MEfflCAL 
 
 Gift of 
 Wallace I, Terry, M.D 
 


 

DR. CARPENTER'S PHYSIOLOGICAL WORKS. 
 
 A MANUAL, OR ELEMENTS OF PHYSIOLOGY, 
 INCLUDING PHYSIOLOGICAL ANATOMY, 
 
 . FOR THE USE OF THE MEDICAL STUDENT. 
 
 With one Hundred and Eighty Illustrations. In one octavo volume of 566 pages. Elegantly 
 printed to match his "Principles of Human Physiology." 
 
 A POPULAR TREATISE ON VEGETABLE PHYSIOLOGY. 
 
 r 
 With numerous Illustrations on Wood. In one neat duodecimo volume. 
 
 (Preparing) 
 
 PRINCIPLES OF GENERAL AND COMPARATIVE 
 PHYSIOLOGY, 
 
 INTENDED AS AN INTRODUCTION TO THE STUDY OF HUMAN PHYSIOLOGY, AND 
 AS A GUIDE TO THE PHILOSOPHICAL PURSUIT OF NATURAL HISTORY. 
 
 With numerous Illustrations on Wood. From the Third London Edition. 
 
 (Preparing) 
 
 PRINCIPLES OF ANIMAL PHYSIOLOGY. 
 
 With about Three Hundred beautiful Illustrations on Wood. 
 
 LEA AND BLANCHARD. 
 
PRINCIPLES 
 
 OF 
 
 HUMAN PHYSIOLOGY, 
 
 WITH THEIR CHIEF APPLICATIONS TO PATHOLOGY, HYGIENE, AND 
 FORENSIC MEDICINE. 
 
 BY 
 
 WILLIAM B.^CARPENTER, M.D., F.R.S., 
 
 FULLEEIAN PROFESSOR OF PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN, CORRESPONDING 
 MEMBER OF THE AMERICAN PHILOSOPHICAL SOCIETY, AND OF THE 
 
 NATIONAL INSTITUTE OF THE UNITED STATES J 
 
 LECTURER ON PHYSIOLOGY AT THE LONDON HOSPITAL MEDICAL SCHOOL, 
 ETC. ETC. 
 
 American, from tjje last 2-ontion 
 
 WITH NOTES AND ADDITIONS, 
 
 
 
 BY 
 
 MEREDITH CLYMER, M.D., 
 
 CONSULTING PHYSICIAN TO THE PHILADELPHIA HOSPITAL; 
 
 LATE PROFESSOR OF THE PRINCIPLES AND PRACTICE OF MEDICINE, AND CLINICAL MEDICINE, IN THE 
 
 FRANKLIN MEDICAL COLLEGE, PHILADELPHIA J FELLOW OF THE 
 
 COLLEGE OF PHYSICIANS, ETC. ETC. ETC. 
 
 THREE HUNDRED AND SEVENTEEN WOOD-CUT AND OTHER ILLUSTRATIONS. 
 
 PHILADELPHIA: 
 LEA AND, BLANCHARD. 
 
 1847. 
 

 Entered according to Act of Congress, in the year 1845, by 
 
 LEA AND BLANCHARD, 
 in the Office of the Clerk of the District Court for the Eastern District of Pennsylvania. 
 
 PHILADELPHIA : 
 T. K. AND P. G. COLLIN^ PRINTERS. 
 
TO 
 
 WILLIAM PULTENEY ALISON, 
 
 M.D., F.R.S.E., &c.&c. 
 
 PROFESSOR OF THE PRACTICE OF MEDICINE OF THE UNIVERSITY OF EDINBURGH. 
 
 MY DEAR SIR, 
 
 I take the liberty of inscribing the following Work to you, as an ex- 
 pression of my grateful remembrance of the value of your instructions, 
 of my respect for those intellectual faculties which render you pre-emi- 
 nent amongst the Medical Philosophers of our time, and of my admira- 
 tion for those moral excellencies which call forth the warm regard of all 
 who are acquainted with your character. 
 
 In many parts of this Treatise, you will find that doctrines, which you 
 have long upheld in opposition to almost the whole Physiological world, 
 are defended with such resources as I could command; and that, in 
 many instances, such convincing evidence of their truth has been afforded 
 by recent observations, that further opposition to them would now seem 
 vain. And if I have presumed to differ from you on some points, it has 
 been in the spirit of that independence which you have uniformly encou- 
 raged in your pupils; yet with a distrust of my own judgment, wherever 
 it came into collision with yours. 
 
 That you may long be spared to be the ornament of your University, 
 and the honour of your City, is the earnest wish of, 
 
 Dear Sir, 
 
 Your obliged Pupil, 
 
 WILLIAM B. CARPENTER. 
 
EDITOR'S PREFACE. 
 
 THE character of the present Work is too well known and established 
 to need any commendation. Within a period of four years, it has passed 
 through three editions both in this country and Great Britain. It will 
 be seen, upon referring to the Author's Preface, that the present edition 
 has been essentially modified and improved ; and, besides attentive re- 
 vision, has undergone material alteration in the arrangement. 
 
 Many of the Notes of the American Editor to former editions have 
 been incorporated by the Author in the text of the present ; others remain ; 
 whilst such additions have been made, as the progress of the science 
 required. 
 
 By the liberality of the Publishers, the Editor has been enabled to add 
 numerous additional illustrations ; which, accompanied by copious refer- 
 ences, will, he trusts, be found to enhance the value of this edition, and. 
 to peculiarly adapt it to the Student of Physiology. There are one 
 hundred and fifteen more wood-cuts in this than in the third English 
 edition, and one hundred and one more than in the last American. 
 
 The new matter added by the American Editor is in smaller type, and 
 is distinguished thus [ M. C.] The new cuts are included between 
 brackets [ ]. M. C. 
 
 230. Spruce Street, Philadelphia, 
 September, 1847. 
 
PREFACE 
 
 TO 
 
 THE TRIED LONDON EDITION. 
 
 THE Author gladly avails himself of the opportunity afforded him by 
 the call for a Third Edition of the following work, to express his grateful 
 acknowledgments for the kind reception it has experienced, both in this 
 country and in the United States. The rapid sale of two large impres- 
 sions on each side of the Atlantic, has been the most satisfactory proof that 
 he had not been in error when he supposed that an opening existed for 
 an additional Treatise on Physiology, notwithstanding the large number 
 of those already before the public; and that he has not been altogether 
 unsuccessful in supplying the deficiency. 
 
 The present Edition has not only undergone a very careful revision ; 
 but has in many parts received large additions, and has been in many 
 others entirely remodelled. By an increase in the size of the page, and in 
 the proportion of small type, the quantity of matter has been augmented 
 by an amount equivalent to the addition of fully a hundred pages. A 
 considerable number of new wood engravings, of first rate execution, 
 have also been introduced. Many of these are from original drawings 
 by Mr. Leonard. 
 
 Among the principal additions will be found a Chapter on the Varie- 
 ties of the Human Race ; intended to convey to those, who have not 
 time or opportunity to peruse Dr. Prichard's elaborate treatises, a general 
 view of his arguments and conclusions. The account of the Primary 
 Tissues, also, which was formerly included in the Chapter on Nutrition, 
 has been extended in a degree commensurate with the Author's estimate 
 of its importance, and has been made to form a distinct Chapter nearer 
 the commencement of the work. Other additions and changes, which 
 constitute, when taken collectively, no inconsiderable proportion of the 
 entire Treatise, are scattered through the volume. The materials of 
 these have been drawn from the numerous contributions to Physiological 
 Science, which have been made within the last two years, and from 
 
X PREFACE. 
 
 among which the Author has endeavoured to select the most import- 
 ant and the most stable ; not rashly introducing changes inconsistent 
 with usually-received views ; nor, on the other hand, showing an un- 
 willingness to reject the statements of those who have taken much pains 
 to arrive at accurate conclusions. He trusts that he may be found to 
 have generally exercised a sound discretion, both as to what he has 
 admitted, and what he has rejected; and that his work will appear to 
 exhibit on the whole, a faithful reflection of the present aspect of Phy- 
 siological Science. He cannot venture to expect, however, that he has 
 succeeded in every instance, so that each of his readers will be in con- 
 stant agreement with him ; since it is impossible that they should all 
 survey the subject from the same point of view. 
 
 Many, however, of the additions and alterations scattered through the 
 work, are the result of the Author's own investigations. He has par- 
 ticularly directed his attention to the settlement of points, which ap- 
 peared to him to be left doubtful by others ; and hence will sometimes be 
 found to have expressed his views with a degree of confidence, which 
 the evidence adduced by them may scarcely appear to warrant. 
 
 The Author feels called upon to express his particular obligations to 
 the valuable Reports on the Progress of Anatomy and Physiology, con- 
 tributed by Mr. Paget, to the British and Foreign Medical Review ; and 
 also to those contained in the Half- Yearly Abstract, edited by Dr. Rank- 
 ing. He has made a point, however, of consulting the original sources 
 of information referred to in these Reports, in every instance in which 
 he could gain access to them. He has derived much assistance, also, 
 from Dr. Day : s Reports on the Progress of Chemistry, published in the 
 second of the works just named ; as well as from the translation of 
 Simon's Animal Chemistry, edited by the same gentleman. 
 
 He would be doing injustice to his own feelings, if he did not specially 
 refer to the admirable "Anatomical and Pathological Observations" of 
 Messrs. Goodsir, as one of the most valuable contributions to Physiolo- 
 gical Science which has been made since the date of his former Edition. 
 
 The subjoined Extracts from the First Edition will explain the plan 
 and scope of his Treatise to those who may now examine it for the first 
 time. 
 
 Stoke Newington, 
 
 October, 1846. 
 
FROM THE 
 
 PREFACE 
 
 TO 
 
 THE FIKST EDITION. 
 
 THE composition of such a Treatise as the following was a part of the 
 original plan of the Author when he first came before the Public as a 
 writer on Physiology. Being desirous, however, of making his first essay 
 in the path which had been previously the most incompletely explored, 
 he deemed it better to await the verdict upon this before proceeding 
 further; and he was not without hope, that some Writer, more fully com- 
 petent to the task, might in the meantime take up the subject of Human 
 Physiology in such a way as to leave nothing for the Student to desire. 
 This, however, has not been accomplished. The previously existing 
 Treatises upon it, which have been every year becoming more antiquated, 
 have not been replaced by any works, that can be considered as at the 
 same time sufficiently elevated in their character, to represent the present 
 condition of Physiological Science, sufficiently compendious in their 
 bulk for the limited time at the disposal of most Students, and suffi- 
 ciently practical in their tendency to lead their readers to the useful 
 applications of the facts and principles they place before them. This is 
 not the opinion of the Author alone, but that of numerous experienced 
 Teachers throughout the country; and he has been led to regard the 
 present as a good time for carrying his purpose into execution. 
 
 The plan and objects of his Treatise may be gathered from the pre- 
 ceding statement of the reasons which have occasioned its production. 
 In this, as in his previous work, it has been his object to place the 
 Reader in the possession of the highest principles, that can be regarded 
 as firmly established, in each department of the Science; and to explain 
 and illustrate these, by the introduction of as many important lacts as 
 could be included within moderate limits. In every instance, he has 
 endeavoured to make his statements clear and precise without being 
 formal or dogmatical; and definite enough to admit of practical applica- 
 
Xll PREFACE. 
 
 tion without appearing to be unimprovable by further inquiry. Physiology 
 is essentially a science of progress ; and it must happen that much of 
 v kit is sirow regarded as established truth, will need great modification 
 to be brought into accordance with the results of new inquiries. It is 
 very desirable, therefore, that the Student should not be made to think 
 so confidently of his acquirements, as to be indisposed to receive new 
 information, even though it should tend to diminish their value. 
 
 The present Treatise is to be regarded as complete in itself, and as 
 quite independent of the Author's " Principles of General and Compara- 
 tive Physiology." That it may be so he has inserted an introductory 
 chapter on the "Place of Man in the Scale of Being," and numerous 
 references to the Comparative Physiology of the lower Animals. Still 
 he does not hesitate to express the opinion that, the greater the amount 
 of the Student's previous general knowledge of the Science, the better 
 will he be prepared to enter upon any department of it, especially that 
 peculiarly complex and difficult branch, the Physiology of Man. On 
 every topic, it has been the author's aim to present the latest and most 
 satisfactory information within his reach ; and he believes that the Volume 
 contains much that will be new to the Physiologist, whose reading has 
 not been tolerably extensive. Its materials have been but little derived 
 from other Systematic Treatises on the subject ; and it will not be found 
 to bear, as a whole, any considerable resemblance to those already Before 
 the public. The author has rather endeavoured to bring together the 
 valuable facts and principles, scattered through the best of the numerous 
 Monographs, that have been recently published on special divisions of 
 Physiology and Medicine ; and to reduce these disjecta membra to that 
 systematic form, which they can only be rightly made to assume, when 
 brought into relation with each other, and shown to be subservient to 
 principles of still higher generality. In regard to this, as to his former 
 Treatise, the Author believes that he may claim a somewhat higher 
 character than that of the mere Compiler ; and that even the well-read 
 Physiologist will find in it many facts and deductions, which have not 
 been previously brought before him in the same form. 
 
 In apportioning the amount of space to be devoted to each division of 
 the subject, the Author has had in view its practical relations, much 
 more than its merely scientific interest; and he has on this account 
 bestowed a much larger share on the organs of Animal life than some 
 may think just when compared with the narrow limits within which other 
 important topics are discussed. But he has endeavoured to keep always 
 in view, that he is writing for the guidance of the Student who is to be- 
 come a Practitioner, rather than for him who makes the pursuit of Science 
 his professed object; and that much that is of the highest interest to the 
 
PREFACE. Xlll 
 
 latter is comparatively valueless to the former. Hence "many topics of 
 great scientific interest are entirely passed over; and it is hoped that 
 such omissions will not be accounted as faults in the estimation of those, 
 who dread lest the attention of the Student should be too much drawn off 
 by the seducing novelties of Science, from his less attractive, but more 
 important objects. 
 
 For a large part of his illustrations, the Author is indebted to the 
 valuable and beautiful Icones Physiologicse of Prof. Wagner. He has 
 indicated the sources of all which are not original. 
 
 In conclusion, the Author would repeat what he has already had oc- 
 casion to state ; that in a work involving many details, it is not to be 
 expected that no error should have crept in ; but that he has endeavoured 
 to secure correctness, by relying only upon such authorities as appeared 
 to him competent, and by comparing their statements with such general 
 principles as he considers well established. For the truth of those 
 principles, he holds himself responsible ; for the correctness of the details, 
 he must appeal to those from whom they are derived, and to whom he 
 has generally referred. He hopes that he will not be found unwilling to 
 modify either, when they have been proved to be erroneous ; nor indis- 
 posed to profit by criticism, when administered in a friendly spirit. 
 
 Bristol, Feb. 1, 1842, 
 
 
TABLE OF CONTENTS 
 
 ; INTRODUCTION. 
 
 i PAGE 
 
 NATURE AND OBJECTS OF PHYSIOLOGICAL SCIENCE - : ( 38 
 
 CHAPTER I. 
 
 OX THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 1. Distinction between Animals and Plants - - - - 39 
 
 , 2. General sub-divisions of the Animal Kingdom - - - - 41 
 
 3. General characters of Radiata ... -42 
 
 4. General characters of Mollusca - 45 
 
 5. General characters of Articulata - - - - . - - -48 
 
 6. General characters of Vertebrata - - 50 
 
 7. General characters of Fishes - - - -'- - - 54 
 
 8. General characters of Reptiles - - 55 
 
 9. General characters of Birds - - - - i.- 58 
 
 10. General characters of Mammalia .... , v . ^ . 62 
 
 11. Chief sub-divisions of Mammalia ... - 65 
 
 12. Characteristics of Man - - - 67 
 
 CHAPTER II. 
 
 OF THE MUTUAL RELATIONS OF THE DIFFERENT BRANCHES OF THE HUMAN 
 
 FAMILY. 
 
 1. General Considerations ---.----76 
 
 2. On the Discrimination of Species - - - 77 
 
 3. On the possible Extent of Variation within the limits of Species ', - ' 79 
 
 4. On the Extremes of Variation among the Races of Men - - - 81 
 
 5. On the value of ^Physiological and Psychological peculiarities as specific distinc- 
 
 tions - - - - -. - * - - 82 
 
 6. On the Comparative Peculiarities of the different Races of Mankind - - 83 
 
 7. Of the Principal Branches of the Human Family - -91 
 
 CHAPTER III. 
 
 OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 1. On Organized Structures in General ...... 99 
 
 2. On the Original Components of the Animal Fabric 102 
 
 3. Of the Elementary Parts of Organized Tissues; Cells, Membrane, and Fibre 108 
 
 4. Of the Simple Fibrous Tissues - " - - ... - 120 
 
XVI CONTENTS. 
 
 PAGE 
 
 5. Of simple Cells, floating in the Animal Fluids - - 124 
 
 6. Of Cells developed upon Free Surfaces - - 137 
 
 7. Of the Compound Membrano-Fibrous Tissues - - 147 
 
 8. Of Simple Isolated Cells, forming Solid Tissues by their aggregation - - 150 
 
 9. Of Tissues consolidated by Earthy deposit. Bones and Teeth - -161 
 
 10. Of Simple Tubular Tissues. Capillary Blood-vessels - - 188 
 
 11. Of Compound Tubular Tissues. Muscle and Nerve - J 192 
 
 CHAPTER IV. 
 
 GENERAL VIEW OF THE FUNCTIONS. 
 
 1. Of Vital Actions, and their mutual dependence - 216 
 
 2. Functions of Vegetative Life - - 224 
 
 3. Functions of Animal Life - 232 
 
 CHAPTER V. 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 1. General Summary v 236 
 
 2. Comparative Anatomy and Physiology of the Nervous System in Invertebrata 247 
 
 3. Nervous System of Vertebrata - .... 265 
 
 4. Functions of the Spinal Cord and its Nerves. Reflex Action - - - 285 
 
 Respiratory Movements ... - 292 
 Deglutition and Defecation - - * - -297 
 
 Movements of the Genital Organs - - - 305 
 
 Protecting Agency of the Spinal Cord - - 305 
 
 Movements of Locomotion - ... 307 
 
 Influence on Muscular Tension ----- 307 
 
 Pathological Phenomena - , - 308 
 Nerves of the Spinal System - - - - -310 
 
 5. Of the Sensory Ganglia and their Functions. Consensual Movements - - 326 
 
 Emotional Actions ....-- 335 
 
 Nerves connected with the Sensory Ganglia ... 339 
 
 Consensual Movements of the Eye - - 344 
 
 6. Functions of the Cerebellum - - 349 
 
 7. Functions of the Cerebrum - - - 357 
 
 8. General Recapitulation, and Pathological Applications - - 376 
 
 CHAPTER VI. 
 
 OF SENSATION, AND THE ORGANS OF THE SENSES. 
 
 1. Of Sensation in General - - - 385 
 
 2. Sense of Touch ' 395 
 
 3. Sense of Taste .... 399 
 
 4. Sense of Smell - - 404 
 
 5. Sense of Vision - - - 407 
 
 6. Sense of Hearing - - - - - - 422 
 
 CHAPTER VII. 
 
 OF MUSCULAR CONTRACTILITY. 
 
 1. Of Contractility in General - - - . - - : - 438 
 
CONTENTS. XVli 
 
 PAGE 
 
 2. Of Muscular Irritability - .... 439 
 
 3. Of Muscular Tonicity - - - - - - - -.449 
 
 4. Energy and Rapidity of Muscular Contraction - - 452 
 
 CHAPTER VIII. 
 
 OF THE VOICE AND SPEECH. 
 
 1. The Larynx, and its Actions r ." 455 
 
 2. Of Articulate Sounds - - 464 
 
 CHAPTER IX. 
 
 INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC FUNCTIONS. 470 
 
 CHAPTER X. 
 
 OF FOOD AND THE DIGESTIVE PROCESS. 
 
 1. Sources of the Demand for Aliment. Hunger and Thirst - - 477 
 
 2. Nature and Destination of the Food of Animals - - 483 
 
 3. Of the Passage of Food along the Alimentary Canal - ' 492 
 
 Mastication 'and Deglutition - - 494 
 
 Action of the Stomach - - - 496 
 
 Action of the Intestinal Tube - - 501 
 
 Act of Defecation - 502 
 
 4. Nature of Chymification and Chylification - 503 
 
 CHAPTER XI. 
 
 OF ABSORPTION AND SANGUIFICATION. 
 
 1. Absorption from the Digestive Cavity - - 509 
 
 2. Absorption from the Body in general - - - - -512 
 
 3. Of the Elaboration of the Nutrient Materials - - -517 
 
 4. Composition and Properties of the Chyle and Lymph - - 523 
 
 5. Physical and Vital Properties of the Blood - 527 
 
 6. Pathological Changes in the Blood - 535 
 
 CHAPTER XII. 
 
 OF THE CIRCULATION OF BLOOD. 
 
 1. Of the. Circulation in General - ,- j 540 
 
 2. Action of the Heart - ' - 546 
 
 3. Movement of the Blood in the Arteries and Capillaries - - 556 
 
 4. Of the Venous Circulation > 566 
 
 5. Peculiarities of the Circulation in different Parts - - - -. ~ 568 
 
 CHAPTER XIII. 
 
 OF RESPIRATION. 
 
 1. Nature of the Function ; and Provisions for its Performance 
 
 2. Effects of Respiration on the Air 
 
 2* 
 
XV111 CONTENTS. 
 
 PAGE 
 
 3. Effects of Respiration on the Blood - - 586 
 
 Exhalation and Absorption by the Lungs ... 589 
 
 4. Effects of Suspension of the Respiratory Process .... 591 
 
 CHAPTER XIV. 
 
 OF NUTRITION. 
 
 1. General Considerations. Selective Power of Individual Parts - - 593 
 
 2. Varying Activity of the Nutritive Processes - - - - - 596 
 
 Reparative Operations - - T " - " *^ 
 
 3. Abnormal Forms of the Nutritive Process - . - ... . " - 604 
 
 4. Varying Duration of Different Parts of the Organism - 609 
 
 5. Of Death, or Cessation of Nutrition - 612 
 
 CHAPTER XV. 
 
 OF SECRETION. 
 
 1. Of Secretion in General - 614 
 
 2. The Liver. Secretion of Bile - 618 
 
 3. The Kidneys. Secretion of Urine - 632 
 
 4. Mammary Gland. Secretion of Milk - - 647 
 
 5. Salivary Glands and Pancreas - ... 655 
 
 6. Lachrymal Gland - 657 
 
 7. The Testis. Spermatic Fluid - - 657 
 
 8. Cutaneous and Mucous Follicles - 661 
 
 CHAPTER XVI. 
 
 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. ANIMAL HEAT. 
 
 1. Review of the Nutritive Processes, with Practical Ajtplications - - 671 
 
 2. Animal Heat - - - 676 
 
 CHAPTER XVII. 
 
 OF REPRODUCTION. 
 
 1. General Character of the Function - - - 687 
 
 2. Action of the Male - 689 
 
 3. Action of the Female - - 692 
 
 4. Development of the Embryo - - 713 
 
 APPENDIX. 
 
 I. ON PHRENOLOGY ... . 731 
 
 II. ON ARTIFICIAL SOMNAMBULISM AND MESMERISM - - 733 
 
* 
 
.TLATLl 
 
EXPLANATION OF PLATES. 
 
 PLATE I. 
 
 The first 16 Figures in this Plate are from Dr. Barry's Embryological Researches in the 
 Philosophical Transactions for 1837, 1839 and 1840. 
 
 FIG. 
 
 1. A very early stage of the formation of the Ovum; the vesicles, the largest of which 
 
 measures only 1-1 12 5th of an inch, are seen in the midst of dark granules or 
 globules ( 906). 
 
 2. A stage somewhat more advanced ; the vesicles are surrounded by envelopes of smaller 
 
 vesicles, amongst which the granules are still seen ( 906). 
 
 3. .A still later stage ; a central vesicle a, is seen, with a spot, 6, upon its walls, and sur- 
 
 rounded with numerous granules ; this has now evidently become the Germinal 
 Vesicle ( 906). 
 
 4. Ovisacs from Human Ovum, 1-2 00th of an inch and upwards, in diameter; the largest 
 
 exhibits the Germinal Vesicle, a, very distinctly ( 906). 
 
 5. Ovisac from Cat, showing its contents when near maturity ; a, ovisac ; 6, its contained 
 
 granules; c,zona pellucida; d, granules of the yolk; e, germinal vesicle ;/, germinal 
 spot; magnified 440 diameters ( 905). 
 
 6. Ovum of Rabbit at the periphery of the Graafian follicle, with part of the membrana 
 
 granulosa removed; g,g, membrana granulosa; ov, ovulum; r, retinacula ( 906, 
 912). 
 
 7. Ovum with its tunica granulosa and retinacula, removed from the Graafian follicle ; a, 
 
 germinal vesicle; 6, germinal spot; c, zona pellucida; d, globules of the yolk; r,r, 
 retinacula; f,g, tunica granulosa ( 906). 
 
 8. Graafian follicle discharging its Ovum, ou, to which the tunica granulosa, tg, and retina- 
 
 cula, r, r, remain attached ( 912). 
 
 9. Ovarium Ovum in preparation for fecundation: a, germinal spot beginning to resolve it- 
 
 self into cells at its margin; 6, germinal vesicle; c, elliptical cells in the place of 
 the yolk ; d, zona pellucida. 100 Diameters ( 915, 916.) 
 
 10. Ovum nearly ready for fecundation : a, germinal spot more fully developed into cells, of 
 
 which concentric layers occupy the germinal vesicle b ; c, elliptical discs or cells ; 
 rf, zona pellucida; e, outer layer of cells of yolk ( 130, 915, 916). 
 
 11. Fecundated Ovum of nine hours; the germinal vesicle, having returned to the centre of 
 
 the ovum, is concealed by the large elliptical discs, which fill the cavity of the 
 zona pellucida ( 916). 
 
 12. Plan of one of these discs or cells: its nucleus, a, has developed itself into concentric 
 
 rings of cells: and in^the most fully developed of these, the nucleus, b, is seen to 
 be commencing the same kind of evolution. In the centre of the original nucleus, 
 a pellucid spot, the nucleolus of Sch wann and Schleiden, is observed ( 130, 916). 
 
XX EXPLANATION OF PLATES. 
 
 Fie. 
 
 13. Ovum from the Uterus, measuring about 1-6 8th of an inch in diameter: a, pair of cells 
 
 now occupying the greater part of the germinal vesicle 6; c, zona pellucida ; d, 
 chorion, a new envelope, separated from the last by the fluid it has absorbed 
 ( 130, 917). 
 
 14. Ovum, of which the essential part, a, the pair of cells occupying the germinal vesicle, 
 
 has advanced farther than in the last case; the other contents of the germinal 
 vesicle have undergone liquefaction. The chorion is here incipient; and the re- 
 mains of the cells of which t it is composed are seen at cho ( 130, 918). 
 
 15. More advanced ovum; the cavity of the germinal vesicle filled with cells, a, that have 
 
 originated in the two represented in the last figure; these cells have nuclei, 6, 
 which are undergoing a corresponding process of evolution into secondary cells; c 
 and d as in Fig. 13 ( 130, 935). 
 
 16. Ovum in a state rather more advanced; a, central cell of the germinal mass, now come 
 
 to the surface, and showing the nucleus b with a pellucid centre, from which most 
 of the embryonic structures are developed ; c, cavity in the germinal mass, caused 
 by the approach of its peripheral cells to the enclosing membrane, d ( 935, 936). 
 
 17. Formation of the Membrana Decidua; a, a, a, interfollicular substance of the mucous 
 
 membrane of the uterus ; 6, cavities of the follicles ; c, uterine vessels prolonged 
 into the decidua and forming loops. After Baer ( 919). 
 
 18. Human Spermatozoa; a, seminal granules. After Wagner ( 902). 
 
 19. Cyst of evolution. After Wagner ( 902). . , 
 
 20. Capsular bundle of Spermatozoa, just previous to their separation. After Wagner 
 
 (902). 
 
 21. Globules from the Chyle; a, ordinary globules; 6, a globule (cytoblast ?) surrounding 
 
 itself with an envelope (a forming cell?); c. minute molecules of chyle; d, a 
 colourless corpuscle from the blood. After Wagner ( 692, 693). 
 
 22. Particles of Blood undergoing multiplication: a, b, c y d, e, successive stages. After Barry 
 
 (S 148). 
 
 23. Extremity of one of the tufts of fostal vessels forming the Placenta; this includes (like 
 
 a branchial tuft) an artery and vein. After Reid ( 922). 
 
 24. Plan of the structure of the Placenta, according to Dr. J. Reid's view of it ; a, a, portion 
 
 of substance of uterus ; 6, i, 6, 6, section of uterine sinuses, some of them opening 
 on the inner surface into the cavity of the placenta; c, curling artery of uterus ; d, rf, 
 ramifications of fetal vessels, some of them sending down prolonged tufts which 
 dip into the uterine sinuses ( 923). 
 
 PLATE II. 
 
 25. Uterine Ovum of Rabbit, showing the Area Pellucida, with the annular nucleus of the 
 
 embryonic cell (Fig. 14, 6) now elongated. In the clear space enclosed by this is a 
 well-marked dark groove, occupying the position in which the nervous centres are 
 subsequently to be developed. The cephalic extremity of this is already rounded 
 and the caudal extremity pointed. After Bischoff ( 937). 
 
 26. More advanced ovum, showing the incipient formation of the Vertebral column; and 
 
 the dilatation of the primitive groove at its anterior extremity. After BischorT 
 ( 937). 
 
PLATE Z. 
 
 Fit 27 
 
EXPLANATION OF PLATES. XXI 
 
 PIff. 
 
 27. More advanced embryo, seen on its ventral side, and showing the first development of 
 the Circulating apparatus. Around the Vascular Area is shown the terminal sinus, 
 o, a, a. The blood returns from this by two superior branches, 6, 6, and two infe- 
 rior, c, c, of the omphalo-meseraic veins, to the heart, <?; which is, at this period, a 
 tube curved on itself, and presenting the first indication of a division into cavities. 
 The two aortic trunks appear, in the abdominal region, as the inferior vertebral 
 arteries, e, c; from which are given off the omphalo-meseraic arteries, /,/, which 
 form a network that distributes the blood over the vascular area. In the cephalic 
 region are seen the anterior cerebral vesicles, with the two ocular vesicles, g. After 
 Bischoff(938). 
 
 
 
 

LIST OF WOOD-ENGRAVINGS. 
 
 FIG. PAGE 
 
 1. Structure of the Star-fish, after Tiedemann - 43 
 
 2. External aspect of Aplysia, after Rang 
 
 3. Structure of Aplysia, after Cuvier 47 
 
 4. Section of Cockchafer, after Strauss-Durckheim - 50 
 
 5. Comparative view of base of Skull of Man, and of Orang-Outan, after Owen - 68 
 
 6. Comparative view of the Skeletons of Man aud the Orang, after Owen 71 
 
 7. Views of Prognathous Skull, after Prichard > 86 
 
 8. Views of Pyramidal Skull, after Prichard 87 
 
 9. View of Oval Skull, after Prichard 
 
 10. Fibrous structure of Exudation-membrane, after Gerber - 107 
 
 11. Fibrous membrane from the Egg-shell - - - 107 
 
 12. Simple Isolated Cells, containing reproductive Molecules - 110 
 
 13. Cells of Zygnema, showing spiral arrangement of nuclear particles, after Hassall 110 
 
 14. Cells of Pelargonium, showing stellate prolongations of nuclei - - - 111 
 
 15. Haematococcus binalis, in various stages of development, after Hassall - - 111 
 
 16. Coccochloris cystifera, in various stages of development, after Hassall - - 111 
 
 17. Haematococcus sanguineus, in various stages of development, after Hassall - 112 
 
 18. Nostoc macrosporum, in two states, after Hassall 
 
 19. Section of branchial Cartilage of young Tadpole, after Schwann 
 
 20. Endogenous cell-growth in cells of a meliceritous tumor, after Goodsir - 
 
 21. Colorless cells with active molecules and fibres of fibrine, after Addison - 118 
 
 22. Arrangement of Fibres in Areolar Tissue 
 
 23. White Fibrous Tissue, from Ligament - 
 
 24. Yellow Fibrous tissue, from Ligamentum nuchse of Calf - 122 
 
 25. Elements of Areolar Tissue, after Todd and Bowman - 
 
 26. Development of Areolar Tissue, after Schwann 122 
 
 27. Red Corpuscles of Human Blood, after Donne - - 124 
 
 28. Red Corpuscles of Frog's Blood, after Wagner - - 125 
 
 29. Production of Red Corpuscles in Chick, after Wagner - - - - 129 
 
 30. Small Venous Trunk, from web of Frog's foot, after Wagner - 
 
 31.. Vertical Section of Epidermis, after Wilson - - 137 
 
 32. Choroid Epithelium, with pigment cells, after Todd and Bowman - - 139 
 
 33. Cells of Pigmentum Nigrum 
 
 34. Section of the nail and its matrix, after Todd and Bowman - - 140 
 
 35. Hairs of Sable and Musk-Deer - - 141 
 
 36. Hair and hair follicles seen in section, after Todd and Bowman - - 141 
 
 37. Structure of Human Hair, after Wilson - - - - 142 
 
 38. Pavement-Epithelium-cells 144 
 
 39. Ciliated Epithelium 
 
 40. Examples of Cilia, after Todd and Bowman - - 145 
 
 41. Secreting Follicles from the Liver of Crab 146 
 
 42. Capillary Network of Skin, after Berres 
 
 43. Capillary Network of Intestinal Villi, after Berres 
 
 44. Capillary Network of Mucous Membrane, after Berres - 
 
 45. Diagram of the Structure of Mucous Membrane, after Todd 
 
 46. Extremity of Intestinal Villi, after Goodsir 
 
 47. Secreting Cells of Human Liver, after Bowman 
 
 48. Shape of Fat Vesicles in close pressure, after Todd and Bowman 
 
 49. Cells of Adipose Tissue ... 
 
 50. Blood Vessels of Fat, after Todd and Bowman - 
 
XXIV LIST OF WOOD-ENGRAVINGS. 
 
 " PAG* 
 
 51. Fat Vesicles from an emaciated subject, after Todd and Bowman - - 154 
 
 52. Section of Branchial Cartilage of Tadpole, after Schwann - - 155 
 v 53. Section of Fibro-Cartilage - - - 155 
 
 54. Ampullary Loops of Vessels of Cartilage, after Toynbee - 1 57 
 
 55. Nutrient Vessels of Cartilage, after Toynbee ..... 157 
 
 56. Nutrient vessels of the Cornea, after Toynbee - - -158 
 
 57. Vertical section of Sclerotica arid Cornea, after Todd and Bowman - - 158 
 
 58. Tubes of the Cornea of an Ox, injected, after Todd and Bowman - - 159 
 
 59. Calcified Areolar Structure from shell of Echinus - - - - 161 
 
 60. Cellular Membrane from Shell of Pinna - - - - - 161 
 
 61. Section of Bone ...... J62 
 
 62. Transverse section of a long Bone, after Todd and Bowman - - 163 
 
 63. Transverse section of a Tibia, after Tomes - -.163 
 
 64. Lacunae of Osseous Substance - 163 
 
 65. Haversian canals in a long Bone, after Todd and Bowman - 164 
 
 66. Section of Cartilage at Seat of Ossification, after Wilson - 168 
 
 67. Vertical section of Cartilage, after Todd and Bowman - 168 
 
 68. Scapula of a Foetus, showing the process of ossification, after Tomes - - 170 
 
 69. Longitudinal section of an Incisor and Molar Tooth - 174 
 
 70. Vertical section of an adult Bicuspid - 174 
 
 71. Vertical Section of an imperfectly developed Incisor - - 174 
 
 72. Hexagonal terminations of Fibres of Enamel, after Retzius - - 174 
 
 73. Fibres of Enamel viewed sideways, after Retzius - - 175 
 
 74. Vertical section of Bicuspid highly magnified - - - 175 
 
 75. Most interior portion of Main Tubes of Dental Bone - 175 
 
 76. Ramifications of the Main Tubes of Dental Bone - - 175 
 
 77. Transverse section of Crown of Bicuspid, highly magnified - -176 
 
 78. Position of the Main Tubes near the Root of Bicuspid - 176 
 
 79. Sections of a Human Incisor, highly magnified, after Todd and Bowman - 176 
 
 80. Transverse sections of Tubules of Dentine, after Todd and Bowman - - 177 
 
 81. Oblique Section of Dentine, after Owen - 177 
 
 82. Vessels of Dental Papilla, after Berres - 180 
 
 83. Diagram of development of Dentine, after Owen - - - 180 
 
 84. Inner surface of cap of dentine, after Owen - - 181 
 
 85. Formation of Enamel, after Owen - 182 
 
 86. Formation of the Cementum, after Owen - - 182 
 
 87. First stage of Formation of Teeth, after Goodsir - - 183 
 
 88. Diagram illustrating subsequent stages of formation of Teeth, after Goodsir - 183 
 
 89. Do. do. do. after Goodsir - 184 
 
 90. Capillary network in Frog's foot, after Wagner 
 
 91. Capillary vessels from pia mater, after Henle - - 190 
 
 92. Formation of capillaries in germinal membrane, after Wagner - - 191 
 
 93. Fasciculus of fibres of Voluntary Muscle, after Baly - - 193 
 
 94. Portion of Human Muscular Fibre, separating into disks, after Bowman - 193 
 
 95. Cleavage of Striped Elementary Fibres - - 194 
 
 96. Muscular Fibre broken across, showing Myolemma, after Bowman - - 194 
 
 97. Transverse Section of Muscular Fibres of Teal, after Bowman - 196 
 
 98. Fragment of Muscular Fibre from Heart of Ox, after Bowman - 197 
 
 99. Structure of ultimate fibrillae of striated Muscular Fibre - 197 
 
 100. Muscular fibre of Dytiscus, contracted in the centre, after Bowman - - 198 
 
 101. Muscular fibre of Skate, in different stages of contraction, after Bowman - 199 
 
 102. Attachment of Tendon to Muscular Fibre in Skate, after Bowman - - 200 
 
 103. Non-striated Muscular Fibre, after Bowman - - 200 
 
 104. Do. showing nodosities, after Wilson 
 
 105. Muscular Fibres from Fcetus, after Bowman ... 202 
 
 106. Do. treated with tartaric acid, after Wilson 
 
 107. Capillary network of Muscles, after Berres 
 
 108. Terminating loops of Nerves in Muscles, after Burdach - 204 
 
 109. Structure of Sympathetic Ganglion, after Valentin - - - 205 
 
 110. Diagram of Tubular Fibre of a Spinal Nerve, after Todd and Bowman 
 
 111. Structure of Nerve-tubes, after Wagner 
 
 112. Primitive fibres and ganglionic globules of human brain, after Purkinje - 208 
 
 113. Nerve-vesicles from the Gasserian ganglion, after Todd and Bowman - 209 
 
 1 14. Caudate nerve-vesicles from the cerebellum and cord, after Todd and Bowman 2 10 
 
LIST OF WOOD-ENGRAVINGS. XXV 
 
 FIG. 
 
 115. View of piece of Otic ganglion of sheep, after Valentin - 210 
 
 116. Two views of the vesicular and fibrous matter of the cerebellum, after Todd 
 
 and Bowman - - - - - - - -211 
 
 117. Vesicular and fibrous matter in the Gasserian ganglion, after Todd and Bowman 211 
 
 118. Primitive Fibres and ganglionic globules, after Wagner - -211 
 
 119. Distribution of tactile nerves in skin, after Gerber - - - - 212 
 
 120. Terminal loops of nerve in the pulp of a tooth, after Valentin - 213 
 
 121. Capillary network of nervous centres, after Berres - 214 
 
 122. Capillary loops in skin of finger, after Berres - - 214 
 
 123. Stages of the development of nerve, after Schwann - - 215 
 
 124. Nervous system of Solen, after Blanchard, ... - 251 
 
 125. Nervous system of Aplysia, after Cuvier - - , 254 
 
 126. Nervous system of larva of Sphinx ligustri, after Newport - - - 256 
 
 127. Portion of ganglionic tract of Polydesmus, after Newport - - 257 
 
 128. Parts of Nervous System of Articulata, after Newport - 259 
 
 129. Stomato-gastric system of Gryllotalpa vulgaris, after Brandt ... 261 
 
 130. A View of the Great Sympathetic Nerve - 267 
 
 131. Roots of a dorsal Spinal Nerve, after Todd and Bowman - - 268 
 
 132. Nervous centres in Frog, after Leuret ... - 270 
 
 133. Transverse sections of Spinal Cord at different points, after Solly - . - 271 
 
 134. Structure of the Spinal Cord, after Stilling - 272 
 
 135. Connection of nerve-roots with the Spinal Cord, after Stilling - 272 
 
 136. A posterior superior view of the Pons Varolii, Cerebellum, &c. - ' 275 
 
 137. An anterior view of the Medulla Oblongata, after Todd and Bowman - 275 
 
 138. A posterior view of the Medulla Oblongata, after Todd and Bowman - 275 
 
 139. Transverse section of the Medulla Oblongata, after Stilling - - - 276 
 
 140. Course of the Motor tract, after Sir C. Bell - - - - 277 
 
 141. Course of the Sensory tract, after Sir C. Bell ..... 278 
 
 142. Analytical diagram of the Encephalon, after Mayo .... 279 
 
 143. Brains of Fox-shark, Cod, and Pike, after Leuret - - 281 
 .144. Human Embryo of 6th week, showing rudiments of Brain, after Wagner - 282 
 
 145. Brain of Turtle, after Solly - - - - - - - 283 
 
 146. Brain of Buzzard, after Leuret - - - - - 283 
 
 147. Brain of Human Embryo at 12th week, after Tiedemann ~ - - - 284 
 
 148. Brain of Squirrel laid open, after Solly - - 284 
 
 149. Upper and under surface of Brain of Rabbit, after Leuret - - 285 
 ,150. Diagram of the distribution of the Fifth Pair - 311 
 
 151. A view of the distribution of the Trifacial nerves - - - - 312 
 
 152. A view of the Third, Fourth, and Sixth Pairs of nerves - 313 
 
 153. Diagram of the distribution of the Seventh Pair - - - 314 
 
 154. Diagram of the distribution of the Eighth Pair - - - 315 
 
 155. A view of the distribution of the Glosso-Pharyngeal, Pneumogastric and Spinal 
 
 Accessory Nerves, or Eighth Pair - - 316 
 
 156. A view of the course and distribution of the Hypoglossal, or Ninth Pair - 324 
 
 157. Base of the Cerebrum and Cerebellum with their nerves - - - 327 
 
 158. A view of the Optic nerve and the origins of seven other pairs - - 340 
 
 159. Plan of the optic tracts and nerves, after Todd and Bowman - - 342 
 
 160. Course of Fibres in the Chiasma, after Todd and Bowman - - 342 
 
 161. Origin and distribution of the Portio Mollis of the Seventh Pair, or Auditory 
 
 Nerve ... ..... 343 
 
 162. Capillary network at margin of lips, after Berres - - 396 
 
 163. Dorsal surface of the Tongue, from Soemmerring - - - 399 
 
 164. Simple papillae near the base of the tongue, after Todd and Bowman - - 400 
 
 165. Vertical section of one of the.circumvallate papillae, after Todd and Bowman 400 
 
 166. Compound and simple papillae of Foramen Ccecum, after Todd and Bowman 400 
 
 167. Capillary network of fungiform papilla of tongue, after Berres - 401 
 
 168. Fungiform papilla with its simple papillae and vessels, after Todd and Bowman 401 
 
 169. Forms of the conical or filiform papillae, after Todd and Bowman - - 401 
 
 170. \ A ' ^ ecti n f f^; m and fu , n g iform P a P ille I after Todd and Bowman - 402 
 B. Structure of filiform papillae 5 
 
 171. Nerves of the papillae of the tongue, after Todd and Bowman 
 
 172. Distribution of Olfactory nerve on Septum Nasi ... - 405 
 
 173. Longitudinal section of globe of the eye - 40 * 
 
 174. Horizontal section of the eyeball 
 
 3 
 
XXVI LIST OF WOOD-ENGRAVINGS. 
 
 FIG. PAGE 
 
 175. Outer surface of retina of Frog, after Treviranus - - - 412 
 
 176. Capillary network of retina, after Berres - - 412 
 
 177. A portion of the retina of an Infant, magnified - 412 
 178.- Vertical section of the Human retina and. Hyaloid membrane, after Todd and 
 
 Bowman - - .... 413 
 
 179. Membrane of Jacob, after Jacob - - - 413 
 
 180. General section of the Ear, after Scarpa ..... 433 
 
 181. Diagram of the Inner wall of Tympanum, after Todd and Bowman - - 424 
 
 182. Axis of Cochlea and Lamina Spiralis - - - - - -425 
 
 183. Cochlea of a new-born Infant, after Arnold - - - - - 425 
 
 184. Section of the Cochlea, after Breschet - .... 426 
 
 185. Papillae of Auditory nerve on spiral lamina of cochlea of young mouse 426 
 
 186. Auditory nerve taken out of the cochlea - 426 
 
 187. Magnified view of the Lamina Spiralis - 427 
 
 188. Plexiform arrangement of cochlear nerves, after Todd and Bowman - - 427 
 
 189. Soft parts of the Vestibule - - 428 
 
 190. Ampulla of the External Semicircular Membranous Canal - 428 
 -191. Labyrinth laid open, after Breschet - - - 433 
 
 192. Labyrinth of the Left Side - ... 434 
 
 193. Left Ear in its natural state - - -s - 435 
 
 194. Anterior view of the External Ear, Meatus Auditorius, &c. - - - 435 
 
 195. External and Sectional views of the Larynx, after Willis - - 456 
 
 196. Bird's-eye view of Larynx from above, after Willis - - 457 
 
 197. Diagram of the direction of the muscular forces of the Larynx, after Willis - 458 
 
 198. Artificial Glottis, after Willis ....... 461 
 
 199. View of the Organs of Digestion in their whole length - - 493 
 
 200. Muscles of the Tongue, Palate, Larynx and Pharynx - - 495 
 
 201. Front view of the Stomach distended - - - - 499 
 
 202. Interior of the Stomach ... . . 499 
 
 203. Interior of the Stomach and Duodenum - - 500 
 
 204. Commencement of Lacteal in Villus. after Krause - - 510 
 
 205. Vessels of Intestinal Villus of Hare, after Dollinger 
 
 206. Do. Do. of Man, after Krause 
 
 207. Diagram of Lymphatic Gland, after Goodsir 
 
 208. Portion of intra-glandular Lymphatic, after Goodsir 
 
 . - - 511 
 
 511 
 517 
 517 
 
 209. Section showing the anatomy of the Thymus gland, after Cooper 
 
 210. Microscopic appearance of Inflammatory Blood, after Addison - 534 
 
 211. Web of Frog's foot, slightly magnified, after Wagner, - - 541 
 
 212. The anatomy of the Heart - - 551 
 
 213. Hsemadynamometer of Poisseuille - - - , - - 555 
 
 214. Gill-tuft of Doris, after Alder and Hancock - 
 
 215. Lung of Triton, slightly magnified, after Wagner 
 
 216. Portion of the same more highly magnified, after Wagner 
 
 217. Capillary Circulation in lung of living Triton, after Wagner - 
 
 218. The Larynx, Trachea and Bronchia .... 
 
 219. Bronchia and Blood-vessels of the Lungs - - - - - 577 
 
 220. Development of Lungs, after Rathke - 
 
 221. Arrangement of Capillaries in Human Lung - 
 
 222. Mammary Gland of Ornithorrhyncus, after Miiller - - 616 
 
 223. Exterior of lobule of liver of Squilla, after Miiller - - 619 
 
 224. Interior of do. do. do. 
 
 225. Inferior Surface of the Liver - - - 620 
 22G. Three Coats of the Gall Bladder ... - - 620 
 
 227. Gall bladder distended, with vessels injected - 
 
 228. Nucleated Cells of Parenchyma of Liver - 621 
 
 229. Lobules of Liver, with branches of Hepatic vein, after Kiernan - 622 
 
 230. Horizontal section of lobules, showing arrangement of their blood-vessels, after 
 
 Kiernan - - ..... 622 
 
 231. Horizontal section of lobules, showing arrangement of their bile-ducts, after 
 
 Kiernan ----- ... 622 
 
 232. Nucleated Cells forming Parenchyma of Liver, after Bowman - - 624 
 
 233. Origin of Liver in Chick, after Miiller - 
 
 234. Lobules in a state of Anemia, after Kiernan ... 625 
 
 235. Do. in first stage of hepatic- venous congestion, after Kiernan - - 625 
 
LIST OF WOOD-ENGRAVINGS. XXV11 
 
 PIG. PAGE 
 
 236. Lobules in second stage of hepatic-venous congestion, after Kiernan - - 625 
 
 237. Do. in a state of portal-venous congestion, after Kiernan - - 625 
 
 238. Hepatic cells loaded with Fat, after Bowman - 627 
 
 239. Right Kidney, with Renal Capsule - - 632 
 
 240. Section of Kidney after Wilson - 632 
 
 241. Half a Kidney, divided vertically - - - 633 
 
 242. Kidney divided vertically, with Arteries injected - - 633 
 
 243. Section of Kidney, after Wagner - - - 634 
 
 244. Portion of Tubuius Uriniferus, after Wagner - - - 634 
 
 245. Section of a Pyramid of Malpighi - 635 
 
 246. Magnified view of small portion of the Kidney, after Wagner - 636 
 
 247. Structure of Malpighian Body, after Bowman - - - . . 637 
 
 248. Diagram of Circulation in the Kidney, after Bowman - - " - - 637 
 
 249. Corpora Wolffiana, after Muller - - 637 
 
 250. Mammary Gland - * . - - 647 
 25.1. Vertical section of Mammary Gland - 647 
 
 252. Distribution of Milk-ducts in Mammary Gland, after Sir A. Cooper - - 648 
 
 253. Termination of portion of milk-duct in a cluster- of follicles, after Sir A. Cooper 648 
 
 254. Mammary follicles, with contained cells, after Lebert - - . 648 
 
 255. Lobule of Parotid Gland, after Wagner - - - 656 
 
 256. Capillary Network of Glandular follicles, after-Berres - - 656 
 
 257. Rudimentary Pancreas of Cod, after Muller .... . 656 
 
 258. The Testicle injected with Mercury - - - 658 
 
 259. Minute structure of the Testis - - . * - . - - 658 
 
 260. Human Testis, injected with Mercury, after Lauth - - - 659 
 
 261. Diagram of the structure of the same - - v - - 659 
 
 262. Sudoriferous Gland, after Wagner - - - - 661 
 
 263. Layer of Sweat-glands of the Axilla, after Todd and Bowman - - 662 
 
 264. Sweat-gland and its blood-vessels, after Todd and Bowman - - ^662 
 
 265. Cuticular portion of a Sweat-duct of the Heel, after Todd and Bowman - 662 
 
 266. Three views of Sebaceous glands and hair-follicles, after Todd and Bowman 664 
 
 267. Cutaneous glands of external Meatus Auditorius, after Wagner 665 
 
 268. Cutaneous follicles of the Axilla, after Homer - - 665 
 
 269. Gastric glands in Human Stomach, after Wagner ... 666 
 27Q. Horizontal section of a Stomach-cell and tubes, after Todd and Bowman - 666 
 
 271. Vertical sections of mucous membrane of Stomach, after Todd and Bowman - 667 
 
 272. Entrances to secreting follicles, after Boyd - 667 
 
 273. Stomach-cells and Epithelium, after Todd and Bowman - 667 
 
 274. Villi and follicles of Lieberkiihn on surface of Ileum - 668 
 
 275. One of the Glandulse solitaries of Peyer, after Boehm - : - 668 
 
 276. Mucous coat of Small Intestine, as altered in Fever, after Boehm - - 668 
 
 277. Glands of Peyer on Small Intestine - ... . 669 
 
 278. Conglomerate gland of Brunner, after Boehm - - 669 
 
 279. Patch of agminated Peyer ian glands, after Boehm .- - 670 
 
 280. Extremity of Placental Villus, after Goodsir - . 705 
 
 281. External membrane and cells of Placental villus, after Goodsir - - 705 
 
 282. Diagram of the arrangement of the Placental Decidua, after Goodsir - - 706 
 
 283. Plan of early Uterine Ovum, after Wagner - ... 715 
 
 284. Diagram of Ovum, showing formation of digestive cavity and of amnion, after 
 
 Wagner - ... . 715 
 
 285. Do. do. still more advanced, the allantois beginning to appear, after 
 
 Wagner - - - - - - 717 
 
 286. Diagram of Ovum in the second month, showing incipient formation of Pla- 
 
 centa, after Wagner - - - - - - - v 717 
 
 287. Section of Uterus, showing ovum, membranes, &c., at the time of formation of 
 
 Placeifta, after Wagner - - - - - - . - 718 
 
 288. Diagram illustrating the Fcetal Circulation - - - ,721 
 
 289. Curve representing the relative Viability of Human Male and Female at dif- 
 
 ferent ages, after Quetelet - - - 727 
 290 Do. do. do. Heights and Weights of the Human Male 
 
 and Female at different ages, after Quetelet - - - 728 
 
 ALSO, 
 Two Lithographic Plates, with 27 figures. 
 
INTRODUCTION.-' 
 
 THE object of the science of Physiology is to bring together, in a sys- 
 tematic form, the phenomena which normally present themselves during the 
 existence of living beings ; and to classify and compare these, in such a man- 
 ner as to deduce from them the general laws or principles, according to which 
 they take place. 
 
 The term Law having been frequently applied to physical and physiological 
 phenomena, in a manner very different from that which sound philosophy 
 sanctions, it is desirable to explain the acceptation (believed by the author to 
 be the only legitimate one) in which it is here employed. The so-called 
 Laws of Nature are nothing else than general expressions of the conditions, 
 under which certain assemblages of phenomena occur ; so far as those con- 
 ditions are known to us. Thus the law of Gravitation, in General Physics 
 (the' most universal in its action of any with which we are acquainted), is 
 nothing else than a simple expression of the fact, that, under all circum- 
 stances, two masses of matter will attract each other with forces directly pro- 
 portional to their respective bulks, and inversely as their distances. So, again, 
 the law of Cell-growth, which seems to hold the same rank in Physiology 
 with that of Gravitation in Physics, embodies these two general facts, that 
 all organised beings originate in cells, and that the various functions of life 
 are carried on, even in the adult condition, by the continued growth and de- 
 velopment of cells. 
 
 In no case can natural phenomena be correctly said to be governed by 
 laws ; since the laws themselves are nothing else than manifestations of the 
 Will of the governing Power. But they may be properly said to take place 
 according to certain laws ; these laws being framed by Man as expressions 
 or descriptions of the slight glimpses he possesses, of the plan according to 
 which the Creator sees fit to operate in the natural world. Thus understood, 
 the use of the term Law can be in no way supposed to imply, that the Deity 
 stands in any other relation to the phenomena of the Universe than as their 
 direct and constantly-operating Cause. 
 
 In order to determine the true laws, t r most general principles, of Phy- 
 siological Science, a very extensive comparison is requisite. Principles, which 
 might seem of paramount importance in regard to one group of living beings, 
 are often found, on a more general review, to be quite subordinate. For 
 example, the predominance of the Nervous System in the higher classes of 
 Animals, and its evidently close connection with many of the functions of 
 life, has led several Physiologists to the opinion, that its influence is essential 
 to the performance of the functions of Nutrition, Secretion, &c. ; but, on 
 turning our attention to the Vegetable kingdom, in which nothing analogous 
 to a nervous system can be proved to exist, we find these functions going on 
 with even greater activity than in animals. It is clear, therefore, they may 
 be performed without it ; and, on a closer examination of the phenomena 
 4 
 
38 INTRODUCTION. 
 
 presented by Animals, it is seen that these may be explained better, on the 
 principle that the nervous system has a powerful influence on such actions, 
 than on the idea that it affords a condition essential to them. Recent inquiries 
 have shown that the agents immediately concerned in these operations are of 
 the same nature in both kingdoms ; the separation of the nutrient materials 
 from the circulating fluids, or the elimination of substances which are to be 
 withdrawn from it, being performed in the animal, as in the plant, by ce//s, in 
 the manner to be explained hereafter. This is only one out of many in- 
 stances, which it would be easy to adduce, in proof of the necessity of bring- 
 ing together all the phenomena of the same kind, in whatever class of living 
 beings they may be presented, before we attempt to erect any general princi- 
 ples in Physiology. 
 
 The object of the present treatise, however, is not to follow out such an 
 investigation ; but to show the detailed application of the principles of which 
 Physiological science may now be said to consist, to the phenomena exhibited 
 by the Human being during the continuance of health or normal life. These 
 phenomena, when they occur in a disturbed or irregular manner, constitute 
 disease or abnormal life; and become the subjects of the science of Pathology. 
 It is impossible to draw a precise line of demarcation, between the states of 
 health and disease ; since many variations may occur, which do not pass the 
 limits of what must be called in some individuals the normal state, but which 
 must be regarded as decidedly abnormal actions in others. The sciences of 
 Physiology and Pathology, therefore, are very closely related to each other; 
 and neither can be pursued with the highest prospect of success, except in 
 connection with the other. 
 
 Equally close is the relation between Hygiene, or the art of preserving 
 the body in health, which is founded on the science of Physiology, and 
 Therapeutics, which is the art of curing disease, founded upon the science of 
 Pathology. In proportion as the science of Physiology is perfected, will the 
 simplicity and certainty of its practical applications increase ; and although 
 we may not anticipate a return of patriarchal longevity, yet the experience of 
 the last century has amply shown, that every general increase of attention to 
 its simple and universally-acknowledged truths is attended with a prolonga- 
 tion of life, and contributes to that not less important object, its emancipation 
 from disease. In like manner, with every advance in Pathological science, 
 will the art of Therapeutics lose its merely empirical character, and become 
 more and more rational; that is, the rules laid down for the treatment of 
 disease will be less and less founded upon the results of a limited experience 
 as to the efficacy of particular remedies in removing certain abnormal phe- 
 nomena ; and will have reference more and more to the nature of the morbid 
 action, which is indicated by the symptoms. Thus, when the urine presents 
 a particular sediment, our inquiries are directed, not so much to the condition 
 of the kidney itself, as to the constitutional state which causes an undue 
 amount of the substance in questio^ to be carried off by the urinary excre- 
 tion, or which prevents it from being (as usual) dissolved in the fluid. 
 
 In proportion as our treatment of disease thus loses its empirical character, 
 and is founded on scientific principles, must it increase in perfection and suc- 
 cess ; and in like proportion will the Medical Profession acquire that dignity 
 to which the nobility of its objects entitles it, and that general estimation 
 \vhich will result from the enlightened pursuit of them. 
 
39 
 
 CHAPTER I. 
 
 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 1. Distinction between Animals and Plants. 
 
 1. IN entering upon the general survey of the Animal Kingdom, which it 
 is desirable to take before we consider in detail any particular member of it, 
 the question naturally arises, how is the Animal distinguished from the 
 Vegetable ? There is no difficulty in replying to this, if we keep in view 
 merely the higher tribes of each division ; no one, for example, would be in 
 any danger of confounding a Whale with a Palm, or an Elephant with an 
 Oak. It is when we descend to the opposite extremity of the scale, that we 
 encounter the greatest difficulty ; from the circumstance that the distinguish- 
 ing characters of each kingdom disappear, one after another, until we are 
 reduced to those which seem common to both. So completely is this the 
 case, that there are many tribes which cannot, in the present state of our 
 knowledge, be referred with certainty to either one division or the other. We 
 are accustomed to think of Animals as beings, which not only grow and 
 reproduce themselves, but which also possess the power of spontaneously 
 moving from place to place, and which are conscious of impressions made 
 upon them : and we usually regard Plants as beings which are entirely des- 
 titute of sensibility and of the power of spontaneous motion, going through 
 all their processes of growth, reproduction and decay, alike unconscious of 
 pleasure and of pain, and devoid of all power of voluntarily changing their 
 condition. Such a definition is probably the most correct that we can employ ; 
 but great difficulties lie in the way of its application. There are many tribes 
 which possess a general structure more allied to that of beings known to be 
 Animals, than to that of any Plants ; and which yet present no decided indi- 
 cations, either of sensibility or of voluntary power. Such is the Sponge, 
 the fabric of which closely corresponds with that of many Alcyonian Polypes, 
 whose animality is undoubted; whilst there are no known Vegetables to 
 which it presents any near resemblance : and yet neither observation nor 
 experiment has ever succeeded in proving that the Sponge feels or spontane- 
 ously moves. On the other hand, many Vegetables perform evident move- 
 ments, which, at first sight, appear to be spontaneous, as if they indicated 
 sensibility on the part of the being that executes them. Such movements, 
 however, can in some instances (as in that of the Sensitive-Plant, or of the 
 Venus's Fly-trap), be referred to a sort of mechanism, the action of which 
 does not involve sensibility, and which may be compared with the many 
 movements (such as that of the heart) that are constantly taking place in the 
 bodies of the highest animals, without their consciousness ; and in other cases 
 (as in the Oscillatoriss) they are so rhythmical, as to impress the observer 
 with the idea that they are rather the result of some physical, than of any 
 mental, influence. In this respect they correspond with the motions of the 
 constantly-vibrating cilia; which cover the surface of the mucous membranes 
 of Animals ; and which have been recently detected in the reproductive par- 
 ticles of certain among the lower tribes of aquatic Plants. 
 
40 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 2. However difficult it may be for us, owing to our imperfect knowledge, 
 to draw the line in individual cases, it cannot be doubted that a boundary does 
 exist ; and, in general, a very simple mark will suffice to establish the dis- 
 tinction. This mark is the presence or absence of a Stomach, or internal 
 cavity for the reception of food. The possession of a stomach cannot be re- 
 garded, however, as in itself an essential distinction between the two kingdoms 
 (as some have represented it) ; for its presence is merely a result, so to speak, 
 of the nature of the food of Animals, and of the mode in which it is obtained. 
 Vegetables are dependent for their support, upon those materials only, which 
 they obtain from the surrounding elements ; carbonic acid, water and ammonia, 
 duly supplied to them, with a small quantity of certain mineral ingredients, 
 affording all the conditions they require for the production of the most mas- 
 sive fabrics, and the greatest variety of secretions. But these same elements, 
 if supplied to Animals, could not be converted by them into the materials of 
 organized structures; for they can only employ them as food, after they have 
 been united into certain peculiar organic compounds ; and Animals are con- 
 sequently dependent, either directly or indirectly, upon the Vegetable kingdom 
 for their means of support. Now they cannot incorporate any alimentary 
 substance into their own tissues, untilit has been reduced to the fluid form; 
 hence they need the means of effecting this reduction, which are supplied by 
 the stomach. Again, they cannot be always in immediate relation with their 
 food ; they have to go in search of it, and need a store-room in which it may 
 be deposited during the intervals ; this purpose also is supplied by the stomach. 
 It is evident, moreover, that the powers of voluntary locomotion and sensa- 
 tion, which Animals enjoy, are connected with the peculiar nature of the food 
 they require ; for if they were fixed in the ground, like Plants, they would 
 not be able to obtain that which they require for their support. It is true that 
 there are some, which seem almost rooted to one spot; but these have the 
 power of bringing their food within their reach, though they cannot go in 
 search of it. Such is the case with many Polypes, which use their outspread 
 tentacula for this purpose ; and with the lower Mollusca, which can create 
 currents by means of ciliary action. 
 
 3. A distinction might probably be erected, between the Animal and Vege- 
 table kingdoms, upon the mode in which the first development of the germ 
 takes place. The seed of the Plant, at the time of fertilisation, principally 
 consists of a store of nourishment prepared by the parent for the supply of 
 the germ, which is introduced into the midst of it. The same may be said of 
 the egg of the Animal. In both instances, the first development of the germ 
 is into a membranous expansion, which absorbs the alimentary materials with 
 which it is in contact; and it prepares these by assimilation, for the nourish- 
 ment of the embryonic structure, the most important parts of which the 
 only permanent parts in the higher classes of Animals and in Phanerogamic 
 Plants are in its centre. Now in Plants, this membranous expansion (the 
 single or double cotyledon) absorbs by its outer surface, which is applied to 
 the albumen of the seed, and takes it more or less completely into its own 
 substance. In Animals, this expansion is developed in such a manner, that 
 it surrounds the albumen, inclosing it in a sac, of which the inner surface 
 only is concerned in absorption. This sac is, then, the temporary stomach 
 of the embryonic structure ; it becomes the permanent stomach of the Radi- 
 ata ; but in the higher classes, only a portion of it is retained in the fabric of 
 the adult, the remainder being cast off, like the cotyledon of Plants, as soon 
 as it has performed its function. Thus, then, the first nisus of Animal de- 
 velopment is towards the formation of a stomach, for the internal reception 
 and digestion of food ; whilst the first processes of Vegetable evolution tend 
 to the production of a leaf-like membrane, which, like the permanent frond of 
 
GENERAL SUBDIVISIONS OF THE ANIMAL KINGDOM. 41 
 
 the lower classes of Plants, absorbs nourishment by its expanded surface 
 only. 
 
 4. Some Physiologists have asserted that the nature of the respiratory pro- 
 cess affords a ground of distinction between Animals and Plants; oxygen 
 being absorbed, and carbonic acid evolved, by the former, and a converse 
 change being effected in the surrounding air by the latter. It is not correct, 
 however, to designate this converse change as a consequence of the respiratory 
 process ; for in Plants, as in Animals, there is a continual absorption of oxygen 
 and evolution of carbonic acid, which constitute the true function of respira- 
 tion; but the effects of this change are masked (as it were), in Plants, by 
 those of the fixation of carbon from the atmosphere, which only takes place 
 under the influence of sun-light, and which is much more analogous to the 
 digestion of Animals. The most valid distinction, in doubtful cases, seems 
 likely to be founded on the chemical constitution of the tissues themselves. 
 In the plant, the whole of the organized structure, when freed from the pro- 
 ducts of secretion which are deposited in it, (many of these containing the 
 same proportion of nitrogen as exists in animal flesh,) is found to have the 
 same composition with starch ; being formed of oxygen, hydrogen, and car- 
 bon only. In the animal, on the other hand, the organised tissues all contain 
 azote -as part of their proper substance ; non-azotised compounds, such as 
 fatty matter, being merely deposited in these, as products of secretion. Hence 
 if the chemical composition of the organised tissues themselves can be cor- 
 rectly determined, the Vegetable or Animal nature of a doubtful body may be 
 ascertained. By this test, the long-disputed question of the nature of the 
 true Corallines has been set at rest ; their tissue, when freed from the lime de- 
 posited in it, being found to have the composition of that of Plants : and upon 
 evidence of the same kind, (the presence of starch in their interior,) a large 
 number of tribes, which have been described by Ehrenberg as Animalcules, 
 are now generally referred to the Vegetable kingdom. 
 
 2. General Subdivisions of the Animal Kingdom. 
 
 5. The animal kingdom was formerly divided into two primary groups, the 
 Vertebratedand. the Invertebrated ; the former comprising those which are dis- 
 tinguished by the possession of a jointed spinal column, consisting of a num- 
 ber of internal bones, termed vertebrae ; and the latter including all those ani- 
 mals which are destitute of this support. It was pointed out by Cuvier, 
 however, that among the Invertebrata there are three types of organization, 
 as distinct from each other as any of them are from the Vertebrate ; and he 
 accordingly distributed the whole under four primary divisions or sub-king- 
 doms : of these, the VERTEBRATA rank highest ; next, the ARTICULATA and 
 the MOLLTISCA, which may be said to form two parallel series, both of them 
 inferior in degree of organization to the Vertebrata, but superior to the lowest 
 group ; and lastly, the RADIATA, which include those animals that border most 
 closely, both in external aspect, and in general character, upon the Vegetable 
 kingdom. The members of these groups are readily separated from each 
 other by the structure of their skeletons, or organs of support and protection ; 
 as well as by many other characters. In the Vertebrata, the skeleton consists 
 of a number of internal jointed bones, which are clothed by the muscles that 
 are attached to them and move them ; these bones are traversed by blood- 
 vessels, and are to be regarded as in all respects analogous to the other living 
 tissues of the body. In the Articulata, the soft parts are supported by a hard 
 external envelope, which is of corresponding form on the two sides of the 
 median line, and which is divided into several pieces, jointed or articulated 
 together by a membrane, in such a manner as still to allow of free motion ; 
 
 4* 
 
42 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 and the muscles, which are numerous and complex, are attached to the inte- 
 rior of these. In the Mollusca, the whole body is quite soft ; and many spe- 
 cies exist, in which it has no external protection ; in a large proportion of the 
 group, however, the surface has the power of producing shelly matter, so as 
 to form a protective habitation, within which the animal can withdraw its 
 body, but which does not exhibit any very definite type of form. In the 
 Radiata, all the parts are arranged in a circular manner, the mouth being in 
 the centre; some of them are protected by firmly-jointed external skeletons, 
 like those of the Articulata ; whilst others deposit calcareous matter in the cen- 
 tre of their soft fleshy structures, as if sketching out the internal skeleton of 
 the Vertebrata. The skeletons of most of the Invertebrata differ, however, 
 from those of Vertebrate animals, in this important character, that they are 
 not permeated by vessels, and are formed only by superficial deposition. 
 Hence they are termed extra-vascular : and it is an obvious result of an ar- 
 rangement of this kind, that parts once formed are never changed, except by 
 the ordinary processes of decay, and that they can only be extended by addi- 
 tion to their exterior ; whilst in Vertebrata, the bones are subject to alterations 
 of any kind, whether of removal or addition, throughout their entire substance. 
 It is not correct to regard them, however, as mere exudations, or as being des- 
 titute of vitality ; since they consist, in all instances, of a regularly-organized 
 tissue, in which the mineral matter, where such exists, is deposited ; and in 
 several cases they are traversed by tubes, which seem to convey a fluid de- 
 stined for their nutrition, if not actual blood. Fabrics of this kind are on the 
 same footing with the dentine and enamel of the teeth of Vertebrata ( 209, 
 210); to which they sometimes bear a very strong resemblance. A more 
 detailed account of the general structure of these sub-kingdoms will now be 
 given, beginning with the lowest. 
 
 3. General characters of Radiata. 
 
 6. The RADIATA possess many points of affinity with the Vegetable king- 
 dom ; and of these, the circular arrangement of their parts is one of the most 
 evident. Many species of Sea-Anemone, for instance, present an appearance 
 so much resembling that of various composite blossoms, as to have been com- 
 monly termed Animal-flowers, a designation to which they further seem 
 entitled, from the small amount of sensibility they manifest, and the evident 
 influence of light upon their opening and closing. But it is in the tendency to 
 the production of compound fabrics, each containing a number of individu- 
 als, w r hich have the power of existing independently, but which are to a cer- 
 tain degree connected with one another, that we recognise the greatest aifinity 
 in structure, between this group and the Vegetable kingdom. Every tree is 
 made up of a large number of buds, which are composed of leaves arranged 
 round a common axis ; each bud has the power of preserving its own life, 
 and of reproducing the original structure, when removed from the parent stem, 
 if placed in circumstances favourable to its growth ; and yet all are connected 
 in the growing tree, by a system of vessels, which forms a communication 
 between them. This is precisely the nature of the structures formed by the 
 animals of that class, which may be regarded as the most characteristic of the 
 Radiate group. Every mass of Coral is the skeleton of a compound animal, 
 consisting of a number of polypes, connected together by a soft flesh, in which 
 vessels are channelled out ; these polypes are capable of existing separately, 
 since each one, when removed from the rest, can in time produce a massive 
 compound fabric, like that of its parent ; but they all contribute to the main- 
 tenance of the composite structure, so long as they are in connection with it. 
 In some instances the skeleton is stony, and is formed by the deposition of 
 
GENERAL CHARACTERS OF RADIATA. 
 
 43 
 
 calcareous matter either in the centre of each fleshy column, so as to form a 
 solid stem, or on its exterior, so as to form a tube. In other cases it is horny ; 
 and then it may be a flexible axis, or a delicate tube. Both the stony and 
 horny Corals frequently possess the form of plants or trees: and as their 
 skeletons are often found with no obvious traces of the animals to which they 
 belonged, they have been accounted Vegetable growths. There is not the 
 least doubt, however, as to the Animal origin of the greater part of these plant- 
 like structures. 
 
 7. The affinity between the lowest Radiata and Plants, in regard to the 
 vital phenomena they exhibit, is still more close than that manifested by their 
 structure. Although, in the higher groups, movements may be constantly 
 witnessed, which evidently indicate consciousness and voluntary power, this 
 is far from being the case in the lower. There are many tribes, whose recep- 
 tion of food, growth, and reproduction, are not known to be accompanied by 
 any phenomena which distinctly indicate their animal character. The most 
 violent lacerations produce no signs of sensibility ; and the movements occa- 
 sionally exhibited by them have not so much of a spontaneous aspect as 
 those which are performed by many plants. This is the case, for example, 
 with the Sponge tribe ; and also with a number of microscopic species. So 
 
 Fig. 1. 
 
 Asterias aurantiaca, with the upper side of the hard envelope removed ; a, central stomach ; b, coeca 
 upon its upper surface, probably answering to the liver; c,c, coecal prolongations of stomach into ray a; 
 c', c', the same empty ; rf, the same opened ; e, under surface, showing vesicles of feet ;/, vesicles con- 
 tracted, showing skeleton between them. 
 
44 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 doubtful is the nature of these beings, that their Animal or Vegetable charac- 
 ter is rather to be decided by their affinity with species known to belong to 
 one or the other kingdom, and by the chemical composition of their tissues, 
 than in any other way. 
 
 8. It is very different, however, in regard to the higher Radiata. Even 
 among the Zoophytes (as the plant-like animals just alluded to are com- 
 monly termed), there are some species which are unattached during the 
 whole period of their lives, and which have a power of voluntarily moving 
 from place to place, such as is never possessed by plants. And in the high- 
 est class, the Echinodermata, including the Star-fish, Sea Urchin, &c., we 
 meet with a considerable degree of complexity of structure, and a correspond- 
 ing variety of actions. Still, except in those species which connect this group 
 with others, the same character of radial or circular symmetry is maintained 
 throughout ; and in no animal is it more remarkable than in the common Star- 
 fish. It is exhibited alike in its internal conformation and in its external 
 aspect. The mouth, placed in the centre of the disk, leads to a stomach 
 which occupies the greatest part of the cavity of the body ; and this sends 
 prolongations into the arms, which are exactly alike in form, and which oc- 
 cupy a precisely similar position in every one. Each arm is furnished, on its 
 under side, with a curious apparatus for locomotion, consisting of a series of 
 short elastic tubes, which are prolonged through apertures in the hard enve- 
 lope, from a series of vesicles placed along the floor (as it may be termed) of 
 the ray. The system of vessels for absorbing nutriment and conveying it 
 through the system, is also disposed upon the same plan; and the same may 
 be said of the nervous system, and of the only organs of special sensation 
 which this animal appears to possess the rudimentary eyes, of which 'one is 
 found at the extremity of each ray. 
 
 9. Amongst other results of the repetition of similar organs, so remarkable 
 in the Radiated group, is this, that one or more of them may be removed with- 
 out permanent injury to the whole structure, and may even develope them- 
 selves into an entire fabric. Thus in the Star-fish, instances are known of the 
 loss of one, two, three, and even four rays, which have been gradually repro- 
 duced ; the whole process appearing to be attended with little inconvenience 
 to the animal. In some species of isolated Polypifera, such as the common 
 Sea- Anemone, and Hydra (Fresh-water Polype), this power of reproduction 
 is much greater. The Hydra may be cut into a large number of pieces (it is 
 said as many as 40) of which every one shall be capable of developing itself 
 in time into a perfect polype. The Sea-Anemone, when divided either trans- 
 versely or vertically, still lives ; and each half produces the other, so as to re- 
 form the perfect animal. This is another character which shows the affinity 
 of the Radiata to the Vegetable kingdom ; and there is yet another, derived 
 from their mode of reproduction. In many Polypifera, we observe a propa- 
 gation by buds, in all respects conformable to that which plants effect, and 
 quite different from the regular multiplication by distinct germs. This gem- 
 miparous reproduction, as it is called, takes place, not only in the compound 
 Polypifera, whose plant-like structures are extended by it, but also in some 
 isolated -species, such as the Hydra ; from the body of which one or more young 
 polypes bud forth at the same time ; and these buds may themselves put forth 
 another generation, previously to their separation from their parent. This 
 kind of reproduction is not seen anywhere else in the whole Animal kingdom, 
 except in a few of the lowest Mollusca and Articulata, which border most 
 closely on the Radiata. 
 
 10. In the lowest animals of this group, such as the simplest forms of Po- 
 lypes, we find the whole body to consist of nothing else than a stomach, fur- 
 
GENERAL CHARACTERS OF MOLLUSCA. 45 
 
 nished with tentacula for drawing food to its orifice.* The nutrient materials 
 are imbibed by the walls of the stomach, and are transmitted by them to the 
 tentacula, without any regular circulation ; and the exposure of the whole of 
 the soft surface of the body to the surrounding liquid, affords all the aeration 
 which is requisite. In the Medusae, or Jelly-fish, we often find the stomach 
 extending itself into a ramified system of tubes, which convey its consents to 
 the thin border of the umbrella-shaped disk, for more effectual aeration ; but 
 there is still no separate circulating system, except in a few instances. In the 
 class of Echinodermata, however, which includes the highest forms of Ra- 
 diated animals (such as the Asterias or Star-fish, Echinus or Sea-Urchin, and 
 Holothuria or Sea-Cucumber), we find the digestive cavity restricted within 
 much narrower limits ; and there is here a distinct system of vessels, adapted 
 to absorb the nutrient fluid from the digestive cavity, and to convey it to the 
 remoter parts of the system for their nutrition, as well as to effect its aeration, 
 by exposing it to the influence of the air contained in the surrounding liquid, 
 in organs especially adapted for that purpose. 
 
 4. General characters of Mollusca. 
 
 11. The range of Animal forms comprehended in the Sub-Kingdom MOL- 
 LUSCA is so great, that it would be difficult to include them in any positive 
 definition which should be applicable to all. They present few traces of the 
 circular disposition of organs around the mouth, which is characteristic of the 
 Radiated classes ; and we seldom meet with any marked approach to the 
 elongation of the body, still seldomer with any indication of that division 
 into segments, which are the chief peculiarities of the Articulata. It is by 
 the absence of these, and of any trace of the Vertebrated structure, that the 
 Mollusca are most readily defined. The variety of form which they present, 
 is less surprising, when it is considered that the bulk of their bodies is almost 
 entirely made up by organs of nutrition ; the organs of sensation and locomo- 
 tion, which they possess, being chiefly subservient to the supply of these. 
 We find, in the lowest tribes of this group, living beings which are fixed to 
 one spot during all but the earliest period of their lives ; and which scarcely 
 possess within themselves so much power of movement, as that enjoyed by 
 the individual Polypes in a compound polypidom ; and yet these exhibit a 
 complex and powerful digestive apparatus, a regular circulation of blood, and 
 an active respiration. We never find, throughout the whole Animal kingdom, 
 that the apparatus of organic life is arranged on any definite plan of its own ; 
 its confirmation being adapted to the type which predominates in the struc- 
 ture of each group, and which is principally manifested in the disposition of 
 the locomotive organs. Thus, the stomach of the Star-fish is circular, and 
 sends a prolongation into each ray ; whilst the digestive cavity of the Articu- 
 lata is prolonged into a tube. In the Mollusca, there is no such definite 
 type, the apparatus of nutrition having the predominance over that of loco- 
 motion ; and the form of the body is, therefore, extremely variable. The re- 
 lative places, even of the most important organs (such as the gills), are found 
 to undergo complete changes, as we pass from one tribe to another ; although 
 their general structure is but little altered. 
 
 12. The lower Mollusca may be characterised as consisting merely of a 
 
 * It is usual to speak of the orifice of the stomach, in the Polypes, as the mouth ; and to 
 regard the tentacula as prolonged lips. It appears to the author much more reasonable, how- 
 ever, to consider this aperture as the cardiac orifice of the stomach ; and to regard the tenta- 
 cula in the light of pharyngeal constrictors, their office being to grasp the food and convey it 
 to the stomach. This view is borne out by the conformation of the superadded parts in the 
 Ciliobrachiate Polypes and Ascidian Molluscs. 
 
46 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 bag of viscera ; they have not even any prominence for the mouth, nor any 
 organs of special sense, such as would distinguish a head; and they are 
 entirely Destitute of symmetry, the radiated arrangements of parts seen in 
 Zoophytes being absent, as well as the bi-lateral correspondence which is 
 characteristic of the higher sub-kingdoms. In the more elevated Mollusca, 
 however, which possess not merely sensitive tentacula, but eyes and even or- 
 gans of smell and hearing, we find these disposed in a symmetrical manner ; 
 so that the head, which is the part concerned peculiarly in animal life, does 
 present a bi-lateral equality of parts, even when the remainder of the body 
 wants it. Further, in the more active among the higher classes, we find this 
 bi-lateral symmetry showing itself in the exterior of the whole body ; evi- 
 dently bearing a pretty close relation to its degree of locomotive power. It 
 is most evident and complete in the Cephalopoda (Cuttle-fish tribe); many 
 of which are adapted to lead the life of Fishes, and resemble them in the 
 general form of the body, as also in the structure of many of the individual 
 organs. It is also manifested in many of the shell-less Gasteropoda, such as 
 the Slug, or the Jjplysia (Sea-Hare) ; as will be seen by the accompanying 
 representation of a species of the latter. But this symmetry does not extend 
 
 Fig. 2. 
 
 Aplysia depilans; a, branchisB or gills. 
 
 to the arrangement of the internal organs ; and appears to be only designed to 
 adapt the body for more convenient locomotion. 
 
 13. As a group, however, the Mollusca are to be characterised rather by 
 the absence, than by the possession, of any definite form; and there is a 
 corresponding absence of any regular organs of support, by which such a 
 form could be maintained. The name they have received designates them 
 as soft animals ; and this they are pre-eminently, as every one knows, who 
 has taken a Slug between his fingers. The shell, where it exists, is to be 
 regarded rather in the light of an appendage, designed for the mere protec- 
 tion of the body, and deriving its shape from the latter, than as a skeleton, 
 giving attachment to muscles, and regulating the form of the whole structure. 
 It is in no instance a fixed point for the muscles of locomotion ; and it is only, 
 indeed, where the body is uncovered by a shell, or where a locomotive organ 
 may be projected beyond it, that any active movements can be executed. 
 This locomotive organ, ihefoot, as it is commonly termed is nothing else 
 than a fleshy mass, formed by the increased development of the muscular 
 portion of one part of the general envelope of the body, termed the mantle, 
 in which the visceral mass is loosely included. The inantle, is not essen- 
 tially different from the skin of other animals ; but it is usually thicker, pos- 
 sessing a considerable amount of muscular fibre interwoven with it, and its 
 
GENERAL CHARACTERS OF MOLLUSCA. 
 
 47 
 
 surface having frequently a glandular character. This general muscular 
 envelope is the only locomotive organ possessed by a large portion of the 
 Mollusca ; but its contractile properties are usually greatest at some particular 
 spot, where it is thickened into a sort of disk, by the alternate contraction 
 and extension of which the animal can slowly propel itself; this is well seen, 
 by causing a Snail or Slug to crawl over a piece of glass, so that the under 
 surface of the disk may be seen whilst it is in operation. The general cha- 
 racter of their locomotion, however, is well expressed by the term sluggish; 
 and there are scarcely any among the typical Mollusca, whose activity is such 
 as to demand for them any higher appellation. 
 
 14. The general development of their organs of Nutrition, however, is 
 
 Fig. 3. 
 
 Aplysia cut open, showing the viscera ; a, the upper part of oesophagus ; 6, penis ; c, c, salivary glands ', 
 dj superior or cephalic ganglion ; e, e, inferior or subresophageal ganglia; f, termination of oasophagus ; 
 .-, g, first stomach ; A, third stomach ; i, second stomach ; &, intestine ; I, I, I, liver ; m, posterior ganglion ; 
 n, aorta; o, hepatic artery; p, ventricle of heart; ?, auricle; r, a, branchiae ; t, testia; w, lower part of 
 intestine 5 v, ovary ; tc, anus. 
 
48 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 much higher than is met with among the Articulata ; and, in proportion to 
 that of the organs of Locomotion, it is much greater than will be elsewhere 
 observed throughout the Animal kingdom. The justice of this statement will 
 be made evident by a slight examination of the preceding figure, in which 
 the interior structure of the rfplysia, showing the general character of that 
 of the group, is displayed. The only distinct set of muscles, possessed by 
 this animal, is that connected with the mouth ; which it is able to push for- 
 wards or to draw back, and which possesses considerable powers of mastica- 
 tion, and is furnished with large salivary glands. The nervous centres (of 
 which more will be said hereafter) are seen to be principally disposed around 
 the oesophagus. The whole digestive apparatus is observed to be very com- 
 plex and highly developed ; the liver alone occupying a considerable part of 
 the cavity. The heart has distinct muscular walls, and is divided into a 
 separate auricle and ventricle ; and a large respiratory organ is developed for 
 the aeration of the blood. The position of the gills, which are external to 
 the cavity, but which are concealed in part by a fold of the mantle, and in 
 part by the rudimentary shell, is seen at a, Fig. 2. The generative apparatus, 
 also, is highly developed. Yet with all this complex organization, the loco- 
 motive power of the animal is not much greater than that of the Slug; no 
 other means being provided for the purpose than the contractility of the gene- 
 ral envelope, which is greatest in the thickened portion on the under side of 
 the body. 
 
 15. The blood of the Mollusca is white, and the number of corpuscles in 
 it is small. Their temperature is low, being seldom more than one or two 
 degrees above that of the surrounding medium ; but many of them are capa- 
 ble of being subjected to extreme variations of heat and cold, without their 
 vitality being thereby destroyed. Their respiration is for the most part aquatic ; 
 and is performed by means of gills, over which a current of water is con- 
 stantly being propelled, by the vibration of the cilia that cover their surface. 
 Many of them are dependent on the same current for their supplies of food ; 
 part of the water so introduced being taken into the stomach ; and a part 
 flowing over the respiratory surface. The higher tribes, however, go in 
 search of their food, and have instruments of mastication for reducing it; but 
 in these, as in the former, the anal orifice of the intestine opens into the 
 passage through which the current that has passed over the respiratory organs 
 finds egress ; so that the faecal matter from the former, and the fluid that has 
 served the purpose of the latter, are discharged together. Although very 
 voracious when supplies of food come in their way, most of the Mollusca are 
 capable of fasting for long intervals, where none offer themselves, a fact 
 which is readily explained by that general inertness of their vital processes, 
 which has been stated to be characteristic of the group. 
 
 5. General characters of Articulata. 
 
 16. The members of the sub-kingdom, ARTICULATA, are distinguished, for 
 the most part, by characters which are exactly opposed to those just enume- 
 rated. Their characteristic form is easily defined ; and in no instance is there 
 any wide departure from it. The body is more or less elongated, and presents 
 throughout a most exact bi-lateral symmetry. It is completely inclosed in an 
 integument of greater density than the rest of the structure, which is divided 
 into distinct rings or segments ; these, being held together by a flexible mem- 
 brane, allow considerable freedom of motion, whilst they firmly protect the 
 soft parts, and afford attachment to numerous muscles. It is in the Centipede, 
 and other such animals, that this division into segments is most distinctly and 
 regularly marked. In the lower Articulata, such as the Leech and the Earth- 
 
GENERAL CHARACTERS OF ARTICULATA. 49 
 
 worm, the integument is altogether so soft, that the intervals of the articulations 
 are not very distinct from the rings themselves ; and in the highest Crusta- 
 cea and Arachnida, the segments are so closely united together, as to be in 
 some instances scarcely recognizable. In the former, the movements of the 
 body are entirely effected by its own flexion ; whilst in the latter, they are 
 committed to members developed for that special purpose. These members 
 also have an articulated external skeleton. The bulk of the body in the Ar- 
 ticulata is made up of the muscles, by which the several segments and theyr 
 various appendages are put in motion ; these muscles have their fixed points 
 on the interior of the hard envelope, just as they are attached in Vertebrated 
 animals to the exterior of the bones ; and they form a system of great com- 
 plexity. 
 
 17. The development of the organs of nutrition in Articulata, would seem 
 to be altogether subservient to that of the Locomotive apparatus, their func- 
 tion being chiefly to supply the nerves and muscles with the aliment necessary 
 to maintain their vigour. The power of the muscles is so great in proportion 
 to the size of the animals, that in energy and rapidity of movement, some of 
 the Articulated tribes surpass all other beings. Their movements are directed 
 by organs of sensation, which, although not developed on so high a plan as 
 those of some Mollusca, are evidently very acute in their powers. There are 
 very few instances of Articulated animals being in any way restrained as to 
 freedom of locomotion ; and these are found in a single group, the Cirrhopoda 
 or Barnacle tribe, which connects this sub-kingdom with the last. In general, 
 they roam freely abroad in search of food, and are supplied with prehensile 
 organs for capturing their prey, and with a complex masticating apparatus for 
 reducing it. Their actions are evidently directed almost solely by instinctive 
 propensities, which are adapted to meet every ordinary contingency, being of 
 similar character in each individual of the same species, and presenting but 
 little appearance of ever being modified by intelligence. Hence these animals 
 seem like machines, contrived to execute a certain set of operations ; many of 
 them producing immediate results, which even Man, by the highest efforts of 
 his reason, has found it difficult to attain. 
 
 18. All the Articulata, save a few of the very lowest species, possess a 
 distinct head at one end of the body, furnished with organs of special sensa- 
 tion, and with lateral jaws for the prehension and reduction of food ; and their 
 movements, being principally guided by the special senses, take place in this 
 direction. The bi-laterai symmetry of the body is not confined to its exte- 
 rior ; for it prevails most completely in the whole muscular apparatus ; and 
 even the organs of nutrition present more distinct traces of it than are to be 
 seen elsewhere. The compact heart of the Mollusca, for instance, is here 
 replaced by a long tube, the dorsal vessel, placed on the median line ; and the 
 respiratory organs, which are usually diffused through the whole system, are 
 uniform on the two sides. Even the intestinal canal partakes of this symme- 
 try ; in some species it runs straight from end to end of the body ; and even 
 where it is otherwise disposed, its appendages are nearly equal on the two 
 sides. The respiration of this group is for the most part aerial ; and the ap- 
 paratus for the purpose consists of a series of chambers or tubes, which are 
 dispersed or extended through the whole body, and which are expanded at 
 certain points, in insects possessing considerable powers of flight, into large 
 air-sacs. By this means, the air, the blood, and the tissue to be nourished, 
 are all brought into contact at the same points ; and a much less vigorous cir- 
 culation is required than would otherwise be needed ; whilst, at the same 
 time, the specific gravity of the body is diminished, and flight thereby rendered 
 more easy. The whole apparatus of nutrition is comprised within a compa- 
 ratively small part of the body ; and the bulk of the organs which compose 
 
 o 
 
50 OX THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 it, is never at all comparable with that which we ordinarily find in the Mol- 
 lusca. Thus, the liver, which in the Oyster forms a large part of the whole 
 substance, is often scarcely recognizable as such in the Insect; and the intes- 
 tinal tube seldom makes many convolutions in its course from one extremity 
 to the other. The blood is usually white, as in the other Invertebrated classes : 
 but it contains a larger number of corpuscles than are seen in that of most of 
 the Mollusca. The temperature varies to a certain degree with that of the 
 atmosphere ; but many Insects have the power of generating a large amount of 
 independent heat, which is strictly proportionable to the quantity of oxygen 
 converted by them into carbonic acid in the respiratory process. All the ac- 
 tions of the Articulata are performed with great energy ; and, at the time of 
 the most rapid increase of the body, the demand for food is so great, that a 
 short suspension of the supply of aliment is fatal. Many of them are capa- 
 ble, however, of being submitted to the influence of very extreme temperatures, 
 with little permanent injury. 
 
 19. The adjoining figure, which displays the muscular apparatus of the 
 interior of the body of a Cock-chafer, will give an idea of its complexity and 
 variety, and of the large portion of the trunk which is occupied by it ; and 
 will also show the division of the skeleton into segments, the number of 
 which in Insects is limited to thirteen. These are nearly equal and similar 
 to each other in the Larva ; but, in the perfect Insect, the three behind the 
 head are united into the thorax, to which the legs and wings are attached; 
 and the remainder form the abdomen, which has little concern in locomotion. 
 
 Section of the trunk of Melolontha vulgaris, (after Strauss-Durckheim.) showing the complexity of the 
 Muscular system. The first segment of the thorax (2) is chiefly occupied by the muscles of the head, 
 and by those of the first pair of legs The second and third segments (3 and 4) contain the very large 
 muscles of the wings, and those of the other two pairs of legs. The chief muscles of ihe abdomen ara 
 the long dorsal and abdominal recti, which move the several segments one upon the other. 
 
 6. General characters of Vertebrata. 
 
 20. In none of the three preceding divisions of the Animal kingdom, does 
 the Nervous System attain such a degree of development, as to give it that 
 predominance in the whole fabric which it evidently possesses in VERTE- 
 BRATA. In the Radiata and Mollusca, its functions are obviously restricted to 
 the maintenance of the nutritive operations ; and to the guidance of the ani- 
 mal, by means of its sensory endowments, in the choice of food, as well as 
 (in some instances) in the search for an individual of the opposite sex: in the 
 
GENERAL CHARACTERS OF VERTEBRATA. 51 
 
 Articulata, its purpose appears similar, but is carried into effect in a different 
 manner, the locomotive organs being the parts chiefly supplied by it. In the 
 Vertebrata, on the other hand, the development of all the other organs appears 
 to be subordinate to that of the Nervous System ; their object being solely to 
 give to it the means of the exercise of its powers. This statement is not, of 
 course, as applicable to the lower Vertebrata, as it is to the higher ; but it is 
 intended to express the general character of the group. The predominance 
 of the nervous system is manifested, not only in the increased size of its cen- 
 tres, but also in the special provision which we here find, for the protection 
 of these from injury. In the Invertebrated classes, wherever the nervous sys- 
 tem is inclosed in any protective envelope, that envelope serves equally for 
 the protection of the whole body. This is the case, for example, in regard 
 to the spiny integument of the Star-fish, the shell of the Mollusca, and the 
 firm jointed rings of the Insect. The only exceptions occur in a few tribes, 
 in which the nervous system is much concentrated ; and in which the general 
 organization approaches that of the Vertebrata.* In Vertebrated animals, we 
 find that the skeleton essentially consists of a series of parts, which are de- 
 stined to inclose the nervous centres, and to give attachment on their exterior 
 to the muscles by which the body is moved ; hence it may be termed the 
 neuro-skeleton ; in contradistinction to the dermo- skeleton, which envelopes 
 the whole body in many Invertebrata, being formed on the basis of their in- 
 tegument. The tissues, bone and cartilage, of which the former is composed, 
 are more closely connected with the vascular system, than are the hard parts 
 of Invertebrata ; and are consequently more capable of undergoing interstitial 
 change. 
 
 21. In considering the essential character of the skeleton of Vertebrata, we 
 should look at its simplest forms, those in which it has the least number of 
 superadded parts. We find these in the Serpent tribe, among Reptiles, and 
 in the Eel and its allies among Fish. If we examine their skeletons, we per- 
 ceive that the Spinal Column, with the Cranium at its anterior extremity, 
 constitutes the essential part of the verteb rated frame-work ; and that the de- 
 velopment of members is secondary to this. The Spinal Column usually 
 consists of a number of distinct bones, the Vertebrae ; each of which is per- 
 forated by a large aperture, in such a manner that, when the whole is united, 
 a continuous tube is formed for the lodgment of the spinal cord. The Cra- 
 nium, which it bears at its upper end, is in reality formed of the same elements 
 as the vertebrae, instead of differing from them completely in structure, as we 
 might be led to suppose by examination of its most developed forms only. 
 The object of this enlargement is to inclose the brain, or mass of cephalic 
 ganglia, which attains a greatly-increased size in the Vertebrata; and also to 
 afford support and protection to the organs of special sense, which are far 
 more highly developed among them than they are in the lower classes. The 
 true nature of the cranium is best seen in those animals, in which the brain 
 bears but a small proportion to the spinal cord, such as the lower Reptiles 
 and Fishes ; and an examination of its structure in these satisfactorily proves 
 the reality of this view, which is further borne out by the history of its de- 
 velopment, and of that of its contained parts, in the higher Vertebrata. 
 
 22. The Vertebral column at its opposite extremity, is usually contracted 
 instead of being dilated, forming a tail, or a rudiment of one, from which 
 the nervous centres are entirely withdrawn ; the development of the tail is 
 
 * Thus, in the highest Crustacea, there is an -internal projection from the shell, on each 
 side of the median line, which forms a sort of arch inclosing the ventral cord ; and in the 
 naked Cephalopoda, the nervous centres are supported, and in part protected, by cartilagi- 
 nous plates, which are evidently the rudiments of the internal skeleton of the Vertebrata. 
 
52 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 commonly seen to be in an inverse proportion to that of the cranium. To 
 this column, the ribs and extremities are merely appendages, which we find 
 more or less developed in the various tribes, and often entirely absent ; whilst 
 t.he vertebral column is never wanting, although reduced in some species to a 
 very rudimentary state. It is interesting to compare its various conditions, 
 with those which have been noticed in the external skeleton of the Articulata. 
 In the lowest animals of the group, locomotion is principally or even entirely 
 performed by flexion of the body itself; and here, as in the worm tribe, we 
 find the skeleton extremely flexible, the whole being comparatively soft, and 
 its divisions indistinct. This is the case, for example, in the Lamprey and 
 other Cyclostome fishes : in which there is no distinct division into vertebrae, 
 the spinal column scarcely possessing even the density of cartilage. In pro- 
 portion, however, as distinct members are developed, and the power of loco- 
 motion is committed to them, we find the firmness of the spinal column in- 
 creasing, and its flexibility diminishing ; and in Birds, in which, as in In- 
 sects, the movements of the body through the air are effected by muscles that 
 must have very firm points of support, the vertebral column is much conso- 
 lidated by the union of its different parts, so as to form a solid frame-work. 
 A.S a general rule, then, the mobility of the extremities, and the firmness of 
 the vertebral column, vary in a like proportion. The number of these ex- 
 tremities in Vertebrata never exceeds four ; and two of them are not unfre- 
 quently absent. The power of locomotion is not developed to nearly the 
 same proportional extent, as in the Articulata ; the swiftest bird, for example, 
 not passing through nearly so many times its own length in the same period, 
 as a large proportion of the Insect tribes : but it is far greater than that, which 
 is characteristic of the Mollusca ; and there is no species that is fixed to one 
 spot, without the power of changing its place. On the other hand, the high- 
 est Mollusca approach them very nearly in the development of organs of spe- 
 cial sense, of which Vertebrata almost invariably possess all four kinds sight, 
 hearing, smell, and taste. 
 
 23. The perfection of the Articulate structure has been shown to consist 
 in the development of those powers which enable the animal to perform 
 actions denoting the highest instinctive faculties. That of the Vertebrata 
 evidently tends to remove the animal from the dominion of undiscerning, 
 uncontrollable, instinct; and to place all its operations under the dominion of 
 an intelligent will. We no longer witness in these operations that uniformity, 
 which has been mentioned as so remarkable a characteristic of instinctive 
 actions. There is evidently, among the higher Vertebrata especially, a power 
 of choice and of determination, guided by a perception of the nature of the 
 object to be attained, and of the means to be employed, constituting the 
 simplest form of the reasoning faculty ; and the amount of this bears so close 
 a relation with the development of the cerebrum, that it is scarcely possible to 
 regard the two as unconnected. In Man, whose cerebrum is far larger in pro- 
 portion to his size, as well as more complex in its structure, than that of any other 
 animal, the reasoning faculties attain the highest perfection that we know to 
 be anywhere manifested by them in connection with a material instrument ; 
 the instinctive propensities are placed under their subjection; and all his acts, 
 excepting those immediately required for the maintenance of his organic func- 
 tions, are put under their control. It is to Man, therefore, that what was just 
 now stated, of the predominance of the nervous system in Vertebrata, parti- 
 cularly applies ; but the same may be noticed, though in a less striking degree, 
 throughout the group. Not only is -the influence of the nervous system to be 
 traced, in the sensible movements which they perform ; but also in various 
 modifications of the organic functions, which take place under the influence 
 of particular states of mind, and the occurrence of which there is no reason 
 
GENERAL CHARACTERS OF VERTEBRATA. 53 
 
 to suspect in the lower tribes of animals. These are even much more strik- 
 ing in Man, than in the lower Vertebrata; indeed the comparative slightness 
 of the influence of the mind upon the body, is one of the causes which ren- 
 der the lower Mammalia more able than Man is to recover from the effects 
 of severe injuries. The Mollusca seem to grow like plants ; their massive 
 organs increasing by their own separate vitality, and being but little depend- 
 ent upon each other. Even the act of respiration, which is in most animals 
 performed by a series of distinct muscular contractions, is there principally 
 effected through the medium of the cilia which clothe the respiratory surface. 
 But in the Vertebrata, the nervous system possesses a distinct and independ- 
 ent rank ; its offices are those which more particularly constitute the active 
 life of the animal ; the organic functions have for their chief object, the main- 
 tenance of the nervous and muscular apparatus in the condition requisite for 
 their activity ; and in consequence, all these different kinds of apparatus are 
 so interwoven together, that their mutual dependence is very close. 
 
 24. The foregoing remarks will be found to have an important bearing on 
 the details subsequently to be given respecting the functions of the Nervous 
 system in Man ; and it is desirable to set out with clear ideas on this subject, 
 since there is no department of Physiology, regarding which more error is 
 prevalent. There is no valid reason for believing that the Organic functions 
 in Animals, any more than the corresponding changes in Plants, are depend- 
 ent on the nervous system for their performance ; but common observation 
 shows, that they are much influenced by it in the higher animals ; and from 
 such a comparison as that which has been just now briefly made, it would 
 appear that, the higher the general development of the nervous system, the 
 closer is their relation with it. 
 
 25. This general character of the Vertebrata harmonises well with what 
 may be observed, on a cursory glance at the structure of their bodies, as to 
 the proportion between the organs of Nutritive and those of Animal life. The 
 former, contained in the cavities of the trunk, are highly developed ; but, as in 
 the Mollusca, they are for the most part unsymmetrically disposed. Of the 
 latter, the nervous system and organs of the senses occupy the head ; whilst 
 the muscles of locomotion are principally connected with the extremities : 
 both are symmetrical, as in the Articulata; but, whilst that part of the nerv- 
 ous centres, which is the instrument of reason, is very largely developed, the 
 portion which is specially destined to locomotion, together with the muscular 
 system itself, bears much the same proportion to the whole bulk of the body, 
 as it does in the Articulated series. Hence we observe that the Vertebrata 
 unite the unsymmetrical apparatus of nutrition, characteristic of the Mollusca, 
 with the symmetrical system of nerves and muscles of locomotion, which is 
 the prominent characteristic of the Articulata; both, however, being rendered 
 subordinate to the great purpose to be attained in their fabric, the develop- 
 ment of an organ, through which intelligence peculiarly manifests itself. For 
 the operations of this, a degree of general perfection is required, which is 
 not met with elsewhere. The higher Vertebrata have a power of constantly 
 keeping the temperature of the body up to a point, which it can only attain 
 occasionally, and under peculiar circumstances, in the Articulata, and which 
 it never reaches in the Mollusca. This involves an energetic performance of 
 the functions of respiration and circulation ; and these again require consider- 
 able activity of digestion. All the Vertebrata have red blood, which is pro- 
 pelled through the system by a distinct muscular heart; and the number of 
 red corpuscles, which any given amount of the fluid contains, bears a nearly 
 constant proportion to the ordinary temperature of the 'animal. They are 
 further distinguished from Articulata by a character which seems of little im- 
 portance, but which is very constant in each group. Whilst the mouth of the 
 
 5* 
 
54 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 latter is furnished with two or three pairs of jaws which open sideways, that 
 of the former has never more than one pair of jaws, which are placed one 
 above or before the other; and these jaws are usually armed with teeth, which 
 are very analogous in their structure to bone. 
 
 7. General characters of Fishes. 
 
 26. The Vertebrata are subdivided into classes, principally according to 
 their mode of performing the functions of respiration and reproduction. Thus, 
 FISHES are at once separated from all other groups, by the circumstances of 
 their being adapted, like the aquatic Invertebrata, to aerate their blood by 
 gills ; and being hence enabled to inhabit water during their whole lives, 
 without the necessity of coming to the surface to breathe. The low amount 
 of their respiration prevents their bodies from ever attaining a temperature 
 much above that of the surrounding medium ; hence they are spoken of as 
 cold-blooded. Further, they are oviparous ; an ovum or egg being deposited 
 by the parent, from which, in due time, the young makes its. way ; or if, as 
 sometimes happens, the ovum is retained within the body of the parent until 
 it is hatched, the young animal, though produced alive, is not subsequently 
 dependent upon its parent for support. In many respects, the organization 
 of Fishes is not much advanced beyond that of the higher Mollusca. Their 
 respiratory apparatus has the same character; and the organs by which the 
 blood is depurated of its superfluous azote, rather correspond with the tem- 
 porary Corpora Wolffiana of higher animals, than with their true Kidneys 
 (CHAP. XV. 3). The vertebral column itself is often very imperfectly deve- 
 loped ; in a large proportion of the group, the skeleton is cartilaginous only ; 
 and in the lowest species, it does not even manifest a trace of division into 
 vertebra. Living habitually in an element, which is nearly of the same speci- 
 fic gravity with their own bodies, Fishes have no weight to support, and have 
 only to propel themselves through the water. Accordingly we find their 
 structure adapted rather for great freedom of motion, than for firmness and 
 solidity ; and as progressive motion is chiefly effected by the lateral action of 
 the spine, the vertebrae are so united, as to move very readily upon one ano- 
 ther. Instead of being articulated together by surfaces nearly flat, as in 
 Mammalia, or by ball-and-socket joints, as in Serpents, they have both their 
 surfaces concave : and these glide over a bag of fluid (the representative of the 
 intervertebral substance in the higher animals), which is interposed between 
 each pair. The tail is flattened vertically ; so as, by its lateral stroke, to pro- 
 pel the Fish through the water. By this character, true Fishes are distin- 
 guished from those aquatic Mammalia, which are adapted to inhabit their 
 element, and which commonly receive the same designation ; for the latter, 
 being air-breathing Animals, are obliged to come frequently to the surface to 
 respire ; and their tail is flattened horizontally, to enable them to do this with 
 facility. The lateral surface of the body of Fish is further extended above, by 
 the projection of the dorsal fin, which is supported on the spinous processes of 
 the vertebra? ; and below, by the abdominal fin, which also is placed on the 
 median line ; these will, of course, increase the power of the lateral stroke of 
 the body, and can only be moved with the spine. The pectoral and ventral 
 fins, on the other hand, the former of which answer to the superior extre- 
 mities, and the latter to the inferior extremities, of Man, serve, by their in- 
 dependent movements, rather as steering than as propelling organs ; and they 
 also assist in raising and depressing the animal through the water. The 
 scales with which the bodies of all Fishes are covered, are frequently of a 
 bony hardness, and sometimes form a firmly-jointed casing, in which the 
 trunk is completely inclosed ; this is especially the case, when the internal 
 
GENERAL CHARACTERS OF REPTILES. 55 
 
 skeleton is imperfectly developed ; so that here we have an approach to the 
 character of the Invertebrata. 
 
 27. The swimming-bladder, as it is commonly termed, of the Fish, is not 
 an organ sui generis ; but is ascertained, by comparison with the pulmonary 
 sacs of the lower Reptiles, to be a rudimentary lung. It does not, however, 
 give any assistance in the aeration of the blood, except in a few instances ; 
 but seems to be in general subservient to the elevation and depression of the 
 body in its element. The heart of the Fish is extremely simple in its con- 
 struction, containing two cavities only; and the course of the circulation is 
 equally simple. The blood which returns from the body in a venous condi- 
 tion, is received into the single auricle or recipient cavity ; and from this it 
 passes into the ventricle or propellent cavity. The latter forces it into a large 
 trunk, which subdivides into branches that are distributed to the branchial 
 arches on each side ; and in these it undergoes aeration. Being collected 
 from the gills by returning vessels, the blood, now become arterial in its cha- 
 racter, is transmitted to the large systemic trunk, the aorta, by which it is dis- 
 tributed through the system, returning again to the heart, when it has passed 
 through the organs and tissues of the body. Hence it is evident that the 
 whole of the blood passes through the gills, before it goes a second time to the 
 system ; by which the imperfection of the aerating process itself is in some 
 degree compensated. There is a special provision, too, for renewing by 
 muscular power the stratum of water in contact with the gills ; continual cur- 
 rents being sent over them from the pharynx, with which their cavity com- 
 municates. It is worth noticing, that whilst, in the Osseous Fishes, there is 
 a single large external-gill opening on either side, with a valve-like opercu- 
 lum or gill-cover, there are, in the Cartilaginous Fishes, several slits on each 
 side of the neck, one corresponding with each branchial arch. Similar aper- 
 tures in the neck may be seen in the embryo of Man and of other Mammalia, 
 as well as of Birds and Reptiles, at the time that the circulation is in the con- 
 dition of that of the Fish, the heart possessing only two cavities, and the 
 blood being first propelled through a series of branchial arches. 
 
 . 8. General characters of Reptiles. 
 
 28. The class of REPTILES is oviparous and cold-blooded, like that of 
 Fishes ; but the animals belonging to it are formed to breathe air, and to 
 inhabit the surface of the earth, the few which are adapted to make the 
 water their dwelling, being obliged to come to the surface to breathe. Al- 
 though they breathe air, however, their respiration is not usually so energetic 
 as that of Fishes, and their general activity is much less. The mechanism 
 for the inflation of their lungs is very imperfect. Being destitute of a dia- 
 phragm, they are obliged to force air into the chest, by a process resembling 
 deglutition or swallowing; so that, strange as it may seem, a Reptile may be 
 suffocated by holding its mouth open. The heart possesses three cavities, 
 one of which receives the blood from the lungs, and another from the general 
 system ; the arterial and the venous blood, contained in these two auricles 
 respectively, are transmitted to the third or propelling cavity, the ventricle, 
 where they are mixed ; and the half-arterialised fluid is then transmitted to 
 the system at large, a part being sent to the lungs. Thus only a portion of 
 the blood expelled from the heart is exposed to the influence of the air ; and 
 that which is transmitted to the body is very imperfectly arterialised. In 
 some of the higher Reptiles, as the Crocodile, the ventricle is double, as in 
 the superior Vertebrata ; and the course of the circulation is so arranged, that 
 pure arterial blood shall go to the head, where it is most required, whilst a 
 mixed fluid is sent to the rest of the 'body. This plan exactly corresponds 
 
56 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 with the one, which is adopted in the circulation of the Human foetus, from 
 the time of the formation of the four cavities in its heart, and of the perma- 
 nent system of vessels, up to the period of birth. The imperfect arterialisa- 
 tion of the blood in Reptiles, causes a great degree of general inertness in 
 their functions. Their motions are principally confined to crawling and 
 swimming ; their general habits are sluggish, and their sensations are obtuse ; 
 and their nutritive functions are very slowly performed. Hence they can 
 exist for a long time, with a very feeble exercise of these functions, under 
 circumstances that would be fatal to animals, in which they are performed 
 with greater activity. In cold and temperate climes, they pass the whole 
 winter in a state of torpidity ; and at other seasons, they may be kept during 
 a long time from their due supplies of food and air, without appearing to suf- 
 fer much inconvenience. 
 
 29. In regard to the structure of their skeleton, and the external form of 
 the body, there is a considerable variation among the several orders of Reptiles. 
 Thus, Tortoises, Lizards, and Serpents, differ from each other so widely, 
 that a common observer would separate them completely ; and yet they not 
 only agree in all the foregoing characters, but pass into one another by links 
 of transition so gradual, that it is even difficult to classify them. They differ, 
 however, more in the configuration of the accessory parts, than in the struc- 
 ture of the essential portion of the skeleton, the, spinal column. This is 
 characterised by the ball-and-socket articulation of the vertebrae, each vertebra 
 having one surface convex and the other concave, a structure which is more 
 strongly marked in Serpents, whose movements are performed chiefly by the 
 flexion of the spinal column itself, than it is in the other tribes. The chief 
 characteristic of the Tortoise tribe, is the shell or case in which the body is 
 contained. The upper arch of this shell, termed the carapace, is formed by 
 a bony expansion from the edges of the ribs, which is covered by a set of 
 horny plates, that are to be regarded (like smaller scales) as epidermic appen- 
 dages. The under portion, termed the plastron, is composed of the sternum, 
 which is in like manner extended laterally. In the Land-tortoises, this usu- 
 ally forms a complete floor ; but in the aquatic species, a part is commonly 
 absent, the interval being filled up by cartilage and membrane. The skeleton 
 of the Lizards is formed more upon the general plan of that of Mammalia, 
 but may be readily distinguished from it. The sternum is usually prolonged 
 over the front of the abdomen, and the ribs are continued through a much 
 larger part of the spinal column ; of these abdominal ribs, the white lines 
 across the recti muscles in the higher Vertebrata, are evidently the rudiments. 
 In the higher Lizards, the power of locomotion is almost entirely delegated 
 to the extremities ; but in the less typical species, the body and tail are much 
 prolonged, so as to present a serpentiform aspect ; and first one pair of feet, 
 and then the other, disappear, until the form is altogether that of the Serpent. 
 Even in Serpents, however, rudiments of extremities are frequently to be 
 found ; but their mode of progression is very different, and these rudiments 
 are of no assistance to them. The most remarkable feature in the Serpent's 
 skeleton, besides the absence of legs, and the large number of ribs and verte- 
 brae, is the deficiency of a sternum ; through the absence of this, the extremi- 
 ties of the ribs are free, and they become in fact the fixed points, on which 
 the animal crawls, when advancing slowly forwards, in a manner which bears 
 a strong resemblance to the progression of the Centipede. 
 
 30. Although the configuration of the cranium varies much in the different 
 orders of Reptiles, yet there is a remarkable agreement in certain general cha- 
 racters, and in the general degree of development. It consists of a much 
 larger number of parts, than are to be found in the cranium of adult Birds or 
 Mammalia ; each principal bone being subdivided, as it were, into smaller ones. 
 
GENERAL CHARACTERS OF REPTILES. 57 
 
 This condition exactly corresponds with that, which may be observed during 
 the process of ossification in higher Vertebrata ; for each of the larger bones 
 of the cranium is formed from several centres of ossification ; so that, if the 
 cranium of a foetus or young infant be macerated, it will fall into a number of 
 pieces nearly corresponding with those of the Reptile's skull. The different 
 orders of Reptiles have a close agreement in various other points ; especially 
 in the degree of development of their several organs of nutrition. Thus, in 
 all of them, the lungs, though commonly of large size, are so little subdivided, 
 as really to expose but a small extent of surface. The glandular structures, 
 too, are formed upon a much more simple type, than is characteristic of the 
 warm-blooded Vertebrata. They all agree, moreover, in having the body 
 covered with scales ; which, though generally small, are sometimes large flat- 
 tened plates. 
 
 31. Between Fishes and true Reptiles, there is a group that remarkably 
 combines the characters of both ; being composed of animals which come 
 forth from the egg in the condition of Fishes, but which afterwards attain a 
 form and structure closely corresponding with that of true Reptiles. This 
 group, consisting of the Frog and its allies, is sometimes associated as an or- 
 der (Batrachia) of the class of Reptiles ; though it should probably take rank 
 as a distinct class, the AMPHIBIA. The Tadpole or larva of the Frog is in 
 every essential respect a Fish. Its respiration and circulation, its digestion 
 and nutrition, its locomotion and sensation, are entirely accordant with those 
 of Fishes. The body is destitute of members for progression, but is propelled 
 through the water by the lateral undulations of the spinal column, which is 
 articulated in the same manner as that of Fishes. At a certain period, a me- 
 tamorphosis commences in which almost every organ in the body undergoes 
 an essential change. Lungs are developed, which take the place (in regard 
 to their function) of the gills ; and the latter are atrophied. The auricle of 
 the heart is divided into two ; and the circulation is performed on the plan of 
 that of the true Reptile. Two pairs of members are usually formed, to which, 
 when they are fully developed, the power of progression is committed, the 
 tail disappearing ; in some species, however, the tail remains, and the extre- 
 mities are small. The digestive system undergoes a remarkable alteration ; 
 the intestinal canal, which was previously of enormous length in proportion 
 to the body, being now considerably shortened, in accordance with the differ- 
 ent kind of food on which the animal has to subsist. The mode of articu- 
 lation of the spinal column also, undergoes a change, which brings it to the 
 type of that of Reptiles. The most obvious point of difference in external 
 characters, between the higher Amphibia and true Reptiles, is the absence of 
 scales or plates on the skin of the former. In this manner, the common Sala- 
 mander or Water-Newt may be recognised as belonging to the Batrachia 
 though its form would otherwise lead us to place it among the Lizards ; and 
 the Ccecilia, which has the form of the Serpent, is in like manner known to 
 be really allied to the Frog. An acquaintance with the history of these ani- 
 mals confirms such an arrangement, by showing that the Salamander and the 
 Co3cilia undergo a metamorphosis ; breathing by gills, and having the general 
 structure of Fishes, in the early part of their lives. 
 
 32. Besides those animals, however, which attain the condition of perfect 
 Reptiles, this group contains several, whose development is arrested, as it 
 were, in an intermediate or transition state ; their adult form presenting a re- 
 markable mixture of the characters of the two classes, which they thus con- 
 nect. This is the case in the Proteus, Siren, and other less known species, 
 which retain their gills through the whole of their lives, whilst their lungs are 
 at the same time developed ; so that, as they can respire in either air or wa- 
 ter, they are the only true amphibious animals. In their general organization, 
 
58 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 they correspond with the Tadpole of the Frog at an advanced period of its 
 metamorphosis ; and it is a most interesting fact (which has been established 
 by the experiments of Dr. W. F. Edwards) that, if Tadpoles be kept in such 
 a manner, as to be amply supplied with food, and exposed to a constantly- 
 renewed current of water, but be secluded from light and from the direct in- 
 fluence of the solar heat, they will continue to grow as Tadpoles ; their me- 
 tamorphosis being checked. The metamorphosis of the Batrachia closely 
 corresponds with that of Insects ; the young animal, in each case, at the time 
 of its emersion from the egg, having a resemblance, in all essential particulars, 
 to a class below that to which it is ultimately to belong. This kind of meta- 
 morphosis is by no means confined to them, however ; for the gradual exten- 
 sion of our knowledge of the early history of the different tribes of animals, 
 is constantly bringing to light new facts of the same kind. The Polypes and 
 lower Mollusca, for instance, come forth from the egg, and swim about for 
 some time, in a condition which can scarcely be termed animal; for there is 
 not even a mouth leading to a digestive cavity ; nor are there any other or- 
 gans of locomotion than the cilia, the action of which is involuntary. And, 
 in tracing the development of the Human embryo, we shall find that it under- 
 goes a series of progressive changes equally remarkable; the principal differ- 
 ence being, that these changes are not so arranged in harmony with each 
 other, as to cause the embryo to present, at any one time, the combination of 
 characters which belong to the Fish, Reptile, &c., or to enable it to sustain an 
 independent existence. 
 
 9. General characters of Birds. 
 
 33. From Reptiles to BIRDS, the transition would seem rather abrupt ; since 
 the latter class is, in almost every respect, the opposite of the former. Never- 
 theless, it would seem to have been effected by the now-extinct Pterodac- 
 tylus, which combined, in a most remarkable degree, the characters of the 
 two groups. Birds are, like Fishes and Reptiles, oviparous Vertebrata ; but 
 they differ essentially from both, in being warm-blooded, and in affording as- 
 sistance by their own heat in the development of the ovum. Birds correspond 
 with Mammalia, in possessing a heart with four cavities, and a complete dou- 
 ble circulation ; by which the whole of the blood that has circulated through 
 the body, is exposed to the influence of the air before being again transmitted 
 to the system. This high amount of oxygenation of the blood is accompa- 
 nied by great activity and energy of all the organic functions, acuteness of the 
 senses, and rapid and powerful locomotion ; as well as by the evolution of a 
 degree of heat, superior to that which we ordinarily meet with among the 
 Mammalia. The temperature of Birds ranges from about 104 to 112. The 
 lowest is in the aquatic species, whose general activity is much less than that 
 of the tribes which spend most of their time in the air ; the highest is among 
 those distinguished for the rapidity and energy of their flight, such as the 
 Swallow. 
 
 34. Birds have been denominated, and not inappropriately, the Insects of 
 the Vertebrated series; as in the animals of that class, we find the whole 
 structure peculiarly adapted to motion, not in water, nor upon solid ground, 
 but in the elastic and yielding air. It is impossible to conceive any more 
 beautiful series of adaptations of structure to conditions of existence, than 
 that which is exhibited in the conformation of the Bird, with reference to its 
 intended mode of life. In order to adapt the Vertebrated animal to its aerial 
 residence, its body must be rendered of as low specific gravity as possible. 
 It is further necessary that the surface should be capable of being greatly ex- 
 tended ; and this by some kind of appendage that should be extremely light, 
 
GENERAL CHARACTERS OF BIRDS. 59 
 
 and at the same time possessed of considerable resistance. The degree of 
 muscular power required for support and propulsion in the air, involves the 
 necessity of a very high amount of respiration ( 275), for which it has been 
 seen that an express provision exists in Insects; and as the general activity 
 of the vital processes depends greatly upon the high temperature, which this 
 energetic respiration keeps up, a provision is required for keeping in this heat, 
 and not allowing it to be carried away by the atmosphere, through which the 
 Bird is rapidly flying. 
 
 35. The first and third of these objects, the lightening of the body, and 
 the extension of the respiratory surface, are beautifully fulfilled in a mode, 
 which will be found to correspond with the plan adopted for the same purpose 
 in Insects. The air which enters the body, is not restricted to a single pair 
 of air-sacs or lungs placed near the throat; but is transmitted from the true 
 lungs, to a series of large air-cells, disposed in the abdomen and in various 
 other parts of the body. Even the interior of the bones is made subservient 
 to the same purpose ; being hollow, and lined with a delicate membrane, over 
 which the blood-vessels are minutely distributed. In this manner, the respi- 
 ratory surface is greatly extended; whilst, by the large quantity of air intro- 
 duced into the mass, its specific gravity is diminished. The subservience of 
 the cavities in the bones to the respiratory function, is curiously shown by 
 the fact, which has been ascertained both accidentally and by a designed ex- 
 periment, that, if the trachea of a Bird be tied, and an aperture be made in 
 one of the long bones, it will respire through this. 
 
 36. The other two objects, the extension of the surface, and the retention 
 of the heat within the body, are also accomplished in combination, by a most 
 beautiful and refined contrivance, the covering of feathers. Like hair or 
 scales, feathers are to be regarded as appendages to the Cutis; the stem is 
 formed from it by an apparatus, which may be likened to a hair-bulb on a 
 very large scale ; but there are some additional parts for the production of the 
 laminae, which form the vane of the feather, and which are joined to the stem 
 during its development. These laminae, when perfectly formed, are connected 
 by minute barbs at their edges, which hook into one another, and thus give 
 the necessary means of resistance to the air. The substance of which feathers 
 consists, is a very bad conductor of heat ; and when they are lying one over 
 the other, small quantities of air are included, which still further obstruct its 
 transmission by their non-conducting power. Thus the two chief objects are 
 fulfilled; power of resistance and slow-conducting properties being obtained, 
 in combination with lightness and elasticity. At the two extremes of the 
 class, however, we meet with remarkable modifications in the typical structure 
 of feathers. In the Penguin, those which cover the surface of the wings 
 have a strong resemblance to scales ; and the wings are not employed to raise 
 this Bird in the air, but only to propel it through water (as fins would do) by 
 their action on the liquid. On the other hand, in the Ostrich tribe, the laminae 
 of the feathers are separated from each other, so as no longer to form a con- 
 tinuous surface ; the feathers more resembling branching hairs. Here the 
 wings are almost or completely absent; the birds of this tribe being constantly 
 upon the ground, propelling themselves by running, and approaching the 
 Mammalia in many points of their conformation. 
 
 37. The bony frame-work of Birds presents many remarkable adaptations 
 to the same purposes. In the first place it is to be remarked, that the faculty 
 of locomotion is here entirely delegated to the extremities; and that the skele- 
 ton of the trunk must be consolidated, in proportion to the power with which 
 they are to be endowed, in order to afford their muscles a firm attachment 
 ( 22). Just as the segments of the external skeleton of the Articulata, 
 therefore, are consolidated in Insects, do we find that the vertebral column 
 
60 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 and its appendages are firmly knit together, in the upper part of the trunk of 
 Birds. The vertebra? are closely united to each other; and the ribs are con- 
 nected with the sternum by bony prolongations of the latter, instead of by 
 cartilages. This union is so arranged, that the state of expansion is natural 
 to the thorax, whilst that of contraction is forced. The diaphragm is absent 
 among birds, as among Reptiles ; except in a few species, which most nearly 
 approach the Mammalia. But its deficiency is compensated by this contriv- 
 ance, which keeps the lungs and air-sacs always full, except when the Bird 
 by a muscular effort, expels the air from them, in order that they may be re- 
 filled by a fresh supply. By this means, also, the specific gravity of the body is 
 more constantly kept down, than it could have been, if the lungs had been 
 subjected to the constantly-alternating contractions and expansions, which they 
 perform in Mammalia. It is worthy of remark, that the air which enters the 
 bones and the air-sacs, passes through the lungs, both on its entrance and 
 return ; so as to yield to their capillaries all the oxygen which they can take 
 from it, and of which the blood that it has elsewhere met with has not de- 
 prived it. It is only in the lungs, that it meets with purely venous blood ; for 
 they alone receive the branches of the pulmonary artery ; the vessels which 
 are distributed upon the respiratory surface of the air-sacs and bones, being 
 a part of the systematic circulating apparatus. Hence we may regard this 
 curious provision, as being partly designed for the aeration of the blood in its 
 course through the system (this, it will be remembered, being the sole mode 
 in which the function is performed in Insects), and partly for supplying the 
 lungs with air, as from a reservoir, during the violent actions of flight. 
 
 38. The articulation of the anterior extremity with the trunk exhibits a 
 peculiar provision for strength and power, which we find in no other Verte- 
 brata. The two clavicles are united together on the central line, forming the 
 furcula or merry-thought ; and the use of this is to keep the shoulders apart, 
 notwithstanding the opposing force exerted by the pectoral muscles in the 
 action of flight. It is generally firm, and its angle open, in proportion to the 
 power of the wings. Besides this bone, there is another connecting the 
 sternum with the scapula on each side ; this is the coracoid bone, which in 
 Man and most other Mammalia is scarcely developed, being merely a short pro- 
 cess which does not reach the sternum. The sternum of Birds usually ex- 
 hibits a very remarkale development on the median line ; an elevated keel or 
 ridge being seen on it, which serves for the attachment of the powerful mus- 
 cles that depress the wings. In the great development of the sternum, Birds 
 have some analogy with the Turtle tribe : which they also resemble in the 
 deficiency of teeth, and in the development of a horny covering to the jaws: 
 but in these, the lateral elements of the sternum are the parts most developed; 
 whilst in Birds it is the central portion which exhibits the peculiarity. From 
 the depth of the keel of the sternum, a judgment may be formed of the thick- 
 ness of the pectoral muscles, and thence of the powers of flight ; in the Os- 
 trich tribe, where the wings are not sufficiently developed to raise the bird 
 off the ground, the sternum is quite flat, as in the Mammalia. The want of 
 flexibility in the trunk is counterbalanced by the length and flexibility of the 
 neck ; the number of cervical vertebra? is very considerable, varying from 12 
 to 23, the highest number being present in the Swan tribe. They are so 
 articulated that the head can be turned completely round, or moved in any 
 direction. The anterior extremities of Birds being solely adapted to sustain 
 them in flight, the posterior are necessarily modified for their support on the 
 ground. They are usually placed rather far back ; but the spine has a posi- 
 tion more inclined than horizontal, so that the weight may not be altogether 
 thrown forwards. The trunk is supported on the thighs by powerful muscles; 
 and there is another series, which passes from the lower part of the spine 
 

 GENERAL CHARACTERS OF BIRDS. 61 
 
 continuously to the toes, turning over the knee and heel, in such a manner 
 that the flexion of these joints shall tighten the tendons ; by this contrivance, 
 the simple weight of the body flexes the toes ; and Birds are thus enabled to 
 maintain their position, by grasping their perch, during sleep, without any 
 active muscular effort. 
 
 39. Not only do Birds resemble Insects in their general structure and 
 mode of life, but also in the peculiar development of the instinctive powers. 
 Under the direction of these, the place for their nests appears to be selected ; 
 their materials collected ; the nest themselves built, and the young reared in 
 them ; the migrations are performed ; and many curious stratagems are em- 
 ployed to obtain food. It is sufficient to indicate these in general terms ; 
 since it is well known that the habits of Birds have peculiarities restricted to 
 each species ; and that in all the individuals of each species ; they are as 
 precisely alike as their circumstances will admit. Nevertheless, there are ob- 
 served in Birds a degree and kind of adaptation to varying conditions, which 
 Insects do not possess, and which display an amount of intelligence far su- 
 perior to what is found in that class ( 17). This is evinced also in their edu- 
 cability ; for no animal can be taught to perform actions which are not 
 natural to it, unless it possesses in a considerable degree the powers of memory 
 and association, at least, if not some of the higher mental faculties, such as 
 the power of perceiving and comparing the relations of ideas. Moreover, 
 in the domesticability of many tribes of Birds, we see this educability com- 
 bined with a degree of that higher form of attachment to Man, which is so 
 strikingly exhibited by certain species of Mammalia. The development of 
 the senses of Birds varies in different tribes, according to the mode in which 
 they are adapted to obtain their prey. The sight is almost always extremely 
 acute, and is their chief means of seeking food ; and where this would be of 
 comparatively little service, as in the nocturnal rapacious birds, it is compen- 
 sated by a much higher development of the faculty of hearing, than is com- 
 mon amongst other tribes. The senses of smell, taste, and touch, do not 
 seem to be usually very acute in Birds ; but there are particular tribes, in 
 which each of these is more developed than in the rest. 
 
 40. As might be expected from the analogy of Birds with Insects, the de- 
 velopment of their organs of nutrition (excepting that of the respiratory organs) 
 is much less striking than is that of the locomotive apparatus. The whole 
 cavity of the trunk, especially in Birds distinguished for their powers of 
 flight, is small in comparison with that of the body ; but what is wanting in 
 the size of the organs, is made up in their energy of function. Hence the 
 demand for food is more active in them than in any other class of animals. 
 It is interesting to observe, that there is more bi-lateral symmetry in the 
 arrangement of the viscera, than we usually find in the class above. This is 
 evidently connected with their active locomotive powers ; as it is obviously 
 necessary, that the two sides of the body should be balanced with perfect 
 equality, and that their energy should be exactly correspondent. The lungs 
 and air-sacs are precisely similar in size and situation on the two sides ; con- 
 sequently the heart is placed on the median line ; and the mode of origin, 
 from the aorta, of the trunks supplying the head and upper extremities, is 
 alike on the two sides. The liver, also, is less asymmetrical than we usually 
 find it in the Mammalia. 
 
 41. It has been remarked, that the assistance afforded by the parent, in 
 the development of the young, is greater in Birds than in the lower Verte- 
 brata ; but is less than in Mammalia. Whilst Reptiles and Fishes show little 
 or no concern for their eggs after they have deposited them, Birds sedulously 
 tend them, affording them not only protection but warmth, by means of their 
 powerful heat-producing apparatus. The yolk-bag of the Bird's egg is so 
 
 6 
 
62 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 suspended in the midst of the white albumen, that, when the egg is laid upon 
 its side, it will always rise to the highest part of it; and the relative weight 
 of the several parts is further adjusted in such a manner, that the cicatricula 
 or germ-spot shall always be at the point nearest the shell, so as to come into 
 the closest proximity with the source of heat, and also to be in the most im- 
 mediate relation with the surrounding air. There are some Birds, inhabiting 
 the equatorial region, which do not always incubate their eggs, trusting to the 
 solar heat for their maturation. It is said that the Ostriches of the intertro- 
 pical deserts are content with covering their eggs with a thin layer of sand, 
 so as to admit the action of the sun by day, and to keep them warm at night ; 
 but that those living under a less constantly elevated temperature, sit upon 
 their eggs if not constantly, at any rate when the solar heat is not sufficient. 
 This statement has been disputed ; but its truth seems to be confirmed by a 
 curious observation made by Mr. Knight, that a Fly-catcher, which built for 
 several years in one of his hot-houses, sat upon its eggs when the temperature 
 was belo\v 72, but left them when it rose above that standard. Certain Birds 
 inhabiting New Holland, deposit their eggs in a sort of hot-bed, composed of 
 decaying vegetable matter ; a number associating together for the construction 
 of this artificial incubating apparatus, although they live separately at other 
 times. The degree of assistance afforded by the parent Birds to their young, 
 after their emersion from the shell, varies much in different tribes ; in general 
 it may be remarked, however, that it is most prolonged in those which ulti- 
 mately attain the highest development, and especially in those whose intelli- 
 gence becomes the greatest. Thus the Chicken and the D.uckling, when just 
 hatched, are able to shift for themselves ; but among the Raptorial and Inses- 
 sorial Birds, which rank far higher in the scale, the young is for a long time de- 
 pendent upon the parent for food ; and in the Parrot tribe, which unquestion- 
 ably surpasses all others in intelligence, the parent not only supplies its young 
 with food which it has obtained for them, but partly nourishes them by a 
 milky secretion from the interior of the craw ; impregnating with this the 
 aliment which it swallows, and which it afterwards disgorges for its offspring. 
 
 10. General characters of Mammalia. 
 
 42. The MAMMALIA are universally regarded as the highest group in the 
 Animal kingdom ; not only from being that to which Man belongs (so far, at 
 least, as his bodily structure is concerned), but also as possessing the most 
 complex organization, adapted to perform the greatest number and variety of 
 actions, and to execute these with the greatest intelligence. The contrast is 
 here extremely strong between the reasoning and the instinctive powers ; 
 even when we put Man out of view. When we compare, for example, the 
 sagacity of a Dog, Monkey, or Elephant, and the great variety of circum- 
 stances in which they will display an intelligent adaptation of means to ends, 
 with the limited operations of Insects, over which the judgment and will seem 
 to have no control, we cannot help being struck with the difference. The 
 former are educable in the highest degree next to Man ; the latter could not 
 be made to change their habits, in any essential degree, by the most prolonged 
 course of discipline. Man is actuated, like the lower animals, by instinctive 
 propensities, which have an immediate bearing on his corporeal wants ; whilst 
 they have, like him, the power of adapting their actions to gain certain ends, 
 of which they are conscious. A Dog or an Elephant may show more real 
 wisdom, in controlling for a time its instinctive propensities, from the desire 
 to accomplish some particular object, than is displayed by many Men, who 
 give free scope to the exercise of their sensual passions, although warned by 
 their reason of the injurious consequences of such indulgence. 
 
GENERAL CHARACTERS OF MAMMALIA. 63 
 
 43. This high development of the intelligence in Mammalia, is evidently 
 connected with the greatly-prolonged connection between the parent and the 
 offspring, which we find to be a characteristic of this class. Mammalia are, 
 like Birds, warm-blooded Vertebrata, possessing a complete double circula- 
 tion ; and some of them are adapted to lead the life of Birds, passing a large 
 part of their time in darting through the air on wings, in pursuit of Insect 
 prey. But they differ from Birds in this essential particular, that they are 
 not oviparous, but viviparous ; producing their young alive, that is, in a 
 condition in which they can perform spontaneous movements, and can appro- 
 priate nourishment supplied to them from without. But they are not distin- 
 guished from all other animals by this character alone ; for there are some 
 species among Reptiles, Fishes, and even Insects, which produce their young 
 alive, the egg being retained within the oviduct and hatched there. The 
 real distinction lies partly in that, which the name of the class imports, the 
 subsequent nourishment of the young by suckling ; and partly in the mode 
 in which the embryo is nourished before its birth. In Mammels, the yolk- 
 bag is very small in proportion to its size in Birds ; and the contents of the 
 ovum, instead of furnishing (as in that class) the materials necessary for the 
 development of the young animal, up to the time when it can ingest food for 
 itself, only serve for the earliest set of changes in which this process con- 
 sists. In the latter stages of the evolution of the embryo, it is supplied with 
 nutriment directly imbibed from its parent. This is at first accomplished 
 by means of a series of root-like tufts, which are prolonged from the surface 
 of the ovum, and insinuate themselves among the maternal vessels, without, 
 however, uniting with them. These tufts absorb, from the maternal fluid, 
 the ingredients necessary for the support of the embryo ; and also convey 
 back to the parent its effete particles, which are received back into her blood, 
 and are then cast out of her system, by the process of secretion, respiration, 
 &c. 
 
 44. The Mammalia may be divided into two sub-classes ; in one of which 
 the structure just described is the greatest advance ever made, in the appa- 
 ratus by which the foetus is nourished ; whilst in the other a more concen- 
 trated form is subsequently assumed by it. The ovuni of the latter is delayed 
 for a longer period, in a cavity formed by the union of the two oviducts, 
 termed the uterus; which can be scarcely said to be developed in the Marsu- 
 pialia and Monotremata, the two orders constituting the first sub-class. The 
 vascular tufts proceeding from the chorion become especially developed at one 
 point, and the vessels of the uterus are extremely enlarged in a corresponding 
 situation ; the tufts dip down, as it were, into a chamber formed by an exten- 
 sion of the inner lining of these vessels, and serve the combined purpose of 
 the roots of plants and of the branchiae of aquatic animals, absorbing from 
 the maternal blood the materials required for the nourishment of the embryo, 
 and aerating the blood of the foetus, by exposing it to the influence of that of 
 the parent. The peculiar organ thus formed is termed the placenta; and the 
 two sub-classes of the Mammalia have thence received the appellations of 
 placental and non-placental. The animals belonging to the latter present 
 many points of affinity to Birds, in the structure of their internal organs. 
 That of the brain is very nearly allied in these two groups ; and their amount 
 of intelligence seems, as far as can be determined, to bear a close correspond- 
 ence. The Ornithorhyncus in particular, has so many marks of alliance to 
 oviparous animals, and its osteology, as well as in its horny bill and in less 
 important particulars, that Naturalists have much debated whether it could 
 really be termed a Mammiferous animal. No positive evidence has yet been 
 obtained that its young are born alive ; but on the other hand, there is a strong 
 reason to believe that they come into the world uninclosed in the ovum, al- 
 
64 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 though in a very imperfect condition. Moreover, it has been satisfactorily 
 ascertained that the young are nourished, for some time after their birth, by 
 a mammary secretion, which the organization of their mouth at that period 
 enables them to obtain from the parent. In the Marsupialia, there is a 
 remarkable compensation for the abrupt termination of the period of uterine 
 gestation, the young being received into a pouch or marsupium, within which 
 the nipple is situated ; this is extremely prolonged, and the mouth of the foetus 
 (for so the being must still be regarded) is adapted to receive and hold on by 
 it; so that the little creature, which looks at first more like an earth-worm 
 than a Mammiferous animal, is thus suspended within the protective pouch, 
 until its development is so far advanced, that it can shift for itself in the same 
 degree as other new-born animals can do. 
 
 45. The period of gestation in the higher sub-class of Mammalia, is usually 
 prolonged, until the foetus is able, on its entrance into the world, to execute 
 regular movements ; some of these being merely indicative of its desire for 
 food, and others evidently designed for the acquirement of it. In many species, 
 the young animal seems to be from the first in the full possession of its senses, 
 and has considerable power of active locomotion ; in general, however, it is 
 very dependent upon its parent ; only being able to obtain food when this is 
 placed within its immediate grasp. Such is the case with the Human infant, 
 which is closely dependent upon its parent, during a larger proportion of its 
 existence, than is the young of any other animal. Here again, therefore, we 
 perceive the application of the general law, that, the higher the grade of 
 development a being is ultimately to assume, the more does it require to be 
 assisted during the early stages of its progress. In the case of Man, the pro- 
 longation of this period has a most important and evident influence upon the 
 social condition of the race; being, in fact, one of the chief means, by which 
 the solitary are bound together in families. 
 
 46. The class Mammalia, taken as a whole, is not characterized so much 
 by the possession of any one particular faculty, like that which has been 
 seen in Birds, as by the perfect combination of the different powers, which 
 renders the animals belonging to it susceptible of a much greater variety of 
 actions, than any others can perform. There are none that can compete with 
 Birds in acuteness of sight ; but there are few that do not possess the senses 
 of smell, taste, and touch in a more elevated degree. There are none which 
 can rival Birds in rapidity of locomotion ; but there are few which cannot per- 
 form several kinds of progression. Several of their movements require a 
 considerable amount of flexibility in the spine ; hence the vertebral column, 
 and the bony framework of the trunk, are never so much consolidated as they 
 are in Birds. On the other hand, the neck is much less movable ; it never 
 consists of more than seven vertebrae, and these are always present ; so that 
 they are sometimes of great length, as in the Giraffe, and sometimes ex- 
 tremely short, as in the Whale, which seems to have no neck at all. In the 
 greatest number of Mammalia, the body is supported upon all the four extre- 
 mities, as in Reptiles ; being adapted for progression along the surface of the 
 earth. There are some species, however, in which the typical structure has 
 undergone a metamorphosis, by which it is made to resemble that of a Bird ; 
 whilst in others it is modified, so as to conform to the character of the Fish. 
 In the Bats, the power of motion is almost entirely delegated to the wings, 
 which are composed of skin, stretched over a bony framework formed of the 
 widely-extended hand ; and the sternum has a projecting keel for the attach- 
 ment of the pectoral muscles, as in Birds. And in the Whale tribe, the power 
 of locomotion is almost completely taken from the extremities, and given 
 back to the trunk, as in Fishes ; for the posterior extremities are entirely ab- 
 sent, and the anterior serve only for guidance : there is this important differ- 
 
CHIEF SUB-DIVISIONS OF MAMMALIA. 65 
 
 ence, however, that the tail, which is flattened vertically in Fishes, is flattened 
 horizontally in the Cetacea, which require the power of frequently coming to 
 the surface to breathe. 
 
 47. The inferior energy of muscular movement in the Mammalia, is ac- 
 companied by an inferior amount of respiration ; the type of the respiratory 
 apparatus, however, is higher than in Birds, a large extent of surface being 
 comprised within a smaller space. The lungs are confined to the cavity of 
 the thorax ; and there is a provision for the regular renewal of the air received 
 into them, by the action of the diaphragm, which here completely separates 
 that cavity from the abdomen. The diminished amount of respiration, again, 
 involves the production of a lower degree of animal heat ; so that the tempe- 
 rature of this class seldom rises above 104. There is, therefore, less need 
 of means for effectually confining the caloric, especially, too, as their greater 
 average size causes their radiating surface to be much less, in proportion to 
 their bulk, than is that of Birds ; and accordingly, we find them provided 
 only with a covering of hair or fur, which is much less warm than that of 
 feathers, and which is thin and scanty in Mammals inhabiting tropical climates. 
 The chief exception to the last rule is in the case of the Sloths and of some 
 Monkeys, which inhabit situations exposed to the most powerful rays of the 
 sun, and which are covered with a long but thin and coarse hair ; the purpose 
 of this is evidently the protection of their skin from the external heat. The 
 inferior energy of the respiration and circulation, involves a diminished activity 
 of the other functions of nutrition, as compared with those of Birds ; and the 
 demand for food appears to be somewhat less constant. Their various organs, 
 however, are developed upon a higher plan ; as we have already observed in 
 regard to those of respiration. 
 
 11. Chief Sub-divisions of Mammalia. 
 
 48. In sub-dividing the truly Viviparous division of the class, so as to sepa- 
 rate Man from the tribes with which he is associated in it, we may be advan- 
 tageously guided, in the first place, by the conformation of the extremities ; 
 since upon the perfection of the organs of touch, will depend much of the 
 address of an animal in executing the actions to which it is prompted by its 
 intelligence. The degree of this perfection is estimated by the number and 
 mobility of the fingers, and by the degree in which their extremities are en- 
 veloped by the nail, claw, or hoof, that terminates them. When the fingers 
 are partly absent, or are consolidated together, and a hoof envelopes all that 
 portion which touches the ground, it is obvious that the sensibility must be 
 blunted, whilst, at the same time, the member becomes incapacitated for pre- 
 hension. The opposite extreme is where (as in Man) a thin nail covers only 
 one side of the extremity of the finger, leaving the other possessed of all its 
 delicacy ; where several such fingers exist, of which one can be opposed to 
 the rest, so as to render prehension more perfect, and to perform a great va- 
 riety of actions : and where the plane of the whole hand can be turned in 
 any position, by the nature of its attachment to the fore-arm. Between these 
 there are many intermediate gradations. By these characters, the viviparous 
 Mammalia may be divided into the Unguiculated, which have separate fin- 
 gers, terminated by distinct nails or claws ; and the Ungulated, in which the 
 fingers are more or less consolidated, and inclosed at their extremity in a hard 
 hoof. Hoofed animals are necessarily Herbivorous, inasmuch as the con- 
 formation of their feet precludes the possibility of their seizing a living prey; 
 and they have flat-crowned grinding teeth for triturating their food, 
 summits of these teeth are usually not covered by a smooth coat of enamel, 
 but present a series of elevations* and depressions ; these are occasioned by 
 
 6* 
 
66 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 the peculiar structure of the teeth, which consist of alternating plates of ena- 
 mel, ivory or dentine, and cementum or crusta petrosa, substances of three 
 different degrees of hardness ; and, as the softer portions will of course wear 
 down first, the harder remain as projecting ridges. In order to give effect to 
 these, there is usually a considerable power of lateral motion possessed by 
 the lower jaw ; so that a regular grinding action may be performed, which is 
 favourable to the complete reduction of the tough vegetable substances that 
 serve as their food. 
 
 49. Animals with Unguiculated fingers are capable of more variety in the cha- 
 racter of their food. In some it is almost exclusively vegetable, as in the Roden- 
 tia ; and here the power of prehension possessed by the extremities is small, 
 the fore-arm not being so constructed as to be capable of the motions of pro- 
 nation and supination. In this order, the mouth is remarkably adapted for 
 grinding down hard vegetable substances ; the molar teeth being furnished with 
 transverse ridges of enamel; and the jaws having a powerful movement back- 
 wards and forwards.* In other orders, again, there is an almost exclusive adap- 
 tation to animal food. The toes are furnished with long and sharp claws ; 
 and the fore-feet may be placed in a variety of positions, by the rotation of 
 the two bones composing the lower part of the leg. The grinding teeth are 
 very narrow, and are formed with sharp points and edges, so as to be adapted 
 for dividing animal flesh ; these are firmly set in short strong jaws, which are 
 fitted together like the blades of a pair of scissors, having no action but a 
 vertical one ; and the constant friction of the edges of the molar teeth against 
 each other, keeps them sharp.! In the Carnivorous group, too, we find the 
 greatest development of the canine teeth, which are commonly absent or but 
 slightly developed among herbivorous quadrupeds ; these are instruments of 
 great power, serving both for the first attack of their prey, and for subse- 
 quently tearing it in pieces. It is evident that the whole structure of the body 
 must undergo modification, in conformity with the nature of the food. The 
 simple stomach and intestinal canal of the Carnivorous animal, adapted only 
 to the digestion of aliment consisting of materials similar to those of its own 
 body, would be totally useless to an animal prevented by its general organi- 
 zation from obtaining any other than vegetable food ; and, on the other hand, 
 the teeth and hoofs of the Herbivorous quadruped would be of little assist- 
 ance to an animal, whose instincts and general conformation adapted it for the 
 pursuit of animal prey. It will be presently seen that, in regard to his or- 
 ganization, Man holds an intermediate place between the purely Herbivorous 
 and the purely Carnivorous tribes ; being capable of subsisting exclusively 
 upon either kind of diet, but being obviously intended by Nature to employ 
 both in combination. 
 
 50. The classification of the Mammalia by Linnaeus, although not strictly 
 natural, affords us the readiest means of separating Man, zoologically, from all 
 other animals. He arranged under his order Primates, all the unguiculated 
 Mammalia which have four incisor teeth and two canines in each jaw; and 
 thus Man, with the Monkeys and the Bats, was distinguished from the re- 
 
 * The action of trituration is chiefly performed by the external pteregoid muscles. When 
 these are in operation together, they draw the whole of the lower jaw forwards, so as to 
 make the lower teeth project beyond the upper; and the jaw being drawn back again by 
 the digastric muscles, a rapid alternate movement may be thus effected, such as is seen in the 
 Rodentia. When only the muscle of one side acts, the condyle of that side is thrown for- 
 wards ; and by the alternating operation of the two, aided by other muscles, that rotatory 
 motion is given which we see especially in Ruminating Quadrupeds. 
 
 f In Carnivorous animals, the muscles which elevate the lower jaw attain a very high 
 degree of development. This is very remarkably seen in the internal pteregoid, which in 
 Man is of subordinate size and importance, but which is a very powerful muscle in the Lion, 
 Tiger, &c. 
 
CHARACTERISTICS OF MAN. 67 
 
 mainder of those Quadrupeds which have separate fingers with distinct nails 
 or claws. This group is now sub-divided into three orders, corresponding 
 with the Linnaean genera, Homo, Simla, and Vespertilio. The last of these 
 orders, named Cheiroptera, consists of the Bat tribe, which is easily separated 
 from all others by the peculiar conformation of the anterior extremities, from 
 which its name is derived. The second, termed Quadrumana, comprehends 
 the Apes, Monkeys, and Baboons, which exhibit a regular series ; the highest 
 approaching Man in general conformation ; and the lowest having much more 
 of the general organization of the inferior carnivorous quadrupeds. They are 
 distinguished from other viviparous Mammalia, by possessing an opposable 
 thumb on all four extremities (whence they are termed four-handed), a cha- 
 racter which is only found elsewhere in the Opossums. Although some of 
 the higher members of this group are capable of maintaining the erect posi- 
 tion without difficulty for some time, even whilst walking, it is certainly not 
 that which is natural to them. The posterior extremity, being formed on 
 the plan of a hand, for prehension rather than for direct support, is destitute 
 of the heel, which is characteristic of Man ; and although Apes can climb 
 trees with facility, they cannot plant the foot firmly on the ground, so as to 
 resist attempts to overthrow them; since the foot rests rather upon the outer 
 side than upon its sole, and the narrowness of the pelvis is unfavourable to an 
 equilibrium. There are many points of striking resemblance to Man, how- 
 ever, in the details of the conformation of the Quadrumana, especially among 
 the most elevated species ; the order being distinguished by the same charac- 
 ters from most others. The structure of their alimentary canal differs ex- 
 tremely little from his. The eyes are directed forwards, when the trunk is 
 erect; and the orbit is completely separated from the temporal fossae, by a 
 bony partition. The mammaa are situated on the thorax ; and the penis is 
 pendent. The coitus, however, is reverse, as in the lower Mammalia. The 
 form of the brain in the higher species corresponds with that of Man in this 
 remarkable character, that it is divided into three lobes, of which the poste- 
 rior is prolonged backwards so as to cover the cerebellum ; this is not the case 
 in the highest of the other Mammalia. 
 
 12. Characteristics of Man. 
 
 51. We shall now review, somewhat in detail, the distinctive characters 
 that separate Man from those animals which present the nearest approach to 
 him in general structure and aspect. These may be advantageously classified 
 according to their obvious purposes ; and the first series we shall notice con- 
 sists of those by which Man is peculiarly adapted to the erect attitude. On 
 examining his cranium we remark that the condyles, by which it is articulated 
 with the spinal column, are so placed that a perpendicular dropped from the 
 centre of gravity of the head would nearly fall between them, so as to be 
 within the base on which it rests. The foramen magnum is not placed in the 
 centre of the base of the skull, but just behind it; in order to compensate for 
 the greater specific gravity of the posterior part of the head, which is entirely 
 filled with solid matter, whilst the anterior part contains many cavities. There 
 is, indeed, a little over-compensation, which gives a slight preponderance to 
 the front of the head; so that it drops forwards and downwards when all the 
 muscles are relaxed. But the muscles which are attached to the back of the 
 head are far larger and more numerous than those in front of the condyles ; 
 so that they are evidently intended to counteract this disposition; and we 
 find, accordingly, that we can keep up the head for the whole day, with so 
 slight and involuntary an effort that no fatigue is produced by it. Moreover, 
 the surfaces of the condyles have a horizontal direction when the head is 
 
68 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 upright ; and thus the weight of the skull is laid vertically by them upon the 
 top of the vertebral column. If these arrangements be compared with the 
 position and direction of the occipital condyles in other Mammalia, it will 
 be found that these are placed in the latter much nearer to the back of the 
 head, and that their plane is more oblique. Thus, whilst the foramen mag- 
 num is situated, in Man, just behind the centre of the base of the skull, it is 
 found in the Chimpanzee and Orang Outan to occupy the middle of the 
 posterior third ; and, as we descend through the scale of Mammalia, we ob- 
 serve that it gradually approaches the back of the skull, and at last comes 
 nearly into the line of its longest diameter, as we see in the Horse. The 
 obliquity of the condyles differs in a similar degree. In all Mammalia except 
 Man their plane is oblique ; so that, even if the head were equally balanced 
 upon them, the force of gravity would tend to carry it forwards and down- 
 wards. In Man, the angle which they make with the horizontal is very 
 small ; in the Orang Outan it is as much as 37; and in the Horse their 
 plane is vertical, making the angle 90. If, therefore, the natural posture of 
 Man were horizontal, he would in this respect be circumstanced like the 
 Horse ; for the plane of his condyles, which is nearly horizontal in the erect 
 position, would then be vertical: and the head, instead of being nearly 
 balanced in the erect position, would hang at the end of the neck, so that its 
 whole weight would have to be supported by some external and constantly- 
 acting power. But for this there is neither in the skeleton, nor in the muscu- 
 lar system of Man, any adequate provision. In, other Mammalia the head is 
 maintained in such a position by a strong and thick ligament (the ligamentum 
 nuchas), which passes from the spines of the cervical and dorsal vertebra? to 
 the most prominent part of the occiput ; but of this there is scarcely any 
 
 Fig. 5. 
 
 View of the base of skull of Man, compared with that of the Orang Outan. 
 
 trace in Man. In the horizontal position, therefore, he would have the heavi- 
 est head, with the least power of supporting it. 
 
 52. The position of the face immediately beneath the brain, so that its 
 front is nearly in the same plane as the forehead, is peculiarly characteristic 
 of Man; for the crania of the Chimpanzee and Orang, which approach 
 nearest to that of Man, are entirely posterior to, and not above, the face. It 
 should be remarked that in the young Ape there is a much greater resem- 
 blance to Man in this respect than there is in the adult. For at the time of 
 the second dentition the muzzle of the Ape undergoes a great elongation, so 
 
CHARACTERISTICS OF MAN. 69 
 
 that it projects much more beyond the forehead ; this is seen in Fig. 5. The 
 whole cast of the features is altered at the same time, so that it approaches 
 much more to that of the lower Quadrumana than would be supposed from 
 observation of the young animal only.* This increased projection of the 
 muzzle is an evidence of want of perfect adaptation to the erect posture : 
 whilst the absence of it in Man shows that no other position is natural to him. 
 Supposing that, with a head formed as at present, he were to move on all 
 fours, so that his^face would be brought into a plane parallel with the ground, 
 as painful an effort would be required to examine with the eyes an object 
 placed in front of the body, as is now necessary to keep the eyes fixed on 
 the zenith ; the nose would be unable to perceive any other odours than those 
 which proceeded from the earth or from the body itself; and the mouth could 
 not touch the ground without bringing the forehead and chin also into contact 
 with it. The oblique position of the condyles in the Quadrumana enables 
 them, without much difficulty, to adapt the inclination of their heads to the 
 horizontal or to the erect position of the body; but the natural position, in 
 the highest among them, is unquestionably one in which the spinal column is 
 inclined, tfre body being partially thrown forwards, so as to rest upon the 
 anterior extremities ; and in this position the face is directed forwards without 
 any effort, owing to the mode in which the head is. articulated with the spine. 
 53. The vertebral column in Man, though not absolutely straight, has its 
 curves so arranged, that, when the body is in an erect posture, a vertical line 
 from its summit would fall exactly on the centre of its base. It increases 
 considerably in size in the lumbar region, so as to be altogether somewhat 
 pyramidal in form. The lumbar portion, in the Chimpanzee and Orang, is 
 not of the same proportional strength; and contains but four vertebrae instead 
 of five. The processes for the attachment of the muscles of the back to this 
 part, are peculiarly large and strong in Man ; and this arrangement is obviously 
 adapted to overcome the tendency, which the weight of the viscera in front 
 of the column would have, to draw it forwards and downwards. On the 
 other hand, the spinous processes of the cervical and dorsal vertebrae, which x 
 are in other Mammalia large and strong, for the attachment of the ligamentum 
 nuchae to support the head, have in Man but little prominence, his head being 
 nearly balanced on the top of the column. The base of the human vertebral 
 column is placed on a sacrum of greater proportional breadth, than that of 
 any other animal; this sacrum is fixed between two widely expanded ilia; 
 and the whole pelvis is thus peculiarly broad. In this manner, the femoral 
 articulations are thrown very far apart, so as to give a wide basis of support; 
 and by the oblique direction of the whole pelvis, the weight of the body is 
 transmitted almost vertically, from the top of the sacrum to the upper part of 
 the thigh bones. The pelvis of every other species of the class is very dif- 
 ferently constructed ; as will be seen in the adjoining Figure (6), in which the 
 skeleton of the Orang is placed in proximity with that of Man. It is much 
 longer and narrower, having a far smaller space between the iliac bones and 
 the lowest ribs ; the sacrum is lengthened and reduced in width ; the alae of 
 the ilia are much less expanded ; and the whole pelvis is brought nearly into 
 a line with the vertebral column. The position of the human femur, in which 
 it is most securely fixed in its deep aoetabulum, is that which it has when 
 supporting the body in the erect attitude. In the Chimpanzee and Orang, its 
 analogous position is at an oblique angle to the long axis of the pelvis, with 
 the body supported obliquely in front of it; in many Mammalia, as in the 
 
 * None but young specimens of the Chimpanzee and Orang Outan have ever been 
 brought alive to this country ; and they have never survived the period of their second 
 dentition. 
 
70 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 Elephant, it forms nearly a right angle ; and in several others, as the Horse, 
 Ox, &c., it forms an acute angle with the axis of the pelvis and spinal column. 
 
 54. The lower extremities of Man are remarkable for their length ; which 
 is proportionally greater than that which we find in any other Mammalia, 
 except the Kangaroo tribe. It is evident that there could be no greater ob- 
 stacle to his prorgession in the horizontal posture, than this length of what 
 would then be his hind legs. Either Man would be obliged to rest on his 
 knees, with his thighs so bent towards the trunk, that the attempt to advance 
 them would be inconvenient, his legs and feet being entirely useless ; or he 
 must elevate his trunk upon the extremities of his toes, throwing his head 
 downwards, and exerting himself violently at every attempt to bring forward 
 the thighs by a rotatory motion at the hip-joint. In either case, the only use- 
 ful joint would be that at the hip; and the legs would be scarcely superior to 
 wooden or other rigid supports. The chief difference in their proportional 
 length, between Man and the semi-erect Apes, is seen in the thigh ; and from 
 the comparative shortness of his arms, his hands only reach the middle of the 
 thighs ; whilst in the Chimpanzee they hang on a level with the knees, and 
 in the Orang they descend to the ancles. The human femur is distinguished 
 by its form and position as well as by its length. The obliquity and length 
 of its neck still further increase the breadth of the hips ; whilst they cause 
 the lower extremities of these bones to be somewhat obliquely directed towards 
 each other, so that the knees are brought more into ike line of the axis of the 
 body. This position is obviously of great use in walking, when the whole 
 weight has to be alternately supported on each limb ; for if the knees had 
 been further apart, the whole body must have been swung from side to side 
 at each step, so as to bring the centre of gravity over the top of each tibia ; 
 and, as a matter of fact, it is noticed that the walk of women, in whom the 
 pelvis is broader and the knees more separated, is less steady than that of 
 men. 
 
 55. There is a very marked contrast between the knee-joint of Man, and 
 that even of the highest Apes. In the former, the opposed extremities of the 
 femur and the tibia are expanded, so as to present a very broad articulating 
 surface; and the internal condyle of the femur is lengthened, so that the two 
 are in the same horizontal plane, in the usual oblique position of the femur. 
 In this manner, the whole weight of the body, in its erect posture, falls verti- 
 cally on the top of the tibia, when the joint is in the firmest position in which 
 it can be placed: and a comparison of the knee-joint of the Orang with that 
 of Man, will make it at once evident, that the former is not intended to serve 
 as more than a partial support. The weight of the body is transmitted through 
 the tibia, to the upper convex surface of the astragalus, and thence to the other 
 bones of the foot. The Human foot is, in proportion to the size of the whole 
 body, larger, broader, and stronger, than that of any other Mammal save the 
 Kangaroo. The sole of the foot is concave, so that the weight of the body 
 falls on the summit of an arch, of which the os calcis and the metatarsal bones 
 form the two points of support. This arched form of the foot, and the na- 
 tural contact of the os calcis with the ground, are peculiar to Man alone. All 
 the Apes have the os calcis small, straight, and more or less raised from the 
 ground; which they touch when starrtling erect, with the outer side only of the 
 foot : whilst in animals more remote from Man, the os calcis is brought still 
 more into the line of the tibia ; and the foot being more elongated and nar- 
 rowed, only the extremities of the toes come in contact with the ground. 
 Hence Man is the only species of Mammal, which can stand upon one leg. 
 If we look at the structure of the upper extremity of Man, we observe simi- 
 lar proofs that it is not intended as an organ of support; being destitute of all 
 these adaptations ; and having a conformation obviously designed for other 
 
CHARACTERISTICS OF MAN. 
 
 71 
 
 Fig. 6. 
 
 Comparative view of the Skeleton of Man and that of the Orang Outan. 
 
72 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 purposes, which could not be possibly answered, if it were not completely 
 relieved from the necessity of bearing the weight of the body. This peculiar 
 conformation will be subsequently considered. 
 
 56. The other parts of the Human body concerned in locomotion are 
 exactly adapted to the peculiar construction of the skeleton. The tibia is 
 kept erect upon the foot by the very powerful muscles which are attached to 
 the heel and form the calf of the leg, a prominence observed in no other 
 animal in nearly the same degree. The flexor longus pollicis pedis, which is 
 attached in the Chimpanzee and Orang to the three middle toes, proceeds in' 
 man exclusively to the great toe, on which the weight of the body is often 
 supported. The extensors of the leg upon the thigh are much more power- 
 ful than the flexors, an arrangement seen in no other animal. The glutaBi, by 
 which the pelvis is kept erect upon the thigh, are of far greater size than is 
 elsewhere seen. The superior power of the muscles tending to draw the 
 head and spine backwards, has been already referred to. In the general form 
 of the trunk, there is a considerable difference between Man and most other 
 Mammalia. His chest is large, but is flattened in front, and expanded late- 
 rally, so that its transverse diameter is greater than its antero-posterior ; a 
 peculiarity in which only the most Man-like monkeys partake. His sternum 
 is short and broad ; and there is a considerable distance between the lower 
 ribs and the ilia, in consequence of the small number of ribs, and the length 
 of the lumbar portion of the vertebral column. The viscera in this space, 
 which in the horizontal position would be but insufficiently held up by the 
 abdominal muscles, are, in the erect attitude, securely supported by the ex- 
 panded pelvis. From all these facts, it is an indisputable conclusion, that the 
 erect attitude and biped progression are natural to Man ; and we must regard 
 as in great degree fabulous, all those histories of supposed wild men, who, it 
 has been said, were found in woods, dumb, hairy, and crawling on all-fours. 
 The most elaborate investigation* of the structure of the anthropoid Apes, 
 and the fullest acquaintance with their habits, concur in proving, that their 
 movements are not easy or agile, unless they employ all their limbs for the 
 support of their bodies. 
 
 57. The name Bimana is the most appropriate that could be found, for an 
 order constituted by the Human species only ; since Man alone is two-handed. 
 " That," says Cuvier, " which constitutes the hand, properly so called, is the 
 faculty of opposing the thumb to the other fingers, so as to seize the most 
 minute objects, a faculty which is carried to its highest degree of perfec- 
 tion in Man, in whom the whole anterior extremity is free, and can be em- 
 ployed in prehension." Some naturalists refuse the term hand to the extremi- 
 ties of the monkey tribe, preferring to call them graspers ; for it is certainly 
 true, that, although usually possessing an opposable thumb, they are destitute 
 of the power of performing many of those actions which we regard as most 
 characteristic of the hand. Such actions are chiefly dependent on the size 
 and power of the thumb ; which is much more developed in Man than it is 
 even in the highest Apes. The thumb of the Human hand can be brought 
 into exact opposition to the extremities of all the fingers, whether singly or 
 in combination ; whilst in those Quadrumana which most nearly approach 
 Man, the thumb is so short and weak, and the fingers so long and slender, 
 that their tips can scarcely be brought into opposition, and can never be op- 
 posed in near contact with each other, with any degree of force. Hence, 
 although admirably adapted for clinging round bodies of a certain size, such 
 as the small branches of trees, &c., the extremities of the Quadrumana can 
 
 * See especially Mr. Owen's paper on the Chimpanzee and the Orang Outan in the Zoolo- 
 gical Transactions, vol. i. 
 
CHARACTERISTICS OF MAN. 73 
 
 neither seize very minute objects with such precision, nor support large ones 
 with such firmness, as are essential to the dexterous performance of a variety 
 of operations for which the hand of Man is admirably adapted. Hence 
 the possession of " four hands" is not, as might be supposed, a character 
 which raises the animals that exhibit it above two-handed Man ; for none of 
 these four hands are adapted to the same variety of actions of prehension of 
 which his are capable ; and all of them are in some degree required for sup- 
 port. In this respect their character approaches much nearer to that of the 
 extremities of the lower Mammalia ; and there are several among them in 
 which, the opposable power of the. thumb being deficient, there is no very 
 marked distinction between the so-called hand, and the foot of some Carni- 
 vora. There is much truth, then, in Sir C. Bell's remark, that " We ought 
 to define the hand as belonging exclusively to Man." There is in him, what 
 we observe in none of the Mammalia that approach him in other respects, 
 a complete distinction in the functional character of the anterior and posterior 
 extremities ; the former being adapted for prehension alone, and the latter for 
 support alone. Thus each function is performed with a much higher degree 
 of perfection than it can be where two such opposite purposes have to be 
 united. The arm of the Ape has as wide a range of motion as in Man, so 
 far as its articulations are concerned ; but it is only when the animal is in the 
 erect attitude, that its arm can have free play. Thus the structure of the 
 whole frame must conform to that of the hand, and must act with reference 
 to it. But it cannot be said with truth (as some have maintained) that Man 
 owes his superiority to his hand alone ; for without the directing mind, the 
 hand would be comparatively valueless. His elevated position is due to his 
 mind and its instruments conjointly ; for if destitute of either, mankind would 
 be speedily extinguished altogether, or reduced to a very subordinate grade of 
 existence. 
 
 58. Thus, then, although the order Bimana cannot be separated from the 
 order Quadrumana by any single obvious structural distinction, like that which 
 characterises the Cetacea or the Cheiroptera, it is really as far removed by 
 the minuter, but not less important, modifications which have been detailed. 
 A few other distinctive characters will now be noticed. With one exception 
 (the fossil genus Anoplotherium, which is allied to the Tapir tribe), Man is 
 distinguished from all other animals, by the equality in the length of all his 
 teeth, and by the equally close approximation of them all in each jaw. Even 
 the anthropoid'Apes have the canine teeth longer than the others, and an in- 
 terval in the line of teeth in each side of the jaw, to receive the canine teeth 
 of the opposite jaw. This is more evident in the adult than in the young 
 animal. The vertical position of the Human teeth, on which one of the most 
 characteristic features of the Human face the prominent chin depends, is 
 also quite peculiar ; and is intimately connected both with his erect attitude, 
 and with the perfection of the hands, by which the food is divided and con- 
 veyed to the mouth. He has no occasion for that protrusion of the muzzle 
 and lips, which, in animals that seize their food with the mouth only, is re- 
 quired to prevent the face from coming into general contact with it. The 
 absence of any weapons of offence, and of direct means of defence, are 
 remarkable characteristics of Man, and distinguish him from other animals. 
 On those to whom Nature has denied weapons of attack, she has bestowed 
 the means either of passive defence, of concealment, or of flight. Yet Man, 
 by his superior reason, has not only been enabled to resist the attacks of other 
 animals, but even to bring them under subjection to himself. His intellect 
 can scarcely suggest the mechanism, which his hands cannot frame ; and he 
 has devised and constructed arms more powerful than those which any other 
 creature wields, and defences so secure as to defy the assaults of all but his 
 7 
 
74 ON THE PLACE OF MAN IN THE SCALE OF BEING. 
 
 fellow-men. We find, on comparing the brain of Man with that of the lower 
 Mammalia, that, as might have been anticipated, its proportional dimensions 
 are much greater, and its structure more complex. The former part of this 
 statement is easily verified by an examination of the cranium alone, comparing 
 the size of its cavity with that of the face. The amount of the facial angle, 
 taken after the manner of Camper, affords a tolerably correct indication of the 
 relative sizes of these parts. In Man, the facial angle is, in the average of 
 Europeans, 80; in Negroes, it is about 70. In the adult Chimpanzee (which 
 approaches in this respect nearest to Man), the facial angle is only 35 ; and 
 in the Orang, it is no more than 30. In other animals it is still less, except 
 when it is increased by the prominence of large frontal sinuses, or by the 
 comparative shortness of the jaws. In regard to the structure of the brain, we 
 shall here only remark generally, that the Encephalon of Man far exceeds that 
 of the highest Quadrumana, in the size of the cerebral hemispheres, in the 
 complexity and development of its internal parts, and in the depth and num- 
 ber of its convolutions^. 
 
 59. Man cannot be regarded as distinguished from other Mammalia, how- 
 ever, either by acuteness of sensibility, or by muscular power. His swiftness 
 in running, and agility in leaping, are inferior to that of other animals of his 
 size, the full-grown Orang for example. The smallness of his face, com- 
 pared with that of the cranium, shows that the portion of the nervous system 
 distributed to the organs of sense, is less developed in him than it is in most 
 other animals ; and the small proportional size of the ganglionic centres, with 
 which these organs are immediately connected, is another indication of the 
 same fact. Accordingly, he is surpassed by many in acuteness of sensibility 
 to light, sound, &c. ; but he stands pre-eminent in the power of comparing 
 sensations, and of drawing conclusions from them. Moreover, although none 
 of his senses are very acute in his natural state, they are all moderately so, 
 which is not the case in other animals ; and they are capable (as is ajso his 
 swiftness of foot) of being much improved by practice, especially when cir- 
 cumstances strongly call for their exercise. This power of adaptation to va- 
 rieties in external conditions, which makes him to a great extent independent 
 of them, is manifested in other features of his structure and economy. He 
 is capable of sustaining the lowest, as well as the highest, extremes of tempe- 
 rature and of atmospheric pressure. In the former of these particulars, he is 
 strikingly contrasted with the anthropoid Apes, such as the Chimpanzee, which 
 is restricted to a few of the hottest parts of Africa, and the Orang-Outan, 
 which is only found in Borneo and Sumatra : these cannot be kept alive in 
 temperate climates, without the assistance of artificial heat ; and even when 
 this is afforded, they speedily become diseased and die. His diet is naturally 
 of a mixed kind ; but he can support himself in health and strength, on either 
 animal or vegetable food exclusively. It is by the demands which his pecu- 
 liar condition makes upon the exercise of his ingenuity, that his mental 
 powers are first called into active operation; but, when once aroused, their 
 development has no assignable limit. The slow growth of Man, and the 
 length of time during which he remains in a state of dependence upon his 
 parents, have been already mentioned as peculiarities, by which he is distin- 
 guished from all other animals. He is unable to seek his own food, during 
 at least the three first years of his life ; and he does not attain to his full 
 stature, until he is more than twenty years of age. In proportion to his size, 
 too, the whole sum of his life is greater than that of other Mammalia. The 
 greatest age of the Horse, for example, which is an animal of much superior 
 bulk, is between thirty and forty years. That of the Orang, which, when full 
 grown, surpasses Man in stature, is about the same, so far as it can be ascer- 
 tained. The age to which the life of Man is frequently prolonged, is well 
 
GENERAL CONSIDERATIONS. 75 
 
 known to be above a hundred years ; and instances of such longevity are to be 
 found in all nations. 
 
 60. Still, however widely Man may be distinguished from other animals, 
 by these and other peculiarities of his structure and economy, he is yet more 
 distinguished by those mental endowments, and the habitudes of life and 
 action thence resulting, which must be regarded as the essential characteris- 
 tics of humanity. In the highest among brutes, the mere instinctive propen- 
 sities (as already defined, 17, 23), are the frequent springs of action; and 
 although the intelligent will is called into exercise to a certain extent, the 
 character never rises beyond that of the child. In fact, the correspondence 
 between the psychical endowments of the Chimpanzee, and those of the 
 Human infant before it begins to speak, is very close. In Man, however, the 
 instinctive propensities only manifest themselves strongly, whilst the intellect 
 is undeveloped ; and nearly all the actions of adult life are performed under 
 the direction of the intelligent will. From the intelligence of Man results his 
 mental improvability ; and his improved condition impresses itself upon his 
 organization. This capability of improvement in the bodily as well as the 
 mental constitution of Man, is the cause of the. comforts now enjoyed by 
 civilised races, and of the means which they possess of still further elevation. 
 In the processes by which these are attained, we observe a remarkable differ- 
 ence between the character of Man, and that of other animals. The arts of 
 which these last are capable, are limited, and peculiar to each species ; and 
 there seems to be no general power of adapting these to any great variety of 
 purposes, or of profiting by the experience of others. Where a particular 
 adaptation of means to ends, of actions to circumstances, is made by an indi- 
 vidual (as is frequently the case, when some amount of intelligence or ration- 
 ality exists), the rest do not seem to profit by it; so that there is no proof 
 that any species or race among the lower animals ever makes a voluntary 
 advance towards an improvement or alteration in its condition. That modifi- 
 cations in structure and instincts may be induced by circumstances, in some 
 of the most improvable species, such as the Dog, has been shown by abun- 
 dant evidence ; and these modifications, if connected with the original habits 
 and instincts of the species, maybe hereditarily transmitted. There is ample 
 proof that the same is the case, in regard both to the corporeal structure and 
 the psychical endowments of Man. Under the influence of education, phy- 
 sical and mental, continued through successive generations, the capabilities of 
 his whole nature, and especially those of his brain, are called out; so that the 
 general character of the race is greatly improved. On the other hand, under 
 the influence of a degraded condition, there is an equally certain retrogression; 
 so that, to bring up the New Holland Savage, or the African Bushman, to the 
 level of the European, would probably require centuries of civilisation. One 
 of the most important aids to the use and development of the human mind, is 
 the power of producing articulate sounds, or language ; of which, as far as 
 we know, Man is the only animal in possession. There is no doubt, that 
 many other species have certain powers of communication between individu- 
 als ; but these are probably very limited, and of a kind very different from a 
 verbal language. 
 
 61. Although, as we have stated, there is nothing in Man's present condi- 
 tion, which removes him from the pale of the Animal kingdom, and although 
 his reasoning powers differ rather in degree than in kind from those of the 
 inferior animals, he seems distinguished by one innate tendency ; to which 
 we have no reason to suppose that anything analogous elsewhere exists ; and 
 which we might term an instinct, were it not that this designation is generally 
 applied to propensities of a much lower character. The tendency here 
 referred to, is that which seems universal in Man, to believe in some unseen 
 
76 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 Existence. This may take various forms, but is never .entirely absent from 
 any race or nation, although (like other innate tendencies) it may be defective 
 in individuals. Attempts have been made by some travellers to prove, that 
 particular nations are destitute of it ; but such assertions have been based 
 only upon a limited acquaintance with their habits of thought, and with their 
 outward observances. For there are probably none, that do not possess the 
 idea of some invisible Power external to themselves ; whose favour they seek, 
 and whose anger they deprecate, by sacrifice and other religious observances. 
 It requires a higher mental cultivation than is always to be met with, to con- 
 ceive of this Power as having a Spiritual existence; but wherever the idea 
 of spirituality can be defined, it seems connected with it. The vulgar readi- 
 ness to believe in demons, ghosts, &c., is only an irregular or depraved 
 manifestation of the same tendency. Closely connected with it, is the desire 
 to share in this spiritual existence ; which has been implanted by the Creator 
 in the mind of Man ; and which, developed as it is by the mental cultivation 
 that is almost necessary for the formation of the idea, has been regarded by 
 philosophers in all ages, as one of the chief natural arguments for the im- 
 mortality of the soul. By this Immortal Soul, the existence of which is thus 
 guessed by Man, but of whose presence within him he derives the strongest 
 assurance from Revelation, Man is connected with beings of a higher order, 
 amongst whom Intelligence exists, unrestrained in its exercise by the imper- 
 fections of that corporeal mechanism, through which it here operates ; and to 
 this state, a state of more intimate communion of mind with mind, and of 
 creatures with their Creator, he is encouraged to aspire, as the reward of 
 his improvement of the talents here committed to his charge. 
 
 CHAPTER II. 
 
 OF THE MUTUAL RELATIONS OF THE DIFFERENT BRANCHES OF THE HUMAN 
 
 FAMILY. 
 
 1. General Considerations. 
 
 62. AMONGST the various tribes of Men, which people the surface of the 
 globe, and which are separated from all other animals by the foregoing cha- 
 racters, there are differences of a very striking and important nature. They 
 are distinguishable from each other, not merely by their language, dress, 
 manners and customs, religious belief, and other acquired peculiarities, but in 
 the physical conformation of their bodies ; and the difference lies, not merely 
 in the colour of the skin, the nature of the hair, the form of the soft parts 
 (such as the nose, lips, &c.,) but in the shape of the skull, and of other parts 
 of the bony skeleton, which might be supposed to be less liable to variation. 
 It is a question of great scientific interest, as well as one that considerably 
 affects the mode in which we treat the races that differ from our own, whe- 
 ther they are all of one species, that is, descended from the same or from 
 similar parentage, or whether they are to be regarded as distinct species, 
 the first parents of the several races having had the same differences among 
 themselves, as those now exhibited by their descendants. 
 
 63. It has been a favourite idea, among those who wished to excuse the 
 horrors of slavery, or the extirpation of savage tribes, that the races thus 
 
ON THE DISCRIMINATION OF SPECIES. 77 
 
 treated might be considered as inferior species, incapable of being raised by 
 any treatment to our own elevation; and as thus falling legitimately under the 
 domination of the superior races, just as the lower animals have been placed 
 by the Creator in subservience to Man. This doctrine, which has had its 
 origin in the desire to justify as expedient what could not be defended as 
 morally right, finds no support from scientific inquiries conducted in an en- 
 larged spirit. In order to arrive at a just conclusion on the subject, it is ne- 
 cessary to take a very extensive survey of the evidence furnished by a number 
 of different lines of inquiry. Thus, in the first place, it is right to investigate 
 what are the discriminating structural marks, by which species are distin- 
 guished among the lower tribes of animals. Secondly, it should be ascer- 
 tained to what extent variation may proceed among races, which are histori- 
 cally known to have a common parentage ; and what are the circumstances 
 which most favour such variations. Thirdly, the .extreme variations, which 
 present themselves among the different races of men, should be compared 
 with those which occur among tribes of animals known to be of the same 
 parentage; and it should be questioned, at the same time, whether the cir- 
 cumstances which favour the production of varieties in the latter case, are in 
 operation in the former. Fourthly, where it is impossible to trace back dis- 
 tinct races to their origin, it is. to be inquired how far agreement in physiolo- 
 gical and psychological peculiarities may be regarded as indicating specific 
 identity, even where a considerable difference exists in bodily conformation ; 
 and this test, if it can be determined on, has to be applied to Man. Fifthly, 
 it must be attempted, by a detailed examination of the varieties of the human 
 race themselves, to ascertain whether their differences in conformation are 
 constant; or whether there are not occasional manifestations, in each race, of 
 a tendency to assume the characters of others ; so as to prevent a definite line 
 being drawn between the several tribes, which together make up the (sup- 
 posed) distinct species.* 
 
 2. On the Discrimination of Species. 
 
 64. Theirs/ of the foregoing questions is a fertile source of perplexity to 
 the Naturalist ; owing to the tendency that exists in certain races of Plants 
 and Animals, to exhibit variations of form much greater than those which 
 are relied upon in other instances as characterizing distinct species. In our 
 ignorance as to the history of the origin of the greater part of the dissimilar 
 forms or races of organized beings, with which the globe is peopled, we are 
 accustomed to regard two races of Plants or animals as of the same species, 
 that is, as Having had the same or similar progenitors, when they are not 
 distinguished from one another by any peculiarities, but such as the one may 
 be supposed to have gained, or the other to have lost, by the influence of 
 external circumstances during a long period of time. On the other hand, two 
 races are regarded as constituting distinct species,' that is, are believed to 
 have descended from dissimilar parents, when a constant well-marked dif- 
 ference exists between them, such as exhibits no tendency to variation in the 
 individuals of either race fleeing equally characteristic of every one), and is 
 not affected by the lapse of time or by change in external conditions. 
 
 65. Thus, if we compare together the different breeds of Dogs, we find 
 
 * This investigation has been most elaborately, and in the Author's opinion most suc- 
 cessfully, worked out by Dr. Prichard, in his profound and philosophical Treatise on the 
 Physical History of Man. The sketch of the argument given above does little more than 
 exhibit the conclusions at which he has arrived ; and for the grounds on which these are 
 based, reference .must be made to that work, or to the abridgment of it published by Dr. 
 Prichard, under the title of the Natural History of Man. 
 
 7* 
 
78 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 that, although they are distinguished by very marked peculiarities, yet that 
 these peculiarities are by no means constant. There is historical evidence of 
 the great change, which may take place in their conformation and habits, 
 under the influence of a change in their external circumstances ; in the case, 
 for example, of the blood-hounds, introduced into the West Indies by the 
 Spaniards, which have now degenerated into a wild race of very different 
 form, and have lost all the distinctive characters of the breed. And there is 
 not that close agreement in the distinctive characters of the several breeds, 
 among the individuals respectively composing them, which is requisite for the 
 establishment of a definite specific distinction ; the characters being shaded 
 off, as it were in individuals, so as to cause a near approximation between the 
 less decided forms of the different races. On the other hand, in spite of the 
 varieties of conformation exhibited by the several races of Dog, (which even 
 affect the number of vertebrae in the tail, as well as the shape and proportions 
 of the bones, we never see any which present so strong a resemblance to the 
 Fox, as to be at all in danger of being mistaken for that animal ; and they 
 may always be distinguished by this obvious character, that the pupil of the 
 eye of the Dog is always round, whilst that of the Fox is oval when con- 
 tracted. This difference may appear a very trifling one, in comparison with 
 the important variations presented in the structure of the different breeds of 
 Dogs ; but it is constant ; and it may therefore be assumed to have existed 
 in the progenitors of each race, as it exists at present in all their descendants. 
 
 66. There are many instances of an opposite character, in which the tend- 
 ency to variation is extremely small ; and in which the Naturalist feels jus- 
 tified in assuming a specific difference, from variations in size or colour, 
 which in themselves are very trifling, but which are important in classifica- 
 tion, because they are constant. Thus, among the several species of the 
 genus Felis (or Cat tribe), there is scarcely any perceptible osteological varia- 
 tion, except in point of size ; so that even Cuvier was unable to find out a 
 positive means of distinguishing the skull of the Lion from that of the Tiger; 
 and the skeleton of a Wild Cat is a reduced copy of that of the largest Felines. 
 There are certain species, which are distinguished by no other external indi- 
 cations, than the markings upon their skins ; characters, which are in other 
 cases subject to extreme uncertainty; but which are here so constant, as to 
 present scarcely the slightest variation amongst the individuals of each race. 
 Thus, if a certain patch or stripe be repeated from generation to generation, in 
 a wild feline race, the Naturalist is inclined to regard this as a sufficient proof 
 of the specific difference of that race from another which is differently marked. 
 The Domestic Cat is the only one of the group, which is liable to any con- 
 siderable variation ; and in this species, as every one knows, the markings 
 characteristic of the several breeds or races are not thus constantly repeated, 
 and therefore cannot be indicative of original difference. Now it is precisely 
 in this species that we should look for such variations ; since it is the only 
 one which can be domesticated; and the capability of domestication implies 
 a power in the original constitution of the animal, to adapt itself to a change 
 of circumstances, and thus to exhibit various departures from its original type. 
 
 67. This striking contrast, between variable and invariable groups of ani- 
 mals nearly allied to each other, is found through the whole kingdom ; every 
 division of it appearing to contain some species, which do not change their 
 forms or other characteristics under any circumstances, but which cease to 
 exist if a change takes place in their conditions, incompatible with the regular 
 performance of their functions ; whilst it also includes others, in whose phy- 
 sical and psychical constitutions there is such a susceptibility of modification, 
 that new forms and new instincts may arise, adapted to a great variety of 
 external conditions, and thus new and very different races may be originated. 
 
EXTENT OF VARIATION IN RACES OF THE SAME SPECIES. 79 
 
 Thus, the Feline races, with a few exceptions, are fitted to maintain life only 
 in tropical climates, and very speedily die in colder countries (unless kept 
 warm by artificial means), in consequence of their deficiency of heat-pro- 
 ducing power, and the want of a close downy fur adapted to retain the caloric 
 generated in their bodies. On the other hand, the Dog is enabled to accom- 
 pany Man, in the coldest as well as the hottest regions of the globe ; his 
 power of generating heat being capable of variation, in accordance with the 
 external temperature ; and his entire organization undergoing modifications, 
 which adapt it to the change in the conditions of its existence. It appears, 
 then, that it is quite impossible to fix upon any difference of structural pecu- 
 liarities, as indications of the distinctness of species ; until it has been ascer- 
 tained by observation, whether they are constant and invariable, the races 
 neither exhibiting any tendency to change in successive generations, nor 
 showing any disposition to mutual approximation, by the occasional modifi- 
 cation of the distinctive characters in the individuals composing them. 
 
 3. On the possible Extent of Variation within the Limits of Species. 
 
 68. We now come to the second point of our inquiry, namely, the 
 amount of variation which may take place in races, historically known to 
 have had a common parentage. There is considerable difficulty in obtaining 
 the most complete evidence upon this subject; owing to the want of accurate 
 observation in the more remote historical periods, when it is probable that 
 most of the varieties or breeds of our domesticated animals were first origi- 
 nated. Still there is an adequate amount of proof, that these races may 
 undergo very considerable modifications, in the course of a few generations ; 
 and that new races or breeds, distinguished by marked peculiarities, may 
 originate even at the present time. Our most satisfactory information is de- 
 rived from the changes, which have taken place in the races of domesticated 
 animals, introduced into the West Indies and South America, by the Span- 
 iards, three centuries since. Many of these races have multiplied exceed- 
 ingly, on a soil and under a climate congenial to their nature ; and several of 
 them have run wild in the vast forests of America, and have lost all the most 
 obvious appearances of domestication. The wild tribes are found to differ 
 physically from the domesticated breeds, from which they are known to have 
 originated ; and there is good reason to regard this change, as a partial restora- 
 tion of the primitive characteristics of the wild stocks, from which the tamed 
 animals originally descended. Thus we find that the Hog, where it has re- 
 turned to its wild state, nearly resembles the Wild Boar, which has never 
 been in a state of domestication. The colour loses the variety found in the 
 domestic breeds ; the Wild Hogs of the American forests being uniformly 
 black. The thin covering of hair and scattered bristles is replaced by a thick 
 fur, often somewhat crisp ; beneath which is found, in those which inhabit 
 the colder regions, a species of wool. The head, too, becomes much larger 
 in these wild races, as in the original Boar; and the differences in the conform- 
 ation of the cranium, between these and the domesticated breeds, are fully 
 equal to anything that is seen in the human race. The variations which pre- 
 sent themselves in other races of domesticated animals introduced into South 
 America at the same period, such as the horse, ass, ox, sheep, goat, dog, 
 cat, and gallinaceous birds, are not less striking. Still more remarkable 
 variations are seen in certain domesticated breeds, which must without doubt 
 have sprung from the same stock with the ordinary ones, although their origin 
 cannot be traced historically ; thus, in some localities we find swine with 
 solid hoofs ; in others, the hoof is cleft into five parts ; and in others, again, 
 the toes are developed to a monstrous length. 
 
80 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 69. Although the numerous examples furnished by the Vegetable Kingdom 
 may seem to have but a remote bearing on the question, it would still be 
 wrong to pass them by without notice ; since the general principles already 
 noticed are recognized by Botanists, as serving for the discrimination or iden- 
 tification of species of Plants ; to which they apply equally with Animals. 
 We have abundant evidence, in the case of our cultivated fruits and flowers, 
 of the origination of new and well-marked varieties from stocks originally the 
 same ; the differences between these races being such, as would undoubtedly 
 have led to their being ranked as distinct species, if their common parentage 
 were not known. Thus, of the numerous widely-different varieties of Apple, 
 Pear, Strawberry, Plum, &c., many have been produced in our own time ; 
 and there is no doubt, that all the forms of each fruit are descended from 
 wild stocks, extremely unlike any one of them. So the Cowslip, Primrose, 
 Oxslip, and Polyanthus, which were formerly regarded as constituting at least 
 two distinct species, have been shown to be all producible from the seeds of 
 one parent. And a single plant of the Orchideous tribe has borne flowers and 
 pseudo-bulbs, which were formerly considered as characteristic of three dis- 
 tinct genera. 
 
 70. Of the origination of entirely new races of animals, distinguished by 
 physical peculiarities, and disposed to become permanent under circumstances 
 favourable to their perpetuation, we have frequent examples at the present 
 time. It is not uncommon to meet with individuals among our domesticated 
 animals, which differ from others of their kind, in some marked feature of 
 their conformation. If this be of a nature which impairs the value of the 
 animal, care is taken that it shall not propagate its race ; but, on the other 
 hand, if it afford a prospect of utility, the skill of the breeder is employed to 
 perpetuate it. One of the most remarkable examples of this kind, is to be 
 Sound in the origin of the Ancon or Otter breed of Sheep, now common in 
 New England. In the year 1791, one of the ewes on the farm of Seth 
 Wright, in the State of Massachusetts, produced a male lamb, remarkable for 
 the singular length of its body, the shortness of its limbs, and the crookedness 
 of its fore-legs. This physical conformation, incapacitating the animal from 
 leaping fences, appeared to the farmers around so desirable, that they wished 
 it continued. Wright consequently determined on breeding from this ram ; 
 but the first year he obtained only two with the same peculiarities. In the 
 following years, he obtained greater numbers ; and when they became capable 
 of breeding with one another, the new race became permanent, the offspring 
 invariably having the JLncon conformation, when both the parents belonged 
 to that breed. In the Human race, it is not uncommon to find particular 
 families distinguished by the possession of six fingers on each hand, and six 
 toes on each foot. If such were to intermarry exclusively with one another, 
 there can be no reasonable doubt that the children would invariably exhibit 
 the same peculiarity; and the six-fingered race, which now tends, whenever 
 it is originated, to merge in the more general form, would then become per- 
 manent. When it is remembered that the influence of a scanty population, in 
 the early ages of the world, would have been precisely the same as that which 
 is now exercised by the breeders of animals, we can understand why the va- 
 rieties, which then arose, should have had a much greater tendency to become 
 permanent, than most of those which now present themselves. At the present 
 time, any peculiarity which may occasionally arise, speedily merges by inter- 
 mixture with the mass, and returns to the common standard; but when popu- 
 lation was scanty, any peculiarities existing in one family would be perpetuated, 
 by the intermixture of its members, rendered necessary by their isolation from 
 others ; and thus a new race would originate. 
 
 71. For the cause of these occasional variations from the common type, 
 
ON THE VALUE OF SPECIFIC DISTINCTIONS. 81 
 
 we must look in part to the original constitution of the species, and in part 
 to the influence of external conditions. As already mentioned, there is a 
 marked difference among various species of animals (even those nearly allied, 
 such as the Domestic Cat and the Tiger), in regard to their respective capa- 
 cities for variation. And among the peculiarities of conformation which oc- 
 casionally present themselves in the Human and other most variable species, 
 there are several, which cannot be in any way attributed to the modifying 
 influence of external conditions; such, for example, as the development of 
 additional fingers or toes, the alteration in the number of the vertebrae in the 
 tail, the unusual consolidation or separation of the toes, &c. But it cannot 
 be doubted, when the known history of the domesticated races is fairly con- 
 sidered, that a change of external circumstances is capable of exerting a very 
 decided influence upon the physical form, upon the habits and instincts, and 
 upon various functions of life. The variations thus induced, extend to con- 
 siderable modifications in the external aspect, such as the colour, the texture, 
 and the thickness of the external covering ; to the structure of limbs, and the 
 proportional size of parts ; to the relative development of the organs of the 
 senses and of the psychical powers, involving changes in the form of the cra- 
 nium ; and to acquired propensities, which, within certain limits (depending, it 
 would appear, on their connection with the natural habits of the species), may 
 become hereditary. 
 
 4. On the Extremes of Variation among the Races of Men. 
 
 72. We have now to inquire, in the third place, how far the same influ- 
 ences might be expected to operate in the Human race ; and whether the ex- 
 treme varieties, which we enconuter among Mankind, are really greater than 
 those, which we meet with in the races of domesticated animals, known to 
 have had a common ancestry. It must be admitted by every one, that both 
 of the conditions just noticed as favouring the origination of peculiarities, ope- 
 rate to their fullest extent in Man. There is no other species of animals, in 
 which an equal tendency to variation exists. The different individuals of the 
 same breed of Dogs, for example, resemble each other far more closely in 
 physical and mental characters, than the individual men of one nation ; and 
 there is no species of animals, which possesses an equal power of maintain- 
 ing life in the remote extremes of climate, atmospheric pressure, &c., which 
 are encountered at different parts of the earth's surface, and at different ele- 
 vations above it. Again, we should expect to find these varieties in external 
 circumstances, together with the change of habits induced by civilization 
 (which is far greater than any change effected by domestication in the condi- 
 tion of the lower animals), producing still more important alterations in the 
 physical form and constitution of the Human body, than those effected in 
 brutes by a minor degree of alteration. And it may be reasonably antici- 
 pated, that, as just now explained, there would be a greater tendency to the 
 perpetuation of these varieties, in other words, to the origination of distinct 
 races, during the earlier ages of the history of the race, than at the present 
 time, when, in fact, by the increasing admixture of races which have long 
 been isolated, there is a tendency to the fusion of all these varieties, and to a 
 return to a common type. Now, when the extreme varieties which are pre- 
 sented by the different races of Man are carefully compared together, it is 
 found that their differences are all of the same kind as those, which present 
 themselves among the breeds of domesticated animals ; and do not by any 
 means exceed them (perhaps not even equalling them in degree. This will 
 be shown in detail hereafter. 
 
 73. It appears, then, that the analogical argument derived from the pheno- 
 
82 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 mena presented by the domesticated species among the lower animals, is de- 
 cidedly in favour of the specific unity of the Human race ; the differences 
 which have sprung up, in course of time, amongst the inhabitants of different 
 parts of the world, being such as we have a fair right to attribute according to 
 the recognized principles of Zoology to the modifying influence of external 
 conditions, acting upon a constitution peculiarly disposed to yield to it. 
 
 5. On the Value of Physiological and Psychological Peculiarities, as 
 Specific Distinctions. 
 
 74. We have now to inquire, in the fourth place, what other arguments ill 
 favour of this position may be drawn from agreement or difference in Physi- 
 ological and Psychological peculiarities. A comparison of the physiological 
 history of two races, is often found to afford a better criterion of their specific 
 difference or identity, than the comparison of their structural characters. 
 Now, in every important point of physiological history, there is a wonderful 
 agreement amongst the different races of Men ; the variations not being greater 
 than are those with which we meet among the different individuals of any 
 one race. Thus, we not only find the average duration of life to be every- 
 where the same, (making allowance for circumstances which are likely to in- 
 duce disease), but the various epochs of life have a close correspondence, 
 such as the times of the first and second dentition, the period of puberty, the 
 duration of pregnancy, the intervals of the catamenia, and the time of their 
 final cessation. And the different races of Man are all subject to the same 
 diseases, both sporadic, contagious, and epidemic ; whilst there are no two 
 really-distinct species among the lower animals, which have more than a very 
 slight conformity in this respect. 
 
 75. The most important physiological test of specific unity or diversity, is 
 derived from the phenomena attending the Reproductive process. It is well 
 known that, in Plants, the stigma of the flower of one species may be fertil- 
 ized with the pollen of an allied species ; and that, from the seeds produced, 
 plants of an intermediate character may be raised. These hybrid plants, 
 however, will not perpetuate the new race ; for, although they may ripen their 
 seed for one or two generations, they will not continue to reproduce them- 
 selves beyond the third or fourth. But, if the intervention of one of the pa- 
 rent species be employed, its stigma being fertilized by the*pollen of the 
 hybrid, or vice versa, a mixed race may be kept up for some time longer ; 
 but it will then have a manifest tendency to return to the form of the parent 
 whose intervention has been employed. Where, on the other hand, the pa- 
 rents themselves were only varieties, the hybrid forms but another variety, 
 and its powers of reproduction are rather increased than diminished ; so that 
 it may continue to propogate its own race, or may be used for the production 
 of other varieties, almost ad infinitum. In this way, many beautiful new 
 varieties of garden flowers have been obtained ; especially among such species 
 as have a natural tendency to change their aspect. Amongst Animals, the 
 limits of hybridity are much more narrow, since the hybrid is totally unable 
 to continue its race with one of its own kind ;* and although it may be fertile 
 with one of its parent species, the progeny will of course approach in cha- 
 racter to the pure breed, and the race will ultimately merge into it. On the 
 other hand, in Animals, as among Plants, the mixed offsprings originating from 
 different races within the limits of the same species, generally exceed in vi- 
 
 * One or two instances have been stated to occur, in which a Mule has produced offspring 
 from union with a similar animal; but this is certainly the extreme limit, since no one has 
 ever maintained that the race can be continued further than the second generation, without 
 admixture with one of the parent species. 
 
DISTINCTIVE PECULIARITIES OF THE RACES OF MAN. 83 
 
 gour, and in the tendency to multiply, the parent races from which they are 
 produced, so as to gain ground upon the older varieties, and gradually to su- 
 persede them. In this manner, by the crossing of the breeds of our domes- 
 ticated animals, many new and superior varieties have been produced. The 
 general principle is, then, that beings of distinct species, or descendants from 
 stocks originally different, cannot produce a mixed race, which shall possess 
 the capability of perpetuating itself; whilst the union of varieties has a tend- 
 ency to produce a race superior in energy and fertility to its parents. 
 
 76. The application of this principle (if it be admitted as such) to the Hu- 
 man races, leaves no doubt with respect to their specific unity ; for, as is well 
 known, not only do all the races of Men breed freely with each other, but the 
 mixed race is generally superior in physical development, and in tendency to 
 rapid multiplication, to either of the parent stocks ; so that there is much rea- 
 son to believe that, in many countries, the mixed race between the Aborigines 
 and European colonizers will ultimately become the dominant power in the 
 community. This is especially the case in India and South America. 
 
 77. Not less conclusive is the result of the test, furnished by agreement 
 or difference in psychological characters. Among the lower animals, we find 
 every species characterised by the possession of instincts and propensities 
 peculiar to itself; and these instincts often differ remarkably in species, which 
 present the closest structural alliance. On the other hand, in the several 
 varieties of domesticated animals, notwithstanding their strongly-marked di- 
 versities of physical structure, we may recognize instincts which are fun- 
 damentally the same, although they have been modified by the continued 
 influence of Man, and by the new circumstances in which the animals are 
 placed. Now from an impartial survey of the psychological characters of the 
 different races of Men, so far as our present knowledge extends, the follow- 
 ing conclusion may be drawn. " We contemplate, among all the diversified 
 tribes, who are endowed whh reason and speech, the same internal feelings, 
 appetencies, and aversions; the same inward convictions, the same sentiments 
 of subjection to invisible powers, and (more or less fully developed) of ac- 
 countableness or responsibility to unseen avengers of wrong and agents of 
 retributive justice, from whose tribunal men cannot even by death escape. 
 We find everywhere the same susceptibility, though not always in the same 
 degree of forwardness or ripeness of improvement, of admitting the cultiva- 
 tion of those universal endowments, of opening the eyes of the mind to the 
 more clear and luminous views which Christianity unfolds, of becoming 
 moulded to the institutions of religion and of civilised life : in a word, the 
 same inward and mental nature is to be recognized in all the races of men.* 
 
 6. On the Comparative Peculiarities of the Different Races of Mankind. 
 
 78. We have now to inquire, fifthly and lastly, whether it is possible, after 
 a detailed and careful examination of the ensemble of the characters of the 
 different races of Men, to make any division of them into distinct groups, 
 capable of being defined by such constant and well-marked features, as shall 
 entitle them to be regarded in the light of distinct species. The general re- 
 sults, only, of this inquiry, can here be given ; and this in a very summary 
 manner. They will be almost entirely drawn from the profound and labo- 
 rious investigations of Dr. Prichard. 
 
 79. The characters which are most relied on for the discrimination of the 
 several races of Mankind, are the colour of the skin, the nature of the hair, 
 and the conformation of the skull and other parts of the skeleton. The Co- 
 
 * Pilchard's Natural History of Man, p. 546. 
 
84 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 lour of the skin exists in the epidermis only; and it depends upon the ad- 
 mixture of certain peculiar cells, termed pigment-cells, with the ordinary 
 epidermic cells. These pigment-cells, as will be shown hereafter ( 163), are 
 distinguished by their power of generating or secreting colouring-matter of 
 various hues ; and all the varied shades of colour, presented by the different 
 races of men, are due to the relative amount of these cells, and to the parti- 
 cular tint of the pigment which they form. It would be easy, by selecting 
 well-marked specimens of each race, to make it appear that colour affords 
 sufficient distinctive marks for their separation : thus, for example, the fair 
 and ruddy Saxon, the jet-black Negro, the olive Mongolian, and the copper- 
 coloured North American, would seem positively separated from each other 
 by this character, propagated, as it seems to be, with little or no perceptible 
 change, from generation to generation. But although such might appear to 
 be the clear and obvious result of a comparison of this kind, yet a more pro- 
 found and comprehensive survey tends to break down the barrier that would 
 be thus established. For, on tracing this character through the entire family 
 of Man, we find the isolated specimens just noticed to be connected by such 
 a series of links, and the transition from one to the other to be so very gradual 
 that it is impossible to say where the line is to be drawn. There is nothing 
 here, then, which at all approaches to the fixed and definite marks, which have 
 been noticed as serving though equally trivial in themselves to establish 
 specific distinctions among other tribes of animals. 
 
 80. But further, there is abundant evidence that these distinctions are far 
 from being constantly maintained, even in any one race. For among all the 
 principal subdivisions, albinoism, or the absence of pigment-cells, occasion- 
 ally presents itself; so that the fair skin of the European may present itself 
 in the offspring of the Negro or of the Red Man. On the other hand, in- 
 stances are by no means rare, of the unusual development of pigment-cells 
 in individuals of the fair-skinned races ; so ; that parts of the body are of a 
 dark red or brown hue, or are even quite black. Such modifications may 
 seem of little importance to the argument; since they are confined to indi- 
 viduals, and may be put aside as accidental. But there is ample evidence, 
 that analogous changes may take place in the course of time, which tend to 
 produce a great variety of shades of colour, in the descendants of any one 
 stock. Thus, in the great Indo-Atlantic family, which may be unquestion- 
 ably regarded as having had a common origin, we find races with fair com- 
 plexion, yellow hair, and blue eyes, others presenting the xanthous or olive 
 hue, and others decidedly black. A similar diversity may be see,n among 
 the American races, which are equally referrible to one common stock ; and 
 it exists to nearly the same extent among the African nations, which are simi- 
 larly related to each other. It may be freely admitted that, among European 
 colonists settled in hot climates, such changes do not present themselves within 
 a few generations ; but in many well-known instances of earlier colonization 
 they are very clearly manifested. Thus the wide dispersion of the Jewish 
 nation, and their remarkable isolation (maintained by their religious observ- 
 ances) from the people among whom they live, render them peculiarly appro- 
 priate subjects for such observations ; and we accordingly find, that the bru- 
 nette complexion and dark hair, which are usually regarded as characteristic 
 of the race, are frequently superseded, in the Jews of Northern Europe, by 
 red or brown hair and fair complexion ; whilst the Jews who settled in India 
 some centuries ago, have become as dark as the Hindoos around them. 
 
 81. The relation of the complexions of the different races of Men to the 
 climates they respectively inhabit, is clearly established by an extended com- 
 parative survey of both. From such a survey the conclusion is inevitable, 
 that the intertropical region of the earth is the principal seat of the black races 
 
DISTINCTIVE PECULIARITIES OF THE RACES OF MAN. 85 
 
 of Men ; whilst the region remote from the tropics is that of the white races ; 
 and that the climates approaching the tropics are generally inhabited by na- 
 tions, which are of an intermediate complexion. To this observation it may 
 be added, that high mountains, and countries of great elevation, are generally 
 inhabited by people of a lighter colour, than are those of which the level is 
 low, such as swampy or sandy plains upon the sea-coast. These distinc- 
 tions are particularly well seen in Africa, where the tropics almost exactly 
 mark out the limits of the black complexion of the inhabitants ; and where 
 the deepest hue is to be seen among the Negroes of the Guinea Coast, whose 
 residence unites both the conditions just mentioned. 
 
 82. The nature of the Hair is, perhaps, one of the most permanent charac- 
 teristics of different races. In regard to its colour, the same statements apply, 
 as those just made with respect to the colour of the skin; the variety of hue 
 being given by pigment-cells, which may be more or less developed under 
 different circumstances. But it has been thought that its texture afforded a 
 more valid ground of distinction ; and it is commonly said that the substance 
 which grows on the head of the African races, and of some other dark-colour- 
 ed tribes (chiefly inhabiting tropical climates), is wool, and not hair. This, 
 however, is altogether a mistake : for microscopic examination clearly de- 
 monstrates, that the hair of the Negro has exactly the same structure with 
 that of the European ; and that it does not bear any resemblance to wool, save 
 in its crispness and tendency to curl. Moreover, even this character is far 
 from being a constant one ; for, whilst Europeans are not unfrequently to be 
 met with, whose hair is as crisp as that of the Negro, there is a great variety 
 amongst the Negro races themselves, which present every gradation from a 
 completely crisp (or what is termed woolly) hair, to merely curled or even 
 flowing locks. A similar observation holds good in regard to the natives of 
 the islands of the great Southern Ocean, where some individuals possess crisp 
 hair, whilst others, of the same race, have it merely curled. It is evident, then, 
 that no characters can be drawn from the colour or texture of the hair in Man, 
 sufficiently fixed and definite to serve for the distinction of races: and this 
 view is borne out by the evident influence of climate, in producing changes 
 in the hairy covering of almost every race of domestic animals ; the change 
 often manifesting itself in the very individuals that are transported from one 
 country to another, and showing itself yet more distinctly in succeeding gene- 
 rations. 
 
 83. It has been supposed, that varieties in the configuration of the Skeleton 
 would afford characters for the separation of the Human races, more, fixed 
 and definite than these derived from differences in the form, colour, and tex- 
 ture of the soft parts which clothe it. And attention has been particularly 
 directed to the skull and the pelvis, as affording such characters. It has been 
 generally laid down as a fundamental principle, that all those notions which 
 are found to resemble each other in the shape of their heads, must needs be 
 more nearly related to each other, than they are to tribes of Men who differ 
 from them in this particular. But if this principle be rigorously carried out, 
 it will tend to bring together races, which inhabit parts of the globe very re- 
 mote from each other, and which have no other mark of affinity whatever : 
 whilst, on the other hand, it will often tend to separate races, which every 
 other character would lead us to bring together. It is to be remembered, 
 moreover, that the varieties in the conformation of the skeleton, presented by 
 the breeds of domesticated animals, are at least equal to those which are ma- 
 nifested in the conformation and colour of their soft parts ; and we might rea- 
 sonably expect, therefore, to meet with similar variations among the Human 
 races. It is probable, however, that climate has not so much influence in 
 producing such changes in the configuration of the body, as is exerted by the 
 
 8 
 
86 
 
 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 peculiar habits and mode of life of the different races ; and Dr. Prichard has 
 pointed out a very remarkable relation of this kind, in regard to the three 
 principal types of form presented by the skull. 
 
 84. Among the rudest tribes of Men, hunters and savage inhabitants of fo- 
 rests, dependent for their supply of food on the accidental produce of the soil 
 or on the chase, among whom are the most degraded of the African nations, 
 and the Australian savages, a form of head is prevalent, which is most aptly 
 distinguished by the term prognathous, indicating a prolongation or forward- 
 Fig. 7. 
 
 Profile and basal views of the prognathous skull of a Negro. 
 
 extension of the jaws. This character is most strongly marked in the Ne- 
 groes of the Gold Coast, whose skulls are usually so formed, as to give the 
 idea of lateral compression. The temporal muscles have a great extent, rising 
 high on the parietal bones ; the cheek-bones project forward, and not out- 
 ward ; the upper jaw is lengthened and projects forwards, giving a similar 
 projection to the alveolar ridge and to the teeth; and the lower jaw has 
 somewhat of the same oblique projection, so that the upper and lower incisor 
 teeth are set at an obtuse angle to each other, instead of being nearly in pa- 
 rallel planes, as in the European. From the shape of the upper jaw alone, 
 would result a marked diminution in the facial angle, measured according to 
 the method of Camper; but this diminution is far from being sufficient to ap- 
 proximate the Ethiopian races to the higher Apes, as some have supposed it 
 to be. For, whilst the average facial angle of the European may be stated at 
 80, and that of the Negro at 70, that of the adult Chimpanzee is only 35, 
 and that of the adult Orang only 30.* Independently of the diminution of 
 the facial angle, resulting from the projection of the upper jaw, it is quite cer- 
 tain that, in the typical prognathous skull, there is a want of elevation of the 
 forehead ; but it does not appear that there is a corresponding diminution in 
 the capacity of the cranial cavity, the retreating form of the forehead being 
 partly due to the general elongation of the skull in the antero-posterior direc- 
 tion. Nor is it true, as stated by some, that the position of the foramen mag- 
 num in the Negro is decidedly behind that, which it holds in the European, 
 in this respect approaching that of the Apes ( 51) : since, if due allowance 
 
 * The different statements made by some writers, who have estimated the facial angle of 
 the higher Apes at from 60 to 64, are due to the measurements having been made upon 
 young skulls; the projection of the jaws, in these animals, undergoing an extraordinary in- 
 crease at the time of the second dentition. 
 
DISTINCTIVE PECULIARITIES OF THE RACES OF MAN. 
 
 87 
 
 be made for the projection of the upper jaw, this aperture is found to have 
 the same position in the prognathous skull as in the oval one, namely, ex- 
 actly behind the transverse line bisecting the antero-posterior diameter of the 
 base of the cranium. The prognathous skull is further remarkable for the 
 large development of the parts connected with the organs of sense, especially 
 those of smell and hearing. The aperture of the nostrils is very wide ; and 
 the internal space allowed for the expansion of the Schneiderian membrane, 
 and for the distribution of the olfactory nerve, is much larger than in most 
 European heads. The posterior openings of the nasal cavity are not less re- 
 markable for their width than the anterior. The external auditory meatus is 
 also peculiarly wide and spacious ; and the orbital cavities have been thought 
 to be of more than ordinary capacity, but this last is by no means a constant 
 character. 
 
 85. A second shape of the head, very different from the preceding, belongs 
 
 Fig 8. 
 
 Front and basal views of the pyamidal skull of an Esquimaux. 
 
 principally to the nomadic races, who wander with their herds and flocks 
 over vast plains ; and to the tribes who creep along the shores of the Icy Sea, 
 and live partly by fishing, and in part on the flesh of their reindeer. This 
 form, designated by Dr. Prichard as the pyramidal, is typically exhibited by 
 various nations of Northern and Central Asia ; and is seen in an exaggerated 
 degree, in the Esquimaux. Its most striking character is the lateral or out- 
 ward projection of the zygoma, which is due to the form of the malar bones. 
 These do not project forwards and downwards under the eyes, as in the pro- 
 gnathous skull ; but take a direction laterally or outwards, forming, with the 
 zygomatic process of the temporal bone, a large rounded sweep or segment 
 of a circle. From this, in connection with the narrowness of the forehead, 
 it results, that lines drawn from the zygomatic arches, touching the temples on 
 either side, instead of being parallel (as in Europeans), meet over the forehead, 
 so as to form with the basis a triangular figure. The upper part of the face 
 being remarkably flat, the nose also being flat, and the nasal bones, as well as 
 the space between the eyebrows, being nearly on the same plane with the 
 cheek-bones, the triangular space bounded by these lines may be compared to 
 one of the faces of a pyramid. The orbits are large and deep ; and the pecu- 
 liar conformation of the bones which surround it, gives to the aperture of the 
 lids an appearance of obliquity, the inner angle seeming to be directed 
 downwards. The whole face, instead of presenting an oval form, as in most 
 Europeans and Africans, is of a lozenge-shape. The greater relative develop- 
 
88 
 
 MUTUAL RELATIONS OE THE HUMAN FAMILY. 
 
 Fig. 9. 
 
 Oval skull of a European. 
 
 merit of the zygomatic bones, and of the bones of the face altogether, when 
 compared with the capacity of the cranium, indicates in the pyramidal skull 
 a more" ample extension of the organs subservient to sensation ; the same 
 effect being thus produced by lateral expansion, as by the forward extension 
 of the facial bones in the prognathous skulls. 
 
 86. The most civilized races, those which live by agriculture and the arts 
 of cultivated life, all the most intellectually-improved nations of Europe and 
 Asia, have a shape of the head, which differs from both the preceding forms, 
 
 and which may be termed oval or 
 elliptical. This at once approves it- 
 self as a more symmetrical form ; no 
 part having an excessive prominence; 
 whilst on the other hand, there is no- 
 where an appearance of undue flat- 
 tening or compression. The head is 
 altogether of a rounder shape than in 
 other varieties; and the forehead is 
 more expanded ; while the maxillary 
 bones and the zygomatic arches are 
 so formed, as to give the face an oval 
 shape, nearly on a plane with the 
 forehead and cheek-bones, and not 
 projecting towards the lower part. 
 Owing to the more perpendicular di- 
 rection of the alveolar processes, the 
 front teeth are fixed in planes, which 
 are nearly or quite parallel to each other. The principal features in 
 this form of cranium are thus of a negative character ; the chief positive dis- 
 tinction is the large development of the cranial cavity, and especially the full- 
 ness and elevation of the forehead, in proportion to the size of the face ;- 
 indicating the predominance of the intellectual powers over those merely 
 instinctive propensities, which are more directly connected with sensations. 
 Among European nations, the Greeks have probably displayed the greatest 
 symmetry and perfection in the form of the head; but various departures 
 may be traced, towards the preceding forms, when we compare the crania of 
 different races, and even of individuals, belonging to the same stock, some 
 approaching the pyramidal form of the Northern Asiatics, whilst others ap- 
 proximate to the prognathous type of the Negro. 
 
 87. The influence of habits of life, continued from generation to generation, 
 upon the form of the head, is remarkably evinced by the transition from one 
 type to another, which may be observed in nations that have undergone a 
 change in their manners, and customs, and have made an advance in civiliza- 
 tion. Thus, to mention but one instance, the Turks at present inhabiting the 
 Ottoman and Persian empires, are undoubtedly, descended from the same stock 
 with the nomadic races, which are still spread through Central Asia. The 
 former, however, having conquered the -countries which they now inhabit, 
 eight centuries since, have gradually settled down to the fixed and regular ha- 
 bits of the Indo-European race, and have made corresponding advances in 
 civilization ; whilst the latter have continued their wandering mode of life, 
 and can scarcely be said to have made any decided advance during the same 
 interval. Now, the long-since civilized Turks have undergone a complete 
 transformation into the likeness of Europeans ; whilst their nomadic relatives 
 retain the pyramidal configuration of the skull in a very marked degree. Some 
 have attributed this change in the physical structure of the Turkish race, to 
 the introduction of Circassian slaves into the harems of the Turks ; but this 
 
DISTINCTIVE PECULIARITIES OF THE RACES OF MAN. 89 
 
 could only affect the opulent and powerful amongst the race ; and the great 
 mass of the Turkish population have always intermarried among themselves. 
 The difference of religion and manners must have kept them separate from 
 those Greeks whom they subdued in the new Ottoman countries ; and in Per- 
 sia, the Tajiks, or real Persians, still remain quite distinct from their Turkish 
 rulers, belonging to a different sect among the Mussulmans, and commonly 
 living apart from them. In like manner, even the Negro head and face may 
 become assimilated to the European, by long subjection to similar influences; 
 thus, in some of our older West Indian Colonies, it is not uncommon to meet 
 with Negroes, the descendants of those first introduced there, who exhibit 
 a very European physiognomy ; and it has even been asserted that a Negro 
 belonging to the Dutch portion of Guiana, may be distinguished from another 
 belonging to the British settlements, by the similarity of his features and ex- 
 pression to those which peculiarly characterize his masters. The effect could 
 not be here produced by the intermixture of bloods, since this would be made 
 apparent by alteration of colour. 
 
 88. Next to the characters derived from the form of the head, those which 
 are founded upon the form of the pelvis seem entitled to rank. These have 
 been particularly examined by Professors Vrolik and Weber. The former 
 concluded from his examinations of this part of the skeleton, that the pelvis 
 of the Negress, and still more that of the female Hottentot, approximates to 
 that of the Simiae in its general configuration ; especially in its length and 
 narrowness, the iliac bones having a more vertical position, so that the ante- 
 rior spines approach one another much more closely than they do in the Euro- 
 pean ; and the sacrum also being longer and narrower. On the other hand, 
 Prof. Weber concludes, from a more comprehensive survey, that no particular 
 figure is a permanent characteristic of any one race. He groups the principal 
 varieties which he has met with, according to the form of the upper opening, 
 whether oval, round, four-sided, or wedge-shaped. The first of these is 
 most frequent in the European races ; the second, among the American races ; 
 the third, most common among the Mongolian nations, corresponds remarka- 
 bly with the 'form of their heads; whilst the last chiefly occurs among the 
 races of Africa, and is in like manner conformable with the oblong com- 
 pressed form usually presented by their cranium. But though there are par- 
 ticular shapes which are most prevalent in each race, yet there are numerous 
 individual deviations ; of such a nature, that every variety of form presents 
 itself occasionally in any given race. 
 
 89. Other variations have been observed by anatomists, in the relative length 
 of the bones, and in the shape of the limbs, between the different races of 
 Man ; but these also seem to have reference to the degree of civilization, and 
 to the regularity of the supply of wholesome nutriment. It is generally to 
 b observed, that the races least improved by civilization, like the uncultivated 
 breeds of animals, have slender, lean, and elongated limbs ; this may be es- 
 pecially remarked in the natives of Australia. In nearly all the less civilized 
 races of Men, the limbs are more crooked and badly formed than the average 
 of those of Europeans; and this is particularly the case in the Negro, the 
 bones of whose legs bow outwards, and whose feet are remarkably flat. It 
 has been generally believed, that the length of the forearm in the Negro is so 
 much greater than in the European, as to constitute a real character of ap- 
 proximation to the Apes. The difference, however, is in reality extremely 
 slight ; and is not at all comparable with that which exists between the most 
 uncultivated races of Men and the highest Apes ( 54). And in regard to all 
 the peculiarities here alluded to, it is to be observed, that they can only be 
 discovered by the comparison of large numbers of one race with correspond- 
 ing numbers of another ; for individuals are found in every tribe, possessing 
 
90 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 the characters which distinguish the majority of the other race. Any such 
 peculiarities, therefore, are totally useless as the foundation of specific charac- 
 ters ; being simply variations from the ordinary type, resulting from causes 
 which might affect the entire race, as well as individuals. 
 
 90. The connection between the general form of the body, on the one hand, 
 and the degree of civilization (involving the regular supply of nutriment) on 
 the other, is made apparent, not merely by the improvement which we per- 
 ceive in the form, development, and vigour of the frame, as we advance from 
 the lowest to the most cultivated of the Human races ; but also by the degra- 
 dation which is occasionally to be met with in particular groups of the higher 
 tribes, which have been subjected for several generations to the influence of 
 depressing causes. Of this class of facts, the following is a very interesting 
 example : " On the plantation of Ulster, and afterwards on the successes of 
 the British against the rebels of 1641 and 1689, great multitudes of the na- 
 tive Irish were driven from Armagh and the south of Down, into the moun- 
 tainous tract extending from the barony of Flews eastward to the sea : on 
 the other side of the kingdom, the same race were expelled into Leitrim, Sligo 
 and Mayo. Here they have been almost ever since, exposed to the worst 
 effects of hunger and ignorance, the two great brutalizers of the human race. 
 The descendants of these exiles are still readily distinguishable from their 
 kindred in Meath, and in other districts where they are not in a state of phy- 
 sical degradation ; being remarkable for open projecting mouths, with prominent 
 teeth and exposed gums ; their advancing cheek-bones and depressed noses 
 bearing barbarism on their very front. In Sligo and northern Mayo, the con- 
 sequences of two centuries of degradation and hardship exhibit themselves in 
 the whole physical condition of the people ; affecting not only the features, 
 but the frame, and giving such an example of human deterioration from known 
 causes, as almost compensates, by its value to future ages, for the suffering 
 and debasement which past generations have endured in perfecting its appall- 
 ing lesson. Five feet two inches upon an average, pot-bellied, bow-legged, 
 abortively-featured, their clothing a wisp of rags, these spectres of a people, 
 that were once well-grown, able-bodied, and comely, stalk abroad into the day- 
 light of civilization, the annual apparitions of Irish ugliness and Irish want. 
 In other parts of the island, where the population has never undergone the 
 influence of the same causes of physical degradation, it is well known that 
 the same race furnishes the most perfect specimens of human beauty and 
 vigour, both mental and bodily."* 
 
 91. From the foregoing survey of the phenomena, bearing upon the ques- 
 tion of the specific unity or diversity of the Human races, the following 
 conclusions may be drawn : 
 
 I. That the physical constitution of Man is peculiarly disposed, like that 
 of the domesticated animals, to undergo variations; some of which can be 
 traced to the influence of external causes ; whilst others are not so explicable, 
 and must be termed spontaneous. 
 
 II. That the extreme variations which present themselves, between the 
 races apparently the most removed from one another, are not greater in degree 
 than those which exist between the different breeds of domesticated animals, 
 which are known to have descended from a common stock; and that they 
 are of the same kind with the variations which present themselves in any 
 one race of Mankind, the difference of degree being clearly attributable, in 
 the majority of cases, to the respective conditions under which each race 
 exists. 
 
 III. That none of the variations, which have been pointed out as existing 
 
 * See Dublin University Magazine, No. XL VIII. 
 

 
 PRINCIPAL BRANCHES OF THE HUMAN FAMILY. 91 
 
 between the different races of mankind, have the least claim to be regarded 
 as valid specific distinctions ; being entirely destitute of that fixity, which is 
 requisite to entitle them to such a rank; and exhibiting, in certain groups of 
 each race, a tendency to pass into the characters of some other. 
 
 IV.. That, in the absence of any valid specific distinctions, we are required, 
 by the universally-received principles of zoological science, to regard all the 
 races of Mankind as belonging to the same species, or (in other words) as 
 having had either an identical or similar parentage ; and that this conclusion 
 is supported by the positive evidence, afforded by the agreement of all the 
 races in the physiological and psychological characters, that most distinguish 
 them from other species, and especially by the ready propagation of mixed 
 breeds or hybrid races. 
 
 7. Principal Branches of the Human Family. 
 
 92. The above conclusions are found to be in entire accordance with those 
 derived from an examination of the relative affinities of the different races of 
 Men at present existing ; as far as these are deducible from the analogies of their 
 language, from their correspondence in peculiar habits and observances, and from 
 traditional or other evidence in regard to their original sources. For it appears, 
 from such investigations, that very great difference in colour, texture of the hair, 
 form of the skull, and other important physical characters, exist among nations, 
 which may be referred with great confidence to a common source ; whilst on 
 the other hand, we find traits of physical resemblance, in tribes which exist 
 under corresponding circumstances in remote parts of the world, and which 
 seem to have nothing else in common. It has been attempted by Blumenbach 
 and Cuvier to arrange the different races of Men under five principal varie- 
 ties; the Caucasian, Mongolian, Ethiopian, Malay, and American. But, for 
 the reason just given, it is impossible to establish any constant distinguishing 
 characters, which shall serve to mark these clearly ouj; ; and it moreover ap- 
 pears that several additional groups must be created, for the reception of tribes, 
 that differ as much from the preceding as these do from each other. In the 
 following brief enumeration, the views of Dr. Prichard will be adopted. 
 
 93. The Caucasian variety of Blumenbach and Cuvier was so named from the 
 idea, that the Caucasian range of mountains might be regarded as the centre 
 or focus of the races belonging to it; and that the Caucasian people present 
 the typical conformation of the variety in the most perfect degree. Neither 
 of these ideas are correct, however; and some other designation might very 
 properly be substituted for that which conveys them. In this variety are pre- 
 sented all the characters of highest physical perfection of the race, such as 
 were, perhaps, most pre-eminently combined among the Ancient Greeks; as 
 well as those of intellectual and moral elevation. No uniformity exists, how- 
 ever, as to colour; for this character presents every intermediate gradation, 
 from the fair and florid hue of the Northern Europeans, to the jet black of 
 many tribes in North Africa and Hindustan. The hair is generally long and 
 flexible ; but departures from the ordinary type present themselves in this 
 respect, also, both among individuals and among whole tribes. Although 
 there is general agreement in these characters among the nations of South- 
 western Asia, Northern Africa, and nearly the whole of Europe, yet we are 
 required by the evidence of ancient history, as well as by the characters de- 
 rived from language, to separate these nations into two groups ; which appeared 
 to have been distinct from each other at the earliest JSriod of which we have 
 any traces ; and which we must regard, therefore, as alike entitled to rank as 
 primary branches of the human family. These are the Syro-Arabian, and the 
 Indo-European groups of nations. 
 
92 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 94. The Syro-Jlrabian nations, distinguished from all others by their very 
 peculiar idiom, originally inhabited the region of Asia intermediate between 
 the countries of the Indo-European and of the Egyptian races ; having as its 
 centre the region watered by the great rivers of Mesopotamia. Several of the 
 nations originally constituting this group have become extinct, or nearly so ; 
 and the Arabs, which originally formed but one subdivision of it, have now 
 become the dominant race, not only throughout the ancient domain of the 
 Syro-Arabian nations, but also in Northern Africa. In the opinion of Baron 
 Larrey, who had ample opportunities for observation, the skulls of the Arabian 
 race furnish, at present, the most complete type of the human head; and he 
 considered the remainder of the physical frame as equally distinguished by 
 its superiority to that of other races of men. The different tribes of Arabs 
 present very great diversities of colour, which are generally found to coincide 
 with variations in climate. Thus the Shegya Arabs, and others living on the 
 low countries bordering on the Nile, are of a dark-brown or even black hue ; 
 but even when quite jetty, they are distinguished from the Negro races by 
 the brightness of their complexions, by the length and straightness of their 
 hair, and by the regularity of their features. The same may be said of the 
 wandering Arabs of Northern Africa ; but the influence of climate and cir- 
 cumstances is still more strongly marked in some of the tribes long settled in 
 that region, whose descent may be traced to a distinct branch of the Syro- 
 Arabian stock, namely, the Berber, to which belong the Kabyles of Algiers 
 and Tunis, the Tuaryks of Sahara, and the Guanches or ancient population 
 of the Canary Isles. Amongst these tribes, whose affinity is indisputably 
 traceable through their very remarkable language, every gradation may be 
 seen, from the intense blackness of the Negro skin, to the more swarthy hue 
 of the inhabitants of the South of Europe. It is remarkable that some of the 
 Tuaryk inhabitants of particular Oases in the great desert, who are almost as 
 insulated from communication with other races as are the inhabitants of 
 islands in a wide ocean, have hair and features that approach those of the 
 Negroes ; although they speak the Berber language with such purity, as to 
 forbid the idea of the introduction of these characters by an intermixture of 
 races. The Jews, who are the only remnants now existing of the once pow- 
 erful Phoenician tribe, and who are now dispersed through nearly every coun- 
 try on the face of the earth, present a similar diversity ; having gradually 
 assimilated in physical characters to the nations among which they have so 
 long resided ( 80). 
 
 95. The affinity of the Indo-European nations, now spread from the 
 mouth of the Ganges to the British Islands and the Northern extremity of 
 Scandinavia, is in like manner proved by the cognate character of their lan- 
 guages ; in spite of the differences in colour and other traits, which present 
 themselves among the inhabitants of that vast tract. The type of physical 
 configuration, however, is the same ; and the differences of colour are such, 
 as may readily be traced to external agencies. Thus among the Hindoo 
 races we find that the distinction of castes (perpetuating the same mode of life 
 in particular families from generation to generation), the marked differences 
 of climate (as between the mountainous regions of Kashmir and Kafiristan, 
 and the plains bordering the great rivers of India), and other circumstances, 
 are accompanied, as in the case of the Arabian race, with diversities in phy- 
 sical conformation, which are now established as belonging to different sections 
 of the people. In majjjf instances, the origin of these varieties can be clearly 
 traced by historical evidence, as well as by affinities of language and con- 
 formation ; and it cannot be questioned, that Hindoos as black as Negroes, 
 others of a copper-colour, others little darker than the inhabitants of Southern 
 Europe, and others of fair complexion with blue eyes and auburn or even red 
 
PRINCIPAL BRANCHES OF THE HUMAN FAMILY. 93 
 
 hair, have all had a common parentage; some having become darker, and 
 others lighter than their ancestors, generally in accordance with changes in 
 their residence and habits. This group seems to have been early divisible 
 into two primary branches ; the northern or Median; and the southern or 
 Indian. Between the original languages of these races, a marked resem- 
 blance can be traced ; and the traditions of both races point to contiguous 
 regions as their original seat, the earliest records of the Persians indicating 
 that they migrated westwards from a spot in the ancient Bactria, not far from 
 Balkh, to the westward of the Indus ; whilst the traditions of the Brahmans 
 refer the origin of the Hindoos to the north-western part of the country lying 
 between the Himalaya and the Vindhya mountains, whence they afterwards 
 moved eastwards and southwards into the Peninsula. Both these races ap- 
 pear to have migrated in a north-westerly direction, at a period long preceding 
 our earliest knowledge of European history ; for the European languages pre- 
 sent indications of affinity to the ancient languages of both Medians and 
 Indians. The classical languages of Greece and Italy appear more referrible 
 to the Sanskrit or ancient Indian, than to the Zend or ancient Median ; whilst, 
 on the other hand, the Germanic languages would seem to have originated 
 rather in the latter. Of all the extant European dialects, the Lettish and 
 Lithuanian approach most nearly to the ancient type. 
 
 a. It may be well to notice here, the nature of the evidence on which statements of this 
 kind are grounded. The extensive and profound inquiries which have been in progress 
 for many years, have enabled Philologists to distinguish, usually with little difficulty, between 
 the intermixture of languages, which may arise from the intercourse of any two nations that 
 happen to be connected by local proximity, commercial intercourse, &c.; and that funda- 
 mental correspondence, which indicates original affinity. The latter is to be sought rather 
 in the analogies of grammatical structure, and in the laws of combination, or the mechanism 
 of speech, than in the vocabulary; and it sometimes happens that a relationship may thus 
 be traced between languages, which have scarcely a single word in common. The most 
 satisfactory evidence, however, is derived from resemblance in those parts of the vocabu- 
 lary, which serve to represent the ideas of a people in the most simple state of existence ; 
 such as terms expressive of family relations; names for the most striking objects of the visi- 
 ble universe; terms distinguishing different parts of the body; nouns of number, up to 5, 10, 
 or 20 ; verbs descriptive of the most common sensations and bodily acts, such as seeing, 
 hearing, eating, drinking, and sleeping. As no nation was ever found destitute of similar 
 expressions ; and as we know by the observation of facts, in addition to abstract probability, 
 that tribes however rude, do not exchange their own stock of primitive words for those of a 
 foreign idiom ; it may be inferred that dialects, which correspond in those parts of their 
 vocabulary, were originally one speech, or the language of one people. 
 
 b. It has been fully demonstrated, tha,t both these indications of affinity or family relation- 
 ship exist between the languages of the several races, from which the great mass of the popu- 
 lation of Europe is derived; and, further, that this affinity not only unites them with each 
 other, but connects them all with the common Eastern stock. 
 
 96. The second primary division of the human family, according to the 
 usual arrangement, is that commonly termed Mongolian. The real Mon- 
 goles, however, constitute but a single and not very considerable member of 
 the group of nations associated under this designation ; which is, therefore, 
 by no means an appropriate one. The original seat of these races appears 
 to have been the great central elevated plain of Asia, in which all the great 
 rivers of that continent have their sources, whatever may be their subsequent 
 direction. Taken as a whole, this division of the human family is charac- 
 terized by the pyramidal form of the skull, and by a xanthous or olive com- 
 plexion; but these characters are only exhibited, in a prominent degree, in 
 the more typical members of the group, and may become so greatly modified 
 as to cease altogether to be recognizable. This has been remarkably the case 
 with regard to the Turkish people, now so extensively distributed. All the 
 most learned writers on Asiatic history are agreed in opinion, that the Turkish 
 
94 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 races are of one common stock ; although at present they vary in physical 
 characters, to such a degree that, in some, the original type has been alto- 
 gether changed. Those which still inhabit the ancient abodes of the race, 
 and preserve their pastoral nomadic life, present the physiognomy and gene- 
 ral characteristics which appear to have belonged to the original Turkomans ; 
 and these are decidedly referrible to the so-called Mongolian type. Before 
 the Mohammedan era, however, the Western Turks or Osmanlis had adopted 
 more settled habits, and had made considerable progress in civilization ; and 
 their adoption of the religion of Islam incited them to still wider extension, 
 and developed that spirit of conquest, which, during the middle ages, dis- 
 played itself with such remarkable vigour. The branches of the race, which, 
 from their long settlement in Europe, have made the greatest progress in 
 civilization, now exhibit in all essential particulars the physical characters of 
 the European model; and these are particularly apparent in the conformation 
 of the skull. In like manner we find that the Ugorian division, which mi- 
 grated towards the northwest at a very early period, planted a colony in 
 Europe, which still tenants the Northern Baltic countries, forming the races 
 of Fins and Lappes. In the time of Tacitus, the Fins were as savage as the 
 Lappes ; but the former, during the succeeding ages, became so far civilized, 
 as to exchange a nomadic life for one of agricultural pursuits, and have gra- 
 dually assimilated with the surrounding people ; whilst the Lappes, like the 
 Siberian tribes of the same race, have ever since continued to be barbarous 
 nomades, and have undergone no elevation in physical characters. The same 
 division gave origin to the Magyars or Hungarians ; a warlike and energetic 
 people, unlike their kindred in the North ; in whom a long abode in the centre 
 of Europe has, in like manner, developed the more elevated characters, phy- 
 sical and mental, of the European nations. The nations inhabiting the south- 
 eastern portion of Asia, also, appear to have had their origin in the Mongolian 
 or Central Asiatic stock; although their features and form of skull by no 
 means exhibit its characteristic marks, but present such departures from it as 
 are elsewhere observable in races that are making advances in civilization. 
 Even the great peninsula of Hindostan appears to have been peopled, long 
 previously to the settlement of the present Hindoo race, by tribes of the 
 Central Asiatic stock, so distinguished by its migratory propensities; and 
 remains of these aborigines are still found in the hilly parts of Northern 
 India, in the Dekhan, and in Ceylon, constituting numerous tribes, which are 
 now for the most part isolated from each other, and which exhibit very dif- 
 ferent degrees of civilization. 
 
 97. According to the usual mode of dividing the Human family, the Ethi- 
 opian or Negro stock is made to include all the nations of Africa, to the 
 southward of the Atlas range. But there is good reason for separating the 
 Hottentots and Bushmen as a distinct race ; and for restricting the designation 
 of Negroes to the nations inhabiting the region southward of the Great Desert, 
 as far as the Hottentot country, the inhabitants of the oases of the desert 
 itself being mostly, as already pointed out, of Syro-Arabian origin, although 
 assimilating closely to the Negro race in physical characters. The nations 
 thus in geographical proximity with each other, are found to have sufficient 
 affinities of language, to justify the belief in their common origin ; and they 
 all present, in a more or less evident degree, the physical peculiarities of the 
 Negro race. But these are far from constituting a sufficient ground for regard- 
 ing the African nations as a distinct race, separated from all other families of 
 men by a broad and definite line of demarcation. Our idea of the Negro 
 character is principally founded upon that division of the people which in- 
 habits the low countries of the Western part of Central Africa, and in which 
 the Negro peculiarities are most strongly marked. There are very few nations 
 
PRINCIPAL BRANCHES OF THE HUMAN FAMILY. 95 
 
 which present in a high degree all the characters that are commonly regarded 
 as typical of the Negro; these being generally distributed among different 
 nations in various ways; and being combined, in each instance, with more 
 or fewer of the characters belonging to the European or Asiatic. Thus the 
 race of Jolofs near the Senegal, and the Guber in the interior of Sudan, have 
 woolly hair and deep black complexions, but fine forms and regular features 
 of a European cast; and nearly the same may be said of the darkest of the 
 Kafirs of Southern Africa. The Bechuna Kafirs present a still nearer ap- 
 proach to the European type ; the complexion being of a light brown, the 
 hair often not woolly but merely curled, or even in long flowing ringlets, and 
 the figure and features having much of the European character. The nations 
 of the northeast of Africa, also, present similar departures Jfrom the typical 
 characters of the Negro. 
 
 98. There is no group which presents a more constant correspondence 
 between external conditions and physical conformation, than that composed 
 of the African nations. As we find the complexion becoming gradually 
 darker, in passing from northern to southern Europe, thence to North Africa, 
 thence to the borders of the Great Desert, and thence to the intertropical re- 
 gion where alone the dullest black is to be met with, so do we find, on 
 passing southwards from this, that the hue becomes gradually lighter in pro- 
 portion as we proceed further from the equator, until we meet with races 
 of comparatively fair complexions among the nations of Southern Africa. 
 Even in the intertropical region, high elevations of the surface have the same 
 effect, as we have seen them produce elsewhere, in lightening the complexion. 
 Thus, the high parts of Senegambia, where the temperature is moderate and 
 even cool at times, are inhabited by Fulahs of a light copper colour; whilst 
 the nations inhabiting the lower regions around them, are of true Negro Mack- 
 ness; and nearly on the same parallel, but at the opposite side of Africa, are 
 the high planes of Enarea and Kaffa, where the inhabitants aye said to be 
 fairer than the natives of Southern Europe. Again, those races which have 
 the Negro character in an exaggerated degree, and which may be said to ap- 
 proach to deformity in persons, the ugliest blacks, with depressed forehead, 
 flat noses, and crooked legs, are in most instances inhabitants of low coun- 
 tries, often of swampy tracts near the sea-coast, where many of them have 
 scarcely any other means of subsistence than shell-fish and the accidental gifts 
 of the sea. Such tribes are uniformly in the lowest stage of society, being 
 either ferocious savages, or stupid, sensual, and indolent. Such are most of 
 the tribes along the Slave Coast. On the other hand, wherever we hear of 
 a Negro state, the inhabitants of which have attained any considerable degree 
 of improvement in their social condition, we constantly find that their phy- 
 sical characters deviate considerably from the strongly-marked or exaggerated 
 type of the Negro. Such are the Ashanti, the Sulima, and the Dahomans of 
 Western Africa; also the Guber of Central Sudan, among which a consider- 
 able degree of civilization has long existed, which are perhaps the finest race 
 of genuine Negroes on the whole continent, and which present in their lan- 
 guage distinct traces of original relationship to the Syro-Arabian nations, not 
 to be accounted for by any subsequent intermixture of races. 
 
 99. The highest civilisation, and the greatest improvement in physical 
 characters, are to be found in those nations, which have adopted the Moham- 
 medan religion; this was introduced, three or four centuries since, into the 
 eastern portion of Central Africa; and it appears that the same people, which 
 were then existing in the savage condition still exhibited by the pagan nations 
 further south, have now adopted many of the arts and institutions of civilized 
 society, subjecting themselves to governments, practising agriculture, and 
 dwelling in towns of considerable extent, many of which contain 10,000, and 
 
96 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 some even 30,000 inhabitants; a circumstance which implies a consider- 
 able advancement in industry, and in the resources of subsistence. This last 
 fact affords most striking evidence of the improvability of the Negro races ; 
 and, taken in connexion with the many instances that have presented them- 
 selves, of the advance of individuals, under favourable circumstances, to at 
 least the average degree of mental development among the European nations, 
 it affords clear proof that the line of demarcation, which has been supposed 
 to separate them intellectually and morally from the races that have attained 
 the greatest elevation, has no more real existence than that, which has been 
 supposed to be justified by a difference in physical characters, and of which 
 the fallacy has been demonstrated. 
 
 100. The Bushmen or Bojesmen of South Africa are generally regarded 
 as presenting the most degraded and miserable condition, of which the human 
 race is capable: and they have been supposed to present resemblances in 
 physical characters to the higher Quadrumana. Yet there is distinct evidence, 
 that this degraded race is but a branch or subdivision of the once extensive 
 nation of Hottentots; and that its present condition is in great part due to the 
 hardships, to which it has been subjected in consequence of European colo- 
 nization. This race differs from all other South African nations, both in lan- 
 guage and in physical conformation. The language cannot be shown to possess 
 affinities with those of any other stock; but in bodily structure there is a re- 
 markable admixture of the characters of the Mongolian with those of the Ne- 
 gro. Thus the face presents the very wide and high cheek-bones, with the 
 oblique eyes and flat nose, of the Northern Asiatics ; at the same time that, in 
 the somewhat prominent muzzle and thick lips, it resembles the countenance 
 of the Negro. The complexion is of a tawny buff or fawn colour, like that 
 of the Negroes diluted with the olive of the Mongoles. The hair is woolly 
 like that of the Negroes, but it grows in small tufts, scattered over the surface 
 of the scalp, instead of covering it uniformly, resembling in its comparative 
 scantiness that of the Northern Asiatics. It is most interesting to observe this 
 remarkable resemblance in physical characters, between the Hottentots and 
 the Mongolian races ; in connexion with the similarity that exists between the 
 circumstances under which they respectively live. No two countries can be 
 more similar, than the vast steppes of Central Asia, and the karroos of South- 
 ern Africa. And the inhabitants of each were nomadic races, wandering 
 through deserts remarkable for the wide expansion of their surface, their scanty 
 herbage, and the dryness of their atmosphere, and feeding upon the milk and 
 flesh of their horses and cattle. Of the original pastoral Hottentots, however, 
 very few now remain. They have been gradually driven, by the encroach- 
 ments of European colonists and by internal wars with each other, to seek 
 refuge among the inaccessible rocks and deserts of the interior ; and they have 
 thus been converted from a mild unenterprising race of shepherds, into wander- 
 ing hordes of fierce, suspicious, and vindictive savages, treated as wild beasts 
 by their fellow-men, until they become really assimilated to wild beasts in their 
 habits and dispositions. This transformation has taken place under the ob- 
 servation of eye-witnesses, in the Koranas, a tribe of Hottentots well known 
 to have been previously the most advanced in all the improvements which 
 belong to pastoral life. Having been plundered by their neighbours and driven 
 out into the wilderness to subsist upon fruits, they have adopted the habits of 
 the Bushmen, and have become assimilated in every essential particular to 
 that miserable tribe. 
 
 101. The American nations, taken collectively, form a group which ap- 
 pears to have existed as a separate family of nations from a very early period 
 in the world's history. They do not form, however, so distinct a variety, in 
 regard to physical characters, as some anatomists have endeavoured to prove ; 
 

 PRINCIPAL BRANCHES OF THE HUMAN FAMILY. 97 
 
 for, although certain peculiarities have been stated to exist in the skulls of the 
 aboriginal Americans, yet it is found, on a more extensive examination, that 
 these peculiarities are very limited in their extent, the several nations spread 
 over this vast continent differing from each other in physical peculiarities, as 
 much as they do from those of the Old World, so that no typical form can be 
 made out among them. In regard to complexion, again, it may be remarked, 
 that although the native Americans have been commonly characterized as 
 " red men," they are by no means invariably of a red or coppery hue, some 
 being as fair as many European nations, others being yellow or brown, and 
 others nearly, if not quite, as black as the Negroes of Africa ; whilst, on the 
 other hand, there are tribes equally red, and perhaps more deserving that epi- 
 thet in Africa and Polynesia. In spite of all this diversity of conformation, 
 it is believed that the structure of their languages affords a decided and 
 clearly-marked evidence of relationship between them. The words, and even 
 the roots, may differ entirely in the different groups of American nations ; 
 but there is a remarkable similarity in grammatical construction amongst them 
 all, which is of a kind not only to demonstrate their mutual affinity, but to 
 separate them completely from all known languages of the old continent. 
 Notwithstanding also their diversities in mode of life, there are peculiarities 
 of mental character, as well as a number of ideas and customs derived from 
 tradition, which seem to be common to them all, and which for the most part 
 indicate a former elevation in the scale of civilization, that has left its traces 
 among them even in their present degraded condition, and that still distin- 
 guishes them from the sensual, volatile, and almost animalized savages, that 
 are to be met with in many parts of the Old Continent. The Esquimaux 
 constitute an exception to all general accounts of the physical characters of 
 the American nations ; for in the configuration of their skulls, in their com- 
 plexion, and in their general physiognomy, they conform to the Mongolian 
 type, even presenting it in an exaggerated degree. Their wide extension 
 along the whole northern coast of America, and the near proximity of this 
 coast to Kamschatka, certainly lend weight to the idea, that they derive their 
 origin from the Northern Asiatic stock ; but, on the other hand, they have a 
 marked affinity, in regard to language, to the other American nations. The 
 Athapascan Indians, various tribes of which inhabit the country south of the 
 Esquimaux country, seem intermediate in physical characters, as they are in 
 geographical position, between the Esquimaux and the ordinary Americans. 
 They have a tradition which seems to indicate, that they are derived from the 
 North-Eastern Asiatics, with whom they have many points of accordance in 
 dress and manners. 
 
 102. It now remains for us to notice the Oceanic races, which inhabit the 
 vast series of islands scattered through the great ocean, that stretches from 
 Madagascar to Easter Island. There is no part of the world, which affords a 
 greater variety of local conditions than this, or which more evidently exhibits 
 the effects of physical agencies on the organization of the human body. 
 Moreover, it affords a case for the recognition of affinities by means of lan- 
 guage, that possesses unusual stability ; since the insulated position of the 
 various tribes, that people the remote spots of this extensive tract, prevents 
 them from exercising that influence upon each others' forms of speech, which 
 is to be observed in the case of nations united by local proximity or by fre- 
 quent intercourse. Tried by this test, it is found that the different groups of 
 people, inhabiting the greater part of these insular tracts, are more nearly con- 
 nected together, although so widely scattered, and so diverse in physical 
 characters, than most of the families of men, occupying continuous tracts of 
 land on the great continents of the globe. The inhabitants of Oceanica seem 
 divisible into three groups, which are probably to be regarded as having con- 
 9 
 
98 MUTUAL RELATIONS OF THE HUMAN FAMILY. 
 
 stituted distinct races from a very early period ; these are the Malayo-Poly- 
 nesian race, the Pelagian Negroes (commonly termed Papuas), and the Alforas 
 or Alfourous. 
 
 103. The Malay ^-Polynesian group is by far the most extensive of the 
 three, and comprehends the inhabitants of the greater part of the Indian and 
 Polynesian Archipelagoes, with the peninsula of Malacca (which is the cen- 
 tre of the Malays proper), and the inhabitants of Madagascar. These are all 
 closely united by affinities of language. The proper Malays bear a strong 
 general resemblance to the Mongolian races, and this resemblance is shared, 
 in a greater or less degree, by most of the inhabitants of the Indian Archi- 
 pelago. They are of a darker complexion, as might be expected from their 
 proximity to the equator ; but in this complexion, yellow is still a large in- 
 gredient. The Polynesian branch of the group presents a much wider 
 diversity ; and if it were not for the community of language, it might be 
 thought to consist of several races, as distinct from each other as from the 
 Malayan branch. Thus the Tahitians and Marquesans are tall and well- 
 made; their figures combine grace and vigour: their skulls are usually re- 
 markably symmetrical ; and their physiognomy presents much of the Euro- 
 pean cast, with a very slight admixture of the features of the Negro. The 
 complexion, especially in the females of the higher classes, who are sheltered 
 from the wind and sun, is of a clear olive or brunette, such as is common 
 among the natives of Central and Southern Europe; and the hair, though 
 generally black, is sometimes brown or auburn, or even red or flaxen. Among 
 other tribes, as the New Zealanders, and the Tonga, and Friendly Islanders, 
 there are greater diversities of conformation and hue ; some being finely pro- 
 portioned and vigorous, others comparatively small and feeble ; some being 
 of a copper-brown colour, others nearly black, others olive, and others almost 
 white. In fact, if we once admit a strongly-marked difference in complexion, 
 features, hair, and general configuration, as establishing a claim to original 
 distinctness of origin, we must admit the application of this hypothesis to 
 almost every group of islands in the Pacific ; an idea of which the essential 
 community of language seems to afford a sufficient refutation. Among the 
 inhabitants of Madagascar, too, all of which speak dialects of the same lan- 
 guage, some bear a strong resemblance to the Malayan type, whilst others 
 present approaches to that of the Negro. 
 
 104. The Pelagian-Negro races must be regarded as a group altogether 
 distinct from the preceding ; having a marked diversity of language ; and 
 presenting more decidedly than any of the Malay o-Polynesians, the characters 
 of the Negro type. They form the predominating population of New Bri- 
 tain, New Ireland, the Louisiade and Solomon Isles, of several of the New 
 Hebrides, and of New Caledonia; and they seem to extend westwards into 
 the mountainous interior of the Malayan Peninsula, and into the Andaman 
 Islands, in the Bay of Bengal. The Tasmanians, or aborigines of Van Die- 
 man's Land, which are now almost completely exterminated, undoubtedly 
 belonged to this group. Very little is known of them, except through the 
 reports of the people of Malayo-Polynesian race inhabiting the same islands ; 
 but it appears that, generally speaking, they have a very inferior physical de- 
 velopment, and lead a savage and degraded life. There is considerable diversity 
 of physical characters among them ; some approximating closely in hair, com- 
 plexion, and features, to the Guinea-Coast Negroes ; whilst others are of 
 yellower tint, straight hair, and better general development. The Papuans, 
 who inhabit the northern coast of New-Guinea, and some adjacent islands, 
 and who are remarkable for their large bushy masses of half-woolly hair, have 
 been supposed to constitute a distinct race ; but there is little doubt that they 
 are of hybrid descent, between the Malays and the Pelagian Negroes. 
 

 ON ORGANIZED STRUCTURES IN GENERAL. 99 
 
 105. Still less is known of the Mfourous, or JLlforian race, which are 
 considered by some to be the earliest inhabitants of the greater part of the 
 Malayan Archipelago, and to have been supplanted by the more powerful peo- 
 ple of the two preceding races, who have either extirpated them altogether, 
 or have driven them from the coasts into the mountainous and desert parts of 
 the interior. They are yet to be found in the central parts of the Moluccas 
 and Philippines ; and they seem to occupy most of the interior and southern 
 portion of New Guinea, where they are termed Endamenes. They are of 
 very dark complexion ; but their hair, though black and thick, is lank. They 
 have a peculiar repulsive physiognomy ; the nose is flattened, so as to give 
 the nostrils an almost transverse position; the cheek-bones project; the eyes 
 are large, the teeth prominent, the lips thick, and the mouth wide. The limbs 
 are long, slender and misshapen. From the close resemblance in physical 
 characters, between the Endamenes of New Guinea, and the aborigines of 
 New Holland, and from the proximity between the adjacent coasts of these 
 two large islands, it may be surmised that the latter belong to the Alforian 
 race; but too little is known of the language of either, to give this inference 
 a sufficient stability. In the degradation of their condition and manner of life 
 the savages of New Holland fully equal the Bushmen of South Africa ; and 
 it is scarcely possible to imagine human beings, existing in a condition more 
 nearly resembling that of brutes. But there is reason to believe, that the 
 tribes in closest contact with European settlers are more miserable and savage 
 than those of the interior ; and even with respect to these, increasing acquaint- 
 ance with their language, and a consequent improved insight into their modes 
 of thought, tend to raise the very low estimate which had been formed and 
 long maintained, in regard to their extreme mental degradation. The latest 
 and most authentic statements enable us to recognize among them the same 
 principles of a moral and intellectual nature, which, in more cultivated tribes, 
 constitute the highest endowments of humanity, and thus to show that they 
 are not separated, by any impassable barrier, from the most civilized and cul- 
 tivated nations of the globe. 
 
 CHAPTER III. 
 
 OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 1. On Organized Structures in General. 
 
 106. THE Human body, in common with the bodies of all the higher Ani- 
 mals, is composed of an immense number of parts, whose structure and 
 whose actions are alike dissimilar ; but which are yet so arranged, as to make 
 up a fabric distinguished by its perfect adaptation to a great variety of pur- 
 poses, whilst their actions, though in a great degree independent of each other, 
 concur in effecting one common object, the maintenance of the integrity of 
 the entire organism. 'In the lowest and simplest forms of living being, such 
 as we meet with among the humblest Cellular Plants, we find a single cell 
 making up the whole fabric. This cell grows from its germ, absorbs and as- 
 similates nutriment, converts a part of this into the substance of its own cell- 
 wall, secretes another portion into its cavity, and produces from a third the 
 reproductive germs that are to continue the race ; and having reached its own 
 
100 OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 term of life, and completed the preparation of these germs, it bursts and sets 
 them free, every one of these being capable, in its turn, of going through 
 the same set of operations. In the highest forms of Vegetable life, we find 
 but a multiplication of similar cells ; amongst which these operations are dis- 
 tributed, as it were, by a division of labour; so that, by the concurrent labours 
 of all, a more complete and permanent effect may be produced. If we ana- 
 lyze the structure of a forest tree, for example, we find that all the soft and 
 growing parts are composed of similar cells ; whose office it is, to absorb and 
 prepare the nutriment, which is afterwards to be applied to the extension of 
 the solid internal skeleton of the trunk and branches. This latter part is not 
 concerned in the functions of vegetation, in any other way than as supporting 
 and connecting the different groups of cells, which form the operative part of 
 the fabric; and it is composed of two forms of tissue, woody-fibre, and vas- 
 cular tissue, each of which may be regarded as originating in the metamor- 
 phosis of cells ( 120). 
 
 107. At the extremities of the roots of all the more perfect Plants, we find 
 a set of soft cells, making up those succulent bodies which are known as the 
 spongioles ; these are specially destined to perform the Absorption of nutri- 
 tious fluid. This fluid, being conveyed by the vessels of the stem and branches 
 to the leaves, is there subjected to the action of the cells which make up the 
 parenchyma of those organs. The crude watery ascending sap is thus con- 
 verted, by a variety of chemical and vital operations, into the thick glutin- 
 ous latex; which, like the blood of animals, contains the materials for the 
 production of new tissue, and also the elements of the various secretions. 
 This process of conversion includes the Exhalation of superfluous liquid; 
 and also that interchange of gaseous ingredients between the sap and the air, 
 which may be termed Aeration ; but it involves, beside these obvious chemi- 
 cal alterations, a new molecular arrangement of the particles of the sap, by 
 which a variety of new products are generated, some of them possessing 
 such a tendency to pass into the form of solid organized tissue, as to present 
 a sort of sketch of this, by a process of coagulation, when withdrawn from 
 the living vessels. To this peculiar converting process, which is such an 
 important step towards the production of perfect living tissue from the crude 
 aliments, the term Assimilation is applied. As the elaborated sap or latex 
 descends in its proper vessels through the stem, it yields up to the growing 
 parts the nutrient materials they respectively require. These growing parts 
 may be either the ordinary tissues, of which the chief part of the fabric is 
 composed, and which are destined to a comparative permanency of duration ; 
 and in the growth and extension of these, the process of Nutrition is com- 
 monly regarded as consisting. On the other hand, certain groups of cells 
 have for their office the separation of peculiar products from the sap, such as 
 oil (fixed or essential), starch, resin, &c. ; which they store up against the 
 time when they may be demanded ; and these are said to perform the act of 
 Secretion. In both cases, however, the act is essentially the same ; for the 
 process of Secretion, like that of Nutrition, consists in the growth of a cellular 
 tissue, and the difference consists only in the destination of the contents of the 
 cells ; which, in the one case, are adapted merely to give firmness and solidity 
 to their walls ; whilst, in the other, they are set apart for some other purpose, 
 to be given up again when required. 
 
 108. It is very important to remark, in regard to all the cells thus actively 
 concerned in the Vegetative functions, by which the development and exten- 
 sion of the permanent fabric is provided for, that they have but a very transi- 
 tory life as individuals. The Absorbent cells at the extremities of the rootlets 
 are continually being renewed ; some of the old ones dying and decaying 
 away, whilst others are converted into the solid texture of the root, and thus 
 
ON ORGANIZED STRUCTURES IN GENERAL. 101 
 
 contribute to its progressive elongation. Of the transitory duration of the 
 Assimilating cells, we have an obvious proof in the "fall of the leaf;" which 
 takes place at intervals (alike in evergreen and deciduous species), to be fol- 
 lowed by the production of a new set of cells, having similar functions. And 
 the Secreting cells have usually a like transitory duration; being destined to 
 give up their contents by the rupture or liquefaction of their walls, whenever 
 called upon to do so, by the demand set up in the growing parts of their 
 neighbourhood, for the peculiar products they have set apart. 
 
 109. Not only are the proper organic functions of all Plants thus dependent 
 upon the agency of cells ; but their Reproduction is likewise. In the lowest 
 tribes of the Cryptogamia, where each cell is an independent individual, every 
 one has the power of preparing within itself the reproductive germs, from 
 which new generations may arise. In the higher tribes, on the other hand, 
 the general principle of the division of labour, which separates the absorbing, 
 assimilating and secreting cells, involves also the setting apart of a distinct set 
 of cells for the preparation of the reproductive germs ; these cells are known 
 in the Cryptogamia as spores, and in the Phanerogamia as pollen-grains. In 
 the higher Plants we find a complex apparatus superadded ; for the purpose 
 of aiding the early development of these germs, by supplying them with nu- 
 triment previously elaborated by the parent; yet still this operation is of a 
 purely accessory kind, and the essential part of the process remains the same. 
 
 110. Now we shall find that, although the fabric of Animals appears to be 
 formed on a plan entirely different from that of Plants, and although the ob- 
 jects to be attained are so dissimilar, there is a much greater accordance 
 amongst their elementary parts, than might have been anticipated. The starting- 
 point of both is the same ; for the embryo of the Animal, up to a certain grade 
 of its development, consists, like that of the Plant, of nothing else than an aggre- 
 gation of cells (Plate I., Fig. 15). And amongst the lowest tribes of animals, as 
 well as among certain of the highest tribes that retain many embryonic peculi- 
 arities, even in the adult condition, (such as the curious Amphioxus or Lancelot,) 
 we find a great proportion of the complete fabric to be possessed of a similar 
 constitution. In most of the higher animals, however, we find that a large 
 proportion of the fabric consists of tissues in which no distinct trace of a cel- 
 lular origin is apparent ; and it has been only since improved powers of ob- 
 servation have been brought to bear upon their analysis, and more especially 
 since they have been examined, not only in their complete state, but in the 
 course of their development, that they have been reduced to the same category 
 with the tissues of Plants and of the lower Animals. Other tissues, which 
 are peculiar to Animals, cannot be referred to the same origin ; but these will 
 be found to have a grade of organization even lower than that of simple iso- 
 lated cells, and to be referrible to the solidification of the plastic or organizable 
 fluid prepared by the assimilating cells, and set free by their rupture. We 
 shall find, however, that (as in Plants) all the tissues most actively concerned 
 in the Vital operations, retain their original cellular form ; and we shall be 
 able to refer to distinct groups of cells in the bodies of Animals, not merely 
 the functions of Absorption, Assimilation, Respiration, Secretion, and Repro- 
 duction, which are common to them with Plants, but also those of Muscular 
 (Contraction, and Nervous Action, which they alone perform. Before procee^^ 
 ing to this investigation, however, it will be desirable to examine into the na- 
 ture of the original components at the expense of which the Animal fabric 
 is built up. Our knowledge of these is principally derived from the researches 
 which have been made into their character in Man and the higher Animals; 
 but there can be little doubt that they are common, with trifling modifications, 
 perhaps, to the entire kingdom. 
 
 9* 
 
102 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 2. On the Original Components of the Animal Fabric. 
 
 111. Putting aside, for the present, the inorganic or mineral matters which 
 enter into the composition of the Animal body, and which are left in the form 
 of an ash, when the organic compounds are decomposed and dissipated by 
 heat, we shall confine our attention to the peculiar characters of the latter. 
 As already stated ( 4), the organized tissues of Plants are found, when en- 
 tirely freed from the contents of their cells, to have a very uniform composi- 
 tion; being entirely made up of Carbon united with the elements of Water in 
 a very simple proportion, that of 8 of the former to 7 of each of the latter; 
 and this simplicity in their chemical character partly accounts for their com- 
 parative durability. There are various compounds found iii the cells of Plants, 
 and elaborated by them for the purpose of affording food to Animals, which 
 do not undergo organization, so long as they are contained in the Vegetable 
 fabric; but these very products, when transferred to the bodies of Animals, 
 form the components of their solid tissues. These substances are distinguished 
 by the presence of Azote or Nitrogen, in considerable amount; and also by the 
 large number of atoms of the four components, which are united in each of 
 them, giving them a much more complex composition, and a much greater 
 tendency to decay, this being brought about by the disposition of the compo- 
 nents to enter into new compounds of a simpler and more permanent nature. 
 A considerable variety of such substances exists in the different parts of the 
 Human body ; but the nature and composition of these may be belter studied, 
 when their structure and actions are being described; and at present we shall 
 confine ourselves to the fundamental or original components, of which all the 
 others may be regarded as modifications. 
 
 112. When we examine the Egg of an Oviparous animal, we find that, 
 putting aside the fatty matter of the yolk (which is destined, not to be con- 
 verted into tissue, but to be stored up in cells), the sole organic constituent is 
 that which is known to Chemists as Albumen. By the wonderful processes 
 of chemical and vital transformation, which take place during the period of 
 incubation, and which are effected by the germ-cell and its descendants, this 
 Albumen is metamorphosed into nerve, muscle, tendon, ligament, membrane, 
 areolar tissue, horny substance, feathers, the organic basis of bone, &c. The 
 same metamorphosis is continually taking place in the adult animal; for every 
 substance of similar composition, that is employed as food, is reduced to the 
 form of Albumen in the digestive process; so that this becomes the essential 
 constituent of whatever fluid is absorbed for the nutrition of the tissues. It 
 is true that Gelatine, taken in as food, may be absorbed and carried into the 
 current of the circulation ; but there is little doubt, that it is incapable of 
 being applied to the reconstruction of any but the gelatinous tissues ; and in 
 these it exists in the very lowest form of organization, if organization it can 
 be called. Moreover, as it is clear, from what has been just stated, that the 
 gelatinous tissues may be formed at the expense of Albumen, we are justified 
 in regarding the latter substance as the common pabulum for all. Hence Albu- 
 men seems to hold very much the same position in the Animal economy, with 
 Gum in the Vegetable. 
 
 ^113. The properties of Albumen may be studied in the White of Egg, or 
 in the Serum of Blood ; from both of which situations it may be obtained in 
 a pure state by very simple means. In the Animal Fluids it exists in a so- 
 luble state ; and even when it has been dried (at a temperature of 126), it 
 is readily dissolved again in water, forming a glairy, colourless, and nearly 
 tasteless fluid. In this condition it is always combined with a small quan- 
 tity of free soda; to the separation of which (whether by the agency of heat 
 or acids), its coagulation is thought by many Chemists to be due. On this 
 
COMPONENTS OF THE ANIMAL FABRIC. ALBUMEN. 
 
 103 
 
 view, pure Albumen is not soluble in water ; its solution being only accom- 
 plished by union with an alkali. When dissolved in water, it coagulates 
 at 158; a very dilute solution, however, does not become turbid until it is 
 boiled. When the coagulation of Albumen takes place rapidly, a coherent 
 mass is formed, which shows no trace whatever of organization ; but, when 
 the process is more gradual, minute granules present themselves, which do 
 not, however, exhibit any tendency towards a higher form of structure. It is 
 thrown down from its solution, in a coagulated state, by Alcohol, Creosote, 
 and by most Acids (particularly nitric) with the exception of the acetic. 
 These precipitates are definite compounds of the Acids with the Albumen, 
 which here acts the part of a base. On the other hand, coagulated Albumen 
 dissolves in caustic Alkalies, and neutralizes them ; so that it must here act 
 as an acid. A solution of Albumen in water is precipitated by acetate of lead, 
 and by many other metallic solutions: and insoluble compounds are formed, 
 of which one the albuminate of the chloride of mercury is of much interest, 
 as being that which is produced by the mixture of a solution of albumen with 
 one of corrosive sublimate. Albumen, both in its soluble and insoluble state, 
 always contains a small amount of Sulphur, which blackens metallic silver ; 
 and also a minute quantity of Phosphorus. Soluble albumen dissolves Phos- 
 phate of Lime ; and about two per cent, of this salt may be separated from it 
 in its coagulated state. 
 
 114. So long as Albumen remains in the state regarded by Chemists as 
 characteristic of it, no tendency to become organized can be discerned in it ; 
 but subsequently to its introduction into the living Animal body, it undergoes 
 a transformation into a compound, termed Fibrine, which is distinguished from 
 it by new and peculiar properties. It appears from the analyses of Mulder 
 and Scherer, that there is no essential difference in the ultimate composition 
 of these two substances ; the relative proportions of the constituents of each 
 being, according to them, as follow: 
 
 MULDER. 
 
 SCHERER. 
 
 Albumen. Fibrine. Albumen. Fibrine. 
 
 Carbon . 
 
 Hydrogen 
 
 Nitrogen 
 
 Oxygen 
 
 Phosphorus 
 
 Sulphur 
 
 54-84 
 
 7-09 
 
 15-83 
 
 21-23 
 
 33 
 
 68 
 
 54-56 
 
 6-90 
 
 15-72 
 
 22-13 
 
 33 
 
 36 
 
 53-850 
 
 6-983 
 
 15-673 
 
 23-494 
 
 53-671 
 
 6-878 
 
 15-763 
 
 23-688 
 
 100-00 100-00 
 
 100-000 100-000 
 
 The wide difference in their properties must be referred, on this view, solely 
 to a change in the molecular arrangement of their ultimate particles. Accord- 
 ing to Dumas, however, there is a marked difference in composition, between 
 Fibrine and the various forms of Albumen; the former having less Carbon, 
 and more Nitrogen, than the latter. The following are the results of his 
 analyses : 
 
 Carbon 
 
 Hydrogen 
 
 Nitrogen 
 
 Oxygen 
 
 Sulphur 
 
 Phosphorus 
 
 ALBUMEN. 
 
 , A 
 
 From serum. From eggs. 
 . 53-32 53-37 
 
 7-29 7-10 
 
 15-70 15-77 
 
 23-69 
 
 23-76 
 
 FIBRINE. 
 
 52-78 
 
 6-96 
 
 16-78 
 
 23-48 
 
 100-00 
 
 100-00 
 
 100-00 
 
104 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 It is not, perhaps, of any great moment whether this difference has a real 
 existence or not; for the conversion of Albumen into Fibrine is unquestion- 
 ably a process much more of vital than of chemical transformation. We 
 shall presently see, that Fibrine may be regarded as Albumen, in which the 
 process of Organization has begun ; its molecules being ready to assume the 
 peculiar arrangement that is so designated : this arrangement takes place 
 most completely, when the fibrinous mass is in contact with a living tissue, 
 and is therefore to a certain degree under its influence. Fibrine, like Albu- 
 men,, may exist in a soluble or in a coagulated state ; its soluble form only 
 occurs, however, in certain living animal fluids, the Chyle, Lymph, and 
 Blood; and it seems to be the intermediate condition between the soluble al- 
 bumen, and the solid organized substances which are formed from it. When 
 withdrawn from the blood-vessels, the Blood soon coagulates, as do also the 
 Chyle and Lymph, when they contain sufficient fibrine; and this coagulation 
 is entirely due to a change in the condition of the Fibrine, the particles of 
 which have a tendency to aggregation in a definite manner. The Fibrine may 
 be obtained in a separate form, by stirring fresh-drawn blood with a stick, to 
 which it adheres in threads ; these contain some fatty matter, which is to be 
 washed out with alcohol. In this condition it possesses the softness and elas- 
 ticity which characterize the flesh of animals ; and contains about three-fourths 
 of its weight of water. It may be deprived of this water in dry air, and then 
 becomes a hard and brittle substance ; but, like flesh, it imbibes water again 
 when moistened, and recovers its original softness and elasticity. When 
 burned, it always leaves, like albumen, a portion of phosphate of lime. Fi- 
 brine is insoluble in alcohol and ether, and also, under ordinary circumstances, 
 in water; but when long boiled in water, especially underpressure, its nature 
 is altered, and it becomes soluble. This change, which may be effected also 
 in coagulated Albumen, is attributed by Mulder to the oxidation of the Pro- 
 teine, which is its principal constituent ( 116, a). When Fibrine is treated 
 with strong acetic acid, it imbibes the acid, and swells up into a transparent 
 colourless jelly, which is soluble in hot water; this solution is precipitated by 
 the addition of another acid. 
 
 115. Fibrine, like Albumen, unites with acids as a base, forming definite 
 compounds ; and with bases as an acid. Its correspondence with Albumen 
 is further indicated by the fact (first stated by M. Denis), that it may be en- 
 tirely dissolved in a solution of nitrate of potash; and that this solution is 
 coagulated by heat, and greatly resembles a solution of Albumen. This is 
 only true, however, Of the ordinary Fibrine of venous blood; for that which 
 is obtained from arterial blood or from the buffy coat, or which has been ex- 
 posed for some time to the air, is not thus soluble. This is an important and 
 interesting circumstance. The difference appears to depend upon the larger 
 quantity of oxygen contained in the latter; for a solution of Venous Fibrine in 
 nitre, contained in a deep cylindrical jar, allows a precipitate in fine flocks to fall 
 gradually, provided the air have access to the surface, but not if it be prevented 
 from coming in contact with the fluid ; this precipitate is insoluble in the solution 
 of nitre, and possesses the properties of 'arterial fibrine. Hence it may be 
 inferred, that the Fibrine of Venous blood most nearly resembles Albumen ; 
 whilst that of Arterial blood, and of the Buffy coat, contains more oxygen, 
 and is more highly animalized. When decomposition commences in a coagu- 
 lum of .Fibrine withdrawn from the body (and even in the greatly-debilitated 
 living body, in which the Fibrine appears to be imperfectly formed), a granu- 
 lar mode of aggregation is evident in the particles of the mass, thus showing 
 its affinity to Albumen, when its peculiar vital characters have departed, or 
 are possessed by it in an inferior degree. 
 
 116. The close chemical relation existing between Albumen and Fibrine 
 
PROTEINE, AND ITS TRANSFORMATIONS. 105 
 
 is further shown by the fact, that from both of them (as well as from various 
 substances used as food, which are furnished by the Vegetable kingdom, 111) 
 an identical substance may be obtained by a simple process. If boiled al- 
 bumen be dissolved in a weak solution of caustic alkali, and the liquid be 
 neutralized by an acid, a precipitate falls down in grayish-white flocks ; this, 
 being collected and washed, is gelatinous, of a grayish colour, and semi-trans- 
 parent; and, when dried, it is yellowish, hard, easily pulverized, tasteless, in- 
 soluble in water and alcohol, and decomposed by heat without fusing. This 
 substance has been termed Proteine^ from an idea that it is the fundamental 
 proximate principle of which Albumen, Fibrine, &c., are modifications. It 
 contains the same proportions of Carbon, Hydrogen, Nitrogen and Oxygen, with 
 Albumen and Fibrine ; but it has been commonly regarded as destitute of their 
 Sulphur and Phosphorus; .the most recent investigations of Liebig, however, 
 render it doubtful whether this is the case. According to Mulder (its dis- 
 coverer), its composition may be represented by the formula 40 C, 31 H, 5 N, 
 12 O ; whilst by Liebig it is represented by the formula 48 C, 36 H, 6 N, 14 O. 
 Either of these correctly represents the relative proportions of tlie elements, 
 as deduced from analysis ; but the formula of Mulder is asserted by him to 
 represent more accurately the combining equivalent of the entire substance, 
 as deduced from the compounds it forms with others. 
 
 a. According to Mulder, Proteine unites with Oxygen in definite proportions, so as to form 
 a binoxide and a tritoxide. These are both produced when Fibrine is boiled in water for 
 some time; the latter being then found in solution, whilst the former remains insoluble. 
 The tritoxide may also be formed by boiling Albumen for some time in water, when it is in 
 like manner taken up in solution ; but the insoluble residue is still albumen. It is further 
 attainable by decomposing the chlorite of proteine with ammonia. In its properties it some- 
 what resembles Gelatine, and has been mistaken for that substance. There is reason to 
 think that this compound really exists as such in the blood; a small quantity of it being 
 formed every time that the blood passes through the lungs, and given out again when it 
 returns to the system ; and a much larger quantity being generated during the inflammatory 
 process, so that it may be easily obtained from the buffy coat by boiling. It is also said to 
 be contained in pus. The binoxide is quite insoluble in water, but dissolves in dilute acids. 
 It may be obtained by dissolving Hair in potash, adding a little acid to throw down the 
 proteine, and then adding a large excess of acid, which precipitates the binoxide. Accord- 
 ing to Mulder, this compound also is produced in small quantity at every respiration; and it 
 enters into the normal composition of several of the animal tissues. These views, however, 
 must still be received with some hesitation. They are liable to the fundamental objection, 
 advanced against them by Liebig; that the binoxide and tritoxide, like proteine itself, contain 
 the sulphur of albumen and fibrine. Still, the production of new and peculiar compounds, 
 by the processes indicated, is an important fact which cannot be overthrown ; whatever 
 may prove to be the case in regard to the ultimate composition of these substances. 
 
 b. One of the most characteristic and important properties of Proteine, is the facility with 
 which it undergoes decomposition, when acted on by other chemical substances, especially 
 by alkalies. If a proteine-compound be brought into contact with an alkali, ammonia is im- 
 mediately disengaged ; indeed the alkaline solution can hardly be made weak enough to 
 prevent the disengagement of ammonia. This is a property, which must be continually 
 acting in the living body ; since the blood has a decidedly alkaline reaction. If either albu- 
 men, or any other proteine compound, be boiled with potash, it is completely decomposed; 
 not, however, being resolved at once into its ultimate constituents, or altogether into simple 
 combinations of them; but in great part into three other organic compounds, Leucin, Protid, 
 and Erythroprotid. Leucin is a crystalline substance, which forms colourless scales, destitute 
 of taste and odour; it is soluble in water and alcohol, and sublimes unchanged. It consists 
 of 12 Carbon, 12 Hydrogen, 1 Nitrogen, and 4 Oxygen. There is not at present any evi- 
 dence, that it is produced in the living body; but considerable interest attaches to it from the 
 fact, that it may be procured from Gelatine, as well as from Proteine; a near relationship 
 between these two substances being thus indicated. The other two compounds, Protid and 
 Erythroprotid, are uncrystalline substances ; the former of a straw-yellow, the latter of a red- 
 dish-brown colour ; they belong to the class of bodies which were formerly included under 
 the vague general term of extractive matter; and they bear a strong resemblance to Gelatine, 
 not only in their solubility in water, but also in their chemical composition, as is shown by 
 the following comparison of their formulae : 
 
106 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 C. H. yr. O. 
 
 Protid . 13 914 
 
 Erythroprotid . 13 8 .1 5 
 
 Gelatine . 13 10 2 5 
 
 Besides these substances and Ammonia, Formic and Carbonic Acids are produced by the 
 decomposition of Proteine with potash ; the acids unite with the potash, whilst the ammonia 
 is set free. 
 
 117. It is very important, however, to bear in mind, that however close 
 may be the chemical approximation between Albumen and Fibrine, there is a 
 wide difference between them, as regards their relations to living organized 
 structures : and this difference is one of which chemistry takes no cogni- 
 zance. To use a rather homely illustration, the relation between Albumen, 
 Fibrine, and Organized Tissue is somewhat of the .same nature as that which 
 exists between the raw cotton, the spun yarn, and the woven fabric. Albu- 
 men shows no tendency to coagulate, except under the influence of purely 
 chemical agents, and its coagulum is entirely destitute of structure, being a 
 mere homogeneous aggregation of particles. On the other hand, Fibrine 
 exhibits a constant tendency to pass into the form of a solid tissue ; and it 
 seems only restrained from doing so by certain influences, whose nature is 
 not understood, to which it is subjected whilst contained in the vessels of the 
 living body. The conversion of Albumen into Fibrine, therefore, is the first 
 great step in the process of Nutrition, by which the materials supplied by the 
 food are made to form part of the living tissues of the body ; and it is the one 
 to which the term Assimilation may be most appropriately applied. As 
 already mentioned, Albumen is always the starting-point; since the fibrinous 
 elements of organized tissues are reduced, by the solvent power of the gas- 
 tric fluid, to the same form with the unorganized coagulum of the albumen of 
 the egg. The first appearance of Fibrine is in the Chyle, or fluid of the 
 Lacteals ; and when this is examined in the neighbourhood of the part where 
 it has been absorbed, the traces of Fibrine which it presents are very slight. 
 As the Chyle flows along the lacteals, however, the proportion of Fibrine in- 
 creases ; and it reaches its maximum at the point where the Chyle is de- 
 livered into the current of the circulating Blood. The proportion of Fibrine 
 in the Blood, as indicated by the firmness of the coagulum which it forms, is 
 much greater than that contained in the Chyle, notwithstanding that there is 
 a constant withdrawal of this element for the purpose of nutrition. And in 
 certain disordered states of the system, in which the formative powers of the 
 Blood are so exalted, as to produce a tendency to the formation of tissue in 
 abnormal situations, the proportion of Fibrine is found to be increased to 
 twice, thrice, or even four times its usual amount. And even where there is 
 no such general increase, a local increase is made evident in the large pro- 
 portion of fibrine, which exists in the exudations poured forth for the repara- 
 tion of injuries ; these exudations, when possessed of a high formative pro- 
 perty (that is, a readiness to produce an organized tissue), are said to be 
 composed of plastic, or coagulable lymph; but this is nothing more than the 
 Liquor Sanguinis, or fluid portion of the Blood,, holding in solution an unu- 
 sual quantity of Fibrine. It is evident, from these facts, that some peculiar 
 agency must exist within the vessels, by which the elaboration of the Fibrine 
 from the Albumen is effected ; and we shall hereafter endeavour to bring 
 together certain facts, which seem to indicate its nature. 
 
 J18. The tissue that is produced by the apposition of the particles of 
 Fibrine, when left to themselves, and solely influenced by their own mutual 
 attraction, is of a very simple character, being composed of fibres interlaced 
 with each other in various directions. This arrangement can be seen in the 
 ordinary Crassamentum, or clot of healthy Blood, by examining thin slices 
 
FIBRILLATION OF COAGULATED FIBRINE. 
 
 107 
 
 Fig. 10. 
 
 under the microscope ; especially after the clot has been hardened by boiling. 
 A number of fibres, more or less distinct, may be seen to cross one another ; 
 forming by their interlacement a tolerably regular network, in the meshes of 
 which the red corpuscles are entangled. This fact was known to Haller ; 
 but it has been generally overlooked by subsequent Physiologists, until atten- 
 tion was drawn to it by the inquiries of Messrs. Addison, Gulliver, and 
 others. It is in the Buffy Coat, however, that the fibrous arrangement is best 
 seen; on account, as it would appear, of the stronger attraction which the 
 particles of fibrine have for one another, when its vitality has been raised by 
 the increased elaboration to which it has been subjected. That there are va- 
 rieties of plasticity in the substance, which, on account of its power of spon- 
 taneously coagulating, we must still c$\\ fibrine, appears from this fact among 
 others, that, in tuberculous subjects, 
 the quantity of fibrine in the blood is 
 higher than usual (Andral and Gavarret), 
 although its plasticity is certainly below 
 par. It is as easy to understand, that 
 its plasticity may be increased, as that it 
 may be diminished; and this either in 
 the general mass of the blood, or in a 
 local deposit. In fact, the adhesions 
 which are formed by the consolidation 
 of coagulable lymph, or in other words, 
 of the fluid portion of the blood, whose 
 plasticity has been heightened by the 
 vital actions that take place within the 
 capillaries of the part on which it has 
 been effused, often acquire very con- 
 siderable firmness, before any vessels 
 have penetrated them ; and this firmness must depend upon that mutual 
 attraction of the particles for one another, which in aplastic deposits is alto- 
 gether wanting, and which in cacoplastic deposits is deficient. A very inte- 
 resting example of a structure entirely composed of matted fibres, and evi- 
 dently originating in the simple consolidation of Fibrine, is found in the 
 membrane adherent to the interior of the Egg-shell (Membrana putaminis) ; 
 and also in that which forms the basis of the Egg- 
 shell itself. Between the two, there is no essen- 
 tial difference ; as may be seen by examining " an 
 egg without shell," as it is commonly termed, (or 
 rather one in which the shell-membrane has been 
 unconsolidated by the deposition of calcareous 
 matter) ; or by treating the egg-shell with dilute 
 acid, so as to remove the particles of carbonate of 
 lime, which are deposited in the interstices of the 
 network. The place of the shell is then found to 
 be occupied by a membrane of considerable firm- 
 ness, closely resembling that which lines the shell 
 and surrounds the albumen of the egg, but thicker 
 and more spongy. After maceration for a few 
 days, either of these membranes may be separated 
 into a number of laminae, each of which (if suffi- 
 ciently thin) will show a beautiful arrangement of reticulated fibres. It is 
 impossible to refuse to such a structure the designation of an organized tis- 
 sue, although it contains no vessels, and must be formed by the simple con- 
 solidation of Fibrine, poured out from the lining membrane of the oviduct of 
 
 Fibrous structure of inflammatory exudation 
 from peritoneum. 
 
 Fig. 11. 
 
 Fibrous membrane from 
 Egg-shell. 
 
108 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 the bird. It is probably in the same manner, that the Chorion of the Mam- 
 miferous animal originates ; since this is a new envelope, formed around the 
 ovum, during its passage along the Fallopian tube. In the latter, for an ulte- 
 rior purpose, vessels are afterwards developed, by extension from the con- 
 tained ovum ; and by the nutrition they supply, its size is increased, and 
 changes take place in its texture. But in the Egg-membrane of the Bird, 
 there is no need of vessels ; because no subsequent change in its texture is 
 required, and its duration is sufficient for the purpose it has to answer. 
 
 119. The completeness of the transformation of Fibrine into simple Fi- 
 brous Tissue, appears to depend upon two circumstances in particular ; the 
 perfect elaboration of the Fibrine itself; and the vitality of the surface upon 
 which the concretion takes place. When the Fibrine is highly elaborated, it 
 will coagulate in the form of a definite network of minute fibrillae, even upon 
 a dead surface, as a slip of glass ; this is the case, for instance, with the Fi- 
 brine of the buffy coat of the Blood, or with that of the Liquor Sanguinis 
 (coagulable lymph) poured out for the reparation of an injured part. But in 
 the ordinary Fibrine of the blood, the fibrillation is less distinct when the con- 
 cretion takes place upon a dead surface. When it occurs in contact with a 
 living surface, however, the coagulation takes place more gradually; and it 
 seems as if the particles, having more time to arrange themselves, become ag- 
 gregated into more definite forms, so that a more regular tissue is produced 
 just as crystals are most perfectly formed when the crystalline action takes 
 place slowly. It was formerly imagined that the Muscular tissue is the only 
 one produced at the expense of the Fibrine of the blood ; the other tissues 
 being formed from its Albumen. This, however, is unquestionably erroneous. 
 There is no proof whatever that Albumen, as long as it remains in that con- 
 dition, ever becomes organized ; whilst, on the other hand, there is abundant 
 evidence, that the plasticity of any fluid deposit that is, its capability of be- 
 ing metamorphosed into organized tissue- is in direct relation with the quan- 
 tity of Fibrine which it contains. Thus the Liquor Sanguinis, or Coagulable 
 Lymph, thrown out for the reparation of injuries, contains a large amount of 
 Fibrine ; and this substance is converted, not at first into muscular fibre, but 
 (whatever may be the. tissue to be ultimately produced in its place) into a 
 fibrous network, which fills up the breach and holds together the surrounding 
 structure. This may be regarded as a simple form of areolar tissue ; which 
 gradually becomes more perfectly organized by the extension of vessels and 
 nerves into its substance ; and in which other forms of tissue may subse- 
 quently make their appearance. This process will be more particularly de- 
 scribed hereafter ; it is at present noticed here as an illustration of the general 
 fact, thatjibrine is to be regarded as the plastic element of the nutritive fluids. 
 
 3. Of the Elementary Parts of Organized Tissues; Cells, Membrane, 
 
 and Fibre. 
 
 120. The cells, which have been spoken of as making up the chief part of 
 the Vegetable Organism, are minute closed sacs; whose walls are composed 
 in the first instance of a delicate membrane, frequently strengthened, at a 
 period long subsequent to their first formation, by some internal deposit. The 
 form of these cells is extremly variable ; and depends chiefly upon the degree 
 and direction of the pressure, to which they may have been subjected at the 
 period of their origin, and subsequently to it. Sometimes they are spheroidal ; 
 sometimes cubical or prismatic ; sometimes cylindrical ; and sometimes very 
 much prolonged. These cells may undergo various transformations. One of 
 the most common, is the conversion of several into a continuous tube or Duct. 
 This is principally seen in the vessels, through which the sap ascends the stem ; 
 
DEVELOPMENT AND METAMORPHOSES OF CELLS. 109 
 
 these appear to have been formed by the breaking-down of the transverse 
 partitions, between a regular series of cylindrical cells laid end to end ; and 
 the remains of such partitions may frequently be seen in them. The ducts 
 which convey the ascending sap, do not inosculate with each other ; their 
 purpose being merely to carry it direct to the leaves ; but the vessels, through 
 which the descending or elaborated sap flows, are of very different character; 
 for their purpose is to distribute the nutritious fluid through the tissues; 
 and they anastomose very freely, just as do the capillaries of Animals. The 
 network which they form, however, can be as clearly traced to an origin in cells, 
 whose cavities were originally distinct, as can the bundles of straight non- 
 communicating ducts. Another important transformation of the original cells, 
 is that by which the Woody Fibres, which compose nearly all the fibrous 
 textures of Vegetables, are produced. These fibres are still cells, but their form is 
 very much elongated ; they have a fusiform or spindle shape, being tubes drawn 
 to a point at each end ; at first they are quite pervious, like ordinary cells ; 
 but in the older wood, their cavity is filled up by interior deposit. 
 
 121. Such deposits may take place in cells of the ordinary form ; and they 
 present many variations in their character, which give corresponding peculi- 
 arities to the cells which contain them. In many instances, they consist merely of 
 concentric layers, one within the other, each layer completely lining the one 
 which preceded it ; and the cavity of the cells being thus gradually but uni- 
 formly contracted in every dimension. In other cases, certain points of the 
 original external cell-membrane are left uncovered by the secondary deposits ; 
 and thus, the same vacuities being left in the successive layers, passages are 
 formed, which stretch out from the central cavity to certain spots of the peri- 
 phery of the cell. Cells of this character are found in certain parts of plants, 
 which are required to possess unusual firmness, without losing the power of 
 transmitting fluid, the former endowment being conferred by the secondary 
 deposits; whilst the latter is retained by the peculiar system of passages just 
 described, the thin or uncovered parts of the wall of one cell being in contact 
 with corresponding spots on the walls of adjacent cells, as we see in the tissue 
 of the stones of fruit, the central gritty matter of the pear, &c. Lastly, the 
 new deposit may present the form of a more or less regular spiral fibre, winding 
 within the cell from end to end ; and this may present itself alike in cells of 
 the ordinary shapes, or in fusiform cells (constituting the proper spiral ves- 
 sels), or in cells that have coalesced into continuous tubes or ducts. The 
 spiral may break up into rings or irregular pieces ; and these may be united 
 again by additional deposits of a still more irregular character, so as completely 
 to obscure their original spiral form. This spiral fibre is very completely gene- 
 rated, in some instances, when the cell-wall itself has not acquired any greater 
 tenacity than that of mucus, very easily dissolved ; which (as we shall presently 
 see) is a stage in the production of cells in general. Such spiral fibres spring 
 out from the external coats of many seeds, when they are moistened with 
 fluids. 
 
 122. So far as is yet known, all Cells originate in germs, that have been pre- 
 pared by some previously-existing cell; and these germs may either be de- 
 veloped within the parent-cell, or may be set free by its rupture, and may be 
 developed quite independently. The latter case, being the simplest, will be 
 first considered ; we have numerous examples of it among the lower Cellular 
 Plants. In the first place, the germ, from which the cell originates, is a mi- 
 nute granule, only to be seen with a good microscope, and apparently quite 
 homogeneous. It has the power of drawing to itself the nutrient elements 
 around, and of combining these into the proximate principles, that may serve 
 as the materials for its development. By the incorporation of these with its 
 own substance, it gradually increases in size, and a distinction becomes ap- 
 
 10 
 
110 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 parent, between its transparent exterior and its coloured interior. Thus we 
 have the first indications of the cell-wall, and the cavity. As the enlarge- 
 ment proceeds, the distinction becomes more obvious ; the cell-wall is seen to 
 be of extreme tenuity, perfectly transparent, and apparently homogeneous in 
 its texture ; whilst the contents of the cavity are distinguished by their colour, 
 which (in the species here alluded to) is commonly either green or bright red. 
 At first they, too, seem to be homogeneous ; but a finely-granular appearance 
 is then preceptible amongst them ; and a change gradually takes place, which 
 
 Fig. 12. 
 
 Simple isolated cells con- 
 taining productive mole- 
 cules. 
 
 seems to consist in the aggregation of the minuter 
 molecules into granules of more distinguishable size and 
 form. These granules, which are the germs of new 
 cells, seem to be at first attached to the inner wall of the 
 parent-cell ; afterwards they separate from it, and move 
 about in its cavity ; and at a later period, the parent- 
 cell bursts and sets them free. Now this is the ter- 
 mination of the life of the parent-cell ; but the com- 
 mencement of the life of a new generation : since every 
 one of these germs may develope itself into a cell, after 
 precisely the foregoing manner ; and will then, in turn, 
 propagate its kind by a similar process. 
 
 123. The development of new cells within the pa- 
 rent, or what may be termed the endogenous mode 
 of cell-growth, takes place in many instances on a plan which differs in no 
 respect from the preceding, except that the parent-cell does not rupture. The 
 granules it contains derive their nutriment from the surrounding fluid, which 
 is included within the cell ; by their progressive increase in size, they gradu- 
 ally fill up the whole cavity of the parent-cell ; and by a further increase, they 
 distend its wall, which becomes thinner and thinner, and at last ceases to be 
 visible around the newly-formed cluster. 
 
 124. In other instances, however, we find that the development of new 
 ,.,. cells proceeds, not from granules scattered through the whole 
 
 interior of the cell, but from a determinate spot or nucleus, 
 which is seen upon its wall. This nucleus is frequently formed 
 very early, by the aggregation of molecules around the original 
 granule or cell-germ, even previously to the first appearance of 
 the distinct cell-membrane ; and by Schleiden, who first ob- 
 served this process, it was thought that the body thus produced 
 was essential to the development of the new cell, whence he 
 gave it the name of cytoblast. It appears, however, from more 
 extended inquiries, that this is not the case ; and that the nu- 
 cleus is rather concerned with the subsequent operations which 
 the cell performs, than with its original development. Fre- 
 quently the nucleus does not make its appearance, until the cell 
 itself has been completely formed. It is chiefly in the higher 
 tribes of Plants, that we find these nucleated cells ; the nucleus 
 in the cells of the lower Cryptogamia being usually more or 
 less expanded or diffused (as it were), through the entire cavity. 
 The destination of the several forms of cells which make up 
 the complex structure of' the higher plants, is very different ; 
 and their office seems in great measure to depend upon the 
 peculiar powers of the nucleus. In some instances, this body 
 seems to be the centre which attracts new deposits ; even the 
 Ceils of zygne- spiral filament being probably formed by its agency. We 
 ma, showing spiral have, in some of the lowest Cellular Plants, a curious fore-sha- 
 arrangementof the d owm g O f the spiral vessels of the most perfect ; the green 
 
 nuclear panicles. 
 
DEVELOPMENT AND MULTIPLICATION OF CELLS. 
 
 Ill 
 
 Fig. 14. 
 
 particles (or diffused nucleus ?) of the cells, in the genus Zygnema, presentin 
 a regular spiral arrangement at one period of their growth (Fig. 13). An 
 in other instances, as in the cells of the petal of 
 the common Geranium (Pelargonium}, we find 
 the nucleus sending out curious stellate or radi- 
 ating prolongations (Fig. 14.) These facts are 
 of much interest, as illustrating some of the more 
 obscure changes which are believed to take place 
 in animal tissues. 
 
 125. But the nucleus may also be the source 
 from which the new cells arise, thai are devel- 
 oped within the cavity of the parent. Several vari- 
 eties in the mode in which this process takes place, 
 are presented to our observation in the simplest of 
 the Cellular Plants, belonging to the group of the 
 Fresh-water Algae ; the growth of which may be 
 studied with peculiar facility. In some of these 
 the cell is destitute of a nucleus, but is filled with 
 a very finely-divided granular matter, the en- 
 dochrome; and the process of cell-multiplication 
 is effected by the subdivision of this matter into 
 two distinct masses, around each of which a pellucid cell-membrane subse- 
 quently makes its appearance, thus forming two new cells within the parent. 
 By a repetition of the same process, each of these new cells may again pro- 
 duce two new ones ; and thus the multiplication may be rapidly effected. 
 
 Fig. 16. 
 
 Cells from the petal of Pelargonium 
 showing stellate prolongations of the 
 nuclei. 
 
 Htmatococcusbinalis, in various stages of devel. 
 opment ; o, a, simple rounded cells ; 6, elongated 
 cell, the endochrome preparing to divide ; c, c, cells 
 in which the division has taken place ; d, large pa- 
 rent cell, in which the process has been repeated 
 a second time, so as to form a cluster of four se- 
 condary cells, such as is often seen in Cartilage. 
 
 CoceoMoris cystifera, showing various stages of 
 development: a, simple globular cells, surround- 
 ed by a well-defined mucous envelope ; 6, elon- 
 gated cell about to divide ; c, cell doubled by di- 
 vision, both the new cells still enclosed in original 
 mucous envelope ; d, further stage of the same 
 process,, one of the secondary cells having again 
 divided, whilst the other has not yet undergone 
 this change, but is about to do so ; e, group of 
 cells formed by the same process, and still re- 
 tained within the original mucous envelope. 
 
 This form of cell-development is best seen in some of the simplest Algae, 
 which consist of isolated cells, and in which the individuals composing the 
 successive generations are quite independent of one another ; and we have a 
 good illustration of it in the Hematococcus binalis, whose various stages of 
 cell-multiplication are shown in Fig. 15. In many other instances, the cells 
 of successive generations, without losing their individuality, are held together 
 
112 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 by a consistent mucous envelope ; so that we may find two, three, four, or a 
 larger number, clustered together within a well-defined investment, which has 
 tenacity enough to prevent them from separating. Of this we have a good 
 example in Coccochloris cystifera (Fig. 16) ; and a yet more remarkable one 
 in Hematococcus sanguineus (Fig. 17). The cells forming such masses of 
 vegetation may be likened to those of Cartilage, which are similarly enveloped 
 by an intercellular substance, and which present the same binary method of 
 multiplication ( 129). In the Confervas we find the cells, which are succes- 
 sively produced in this manner, remaining in connection with each other, so 
 as to form articulated filaments. The terminal cell of each filament is con- 
 tinually undergoing subdivision in the manner just described, and thus the 
 filament is elongated ; whilst other cells produce regular reproductive granules, 
 which are set free by an opening that forms in the cell-wall, and which devel- 
 ope themselves into new individuals without any further aid from the parent 
 structure, in the manner already described. The difference between these 
 two modes of propagation seems to have reference to the age and degree of 
 development of the cell ; the binary division being characteristic of cells which 
 are in a growing state, and being destined to extend the original structure; 
 whilst the formation and' emission of a number of reproductive granules is the 
 function of the mature cell, and is destined to give origin to new individuals. 
 These processes are analogous in the higher plants, the first to the develop- 
 ment of leaf-buds, the second to the production of seeds. In the Nostoc we 
 find the moniliform filaments, which are composed of a linear series of cells, 
 invested by dense gelatinous sheaths of definite extent, looking almost like 
 
 Fig. 17. 
 
 Hematococcus sanguineus in various stages of development , a, a single cell, enclosed in its mucous 
 envelope ; 6, c, clusters formed by division of parent-cell ; d, more numerous cluster, its component cells 
 in various stages of division ; , large mass of young cells, formed by continuance of the same process. 
 and enclosed within common gelatinous envelope. 
 
 large parent-cells (Fig. 18, B) ; and the extension of the filaments may so dis- 
 tend their sheaths as to give them the appearance of capacious globular cells 
 (Fig. 18, A). There is reason to believe that the long convoluted filaments 
 then separate into a cluster of shorter ones, each having its own share of the 
 mucous envelope. 
 
 126. The history of the Animal cell, in its simplest form, is precisely that 
 of the Vegetable cell of the lowest kind. It lives for itself and by itself, and 
 
DEVELOPMENT AND MULTIPLICATION OF CELLS. 
 
 113 
 
 is dependent upon nothingjbut a due supply of nutriment and a proper tem- 
 perature for the continuance of its growth, and for the due performance of its 
 functions, until its term of life is expired. It originates from a reproductive 
 granule, previously formed by some other cell ; this granule attracts to itself, 
 assimilates, and organizes, the particles of the nutrient fluid in its neighbour- 
 hood ; and converts some of them into the substance of the cell-wall, whilst 
 it draws others into the cavity of the cell. In this manner the cell gradually 
 increases in size ; and whilst it is 
 itself approaching the term of its 
 life, it usually makes preparation 
 for its renewal, by the develop- 
 ment of reproductive granules in 
 its interior ; which may become 
 the germs of new cells, when set 
 free from the cavity of the parent, 
 by the rupture of its cell-wall. 
 There is an important difference, 
 however, in the endowments of 
 the Animal and Vegetable cell. 
 The latter can in general obtain 
 its nutriment, and the materials for 
 its secretion, by itself combining 
 inorganic elements into organic 
 compounds. The former, how- 
 ever, is totally destitute of this 
 power ; it can produce no organic 
 compound, and we have yet to 
 learn how far its power of con- 
 verting one compound into an- 
 other may extend ; its chief en- 
 dowment seems to be that of at- 
 tracting or drawing to itself some 
 of the various substances, which 
 are contained in the nutritive fluid 
 in relation with it. This fluid, as 
 we shall hereafter see, is a mixture 
 of a great number of components ; 
 and different sets of cells appear 
 destined severally to appropriate 
 these, just as the different cells of 
 a parti-coloured flower have the 
 power of drawing to themselves 
 the element of their several colour- 
 ing matters. As far as it is yet 
 known, however, the composition 
 of the cell-wall is everywhere the 
 same, being that of Proteine. It 
 is in the nature of the contents of 
 the cell (as among the cells of Plants), that the greatest diversity exists ; and 
 we shall find that the purposes of the different groups of cells, in the general 
 economy of the Animal, depend upon the nature of the products they secrete, 
 and upon the length of time during which these products are retained by them. 
 127. Of the general account just given, the development of certain cells, 
 which float in the Chyle, Lymph, and Blood, may be adduced as an exam- 
 ple ; these, which are known as the Chyle arid Lymph corpuscles, and as the 
 
 10* 
 
 Nostoc macrosporum:A, a long convoluted filament, 
 composed of linear series of minute cells, enclosed in 
 general mucous envelope ; B, group of shorter fila- 
 ments, each with its own gelatinous envelope, pro- 
 bably formed by the division of the preceding. 
 
114 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 Colourless corpuscles of the Blood, have no single nucleus, but contain seve- 
 ral scattered particles, each of which seems to be a reproductive granule ; and 
 they emit these by the bursting or liquefaction of their wall, a change which 
 may be effected in them at any time, by the application of chemical reagents. 
 The granules thus set free appear to float in the current of fluid, and to be in 
 their turn developed into cells at the expense of the materials it affords. The 
 exudations of the plastic or organizable matter of the blood, which are thrown 
 out upon inflamed or wounded surfaces, appear to contain some of these gra- 
 nules ; for similar cells are speedily developed in these exudations, giving rise, 
 in their turn, to new generations, when their own term of life is ended. 
 
 128. In general, however, we find the cells of Animal tissues furnished with 
 a nucleus; and this may be formed, as in Plants, either at an early stage of 
 the development of the cell, by the aggregation of minute molecules around 
 the original granular germ (which germ seems to be the nucleolus of some 
 authors) ; or after the cell has attained its full size. The nucleus, where it 
 exists, appears to be the chief instrument in the functions of the cell; the 
 cell-membrane probably having little else, than the mechanical office of 
 bounding or limiting the contents of the cell. In some cells the function is 
 restricted to the attraction of certain constituents, by which the cavity of the 
 cell is filled. These constituents may be of a nature to give solidity and 
 permanence to the texture ; thus, the cells of the Epidermis are strengthened 
 by a deposit of horny matter, those of Shell by the deposit of carbonate of 
 lime; those of Bones and Teeth by a mixture of mineral and earthy matter, 
 &c. Or they may be of a fluid nature, readily passing into decomposition, 
 and destined to be retained only for a short time ; being given up again by 
 the rupture or liquefaction of the cell-wall, as in the case with the cells of 
 Glandular structures in general. Now such cells do not usually reproduce 
 themselves, but successive crops of them are generated as fast as required 
 from other sources; and the function of their nuclei appears to be limited to 
 their chemical agency upon the materials which they select. It would seem, 
 
 in fact, as if the direction of the nisus 
 
 Fig. 19 - or power of the cell to this object, 
 
 prevented the exercise of its repro- 
 ductive powers ; and where we find 
 these last most strongly manifested, 
 it is usually observable that the cell 
 performs little or no other duty. 
 
 129. In the endogenous develop- 
 ment of Animal cells, the nucleus 
 seems always to perform an important 
 part, where it has a distinct existence. 
 In many cases, the multiplication can 
 be clearly perceived to take place, by 
 the division of the nucleus into two 
 or more portions ; each part giving 
 origin to a new cell. This seems to 
 be the case, for example, in the ordi- 
 nary production of Cartilage-cells ; for 
 on examining sections of cartilage that 
 is undergoing rapid extension, we find 
 groups of cells, in all respects corre- 
 sponding with those of the simple 
 cellular plants, which can be seen to 
 increase in the same way. Thus in 
 Fig. 19, which represents a section of one of the branchial cartilages of the 
 
 Section of branchial Cartilage of young Tadpole ; 
 a, b, c, intercellular substance ; d, single nucleus; e, 
 nucleus dividing into two ; d', e', two nuclei in one 
 cell, formed by division of single nucleus;/, second- 
 ary cell, forming around nucleus g; h, two nuclei 
 within single secondary cell ; i, three secondary 
 cells, within one primary cell. 
 
DEVELOPMENT AND METAMORPHOSES OF CELLS. 
 
 115 
 
 Fig. 20. 
 
 Tadpole, we observe, within the large parent-cells that are held together by 
 intercellular substance, , b, c, secondary cells in various stages of develop- 
 ment: at d, the nucleus is single ; at e it is dividing into two ; in the adjoining 
 cell, the division into two nuclei, d' and e', is complete ; at h, two such nuclei 
 are inclosed within a common cell-membrane ; at i, we see three new cells 
 (one of them elongated, and itself probably about to subdivide) within the 
 parent ; and in each of the two groups at the top and bottom of the figure, 
 we have four small cells, now separated by partitions of intercellular sub- 
 stance, but having manifestly originated from one parent cell. (See also Fig. 
 43.) 
 
 130. In other cases, the granular nucleus subdivides into a greater number 
 of parts, so as to give origin to a cluster of young cells, which may completely 
 fill the parent-cell ; various stages of 
 this process are seen in Fig. 20. 
 This process seems to be adopted, 
 where rapid multiplication is need- 
 ed, and where the new or secondary 
 cells are not destined to possess any 
 great duration. The same nuclei 
 or "germinal centres," continually 
 drawing new materials from the 
 blood, may thus develope many suc- 
 cessive crops of new cells, when an 
 opening in the wall of the parent- 
 cell permits them to be discharged 
 as fast as they are formed ; and this 
 we shall find to be the way in which 
 the cells of the secreting structures 
 are developed within the glandular 
 follicles. According to Dr. Barry, it 
 is not uncommon for several annuli 
 of young cells to be generated from 
 the periphery of the nucleus, and to 
 attain a certain degree of develop- 
 ment within the parent cell, the first- 
 formed being the largest, as shown 
 in Plate I., Fig. 10, , b; some of 
 these, moreover, having distinct nu- 
 clei of their own, from which a third 
 generation is being developed on the 
 same plan (Fig. 12,6); and yet for all these to disappear by liquefaction, 
 leaving the cavity of the parent-cell unoccupied, except by a pair of cells ori- 
 ginating in the central part of the nucleus (Fig. 13). If this account be cor- 
 rect, it is probable that these temporary cells perform the office of preparing 
 the contents of the parent-cell for the nutrition of the offspring which is to 
 succeed it ; and each of these twin cells, in its turn, going through the same 
 series of changes (Fig. 14), gives origin to a new pair; the continuance of 
 which process generates a cluster. This is the mode, according to Dr. Barry, 
 in which the first cells of the embryo are developed into the " mulberry mass" 
 (Fig. 15), by whose subsequent development and metamorphoses, the tissues 
 and organs of the fetus are progressively evolved. 
 
 131. Notwithstanding the numerous varieties that exist, in the particular 
 modes in which the cells are developed, it seems to be well established as a 
 simple general principle, that all cells take their origin in germs prepared by 
 a previously-existing cell; and that these germs may be developed, either 
 
 Endogenous cell-growth in cells of a meliceritous 
 tumour; a, cells presenting nuclei in various stages 
 of development into a new generation; &, parent- 
 cell filled with a new generation of young cells, 
 which have originated from the granules of the nu- 
 cleus. 
 
116 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 within the parent-cell, or when set free by its rupture. The difference ob- 
 servable in the several cases that have been enumerated, and in others that 
 might be mentioned, seems to have reference chiefly to the degree of prepara- 
 tion that is effected in the nutriment with which the young cells are supplied; 
 some drawing it directly from the blood ; whilst others receive it through 
 the medium of the parent-cell, which probably exerts a certain degree of pre- 
 paring influence upon it; and others, again, requiring a further preparation 
 to be effected, by the elaborating or assimilating influence of a group of tem- 
 porary cells, expressly developed for this purpose. 
 
 132. We shall find, as we proceed, that all the tissues most actively con- 
 cerned in the maintenance of the Vital functions of the Human body, both 
 those of a Vegetative nature, and those which are peculiarly Animal, are 
 composed of Cells which have undergone no considerable metamorphosis, 
 and of which one generation is produced after another with a rapidity that is 
 proportioned to the activity of the function. But there are other structures 
 of an accessory character, in which a departure from the original type is to 
 be traced, sometimes so complete, as to prevent their real nature from being 
 understood, except by a very careful scrutiny into their history. This depart- 
 ure is the result of various kinds of metamorphosis of the cells and of their 
 nuclei ; of which the following are the principal. The cells, originally sphe- 
 roidal, oval, or polygonal, may become elongated to such a degree, as to as- 
 sume the spindle or fusiform shape ; thus resembling woody fibres. They 
 may at the same time lose their nuclei ; and their cavities may be occupied 
 by internal deposits, so that they may be mistaken for solid fibres. Such 
 fusiform cells are often found in exudation-membranes. Again, the cells may 
 shoot out prolongations, either in a radiating manner, so that they assume a 
 stellate form ; or in no definite direction, so that their shape becomes altogether 
 irregular. Such forms are seen amongst the pigment-cells of the Batrachia 
 and Fishes, and among the vesicles of the gray matter of the nervous system. 
 Further, the original boundaries of the cells may be altogether lost, by their 
 coalescence with each other. This is the case with many membranes that 
 seem to have originated in a layer of flat cells ; the situation of which is rather 
 to be traced by their nuclei, than by their former boundaries, which have alto- 
 gether disappeared. It is often the case, too, with the horny cells, of which 
 the nails, hoof, &c., are made up ; and still more with the cells of shell, bone, 
 tooth, &c., which have been consolidated by the deposition of a calcifying 
 deposit. Lastly, the character of the original cell may be completely altered 
 by a solution in the continuity of its wall, in one or more spots, so that its 
 cavity is laid open, and coalesces with some other. In this manner, by the 
 disappearance of the partitions between cells laid in apposition, end to 
 end, may be formed a tube ; and this tube may coalesce with others, in like 
 manner, so as to form a capillary network for the circulation of the blood. 
 Or the tube may form a simple straight fibre ; and the nuclei of its component 
 cells may give origin to a new deposit, either in an amorphous condition, as 
 in the fibrous portion of nervous tissue, or in the form of an aggregation of 
 new cells, as in the most perfect kind of muscular fibre. In these cases, also, 
 the original composition of the tubes may be frequently traced by the nuclei 
 that remain in their interior. In the follicles of glands, the solution of con- 
 tinuity takes place at one point only, which establishes a communication be- 
 tween the cavity of the parent-cell, and some canal by which its contents may 
 be discharged ; and the nucleus situated at the blind or closed extremity of the 
 follicle, may then continue to form successive generations of secondary cells, 
 which are discharged by this outlet. 
 
 133. The metamorphoses of the nucleus are not less important, though 
 not as numerous. In some instances we find it sending out radiating prolonga- 
 
FIBROUS TISSUES. BASEMENT MEMBRANE. 117 
 
 tions, so that it assumes a stellate form, like that of the cells of the Geranium- 
 petal ; this seems to be the case in regard to the nuclei of the Bone-cells. 
 In other instances it appears to resolve itself into a fasciculus of fibres ; and 
 this is stated by Henle to be the origin of the yellow fibrous tissue. Further, 
 it may separate into a number of distinct fibres, each composed (like those of 
 the Nostoc, Fig. 18,) of a linear aggregation of granules; it seems to be in 
 this manner, that the tubuli of the Dental structure are formed. Lastly, it 
 may disperse itself still more completely into its component granules ; by the 
 reunion of which, certain peculiar vibrating filaments (the so-called Sperma- 
 tozoa) may be formed, possessing motor powers analogous to those of the 
 Oscillatoriae and other corresponding filamentous products of humble Crypto- 
 gamic vegetation, but destined to perform most important offices in the func- 
 tion of Reproduction. 
 
 134. We have seen that, in the Vegetable structure, the component cells, 
 tubes, woody fibres (or elongated cells), &c., are held together by simple ad- 
 hesion ; a gummy intercellular substance, which answers the purpose of a 
 cement, being often interposed, sometimes in considerable quantity. But in 
 the Animal body, of which the several parts are destined to move with greater 
 or less freedom upon one another, the aggregations of cells that make up its 
 chief part, either in their original or in their metamorphic form, could not be 
 held together in their constantly-varying relative positions, without some in- 
 tervening substance of an altogether different character. It must be capable 
 of resisting tension with considerable firmness and elasticity ; it must admit 
 free movement of the several parts upon one another ; and it must still hold 
 them sufficiently close together to resist any injurious strain upon the deli- 
 cate vessels, nerves, &c., which pass from one to another, as well as to pre- 
 vent any permanent displacement. Now all these offices are performed in a 
 remarkably complete degree, by the Areolar Tissue ( 138); the reason of 
 whose restriction to the Animal kingdom is thus evident. And as necessity 
 arises, in certain parts, for tissues which shall exercise a still greater power 
 of resistance to tension, and which shall thus communicate motion (as in the 
 case of Tendons), or shall bind together organs that require to be united (as 
 in the case of Ligaments and Fibrous Membranes), so do we find peculiar 
 tissues developed that shall serve these purposes in the most effectual manner. 
 Hence these tissues also, although not endowed with any properties that are 
 peculiarly animal, are nevertheless restricted to the Animal Kingdom, as 
 completely as are the Muscular and Nervous Tissues, which make up the 
 essential parts of the apparatus of Animal Life. 
 
 135. That all the Animal tissues are in the first instance developed from 
 Cells, was the doctrine put forth by Schwann, who first attempted to gene- 
 ralize on this subject. By subsequent research, however, it has been shown 
 that this statement was too hasty ; and that, although many tissues retain their 
 origin cellular type, through the whole of life, and many more are evidently 
 generated from Cells and are subsequently metamorphosed, there are some, 
 in which no other cell-agency can be traced, than that concerned in the pre- 
 paration of the plastic material. This would appear to be the case, in certain 
 forms of the very delicate structureless lamella of membrane, now known 
 under the name of Basement or Primary Membrane, which is found beneath 
 the Epidermis or Epithelium, on all the free surfaces of the body. In many 
 specimens of this membrane, no vestige of cell-structure can be seen ; and it 
 would rather appear to resemble that, of which the walls of the cells are them- 
 selves constituted.* In some instances, it presents a somewhat granular ap- 
 
 * See a Paper by the Author, on the Microscopic Structure of Shells, &c., in the Annals 
 of Natural History, Dec. 1843. The inner layer of the Shells of Mollusca, after treatment 
 
118 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 pearance ; and it is then supposed by Henle to consist of the coalesced nuclei 
 of cells, whose development has been arrested : or, in other words, such 
 Basement-Membrane is formed by the consolidation of a layer of the plastic 
 element, that includes a large number of the granules, which may serve for 
 the development of new cells. Other forms of the Basement-Membrane can 
 be distinctly seen to consist of flattened polygonal cells, closely adherent by 
 their edges ; every one having its own granular nucleus.* It seems to be from 
 these granular germs, sometimes scattered through the membrane, and in other 
 instances collected into certain spots, that the cells of the superjacent Epithe- 
 lium or Epidermis take their origin ; and if this be the case, we must regard 
 the Basement-Membrane as a transitional rather than as a permanent struc- 
 ture, continually disintegrating, and yielding up its contained cell-germs on 
 its free surface, and as constantly being renewed from the blood beneath. 
 For the epidermic structures appear to constitute an exception to the general 
 rule, that the Tissues reproduce themselves ; since they are cast off, without 
 leaving their germs behind them ; and the cells which replace them must be 
 derived from new germs, more directly supplied from the blood than is else- 
 where the case. In the ease of the other tissues, whose disintegration takes 
 place inter stitially (so to speak), it would seem probable that, in the very 
 act of the dissolution of the parent-structure, the germs of the new structures 
 destined to replace it are set free ; as happens in the reproduction of the sim- 
 ple Cellular Plants. 
 
 136. It would seem doubtful, also, in regard to the simple Fibrous tissues, 
 whether they are generated by a metamorphosis of Cells, in the same manner 
 as the Osseous, Muscular and Nervous ; or whether they are not produced, 
 like the Basement-Membrane, by the consolidation of a plastic fluid, which 
 has been elaborated by cells. The latter view is the one which the Author 
 has been led to regard as most probable, from the results of his own observa- 
 tions, coupled with those of Messrs. Addison and Gulliver previously adverted 
 to. The Membrane of the Egg-shell, whose structure has been already 
 described ( 118), appears to him to have essentially the same character with 
 the simple Fibrous tissues, which it resembles also in its tenacity (compare 
 Fig. 11 with Fig. 22) ; whilst its origin can scarcely be supposed to be different 
 from that of the fibrous network in the buffy coat of the Blood, or in the 
 bands formed by the coagulation of Lymph upon an 
 Fig. 21. inflamed surface. The occasional vestiges of cells, 
 
 which the purely Fibrous tissues display ( 138), 
 and which have been adduced in support of their 
 cellular origin, are not inconsistent with this view. 
 For in the reticulated structures just adverted to, 
 certain bodies are seen, which appear to be nuclei 
 or imperfectly-formed cells (originating probably in 
 germs set free by the rupture of the colourless cor- 
 puscles of the blood), and which closely correspond 
 with the nuclear corpuscles that may be brought 
 into view in the Fibrous tissue. Mr. Addison's 
 observation, too, that the fibres formed in the 
 Liquor Sanguinis, and in plastic exudations, during 
 coagulation, often seem to radiate from the remains 
 of the white corpuscles that have ruptured, or from 
 the little aggregations of granules they contained, 
 gives the explanation of several of the appearances, which have led to the 
 
 with a dilute acid, yields specimens of Basement-Membrane, in a form well adapted for 
 examination. 
 
 * See J. Goodsir, in " Anatomical and Pathological Observations," Chap. I. 
 
 Colourless cells, with ac- 
 tive molecules, and fibres, of 
 fibrine, from Herpes labialis. 
 
CLASSIFICATION OF HUMAN ELEMENTARY TISSUES. 119 
 
 belief in the production of the Areolar and other fibrous tissues by Cell-trans- 
 formation. An additional argument in favour of this view, may be found in 
 the appearances presented by the semi-fibrous Cartilages. In the Cartilages 
 of the ribs, for instance, a more or less distinct fibrous appearance may often 
 be seen in the intercellular substance, which is elsewhere quite homogene- 
 ous ; this appearance is sometimes so faint, that it might be considered as 
 an illusion, occasioned by the manipulation to which the section has been 
 subjected; but it is often so well defined, as to present the aspect of true 
 fibrous tissue. No indication of the direct operation of cells, in the develop- 
 ment of these fibres, has ever been witnessed ; and we can scarcely do other- 
 wise than regard them as produced by the regular arrangement and con- 
 solidation of the particles of the intercellular substance, in virtue of its own 
 inherent powers. 
 
 137. The following arrangement of the Human Tissues will be here adopt- 
 ed as expressing their respective relations to the fundamental elements which 
 have been now described ; namely, simple Membrane, fibres, and Cells. 
 
 a. Simple Membranous Tissues. Of these there are scarcely any examples 
 in the Human body, except in the posterior layer of the cornea and thec cap- 
 sule of the crystalline lens. The membranous element is largely found, how- 
 ever, in the compound Membrane-fibrous tissues. 
 
 b. Simple Fibrous Tissues. Under this head may be classed the White 
 and Yellow Fibrous Tissues, and Areolar Tissue. 
 
 c. Simple Cells floating separately and freely in the fluids. Such are the 
 Corpuscles of the Blood, Chyle, and Lymph. 
 
 d. Simple Cells developed on the free surfaces of the body. Such are the 
 Epidermis and Epithelium. 
 
 e. Compound Membrano-Fibrous Tissues, composed of a layer of simple 
 membrane, developing Cells on its free surface, and united on the other to a 
 fibrous or areolar structure. Of this kind are the Skin, the Mucous Mem- 
 branes, the Serous and Synovial membranes, the lining membranes of the 
 Blood-vessels, &c. 
 
 f. Simple Isolated Cells, forming solid tissues by their aggregation. Un- 
 der this head we may rank the Fat-cells, the Vesicles of Gray Nervous matter,* 
 the Absorbent cells at the extremities of the Intestinal villi, and the cellular 
 parenchyma of the Spleen and similar bodies ; the cells being held together, 
 in all these cases, by the blood-vessels and areolar tissue which pass in amongst 
 them. In Cartilage, and certain tissues allied to it in structure, the cells are 
 united by intercellular substance, which may be quite homogeneous, or may 
 have a fibrous character. 
 
 g. Sclerous or Hard Tissues, in which the cells have been consolidated by 
 internal deposit, and have more or less completely coalesced with each other. 
 Such is the case with the substance of Hair, Nails, &c., which may be more 
 properly ranked under the Epidemic Tissues ; but the result is most charac- 
 teristically seen in Bones and Teeth. 
 
 h. Simple Tubular Tissues, formed by the coalescence of the cavities of 
 cells, without secondary internal deposit. The Capillary blood-vessels, and 
 probably also the smallest Lymphatics and Lacteals, seem to be formed in this 
 manner. 
 
 i. Compound Tubular Tissues ; in which, subsequently to the coalescence 
 of the original cells, a new deposit has taken place within their cavities. In 
 the tubuli of the White or Medullary Nervous matter, and in those of the least 
 
 * As it is undesirable to separate from each other the descriptions of the two elementary 
 forms of Nervous structure, on account of their close functional connection, the gray or vesi- 
 cular nervous matter will be described together with the white or tubular, in the last section 
 of this chapter. 
 
120 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 perfect form of Muscular Fibre, the secondary deposit has only a granular or 
 amorphous character ; but in the striated Muscular fibre, it is composed of 
 minute cells. 
 
 As it is not requisite here to say anything further of simple Elementary 
 Membrane, we shall at once pass on to the second group of Tissues ; one of 
 great extent and importance in the bodies of all the higher Animals. 
 
 4. Of the Simple Fibrous Tissues. 
 
 138. A very large proportion of the body, in the higher Animals, is com- 
 posed of a tissue, to which the name of " Cellular" was formerly given. This 
 term, however, is so much more applicable to those structures, which are 
 composed of a congeries of distinct Cells, and the use of it for both purposes 
 is likely to engender so much confusion, that it is to be wished that its appli- 
 cation to this purpose should be altogether discontinued. The tissue in ques- 
 tion, now generally designated the Areolar, is found, when examined under 
 the Microscope, to consist of a network of minute fibres and bands, inter- 
 woven in every direction, so as to leave innumerable interstices, which com- 
 municate with each other. The two kinds 
 of Fibrous tissue, which elsewhere exist se- 
 parately, the white, and the yellow, may 
 be detected in Areolar tissue ; as was first 
 pointed out by Messrs. Todd and Bowman. 
 The White presents itself in the form of 
 inelastic bands of variable size, the largest 
 1 -500th of an inch in breadth, somewhat 
 wavy in their direction, and marked longitu- 
 dinally by numerous streaks (Fig. 23); these 
 streaks are rather the indications of a longi- 
 tudinal creasing, than a true separation into 
 component fibres ; for it is impossible by any 
 
 ArrangementofFibresin Areolar Tissue- art tO tGEr U P *e band into filaments of a de- 
 Magnified 135 diameters. terminate size, although it manifests a decided 
 tendency to tear lengthways. Sometimes, 
 
 however, distinct fibres may be traced, whose diameter varies from about 
 l-15,000th to l-20,000th of an inch. The Yellow fibrous element exists in 
 the form of long, single, elastic, branched filaments, with a dark decided bor- 
 der, and disposed to curl when not put on the stretch (Fig. 24). These inter- 
 lace with the others, but appear to have no continuity of substance with them. 
 They are for the most part between l-5000th and 1-10,000 of an inch in 
 thickness ; but they are often met with both larger and smaller. The pro- 
 portion of this element varies greatly in different parts ; being greatest in those 
 situations, in which the greatest elasticity is required. Sometimes we find 
 elastic fibres passing round the fasciculi of the white tissue, constricting them 
 with distinct rings, or with a continuous spiral ; such are termed by Henle 
 nucleus-filaments, from his idea of their origin ( 133). This remarkable 
 disposition of the yellow fibres is best seen in the areolar tissue, that accom- 
 panies the arteries at the base of the brain. The effect of Acetic acid upon 
 these two elements is very different; the white immediately swells up, and 
 becomes transparent; whilst the yellow remains unchanged. This agent fre- 
 quently brings into view certain oval corpuscles, which lie in the midst of 
 the bands and threads, and which sometimes appear to have delicate prolonga- 
 tions among them. These are usually supposed to be the persistent nuclei 
 of the cells, from which the tissue was developed ; but, as already pointed 
 out, it is doubtful whether the fibres of this tissue are ever formed by the me- 
 
SIMPLE FIBROUS TISSUES; AREOLAR TISSUE. 121 
 
 tamorphosis of cells, their origin being rather, it seems more probable, in the 
 fluid blastema ( 136). The interstices of Areolar tissue are filled during life 
 with a fluid, which resembles a very dilute Serum of the blood ; it consists 
 chiefly of water, but contains a sensible quantity of common salt and albumen, 
 and (when concentrated) a trace of alkali sufficient to affect test-paper. The pre- 
 sence of this fluid seems to result from an act of simple physical transudation; 
 for it has been found that, when the serum of the blood is made to percolate 
 through thin animal membranes, the water charged with saline matter passes 
 through them much more readily than the albumen, a part of which is kept 
 back. 
 
 139. The great use of Areolar tissue appears to be, to connect together 
 organs and parts of organs, which require a certain degree of motion upon 
 one another : and to envelope, fix, and protect, the blood-vessels, nerves, and 
 lymphatics with which these organs are to be supplied. It can scarcely be 
 said to enjoy any vital powers, and is connected solely with physical actions 
 ( 134). It is extensible in all directions, and very elastic, in virtue of the 
 physical arrangement of its elements ; and it possesses no contractility, be- 
 yond that of the vessels which are distributed through it. It cannot be said 
 to be endowed with sensibility ; for the nerves which it contains seem to be 
 merely en route to other organs, and not to be distributed to its own elements. 
 And its asserted powers of absorption and secretion appertain rather to the 
 walls of the capillary blood-vessels, than to the threads and bands of which 
 it is composed. It is regenerated more readily than any other tissue, save 
 the Epithelium; being produced, it would appear, by the simple consolida- 
 tion of the blastema, that is poured out (in the form of organizable lymph) in 
 situations where there has been a breach of substance. It is also formed in 
 the effusions of a similar fluid, which are deposited on the surfaces 1 , or in 
 the substance, of inflamed tissues. Areolar tissue yields Gelatine by boiling ; 
 but this is derived from the White Fibrous element only ; the Yellow not 
 being affected by the process. 
 
 140. The White Fibrous tissue exists alone in Ligaments, Tendons, Fi- 
 brous Membranes, Aponeuroses, &c. ; where it presents the same characters 
 as those just described, except that the bands are less wavy, and frequently 
 quite straight, so that it is inextensible. It receives very few blood-vessels, 
 and still fewer nerves ; indeed it would seem that, in many structures (as ten- 
 dons), it is totally insensible. It seems entirely destitute of any vital pro- 
 perty ; and its chemical nature is such, that it needs very little interstitial 
 change to maintain its normal composition. If^tried, it has not the least tend- 
 ency to putrefy ; and when moist, it resists the putrefactive process more 
 strongly than almost any of the softer textures. The peculiar and important 
 property of this tissue, is its capability of resisting extension ; and we find it 
 in situations, where a firm resistance is to be made to traction. If the traction 
 be applicable in one direction only, as in Tendons and most Ligaments, we 
 find the bundles of fibres or bands arranged side by side ; but if it be exerted in 
 various directions, the fasciculi cross one another, as in Fibrous Membranes. 
 The reparation of this tissue is effected by the interposition of a new substance, 
 every way similar to the original, except that it wants its peculiar glistening 
 aspect, and is more bulky and transparent. The Yellow Fibrous tissue exists 
 separately in the middle coat of the Arteries, the Chordae Vocales, the Liga- 
 mentum Nuchae (of quadrupeds) and the Ligamenta subflava ; and it enters 
 largely into the composition of some other parts. It differs remarkably from 
 the white, in the possession of a high degree of elasticity ; so that the tissues, 
 which are composed of it alone, are among the most elastic of all known sub- 
 stances. It is, however, much more brittle than the white ; and its fibrdfc 
 usually exhibit a marked tendency to curl at their broken ends. Their size 
 
 11 
 
122 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 varies from about 1 -4000th, to 1 -24,000th of an inch ; in the ligamenta sub- 
 flava, it is usually about l-7500th. There is less tendency to spontaneous 
 
 Fig. 23. 
 
 Fig. 24. 
 
 White Fibrous Tissue, from Ligament. 
 Magnified 65 diameters. 
 
 [Fig. 25. 
 
 Yellow Fibrous Tissue, from Ligamentum 
 Nuchae of Calf. Magnified 65 diameters. 
 
 [Fig. 26. 
 
 The two elements of Areolar tissue, in their natural rela- 
 tions to one another; 1, the white fibrous element, with 
 cell-nuclei, 9, sparingly visible in it ; 2, the yellow fibrous 
 element, showing the branching or anastomosing charac- 
 ter of its fibrillse ; 3, fibrillae of the yellow element, far 
 finer than the rest, but having a similar curly character, 
 8, nucleolated cell-nuclei, often seen apparently loose. 
 From the areolar tissue under the pectoral muscle, mag- 
 nified 320 diameters.] 
 
 Development of the Areolar tissue, 
 (white fibrous element;) 4, nucleated 
 cells, of a rounded form ; 5, 6, 7, the 
 same, elongated in different degrees, 
 and branching. At 7, the elongated ex- 
 tremities have joined others, and are 
 already assuming a distinctly fibrous 
 character. (After Schwann.)] 
 
 decomposition in this tissue, than in almost any other part of the fabric, at 
 dfeast, of its soft and moist portions ; it requires but little renovation, therefore, 
 in the living body ; and is but very sparingly supplied with blood-vessels. 
 
COMPOSITION AND PROPERTIES OF GELATINE. 123 
 
 141. The composition of the White fibrous tissues is very different from 
 that of most others; for they yield to boiling water the substance called 
 Gelatine, which does not seem capable of the same degree of organization 
 with the Proteine-compounds. This may be obtained by boiling portions of 
 Skin, Areolar tissue, Serous membrane, Tendon, Ligament, &c., in water, for 
 some time ; after which the decoction is allowed to cool, when it solidifies 
 into a jelly of greater or less thickness. Some tissues dissolve readily in this 
 manner, and little residual substance is left ; this is especially the case with 
 areolar tissue, serous membranes, and (in a less degree) with skin. Others 
 require a long boiling for the extraction of any Gelatine ; and even then it is 
 obtained in but small quantity ; of this kind are the Elastic fibrous tissue, 
 and some forms of Cartilage. A peculiar modification of this principle 
 exists in most of the permanent cartilages ; and has received the name of 
 Chondrine. Gelatine is not found in the blood, nor in any of the healthy 
 fluids ; and some Chemists are of opinion, that it is rather a product of the 
 operation practised to separate it, than a real constituent of the living solids. 
 This idea seems inconsistent, however, with the fact, that the gelatinous tis- 
 sues will exhibit, without any preparation, the best marked of the chemical 
 properties which are regarded as characteristic of Gelatine, that, namely, of 
 forming a peculiar insoluble compound with Tannin; and the Tanno-Gelatine, 
 which may be obtained by precipitating Gelatine from a solution, and that 
 which results from the action of Tannin on Animal membrane, appear to be 
 precisely analogous in every respect, save in the presence of structure in the 
 latter, which is absent in the former. Moreover, the Gelatinous tissues are 
 found, when submitted to ultimate analysis, to possess exactly the same com- 
 position with Gelatine itself. Still it seems probable, that the arrangement of 
 the component particles is in some degree altered by the process of boiling ; 
 for it is found that, the more distinct the fibrous structure of the tissue, the 
 less it is affected by the prolonged action of cold water, and the longer it must 
 be boiled, before it is resolved into Gelatine. 
 
 a. Gelatine is very sparingly soluble in cold water ; by contact with which, however, it is 
 caused to swell up and soften. It is readily dissolved by hot water ; and forms so strong a 
 jelly on cooling, that 1 part in 100 of water becomes a consistent solid. Its reaction with 
 Tannic acid is so distinct, that 1 part in 5000 of water is at once detected by infusion of 
 Galls. The following are the results of four analyses of Gelatine by Scherer and Mulder. 
 
 SCHEREB. 
 
 Carbon . . . 50-557 50-774 50-048 50-048 
 
 Hydrogen . . 6-903 7-152 6-477 6-643 
 
 Nitrogen . .18-790 18-320 18-350 18-388 
 
 Oxygen . . 23-750 23-754 25-125 24-921 
 
 The formula deduced by Mulder from this composition, and from the combinations of 
 Gelatine with Tannic and Chlorous acids, is 13 C,10 H,2 N, 5 0. When Gelatine is boiled 
 for some time, it loses its power of forming a jelly on cooling ; and it is stated by Mulder, 
 that this is due to its union with an additional amount of water, a true Hydrate of Gelatine 
 being formed by the combination of 4 Equiv. of Gelatine, with 1 Equiv. of Water. The 
 same product is obtained by adding Ammonia to the Chlorite of Gelatine, and removing by 
 Alcohol the Sal Ammoniac thus formed. 
 
 b. It is not yet known how Gelatine is produced in the Animal body. There cannot be 
 a doubt that it may be elaborated from Albumen ; since we find a very large amount of it 
 in the tissues of young animals, which are entirely formed from albuminous matter ; and 
 also in the tissues of herbivorous animals, which cannot receive it in their food, since Plants 
 yield no substance resembling Gelatine in composition. It has been suggested by Mulder, 
 that Gelatine may be formed by the decomposition of Proteine, which has been already 
 mentioned as taking place from the agency of weak alkaline solutions (116 6), and which 
 must probably, therefore, be continually occurring in the Blood. For, if to each atom of Pro- 
 tid and Erythroprotid, we add one of the atoms of Ammonia which are given off in that 
 
124 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 decomposition, we have compounds, of which the former differs from Gelatine only by the 
 presence of two additional atoms of hydrogen and the deficiency of one of oxygen, whilst 
 the only difference in the latter consists in the presence of one additional atom of hydrogen. 
 Thus the ammoniated Erythroprotid, when exposed to oxygenation in the lungs, may have 
 its one superfluous atom of hydrogen carried off in the form of water, and will then have 
 the composition of Gelatine ; and the same result will be attained from the ammoniated 
 Protid, by the addition of three atoms of oxygen, which will convert it into Gelatine with 
 two atoms of water. According to this formula, the substances produced from the decom- 
 position of the proteine in blood, merely through the action of the alkali in the serum, and 
 the oxydizing influence of the atmosphere, are carbonic acid, water, gelatinous 'tissue, and 
 leucin. The carbonic acid passes off through the lungs ; and the water, either by the kid- 
 neys, or by exhalation from the lungs or skin. The Gelatine only requires form, to become 
 Fibrous tissue. Leucin, however, has not yet been found in the body ; and until it shall 
 have been discovered, or the products of its decomposition shall have been detected, any 
 such attempt to explain the formation of Gelatine, must be regarded as altogether theoretical.* 
 c. The relation of Gelatine to the Proteine-compounds is further shown by the fact, that 
 Leucin may be produced from the former, as well as from the latter. When Gelatine is 
 boiled, either with alkalies or with dilute sulphuric acid, Leucin is formed ; together with 
 extractive matters, and a peculiar sugar termed Glycicoll. This substance crystallizes in large 
 colourless prisms, which have a sweet taste, and feel gritty between the teeth ; it is soluble 
 in 4^ parts of water, and is taken up in small quantity by Alcohol. This fact is one of much 
 interest in regard to certain Pathological relations of Gelatine. 
 
 142. The Yellow Fibrous tissue, on the contrary, undergoes scarcely any 
 change by long boiling; a very small quantity of Gelatine being alone yielded 
 by it; and this being probably derived from the Areolar tissue, by which it is 
 penetrated. It is unaffected by the weaker acids, and undergoes no solution 
 in the gastric fluid ; and it preserves its elasticity for an almost unlimited pe- 
 riod. According to Scherer, the yellow fibrous tissue from the middle coat 
 of the Arteries consists of 48 C, 38 H, 6 N, 16 ; which (taking Liebig's 
 formula for Proteine) may be regarded as 1 Proteine + 2 Water. When 
 burned, it leaves 1*7 per cent, of ash. 
 
 5. Of Simple Cells, floating in the Minimal Fluids. 
 
 143. The red colour, which is characteristic of the Blood of Vertebrated 
 animals, is entirely due to the presence, in that fluid, of a very large number of 
 floating cells, which have the power of forming a secretion in their interior, 
 that is distinguished by its peculiar chemical nature, as well as by its hue. 
 The red Blood-corpuscles (commonly, but erroneously termed globules) are 
 
 flattened Discs, which, in Man and most 
 
 Fig. 27. of the Mammalia, have a distinctly cir- 
 
 cular outline. In the discs of Human 
 blood, when examined in its natural con- 
 dition, the sides are somewhat concave ; 
 and there is a bright spot in the centre, 
 which has been regarded by many as in- 
 dicating the existence of a nucleus ; though 
 it is really nothing else than an effect of 
 refraction, and may be exchanged for a 
 dark one by slightly altering the focus of 
 the Microscope. The form of the disc 
 
 Red Corpuscles of Human Blood represent- j g much ^^ fa yarious ntfl . 
 
 ed at a, as they are seen when rather beyond J . J . 
 
 the focus of the microscope ; and at b as they for the membrane which COmpOSCS Its ex- 
 appear when within the focus. Magnified 400 tenor or cell-well, is readily permeable by 
 diameters. liquids ; so as to admit a passage of li- 
 
 quid, according to the laws of Endos- 
 mose, either inwards or outwards, as the relative density of the contents of 
 
 * See Mulder's Chemistry, p. 326. 
 
SIMPLE ISOLATED CELLS; RED BLOOD-CORPUSCLES. 125 
 
 the cell and of the surrounding fluids may direct. Thus, if the Red corpus- 
 cles be treated with water, there is a passage of that liquid into the cell ; the 
 disc becomes first flat, and then double-convex, so that the central spot disap- 
 pears ; and by a continuance of the same process, at last becomes globular, 
 and finally bursts, the cell-wall giving way, and allowing the diffusion of the 
 contents through the surrounding liquid. On the other hand, when the Red 
 corpuscles are treated with a thick syrup or solution of albumen, they will be 
 more or less completely emptied, and caused to assume a shrunken appear- 
 ance ; the first effect of the process being to increase the concavity, and to 
 render the central spot more distinct. It is probable that the Blood-corpuscles, 
 even whilst they are circulating in the living vessels, are liable to alterations 
 of this kind, from variations in the density of the fluid in which they float ; 
 and that such alterations may be constantly connected with certain disordered 
 states of the system.* We hence see the necessity, in examining the Blood 
 microscopically, for employing a fluid for its dilution, that shall be as nearly 
 'as possible of the same character with ordinary liquor sanguinis.t 
 
 144. Microscopic observers have been much divided upon the question, 
 whether or not the Red corpuscles of the Blood of Man and other Mammalia 
 contain a nucleus. There seems every probability from analogy, that a nu- 
 cleus exists in them, as it does in the red corpuscles of all other animals ; 
 but it cannot be brought into view by any of the ordinary methods, which 
 render it distinctly visible in the oval blood-discs of Oviparous Vertebrata ; 
 and of late the general opinion has been, that nothing resembling their nuclei 
 could be present in the blood-discs of Man and Mammalia. Dr. G. O. Rees 
 states, however, that, by carefully examining the ruptured cell-walls, which 
 fall to the bottom of the water when red corpuscles have been diffused 
 through it, he could distinguish appearances on them, that indicated the ex- 
 istence of nuclei ; although they escape observation when within the corpus- 
 cles themselves, on account of their high refractive power. He describes 
 them as being circular and flattened, like the Red corpuscles themselves ; and 
 as about two-thirds of their diameter. 
 
 145. In all Oviparous Vertebrata, without any known exception, the red 
 corpuscles are oval, the proportion between their long and short diameters, 
 however, being much subject to varia- 
 tion ; and their nuclei may always be Fig. 28. 
 
 brought into view, by treatment with 
 acetic acid, when not at first visible. In 
 the red particles of the Frog, which are 
 far larger than those of Man, a nucleus 
 can be observed to project somewhat 
 from the central portion of the oval, 
 even during their circulation ; and it 
 is rendered extremely distinct by the 
 action of acetic acid ; this renders the 
 remainder of the particle extremely Particles of ^ blood; i,u, thfeir flattened 
 
 , ., A *. . . J , face ; 2, particle turned nearly edgeways ; 3, 
 
 transparent, whilst it gives increased lymph . globule ; 4 , blood-corpuscles altered by di- 
 
 Opacity tO the nucleus. Which is then lute acetic acid. Magnified 500 diameters. 
 
 seen to consist of a granular substance. 
 
 In the still larger blood-disc of the Proteus and Siren, this appearance is yet 
 
 * See Dr. G. O. Rees' Gulstonian Lectures, for 1845. 
 
 t By Wagner, the filtered serum of frog's blood is recommended for this purpose. Weak 
 solutions of salt or sugar, and urine, answer tolerably well ; but Mr. Gulliver remarks that 
 all addition must be avoided, when it is intended to measure the corpuscles, or to ascertain 
 their true forms ; as the serum of one Mammal reacts injuriously on the blood of another. 
 See Philos. Magaz., Jan. and Feb. 1840. 
 
126 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 more distinct ; the structure of the nucleus being so evident without the addi- 
 tion of acetic acid, that its granules can be counted.* 
 
 146. The form, of the Red Corpuscles is not unfrequently seen to 
 change during their circulation ; but this is generally in consequence of 
 pressure: from the effects of which, however, they quickly recover them- 
 selves. In the narrow capillary vessels, they sometimes become suddenly 
 elongated, twisted, or bent, through a narrowing of the channel ; and this 
 may take place to such a degree, as to enable the disc to pass through an 
 aperture, which appears very minute in proportion to its diameter. When 
 undergoing spontaneous decomposition, the blood-discs become granulated, 
 and sometimes (as long ago noticed by Hewson) even mulberry-shaped ; and 
 particles in which these changes appear to be commencing, may be found in 
 the blood at all times. It has been ascertained that bile and urea exert a pecu- 
 liar solvent power on the blood-corpuscles ; and hence we can understand 
 one of the modes in which a retention of these substances in the circulating 
 fluid (Chap. XV., Sect. 1) proves so injurious. The size of the blood-discs 
 is liable to considerable variation, even in the same individual ; some being 
 met whh as much as one-third larger, whilst others are one-third smaller, than 
 the average. The diameter of the corpuscles bears no constant relation to the 
 size of the animal, even within the limits of the same class ; thus, although 
 those of the Elephant are the largest among Mammalia (as far as is hitherto 
 known), those of the Mouse tribe are far from being the smallest, being in 
 fact more than three times the diameter of those of the Musk Deer. There 
 is, however, a more uniform relation between the size of the animal and that 
 of its blood-discs, when the comparison is made within the limits of the same 
 order. In Man, the diameter varies from about 1 -4000th to 1 -2800th of an 
 inch; the average diameter is probably about l-3200th. 
 
 a. The following measurements of the blood-discs of various animals are chiefly given 
 on the authority of Mr. Gulliver. The diameter of the corpuscles in the Quadrumana is 
 generally about the same with that of the Human blood-discs ; there is, however, a slight 
 diminution among the Lemurs, and there is more variation among them, than among the 
 Monkeys. Among the Cheiroptera, the diameter of the corpuscles is somewhat less than in 
 the preceding order, the average being about l-4300th of an inch. Passing to the Insecti- 
 vora, we find the blood-discs of the Mole to be still smaller, averaging only the l-4747th of 
 an inch ; those of the Hedgehog, however, are larger, being about l-4085th. In the corpus- 
 cles of the different families of the Carnivora, there is siidi a well-marked diversity in the 
 size of the corpuscles, that the fact may be used as a help to classification.! In the Seals, 
 
 * As Professor Owen's interesting account of the blood-discs of the Siren may not be 
 generally accessible (Penny Cyclopaedia, Art. Siren), the leading facts in it will be here 
 stated. This animal agrees with the Proteus and other species in being perennibranchiate 
 ( 32) ; and, as in all its congeners yet examined, the blood-discs are of very large dimen- 
 sions. They are usually of an oval form, the long diameter being nearly twice the short; 
 and the nucleus projects slightly from each of the flattened surfaces. Considerable variety 
 in the form of the disc presents itself, some of the corpuscles being much less oval than 
 others; but the nuclei^do not partake of these variations in nearly the same degree. The 
 nucleus is clearly seen to consist of a number of moderately-bright spherical granules, of 
 which from 20 to 30 could be seen in one plane or focus, the total number being of course 
 much greater. When removed from the capsule, the nuclei are colourless, and the compo- 
 nent granules have a high refracting power. Viewed in situ, they present a tinge of colour 
 lighter than that of the surrounding fluid, and dependent upon the thin layer of that fluid 
 interposed between the nucleus and the capsule. As the fluid contents of the blood-disc in 
 part evaporate during the process of desiccation, the capsule falls into folds in the interspace 
 between the nucleus and the outer margin ; these folds generally take the direction of straight 
 lines, three to seven in number, radiating from the nucleus. 
 
 f Two facts of much interest in Zoology have been brought to light by Mr. Gulliver's 
 examination of the diameter of the blood-corpuscles of this tribe. The difference between 
 those of the Dog and the Wolf is not greater than that which exists among the varieties of 
 the Dog ; whilst the discs of the Fox are much smaller. The discs of the Hyaena are far 
 more approximate to those of the Canidse, than they are to those of the Felidoe. 
 
COMPARATIVE SIZES OF RED CORPUSCLES OF BLOOD. 127 
 
 the diameter averages l-3280th of an inch; in the Dog, l-3540th ; in the Bear, about 
 1 -3700th; in the Weasel, l-4200th; in the Cat, l-4400th ; and in the Viverrae, l-5365th. In 
 two species only of the Cetacea, have the blood-discs been yet examined ; the Dolphin, in 
 which their diameter averages l-3829th of an inch ; and the great Rorqual (the largest known 
 Mammal), in which they are only l-3100th of an inch, or scarcely larger than those of Man. 
 Among the Pachydermata, the average excluding the Elephant (the diameter of whose blood- 
 discs is about l-2745th of an inch), and the Rhinoceros (in which they are about l-3765th), 
 may be stated at about l-4200th; and there is less variation than might have been expected, 
 from the different size and conformation of the several species examined. Among the Ru- 
 minantia, the corpuscles are for the most part smaller than in other orders ; and there is more 
 relation between their diameter and the size of the animal, than is elsewhere observable. 
 Excluding the Camelidae (which are zoologically intermediate between the Ruminantia and 
 Pachydermata), we find a range of sizes extending from the l-3777th to the l-12,325th of 
 an inch ; the former is the diameter in one of the larger Deer ; the latter in the Musk Deer, 
 which is the smallest in the whole order. In the Camel tribe, the average of the long dia- 
 meter of the corpuscles is about l-3300th of an inch , whilst that of the short diameter is 
 l-6300th ; and this is nowhere widely departed from : the length of the discs is, therefore, 
 not quite twice their breadth. Among the Rodentia, the discs are rather large, especially 
 considering the small size of most of the species. In the Capybara, which is the largest 
 animal of the order, they average 1-3 190th; and in the Mouse family (the smallest of Mam- 
 malia), they are as much as 1-38 14th. In the Squirrels, the diameter is rather less ; but in 
 scarcely any of the whole order is it under l-4000th. Among the Edentata, the Two-toed Sloth 
 has been found to have corpuscles of the unusually large diameter of l-2865th of an inch; 
 whilst in the Armadilloes they average about l-3400th. In the Marsupialia the range is 
 nearly the same as among the Rodentia. .- 
 
 b. In BIRDS, according to the observations of Mr. Gulliver, the long and short diameters 
 of the corpuscles usually bear to each other the proportion of Ijt or 2, to 1; and this is the 
 general relation among Oviparous Vertebrata, with the exception of some of the Crocodile 
 tribe, in which the length is sometimes three times the breadth. The size of the corpuscles 
 of Birds has generally more relation to that of the species, than it has in Mammalia. No 
 instance has yet been detected, of the occurrence of comparatively small corpuscles in the 
 larger species, and of large corpuscles among smaller animals, which has been seen to be 
 common among the former class ; the blood of the Humming-birds, however, has not yet 
 been examined. ; The largest discs are found among the Cursores ; those of the Ostrich have 
 an average long diameter of l-1649th of an inch, and a short diameter of l-3000th; and 
 among the larger Raptores, Grallatores, and Natatores, the dimensions are but little inferior. 
 The least dimensions hitherto observed are among the small Passerine birds ; in which the 
 corpuscles have a long diameter of about l-2400th of an inch, and a transverse diameter of 
 from l-3800th to l-4800th. Circular discs may be occasionally observed in some species, 
 agreeing with the others in every particular but their form ; and every gradation may be no- 
 ticed between these and the regular oval corpuscles. 
 
 c. The large size of the blood-discs in REPTILES, especially in ttatrachia, and above all, 
 in the Perennibranchiate species of the latter, has been of great service to the Physiologist ; 
 by enabling him to ascertain many particulars regarding their structure, which could not 
 have been otherwise determined with certainty. Among other facilities which this occa- 
 sions, is that of procuring their separation from the other constituents of the blood ; for they 
 are too large to pass through the pores of ordinary filtering-paper, and are therefore re- 
 tained upon it, after the liquor sanguinis has flowed through. The blood-discs of the warm- 
 blooded Vertebrata cannot be thus separated. The oval corpuscles of the Frog have a long 
 diameter of about 1-1 108th, and a transverse diameter of about l-1800th of an inch; those 
 of the Salamander or Water-newt are still larger. The long diameter of the corpuscles of the 
 Proteus is stated by Wagner at l-337th of an inch ; that of the Siren is about l-435th, the 
 short diameter being about l-800th of an inch ; the extremes of variation, however, are very 
 wide. The long diameter of the nuclei is about l-1000th or 1-1 100th, and the short diame- 
 ter about l-2000th; hence it is about three times as long, and nearly twice as broad, as the 
 entire Human blood-disc, thus having six times its superficies; its thickness is about l-3800th 
 of an inch. 
 
 d. The number of FISHES, in which the diameters of the blood-discs have been examined, 
 is still inconsiderable. In the common Perch, they average 1-2 100th by 1-2824 ; in the Carp, 
 they are l-2142nd of an inch by l-3429th; in the Gold-Fish, though of the same genus and 
 of much smaller size, they are as much as l-1777th by l-2824th; in the Pike, l-2000th by 
 l-3555th; and in the Eel, 1-1 745th by 1 -2842nd.* 
 
 * A summary of Mr. Gulliver's numerous and valuable observations is contained in the 
 Proceedings of the Zoological Society, No. CLII. 
 
128 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 147. In speaking of the Chemical constitution of the Red Corpuscles of 
 Blood, it is necessary to distinguish the substance of their walls and nuclei 
 from their fluid contents. These may be separated by treating them with 
 water ; which, as already mentioned, occasions the rupture of the cells, the 
 walls of which sink to the bottom, whilst their contents are diffused through 
 the liquid. The substance obtained from the former has been termed Globu- 
 line; but it does not seem to differ in any essential character from other sub- 
 stances, that result from the organization of the proteine-compounds. The 
 compound which forms the contents of the red corpuscles, however, and 
 which gives them their characteristic hue, is very different both in its sensi- 
 ble properties, and in its composition ; and has received the designation of 
 Hsematine. When separated from albuminous matter, it is of a dark-brown 
 hue, and is tasteless and insoluble in water, alcohol, and ether ; but it is rea- 
 dily soluble in water or alcohol, that contains alkalies or acids ; whence it may 
 be supposed to unite with these, like albumen, as an acid or a base. In 
 composition, however, it differs considerably from that of the proteine-com- 
 pounds ; its formula being 44 C, 22 H, 3 N, 6 O, with a single proportional 
 of iron. When burned, it yields a notable quantity of peroxide of iron ; and 
 one atom of this is considered to be present in combination with each equiva- 
 lent of the animal compound. The red colour is not due, however, as for- 
 merly supposed, to the presence of this peroxide ; for M. Scherer has proved, 
 that the metal may be entirely dissolved away by the agency of acids, and 
 that the animal matter, afterwards boiled in alcohol, colours the spirit intensely 
 red. On the other hand, the iron is most certainly united firmly with the 
 constituents of the Haematine, as contained in the red corpuscles ; for this sub- 
 stance may be digested in dilute sulphuric or muriatic acid for several days, 
 without the least diminution in the quantity of iron, the usual amount of which 
 may be obtained by combustion from the Haematine that has been subjected 
 to this treatment. When diffused through water, in the manner just describ- 
 ed, the Haematine exhibits the same changes of colour under the influence of 
 oxygen, acids, saline matter, &c., as the Blood undergoes in similar circum- 
 stances. 
 
 148. The question of the origin of the red Blood-corpuscles is a very inte- 
 resting one, and cannot yet be regarded as completely determined. That they 
 are to be regarded as nucleated cells, conformable in general character with the 
 isolated cells, which constitute the whole of the simplest Plants ( 125), and 
 having each an independent life of its own, the duration of which is limited, 
 there can now be no reasonable doubt. From this we should infer that they 
 have the power of reproducing themselves ; and the recent observations of 
 Dr. Barry and other Microscopists seem to confirm the statement long ago 
 made to that effect by Leeuwenhoek. The first change said to take place, is 
 the appearance of delicate radiating lines between the nucleus and the peri- 
 phery ; dividing the disc into several segments, usually six in number (Plate I., 
 Fig. 22.) The margin is soon observed to become crenated, by indentations 
 at corresponding points ; and these indentations become deeper, until a com- 
 plete separation takes place, setting free six young cells or discs (, 6, c, rf, e), 
 which seem to have been formed around the margin of the nucleus of the pa- 
 rent cell. Between the small newly-generated disc, and the full-sized corpus- 
 cle, we should expect to find every intermediate size ; and this is affirmed by 
 these observers to be the case. It has been lately asserted by Dr. G. O. Rees, 
 that, when examining a portion of Blood maintained at about its natural tem- 
 perature, he observed some of the corpuscles to assume an hour-glass form, 
 by a contraction across their middle ; and that, by the increase of this contrac- 
 tion, producing the complete division of the corpuscles, two unequal-sized* 
 circular bodies were eventually produced from each ; which, when treated 
 
ORIGIN AND MULTIPLICATION OF RED CORPUSCLES. 129 
 
 with a strong saline solution, were emptied of their contents, like ordinary 
 blood-discs. It is not at all improbable, that both these methods of multi- 
 plication may be followed ; and it can scarcely be doubted that, by one or 
 both, a continual succession of Red corpuscles is kept up. That the corpus- 
 cles may be generated with great rapidity under peculiar circumstances, will 
 hereafter appear (Chap. XL, Sect. 6) ; and their amount may undergo a rapid 
 diminution also, without any evident abstraction of them from the circulating 
 fluid. This diminution seems to be traceable in some instances to a too low 
 specific gravity of the serum ; which will cause the Red corpuscles to rupture 
 by endosmose, just as when they are treated with water. Appearances have 
 been seen by Wagner, Gulliver, and others, in the blood of Batrachia, which 
 might seem to indicate that the Colourless corpuscles ( 151) serve as the 
 nuclei of cells, which,, when fully developed, may become Red blood-discs ; 
 but in the Mammalia, it is scarcely possible to imagine that this can occur ; 
 since the diameter of the colourless corpuscles is very constant ; whilst that 
 of the Red blood-discs is so variable, that the former, though sometimes the 
 smaller, are in other instances far larger than the latter. If it be admitted 
 that the Red corpuscles have the power of reproduction, like other isolated 
 cells, it does not seem necessary to seek elsewhere for the source of their con- 
 stant renewal ; and various facts, hereafter to be stated, appear to the Author 
 strongly indicative of the entire functional as well as structural difference, 
 between the red and the colourless corpuscles of the blood of Vertebrata. 
 
 149. That the Red blood-discs, when first formed in the embryo, have an 
 origin common to that of all other tissues, cannot be doubted. They are pro- 
 duced, in the embryo of the Bird, in the portion of the germinal membrane 
 which afterwards becomes the area vasculosa ; this consists of delicate cells 
 very uniformly disposed: and whilst capillary vessels are being formed by 
 the union of the cavities of these, blood-discs seem to be developed from 
 
 Fig. 29. 
 
 
 
 Production of blood-corpuscles in Chick, on the fourth day of incubation ; a, particles fully formed; 
 6, particles in progress of formation; c, similar particles altered by dilute acetic acid, so as to display their 
 nuclei. 
 
 the granules or cell-germs they contain. These changes take place about the 
 second or third day of incubation ; but it is not until some days afterwards, 
 that the discs assume their characteristic form. 
 
 a. Mr. Macleod gives the following history of the development of the blood-corpuscles 
 in the Chick. In blood withdrawn from the heart, on the third day, and diluted with se- 
 rum, or from the germinal membrane or allantois, and diluted with fluid albumen, " a num- 
 ber of small granules are seen floating about the field : these enlarge and become clearer in 
 the centre ; this enlargement goes on very rapidly, and when they have gained to about twice 
 their original size, the central clear part becomes dull. This dullness slightly increases, and 
 in a short time it is seen to be distinctly granular; whilst the borders are observed to be 
 well-defined, smooth, and clearer than the central part. The enlargement of these bodies, 
 with the granular appearance of their centre, seems not to depend on the aggregation of 
 granules round a centre one, but on a property which they have in themselves of enlarging 
 and presenting that figure. During all this time they are quite spherical and of good con- 
 sistence, as they do not lose their form by considerable pressure. In the second stage, the 
 central portion gradually becomes less opaque, and ceases to appear granular, the external 
 
130 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 portion at the same time separating in some degree from the central part. The blood-cor- 
 puscle, in this stage of development, has the appearance of a slightly flattened round cell, 
 formed of a somewhat delicate but elastic membrane, with a nucleus in the centre. At this 
 time a number of these bodies, being close together in the field, presents a yellowish colour. 
 The cell is disc-like, rather concave, but the nucleus convex. In the third stage, one side of 
 the corpuscle gradually elongates, giving it a pear-shaped appearance ; the opposite side then 
 elongates itself in a similar manner, and to the same degree. The concavity between the 
 nucleus and border disappears, and the whole becomes slightly convex. The hue at the 
 same time gradually becomes redder."* 
 
 The corpuscles are generally larger in the embryo than in the adult, espe- 
 cially soon after the period of their first formation ; it was remarked by M. 
 Prevost, that in the foetal goat they were at first twice the size of those of the 
 mother. Mr. Gulliver has observed, however, that at a later period of utero- 
 gest^tion they are sometimes smaller than the average dimension of the adult; 
 but perhaps all such observations are to be received with hesitation, owing to 
 the fact mentioned by him, that the variety in the magnitude of the foetal cor- 
 puscles is much greater than in the full-grown animal. 
 
 150. In regard to the uses of the Red corpuscles of the Blood, in the Ani- 
 mal economy, it appears to the Author that a definite conclusion may be now 
 arrived at. Their existence in the circulating fluid is nearly confined to* the 
 Vertebrated classes ; the corpuscles which are seen in the blood of the Inver- 
 tebrated, being mostly analogous rather to the Colourless corpuscles, presently 
 to be described as present in the blood of the higher animals. Among the 
 lower Invertebrata, indeed, the Red corpuscles seem to be altogether wanting ; 
 and the same may be said of the embryos of the highest animals, at an early 
 period of their development ; as well as of the early state of parts that are 
 being newly formed, at any period of their lives. Hence the inference ap- 
 pears highly probable, that they are not essentially necessary to the produc- 
 tion of the organizable elements of the blood, or of the organized tissues ; in 
 other words, to the simple acts of growth and nutrition. The Red corpuscles 
 are most abundant in those classes among Vertebrata, which maintain the 
 highest temperature ; thus, they are somewhat more numerous, in proportion 
 to the whole bulk of the Blood, in Birds than in Mammalia ; and far more in 
 the latter, than in Reptiles and Fishes. As it is evident that they undergo 
 very important changes in the pulmonary and systemic capillaries, their co- 
 lour being changed from purple to red in the former, and from red to purple 
 in the latter, it seems highly probable that they have as their principal office, 
 the introduction of oxygen into the blood that circulates through the systemic 
 capillaries, and the removal of the carbonic acid set free there ; serving, in 
 fact, as the medium for bringing the tissues into relation with the air, the in- 
 fluence of which is necessary for the maintenance of their vital activity. In 
 the Invertebrata generally, whose respiration is very feeble, this end will be 
 sufficiently answered by the fluid plasma of the blood ; the alterations in which, 
 under the influence of the air, have been already noticed ( 115, 116 a). And 
 in Insects, the only class whose respiration is at all active, we find the air 
 directly conveyed into the tissues ; the circulating fluid not being employed as 
 its carrier ( 18). We shall hereafter find, that the influence of oxygen upon 
 the Nervous and Muscular systems is essential to their vital activity ; and it 
 seems to be by their agency in bringing these into relation, that the Red cor- 
 puscles possess that intimate connection with the Animal functions, which we 
 find them to possess. The animals whose temperature is the highest, are 
 also those whose senses are most acute, and whose movements are most ener- 
 getic : whilst, on the other hand, if there be any unusual diminution in the 
 
 * London and Edinburgh Monthly Journal, September, 1842. 
 
COLOURLESS CORPUSCLES OF BLOOD. 131 
 
 proportion of Red corpuscles, it is invariably accompanied by muscular de- 
 bility and deficient nervous power. 
 
 a. By Liebig it is supposed, that the iron in the red corpuscles is the real agent in the 
 respiratory process : for if its original state be the protoxide, it may become the peroxide 
 by uniting with an additional atom of oxygen, or the protocarbonate by the addition of an 
 atom of carbonic acid. The former change is supposed by him to take place in the lungs, 
 to which the blood comes charged with carbonic acid ; the carbonic acid is given up by the 
 iron, and replaced by an equivalent of oxygen taken in from the air : whilst in the syste- 
 mic capillaries, the converse change takes place, the oxygen being imparted to the tissues, 
 and being replaced by carbonic acid which is given up by them to be conveyed out of the 
 system. It is stated by Liebig that there is far more than sufficient iron in the whole mass 
 of the blood, to convey in this manner all the oxygen and carbonic acid, which are inter- 
 changed between the pulrrionary and systemic capillaries. The speculation is certainly an 
 ingenious one ; but it can scarcely be yet received as a physiological fact. 
 
 151. Besides the red particles of the Blood, there are others which possess 
 no colour, and which seem to have a function altogether different ; these are 
 known as the White or Colourless corpuscles. Their existence has long 
 been recognized in the blood of the lower Vertebrata, where, from being much 
 smaller than the red corpuscles, they could readily be distinguished. But it 
 is only of late, chiefly through the researches of Gulliver, Addison,* and 
 others, that they have been recognized in the blood of Man and other Mam- 
 malia ; their size being nearly the same with that of the red corpuscles ; and 
 the general appearance of the two (owing to the circular form of the latter, 
 and the absence of a proper nucleus,) being less distinct. It is remarkable 
 that, notwithstanding the great variations in the size of the red corpuscles in 
 the different classes of Vertebrata, the dimensions of the colourless corpuscles 
 are extremely constant throughout ; their diameter seldom being much greater 
 or less than l-3000th of an inch. This has been observed even in those ani- 
 mals, the Musk-deer, and the Proteus, which present the widest departure 
 from the general standard in the size of their red corpuscles : so that the 
 colourless corpuscle is as much as four times the diameter of the red, in one 
 instance ; whilst it is not one-eighth of the long diameter of the red, in the 
 other. Hence it would seem very improbable, that the red can never be con- 
 verted into the white, or the white into the red. The aspect of the two, under 
 the Microscope, is very different. Instead of presenting a distinct central 
 nucleus, like the red corpuscles of the Oviparous Vertebrata, or being en- 
 tirely destitute of granular contents, as are those of Mammalia when unaffected 
 by reagents, the colourless corpuscles are studded with minute granules, 
 which may be occasionally seen in active motion within them, and which are 
 discharged when the corpuscles are treated with liquor potassae. They pos- 
 sess, moreover, a higher refracting power than the red corpuscles ; and are 
 further distinguished from them, by their greater firmness, and by the ab- 
 sence of any disposition to adhere to each other ; so that, when a drop of recent 
 blood is placed between two strips of glass, and these are gently moved over 
 one another, the white corpuscles may be at once recognized by their soli- 
 tarirress, in the midst of the rows and irregular masses formed by the aggre- 
 gation of the red. This is still better seen in inflamed blood ; in which the 
 Red corpuscles have a peculiar tendency to adhere to one another, whilst the 
 White are present in unusual number. 
 
 152. The Colourless corpuscles may be readily distinguished in the cir- 
 culating Blood, in the capillaries of the Frog's foot ; and it is then observa- 
 ble, that they occupy the exterior of the current, where the motion of the fluid 
 is slow, whilst the red corpuscles move rapidly through the centre of the tube. 
 
 * Transactions of the Provincial Medical Association, 1842 and 1843. 
 
132 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 Fig. 30. 
 
 A small venous trunk, a, from the Web of 
 the Frog's foot, magnified 350 Diam ; 6, b, cells 
 of the pavement-epithelium, containing nuclei. 
 In the space between the current of oval blood- 
 corpuscles, and the walls of the vessel, the rouud 
 transparent white corpuscles are seen. 
 
 The Colourless corpuscles, indeed, often show a disposition to adhere to the 
 walls of the vessels ; which is manifestly increased on the application of an 
 irritant. Hence the idea naturally arises, that (to use the words of Mr. Whar- 
 
 ton Jones) " there is some reciprocal re- 
 lation between the colourless corpuscles, 
 and the parts outside the vessels, in the 
 process of nutrition." What that rela- 
 tion is, we shall now proceed to inquire. 
 153. In regard to the purpose of the 
 Colourless corpuscles in the Animal eco- 
 nomy, a view has been brought forward 
 by the Author,* which increased consi- 
 deration has only served to strengthen ; 
 and which he advances here, with some 
 degree of confidence that it will be found, 
 on attentive examination, warranted by 
 a large number of physiological analo- 
 gies, though not capable of being direct- 
 ly proved. That it may be rightly un- 
 derstood, a general sketch of certain 
 known operations of cells in Plants and 
 Animals will be first given. It is not 
 difficult, on taking a comprehensive sur- 
 vey of the Assimilating processes, to 
 find a number of examples, in which 
 cells are developed in a temporary man- 
 ner ; growing, arriving at maturity, and 
 then disappearing, apparently without having performed any particular 
 function. In the albumen of the Seed, for instance, this often takes place to 
 a remarkable extent. In the Yolk of the Egg, there is a similar transitory 
 development of cells, of which several generations succeed each other, without 
 any permanent structure being the result ; and we have seen that, according 
 to Dr. Barry ,t a process of the same nature takes place within the germinal 
 vesicle, and in the primary embryonic cells and their descendants ( 130). 
 It can scarcely be imagined by the well-judging Physiologist, that all this 
 cell-life comes into existence without some decided purpose ; and if we can 
 assign to it an object, the fulfilment of which is consistent with the facts sup- 
 plied by analogy elsewhere, this may be reasonably considered as having a 
 fair claim to be received as a physiological induction. In all these instances, 
 and in many more which might be quoted, the crude alimentary materials are 
 being prepared to undergo conversion into permanent and regularly-organized 
 structures. We have seen that the very first union of the inorganic elements, 
 into the simplest proximate principles, is effected by the cell-life of Plants. 
 The change of these principles into the peculiar compounds, which form the 
 characteristic secretions of Plants, is another result of their cell-life. And 
 there seems equal ground for the belief that the change of these proximate 
 principles into the peculiar glutinous sap, which is found wherever a forma- 
 tion of new tissue is taking place, is equally dependent upon the agency of 
 cells. Thus, the starchy fluid, which is contained in the ovule previously to 
 its fecundation, is probably not in the state in which it can be immediately 
 rendered subservient to the nutrition of the embryo ; and the development of 
 successive generations of cells, which exert upon it their vitalizing influence, 
 
 * Report on Cells, in British and Foreign Medical Review, Jan. 1843. 
 j" Embryo] ogical Researches. Third Series. 
 
COLOURLESS CORPUSCLES OF BLOOD. 133 
 
 may be reasonably regarded as the means, by which the requisite change is 
 effected. Exactly the same may be said of the Albuminous matter contained 
 in the Yolk .of the Egg, which is certainly not in a condition in which it can 
 be immediately applied to the purposes of nutrition ; and its conversion may 
 be regarded as commencing with the development of transitory cells within 
 its own substance, and as being completed by means of the cells forming the 
 inner layer of the germinal membrane, by which it is subsequently taken up 
 and introduced into the current of blood flowing through the vascular area 
 ( 149). A similar purpose is probably answered by the transitory cells de- 
 veloped within the germinal vesicle ; and by those which appear at a similar 
 period, in the evolution of the descendants of the " twin cells" produced in 
 it. Many similar examples have been elsewhere adduced. 
 
 a. There are probably cases, however, in which cells are very rapidly called into exist- 
 ence, without that preparatory elaboration of their nutrient materials, which we regard as 
 due to the vital operations of a preceding generation. Thus the Sovista giganteum, a large 
 fungus of the Puff-ball tribe, has been known to increase, in a single night, from a mere point 
 to the size of a huge gourd, estimated to contain 47,000,000,000 cellules. In such a case it 
 is difficult to suppose that any but the most rapid mode of generating cells ean have been in 
 operation ; and the idea that these could not have been developed by any such elaborate 
 process as that just alluded to, is borne out by the fact of their extremely transitory charac- 
 ter, the decay of such a structure being almost as rapid as its production. The same may be 
 remarked of those fungous growths, in the Animal body, which sprout forth most rapidly. 
 Hence the apparent exception assists in proving the rule. 
 
 154. We have thus a class of facts, which indicates that the conversion of 
 the Chemical compound into the organizable principle the aplastic into the 
 plastic material is effected, in the particular situations where it is most 
 wanted, by the vital agency of transitory cell-life ; that is, by the production 
 of cells, which are not themselves destined to form an integral part of any 
 permanent structure, but which, after attaining a certain maturity, reproduce 
 themselves and disappear ; successive generations thus following one another, 
 until the object is accomplished, after which they altogether vanish. We 
 shall now consider another class of facts, which seem to indicate that a change 
 of this kind is being continually effected in the nutritious fluids of Animals, 
 during their circulation through the body : by Cells, which are either carried 
 about with them, or which are developed for the purpose in particular situa- 
 tions, as in Plants. The former is the nrore common occurrence ; since the 
 conditions, of Anirnal life, usually involving a general movement of the body, 
 require also a constant general reparation of its parts, and therefore an adapt- 
 ation of the circulating fluid to the wants of the whole fabric. 
 
 155. It is not in the Blood alone, that floating cells are met with; for Cells, 
 which seem identical with the Colourless corpuscles of the blood, are found 
 in the Chyle and Lymph fluids in which, as in the Blood, the elaboration 
 of plastic Fibrine from unorganizable Albumen is continually taking place, to 
 make up for the constant withdrawal of the former substance by the nutrient 
 processes. Hence there would seem reason for attributing this important 
 function to these floating cells ; the number of which present in the fluids, 
 seems to bear a very close relation with the energy of the elaborating process. 
 It is a fact of great physiological interest and importance, that, whilst the 
 colourless corpuscles are to be met with in the nutritious' fluids of all Animals 
 which possess a distinct circulation, the red corpuscles are nearly restricted to 
 the blood of Vertebrata. This observation, which was first put forth by 
 Wagner,* has been confirmed by the Authos, who had been previously struck 
 with the very close analogy between the floating cells carried along in the 
 
 * [Elements of Physiology, translated by R. Willis.] 
 12 
 
134 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 current of the circulation in some of the very transparent aquatic larvae (espe- 
 cially those of the Culicidae), and the lymph-corpuscles of the Frog. Now 
 it is evident from this fact, that, as the Blood of Vertebrata is distinguished 
 from their Chyle chiefly by the presence of red corpuscles in the former, and 
 by the absence of those bodies in the latter, the nutritious fluid of Inverte- 
 brated animals is rather analogous (as Wagner has remarked) to the Chyle 
 and Lymph, than to the Blood of Vertebrata. Or, to put the same idea in 
 another form, the presence of the colourless corpuscles in the nutritious fluid 
 appears to be the most general fact in regard to its character throughout the 
 whole Animal scale; whilst the presence of red corpuscles in that fluid is 
 limited to the Vertebrated classes and the higher Invertebrata. Hence it 
 would not be wrong to infer, that the function of the colourless corpuscles 
 must be of a general character, and intimately connected with the nutritious 
 properties of the circulating fluid ; whilst the function of the red corpuscles 
 must be of a limited character, being only required in one portion of the ani- 
 mal kingdom. 
 
 156. Further, it has been noticed by Mr. Gulliver, that in the very young 
 embryo of the Mammalia, the white globules are nearly as numerous as the 
 red particles: this, Mr. Gulliver has frequently observed in foetal deer of about 
 1| inch long. In a still smaller foetus, the blood was pale, from the prepon- 
 derance of the white corpuscles. It is, therefore, a fact of much interest, 
 that, even in the Mammiferous embryo, at the period when growth is most 
 rapid, the circulating fluid has a strong analogy to that of the Invertebrata. 
 It then, too, bears in other respects the most striking analogy to Chyle; since 
 it consists of the fluid elaborated from the organizable matter supplied by the 
 parent, and directly introduced into the current of the circulation. The func- 
 tion of the placental vessels may be regarded as double : for they are at the 
 same time the channel, through which the alimentary materials supplied by 
 the parent are introduced into the circulating system of the foetus ; and the 
 medium of aerating the fluid, which has traversed the foetal system. Hence 
 the placenta may be regarded as at once the digestive and the respiratory 
 apparatus of the foetus ; and the fluid circulating through the cord, as at once 
 chyle and blood. It is not until the pulmonary and lacteal vessels of the 
 embryo have commenced their independent operation, that the distinction be- 
 tween the blood and the chyle of the foetus becomes evident; and we should 
 expect, therefore, to find that the circulating fluid, up to the time of birth, 
 contains a large proportion of white corpuscles, which is actually the case. 
 There is a gradual decrease, however, in their proportional number, from the 
 earlier to the later stages of embryonic life ; in accordance with the diminish- 
 ing energy of the formative processes. The recent observations of Mr. New- 
 port upon the Blood of Insects,* present a remarkable correspondence with 
 the foregoing. He finds in the circulating fluid of the Larva, a number of 
 " oat-shaped" corpuscles or floating cells; which he regards as analogous to 
 the Colourless corpuscles of Vertebrata. These are most numerous at the 
 period immediately preceding each change of skin; at which time the blood 
 is extremely coagulable, and evidently possesses the greatest formative power. 
 The smallest number are met with soon after the change of skin; when the 
 nutrient matter of the blood has been exhausted in the production of new 
 epidermic tissue. In the Pupa state, the greatest number are found at about 
 the third or fourth day subsequent to the change ; when preparations appear 
 to be most actively going on, for the development of the new parts that are 
 to appear in the perfect Insect. 'After this, there is a gradual diminution; the 
 plastic element being progressively withdrawn by the formative processes ; 
 
 * Philosophical Magazine, May 1845. 
 
COLOURLESS CORPUSCLES OF BLOOD. 135 
 
 until, in the perfect Insect, very few remain. When the wings are being 
 expanded, however, and are still soft, a few oat-shaped corpuscles circulate 
 through their vessels ; but as the wings become consolidated, these corpuscles 
 appear to be arrested and to break down in the circulating passages ; supply- 
 ing, as Mr. N. thinks, the nutrient material for the completion of these struc- 
 tures, which subsequently undergo no change. In the perfect Insect, a differ- 
 ent set of corpuscles makes its appearance; which is rather analogous to the 
 red corpuscles of Vertebrata. This last fact completely harmonizes with the 
 views already expressed ; since the formative processes are now reduced to 
 their lowest condition in the Insect; whilst the respiration attains its highest 
 grade. 
 
 157. Even in adult animals, however, variations in formative power may 
 be detected; which correspond with variations in the number of the Colour- 
 less corpuscles. Thus it has been observed by Wagner,* that the number of 
 these corpuscles is always remarkably great, in the blood of well-fed Frogs 
 just caught in the summer season; whilst it is very small in those which have 
 been long kept without food, or which are examined during the winter. In 
 the reparation of injuries, too, which is effected in cold-blooded animals by a 
 process of simple growth without inflammation, it would seem that the Co- 
 lourless corpuscles perform an important part; as they are observed in great 
 numbers, and in a nearly stationary condition, in the vessels surrounding the 
 spot where the new tissue is being formed; apparently having the same action 
 as in the first development of parts altogether new, such as the toes of the 
 larva of the Water-Newt. 
 
 158. A remarkable confirmation <of this view of the connection between the 
 generation of Colourless corpuscles in the Blood, and the production of Fi- 
 brine, is derived from the phenomena of Inflammation. A decided increase 
 in the normal proportion of Fibrine in the Blood (from 2 to 3% parts in 1000), 
 may probably be looked upon as the essential indication of the existence of 
 the Inflammatory condition. That this production of Fibrine is due to a local 
 change, can scarcely be doubted ; since it is frequently observed to commence, 
 before any constitutional symptoms manifest themselves : and it may be re- 
 garded, in fact, as one cause of these symptoms. Now the microscopic ob- 
 servations of Mr. Addisont and Dr. Williams,;}: made independently of each 
 other, have established the important fact, that a great accumulation of Colour- 
 less corpuscles takes place in the vessels of an inflamed part : this seems to 
 be caused at first, by a determination of those already existing in the circu- 
 lating fluid, towards the affected spot; but partly by an actual increase or 
 generation of these bodies, which appear to have the power of very rapidly 
 multiplying themselves. The accumulation of Colourless corpuscles may be 
 easily seen, by applying irritants to the web of a 'Frog's foot. Mr. Addison 
 has noticed it in the Human subject, in blood drawn by the prick of a needle 
 from an inflamed pimple, the base of a boil, the skin in scarlatina, &c. And 
 the Author, without any knowledge of these observations, had remarked a 
 very obvious difference between the proportions of Colourless corpuscles, in 
 blood drawn from a wound in the skin of a Frog immediately upon the in- 
 cision being made, and in that drawn a few minutes after ; and had been led, 
 like the observers just quoted, to refer this difference to a determination of 
 Colourless corpuscles to a part irritated. The absolute increase, sometimes 
 to a very considerable amount, in the quantity of Colourless corpuscles in the 
 blood of an inflamed subject, has been verified by Mr. Gulliver and several 
 
 * [Elements of Physiology, translated by R. Willis.] 
 
 |- Medical Gazette, Dec. 1840; Jan. and March, 1841. 
 
 Medical Gazette, July, 1841 ; and Principles of Medicine, [Am. Ed., by Dr. Clymer, pp. 
 
136 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 other observers. These facts, therefore, afford strong ground for the belief, 
 that the production of Fibrine 'in the blood is closely connected with the de- 
 velopment of the Colourless corpuscles ; and when we consider them in con- 
 nection with the facts previously urged, there scarcely appears to be a rea- 
 sonable doubt that the elaboration of Fibrine is a consequence of this form of 
 cell-life, and is, in fact, its express object. 
 
 159. This view derives further confirmation from the following recent 
 experiment of Mr. Addison's.* " Provide six or eight slips of glass, such as 
 are usually employed for mounting microscopical objects ; and as many 
 smaller pieces. Having drawn blood from a person with rheumatic fever, 
 or any other inflammatory disease, place a drop of the colourless liquor san- 
 guinis, before it fibrillates, on each of the large slips of glass ; cover one im- 
 mediately with one of the smaller slips, and the others one after another at 
 intervals of thirty or forty seconds: then, on examining them by the micro- 
 scope, the first will exhibit colourless blood-corpuscles in various conditions, 
 and numerous white molecules distributed through a more or less copious 
 fibrous network ; and the last will be a tough, coherent, and very elastic 
 membrane, which cannot be broken to pieces nor resolved into smaller frag- 
 ments, however roughly or strongly the two pieces of glass be made to rub 
 against each other. This is a ' glaring instance' of a compact, tough, elastic, 
 colourless, and fibrous tissue, forming from the colourless elements of the 
 blood ; and the several stages of its formation may be actually seen and 
 determined. Numerous corpuscles may be observed, in all these prepara- 
 tions, to have resolved themselves, or to have fallen down into a number of 
 minute molecules, which are spread out over a somewhat larger area than that 
 occupied by the entire corpuscles ; and although still retaining a more or less 
 perfectly circular outline, yet refracting the light at their edges, in a manner 
 very different from that in which the corpuscles themselves are seen to do. 
 It is from these and various other larger and more irregular masses of mole- 
 cules or disintegrated corpuscles, that the fibrinous filaments shoot out on all 
 sides, as from so many centres ; or frequently the filaments are more copious 
 in two opposite directions." 
 
 a. A different view of the cause of the production of Fibrine, however, has been enter- 
 tained by some eminent Physiologists ; and it does not seem right to allow the opinions of 
 Wagner, Henle, and Wharton Jones to pass without notice, even though they appear to the 
 Author to be. easily set aside. By these observers, the elaboration of Fibrine has been at- 
 tributed to the red corpuscles, and has been regarded as one, at least, of their special func- 
 tions. Nearly all the arguments, however, which have led us to assign this duty to the 
 Colourless corpuscles, tell equally against the doctrine now under consideration. In the first 
 place, the contents of the Red corpuscles have no resemblance whatever to liquid Fibrine j 
 but are characterized by the presence of a substance altogether different: whilst, as shown 
 above, the Colourless corpuscles" emit, on bursting, a fibrillating matter. If, then, Fibrine be 
 elaborated by the Red corpuscles, it must be by forming part of their walls : a method alto- 
 gether unusual. Again, the entire absence of Red corpuscles in the blood of the lower 
 Invertebrata, and in that of the larva and pupa of the Insect, the small proportion in which 
 they are present in the blood of any Invertebrata, and their occurrence to any large amount 
 in the blood of Vertebrata only, seem to show that they cannot be Concerned in a function 
 so constant and essential as the elaboration of the plastic element. The number of the Red 
 corpuscles, as stated above, bears a regular proportion to the amount of oxygen introduced 
 into the system, and thus to the heat developed, and to the activity of the Animal functions ; 
 but it does not bear the same relation to the activity of the formative processes^ which take 
 place most energetically in a state of functional quiescence. Further, although the quantity 
 of Fibrine is so remarkably increased in Inflammation, the number of Red corpuscles under- 
 goes no decided change. Such an augmentation is even compatible with a Chlorotic state of 
 the blood ; the peculiar characteristic of which is a great diminution in the proportion of Red 
 corpuscles. By such alterations, the nprmal proportion between the Fibrine and the Red 
 corpuscles, which may be stated as A. : B, may be so much altered as to become, in Inflam- 
 
 * Transactions of the Provincial Medical Association, 1843. 
 
EPIDERMIC CELLS. 
 
 137 
 
 Fig. 31. 
 
 mation, 4 A : B ; or, in Chlorosis, A : J B. In Fever, the characteristic alteration in the con* 
 dition of the blood, appears to be an increase, in the amount of Red corpuscles, with a dimi- 
 nution in the quantity of Fibrine ; yet if a local inflammation should establish itself during 
 the course of a fever, the proportion of fibrine will rise ; and this without any change in the 
 amount of corpuscles. Lastly, the effect of Loss of Blood has been shown by Andral's in- 
 vestigations, to be a marked diminution in the number of Red corpuscles, with no decided 
 reduction in the quantity of Fibrine, even when this is much above its normal standard; and 
 in this condition of the blood, it has been observed by Remak that the Colourless corpuscles 
 are very numerous. 
 
 6. Of Cells developed upon Free Surfaces. 
 
 160. Next in independence to the cells or corpuscles floating in the animal 
 fluids, are those which cover the free membranous surfaces of the body, and 
 which form the Epidermis and Epithelium. Between these two structures 
 there is no essential difference, either in regard to their origin, their mode of 
 development, their situation, or their individual history ; but there is an im- 
 portant difference in the purposes which they respectively serve in the eco- 
 nomy. They both consist of cells, which are developed from germs furnished 
 by the subjacent membrane, which are nourished by its vessels, and which 
 are after a time cast off from its free surface to be replaced by a succeeding 
 generation ; but the contents of the cells vary in different situations, and give 
 peculiar characters to the tissue. The differences, however, are not more 
 striking between the Epidermis, or cellular covering of the external surface, 
 and the Epithelium, or cellular lining of the internal cavities, than those which 
 exist between the different portions of the Epithelium itself. For although 
 the Epidermis is distinguished by its comparatively 
 
 hard, dry, horny character, whilst the Epithelium 
 is soft, moist, and deficient in tenacity ; yet we shall 
 hereafter find that, as all the Secretions of the body 
 are elaborated by the agency of the cells of the 
 latter, there must be as many varieties of endow- 
 ment, in these important bodies, as there are differ- 
 ences in the results of their action. 
 
 161. The Epidermis, which usually forms a 
 thin semi-transparent pellicle, in close apposition 
 with the surface of the true Skin, but occasionally 
 presents a great increase in thickness, consists of 
 a series of flattened scale-like cells ; which, when 
 first formed, are spherical ; but which gradually dry 
 up, their nucleus usually remaining visible. These 
 form several layers ; of which the deeper can be 
 seen very distinctly to possess the cellular character, 
 whilst the external layers are scaly ; and between 
 these, all stages of transformation may be traced. 
 The outer layers are continually being thrown off 
 by desquamation ; and new ones are as constantly 
 being formed below. They would seem to origi- 
 nate in germs supplied by the basement-membrane, 
 on whose surface they make their first appearance; 
 and their continued development takes place at the 
 expense of nutriment, which they draw through 
 that membrane, from the subjacent vessels. The 
 Epidermis is not itself traversed by vessels or 
 nerves ; but it is pierced by the excretory ducts of 
 the sebaceous and sweat glands, and also by the 
 shafts of the hairs ; being, however, at the same 
 
 12* 
 
 Vertical section of Epidermis, 
 from palm of the hand ; a, outer 
 portion, composed of flattened 
 scales ; 6, inner portion, consist- 
 ing of nucleated cells ; c, tortu- 
 ous perspiratory tube, cut across 
 by the section higher up. Mag- 
 nified 155 diameters. 
 
138 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 time continuous with the epithelial linings of these. The soft layer which 
 lies in immediate contact with the true skin, was formerly supposed to be a 
 substance of distinct nature, and was described under the name of rete muco- 
 sum ; it has been proved by microscopic examination, however, to consist of 
 the same elements with the ordinary epidermis, in an early stage of their 
 development; and, so far from being the exclusive seat of the colour of the 
 skin, as was formerly supposed, it only participates with the fully-formed 
 epidermis in the possession of pigment-cells ( 163). The thickness of the 
 Epidermis, and consequently the number of layers of which it is composed, 
 vary greatly in different parts ; being usually found to be greatest, where there 
 is most pressure or friction, as on the palms of the hands of the labouring 
 man, and on the soles of the feet, particularly at the heel, and the ball of the 
 great toe. It would seem as if the irritation of the true skin produced an 
 augmented determination of blood to the part, and consequently an increased 
 development of epidermic cells. The Epidermis covers the whole exterior of 
 the body, not excepting the Cornea and the Conjunctival membrane; on the 
 latter, however, it has more the character of an Epithelium. This continuity 
 is well seen in the cast skin or slough of the Snake ; in which the covering 
 of the front of the eye is found to be as perfectly exuviated as that of any part 
 of the body. 
 
 162. The Epidermis appears solely destined for the protection of the true 
 Skin, from the mechanical injury and the pain occasioned by the slightest 
 abrasion, and from the irritating influence of exposure to air and of changes 
 of temperature. We perceive the value of this protection, when the Epider- 
 mis has been accidentally removed. It is very speedily replaced, however; 
 the increased determination of blood to the Skin, which is the consequence of 
 the irritation, being favourable to the rapid production of Epidermic cells from 
 its surface. The peculiar character of the tissue appears to depend upon the 
 property possessed by its cells, of secreting horny matter into their cavity ; 
 and this process seems to take place at a period subsequent to the first forma- 
 tion of the cells. For if a thin vertical section of the Epidermis be treated 
 with Acetic acid, or with a strong solution of Potass, it is found that the inner 
 newly-formed layers are dissolved by the re-agent, whilst the outer or scaly 
 ones are unaffected. Recent analysis has shown, that the dense Epidermis 
 from the sole of the foot, and the compact Horny matter of which Nails, 
 Hoofs, Horns, Hair, and Wool, are composed, have the same composition; 
 the formula of all of them being 48 Carbon, 39 Hydrogen, 7 Nitrogen, and 
 17 Oxygen. It is probable that, here as elsewhere, if we could isolate the 
 wall of the cell from its contents, we should find the former to consist of a 
 proteine-compound. 
 
 163. Mingled with the Epidermic cells, we find others which secrete Co- 
 louring-matter instead of Horn ; these are termed Pigment-cells. They are 
 not readily distinguishable in the Epidermis of the fair races of mankind, 
 except in certain parts, such as the areola around the nipple, and in freckles, 
 naevi, &c. But they are very obvious, on account of their dark hue, in the 
 newer layers of the Epidermis of the Negro and other coloured races ; .and, 
 like true Epidermic cells, they dry up and become flattened scales in passing 
 towards the surface, thus constantly remaining dispersed through its substance, 
 and giving it a dark tint when it is separated and held up to the light. In all 
 races of men, however, we find the most remarkable development of Pigment- 
 cells on the inner surface of the Choroid coat of the eye : where they form 
 several layers, known as the Pigmentum nigrutn. When examined sepa- 
 rately, these are found to have a polygonal form, and to have a distinct nucleus 
 in their interior. The black colour is given by the accumulation, within the 
 cell, of a number of flat, rounded or oval granules, measuring about 1-20, 000th 
 

 PIGMENT-CELLS. 
 
 139 
 
 of an inch in diameter, and a quarter as much in thickness ; these, when 
 separately viewed, are observed to be transparent, not black and opaque ; and 
 
 [Fig. 32. 
 
 Fig. 33. 
 
 B 
 
 A. Choroid Epithelium, with the cells filled with 
 pigment, except at a, where the nuclei are visi- 
 ble. The irregularity of the pigment-cells is seen. 
 b. Grains of pigment. 
 
 B. Pigment-cells from the substance of the Cho- 
 roid. A detached nucleus is seen. Magnified 
 320 diameters.] 
 
 Cells from Pigmentum Ni- 
 grum; a, pigmentary gra- 
 nules concealing the nu- 
 cleus; fc, the nucleus distinct. 
 Magnified 410 diameters. 
 
 they exhibit an active movement when set free from the cell, and even whilst 
 inclosed within it. The Pigment-cells are not always of a simple rounded or 
 polygonal form; they sometimes present remarkable stellate prolongations, 
 such as those seen in the skin of the Frog (Fig. 88) ; and occasionally, the 
 cells being more nearly approximated to each other, these prolongations com- 
 municate, so as to form a kind of network. The Chemical nature of the Black 
 pigment has not yet been distinctly ascertained ; it has been shown, however, 
 to have a very close relation with that of the Cuttle-fish ink, or Sepia, which 
 derives its colour from the pigment-cells of the ink-bag; and to include a 
 larger proportion of carbon than most other organic substances, every 100 
 parts containing 58| of that element. 
 
 164. It cannot be doubted that the development of the Pigment-cells of 
 the skin is very much influenced by exposure to light ; and in this respect 
 there is a remarkable correspondence between Animals and Plants, the 
 coloration of the latter, as is well known, being entirely due to that agent. 
 Thus, it is a matter of familiar experience, that the influence of light upon 
 the skin of many individuals, causes it to become spotted with brownfreckles ; 
 these freckles being aggregations of brown pigment-cells, which either owe 
 their development to the stimulus of light, or are enabled by its agency to 
 perform a decided chemical transformation, which they could not otherwise 
 effect. In like manner, the swarthy hue, which many Europeans acquire 
 beneath exposure to the sun in tropical climates, is due to a development of 
 dark pigment-cells, and to this we usually find the greatest disposition in in- 
 dividuals or races, that are already of a somewhat dark complexion. The 
 deep blackness of the Negro skin seems dependent upon nothing else than a 
 similar cause, operating through successive generations ( 80). It is well 
 known that the new-born infants of the negro and other dark races, do not ex- 
 hibit nearly the same depth of colour in their skins, as that which they present 
 after the lapse of a few days, when light has had time to exert its influence 
 upon their surface ; and further, that in those individuals who keep them- 
 selves during life most secluded from its influence, we observe the lightest 
 hue of the epidermis. Thus among the intertropical nations, the families of 
 Chiefs, which are not exposed to the sun in the same degree with the com- 
 
140 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 [Fig. 34. 
 
 mon people, almost always present a lighter hue ; and in some of the islands 
 of the Polynesian Archipelago, bordering on the Equator, they are not darker 
 than the inhabitants of Southern Europe. An occasional development of dark 
 pigment-cells takes place during pregnancy, in some females of the fair races ; 
 thus it is very common to meet with an extremely dark and broad areola 
 round the nipple of pregnant women ; and sometimes large patches of the 
 cutaneous surface, on the lower part of the body especially, become almost 
 as dark as the skin of a Negro.- On the other hand, individuals are occasion- 
 ally seen with an entire deficiency of pigment-cells, or at least of their proper 
 secretion ; and this not merely in the skin, but in the eye ; such are termed 
 Albinoes ; and they are met with alike among the fair, and among the dark 
 races. The absence of colour usually shows itself also in the hair ; which 
 is almost white. 
 
 165. The Nails, like Hoof, Horn, &c., may be regarded as nothing more 
 than an altered form of Epidermis. When their newest and softest portions 
 are examined, they are found to consist of nucleated particles, resembling 
 those of the newer layers of Epidermis ; in the more superficial laminae, 
 however, no distinct structure can be made out; but, when treated with acetic 
 acid, some traces of nuclei may be detected in them. The Nail is produced 
 from the surface of the true skin that lies beneath it, which is folded into a 
 
 groove at its root; this surface is highly vascular. 
 The increase in length is effected by successive 
 additions at the root, causing the whole nail to 
 shift onwards ; but as it moves, it receives ad- 
 ditional layers from the subjacent skin, which 
 increases its thickness. The nail is continuous 
 with the true. Epidermis at every part, except 
 its free projecting edge ; and in the foetus, the 
 continuity is maintained there also. 
 
 166. The Hair, as originally consisting of 
 Epidermic cells, may be properly described 
 here ; although, when fully formed, it departs 
 widely (in Man at least) from the cellular type. 
 It has been imagined until recently, that the 
 Hair, in common with the other Epidermic tis- 
 sues, is a mere product of secretion ; its mate- 
 rial, which is chiefly horny matter of the same 
 composition with that of the Epidermis and its appendages, being elaborated 
 from the surface of the pulp at its base. It is not known, however, to con- 
 tain a distinctly organized structure ; and to be formed by the conversion of 
 a cellular mass at its root. The Hair originates within a follicle, which is 
 formed by a little depression of the Skin, and which is lined by a continua- 
 tion of the Epidermis. From the bottom of this follicle, there rises up a 
 cluster of cells, which may be regarded as an increased development of Epi- 
 dermic cells ; the exterior of this cluster, which is the densest part, is known 
 as the bulb ; whilst the softer interior is termed the pulp. The follicle itself 
 is extremely vascular ; and even the bulb is reddened by minute injection, 
 though no distinct vessels can be traced into it. Although the Hairs of differ- 
 ent animals vary considerably in the appearances they present, we may gene- 
 rally distinguish in them two elementary parts ; a cortical or investing sub- 
 stance, of a fibrous horny texture ; and a medullary or pith-like substance, 
 occupying the interior. The fullest development of both substances is to be 
 found in the spiny Hairs of the Hedgehog, and in the quills of the Porcu- 
 pine ; which are but hairs on a magnified scale. The cortical substance 
 forms a dense horny tube, to which the firmness of the structure seems chiefly 
 
 Section of the skin on the end of 
 the finger: The cuticle, and nail, n, 
 detached from the cutis and matrix, m.} 
 
STRUCTURE OF HAIR. 
 
 141 
 
 due ; whilst the medullary substance is composed of an aggregation of very 
 large cells, which seem not to possess any fluid contents in the part of the 
 hair which is completely formed. The structure of the feather of Birds is 
 precisely analogous ; the cortical horny tube existing alone in the quill ; but 
 being filled with a cellular medulla in the stem of the feather itself. In the 
 hair of the Mouse and other small Rodents, we see the horny tube crossed 
 at intervals by partitions, which are sometimes complete, sometimes only par- 
 tial ; these are the walls of the single or double line of cells, of which the 
 medullary substance is made up. In the Sable, we sometimes meet with 
 hairs, in which the medulla is made up of rounded cells ; whilst the cortical 
 substance is composed of imbricated Epidermic scales (Fig. 35, B). In some 
 instances, however, there is scarcely any medulla to be traced ; whilst in 
 other animals, as the Musk-deer (Fig. 35, A), the entire hair seems to be made 
 up of it. 
 
 Fig. 35. 
 
 [Fig. 36. 
 
 A, hair of Musk-Deer 
 consisting almost entirely 
 of polygonal cells; B, hair 
 of Sable, showing large 
 rounded cells in its inte- 
 rior, covered by imbrica- 
 ted scales, or flattened 
 cells. 
 
 Bulb of a small black hair, from the scrotum, seen 
 in section, a. Basement membrane of the follicle, b. 
 Layer of epidermic cells resting upon it, and becoming- 
 more scaly as they approach c, a layer of imbricated 
 cells, forming the outer lamina, or cortex, of the hair. 
 These imbricated cells are seen more flattened and 
 compressed, the higher they are traced on the bulb. 
 Within the cortex is the proper substance of the hair, 
 consisting at the base, where it rests on the base- 
 ment membrane, of small angular cells scarcely larger 
 than their nuclei. At d, these cells are more bulky, 
 and the bulb consequently thicker ; there is also pig- 
 ment developed in many of them more or less abun- 
 dantly. Above d, they assume a decidedly fibrous cha- 
 racter, and become condensed, e. A mass of cells in 
 the axis of the hair, much loaded with pigment] 
 
 167. In the Human hair, the representation of the cortical sheath of the hair 
 of other animals is found in a thin transparent horny film ; which is composed 
 of flattened cells or scales, arranged in an imbricated manner, their edges 
 (Fig. 36) forming delicate lines upon the surface of the hair, which are some- 
 times transverse, sometimes oblique, and sometimes apparently spiral (Fig. 
 37, A). Within this, we find a cylinder of fibrous texture ; which forms the 
 
142 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 principal part of the shaft of the hair ; whilst the centre is frequently more 
 distinctly cellular. The constituent fibres of the shaft are marked out by 
 delicate longitudinal striae, which may be traced in vertical sections of the 
 hair (Fig. 37, B.) ; but they may be still more completely demonstrated by 
 crushing the hair, after it has been macerated for some time in dilute acid. 
 In dark hairs, pigmentary granules are frequently scattered between the fibres; 
 but they are usually found in greater abundance in the central cells. The 
 Hair of Man is commonly reputed to be tubular ; but this is seldom if ever 
 the case, as is shown by microscopical examination of thin transverse sec- 
 tions (Fig. 37, c). The mistake has arisen from a misinterpretation of the 
 appearance of a dark band in the interior of the hair, when viewed by trans- 
 mitted light ; which is really due, partly to the presence of pigmentary mat- 
 ter in the central portion of the shaft, and partly to the refraction of light by 
 the cylindrical surface. The chemical composition of Hair, as already stated, 
 
 Structure of Human Hair; A, external surface of the shaft, showing the transverse striae and jagged 
 boundary, caused by the imbrications of the scaly cortex ; B, longitudinal section of the shaft, showing 
 the fibrous character of the medullary substance, and the arrangement of the pigmentary matter; c, 
 transverse sections, showing the distinction between the cortical and medullary substance, and the cen- 
 tral collection of pigmentary matter, sometimes found in the latter. Magnified 310 diameters. 
 
 is precisely the same with that of the horny Epidermis ( 162). Its colour- 
 ing matter seems related to HaBinatine ; it is bleached by Chlorine ; and its 
 hue appears to be dependent in part upon the presence of iron, which is found 
 in larger proportion in dark than in light hair. 
 
 168. The real nature of the different elements of the Hair is ascertained, 
 by examining them at its base, where they become continuous with those of 
 the bulb. It is then seen, that the fibres of the shaft are identical with the 
 cells of the bulb ; these undergoing elongation, as they are pushed upwards 
 towards the mouth of the follicle, by the development of additional cells be- 
 neath ; and being proportionably diminished in diameter. Hence the shaft of 
 the hair is considerably narrower than the bulb. The central part of the hair 
 which more distinctly exhibits the cellular character, is derived from the pulp 
 or internal portion of the bulb ; whose constituent cells undergo Tess change. 
 And the imbricated layer of cells, that forms its fibrous envelope, may be said 
 to be a prolongation of the ordinary Epidermis over the surface of the hair ; 
 being developed from the external portion of the bulb, where it is continuous 
 with the epidermic lining of the follicle. Thus we see that the whole tissue 
 of the Hair is derived from Epidermic cells, developed in peculiar abundance 
 from the base of the follicle ; some of these cells, however, retaining their 
 original form ; whilst others are transformed into fibres, and others converted 
 (like those of ordinary Epidermis) into flattened cells. They all have the 
 power, however, of drawing horny matter into their cavities ; and resist the 
 
STRUCTURE OF HAIR. EPITHELIUM. 143 
 
 solvent power of chemical re-agents, except when these are employed in un- 
 usual strength. The Hair is constantly undergoing elongation, by the addi- 
 tion of new substance at its base; and the part which has been once fully 
 formed, and which has emerged from the follicle, usually undergoes no sub- 
 sequent alteration. There is evidence, however, that it may be affected by 
 changes at its base, the effect of which is propagated along its whole extent : 
 thus, it is well known that cases are not unfrequent, in which, under the in- 
 fluence of strong mental emotion, the whole of the hair has been turned to 
 gray, or even to a silvery white, in the course of a single night; a change 
 which can scarcely be accounted for in any other way than by supposing that 
 a fluid, capable of chemically affecting the colour, is secreted at the base of 
 the hair, and transmitted by imbibition through the medullary substance to 
 the opposite extremity. Another evidence of their retention of a degree of 
 vitality, is found in the fact of Hairs having a tendency to become pointed,' 
 after having been cut short off. In the hairs of some animals (particularly 
 the whiskers of the Seal and other Carnivora) the base is hollow, and con- 
 tains a true papilla, or elevation of the cutis, furnished with nerves and blood- 
 vessels ; this is separated by a layer of basement-membrane from the proper 
 tissue of the Hair. In such cases, there is bleeding from the stumps of the 
 hairs, when they are shaved off close to the skin. There is an approach to 
 this papillary structure in Man; and it may perhaps be an abnormal develop- 
 ment of it, which occasions the hair to bleed in the disease termed Plica Po- 
 lonica. The hair of individuals affected with it is further disposed to split 
 into fibres, often at a considerable distance from the roots, and to exude a 
 glutinous substance ; these two causes unite in occasioning that peculiar mat- 
 ting of the hair, which has given origin to the name of the disease. 
 
 169. The layer of cells covering the internal free surfaces of the body, is 
 known under the name of Epithelium. In some instances it appears to serve 
 to the subjacent membranes, like the Epidermis to the Cutis, merely as a pro- 
 tection; whilst in other cases, as we shall presently find, it answers purposes 
 of far greater importance. It has long been known that the epidermic layer 
 might be traced continuously from the lips to the mucous membrane of the 
 mouth, and thence down the oesophagus into the stomach ; and that, in the 
 strong muscular stomach or gizzard of the granivorous birds, it becomes quite 
 a firm horny lining. But it has been only since the application of the Mi- 
 croscope to this investigation, that a continuous layer of cells has been traced, 
 not mereTy along the whole surface of the mucous membrane lining the ali- 
 mentary canal, but likewise along the free surfaces of all other Mucous Mem- 
 branes, with their prolongations into follicles and glands ; as well as on the 
 Serous and Synovial membranes, and the lining membrane of the heart, blood- 
 vessels, and absorbents. 
 
 170. The forms presented by the Epithelium cells are various. The two 
 chief, however, are the tesselated, forming the pavement- epithelium; and the 
 cylindrical, forming the cylinder-epithelium. The Tesselated Epithelium 
 covers the serous and synovial membranes, the lining membrane of the blood- 
 vessels, and the ultimate follicles or tubuli of most glandular structures con- 
 nected with the skin or mucous membranes, as also the mucous membranes 
 themselves, where the cylinder-epithelium does not exist. The cells compos- 
 ing it are usually flattened and polygonal (Fig. 38, A.) so as to come into con- 
 tact with each other at their edges, like the pieces of a tesselated pavement 
 (Fig. 30) ; but they sometimes retain their rounded or oval form, and are se- 
 parated from each other by considerable interstices. (Fig. 38, B.) This last 
 form seems to be the commonest, where the cells are most actively renewed, 
 so that they have not time (so to speak) to be developed into a continuous 
 stratum. The number of layers is commonly small; and sometimes there is 
 
144 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 only a single one. The Cylinder-Epithelium is very differently constituted. 
 Its component cells are cylinders, which are arranged side by side ; one extre- 
 
 Fig. 38. 
 
 B. 
 
 Separated Epithelium cells, a, with 
 nuclei, 6, and nucleoli, c, from mucous 
 membrane of mouth. 
 
 Pavement-Epithelium of 
 the Mucous Membrane of the 
 smaller bronchial tubes; a, 
 nuclei with double nucleoli. 
 
 mity of each cylinder resting upon the basement-membrane, whilst the other 
 forms part of the free surface. The perfect cylindrical form is only shown, 
 however, when the surface on which the cylinders rest is flat or nearly so. 
 When it is convex, the lower ends or basements of the cells are of much smaller 
 diameter than the upper or free extremities ; and thus each has the form of a 
 truncated cone, rather than of a cylinder ; as is well seen on the cells covering 
 the villi of the intestinal canal. (Fig. 45.) On the other hand, where the cy- 
 linder-epithelium lies upon a concave surface, the free extremities of the cells 
 may be smaller than those which are attached. Sometimes each cylinder is 
 formed from more than one cell, as is shown by its containing two or more 
 nuclei ; although its cavity seems to be continuous from end to end. And 
 occasionally the cylinders arise by stalk-like prolongations, from a pavement- 
 epithelium beneath. The two forms of Epithelium pass into one another at 
 various points ; and various transition-forms are then seen, the tesselated 
 scales appearing to rise more and more from the surface, until they project as 
 long-stalked cells, truncated cones, or cylinders. The Cylinder-Epithelium 
 covers the mucous membrane of the alimentary canal, from the cardiac orifice 
 downwards ; it is found also in the larger ducts of the glands which open into 
 it, or upon the external surface such as the ductus choledochus, the salivary 
 ducts, those of the prostate and Cowper's glands, the vas deferens, and urethra. 
 In all these situations, it comes into connection with the Tesselated Epithe- 
 lium, which usually lines the more delicate canals of the glands, as well as 
 their terminal follicles. 
 
 171. Both these principal forms of Epithelial cells are frequently observed 
 to be fringed at their free margins with delicate filaments, which are termed 
 Cilio ; [from cilium, an eyelash,] and these, although of extreme minuteness, 
 are organs of great importance in the animal economy, through the extraordi- 
 nary motor power with which they are endowed. The form of the Ciliary 
 
 filaments is usually a little flattened, and ta- 
 pering gradually from the base to the point. 
 Their size is extremely variable ; the largest 
 that have been observed being about l-500th 
 of an inch in length, and the smallest about 
 l-13,000th. When in motion, each fila- 
 ment appears to bend from its root to its 
 point, returning again to its original state, 
 like the stalks of corn when depressed by 
 the wind ; and when a number are affected 
 in succession with this motion, the appear- 
 ance of progressive waves following one 
 
 Fig, 39. 
 
 Vibratile or ciliated Epithelium ; a, nu- 
 cleated cells, resting on their smaller ex- 
 tremities ; ft, cilia. 
 
EPITHELIUM; CILIARY MOVEMENT. 
 
 145 
 
 another is produced, as when a corn-field is agitated by frequent gusts. 
 When the Ciliary motion is taking place in full activity, however, nothing 
 whatever can be distinguished, but the whirl of particles in the surrounding 
 fluid ; and it is only when the rate of movement slackens, that the shape 
 and size of the Cilia, and the manner in which their stroke is made, can be 
 clearly seen. The motion of the Cilia is not only quite independent (in all 
 the higher animals at least) of the will of the animal, but is also independent 
 even of the life of the rest of the body ; being seen after the death of the 
 animal ; and proceeding with perfect regularity in parts separated from the 
 body. The isolated epithelium cells have been seen to swim about actively 
 in water, by the agency of their cilia, for some hours after they have been de- 
 tached from the mucous surface of the nose ; and the Ciliary movement has 
 been seen fifteen days after -death in the body of a Tortoise, in which putre- 
 faction was far advanced. In the gills of the River-Mussel, which are among 
 the best objects for the study of it, the movement endures with similar per- 
 tinacity. 
 
 172. The purpose of this Ciliary movement is obviously to propel fluids 
 over the surface on which it takes place ; and it is consequently limited in 
 the higher animals to the internal surfaces of the body, and always takes 
 place in the direction of the outlets, towards which it aids in propelling the 
 various products of secretion. The case is different, however, among animals 
 of the lower classes, especially those inhabiting the water. Thus the external 
 surface of the gills of Fishes, Tadpoles, &c., is furnished with cilia; the con- 
 tinual movement of which renews the water in contact with them, and thus 
 promotes the aeration of the blood. In the lower Mollusca, and in many 
 Zoophytes, which pass their lives rooted to one spot, the motion of the Cilia 
 serves not merely to produce currents for respiration, but likewise to draw 
 into the mouth the minute particles that serve as food. [Fig. 107, 2, 5.] 
 And in the free-moving Animalcules, 
 
 of various kinds, the Cilia are the [Fig. 40. 
 
 sole instruments which they possess, 
 not merely for producing those cur- 
 rents in the water, which may bring 
 them the requisite supply of air and 
 food, but also for propelling their 
 own bodies through the liquid ele- 
 ment. This is the case, too, with 
 many larger animals of the class 
 Acalepha (Jelly fish), which move 
 through the water, sometimes with 
 great activity, by the combined ac- 
 tion of the vast numbers of cilia, that 
 clothe the margins of their external 
 surfaces. In these latter cases, it 
 
 11 'PI /^1*l* in.*-' ^^t*-miAoov^ij JLWJ. y ttvvvisct c.',< in^o, ouwwuig k;iUtX fill 1C 31 
 
 WOuld seem as if the Ciliary move- and in motion; 2, ciliated epithelium particles from the 
 
 ment were more under the control 
 of the will of the animal, than where 
 it is concerned only in the organic 
 functions. In what way the will 
 can influence it, however, it does 
 not seem easy to say ; since the 
 ciliated epithelium-cells appear to be perfectly disconnected from the surface 
 on which they lie, and cannot, therefore, receive any direct influence from 
 their nerves. Of the cause of the movement of the Cilia themselves, no ac- 
 count can be given ; they are usually far too small to contain even the minutest 
 13 
 
 ^xamplesof Cilia; l,poriionof abarofthe gtllof 
 the sea-mussel, Mytilus edulis, showing ciha at rest 
 
 frog's mouth; 3, ciliated epithelium particles from in- 
 ner surface of human membrana tympani ; 4, ditto, 
 ditto, from the human bronchial mucous membrane 
 5, Leucophrys patula, a polygastric infusory animal- 
 cule; to show its surface covered with cilia, and the 
 mouth surrounded by them.] 
 
146 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 fibrillae, of muscle; and we must regard them as being, like those fibrillae, 
 organs sui generis, having their own peculiar endowment, which is, in the 
 higher animals at least, that of continuing in ceaseless vibration, during the 
 whole term of the life of the cells to which they are attached. 
 
 [That this movement is truly molecular and independent of muscular influence and of 
 both the vascular and nervous systems has been proved by experiment. For, besides continu- 
 ing to manifest itself in a single particle for many hours a%r it has been isolated from 
 the rest of the system, a ciliated surface continues unaffected in its movements though the 
 supply of blood to the subjacent tissues be completely cut off. Neither do hydrocyanic 
 acid, opium, strychnine, belladonna, substances which affect powerfully the nervous sys- 
 tem, exert any influence on ciliary motion ; this phenomenon continuing in the bodies of 
 animals killed by these poisons. And lastly, shocks of electricity passed through the ciliated 
 parts, even the removal of the brain and spinal marrow in frogs, extinguishing as it does 
 muscular motion, do not destroy the action of cilia. M. C.] 
 
 The length of time during which the Ciliary movement continues after the 
 general death of the body, is much less in the warm-blooded than in the cold- 
 blooded animals; and in this respect it corresponds with the degree of per- 
 sistence of muscular irritability, and of other vital endowments. 
 
 173. A layer of Ciliated epithelium, of the Tesselated form, is found upon 
 the delicate pia mater which lines the cerebral cavities, not even excepting the 
 infundibulum and the aqueduct of Sylvius ; and it is also found in the termi- 
 nal* ramifications of the bronchial tubes. A Cylindrical epithelium furnished 
 with Cilia is found lining the nasal cavities, the frontal sinuses, the maxillary 
 antra, the lachrymal ducts and sac, the posterior surface of the velum pendu- 
 lum palati, and fauces, the Eustachian tube, the larynx, trachea, and bronchi 
 to their finest divisions, the upper portion of the vagina, the uterus, and the 
 Fallopian tubes. The function of the Cilia in all these cases appears to be 
 the same; that of propelling the secretions, which would otherwise accumu- 
 late on these membranes, towards the exterior orifices, whence they may be 
 carried off. 
 
 174. The Epithelium-cells, like the scales of the Epidermis, are continually 
 being cast off and renewed from the subjacent surface; but the rapidity of 
 this renewing process varies according to the particular function of the part. 
 Thus we shall hereafter find it to be greater on the Mucous Membranes, 
 which are actively engaged in the introduction of nutrient materials and in the 
 separation of effete matter, than it is on the Serous surfaces, which are com- 
 paratively inert. The epithelial cells that cover the plane surfaces, seem to 
 be developed from granular germs, scattered through the subjacent basement 
 membrane ; but it is different in regard to the cells of the glandular follicles, 
 which usually seem to originate in a single " germinal spot," composed of a 
 mass of granules, at the blind extremity of the follicles. In fact, each of these 
 follicles may be regarded as a parent-cell, which was closed at an earlier 
 period of its existence, and which, even after it has ruptured and given exit 
 to its contents, goes on forming a succession of new generations from, its 
 
 nucleus. The accompanying figure represents 
 Fig. 41. two follicles of the liver of the common Crab, 
 
 which are seen to be filled with secreting cells ; 
 and it is evident, from a comparison of the sizes 
 of the cells at different parts, that they originate 
 at the blind extremity of the follicle, where there 
 is a germinal spot ; and that, as they recede 
 from that point and approach the outlet of the 
 TWO follicles from the liver of Car- follicle, they gradually increase in size and be- 
 dnus nuznas (Common Crab), with come filled with their characteristic secretion ; be- 
 their contained secreting cells. ing at the same time pushed onwards towards 
 
 
SECRETING CELLS. SEROUS AND SYNOVIAL MEMBRANES. 147 
 
 the outlet, by the continual new growth of cells at the germinal spot.* It is 
 by the continual growth and exuviation of the cells which line the glandular 
 follicles, that the various products of Secretion are separated from the blood ; 
 and it is in cells occupying a similar position, that the Spermatozoa or Repro- 
 ductive particles are developed (Plate I., Fig. 18). In each case, the growth 
 of the cell, and the nature of its product, depend upon its own peculiar 
 vital properties; and it is a curious fact that'the seminal cells, in which the 
 -Spermatozoa are formed, are ejected from the gland in the Decapod Crusta- 
 ceous animals, not only before they have burst and set free the Spermatozoa, 
 but even long before the development of the Spermatozoa in their interior is 
 completed, the process being perfected, after the cells have been deposited 
 in the generative passages of the female.t 
 
 7. Of the Compound Membrano- Fibrous Tissues. 
 
 175. Having now considered the Elementary components of the Tissues 
 of the Human body, namely, Membranes, Fibres, and Cells, we proceed 
 to notice certain structures, in which these elements are united in their sim- 
 plest form ; and, in the first place, those termed Serous and Synovial Mem- 
 branes. When examined with the Microscope, their free surface is found to 
 be covered with a single layer of Pavement-Epithelium, which lies on a con- 
 tinuous sheet of Basement-Membrane. Beneath this last is a layer of con- 
 densed Areolar tissue, which constitutes the chief thickness of the membrane, 
 confers upon it its strength and elasticity ; this gradually passes into that 
 laxer variety, by which the membrane is attached to the parts it lines, and 
 which is commonly known as the subserous tissue. The yellow fibrous 
 element enters largely into the composition of the membrane itself; and its 
 filaments interlace into a beautiful network, which confers upon it equal elas- 
 ticity in every direction. The membrane is traversed by blood-vessels, nerves, 
 and lymphatics, in varying proportions. The Serous and Synovial mem- 
 branes form, as is well known, closed sacs, which contain a greater or less 
 proportion of fluid. The liquid effused from the Serous membranes is nearly 
 the same with the Serum of the blood; containing as much as 7 or 8 per cent. 
 
 . of albumen and salts ; and being distinctly alkaline, from the presence of 
 carbonate or albuminate of soda. There is no reason for regarding it in any 
 other light, than as a simple product of transudation. The fluid contained 
 in the Synovial capsules, and in the Bursae Mucosae, may be considered as 
 serum with from 6 to 10 per cent, of additional albumen; it shows an alka- 
 line reaction.^ The fluid of Dropsy (at least in some forms of this disease) 
 contains in addition urea, and cholesterine suspended in fine plates; also 
 (according to Dr. Kane) stearine and elaine. 
 
 176. The general term Mucous Membrane may be applied to that great 
 system of membranous expansions, which forms the external tegument, or 
 Skin, the lining of the internal cavities whose walls are continuous with it, 
 or Mucous Membrane proper, and the prolongations of this into the secre- 
 ting organs, forming the tubes and follicles of the Glands. These all consist, 
 as Mr. Bowman has justly remarked, "of certain elements, which the 
 Anatomist may detect and discriminate; some of them being essential, others 
 appended or superadded : and the broad characteristic distinctions between 
 
 * Goodsir, in Anatomical and Pathological Observations, Chap. v. 
 
 t Op. Cit. p. 39. 
 
 J This is probably a true secretion, formed by the agency of the epithelium-cells that cover 
 certain delicate highly-vascular fringe-like projections, which hang down into the sy no vial 
 capsules. 
 
 Cyclopedia of Anatomy and Physiology, vol. iii. p. 485. 
 
148 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 these structures, appreciable to ordinary sense as well as the innumerable 
 gradations by which they everywhere blend insensibly with one another, 
 are solely due to various degrees and kinds of modification wrought in the 
 form, quantity, and properties of these respective elementary parts." The 
 Mucous Membrane may be said, like the Serous, to consist of three chief 
 parts, the epithelium or epidermis covering its free surface, the subjacent 
 basement-membrane, and the areolar tissue, with its vessels, nerves, &c., 
 which forms the thickness of the membrane, and connects it to the adjacent 
 parts. Of the Epithelium and Epidermis, a general description has been 
 given in the preceding Section. The Basement-Membrane may be fre- 
 quently demonstrated with very little trouble, in the tubuli of the glands, 
 especially the kidney ; which are but very slightly adherent, by their exter- 
 nal surface, to the surrounding tissue. Its existence on the Skin, and on 
 many parts of the proper Mucous Membrane, has not yet been fully proved ; 
 but there can be no reasonable doubt of its continuity in these situations. 
 These two elements may be regarded as the essential constituents of Mucous 
 membrane ; which is thus found to be, strictly speaking, extra-vascular. Its 
 difference from Serous Membrane must be considered, therefore, as depend- 
 ing rather upon its arrangement, and upon the peculiar secretion of its epithe- 
 lium-cells, than upon any decided anatomical character. 
 
 177'. The tissues appended to these elements, and less essential to the 
 character of Mucous Membrane, are Capillary Blood-vessels, Absorbents, 
 
 Distribution of Capillaries at the sur- 
 face of the skin of the ringer. 
 
 Distribution of Capillaries in the 
 Villi of the Intestine. 
 
 Fig. 44. 
 
 Nerves, and Areolar tissue. The former are almost everywhere abundant ; 
 in the Skin they seem chiefly destined to supply the nervous papillae, and 
 thus minister to its acute sensibility ; whilst in the Mucous Membrane 
 of the Alimentary canal, they seem more concerned in the functions of Ab- 
 sorption and Secretion ; and in the Glandular organs, they supply the mate- 
 rials for the last-named process. The Absorb- 
 ents are most abundant, as Lymphatics, in the 
 Skin ; and as Lacteals, in the Mucous Mem- 
 brane of the first part of the Intestinal canal ; 
 but the Lymphatics are also largely distributed 
 through some of the Glandular organs. The 
 Skin is the only part of this system, which is 
 largely supplied with Nerves ; except the Con- 
 junctival Membrane, and the Mucous Mem- 
 brane of the ]Vose : hence the sensibility of this 
 structure is usually low, although its import- 
 ance in the organic functions is so great. The 
 Areolar tissue of Mucous Membranes usually 
 makes- up the greatest part of their thickness ; and is so distinct from the sub- 
 jacent layers, as to be readily separable from them. It differs not, however, 
 
 Distribution of Capillaries around 
 follicles of Mucous Membrane. 
 
STRUCTURE AND OFFICES OF MUCOUS MEMBRANE. 
 
 149 
 
 in any important particular, from the same tissue elsewhere; and the white 
 and the yellow fibrous elements may be detected in it, in varying propor- 
 tions, in different parts, the latter being especially abundant in the Skin and 
 the Lungs, which owe to it their peculiar elasticity. Hence the Mucous 
 Membranes for the most part yield Gelatine, on being boiled. There is some 
 reason to believe, that the Skin also contains non-striated muscular fibres 
 scattered through it. .The regeneration of all the forms of Mucous Mem- 
 brane, after loss of substance by disease or injury, is very complete, and takes 
 place with considerable rapidity. 
 
 178. The essential character of the Mucous Membranes, in regard alike to 
 their offices and their arrangement, is altogether different from that of the 
 Serous and Synovial membranes. For, whilst the latter form shut sacs, 
 whose contents are destined to undergo little change, the former either cover 
 the external surface of the body, or line tubes and cavities in its interior, 
 which have free outward communications; and they thus constitute the me- 
 dium, through which all the changes are effected, that take place between the 
 living organism and the external world. Thus, in the gastro-intestinal mucous 
 membrane, we find a provision for reducing the food, by means of a solvent, 
 fluid poured out from its follicles ; whilst the villi, or root-like filaments, 
 which are closely set upon the surface of that same membrane, are specially 
 adapted to absorb the nutrient materials thus reduced to the liquid state. This 
 same membrane, at its lower part, constitutes an outlet through which are cast 
 out, not merely the indigestible residuum of the food, but also the excretions 
 from numerous minute glandulse in the intestinal wall, which result from the 
 
 Fig. 45. 
 
 Diagram of the structure of an involuted Mucous Membrane, showing the continuation of its elements 
 in the follicles and villi ; F, F, two follicles ; b. basement membrane ; c, submucous tissue ; e, epithelium ; 
 r, vascular layer ; n, nerve ; v, villus, covered with epithelium; v', villus whose epithelium has been shed. 
 
 decomposition of the tissues, and which must be separated and cast forth from 
 them to prevent further decay. Again, the bronchio-pulmonary mucous mem- 
 brane serves for the introduction of oxygen from the air, and for the exhala- 
 tion of water and carbonic acid. The mucous membranes prolonged into the 
 
 13* 
 
150 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 interior of the various glands, are the instruments by which their respective 
 products are eliminated from the blood. And lastly, the Skin is concerned 
 in- two great classes of changes; the excretion of various matters from its 
 surface, and from the glandulae in its substance; and the reception of impres- 
 sions upon the nerves, with which it is so copiously supplied. 
 
 179. The character of the secretions formed by the Mucous Membranes, 
 is different in almost every part; and is dependent, as will be shown here- 
 after, upon the properties of the Epithelium-cells which cover them. These 
 cells, instead of forming a comparatively permanent stratum, like that which 
 covers the surface of serous membranes, are in a state of continual change 
 and renewal; the older layers falling off, whilst new ones are produced in 
 immediate contact with the subjacent membrane, and this, not merely on its 
 simple plane surfaces, but on its prolongations, whether these form the cover- 
 ings of villi, or the lining of follicles. The purpose of the cells which form 
 the Epidermis, is simply to protect the sensitive surface of the true skin; and 
 these cells have the power of drawing a horny matter into their interior. On 
 the other hand, the Epithelium cells of the ultimate tubuli or vesicles of glands, 
 contain the substances which characterize the secretions of those glands. It 
 is chiefly on the bronchio-pulmonary and gastro-intestinal mucous membranes, 
 that we meet with the peculiar secretion termed Mucus; which appears to be 
 expressly formed to shield them from the irritation they would suffer through 
 the contact of air, or of solids or liquids. This secretion is also found on 
 the lining membrane of the larger excretory ducts of most of the glands ; and 
 it is mixed, in greater or less amount, with most of the secretions discharged 
 by them. It is found also upon the lining membrane of the gall-bladder, 
 and of the urinary bladder. When these membranes are in a state of unusual 
 irritation, the amount of mucus which they discharge is very considerable; 
 but it ordinarily forms an extremely thin layer. The characters of Mucus, 
 obtained from various sources, are by no means invariable. In general, how- 
 ever, it may be described as a fluid pf peculiar viscidity, either colourless or 
 slightly yellow, transparent or nearly so, incapable of mixing with water, and 
 sinking in it, except when buoyed up by bubbles entangled in its mass, 
 which is commonly the case with the bronchial and nasal mucus. This 
 fluid contains from 4 to 65 per cent, of solid matter, of which a small part 
 consists of salts resembling those of the blood : whilst the chief organic con- 
 stituent is a substance termed Mucin, to which the characteristic properties of 
 the secretion are due. This appears to be an albuminous compound, altered 
 by the action of an alkali ; for as Dr. Babington has shown, any albuminous 
 fluid may be made to present the peculiar viscidity of mucus, by treating it 
 with liquor potassae. ' That the mucin of Mucus is held in solution by an 
 alkali, appears from this, that it is readily precipitated by acids, which neu- 
 tralize the base ; and that a sort of faint coagulation may be induced even by 
 water, which withdraws the base from it. When Mucus is examined with 
 the Microscope, it is found to contain numerous epithelium-scales (or flattened 
 cells) ; together with round granular corpuscles, considerably larger than 
 those of the blood, and closely resembling the nuclei of the epithelium-cells, 
 which are commonly termed mucus-corpuscles. In the more opaque mucus, 
 discharged from membranes in -a state of irritation or inflammation, these cor- 
 puscles are present in greatly-increased amount ; and cells are often developed 
 around them. 
 
 8. Of Simple Isolated Cells, forming Solid Tissues by their Aggregation. 
 
 180. We now proceed to a class of Cells, which are equally independent 
 of each other, which begin and end their lives as cells without undergoing any 
 
PERSISTENT CELLULAR PARENCHYMA. PLACENTAL CELLS. 151 
 
 transformation, but which form part of the substance of tire fabric, instead of 
 lying upon its free surfaces and being continually cast off from them. Still 
 their individual history is much the same as that of the cells already noticed ; 
 and they differ chiefly in regard to the destination of their products^ There 
 are many animals, in which such aggregations of cells make up a much larger 
 part of the fabric, than they do in Man ; and this in consequence of their re- 
 taining more of the embryonic type of structure in their adult condition. 
 Thus in the Myxinoid family of Fishes, there is no true Vertebral column ; 
 but its place is supplied by a gelatinous tube, termed the chorda dorsalis ; 
 which consists of nucleated cellular tissue, and which is precisely analogous 
 to the structure occupying the same position in the early embryo of higher 
 animals. In the Short Sunfish, a corresponding form of tissue forms a thick 
 covering to the body, replacing the true skin. And in the Lancelot (a little 
 Fish which is deficient in so many of the characters of the Vertebrated di- 
 vision, that many naturalists have doubted its right to a place in the class), a 
 considerable portion of the fabric is made up of a like cellular parenchyma. 
 
 181. The first group of this class deserving a separate notice, is that which 
 effects the introduction of aliment into the body ; of those kinds of aliment, 
 at least, which are not received in solution by any more direct means. These 
 cells (first pointed out by Mr. J. Goodsir) form a cluster at the extremity of 
 each of the villi of the intestinal tube ; the origin of the lacteal being lost in 
 the midst of it. If examined whilst the absorbent process is going on, they 
 are found to be turgid with a milky fluid, which is evidently the same with 
 that of the lacteals ; and to have a diameter of from 1 -2000th to 1-1 000th of 
 an inch (Fig. 46, A). In the intervals of the digestive process, the extremities 
 of the villi are comparatively flaccid : and instead of cells, they show merely 
 
 
 
 Fig. 46. 
 
 Extremity of intestinal villus; seen at A, during absorption, and showing absorbent cells and lacteal 
 trunks, distended with chyle ; at B, during interval of digestion, showing peripheral network of lacteals, 
 with granular germs of absorbent cells, as yet undeveloped, lying between them. 
 
 a collection of granular germs (Fig. 46, b). These begin to develope them- 
 selves, as soon as the food has been dissolved in the stomach and transmitted 
 to the intestine ; and their development goes on so long as they are surrounded 
 with nutrient matter. The cells grow, select, absorb, and prepare the nu- 
 tritious matter, by making it a part of themselves ; and, when their work is 
 accomplished, they deliver it to the lacteals by their own rupture or deliques- 
 cence, at the same time, it is probable, setting free the germs, from which a 
 new generation maybe developed, when the next supply of chyle is prepared. 
 182. Although the mucous membrane- of the intestinal tube is the only 
 channel, through which insoluble nutriment can be absorbed in the completely- 
 formed Mammal, and the only situation, therefore, in which we meet with 
 these absorbent cells, there are other situations, in which similar cells perform 
 analogous duties in the embryo. Thus, the Chick derives it nutriment, whilst 
 in the egg, from the substance of the yolk, by absorption through the blood- 
 vessels, spread out in the vascular layer of the germinal membrane that sur- 
 rounds it ; which vessels answer to the blood-vessels and lacteals of the per- 
 
152 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 manent digestive cavity, and are raised into folds or villi, as the contents of 
 the yolk-bag are diminished. Now the ends of the vessels are separated 
 from the fluid contents of the yolk-bag by a layer of cells, which is filled 
 with matter of a yellow-colour; and which seems to have for its office, to 
 select and prepare the materials supplied by the yolk, for being received into 
 the absorbent vessels. In like manner, me embryo of the Mammal is nou- 
 rished, up to the time of its birth, through the medium of its umbilical ves- 
 sels ; the ramifications of which form tufts, that dip down (as it were) into 
 the maternal blood, and receive from it the materials destined for the nutrition 
 of the foetus ; besides effecting the aeration of the blood of the latter, by 
 exposing it to the more oxygenated blood of its mother. Now around the 
 capillary loop of the fetal tuft there is a layer of cells, closely resembling the 
 absorbent cells of the villi ; and these are inclosed in a cap of basement-mem- 
 brane, which completes the fetal portion of the tuft, and renders it comparable, 
 in all essential respects, to the intestinal villus. It is again surrounded, however, 
 by another layer of membrane and of cells, belonging to the maternal sys- 
 tem ; the derivation of which will be explained hereafter (Chap. XVII). 
 
 183. The cells which make up the parenchyma of the Liver in the higher 
 animals, seem to be developed under conditions somewhat similar. In the 
 Invertebrata, the Liver is constructed upon the type of the glands in general ; 
 its secreting cells being developed as an epithelium upon the inner wall of the 
 hepatic ducts. This does not appear to be the case, however, in Man and the 
 Mammalia : the substance of whose liver is made up of an aggregation of 
 cells, which lie so far as can be ascertained upon the 
 Fig. 47. outside of the terminal ramifications of the hepatic ducts. 
 
 That these cells are the efficient instruments in the secre- 
 ting process, is evident from the nature of their contents, 
 which consist of biliary matter with oil globules. Their 
 diameter is usually from 1-1 500th to l-200th of an inch ; 
 and they generally contain a very distinct nucleus. Their 
 connexion with the secreting process is further marked by 
 the fact, that, in some instances in which the bile has not 
 been eliminated, and death has been the result, Microscopic 
 examination has proved that the hepatic cells were either 
 very imperfectly formed or were almost entirely deficient. 
 Further, in cases of Fatty Liver, the cells have been found to contain an un- 
 usual amount of Adipose matter. 
 
 184. The Fat-cells, of which Adipose tissue 
 is composed, also permanently exhibit the original 
 type of structure in .its simplest form. This tis- 
 sue is usually difFuse'd over the whole body, filling 
 up interstices, and forming a kind of pad or 
 cushion for the support of moveable parts. Even 
 in cases of great emaciation, some Fat is always 
 left ; especially at the base of the heart, around 
 the origin of the large vessels ; in the orbit of the 
 eye ; in the neighbourhood of the kidney ; in the 
 interior of the bones ; and within the spinal ca- 
 nal, between the periosteum and the dura mater. 
 The Fat Cells are usually spherical or spheroidal ; 
 sometimes, however, when closely pressed toge- 
 ther without the intervention of any intercellular 
 substance, they become polyhedral. The nucleus 
 is not always to be distinguished ; perhaps in 
 consequence of its having passed to the interior of 
 
 Secreting Cells of 
 Human Liver ; o, nu- 
 cleus; 6, nucleus ; c, 
 oil-particles. 
 
 [Fig. 48. 
 
 Fat vesicles, assuming the poly- 
 hedral form from pressure against 
 one another. The capillary ves- 
 sels are not represented. From 
 the omentum ; magnified about 300 
 diameters.] 
 
FAT CELLS ; COMPOSITION AND USES OF FAT. 
 
 153 
 
 the cell ; it has been seen, however, in the fat-cells of the embryo. The dia- 
 meter of the greater number of fat-cells, is between l-300th and l-600th of 
 an inch ; but larger and smaller sizes are frequently to be met with. These 
 bodies frequently present themselves in an isolated condition, dispersed among 
 the meshes of Areolar tissue ; but when they are aggregated so as to form 
 masses of fat, they are first collected into little lobular clusters, each of which 
 has a delicate membranous invest- 
 ment ; and these are again united into Fig. 49. 
 larger clusters, visible to the naked 
 eye. The aggregation of these often 
 forms masses of considerable size ; 
 the component parts being held toge- 
 ther by Areolar tissue, and also by the 
 blood-vessels which penetrate them, 
 and which ramify minutely among 
 them, forming a capillary network, 
 not only upon the surface of the 
 smallest lobules, but even (it would 
 appear) between their contained fat- 
 cells. In some forms of Adipose tis- 
 sue, such as the marrow of bones, it 
 
 would seem that very little areolar tissue exists, or that it is even entirely 
 absent ; and here the capillary plexus forms the principal bond of union be- 
 tween the fat-cells. No lymphatics have been detected in Adipose tissue ; 
 and it would seem to be equally destitute of nerves, excepting such as are 
 passing through it on their way to other textures ; thus accounting for the 
 known fact of its being insensible, except when those trunks are injured. 
 
 ' [Fig. 50. 
 
 Cells of Adipose Tissue ; magnified 135 diameters. 
 
 Blood-vessels of Fat; 1, minute flattened fat-lobule, in which the vessels only are represented ; 3, the 
 terminal artery ; 4, the primitive vein ; 5, the fat vesicles of one border of the lobule, separately repre- 
 sented, magnified 100 diameters; 2, planof the arrangement of the capillaries on the exterior of the 
 vesicles, more highly magnified.] 
 
 185. The consistency of the substance contained in the Fat-vesicles, varies 
 in different animals, according to the proportions of the organic elements, that 
 "enter into its composition. These elements are known under the names of 
 Stearine, Margarine, and Oleine: the two former, which are solid when sepa- 
 
154 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 [Fig. 51. 
 
 Fat vesicles from an emacia- 
 *ed subject; 1, 1, the cell-mem- 
 brane; 2,2,2, the solid portion 
 collected as a star-like mass> 
 with the elaine in connection 
 with it, but not filling the cell.] 
 
 rate, being dissolved in the latter, at the ordinary 
 temperature of the body. That the thick oil thus 
 formed does not escape from the fat-cells during 
 life, may be attributed to the moistening of their 
 walls by the aqueous fluid circulating through the 
 vessels. In all fixed oils, which are fluid at com- 
 mon temperatures, a portion of the solid constitu- 
 ents of fat exists ; these may be separated by ex- 
 posure to cold, which congeals them, leaving the 
 Oleine fluid. All these substances are regarded 
 by chemists in the light of salts ; being compounds 
 of acids the Stearic, Margaric, and Oleic with 
 a common base, to which, from its sweetish taste, 
 the name of Glycerine has been given. 
 
 a. Stearine is the essential constituent of nearly all solid fats, and preponderates in propor- 
 tion to their consistence. It exists largely in mutton-suet ; from this it may be obtained by 
 the action of ether, which takes up all the oily matter. It is crystalline, like spermaceti ; 
 it is not at all greasy between the fingers, and melts at about 130. It is insoluble in water, 
 and in cold alcohol and ether; but it dissolves in boiling alcohol or ether, crystallizing as it 
 cools. Stearic acid (the substance of which the stearine candles are composed) may be sepa- 
 rated, by causing it to combine with a stronger base, such as lime or potash, and then setting 
 it free from this by a stronger acid. It crystallizes in milk-white needles ; is soluble in its 
 own weight of cold alcohol, and in all proportions at a boiling heat; and fuses at about 158. 
 Its acid powers are sufficient to decompose the alkaline carbonates. Margarine exists in 
 small quantity, along with Stearine, with most fats ; but it is the principal solid constituent 
 of Human fat, which in this respect resembles olive oil rather than the other animal fats. It 
 corresponds with Stearine in many of its properties ; but it is much more soluble in alcohol 
 and ether; and it melts at 116. Margaric acid closely resembles stearic acid in most of its 
 properties; but it is more soluble in cold alcohol; and has a lower melting-point, viz., 140, 
 or thereabouts. It may be- procured from stearic acid, by subjecting the latter to a dry dis- 
 tillation. Oleine exists in small quantity in the various solid fats ; but it constitutes the great 
 mass of the liquid fixed oils. The tendency of these to solidification by cold, depends upon 
 the proportion of stearine or margarine they may contain ; for oleine itself remains fluid 
 at the zero of Fahrenheit's thermometer. It is soluble in cold ether, from which it can only 
 be separated by the evaporation of the latter. Oleic acid much resembles oleine in physical 
 characters, being colourless, lighter than water, and not prone to solidify j but it has a dis- 
 tinct acid reaction, and a sharp taste, and is miscible with cold alcohol in all proportions. 
 Glycerine, the base of all the fatty acids, may be obtained from any fatty matter, by saponi- 
 fying it with an alkaline base, by which this compound is set free. It cannot be obtained 
 in a solid form, but maybe brought to the consistence of a thick syrup. It dissolves in 
 water and alcohol ; but is insoluble in ether. It has a sweetish taste, whence its name is 
 derived ; and it is remarkable for its solvent powers, which are scarcely inferior to those of 
 water. The following table shows the 'atomic composition. of the fatty acids, and of their 
 base. 
 
 Stearic Acid ... .68 Carbon, 66 Hydrogen, 5 Oxygen. 
 
 Margaric Acid ... 68 Carbon, 66 Hydrogen, 6 Oxygen. 
 
 Oleic Acid . . . . 44 Carbon, 39 Hydrogen, 4 Oxygen. 
 
 Glycerine 6 Carbon, 8 Hydrogen, 6 Oxygen. 
 
 The following results of the ultimate analysis of different kind of Fat, show the close 
 correspondence in their composition ; and at the same time make apparent the very large 
 proportion of carbon which they all contain. 
 
 Carbon . . 
 Hydrogen . 
 Oxygen 
 
 Hog's Lard. 
 . 79-098 
 . 11-146 
 9-756 
 
 100-000 
 
 Mutton Fat. 
 
 78-996 
 
 11-700 
 
 9-304 
 
 100-000 
 
 Human Fat. 
 
 79-000 
 
 11-416 
 
 9-584 
 
 100-000 
 
 186. Besides the support, combined with facility, of movement, which Fat 
 affords to the moving parts of the body, it answers the important purpose of 
 assisting in the retention of the animal temperature, by its non-conducting 
 power; and the still more important object, of serving as a kind of reservoir 
 of combustible matter against the time of need. Herbivorous animals, whose 
 
STRUCTURE AND COMPOSITION OF CARTILAGE. 
 
 155 
 
 Fig. 52. 
 
 food is scanty during the winter, usually exhibit a strong tendency to such an 
 accumulation, during the latter part of the summer, when their food is most 
 rich and abundant ; and the store thus laid up is consumed during the winter. 
 This is particularly evident in the hybernating Mammalia, which take little or 
 no food during their seclusion. Fat appears to be deposited, only where there 
 is an excess, in the alimentary matter introduced into the body, of non-azo- 
 tized compounds which may be converted into it. But the-ingestion of a large 
 quantity of these in the food, is by no means sufficient for the production of 
 Fat ; for they may not be absorbed into the vessels ; and, if absorbed, there 
 may be a want of power to generate Adipose tissue, so that they would ac- 
 cumulate injuriously in the blood, if not drawn off by the Liver. Hence 
 some persons never become fat, however large the quantity of oily matter 
 ingested ; and it is in such persons, that the tendency to disorder of the Liver 
 from over-work is most readily manifested ; hence they are obliged to abstain 
 from the use of fat-producing articles of food. 
 
 187. In Cartilage, also, the simple cellular structure is very obviously re- 
 tained, and frequently exists alone ; although in some forms of this tissue, it 
 is united with the fibrous, or partly 
 replaced by it. In all, however, the 
 early stage of formation appears to 
 be the same. The structure origi- 
 nates in cells, analogous to those of 
 which the rest of the fabric is com- 
 posed ; but between these cells, a 
 larger quantity than usual of hyaline 
 or intercellular substance is depo- 
 sited ; and the amount of this sub- 
 stance continues increasing, simul- 
 taneously with the bulk of the cells. 
 The original cells are pushed far- 
 ther and farther from one another ; 
 but new cells arise between them 
 from germs which are contained in 
 the hyaline substance. The first 
 cells frequently produce two or more 
 young cells from their nuclei ; and 
 thus it is very common to meet with 
 
 groups of such cells or corpuscles, consisting of two, three, or four. The 
 varieties in the permanent Cartilages principally depend upon the degree of 
 
 c 
 
 Section of the Branchial cartilage of Tadpole; a f 
 group of four cells, separating from each other; 6, 
 pair of cells in' apposition ; c, c, nuclei of cartilage 
 cells ; d, cavity containing three cells. 
 
 organization, which subsequently 
 takes place in the intercellular sub- 
 stance. If a mass of Fibres, analo- 
 gous to those of the fibrous mem- 
 branes ( 138), should originate in 
 it, the Cartilage presents a more or 
 less fibrous aspect; in some instan- 
 ces the Fibrous structure is deve- 
 loped so much, at the expense of 
 the Cells, that the latter disappear 
 altogether, and the whole structure 
 becomes fibrous. Sometimes the 
 fibres which are developed, are 
 rather analogous to those of the 
 Elastic tissue ( 140) ; these are dis- 
 posed around the cells, forming a 
 kind of network, in the areolae of 
 
 Fig. 53. 
 
 Section of Fibro-Cartilage ; showing disposition of 
 cartilage cells, in areolae of fibrous tissue. 
 
1.56 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 which they lie; and this kind of cartilage may be termed the elastic or 
 reticular. The primitive cellular organization is for the most part retained 
 in the ordinary articular cartilages,* the cartilaginous septum narium, the car- 
 tilages of the alas and point of the nose, the semilunar cartilage of the eye- 
 lids, the cartilages of the larynx (with the exception of the epiglottis), the 
 cartilage of the trachea and its branches, the cartilages of the ribs (in Man) 
 and the ensiform cartilage of the sternum ; and it is seen also in the tempo- 
 rary cartilages, or those which are destined to undergo ossification. The 
 fibrous structure is seen in all those Cartilages, which unite the bones by 
 synchondrosis ; this is the case in the vertebral column and pelvis, the 
 cartilages of which are destitute of corpuscles, except in and near their cen- 
 tres. In the lower Vertebrata, however, and in the early condition of the 
 higher, the fibrous structure is confined to the exterior, and the whole interior 
 is occupied by the ordinary cartilaginous corpuscles. The reticular structure 
 is best seen in the epiglottis and in the concha auris : in the former of- these, 
 scarcely any trace of cartilage-cells remains ; in the latter, the fibrous net- 
 work disappears by degrees towards the extremity of the concha, and the 
 structure gradually passes into the cellular form.t 
 
 a. The substance that gives to the Cellular Cartilages their peculiar character, has received 
 the designation of Chondrine. It bears much resemblance to ordinary Gelatine, but requires 
 longer boiling in water for its solution ; the solution fixes on cooling, like that of gelatine ; 
 and when it becomes dry by evaporation, it has the appearance of solid glue. Chondrine 
 is not precipitated, however, by tannic acid; on the other hand, it gives precipitates with 
 acetic acid, alum, acetate of lead, and proto-sulphate of iron, which do not disturb a solution 
 of Gelatine. That the Chondrine obtained by boiling Cartilage is an actual component of 
 that tissue, and is not a product of the operation, appears from the agreement between its 
 elementary composition and that of cartilage, when analyzed by combustion. According to 
 Mulder, the proportions of the elements, as- deduced from the definite compound which 
 Chondrine forms with Chlorine, are 32 C, 26 H, 4N, 14 0, with l-10th of an equivalent of 
 Sulphur. Chondrine agrees much more nearly with the proteine-compounds, in its element- 
 ary composition, than does Gelatine ; and may be considered as a sort of intermediate stage 
 between the two. Chondrine is not obtainable from any of the Fibro-cartilages ; these 
 yield gelatine, on boiling, exactly similar to that of the tendons. The Elastic cartilages, 
 after being boiled for several days, yield a small quantity of an extract, which does not form, 
 a jelly, but which has the other chemical properties of Chondrine. .The cartilage of Bone, 
 before ossification, yields only Chondrine ; after ossification, however, it affords only Gelatine; 
 and it is curious that, even when bony deposits take place in the permanent cartilages, the 
 ossified portion contains ordinary Gelatine in the place of Chondrine. Many of the carti- 
 lages naturally contain a large proportion of mineral matter ; in the costal cartilages, frac- 
 tures in which are generally repaired by osseous substance, from 3 to 7 per cent, of ash is 
 left by calcination. This contains a large proportion of the carbonate and sulphate of soda, 
 together with carbonate of lime and a small proportion of phosphate ; as age advances, the 
 phosphate of lime predominates, and the soluble compounds diminish. 
 
 188. Cartilage (at least in its simplest form) is nourished, without coming 
 into direct relation with the Blood through the medium of blood-vessels ; the 
 cellular Cartilages not being penetrated by vessels in the healthy state; al- 
 though in certain diseased conditions they become distinctly vascular. They 
 are, however, surrounded by Blood-vessels ; which form large ampullae or 
 varicose dilatations at their edges or on their surfaces (Fig. 54) : and from 
 these the Cartilages derive their nourishment .by imbibition ; in exactly the 
 same manner as the frond of a Sea-weed (the structure of which is alike cel- 
 lular) draws into itself the requisite fluid from the surrounding medium. In 
 the thicker masses of cartilaginous tissue, however, such as the cartilages of 
 
 * The articular cartilages, at the points where tendons are implanted into them, have all 
 the characters of fibro-cartilage ; the fibres of the tendon being spread through the intercel- 
 lular substance of the cartilage, for some distance, and gradually coalescing with it. 
 
 f See Mr. Toynbee's Memoir on the Non- Vascular Tissues, Phil. Trans. 1841. 
 
STRUCTURE AND COMPOSITION OF CARTILAGE. 
 
 157 
 
 the ribs, we find canals excavated at wide distances from each other ; which 
 are lined by a continuation of the perichondrium or investing membrane of 
 the cartilage, and which thus allow 
 
 its vessels to come into nearer prox- Fig. 54 - 
 
 imity with parts, that would be other- 
 wise too far removed from them. 
 The vessels, however, nowhere pass 
 from the walls of these canals into 
 the substance of the cartilage. Si- 
 milar vascular canals are found in the 
 temporary cartilages, near the points 
 where the ossifying process is taking 
 place ; this is well seen in the long 
 bones, towards their extremities. At 
 an early period of foetal life, there is 
 HO distinction between the cartilage that is ultimately to become the Osseous 
 Epiphysis, and*that which is to remain as Articular Cartilage ; both are alike 
 cellular ; and the vessels that supply them with nutrient materials penetrate 
 no further than their surfaces. At a subsequent period, however, when the 
 ossification of the epiphysal cartilage is about to commence, vessels are 
 prolonged into it ; and a distinct line of demarcation is seen betwixt the vas- 
 cular portion, which is to be converted into Bone, and the non-vascular part, 
 which is to remain as Cartilage. At this period, the Articular Cartilage is 
 
 Fig. 55. 
 
 Vessels between the Articular Cartilage and attached 
 Synovial Membrane. (After Toynbee.) 
 
 Vessels situated between the attached synovial membrane, and the articular cartilage, at the point 
 where the ligamentum teres is inserted in the head of the os femoris of the human subject, between the 
 third and fourth months of foetal life ; a, the surface of the articular cartilage ; 6, the vessels between the 
 articular cartilage and the synovial membrane ; c, the surface to which the ligamentum teres was at- 
 tached ; d, the vein ; , the artery. 
 
 nourished by a plexus of vessels spread over its free surface, beneath its sy- 
 novial membrane; as well as by the vessels, with which it comes in contact 
 at its attached extremity. Towards the period of birth, however, the sub-sy- 
 novial vessels gradually recede from the surface of the articular cartilage ; and 
 at adult age they have entirely left it, though they still form a band which 
 surrounds its margin. The Fibrous cartilages are somewhat vascular ; but 
 the vessels do not extend to the cellular portions, where such exist. 
 
 189. No vessels can be traced (according to Mr. Toynbee) into the sub- 
 stance of the true Cornea ; which, contrary to the statement of Miiller, is a 
 cellular rather than a fibrous cartilage. The cells are not so numerous as are 
 those of the articular cartilages; and they are surrounded by a plexus of bright 
 14 
 
158 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 Fig. 56. fibres, laxly connected together, so as to re- 
 
 semble areolar tissue. Two sets of vessels, a 
 superficial and a deep-seated, surround the mar- 
 gin of the cornea. The arteries of the former 
 are prolonged for a short distance upon the 
 Conjunctival membrane, which forms the outer 
 lamina of the cornea ; but they terminate in 
 veins at from a to a line from its margin. 
 The deep-seated vessels belong to the Cornea 
 proper ; but they do not enter it, the arteries 
 terminating in veins just where the tissue of 
 the Sclerotic becomes continuous with that of 
 the Cornea. In diseased conditions of the 
 Cornea (as of the articular cartilages), both sets 
 of vessels extend themselves through it ; the 
 superficial not unfrequently form a dark band 
 of considerable breadth round its margin ; 
 whilst the deep-seated are prolonged into its 
 entire substance. Notwithstanding the absence 
 of vessels in the healthy condition of this struc- 
 ture, incised wounds commonly heal very rea- 
 dily, as is well seen after the operation of ex- 
 traction of Cataract ; but the foregoing details 
 make evident the importance of not carrying 
 
 the incision further round than is necessary ; since the corneal tissue should 
 not be cut off from the supply of nourishment, afforded by the vessels in its 
 immediate proximity. 
 
 [This structure has been recently studied by Messrs. Todd and Bowman, and is described 
 by them with great accuracy. We subjoin their description. " The cornea, though a beau- 
 tifully transparent substance, and appearing at first sight as homogeneous as glass, is never- 
 theless full of elaborate structure. It is in fact composed of five coats or layers, clearly 
 distinguishable from one another. These are, from before backwards, the conjunctival layer 
 of epithelium, the anterior elastic lamina, the cornea proper, the posterior elastic lamina, and the 
 epithelium of the aqueous humour, or posterior epithelium. The cornea, when uninflamed, con- 
 tains no blood-vessels; those of the surrounding parts running back in loops, as they arrive 
 at its border. 
 
 On the coj-nea proper, or lamellated cornea, the thickness and strength of the cornea mainly 
 depend. It is a peculiar modification of the white fibrous tissue, continuous with that of the 
 sclerotic. At their line of junction (fig. 57), the fibres, which in the sclerotic have been 
 
 Fig. 57. 
 
 Nutrient Vessels of the cornea. A, 
 superficial vessels belonging to the 
 Conjunctival membrane, and continu- 
 ed over the margin of the Cornea ; B, 
 vessels of the Sclerotic, returning at 
 the margin of the Cornea. 
 
 Vertical section of the Sclerotic and Cornea, showing the continuity of their tissue between the dotted 
 lines: a. Cornea, b. Sclerotic. In the cornea the tubular spaces are seen cut through, and in the 
 sclerotic the irregular areolce. Cell-nuclei, as at c, are seen scattered throughout, rendered more plain 
 by acetic acid. Magnified 320 diameters. 
 
CORNEA, AND CRYSTALLINE LENS. 
 
 159 
 
 densely interlaced in various directions, and mingled with elastic fibrous tissue, flatten out 
 into a membranous form, so as to follow in the main the curvatures of the surfaces of the 
 cornea, and to constitute a series of more than sixty lamellae, intimately united to one ano- 
 ther by very numerous processes of similar structure, passing from one to the other, and 
 making it impossible to trace any one lamella over even a small portion of the cornea. The 
 resulting areolae, which in the sclerotic are irregular, and on all sides open, are converted in 
 the cornea into tubular spaces, which have a very singular arrangement, hitherto undescribed. 
 They lie in superposed planes, the contiguous ones of the same plane being for the most part 
 parallel, but crossing those of the neighbouring planes at an angle, and seldom communica- 
 ting with them (fig. 58). The arrangement and size of these tubes can be shown by 
 
 Fig. 58. 
 
 Tubes of the Cornea Proper, as shown in the eye of the Ox by mercurial injection. Slightly magnified. 
 
 driving mercury, or coloured size, or air, into a small puncture made in the cornea. They 
 may also be shown under a high power by moistening a thin section of a dried cornea, and 
 opening it out by needles. The tissue forming the parietes of these tubes is membranous 
 rather than fibrous, though with the best glasses a fibrous striation may be frequently seen, 
 both in the laminae separating the different series of tubes, and in that dividing those of the 
 same layer from each other. By acetic acid, also, the structure swells, and displays corpus- 
 cles resembling those apparent in the white fibrous tissue. Such is the lamellar structure of 
 the cornea, which makes it so much easier to thrust an instrument horizontally than verti- 
 cally into its substance. The tubes or elongated spaces of which we have spoken, are not 
 distended with any fluid, but are merely moistened in the same way as the areolae of ordi- 
 nary areolar tissue. A perfectly fresh and transparent cornea is rendered opaque by pres- 
 sure, but it regains its brilliance on the removal of the compressing force. Some have sup- 
 posed this to result from the expulsion of fluid from between its laminae ; but that the opa- 
 city is owing simply to a derangement of the elementary parts of its structure is plain from 
 the fact, that the same phenomena are exhibited by a section, however thin, immersed in 
 water, and deranged by stretching.] 
 
 190. In connection with the cornea, it is natural to allude to the Crystal- 
 line lens and Vitreous humour, which have a structure essentially the same. 
 The structure of the Crystalline lens has long been known to be fibrous ; and 
 Sir D. Brewster has shown, by the aid of polarized light, the very beautiful 
 manner in which the fibres are arranged.* They are united into laminae, by 
 means of numerous teeth or sinuosities at their edges, which lock into one 
 another. That these fibres originate in cells, has been clearly ascertained ; 
 but the nature of the metamorphosis has been differently stated by two emi- 
 nent observers, Schwann and Barry. By the former, the fibres are considered 
 to be prolonged cells : whilst the latter regards them as rather formed upon 
 the plan of the tubes of muscular fibre ( 235), several cells coalescing into 
 one ; in this he is supported by Mr. Toynbee* who states that he has fre- 
 quently seen the fibres, towards the margin of the lens, made up of such cells. 
 After it is fully formed, however, it is not permeated by blood-vessels ; these 
 being confined to the capsule. During the early part of foetal life, and in in- 
 flammatory conditions of this membrane, both the anterior and posterior por- 
 tions of the capsule are distinctly vascular; but at a later period, according to 
 
 * Philosophical Transactions, 1833. 
 
160 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 Mr. Toynbee, the posterior half only O f the capsule has vessels distributed 
 over it surface ; and these are derived from the Arteria centralis retinae. 
 From optical experiments which have been suggested to him by this circum- 
 stance, he infers that "objects (radiating lines for instance), situated on the 
 anterior surface of the crystalline lens, produce an indistinctness in the image 
 which is formed upon the retina; whereas, when these lines exist upon the 
 posterior surface of the lens, the image is clear." The substance of the Lens 
 contains about 42 per cent, of animal matter, with 58 parts of water. Nearly 
 the whole of the former may be dissolved in cold water by trituration ; the 
 solution is coagulated by heat, and forms a granular but not coherent mass; 
 alcohol and acids produce the same effect. Hence it appears that the Lens 
 chiefly consists of albumen in its soluble form ; and this may be supposed 
 to be contained in the cavities of the cells, as it is in those of the vitreous 
 humour. From the latest analyses, it appears that the substance of the lens 
 corresponds most with that modification of albumen, which forms the Glo- 
 buline of the blood ( 147). In the Vitreous humour, we have an example 
 of a very loose form of cellular tissue ; strongly resembling that which con- 
 stitutes the entire structure of Acalephae (Jelly-fish). That the cells com- 
 posing it have no open communication with each other, is evident from the 
 fact that, when the general enveloping membrane is punctured in several 
 places, it is long before the contained fluid entirely drains away. This 
 fluid is analogous to that of the Aqueous humour ; being little else than Wa- 
 ter, holding a small quantity of Albumen and Saline water in solution. From 
 Mr. Toynbee's inquiries it would appear, that the vessels which pass through 
 the Vitreous humour do not send branches into its substance ; but that it is 
 nourished by the vessels, which are minutely distributed upon its general en- 
 velope. The Ciliary processes of the Choroid membrane are almost entirely 
 composed of large, plexiform vessels, closely resembling those of synovial 
 membrane (Fig. 54), which allow a great quantity of blood to circulate through 
 them ; and these have probably an important share in the nutrition of the Vi- 
 treous body. 
 
 191. Cartilage is perfectly insensible ; and neither nerves nor lymphatics 
 can be traced into its substance. Its functions are purely mechanical ; the 
 consolidation of its texture by internal deposit renders it little disposed to 
 change by spontaneous decay ; and it is protected by its toughness and elas- 
 ticity from those injuries, to which softer or more brittle tissues are liable. 
 These very circumstances, however, interfere with the activity of its nutrition. 
 Cells which are choked up with interior deposit do not readily transmit fluid : 
 it is doubtful whether any interstitial change can take place in the interior of 
 a permanent Cartilage (except when it has become vascular by disease, or 
 undergoes ossification), through the whole of life; and there seems ground to 
 believe that, when it has been injured by disease or accident, the loss of sub- 
 stance is not repaired by real cartilaginous tissue. In the process of uleera- 
 tion of Cartilage (as observed by Mr. J. Goodsir),it appears that the formation 
 of depressions on the surface is due, not so much to any change originating 
 in the substance of the cartilage, as to the eroding action of the cells of the 
 false membrane, which is the product of inflammatory action upon its surface ; 
 and it is in this false membrane that the new vessels are formed, which dip 
 down into nipple-like prolongations of the membrane, entering corresponding 
 hollows excavated in the cartilage. On the other hand, the softer tissues of 
 the Eye are capable of complete regeneration. Every oculist is aware that 
 a great loss of Vitreous humour may take place without permanent injury; 
 and it has been found that even the Crystalline lens may be completely rege- 
 nerated, after it has been entirely removed by extraction. 
 
CALCIFICATION OF FIBRES AND CELLS. 
 
 161 
 
 Fig. 59. 
 
 9. Tissues consolidated by Earthy deposit. Bones and Teeth. 
 
 192. Both the Fibres and Cells of the Animal tissue, there is reason to be- 
 lieve, may be consolidated by mineral deposits ; these being chemically united 
 with the Gelatine of the Fibres ; or secreted, either alone, or in combination 
 with gelatine, into the cavities of the 
 Cells, by their own inherent powers. 
 We have an example of the form- 
 ation of a skeleton by the consoli- 
 dation of fibres, in the shell and 
 other hard parts of the Echinoder- 
 mata ; the intimate structure of which, 
 as shown by the Microscope, strong- 
 ly reminds us of Areolar tissue that 
 might have undergone the calcifying 
 process. Again, we have an exam- 
 ple of the formation of a skeleton 
 by the deposit of mineral matter in 
 the cavities of cells, in the shells of 
 Mollusca; in many of which (espe- 
 cially among the Bivalves) the cellu- 
 lar character is permanently shown, 
 a consistent membrane being left, 
 after the Carbonate of Lime that consolidated 
 away by an acid. An arrange- 
 ment precisely similar, as regards 
 the animal constituent, is found 
 in the Enamel of Teeth ( 215) ; 
 the only difference being in the 
 consolidating material, which is 
 chiefly the Phosphate of Lime, 
 a mineral far harder than the 
 
 Calcified Areolar Structure, of which the Skele- 
 ton of the Echinodermata is composed ; from the 
 Spine of an Echinus. Magnified 150 diameters. 
 
 the cell has been dissolved 
 
 Fig. 60. 
 
 Cellular membrane, left after the removal of the Cal- 
 careous matter from the shell of Pinna. Magnified 185 
 diameters. 
 
 Carbonate. It is not always, 
 however, that the original cells 
 preserve their character so dis- 
 tinctly; for it is very commonly 
 found, that they have coalesced 
 with each other, in such a man- 
 ner as not to be distinguishable 
 in the fully-formed tissue. We 
 also frequently observe, in the 
 skeletons of Vertebrata, that the 
 
 whole substance is not consolidated, but that cavities and channels are left in 
 it ; which seem destined to perform some office connected with the interstitial 
 changes, that continue to take place in the tissues subsequently to their first 
 formation. It has been already pointed out ( 5), that the internal bony ske- 
 letons of Vertebrated animals are destined to undergo a degree of interstitial 
 change (in order to adapt them to the progressive growths of the parts that 
 cover them), which is not required in the external envelopes of Invertebrated 
 animals ; these being capable of sufficient enlargement by addition to their 
 edges merely ; or else being periodically thrown off, and renewed upon a 
 larger scale. It is obvious that, if the whole substance be consolidated by 
 calcareous deposit, there can be no permeation of nutritive fluid through it; 
 but, on the other hand, if it be traversed by tubuli, commencing from the near- 
 est vascular surface ; or if a series of minute chambers, connected by still 
 
 14* 
 
162 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 more minute passages, be excavated in its substance, it is evident that, even 
 though blood cannot circulate through it, a nutritive fluid drawn from the 
 blood, may be carried into its minutest parts. This is the kind of structure 
 which we find in Bone, and in the principal substance of Teeth. The mode 
 in which it is generated, will become the subject of inquiry hereafter. 
 
 193. When examined with the naked eye, it is seen that Bone possesses 
 in some degree a laminated texture : in the long bones, the external and in- 
 
 Fig. 61. 
 
 Portion of Transverse Section of Human Clavicle, showing the orifices of the Haversian canals, and 
 the concentric arrangement of the laminae of bony matter, and of the lacunas, around them. Magnified 
 85 diameters. 
 
 ternal laminae are arranged concentrically round the medullary canal ; and in 
 the flat bones, they are parallel to the surface. Towards the extremities of 
 the long bones, and between the external plates of the flat bones, are a num- 
 ber of cancelli, or small hollows bounded by very thin plates of bone ; these 
 communicate with the medullary canal where it exists ; having, like it, an 
 extremely vascular lining membrane ; and their cavities being filled with a 
 peculiar adipose matter. The hard substance of the bone also is traversed by 
 canals, on which the name of Haversian has been bestowed, after their disco- 
 verer ; these canals run for the most part in the direction of the laminee ; but 
 they have many transverse communications, both with each other and with 
 the medullary cavity, so that they form a complete network, which is lined 
 by a continuation of the membrane of the latter. Their diameter varies from 
 l-200th to 1 -2000th of an inch; the average being probably about 1-500. 
 The smaller ones contain only a single capillary vessel ; but several such ves- 
 sels seem to exist in the larger ones, together with adipose matter. When a 
 thin transverse section of a long bone is made, and is highly magnified, it is 
 seen that the bony matter of the greater part of its thickness is arranged in 
 concentric circles round the orifices of the canals ; these circles are marked 
 by a series of stellated points ; and when the latter are magnified still more 
 highly, it is seen that they are cavities or lacunae of a peculiar form, which 
 seems characteristic of Bone. They are usually oval or lenticular in form ; 
 and are so placed, that one of their largest surfaces is turned from, and the 
 
STRUCTURE OF BONE. , 163 
 
 other towards, the Haversian canal. Their long diameter is commonly from. 
 [Fig. 62. [Fig. 63. 
 
 Transverse section of the compact tissue 
 of along Bone; showing 1, the periosteal 
 layer; 2, the medullary layer, and the inter- 
 mediate Haversian systems of lamellae, each 
 perforated by an Haversian canal. Mag- 
 nified about 15 diameters.] 
 
 Transverse section of the compact tissue of a Tibia 
 from an aged subject, treated with acid ; showing the 
 appearance of lamellae surrounding the Haversian ca- 
 nals. Portions of several systems of lamellae are seen. 
 The appearance of the lacunae, when their pores are 
 filled with fluid, is also seen, as well as the radiation 
 from the canals which then remain. From Mr. Tomes.] 
 
 
 1 -2400th to 1-1 600th of an inch ; their short diameter is about one-third, and 
 their thickness about one-sixth, of their length. 
 
 a. It has been lately shown by Mr. J. Quekett, that there are differences in the form and 
 size of the lacunae, in the several classes of animals, sufficiently characteristic to allow of the 
 assignment of minute fragments of bone, with the aid of the microscope, to their proper class. 
 The lacunse of Reptiles are distinguishable by their large size, and long oval form; and those 
 of Fish, by their angular form and the fewness of the radiating canaliculi. The osseous 
 lacume of the Bird may be distinguished from those of the Mammal, partly by their smaller 
 size, but chiefly by the remarkable tortuosity of their canaliculi, which wind backwards and 
 forwards in such a manner, as frequently to destroy the concentric lamellar appearance. It 
 is interesting to remark further, that the sizes of the lacunse in the four classes of the Verte- 
 b rated animals, bear a close relation to the sizes of their blood-corpuscles. Here, as else- 
 where, the dimensions of the ultimate parts of the tissue are tolerably constant in each group 
 of animals, and show little variation in accordance with the size of the species ; thus there 
 is little or no perceptible difference in the size of the elements of the osseous tissue of the 
 enormous extinct Iguanodon, and of the smallest Lizard now inhabiting the earth. 
 
 Fig. 64. 
 
 194. From all parts of these cavities, 
 but especially from their two largest 
 surfaces, proceed a large number of 
 minute tubuli, which traverse the sub- 
 stance of the bone, and communicate 
 irregularly with one another. Their 
 direction, however, possesses a certain 
 degree of determinateness ; for those 
 passing off from the inner surface con- 
 verge towards the Haversian canal ; 
 whilst those passing off from the outer 
 
 c i- ,1 j. ijacunae 01 osseous ouosiance ; masrinueu 
 
 surface diverge in the contrary direc- ^ diameters: central c u avity . 6> ' it8 ramifica . 
 
 tion, so as to meet and inosculate with tions. 
 
 those proceeding inwards from the 
 
 cavities of the next annulus. In this manner, a communication is kept up 
 
 between the Haversian canal, and the most external of its concentric lamellae 
 
 Lacunae of Osseous Substance; magnified 
 
164 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 Haversian canals, seen on a 
 longitudinal section of the com- 
 pact tissue of the shaft of one of 
 the long bones: 1, arterial canal; 
 2, venous canal ; 3, dilatation of 
 another venous canal.] 
 
 of bone. It is not to be imagined, however, that blood can be conveyed by 
 these tubuli, their size being far too small ; for 
 [Fig. 65. their diameter, at their largest part, is estimated at 
 
 from 1-1 4,000th to l-20,000th of an inch, whilst 
 that of the smaller branches is from l-40,000th to 
 l-60,000th of an inch ; so that the blood-corpus- 
 cles could not possibly enter them. But it may be 
 surmised that they draw fluid from the nearest 
 blood-vessels, and thus keep up a sort of circulation 
 through the osseous substance, which may con- 
 tribute to its growth, and may keep it in a state fit 
 for repairing itself, when injured by disease or vio- 
 lence. The lacunas, however, do not seem to be 
 unoccupied in the living bone ; for each contains 
 (according to Mr. J. Goodsir) a minute granular 
 substance, which seems to be identical with the 
 nucleus of the original bone-cell, and which pro- 
 bably serves as a " nutritive centre," attracting to 
 itself, through its own system of canaliculi, the 
 nutritive materials supplied by the blood-vessels of 
 the nearest surface, and diffusing these through the 
 surrounding substance.* 
 
 195. Although a large quantity of blood is sent 
 to Bone, the vessels do not penetrate its minute 
 parts ; being confined to the Medullary cavity, 
 and to the Haversian Canals, and Cancelli, which 
 are prolongations of it. The substance of the Bone, 
 therefore, is really as non-vascular as that of Carti- 
 lage ; the only difference being, that it is channelled out by more numerous 
 inflexions of the external surface, and that the vessels are thus brought into 
 nearer proximity with its several parts. The delicate osseous lamella, which 
 form the walls of the cancelli, and of the large cells excavated in some of the 
 cranial bones, have a structure precisely analogous to that of the cylindrical 
 laminae surrounding the Haversian canals of the long bones ; and derive their 
 nourishment from the vascular membrane covering their surface, through the 
 medium of a similar set of lacunas and canaliculi. They do not themselves 
 contain Haversian canals or cancelli ; because no part of their substance is far 
 removed from a vascular membrane. The cylindrical rods, that make up the 
 hollow shaft of a long bone, are connected together by solid osseous sub- 
 stance, which is composed of lamellae running parallel to the external surface 
 of the bone ; and these derive their nutriment either from the periosteum, or 
 from the membrane lining the great central medullary cavity ; according as 
 they are nearest to one or to the other. The membranous lining of the canals 
 of Bone appears to be supplied with lymphatics, and also with nerves ; but 
 with both in a very limited amount. The periosteum seems to be scarcely 
 (if at all) sensible in the state of health, although painfully, so-when inflamed ; 
 and the same may be said of the membrane lining the Haversian canals and 
 cancelli. The membrane lining the central medullary cavity, however, is more 
 
 * The lacunae and canaliculi of Bone were formerly supposed, on account of the black 
 appearance th/ey exhibit under the Microscope, to be filled with opaque matter 5 but this ap- 
 pearance is common to all cavities excavated in a highly-refracting substance (being shown 
 by a bubble of air in water), and ceases when a very thin section of Bone is examined, es- 
 pecially if it have been placed in Canada Balsam. In the Bones of Mummies, they are found 
 to be filled with a waxen material ; and in those which have lain in bogs, they are rendered 
 peculiarly distinct by the infiltration of some of the surrounding black matter : so that their 
 power of imbibing liquids is clearly proved. 
 
STRUCTURE AND COMPOSITION OF BONE. 165 
 
 sensitive ; since unequivocal signs of pain are manifested by an animal, when, 
 a bone having been sawn across, a probe is passed up the cavity, or an acrid 
 fluid is injected into it. 
 
 196. The ultimate substance of Bone, lying between the lacunae and cana- 
 liculi, appears to be usully granular ; the granules are stated by Mr. Tomes* 
 to be often distinctly visible without any artificial preparation, in the sub- 
 stance of the delicate spicula of the cancelli, when they are viewed with a 
 high power ; and to be made very evident by prolonged boiling in a Papin's 
 digester. They vary in diameter from 1 -6000th to 1-1 4,000th of an inch ; 
 their shape is oval or oblong, often angular; and they cohere firmly together, 
 possibly by the medium of some different material. Their own substance, 
 however, appears to be perfectly homogeneous ; but it is made up of several 
 components, as appears from the following statements regarding the chemical 
 composition of Bone. 
 
 a. When the Calcareous matter of Bone has been dissolved away by the action of an acid, 
 the Animal substance which remains is almost entirely dissolved by a short boiling in water; 
 yielding to it a large quantity of Gelatine. This, indeed, may be obtained by long boiling 
 under pressure, from previously-unaltered Bone ; and the calcareous matter is then left almost 
 pure. The Lime of bones is, for the most part, in the state of Phosphate, especially among 
 the higher animals; it is curious, however, that in callus and exostosis, there is a much larger 
 proportion of Carbonate of lime, than in the sound bone ; in which respect these formations 
 correspond with the bones of the lower animals ; but in caries, the quantity of the carbonate 
 is much smaller than usual. The composition of the Phosphate of Lime in Bones is peculiar ; 
 8 equiv. of the base being united with 3 of the acid. According to Prof. Graham, it is to be 
 regarded as a compound of two tribasic phosphates ; namely, 2 Ca, O, H 0, P 5 -f-2 (3 Ca 0, 
 P O 5 ) ; with the addition of an equiv. of water, which is driven off by calcination. The fol- 
 lowing are the results of some of the most recent and careful analyses of Human Bone, by 
 Marchand and Lehmann: those of the former were made on the compact substance of the 
 femur of a man aged 30 ; and those of the latter on the long bones of the arm and leg of a 
 man of 40 years of age. 
 
 Organic matter. MARCHATTD. LEHMANK. 
 
 Cartilage insoluble in hydrochloric acid . . . 27-23 } 
 
 Cartilage soluble in hydrochloric acid . . . 5-02 V 32-56 
 
 Vessels . 1-01 ) 
 
 Inorganic matter. 
 
 Phosphate of lime 52*26 ) -.^ 
 
 Fluoride of calcium . . . . . . TOO ( 
 
 Carbonate of lime 10'21 9'41 
 
 Phosphate of magnesia 1-05 T07 
 
 Soda -92 Ml 
 
 Chloride of sodium 0-25 0'38 
 
 Oxide of iron and manganese, and loss . . 1-05 -86 
 
 100-00 100-00 
 
 b. According to Dr. Stark,f the relative proportions of cartilaginous and earthy matter, in 
 the bones of different animals, in the bones of the same animals at different ages, and in the 
 different bones of the same body, never depart widely from the preceding standard; the 
 amount of earthy matter being always found to be just double that of the cartilaginous basis, 
 when the bones have been carefully freed from oily matter, and completely dried, previously 
 to the analysis. The hardness of bone, he maintains, does not at all depend upon the pre- 
 sence of an unusually large proportion of earthy matter; nor does their increased flexibility 
 and transparency indicate a deficiency of the mineral ingredients ; for the transparent readily- 
 cut bones of fish contain the same amount of earthy matter, in proportion to their gelatinous 
 basis, as do the dense ivory-like leg-bones of the deer or sheep. The same holds good of 
 the bones even of the so-called Cartilaginous Fish. The difference seems to depend upon 
 the molecular arrangement of the ultimate particles ; and especially, it seems likely, upon 
 the relative amount of water which the bones contain. 
 
 * Todd and Bowman's Physiological Anatomy, p. 108, and Cyclopaedia of Anatomy, art. 
 Osseous Tissue. 
 
 f Edinburgh Med. and Surg. Journal, April 1845. 
 
166 
 
 OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 c. Probably the most exact and comprehensive analyses yet made of Bone, are those of 
 Von Bibra;* whose laborious investigations may be said to have almost exhausted the sub- 
 ject. The following table shows the relative proportions of the principal ingredients in some 
 of the principal bones of a woman aged 25 years. 
 
 Occipital 
 
 Scapula. 
 Organic matter. 
 Cartilage 
 Fat . 
 
 Inorganic matter. 
 Phosphate of lime } 
 
 54-75 
 
 Femur. 
 
 29-54 
 1-82 
 
 bone. 
 
 29-87 
 1-40 
 
 Os innomi- 
 natum. Vertebra. Sternum. 
 
 32-90 
 1-73 
 
 33-06 
 2-37 
 
 38-26 
 1-77 
 
 43'44 
 2-31 
 
 46-57 
 2-00 
 
 with a little fluo- > 57-42 57-66 54-75 52-91 
 
 ride of calcium. ) 
 
 Carbonate of lime . 8-92 8-75 8'58 8-66 
 
 Phosphate of magnesia 1-70 1-69 1-53 1-40 
 
 Soluble salts . . 0-60 0-63 0-51 0-60 
 
 49-72 44-28 
 
 42-63 
 
 8-08 
 1-57 
 0-60 
 
 8-00 
 1-44 
 0-53 
 
 100-00 100-00 100-00 100-00 100-00 100-00 
 
 The analyses of the long bones of the arm and leg correspond closely with that of the 
 femur ; but we observe that the proportions of ingredients in the more spongy bones are 
 widely different. It is difficult, however, to say how far this variation is due to a difference 
 in the proportions of gelatine and earthy matter, in the actual osseous substance ; or how far 
 it may be accounted for by the presence of an increased proportion of membrane, forming 
 the lining of the cancelli. The same uncertainty must attend the explanation of the differ- 
 ences that present themselves at different ages 5 as shown in the following table, which gives 
 the comparative analyses of the long bones (generally the femur) at different ages. 
 
 Foetus Foetus Child Child Man Woman 
 
 6 months. 7 months. 2 months. 5 years. 25 years. 62 years. 
 Organic matter. 
 
 Cartilage 40-38 34-18 33-86 31-28 29-70 28-03 
 
 Fat a trace 0-63 0-82 0-92 1-33 2-15 
 
 Inorganic matter. 
 Phosphate of lime ) 
 
 with a little fluo- V . . 53-46 57-63 57-54 59-96 59-63 63-17 
 
 ride of calcium. ) 
 
 Carbonate of lime . . . 3-06 5-86 6-02 5-91 7-33 4-46 
 
 . 2-10 1-10 1-03 1-24 1-32 1-29 
 
 1-00 0-60 0-73 0-69 0-69 0-90 
 
 Phosphate of magnesia 
 Soluble salts 
 
 100-00 100-00 100-00 100-00 100-00 100-00 
 
 From this it will be seen that there is a gradual diminution in the proportion of animal 
 matter, through life; and a corresponding increase in the proportion of the earthy components. 
 But this is not nearly so great as is usually supposed ; and the greater solidity of the bones 
 of old persons is doubtless owing chiefly to the fact, that their cavities are progressively con- 
 tracted, by the addition of new bony matter (201). 
 
 d. The following comparative analysis of the bones of different animals, are selected from 
 the very extensive series given by Von Bibra; which contains 143 of Mammalia (independ- 
 ently of Man), 151 of Birds, 31 of Reptiles, and 23 of Fishes. They were mostly made 
 upon the long bones ; except in the case of Fishes, in which they were made upon the Ver- 
 tebrae. 
 
 Sheep. Horse. Wolf. Thrush. Frog. Cod. Salmon. 
 
 Organic matter. 
 
 Cartilage 
 
 Fat 
 
 Inorganic matter. 
 
 Phosphate of lime with 
 a little fluoride of cal- 
 cium. 
 
 Carbonate of lime 
 
 Phosphate of magnesia 
 
 Soluble salts 
 
 29-68 
 0-70 
 
 27-99 
 3-11 
 
 27-44 
 1-45 
 
 28-02 
 1-54 
 
 30-19 
 5-31 
 
 31-90 
 2-34 
 
 21-80 
 
 38-82 
 
 55-94 54-37 57-87 62-65 59-48 57-65 36-84 
 
 12-18 12-00 
 1-00 1-83 
 0-50 0-70 
 
 11-09 
 1-13 
 1-02 
 
 6-05 
 0-90 
 0-84 
 
 2-25 
 0-99 
 1-78 
 
 4-81 
 2-30 
 1-00 
 
 1-01 
 0-70 
 0-83 
 
 100-00 100-00 100-00 100-00 100-00 100-00 100-00 
 
 * Chemische Untersuchungen iiber die Knochen und Ziihne des Menschen, und der Wir. 
 belthiere. 
 
COMPOSITION AND DEVELOPMENT OF BONE. 167 
 
 It will be observed that, in all cases, the proportion between the cartilaginous basis and 
 the earthy matter is very nearly the same ; being almost' exactly as 1 to 2, even where the 
 composition of the bone is most altered, by the presence of an unusual quantity of fatty mat- 
 ter. Hence there is strong reason to believe, that a definite chemical compound is formed 
 by the union of the Gelatine and Earthy salts ; and this corresponds well with the fact 
 already noticed, in regard to the homogeneousness of the ultimate particles of bone. 
 
 197. The first Development of Bone may take place in the substance, 
 either of Membrane, or of Cartilage.* The tabular bones forming the roof 
 of the cranium afford a good example of the first, or intramembranous form 
 of Ossification ; for their place is but in part pre-occupied by cartilage ; only 
 a membrane being elsewhere interposed between the dura mater and the in- 
 teguments. This membrane is chiefly composed of fibrous fasciculi, corre- 
 sponding with those of the white fibrous tissues ; but amongst these are seen 
 numerous cells, some about the size of blood-discs, but others two or three 
 times larger, containing granular matter ; and a soft amorphous or faintly- 
 granular matter is also found interposed amidst the fibres and cells. In cer- 
 tain parts, the fibres predominate ; and in others, the cells. The process of ossi- 
 fication here seems at first to consist in the consolidation of the fibres by earthy 
 matter ; for the first bony deposit consists of an irregular reticulation, very loose 
 and open towards its edges, and there frequently presenting itself in the form 
 of distinct spicula, which are continuous with fasciculi of fibres in the sur- 
 rounding membrane. The limits of the calcifying deposit may be traced by 
 the opaque and granular character of the parts affected by it, and it gradually 
 extends itself, involving more and more of the surrounding membrane, until the 
 foundation is laid for the entire bone. Everywhere the part most recently 
 formed consists of a very open reticulation of fibro-calcareous spicula ; whilst 
 the older part is rendered harder and more compact, by the increase in the 
 number of these spicula, and perhaps also by the calcification of the interve- 
 ning cells. As the process advances, and the plate of bone thickens, a series 
 of grooves or furrows, radiating from the ossifying centre, are found upon its 
 surface ; and these by a further increase in thickness, occasioned by a deposit 
 of ossific matter all around them, are gradually converted into closed canals 
 (the Haversian), which contain blood-vessels, supported by processes of the 
 investing membrane. Further deposits subsequently take place in the interior 
 of these canals ; which thus gradually produce a diminution of their calibre, 
 and a consolidation of the bone ; and in this manner its two surfaces acquire 
 their peculiar density, whilst the intervening layer or diploe retains a charac- 
 ter more resembling that of the original osseous reticulation. The mode in 
 which the peculiar lacunae and canaliculi are formed, in the concentric layers 
 around the Haversian canals, probably corresponds with that in which they 
 are generated in the intracartilaginous form of ossification, to which we shall 
 next proceed. 
 
 198. In a very large proportion of the skeleton, the appearance of the Bones 
 is preceded by that of Cartilages ; which present the same form, and which 
 seem destined to afford a certain degree of support, to the surrounding soft 
 parts, until the production of Bone has taken place. As already mentioned 
 ( 187), the temporary cartilages differ in no essential particular from the per- 
 manent. They present the same irregular scattering of cells through a homo- 
 geneous intercellular substance, and there is the same absence of any vascu- 
 
 * In recent times, the development of Bone from Cartilage has received almost exclusive 
 attention ; but the older opinion, that Bone is often developed in Membrane, has been lately 
 brought again into notice by Dr. Sharpey (Introduction to Fifth Edition of Quain's Anatomy), 
 who has demonstrated its truth by Microscopic research. The statements in the text, upon 
 this part of the subject, are derived from Dr. Sharpey's observations, which the author has 
 since confirmed. 
 
168 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 larity in the Cartilaginous tissue itself. In all considerable masses, how- 
 ever, we find a coarse network of canals, lined by an extension of the peri- 
 chondrium or investing membrane ; and these canals, which may be regarded 
 as so many involutions of the external surface, allow the vessels to come into 
 nearer relation with the interior parts of the Cartilaginous structure, than 
 they would otherwise do. They are especially developed at certain points, 
 
 Fig. 66. 
 
 [Fig. 67. 
 
 Section of Cartilage at the seat of 
 ossification ; the clusters of cells are 
 arranged in columns ; the intercellular 
 spaces between the columns being 
 l-3250th of an inch in breadth. At the 
 lower end of the figure, osseous fibres 
 are seen occupying the intercellular 
 spaces, at first bounding the clusters 
 laterally, then splitting them longitudi- 
 nally and encircling each separate cell. 
 The greater opacity of this portion is 
 due to a threefold cause; the increase of 
 osseous fibres, the opacity of the con- 
 tents of the cells, and the multiplica- 
 tion of oil-globules. 
 
 Vertical section of Cartilage near the surface of ossifi- 
 cation; 1, ordinary appearance of the temporary cartilage; 
 1', portion of the same more highly magnified; 2, the cells 
 beginning to assume the linear direction; 2', portion more 
 magnified; opposite 3, the ossification is extending in the 
 intercellular spaces, and the rows of cells are seen resting 
 in the cavities so formed, the nuclei being more separated 
 than above; 3', portion of the same more highly magnified. 
 From a new-born rabbit which had been preserved in 
 spirit.] 
 
 which are to be the centres of the ossifying process ; and it is always observ- 
 able, that the vascularity is greatest at the zone, in which the conversion of 
 cartilage into bone is actually taking place. During the extension of the vas- 
 cular canals into the Cartilaginous matrix, certain changes are taking place 
 
OSSIFICATION OF CARTILAGE. 169 
 
 in the substance of the latter, which are preparatory to its conversion into 
 Bone. Instead of single isolated cells, or groups of two, three, or four, such 
 as we have seen to be characteristic of ordinary Cartilage (Fig. 52), we find, 
 as we approach the centre or line of ossification, clusters made up of a larger 
 number arranged in a linear manner ; which seem to be formed by a continu- 
 ance of the same multiplying process as that formerly described (Fig. 66). 
 And when we pass still nearer, we see that these clusters are composed of a 
 yet greater number of cells, which are arranged in long rows, whose direc- 
 tion corresponds to the longitudinal axis of the bone ; these clusters are still 
 separated by intercellular substance ; and it is in this, that the ossific matter 
 is first deposited. If we separate the cartilaginous and the osseous substance 
 at this stage of the process, we find that the ends of the rows of cartilage- 
 cells are received into deep narrow cups of bone, formed by the calcification 
 of the intercellular substance between them. Thus the Bone first formed in 
 the cartilaginous matrix, is seen to consist of a series of lamellae of a some- 
 what cylindrical form ; inclosing oblong areola?, or short tubular cavities, 
 within which the piles of cartilage-cells yet lie : and it thus corresponds 
 closely with the reticular structure, which first makes its appearance in the 
 intra-membranous form of the process. So far it would appear that the blood- 
 vessels are not directly concerned in the operation; for although they advance 
 to the near neighbourhood of the first ossific deposit, they do not make their 
 way into its substance, or even into the intervening areolae. 
 
 199. This state of things, however, speedily gives place to another. On 
 examining the subjacent portion, in which the ossification has advanced further, 
 it is found that the original closed cavities have coalesced to a certain extent 
 (probably by the absorption of their walls), both laterally and longitudinally; 
 and that they now receive numerous blood-vessels, prolonged into them from 
 the previously-ossified portion. The groups of cartilage-cells, which origi- 
 nally occupied the cavities, are no longer seen ; and their place is filled with 
 a blastema, composed of cells, containing a granular matter, and closely re- 
 sembling those seen in the intra-membranous ossification, with a few fibres 
 scattered amongst them. It is by a change in this blastema, that the walls of 
 the cavities are gradually consolidated; new deposits of ossific matter being 
 formed in their interior, which occasion the gradual contraction of the cavities, 
 and give an increasing density to the bone. The cancellated structure, which 
 remains for a time in the interior of the long bones, and which continues to 
 occupy their extremities, represents the early condition of the ossifying sub- 
 stance, with very little change ; whilst the cavities, which have formed more 
 regular communications with each other, and which have been gradually con- 
 tracted by the subsequent deposit of concentric lamella?, one within another, 
 form the original Haversian canals. Thus we see that they all form one 
 system in their origin ; as they may be considered to do, notwithstanding 
 the difference of their form, in the complete bone. 
 
 200. The original osseous lamella?, formed by the consolidation of the car- 
 tilaginous substance, are entirely composed of granular matter ; and exhibit 
 none of the lacuna? and canaliculi, which are commonly regarded as charac- 
 teristic of Bone. These excavations present themselves, however, in all the 
 subsequent deposits ; and into the origin of these, we have now to inquire. 
 According to the views of some Microscopists, the cells of the blastema fill 
 themselves with ossific matter, except at the points occupied by the nuclei ; 
 at the same time, they become flattened against the walls of the canals, and 
 their nuclei send out radiating prolongations ; so that, when the calcification 
 of the cell has been completed, a stellate cavity is left in the hard deposit, 
 which is occupied by the granular matter of the nucleus. The centre of this 
 cavity forms the lacuna, in which the original granular matter may frequently 
 
 15 
 
170 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 be found remaining, and presenting an appearance as if developed into a cluster 
 of minute cells; whilst its prolongations form the canaliculi, from which the 
 nuclear matter seems afterwards to disappear altogether. This view is sup- 
 ported by several considerations ; amongst others, by the fact of the existence 
 of such stellate nuclei in many Vegetable cells (Fig. 14); and by the corre- 
 sponding appearances witnessed by Professor Owen in the formation of the 
 Cementum of Teeth, a structure identical with bone, and produced by the 
 calcification of the capsule ( 216). Others, again, regard the lacunae and 
 their radiating prolongations as themselves constituting cells ; and examples 
 are not wanting of similar forms in bodies known to have this character, as 
 the pigment-cells of the skin of Batrachia (Fig. 90, c). Dr. Sharpey, on the 
 other hand, states as the result of his observations, that the concentric layers 
 within the Haversian canals are formed by a process analogous to the intra- 
 inembranous ossification ; namely, by the calcification of successive layers of 
 fibres, generated in the blastema, and possibly derived from the granular cells. 
 These fibres, being arranged in a reticular manner, may here and there include 
 an entire cell or cell-nucleus, the presence of which may determine the posi- 
 tion of a lacuna; whilst the canalicula may result from the apposition of the 
 minute apertures, existing between the other reticulations of the decussating 
 fibres. This view seems to derive confirmation from the appearances pre- 
 sented by very thin shreds of the gelatinous matrix, left after the removal of 
 the calcareous matter by acid ; for these, according to Dr. S., are plainly com- 
 posed of transparent fibres, resembling those of the white fibrous tissues, in- 
 tersecting one another at acute angles, and forming a network, in the meshes 
 of which are minute perforations, that are nothing else than transverse sections 
 of the canaliculi. 
 
 201. In the formation of a long bone, we usually find one centre of ossifi- 
 cation in the shaft, and one in each of the epiphyses ; in the flat bones, there 
 is one in the middle of the surface, and one in each of the principal processes. 
 The ossification usually proceeds to a considerable 
 [Fig. 68. extent, however, in the main centre, before it com- 
 
 mences in the extremities or processes ; and these 
 remain distinct from the principal mass of the bone, 
 long after this has acquired solidity. During the 
 spread of the ossifying process, the cartilaginous 
 matrix continues to grow, like cartilage in other 
 parts; but after the bony deposit has pervaded its 
 entire substance, in the manner just described, a 
 change takes place in the method adopted. The 
 osseous laminae, that subdivide the whole texture, 
 are removed by absorption from the interior of the 
 shaft, so as to leave the great central medullary 
 cavity ; whilst, on the other hand, they receive pro- 
 gressive additions in the external portion, which is 
 Scapula of a Fcetus at the thus gradually consolidated into the dense bone, 
 seventh month ; showing the pro- that forms the hollow cylinder of the shaft. This 
 gress of ossification. Natural consolidation is effected by the deposit of a series 
 
 size. The light parts are epiphy- Qf concentric l amimfi one wilhin another, On the 
 ses as yet cartilaginous.- From ,. . , TT ' 
 
 the Museum of King's College, hnin g of the Haversian canals. The bone con- 
 London.] tinues to increase in diameter, by the formation of 
 new layers upon its exterior ; and Dr. Sharpey has 
 
 pointed out that these layers are formed, not (as usually stated) in a cartila- 
 ginous matrix, but in the substance of a membrane, consisting of fibres and 
 granular cells, and exactly resembling that in which the flat bones of the roof 
 of the skull are developed. The Haversian canals, too, of these new layers 
 
DEVELOPMENT AND GROWTH OF BONE. 171 
 
 are formed in the same manner as those of the tabular bones of the skull ; the 
 osseous matter being not only laid on in strata parallel to the surface, but also 
 being deposited around processes of the vascular membranous tissue, which 
 extend obliquely from the surface into the substance of the shaft; the canals, 
 in which these membranous processes lie, becoming narrowed by the depo- 
 sition of concentric osseous laminae, and at last remaining as the Haversian 
 canals. Whilst this new deposition is taking place on the exterior of the 
 shaft, absorption of the inner and older layers goes on : so that the central 
 cavity is proportionably enlarged. The increase of the bone in length ap- 
 pears due to the growth of the cartilage between the shaft and the epiphyses, 
 so long as this remains unconsolidated by ossific deposit ; and this state con- 
 tinues, until the bone has acquired nearly its full dimensions. What further 
 increase it gains, seems chiefly if not entirely due to the progressive ossifica- 
 tion of the articular cartilage covering the extremities ; which progressively 
 diminishes in thickness during the whole of life, and which in old age some- 
 times appears to have been almost completely converted into bone. 
 
 202. It thus appears doubtful, whether there be anything like a proper 
 interstitial growth in bone ; that is, whether the part, through which the 
 ossific process has made its way, is capable of any further extension than by 
 addition to its surface. By the admirable system of prolongations, however, 
 by which the vascular membrane is conveyed into its intimate substance, we 
 find this method of superficial deposit adapted to the consolidation of parts, at 
 first sketched out (as it were) by a slight osseous reticulation ; whilst by the 
 facility with which the bony matter is absorbed in the internal part of the shaft, 
 whilst it is being deposited upon its exterior, the same effect is produced, as 
 if the whole cylinder could enlarge uniformly by a proper interstitial growth, 
 in the manner of the softer tissues. Much of our information regarding the 
 mode in which new bony matter is deposited, is derived from observations 
 made upon the bones of animals that have been fed with madder ; for this 
 colon ring-matter, having a strong affinity for bone-earth, tinges all those parts 
 which are in close relation with the vascular surfaces. In very young ani- 
 mals, a single day serves to colour the entire substance of the bones ; for 
 there is in them no osseous matter far removed from a vascular surface. 
 At a later period, however, the colouring matter is deposited less rapidly ; and 
 is found to be confined to the innermost of the concentric laminaa of bone, 
 surrounding each Haversian canal, showing that this is the last formed. 
 When madder is given to a growing animal, the external portion of the bone 
 is first reddened ; showing that the new deposit takes place exclusively in 
 that situation. And if, when time has been allowed for this part to become 
 tinged, the administration of the madder be discontinued, and the animal be 
 killed some weeks afterwards, the red stratum is surrounded by a colourless 
 one of subsequent formation ; whilst the colourless layer internal to the red 
 one, and formed previously to it, is thinned by absorption from within. By 
 alternately administering and withholding the madder, a succession of coloured 
 and colourless cylinders may thus be formed in the shaft of a long bone ; 
 which present themselves as concentric rings in its transverse section. 
 
 203. The nature of the Ossifying process receives some additional light 
 from the abnormal forms in which it occasionally presents itself in Cartilages 
 that are usually permanent ; as well as in various softer tissues, such as the 
 coats of the arteries, fibrous and serous membranes, muscular substance, &c. 
 In these cases, the ossific deposit may often be seen to take place, in the first 
 instance, in the form of distinct granules, which gradually coalesce ; or in the 
 form of spicular fibres, to which additions are progressively made; until a 
 solid mass is produced. This adventitious bone, however, almost invariably 
 differs from true or normal bone, in the want of a regular Haversian system 
 
172 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 with concentric laminae, and in the absence of the characteristic lacunae and 
 canaliculi. Irregular cavities, however, are scattered through them ; which 
 may in some degree answer the same purpose. The osseous plates not un- 
 frequently found in the dura mater, are stated by Mr. Tomes to possess a 
 structure more closely allied to that of true bone ; which may be connected 
 with the fact that, in some of the lower Mammalia, certain parts of this mem- 
 brane (the falx and tentorium) are normally ossified. 
 
 204. The Regeneration of Bone, after loss of its substance by disease or 
 injury, is extremely complete ; in fact, there is no other structure of so com- 
 plex a nature, which is capable of being so thoroughly repaired. Much dis- 
 cussion has taken place with respect to the degree in which the different 
 membranous structures, that surround bone and penetrate its substance, con- 
 tribute to its regeneration ; but the fact seems to be, that any or all these 
 membranes may contribute to the formation ff new bone, in proportion to 
 their vascularity, the new structure, however, being most readily produced 
 in continuity with the old. Thus, when a portion of the shaft of the bone 
 is entirely removed, but the periosteum is left, the space is filled up with 
 bony matter in the course of a few weeks ; though, if the periosteum also be 
 removed, the formation of new osseous matter will be confined to a small 
 addition in a conical form to the two extremities, a large interspace being left 
 between them. The production of new bony tissue, in this experiment, as 
 in cases where the periosteum has been detached by disease and remains alive 
 while the shaft dies, is in continuity with minute spicula of original bone, 
 which still adhere to the membrane; and it is well known that, in comminuted 
 fractures, every portion of the shattered bone, that remains connected with 
 the vascular membranes, whether these be internal or external, becomes the 
 centre of a new formation ; the loss of substance being filled up the more ra- 
 pidly, in proportion to the number of such centres. 
 
 205. The most extensive reparation is seen, when the shaft of a long bone 
 is destroyed by disease. If violent inflammation occur in its tissue, the death 
 of the fabric is frequently the consequence ; apparently through the blocking- 
 up of the canals with the products of inflammatory action, and the consequent 
 cessation of the supply of nutriment. It is not often that the whole thickness 
 of the bone becomes necrosed at once ; more commonly this result is confined 
 to its outer or to its inner layers. When this is the case, the new formation 
 takes place from the part that remains sound ; the external layers, which 
 receive their vascular supply from the periosteum, and from the Haversian 
 canals continued inwards from it, throwing out new matter on their interior, 
 which is gradually converted into bone ; whilst the internal layers, if they 
 should be the parts remaining uninjured, do the same on their exterior, de- 
 riving their materials from the medullary membrane, and from its prolonga- 
 tions into their Haversian canals. But it sometimes happens that the whole 
 shaft suffers necrosis; and as the medullary membrane and the entire Haver- 
 sian system have lost their vitality, reparation can then only take place from 
 the splinters of bone which may remain attached to the periosteum, and from 
 the living bone at the two extremities. This is consequently a very slow 
 process ; more especially as the epiphyses, having been originally formed as 
 distinct parts from the shaft, do not seem able to contribute much to the re- 
 generation of the latter. 
 
 206. When the shaft of a long bone has been fractured through, and the 
 extremities have been brought evenly together, it is found that the new matter 
 first ossified is that which occupies the central portion of the deposit, and 
 which thus connects the medullary cavities of the broken ends, forming a kind 
 of plug that enters each. This was termed by Dupuytren, by whom it was 
 first distinctly described, the provisional callus, and it is usually formed in 
 
REPARATION OF BONE. 173 
 
 the course of five or six weeks, or less, in young persons. At that period, 
 however, the contiguous surfaces of the bone itself are not cemented by bony 
 union ; and the formation of the permanent callus occupies some months ; 
 during which the provisional callus is gradually absorbed, and the continuity 
 of the medullary canal is thus restored, in the manner in which it was first 
 established. Mr. Gulliver has remarked that, when the broken portions of 
 bone form an angle, there is quite a distinct centre of ossification in the new 
 matter ; from which that portion of it is ossified, that lies between the sides 
 of the angle ; thus forming what has been termed an accidental callus, and 
 giving support to the two portions of the shaft, in a situation which is exactly 
 that^of the greatest mechanical advantage. Though for some time quite uncon- 
 nected with the old bone, it soon becomes united to the regular callus. This 
 instance proves, that continuity with previously-formed bone is not absolutely 
 requisite for the production of new osseous structure; although the process 
 is decidedly favoured thereby. 
 
 207. The reparation of Bone, after disease or injury, seems to take place 
 upon a plan essentially the same as that of its first formation. A plastic or 
 organizable exudation is first poured out from the neighbouring blood-vessels ; 
 and thus forms a sort of bed or matrix, in which the subsequent processes 
 take place. The next stage, in young animals, is the formation of a true car- 
 tilaginous substance, exactly resembling their temporary cartilages ; and this 
 is gradually converted into bone, in the manner in which those cartilages are 
 consolidated in the first instance. In older animals, however, the new struc- 
 ture appears to be rather of a membranous character; and the ossifying pro- 
 cess would therefore correspond rather with that by which the normal in- 
 crease of their bones is effected. Mr. Tomes states* that he has examined 
 various cases of fracture of the neck or shaft of the femur, in which union 
 had not been effected, in consequence of the patient's advanced age; and that 
 he found in these no intervening cartilage, and but a scanty amount of con- 
 densed areolar tissue. In this latter, traces of an attempt at repair may be 
 generally found, in the presence of osseous matter in granules or granular 
 masses ; but in these there is no arrangement of tubes or bone-cells of definite 
 character ; indeed, such osseous masses are generally small, and are deficient 
 in density, owing to the want of union between the individual granules. 
 
 208. The Teeth are nearly allied to Bone in structure ; and in some of the 
 lower Vertebrata, there is an actual continuity between the bone of the jaw, 
 and the teeth projecting from it, notwithstanding that the latter form part of 
 the dermal skeleton, whilst the former belongs to the neural or internal. In 
 Man and the higher animals, however, there is an obvious difference in their 
 structure ; as in their mode of development. These subjects have lately re- 
 ceived much attention; and the practical importance of an acquaintance with 
 them, renders it desirable that they should be here treated somewhat fully. 
 The Teeth of Man, and of most of the higher. animals, are composed of three 
 very different substances ; Dentine (known as ivory in the tusk of the Ele- 
 phant), Enamel and Cementum or Crusta Petrosa. These are disposed in 
 various methods, according to the purpose which the Tooth is to serve : in 
 Man, the whole of the crown of the tooth is covered with Enamel ; its root or 
 fang is covered with Cementum; whilst the substance or body of the tooth is 
 composed of Dentine. In the molar Teeth of many Herbivorous animals, 
 however, the Enamel and Cementum form vertical plates, which alternate 
 with plates of Dentine, and present their edges at the grinding surface of the 
 tooth ; and the unequal wear of these substances, the Enamel being the 
 hardest, and the Cementum the softest, occasions this surface to be always 
 kept rough. 
 
 * Cyclopaedia of Anatomy and Physiology, vol. iii., p. 857. 
 15* 
 
174 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABUIC. 
 
 [Fig. 69. [Fig> 7a 
 
 A view of an Incisor and of a Molar Tooth, 
 given by a longitudinal section, and showing 
 that the enamel is striated, and that the strise 
 are all turned to the centre; the internal 
 structure is also seen ; 1, the enamel ; 2, the 
 ivory ; 3, the cavitas pulpi.] 
 
 209. The Enamel is composed 
 an inch in diameter, arranged side 
 
 [Fig. 71. 
 
 A vertical section of an adult Bicuspid, cut from 
 without inwards magnified 4 times ; 1, 1, the cor- 
 tical substance which surrounds the root up to the 
 commencement of the enamel ; 2, 2, the ivory of 
 the tooth, in which are seen the greater parallel 
 curvatures, as well as the position of the main 
 tubes; 3, apex of the tooth, where the tubes are al- 
 most perpendicular ; 4, 4, the enamel ; 5, the cavity 
 of the pulp, in which are seen, by means of the 
 glass, the openings of the tubes of the dental bone.] 
 
 of solid prisms or fibres, about l-5600th of 
 by side, and closely adherent to each other ; 
 
 [Fig. 72. 
 
 A vertical section of an imperfectly developed Incisor, 
 taken from the follicle in which it was enclosed; this 
 section is meant to show the position of the enamel 
 fibres, and also that a part of the appearances which are 
 seen in this substance under a less magnifying power, 
 originate in parallel curvatures of the fibres ; 1, 1, the 
 enamel ; 2, 2, the dental bone, or ivory; 3, 3, the minute 
 indentations and points on the surface of the ivory, on 
 which the enamel fibres rest ; 4, 4, brown parallel fibres; 
 5, parallel flexions of the fibres of the dental bone in these 
 stripes ] 
 
 A portion of the surface of the Enamel 
 on which the hexagonal terminations 
 of the fibres are shown highly magni- 
 fied ; 1, 2, 3, are more strongly marked 
 dark crooked crevices, running be- 
 tween the rows of the hexagonal 
 fibres.] 
 
STRUCTURE OF TEETH; ENAMEL, DENTINE, 
 
 175 
 
 their length corresponds with the thickness of the layer which they form ; 
 and the two surfaces of this layer present the ends of the prisms, which are 
 usually more or less regularly hexagonal. The course of these prisms is 
 generally wavy ; but their curves are for the most part parallel to each other. 
 In the perfect state, the Enamel contains but an extremely minute quantity of 
 animal matter ; but if a young tooth be examined, it is found that, after the 
 
 [Fig. 73. 
 
 [Fig. 74. 
 
 The Fibres of the Enamel viewed sideways A small portion of fig. 70 covered with turpentine 
 
 under a magnifying power of 350 times; 1,1, varnish, viewed under a magnifying power of 350 
 
 the enamel fibres ; 2, 2, the transverse stripes times; 1. 2, 3, are the tubes containing a powdery, 
 
 upon them.] lumpy substance. They are regular, and closely un- 
 
 dulating; but the branches do not appear, because 
 they are penetrated by the varnish.] 
 
 calcareous matter of the tooth has been dissolved away by an acid, there re- 
 mains a set of distinct prismatic cells, which formed (as it were) the moulds 
 in which the mineral substance was deposited.* The Enamel is the least 
 constant of the dental tissues ; being more frequently absent than present in 
 the teeth of Fishes ; being deficient in the whole order of Serpents ; and form- 
 ing no part of the teeth of the Edentate and Cetacean Mammals. 
 
 210. The Dentine} consists of a firm substance, in which mineral matter 
 largely predominates, though to a less degree than in the enamel. It is tra- 
 
 [Fig. 75. [Fig. 76. 
 
 A view of the most interior portion of the main 
 tubes of the dental bone in an incisor of a child 
 two years old, close to their commencement in the 
 cavitas pulpi, in order to show their first division.] 
 
 A view of the external portion of the tubes of 
 the same tooth, exhibiting their more minute ra- 
 mifications, which, for the most part, turn towards 
 the crown.] 
 
 versed by a vast number of very fine cylindrical branching wavy tubuli ; which 
 
 * The Author has discovered a structure precisely resembling this, in the shells of many 
 Mollusca. See Annals of Natural History, December, 1 843. 
 
 t A structure exactly resembling Dentine has been found by the Author in the shell of 
 the Crab, especially at the tips of the claws; and a less regular structure of the same kind 
 in the shells of many Mollusca. (Loc. cit.) 
 
176 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 commence at the pulp-cavity (on whose wall their openings may be seen), 
 and radiate towards the surface. In their course outwards, the tubuli occa- 
 sionally divide dichotomously ; and they frequently give off minute branches, 
 which again send off smaller ones. In some animals, these tubuli may be 
 traced at their extremities into cells exactly resembling the lacuna? of bone; 
 and here the Ivory must be considered as presenting a form of transition into 
 
 [Fig. 77. 
 
 [Fig. 78. 
 
 A view of a small portion of a transverse section of 
 the crown of the Tooth seen in fig. 70, viewed under a 
 magnifying power of 350 times ; 1, 2, 3, are the round 
 openings of the tubes, with parietes of a peculiar sub- 
 stance ; 4, 5, 6, are the tubes cut more obliquely, in 
 consequence of their more external position ] 
 
 A view of the position of the same main 
 tubes, in a transverse section near the root 
 of a bicuspid, magnified 5 diameters. The 
 dark patches in this figure mark the places 
 in which the bone was especially white and 
 less transparent than in the clear interme- 
 diate tracts.] 
 
 [Fig. 79. 
 
 Sections of a human incisor, showing: 
 
 A. Junction of dentine and enamel near the neck of the tooth, a. Tubes of the dentine, dividing and 
 ending on b b, the cupped surface on which the enamel rods vertically rest. c. Free surface of the ena- 
 mel. The enamel rods are crossed by transverse lines and also by oblique dark lines. 
 
 B. Bifurcation of the tubuli of the dentine, soon after their commencement on d the surface of the pulp- 
 cavity. 
 
 c. Branching of the tubuli of the fang, and their termination in the small irregular lacunae of the " gra- 
 nular layer." 
 
 In these longitudinal views of the tubuli, their cavities only, and not their walls, are visible. 
 Magnified 300 diameters.] 
 
STRUCTURE OF TEETH; ENAMEL, DENTINE. 
 
 177 
 
 the substance next to be described. The tubuli, in their radiating course, de- 
 scribe two, three, or more curvatures, appreciable by a low magnifying power; 
 these are termed by Prof. Owen, the " primary curvatures." With a higher 
 power, the tubes are seen to be bent, throughout the whole of their flexuous 
 course, into minute and equal oblique undulations, of. which 100 may be 
 counted within the space of l-10th of an inch ; these are the " secondary cur- 
 vatures" of Prof. Owen. Both the primary and the secondary curvatures of 
 one tube are usually parallel with those of the contiguous tubes ; and from 
 the radiating course of the tubuli, the rows of curvatures have the appearance 
 of lines running parallel with the external contour of the tooth. The dia- 
 meter of the tubuli in their largest part averages about 1-1 0,000th of an inch ; 
 their smallest branches are immeasurably fine. It is impossible that they 
 can receive blood; but it may be surmised that, like the canaliculi of bone, 
 they absorb matter from the vascular lining of the pulp-cavity, which aids in 
 the nutrition of the tooth. Although, when once fully formed, the Tooth un- 
 dergoes little or no change, there is evidence that it possesses a certain power 
 of repairing the effects of disease ; a new layer of hard matter being some- 
 times thrown out on a surface, which has been laid bare by Caries. It has 
 been found, too, that the Dentine is sometimes tinged by colouring* matters 
 contained in the blood. This is most evident, when a young animal is fed 
 upon madder, during the period of the formation of the tooth ; but even in an 
 adult, some tinge will result from a prolonged use of this substance ; and it 
 has been noticed that the teeth of persons, who have long suffered from Jaun- 
 
 [Fig. 80. 
 
 Fig. 81. 
 
 
 Transverse sections of tubules of dentine, 
 showing their cavities, their walls, and the 
 intertubular tissue. 
 
 a. Ordinary distance apart. 
 
 b. More crowded. 
 e. Another view. 
 
 Human molar. Magnified 400 diameters.] 
 
 Oblique section of Dentine of human 
 tooth, highly magnified, showing the calci- 
 gerous tubuli, and the outlines of the original 
 cells. 
 
 dice, sometimes acquire a tinge of bile. Attention has been particularly di- 
 rected by Prof. Owen, to appearances which he regards as indicating the 
 
178 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 boundaries of the original cells of the dentinal pulp (213) that have not been 
 obliterated by the process of calcification.* These are particularly evident 
 in the teeth of the Dugong, and of the extinct Mylodon; but they occasionally 
 present themselves in the Dentine of Man (Fig. 81). In certain Mammals 
 and Reptiles, and in a large number of Fishes, the Dentine is traversed by 
 canals, which are prolonged into it from the central pulp-cavity, and which 
 are lined (like the pulp-cavity itself) by a highly-vascular membrane ; and it 
 is then distinguished as Vascular Dentine. These canals are obviously ana- 
 logous to the medullary or Haversian canals of bone ; and the tubuli usually 
 radiate from them, rather than from the central cavity. In some instances, 
 there is no central cavity whatever ; but the whole tooth is traversed by an 
 irregular network of these medullary canals, which become continuous with 
 the Haversian canals of the subjacent bone. A substance still more resem- 
 bling bone, but formed from the dentinal pulp, is found in the interior of the 
 teeth of certain Reptiles and Mammalia, and occasionally in the teeth of 
 Man, especially at the later periods of life. This substance possesses not 
 only vascular or medullary canals, but also the stellate lacunre and radiating 
 canaliculi of true bone. It sometimes occupies the whole of the cavity of the 
 pulp, and is formed by the ossification of its cellular parenchyma ; but in 
 other cases, it forms merely a thin shell upon the interior of the ordinary 
 Dentine. 
 
 211. The Cementutn or Crusta Petrosa corresponds in all essential parti- 
 culars with Bone ; possessing its characteristic lacunae ; and being also tra- 
 versed by vascular medullary canals, wherever it occurs of sufficient thickness, 
 as in the exterior of the tooth of the extinct Megatherium, and in the thick 
 plates interposed within the islands of Enamel in the teQth of Ruminants, Ro- 
 dents, &c. The varieties of microscopic structure presented by the Cemen- 
 tum in different classes of animals, correspond with the modifications of the 
 osseous tissue, which exist in the skeletons of those animals respectively. 
 The Cementum was formerly supposed to be restricted to the compound 
 teeth of Herbivorous animals ; and its presence in the simple teeth of Man 
 and the Carnivora can be shown only by the application of the Microscope. 
 In the latter it forms a layer, which invests the fang, and which decreases in 
 thickness as it approaches the crown of the tooth ; at the time of the first 
 emersion of the tooth, it covers the crown with a very thin lamina ; but this 
 is speedily worn away by use ; on the other hand, its thickness around the 
 apex of the fang often undergoes a subsequent increase, especially when chro- 
 nic inflammation and thickening take place in the membranous contents of the 
 socket. 
 
 212. The following are the results of the most recent Chemical Analyses 
 of the component structures of Human Teeth : t 
 
 . Incisors of Adult Man. 
 
 Dentine. Enamel. Cementum. 
 
 Organic matter . . . 28-70 3-59 29-27 
 
 Earthy matter . . 71-30 96-41 70-73 
 
 100-00 100-00 100-00 
 
 The proportion of these two components varies considerably in different species; thus the 
 organic basis of the Elephant's tusk forms as much as 43 per cent, of the whole. It would 
 seem even to vary considerably in different individuals of the same species : thus in the 
 molar teeth of one man,Bibra found, the organic matter to constitute as little as 21 per cent., 
 
 * See Prof. Owen's Odontography, Introduction. 
 
 f Op. Cit. ; and Bibra's " Chemische Untersnchungen xiber die Knochen und Ziihne." 
 

 COMPOSITION AND DEVELOPMENT OF TEETH. 179 
 
 whilst in another it was 28. The following analyses afford a more particular view of the 
 components of each substance : 
 
 Molars of Mult Man. 
 
 Dentine. Enamel. 
 
 Phosphate of Lime, with traces of fluate of lime . 66-72 89'82 
 
 Carbonate of Lime 3-36 437 
 
 Phosphate of Magnesia 1 08 1-34 
 
 Other Salts O83 OSS 
 
 Chondrine . . , . - 27-61 339 
 
 Fat 0-40 020 
 
 lOO'OO 100-00 
 
 Incisors of Ox. 
 
 Dentine. Enamel. Cement. 
 Phosphate of Lime, with trace of fluate 
 
 of lime 59-57 81-86 58-73 
 
 Carbonate of Lime . . . 7-00 9-33 7-22 
 
 Phosphate of Magnesia . . .099 1-20 0-99 
 
 Salts 0-91 0-93 0-82 
 
 Chondrine 30-71 6-66 31-31 
 
 Fat ' . 0-82 0-02 0'93 
 
 100-00 100-00 100-00 
 
 213. The Dentine and its modifications, the Enamel, and the Cementum, 
 originate in three distinct structures ; which may be termed respectively, the 
 dentinal-pulp, the enamel-pulp, and the capsule or cemental-pulp ; the whole 
 forming the " matrix'* from which the entire tooth is evolved. The Dentinal 
 pulp is always the first-developed part of the matrix ; and it makes its appear- 
 ance in the form of a papilla, budding out from the free surface of a fold or 
 groove of the mucous membrane of the mouth. This may be converted into 
 dentine, without ever becoming inclosed within .a capsule; as we see in the 
 Shark, whose dentition never advances beyond this papillary stage. The 
 dentinal pulp consists of a mass of nucleated cells, imbedded in a semi-fluid 
 granular blastema, and the whole inclosed in a dense structureless pellucid 
 membrane. This substance is copiously supplied with blood-vessels, origin- 
 ating in a trunk that enters the base of each papilla; the branches ramify and 
 diverge in their progress through the pulp ; and at last they form a capillary 
 network, which terminates in loops near the apex of the pulp (Fig. 82). 
 These vessels are accompanied by nerves; which also have looped termina- 
 tions. The following is the substance of the account given by Prof. Owen, 
 of the conversion of the dentinal pulp into dentine ; based upon his observa- 
 tion of this process as it occurs in the foetal Shark. The primary cells, which 
 are smallest at the base of the pulp, and have large simple sub-granular nuclei, 
 soon fall into linear series, directed towards the periphery of the pulp ; and 
 those which are nearest to the periphery become closely aggregated, increase 
 in size, and present a series of important changes in their interior (Fig. 83, a). 
 A pellucid point appears in the centre of the nucleus ; and the latter increases 
 in size, and becomes more opaque around it. A division of the nucleus in 
 the course of its long axis is next observed (6) ; and in the larger and more 
 elongated cells, still nearer the periphery of the pulp, a further subdivision of 
 the nuclei is observed, in a transverse as well as a longitudinal direction (e* c), 
 the subdivisions becoming elongated, with their long axes vertical, or nearly 
 so, to the surface of the pulp. The subdivided and elongated nuclei become 
 attached by their extremities to the corresponding nuclei of the cells in ad- 
 vance; and the attached extremities become confluent (</); so that lines or 
 
180 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 Fig. 82. Fig. 83. 
 
 f 
 
 OOD 
 
 Vessels of Dental Papilla. 
 
 files of nuclear matter are formed, which 
 present an unbroken continuity from 
 one primary cell to another. While 
 these changes are proceeding, the cal- 
 careous salts furnished by the blood 
 begin to be accumulated in the interior 
 of the cells, and to be aggregated in a 
 semi-transparent state around the cen- 
 tral granular part of the elongated nu- 
 clei, which now present the character 
 of rows of minute secondary cells ; and 
 the salts occupy, in a still clearer and 
 more compact state, the cavity of the 
 primary cell not occupied by the trans- 
 formed nuclei. The rows of minute 
 secondary cells (which appear scarcely 
 to advance beyond the condition of 
 simple granules) remain uncalcified in 
 the midst of the solid calcareous sub- 
 stance ; and thus constitute the tubuli 
 of the dentine, in which a granular or 
 bead-like aspect may generally be traced. 
 
 214. Around the tubes, in a transverse section, is a small circular space 
 (Fig. 84, 6,) manifestly distinct from the intertubular substance; and this is 
 regarded by Professor Owen as the indication of a membrane surrounding 
 the elongated and coalesced secondary cells. The traces of the original 
 boundary of the primary or parent-cells (Fig. 84, a, a), are generally lost; 
 but, as already remarked (210) they are sometimes preserved with suffi- 
 cient distinctness to be quite recognizable. The " primary curvatures" ob- 
 servable in the tubuli are due to the arrangement of the original linear series 
 
 Diagram of development of Dentine ; a, end 
 of a linear series of primary dentinal cells; 6, 
 cells with nuclei dividing; c, subdivision and 
 elongation of nuclear matter; d, elongated 
 nuclei uniting to form the areee of dentinal 
 tubes; e, e, calcified cap of dentine, formed by 
 the mtus-susception of the clear hardening 
 salts into the walls and cavities of the cells 
 and intercellular blastema i, e, and by their 
 partial exclusion from the moniliform nuclear 
 tracts/" f; g-, union of two peripheral nucle- 
 olar or secondary cells with one nearer the 
 centre of the pulp. 
 
DEVELOPMENT OF DENTINE. 
 
 181 
 
 
 SKI 
 
 m 
 
 Inner surface of portion of calcified dentinal pulp, 
 forming cap of dentine ; a, intervals and walls of pri- 
 mary dentinal cells ; 6, walls of dentinal tubes ; c, nu- 
 clear matter, establishing areas of dentinal tubes. 
 For clearer demonstration, the number of tubes iu 
 the area of each cell is made less than in nature. 
 
 of parent cells ; whilst the " se- 
 condary curvatures" are accounted for 
 by the fact, that the elongated nuclei 
 usually unite with each other at ob- 
 tuse angles, and not in perfectly straight 
 lines, (Fig. 83, d.) Thus we are to 
 regard the Dentine as composed of the 
 original cells of the pulp, which have 
 become consolidated by the calcifying 
 process, in every part save that which 
 is occupied by the rows of granules 
 or incipient cells, developed from the 
 metamorphosed nuclei. The calca- 
 reous matter appears to be chemically 
 united, as in Bone, with an animal 
 base; the cavity of each cell being 
 pervaded by both ; so that, when the 
 whole of the calcareous matter is re- 
 moved by dilute acid, a cartilaginous- 
 looking mass remains, which preserves 
 the form of the tooth. The calcifying process takes place first on the exterior 
 of the pulp, and gradually extends inwards ; and the capillary blood-vessels alto- 
 gether retreat from the calcifying portion, and form their terminal loops upon 
 the surface of the part which still remains unconsolidated. As the calcifica- 
 tion extends inwards, the pulp, of course, progressively decreases ; fewer 
 nuclei are formed in the cells ; and these do not acquire so large a size. Here 
 and there it is seen, that the inner extremities of two of the granular tracts, 
 in the part last calcified, converge, and connect themselves with a single tract 
 in the layer nearer the centre of the pulp, (Fig. 83, g) ; in which we see the 
 origin of the bifurcation of the tubuli. This bifurcation becomes more fre- 
 quent, as the calcifying process approximates towards the centre and base of 
 the pulp ; and it is thus that the main tubes are formed. In some of the cells, 
 at and near the central and basal part of the pulp, the nucleus undergoes no 
 division ; but it merely elongates, and sometimes becomes angular or radiated, 
 thus showing a form of transition to the stellate nucleus of the bone-cells. 
 As already stated, we occasionally find modifications of the dentine in this 
 situation, which closely resemble true bone in structure. 
 
 215. The Enamel-pulp is not formed until after the dental papilla has 
 become inclosed in a capsule, by the process to be presently described ( 217, 
 c). It differs from the dentinal pulp, at its first formation, in the more fluid 
 state of its blastema ; and in containing fewer and more minute cells. The 
 enamel-pulp is derived from the free inner surface of the capsule ; of which 
 we may regard its cells as the epithelium. The cells are largest and most 
 numerous in that portion of the pulp which most nearly approaches the den- 
 tal papilla ; and many of them show a nuclear spot (Fig. 85, /, h). In the 
 portion of the enamel-pulp most distant from the capsule, the cells, at first 
 spherical, become impacted against one another, and are pressed into hexago- 
 nal or polygonal forms (i, i) ; the fluid blastema being now almost excluded from 
 between them. In the part in closest contiguity with the surface of the den- 
 tinal pulp, the cells increase in length, either by the elongation of each indi- 
 vidual cell, or by the coalescence of several (j) ; the nuclei (k) disappear ; and 
 the cells, now forming long prisms (/), absorb into themselves calcareous salts, 
 which henceforth completely fill them, in a clear and crystalline form. These 
 salts would not seem to be united, as in bone and dentine, with any organic 
 matters; the small quantity of this existing in Enamel, being probably em- 
 
182 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC, 
 
 Fig. 85. Fig. 86. 
 
 Formation of the Cementum ; m, primary cells ; p, their 
 granular nuclei; n, more minutely granular blastema; o, the 
 primary cell enlarged, and receiving the hardening salts ; n' ' 
 calcined blastema; P')P', stellate nuclei of fully-formed ce- 
 mental cells. 
 
 ployed wholly in forming the walls of the pris- 
 matic cells. The disappearance of the nucleus, 
 previously to the calcification of the cell, is 
 evidently the reason of the absence of any 
 permanent space or tube in its interior unoccu- 
 pied by mineral matter. The islands of Ena- 
 mel, which are found in the midst of the dentine, 
 in the compound teeth of Herbivorous animals, 
 are formed from extensions of the same ena- 
 mel-pulp, with that which gives origin to the 
 general envelope of the tooth ( 217, c). 
 
 216. The "Cemental pulp," or matrix of 
 the Crusta Petrosa, is in fact nothing else than 
 the capsule itself; in which, at an early period, 
 nucleated cells are found, distributed in the 
 midst of a granular blastema, which is copi- 
 ously supplied by vessels. The process of 
 calcification begins in the portion nearest the 
 dentine ; and consists, as elsewhere, in the 
 absorption of calcareous matter into the cavi- 
 ties of the cells, in the more close aggregation 
 of the cells with each other, and in the changes which take place coincidently 
 in their nuclei. These, which are at first large granular spots of a rounded 
 form, send out radiating prolongations, which extend quite to the borders of 
 the cell; and as the calcareous salts which penetrate the cell, are not depo- 
 sited in the space occupied by the nuclei, the stellate cavities, or lacunae and 
 diverging canaliculi, are left, which are so analogous to those of bone, as to 
 serve to identify the two tissues. In the cementum, as in Bone and Dentine, 
 the consolidating substance appears to consist of mineral and organic matter 
 in a state of chemical union. The boundaries of the original cells usually 
 disappear in this, as in similar cases ; so that nothing remains in the fully- 
 formed cementum, to mark its cellular origin, save the stellate lacuna which 
 represent the positions of the formerly-existing nuclei. 
 
 Formation of Enamel ; h. primary 
 cells suspended in fluid blastema g; 
 t, the same more fully developed and 
 become angular; ./, the same be- 
 coming prismatic ; fc, the nucleus 
 disappearing; J, the modified pris- 
 matic cells, filled with calcareous 
 salts, forming the spicula and fibres 
 of enamel. 
 
DEVELOPMENT OF THE TEETH. 
 
 183 
 
 217. As it is of much practical importance to understand the origin of the 
 several kinds of Human Teeth, and the times of their appearance, some de- 
 tails upon these subjects will be given ; those which relate to the mode of de- 
 velopment being principally derived from the researches of Mr. J. Goodsir.* 
 
 a. At the sixth week of Foetal life, a deep narrow groove may be perceived, in the upper 
 jaw of the Human embryo, between the lip and the rudimentary palate; this is speedily 
 divided into two by a ridge, which afterwards becomes the external alveolar process ; and 
 it is in the inner groove, that the germs of the teeth subsequently appear. Hence this may 
 be termed the primitive dental groove. At about the seventh week, an ovoidal papilla, 
 consisting of a granular substance, makes its appearance on the floor of the groove, near 
 its posterior termination ; this papilla is the germ of the Anterior superior Milk Molar 
 tooth. About the eighth week, a similar papilla, which is the germ of the Canine tooth, 
 arises in front of this; and during the ninth week the germs of the Incisors make their ap- 
 pearance under the same form. During the tenth week, processes from the sides of the 
 dental groove, particularly the external one, approach each other, and finally meet before 
 and behind the papilla of the anterior Molar ; so as to inclose it in a follicle, through the 
 mouth of which it may be seen. By a similar process, the 
 other teeth are gradually inclosed in corresponding follicles. 
 The germ of the Posterior milk Molar also appears during 
 the tenth week, as a small papilla. By the thirteenth week, 
 the follicle of the Posterior Molar is completed ; and the 
 several papillae undergo a gradual change of form. Instead 
 of remaining, as hitherto, simple, rounded, blunt masses of 
 granular matter, each of them assumes a particular shape ; 
 the Incisors acquire in some degree the form of the future 
 teeth ; the Canines become simple cones ; and the Molars 
 become cones flattened transversely, somewhat similar to 
 carnivorous molars. During this period, the papillae grow 
 faster than the follicles ; so that the former protrude from 
 the mouth of the latter. At this time, the mouths of the 
 follicles undergo a change, consisting in the development of 
 their edges, so as to form Opercula; which correspond in 
 some measure with the shape of the crowns of the future 
 teeth. There are two of these opercula in the Incisive follicles, three for the Canines, and 
 
 Fig. 88. 
 
 Fig. 87. 
 
 Upper jaw of human embryo 
 at 6th week ; showing b, the primi- 
 tive Dental Groove, behind a, the 
 Lip. 
 
 Diagrams illustrative of the formation of a Temporary, and its corresponding Permanent Tooth, from 
 
 a Mucous Membrane. 
 
 four or five for the Molars. At the fourteenth week, the inner lip of the dental groove has 
 increased so much, as to meet and apply itself in a valvular manner to the outer lip or 
 
 Edin. Med. and Surg. Journal, vol. li. 
 
184 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 ridge, which has been also increasing. The follicles at this time grow faster than the pa- 
 pilla?, so that the latter recede into the former. The primitive dental groove then contains 
 ten papilla-, inclosed in as many follicles; and thus all necessary provision is made for the 
 production of the first set of teeth. (This series of changes is represented in Fig. 88, a g.) 
 The groove is now situated, however, on a higher level than at first 5 and it has undergone 
 such a change by the closure of its edges, as to entitle it to the distinctive appellation of 
 secondary dental groove. It is in this secondary groove that those structures originate, which 
 are destined for the development of the Second or Permanent set of Teeth, of those at 
 least which replace the Milk Teeth. This is accomplished in the following manner. 
 
 b. At about the fourteenth or fifteenth week, a little crescentic depression may be observed, 
 immediately behind the inner Opercula of each of the Milk-tooth follicles. This depres- 
 sion gradually becomes deeper, and. constitutes what maybe termed a cavity of reserve ; 
 adapted to furnish delicate mucous membrane, for the future formation of the sacs and pulps 
 of the ten anterior Permanent teeth. These cavities of reserve are gradually separated 
 from the secondary dental groove, by the adhesion of their edges; and they thus become 
 minute compressed sacs, situated between the surface of the gum and the milk-sacs. They 
 gradually recede, however, from the surface of the gum, so as to be posterior instead of in- 
 ferior to the milk sacs; and at last they imbed themselves in the submucous cellular tissue, 
 which has all along constituted the external layer of the milk-sac. The implantation of the 
 Permanent tooth-sacs in the walls of the Temporary follicles, gives to the former the appear- 
 ance of being produced, by a gemmiparous process from the latter. This series of changes 
 is represented in Fig. 88, g n. 
 
 c. We now return to the Milk-teeth, the papillae of which, from the time that their follicles 
 close, become gradually moulded into their peculiarly Human shape. The Molar pulps be- 
 gin to be perforated by three canals, which, proceeding from the surface towards the centre, 
 gradually divide their primary bases into three secondary bases ; and these become deve- 
 loped into the fangs of the future teeth. Whilst this is going on, the sacs grow more rapidly 
 than the papilla?, so that there is an intervening space, which is filled with a gelatinous gra- 
 nular substance the enamel blastema ; this closely applies itself to the surface of the pa- 
 pilla, but does not adhere to it. The branch of the dental artery which proceeds to each 
 sac, ramifies minutely in its proper membrane, but does not send the smallest twig into the 
 granular substance. At this period, the tubercles and apices of the papillas or pulps become 
 converted into real dentine or tooth-substance, in the manner already stated ( 213) ; and the 
 granular matter is absorbed as fast as this appears ; so that, when the process of conversion 
 has reached the base of the pulp, the interior of the dental sac is left in the villous and vas- 
 cular condition of a true Mucous membrane, having upon it a very thin layer of the granular 
 substance, or enamel pulp, which may be considered as a sort of Epithelium ; and it is by 
 the deposition of calcareous matter in the long prismatic cells of this, that the enamel is 
 
 00 
 
 
 Diagrams illustrative of the formation of the three Permanent Molar teeth, from the non-adherent 
 portion of the Dental Groove. 
 
 formed. The opercula, which close the mouth of the dental sac, attain a much greater de- 
 velopment in the Molar teeth of Herbivorous animals; where they dip down into the midst 
 of the dentinal pulp, and give origin to insulated spots both of enamel and cementum. It 
 has been remarked by Mr. Lintott, that the lines along which the opercula meet, on the 
 
DEVELOPMENT OF THE TEETH. 185 
 
 crown of the Human molar teeth, that is to say. the groove which separates their tubercles, 
 is by far the most frequent seat of incipient decay ; probably from its tissue having been 
 at the first less perfectly formed than that of the remainder. 
 
 d. Whilst these changes are going on, other important preparations are being made for the 
 Permanent set. The general adhesion of the edges of the Primitive Dental Groove, ( a) 
 does not invade the portion which is situated behind the Posterior Milk follicle ; this retains 
 its original appearance for a fortnight or three weeks longer, and affords a nidus for the de- 
 velopment of the papilla and follicle of the Anterior Permanent Molar tooth, which is de- 
 veloped in all respects on the same plan with the Milk teeth. After its follicle has closed, 
 the edges of the dental groove meet over its mouth ; but as the walls of the groove do not 
 adhere, a considerable cavity is left between the sac of the tooth and the surface of the 
 gum. The cavity is a reserve of delicate mucous membrane, to afford materials for the 
 formation of the Second Permanent Molar, and of the Third Permanent Molar, or Wisdom- 
 tooth. The process just described is represented in Fig. 89, a c. It will be convenient 
 here to continue the account of the development of these teeth, although it takes place at a 
 much later period. Towards the end of fretal life, the increase of the bulk of the Milk-tooth 
 sacs takes place so much more rapidly than the growth of the jaw, that the sac of the An- 
 terior Permanent Molar is forced backwards and upwards, into the maxillary tuberosity 5 
 and thus it not only draws the surface of the gum in the same direction, but lengthens out 
 the great cavity of reserve (Fig. 99, e?). During the few months which succeed birth, how- 
 ever, the jaw is greatly lengthened ; and when the infant is eight or nine months old, the 
 Anterior Permanent Molar resumes its former position in the posterior part of the dental 
 arch ; and the great cavity of reserve returns to its original size and situation (c). This 
 cavity, however, soon begins to bulge out at its posterior side, and projects itself, as a sac, into 
 the maxillary tuberosity (y) ; a papilla or pulp appears in its fundus ; and a process of con- 
 traction separates it from the remainder of the cavity of reserve. Thus the formation of 
 the Second Permanent Molar from the first, takes place on precisely the same plan with the 
 formation of the Permanent Bicuspids from the Temporary Molars. The new sac at first 
 occupies the maxillary tuberosity (g) ; but the lengthening of the jaw gradually allows it to 
 fall downwards and forwards, into the same line, and on a level, with the rest (A). Before 
 it leaves the tuberosity altogether, the posterior extremity of the remainder of the cavity of 
 reserve sends backwards and upwards its last offset the sac and pulp of the Wisdom-tooth 
 (i) ; this speedily occupies the tuberosity after the second molar has left it (j) ; and ulti- 
 mately, when the jaw lengthens for the last time, at the age of nineteen or twenty, it takes 
 its place at the posterior extremity of the range of the adult teeth (&). Thus, the Wisdom- 
 teeth are the second products of the posterior or great cavities of reserve ; and the final effects 
 of development in the secondary dental groove. In the Elephant, in which there is a con- 
 tinual new production of molar teeth at the back of the jaw, it is probable that from each 
 sac a cavity of reserve is formed, which produces the succeeding tooth ; and thus the only 
 essential difference between its dentition and that of Man, consists in the degree of continu- 
 ance of this gemmiparous process ; which ceases in Man, after being twice performed, but 
 is repeated in the Elephant until nearly the close of its life. 
 
 e. We have thus sketched the history of the Development of the Teeth, up to the time 
 when they prepare to make their way through the gurn. The first stage of this development 
 may be termed the papillary and the second the follicular. The latter terminates when the 
 papillae are completely hidden by the closure of the mouths of the follicles, and of the groove 
 itself. The succeeding stage, which has long been known as the saccular, is the one during 
 which the whole formation of the Tooth-substance, and of the Enamel, takes place. It is 
 during this period, also, that the ossification of the jaw is being effected ; and that the bony 
 sockets are formed for the teeth, by the consolidation of the anterior and posterior ridges 
 bounding the alveolar groove (in which the dental groove was originally imbedded), and of 
 the interfollicular septa, which are produced by the meeting of transverse projections from 
 these ridges. The history of development in the Lower Jaw is very nearly the same; the 
 chief difference being in the origin and situation of the primitive dental groove. 
 
 /. We have now only to consider the fourth or eruptive stage, that in which the Teeth 
 make their way through the gum. This process chiefly results from the lengthening of the 
 fang, by the addition of new bony matter ; and the crown of the tooth is thus made to press 
 against the closed mouth of the sac (Fig. 98, m). This at last gives way, so that the sac as- 
 sumes its previous condition of an open follicle. When the edge of the tooth has once made 
 its way through the gum, it advances more rapidly than can well be accounted for by the 
 usual rate of lengthening of its fang; and this appears to be due to the separation of the 
 bottom of the sac from the fundus of the alveolus ; so that the whole tooth-apparatus is car- 
 ried nearer to the surface, leaving a space at the bottom of the alveolar cavity, in which the 
 further lengthening of the root can take place (). The open portion of the sac remains as 
 the narrow portion of the gum, which forms a vascular border arid groove round the neck 
 of the perfected tooth (o). The deeper portion of the sac adheres to the fang of the tooth, 
 
 16* 
 
186 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 and is converted by ossification into the Cementum or Crusta Petrosa ( 216). What is 
 Commonly denominated the Periosteum of the Tooth, really belongs as much to the Alveolus. 
 It is connected with the tooth by the submuoous cellular tissue, which originally intervened 
 between the tooth-sac and the walls of the osseous cavity. It appears from Mr. Nasmyth's 
 researches, that the inner layer of the portion of the capsule which covered the crown of 
 the tooth, remains adherent to it; forming a thin coating of Crusta Petrosa (most of which 
 is, however, soon worn off) over the Enamel. During the period that the Milk-teeth have 
 been advancing, along with their sockets, to their perfect state and ultimate position, the Per- 
 manent sacs have been receding in an opposite direction, and have with their bony crypts 
 been enlarging; and at last they occupy a position almost exactly below the former (n ando). 
 They still retain a communication with the gum, however; the channel by which they de- 
 scended not having completely closed up, arid the neck of the sac being elongated into a 
 cord which passes through this. The channels may afterwards serve as the itinera dentium, 
 and the cords as gubernacula ; but it is uncertain whether they really afford any assistance in 
 directing the future rise of the tooth to the surface ; the successive stages of which are repre- 
 sented in Fig. 98, p t. The sacs of the permanent teeth derive their first vessels from the 
 gums ; ultimately they receive their proper dental vessels from the Milk-sacs ; and, as they 
 separate from the latter into their own cells, the newly-formed vessels, conjoining into com- 
 mon trunks, also retire into permanent dental canals, and gradually become the most direct 
 channels for the blood transmitted through the jaw. 
 
 g. The following interesting generalizations respecting the development of the teeth, result 
 from Mr. Goodsir's researches. 1. The Milk-teeth are formed on both sides of either jaw 
 in three divisions, a Molar, a Canine, and an Incisive ; in each of which, dentition pro- 
 ceeds in an independent manner. 2. The dentition of the whole arch proceeds from 
 behind forwards; the Molar division commencing before the Canine, and the Canine 
 before the Incisive. 3. The dentition of each of the divisions proceeds in a contrary direc- 
 tion, the Anterior Molar appearing before the Posterior, the Central Incisor before the La- 
 teral. 4. Two of the subordinate phenomena of nutrition also obey this inverse law ; 
 the follicles closing by commencing at the median line and proceeding backwards ; and the 
 dental groove disappearing in the same direction. 5. Dentition commences in the Upper 
 Jaw, and continues in advance during the most important period of its progress. The 
 development of the Superior Incisors, however, is- retarded by a peculiar cause; so that the 
 Inferior Incisors have the priority in the time of their completion and appearance. 6. The 
 germs of the Permanent teeth, with the exception of that of the Anterior Molar, appear in a 
 direction from the median line backwards. 7. The Milk-teeth originate, or are developed, 
 from mucous membrane. 8. The Permanent teeth, also originating from mucous membrane, 
 are of independent origin, and have no connection with the milk-teeth. 9. A tooth-pulp 
 and its sac must be referred to the same class of organs, as the combined Papilla and Folli- 
 cle from which a hair or feather is developed. 
 
 h. The following is the usual order and period of appearance, of the several pairs of Milk- 
 teeth. The Four Central Incisors first present themselves, usually about the seventh month 
 after birth ; but frequently much earlier or later : those of the Lower Jaw appear first. 
 The Lateral Incisors next show themselves, those of the Lower Jaw coming through before 
 those of the upper ; they usually make their appearance between the seventh and tenth months. 
 After a short interval, the Anterior Molars present themselves. generally soon after the 
 commencement of the Second Year ; and these are followed by the Canines, which usually 
 protrude themselves between the fourteenth and twentieth months. The Posterior Molars are 
 the last, and the most uncertain in regard to their time of appearance ; this varying from 
 the eighteenth to the thirty-sixth month. In regard to all except the front teeth, there is no 
 settled rule as to the priority of appearance of those in the Upper or Under Jaw ; some- 
 times one precedes, and sometimes the other; but in general it may be stated, that, when- 
 ever one makes its appearance, the other cannot be far off. The same holds good in re- 
 gard to the two sides, in which development does not always proceed exactly pari passu. 
 The period of Dentition is one of considerable risk to the Infant's life. The pressure upon 
 the nerves of the gum, which necessarily precedes the opening of the sac and the eruption 
 of the tooth, is a fruitful source of irritation ; producing disorder of the whole system, espe- 
 cially of the Digestive organs, and not unfrequently giving origin to fatal Convulsive affec- 
 tions. These last have been particularly studied by Dr. M. Hall, who recommends the free 
 use of the gum-lancet, as a most important means of prevention and cure. Even where 
 Dentition proceeds quite naturally and is not itself a cause of diseased action, it induces an 
 irritable state of the whole constitution, which aggravates the effects of other morbific causes. 
 It is, therefore, of the greatest consequence that the infant should be withdrawn during this 
 period, from all injurious influences ; and that no irregularity of diet, or deficiency of fresh 
 air and exercise, should operate to its disadvantage. 
 
 i. After the lapse of a few years, the further elongation of the jaw permits the appear- 
 ance of the First True Molar; which, as already remarked, is really a Milk-tooth, so far as 
 its formation is concerned. This commonly presents itself about the middle or end of the 
 
DEVELOPMENT OF THE TEETH. 187 
 
 Seventh Year; sometimes preceding, and sometimes following, the exchange of the Central 
 Incisors, which takes place about the same time. When the Permanent Teeth have so 
 much enlarged, that they can no longer be contained within their own alveoli, they press 
 upon the anterior parietes of those cavities, and cause their absorption ; so that each tooth 
 is allowed to come forwards, in some degree, into the lower part of the socket of the cor- 
 responding Temporary tooth. The root of the temporary tooth now begins to be absorbed, 
 generally at the part nearest its successor ; and this absorption proceeds as the new tooth 
 advances, until the root of the Milk-tooth is completely removed: when its crown falls off, 
 leaving room for the permanent tooth to supply its place (Fig. 88, p ). This absorption 
 is usually regarded as due to the pressure of the Permanent tooth, but this does not appear 
 to be the case ; for it is mentioned by Mr. Bell, that it is not an uncommon occurrence for 
 the root of the temporary tooth to be wholly absorbed, and for the crown to fall out spon- 
 taneously, long before the succeeding tooth has approached the vacant space. The same 
 has been remarked by Mr. Bell, of the cavity in the jaw which is formed for the reception 
 of the sac of the Permanent tooth, at the time that it buds off from that of the milk-tooth 5 
 the excavation being often seen to commence before the new sac is formed. Hence, although 
 the two processes, growth, and absorption, are usually contemporaneous in each instance, 
 they are by no means dependent on each other. Still it would seem that the existence, if 
 not the pressure of the new Tooth is necessary to determine the absorption of the old ; for 
 cases are not unfrequent, in which the Temporary teeth retain their situation in the mouth, 
 with considerable firmness, until adult age, the corresponding permanent ones not having 
 been formed. 
 
 k. In the successive replacement of the Milk-teeth by the Permanent set, a very regular 
 order is usually followed. The Middle Incisors are first shed and renewed, and then the 
 Lateral Incisors. The Anterior Milk Molars next follow ; and these are replaced by the An- 
 terior Bicuspid teeth. About a year afterwards, the Posterior Milk Molars are shed, and are 
 replaced in like manner by Bicuspid teeth. The Canines are the last of the Milk-teeth to 
 be exchanged ; the development of the new ones not taking place until the 12th year. In 
 the succeeding year, the Second pair of the True Molars appears ; the third pair, or denies 
 sapientuK, are seldom developed until three or four years subsequently, and often much 
 longer. It has been recently proposed* (and, from the evidence adduced in its favour, the 
 proposition would seem entitled to considerable attention) to adopt the successive stages in 
 the Second Dentition, as standards for estimating the physical capabilities of Children, es- 
 pecially in regard to those two periods which the Factory Laws render it of the greatest 
 importance to determine, namely, the ages of nine and thirteen years. Previously to the for- 
 mer, a child is not permitted to work at all ; and up to the latter, it may be only employed 
 during 9 hours a day. The necessities or the cupidity of Parents are continually inducing 
 them to misrepresent the ages of their children; and it has been found desirable, therefore, 
 to seek for some test, by which the capability of the Child may be determined, without a 
 knowledge of its age. A standard of Height has been adopted by the Legislature for this 
 purpose; but upon grounds which, Physiologically considered, are very erroneous ; since, as is 
 well known, the tallest children are frequently the weakliest. According to Mr. Saunders, 
 the degree of advance of the Second Dentition may be regarded as a much more correct 
 standard of the degree of general development of the organic frame, and of its physical 
 powers ; and it appears from his inquiries, that it may be relied on as a guide to the real 
 age, in a large proportion of cases ; whilst no serious or injurious mistake can ever arise 
 from its use. It may happen that local or constitutional causes may have slightly retarded 
 the development of the Teeth ; in which case the age of the individual would rather be 
 under-estimated, and no harm could ensue : on the other hand, instances of preiTiature de- 
 velopment of the Teeth very rarely, if ever, occur : so that there is no danger of imputing 
 to a Child a capability for exertion which he does not possess, as the test of height is con- 
 tinually doing. Moreover, if such an advance in Dentition should occur, it might probably 
 be regarded as indicative of a corresponding advance in the development of the whole or- 
 ganism ; so that the real capability would be such as the teeth represent it. 
 
 /. The following is Mr. Saunders' statement of the Ages at which the Permanent teeth 
 respectively appear. The first True Molars usually make their appearance towards the end 
 of the 7th year. Occasionally one of them protrudes from the gum at 6, or more frequently 
 at 6$ years of age ; but the evolution of the whole of them may be regarded as an almost 
 infallible sign of the Child's being 7 years old. In other instances, however, where the tooth 
 on one side of the mouth is freely developed, it is fair to reckon the two as having emerged 
 from their capsule ; since the development of the other must be considered as retarded. This 
 rule only holds good, however, in regard to teeth in the same row ; for the development of 
 the teeth in either jaw must not be inferred from that of the corresponding teeth in the other. 
 
 * "The Teeth a Test of Age, considered with reference to the Factory Children." By 
 Edwin Saunders. 
 
188 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 With this understanding, the results of the application of the following table will probably 
 be very near the truth. 
 
 Central Incisors developed at .... 8 years. 
 Lateral Incisors . . . . . . 9 
 
 First Bicuspid 10 
 
 Second Bicuspid 11 
 
 Canines 12 to 12^ 
 
 Second Molars 12^ to 14 
 
 The following are the results of the application of this test, in a large number of cases 
 examined by Mr. Saunders. Of 708 children of nine years old, 530 would have been pro- 
 nounced by it to be near the completion of their ninth year ; having the central, and either 
 three or four lateral, incisors fully developed. Out of the remaining 178, it would have in- 
 dicated that 126 were 8 years old, as they presented one or two of the Lateral Incisors; 
 and the 52 others would have been pronounced 8 years old, all having three or four of the 
 Central Incisors. So that the extreme deviation is only 12 months ; and this in the incon- 
 siderable proportion (when compared with the results obtained by other means) of 52 in 708, 
 or 7^ per cent. Again, out of 338 children of 13 years of age, 294 might have been pro- 
 nounced with confidence to be of that age, having the Canines, Bicuspid, and Second Molars, 
 either entirely developed, or with only the deficiency of one or two of either class. Of the 
 44 others, 36 would have been considered as in their 13th year, having one of the Posterior 
 Molars developed ; and 8 as near the completion of the 12th, having two of the Canines, 
 and one or two of the Second Bicuspid. In all these instances, the error is on the favourable 
 side, that is, on the side on which it is calculated to prevent injury to the objects of the 
 inquiry ; in no instance did this test cause a Child to be estimated as older or more fit for 
 labour than it really was. 
 
 m. The value of this test, as compared with that of Height, is manifested by a striking ex- 
 ample adduced by Mr. Saunders. The height of one lad, J. J., aged 8 years and 4 months, 
 was 4 feet and of an inch ; that of another boy, aged 8 years and 7 months, was only 3 
 feet 7 inches. According to the standard of height adopted by the Factory Commissioners 
 (namely, 3 feet 10 inches), the taller lad would have been judged fit for labour, whilst the 
 shorter would have been rejected. The Dentition of the latter, however, was further ad- 
 vanced than that of the former; for he had two of the Lateral Incisors, whilst the former 
 had only the Central ; and the determination of their relative physical powers, which would 
 have been thus formed, would have been in complete accordance with the truth. The elder 
 boy, though shorter than the other by 5 inches, possessed a much greater degree both of 
 corporeal and mental energy, and his pulse was strong and regular ; whilst that of the 
 younger lad, who was evidently growing too fast, was small and frequent. An instance 
 even more striking has come under the Author's own observation. 
 
 10. Simple Tubular Tissues. 
 
 218. We have seen that all the Animal Tissues, whose structure has been 
 yet considered, derive the materials of their growth and renovation from the 
 nutrient fluid ; which is brought into a more or less close relation with their 
 elementary parts, by means of Capillary blood-vessels. These seem to have 
 a claim to be regarded as among the elementary parts of the fabric; since they 
 are formed quite independently of the larger trunks, and have little in common 
 with them in their function. All those changes which take place between 
 the blood and the surrounding parts, whether ministering to the functions of 
 Nutrition, Secretion, or Respiration, occur during its movement through the 
 Capillary vessels: and the function of the larger trunks is merely to bring to 
 them a constant supply of fresh blood, regulated according to the demand 
 created by the actions to which it is subservient ; and to remove the fluid 
 which has circulated through them. When we examine into the structure of 
 the Circulating apparatus in Plants and in the lower Animals, we find that 
 the canals, which convey the nutritive fluid, are of two kinds ; either simple 
 excavations in the solid tissues or unfilled vacuities ; or tubes with definite 
 membranous walls. The former are known, in Plants, under the name of 
 inter-cellular passages ; and, among the lower tribes in particular, they have 
 a large share in the conveyance of the nutritious fluid from one part of the 
 
STRUCTURE OF CAPILLARY BLOOD-VESSELS. 
 
 189 
 
 structure to the other. Similar passages exist to a great extent among the In- 
 vertebrata ; the venous circulation in particular being mainly carried on by 
 them. We have an example of them, even in Man, in the Sinuses through 
 which the venous blood is returned from the Brain ; these sinuses being simple 
 passages formed by the folds of the Dura Mater. In the higher Plants, however, 
 the circulation of fluid is for the most part carried on through Ducts, having 
 distinct membranous parietes ; and these ducts may be either straight and 
 simple tubes, as are those of the interior of the stem through which the sap 
 ascends ; or they may form a network by their mutual anastomosis, such as 
 that by which the sap descends through the bark and newer wood. Both of 
 these forms of ducts appear to be formed by the coalescence of cells ; the 
 straight cylindrical ducts being formed from cells, arranged in a simple linear 
 manner ; and the network of vessels for the descent of the elaborated sap, 
 being produced by the junction, at various points, of cells of less regular form, 
 which stretch out to meet each other. 
 
 219. In all the higher Animals, in their adult condition at least, the 
 Capillary circulation is entirely carried on through tubes having distinct mem- 
 branous parietes. These tubes commonly form a minutely-anastomosing net- 
 work ; into which the blood is brought by the ramifications of the arteries on 
 one side, and from which it is returned by the radicles of the veins on the other. 
 The walls of the tubes are composed of a delicate membrane, in which an 
 appearance of transverse striation (as if produced by minute annular fibres) 
 can sometimes be discerned. The diameter of the Capillaries varies in dif- 
 ferent animals, in accordance with that of their blood-corpuscles ; thus the 
 
 Fig. 90. 
 
 Capillary circulation in a portion of the web of a Frog's foot, magnified 110 diameters ; 1, trunk of 
 vein ; 2, 2, its branches ; 3, 3, pigment cells. 
 
 Capillaries of the Frog are of course much larger than those of Man. The 
 diameter of the latter appears, from the measurements of Weber, Mu'ller, and 
 others, to vary from about the 1 -3700th to the 1 -2500th of an inch ,- but as 
 they can only be examined after death, it is probable that these statements are 
 
190 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 not altogether exact, particularly as tubes of the smallest of the above sizes 
 would not admit ordinary blood-corpuscles. The dimensions of the individual 
 vessels, indeed, are by no means constant ; as may be seen by watching the 
 Circulation in any transparent part, for some little time. Putting aside the 
 general changes, in diameter, which result from circumstances affecting all the 
 capillaries of a part, it may be observed that a single capillary will sometimes 
 enlarge or contract by itself without any obvious cause. Thus, the stream 
 of blood will sometimes be seen to run into passages, which were not before 
 perceived ; and it has hence been supposed that they were new excavations, 
 formed by the retreating or removal of the solid tissue through which it passes. 
 But a more attentive examination shows, that such passages are real capilla- 
 ries, which did not, at the time of the first observation, admit the stream of 
 blood-corpuscles, in consequence of the contraction of their calibre, or of some 
 other local impediment ; and that they are brought into view by the simple 
 increase in their diameter. The compression of one of the small arteries 
 will generally occasion an oscillation of the corpuscles of blood in the small- 
 est capillaries, which will be followed by the disappearance of some of them ; 
 but when the obstruction is removed, the blood soon regains its former velocity 
 and force, and flows exactly into the same passages as before. 
 
 220. The opinion was long entertained, that there are vessels adapted to sup- 
 ply the white or colourless tissues ; carrying from the arteries the Liquor 
 Sanguinis, or fluid portion of the blood; and leaving the Corpuscles behind, 
 through inability to receive them. But such a supposition is altogether 
 groundless. Some of the white tissues, as Cartilage, are altogether destitute 
 of vessels ; and in others, the supply of blood is so scanty, as not to commu- 
 nicate to them any decided hue. It is evident from what has been already 
 stated, that the idea that Nutrition can only be carried on by means of Capil- 
 lary vessels, is entirely gratuitous. There is no essential difference, in fact, 
 between the nutrition of the non-vascular tissues, and that of the islets in the 
 midst of the network of capillary vessels, which traverses the most vascular. 
 
 Fig. 91. 
 
 Capillary vessels from the pia mater ; o. calibre of the tube, partly occupied by oval nuclei, alter- 
 nately arranged lengthways, and epithelial in their character; 6, b, b, nuclei projecting on the exterior 
 of the tube ; c, c, walls, and d, calibre, of a large branch ; /,/, oval nuclei, arranged transversely. Mag- 
 nified 410 diameters. 
 
FORMATION OF CAPILLARY BLOOD-VESSELS. 191 
 
 In both cases, the nutrient materials conveyed by the blood are absorbed by 
 the cells or other elementary parts of the tissue immediately adjoining the 
 vessels, and are imparted by them to others which are further removed ; and 
 the only variation which exists, is in the amount of the portion of tissue that 
 has to be thus traversed. There is great variety in this respect, as we 
 have seen, among the vascular tissues ; and we are only required to extend 
 our ideas, from the largest of the islets which we find in these, to the still 
 more isolated structures, of which the non-vascular tissues are composed. 
 The distribution of Capillaries through the vascular tissues, and the character 
 of the reticulation which they form, vary so greatly in the different parts of 
 the fabric, that it is possible to state with tolerable certainty the nature of the 
 part from which any specimen has been detached, whether a portion of 
 skin, mucous membrane, serous membrane, muscle, nerve, fat, areolar tissue, 
 gland, &c. But the arrangement of vessels peculiar to each evidently has 
 reference only to the convenience of the distribution of blood among the 
 elementary parts of the tissue, and varies with their form. It is not possible 
 to imagine that it has any other relation than this to their function ; since, as 
 already shown, the function of each separate element of the organ, of which 
 that of the entire organ is the aggregate, is due to its own inherent vital 
 powers, the supply of blood being only required as furnishing the material, 
 on which these are to be exercised. 
 
 221. It has been rendered highly probable, by the observations of Schwann 
 and other Physiologists, that the Capillaries of Animals originate in cells, like 
 the straight and anastomosing Ducts of Plants. Bodies having the appear- 
 ance of cell-nuclei may frequently be seen in the walls of the capillaries of 
 embryos and of tadpoles ; and these are too wide apart to warrant the idea, that 
 they are the nuclei of epithelial cells, such as those which line the larger 
 vessels. Similar nuclei may be brought into view in the capillaries of adult 
 animals, by treating them with acetic acid ; and they are particularly well 
 seen in the Pia Mater, which consists almost entirely of a congeries of blood- 
 vessels (Fig. 91). The accompanying figure shows the contrast between the 
 long oval nuclei b, 6, imbedded at intervals in the walls of the true capillaries, 
 and rather projecting on their exterior ; and the nuclei of the epithelium-cells, 
 
 y, /, lining the interior of a larger branch, which last are more numerous and 
 of less regular form, and are sometimes placed transversely to the direction of 
 the tube. 
 
 222. The first formation of the Capillary blood-vessels in the vascular 
 area in the Bird's egg, is described by Schwann as being 
 
 affected entirely by the coalescence of cells, which send 
 
 off prolongations in various directions, in the manner of 
 
 stellate pigment-cells, such as those seen at c, c, Fig. 90. 
 
 By the junction of these prolongations, a network of tubes 
 
 is formed, which is at first very irregular in its character ; 
 
 the greatest diameter of the tubes being in the situation 
 
 of the centres or bodies of the original cells; whilst be- 
 
 tween these, at the points where their prolongations coa- 
 
 lesced, they are much contracted. The calibre of the ves- 
 
 sels, however, gradually becomes equalized (Fig. 92) ; and 
 
 the network becomes connected with the larger trunks, and 
 
 bears a part in the general circulation. Appearances indica- First appearance of 
 
 tive of a similar process, have been seen in the tail of very blood-vessels in the 
 
 young Tadpoles ; so that it may probably be regarded as the vascular layer of the 
 
 general method, by which new capillaries are formed in germinal membrane of 
 
 the natural process of growth. Observations upon the ? Fowl at the 3fith hour 
 
 history of the operations, which are performed for the ofincubatkm - 
 
192 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 repair of injuries, lead to precisely the same conclusions. The first appear- 
 ance of the vascular network in the newly-forming tissue, is in the form of 
 transparent arborescent streaks ; which push out extensions on all sides ; these 
 encounter one another, and form a complete series of capillary reticulations, 
 some of which come into connection with the vessels of the surrounding parts. 
 According to the observations of Mr. Travers,* isolated corpuscles enter these 
 newly-formed capillaries, and perform an oscillating movement in them for 
 some hours, before any series of them passes into it ; so that we cannot re- 
 gard the new channel as burrowed out by a string or file of red corpuscles, 
 pushed forth from the nearest capillary by vis a tergo, as some have main- 
 tained. 
 
 11. Compound Tubular Tissues. 
 
 223. There now remain to be described two elements of the Animal fabric, 
 to which there is scarcely anything that bears the least analogy in the struc- 
 ture of Plants ; namely, the Muscular and Nervous tissues. We have seen 
 that, putting aside the Simple Fibrous tissues, whose function is purely me- 
 chanical, the Animal fabric, so far as we have yet passed its elements under 
 review, is constructed upon the very same type with that of Plants ; all the 
 parts actively concerned in the processes of nutrition, secretion, reproduction, 
 &c., retaining their original cellular character ; the vessels that serve for the 
 conveyance of fluid, having their origin in cells, whose cavities have coalesced ; 
 whilst the more solid portions of the frame- work are made up of united cells, 
 whose cavities are occupied by internal deposit. Now the purpose of the 
 Muscular and Nervous system is entirely different. The former is the one, 
 by which all the sensible movements of the body are immediately effected ; 
 and it is only amongst a small number of Plants, that any such movements 
 are exhibited. The latter serves as the instrument by which sensations are 
 received ; and by which the instincts, emotions, or volitions, excited by these 
 sensations, act upon the muscles : a class of functions which we have no 
 reason whatever to regard as performed by Plants. In fact, as already pointed 
 out ( 1 4), the distinction between the two kingdoms is more properly 
 founded upon the presence of these functions and of their instruments in the 
 Animal, and upon their absence in the Plant, than upon any other structural 
 character. 
 
 224. Now it might have not been unreasonable to expect, that tissues alto- 
 gether so dissimilar in their properties, and in the purposes to which they are 
 destined, should have a structure departing widely from the type of the simple 
 Cell. Yet it does not appear that this is the case. That portion of the Nerv- 
 ous matter, by which its most active functional changes are effected, retains 
 its original cellular character without alteration ; and the so-called fibres, 
 which constitute the Nerve-trunks, and which convey the influence of these 
 changes, are in reality tubes, formed as it would seem by the coalescence of 
 a linear series of cells, and chiefly distinguished by the peculiar nature of 
 their internal deposit. In like manner, we shall find that the ultimate Mus- 
 cular Fibre is also a tube, formed out of the same elements, and distinguished 
 by the nature of its contents ; which, in the most perfect form of the tissue, 
 are composed of linear series of extremely minute secondary cells. 
 
 225. Muscular tissue exists under two forms ; one in which the ultimate 
 fibres are marked by transverse striae ; and the other in which they are plain 
 or unstriped. The former is chiefly employed in performing the various move- 
 ments, which are effected through the agency of the Nervous system, and which 
 
 * Physiology of Inflammation and the Healing Process. 
 
STRIATED MUSCULAR FIBRE. 
 
 193 
 
 Fig. 93. 
 
 are connected with the peculiarly Animal powers of the being. The latter is 
 with difficulty called into action through the nervous system, but is much 
 more readily excited by stimuli applied to itself; and this is employed to per- 
 form various movements, which are more immediately concerned in the Vege- 
 tative or organic functions.* 
 
 226. When we examine an ordinary Muscle (from one of the extremities, 
 for example) with the naked eye, we observe that it presents a fibrous ap- 
 pearance ; and that the fibres are arranged with great regularity, in the direc- 
 tion in which the muscle is to act. Upon further examination it is found, 
 that these fibres are arranged in fasciculi or bundles of larger or smaller size, 
 connected by means of areolar tissue ; and when the Microscope is applied to 
 the smallest fibre which can be seen with the naked eye, it is seen itself to 
 consist of a fasciculus, composed of a number of cylindrical fibres lying in a 
 parallel direction, and closely bound to- 
 gether. These primitive fibres present 
 two sets of markings or stride; one set 
 longitudinal, the other transverse or 
 annular. By more closely examining 
 these fibres, when separated from each 
 other, it is frequently seen that each may 
 be resolved into fibrillse, by the splitting 
 of its contents in a longitudinal direction, 
 as shown in Fig. 93. These fibrillae have 
 a peculiar beaded appearance, which will 
 be presently noticed more particularly. 
 It not unfrequently happens, however, that 
 when a fibre is drawn apart, its contents 
 separate in the direction of the transverse stria3 ; forming a series of discs, as 
 shown in Figs. 94 and 95. This cleavage is just as natural as the former, 
 though less frequent; and it leads us to a view of the composition of Muscu- 
 lar Fibre, somewhat different from the one commonly adopted. To use the 
 
 Fig. 94. 
 
 Fasciculus of Fibres of Voluntary Muscle; 
 the fibres separated at one end, into brush- 
 like bundles of fibrillae. 
 
 Portion of Human Muscular fibre, separating into discs, by cleavage in direction of transverse striae. 
 
 words of Mr. Bowman,t it would be as proper to say, "that the fibre is a pile 
 of discs, as that it is a bundle of fibrillse ; but in fact it is neither the one nor 
 the other, but a mass in whose structure there is an intimation of the existence 
 of both, and a tendency to cleave in the two directions. If there were a gene- 
 ral disintegration along all the lines in both directions, there would result a 
 
 * By some, the two classes have been spoken of as those of Voluntary and Involuntary 
 muscles; but this distinction is not correct; since every muscle ordinarily termed voluntary, 
 may be called into action involuntarily. 
 
 t See Bowman on the Minute Structure and Movements of Voluntary Muscle; in Phil. 
 Trans. 1840. 
 
 17 
 
194 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 series of particles, which may be termed primitive particles or sarcous ele- 
 ments, the union of which constitutes the mass of the fibre. These elementary 
 
 [Fig. 95. 
 
 Fragments of Striped Elementary Fibres, showing a cleavage in opposite directions ; magnified 300 
 diameters; 1, longitudinal cleavage; the longitudinal and transverse lines are both seen; some longitu- 
 dinal lines are darker and wider than the rest, and are not continuous from end to end ; this results from 
 partial separation of the fibrillae; 6, fibriHee, separated from one another by violence at the broken end 
 of the fibre, and marked by transverse lines equal in width to those on the fibre ; 7, 8 represent two ap- 
 pearances commonly presented by the separated single fibrilla, (more highly magnified;) at 7 the borders 
 and transverse lines are all perfectly rectilinear, and the included spaces perfectly rectangular; at 8 the 
 borders are scalloped, the spaces bead-like ; when most distinct and definite, the fibrilla presents the 
 former of these appearances ; 2, transverse cleavage ; the longitudinal lines are scarcely visible ; 3, in- 
 complete fracture following the opposite surfaces of a disc, which stretches across the interval and re- 
 tains the two fragments in connection ; the edge and surface of this disc are seen to be minutely granular, 
 the granules corresponding in size to the thickness of the disc, and to the distance between the faint 
 longitudinal lines; 4, another disc nearly detached; 5, detached disc more highly magnified, showing the 
 sarcous elements.] 
 
 Fig. 96. 
 
 particles are arranged and united together in the two directions. All the re- 
 sulting discs, as well as fibrillae, are equal to one another in size ; and con- 
 tain an equal number of particles. The same particles compose both. To 
 detach an entire fibrilla, is to abstract a particle of every disc; and vice versa." 
 227. The elements of Muscular Fibre are bound together, in the perfect 
 condition of the fibre, by a very delicate tubular sheath. This cannot always 
 be readily brought into view ; but it is occasionally seen with great distinct- 
 ness : thus, when the two ends of a fibre are drawn apart, its contents will 
 
 sometimes separate without the rupture 
 of the sheath, which then becomes evi- 
 dent ; and this, during the act of con- 
 traction, may sometimes be observed 
 to rise up in wrinkles upon the surface 
 of the fibre, as seen in Fig. 100. This 
 sheath is quite distinct from the areolar 
 tissue, which binds the fibres into fasci- 
 culi; and it has been termed, for the 
 sake of distinction, the Myolemma. Its existence may be demonstrated in 
 any Muscular fibre, by subjecting it to the action of fluids, which occasion a 
 swelling of its contents ; this is especially the effect of acids and alkalies, and 
 may be well produced by the citric and tartaric acids, and by potash. For a 
 time, the Myolemma yields to the distention which takes place from within ; 
 but at last it bursts at particular points, and a sort of hernia of its contents 
 takes place, making the existence of a perfect envelope in all other parts quite 
 
 Fibre of Human Muscle broken across; the 
 fragments connected by the untorn Myolemma. 
 
STRIATED MUSCULAR FIBRE. 195 
 
 evident. This membrane is itself perfectly transparent, and has nothing to do 
 with the production of either the longitudinal or the transverse striae. There is 
 no reason to believe that it is perforated either by nerves or by capillary ves- 
 sels ; in fact it seems to be an effectual barrier between the real elements of 
 Muscular structure, and the surrounding parts. That it has no share in the 
 contraction of the fibre, is evident from the fact just mentioned, respecting the 
 condition which it occasionally presents when the fibre is much shortened. 
 
 228. Muscular Fibres are commonly described as cylindrical ; but there is 
 reason to believe that they are rather of a polygonal form, their sides being 
 flattened against those of adjoining fibres (Fig. 97). In some instances the 
 angles are sharp and decided ; in others they are rounded off, so as to leave 
 spaces between the contiguous fibres for the passage of vessels. In Insects, 
 the fibres often present the form of flattened bands. The average diameter of 
 the fibres in Man maybe stated at about l-400th of an inch; being somewhat 
 greater than this in the Male, and less in the Female. Their size varies con- 
 siderably, however, in different classes of animals ; and even in the same ani- 
 mal, and the same muscle. The following table gives illustrations of these 
 varieties; the extremes are those met with by Mr. Bowman himself; but 
 other observers speak of dimensions more widely separated. 
 
 Fractions of an inch. 
 
 *"" j"te : : ; E t 
 
 MAMMALU . ^ ;;; W ij, 
 
 Mole j^j to T { F 
 
 Mouse ? J- F 
 
 Owl T7 ,i ff?r to 
 
 BIRDS . 
 
 REPTILES 
 
 FISH 
 
 INSECTS 
 
 Chaffinch ^ to ^ 
 
 Heron T ^ to TTTIF 
 
 Fro ? ToVir to sffs- 
 
 Lizard ^ 
 
 Boa *i* to T , 
 
 Skate ^ to & 
 
 Cod ....'.... Tjjg- tO 
 
 Sprat , ^^ to 
 
 Staghorn Beetle .... 5 y to 
 
 Blue-bottle Fly 7 y to 
 
 f 
 
 4UT 
 
 It is interesting to remark, upon this table, that the Muscular Fibre of Rep- 
 tiles and Fishes is upon the whole much larger than that of other Vertebrata, 
 and that its dimensions present the greatest extremes of variation ; whilst in 
 Birds, it is much smaller than in all other Vertebrata, and its dimensions are 
 also less variable. Further, the size of the fibres bears no proportion to that 
 of the animal; for we observe that in the Chaffinch they are larger than in 
 the Owl, in the Cat larger than in the Horse, and in the Frog often larger 
 than in the Boa. Moreover in Insects, the diameter of the fibres is even 
 greater than it is in Mammalia. The average distance of the transverse striae, 
 in the muscular fibre of different animals, is very nearly uniform ; as will be 
 seen from the following table. Between the extremes, however, there is con- 
 siderable variation ; and this will be presently shown to depend upon the con- 
 dition of the muscle, at the time of examination. The distance is not only 
 often different in the same muscle and the same fasciculus, but even in the 
 same fibre in different parts of its length. The figures indicate the number of 
 striae in l-1000th of an inch. The extremes in the same specimen, however, 
 are in no instance so widely apart, as the table indicates for the Class ; the 
 
196 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 greatest proportion between the maximum and minimum being, except in In- 
 sects, as 2 to 1. 
 
 Mean. 
 
 9-4 
 10-9 
 104 
 111 
 11-1 
 
 9-5 
 
 229. It has been maintained by some, that each Muscular Fibre is a hol- 
 low bundle of fibrillae ; but the appearance presented by transverse sections 
 proves that this is not the case, the whole area of the tube being occupied by 
 fibrillae, without any trace of central cavity. The extremities of the cut fibrillae, 
 however, cannot always be distinguished in Mammalia, in consequence, as it 
 would seem, of their close and intimate lateral union ; but they are very evi- 
 
 Fig. 97. 
 
 
 Maximum. 
 
 Minimum. 
 
 Human 
 
 . 15-0 
 
 6-0 
 
 Other Mammalia . 
 
 . 15-0 
 
 6-7 
 
 Birds 
 
 . 140 
 
 7-0 
 
 Reptiles 
 
 . 20-0 
 
 G-7 
 
 Fish 
 
 . 18-0 
 
 7-5 
 
 Insects 
 
 . 16-0 
 
 4-5 
 
 Transverse section of Muscular fibres from pectoral muscle of Teal ; showing the irregular form of the 
 fibres, and the aggregation of circular particles, with which they are completely filled. 
 
 dent in Birds, Reptiles, and Fishes (Fig. 97). The addition of an acid in- 
 creases the distinctness of the fibrillae, by widening the interstices between 
 them. 
 
 230. When the fibrilla3 are separately examined, they are found to present 
 an alternation of dark and light spaces, corresponding with the transverse 
 striae of the fibre, and the lighter intervals between them. It is this alterna- 
 tion, which gives to the fibrillae the beaded appearance they present, when 
 their outline is not perfectly seen. When good specimens, however, are 
 carefully examined under a sufficient magnifying and good defining power, it 
 is seen that the border of the fibrillae is straight or nearly so ; so that the 
 beaded appearance is an optical illusion. Moreover, each of the light spaces 
 is seen to be crossed by a delicate but distinct line, separating it into two 
 equal parts; and -upon attentive examination it is seen, that a transparent 
 border, equal in breadth to either of these parts, is seen at the sides, as well 
 as between the ends, of the dark spaces. Thus each dark space is completely 
 surrounded by this pellucid border ; and it can scarcely be doubted that the 
 whole constitutes a complete though minute cell, and that the entire fibrilla 
 
STRIATED MUSCULAR FIBRE. 
 
 197 
 
 Fig. 99. 
 
 7> 
 
 Fragment of Muscular fibre 
 from macerated heart of Ox, 
 showing formation of strise by 
 the aggregation of fibrillse. 
 
 I 
 
 is made up of a linear aggregation of such cells.* When the fibril is in a 
 state of relaxation, as seen at , the diameter of the cells is greatest in the 
 longitudinal direction ; but when it 
 is contracted, the fibril increases in 
 diameter as it diminishes in length ; 
 so that the transverse diameter of 
 each cell equals or even exceeds the 
 longitudinal diameter, as seen at b. 
 The difference between the two 
 states is frequently much more strik- 
 ing than is represented in the figure. 
 Thus the act of Muscular contrac- 
 tion seems to consist in a change of 
 
 form in the cells of the ultimate fibrillae, consequent upon an 
 attraction between the walls of their two extremities, or per- 
 haps between their nuclei; and.it is interesting to observe 
 how very closely it thus corresponds with the contraction of 
 certain Vegetable tissues, of which the component cells change 
 their form when irritated, and thus produce a movement ( 1). 
 The essential difference, therefore, between the striated mus- 
 cular tissue of Animals, and the contractile tissues of Plants, 
 consists in the subjection of the former to nervous influence. 
 The diameter of the ultimate fibrillae, and the length of the 
 component cells, will of course vary according to the contract- St 
 
 , , T r- i /*i i . -u >L- ultimate fibrillae of 
 
 ed or relaxed condition of the fibre ; but they otherwise seem 
 to be tolerably uniform in different animals. The average 
 diameter may be stated at about l-10,000th of an inch; but 
 it has been observed as high as l-5000th, and as low as 1- 
 20,000th, even when not put upon the stretch. The length of 
 the component cells corresponds, of course, to the distance of 
 the striae on the entire fibre ; and this also has been just shown 
 to average about 1-1 0,000th of an inch. 
 
 231. The general opinion as to the disposition of the fibres during the con- 
 traction of Muscle, has been, until lately, that of Prevost and Dumas, who 
 stated that they were thrown into a sinuous or zig-zag flexure. Recent ob- 
 servations, however, have fully demonstrated the incorrectness of this view ; 
 the improbability of which might have been suspected from the consideration, 
 
 * This account of the ultimate structure of Muscular Fibre was first published simulta- 
 neously (March, 1846), by the Author of this Treatise, in his Manual of Physiology, and by 
 Dr. Sharpey, in his new edition of Dr. Quain's Anatomy. Both of these statements, which 
 were completely independent of each other, were founded upon the examination of the very 
 beautiful preparations of Muscular Fibre, made by Mr. Lealand the Optician ; who appears 
 to have been the first to direct attention to the transverse line dividing the bright space, and 
 to the bright border edging the dark spot. A similar delineation had previously been pub- 
 lished, however, by Dr. Goodfellow (Physiological Journal, No. IV.) ; but his interpretation 
 of the appearances was altogether different; for he considered the dark spaces as the " sar- 
 cous elements" of Mr. Bowman, and regarded them as separately inclosed within partitions 
 formed by internal prolongations of the general investing Myolemma. By Mr. Erasmus 
 Wilson, again, the appearances were described as leading to the belief that two kinds of 
 cells exist in each fibrilla, a dark and a light ; a pair of light cells, separated by the delicate 
 transverse line just spoken of, being interposed between each pair of dark ones [System of 
 Anatomy, 3d Am. Edit, p. 183]. The bright edging to the dark spots was overlooked by 
 him. The view taken by Dr. Sharpey and the Author has the entire concurrence of several 
 of the most eminent Microscopists in London and elsewhere; and it is confirmed by the 
 remarkable similarity between the aspect of the Muscular fibrilla, and that of a minute Con- 
 ferva, seen under the same magnifying power, the cellular constitution of the latter being 
 indubitable. 
 
 17* 
 
 striated muscular 
 fibre : a, a fibril 
 in a state of ordi- 
 nary relaxation ; 
 6, a fibril in a state 
 of partial contrac- 
 tion. 
 
198 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 that fibres in this state of flexure could scarcely be imagined to be exerting 
 any force of traction. Prof. Owen has noticed that, in the contracted state of 
 the very transparent muscles of some Entozoa, each separate fibre, which 
 may be seen with great distinctness, presents a knot or swelling in the middle, 
 besides being generally thickened ; but that it is simply shortened, without 
 falling out of the straight line. Dr. A. Thomson remarked the same thing in 
 the Frog; single fibres, whilst continuing in contraction, being simply short- 
 ened, without falling into zig-zag lines: and he was led to suspect, from this 
 and other circumstances, that the zig-zag arrangement was not produced, until 
 the act of contraction had ceased. The recent inquiries of Mr. Bowman 
 have proved most satisfactorily, that, in the state of contraction, there is an 
 approximation of the transverse stria3, and a general shortening of the fibre ; 
 and that its diameter is at the same time increased; but that it is never thrown 
 out of the straight line, except when it has ceased to contract, and its two 
 extremities are still held in proximity by the contraction of other fibres. The 
 whole process may be distinctly seen under the Microscope, in a single fibre 
 isolated from the rest : it is, of course, desirable to select the specimen from 
 those animals, in which the contractility of the Muscle is retained for the 
 longest period after death, which is particularly the case in Reptiles among 
 Vertebrata, and in most Invertebrata (Mr. Bowman particularly recommends 
 the Crab and Lobster) ; but the change has been fully proved to differ in no 
 essential degree, in the warm-blooded Vertebrata. The contraction usually 
 commences at the extremities of the fibre; but it frequently occurs also at one 
 or more intermediate points. The first appearance is a spot more opaque 
 than the rest, caused by the approximation of a few of the dark points of 
 some of the fibrilla3 : this spot usually extends in a short time through the 
 whole diameter of the fibre ; and the shading, caused by the approximation 
 of the transverse striae, increases in intensity. The stria? are found to be 
 two, three, or even four times as numerous, in the contracted, as in the un- 
 contracted part ; and are also .proportionally narrower and more delicate. 
 The line of demarcation between the contracted and uncontracted portions is 
 well defined; but, as the process goes on, fresh stria3 are absorbed (as it 
 were) from the latter into the former. The contracted part augments in thick- 
 ness ; but not in a degree commensurate with its diminished length ; so that 
 its solid parts lie in smaller compass than before, the fluid which previously 
 intervened between them, being pressed out in bullae under the myolemma 
 (Fig. 100). The force with which the elements of the fibre thus tend to ap- 
 proximate is evidently considerable ; for if the two extremities be held apart, 
 
 Fig. 100. 
 
 Muscular fibre of Dytiscus, contracted in the centre; the striae approximated ; the breadth of the fibre 
 increased ; and the sarcolemma raised in bullae on its surface. 
 
 the fibre is not unfrequently ruptured. This corresponds with the appear- 
 ances found in the muscles of persons who have died from tetanus ; for in 
 the ruptured fibres of those muscles, which have been the subjects of the 
 spasmodic action, the striae have been observed to approximate so closely, 
 as to.be scarcely distinguishable. When the contraction is not very decided, 
 the dark and elevated spot appears to play like a wave along the fibre, before 
 it involves the whole diameter in any part (Fig. 101, 2) ; and even when con- 
 
STRIATED MUSCULAR FIBRE. 
 
 199 
 
 Fig. 101, 
 
 3 
 
 
 siderable traction is being exercised, there is continual interchange in the ele- 
 ments by which it is effected, the discs at one end of the contracted part 
 receding from each other, whilst at the other end new discs are being re- 
 ceived into it. 
 
 232. The foregoing description is chiefly 
 derived from the appearances presented by 
 muscular fibre, when spontaneously passing 
 into that state of contraction, which is termed 
 the rigor mortis ; but there can be no rea- 
 sonable doubt, that the phenomena of con- 
 traction, excited by the agency of the nerves, 
 are precisely similar. Mr. Bowman has re- 
 marked, that stimuli of various kinds, direct- 
 ly applied to them, produce corresponding 
 effects, although, in the case of galvanism, 
 the change is too rapid for its steps to be 
 followed ; and that, from the appearances 
 presented by muscles which have been af- 
 fected with tetanic spasms, the contraction 
 produced by nervous agency may be inferred 
 to correspond in character. It now remains, 
 therefore, to inquire what is the cause of the 
 zig-zag arrangement, which is often seen in 
 the fibres. This may be easily produced, by 
 approximating the ends of a fasciculus, after 
 the irritability of its fibres has ceased ; and 
 it would not seem unlikely, that the passage 
 of vessels or nerves should determine the 
 points at which the flexures take place. 
 Hence it appears, that the sinuous or zig-zag 
 arrangement is that into which fibres are 
 naturally thrown, if, on elongation following 
 
 contraction, they are not at once stretched by antagonist muscles,* Many 
 facts support the opinion, which has long been held by several Physiologists, 
 that, when an entire muscle is contracting, all its fasciculi are not in con- 
 traction at once ; but that there is a continual interchange in the parts, 
 by which the tension is effected ; some relaxing, whilst others are short- 
 ening. When the ear is applied to a muscle in vigorous action, an exceed- 
 ingly rapid faint silvery vibration is heard ; which seems to be attributable to 
 this constant movement in its substance. Now, on examining a muscle, of 
 which some fasciculi present the zig-zag arrangement, others will be seen (if 
 the two extremities have not been purposely approximated) to be quite straight, 
 and in a state of contraction ; and it thence appears, that the former appear- 
 ance is presented by bundles of fibres, which have either not yet entered into 
 contraction, or which have relaxed after undergoing it ; but of which the ex- 
 tremities are still approximated, by the agency of other contracting fibres. 
 The result of various experiments made for the purpose, leads to the conclu- 
 sion, that the total bulk of a muscle in contraction is not less than when it is 
 in a relaxed state ; or that the difference, if any exist, is extremely trifling. 
 
 233. Every Muscular Fibre, of the striated kind at least, is attached at its 
 extremities to white fibrous tissue ; through the medium of which it exerts its 
 contractile power on the bone or other substance, which it is destined to move. 
 
 Muscular'fibre of Skate, in'a state of 
 rest (1), and in three different stages of 
 contraction (2, 3, 4). 
 
 * Mr. Bowman's conclusions have recently been confirmed by Prof. E. Weber. (Archives 
 d' Anatomic Generate, Jan. 1846.) 
 
200 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 The whole fasciculus of fibrillae usually seems to end abruptly in a perfect 
 disk ; and the myolemma terminates there. The tendinous fibres are attached 
 to the whole surface of the disk; and probably become continuous with the 
 
 Fig. 102. 
 
 Attachment of Tendon to Muscular Fibre, in Skate. 
 
 myolemma. Thus the whole muscle is penetrated by minute fasciculi of tendi- 
 nous fibres ; and these collect at its extremities into a Tendon. Sometimes the 
 muscular fibres are attached obliquely to the tendon, which forms a broad 
 band that does not subdivide ; this is seen in the legs of Insects and Crusta- 
 cea, in which the muscular fibres have apenniform arrangement; being inserted 
 into the tendon, on either side, like the laminae of a feather into its stem. 
 
 234. The Muscular Fibre of Organic Life is very different from the pre- 
 ceding. It consists of a series of tubes, which do not present transverse 
 
 Fig. 103. 
 
 [Fig. 104.] 
 
 Non-striated Muscular Fibre; at 
 ft, in its natural state ; at a, show- 
 ing the nuclei after the action of 
 acetic acid. 
 
 4, A muscular fibre 
 of Organic Life with 
 two of its nuclei ; 
 taken from the uri- 
 nary bladder, and 
 magnified 600 diam- 
 eters ; 5, muscular 
 fibre of organic life 
 from the stomach, 
 magnified the same.] 
 
 strife, and in which the longitudinal striae are very faint ; these tubes are 
 usually much flattened, and cannot be shown to contain distinct fibrillee. 
 
NON-STRIATED MUSCULAR FIBRE. 201 
 
 Their size is usually much less than that of the fibres of Animal life ; but, 
 owing to the extreme variation in the flattening which they undergo, it is dif- 
 ficult to make a precise estimate of their dimensions. Those of the aliment- 
 ary canal are stated by Dr. Baly to measure from about the 1 -2500th to the 
 l-5600th of an inch; in the foot of the common Mussel, the Author has 
 found them to be as much as the 1 -1920th of an inch ; whilst in the respira- 
 tory sac of a Phallusia (an Ascidian Mollusk), their diameter is no more than 
 1 -8400th. They sometimes present markings, which indicate a granular ar- 
 rangement in their interior ; and these markings have occasionally a degree 
 of regularity, which approaches that of the striae on the striped Muscular fibres. 
 They frequently present nodosities at intervals, which are the nuclei of their 
 original component cells ; and, where these nuclei are not otherwise visible, 
 they may be brought into sight by acetic acid (Fig. 103, a). The plain or 
 non-striated fibres, like those of the other muscles, are usually arranged in a 
 parallel manner, into bands or fasciculi ; but these fasciculi are generally in- 
 terwoven into a net-work, not having any fixed points of attachment, but con- 
 tracting against each other. It is of this kind of structure, that the muscular 
 substance of the walls of the oesophagus, stomach, intestinal tube, bladder, 
 and uterus, is composed ; it occurs also in the bronchial tubes, in the ureters, 
 and most of the larger gland-ducts, and in the irjs. In the Heart, are found 
 various forms of Muscular fibre ; some being distinctly striated, others quite 
 plain ; and others of intermediate character. The average size of the fibres 
 is less than that of the fibre, of which the voluntary muscles are composed ; 
 and the fasciculi, instead of being straight and parallel, are considerably in- 
 terlaced. This intermediate character accords well, as we shall hereafter see, 
 with the actions of the organ ; which correspond in their energy and rapidity, 
 with the contractions of voluntary muscles ; whilst they agree with those of 
 the non-striated kind, in being but little influenced by the nervous system. 
 The middle coat of the Arteries contains a contractile tissue, very similar to 
 that of unstriped muscle ; and fibres of a similar nature are interwoven with 
 other fibrous tissues in the Skin, and especially in the Dartos, giving rise in 
 the former to the state termed cutis anserina, under the influence of cold or 
 of depressing emotions ; and in the latter to the wrinkling of the scrotum. 
 There are certain points, at which the one system of fibres comes into close 
 connection with the other. This is the case, for example, in the oesophagus; 
 the upper part of which contains striated fibres, and is thrown into contrac- 
 tion by nerves ; whilst the muscular wall of the lower part seems entirely 
 composed of non-striated fibres, and acts for the most part independently of 
 the nerves. The point of transition varies in different animals ( 386) ; and 
 seems not to be constant among individuals of the human species. 
 
 235. The Myolemma of the Muscular Fibre appears to be the part first 
 formed ; being distinctly visible long before any traces of fibrillaB can be ob- 
 served in it. This tube seems to take its origin, like the ducts of Plants, in 
 cells laid end to end, the cavities of which coalesce, by the disappearance of 
 the partitions, at a subsequent period ; and the nuclei of these original cells 
 may be distinctly seen, for some time after the appearance of the striae, which 
 indicate the formation of the fibrillae in their interior. In an early stage of 
 the development of the fibres, indeed, these bodies project considerably from 
 their sides : in this respect, as well as in others, there is a close correspond- 
 ence between the temporary character of the Muscular fibre of Animal life, 
 and the permanent condition of that of Organic life. In the fully formed 
 muscle of Animal life, they are not perceptible, except when a peculiar me- 
 thod has been adopted for bringing them into view. This method consists in 
 treating the fibre with weak acids, which render the nuclei more opaque, 
 whilst the surrounding structure becomes more transparent. They are usually 
 
202 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 numerous in proportion to the size of the fibre. There is every probability 
 that these nuclei continue to act, like the " germinal spots" of the glandular 
 
 Fig. 105. 
 
 Fig. 106. 
 
 Muscular fibres from foetal pectoral is ; 
 A, from Calf at two months ; B, from hu- 
 man foetus of nine months. 
 
 Mass of ultimate fibres from 
 the pectoralis major of the hu- 
 man fetus, at nine months. 
 These fibres have been im- 
 mersed in a solution of tartaric 
 acid ; and their " numerous cor- 
 puscles, turned in various direc- 
 tions, some presenting nucle- 
 oli," are shown. 
 
 follicles or parent-cells, as centres of nutrition ; from which the minute 
 secondary cells, that compose the fibrillae, are developed as they are re- 
 quired. The diameter of the Muscular fibre of the foetus is not above one- 
 third of that which it possesses in the adult ; and as the size of their ultimate 
 particles is the same in both cases, their number must be greatly multiplied 
 during the growth of the structure. But we shall find reason to believe, that 
 a decay is continually taking place in the component cells, with a rapidity 
 proportional to the functional activity of the Muscle, and their generation, 
 which occurs as constantly when the nutrient operations proceed in their 
 regular course, is probably accomplished by a development from these cen- 
 tres, at the expense of the blood, with which the muscle is copiously supplied. 
 
 236. From the preceding history it appears, that there is no difference, at 
 an early stage of development between the striated and non-striated forms of 
 Muscular fibre. Both are simple tubes, containing a granular matter, in which 
 no definite arrangement can be traced, and presenting enlargements occasioned 
 by the presence of the nuclei. But whilst the striated fibre goes on in its 
 development, until the fibrillae, with their alternation of light and dark spaces, 
 are fully produced, the non-striated fibre retains throughout life its original 
 embryonic character. 
 
 237. Notwithstanding the energy of growth in Muscular Fibre, and the 
 constant interstitial change which seems to take place in its contents, it is 
 doubtful if it is ever regenerated, when there has been actual loss of substance. 
 Wounds of muscles are united by Areolar tissue, which gradually becomes 
 condensed; but its fibres never acquire any degree of contractility. 
 
 238. The Chemical Composition of Muscular Fibre seems to be very uni- 
 form, from whatever source it is obtained. It is impossible, however, to de- 
 termine it with precision ; on account of the difficulty of completely isolating 
 the substance of the fibres from the areolar tissue, vessels, and nerves, that 
 are blended with them. The proper muscular substance differs from the 
 simple fibrous tissues, in not being resolvable into gelatine by the prolonged 
 action of boiling water; and in being soluble in acetic acid, from which it is 
 
CHEMICAL COMPOSITION OF MUSCLE. 203 
 
 precipitated by ferrocyanide of potassium, showing that it belongs to the pro- 
 teine-compounds. The following analyses of Muscle by Berzelius corre- 
 sponds very exactly with those since made by Braconnot, Schultz, Marchand, 
 and other Chemists : 
 
 Fibrine (from the proper muscular substance) . 
 
 Gelatine (from areolar tissues) 
 
 Albumen and hsematine 
 
 Phosphate of lime, with albumen ..... 
 
 Alcoholic extract, with salts (lactates?) .... 
 
 Watery extract, with salts ....... 
 
 Water, and loss 
 
 100-00 
 
 Thus something less than 23 percent, of solid matter exists in ordinary meat; 
 and in 100 parts of this solid mattter, there are about 7k parts of fixed salts. 
 
 \Kreatine (from xfsa?, flesh), originally discovered by Chevreul, in 1835, has been proved 
 by the recent investigations of Liebig to be a constant ingredient of the muscles of all the 
 higher classes of animals. Schlossberger found it in the flesh of the alligator. Its crystals 
 are colorless, perfectly transparent, and of great lustre. They form groups, the character 
 of which is exactly similar to that of sugar of lead. Its formula is C 8 N 3 H n 6 . It dissolves 
 easily in boiling water, and a solution saturated at 212 forms on cooling a mass of small bril- 
 liant crystals, and is nearly insoluble in cold alcohol. It is neither acid nor basic. From the 
 action of strong mineral acids, a new body of totally different chemical qualities, a true or- 
 ganic alkali is formed, which Liebig has called Kreatinine. It is easily obtained from the 
 hydrochlorate or the sulphate. Kreatinine is more soluble both in cold and hot water than 
 kreatine; it dissolves in boiling alcohol, and crystallizes on cooling. In its chemical cha- 
 racter it is analogous to ammonia. Its formula is C 8 N 3 H 7 2 . Researches on the Chemistry 
 of Food, by J. Liebig. London, 1847. M. C.] 
 
 a. The exact correspondence in ultimate composition, between dried Muscle, and dried 
 Blood, according to the analyses of Playfair and Bockmann, is not a little remarkable. The 
 following are their results. 
 
 PLAYFAIII. BOCKMASTN. 
 
 Muscle. Blood. Muscle. Blood. 
 
 Carbon . . . 51-83 51-95 51-89 51-96 
 
 Hydrogen . . . 7-57 7-17 7-59 7-33 
 
 Nitrogen . . . 15-01 15-07 15-05 1508 
 
 Oxygen ... 21'36 21-39 21-24 21-21 
 
 Ashes . . . 4-23 4-42 4-23 4-42 
 
 It may be questioned, from these results, whether the amount of Haematine in Muscle is not 
 greater than that which is represented by the previous analysis ; since a tissue composed of 
 Fibrine and Albumen alone, could not possess the same ultimate composition with one, in 
 which Haematine is present in large proportion. 
 
 b. Some very interesting researches have lately been made by Helmholtz,| on the changes 
 induced in the tissue by Muscular action. Powerful contractions were induced by electricity 
 in the amputated leg of a Frog ; and were kept up as long as the irritability was retained. 
 The flesh of the two limbs was then analyzed; and it was found that, in every instance the 
 water-extractive was diminished in the electrized muscle, to the extent of from 20 to 24 per 
 cent.; whilst the alcoholic extract was increased to about the same amount. Similar results 
 were obtained from experiments on warm-blooded animals ; the amount of change, how- 
 ever, being less, on account of the shorter duration of their muscular irritability. 
 
 239. Muscular tissue, properly so called, is as extra-vascular as cartilage 
 or dentine ; for its fibres are not penetrated by vessels ; and the nutriment 
 required for the growth of its contained matter must be drawn by absorption 
 through the myolemma. But the substance of Muscle, as a whole, is ex- 
 
 * [The recent researches of Liebig make it exceedingly probable that lactic acid is a con- 
 stituent of muscle. Its purpose in the animal organism will be alluded to hereafter. M. C.] 
 t Mullet's Archiv., 1845. 
 
204 
 
 OX THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 Capillary net- work of Muscle. 
 
 tremely vascular, the capillary vessels being distributed in parallel lines, united 
 
 by transverse branches, in the minute inter- 
 spaces between the fibres (Fig. 107); so that it 
 is probable that there is no fibre, which is not in 
 close relation with a capillary. The number 
 of blood-vessels in a given space will of course 
 be greater, where the fibres and the capilla- 
 ries are both small, as in Mammals and Birds, 
 than where they are of larger diameter, as in 
 Reptiles and Fishes ; and the former condition 
 will obviously be the one most favourable to 
 the performance of active changes between the 
 blood and the muscle. These changes consist, 
 it would appear, not merely in the nutrition of 
 
 the tissue; but in the supply of oxygen, which is a necessary condition of 
 the excitement of its activity. We shall hereafter see, indeed, that every 
 muscular contraction probably involves the disintegration of a certain amount 
 of its substance, through the union of oxygen, supplied by arterial blood, 
 with its elements ; and that the great demand for nutrition, which is occa- 
 sioned by muscular activity, is for the purpose of repairing this loss. The 
 muscles of warm-blooded animals speedily lose their irritability, after the 
 supply of arterial blood has been suspended, either through the cessation of 
 the general circulation, or by deficient aeration of the fluid. But the muscles 
 of cold-blooded animals, which are very inferior in the energy and rapidity 
 of their action, preserve their properties for a much longer period, after the 
 deprivation of their supply of arterial blood ; in accordance with the general 
 principle, that, the lower the usual amount of vital energy, the longer is its 
 persistence, after the withdrawal of the conditions on which it is dependent. 
 The very indisposition to a change of composition, on which the less ready 
 action depends, produces a longer retention of the power of acting. 
 
 240. The Muscles of Animal life are, of all the tissues except the skin, 
 those most copiously supplied with Nerves. These, like the blood-vessels, 
 lie on the outside of the Myolemma of the several fibres ; and their influence 
 must consequently be excited through it. The general arrangement of these 
 nerves is shown in Fig. 108. Their ultimate fibres or tubes cannot be said 
 
 Fig. 108. 
 
 Form of the terminating loops of the nerves in the muscles. 
 
 to terminate anywhere in the Muscular substance; for after issuing from the 
 trunks, they form a series of loops, which return either to the same trunk, or 
 
NERVOUS SYSTEM; ITS GENERAL STRUCTURE. 
 
 205 
 
 to an adjacent one. The occasional appearance of a termination to a nervous 
 fibril is caused by its dipping down between the muscular fibres, to pass to- 
 wards another stratum. The nerves are almost exclusively of the motor 
 kind; but a few sensory are blended with them. We see this most clearly 
 in cases in which the motor and sensory trunks supplying the muscles are 
 distinct ; as in the muscles of the orbit. The non-striated muscles are very 
 sparingly supplied with nerves ; and these are derived (for the most part, if 
 not entirely), from the Sympathetic system, rather than from the Cerebro- 
 Spinal. 
 
 241. We have, lastly, to consider the structure, composition, actions, and 
 mode of growth and regeneration of the Nervous Tissue ; the one which is 
 most distinctive of the Animal fabric, and which serves as the instrument of 
 the operations that are most peculiar to it. Wherever a distinct Nervous Sys- 
 tem can be made out (which has not yet been found possible in the lowest of 
 those beings, that, from their general structure and habits of life, are unques- 
 tionably to be ranked in the Animal Kingdom), it consists of two very different 
 forms of structure ; the presence of both of which, therefore, is essential to 
 our idea of it as a whole. We observe, in the first place, that it is formed of 
 trunks, which are distributed to different parts of the body, and especially to 
 the muscles and to the sensory surfaces ; and of ganglia, or masses with 
 which the central terminations of those trunks come into connexion. It is 
 easily established by experiment, that the trunks themselves have no power 
 of originating changes ; and that they only serve to conduct or convey the in- 
 fluence of operations which take place at their central or peripheral extremi- 
 ties. For if a trunk be divided in any part of its course, all the parts to which 
 the portion thus cast off from the ganglion is distributed, are completely para- 
 lyzed ; that is, no impression made upon them is felt as a sensation ; and no 
 motion can be excited in them by any act of the mind. Or, if the substance 
 of the ganglion be destroyed, all the parts which are exclusively supplied by 
 nervous trunks proceeding from it, are in like manner paralyzed. But if, 
 
 Fig. 109. 
 
 Dorsal ganglion of Sympathetic nerve of Mouse ; a, 6, cords of connection with adjacent sympathetic 
 ganglia ; c, c, c, c, branches to the viscera and spinal nerves ; d, ganglionic globules or cells ; e, nervous 
 fibres traversing the ganglion. 
 
 when a trunk is divided, the portion still connected with the ganglion be pinched 
 or otherwise irritated, sensations are felt which are referred to the points sup- 
 plied by the separated portion of the trunk ; which shows that the part re- 
 maining in connexion with the ganglion is still capable of conveying impres- 
 18 
 
206 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 sions, and that the ganglion itself receives these impressions, and makes them 
 felt as sensations. On the other hand, if the separated portion of the trunk 
 be irritated, motions are excited in the muscles which it supplies ; showing 
 that it is still capable of conveying the motor influence, though cut off from 
 the usual source of that influence. 
 
 242. In the ordinary Nerve-trunks, we find only one form of Nervous tis- 
 sue ; that which may be designated as the fibrous or tubular. In the Gan- 
 glia, we find, in addition to this, a substance made up of peculiar cells or 
 vesicles ; which may be distinguished as the vesicular nervous matter. In 
 fact, the character of a Ganglionic centre (which is frequently not otherwise 
 clearly distinguished as such) is derived from the presence of this vesicular 
 substance. 
 
 243. The ultimate Nerve-fibre, in its most complete form, such as is pre- 
 sented to us in the ordinary spinal nerves, is distinctly tubular ; being com- 
 posed of an external cylindrical membranous sheath, within which the peculiar 
 nervous matter is contained. This membranous tube, like the Myolemma of 
 muscular fibre, is extremely delicate and transparent ; and is nearly or quite 
 
 $ c I 
 
 A. Diagram of tubular fibre of a spinal nerve ; a. Axis cylinder, b. Inner border of white substance, 
 e, e. Outer border of white substance, d, d. Tubular membrane. B. Tubular fibres ; e, in a natural 
 state, showing the parts as in A. /. The white substance and axis cylinder interrupted by pressure, 
 while the tubular membrane remains, g. The same, with varicosities. h. Various appearances of the 
 white substance and axis cylinder forced out of the tubular membrane by pressure, i. Broken end of a 
 tubular fibre, with the white substance closed over it. k. Lateral bulging of white substance and axis 
 cylinder, from pressure. I. The same more complete, g'. Varicose fibres of various sizes, from the 
 cerebellum, c. Gelatinous fibres from the solar plexus, treated with acetic acid, to exhibit their cell- 
 nuclei. B and c magnified 320 diameters.] 
 
 homogeneous. It is not penetrated by blood-vessels ; nor is it ever seen to 
 branch or anastomose with others ; so that there is reason to regard it as form- 
 
TUBULAR NERVOUS TISSUE. 
 
 207 
 
 ing one continuous sheath, that isolates the contained matter from the surround- 
 ing tissue, along the whole course of the nerve-trunk, from its central to its 
 peripheral extremity. When the nerve-fibres are examined in a very fresh 
 state, their contents appear pellucid and homogeneous, and of a fluid consist- 
 ence ; so that each tube or fibre looks like a cylinder of clear glass, with sim- 
 ple, well-defined, dark edges. But a kind of coagulation soon takes place in 
 the contained substance, making it easily distinguishable from the tube itself; 
 for the latter is then marked by a double line, as shown in Fig. Ill, A. The 
 substance which is in immediate contact with the inner wall of the nerve-tube, 
 is more opaque than that which occupies its centre, and of a different refract- 
 ing power; and thus it forms a hollow cylinder, which surrounds the latter, 
 and which is known under the name of the White substance of Schwann. The 
 centre or axis of the tube is occupied by a substance that preserves its trans- 
 parency ; and this is the axis-cylinder of Rosenthal and Purkinje. It may be 
 surmised that the White substance of Schwann, which exhibits much variety 
 in thickness in different parts of the nervous system, chiefly serves, like the 
 membranous investment, to isolate the interior matter ; which last seems to be 
 the essential constituent of the nervous fibre. The whole of the matter con- 
 tained in the tubular sheath is extremely soft; yielding to very slight pressure, 
 and readily escaping from the cut extremities of the tubes. The tubular sheath 
 itself varies in density in different parts ; being stronger in the nervous trunks 
 than in the substance of the brain and spinal cord. In the former, it is not 
 difficult to show that the regular form of the nerve-tube is a perfect cylinder ; 
 though a little disturbance will cause an alteration in this, a small excess of 
 pressure in one part forcing the contents of the tube towards another portion, 
 
 Fig. 111. 
 
 
 Structure of nerve-tubes, magnified 350 diameters. A. Cylindrical tubuli from nerve. B, Varicose 
 tubuli from brain, c, Nerve-tubes, of which one exhibits the remains of nuclei in its walls. 
 
 where they are more free to distend it, and thus producing a swelling. The 
 greater delicacy of the tubular sheath in the latter, causes this result to take 
 place with yet more readiness ; so that a very little manipulation exercised 
 upon the fibres of the Brain or Spinal Cord, or on those of special sense, occa- 
 sions them to assume a varicose or beaded appearance (Fig. Ill, B), which, 
 when first observed by Ehrenberg, was thought to be characteristic of them. 
 When the fibres of these parts are examined, however, without any such pre- 
 paration, they are found to be as cylindrical as the others. The diameter of the 
 tubular fibres of the cerebro-spinal nerve-trunks in Man, usually varies from 
 about l-2000th to l-4000th of an inch, being sometimes as great, however, 
 as 1-1 500th of an inch ; and sometimes much below the least of the above 
 
208 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 dimensions. The fibres decrease in size as they approach the brain, either 
 directly, or through the medium of the spinal cord ; and in the brain itself they 
 continue to diminish, as they pass through the medullary towards the cortical 
 portion ; so that they are very commonly found of no more than 1 -7000th or 
 l-8000th of an inch in diameter, and sometimes as little as l-14,000th. Like 
 most other elementary structures, they are of considerably larger dimensions 
 in Reptiles and Fishes ; varying, according to Dr. Todd, from l-1260th to 
 l-2280th of an inch in the Frog; being in the Eel as much as the l-1040th 
 of an inch ; and in the optic nerve of the Cod, no less than l-650th of an inch 
 in diameter.* 
 
 244. Besides these proper tubular nerve-fibres, of which, in combination 
 with areolar and fibrous tissue, blood-vessels, &c., a large proportion of the 
 cerebro-spinal nerve-trunks are made up, there are certain other fibres, which 
 are peculiarly abundant in the trunks of the Sympathetic system, and which 
 are of different character from the preceding. They are chiefly distinguished 
 by their small size, their diameter not being above half or one-third of that of 
 the ordinary nervous tubuli. They are destitute of the double contour, which 
 has been shown to result in the preceding case from the presence of two dis- 
 tinct substances within the tubular investment; and their contents appear to 
 be homogeneous. And when they are aggregated in bundles, they possess a 
 yellowish-grey colour. Although these fine fibres exist in greater proportion 
 in the Sympathetic system than in the Cerebro-spinal, yet they are present 
 in great numbers in some of the nerves of the latter; and it is even question- 
 
 Primitive fibres and ganglionic vesicles of human brain, after Purkinje. A, ganglionic vesicles lying 
 amongst nerve-tubes and blood-vessels, in substance of optic thalamus ; a, vesicle more enlarged ; 6, 
 vascular trunk. B, B, vesicles with variously-formed processes, from dark portion of crus cerebri. Mag- 
 nified 350 diameters. 
 
 able, whether they may not be continuous with the ordinary tubular fibres. 
 They may be traced into the ganglia of the Sympathetic, into the ganglia on 
 the posterior roots of the Spinal nerves, and even to the ganglionic matter of 
 the Brain and Spinal Cord.t 
 
 * Cyclopaedia of Anatomy and Physiology, Vol. in., p. 593. 
 
 f Much controversy has recently taken place in Germany, regarding the existence of a 
 set of fibres peculiar to the Sympathetic system. The grey or gelatinous fibres, described by 
 Remak, and (following him) by Miiller and others, as essentially constituting the Organic 
 system of Nerves, are now generally admitted not to be entitled to the designation of nerve- 
 
VESICULAR NERVOUS TISSUE. 
 
 209 
 
 113. 
 
 245. The second primary element of the Nervous system, without which 
 the fibrous portion would seem to be totally inoperative, is composed of nu- 
 cleated cells, consisting of a finely granular substance, and lying somewhat 
 loosely in the midst of a minute plexus of blood-vessels. Their original form 
 may be regarded as globular ; whence they have been called ganglion-globules. 
 This, however, is liable to alteration; sometimes, perhaps, from external com- 
 pression ; but more commonly through their own irregular mode of growth. 
 They frequently extend themselves into long processes, which may give 
 them (according to the number thus projecting) a caudate or a stellate aspect, 
 resembling that of the pigment-cells of the Batrachia. These processes are 
 composed of a finely-granular substance, resembling that of the interior of the 
 vesicle, with which they seem to be distinctly continuous. They are very 
 liable to break off near the vesicle ; but if traced to a distance, they are found 
 to divide and subdivide, and at last to 
 
 give off some extremely fine transpa- 
 rent fibres ; some of which seem to in- 
 terlace with those of other stellate cells, 
 whilst others become continuous with 
 the axis-cylinders of the nerve-tubes. 
 Such vesicles have been seen alike in 
 the ganglionic masses of the Cerebro- 
 spinal, and in those of the Sympathetic 
 system.* Besides the finely-granular 
 substance just mentioned, these cells 
 usually contain a collection of pigment- 
 granules, which especially cluster round 
 the nuclei, and give them a reddish or 
 yellowish-brown colour. This pigment 
 seems to have some resemblance to 
 the hasmatine of the blood ; and it is 
 usually, if not invariably, deficient 
 among the In vertebra ta, as well as less 
 abundant in Reptiles and Fishes. The 
 vesicles are sometimes covered with a 
 layer of a soft granular substance, which adheres closely to their exterior and 
 to their processes ; this is the case in the outer part of the cortical substance 
 of the human brain. In other instances, each cell is inclosed in a distinct en-' 
 velope composed of smaller cells, closely adherent to each other, and to the 
 contained cell ; such an arrangement is common in the smaller ganglia, and 
 in the inner portion of the cortical substance of the brain. The diameter of 
 the vesicles is extremely variable, owing to the changes of form above de- 
 scribed ; that of the globular ones is usually between l-300th and l-1250th of 
 an inch. 
 
 246. In the central or ganglionic masses of the Nervous system, we find 
 these vesicles aggregated together, and imbedded in a finely-granular matter; 
 the whole being traversed by a minute plexus of capillary blood-vessels. 
 The entire substance, made up of these distinct elements, is commonly known 
 as the cineritious or cortical substance ; being distinguished by its colour, in 
 
 fibres, but to be a form of simple fibrous tissue. The peculiar fibres described above, were 
 first pointed out by Bidder and Volkmann ; whose statements in regard to them have re- 
 cently been confirmed by the laborious and impartial researches of Kdlliker. (See his work 
 "Die Selbstiindigkeit und Abhangigkeit des Sympathischen Nervensystems," 1844; and the 
 abstract of his results in Mr. Paget's able Report, in Brit, and For. Med. Review, July, 1846, 
 p. 271.) 
 
 * See Todd and Bowman's Physiological Anatomy, Vol. I., p. 214. See also Kolliker, loc. 
 cit.; and Dr. Radclyffe Hall, in Edinburgh Med. & Surg. Journal, April, 1846. 
 
 18* 
 
 Nerve-vesicles from the Gasserian ganglion of 
 the human subject : a. A globular one with de- 
 fined border; 6, its nucleus; c, its nucleolus. d. 
 Caudate vesicle, e. Elongated vesicle, with two 
 groups of pigment particles. /. Vesicle surround- 
 ed by its sheath, or capsule, of nucleated particles. 
 g. The same, the sheath only being in focns. 
 Magnified 300 diameters.] 
 
210 
 
 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 [Fig. 114. 
 
 Ganglion globules, with their processes, nuclei, and nucleoli: a. a. From the deeper part of the gray 
 matter of the convolutions of the cerebellum. The larger processes are directed towards the surface 
 of the organ, b. Another from the cerebellum, c. d. Others from the post, horn of gray matter of the dor- 
 sal region of the cord. These contain pigment, which surrounds the nucleus in c. In all these specimens 
 the processes are more or less broken. Magnified 200 diameters.] 
 
 Man and the higher animals at least, from the white substance composed of 
 nerve-tubes, of which the trunks of the nerves, as well as a large part of the 
 brain and spinal cord, are made up ; and occupying in the brain a position 
 external to the latter, which is often termed the medullary substance. This 
 position, however, is quite an exceptional one; for in the spinal cord and in 
 the scattered ganglia of Vertebrated animals, and in all the ganglionic centres 
 of ^Invertebrata, everywhere, in fact, except in the Brain, the vesicular 
 nerve substance occupies the centres of the ganglia; consequently the terms 
 
 cortical and medullary, as applied to the vesi- 
 [Fag. 115. cular and tubular substances respectively, are 
 
 quite inappropriate. Nor are the designations 
 that have reference to their colour, much more 
 uniformly correct: for, as we have seen, 
 the vesicular substance may be destitute of 
 internal pigment-granules, and the blood in 
 its capillary plexus may be pale or colourless, 
 so that the reddish-grey hue, which is ex- 
 pressed by the term cineritious, may be entirely 
 wanting ; whilst, on the other hand, we have 
 seen that certain of the nerve-fibres, making 
 up what is commonly termed the white sub- 
 stance, are of a grey colour. Hence the only 
 valid distinction between these two kinds of 
 nervous matter, is that which has reference to 
 their constitution; as consisting of cells or 
 vesicles on the one hand ; or of tubes or fibres, 
 on the other. 
 247. The connection between the fibrous and 
 
 A small piece of the otic ganglion of 
 the sheep, slightly compressed ; show- 
 ing the interlacement of the internal 
 fibres, and the vesicular matter. 
 (After Valentin.)] 
 
CONNECTION OF FIBROUS AND VESICULAR SUBSTANCES. 
 
 211 
 
 vesicular nervous elements, in the nervous centres, has not yet been tho- 
 roughly elucidated. It seems certain, on the one hand, that some of the 
 
 [Fig. 116. 
 
 [Fig. 117. 
 
 A. Blending of the vesicular and fibrous nervous 
 matter in the dentate body of the cerebellum: a, 
 Ganglion globule, with its nucleus and nucleolus. 
 b. Nerve-tube, slightly varicose, in close contact 
 with the ganglion globule, b'. Smaller nerve-tubes. 
 These parts all lie in a finely granular matrix in- 
 terspersed with nuclei, c. B. Vesicular and fibrous 
 matter of the laminae of the cerebellum, a. Gan- 
 glion globule, b. Very minute nerve-tubes tra- 
 versing a finely granular matrix, in which are 
 numerous rounded nuclei, c.] 
 
 From the Gasserian ganglion of an adult: a. a. 
 Ganglion globules with their nucleus, nucleated 
 capsule, and pigment, t. Tubular fibres, running 
 among the globules in contact with their capsule. 
 g. Gelatinous fibres also in contact with the gan- 
 glion globules. Magnified 3*20 diameters.] 
 
 fibres come into direct continuity with caudate prolongations of the ganglionic 
 corpuscles, and may thus be said to originate from them. This appears to 
 
 Fig. 118. 
 
 Primitive fibres and ganglionic vesicles. A, from sympathetic ganglion ; * a separate vesicle, show- 
 ing its pellucid nucleus and nucleolus. B, from grey substance of human cerebellum ; a, 6, plexus of 
 primitive fibres ; c, nucleated globules ; * a separate globule from human Gasserian ganglion. Magni- 
 fied 350 diameters. 
 
 be especially the case, with regard to the class of/ne fibres ( 244). On the 
 
212 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 other hand, it seems equally certain that there are many nerve-tubes which 
 simply enter the ganglionic masses, pass round and amongst the cells, and 
 then emerge from them, without having undergone any distinct change, save 
 that they present a soft and varicose appearance, whilst threading their way 
 through the cells. And it is equally certain that there are many ganglionic 
 corpuscles, which never acquire the caudate prolongations, and which appear 
 specially destined to act upon this class of nerve fibres. Some observations 
 which have been made upon the nervous system of foetuses, in which the 
 brain and spinal cord were wanting, present a remarkable confirmation of this 
 view.* The nervous cords were for the most part developed ; and at their 
 (so called) origins or central extremities, they were found to hang as loose 
 threads in the cavities of the cranium and spine. On examining these threads, 
 it was found that the nerve-tubes, of which they consisted, formed distinct 
 loops ; each of which was composed of a fibre that entered the cavity, and 
 then returned from it. These loops were imbedded in granular matter, 
 resembling that interposed between the vesicles in the cortical substance of 
 the brain ; and perhaps to be regarded as vesicular matter in an early stage 
 of its formation. All that is known of the laws regulating the formation of 
 such irregular productions, leads to the belief, that we may rightly consider 
 this arrangement of the nerve-tubes as one which exists in the nervous cen- 
 tres, when they are normally developed. But it may not be the only one; 
 for, as already pointed out, some of the nerve-fibres appear to originate from 
 the filamentous prolongations of certain ganglionic cells. Additional informa- 
 tion is much needed upon this point. 
 
 248. The arrangement of the nerve-fibres, at their peripheral extremities, 
 seems to be essentially of the same character. It has been already shown 
 that the motor fibres, which are distributed to the muscles, have no proper 
 terminations ; a series of loops, returning into themselves or joining others, 
 being formed by the ultimate ramifications of the main trunks. The arrange- 
 ment of the sensory fibres seems to be usually of the same nature. The 
 principal trunks subdivide into numerous anastomosing branches, forming a 
 sort of plexus in the substance of the skin ; and from this, single filaments 
 detach themselves at intervals, rising up into the papillary elevations of its 
 surface, and then returning again into the plexus, after making a series of 
 
 Fig. 119. 
 
 Distribution of the tactile nerves at the extremity of the human thumb, as seen 
 in a thin perpendicular section of the skin. 
 
 loops, in which a sort of varicose enlargement of the fibre may often be 
 noticed. Similar looped terminations have been traced in the nerves supply- 
 
 * Dr. Lonsdale, in Edinb. Med. and Surg. Journal, No. CLTII. ; and Mr. Paget in Brit, and 
 For. Med. Rev., No. XLIII. p. 273. 
 
CONNECTION OF FIBROUS AND VESICULAR SUBSTANCES. 
 
 213 
 
 Terminal nerves on the sac of the second 
 molar tooth of the lower jaw in the sheep, 
 showing the arrangement in loops. (After 
 Valentin.)] 
 
 ing the dental sacculi, in the expansions of [Fig. 120. 
 
 the auditory nerve distributed upon the de- 
 licate membrane lining the cavities of the 
 internal ear, and elsewhere. It would yet, 
 however, be premature to say, that this ar- 
 rangement is universal. The peripheral 
 extremities may be really considered as 
 the origins of the sensory nerves ; since 
 it is in them that those changes are ef- 
 fected which it is the office of the trunks 
 to conduct towards the centres ; and it may 
 be reasonably inquired, whether anything 
 like the vesicular substance of the ganglia 
 can be detected in them. In examining 
 the retina microscopically, it is found to 
 be almost entirely made up of a layer of 
 ganglionic cells, very closely resembling 
 those of the grey matter of the brain ; and 
 these are in apposition with the vascular 
 layer; so that we have here precisely the 
 same provision for exciting a change, that 
 is to be conducted towards the centres, as 
 we have in the brain for exciting a change, 
 whose influence is to be conveyed towards 
 the periphery. Something of the same 
 kind has been seen in connection with the 
 corresponding expansions of the olfactive 
 and auditory nerves ; and it is probable 
 that similar elements exist in the papillae 
 
 of the skin and tongue, to which the nerves of taste and touch are distributed. 
 In these papillae we find loops of capillary vessels in close contiguity with 
 the extremities of the nerve-tubes. Hence we may state it as a general fact, 
 that wherever a change is to be originated, we find some form of Vesicular 
 matter, with capillary blood-vessels ; whilst for the conduction of such a 
 change to distant parts, the Fibrous structure is alone required. 
 
 249. The Chemical constitution of the Nervous matter is peculiar ; and 
 an acquaintance with its general features is of importance, in leading us to 
 recognize in the excretions the results of its decomposition. 
 
 a. The following, according to L'Heritier, is the relative proportion of the different con- 
 stituents in individuals of different classes : 
 
 Aged 
 
 Infants. Youths. Adults. Persons. Idiots. 
 
 Water .... 82-79 74-26 72-51 73-85 70-93 
 Albumen . . . 7-00 10-20 9-40 8-65 8-40 
 
 Fat 3-45 5-30 6-10 4-32 5-00 
 
 Osmazome (?) and Salts 5-96 8-59 10-19 12-18 14-82 
 
 Phosphorus . . . 0-80 1-65 1-80 1-00 0-85 
 
 It appears from the researches of M. Fremy, that the Phosphorus is combined with part of 
 the fatty matter; and forms with it two peculiar fatty acids, termed by him the Cerebric and 
 Oleophosphoric. Cerebric acid, when purified, is white, and presents itself in crystalline 
 grains. It contains a small proportion of Phosphorus ; and differs from the ordinary fatty 
 matter, in being partly composed of Nitrogen. It consists of 66-7 per cent, of Carbon, 10'6 
 of Hydrogen, 2-3 of Nitrogen, 19-5 of Oxygen, and 0-9 of Phosphorus; and thus differs from 
 ordinary fat, not only in containing Phosphorus and Nitrogen, but in possessing more than 
 twice their proportion of Oxygen.* Oleophosphoric acid is separated from the former by its 
 
 * It is probable that, in the above analysis of L'Heritier, the Cerebric acid, which is not 
 soluble in ether, is included under the head of Osmazome ; for the analyses of Denis and 
 
214 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 
 
 solubility in ether : it is of a viscid consistence ; but when boiled for a long time in water or 
 alcohol, it gradually loses its viscidity, and resolves .itself into a fluid oil, which is pure 
 Oleine, whilst phosphoric acid remains in the liquor. The proportion of Phosphorus which 
 this oil contains is about 2 per cent. Cholesterine has also been extracted from the brain by 
 M. Fremy in considerable quantity. The proportion of Fixed Salts is small; not being 
 above 3 parts in 100 of Dry Cerebral matter ; which is less than half the proportion that 
 exists in Muscle. According to Lassaigne, the chemical composition of the Cortical and 
 Medullary substances of the brain is essentially different; the former containing 85 per 
 cent, of water, whilst the latter has only 73; the cortical substance having also 3-7 per cent, 
 of a red fatty matter, of which the medullary has scarcely any; and being almost entirely 
 destitute of the white fatty matter, which exists in large proportion in the latter. 
 
 The Albuminous matter in the above analyses, is probably that of which 
 the walls of the nerve-cells and nerve-tubes, and of the capillary blood-vessels 
 are composed. The contents of these cells and tubes are represented chiefly, 
 if not entirely, by the phosphorized fats ; and there are many reasons for re- 
 garding these as the active agents in the operations of the Nervous system. 
 It will be remarked, that the amount of phosphorus is the greatest at the 
 period of greatest mental vigour ; and that in infancy, old age, and idiocy, the 
 proportion is not above half that which is present during the adolescent and 
 adult periods. 
 
 250. The Nervous System is very copiously supplied with blood-vessels ; 
 the arrangement of which varies according to the form of the elementary parts, 
 in which they are distributed. Thus in the Vesicular substance of the ner- 
 vous centres, the capillaries form a minute net-work, in the interstices of which 
 the ganglionic cells are included. In the tubulo-fibrous substance, the capilla- 
 ries are distributed much on the same plan as in Muscular tissue ; the net- 
 work being composed of straight vessels, which run along the course of 
 the fibres, passing between the nerve-tubes, and which are connected at 
 intervals by transverse branches. And at the sensory extremities of the 
 
 Fig. 121. 
 
 Capillary net- work of Nervous Centres. Distribution of Capillaries at the sur- 
 
 face of the skin of the finger. 
 
 nerves we find loops of Capillaries arching over their terminal and probably 
 looped filaments. The Brain of Man, taken en masse, has been estimated to 
 receive one-sixth of the whole amount of blood, although its weight is not 
 usually more than a-fortieth part of that of the entire body. Whether or not 
 this estimate be precisely correct, there can be no doubt that it receives far 
 more blood, than any other part containing the same amount of solid matter. 
 Now this copious supply of blood evidently has reference to two distinct ob- 
 jects ; first, to supply the necessary conditions for the action of the Nervous 
 system ; and, secondly, to maintain its nutrition. Many circumstances lead 
 to the conclusion that, in the Nervous as in the Muscular system, every vital 
 operation is necessarily connected with a certain change of composition, so 
 
 other chemists give a much higher proportion to the phosphorized fat, and a much smaller 
 one to the ill-defined compounds represented by the designation Osmazome. 
 
SUPPLY OF BLOOD TO NERVOUS TISSUE. 
 
 215 
 
 that no manifestation of nervous power can take place, unless this change can 
 be effected. There is strong reason to believe, further, that this change es- 
 sentially consists in the union of oxygen conveyed by the arterial blood, with 
 the elements of the proper nervous matter ; and that this union consequently 
 involves the death and disintegration of a certain amount of the nervous tis- 
 sue, the reproduction of which will be requisite, in order that the systsm 
 may be maintained in a state fit for action. This reproduction is effected by 
 the nutritive process, which takes place at the expense of other constituents 
 of the blood; and it will proceed most vigorously in the intervals, when the 
 active powers of the nervous system are not being called into operation ( 292 
 296). 
 
 251. The proofs of this continual waste and reproduction of the Nervous 
 substance, will be partly found in the appearance of the products of its de- 
 composition in the excretions, and in the demand which is set up for the ma- 
 terials for its reparation; these being found to accord in amount, as will be 
 shown hereafter, with the degree of its functional activity. But evidence of 
 another kind may be drawn from the microscopic appearances observable in 
 the cortical substance of the Brain. It seems probable, from the observations 
 of Henle, that there is as continual a succession of nerve-cells, as there is of 
 epidermic cells; their development commencing at the surface, where they 
 are most copiously supplied with blood-vessels from the pia mater; and pra- 
 ceeding as they are carried towards the inner layers, where they come into 
 more immediate relation with the tubular portion of the nervous tissue. This 
 change of place is probably due to the continual death and disintegration of 
 the mature cells, where they are connected with the fibres, and the equally 
 rapid production of new generations at the external surface ; the newly- 
 formed epidermic cells being thus carried inwards, in precisely the same man- 
 ner that the epidermic cells are carried outwards. 
 
 252. The first development of the Nerve-tubes appears to take place, like 
 that of Muscular fibre, by the coalescence of a number of primary cells into 
 a continuous tube ; for although the primary nervous cell has not yet been 
 made out with precision, the nuclei of what seem to be the original cells may 
 frequently be seen in the fully- 
 formed tube, lying between the'ir [Fig. 123. 
 membranous walls, and the white 
 
 substance of Schwann (111, c). 
 When first a nerve-fibre can be re- 
 cognized as such, it has a strong re- 
 semblance to the gelatinous fibres 
 of the sympathetic trunks ; being a 
 cord of small diameter, without any 
 clear distinction between the tube 
 and its contents, of granular consist- 
 ence, and having nuclei at no great 
 distance from each other. The 
 substance of the fibre, at this pe- 
 riod, seems to correspond with the 
 axis-cylinder of the fully-formed 
 nerve-tube ; the white substance of 
 Schwann is subsequently deposited 
 around it, separating it from the 
 membranous tubular envelope. 
 The first development of the vesi- 
 cular substance appears to take place on the same plan with its subsequent 
 renewal. 
 
 Various stages of the development of nerve ; a. 
 Earliest stage, b. Detached fibre, c. Nucleated fibre 
 in the lower part of which, d, the white substance of 
 Schwann has begun to be deposited, e. Nucleus in a 
 more fully-formed fibre between the white substance 
 and tubular membrane. /.Displays the tubular mem- 
 brane, the contained matter having given way. (After 
 Schwann.)] 
 
216 GENERAL VIEW OF THE FUNCTIONS. 
 
 253. The regeneration of Nervous tubuli that have been destroyed, takes 
 place in continuity with that which has been left sound. This may be more 
 easily proved by the return of the sensory and motor endowments of the part 
 whose nerves have been separated, than by microscopic examination of the 
 reunited trunks themselves, which is not always satisfactory. All our know- 
 ledge of the functions of the Nervous System leads to the belief, that perfect 
 continuity of the nerve-tubes is requisite for the conduction of an impression 
 of any kind, whether this be destined to produce motion or sensation ; and 
 various facts, well known to Surgeons, prove that such restoration may be 
 complete. In the various operations which are practised for the restoration 
 of lost parts, a portion of tissue removed from one spot, is grafted as it were 
 upon another ; its original attachments are more or less completely severed, 
 frequently altogether destroyed, and new ones are formed. Now in such a 
 part, so long as its original connections exist, and the new ones are not com- 
 pletely formed, the sensation is referred to the spot from which it was taken ; 
 thus, when a new nose is made, by partly detaching and bringing down a piece 
 of skin from the forehead, the patient at first feels, when anything touches the 
 tip of his nose, as if the contact were really with the upper part of his fore- 
 head. After time has been given, however, for the establishment of new 
 connections with the parts into whose neighbourhood it has been brought, the 
 old connections of the grafted portion are completely severed, and an interval 
 ensues, during which it frequently loses all sensibility ; but after a time its 
 power of feeling is restored, and the sensations received through it are referred 
 to the right spot. A more familiar case is the regeneration of Skin, contain- 
 ing sensory nerves, which takes place in the well-managed healing of wounds 
 involving loss of substance. Here there must obviously be, not merely a pro- 
 longation of the nerve-tubes from the subjacent and surrounding trunks, but 
 also a formation of new sensory papillae. A still more striking example of 
 the regeneration of Nervous tissue, however, is to be found in those cases (of 
 which there are now several on record), in which portions of the extremities, 
 that have been completely severed by accident, have been made to adhere to 
 the stump, and have, in time, completely recovered their connection with the 
 Nervous as with the other systems, as indicated by the restoration of their 
 motor and sensory endowments. 
 
 CHAPTER IV. 
 
 GENERAL VIEW OF THE FUNCTIONS. 
 
 1. Of Vital Actions, their conditions, and their mutual dependence. 
 
 254. THE idea of Life, in its simplest and most correct acceptation, is that 
 of Vital Action ; and obviously, therefore, involves that of change. We do 
 not consider any being as alive, which is not undergoing some continual alte- 
 ration, that may be rendered perceptible to the senses. This alteration may 
 be evidenced only by the growth and extension of the organic structure, or 
 the development of new parts ; and it may take place so slowly as to be im- 
 perceptible, except by comparing observations made at long intervals. Thus 
 the scaly Lichen, that forms the grey or yellow spots upon old walls, might 
 be thought an inert substance, did we not know that a sufficiently-prolonged 
 
CONDITIONS OF VITAL ACTIONS. 217 
 
 acquaintance with its history would detect its progressive though tardy exten- 
 sion, and would ascertain that it multiplies its race by an humble yet effectual 
 process of fructification. Or the change may be rather evidenced, by the 
 performance of some kind of movement, for which the ordinary physical 
 laws of matter will not account ; yet, for the detection of this, a close and 
 careful scrutiny will be frequently required. Thus the Oyster that is lying 
 motionless in its massive bed, or the Ascidia that clusters upon the faces of 
 sea-beaten rocks, may seem totally destitute of activity ; yet it would be found 
 upon close examination, that their internal surfaces are covered with cilia 
 which are in continual vibration, that by this means water is drawn into 
 the stomach and caused to traverse the respiratory organs, yielding to the 
 former the animalcules it may contain, and to the latter the oxygen dissolved 
 in it, that the food thus introduced into the stomach undergoes digestion, and 
 is converted into materials adapted to nourish the body, which are then con- 
 veyed to its different parts by a circulating apparatus, that in due time em- 
 bryos are produced, which are endowed with powers of active motion, and 
 which swim forth from within the parent-envelopes and locate themselves 
 elsewhere, and that, apathetic as these creatures may seem, they may be 
 excited by certain kinds of stimuli to movements which seem to evince sen- 
 sation ; the Oyster clbsing its shell, and the Ascidia contracting its muscular 
 tunic, when it receives any kind of mechanical irritation ; and the former, 
 whilst lying undisturbed in its native haunts, drawing together its valves, if a 
 shadow passes between itself and the sun. From what has been already 
 stated, regarding the nature of the actions of the Nervous and Muscular sys- 
 tems, by which the movements of Animals are chiefly effected, it would ap- 
 pear that these, in common with the Vegetative functions, involve a chemical 
 alteration in the structure performing them ; so that it may be stated as a 
 general proposition, that a change in Chemical composition is an essential 
 condition of every Vital phenomenon. 
 
 255. If change be essential to our idea of Life, it may be asked, what is 
 the condition of a seed, which may remain unaltered during a period of many 
 centuries ; vegetating at last, when placed in favourable circumstances, as 
 if it had only ripened the year before. Such a seed is not alive; for it is not 
 performing any vital operations. But it is not dead, for it has undergone no 
 decay ; and it is still capable of being aroused into active life, when the proper 
 stimuli are applied. And the most correct designation of its state seems to 
 be that of dormant vitality. The condition of an animal reduced to a state of 
 complete torpidity and inaction, is precisely similar ; into such a condition, 
 the Frog may be brought by cold, and the Wheel-Animalcule by deprivation 
 of moisture. And the condition of a Human being, during sleep, is precisely 
 similar, so far as his psychical powers are concerned ; he is not then a feel- 
 ing, thinking Man ; but he is capable of feeling and thinking, when his 
 brain is restored to a state of activity, and its powers are called into operation 
 by the impressions of external objects. 
 
 256. There can be no doubt whatever, that, of the many changes which 
 take place during the life, or state of vital activity, of an Organised being, 
 and which intervene between its first development and its final decay, a large 
 proportion are effected by the direct agency of those forces which operate in 
 the Inorganic world; and there is no necessity whatever for the supposition, 
 .that these forces have any other operation in the living body, than they would 
 have out of it under similar circumstances. But after every possible allowance 
 has been made for the operation of Physical and Chemical forces in the living 
 Organism, there still remain a large number of phenomena, which cannot be 
 in the least explained by them ; and which we can only investigate with suc- 
 cess, when we regard them as resulting from the agency of forces, as distinct 
 
 19 
 
218 GENERAL VIEW OF THE FUNCTIONS. 
 
 from those of Physics and Chemistry, as these are from each other. It is to 
 such phenomena, that the name of Vital is properly restricted ; the forces 
 from whose operation we assume them to result, are termed vital forces; and 
 the properties, which we must attribute to the substances exerting those forces, 
 are termed vital properties. Thus we say that the contraction of Muscle is 
 a Vital phenomenon ; because its character and conditions appear to be to- 
 tally distinct from those of Chemical or Physical phenomena. The act is 
 the manifestation of a certain Force ; the possession of which is peculiar to 
 the muscular structure, and which is named the Contractile force. Further, 
 that force may remain dormant (as it were) in the muscular structure ; not 
 manifesting itself for a great length of time, and yet resting capable of being 
 called into operation at any moment. This dormant force is termed a Pro- 
 perty ; thus we regard it as the essential peculiarity of living muscular tissue, 
 that it possesses the vital property of Contractility. Or, to reverse the order, 
 the Muscle is said to possess the property of Contractility ; the property, 
 called into operation by the appropriate stimulus, gives rise to the Contractile 
 force ; and the force produces, if its operation be unopposed, the act of Con- 
 traction. 
 
 257. These distinctions, though apparently verbal only, are of importance 
 in leading us to the correct method of investigating Vital Phenomena, and of 
 comparing them with those of the Inorganic world. It is now almost uni- 
 versally admitted by intelligent Physiologists, that we gain nothing by the 
 assumption of some general controlling agency, or Vital Principle, distinct 
 from the organized structure itself; and that the Laws of Life are nothing else 
 than general expressions of the conditions under which Vital operations take 
 place, expressions analogous to those which constitute the laws of Physics 
 or Chemistry, and to be arrived at in the same manner, namely, by the col- 
 lection and comparison of phenomena. The difficulty of thus generalising in 
 Physiology results merely from the complex nature of the phenomena, and 
 the consequent difficulty of precisely determining their conditions. We have 
 as much ground for believing in the fixity and constancy of Physiological 
 phenomena, when the causes and conditions are the same, as we have in those 
 of any other department of science ; and the apparent uncertainty of the 
 actions of the living body, results merely from the influence of differences in 
 those conditions, so trivial in appearance as frequently to elude observation, 
 and yet sufficiently powerful in reality to produce an entire change in the 
 result. 
 
 258. All Vital phenomena are dependent upon at least two sets of condi- 
 tions; an Organized structure, possessed of peculiar properties ; and certain 
 Stimuli, by which these properties are called into action. Thus, to revert to 
 the example just cited, the Contraction of a Muscle is due to the inherent 
 Contractility of the Muscular tissue, called into operation by the stimulus of 
 innervation ; other conditions, as a certain elevated temperature, a supply of 
 oxygen, &c., being at the same time requisite. The Microscopical and 
 Chemical researches of recent years, have given increased stability to the 
 position, that the peculiar properties, which we term Vital, are dependent 
 upon those peculiar modes of combination and aggregation of the elementary 
 particles, which are characteristic of Organized structures. We have no evi- 
 dence of the existence of Vital properties in any other form of matter than 
 that which we term Organized; whilst, on the other hand, we have no reasoa 
 to believe that Organized matter can possess its normal constitution, and be 
 placed in the requisite conditions, without exhibiting Vital Actions. The 
 advance of Pathological science renders it every day more probable (indeed, 
 the probability may now be said to amount almost to positive certainty), that 
 derangement m function, in other words, an imperfect or irregular action, 
 

 CONDITIONS OF VITAL ACTIONS. 219 
 
 always results, either from some change of structure or composition in the 
 tissue itself, or from some corresponding change in the external conditions, 
 under which the properties of the organ are called into action. Thus, when 
 a Muscle has been long disused, it can scarcely be excited to contraction by 
 the usual stimulus, or may even be altogether powerless ; and minute exami- 
 nation of its structure shows it to have undergone- a change, which is obvious 
 to the Microscope (the fibres being as it were shrunken, and the fibrillae in- 
 distinct), though it may not be perceptible to the naked eye, and which results 
 from imperfect nutrition. Or, again, convulsive or irregular actions of the 
 Nervous System may be produced, not by any change in its own structure 
 or composition, but by the presence of various stimulating substances in the 
 blood (such as urea or strychnine), although their quantity may be so small, 
 that they cannot be detected without great difficulty. Further, whenever the 
 peculiar properties of an Organized structure can no longer be excited by the 
 requisite stimuli, we find that it has undergone some incipient change of com- 
 position, or that some of the other conditions are wanting. Thus, the depar- 
 ture of the contractility from the muscles of warm-blooded animals, at no long 
 period after the cessation of the circulation, is due in part to the lowering of 
 their temperature, and in part to the cessation of the supply of oxygen to the 
 elementary parts of their substance ; either of which would alone suffice to 
 prevent their respondence to the stimuli, that would ordinarily produce ener- 
 getic contractions. Lastly, we find special properties constantly associated 
 with distinct forms of organized tissue ; thus we never find contractility exist- 
 ing in the fibres of Nerve ; nor do we ever find the power of conducting 
 impressions to exist in the fibres of Muscle. The details given in the pre- 
 ceding Chapter make it evident that each tissue, distinguished from others by 
 its peculiar composition, and by the form of its elementary parts, has some- 
 thing peculiar in its properties ; and this is true, as well of properties that are 
 simply physical, as of those that belong to a different category: thus the 
 Yellow Fibrous tissue is distinguished from the White as much by its elas- 
 ticity, as by its peculiar composition ; and it does not lose its elasticity, until 
 it is in a state of evident decay. 
 
 259. By the study of the various forms of Elementary Tissue, of which 
 the Human fabric (or any other of similar complexity) is made up, we are led 
 to the very same conclusion, with that which we should derive from the 
 observation of the simplest forms of organized being, or from the scrutiny 
 into the earliest condition of the most complex ; namely, that the simple 
 Cell may be regarded as the type of Organization; and that its actions 
 constitute the simplest idea of Life. Between the humblest Oonfervoid Plant, 
 and the highest Animal, there is originally no perceptible difference ; they may 
 be said to have a common starting-point ; and the subsequent difference of 
 their course consists essentially in this, that the successive generations of 
 cells, which are the descendants of the former, are all similar to it, each cell 
 being capable of existing by itself, and therefore ranking as an independent 
 individual ; whilst the subsequent generations, which originate from the 
 latter, undergo various departures from the primary type, and lose the power 
 of independent existence, their several actions being mutually dependent upon 
 each other, so that the integrity of the whole fabric is essential to the con- 
 tinued life of any individual cell. Every individual part, however, even in 
 the most complex and highly-organized fabric, has its own power of develop- 
 ment; and the properties which it possesses are the result of the exercise of 
 that power. But instead of the power of cell-growth being exerted, as in the 
 Plant, upon the inorganic elements around, it can only be put in action, in 
 the Animal, upon certain peculiar compounds, having the same chemical com- 
 position with its own substance ; and it is for the reception of these, for their 
 
220 GENERAL VIEW OF THE FUNCTIONS. 
 
 preparation, and for their maintenance in the requisite state of purity, that a 
 large part of the fabric of the Animal is destined. But if we could imagine 
 its several tissues to be supplied with nutriment in any other manner, and 
 maintained in other respects in their normal circumstances (as regards warmth, 
 air, &c.), we have every reason to believe that their independent vitality would 
 manifest itself by their continued development, and by the regular exhibition 
 of their ordinary properties. An approach to this condition is made, in the 
 experiment of entirely detaching a limb from the body, but keeping up the 
 circulation of blood through it, by means of tubes connecting its main artery 
 and vein with those of the stump. Notwithstanding the prejudicial effect of 
 such severe injuries, the increased duration of the muscular irritability in the 
 separated part, is a sufficient proof of the continuance of the normal actions of 
 nutrition, although of course in a diminished degree. And the occasional 
 reunion of a member which has been entirely separated, when decomposing 
 changes have not yet commenced in it, most clearly shows, that nothing but 
 the restoration of its supply of nutriment is requisite for the preservation of 
 its vitality, and that its powers of growth and renovation are inherent in itself, 
 only requiring a due supply of the nutrient material, with certain other con- 
 current conditions. 
 
 260. In every living structure of a complex nature, therefore, we see a great 
 variety of actions, resulting from the exercise of the different properties of its 
 several component parts. If we take a general survey of them, with reference 
 to their mutual relations to each other, we shall perceive that they may be 
 associated into groups; each consisting of a set of actions, which, though 
 different in themselves, concur in effecting some positive and determined pur- 
 pose. These groups of actions are termed Functions. Thus, one of the 
 most universal of all the changes necessary to the continued existence of a 
 living being, is the exposure of its nutritious fluid to the air; by the action of 
 which upon it, certain alterations are effected. For the performance of this 
 aeration, simple as the change appears, many provisions are required. In the 
 first place, there must be an aerating surface, consisting of a thin membrane, 
 permeable to gases ; on the one side of which the blood may be spread out, 
 whilst the air is in contact with the other. Then there must be a provision 
 for continually renewing the blood which is brought to this surface; in order 
 that the whole mass of fluid may be equally benefited by the process. And, 
 in like manner, the stratum of air must also be renewed, as frequently as its 
 constituents have undergone any essential change. We include, therefore, in 
 speaking of the Function of Respiration, not only the actual aerating process, 
 but also the various changes which are necessary to carry this into effect, and 
 which obviously have it for their ultimate purpose. 
 
 261. On further examining and comparing these Functions, we find that 
 they are themselves capable of some degree of classification. Indeed the dis- 
 tinction between the groups into which they may be arranged, is one of essen- 
 tial importance in Animal Physiology. If we contemplate the history of the 
 Life of a Plant, we perceive that it grows from a germ to a fabric of sometimes 
 gigantic size, generates a large quantity of organised structure, as well as 
 many organic compounds, which form the products of secretion, but which do 
 not undergo organization, and multiplies its species, by the production of 
 germs similar to that from which it originated; but that it performs all these 
 complex operations, without (so far as we can perceive) either feeling or think- 
 ing, without consciousness or will. All the functions of which its Life is com- 
 posed, are, therefore, grouped together under the general designation of Func- 
 tions of Organic or Vegetative life : and they are subdivided into those con- 
 cerned in the maintenance of the structure of the individual, which are termed 
 functions of Nutrition ; and those to which the Reproduction of the species 
 
CLASSIFICATION OF VITAL ACTIONS INTO FUNCTIONS. 221 
 
 is due. The great feature of the Nutritive operations in the Plant, is their 
 constructive character. They seem as if destined merely for the building-up 
 and extension of the fabric; and to this extension there may be no definite 
 limit. But it is very important to remark, that the growth of the more per- 
 manent parts of the structure is only attained by the continual development, 
 decay, and renewal of parts, whose existence is temporary. No fact is better 
 established in Vegetable Physiology, than the dependence of the formation of 
 wood upon the action of the leaves. It is in their cells, that those important 
 changes are effected in the sap, by which it is changed, from a crude watery 
 fluid containing very little solid matter, to a viscid substance including a great 
 variety of organic compounds, destined for the nutrition of the various tissues. 
 The "fall of the leaf" results merely from the death and decay of its tissue; 
 as is evident from the fact, that, for some time previously, its regular functions 
 cease, and that, instead of a fixation of carbon from the atmosphere, there is a 
 liberation of carbonic acid (a result of their decomposition) in large amount. 
 The process takes place in evergreens equally with deciduous trees ; the only 
 difference being, that the leaves in the latter are all cast off and renewed to- 
 gether, whilst in the former they are continually being shed and replaced, a 
 few at a time. It appears as if the nutritious fluid of the higher Plants can 
 only be prepared by the agency of cells, whose duration is brief; for we have 
 n'o instance, in which the tissue concerned in its elaboration possesses more 
 than a very limited term of existence. But by its active vital operations, it 
 produces a fluid adapted for the nutrition of parts which are of a much more 
 solid and permanent character, and which undergo little change of any kind 
 subsequently to their complete development ; the want of tendency to decay 
 being the result of the very same peculiarity of constitution as that which 
 renders them unfit to participate in the proper vital phenomena of the organism. 
 Thus the final cause or purpose of all the Nutritive functions of the Plant, so 
 far as the individual is concerned, is to produce an indefinite extension of the 
 dense, woody, almost inert, and permanent portions of the fabric, by the con- 
 tinued development, decay, and renewal of the soft, active, and transitory 
 cellular parenchyma. The Nutritive functions, however, also supply the 
 materials for the continuance of the rce, by the generation of new individuals; 
 since a new germ cannot be formed, any more than the parent structure can 
 be extended, without organizable materials, prepared by the assimilating pro- 
 cess, and supplied to the parts where active changes are going on. 
 
 262. On analyzing the operations which take place in the Animal body, we 
 find that a large number of them are of essentially the same character with the 
 foregoing, and differ only in the conditions under which they are performed ; 
 so that we may, in fact, readily separate the Organic functions, which are 
 directly concerned in the development and maintenance of the fabric, from the 
 Jlnimal functions, which render the individual conscious of external impres- 
 sions, and capable of executing spontaneous movements. The relative de- 
 velopment of the organs destined to these two purposes, differs considerably 
 in the several groups of Animals, as we have already in part seen (Chap. I.). 
 The life of a Zoophyte is upon the whole much more vegetative than animal ; 
 and we perceive jn it, not merely the very feeble development of those powers 
 which are peculiar to the Animal kingdom, but also that tendency to indefinite 
 extension which is characteristic of the Plant. In the Insect we have the 
 opposite extreme ; the most active powers of motion, and sensations of which 
 some (at least) are very acute, with a low development of the organs of nutri- 
 tion. In Man, and in the higher classes generally, we have less active powers 
 of locomotion, but a much greater variety of Animal powers ; and the instru- 
 ments of the organic or nutritive operations attain their highest development, 
 and their greatest degree of mutual dependence. "We see in the fabric of all 
 
 19* 
 
222 GENERAL VIEW OF THE FUNCTIONS. 
 
 things, in which the Animal powers are much developed, an almost entire 
 want of that tendency to indefinite extension, which is so characteristic of the 
 Plant; and when the large amount of food consumed by them is considered, 
 the question naturally arises, to what purpose this food is applied, and what 
 is the necessity for the continued activity of the Organic functions, when once 
 the fabric has attained the limit of its development. 
 
 263. The answer to this question lies in the fact, that the exercise of the 
 Minimal functions is essentially destructive of their instruments ; every ope- 
 ration of the Nervous and Muscular systems requiring, as its necessary con- 
 dition, a disintegration of a certain part of their tissues, probably by their ele- 
 ments being caused to unite with oxygen. The duration of the existence of 
 those tissues (as stated in the preceding Chapter) varies inversely to the use 
 that is made of them ; being less as their functional activity is greater. Hence, 
 when an Animal is very inactive, it requires but little nutrition ; if in mode- 
 rate activity, there is a moderate demand for food ; but if its Nervous and 
 Muscular energy be frequently and powerfully aroused, the supply must be 
 increased, in order to maintain the vigour of the system. In like manner, the 
 amount of certain products of excretion, which result from the disintegration 
 of the Nervous and Muscular tissues, increases with their activity, and dimin- 
 ishes in proportion to their freedom from exertion.* We are not to measure 
 the activity of the Nervous system, however, like that of the Muscular, only 
 by the amount of movement to which it gives origin. For there is equal evi- 
 dence, that the demand for blood in the brain, the amount of nutrition it re- 
 ceives, and the degree of disintegration it undergoes, are proportional likewise 
 to the energy of the purely psychical operations ; so that the vigorous exercise 
 of the intellectual powers, or a long-continued state of agitation of the feelings, 
 produces as great a waste of Nervous matter, as is occasioned by active bodily 
 exercise. From this and other considerations, we are almost irresistibly led 
 to the belief, that every act of Mind is inseparably connected, in our present 
 state of being, with material changes in the Nervous System; a doctrine not 
 in the least inconsistent with the belief in the separate immaterial existence of 
 the Mind itself, nor with the expectation of a future state, in which the com- 
 munion of Mind with Mind shall be more direct and unfettered. 
 
 264. Thus in the Animal fabric, among the higher classes at least, the func- 
 tion or purpose of the organs of Vegetative life is not so much the extension 
 of the fabric, for this has certain definite limits, as the maintenance of its in- 
 tegrity, by the reparation of the destructive effects of the exercise of the 
 purely Animal powers. Thus, by the operations of Digestion, Assimilation, 
 and Circulation, the nutritious materials are prepared and conveyed to the 
 points where they are required ; the Circulation of Blood also serves to convey 
 oxygen, which is introduced by the Respiratory process ; and it has further 
 for its office to convey away the products of the decomposition of the Muscular 
 and Nervous tissues that results from their functional activity, these products 
 being destined to be separated by the Respiratory and other Excreting opera- 
 tions. In the performance of the Organic functions of Animals, as in those 
 of Plants, there is a continual new production, decay, exuviation, and renewal, 
 of the cells, by whose instrumentality they are effected ; which altogether effect 
 a change not less complete than of the leaves in Plants. But it takes place in 
 the penetralia of the system, in such a manner as to elude observation, except 
 that of the most scrutinizing kind ; and it has been in bringing this into view, 
 that the Microscope has rendered most essential service in Physiology. 
 
 * This doctrine, though propounded in general terms by previous writers, was first point- 
 edly stated by Prof. Liebig, so far as regards Muscular tissue, in his Treatise on Animal 
 Chemistry. It will be hereafter shown, however, to be equally applicable to the Nervous 
 substance. 
 
MUTUAL DEPENDENCE OF VITAL OPERATIONS. 223 
 
 265. The regular maintenance of the functions of Animal life is thus entirely 
 dependent upon the due performance of the Nutritive operations ; a considera- 
 tion of great importance in practice, since a very large proportion of what are 
 termed functional disorders (of the Nervous system especially) are immediately 
 dependent upon some abnormal condition of the Blood. But there also exists 
 a connection of an entirely reverse kind, between the Organic and Animal func- 
 tions; for the conditions of Animal existence render the former in great degree 
 dependent on the latter. Thus, in regard to the acquisition of food, the Animal 
 has to make use of its senses, its psychical faculties, and its power of locomotion, 
 to obtain that which the Plant, from the different provision made for its support, 
 can derive without any such assistance. Moreover, the propulsion of the food 
 along the alimentary canal is effected by a series of operations, in which the 
 Nervous and Muscular systems are together involved at the two extremes ; 
 though simple Muscular contractility is alone employed through the greater 
 part of the intestinal canal. Thus, the change in the conditions required for 
 the ingestion of food by Animals, has rendered necessary the introduction of 
 an additional element in the apparatus, to which nothing comparable was to 
 be found in Plants. Again, in the function of Respiration as performed in the 
 higher Animals, the Nervous and Muscular systems are alike involved; for the 
 movements, by which the air in the lungs is being continually renewed, are 
 dependent upon the action of both ; and those by which the blood is propelled 
 through the respiratory organs, are chiefly occasioned by the contractility of a 
 muscular organ, the heart. But in regard to the simple contractility of mus- 
 cular fibre, upon the direct application of a stimulus to it, which is the agent 
 in the movements of the heart and of the alimentary canal, it may be remarked, 
 that it does not differ in any essential particular from that which is witnessed 
 in many Vegetables : so that it strictly belongs to the functions of Organic life. 
 And with respect to those concerned in the act of Respiration, as well as those 
 which govern the two orifices of the alimentary tube, it will hereafter appear 
 that they result, equally with the former, from the application of a stimulus ; 
 and that they may be performed without any consciousness on the part of the 
 individual (though ordinarily accompanied by it) : the difference being, that 
 in the former the stimulus is applied to the contractile part itself, whilst in the 
 latter it is applied to an organ with which this is connected by nerves only. 
 Now we have, even in Vegetables, instances of the propagation of an irritation 
 from one part to another, so that a motion results in a part distant from that 
 stimulated, as in the case of the Sensitive Plant or Venus's Fly-trap. The 
 only essential difference, therefore, between those movements of Animals, 
 which are thus closely connected with the maintenance of the organic func- 
 tions, and those of Plants, consists in the medium through which they are 
 performed, this being in Animals a distinct Nervous and Muscular apparatus, 
 whilst in Plants it is only a peculiar modification of the ordinary structure. 
 
 266. From what has been said, then, it appears that all the functions of the 
 Animal body are so completely bound up together, that none can be suspended 
 without the cessation of the rest. The properties of all the tissues and organs 
 are dependent upon their regular Nutrition, by a due supply of perfectly-ela- 
 borated blood ; this cannot be effected unless the functions of Circulation, 
 Respiration, and Secretion, be performed with regularity, the first being ne- 
 cessary to convey the supply of nutritious fluid, and the two latter to separate 
 it from its impurities. The Respiration cannot be maintained without the in- 
 tegrity of a certain part of the nervous system; and the due action of this, 
 again, is dependent upon its regular nutrition. The materials necessary for 
 the replacement of those which are continually being separated from the blood, 
 can only be derived by the Absorption of ingested aliment ; and this cannot 
 be accomplished without the preliminary process of Digestion. The intro- 
 
224 GENERAL VIEW OF THE FUNCTIONS. 
 
 duction of food into the stomach, again, is dependent, like the actions of Re- 
 spiration, upon the operations of the muscular apparatus and of a part of the 
 nervous centres; and the previous acquirement of food necessarily involves 
 the purely Animal powers. Now it will serve to show the distinction between 
 these powers, and those which are merely subservient to Organic life, if we 
 advert to thfe case, which is of no unfrequent occurrence, of a human being, 
 deprived, by some morbid condition of the brain, of all the powers of Animal 
 life, Sensation, Thought, Volition, &c. ; and yet capable of maintaining a 
 vegetative existence, all the organic functions going on as usual, the morbid 
 condition not having affected the division of the nervous system, that is con- 
 cerned in the movements on which some of them depend. It is evident that 
 we can assign no definite limits to such a state, so long as the necessary food 
 is placed within reach of the grasp of the muscles, that will convey it into the 
 stomach ; as a matter of fact, however, it is seldom of long continuance ; 
 since the disordered state of the brain is sure to extend itself, sooner or later, 
 to the rest of the nervous system. This condition may be experimentally 
 imitated, however, by the removal of the brain in many of the lower animals, 
 whose bodies will sustain life for many months after such a mutilation ; but 
 this can only take place when that food is conveyed by external agency 
 within the pharynx, which they would, if in their natural condition, have ob- 
 tained for themselves. A similar experiment is sometimes made by Nature 
 for the Physiologist, in the production of fetuses, as well of the human as of 
 other species, in which the brain is absent ; these can breathe and suck and 
 swallow, and perform all their organic functions ; and there is no assignable 
 limit to their existence, so long as they are duly supplied with food. Hence 
 we may learn the exact nature of the dependence of the Organic functions 
 upon those of purely Animal life ; and we perceive that, though less imme- 
 diate than it is upon the simple organic operations of the nervous and muscu- 
 lar systems, it 'is not less complete. On the other hand, the functions of 
 Animal life are even more closely dependent upon the Nutritive actions than 
 are those of organic life in general ; for many tissues will retain their several 
 properties, and their power of growth and extension, for a much longer pe- 
 riod after a general interruption of the circulation, than will the Nervous 
 structure ; which is, indeed, instantaneously affected by a cessation of the due 
 supply of blood, or by the depravation of its quality. 
 
 267. It is of little consequence, then, with which group of functions we 
 commence the detailed study of the phenomena, which in their totality make 
 up the life of Man. In viewing him merely as one of the widely-extended 
 group of organized beings, it would be natural to commence with those phe- 
 nomena which are common to all ; and to make, therefore, the Organic func- 
 tions the first object of our consideration. On the other hand, regarding Man 
 as a being in some degree isolated from all these by his peculiar character- 
 istics, it seems right to inquire into the latter in the first instance ; more 
 especially as, in a general view of his life, these occupy the most prominent 
 place. It will be necessary, however, previously to entering upon them, to 
 take a more detailed survey than we have hitherto done, of the vital opera- 
 tions performed by his several organs, and of their connections with each 
 other. We shall commence with those of Vegetative Life. 
 
 2. Functions of Vegetative Life. 
 
 268. It is one of the most peculiar characteristics of Organized structure, 
 that its elements have a constant tendency (under ordinary circumstances at 
 least) to separate into more simple combinations ; and although it has been 
 ordinarily considered, that their living state prevents such a change, and that 
 
FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE. 225 
 
 they have no tendency to it except when dead, reason will hereafter be given 
 for the belief that no such distinction exists (Chap. XIV., Sect. 4). The 
 maintenance of the vital properties of all organized structure then, requires 
 either that this structure should be completely secluded from air, moisture, 
 warmth, and other agents which tend to its decomposition; or that it should 
 be renewed as fast as it decays. Now the exclusion of these decomposing 
 agents would prevent any vital actions from being called into operation; 
 since they are the ordinary stimuli which are necessary to them. For 
 instance, a seed which is buried so deep in the soil as to be excluded from 
 the contact of air, and from the warmth of the sun, will not vegetate, although 
 it may retain its power of germinating when placed in more favourable cir- 
 cumstances ; and it will not decay, because secluded from the air and warmth 
 which are necessary to its decomposition. But as a certain change of com- 
 position appears to be a necessary condition of its vital activity, it is obvi- 
 ously requisite that a provision should be made, for removing from the 
 organism all those particles which are manifesting an incipient tendency to 
 decay, and are thus losing their vital properties ; and for replacing these by 
 newly-combined particles, which in their turn undergo the same process. 
 Thus we find that, in the softest parts of the Animal frame-work, as in those 
 of the Plant, there is much less permanency than there is in those harder and 
 more solid portions, which often seem altogether to defy the lapse of time. 
 Now it is in the former that the most active vital changes take place, those 
 of the nervous system, for example; whilst of the latter, the function is 
 chiefly, if not entirely, that of giving mechanical support to the structure. 
 The former organs are renewed many times, whilst the fabric of the latter is 
 not once completely changed; and thus a very interesting correspondence is 
 shown between the degree in which the action of any organized structure is 
 removed from, or is similar to, that of a mere inorganic substance, and the 
 amount of tendency to decomposition which that structure exhibits ; since 
 this constant renewal can scarcely serve any other purpose than that of 
 making up for the effects of decay. 
 
 269. One of the most important purposes of the supply of aliment, there- 
 fore, which all living beings continually require, is the replacement of the 
 portions of the fabric that are thus lost. The effects of the process of decay, 
 when uncompensated by that of renovation, are remarkably seen in cases of 
 starvation ; for it is a very constant indication of this condition, that the body 
 exhales a putrescent odour, even before death, and that it subsequently passes 
 very rapidly into decomposition. This, it may be considered, is the reason 
 why a constant supply of aliment is still required for the maintenance of 
 every organic structure, though it may have arrived at its full growth; and it 
 also affords one source of explanation of the fact, that old people require less 
 food than adults, since their tissues are more consolidated, and thus become 
 at the same time unable to perform their usual actions with their pristine 
 energy, whilst their tendency to decomposition is less. In the growing state, 
 however, an additional important source of demand for food obviously exists, 
 in the extension which the tissues themselves are constantly receiving ; yet 
 this, perhaps, does not make so great a difference, as it appears to do, in the 
 supply which is requisite. For if the addition which is made by growth to 
 the body in any given time, be compared with the amount of exchange which 
 has taken place in the same time. the latter being judged of by the quantity 
 of matter excreted from the lungs, liver, kidneys, skin, &c., it will be found 
 to bear but a very small proportion to it; except during foetal life, when the 
 growth is very rapid, and a large proportion of the effete particles are com- 
 municated to the maternal blood, to be excreted from it. The real cause of 
 the increased demand for nutriment, during the early part of life, is rather 
 
226 GENERAL VIEW OF THE FUNCTIONS. 
 
 this, that the tissues are far from having acquired that firmness and consoli- 
 dation which they gain at adult age; and that they are, therefore, more prone 
 to decomposition, at the same time that their vital activity is greater, as is well 
 known to be the case. The feeling of hunger or desire for food originates, 
 we shall hereafter find reason to believe (Chap. X., Sect. 1), not so much in 
 the stomach itself, as in the system at large; of whose condition, in regard to 
 the requirement of an increased supply of aliment, it may, during the state of 
 health, be considered as a pretty faithful index. The same may be said of 
 thirst. The feeling of hunger, then, is the stimulus to the mental operations, 
 which have for their object the acquisition of food; whether these be of a 
 voluntary or of a purely instinctive kind. In Man they are obviously the 
 former, during all but infant life. 
 
 270. The food received into the mouth, and prepared there by the acts of 
 mastication and insalivation (the movements concerned in which are dependent 
 upon the brain, and can only be performed when it is in a condition of some 
 activity), is brought by them within reach of the pharyngeal muscles, whose 
 contraction cannot be effected by the will, but is purely excilo-motor, result- 
 ing merely from the impression made upon the fauces by the contact Sf the 
 substance swallowed, which impression is conveyed to the medulla oblongata 
 and reflected back to the muscles ( 383). By these it is propelled down 
 the oesophagus ; and, after their action has ceased, it is taken up (as it were) 
 by the muscular coat of the oesophagus itself, and conveyed into the stomach. 
 How far the movements of the lower parts of the oesophagus and of the 
 stomach are in Man dependent upon reflex action, is uncertain; the facts 
 which have been ascertained on this point, by experiment on animals, will be 
 detailed in their proper place ( 390). In the stomach the food is subjected 
 to the gastric secretion ; the chemical action of which, aWed by the con- 
 stantly-elevated temperature of the interior of the body, and by the continual 
 agitation effected by the contractions of the parietes of the organ, effects a 
 more or less complete solution of it. The mixture of the biliary and pan- 
 creatic secretions with the chyme thus produced, occasions a separation of its 
 elements into those adapted for nutrition, and those of which the character is 
 excrementitious ; and this separation can scarcely be regarded in any other 
 light than as a chemical precipitation. By the agency of the biliary secre- 
 tion, moreover, certain elements of the food that would otherwise be rejected, 
 are reduced to a form in which they can be absorbed. The nutritious por- 
 tion is taken up by the Blood-vessels and by the Absorbent vessels (or Lac- 
 teals), which are distributed on the walls of the alimentary canal ; whilst the 
 remainder is propelled along the intestinal tube by the simple contractility of 
 its walls, undergoing at the same time some further change, by which the 
 nutritive materials are still more completely extracted from it. And at last, 
 the excrementitious matter, consisting not only of a portion of the food 
 taken into the stomach, but also of part of the secretion of the liver, and of 
 that of the mucous surface of the intestines and of their glandulse, is avoided 
 from the opposite extremity of the canal, by a muscular exertion, which is 
 partly reflex, like that of deglutition, but is partly voluntary, especially (as it 
 would appear) in Man. 
 
 271. There seems no doubt that fluid containing saline, albuminous, or 
 other soluble matters, may be absorbed by the Blood-vessels, with which the 
 mucous membrane of the alimentary canal is so copiously supplied ; and this 
 simple process of Imbibition probably takes place according to the physical 
 laws of Endosmose. But the Selection and Absorption of certain nutritious 
 elements appear to be performed, not by vessels, but by the growth and de- 
 velopment of cells ( 181); which, by their subsequent disintegration, give it 
 up to the Lacteals. The absorbed fluid, which now receives the name of 
 
FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE. 227 
 
 Chyle, is propelled through the Lacteals, by the contractility of their walls ; 
 aided in part, perhaps, by a vis a tergo derived from the force of the absorp- 
 tion itself. With the reception of the nutritious fluid into the absorbent ves- 
 sels, commences its real preparation for Organization. Up to that period, it 
 cannot be said to be in any degree vitalised; the changes which it has under- 
 gone being only of a chemical and physical nature, and such as merely prepare 
 it for subsequent assimilation. But in its passage through the long and tor- 
 tuous system of absorbent vessels and glands, it undergoes changes which, 
 with little chemical difference, manifest themselves by a decided alteration in 
 its properties ; so that the chyle of the thoracic duct is evidently a very dif- 
 ferent fluid from the chyle of the lacteals, approaching much nearer to blood 
 in its general characters. These characters are such as indicate that the pro- 
 cess of organization and vitilization has commenced; as may be known alike 
 from the microscopic appearance of the fluid, and from the actions it per- 
 forms when removed from the body. There is reason to believe that the 
 changes, which the Chyle undergoes in its progress through the lacteals, are 
 due to the action of certain cells which are seen to be diffused through the 
 liquid ( 155) ; these, by their own independent powers of growth, are con- 
 tinually absorbing into themselves the fluid in which they float ; whilst, by 
 bursting or liquefying, as soon as their term of life is completed, they give 
 this back in an altered state. The Chyle thus modified is conveyed into the 
 Sanguiferous system of vessels, and flows directly to the heart; by which it is 
 transmitted with the mass of the blood, to the lungs. It there has the oppor- 
 tunity of excreting its superfluous carbonic acid, and of absorbing oxygen ; 
 and probably acquires gradually the properties, by which the blood previous- 
 ly formed is distinguished, thus becoming the pabulum vitse for the whole 
 system. 
 
 272. The Circulation of the Blood through the tissues and organs which 
 it is destined to support, is a process evidently necessary for the conveyance 
 to them of the nutritious materials, which are provided for the repair of their 
 waste ; and for the removal of those elements of their fabric, which are in a 
 state of incipient decomposition. In the lowest classes of organized beings, 
 every portion of the structure is in direct relation with its nutritive materials ; 
 it can absorb for itself that which is required ; and it can readily part with 
 that of which it is desirable to get rid. Hence in such, no general circulation 
 is necessary. In Man, on the other hand, the digestive cavity occupies so 
 small a portion of the body, that the organs at a distance from it have no other 
 means, than their vascular communication affords, of participating in the re- 
 sults of its operations ; and it is moreover necessary that they should be 
 continually furnished with the organizable materials, of which the occasional 
 operation of the digestive process would otherwise afford only an intermitting 
 supply. This is especially the case, as already mentioned, with the Nervous 
 system, which is so predominant a feature in the constitution of Man ; and 
 we accordingly find both objects provided for, in the formation of a large 
 quantity of a semi-organized product, which contains within itself" the mate- 
 rials of all the tissues, and is constantly being carried into relation with them. 
 Blood has been not unaptly termed chair coulante, or liquid flesh ; and al- 
 though it has been heretofore much questioned, whether it could be regarded 
 as either organized or endowed with vital properties, there now appears to be 
 sufficient reason for admitting, that this is the case to a very considerable 
 extent. The propulsion of the blood through the large trunks, which subse- 
 quently divide into capillary vessels, is due to the contractions of a hollow mus- 
 cular organ, the Heart; but these, like the peristaltic movements of the ali- 
 mentary canal, are quite independent of (though frequently influenced by) the 
 
228 GENERAL VIEW OF THE FUNCTIONS. 
 
 agency of the Nervous system ; and are therefore to be referred to the class 
 of Organic movements, such as occur in Vegetables. 
 
 273. Upon the circulation of the blood through all parts of the fabric, de- 
 pends, in the first place, the Nutrition of the tissues. Upon this subject, for- 
 merly involved in the greatest obscurity, much light has recently been thrown 
 by Microscopic discovery ; it being now understood (as explained in the 
 preceding Chapter), that the continued growth and renewal of each tissue are 
 effected by a continuation of a process of cell-growth, similar to that by which 
 it was first developed. Even where the primary cells have changed their 
 character, their nuclei remain persistent; and may be regarded (in the lan- 
 guage of Mr. J. Goodsir) as so many "germinal centres," for giving origin to 
 new products. The greatest difficulty, in the present condition of our know- 
 ledge of this most interesting subject, is to comprehend the reason why such a 
 variety of products should spring up ; when the cells in which they all origi- 
 nate, appear to be so exactly alike. The important discoveries now referred 
 to are not confined to healthy structures ; for it has been ascertained, that dis- 
 eased growths have a similar origin and mode of extension ; and that the ma- 
 lignant character, assigned to Cancer, Fungus Haematodes, and other such 
 productions, is to be traced to the fact, that they are composed of cells which 
 undergo little metamorphosis, and retain their reproductive power ; so that 
 from a single cell, as from that of a Vegetable Fungus, a large structure may 
 rapidly spring up, the removal of which is by no means attended with any 
 certainty that it will not speedily re-appear, from some germs left in the sys- 
 tem. 
 
 274. The independent character of the cells in which all organized tissues 
 originate, might be of itself a satisfactory proof that, in Animals, as in Plants, 
 the actions of Nutrition are performed by the powers with which they are 
 individually endowed ; and that, whatever influence the Nervous system may 
 have upon them, they are not in any way essentially dependent upon it. More- 
 over, there is an evident improbability in the idea, " that any one of the solid 
 textures of the living body should have for its office, to give to any other the 
 power of taking on any vital actions :" and the improbability becomes an im- 
 possibility, when the fact is made known, that no formation of nervous matter 
 takes place in the embryonic structure, until the processes of Organic life 
 have been for some time in active operation. The influence which the Nerv- 
 ous System is known to have upon the Function of Nutrition, is probably ex- 
 erted, rather through the medium of its power of regulating the diameter of the 
 arteries and capillaries, by which it controls in some degree the afflux of blood, 
 and of affecting those preliminary actions on which the quantity and quality of 
 the nutritious fluid depend ; than in any more direct manner. At any rate, 
 it may be safely asserted, that no such proof of its more direct influence, as 
 is required to counterbalance the manifest improbability which has been shown 
 to attend it, has yet been given ; all the facts which have been adduced in 
 support of this hypothesis being equally explicable on the other, which, being 
 in itself more probable, ought to be preferred. 
 
 275. The renewal which the various tissues of the body are continually 
 undergoing, has for its chief object the counteraction of the decay into which 
 they would otherwise speedily pass; and it is obviously required, that a means 
 should be provided for conveying away the waste, as well as for supplying 
 the new material. This is partly effected by the Venous circulation ; which 
 takes up a large part of the products of incipient decomposition, and conveys 
 them to organs of Excretion, by which they may be separated and cast forth 
 from the body. The first product of the decay of all organized structures, 
 is carbonic acid ; and this is the one which is most constantly and rapidly 
 accumulating in the system, and the retention of which, therefore, within the 
 
FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE. 229 
 
 body, is the most injurious. Accordingly, we find two large organs the 
 Lungs and the Liver adapted to remove it ; and to both these Venous blood 
 passes, before it is again sent through the system. The function of the Lungs 
 is so important in warm-blooded animals, that a special heart is provided for 
 propelling the blood through them ; in addition to the one possessed by most 
 of the lower animals, the function of which is the propulsion of the blood 
 through the system. In these organs, the blood is subjected to the influence 
 of the atmosphere, by which the carbonic acid with which it was charged, is 
 removed and replaced by oxygen ; and this change takes place, through the 
 delicate membrane that lines the air-cells of the lungs, according to the physi- 
 cal law of the mutual diffusion of gases. The introduction of oxygen into 
 the blood is necessary for the maintenance of those peculiar vivifying powers, 
 by which the Nervous and Muscular systems are kept in a state fit for activity ; 
 and its union with their elements appears to be a necessary condition of the 
 manifestation of their peculiar powers. Of this union, carbonic acid is one 
 of the chief products ; and we shall find that the demand for oxygen, and the 
 excretion of carbonic acid, vary according to the amount of nervous and mus- 
 cular action. The continual formation of carbonic acid, in this and other in- 
 terstitial changes, appears to have a most important purpose in the vital eco- 
 nomy, that of keeping up its temperature to a fixed standard; for the union 
 of carbon and oxygen in this situation may be compared to a process of slow 
 combustion ; and it is well known that, the more energetic this is, the higher 
 is the temperature. Thus, in Birds, whose muscular and nervous activity is 
 so great, and whose respiration is so energetic, the temperature is constantly 
 maintained at a point higher than that which other animals ever attain, in the 
 healthy state at least ; whilst in Reptiles, which present a condition exactly 
 the reverse of this, the temperature is scarcely above that of the surrounding 
 medium. The function of the Liver is, like that of the lungs, twofold ; it 
 separates from the blood a large quantity of the superfluous hydro-carbon, 
 which it acquires by circulating through the tissues ; and it combines that 
 carbon with other elements, into a secretion, which, as we have seen, is of 
 great importance in the digestive process. The hepatic circulation, however, 
 is not kept up by a distinct impelling organ ; but the venous blood from the 
 abdominal viscera (and, in the lower Vertebrata, that from the posterior part 
 of the body) passes through the Liver on its return to the heart. 
 
 276. All animal substances have a tendency, during their decomposition, 
 to throw off nitrogen, as well as carbon ; and this nitrogen may take the form 
 either of cyanogen, by going off in combination with carbon, or of ammo- 
 nia, by uniting at the time of its liberation with hydrogen. The chief function 
 of the Kidneys is evidently to separate the azotized products of decay from 
 the circulating fluid ; for the secretion which is characteristic of them, namely 
 urea, contains a larger proportion of nitrogen than is found in any other 
 organic compound ; it is identical in its chemical nature with cyanate of am- 
 monia, and maybe considered as the result of the union of these two products 
 of animal decomposition. The action of the kidneys is equally essential to 
 the continued performance of the other vital functions, with that of the lungs 
 and liver ; since death invariably follows its suspension, unless some other 
 means be provided by Nature (as occasionally happens), for the separation of 
 its characteristic excretion from the circulating blood. 
 
 277. There seems reason to believe, however, that, of the products of 
 decomposition which are set free in the various tissues and organs of the 
 body, only a part is destined to be immediately excreted ; and that it is this 
 part, which is taken up by the Veins, and conveyed, by the general vascular 
 apparatus, to the several glands which are to separate it. The remainder, 
 consisting of substances which are fit to be re-assimilated, appears to be 
 
 20 
 
230 GENERAL VIEW OF THE FUNCTIONS. 
 
 taken up by a distinct system of vessels, termed Lymphatics; which may be 
 considered as an extension of the Lacteal system through the fabric at large. 
 There is good reason to believe, that the special function of the Lymphatics 
 is, like that of the Lacteals, to minister to Nutritive absorption (although 
 other substances may find their way into them, by the mere physical process 
 of imbibition); the latter being especially destined to take up assimilable 
 matter from the digestive cavity, whilst the former absorb the products of the 
 secondary digestion, which seems to be continually going on in every part of 
 the body. (See Chap. XL, Sects. 1 and 2.) Of these, however, a portion 
 may still be destined to immediate excretion. 
 
 278. The various Secretions which have not already been adverted to, 
 appear for the most part to have for their object the performance of some 
 special function in the system, rather than the conveyance out of it of any 
 substances which it would be injurious to retain. This is the case, for 
 example, in regard to the secretion of the Lachrymal, Salivary, and Mam- 
 mary Glands, as well as with that of the Mucous and Serous Membranes. 
 The Excretion of fluid from the cutaneous surface, however, appears to 
 answer two important purposes, the removal from the body of a portion of 
 its superfluous fluid, and the regulation of its temperature. Just as, by the 
 action of the Lungs, the conditions are supplied, by which the temperature of 
 the body is kept up to a certain standard, so, by that of the Skin, it is pre- 
 vented from rising too high ; for by the continual excretion from its surface, 
 of fluid which has to be carried off by evaporation, a degree of cold is gene- 
 rated, which keeps the calorific processes in check; and this excretion is 
 augmented, in proportion to the elevation of the external temperature, which 
 seems, in fact, the direct stimulus to the process. In all forms of true Secre- 
 tion, the selection of the materials to be separated from the blood, is accom- 
 plished, like selective Absorption, by the agency of cells. These are de- 
 veloped in the interior of the secreting organ ; and when they are distended 
 with the fluid they have imbibed, their term of life appears to have expired, 
 so that they burst or liquefy, yielding their contents to the ducts, by which 
 the secreted product is conveyed away. In the case of Adipose tissue, we 
 have an instance in which the secreted product (separated from the blood by 
 the cells of which this tissue essentially consists) is not carried out of the 
 body, but remains to form a constituent part of it. The regulation of the 
 amount of fluid in the vessels, is provided in a kind of safety-valve structure, 
 which has been lately shown to exist in the Kidneys. This readily permits 
 the escape of aqueous fluid from the capillary vessels, into the urinary canals, 
 by a process altogether distinct from the secretion of the solid matter, which 
 it is the office of the kidneys to separate from the circulating fluid. Hence, 
 if the excretion of fluid from the skin be checked by cold, so that an accumu- 
 lation would take place in the vessels, the increased pressure within them 
 causes an increased escape of water through the kidneys. The relation 
 between the true process of Secretion, which is performed by the selective 
 power of cells, and that of simple Transudation, is the same as that which 
 has been already pointed out, between Selective Absorption and simple 
 Imbibition ( 271). 
 
 279. There is no sufficient reason to believe, that the Nervous System has 
 any more direct influence on the process of Secretion, than it has been stated 
 to have on that of Nutrition. That almost every secretion in the body is 
 affected by states of mind, which must operate through the nerves, daily 
 experience teaches ; but the very remarkable degree of control, which the 
 Nervous system' possesses over the Circulation, appears sufficient to explain 
 any of these effects, whether they be local or general. The flow of the 
 secreted fluids through their efferent ducts, seems to be principally caused by 
 
FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE. 231 
 
 the proper contractility of these, which (like that of the heart and alimentary 
 canal) is directly stimulated by the contact of their contents; but there is 
 also evidence that this contractility may be affected (as it is in those two 
 instances) by the nervous system; and thus we have an additional means of 
 influence, by which the nervous system can operate on these processes, since 
 its power is probably not confined to the large ducts, but extends to their 
 ultimate ramifications. Where, as happens in the case of the urinary excre- 
 tion, there is a reservoir into which it is received as fast as it is formed, for 
 the purpose of preventing the inconvenience which its constant passage from 
 the body would otherwise occasion, the power of emptying this reservoir is 
 usually placed in some degree under the dominion of the will, although 
 chiefly governed by reflex action. It is obvious that such a provision is by 
 no means essential to the function ; and that it has for its object the adapta- 
 tion, merely, of that function, to the conditions of Animal existence. 
 
 280. Thus we see that, when we enter, as it were, into the penetralia of 
 the Animal system, and study those processes, of which the development and 
 maintenance of the material fabric essentially consist, we find them performed 
 under conditions essentially the same as those which obtain in Plants; and 
 we observe that the operations of the Nervous System have none but an 
 indirect influence or control over them. It is, therefore, quite philosophical 
 to distinguish these Organic Functions, or phenomena of Vegetative Life, 
 from those concerned in the Life of Relation, or Animal Life. The distinc- 
 tion is, indeed, of great practical importance, and lies at the foundation of all 
 Physiological Science ; yet it is seldom accurately made, and a very confused 
 notion on the subject is generally prevalent. It is commonly said, for ex- 
 ample, that the function of Respiration is the connecting link between the 
 two: the fact being, however, that the true process of Respiration is no 
 more a function of Animal life, tha'n is any ordinary process of secretion ; but 
 that, in order to secure the constant interchange of air, which is necessary to 
 its performance, the assistance of the nervous and muscular systems is called 
 in, though not in a manner which necessarily involves either consciousness 
 or will. 
 
 281. The process of Reproduction, like that of Nutrition, has been until 
 recently involved in great obscurity ; and although it cannot be said to be yet 
 fully elucidated, it has been brought, by late investigations, far more within 
 our comprehension, than was formerly deemed possible. The close connec- 
 tion between the Reproductive and Nutritive operations, both as regards their 
 respective characters, and their dependence upon one another, has long been 
 recognized; and it is now rendered still more evident. Nutrition has not been 
 unaptly designated " a perpetual reproduction ;" and the expression is strictly 
 correct. In the fully-formed organism, the supply of alimentary material to 
 every part of the fabric, enables it to produce a tissue resembling itself; thus 
 we only find true bone produced in continuity with bone, nerve with nerve, 
 muscle with muscle, and so on. Hence it would appear that, when a group 
 of cells has once taken on a particular kind of development, it continues to 
 reproduce itself on the same plan. But in the Reproductive process it is 
 different. A single cell is generated by certain preliminary actions, from 
 which single cell, all those which subsequently compose the embryonic struc- 
 tures, take their origin ; and it is not until a later period, that any distinction 
 of parts can be traced, in the mass of vesicles which spring from it. Hence 
 the essential character of the process of Reproduction consists in the forma- 
 tion of a cell, which can give origin to others, from which again others spring ; 
 and in the capability of these last to undergo several kinds of transforma- 
 tion, so as ultimately to produce a fabric, in which the number of different 
 parts is equal to that of the functions to be performed, every separate part 
 
232 GENERAL VIEW OF THE FUNCTIONS. 
 
 having a purpose distinct from that of the rest. Such a fabric is considered 
 as a very heterogeneous one ; and is eminently distinguished from those homo- 
 geneous organisms, in which every part is but a repetition of the rest. Of all 
 Animals, Man possesses, as already shown, the greatest variety of endow- 
 ments, the greatest number of distinct organs ; and yet Man, in common with 
 the simplest Animal or Plant, takes his origin in a single cell. It is in the 
 almost homogeneous fabrics of the Cellular Plants, that we find the closest 
 connection between the function of Nutrition, and that of Reproduction; for 
 every one of the vesicles which compose their fabric, is endowed with the 
 power of generating others similar to itself; and these may either extend the 
 parent structure, or separate into new and distinct organisms. Hence it is 
 scarcely possible to draw a line, in these cases, between the Nutrition of the 
 individual, and the Reproduction of the species. 
 
 282. But, it will be inquired, how and where in the Human body (and in 
 the higher Animals in general) is this embryonic vesicle produced, and what 
 are the relative offices of the two sexes in its formation ? This is a question 
 which must still be answered with some degree of doubt ; and yet observed 
 phenomena, if explained by the aid of analogy, seem to lead to a very direct 
 conclusion. The embryonic vesicle itself, like other cells, must arise from a 
 germ ; and reasons will be hereafter given for the belief, that the germ is sup- 
 plied by the male parent, and that the female supplies only the materials for 
 its development. Here, as in the Nutritive processes, we find that the opera- 
 tions immediately concerned in this function, namely, the act of fecundation, 
 and the development of the ovum, are not directly influenced in any way by 
 the nervous system ; and that the functions of Animal Life are called into play, 
 only in the preliminary and concluding steps of the process. In many of the 
 lower Animals, there is no. sexual congress, even where the concurrence of 
 two sets of organs (as in the Phanerogamic Plants) is necessary for the pro- 
 cess; the ova are liberated by one, and the spermatozoa by the other; and 
 the accidental meeting of the two produces the desired result. In many Ani- 
 mals higher in the scale, the impulse which brings the sexes together is of a 
 purely instinctive kind. But in Man, it is of a very compound nature. The 
 instinctive propensity, unless unduly strong, is controlled and guided by the 
 will, and serves (like the feelings of hunger and thirst) as a stimulus to the 
 reasoning processes, by which the means of gratifying it are obtained; and a 
 moral sentiment or affection of a much higher kind is closely connected with 
 it, which acts as an additional incitement. Those movements, however, 
 which are most closely connected with the essential part of the process, are, 
 like those of deglutition, respiration, &c., simply reflex and involuntary in their 
 character; and thus we have another proof of the constancy of the principle, 
 that, where the action of the apparatus of Animal Life is brought into near 
 connection with the Organic functions, it is not such as requires the operation 
 of the purely animal powers, sensation and volition. Thus, then, as it has 
 been lucidly remarked, "the Nervous System lives and grows within an Ani- 
 mal, as a parasitic Plant does in a Vegetable ; with its life and growth, certain 
 sensations and mental acts, varying in the different classes of Animals, are 
 connected by nature in a manner altogether inscrutable to man ; but the ob- 
 jects of the existence of Animals require, that these mental acts should exert 
 a powerful controlling influence over all the textures and organs of which they 
 are composed." 
 
 3. Functions of Animal Life. 
 
 283. The existence of consciousness, by which the individual (le moi, in 
 the language of French physiologists) becomes sensible of impressions made 
 
FUNCTIONS OF ANIMAL LIFE. 233 
 
 upon its bodily structure, and the power of spontaneously exciting contrac- 
 tions in its tissues, by which evident motions are produced, have been already 
 stated to be the peculiar attributes of the beings composing the Animal king- 
 dom. The evident motions exhibited by some Plants, cannot be regarded as 
 indicating the existence of any psychical endowments in the beings included 
 in the Vegetable kingdom ; for they are usually to be referred without difficulty 
 to the action, either direct or indirect, of an external stimulus, upon a contrac- 
 tile tissue ; and even where no such action evidently takes place, there is good 
 reason to suppose its existence. To refer, therefore, the movements of Vege- 
 tables to a Nervous system, of which no traces can be found, still more to 
 suppose them endowed with consciousness and will, as some have done, is 
 to violate most grossly a well-known rule in philosophy, which cannot be too 
 steadily kept in view in prosecuting physiological inquiries non finger e hy- 
 potheses. 
 
 284. There are in Animals, however, many movements which are equally 
 dependent upon direct stimuli for their production ; such are (as we have 
 seen), even in the highest, the actions of the heart and of the alimentary canal. 
 These, in the lowest tribes, probably bear a much greater proportion to the 
 whole amount of those exhibited by the beings, than they do in the higher; 
 whilst those, which we may regard as specially dependent on a nervous sys- 
 tem, appear to constitute but a small part of their general vital actions. The 
 life of such beings, therefore, bears a much closer resemblance to that of the 
 Vegetable, than to that of the higher-Animal. Their organic functions are 
 performed with scarcely more of sensible movement, than is seen in plants ; 
 and of the motions which they do exhibit (nearly all of them immediately 
 concerned in the maintenance of the organic functions), it is probable that 
 many are the result of the simple contractility of their tissues, called into 
 action by the stimuli directly applied to them. It is scarcely possible to ima- 
 gine that such beings can enjoy any of those higher mental powers, which 
 Man recognizes by observation on himself, and of which he discerns the ma- 
 nifestations in those tribes, which, from their nearer relation to himself, he 
 regards as more elevated in the scale of existence. If we direct our attention 
 on the other hand, to the psychical* operations of Man, as forming part of 
 his general vital actions, we perceive that the proportion is completely re- 
 versed. So far from his organic life exhibiting a predominance, it appears 
 entirely subordinate to his animal functions, and seems destined only to afford 
 the conditions for their performance. If we could imagine his nervous and 
 muscular systems to be isolated from the remainder of his corporeal structure, 
 and endowed in themselves with the power of retaining their integrity and 
 activity, we should have all that is essential to our idea of Man. But, as at 
 present constituted, these organs are dependent, for the maintenance of their 
 integrity and functional activity, upon the nutritive apparatus ; and the whole 
 object of the latter appears to be the supply of those conditions, which are 
 necessary to the exercise of the peculiarly animal functions. That his men- 
 tal activity should be thus made dependent upon the due supply of his bodily 
 wants, is a part of the general scheme of his probationary existence ; and the 
 first excitement of his intellectual powers is in a great degree dependent upon 
 this arrangement. 
 
 285. The most simple or elementary function of the Nervous System is, as 
 already observed, the establishment of a communication between a part which 
 is susceptible of impressions, and another which can perform contractile move- 
 
 * Here and elsewhere this term will be employed in its most extended sense, to designate 
 all the mental operations, whether intellectual, emotional or instinctive, of which Man's 
 nervous system is the instrument. 
 
 20* 
 
234 GENERAL VIEW OF THE FUNCTIONS. 
 
 ments ; so that a stimulus applied to one may immediately excite a respondent 
 action in the other, however great may be its distance. Hence it may be said 
 to have an internuncial function ; but this, so far as it is performed without 
 the necessary participation of the consciousness or will of the individual, is 
 not essentially higher in character, than the corresponding function in Plants, 
 although the latter is affected by a different apparatus. The ministration of 
 the nervous system to purely Animal life, obviously consists in its rendering 
 the mind cognizant of that which is taking place around, and in enabling it to 
 act upon the material world, by the instruments with which the body is pro- 
 vided for the purpose. It is important to observe, that every method at pre- 
 sent known, by which Mind can act upon Mind, requires muscular contraction 
 as its medium, and sensation as its recipient. This is the case, for example, 
 not only in that communication which takes place by language, whether 
 written or spoken ; but in the look, the touch, the gesture, which are so fre- 
 quently more expressive than any words can be ; and thus we trace the limi- 
 tation, which, even in communication that appears so far removed from the 
 material world, constantly bounds the operations of the most powerful intel- 
 lect, and the highest flights of the imagination. That in a future state of being', 
 the communion of mind with mind will be more intimate, and that Man will 
 be admitted into more immediate converse with his Maker, appears to be alike 
 the teaching of the most comprehensive Philosophical inquiries, and of the 
 most direct Revelation of the Divinity. 
 
 286. The Organs of Sense are instruments, which are adapted to enable 
 particular nerves to receive impressions from without; of a kind, and in a de- 
 gree, of which they would not otherwise be sensible. Thus, although the 
 simple contact of a hard body with the nerve may be readily conceived to 
 produce a material change in it, of such a kind as would be easily propagated 
 to the central sensorium, it is evident that a nerve must be peculiarly modi- 
 fied, to receive and conduct sonorous impressions from the undulations of the 
 air ; still more to be susceptible of the impressions produced by those un- 
 dulations, to which most Natural Philosophers now attribute the transmission 
 of light. And, even when this difficulty has been provided for, by some mo- 
 dification in the structure of the nerve itself, there is evidently another still 
 remaining, that of understanding how distinct images of the form, colour, 
 &c., of external objects can be communicated to the nerve of sight; or ideas 
 of the direction, pitch, quality, &c., of sonorous undulations, can be obtained 
 through the auditory nerve. There is reason to believe that many among 
 the lower Animals, which do not see objects around them, are conscious of 
 the influence of light ; and thus the distinction between the mere reception of 
 the impression, and the communication of the optical image, becomes evident. 
 The former may take place through the intervention of nerves, whose sensory 
 extremities offer no peculiarities : the latter can only be received through the 
 medium of an instrument, which shall, from the mixture of rays falling 
 equally upon every part of a surface, produce an optical image, and then 
 impress it upon the expanded surface of the nerve ; so that each fibril may 
 receive a distinct impression, the image presented to the mind being formed 
 by the combination of the whole. That this is, in fact, the share which the 
 organs of special sense bear in the general endowments of the whole appa- 
 ratus, may be inferred especially from the conformation of the Eye ; which 
 is in every respect a merely optical instrument, of the greatest beauty and 
 perfection, adapted to present to the nerve, in the most advantageous manner, 
 the images of surrounding objects in all their variations. And we might con- 
 ceive that, if it were possible for the interior of the living eye to be replaced 
 by one constructed of inorganic materials by the hand of man, without de- 
 stroying the functional power of the retina, the sense of sight would be but 
 
FUNCTIONS OF ANIMAL LIFE. 235 
 
 little impaired, except through the incapability, on the part of any piece of 
 human mechanism, to imitate those wondrous contrivances of Infinite Skill, 
 which have for their object the adaptation of the instrument to varieties of dis- 
 tance, of intensity of light, &c. There can be little doubt, that the structure 
 of the Ear is arranged to do the same for the sonorous vibrations, which the 
 eye does for the rays of light; that is, through its means, the undulations 
 which strike upon the external surface of the organ are separated and distin- 
 gished, those of a like kind being brought together upon one division of the 
 nerve, and those of another order upon a different set of fibres ; so that the 
 different kinds of sound, and the peculiar quality and direction of each, may 
 be discriminated ; whilst, by the concentration of all the impressions of the 
 same character, a higher amount of force is given to them. Of the sense of 
 Smell, no similar account can be given; since the medium by which odours are 
 propagated is not known. If, as is generally believed, this is accomplished by 
 the diffusion through space, of minute particles of the odoriferous body itself 
 (which supposition seems to derive support from the general fact, that the 
 most volatile substances are usually most odoriferous), smell may be regarded, 
 as taste also is probably to be considered, in the light of a refined kind of 
 touch. 
 
 287. Thus, the general rule holds good, here as elsewhere, that the pro- 
 cesses, by which the organism is immediately brought into relation with the 
 external world, are performed in obedience to physical laws ; the living struc- 
 ture only affording certain peculiar conditions, which may be imitated in a 
 great degree by other means. This is the case, for example, with regard to 
 Digestion, which is in itself a simply Chemical process, that will take place 
 out of the body as well as in it, if the materials and the necessary solvent be 
 submitted to the same circumstances, as those to which they are exposed in 
 the stomach ; and in regard also to the act of Respiration, which depends 
 upon the physical tendency to mutual diffusion, inseparable from the exist- 
 ence of gases ; and we notice the prevalence of the same general fact in the 
 Animal as in the Organic functions. We cannot become cognizant of the 
 changes, or even of the existence, of the external world, unless some mate- 
 rial effect be produced by it on our organs of sense ; nor can we produce any 
 alteration in its condition, except by powers which act according to purely 
 mechanical principles. 
 
 288. In regard to the Muscular System, it has already been sufficiently 
 explained that it forms a part of the apparatus of Animal life, no otherwise 
 than as the instrument by which nervous energy operates upon external 
 objects. The contractility which it manifests on the application of a stimulus, - 
 is an endowment which it derives from its own structure, and not from the 
 nervous system ; for it will be clearly proved in its appropriate place, that 
 the presence of this contractility is connected with the healthy nutrition of 
 the tissue, and with its due supply of arterial blood ; and that the complete 
 separation of any muscular part from all its nervous connections, has none 
 but an indirect influence on its properties. 
 
236 
 
 CHAPTER V. 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 1. General Summary. 
 
 289. OUR fundamental idea of a Nervous System includes a central organ 
 or ganglion, essentially composed of vesicles or cells, with a plexus of capil- 
 lary vessels distributed amongst these ; and a set of trunks and ramifying 
 branches, composed of tubular fibres, and connecting the ganglion with differ- 
 ent parts of the fabric. These branches are for the most part distributed, on 
 the one hand, to the sensory surfaces and organs ; and, on the other, to the 
 muscles or motor organs. The former serve for the conveyance of impres- 
 sions, made upon the periphery, towards the centre ; and they may thence 
 be denominated afferent fibres.* The latter, on the other hand, serve to con- 
 vey an influence, originating in the central ganglion, to the muscles, which 
 are thereby thrown into contraction ; and these are distinguished as efferent 
 or motor fibres. Although the distinctness of these two sets of fibres has 
 only been proved in the Vertebrata, yet there can be no reasonable doubt of 
 its universality. Now this fundamental idea of a Nervous apparatus, which 
 is based upon what are believed to be the relative offices of its several com- 
 ponent parts (as formerly explained 248), is found to be exactly realized in 
 the simple forms of that system, which we find in the lowest animals in which 
 Nervous structure can be discovered at all ; and even where the apparatus 
 has, to all appearance, a character of much greater complexity, it may still be 
 reduced to the same simple idea, by taking it to pieces (so to speak) and exa- 
 mining its component parts. For it will then be found, that the multiplica- 
 tion of ganglia and trunks is principally due to the multiplication of the 
 organs to be supplied ; as in the case of the nervous ring of the Star-fish, 
 where the ganglia, all of them apparently identical in function, and similar in 
 the distribution of their branches, are repeated in conformity with the num- 
 ber of the radiating parts of the body ; or in the case of the ventral nervous 
 cord of an Articulated animal, in which the ganglia are in like manner re- 
 peated longitudinally, in accordance with the number of segments of the body, 
 and of the pairs of members connected with them. In other instances, the 
 multiplication of ganglia is due to the increased complexity of the functions 
 performed by a set of organs ; of this we shall see numerous examples in 
 the higher Vertebrata. In all cases, the individual ganglia remain to a great 
 extent independent of each other; so that the removal of any one (if it can 
 be accomplished without injury to the rest) affects only the particular organ 
 with which it may be connected, and the special function of that organ to 
 which alone it ministers. 
 
 290. Before proceeding to inquire into the operations of the Nervous Sys- 
 tem as a whole, it is desirable that we should stop to consider the conditions 
 
 * Such are commonly denominated sensory fibres ; but this designation is objectionable, 
 in as much as many of them serve to excite reflex actions, without necessarily producing 
 sensations. 
 
DEPENDENCE OF NERVOUS POWER ON SUPPLY OF BLOOD. 237 
 
 on which its functional activity is dependent. The chief of these, is a con- 
 stant supply of oxygenated blood ; which is more necessary for the mainte- 
 nance of the Nervous power, than it is for that of any other tissue whatever. 
 This supply is peculiarly required at those points at which changes originate ; 
 not being, it would appear, so necessary for the mere conduction of impres- 
 sions. Consequently we find that the greatest supply of blood is afforded to 
 the nervous centres, and to the peripheral extremities or origins of the affe- 
 rent nerves ; and that the effects of any interruption to the supply are mani- 
 fested in an immediate and most striking manner. Thus, if the circulation 
 through the Brain be suspended but for an instant, insensibility and loss of 
 voluntary power supervene, and continue until it is restored. This was 
 shown by the following experiment of Sir A. Cooper's. After having tied 
 both carotid arteries in a dog, he compressed the Vertebral trunks ; and im- 
 mediate insensibility came on, the animal at the same time falling powerless. 
 But convulsive movements occurred at the same time ; showing that the func- 
 tions of the spinal cord were not suspended, but only deranged. As soon as 
 the blood was re-admitted to the brain, the animal recovered its consciousness 
 and voluntary power, and stood on its legs again ; the convulsive movements 
 ceased at the same time. In Syncope, the circulation through the Spinal 
 cord is weakened, by the failure of the heart's action, to the same extent as 
 the flow of blood through the Brain ; and a general cessation, not merely of 
 muscular movement, but of all power of exciting it, is the immediate result. 
 No sooner, however, is the circulation fully re-established, than the power of 
 the Nervous centres is restored. Again, the influence of diminished circula- 
 tion, at the origins of the afferent nerves, is shown in the deficient impressi- 
 bility of the nerves, at the part affected. Thus, if the movement of blood 
 through the capillaries of a limb be stagnated, whether by pressure on the 
 arterial trunks, by cold, or by any other cause, it is at once made apparent 
 by the numbness of the surface ; and a complete stagnation produces com- 
 plete insensibility. The power of receiving impressions, that are to excite 
 reflex movements, is diminished in the same degree. 
 
 291. On the other hand it is found, that increased circulation through the 
 same parts, is attended with an exaltation of their function. This is particu- 
 larly noticed in those affections of the brain and spinal cord, closely border- 
 ing on inflammation, to which the terms active congestion and determination 
 of blood have been applied. We have, in such cases, extreme acuteness of 
 sensation, excessive activity of the mental functions, or violent excitement of 
 the motor powers ; according (it would seem) to the particular division of the 
 nervous centres most affected. Again, we find that an increase in the circu- 
 lation through any organ, from which afferent nerves arise, increases their 
 readiness to receive impressions ; thus the sensibility of the genital organs of 
 animals during the period of heat, and of those of man in a state of venereal 
 excitement, are greatly augmented ; and the tendency of impressions, made 
 upon them, to excite reflex movements, is similarly exalted. 
 
 292. The due activity of the Nervous System is not merely dependent 
 upon a constant and ample supply of Blood ; but it requires that this blood 
 should be in a state of extreme purity, and more especially that it should 
 contain a due supply of oxygen, and should be depurated of its carbonic acid, 
 and of other products of the decomposition of the body. The final cessa- 
 tion of nervous power, in death by Asphyxia, is partly due (as will be shown 
 hereafter, Chap. XIIL, Sect. 3), to a positive deficiency in the supply of blood ; 
 but the obtuseness of sensibility which gradually increases until a state of 
 unconsciousness comes on, may be clearly traced in the first instance to the 
 deficient aeration of the blood, which is gradually deprived of its oxygen, and 
 charged with more and more carbonic acid. Corresponding but less severe 
 
238 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 symptoms occur, when the excretion of carbonic acid is not checked, but only 
 slightly impeded ; provided the impediment be in operation for a sufficient 
 length of time, as. in the case of an ill-ventilated apartment; an indisposition 
 to mental exertion, a deficiency of muscular power, and an obtuseness of the 
 intellectual and moral faculties, being the general result. These facts are 
 readily explained upon the hypothesis (which seems now to have a sufficiently 
 wide foundation, to be entitled to rank as physiological truth, although no 
 very direct proof of it can be given), that the functional activity of the nerv- 
 ous system is mainly dependent upon the combination of the oxygen sup- 
 plied by the blood, with its elements', the production of the nervous force, 
 whatever be its nature, being a result of this change of composition. The 
 chief grounds for this doctrine will now be enumerated. 
 
 293. In the first place, the dependence of nervous energy upon the con- 
 stant circulation of blood through the tissue, is much more close and imme- 
 diate than can be accounted for on the idea that the relation is one of mere 
 nutrition or development. On the contrary, where these last changes are 
 taking place most actively, we often find rather a disposition to stagnation of 
 the current, to give time for the elaboration of the nutrient materials that are 
 to be withdrawn from it; and in no case does the process so instantaneously 
 cease, when the flow is suspended. From this it would appear, that some 
 combination takes place between the elements of the nervous tissue, and some 
 material supplied by the blood ; which is much more rapid in its character, 
 than the process of cell-development ; and which is essentially concerned in 
 the production and maintenance of the active condition of the nervous sys- 
 tem. Again, that the material supplied by the blood for this purpose is Oxy- 
 gen, would appear from a variety of considerations. A general survey of 
 the Animal kingdom shows, that oxygen is essential to the maintenance of 
 animal life, as distinct from vegetative; and a more particular comparison 
 of different tribes demonstrates most unequivocally, that the consumption of 
 oxygen is in direct relation to the development of the animal powers in each. 
 These facts harmonize completely with what has been just stated, respecting 
 the effects of a suspension of the oxygenating process. 
 
 294. Further, in proof that the activity of the Nervous system is immedi- 
 ately dependent, not upon a process of development or nutrition, but upon 
 one of disintegration or destruction, it may be urged, that it is impossible for 
 this state of activity to be maintained, in a large portion of it, without an in- 
 terval of repose, which we know to be favourable to the vegetative or repa- 
 rative processes. There are certain parts of the Nervous System, particularly 
 those that put in action the respiratory muscles, which are in a state of un- 
 ceasing though moderate activity ; and in these, the constant nutrition is suffi- 
 cient to repair the effects of the constant decay. But those parts which 
 operate in a more powerful and energetic manner, and which are therefore 
 more rapidly disintegrated when in action, need a season of rest for their re- 
 paration. Hence the sense of fatigue which is experienced when the mind 
 has been long acting through its instrument, the Brain ; and the irresistible 
 tendency to sleep, which usually supervenes after any unusual exertion of this 
 kind. In the healthy state of the body, when the exercise of the nervous system 
 by day does not exceed that which the repose of the night may compensate, 
 the Nervous System is maintained in a condition which fits it for constant 
 moderate exercise ; but unusual demands upon its powers, whether by long- 
 continued and severe exercise of the intellect, by excitement of the emotions, 
 or by the combination of both, in that state of anxiety which the circum- 
 stances of man's condition too frequently induce, occasion an unusual waste, 
 and require a prolonged repose and uninterrupted nutrition, for the complete 
 restoration of its powers. There can be no doubt that (from causes which 
 
DISINTEGRATION OF NERVOUS MATTER WITH USE. 239 
 
 are not known) the amount of sleep required by different persons, for the 
 maintenance of a healthy condition of the Nervous System, varies consider- 
 ably ; some being able to dispense with it to a degree which would be exceed- 
 ingly injurious to other individuals, who do not surpass them in mental activity. 
 Where a prolonged exertion of the mind has been made, and the natural tend- 
 ency to sleep has been habitually resisted, by a strong effort of the will, 
 injurious results are sure to follow. The bodily health breaks down; and too 
 frequently the mind itself is permanently enfeebled. It is obvious that the 
 Nutrition of the Nervous System becomes completely deranged ; and that the 
 tissue is no longer formed in a manner requisite for the discharge of its healthy 
 functions. The same may be said of the state of Mania ; in which there is, 
 for a time, an extraordinary degree of activity (though manifested in an irregu- 
 lar manner) of the cerebral functions, and an absence of disposition to sleep. 
 Such a state may continue for some time; but the subsequent exhaustion of 
 nervous power is proportioned to the duration of the excitement, and frequent 
 attacks of mania almost invariably subside at last into imbecility. 
 
 295. Additional evidence for the belief that the functional activity of the 
 Nervous tissue involves disintegration of its tissue by the agency of Oxygen, 
 is found in the increase of phosphatic deposits in the urine, and especially 
 of those having alkaline bases, when there has been any unusual demand 
 upon the nervous power. No others of the soft tissues contain any large 
 amount of phosphorus ; and the marked increase in these deposits, which has 
 been continually observed to accompany long-continued wear of mind, whether 
 by intellectual exertion, or by the excitement of the feelings, and which fol- 
 lows any temporary strain upon its powers, can scarcely be set down to any 
 other cause. The most satisfactory proof is to be found in cases, in which 
 there is a periodical demand upon the mental powers ; as, for example, among 
 Clergymen, in the preparation for and discharge of their Sunday duties. This 
 is found to be almost invariably followed by the appearance of a large quantity 
 of the alkaline phosphates in the urine. And in cases in which constant and 
 severe intellectual exertion has impaired the nutrition of the brain, and has 
 consequently weakened the mental power, it is found that any premature at- 
 tempt to renew the activity of its exercise, causes the re-appearance of the 
 excessive phosphatic discharge indicative of an undue waste of nervous mat- 
 ter.* 
 
 296. There is not the same evidence of constant change, however, in re- 
 gard to the fibrous element of the Nervous System; and its conducting power 
 appears to be much less dependent upon the supply of blood, than is the ori- 
 ginating power of the vesicular matter. It remains, with little decrease, for 
 some time after death ; especially in cold-blooded animals ; for we can, by 
 pinching, pricking, or otherwise stimulating the motor trunks, give rise to con- 
 tractions in the muscles supplied by them, exactly as during life. Its earlier 
 departure in warm-blooded animals, may be partly due to the cooling of the 
 body. 
 
 297. Of the actual nature of the changes by which impressions are received 
 upon the peripheral origins of the afferent nerves, or are communicated to the 
 
 * A large amount of evidence confirmatory of the above views, and showing the im- 
 portance of carefully distinguishing between the alkaline and earthy phosphates, has been 
 adduced by Dr. Bence Jones, in a Paper lately read to the Royal Society. The quantity of 
 the latter, which is present in the urine, is found to bear a constant relation to that which is 
 contained in the food. On the other hand, the amount of the former varies with different 
 conditions of the nervous system, in such a manner as to warrant the inference that its pro- 
 duction is a result of the disintegration of nervous matter; being due to the union of the 
 phosphoric acid thus set free, with alkaline bases present in the blood in a state of feeble 
 combination. 
 
240 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 central origins of the motor, and by which they are conducted along each to 
 their opposite extremities, Physiologists have no certain knowledge. That 
 they are Electrical in their character, has been, and still continues to be, a 
 favourite theory with some; and the idea seems to derive support from the 
 marked degree in which Electricity, transmitted along the Nervous trunks, 
 can excite the changes to which those nerves are ordinarily subservient. 
 Thus, a feeble galvanic current, transmitted along the motor nerves of an ani- 
 mal recently killed, will call the muscles supplied by it into contraction ; whilst, 
 on the other hand, a similar current transmitted along an afferent nerve, shall 
 excite reflex movements through its ganglionic centre. Further, if the cur- 
 rent be transmitted along an afferent nerve, in a living animal, it will excite 
 sensations which are referred to the part whence the nerve arises ; and, as 
 will be shown hereafter (Chap. VI., Sect. 1), Electricity is capable of thus 
 producing sensations of a special kind, as well as those of a general nature. 
 Moreover, in the instantaneousness of the transmission of Nervous agency 
 from one part of the system to another, there is more analogy to Electricity, 
 than to any other known force. But these and similar arguments do not prove 
 the identity of Nervous agency with Electricity ; since the effects of the for- 
 mer may be imitated to a certain extent, not merely by Electricity, but by 
 mechanical and chemical stimulation of various kinds. Further, there are 
 powerful arguments against such a supposition, the validity of which cannot 
 be easily set aside. All attempts to prove the existence of an Electric current, 
 in a Nervous trunk that is actively engaged in conveying motor influence, 
 have completely failed, though made with the greatest precaution. Thus, Mat- 
 teucci has lately experimented upon the very large crural nerve of a Horse, 
 which was caused, by stimulating its roots, to throw the muscles of the leg 
 into violent contraction ; nevertheless, although he used instruments of such 
 delicacy, as to be capable of detecting an infinitesimally-small disturbance of 
 the electric equilibrium, no such disturbance was apparent. Further, it is well 
 known that the conducting power of the nerves is destroyed, not merely by 
 dividing the trunk, but also by putting a ligature round it ; which last opera- 
 tion does not diminish its powers as a conductor of Electricity. Moreover, 
 the various fibrils are not as completely insulated from each other in regard to 
 Electricity, as we know them to be with respect to nervous agency ; for the 
 first of these forces, when transmitted along a nervous trunk, cannot be re- 
 stricted to any fibre or fasciculus of fibres, but spreads through the entire 
 trunk, and even to the neighbouring parts in which it is imbedded; whilst the 
 latter is continually restricted to a small portion of the trunk, as is manifested 
 by its results. Again, if a small piece of nervous trunk be cut out, and be 
 replaced by an electric conductor, electricity will still pass along the nerve ; 
 but no nervous force, excited by stimulus above the section, will be propa- 
 gated through the conductor to the parts below. And lastly, the conducting 
 power of Nerve for Electricity is stated by Matteucci to be not more than 
 one-fourth that of Muscle ; whilst Messrs. Todd and Bowman give it as the 
 result of their experiments, that both Nerve and Muscle are both infinitely 
 worse conductors than copper ; their power of conduction not ranking above 
 that of water holding in solution a small quantity of saline matter. 
 
 a. Although, for the sake of convenience, Electricity and Nervous power are spoken of, 
 here and elsewhere, as actual entities or agents, traveling along the wires or cords that con- 
 duct them, it must not be forgotten that the present tendency of scientific inquiry leads us 
 to abandon such an idea, in the former case at least ; what is commonly termed the trans- 
 mission of electricity being the result of a molecular change, instantaneously occurring along 
 the whole length of the conducting body, in virtue of a disturbance, in the polar arrangement 
 of its particles, at one extremity, which causes a similar disturbance to manifest itself at the 
 other. Thus if 
 
 ab ab ab ab ab ab ab ab 
 
LAWS OF NERVOUS TRANSMISSION. 241 
 
 represent the arrangement of the particles, in the condition of equilibrium or quiescence, and 
 this condition be disturbed at one extremity, by the operation of a new attraction upon the 
 first particle a, a new arrangement will instantaneously take place throughout: this may be 
 represented by 
 
 a ba ba ba ba ba ba ba b 
 
 which shows b in a free state at the opposite end, ready to exert its influence upon anything 
 submitted to it. It is probable that in this respect there is an analogy between the Nervous 
 and electrical forces ; and that, instead of speaking of the "transmission of nervous influence" 
 along a nerve, we should describe the change as the production of a " polar state" in the 
 nervous trunk; as first pointed out by Messrs. Todd and Bowman (Physiological Anatomy, 
 vol. i. p. 240). 
 
 298. Every fibre, there is reason to believe, runs a distinct course between 
 the central organ, in which it loses itself at one extremity, and the muscle or 
 organ of sense in which it terminates at the other. Each Nervous Trunk is 
 made up of several fasciculi of these fibres ; and each fasciculus is composed 
 of a large number of the ultimate fibres themselves. Although the fasciculi 
 occasionally intermix and exchange fibres with one another (as occurs in what 
 is termed a plexus), the fibres themselves never inosculate. Each fibre would 
 seem, therefore, to have its appropriate office, which it cannot share with 
 another. The objects of a plexus are twofold. In some instances it serves 
 to intermix fibres, which have endowments fundamentally different : for 
 example, the Spinal Accessory nerve, at its origin, appears to be exclusively 
 motor, and the roots of the Par Vagum are as exclusively afferent ; but by 
 the early admixture of these, a large number of motor fibres are imparted to 
 the Par Vagum, and are distributed in variable proportion, with its different 
 branches ; whilst few of its sensory filaments seem to enter the Spinal Acces- 
 sory. In other instances, the object of a plexus appears to be, to give a more 
 advantageous distribution to fibres, which all possess corresponding endow- 
 ments. Thus the Brachial plexus mixes together the fibres arising from five 
 segments of the spinal cord, and sends off five principal trunks to supply the 
 arm. Now if each of these trunks had arisen by itself, from a distinct seg- 
 ment of the spinal cord, so that the parts on which it is distributed had only 
 a single connection with the nervous centres, they would have been much 
 more liable to paralysis than at present. By means of the plexus, every part 
 is supplied with fibres arising from each segment of the spinal cord ; and the 
 functions of the whole must therefore be suspended, before complete paralysis 
 of any part can occur, from a cause which operates above the plexus. Such 
 a view is borne out by direct experiment; for it has been ascertained by 
 Panizza that, in Frogs, whose crural plexus is much less complicated than 
 that of Mammalia, section of the roots of one of the three nerves which enter 
 into it, produces little effect on the general movements of the limb ; and that, 
 even when two are divided, there is no paralysis of any of its actions, all 
 being weakened in a nearly similar degree. It is not unlikely also that, by 
 this arrangement, a consentaneousness of action is in some degree favoured, as 
 is supposed by Sir C. Bell; for comparative anatomy shows that something 
 resembling it may be traced, wherever a similar purpose has to be attained. 
 Thus, in the Hymenoptera, there is a similar interlacement between the nerves 
 of the anterior and posterior pairs of wings, which act very powerfully to- 
 gether; whilst in the Coleoptera, in which the anterior wings are converted 
 into elytra, and are motionless during flight, the nerves supplying each pair 
 run their course distinctly. In the Octopus, or Poulp, again, the trunks which 
 radiate from the cephalic mass to the eight large arms surrounding the head, 
 are connected by a circular band ; forming a kind of plexus, which seems to 
 contribute to the very powerful and harmonious movements of the arms of 
 this Cephalopod. 
 
 299. The following statements, in which the language of Miiller is adopted 
 21 
 
242 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 with some modification, embody the general principles ascertained by ex- 
 periment, respecting the transmission of sensory and motor impressions. 
 Their rationale will be at once understood, from the facts already mentioned 
 in regard to the isolated characters of each fibril, and the identity of its 
 endowments through its whole course, i. When the whole trunk of a sensory 
 nerve is irritated, a sensation is produced, which is referred by the mind to 
 the parts to which its branches are ultimately distributed ; and if only part of 
 the trunk be irritated, the sensation will be referred to those parts only, whicli 
 are supplied by the fibrils it contains. This is evidently caused by the pro- 
 duction of a change in the sensorium, corresponding with that which would 
 have been transmitted from the peripheral origins of the nerves, had the 
 impression been made upon them. Such a change only requires the integrity 
 of the afferent trunk, between the point irritated and the sensorium ; and is 
 not at all dependent upon the state of the extremity, to which the sensations 
 are referred : for this may have been paralyzed by the division of the nerve ; 
 or altogether separated, as in amputation; or the relative position of its parts 
 may have been changed. It results from the foregoing, that, when different 
 parts of the thickness of the same trunk are separately subjected to irritation, 
 the sensations are successively referred to the several parts supplied by these 
 divisions. This may be easily shown by compressing the ulnar nerve, in 
 different directions, where it passes at the inner side of the elbow-joint. 
 
 ii. The sensation produced by irritation of a branch of the nerve, is con- 
 fined to the parts to which that branch is distributed, and does not affect the 
 branches which come off from the nerve higher up. The rationale of this 
 law is at once understood: but it should be mentioned that there are certain 
 conditions, in which the irritation of a single nerve will give rise to sensations 
 over a great extent of the body. This seems due, however, to a particular 
 state of the central organs ; and not to any direct communication among the 
 sensory fibres. 
 
 in. The motor influence is propagated only in a centrifugal direction, never 
 in a retrograde course. It may originate in a spontaneous change in the 
 central organs: or it may be excited by an impression conveyed to them 
 through afferent nerves ; but in both cases its law is the same. 
 
 iv. When the whole trunk of a motor nerve is irritated, all the muscles 
 w r hich it supplies are caused to contract: but when only a part of the trunk 
 or a branch is irritated, the contraction is confined to the muscles, which 
 receive their nervous fibres from it. This contraction evidently results from 
 the similarity between the effect of an artificial stimulus applied to the trunk 
 in its course, and that of the change in the central organs by which the motor 
 influence is ordinarily propagated. In this instance, as in the other, there is 
 no lateral communication between the fibrils. 
 
 300. Various methods of determining the functions of particular nerves 
 present themselves to the Physiological inquirer. One source of evidence is 
 drawn from their anatomical distribution. For example, if a nervous trunk 
 is found to lose itself entirely in the substance of muscles, it may be inferred 
 to be chiefly, if not entirely, motor or efferent. In this manner, Willis long 
 ago determined that the third, fourth, sixth, portio dura of the seventh, and 
 ninth cranial nerves, are almost entirely subservient to muscular movement; 
 and the same had been observed of the fibres proceeding from the small root 
 of the fifth pair, before Sir C. Bell experimentally determined the double 
 function of that division of the nerve, into which alone it enters. Again, 
 where a nerve passes through the muscles, with little or no ramification among 
 them, and proceeds to a cutaneous or mucous surface, on which its branches 
 are minutely distributed, there is equal reason to believe that it is of a sensory, 
 or rather of an afferent, character. In this manner Willis came to the con- 
 
' 
 
 DETERMINATION OF FUNCTIONS OF NERVES. 243 
 
 elusion, that the fifth pair of cranial nerves differs from those previously 
 mentioned, in being partly sensory. Further, where a nerve is entirely dis- 
 tributed upon a surface adapted to receive impressions of a special kind, as 
 the Schneiderian membrane, the retina, or the membrane lining the internal 
 ear, it may be inferred that it is not capable of transmitting any other kind 
 of impressions; for experiment has shown, that the special sensory nerves do 
 not possess common sensibility. The case is different, however, in regard to 
 the sense of taste, which originates in impressions not far removed from those 
 of ordinary touch; and it is probable that the same nerves minister to both. 
 Anatomical evidence of this kind is valuable also, not only in reference to the 
 functions of a principal trunk, but even as to those of its several branches, 
 which, in some instances, differ considerably. Thus, some of the branches of 
 the Par Vagum are especially motor, and others almost exclusively afferent; and 
 anatomical examination, carefully prosecuted, not only assigns the reasons for 
 these functions, when ascertained, but is in itself nearly sufficient to determine 
 them. Thus the superior laryngeal branch is distributed almost entirely upon 
 the mucous surface of the larynx, the only muscle it supplies being the crico- 
 thyroid ; whilst the inferior laryngeal or recurrent is almost exclusively dis- 
 tributed to the muscles. From this we should infer, that the former is an 
 afferent, and the latter a motor nerve ; and experimental inquiries (hereafter to 
 be detailed) fully confirm this view. In like manner it may be shown, that 
 the Glosso-pharyngeal is chiefly an afferent nerve, since it is distributed to the 
 surface of the tongue and pharynx, and scarcely at all to the muscles of those 
 parts ; whilst the pharyngeal branches of the Par Vagum are chiefly if not 
 entirely, motor. Lower down, however, the branches of the glosso-pharyn- 
 geal cease, and the oesophageal branches of the par vagum are distributed both 
 to the mucous surface and to the muscles ; from which it may be inferred that 
 they are both afferent and motor a deduction which experiment confirms. 
 
 301. We perceive, therefore, that much knowledge of the function of a 
 nerve may be obtained, from the attentive study of its ultimate distribution: 
 but it is necessary that this should be very carefully ascertained, before it is 
 made to serve as the foundation for physiological inferences. As an example 
 of former errors in this respect, may be mentioned the description of the 
 Portio Dura of the seventh, at first given by Sir C. Bell: he stated it to be 
 distributed to the skin as well as to the muscles of the face, and evidently 
 regarded it as in part an afferent nerve, subservient to respiratory impressions 
 as well as to motions. In the same manner, from inaccurate observation of 
 the ultimate distribution of the Superior Laryngeal nerve, it was long re- 
 garded as that which stimulated to action the constrictors of the glottis. But 
 the knowledge obtained by such anatomical examinations alone is of a very 
 general kind ; and requires to be made particular, to be corrected and modi- 
 fied by other sources of information. One of these relates to the connection 
 of the trunks with the central organs. The evidence derived from this 
 source, however, is seldom of a very definite character; and, in fact, the 
 functions of particular divisions of the nervous centres have rather been 
 hitherto judged of, by those of the nerves with which they are connected, 
 than afforded aid in the determination of the latter. Still, this kind of 
 examination is not without its use, when there is reason to believe that a 
 particular tract of fibrous structure has a certain function, and when the office 
 of a nerve whose roots terminate in it is doubtful. Here again, however, 
 very minute and accurate examination is necessary, before any sound physio- 
 logical inferences can be drawn from facts of this description ; and many 
 instances might be adduced to show, that the real connections of nerves and 
 nervous centres are often very different from their apparent ones, 
 
 302. Experimental inquiries into the functions of particular nerves are also 
 
244 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 liable to give fallacious results, unless they are prosecuted with a full know- 
 ledge of all the precautions necessary to insure success. Some of these will 
 be here explained. Suppose that, upon irritating the trunk of a nerve, whilst 
 still in connection with its centre, muscular movements are excited ; it must 
 not be hence concluded that the nerve is an efferent one,- for it may have no 
 directly motor powers. The next step would be to divide the trunk, and to 
 irritate each of the cut extremities. If, upon irritating the end separated 
 from the centre, muscular contractions are produced, it may be safely inferred 
 that the nerve is, in part at least, of an efferent character. Should no such 
 result follow, this would be doubtful. If, on the other hand, muscular move- 
 ment should be produced by irritating the extremity in connexion with the 
 centre, it will then be evident, that it is occasioned by an impression conveyed 
 towards the centre by this trunk, and propagated to the muscles by some 
 other; in other words, to use the language of Dr. M. Hall, this nerve is an 
 excitor of motion, not a direct motor nerve. The glosso-pharyngeal nerve 
 has been satisfactorily determined to be chiefly, if not entirely, an efferent 
 nerve, by experiments of this kind, performed by Dr. J. Reid. 
 
 303. It has been from the want of a proper mode of experimenting, that 
 the functions of the posterior roots of the Spinal nerves have been regarded 
 as in any degree motor. If they be irritated, without division of either root, 
 motions are often excited; but if they be divided, and their separated trunks 
 be then irritated, no motions ensue; nor are any movements produced by 
 irritation of the roots in connexion with the spinal cord, if the anterior roots 
 have been divided. Hence it appears that the motor powers of these fibres 
 are not direct, but that they convey an impression to the centre, which is 
 reflected to the muscles through the anterior roots. Another source of fallacy 
 is to be guarded against, arising from the communication to a nerve, in its 
 course, of properties it did not possess at its root, by inosculation with an- 
 other nerve. Of this many instances will hereafter present themselves. 
 
 304. The same difficulties do not attend the determination of the sensory 
 properties of nerves. If, when the trunk of a nerve be pricked or pinched, 
 the animal exhibits signs of pain, it may be concluded that the nerve is sen- 
 sible to ordinary impressions at its peripheral extremity. But not unfre- 
 quently this sensibility is derived by inosculation with another nerve ; as is 
 the case with the portio dura, which is sensory after it has passed through 
 the parotid gland, having received there a twig from the fifth pair. A similar 
 inosculation explains the apparent sensibility of the anterior roots of the 
 spinal nerves. If these be irritated, the animal usually gives signs of uneasi- 
 ness ; but if they be divided, and the cut ends nearest the centre be irritated, 
 none such are exhibited ; whilst they are still shown, when the farther ends 
 are irritated, but not if the posterior roots are divided. This seems to indi- 
 cate that, from the point of junction of the two roots, sensory fibres derived 
 from the posterior root pass backwards (or towards the centre) in the anterior; 
 and thus its apparent sensory endowments are entirely dependent upon its 
 connexion with the posterior column of the spinal cord, through the posterior 
 roots. 
 
 305. The fallacies to which all experiments upon the nerves are subject, 
 arising from the partial loss of their powers of receiving and conveying im- 
 pressions, and of exciting the muscles to action, after death, are too obvious 
 to require particular mention here; yet they are frequently overlooked. Of 
 a similar description are those arising from severe disturbance of the system, 
 in consequence of operations; which also have not been enough regarded by 
 experimenters. 
 
 306. All our positive knowledge of the functions of the Nervous System 
 in general, save that which results from our own consciousness of what passes 
 
DETERMINATION OF FUNCTIONS OF NERVES. 245 
 
 within ourselves, and that which we obtain from watching the manifestations 
 of disease in Man, is derived from observation of the phenomena exhibited 
 by animals made the subjects of experiments; and it is desirable to preface 
 our general summary of the results of these, by some remarks upon the in- 
 ferences to be drawn from them. In the first place it must be constantly 
 borne in mind that, except through the movements consequent upon them, 
 we have no means of ascertaining, whether or not particular changes in the 
 Nervous System, whose character we are endeavoring to determine, are 
 attended with Sensation; since we have no power of judging whether or not 
 this has been excited, save by the cries and struggles of the animal made the 
 subject of experiment. Now although such cries and struggles are ordinarily 
 considered as indications of pain, yet it is not right so to regard them in every 
 instance; and the only unequivocal evidence is derived from observation of 
 the corresponding phenomena in the Human subject; since we can there 
 ascertain, by the direct testimony of the individual affected, what impressions 
 produce sensation, and what excite movements independently of sensation. 
 Further, we are not justified in assuming that consciousness is excited by an 
 irritation, still less that the intelligence and will are called into exercise by 
 it, merely because movements, evidently tending to get rid of this, are per- 
 formed in respondence to it. We know that the contractions of the heart 
 and alimentary tube are ordinarily excited by a stimulus, without any sensa- 
 tion being involved; and these movements, like all that are concerned in the 
 maintenance of the Organic functions, have an obvious design, when con- 
 sidered either in their immediate effects, or in their more remote consequences. 
 The character of adaptiveness, then, in Muscular movements excited by 
 external stimuli, is no proof that they are performed in obedience to sensa- 
 tion ; much less, that they have a voluntary character. In no case is this 
 adaptiveness more remarkable, than in some of those actions, which are not 
 only performed without any effort of the will, but which the will cannot 
 imitate. This is the case, for example, with the act of Deglutition; the 
 muscles concerned in which cannot be thrown into contraction by a voluntary 
 impulse, being stimulated only by impressions conveyed from the mucous 
 surface of the fauces to the medulla oblongata, and thence reflected along the 
 the motor nerves. No one can swallow without producing an impression of 
 some kind upon this surface, to which the muscular movements will imme- 
 diately respond. Now it is impossible to conceive any movements more 
 perfectly adapted to a given purpose than those of the parts in question ; and 
 yet they are independent, not only of Volition, but of Sensation, being still 
 performed in cases in which consciousness is completely suspended, or 
 entirely absent. 
 
 307. There is much difficulty, then, in ascertaining the really elementary 
 functions of the Nervous System, by experiments upon animals ; and it is 
 only when their results are corrected and explained by pathological observa- 
 tion on Man, the sole case in which we can obtain satisfactory evidence of 
 the presence or absence of sensation, that they have much value to the phy- 
 siological inquirer. From these combined sources, however, a vast amount 
 of knowledge of the functions of the nervous system has recently been gained; 
 and the general purposes to which it is subservient, may be advantageously 
 stated in a systematic form, before we enter upon any detailed examination of 
 them. 
 
 i. The Nervous System receives impressions, which, being conveyed by 
 its afferent fibres to the Sensorium, are there communicated to the conscious 
 Mind, and thus give origin to Sensations. The Nervous structure is further 
 subservient, in some way, to the acts of that mind ; as the result of which, a 
 motor impulse is transmitted along the efferent trunks, to particular Muscles, 
 
246 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 exciting them to contraction. There is reason to believe, however, that this 
 motor impulse may proceed from at least two distinct sources; being either 
 the direct consequence of the sensation, acting involuntarily as an emotional 
 or instinctive impulse ; or resulting from a more or less complicated series 
 of intellectual operations, which terminate in an act of volition or will. To 
 these functions, taken collectively, the Encephalon, and the nerves connected 
 with it, are alone subservient ; and we may probably assign the group of sim- 
 ple consensual or involuntary actions to the ganglia which receive the nerv- 
 ous trunks from the organs of sense, and which make up nearly the whole 
 of the Cephalic masses of ganglia in the Invertebrata ; whilst the Cerebral 
 hemispheres of Vertebrata are the instruments of the intellectual operations 
 and of the mandates of the will. 
 
 ii. Certain parts of the Nervous System receive impressions which are 
 propagated along afferent fibres, that terminate in ganglionic centres distinct 
 from the sensorium; and in these a reflex motor impulse is excited, which, 
 being conveyed along the efferent trunks proceeding from them, excites mus- 
 cular contraction, without any necessary intervention of sensation or volition. 
 Of this function (called by Dr. Hall, to whom the discovery of it is in a great 
 part due, the reflex function), we shall find that the portion of the Spinal 
 Cord of Vertebrata, which is not continuous with the fibrous structure of the 
 brain, together with the portion of the nervous trunks which are connected 
 with it alone, is the instrument: whilst, in the Invertebrata, the same office 
 is performed by ganglia still more obviously disconnected from the cephalic 
 mass. 
 
 in. Another division of the Nervous System appears to have for its object, 
 to combine and harmonize the muscular movements immediately connected 
 with the maintenance of Organic life ; and to bring these into relation with 
 certain conditions of the mind. There is reason to believe (though this is 
 less certain) that it also influences, and brings into connection with each other, 
 the processes of Nutrition. Secretion, &c. ; though these, like the muscular 
 movements just mentioned, are essentially independent of it. This portion 
 of the nervous apparatus is commonly known under the name of the Sympa- 
 thetic system. 
 
 308. "Now, in reference to the first of these classes of operations, it is well 
 to explain that though the Physiologist speaks of the intellectual powers, 
 moral feelings, &c., as functions of the Nervous System, they are not so in 
 the sense in which the term is employed in regard to other operations of the 
 bodily frame. In general, by the function of an organ, we understand some 
 change which may be made evident to the senses ; as well in our own sys- 
 tem, as in the body of another. Sensation, Thought, Emotion, and Volition, 
 however, are changes imperceptible to our senses, by any means of observa- 
 tion we at present possess. We are cognizant of them in ourselves, without 
 the intervention of those processes by which we observe material changes 
 external to our minds ; but we judge of them in others, only by inferences 
 founded on the actions to which they give rise, when compared with our own. 
 When we speak of sensation, thought, emotion or volition, therefore, as func- 
 tions of the Nervous System, we mean only that this system furnishes the 
 conditions under which they take place in the living body ; and we leave the 
 question entirely open, whether the "Vvzy has or has not an existence independ- 
 ent of that of the material organism, by which it operates in Man, as he is 
 at present constituted. 
 
 309. In regard to the second class of actions, it may be remarked, that they 
 are nearly all connected, more or less closely, with the maintenance of the 
 Organic functions, or with the protection of the body from danger. Thus 
 the movements of the pharynx supply to the stomach the alimentary materi- 
 
COMPARATIVE ANATOMY AND PHYSIOLOGY. RADIATA. 247 
 
 als, which it has to prepare for the nutrition of the body ; and those of the 
 muscles of the thorax, &c., maintain that constant interchange of air in the 
 lungs, which is necessary for the aeration of the blood : whilst those, by 
 which a limb is involuntarily retracted from any cause of pain or irritation, are 
 obviously adapted to the latter of these two ends. 
 
 2. Comparative Anatomy and Physiology of the Nervous System in 
 Invertebrated Animals. 
 
 310. Although the structure and distribution of the Nervous System in the 
 different classes of Animals have been, until recently, but little appealed to 
 in the determination of its functions, they are capable of supplying evidence 
 regarding some of these, not less important in its character than that which 
 Comparative Anatomy affords to other departments of Physiology. Some of 
 the principal of these contributions will now be pointed out. 
 
 311. In the lowest tribes of the RADIATED division of the animal kingdom, 
 no Nervous System has yet been discovered. These have, therefore, been 
 separated by some naturalists into a new primary group, to which the desig- 
 nation of Jicrita has been given, on account of the (supposed) "indistinct, 
 diffused, or molecular character of their nervous system." This idea of a 
 "diffused nervous system" seems to be regarded by many Physiologists as 
 well as Naturalists as the necessary alternative, resulting from the want of 
 any definite indications of its presence. It may be said, however, to be based 
 on very erroneous notions, as to the true offices of the nervous apparatus. 
 Its influence is not required to endow the tissues with contractility $ a pro- 
 perty possessed in a high degree by the structures of many Plants, to which 
 these beings present a much greater general resemblance, than they bear to 
 the higher Animals; and, even in the latter (as will be shown hereafter), this 
 property is independent of nervous agency, although generally called into 
 exercise by it. That a nervous system is not required by them for the per- 
 formance of the functions of Nutrition and Reproduction, otherwise than to 
 supply, by its locomotive actions, the conditions of those functions, would 
 also appear from its absence in Pfants. It is on the sensible movements of 
 these beings, that our belief in their possession of a nervous system must be 
 founded, when we cannot render it cognizable by our senses. But we must 
 be careful not to draw hasty inferences from such phenomena. Sensible move- 
 ments are, as we have seen, performed by the Dionaea and Sensitive plant, in 
 respondence to external stimuli acting on distant organs ; and they are also 
 exhibited, in a very remarkable manner, by the reproductive particles of many 
 of the simpler Plants, as well as by numerous beings now generally referred 
 to the Vegetable kingdom. It is to be remarked, however, that such motions 
 are of a very simple description. In objects of the latter class, they are of 
 a rhythmical character, and do not seem to be in direct dependence on any 
 external influences. And even where they are performed solely in respond- 
 ence to external stimuli, there is usually such a uniformity in their character, 
 as indicates that the means by which the influence is propagated are of a very 
 mechanical nature. On the other hand, those movements of Polypes, which 
 are performed in respondence to external stimuli, are of a much more varied 
 character; and there are others, which seem to indicate a certain degree of 
 voluntary power, and therefore to display a consciousness of impressions made 
 upon the body. These phenomena, then, would lead us to suspect the ex- 
 istence of a Nervous System in the beings which exhibit them ; not, however, 
 in a "diffused" condition, but in the form of connected filaments. For, what 
 consentaneousness of action can be looked for in a being whose nervous 
 matter is incorporated in the state of isolated globules with its tissues? How 
 
248 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 should an impression made on one part be propagated by these to a distance ? 
 And how can that consciousness and will, which are one in each individual, 
 exist in so many unconnected particles ? If, then, we allow any sensibility, 
 consciousness, and voluntary power, to the beings of this group of Acrita 
 to deny which would be in effect to exclude them from the Animal Kingdom 
 we must regard these faculties as associated with nervous filaments, of such 
 delicacy as to elude our means of research. When the general softness of 
 the textures, and the laxity of structure that characterizes the nervous fibres, 
 in the lowest animals in which they can be traced, are kept in view, little 
 difficulty need be felt in accounting for their apparent absence. The case is 
 very different from that of Vegetable structure ; the greater consistency of 
 which enables us to place much more reliance upon the negative evidence 
 afforded by anatomical research. 
 
 312. The correctness of this view (which has been here dwelt on the longer, 
 because it involves a fundamental question in Nervous Physiology), is borne 
 out by the fact, that, in those members of the group whose size and consist- 
 ency allow their structures to be sufficiently examined, a definite nervous 
 system has been detected ; in the position which it might, a priori, be ex- 
 pected to occupy, according to the type of the individual. Thus, in the large 
 fleshy isolated polype, commonly known as the Sea-Anemone (Jictinia), a 
 nervous ring has been discovered, surrounding the mouth as in other Radiata, 
 and sending off branches to the tentacula, with a minute ganglionic enlarge- 
 ment at the base of each. In the higher Radiata, as the Star-Fish, the nerv- 
 ous system has the same regular form as that which prevails through the 
 other organs. The mouth is surrounded by a filamentous ring, which presents 
 a regular series of ganglionic enlargements, one of them corresponding with 
 each segment of the body. From every one of these, a branch is transmitted 
 to the corresponding ray ; and two smaller ones proceed to the viscera included 
 in the central disk. 
 
 313. The POLYPIFERA being the lowest of the Radiated classes, in which 
 there is a regularly-organized digestive apparatus, and which perform move- 
 ments of a character ascribable only to a Nervous System, it will be desir- 
 able to inquire a little more particularly mto the phenomena they exhibit, and 
 the degree in which these necessarily involve the possession of the higher 
 mental endowments. In this inquiry we shall refer principally to the little 
 Hydra, or fresh-water Polype ; the habits of which are better known than 
 those of any other species. Although no nervous filaments have been de- 
 tected in this, we have a right to infer their presence for the reasons already 
 given ; and they probably form a ring around the mouth, as in the Actinia, 
 sending filaments to the tentacula. This interesting little being may be re- 
 garded as essentially a stomach; and the orifice of this is provided with 
 tentacula, which contract when irritated by the touch of any adjacent body, 
 and endeavour to draw it towards the entrance Now, the action in the Hu- 
 man body, to which this is most allied, is evidently that of the muscles of 
 Deglutition ; which lay hold, as it were, of the food that has been conveyed 
 to the fauces, and carry it into the stomach. These muscles are called into 
 action, not by an effort of the will, but by the contact of the food with the 
 lining membrane of the pharynx. This impression is propagated by the 
 glosso-pharyngeal nerve to the medulla oblongata. where a respondent motor 
 impulse is excited, which is transmitted through the pharyngeal branches of 
 the par vagum to the muscles of deglutition, and causes their contraction. 
 This phenomenon will be more fully examined hereafter ; it is here adduced 
 simply as an instance of the important class of reflex movements, which are 
 independent of the brain (though, to a certain extent, controlled by it), which 
 are altogether involuntary, and which do not necessarily involve the produc- 
 
MOVEMENTS OF POLYPES. 249 
 
 tion of sensation. There would appear to be little difference in the character 
 of this movement, between the simple Hydra and the most perfect Vertebrated 
 animal. In the latter, however, another set of muscles are superadded to 
 these, for the purpose of preparing the aliment by mastication for the opera- 
 tion of the stomach, and of bringing it within reach of the pharyngeal con- 
 striction. But, it has been urged, the inactivity of the tentacula when the 
 Hydra is gorged with food, proves that they are excited to action by the will 
 of the animal. This inference, however, may be easily disproved. The 
 muscles of deglutition in Man are not called into action with nearly the same 
 readiness and energy, when the stomach is distended, as when it is empty; a 
 fact of which any one may convince himself, by observing the relative facility 
 of swallowing, at the commencement and the termination of a full meal. No 
 one will assert that this variation is an effect of the will; indeed, it is often 
 opposed to it; being one of those beautiful adaptations, by which the welfare 
 of the economy is provided for, but which the indulgence of the sensual appe- 
 tites opposes. Most of the movements of this animal, and of others of the 
 class, appear to be equally the result of external stimuli, with that already 
 described; and it is only in a few instances, principally those of absolute 
 locomotion or change of place, that any evidence of voluntary action can be 
 discerned. It may be occasionally remarked, however, that one or more of 
 the tentacula are retracted or extended, without the slightest appreciable 
 change in any of those external circumstances, which seem ordinarily to 
 affect the motions of the animal ; and this action we can scarcely regard as 
 otherwise than voluntary. 
 
 314. Thus in the Nervous System of Radiated Animals, we have an in- 
 stance of that community of function, which is so remarkable in the organism 
 of the lower tribes, when contrasted with the separation, which is perceptible 
 in those at the opposite extremity of the scale. The visceral nerves of the 
 Asterias are not isolated at their central terminations from those which are 
 connected with the sensorial and locomotive functions : nor are the nerves 
 which minister to the instinctive actions separable from those which convey 
 the influence of the will. Every segment of the body appears equal in its 
 character and endowments to the remainder; each has a ganglion appropriated 
 to it ; and, as the ganglia, like the segments, are all alike, neither of them can 
 be regarded as having any presiding character. 
 
 315. From the Radiated we now pass to the MOLLUSCOUS classes; the 
 general character of which, as a natural group, is the remarkable predomi- 
 nance of the Nutritive system over that of Animal life. There is not in the 
 Mollusca, as in the Radiata, any repetition of parts around a common centre; 
 and we do not therefore meet in them with a number of ganglia, nearly or 
 altogether alike in endowments. In some of the higher species, there is a 
 conformity between the two sides of the body, or a lateral symmetry ; which 
 involves a subdivision of some of the ganglia, that are single in the inferior 
 tribes, into two masses, which always remain in connexion with each other. 
 With this exception, it may be observed, that all the principal ganglia, to the 
 number of four or five, which we meet with in the higher Mollusca, appear 
 to have distinct functions; as may be determined by tracing the distribution 
 of their nerves. Thus we find a pair of cephalic ganglia, situated above the 
 03sophagus, connected with the organs of special sensation, and sending motor 
 nerves (as we shall see reason to believe) to all parts of the body. This is 
 obviously analogous to the brain of Vertebrata. Below the oesophagus there 
 is generally a small ganglion, connected with the apparatus of deglutition, 
 which may be called the stomato- gastric ganglion. In connexion with the 
 gills we have always one ganglion, sometimes a pair, which may be termed 
 the branchial ganglion. Another is found at the base of the foot, which may 
 
250 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 be called the pedal ganglion. And there is sometimes another, which espe- 
 cially supplies the mantle with nerves ; and this may be called the palleal 
 ganglion. The distribution of their nerves to the different organs, would 
 alone indicate the respective functions of these ganglia; but these are placed 
 beyond doubt, by that very great variety in the disposition of these organs, 
 which is characteristic of the Mollusca. The development of the sensory 
 organs, the situation of the gills, the structure and position of the foot, the 
 conformation and uses of the mantle, are well known to differ in the most 
 obvious manner, in genera which are closely allied to each other. Hence 
 the anatomist is enabled, by the discovery of corresponding changes in the 
 nervous system, to satisfy himself of the particular functions of its different 
 centres.* 
 
 316. It is only in the higher tribes, however, that this separation of function 
 is evident ; for in the lowest, we find the Nervous System in its least deve- 
 loped form. This is the case in the class TUNICATA; composed of animals, 
 in which the whole body is enclosed in a tunic or bag, having two orifices, 
 through one of which the water is drawn in by ciliary action, whilst through 
 the other it is expelled. This bag incloses a large chamber, the lining of 
 which is devoted to the respiratory function ; and at the bottom of it lies the 
 mass of the viscera, on which is the entrance to the stomach. A part of the 
 water which is taken into the respiratory chamber flows into this, and passes 
 through the intestinal canal ; being discharged along with that, which has 
 only served the purpose of aerating the blood. These animals have no power 
 of motion, but such as is effected by the general contraction of the respiratory 
 sac; this is effected by a single ganglion placed between its orifices, which is 
 therefore chiefly a branchial ganglion, and is the only nervous centre they 
 possess. The trunks connected with it send branches over the muscular 
 envelope of the respiratory sac, and to the sphincters which surround its 
 orifices ; whilst other branches proceed to the membrane lining the orifices, 
 and especially to the tentacula, or lips, which are situated at the oral entrance. 
 The maintenance of the regular current is effected, as just stated, by ciliary 
 action ; but when any substance is being drawn in, the entrance of which 
 would be injurious, its contact with the tentacula excites a general contraction 
 of the muscular envelope, and causes a jet of water to issue from one or both 
 orifices, which carries the offending body to a distance. And, in the same 
 manner, if the exterior of the body be touched, the mantle suddenly and vio- 
 lently contracts, and expels the contents of the sac. These are the chief, if 
 not the only actions, which the Nervous System of these animals is destined 
 to perform ; and they are evidently of a reflex character ; bearing a close 
 correspondence with the acts of coughing and sneezing in Man, which are in 
 like manner destined to expel injurious substances from the respiratory pas- 
 sages. By the contact of such substances with the tentacula that guard the 
 oral orifice, or with the lining of the respiratory sac, or by irritation of the 
 external surface of the body, an impression is produced on the afferent fibres ; 
 which, being conveyed to the central ganglion, excites there a reflex motor 
 impulse ; and the propagation of this impulse along the afferent fibres, to the 
 muscular fibres of the contractile sac, and to the sphincters, produces the 
 movements in question. 
 
 317. In the CONCHIFERA, or Mollusks inhabiting bivalve shells, there are 
 invariably two ganglia, having different functions. The larger of these (Fif 
 
 124, c), corresponding to the single ganglion of the Tunicata, is situated towards 
 the posterior end of the body (that is, the end most distant from the mouth), 
 
 * See Mr. Garner on the Nervous System of the Mollusca, in the Linnsean Transactions, 
 Vol. xvn. 
 
NERVOUS SYSTEM OF THE LOWER MOLLUSC A. 
 
 251 
 
 Fig. 124. 
 
 in the neighbourhood of the posterior adductor muscle ; and its branches are 
 distributed to that muscle, to the mantle, to the gills, and to the siphons 
 through which the water is introduced 
 and carried off. But we find another 
 ganglion, or rather pair of ganglia, a, 
 a, situated near the front of the body, 
 either upon the resopliagus, or at its 
 sides ; these ganglia are connected 
 with the very sensitive tentacula 
 which guard the mouth ; and they 
 may be regarded as presenting the 
 first approach, both in position and 
 functions, to the brain of higher ani- 
 mals. In the Oyster, and others of 
 the lower Conchifera which have no 
 foot, which is a muscular tongue- 
 like organ, we find an additional 
 ganglion (b) connected with it. This 
 is the case in the Solen, or animal of 
 the Razor-shell ; whose foot is a very 
 powerful boring instrument, enabling 
 it to penetrate deeply into the sand. 
 Here, then, we have three distinct 
 kinds of ganglionic centres ; every one 
 of which may be doubled, or repeated 
 on the two sides of the body. First, 
 the cephalic ganglia, a, a, which are 
 probably the sole instruments of sen- 
 sation and of consensual movements; 
 as well as of whatever voluntary 
 power the animal may possess : these 
 are almost invariably double, being 
 connected together by a transverse 
 band, which arches over the oesopha- 
 gus. Second, the pedal ganglion, b, 
 which is usually single, in conformity 
 with the single character of the organ 
 it supplies ; but in one very rare Bi- 
 valve Mollusk, the foot is double, and 
 the pedal ganglion is double also. 
 Third, the respiratory ganglion, c, 
 which frequently presents a form that 
 indicates a partial division into two 
 halves, corresponding with the repe- 
 tition of the organs it supplies, on the 
 two sides of the body. Besides these 
 principal centres, we meet with nu- 
 merous smaller ones upon the nervous 
 cords (/, /, and g, g), which proceed from them to the different parts of the 
 general muscular envelope or mantle. 
 
 318. Now it will be observed, that the two cephalic ganglia a, a, are con- 
 nected with the pedal ganglion, b, by means of a pair of trunks, e, proceeding 
 from the former to the latter ; and that they are, in like manner, separately 
 connected with the respiratory or branchial ganglion c. It is found, upon 
 
 Nervous system of Solen; a, a, cephalic ganglia, 
 connected by a transverse band passing over the 
 oesophagus; 6, pedal ganglion, the branches of 
 which are distributed to the powerful muscular 
 foot; c, branchial ganglion, the branches of which 
 proceed to the gills g, the siphons i, t, and other 
 parts ; A, anus : e, trunks connecting cephalic and 
 branchial ganglia; /-/././, minute ganglia on the 
 branches distributed to the mantle. 
 
252 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 careful dissection, that these cords do not serve merely to bring the ganglia 
 into relation ; but that a part of them pass through the ganglion into the trunks 
 proceeding from it. Thus, of the nerves which supply the large fleshy foot, 
 and which appear to proceed from the pedal ganglion, 6, a part are undoubt- 
 edly connected with that ganglion alone, coming into relation with its vesicu- 
 lar substance ; but a part also pass on to the cephalic ganglia, by the connecting 
 trunks, so that these, rather than the pedal ganglion, constitute their centre. 
 The same may be said of the nerves proceeding from the branchial ganglion : 
 a portion of them having their centre in the vesicular matter of that ganglion ; 
 whilst another portion has no relation to it whatever (beyond that of prox- 
 imity), but passes through or over it, to become connected with the cephalic 
 ganglia. There is good reason to believe, that the pedal and branchial gan- 
 glia minister to the purely reflex actions of the organs they respectively sup- 
 ply; and that they would serve this purpose as well, if altogether cut off from 
 connection with the cephalic ganglia : whilst the latter, being the instruments 
 of the actions which are called forth by sensation (whether these be of a con- 
 sensual or of a voluntary nature), exert a general control ancT direction over 
 the movements of the animal. 
 
 319. The animals of the class GASTEROPODA, whether furnished with uni- 
 valve shells, or entirely destitute of such protection, are, for the most part, 
 much more highly organized than the preceding; possessing not merely 
 greater locomotive power, but organs of special sense, which are situated in 
 the neighbourhood of the mouth, upon a projecting part of the body, which is 
 thus constituted a head. Their nervous system consists of at least three dis- 
 tinct centres ; the relative position of which varies with that of the organs 
 supplied by them. The anterior or cephalic ganglia are larger in proportion 
 to the rest, than they are in the Conchifera ; and they exhibit a tendency to 
 gain a position anterior to the oesophagus, and to approximate towards each 
 other, so as to meet and form a single ganglionic mass on the median line. 
 The branchial ganglion is constantly to be met with ; but its position is ex- 
 tremely variable. This centre, however, always bears a close relation with 
 the gills, both in situation and in degree of development ; and even where 
 conjoined, as it frequently is, with the pedal ganglion, it may be distinguished 
 from it by the distribution of its nerves, as well as by its separate connection 
 with the cephalic ganglia, which is always noticed in such cases. This may 
 be observed in the Patella (limpet) and Limax (slug). Sometimes the func- 
 tions of this ganglion are subdivided between two ; of which one is still ap- 
 propriated to the branchiae ; whilst the other is connected with the general 
 surface of the mantle, and with the respiratory passages which are prolonga- 
 tions of it, and hence may be called the palleal ganglion. The position of 
 the pedal ganglion (which is generally double in the Gasteropoda, though the 
 foot is single), also varies, but in a less degree, since it is generally in the 
 neighbourhood of the head. Besides these nervous centres, we find, in many 
 of the Gasteropoda, a separate system connected with a very important set 
 of organs, the gustatory and manducatory, which are but slightly shadowed 
 out among the Conchifera. In these higher tribes, the oesophagus is dilated 
 at its commencement into a muscular cavity (Fig. 3, a); containing a curious 
 rasp-like tongue, often supported upon cartilages, which serves to reduce the 
 food; and sometimes furnished with horny maxillae. The nerves which sup- 
 ply these do not proceed directly from the cephalic ganglia, but from a dis- 
 tinct centre; and their ramifications proceed along the oesophagus and sto- 
 mach, and are occasionally connected with the other nerves by inosculating 
 filaments. This set of ganglia and nerves, which is even more important 
 from its relative development in some other classes, and into the analogies of 
 
NERVOUS SYSTEM OF HIGHER MOLLUSCA. 253 
 
 which in the nervous system of Vertebrata we shall hereafter inquire, may be 
 called, from its distribution, the stomato- gastric system. 
 
 320. The ganglia first described may be regarded as corresponding with 
 those parts of the nervous centres in the Vertebrata, the distribution of whose 
 nerves is analogous. Thus the branchial ganglion obviously corresponds 
 with that portion of the Medulla Oblongata which is the centre of their respi- 
 ratory actions ; and the pedal ganglion is analogous to that division of the 
 Spinal Cord from which the nerves of the anterior or posterior extremities 
 pass off. It is well known that such portions of the spinal cord may be com- 
 pletely isolated, without destroying the functions to which they minister. 
 Thus, the brain and lower part of the spinal cord may be removed, that 
 portion only of the cerebro-spinal axis being left, which is connected with the 
 principal respiratory nerves, in fact the respiratory ganglion, and yet the 
 animal may continue to exist for some time. It is then reduced to a condi- 
 tion similar to that of the Tunicata; whose single ganglion, though combining 
 in some degree the functions of those which exist separately in the higher 
 tribes, has evidently the regulation of the respiratory movements for its chief 
 object. In the same manner, the integrity of the segment of the cord, with 
 which the nerves of the extremities are connected, will enable them to execute 
 those movements of a reflex character, which depend upon its power as their 
 centre; even though it be isolated from every other part of the nervous ap- 
 paratus. The cephalic ganglia must be regarded as chiefly analogous to those 
 portions of the Encephalon of Vertebrata, which are immediately connected 
 with the nerves of sense. We find nerves of special sensation proceeding 
 from them, certainly to eyes and an auditory apparatus, perhaps also to 
 olfactive organs ; as well as others of common sensation, supplying the ten- 
 tacula and mouth. Hence we must admit, that they perform the functions of 
 the optic ganglia of Vertebrata, and perhaps also of the olfactory lobes ; as 
 well as of the portion of the medulla oblongata, in which the sensory portion 
 of the fifth pair terminates. Moreover, they certainly give origin also to 
 motor nerves ; and must thus perform the functions of the Medulla Oblongata, 
 from which the corresponding nerves arise in Vertebrata ; as well as, perhaps, 
 of the Cerebellum. It is obvious that the portion of the Nervous system of 
 the Gasteropod Mollusca, into the analogies of which we have thus inquired, 
 cannot in the least be compared as a whole with the Sympathetic system of 
 the Vertebrata, which it was formerly imagined to resemble. The distribu- 
 tion of some of its nerves to the viscera, however, may indicate that it partly 
 performs the functions of that system; with which it is structurally inter- 
 mixed, even in Vertebrata. But the stomato-gastric system may, perhaps, 
 with more probability, be considered as executing its offices. Into the pecu- 
 liar character of that system we shall be more competent to inquire when we 
 have traced it through other classes of Invertebrata. 
 
 321. Having thus separately considered the nervous centres of the Gaste- 
 ropoda, and determined their special functions by their structural relations, we 
 shall inquire into the mode in which these functions are combined, so as to 
 enable them to act in harmony. This is an inquiry of much interest, in re- 
 ference to the determination of the offices of the different parts of the nervous 
 centres in Articulated and Vertebrated animals. If we examine the mode in 
 which the different ganglia are united by connecting trunks, we are led to per- 
 ceive the important fact, that, while they have little or no communication with 
 each other, they are all directly connected with the cephalic ganglia ; which 
 seem thus to harmonize and control their individual actions. Frequently a 
 communication with one another appears to exist, where there is really none. 
 Thus, in the Jlplysia,^. cord passes from the branchial ganglion (Fig. 125, D), 
 
 22 
 
254 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Fig. 125. 
 
 which is situated in the posterior part of the body, to the pedal ganglion of 
 each side, (c, c). Where such is the case, the trunk is not united with that 
 
 proceeding from the ganglion through 
 which it passes ; but the two remain 
 distinct, though running in the same 
 direction. Moreover, the double func- 
 tion of a ganglion may be sometimes 
 recognized, by its being connected 
 with the cephalic mass by a double 
 trunk. Thus, in the Aplysia, that 
 which has been termed the pedal gan- 
 glion is really made up of a pedal and 
 palleal ganglion, as is proved by the 
 distribution of its branches; and in 
 conformity with this double function, 
 we find it communicating with the 
 cephalic mass by two cords, besides 
 the one which has been just mentioned 
 as passing through it, and which ap- 
 pears as a third. In the Bullsea, 
 whose nervous system is disposed on 
 the same general plan, the pedal and 
 palleal ganglia are separately connected 
 with the cephalic ; the cord from the 
 branchial ganglion passing through the 
 palleal. 
 
 322. Further, a careful examination 
 of these ganglia, and of their connecting 
 cords, discloses this important fact, 
 which is peculiarly evident in the case 
 of the pedal ganglia that the cords 
 proceeding from the cephalic mass do 
 not lose themselves in the grey matter 
 of these ganglia; but divide themselves 
 into filaments, which mix with those 
 proceeding from them, to form the 
 
 nervOUS trunks which they distribute. 
 
 Ttf e can scarcely, then, fail to infer, 
 
 h h , j ^ngUon, with the nerv- 
 
 ,., ., 6 * * 
 
 OUS fibnls proceeding from itself, IS the 
 
 SOUTCe of the reflex actions of this Or- 
 gan; whilst the filaments whichare con- 
 
 tinuous with those of the connecting 
 
 Nervous system of Aplysia. A, pharyngeal gan- 
 
 giion; B, cephalic ganglion. The cephalic is con- 
 
 nected, by three distinct cords on each side, with 
 the lateral masses, c c, which combine the functions 
 of pedal and palleal ganglia; these are united with 
 each other by two transverse bands, between which 
 the aorta passes. From the lateral ganglia, a con- 
 necting cord passes backwards on each side to the 
 
 with the nucleus of the cephalic gang- 
 lia, are the channels of sensory impres- 
 sions, and of the motor impulses prompted by them. This is well illustrated 
 in the curious disposition of parts, which we find in the arms of the Cuttle-fish. 
 These are provided, it is well known, with a series of suckers, which are to 
 the animal important instruments of locomotion and prehension. It has been 
 observed by Dr. Sharpey, that the nerves which supply these arms are fur- 
 nished with ganglionic enlargements, of which one corresponds with each 
 sucker; and that each trunk consists of two tracts, in one of which the gan- 
 glionic enlargements exist; whilst the other passes continuously over these, 
 but sends off nervous filaments, which help to form the branches going to the 
 
NERVOUS SYSTEM OF MOLLUSCA AND ARTICTJLATA. 255 
 
 several suckers. When the animal endeavours to embrace any object firmly 
 with its arm, it brings all the suckers simultaneously to bear upon it. There 
 can be little doubt that this action is occasioned by a motor impulse, propa- 
 gated from the cephalic masses by the non-ganglionic portion of the cord, 
 which supplies all the suckers alike. On the other hand, any individual 
 sucker may be made to attach itself, by placing a substance in contact with 
 it alone ; this action is independent of the cephalic ganglia, as is evident from 
 the fact, that it will take place when the arm is severed from the body, or even 
 in a small piece of the arm, if recently separated; and it can scarcely be doubted, 
 that it is due to the reflection of the impression made upon the sucker, through 
 the small ganglion in its own neighbourhood, where it excites a motor impulse. 
 The operation of these independent centres appears, in the entire living animal, 
 to be controlled, directed, and combined, by the cephalic ganglia ; through the 
 medium of the fibrous band which passes over them, and which mixes its 
 branches with theirs. A very similar arrangement will be presently shown 
 to exist in the double nervous column of the Articulata. 
 
 323. Upon reviewing all the anatomical facts hitherto stated, it will be per- 
 ceived that ganglionic masses, characterized by nuclei of grey matter, or of 
 something equivalent to it, seem to exist, wherever it is desirable that impres- 
 sions made upon the afferent nerves should excite motions ; and that, as we 
 rise dn the scale, there is an increase in the number of centres possessing a 
 diversity of functions. We have seen that sometimes these centres are, for 
 the sake of convenient disposition, united into one mass ; whilst on the other 
 hand, when the organs are multiplied, they also are repeated to a like extent ; 
 especially when it is desirable that they should be able to act independently 
 of one another, as in the case of the suckers of the Cuttle-fish. It may further 
 be remarked, that wherever the presence of special sensory organs, confined 
 to one part of the body, gives to that part a predominance over the remainder 
 (the entrance to the alimentary canal being always in this neighbourhood), we 
 find the ganglia with which they are connected possessing a special relation 
 with all the rest, which these do not possess with each other. It is obvious 
 that, where visual organs are developed, the impressions made upon these will 
 determine the movements of the animal, more than those of any other kind ; 
 and it would seem to be chiefly owing to the information they communicate, 
 that the cephalic ganglion has such an evident presiding influence over the rest, 
 even when smaller than any of them. This is, however, more the case in 
 animals whose movements are rapid, and in which, therefore, the perception 
 of distant objects is more important as in the Insect tribes. Except in the 
 Cephalopoda, the subservience of the nervous system to the nutritive functions 
 of the Mollusca is so great that it might almost be regarded as an appendage to 
 the digestive organs, destined for the selection and prehension of aliment. 
 But in the more active members of that class it derives a more elevated cha- 
 racter, from the development of organs of special sensation and of active loco- 
 motion. 
 
 324. The animals composing the group ARTICULATA all present, in a more 
 or less evident degree, a division into segments, which have an obvious tend- 
 ency to resemble one another, as in the Radiata ; these are disposed, however, 
 not in a circle, as in the Radiata, but in a continuous line. In those in which 
 these segments differ but little (as in the Centipede, or the Caterpillar of the 
 Insect), the nervous system is a repetition of similar parts ; the most anterior 
 of the ganglia, however, has an evident predominating influence over the 
 rest, for the reason just specified ; and this influence will be found, by com- 
 parison in other classes, to diminish with the loss* and to increase with the de- 
 velopment, of the faculties of special sensation, which have their seat there. 
 The locomotive power's are just as predominant in the Articulated series, as 
 
256 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Fig. 126. 
 
 Nervous System of Larva of Sphinx Ugus. 
 
 distances ; the last is formed by the consoli- 
 dation of the llth and 12th. 
 
 are the nutritive functions among the Mol- 
 lusca. Accordingly, we find the deve- 
 lopment of the Nervous system to bear a 
 special reference to them ; and the sensori- 
 motor divisions of it can be more distinctly 
 separated, than in the Mollusca, from the 
 portion which ministers to the organic func- 
 tions. 
 
 325. The general arrangement of the 
 Nervous System differs so little, except as 
 to the degree of concentration of the ganglia, 
 in the different classes of this sub-king- 
 dom, that it is of little consequence what 
 example we select. It will be convenient 
 to take for illustration that of the Larva of 
 the Sphinx ligustri, or Privet Hawk-Moth, 
 which has been minutely described by Mr. 
 Newport. Here we observe a chain of 
 ganglia running from one extremity of the 
 body to the other, along the ventral sur- 
 face, and in the median line. These gan- 
 glia are connected by trunks, which, on 
 close examination, are seen to consist of 
 two cords closely united. The cephalic 
 ganglion is bilobed ; evidently consisting 
 of two masses, which are united on the 
 median line. These receive the nerves of the 
 eyes and antennae ; but they are still of small 
 size, in accordance with the low develop- 
 ment of the sensory organs. The ganglia 
 of the longitudinal cord are nearly equal 
 from one extremity of the body to the 
 other. Each sends off nerves to its re- 
 spective segments ; and the branches pro- 
 ceeding from the different ganglia have 
 little communication with each other. The 
 highest of them, situated just beneath the 
 oesophagus, is connected with the cephalic 
 masses by two cords ; between which that 
 canal passes, encircled, as it were, in a ring. 
 
 326. The most detailed account of the 
 conformation of the Nervous Centres in 
 the Articulata, is that recently given by 
 Mr. Newport, in regard to the lulus, and 
 other animals of the class MYRIAPODA.* 
 Their general arrangement corresponds 
 with that which has been just described 
 in the Iarva3 of the Sphinx ligustri ; but 
 the number of ganglia is much greater. In 
 each lateral half of the cord, two distinct 
 tracts or layers of fibres can be detected : 
 of these, one known as the fibrous tract 
 is continuous with the 
 
 * Philosophical Transactions, 1843. 
 
NERVOUS SYSTEM OF ARTICULATA. 
 
 257 
 
 Portion of the gang] ionic tract of Po- 
 lydesmus maculalus ; b, inter-ganglionic 
 cord ; c, anterior nerves ; d, posterior 
 nerves; /, &, fibres of reinforcement; 
 g-, h, commissural fibres ; i, longitudinal 
 fibres, softened and enlarged, as they 
 pass through ganglionic matter. 
 
 and contains no vesicular matter ; whilst the other known as the ganglionic 
 tract has vesicular matter deposited at intervals amongst its fibres, some of 
 which are continuous with the brain, whilst others do not reach it. (Fig. 128, 
 A.) Every nerve that is given off from this ventral column, is connected with 
 both tracts ; and thus it has two sets of roots, one proceeding to the brain, the 
 other entering the ganglion near which it arises. Of this last division, a part 
 crosses to the opposite side, forming the 
 commissural fibres which unite together the 
 lateral halves of the cord ; whilst another 
 bundle of fibres runs along the side of the 
 ganglionic tract, for a greater or less propor- 
 tion of its length, and then emerges again 
 forming part of another nervous trunk. In 
 Fig. 127 is seen Mr. N.'s representation of 
 one of the ventral ganglia, and part of the 
 cord, of Polydesmus maculalus; showing 
 the longitudinal and commissural fibres, to- 
 gether with those to which he has given the 
 name of fibres of reinforcement. These 
 lateral fibres, which do not pass on to the 
 brain, but issue again from the ventral cord 
 at a point a little distant from their entrance, 
 seem to be more numerous in the hinder part 
 of the body of the Centipede tribe, than in 
 its front portion : and thus it is, that the whole 
 size of the cord remains nearly the same 
 along its entire length ; whilst that of the por- 
 tion which passes backwards from the brain, must be continually diminishing, 
 as it gives off' fibres to the nerves. 
 
 327. After what has been said of the offices which the ganglia perform in 
 the Mollusca, and of the relation which they bear to the cephalic mass, we 
 shall have little difficulty in understanding the character of the nervous appa- 
 ratus in the Articulata, if our minds be unoccupied by any preconceived 
 notion. When we examine into the actions of the ventral cord, we perceive 
 that those of all its ganglia are similar to each other; being related only to 
 the movements of their respective segments, and of the members which belong 
 to them. In fact, these ganglia may be regarded as so many repetitions of 
 the pedal or locomotive ganglion of the Mollusca. It is easily proved, that 
 the movements of each pair of feet may be produced by that ganglion alone, 
 with which it is connected ; since a single segment, isolated from the rest, 
 will continue to perform these movements for some time, under favourable 
 circumstances. But it is evident that they must be placed, in the living ani- 
 mal, under some general control ; by which the consentaneousness of action, 
 that is essential to regular locomotion, may be produced. This is proved by 
 the experiments to be presently quoted. We can scarcely account for the 
 exercise of such a general control, otherwise than by attributing it to the 
 fibrous portion of the cord,* which directly connects each of the nervous 
 
 * It is believed by Mr. Newport, that the fibrous portion of the ganglionic tract, which lies 
 nearest the surface of the body, may be the channel by which sensory impressions are con- 
 veyed to the brain; whilst the fibrous tract itself may convey downwards the motor impulses 
 which originate in the cephalic ganglia. The chief reason for this supposition, is the corre- 
 spondence in position, relatively to each other, and to the rest of the body, between the 
 fibrous and ganglionic columns in Articulata, and the portions of the Spinal Cord of Verte- 
 tebrata, from which the anterior or motor roots, and the posterior or sensory, respectively 
 arise. But the fibres which are peculiar to the ganglionic tract, obviously form a distinct 
 system. 
 
 22* 
 
258 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 trunks with the cephalic ganglia, as in the Mollusca; and this must, there- 
 fore, conduct to the sensorium (whose seat is probably in the latter) the im- 
 pressions which there produce sensations, and must convey downwards the 
 locomotive impulse; whilst the ganglion of each segment, with the filaments 
 connected with its nucleus, will form the circle necessary for the simply- 
 reflex actions of its members. The independence of the segments of the 
 Articulata, as far as their reflex actions are concerned, and their common sub- 
 ordination to one presiding centre of the will, are fully explained on this sup- 
 position. It is also quite conformable to the analogy, both of Mollusca, and 
 of Vertebrata. 
 
 328. The number and variety of the reflex actions, which take place in the 
 Articulata after decapitation, are very remarkable ; and they seem to have a 
 consentaneousness, proportioned to the closeness of the relation between the 
 nervous centres in the respective species. Thus, in the Centipede, we find 
 the ganglia of the several segments distinct, but connected by a commissural 
 trunk. Here an impression made equally upon the afferent nerves of all the 
 ganglia, will produce a consentaneous action. Thus, if the respiratory ori- 
 fices on one side of a decapitated Centipede be exposed to an irritating vapour, 
 the body will be immediately flexed in the opposite direction ; and if the 
 stigmata of the other side be then similarly irritated, a contrary movement 
 will occur. But different actions may be excited in different parts of the 
 cord, by the proper disposition of the irritating cause. In the higher classes, 
 however, where the ganglia of the locomotive organs are much concentrated, 
 the same irritation will produce consentaneous motions in several members, 
 similar to those which the unmutilated animal performs. In the Mantis 
 religiosa, for example, which ordinarily places itself in a very curious 
 position, especially when threatened or attacked, resting upon its two pos- 
 terior pairs of legs, and elevating its thorax with the anterior pair, which are 
 armed with powerful claws, if the anterior segment of the thorax, with its 
 attached members, be removed, the posterior part of the body will still remain 
 balanced upon the four legs which belong to it, resisting any attempts to over- 
 throw it, recovering its position when disturbed, and performing the same 
 agitated movements of the wings and elytra, as when the unmutilated animal 
 is irritated: on the other hand, the detached portion of the thorax, which con- 
 tains a ganglion, will, when separated from the head, set in motion its long 
 arms, and impress their hooks on the fingers which hold it. These facts 
 prove unequivocally, that the combined automatic movements of these parts, 
 which are performed in direct respondence to external expressions, are only 
 dependent for their stimulation upon that ganglionic centre, with which the 
 nerves that excite them are immediately connected. Another instance, related 
 by Burmeister, is still more satisfactory in regard to the manner in which 
 these movements are excited. A specimen of the Dytiscus Sulcatus, from 
 which the cephalic ganglia had been removed, and which remained in a 
 motionless condition whilst lying with its abdomen on a dry hard surface, 
 executed the usual swimming motions, when cast into water, with great 
 energy and rapidity, striking all its comrades to one side by its violence, and 
 persisting in this for half an hour. 
 
 329. These conclusions are also fully confirmed by the experiments of 
 Mr. Newport, upon various Insects and Myriapoda; the results of which 
 have been recently made public.* The following, upon the lulus terrestris, 
 is particularly interesting. " The cord was divided in the fourteenth, and 
 also the twentieth segment; and the intervening portion was destroyed, by 
 breaking it down with a needle. The animal exhibited in the anterior part 
 
 * Philos. Trans., 1843, p. 267. 
 
REFLEX ACTIONS OF ARTICULATA. 
 
 259 
 
 of its body all the evidences of perfect volition. It moved actively along, 
 turning itself back on either side repeatedly, as if to examine the anterior 
 wounded portion, which it felt again and again with its antennae: and when 
 attempting to escape, frequently turned back as if in pain and aware of some 
 hindrance to its movements ; but it seemed perfectly unconscious of the 
 existence of the posterior part of its body, behind the first incision. In those 
 segments, in which the cord was destroyed, the legs were motionless ; while 
 those of the posterior division, behind the second incision, were in constant 
 but involuntary motion, the movements being similar to those of walking or 
 running, uniformly continued, but without any consentaneous action with 
 those of the anterior part, by which locomotion was performed, dragging the 
 posterior divisions of the body after them. When the animal was held by 
 the posterior segments, reflex actions were excited in the legs, and powerful 
 contractions and gyrations of the whole animal were performed in those seg- 
 ments ; but these movements appeared to be entirely the result of reflex 
 actions of the muscles, since exactly similar ones took place in the whole 
 body of decapitated specimens. At the expiration of twelve hours, the most 
 perfectly voluntary acts were performed by the head and anterior division of 
 
 Fig. 128. 
 
 Parts of Xervous System of Articulata. A, single ganglion of Centipede, much enlarged, showing the 
 distinctness of the purely fibrous tract, 6, from the ganglionic column, a. B, portion of the double cord 
 from thorax of Pupa of Sphinx ligustri, showing the respiratory ganglia and nerves, between the gan- 
 glia (2, 3, 4), and the separated cords of the symmetrical system, c, view of two systems combined, 
 showing their arrangement in the Larva; a, ganglion of venial column ; 6, fibrous tract passing over 
 it; c c, respiratory system of nerves distinct from both. 
 
 the body, such as locomotion forwards or to either side, avoidance of any 
 obstacle, touching it with the antennae, (which were in rapid action, as in an 
 uninjured animal,) and attempting to reach and to climb up an object pre- 
 
260 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 sented to it, but not in immediate contact with it. But reflex movements 
 alone existed in the posterior division, in which the legs were very slowly 
 moved, even when the animal was not progressing. Brisk actions were now 
 more easily excited in them than at first, either by contact with the segments, 
 by irritation of one or two of the legs themselves, or by a sudden current of 
 air. By these means, when the animal was lying still, actions were imme- 
 diately excited in all the legs of the posterior parts of the body, anterior and 
 posterior to those which were irritated ; and these actions were induced in 
 those of both sides of the body, but appeared to commence on the opposite 
 side, in the legs corresponding to those which were first irritated. In eighteen 
 hours, the anterior part of the body was quite dead, so that no motions what- 
 ever could be excited in it, either voluntary or reflex; but reflex actions were 
 then readily excited in the posterior, and also slightly so by mechanical irrita- 
 tion, even at twenty-four hours." It would appear, then, that we may obtain 
 more decided proof, in the Articulated series, of the real character of reflex 
 actions, and of their dependence upon a distinct system of nerves, than we 
 can draw from any other class of animals. In the Vertebrata, it is easy to 
 distinguish the sensory from the motor the afferent from the efferent 
 fibres; but the distinctness of the excito-motor system from the sensori-voli- 
 tional, is not so clearly made out. Here, however, the afferent and efferent 
 fibres cannot'be readily distinguished; but it is obvious that the reflex actions, 
 which manifest themselves when the communication with the cephalic ganglia 
 is cut off, are to be attributed to those fibres, which enter the cord under the 
 afferent character, pass into the edge of the ganglion as ihe fibres of rein- 
 forcement, or cross it as commissural fibres, and then emerge again as 
 efferent fibres, either in the nerves of the same segment, or in those of another 
 more or less distant. By traversing the cord along a part of its length, and 
 thus placing the several segments in communication with each other, the 
 fibres of reinforcement thus constitute a part of the longitudinal filaments of 
 the cord, the remainder consisting of the fibres continuous with the cephalic 
 ganglia. 
 
 330. Hitherto we have spoken only of that division of the nervous system 
 of the Articulata, which may be regarded as corresponding with the sensory 
 and locomotive ganglia of the Mollusca ; we have next to inquire what we 
 find corresponding with the branchial ganglion. It is to be recollected, that the 
 respiratory apparatus of Insects is diffused throughout the whole body, so that its 
 presiding system of nerves must be proportionally extended; and we are, there- 
 fore, prepared to find the branchial ganglion of the Mollusca repeated, like 
 the pedal, in each segment. Besides the nervous trunks proceeding from the 
 ventral cord at its ganglionic enlargement, we find, in most of the Articulated 
 classes, a series of smaller nerves, given off at intermediate points, without 
 any apparent swelling at the points of divergence. The connections of these 
 are most distinctly traced in the thoracic region, just as the Larva is passing 
 into the Pupa state ; for the cords of the ventral column then diverge, so that 
 an additional tract may be seen which occupies the central line. By a close 
 scrutiny, this tract may be found in the perfect Insect, on the superior or vis- 
 ceral aspect of the cord ; and its nerves are given off from minute ganglionic 
 enlargements upon it. It seems to be quite unconnected, along its whole 
 course, with the column upon which it lies. Its nerves, however, communi- 
 cate with those of the sensori-motor system ; but they have a separate distri- 
 bution, being transmitted especially to the tracheae, on the parietes of which 
 they ramify minutely, and also to the muscles concerned in the respiratory 
 movements. (The latter, however, being a part of the general locomotive 
 apparatus, are also supplied from the principal ganglionic column.) These 
 nerves, then, which are evidently analogous to those of the gills and siphonic 
 
KESPIRATORY AND STOMATO-GASTRIC SYSTEMS OF INSECTS. 
 
 261 
 
 Fig. 129. 
 
 apparatus in the Mollusca, may be regarded as corresponding with the pneu- 
 monic portion of the Par Vagum in Vertebrata (which is in like manner dis- 
 tributed on the air passages), and with its associated motor nerves. 
 
 331. In comparing the nervous system of Insects with that of the higher 
 Mollusca, it will be seen that they differ more in the arrangement and in the 
 relative proportion of their parts, than in their essential character. In both 
 there is a Cephalic division of the ganglionic centres, in which sensibility and 
 psychical power appear to reside more particularly, if not entirely. In both 
 there is a division specially appropriated to the Locomotive apparatus, differ- 
 ing only in the multiplication of the centres in Insects, conformably with the 
 arrangement of the members they supply ; and sometimes consolidated to 
 nearly the same degree. In both, also, we find a division appropriated to the 
 Respiratory apparatus, in which there is a corresponding multiplicity of 
 centres in the Articulata, in harmony with the universal distribution of their 
 tracheal system. And in both, as we shall now see, 
 
 there is a separate system of nerves, distributed to the 
 alimentary apparatus, and supplying the organs of mas- 
 tication (with the salivary glands), of deglutition, and of 
 digestion. 
 
 332. Of the stomato- gastric system, some traces may 
 be found in nearly all the Articulated classes. Thus, 
 in the Leech, we find a minute ganglion existing at the 
 base of each of the three teeth which form the mouth ; 
 these ganglia are connected together, and, to the cephalic 
 by slender filaments ; and they seem also to be in con- 
 nection with other filaments, which may be traced on the 
 alimentary canal. As a specimen of its highly-deve- 
 loped form, we shall describe that of the Gryllotalpa 
 vulgaris (Common Mole-Cricket). Here we find it con- 
 sisting of two divisions; one placed on the median 
 line, which may hence be called the median system ; 
 the other running on each side at some little distance, 
 and hence called the lateral system. The median sys- 
 tem appears to originate in a small ganglion, situated an- 
 teriorly and inferiorly to the cephalic mass, with which 
 it communicates by a connecting branch on each side. 
 From this ganglion, nerves proceed to the walls of the 
 buccal cavity, the mandibles, &c. Its principal trunk, 
 however, (the recurrent of authors,) is sent backwards 
 beneath the pharynx. The ramifications of this are 
 distributed along the cesophageal tube and dorsal ves- 
 sel ; whilst the trunk passes downwards to the stomach, 
 where its branches inosculate with those supplied by 
 the lateral system, and seem to assist in forming a 
 pair of small ganglia, from which most of the visceral 
 nerves radiate. The ganglia of the lateral system are 
 two on each side, lying behind and beneath the cephalic 
 masses. The anterior pair are the largest, and meet on 
 the median line, just behind the cephalic ganglia, with 
 which they communicate. Posteriorly to these lie the 
 second pair, which are in connection with them. Two 
 cords pass backwards on each side ; one derived from 
 the anterior, the other from the posterior, of these gan- 
 glia. They run along the sides of the oesophagus and 
 
 dorsal vessel ; and, after inosculating with the branches of the central system 
 
 IV 
 
 Stomato-gastric system 
 of Gryllotalpa vulgaris ; 
 AA, cephalic ganglia; a, 
 anterior median ganglion 
 with the recurrent trunk 
 passing downwards from 
 it ; 66, and ec, lateral gan- 
 glia ; d, visceral ganglia. 
 
262 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 enter the two cceliac ganglia, from which branches radiate to the abdominal 
 viscera. 
 
 333. This system of ganglia and nerves has an evident affinity with the 
 Sympathetic system of Vertebrate, as well as with some parts of the Cerebro- 
 spinal system, more especially with the Par Vagum. It is to be remembered, 
 that the Pneumogastric nerve of Vertebrata is distributed to three separate 
 systems the respiratory, the circulating and the digestive. As we know 
 that the ultimate fibrils of nerves never anastomose, there can be no doubt 
 that these branches might be separately traced backwards into their ganglionic 
 centres ; and they may thus be regarded as functionally three distinct nerves, 
 though bound up in a single trunk. There is no difficulty, then, in under- 
 standing that the respiratory system of nerves, in Insects, and other In- 
 vertebrata, may be analogous with the pneumonic portion of the Par Vagum ; 
 although it bears no relation with the cardiac and gastric divisions of the 
 nerve. To the latter divisions, the analogy of the recurrent nerve becomes 
 sufficiently plain, when we look at its distribution upon the dorsal vessel, 
 oesophagus, and stomach ;* but its commencement in the anterior ganglion, 
 which also supplies the mouth and pharynx, might seem to place it on a dif- 
 ferent footing, until we have determined the true analogy of this last centre. 
 It may be inferred from its situation, and from the distribution of its nerves, 
 that this anterior ganglion is analogous both to the labial and pharyngeal 
 ganglia of the higher Mollusca. These appear to form a division of the 
 nervous system, by whichfthe actions immediately concerned in the prehen- 
 sion of food are performed ; and these seem almost as independent of the 
 cephalic ganglia, as are those of respiration. There is evidently, however, 
 a greater tendency towards the union of these centres with the oesophageal 
 collar, than of those presiding over the respiratory function, which is more 
 independent of the will. 
 
 334. The division of the nervous system of Vertebrata with which the 
 central portion of this system corresponds, is a question of some apparent 
 difficulty; but, if we bring into comparison not only the highest but the 
 lowest forms of the cerebro-spinal apparatus, the chief difficulties will be 
 removed. The analogies drawn from the distribution of the nervous branches 
 would lead us to infer, that the third division of the Fifth pair (including its 
 sensory and motor origins), the Glosso-Pharyngeal, and the gastric portion of 
 the Par Vagum, would most nearly represent its central portion. Now, when 
 the fifth pair is traced back to its true origin, it is found to be not a cerebral 
 but a spinal nerve; and it is then seen to arise from the Medulla Oblongata, 
 in such close approximation with the par vagum and glosso-pharyngeal, as to 
 show that, if this portion of the nervous centres were isolated from the rest, 
 the nerves which proceed from it would form, anatomically as well as func- 
 tionally, a natural group. The fifth pair, like other spinal nerves, may act in 
 a simply-reflex character; although, in Man, it is usually under the dominion 
 of the will. In the lower animals we find these reflex actions bearing a much 
 larger proportion to the voluntary, than in Man; and even in him we not 
 unfrequently meet with cases, in which the functions of the cerebral hemi- 
 spheres seem suspended, whilst those of the spinal cord are unimpaired ; so 
 that the prehension of food by the lips may take place without any effort of 
 the will. This has been observed in anencephalous fetuses, in puppies from 
 which the brain has been removed, and in profound apoplexy. Further, the 
 connection between the fifth pair and par vagum is very intimate in fishes ; the 
 class which approaches nearest, in the character of its nervous system, to 
 Invertebrata. We may reasonably infer, then, that the anterior ganglion is 
 
 * See Newport, in Phil. Trans., 1832, p. 386. 
 
STOMATO-GASTRIC SYSTEM OF INVERTEBRATA. 263 
 
 the principal centre of the reflex actions of those nerves, which correspond to 
 the third branch of the fifth pair, to the glosso-pharyngeal, and to the gastric 
 portion of the par vagum, in Vertebrata ; whilst the branches which connect 
 them with the cephalic ganglia, bring these nerves more or less under the 
 influence of the latter. The lateral ganglia seem more analogous to the 
 centres of the Sympathetic system in Vertebrata; especially in the connection 
 of their branches with all the other systems of nerves; and in the share 
 which they have in the formation of the coeliac ganglia. This view of the 
 relative functions of these two divisions of the stomato-gastric system, is 
 strengthened by the fact, that the connection between the Sympathetic system 
 of Fishes and the Par Vagum is much more intimate than in the higher 
 Vertebrata; although, even in the latter, as will be shown hereafter, it is by no 
 means so slight as it appears.* 
 
 335. Upon taking a general review of the facts which have been stated, 
 and of the inferences which have been erected upon them, we perceive that 
 a gradual elevation may be traced, in the character of the actions to which the 
 Nervous System is subservient, as we ascend from the lower to the higher 
 parts of the Animal Scale. In the Radiata and lower Mollusca, in which no 
 organs of special sensation exist, all, or nearly all, of the movements which 
 are witnessed, may be legitimately regarded as simply reflex in their character ; 
 being analogous to those, which are unquestionably so in the higher animals ; 
 and being performed by the instrumentality of a nervous apparatus, that 
 seems to have little else than an internuncial purpose. But when, as in 
 the higher Mollusca and in nearly all the Articulata, we meet with distinct 
 organs of special sensation, it becomes evident that the consciousness of the 
 animal must be 'concerned in the direction of its actions; since no impressions 
 upon these organs (the eyes, for example) can exert any motor influence on 
 the muscles, except by producing sensations ; that is, if we may apply to 
 the lower tribes the laws deduced from the study of the higher. Whilst, 
 therefore, a large proportion of the actions of the higher Invertebrata still 
 continues to be reflex (as we have especially seen in the Articulata), a new 
 group is superadded to these; and this, consisting of actions, which are 
 directly stimulated by sensations, and in which no Reasoning powers nor 
 Will appear to have any direct participation, may be termed consensual. 
 They require, as their instruments, a set of ganglia to receive the trunks which 
 originate in the organs of sense, and to issue motor nerves to the several parts 
 of the body. These last are distributed along with the trunks, which are 
 connected with the ganglia belonging to each particular organ ; thus the legs 
 and wings of an Insect appear to derive their motor nerves, partly from the 
 ganglia of the ventral cord, which minister to their reflex actions, and partly 
 from the cephalic ganglia, which seem to harmonize, to control, and even to 
 antagonize, the influence of the former. In like manner, the parts of the 
 body, which are capable of receiving sensory impressions, appear to have a 
 double connection; one with the ganglia of the ventral cord, for the purpose 
 of conveying thither those impressions which are destined to excite reflex 
 actions ; and the other with the cephalic ganglia, in order to originate sensa- 
 tions. Of this double system of nerves and ganglia, the one connected solely 
 
 * The view given above of the comparative structure and offices of the Nervous System, 
 in the Invertebrated animals, is chiefly abridged from the Author's Prii.3 Thesis on this 
 subject; in which additional details will be found, as well as many other illustrative figures 
 and references to authorities. He has there, also, discussed the physiological explanation 
 which had been previously given of the double nervous cord of the Articulata ; and having 
 shown that it is neither consistent with itself, nor capable of being applied to the other 
 Invertebrata, he has deemed it unnecessary to complicate the present sketch by introducing it. 
 
264 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 with the reflex actions, and the other with the consensual, the existence in 
 Articulata seems to be clearly established by Mr. Newport's researches 
 ( 326) ; and although the distinction between the afferent and motor fibres, 
 of each system respectively, has not here been clearly made out, there can be 
 no reasonable doubt of its existence. 
 
 336. The class of consensual actions evidently becomes more predominant, 
 in proportion as the special sensory organs are more evolved, and as the 
 ganglia in immediate connection with them (and altogether forming the cephalic 
 mass) present an increase in their proportionate development. This is 
 especially the case in the higher Articulata ; in which the Instinctive group of 
 actions attains its highest perfection and predominance. The propriety of 
 referring these to the consensual group, will be obvious upon a little considera- 
 tion. They are as evidently prompted by particular sensations, as are the 
 reflex actions by particular impressions; and the respondence is as uniform 
 in the one case, as in the other. Although in these movements, there is a 
 most remarkable adaptation of means to ends, (as in the construction of 
 habitations by various Insects, and especially by the social Hymenoptera,) 
 yet few persons will maintain that this adaptation is performed by the reason 
 of the animal; since, on this supposition, every Bee solves a problem which 
 has afforded scope for the laborious inquiries of the acutest human mathe- 
 matician.* The adaptation is in the original construction of a nervous system, 
 which should occasion particular movements to be performed under the in- 
 fluence of particular sensations ; and the constancy with which these are 
 performed by different individuals of the same species, when placed in the 
 same conditions, leads at once to the belief, that they must be independent of 
 any operations so variable as those of judgment and voluntary exertion. 
 
 337. On the other hand, in the Vertebrata, we shall find the purely reflex 
 and consensual movements forming a smaller proportion of their actions, and 
 brought under a more complete subjection to the Volitional system. This is 
 evident, from the greater variety which the actions exhibit ; from the mode in 
 which they are adapted to peculiar circumstances ; from the degree in which 
 they may be modified by education ; and from various other indications of a 
 superior kind of Intelligence. At last, in adult Man, we perceive that all the 
 movements, which are elsewhere involuntary, but which are not immediately 
 requisite (as are those of deglutition, respiration, <fcc.) for the maintenance of 
 
 * The hexagonal form of the cell is the one in which the greatest strength, and the nearest 
 approach to the cylindrical cavity required for containing the larva, are attained, with the 
 least expenditure of material. But the instinct which directs the Bees in the construction 
 of the partition that forms the bottom or end of the cell, is of a nature still more wonderful 
 than that which governs its general shape. The bottom of each cell rests upon three parti- 
 tions of cells upon the opposite side of the comb ; so that it is rendered much stronger, than 
 if it merely separated the cavities of two cells opposed to one another. The partition is not 
 a single plane surface; but is formed by the union of three rhomboidal planes, uniting in the 
 centre of each cell. The angles formed by the sides of these rhombs, were determined by 
 the measurements of Maraldi to be 109 28' and 72 32'; and these have been shown, by 
 mathematical calculation, to be precisely the angles, at which the greatest strength and capa- 
 city can be attained, with the least expenditure of wax. The solution of the problem was 
 first attempted by Koenig, a pupil of the celebrated Bernouilli ; and as his result proved to 
 differ from the observed angle by only two minutes of a degree, it was presumed that the 
 discrepancy was due to an error of observation, which it was easy to account for by the 
 smallness of the surfaces whose inclination had to be measured. The question has been 
 since taken up, however, by Lord Brougham (Appendix to his Illustrated edition of Paley's 
 Natural Theology) ; who has worked it out afresh, and has shown that, when certain small 
 quantities, neglected by Koenig, are properly introduced into the calculation, the result is . 
 exactly accordant with observation, the Bees being thus proved to be right, and the Mathe- 
 matician wrong. 
 
NERVOUS SYSTEM OF VERTEBRATA. 265 
 
 the Organic functions, are placed under the control of the Will, guided by the 
 reasoning faculties. This is especially true of the locomotive organs, whose 
 reflex actions are entirely governed by the will ; being only distinguishable as 
 such, when, from peculiar states of the system, the immediate influence of 
 the controlling power is suspended. We shall find ground to believe, that 
 the exercise of the Reasoning faculties, and the resulting operations of the 
 Will, take place through the instrumentality of another division of the nervous 
 centres ; to which there is nothing distinctly analogous among the Inverte- 
 brata ; but which seems to bear a constant proportion in size and importance, 
 among Vertebrated animals, to the development of the Intelligence and its 
 influence on the movements of the body : namely, the Cerebral ganglion. 
 
 338. There is another aspect, however, under which we are to consider 
 the Nervous System ; and this becomes more important in the highest division 
 of the Animal kingdom, on which we are now about to dwell. We have 
 hitherto spoken only of its influence on the contractile properties of the tis- 
 sues, to which it is distributed. It has, however, an important and direct 
 connection with the purely organic functions of Nutrition and Secretion; and 
 we shall see reason to regard it as the means, not only of placing the animal 
 in relation with the external world, but of harmonizing and controlling the 
 organic changes taking place in its own structure, and of bringing these under 
 the influence of particular mental conditions. The opinion is entertained by 
 many, that all the Organic Functions are dependent upon the innervation, 
 supplied to them by the system of nerves, which has been termed Sympathetic 
 or visceral. It is incumbent, however, on those who uphold the necessity of 
 this nervous power, to prove it definitively ; since all analogy leads to an 
 opposite conclusion. We may regard the capability of separating a particular 
 secretion from the blood, as a peculiar property inherent in the glandular cells, 
 just as contractility is the inherent property of muscular fibre. But as the 
 peculiar arrangement of the excitable and contractile tissues in Animals, 
 requires a nervous system to act as a conductor between them, and to blend 
 their actions; so may the complicated Organic functions of Animals require 
 to be harmonized and kept in sympathy with each other, by some mode of 
 communication more direct and certain than that afforded by the circulating 
 system, which is their bond of union in Plants. We have seen, in the fore- 
 going sketch, that the Visceral system does not exist in a distinct form in the 
 lower classes of Invertebrated animals ; and also that the nervous system of 
 these classes cannot, as a whole, be compared with it, although it may be 
 regarded as containing some rudiments of it. As the divisions of this system 
 become more evident, however, and the organic functions more complicated, 
 some appearance of a separate Sympathetic system presents itself; but this is 
 never so distinct as in Vertebrata. Hence, it may fairly be inferred that, as 
 the Sympathetic system is not developed in proportion to the predominant 
 activity of the functions of organic life (which is so remarkable in the Mol- 
 lusca when contrasted with the Articulata), but in proportion to the develop- 
 ment of the higher divisions of the nervous system, its office is not to 
 contribute to these functions anything essential to their performance ; but 
 rather to exercise that general control over them which becomes the more 
 necessary as they become more independent of one another; and to bring 
 them into relation with the system of Animal life. 
 
 3. Nervous System of Vertebrata. 
 
 339. When we direct our attention to the Nervous System of the Verte- 
 brated classes, we are immediately struck by two remarkable differences which 
 its condition presents, from that under which we have seen it to exist in the 
 
 23 
 
266 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Invertebrata. In the latter it has seemed but a mere appendage to the rest of 
 the organism, a mechanism superadded for the purpose of bringing its various 
 parts into more advantageous relation. On the other hand, in the Vertebrata 
 the whole structure appears subservient to it, and designed but to carry its 
 purposes into operation. Again, in the Invertebrata, we do not find any 
 special adaptation of the organs of support, for the protection of the Nervous 
 System. It is either inclosed, with the other soft parts of the body, in one 
 general hard tegumentary envelope, as in the Echinodermata and Articulata; 
 or it receives a still more imperfect protection, as in the Mollusca. In the 
 latter, the naked species are destitute of any means of passive resistance, and 
 the Nervous System shares the general exposed condition of the whole body ; 
 and it is not a little remarkable that, in the testaceous kinds, the portion of 
 the body containing the most important nervous centres should be protruded 
 beyond the shell, whilst the principal viscera are retained within it. Now, 
 in the Vertebrata, we find a special and complex bony apparatus, adapted in 
 the most perfect manner for the protection of the Nervous System ; and it is, 
 in fact, the possession of a jointed spinal column, and of its cranial expansion, 
 which best characterizes tiie group. 
 
 340. When we look more particularly at the Nervous Centres themselves, 
 we perceive that they combine the general characters of those of the Articulata 
 with those of the Mollusca ; the locomotive powers of the former (compara- 
 tively reduced, however, in activity) being united with the complex nutritive 
 system of the latter ; and we find this combination manifested, not only in 
 the organs themselves, but in the Nervous System, which stands in so close 
 a relation with them. The Spinal Cord of Vertebrata is evidently the ana- 
 logue of the ventral columns of Articulata. It is a continuous ganglion, con- 
 taining two portions as distinct as the two tracts in the Articulata ; a fibrous 
 structure, which is continuous between the Brain and the spinal nerves, and 
 thus resembles the white tract in Insects ; and a ganglionic portion, princi- 
 pally composed of gray matter. Into this gray matter, as in the ventral gan- 
 glia of Insects, a part of the roots of the spinal nerves may be traced ; whilst 
 others seem to pass on continuously to the brain. At the upper extremity of 
 the Spinal cord (commonly termed the Medulla Oblongata] we find the 
 ganglia and nerves of special sensation; and the organs which these supply 
 are placed in immediate proximity with the entrance to the alimentary canal, 
 holding the same relation to it as in the Mollusca. But in addition to these 
 we find two ganglionic masses in all Vertebrata, to which we have no distinct 
 analogue in the lower classes the Cerebral Hemispheres, and the Cerebel- 
 lum. With the development of the former of these, as already remarked, 
 the perfection of the reasoning powers appears to hold a close relation ; that 
 of the latter seems connected with the necessity which exists, for the adjust- 
 ment and combination of the locomotive powers, when the variety of move- 
 ments performed by the animal is great, and the harmony required among 
 them is more perfect. Upon these points, however, we shall hereafter 
 dwell. 
 
 341. The Visceral system of nerves now assumes a more distinct form. 
 It does not share the protection of the Spinal column; but its ganglia lie for 
 the most part in the general cavity of the trunk. These ganglia, which 
 are doubtless the independent centres of some of the nerve-fibres proceed- 
 ing from them, are much more numerous than is commonly supposed. It 
 appears from recent researches, that we are to regard as belonging to the 
 Visceral or Sympathetic system, not only the Semilunar and Cardiac ganglia 
 (which seem to be its principal centres), with the chain of cranial, cervical, 
 thoracic, lumbar, and sacral ganglia, which are in nearer proximity to the 
 
NERVOUS SYSTEM OF VERTEBRATA. 
 
 267 
 
 [Fig. 130. 
 
 Cerebro-spinal system, but also nu- 
 merous minute ganglia, which are 
 to be found on its branches in vari- 
 ous parts, and, in addition, the gan- 
 glia upon the posterior roots of the 
 Spinal nerves. If, indeed, we are 
 to regard the fine nerve - fibres, 
 wherever they present themselves, 
 as belonging to the Visceral sys- 
 tem, we must regard this as still 
 largely interwoven with the Cere- 
 bro-spinal system, notwithstanding 
 that the former has its own set of 
 ganglionic centres ; since, as already 
 mentioned ( 244), these peculiar 
 fibres are found in considerable 
 numbers in all the Cerebro-spinal 
 nerves, and may be shown to origi- 
 nate in the caudate corpuscles of 
 the Brain and Spinal Cord. On 
 the other hand, there unquestion- 
 ably exist numerous fibres in the 
 Visceral system, which proceed 
 into it from the Cerebro-spinal sys- 
 tem; these, however, are not uni- 
 formly distributed, for some of the 
 Visceral nerves contain few or none 
 of them, whilst in others they are 
 numerous. The branches by which 
 the Sympathetic system communi- 
 cates with the Cerebro-spinal, and 
 which were formerly considered as 
 the roots of the Sympathetic sys- 
 tem, contain fibres of both kinds : 
 i. e., Cerebro-spinal fibres passing 
 into the Sympathetic, and Sym- 
 pathetic fibres passing into the 
 Cerebro - spinal. The latter are 
 chiefly, if not entirely, transmit- 
 ted into the anterior branches of 
 the Spinal nerves; the posterior 
 branches being principally supplied 
 with fine fibres, from the ganglia on 
 
 A view of the Great Sympathetic Nerve. 1, the plexus on the carotid artery in the carotid foramen; 
 2, sixth nerve (motor externus); 3, first branch of the fifth or ophthalmic nerve ; 4, a branch on the sep- 
 tum narium going to the incisive foramen ; 5. the recurrent branch or vidian nerve dividing into the 
 carotid and petrosal branches; 6, posterior palatine branches; 7, the lingual nerve joined by the corda 
 tympani; 8, the portio dura of the seventh pair or the facial nerve; 9, the superior cervical ganglion; 
 10, the middle cervical ganglion ; 11, the inferior cervical ganglion ; 12, the roots of the great splanchnic 
 nerve arising from the dorsal ganglia; 13, the lesser splanchnic nerve; 14, the renal plexus; 15, the solar 
 plexus; 16, the mesenteric plexus ; 17, the lumbar ganglia; 18, the sacral ganglia; 19, the vesical plexus; 
 20, the rectal plexus; 21, the lumbar plexus (cerebro-spinal) ; 22, the rectum; 23, the bladder; 24, the 
 pubis; 25, the crest of the ileum; 26, the kidney; 27, the aorta; 28, the diaphragm; 29, the heart; 30, the 
 larynx ; 31, the sub-maxillary gland ; 32, the incisor teeth ; 33, nasal septum ; 34. globe of the eye ; 35, 
 36, cavity of the cranium.] 
 
268 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 [Fig. 131. their posterior roots. Some of these 
 
 last fibres also pass, with the ordi- 
 nary large nerve-tubes, from the 
 Cerebro-spinal into the Sympathetic 
 system. By these communications 
 the two systems of fibres are so 
 blended with each other, that it is 
 impossible to isolate them; and all 
 that can be said is, that the large 
 tubular fibres predominate in the 
 former, and the fine homogeneous 
 fibres in the latter. 
 
 342. The branches proceeding 
 from the Semilunar ganglia are dis- 
 tributed upon the abdominal viscera; 
 and those of the Cardiac ganglia 
 upon the heart and the vessels pro- 
 ceeding from it. The latter seem 
 to accompany the arterial trunks 
 through their whole course, rami- 
 fying minutely upon their surface; 
 and it can scarcely be doubted, that 
 they exercise an important influ- 
 ence over their functions. What 
 the nature of that influence is, how- 
 ever, will be a subject for future 
 inquiry. It is so evidently con- 
 Roots of a dorsal spinal nerve, and its union with necte d" with the operations of nutri- 
 sympathetic:- C ,c. Anterior fissure of the spinal cord. ^ sec retion, &C., that the de- 
 
 a. Anterior root. p. Posterior root, with its ganglion. r ,. ,, 
 
 '. Anterior branch. '. Posterior branch. ,. Sympa- SlgnatlOn of nervOUS System of 
 thetic. e. Its double junction with the anterior branch Organic life, as applied to this SVS- 
 of the spinal nerve by a white and a grey filament] tem does not Seem objectionable, 
 
 provided that we do not understand 
 
 it as denoting the dependence of these functions upon it. Even in Vertebrata, 
 however, we do not always find the distribution of the visceral trunks distinct 
 from those of the cerebro-spinal. In the Cyclostome Fishes, the par vagum 
 supplies the intestinal canal along its whole length, as well as the heart; and 
 no appearance of a distinct sympathetic can be discovered. In Serpents, 
 again, the lower part of the alimentary canal is supplied from the spinal cord, 
 and the upper part by the par vagum; and though the lateral cords of the 
 sympathetic may be traced, they are almost destitute of ganglia. Even in 
 the highest Vertebrata, some of the glands, of which the secretion is most 
 directly influenced by the condition of the mind, are supplied with most of 
 their nerves from the cerebro-spinal system ; thus, the lachrymal and sublin- 
 gual glands receive large branches from the fifth pair, and the mammary 
 glands from the intercostal nerves. But it appears probable, from what has 
 just been stated, that the influence is conveyed through the visceral fibres, 
 contained in these nerves, and either originating in the ganglia at their roots, 
 or derived from the Sympathetic system. 
 
 343. The Spinal Cord, with its encephalic continuation the Medulla Ob- 
 longata, may be regarded as constituting the essential part of the nervous 
 system of Vertebrata. Although the Cerebral Hemispheres in Man bear so 
 large a proportion to it in size, that the Spinal Cord seems but a mere ap- 
 pendage to them, the case is reversed when we look at the other extremity of 
 the scale; the Cerebral Hemispheres, in many Fishes, being but ganglionic 
 
NERVOUS SYSTEM OF VERTEBRATA. 269 
 
 protuberances from the Medulla Oblongata. Moreover, the fact that animals 
 are capable of living without the brain, whilst they at once die if deprived of 
 the spinal cord, sufficiently demonstrates this. The spinal cord, then, when 
 viewed in relation to the nervous system of the Invertebrata, may be regarded 
 as including their respiratory, stomato-gastric, and pedal ganglia. That these 
 should be associated together, can scarcely be considered remarkable. It is 
 obviously convenient that they should all be inclosed in the bony sheath pro- 
 vided for their protection ; and their closer relation favors that sympathy of 
 action, which is so important in animals of such complex structure and 
 mutually dependent functions, as the higher Vertebrata. An animal either 
 congenitally or experimentally deprived of its cerebral hemispheres, is very 
 much in the condition of one of the Acephalous Mollusca. It can perform 
 those respiratory movements, on which depend the maintenance of its circu- 
 lation, and consequently its whole organic life ; it can swallow food brought 
 within its reach, and it can, in some degree, exert its locomotive powers to 
 obtain it; but it is unconscious of the direction in which these can be best 
 employed, and is dependent upon the supplies of food that come within its 
 grasp. The Acephalous Mollusca are so organized, that they find support 
 from the particles brought in by their respiratory current; but the more 
 highly-organized Vertebrata are not capable of so existing, and they must 
 have their food provided for them by an exertion of the mental powers. So 
 long as an anencephalous Vertebrated animal is duly supplied with its requi- 
 site food, so long may it continue to exist, although in a state analogous to 
 that of profound sleep; and thus it is seen, that the operations of the Brain 
 are not immediately connected with the maintenance of the organic functions ; 
 the movements requisite for these being carried on, as in the lower animals, 
 through the instrumentality of ganglionic centres and nerves specially appro- 
 priated to them. 
 
 344. It is only in the Vertebrata, that the difference between the afferent 
 and efferent fibres of the nerves, has been satisfactorily determined. The 
 merit of this discovery is almost entirely due to Sir C. Bell. He was led to 
 it by a chain of reasoning of a highly philosophical character; and though 
 his first experiments on the Spinal nerves were not satisfactory, he virtually 
 determined the respective functions of their two roots, by experiments and 
 pathological observations upon the cranial nerves, before any other physiolo- 
 gist came into the field.* Subsequently his general views were confirmed 
 by the very decided experiments of Muller ; but, until very recently, some 
 obscurity hung over a portion of the phenomena. It was from the first main- 
 tained by Magendie, and has been subsequently asserted by other physiolo- 
 gists, that the anterior and posterior roots of the nerves were both concerned 
 in the reception of sensations and in the production of motions ; for that, 
 when the anterior roots were touched, the animal gave signs of pain, at the 
 same time that convulsive movements were performed ; and that, on touching 
 the posterior roots, not only the sensibility of the animal seemed to be affected, 
 but muscular motions were excited. These physiologists were not willing, 
 therefore, to admit more, than that the anterior roots were especially motor, 
 and the posterior especially sensory. But the recently attained knowledge of 
 the reflex function of the spinal cord, enables the latter portion of these phe- 
 nomena to be easily explained. The motions excited by irritating the pos- 
 terior root are entirely dependent upon its connection with the spinal cord, 
 and upon the integrity of the anterior roots and of the trunks into which they 
 enter; whilst they are not checked by the separation of the posterior roots 
 from the peripheral portion of the trunk. It is evident, therefore, that excita- 
 
 * See British and Foreign Medical Review. Vol. ix., p. 140, &c. 
 23* 
 
270 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 tion of the posterior root does not act immediately upon the muscles through 
 the trunk of the nerve, which they contribute to form; but that it excites a 
 motor impulse in the Spinal Cord, which is propagated through the anterior 
 roots 'to the periphery of the system. Thp converse phenomenon, the appa- 
 rent sensibility of the anterior roots, has been still more recently explained 
 by the experiments of Dr. Kronenberg;* which seem to prove, that it is de- 
 pendent upon a branch of the posterior root passing into the anterior root at 
 their point of inosculation, and then directing itself towards the cord ( 304). 
 345. On the other hand, the distinctness of the system of nerves concerned 
 in the simply-reflex actions, from those which minister to sensation, emotion, 
 and volition by their connection with the brain, is by no means so obvious as 
 in the Invertebrated classes. When first pointed out by Dr. Marshall Hall, 
 who had grounded his opinion more upon physiological phenomena than 
 upon anatomical facts, the statement did not command general assent; since, 
 while the phenomena were admitted, the inferences which he drew from them 
 were not regarded as necessary results. When, however, the anatomy of 
 the Nervous centres in Vertebrata was more closely inquired into (by Mr. 
 Grainger, who had been partly anticipated by Bellingeri), it was found to 
 present certain phenomena which might be regarded as supporting Dr. M. 
 Hall's views; and when the inquiry was extended to the Invertebrated classes, 
 the confirmation was found to be still more decisive. In our previous sketch 
 these doctrines have been treated as established; since they have been found 
 not only to correspond with the facts disclosed by anatomical research, but to 
 be required by them. We shall now apply them to the nervous apparatus of 
 the Vertebrata. 
 
 346. The Spinal Cord consists of two lateral halves ; 
 Fig. 132. these are partially separated, in the higher classes, by 
 
 the superficial anterior and posterior fissures ; and in 
 Fishes by an internal canal, which is continuous with the 
 fourth ventricle.! This canal is evidently the indication 
 of that complete separation of the two columns, which 
 exists in the lower Articulata; and the fourth ventricle, 
 which in many Fishes remains unclosed (the cerebellum 
 not being sufficiently developed to overlap it), corre- 
 sponds with the passage between the cords uniting the 
 cephalic ganglia, with the first sub-oesophageal, through 
 which the cesophagus passes in all the Invertebrata. 
 The two lateral halves have little connection with each 
 other in Fishes, and the pyramidal bodies at their apex 
 scarcely decussate ; but in ascending towards the higher 
 classes, the communication between the two sides is more 
 intimate, and a larger proportion of the pyramidal fibres, 
 crosses to the opposite side. In all the Vertebrata, the 
 true Spinal Cord contains grey substance, or something 
 equivalent to it ; thus possessing the character of a con- 
 tinuous ganglion. The proportion of the vertebral column 
 Frog; A, oifactive ganglia; which this ganglion ic portion occupies, is, however, ex- 
 B, cerebral hemispheres ; tremely variable ; depending principally on the position 
 c, optic ganglia; D, cere- O f tne c hief organs of locomotion. Thus, in the Eel, 
 beiium, so small as not to and other Vermiform Fishes, it is continued through 
 
 cover the 4th ventricle, or , , , ., , , ., . IT-L- j 
 
 cavity left by the diver- the whole spinal canal ; whilst in the Lophius and 
 gence of the columns of Tetraodon, whose body is less prolonged, and more 
 the Spinal Cord. dependent for its movements upon the anterior extremi- 
 
 * Miiller's Archiv., 1839, Heft v.; and Brit, and For. Med. Rev., vol. ix. p. 547. 
 f This canal may be traced in the Spinal Cord of Man and other Mammalia; but it is 
 nearly obliterated. 
 
 Nervous centres in 
 
SPINAL CORD OF VERTEBRATA. 
 
 271 
 
 ties, the true Spinal Cord scarcely passes out of the cranium. The quan- 
 tity of grey matter is nearly uniform in every part of the cord, where 
 there is no great diversity in the functions of the nerves which originate 
 from each portion. In most Fishes, for example, the body is propelled 
 through the water more by the lateral action of the flattened trunk (whose 
 surface is extended by the dorsal and caudal fins erected upon prolonga- 
 tions of its vertebra), than by the movements of its extremities, which serve 
 principally to guide it. Hence we usually find the amount of grey mat- 
 ter varying but little in different parts of the cord. But in the Flying-fish, 
 and others whose pectoral fins are unusually powerful, a distinct ganglionic 
 enlargement of the cord takes place where the nerves are given off. In Ser- 
 pents, again, the spinal cord is nearly uniform throughout its entire length ; 
 whilst in Amphibia it is so during the Tadpole condition, but presents enlarge- 
 ments corresponding to the anterior and posterior extremities, when these are 
 developed; at the same time becoming much shortened, as the tail is less im- 
 portant to locomotion, or is altogether atrophied. In Birds, the ganglionic 
 enlargements are generally very perceptible ; and bear a close relation in 
 size, with the development of the locomotive organs with which they are 
 connected. Thus, in birds of active flight, and short powerless legs, the an- 
 terior enlargement is the principal ; but in those which are more adapted to 
 run on hand than to wing their way through the air, such as the whole tribe 
 of Struthious birds, the size of the posterior enlargement is very remarkable. 
 Hence we have a right to infer, that the increase in the quantity of grey mat- 
 ter in the cord has some connection with the amount of power to be supplied ; 
 and this exactly corresponds with what has been observed in the Articulated 
 classes, and especially in watching the metamorphosis of Insects. In Birds 
 and Mammalia, however, the whole amount of the grey matter in the spinal 
 cord does not bear so large a proportion to the bulk of the nerves proceeding 
 from it, as in the lower Vertebrata ; and the reason of this seems obvious. 
 The actions of the locomotive 
 
 organs are less and less of a Fig. 133. 
 
 reflex character, and are more 
 directly excited by the will, 
 and consequently by the brain 
 than in the inferior tribes ; and 
 just in proportion, therefore, 
 to the development of the 
 Brain, will it become the cen- 
 tre of all the actions performed 
 by the animal, and the Spinal 
 Cord a mere appendage to it. 
 Still, in all the Mammalia, even 
 in Man, do we find these gan- 
 glionic enlargements of the 
 spinal cord ; and in Man it is 
 the posterior one (or rather the 
 inferior), which contains the 
 largest quantity of grey mat- 
 ter. In the cord of this class, 
 too, the lateral halves are much 
 more intimately united, than in 
 the classes below ; for not only is the central canal for the most part absent, 
 but the two crescent-shaped plates of grey matter are united by a transverse 
 lamella, which connects their centres like a commissure. 
 
 347. The Cord is transversed, not only by the anterior and posterior fis- 
 
 Transverse sections of human Spinal Cord at different 
 points, showing the proportional quantity and arrangement 
 of grey arid white matter at each : 1, opposite llth dorsal ver- 
 tebra; 2, opposite 10th dorsal ; 3, opposite 8th dorsal; 4, op- 
 posite 5th dorsal ; 5, opposite 7th cervical ; 6, opposite 4th 
 cervical; 7, opposite 3d cervical; 8, section of medulla ob- 
 longata through centre of corpus olivare. 
 
272 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 sures, but by two furrows on each side, marking out three columns upon Jt. 
 We have, therefore, on each half of the cord, an anterior middle or lateral 
 and posterior column. The points of the crescentic lamellae of grey matter 
 approach these furrows pretty closely ; but elsewhere the grey matter is 
 covered deeply by the fibrous columns. Each spinal nerve arises from two 
 sets of roots. The anterior roots join the spinal cord, near the anterior fur- 
 row ; and the posterior, near the posterior furrow. Respecting their intimate 
 connection with the principal divisions of the cord, a considerable diversity 
 has existed among the statements of anatomists ; but it seems to be now 
 generally admitted, that, as in the Articulata, a part of each root enters the 
 
 [Fig. 134. 
 
 Fig. 135. 
 
 Transverse section of human spinal cord, close to 
 the third and fourth cervical nerves ; magnified ten 
 diameters, (from Stilling;)-/. Posterior columns, ii. 
 Gelatinous substance of the posterior horn. k. Pos- 
 terior root. I. Supposed anterior roots, a. Anterior 
 fissure, c. Posterior fissure. 6. Grey commissure, in 
 which a canal is contained, which, according to these 
 writers, extends through the length of the cord. g. 
 Anterior horn of grey matter containing caudate vesi- 
 cles, e. Antero-lateral column (from k to a)]. 
 
 Passage of Nerve-fibres through the 
 Spinal Cord, according to Stilling; A, 
 posterior fibres continuous with the 
 anterior of the same side, through the 
 nucleus of the cord ; B, posterior fibres 
 continuous with the anterior of the 
 opposite side. 
 
 grey matter or ganglionic portion of the cord, whilst a part is continuous 
 with its white or fibrous columns. The course of the fibres which enter the 
 grey matter, has been lately displayed, in part, at least, by the researches of 
 Dr. Stilling.* It appears that of the fibres of the posterior roots, some form 
 loops in the grey matter, and become continuous with those of the anterior 
 roots of the same side, as seen at A, fig. 135. Others cross the grey matter, 
 and become continuous with those of the anterior roots of the opposite side, 
 as seen at B. It can scarcely be doubted that these fibres, being unconnected, 
 with the brain, constitute the system to which reflex actions are due. Although 
 Dr. Stilling's inquiries have not proved the fact,t yet it may be inferred from 
 physiological phenomena, as well as from the facts recently shown by Mr. 
 Newport ( 326), that there are other fibres, which pass from the posterior 
 
 * Ueber die Textur und Function der Medulla Oblongata. 
 
 f It may be thought that the mode of examination which he adopted, that of making 
 very thin transverse sections of the Spinal Cord, is not well fitted to display the connections 
 of the roots with longitudinal fibres. The subsequent observations of Budge (Muller's Ar- 
 chiv., 1844, p. 160), seem to have established the fact of the continuity of a portion of each 
 root with the longitudinal fibres of the cord. 
 
SPINAL CORD OF VERTEBRATA. 273 
 
 roots into the anterior roots of other nerves above and below, both on the 
 same side and on the opposite. Of the portions of the roots which are con- 
 tinuous with the fibrous columns, the anterior would seem to have a connec- 
 tion with both the anterior and lateral columns ; and the posterior cannot be 
 said to be restricted to the lateral column, some of their fibres entering the 
 posterior division of the cord. 
 
 348. If the white or fibrous portion of the Spinal Cord be really continu- 
 ous with the medullary matter of the Brain, the roots of the nerves which 
 enter it are in reality thus brought into connection with the Cerebral Hemi- 
 spheres and Cerebellum ; and the posterior division of these may, therefore, 
 be regarded as conducting to the Sensorium those impressions, which there 
 become sensations ; whilst the anterior roots convey the motive influence, 
 which has been propagated, by a voluntary or emotional impulse, down the 
 tract of the Spinal Cord with which they are continuous. On the other hand, 
 the passage of one portion of each set of roots through the grey matter of 
 the Cord, completes the nervous circle required for the performance of reflex 
 actions ; and by this they would seem to take place in Vertebrated animals, 
 just as through the distinct system of excito-motor fibres in the Articulata 
 ( 328.) The fibres which pass continuously from the posterior to the ante- 
 rior roots of the nerves on the same side, probably constitute the channel of 
 those reflex actions, which can be excited in apart supplied by any compound 
 nerve, by stimulating its afferent fibres, and thus causing a motor impulse to 
 be transmitted from the Spinal Cord along its afferent portion. The fibres 
 which cross to the opposite side, will produce similar movements in its cor- 
 responding parts. And the fibres, if such there be, that pass from the pos- 
 terior (afferent) roots of each nerve, into the anterior (motor) roots of distant 
 nerves, would convey to a great variety of muscles, the influence of a stimulus 
 applied to a single afferent nerve. It follows, then, on this view of the cha- 
 racter of the Spinal Cord, that the continuity of the fibrous tracts is all that 
 is required, to convey the influence of the brain to the parts below ; whilst 
 the completeness of the nervous circle is all that is necessary, for the perform- 
 ance of reflex actions excited through it. This is found to be strictly true ; 
 the former having been observed in cases of disease, and the latter having 
 been proved by experiment. As far as simple reflex actions are concerned, 
 there is as much segmental independence in Vertebrata, as in the Articulata ; 
 but these actions seldom have so completely the character of adaptation, and 
 are of a more irregular and convulsive nature. Still, however, there is an 
 essential correspondence between them ; and we may, therefore, regard the 
 distinction between the reflex and voluntary movements as the same in each 
 group ; the former predominating in Articulata ; the latter in Vertebrata. On 
 this view, then, each spinal nerve contains at least four sets of fibres. 
 
 i. A sensory bundle passing upwards to the Brain. 
 
 ii. A motor set, conveying the influence of volition and emotion down- 
 wards/rom the Brain. 
 
 in. A set of excitor or centripetal fibres, terminating in the true Spinal 
 Cord or ganglion, and conveying impressions to it. 
 
 iv. A motor or centifrugal set, arising from the same Ganglionic centre, 
 and conveying the motor impulse reflected/row it to the muscles. 
 
 Of these, the first and third are united in the posterior or afferent roots ; 
 the second and fourth in the anterior or efferent roots. 
 
 349. It is difficult to trace the course of the fibres within the Spinal Cord; 
 but it is now proved, that Sir C. Bell was not altogether correct in his idea, 
 that the functions of the columns of the Cord are respectively similar to those 
 of the roots connected with them. Cases, indeed, are of no unfrequent oc- 
 currence, in which a portion of one of the columns has been almost entirely 
 
274 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 destroyed by injury or disease, without any corresponding loss of the func- 
 tion attributed to it.* Such cases have kept alive, in the minds of many emi- 
 nent practical men, a considerable distrust of the accuracy of Sir C. Bell's 
 conclusions. We have seen that, in regard to the roots of the nerves, his 
 first statements have been confirmed, and rendered more precise, by subse- 
 quent researches ; but it is not so in regard to the functions of the anterior 
 and posterior divisions of the Spinal Cord. Bellingeri was led, by experi- 
 ments on the spinal cord, to the conclusion, that the anterior roots of the 
 nerves were for the flexion of the various articulations, and the posterior for 
 their extension. He also was wrong, in extending an inference, founded on 
 experiments on the Cord, to the roots of the nerves. The recent experiments 
 of Valentin, whilst they fully confirm Sir C. Bell's determination of the func- 
 tions of the roots of the nerves, coincide, to no small degree, with Bellingeri's 
 opinion, in regard to the offices of the anterior and posterior divisions of the 
 Cord. He obtained reason to believe that, in the Frog, neither the superior 
 nor inferior strand of the cord (posterior and anterior columns in Man) solely 
 possesses motor functions ; but he found that, when the former were irritated, 
 sensations predominated ; and when the latter, motions were chiefly excited. 
 He further states that, if the superior strand (posterior column) be irritated 
 at the point at which the nerves of either extremity are given off, that ex- 
 tremity is extended ; and that if the inferior strand (anterior column) be irri- 
 tated, the extremity is flexed. At their entrance into the spinal cord, there- 
 fore, it would appear that the motor fibres of the extensors pass towards the 
 superior stratum (posterior column in Man), whilst those of the flexors are 
 continuous with the inferior stratum (inferior column) ; their course being 
 more altered, however, when they are examined far from the point of issue. 
 This doctrine was confirmed by experiments on Mammalia ; and is borne out 
 (according to Valentin) by pathological phenomena observed in Man. Accord- 
 ing to this eminent physiologist, also, relaxation of the sphincters is analogous 
 to the extended state of the extremities ; and he has noticed a manifest relaxa- 
 tion of the sphincter ani in the frog, when the superior part of the spinal 
 cord was irritated, so as to produce extension of the limbs. These state- 
 ments are entitled to considerable weight, on account of the quarter from 
 which they come ; but they are not, perhaps, to be received altogether with- 
 out hesitation, until confirmed by other physiologists, especially whilst the 
 phenomena of reflex action are still so imperfectly known. For it is quite 
 possible that, whilst stimulation of the anterior part of the cord may excite 
 direct motions of flexion, in preference to those of extension, the movements 
 of extension produced by stimulating the posterior column may be of a reflex 
 character. 
 
 350. There is no reason to believe, that the functions of the Spinal Cord 
 are essentially different along its whole length. Everywhere it appears to 
 consist of a ganglionic centre, supplying nerves to its particular segment ; 
 and of connecting fibres, by which the nerves proceeding from any one divi- 
 sion are brought into relation with distant portions of the organ, and with the 
 large ganglionic masses at its anterior extremity. In this respect, then, it 
 corresponds precisely with the double nervous cord of the Articulata ; the 
 only prominent difference between the two being, that in the former the gan- 
 glionic matter is continuous from one extremity of the organ to the other; 
 whilst in the latter it is interrupted at intervals ; and in the Mollusca, the 
 centres are still further separated from each other. The connection of the 
 
 * See especially a case recorded by Dr. Webster (Medico-Chirurgical Transactions, vol . 
 xxvi.), in which there was complete destruction of the posterior columns in the lower part 
 of the cervical region ; which was not attended with loss of sensibility in the parts below, 
 but, on the contrary, with loss of power of voluntary motion. 
 
SPINAL CORD OF VERTEBRATA. 
 
 275 
 
 Spinal Cord with the large ganglia 
 contained within the cavity of the 
 cranium, is effected by means of 
 processes from its superior extre- 
 mity, the arrangement of which is 
 somewhat complex. This portion 
 of the cord, which also lies within 
 the cavity of the cranium, has been 
 termed the Medulla Oblongata. 
 It has been supposed to be the 
 peculiar seat of vitality ; but the 
 only real foundation of this idea 
 is, that it is the great centre of the 
 Respiratory actions, on the conti- 
 nuance of which all the other 
 functions are dependent. The 
 Brain may be removed from above, 
 and nearly the whole Spinal Cord 
 from below, without an immediate 
 check being put upon all the phe- 
 nomena of life. In this Medulla 
 Oblongata,/owr different parts may 
 be distinguished on each side: 1, 
 The Anterior Pyramids, or Cor- 
 pora Pyramidalia; 2, The Oli- 
 vary Bodies, or Corpora Oliva- 
 ria; 3, The Restiforrn bodies, or 
 Corpora Restiformia ; otherwise 
 called Processus a Cerebello ad 
 Medullam Oblongatam; 4, The 
 
 [Fig. 137. 
 
 [Fig. 136. 
 
 A posterior superior view of the Pons Varolii, the 
 Cerebellum, and the Medulla Oblongata and Spinalis. 
 1,1, the crura cerebrij 2, the pons varolii or tuber- 
 annularis; 3, its middle fossa; 4, an oblique band of 
 medullary matter seen passing from its side ; 5, the 
 external surface of the crus cerebelli in its natural 
 state ; 6, the same portion deprived of outer layer ; 7, 
 the nervous matter which united it to 4; 8, the trige- 
 minus or fifth pair of nerves ; 9, portion of the audi- 
 tory nerve the white neurine is seen passing from 
 the oblique band which comes from the corpus resti- 
 forme to the trigeminus nerve in front, and the auditory 
 nerve behind ; 10, 11, the superior portion of the hemi- 
 spheres of the cerebellum; 12, lobulus amygdaloides ; 
 13, corpus olivare ; 14, corpus pyramidale ; 15, medulla 
 spinalis.] 
 
 [Fig. 138. 
 
 Front view of the medulla oblon- 
 gata : p, p. Pyramidal bodies, de- 
 cussating at d. 0,0. Olivary bodies. 
 r, r. Restiform bodies, a, a. Arci- 
 form fibres, v. Lower fibres of the 
 Pons Varolii.] 
 
 Posterior view of the medulla oblongata :pp. Posterior 
 pyramids, separated by the posterior fissure, rr. Restiform 
 bodies, composed of cc, posterior columns, and dd, lateral 
 part of the antero-lateral columns of the cord. aa. Olivary 
 columns, as seen on the floor of the fourth ventricle, sepa- 
 rated by s, the median fissure, and crossed by some fibres 
 of origin of nn, the seventh pair of nerves.] 
 
276 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Posterior Pyramids, or Corpora Pyramidalia Posteriora. The connections 
 of these with the Brain above, and with the Spinal Cord below, will be now 
 traced.* 
 
 [Fig. 139. 
 
 Transverse section of the medulla oblongata through the lower third of the olivary bodies. (From Stil- 
 ling.) Magnified 4 diameters. 
 
 a. Anterior fissure, b. Fissure of the calamus scriptorius. c. Raphe". d. Anterior columns, e. La- 
 teral columns. /. Posterior columns, g Nucleus of the hypoglossal nerve, containing large vesicles. 
 A. Nucleus of the vagus nerve, i, i. Gelatinous substance. &,&. Roots of the vagus nerve. I. Roots of 
 the hypoglossal, or ninth nerve, m. A thick bundle of white longitudinal fibres connected with the root 
 of the vagus, n. Soft column (Zartstrang, Stilling), o. Wedge-like column (Keelstrang, Stilling), p. 
 Transverse and arciform fibres, q. Nucleus of the olivary bodies, r. The large nucleus of the pyramid, 
 s, s, s. The small nuclei of the pyramid, u. A mass of grey substance near the nucleus of the olives 
 (Oliven-Nebenkern). u. q, r, are traversed by numerous fibres passing in a transverse semicircular direc- 
 tion, v, w. Arciform fibres, x. Grey fibres.] 
 
 351. As our object, however, is rather Physiological than purely Anato- 
 mical, we shall commence with a description of the motor and sensory tracts, 
 which may, according to Sir C. Bell,t be very distinctly separated in the Pons 
 
 * Great diversities will be found in the accounts given of those connections by different 
 Authors ; some of which are attributable to a variation in the use of terms, which must not 
 pass unnoticed. By the majority of Anatomists, the name of Corpora Restiformia is given to 
 the Cerebellar Columns; and its designation, therefore, it seems advisable to retain. Some, 
 however, and amongst them Dr. J. Reid, in his late very excellent description of the Ana- 
 tomy of the Medulla Oblongata (Edinb. Med. & Surg. Journal, Jan. 1841), give the name to 
 the columns that pass up from the posterior division of the spinal cord into the crus cerebri, 
 which are here called (after Sir C. Bell) the posterior pyramids; and apply the terms 
 Posterior Pyramids to the Cerebellar column. The truth is that, as Sir C. Bell has justly 
 observed, all the tracts of fibrous matter connecting the Brain with the Spinal Cord, have a 
 somewhat pyramidal form ; and it might be added that all have something of a restiform or 
 cord-like-aspect. 
 
 f Philosophical Transactions, 1835. 
 
STRUCTURE AND CONNECTIONS OF MEDULLA OBLONGATA. 
 
 277 
 
 Varolii. The Pons has been correctly designated as the great Commissure 
 of the Cerebellum, inclosing the Crura Cerebri; and its transverse fibres not 
 only surround the longitudinal bands which connect the Cerebrum with the 
 Spinal Cord, but pass through them ; so as in some degreee to isolate the 
 
 Fig. 140. 
 
 
 Course of the Motor tract, according to Sir C. Bell. A, A, fibres of the hemispheres, converging to form 
 the anterior portion of the crus cerebri ; B, the same tract where passing the crus cerebri ; c, the right 
 pyramidal body, a little above the point of decussation ; D, the remaining part of the pons Varolii, a por- 
 tion having been dissected off to expose B.l, olfactory nerve, in outline; 2, union of optic nerves; 
 3. motor oculi ; 4, 4, patheticus ; 5, 5, trigeminus ; 6, 6, its muscular division ; 7, 7, its sensory root ; 8, ori- 
 gin of sensory root from the posterior part of the medulla oblongata ; 9, abducens oculi ; 10, auditory 
 nerve ; 11, facial nerve ; 12, eighth pair ; 13, hypoglossal ; 14, spinal nerves ; 15, spinal accessory of right 
 side, separated from par vagum and glosso-pharyngeal. 
 
 two lateral halves from one another, and to form a complete septum between 
 the anterior and posterior portions of each. The Motor tract is brought into 
 view, by simply raising the superficial layer of the Pons, and tracing upwards 
 and downwards the longitudinal fibres which then present themselves. It is 
 24 
 
 
278 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 then found, that these fibres may be traced upwards, chiefly into the Corpora 
 Striata, whence they radiate to the Hemispheres ; and downwards, chiefly into 
 the Anterior Pyramids. From this tract arise all the Motor nerves usually 
 reckoned as Cranial; as will be seen in the accompanying Figure. The 
 Sensory tract is displayed, by opening the Medulla Oblongata on its posterior 
 aspect ; and then separating and turning aside the Restiform Columns, so as 
 to bring into view the Posterior Pyramids, which lie on the outside of the ca- 
 lamus scriptorius. On tracing their fibres upwards, it is found that they form 
 a part of the posterior layer of the Crura Cerebri, ultimately passing on to the 
 Thalami optici, whence they radiate to the Hemispheres. From this tract, 
 no motor nerves arise ; but on tracing it downwards into the Spinal Cord, it 
 is found that the sensory root of the fifth pair terminates in it, and that the 
 
 Fig. 141. 
 
 Course of the Sensory tract according to Sir C. Bell. A. Pons Varolii : B, B, sensory tract separated ; 
 c, union and decussation of posterior columns ; D, D, posterior roots of spinal nerves ; E, sensory roots of 
 fifth pair. 
 
 posterior roots of the spinal nerves are evidently connected with its continua- 
 tion. Also forming part of the posterior division of the crus cerebri, and se- 
 parated from the anterior by the transverse septum, is a layer of fibres which 
 ascends from the Olivary bodies, some of which terminate in the Corpora 
 Quadrigemina. 
 
 352. On tracing upwards the four divisions of the Medulla Oblongata, the 
 following are found to be their chief connections with the Brain. 1. The 
 fibres of the Anterior Pyramids for the most part enter thevCrura Cerebri, 
 passing through the Pons Varolii, and traversing the Optic Thalami (which, 
 it must be carefully borne in mind, have scarcely any real connection with 
 the Optic Nerves, or with the sense of sight) ; after which they diverge and 
 become intermingled with grey matter, thus forming the Corpora Striata, and 
 finally radiate to the convolutions of the Cerebrum. 2. The fibres of the 
 Olivary body also pass into the Pons Varolii, and there divide into two bands ; 
 
STRUCTURE AND CONNECTIONS OF MEDULLA OBLONGATA. 
 
 279 
 
 of which one proceeds upwards and forwards to join the Crus Cerebri, 
 thence to pass to the Optic Thalami ; whilst the other passes upwards and 
 backwards into the Corpora Quadrigemina. 3. Of the true Restiform bodies, 
 the fibres pass entirely into the Cerebellum. 4. Finally, of the Posterior 
 Pyramids, the fibres pass directly onwards through the Crura Cerebri into 
 the Thalami, whence they radiate to the convolutions. 
 
 353. The downward course of these fibres into the Spinal Cord now re- 
 mains to be traced; and their arrangement is by no means a simple one. 1. 
 The Anterior Pyramids decussate, as is well known, at their lower extremity ; 
 
 [Fig. 142. 
 
 
 Analytical diagram of the encephalon in a vertical section. (After Mayo.) 
 
 s. Spinal cord. r. Restiform bodies passing to, c the cerebellum, d. Corpus dentatum of the cerebel- 
 lum, o. Olivary body. f. Columns continuous with the olivary bodies and central part of the medulla 
 oblongata, and ascending to the tubercular quadrigemina and optic thalami. p. Anterior pyramids, v. 
 Pons Varolii. n, b. Tubercular quadrigemina. g. Geniculate body of the optic thalamus. t. Pro- 
 cessus cerebelli ad testes. a. Anterior lobe of the brain, q. Posterior lobe of the brain.] 
 
 the principal part (but not the whole) of the fibres on each side, passing over 
 to the other. The decussating fibres pass backwards as well as downwards, 
 and enter, not the anterior column of the spinal cord, (as commonly stated,) 
 but the lateral column. The smaller bundle of fibres, which do not decus- 
 sate, passes downwards, along with those of the olivary bodies, to form the 
 anterior column. 2. The fibres descending from the Olivary bodies converge 
 
280 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 as those of the pyramids pass backwards from between them, until they meet 
 on the median line, forming the greater part of the anterior column. 3. The 
 fibres of the Restiform, or Cerebellar columns, which, like those of the 
 Olivary columns, do not decussate, mostly pass downwards into the posterior 
 columns ; but a band (which has been termed, from its curved aspect, the 
 arciform layer) passes forwards into the anterior columns : and another 
 small fasciculus enters the lateral columns. 4. The fibres of the Posterior 
 Pyramids are stated by Sir C. Bell to decussate like those of the anterior; 
 they pass down chiefly into the posterior part of the lateral column, forming 
 part also of the posterior. 
 
 354. The following tabular view may assist, better than any delineations 
 could do, in the comprehension of this very intricate piece of Anatomy ; the 
 knowledge of which can be readily applied to the explanation of many curious 
 pathological phenomena, and cannot but assist in the elucidation of others, 
 whose rationale is as yet obscure. 
 
 SPIRAL CORD. MEDULLA OBLONGATA. BRAIX. 
 
 ( Arciform fibres of Cerebellar Columns . . ) Cerebellum 
 Anterior Column < Olivary Columns ...... $ Corpora Quadrigemina 
 
 Non-decussating portion of Ant. Pyramids . ) r <> 
 
 ' 
 
 355. The Medulla Oblongata is not to be viewed, however, solely as a series 
 of connecting bands or commissures, between the Brain and Spinal Cord; for 
 it contains vesicular matter of its own, in virtue of which it serves as a gan- 
 glionic centre to nerves that are specially connected with it. The vesicular 
 matter is partly found in a situation corresponding to that which it occupies 
 in the spinal cord ; and it forms a tract, which is continuous above with the 
 grey nucleus of the Corpora Quadrigemina, and below with that of the Spinal 
 Cord ; and which is opened out to view (as it were) on the floor of the fourth 
 ventricle, forming the calamus scriptorius. Besides this central portion, 
 there are other outlying masses, which are continuous with it. Thus the 
 bulk of the Olivary body is principally due to the presence of a ganglionic 
 mass in its interior ; inclosed in the fibres of which the olivary column is 
 composed, and which, for the most part, pass over and around it without en- 
 tering it. This mass consists of a layer of grey matter, spread in a thin pli- 
 cated stratum over a centre of white substance, and altogether forming what 
 is known as t^je corpus dentatum. There is a considerable amount of ve- 
 sicular substance in the Restiform bodies also ; and this is continuous with 
 the grey matter forming the posterior cornua in the Spinal Cord. 
 
 356. We have now to inquire into the character of the ganglionic masses, 
 which form, with the Medulla Oblongata, the Encephalon of Vertebrated ani- 
 mals. We should be liable to form a very erroneous conception of the rela- 
 tive importance, and of the real nature, of these, if we were to study them 
 only in the Brain of Man and of the higher animals ; for the great develop- 
 ment of their Cerebrum and Cerebellum throws into the shade (so to speak) 
 certain other ganglionic centres, which constitute yet more essential parts of 
 the nervous apparatus. It is one of the most interesting results of the com- 
 parison of the Human Brain with that of the lower tribes of Vertebrata, that 
 the great change in the relative proportions of the parts, which we encounter 
 in the latter, makes evident the real nature and importance of what would 
 otherwise have been considered as subordinate appendages : whilst, at the 
 same time, they afford us the connecting links, by which we are enabled 
 to trace the real analogies of the different parts of the Encephalon with the 
 ganglionic masses which represent it among Invertebrated animals. 
 
ENCEPHALON OF FISHES. 
 
 281 
 
 357. Commencing with FISHES, we find a series of four distinct ganglionic 
 masses, arranged in a line which is nearly continuous, from behind forwards, 
 with that of the Spinal Cord ; of these, the posterior is usually single, and 
 on the median plane, whilst the others are in pairs. The posterior, from its 
 position and connections, is evidently to be regarded in the light of a Cere- 
 bellum ; and it bears a much larger proportion to the rest, in this class, than 
 in any other. The pair in front of this are not the hemispheres of the Ce- 
 rebrum, as their large size in some instances (the Cod for instance) might 
 lead us to suppose ; but they are immediately connected with the Optic nerve, 
 which, in fact, terminates in them, and are therefore to be considered (like the 
 chief part of the cephalic masses of Invertebrated animals) as' Optic Ganglia. 
 In front of these are the Cerebral Hemispheres, which are small, generally 
 destitute of convolutions, and possess no ventricle in their interior, except 
 in the Sharks and Rays, in which they are much more highly developed than 
 in the Osseous Fishes. Anterior to these is another pair of ganglionic en- 
 largements, from which the Olfactory nerves arise ; and these are, therefore, 
 correctly designated as the Olfactive tubercles or ganglia. In some instances, 
 these ganglia are not immediately seated upon the prolonged spinal cord, but 
 are connected with it by long peduncles ; this is the case in the Sharks ; and 
 we are thus led to perceive the real nature of the portion of the trunk of the 
 Olfactory nerve in Man, which lies within the cranium, and of its bulbous 
 expansion on the Ethmoid bone. Besides these principal ganglionic enlarge- 
 ments, there are often smaller ones, with which other nerves are connected. 
 Thus, in the Shark, we find a pair of tubercles of considerable size, at the 
 origin of the Trifacial nerves ; and another pair, in most Fishes, at the roots 
 of the Vagi. In some instances, too, distinct Auditory ganglia present them- 
 selves ; as in the Carp. 
 
 Pike. 
 
 Cod. 
 
 Fig. 143. 
 
 Fox- shark. 
 
 Brains of Fishes. A. olfactive lobes or ganglia; B, cerebral hemispheres ; c, optic lobes ; D, cerebel- 
 lum ; ol, olfactory nerve ; op, optic nerve ; pa, pathelicus ; no, motor oculi ; a&, abducens ; tri, trifacial ; 
 /a, facial ; vag, vagus ; , tubercles or ganglia of the trifacial ; w, tubercles of the vagus. 
 
 358. The Optic Lobes of Fishes have no analogy whatever with the Tha- 
 lami optici of Mammalia ; the connection of which, with the Optic nerves, is 
 
 24* 
 
282 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 very slight. They are rather to be compared with the Tubercula Quadri- 
 gemina, which are the real ganglia of the Optic nerve. Their analogy is not 
 so complete, however, to these bodies in the fully formed Brain of Man, as 
 it is to certain parts which occupy their place at an earlier period. The Third 
 Ventricle, which is quite distinct from the Corpora Quadrigemina, is hollowed 
 out, as it were, from the floor of the Optic Lobes of Fishes ; and the Anterior 
 Commissure bounds its front; hence these must be considered as analogous 
 to the parts surrounding the Third Ventricle, as well as to the Corpora Quad- 
 rigemina. This is made evident by the fact, observed by Miiller, that, in the 
 Lamprey, there is a distinct Lobe of the third ventricle, replacing the Optic 
 Lobes of other Fishes, and partly giving origin to the optic nerves ; and a 
 separate vesicle, analogous to the Corpora Quadrigemina. With this condition, 
 the early state of the Brain in the embryo of the Bird and Mammiferous ani- 
 mal, and even in Man himself, bears a very close correspondence. The En- 
 cephalon consists at this time of a series of vesicles, arranged in a line with 
 
 each other, of which those that represent 
 
 Fig. 144. the Cerebrum are the smallest, whilst that 
 
 which represents the Cerebellum is the 
 largest. The latter, as in Fishes, is single, 
 covering the fourth ventricle on the dorsal 
 surface of the Medulla Oblongata. Ante- 
 rior to this, is the single vesicle of the 
 Corpora Quadrigemina, from which the 
 Optic nerve chiefly arises; this has in its 
 interior a cavity, the ventricle of Sylvius, 
 which exists even in the adult Bird, where 
 the Corpora Quadrigemina are pushed, as 
 it were, from each other by the increased 
 development of the Cerebral hemispheres. 
 In front of this is the vesicle of the Third 
 Ventricle, which contains also the Thala- 
 T' Development proceeds this like 
 6, vesicle of cerebral hemi- the preceding, is covered by the enlarged 
 
 spheres; c, vesicle of thalami optici and hemispheres ; whilst its roof becomes 
 
 third ventricle ; rf, vesicle for cerebellum cleft anteriorly on the median line, so as 
 
 and medulla oblongata; e, auditory vesicle ; ^ form tfae ante rior entrance to the Cavity. 
 f, olfactory fossa ; h, liver; ** caudal extre- ^ .,, , . ., j , i 
 
 mity Still more anteriorly is the double vesicle, 
 
 which represents the hemispheres of the 
 
 Cerebrum ; this has a cavity on each side, the floor of which is formed by the 
 corpora striata. The cavity of the cerebral vesicles has at first no opening, 
 except into that of the third ventricle; at a later period is formed that fissure 
 on the inferior and posterior side, which (under the name of the fissure of 
 Sylvius)enables the membranes enveloping the brain to be reflected into the 
 lateral ventricles. 
 
 359. Thus it will be seen that the real analogy between the brain of the 
 Human foetus, and that of the adult Fish, is not so close as, from the resem- 
 blance in their external form, might have been supposed. In the small pro- 
 portion which the Cerebral Hemispheres bear to the other parts, there is evi- 
 dently a very close correspondence ; and this extends also to the general 
 simplicity of their structure, the absence of convolutions, and the deficiency of 
 commissures. But there is a much nearer analogy between the foetal brain 
 of the Fish, and ihefostal brain of the Mammal ; indeed, at the earliest period 
 of their formation, they could not be distinguished ; during their advance to the 
 permanent condition, however, each undergoes changes, which are so much more 
 decided in the higher animals than in the lower, that in the latter there seems 
 but little departure from the foetal condition, whilst in the former the condition 
 
ENCEPHALON OF REPTILES AND BIRDS. 283 
 
 appears entirely changed. Hence it is not correct to assert, as is frequently 
 done, that the Brain, or any other organ, in the higher animals, passes 
 through a series of forms, which are parallel to the permanent forms of the 
 same organ in different parts of the animal scale ; since the fact is rather, that 
 the more nearly all are traced back to their first origin, the closer will their 
 conformity be found to be ; the subsequent development of each taking place 
 not only in various degrees, but in different modes or directions ; so that the 
 resemblances presented by the higher, at different epochs of their evolution, 
 to the permanent conditions of the lower, are often far from being complete.* 
 This we have seen to be the case in the present instance ; the vesicle of the 
 Corpora Quadrigemina, and that of the third Ventricle, uniting to form the 
 Optic Lobes of Fishes, whilst in the higher Vertebrata they remain distinct ; 
 so that there is no single part, with which the Optic Lobes can be properly 
 compared, either in the foetal or perfect state of the Human Brain. 
 
 360. The Brain of REPTILES does not show any considerable advance in 
 its general structure above that of Fishes ; but the Cerebral Hemispheres are 
 usually much larger in proportion to the Optic lobes ; whilst the Cerebellum 
 is smaller. The very low development of the Cerebellum is especially seen 
 in the Frog (Fig. 132), in which it is so small as not even to cover-in the 
 Fourth Ventricle; but it is common to nearly the whole group. The defi- 
 ciency in commissures still exists to a great extent. The anterior Commissure 
 in front of the third ventricle, is the only uniting band which can be distinctly 
 traced in Fishes ; and Reptiles have, in addition to this, a layer of uniting 
 fibres which may be compared to the Fornix ; but as yet, there is no vestige 
 of a true Corpus Callosum, or great transverse commissure of the hemi- 
 spheres. The distinction between the tubercula quadrigemina, and the parts 
 inclosing the third ventricle, is more obvious than in Fishes ; in fact the Optic 
 ganglia of Reptiles correspond pretty closely with the Vesicle of the tubercula 
 quadrigemina in the brain of the fetal Mammal. 
 
 Fig. 145. Fig. 146. 
 
 Brain of Turtle; A, olfactive Brain of Buzzard; the olfactive ganglia 
 
 ganglia; B, cerebral hemi- are concealed beneath B, the hemispheres; 
 
 spheres; c, optic ganglia; D, c, optic ganglia; D, cerebellum ; g, pineal 
 
 cerebellum. gland 
 
 * For a fuller examination of this interesting question, see General and Comparative Phy- 
 siology, 244. 
 
284 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 361. This is still more evident in BIRDS, in whose Encephalon the Tuber- 
 cula Quadrigemina or Optic Ganglia, and the Thalami with their included 
 ventricle, are obviously very distinct parts. The Cerebral Hemispheres 
 attain a great increase of development, and arch backwards, so as partly to 
 cover the Optic ganglia ; and these are separated from one another, and thrown 
 to either side. The Cerebellum also is much increased in size, proportion- 
 ably to the Medulla Oblongata and its ganglia ; and it is sometimes marked 
 with transverse lines, which indicate the intermixture of grey and white mat- 
 ter in its substance ; there is as yet, however, no appearance of a division 
 into hemispheres. On drawing apart the hemispheres of the Cerebrum, the 
 Corpora Striata, Optic Thalami, and Tubercula Quadrigemina or Optic Gan- 
 glia, are seen beneath them ; the size of the last still bears a considerable pro- 
 portion to that of the whole Encephalon. The Optic Ganglia are still hollow, 
 as they are in the embryo condition of Man. Indeed the Brain of the Human 
 foetus about the twelfth week will bear comparison, in many respects, with 
 that of the Bird. The Cerebral hemispheres, much increased in size, and 
 arching back over the Thalami and Optic ganglia, but destitute of convolutions, 
 and imperfectly connected by commissures, the large cavity still existing in 
 
 Fig. 147. 
 
 Fig. 148. 
 
 Brain of Human Embryo at twelfth week. A, seen from behind ; B, side view ; c, sectional view ; a, 
 corpora quadrigemina; bb, hemispheres; d, cerebellum; -e, medulla oblongata ; ./, optic thalamus; g, 
 floor of third ventricle; i, olfactory nerve., 
 
 the Optic ganglia, and freely communicating with the third ventricle, and 
 the imperfect evolution of the Cerebellum, make the correspondence in the 
 general condition of the two very considerable. 
 
 362. The Brain of the lowest MAMMALIA presents but a slight advance 
 
 upon that of Birds, in regard both to the rela- 
 tive proportions of its parts, and to their degree 
 of development. Thus, in the Marsupialia, the 
 Cerebral hemispheres exhibit no convolutions ; 
 and the great transverse commissure, the 
 Corpus Callosum, is deficient. There is gra- 
 dually to be noticed, however, in ascending the 
 scale, a backward prolongation of the Cerebral 
 hemispheres ; so that first the Optic ganglia, 
 and then the Cerebellum, are covered by them. 
 The latter partly shows itself, however, in all 
 but the Quadrumana, when we look at the 
 brain from above downwards; in the Rabbit, 
 which is in this respect among the lowest of 
 the true Viviparous Mammalia, nearly the 
 whole of the Cerebellum is uncovered. In 
 proportion to the increase of the Cerebral 
 hemispheres, there is a diminution in the size 
 of the ganglia immediately connected with the 
 organs of sense ; and this in comparison, not 
 only with the rest of the Encephalon, but even 
 
 Brain of Squirrel, laid open ; the 
 hemispheres, B, being drawn to either 
 side to show the subjacent parts; c, 
 the optic lobes ; D, cerebellum ; thai, 
 thalamus opticus ; cs, corpus striatum. 
 
ENCEPHALON OF MAMMALIA. 
 
 285 
 
 with the Spinal Cord ; so that in Man the Tubercula Quadrigemina are abso- 
 lutely smaller than they are in many animals of far inferior size. The inter- 
 Fig. 149. 
 
 Upper and under surface of Brain of Rabbit, A, B, D, as before ; oJ, olfactive lobes; op, optic nerve ; 
 mo, motor oculi ; cm, corpora mamillaria; cc, crus cerebri ; pv, pons varolii ; pa, patheticus; tri, trifa- 
 cial ; ab, abducens ; fac, facial ; au, auditory ; vag, vagus ; s, spinal accessory ; hyp, hypoglossal. 
 
 nal structure of the hemispheres becomes more complex, in the same propor- 
 tion as their size and the depth of the convolutions increase; and in Man all 
 these conditions present themselves in a far higher degree, than in any other 
 animal. In fact it is only among the Ruminantia, Pachydermata, Carnivora, 
 and Quadrumana, that regular convolutions can be said to exist. The cor- 
 respondence between the bulbous expansion of the Olfactive Nerves in Mam- 
 malia, and the Olfactive lobes of the lower Vertebrata, is made evident by the 
 presence, in both instances, of a cavity which communicates with the lateral 
 ventricle on each side ; it is in Man only that this cavity is wanting. The 
 external form of the Corpora Quadrigemina of Mammalia, differs from that of 
 the Optic ganglia of Birds, owing to the division of the former into anterior 
 and posterior eminences, (the nates and testes ;) and there is also an internal 
 difference, occasioned by the contraction of the cavity or ventricle, which now 
 only remains as the Aqueduct of Sylvius. The Cerebellum is chiefly re- 
 markable for the development of its lateral parts or hemispheres ; the central 
 portion, sometimes called the vermiform process, is relatively less developed 
 than in the lower Vertebrata, in which it forms the whole of the organ. 
 
 4. General Functions of the Spinal Cord. Reflex Action. 
 
 363. The functions of the Nervous System in Vertebrated Animals are so 
 complex in their nature, and our means of analyzing them are so imperfect, 
 that the inquiry is confessedly one of the greatest difficulty, and needs all the 
 light which can be thrown upon it from any source. The great accession to 
 our knowledge of them, which has been made within the last few years, 
 chiefly by the labours of Sir C. Bell, and Dr. M. Hall, has so far changed 
 the aspect of this department of Physiological Science, as to render it neces- 
 sary for those who had previously studied it, to begin de novo. This is espe- 
 cially the case in regard to the actions dependent on the Spinal Cord ; which 
 it seems desirable to consider in the first instance, in order that it may be 
 
286 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 clearly defined what the Brain does not do. By many, even in recent times, 
 the Spinal Cord has been considered as a mere appendage to the Brain ; but 
 the phenomena of its independent action render such an idea quite inadmis- 
 sible. These phenomena have been especially pointed out by Dr. M. Hall ; 
 and it is mainly owing to his arguments, that Physiologists are now for the 
 most part agreed in the general fact, that the Spinal Cord constitutes a dis- 
 tinct centre, or rather a collection of centres, of nervous influence, and that 
 its operations are carried on through the nervous trunks with which it is con- 
 nected. It is further generally admitted that its functions are independent of 
 the will; and that they are in effect frequently opposed to those of the Brain, 
 which operates on the muscles, either by a volitional, or by an emotional 
 impulse. And lastly, its actions are always (except when excited by a physi- 
 cal irritation directly applied to itself) entirely of a reflex character; that is 
 to say, the motor impulses which originate in it are not spontaneous, but re- 
 sult from the stimulus of impressions, conveyed to it by the afferent trunks, and 
 operating upon it, to use the expression of Prochaska, according to certain 
 "peculiar laws written, as it were, by nature on its medullary pulp." It is 
 not, however, universally admitted that these actions are independent of sen- 
 sation; and some eminent physiologists, among whom may be named Dr. 
 Alison, still hold that the intervention of sensation is necessary in the case 
 at least, of the ordinary associated movements, which "have definite ends in 
 view, and follow one another in regular succession, as those of Respiration, 
 for an impression to give rise to that organic change in the Spinal Cord, which 
 shall terminate in a muscular motion.* It will be desirable, therefore, to con- 
 sider the evidence upon which the statement rests, that reflex actions are in- 
 dependent of sensation, though ordinarily accompanied by it. 
 
 364. In the first place, then, it has long been well known that, in the 
 Human being, the Spinal Cord does not by itself possess, in the remotest 
 degree, the power of communicating sensory impressions to the mind; since, 
 when its lower portion has been severed from the brain by injury or disease, 
 there is complete anaesthesia of all the parts of the body, which derive their 
 nerves exclusively from it. Hence it might be inferred, that throughout the 
 Vertebrated classes, the spinal cord is equally destitute of sensibility ; and 
 that any movements produced by stimuli acting through it, are the results of a 
 physical, and not of a sensorial change. This inference, however, has been 
 disputed ; and, if unsupported by other evidence, it would not, perhaps, be 
 entitled to rank as an ascertained truth. The very performance, by decapi- 
 tated animals of inferior tribes, of actions which had not been witnessed in 
 Man under similar circumstances, has been held to indicate, that the spinal 
 cord in them has an endowment which his does not possess. The possibility 
 of such an explanation however unconformable to that analogy throughout 
 organized nature, which the more it is studied, the more invariably is found 
 to guide to truth could not be disproved. Whatever experiments on decapi- 
 tated animals were appealed to, in support of the doctrine that the brain is 
 the only seat of sensibility, could be met by a simple denial that the spinal 
 cord is everywhere as destitute of that endowment, as it appears to be in Man. 
 The cases of profound sleep and apoplexy might be cited, as examples of 
 reflex action without consciousness ; and these might be met by the assertion, 
 that in such conditions sensations are felt, though they are not remembered. 
 It is difficult, however, to apply such an explanation to the case of anence- 
 
 * See Outlines of Physiology, 3d edit, 211. By many of the German Physiologists, also, 
 it is maintained that Sensation is a necessary link in the chain of reflex actions ; but as they 
 employ the term sensation in a sense which does not involve consciousness, it is obvious that 
 their dissent from Dr. Hall's views is chiefly verbal. 
 
FUNCTIONS OF THE SPINAL CORD. REFLEX ACTION. 287 
 
 phalous human infants (in which all the ordinary reflex actions have been ex- 
 hibited, with an entire absence of brain), without supposing that the Medulla 
 Oblongata is the seat of a sensibility which we know that the lower part of 
 the Spinal Cord does not possess ; and of this there is no evidence whatever. 
 
 365. Experiments on the lower animals, then, and observation of the phe- 
 nomena manifested by apoplectic patients and anencephalous infants, might 
 lead to the conclusion, that the Spinal Cord does not possess a sensibility, 
 and that its reflex actions are independent of sensation. At this conclusion, 
 Prochaska, Sir G. Blane, Flourens, and other physiologists, had arrive* ; but 
 it was not until special attention was directed to the subject by Dr. M. Hall, 
 that facts were obtained by which a positive statement of it could be supported. 
 For the question might have been continually asked, If the spinal cord in 
 Man is precisely analogous in function to that of the lower Vertebrata, why 
 are not its reflex phenomena manifested, when a portion of it is severed from 
 the rest by disease or injury ? The answer to this question is twofold. In 
 the first place, simple division of the cord with a sharp instrument leaves the 
 separated portion in a state of much more complete integrity, and therefore 
 in a state much more fit for the performance of its peculiar functions, than it 
 ordinarily is after disease or violent injury ; and as the former method of di- 
 vision is one with which the Physiologist is not likely to meet in Man as a 
 result of accident, and which he cannot experimentally put in practice, the 
 cases in which reflex actions are manifested, are likely to be comparatively few. 
 But, secondly, a number of such instances have now been accumulated, sufficient 
 to prove that the occurrence is by no means so rare as might have been sup- 
 posed; and that nothing is required but patient observation, to throw great 
 light on this interesting question, from the phenomena of disease. A most 
 valuable collection of such cases, occurring within his own experience, has 
 been published by Dr. W. Budd ;* and the leading facts observed by him will 
 be now enumerated. 
 
 366. In the first case, paraplegia was the result of angular distortion of the 
 spine in the dorsal region. The sensibility of the lower extremities was ex- 
 tremely feeble, and the power of voluntary motion was almost entirely lost. 
 " When, however, any part of skin is pinched or pricked, the limb that is 
 thus acted on jumps with great vivacity; the toes are retracted towards the 
 instep, the foot is raised on the heel, and the knee so flexed as to raise it off 
 the bed ; the limb is maintained in this state of tension for several seconds 
 after the withdrawal of the stimulus, and then becomes suddenly relaxed." 
 " In general, while one leg was convulsed, its fellow remained quiet, unless 
 stimulus was applied to both at once." " In these instances, the pricking and 
 pinching were perceived by the patient ; but much more violent contractions 
 are excited by a stimulus, of whose presence he is unconscious. "When a 
 feather is passed lightly over the skin, in the hollow of the instep, as if to 
 tickle, convulsions occur in the corresponding limb, much more vigorous than 
 those induced by pinching or pricking; they succeed one another in a rapid 
 series of jerks, which are repeated as long as the stimulus is maintained." 
 "When any part of the limb is irritated in the same way, the convulsions 
 which ensue are very feeble, and much less powerful than those induced by 
 pricking or pinching." " Convulsions, identical with those already described, 
 are at all times excited by the acts of defecation and micturition. At these 
 times, the convulsions are much more vigorous than under any other circum- 
 stances, insomuch that the patient has been obliged to resort to mechanical 
 means to secure his person while engaged in these acts. During the act of 
 expulsion, the convulsions succeed one another rapidly, the urine is discharged 
 
 * Medico-Chirurgical Transactions, vol. xxii. 
 
288 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 in interrupted jets, and the passage of the faeces suffers a like interruption." 
 The convulsions are more vigorous, the greater the accumulation of urine ; 
 and involuntary contractions occur whenever the bladder is distended, and 
 also when the desire to relieve the rectum is manifested. "In all these cir- 
 cumstances, the convulsions are perfectly involuntary ; and he is unable, by 
 any effort of the will, to control or moderate them." The patient subse- 
 quently regained, in a gradual manner, both the sensibility of the lower ex- 
 tremiges, and voluntary power over them ; and as voluntary power increased, 
 the susceptibility to involuntary movements, and the extent and power of these, 
 diminished. 
 
 367. This case, then, exhibits an increased tendency to perform reflex actions, 
 when the control of the brain was removed ; and it also shows that a slight 
 impression upon the surface, of which the patient was not conscious, was 
 more efficacious in exciting reflex movements, than were others that more 
 powerfully affected the sensory organs. This is constantly observed in ex- 
 periments upon the lower animals ; and it harmonizes, also, with the important 
 fact, that, when the trunk of an afferent nerve is pinched, pricked, or other- 
 wise irritated, the reflex function will not be nearly so strongly excited, as 
 when a gentler impression is made on a surface supplied by the branches of 
 this nerve. The former produces pain, whilst the latter does not; the amount 
 of sensation, therefore, does not at all correspond with the intensity of reflex 
 action, but rather bears a converse relation to it. Mr. Grainger found, that 
 he could remove the entire hind leg of a Salamander with the scissors, with- 
 out the creature moving, or giving any expression of suffering, if the spinal 
 cord had been divided : yet that, by irritation of the foot, especially by heat, 
 in an animal similarly circumstanced, violent convulsive actions in the leg and 
 tail were excited. It should be added that, in the foregoing case, the nutrition 
 of the lower extremities was not impaired, as in most cases of paraplegia. 
 The rationale of this phenomenon, which is to be constantly observed when 
 the reflex actions of the part remain entire, will be hereafter noticed (Chap. 
 VIL). 
 
 368. In another case, the paralysis was more extensive, having been pro- 
 duced by an injury (resulting from a fall into the hold of a vessel) at the lower 
 part of the neck. There was at first total loss of voluntary power over the 
 lower extremities, trunk, and hands ; slight remaining voluntary power in the 
 wrists, rather more in the elbows, and still more in the shoulders. The 
 intercostal muscles did not participate in the movements of respiration. The 
 sensibility of the hands and feet was greatly impaired. There were retention 
 of urine, and involuntary evacuation of the faeces. Recovery took place very 
 gradually ; and during its progress, several remarkable phenomena of reflex 
 action were observed. At first, tickling one sole excited to movement that 
 limb only which was acted upon ; afterwards, tickling either sole excited both 
 legs, and, on the 26th day, not only the lower extremities, but the trunk and 
 other extremities also. Irritating the soles, by tickling or otherwise, was at 
 first the only method, and always the most efficient one, by which convulsions 
 could be excited. From the 26th to the 69th day, involuntary movements in 
 all the palsied parts continued powerful and extensive, and were excited by 
 the following causes: In the lower extremities only, by the passage of flatus 
 from the bowels, or by the contact of a cold urinal with the penis ; convulsions 
 in the upper extremities and trunk, attended with sighing, by plucking the 
 hair of the pubes. On the 41st day, a hot plate of metal was applied to the 
 soles, and found a more powerful excitor of movement than any before tried. 
 The movements continued as long as the hot plate was kept applied ; but the 
 same plate, at the common temperature, excited no movements after the first 
 contact. The contact was distinctly felt by the patient ; but no sensation of 
 
FUNCTIONS OF THE SPINAL CORD. REFLEX ACTION. 289 
 
 heat was perceived by him, although the plate was applied hot enough to 
 cause vesication. At three different intervals, the patient took one-eighth of 
 a grain of strychnia three times a day. Great increase of susceptibility to 
 involuntary movements immediately followed, and they were excited by the 
 slightest causes. No convulsions of the upper extremities could ever be pro- 
 duced, however, by irritating their integument; though, under the influence of 
 strychnia, pulling the hair of the head, or tickling the chin, would occasion 
 violent spasmodic actions in them. Spontaneous convulsions of the palsied 
 parts, which occurred at other times, were more frequent and more powerful 
 after the use of strychnia. On the first return of voluntary power, the 
 patient was enabled to restrain in some measure the excited movements ; but 
 this required a distinct effort of the will ; and the first attempts to walk were 
 curiously affected, by the persistence of the susceptibility to excited involun- 
 tary movements. When he first attempted to stand, the knees immediately 
 became forcibly bent under him ; this action of the legs being excited by 
 contact of the soles with the ground. On the 95th day this effect did not 
 take place, until the patient had fciade a few steps ; the legs then had a 
 tendency to bend up, a movement which he counteracted by rubbing the 
 surface of the belly : this rubbing excited the extensors to action, and the legs 
 became extended with a jerk. A few more steps were then made ; the 
 manoeuvre repeated, and so on. This susceptibility to involuntary movements 
 from impressions on the soles, gradually diminished ; and on the 141st day, 
 the patient was able to walk about, supporting himself on the back of a chair 
 which he pushed before him ; but his gait was unsteady, and much resembled 
 that of chorea. Sensation improved very slowly : it was on the 53d day 
 that he first slightly perceived the heat of the metal plate. 
 
 369. This important case suggests many interesting reflections. Common 
 sensation was not so completely abolished as in the former instance; but of 
 the peculiar kind of impression, which was found most efficacious in exciting 
 reflex movements, no consciousness whatever was experienced. Not less 
 interesting was the circumstance, that convulsions could be readily excited by 
 impressions on surfaces above the seat of injury; as, by pulling the hair of 
 the scalp, a sudden noise, and so on. This proves two important points : 
 first, that a lesion of the cord may be such, as to intercept the transmission of 
 voluntary influence, and yet may allow the transmission of that reflected from 
 incident nerves. Secondly, that all influences from impressions on incident 
 nerves are diffused through the cord; for, in the instance adduced, the reflected 
 influence was undoubtedly not made to deviate into the cord by the morbid 
 condition of that organ, but followed its natural course of diffusion, being 
 rendered manifest in this case by the convulsions which were excited, in con- 
 sequence of increased activity of the motor function of the cord. It is further 
 interesting to remark, that, in the foregoing case, the reflex actions were very 
 feeble during the first seven days, in comparison with their subsequent energy; 
 being limited to slight movements of the feet, which could not always be 
 excited by tickling the soles. In another case of very similar character, it was 
 three days after the accident, before any reflex actions could be produced. It 
 is evident, then, that the spinal cord must have been in a state of concussion, 
 which prevented the manifestation of its peculiar functions, so long as this 
 effect lasted; and it is easy, therefore, to perceive, that a still more severe 
 shock might permanently destroy its power, so as to prevent the exhibition of 
 any of the phenomena of reflex action. 
 
 370. It seems well established, then, by such cases, that the Spinal Cord, 
 or small segments of it, may serve in Man as the centre of very energetic 
 reflex actions ; when the voluntary power exercised through the Brain, over 
 the muscular system, is suspended or destroyed. And it is further evident, 
 
 25 
 
290 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 that these movements are produced by a mere physical change in the nervous 
 centres ; the consciousness of the individual not being affected in their per- 
 formance, and sensation having therefore no necessary participation in them. 
 As the movements witnessed in the lower animals, under the same circum- 
 stances, are altogether of a similar character, there seems no good reason to 
 attribute to their Spinal Cord an attribute, of which it is certainly destitute in 
 Man. There is no essential difference, either in structure, or in the nature of 
 the actions performed by them, between the Spinal Cord and the Medulla 
 Oblongata, which can warrant us in assigning to the latter a function that the 
 former does not possess: and if the reflexions of the Spinal Cord do not 
 involve sensation, there is good reason for concluding, that this change is not 
 a necessary element in those of the Medulla Oblongata. It is perfectly true, 
 that it usually accompanies in us the greater number of actions, to which that 
 division of the centre is subservient; for example, those of respiration and 
 deglutition : and it is scarcely possible for such an accident to occur in the 
 Human being, as the separation of the Medulla Oblongata from the brain, 
 without the destruction of the independent functions of both. It is not likely 
 that we can ever have the power of ascertaining, by the testimony of a patient 
 so affected, that the Respiratory movements are performed without the neces- 
 sary intervention of sensation ; as we have been able to do in regard to other 
 reflex movements. But as the general fact is, that there is no positive ground 
 whatever for regarding any part of the Spinal Cord as a sensorium independent 
 of the brain, and that the Respiratory movements certainly correspond in all 
 their conditions with the actions denominated reflex, there would seem no 
 good reason for maintaining that sensation is an element in their production, 
 whilst it is admitted to be not essential in the case of the less regular con- 
 vulsive actions already described. The character of adaptiveness to a designed 
 end, in regard to their combination and succession, which the movements of 
 respiration and deglutition exhibit, has been shown to be no proof of their 
 dependence on sensation. 
 
 - 371. The question has been often put to those who advocate this view, 
 wrfy the sensation should be so constantly associated with these changes, if 
 not essential to produce the motion? An objection might fairly be made to 
 any reasoning from final causes, in a question of facts ; but the inquiry may 
 be easily answered. In many instances the production of sensations is the 
 stimulus necessary for the excitement of other actions, which are required 
 for the continued maintenance of those in question. This may be rendered 
 more comprehensible by a simple illustration. A cistern filled with water 
 may be speedily emptied by a cock occasionally opened at the bottom ; but, 
 if it communicate with a reservoir, by means of a valve opened by a ball 
 floating on the surface of the water it contains, it may be kept constantly full. 
 The lower cock is opened, and the water flows out ; and, in consequence of 
 the lowering of the surface thus produced, the floating valve above is opened, 
 and the cistern is refilled from the reservoir. Now here the action of the ball- 
 cock at the top is not essential to the flow of water at the bottom, but is 
 rather consecutive upon it. Just so is it with regard to those movements of 
 Animals, which are concerned in the ingestion of their food. The muscular 
 contractions required to propel it along the alimentary canal, from the stomach 
 downwards, are provided for, without even the intervention of the nervous 
 system. To bring it within reach of these, a muscular apparatus is provided, 
 by which anything that comes within its grasp is conveyed downwards, 
 through a reflex operation, originating in the impression made upon the sur- 
 face of the pharynx. Now this action, in the ordinary condition, may be 
 considered as attended with sensation, in order that the Animal may be called 
 upon to execute those other movements, which will bring food within the 
 
FUNCTIONS OF THE SPINAL CORD. REFLEX ACTION. 291 
 
 reach of the apparatus of deglutition. The Polype is dependent for its sup- 
 plies of aliment, upon what the currents in the surrounding fluid, or other 
 chances, bring into its neighbourhood ; but anything which touches its ten- 
 tacula, is entrapped and conveyed into its stomach. The anencephalous 
 Infant, again, can swallow, and even suck; but it can execute no other move- 
 ments adapted to obtain the supply of food continually necessary for mainte- 
 nance, because it has not a mind which sensations could awake into activity. 
 
 372. The sensation connected with reflex actions has not only this import- 
 ant end, but it frequently contributes to enjoyment, as in suction and ejaculatio 
 seminis. Now there is evidence that the latter of these processes, involving 
 though it does the combined action of a number of muscles, and dependent 
 as it seems upon sensation of a very peculiar kind, may take place without 
 consciousness on the part of the individual. Brachet mentions a case of this 
 kind in the Human subject, in which the patient's own testimony could be 
 adduced; and he ascertained that emission could be produced in dogs, in 
 which the spinal cord had been divided in the back, and in which, therefore, 
 it can scarcely be doubted that the sensibility of the genital organs was de- 
 stroyed. Such cases, it might be thought, are sufficient to prove, that the 
 Reflex power, operating independently of sensation, is not confined to such 
 irregular convulsive movements as are seen in Man after disease or injury; 
 but is exercised in producing the regular combined actions which are neces- 
 sary for the maintenance of the organic functions. The sensation accompa- 
 nying these actions, moreover, frequently affords premonition of danger, or 
 gives excitement to supplementary actions destined to remove it, as in the 
 case of respiration ; for where anything interferes with the due discharge of 
 the function, the uneasy sensation that ensues occasions unwonted move- 
 ments, which are more or less adapted to remove the impediment, in propor- 
 tion as they are guided by judgment as well as by consciousness. Again, 
 sensation often gives warning against inconvenience, as in the excretory func- 
 tions; and here it is very evident, that its object is not only (if it be at all) to 
 excite the associated muscles necessary for the excretion, but actually to make 
 the Will set up the antagonizing action of the sphincters, as will be hereWter 
 explained ( 391). There is one unequivocal case, in the ordinary condition 
 of the human body, of reflex action without sensation ; this is the muscular 
 contraction, by which the food is propelled from the bottom of the pharynx 
 to the stomach. Unless the morsel be very bulky, so as to press on the sur- 
 rounding parts, or be very different in temperature from the surface it touches, 
 or have any peculiar irritating quality, we are not more conscious of its pre- 
 sence, whilst it is passing down the lower part of the resophagus, than when 
 it is being propelled along the intestinal tube; and yet, as Dr. J. Reid's ex- 
 periments* have shown, this contraction is of a reflex character, not being 
 stimulated by direct contact, but requiring the completeness of the nervous 
 circle for its performance. 
 
 373. We shall now separately consider the chief operations, in which the 
 Spinal Cord and its system of nerves are usually concerned, in the ^ordinary 
 course of the vital actions of the Human body. Upon taking a general sur- 
 vey of these, it will be found that their principal function is, to supply the 
 conditions requisite for the maintenance of the various Organic processes. 
 Thus, the aeration of the blood, which takes place whenever that fluid is 
 placed in relation with the atmosphere, can only be carried on, by the regular 
 exchange of the small quantity of the gas contained in the lungs; if this 
 cease, the circulation is soon brought to a stand, and loss of vitality of the 
 whole system speedily results. Hence this is the most constantly necessary 
 
 * Edinb. Med. and Surg. Journ., vol. xlix. 
 
292 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 of all the actions of the Spinal Cord ; and we find its maintenance, in spite 
 of accident or disease of the spine, remarkably provided for, in the location of 
 the centre of the respiratory movements, which occupies a position where it 
 receives the greatest possible amount of protection. The supply of the di- 
 gestive apparatus, again, is immediately dependent upon the Spinal system ; 
 and this, being another essential function, has its centre equally protected. 
 The outlets of the cavities are also controlled by the Spinal system ; but this 
 control, although essential to the comfort of life, is less necessary to its main- 
 tenance ; and we find it dependent upon a portion of the Cord, which is 
 more liable to lose its powers by disease or injury. It is possible, as will 
 hereafter be shown, that several actions, which are at first voluntary, may be 
 effected, when so frequently performed as to become habitual, through the 
 medium of the Spinal system ; of this kind seem to be the movements of 
 locomotion, which are continued involuntarily, when the whole attention of 
 the mind is given to other objects, but which the Will can check at any time. 
 We shall commence our particular survey of the Reflex movements in Man, 
 with the consideration of those of Respiration, which are well adapted for 
 illustrating their general character. 
 
 374. Respiratory Movements. The centre of these is the upper part of 
 the Medulla Oblongata; into this may be traced the excitor nerves, that con- 
 vey the stimulus on which the movements are dependent; and from it pro- 
 ceed, either directly or indirectly, the motor nerves by which they are carried 
 into effect. The chief Excitor of the respiratory movements is unquestion- 
 ably the Par Vagum. When this is divided on both sides, according to the 
 experiments of Dr. Reid,* the number of respiratory movements is considera- 
 bly diminished, usually about one-half. Now if this nerve excites the motions 
 of respiration by its powerful action in producing sensation, we should ex- 
 pect to find its trunk endowed with considerable sensibility, which is not the 
 case ; for all experimenters agree in stating that, when its trunk is pinched or 
 pricked, the animal does not exhibit signs of pain nearly so acute, as when 
 the trunks of the ordinary spinal nerves, or of the fifth pair, are subjected to 
 sircar treatment. It cannot be questioned, however, that its power as an 
 excitor of respiration is very great ; since, besides the fact of the diminution 
 in the number of inspirations which occurs immediately on section of it, 
 irritation of its trunk in the neck is instantly followed by an act of inspira- 
 tion. It is evident that this power must arise from impressions made upon 
 its peripheral extremities. The impression is probably due to the presence 
 of venous blood in the capillaries of the lungs ; or, as Dr. M. Hall thinks, to 
 the presence of carbonic acid in the air-cells. Either or both may be true. 
 The Pneumogastric nerve, however, is not the only excitor of the respiratory 
 movements ; since, when the nerve is cut on each side, they still continue. 
 Dr. Reid has satisfactorily shown the statement of many experimenters, that 
 the inspirations are increased in frequency after this operation, to be erroneous ; 
 this idea having originated in their very prolonged and laborious character. 
 The removal of the Encephalon, also, diminishes the frequency of the respi- 
 ratory movements, whether it be performed before or after the section of the 
 Vagi. Dr. Reid found that, in a kitten of a day old, in which the inspira- 
 tions were 100 per minute, they fell to 40 when the Encephalon was re- 
 moved ; and on subsequently cutting the Pneumogastrics, the number of 
 inspirations instantly fell to between 3 and 4 in the minute, and continued so 
 -for some time. Hence it appears that the respiratory movements are partly 
 dependent upon sensation, and a motor influence excited by it; and this may 
 also be learned from the prolonged and laborious character of the inspirations 
 
 * Edinb. Med. and Surg. Journ., vol. li. 
 
REFLEX ACTIONS. RESPIRATORY MOVEMENTS. 293 
 
 during sleep or profound attention, when the influence of the Encephalon is 
 more or less suspended. 
 
 375. But why (it may be asked) do the movements continue, when the 
 Pneumogastrics have been divided, and the Encephalon has been removed ? 
 It is evident that there must be other excitors to the action of the respiratory 
 muscles. Amongst these, the nerves distributed to the general surface, and 
 particularly to the face, probably perform an important part; and in exciting 
 the first inspiration, the Fifth pair seems the principal agent. It has long 
 been a well-known fact, that the first inspiratory effort of the new-born infant 
 is most vigorously performed, when the cool external air comes into contact 
 with the face ; and that impressions on the general surface, such as a slap of 
 the hand on the nates, are often effectual in exciting the first inspiratory 
 movements, when they would not otherwise commence. Dr. M. Hall relates 
 an interesting case, in which the first inspiration was delayed, simply because 
 the face was protected by the bed-clothes from the atmosphere ; and, on lift- 
 ing t up these, the infant immediately breathed. Dr. M. Hall has recently 
 mentioned the important fact, that if the cerebrum be removed, and the pneu- 
 mogastrics be divided, in a young kitten, the number of acts of respiration 
 will be reduced to four in a minute; but by directing a stream of air on the 
 animal, or by irritating various parts of the general surface, we may excite 
 twenty or thirty acts of respiration within the same space of time. He 
 further remarks, that in the very young warm-blooded animal, as in the cold- 
 blooded animal, the phenomena of the excito-motor power are far more vividly 
 manifested, than in the older and the warm-blooded. In the very young 
 .kitten, even when asphyxiated to insensibility, every touch, contact, or slight 
 blow, every jar of the table, any sudden impression of the external air, or 
 that of a few drops of cold water, induces at once energetic reflex movements, 
 and acts of inspiration. This may be looked upon as Nature's provision for 
 the first establishment of the acts of inspiration in the new-born animal. 
 But the influence of the nerves of the general system is by no means want- 
 ing in the adult; as the following experiment of Dr. J. Reid's demonstrates. 
 After dividing the pneumogastrics, and removing the cerebrum and ceflUbel- 
 lum, he divided the spinal cord high up in the neck, so as to cut off the com- 
 munication between the spinal nerves and the Medulla Oblongata; and he 
 found that the frequency of the respiratory movements was still further 
 diminished, although they were not even then entirely suspended. Every 
 one knows the fact, that the first plunge into cold water, the first descent of 
 the streams of the shower-bath, or even the dashing of a glass of cold water 
 in the face, will produce inspiratory efforts ; and this fact has many important 
 practical applications. Thus in the treatment of Asphyxia, whether congeni- 
 tal, or the result of narcotic poisoning, drowning, &c., the alternate applica- 
 tion of cold and heat is found to be one of the most efficacious means of 
 restoring the respiratory movements; and a paroxysm of hysteric laughter 
 may be cut short, by dashing a glass of cold water in the face. It may be 
 surmised that the Sympathetic nerve, which derives many filaments from the 
 Cerebro-Spinal system, and which especially communicates with the Pneu- 
 mogastric nerves, is one of the excitors to this function; and this, perhaps, 
 not only through its ramifications in the lungs, which are considerable, but 
 also by its distribution on the systemic vessels ; so that it may convey to the 
 Spinal Cord the impression of imperfectly-arterialized blood, circulating in 
 these, such as the Pneumogastric is believed to transmit from the lungs. It 
 will hereafter be shown, that an impression of a corresponding kind is more 
 probably the cause of the sense of Hunger and Thirst, than any which origi- 
 nates in the stomach alone (Chap. X., Sect. 1). 
 
 376. The Motor or Efferent nerves concerned in the function of Respira- 
 
 26* 
 
294 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 tion, are those which Sir C. Bell has grouped together in his respiratory 
 system. The most important of these, the Phrenic, arises from the upper 
 part of the Spinal Cord; the Intercostals much lower down; whilst the Facial 
 nerve and the Spinal Accessory, to the latter of which, as will hereafter be 
 stated ( 408), the motor powers of the par vagum are chiefly due, take their 
 origin in the Medulla Oblongata itself. But we must not decide upon the 
 connection of a particular nerve with a particular segment of the Spinal Cord, 
 simply because it diverges from it at that point. It has been shown that, in 
 the Mollusca, a nerve passing to, or proceeding from, one ganglion, frequently 
 passes through or over another which lies in its course ; and in the Articulata, 
 this is a still more constant occurrence. It is by no means improbable, then, 
 that the connection of the intercostal nerves is really in part with the grey 
 matter of the Medulla Oblongata; at any rate, such a connection has not been 
 disproved. The white columns of the Spinal Cord consist of fibres, which 
 bring the spinal nerves into connection, not only with the brain, but also with 
 other segments of the ganglionic portion of the cord; being analogous in junc- 
 tion, not merely to the distinct fibrous tract of the ventral column of the Arti- 
 culata, but also to the fibrous bands that connect the ganglia themselves. And 
 as the Medulla Oblongata, in Vertebrated animals, is the chief centre of the 
 actions of Respiration, it can scarcely be doubted that all the nerves concerned 
 in that function have a direct structural connection with it. 
 
 377. That the Respiratory movements, as ordinarily performed, are essen- 
 tially independent of the Will, appears not only from our own consciousness, 
 but also from cases of paralysis; in some of which, the power of the will over 
 the muscles has been lost, whilst the movements have been kept up by the 
 reflex action of the Medulla Oblongata or respiratory ganglion ; whilst in 
 others, some of the respiratory muscles have been motionless during ordinary 
 breathing, and yet have remained under the power of the will. Such cases 
 are mentioned by Sir C. Bell, in the Appendix to his work on the Nervous 
 System, That consciousness is not a necessary link in the chain of causes, 
 which produce the respiratory movements, we are enabled to judge from the 
 phenomena presented by the human being in sleep and coma, by anencephalous 
 foetuses, and by decapitated animals. Further, Dr. Ley* has put on record a 
 case, which confirms this particular inference, just in the same manner as the 
 cases already related confirm the general doctrine of the non-existence of sen- 
 sibility in the Spinal Cord. He had under his care a patient, in whom the 
 par vagum appeared to be diseased; the lungs suffered in the usual way in 
 consequence, and the patient had evidently laborious breathing; but he dis- 
 tinctly said that he felt no uneasiness in his chest. The experience of every 
 one informs him, that Respiratory movements are partly under the control 
 and direction of the will, though frequently unrestrainable by it. In ordinary 
 circumstances, when the blood is being perfectly aerated, and there is a suffi- 
 cient amount of arterial blood in the system to carry on the functions of life 
 for a short time, we can suspend the respiratory actions during a few seconds 
 without any inconvenience. If, however, we endeavour to prolong the sus- 
 pension, the stimulus conveyed by the excitor nerves to the Medulla Oblon- 
 gata becomes too strong, and we cannot avoid making inspiratory efforts ; and 
 if the suspension be still further prolonged, the whole body becomes agitated 
 by movements, which are almost of a convulsive nature ; and no effort of the 
 will can then prevent the ingress of air.t It is easy to understand why, in 
 
 * On Laryngismus Stridulus, p. 417. 
 
 t It is asserted by M. Bourdon (Recherches sur le Mecanisme de la Respiration, p. 81), 
 that no person ever committed suicide, though many have attempted to do so, by simply 
 holding the breath; the control of the will over the respiratory muscles not being sufficiently 
 great, to antagonize the stimulus of the " besoin de respirer," when this has become aggra- 
 
REFLEX ACTIONS. RESPIRATORY MOVEMENTS. 295 
 
 the higher animals at least, and more especially in Man, the respiratory actions 
 should be thus placed under the control of the will : since they are subser- 
 vient to the production of those sounds, by which individuals communicate 
 their feelings and desires to each other ; and which, when articulate, are capa- 
 ble of so completely expressing what is passing in the mind of the speaker. 
 If the respiratory mucles of Man were no more under his control, than they 
 appear to be in the Insect or Molluscous animal, he might be provided with 
 the most perfect apparatus of speech, and yet he would not be able to employ 
 it to any advantage. 
 
 378. The motor, power of the Respiratory nerves is exercised, however, 
 not only on the muscles which perform the inspiratory and expiratory move- 
 ments, but on those which guard the entrance to the windpipe, and also on 
 certain other parts. The movements of the internal respiratory apparatus 
 are chiefly, if not entirely, effected through the medium of the motor fibres, 
 which the Par Vagum contains. These motor fibres exist in very different 
 amount in its different branches. For example, the pharyngeal and resopha- 
 geal branches, by which (as will hereafter appear) the muscles of deglutition 
 are excited to contraction, possess a much larger proportion of them, and 
 exhibit much less sensibility when irritated, than do other divisions of the 
 trunk. Between the superior and inferior laryngeal nerves, again, there is an 
 important difference, which anatomical and experimental research has now 
 very clearly demonstrated. It has long been known, that section of the Par 
 Vagum in the neck, above the inferior laryngeals, is frequently followed by 
 suffocation, resulting from closure of the glottis ; and hence it has been in- 
 ferred, that the office of the inferior laryngeals was to call into action the 
 dilators of the larynx, whilst the superior laryngeals were supposed to stimu- 
 late the constrictors. This view, however, is incorrect. It is inconsistent 
 with the results, just stated, of anatomical examination into the respective 
 distribution of these two trunks ; and it has been completely overthrown by 
 the very careful and satisfactory observations and experiments of Dr. J. Reid, 
 which have established that, whilst the inferior laryngeal is the motor nerve 
 of nearly all the laryngeal muscles, the superior laryngeal is the excitolf or 
 afferent nerve, conveying to the Medulla Oblongata the impressions by which 
 muscular movements are excited. Its motor endowments are limited to the 
 crico-thyroid muscle, to which alone of all the muscles its filaments can be 
 traced, the remainder being distributed beneath the mucous surface of the 
 larynx ; and its sensibility is very evident, when it is pinched or irritated 
 during experiments upon it. On the other hand, the motor character of the 
 inferior laryngeal branch is shown by its very slight sensibility to injury, its 
 nearly exclusive distribution to muscles, and its influence in exciting contrac- 
 tion of these when its separated trunk is stimulated. 
 
 379. It has been ascertained by Dr. Reid that, if the inferior laryngeal 
 branches be divided, or the trunk of the par vagum be cut above their origin 
 from it, there is no constriction of the glottis, but a paralyzed state of its mus- 
 cles. After the first paroxysm occasioned by the operation, a period of qui- 
 escence and freedom from dyspnoea often supervenes, the respirations being 
 performed with ease, so long as the animal remains at rest; but an unusual 
 respiratory movement, such as takes place at the commencement of a struggle, 
 induces immediate symptoms of suffocation, the current of air carrying in- 
 wards the arytenoid cartilages, which are rendered passive by the paralyzed 
 
 vated by the temporary cessation of the action. But such persons have succeeded better, by 
 holding the face beneath the surface of water; because here another set of muscles is called 
 into action, which are much more under the control of the will, than are those of respiration ; 
 and a strong volition applied to these can prevent all access of air to the lungs, however 
 violent may be the inspiratory efforts. 
 
296 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 state of their muscles; and these, falling upon the opening of the glottis, like 
 valves obstruct the entrance of air into the lungs. The more effort is made, 
 the greater will be the obstruction: and accordingly, it is generally necessary 
 to counteract the tendency to suffocation, when it is desired to prolong the life 
 of the animal after this operation, by making an opening into the trachea. Dr. 
 Reid further ascertained that the application of a stimulus to the inferior 
 laryngeal nerves, when separated from the trunk, would occasion distinct 
 muscular contractions in the larynx; whilst a corresponding stimulus applied 
 to the superior laryngeal occasioned no muscular movement, except in the 
 crico-thyroid muscle. But when the superior laryngeals were entire, irritation 
 of the mucous surface of the larynx, or of the trunks themselves, produced 
 contraction of the glottis and efforts to cough ; effects which were at once pre- 
 vented by dividing those nerves, and thereby cutting off their communication 
 with the Medulla Oblongata. There can be no doubt, then, that the superior 
 and inferior laryngeal branches constitute the circle of incidents and motor 
 nerves, by which the aperture of the glottis is governed, and by which any 
 irritation of the larynx is made to close the passage, so as to prevent the 
 entrance of improper substances; whilst the superior laryngeal nerve also ex- 
 cites the muscles of expiration, so as to cause the violent ejection of a blast of 
 air, by which the offending gas, fluid, or solid, may be carried off. The effect 
 of carbonic acid in causing spasmodic closure of the glottis is well known ; 
 and affords a beautiful example of the protective character of this system of 
 nerves. The mucous surface of the trachea and bronchi appears, from the 
 experiments of Valentin, to be endowed with excitability, so that stimuli ap- 
 plied to it produce expiratory movements; and this evidently operates through 
 the branches of the par vagum distributed upon the membrane. Here, as 
 elsewhere, we find that a stimulus applied to the surface has a much more 
 decided influence than irritation of the trunk of the nerve supplying it. 
 
 380. The actions of sighing, yawning, sobbing, laughing, coughing, and 
 sneezing, are nothing else than simple modifications of the ordinary movements 
 of respiration, excited either by mental emotions, or by some stimulus originat- 
 ing in the respiratory organs themselves. Sighing is nothing more than a very 
 long-drawn inspiration, in which a larger quantity of air than usual is made to 
 enter the lungs. This is continually taking place to a moderate degree ; and 
 we notice it particularly, when the attention is released, after having been 
 fixed upon an object; which has excited it strongly, and which has prevented 
 our feeling the insufficiency of the ordinary movements of respiration. Hence 
 this action is only occasionally connected with mental emotion. Yawning is 
 a still deeper inspiration, which is accompanied by a kind of spasmodic con- 
 traction of the muscles of the jaw, and also by a very great elevation of the 
 ribs, in which the scapulae partake. The purely involuntary character of this 
 movement is sometimes seen, in a remarkable manner, in cases of palsy; in 
 which the patient cannot raise his shoulder by an effort of the will, but does 
 so in the act of yawning. Nevertheless this act may be performed by the 
 will, though not completely; and it is one that is particularly excited by 
 an involuntary tendency to imitation ; as every one must have experienced, 
 who has ever been in company with a set of yawners. Sobbing is the con- 
 sequence of a series of short convulsive contractions of the diaphragm ; and it 
 is usually accompanied by a closure of the glottis, so that no air really enters. 
 In Hiccup, the same convulsive respiratory movement occurs ; and the glottis 
 closes suddenly in the midst of it; the sound is occasioned by the impulse of 
 the column of air in motion, against the glottis. In Laughing, a precisely 
 reverse action takes place ; the muscles of expiration are in convulsive move- 
 ment, more or less violent, and send out the breath in a series of jerks, the 
 glottis being open. This sometimes goes on, until the diaphragm is more 
 
REFLEX ACTIONS. RESPIRATORY MOVEMENTS. 297 
 
 arched, and the chest is more completely emptied of air, than it could be by 
 an ordinary movement of expiration. The act of Crying, though occasioned 
 by a contrary emotion, is, so far as the respiration is concerned, very nearly 
 the same as the last. Every one knows the effect of mixed emotions, in pro- 
 ducing an expression of them, which is " between a laugh and a cry." The 
 greater part of the preceding movements seem to belong as much to the con- 
 sensual or emotional, as to the purely reflex group of actions ; for whilst they 
 are sometimes the result of peculiar states of the respiratory organs, or of the 
 bodily system in general, they may also be called forth by influences, which 
 operate directly through the senses, or which excite the emotions. Thus, 
 whilst Sighing and Yawning often occur as simple results of deficient aeration, 
 they may be brought on, the former by a depressed state of the feelings, 
 the latter by the mere sight of the act in another person. The actions of 
 Laughter and Crying never seem to originate in the respiratory system ; but 
 to be always either expressions of the emotions, or simple results of sensa- 
 tions, crying being connected with the sense of pain, and laughter with that 
 of tickling. The origin of the act of Hiccup does not seem very clear ; but 
 the movement is probably of a purely reflex nature. 
 
 381. The purposes of the acts of Coughing and Sneezing are, in both 
 instances, to expel substances from the air-passages, which are sources of irri- 
 tation there ; and this is accomplished in both, by a violent expiratory effort, 
 which sends forth a blast of air from the lungs. Coughing occurs, when the 
 source of irritation is situated at the back of the mouth, in the trachea, or 
 bronchial tubes. The irritation may be produced by acrid vapours, or by 
 liquids or solids, that have found their way into these passages ; or by secre- 
 tions which have been poured into them in unusual quantity, as the result of 
 disease; or by the simple entrance of air (especially if cold), when the mem- 
 brane is in a peculiarly irritable state. Any of these causes may produce an 
 impression upon the excitor fibres of the Par Vagum, which, being conveyed 
 to the Medulla Oblongata, shall give rise to the transmission of motor impulses 
 to the several muscles, that shall combine them in the act of coughing. This 
 act consists, 1st, in a long inspiration, which fills the lungs; 2d, in the 
 closure of the glottis at the moment when expiration commences ; and 3d, in 
 the bursting open (as it were) of the glottis, by the violence of the expiratory 
 movement; so that a sudden blast of air is forced up the air-passages, carrying 
 before it anything that may offer an obstruction. The difference between 
 coughing and Sneezing consists in this, that in the latter, the communication 
 between the larynx and the mouth is partly or entirely closed, by the drawing 
 together of the sides of the velum palati over the back of the tongue; so that 
 the blast of air is directed, more or less completely, through the nose, in such 
 a way as to carry off any source of irritation that may be present there. It is 
 difficult to say how far these actions are simply reflex ; or how far they may 
 require the stimulus of sensation for their performance. 
 
 382. Deglutition and Defecation. Another very important function of the 
 Spinal Cord (and of the ganglia corresponding to it in the Invertebrata), is the 
 control which it exercises over the entrance and termination of the Alimentary 
 Canal; and this reflex action might probably be traced in some animals, in 
 which the necessity for that of Respiration does not exist. In all beings which 
 are unequivocally of an animal character, a stomach or digestive cavity exists ; 
 and a means must be provided for the introduction of food into it. This is 
 partly accomplished by the power, with which its entrance is endowed, of 
 contracting upon, and of attempting to draw inwards, whatever comes in con- 
 tact with it; as we may readily observe in the Star-Fish, or Sea-Anemone, 
 where what is commonly regarded as the mouth, is really the aperture of the 
 stomach. But we almost always find some more special apparatus, for bring- 
 
298 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 ing food within reach of this orifice. In the Sea-Anemone, the Hydra, and 
 other Polypes, for example, we find that aperture surrounded by tentacula; 
 which have an evident tendency to lay hold of anything that touches them, so 
 as to bring it, by their contraction, within reach* of the muscles immediately 
 surrounding the aperture. This is just the purpose of the pharyngeal muscles 
 of Man. The lower part of the oesophagus, near its termination in the sto- 
 mach, has the same simple tendency to contraction from above downwards 
 (so as to convey into the stomach anything which is brought within its reach), 
 as have the muscles surrounding the mouth of the Polype; but there is need 
 of some more complex apparatus, for the purpose of laying hold of the food, 
 and of conducting it into its grasp. This is provided for, in the higher animals, 
 in the muscles of that funnel-like entrance to the oesophagus, which is called 
 the Pharynx. The actions of these are most distinctly reflex; and it is inte- 
 resting to remark, that the movements can neither be caused nor controlled by 
 the direct influence of the will. In the case of the movements of respiration, 
 we found sufficient provision made for their constant maintenance; and yet, 
 for secondary purposes, they were placed in a considerable degree under the 
 control of the brain. But here there are no secondary purposes to be an- 
 swered ; the introduction into the stomach of food, brought by the will within 
 reach of the pharyngeal muscles, is the only object contemplated by them; 
 and they are accordingly placed under the sole government of the Spinal Cord. 
 
 383. No attempts, on our own part, will succeed in producing a really 
 voluntary act of Deglutition. In order to excite it, we must supply some 
 stimulus to the fauces. A very small particle of solid matter, or a little fluid 
 (saliva, for instance), or the contact of the back of the tongue itself, will be 
 sufficient ; but without either of these we, cannot swallow at will. Nor can 
 we restrain the tendency, when it is thus excited by a stimulus ; every one 
 knows how irresistible it is, when the fauces are touched in any unusual man- 
 ner ; and it is equally beyond the direct control of the will, in the ordinary 
 process of eating, voluntary as we commonly regard this. The only mode 
 in which the will can influence it, is by regulating the approach of the stimu- 
 lus necessary to excite it; thus, we voluntarily bring a morsel of food, or a 
 little fluid, into contact with the surface of the fauces, and an act of deglutition 
 is then involuntarily excited : or we may voluntarily keep all stimulus at a 
 distance ; and no effort of the will can then induce the action. Moreover, 
 this action is performed, like that of respiration, when the power of the will 
 is suspended, as in profound sleep, or in apoplexy affecting only the brain; 
 and it does not seem to be at all affected by the entire removal of the brain, 
 in an animal that can sustain the shock of the operation ; being readily ex- 
 citable, on stimulating the fauces, so long as the nervous structure retains its 
 functions. This has been experimentally proved by Dr. M. Hall; and it 
 harmonizes with the natural experiment sometimes brought under our notice 
 in the case of an anencephalous infant, in which the power of swallowing 
 seems as vigorous as in the perfect one. But, if the nervous circle be de- 
 stroyed, either by division of the trunks, or by injury of any kind to the por- 
 tion of the nervous centres connected with them, the action can no longer be 
 performed; and thus we see that, when the effects of apoplexy are extending 
 themselves from the brain to the spinal cord, whilst the respiration becomes 
 stertorous, the power of Deglutition is lost, and then respiration also speedily 
 ceases. 
 
 384. Our knowledge of the nerves specially concerned in this action is 
 principally due to the very careful and well-conducted experiments of Dr. J. 
 Reid.* The distribution of the Glosso-Pharyngeal evidently points it out as 
 
 * Edinb. Med. and Surg. Journ., vol. xlix. 
 
ACTIONS PRELIMINARY TO DEGLUTITION. 299 
 
 in some way connected with it ; and this, when carefully examined, discloses 
 the important fact, that the nerve scarcely sends any of its branches to the 
 muscles which they enter ; but that these mostly pass through them, to be 
 distributed to the super] acent mucous surface of the tongue and fauces. 
 Further, when the trunk is separated from the nervous centres, irritation 
 scarcely ever produces muscular movements. Hence it is not in any great 
 degree an efferent or motor nerve ; and its distribution would lead us to sup- 
 pose its function to be, the conveyance of impressions from the surface of the 
 Fauces to the Medulla Oblongata. This inference is fully confirmed by the 
 fact, that, so long as its trunk is in connection with the Medulla Oblongata, 
 and the other parts are uninjured, pinching, or other severe irritation of the 
 Glosso-Pharyngeal, will often excite distinct acts of deglutition. Such irrita- 
 tion, however, may excite only convulsive twitches, instead of the regular 
 movements of swallowing; and it is evident that, here, as elsewhere, the 
 impressions made upon the extremities of the nerves are much more power- 
 ful exciters of reflex movement, than those made upon the trunk, though the 
 latter are more productive of pain. It was further observed by Dr. Reid, that 
 this effect was produced by pinching the pharyngeal branches only ; no irrita- 
 tion of the lingual division being effectual to the purpose. 
 
 385. If, then, the muscles of deglutition are not immediately stimulated to 
 contraction by the Glosso-Pharyngeal nerve, it remains to be inquired, by 
 what nerve the motor influence is conveyed to them from the Medulla Oblon- 
 gata ; and Dr. Reid has been equally successful in proving, that this function 
 is chiefly performed by the pharyngeal branches of the Par Vagum. Ana- 
 tomical examination of their distribution shows, that they lose themselves in 
 the muscles of the pharynx ; and whilst no decided indications of suffering 
 can be produced by irritating them, evident contractions are occasioned, when 
 the trunk, separated from the brain, is pinched or otherwise stimulated. It 
 appears, however, that neither is the Glosso-Pharyngeal the sole excitor 
 nerve, nor are the pharyngeal branches of the Par Vagum the sole motor 
 nerves, concerned in deglutition ; for after the former has been perfectly di- 
 vided on each side, the usual movements can still be excited, though with less 
 energy; and, after the latter have been cut, the animal retains the means of 
 forcing small morsels through the pharynx, by the action of the muscles of 
 the tongue and neck. From a careful examination of the actions of degluti- 
 tion, and of the influence of various nerves upon them, Dr. Reid draws the 
 following conclusions : The excitor impressions are conveyed to the Me- 
 dulfa Oblongata chiefly through the Glosso-Pharyngeal, but also along the 
 branches of the Fifth pair distributed upon the fauces, and probably along the 
 branches of the Superior Laryngeal distributed upon the pharynx. The 
 motor influence passes chiefly along the pharyngeal branches of the Vagus ; 
 along the branches of the Hypo-glossal, distributed to the muscles of the 
 tongue, and to the sterno-hyoid, sterno-thyroid, and thyro-hyoid muscles ; 
 along the motor filaments of the Recurrents, ramifying upon the larynx ; 
 along some of the branches of the Fifth, supplying the elevator muscles of the 
 lower jaw; along the branches of the Portio Dura, ramifying upon the digas- 
 tric and stylo-hyoid muscles, and upon the muscles of the lower part of the 
 face ; and probably along some of the branches of the Cervical plexus, which 
 unite themselves to the descendens noni. 
 
 386. When the food has been propelled downwards by the Pharyngeal 
 muscles as far as their action extends, its further progress through the (Eso- 
 phagus is effected by the peristaltic movement of the muscular coat of the 
 tube itself. This movement is not, however, due only to the direct stimulus 
 of the muscular fibre by the pressure of the food, as it seems to be in the 
 lower part of the alimentary canal ; for Dr. J. Reid has found, by repeated 
 
300 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 experiment, that the continuity of the oesophageal branches of the Par Vagum 
 with the Spinal Cord, is necessary for the rapid propulsion of the food ; so 
 that it can scarcely be doubted, that an impression made upon the mucous 
 surface of the oesophagus, conveyed by the afferent fibres of these nerves to 
 the Medulla Oblongata, and reflected downwards along the motor fibres, is 
 the real cause of the muscular contraction. If the Par Vagum be divided in 
 the rabbit, on each side, above the cesophageal plexus, but below the pharyn- 
 geal branches, and the animal be then fed, it is found that the food is delayed 
 in the oesophagus, which becomes greatly distended. Further, if the lower 
 extremity of the par vagum be irritated, distinct contractions are seen in the 
 cesophageal tube, proceeding from above downwards, and extending over the 
 cardiac extremity of the stomach. We have here, then, a distinct case of 
 reflex action without sensation, occurring as one of the regular associated 
 movements in the natural condition of the animal body ; and it is very inte- 
 resting to find this following upon a reflex action with sensation (that of the 
 pharynx), and preceding a movement which is altogether unconnected with 
 the Spinal Cord (that of the lower part of the alimentary canal). The use of 
 sensation in the former case will presently appear. The muscular fibres of 
 the oesophagus are also excitable, though usually in a less degree, by direct 
 stimulation ; for it appears that, in some animals (the Dog, for example), 
 section of the pneumogastric does not produce that check to the propulsion of 
 the food, which it occasions in the Rabbit; and even in the Rabbit, as Dr. 
 M. Hall* has remarked, the simple contractility of the muscular fibre occa- 
 sions a distinct peristaltic movement along the tube, after its nerves have been 
 divided; causing it to discharge its contents, when cut across. Such a move- 
 ment, indeed, seems to take place in something of a rhythmical manner (that 
 is, at short and tolerably regular intervals), whilst a meal is being swallowed; 
 but as the stomach becomes full, the intervals are longer, and the wave-like 
 contractions less frequent. These movements are reversed in Vomiting ; and 
 this reversion has been observed, even after the separation of the stomach 
 from the oesophagus, as a consequence of the injection of tartar emetic into 
 the veins. 
 
 a. It will be desirable here to revert for a short time to the actions, which, in the higher 
 animals, precede those of Deglutition. There can be no doubt that, in the Human being, 
 the motions adapted to the Ingestion and Mastication of aliment originally result, in part at 
 least, from distinct operations of the Will ; but it would appear almost equally certain that, 
 in time, they come to be of so habitual a character, that the will only exerts a general con- 
 trolling influence over them, each individual act being directly excited by sensation. Every 
 one is conscious that the act of mastication may be performed as well, when the mind is 
 attentively dwelling on some other object, as when directed to it ; but, in the former case, 
 one is rather apt to go on chewing and rechewing what is already fit to be swallowed, 
 simply because the will does not exert itself to check the action, and to carry the food back- 
 wards within the reach of the muscles of deglutition. We now see why sensation should 
 be associated unth the latter process, though not essential to it. The conveyance of food back- 
 wards to the fauces is a distinctly voluntary act; and it is necessary that it should be guided 
 by the sensation, which there results from the contact it induces. If the surface of the 
 pharynx were as destitute of sensation, as is the lower part of the oesophagus, we should not 
 know when we had done what was necessary to excite its muscles to operation. The 
 muscles concerned in the Mastication of food are nearly all supplied by the third branch of 
 the Fifth pair, a large proportion of which is well known to have a motor character. Many 
 of these muscles, especially those of the cheeks, are also supplied by the Portio Dura of the 
 Seventh; and yet, if the former be paralyzed, this cannot stimulate them to the necessary 
 combined actions. Hence we see that the movements are of an associated character, their 
 due performance being dependent on the part of the nervous centres, from which the motor 
 influence originates. If the Fifth pair, on the other hand, be uninjured, whilst the Portio 
 Dura is paralyzed, the movements of Mastication are performed without difficulty ; whilst 
 those connected in any way with the Respiratory function, or with Expression, are para- 
 lyzed. 
 
 * Third Memoir on the Nervous System, 201. 
 
ACTIONS PRELIMINARY TO DEGLUTITION. 301 
 
 b. Comparative Anatomy supplies us with the key to the explanation of these phenomena. 
 It has been seen that, in the lower animals, the Respiratory organs are completely uncon- 
 nected with the mouth, and that a very distinct set of muscles is provided to keep them in 
 action. These muscles have distinct ganglia as the centres of their operations ; and these 
 ganglia are only connected indirectly with those of the sensori-motor system. The same 
 would appear to be the case, in regard to the introduction of the food into the digestive 
 apparatus. It has been shown that the muscles concerned in this operation have their own 
 centres, the Stomato-gastric and Pharyngeal ganglia, which are not very closely connected 
 with the cephalic, or with the respiratory, or with those of general locomotion. Now in the 
 Vertebrata, the distinct organs have been so far blended together, that the same muscles 
 serve the purposes of both; but the different sets of movements of these muscles are excited 
 by different nerves; and the effect of division of either nerve, is to throw the muscle out of 
 connection with the function, to which that nerve previously rendered it subservient, as 
 much as if the muscle were separated from the nervous system altogether. There is an 
 apparent exception to this view of the matter, in the case of the Portio Dura; this being the 
 source of those movements of the upper lip, which, in many animals, are essential to the 
 prehension of food. These movements, however, are dependent upon sensations conveyed 
 through the Fifth pair.* being completely checked by division of its infra-orbital trunk; and 
 it can scarcely be doubted, from their general character, that they are of a strictly voluntary 
 nature, and are not to be regarded as part of the reflex associated movements in which that 
 nerve is concerned. 
 
 c. Now although, in the adult Human being, the movements required to convey the food 
 to the pharynx are under the control of the Will, if not constantly dependent upon it, there 
 is good reason to believe that this is not the case in regard to those remarkable associated 
 movements, which constitute the act of suction in the Infant. The experiments provided 
 for us by nature, in the production of anencephalous monstrosities, fully prove that the 
 nervous connection of the lips and respiratory organs with the Spinal Cord, is alone sufficient 
 for its execution; and Mr. Grainger has sufficiently established the same, by experiment 
 upon puppies whose brain had been removed. He adds that, as one of the puppies lay on 
 its side, sucking the finger which was presented to it, it pushed out its feet in the same 
 manner as young pigs exert theirs against the sow's dugs. On the whole, however, the act 
 of suction belongs more to the Respiratory ganglion (so to speak) than to the Stomato-gastric 
 system of nerves ; and hence we can understand why, even in the highest animals, it should 
 be purely reflex; the movements of Respiration being so from the first, whilst those ordi- 
 narily concerned at a later period in the Ingestion of the food are more directed by sensa- 
 tion and volition. The actions of the mammary foetus of the kangaroo, described by Mr. 
 Morgan, furnish a very interesting exemplification of the same function of the Spinal Cord; 
 this creature, resembling an earth-worm in appearance, and only about fourteen lines in 
 length, with a brain corresponding in degree of development to that of a human foetus of 
 the ninth week, executes regular, but slow, movements of respiration, adheres firmly to the 
 point of the nipple, and moves its limbs when disturbed. The milk is forced into the oeso- 
 phagus by a compressor muscle, with which the mamma of the parent is provided. " Can it 
 be imagined," very justly asks Mr. Grainger, "that in this case there are sensation and vo- 
 lition, in what can be proved anatomically to be a foetus?" 
 
 387. The Sphincter muscle, which guards the Cardiac orifice of the 
 stomach, appears to be under the influence of the Spinal system of nerves. 
 It is usually closed; but it opens when there is a sufficient pressure on it, 
 made by the accumulated food propelled by the movements of the oesophagus 
 above; and it then closes again, so as to retain the food in the stomach. 
 That this closure is due to reflex action appears from the fact that, when the 
 nerves supplying the muscle are divided, the sphincter no longer contracts, 
 and the food regurgitates into the oesophagus. The opening of the cardiac 
 orifice is one of the first of the changes, which occur in the act of vomiting. 
 With regard to the degree, in which the movements of the Stomach, that have 
 so important a share in the Digestive operation, are dependent upon the Spinal 
 system, and are consequently of a reflex nature, it is difficult to speak with 
 
 * Hence originated one of Sir C. Bell's early errors. He found that an ass, in which the 
 infra-orbital branch of the fifth was divided, would not pick up oats with its lip, although 
 they were in contact with it; hence he concluded that its power of motion was destroyed, 
 when it was in reality only the sensation necessary to excite the will to cause the motion, 
 that was deficient. 
 26 
 
302 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 certainty, owing to the contradictory results obtained by different experi- 
 menters. These contradictions, however, seem partly due to a diversity in 
 the nature of the animals experimented on. It seems to be well established, 
 by the researches of Reid, Valentin, and others, that distinct movements may 
 be excited in the Stomach of the Rabbit, if distended with food, by irritating 
 the Par Vagum soon after the death of the animal; these movements seem to 
 commence from the cardiac orifice, and then to spread themselves in a sort 
 of peristaltic manner along the walls of the stomach; but no such movements 
 can be excited if the stomach be empty. Various experiments upon living 
 animals have led to a similar conclusion ; food taken in shortly before or sub- 
 sequently to its division, having been found to be only dissolved on the sur- 
 face of the mass, where it was in contact with the mucous membrane. But 
 these experiments have been made for the most part upon Herbivorous 
 animals, such as horses, asses, and rabbits ; whose food is bulky and difficult 
 of solution, requiring to be constantly changed in its position, so that every 
 part of it may be successively brought to the exterior. On the other hand, 
 Dr. Reid found, in his experiments upon Dogs, that, after the first shock of 
 the operation had gone off, solution of the food in the stomach, and absorp- 
 tion of chyle, might take place; and hence it may be inferred, that no influ- 
 ence of this nerve upon the muscular parietes of the stomach is essential to 
 digestion in that species. This conclusion harmonizes well, therefore, with 
 , the^fact already stated respecting the absence of such influence in the lower 
 parts of its oesophagus ; and it may, perhaps, be explained by the considera- 
 tion, that the natural food of the dog is much less bulky and more easy of 
 solution, than that of the animals already named ; so that there is not so much 
 need of the peculiar movement, which is in them so important an aid to the 
 process of reduction. The muscular walls of the stomach appear to be called 
 into reflex contraction in the act of Vomiting; the mechanism of which will 
 be considered hereafter ( 505). 
 
 388. That the ordinary peristaltic movements of the Intestinal canal, from 
 the stomach to the rectum, may take place without any connection with the 
 nervous system, being due to the direct stimulation of the contact of food, 
 there is now ample evidence ; and though some may yet be found to deny the 
 Hallerian doctrine, that muscular fibre possesses in itself the property of con- 
 tractility, so much additional evidence of its truth has been recently adduced 
 whilst the doctrine itself is so conformable to the analogy supplied by other 
 vital phenomena, that it will be here unhesitatingly adopted. (See Chapter V.) 
 Some Physiologists still suppose, that the peristaltic movements of the ali- 
 mentary canal are due to a sort of reflex action, taking place through the 
 ganglia of the Sympathetic system of nerves, especially, of course, the semi- 
 lunar. This supposition, however, has little or no evidence to support it; for 
 it has been fully proved that the muscular contractions will continue, long 
 after the tube has been separated from its nervous connections through its 
 whole extent ; and the only evidence in its favour is derived from the con- 
 tractions, which may sometimes be induced in parts of the tube which are at 
 rest, when the Sympathetic nerves supplying them are irritated. The ex- 
 periments of Valentin, however, by which the fact that such contractions 
 may be induced (which has been denied by some) is clearly substantiated, 
 also show that the motor influence does not originate in the Sympathetic gan- 
 glia, but in the Spinal Cord. The following are the general results of up- 
 wards of three hundred experiments, so far as they apply to this subject. 
 The pharynx may not only be excited to contraction by irritation of the pha- 
 ryngeal branches of the !Par Vagum, or of the roots of the Spinal Accessory, 
 from which their motor power is derived (as will be hereafter explained), but 
 also by stimulating the roots of the first two Cervical nerves ; and the lower 
 * 
 
REFLEX ACTIONS. MOVEMENTS OF STOMACH. 303 
 
 part of the oesophagus in the neck is made to contract peristaltically from 
 above downwards, by irritation of the roots of the first three Cervical nerves, 
 and of the cervical portion of the Sympathetic, through which last the former 
 evidently operate. The thoracic portion of the O3sophagus is made to con- 
 tract, by irritation of the lowest Sympathetic ganglion of the neck, and of 
 the higher thoracic ganglia, and also of the roots of the lower Cervical spinal 
 nerves. Muscular contractions of the stomach are produced, by irritation of 
 the roots of the 4th, 5th, 6th, and 7th Cervical nerves, and of the first tho- 
 racic in the rabbit ; so that a distinct furrow is evident between the cardiac 
 and pyloric portion of the viscus ; and the lower the nerve irritated, the 
 nearer the pylorus do the contractions extend. Irritation of the first thoracic 
 ganglion of the Sympathetic produces the same effect. Contractions of the 
 intestinal tube, varying in place according to the part of the Spinal Cord ex- 
 perimented on, may be excited by irritation of the roots of the dorsal, lumbar, 
 and sacral nerves, and of the trigeminus ; and similar effects are produced by 
 irritation of the lower part of the thoracic portion, of the lumbar, and of the 
 sacral portions of the Sympathetic, also of the splanchnic, and of the gastric 
 plexus. 
 
 389. From these facts it is evident, that the movements of the Intestinal 
 tube may be influenced by the Spinal Cord ; and that what is commonly 
 termed the Sympathetic nerve, is the channel of that influence, by the fibres 
 which it derives from the Spinal system. But it by no means thence follows, 
 that the ordinary peristaltic actions of the muscles in question are dependent 
 on a stimulus reflected through the spinal cord, rather than on one directly 
 applied to themselves. It is clear that, although these movements are of the 
 first importance to the welfare of the system, such means of sustaining them 
 are feeble, compared to those which we find provided for the maintenance of 
 the distinctly-reflex actions of deglutition, respiration, &c. The difficulty 
 with which any evidence can be obtained of the connection, is a sufficient 
 proof of this. On the other hand, we do know that these peristaltic move- 
 ments are influenced by particular states of mind, or by conditions of the bodily 
 system ; and the connection just traced satisfactorily accounts for this, and is 
 itself sufficiently explained. The intestinal tube, then, from the stomach to 
 the rectum is not dependent upon the Spinal cord for its contractility, but is 
 enabled to propel its contents by its own inherent powers ; still we find that 
 here, as in other instances, the nervous centres exert a general control over 
 even the Organic functions, doubtless for the purpose of harmonizing them 
 with each other, and with the conditions of the organs of Animal life. 
 
 390. The Muscular Coat of the Bladder appears, like that of the Intestinal 
 tube, to be ordinarily excited to contraction, rather by direct stimulation than 
 by the agency of the Spinal nerves. It is not, however, altogether removed 
 from the influence of the Spinal Cord ; for the experiments of Valentin have 
 shown that a connection exists, as in the former case, through the Sympathetic 
 nerve, affecting not only the bladder but also the ureters. That physiologist 
 states, that a very distinct and powerful peristaltic action of the ureter, pro- 
 ceeding from the kidneys to the bladder, may be produced, by irritating the 
 abdominal ganglia of the Sympathetic, or the roots of the superior abdominal 
 Spinal nerves ; and that strong contractions of the bladder are excited, by irri- 
 tation of the inferior portion of the abdominal Sympathetic, but especially of 
 its sacral portion, and of the roots of the middle and inferior nerves of the 
 Spine. In these, as in former cases, no effect is produced by irritation of the 
 Spinal Nerves, unless the portion of the Sympathetic connected with the par- 
 ticular organ be entire. 
 
 391. On examining the outlets by which the excretions are voided, we find 
 that they are placed, like the entrances, under the guardianship of the Spinal 
 Cord; subject, however, to some control on the part of the Will. In the 
 
304 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 lowest animals, the act of discharging excrementitious matter is probably as 
 involuntary, as are the acts immediately concerned in the introduction of nu- 
 triment ; and it is performed as often as there is anything to be got rid of. 
 In the higher classes, however, such discharges are much less frequent ; and 
 reservoirs are provided, in which the excrementitious matter may accumulate 
 in the intervals. The associated movements required to empty these, are 
 completely involuntary in their character ; and are excited by the quantity, 
 or stimulating quality, of the contents of the reservoir. But, had volition no 
 control over them, great inconveniences would ensue ; hence sensation is ex- 
 cited by the same stimulus, which produces the movements; in order that, 
 by arousing the will, the otherwise involuntary motions may be restrained 
 and directed. There can be little doubt, from the experiments of Dr. M. 
 Hall, as well as from other considerations, that the associated movements, by 
 which the contents of the rectum and bladder are discharged, correspond 
 much with those of Respiration ; being in their own nature excito-motor, but 
 capable of a certain degree of voluntary restraint and assistance. The acts 
 of Defecation and Urination chiefly depend upon the combined contraction 
 of the abdominal muscles, similar to that which is concerned in the expiratory 
 movement ; but, the glottis being closed, and the diaphragm fixed, the expulsor 
 power is restricted to the contents of the abdominal cavity ; and so long as the 
 sphincter of the cardia remains closed, the force must act downwards, upon 
 the walls of the rectum and bladder, the contents of the one or the other of 
 these cavities, or of both, being expelled, according to the condition of their 
 respective sphincters. These actions are doubtless assisted by the contrac- 
 tion of the walls of the rectum and bladder themselves; for we sometimes find 
 their agency sufficient to expel the contents of the cavities, when there is a 
 total paralysis of the ordinary expulsors, provided that the sphincters be at 
 the same time sufficiently relaxed. This is more especially the case, when 
 their power is augmented by increased nutrition. For example, in many 
 cases of disease or injury of the Spinal Cord, the bladder ceases to expel 
 its contents, through the interruption of the circle of reflex actions ; but after 
 a time, the necessity for drawing off the urine by the catheter is found to 
 exist no longer; the fluid is constantly expelled as soon as it has accumulated 
 in small quantities. In such cases, the mucous coat is found after death to 
 be thickened and inflamed; and the muscular coat to be greatly increased in 
 strength, and contracted upon itself. It would seem, then, that the abnormal 
 irritability of the mucous membrane, and the increased nutrition of the mus- 
 cular substance which appears consequent upon it, enable the latter to expel 
 the urine without the assistance of the ordinary expulsors. 
 
 392. On the other hand, the sphincters which antagonize the expellent ac- 
 tion, are usually maintained in a state of moderate contraction, so as to afford 
 a constant check to the egress of the contents of the cavities ; and this con- 
 dition has been fully proved by Dr. M. Hall, to result from their connection 
 with the Spinal Cord, ceasing completely when this is interrupted. But the 
 sphincters are certainly in part controlled by the will, and are made to act in 
 obedience to the warning given by sensation ; and this voluntary power is 
 frequently destroyed by injuries of the Brain, whilst the Spinal Cord remains 
 able to perform all its own functions, so that discharge of the urine and 
 fa3ces occurs. In their moderate action, the expulsors and the sphincters 
 may be regarded as balancing one another, so far as their reflex action is 
 concerned, the latter having rather the predominance, so as to restrain the 
 operation of the former. But, when the quantity or quality of the contents 
 of the cavity gives an excessive stimulus to the former, their action pre- 
 dominates, unless the will is put in force to strengthen the resistance of 
 the sphincter ; this we are frequently experiencing, sometimes to our great 
 
REFLEX ACTIONS. MOVEMENTS OF GENITAL ORGANS, ETC. 305 
 
 discomfort. On the other hand, if the stimulus is deficient, the will must 
 aid the expulsors, in order to overcome that resistance which is due to the 
 reflex contraction of the sphincters; of this also we may convince ourselves, 
 when a sense of propriety, or a prospective regard to convenience, occasions 
 us to evacuate the contents of the rectum or bladder without a natural call to 
 do so. 
 
 393. Movements of the Genital Organs. The muscular contractions in- 
 volved in the Emissio Seminis are clearly of a reflex nature ; being inde- 
 pendent of the will and not capable of restraint by it, when once fully excited; 
 and being producible in no other way, than (like those concerned in Degluti- 
 tion) by a particular local irritation. That this irritation need not amount to 
 a sensation, is proved by cases already referred to ( 372) ; and it has been 
 also shown by experiment, that section of the Spinal Cord in the lumbar 
 region does not prevent the act from being performed, the lower division only 
 being concerned in the reflexion of the impression. It further appears, from 
 the experiments of Valentin, that the Spinal Cord may operate on the Genital 
 organs through the Sympathetic system. Contractions were excited in the 
 vas deferens vesiculae seminales, especially of the Guinea Pig at the time of 
 heat, by irritation of the inferior lumbar and highest sacral portions of the 
 Sympathetic; and the Fallopian tubes, as well as the Uterus itself, may be 
 excited to contraction, by irritation of the same nerves as those which excite 
 the rectum, namely, the lower lumbar and first sacral nerves of the Spine. 
 This last fact is important, in regard to the rationale of the operation of certain 
 medicines, such as aloes, which are known to have an influence on both 
 parts. In regard to the act of Parturition, there would seem reason to believe, 
 from the evidence of cases of paraplegia, that, of-the muscles whose operation 
 is associated in it, the diaphragm, abdominal muscles, &c., are called into 
 action (as in defecation) through the Spinal Cord ; but that the contractions 
 of the Uterus itself are but little dependent on its connection with the nervous 
 centres. Of the reason why the muscles, which were up to that time inert, 
 should then combine in this extraordinary mariner, and with such remarkable 
 energy, Physiology can afford no certain information. There can be little 
 doubt, however, that the stimulus usually originates in the uterus, or in some 
 of the neighbouring organs which are incommoded by the pressure ; but it 
 may also result from some condition of the general system, in which the 
 uterus itself is but little concerned. It is an interesting fact, which has been 
 more than once observed, that the foetus may be expelled from the dying body 
 of the mother, even after the respiratory movements have ceased. This would 
 appear due to the contraction of the Uterine fibres alone, which, like those of 
 the heart and alimentary canal, retain their irritability longer than those ot 
 the muscles supplied by the cerebro-spinal nerves; and, the power of these 
 would be unopposed by the resistance which they ordinarily have to en- 
 counter ; since the tension of all the muscles surrounding the outlet would be 
 destroyed, by the cessation of the activity of the Spinal system of nerves 
 (398). 
 
 394. Protecting Agency of the Spinal Cord. From the foregoing details 
 it appears, that one of the chief functions of the Spinal Cord is to control the 
 orifices of the various open cavities of the body; and this function evidently 
 has safety, as well as convenience, in view. It has been manifestly designed 
 by the All-wise Creator, that the Glottis should close against agents injurious 
 to the organs within; and that the effort to vomit should be excited by the 
 attempt to swallow substances so nauseous as to induce loathing. There is 
 another protective influence exerted by it, of a still more remarkable nature. 
 It has been ascertained by Dr. M. Hall that, if the functions of the Brain be 
 suspended or destroyed, without injury to the Spinal system of nerves, the 
 
 26* 
 
306 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Orbicularis muscle will contract, so as to occasion the closure of the eyelids, 
 upon the tarsal margin being touched with a feather. This fact is interesting 
 in several points of view. In the first place, it is a characteristic example of 
 pure reflex action ; occurring under circumstances in which volition cannot be 
 imagined to guide it, and in which there is no valid reason to believe that sen- 
 sation directs it. Further, it explains the almost irresistible nature of the tend- 
 ency to winking, which is performed at short intervals by the contraction of the 
 Orbicularis muscle; this is evidently a Spinal action, capable of being in some 
 degree restrained (like that of respiration) by the will, but only until such time 
 as the stimulus (resulting perhaps from the -collection of minute particles of 
 dust upon the eyes, or from the dryness of its surface in consequence of 
 evaporation), becomes too strong to be any longer resisted. Again, we have 
 in sleep or in apoplexy an example of this purely spinal action, unbalanced 
 by the influence of the will, which, in the waking state, antagonizes it by 
 calling -the levator palpebra into action. As soon as the will ceases to act, the 
 lids droop, and close over the eye in order to protect it; and if those of a 
 sleeping person be separated by the hand, they will be found presently to 
 return. Here, as in studying the respiratory and other movements, we are 
 led to perceive, that it is the Brain alone, which is torpid during sleep, and 
 whose functions are affected by this torpidity. As Dr. M. Hall very justly 
 remarks, the Spinal system never sleeps; it is constantly in activity; and it is 
 thus that, in all periods and phases of Life, the movements which are essential 
 to its continued maintenance are kept up without sensible effort. 
 
 395. The closure of the Pupil against a strong light, is another movement 
 of the same protective tendency. The channel, through which that just 
 named is performed, is completed by the first branch of the Fifth and the 
 Portio Dura of the seventh. The contraction of the pupil is immediately 
 caused by the Third pair, or Motor Oculi; as is easily shown by irritating the 
 trunk of that nerve and observing the result. But it is not easy to speak with 
 certainty as to the afferent nerve, by which the motor influence is excited. 
 Although the contraction of the pupil is usually in close accordance with the 
 sensation occasioned by the impression of light upon the retina, yet there is 
 no want of evidence to prove that the sensation of light is not always neces- 
 sary ; for, even when the sight of both eyes has been entirely destroyed by 
 amaurosis, the regular actions have been witnessed in the pupil, in accordance 
 with varying degrees of light impinging on the retina. This fact may be 
 explained in two ways. It may either be imagined that the requisite stimulus 
 is not that of light conveyed through the Optic nerve ; but that of heat con- 
 veyed through the ophthalmic branch of the Fifth pair. Or it may be still 
 supposed, that the motion results from an impression upon the retina, which 
 impression, being conducted to the Sensorium, ordinarily produces a sensation; 
 whilst in these curious cases, no sensation is produced, on account of a dis- 
 ordered state of the part of the ganglionic centre in which the Optic nerve 
 terminates; though some filaments of that nerve, being connected with the 
 Third pair by means of a distinct tract of vesicular matter, can produce a 
 reflex action through it, although no sensation intervene. In either view, the 
 rarity of the occurrence is at once accounted for ; since in most cases of 
 amaurosis, the disease lies in the trunk of the nerve, and thereby checks both 
 its spinal and its encephalic actions. 
 
 396. The Physiologist has not at present any knowledge of any similar 
 protective movements, in the Human being, designed to keep the organ of Hear- 
 ing from injury ; but there can be little doubt that those which we are constantly 
 witnessing in other animals, possessing large external ears, are reflex actions 
 excited by the irritation applied to them. In regard to the Nose, we find a 
 remarkably complex action that of Sneezing adapted to drive off" any cause 
 
REFLEX ACTIONS. MOVEMENTS OF LOCOMOTION. 307 
 
 of irritation ( 381). It will hereafter be shown that the stimulus is conveyed, 
 in this case, not through the Olfactory nerve, but through the Fifth pair; so 
 that it is not dependent upon the excitement of the sensation of Smell. The 
 act of Coughing, also, may be regarded as of a protective character ; being 
 destined to remove sources of irritation from the air-passages. The automatic 
 movements, performed by the limbs of Frogs and other animals, when their 
 connection with the brain has been cut off ( 306, 370) appear destined to 
 remove these parts from sources of irritation or injury; and they may thus be 
 rightly placed under the same category. 
 
 397. Movements of Locomotion. Lastly, we have to inquire how far the 
 Reflex function of the Spinal Qord is concerned in the locomotive -actions of 
 
 "the lower extremities in Man. It will be remembered that, in the Dytiscus 
 whose head had been removed ( 328), the stimulus of the contact of water 
 immediately excited regular and continued locomotive actions which lasted 
 for some time. So in the cases already quoted ( 366- 368), when the con- 
 trol of the will over the lower extremities was lost, powerful muscular actions 
 were excited in them, through the Spinal Cord alone. In the healthy con- 
 dition of the Human system, when the Will is controlling all the movements, 
 which are not immediately concerned in the maintenance and regulation of 
 the organic functions, no such actions can be excited : but in proportion as its 
 control is lost, does the independent power of the Spinal Cord manifest itself. 
 The more such actions are of a simple rhythmical character, similar to those 
 of Respiration, the more does it seem that they may with probability be re- 
 ferred to the Spinal system ; and if we attribute to this (as we can scarcely 
 help doing) the rapid vibration of the wings of Insects, there seems no reason 
 why we should riot extend the same view to the wings of Birds. Such an 
 explanation of their movements will account for their occasional continuance, 
 without apparent fatigue, during a period through which no known voluntary 
 effort can endure; for it is one of the attributes of the Spinal system of 
 nerves, well pointed out by Dr. M. Hall, that the exercise of the muscles 
 excited by it does not occasion fatigue, the sense of which is Cerebral only. 
 It would seem to the Author more probable, however, that those movements 
 which guide the body, and which must themselves be directed by Sensation, 
 are to be referred to a class intermediate between the Voluntary and the Re- 
 flex, which may be properly termed Consensual. Numerous actions, in Man, 
 which were at first Voluntary, appear, at last to be performed as instinctively 
 or intuitively, as they are in the lower animals from the commencement of 
 their existence. (See the next Section.) 
 
 398. Influence on Muscular Tension. The various muscles of the body, 
 even when there is the most complete absence of effort, maintain, in the 
 healthy state of the system, a certain degree of firmness, by their antagonism 
 with each other ; and if any set of muscles be completely paralyzed, the op- 
 posing muscles will draw the part on which they act, out of its position of 
 repose ; as is well seen in the distortion of the face, which is characteristic 
 of paralysis of the facial nerve on one side. This condition has been desig- 
 nated as the tone of the Muscles ; but this term renders it liable to be con- 
 founded with their tonic contraction, which is also concerned in maintaining 
 their firmness, but which operates in a very different manner. The latter is 
 dependent upon the simple contractility of the muscle ; and is exhibited alike 
 by the striated and the non-striated forms of muscular fibre, but more espe- 
 cially by the latter ( 593). On the other hand, the condition now alluded to, 
 which may perhaps be appropriately termed their tension, is the result of a 
 moderate though continued excitement of that contractility, through the nerv- 
 ous centres. It has been proved by Dr. M. Hall, that the Muscular Tension 
 is not dependent upon the influence of the Brain ; but upon that of the Spinal 
 
308 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Cord ; as the following experiments demonstrate. " Two Rabbits were taken ; 
 from one the head was removed ; from the other also the head was removed, 
 and the spinal marrow was cautiously destroyed with a sharp instrument: the 
 limbs of the former retained a certain degree of firmness and elasticity; 
 those of the second were perfectly lax." Again : " The limbs and tail of a 
 decapitated Turtle possessed a certain degree of firmness or tone, recoiled on 
 being drawn from their position, and moved with energy on the application of 
 a stimulus. On withdrawing the spinal marrow gently out of its canal, all 
 these phenomena ceased. The limbs were no longer obedient to stimuli, and 
 became perfectly flaccid, having lost all their resilience. The sphincter lost 
 its circular form and contracted state, becoming lax, flaccid, and shapeless. - 
 The tail was flaccid, and unmoved on the application of stimuli." It is further* 
 remarked by Messrs. Todd and Bowman, that ' a decapitated frog will con- 
 tinue in the sitting posture through the influence of the spinal cord ; but im- 
 mediately this organ is removed, the limbs fall apart." 
 
 399. This operation of the Spinal Cord is doubtless but a peculiar mani- 
 festation of its ordinary reflex function. We shall hereafter see (Section 5) 
 how much the influence of the will in producing the active contraction of a 
 muscle, is connected with sensations received from it; and it seems highly 
 probable, that the impression of the state of the muscle, conveyed by the 
 afferent fibres proceeding from it to the spinal cord, is sufficient to excite this 
 state of moderate tension through the motor nerves, arising from the latter. 
 Such a view derives probability from the fact, which must have fallen under 
 the observation of almost every one, that most reflex actions become increased 
 in energy if resistance is made to them. Of this we have familiar examples 
 in the action of the expulsor muscles, which operate in defecation, urination, 
 and parturition, if, when they are strongly excited, their efforts be opposed 
 by the will acting on the sphincters, or by mechanical means. Many forms 
 of convulsive movement exhibit the same tendency ; their violence being pro- 
 portional to the mechanical force used to restrain them.* Here it is evident 
 that the impression of resistance, conveyed to the Spinal Cord, is the source 
 of the increased energy of its motor influence ; from which we may fairly 
 infer that the moderate resistance, occasioned by the natural antagonism of the 
 muscles, is the source of their continued and moderate tension, whilst they 
 are under the influence of the Spinal Cord. This constant though gentle 
 action serves to keep up the nutrition ef the muscles, which are paralyzed to 
 the will ; and this is still more completely maintained, if the portion of the 
 nervous centres, with which they remain connected, is so unduly irritable, 
 that the muscles are called into contraction upon the slightest excitation, and 
 are thus continually exhibiting twitchings, starlings, or more powerful convuls- 
 ive movements. It is upon the state of nutrition of the muscles, that their 
 contractility depends, as will be shown hereafter ( 588) ; and hence the 
 Spinal Cord has an indirect influence upon this peculiar property, which is 
 more likely to be retained, when the muscle is still subject to the influence of 
 the Spinal Cord, though cut off from that of the Brain, than when it is com- 
 pletely paralyzed by the entire cessation of the influence of the nervous 
 centres. 
 
 400. Pathological Phenomena. It would not be right to conclude this 
 account of the principal functions of the Spinal Cord, without adverting to 
 some of the leading Pathological applications of the physiological doctrines 
 
 * Hence the absurdity of the common practice of endeavouring to prevent the move- 
 ments of the limbs and tody, in convulsive paroxysms, by mechanical constraint. Nothing 
 should be attempted but what is requisite to prevent the sufferer from doing himself an in- 
 jury. 
 
REFLEX ACTIONS. PATHOLOGICAL PHENOMENA. 309 
 
 which have been developed in it; although they will hereafter be passed 
 under a more general review (Section 8). A large part of these were first 
 pointed out by Dr. M. Hall;* and they are receiving continual and important 
 extensions from his own labours and those of other practical inquirers. It 
 may be remarked, in the first place, that the power of the whole Spinal sys- 
 tem is capable of being morbidly diminished or augmented. It may even be 
 for a time almost completely suspended, as in Syncope ; which state may be 
 induced by sudden and violent impressions, either of a mental or physical 
 nature, that operate upon the whole nervous system at once, commencing, 
 however, in the brain. It is to be remarked that, in recovering from these, it 
 is the Spinal system of which the activity is first renewed, the respiratory 
 movements recommencing, and the power of swallowing being restored, 
 before any voluntary actions can be performed. A corresponding state may 
 be induced in particular portions of the system by concussion ; as is seen in 
 severe injuries of the Spinal Cord, which are almost invariably followed for 
 a time by the suspension of its functions. Again, the power of the whole 
 Spinal Cord may be diminished by various causes, such as enfeebled circula- 
 tion, pressure, &c. ; and then we have torpidity of the whole muscular sys- 
 tem. If oppression exists in the Brain, the functions of the Medulla oblon- 
 gata will be especially affected; and if it be prolonged and sufficiently severe, 
 Asphyxia will result from the interruption of the respiratory movements which 
 it occasions. 
 
 401. On the other hand, the excitability of the whole Cord, or of particu- 
 lar parts of it, may be .morbidly increased. This is especially seen in ordi- 
 nary Tetanus and the artificial Tetanus induced by Strychnine; in which the 
 slightest external stimulus is sufficient to induce reflex actions in their most 
 terrific forms. It is interesting to remark, that in this formidable disease the 
 functions of the muscles controlling the various orifices are those most affected ; 
 and it is by the spasms affecting the organs of respiration or deglutition, that 
 life is commonly terminated. Various remedial agents will probably be found 
 to operate, by occasioning increased excitability in some particular segments 
 of the Cord; so that the usual stimuli applied to the parts connected with 
 these, will occasion increased muscular tension. This seems to be the case, 
 for example, in regard to the influence of aloes on the rectum and uterus, 
 cantharides on the neck of the bladder and adjoining parts, and secale cornu- 
 tum on the uterus. The mode of influence of cantharides is illustrated by a 
 curious case, related by Dr. M. Hall, of a young lady who lost the power of 
 retention of urine, in consequence of a fatty tumour in the spinal canal, which 
 gradually severed the Spinal Cord, and induced paraplegia. The power of 
 retaining the urine was always restored for a time by a dose of tincture 
 of cantharides, which augmented the excitability of the segment of the cord, 
 with which the sphincter vesica3 is connected. The researches of Valentin, 
 when grafted (as it were) on the doctrines of Dr. M. Hall, afford the key to 
 the explanation of the numberless sympathetic influences of the organs of 
 nutrition, &c., upon one another; by showing that they are all connected with 
 the Spinal Cord ; and that the muscular structure, with which they are all 
 provided, may be excited to contraction through it. And, lastly, the more 
 recent observations of Dr. M. Hall, in regard to the peculiar excitor power 
 that belongs to the nervous fibres distributed on various serous and fibrous 
 membranes, will probably lead, when they have been fully carried out, to the 
 explanation of the various convulsive actions, that result from pressure or 
 irritation affecting these parts. 
 
 * See especially his Treatise on the Diseases and Derangements of the Nervous System. 
 
310 FUNCTIONS OF THE NEllVOUS SYSTEM. 
 
 a. It has been pointed out by Messrs. Todd and Bowman (Physiological Anatomy, Vol. I. 
 p. 315), that the Spinal Cord of the male frog, at the season of copulation, naturally pos- 
 sesses a state of most extraordinary excitability. The thumb of each anterior extremity at 
 this season, becomes considerably enlarged; as is well known to Naturalists. " This enlarge- 
 ment is caused principally by a considerable development of the papillary structure of the 
 skin which covers it; so that large papillas are formed all over it. A male frog, at this 
 season, has an irresistible propensity to cling to any object, by seizing it between his anterior 
 extremities. It is in this way that he seizes upon, and clings to the female ; fixing his 
 thumbs to each side of her abdomen, and remaining there for weeks, until the ova have been 
 completely expelled. An effort of the Will alone could not keep up the grasp uninterrupt- 
 edly for so long a time, yet so firm is the hold, that it can with difficulty be relaxed. What- 
 ever is brought in the way of the thumbs, will be caught by the forcible contraction of the 
 anterior limbs ; and hence we often find frogs clinging blindly to a piece of wood, or a dead 
 fish, or some other substance which they may chance to meet with. If the finger be placed 
 between the, anterior extremities, they will grasp it firmly ; nor will they relax their grasp 
 until they are separated by force. If the animal be decapitated, whilst the finger is within 
 the grasp of its anterior extremities, they still continue to hold on firmly. The posterior half 
 of the body may be cut away, and yet the anterior extremities will still cling to the finger; 
 but immediately that the segment of the cord, from which the anterior extremities derive 
 their nerves, has been removed, all their motion ceases. This curious instinct only exists 
 during the period of sexual excitement; for at other periods the excitability of the anterior 
 extremities is considerably less than that of the posterior." 
 
 402. Nerves of the Spinal System. The nerves which minister to the 
 functions of the Spinal Cord, conveying to it the impressions made on the 
 periphery, and transmitting its motor influence to the muscles, are not those 
 alone which are ordinarily designated as Spinal nerves; for several of those, 
 which pass forth through the base of the cranium, and which are commonly 
 described as Cephalic nerves, belong to the same category. The general 
 characters of the Spinal nerves, their mode of connection with the Spinal 
 Cord by two sets of roots, and the presence of ganglion upon the posterior 
 root, have already been adverted to ( 344). The anterior roots are usually 
 the smaller ; and this is particularly the case with those of the cervical nerves, 
 in which the posterior roots are of remarkable comparative size. In the First 
 Cervical or Sub-occipital pair, the anterior roots are sometimes wanting ; but 
 there is then a derivation of fibres from the Spinal Accessory, or from the 
 Hypoglossal, or from both. The two roots of the ordinary Spinal nerves 
 unite immediately beyond the ganglion, which is situated on the posterior one; 
 and the trunk thus formed separates immediately into two divisions, the an- 
 terior and posterior, each of which Contains both afferent and motor fibres. 
 These divisions, of which the anterior is by far the larger, proceed to the ante- 
 rior and posterior parts of the body respectively ; and are chiefly distributed to 
 the skin and the muscles. The anterior branch is that which communicates 
 with the sympathetic nerve. 
 
 403. The pair of nerves commonly designated as the Fifth of the Cephalic 
 series, or as the Trifacial, is the one which more nearly resembles the ordi- 
 nary Spinal nerves (as was long since pointed out by Sir C. Bell), than does 
 any other of those originating within the cranium. It possesses two distinct 
 sets of roots, of which one is much larger than the other ; on the larger root, 
 as on the posterior and larger root of the Spinal nerves, is a distinct ganglion; 
 and the fibres arising from the smaller root do not blend with the others, until 
 after the latter have passed through this ganglion. The trunk of the nerve 
 separates, as is well known, into three divisions, the Ophthalmic, the Supe- 
 rior Maxillary, and the Inferior Maxillary ; and it can be easily shown, by 
 careful dissection, that the fibres of the smaller root pass into the last of these 
 divisions alone. When the distribution of this nerve is carefully examined, 
 it is found that the first and second divisions of it proceed almost entirely to 
 the skin and mucous surfaces ; a very small proportion, only, of their fibres 
 being lost in the muscles : whilst of the branches of the third division, a large 
 number are distinctly muscular. Hence analogy, and the facts supplied by 
 
SPINAL NERVES. FIFTH PAIR, OR TRIFACIAL. 
 
 311 
 
 anatomical research, would lead to the conclusion, that the first two divisions 
 are nerves of sensation only, and that the third division combines sensory and 
 motor endowments. Such an inference is fully borne out by experiment. 
 When the whole trunk is divided within the cranium by the penetration of a 
 sharp instrument (which Magendie, by frequent practice, has been able to ac- 
 complish), evident signs of acute pain are given. After the incision has been 
 made through the skin, the animal remains quiet until the nerve is touched ; 
 and when it is pressed or divided, doleful cries are uttered, which continue 
 for some time, showing the painful effect of the irritated state of the cut ex- 
 tremity. The common sensibility of all the parts supplied by this nerve is 
 entirely destroyed on the affected side. The jaw does not hang loosely, be- 
 cause it is partly kept up by the muscles of the other side ; but it falls in a 
 slight degree ; and its movements are seen, when carefully observed, to be 
 somewhat oblique. If the trunk be divided on each side, the whole head is 
 deprived of sensibility ; and the animal carries it in a curious vacillating man- 
 ner, as if it were a foreign body. 
 
 Fig. 150. 
 
 A diagram showing the Fifth pair of nerves with its branches. 1. The origin of the nerve by two roots, 
 2. The nerve escaping from the crus cerebelli. 3. The Gasserian ganglion. 4. Its ophthalmic division. 
 5. The frontal nerve, giving off the supra-trochlear branch, and escaping on the forehead through the 
 supra-orbital foramen. 6. The lachrymal nerve. 7. The nasal nerve, passing at 8 through the anterior 
 ethmoidal foramen, and giving off the infra- trochlear branch. 9. The communication of the nasal nerve 
 with the ciliary ganglion. 10. A small portion of the third nerve with which the ganglion is seen com- 
 municating; the ganglion gives off the ciliary branches from its anterior aspect. 11. The superior maxil- 
 lary nerve. 12. Its orbital branch. 13. The two branches communicating with Meckel's ganglion ; the 
 three branches given off from the lower part of the ganglion are the posterior palatine nerves. 14, 14. 
 The superior dental nerves, posterior, middle, and anterior. 15. The infra-orbital branches distributed 
 upon the cheek. 16. The inferior maxillary nerve. 17. Its anterior or muscular trunk. 18. The pos- 
 terior trunk ; the two divisions are separated by an arrow. 19. The gustatory nerve. 20. The corda 
 tympani joining it at an acute angle. 21. The submaxillary ganglion. 22. The inferior dental nerve. 
 23. Its mylo-hyoidean branch. 24. The auricular nerve, dividing behind the articulation of the lower 
 jaw, to reunite and form a single trunk. 25. Its branch of communication with the facial nerve. 26. Its 
 temporal branch. 
 
 404. If the anterior or Ophthalmic branch only be divided, all the parts 
 supplied by it are found to have lost their sensibility, but their motions are 
 unimpaired ; and all experiments and pathological observations concur in at- 
 
312 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 tributing to it sensory endowments only. The only apparent exception is in 
 the case of the Naso-Ciliary branch; since there is good reason to believe that 
 the long root of the ciliary ganglion, and the long ciliary nerves, possess motor 
 
 [Fig. 151. 
 
 A view of the distribution of the Trifacial or Fifth 
 pair; 1, orbit; 2, antrum highmorianum ; 3, tongue; 
 4, lower jaw-bone; 5, root of the fifth pair, forming 
 the ganglion of Gasser ; 6, first branch of the fifth pair, 
 or ophthalmic ; 7, second branch of the fifth pair, or 
 superior maxillary ; 8, third branch of the fifth pair, or 
 inferior maxillary ; 9, frontal branch, dividing into ex- 
 ternal and internal frontal nerves; 10, lachrymal 
 branch of the fifth pair ; 11, nasal branch ; just under 
 the figure is the long root of the lenticular or ciliary 
 ganglion and a few of the ciliary nerves; 12, internal 
 nasal nerve, disappearing through the anterior eth- 
 moidal foramen; 13, external nasal nerve; 14, external 
 and internal frontal nerve ; 15, infra-orbitary nerve ; 
 16, posterior dental branches ; 17, middle dental 
 branch; 18, anterior dental nerve: 19, terminating 
 branches of the infra-orbital nerve,*called the labial 
 and palpebral nerves; 20, subcutaneous malae, oror- 
 bitar branch ; 21, pterygoid, or recurrent nerve, from 
 Meckel's ganglion; 22, five anterior branches of the 
 third branch of the fifth pair; 23, lingual branch of the 
 fifth, joined by the chorda tympani ; 24, inferior dental 
 nerve ; 25, its mental branches ; 26, superficial tempo- 
 ral nerve; 27, auricular branches; 28, mylo-hyoid 
 branch.] 
 
 powers ; but these appear to be derived from the Sympathetic nerve. When 
 the whole nerve, or its anterior branch, is divided in the rabbit, the pupil is 
 exceedingly contracted, and remains immovable ; but in dogs and pigeons it 
 is dilated. The pupil of the other eye is scarcely affected ; or, if its dimen- 
 sions be changed, it soon returns to its natural state. The eyeball speedily 
 becomes inflamed, however; and the inflammation usually runs on to suppu- 
 ration and complete disorganization. The commencement of these changes 
 may be commonly noticed within twenty-four hours after the operation ; and 
 they appear to be due to the want of the protective secretion, which (as will 
 be explained when the direct influence of the nervous system upon the organic 
 functions is considered), is necessary to keep the mucous surface of the eye 
 in its healthy condition, and which is not formed when the sensibility of that 
 surface is destroyed. The Superior Maxillary branch, considered in itself, 
 is equally destitute of motor endowments with the ophthalmic ; but its con- 
 nections with other nerves, through the spheno-palatine ganglion and its anas- 
 tomosing twigs, may introduce a few motor fibres into it. The Inferior 
 Maxillary branch is the only one which possesses motor as well as sensory 
 endowments from its origin; but its different subdivisions possess these endow- 
 ments in varying proportions, some being almost exclusively motor, and others 
 as completely of a sensory character. The latter is probably the nature of 
 the Lingual branch ; and there seems good reason to believe, as will hereafter 
 be shown, that this ministers not only to the tactile sensibility of the tongue, 
 but to the sense of Taste. The muscles put in action by this division of the 
 Fifth pair, are solely those concerned in the masticatory movements. 
 
 405. The Third, Fourth, and Sixth pairs, together make up the appara- 
 tus of motor nerves, by which the muscles of the Orbit are called into ac- 
 tion. The Third pair supplies the greater number of the muscles ; the Fourth 
 
CRANIAL NERVES. THIRD TO SEVENTH. 
 
 313 
 
 being confined to the superior ob- [Fig. 152. 
 
 lique, and the Sixth to the abdu- 
 cens. Of these nerves, the Third 
 pair is the only one which exhibits 
 any appearance of sensibility, when 
 its trunk is irritated ; but this sen- 
 sibility is not nearly so great as 
 that of the Fifth pair ; and it may 
 be doubted whether it is really pos- 
 sessed by the Third, in virtue of 
 its direct connection with the nerv- 
 ous centres, or whether it is not 
 imparted by the anastomosis of that 
 nerve with the Fifth, some fila- 
 ments of which may pass back- 
 wards as well as forwards, so as to 
 confer sensibility on the trunk of 
 the Third, above as well as beyond 
 their point of entrance. The pe- 
 culiar mode in which these motor 
 nerves ordinarily excite the mus- 
 cles to action, will be considered 
 in the next Section. Although 
 commonly ranked as cephalic 
 nerves, they have no direct con- 
 nection with the Cerebrum ; their 
 real origin being from the upper 
 part of the Medulla Oblongata, and 
 those prolongations of it which are 
 known as the Crura Cerebri. The 
 
 roots of the Third pair may be traced into direct connection with the Cor- 
 pora Quadrigemina; a fact of considerable physiological importance, as will 
 hereafter appear. The chief actions of a purely reflex nature, to which this 
 group of nerves ordinarily ministers, are the government of the diameter of 
 the pupil, which is accomplished through the Third pair ; and the rolling of 
 the eyeball beneath the upper lid during sleep, as well as in the efforts of 
 sneezing, coughing, &c. But irregular movements of the eyeballs, which 
 must be referred to the same group, are continually seen to accompany various 
 other forms of convulsive action. 
 
 406. The Portio Dura of the Seventh pair, or Facial nerve, has been 
 supposed, since the first researches of Sir C. Bell, to be a nerve of motion 
 only ; but some recent physiologists have maintained, that it both possesses 
 sensory endowments, and arises by a double root. According to Valentin, 
 however, who experimented on the roots exposed within the cranium, it pos- 
 sesses no sensory endowments at its origin ; since, when these roots were 
 touched, the animals gave no signs of pain, though violent muscular move- 
 ments were excited in the face. Subsequently to its first entrance into the 
 canal by which it emerges, however, it anastomoses with other nerves ; and 
 thus sensory fibres are introduced into it from many different sources, ante- 
 riorly, from the Fifth pair, and posteriorly, from the Cervical nerves, which 
 cause irritation of several of its branches to produce pain. The number 
 and situation of the anastomoses vary much in different animals ; so that it 
 is impossible to make any very comprehensive statement in regard to them. 
 Experimental researches leave no doubt that the Portio Dura is the general 
 motor nerve of the face ; ministering to the influence of volition and Emo- 
 27 
 
 A view ofthe Third, Fourth and Sixth pairs of 
 Nerves; 1, ball ofthe eye and rectus externus muscle; 
 2, the superior maxilla; 3, the third pair, or motores 
 oculi, distributed to all the muscles of the eye except 
 the superior oblique and external rectus; 4, the fourth 
 pair, or pathetici. going to the superior oblique muscle; 
 5, one of the branches of the seventh pair ; 6, the sixth 
 pair, or motor externus, distributed to the external 
 rectus muscle ; 7, spheno-palatine ganglion and 
 branches; 8, ciliary nerves from the lenticular gan- 
 glion, the short root of which is seen to connect it with 
 the third pair.] 
 
314 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Fig. 153. 
 
 The distribution of the Facialjierve, and the branches of the Cervical plexus. 1 .The facial nerve, 
 escaping from the stylo-mastoid foramen, and crossing the ramus of the lower jaw; the parotid gland 
 has been removed in order to see the nerve more distinctly. 2. The posterior auricular branch; the 
 digastric and stylo-mastoid filaments are seen near the origin of this branch. 3. Temporal branches, 
 communicating with (4) the branches of the frontal nerve. 5. Facial branches, communicating with 
 (6) the infra-orbital nerve. 7. Facial branches, communicating with (8) the mental nerve. 9. Cervico- 
 facial branches, communicating with (10) the superficialis colli nerve, and forming a plexus (11) over 
 the sub-maxillary gland. The distribution of the branches of the facial in a radiated direction over the 
 side of the face, constitutes the pes anserinus. 12. The auricularius magnus nerve, one of the ascending 
 branches of the cervical plexus. 13. The occipitalis minor, ascending along the posterior border of the 
 sterno-mastoid muscle. 14. The superficial and deep descending branches of the cervical plexus. 15. 
 The spinal accessory nerve, giving oft' a branch to the external surface of the trapezius muscle. 16. 
 The occipitalis major nerve, the posterior branch of the second cervical nerve. 
 
 tion, and also being the channel of the Reflex movements concerned in respi- 
 ration and other associated movements of the muscles ; but not being in the 
 least concerned in the act of mastication. 
 
 a. The distinctness of the Spinal and Encephalic actions of this nerve, is made evident 
 by the not unfrequent occurrence of paralysis in either of them, without the other being 
 affected. Thus we may see the mouth drawn to one side (in consequence of the loss of 
 tone, which the muscles have experienced), and all the Reflex and Emotional actions of 
 the face performed only on one side ; and yet Voluntary power may remain unaffected ; so 
 that, in ordinary winking, the lid of the affected side does not close ; though the patient can 
 shut the eye by an effort of the will. OH the other hand, the tension of the muscles may 
 remain unimpaired, and all their Reflex and Emotional actions may be performed as usual 
 and yet distortion may be at once apparent, when Voluntary actions are attempted; in con- 
 sequence of paralysis of the Cerebral portion of the nerve on one side. 
 
 407. The functions of the Glosso-Pharyngeal nerve have been heretofore 
 alluded to in part ; but there still remain several questions to be discussed in 
 regard to them. Reasons have been given for the belief that it is chiefly an 
 afferent nerve, scarcely having any direct power of exciting muscular con- 
 traction, but conveying impressions to the Medulla Oblongata, which produce 
 reflex movements of the other nerves ( 384). This view of its function has 
 been deduced by Dr. Reid from minute anatomical investigation, and from a 
 large number of experiments. Some experimenters assert, that they have 
 succeeded in exciting direct muscular actions through its trunk ; but these ac- 
 tions seem to be limited to the stylo-pharyngei and to the palato-glossi mus- 
 
FUNCTIONS OF THE PAR VAGUM. 315 
 
 cles. Much controversy has taken place on the question, whether this nerve is to 
 be regarded as ministering, partly or exclusively, to the sense of Taste ; and 
 many high authorities have ranged themselves on each side. The question 
 involves that of the function of the Lingual branch of the Fifth pair; and it is 
 partly to be decided by the anatomical relations of the two nerves respectively. 
 The glosso-pharyngeal is principally distributed on the mucous surface of the 
 fauces, and on the back of the tongue. According to Valentin, it sends a 
 branch forwards, on either side, somewhat beneath the lateral margin, which 
 supplies the edges and inferior surface of the tip of the tongue, and inosculates 
 with the Lingual branch of the Fifth pair. On the other hand, the upper sur- 
 face of the front of the tongue is supplied by this lingual branch. The experi- 
 ments of Dr. Alcock, whose conclusions are borne out by Dr. J. Reid, de- 
 cidedly support the conclusion, that the gustative sensibility of this part of 
 the tongue is due to the latter nerve, being evidently impaired by division of 
 it. Moreover, cases are by no means rare, in which the gustative sensibility 
 of the anterior part of the tongue has been destroyed, with its tactual sensi- 
 bility; when there was no reason to suppose that any other than the Fifth 
 pair of nerv.es was involved.* On the other hand, it is equally certain, that 
 the sense of taste is not destroyed by section of the Lingual nerve on each 
 side; and it seems also well ascertained, that it is impaired by section of the 
 Glosso-pharyngeal nerve. Considering how nearly allied is the sense of 
 Taste to that of Touch, and bearing in mind the respective distribution of 
 these two nerves, it does not seem difficult to arrive at the conclusion, that both 
 nerves are concerned in this function ; but there seems good reason to believe 
 the Glosso-pharyngeal to be exclusively that through which the impressions 
 made by disagreeable substances taken into the mouth are propagated to the 
 Medulla Oblongata, so as to produce nausea, and to excite efforts to vomit. 
 
 408. The functions of the Par Vagum at its roots have lately been made 
 the subject of particular examination by various experimenters ; some of 
 whom (for instance, Bischoff, Valentin, Longet, and Morgan ti), have concluded 
 that it there possesses no motor power, but is entirely a sensory, or rather, an 
 afferent nerve. According to these, if the roots be carefully separated from 
 those of the Glosso-Pharyngeal, and (which is a matter of some difficulty) 
 from those of the spinal Accessory nerve, and be then irritated, no movements 
 of the organs supplied by it can be observed ; whilst, if the roots be irritated 
 when in connection with the nervous centres, muscular contractions, evidently 
 of a reflex character, result from the irritation ; and strong evidences of their 
 sensibility are also given. It has been further asserted that, when the roots 
 of the Spinal Accessory nerve are irritated, no indications of sensation are 
 given ; but that the muscular parts supplied by the Par Vagum, as well as by 
 its own trunk, are made to contract, even when the roots are separated from 
 the nervous centres ; so that these roots must be regarded as the channel of 
 the motor influence, transmitted to them from the Medulla Oblongata. When 
 the Par Vagum swells into the jugular ganglion, an interchange of fibres takes 
 place between it and the Spinal Accessory ; and it seems clear that the pha- 
 ryngeal branches, which are among the most decidedly motor of all those 
 given off from the Pneumogastric, may in great part be traced backwards into 
 the Spinal Accessory. These statements confirm the idea of Arnold and 
 Scarpa, that the Par Vagum and Spinal Accessory are together analogous to 
 a spinal nerve, the former answering to the posterior roots, and the latter to 
 the anterior. But, on the other hand, an equally numerous and trustworthy 
 set of experimenters (among whom may be mentioned J. Reid, Miiller, Volk- 
 mann, and Stilling) are opposed to this opinion ; maintaining that the Par Va- 
 gum has motor roots of its own, and that the Spinal Accessory possesses sen- 
 
 * Romberg, in Mxiller's Archiv., 1838, Heft HI. 
 
316 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Fig. 154. [Fig. 155 . 
 
 Origin and distribution of the Eighth pair of nerves. 
 1, 3, 4, the medulla oblongala; 1, the corpus pyrami- 
 dale of one side ; 3, the corpus olivare ; 4, ihe cor- 
 pus restiforme ; 2, the pons Varolii ; 5, the facial 
 nerve ; 6, the origin of the glosso-pharyngeal nerve ; 
 7, the ganglion of Andersch ; 8, the trunk of the nerve; 
 9, the spinal accessory nerve; 10, the ganglion of the 
 pneumogastric nerve; 11, its plexiform ganglion; 
 12, its trunk; 13, its pharyngeal branch forming the 
 pharyngeal plexus (14) assisted by a branch from the 
 glosso-pharyngeal (8) and one from the superior la- 
 ryngeal nerve (15) ; 16, cardiac branches; 17, recur- 
 rent laryngeal branch ; 18, anterior pulmonary 
 branches; 19, posterior pulmonary branches; 20, 
 03sophageal plexus ; 21, gastric branches ; 22, origin 
 of the spinal accessory nerve; 23, its branches dis- 
 tributed to the sterno-mastoid muscle j 24, its branches 
 to the trapezius muscle. 
 
 A view of the distribution of the Glosso-Pha 
 ryngeal Pneumogastric and Spinal Accessory 
 Nerves, or the Eighth pair ; 1, the inferior max- 
 illary nerve; 2, the gustatory nerve; 3, the 
 chorda-tympani ; 4, the auricular nerve ; 5, its 
 communication with the portio dura; 6, the fa- 
 cial nerve coming out of the stylo-mastoid fora- 
 men ; 7, the glosso-pharyngeal nerve ; 8, branch- 
 es to the stylo-pharyngeus muscle; 9, the pha- 
 ryngeal branch of the pneumogastric nerve 
 descending to form the pharyngeal plexus; 10, 
 branches of the glosso-pharyngeal to the pha- 
 ryngeal plexus ; 11, the pneumogastric nerve , 
 12, the pharyngeal plexus ; 13, the superior la- 
 ryngeal branch ; 14, branches to the pharyngeal 
 plexus; 15, 15, communication of the superior 
 and inferior laryngeal nerves ; 16, cardiac 
 branches ; 17, cardiac branches from the right 
 pneumogastric nerve ; 18, the left cardiac gan- 
 glion and plexus ; 19, the recurrent or inferior 
 laryngeal nerve; 20, branches sent from the 
 curve of the recurrent nerve to the pulmonary 
 plexus; 21, the anterior pulmonary plexus; 22, 
 22, the oesophageal plexus.] 
 
FUNCTIONS OF THE PAR VAGUM. 317 
 
 sory roots ; and affirming that irritation of the roots of the Spinal Accessory 
 produces little or no effect on the muscles supplied by the trunk of the Par 
 Vagum. The fact appears to be, that the roots of these two nerves are so 
 commingled, that it is difficult to say what belong exclusively to each. Some 
 of the fibres usually considered to belong to the Spinal Accessory, are occa- 
 sionally seen to connect themselves with the roots of the Par Vagum, even 
 before the ganglion is found upon it. And it seems most probable, that the 
 roots of the Spinal Accessory are chiefly motor, and those of the Par Vagum 
 chiefly afferent ; that they inosculate with each other in a degree which may 
 vary in different species, and even in different individuals ; and that the Par 
 Vagum may thus derive additional motor fibres from the Spinal Accessory, 
 whilst it supplies that nerve with additional afferent fibres. In regard to its 
 trunk, there can be no doubt that the Par Vagum is to be considered as a 
 nerve of double endowments ; although it is certain that these endowments 
 are very differently distributed amongst its branches. That the nerve is capa- 
 ble of conveying those impressions which become sensations when commu- 
 nicated to the sensorium, is experimentally proved by the fact that, when its 
 trunk is pinched, the animal gives signs of acute pain ; but it is also evident 
 from the painful consciousness we occasionally have of an abnormal condition 
 of the organs which it supplies. Thus, the suspension of the respiratory 
 movements gives rise to a feeling of the greatest uneasiness, which must be 
 excited by impressions conveyed through this nerve from the lungs ; and an 
 inflamed state of the walls of the air-passages causes the contact of cold and 
 dry air to produce distressing pain and irritation. Yet, of the ordinary im- 
 pressions conveyed from these organs, which are concerned in producing the 
 respiratory movements, and in regulating the actions of the glottis, we are not 
 conscious. The same may be said of the portion of the nerve distributed 
 upon the alimentary tube. The pharyngeal branches are almost exclusively 
 motor, the afferent function being performed by the Glosso-pharyngeal ; whilst 
 the oesophageal and gastric are both afferent and motor, conveying impressions 
 which excite reflex movements in the muscles of those parts, but which do 
 not become sensations except under extraordinary circumstances. 
 
 409. The section of the Par Vagum produces, as would readily be expected, 
 great disorder of the functions of Respiration and Digestion, to which it minis- 
 ters. It is an operation which has been very frequently performed ; and the 
 statements of its results vary considerably amongst each other, being generally 
 influenced, in some degree, by the preconceived views of the experimenter.* 
 The section of the Par Vagum, when practised with the view of ascertaining 
 the influence of the nerve upon the lungs and stomach, is usually made in the 
 neck, between the origins of the superior and inferior (or recurrent) laryngeal 
 branches. Hence the muscles of the larynx are paralyzed ( 379) ; and, if the 
 animal should struggle violently, the ingress of air is likely to be obstructed 
 by the flapping down of the arytenoid cartilages, and by the closure of the 
 glottis. This is especially the case in young animals, in which the larynx is 
 small. But in those that are full grown, and have a large larynx, an adequate 
 quantity of air may still find its way through the aperture, if the animal refrain 
 from any violent effort. In a considerable number of Dr. Reid's experiments, 
 therefore, he did not find it necessary to introduce the trachea-tube, which 
 other experimenters have generally employed ; an opening was made into the 
 trachea, however, in those instances in which, from any cause, the entrance of 
 air was obstructed. . 
 
 * The Author employs, as in his opinion the most worthy of confidence, the experiments 
 of Dr. J. Reid (Edinb. Med. and Surg. Journ., vols. xlix. and li.), on whose accuracy he has 
 strong personal reasons for placing reliance; and whose anatomical and pathological attain- 
 ments are such as to render him fully competent to the task. 
 
 27* 
 
318 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 410. The functions of the Pharyngeal and Laryngeal branches of the Pneu- 
 mogastric having been already explained ( 378, 379, and 385), we may now 
 proceed to its Pulmonary division. In regard to this, we have to notice, that 
 its endowments are chiefly afferent; its most important office being, to con- 
 vey to the Medulla Oblongata the impression produced by venous blood in 
 the capillaries of the lungs, or of carbonic acid in the air-cells. This impres- 
 sion may give rise, as we have seen, to respiratory movements, without pro- 
 ducing sensation; but if it be from any cause stronger than usual, the sense of 
 uneasiness which it occasions is very distressing. The impression may be 
 imitated by pressure on the nerve ; which occasions an immediate inspiratory 
 movement. Hence the chief function of the afferent portion of the pulmonary 
 division of the Par Vagum, is to serve as an excitor to the respiratory move- 
 ments ; which are consequently diminished in frequency, when the trunk is 
 divided on both sides. But this division also contains motor fibres, which 
 are distributed upon the muscular fibres surrounding the bronchial tubes ; and 
 the experiments of Dr. Williams, which have been recently confirmed by 
 Longet and Volkmann, agree in proving, that the calibre of the bronchial tubes 
 can be caused to contract in a very considerable degree, by stimuli applied to 
 this nerve, and especially by electricity. 
 
 411. Various alterations are produced in the Lungs, by section of the Pneu- 
 mogastric nerves. The order in which these arise, and the causes to which 
 they are immediately due, constitute very interesting subjects of investigation; 
 and the knowledge of them will probably throw light upon many ill-understood 
 morbid phenomena. 
 
 a. In the first place, it has been fully established by Dr. Reid, that section of the Vagus 
 on one side only does not necessarily, or even generally, induce disease of that lung; and 
 hence the important inference may be drawn, that the nerve does not exercise any immediate 
 influence on its functions. When both Vagi are divided, however, the animal rarely survives 
 long; but its death frequently results from the disorder of the digestive functions. Never- 
 theless, the power of digestion is sometimes restored sufficiently to re-invigorate the animals ; 
 and their lives may then be prolonged for a considerable time. In fifteen out of seventeen 
 animals experimented on by Dr. Reid, the lungs were found more or less unfit for the 
 healthy performance of their functions. The most common morbid changes were a congested 
 state of the blood-vessels, and an effusion of frothy serum into the air-cells and bronchial tubes. 
 In eight out of the fifteen, these changes were strongly marked. In some portions of the 
 lungs, the quantity of blood was so great as to render them dense. The degree of conges- 
 tion varied in different parts of the same lung; but it was generally greatest at the most 
 depending portions. The condensation was generally greater, than could be accounted for 
 by the mere congestion of blood in the vessels; and probably arose from the escape of the 
 solid parts of the blood into the tissue of the lung. In some instances the condensation was 
 so great, that considerable portions of the lung sank in water, and did not crepitate ; but 
 they did not present the granulated appearance of the second stage of ordinary pneumonia. 
 In five cases in which the animals had survived a considerable time, portions of the lungs 
 exhibited the second, and even the third stages of pneumonia, with puriform effusion into 
 the small bronchial tubes ; and in two, gangrene had supervened. 
 
 6. One of the most important points to ascertain, in an investigation of this kind, is the 
 first departure from a healthy state ; to decide whether the effusion of frothy reddish serum, 
 by interfering with the usual change in the lungs, causes the congested state of the pulmo- 
 nary vessels and the laboured respiration ; or whether the effusion is the effect of a pre- 
 viously congested state of the blood-vessels. The former is the opinion of many physiolo- 
 gists, who have represented the effusion of serum as a process of morbid secretion, directly 
 resulting from the disorder of that function produced by the section of the nerve ; the latter 
 appears the unavoidable inference from the carefully-noted results of Dr. Reid's experiments. 
 In several of these, only a very smalt quantity of frothy serum was found in the air-tubes, 
 even when the lungs were found loaded with blood, and when the respiration before death 
 was very laboured. This naturally leads us to doubt, whether the frothy serum is the cause 
 of the laboured respiration, and of the congested state of the pulmonary vessels, in those 
 cases where it is present ; though there can be no doubt that, when once it is effused, it must 
 powerfully tend to increase the difficulty of respiration, and still further to impede the cir- 
 culation through the lungs. Dr. R. has satisfied himself of an important point, which has 
 
FUNCTIONS OF THE PAR VAGTJM. 319 
 
 been overlooked by others that this frothy fluid is not mucus, though occasionally mixed 
 with it ; but that it is the frothy serum so frequently found in cases where the circulation 
 through the lungs has been impeded before death. From this and other facts, Dr. R. con- 
 cludes " that the congestion of the blood-vessels is the first departure from the healthy state 
 of the lung, and that the effusion of frothy serum is a subsequent effect." 
 
 c. The next point, therefore, to be inquired into, is the cause of this congestion ; and this 
 is most satisfactorily explained, upon the general principles regulating the circulation of the 
 blood, by remembering that section of the Par Vagum greatly diminishes the frequency of 
 the respiratory movements, and that the quantity of air introduced into the lungs is, there- 
 fore, very insufficient for the due aeration of the blood. We shall hereafter see reason to 
 regard it as one of the best established principles in Physiology, that the activity of the 
 changes which the blood undergoes in the capillary vessels, does, in some way or other, 
 regulate its movement through them ; that, when these changes are proceeding with ac- 
 tivity, the capillary circulation is proper tionably accelerated ; and that when they are ab- 
 normally low in degree, the movement of the blood in the capillaries is stagnated. There 
 is now abundant evidence, in regard to the Pulmonary circulation in particular, that, to pre- 
 vent the admission of oxygen in the lungs, either by causing the animal to breathe pure 
 nitrogen or hydrogen, or by occlusion of the air-passages, is to bring the circulation through 
 their capillaries to a speedy check. Hence we should at once' be led to infer, that diminu- 
 tion in the number of Respiratory movements would produce the same effect; and as little 
 or no difference in their frequency is produced by section of one Vagus only, the usual ab- 
 sence of morbid changes in the lung supplied by it is fully accounted 'for. The congestion 
 of the vessels, induced by insufficient aeration, satisfactorily accounts not only for the effusion of 
 serum, but also for the tendency to pass into the inflammatory condition, sometimes pre- 
 sented by the lungs, as by other organs similarly affected. Dr. Reid confirms this view, by 
 the particulars of cases of disease in the human subject, in which the lungs presented after 
 death a condition similar to that observed in the lower animals after section of the Vagi ; 
 and in these individuals, the respiratory movements had been much less frequent than natu- 
 ral during the latter part of life, owing to a torpid condition of the nervous centres. The 
 opinion (held especially by Dr. Wilson Philip) that section of the par vagum produces the 
 serous effusion, by its direct influence on the function of Secretion, is further invalidated by 
 the fact stated by Dr. Reid, that he always found the bronchial membrane covered with its 
 true mucus, except when inflammation was present. 
 
 " The experimental history of the Par Vagum," it is justly remarked by 
 Dr. Reid, "furnishes an excellent illustration of the numerous difficulties with 
 which the physiologist has to contend, from the impossibility of insulating 
 any individual organ from its mutual actions and reactions, when he wishes 
 to examine the order and dependence of its phenomena." In such investi- 
 gations, no useful inference can be drawn from one or two experiments only; 
 in order to avoid all sources of fallacy, a large number must be made ; the 
 points in which all agree must be separated from others, in which there is a 
 variation of results ; and it must be then inquired, to what the latter is due. 
 
 412. These observations apply equally to the other principal subject of in- 
 quiry in regard to the functions of the Par Vagum, its influence upon the 
 process of Digestion. The results obtained by different experimenters have 
 led to differences of opinion as to its action, no less remarkable than those 
 which have prevailed on the question just discussed. Thus, in regard to the 
 afferent fibres of the Gastric division of the nerve, some physiologists main- 
 tain it to be by impressions on them alone, that the sense of hunger or satiety 
 is excited; whilst others deny that they have any power of transmitting such 
 impressions, which, according to them, do not originate in the stomach at all. 
 Dr. Reid has arrived at the conclusion, from his numerous experiments, that 
 the Par Vagum is the channel through which the mind becomes cognizant of 
 the condition of the stomach ; but that it is not the sole excitor of the sense 
 of hunger. Animals, which have sustained section of the nerve on both sides, 
 will eagerly take food, if they have not received too great a shock from the 
 operation ; but they seem to experience no feeling of satiety when the sto- 
 mach is loaded. This inference is confirmed by Valentin, who mentions that 
 puppies after the operation will take three times the same quantity of milk, 
 as uninjured individuals of the same age, so as greatly to distend the abdomen. 
 
320 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 The act of Vomiting has been proved to be excitable by impressions trans- 
 mitted through the Gastric branches of the Par Vagum ; although they con- 
 stitute by no means the only channel, through which the various muscles con- 
 cerned in it may be called into combined action ( 505). 
 
 413. The question of the influence of the motor fibres of the Pneumo- 
 gastric, upon the muscular walls of the stomach, has been already in part dis- 
 cussed ( 387). Although it seems unquestionable that they have the power 
 of stimulating these muscles to contraction, yet there is evidence that the 
 movements of the stomach, which are most essential to digestion, may take 
 place without it. Thus Dr. Reid found, in several of his experiments, that 
 food was not only digested in the Stomach, but propelled into the Duodenum, 
 subsequently to the operation. It seems very probable, however, that a tem- 
 porary suspension of these movements (as of other independent functions of 
 the stomach) may be the first effect of the operation. 
 
 414. It is necessary here to stop to notice, on account of the currency 
 which it has obtained, the doctrine of Dr. Wilson Philip ; that the Par Va- 
 gum controls the secretion of the Gastric fluid ; and that its division checks 
 the secretion. He further stated, that the influence of Galvanism propagated 
 along the nerve, would re-establish the secretion. This statement has been quoted 
 and re-quoted, as an established physiological position ; and, when united with 
 the well-known fact, that galvanism would excite muscular contraction, it has 
 seemed to Dr. W. Philip and other physiologists sufficient to establish the 
 important position, that galvanism and nervous influence are identical. It has 
 been disputed, however, by many other experimenters ; who have satisfied 
 themselves that the secretion of gastric juice continues after the operation ; 
 and consequently, that the elaboration of this product cannot be dependent on 
 nervous influence supplied by the Par Vagum, though doubtless in part regu- 
 lated by it. The first effects of the operation, however, are almost invariably 
 found to be vomiting (in those animals capable of it), loathing of food, ami 
 arrestment of the digestive process ; and it is not until after four or five days, 
 that the power seems re-established. In the animals which died before that 
 time, no indication of it could be discovered by Dr. R. ; in those which survived 
 longer, great emaciation took place ; but when life was sufficiently prolonged, the 
 power of assimilation seemed almost completely restored. This was the 
 case in four out of the seventeen dogs experimented on ; and the evidence of 
 this restoration consisted in the recovery of flesh and blood by the animals, 
 the vomiting of half-digested food permanently reddening litmus paper, the 
 disappearance of a considerable quantity of alimentary matter from the intes- 
 tinal canal, and the existence of chyle in the lacteals. It may serve to account 
 in some degree for the contrary results, obtained by other experimenters, to 
 state that seven out of Dr. R.'s seventeen experiments were performed before 
 he obtained any evidence of digestion after the operation ; and that the four 
 which furnished this followed one another almost in succession ; so that it is 
 easy to understand why those who were satisfied with a small number of 
 experiments, should have been led to deny it altogether. 
 
 [M. Bernard has instituted fresh experiments to determine this still-debated question, 
 making use of the artificial fistulous openings into the stomach, invented by M. Blondlot. 
 A dog's digestion had been thus watched for eight days, and had always been well effected. 
 On the ninth day, after a day's fast, M. Bernard sponged out the stomach, which contracted 
 on the contact of the sponge, and at once secreted a large quantity of gastric fluid ; he then 
 divided the pneumogastric nerves in the middle of the neck, and immediately the mucous 
 membrane, which had been turgid, became pale, as if exsanguine, its movements ceased, 
 the secretion of gastric fluid was instantaneously put a stop to, and a quantity of ropy neutral 
 mucus was soon produced in its place. After this, no digestion was duly performed, and 
 milk was no longer coagulated; raw meat remained unchanged, and the food (meat, milk, 
 bread and sugar, which the dog had before thoroughly digested) remained for a long time 
 
FUNCTIONS OF THE PAR VAGUM. 321 
 
 neutral, and at last acquired acidity only from its own transformation into lactic acid. In 
 the stomachs of otljer dogs after the division of the nerves, he traced the transformation of 
 cane-sugar into grape-sugar in three or four hours ; and in ten or twelve hours the trans- 
 formation into lactic acid was complete. In others, when the food was not capable of an 
 acid transformation, it remained neutral to the last. In no case did any part of the food pass 
 through the peculiar changes of chymification. In a last experiment, he gave to each of two 
 dogs, in one of which he had cut the nerves, a dose of emulsine, and half an hour after, a 
 dose of am ygdaline (substances which are innocent alone, but when mixed produce hydro- 
 cyanic acid). The dog, whose nerves were cut, died in a quarter of an hour, the sub- 
 stances being absorbed unaltered and mixing in the blood: in the other, the emulsine was 
 changed by the action of the gastric fluid before the amygdaline was administered, and it 
 survived. Gazette Med., Juin 1, 1844,/rom tlie Report of the jlcad. des Sri., seance du 27 Mai, 
 1844. M. C.] 
 
 a. Another series of experiments was performed by Dr. Reid, for the purpose of testing 
 the validity of the results obtained by Sir B. Brodie, relative to the effects of section of the 
 Par Vagum upon the secretions of the stomach, after the introduction of arsenious acid into 
 the system. According to that eminent Surgeon and Physiologist, when the poison was 
 introduced after the Par Vagum had been divided on each side, the quantity of the pro- 
 tective mucous and watery secretions was much less than usual, although obvious marks of 
 inflammation were present. In order to avoid error as much as possible, Dr. Reid made five 
 sets of experiments, employing two dogs in each, as nearly as possible of equal size and 
 strength, introducing the same quantity of the poison, into the system of each in the same 
 manner, but cutting the Vagi in one, and leaving them entire in the other. This comparative 
 mode of experimenting is obviously the only one admissible in such an investigation. Its 
 result was in eveiy instance opposed to the statements of Sir B. Brodie ; the quantity of the 
 mucous and watery secretions of the stomach being nearly the same, in each individual of 
 the respective pairs subjected to experiment; so that they can no longer be referred to the 
 influence of the Eighth pair of nerves. Moreover, the appearances of inflammation were, in 
 four out of the five cases, greatest in the animals whose Vagi were left entire ; and this seemed 
 to be referrible to the longer duration of their lives after the arsenic had been introduced. 
 The results of Sir B. Brodie's experiments may perhaps be explained, by the Speedy occur- 
 rence of death in the subjects of them, consequent (it may be) upon the want of suffi- 
 ciently free respiration, which was carefully guarded against by Dr. Reid. 
 
 415. So far as the results of Dr. Reid's experiments may be trusted to, 
 therefore, (and the Author is himself disposed to rely on them almost im- 
 plicitly,) all the arguments which have been drawn in favour of the doctrine 
 that Secretion depends upon Nervous agency, from the effects of lesion of the 
 Vagi upon the functions of the Stomach, must be set aside. That this nerve 
 has an important influence on the gastric secretion, is evident from the defi- 
 ciency in its amount soon after the operation, as well as from other facts. 
 But this is a very different proposition from that just alluded to; and the 
 difference has been very happily illustrated by Dr. R. "The movements of' 
 a horse," he observes, " are independent of the rider on his back, in other 
 words, the rider does not furnish the conditions necessary for the movements 
 of the horse; but everyone knows how much these movements maybe 
 influenced by the hand and heel of the rider." It may be hoped, then, that 
 physiologists will cease to adduce the oft-cited experiments of Dr. Wilson 
 Philip, in favour of the hypothesis (for such it must be termed) that secretion 
 is dependent upon nervous influence, and that this is identical with galvan- 
 ism. Additional evidence of their fallacy is derived from the fact mentioned 
 by Dr. Reid, that the usual mucous secretions of the stomach were always 
 found; and they are further invalidated by the testimony of Miiller, who 
 denies that galvanism has any peculiar influence in re-establishing the gastric 
 secretion, when it has been checked by section of the nerves. 
 
 416. It only remains to notice the influence of section of the Vagi upon 
 the actions of the Heart. It has been asserted by Valentin and other experi- 
 menters, that mechanical irritation of these nerves, especially at their roots, 
 has a tendency to excite or accelerate the heart's action ; other experimenters, 
 however, have obtained none but negative results. Admitting, what seems 
 probable, that the Cardiac branches of the Pneumogastric have some influence 
 
322 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 upon the Heart's action, it remains to inquire whether that influence is essen- 
 tial to its movements ; and whether these nerves form the channel, through 
 which they are affected by emotions of the mind, or by conditions of the 
 bodily system. In regard to the first point, no doubt can be entertained; 
 since the regular movements of the heart are but little affected by section of 
 the Vagi. With respect to the second, there is more difficulty ; since the 
 number of causes, which may influence the rapidity and pulsations of the 
 heart, is very considerable. For example, when the blood is forced on more 
 rapidly towards the heart, as in exercise, struggling, &c., the stimulus to its 
 contractions is more frequently renewed, and they become more frequent; 
 and when the current moves on more slowly, as in a state of rest, their fre- 
 quency becomes proportionably diminished. If the contractions of the heart 
 were not dependent upon the blood, and their number were not regulated by 
 the quantity flowing into its cavities, very serious and inevitably fatal dis- 
 turbances of the heart's action would soon result. That this adjustment takes 
 place otherwise than through the medium of the nervous centres, is evident 
 from the fact that, in a dog, in which the par vagum and sympathetic had 
 been divided in the neck on each side, violent struggling, induced by alarm, 
 raised the number of pulsations from 130 to 260 per minute. It is difficult 
 to ascertain, by experiment upon the lower animals, whether simple emotion, 
 unattended with struggling or other exertion, would affect the pulsation of the 
 heart, after section of the Vagi; but when the large proportion of the Sympa- 
 thetic nerves proceeding to this organ is considered, and when it is also re- 
 membered that irritation of the roots of the upper cervical nerves stimulates 
 the action of the heart through these, we can scarcely doubt that both may 
 serve as the channels of this influence, especially in such animals as the dog, 
 in which the two freely inosculate in the neck. 
 
 417. In regard to the functions of the Spinal Accessory nerve, also, there 
 has been great difference of opinion ; the peculiarity of its origin and course 
 having led to the belief, that some very especial purpose is answered by it. 
 The predominance of motor fibres in its roots, its inosculation with the Par 
 Vagum, and its probable reception of sensory fibres from the latter whilst 
 imparting to it motor filaments, have been already referred to ( 408). As its 
 trunk passes through the foramen lacerum, it divides into two branches; of 
 which the internal, after giving off some filaments that assist in forming the 
 pharyngeal branch of the Par Vagum, becomes incorporated with the trunk of 
 that nerve; whilst the external proceeds outwards, and is finally distributed to 
 the sterno-cleido-mastoideus and trapezius muscles, some of its filaments 
 inosculating with those of the cervical plexus. When the external branch is 
 irritated, before it perforates the sterno-mastoid muscles, vigorous convulsive 
 movements of that muscle, and of the trapezius, are produced; and the animal 
 does not give any signs of pain, unless the nerve is firmly compressed between 
 the forceps, or is included in a tight ligature. Hence it may be inferred, that 
 the functions of this nerve are chiefly motor, and that its sensory filaments are 
 few in number. Further, when the nerve has been cut across, or firmly tied, 
 irritation of the lower end is attended by the same convulsive movements of 
 the muscles ; whilst irritation of the upper end, in connection with the spinal 
 cord, is unattended with any muscular movement. Hence it is clear that the 
 motions occasioned by irritating it are of a direct, not of a reflex character. 
 The same muscular movements are observed on irritating the nerve in the 
 recently-killed animal, as during life. 
 
 a. According to Sir C. Bell, the Spinal Accessory is a purely Respiratory nerve, whose office 
 it is to excite the involuntary or automatic movements of the muscles it supplies, which 
 share in the act of respiration ; and he states that the division of it paralyzes the muscles to 
 which it is distributed, as muscles of respiration ; though they still perform the voluntary 
 
HYPOGLOSSAL NERVE. 323 
 
 movements, through the medium of the spinal nerves. Both Valentin and Dr. Reid, however, 
 positively deny that this is the case. Dr. Reid's method of experimenting was well adapted 
 to test the truth of the assertion. Considering that, in the ordinary condition of the animal, 
 it might be difficult to distinguish the actions of particular muscles, beneath the skin, when 
 those in the neighbourhood were in operation ; and also that the usual automatic movements 
 might be simulated by voluntary action, when the breathing might be rendered difficult ; he 
 adopted the following plan : A small dose of prussic acid was given to an animal, in which 
 the Spinal Accessory had been previously divided on one side ; and after the convulsive 
 movements produced by it had ceased, the animal was generally found in a state similar to 
 that which we sometimes see in apoplexy, the action of the heart going on, the respirations 
 being slow and heaving, and the sensorial functions appearing to be completely suspended. 
 The Respiratory movements always ceased before the action of the heart; but they con- 
 tinued, in several of the animals experimented on, sufficiently long to allow the muscles Of 
 the anterior part of the neck to be laid bare, so that accurate observations could be made 
 upon their contractions. In the dog and cat, the sterno-mastoid does not appear to have 
 much participation in the ordinary movements of respiration ; for in several instances it 
 could not be seen to contract on either side, though the head was forcibly pulled towards the 
 chest at each inspiratory movement, chiefly by the action of the sterno-hyoid and thyroid 
 muscles. In two dogs and one cat, however, in which the head was fixed, and these 
 respiratory movements were particularly vigorous, distinct contractions were seen in the 
 exposed sterno-mastoid muscles, synchronous, with the other movements of respiration : these 
 were, perhaps, somewhat weaker on the side on which the nerve had been cut, but were 
 still decidedly present. In one of these dogs, similar movements were observed in the 
 trapezius, on the side on which the nerve had been divided. As the condition of the animal 
 forbade the idea that volition could be the cause of these movements, it can scarcely be ques- 
 tioned that Sir C. Bell's statement was an erroneous one. As far, therefore, as these experi- 
 ments afford any positive data, in regard to the functions of this nerve, it may be concluded 
 that they are the same as those of the cervical plexus, with which it anastomoses freely. 
 "Future anatomical researches," as Dr. Reid justly remarks, "may perhaps explain to us how 
 it follows this peculiar course, without obliging us to suppose that it has a reference to any 
 special function in the adult of the human species." Thus, the study of the history of 
 development has accounted satisfactorily for the peculiar course of the recurrent laryngeal, 
 which may be traced passing directly from the par vagum to the larynx, at a time when the 
 neck can scarcely be said to exist, and when that organ is buried in the thorax. As this 
 rises in the neck, the nerve, which at first came off below the great transverse blood-vessels, 
 has both its origin and its termination carried upwards ; whilst it is still tied down by these 
 vessels in the middle of its course. 
 
 418. The Hypo glossal nerve, or Motor Linguae, is the only one which, 
 in the regular order, now remains to be considered. That the distribution of 
 this nerve is restricted to the muscles of the tongue, is a point very easily 
 established by anatomical research ; and accordingly we find that, long before 
 the time of Sir C. Bell, Willis spoke of it as the nerve of the motions of 
 articulation, whilst to the Lingual branch of the fifth pair he attributed the 
 power of exercising the sense of taste ; and he distinctly stated, that the 
 reason of this organ being supplied with two nerves is its double function. 
 The inference that it is chiefly, if not entirely, a motor nerve, which has been 
 founded upon its anatomical distribution, is supported also by the nature of 
 its origin, which is usually from a single root, corresponding to the anterior 
 root of the Spinal nerves. Experiment shows that, when the trunk of the 
 nerve is stretched, pinched, or galvanized, violent motions of the whole tongue, 
 even to its tip, are occasioned; and also, that similar movements take place 
 after division of the nerve, when the cut end most distant from the brain is 
 irritated. In regard to the degree in which this nerve possesses sensory pro- 
 perties, there is some difference of opinion amongst physiologists, founded, as 
 it would seem, on a variation in this respect between different animals. 
 Indications of pain are usually given, when the trunk is irritated after its exit 
 from the cranium; but these may proceed from its free anastomosis with the 
 cervical nerves, which not improbably impart sensory fibres to it. But in 
 some Mammalia, the hypoglossal nerve has been found to possess a small 
 posterior root with a ganglion: this is the case in the ox, and also in the rabbit; 
 
324 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 and in the latter animal, Valentin states that the two trunks pass out from the 
 cranium through separate orifices, and that, after their exit, one may be shown 
 
 [Fig. 156. 
 
 The course and distribution of the Hypo-Glossal or Ninth pair of nerves ; the deep-seated nerves of 
 the neck are also seen ; 1, the hypo-glossal nerve ; 2, branches communicating with the gustatory nerve ; 
 3, a branch to the origin of the hyoid muscles ; 4, the descendens noni nerve ; 5, the loop formed with the 
 branch from the cervical nerves ; 6, muscular branches to the depressor muscles of the larynx ; 7, a 
 filament from the second cervical nerve, and 8, a filament from the third cervical, uniting to form the 
 communicating branch with the loop from the descendens noni ; 9, the auricular nerve ; 10, the inferior 
 dental nerve ; 11, its mylo-hyoidean branch; 12, the gustatory nerve ; 13, the chorda-tympani passing to 
 the gustatory nerve; 14, the chorda-tympani leaving the gustatory nerve to join the sub-maxillary 
 ganglion; 15, the sub-maxillary ganglion; 16, filaments of communication with the lingual nerve; 17, 
 the glosso-pharyngeal nerve ; 18, the pneumogastric or par vagum nerve; 19, the three upper cervical 
 nerves; 20, the four inferior cervical nerves; 21, the first dorsal nerve; 22, 23, the brachial plexus ; 24, 
 25, the phrenic nerve; 26, the carotid artery; 27, the internal jugular vein.] 
 
 to be sensory, and the other to be motor. Hence, this nerve, which is the 
 lowest of those that originate in the cephalic prolongation of the spinal cord, 
 generally known as the medulla oblongata, approaches very closely in some 
 animals to the regular type of the spinal nerves ; and though in Man it still 
 manifests an irregularity, in having only a single root, yet this irregularity is 
 often shared by the first cervical nerve, which also has sometimes an anterior 
 root only. 
 
 419. The Hypoglossal nerve is distributed not merely to the tongue, but to 
 the muscles of the neck which are concerned in. the movements of the larynx ; 
 and the purpose of this distribution is probably to associate them in those 
 actions, which are necessary for articulate speech. Though all the motions 
 of the tongue are performed through the medium of this nerve, yet it would 
 appear, from pathological phenomena, to have at least two distinct connec- 
 tions with the nervous centres ; for in many cases of paralysis, the masticatory 
 movements of the tongue are but little affected, when the power of articula- 
 tion is much injured or totally destroyed : and the converse may be occasion- 
 ally noticed. When this nerve is paralyzed on one side, in hemiplegia, it 
 will be generally observed that the tongue, when the patient is directed to put 
 
CEPHALIC NERVES IN GENERAL. 325 
 
 it out, is projected towards the palsied side of the face : this is due to the 
 want of action of the lingual muscles of that side, which do not aid in pushing 
 forward the tip ; the point is consequently directed only by the muscles of 
 the other side, which will not act in a straight direction, when unantagonized 
 by their fellows. It is a curious fact, however, that the hypoglossal nerve 
 seems not to be always palsied on the same side with the facial, but sometimes 
 on the other. This has been suggested to be due to the origination of the 
 roots of this nerve from near the point, at which the pyramids of the medulla 
 oblongata decussate ; so that some of its fibres come off, like those of the 
 spinal nerves, without crossing ; whilst others are transmitted to the opposite 
 side, like those of the higher cerebral nerves ; and the cause of paralysis may 
 affect one or other of these sets of roots more particularly. Whatever may 
 be the validity of this explanation, the circumstance is an interesting one, and 
 well worthy of attention.* 
 
 420. The general character and arrangement of the Cephalic nerves, as 
 distinguished from the ordinary Spinal, constitute a study of much interest, 
 when considered in relation to Comparative Anatomy, and to Embryology. It 
 appears, from what has been already stated, that the Par Vagum, Spinal 
 Accessory, Glosso-pharyngeal, and Hypoglossal nerves, may be considered 
 nearly in the light of ordinary Spinal nerves. They all take their origin ex- 
 clusively in the Medulla Oblongata ; and the want of correspondence in posi- 
 tion, between their roots and those of the Spinal nerves, is readily accounted 
 for by the alteration in the direction of the columns of the Spinal Cord, 
 which, as long since pointed out by Rosenthal, and lately stated prominently 
 by Dr. Reid, not only decussate laterally, but, as it were, antero-posteriorly 
 ( 353). The Hypoglossal, as just stated, not unfrequently possesses a sen- 
 sory in addition to its motor root. The Glosso-pharyngeal, which is princi- 
 pally an afferent nerve, is stated by Arnold and others to have a small motor 
 root; at any rate, the motor fibres which answer to it are to be found in the 
 Par Vagum. That the Par Vagum and a portion of the Spinal Accessory 
 together make up a spinal nerve, has been already stated as probable. 
 
 421. Leaving these nerves out of the question, therefore, we proceed to the 
 rest. Comparative anatomy, and the study of Embryonic development, alike 
 show that the Spinal cord and Medulla Oblongata constitute the most essen- 
 tial part of the nervous system in Vertebrata ; and that the Cerebral Hemi- 
 spheres are superadded, as it were, to this. At an early period of develop- 
 ment, the Encephalon consists chiefly of three vesicles, which correspond 
 with the ganglionic enlargements of the nervous cord of the Articulata, and 
 mark three divisions of the cerebro-spinal axis ; and, in accordance with this 
 view, the Osteologist is able to trace, in the bones of the cranium, the same 
 elements which would form three vertebrae, in a much expanded and altered 
 condition. However improbable such an idea might seem, when the cranium 
 of the higher Vertebrata alone is examined, it at once reconciles itself to our 
 reason, when we direct our attention to that of Reptiles and Fishes ; in 
 which classes the size of the Cerebral or hemispheric ganglia is very small, 
 in comparison with that of the Ganglia of special sensation; and in which the 
 latter evidently form but a continuation of the Spinal Cord, modified in its 
 function ; so that, when we trace upwards the cavity of the spinal column 
 into that of the cranium, we encounter no material change, either in its size or 
 
 * It may be questioned, however, whether the Hypoglossal is really paralyzed on the op- 
 posite side from the facial in such cases. An instance has been communicated to the Author 
 by Dr. W. Budd, in which the hypoglossal nerve was completely divided on one side; and 
 yet the tip of the tongue, when the patient was desired to put it out, was sometimes directed 
 from and sometimes towards the palsied side ; showing that the muscles of either half are 
 sufficient to give any required direction to the whole. 
 28 
 
326 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 direction. The three pairs of nerves of special sensation make their way 
 out through these three cranial vertebrae respectively. At a later period of 
 development, other nerves are interposed between these ; which, being inter- 
 vertebral, are evidently more analogous to the Spinal nerves, both in situation 
 and function. A separation of the primitive fibres of these takes place, how- 
 ever, during the progress of development, so that their distribution appears 
 irregular. Thus the greater part of the sensory fibres are contained in the 
 large division of the Trigeminus ; whilst, of the motor fibres, the anterior 
 ones chiefly pass forwards as the Oculo-motor and Patheticus ; and of the 
 posterior, some form the small division of the Trigeminus, and others unite 
 with the first pair from the Medulla Oblongata to form the Facial. This last 
 fact explains the close union which is found in Fishes and some Amphibia, 
 between that nerve and those proceeding more directly from the Medulla Ob- 
 longata. According to Valentin, the Glosso-pharyngeal is the sensory por- 
 tion of the first pair from the Medulla Oblongata, of which the motor part is 
 chiefly comprehended in the Facial nerve. It is very interesting to trace this 
 gradual metamorphosis from the character of the Spinal nerves, which is ex- 
 hibited in the Cephalic, when they are traced upwards from the Medulla Ob- 
 longata ; and this is shown also, in some degree, in the nerves of special sen- 
 sation ( 446, a). Although we are accustomed to consider the Fifth pair as 
 par eminence the Spinal nerve of the head, the foregoing statements, founded 
 upon the history of development, show that the nerves of the Orbit really 
 belong to its motor portion ; they may consequently be regarded as altogether 
 forming the first of the inter vertebral or Spinal nerves of the cranium.. The 
 Facial and Glosso-pharyngeal appear to constitute the second ; whilst the Par 
 Vagum and Spinal Accessory, forming the third pair, intervene between this 
 and the true spinal, of which the Hypoglossal may be considered as the first. 
 
 5. Of the Sensory Ganglia and their Functions. Consensual Movements. 
 
 422. At the base of the Brain in Man, concealed by the Cerebral Hemi- 
 spheres, but still readily distinguishable from them, we find a series of gan- 
 glionic masses ; which are in direct connection with the nerves of Sensation; 
 and which appear to have functions quite independent of those of the other 
 components of the Encephalon. Thus anteriorly we have the Olfactive 
 ganglia, in what are commonly termed the bulbous expansions of the Olfactive 
 nerve. That these are real ganglia, is proved by their containing grey or ve- 
 sicular substance ; and their separation from the general mass of the Encepha- 
 lon, by the peduncles or footstalks commonly termed the trunks of the Olfac- 
 tory nerves, finds its analogy in many species of Fish ( 357). The ganglionic 
 nature of these masses is more evident in many of the lower Mammalia, in 
 which the organ of smell is highly developed, than it is in Man, whose olfac- 
 tive powers are comparatively moderate. At some distance behind these, we 
 have the representatives of the Optic ganglia, in the Tubercula Quadrigemina, 
 to which the principal part of the roots of the Optic nerve may be traced. 
 Although these bodies are so small in Man, in comparison to the whole En- 
 cephalic mass, as to be apparently insignificant, yet they are much larger, and 
 form a more evidently important part of it in many of the lower Mammalia ; 
 though still presenting the same general aspect. The Auditory ganglia do 
 not form distinct lobes or projections ; but are lodged in the substance of the 
 Medulla Oblongata. Their real character is most evident in certain Fishes, as the 
 Carp ; in which we trace the Auditory nerve into a ganglionic centre as distinct 
 as the Optic ganglion. In higher animals, however, and in Man, we are able 
 to trace the Auditory nerve into a small mass of vesicular matter, which lies 
 on each side of the Fourth Ventricle ; and although this is lodged in the midst 
 
SENSORY GANGLIA. CONSENSUAL ACTIONS. 327 
 
 of parts whose function is altogether different, yet there seems no reason for 
 doubting that it has a character of its own, and that it is really the ganglionic 
 
 [Fig. 157. 
 
 A view of the base of the Cerebrum and Cerebellum, together with their nerves ; 1, anterior extremity 
 of the fissure of the hemispheres of the brain ; 2, posterior extremity of the same fissure ; 3, the anterior 
 lobes of the cerebrum; 4, its middle lobe ; 5, the fissure of Sylvius; 6, the posterior lobe of the cerebrum; 
 7, the point of the infundibulum ; 8, its body; 9, the corpora albicantia; 10, cineritious matter; 11, the 
 crura cerebri ; 12, the pons Varolii ; 13, the top of the medulla oblongata; 14. posterior prolongation of 
 the pons Varolii; 15, middle of the cerebellum ; 16, anterior part of the cerebellum ; 17, its posterior part 
 and the fissure of its hemispheres ; 18, superior part of the medulla spinalis ; 19, middle fissure of the 
 medulla oblongata ; 20, the corpus pyramidale ; 21, the corpus restiforme ; 22, the corpus olivare ; 23, the 
 olfactory nerve ; 24, its bulb ; 25, its external root ; 26, its middle root ; 27, its internal root ; 28, the op- 
 tic nerve beyond the chiasm; 29, the optic nerve before the chiasm; 30, the motor oculi, or third pair 
 of nerves ; 31, the fourth pair or pathetic nerves ; 32, the fifth pair, or trigemini nerves ; 33, the sixth 
 pair, or motor externus ; 34, the facial nerve ; 35, the auditory the two making the seventh pair ; 36, 
 37, 38, the eighth pair of nerves. (The ninth pair is not here seen.)] 
 
 centre of the Auditory nerve. In like manner, we may probably fix upon a 
 collection of vesicular matter, imbedded in the Medulla Oblongata, which is 
 considered by Stilling to be the nucleus of the Glosso-pharyngeal nerve, and 
 to which a portion of the sensory root of the Fifth pair may be traced, as 
 representing the Gustatory ganglion. 
 
 423. At the base of the Cerebral Hemispheres, we find two other large 
 ganglionic masses, on either side ; into which all the fibres appear to pass, 
 which connect the Hemispheres with the Medulla Oblongata. These are the 
 Thalami Optici, and the Corpora Striata. Now, although these are com- 
 monly regarded in the light of appendages, merely, to the Cerebral Hemi- 
 spheres, it is evident, from the large quantity of vesicular matter they contain, 
 that they have an independent character ; and that, even if the Cerebral fibres 
 simply pass through them, other fibres have their proper ganglionic centres 
 
328 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 in them. Such an idea is further warranted by the history of their develop- 
 ment ; for we find, in the Human embryo of the sixth week, a distinct vesi- 
 cle for the Thalami Optici, interposed between the vesicle of the Corpora 
 Quadrigemina, and that which gives origin to the Cerebral Hemispheres ; 
 whilst the Corpora Striata constitute the floor of the cavity or ventricle, which 
 exists in the latter. Now, as already pointed out, we may distinguish in the 
 Medulla Oblongata and Crura Cerebri, a sensory and a motor tract; by 
 the endowments of the nerves which issue from them. The sensory tract 
 may be traced upwards from the Olivary columns, until it almost entirely 
 spreads itself through the substance of the Thalamus. Moreover, the Optic 
 nerves, and the peduncles of the Olfactive, may be shown to have a distinct 
 connection with the Thalami ; the former by the direct passage of a portion 
 of their roots into these ganglia; and the Blatter through the medium of the 
 Fornix. Hence we may fairly regard the Thalami Optici as the chief focus 
 of the Sensory nerves ; and more especially as the ganglionic centre of the 
 nerves of common sensation, which ascend to it from the Medulla Oblongata 
 and Spinal Cord. On the other hand, the Corpora Striata are implanted on 
 the motor tracts of the Crura Cerebri, which descend into the Pyramidal co- 
 lumns ; and their connection with the motor function is very generally admit- 
 ted, from the constancy with which paralysis is observed to accompany lesions 
 of these bodies, even when they are affected to a very trifling extent. 
 
 424. The Thalami Optici, and the Corpora Striata, as is well known, are 
 very closely connected with each other by commissural fibres ; and, if the 
 preceding account of (heir respective offices be correct, they may be regarded 
 as having much the same relation to each other, as that which exists between 
 the posterior and anterior peaks of vesicular matter in the Spinal Cord ; the 
 latter issuing motor impulses in respondence to sensations excited through 
 the former. They are also closely connected with other ganglionic masses 
 in their neighbourhood, such as the locus niger, and the vesicular matter of 
 the pons; which again, are in close relation with the vesicular matter of the 
 medulla oblongata. Altogether it is very evident, that an extensive tract of 
 ganglionic matter exists at the base of the Encephalon, which is really just as 
 distinct from either the Cerebrum or Cerebellum, as these are from each 
 other ; and we have next to inquire, what functions are to be assigned to it. 
 
 425. The determination of these may seem the more difficult, as it is im- 
 possible to make any satisfactory experiments upon the ganglionic centres in 
 question, by isolating them from the Cerebral Hemispheres above, and from the 
 Medulla Oblongata and Spinal Cord below. But the evidence derived from 
 Comparative Anatomy appears to be in this case particularly clear; and, 
 rightly considered, seems to afford us nearly all the information we require. 
 In the series of " experiments prepared for us by nature," which is presented 
 to us in the descending scale of Animal life, we witness the effects of the 
 gradual change of the relative development of the Sensory ganglia and Cerebral 
 Hemispheres, which are presented to us in the Vertebrated classes ; and the results 
 of the entire "withdrawal of the latter, and of the sole operation of the former, 
 which are presented in the higher Invertebrata. Tn the sketch already given 
 of the Comparative Anatomy of the Encephalon in Vertebrata, it has been 
 shown that the Sensory ganglia gradually increase, whilst the Cerebral hemi- 
 spheres as regularly diminish, in relative size and importance, as we descend from 
 the higher Mammalia to the lower, from these to Birds, thence to Reptiles, 
 from these, again, to the higher Fishes, in which the" aggregate size of the 
 Sensory ganglia equals that of the Cerebrum, thence to the lower Fishes, 
 in which the size of the Cerebral lobes is no greater than that of a single pair 
 of sensory ganglia, the Optic, and frequently even inferior, and lastly, to the 
 jZmphioxus or Lancelot, the lowest Vertebrated animal of which we have 
 
FUNCTIONS OF SENSORY GANGLION. 329 
 
 any knowledge, in which there is not the rudiment of a Cerebrum, the En- 
 cephalon being only represented by a single ganglionic mass, which, from its 
 connection with the nerves of sense, must obviously be regarded as analogous 
 to the congeries of ganglia that we find in the higher forms of the class. 
 
 a. It has been supposed, from the results of an imperfect examination of this very remarka- 
 ble animal, that it is altogether destitute of Encephalon; and that it possesses no ganglionic 
 centre, except the Spinal Cord and Medulla Oblongata. The researches of M. de Quatre- 
 fages, however, indicate that the most anterior of the ganglionic enlargements exhibited by 
 its Cerebro-Spinal axis, is of a more special character than the rest; uniting in itself the 
 characters of several distinct ganglionic centres. The ganglionic enlargements, arranged in 
 a linear series, which altogether represent the Spinal Cord, each give origin to a single pair 
 of nerves ; but the cephalic ganglion is the centre of Jive pairs. Of these, the first pair is 
 distinctly an Optic nerve; being exclusively distributed to an organ, which has the structure 
 of a rudimentary Eye, though lodged within the dura mater; reminding us, in its situation, 
 of the Auditory apparatus of the Gasteropod Mollusks, which is actually imbedded in the 
 posterior part of the Cephalic ganglia. The second pair seems to correspond in its distribu- 
 tion with the Facial; whilst the third represents the Fifth pair and the Pneumogastric con- 
 jointly. The fourth and fifth pairs are distributed to the fin-like expansion, which forms the 
 margin of the head as well as of the body; and seem to hold the same relation to the two 
 preceding pairs, as the dorsal branches of the Spinal nerves bear to the ventral, or, in Man, 
 the posterior to the anterior. Hence we see that this single ganglion is made up of at least 
 three centres; of which the first corresponds to the Optic ganglion of higher Vertebrata; 
 whilst the second and third are analogous to certain parts of the Medulla Oblongata in im- 
 mediate connection with them. Moreover, this little animal possesses an organ of Smell, 
 much more distinct than the rudimentary eye ; and although its connection with the anterior 
 part of the cephalic ganglion has not yet been traced (owing to the extreme minuteness of 
 the parts, and the difficulty resulting from the interposition of the dura mater, which is in 
 equally close contact with the nervous mass which it incloses, and with the olfactive organ 
 which abuts upon its exterior), there can be little doubt that such a connection exists, and 
 that the Cephalic mass unites within itself also the characters of an Olfactive ganglion. But 
 no part whatever can be traced, which bears any resemblance to the Cerebral hemispheres ; 
 and as these, wherever they exist, are completely isolated from the Sensory ganglia, their 
 absence may be stated as an almost certain fact. Hence, in this particular, the Amphioxus 
 evidently corresponds with the Invertebrata ; to which its affinity is so close in other particu- 
 lars, that many Naturalists have hesitated to assign it a place in the Vertebrated series at all ; 
 and, as will be seen in the next paragraph, the union of several really distinct ganglionic 
 centres into one Cephalic mass, is a fact which is capable of actual demonstration. (See 
 the Memoir on the Branchiostoma or Amphioxus, by M. de Quatrefages, in the Annales des 
 Sciences Naturelles, 3 me Serie, Zoologie, torn, iv.) 
 
 426. Descending to the Invertebrated series, we find that, except in a few 
 of those which border most closely upon Vertebrata (such, for example, as 
 the Cuttle-Fish), the whole Cephalic mass appears to be made up of ganglia, 
 in immediate connection with the nerves of sense. These may appear to 
 form but a single pair ; yet they are in reality composed of several pairs, 
 fused (as it were) into one mass. Of this we may judge by determining the 
 number of distinct pairs of nerves which issue from them ; and also by the 
 investigation of the history of their development, the results of which bear a 
 close correspondence with those obtained in the preceding method. 
 
 a. Thus, Mr. Newport has shown, by studying the development of the head in certain 
 species of the class Myriapoda, that it is originally composed of no less than eight segments; 
 each having its peculiar appendages; and each possessing (like the segments of the body) 
 its own pair of ganglionic centres. These segments afterwards coalesce into two portions ; 
 of which the most anterior, made up by the union of four sub-segments, is termed the pro- 
 per cephalic; whilst the posterior, also made up of four sub-segments, is termed the basilar. 
 The four pairs of ganglia belonging to the cephalic portion coalesce into the one pair of 
 cephalic ganglia; whilst the other four pairs unite to form the first sub-cesophageal ganglia. 
 The first of the original sub-segments had, as its proper appendages, the antennae; and the 
 ganglia contained in it were evidently the proper centres of the antennal nerves. The 
 second had no movable appendages, but contained the eyes ; and its ganglia were evidently 
 the proper centres of the optic nerves. To the third belonged the first pair of jaws, the 
 maxillae; and to the fourth, the maxillary palpi: and these organs derived nerves from their 
 
 28* 
 
330 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 own ganglionic centres, belonging to their respective segments. Now as all these nerves 
 are found to proceed, in the adult animal from the single pair of Cephalic ganglia, it is 
 obvious that these combine the functions of the ganglionic centres of the nerves of the 
 antennae, eyes, and palpi, which are all sensory organs, aa well as of the maxillary nerves, 
 which must be chiefly motor. And it is equally obvious, that there is nothing in such an 
 animal, which can be compared to a pair of Cerebral hemispheres; since all the ganglia 
 of the original segments are directly connected with the appendages of those segments 
 respectively. 
 
 427. It is further to be remarked, that the development of the Cephalic 
 ganglia in the Invertebrata always bears an exact proportion to the develop- 
 ment of the eyes ; the other organs of special sense being comparatively 
 undeveloped ; whilst these, in all the higher classes at least, are instruments 
 of great perfection, and evidently connected most intimately with the direc- 
 tion of the movements of the animals. Of this fact we have a remarkable 
 illustration in the history of the metamorphoses of Insects ; the eyes being 
 almost rudimentary, and the Cephalic ganglia comparatively small, in most 
 Larvae ; whilst both these organs attain a high development in the Imago, to 
 whose actions the faculty of sight is essential. 
 
 428. Now upon making a similar comparison of the psychical operations 
 of these different classes of animals, we are led to perceive that, as we de- 
 scend from the higher to the lower Vertebrata, we gradually lose the indica- 
 tions of Intelligence and Will, as the sources of the movements of the animal; 
 whilst we see a corresponding predominance of those, which are commonly 
 denominated Instinctive, and which are performed (as it would appear) in 
 immediate respondence to certain sensations, without any intentional adapta- 
 tion of means to ends on the part of the individual, although such adaptive- 
 ness doubtless exists in the actions themselves, being a consequence of the 
 original constitution of the nervous system of each animal performing them. 
 It cannot be doubted by any person who has attentively studied the charac- 
 ters of the lower animals, that many of them possess psychical endowments, 
 corresponding with those which we term the intellectual powers and moral 
 feelings in Man; but in proportion as these are undeveloped, in that propor- 
 tion is the animal under the dominion of those Instinctive impulses, which, 
 so far as its own consciousness is concerned, may be designated as blind and 
 aimless, but which are ordained by the Creator for its protection from danger, 
 and for the supply of its natural wants. The same may be said of the Human 
 infant, or of the Idiot, in whom the reasoning powers are undeveloped. In- 
 stinctive actions may in general be distinguished from those which are the 
 result of voluntary power guided by reason, chiefly by the two following 
 characters: 1. Although, in many cases, experience is required to give the 
 Will command over the muscles concerned in its operations, no experience 
 or education is required, in order that the different actions, which result from 
 an Instinctive impulse, may follow one another with unerring precision. 2. 
 These actions are always performed by the same species of animal, nearly, 
 if not exactly, in the same manner; presenting no such variation in the means 
 adapted to the object in view, and admitting of no such improvement in the 
 progress of life, or in the succession of ages, as we observe in the habits of 
 individual men, or in the manners and customs of nations, that are adapted to 
 the attainment of any particular ends, by those voluntary efforts which are 
 guided by reason. The fact, too, that these instinctive actions are often seen 
 to be performed under circumstances rendering them nugatory, as reason 
 informs us, for the ends which they are to accomplish (as when the Flesh-fly 
 deposits her egg on the Carrion-plant instead of a piece of meat, or when the 
 Hen sits on a pebble instead of her egg) is an additional proof, that the 
 Instinctive actions of animals are prompted, like the consensual movements 
 
SENSORY GANGLIA. CONSENSUAL ACTIONS. 331 
 
 we have been recently inquiring into, by an impulse which immediately 
 results from a particular sensation being felt, and not by anticipation of the 
 effect which the action will produce. 
 
 429. The highest development of the purely Instinctive tendencies, is to be 
 found in the class of Insects ; and above all in the order Hymenoptera, and in 
 that of Neuroptera, which is nearly allied to it. It is in this division of the 
 class, that we find the highest development of the sensory organs and of the 
 cephalic ganglia, and the most active powers of locomotion. We may here 
 trace the operations of Instinct, with the least possible interference of Intelli- 
 gence. It is, of course, impossible to draw the line between the two sources 
 of action, with complete precision ; but we observe, in the habits of Bees and 
 other social Insects, every indication of the absence of a power of choice, and 
 of the entire domination of instinctive propensities called into action by sen- 
 sations. Thus, although Bees display the greatest art in the construction of 
 their habitations, and execute a variety of curious contrivances, beautifully 
 adapted to variations in their circumstances, the constancy with which indi- 
 viduals and communities will act alike under the same conditions, appears to 
 preclude the idea of their possessing any inherent power of spontaneously de- 
 parting from the line of action, to which they are tied down by the constitution 
 of their Nervous system. We do not find one individual or one community 
 clever, and another stupid; nor do we ever witness a disagreement, or any 
 appearance of indecision, as to the course of action to be pursued by the 
 several members of any republic.* For a Bee to be destitute of its peculiar 
 tendency to build at certain angles, would be as remarkable as for a Human 
 being to be destitute of the desire to eat, when his system should require 
 food. It may be doubted, on the other hand, whether there was ever a case, 
 in which an Insect of any kind could be taught to recognize any one, who had 
 been in the habit of feeding it; or to show any other unequivocal indications 
 of intelligence. 
 
 a. Such anecdotes have been related of Spiders; but these animals are the highest of the 
 Articulated series, having many points of approach to Vertebrata. It is probable, therefore, 
 that they may possess the rudiment of a Cerebrum ; a similar rudiment making its appear- 
 ance in the higher Cephalopods, which occupy a corresponding place in the Molluscous 
 series. 
 
 b. The only manifestation of educability, which the Author has ever noticed, during a 
 pretty long familiarity with the habits of Bees, is the acquirement of a power of distinguish- 
 ing the entrance of their hive from that of others around. When a swarm is first placed in 
 a new box, and the Bees have gone forth in search of food, they often seem puzzled on their 
 return, as to which is their own habitation ; more especially if there be several hives r with 
 similar entrances, in one bee-house ; and it has been proposed to paint these entrances of 
 different colours, in order to enable the Bee to distinguish them more readily. In a short 
 time, however, even without such aid, the Bees are seen to dart from a considerable height 
 in the air, directly down to their proper entrances ; showing that they have learned to dis- 
 tinguish these, by a memorial power. This the Author has observed most remarkably, in a 
 case in which a hive is placed in the drawing-room of a house, the entrance to it being be- 
 neath one of the windows ; the adjoining houses have windows precisely similar, except in 
 the absence of this small passage; and he has often noticed that, when a new stock has been 
 placed in this hive, the Bees are some days in learning the exact position of their house, con- 
 siderably annoying the neighbours by flying in at their windows. 
 
 * The community of Bees, though commonly reputed to be a monarchy, governed by a 
 sovereign, is really a republic, in which every individual performs its own independent part. 
 The function of the queen is simply that of breeding ; and as (among the Hive-Bees at least) 
 she is the only female, the purpose of the instinct, 'which leads the workers to treat her with 
 peculiar attention, is very obvious. But the idea that she directs the operations of the hive, 
 of exerts any peculiar control over the ordinary Bees, is entirely destitute of foundation. The 
 actions of the latter all tend to one common end ; simply because they are performed in re- 
 spondence to impulses, which all alike share. 
 
332 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 430. Thus the analysis of such of the actions of these animals, as are evi- 
 dently of a higher order than the simply-reflex, terminates in referring them to 
 the immediate directing influence of Sensations ; which, being received by the 
 cephalic ganglia through the sensory nerves, excite respondent motor impulses, 
 which are propagated to the various muscles of the body, through those por- 
 tions of the motor trunks that issue from them. As the term Instinctive has 
 been employed in a great variety of significations, and is very indefinite in its 
 character, we may more appropriately apply the designation Consensual to the 
 actions of this group. We have now to inquire, whether there is any class of 
 movements in Man and the higher Vertebrata, which seems to possess a simi- 
 lar character, and which may be regarded as the special function of the gangli- 
 onic centres under consideration. By far the larger part of the movements of 
 these animals (putting aside the simply-reflex) are performed under the direc- 
 tion of the Intelligence ; to which the sensations are communicated ; by which 
 a reasoning process is founded upon them ; and from which, at last, issues 
 that mandate, which is called the Will. Consequently, there are compara- 
 tively few movements, in the adult at least, which can be clearly distinguished 
 as neither voluntary, on the one hand, nor reflex on the other. Such actions, 
 however, do exist ; and serve to show that, although the Instinctive propensities 
 are in great measure superseded by the Intelligence, they may still operate 
 independently of it. As examples of this group, we may advert to the act of 
 Vomiting, produced by various causes which act through the organs of sense; 
 such as the sight of a loathsome object, a disagreeable smell, or a nauseous 
 taste. The excitement of the act of Sneezing by a dazzling light, is another 
 example of the same kind; for even if it be granted, that the act of sneezing 
 is ordinarily excited through the reflex system alone (which is by no means 
 certain), there can be no doubt that in this instance it cannot be brought into 
 play without a sensation actually felt. The same may be said of the Laughter 
 which sometimes involuntarily bursts forth, at the provocation of some sight 
 or sound, to which no distinct ludicrous idea or emotion can be attached ; and 
 of that resulting from the act of tickling, in which case it is most certainly 
 occasioned by the sensation, and by that alone. 
 
 431. The direct influence of Sensations, in occasioning and governing move- 
 ments, which are neither reflex nor voluntary, is most remarkably manifested 
 in many phenomena of disease. Thus in cases of excessive irritation of the 
 retina, which renders the eye most painfully sensitive to even a feeble amount 
 of light, the state designated as photophobia, the eyelids are drawn together 
 spasmodically, with such force as to resist very powerful efforts to open them ; 
 and if they be forcibly drawn apart, the pupil is frequently rolled beneath the 
 upper lid (apparently by the action of the inferior oblique muscle), much fur- 
 ther than it could be carried by a voluntary effort. And in Pleuritis, Pericar- 
 ditis, and other painful affections of the parietes of the chest, we may observe 
 the usual movements of the ribs to be very much abridged ; the dependence of 
 this abridgement upon the painful sensation which they occasion, being most 
 evident in those instances in \vhich the affection is confined to one side, for 
 there is then a marked curtailment in its movements, whilst those of the other 
 side may take place as usual ; a difference which cannot be reflex, and which 
 the Will cannot imitate. Again, in some Convulsive disorders, we observe 
 that the paroxysms are excited by causes, which act through the organs of 
 special sense ; thus in Hydrophobia, we observe the immediate influence of 
 the sight or the sound of liquids, and of the slightest currents of air ; and in 
 many Hysteric subjects, the sight of a paroxysm in another individual is the 
 most certain means of inducing it in themselves. 
 
 432. The results of experiments, so far as any reliance can be placed upon 
 them, confirm these views ; by showing that any disturbance of the usual 
 
SENSORY GANGLIA. CONSENSUAL ACTIONS. 333 
 
 actions of the organs of sense, and of the nervous centres with which they are 
 connected, in animals whose movements are directly governed by the sensations 
 received through these, is followed by abnormal movements. Thus it has 
 been ascertained by Flourens, that a vertiginous movement may be induced in 
 pigeons, by simply blindfolding one eye ; and Longet has produced the same 
 effect, by evacuating the humours of one eye. These vertiginous movements 
 are more decided and prolonged, when, instead of blinding one eye, one of 
 the tubercula quadrigemina is removed ; the animal continuing to turn itself 
 towards the injured side, as if rotating on an axis. The results of the experi- 
 ments of M Flourens upon the portion of the Auditory nerve proceeding to 
 the Semi-circular canals, are still more extraordinary. Section of the hori- 
 zontal semi-circular canal in Pigeons, on both sides, induces a rapid jerking 
 horizontal movement of the head, from side to side ; and a tendency to turn 
 to one side, which manifests itself whenever the animal attempts to walk for- 
 wards. Section of a vertical canal, whether the superior or inferior, of both 
 sides, is followed by a violent vertical movement of the head. And section of 
 the horizontal and vertical canals at the same time, causes horizontal and ver- 
 tical movements. Section of either canal on one side only, is followed by the 
 same effect as when the canal is divided on both sides ; but this is inferior in 
 intensity- The movements continue to be performed during several months. 
 In Rabbits, section of the horizontal canal is followed by the same movements, 
 as those exhibited by pigeons ; and they are even more constant, though less 
 violent. Section of the anterior vertical canal causes the animal to make con- 
 tinued forward somersets; whilst section of the posterior vertical canal occa- 
 sions continual backward somersets. The movements cease when the animal 
 is in repose ; and they recommence when it begins to move, increasing in 
 violence as its motion is more rapid. These curious results are supposed by 
 M. Flourens to indicate, that the nerve supplying the semi-circular canals does 
 not minister to the sense of hearing, but to the direction of the movements of 
 the animal: but they are fully explained upon the supposition that the normal 
 function of the semi-circular canals is to indicate to the animal the direction 
 of sounds, and that its movements are partly determined by these; so that a 
 destruction of one or other of them will produce an irregularity of movement 
 (resulting, as it would seem, from a sort of giddiness on the part of the animal), 
 just as when one of the eyes of a bird is covered or destroyed, as in the ex- 
 periments just cited. 
 
 433. But we may trace the influence of the Sensory ganglia, not merely in 
 their direct and independent operation on the muscular system, but also in the 
 manner in which they participate in all Voluntary actions. There can be no 
 doubt that, in every exertion of the will upon the muscular system, we are 
 guided by the sensations communicated through the afferent nerves, which 
 indicate to the Sensorium the state of the muscle. Many interesting cases 
 are on record, which show the necessity of this Muscular Sense, for determin- 
 ing voluntary contraction of the muscle. Thus, Sir C. Bell (who first promi- 
 nently directed attention to this class of facts, under the designation of the 
 Nervous Circle), mentions an instance of a woman, who was deprived of it in 
 her arms, without losing the motor power; and who stated, that she could not 
 sustain anything in her hands (not even her child), by the strongest effort of 
 her will, unless she kept her eyes constantly fixed upon it; the muscles losing 
 their power, and the hands dropping the object, as soon as the eyes were 
 withdrawn from it. Here the employment of the visual sense supplied the 
 deficiency of the muscular ; but instead of being inseparably connected, as the 
 latter is in the state of health, with the action of the muscle, the former could 
 be only brought to bear by an effort of the will ; and the sustaining power was 
 therefore dependent, not upon the immediate influence of the will upon the 
 
334 FUNCTIONS or THE NERVOUS SYSTEM. 
 
 muscle, but upon the voluntary direction of the Sight towards the object to be 
 supported. Again, in the production of vocal sounds, the nice adjustment of 
 the muscles of the larynx, which is requisite to produce determinate tones, 
 can only be learned in the first instance under the guidance of the sensation 
 of the sounds produced, and can only be effected by an act of the will, in 
 obedience to a mental conception (a sort of inward sensation) of the tone to 
 be uttered, which conception cannot be formed, unless the sense of hearing 
 has previously brought similar tones to the mind. Hence it is, that persons 
 who are born deaf, are also dumb. They may have no malformation of the 
 organs of speech ; but they are incapable of uttering distinct vocal sounds or 
 musical tones, because they have not the guiding conception, or recalled sen- 
 sation, of the nature of these. By long training, and by efforts directed by the 
 muscular sense of the larynx itself, some persons thus circumstanced have 
 acquired the power of speech ; but the want of a sufficiently definite control 
 over the vocal muscles, is always very evident in their use of the organ. 
 
 434. The conjoint movements of the two eyes, which concur to direct 
 their axes towards the same object, are among the most interesting of these 
 actions, in which Volition and Consensual action are alike concerned ; and 
 they afford an excellent illustration of the necessity for guiding sensations, 
 to determine the actions of muscles. The sensations, however, are not so 
 much those of the muscles themselves, as those received through the visual 
 organ; but the former appear capable of continuing to guide the harmonious 
 movements of the eyeballs, when the sense of sight has been lost. It is a 
 striking peculiarity of these movements, that, in the majority of them, two 
 muscles or combinations of muscles of opposite action are in operation at 
 once ; thus, when the eyes are made to rotate in a horizontal plane, the in- 
 ternal rectus of one side acts with the external rectus of the other. In most 
 other cases, there is a difficulty in performing two opposite movements, on 
 the two sides at the same time. Thus, if we move the right hand as if wind- 
 ing on a reel, and afterwards make the left hand revolve in a contrary direc- 
 tion, no difficulty is experienced; but if we attempt to move the two at the 
 same time in contrary directions, we shall find it almost impossible. As the 
 Consensual movements of the Eyes are of sufficient interest and importance, 
 to require a detailed consideration, they will be examined more fully at the 
 close of the present section ( 450 456). 
 
 435. If the preceding views be correct, we may regard the series of Gan- 
 glionic centres which have been enumerated ( 422, 423), as constituting the 
 real Sensorium ; each ganglion having the power of cummunicating to the 
 mind the impressions derived from the organ, with which it is connected, and 
 of exciting automatic muscular movements in respondence to these sensations. 
 If this position be denied, we must either refuse the attribute of consciousness 
 to those animals, which possess no other encephalic centres than these ; or 
 we must believe that the addition of the Cerebral hemispheres, in the Verte- 
 brated series, alters the endowments of the Sensory ganglia, an idea which 
 is contrary to all analogy. So far as the results of experiments can be relied 
 on, they afford a corroboration of these views. The degree in which animals 
 high in the scale of organization can perform the functions of life, without 
 any other centre of action than the Ganglia of Special sense, the Medulla 
 Oblongata/and the Cerebellum, appears extraordinary to those who are accus- 
 tomed to regard the Cerebral Hemispheres as the centre of all energy. From 
 the experiments of Flourens, Hertwig, Magendie, and others, it appears that 
 not only Reptiles, but Birds and Mammalia, may survive for many weeks or 
 months (if their physical wants be duly supplied) after the removal of the 
 whole Cerebrum. It is difficult to substantiate the existence in them of 
 actual Sensation; but some of their movements appear to be of a higher kind 
 
SENSORY GANGLIA. CONSENSUAL AND EMOTIONAL ACTIONS. 335 
 
 than those resulting from mere Reflex action. One of the most remarkable 
 phenomena exhibited by such a being, is the power of maintaining its equili- 
 brium, which could scarcely exist without consciousness. If it be laid upon 
 the back, it rises again; if pushed, it walks. If a Bird thus mutilated be 
 thrown into the air, it flies; if a Frog be touched, it leaps. It swallows food 
 and liquid, when they are placed in its mouth; and the digestive operations, 
 the acts of excretion, &c., take place as usual. In the case of a Pigeon ex- 
 perimented on by Malacorps, which is recorded by Magendie, there appears 
 sufficient proof of the persistence of a certain amount of sensation. Although 
 the animal was not affected by a strong light suddenly made to fall upon its 
 eyes, it was accustomed, when confined in a darkened or partially-illuminated 
 room, to seek out the light parts ; and it avoided objects that lay in its way. 
 In the same manner, it did not seem to be affected by sudden noises; but at 
 night, when it slept with closed eyes and its head under its wing, it would 
 raise its head in a remarkable manner, and open its eyes, on the slightest 
 noise ; speeflily relapsing into a state of complete unconsciousness. Its 
 principal occupation was to prune its feathers and scratch itself. The con- 
 dition of such a being seems to resemble that of a Man, who is in a slumber 
 sufficiently deep to lose all distinct perception of external objects, but who is 
 yet conscious of sensations, as appears from the movements occasioned by 
 light or by sounds, or from those which he executes to withdraw the body 
 from an uneasy position.* 
 
 436. Among the ganglia of special sensation, the functions of the Optic 
 Lobes, or Corpora Quadrigemina, have been chiefly examined. The re- 
 searches of Flourens and Hertwig have shown, that their connection with 
 the visual function, which might be inferred from their anatomical relations, 
 is substantiated by experiment. The partial loss of the ganglion on one 
 side produces partial loss of power and temporary blindness on the opposite 
 side of the body, without necessarily destroying the mobility of the pupil; 
 but the removal of a larger portion, or complete extirpation of it, occasions 
 permanent blindness and immobility of the pupil, with temporary muscular 
 weakness, on the opposite side. This temporary disorder of the muscular 
 system sometimes manifests itself (as already stated) in a tendency to move on 
 the axis, as if the animal were giddy. No disturbance of consciousness ap- 
 pears to be produced; and Hertwig states that he never witnessed the con- 
 vulsions, which Flourens mentions as a consequence of the operation, and 
 which were probably occasioned by his incision having been carried too 
 deeply. These results are confirmed by pathological phenomena in Man; 
 for there are many instances on record, in which blindness has been one of 
 the consequences of diseased alterations in one or both tubercles ; and in 
 some of the cases, in which the lesion extended to parts seated beneath the 
 tubercles, disturbed movements were observed. No definite conclusions can 
 be drawn, either from experiment or from pathological observation, in regard 
 to the functions of the Thalami Optici and Corpora Striata; but there is 
 nothing in these sources of information to oppose the views already offered, 
 which are based on other foundations. 
 
 437. Emotional Actions. There appears strong reason for regarding the 
 Ganglionic tract, which is the instrument of Consensual actions, as the imme- 
 diate centre also of those movements which directly result from the excite- 
 ment of the Emotions. Several considerations tend' to establish this position. 
 
 * It must not be forgotten that, in such experiments, the severity of the operation will of 
 itself occasion a suspension or disturbance of the functions of parts that remain ; so that the 
 loss of a power must not be at once inferred from the absence of its manifestations. But the 
 persistence of a power, after the removal of a particular organ, is a clear proof that it cannot 
 be the peculiar attribute of that organ. 
 
336 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 In the first place, that the channel through which the direct impulses of the 
 Emotions are conveyed to the Muscles, is not the same with that which con- 
 veys to them the mandates of the Will, appears sufficiently established by 
 Pathological observation ; since cases of paralysis not unfrequently occur, in 
 which the muscles are obedient to an emotional impulse, though the will exerts 
 no power over them ; whilst, on the other hand, the will may have its due 
 influence, and yet the emotional state cannot manifest itself. This is espe- 
 cially remarkable in the different forms of paralysis of the Facial nerve ; since 
 the facial muscles manifest the ordinary influence of the Emotions, more evi- 
 dently than any others. But it is not, however, confined to them; thus, for 
 example, the arm of a man, which no effort of his will could move, has been 
 seen to be violently agitated at the sight of a friend. Dr. M. Hall has inferred 
 from cases of this kind, that the Spinal system of nerves constitutes the chan- 
 nel of the Emotional actions; but all which is proved by them is, that these 
 are not effected through the same agency with the Volitional ; and the idea 
 that they are of the same character with Reflex actions is distinctly negatived 
 by the fact, that in a great majority of instances, they are excited through the 
 organs of special sense, and that consciousness is a distinct element in the 
 series of changes which ends in their performance. These facts would lead 
 us to infer, that the Emotional actions are dependent on a set of centres, in- 
 termediate between the Cerebrum and the Spinal Cord ; a position which is 
 precisely that of the ganglionic tract under consideration. In the next place 
 it may be remarked, that the Emotions are so closely linked with Sensations, 
 as to be regarded by many Metaphysicians as almost identical with them ; and 
 this connection is universally recognized in the term Feelings popularly ap- 
 plied to both. Like the Instinctive tendencies of Animals, the Emotional 
 states follow directly and necessarily upon Sensations, without any interven- 
 ing process of ratiocination ; and there is such a marked correspondence in 
 the'character of the actions, which flow from these sources, as to point to the 
 conclusion of the identity of the conditions on which they immediately de- 
 pend. Of this, an example will be presently given. We have seen that the 
 Sensory ganglia must necessarily be regarded as the instruments of the In- 
 stinctive actions ; and a probable inference may therefore be drawn from this 
 fact, in regard to their relation to those which (in Man) are designated as 
 Emotional.* A third argument in support of this view may be drawn from 
 the fact, of the very close connection of this division of the nervous centres, 
 with the nervous trunks, through which the emotional states are excited, and 
 the respondent muscular actions are stimulated. For the Sensory ganglia re- 
 ceive all those nerves, which communicate the Sensations through whose 
 immediate agency the Emotion is excited ; and the nerves of the Orbit, the 
 Face, and the Respiratory organs, those most concerned in producing the 
 movements, by which the emotions are expressed or manifested, arise in 
 their immediate proximity. It is chiefly through these nerves, too, that the 
 
 * It seems by no means certain, that we are always to attribute to the lower animals the 
 Emotions which we ourselves feel, because they perform movements analogous to those by 
 which we ordinarily express them: for the movements may be directly excited by the Sen- 
 sations, without the intervention of the Emotion ; just as in ourselves, involuntary laughter 
 is occasioned by tickling, although no ludicrous emotion be excited ; or as Vomiting results 
 from the sight of a loathsome object, rather in respondence to the sensation of nausea, than 
 to the emotion of disgust which it concurrently excites. We might, on equally valid grounds, 
 assert, that the Bee goes through a process of mathematical ratiocination, before it commences 
 the construction of its cell. The purpose of the Emotion, in animals possessed of Intelligence, 
 may be rather to act upwards upon it and, although closely connected with the sensation 
 which excites it ; it may be no more necessary to the resulting muscular movement, than 
 sensation is to reflex action. On this view, all actions of the directly Emotional character 
 would be in reality purely Consensual. 
 
EMOTIONAL AND INSTINCTIVE ACTIONS. 337 
 
 abnormal movements are effected, in those disorders of the Nervous centres, 
 which may be most distinctly referred to the Emotional system ; such as 
 Chorea and Hysteria. 
 
 438. The correspondence between the purely Emotional actions in Man, 
 and those actions in the lower animals to which we give the name of Instinc- 
 tive, may be made evident by a very simple illustration. The Cuttle-fish is 
 well known to discharge its ink, when pursued, and to tinge the water around 
 with a colour so deep, as to enable it to escape under the cloud thus formed. 
 Now it is not to be supposed, that the Cuttle-fish has any notion of the pur- 
 pose which this act will serve ; since its constancy and uniformity, and the 
 provision for its performance immediately on the emersion of the young ani- 
 mal from the egg, forbid our regarding it as the result of any act of reasoning. 
 Further, the ink is an excretion which corresponds to the urine (having been 
 found to contain urea) ; and every one knows how strong an impulse to dis- 
 charge this, is frequently caused by mental emotion. The same may be said 
 of the strongly odorous secretions possessed by many Mammalia, which are 
 discharged under similar circumstances, and evidently with^ the same object; 
 though of that object, the animal itself be not conscious. The emotion of 
 fear involuntarily opens the sphincters, and causes the contraction of the recep- 
 tacle, in one case as in the other ; and the great difference between the condi- 
 tion of Man, and that of the lower animals, in this respect, is simply that, in 
 the former, the purely Emotional or Instinctive actions are few in comparison 
 with the whole, whilst in the latter they constitute by far the largest part; and 
 also that Man has much greater power of controlling these actions by a volun- 
 tary effort, than that which the lower animals possess, although even he is not 
 unfrequently compelled by the strength of his Emotions to act against his 
 Will.- Thus, we see or hear something ludicrous, which involuntarily pro- 
 duces laughter, although we may have the strongest motives for desiring to 
 restrain it. 
 
 a. It is a very interesting question, how far actions at first performed voluntarily by Man, 
 may by habit cease to require an effort of the Will; being prompted, like the movements of 
 the Consensual class, by the direct impulse of sensations. Thus we all know that, in walking 
 along an accustomed road, we frequently occupy our minds with some continuous train of 
 thought, and yet our limbs continue to move under us with regularity, until we are surprised 
 by finding ourselves at the place of our destination, or perhaps at some other which we had 
 not intended to visit, but to which habit has conducted us. Or we may read aloud for a 
 long time, without having in the least degree comprehended the meaning of the words we 
 have uttered ; our attention having been closely engaged by some engrossing thoughts or 
 feelings within. Or a Musician may play a well-known piece of music, whilst carrying on 
 an animated conversation ; the Author has known a skilful performer who could play at 
 sight whilst thus occupied. Now in such a case it would be said by some Metaphysicians 
 (acknowledging, as most do, that the mind cannot will two different things at the same time) 
 that the Volition is in a sort of vibratory condition between the two sets of actions, now 
 prompting one, and now the other! But it would seem much more conformable to the 
 analogy afforded by other psychical phenomena, to refer the habitual series of actions to the 
 same operation of the Nervous System with the Instinctive ; and perhaps the term Automatic 
 may be fairly applied to the whole of this group. It is well known that in cases of severe 
 injury of the brain, in which Intelligence and Will seem completely in abeyance, habitual 
 actions may be often excited. Thus, Dr. Perceval, in his Essay on habit, mentions the case 
 of a snuff-taking Countess, in whom, when seized with apoplexy, irritation of the -nose with 
 a feather produced contraction of the fore-finger and thumb of the right Jtiand; and Mr. 
 Traverse has recorded a similar fact in the case of a boy, who, when apparently insensible 
 from depressed fracture of the skull, assisted in removing his clothes, preparatorily to the 
 required operation. 
 
 439. The purely Emotional actions are not always directly excited, however, 
 by external sensations ; for they may result from the operations of the Mind 
 itself. Thus involuntary laughter may result from a ludicrous idea, called up 
 by some train of association, and having no obvious connection with the sen- 
 
 29 
 
338 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 sation which first set this process in operation; and the various movements 
 of the face and person, by which Actors endeavour to express strong Emotions, 
 are only effectual in conveying their meaning, when they result from the actual 
 working of the emotions in the mind of the performer, who has, by an effort 
 of the will, identified himself (so to speak) with the character he personates. 
 A still more remarkable case is that, in which paroxysms of Hysterical con- 
 vulsion, in themselves beyond the power of the Will to excite or to control, 
 are brought on by a voluntary effort; which seems to act by "getting up," so 
 to speak, the state of feeling, which is the immediate cause of the disordered 
 movements. In all these instances, and others of like nature, it would seem 
 as if the agency of the Cerebrum produced the same condition in the Sensory 
 ganglia and their motor fibres, as that which is more directly excited by sen- 
 sations received through their own afferent nerves. It may be reasonably 
 surmised, that the Sensory ganglia, like the Cephalic ganglia which are the 
 instruments of the Instinctive actions of the lower animals, can only be excited 
 to action by stimuli immediately operating upon them ; but that these stimuli 
 may be either Sensations directly originating in external objects, or Concep- 
 tions resulting from the remembrance of those objects, of which there is strong 
 reason to believe that the Cerebrum is the storehouse. 
 
 440. The Emotions are concerned in Man, however, in many actions, which 
 are in themselves strictly voluntary. Unless they be strongly excited, so as 
 to get the better of the Will, they do not operate directly through the nervous 
 trunks, but are subservient to the intellectual operations; to which they supply 
 materials, or motives. Thus, of two individuals, with differently constituted 
 minds, one shall judge of everything through the medium of a gloomy morose 
 temper, which, like a darkened glass, represents to his judgment the whole 
 world in league to injure him ; and all his determinations, being based upon 
 this erroneous view, exhibit the indications of it in his actions ; which are 
 themselves, nevertheless, of an entirely voluntary character. On the other 
 hand, a person of a cheerful, benevolent disposition, looks at the world around 
 as through a Claude Lorraine glass, seeing everything in its brightest and 
 sunniest aspect; and, with intellectual faculties precisely similar to those of 
 the former individual, he will come to opposite conclusions ; because the 
 materials, which form the basis of his judgment, are submitted to it in a very 
 different condition. Various forms of Moral Insanity exhibit the same con- 
 trast in a yet more striking light. We not unfrequently meet with individuals, 
 still holding their place in society, who are accustomed to act so much upon 
 feeling, and to be so little guided by reason, as to be scarcely regarded as 
 sane ; and a very little exaggeration of such a tendency causes the actions to 
 be so injurious to the individual himself, or to those around him, that restraint 
 is required, although the intellect is in no way disordered, nor are any of the 
 feelings perverted. Not unfrequently we may observe similar inconsistencies 
 resulting from the habitual indulgence of one particular feeling, or a morbid 
 exaggeration of it. The mother who, through weakness of will, yields to her 
 instinctive fondness for her offspring, in allowing it gratifications which she 
 knows to be injurious to it, is placing herself below the level of many less 
 gifted beings. The habit of yielding to a natural infirmity of temper often 
 leads into paroxysms of ungovernable rage, which, in their turn, pass into a 
 state of maniacal excitement. It is not unfrequently seen, that a delusion of 
 the intellect (constituting what is commonly known as Monomania) has in 
 reality resulted from a disordered state of the feelings, which have represented 
 every occurrence in a wrong light to the mind of the individual. All such 
 conditions are of extreme interest, when compared with those which are met 
 with amongst idiots, and animals enjoying a much lower degree of intelligence : 
 for the result is much the same, in whatever way the balance between the 
 

 NERVES OF SPECIAL SENSE. OLFACTIVE. 339 
 
 feelings and the judgment (which is so beautifully adjusted in the well-ordered 
 mind of Man) is disturbed ; whether by a diminution of the intelligence, or 
 by an exaltation of the feelings. These views will probably be found correct, 
 whatever be the truth of the speculation with which they have been here con- 
 nected, as to the part of the Nervous system concerned in the performance of 
 the purely Emotional actions. That their channel is alike distinct, however, 
 from that of the Voluntary movements, and from that of Reflex operations, 
 must be apparent to any one who fairly weighs the evidence. 
 
 441. Nerves connected with the Sensory Ganglia. That the First pair, 
 or Olfactory nerves, minister to the sense of smell, has long been known, 
 yet it could not be predicted without experimental inquiry, that it is not a 
 conductor of the impressions which produce ordinary sensation; nor that it 
 is destitute of all power of exciting muscular movement, either by direct or 
 reflex action. Anatomical examination of the distribution of this nerve, proves 
 that it is not one which directly conveys motor influence to any muscles ; 
 since all its branches are distributed to the membrane lining the nasal cavity. 
 Experimental inquiry leads to the same result ; for no irritation of the pedun- 
 cles or branches excites any muscular movement. Further, no irritation of 
 any part of this nerve excites reflex actions through other nerves. Again, it 
 is not a nerve of common sensation ; for animals exhibit no sign of pain, 
 when it is subjected to any kind of irritation. Neither the division of the 
 nerve, nor the destruction of the olfactive ganglia, seems to inconvenience 
 them materially. They take their food, move with their accustomed agility, 
 and exhibit the usual appetites of their kind. The common sensibility of the 
 parts contained in the olfactive organ is in no degree impaired, as is shown 
 by the effect of irritating vapours ; but the animals are destitute of the sense 
 of smell, as is shown by the way in which these vapours affect them. At 
 first they appear indifferent to their presence, and then suddenly and vehe- 
 mently avoid them, as soon as the Schneiderian membrane becomes irritated. 
 Moreover, if two dogs, with the eyes bandaged, one having the olfactory 
 nerves and ganglia sound, and the other having had them destroyed, are 
 brought into the neighbourhood of the dead body of an animal, the former 
 will examine it by its smell ; whilst the latter, even if he touches it, pays no 
 attention to it. This experiment Valentin states that he has repeated several 
 times, and always with the same results. Further, common observation 
 shows that sensibility to irritants, such as snuff, and acuteness of the power 
 of smell, bear no constant proportion to one another ; and there is ample 
 pathological evidence, that the want of this sense is connected with some 
 morbid condition of the olfactory nerves or ganglia. It is well known that 
 Magendie has maintained, that the Fifth pair in some way furnishes conditions 
 requisite for the enjoyment of the sense of smell; asserting that, when it is 
 cut, the animal is deprived of this. But his experiments were made with ir- 
 ritating vapours, which excite sternutation or other violent muscular actions, 
 not through the Olfactory nerve, but through the Fifth pair ; and the experi- 
 ments of Valentin, just related, fully prove that the animals are not sensitive 
 to odours, strictly so called, after the Olfactory has been divided. It is by 
 no means improbable, however, that the acuteness of the true sense of smell 
 may be diminished by section of the Fifth pair; since the olfactory mem- 
 brane is no longer duly moistened by its proper secretion; and, when dry, it is 
 not so susceptible of the impressions made by those minute particles of odori- 
 ferous substances, to which the excitement of the sensation must be referred. 
 
 442. That the Second pair, or Optic nerves, have an analogous character, 
 appears alike from anatomical and experimental evidence. No chemical or 
 mechanical stimulus of the nerve produces direct muscular motion ; nor does 
 it give rise, as far as can be ascertained, to indications of pain ; whence it may 
 
340 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 [Fig. 158. 
 
 be concluded, that this nerve is not one of common sensation. That the ordi- 
 nary sensibility of the eyeball remains, when the functions of the Optic nerve 
 are completely destroyed, is well known ; as is also the fact, that division of 
 it puts an end to the power of vision. Valentin states that, although the Optic 
 nerve may, like other nerves, be in appearance completely regenerated, he has 
 
 never been able to obtain any evi- 
 dence that the power of sight has 
 been in the least degree recovered. 
 He remarks that animals suddenly 
 made blind exhibit great mental dis- 
 turbance, and perform many unaccus- 
 tomed movements ; and that the com- 
 plete absence of the power of vision 
 is easily ascertained. Morbid changes 
 are sometimes observed to take place 
 in eyes, whose Optic nerve has been 
 divided ; but these are by no means 
 so constant or so extensive, as when 
 the Fifth pair is paralyzed ; and they 
 may not improbably be attributed to 
 the injury, occasioned by the opera- 
 tion itself, to the parts within the or- 
 bit. It is well known that, when 
 amaurosis is produced by a morbid 
 condition of the Optic nerve alone, 
 the eye retains its usual appearance ; 
 but, if the amaurosis be complete, the 
 texture of the Retina undergoes a re- 
 markable change, ceasing to exhibit 
 that peculiar structure which normally 
 characterizes it. Neither primitive 
 nervous fibrils, nor nucleated vesicles, 
 can be distinguished in it, and the 
 yellow spot of Soemmering becomes 
 paler, and is at last undistinguishable. 
 But if a very slight degree of sensi- 
 bility to light remain, these changes 
 are much less decided. Further, it is 
 well known that, when the sight is 
 destroyed by a disease or injury, 
 which prevents the passage of light through the pupil, the whole eye becomes 
 more or less atrophied ; and the Retina and Optic nerve, although previously 
 sound, are found after death, (if the morbid condition have lasted sufficiently 
 long) to have lost their characteristic structure. It seems evident, then, that 
 the continuance of the functional operations of nerves, is a necessary condi- 
 tion of the maintenance of their normal organization; and we can very well 
 understand that this should be the case, from the analogy of other parts of the 
 system. 
 
 443. The Optic nerve, though analogous to the Olfactory in all the points 
 hitherto mentioned, differs from it in one important respect ; that it has the 
 power of conveying impressions which shall excite reflex muscular motions. 
 This is especially the case in regard to the Iris, the ordinary actions of which 
 are regulated by the degree of light impinging on the retina. When the optic 
 nerve is divided, a contraction of the pupil takes place; but this does not 
 occur, if the connection of this nerve with the third pair, through the nerv- 
 
 A view of the 2d pair or optic, and the origins of 
 seven other pairs. 1, 1. Globe of the eye, the one 
 on the left hand is perfect, but that on the right has 
 the sclerotic and choroid removed to show the 
 retina. 2. The chiasm of the optic nerves. 3. The 
 corpora albic an tia. 4. The infundibulura. 5. The 
 Pons Varolii. 6. The medulla oblongata. The 
 figure is on the right corpus pyramidale. 7. The 
 3d pair, motores oculi. 8. 4th pair, pathetici. 9. 
 5th pair,trigemini. 10. 6th pair, abducentes. 11. 
 7th pair, auditory and facial. 12. 8th pair, pneumo- 
 gastric, spinal accessory, andjglosso-pharyngeal. 
 13. 9th pair, hypoglossal. ] 
 
NERVES OF SPECIAL SENSE. OPTIC. 341 
 
 ous centres, be in any way interrupted. After such division (if complete), 
 the state of the pupil is not affected by variations in the degree of light im- 
 pinging on the retina ; except in particular cases, in which it is influenced 
 through other channels. Thus, in a patient suffering under amaurosis of one 
 eye, the pupil of the affected eye is often found to vary in size, in accord- 
 ance with that of the other eye ; but this effect is produced by the action of 
 light on the retina of the sound eye, which produces a motor change in the 
 third pair on both sides. Further, as has been formerly stated ( 395), the 
 impression only of light upon the retina may give rise to contraction of the 
 pupil, by reflex action, when the optic nerve is itself sound ; whilst no sen- 
 sations are received through the eye, in consequence of disease in the sen- 
 sorial portion of the nervous centres. Although the contraction of the pupil 
 is effected by the influence of motor fibres, which proceed to the sphincter 
 of the Iris from the third pair of nerves, through the Ophthalmic ganglion, 
 there is evidence that its dilatation depends rather upon the influence it de- 
 rived from that ganglion itself, and from the Sympathetic system, of which it 
 forms part. Some have attempted to show, that the actions of the iris are in 
 a slight degree voluntary, because, by an effort of the will, they could occa- 
 sion contraction of the pupil ; but this so-called voluntary contraction is al- 
 ways connected with a change in the place of the eyeball itself, occasioned 
 by an action of some of its muscles. It is principally noticed under the two 
 following conditions : 1. When an object is brought very near the eye, and we 
 steadily fix our attention upon it, the axes of the two eyes are made to con- 
 verge ; and if this convergence be carried to a considerable extent, so that the 
 pupils of both eyes are sensibly directed towards the inner canthus, a con- 
 traction of the pupil takes place. The final cause or purpose of this contrac- 
 tion is very evident. When an object is brought near the eye, the rays pro- 
 ceeding from it would enter the pupil (if it remained of its usual size) at an 
 angle of divergence, so much greater than that which would allow them to 
 be properly refracted to a focus, that indistinct vision \vould necessarily re- 
 sult. By the contraction of the pupil, however, the extreme or most diver- 
 gent rays are cut off, and the pencil is reduced within the proper angle. The 
 principle is precisely the same as that on which the optician applies a stop 
 behind his lenses, which reduces their aperture in proportion to the shortness 
 of their focal distance. 2. Contraction of the pupil is also noticed, when the 
 eyeball is performing that rotation upwards and inwards, which, when per- 
 formed along with violent respiratory actions, or during sleep, mus't be regarded 
 as involuntary. This rotation also takes place, to a slight degree, when the 
 eyelid is depressed, as in ordinary winking ; and it is obvious that, in this 
 manner, the surface of the eye is more effectually swept free from impurities 
 which may have gathered upon it, than it would be by the downward motion 
 of the lid alone. But the pupil is not contracted, when the eyeball is volun- 
 tarily rotated upwards and inwards. 
 
 444. Besides the contractions of the pupil, another action, which has been 
 sometimes spoken of as reflex, is produced through the Optic nerve, the 
 contraction of the Orbicularis muscle under the influence of strong light, or 
 when a foreign body is suddenly brought near the eye. But this cannot be 
 produced by any mechanical stimulation, and it evidently involves sensation ; 
 in fact, it is a movement of a consensual kind, produced by the painful effect 
 of light, which gives rise to the condition well characterized by the term 
 photophobia. The involuntary character of it must be evident to every one, 
 who has been engaged in the treatment of diseases of the eyes; and the effect 
 of it is aided by a similarly-involuntary movement of the eyeball itself, which 
 is rotated upwards and inwards, to a greater extent than the Will appears able 
 to effect. 
 
 29* 
 
342 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 445. There is a further peculiarity, of a very marked kind, attending the 
 course of the Optic nerves; this is the crossing or decussation which they 
 
 [Fig. 159. 
 
 [Fig. 160. 
 
 Plan of the optic nerves on a 
 small scale, showing their diver- 
 gence from the chiasma, c, and 
 their junction with the globe, on 
 the inner side of the axis of the 
 humors.] 
 
 Course of fibres }n the chiasma, as exhibited by 
 tearing off the superficial bundles from a specimen 
 hardened in spirit, a. Anterior fibres, commissural 
 between the two retinse. -p. Posterior fibres, com- 
 missural between the thalami. a', p'. Diagram of 
 the preceding.] 
 
 undergo, more or less completely, whilst proceeding from their ganglia to the 
 eyes. In some of the lower^ animals, in which the two eyes (from their lateral 
 position) have entirely different spheres of vision, the decussation is complete ; 
 the whole of the fibres from the right optic ganglion passing into the left eye, 
 and vice versa. This is the case, for example, with most of the Osseous 
 Fishes (as the cod, halibut, &c.) ; and also, in great part at least, with Birds. 
 In the Human subject, however, and in animals which, like him, have the two 
 eyes looking in the same direction, the decussation seems less complete ; but 
 there is a very remarkable arrangement of the fibres, which seems destined to 
 bring the two eyes into peculiarly consentaneous action. The posterior border 
 of the Optic Chiasma is formed exclusively of commissural fibres, which pass 
 from one optic ganglion to the other, without entering the real optic nerve. 
 Again, the anterior border of the Chiasma is composed of fibres, which seem, 
 in like manner, to act as a commissure between the two retinas; passing from 
 one to the other, without any connection with the optic ganglia. The tract 
 which lies between the two borders, and occupies the middle of the Chiasma, 
 is the true Optic Nerve ; and in this it would appear that a portion of the fibres 
 decussates, whilst another portion passes directly from each Optic ganglion 
 into the corresponding eye. The fibres which proceed from the ganglia to 
 the retinae, and constitute the proper Optic Nerves, may be distinguished into 
 an internal and an external tract. Of these, the external on each side, passes 
 directly onwards to the eye of that side ; whilst the internal crosses over to 
 the eye of the opposite side. The distribution of these two sets of fibres in 
 the retina of each eye respectively, is such that, according to Mr. Mayo, the 
 fibres from either optic ganglion will be distributed to its own side of both 
 eyes ; the right optic ganglion being thus exclusively connected with the outer 
 part of the retina of the right eye, and with the inner part of the retina of the 
 left eye ; and the left optic ganglion being, in like manner, connected exclu- 
 sively with the outer side of the left retina, and with the inner side of the 
 right. Now as either side of the eye receives the images of objects, which 
 are on the other side of its axis, it follows, if this account of their distribution 
 be correct, that in Man, as in the lower animals, each ganglion receives the 
 sensations of objects situated on the opposite sides of the body. The purpose 
 of this decussation may be, to bring the visual impressions, which are so im- 
 portant in directing the movements of the body, into proper harmony with the 
 
NERVES OF SPECIAL SENSE. AUDITORY AND GUSTATORY. 
 
 343 
 
 [Fig. 161. 
 
 apparatus ; so that, the decussation of the motor fibres in the pyramids being 
 accompanied by a decussation of the optic nerves, the same effect is produced 
 as if neither decussated, which last is the case with Invertebrated animals in 
 general. 
 
 446. The functions of the Auditory nerve, or Portio Mollis of the Seventh, 
 are easily determined, by anatomical examination of its distribution, and by 
 observation of pathological phenomena, to be analogous to those of the two 
 preceding, Atrophy or lesion of the trunk destroys the sense of Hearing; 
 whilst irritation of it produces auditory sensations, but does not occasion pain. 
 From experiments made upon the 
 
 nerve before it leaves the cranial 
 cavity, it appears satisfactorily as- 
 certained, that this nerve is not 
 endowed either with common sen- 
 sibility, or with the power of di- 
 rectly stimulating muscular move- 
 ment. Nor can any obvious reflex 
 actions be executed by irritation of 
 this nerve; but it seems neverthe- 
 less by no means improbable, that 
 the muscles which regulate the ten- 
 sion of the tympanum, are called 
 into action by impressions made 
 upon it and reflected through the 
 auditory ganglion, in the same man- 
 ner as the diameter of the pupil is A view of the origin and distribution of the Portio 
 regulated through the Optic nerve. Mollis of the Seventh pair or Auditory Nerve ; 1, the 
 
 It has been attempted by FloU- medulla oblongata; 2, the pons Varolii ; 3, 4,thecrura 
 
 reilS to Show, that the division of cerebelli of the right side; 5 the eighth pair of nerves; 
 
 .. ,. , 6, the ninth pair; 7, the auditory nerve distributed to 
 
 the Auditory nerve, Which proceeds thec0 chlea and labyrinth; 8, the sixth pair of nerves; 
 
 tO the Semi-circular Canals, has 9, the portio dura of the seventh pair; 10, the fourth 
 
 functions altogether different from pair; n, the fifth pair.] 
 that portion which supplies the Ves- 
 tibule and Cochlea. This inference, however, is grounded only upon the 
 movements exhibited by animals, in which these nerves are irritated ; which 
 movements are capable of a different explanation ( 432). 
 
 a. It is interesting to remark, that microscopic examination of the structure of the Audi- 
 tory nerve clearly indicates its intermediate character between the nerves of special sensa- 
 tion issuing from the anterior part of the cranium (namely, the Optic and Olfactory), and 
 those whose function is to minister, either to common sensation, or to that of Taste, which 
 approaches nearly to it, (namely, the Fifth pair and the Glosso-pharyngeal,) which issue 
 from the posterior part of the Encephalon, and are more nearly analogous to the Spinal 
 nerves. The primitive fibres are not so soft as those of the Olfactive, nor so slender as 
 those of the Optic ; and they are softer than those of the Glosso-pharyngeal. Moreover, the 
 Auditory nerve forms a plexus with the Facial, to which there is no analogy in the Optic 
 and Olfactive nerves, but to which a similar one exists in the Glosso-pharyngeal. This 
 intermediate structural character is interesting, when we compare it with the intermediate 
 character of the function; for the impressions made upon the sense of Hearing are pro- 
 duced through vibrations of a material fluid, instead of being, as in the case of Sight, the 
 result of changes so subtle as to be almost inscrutable to our means of research, or, as in 
 the case of Taste and Touch, being produced by the direct contaA of the substance which 
 gives rise to the sensation. 
 
 447. The nerves which minister to the sense of Taste, as already men- 
 tioned, are destitute of the peculiarities which distinguish the preceding; 
 being no other than certain branches of ordinary afferent nerves, the Fifth 
 Pair and Glosso-pharyngeal, the peculiar endowments of which seem to 
 
344 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 depend rather upon the structure and actions of the papillae at their peripheral 
 extremities, than upon anything special in their own characters. From the 
 recent observations and experiments of M. Ch. Bernard, it appears that the 
 Facial nerve (Portio Dura of the 7th) supplies some condition requisite for 
 the sense of Taste, through the branch known as the Chorda Tympani, which 
 is the motor nerve of the Lingualis muscle. When paralysis of the Facial 
 exists in Man, the sense of taste is very much impaired on the corresponding 
 side of the tongue, provided the cause of the paralysis be seated above the 
 origin of the Chorda Tympani from its trunk. Similar results have been ob- 
 tained from experiments upon other animals. The nature of the influence 
 afforded by this nerve is entirely unknown ; and it is the more obscure, as the 
 Chorda Tympani contains no sensory filament. 
 
 448. To the sense of Touch, all the afferent nerves of the body (save the 
 nerves of special sense) appear to minister; in virtue according to the hypo- 
 thesis here upheld of the direct connection of certain of their fibrils with the 
 Sensorium commune. But the degree in which they are capable of producing 
 Sensations, does not bear any constant relation to their power of exciting 
 Reflex actions. Thus, the Glosso-pharyngeal is not nearly so sensitive as 
 the Fifth pair; though more powerful as an excitor nerve. The Par Vagum 
 appears to have even less power of arousing sensory changes ; although it is 
 the most important of all the excitors to reflex action. So again, the afferent 
 nerves of the inferior extremities, in Man, are less concerned in ministering 
 to sensations, than are those of the superior ; and yet they appear to be much 
 more efficient as excitors to muscular action. These differences may be ac- 
 counted for, by supposing that the proportion which the fibres, having their 
 centre in the ganglionic matter of the Spinal Cord, bear to that of the fibres 
 which pass on to the Sensorium, is not constant, but is liable to variation ; 
 the former predominating in the Par Vagum and the Glosso-pharyngeal ; 
 whilst the latter are more numerous in the Fifth Pair, and in most of the Spi- 
 nal nerves. 
 
 449. It appears, from what has been already stated, that all the motor fibres 
 of the Cerebro-spinal system, not exclusively concerned in Reflex movements, 
 must be in connection with the Sensory ganglia ; since we find that their 
 actions, whether simply consensual, emotional, or volitional, are dependent 
 upon guiding sensations. Of these sensations, the greater proportion are 
 received from the muscles themselves ; but there are certain cases, as we have 
 seen, in which the guiding influence is communicated rather by the organs 
 and nerves of Special sense. Of these, a good example is afforded by the 
 movements of the Eyeball, presently to be examined in detail ; and another 
 is to be found in those of the Larynx, to be fully treated of hereafter (Chap, 
 viii.). The Emotions, in like manner, may operate upon all the motor nerves 
 of the body; as we see in the violent movements of unrestrained passion, or 
 in the increased power given to voluntary efforts, by the simultaneous excite- 
 ment of certain emotional states. But, as already remarked, their ordinary 
 action is most displayed through the motor nerves of the face and respiratory 
 organs. 
 
 450. Consensual Movements of the Eye. It will be recollected that, in 
 the Human Orbit, six muscles for the movements of the eyeball are found, 
 the four recti, and the, two oblique muscles. The precise actions of these are 
 not easily established by experiment on the lower animals ; for in all those 
 which ordinarily maintain the horizontal position, there is an additional mus- 
 cle, termed the retractor, which embraces the whole posterior portion of the 
 globe, and passes backwards to be attached to the bottom of the orbit. This 
 muscle is most developed in Ruminating animals, which, during their whole 
 time of feeding, carry their heads in a dependent position. In most Carni- 
 
CONSENSUAL MOVEMENTS OF THE EYE. 345 
 
 vorous animals, instead of the complete hollow muscular cone (the base inclos- 
 ing the eyeball, whilst the apex surrounds the optic nerve) which we find in 
 the Ruminants, there are four distinct strips, almost resembling a second set 
 of recti muscles, but deep-seated, and inserted into the posterior instead of the 
 anterior portion of the globe. It is obvious that the actions of these must 
 greatly affect the results of any operation, which we may perform upon the 
 other muscles of the Orbit; and, as it is impossible to divide the former, 
 without completely separating the eye from its attachments, we have no means 
 of correcting such results, but by reasoning alone. Experiments upon ani- 
 mals of the order of Quadrumana, most nearly allied to Man, would be more 
 satisfactory ; as in them, the retractor muscle is almost or entirely absent. 
 If the origin and insertion of the four Recti muscles be examined, however, 
 no doubt can remain that each of them, acting singly, is capable of causing 
 the globe to revolve in its own direction, the superior rectus causing the pupil 
 to turn upwards, the internal rectus causing it to roll towards the nose, and 
 so on. A very easy and direct application of the laws of mechanics will fur- 
 ther make it evident to us, that the combined action of any two of the Recti 
 muscles will cause the pupil to turn in a direction intermediate between the 
 lines of their single action ; and that any intermediate position may thus be 
 given to the eyeball by these muscles alone. This fact, which has not 
 received the attention it deserves, leads us to perceive, that the Oblique mus- 
 cles must have some supplementary function. It may be objected that this is 
 a theoretical statement only ; and that there may be some practical obstacle 
 to the performance of diagonal movements by the Recti muscles, which ren- 
 ders the assistance of the Obliques essential for this purpose. But to this it 
 may be replied, that no single muscle can direct the ball either downwards 
 and inwards, or upwards and outwards; and that, as we have good reason to 
 believe these movements to be effected by the combination of the Recti mus- 
 cles, there is no reason why the other diagonal movements should not also be 
 due to them. 
 
 451. The most probable account of the functions of the Oblique muscles of 
 the eye, seems to be that which was long ago suggested by John Hunter, and 
 which has received confirmation from the recent experiments of Dr. G. John- 
 son.* It has been just shown that the action of the Recti muscles upon the 
 pupil, is such as to cause it to revolve in any given direction ; and they are 
 put in action, not merely to alter the range of vision, the head remaining 
 stationary, but also to keep the range of vision the same, and to cause the 
 images of the objects, upon which our gaze is fixed, still to fall upon the 
 same parts of the retinae, by maintaining the position of the eyes when the 
 head is moved upwards, downwards, from side to side, or in any intermediate 
 direction. But these muscles are not able to rotate the eyeball upon its antero- 
 posterior axis ; and such rotation is manifestly necessary to preserve the fixed 
 position of the eyeball, and consequently to keep the image of the object un- 
 der survey upon the same part of the retina, when the head is inclined side- 
 ways, or bowed towards one shoulder and then towards the other. It appears 
 from the experiments of Dr. G. Johnson, that the action of the Oblique mus- 
 cles is exactly adapted to produce such a rotation; the Inferior oblique, in its 
 contraction, causing the eyeball to move upon its antero-posterior axis, in such 
 a manner that a piece of paper, placed at the outer margin of the cornea, passed 
 downwards and then inwards towards the nose; and the Superior oblique 
 effecting precisely the reverse action, the paper at the outer margin of the cor- 
 nea passing first upwards and then inwards. There was not the slightest 
 appearance, in these experiments, of elevation, depression, abduction, or ad- 
 
 * Cyclopaedia of Anatomy and Physiology, vol. iii. p. 790. 
 
346 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 duction, of the cornea, as a result of the action of the Oblique muscles ; all 
 these movements being attributable to the Recti alone. 
 
 452. On studying the conjoint movements of the Eyeball, we are led to 
 observe the very curious fact, that they are not so much symmetrical as har- 
 monious; that is to say, the corresponding muscles on the two sides are rarely 
 in action at once ; whilst such a harmony or consent exists between the ac- 
 tions of the muscles of the two orbits, that they work to one common purpose, 
 namely, the direction of both eyes towards the required objects. In order to 
 study them properly, it is necessary to reduce them to some kind of classifica- 
 tion. We may divide them into the Voluntary and the Involuntary ; and the 
 former, being numerous, require to be further classified. They may be ar- 
 ranged under two groups ; the first comprising those which are alike har- 
 monious and symmetrical ; the second including those which are harmonious 
 but not symmetrical. To the first group belong the following: 1. Both 
 eyeballs are elevated by the contraction of the two Superior Recti. 2. Both 
 eyeballs are depressed by the conjoint action of the Inferior Recti muscles. 
 3. Both are drawn directly inwards, or inwards and downwards, as when 
 we look at an object placed on or near the nose ; this movement is effected by 
 the action of the Internal Recti of the two sides, with or without the Inferior 
 Recti. It is evidently symmetrical, but might seem at first sight not to be 
 harmonious, because the eyes do not move together towards one side or the 
 other; it is, however, really harmonious, since their axes are directed towards 
 the same point. Now it is to be observed, with regard to these movements, 
 that we can never effect them in antagonism with each other, or with those of 
 other muscles. We cannot, for example, raise one eye and depress the other ; 
 nor can we raise or depress one eye, when we adduct or abduct the other. 
 The explanation of this will be found in the fact, that we can never, by so 
 doing, direct the eyes to the same point. The harmonious but unsymmetrical 
 movements, forming the second class, are those in which the Internal and Ex- 
 ternal Recti of the two sides are made to act together, either alone, or in con- 
 junction with the Superior and Inferior Recti. They are as follows. 4. One 
 eye is made to revolve directly inwards, by the action of its Internal Rectus, 
 whilst the other is turned outwards by the action of its External Rectus. 5. 
 One eye is made to revolve upwards and inwards, by the conjoint action of 
 the Internal and Superior Recti ; the other, upwards and outwards, by the 
 conjoint action of the External and Superior Recti. 6. One eye is made to 
 revolve downwards and inwards, by the conjoint action of the Internal and 
 Inferior Recti ; the other, downwards and outwards, by the conjoint action 
 of the External and Inferior Recti. In these movements, two different mus- 
 cles, the Abducens and Adducens, are called into action on the two sides; but 
 they are so employed for the purpose of directing the axes of the eyes towards 
 the same point. 
 
 453. The normal Involuntary movements of the eyeballs are only of two 
 kinds. 1. The rotation of the two eyeballs on their own axes, which takes 
 place when the head is moved in certain directions ( 451) ; this is effected 
 in direct respondence to certain guiding sensations, and without any influ- 
 ence or control on the part of the will; it is therefore a purely consensual 
 action. 2. The revolution of both eyes upwards and inwards, which takes 
 place in the acts of coughing, sneezing, winking, &c. ; this is altogether inde- 
 pendent of visual sensations, and is commonly, like the other movements 
 associated in these actions, of a reflex nature. Many abnormal movements 
 of the eyeballs, in which there is neither harmony nor symmetry in the 
 actions of the muscles, present themselves in convulsive diseases. 
 
 454. It may be stated as a physiological fact, that Single Vision with two 
 eyes is dependent upon the formation of the image upon parts of the two 
 
CONSENSUAL MOVEMENTS OF THE EYE. 347 
 
 retinae, which are accustomed thus to act with each other. In many physio- 
 logical works it is asserted, that single vision is the result of the impressions 
 being made on corresponding parts of the two retinae, that is to say, on 
 parts equally distant from the axis, on one side or the other : but this seems 
 to be disproved by the fact, that patients who have been long affected with 
 Convergent Strabismus, and who see equally well with both eyes (as many 
 do), are not troubled with double vision. On the other hand, when a person 
 whose eyes look straight before him, is the subject of a disorder which 
 renders their motions in any degree irregular, he is at once affected with 
 double vision ; and the same has been noticed to be a common immediate 
 result of the successful operation for the cure of strabismus, where vision is 
 good in both eyes. Although the images were previously formed on parts of 
 the retinae which were very far from corresponding with each other, yet no 
 sooner is the position of the eyes rectified (so that the relation between the 
 situation of the images is the same as it would have been in a sound eye), 
 than the patient sees double. Now in these cases the difficulty very speedily 
 diminishes, and the patient soon learns to see single. It can scarcely be 
 imagined, then, that to any other cause than habit, is to be attributed the 
 long-discussed phenomenon of single vision with two eyes. The mind re- 
 ceives the two images, frequently combining them together (as Mr. Wheat- 
 stone's ingenious experiments with the Stereoscope have most satisfactorily 
 shown, 547) to produce a picture in relief; and so long as these are con- 
 veyed to it in the accustomed manner, it reconciles them together, even if the 
 parts of the retinae on which they are formed do not correspond; but if any 
 circumstance break this chain, and cause the images to be transmitted to the 
 sensorium through a irew channel, the mind requires some little time to 
 adapt itself to this impression, as it does by habit to almost every other. 
 
 a. That there is a greater tendency to consent between the images, when they are formed 
 upon corresponding parts of the retinae, the Author readily admits ; and he thinks that this 
 is a principle of some importance, in explaining the re-adjustment of the eyes, after the 
 operation for Strabismus. Every one who has seen much of this operation is aware, that 
 the re-adjustment of the eye is not always immediate, but that, after the muscle has been 
 freely divided, the eye often remains somewhat inverted for a few days, gradually acquir- 
 ing its straight position. The Author has known one case, in which, after such a degree of 
 temporary inversion as seemed to render the success of the operation very doubtful, e ver- 
 sion actually took place for a short time to a considerable extent ; after which the axes be- 
 came parallel, and have remained so ever since. 
 
 b. Another argument, derived from the results of this operation, in favour of the con- 
 sensual movement being chiefly dependent upon the place of the impressions on the retina > 
 is, that it is much more successful in those cases, in which the sight of the most displaced 
 eye is good, than in those in which, (as not unfrequently happens from long disuse) it is 
 much impaired. In cases of the latter class, the cure is seldom complete. There is another 
 curious fact, which may be adverted to in reference to this subject : Strabismus not unfre- 
 quently arises from the formation of an opaque spot on the centre of the cornea, which pre- 
 vents the formation of any images on the retina, except by the oblique rays ; and nature 
 seems to endeavour (so to speak) to repair the mischief, by causing the eye to assume the 
 position most favourable for the reception of these. 
 
 c. To one more point only, connected with the subject of Strabismus, would the Author 
 now allude. He is well convinced, from repeated observation, that those Surgeons are in the 
 right, who have maintained, in a recent controversy, that, in a large proportion of cases, 
 strabismus is caused by an affection of both sets of muscles or nerves, and not of one only ; 
 and that it then requires, for its perfect cure, the division of the corresponding muscle on 
 both sides. Cases will be frequently met with, in which this is evident ; the two eyes 
 being employed to nearly the same extent, and the patient giving to both a slight inward 
 direction, when desired to look straight forwards. In general, however, one eye usually 
 looks straight forwards, whilst the other is greatly inverted; and the sight of the inverted 
 eye is frequently affected to a considerable degree by disuse ; so that, when the patien: 
 voluntarily rotates it into its proper axis, his vision with it is far from being distinct. Some 
 Surgeons have maintained, that the inverted eye is usually the only one in fault, and con- 
 sider that the division of the tendon of its Internal Rectus is sufficient for the cure. They 
 
348 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 would even divide its other tendons, if the parallelism be not restored, rather than touch 
 the other eye. The Author is himself satisfied, however, that the restriction of the abnor- 
 mal state to a single eye, is the exception, and not the rule, in all but very slight cases of 
 strabismus ; and to this opinion he is led both by the consideration of the mode in which 
 strabismus first takes place, and by the results of the operations which have come under his 
 notice. If the eyes of an infant affected with cerebral disease be watched, there will fre- 
 quently be observed in them very irregular movements; the axes of the two being some- 
 times extremely convergent, and then very divergent. This irregularity is rarely or never 
 seen to be confined to one eye. Now, in a large proportion of cases of Strabismus, the 
 malady is a consequence of some cerebral affection during infancy or childhood, which we 
 can scarcely suppose to have affected one eye only. Again, in other instances we find the 
 Strabismus to have resulted from the constant direction of the eyes to very near objects, as 
 in short-sighted persons ; and here, too, the cause manifestly affects both. 
 
 d. Now it is easy to understand, why one eye of the patient should appear to be in its 
 natural position, whilst the other is greatly inverted. The cause of strabismus usually 
 affects the two eyes somewhat unequally, so that one is much more inverted than the other. 
 We will call the least inverted eye A, and the other B. In the ordinary acts of vision, the 
 patient will make most use of the least inverted eye, A, because he can most readily look 
 straight forwards or outwards with it ; but to bring it into the axis, or to rotate it outwards, 
 necessitates a still more decided inversion of B. This remains the position of things, the 
 patient usually looking straight forwards with A, which is the eye constantly employed for 
 the purposes of vision, and frequently almost burying under the inner canthus the other 
 eye, B, the vision in which is of very little use to him. When, therefore, the tendon of the 
 internal rectus of B is divided, the relative position of the two is not entirely rectified. 
 Sometimes it appears to be so for a time ; but the strabismus then begins to return, and it 
 can only be checked by division of the tendon of the other eye, A; after which the cure is 
 generally complete and permanent. That it has not been so, in many of the cases on 
 which operations have been performed, the Author attributes, without the slightest doubt in 
 his own mind, to the neglect of the second operation. As just now stated, the sight of the 
 most inverted eye is frequently very imperfect ; indeed it is sometimes impaired to such an 
 extent, that the patients speak of it as entirely useless. That this impairment results in part 
 from disuse merely, seems very evident, from the great improvement which often succeeds 
 the rectification of the axes. The Author cannot help thinking it probable, however, that 
 the same cause which produced the distortion of the eye may, in some -instances at least, 
 have affected the Optic nerve, as well as the Motor nerves of the orbit ; and this idea is 
 borne out by the fact of the restoration of sight, in certain cases of Amaurosis, by division of 
 one or more tendons, where no Strabismus previously existed. (See Adams on Muscular 
 Amaurosis.) It is interesting to remark that, in these cases, Strabismus was usually the 
 first effect of the operation ; but that the eye generally recovered its ordinary position within 
 a short time, especially when the sight was improving. 
 
 455. If this be admitted, we gain an important step in the explanation of 
 the Consensual movements of the Eye. The object to be attained is evidently 
 this, that the usual axes of the eye should always be directed towards the 
 object to be viewed ; and this, as we have seen, involves the necessity (in a 
 great majority of cases), of unsymmetrical movements being performed by 
 the two eyeballs. The combination of these movements is involuntary or 
 automatic ; and appears to be regulated by the sensations received through 
 the retinae. It is well known that, in children born blind, the movements are 
 not consensual ; they are frequently very far from being so, in cases of con- 
 genital cataract, where a considerable amount of light is evidently admitted, 
 but where no distinct image can be formed ; and in such cases, the movements 
 are most consensual where the object is bright and luminous, and a more vivid 
 impression therefore made upon the retina. It is no objection to this theory 
 to say, that persons who have become blind may still move their eyes in a 
 consensual manner ; since, the habit of the association of particular move- 
 ments having been once acquired, the guidance of the muscles may be effected 
 by sensations derived from themselves, in the manner in which it takes place 
 in the laryngeal movements of the deaf and dumb ; and, as a matter of fact, 
 a want of consent may be often noticed where the blindness is total. The 
 peculiar vacant appearance, which may be noticed in the countenances of per- 
 sons completely deprived of sight by amaurotic or other affections, which do 
 
FUNCTIONS OF THE CEREBELLUM. 349 
 
 not alter the external aspect of the eyes, seems to result from this, that their 
 axes are parallel, as if the individual were looking into distant space, instead 
 of presenting that slight convergence which must always exist between them, 
 when the eyes are fixed upon a definite object. This convergence, which is 
 of course regulated by the Internal Recti, varies in degree according to the 
 distance of the object, and it is astonishing how minute an alteration in the 
 axes of the eyes is perceptible to a person observing them. For instance, A. 
 sees the eyes of B directed towards his face, but he perceives that B is not 
 looking at him ; he knows this by a sort of intuitive interpretation of the 
 fact, that his face is not the point of convergence of B's eyes. But if B, who 
 might have been previously looking at something nearer or more remote than 
 A's face, fix his gaze upon the latter, so that the degree of the convergence of 
 the axes is altered, without the general direction of the eyes being in the least 
 affected, the change is at once perceived by the person so regarded ; and the 
 eyes of the two then meet. 
 
 456. The foregoing considerations maybe summed up in this simple state- 
 ment : that, when we voluntarily direct our eyes towards any object, the 
 actions of the several muscles concerned, are guided by the visual sensations, 
 rather than by the ordinary muscular sense, through which other voluntary 
 movements are regulated. In this manner are accomplished, not merely the 
 revolutions of the eyeballs from side to side, upwards and downwards, or in 
 any direction that is required to cause the image to fall most advantageously 
 upon the two retinae ; but also that rotation on their axes, which keeps the 
 images in the same position upon the' 1 retina, when the head moves in a plane 
 perpendicular to their axes ; and likewise that exact convergence of the two 
 axes which shall cause them to meet in the object on which the attention is 
 fixed, and which consequently varies with its distance. Of all the movements 
 of the eyes, there is none which exhibits the necessity of the guiding visual 
 sensations so much as the revolution of both eyes inwards. Some persons 
 can effect this voluntarily to a greater extent than others ; but even then, they 
 can only accomplish it by fixing the gaze upon some object situated between 
 the eyes ; and cannot call the adductor muscles into combined action in per- 
 fect darkness, or if the lids be closed. Even those who have the least power 
 of effecting this extreme convergence, by at once directing the eyes towards 
 a very near object, can accomplish it by looking at an object placed at a mo- 
 derate distance, and gradually bringing this nearer to the nose, keeping the 
 eyes steadily fixed upon it. The unwonted character of the movement is 
 shown in this, that it can only be maintained, even for a short time, by a 
 strong effort, producing a sense of fatigue. No effort whatever can call into 
 simultaneous action the two external Recti ; and this fact is an additional 
 proof of the necessity of a guiding visual sensation ; since it is evident, that 
 no object can ever be placed in such a position, as to require this action for 
 the direction of the axes of the eyes towards it. 
 
 6. Functions of the Cerebellum. 
 
 457. That the Cerebellum has some special function, distinct from that of 
 the Cerebral Hemispheres, can scarcely be doubted ; since its peculiar struc- 
 ture and position, its independent connections with the Medulla Oblongata, 
 and its extremely variable size relatively to the remainder of the Encephalon, 
 point it out as an instrument adapted to some particular purpose. We shall 
 inquire briefly into the nature of the evidence respecting its function, which 
 is supplied to us by Comparative Anatomy, by Experiment, and by Patholo- 
 gical phenomena. A Cerebellum is found in all Vertebrated animals; although 
 it is in some extremely small, looking like a little prominence on the Medulla 
 
 30 
 
350 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Oblongata. When this is the case, it is observed that the whole mass is not 
 a miniature (so to speak) of the large Cerebellum of Man, but that the central 
 portion (termed the vermiform process) is the part most developed; the lobes 
 not presenting themselves until the organ has acquired an increased dimension. 
 The following table, constructed from materials contained in M. Serres' most 
 valuable Comparative Anatomy of the Brain, will afford some idea of the ma- 
 terials for speculating on the nature of the function of the Cerebellum, which 
 we obtain from this source. The first column gives the diameter of the Spinal 
 Cord, at the second cervical vertebra ; in the two succeeding columns are 
 stated the transverse and the antero-posterior diameters of the Cerebellum ; 
 these dimensions are stated in hundred-thousandths of a metre. The fourth 
 column expresses, in round numbers, the proportion which the diameters of 
 the Cerebellum bear to that of the Spinal Cord ; the latter being reckoned as 1. 
 
 MAMMALIA. 
 
 Diam. of Spinal 
 Cord at 2d Cervical 
 Vertebra. 
 
 Transverse Diam. 
 of Cerebellum. 
 
 Antero-posterior 
 Diameter 
 of Cerebellum. 
 
 Proportions. 
 
 Man . 
 
 1,100 
 
 12,000 
 
 6,000 
 
 11 5 
 
 Simia Rubra . 
 
 900 
 
 4,500 
 
 2,443 
 
 5 24 
 
 Bear . 
 
 1,300 
 
 5900 
 
 3,500 
 
 4i-2| 
 
 Dog . 
 
 1.100 
 
 4,200 
 
 2,525 
 
 3$ 2* 
 
 Dromedary . 
 
 1,900 
 
 .7,100 
 
 4,600 
 
 3$ 2i 
 
 Kangaroo 
 
 1.200 
 
 3.800 
 
 2^600 
 
 3^-2^ 
 
 BIRDS. 
 
 
 
 
 
 Falcon . 
 
 400 
 
 1,350 
 
 1,100 
 
 3 2| 
 
 Swallow 
 
 3,175 
 
 500 
 
 600 
 
 3 3i 
 
 Turkey . 
 
 500 
 
 1,350 
 
 1,600 
 
 2f 24 
 
 Ostrich . 
 
 700 
 
 1,750 
 
 2,500 
 
 2i 3i 
 
 REPTILES. 
 
 
 
 
 
 Crocodile 
 
 300 
 
 500 
 
 400 
 
 If li 
 
 Frog . 
 
 300 
 
 300 
 
 200 
 
 1-t 
 
 FISHES. 
 
 
 
 , ! 
 
 
 Shark , 
 
 700 
 
 1,700 
 
 3,100 
 
 2 4 
 
 Cod . 
 
 575 
 
 1.350 
 
 1,700 
 
 2i 3 
 
 Turbot . 
 
 500 
 
 750 
 
 900 
 
 li-lf 
 
 Lamprey 
 
 275 
 
 225 
 
 100 
 
 t-i 
 
 458. This table affords us much scope for interesting speculation, and may 
 be applied to the correction of hypotheses erected upon other foundations. 
 Before we proceed to these, however, a few general remarks may be made 
 upon it. In the first place, the proportional development of the Cerebellum 
 is seen to be smallest in the Vermiform Fishes, which approach most nearly 
 to the Invertebrate ; but it is much greater in the higher Fishes than it is in 
 Reptiles. If we consider in what particular, that may be reasonably supposed 
 to have a connection with this organ, the former surpass the latter, we should 
 at once be struck with their superiority in activity and variety of movement. 
 Passing on to Birds, we remark that the average dimensions of the Cerebel- 
 lum greatly surpass those of the organ in Reptiles ; but that they do not exceed 
 those occasionally met with in Fishes. The greatest size is not found in those 
 
FUNCTIONS OF THE CEREBELLUM. 351 
 
 
 
 species which approach most nearly to the Mammalia in general conformation, 
 such as the Ostrich; but in those of most active and varied powers of flight. 
 Lastly, on ascending the scale of Mammiferous animals, we cannot but be 
 struck with the rapid advance in the proportional size of the Cerebellum, that 
 we observe, as we rise from the lowest, which are surpassed in this respect 
 by many Birds, towards Man, in whom it attains a development which appears 
 enormous, even when contrasted with that of the Quadrumana. 
 
 459. We have next to inquire what evidence can be drawn from Experi- 
 mental investigations on the same subject': and in reference to this it is desirable 
 to remark, in the first place, that the experimental mode of inquiry is perhaps 
 more applicable to this organ than to other parts of the Encephalon ; inasmuch 
 as it can be altogether removed, with little disturbance of the actions imme- 
 diately essential to life; and the animals soon recover from the shock of the 
 operation, and seem but little affected, except in some easily-recognized par- 
 ticulars. The principal experimenters upon this subject have been Rolando, 
 Flourens, Magendie, Hertwig, and Longet. It is not to be expected, that there 
 should be an exact conformity among the results obtained by all. Every one 
 who has been Engaged in physiological experiments, is aware of the amount 
 of difference caused by very minute variations in their circumstances; in no 
 department of inquiry is this more the case than in regard to the Nervous 
 System ; and such differences are yet more likely to occur, in experiments 
 made upon the Nervous Centres, than in those which concern their trunks. 
 The investigations of Flourens are the most clear and decisive in their results ; 
 and of these we shall accordingly take a general survey. He found that, when 
 the Cerebellum was mechanically injured, the animals gave no signs of sensi- 
 bility, nor were they affected with convulsions. When the Cerebellum was 
 being removed by successive slices, the animals became restless, and their move- 
 ments were irregular ; and by the time that the last portion of the organ was cut 
 away, the animals had entirely lost the powers of springing, flying, walking, 
 standing, and preserving their equilibrium, in short, of performing any com- 
 bined muscular movements, which are not of a simply-reflex character. When 
 an animal in this state was laid upon the back, it could not recover its former 
 posture; but it fluttered its wings and did not lie in a state of stupor. When 
 placed in the erect position, it staggered and fell like a drunken man, not, how- 
 ever, without making efforts to maintain its balance. When threatened with a 
 blow, it evidently saw it, and endeavoured to avoid it. It did not seem that the 
 animal had in any degree lost voluntary power over its several muscles ; nor did 
 sensation appear to be impaired. The faculty of combining the actions of the 
 muscles in groups, however, was completely destroyed ; except so far as those 
 actions (as that of respiration) were dependent only upon the Reflex function 
 of the Spinal Cord. The experiments afforded the same results, when made 
 upon each class of Vertebrated animals ; and they have since been repeated, 
 with corresponding effects, by Bouillaud and Hertwig. The latter agrees with 
 Flourens, also, in stating that the removal of one side of the Cerebellum affects 
 the movements of the opposite side of the body; and he further mentions 
 that, if the mutilation of the Cerebellum have been partial only, its function is 
 in great degree restored. 
 
 460. All these results are objected to by those who assert that the Cerebel- 
 lum is the seat of the sexual instinct; on the ground that the observed aberra- 
 tions of the motor functions are sufficiently accounted for, by the general 
 disturbance which an operation so severe must necessarily induce. The 
 fallacy of this objection, however, is shown by the fact, that the much more 
 severe operation of removing the Hemispheres does not occasion such an 
 aberration; the power of performing the associated movements, and of main- 
 
352 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 
 
 taining the equilibrium, being remarkably preserved after the loss of them 
 (435). 
 
 461. Upon comparing these results with the preceding table, a remarkable 
 correspondence will be observed between them. The classes which have the 
 greatest variety of movements, and which require for them the most perfect 
 combination of a large number of separate muscular actions, have, taken col- 
 lectively, the largest Cerebellum. Of all classes of Vertebrata, Reptiles are 
 the most inert ; and their motions require the least co-ordination. The active 
 predaceous Fishes far surpass them in this respect; and may be compared 
 with Birds, in the energy of their passage through the water, and in their 
 facility of changing their direction during the most rapid progression. The 
 Cerebellum, accordingly, bears to the Spinal Cord in them, very much the 
 same proportion as it does in Birds. On the other hand, the Flat Fish, which 
 lie near the bottom of the ocean, and which have a much less variety of move- 
 ment, have a very much smaller cerebellum : and the Vermiform Fishes, which 
 are almost all completely destitute of fins, and whose progression is accom- 
 plished by flexion of the body, have a Cerebellum so small as to be scarcely 
 discoverable : their motion being, like that of the Articulata, almost entirely of 
 a reflex character, each segment being influenced by its own ganglionic cen- 
 tre, and the Spinal Cord constituting by far the largest proportion of the nervous 
 centres. On looking at the class of Birds, we observe that the active preda- 
 ceous Falcons, and the Swift-winged Swallows (the perfect control possessed 
 by which over their complicated movements must have been observed by every 
 one), have a Cerebellum much larger in proportion than that of the Gallina- 
 ceous birds, whose powers of flight are small, or than that of the Struthious 
 tribe, in which they are altogether absent. Lastly, on comparing its propor- 
 tional size in the different orders of Mammalia, with the number and variety 
 of muscular actions requiring combined movements, of which they are respect- 
 ively capable, we observe an even more remarkable correspondence. In the 
 hoofed Quadrupeds, in which the muscular apparatus of the extremities is 
 reduced to its greatest simplicity, and in which the movements of progression 
 are simple, the Cerebellum is relatively smaller than it is found to be in some 
 Birds ; but in proportion as the extremities acquire the power of prehension, 
 and together with this a power of application to a great variety of purposes, 
 still more, in proportion as the animal becomes capable of maintaining the 
 erect posture, in which a constant muscular exertion, consisting of a number 
 of most elaborately-combined parts, is required, do we find the size of the 
 Cerebellum, and the complexity of its structure, undergoing a rapid increase. 
 Thus, even between the Dog and the Bear there is a marked difference ; the 
 latter being capable of remaining for some time in the erect posture, and often 
 spontaneously assuming it ; whilst to the former it is anything but natural. 
 In the semi-erect Apes, again, there is a very great advance in the proportional 
 size of the Cerebellum ; and those which most approach Man in the tendency 
 to preserve habitually the erect posture, also come nearest to him in the di- 
 mensions of this organ. 
 
 462. Now it is evident that Man, although far inferior to many of the lower 
 animals in the power of performing various particular kinds of movement, far 
 surpasses them all, in the number and variety of the combinations which he 
 is capable of executing, and in the complexity of the combinations themselves. 
 Thus, if we attentively consider the act of walking in man, we shall find that 
 there is scarcely a muscle of the trunk or extremities which is not actually 
 concerned in it ; some being engaged in performing the necessary movements, 
 and others in maintaining the equilibrium of the body, which is disturbed by 
 them. On the other hand, in the horse or Camel, the muscular movements 
 are individually numerous, but they do not require nearly the same perfect 
 

 FUNCTIONS OF THE CEREBELLUM. 353 
 
 co-ordination. And in the Bird, the number of muscles employed in the 
 movements of flight, and in directing the course of these, is really comparatively 
 small; as may at once be perceived, by comparing the rigidity of the skeleton 
 of the trunk of the Bird wi % th that of Man, and by remembering the complete 
 inactivity of the lower extremities during the active condition of the upper. 
 In fact, the motions of the wings are so simple and regular, as to suggest the 
 idea, that, as in Insects, their character is more reflex than directly voluntary : 
 an idea which is supported by the length of time during which they can be 
 kept up without apparent fatigue, and also by the important facts already men- 
 tioned, which experimental research has disclosed ( 435). It is seen, then, 
 that Comparative Anatomy fully confirms the idea, which Experimental physi- 
 ology suggests, respecting the chief functions of the Cerebellum. 
 
 463. Some of Magendie's experiments indicate a further connection of 
 this organ with the motor function, the nature of which is still obscure. This 
 physiologist asserts that, if a wound be inflicted on the Cerebellum, the animal 
 seems compelled by an inward force to retrograde movement, although mak- 
 ing an effort to advance; and that, if the Crus Cerebelli on one side be injured, 
 the animal is caused to roll over towards the same side. Sometimes (if Ma- 
 gendie's statements can be relied on), the animals make sixty revolutions in a 
 minute, and continued this movement for a week without cessation. Division 
 of the second Crus Cerebelli restored the equilibrium. Hertwig observed the 
 same phenomenon, when the Pons Varolii (which is nothing more than the 
 commissure of the Cerebellum, surrounding the Crura Cerebri) was injured on 
 one side ; and he has also remarked, that the movements of the eyes were no 
 longer consensual. 
 
 464. On turning to Pathology for evidence of the functions of the Cerebel- 
 lum, we meet with much that seems contradictory. It must be remembered 
 that a sudden effusion of blood, even to a small extent, in any part of the En- 
 cephalon, is liable to produce the phenomena of apoplexy or paralysis ; and 
 inferences founded upon the phenomena exhibited after sudden lesions of this 
 description are, therefore, much less valid, than those based on the results of 
 more chronic affections. In regard to these last, however, it is to be observed, 
 that we are not yet in a condition to be able to state with precision, what 
 amount of morbid alteration in any part of the nervous centres, is compatible 
 with but slightly-disturbed performance of its function ; and that cases are 
 every now and then occurring, which would upset all our previous notions, if 
 we were not aware, that the same difficulty presents itself, even in regard to 
 the best-established results in Neurology. It is also to be remembered, that 
 the results of disease, occasioning pressure, will be peculiarly liable to affect 
 the Medulla oblongata, as well as the Cerebellum ; and will thus occasion a 
 greater loss of motor power than would be occasioned by the mere suspension 
 of the function of the latter. 
 
 465. Pathological phenomena, when examined with these reservations, 
 appear to coincide with the results of experiment, in supporting the conclu- 
 sion, that the Cerebellum is not in any way the instrument of psychical ope- 
 rations. Inflammation of the membranes covering it, if confined to that part, 
 does not produce delirium ; and its almost complete destruction by gradual 
 softening, does not appear necessarily to involve loss of intellectual power. 
 "But," remarks Andral, " whilst the changes of intelligence were variable, 
 inconstant, and of little importance, the lesions of motion, on the contrary, 
 were observed in all the cases [of softening which had come under his no- 
 tice] except one ; and in this it is not quite certain that motion was not inter- 
 fered with." In general, apoplexy of the Cerebellum is accompanied by para- 
 lysis ; but this is by no means usual in cases of chronic disease, in which 
 there is rather an irregularity of movement, with a degree of restlessness re- 
 
 30* 
 
354 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 sembling that described by Flourens as resulting from partial injury of this 
 organ. In a few cases in which both lobes of the Cerebellum have been 
 seriously affected, the tendency to retrograde movement has been observed ; 
 and instances are also on record, of the occurrence of rotatory movement, 
 which has been found to be connected with lesion of the Crus Cerebelli on 
 the same side. So far as they can be relied on, therefore, the results of the 
 three methods of investigation bear a very close correspondence ; and it can 
 scarcely be doubted that they afford us some approximation to truth. 
 
 466. We have now to examine, however, another doctrine regarding the 
 functions of the Cerebellum, which was propounded by Gall, and which is 
 supported by the Phrenological school of physiologists. This doctrine 
 that the Cerebellum is the organ of the sexual instinct is by no means in- 
 compatible with the other; and by some it has been held in combination with 
 it. The greater number of Phrenologists, however, regard this instinct as the 
 exclusive function of the Cerebellum ; and assert that they can judge of its 
 intensity, by the degree of development of the organ. We shall now exam- 
 ine the evidence in support of this position, afforded by the three methods of 
 inquiry which have been already indicated. The results of fair observation 
 as to the comparative size of the Cerebellum in different animals, can scarcely 
 be regarded as otherwise than very unfavourable to the doctrine in question. 
 In the greatest number of Fishes, it is well known that no sexual congress 
 takes place ; the seminal fluid being merely effused, like any other excretion, 
 into the surrounding water ; and being thus brought into accidental contact 
 with the ova, of which a large proportion are never fertilized. But there are 
 certain Fishes, as the Sharks, Rays and Eels, in which copulation takes place 
 after the ordinary method. Now on contrasting these two groups, we find no 
 corresponding difference in the size of the Cerebellum. It is true that this 
 organ is of large size in the Sharks ; but it is very small in the Rays ; and 
 almost rudimentary in the Eels : in this respect bearing a precise correspond- 
 ence with the variety and complexity of their movements. Further, in many 
 ordinary Fishes, which do not copulate, such as the Cod, the Cerebellum is 
 not only larger, but more complex in structure, than it is in the generality of 
 Reptiles, in which the sexual instinct is commonly strong ; the whole spinal 
 system of the Frog possessing, at the season of reproduction, an extraordinary 
 degree of excitability, which is evidently destined to aid in the performance 
 of the function (401, ). Again, in comparing the Gallinaceous Birds, 
 which are polygamous, with the Raptorial and Insessorial tribes which live 
 in pairs, we find that the former, instead of having a larger cerebellum, have 
 one of inferior size. Further on looking at the Mammalia, the same dispro- 
 portion may be noticed. A friend who kept some Kangaroos in his garden, 
 informed the Author that they were the most salacious animals he ever saw ; 
 yet their Cerebellum is one of the smallest to be found in the class. Every 
 one knows, again, the salacity of Monkeys ; there are many which are excited 
 to violent demonstrations by the sight even of a human female; and there 
 are few which do not practise masturbation, when kept in solitary confinement : 
 yet in them the Cerebellum is much smaller than in Man, in whom the sexual 
 impulse is much less violent. It has been supposed that the large size of the 
 organ in Man is connected with his constant possession of the appetite, which is 
 only occasional in others ; but this does not hold good; since among domestic 
 animals, there are many which are ready to breed throughout the year,- Cats 
 and Rabbits for instance ; and in these we do not find any peculiar difference 
 in the size of the Cerebellum. It is asserted, however, that the results, of 
 observation in Man lead to a positive conclusion, that the size of the Cere- 
 bellum is a measure of the intensity of the sexual instinct in the individual. 
 This assertion has been met by the counter-statement of others, that no 
 

 FUNCTIONS OF THE CEREBELLUM. 355 
 
 such relation exists. It is unfortunate that here, as in many other instances, 
 each party has registered the observations favourable to their own ,views, 
 rather than those of an opposite character ; so that until some additional 
 evidence of a less partial nature has been collected, we must consider the 
 question as sub judice. ' The Author is by no means disposed to deny 
 that such a correspondence may exist; but on contrasting the degree of sup- 
 port which this part of phrenology really derives from pathological evidence, 
 with that which the upholders of this view represent it to receive, he cannot 
 but look with much distrust at all their observations on the subject. 
 
 467. It is stated in Phrenological works, as an ordinary result of disease 
 of the Cerebellum, that there is an affection of the genital organs, manifest- 
 ing itself in priapism, turgescence of the testes, and sometimes in seminal 
 emissions. Now it is quite true that, in cases of apoplexy, in which these 
 symptoms manifest themselves, there is very commonly found to be effusion 
 upon the Cerebellum or in its substance ; but it is to be remembered, that in 
 all such lesions the Medulla Oblongata is involved, and these symptoms, 
 equally with paralysis, may be due to affection of that organ.* Further, the 
 converse does not by any means hold good ; for the proportion of cases of 
 disease of the Cerebellum, in which there is any manifest affection of the 
 sexual organs, is really very small, being, according to the calculations of 
 Burdach, not above one in seventeen. The same physiologist states that such 
 affections do present themselves, although very rarely, when the Cerebrum is 
 the seat of the lesion. A large number of facts adduced by Phrenologists in 
 support of their views such as the erections and emissions which often take 
 place during hanging may be explained as well, or even better, on the hypo- 
 thesis that the Cerebro-spinal axis (that is, the Spinal cord with the Medulla 
 Oblongata) is the seat of this instinct. And this hypothesis is much more con- 
 formable to the results of experiment and disease, than that which locates it in 
 the Cerebellum. For it has been found that mechanical irritation of the Spinal 
 Cord, and disease in its substance, much more frequently produce excitement 
 of the genital organs, than do lesions of the Cerebellum. This view is en- 
 tertained by Miiller, and by most physiologists who have taken a compre- 
 hensive and unbiassed survey of the phenomena in question. 
 
 468. Among the arguments adduced by Gall and his followers in proof of 
 the connection between the Cerebellum and the sexual instinct, is one which 
 would deserve great attention, if the facts stated could be relied on. It has 
 been asserted, over and over again, that the Cerebellum, in animals which have 
 been castrated when young, is much smaller than in those which have retained 
 their virility, being, in fact, atrophied from want of power to act. Now, it 
 is unfortunate that vague assertion, founded on estimates formed by the eye 
 from the cranium alone, is all on which this position rests ; and it will be pre- 
 sently shown, how very liable to error such an estimate must be. The fol- 
 lowing is the result of a series of observations on this subject, suggested by 
 M. Leuret,t and carried into effect by M. Lassaigne : The weight of the 
 Cerebellum, both absolutely and as compared with that of the Cerebrum, was 
 adopted as the standard of comparison. This was ascertained in ten Stal- 
 lions, of the ages of from nine to seventeen years ; in twelve Mares, aged 
 
 * A case has been recently communicated to the Author, in which the sexual desire, 
 which had been always strong through life, but which had been controlled within the limits 
 of decency, manifested itself, during a period of some months preceding death, in a most 
 extraordinary degree : on post-mortem examination a tumour was found on the Pons Varolii. 
 This fact harmonizes with the view given in the text ( 470), that the sexual instinct, if con- 
 nected with the Cerebellum at all, has its seat in the central lobe: but it also corresponds 
 equally well with the idea, that the Medulla Oblongata is its centre. 
 
 t Anat. Comp. du Systeme Nerveaux, torn, i., p. 427. 
 
356 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 from seven to sixteen years ; and in twenty-one Geldings, aged from seven 
 to seventeen years. The average weight of the Cerebellum in the Stallions 
 was 433 grammes; the greatest being 485 gr., and the least (which was in a 
 horse of ten years old) being 350. The average weight of the Cerebellum 
 was 61 gr. ; the greatest being 65 gr., and the least 56 gr. The average pro- 
 portion borne by the weight of the Cerebellum to that of the Cerebrum, was, 
 therefore, 1 to 7*07 ; the highest (resulting from a very small Cerebrum) being 
 1 to 6'25 ; and the lowest (resulting from an unusually large Cerebrum) being 
 1 to 7*46. Throughout it might be observed, that the variation in the size of 
 the Cerebellum was much less than in that of the Cerebrum. In the twelve 
 Mares, the average weight of the Cerebrum was 402 gr. ; the highest being 
 432 gr., and the lowest 363 gr. That of the Cerebellum was 61 gr. ; the high- 
 est being 66 gr., (which was in the individual with the smallest Cerebrum), 
 and the lowest 58 gr. The average proportion of the weight of the Cerebel- 
 lum to that of the Cerebrum was 1 to 6'59 ; the highest being 1 to 5'09, and 
 the lowest 1 to 7. The proportion was, therefore, considerably higher in the 
 perfect female, than in the perfect male. In the twenty-one Geldings, the 
 average weight of the Cerebrum was 419 gr. ; the highest being 566 gr., and 
 the lowest 346 gr. The average of the Cerebellum was 70 gr. ; the highest 
 being 76 gr., and the lowest 64 gr. The average proportion was, therefore, 
 1'to 5*97; the highest being 1 to 5'16, and the lowest 1 to 7*44. It is curi- 
 ous, that this last was in the individual which had the largest Cerebellum of 
 the whole ; but the proportional weight of the Cerebrum was still greater. 
 
 4Q9. Bringing together the results of these observations, they are found to 
 be quite opposed to the statement of Gall. The weight of the Cerebrum, 
 reckoning the Cerebellum as 1, is thus expressed in each of the foregoing de- 
 scriptions of animals : 
 
 Average. Highest. Lowest. 
 
 Stallions .... 7-07 7-46 6-25 
 
 Mares .... 6-59 . 7-00 5;09 
 
 Geldings . . . .5-97 7-44 5 : 16 
 
 The average proportional size of the Cerebellum in Geldings, therefore, is so 
 far from being less than that which it bears in entire Horses and Mares, that 
 it is positively greater ; and this depends not only on diminution in the rela- 
 tive size of the Cerebrum, but on its own larger dimension, as the following 
 comparison of absolute weights will show : 
 
 Average. Highest. Lowest. 
 
 Stallions 61 65 56 
 
 Mares .... 61 66 58 
 
 Geldings .... 70 76 64 
 
 The difference is so remarkable, and appears, from examination of the indi- 
 vidual results, to be so constant, that it cannot be attributed to any accidental 
 circumstance, arising out of the small number of animals experimented on. 
 The average weight of the Cerebellum in the ten Stallions and twelve Mares, 
 is seen to be the same ; and the extremes differ but little in the two ; whilst 
 the average in the Gelding is more than one-seventh higher, and the lowest is 
 considerably above the average of the preceding, while the highest far exceeds 
 the highest amongst the entire Horses. It is curious that Gall would have 
 been much nearer the truth, if he had said that the dimensions of the Cere- 
 brum are usually reduced by castration ; for it appears from the following 
 table that this is really the case : 
 
 Average. Greatest. Least. 
 
 Stallions .... 433 485 350 
 
 Mares .... 402 432 336 
 
 Geldings .... 419 566 346 
 
FUNCTIONS OF THE CEREBRUM. 357 
 
 The weight of the largest Cerebrum of the Gelding is far above the highest of 
 the Stallions ; but it seems to be an extraordinary case, as in no other was the 
 weight above 490 gr. If this one be excluded, the average will be reduced 
 still further, being then about 412 ; this may be seen, by looking over the 
 whole table, to give a very fair idea of the usual weight in these animals, 
 which is therefore less, by about one-twentieth, than the average of the Stal- 
 lions. The increased size of the Cerebellum in Geldings may perhaps be 
 accounted for by remembering that this class of horses is solely employed 
 for its muscular power, and that the constant exercise of the organ is not un- 
 likely to develop its size ; whilst Stallions, being kept especially for the pur- 
 pose of propagation, are much less applied to occupations which call forth 
 their motor faculties. 
 
 470. The Author is far from denying in toto, that any peculiar connection 
 exists between the Cerebellum and the Genital system ; but if the evidence 
 at present adduced in support of the Phrenological position be held sufficient 
 to establish it, in defiance of so many opposing considerations, we must bid 
 adieu to all safe reasoning in Physiology. The weight of testimony appears 
 to him to be quite decided, in regard to the connection of the Cerebellum with 
 the regulation of the motor function. How far this invalidates the moderate 
 phrenological view, which does not regard the function of the Cerebellum as 
 exclusively devoted to the sexual instinct, is a question well deserving of at- 
 tention. There is nothing opposed to such an idea in the results of the ex- 
 periments already adverted to ( 459) ; since there is no evidence that sexual 
 instinct remained after the removal of the Cerebellum ; but, on the other hand, 
 there is no proof that it was destroyed. A circumstance which has been 
 several times mentioned to him, that great application to gymnastic exercises 
 diminishes for a time the sexual vigour, and even totally suspends desire, 
 seems worthy of consideration in reference to such a view. If the Cerebellum 
 be really connected with both kinds of functions, it does not seem unreasona- 
 ble that the excessive employment of it upon one should dimmish its energy 
 in regard to the other. Further, it would seem by no means improbable, that 
 the Lobes are specially connected with the regulation and co-ordination of 
 movements ; whilst the Vermiform processes, which are very large in many 
 animals in which the former scarcely present themselves, are the parts con- 
 nected with the sexual function. As an additional argument in favour of the 
 former part of this view, it may be stated, that in Man the lobes bear a larger 
 proportion to the Vermiform processes than in any other animal ; and that 
 they undergo their most rapid development during the first few years of life, 
 when a large number of complex voluntary movements are being learned by 
 experience, and are being associated by means of the muscular sensations 
 accompanying them : whilst in those animals which have, immediately after 
 birth, the power of regulating their voluntary movements for definite objects, 
 with the greatest precision, the Cerebellum is more fully developed at the 
 time of birth. In both instances it is well formed and in active operation (so 
 far as can be judged of by the amount of circulation through it), long before 
 the sexual instinct manifests itself in any perceptible degree. 
 
 7. Functions of the Cerebrum. 
 
 471. We come, in the. last place, to consider the functions of that portion 
 of the Nervous Centres, \fhich is evidently, in Man, the predominant organ 
 of his whole system ; being not merely the instrument of his reasoning facul- 
 ties, but also possessing a direct or indirect control over nearly all the actions 
 of his corporeal frame, save those purely vegetative processes, which are most 
 
358 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 completely isolated from his animal powers. We should be in great danger, 
 however, of coming to an erroneous conclusion as to the real character of the 
 Cerebrum and of its operations, if we confined ourselves to the study of the 
 Human organism ; and the history of Physiological science shows, that every 
 advance of knowledge respecting its functions, has tended to limit them, whilst 
 at the same time rendering them more precise. Thus the Brain (this term, in 
 the older Anatomy, being chiefly appropriated to the Cerebrum) was accounted, 
 not merely the centre of all motion and sensation, but also the source of all 
 vitality ; the different processes of nutrition, secretion, &c., being maintained, 
 it was supposed, by a constant supply of " animal spirits," propagated from 
 the brain, along the nerves, to each individual part. The more modern doc- 
 trine, that the Sympathetic System has for its special function to supply the 
 nervous influence requisite for the maintenance of the functions of Organic 
 life, was the first step in the process of limitation ; still the Brain was regarded 
 as the centre of all the Animal functions ; and no other part was admitted to 
 possess any power independently of it. By experiments and pathological 
 observations, however, the powers of the Spinal Cord as an independent 
 centre of action were next established ; and it was thus shown, that there is 
 a large class of motions, in which the Brain has no concern, and that the re- 
 moval of the Cerebral hemispheres is not incompatible (even among the higher 
 Vertebrata) with the prolonged maintenance of a sort of inert and scarcely 
 conscious life. Still, it has been usually maintained, and with great show of 
 reason, that the Cerebrum is the instrument of all psychical operations ; and 
 of all the movements which could not be assigned to the reflex action of the 
 Spinal Cord. An attempt has been made, however, in the preceding pages, 
 to show that this view is not altogether correct ; and that there is a class of 
 actions, neither reflex nor voluntary, but directly consequent upon Sensations 
 and upon the instinctive and emotional propensities associated with these, 
 which may be justly assigned to certain ganglionic centres, not less inde- 
 pendent of the Cerebrum than is the Spinal Cord itself. It has been advanced, 
 that the Cerebrum must be considered in the light of an organ super added 
 for a particular purpose or set of purposes, and not as one which is essential 
 to life ; that it has no representative among the Invertebrata (except in a few 
 of the highest forms, which evidently present a transition towards the Verte- 
 brated series) ; and that, at its first introduction, in the class of Fishes, it evi- 
 dently performs a subordinate part in the general actions of the Nervous 
 System. Hence, whatever be the function, or set of functions, we assign to 
 the Cerebrum, we must keep in view the special character of the organ ; and 
 must never lose sight of the fact, that its predominance in Man does not de- 
 prive other parts of their independent powers, although it may keep the exer- 
 cise of those powers in check, and may considerably modify their manifesta- 
 tions. 
 
 472. Before proceeding to inquire into the Physiology of the Cerebrum, 
 we may advantageously take notice of some of the leading features of its struc- 
 ture. In the first place, it forms an exception to the general plan, on which 
 the elements of ganglionic centres are arranged ; in having its vesicular sub- 
 stance on the exterior, instead of in the central part of the mass. The pur- 
 pose of this is probably to allow the vesicular matter to be disposed in such 
 a manner, as to present a very large surface, instead of being aggregated to- 
 gether in a more compact manner ; and by this means, to admit the more 
 ready access, on the one side, of the blood-vessels* which are so essential to 
 the functional operations of this tissue, as well as the more ready communi- 
 cation, on the other, with the vast number of fibres, by which its influence is 
 to be propagated. There is no reason whatever to believe, that the functions 
 
FUNCTIONS OF THE CEREBRUM. 359 
 
 of the vesicular and fibrous substances are in the least altered by this change 
 in their relative position ; indeed the results of observation upon the pheno- 
 mena of disordered Cerebral action are such, as to afford decided confirmation 
 to the idea already propounded, that the action of the vesicular matter con- 
 stitutes the source of nervous power ; whilst the fibrous structure has for its 
 office, to conduct the influence generated in the ^preceding, towards the points 
 at which it is to operate. The purpose of this arrangement is further evi- 
 denced by the fact, that, in all the higher forms of Cerebral structure, we find 
 a provision for a still greater extension of the surface, at which the vesicular 
 matter and the blood-vessels may come into relation ; this being effected, by 
 the plication of the layer of vesicular matter into " convolutions," into the 
 sulci between which, the highly vascular membrane known as the pia mater 
 dips down, sending multitudes of small vessels from its inner surface into the 
 substance it invests. In the fibrous or medullary substance of which the 
 great mass of the Cerebrum is composed, three principal sets of fibres may 
 be distinguished. These are, -first, the radiating fibres, which connect the 
 vesicular matter of the cortical substance of the hemispheres with the Thala- 
 mi Optici, and which, if our view of the function of the latter be correct, 
 may be regarded as ascending or sensory ; second, the radiating fibres, 
 which connect the vesicular matter of the cortical substance of the hemi- 
 spheres with the Corpora Striata, and which, on similar grounds, may be re- 
 garded as descending or motor ; and third, the Commissural fibres, which 
 establish the connection between the opposite hemispheres, and between the 
 different parts of the vesicular substance of the same side, especially between 
 that disposed on the surface of each hemisphere, and those isolated patches 
 which are found in its interior. It is on the very large proportion which 
 the Commissural fibres bear to the rest, that the bulk of the Cerebrum of 
 Man and of the higher animals seems chiefly to depend ; and it is easy to 
 conceive, that this condition has an important relation with the operations of 
 the Mind, whatever be our view of the relative functions of different parts of 
 the Cerebrum. It appears from the late researches of M. Baillarger, that the 
 surface and the bulk of the cerebral hemispheres are so far from bearing any 
 constant proportion to each other, in different animals, that, notwithstanding 
 the depth of the convolutions in the Human Cerebrum, its bulk is 2| times 
 as great in proportion to its surface, as it is in the Rabbit, the surface of whose 
 Cerebrum is smooth. The entire surface of the Human Cerebrum, when the 
 convolutions are unfolded, is estimated by him at about 670 square inches.* 
 
 473. With regard to the Radiating fibres, which connect the Corpora 
 Striata and Thalami Optici with the vesicular surface of the Cerebral hemi- 
 spheres, it must be admitted that no positive proof has yet been obtained of 
 their direct continuity with those, which enter into the composition of the 
 nerves proceeding from the Spinal Cord and Medulla Oblongata ; and how- 
 ever probable such a continuity may be regarded on some grounds, there are 
 certain phenomena, which may perhaps be better explained on the idea, that 
 these radiating fibres are of a Commissural nature only, serving to connect the 
 vesicular matter of the Cerebrum with that of the different portions of the Cranio- 
 $pinal Jlxis (under which term are included the Spinal Cord, the Medulla 
 
 * The inference drawn by M. Baillarger from the facts he has collected. namely, that 
 the proportional surface of vesicular matter in different animals, whether considered abso- 
 lutely, or relatively to the volume of the Cerebrum, has no correspondence with their intel- 
 lectual capability, is far too sweeping an assumption ; since, as above shown, the increase 
 in the commissural fibres, causing an augmentation of the bulk of the Cerebrum, may be alike 
 the cause of increased intelligence and of a diminished proportional amount of vesicular mat- 
 ter ; though the latter still remains as the original source of power. 
 
360 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Oblongata, and the chain of Sensory Ganglia at the summit of the latter), 
 and thus brought, through the medium of the latter, into relation with the cen- 
 tral terminations of the afferent nerves, and the origins of the motor. On this 
 view, the Cerebrum would receive all its sensory impressions, by the commis- 
 sural fibres that connect it with the ganglia, which are the real centres of these 
 nerves ; whilst it would call the motor trunks into action, by exciting, through 
 another set of commissural fibres, the vesicular matter of the ganglionic cen- 
 tres from which they pass forth.* This question cannot be determined until 
 it shall have been shown, whether there is, or is not, a direct continuity be- 
 tween any of the fibres of the trunks connected with the Cranio-Spinal Axis, 
 and any of the radiating fibres of the Cerebral hemispheres. But the latter 
 view is certainly favoured by the very remarkable fact, in which the results 
 of all experiments agree, that no irritation or injury of the Cerebral fibres 
 themselves, produces either sensation or motion. Even the Thalami and Cor- 
 pora Striata may be wounded, without the excitement of convulsive actions ; 
 but if the incisions involve the Tubercula Quadrigemina or the Medulla Ob- 
 longata, convulsions uniformly occur. These results are borne out by patho- 
 logical observations in Man ; for it has been frequently remarked, when it 
 has beeri necessary to separate protruded portions of the Brain from the 
 healthy part, that this has given rise to no sensation, even in cases in which 
 the mind has been perfectly clear at the time. 
 
 474. The Commissural fibres constitute two principal groups, the trans- 
 verse, and the longitudinal; the former connecting the two Hemispheres with 
 each other; the latter uniting the different parts of the same Hemisphere. 
 Of the transverse commissures, the Corpus Callosum is the most important. 
 This consists of a mass of fibres very closely interlaced together; which may 
 be traced into the substance of the hemispheres on each side, particularly at 
 their lower part, where their connections are the closest with the Thalami 
 Optici and Corpora Striata. It is difficult, if not impossible, to trace its fibres 
 any further; but there can be little doubt that they radiate, with the fibres 
 proceeding from the bodies just named, to different parts of the cortical sub- 
 stance of the Hemispheres. This commissure is altogether wanting in Fish, 
 Reptiles, and Birds ; and it is partially or completely wanting in those Mam- 
 mals, whose Cerebrum is formed upon the least complex plan the Rodents 
 and Marsupials. The anterior commissure particularly unites the Corpora 
 Striata of the two sides : but many of its fibres pass through those organs, 
 and radiate towards the convolutions of the Hemispheres, especially those of 
 the middle lobe. This commissure is particularly large in those Marsupials, 
 in which the Corpus Callosum is deficient. The posterior commissure is a 
 band of fibres which connects together the Thalami optici; crossing over from 
 the posterior extremity of one to that of the other. Besides these, there are 
 other groups of fibres, which appear to have similar commissural functions, 
 but which are intermingled with vesicular substance. Such are the soft 
 commissure, which also extends between the Thalami; the Pons Tarini, 
 which extends between the Crura Cerebri; and the Tuber Cinereum, which 
 seems to unite the optic tracts with the thalami, the corpus callosum, the for- 
 nix, &c., and to be a common point of meeting for several distinct groups .of 
 fibres. Of the longitudinal commissures, some lie above, and others below, 
 the Corpus Callosum. Upon the transverse fibres of that body, there is a 
 longitudinal tract on each side of the median line, which serves to connect 
 
 * See Messrs. Todd and Bowman's Physiological Anatomy, Chap. XL for a fuller state- 
 ment of this view, and of the arguments in* its favour. See also the General Summary at 
 the conclusion of the present Chapter. 
 
FUNCTIONS OF THE CEREBRUM. 361 
 
 the convolutions of the anterior and posterior Cerebral lobes. Above this, 
 again, is the superior longitudinal commissure, which is formed by the fibrous 
 matter of the great convolutions nearest the median plane on the upper sur- 
 face of the Cerebrum, and which connects the convolutions of the anterior and 
 middle lobes with those of the posterior. Beneath the Corpus Callosum, we 
 find the most extensive of all the longitudinal commissures, the Fornix. This 
 is connected in front with the Thalami optici, the Corpora mammillaria, the 
 tuber cinereum, &c. ; and behind it spreads its fibres over the hippocampi 
 (major and minor), which are nothing else than peculiar convolutions that 
 project into the posterior and descending cornua of the lateral ventricles. 
 The fourth longitudinal commissure is the Tsenia semicircularis, which 
 forms part of the same system of fibres with the fornix ; connecting the cor- 
 pus mammillare and thalamus opticus of each side with the middle lobe of 
 the cerebral hemisphere. If, as Dr. Todd has remarked,* we could take 
 away the corpus callosum, the grey matter of the internal convolution, and 
 the ventricular prominence of the optic thalami, then all these commissures 
 would fall together, and would become united in the same series of longitu- 
 dinal fibres. Experiment does not throw any light upon the particular func- 
 tions of the Corpus Callosum and other Commissures; since they can 
 scarcely be divided without severe general injury. It would appear, how- 
 ever, that the partial or entire absence of these parts, reducing the Cerebrum 
 (in this respect at least) to the level of that of the Marsupial Quadruped, or of 
 the Bird, is by no means an unfrequent cause of deficient intellectual power. 
 
 a. The following case of deficient commissures, lately recorded by Mr. Paget, is of much 
 interest. The middle portion of the Fornix, and the whole of the Septum Lucidum, were 
 absent; and in place of the Corpus Callosum, there was only a thin fasciculated layer of 
 fibrous matter, 1/4 inch in length, but of which the fibres extended to all the parts of the brain, 
 into which the fibres of the healthy corpus callosum can be traced. The Middle commissure 
 was very large ; and the lateral parts of the Fornix, with the rest of the Brain, were quite 
 healthy. The patient was a servant-girl, who died of pericarditis. She had displayed, during 
 her life, nothing very remarkable in her mental condition, beyond a peculiar want of forethought, 
 and power of judging of the probable event of things. Her memory was good ; and she possessed 
 as much ordinary knowledge as is commonly acquired by persons in her rank of life. She 
 was of good moral character, trustworthy, and fully competent to all the duties of her station, 
 though somewhat heedless ; her temper was good, and disposition cheerful. The mental de- 
 ficiencies in the few other cases of which the details have been recorded, seem to have been 
 of the same order; and this is exactly what might have been anticipated; since the depriva- 
 tion of these parts takes away that, which is most characteristic of the Cerebrum of Man and 
 of the higher Mammalia; and their intellectual operations are peculiarly distinguished by that 
 application of past experience to the prediction of the future, which constitutes the highest effort 
 of Intelligence. 
 
 475. The weight of the entire Encephalon in the adult Male usually ranges 
 between 46 and 53 ounces; and in the Female, from 41 to 47 ounces. The 
 maximum of the healthy brain seems to be about 64 ounces, or four pounds; 
 and the minimum about 31 oz., or something less than two pounds. But in 
 cases of idiocy, the amount is sometimes much below this; as low a weight 
 as 20 oz. having been recorded. It appears, from the recent investigations 
 of M. Bourgery, that the relative sizes of the different component elements 
 of the Human Encephalon are somewhat as follows. Dividing the whole 
 into 204 parts, the weight of the Cerebrum will be represented by about 170 
 of those parts, that of the Cerebellum by 21, and that of the Medulla Oblon- 
 gata with the Optic Thalami and Corpora Striata at 13. The weight of the 
 Spinal Cord would be, on the same scale, 7 parts. Hence the Cerebral He- 
 mispheres of Man include an amount of nervous matter, which is four times 
 
 * Anatomy of the Brain, Spinal Cord, &c., p. 234. 
 31 
 
362 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 that of all the rest of the Cerebro-spinal mass, more than eight times that of 
 the Cerebellum, thirteen times that of the Medulla Oblongata, &c., and twenty- 
 four times that of the Spinal Cord. The average weight of the whole En- 
 cephalon, in proportion to that of the body, in Man, taking the average of a 
 great number of observations, is about 1 to 36. This is a much larger propor- 
 tion than that which obtains in most other animals; thus the average of Mam- 
 malia is stated by M. Leuret to be 1 to 186, that of Birds 1 to 212, that of 
 Reptiles 1 to 1321, and that of Fishes 1 to 5668. It is interesting to remark, 
 in reference to these estimates, that the Encephalic prolongation of the Me- 
 dulla Oblongata in Man (being about one-sixteenth of the weight of the whole 
 Encephalon) is alone more than twice as heavy in proportion to his body, as 
 the entire Encephalon of Reptiles, and ten times as heavy as that of Fish. 
 But there are some animals in which the weight of the Encephalon bears a 
 higher proportion to that of the body than it does in Man ; thus in the Blue- 
 headed Tit, the proportion is as 1 to 12, in the Goldfinch as 1 to 24, and in 
 the Field-Mouse as 1 to 31. It does not hence follow, however, that the Ce- 
 rebrum is larger in proportion ; in fact, it is probably not nearly so large ; for 
 in Birds and Rodentia, the sensory ganglia form a very considerable propor- 
 tion of the entire Encephalon. The importance of distinguishing between the 
 several parts of this mass, which are marked out as distinct, alike by their 
 structure and connections, as by the history of their development, has not been 
 by any means sufficiently attended to. 
 
 476. The Encephalon altogether receives a supply of Blood, the amount 
 of which is very remarkable, when its comparative bulk is considered ; the 
 proportion which it receives being, according to the estimate of Haller, as 
 much as one-fifth of the whole. The manner in which this blood is con- 
 veyed to the Brain, and the conditions of its distribution, offer some pecu- 
 liarities worthy of notice. The two Vertebral and two Carotid arteries, by 
 which the blood enters the cavity of the cranium, have a more free communi- 
 cation by anastomosis, than any similar set of arteries elsewhere ; and this is 
 obviously destined to prevent an obstruction in one trunk from interrupting 
 the supply of blood to the parts, through which its branches are chiefly dis- 
 tributed, the cessation of the circulation through the nervous matter being 
 immediately productive (as formerly shown, 290) of suspension of its 
 functional activity. Not only must there be a sufficient supply of blood, but 
 it must make a regulated pressure on the walls of the vessels. Now the 
 Encephalon is differently circumstanced from other vascular organs, in being 
 inclosed within an unyielding bony case ; and it has been supposed that the 
 total amount of blood circulating through it must consequently be invariable, 
 any disturbance of the circulation being due to an undue turgidity of the 
 arteries and corresponding emptiness of the veins, or vice versa. But this is 
 by no means the case ; for, independently of the fact that varying states of 
 functional activity will doubtless produce a considerable variation in the entire 
 bulk of the nervous mass, we find a special provision for equalizing the bulk 
 of the contents of the cranial cavity, and for counterbalancing the results of 
 differences in the functional activity of the brain and in its supply of blood. 
 This is the existence of a fluid, which is found beneath the arachnoid, 
 wherever pia mater exists in connection with the brain and spinal cord; 
 whether on the surfaces of these organs, or in the ventricles of the latter. 
 The amount of this fluid seems to average about two ounces ; but in cases of 
 atrophy of the brain, as much as twelve ounces of fluid may sometimes be 
 obtained from the cranio-spinal cavity ; whilst in all instances, in which the 
 bulk of the brain has undergone an increase, whether from the production of 
 additional nervous tissue, or from undue turgescence of the vessels, there is 
 
FUNCTIONS OF THE CEREBRUM. 363 
 
 either a diminution or a total absence of this fluid. It appears from the ex- 
 periments of Magendie (to whom our knowledge of the importance of this 
 fluid is chiefly due), that its withdrawal in living animals causes great dis- 
 turbance of the cerebral functions, probably by allowing undue distention of 
 the blood-vessels ; it is, however, capable of being very rapidly regenerated ; 
 and its reproduction restores the nervous centres to their natural state. 
 
 477. As the cerebro-spinal fluid can readily find its way from the sub- 
 arachnoid spaces of the cranial cavity into those of the spinal, and as the 
 latter are distensible, to a very considerable extent, it evidently serves as an 
 equalizer of the amount of pressure within the cranial cavity ; admitting the 
 distention or contraction of the vessels to take place, within certain limits, 
 without any considerable change in the degree of compression to which the 
 nervous matter is subjected. That this uniformity is of the greatest import^ 
 ance to the functional exercise of the brain, is evident from a few well-known 
 facts. If an aperture be made in the skull, and the protruding portion of the 
 brain be subjected to pressure, the immediate suspension of the activity of 
 the whole organ is the result ; in this manner, a state resembling profound 
 sleep can be induced in a moment; and the normal activity is renewed as 
 momentarily, as soon as the pressure is withdrawn. This phenomenon has 
 often been observed in the Human subject, in cases in which a portion of the 
 cranial envelope has been lost by disease or injury. The various symptoms 
 of Cerebral disturbance, which are due to a state of general Plethora, are 
 evidently owing to an excess of pressure within the vessels; but an undue 
 diminution of pressure is no less injurious, as appears from the disturbance in 
 the Cerebral functions, which results from the very opposite cause, namely, 
 a depression of the power of the heart, or a deficiency of blood in the ves- 
 sels. It is of peculiar importance to bear in mind the disturbance of the 
 Cerebral functions, which is occasioned by internal pressure, when we are 
 endeavouring to draw inferences from the phenomena presented by disease. 
 
 478. We shall now proceed with our Physiological inquiry into the func- 
 tions of the Cerebrum ; confining ourselves, in the present Section, to certain 
 general positions, with regard to which most Physiologists are agreed ; and 
 referring to the Appendix for a notice of the more detailed system of Cerebral 
 Physiology, first propounded by Dr. Gall. We shall, as before, apply to 
 Comparative Anatomy, to Experiment, and to Pathology, for our chief data. 
 Any general inferences, founded only upon observation of the phenomena pre- 
 sented by Man, must be looked upon with suspicion; since every advance in 
 Comparative Physiology leads us to perceive, how close is the functional rela- 
 tion between organs, that are really of analogous nature in different classes of 
 animals ; and how necessary, therefore, it is, to examine and contrast all the 
 facts which we can attain in regard to them, in order to impart to our con- 
 clusions the utmost validity of which they are capable. Our first general 
 proposition is, that the Cerebrum is the sole instrument of intelligence ; by 
 which term is implied the intentional adaptation of means to ends, in a man- 
 ner implying a perception of the nature of both. The actions performed by 
 the lower animals are often such, as to leave us in doubt, whether they are 
 the result of a mere Instinctive impulse, or of an Intelligent adaptation of 
 means to ends ; and we are guided in our determinations, chiefly by the uni- 
 formity of these actions, in the several individuals of the same species. If 
 we analyze any of our own instinctive actions, we shall perceive the same 
 absence of design on our own parts, as that which we attribute to the lower 
 animals. No one would assert that the tendency to sexual intercourse is the 
 result of a knowledge of its consequences, and of a voluntary adaptation of 
 means to ends ; or that, if we can imagine a man newly coming into the 
 

 364 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 world in the full possession of all his powers, he would wait to eat when 
 hungry, until experience had taught him that the swallowing of food would 
 relieve the uneasy feeling. It has been already shown, that, in the infant, 
 the act of sucking may be performed even without a Cerebrum ( 386, c) ; 
 and for this and other similar actions, therefore, it is doubtful whether con- 
 sciousness is a requisite condition. Adult animals, whose Cerebral hemi- 
 spheres have been removed, will eat food that is put into their mouths, although 
 they will not go to seek it; and this is the case with many Human idiots. 
 When the functions of the Brain are disturbed, or in partial abeyance, as in 
 fever, we often see a remarkable return to the instinctive propensities in 
 regard to food ; and the Physician frequently derives important guidance as 
 to the patient's diet and regimen (particularly as to the administration of 
 wine), from the inclination or disinclination which he manifests. 
 
 479. The difference between actions of a purely Instinctive character, and 
 those which rather result from the Intellectual faculties prompted by the in- 
 stinctive propensities, is well seen in comparing Birds with Insects. Their 
 Instinctive tendencies are of nearly the same kind ; and the usual arts which 
 they exhibit in the construction of their habitations, in procuring their food, 
 and in escaping from danger, must be regarded as intuitive, on account of the 
 uniformity with which they are practised by different individuals of the same 
 species, and the perfection with which they are exercised on the very first 
 occasion. But in the adaptation of their operations to peculiar circumstances, 
 Birds display a variety and fertility of resource, far surpassing that which is 
 manifested by Insects ; and it is not doubted, by those who have attentively 
 observed their habits, that in such adaptations they are often guided by real 
 Intelligence. This must be the case, for example, when they make trial of 
 several means, and select that one which best answers the purpose ; or when 
 they make an obvious improvement from year to year in the comforts of their 
 dwelling ; or when they are influenced in the choice of a situation, bv pecu- 
 liar circumstances, which, in a state of nature, can scarcely be supposed to 
 affect them. The complete domesticability of many Birds is in itself a proof 
 of their possessing a certain degree of intelligence ; but this alone does not 
 indicate the possession of more than a very low amount of it ; since many of 
 the most domesticable animals are of the humblest intellectual capacity, and 
 seem to become attached to Man, principally as the source on which they 
 depend for the supply of their animal wants. This is the case with most 
 Herbivorous quadrupeds, and with Rabbits, Guinea-pigs, &c. ; as well as with 
 the Gallinaceous Birds. 
 
 480. The attachment which is formed to Man, by certain Mammalia of 
 higher orders, such as the Dog, the Horse, and the Elephant, is evidently of 
 a more elevated kind, and involves a much larger number of considerations. 
 The Intelligence of such animals is peculiarly exhibited in their Educability ; 
 that is, in the facility with which their natural habits may be changed by 
 the new influences to which they are subjected, and the complication of the 
 mental processes which they appear to perform under their altered circum- 
 stances. Their actions are evidently the result, in many instances, of a com- 
 plex train of reasoning, differing in no essential respect from that which Man 
 would perform in similar circumstances ; so that the epithet, "half reason- 
 ing," commonly applied to these animals, does not express the whole truth ; 
 for their mental processes are of the same kind with those of Man, and differ 
 more in the degree of control which the animal possesses over them, than they 
 do in their own character. We have no evidence, however, that any of the 
 lower animals have a voluntary power of guiding, restraining, or accelerating 
 their mental operations, at all similar to that which Man possesses ; these 
 
FUNCTIONS OF THE CEREBRUM. 365 
 
 operations, indeed, seem to be of very much the same character as those 
 which we perform in our dreams, different trains of thought commencing as 
 they are suggested, and proceeding according to the usual laws, until some other 
 disturb them. Although it is customary to regard the Dog and the Elephant as 
 the most intelligent among the lower animals, it is not certain that we do so 
 with justice; for it is very possible that we are misled by that peculiar attach- 
 ment to Man, which in them must be termed an instinct, and which enters as 
 a motive into a large proportion of their actions ; and that, if we were more 
 acquainted with the psychical characters of the higher Quadrumana, we should 
 find in them a greater degree of mental capability than we now attribute to 
 them. One thing is certain, that, the higher the degree of intelligence 
 which we find characteristic of a particular race, the greater is the degree of 
 variation which we meet with in the characters of individuals ; thus every one 
 knows that there are stupid Dogs and clever Dogs, ill-tempered Dogs and 
 good-tempered Dogs, as there are stupid Men and clever Men, ill-tempered 
 Men or good-tempered Men. But no one could distinguish between a stupid 
 Bee and a clever Bee, or between a good-tempered Wasp and an ill-tempered 
 Wasp, simply because all their actions are prompted by an unvarying instinct. 
 481. It is important to bear in mind the view to which we have been con- 
 ducted, in regard to the relative offices of the vesicular and fibrous matter, 
 when forming our opinions upon the functions of the Cerebrum in general, or 
 of its several parts ; from the various data supplied to us by Comparative 
 Anatomy, by the comparison of the Cerebra of different individuals of the 
 Human race with each other and with their respective psychical manifestations, 
 and by experimental and pathological inquiry. For in regard to the first of 
 these sources it is to be remarked, that the size of the brain does not, con- 
 sidered alone, afford a means of judgment as to its power. The quantity of 
 vesicular matter on its surface should rather be our guide ; and this we may 
 judge of, not only by the depth of the layer, but by the complexity of the 
 convolutions by which the surface is extended. In no class, save in Mam- 
 malia, do we find the surface marked with convolutions; and in general 
 we do not meet with that fissure between the hemispheres, which greatly 
 increases the extent of surface. In forming comparisons as to the con- 
 nection between the size of the Cerebrum, and the Intelligence, in different 
 animals, we must not be at all guided by its simple proportional dimensions ; 
 since it is very evident, that it is rather the proportion of the bulk of the 
 brain to that of the whole body, upon which we should found our compari- 
 son. But even this is not altogether a safe guide; and many Physiologists 
 have endeavoured to compare the size of the brain, with the aggregate bulk 
 of the nerves proceeding from it. This is a much fairer measure; but it 
 cannot be taken without great difficulty. For all practical purposes, the 
 comparison of the bulk of the Cerebrum with that of the Spinal Cord will 
 probably answer very well. The following table, the materials of which 
 are drawn from M. Serres' Comparative Anatomy of the Brain, exhibits 
 the three diameters of the Cerebrum .of a number of different animals, 
 and the diameter of the Spinal Cord at the second cervical vertebra. The 
 last three columns present in round numbers, the three diameters of the 
 Cerebrum, reckoning that of the Spinal Cord as 1, for the sake of easy com- 
 parison. 
 
 31* 
 
386 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 
 Diameter 
 of Spinal 
 Cord. 
 
 DIMENSIONS OF CEREBRUM. 
 
 Proportional Dimensions. 
 
 Anti.-post. 
 
 Transv. 
 
 Vertical. 
 
 Man 
 
 1,100 
 
 17,000 
 
 7.500 
 
 9,000 
 
 11 5 
 
 l-6f 
 
 181 
 
 Dolphin 
 
 1,100 
 
 9,500 
 
 5', 8 50 
 
 8,200 
 
 l-9i 
 
 1-H 
 
 1-8* 
 
 Mandril 
 
 950 
 
 8,100 
 
 3,200 
 
 4,900 
 
 1 8i 
 
 13* 
 
 15 
 
 Tiger 
 
 1,600 
 
 9,400 
 
 4,250 
 
 6,400 
 
 15* 
 
 l-2f 
 
 14 
 
 Dromedary 
 
 1,900 
 
 10,500 
 
 5,050 
 
 5,800 
 
 1 5i 
 
 1 2f 
 
 13 
 
 Kangaroo 
 
 1,200 
 
 5,300 
 
 2,350 
 
 3,800 
 
 l-4f 
 
 12 
 
 1-3* 
 
 Vulture 
 
 800 
 
 3,200 
 
 2.200 
 
 1,550 
 
 14 
 
 l-2 
 
 12 
 
 Falcon 
 
 500 
 
 1,900 
 
 1,450 
 
 1,200 
 
 l_3f 
 
 13 
 
 92 
 
 Swallow 
 
 175 
 
 1,000 
 
 600 
 
 550 
 
 1 5f 
 
 13* 
 
 3 T 
 
 Pie 
 
 450 
 
 2,000 
 
 1,400 
 
 1.200 
 
 1 4f 
 
 13 
 
 2| 
 
 Turkey 
 
 500 
 
 1,750 
 
 1,250 
 
 1)200 
 
 1 3 
 
 12* 
 
 2| 
 
 Parroquet 
 
 400 
 
 2,900 
 
 1,400 
 
 1,700 
 
 1 7i 
 
 1-3* 
 
 4i 
 
 Tortoise 
 
 300 
 
 1,600 
 
 500 
 
 
 1-5* 
 
 i H 
 
 
 Crocodile 
 
 300 
 
 800 
 
 500 
 
 
 l-2f 
 
 i if 
 
 
 Viper 
 
 200 
 
 600 
 
 300 
 
 
 12 
 
 i i* 
 
 
 Frog 
 
 300 
 
 500 
 
 400 
 
 
 1-lf 
 
 11* 
 
 
 Shark 
 
 710 
 
 2,300 
 
 1,100 
 
 
 13| 
 
 i if 
 
 
 Cod 
 
 575 
 
 725 
 
 800 
 
 
 .1 U 
 
 i if 
 
 
 Lamprey 
 
 275 
 
 400 
 
 300 
 
 
 1 li 
 
 i U 
 
 
 Angler 
 
 400 
 
 400 
 
 300 
 
 
 11 
 
 1-2 
 
 
 i 
 
 
 
 
 
 
 
 
 482. As might be expected, the Cerebrum of Man bears by far the highest 
 proportion ; but this proportion is not so large in the transverse and vertical 
 diameters, as in the antero-posterior; in fact, in the proportion of the vertical 
 diameter the Cerebrum of Man is equalled by that of the Dolphin, and nearly 
 so in that of the transverse- diameter. In the complexity of the convolutions, 
 however, and in the thickness of the grey matter, the Cerebrum of Man 
 far surpasses that of this Cetaceous animal. In these respects the higher 
 Quadrumana present the nearest approach to it; but their brain is much infe- 
 rior in size. In descending the scale of Mammalia, there may be observed a 
 gradual simplification in the general structure of the Cerebrum, depending 
 upon a great diminution in the amount of commissural fibres ; until in the 
 Marsupialia the Brain presents nearly the same condition which it offers in 
 Birds ( 361). These animals manifest a much lower degree of Intelligence 
 than many Birds evidently possess; and it is interesting to remark, that their 
 Cerebral hemispheres are proportionably smaller than those which we find in 
 many Birds : the diminution in their relative size not being counterbalanced 
 (as it is in some other instances) by increased complexity of structure. In 
 the class of Birds, we observe that the Vulture and the Falcon, whose preda- 
 ceous instincts give them a considerable amount of general energy, are much 
 inferior in the size of their brains to the Insessorial Birds, which are more 
 intelligent ; and that of all, there is none in which the brain is so proportion- 
 ably large, as it is in the Parrot tribe, the educability of which is familiar to 
 every one ; whilst the easily-domesticable, but unintelligent Turkey, has a brain 
 of scarcely half the proportional size. The very small size of the Cerebrum 
 in Reptiles and Fishes, completely harmonizes with the same view; these 
 animals presenting for the most part but feeble indications of intelligence. 
 Among Reptiles, the Tortoise has a Cerebrum comparable in length to that 
 of Birds; but its breadth and depth are far less. The largest Cerebra among 
 Fishes are found in the Shark tribe ; the superior intelligence of which is 
 
FUNCTIONS OF THE CEREBRUM. 367 
 
 well known to those who have had the opportunity of observing their habits : 
 and it is interesting to remark, that their surface occasionally presents an ap- 
 pearance of rudimentary convolutions. 
 
 483. Comparative Anatomy, then, fully bears out the general doctrine, that 
 the Cerebrum constitutes the organ of Intelligence, as distinguished from those 
 mere Instincts, by which many of the lower animals seem to be almost en- 
 tirely guided. By Intelligence, we do not mean, however, the reasoning 
 faculties only ; but the combination of those powers which are of an educable 
 character, and which become the springs of voluntary action, in varying pro- 
 portions in different animals of the same tribe; as distinguished from those, 
 which have more immediate relation to the wants of the corporeal system, 
 and which are automatic and invariable in. the several individuals of the same 
 species. This definition does not leave out of view the operation of the Pas- 
 sions, Feelings, and Emotions; which are all but modifications of Instinctive 
 Propensities, to which different names are assigned. The true character of 
 these, however, can only be understood, by studying the mode of their action 
 on the bodily system. This action is of two kinds; the one direct, irrational 
 and involuntary ; the other indirect, rational, and voluntary. In the former, 
 the action is the immediate result of the Emotion, following closely upon the 
 Sensation which excited it, and consequently belongs to the Consensual group 
 already discussed (Sect. 5) ; it is executed without any consciousness of the 
 purpose to be answered by it ; and the power of the Will is only exerted to direct 
 or restrain it. In the latter, as will be presently shown ( 494), the action 
 is but remotely the result of the Emotion, being altogether of the Intelligent 
 class; it is executed with a view to a distinct purpose, which has been deter- 
 mined on by the reasoning powers, and of which, therefore, the mind is fully 
 conscious; and it is purely an act of the Will, however strongly the Emotions 
 may have acted in supplying motives to it and exciting the intellectual powers 
 to action. 
 
 .484. The general inferences drawn from Comparative Anatomy, are borne 
 out by observation of the Human species. When the Cerebrum is fully 
 developed, it offers innumerable diversities of form and size, among various 
 individuals ; and there are as many diversities of character. It may be doubted 
 if two individuals were ever exactly alike in this respect. That a Cerebrum 
 which is greatly under the average size, is incapable of performing its proper 
 functions, and that the possessor of it must necessarily be more,or less idiotic, 
 there can be no reasonable doubt. On the other hand, that a large well-de- 
 veloped Cerebrum is found to exist in persons, who have made themselves con- 
 spicuous in the world by their attainments or their achievements, may be stated 
 as a proposition of equal generality. In these opposite cases, we witness most 
 distinctly the antagonism between the Instinctive and Voluntary powers. Those 
 unfortunate beings, in whom the Cerebrum is but little developed, are guided al- 
 most solely by their instinctive tendencies ; which frequently manifest them- 
 selves with a degree of strength that would not have been supposed to exist; 
 and occasionally new instincts present themselves, of which the Human being 
 is ordinarily regarded as 'destitute.* On the other hand, those who have obtained 
 most influence over the understandings of others, have always been themselves 
 persons of strong intellectual and volitional powers ; in whom the instinctive 
 tendencies have been subordinate to the reason and will, and who have given 
 their whole energy to the particular object of their pursuit. It is very different, 
 
 * A remarkable instance of this has been recently published. A perfectly idiotic girl, in 
 Paris, having been seduced by some miscreant, was delivered of a .child without assistance. 
 It was found that she had gnawed the umbilical cord in two, in the same manner as is prac- 
 tised by the lower animals. It is scarcely to be supposed that she had any idea of the object 
 of this separation. 
 
368 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 however, with those who are actuated by what is ordinarily termed genius ; 
 and whose influence is rather upon i\\e feelings, than upon the understandings, 
 of those around them. Such persons are often very deficient in the power of 
 even comprehending the ordinary affairs of life : and still more commonly, 
 they show an extreme want of judgment in the management of them, being 
 under the immediate influence of their passions and emotions, and not having 
 brought these under the control of their intelligent will. The life of a genius, 
 whether his bent be towards poetry, music, painting, or pursuits of a more 
 material character, is seldom one which can he held up for imitation. In 
 such persons, the general power of the mind being low, the Cerebrum is not 
 usually found of any great size. The mere comparative size of the Cerebrum, 
 however, affords no accurate measure of the amount of mental power ; we not 
 unfrequently meet with men possessing large and well-formed heads, whilst 
 their physical capability is not greater than that of others, the dimensions of 
 whose crania have the same general proportion, but are of much less absolute 
 size. Large brains, with deficient activity, are commonly found in persons of 
 what has been termed the phlegmatic temperament, in whom the general pro- 
 cesses of life seem in a torpid and indolent state ; whilst small brains and great 
 activity, betoken what are known as the sanguine and nervous temperaments. 
 These distinctions come to be very important, where we proceed further in 
 our inquiries, and attempt to determine the particular modes of development 
 of the Brain, which coincide with certain manifestations of the mind. 
 
 485. Having now inquired into the evidence of the general functions of the 
 Cerebrum, which may be derived from examination of its Comparative deve- 
 lopment, we proceed to our other sources of information ; Experiment, and 
 Pathological phenomena. From neither of these, however, is much informa- 
 tion to be derived. The effects of the entire removal of the Cerebral Hemi- 
 spheres have been already stated ( 435). So far as any inferences can be 
 safely drawn from them, they fully bear out the conclusion, that the Cerebrum 
 is the organ of Intelligence ; since the animals which have suffered this muti- 
 lation appear to be constantly plunged in a profound sleep, from which no 
 irritation ever seems able to arouse them into full activity. It may even be 
 argued, that the phenomena which they exhibit do not imply the persistence 
 of consciousness; and that this also must be regarded as the attribute of the 
 Cerebral hemispheres, being destroyed by their ablation. But a careful ana- 
 lysis of them seems to show, that sensibility still exists, although it is much 
 deadened; for' in no other way can we legitimately explain the efforts made 
 by the animals to balance themselves and maintain their position, which are of 
 a' much higher character than the mere reflex movements exhibited by the 
 same animals after the removal of the entire Encephalon, and which can 
 scarcely be explained without attributing to them a degree of sensation. That 
 their sensibility should be greatly blunted, however, is to be anticipated from 
 the fact, that it is almost impossible to remove the Hemispheres, without doing 
 great injury to the other ganglionic centres, especially to the Thalami Optici 
 and Corpora Striata ; which, if the preceding views be correct, form a most 
 important part of the Sensori-Motor apparatus, and which, in the experiments 
 referred to, appear to have been generally removed with the Cerebral Hemi- 
 spheres. The entire and permanent removal of all vascular pressure, too, 
 which is consequent upon the laying-open of the cranial cavity, is another 
 source of permanent disturbance in the functions of the parts which are left. 
 So far as they go, therefore, the results of such experiments confirm the de- 
 ductions drawn from Comparative Anatomy, in regard to the general functions 
 of the Cerebrum ; but we must be careful not to infer too much from them, as 
 to the extent to which the animal functions are brought to a close by the 
 operation in question. In the most recent experiments, those of MM. Bouil- 
 
FUNCTIONS OF THE CEREBRUM. 369 
 
 laud and Longet, it was the opinion of the observers, that sensibility was 
 retained, after the complete removal of the Cerebrum ; although the animals 
 appeared unable to attach any ideas to their sensations.* The results of par- 
 tial mutilations are usually, in the first instance, a general disturbance of the 
 Cerebral functions ; which subsequently, however, more or less subsides, leav- 
 ing but little apparent affection of the animal functions, except muscular weak- 
 ness. The whole of one Hemisphere has been removed in this way, without 
 any evident consequence, save a temporary feebleness of the limbs on the 
 opposite side of the body, and what was supposed to be a deficiency of sight 
 through the opposite eye. The former was speedily recovered from, and the 
 animal performed all its movements as well as before ; the latter, however, 
 was permanent, but the pupil remained active. When the upper part, only, 
 of both Cerebral Hemispheres was removed by Hertwig, the animal was re- 
 duced, for fifteen days, to nearly the same condition with the one from which 
 they had been altogether withdrawn ; but afterwards, sensibility evidently re- 
 turned, and the muscular power did not appear to be much diminished. 
 
 486. The information afforded by Pathological phenomena is equally far 
 from being definite. Many instances are on record, in which extensive dis- 
 ease has occurred in one Hemisphere, so as almost entirely to destroy it, 
 without either any obvious injury to the mental powers, or any interruption 
 of the influence of the mind upon the body. But there is no case on record 
 of severe lesion of both hemispheres, in which morbid phenomena were not 
 evident during life. It is true, that in Chronic Hydrocephalus, a very remark- 
 able alteration in the condition of the Brain sometimes presents itself which 
 might a priori have been supposed destructive to its power of activity ; the 
 ventricles being so enormously distended with fluid, that the cerebral matter 
 has seemed like a thin lamina, spread over the interior of the enlarged cra- 
 nium. But there is no proof that absolute destruction of any part was thus 
 occasioned ; and it would seem that the very gradual nature of the change, 
 gives to the structure time for accommodating itself to it. This, in fact, is 
 to be noticed in all diseases of the Encephalon. A sudden lesion, so trifling 
 as to escape observation, unless this be very carefully conducted, will occasion 
 very severe symptoms ; whilst a chronic disease may gradually extend itself, 
 without any external manifestation. It will usually be found that sudden 
 paralysis, of which the seat is in the Brain, results from some slight effusion 
 of blood in the substance or neighbourhood of the Corpora Striata ; whilst, 
 if it follow disorder of the Brain of long standing, a much greater amount of 
 lesion will usually present itself. In either case, the paralysis occurs in the 
 opposite side of the body, as we should expect from the decussation of the 
 pyramids ; but it may occur either in the same, or on the opposite side of the 
 face, the cause of which is not very apparent. If convulsions accompany 
 the paralysis, we may infer that the Corpora Quadrig6mina, or the parts below, 
 are involved in the injury ; and in this case it is usually found, that the con- 
 vulsions are on the paralyzed side of the body, the effect of the lesion, both 
 of the Cerebrum and of the Corpora Quadrigemina, being propagated to the 
 opposite side, by the decussation of the Pyramids. Where, as not unfre- 
 quently happens, there is paralysis of one side, accompanying convulsions on 
 the other, it is commonly the result of a lesion affecting the base of the Brain 
 and Medulla Oblongata, on the side on which the convulsions take place ; 
 here the effect of the lesion has to cross from the Brain, whilst its influence 
 
 * It is worthy of remark, also, that M. Flourens, who in the first instance maintained that 
 sensation is altogether destroyed by the removal of the Cerebrum, has substituted, in the 
 Second Edition of his Researches, the word perception for sensation: apparently implying ex- 
 actly what is maintained above. See 435. 
 
 
370 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 on the Medulla Oblongata is shown on the same side. Many apparent ano- 
 malies present themselves, however, which are by no means easy of expla- 
 nation, in the present state of our knowledge. The disturbance of the Cere- 
 bral functions, occasioned by those changes in its nutrition which are com- 
 monly included under the general term of Inflammation, presents a marked 
 diversity of character, according to the part it affects. Thus it is well known 
 that the delirium of excitement is usually a symptom of inflammation of the 
 cortical substance or of the membranes of the hemispheres. This, is exactly 
 what might be anticipated from the foregoing premises, since this condition 
 is a perversion of the ordinary mental operations, which are dependent upon 
 the instrumentality of the vesicular matter ; and it is evidently impossible for 
 the membranes to be affected with inflammation without the nutrition of this 
 substance being impaired, since it derives all its vessels directly from them. 
 On the other hand, inflammation of the fibrous portion of the Cerebrum is 
 usually attended rather with a state of torpor than with excitement ; and with 
 diminished power of the will over the muscles. It is stated by Foville, that 
 in acute cases of Insanity, he has usually found the cortical substance in- 
 tensely red, but without adhesion to the membranes ; whilst in chronic cases, 
 it is indurated and adherent : but where the Insanity has been complicated 
 with Paralysis, he has usually found the medullary portion indurated and 
 congested. 
 
 487. The general result of such investigations is, that the Cerebrum is 
 the organ through which all those impressions are received which give rise to 
 the operations of the Intellect; and that it affords the power of occasioning 
 muscular contraction, in obedience to the influence of the Will, which is the 
 result of those operations. That all the operations of the Intellect are ori- 
 ginally dependent upon the reception of Sensations, is a position that can 
 scarcely be denied. If it were possible for a Human being to come into the 
 world, with a Brain perfectly prepared to be the instrument of mental opera- 
 tions, but with all the inlets to sensation closed, we have every reason to be- 
 lieve that the Mind would remain dormant, like a seed buried deep in the 
 earth. For the attentive study of cases, in which there is congenital defi- 
 ciency of one or more sensations, makes it evident that the Mind is uttterly 
 incapable of forming any definite ideas, in regard to those properties of ob- 
 jects, of which those sensations are particularly adapted to take cognizance. 
 Thus the man who is born blind can form no conception of colour ; nor the 
 congenitally-deaf, of musical tones. And in those lamentable cases, in which 
 the sense of touch is the only one through which ideas can be introduced, it 
 is evident that the mental operations would remain of the simplest and most 
 limited character, if the utmost attention be not given by a judicious instructor, 
 to the development of the intellectual faculties, and the cultivation of the 
 moral feelings, through the restricted class of ideas which there is a possi- 
 bility of exciting. The activity of the Mind, then, is just as much the result 
 of its consciousness of external impressions by which its faculties are called 
 into play, as the Life of the body is the consequence of the excitement of its 
 several vital properties by external stimuli. If these stimuli are prevented 
 from acting in the first instance, the state of inaction continues ; but when 
 once the mind has been aroused, the sensations which it receives are treasured 
 up by the Memory: and they may thus continue to be the sources of new 
 ideas, long after the complete closure of the inlets, by which new sensations 
 are ordinarily received. We have remarkable examples of this, in the vivid 
 conceptions which may be formed from the description of a landscape or a 
 picture, by those who have once enjoyed sight ; or in the composition of 
 music, even such as involves new combinations of sounds, by those who have 
 become deaf, as in the remarkable case of Beethoven. The mind thus 
 
FUNCTIONS OF THE CEREBRUM. 371 
 
 feeds, as it were, upon the store which has been laid up during the activity 
 of its sensory organs ; but instead of diminishing, like material food, these 
 sensations become more and more vivid, the oftener they are recalled to the 
 mind. 
 
 488. But the operations of the Intellect are immediately founded, not upon 
 Sensations, but upon the Ideas they excite in the Mind.* Some ideas are so 
 simple, and so constantly excited by certain sensations, that we can scarcely 
 do otherwise than attribute them to original or fundamental properties of the 
 mind, called into activity by the sensations in question ; others, however, are 
 of a much more complex nature, and vary according to the peculiar character 
 of the individual mind, the general habits of thought, and its particular condi- 
 tion at the time. In either case, the formation in the mind of an elementary 
 notion respecting the object of the Sensation, is the first operation in which 
 the Cerebrum can be said to be necessarily concerned, and is introductory to 
 all the rest. The process, whether simple or complex, is termed Perception; 
 and the designation is applied, like Secretion, not merely to the act, but to its 
 result, being used to indicate the notion thus produced, whether it be simple 
 and directly-excited, or more complex and the result of a succession of mental 
 operations. 
 
 489. The difference between Perception and Sensation maybe easily made 
 evident. In order that a sensation should be produced, a conscious state of 
 the mind is all that is required. Its whole attention may be directed towards 
 some other object, and the sensation calls up no new ideas whatever ; yet it 
 will produce some change in the Sensorium, which causes it to be (as it were) 
 registered there for a time, and which may become the object of subsequent 
 attention ; so that, when the mind is directed towards it, that idea or notion 
 of the cause of the sensation is formed, which constitutes a perception. For 
 example, a student, who is directing his thoughts to some object of earnest 
 pursuit, does not receive any intimation of the passage of time, from the 
 striking of a clock in his room. The sensation must be produced, if there 
 be no defect in his nervous system ; but it is not attended to, because the mind 
 is bent upon another object. It may produce so little impression on the mind, 
 as not to recur spontaneously, when the train of thought which previously 
 occupied the mind has been closed, leaving the attention ready to be directed 
 to any other object; or, the impression having been stronger, it may so recur, 
 and at once excite an idea in the mind. Again, the individual may then be 
 able only to say, that he heard the clock strike ; or he may be able to retrace 
 the number of strokes. Now, in either case, a complex perception is formed, 
 without his being aware that any mental operation has intervened. He would 
 say that he remembers hearing the clock strike ; but this would not express 
 the truth. That which he remembers is a certain series of sonorous impres- 
 sions, which was communicated to his mind ; and he recognizes them as the 
 striking of a clock, by a process in which memory and judgment are com- 
 bined, which process may further inform him, that the sounds proceeded 
 from his own particular clock. If he had never heard a clock strike, and the 
 sound produced by it had never been described to him, he would not have 
 been able to form that notion of the object giving rise to the sensation, which, 
 simple as it appears to be at the time, is the result of complex mental opera- 
 tions. But when these operations have been frequently performed, the per- 
 
 * Some Metaphysicians have spoken of ideas as transformed sensations ; but this is a gross 
 absurdity. The idea is excited by the sensation, in accordance with the original properties of 
 the mind, and the laws of their operation, just as muscular contraction is excited by the sti- 
 mulus of electricity or innervation ; but it would be just as correct to speak of a muscular 
 contraction as transformed electricity or innervation, because excited by either of these stimuli, 
 as it is to call an idea a transformed sensation. 
 
372 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 ception or notion of the object becomes inseparably connected with the sen- 
 sation ; and thus it is excited by the latter, without any knowledge on the 
 part of the individual, that a mental operation has taken place. 
 
 490. Such Perceptions are termed acquired, in contradistinction to the in- 
 tuitive perceptions, of which the lower animals seem to possess a large num- 
 ber. The idea of the distance of an object, for example, is one derived in 
 Man from many sources, and is the result of a long experience ; the infant, 
 or the adult seeing for the first time, has to bring the senses of sight and of 
 touch to bear upon one another, in order to obtain it ; but, when once the 
 power of determining it is acquired, the steps of the process are lost sight of. 
 In the lower tribes of animals, however, in which the young receive no assist- 
 ance from their parents, there is an evident necessity for some immediate 
 power of forming this determination ; since they would not be able to obtain 
 their food without it. Accordingly, they manifest in their actions a percep- 
 tion or governing idea of distances, which can only be gained by Man after 
 long experience. A fly-catcher, for instance, just come out of its shell, has 
 been seen to peck at an insect, with an aim as perfect as if it had been all its 
 life engaged in learning the art. In some cases, animals seem to learn that 
 by intuitive perception, at which Man could only arrive by the most refined 
 processes of reasoning, or by the careful application of the most varied expe- 
 rience. Thus, a little fish, named the Chsetodon rostratus, is in the habit of 
 ejecting from its prolonged snout, drops of fluid, which strike insects that hap- 
 pen to be near the surface of the water, and causes them to fall into it, so as 
 to come within its own reach. Now, by the laws of refraction of light, the 
 place of the Insect in the air, will not really be that at which it appears to 
 the Fish in the water ; but it will be a little below its apparent place, and to 
 this point the aim must be directed. But the difference between the real and 
 the apparent place will not be constant ; for the more perpendicularly the rays 
 enter the water, the less will be the variation ; and, on the other hand, the 
 more oblique the direction, the greater will be the difference. Now it is im- 
 possible to imagine but that, by an intuitive perception, the real place of the 
 Insect is known to the Fish in every instance, as perfectly as it could be to 
 the most sagacious Human mathematician, or to a clever marksman, who had 
 learned the requisite allowance in each case by a long experience. 
 
 490*. In Man, the acquirement of perceptions is clearly a Cerebral opera- 
 tion ; but their intuitional formation in the lower animals is probably to be 
 regarded as one of those processes to which the Sensory ganglia are subserv- 
 ient. The same may be said of many of the intuitive perceptions in Man ; 
 which, if analyzed, are found to be connected rather with the instinctive and 
 emotional tendencies, than with the intellectual powers ; the perceptions 
 which minister to the exercise of these last, being the result of experience. 
 Thus, it has been well remarked by Dr. Alison, that the changes which Emo- 
 tions occasion in the countenance, gestures, &c., of one individual, are instinc- 
 tively interpreted by others ; for these signs of mental affection are very early 
 understood by young children, sooner than any associations can be supposed 
 to have been formed, by experience, of their connection with particular modes 
 of conduct ; and they affect us more quickly and strongly, and with nicer 
 varieties of feeling, than when it is attempted to convey the same feelings in 
 words, which are signs addressed to the intellect. 
 
 491. By a certain retentive power, which appears to be peculiar to the 
 Cerebrum, Sensations and the simple ideas or Perceptions they excite, are 
 stored up (so to speak) in such a manner, as to become the subjects of further 
 mental operations at a time more or less remote. They then present them- 
 selves as renewed images of past sensations ; and these may recur, either 
 involuntarily, or by a special direction of the mind towards them by an effort 
 
FUNCTIONS OF THE CEREBRUM. 373 
 
 of Recollection. In either case, the Memory of them is probably due to the 
 operation of the principle of Association ; by which sensations and the ideas 
 they excite become linked together, in such a manner that the recurrence of 
 one shall be the means of the recal of others which are connected with it. 
 There seems much ground for the opinion, that every Sensation actually ex- 
 perienced may become the subject of a Perception at any future time, though 
 beyond the voluntary power of the memory to retrace ; and the phenomena of 
 dreams and delirium, in which these sensations often recur with extraordinary 
 vividness, afford much support to this doctrine. Some of the instances upon 
 record are remarkable, as proving that the sensations may be thus remembered, 
 without any perceptions being attached to them ; these sensations having been 
 of such a nature as not to excite any notion or idea in the mind of the indi- 
 vidual. A very extraordinary case of this kind has been recorded, in which a 
 woman, during the delirium of fever, continually repeated sentences in lan- 
 guages unknown to those around her, which proved to be Hebrew and Chal- 
 daic ; of these she stated herself, on her recovery, to be perfectly ignorant ; but 
 on tracing her former history, it was found that, in early life, she had lived as 
 servant with a clergyman, who had been accustomed to walk up and down 
 the passage, repeating or reading aloud sentences in these languages, which 
 she must have retained in her memory unconsciously to herself. Of the 
 nature of the change, by which sensations are thus registered,, it is in vain to 
 speculate ; and it does not seem likely that we shall ever become acquainted 
 with it. This is certain, however, that disease or injury of the brain will 
 destroy this power, or will affect it in various remarkable modes. We not un- 
 frequently meet with cases in which the brain has been weakened by attacks 
 of epilepsy or apoplexy, in such a manner as to prevent the reception of any 
 neiv impressions ; so that the patient does not remember anything that passes 
 from day to day ; whilst the impressions of events, which happened long 
 before the commencement of his malady, recur with greater vividness than 
 ever. On the other hand, the memory of the long-since-past is sometimes 
 entirely destroyed ; wBilst that of events which have happened subsequently 
 to the malady is but little weakened. The memory ,of particular classes of ideas 
 is frequently destroyed ; that of a certain language, or some branch of science, 
 for example. The loss of the memory of words is another very curious 
 form of this disorder, which is not unfrequently to be met with : the patient 
 understands perfectly well what is said, but is not able to reply in any other 
 terms than yes or wo, not from any paralysis of the muscles of articulation, 
 but from the incapability of expressing the ideas in language. Sometimes the 
 memory of a particular class of words only, such as nouns or verbs, is de- 
 stroyed ; or it may be impaired merely, so that the patient mistakes the proper 
 terms, and speaks a most curious jargon. These cases have a peculiar interest, 
 in reference to the inquiry into the functions of different parts of the Cere- 
 brum. 
 
 492. To the formation of vivid ideas of sensible objects, whether these have 
 actually presented themselves in the same form at some previous time, or are 
 modifications of the forms which had a real existence, the term Conception is 
 applied ; and this designation, like Perception, is also applied to the result of 
 the operation, that is, to the idea which is thus formed. The novelty of the 
 Conception may depend upon the new combination or correlation of the 
 objects it includes ; or it may result from a sort of decomposition of former 
 complex ideas, and the re-assemblage of their elements under a different form. 
 These processes, like the Memory, of which they are modifications, may be 
 either spontaneous or voluntary ; and in both forms they are continually em- 
 ployed by almost every one, the tendency to the exact reproduction of former 
 32 
 
374 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 ideas, however, being most evident in some minds, whilst the tendency to the 
 modification of them is more obvious in others. The latter is one source of 
 that faculty, to which the term Imagination is given. 
 
 493. The Mind, however, is not restricted to external sources, for objects 
 of perception ; since, when once in activity, it perceives its own operations, 
 and traces the various relations and connections among its objects of thought. 
 The power of doing this maybe termed Internal Perception. The mind 
 often has internal perceptions without any direct effort of the will, just as it 
 receives perceptions from external objects ; but its power of cognizance is not 
 unfrequently directed inwards by express volition ; and the act is then pecu- 
 liarly termed Reflection, or perhaps better, Introspection. Now by this pro- 
 cess, a new class of ideas is excited, of a very different character from those 
 which are called up by external objects ; and these, being entirely dependent 
 upon the operation of the Intellectual powers, and having no dependence upon 
 Sensations except as the original springs of those operations, may be termed 
 Intellectual Ideas, in contradistinction to the Sensational Ideas. The former, 
 like the latter, become the subjects of the Associating tendency; and thus are 
 combined in Trains of Thought. Some of these intellectual ideas appear to 
 be so necessarily excited by mental operations, even of the simplest kind, and 
 to be so little dependent on individual peculiarities either inherent or acquired, 
 that they take rank as fundamental axioms or principles of Human Thought. 
 Such are, the belief in our own present existence, or the faith which we re- 
 pose in the evidence of Consciousness ; this idea being necessarily associated 
 with every form and condition of mental activity, the belief in our past ex- 
 istence, and in our personal identity so far as our memory extends, which is 
 necessarily connected with the act of Recollection ; with this, again, is con- 
 nected the general idea of Space : the belief in the external and independent 
 existence of the causes of our sensations, which results from Perception, or 
 the direction of the mind to the ideas originating in them ; with this is con- 
 nected the general idea of Space : the belief in the existence of an efficient 
 cause for the changes which we witness around us, which springs from the 
 Perception of those changes ; whence is derived our idea of Power, the be- 
 lief in the stability of the order of nature, or in the invariable sequence of 
 similar effects to similar causes, which also springs directly from the Percep- 
 tion of external changes, and seems prior to all reasoning upon the results of 
 observation of them (being observed to operate most strongly in those whose 
 experience is most scanty, and in relation to subjects that are perfectly new 
 to them) ; but which is the foundation of all applications of our own experience 
 or that of others, to the conduct of our lives, or to the extension of our know- 
 ledge : lastly, the belief in our own free will, involving the general idea of 
 Voluntary Power ; which is in like manner a direct result of our Internal 
 Perception of those mental changes which are excited by sensations. Hence 
 it is evident, that " the only foundation of much of our belief, and the only 
 source of much of our knowledge, is to be found in the constitution of our own 
 minds ;" but it must be steadily kept in view, that these fundamental axioms 
 are nothing else than expressions of the general fact, that the ideas in question 
 are uniformly excited (in all ordinarily-constituted minds, at least) by simple 
 attention to the changes in which they originate. 
 
 494. Upon the Sensational and Intellectual Ideas thus brought under the 
 cognizance of the Mind, all acts of reasoning are founded. These consist, 
 for the most part, in the aggregation and collocation of ideas ; the decompo- 
 sition of complex ideas into more simple ones, and the combination of simple 
 ideas into general expressions ; in which are exercised the faculty of Com- 
 parison, by which the relations and connections of ideas are perceived, that 
 
FUNCTIONS OF THE CEREBRUM. 375 
 
 of Abstraction, by which we fix our attention on any particular qualities of 
 the object of our thought, and isolate it from the rest, and that of Generali- 
 zation, by which we fix in our minds some definite notions in regard to the 
 general relations of those objects. These are the processes chiefly concerned 
 in the simple acquirement of Knowledge ; with which class of operations, the 
 Emotional part of our nature has very little participation. But in those 
 modes of exercise of our reasoning powers, which are chiefly concerned in 
 the determination of our actions, the Emotions, &c., are largely concerned. 
 As formerly explained ( 440), they chiefly (if not solely) act upon the reason- 
 ing powers, by modifying the form in which the ideas are presented to the 
 mind, whether these ideas are directly excited by external sensations, or 
 whether they are called up by an act of the Memory, or result from the 
 exercise of the Imagination.* If we closely scrutinize our Emotions, indeed, 
 we shall find that they consist chiefly, if not entirely, of feelings of pleasure 
 and pain, connected with certain classes of ideas ; the former producing a 
 desire of the objects to which they relate ; the latter a repugnance to them. 
 They thus have a most important influence upon the Judgment, which is 
 formed by the comparison of certain kinds of ideas; and they may conse- 
 quently modify the Volitional determination, or act of the Will, which is con- 
 sequent upon this, and which may either be directed towards the further 
 operations of the mind itself, or may exert an immediate influence on the 
 bodily frame, by the agency of the Nervous System. In either case, it is the 
 characteristic distinction of a Volitional operation, that means are intention- 
 ally adapted to ends, in accordance with the belief of the mind as to their 
 mutual relations. Upon the correctness of that decision, will depend the 
 power of the action to accomplish what the mind had in view. 
 
 495. The faculty of Imagination is in some respects opposed in its cha- 
 racter to that of Reason; being concerned about fictitious objects, instead of 
 real ones. Still it is in a great degree an exercise of the same powers, though 
 in a different manner. Thus it is partly concerned in framing new combi- 
 nations of ideas relating to external objects, and is thus an extended exercise 
 of Conception, placing us, in idea, in scenes, circumstances, and relations, 
 in which actual experience never placed us, and thus giving rise to a new 
 set of objects of thought. In fact, every Conception of that which has not 
 been itself an object of perception, may, strictly speaking, be regarded as the 
 result of the exercise of Imagination. Now the new Conceptions or mental 
 creations thus formed take their character, in great degree, from the Emo- 
 tional tendencies of the mind ; so that the previous development of particular 
 feelings and affections will influence, not merely the selection of the objects, 
 but the mode in which they are thus idealized. In the higher efforts of the 
 Imagination, the mind is concerned, not so much with the class of Sensa- 
 tional ideas, but with those of the Intellectual character; and the collocation, 
 analysis, and comparison of these, by which new forms of combinations are 
 suggested to the mind, involve the exercise of the same powers, as those con- 
 cerned in acts of Reasoning, but they are exercised in a different way. 
 Whilst the Imagination thus depends upon the Intellectual powers for all its 
 higher operations, the Understanding may be said to be equally indebted to 
 the Imagination ; for the ideal combinations, which are the results of the 
 action of the latter, do not merely engage the attention of the Artist, who 
 aims to develop them in material forms, but are the great sources of the im- 
 
 * The recal of past sensations and ideas may produce purely Emotional actions ; by ex- 
 citing in the centres, from which those actions proceed, a condition corresponding with that 
 which would be excited by the present sensation ( 439). 
 
376 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 provement of the knowledge and happiness possessed by our race, operat- 
 ing alike in the common affairs of life, by suggesting those pictures of the 
 future which are ever before our eyes, and are our animating springs of action, 
 with their visions of enjoyment never perhaps to be fully realized, and their 
 prospects of anticipated evil that often prove to be an exaggeration of the 
 reality, prompting the investigations of Science, that are gradually unfolding 
 the sublime plan on which the Universe is governed, and leading to a con- 
 tinual aspiration after those highest forms of Moral and Intellectual beauty, 
 which are inseparably connected with purity and love. 
 
 8. General Recapitulation and Pathological Applications. 
 
 496. A general Summary of the views here propounded, in regard to the 
 Functions of the Cerebro-Spinal division of the Nervous system, may proba- 
 bly be useful in assisting the Student to gain clear ideas regarding them. 
 The fibres of the nervous trunks may be divided, according to the direction 
 of their influence, into two classes, the afferent or centripetal, and the effe- 
 rent or centrifugal. The afferent may be said to commence at the periphery, 
 especially on the skin, mucous surfaces, &c., and to terminate in the vesicu- 
 lar matter of the nervous centres ; whilst the efferent originate in that vesicu- 
 lar matter, and terminate in the muscles.* Every fibre runs a distinct course 
 from its origin to its termination; and it is not improbable that there are 
 several distinct endo\vments in the different fibres composing each trunk. 
 There is no evidence that the fibrous structure serves any different purpose 
 than that of a mere conductor; and there seems good reason to believe that 
 all the active operations, of which the nervous system is the instrument, ori- 
 ginate in the vesicular matter. A mass of vesicular matter, connected with 
 nervous trunks, forms a ganglion. In the Invertebrata, the ganglia are fre- 
 quently numerous, and are scattered through the system, without much con- 
 nection with each other ; each having an independent action, although its 
 function may be but a repetition of that of others. In Vertebrated animals, 
 on the other hand, they are united into one mass ; partly, it would seem, for 
 the sake of the protection afforded them by the bony skeleton ; and partly, 
 in order that more complete consentaneousness of action may be attained. 
 Still, certain divisions may be traced in the central masses of the Cerebro- 
 Spinal system ; both by the determination of their respective functions, as 
 indicated by observation and experiment ; and by the study of the distribution 
 of the nerves proceeding from them. In this manner we arrive at the know- 
 ledge of several distinct ganglionic centres, of which the following may be 
 considered as a general account. 
 
 i. The True Spinal Cord, consisting of a nucleus of vesicular matter, re- 
 ceiving afferent fibres, and giving origin to efferent ; by these it is connected 
 with all parts of the body, but especially with the surface and muscles of the 
 extremities. The actions of this centre maybe performed without conscious- 
 ness on the part of the individual ; and they consist in the reflexion of a motor 
 impulse along an efferent nerve, on the reception of a stimulus conveyed by an 
 afferent or excitor nerve. These reflex movements can be best excited, when 
 the muscles are removed from the control of the Will, which otherwise gene- 
 rally antagonizes them. Some of them are connected with the maintenance 
 
 * The terms originate, and terminate cannot be used with strict correctness; since, as for- 
 merly explained ( 548), many fibres seem to have no actual termination, either in the mus- 
 cles or in vesicular matter : but they cease to run in their previous direction, after forming 
 their terminal loops ; and their course as afferent or efferent fibres may consequently be said 
 to begin or to end at these points. 
 
GENERAL SUMMARY. 377 
 
 of the Organic functions ; others with locomotion ; and others with the pro- 
 tection or withdrawal of the body from injury. Muscular movements may 
 also be excited by a stimulus directly applied to the Spinal Cord itself ( 
 363373). 
 
 ii. The Medulla Oblongata, or cranial prolongation of the Spinal Cord. 
 The actions of this do not essentially differ from those of the true Spinal 
 Cord ; but they are connected with different organs. This part consists 
 chiefly of the centres of the nerves of Respiration and Deglutition, two 
 functions, of which the continual maintenance is essential to the life of the 
 being ; and it would seem as if these were placed within the cranium, to be 
 more secured from accidental injury. The movements concerned in Respira- 
 tion and Deglutition are, like those excited through the true Spinal Cord, of a 
 strictly reflex character, being in all instances due to an impression or stimulus 
 originating in the periphery of the system, which, being conveyed to the cen- 
 tre, excites there a motor impulse ; and they, also, are independent of Sensa- 
 tion ( 374387). 
 
 in. The Ganglia of the nerves of Sensation, common and special, which 
 form, as it were, the continuation of the Medulla Oblongata. These appear 
 to minister to actions, which, like the Reflex, are almost necessarily excited 
 by certain stimuli, and are only in a degree controllable by the Will : but 
 which differ from those of which the Spinal Cord is the centre, in being only 
 excitable through Sensation. Reasons have been given for the belief, that 
 these ganglia are the centres of those actions, which are commonly termed 
 instinctive in the lower animals, and consensual and emotional in ourselves ; 
 these all correspond, in being performed without any idea of a purpose, and 
 without any direction of the Will, being frequently in opposition to it ( 
 422460). 
 
 iv. The Cerebral Hemispheres or Ganglia, which are evidently the instru- 
 ments or organs of the intellectual faculties. It is probably by them alone, 
 that Ideas or notions of surrounding objects are acquired, and that these ideas 
 are made the groundwork of mental operations. They would seem, also, to 
 be the exclusive seat of Memory. The results of these operations are mani- 
 fested on the bodily frame, through the Will ; which is capable of acting, in 
 greater or less degree, on all the muscles forming part of the system of Ani- 
 mal life ( 471495). 
 
 v. The Cerebellum, which appears to be concerned in the regulation and 
 harmonization of Muscular movements, especially those of. a voluntary cha- 
 racter ( 457470). 
 
 497. The arrangement and connections of these parts may be thus con- 
 cisely expressed : 
 
 Tabular view of the Nervous Centres. 
 
 Cerebral Ganglia, 
 , the centres of the operations 
 of Intelligence and Will. 
 
 Nerves of Special senO c r> r f Nerves of Special sen- 
 
 sation _ Motor fibres I ^ ^^Co^Asual, ~ * 
 
 r I ^-ive.andE^ona! actions. 
 
 Cerebellic Ganglia, 
 
 for harmonization of general 
 
 muscular actions. 
 
 32* 
 
378 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 Afferent and Motor Nerves 
 of. Respiration, Deglutition, 
 &c. 
 
 Respiratory and 
 Stomato-gastric Ganglia, 
 in Medulla Oblongata. 
 
 I 
 -t 
 
 Afferent and Motor Nerves 
 of Respiration, Deglutition, 
 
 Trunks of Spinal nerves, composed of 
 afferent and motor fibres from true 
 Spinal Cord and Medulla Oblongata ; 
 and probably also of sensory and 
 motor fibres, connected by the longi- 
 tudinal strands of the Cord., with 'the 
 Sensory Ganglia. 
 
 VM c H 
 
 '.sf.2 I 
 
 ~ 5 * o 
 
 
 i 
 
 Trunks of Spinal Nerves, composed of 
 afferent and motor fibres from true 
 Spinal Cord and Medulla Oblongata ; 
 and probably also of sensory and 
 motor fibres, connected by the longi- 
 tudinal strands of the Cord, with the 
 ^Sensory Ganglia. 
 
 The Spinal Cord, the Medulla Oblongata, and Sensory Ganglia, seem to 
 constitute one continuous group of ganglionic centres ; which must be regarded 
 as the fundamental portion of the Nervous System. In descending the Verte- 
 brated series, we find the Cerebrum and Cerebellum gradually diminishing in 
 size and importance, and at last, in the Jlmphioxus, disappearing altogether ; 
 and the Cranio- Spinal axis, which then remains, differs in nothing but the 
 continuity of its vesicular structure, from the nervous system characteristic of 
 the Articulata, in which the vesicular matter is broken up (so to speak) into 
 distinct centres. In this Cranio-Spinal Axis, all the nerves have their termi- 
 nation ; and, from what has been ascertained of the anatomy of the gangliated 
 cord in the Articulata, there seems much reason to believe, that their fibres 
 may pass, in the longitudinal strands of the Cord, to great distances from their 
 points of entrance or emersion ; so that we may have, in the nerves connected 
 with every part of the Cord, sensory fibres, whose real termination is in the 
 Sensory ganglia at its summit, and motor fibres, which originate from these 
 centres, and are the instruments of all the actions to which they minister. 
 The great difficulty of tracing the individual fibres of the Spinal Cord, for any 
 considerable part of its length, renders it impossible, however, to say with 
 certainty that this is their real disposition ; but it is known that one at least 
 of the nerves, the Third pair, has this double connection with the Sensory 
 Ganglia and the Spinal Cord (or rather the Medulla Oblongata), and it is 
 likely that the same is true of the other motor nerves of the Orbit. Hence 
 there is no improbability in the idea, that of the afferent fibres of the Spinal 
 nerves, some are connected with the vesicular matter of the part of the Spinal 
 Cord through which they pass, and others with the Sensory Ganglia in the 
 Encephalon ; the relative numbers entering these centres being accordant with 
 the chief purposes of the trunk, whether as an excitor of reflex actions, or as 
 destined to arouse sensations : and that the like is true of the motor fibres, 
 the relative proportions of those derived from the two sources having reference 
 to the character of the motions, whether simply-reflex or consensual, to 
 which the trunk is destined to minister. But there is by no means the same 
 evidence, that any fibres contained in the nerves actually go on to the Cere- 
 brum and the Cerebellum; and the probability seems rather, that the fibres 
 which connect these masses with the Cranio-spinal Axis are of a commissural 
 

 GENERAL SUMMARY. 379 
 
 nature, and are destined to enable them to receive communications, and to act 
 on the muscular system, through the mediation of the latter, than that they 
 are actually continuous with any of the fibres in the nerve-trunks connected 
 with it (see 473). 
 
 498. According to these views, the following will be the mechanism of the 
 different classes of actions, in which the Cerebro-Spinal apparatus is directly 
 concerned. 
 
 i. In Reflex movements, a stimulus acting through the excitor fibres upon 
 the vesicular matter of certain parts of the Spinal Cord, causes the transmis- 
 sion of a reflex impulse through the motor fibres that proceed from it ; and 
 this gives occasion to muscular contraction. With this operation, sensation 
 will be coincident, if the stimulus act upon any of the fibres that pass on to 
 the Sensory ganglia; but this is not essential to it; and will not be aroused 
 if the connection does not exist, or the Sensory ganglia be in a state of torpor. 
 
 ii. In Sensation, the stimulus acts upon fibres which have their termina- 
 tion in the chain of ganglia that lies at the base of the cranial cavity in Man, 
 and is closely connected with the Medulla Oblongata. The series is collect- 
 ively termed the Sensorium ; but it is probable that each is the instrument, 
 by which the animal becomes cognizant of Sensations of a particular class, 
 the Olfactive, Optic, and Auditory ganglia, for those of Smell, Light, and 
 Hearing respectively, the Thalami Optici for those of Touch, and certain parts 
 of the Medulla Oblongata for those of Taste. 
 
 in. In Consensual movements, the stimulus conveyed by the Sensory fibres 
 becomes the direct source of motor impulses ; which are conveyed through the 
 agency of fibres that issue from the Sensory ganglia and Corpora Striata. 
 All the movements which are neither reflex nor voluntary, seem to belong to 
 this class; which will include, therefore, the instinctive actions of .the lower 
 animals, with the automatic and purely emotional movements in Man. 
 
 iv. In the act of Perception, or the formation of ideas from Sensations, in 
 Memory, and in all the higher acts of Mind, the Cerebrum seems to be con- 
 cerned ; the vesicular matter which constitutes its active portion, receiving the 
 stimulus to its operations, through the ascending and commissural fibres that 
 connect its different parts with the Sensory Ganglia at its base. As the con- 
 ducting power of these fibres acts from, not towards, the Sensory ganglia, we 
 should not expect that irritation of them should produce Sensation ; and this 
 is precisely what experiment shows to be the case. 
 
 v. In the act of Voluntary movement, which results from mental operations, 
 the vesicular matter of the Cerebrum operates, through the descending and 
 commissural fibres, upon the motor portion of the Sensory ganglia ; the 
 stimulus transmitted downwards by Volition producing the same kind of state 
 in its vesicular matter, as that which is transmitted upwards by Sensation. 
 In the same manner, the recal of past Sensations and Ideas may reproduce, in 
 the Sensory ganglia, the condition which gives occasion to the purely Emo- 
 tional movements. 
 
 vi. The combination and harmonization of the separate acts of Voluntary 
 Muscular movement, which is the function here attributed to the Cerebellum, 
 appears to be prompted by the guiding sensations, of which the Sensory 
 ganglia are the seat; the influence of these will be propagated along the com- 
 missural fibres known as the processus a cerebello ad testes; and the motor 
 influence, resulting from the action thus excited in the vesicular matter of the 
 Cerebellum, will be propagated downwards by its connections with the various 
 columns of the Spinal Cord. 
 
 499. The distinctness of the operations of these several centres is shown 
 in various ways : but especially by conditions of the bodily system, in which 
 one or more of them is in a state of inaction, whether temporary or permanent; 
 
380 
 
 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 or is prevented, by the interruption of the usual channel of communication, 
 from operating on particular parts. Thus, in ordinary profound Sleep, which 
 is a state of complete unconsciousness, it is evident that the Cerebral Hemi- 
 spheres, and the Sensory Ganglia, are at rest; as the Cerebellum, also, may be 
 considered to be: but the Medulla Oblongata and Spinal Cord must be in com- 
 plete functional activity. The same is the case in profound Coma, resulting 
 from effusion of blood, or from narcotic poisons, but not affecting the power 
 of breathing or swallowing. It may be frequently observed, that the sleep is 
 not so profound as entirely to suspend the consciousness of the individual ; 
 and that various movements of an adaptive character are performed, tending 
 to relieve uneasiness resulting from various causes. In this condition it seems 
 not improbable, that the Sensory ganglia are in some degree awake, and that 
 the movements are of an instinctive nature ; the mind of the individual not 
 being sufficiently active to discern the cause of the uneasiness, or to employ 
 his intelligence in the removal of it. Whenever Dreaming takes place, it is 
 evident that the Cerebrum is in a state of partial activity. The states of 
 Dreaming and Delirium, and many forms of Insanity, have considerable 
 analogy with each other; especially in the absence of the power which is so 
 characteristic of the well-regulated mind of Man, of controlling and regulating 
 the current of thought. One idea calls up another, according to their previous 
 associations; and the most incongruous combinations are frequently the result; 
 but it will generally, if not always, be found, that the ideas themselves have 
 been previously in the mind, and that no entirely new train of thought is 
 started. Of the degree in which, when the mind is thus closed to the external 
 world, the hidden stores of Memory are opened to its search, many very 
 curious instances are recorded. 
 
 500. The state of Somnambulism appears to be nearer to that of wakeful 
 activity of the whole mind, than is that of Dreaming. In the latter condition, 
 the individual is unconscious of external objects ; for, if thfey produce an effect 
 upon him, it is in modifying the current of ideas, frequently in some very 
 extraordinary manner : and he does not form any true perception or idea of 
 their nature. But in Somnambulism, his senses are partly awake, so that im- 
 pressions made upon them may be properly represented to the mind, and 
 excite there the ideas with which they are connected ; moreover the Cere- 
 bellum is also awake, so that the movements which the individual performs, 
 are perfectly adapted to their object; indeed, it has frequently occurred, that 
 the power of balancing the body has been so remarkably exercised in this 
 condition, that sleep-walkers have traversed narrow and difficult paths, over 
 which they could not have passed in open day, when conscious of their danger. 
 In Somnambulism, as in Dreaming, there is an evident want of voluntary 
 control over the thoughts; their succession is more influenced, however, by 
 impressions received from without, than it is in dreaming ; and hence the mind 
 may sometimes be easily guided into a particular train, by properly directing 
 the impressions made upon the sensory organs. It may often be remarked, 
 however, that impressions which do not in some degree harmonize with the 
 train of ideas, are not received by the mind; or, at any rate, they are not 
 applied to the correction of the erroneous notions which possess it. But there 
 are many different shades in the condition of the mind, between Dreaming 
 and Somnambulism; the individual being, in some cases, much less conscious 
 of external objects, than he is in others. In some instances it appears as if 
 the mind was so wholly engrossed in a particular train of thought, that it could 
 not be affected by any new sensations, so that there is even an unconsciousness 
 of those which produce pain; this has its parallel in the waking state. A 
 very remarkable characteristic of the state of Somnambulism, is the complete 
 isolation which commonly exists, between the trains of thought which then 
 
GENERAL SUMMARY. PATHOLOGICAL APPLICATIONS. 381 
 
 occupy the mind, and its operations during the waking hours ; so that in neither 
 state is there a remembrance of what passes in the other. There is usually 
 this difference, however; that the mental operations which take place in 
 Somnambulism are, like those of dreaming, frequently suggested by what has 
 previously been occupying the mind ; whilst these seem to leave no impression 
 to be retraced in the waking state, though all that passes in one fit of Som- 
 nambulism may be recollected in the next. This has been most remarkably 
 observed in the phenomena of that curious state, which is known under the 
 name of Double Consciousness ;* in this, the form of Somnambulism in which 
 there is a consciousness of external, impressions, seems to alternate with the 
 condition of ordinary mental activity, and the individual leads (as it were) two 
 distinct lives, recollecting in each condition what happened in previous states 
 of the same character, but knowing nothing of the occurrences of the other. 
 In regard to the curious forms of these affections, which are produced by 
 the so-called Mesmeric influence, the present views of the Author will be 
 stated in the Appendix. 
 
 501. We have thus witnessed several varieties in the condition of the bo- 
 dily system, depending upon partial or complete suspension of the functional 
 activity of the Cerebrum, Cerebellum, and Sensory ganglia. There is no 
 normal condition of the Spinal system, which at all corresponds with these ; 
 since its operations are so closely connected with the maintenance of the Or- 
 ganic functions, that the suspension of them necessarily induces the cessation 
 of the latter. This is especially the case, however, in regard to the Respira- 
 tory ganglion ; for the whole remainder of the Spinal Cord may be removed, 
 without the interruption of the movements which are dependent on that seg- 
 ment of it. Cases have occurred, however, in which the natural performance 
 even of these has been partially or entirely suspended ; and in which the 
 maintenance of life has for a time been effected, by a voluntary exertion of 
 the muscles of Respiration. The influence of the Will upon the general mo- 
 tor apparatus of Man, seems to predominate so greatly over the Reflex action 
 of the Spinal Cord, that few phenomena which are attributable to the latter 
 ordinarily present themselves ; these are manifested, however, when the in- 
 fluence of the Brain over any part is cut off, as is seen in certain cases of pa- 
 ralysis. These morbid conditions present us, also, with illustrations of other 
 effects of the interruption of the communication between the nervous centres 
 and particular sets of muscles. Thus, the influence of the Will may be cut 
 off, although that of the Instincts, Emotions, and Reflex Function may remain ; 
 or the respondence of the muscles to Emotion may be prevented, whilst they 
 are still capable of Voluntary control, or of Reflex action. Such cases seem 
 to point very clearly to three distinct primary centres of nervous agency ; 
 and to these, the Cerebrum Sensory Ganglia, and Spinal Cord (including the 
 Medulla Oblongata) have been here assigned as the instruments. We shall 
 next inquire into some other morbid conditions of the system, which seem 
 due to the irregular action of these; and in this we shall be chiefly guided by 
 the researches of Dr. M. Hall, which have been already slightly glanced at 
 ( 400, 401). 
 
 502. Of the Convulsive diseases, it appears that the greater part, if not the 
 whole, may be attributed to a morbid state of the Spinal System of nerves. 
 So completely does the power of producing convulsive movements appear 
 limited to that and to the Sensori-motor system, (no mechanical irritation of 
 the Cerebral substance being effectual in exciting such movements, 473,) 
 that, where convulsions present themselves during diseases which appear 
 
 * Much interesting information on this and other subjects, alluded to in this Section, may 
 be found in Dr. Abercrombie's Treatise on the Intellectual Functions. 
 
382 
 
 FUNCTIONS^)F THE NERVOUS SYSTEM. 
 
 limited to the Brain, we may infer that one of these systems is involved. Dr. 
 M. Hall has recently pointed out, that this complication is due to the impres- 
 sions made upon the fibres of the Spinal nerves distributed upon the Dura 
 Mater, and other serous and fibrous membranes ; for convulsive actions may 
 be induced by pinching these membranes, or otherwise irritating them. Of 
 the distinct forms or combinations, of which the class of convulsive disorders 
 is composed, Tetanus is one of the most interesting and instructive. This 
 disease is evidently dependent upon a state of undue excitability of the whole 
 Spinal System ; and this may be produced by different causes. That which 
 is termed the idiopathic form of the disease has its origin in the centres ; it 
 may result in Man from the operation of various predisposing and exciting 
 causes: and may be artificially induced in Animals by the administration of 
 Strychnia. In the traumatic form of the disease, the morbid state has its 
 origin in a local injury; and the irritation propagated from this, and operating 
 through the Spinal Cord, may be itself a cause of many of the convulsive 
 movements. But, when the irritable state is once established in the nervous 
 centres, convulsive action of the muscles may be excited by any stimuli, and 
 even almost entirely without external causes. Hence it is that, whilst the 
 amputation of the injured part is not unfrequently the means of saving the 
 patient, if performed sufficiently early, it is attended with no benefit if delayed. 
 The Cerebral apparatus is entirely unaffected in this disorder ; but the nerves 
 of deglutition are usually those first influenced by it; those of respiration, 
 hbwever, being soon affected, as also those of the trunk in general. The 
 condition termed Hydrophobia is nearly allied to that of traumatic Tetanus, 
 differing chiefly in the mode in which the cranio-spinal axis is affected. The 
 irritable state of the nervous centres results from a local injury of a peculiar 
 kind; and here, too, the early removal of the part is very desirable as a means 
 of prevention ; although, when the malady has once reached the centres, it is 
 of no use. The muscles of respiration and deglutition are, as in Tetanus, 
 those spasmodically affected in the first instance ; but there is this curious 
 difference in the mode in which they are excited to action, that, whilst in 
 Tetanus the stimulus operates through the true Spinal Cord (either centrally, or 
 by being conveyed from the periphery), in Hydrophobia it is often conducted 
 from the ganglia of Special Sense, or even from the Cerebrum ; so that the 
 sight or sound of fluids, or even the idea of them, occasions equally with their 
 contact, or with that of a current of air the most distressing convulsions. It 
 would seem, therefore, as if the Serisori-motor system of nerves was involved 
 in it.* In these and other general convulsive diseases, it is probable that the 
 whole vesicular matter of the centres involved is in so excitable a state, that 
 a stimulus applied to any part of it may produce a reaction through the whole. 
 In no other way would it be easy to explain the great number and variety of 
 movements, which a small degree of local irritation may excite. 
 
 503. Epilepsy is another convulsive disease, principally involving the Spinal 
 Cord, but partly affecting the Brain. The predisposition to convulsive move- 
 ments may depend upon many causes ; but the movements themselves are in 
 general immediately excited by some local irritation, as by the presence of 
 undigested matter in the stomach, of worms in the intestines, &c., although 
 frequently also from causes purely mental. The convulsive movements usually 
 affect the muscular system very extensively ; acting especially upon the mus- 
 cles of ingestion and egestion. The Brain is evidently much concerned in 
 the disease, however; as is evident from the numerous instances in which it 
 has been clearly traced to some local affection of that organ, as well as from 
 
 * For an interesting case of the excitement of involuntary muscular movements, by sen- 
 sations received through the eye and ear, see Dr. Cowan, in Lancet for 1845, Vol. II., p. 364. 
 
GENERAL SUMMARY. PATHOLOGICAL APPLICATIONS. 383 
 
 the loss of consciousness which accompanies the convulsion. Many forms 
 of that protean malady, Hysteria, are attended with a similar irritability of 
 the Nervous Centres ; but there is this remarkable difference in the two cases, 
 that the morbid phenomena of Hysteria, whilst they often simulate those 
 of Tetanus, Hydrophobia, Epilepsy, &c., are evidently dependent upon a state 
 of the system of a much less abnormal character, being frequently relieved 
 by very mild remedies, and -being often capable of prevention by a strong 
 effort of the will. Dr. Hall has pointed out an important distinction between 
 Epilepsy and Hysteria, which materially influences the proximate danger of 
 the paroxysm of each respectively ; in the former, the larynx is convulsively 
 closed, and partial asphyxia is the necessary result, if the access of air be too 
 long prevented, so that venous congestion ensues, increasing the disorder of 
 the nervous centres even to a fatal degree ; in Hysteria, on the contrary, much 
 as the larynx is affected, it is not usually closed. Cases sometimes present 
 themselves, however, in which the Hysteric paroxysm assumes the Epileptic 
 character, the larynx being closed during expiration, so as to produce alarming 
 results. The disordered state of the Nervous Centres, to which these con- 
 vulsive actions are due, seems to be peculiarly connected with Emotional con- 
 ditions of the mind, and with functional derangements of the sexual organs. 
 
 504. The foregoing are the chief general spasmodic diseases in which the 
 Spinal system of nerves is evidently involved ;* but there are many others of 
 a more local character. Such are the various forms of Spasmodic Asthma, 
 the attacks of which generally result from some internal irritation, either in 
 the lungs themselves or in the digestive system, producing a reflex action upon 
 the muscular fibres of the bronchial tubes. The Croup-like Convulsion, or 
 Crowing Inspiration of Infants, again, is an obstruction to the passage of the 
 air through the glottis, by a spasmodic contraction of the constrictors of the 
 larynx. This spasmodic action may be induced by various kinds of irritation ; 
 such as that occasioned by teething, by the presence of undigested food, or by 
 intestinal disorder. In the crowing inspiration, the larynx is partially closed ; 
 when the spasm is severe, however, there is complete occlusion of the pas- 
 sage ; and forcible efforts at expiration are made, which induce, as in epilepsy, 
 a severe degree of venous congestion, and this reacts upon the nervous cen- 
 tres, aggravating the previous disorder of their condition. The present in- 
 creased knowledge of the functions of the laryngeal nerves, and of the symp- 
 toms of this disease, appears to render inadmissible the explanation of it given 
 not long since by Dr. H. Ley, who attributed it to paralysis of the pneumo- 
 gastric nerves occasioned by pressure. Spasmodic closure of the larynx may 
 occur from other causes. When the rima-glottidis is narrowed, by effusion 
 of fluid into the substance of its walls, it is very liable to be completely closed, 
 by spasmodic action, to which the unduly irritable condition of the mucous 
 membrane will furnish many sources of excitement. Choking, again, does 
 not result so much from the pressure of the food on the air-passages them- 
 
 * Chorea is ranked by Dr. M. Hall as a disease of the Spinal System of nerves ; but this 
 can scarcely be regarded as a correct determination. It is true that there is considerable 
 irregularity in the ordinary Reflex actions ; but the irregularity is still greater in those, to 
 which Volition or Emotion are the stimuli. Moreover, the body is at rest during sleep ; and 
 "the Spinal system never sleeps." The frequent origin of the disease in causes which have 
 excited strong mental emotions, and the effect of even moderate excitement of the feelings 
 in greatly aggravating the movements of the body, seem to indicate the connection of this 
 disease with the Sensori-motor system of nerves. Stammering maybe regarded as a sort of 
 Chorea affecting the muscles of voice ; of this more hereafter (CHAP. vi). In Paralysis Agitans, 
 it may be usually observed, that the voluntary actions are much more affected than the reflex ; 
 the latter, indeed, not in general manifesting any disturbance. An interesting and well marked 
 case of this disease has been mentioned to the author by Dr. W. Budd, in which softening 
 was found in the Crura Cerebri. 
 
384 FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 selves, as from the spasmodic action of the larynx, excited by this ; and the 
 dislodgement of the morsel by an act of vomiting, is the most effectual means 
 of obtaining relief. Tenesmus and Strangury are well-known forms of spas- 
 modic muscular contraction, excited by local irritation acting through the 
 Spinal system. The abnormal action which leads to Abortion is frequently 
 excited in the same manner ; how far the uterus itself is called into contrac- 
 tion by the ordinary spinal nerves, is a question as yet undecided ; but the 
 facts already stated leave no doubt, that stimuli operating on these may act 
 upon it through the Sympathetic, into which their fibres pass ( 393). It will 
 be borne in mind, however, that, in abortion, as in ordinary parturition, many 
 muscles are called in, to aid the contractions of the uterus, which are strictly 
 under the dominion of the Spinal system. There is a form of Incontinence 
 of urine, which is very analogous to the morbid action just described ; the 
 sphincter has its due power ; but the stimulus to the evacuation of the bladder 
 is excessive in strength and degree, owing to the acridity of the urine or other 
 causes. The part of the bladder upon which this appears chiefly to act, is 
 the trigonum (which is well known to be more sensitive to the irritation of 
 calculi, than the rest of the internal surface) ; and Sir C. Bell advises young 
 persons who suffer during the night from this very disagreeable complaint, to 
 lie upon the belly instead of the back, so that the contact of the urine with 
 the trigonum may be delayed as long as possible. 
 
 505. One of the most familiar examples of the pathological excitement of 
 the true Spinal system is the act of Vomiting; and, as Dr. M. Hall justly 
 remarks, the special function of this system nowhere receives better illustra- 
 tion. The act may be excited in various ways. Thus, it results from the 
 tickling of the fauces with a feather or with the finger ; but if the feather be 
 carried too far down, an act of deglutition is induced instead of vomiting.* 
 In this instance the glosso-pharyngeal, and perhaps also the fifth pair, are the 
 nerves by which the stimulus is conveyed to the Medulla Oblongata. Vomit- 
 ing, again, may be induced by substances introduced into the stomach ; and 
 here the pneumogastric is evidently the excitor. When it takes place as a 
 result of pregnancy, or of some intestinal irritation, the stimulus must be con- 
 veyed, either through one of the ordinary Spinal nerves, or through the Sym- 
 pathetic. But it may also be occasioned by the sight, smell, or taste of any 
 disagreeable object, or by the mere conception of it, or by mental emotion 
 simply. In this case, the stimulus appears to be received by the ganglia of 
 special sense, and to be transmitted by them to the muscles concerned, as by 
 the Spinal Cord or Medulla Oblongata in the former case. When Vomiting 
 is excited by the introduction of emetic substances into the blood, it is proba- 
 ble that their stimulation chiefly operates through the extended plexus of 
 nerves, spread out by the Sympathetic upon the walls of the blood-vessels ; 
 but the irritant action of the substance upon the nervous centres may be also 
 concerned. In regard to the mechanism by which the act of Vomiting is 
 produced, considerable difference of opinion has existed. The old doctrine 
 was, that it was solely occasioned by the contraction of the stomach itself; 
 but Magendie proved that this could not be the case, by substituting a bladder 
 for the stomach of an animal, and then injecting a solution of tartarized anti- 
 mony into its blood, which immediately caused the emptying of the bladder, 
 by the pressure of the surrounding muscles ; these muscles he considered to 
 
 * This has been the cause of many accidents. Patients have tickled the fauces with a 
 feather in order to excite vomiting ; and, having introduced it too far into the pharynx, it has 
 been drawn out of their fingers by the muscles of deglutition, and carried into the oesophagus. 
 Similar accidents have occurred with the rectum-bougie, and female catheter, as well as with 
 probes, &c., introduced into the male urethra ; all the orifices being furnished with a kind of 
 ingestive power, which is clearly the result of Reflex action. 
 
OF SENSATION IN GENERAL. 385 
 
 be the diaphragm and abdominal muscles, the conjoint actions of which would 
 be a peculiarity observed in no other instance. By Dr. M. Hall, on the other 
 hand, it is maintained that the act of vomiting is, like the expulsion of the 
 foetus, urine, faeces, &c., an expiratory effort, modified in its effects by the pe- 
 culiar condition of the sphincters. It bears, indeed, great resemblance to the 
 act of coughing ; differing chiefly in this, that in vomiting, the larynx is closed 
 during the whole operation, whilst it is only closed momentarily in coughing ; 
 and also, that in coughing, the cardiac orifice of the stomach is closed, whilst 
 in vomiting it is opened. In this view, the accuracy of which has been proved 
 by experiment, the diaphragm is quite inert. A curious case has been re- 
 corded by Drs. Graves and Stokes,* in which vomiting took place from the 
 stomach of a man, who was found after death to be the subject of a very re- 
 markable change in the relative position of the viscera, -the stomach lying in 
 the thorax, which cavity communicated with the abdomen, by an opening in 
 the diaphragm, giving passage to the oesophagus and duodenum. This case 
 was regarded by its reporters as proving that vomiting might take "place by 
 the action of the stomach alone ; but it can scarcely be held to justify this 
 conclusion ; since, the diaphragm being entirely passive, the abdominal mus- 
 cles would have the same power of emptying the stomach, as they would 
 possess over the lungs. There can be little doubt, however, that the walls of 
 the stomach participate in the action ; for even the oesophagus is thrown into 
 a state of reversed peristaltic movement. 
 
 
 CHAPTER VI. 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 1. Of Sensation in General. 
 
 506. BY the term Sensation is rightly understood that change in the con- 
 dition of the mind, by which we become aware of an impression made upon 
 some part of the body; or, in a briefer form of expression, it may be denned 
 to be the consciousness of an impression. Some physiologists have, it is 
 true, spoken of a sensation without consciousness ; but it seems very de- 
 sirable thus to limit the term ; since the word impression may be very well 
 applied to designate the change produced in the afferent nerves by an external 
 cause, up to the point at which the mind becomes conscious of it. We have 
 seen reason to believe, that the impressions communicated to the Spinal Cord 
 may there excite motor actions, without occasioning true Sensation ; and it 
 would seem to be with the Encephalon only, that the Mind possesses the 
 relation necessary for the production of such a change in it. Hence this 
 organ is spoken of as the Sensorium. For the reasons already given ( 435), 
 it seems probable that the ganglia of Special Sensation are rather the essential 
 instruments of this function, than the Cerebral Hemispheres. The afferent 
 nervous fibres, which connect the various parts of the body with the Senso- 
 rium, are termed sensory. This term has also been applied to those which 
 terminate in the Spinal Cord ; but as the impressions which these convey do 
 not produce sensations, it seems desirable to avoid thus designating them ; 
 
 * Dublin Hospital Reports, Vol. v. 
 
386 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 and the term excitor, proposed by Dr. M. Hall, is much preferable. Every 
 afferent spinal nerve, therefore, is made up of sensory and of excitor fibres ; 
 and these may be distributed in very different proportions to different parts. 
 Of the excitor fibres, enough has been already said. Those parts of the body 
 which are endowed with sensory fibres, and impressions on which, therefore, 
 give rise to sensation, are ordinarily spoken of as sensible, and different parts 
 are spoken of as sensible in different degrees, according to the strength of the 
 sensation which is produced by a corresponding impression on each. 
 
 507. In accordance with what was formerly stated ( 250) of the depend- 
 ence of all nervous action on the continuance of the capillary Circulation, 
 especially at the extremities of the fibres, it is found that the sensory nerves 
 are distributed pretty much in the same proportion as the blood-vessels ; that 
 is to say, in the non-vascular tissues, such as the epidermis, hair, nails, car- 
 tilage, and bony substance of the teeth, no nerves exist, and there is an en- 
 tire absence of sensibility ; and in those whose vascularity is trifling, the sen- 
 sibility is dull, as is the case with bones, tendons, ligaments, fibrous mem- 
 branes, and other parts whose functions are simply mechanical, and even with 
 serous and areolar membranes. Many of these textures are acutely sensible, 
 however, under certain circumstances ; thus, although tendons and ligaments 
 may be wounded, burned, &c., with little or no consciousness of the injury, 
 they cannot be stretched without considerable pain ; and the fibrous, serous 
 and areolar tissues, when their vascularity is increased by inflammation, also 
 become extremely susceptible of painful impressions. All very vascular parts, 
 however, do not possess acute sensibility; the muscles, for instance, are fur- 
 nished with a large supply of blood, to enable them to perform their peculiar 
 function ; but they are not sensible in by any means the same proportion. 
 Even the substance of the brain and of the nerves of special sensation, ap- 
 pears to be destitute of this property ; and the same may be said of the mu- 
 cous membranes, lining the interior of the several viscera, which, in the ordi- 
 nary condition, are much less sensible than the membranes which cover those 
 viscera, although so plentifully supplied with blood for their especial purposes. 
 The most sensible of all parts of the body, is the Skin, in which the sensory 
 nerves spread themselves out into a minute net- work ; and even of this tissue, 
 the sensibility differs greatly in different parts. The organs of special sensa- 
 tion are, by the peculiar character of the nerves with which they are sup- 
 plied, rendered sensible to impressions of a particular kind : thus, the eye is 
 sensible to light, the ear to sound, &c. ; and whatever amount of ordinary 
 sensibility they possess, is dependent upon other sensory nerves. The eye, 
 for example, contrary to the usual notions, is a very insensible part of the 
 body, unless affected with inflammation ; for though the mucous membrane 
 which covers its surface, and which is prolonged from the skin, is acutely 
 sensible to some kinds of impressions, the interior is by no means so, as is 
 well known to those who have operated much on the eye. And there are 
 many parts of the body, that are supplied with the common sensory nerves 
 which convey to the mind impressions of particular kinds, with much greater 
 readiness than they communicate those of a different description. 
 
 508. It appears, then, that the vascularity of a part is an essential condition 
 of its sensibility; but it does not follow that a tissue should be peculiarly sen- 
 sible, because it is highly vascular; since its large supply of blood may be 
 required for other purposes. It is not simple vascularity, however, which is 
 necessary, but rather an active capillary circulation ; any cause which retards 
 this, deadens the sensibility, as is well seen in regard to cold; and, on the 
 other hand, an increase in its energy produces a corresponding increase in the 
 sensibility, as is peculiarly evident in the active congestion which usually pre- 
 cedes inflammation. Acute sensibility to external impressions may arise, 
 

 
 OF SENSATION IN GENERAL. 387 
 
 however, not only from abnormal activity of the circulation in the organ or 
 part itself, but from the same condition affecting that part of the sensorium in 
 which the impressions are received. Thus in active congestion and inflam- 
 mation of the brain, the most ordinary external impressions produce sensations 
 of an unbearable violence ; and there are some peculiar conditions of the 
 nervous system, known under the name of hysterical, in which the patients 
 manifest the same discomfort, even when the circulation is in a feeble, rather 
 than an excited state. It is remarkable that the sensibility of the mucous 
 membranes lining the internal organs, is less exalted by the state of inflamma- 
 tion, than is that of most other parts ; and in this arrangement we may trace 
 a wise and beneficent provision ; since, were it otherwise, the functions neces- 
 sary to life could not be performed without extreme distress, with a very 
 moderate amount of disorder in the viscera. If a joint is inflamed, we can 
 give it rest ; but to the actions of the alimentary canal we can give little volun- 
 tary respite. 
 
 509. The feelings of Pain or Pleasure, which are connected with particular 
 sensations, cannot (for the most part at least) be explained upon any other 
 principle than that of the necessary association of these feelings, by an original 
 law of our nature, with the sensations in question. As a general rule, it may 
 be stated, that the violent excitement of any sensation is disagreeable, even 
 when the same sensation in a moderate degree may be a source of extreme 
 pleasure. This is the case alike with those impressions, which are communi- 
 cated through the organs of sight, hearing, smell and taste, as with those that 
 are received through the nerves of common sensation ; and there can be no 
 doubt that the final cause, or purpose, of the association of painful feelings 
 with such violent excitement, is to stimulate the individual to remove himself 
 from what would be injurious in its effects upon the system. Thus, the pain 
 resulting from violent pressure on the cutaneous surface, or from the proximity 
 of a heated body, gives warning of the danger of injury, and excites mental 
 operations destined to remove the part from the influence of the injurious 
 cause ; and this is shown by the fact, that loss of sensibility is frequently the 
 indirect occasion of severe lesions, the individual not receiving the customary 
 intimation that an injurious process is taking place. Instances have occurred, 
 in which severe inflammation of the membrane lining the air-passages has re- 
 sulted from the effects of ammoniacal vapours, introduced into them during a 
 state of syncope, the patient not receiving that notice of the irritation, which 
 would, in an active condition of his nervous system, have prevented him from 
 inhaling the noxious agent. 
 
 a. The following case, recorded in the "Journal df a Naturalist," affords a remarkable 
 instance of this general fact. The correctness of the statement having been called in question, 
 it was fully confirmed by Mr. Richard Smith, the late senior surgeon of the Bristol Infirmary, 
 under whose care the sufferer had been. "A travelling man, one winter's evening, laid 
 himself down upon the platform of a lime-kiln, placing his feet, probably numbed with cold, 
 upon the heap of stones, newly put on to burn through the night. Sleep overcame him in 
 this situation ; the fire gradually rising and increasing, until it ignited the stones upon which 
 his feet were placed. Lulled by the warmth, the man slept on; the fire increased until it 
 burned one foot (which probably was extended over a vent-hole) and part of the leg above 
 the ankle entirely off, consuming that part so effectually, that a cinder-like fragment was 
 alone remaining, and still the wretch slept on ! and in this state was found by the kiln-man 
 in the morning. Insensible to any pain, and ignorant of his misfortune, he attempted to rise 
 and pursue his journey, but missing his shoe, requested to have it found ; and when he was 
 raised, putting his burnt limb to the ground to support his body, the extremity of his leg-bone, 
 the tibia, crumbled into fragments, having been calcined into lime. Still he expressed no 
 sense of pain, and probably experienced none ; from the gradual operation of the fire, and his 
 own torpidity during the hours his foot was consuming. This poor drover survived his mis- 
 fortunes in the hospital about a fortnight ; but the fire having extended to other parts of his ' 
 body, recovery was hopeless." 
 
388 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 510. It is a general rule, with regard to all sensations, that their intensity 
 is much affected by habit; being greatly diminished by frequent and continual 
 repetition. This is not the case, however, with regard to those sensations to 
 which the attention is peculiarly directed ; for these lose none of their acute- 
 ness by frequent repetition; on the contrary, they become much more readily 
 cognizable by the mind. We have a good example of both facts, in the ef- 
 fects of sounds upon a sleeping person. If they are sounds which he has 
 been accustomed to hear, and to disregard, they may not awake him, however 
 loud they be : thus, the strokes of a forge-hammer, the firing of guns, the 
 shouts of a multitude, or the loudest music, may neither prevent the acces- 
 sion of sleep, nor arouse the already unconscious sleeper ; indeed, it oftener 
 happens that individuals are prevented from sleeping by the want of some 
 accustomed sound, or are awoke by its cessation. On the other hand, a very 
 slight sound, the nature of which excites the attention, is sufficient to prevent 
 sleep ; thus, the buzz of a single musquito, in the stillness of the night, is 
 most effectual in dispelling repose ; and, in like manner, a person in a state 
 of the profoundest unconsciousness may be aroused by a whisper, if the sound 
 be one to which he has been accustomed to pay regard. 
 
 a. The following circumstance has been communicated to the Author by a Naval Officer 
 of high rank : When a young man he was serving as signal-lieutenant under Lord Hood ; 
 and being desirous of obtaining the favourable notice of his commander, he devoted him- 
 self to his duty with the greatest energy and perseverance, often remaining on deck nineteen 
 hours out of the twenty-four, with his attention continually on the stretch. During the few 
 hours which he spent in repose, his sleep was so profound, that no noise of an ordinary 
 kind, however loud, would awake him. But if the word " signal" was softly uttered in his 
 ear, he was instantly aroused. 
 
 511. The general law, that Sensations, not attended to, are blunted by fre- 
 (juent repetition, may perhaps be connected with certain other general facts, 
 which lie under the observation of every one. It is well known, that the 
 vividness of sensations depends rather on the degree of change which they 
 produce in the system, than on the absolute amount of the impressing cause; 
 and this is alike the case with regard to the special and the ordinary sensa- 
 tions. Thus, our sensations of heat and cold are entirely governed by the 
 previous condition of the parts affected ; as is shown by the well-known ex- 
 periment, of putting one hand in hot water, the other in cold, and then trans- 
 ferring both to tepid water, which will seem cool to one hand, and warm to 
 the other. Every one knows, too, how much more we are affected by a warm 
 day at the commencement of the summer, than by an equally hot day later 
 in the season. The same is the case in regard to light and sound, smell and 
 taste. A person going out of a totally dark room into one moderately bright, 
 is for the time painfully impressed by the light, but soon becomes habituated 
 to it ; whilst another, who enters it from a room brilliantly illuminated, will 
 consider it dark and gloomy. Those who are constantly exposed to very loud 
 noises, become almost unconscious of them, and are even undisturbed by them 
 in illness; and the medical student well knows, that even the effluvia of the 
 dissecting-room are not perceived, when the organ of smell is habituated to 
 them, although an intermission of sufficient length would, in either instance, 
 occasion a renewal of the first unpleasant feelings, when the individual is 
 again subjected to the impression. 
 
 512. Again, it is a well-known fact, that impressions made upon the organs 
 of sense continue for a time, after the cause of the impression has ceased. 
 It is in this manner that a musical tone, which seems perfectly continuous, 
 results from a series of consecutive vibrations, following each other with a 
 certain rapidity ; and that a line or circle of light is produced by a luminous 
 body moving with a certain velocity. Now there is reason to believe that 
 
OF SENSATION IN GENERAL. 389 
 
 changes, of which the effects thus transiently remain upon the nerves of sense, 
 are more permanently impressed upon the Sensorium; since, as formerly 
 shown ( 491), we can only in this manner account for the phenomena of 
 Memory, and for the effects produced upon this power, by material changes 
 in the brain. Hence, the diminution in the force of sensations, which is the 
 consequence of their habitual recurrence, may be considered as resulting from 
 these two general facts, the persistence of the impression made by them 
 upon the sensorium, and the consequent absence of a change in its state, 
 when a sensory impression is brought to it, which is of the same nature with 
 one already registered there : the degree in which the consciousness is ex- 
 cited, being dependent, as just stated, not upon the absolute degree of the 
 impressing cause, but upon the amount of change which it produces in the 
 sensorial apparatus. In this respect there is a perfect conformity between 
 the law of sensation, and that of muscular contraction ; for stimuli which ex- 
 cite the latter, usually lose their force in proportion to the frequency of their 
 repetition. Indeed, both may be considered as results of the more general 
 laws of vitality ; for the actions of other tissues follow the same rule, as is 
 shown by the tolerance, that may be gradually established in the system, of 
 medicinal agents, poisons, &c., which would have at first produced the most 
 violent effects, when given in the same amount. 
 
 513. It is curious, also, that the feelings of Pain or Pleasure, which unac- 
 customed sensations excite, are often exchanged for each other, when the sys- 
 tem is habituated to them ; this is especially the case, in regard to impressions 
 communicated through the organs of smell and taste. There are many arti- 
 cles in common use among mankind, such as Tobacco, Fermented Liquors, 
 <fcc., the use of which cannot be said to produce a natural enjoyment, since 
 it is at first unpleasant to most persons ; and yet it first becomes tolerable, 
 then agreeable ; and at last the want of them is felt as a painful privation, and 
 the stimulus must be applied in an increasing degree, in order to produce 
 the usual effect. 
 
 514. It is through the medium of Sensation, that we acquire a knowledge 
 of the material world around us ; and that its changes excite mental operations 
 in ourselves. The various kinds or modes of Sensation excite in us various 
 ideas regarding the properties of matter ; and these properties are known to 
 us, only through the changes which they produce in the several organs. Thus 
 a man totally blind from birth can form no idea of the nature of light or co- 
 lours; nor could one completely deaf have any just conception of musical 
 tones. It is well known that instances exist, in which, from some imperfection 
 of the organization, there is an incapacity for distinguishing colours or musi- 
 cal tones, whilst there is no want of sensibility to light or sound ; and that 
 some persons are naturally endowed with a much greater range of the sen- 
 sory faculties, than others possess. Hence it does not seem at all improbable, 
 that there are properties of matter, of which none of our senses can take 
 immediate cognizance ; and which other beings might be formed to perceive, 
 in the same manner as we are sensible to light, sound, &c. Thus, it is well 
 known, that many animals are affected by atmospheric changes, in such a 
 manner, that their actions are regarded by Man as indications of the probable 
 state of the weather ; and the same is the case in a less degree with some 
 of our own species ; who are peculiarly susceptible of the same influences. 
 Now the most universal of all the qualities or propensities of matter, 
 that, in fact, on which our notion of it is founded, is resistance ; and 
 it is this quality, of which the knowledge seems most universally diffused 
 throughout the Animal kingdom. In the lowest tribes, we find that contact, 
 between their surface and some material body, is required to produce sensa- 
 
 33* 
 
390 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 tion ; and beings which cannot be made conscious, in this manner, of the 
 existence of something external to themselves, do not deserve to be ranked 
 in the Animal kingdom. Our difficulty lies (as heretofore remarked, 1), 
 in ascertaining what are to be regarded, in such beings, as unequivocal indi- 
 cations of consciousness. Those animals which are fixed to one spot, can 
 have few other ideas of matter than this most general one ; but in those 
 which have the power of locomotion, the general sensibility of the surface 
 doubtless communicates to them some notion of the character of the body 
 over which they move, in the same manner as we learn it by passing the 
 hand over its exterior. We shall presently see, however, that the idea of 
 the shape of a body which we form from the touch, results from a very com- 
 plex process ; which animals of the lowest grade can scarcely be supposed 
 to exercise. There can be no doubt that, next to the mere sense of resistance, 
 sensibility to temperature is the most universally diffused through the Ani- 
 mal kingdom ; and probably the consciousness of luminosity is the next in 
 the extent of its diffusion. There is good reason to believe, from observation 
 of their habits, that many animals are susceptible of the influence, and are 
 directed by the guidance of light ; whilst their organs are not adapted to re- 
 ceive true visual impressions, or to form optical images ; and such would 
 seem to be the function of the red spots, frequently seen on prominent parts 
 of Animalcules, the lower Articulata and Mollusca, and even of some Radiata. 
 Wherever these are of sufficient size to allow their structure to be examined, 
 they are found to be largely supplied with nerves, but to be destitute of the 
 peculiar organization which alone constitutes a true eye. The 'sense of Taste 
 may be considered as a refined modification of that of Touch ; and it is 
 probable that this exists very low down in the animal scale, being obviously 
 of great importance in the selection of food ; but the Anatomist has no means 
 of ascertaining where this refinement exists, and where it does not ; since the 
 organs of taste and touch are so similar. The sense of Hearing does not 
 seem to be distinctly present among the Invertebrate animals, except in such 
 as approach most nearly to the Vertebrata ; it is not improbable, however, 
 that sonorous vibrations may produce an effect upon the system of those ani- 
 mals which do not receive them as sound; and this would appear, from a 
 fact subsequently to be mentioned ( 526), to be not improbably the case, 
 with regard especially to aquatic animals. The sense of Smell, which is con- 
 cerned with one of the least general properties of matter, appears to be the 
 least widely diffused among the whole ; being only possessed in any high 
 degree by Vertebrated animals, and being "but feebly present in a large pro- 
 portion of these. 
 
 515. Besides the various kinds of sensibility which have been just enume- 
 rated, there are others which are ordinarily associated together, along with 
 the sense of material resistance (and its several modifications), and the sense 
 of temperature, under the head of Common Sensation ; but several of them, 
 especially those which originate in the body itself, can scarcely be regarded 
 in this light. Such are the feelings of Hunger and Thirst; that of Nausea; 
 that of distress resulting from suspended aeration of the blood ; that of " sink- 
 ing at the stomach," as it is vulgarly but expressively described, which results 
 from strong mental emotion ; that of the venereal excitement, and perhaps 
 some others. Now in regard to all these, it is impossible in the present state 
 of our knowledge to say, whether their peculiarity results from the particular 
 constitution of the nerves that receive and convey them, or only from a modi- 
 fication in the impressing causes, and in the mode in which they operate. 
 Thus we have no evidence that the nervous fibrils, which convey from the 
 lungs the sense of distress resulting from deficient aeration, may not be of a 
 different character from those which convey from the surface of the air-pas- 
 
OF SENSATION IN GENERAL. 391 
 
 sages the sense of the contact of a foreign body. But as we know that all 
 the trunks, along which these peculiar impressions travel, do minister to ordi- 
 nary sensation, whilst the nerves of truly special sensation are not sensible 
 to common impressions, it is evident that the probability is in favour of the 
 identity of the fibres, which minister to these sensations, with those of the 
 usual sensory character. For the sense of temperature, however, it is not by 
 any means certain that a special set of fibres does not exist ; for many cases 
 are on record, in which it has been lost, whilst the ordinary sense of tact 
 remained; and it is sometimes preserved, when the anaesthesia is in other 
 respects complete. 
 
 516. With regard to all kinds of Sensation it is to be remembered, that the 
 change of which the mind is informed, is not the change at the peripheral 
 extremities of the nerves, but the change communicated to the sensorium ; 
 hence it results, that external agencies can give rise to no kind of sensation, 
 which cannot also be produced by internal causes, exciting changes in the 
 condition of the nerves in their course. This very frequently happens in 
 regard to the senses of sight and hearing ; flashes of light being seen, and 
 ringing sounds in the ears being heard, when no external stimulus has pro- 
 duced such impressions. The production of odorous and gustative sensations 
 from internal causes, is perhaps less common ; but the sense of nausea is 
 more frequently excited in this manner, than by the direct contact of the nau- 
 seating substance with the tongue or fauces. The various phases of common 
 sensibility often originate thus ; and it is an additional evidence in favour of 
 the distinctness of the fibres which convey the impressions of temperature, 
 that these are frequently affected, a person being sensible of heat or of chil- 
 liness in some part of his body, without any real alteration of its temperature, 
 whilst there is no corresponding affection of the tactual sensations. The 
 most common of the internal causes of these subjective sensations (as they 
 have been termed, in contradistinction to the objective, which result from a 
 real material object), is congestion or inflammation ; and it is interesting to 
 remark that this cause, operating through each nerve, produces in the senso- 
 rium the changes to which that nerve is usually subservient. Thus, conges- 
 tion in the nerves of common sensation gives rise to feelings of pain or un- 
 easiness ; but when occurring in the retina and optic nerve it produces flashes 
 of light; and in the auditory nerve it occasions "a noise in the ears." It 
 may be observed, also, of some external causes, that they may excite changes 
 in the sensorium through several different channels ; and that in each case the 
 sensation is characteristic of the particular nerve, on which the impression is 
 made. Thus pressure, which produces through the nerves of common sensa- 
 tion the feeling of resistance, is well known to occasion, when exerted on the 
 eye, the sensation of light and colours ; and, when made with some violence 
 on the ear, to produce tinnitus aurium. It is not so easy to excite sensations 
 of taste and smell, by mechanical irritation ; and yet, as Dr. Baly* has shown, 
 it may readily be accomplished in regard to the former. The sense of nau- 
 sea may be easily produced, as is familiarly known, by mechanical irritation 
 of the fauces. The stimulus of Electricity still more completely possesses 
 the power of affecting all the sensory nerves, with the changes which are pe- 
 culiar to them; for, by proper management, an individual may be made con- 
 scious at the same time of flashes of light, of distinct sounds, of a phosphoric 
 odour, of a peculiar taste, and of pricking sensations, all excited by the same 
 cause, the effects of which, are modified, according to the respective peculi- 
 arities of the instruments through which it operates. But although there are 
 some stimuli which can produce sensory impressions on all the nerves of 
 
 * Translation of Mviller's Physiology, p. 1062, note. 
 
392 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 sensation, it will be found that those, to which any one organ is peculiarly 
 fitted to respond, produce little or no effect upon the rest. Thus the ear can- 
 not distinguish the slightest difference between a luminous and a dark object. 
 A tuning-fork, which, when laid upon the ear whilst vibrating, produces a dis- 
 tinct musical tone, excites no other sensation when placed upon the eye than 
 a slight jarring feeling. The most delicate touch cannot distinguish a sub- 
 stance which is sweet to the taste from one which is bitter; nor can the taste 
 (if the communication between the mouth and the nose be cut off) perceive 
 anything peculiar, in the most strongly odoriferous bodies. 
 
 517. It may hence be inferred that no nerve of special sensation can, by 
 any possibility, take on the function of another. How far the nerves of com- 
 mon sensation, can, under any circumstances, perform the offices usually 
 delegated to those of special sense, we are not yet in a condition to deter- 
 mine. Comparative Anatomy seems to show that, in the lowest animals in 
 which the rudiments of eyes can be detected, there is no distinction between 
 the nerves proceeding to these organs, and the rest ; and there would appear 
 some ground for the belief that, as in other cases, the special organs of sensi- 
 bility are gradually elaborated, in ascending the Animal scale, from the more 
 general apparatus, and are not merely superadded to it.' Hence we may con- 
 ceive the possibility (though there is no proof of the fact) that states of the 
 system might occur, in which a change in the common sensory nerves might 
 produce the sensation of light, sound, &c. But it is quite impossible (so far 
 at least as our present knowledge of physical phenomena permits us to decide 
 upon the impossibility of anything) that distinct visual impressions should be 
 communicated to a nerve, except through the mediation of such an optical 
 instrument as the eye ; or distinct sonorous impressions, except through such 
 an acoustic instrument as the ear. Hence we must receive with the greatest 
 caution the wonderful accounts of transference of sensation, many of which 
 have undoubtedly been the offspring of deception. Still it may be objected 
 that, since we are so totally destitute of real knowledge, as to the mode in 
 which vision is ordinarily produced by inverted images upon the retina, we 
 have no right to assert that it may not take place in some other way ; and 
 perhaps this objection should lead us to consider the phenomenon rather as 
 extremely improbable, than as impossible. But the improbability may be 
 compared to that of a stone ascending like a balloon, or a piece of lead float- 
 ing on the water ; for we have no more knowledge of the ultimate cause of 
 that which we term the force of Gravitation, than we have of the nature of 
 Sensation. 
 
 518. The peculiar aptitudes of the different Sensory nerves, to receive 
 and convey impressions of various kinds, must be regarded as the result of 
 properties inherent in themselves ; just as we consider the difference between 
 the afferent nerves in general, and the motor nerves, to be one belonging to 
 their own constitution. But it is probable that there are also different locali- 
 ties in the Sensorium, in which the changes to which they give rise are per- 
 formed. This may be judged of from the fact, that the phenomena of sub- 
 jective sensation frequently originate in peculiar conditions of the encephalon 
 itself, and not in the nervous trunks or organs of sense ; thus, in dreaming, 
 we have frequently very vivid pictures of external objects presented to our 
 minds; and we sometimes distinctly hear voices and musical tones, or have 
 perceptions (though this is less common) of tastes and odours. The phe- 
 nomena of spectral illusions are very nearly connected with those of dream- 
 ing; both may be in some degree influenced by external causes, acting upon 
 the organs of sensation, which are misinterpreted (as it were) by the mind, 
 owing to its state of imperfect operation ; but both also may entirely originate 
 in the central organs. There seems to be no difference, in the feelings of the 
 
OF SENSATION IN GENERAL. 393 
 
 individual, between the sensations thus originating, and those which are pro- 
 duced in the usual manner ; for we find that, unless otherwise convinced by 
 their own reason, persons who witness spectral illusions believe as firmly in 
 the reality of the objects that come before their minds, as if the images of 
 those objects were actually formed on their retinae. This is another proof, if 
 any were wanting, that the organ of sense, and the nerve belonging to it, are 
 but the instruments by which certain changes are produced in the sensorium; 
 of which changes, and not of the immediate impression of the object, the 
 sensation really consists. It seems to be by an innate law of our constitution, 
 that these subjective sensations, whether originating in the central organs, or 
 in the course of the nervous trunks, should be referred by the mind to the 
 ordinary situations of the peripheral terminations of those nerves ; even 
 though these should not exist, or should be destitute of the power of receiv- 
 ing impressions. Thus after amputations, the patients are for some time 
 affected with sensations (originating probably in the cut extremities of the 
 nerves), which they refer to the removed extremities; the same has been 
 noticed in regard to the eye, as well when it has been completely extirpated, 
 as when its powers have been destroyed by disease. The effects of the 
 Taliacotian operation also exhibit the operation of this law in a curious man- 
 ner; for until the flap of skin, from which the new nose is formed, obtains 
 vascular and nervous connections in its new situation, the sensation produced 
 by touching it is referred to the forehead. Another interesting illustration of 
 it may be obtained by the following very simple experiment : if the middle 
 finger of either hand be crossed behind the fore-finger, so that its extremity is 
 on the radial side of the latter, and the ends of the two fingers thus disposed 
 be rolled over a marble, pea, or other round body, a sensation will be pro- 
 duced, which, if uncorrected by reason, would cause the mind to believe in 
 the existence of two distinct bodies ; this is due to the impression being made 
 at the same time upon the radial side of the fore-finger, and the ulnar side of 
 the middle finger, two joints which, in the natural position, are at a con- 
 siderable distance. 
 
 519. The acuteness of particular sensations is influenced in a remarkable 
 degree by the attention they receive from the mind. If the mind be entirely 
 inactive, as in profound sleep, no sensation whatever is produced by ordinary 
 impressions ; on the other hand, when the mind is from any cause strongly 
 directed upon them, impressions very feeble in themselves produce sensations 
 of even painful acuteness. Every one knows how much a slight itching of 
 some part of the surface may be magnified, by the direction of the thoughts 
 to it; whilst as soon as they are forced by some stronger impression into ano- 
 ther channel, the irritation is no longer felt. Every one is aware how vividly 
 sounds are perceived, when they break in upon the stillness of the night; being 
 increased in strength, not only by the contrast, but by absorbing the whole 
 attention. An interesting experiment is mentioned by Miiller, which shows 
 how completely the mind may be unconscious of impressions communicated 
 to it by one organ of sense, when occupied, even without a distinct effort of 
 the will, by those received through another. If we look at a sheet of white 
 paper through two differently-coloured glasses at the same time one being 
 placed before each eye, the resulting sensation is seldom that of a mixture 
 of the colours : if the experiment be tried with blue and yellow glasses, for 
 example, we do not see the paper of an uniform green ; but the blue is pre- 
 dominant at one moment, and the yellow at another; or blue nebulous spots 
 may present themselves on a yellow field, or yellow spots on a blue field. 
 We perceive from this experiment, that the attention may not only be directed 
 to the impressions made on either retina, to the complete exclusion of those of 
 
394 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 the other, but it may be directed to those made on particular spots of either. 
 This may be noticed, again, in the process by which we make ourselves ac- 
 quainted with a landscape or a picture ; if our attention be directed to the whole 
 field of vision at once, we see nothing distinctly ; and it is only by abstracting 
 ourselves from the contemplation of the greater part of it, and by directing 
 our attention to smaller portions in succession, that we can obtain a definite 
 conception of the details. The same is the case in regard to auditory impres- 
 sions ; and here the power of attention, in causing one sensation or series of 
 sensations to predominate over others which are really more intense, is often 
 most remarkably manifested. When we are listening to a piece of music 
 played by a large orchestra, for example, we may either attend to the combined 
 effect of all the instruments, or we may single out any one part in the har- 
 mony, and follow this through all its mazes ; and a person with a practised ear 
 (as it is commonly but erroneously termed, it being not the ear but the mind 
 that is practised), can even distinguish the sound of the weakest instrument 
 in the whole band, and can follow its strajn through the whole performance. 
 This attention to a single element can only be given, however, by withdrawing 
 the mind from the perception of the rest ; and a musician who thus listens, 
 will have very little idea of the rest of the harmonic parts, or of the general 
 effect. In fact, when the mind is thus directed, by a strong effort of the will, 
 into a particular channel, it may be almost considered as unconscious quoad 
 any other impressions. 
 
 520. The effects of this principle are manifested. in regard to the sensations 
 which originate within the system ; as well as in respect to those which are 
 excited by external impressions. Every one is aware how difficult it is to 
 keep the body perfectly quiescent,* especially when there is a particular mo- 
 tive for doing so, and when the attention is strongly directed to the object. 
 This is experienced even whilst a Photogenic likeness is being taken, when 
 the position is chosen by the individual, and a support is adapted to assist 
 him iii retaining it; and it is still more strongly felt by the performers in the 
 Tableaux Vivans, who cannot keep up the effort for more than three or four 
 minutes. Now it is well known that, when the attention is strongly directed 
 to an entirely different object (when we are listening, for example, to an elo- 
 quent sermon, or an interesting lecture), the body may remain perfectly mo- 
 tionless for a much longer period j the uneasy sensations, which would other- 
 wise have occasioned the individual to change his position, not being felt; but 
 no sooner is the discourse ended, than a simultaneous movement of the whole 
 audience takes place, every one then becoming conscious of some discomfort, 
 which he seeks to relieve. This is the case, also, in regard to the respiratory 
 sensation ; in general it may be observed, that the usual reflex movements are 
 not enough for the perfect aeration of the blood, and that a more prolonged 
 inspiration prompted by an uneasy feeling, takes place at intervals ; but under 
 such circumstances as those just alluded to, this feeling is not experienced, until 
 the attention ceases to be engaged by a more powerful stimulus, and then it 
 manifests itself by the deep inspirations which accompany, in almost every 
 individual, the general movement of the body. 
 
 52 1 . It is curious that the constant direction of the attention to internal 
 sensations of & subjective kind, should sometimes occasion actual disorder of 
 the parts to which these sensations are referred ; and yet this seems the only 
 way of accounting for some of the phenomena of disease. Sometimes the 
 cause of the sensation may exist in the trunk of the nerve, in some part of its 
 course; whilst in other instances, it may be confined to the sensorium. Pain 
 
 * Of course the movements of respiration and winking are left out of the question. 
 
SENSE OF TOUCH. 395 
 
 of the testicle, for example, may be occasioned by irritation having its seat 
 in the lower part of the spine, the organ itself being perfectly sound ; yet if 
 that pain continue, it may become diseased. The following are some very 
 interesting remarks on this subject, from the able pen of Dr. Holland.* 
 " There is cause to believe the action of the heart to be quickened or other- 
 wise disturbed, by the mere centering of consciousness upon it, without any 
 emotion or anxiety." This is especially the case where its impulses are 
 irregular, or are so loud as to be audible. " The same may be said of the 
 parts concerned in respiration. If this act be expressly made the subject of 
 consciousness, it will be felt to undergo some change ; generally to be retarded 
 at first, and afterwards quickened." " The act of swallowing is manifestly 
 rendered more difficult, by the attention being fixed upon it ; and the same 
 cause will often be found to render articulation less distinct, especially when 
 there exists already some impediment to the function. A similar direction of 
 consciousness to the region of the stomach, creates in this part a sense of 
 weight, oppression, or other less definite uneasiness ; and, when the stomach 
 is full, appears greatly to disturb the due digestion of the food. The state 
 and action of the bowels are much influenced by the same cause." A pecu- 
 liar sense of weight and restlessness approaching to cramp, is felt in a limb, 
 to which the attention is particularly directed. " The attention concentrated, 
 for so by an effort of will it may be, on the head or sensorium, gives certain 
 feelings of tension and uneasiness, caused possibly by some change in the 
 circulation of the part ; though it may be an effect, however difficult to be 
 conceived, on the nervous system itself. Persistence in this effort, which is 
 seldom indeed possible beyond a short time without confusion, produces results 
 of much more complex nature, and scarcely to be defined by any common terms 
 of language." These phenomena have an evident affinity, on the one hand, 
 with the exaltation of external or objective sensations, to which the attention 
 is peculiarly directed; and on the other with those of several morbid condi- 
 tions. The explanation of them all is probably to be sought in some change 
 in the circulation of the part, to which the sensation is referred. Thus the 
 hypochondriac patient, ** in fixing his consciousness with morbid intentness on 
 certain organs, creates not merely disordered sensations, but often also disor- 
 dered actions in them. There may be palpitation of the heart, hurried or 
 choked respiration, flatulence and other distress of stomach, irritation of the 
 bladder; all arising from this morbid direction of attention to the organs in 
 question." In hysteria, again, " the instances are frequent, of attacks brought 
 on by the mere expectation of them ; or by irritation ; or occasionally even a 
 sort of morbid solicitation of the organs to these singular actions." These 
 facts go a long way to explain the phenomena of Mesmerism, many of which 
 are obviously to be referred to the exaggerated operation of the same principle. 
 (See Appendix.) We now proceed to consider in more detail the functions of 
 the several Organs of the Senses, and shall commence with that of the most 
 general character. 
 
 2. Sense of Touch. 
 
 522. By the sense of Touch, as commonly understood, is meant that mo- 
 dification of the common sensibility of the body, of which the Cutaneous sur- 
 face is the especial seat. It derives its peculiar power simply from the large 
 amount of sensory nervous fibres, which are distributed in its substance; and 
 especially through the terminations (or rather the origins) of these in the pa- 
 pillae, which are little elevations of the surface of the cutis, easily perceptible 
 
 * Medical Notes and Reflections, Chap, v. 
 
396 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 162. 
 
 Capillary net-work at margin of 
 lips. 
 
 by the aid of a lens, and each chiefly composed of a vascular loop overlapping 
 
 the extremity of the nervous fibril. The pre- 
 cise arrangement of the nerve-fibres in the cuta- 
 neous papillae, has not been indisputably ascer- 
 tained ; but the opinion that they form loops 
 (Fig. 119) is the one most generally adopted. 
 The number of these papillae within any given 
 area, pretty closely corresponds with the degree 
 of sensibility of that part of the surface ; thus 
 we find them most abundant on the hands, es- 
 pecially towards the points of the fingers, and 
 on the lips and tongue. In some animals, es- 
 pecially those of the Feline tribe, the long vi- 
 brissas (commonly termed whiskers) evidently 
 minister to sensation; and it has been demonstrated that their pulps are 
 largely supplied with nerves from the fifth pair. Some interesting observa- 
 tions have been made by Prof. Weber, on the sensibility of different parts of 
 the skin. His mode of ascertaining this, was to touch the surface with the 
 legs of a pair of compasses, the points of which were guarded with pieces of 
 cork ; the eyes being closed at the time, the legs were approximated to each 
 other, until they were brought within the smallest distance, at which they 
 could be felt to be distinct from one another. The following are some of the 
 results of the experiments. With the extremities of the fingers and the 
 point of the tongue, the distance could be distinguished most easily in the 
 longitudinal direction ; on the dorsum of the tongue, the face, neck, and ex- 
 tremities, the distance could be recognized best when the points were placed 
 transversely. 
 
 Point of middle finger . . of a line 
 
 Point of tongue . . . $ of a line 
 
 Palmar surface of third finger 1 line 
 
 Red surface of lips . . 2 lines 
 Palmar surface of middle finger 2 
 
 Dorsal surface of third finger 3 
 
 Tip of the nose . . 3 ,, 
 
 Dorsum and edge of tongue 4 
 
 Part of lips covered by skin 4 
 
 Palm of hand . . . 5 
 
 Skin of cheek . . 5 
 
 Extremity of great toe . 5 
 
 Hard palate . . . 6 
 
 Dorsal surface of forefinger . 7 
 
 Dorsum of hand . 8 , 
 
 Mucous Membrane of gums 
 
 Lower part of forehead 
 
 Lower part of occiput 
 
 Back of hand . 
 
 Neck, under lower jaw 
 
 Vertex . 
 
 Skin over Patella 
 
 Sacrum . 
 
 Dorsum of foot 
 Skin over sternum . 
 Skin beneath occiput 
 Skin over spine, in back 
 Middle of the arm . 
 thigh 
 
 9 lines 
 
 10 
 
 12 
 
 14 
 
 15 
 
 15 
 
 16 
 18 
 18 
 18 
 20 
 24 
 30 
 30 
 30 , 
 
 It is curious that the distance between the legs of the compasses seemed to 
 be greater (although really so much less), when it was felt by the more sensi- 
 tive parts, than when it was estimated by parts of less distinct sensibility. As 
 a general fact, it seems that the sensibility of the trunk is greater on the me- 
 dian line, both before and behind, and less at the sides. Differences of tem- 
 perature, and the weight of bodies, were, according to Prof. Weber's observa- 
 tions, most accurately recognized at the parts, which were determined to be 
 most sensible by the foregoing method of inquiry. 
 
 523. As already stated( 514), the only idea communicated to our minds by 
 the sense of Touch, when exercised in its simplest form, is that of Resistance ; 
 but when the sensory surface and the substance touched are made to change 
 their place in regard to each other, we obtain the additional notion of Extension 
 or Space. By the various degrees of resistance which the sensory surface 
 encounters, we estimate the hardness or softness of the body; but in this we 
 
SENSE OF TOUCH. v 397 
 
 are assisted by the muscular sense ( 433), which makes us conscious of the 
 degree of pressure we are employing. By the impressions made upon the 
 papillae, during the movement of the tactile surface over that which is being 
 examined, the roughness, smoothness, or other peculiar characters, of the lat- 
 ter are estimated, Our knowledge of form, however, is a very complex pro- 
 cess, requiring not merely the exercise of the sense of touch, but. also great 
 attention to the muscular sensations. It is chiefly, as formerly remarked, in 
 the variety of movements of which the hand of Man is capable, that it is 
 superior to that of any other animal ; and it cannot be doubted that this affords 
 a very important means of acquiring information in regard to the external 
 world, and especially of correcting many vague and fallacious notions, which 
 we should derive from the sense of Sight, if used alone. On the other hand, 
 it must be confessed, that our knowledge would have a very limited range, if 
 this sense were the only medium, through which we could acquire ideas. It 
 is probably on the sensations communicated through the touch, that the idea 
 of the material world, as something external to ourselves, chiefly rests ; but 
 this idea is by no means a direct result of these sensations, being rather an 
 instinctive or intuitive perception excited by them. Every person who directs 
 the least attention to the subject must perceive, how completely different are 
 those notions of the primary or elementary properties of matter, which we 
 base upon the information thus communicated to us, from the sensations them- 
 selves ; and, as Dr. Alison has justly remarked, "a decisive proof of this being 
 the true representation of this part of our mental constitution, is obtained by 
 attending to the idea of extension or space ; which is undoubtedly formed 
 during the exercise of the sense of touch ; and is no sooner formed, than it 
 ' swells in the human mind to Infinity,' to which certainly no human sensation 
 can bear any resemblance." 
 
 524. That the conditions under which certain of the modifications of com- 
 mon sensation operate, are in some respects different from those of ordinary 
 Touch, is very easily shown. Thus, the feeling of tickling is excited most 
 readily in parts, which have the least tactual sensibility, the armpits, flanks, 
 and soles of the feet ; whilst in the points of the fingers it cannot be excited. 
 Moreover, the nipple is very moderately endowed with ordinary sensibility ; 
 yet by a particular kind of irritation, a very strong feeling may be excited 
 through it. Again, in regard to temperature, it is remarked by Weber, that 
 the left hand is more sensitive than the right ; although the sense of touch is 
 undoubtedly the most acute in the latter. He states that, if the two hands, 
 previously of the same temperature, be plunged into separate basins of warm 
 water, that in which the left hand is immersed will be felt as the warmest, 
 even though its temperature is somewhat lower than that of the other. In 
 regard to the sensations of heat and cold, he points out another curious fact, 
 that a weaker impression made on a large surface, seems more powerful than 
 a stronger impression made on a small surface ; thus, if the forefinger of one 
 hand be immersed in water at 104, and the whole of the other hand be 
 plunged in water at 102, the cooler water will be thought the warmer; 
 whence the well-known fact, that water in which a finger can be held, will 
 scald the whole hand. Hence it also follows, that minute differences in tem- 
 perature, which are imperceptible to a single finger, are appreciated by plung- 
 ing the whole hand into the water ; in this manner, a difference of one-third 
 of a degree may readily be detected, when the same hand is placed succes- 
 sively in two vessels. The judgment is more accurate, when the temperature 
 is not much above or below the usual heat of the body ; just as sounds are 
 best discriminated, when neither very acute nor very grave. 
 
 525. The improvement in the sense of Touch, in those persons whose de- 
 pendence upon it is increased by the loss of other senses, is well known ; this 
 
 34 
 
398 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 is doubtless to be in part attributed (as already remarked) to the increased 
 attention which is given to the sensations, and in part to an increased develop- 
 ment of the tactile organs themselves, resulting from the frequent use of them. 
 The case of Saunderson, who, although he lost his sight at two years old, be- 
 came Professor of Mathematics at Cambridge, is well known ; amongst his 
 most remarkable faculties, was that of distinguishing genuine medals from 
 imitations, which he could do more accurately than many connoisseurs in full 
 possession of their senses. The process of the acquirement of the power of 
 recognizing elevated characters by the touch, is a remarkable example of this 
 improveability. When a blind person first commences learning to read in this 
 manner, it is necessary to use a large type ; and every individual letter must 
 be felt for some time, before a distinct idea of its form is acquired. After a 
 short period of diligent application, the individual becomes able to recognize 
 the combinations of letters in words, without forming a separate idea of each 
 letter ; and can read line after line, by passing the finger over each, with con- 
 siderable rapidity. Now when this power is once thoroughly acquired, it is 
 found that the size of the type may be gradually diminished ; and this seems 
 to indicate, that the sensations themselves are rendered more acute, by the 
 frequent application of them in this direction. As an instance of the correct 
 notions which may be conveyed to the mind, of the forms and surfaces of a 
 great variety of objects, and of the sufficiency of these notions for accurate 
 comparison, the Author may mention the case of a blind friend of his own, 
 who has acquired a very complete knowledge of Conchology, both recent and 
 fossil ; and who is not only able to recognize every one of the numerous spe- 
 cimens in his own Cabinet, but to mention the nearest alliances of a Shell 
 previously unknown to him, when he has thoroughly examined it by his 
 touch. Many instances are on record, of the acquirement, by the blind, of 
 the power of distinguishing the colours of surfaces, which were similar in 
 other respects ; and, however wonderful this may seem, it is by no means 
 incredible. For it is to be remembered that the difference of colour depends 
 upon the position and arrangement of the particles composing the surface, 
 which render it capable of reflecting one ray whilst it absorbs all the rest ; and 
 it is quite consistent with what we know from other sources, to believe that 
 the sense of Touch may become so refined, as to communicate a perception 
 of such differences. 
 
 526, The examples of peculiar acuteness of this sense, which we occa- 
 sionally meet with among the lower animals, are very interesting, when 
 viewed in connection with its improveability in Man. It was found by Spal- 
 lanzani, that Bats, when deprived of sight, and (as far as possible) of hearing 
 and smelling also, still flew about with equal certainty and safety, avoiding 
 every obstacle, passing through passages only just large enough to admit them, 
 and flying about places previously unknown, with the most unerring accuracy, 
 and without coming into collision with the objects near which they passed. 
 He also stretched threads in various directions across the apartment, with the 
 same result. So astonished was he at these curious facts, that he was led to 
 attribute the phenomenon to the possession of a sixth sense, unknown to Man. 
 Cuvier was the first to appreciate the real value of these experiments, as afford- 
 ing a proof of the existence of the most exquisite tactile sensibility, over the whole 
 surface of the flying membrane ; the naked surface and delicate structure of 
 which, appear well adapted to constitute the seat of so important a function. 
 From this view, therefore, it would appear that it is by means of the pulsation of 
 the wings on the air, that the propinquity of solid bodies is perceived, through 
 the manner in which the air reacts on their surface. It is curious that the 
 instance which (so far as we at present know) is most analogous to this, 
 should be met with among the inhabitants of the deep. It is a fact well 
 
SENSE OF TASTE. 
 
 399 
 
 known to Whale-fishers, especially to those who pursue the Spermaceti 
 Whale, that these animals have the power of communicating with each other 
 at great distances. It has often been observed, for example, that when a 
 straggler is attacked, at the distance of several miles from a shoal, a number 
 of its fellows bear down to its assistance, in an almost incredibly short space 
 of time. It can scarcely be doubted, then, that the communication must be 
 made through the medium of the vibrations of the water, excited by the 
 struggles of the animal, or perhaps by some peculiar movements especially 
 designed for this purpose, and propagated through the fluid to the large cuta- 
 neous surface of the distant Whales ; and this idea is fully confirmed by 
 the fact, that the nerves which proceed to the skin, pass through the inner 
 layers of blubber with scarcely any subdivision, but spread out into a net- 
 work of extreme minuteness, as soon as they arrive at the surface. 
 
 3. Sense of Taste. 
 
 527. That this sense may be really considered as a peculiar modification 
 of that of Touch, appears from several considerations. In the first place, the 
 actual contact of the object of sense, with the organ through which the im- 
 pression is received, is here necessary ; and this is the case in regard to no 
 other sense. Moreover the intimate 
 structure of the organ is nearly the 
 same in both instances. Again, it ap- 
 pears from the considerations formerly 
 alluded to ( 407), that there is no 
 special nerve of taste ; the gustative 
 impressions made upon the front of 
 the tongue, being conveyed by the 
 lingual branch of the fifth pair ; whilst 
 those made upon the back of the organ, 
 are conveyed by the glosso-pharyngeal. 
 The first of these nerves also ministers 
 to ordinary tactile sensibility ; the se- 
 cond appears to convey the impres- 
 sions which produce nausea. The 
 papillae of the Tongue are essentially 
 the same in structure with those of 
 the Skin ; but many of them are of a 
 peculiarly complex nature. 
 
 a. The characters of the papillae of the 
 tongue have recently undergone a very careful 
 examination by Messrs. Todd and Bowman 
 (Physiological Anatomy, Chap. xv.). They 
 may be divided, in the first place, into the 
 simple and the compound; the former of which 
 had previously escaped observation, through 
 not forming any apparent projection. The 
 Simple papillae are scattered in the intervals of 
 compound, over the general surface of the 
 tongue; and they occupy much of the surface 
 behind the circumvallate variety, where no 
 compound papillas exist. They are com- Tongue, seen on its upper surface : a. One of 
 
 pletely buried and concealed beneath .the the circumvallate papillce. b. One of the fungi- 
 continuous sheet of epithelium, and can only form papillae. Numbers of the conical papillae 
 be detected, when this membrane has been are seen about d, and elsewhere, e. Glottis, epi- 
 removed by maceration; they are then found glottis, and glosso-epiglottidean folds of mucous 
 
 membrane. From Scemmering.] 
 
400 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 to have the general characters of the cutaneous papillae, but nerve-tubes have not yet been 
 detected in them. 
 
 [Fig. 164. 
 
 A 
 
 Simple papillae near the base of the tongue: A. a, concealed under the epithelium'; 6, uncovered by 
 it. Magnified 10 diameters. B. a. Arterial twig, supplying their capillary loops, v. Vein. The vessels 
 are all contained within the line b, b, of basement membrane, c, c. Deeper epithelial particles resting 
 on the basement membrane, d. Scaly epithelium on the surface. The granular interior of the papillee 
 is represented at e. c. Papillae in which the basement membrane is not visible; and the deep layer of 
 epithelium seems to rest on the capillary loop. Magnified 200 diam.] 
 
 [Fig. 165. 
 
 Vertical section of one of the circumvallate 
 papillae : a. Central part. b, b. Border, c, e. 
 Fissure between centre and border. The se- 
 condary papillae are seen covered by the epi- 
 thelium. Similar papillae are seen, d, d, on the 
 membrane beyond. Magn. 8 diam.] 
 
 A. Compound papillae on the side of the foramen caecum, injected: a, a. Arterial twigs, v, v. Veins. 
 The capillary loops indicate the simple papillae ; in one of which, &, the injected matter has been extra- 
 vasated within the basement membrane of the papillae, the outline of which is thus distinguished, c. 
 Capillary plexus, where no papillae exist, e, e. External surface of the epithelium of the papilla. 
 Magn. 15 diam. 
 
 B. One of the simple papillae of A : a, v, v. Arterial and venous sides of the capillary loops. 6, 6. 
 Basement membrane, d. Deeper epithelial particles resting on the basement membrane, s. Scaly epi- 
 thelium on the surface. Magnified 300 diameters.] 
 
SENSE OF TASTE. 
 
 401 
 
 Fig. 167. 
 
 b. The Compound papillae are visible to the naked eye; and have been classified, accord- 
 ing to their shape, into the rircumvallate, the fungiform, and the filiform. The Circumval- 
 late or calyci/brm papillae are eight or ten in number, and are situated in a V-shaped line 
 at the base of the tongue. Each consists of a central flattened circular projection of the 
 mucous membrane, surrounded by a tumid ring of about 
 the same elevation, from which it is separated by a narrow 
 circular fissure. The surface of both centre and border 
 is smooth, and invested by scaly epithelium, which con- 
 ceals a multitude of simple papillae. The Fungiform pa- 
 pillse are scattered singly over the tongue, chiefly upon its 
 sides and tip. They project considerably from the surface, 
 and are usually narrower at the base than at their summit. 
 They contain a complex capillary plexus, the terminal 
 loops of which enter the numerous simple papillae that 
 clothe the surface of the fungiform body. They contain 
 nerve-tubes, in which a looped arrangement can be traced ; 
 and the epithelium which covers them is so thin, as to allow 
 the red colour of the blood to be seen through it. In this 
 manner they are readily distinguished from the filiform pa- 
 pillse, among which they lie. The Filiform papillae, like the preceding, contain a plexus of 
 
 [Fig. 168. 
 
 Capillary net- work of fungiform 
 papilla of the tongue. 
 
 
 A. Fungiform papilla, showing the secondary papillae on its surface, and at a its epithelium covering 
 them over. Magnified 35 diameters. 
 
 B. Another, with the capillary loops of its simple papilla? injected, a. Artery, v. Vein. The groove 
 around the base of some of the fungiform papillae is here represented, as well as the capillary loops, c, c, 
 of some neighbouring simple papilla?. Magnified 18 diameters.] 
 
 capillaries, and a bundle of nerve-fibres, both terminating in loops, which enter the simple 
 papillae that clothe the surface of the compound body; but instead of being covered with 
 a thin scaly epithelium, they are furnished with bundles of long pointed processes, some of 
 which approach hairs in their stiffness and structure. These are immersed in the mucus of 
 the mouth, and may be moved in any direction, though they are generally inclined back- 
 wards. 
 
 [Fig. 169. 
 
 Various forms of the conical compound papillae deprived of their epithelium : a, &, and especially c, 
 are the best marked, and were provided with the stiflfest and longest epithelium; their simple papillae 
 are more acuminated, d> approaches the fungiform variety : e.f, come near the simple papillae. Mag- 
 nified 20 diameters.] 
 
 34* 
 
402 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 c. The Simple papillae which occur in an isolated manner, with those which are aggre- 
 gated in the Circumvallate and Fungiform bodies, doubtless minister to the sense of Taste; 
 but there seems much reason to coincide in the opinion of Messrs. Todd and Bowman, with 
 regard to the different office of the Filiform papillae. "The comparative thickness of their 
 
 [Fig. 170. 
 
 A. Vertical section near the middle of the dorsal surface of the tongue : a, a. Fungiform papillse. b, 
 Filiform papillae, with their hair-like processes, c. Similar ones deprived of their epithelium. Magni- 
 fied 2 diameters. 
 
 B. Filiform compound papillae : a. Artery, v. Vein. c. Capillary loops of the secondary papillae. 
 b. Line of basement membrane, d. Secondary papillae, deprived of e, e, the epithelium, f. Hair-like 
 processes of epithelium capping the simple papillae. Magnified 25 diameters, g. Separated nucleated 
 particles of epithelium, magnified 300 diameters. 
 
 1, 2. Hairs found on the surface of the tongue. 3, 4, 5. Ends of hair-like epithelial processes, showing 
 varieties in the imbricated arrangement of the particles, but in all a coalescence of the particles towards 
 the point. 5, encloses a soft hair. Magnified 160 diameters.] 
 
 protective covering, the stiffness and brush-like arrangement of their filamentary productions, 
 their greater development in that portion of the dorsum of the tongue which is chiefly em- 
 ployed in the movements Of mastication, all evince the subservience of these papilla? to the 
 latter function, rather than to that of taste ; and it is evident that their isolation and partial 
 mobility on one another, must render the delicate touch with which they are endowed, more 
 available in directing the muscular actions of the organ. The almost manual dexterity of the 
 organ, in dealing with minute particles of food, is probably provided for, as far as sensibility 
 conduces to it, in the structure and arrangement of these papillae." It may be added, that 
 the filiform papillae of Man seem to be the rudimentary forms of those horny epithelial pro- 
 cesses, which acquire so great a development in the tongues of the Carnivora, and which are 
 of such importance in the abrasion of their food. 
 
SENSE OF TASTE. 
 [Fig. 171. 
 
 403 
 
 
 A. Secondary papilla of the conical class, treated with acetic acid : a. Its basement membrane. 6. 
 Its nerve-tube forming a loop. c. Its curly elastic tissue. The epithelium in this instance is not abund- 
 ant ; but the vertical arrangement of its particles over the apex of the papilla is well seen, d, and illus- 
 trates the mode of formation of the hair-like processes described in the text. Mag. 160 diam. 
 
 B. A similar papilla, deprived of its epithelium : a. Basement membrane, b. Tubular fibre, probably 
 forming a loop, but its arch not clearly seen, c, c. Elastic fibrous tissue at its base and in its interior. 
 Magnified 320 diameters. 
 
 c. Nerves of a compound papilla near the point of the tongue, in which their loop-like arrangement is 
 distinctly seen. Magnified 160 diameters.] 
 
 528. As a general rule, it is a necessary condition of the sense of Taste, 
 that the object should either be in a state of solution, or should be soluble in 
 the moisture covering the tongue ; if this be not the case, or if the tongue be 
 dry, a simple feeling of contact is all that is produced. As in the case of 
 touch, the idea of the character of the sapid body is very imperfect, unless it 
 is made to move over the gustative surface ; and thus the taste is very much 
 heightened, by the compression and friction of the substance between the 
 tongue and the palate. From all these circumstances it appears indisputable, 
 that a very strong analogy exists between Taste and Touch ; indeed it may 
 be questioned, whether they are not in reality more closely allied, than is the 
 sense of Temperature with that of Resistance. 
 
 529. Although the Tongue seems to be the chief seat of Gustative sensi- 
 bility, yet this is also possessed, though in a less degree, by the palate. But 
 it is to be remarked that the sensations produced by most sapid substances 
 are of a complex kind ; and are in great part due to the organ of Smell. Of 
 this any one may convince himself, by closing the nostrils, and inspiring and 
 expiring through the mouth only, when holding in the mouth, or even rub- 
 bing between the tongue and the palate, some sapid substance ; of which the 
 taste is then scarcely recognized, although it is immediately perceived, when 
 its effluvia.are drawn into the nose. It is well known too, that, when the 
 
404 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 sensibility of the Schneiderian membrane is blunted by inflammation (as in 
 an ordinary cold in the head), the power of distinguishing flavours is very 
 much diminished. In fact, some Physiologists are of opinion that all our 
 knowledge of the flavor of sapid substances is received through the Smell ; 
 and this is not improbably true : but it is to be remembered, that, besides 
 flavor, a sapid body may excite various other sensations, as those of irritation 
 and pungency ; and of these, it seems to be the true function of the sensory 
 surface of the mouth, to take cognizance. Such sensations are evidently not 
 far removed from those of ordinary touch ; and correspond with those which 
 may be excited in the nostrils, through the medium of the Fifth pair. Taken 
 in its ordinary compound acceptation, the sense of Taste has for its object to 
 direct us in the choice of food, and to excite the flow of the mucus and saliva, 
 which are destined to aid in the preparation of the food for Digestion. Among 
 the lower Animals, the instinctive perceptions connected with this sense are 
 much more remarkable than our. own; thus an omnivorous Monkey will 
 seldom touch fruits of a poisonous character, although their taste may be 
 agreeable ; and animals, whose diet is restricted to some one kind of food, 
 will decidedly reject all others. As a general rule, it may be stated, that 
 substances of which the taste is agreeable to us, are useful in our nutrition ; 
 and vice versa : but there are many signal exceptions to this. 
 
 530. Like other senses, that of Taste is capable of being rendered more 
 acute by education ; and this on the principles already laid down in regard to 
 touch. The experienced wine-taster can distinguish differences in age, purity, 
 place of growth, &c., between liquors that to ordinary judgments are alike ; 
 and the epicure can give an exact determination of the spices that are com- 
 bined in a particular sauce, or of the manner in which the animal, on whose 
 flesh he is feeding, was killed. As in the case of other senses, moreover, 
 impressions made upon the sensory surface remain there for a certain period : 
 and this period is for the most part longer than that which is required for 
 the departure of the impressions made upon the eye, the ear, or the organ of 
 smell. Every one knows how long the taste of some powerful substances 
 remains in the mouth ; and even of those which make less decided impres- 
 sions, the sensation remains to such a degree that it is difficult to compare 
 them at short intervals. Hence if a person be blindfolded, and be made to 
 taste substances of distinct, but not widely different flavours (such as various 
 kinds of wine or of spirituous liquors), one after another in rapid succession, 
 he soon loses the power of discriminating between them. In the same man- 
 ner, the difficulty of administering very disagreeable medicines may be some- 
 times got over, by either previously giving a powerful aromatic, or by com- 
 bining the aromatic with the medicine ; its strong impression in both cases 
 preventing the unpleasant taste from exciting nausea. 
 
 4. Sense of Smell. 
 
 531. Of the nature of Odorous emanations, the Natural Philosopher is so 
 completely ignorant, that the Physiologist cannot be expected to give a defi- 
 nite account of the mode, in which they produce sensory impressions. Al- 
 though it may be surmised that they consist of particles of extreme minuteness, 
 dissolved as it were in the air, and although this idea seems to derive confir- 
 mation from the fact that most odorous substances are volatile, and vice versa, 
 yet the most delicate experiments have failed to discover any diminution in 
 weight, in certain substances (as musk) that have been impregnating with their 
 effluvia a large quantity of air for several years ; and there are some volatile 
 fluids, such as water, which are entirely inodorous. The true Olfactory 
 nerves pass down from the Olfactory Ganglion ( 422) in the fo.rm of very 
 
SENSE OF SMELL. 405 
 
 numerous minute threads, which form a plexus upon the surface of the 
 Schneiderian or Pituitary membrane. Nothing satisfactory is known in re- 
 gard to their ultimate arrangement ; but it is probable that they form loops, 
 
 Fig. 172. 
 
 The Olfactory nerve, with its distribution on the septum nasi. The nares have been divided by a longi- 
 tudinal section made immediately to the left of the septum, the right nares being preserved entire. 1. 
 The frontal sinus. 2. The nasal bone. 3. The crista galli process of the ethmoid bone. 4. The sphe- 
 noidal sinus of the left side. 5. The sella turcica. 6. The basilar process of the sphenoid and occipital 
 bones. 7. The posterior opening of the right nares. 8. The opening of the Eustachian tube in the upper 
 part of the pharynx. 9. The soft palate, divided through its middle. 10. Cut surface of the hard palate, 
 a. The olfactory peduncle, b. Its three roots of origin, c. Olfactory ganglion, from which the filaments 
 proceed that spread out in the substance of the pituitary membrane, d. The nasal nerve, a branch of 
 the ophthalmic nerve, descending into the left nares from the anterior foramen of the cribriform plate, and 
 dividing into its external and internal branch, e. The naso-palatine nerve, a branch of the spheno-pala- 
 tine ganglion distributing twigs to the mucous membrane of the septum nasi in its course to (/) the ante- 
 rior palatine foramen, where it forms a smali gangliform swelling (Cloquet's ganglion) by its union with 
 its fellow of the opposite side. g. Branches of the naso-palatine nerve to the palate. A. Posterior pala- 
 tine nerves, i, i. The septum nasi. 
 
 similar to those of the cutaneous nerves. It would appear that every part of 
 the Schneiderian membrane is not equally endowed with the faculty of dis- 
 tinguishing odours, which is a very different power from that of becoming 
 sensible of irritation from them. The Olfactory nerves cannot be traced to 
 the membrane covering the middle and inferior spongy bones, or to that which 
 lines the different sinuses, these parts of the surface being supplied by the 
 Fifth pair only ; and it is a matter of common experience, that we cannot dis- 
 tinguish faint odours, unless, by a peculiar inspiratory effort, we draw the air 
 charged with them to the upper part of the nose. In animals living in the 
 air, it is a necessary condition of the exercise of the sense of Smell, that the 
 odorous matter should be transmitted by a respiratory current through the 
 nostrils; and that the membrane lining these should be in a moist state. 
 Hence, by breathing through the mouth, we may avoid being affected by 
 odours even of the strongest and most disagreeable kind; and in the first stage 
 of a catarrh, when the ordinary mucous secretion is suspended, the sense of 
 smell is blunted from this cause, as it afterwards is from the excess in the 
 quantity of the fluid, which prevents the odoriferous effluvia from coming 
 into immediate relation with the sensory extremities of the nerves. Hence 
 we may easily comprehend, that section of the Fifth pair, which exercises a 
 
406 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 considerable control over the secretion's, will greatly diminish the acuteness of 
 the smell ; and it will have the further effect of preventing the reception of 
 any impressions of irritation from acrid vapours, which are entirely different 
 in their character from true odorous impressions, and which are not trans- 
 mitted through the Olfactory nerve ( 441). The nasal passages may indeed 
 be considered as having, in the air-breathing Vertebrata, two distinct offices ; 
 they constitute the organ of smell, through the distribution of the olfactory 
 nerve upon a part of their surface ; but they also constitute the portals of the 
 respiratory organs, having for their office to take cognizance of the aeriform 
 matter which enters them, and to give warning of that which would be inju- 
 rious ; this latter function is performed by the Fifth pair, as by the Par Vagum 
 in the glottis. It is through this nerve, that the act of sneezing is excitable : 
 the evident purpose of which, is the ejection of a strong blast of air through 
 the nasal passages, in such a manner as to drive out any offending matter 
 they may contain. 
 
 532. The importance of the sense of Smell among many of the lower 
 Animals, in guiding them to their food, or in giving them warning of danger 
 and also in exciting the sexual feelings, is well known. To Man its utility 
 is very subordinate under ordinary circumstances ; but it may be greatly in- 
 creased when other senses are deficient. Thus, in the well-known case of 
 James Mitchell, who was deaf, blind and dumb, from his birth, it was the 
 principal means of distinguishing persons, and enabled him at once to per- 
 ceive the entrance of a stranger. It is recorded that a blind gentleman, who 
 had an antipathy to cats, was possessed of a sensibility so acute in this re- 
 spect, that he perceived the proximity of one that had been accidentally shut 
 up in a closet adjoining his room. Among Savage tribes, whose senses are 
 more cultivated than those of civilized nations, more direct use being made of 
 the powers of observation, the scent is almost as acute as in the lower Mam- 
 malia; it is asserted by Humboldt, that the Peruvian Indians in the middle of 
 the night can thus distinguish the different races, whether European, Ameri- 
 can-Indian, or Negro.* The agreeable or disagreeable character assigned to 
 particular odours, is by no means constant amongst different individuals. 
 Many of the lower Animals pass their whole lives in the midst of odours, 
 which are to Man (in his civilized condition at least) in the highest degree 
 revolting ; and will even refuse to touch food, until it is far advanced in pu- 
 tridity. It more frequently happens in regard to odours and savours, than 
 with respect to other sensory impressions, that habit makes that agreeable, 
 and even strongly relished, which was at first avoided; the taste of the epi- 
 cure for game that has acquired ihefumet, for olives, for assafoetida, &c., 
 are instances of this. As to the length of time, during which impressions 
 made upon the organ of smell remain upon it, no certain knowledge can .be 
 obtained. It is difficult to say that the effluvia have been Completely removed 
 from the nasal passages ; since it is not improbable that the odorous particles 
 (supposing such to exist) are absorbed or dissolved by the mucous secretion ; 
 it is probably in this manner that we may account for the fact, well known to 
 every medical man, that the cadaverous odour is frequently experienced for 
 days after a post-mortem examination.t 
 
 * The author has been assured by a competent witness, that a lad in the state of Som- 
 nambulism, had his sense of .smell so remarkably heightened, as to be able to assign (with- 
 out the least hesitation) a glove placed in his hand, to its right owner, in the midst of 
 about thirty persons, the boy himself being blindfolded. 
 
 f This may partly be attributed also to the effluvia adhering to the dress. It has been 
 remarked that dark cloths retain these more strongly than light. 
 
SENSE OF VISION. 407 
 
 5. Sense of Vision. 
 
 533. The objects of this sense are bodies, which are either in themselves 
 luminous, or which become so by reflecting the light that proceeds from others. 
 Whether their light is transmitted by the actual emission of rays, or by the 
 propagation of undulations analogous to those of sound, is a j^uestion at pre- 
 sent keenly debated amongst Natural Philosophers ; but it is of little conse- 
 quence to the Physiologist, which is the true solution; since it is only with 
 the laws, which actually regulate the transmission of light, that he is concerned. 
 These laws it may be desirable here briefly to recapitulate. 
 
 534. Every point of a luminous body sends off a number of rays, which 
 diverge in every direction, so as to form a cone, of which the luminous point 
 is the apex. So long as these rays pass through a medium of the same dens- 
 ity, they proceed in straight .lines ; but, if they enter a medium of different 
 density, they are refracted or bent, towards the perpendicular to the surface 
 at the point at which they enter, if they pass from a rarer into a denser me- 
 dium, and from the perpendicular, when they pass from a denser medium 
 into a rarer. It is easily shown to be a result -of this law, that, when parallel 
 rays passing through air fall upon a convex surface of glass, they will be 
 made to converge ; so as to meet at the opposite extremity of the diameter of 
 the circle, of which the curve forms part. If, instead of continuing in the 
 glass, they pass out again, through a second convex surface, of which the di- 
 rection is the reverse of the first, they will be made to converge still more, so 
 as to meet in the centre of curvature. Rays which are not parallel, but which 
 are diverging from a focus, are likewise made to converge to a point or focus ; 
 but this point will be more distant from the lens, in proportion as the object 
 is nearer to it, and the angle of divergence consequently greater. The rays 
 diverging from the several points of a luminous object, are thus brought to a 
 corresponding focus ; and the places of all these foci hold exactly the same re- 
 lation to each other, with that of the points from which the rays diverged; so 
 that a perfect image of the object is formed upon a screen held in the focus 
 of the lens. This image, however, will be inverted; and its size, in pro- 
 portion to that of the object, will depend upon their respective distances from 
 the lens. If their distances be the same, their size will also be the same ; if 
 the object be distant, and the image near, the latter will be much the smaller ; 
 and vice versa. 
 
 535. There are two circumstances, however, which interfere with the per- 
 fection of an image thus formed by a convex lens. The one is, that, if the 
 lens constitute a large part of the sphere from which it is taken, the rays 
 which fall near its margin are not brought to a focus at the same point with 
 those which pass through its centre ; but at a point nearer the lens. This 
 difference, which must obviously interfere greatly with the distinctness of the 
 image, is termed Spherical Aberration ; it maybe corrected by the combi- 
 nation of two or more lenses, of which the curvatures are calculated to ba- 
 lance one another, in such a manner that all the rays shall be brought to the 
 same focus ; or by diminishing the aperture of the lens by means of a stop 
 or diaphragm, in such a manner that only the central part of it shall be used. 
 The latter of these methods is the one employed, where the diminution in 
 the amount of light transmitted is not attended with inconvenience. The 
 nearer the object is to the lens (and the greater, therefore, the angle of diverg- 
 ence of its rays), the greater will be the spherical aberration, and the more 
 must the aperture of the diaphragm be contracted in order to counteract it. 
 The other circumstance that interferes with the distinctness of the image, is 
 the unequal refrangibility of the differently-coloured rays, which together 
 
408 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 make up white or colourless light ; the violet being more bent from their 
 course than the blue, the blue more than the yellow, and the yellow more 
 than the red ; the consequence of which will be, that the violet rays are 
 brought to a focus much nearer to the lens than the blue, and the blue nearer 
 than the red. If a screen be held to receive the image, in the focus of any 
 of the rays, the others will make themselves apparent as fringes round its 
 margin. This difference is termed Chromatic Aberration. It is corrected in 
 practice, by combining together lenses of different substances, of which the 
 dispersive power (that is, the power of separating the coloured rays) differs 
 considerably. This is the case with flint and crown glass, for instance, the 
 dispersive power of the former being much greater than that of the latter, 
 whilst its refractive power is nearly the same: so that, if a convex lens of 
 crown glass be united with a concave of flint whose curvature is much less, 
 the dispersion of the rays effected by the former will be counteracted by the 
 latter, which diminishes in part only its refractive power. 
 
 536. The Eye may be regarded as an optical instrument of great perfec- 
 tion, adapted to produce, on the expanded surface of the optic nerve, a com- 
 plete image or picture of luminous objects brought before it; in which the 
 forms, colours, lights and shades, &c., of the object are all accurately repre- 
 sented. By the different refractive powers of the transparent media, through 
 which the rays of light pass, and by the curvatures given to their respective 
 surfaces, both the Spherical and Chromatic aberrations are corrected in a de- 
 gree sufficient for all practical purposes; so that, in a well-formed eye, the 
 picture is quite free from haziness, and from false colours. The power by 
 which it adapts itself to variations in the distance of the object, so as to 
 form a distinct image of it, whether it be six inches, six yards, or six miles 
 off, is extremely remarkable, and cannot be regarded as hitherto completely 
 explained. It is obvious that, if we fix upon any distance as that for which 
 the eye is naturally adjusted (say 12 or 14 inches, the distance at which we 
 
 (Fig. 173. 
 
 A longitudinal section of the globe of the Eye ; 1, the sclerotic, thicker behind than in front ; 2, the 
 cornea, received within the anterior margin of the sclerotic, and connected with it by means of a be- 
 veled edge ; 3, the choroid, connected anteriorly with (4) the ciliary ligament, and (5) the ciliary pro- 
 cesses ; 6, the iris ; 7, the pupil ; 8, the third layer of the eye, the retina, terminating anteriorly by an 
 abrupt border at the commencement of the ciliary processes ; 9, the canal of Petit, which encircles the 
 lens (12) ; the thin layer in front of this canal is the zonula ciliaris, a prolongation of the vascular layer 
 of the retina to the lens. 10, the anterior chamber of the eye, containing the aqueous humour; the 
 lining membrane by which the humour is secreted is represented in the diagram ; 11, the posterior; 12, 
 the lens more convex behind than before, and enclosed in its proper capsule ; 13, the vitreous humour 
 enclosed in the hyaloid membrane, and in cells formed in its interior by that membrane ; 14, a tubular 
 sheath of the hyaloid membrane, which serves for the passage of the artery of the capsule of the lens ; 
 15, the neurilerama of the optic nerve ; 16, the arteria centralis retinae, imbedded in its centre.] 
 
SENSE OF VISION. 
 [Fig. 174. 
 
 409 
 
 A Horizontal Section of the Eyeball ; 1, sclerotic coat ; 2, sheath of the optic nerve, or canal of Pon- 
 tana; 3, circular venous sinus of the iris; 4, proper substance of the cornea; 5, arachnoidea oculi ; 6, 
 membrane of the anterior chamber of the aqueous humour ; of the two dotted lines one points to the 
 
 35 
 
410 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 supposed membrane of Descemet, the other to the supposed continuation of that membrane over the 
 anterior surface of the iris; 7, choroid coat; 8, annulus albidus; 9, ciliary ligament ; 10, 10', ciliary body, 
 consisting of (10') a pars non-fimbriata, and (10) a pars fimbriata formed by the ciliary process; 11, ora 
 serrata of the ciliary body ; 12, iris ; 13, pupil ; 14, membrane of the pigment ; 15, delicate membrane lining 
 the posterior chamber of the aqueous humour ; 16, membrane of Jacob ; 17, the optic nerve surrounded 
 by its neurilemma; 17', the fibres of the optic nerve consisting of fasciculi of primitivet ubules; 18, cen- 
 tral artery of the retina; 19, papilla cornica of the optic nerve ; 20, retina; the situation of its vascular 
 layer is indicated by a dotted line ; 21, central transparent point of the retina; 22, vitreous humour ; 23, 
 the hyaloid membrane ; 24, canalis hyaloideus ; 25, zonula ciliaris; in the plate, none of its fimbriated 
 part is seen, being concealed by the ciliary processes; 26, canal of Petit; 27, crystalline lens; 28, an- 
 terior wall of the capsule of the lens ; 29, posterior wall of the capsule of the lens; 30, posterior chamber 
 of the aqueous humour ; 31, anterior chamber of the aqueous humour.] 
 
 ordinarily read), the rays proceeding from an object, placed nearer to the 
 eye than this, would not be brought to a focus upon the retina, but would 
 converge towards a point behind it ; whilst on the contrary, the rays from an 
 object at a greater distance would meet before they reached the retina, and 
 would have again diverged from each other when they impinge upon it ; so 
 that in either case, vision would be indistinct. Now two methods of adapta- 
 tion suggest themselves to the Optician. Either he may vary the distance 
 between the refracting surface and the screen on which the image is formed,, 
 in such a manner, that the latter shall always be in the focus of the converg- 
 ing rays ; or, the distance of the screen remaining the same, he may vary the 
 convexity of his lens, i such a manner as to adapt it to the distance of the object. 
 It is not improbable, that both of these methods are employed in the Eye, 
 though no distinct evidence has been obtained of the operation of either. Seve- 
 ral hypotheses have been proposed, to account for the phenomenon : it is* 
 easily proved that no one of them can alone be true ; but it cannot be readily 
 shown that any of them is entirely false : and it would not seem unlikely, 
 therefore, that all may participate, in various degrees, in the effect. The fol- 
 lowing are the principal of these. 1. An alteration in the form of the globe 
 of the eye by the action of the muscles, so that its antero-posterior diameter 
 may be increased or diminished.* 2. A change in the convexity of the cor- 
 nea. This might be very well connected with the last ; since, if the globe 
 were converted into a spheroid, of which the antero-posterior diameter would 
 be the longest, the curvature of the cornea would be increased ; whilst, if the 
 antero-posterior diameter were shortened, the curvature would be diminished. 
 
 3. Change of position of the crystalline lens, by means of the ciliary processes. 
 
 4. Change of figure of the lens itself. That one or both of the last two are 
 concerned in the effect, would appear from the fact, well known to every Oculist, 
 that, after the removal of a cataract, the power of adapting the eye to dis- 
 tances is greatly diminished. 5. Change in the aperture of the pupil ; the 
 mode in which this could assist in accommodating the eye to variations of 
 distance, is not very obvious. 
 
 537. Some curious circumstances, relative to the connection between the 
 optical adaptation of the eye to distances, and the changes in the direction of the 
 axes of the two eyes, have been pointed out by Miiller. When both eyes are 
 fixed upon an object, their axes must converge (as formerly explained, 455) 
 so as to meet in it. The nearer the object, the greater must be the degree of 
 convergence; and when the object is brought within the ordinary distance of 
 distinct vision, the convergence must very rapidly increase. Now this is 
 precisely what takes place, in regard to alterations in the focus of the eye ; for 
 little change is required, when the object is made to approach from a considera- 
 ble distance to a moderate distance; but, when it is brought near the eye, the 
 
 * The influence of the muscles in altering the form of the globe may be better compre- 
 hended, now that we know the mode in which this is kept in its place in the front of the 
 orbit, by a fascia passing behind it, and attached anteriorly to the lids. 
 
SENSE OF VISIOX. 411 
 
 focus must be considerably lengthened, or the convexity of the eye increased, 
 to cause the rays to meet on the retina: and hence it may be surmised, that 
 the same cause is acting to produce both changes. But that the convergence 
 of the axes is not itself in any way the occasion of the alteration of the focus 
 of the eye, is shown by the fact, that the adaptation is as perfect, in a person 
 who only possesses or uses one eye, as it is when both are employed ; and 
 also by the power, which is possessed by some persons, of altering the focus 
 of the eye by an effort of the will, whilst the convergence remains the same. 
 In regard to the adaptation of the eyes to varying distances, it is further to be 
 remarked, that, when an object is being viewed as near to the eye as it can be 
 distinctly seen, the pupil contracts in a considerable degree. The final cause 
 of this change, is evidently to exclude the outer rays of the cone or pencil, 
 which, from the large angle of their divergence, would fall so obliquely on the 
 convex surface of the eye, as to be much affected by the spherical aberration ; 
 and to allow the central rays only to enter the eye, so as to preserve the clear- 
 ness of the image. The channel through which it is effected is evidently the 
 same, as that by which the convergence of the eyes is produced, namely, 
 the inferior branch of the third pair of nerves; to the action of which, the 
 sensations upon the retina form the stimulus, in the same manner as they do 
 to the ordinary variation in the diameter of the pupil under the influence of 
 light. 
 
 538. The ordinary forms of defective vision, which are known under the 
 names of myopia and presbyopia, or short-sightedness and long-sightedness, 
 are entirely attributable to defects in the optical adaptation of the eye. In the 
 former, its refractive power is too great; the rays from objects at the usual 
 distance are consequently brought too soon to a focus, so as to cross one 
 another and diverge, before they fall upon the retina; whilst the eye is adapted 
 to bring to their proper focus on the retina, only those rays which were pre- 
 viously diverging at a large angle, from an object in its near proximity. Hence 
 a short-sighted person, whose shortest limit of distinct vision is not above half 
 that of a person of ordinary sight, can see minute objects more clearly; his 
 eyes having, in fact, the same magnifying power, which those of the other 
 would possess, if aided by a convex glass, that would enable him to see the 
 object distinctly at the shorter distance. But as the myopic structure of the 
 eye incapacitates its possessor from seeing objects clearly, at even a moderate 
 distance, it is desirable to apply a correction; and this is done, by simply inter- 
 posing a concave lens, of which the curvature is properly adapted to compen- 
 sate for the excess of that of the organ itself, between the object and the eye. 
 On the other hand, in the presbyopic eye, the curvature and refractive power 
 are not sufficient to bring to a focus on the retina, rays which were previously 
 divergent in a considerable or even in a moderate degree ; and indistinct vision 
 in regard to all near objects is, therefore, a necessary consequence, whilst 
 distant objects are well seen. This defect is remedied by the use of convex 
 lenses, which make up for the deficiency of the curvature. We commonly 
 meet with myopia in young persons, and with presbyopia in old; but this is 
 by no means the invariable rule; for even aged persons are sometimes short- 
 sighted; and long-sightedness is occasionally met with amongst the young. 
 In choosing spectacles, for the purpose of correcting the errors of the eye, it 
 is of great consequence not to make an over-compensation; for this has a 
 tendency to increase the defect, besides occasioning great fatigue in the employ- 
 ment of the sight. It may be easily found, when a glass of the right power 
 has been selected, by inquiring of the individual, whether it alters the apparent 
 size of the objects, or only renders them distinct. If it alter the size (in- 
 creasing it if it be a convex lens, and diminishing it if it be a concave), its 
 curvature is too great ; whilst if it do not disperse the haze, it is not sufficiently 
 
412 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 powerful. In general it is better to employ a glass which somewhat under- 
 compensates the eye, than one which is of a curvature at all too high ; since, 
 with the advance of years in elderly persons, a progressive increase in power 
 is required ; and, as young persons grow up to adult age, they should endeavour 
 to dispense with the aid of spectacles. 
 
 539. Many other interesting inquiries, respecting the action of the eye as 
 an optical instrument, suggest themselves to the physical philosopher; but the 
 foregoing are the chief in which the Physiologist is concerned ; and we shall 
 now proceed, therefore, to consider the share, which the Retina and Optic 
 
 Fig. 175. Fig. 176. 
 
 Part of the Retina of a Frog, seen 
 from the outer surface. Magnified 300 
 times. 
 
 Distribution of Capillaries in Vascu- 
 lar layer of Retina. 
 
 [Fig. 177. 
 
 Nerve perform in the phenomena of vision. The optic nerve, at its entrance 
 into the eye, divides itself into numerous small fasciculi of ultimate fibrils; 
 
 and these appear to spread themselves out, 
 and to inosculate with each other by an ex- 
 change of fibrils, so as to form a net-like 
 plexus. There is considerable difficulty, 
 however, in the precise determination of the 
 course of the nerve-fibres in the Retina; on 
 account of their minute size, and the absence 
 of their distinctive characters. According to 
 Mr. Bowman, the tubular membrane and the 
 white substance of Schwann are deficient; 
 and only the central part of the nerve-fibre, or 
 axis-cylinder, is continued into this expansion. 
 The plexus of nerve-fibres comes into relation 
 with a plexus of capillary vessels, very minute- 
 ly distributed ; and also with a layer of cells, 
 so closely resembling those of the cortical sub- 
 stance of the brain, that there can be no rea- 
 sonable doubt of their correspondence in func- 
 tion. This layer of cells, constitutes the in- 
 ternal layer of the true retina. We have here, 
 then, all "the' elements of an apparatus for the 
 origination of changes in the nervous trunks, 
 in a fully displayed form ; and it can scarcely 
 be doubted that the essential parts of the same 
 structures exist in the papillae of the cutaneous 
 and other sensory surfaces. The true Retina 
 is covered externally by a very peculiar in- 
 vestment, the Membrane of Jacob, which 
 
 A portion of the Retina of an Infant, 
 with its vessels injected and magnified 
 25 diameters. An outline of the natural 
 size of this piece is seen just below the 
 main cut.] 
 
SENSE OF VISION. 
 
 413 
 
 separates it from the pigmentary layer. This seems to be composed of cells 
 having a cylindrical form. These are sometimes arranged vertically to the 
 
 [Fig. 178. 
 
 Vertical section of the Human Retina and Hyaloid Membrane, h. Hyaloid membrane, h'. Nuclei 
 on its inner surface, c. Layer of transparent cells, connecting the hyaloid and retina, c'. Separate 
 cell enlarged by imbibition of water, n. Gray nervous layer, with its capillaries. 1. Its fibrous lamina. 
 2. Its vesicular lamina. 1'. Shred of fibrous lamina detached. 2'. Vesicle and nucleus detached, g. Granu- 
 lar layer. 3. Light lamina frequently seen. g'. Detached nucleated particle of the granular layer. 
 m. Jacob's membrane, m'. Appearance of its particles, when detached, m". Its outer surface. Mag- 
 nified 320 diameters.] 
 
 [Fig. 179. 
 
 surface of the membrane, so that their extremities only are seen ; whilst in 
 other instances they are found to present an 
 imbricated arrangement, lying over each other 
 obliquely, in which case they are of conside- 
 rable length (Fig. 175). They are remarka- 
 ble for the rapidity with which they undergo 
 alterations after death ; and especially for the 
 changes in their form, which are produced 
 by the action of water. 
 
 540. The following statements on the 
 Limits of Human Vision, in regard to the 
 possible minuteness of the objects of which 
 it can take cognizance, comprehend the re- 
 sult of numerous inquiries made by Ehren- 
 berg, with the view of calculating the ulti- 
 mate power of the Microscope.* In opposi- 
 tion to the generally-received opinion, Ehren- 
 berg arrived at the conclusion that, in regard 
 to the extreme limits of vision, there is little difference amongst persons of 
 ordinarily good sight, whatever may be the focal distance of their eyes. The 
 smallest square magnitude usually visible to the naked eye, either of white 
 particles on a black ground, or of black upon a white or light-coloured ground, 
 is about the l-405th of an inch. It is possible, by the greatest condensation 
 of light, and excitement of the attention, to recognize magnitudes between the 
 1 -405th and l-540th of an inch ; but without sharpness or certainty. Bodies 
 which are smaller than these, cannot be discerned with the naked eye when 
 single ; but may be seen when placed in a row. Particles which powerfully 
 reflect light, however, may be distinctly seen, when not half the size of the 
 
 Outer surface of the Retina, showing 
 the membrane of Jacob, partially detach- 
 ed. After Jacob.] 
 
 Taylor's Scientific Memoirs. 
 35* 
 
 Vol. i. p. 576. 
 
414 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 least of the foregoing ; thus, gold dust* of the fineness of 1-1 125th of an inch, 
 may be discerned with the naked eye in common daylight. The delicacy of 
 vision is far greater for lines than for single articles ; opaque threads of 1 -4900th 
 of an inch in diameter may be discerned with the naked eye, when held to- 
 wards the light. Such threads are about half the diameter of the Silk-worm's 
 fibre. The degree in which the attention is directed to them, has a great 
 influence on the readiness with which very minute objects can be perceived; 
 and Ehrenberg remarks that there is a much greater difference amongst indi- 
 viduals in this respect, than there is in regard to the absolute limits of vision. 
 Many persons can distinctly see such objects, when their situation is exactly 
 pointed out to them, who cannot otherwise distinguish them ; and the same 
 is the case with persons of acuter perception, with respect to objects at dis- 
 tances greater than those, at which they can see most clearly. " I myself," 
 says Ehrenberg, " cannot see l-2700th of an inch, black on white, at twelve 
 inches distance ; but having found it at from four to five inches distance, I 
 can remove it to twelve inches, and still see the object plainly." Similar 
 phenomena are well known in regard to a balloon, or a faint star, in a clear 
 sky; or a ship in the horizon: we easily see them after they have been 
 pointed out to us; but the faculty of rapidly descrying depends on the habit 
 of using the eyes in search of such objects ( 519). 
 
 541. The sense of Vision depends, in the first place, on the transference 
 to our minds of the picture which is formed upon the retina ; this picture puts 
 us in possession of the outlines, lights and shades, colours, and relative posi- 
 tions of the objects before us ; and all the ideas respecting the real forms, 
 distances, &c., of bodies, which we found upon these data, must be considered 
 in the light of perceptions, either instinctive or acquired. Many of these are 
 derived through the combination, in our minds, of the Visual sensations, with 
 those derived from the sense of Touch. Thus, to take a most simple illustra- 
 tion, the idea of smoothness is one essentially tactile ; and yet it constantly 
 occurs to us, on looking at a surface which reflects light in a particular man- 
 ner. But, if it were not for the association, which experience leads us to 
 form, of the connection between polish as seen by the eye, and smoothness 
 as felt by the touch, we should not be able to determine, as we now can do, 
 the existence of both these qualities from an impression communicated to us 
 through either sense singly. The general fact that, in Man, the greater part 
 of those notions of the external world by which his actions in the adult state 
 are guided, are acquired by the gradual association of the sensations commu- 
 nicated by the sight and by touch, is substantiated by amply-sufficient evidence. 
 This evidence is chiefly derived from observations made upon persons born 
 blind, to whom sight has been communicated by an operation, at a period of life 
 which enabled them to give an accurate description of their sensations. The 
 case recorded by Cheselden is one of the most interesting of these. The 
 youth (about 12 years of age), for some time after tolerably distinct vision had 
 been obtained, saw everythingjtfotf, as in a picture ; simply receiving the con- 
 sciousness of the impression made upon his retina ; and it was some time be- 
 fore he acquired the power of judging, by his sight, of the real forms and 
 distances of the objects around him. An amusing anecdote recorded of him, 
 shows the complete want of natural or intuitive connection which there is in 
 Man, between the ideas formed through visual and through tactile sensations. 
 He was well acquainted with a Dog and a Cat by feeling ; but could not re- 
 member their respective characters when he saw them. One day, when thus 
 puzzled, he took up the Gat in his arms, and felt her attentively, so as to as- 
 
 * Ehrenbsrg mentions that he obtained the finest particles of gold, by scraping gilt brass ; 
 by filing pure gold, he always obtained much coarser particles. 
 
SENSE OF VISION. 
 
 415 
 
 sociate the two sets of ideas ; and then, setting her down, said, " So, puss, I 
 shall know you another time." A similar instance has come under the Au- 
 thor's own knowledge ; but the subject of it was scarcely old enough to pre- 
 sent phenomena so striking. One curious circumstance was remarked of him, 
 which fully confirms (if confirmation were wanting) the view here given. 
 For some time after the sight was tolerably clear, the lad preferred finding his 
 way through his father's house, to which he had been quite accustomed when 
 blind, by touch rather than by sight, the use of the latter sense appearing to 
 perplex rather than to assist him ; but, when learning a new locality, he em- 
 ployed his sight, and evidently perceived the increase of facility which he de- 
 rived from it. 
 
 542. The question has been proposed, whether a person born blind, who 
 was able by the sense of Touch to distinguish a cube from a sphere, would, 
 on suddenly obtaining his Sight, be able to distinguish them by the latter 
 sense. This question was answered by Locke in the negative; and probably 
 with justice. It is no real objection to such a reply, that a new-born animal 
 seeks the nipple of its mother, when informed of its proximity by sight ; for 
 all that is indicated by this fact is, that the sensation excites an intuitive feel- 
 ing of desire, which gives rise to movements adapted to gratify it. Such in- 
 stinctive actions, founded upon intuitive perceptions, are, as already pointed 
 out, much more numerous in the lower Animals than in the higher, and in the 
 young of the Human species than in the adult ( 428) ; and they do not afford 
 any proof that definite notions, such as we acquire, of the forms and proper- 
 ties of external objects, are possessed by the animals which exhibit them. 
 We shall now examine, a little more in detail, into the means by which we 
 gain such notions, and the data on which they are founded. 
 
 543. The first point to be determined, is one which has been a fruitful 
 source of discussion, the cause of erect vision, the picture Upon the retina 
 being inverted. Many solutions of it have been attempted; but they are for the 
 most part rather specious than really satisfactory. That which has been of late 
 years the most in vogue, is founded upon what was styled the Law of Visible 
 Direction, which has been supported by Sir D. Brewster, and other eminent 
 Philosophers. This law affirms, that every object is seen in the direction of 
 the perpendicular to that point of the retina, on which its image is formed ; 
 or, in other words* that, as all the perpendiculars to the several points of the 
 inner surface of a sphere meet in the centre, the line of direction of any ob- 
 ject is identical with the prolonged radius of the sphere, drawn from the point 
 at which its image is made upon the retina. Upon close examination, how- 
 ever, it is found that this law cannot be optically correct ; since the lines of 
 direction cross each other at a point much anterior to the centre of the globe ; 
 as may be determined by drawing a diagram upon a large scale, and laying 
 down the course of the rays received by the eye, according to the curvatures 
 and refractive powers of its different parts. In this manner it has been deter- 
 mined by Volkraann, that the lines of direction cross each other in a point a 
 little behind the crystalline lens ; and that they will thus fall at such differ- 
 ent angles on different points of the retina, that no general law can be laid 
 down respecting them. It may be questioned, moreover, whether such a law 
 would afford any assistance in explaining the phenomenon ; since, after all, 
 it is requisite to assume an intuitive application of it, in supposing the mind 
 to derive its ideas of the relative situations of objects, from the imagined line 
 of direction. A much simpler and more direct explanation may be given. 
 We must remember that, which we have had occasion to notice in regard to all 
 the other senses, the broad line of distinction between the sensation and the 
 perception or elementary notion; and this is still more clearly shown by the 
 complete absence of any relation, but such as experience developes, between 
 
416 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 the perceptions derived through the sight, and those acquired from the touch. 
 Hence there is no more difficulty in understanding, that an inverted picture 
 upon the retina should convey to us a notion of the external world, which 
 harmonizes with that acquired through the sense of touch, than there is in 
 comprehending the formation of any of those intuitive perceptions of animals, 
 which are so much more removed from the teachings of our own experience 
 ( 490). It is justly remarked by Miiller that, " if we do see objects inverted [or 
 rather, if the picture on the retina is inverted] the only proof we can possibly 
 have of it, is that afforded by the study of the laws of Optics ; and, if everything 
 is seen reversed, the relative position of the objects remains unchanged. Hence 
 it is, also, that no discordance arises between the sensations of inverted vision 
 and those of touch, which perceives everything in its erect position ; for the 
 images of all objects, even of our own limbs, on the retina, are equally in- 
 verted, and therefore maintain the same relative position* Even the image of 
 our hand, wJien used in touch, is inverted." From what has been stated, it 
 would appear quite conceivable, that a person just endowed with sight, should 
 not at first know by his visual powers, whether a pyramid placed before his 
 eyes is the same body, and in the same position, as one with which he has 
 become acquainted by the touch ; and, if this be admitted, the inference ne- 
 cessarily follows, that the notion of erectness, which we form by the combined 
 use of our eyes and our hands, is really the product of experience in ourselves, 
 whilst it is probably innate or intuitional in the lower Animals. 
 
 544. The cause of single vision with the two eyes has, in like manner, 
 been the subject of much discussion; since the mode in which we are affected 
 by the two simultaneous impressions, is quite different from that, in which 
 we derive our knowledge of external things through the other senses. Some 
 have even asserted, that we do not really employ both eyes simultaneously, 
 but that the mind is affected by the image communicated by one only; and 
 this idea might seem to be confirmed by the fact heretofore mentioned ( 519), 
 respecting the alternate use of the two eyes, when they are looking through 
 two differently-coloured media. But it is easily disproved in other ways. 
 It will presently be shown, that all our estimates of the forms of bodies, de- 
 pend on the combination by the mind, of the images simultaneously transmit- 
 ted by the two eyes ; and our knowledge of distances is in great part obtained 
 in like manner. The condition of Single Vision has been already stated 
 ( 454) to be probably this,' that the two images of the object should be 
 formed on parts of the two retinae, which are accustomed to act in concert ; 
 and reasons were given for the belief, that habit is the chief means by which 
 this conformity is produced. There can be no doubt, however, that double 
 images are continually being conveyed to our minds ; but that, from their 
 want of force and distinctness, and from the attention being fixed on something 
 else, we do not take cognizance of them. This may be shown by a very 
 simple experiment. If two fingers be held up before the eyes, one in front 
 of the other, and vision be directed to the more distant, so that it is seen 
 singly, the nearer will appear double ; while, if the nearer one be regarded 
 more particularly, so as to appear single, the more distant will be seen double. 
 A little consideration will show, therefore, that our minds must be continually 
 affected with sensations, which cannot be united into the idea of a single 
 image ; since, whenever we direct the axes of our eyes towards any object, 
 everything else will be represented to us as double; but we do not ordinarily 
 perceive this, from our minds being fixed upon a clear and distinct image, and 
 disregarding, therefore, the vague undefined images formed by objects at a 
 different focus. Of this it is very easy to convince oneself. It is moreover 
 evident from this experiment, that double vision cannot result from want of 
 symmetry in the position of the images upon the retina, to which some have 
 
SENSE OF VISION. 417 
 
 attributed it ; for it answers equally well, if the line of the two fingers be pre- 
 cisly in front of the nose, so that the inclination of both eyes towards either 
 object is equal ; the position of the images of the second object must then be 
 at the same distance on each side from the central line of the retina, and yet 
 they are represented to the mind as double. It is, moreover, easily shown, 
 that, in the lower animals whose orbits are not directed forwards as in us, but 
 sideways in a greater or less degree, whenever an object is so situated as to 
 be seen by both eyes, the points of the two retinae on which its images are 
 formed, must be very far from possessing this symmetry. 
 
 545. Many attempts have been made to explain the phenomena of Single 
 Vision by the peculiar decussation of the Optic nerves ( 445) ; and an inte- 
 resting correspondence between the varieties in the degree of decussation, and 
 the position of the eyes, in several animals, has been pointed out by Mr. Solly 
 and Mr. Mayo. From these and other data, it has been concluded, that each 
 nerve is used in looking towards the opposite side. This is evidently true of 
 the Osseous Fishes, whose two eyes, being directed sideways, have two en- 
 tirely different spheres of vision. And it is also true of Man, if Mr. Mayo's 
 account of the distribution of the nerve be correct ; since, when we look at 
 an object held directly in front of the face, at the level of the eyes, and at the 
 nearest point for distinct vision, almost the whole of that portion of the right 
 retina, which lies to the outside of the entrance of the optic nerve, is directed 
 to the left; and the exactly different, complementary, or inner portion of the 
 left retina, which is supplied by the same nerve, is likewise directed to the 
 left. On this supposition, all the rays entering the two eyes from any one 
 point, will be brought to a focus on fibrils belonging to the nerve of the same 
 side ; though these are in Man, as in other animals whose spheres of vision 
 are nearly or partly coincident, distributed to distinct visual organs.* It is 
 obvious, however, that this or any similar explanation, must be insufficient to 
 explain the phenomenon of single vision ; since the images formed upon the 
 two retinas are necessarily different, and must be combined or harmonized by 
 an act of the mind, as will be shown in the succeeding paragraphs. 
 
 546. We shall next consider the mode, in which our notion of the solid 
 forms and relative projection of objects is acquired ; on which great light has 
 
 recently been thrown by the interesting experiments of Mr. Wheatstone.t It 
 is perfectly evident, both from reason and experience, that the flat picture upon 
 the retina, which is the only object of our sensation, could not itself convey to 
 our minds any notion, but that of a corresponding plane surface. In fact, any 
 notion of solidity, which might be formed by a person, who had never had 
 the use of more than one eye, would entirely depend upon the combination of 
 his visual and tactile sensations. This idea is fully confirmed by the case 
 already referred to, as recorded by Cheselden. The first visual idea formed 
 by the youth was, that the objects around him formed a flat surface, which 
 touched his eyes, as they had previously been in contact with his hands ; and 
 after this notion had been corrected, through the education of his sight by his 
 touch, he fell into the converse error of supposing that a picture, which was 
 shown to him, was the object itself represented in relief on a small scale. But 
 where both eyes are employed, it has been ascertained by Mr. Wheatstone, 
 
 * The late Dr. Wollaston was subject to a curious affection of vision, which consisted in 
 his not being able to see more than half an object, the loss being sometimes on one side, 
 and sometimes on the other. The Author has met with several cases of this disorder, which 
 has been termed hemiopia. Dr. W. thought that they might be explained by the decussation 
 of the optic nerve ; but Mr. Mayo states that he has known instances of a parallel affection, 
 involving alternately the centre and the circumference of the retina, and therefore not attribut- 
 able to any such structural arrangement. 
 
 f Philosophical Transactions, 1838. 
 
418 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 that they concur in exciting the perception of solidity or projection, which 
 arises from the combination of two different images in the mind. It is easily 
 shown, that any near object is seen in two different modes by the two eyes. 
 Thus let the reader hold up a thin book, in such a manner that its back shall 
 be exactly in front of his nose, and at a moderate distance from it ; he will 
 observe, by closing first one eye and then the other, that his perspective view 
 of it (or the manner in which he would represent it on a plane surface) is very 
 different, according to the eye with which he sees it. With the right eye he 
 will see its right side, very much foreshortened ; with the left, he will gain a 
 corresponding view of the left side ; and the apparent angles, and the lengths 
 of the different lines, will be found to be very different in the two views. On 
 looking at either of these views singly, no other notion of solidity can be 
 acquired from it, than that to which the mind is conducted, by the association 
 of such a view with the touch of the object it represents. But it is capable of 
 proof, that the mental association of the two different pictures upon the retina*, 
 does of itself give rise to the idea of solidity. This proof is afforded by Mr. 
 Wheatstone's ingenious instrument, the Stereoscope. 
 
 547. The Stereoscope essentially consists of two plane mirrors, inclined 
 with their backs to one another at an angle of 90. If two perspective draw- 
 ings of any solid object, as seen at a given distance with the two eyes respect- 
 ively, be placed before these mirrors, in such a manner that their images shall 
 be made to fall upon the corresponding parts of the two retinas, in the same 
 manner as the two images formed by the solid object itself would have done, 
 the mind will perceive, not a single representation of the object, nor a confused 
 union of the two, but a body projecting in relief, the exact counterpart of 
 that from which the drawings were made. Mr. Wheatstone further shows by 
 means of the Stereoscope, that similar images, differing to a certain extent in 
 magnitude, when presented to the corresponding parts of the two retina, give 
 rise to the perception of a single object, intermediate in size between the two 
 monocular pictures. Were it not for this, objects would appear single, only 
 when at an equal distance from both eyes, so that their pictures upon the 
 retina are of the same size ; which will only happen, when they are directly 
 in front of the median line of the face. Again, if pictures of dissimilar objects 
 be simultaneously presented to the two eyes, the consequence will be similar 
 to that which is experienced, when the rays come to the eye through two 
 differently-coloured media; the two images do not coalesce, nor do they 
 appear permanently superposed upon one another : but at one time one image 
 predominates to the exclusion of the other, and then the other is seen alone ; 
 and it is only at the moment of change, that the two seem to be intermingled. 
 It does not appear to be in the power of the will, Mr. Wheatstone remarks, 
 to determine the appearance of either ; but, if one picture be more illuminated 
 than the other, it will be seen during a larger proportion of the time. Many 
 other curious experiments with this simple instrument are related by Mr. 
 Wheatstone ; and they all go to confirm the general conclusion, that the com- 
 bination of the images furnished by the two eyes is a mental act, resulting 
 from an inherent law of our psychical constitution ; and that our perceptions of 
 the solidity and projection of objects, near enough to be seen in different views 
 with the two eyes, result from this cause. In regard to distant objects, how- 
 ever, the difference in the images formed by the two eyes is so slight, that it 
 cannot aid in the determination ; and hence it is, that, whilst we have no dif- 
 ficulty in distinguishing a picture, however well painted, from a solid object, 
 when placed near our eyes, (since the idea, which might be suggested by the 
 image formed on one eye, will then be corrected by the other,) we are very 
 liable to be misled by a delineation, in which the perspective, light and shade, 
 <fcc., are faithfully depicted, if we are placed at a distance from it, and are pre- 
 

 SENSE OF VISIOX. 419 
 
 vented from perceiving that it is but a picture. In this case, however, a slight 
 movement of the head is sufficient to undeceive us ; since by this movement 
 a great change would be occasioned in the perspective view of the object, sup- 
 posing it to possess an uneven surface ; whilst it scarcely affects the image 
 formed by a pictiire. In the same manner, a person who only possesses one eye, 
 obtains, by a slight motion of his head, the same idea of the form of a body, 
 which another would acquire by the simultaneous use of his two eyes. 
 
 548. The appreciation of the distance of objects, may be easily shown to 
 be principally derived from the association, in the mind, of visual and tactual 
 sensations ; assisted, in regard to near objects, by the muscular sensations de- 
 rived from the convergence of the eyes. Thus, an infant, or a person who 
 has but recently acquired sight, evidently forms very imperfect ideas regarding 
 the distance of objects ; and it is only after long experience that a correct no- 
 tion is formed. The assistance which is given by the joint use of both eyes, 
 is evident from the fact, that, if we close one eye, we are unable to execute 
 with certainty many actions, which require a precise appreciation of the dis- 
 tance of near objects, such as threading a needle, or snuffing a candle. In. 
 regard to distant objects, our judgment is chiefly founded upon their apparent 
 size, if their actual size be known to us ; but, if this is not the case, and if we 
 are so situated that we cannot judge of the intervening space, we principally 
 form our estimate from the greater or less distinctness of their colour and out- 
 line. Hence this estimate is liable to be greatly affected by varying states of 
 the atmosphere ; as is well known to every one who has visited warmer lati- 
 tudes. The extreme clearness of the air sometimes brings, into an apparently 
 near proximity, a hill that rises beyond some neighbouring ridge (the inter- 
 vening space being hidden, so as not to afford any datum for the estimate of 
 the distance of the remote hill) ; and which, by a slight haziness, is carried to 
 three or four times the degree of apparent remoteness. It is probable that, in 
 the lower Animals, the perception of distance is much more intuitive than it is 
 in ourselves. 
 
 549. Our estimate of the real size of an object is manifestly connected with 
 that of its distance. The apparent size is dependent upon the angle at which 
 its rays diverge, to impinge upon the cornea ; this angle increases with the 
 proximity, and diminishes with the remoteness, of the object. Our estimate 
 of the comparative size of near objects, of whose distances we can become 
 aware by the inclination of the optic axes, is much more correct than that 
 which we form, when one or both are far removed; since, when we are un- 
 certain as to its distance, we cannot form a judgment of the real size of a body, 
 from the angle at which its rays diverge. Hence our estimate of the size of 
 objects even moderately distant, is much influenced by states of the atmosphere. 
 Thus, if we walk across a common in a fog, a child approaching us appears 
 to have the size of a man, and a man seems like a giant; since the indistinct- 
 ness of the outline excites in the mind the idea of distance; and an object 
 seen under a given visual angle at a distance, must of necessity be much larger 
 than one, of which the apparent size is the same, but which is much nearer. 
 The want of innate power in Man to form a true conception of either size or 
 distance, is well shown by the effect produced on the mind unprepared for 
 such delusions, by a skilfully-painted picture ; the view of which is so con- 
 trived, that its distance from the eye cannot be estimated in the ordinary man- 
 ner; the objects it represents are invested by the mind with their real sizes 
 and respective distances, as if their peal image was formed upon the retina.* 
 
 * This delusion has been extremely complete, in some of those who have seen the pano- 
 ramic view of London in the Coliseum. A lively and interesting account of it is given in 
 the Journal of the Parsee Shipbuilders, who visited England some time ago. 
 
420 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 550. From all these considerations, we are led to perceive the truth of the 
 quaint observation made by Dr. Brown, that "vision is, in fact, the art of 
 seeing things which are invisible ;" that is, of acquiring information, by means 
 of the eye, which is neither contained in the sensations of sight themselves, 
 nor logically deducible from the intimations which those sensations really 
 convey. We cannot too constantly bear in mind, in treating of this subject, 
 that we do not take cognizance by our optic nerves, as we do by the nerves 
 of touch, of material bodies themselves, but of the pictures or images formed 
 by those objects ; and whatever be the notions suggested by the picture, that 
 can never be transformed into anything else. These notions appear to be, in 
 the lower Animals, entirely of an intuitional or instinctive character; in Man 
 they are so in a much less degree ; and although it is impossible to come to a 
 precise conclusion on the subject, from the want of sufficient data, it is indu- 
 bitable that a large part of the knowledge of the external world, which he de- 
 rives in the adult condition from the use of his eyes alone, is really dependent 
 upon the early education of his perceptive powers, in which process, the sen- 
 sations conveyed by .different organs are brought to bear upon one another. 
 
 551. The persistence, during a certain interval, of impressions made upon 
 the retina, gives rise to a number of curious visual phenomena. The pro- 
 longation of the impression will be governed, in part, by its previous duration. 
 Thus, when we rapidly move an ignited point through a circle, the impression 
 itself is momentary, and remains but for a short time; whilst, if we have been 
 for some time looking at a window, and then close our eyes, the impression of 
 the dark bars traversing the illuminated space is preserved for several seconds. 
 Such phenomena can here be only briefly adverted to. One of these is the 
 combination, into one image, of two or more objects presented to the eye in 
 successive movements ; but these must be of a kind which can be united, other- 
 wise a confused picture is produced. Thus in a little toy, called the Thauma- 
 trope, which was introduced some years ago, the two objects were painted on 
 the opposite sides of a card, a bird, for instance, on one, and a cage on the 
 other; and, when the card was made (by twisting a pair of strings) to revolve 
 about one of its diameters, in such a manner as to be alternately presenting 
 the two sides to the eye at minute intervals, the two pictures were blended, 
 the bird being seen in the cage. A far more curious illusion, however, was 
 that first brought into notice by Mr. Faraday ; who showed that, if two toothed 
 wheels, placed one behind the other, be made to revolve with equal velocity, 
 a stationary spectrum will be seen; whilst if one be made to revolve more 
 rapidly than the other, or the number of teeth be different, the spectrum also 
 will revolve. The same takes place when a single wheel is made to revolve 
 before a mirror ; the wheel and its image answering the purpose of the two 
 wheels in the former case. On this principle, a number of very ingenious 
 toys have been constructed; in some of these, the same figure or object is 
 seen in a variety of positions ; and the impressions of these, passing rapidly 
 before the eye, give rise by their combination to the idea, that the object is 
 itself moving through these positions. Similar illusions may be produced in 
 regard to colour. 
 
 552. When the Retina has been exposed for some time to a strong im- 
 pression of some particular kind, it seems less susceptible of feebler impres- 
 sions of the same kind. Thus, if we look at any brightly luminous object, 
 and then turn our eyes on a sheet of white paper, we shall perceive a dark 
 spot upon it; the portion of the retina, which had been affected by the bright 
 image, not being able to receive an impression from the fainter rays reflected 
 by the paper. The dark spectrum does not at once disappear, but assumes 
 different colours in succession, these being expressions of the states through 
 which the retina passes, in its transition to the natural condition. If the eye 
 
SENSE OF VISION. 421 
 
 has received a strong impression from a coloured object, the spectrum exhibits 
 the complementary colour;* thus, if the eye be fixed for any length of time 
 upon a bright red spot on a white ground, and be then suddenly turned so as 
 to rest upon the white surface, we see a spectrum of a green colour. The 
 same explanation applies to the curious phenomenon of coloured shadows. 
 It may not unfrequently be observed at sunset, that, when the light of the sun 
 acquires a bright orange colour from the clouds through which it passes, the 
 shadows cast by it have a blue tint. Again, in a room with red curtains, the 
 light which passes through these produces green shadows. In both instances, 
 a strong impression of one colour is made on the general surface of the retina; 
 and at any particular spots, therefore, at which the light is colourless but very 
 faint, that colour is not perceived, its complement only being visible. The 
 correctness of this explanation is proved by the fact, that, if the shadow be 
 viewed through a tube, in such a manner that the coloured ground is excluded, 
 it seems like an ordinary shadow. It is not unlikely that, as Miiller suggests, 
 the predominant action of one colour on the retina disturbs (as it were) the 
 equilibrium of 'its condition, and excites in it a tendency to the development 
 of a state, corresponding to that which is produced by the impression of the 
 complementary colour; for the latter is, according to him, perceived even 
 ^vhere it does not exist; as when the eye, after receiving a strong impression 
 from a coloured spot, and directed upon a completely dark surface or into a 
 dark cavity, still perceives the spectrum. Upon these properties of the eye 
 are founded the laws of harmonious colouring, which have an obvious analogy 
 with those of musical harmony. All complementary colours have an agreeable 
 effect, when judiciously disposed in combination; and all bright colours, which 
 are not complementary, have a disagreeable effect, if they are predominant: this 
 is especially the case in regard to the simple colours, strong combinations of 
 any two of which, without any colour that is complementary to either of them, 
 are extremely offensive. Painters who are ignorant of these laws, introduce 
 a large quantity of dull grey into their pictures, in order to diminish the glaring 
 effects, which they would otherwise produce; but this benefit is obtained by 
 a sacrifice of the vividness and force, which may be secured in combination 
 with the richest harmony, by a proper attention to physiological principles. 
 
 553. Some persons, who can perfectly distinguish forms, are deficient, 
 through some original peculiarity in the constitution of the retina, in the 
 power of discriminating colours. This is most commonly seen in regard to the 
 complementary colours, especially red and green ; such persons not being 
 able to perceive cherries amidst the leaves on a tree, except by the difference 
 of their form. Several distinct varieties of this affection may be distinguished, 
 however. These have been classified by Seebeck and Wartmann.t 
 
 554. Amongst other curious phenomena of Vision, is the vanishing of 
 images which fall at the entrance of the optic nerve ; as is shown in the fol- 
 lowing experiment. Let two black spots be made upon a piece of paper, 
 about four or five inches apart ; then let the left eye be closed, and the right 
 eye be strongly fixed upon the left-hand spot. If the paper be then moved 
 backwards and forwards, so as to change its distance from the eye, a point will 
 be found, at which the right-hand spot is no longer visible; though it is clearly 
 seen, when the paper is brought nearer or removed further. In this position 
 of the eye and object, the rays from the right-hand spot cross to the nasal 
 
 * By the complementary colour is meant that, which would be required to make white or 
 colourless light, when mixed with the original. As red, blue, and yellow are the primary 
 or elementary colours, red is the complement of green (which is composed of yellow and 
 blue); blue is the complement of orange (red and yellow); and yellow of purple (red and blue); 
 and vice versa in all instances. 
 
 t Miiller's Physiology, p. 1213; Taylor's Scientific Memoirs, Vol. iv. p. 156, et seq. 
 3G 
 
422 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 side of the globe, and fall upon the point of the retina, which has just been 
 mentioned. The phenomenon is not confined to that spot, however ; nor is 
 it correct to say, as is sometimes done, that the retina is not sensible to light 
 at that point ; since, if such were the case, we should see a dark spot in our 
 field of view, whenever we use only one eye. The fact is, that a similar 
 phenomenon may occur under somewhat different conditions, in any division 
 of the retina, especially in its lateral parts. Thus, if we fix the eye for some 
 time, until it is fatigued, upon a strip of coloured paper lying upon a white 
 surface, the image of the coloured object will in a short time disappear, and 
 the white surface will be seen in its place ; the disappearance of the image, 
 however, is only of a few seconds duration. The truth seems to be, that 
 there is a tendency in the retina, to the propagation over neighbouring parts, 
 of impressions which occupy a large proportion of its surface ; and that this 
 tendency is the strongest, around the point at which the optic nerve enters, 
 so that the state of this part will generally become similar to that of the sur- 
 rounding portion of the retina. Hence, when we are using one eye only, 
 we do not perceive any dark spot in the field, but only a certain degree of in- 
 distinctness in a portion of the image. 
 
 555. Under particular circumstances, we may receive a visual representa- 
 tion of the retina itself; as is shown by the experiments of Purkinje. " If^ 
 in a room otherwise dark, a lighted candle be moved to and fro, or in a circle, 
 at a distance of six inches before the eyes, we perceive, after a short time, a 
 dark arborescent figure ramifying over, the whole field of vision ; this appear- 
 ance is produced by the vasa centralia distributed over the retina, or by the 
 parts of the retina covered by those vessels. There are, properly speaking, 
 two arborescent figures, the trunks of which are not coincident, but on the 
 contrary arise in the right and left divisions of the field, and immediately 
 take opposite directions. One trunk belongs to each eye, but their branches 
 intersect each other in the common field of vision. The explanation of this 
 phenomenon is as follows : By the movement of the candle to and fro, the 
 light is made to act, on the whole extent of the retina, and all the parts of the 
 membrane which are not immediately covered by the vasa centralia are feebly 
 illuminated ; those parts, on the contrary, which are covered with those vessels 
 cannot be acted on by the light, and are perceived, therefore, as dark arbore- 
 scent figures. These figures appear to lie before the eye, and to be suspended 
 in the field of vision."* We have thus another demonstration of the fact 
 that, in ordinary vision, the immediate object of our sensation is a certain 
 condition of the retina, which is excited by the formation of a luminous 
 image. 
 
 6. Sense of Hearing. 
 
 556. In the Ear, as in the Eye, the impressions made upon the sensory 
 nerve are not at once produced by the body which originates the sensation ; 
 but they are propagated to it, through a medium capable of transmitting them. 
 Here too, therefore, we take cognizance by the mind, not of the sonorous ob- 
 ject, but of the condition of the auditory nerve ; and all the ideas we form of 
 sounds, as to their nature, intensity, direction, &c., must be based upon the 
 changes which they produce in it. The complex contrivances, which we 
 meet with in the organ of Hearing among higher animals, are evidently in- 
 tended to give them greater power of discriminating sounds, than is possessed 
 by the lower tribes ; in which last it is reduced to a form so simple, that it may 
 be questioned whether they can be said to possess an organ of hearing, if 
 by this term we imply anything more than the mere consciousness of sono- 
 
 * Muller's Physiology, p. 1163. 
 
SENSE OF HEARING. 423 
 
 rous vibrations. There is a considerable difference, however, between the 
 Eye and the Ear, in regard to the special purposes for which they are respect- 
 ively adapted. In the former we have seen, that the whole object of the in- 
 strument is to direct the rays of light received by it, in such a manner, as to 
 occasion them to fall upon the expansion of the optic nerve in a similar rela- 
 tive position, and with corresponding proportional intensity, to that which 
 they possessed when issuing from the object. We have no reason to believe 
 anything of this kind to be the purpose of the Ear ; indeed, it would be in- 
 consistent with the laws of the propagation of sound. Sonorous vibrations 
 having the most various directions, and the most equal rate of succession, are 
 transmitted by all media without modification, however numerous their lines 
 of intersection ; and wherever these undulations fall upon the auditory nerve, 
 they must cause the sensation of corresponding sounds. Still it is probable 
 that some portions of the complex organ of hearing, in Man and in the higher 
 animals, are more adapted than others to receive impressions of a particular 
 character ; and that thus we may be especially informed of the direction of "a 
 sound by one part of the organ, of its musical tone by another, and of some 
 other of its qualities by a third. In our inquiries into this ill-understood sub- 
 ject, we shall commence with a brief survey of the comparative structure of 
 the organ. 
 
 557. The essential part of an Organ of Hearing being obviously a nerve, 
 endowed with the peculiar property of receiving and transmitting sonorous 
 undulations, it is by no means indispensable that a special provision should 
 be made for this purpose ; since the Auditory nerve, if merely in contact with 
 the solid parts of the head, will be affected by the vibrations, in which it is 
 continually participating. Hence we must not imagine the sense to be absent, 
 wherever we cannot discover a special organ. It is among the highest only 
 of the Invertebrate animals, that any such special organ presents itself; and 
 then only in a very simple form. Thus in the Crustacea and Cephalopoda, 
 
 [Fig. 180. 
 
 General view of the external, middle, and internal ear, as seen in a prepared section through a, the 
 auditory canal, b. The tympanum or middle ear. c. Eustachian tube, leading to the pharynx, d. Coch- 
 lea; and e. Semicircular canals and vestibule, seen on their exterior, as brought into view by dissecting 
 away the surrounding petrous bone. The styloid process projects below; and the inner surface .of the 
 carotid canal is seen above the Eustachian tube. From Scarpa.] 
 
424 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 the ear consists of a small cavity excavated in the solid frame-work of the 
 head ; this cavity is lined with a membrane, on which the nerve is distri- 
 buted ; and it is filled with a watery fluid. In some instances, the cavity is 
 completely shut in by its solid walls ; and the sonorous vibrations can then 
 only be communicated through these : but in the higher forms of this appa- 
 ratus, there is a small aperture covered with a membrane, upon which the 
 external medium can at once act. In tracing this most simple into the more 
 complex forms, it is at once seen, that the cavity corresponds with the vesti- 
 bule of the ear of higher animals, and its opening with the fenestra ovalis. 
 In the lowest Cyclostome Fishes, the organ is but little more complicated ; 
 from the vestibule proceeds a single annular passage, which may be consi- 
 dered as a semicircular canal; and the auditory nerve is distributed minutely 
 upon its lining membrane, as upon that of the vestibule itself. In species 
 a little higher in the scale, two such canals exist ; these are present in the 
 Lamprey. And in all the rest of the class, three semicircular canals are 
 found; holding the same direction in regard to each other, as they do in Man. 
 Within the vestibular sac of Fishes are found calcareous concretions, which 
 are pulverulent in the Cartilaginous, but hard and stony in the Osseous tribes; 
 to these the name of Otolithes has been given. Some rudiments of a tympa- 
 nic cavity may be found in Fishes ; but there is no vestige of a cochlea : in 
 several tribes, the organ of hearing possesses a peculiar connection with the 
 air-bladder, which appears to be a foreshadowing of the Eustachian tube of 
 higher classes. 
 
 558. In the true Reptiles, a considerable advance is constantly to be found 
 in the character of the Ear; a tympanic cavity being added, with a drum and 
 a chain of bones ; and a rudiment of the cochlea being generally discoverable. 
 Among the Amphibia, however, which are in so many respects intermediate 
 
 [Fig. 181. 
 
 Diagram of the inner wall of the tympanun after maceration, the outer wall and ossicles being re- 
 moved, a. Fenestra ovalis. b. Fenestra rotunda, c. Promontory, d. Pryramid, with the orifice at its 
 apex, e. Projection of the aqueductus Fallopii. f. Some of the mastoid <:ells communicating with the 
 tympanum, g. Processus cochleariformis, bounding i, the canal for the tensor tympani muscle : the an- 
 terior pyramid is broken off, if it existed, h. Commencement of the Eustachian tube. j. Jugular-fossa, 
 immediately below the tympanum. &, k. Carotid canal, with the artery in outline, to show its course in 
 relation to the tympanum and Eustachian tube. I Portio dura of the seventh pair of nerves, as it would 
 be seen in the terminal part of the aqueduct of Fallopius. m. Chorda tympani, leaving the portio dura, 
 and entering a short canal, which opens in the tympanum, at the base of the pyramid, n. Grooves for 
 the tympanic plexus.] 
 
SENSE OF HEARING. 
 
 425 
 
 between the true Reptiles and Fishes, there is a remarkable variation in this 
 respect, some having a tympanum, and some being completely destitute of 
 it. Wherever a tympanic cavity distinctly exists, there is an Eustachian tube 
 connecting it with the fauces. This cavity, in the true Reptiles, not only 
 possesses ihefenestra ovalis (or opening into the vestibule), but the fenestra 
 rotunda (or opening into the cochlea). The membrana tympani is usually 
 
 [Fig. 182. 
 
 A view of the axis of the Cochlea and the Lamina Spiralis, showing the arrangement of the three 
 Zones; theosseous zone and the membraneof the vestibule have been removed; 1, the natural size of the 
 parts ; the other figure is greatly magnified ; 2, trunk of the auditory nerve ; 3, the distribution of its fila- 
 ments in the zona ossea ; 4, the nervous anastomosis of the zona vesicularis ; 5, the zona membranacea; 
 0, the osseous tissue of the modiolus ; 7, the opening between the two scalse.] 
 
 visible externally ; but it is sometimes covered by the skin. In Birds, the 
 structure of the ear is essentially the same as in the higher Reptiles. A dis- 
 tinct cochlea exists, though its form is not spiral but nearly straight : of its 
 character, however, there can be no doubt ; a division into two passages, by 
 a membranous partition on which the nerve is spread out, being evident. 
 Moreover the tympanum communicates with cavities in the cranial bones, 
 which are thus filled with air ; and these, by increasing the extent of surface, 
 produce a more powerful resonance. There is no external ear, except in a 
 few species of nocturnal Birds. In Mammalia, the organ of hearing is usually 
 
 [Fig. 183. 
 
 Cochlea of a pew -born infant, opened tm the side towards the apex of the petrous bone. It shows the 
 general arrangement of the two scalse, the lamina spiralis, and the distribution of the cochlear nerve. At 
 the apex is seen the modiolus expanding into the cupola, where the spiral canal terminates in a cul-de- 
 sac. The helicotrema is not visible in this view. From Arnold.] 
 
 36* 
 
426 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 formed upon the same plan, as it presents in Man ; in the Monotremata, how- 
 ever, it more approaches that of Birds. The cochlea of the Mammalia in 
 general is a spiral, forming about two turns and a half; the partition which 
 
 [Fig. 184. 
 
 The Cochlea divided parallel with its axis, through the centre of the Modiolus ; after Breschet; 1, the 
 modiolus ; 2, the infundibulum in which the modiolus terminates ; 3, 3, the cochlear nerve, sending its fila- 
 ments through the centre of the modiolus ; 4, 4, the scala tympani of the first turn of the cochlea ; 5, 5, the 
 scala vestibula of the first turn; 6, section of the lamina spiralis, its zonulaossea; one of the filaments of 
 the cochlear nerve is seen passing between the two layers of the lamina spiralis to be distributed upon the 
 membrane which invests the lamina; 7, the membranous portion of the lamina spiralis; 8, loops formed by 
 the filaments of the cochlear nerve ; 9, 9, scala tympani of the second turn of the cochlea; 10, 10, scala 
 vestibula of the second turn ; the septum between the two is the lamina spiralis; 11, the scala tympani of 
 the remaining half turn ; 12, the remaining half turn of the scala vestibula; the dome placed over this half 
 turn is the cupola : 13, the lamina of bone which forms the floor of the scala vestibula curving spirally 
 round to constitute the infundibulum (2) ; 14, the helicotrema through which a bristle is passed ; its lower 
 extremity issues from the scala tympani of the middle turn of the cochlea.] 
 
 divides its canal is partly osseous, partly membranous ; and its two passages 
 communicate with the tympanic cavity and the vestibule respectively. The 
 cavity of .the tympanum is very large in some species, extending even into the 
 contiguous bones. All the Mammalia, except the aquatic tribes, have an ex- 
 ternal ear ; and this is sometimes of an enormous size in proportion to the 
 dimensions of the body, as it is in the Bats. The labyrinth of the higher 
 Vertebrata contains no otolithes. 
 
 559. The ultimate terminations of the fibres of the Auditory nerve, are 
 
 Fig. 185. 
 
 [Fig. 186. 
 
 Papillae (?) of the Auditory nerve, 
 on a segment of the spiral lamina of 
 the cochlea of a young Mouse ; the 
 lower portion is the osseous, and the 
 higher the membranous part of the 
 lamina. Magnified 300 times. 
 
 The Auditory Nerve taken out of the Cochlea ; 1, 1, 1, 
 the trunk of the nerve; 2, 2, its filaments in the zona ossea 
 of the lamina spiralis ; 3, 3. its anastomoses in the zona 
 vesicularis.] 
 
SENSE OF HEARING. 
 
 427 
 
 best seen in the lamina spiralis of the cochlea, and its membranous prolon- 
 gation. Much diversity exists, however, as to the interpretation of the ap- 
 
 [Fig. 187. 
 
 [Fig. 188. 
 
 A highly magnified view of a small piece of the Lamina Spiralis, 
 showing the globular structure of the Nerves, and the manner in 
 which they leave their Neurilemma as they anastomose; the natural 
 size of the piece is seen on the side of the figure; 1, portion of the 
 auditory nerve, 2, 2, osseous canals in the zona ossea of the lamina 
 spiralis; 3, 3, anastomoses in the zona mollis; 4, 4, the neurilemma 
 leaving the nervous loops and interlocking to form the layer of the 
 zona membranacea.] 
 
 Plexiform arrangement of the 
 cochlear nerves seen in the basal 
 coil of the lamina spiralis, treated 
 with hydrochloric acid. There 
 are no ganglion globules in this 
 plexus, which consists of tubular 
 fibres, a. Twig of cochlear nerve 
 in the modiolus, its fibres diverging 
 and reuniting in 6, a band in the 
 plexus taking a direction parallel 
 to the zones. From this other 
 twigs radiate, and again and again 
 branch and unite as far as the mar- 
 gin of the osseous zone c, where 
 they terminate. From the sheep. 
 Magnified 30 diameters.] 
 
 pearances there seen ; some observers affirming that there are no free or 
 papillary terminations, and that the nervous fibres all return by loops ; whilst 
 others state that the papillae are clearly to be distinguished. The fact appears 
 to be that, as in the retina, the fibres do form a minute plexus; but that fibres 
 are connected with this, which end, or rather commence in papillae. The 
 Auditory nerve is also very minutely distributed on the membrane lining the 
 vestibule and semicircular canals ; and in the ampullae or dilated extremities 
 of the latter, there are little projections of this membrane internally, which 
 are largely supplied with nerves. 
 
 560. In order to gain any definite idea of the uses of different parts of the 
 Ear, it is necessary to bear in mind, that sounds may be propagated amongst 
 solid or fluid bodies in three ways, by reciprocation, by resonance, and by 
 conduction. 1. Vibrations of reciprocation are excited in a sounding body, 
 when it is capable of yielding a musical tone of definite pitch, and another 
 body of the same pitch is made to sound near it. Thus if two strings of the 
 same length and tension be placed along side of each other, and one of them 
 be sounded with a violin-bow, the other will be thrown into reciprocal vibra- 
 tion ; or if the same tone be produced near the string in any other manner, 
 as by a flute, or a tuning-fork, the same effect will result. 2. Vibrations of 
 resonance are of somewhat the same character; but they occur when a sound- 
 
428 
 
 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 [Fig. 189. 
 
 The soft parts of the Vestibule taken out of their bony case, so as to show the distribution of the Nerves 
 in the Ampullae ; 1, the superior semicircular membranous canal or tube ; 2, the external semicircular 
 lube ; 3, the inferior semicircular tube ; 4, the tube of union of the superior and inferior canals ; 5, the 
 sacculus ellipticus ; 6, the sacculus sphericus ; 7, the portio dura nerve ; 8, the anterior fasciculus of the 
 auditory nerve ; 9, the nerve to the sacculus sphericus ; 10, 10, the nervous fasciculi to the superior and 
 external ampullae ; 11, the nerve to the sacculus ellipticus ; 12, the posterior fasciculus of the auditory 
 nerve, furnishing 13, the filaments of the sacculus sphericus, and 14, the filaments of the cochlea, cut off.] 
 
 [Fig. 190. 
 
 The Ampulla of the External Semicircular Membranous Canal, showing the Mode of termination of its 
 Nerve.] 
 
 ing body is placed in connection with any other, of which one or more parts 
 may be thrown into reciprocal vibration, even though the tone of the whole 
 be different, or it be not capable of producing a definite tone at all. This is 
 the case, for example, when a tuning-fork in vibration is placed upon a sound- 
 board ; for even though the whole board have no definite fundamental note,* 
 
 * The fundamental note of a body is the lowest tone which it will yield, when the whole 
 of it is in vibration together. By dividing the body into two or more distinct parts, it may 
 
SENSE OF HEARING. 429 
 
 it will divide itself into a number of parts, which will reciprocate the original 
 sound, so as greatly to increase its intensity; and the same sound-board will 
 act equally well for tuning-forks of several different degrees of pitch. When 
 a smaller body is used for resonance, however, it is essential that there should 
 be a relation between its fundamental note and that of the sonorous body ; 
 otherwise no distinct resonance is produced. Thus, if a tuning-fork in vibra- 
 tion be held over a column of air in a tube, of such a length that the same note 
 would be given by its vibration, its sound w r ill be reciprocated. And if it be 
 held over a pipe, the column of air in which is a multiple o,f this, the column 
 will divide itself into that number of shorter parts, each of which will recipro- 
 cate the original sound, and the total action will be one of resonance. But if 
 the length of the pipe bear no such correspondence with the note sounded by 
 the tuning-fork, no resonance is given by the column of air it contains. 3. 
 Vibrations of conduction are the only ones by which sounds can strictly be 
 said to be propagated. These are distinguishable into various kinds, into 
 which it is not requisite here to inquire. It should be remarked, however, 
 that all media, fluid, liquid, or solid, are capable of transmitting sound in this 
 manner, a vacuum being the only space through which it cannot pass. 
 The transmission is usually much more rapid through solid bodies, than 
 through liquid ; and through liquid, than through gaseous. The greatest 
 diminution in the intensity of sound is usually perceived, when a change takes 
 place in the medium through which it is propagated, especially from the aeri- 
 form to the liquid. 
 
 561. The detailed application of these principles has been most elaborately 
 worked out by Miiller ; and the following statement of what may be regarded 
 as the present condition of our knowledge of the subject, is little more than 
 an abstract of his results. Considering it desirable, in the first place, to estab- 
 lish the conditions under which those animals hear that are constantly im- 
 mersed in water, he made a series of experiments, from which he draws the 
 following conclusions : i. Sonorous vibrations, excited in water, are imparted 
 with considerable intensity to solid bodies. n. Sonorous vibrations of solid 
 bodies are communicated with greater intensity to other solid bodies brought 
 in contact with them, than to water ; but with much greater intensity to 
 water, than to atmospheric air. in. Sonorous vibrations are communicated 
 from air to water with great difficulty, with very much greater difficulty 
 than they are propagated from one part of the air to another ; but their transi- 
 tion from air to water is much facilitated, by the intervention of a membrane 
 extended between them. iv. Sonorous vibrations are not only imparted from 
 water to solid bodies with definite surfaces, which are in contact with the 
 water, but are also returned with increased intensity by these bodies to the 
 water ; so that the sound is heard loudly in the vicinity of those bodies, in 
 situations where, if it had its origin in the conducting power of the water 
 alone, it would be faint. v. Sonorous undulations, propagated through water, 
 are partially reflected by Jhe surfaces of solid bodies. vi. Thin membranes 
 conduct sound in water without any loss of its intensity, whether they be 
 tense or lax. From in., iv., and vi., we learn the mode in which the sound 
 
 be made to give a great variety of sounds. Thus, if a stretched string be divided by a bridge 
 into two equal parts, each will sound the octavo of the fundamental note, or the 8th note 
 above it. If it be divided into three parts, each will give the 12th above the fundamental 
 note; if into four, the 15th or double octave will be heard; if into five, the 17th; if into six, 
 the 19th ; if into seven, the 20^th (flat seventh above the second octave); if into eight, the 
 22d or triple octave. A string forcibly set in vibration has a tendency to sound these har- 
 monics with the fundamental note, by spontaneous division into several distinct segments of 
 vibration ; as may be easily made evident by striking one of the lower keys of the piano, 
 and listening to the sounds heard whilst the fundamental note is dying away. 
 
430 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 is conducted to the ear, in aquatic animals not breathing atmospheric air. 
 The labyrinth of such is either entirely inclosed within the bones of the head, 
 as in the Cephalopoda, and in the Cyclostome and Osseous Fishes ; or, its 
 cavity being prolonged to the surface of the body, it is there brought into 
 communication with the conducting medium, by means of a membrane, be- 
 sides receiving the vibrations through the medium of the solids of the body, 
 as is the case in Cartilaginous Fishes and Crustacea. It would seem as if, 
 in the Osseous Fishes, the resonance of the cranial bones, in which the laby- 
 rinth is imbedded, were sufficient to give the requisite increase of intensity to 
 the sound ; whilst in the Cartilaginous orders, the softness of these bones 
 renders some other means necessary. In addition to this, we find in many 
 Fishes a communication with the air-bladder; which indeed seems to have, 
 in these, but little other use. The mode in which this increases by resonance 
 the intensity of the sounds, will appear from the following experimental con- 
 clusions. vii. When sonorous vibrations are communicated from water to 
 air inclosed in membranes or solid bodies, a considerable increase in the in- 
 tensity of the sound is produced, by the resonance of the air thus circum- 
 scribed. vin. A body of air inclosed in a membrane, and surrounded by 
 water, also increases the intensity of the sound by resonance, when the sono- 
 rous undulations are communicated to it by a solid body. From these ob- 
 servations, it may be concluded, that the air-bladder of Fishes, in addition to 
 other uses, serves the purpose of increasing by resonance the intensity of the 
 sonorous undulations, communicated from the water to the body of the Fish. 
 Moreover, as the conducting and resonant power of the air in the air-bladder 
 is greater in proportion to its density, the influence of this organ on the per- 
 ception of sounds will, of course, be greater in deep waters, where the pres- 
 sure upon it is considerably increased. 
 
 562. Most animals living in air, are provided with an opening into the ves- 
 tibule, covered by a thin membrane; and, in the majority of cases, with the 
 tympanic apparatus also. The following experimental results bear upon the 
 manner in which the Ear of such animals is affected by sound. ix. Sono- 
 rous undulations, in passing from air directly into water, suffer a considerable 
 diminution in their strength ; while, on the contrary, if a tense membrane 
 exists between the air and the water, the sonorous undulations are communi- 
 cated from the former to the latter medium with great intensity. x. The so- 
 norous vibrations are also communicated without any perceptible loss of in- 
 tensity, from the air to the water ; when, to the membrane forming the me- 
 dium of communication, there is attached a short solid body, which occupies 
 the greater part of its surface, and is alone in contact with the water. xi. A 
 small solid body, fixed in an opening by means of a border of membrane, so 
 as to be movable, communicates sonorous vibrations, from air on one side, to 
 water or the fluid of the labyrinth on the other, much better than solid media 
 not so constructed. But the propagation of sound to the fluid is rendered 
 much more perfect, if the solid conductor, thus occupying the opening, is by 
 its other end fixed to the middle of the tense membrane, which has atmo- 
 spheric air on both sides. The fact stated in ix. is evidently one of great im- 
 portance in the physiology of hearing ; and fully explains the nature of the 
 process in those animals which receive the sonorous vibrations through air, 
 but which have no tympanic apparatus. In x. we have the elucidation of the 
 action of the fenestra ovalis, and of the movable plate of the stapes which 
 occupies it, in animals living in air, but destitute of tympanic apparatus ; this 
 is naturally the case in many Amphibia ; and it may happen as the result of 
 disease in the Human subject. In xi. we have a very interesting demonstra- 
 tion of the purpose and action of the tympanum, in the more perfect forms of 
 the auditory apparatus. We are now prepared to inquire, in somewhat more 
 

 SENSE OF HEARING. 431 
 
 of detail, into the action of the different parts of this apparatus ; and it will be 
 better to commence with that of the Internal Ear, the accessory organs being 
 afterwards considered. 
 
 563. The object of the Membrana Tympani is evidently to receive the 
 sonorous undulations from the air, in such a manner as to be thrown by them 
 into a recriprocal vibration, which is to be communicated to the chain of bones. 
 This membrane is, in its usual state, rather lax than tense; and this laxity is 
 found by experiment to be, for a small membrane, the best condition for the 
 propagation of ordinary sounds. This is easily rendered sensible in one's 
 own person ; for an increased tension may be given to the membrana tym- 
 pani, either by holding the breath and forcing air into the Eustachian tube, so 
 as to distend it from within, or by exhausting the cavity, so as to cause the 
 external air to make increased pressure upon it. In either case the hearing is 
 found immediately to become indistinct. It is observed, however, that grave 
 and acute sounds are not equally affected by this action ; for the experimenter 
 renders himself deaf to grave sounds, whilst acute sounds are heard even more 
 distinctly than before. This fact is easily understood by referring to the laws 
 of Acoustics already mentioned. The greater the tension to which the mem- 
 brana tympani is subjected, the more acute will be its fundamental tone; and 
 as no proper reciprocation can take place in it, to any sound lower than its 
 fundamental tone, its power of repeating perfectly the vibrations proper to the 
 deeper notes will diminish. The nearer a sound approaches to the funda- 
 mental note proper to the tense membrane, the more distinctly will it be heard. 
 On the other hand, when the membrane is in its natural lax condition, its fun- 
 damental note is very low, and it is capable of repeating a much greater vari- 
 ety of sounds ; for, when it receives undulations of a higher tone, than those 
 to which the whole membrane would reciprocate, it divides itself into distinct 
 segments of vibration, which are separated by lines of rest; and every one of 
 these reciprocates the sound;* at the same time rendering it more intense by 
 multiplication. These facts enable us to understand the influence of the ten- 
 sor tympani muscle, in modifying the tension of the membrane, and thus caus- 
 ing it to vibrate in reciprocation to sounds having a great variety of funda- 
 mental notes. Moreover, the fact that some persons are deaf to grave sounds, 
 whilst they readily hear the more acute, is thus accounted for. The tensor 
 tympani, like the iris, is probably excited to operation by a reflex action ; and 
 it is by no means improbable that one of its functions may be, to prevent the 
 internal ear from being too violently affected by loud sounds, by putting the 
 membrana tympani into such a state of tension, as not readily to reciprocate 
 them. 
 
 564. The uses of the Tympanic cavity are very obvious. One of its pur- 
 poses is, to render the vibrations of the membrane quite free ; and the other, 
 to isolate the chain of bones, in such a manner as to prevent their vibrations 
 from being weakened, by diffusion through the surrounding solid parts. As to 
 the objects of the Eustachian tube, however, opinions have been much divided. 
 From the experiments of Muller it appears, that it does not increase the intens- 
 ity of sound, but that it prevents a certain degree of dulness, which would 
 attend it, if the cavity of the tympanum were completely closed ; of this dul- 
 ness we are conscious, when any tumefaction of the fauces causes an occlusion 
 of the extremity of the tube. It has been supposed that, among other uses, 
 
 * This is very eas.ily proved by experiments on a membrane stretched over a resonant 
 cavity 5 if light sand be strewed upon it, and a strong musical tone be produced in its vicinity, 
 the membrane will immediately be set in vibration, not as a whole (unless its fundamental note 
 be in unison with that sounded), but in distinct segments, of which every one reciprocates the 
 sound ; from the vibrating parts, the sand will be violently thrown off; but it will settle on the in- 
 termediate linesof rest, forming a variety of curious figures, which, are known as the nodal lines. 
 
432 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 this canal serves for the conduction of the speaker's voice to his ears ; but this 
 is certainly not the case in any considerable degree ; for, when the Eustachian 
 tubes are obstructed by disease, the patient hears his own voice well, though 
 other sounds are indistinct; and it is easily shown, that its transmission is 
 chiefly accomplished in other ways. The common idea is, that it serves the 
 same purpose with the hole in an ordinary drum ; the effect of which is gene- 
 rally supposed to be, the removal of the impediment to the vibrations of the 
 membrane, that would be offered by the complete inclosure of the air within. 
 It does not appear, however, that any such impediment is really offered ; and 
 the effect of the hole in the drum seems rather to be the communication, to 
 the ear of the auditor, of the sonorous vibrations of the contained air ; which 
 are thus transmitted directly through the atmosphere, instead of being weak- 
 ened by transmission through the walls of the instrument. Hence there is no 
 real analogy in the two cases. The principal object of the Eustachian tube 
 (which is always found where there is a tympanic cavity), seems to be, the 
 maintenance of the equilibrium between the air within the tympanum and the 
 external air ; so as to prevent inordinate tension of the membrana tympani, 
 which would be produced by too great or too little pressure on either side, 
 and the effect of which would be imperfection of hearing. It also has the 
 office of conveying away mucus secreted in the cavity of the tympanum, by 
 means of cilia vibrating on its lining membrane ; and the deafness, conse- 
 quent on occlusion of this tube, is in part explicable by the accumulation, 
 which will then take place in the tympanum. 
 
 565. From what has been stated, it is evident that sonorous undulations 
 taking place in the air, will be propagated to the fluid contained in the laby- 
 rinth, through the tympanum, the chain of bones, and the membrane of the 
 fenestra ovalis to which the stapes is attached, without any loss, but rather 
 an increase, of intensity. Why water should be chosen as the medium through 
 which the impression is to be made upon the nerve, it is impossible for us to 
 say with anything like certainty, in our present state of ignorance as to the 
 physical character of that impression. But, the problem being, to communi- 
 cate to water the sonorous undulations of air, the experimental results already 
 detailed satisfactorily prove that, whilst this may be accomplished, in a de- 
 gree sufficient for the wants of the inferior animals, by the simple interposition 
 of a tense membrane between the air and the fluid, the tympanic apparatus 
 of the higher classes is most admirably adapted for this purpose. The fenes- 
 tra ovalis is not, however, the only channel of communication between the 
 tympanum and the labyrinth ; for there is, in most animals, a second aperture, 
 the fenestra rotunda, leading into the cochlea, and simply covered with a mem- 
 brane. It is generally supposed that, the labyrinth being filled with a nearly 
 incompressible fluid, this second aperture is necessary to allow of the free 
 vibration of that fluid, the membrane of the fenestra rotunda being made to 
 bulge out, as that of the fenestra ovalis is pushed in. It may, however, be 
 easily shown by experiment, as well as by reference to comparative anatomy, 
 that no such contrivance is necessary ; for sonorous undulations may be ex- 
 cited in a non-elastic fluid, completely inclosed within solid walls at every 
 part, except where these are replaced by the membrane through which the 
 vibrations are propagated ; and this is precisely the condition, not only of the 
 Invertebrated animals, but even of Frogs ; in which last a tympanic apparatus 
 exists, without a second orifice into the labyrinth. Moreover it is certain, that 
 the vibrations of the air in the cavity of the tympanum, must of themselves 
 act upon the membrane of the fenestra rotunda; and this is perhaps the most 
 direct manner in which the fluid in the cochlea will be affected ; although it 
 will ultimately be thrown into much more powerful action, by the transmission 
 of vibrations from the vestibule. For it has been satisfactorily determined by 
 
SENSE OF HEARING. 
 
 [Fig. 191. 
 
 433 
 
 The labyrinth of the Left Ear, laid open in order to show its cavities and the Membranous Labyrinth ; 
 after Breschet ; 1, the cavity of the vestibule, opened from its anterior aspect in order to show the three- 
 cornered form of its interior, and the membranous labyrinth which it contains ; the figure rests upon the 
 common saccule of the membranous labyrinth the sacculus communis ; 2, the ampulla of the superior 
 or perpendicular semicircular canal, receiving a nervous fasciculus from the superior branch of the 
 vestibular nerve ; 3, 4, the superior or perpendicular canal with its contained membranous canal ; 5, the 
 ampulla of the inferior or horizontal semicircular canal, receiving a nervous fasciculus from the superior 
 branch of the vestibular nerve ; 6, the termination of the membranous canal of the horizontal semicircular 
 canal in the sacculus communis ; 7, the ampulla of the middle or oblique semicircular canal, receiving a 
 nervous fasciculus from the inferior branch of the vestibular nerve ; 8, the oblique semicircular canal 
 with its membranous canal ; 9, the common canal, resulting from the union of the perpendicular with 
 the oblique semicircular canal ; 10, the membranous common canal terminating in the sacculus com- 
 munis ; 11, the otoconite of the sacculus communis seen through the membranous parietes of that sac ; a 
 nervous fasciculus from the inferior branch of the vestibular nerve is seen to be distributed to the saccu- 
 lus communis near to the otoconite ; the extremity of the sacculus above the otoconite is lodged in the 
 superior ventricle of the vestibule, and that below it in the inferior ventricle ; 12, the sacculus proprius 
 situated in the anterior ventricle ; its otoconite is seen through its membranous parietes, and a nervous 
 fasciculus derived from the middle branch of the vestibular nerve, is distributed to it ; the spaces around 
 the membranous labyrinth are occupied by the aqua labyrinthi; 13, the first turn of the cochlea; the 
 figure is situated in' the scala tympani; 14, the extremity of the scala tympani corresponding with the 
 fenestra rotunda; 15, the lamina spiralis ; the figure is situated in the scala vestibuli ; 16, the opening of 
 the scala vestibuli into the vestibule; 17, the second turn of the cochlea; the figure is placed upon the 
 lamina spiralis, and, therefore, in the scala vestibuli, the scala tympani being beneath the lamina; 18, 
 the remaining half turn of the cochlea ; the figure is placed in the scala tympani; 19, the lamina spiralis 
 terminating in a falciform extremity ; the dark space included within the falciform curve of the extremity 
 of the lamina spiralis is the helicotrema; 20, the infundibulum.] 
 
 experiment (xii.), that vibrations are transmitted with very much greater in- 
 tensity to water, when a tense membrane, and a chain of insulated solid bodies 
 capable of free movement, are successively the conducting media, than when 
 the media of communication between the vibrating air and the water are the 
 same tense membrane, air, and a second membrane : or, to apply this fact 
 to the organ of hearing, the same vibrations of the air act upon the fluid of the 
 labyrinth with much greater intensity, through the medium of the chain of 
 auditory bones and the fenestra ovalis, than through the medium of the air of 
 the tympanum and the membrane closing the fenestra rotunda. The fenestra 
 rotunda is not to be considered as having any peculiar relation with the cochlea ; 
 since, in the Turtle tribe, the former exists without the latter. 
 
 566. In regard to the functions of particular parts of the labyrinth, no cer- 
 tainty can be said to exist. From the experimental results already stated, it 
 appears likely that, the greater the extension of the cavity into the dense sub- 
 stance of the bone, the greater will be the resonance communicated to the 
 fluid, and thence transmitted to the nerves exposed to its influence. It is 
 37 
 
434 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 [Fig. 192. 
 
 A view of the labyrinth of the Left Side, laid open in its whole extent so as to show its Structure ; these 
 figures are all magnified ; 1, the thickness of the outer covering of the cochlea; 2, 2, the scala vestibuli 
 or upper layer of the lamina spiralis ; 3, 3, the scala tympani or lower layer of the lamina spiralis ; 4, the 
 hamulus cochleae ; 5, centre of the infundibulum ; 6, the foramen rotundum communicating with the tym- 
 panum ; 7, the thickness of the outer layer of the vestibule ; 8, the foramen rotundum ; 9, the fenestra 
 ovalis ; 10, the orifice of the aqueduct of the vestibule ; 11, the inferior semicircular canal ; 12. the superior 
 semicircular canal ; 13, the external semicircular canal ; 14, the ampulla of the inferior canal ; 15, the 
 ampulla of the superior canal ; 16, the common orifice of the superior and inferior canals ; 17, the ampulla 
 of the external canal.] 
 
 commonly supposed that the Semicircular Canals have for their peculiar func- 
 tion, the reception of the impressions by which we distinguish the direction of 
 sounds; and it is certainly a powerful argument in support of this view, that, 
 in almost every instance in which these parts exist at all, they hold the same 
 relative position to each other as in Man, their three planes being nearly at 
 right angles to one another. The idea, however, must be regarded as a mere 
 speculation, the value of which cannot be decided without an increased know- 
 ledge of the laws, according to which sonorous vibrations are transmitted. 
 Regarding the special function of the Cochlea, there is precisely the same un- 
 certainty. This part of the organ is peculiar in one respect, that the expan- 
 sion of the auditory nerve is here spread out (upon the lamina spiralis) in 
 closer proximity with the bone itself, than it is in any other part of the laby- 
 rinth ; so that the vibrations of the bone will be more directly communicated 
 to the nerve. It is not easy to see, however, what can be the peculiar object 
 of this disposition, in regard to the function of hearing. By M. Duges it is 
 surmised, that by the cochlea we are especially enabled to estimate the pitch 
 of sounds, particularly of the voice ; and he adduces, in support of this idea, 
 the fact, that the development of the cochlea follows a very similar proportion 
 with the compass of the voice. This is much the greatest in the Mammalia; 
 less in Birds ; and in Reptiles, which have little true vocal power, the cochlea 
 is reduced to its lowest form, disappearing entirely in the Amphibia. That 
 there should be an acoustic relation between the voice and ear of each species 
 of animal, cannot be regarded as improbable ; but the speculation of M. Duges 
 can at present only be received as a stimulus to further inquiry. 
 
 567. We have now to consider the functions of the accessory parts, the 
 External Ear, and the Meatus. The Cartilage of the external ear may pro- 
 
SENSE OF HEARING. 
 
 435 
 
 pagate sonorous vibrations in two ways, by reflection, and by conduction. 
 In reflection, the concha is the most important part, since it directs the reflected 
 undulations towards the tragus, whence they are thrown into the auditory 
 passage. The other inequalities of the external ear cannot promote hearing 
 by reflection ; and the purpose of the extension of its cartilage is evidently to 
 receive the sonorous vibrations from the air, and to conduct them to its point 
 of attachment. In this point of view, the inequalities become of importance ; 
 for those elevations and depressions upon which the undulations fall perpen- 
 dicularly, will be affected by them in the most intense degree ; and in conse- 
 
 [Fig. 193. 
 
 [Fig. 194. 
 
 A view of the Left Ear in its natural state ; 1, 2, 
 the origin and termination of the helix ; 3, the anti- 
 helix ; 4, the anti-tragus ; 5, the tragus ; 6, the lobus 
 of the external ear ; 7, points to the scapha and is on 
 the front and top of the pinna ; 8, the concha; 9, the 
 meatus auditorius externus.] 
 
 An anterior view of the External Ear, as well 
 as of the Meatus Auditorius, Labyrinth, &c. ; 1, 
 the opening into the ear at the bottom of the con- 
 cha ; 2, the meatus auditorius externus or car- 
 tilaginous canal ; 3, the membrana tympani 
 stretching upon its ring ; 4, the malleus ; 5, the 
 stapes ; 6. the labyrinth.] 
 
 quence of the varied form and position of these inequalities, sonorous undula- 
 tions, in whatever direction they may come, must fall advantageously upon 
 some of them. The functions of the Meatus appear to be threefold. The 
 sonorous undulations entering from the atmosphere are propagated directly, 
 without dispersion, to the membrana tympani : the sonorous undulations 
 received on the external ear, are conveyed along the walls of the meatus to 
 the membrana tympani: the air which it contains, like all insulated masses 
 of air, increases the intensity of sounds by resonance. That, in ordinary 
 hearing, the direct transmission of atmospheric vibrations to the membrana 
 tympani, is the principal means of exciting the reciprocal vibrations of the 
 latter, is sufficiently evident ; the undulations which directly enter the passage, 
 will pass straight on to the membrane ; whilst those that enter obliquely will 
 be reflected from side to side, and at last will fall obliquely on the membrane, 
 thus perhaps contributing to the notion of direction. The power of the lining 
 of the meatus to conduct sound from the external ear, is made evident by the 
 fact, that, when both ears are closely stopped, the sound of a pipe having its 
 lower extremity covered by a membrane, is heard more distinctly, when it is 
 applied to the cartilage of the external ear itself, than when it is placed in con- 
 tact with the surface of the head. The resonant action of the air in the tube 
 is easily demonstrated, by lengthening the passage by the introduction of 
 
436 ON SENSATION, AND THE ORGANS OF THE SENSES. 
 
 another tube ; the intensity of external sounds, and also that of the individual's 
 own voice, as heard by himself, is then much increased. 
 
 568. Many facts prove, however, that the fluid of the labyrinth may be 
 thrown into vibration in other ways, than by the tympanic apparatus. Thus 
 in Osseous Fishes, it is only by the vibrations transmitted through the bones 
 of the head, that hearing can take place. There are many persons,' again, 
 who can distinctly hear sounds which are thus transmitted to them ; although, 
 through some imperfection of the tympanic apparatus, they are almost insen- 
 sible to those which they receive in the ordinary way. It is evident, where 
 this is the case, that the nerve must be in a state fully capable of functional 
 activity ; and, on the other hand, where sounds cannot thus be perceived, 
 there will be good reason to believe that the nerve is diseased. 
 
 569. A single impulse communicated to the Auditory nerve, in any of the 
 foregoing modes, seems to be sufficient to excite the momentary sensation of 
 sound; but most frequently a series of such impulses is concerned, there 
 being but few sounds which do not partake, in a greater or less degree, of 
 the character of a tone. Any continuous sound or tone is dependent upon a 
 succession of such impulses ; and its acuteness or depth is governed by the 
 rapidity with which they succeed one another. 
 
 a. It. is not difficult to ascertain by experiment, what number of such impulses or undula- 
 tions are required, to give every tone which the ear can appreciate. Thus, if a circular plate, 
 with' a number of apertures at regular intervals, be made to revolve over the top of a pipe 
 through which air is propelled, a succession of short pvffs will be allowed to issue from this; 
 and, if the revolution is sufficiently rapid, these impulses will unite into a definite tone. In 
 the same manner, if a spring be fixed near the edge of a revolving toothed wheel, in such 
 a manner as to be caught by every tooth as it passes, a succession of clicks will be heard ; 
 and these too, if the revolution of the wheel be sufficiently rapid, will produce a tone. The 
 number of apertures in the plate, which pass the orifice of the pipe in a given time, or the 
 number of teeth which pass the spring, being known, it is easy to see, that this must be the 
 number of impulses required to produce the given tone. Each impulse produces a double 
 vibration, forwards and backwards (as is seen when a string is put in vibration, by pulling 
 it out of the straight line) ; hence the number of impulses is always half that of the single 
 vibrations. The maximum and minimum of the intervals of successive pulses, still appre- 
 ciable by the ear as determinate sounds, have also been determined by M. Savart, more satis- 
 factorily and more accurately than had previously been done. If their intensity is great, 
 sounds are still audible which result from the succession of 24,000 impulses in a second ; 
 and this, probably, is not the extreme limit to the acuteness of sounds perceptible by the ear. 
 From some observations of Dr. Wollaston's, it seems probable that the ears of different indi- 
 viduals are differently constituted in this respect, some not being able to hear very acute 
 tones produced by Insects, or even Birds, which are distinctly audible to others. Again, the 
 sound resulting from 16 impulses per second, is not, as has been usually supposed, the lowest 
 appreciable note ; on the contrary, M. Savart has succeeded in rendering tones distinguisha- 
 ble, which are produced by only 7 or 8 impulses in a second; and continuous sounds of a 
 still deeper tone could be heard, if the individual pulses were sufficiently prolonged. In 
 regard, however, to the precise time during which a sonorous impression remains upon the 
 ear, it is difficult to procure exact information, since it departs more gradually than do visual 
 impressions from the eye. This is certain, however, that it is much longer than the interval 
 between the successive pulses in the production of tones; since it was found by M. Savart, 
 that one or even several teeth might be removed from the toothed wheel, without a percep- 
 tible break in its sound, showing that, when the tone was once established, the impression 
 of it remained during an intermission of some length. 
 
 570. The Ear may, like the Eye, vary considerably, as regards general 
 acuteness amongst different individuals; and its power may be much increased 
 by practice. A part of this increase depends, however, as in other instances, 
 upon the greater attention which its fainter indications receive ; but a part, 
 also, upon an increased use of the organ. The power of hearing very faint 
 sounds, is as different from the power of distinguishing musical tories, as the 
 power of discerning very minute objects, or of seeing with very faint degrees 
 of light, is from that of distinguishing colours. Many persons are altogether 
 
SENSE OF HEARING. 437 
 
 destitute of what is termed a musical ear ; whilst others are endowed with it 
 in a degree, which is a source of great discomfort to them, since every discord- 
 ant sound is a positive torment. The power of distinguishing the direction 
 of sounds appears to be, in Man, at least, for the most part acquired by habit. 
 It is some time before the infant seems to know anything of the direction of 
 noises, which attract his attention. Now although there can be no question, 
 that this perception is acquired by attention to certain variations in the impres- 
 sion made upon the nerve, through the medium either of the tympanic appa- 
 ratus, or of the bones of the head, yet it is equally evident, that there can be 
 nothing in these variations themselves adequate to excite the idea, and that it 
 must therefore be either intuitive or acquired by habit. This is a considera- 
 tion of some importance, in regard to the similar question as to the sense of 
 Visual direction. In some cases we are probably assisted by the relative in- 
 tensity of the sensations, communicated by the two ears respectively. The 
 idea of the distance of the sonorous body is another acquired perception, de- 
 pending principally upon the loudness or faintness of the sound, when we 
 have no other indications to guide us. In this respect, there is a great simi- 
 larity between the perception of the distance of an object, through the Eye, 
 by its size, and through the Ear, by the intensity of its sound. When we 
 know the size of the object, or are acquainted with the usual intensity of its 
 sound, we can judge of its distance ; and vice versa, when we know its dis- 
 tance, we can at once form an idea of its real from its apparent size, and of 
 its real strength of tone from that which affects our ears. In this manner, 
 the mind may be affected with corresponding deceptions through both senses ; 
 thus, in the Phantasmagoria, the figure is gradually diminished whilst its dis- 
 tance remains the same, and it appears to the spectators to recede, the illu- 
 sion being more complete, if its brightness be at the same time diminished ; 
 and the effect of a distant full military band gradually approaching, may be 
 alike given by a corresponding crescendo of concealed instruments. It is upon 
 the complete imitation of the conditions which govern our ideas of the intensity 
 and direction, as well as of the character, of sounds, that the deceptions of the 
 Ventriloquist are founded. 
 
 571. Some facts of much interest have lately been ascertained, in regard to 
 an occasional variation in the rapidity of the perception of sensory impres- 
 sions, received through the Eye and through the Ear. These facts are the 
 result of comparisons made amongst different astronomical observers, who 
 may be watching the same visual phenomena, and timing their observations 
 by the same clock ; for it has been remarked, that some persons see the same 
 phenomenon, a third or even half of a second earlier than others. There is 
 no reason to suppose from this, however, that there is any difference in the 
 rate of transmission of the sensory impressions in the two nerves. The fact 
 seems rather to be, that the sensorium does not readily perceive two different 
 impressions with equal distinctness ; and that, when several impressions are 
 made on the nerves at the same time, the mind takes cognizance of one only, 
 or perceives them in succession. When, therefore, both sight and hearing are 
 directed simultaneously to one object, the communication of the impression 
 through one sense will necessarily precede that made by the other. The in- 
 terval between the two sensations is greater in some persons than in others ; 
 for some can receive and be conscious of many impressions, seemingly at 
 the same moment ; whilst in others a perceptible space must elapse. 
 
 572. Amongst other important offices of the power of Hearing, is that of 
 supplying the sensations by which the Voice is regulated. It is well known 
 that those who are born entirely deaf, are also dumb, that is, destitute of the 
 power of forming articulate sounds ; even though not the least defect exist in 
 their organs of* voice. Hence it appears that the vocal muscles can only be 
 
 37* 
 
438 OF MUSCULAR CONTRACTION. 
 
 guided in their action by the sensations received through the Ears, in the same 
 manner as other muscles are guided by the sensations received through them- 
 selves ( 433). On this point, more will be said hereafter ( 611). 
 
 C H APTE R VII. 
 
 OF MUSCULAR ACTIpN. 
 
 I. Of Contractility in General. 
 
 573. THE Nervous System has no power of occasioning movement in any 
 part of the body, save by exciting to contraction certain structures, to which 
 the term Muscular is given. That one tissue should possess within itself the 
 property of Contractility on the application of a stimulus, is no more wonderful, 
 than that another should be capable of conveying sensory or motor influences, 
 or another of separating a peculiar secretion from the blood. Such contractile 
 tissues are found in Vegetables, as well as in Animals ; and they appear to 
 consist, in both instances, of cells, whose peculiar property it is to change 
 their form, when subjected to certain kinds of irritation ( 230). The only 
 essential difference in function, between the Contractility of the cells compos- 
 ing the ultimate fibrillae of Muscular Fibre, and that of the cells composing 
 the intumescence of the Sensitive Plant, consists in the susceptibility of the 
 former to a stimulus, which does not operate on the latter. Both can be made 
 to change their form by stimuli of various kinds, mechanical, chemical, 
 electrical, &c., directly applied to themselves ; but the contractility of Mus- 
 cular fibre is excited, in addition, by the stimulus of Innervation, which has 
 no operation in the Plant ; and it is when its peculiar property is thus excited, 
 that the Muscular tissue becomes the instrument of the operation of the Nerv- 
 ous system upon the external world, and thus performs an important part in 
 the purely Animal Functions. The Muscular tissue, however, is not always 
 thus called into activity through the medium of the Nervous system ; for it is 
 employed to execute numerous movements, which are immediately connected 
 with the maintenance of the Organic functions, and in which the influence of 
 Innervation seems to be but little concerned ; its contractility being excited to 
 action by stimuli directly applied to itself. We have seen that there are two 
 forms of Muscular tissue, the striated and the non-striated, which are appro- 
 priated to these two purposes ; the former being the kind most readily acted 
 on through the Nervous System, and invariably employed in the Muscles that 
 are called into action by its influence ; whilst the latter (which seems a less 
 perfectly-developed form of the tissue) is with difficulty excited to contraction 
 through the Nervous System, and is usually employed in Muscles, whose 
 action is altogether uncontrollable by the will ( 225 234). 
 
 574. The general property of Contractility shows itself under two forms ; 
 which are alike distinct in the mode of their action, and in the conditions 
 requisite for its excitation. Its most obvious and striking manifestations pre- 
 sent themselves in the Voluntary muscles and in the Heart ; which, when in 
 activity, exhibit powerful contractions tending to alternate with relaxations. 
 The modification of contractility which is concerned in producing these, is 
 distinguished as Irritability. On the other hand, we find that the muscles 
 
OF MUSCULAR IRRITABILITY. 439 
 
 exhibit a tendency to a moderate and permanent contraction, which is not 
 shown by them when they are dead, and which cannot, therefore, be the re- 
 sult of elasticity, or of any simple physical property ; and the contraction, 
 instead of being a result of stimulation through the nerves, is especially ex- 
 cited by changes of temperature in the tissue itself. This endowment, which 
 seems to exist in the greatest amount in certain forms of the non-striated 
 muscle, is called Tonicity. These two modifications of Muscular Contract- 
 ility require a separate consideration. 
 
 2.' Of Muscular Irritability. 
 
 575. All Muscular Fibres, which are in possession of vital activity, may be 
 caused to contract by stimuli directly applied to themselves ; and these stimuli 
 may be of different kinds. The simplest is the contact of a solid substance, 
 especially if it be pointed ; thus we may excite contractions in Muscular 
 fibres, by simply touching them with the point of a needle or of a scalpel. 
 Most substances of strong chemical action, such as acids and alkalies, will ex- 
 cite the fibres to contraction, when directly applied to themselves ; but the 
 most powerful agent of all is Electricity. If we thus irritate a portion of a 
 muscle composed of striated fibre, the biceps, for example, the fasciculus of 
 fibres which is touched will immediately contract, and that one only ; and the 
 contracted fasciculus will soon relax, without communicating its movements 
 to any other. In fact, the only way to call the entire muscle into contraction 
 at once (since it would be impossible to apply direct irritation to every fasci- 
 culus), is to stimulate it through its nerves. On the other hand, if we apply 
 a similar irritation to a portion of non-striated fibre, as that of the Intestinal 
 canal, the fasciculus which is stimulated will contract less suddenly, but ulti- 
 mately to a greater amount ; its relaxation will be less speedy ; and, before it 
 takes place, other fasciculi in the neighbourhood begin to contract ; their con- 
 traction propagates itself to others ; and so on. In this manner, successive 
 contractions and relaxations may be produced through a considerable part of 
 the canal, by a single prick with a scalpel ; a sort of wave of contraction being 
 transmitted in the direction of its length, and being followed by relaxation. 
 Again, in the Muscular structure of the Bladder and Uterus (which is of the 
 non-striated kind), direct irritation excites immediate and powerful contractions, 
 which extend beyond the fasciculus actually irritated, and produce a great 
 degree of shortening ; but they do not alternate in the healthy state with any 
 rapid arjd decided elongation. In the Heart, which is composed of a mixture 
 of striated and non-striated fibre, the Muscular substance of a large part of the 
 organ is thrown into rapid and energetic contraction, by a stimulus applied at 
 any one point ; and this contraction is speedily followed by relaxation, which 
 is again succeeded by a number of alternating contractions and relaxations. 
 And in the muscular tissue of the middle coat of the Arteries, which is of the 
 non-striated character, the contraction takes place rather after the manner of 
 that of the bladder and uterus ; a considerable degree of shortening being 
 effected, by the contraction of other fasciculi than those directly irritated, and 
 this shortening not giving way speedily to relaxation ; but a prolonged appli- 
 cation of the stimulus is often necessary to produce the effect. 
 
 576. On the other hand, when the stimuli which excite Muscular Contrac- 
 tility are applied to the nerves, which supply any muscle composed of striated 
 fibre (the Heart only excepted), they produce a simultaneous contraction in the 
 whole muscle ; the effect of the stimulus being at once exerted upon every part 
 of it. The contraction speedily alternates with relaxation, unless the operation 
 of the stimulus be continued, as when an electric current is propagated with- 
 out intermission along the nerve-trunks, in which case the contraction lasts as 
 
440 OF MUSCULAR CONTRACTION. 
 
 long as the stimulus is continuously applied, but ceases as soon as it is with- 
 drawn. But it has been lately stated by Volkmann,* that, if the electric 
 stimulus be applied to the central organs, from which the motor nerves arise, 
 the muscular contraction continues for some time after its renewal. If this 
 should prove to be a universal fact, it will afford a valuable means of distin- 
 guishing what are the real centres of the motor nerves of particular organs. 
 Further, when the continuous electric current was passed through incident or 
 excitor nerves, it produced alternating movements of contraction and relaxa- 
 tion, in the muscles which were thus called into play by reflex stimulation. 
 The ordinary actions of the non-striated fibre, on' the other hand, are not 
 easily excitable by stimuli applied to their nerves ; indeed many Physiologists 
 have denied the possibility of producing them through this channel. Positive 
 evidence to this effect, however, has been already given ( 388). The results 
 of Volkmann's recent electrical experiments upon the Heart and the Intesti- 
 nal Canal are of much interest. He found that neither of these organs is 
 thrown into fixed contraction, when the continuous electric current is applied 
 to the Brain and Spinal Cord; whence he concludes that these organs are not 
 the centres of their motor nerves. On the other hand, alternating contrac- 
 tions and relaxations were produced on applying the continuous current to 
 the spinal cord, the par vagum, and the sympathetic nerves ; whence it may 
 be concluded that these parts contain afferent fibres, which excite motion 
 through centres that can scarcely be any others than the ganglia of the Sym- 
 pathetic system. When the Heart is removed from the body, and is left en- 
 tire, it may be thrown into a state of fixed contraction, which lasts after the 
 cessation of the current ; whence it may be concluded, that it contains the 
 centre of its own motor nerves.t These experiments, however, by no means 
 warrant the conclusion, that the ordinary actions of these muscular organs are 
 dependent upon the agency of their nerves ; which is opposed by a variety of 
 evidence. 
 
 577. The general fact, that Muscular Contraction alternates with Relaxa- 
 tion at no longer intervals, is most evident in the rhythmical movements of 
 the Heart, and in the peristaltic action of the Intestinal canal ; since in those 
 parts, the whole or a large proportion of the fibres seem to contract together, 
 and then shortly relax. But it is probably no less true, as formerly stated 
 ( 232), of the individual fibres of those muscles, which are kept in a state 
 of contraction by a stimulus transmitted through their nerves ; since none of 
 them appear, under ordinary circumstances at least, to remain in a contracted 
 state for any length of time, a constant interchange of condition taking place 
 among the fibres, some contracting whilst others are relaxing, and vice versa. 
 It is difficult to speak with confidence, however, in regard to the condition of 
 the individual fibres of a muscle, that is thrown into a state of continued 
 spasmodic contraction ; such as that produced by the application of the elec- 
 tric current to the centre of its motor nerves ( 576). A state of this kind is 
 often of considerable duration. Thus the Author has known a case of Hys- 
 teric Trismus, in which the jaws remained closed with the greatest violence 
 during five days. Whether the individual fibres, in such instances, maintain 
 a state of contraction without intermission, or whether the -contraction of the 
 entire muscle is kept up by a continual interchange of the fibres actually en- 
 gaged, is a very curious subject for inquiry. 
 
 578. Muscles do not lose their Irritability immediately on the general 
 death of the system, which must be considered as taking place, when the cir- 
 culation ceases without a power of renewal ; in cold-blooded animals it is re- 
 
 * Muller's Archiv., 1844, No. 5, p. 407. 
 
 t Op. cit.j and Mr. Paget's Report for 1845, in Brit, and For. Med. Rev., July, 1846. 
 
LOSS OF IRRITABILITY BY AFFECTIONS OF THE NERVOUS SYSTEM. 441 
 
 tained much longer after this period than in the higher Vertebrata, in some 
 of which it disappears within an hour. The muscles of young animals 
 generally retain their irritability for a longer time than those -of adults ; on 
 the other hand, those of Birds lose their irritability sooner than those of Mam- 
 malia. Hence, as a general rule, the duration of the irritability is inversely 
 as the amount of respiration. From experiments on the bodies of executed 
 criminals, who were previously in good health, Nysten ascertained that, in 
 the Human subject, the irritability of the several muscular structures departs 
 in the following time and order. The left ventricle of the heart first ; the in- 
 testinal canal at the end of 45 or 55 minutes ; the urinary bladder nearly at 
 the same time ; the right ventricle after the lapse of an hour ; the ossophagus 
 at the expiration of an hour and a half; the iris a quarter of an hour later ; 
 the muscles of Animal life somewhat later ; and lastly, the auricles of the 
 heart, especially the right, which in one instance contracted under the influ- 
 ence of galvanism 16 hours after death. 
 
 579. Muscular Irritability is deadened by many substances, especially by 
 those which have a narcotic or sedative action on the Nervous system. In 
 carbonic acid gas, hydrogen, carbonic oxide, or sulphurous acid gas, muscles 
 contract very feebly, or not at all, when stimulated ; whilst in oxygen they 
 retain their irritability longer than usual. Narcotic substances, such as a watery 
 solution of opium, when applied directly to the muscles, have an immediate 
 and powerful effect in diminishing or even destroying their irritability ; this 
 effect is also produced, though in a less powerful degree, by injecting these 
 substances into the blood. In the same manner, venous blood, charged with 
 carbonic acid, and deficient in oxygen, has the effect of a poison upon 
 muscles ; diminishing their irritability, when it continues to circulate through 
 them, to such a degree, that they sometimes lose it almost as soon as the cir- 
 culation ceases, as is seen in those who have died from gradual and therefore 
 prolonged Asphyxia. The unfavourable influence of venous blood is also 
 shown in the Morbus Co3ruleus ; patients affected with which are incapable 
 of any considerable muscular exertion. Although most of the stimuli which 
 occasion the contraction of muscles, when directly applied to their fibres, ope- 
 rate also when applied to their motor nerves, the same does not hold good in 
 regard to those agents which diminish irritability. It is a fact of some im- 
 portance, in relation to the disputed question of the connection of muscular 
 irritability with the nervous system, that when, by the application of narcotic 
 substances to the Nerves, their vital properties are destroyed, the irritability 
 of the Muscle may remain for some time longer, showing that the latter 
 must be independent of the former. 
 
 580. We find, however, that sudden and severe injuries of the Nervous 
 Centres have power to impair, directly and instantaneously, or even to destroy? 
 the Contractility of the whole Muscular system ; so that death immediately 
 results, and no irritability subsequently remains. It is in this manner, that 
 the sudden destruction of the Brain anid Spinal Cord, especially of the latter, 
 occasions the immediate cessation of the Heart's action ; though they may be 
 gradually removed, without any considerable effect upon it. Severe concus- 
 sion has the same effect ; hence the Syncope which immediately displays it- 
 self. It is sometimes an important question in Forensic Medicine, whether 
 an individual, who has died from the effects of a blow upon the head, could 
 have moved from the place where the blow was inflicted. If there be found, 
 as is frequently the case, no sensible disorganization of the Brain, the death 
 must be attributed to the concussion, and must have been in that case imme- 
 diate. If, on the other hand, effusion of blood has taken place within the 
 cranium, to any considerable extent, it is probable that the first effects of the 
 blow were in some degree recovered from, and that the circulation was re- 
 
442 OF MUSCULAR CONTRACTION. 
 
 established. It is not essential, however, that the impression should be prima- 
 rily made upon the Cerebro-Spinal system. The well-known fact of sudden 
 death not unfrequently resulting from a blow on the stomach, especially after 
 a full meal, without any perceptible lesion of the viscera, clearly indicates that 
 an impression upon the widely-spread coeliac plexus of Sympathetic nerves 
 (which will be much more extensively communicated to them, when the sto- 
 mach is full, than when it is empty), may cause the immediate cessation of 
 the Heart's action, in the same manner as a violent injury of the Brain or 
 Spinal Cord. Now it is interesting to remark that, in all these cases, the 
 whole vitality of the system appears to be destroyed at once ; for the pro- 
 cesses which would otherwise succeed the injury, and which, after other kinds 
 of death, less sudden in their character, produce evident changes in the part 
 of the surface that has immediately received it, are here entirely prevented. 
 An instance is on record, in which a criminal under sentence of death deter- 
 mined to anticipate the law by self-destruction. Having no other means of 
 accomplishing his purpose, he stooped his head and ran violently against the 
 wall of his cell ; he immediately fell dead ; and no mark of contusion showed 
 itself on his forehead. The same absence of the usual results is to be noticed 
 in the case of blows on the stomach. Yet it is well known, that many of the 
 ordinary vital processes will take place in the injured parts, after death of a 
 more lingering nature ; the vitality of the individual organs not being destroyed 
 immediately on the severance of the chain which binds together the different 
 functions. Hence the Irritability of Muscle is not shown, by the foregoing 
 facts, to have any closer dependence upon the Nervous system, than have the 
 peculiar vital properties of any other tissue. 
 
 581. The influence of severe impressions on the Nervous System, in di- 
 minishing, where it does not altogether destroy, Muscular Irritability, is well 
 seen in the effect of severe injuries affecting vital organs, or extending over a 
 large part of the surface, in depressing the Heart's action. This is a well- 
 known result of severe burns, especially in children, whose nervous system 
 is more susceptible of such impressions than that of the adult; also of the 
 rupture of the alimentary canal, of the bladder or uretus ; and of the shatter- 
 ing of one of the extremities, by violence affecting a large part of their sub- 
 stance. In all these cases, the sufferer is in the same condition with one who 
 has received a severe blow on the head, that does not quite stun him ; the 
 shock immediately diminishes the muscular contractility of the whole sys- 
 tem ; and its influence on the heart, which of course manifests itself most 
 conspicuously, produces a degree of depression which is frequently never re- 
 covered from, and which, at any rate, renders necessary the employment of 
 stimulants, for the purpose of counteracting this very dangerous effect.* Ex- 
 fcessive mental emotion, of a kind not in itself depressing, may occasion the 
 sudden cessation of the Heart's action, and a general loss of muscular Irrita- 
 bility; and it is well known that muscular power is greatly diminished by 
 emotions, which produce no other direct action. 
 
 582. There is no evidence that Muscular Irritability can be increased by 
 any cause operating through the Nervous system. It is quite true that, under 
 
 * The large quantity of stimulus which can be borne even by children, suffering under 
 severe burns, is very extraordinary. There can be no doubt that many lives have been 
 saved by the judicious administration of them, to an amount which would, iH> priori, have 
 been judged in itself fatal ; but that many more have been sacrificed to neglect, even on the 
 part of those whose duty it is to watch the indications with the closest attention. The Au- 
 thor's observation leads him to believe, that Hospital-Nurses very commonly make up their 
 minds, that children, who have met with severe burns, must die ; and that, unless closely 
 watched, they neglect the means of which Science and Experience alike dictate the free em- 
 ployment. 
 
INFLUENCE OF ARTERIAL BLOOD. 443 
 
 the stimulus of alcohol, nitrous oxide, &c., or of some purely mental excite- 
 ment, individuals can perform actions requiring a degree of strength, which 
 they cannot exert under any other circumstances. But it does not hence fol- 
 low, that the irritability is increased ; since the energy of the action may be 
 due solely to the power of the stimulus by which it is excited, and to the un- 
 usual number of fibres called into simultaneous contraction. It is well known 
 that stimulating agents, which thus temporarily increase Muscular power, pri- 
 marily excite the Nervous system ; as is shown by the increased mental acti- 
 vity which results from the moderate use of alcohol, nitrous oxide, opium, 
 &c. ; and it does not seem necessary, therefore, to go further in search of an 
 explanation of their effect on muscular action. It is worthy of remark that, 
 whilst the influence of general depressing causes acting through the Nervous 
 System, is primarily manifested on the muscles of Organic life, that of stimu- 
 lants chiefly shows itself in the muscles subjected to the Will. 
 
 583. There can be no question that, in the living body, the energy of Mus- 
 cular contraction is determined (other things being equal), by the supply of 
 Arterial Blood, which the muscle receives. It is well known that, when a 
 ligature is applied to a large arterial trunk in the Human subject, there is not 
 only a deficiency of sensibility in the surface, but also a partial or complete 
 suspension of muscular power, until the collateral circulation is established. 
 The same result has been constantly attained, in experiments upon the lower 
 Animals ; the contractility of the muscle being impaired or altogether ex- 
 tinguished, when the flow of blood into it was arrested ; and being recovered 
 again, when the supply of blood was restored. The influence of this supply 
 of arterial blood is twofold ; it affords the materials for the nutrition of the 
 tissue ; and it furnishes (what is perhaps more immediately necessary) the 
 supply of oxygen required for that metamorphosis of the tissue, which seems 
 to be an essential condition of the generation of its contractile force. As this 
 oxygen is taken in through the lungs, and as the greater part of it is thrown 
 off when united with carbon into carbonic acid by the same channel, we 
 should expect to find a very close correspondence between the amount of 
 muscular power developed in an animal, and the quantity of oxygen consumed 
 in its Respiration : and this is in reality the case. We find, for example, that 
 in Birds and Insects, whose respiration is the highest, the muscular power is 
 greater in proportion to their size, than in any other animals. In the Mam- 
 malia, and certain Fishes that might be almost called warm-blooded, it is only 
 in a degree inferior. But in the cold-blooded Reptiles, Fishes, and Moljusca, 
 the muscular power is comparatively feeble ; though even here we trace gra- 
 dations, which accord well with the relative quantities of oxygen consumed. 
 But in proportion to the feebleness of the power, do we usually find its dura- 
 tion greater ( 578) ; so that it is not so immediately dependent upon the 
 supply of oxygen, in cold-blooded, as in warm-blooded animals. Thus, it is 
 found that Frogs are still capable of voluntary movement, after the heart has 
 been cut out ; they can move limbs which are connected with the trunk by 
 the nerves alone : and that this power is not altogether due to the blood which 
 may remain in the capillary vessels, is shown by the experiment of Muller, 
 who found the muscles still contractile, after he had expelled all the blood, 
 by forcing a current of water into an artery, until it escaped from the divided 
 veins. 
 
 584. It seems probable that the Muscles of Organic life are less dependent 
 upon a supply of arterialized blood, than are those of Animal life ; for the 
 Heart will continue to contract, when the blood in its vessels is entirely ven- 
 ous, and when the circulation in it has come to a stand. Still the dependence 
 of its action upon a constant supply of arterial blood, is very close ; and in all 
 animals, however different the plans of their circulation, we find a provision 
 
444 OF MUSCULAR CONTRACTION. 
 
 for this supply, by a special arrangement of the coronary arteries.* That the 
 heart's action comes to an end much sooner, after the destruction of animal 
 life by pithing, when the coronary arteries have been tied, than when they 
 are left untouched, has been proved by the experiments of Mr. Erichsen.t 
 In an animal that has been pithed, but whose heart has been left intact, artificial 
 respiration will easily keep up its action for an hour, or an hour and a half. 
 But when the coronary arteries were tied, a mean of six experiments gave a 
 duration, for the ventricular action, of only 23 minutes after the ligatures 
 were applied, and 32| minutes after the pithing; and in no instance was it 
 prolonged more than 31 minutes after the application of the ligature, or 37 
 minutes after the pithing. On the other hand, when the aorta was tied, so 
 that the coronary arteries were distended with blood, the circulation being 
 carried on through them alone, the right ventricle continued to act up to the 
 82d minute. 
 
 585. There is a remarkable difference in the degree of Irritability in the two 
 sides of the heart, to which Dr. M. Hall has directed attention. In the warm- 
 blooded Vertebrata, the right side of the heart will act on the stimulus of ven- 
 ous blood ; whilst the left side requires the stimulus of arterial. In Fishes, 
 on the other hand, whose heart corresponds to the right side only of that of 
 Man, the whole is put in action by venous blood. In Reptiles, one auricle is 
 sufficiently stimulated by venous blood, whilst the other requires arterial ; and 
 the ventricle is excited to action by a mixed fluid. In all these cases, there 
 must be a marked difference in the properties of the several parts ; some being 
 sufficiently affected by a stimulus, which is totally inoperative on others. 
 This is still more remarkably exemplified by the fact, that the muscular fibre 
 of Frogs would be thrown into a state of permanent and rigid contraction 
 (through the powerful operation of its property of Tonicity), by the stimulus 
 of a fluid no hotter than the blood, which ordinarily bathes the muscles of 
 Birds. Now in those warm-blooded animals which pass the winter in a state 
 of torpidity, the respiration is very slow and imperfect, and the blood is very 
 imperfectly arterialized. There must, therefore, be a change in the properties 
 of the left ventricle, by which it becomes capable of action on a more feeble 
 stimulus, thus resembling the ventricle of Reptiles. 
 
 a. This change Dr. M. Hall designates as an increase of Irritability ; considering that, 
 if muscular action be excited by a more feeble stimulus, the property to which that action is 
 due, must be itself more exalted. Physiologists have been so long accustomed, however, to 
 consider the irritability of the muscles in warm-blooded animals as greater than that of cold- 
 blooded, on account of the greater energy and rapidity of their contractions when excited, 
 that it seems undesirable to modify the term in the manner proposed by Dr. Hall. No one 
 will assert that the vitality of the Muscle is exalted, when it is reduced to the condition of that 
 of the Reptile; and, as Irritability is strictly a vital property, it cannot be correctly spoken of 
 in that manner. The general principle, however, laid down by Dr. M. Hall, that the facility 
 with which the muscular system may be excited to contraction, or in other words the feeble- 
 ness of the stimulus required for the purpose, is inversely as the respiration of the animal, 
 is, no doubt, generally correct. 
 
 586. The doctrine, now generally accepted as a Physiological truth, that the 
 active exercise of the Contractility of Muscle, is attended with a waste or dis- 
 integration of its tissue, rests upon a great variety of evidence. The increase 
 of the demand for food, occasioned by Muscular activity ( 263), is an indica- 
 tion that the nutritive operations are excited by it ; and the purpose of these 
 can scarcely be anything else, than the reparation of the loss which the Mus- 
 cle has sustained. Again, it has been just shown, that the presence of Oxygen 
 is essential to the development of the Contractile force ; and there is evidence 
 that, in this development, a chemical change is effected in the substance of the 
 
 * Dr. M. Hall's Gulslonian Lectures, pp. 23, 24. t Medical Gazette, July 8, 1842. 
 
DISINTEGRATION AND NUTRITION OF MUSCLE. 445 
 
 Muscle, which is of a nature destructive to its integrity as an organized tissue. 
 For, in the first place, the researches of Helmholtz, formerly referred to 
 ( 238, 6), indicate such a change, from the comparative results of Chemical 
 analysis of the muscle, before and after the violent excitement of its contrac- 
 tility. But it is still more decidedly shown, by the increase in the excretions, 
 which is consequent upon Muscular activity ; and especially by the augmenta- 
 tion of the Carbonic acid set free from the respiratory organs, and by that of 
 the Urea set free from the kidneys. The amount of the latter, indeed, may be 
 regarded, casteris paribus, as an approximative indication of the quantity of 
 Muscular tissue which has undergone disintegration ; being increased or 
 diminished, in precise proportion to the degree of exertion to which the 
 Muscular system has been subjected. It cannot but be regarded as a probable 
 inference from these facts, that the development of the Contractile force is in 
 some way dependent upon the Chemical change, which seems to be so essen- 
 tial a condition of it ; just as the development of the Electric force of the 
 Galvanic battery is dependent upon the new chemical arrangements, which 
 take place between the bodies brought to act upon one another in its trough. 
 
 587. The frequently-renewed exercise of Muscles, by producing a deter- 
 mination of blood towards them, occasions an increase in their nutrition ; so 
 that a larger amount of new tissue becomes developed, and the muscles are 
 increased in size and vigour. This is true, not only of the whole Muscular 
 system when equally exercised; but also of any particular set of muscles, 
 which is more exercised than another. Of the former we have examples in 
 those who practise a system of Gymnastics adapted to call the various mus- 
 cles alike into play ; and of the latter, in the limbs of individuals who follow 
 any calling, that habitually requires the exertion of either pair, to the partial 
 exclusion of the other, as the arms of the Smith, or the legs of the Opera- 
 dancer. But this increased nutrition cannot take place, unless an adequate 
 supply of food be afforded ; and if the amount of nutritive material be insuffi- 
 cient, the result will be a progressive diminution in the size and power of the 
 muscles ; which will manifest itself the more rapidly, as the amount of exer- 
 tion, and consequently the degree of waste, are greater. Nor can it be effected, 
 if the exercise be too constant ; for it is during the intervals of repose that 
 the reparation of the muscular tissue occurs; and the Muscular system, like 
 the Nervous ( 294), may be worn out by too constant use. The more violent 
 the action, the longer is the period of subsequent repose, which is required for 
 the reparation of the tissue : and the longest will, of course, be requisite, when 
 (as sometimes occurs) the contractility of the muscle is so completely ex- 
 hausted by excessive stimulation, that no new manifestation of it can be ex- 
 cited. Nevertheless it is certain, that there must be a provision in some Mus- 
 cles, for the continuance of their nutrition during their state of activity; for in 
 no other way could the Heart and Respiratory Muscles, which are in unceas- 
 ing action during the whole of life, be kept in a state fit for the discharge of 
 
 their functions. 
 
 588. On the other hand, Muscular Irritability, like the vital properties of 
 other parts, is diminished by want of action ; and in this, as in other cases, it 
 is quite clear that the cause of its loss is to be found in the alteration of the 
 nutritive processes, which is the uniform result of the cessation of the usual 
 operations of any part. The Muscular tissue, like all other soft organized 
 substances, has a constant tendency to spontaneous disintegration, especially 
 at the high temperature of the body in warm-blooded animals ; and it is con- 
 sequently subject to a slow and regular waste, quite irrespectively of that pro- 
 duced by its vital activity.* Now when a Muscle or set of Muscles, in a 
 
 * This does not occur with nearly the same rapidity in cold-blooded Animals, nor in the 
 38 
 
446 OF MUSCULAR CONTRACTION. 
 
 warm-blood animal, is reduced to a state of prolonged inactivity, from what- 
 ever cause, its supply of blood is diminished, and its spontaneous decay is 
 not compensated by an equally active renewal ; so that, in time, the characters 
 of the structure are changed, and its distinguishing properties are no longer 
 presented. Thus in persons whose lower extremities have been long disused, 
 the muscles first become pale and flabby ; their bulk gradually diminishes ; 
 their contractile force progressively decreases, and at last departs altogether ; 
 and their proper structure is replaced by a deposit of fat, intermixed with 
 ordinary fibrous tissue, in which few or no characteristically-striated muscular 
 fibres can be detected. 
 
 589. The continual and evident influence of the Nervous System upon 
 Muscular Irritability, has led many Physiologists to the belief, that the latter 
 is dependent upon the agency of the former. Two views upon this question 
 have been commonly taught, to both of which it seems necessary to devote a 
 brief consideration. The first of these is, that Muscular Irritability is derived 
 from some influence or energy communicated from the Brain or Spinal Cord. 
 
 a. This opinion is evidently analogous to that which attributes the vital properties of 
 other parts to the Nervous System alone; and it is open to the same objection, in famine, 
 which has been applied to the latter, the improbability that any one of the solid textures of the 
 living body, should haVe for its office to give to any other the power of performing any vital 
 action. Moreover it is inconsistent with the fact that, in Vegetables, tissues endowed with 
 a high degree of contractility exist, and manifest their property when a stimulus is directly 
 applied to themselves; which, nevertheless, can haVe no dependence whatever upon a 
 nervous system. In the lower classes of Animals, too, there is good reason to believe, that 
 the property is much more universally diffused through their tissues, than nervous agency 
 can be. Again, the action of the heart may be kept up, in the highest Animals, by taking 
 care that the current of the circulation be not interrupted, for a long time after the removal 
 of the brain and spinal cord ; it may even continue when completely separated from the 
 body, which shows that the great centres of the ganglionic system cannot supply any influ- 
 ence necessary to it; and there are many instances, in which the human fetus has come to 
 its full size, so that its heart must have regularly acted, without the existence of a brain or 
 spinal cord. Further, the irritability of muscles of the first class continues for a long time 
 after their nerves are divided, and may be called into action by stimuli directly applied to 
 the parts themselves, or. to their nerves below the section, so long as their nutrition is unim- 
 paired. 
 
 6. The loss of the irritability of Muscles, within a few weeks after the section of their 
 nerves, on which great stress has been laid by Miiller in support of a modified form of the 
 above doctrine, (it being maintained by this distinguished physiologist, that, if muscular irri- 
 tability is not dependent on the Brain and Spinal Cord, they supply some influence essential 
 to its exercise,) is clearly due to the alteration in their nutrition, consequent upon their dis- 
 use. This has been recently proved to demonstration, by the very ingenious experiments of 
 Dr. J. Reid.* "The spinal nerves were cut across, as they lie in the lower part of the spinal 
 canal, in four frogs ; and both posterior extremities were thus insulated from their nervous 
 connections with the spinal cord. The muscles of one of the paralyzed limbs were daily 
 exercised by a weak galvanic battery ; while those of the other limb were allowed to remain 
 quiescent. This was continued for two months ; and at the end of that time, the muscles of 
 the exercised limb retained their original size and firmness and contracted vigorously, while 
 those of the quiescent limb had shrunk to at least one-half of their former bulk, and pre- 
 sented a marked contrast with those of the exercised limb. The muscles of the quiescent 
 limb still retained their contractility, even at the end of two months ; but there can be little 
 doubt that, from their imperfect nutrition, and the progressing changes in their physical 
 structure, this would in no long time have disappeared, had circumstances permitted the 
 prolongation of the experiment."f This experiment satisfactorily explains the fact ob- 
 
 hybernating condition of certain warm-blooded Mammalia ; indeed, when the temperature 
 of the body is reduced to within a few degrees of the freezing point, no chemical change 
 seems possible in muscle, its spontaneous decay, and its vital activity, being alike checked. 
 
 * Edinburgh Monthly Journal of Medical Science, May, 1841. 
 
 j- A fact of an exactly parallel character has fallen under the Author's observation, in a 
 case of Hysteric Paraplegia, in which one leg was occasionally affected with severe cramps. 
 The muscles of this leg suffered much less diminution of size and firmness, than those of 
 

 INHERENT IRRITABILITY OF MUSCULAR FIBRE. 447 
 
 served by Dr. M. Hall, and heretofore adverted to ( 399), that in cases in which the 
 cause of the paralysis is situated in the Brain, and in which the Spinal Cord and its 
 nerves are unaffected, the irritability of the muscles of the paralyzed part is not destroyed, 
 even after a considerable lapse of time. For, if the capability of performing reflex actions 
 still exist, on the part of the nervous system, it is manifest that the muscles will be occa-" 
 sionally excited to action through this channel; and that their nutrition and vital properties 
 will thereby be preserved, as they were in Dr. Reid's experiments by the artificial excite- 
 ment of galvanism. Hence Dr. M. Hall's opinion, that the property of Muscular contrac- 
 tility is derived from the Spinal Cord, is no more tenable than that which locates it in the 
 Brain. 
 
 c. The loss of irritability from section of the nerves, takes place more speedily in warm- 
 blooded Vertebrata, all whose vital operations are performed with a much greater activity, 
 than in Reptiles, and other cold-blooded animals. Dr. Reid found that, in a Rabbit, a por- 
 tion of whose sciatic nerve had been removed on one side, the muscles of that leg were but 
 very feebly excited to contraction by Galvanism, after the lapse of seven weeks. The change 
 in their nutrition was evident to the eye, and was made equally apparent by the balance. 
 The muscles of the paralyzed limb were much smaller, paler, and softer, than the corre- 
 sponding muscles of the opposite leg; and they scarcely weighed more than half, being 
 only 170 grains, whilst the others were 327 grains. It was found, also, that a perceptible 
 difference existed in the size of the bones of the leg, even after so short an interval had 
 elapsed; the tibia and fibula of the paralyzed limb weighing only 81 grains, whilst those of 
 the sound limb weighed 89 grains. On examining the muscular fibres with the microscope, 
 it was found that those of the paralyzed leg were considerably smaller than those of the 
 sound limb, and presented a somewhat shrivelled appearance; and that the longitudinal and 
 transverse striae were much less distinct. 
 
 d. Another equally satisfactory proof, that the loss of Irritability, which follows the sever- 
 ance of the connection between the Nervous centres and the Muscle, is not immediately due 
 to the interruption of any influence communicated by the former, has been given by the ex- 
 periments of Dr. J. Reid. He has proved, that if the irritability of Muscles be exhausted by 
 means, which have no tendency to impair their healthy nutrition, and the other conditions 
 favour the normal performance of the nutrient processes, the irritability is restored, and re- 
 mains for some time. His first experiments were on cold-blooded animals, and they would 
 in themselves be sufficiently satisfactory; but he has since repeated them in the Rabbit, and 
 established the fact beyond all doubt.* " The sciatic nerve was divided in the Rabbit, 
 and a portion of it removed. One wire from two galvanic batteries consisting of thirty 
 pairs of plates, was applied over the course of the nerve ; and the other wire was applied 
 over the foot, which was kept moist, until the muscles had ceased to contract. Three 
 days after this, a weaker battery was used, and the muscles of the limb had recovered 
 their contractility, and contracted powerfully. The more powerful battery was used as 
 before, until the muscles had ceased to respond to the excitement ; and three days after 
 this, they had again recovered their contractility." It seems scarcely possible to draw any 
 other inference from these experiments, than that Irritability is a property inherent in Mus- 
 cular tissue, and that the agency of the Nervous system upon it is merely to call it into 
 active operation. 
 
 590. The second doctrine referred to, as having been taught by some Phy- 
 siologists, is, that Muscles, though not dependent on nerves for their peculiar 
 vital power, are yet dependent upon them for the exercise of that power; 
 all stimuli, which excite muscles to contraction, operating first on the nervous 
 filaments which enter muscles, and through them on the muscular fibres. 
 
 a. The facts which have been already stated, in regard to the ordinary action of the Mus- 
 cles of Organic life, furnish a sufficient answer to this hypothesis. It is with great difficulty 
 that these can be made to display their irritability, by any stimuli applied to their nerves; 
 whilst they manifest it strongly, when the stimulus is directly applied to themselves. Even 
 in the Muscles of Animal life, individual fasciculi may be thrown into action in the same 
 manner; although the entire mass cannot be put into combined operation, except by a stimu- 
 lus simultaneously communicated to the whole, which the nerve affords the readiest means 
 of effecting. Perhaps the most satisfactory disproof of it, however, is to be found in the ob-' 
 
 the other; so that there was a difference of more than an inch in the circumference of the 
 limbs. But since the paraplegia has been recovered from, voluntary power having been es- 
 tablished in both limbs, and the muscles of both having been exercised in the same degree, 
 they have greatly improved in size and firmness, and there is no longer any perceptible dif- 
 ference between them. * Loc. cit. 
 
448 OF MUSCULAR CONTRACTION. 
 
 servation of Mr. Bowman already cited (231), that a single fibre, completely isolated from 
 all its connections, may be seen with the microscope to pass into a state of contraction, under 
 the influence of direct irritation. Further, it has been experimentally ascertained, that there 
 are some chemical stimuli, which will produce the contraction of muscles when directly ap- 
 plied to them, but of which the influence cannot be transmitted through the nerves ; this is 
 especially the case with regard to acids. 
 
 591. When all these considerations are allowed their due weight, we can 
 scarcely do otherwise than acquiesce fully in the doctrine of Haller, which 
 involves no hypothesis, and which is perfectly conformable to the analogy of 
 other departments of Physiology. He regarded every part of the body which 
 is endowed with Irritability, as possessing that property in and by itself; but 
 considered that the property is subjected to excitement and control from the 
 Nervous System, the agency of which is one of the stimuli that can call it 
 into operation. It may be desirable briefly to recapitulate the facts, by which 
 this doctrine is supported. 1. The existence in Vegetables of irritable tissues, 
 which are excited to contraction by stimuli directly applied to themselves, 
 and which can be in no way dependent upon, or influenced by, a Nervous 
 system. 2. The existence in Animals of a form of Muscular tissue, which 
 is especially connected with the maintenance of the Organic functions, and 
 which is much more readily excited to action by direct stimulation, than it is 
 by Nervous agency. 3. The fact that, by the agency of these, the Organic 
 functions may go on (as long as their other requisite conditions are supplied) 
 after the removal of the nervous centres, and when none were ever present ; 
 rendering it next to certain, that their ordinary operations are not dependent 
 upon any stimuli received through the nerves, but upon those directly applied 
 to themselves. 4. The persistence of irritability in muscles, for some time 
 after the nerves have ceased to be able to convey them the effects of stimuli ; 
 this is constantly seen in regard to the Sympathetic system of nerves, and 
 the muscles of Organic life upon which they operate; and it may also be 
 shown to occur with respect to the Cerebro-Spinal system, and the muscles 
 of Animal life, by the agency of narcotics. 5. The persistence of irritability 
 in the muscles, after their complete isolation from the nervous centres, so 
 long as their nutrition is unimpaired; and the effects of frequent exercise, in 
 preventing the impairment of the nutrition and the loss of irritability. 6. 
 The recovery of the irritability of muscles, when isolated from the nervous 
 centres, after it has been exhausted by repeated stimulation; this also depends 
 upon the healthy performance of the nutritive actions. 7. The contraction 
 of muscular fibre under the microscope, when completely isolated from all 
 other tissues. In the words of Dr. Alison, then, " the only ascertained final 
 cause of all endowments bestowed on Nerves in relation to Muscles, in the 
 living body, appears to be, not to make Muscles irritable, but to subject their 
 irritability, in different ways, to the dominion of the acts and feelings of the 
 Mind," to its volitions, emotions, and instinctive determinations. 
 
 592. A curious question has been lately raised, the decision on which is of 
 some importance in our determination of the nature of the force, by which 
 the contraction of muscles is occasioned. This is, whether the power of a 
 muscle is greater or less at different degrees of contraction, the same stimulus 
 being applied. This seems to have been determined, by the ingeniously-de- 
 vised experiments of Schwann.* He contrived an apparatus, which should 
 Accurately measure the length of the muscle, and, at the same time, the weight 
 which it would balance by its contraction. Having caused the muscle of a 
 Frog to shorten to its extreme point, by the stimulus of galvanism applied to 
 the nerve, so that no further stimulation could lift a weight placed in the oppo- 
 site scale, he allowed the muscle to relax until it was extended to a certain 
 
 * Miillefs Physiology, p. 903. 
 
TONIC CONTRACTION OF MUSCLES. 449 
 
 point, and then ascertained the weight which would balance its power. The 
 same was several times repeated, as in the following manner : The length of 
 the muscle in its extreme state of contraction, at which no additional force 
 could be exerted by it, being represented by 14, it was found that, when it 
 had been extended to 17, it would balance a weight of 60; when its length 
 increased to 19'6, it would balance a weight of 120; and at 22*5, it would 
 balance 180. In another experiment, the muscle at 13*5, balanced 0; at 18*8, 
 it balanced 100 ; and at 23*4, it balanced 200. Hence it appears that a uni- 
 form increase of force corresponds with a nearly uniform increase in the 
 length of the muscle ; or, in other words, that when the muscle is nearly at 
 its full length, its contractile power is the greatest. In later experiments upon 
 the same muscle, this uniform ratio seemed to be departed from ; but, by 
 comparing the results in a considerable number of instances, it was constantly 
 found that, in those experiments which were performed the soonest after the 
 preparation of the frog, and in which, therefore, the normal conditions of the 
 system were the least disturbed, the ratio was very closely maintained. It 
 has been ascertained by Valentin, on repeating these experiments, that, by 
 repeated equal irritations, the strength of the muscles in beheaded frogs de- 
 creases in a regular and corresponding ratio ; losing the same amount in each 
 successive period of time. He also found that, when all the Irritability has 
 ceased, the muscles tear with a far less weight, than they were previously 
 able, when galvanized, to draw. 
 
 a. It has been inferred by Miiller, from Schwann's experiments, that the power which 
 causes the contraction of a Muscle, must be very different in its character, from any of the 
 forces of attraction known to us ; since these all increase in energy as the attracted parts ap- 
 proach each other, in the inverse ratio of the square of the distance ; so that the power of a 
 Muscle, if operated on by any of these, ought to increase, instead of regularly diminishing, 
 with its degree of contraction. But it is to be remembered that, as the observations of Mr. 
 Bowman have clearly shown, there must be a considerable displacement of the constituents 
 of every fibre during contraction ( 231); so that it is easy to understand that, the greater 
 the contraction, the more difficult must any further contraction become. If, between a mag- 
 net and a piece of iron attracted by it, there were interposed a spongy elastic tissue, the iron 
 would cease to approach the magnet at a point, at which the attraction of the magnet would 
 be balanced by the force, needed to compress still further the intermediate substance. 
 
 3. -Of Muscular Tonicity. 
 
 593. We have now to consider the other form of Contractility, which pro- 
 duces a constant tendency to contraction (varying, however, as to its degree) 
 in the Muscular fibre ; but which is so far different from simple Elasticity, 
 that it abates after death, before decomposition has taken place. This Toni- 
 city is to be distinguished from the Muscular Tension, which is the result of 
 the reflex operation of the nervous centres ( 398) ; being manifested as well 
 when the muscle is altogether removed from nervous influence, as when sub- 
 jected to it, and being, like Irritability, an inherent property of the tissue itself, 
 the presence of which is characteristic of its living state. It manifests itself 
 in the retraction which takes place in the ends of a living muscle, when it is 
 divided (as is seen in amputation) ; this retraction being permanent, and 
 greater than that of a dead muscle. But its effects are much more remarkable 
 in the non-striated, than in the striated form of Muscular Fibre ; and are par- 
 ticularly evident in the contractile coat of the Arteries, causing the almost 
 entire obliteration of their tubes, when they are no longer distended with 
 blood. The disposition to tonic contraction is increased by any considerable 
 change of temperature ; the power of Heat is well seen in the following ex- 
 periments of John Hunter's : " As soon as the skin could be removed from 
 a sheep that was newly killed, a square piece of muscle was cut off, which 
 
 38* 
 
450 OF MUSCULAR CONTRACTION. 
 
 was afterwards divided into three pieces, in the direction of the fibres ; each 
 piece was put into a Basin of water, the water in each basin being of different 
 temperatures, viz., one about 125, about 27 warmer than the animal; an- 
 other 98, the heat of the animal; and the third 55, about 43 colder than 
 the animal. The muscle in the water heated to 125 contracted directly, so 
 as to be half an inch shorter than the other two, and was hard and stiff. The 
 muscle in the water heated to 98 after six minutes began to contract and 
 grow stiff; and at the end of twenty minutes it was nearly, though not quite, 
 as short and hard as the above. The muscle in the water heated to 55 after 
 fifteen minutes, began to shorten and grow hard ; after twenty minutes it was 
 nearly as short and as hard as that in the water heated to 98. At the end 
 of twenty-four hours, they were all found to be of the same length and stiff- 
 ness."* The agency of Heat in producing this contraction is also remarkably 
 shown in the fact, that if a Frog be immersed in water of the temperature of 
 110, the muscles of its body and limbs will be thrown into a state of perma- 
 nent and rigid contraction. But it would seem that these effects are chiefly, 
 if not entirely, exerted upon the striated form of Muscular fibre ; and that the 
 tonicity of the non-striated fibre is called into play by Cold, rather than by 
 heat. For if a Tadpole or Frog be immersed in water, the temperature of 
 which is gradually raised, until this state of contraction comes on, the Heart 
 will be found to continue pulsating for many hours afterwards, not being 
 affected by the heat. On the other hand, if an artery in a living warm-blooded 
 animal be exposed to cold air for some time, the lowering of its temperature 
 occasions its contraction to such an extent, that its cavity becomes almost 
 obliterated. The influence of warmth in diminishing, and of cold in increas- 
 ing, the tonicity of the arterial system, will be adverted to hereafter (Chap, 
 xii., Sect. 3). 
 
 594. The distinctness of the Tonicity of Muscles from their Irritability, is 
 further shown by the fact that the former commonly survives the latter ; and 
 that it is not destroyed by treatment, which occasions the complete departure 
 of the Irritability. The first of these statements finds its proof in the pheno- 
 mena of the Rigor Mortis, presently to be adverted to. Of the latter, the fol- 
 lowing remarkable experiment of John Hunter's is an ample demonstration : 
 " From a straight muscle in a bullock's neck, a portion, three inches in length, 
 was taken out immediately after the animal had been knocked down, and was 
 exposed between two pieces of lead, to a cold below 0, for fourteen minutes ; 
 at the end of this time it was found to be frozen exceedingly hard, was be- 
 come white, and was now only two inches long; it was thawed gradually, and 
 in about six hours after thawing, it contracted so as only to measure one inch 
 in length ; but irritation did not produce any sensible motion in the fibres. 
 Here, then, were the juices of muscles frozen, so as to prevent all power of 
 contraction in their fibres, without destroying their life ; for when thawed, 
 they showed the same life which they had before ; this is exactly similar to 
 the freezing of blood too fast for its coagulation, which, when thawed, does 
 afterwards coagulate, as it depends in each on the life of the part not being 
 destroyed. "t 
 
 595. The Rigor Mortis, or death-stiffening of the muscles, is probably to 
 be regarded as the final manifestation of this property ; occurring after all the 
 Irritability of the muscles has departed, but before any putrefactive change 
 has commenced. This phenomenon is rarely absent ; though it may be so 
 slight, and may last for so short a time, as to escape observation. The period 
 which elapses before its commencement, is as variable as its duration ; and 
 
 * General Principles of the Blood, in Hunter's Works, Vol. iii., p. 110. 
 f Op. tit, p. 109. 
 
RIGOR MORTIS. 451 
 
 both appear to be in some degree dependent upon the vital condition of the 
 body at the time of death. When the fatal termination has supervened on slow 
 and wasting disease, occasioning great general depression of the vital powers, 
 the rigidity usually developes itself very early, and lasts for a short time. In 
 diseases which powerfully affect the nervous energy, such as Typhus, this is 
 often the case ; even though they have not been of long duration. Thus, 
 after death from Typhus, the limbs have been sometimes known to stiffen 
 within fifteen or twenty minutes. The same is observed in infants and in old 
 people. On the other hand, where the general energy has been retained up 
 to a short period before death, the rigidity is much later in coming on, and 
 lasts longer ; this happens, for example, in many cases of Asphyxia and Poi- 
 soning, in which it has been said not to occur at all. The commencement of 
 the rigidity, however, is not usually prolonged much beyond seven hours ; 
 but twenty or even thirty hours may elapse, before it shows itself. Its gene- 
 ral duration is from twenty-four to thirty-six hours ; but it may pass off much 
 more rapidly ; or it may be prolonged through several days. An attempt has 
 been made to connect it with the lowering of the temperature of the dead 
 body ; but with this it does not seem to have any relation. It occurs in cold- 
 blooded Vertebrata, and even in Invertebrata, as well as in warm-blooded ani- 
 mals ; and it has frequently been noticed to commence in the latter, long be- 
 fore the heat has entirely departed from the body. Moreover, it appears first 
 upon the trunk, which is the region last deserted by the caloric. It first affects 
 the neck and lower jaw, and seems gradually to travel downwards ; but ac- 
 cording to some observers, the lower extremities are stiffened before the upper. 
 In its departure, which is immediately followed by decomposition, the same 
 order is observed. It affects all the muscles nearly alike ; but the flexors are 
 usually more contracted than the extensors, so that the fingers are somewhat 
 flexed on the palm, and the fore-arm on the arm ; and the lower jaw, if pre- 
 viously drooping, is commonly drawn firmly against the upper. It is remark- 
 able, that it is equally intense in muscles which have been paralyzed by He- 
 miplegia; provided that no considerable change has taken place in their 
 nutrition. When very strong, it renders the muscles prominent, as in volun- 
 tary contraction. 
 
 596. The ordinary Irritability of the muscles appears to be almost invaria- 
 bly lost, or greatly diminished, before the Rigor Mortis commences. This 
 statement holds good in regard to animals of different classes, as well as with 
 respect to Man under various conditions. Thus, in Birds, whose muscles 
 most speedily lose their contractility, the cadaveric rigidity is most quickly 
 exhibited ; whilst in Reptiles it is much longer in commencing, the irritability 
 of the muscles being more persistent. The interval between the cessation of 
 the Irritability and the accession of the Rigidity, is sometimes very consider- 
 able ; and in such cases, the rigidity, when it does occur, is usually very de- 
 cided and prolonged. An attempt has been made to show a correspondence 
 between the rigor mortis, and the coagulation of the blood in the vessels ; and 
 there is certainly evidence enough to make it appear, that some analogy exists 
 between these two actions, though they are far from being identical. After 
 those forms of death in which the blood does not coagulate, or coagulates 
 feebly, the rigidity commonly manifests itself least ; but this is by no means 
 an invariable rule. It seems probable that, as the coagulation of the blood 
 will be shown to be the last act of its vitality, so the stiffening of the muscles 
 is the expiring effort of theirs. 
 
 a. It is necessary to bear in mind, when the phenomena of cadaveric rigidity are brought 
 into question in juridical investigations, that a state at first sight corresponding to it may 
 supervene immediately upon death, from some peculiar condition of the nervous and muscular 
 systems at the moment. This has been observed in some cases of Asphyxia; but chiefly 
 when death has resulted from apoplexy following chronic ramottissement of the brain or spinal 
 
452 OF MUSCULAR CONTRACTILITY. 
 
 cord. This contraction, which is obviously of a tetanic character, ceases after a few hours, 
 and is then succeeded by a state of flexibility, after which the ordinary rigidity supervenes. 
 The following case illustrates the nature of the inquiries, to which this condition may give 
 rise.* The body of a man was found in a ditch, with the trunk and limbs in such a relative 
 position, as could only be maintained by the stiffness of the articulations. This stiffness must 
 have* come on at the very moment when the body took that position ; unless it could be 
 imagined that the body had been supported by the alleged murderers, until the joints were 
 locked by cadaveric stiffness. A post-mortem examination showed, that there was no neces- 
 sity for this supposition, obviously a very improbable one in itself; by affording sufficient 
 evidence, that apoplexy, resulting from chronic disease, was the cause of death. A case 
 occurred a few years since in Scotland, in which the same plea was raised. The body was 
 found in a position in which it could have only been retained by rigidity of the joints ; and 
 it was pleaded on the part of the prisoner, that death had been natural, and had resulted 
 from fracture of the processus dentatus, causing sudden pressure upon the spinal cord, whence 
 the spasmodic rigidity would naturally result. Proof was deficient, however, as to the 
 existence of this lesion before death ; and the position of the body rather resembled that into 
 which it might have been forced during the rigidity, than that in which it would probably 
 have been at the moment of death. There were also marks of violence, and many other 
 suspicious circumstances; but the prisoner was acquitted, chiefly from want of evidence 
 against him. What seemed to indicate that the rigidity was of the ordinary cadaveric nature, 
 was, that there was no evidence of the body having become flexible and again stiffened ; as 
 it would probably have done, had the rigidity been of the spasmodic character. 
 
 597. As the property of Tonicity manifests itself most decidedly in the non- 
 striated muscles in the living body, so do we find this post-mortem contraction 
 most remarkable in them. As soon as the muscular walls of the several cavi- 
 ties lose their irritability, they begin to contract firmly upon their contents, 
 and thus become stiff and firm, though they were previously flaccid. In this 
 manner the ventricles of the heart, which are the first parts to lose their 
 irritability, become rigid and contracted within an hour or two after death ; 
 and usually remain in that state for ten or twelve hours, sometimes for 
 twenty-four or thirty-six, then again becoming relaxed and flaccid. This 
 rigid contracted state of the heart, in which the walls are thickened and the 
 cavities diminished, was formerly supposed to be a result of disease, and 
 was termed concentric hypertrophy; but it is now known, from the inquiries 
 of Mr. Paget, to be the natural condition of the organ, at the period when the 
 rigor mortis occurs in it. The contraction of the arterial tubes is so great, as 
 to produce for the time a great diminution in their calibre ; and this doubtless 
 contributes to the passage of the blood from the arterial into the venous sys- 
 tem, which almost invariably takes place within a few hours after death. The 
 arteries, then enlarge again, and become quite flaccid, their tubes being emptied 
 of their previous contents ; and it was from this circumstance, that the ancient 
 Physiologists were led to imagine, that the arteries are not destined to carry 
 blood, but air. 
 
 4. Energy and Sapidity of Muscular Contraction. 
 
 598. The energy of Muscular contraction is of course to be most remarkably 
 observed in those instances in which the continual exercise of particular parts 
 has occasioned an increased determination of blood towards them, and in con- 
 sequence a permanent augmentation in their bulk. This has been the case, 
 for example, with persons who have gained their livelihood by exhibiting 
 feats of strength. Much will, of course, depend on the mechanically-advantage- 
 ous application of muscular power ; and in this mariner, effects may be pro- 
 duced, even by persons of ordinary strength, which would not have been 
 thought credible. In lifting a heavy weight in each hand, for example, a per- 
 son who keeps his back perfectly rigid, so as to throw the pressure vertically 
 upon the pelvis, and only uses the powerful extensors of the thigh and calf, 
 by straightening the knees (previously somewhat flexed), and bringing the leg 
 to a right angle with the foot, will have a great advantage over one who uses 
 
 * Annales d'Hygiene, torn. vii. 
 
ENERGY AND RAPIDITY OF MUSCULAR CONTRACTION. 453 
 
 his lumbar muscles for the purpose. A still greater advantage will be gained, 
 by throwing the weight more directly upon the loins, by means of a sort of 
 girdle, shaped so as to rest upon the top of the sacrum and the ridges of the 
 ilia ; and by pressing with the hands upon a frame, so arranged as to bring 
 the muscles of the arms to the assistance of those of the legs : in this manner, 
 a single Man of ordinary strength may raise a weight of 2000 Ibs. ; whilst few 
 who are unaccustomed to such exertions, can lift more than 300 Ibs. in the 
 ordinary mode. A man of great natural strength, however, has been known 
 to lift 800 Ibs. with his hands ; and the same individual performed several 
 other curious feats of strength, which seem deserving of being here noticed. 
 " 1. By the strength of his fingers, he rolled up a very large and strong pewter 
 dish. 2. He broke several short and strong pieces of tobacco-pipe, with the 
 force of his middle finger, having laid them on the first and third finger. 3. 
 Having thrust in under his garter the bowl of a strong tobacco-pipe, his legs 
 being bent, he broke it to pieces by the tendons of his hams, without altering 
 the bending of the knee. 4. He broke such another bowl between his first 
 and second fingers, by pressing them together sideways. 5. He lifted a table 
 six feet long, which had half a hundred-weight hanging at the end of it, with 
 his teeth, and held it in that position for a considerable time. It is true, the 
 feet of the table rested against his knees ; but, as the length of the table was 
 much greater than its height, that performance required a great strength to be 
 exerted by the muscles of his loins, neck, and jaws. 6. He took an iron 
 kitchen poker, about a yard long, and three inches in circumference, and, hold- 
 ing it in his right hand, he struck it on his bare left arm between the elbow 
 and the wrist, till he bent the poker nearly to a right angle. 7. He took such 
 another poker, and, holding the ends of it in his hands, and the middle of it 
 against the back of his neck, he brought both ends of it together before him ; 
 and, what was yet more difficult, he pulled it straight again."* Haller men- 
 tions an instance of a man, who could raise a weight of 300 Ibs. by the action 
 of the elevator muscles of his jaw: and that of a slender girl, affected with 
 tetanic spasm, in whom the extensor muscles of the back, in the state of tonic 
 contraction or opisthotonos, resisted a weight of 800 Ibs., laid on the abdomen 
 with the absurd intention of straightening the body. It is to be recollected, 
 that the mechanical application of the power developed by muscular contrac- 
 tion, to the movement of the body, is very commonly disadvantageous as re- 
 gards force; being designed to cause the part moved to pass over a much 
 greater space, than that through which the muscle contracts. Thus the tem- 
 poral muscle is attached to the lower jaw, at about one-third of the distance 
 between the condyle and the incisors ; so that a shortening of the muscle to 
 the amount of half an inch, will draw up the front of the jaw through an inch 
 and a half; but a power of 900 Ibs. applied by the muscle, would be required 
 to raise 300 Ibs. bearing on the incisors. In the case of the forearm and leg, 
 the disproportion is much greater ; the points of attachment of the muscles, 
 by which thfe knee and elbow-joints are flexed and extended, being much 
 closer to the fulcrum, in comparison with the distance of the points on which 
 the resistance bears. 
 
 599. The energy of muscular contraction appears to be greater in Insects, 
 in proportion to their size, than it is in any other animals. Thus a Flea has 
 been known to leap sixty times its own length, and to move as many times 
 its own weight. The short-limbed Beetles, however, which inhabit the 
 ground, manifest the greatest degree of muscular power. The Lucanus cer- 
 vi& (Stag Beetle) has been known to gnaw a hole of an inch diameter, in the 
 side of an iron canister in which it had been confined. The Geotrupes ster- 
 corarius (Dung or shard-born Beetle) can support uninjured, and even elevate 
 
 * Desaguliers' Philosophy, Vol. ii. 
 
454 OF MUSCULAR CONTRACTILITY. 
 
 a weight equal to at least 500 times that of its body. And a small Carabus 
 has been seen to draw a weight of 85 grains (about 24 times that of its body) 
 up a plane of 25 ; and a weight of 125 grains (36 times that of its body) 
 up a plane of 5 ; and in both these instances the friction was considerable, 
 the weights being simply laid upon a piece of paper, to which the insect was 
 attached by a string. 
 
 600. The rapidity of the changes of position of the component particles 
 of muscular fibres, may, as Dr. Alison justly remarks,* be estimated, though 
 it can hardly be conceived from various well-known facts. The pulsations of 
 the heart can sometimes be distinctly numbered in children, at more than 200 
 in the minute; and as each contraction of the ventricles occupies only one- 
 third of the time of the whole pulsation, it must be accomplished in l-600th 
 of a minute, or l-10th of a second. Again, it is certain that, by the move- 
 ments of the tongue and other organs of speech, 1500 letters can be distinctly 
 pronounced by some persons in a minute : each of these must require a sepa- 
 rate contraction of muscular fibres ; and the production and cessation of each 
 of the sounds, imply that each separate contraction must be followed by a 
 relaxation of equal length ; each contraction, therefore, must have been ef- 
 fected in l-1000th part of a minute, or in the l-10th of a second. Haller 
 calculated that, in the limbs of a dog at full speed, muscular contractions must 
 take place in less than the l-200th of a second, for many minutes at least in 
 succession.-^All these instances, however, are thrown into the shade, by those 
 which may be drawn from the class of Insects. The rapidity of the vibra- 
 tions of the wings may be estimated from the musical tone which they pro- 
 duce ; it being easily ascertained by experiments, what number of vibrations 
 are required to produce any note in the scale. From these data, it appears 
 to be the necessary result, that the wings of many Insects strike the air many 
 hundred, or even many thousand, times in every second. The minute pre- 
 cision with which the degree of muscular contraction can be adapted to the 
 designed effect, is in no instance more remarkable than in the Glottis. The 
 musical pitch of the tones produced by it, is regulated by the degree of ten- 
 sion of the chordae vocales, which are possessed of a very considerable de- 
 gree of elasticity ( 603). According to the observations of Miiller,t the 
 average length of these, in the male, in a state of repose, is about 73-100ths 
 of an inch ; whilst, in the state of greatest tension, it is about 93-100ths ; the 
 difference being therefore 20-100ths, or one-fifth of an inch : in the female 
 glottis, the average dimensions are about 51-100ths, and" 63-100ths respect- 
 ively ; the difference being thus about one-eighth of an inch. Now the natu- 
 ral compass of the voice, in most persons who have cultivated the vocal 
 organ, may be stated at about two octaves, or 24 semitones. Within each 
 semitone, a singer of ordinary capability could produce at least ten distinct 
 intervals ; so that of the total number, 240 is a very moderate estimate. There 
 must, therefore, be at least 240 different states of tension of the vocal cords, 
 every one of which is producible by the will, without any previous trial ; and 
 the whole variation in the length of the cords being not more than one-fifth 
 of an inch even in man, the variation required to pass from one interval to 
 another, will not be more than one twelve-hundredth of an inch. And yet 
 this estimate is much below that which might be truly made from the per- 
 formances of a practised vocalist.^ 
 
 * Cyclopaedia of Anatomy and Physiology, Art. Contractility. 
 
 t Physiology, 1018. 
 
 J It is said that the celebrated Made. Mara was able to sound 100 different intervals*e- 
 tween each tone. The compass of her voice was at least three octaves, or 22 tones ; so that 
 the total number of intervals was 2200, all comprised within an extreme variation of one- 
 eighth of an inch 5 so that it might be said that she was able to determine the contractions 
 of her vocal muscles to the seventeen-thousandth of an inch. 
 
4 OF THE VOICE AND SPEECH. 455 
 
 601. Of the different associations of Muscular actions, which are em- 
 ployed for various purposes in the living body, it would be out of place here 
 to speak ; since these associations depend upon the Nervous rather than upon 
 the muscular system ; and the most important of them have already been con- 
 sidered in detail. It may be mentioned, however, that the aptitude which is 
 acquired by practice, for the performance of particular actions, that were at 
 first accomplished with difficulty, seems to result as much from a change, 
 which the continual repetition of them occasions in the Muscle, as in the 
 habit which the Nervous system acquires, of exciting their performance. 
 Thus almost every person learning to play on a musical instrument, finds a 
 difficulty in causing the two shorter fingers to move independently of each 
 other and of the rest ; this is particularly the case in regard to the ring-finger. 
 Any one may satisfy himself of the difficulty, by laying the palm of the hand 
 flat on a table, and raising one finger after the other, when it will be found, 
 that the ring-finger cannot be lifted without disturbing the rest, evidently 
 from the difficulty of detaching the action of that portion of the extensor 
 communis digitorum, by which the movement is produced, from that of the 
 remainder of the muscle. Yet to the practised musician, the command of the 
 will over all the fingers becomes nearly alike ; and it can scarcely be doubted 
 that some change takes place in the structure of the muscle, which favours the 
 isolated operation of its several divisions. 
 
 CHAPTER VIII. 
 
 OF THE VOICE AND SPEECH. 
 
 1. The Larynx, and its Actions. 
 
 602. THE sounds produced by the organ of Voice constitute the most im- 
 portant means of communication between Man and his fellows ; and the 
 power of speech has, therefore, a primary influence, as well on his physical 
 condition, as on the development of his mental faculties. Hence, although it 
 only depends on one particular application of muscular force, comparable 
 to that by which other volitional or emotional movements are effected, it 
 seems right, in treating of the Physiology of man, to make it an object of 
 special consideration. In order to understand the nature of the Organ of 
 Voice as a generator of Sound, it is requisite to inquire, in the first, instance, 
 into the sources from which sounds at all corresponding to the human voice 
 are elsewhere obtained. It is necessary to bear in mind, that Vocal Sounds, 
 and Speech or Articulate Language, are two things entirely different; and 
 that the former may be produced in great perfection, where there is no ca- 
 pability for the latter. Hence we should at once infer, that the instrument 
 for the production of Vocal Sounds was distinct from that by which these 
 sounds are modified into articulate speech ; and this we easily discover to be 
 the case, the Voice being unquestionably produced in the Larynx, whilst 
 the modifications of it, by which language is formed, are effected for the most 
 part in the Oral cavity. The structure and functions of the former, then, first 
 claim our attention. 
 
 603. It will be remembered that the Windpipe is surmounted by a stout 
 cartilaginous annulus, termed the Cricoid cartilage ; which serves as a founda- 
 
456 
 
 OF THE VOICE AND SPEECH. 
 
 tion for the super] acent mechanism. This is embraced (as it were) by the 
 Thyroid, which is articulated to its sides by its lower horns, round the ex- 
 tremities of which it may be regarded as turning, as on a pivot. In this man- 
 
 External and sectional views of the Larynx. A n B, the cricoid cartilage ; E c G, the thyroid cartilage ; 
 G, its upper horn ; c, its lower horn, where it is articulated with the cricoid ; F, the arytenoid cartilage ; 
 E, F, the vocal ligament ; A. K, crico-thyroideus muscle ; F e m, thyro-arytenoideus muscle ; x e, crico-ary- 
 tenoideus lateralis ; s, transverse section of arytenoideus transversus ; m n, space between thyroid and 
 cricoid ; B L, projection of axis of articulation of arytenoid with thyroid, 
 
 ner the lower front border of the thyroid cartilage, which is ordinarily sepa- 
 rated by small intervals from the upper margin of the cricoid, may be made to 
 approach it or recede from it ; as any one may easily ascertain, by placing 
 his finger against the little depression which may be readily felt externally, 
 and observing its changes of size, whilst a range of different tones is sounded ; 
 it will then be observed that, the higher the note, the more the two cartilages 
 are made to approximate, whilst they seperate in proportion to the depth of 
 the tones.* Upon the upper surface of the back of the cricoid, are seated 
 the two small Arytenoid cartilages ; these are fixed in one direction by a 
 bundle of strong ligaments, which tie them to the back of the cricoid ; but 
 they have some power of moving in other directions upon a kind of articulat- 
 ing surface. The direction of the surface, and the mode in which these car- 
 tilages are otherwise attached, cause their movement to be a sort of rotation 
 in a plane, which is nearly horizontal, but partly downwards ; so that their 
 vertical planes may be made to separate from each other, and at the same 
 time to assume a slanting position. This change of place will be better un- 
 derstood, when the action of the muscles is described. To the summit of 
 the arytenoid cartilages are attached the chordss vocales or Vocal Ligaments, 
 which stretch across to the front of the thyroid cartilage ; and it is upon the 
 condition and relative situation of these ligaments, that their action depends. It 
 
 * In making this observation, it is necessary to put out of view the general movement to 
 the larynx itself, which the finger must be made to follow up and down. 
 
STRUCTURE AND ACTIONS OF THE LARYNX. 
 
 457 
 
 Bird's-eye view of larynx from above. G E H, 
 the thyroid cartilage, embracing the ring of the 
 
 is evident that they may be rendered more or less tense by the movement of 
 the Thyroid cartilage just described; 
 
 being tightened by the depression of Fig. 196. 
 
 its front upon the Cricoid cartilage, and 
 slackened by its elevation. On the 
 other hand, they may be brought into 
 more or less close apposition, by the 
 movement of the Arytenoid cartilages ; 
 being made to approximate closely, or 
 to recede in such manner as to cause 
 the rima glottidis to assume the form 
 of a narrow V, by the revolution of 
 these cartilages. We shall now in- 
 quire into the actions of the muscles 
 upon the several parts of this apparatus; 
 and first into those of the larynx alone. 
 604. The depression of the front of 
 the Thyroid cartilage, and the conse- 
 quent tension of the Vocal Ligaments, 
 are occasioned by the conjoint action of 
 the Crico-thyroidei on both sides ; and 
 the chief antagonists to these are the 
 Thyro-arytenoidei, which draw the 
 
 front of the Thyroid back towards the cricoid r u x w, and turning upon the axis x z, 
 
 Arytenoid Cartilages, and thus relax the which passes through the lower horns, c, Fig. 113, 
 
 VOCal Hp-amentS. These tWO pairs of N F ' N F ' the ai T tenoid cartilages, connected by 
 
 muscles may be regarded as the prin- ^ arytenoideus transversus ; T v, x v the vocal 
 
 f P . , r , ligaments; N x, the right cnco-arytenoideus late- 
 
 cipal governors of the pitch of the notes, ralis (the left being removed) . v kf) the left thyro . 
 
 which, as we shall hereafter see, is al- arytenoideus (the right*being removed) ; N I, N ?, 
 most entirely regulated by the tension the crico-arytenoidei posticij B, B, the crico-ary- 
 
 of the ligaments ; their action is as- tenoid ligaments, 
 sisted, however, by that of other muscles 
 
 presently to be mentioned. The Arytenoid cartilages are made to diverge 
 from each other, by means of the Crico-arytenoideus posticus of each side, 
 which proceeds from their outer corner, and turns somewhat round the edge 
 of the Cricoid, to be attached to the lower part of its back ; its action is to 
 draw the outer corner backwards and downwards, so that the points to which 
 the vocal ligaments are attached, are separated from one another, and the 
 Rima Glottidis is thrown open. This will be at once seen from the succeed- 
 ing diagram, in which the direction of traction of the several muscles is laid 
 down. The action of this muscle is partly antagonized by that of the Crico- 
 arytenoideus lateralis, which runs forwards and downwards from the outer 
 corner of the Arytenoid cartilage ; and its action, with that of its fellow, will 
 be to bring the anterior points of the Arytenoid cartilages into the same 
 straight line, at the same time depressing them, and thus to close the Glottis. 
 This muscle is assisted by the Arytenoideus transversus, which connects 
 the posterior faces of the Arytenoid cartilages, and which, by its contraction* 
 will draw them together. By the conjoint action, therefore, of the Crico-ary- 
 tenoideus lateralis, and of the Arytenoideus transversus, the whole of the ad- 
 jacent faces of the Arytenoid cartilages will be pressed together; and the 
 points to which the vocal ligaments are attached, will be depressed. But if 
 the Arytenoideus be put in action in conjunction with the Crico-arytenoidei 
 postici, the tendency of the latter to separate the Arytenoid cartilages being 
 antagonized by the former, its backward action only will be exerted ; and thus 
 it maybe caused to aid the Crico-thyroideus in rendering tense the vocal 
 39 
 
458 
 
 OF THE VOICE AND SPEECH. 
 
 ligaments. This action will be further assisted by the Sterno-thyroideus, 
 which tends to depress the Thyroid cartilage, by pulling from a fixed point 
 below ;* and the Thyro-hyoideus will be the antagonist of this, when it acts 
 
 Part of Fig. 196 enlarged, to show the direction of the muscular forces, which act on the Arytenoid 
 cartilage. Q N v s, the right Arytenoid cartilage ; T v, its vocal ligament ; B R s, bundle of ligaments unit- 
 ing it to Cricoid ; o p, projection of its axis of articulation ; h g, direction of the action of the Thyro-ary- 
 tenoideus; N x, direction of Crico-arytenoideus lateralis ; N w, direction of Crico-arytenoideus posticus; 
 N y, direction of Crytenoideus transversus. 
 
 from a fixed point above, the Os Hyoides being secured by the opposing con- 
 traction of several other muscles. The respective actions of these muscles 
 will be best comprehended by the following Table. 
 
 Govern the pitch of the notes. 
 
 CRICO-THYROIDEI 
 STERNO-THYBOIDEI 
 
 THYRO-ARYTENOIDEI 
 THTHO-HTOIDEI 
 
 ! 
 
 b 
 
 Depress the front of the Thyroid cartilage on the 
 Cricoid, and stretch the vocal ligaments; assisted 
 by the Arytenoideus and Crico-arytenoidei postici. 
 
 Elevate the front of the Thyroid cartilage, and draw 
 it towards the Arytenoids, relaxing the vocal liga- 
 ments. 
 
 Govern the Aperture of the Glottis. 
 CHICO-ARYTEHOIDEI PosTici Open the Glottis. 
 
 C CRICO-ARYTElfOIDEI LATEHA1ES 
 ARYTETSTOIDEUS 
 
 C Press together the inner edges of the Ary- 
 tenoid cartilages, arid dose the Glottis. 
 
 605. The muscles which stretch or relax the Vocal ligaments, are entirely 
 concerned in the production of Voice ; those which govern the aperture of 
 the Glottis have important functions in connection with the Respiratory 
 actions in general, and stand as guards (so to speak) at the entrance to the 
 lungs. Their separate actions are easily made evident. We can close the 
 aperture, of the Glottis, by an exertion of the will, either during inspiration or 
 expiration ; and it is a kind of spasmodic movement of this sort, which is 
 
 * This is not usually reckoned as one of the principal muscles concerned in regulating the 
 voice ; but that it is so, any one may convince himself by placing his finger just above the 
 sternum, whilst he is sounding high notes ; a strong feeling of muscular tension is then at 
 once perceived. 
 
STRUCTURE AND ACTIONS OF THE LARYNX. 459 
 
 concerned in the acts of Coughing and Sneezing ( 381), as well as in the 
 more prolonged impediments to the ingress and egress of air, which have been 
 already noticed as resulting from disordered states of the Nervous system 
 ( 504). A slight examination of the recent Larynx is sufficient to make it 
 evident that, when once the borders of the Rima Glottidis are brought toge- 
 ther by muscular action, the effect of strong aerial pressure on either side, 
 whether produced by an expulsory blast from below, or by a strong inspiratory 
 effort, occasioning a partial vacuum below, and consequently an increased 
 pressure above, will be to force them into closer apposition. With this 
 action, then, the muscles which regulate the tension of the vocal ligaments 
 have nothing to do. In the ordinary condition of rest, it seems probable that 
 the Arytenoid cartilages are considerably separated from each other ; so as to 
 cause a wide opening to intervene between their inner faces, and between the 
 vocal ligaments, through which the air freely passes ; and the vocal ligaments 
 are at the same time in a state of complete relaxation. In order to produce 
 a vocal sound, it is not sufficient to put the ligaments into a state of tension ; 
 they must also be brought nearer to each other. That the aperture of the 
 Glottis is greatly narrowed during the production of sounds, is easily made 
 evident to one's self, by comparing the time occupied by an ordinary expiration, 
 with that required for the passage of the same quantity of air during the sus- 
 tenance of a vocal tone. Further, the size of the aperture is made to vary in 
 accordance with the note which is being produced ; of this, too, any one may 
 convince himself, by noting the time during which he can hold out a low and 
 a high note ; from which it will appear, that the aperture of the Glottis is so 
 much narrowed in producing a high note, as to permit a much less rapid pas- 
 sage of air, than is allowed when a low one is sounded. This adjustment of 
 the aperture to the tension of the Vocal Ligaments, is a necessary condition 
 for the production of a clear and definite tone. It further appears that, in the 
 narrowing of the Glottis, which is requisite to bring the vocal ligaments into 
 the necessary approximation, the upper points of the Arytenoid cartilages are 
 caused to approximate, not only by being made to rotate horizontally towards 
 each other, but also by a degree of elevation ; so that the inner faces of the 
 Vocal Ligaments are brought into parallelism with each other, a condition 
 which may be experimentally shown to be necessary, for their being thrown 
 into sonorous vibration. 
 
 606. We have now to inquire what is the operation of the Vocal Ligaments 
 in the production of sounds ; and in order to comprehend this, it is necessary 
 to advert to the conditions under which tones are produced, by instruments of 
 various descriptions, having some analogy with the Larynx. 
 
 a. These are chiefly of three kinds, strings, flute-pipes, and reeds or tongues. The Vocal 
 Ligaments were long ago compared by Ferrein to vibrating Strings ; and at first sight there 
 might seem a considerable analogy, the sounds produced by both being elevated by increased 
 tension. This resemblance disappears, however, on more accurate comparison ; for it may 
 be easily ascertained by experiment, that no string so short as the vocal ligaments could give 
 a clear tone, at all to be compared in depth with that of the lowest notes of the human voice ; 
 and also, that the scale of changes produced by increased tension is fundamentally different. 
 When strings of the same length, but of different tension, are made the subject of comparison, 
 it is found that the number of vibrations is in proportion to the square roots of the extending 
 forces. Thus, if a string extended by a given weight produce a certain note, a string extended 
 by four times that weight will give a note, in which the vibrations are twice as rapid, and 
 this will be the octave of the other. If nine times the original weight be employed, the 
 vibrations will be three times as rapid as those of the fundamental note, producing the 
 twelfth above it. Now by fixing the larynx in such a manner, that the vocal ligaments can 
 be extended by a known weight, Miiller has ascertained that the sounds produced by a varia- 
 tion of the extending force will not follow the same ratio ; and therefore the condition of 
 these ligaments cannot be simply that of vibrating ,cords. Further, a cord of a certain length, 
 which is adapted to give out a clear and distinct note, equal in depth to the lowest of the 
 
460 OF THE VOICE AND SPEECH. 
 
 human voice, may be made by increased tension to produce all the superior notes, which, 
 in stringed instruments, are ordinarily obtained by shortening the strings.* But it does not 
 follow that a short string, which, with moderate tension, naturally produces a high note, 
 should be able, by a diminution of the tension, to give out a deep one; for, although this 
 might be theoretically possible, yet it cannot be accomplished in practice ; since the vibrations 
 become irregular on account of the diminished elasticity .j" These considerations are in them- 
 selves sufficient to destroy the supposed analogy ; and to prove that the Chordae Vocales can- 
 not be reduced to the same category with vibrating strings. 
 
 b. The next kind of instrument, with which some analogy might be suspected, is the 
 Flute-pipe, in which the sound is produced by the vibration of an elastic column of air con- 
 tained in the tube ; and the pitch of the note is determined almost entirely by the length of the 
 column, although slightly modified by its diameter, and by the nature of the embouchure or 
 mouth from which it issues. This is exemplified in the German Flute, and in the English 
 Flute or Flageolet; in both of which instruments, the acting length of the pipe is determined, 
 by the interval between the embouchure and the nearest of the side apertures ; by opening 
 or closing which, therefore, a modification of the tone is produced. In the Organ, of which 
 the greater number of pipes are constructed upon this plan, there is a distinct pipe for every 
 note ; and their length increases in a regular scale. It is, in fact, with flute-pipes as wim 
 strings, that a diminution in length causes an increase in the number of vibrations, in an 
 inverse proportion ; so that of two pipes, one being half the length of the other, the shorter 
 will give a tone which is the octave above the other, the vibrations of its column of air being 
 twice as rapid. Now there is nothing in the form or dimensions of the column of air be- 
 tween the larynx and the mouth, which can be conceived to render it at all capable of such 
 vibrations, as are required to produce the tones of the Human voice ; though there is some 
 doubt, whether it is not the agent in the musical tones of certain Birds. The length of an 
 open pipe necessary to give the lowest G of the ordinary bass voice, is nearly six feet ; and 
 the conditions necessary to produce the higher notes from it, are by no means those which 
 we find to exist in the process of modulating the human voice. 
 
 c. We now come to the third class of instruments, in which sound is produced by the 
 vibration of Reeds or Tongues; these may either possess elasticity in themselves, or be made 
 elastic by tension. The reeds of the Mouth-Eolina, Accordion, Seraphine, &c., are examples 
 of instruments of this character, in which the lamina vibrates freely in a sort of frame, that 
 allows the air to pass out on all sides of it through a narrow channel, thus increasing the 
 strength of the blast : whilst in the Hautboy, Bassoon, &c., and in Organ-pipes of similar con- 
 struction, the reed is attached to one end of a pipe. In the former kind, the sound is pro- 
 duced by the vibration of the tongue alone, and is regulated entirely.by its length and elasti- 
 city; whilst in the latter, its pitch is dependent upon this conjointly with the length of the 
 tube, the column of air contained in which is thrown into simultaneous vibration. Some 
 interesting researches on the effect produced on the pitch of a sound given by a reed, through 
 the union of it with a tube, have been made by M. W. Weber ; and, as they are important 
 in furnishing data, by which the real nature of the vocal organ may be determined, their 
 chief results will be here given. i. The pitch of a reed may be lowered, but cannot be 
 raised, by joining it to a tube. u. The sinking of the pitch of the reed thus produced, is at 
 the utmost not more than an octave, in. The fundamental note of the reed thus lowered, may 
 be raised again to its original pitch, by a further lengthening of the tube : and by a further 
 increase is again lowered, iv. The length of tube, necessary to lower the pitch of the in- 
 strument to any given point, depends on the relation which exists between the frequency of 
 the vibrations of the tongue of the reed, and those of the column of air in the tube, each 
 taken separately. From these data, and from those of the preceding paragraph, it follows 
 that, if a wind-instrument can, by the prolongation of its tube, be made to yield tones of any 
 depth in proportion to the length of the tube, it must be regarded as a flute-pipe ; whilst, if 
 its pitch can only be lowered an octave or less (the embouchure remaining the same) by 
 lengthening the tube, we may be certain that it is a reed instrument. The latter proves to 
 be the case in regard to the Larynx. 
 
 607. It is evident from the foregoing considerations, that the action of the 
 Larynx has more analogy to that of reed instruments, than it has to that either 
 
 * Thus in the Piano-forte, where there are strings for each note, a gradual shortening is 
 seen from the lowest to the highest; and in the Violin the change of tone is produced by 
 stopping the strings with the finger, so as to diminish their acting length. 
 
 f Thus it would be impossible to produce good Bass notes on the strings of a Violin, by 
 diminishing their tension; the length afforded by the Violoncello or Double Bass is requisite. 
 The striking difference between the tone of the Bass strings in the Grand Piano-forte and the 
 small upright Piccolo, is another exemplification of the same principle ; being chiefly due to 
 the length and tension of the former, as contrasted with the shortness and slackness of the 
 latter. 
 
ACTIONS OF THE LARYNX. 
 
 461 
 
 of vibrating strings, or of flute, pipes. There would seem, at first sight, to be 
 a marked difference in character, between the Chords Vocales, and the tongue 
 of any reed instrument ; but this difference is really by no means considera- 
 ble. In a reed, elasticity is a property of the tongue itself, when fixed at one 
 end, the other vibrating freely ; but by a membranous lamina, fixed in the 
 same manner, no tone would be produced. If such a lamina, however, be 
 made elastic by a moderate degree of tension, and be fixed in such a manner 
 as to be advantageously acted on by a current of air, it will give a distinct 
 tone. It is observed by Miiller, that membranous tongues made elastic by 
 tension, may have either of three different forms, i. That of a band extended 
 by a cord, and included between two firm plates, so that there is a cleft for 
 the passage of air on each side of the tongue, n. The elastic membrane 
 may be stretched over the half or any portion of the end of a short tube, the 
 other part being occupied by a solid plate, between which and the elastic 
 membrane a narrow fissure is left. in. Two elastic membranes may be ex- 
 tended across the mouth oY a short tube, each covering a portion of the opening, 
 and having a chink left open between them. This last is evidently the form 
 most allied to the Human Glottis ; but it may be made to approximate still more 
 closely, by prolonging the membranes in a direction parallel to that of the cur- 
 rent of air, so that not merely their edges, but their whole planes, shall be 
 thrown into vibration. Upon this principle, a kind of artificial Glottis has 
 been constructed by Mr. Willis ; the conditions of action, and the effects of 
 which, are so nearly allied to that of the real instrument, that the similar cha- 
 racter of the two can scarcely be doubted. The following is his description 
 of it. "Let a wooden pipe be prepared of the form of Fig. 198 a, having a 
 foot, c, like that of an organ-pipe, and an upper opening, long and narrow, as 
 at B, with a point A, rising at one 
 
 end of it. If a piece of leather, or Fig. 198. 
 
 still better, of sheet India-rubber, be a & 
 
 doubled round this point, and secur- 
 ed by being bound round the pipe 
 at D with strong thread, as in Fig. 
 198, &, it will give us an artificial 
 glottis, with its upper edges G H, 
 which may be made to vibrate or 
 not, at pleasure, by inclining the 
 planes of the edges. A couple of 
 pieces of cork, E, F, may be glued 
 to the corners, to make them more 
 manageable. From this machine, 
 various notes may be obtained, by 
 stretching the edges in the direction 
 of their length, G H ; the notes rising 
 in pitch with the increased tension, 
 although the length of the vibrating 
 edge is increased. It is true, that a 
 scale of notes equal in extent to that 
 'of the human voice, cannot be ob- Artificial Glottis. 
 
 tained from edges of leather; but 
 
 this scale is much greater in India-rubber than in leather ; and the elasticity 
 of them both is so much inferior to that of the vocal ligaments, that we may 
 readily infer that the great scale of the latter is due to its greater elastic pow- 
 ers." By other experimenters, the tissue forming the middle coat of the arte- 
 ries has been used for this purpose, in the moist state, with great success ; 
 with this, the tissue of the vocal ligaments is nearly identical. It is worthy 
 
 39* 
 
462 OF THE VOICE AND SPEECH. 
 
 of remark that, in all such experiments, it is found that the two membranes 
 may be thrown into vibration, when inclined towards each other in various 
 degrees, or even when they are in the same plane, and their edges only ap- 
 proximate ; but that the least inclination from each other (which is the posi- 
 tion the vocal ligaments have during the ordinary state of the glottis, 605,) 
 completely prevents any sonorous vibrations from being produced. 
 
 608. The pitch of the note produced by membranous tongues, may be 
 affected in several ways. Thus, an increase in the strength of the blast, which 
 has little influence on metallic reeds, raises their pitch very considerably ; 
 and in this manner the note of a membranous reed may be raised by semitones, 
 to as much as a fifth above the fundamental. The addition of a pipe has 
 nearly the same effect on their pitch, as on that of metallic reeds ; but it can- 
 not easily be determined with the same precision. The effect of the junction 
 of a pipe with a double membranous tongue, is well shown in the Trumpet, 
 Horn, and other instruments ; which require the vibration of the lips, as well 
 as a blast of air, for the production of their sound,' having no reed of their 
 own. By some, these instruments have been classed with Flute-pipes ; but 
 the conditions of their action are entirely different. The mouth-piece of the 
 horn or trumpet is incapable of yielding any tone, when a current of air is 
 merely blown through it ; and the lips are necessary to convert it into a musi- 
 cal reed, being rendered tense by the contraction of their sphincter, partly 
 antagonized by the slightly-dilating action of other muscles. The variation 
 of the tension of the lips is effected by muscular effort ; and several different 
 notes may be produced with a pipe of the same length ; but there is a certain 
 length of the column of air, which is the one best adapted for each tone ; and 
 different instruments possess various contrivances for changing this. It has 
 been recently ascertained, that the length of the pipe prefixed to the reed, has 
 also a considerable influence on its tone, rendering it deeper in proportion as 
 it is prolonged, down to nearly the octave of the fundamental note ; but the 
 pitch then suddenly rises again, as in the case of the tube placed beyond the 
 reed. The researches of Miiller, however, have not succeeded in establishing 
 any very definite relation between the length of the two tubes, in regard to 
 their influence on the pitch of the reed placed between them. 
 
 609. From the foregoing statements it appears, that the true theory of the 
 Voice may now be considered as well established, in regard to this essential 
 particular, that the sound is the result of the vibrations of the vocal ligaments, 
 which take place according to the same laws with those of metallic or other 
 elastic tongues : and that the pitch of the notes is chiefly governed by the 
 tension of these laminae. With respect, however, to the modifications of these 
 tones, induced by the shape of the air-passages, both above and below the 
 larynx, by the force of the blast, and by other concurrent circumstances, little 
 is certainly known. Hence it is, that on the theory of the production of what 
 are called falsetto notes, there is much difference of opinion amongst Physi- 
 ologists. Some have contended, that these tones are produced by the vibra- 
 tion of the vocal ligaments along only a part of their length ; but this is cer- 
 tainly untrue. By Miiller it is believed, that in the falsetto notes merely the 
 thin border of the glottis vibrates, so that the fissure remains distinctly visible ; 
 whilst in the production of the ordinary vocal tones, the whole breadth of the 
 vocal ligaments is thrown into strong vibrations, which traverse a wider sphere, 
 so that a confused motion is seen in the lips of the glottis, rendering its fissure 
 obscure. That the tension of the vocal cords is not diminished (as it ought 
 to be if only a part of their length were being used), but is progressively in- 
 creased, as we pass from the ordinary to the falsetto scale, any one may con- 
 vince himself, by placing his finger on the interval between the thyroid and 
 
ACTIONS OF THE LARYNX. 463 
 
 cricoid cartilages, as formerly described ( 603).* A very important adjunct 
 to the production of the higher notes, has been pointed out by Miiller, as 
 being afforded by the modification in the space included between the two 
 sides of the thyroid cartilage, which is effected by the thyro-arytenoidei. He 
 had experimentally ascertained, that the introduction of a hollow plug into the 
 upper end of the pipe beneath his artificial larynx (and therefore just below 
 the reed), by diminishing its aperture, produced a considerable elevation of 
 the tone. The action may be imitated in the human larynx, when made the 
 subject of experiment, by compressing the thyroid cartilage laterally; and in 
 this manner, the natural voice could be made to extend through a range, that 
 could otherwise be only reached by a falsetto. 
 
 610. The strength of the tone produced in the larynx, is much increased 
 by the resonance of the elastic tissue, which it contains in various other parts ; 
 but still more, perhaps, by that produced by the air in the trachea, bronchi, 
 and pulmonary cells. This comes to be of great importance in the pheno- 
 mena of auscultation. The aerial resonance is loudest where any large body 
 of air is collected together, as in the trachea, the larger bronchi, an emphyse- 
 matous dilatation, or a cavity resulting from tubercular softening. On the 
 other hand, solidification of the pulmonary tissue will produce a resonance of 
 a somewhat different kind. The influence of the prefixed and superadded 
 tubes, in modifying the tones produced by the Human larynx, has been found 
 by Prof. Miiller not to be at all comparable to that which they exercised 
 over the artificial larynx ; the reason of which difference does not seem very 
 apparent. It appears, however, that there is a certain length of the prefixed 
 tube, as there is a certain distance of the vibrating lamina?, and a certain 
 length or form of the tube above, which is most favourable to the produc- 
 tion of each note ; and the downward movement of the whole vocal organ, 
 which takes place when we are sounding deep notes, and its rise during the 
 elevation of the tones, have been supposed to have the purpose of making this 
 adjustment in the length of the trachea; but this requires the supposition, 
 that the real length of the trachea is shortened whilst it appears extended, 
 for which there seems no foundation. It is considered by Mr. Wheatstone, 
 that the column of air in the trachea may divide itself into harmonic lengths, 
 and may produce a reciprocation of the tone given by the vocal ligaments 
 ( 560) ; and in this manner he considers that the falsetto notes are to be 
 explained. It may be added, that the partial closing of the epiglottis seems 
 to assist in the production of deep notes, just as the partial covering of the 
 top of a short pipe fixed to a reed will lower its tone ; and that something of 
 this kind takes place during natural vocalization, would appear, from the re- 
 traction and depression of the tongue which accompany the lowering of the 
 front of the head, when the very lowest notes are being sounded. The arches 
 of the palate and uvula become contracted during the formation of the higher 
 tones ; but no difference can be perceived in their state, whether these tones 
 be falsetto or not; hence it would appear that they have no concern in this 
 peculiarity ; and the purpose of their increased tension is probably to main- 
 tain their power of resonance. The experiments of Savart have shown, that 
 a cavity which only responds to a shrill note, when its walls are firm and dry, 
 may be made to afford a great variety of lower tones, when its walls are 
 
 * That the falsetto voice differs in some essential particular from the natural, is evident 
 from this, that many persons who possess a considerable range of both, are yet unable to 
 unite them, so as to sing through the whole scale without a marked interruption. Thus a 
 gentleman of the Author's acquaintance has a bass voice, ranging from the lowest D of the 
 Square Piano to the second D above; and a falsetto ranging from the A below this to the E 
 of the octave above, so as to give a compass of more than three octaves on the whole ; yet . 
 the two registers cannot be smoothly blended. 
 
464 OF THE VOICE AND SPEECH. 
 
 moistened and relaxed in various degrees. This observation may probably 
 be applied also to the trachea. 
 
 611. These and numerous other muscular actions, which are employed in 
 the production and regulation of the voice, are effected by an impulse which 
 can scarcely be termed Voluntary, and the nature of which is a curious sub- 
 ject for inquiry. It may be safely affirmed, that the production of sounds is 
 in itself an Instinctive action; although the combination of these, whether into 
 music or articulate language, is a matter of acquirement. Now it might be 
 supposed that the Will has sufficient power over the vocal muscles, to put 
 them into any state requisite for its purposes, without any further condition : 
 but a little self-experiment will prove that this is not the case. No definite 
 tone can be produced by a Voluntary effort, unless that tone be present to the 
 mind, during however momentary an interval, either as immediately conveyed 
 to it by an act of Sensation, recalled by an act of Conception, or anticipated 
 by an effort of the imagination. When thus present, the Will can enable the 
 muscles to assume the condition requisite to produce it; but under no other 
 circumstances does this happen, except by a particular mode of discipline 
 presently to be adverted to. The action itself, therefore, must be reduced to 
 the class of consensual movements ; and we must suppose that the will is 
 exercised in preparing the conditions requisite for it, rather than in directly 
 exciting it. That those who are unfortunately labouring under congenital 
 deafness, are thence debarred from learning the use of Voice in the ordinary 
 manner, is well known; the consensual action cannot be excited, either 
 through sensations of the present, or conceptions of the past ; and the imagi- 
 nation is entirely destitute of power to suggest that which has been in no 
 shape experienced. But such persons may be taught to speak in an imperfect 
 manner, by causing them to imitate particular muscular movements, which 
 they may be made to see; and it is evident, that they must be guided in the 
 imitation and ordinary performance of those movements, by the common 
 muscular sensations which accompany them, and not by the sensations con- 
 veyed through the Auditory nerve, which are ordinarily by far the most pre- 
 cise guides. Many instances, indeed, are on record, in which persons entirely 
 deaf were enabled to carry on a conversation in the regular way; judging of 
 what was said, by the movements of the lips and tongue, which they haol 
 learned to connect with particular syllables ; and regulating their own voices 
 in reply, by their voluntary power, guided by muscular sensation.* 
 
 [In the foregoing account of the Physiology of Voice, the author has been chiefly guided 
 by the excellent paper by Mr. Willis in the Transactions of the Cambridge Philosophical 
 Society, vol. iv. ; and by the elaborate investigations of Miiller and his coadjutors, as detailed 
 in the Fourth Book of his Physiology.] 
 
 %>Of Articulate Sounds. 
 
 612. The larynx, as now described, is capable of producing those tones of 
 which Voice fundamentally consists, and the sequence of which becomes 
 Music : but Speech consists in the modification of the laryngeal tones, by 
 other organs, intervening between the Glottis and the Os Externum ; so as 
 to produce those articulate sounds, of which Language is formed. It cannot 
 be questioned that Music has its language ; and that it is susceptible of ex- 
 pressing the emotional states of the mind, among those at least who have 
 been accustomed to associate these with its varie4 modes, to even a higher 
 degree than articulate speech. But it is incapable of addressing the intellect, 
 by conveying definite ideas of objects, properties, actions, &c,, in any other 
 
 * See Johnstone on Sensation, p. 128. 
 
OF ARTICULATE SOUNDS. 465 
 
 way than by a kind of imitation, which may be compared to the signs used 
 in hieroglyphic writing. These ideas it is the peculiar province of articulate 
 language to convey ; and we find that the vocal organ is adapted to form a 
 large number of simple sounds, which may be readily combined into groups, 
 forming words. The number of combinations which can be thus produced, 
 is so inexhaustible, that every language has its own peculiar series ; no dif- 
 ficulty being found in forming new ones to express new ideas. There is con- 
 siderable diversity in different languages, even with regard to the use of the 
 simplest of these combinations ; some of them are more easy of formation 
 than others, and these accordingly enter into the composition of all languages ; 
 whilst of the more difficult ones, some are employed in one language, some 
 in another, no one language possessing them all. Without entering into any 
 detailed account of the mechanism required to produce each of these simple 
 sounds, a few general considerations will be offered in regard to the classifi- 
 cation of them ; and the peculiar defect of Articulation, termed Stammering, 
 will be briefly treated of. 
 
 613. Vocal sounds are divided into Vowels and Consonants ; and the dis- 
 tinctive characters of these are usually considered to be, that the Vowels are 
 produced by the Voice alone, whilst the sound of the Consonants is formed 
 by some kind of interruption to the voice, so that they cannot be properly 
 expressed, unless conjoined with a vowel. The distinction may be more 
 correctly laid down, however, in this manner : the Vowel sounds are con- 
 tinuous tones, modified by the form of the aperture through which they pass 
 out ; whilst in sounding Consonants, the breath suffers a more or less com- 
 plete interruption, in its passage through parts anterior to the larynx. Hence 
 the really simple Vowel sounds are capable of prolongation during any time 
 that the breath can sustain them ; this is not the case, however, with the 
 real Diphthongal sounds (of which it will presently appear that the English i 
 is one) ; whilst it is true of some Consonants. It seems to have been for- 
 gotten by many of those who have written upon this subject, that the laryn- 
 geal voice is not essential to the formation of either vowels or consonants; for 
 all may be sounded in a whisper. It is very evident, therefore, that the 
 larynx is not primarily concerned in their production ; and this has been fully 
 established by the following experiment. A flexible tube was introduced by 
 M. Deleau through his nostril into the pharynx, and air was impelled by it 
 into the fauces ; then, closing the larynx, he threw the fauces into the differ- 
 ent positions requisite for producing articulate sounds, when the air impelled 
 through the tube became an audible whisper. The experiment was repeated, 
 with this variation, that laryngeal sounds were allowed to pass into the 
 fauces ; and each articulated letter was then heard double, in a proper voice 
 and in a whisper. 
 
 614. That the Vowels are produced by simple modifications in the form 
 of the external passages, is easily proved, both by observation and by imita- 
 tive experiment. When the mouth is opened wide, the tongue depressed, 
 and the velum palati elevated, so as to give the freest possible exit to the 
 voice, the vowel a in its broadest form (as in ah) is sounded.* On the other 
 hand, if the oral aperture be contracted, the tongue being still depressed, the 
 sound oo (the continental u) is produced. If attention be paid to the state of 
 the buccal cavity, during the pronunciation of the different vowel sounds, it 
 will be found to undergo a great variety of modifications, arising from varieties 
 of position of the tongue, the cheeks, the lips, and velum palati. The posi- 
 
 * Thi^ sound of the vowel a is scarcely used in our language, though very common in 
 most of the continental tongues ; the nearest approach to it in English is the a in far : but 
 this is a very perceptible modification, tending towards au. 
 
466 OF THE VOICE AND SPEECH. 
 
 tion of the tongue is, indeed, one of the primary conditions of the variation 
 of the sound ; for it may be easily ascertained that, by peculiar inflexions of 
 this organ, a great diversity of vowel sounds may be produced, the other parts 
 remaining the same. Still there is a certain position of all the parts, which 
 is most favourable to the formation of each of these sounds ; but this could 
 not be expressed without a lengthened description. The following table, 
 slightly altered from that of Kempelen, expresses the relative dimensions of 
 the buccal cavity and of the oral orifice, for some of the principal of these ; 
 the number 5 expressing the largest size, and the others in like proportion : 
 
 Vowel. Sound. Size of oral opening. Size of buccal cavity. 
 
 a as in ah 5 5 
 
 a as in name 4 2 
 
 e as in theme 3 1 
 
 o as in cold 2 4 
 
 oo as in cool 1 5 
 
 These are the sounds of the five vowels, a, e, i, o, u, in most Continental 
 languages ; an(J it cannot but be admitted, that the arrangement is a much more 
 natural one than that of our own vowel series. The English a has three dis- 
 tinct sounds capable of prolongation:* the true broad a of ah, slightly modi- 
 fied in far; the a of fate, corresponding to the e of French; and the a of fall, 
 which should be really represented by au. This last is a simple sound, though 
 commonly reckoned as a diphthong. In Kempelen's scale, the oral orifice 
 required to produce it would be about 3, and the size of the buccal cavity 4.t 
 On the other hand, the sound of the English i cannot, like that of a true vowel, 
 be prolonged ad libitum; it is in fact a sort of Diphthong, resulting from the 
 transition from a peculiar indefinite murmur to the sound of e, which takes 
 its place when we attempt to continue it. The sound oy or oi, as in oil, 
 is a good example of the true diphthong; being produced by the transition 
 from au to e. In the same manner, the diphthong ou, which is the same with 
 ow in owl, is produced in the rapid transition from the broad a of ah, to the 
 oo of cool. Much discussion has taken place as to the true character of y, 
 when it commences a^ word, as in yet, yawl, &c. ; some having maintained 
 that it is a consonant, (for the very unsatisfactory reason, that we are in the 
 habit of employing a rather than an, when we desire to prefix the indefinite 
 article to such words,) whilst others regard it as a peculiar vowel. A slight 
 attention to the position of the vocal organs during its pronunciation, makes it 
 very clear, that its sound in such words really corresponds with that of the 
 long (English) e; the pronunciation of the word yawl being the same as that 
 of eaul, when the first sound is not prolonged, but rapidly transformed into 
 the second. The sound of the letter tu, moreover, is really of the vowel 
 character, being formed in the rapid transition from oo to the succeeding 
 vowel ; thus wall might be spelt ooall. Many similar difficulties might be 
 removed, and the conformity between spoken and written language might be 
 greatly increased (o as to render far more easy the acquirement of the former 
 from the latter), by due attention to the state of the vocal organs in the pro- 
 duction of the simple sounds. 
 
 * The short vowel sounds, as a in fat, e in met, o in pot, &c., are not capable of prolonga- 
 tion. 
 
 f" The mode of making a determination of this kind may here be given, for the sake of 
 example. If the broad a be sounded, the mouth and fauces being opened wide, and we 
 contract the oral orifice by degrees, at the same time slightly elevating the point of the 
 tongue, we gradually come to the sound of au; by still further contracting the orifice, and 
 again depressing the tongue, we form oo. On the other hand, in sounding e, the tongue is 
 raised nearly to the roof of the mouth ; if it be depressed, without the position of the lips 
 being altered, au is given. 
 
OF ARTICULATE SOUNDS. 467 
 
 615. It is not very difficult to produce a tolerably good artificial imitatijp 
 of the Vowel sounds. This was accomplished by Kempelen, by means of an 
 India-rubber ball, with an orifice at each end, of which the lower one was 
 attached to a reed; by modifying the form of the ball, the different vowels 
 could be sounded during the action of the reed. He also employed a short 
 funnel-like tube, and obtained the different sounds by covering its wide open- 
 ing to a greater or less extent. This last experiment has been repeated by 
 Mr. Willis ; who has also found that the vowel sounds might be imitated, by 
 drawing out a long straight tube from the reed. In this experiment he arrived 
 at a curious result: with a tube of a certain length, the series of vowels, i, e, 
 a, o, u, was obtained, by gradually drawing it out; but, if the length was in- 
 creased to a certain point, a further gradual increase would produce the same 
 sequence in an inverted order, w, o, , c, i; a still further increase would pro- 
 duce a return to the first scale, and so on. When the pitch of the reed was 
 high, and the pipe short, it was found that the vowels o and u could not be 
 distinctly formed, the proper tone being injured by the elongation of the 
 pipe necessary to produce them ; and this, Mr. Willis remarks, is exactly the 
 case in the Human voice, most singers being unable to pronounce u and o 
 upon their highest notes. 
 
 616. The most natural primary division of the Consonants is into those 
 which require a total stoppage of the breath at the moment previous to their 
 being pronounced, and which, therefore, cannot be prolonged ; and those in 
 pronouncing which the interruption is partial, and which can, like the vowel 
 sounds, be prolonged ad libitum. The former have received the designation 
 of explosive; and the latter of continuous. In pronouncing the explosive 
 consonants, the posterior nares are completely closed, so that the exit of air 
 through the nose is altogether prevented; and the current may be checked in 
 the mouth in three ways, by the approximation of the^lips, by the approxi- 
 mation of the point of the tongue to the front of the palate, and by the ap- 
 proximation of the middle of the tongue to the arch of the palate. In the first 
 of these modes, we pronounce the letters 6, and p; in the second, d and t; 
 in the third, the hard g, and k. The difference between 6, </, and g, on the 
 one hand, and p, /, and &,* on the other, seems to depend on this ; that in 
 the former group the approximating surfaces are larger, and the breath is sent 
 through them more strongly at the moment of opening, than in the latter. 
 The continuous consonants may be again subdivided, according to the degree 
 of freedom with which the air is allowed to make its exit, and the compression 
 which it consequently experiences, i. The first class includes those, in which 
 no passage of air takes place through the nose, and in which the parts of the 
 mouth that produce the sound are nearly approximated together, so that the 
 compression is considerable. This is the case with v andjf, which are pro- 
 duced by approximating the upper incisors to the lower lip; and which stand 
 in nearly the same relation to each other, as that which exists between d and 
 /, or b and/?. The sibilant sounds z and s, stand in nearly the same relation 
 to each other; they are produced by the passage of air between the point of 
 the tongue and the front of the palate, the teeth being at the same time nearly 
 closed. The simple sound sh is formed, by narrowing the channel between 
 the clorsum of the tongue and the palate ; the former being elevated towards 
 the latter, through a considerable part of its length. If, in sounding s, 
 we raise the point of the tongue a very little, so as to touch the palate, the 
 sound of / is evolved; and in the same manner d is produced from z. This 
 class also includes the th; which, being a perfectly simple sound, ought to be 
 expressed by a single letter, as in Greek; instead of by two, of which the 
 
 * For the sake of proper comparison, this letter should be sounded not as kay but as key. 
 
468 OP THE VOICE AND SPEECH. 
 
 combination does not really produce anything like it. For producing this 
 sound, the point of the tongue is applied to the back of the incisors, or to the 
 front of the palate, as in sounding t;* but, whilst there is complete contact of 
 the tip, the air is allowed to pass out around it. n. In the second class of 
 continuous consonants, including the letters ra, n, /, and r, the nostrils are not 
 closed; and the air thus undergoes very little compression, even though the 
 passage of air through the oral cavity is almost or completely checked. In 
 pronouncing m and n, the breath passes through the nose alone; and the dif- 
 ference of the sound of these two letters, must be due to the variation in the 
 form of the cavity of the mouth, which acts by resonance. The letter m is a 
 labial, like b ; and the only difference between the two is, that in the former 
 the nasal passage is open, whilst the mouth remains closed; whilst in the 
 latter, the nose is entirely closed, and the sound is formed at the moment of 
 opening the mouth. The same correspondence exists between n and t, or n 
 and g (the particular part of the tongue approximated to the palate not being 
 of much consequence in the pronunciation of n}\ and hence it is that the 
 transition from n to t, or from n to g, is so easy, that the combinations nt and 
 ng are found abundantly in most languages. The sound of / is produced, by 
 bringing the tip of the /tongue into contact with the palate, and allowing the 
 air to escape around it, at the same time that a vocal tone is generated in the 
 larynx ; it differs, therefore, from th in the position at which the obstruction 
 is interposed, as well as in the slight degree of the compression of the air 
 which it involves. The sound of the letter r depends on an absolute vibration 
 of the point of the tongue, in a narrow current of air forced between the tongue 
 itself and the palate, m. The sounds of the third class are scarcely to be 
 termed consonants, since they are merely aspirations, caused by an increased 
 force of breath. These are A, and the cAt of most foreign languages (the 
 Greek %). The first i$ a simple aspiration ; the second, an aspiration modified 
 by the elevation of the tongue, causing a slight obstruction to the passage of 
 air, and an increased resonance in the back of the mouth. This sound would 
 become either g or A;, if the tongue, whilst it is being produced, were carried 
 up to touch the palate.^ 
 
 617. These distinctions come to be of much importance, when we apply 
 ourselves to the treatment of defects of articulation. Great as is the number 
 of muscles employed in the production of definite vocal sounds, the number 
 is much greater for those of articulate language ; and the varieties of combina- 
 tion, which we are continually forming unconsciously to ourselves, would not 
 be suspected, without a minute analysis of the separate actions. Thus, in ut- 
 tering the explosive sounds, we check the passage of air through the posterior 
 nares, in the very act of articulating the letter ; and yet, this important move- 
 ment commonly passes unobserved. We must regard the power of forming 
 the several articulate sounds which have been adverted to, and their simple 
 combinations, as so far resulting from intuition, that it can in general be more 
 readily acquired by early practice, than other actions of the same complexity ; 
 so that we may consider these movements as having somewhat of the same 
 consensual character as that which has been attributed to the purely vocalizing 
 actions ( 611). But there is in many individuals a deficiency of the power 
 of rightly combining them ; from which Stammering and other imperfections 
 result. 
 
 618. Many theories regarding the nature of Stammering have been pro- 
 posed ; and there can be little doubt, that the impediment may be attributed to 
 
 * Hence it is easy to understand the substitution of t or d, for the English th, by foreigners, 
 f The English ch is merely a combination of t with sh; thus chime might be spelt tshime. 
 j The general classification proposed by Dr. M. Hall is here adopted, with some modifica- 
 tion as to the details. 
 
OF ARTICULATE SOUNDS. 469 
 
 a great variety of exciting causes. A disordered action of the nervous cen- 
 tres must, however, be regarded as the proximate cause ; though this may be 
 (to use the language of Dr. M. Hall) either of centric or of excentric origin, 
 that is, it may result from a morbid condition of the ganglionic centre, or 
 from an undue excitement conveyed through its afferent nerves. When of 
 centric origin (and this is probably the most general case), the phenomena of 
 Stammering and Chorea have a close analogy to each other ; in fact, stammer- 
 ing is frequently one of the modes in which the disordered condition of the 
 nervous system in Chorea manifests itself. It is in the pronunciation of the 
 Consonants of the explosive class, that the stammerer experiences the greatest 
 difficulty. The total interruption to the breath which they occasion, frequently 
 becomes quite spasmodic ; and the whole frame is thrown into the most dis- 
 tressing semi-convulsive movement, until relieved by expiration.* In the pro- 
 nunciation of the continuous Consonants of the first class, the stammerer 
 usually prolongs them, by a spasmodic continuance of the same action; and 
 there is, in consequence, an impeded, but not a suspended respiration. The 
 same is the case with the / and r in the second class. In pronouncing the m 
 and n, on the other hand, as well as the aspirates and vowels, it is sometimes 
 observed that the stammerer prolongs the sound, by a full and exhausting ex- 
 piration. In all these cases, then, it seems as if the muscular sense, resulting 
 from each particular combination of actions, became the stimulus to the invo- 
 luntary prolongation of that action. In some instances, it is possible that the 
 defect may result from malformation of the parts about the fauces, producing 
 an abnormal stimulus of this kind, in some particular positions of the organ ; 
 and such cases may be really benefited by an operation for the removal of 
 these parts. But the effect of the operation is evidently for the most part upon, 
 the Nervous System ; and it coincides with what may be frequently observed, 
 that the Stammering is increased under any unusual excitement, especially 
 of the Emotional kind. 
 
 619. The method proposed by Dr. Arnott for the prevention of Stammer- 
 ing, consists in the connection of all the words by a vocal intonation, in such 
 a manner, that there shall never be an entire stoppage of the breath. It is 
 justly remarked by Miiller, however, that this plan may afford some benefit, 
 but cannot do everything; since the main impediment occurs in the middle of 
 words themselves. One important remedial means, on which too much stress 
 cannot be laid, is to study carefully the mechanism of the articulation of the 
 difficult letters, and to practise their pronunciation repeatedly, slowly, and 
 analytically. The patient would at first do well to practise sentences, from 
 which the explosive consonants are omitted ; his chief difficulty, arising from 
 1he spasmodic suspension of the expiratory movement, being thus avoided. 
 Having mastered these, he may pass on to others, in which the difficult letters 
 are sparingly introduced ; and may finally accustom himself to the use of 
 ordinary language. One of the chief points to be aimed at, is to make the 
 patient feel that he has command over his muscles of articulation ; and this 
 is the best done, by gradually leading him from that which he finds he can 
 do, to that which he fears he cannot. The fact that stammering people are 
 able to sing their words better than to speak them, has been usually explained 
 on the supposition that, in singing, the glottis is kept open, so that there is 
 less liability to spasmodic action ; if, however, as here maintained, the spas- 
 modic action is not in the larynx, but in the velum palati and the muscles of 
 articulation, the difference must be due to the direction of the attention rather 
 
 * By Dr. Arnott this interruption is represented as taking place in the larynx ; that such is 
 not the case, the Author believes that a little attention to the ordinary phenomena of voice will 
 satisfactorily prove. 
 
 40 
 
470 INFLUENCE OF THE NERVOUS SYSTEM 
 
 to the muscles of the larynx than to those of the mouth. Every one must 
 have noticed how much the impediment of Stammerers is increased, when 
 they are particularly anxious to speak fluently. 
 
 CHAPTER IX. 
 
 INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC FUNCTIONS. , 
 
 620. OF the modes in which the Nervous System influences the Organic 
 Functions, a part have been already considered. It has been shown ( 183) 
 that it is concerned in providing the conditions, either immediate or remote, 
 under which alone these functions can be performed ; so that, when its ac- 
 tivity ceases, they cannot be much longer maintained. The* first mode in 
 which it operates upon them is, therefore, by producing sensible movements 
 in the Muscles or other contractile organs, which can be stimulated to action 
 through it ; and the contractions thus induced have usually an important effect 
 upon them, which varies, however, in each individual case. Thus, the pro- 
 cess of Nutritive Absorption, which is the very first stage in the operations of 
 Vegetative Life, and which is accomplished in Plants by the accidental con- 
 tact of the alimentary materials with the radical fibres, cannot take place in 
 Animals, until the muscular apparatus of prehension has been set in action by 
 the Will, that of deglutition by the Reflex Function, and that of the intestinal 
 canal by direct stimulation, the two former kinds of contraction being ac- 
 complished entirely through the Nervous System, and the latter being influ- 
 enced by it. The Circulation of Blood, too, is chiefly effected, in the higher 
 Animals at least, by the contractions of a muscular organ of impulsion ; which 
 contractions, though not essentially dependent upon Nervous action, are 
 nevertheless greatly influenced by it. The function of Respiration, again, 
 cannot be maintained even for a short time, without muscular movement, ex- 
 cited through the Nervous System. The functions of Nutrition and Secre- 
 tion are more independent of it ; taking place, as in Plants, so long as the 
 conditions are supplied by other functions, without any sensible movements 
 being actually concerned in them. We shall presently see, however, that 
 they are subject to a peculiar kind of Nervous influence, which does not 
 manifest itself in obvious movement, but in altered performance of the inti- 
 mate processes themselves ; showing itself in the character of the organized 
 tissue, or of the secreted product. The act of Excretion is, like ingestion, 
 entirely performed by Muscular movement, dependent upon Nervous agency. 
 Now, wherever such movements of distant organs are usually performed in 
 connection with each other, there is an obvious channel for one kind of sym- 
 pathy between them ; an interesting example of this, is the contraction of the 
 Uterus, which may be frequently made to occur, when that organ is in a re- 
 laxed state at the conclusion of labour, by applying suction or other irritation 
 to the nipple. 
 
 621. Sympathetic movements of this kind may be excited either through 
 the Cerebro-Spinal, or the Ganglionic systems ; and we shall be guided in 
 our determination of their channel in each particular case, by the distribution 
 of these systems respectively to the organ affected. The sympathetic move- 
 ments of the Muscles of Animal life appear to be chiefly, if not entirely, ex- 
 
ON THE ORGANIC FUNCTIONS. 471 
 
 cited through the Cerebro-Spinal system ; whilst those of the contractile tis- 
 sues of the Viscera ( 234) are probably excited through nerves, which, 
 though connected with the Cerebro-Spinal system, act under peculiar condi- 
 tions, and are commonly spoken of as forming part of the Sympathetic 
 system. It has been shown ( 388 393) that all the contractile organs, 
 which may be excited through the Sympathetic or Visceral system of nerves, 
 may also be made to act by stimuli applied to the roots of the Spinal nerves ; 
 but that each Cerebro-Spinal fibre appears to pass through several Ganglia, 
 before being distributed to the organs which it supplies. 
 
 a. Many speculations have been hazarded, as to the reasons why the Visceral nerves 
 are destitute of sensibility ; and, at the time when the Sympathetic was supposed to be 
 merely an offset from the Cerebro-Spinal system, it was imagined that the use of the gan- 
 glia upon the roots of the spinal nerves was to " cut off sensation" from those concerned in 
 the " vital and involuntary motions." The influence of Bichat's ingenious hypothesis, that 
 the Sympathetic system is complete and independent, ministering to the functions of Or- 
 ganic Life, as the Cerebro-Spinal does to those of Animal Life for a time caused this idea 
 to be abandoned. Since, however, it has been anatomically proved, that a large proportion 
 of the filaments of the visceral nerves are derived from the Spinal cord, this opinion has 
 been revived, in a somewhat modified form.* Nevertheless the evidence in its support is 
 somewhat vague ; especially if the truth of the doctrine formerly urged, that the Spinal 
 Cord is not itself a centre of sensation, be admitted. For it is only necessary to suppose, 
 that the white fibres of the Sympathetic nerve terminate in the true Spinal Cord, without 
 proceeding to the Brain, to have an explanation of the absence of sensory endowments in 
 the organs to which they are distributed, and of the complete removal of the muscles sup- 
 plied by their motor nerves, from voluntary control. That a few fibres, of which the actions 
 cannot be excited under ordinary circumstances, pass on to the Brain, would seem probable 
 from the fact of the sensibility of some parts, in disease, which are totally insensible in their 
 normal condition j a fact in the explication of which, the hypothesis just alluded to affords 
 no assistance. 
 
 622. It appears, then, that it may be stated as a general proposition, that 
 all the evident movements which can be excited, by irritation applied to one 
 part of the body, in the contractile organs or tissues of another, are really 
 effected through the true Spinal Cord ; whether the contractile organ be a 
 powerful muscle, or a thin and feeble layer of fibres around a blood-vessel or 
 duct. Upon the reasons why the fibres of the Visceral nerves should be so 
 peculiarly separated from the rest, we can at present only speculate ; but it 
 may not be considered improbable that, by their peculiar plexiform arrange- 
 ment in the various ganglia through which they pass, connections are estab- 
 lished between remote organs, which tend to bring their actions into closer 
 relation with each other, than would otherwise be the case. The existence 
 of such connections for the purpose of harmonizing the several movements 
 of the Viscera, which are concerned in the various and complex operations of 
 Digestion and its attendant processes, may be inferred from the perfect con- 
 formity which exists between them, during all their different states of regular 
 action ; and still more, perhaps, from the phenomena of their disordered con- 
 ditions. The study of these Sympathies is one of those departments of Phy- 
 siology, in which it maybe expected that much will be gained by patient and 
 well-directed investigation. 
 
 623. The movements immediately concerned in the Organic Functions, how- 
 ever, are not influenced by Reflex action alone, but also by Emotional condi- 
 tions of the mind. This is most obvious in regard to the Heart. Every one 
 must have experienced the disturbance of its pulsations, consequent upon ex- 
 citement of the feelings, of almost any description. But other organs probably 
 experience similar changes, although of a less manifest character. It is well 
 known that the Sympathetic system is largely distributed upon the trunks of 
 
 * See Dr. Alison on the Nerves of the Orbit; Edin. Phil. Trans., vol. xv.; and Med. Gaz. 
 vol. xxviii. p. 378. 
 
472 INFLUENCE OF THE NERVOUS SYSTEM 
 
 the blood-vessels, accompanying them to their minutest ramifications ; and it 
 will be hereafter shown ( 732), that the fibrous tissue of the walls of the ar- 
 teries is probably susceptible of influence from these nerves. There can be 
 little doubt, therefore, that they constitute the channel through which Emo- 
 tions operate, in producing sudden distension of particular parts of the vascu- 
 lar system, as in blushing, erection, &c. And to the same kind of influence, 
 more gradually exerted, we may very probably attribute the regulation of the 
 supply of blood which passes to different secreting organs, in varying condi- 
 tions of the system. 
 
 624. But the Sympathetic System does not consist of Cerebro-Spinal fila- 
 ments alone ; nor is its influence exerted only upon the motor or contractile 
 tissues of the body. There is good evidence, that the Nervous System has 
 an immediate action upon the molecular changes, which constitute the func- 
 tions of Nutrition, Secretion, &c. ; and the channel of such influence is pro- 
 bably to be found in that system of peculiar fibres formerly described ( 244), 
 which constitutes a considerable proportion of the Visceral nerves, existing 
 much more sparingly in most of the Cerebro-Spinal, but being abundant in 
 the Fifth pair. There is no valid reason, however, to believe that any of the 
 processes of Nutrition and Secretion are dependent upon this, or any other, 
 kind of Nervous agency. These processes go on with great rapidity and 
 energy in the Vegetable kingdom, in which nothing approaching to a Nervous 
 System exists ; and in the Animal kingdom they take place with equal vigour, 
 long before the least vestige of it appears. The Embryological researches 
 of Dr. Barry have fully proved, that in the earliest condition of foetal life, the 
 germ consists but of a congeries of cells, which have all originated in a single 
 one ; and from this mass, the several tissues are gradually generated, by a 
 process which is technically called histological* transformation, one set of 
 cells being converted into muscular tissue, anther into nervous tissue, another 
 into mucous membrane, and so on. Now since this is the case, it is evident 
 that all these processes of development must take glace, in virtue of the inhe- 
 rent properties of the primary tissue itself; since no nervous influence can be 
 supposed to operate, before nerves are called into existence. Throughout the 
 Animal body, it may be observed that, the more Vegetative the nature of any 
 function, the less is it connected with the Nervous System ; and all the ex- 
 periments, which have been regarded as proving that the Organic functions 
 are dependent upon Nervous influence, are really explicable, fully as well, 
 upon the supposition that they are capable of being affected by it, either in 
 the way of excitement or retardation (see 415). Moreover, there is abundant 
 evidence, that Secretion may take place after the death of the general system, 
 through the persistence of certain molecular changes, of which the essential 
 conditions are not immediately altered; thus Mr. T. Bell mentions that, in 
 dissecting the poison apparatus of a Rattle-snake, which had been dead for 
 some hours, the poison continued to be secreted, so fast as to require being 
 occasionally dried off. This is precisely what might have been anticipated, 
 from the independent power of growth in the secreting cells ; and other acts 
 of Nutrition are recorded to have occurred under similar circumstances. In 
 such a case, the Animal body is reduced to the condition of a Plant ; since 
 the influence of the Nervous system must then be entirely extinct. Upon 
 those who maintain that Nervous agency is a condition essential to those mo- 
 lecular actions, of which Nutrition and Secretion consist, it is incumbent, 
 therefore, to offer some more unexceptionable proof of their position than has 
 yet been given ; since their doctrine is opposed by so many considerations of 
 great weight. 
 
 * This term is used in contradistinction to morphological, which applies to the alterations 
 in the form of the several parts of the embryo. 
 
ON THE ORGANIC FUNCTIONS. 473 
 
 625. That many of the Organic Functions, however, are directly influenced 
 by the Nervous System, is a matter which does not admit of dispute ; and 
 this influence, exerted sometimes in exciting, sometimes in checking, and 
 sometimes in otherwise modifying them, may well be compared to that, 
 which the hand and heel of the rider have upon his horse, or which the en- 
 gine-driver exerts over a locomotive. It is most remarkably manifested in the 
 result of severe injury of the Nervous centres, such as concussion of the 
 Brain, or of the Solar plexus ( 580) ; for this does not merely produce a sus- 
 pension of the respiratory and other movements, which minister to the or- 
 ganic functions, and hence a gradual stagnation of the latter, but a sudden 
 and complete cessation of the whole train of action ; which cannot be attri- 
 buted to any other cause than a positive depressing influence of some kind, 
 propagated through the Nervous System. It will hereafter appear ( 701), 
 that in such cases even the vitality of the Blood is often affected; the usual 
 coagulation not taking place after death, so long, at least, as the blood remains 
 within the vessels. A similar general depression may result from Mental 
 Emotion, operating through the same channel ; but this more commonly 
 has rather a local action, or operates more gradually. The influence of the 
 Nervous System is often especially exerted, in giving temporary excitement 
 to a Secreting process ; which need not be kept in constant activity, or of 
 which circumstances may occasionally require an increase. This- is the 
 case, for example, in regard to the secretions connected with the process of 
 digestion, the Saliva, Gastric fluid, Bile, Pancreatic fluid, &c. ; all of these 
 being excited by the contact of the substances on which they act, with the 
 surfaces on which their respective ducts open. The secretion of Milk, again, 
 in a nursing female, may be excited by irritation of the nipple ; and the de- 
 termination of blood to the Mammae during pregnancy, must be due to in- 
 creased action in the part, excited by the changes occurring in the Uterus, 
 which can scarcely operate otherwise than through the Nervous System. No 
 other channel of influence can be well imagined for most of these operations, 
 than the Sympathetic system of Nerves ; since the organs in question are for 
 the most part supplied by it. There is an apparent exception, however, in 
 the case of the Salivary and Lachrymal glands, which are supplied by the 
 Fifth pair ; but this nerve contains so many organic filaments, and is so inti- 
 mately connected with the Sympathetic, as evidently to supply (in the head) 
 the place of a separate ganglionic system. It is by Nervous influence, that 
 the mucous secretion covering the membranes is caused to be regularly formed 
 for their protection ; for it is shown, by pathological facts, that, when this 
 influence is interrupted, and the secretion is no longer supplied, the membrane 
 losing its protection, is irritated by the air or the fluids with which it may be 
 in contact, and passes into an inflammatory condition. This is the explana- 
 tion of the fact, which has been well ascertained, that the Eye is liable to 
 suppurate when the Fifth pair has been divided ; and that the mucous Mem- 
 brane of the bladder becomes diseased in Paraplegia. 
 
 626. The influence of particular conditions of the mind, in exciting various 
 Secretions, is a matter of daily experience. The flow of Saliva, for exam- 
 ple, is stimulated by the idea of food, especially that of a savoury character. 
 The Lachrymal secretion, again, which is continually being formed to a small 
 extent, for the purpose of bathing the surface of the eye, is poured out in 
 great abundance under the moderate excitement of the emotions, either of 
 joy, tenderness, or grief. It is checked, however, by violent emotions ; hence 
 in intense grief the tears do not flow. It is a well-known proof of moderated 
 sorrow, when this takes place ; tears, however, do not bring relief, as is com- 
 monly believed, but they indicate that it has been brought. Violent emotion 
 may also suspend the Salivary secretion ; as is shown by the well-known test, 
 
 40* 
 
474 INFLUENCE OF THE NERVOUS SYSTEM 
 
 often resorted to in India, for the discovery of a thief amongst the servants of 
 a family, that of compelling all the parties to hold a certain quantity of rice 
 in the mouth during a few minutes, the offender being generally distin- 
 guished by the comparative dryness of his mouthful, at the end of the ex- 
 periment. The influence of the emotion of love-of-offspring, in increasing 
 the secretion of Milk, is well known. The formation of this fluid is con- 
 tinually going on during the period of lactation ; but it is greatly increased 
 by the sight of the infant, or even by the thought of him, especially when as- 
 sociated with the idea of suckling : this gives rise to the sudden rush of blood 
 to the gland, which is known by nurses as the draught, and which occasions 
 a greatly-increased secretion. The strong desire to furnish milk, together 
 with the irritation of the gland through the nipple, has often been effectual 
 in producing the secretion in girls and old women, and even in men ( 853, d). 
 The quantity of the Gastric secretion is increased by exhilaration ; at least 
 if we may judge from the increase of the digestive powers, under such cir- 
 cumstances. Freedom from mental anxiety favours the secretion of fat ; 
 whilst continual solicitude effectually checks the disposition. It has been 
 stated that total despair has an equal tendency, with absence of care, to pro- 
 duce this effect ; persons left long to pine in condemned cells, without a shadow 
 of hope, frequently becoming remarkably fat in spite of their slender fare.* 
 The odoriferous secretion of the Skin, which is much more powerful in some 
 individuals than in others, is increased under the influence of certain mental 
 emotions (as fear or bashfulness), and commonly also by sexual desire. The 
 Sexual secretions themselves are strongly influenced by the condition of the 
 mind. When it is frequently and strongly directed towards objects of passion, 
 these secretions are increased in amount to a degree which may cause them 
 to be a very injurious drain on the powers of the system. On the other hand, 
 the active employment of the mental powers on other objects, has a tendency 
 to render less active, or even to check altogether, the processes by which they 
 are elaborated.! 
 
 * Fletcher's Physiology, Part II., 6, p. 11. 
 
 } This is a simple physiological fact, but of high moral application. The Author would 
 say to those of his younger readers, who urge the wants of Nature as an excuse for the il- 
 licit gratification of the sexual passion: " Try the effects of close mental application to some 
 of those ennobling pursuits, to which your profession introduces you, in combination with 
 vigorous bodily exercise (for the effects of which see 470), before you assert that the ap- 
 petite is unrestrainable, and act upon that assertion. Nothing tends so much to increase 
 the desire, as the continual direction of the mind towards the objects of its gratification. The 
 following observations, which the Author believes to be strictly correct, are extracted from 
 a valuable little work (anonymous) entitled, "Be not deceived," addressed to Young Men; 
 they are directed to those who maintain that, the married state being natural to Man, illicit 
 intercourse is necessary for those who are prevented by circumstances from otherwise grati- 
 fying the sexual passion. " When the appetite is naturally indulged, that is, in marriage, the 
 necessary energy is supplied by the nervous stimulus of its natural accompaniment of love 
 before referred to, which prevents the injury which would otherwise arise from the in- 
 creased expenditure of animal power : and in like manner, also, the function being in itself 
 grateful, this personal attachment performs the further necessary office of preventing im- 
 moderate indulgence, by dividing the attention, through the numerous other sources of sym- 
 pathy and enjoyment which it simultaneously opens to the mind. But, when the appetite 
 is irregularly indulged, that is in fornication, for want of the healthful vigour of true love, 
 its energies become exhausted ; and from the want of the numerous other sympathetic 
 sources of enjoyment in true love, in similar thoughts, common pursuits, and above all in 
 common holy hopes, the mere gross animal gratification of lust is resorted to with unnatural 
 frequency, and thus its powers become still further exhausted, and, therefore, still more 
 unsatisfying, while, at the same time, a habit is thus created, and these jointly cause an 
 increased craving; and the still greater deficiency in the satisfaction experienced in its indulg- 
 ence further, continually, ever in a circle, increases the habit, demand, indulgence, conse- 
 quent exhaustion, diminished satisfaction, and again demand, till the mind and body alike 
 become disorganized." Such considerations as these may, to some persons, appear misplaced 
 
ON THE ORGANIC FUNCTIONS. 475 
 
 627. No secretion so evidently exhibits the influence of the depressing 
 Emotions, as that of the Mammae ; but this may be partly due to the fact, that 
 the digestive system of the Infant is a more delicate apparatus for testing the 
 qualities of that secretion, than any which the Chemist can devise ; affording 
 proof, by disorder of its function, of changes in the character of the Milk, 
 which no examination of its physical properties could detect. The following 
 remarks on this subject are abridged from Sir A. Cooper's valuable work on 
 the Breast. " The secretion of milk proceeds best in a tranquil state of 
 mind, and with a cheerful temper : then the milk is regularly abundant, and 
 agrees well with the child. On the contrary, a fretful temper lessens the 
 quantity of milk, makes it thin and serous, and causes it to disturb the child's 
 bowels, producing intestinal fever and much griping. Pits of anger produce 
 a very irritating milk, followed by griping in the infant, with green stools. 
 Grief has a great influence on lactation, and consequently upon the child. 
 The loss of a near and dear relation, or a change of fortune, will often so 
 much diminish the secretion of milk, as to render adventitious aid necessary 
 for the support of the child. Anxiety of mind diminishes the quantity, and 
 alters the quality of the milk. The reception of a letter which leaves the 
 mind in anxious suspense, lessens the draught, and the breast becomes empty. 
 If the child be ill, and the mother is anxious respecting it, she complains to 
 her medical attendant that she has little milk, and that her infant is griped, 
 and has frequent green and frothy motions. Fear has a powerful influence 
 on the secretion of milk. I am informed by a medical man who practices 
 much among the poor, that the apprehension of the brutal conduct of a 
 drunken husband, will put a stop for a time to the secretion of milk. When 
 this happens, the breast feels knotted and hard, flaccid from the absence of 
 milk, and that which is secreted is highly irritating, and some time elapses 
 before a healthy secretion returns. Terror, which is sudden and great fear, 
 instantly stops this secretion." Of this, two striking instances, in which the 
 secretion, although previously abundant, was completely arrested by this emo- 
 tion, are detailed by Sir A. C. " Those passions which are generally sources 
 of pleasure, and which, when moderately indulged, are conducive to health, 
 will, when carried to excess, alter, and even entirely check the secretion of 
 milk." 
 
 a. The following is perhaps the most remarkable instance on record, of the effect of strong 
 mental excitement on the Mammary secretion ; the event could hardly be regarded as more 
 than a simple coincidence, if it were not borne out by the less striking, but equally decisive 
 facts already mentioned. "A Carpenter fell into a quarrel with a Soldier billeted in his house, 
 and was set upon by the latter with his drawn sword. The wife .of the carpenter at first 
 trembled from fear and terror, and then suddenly threw herself furiously between the combat- 
 ants, wrested the sword from the soldier's hand, broke it in pieces, and threw it away. During 
 the tumult, some neighbours came in and separated the men. While in this state of strong 
 excitement, the mother took up her child from the cradle, where it lay playing, and in the 
 most perfect health, never having had a moment's illness; she gave it the breast, and in so 
 
 in a Physiological Treatise yet the Author feels sure that, by his well-judging readers, he 
 will not be blamed for adverting to this subject, or for the introduction of the above quota- 
 tion from a writer, of whom he has no personal knowledge, but whose object must be con- 
 fessed by all to be laudable. There seems to be something in the process of training young 
 men for the Medical Profession, which encourages in them a laxity of thought and expres- 
 sion on these matters, that generally ends in a laxity of action and of principle. It might 
 have been expected that those who are so continually witnessing the melancholy conse- 
 quences of the violation of the Divine law in this particular, "would be the last to break it 
 themselves : but this is unfortunately very far from being the case. The Author regrets to 
 be obliged further to remark, that some recent works which have issued from the Medical 
 press, contain much that is calculated to excite, rather than to repress, the propensity ; and 
 that the advice sometimes given by practitioners to their patients is immoral as well as un- 
 scientific. 
 
476 INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC FUNCTIONS. 
 
 doing sealed its fate. In a few minutes the infant left off sucking, became restless, panted, 
 and sank dead upon its mother's bosom. The physician who was instantly called in, found 
 the child lying in the cradle, as if asleep, and with its features undisturbed ; but all his re- 
 sources were fruitless. It was irrecoverably gone."* In this interesting case, the milk must 
 have undergone a change, which gave it a powerful sedative action upon the susceptible 
 nervous system of the infant. 
 
 b. The following, which occurred within the Author's own knowledge, is perhaps equally 
 valuable to the Physiologist, as an example of the similarly-fatal influence of undue emotion 
 of a different character; and both should serve as a salutary warning to mothers, not to 
 indulge either in the exciting or depressing passions. A Lady having several children, of 
 which none had manifested any particular tendency to cerebral disease, and of which the 
 youngest was a healthy infant a few months old, heard of the death (from acute hydroce- 
 phalus) of the infant child of a friend residing at a distance, with whom she had been on, 
 terms of close intimacy, and whose family had increased almost contemporaneously with 
 her own. The circumstance naturally made a strong impression on her mind ; arid she 
 dwelt upon it the more, perhaps, as she happened, at that period, to be separated from the 
 rest of her family, and to be much alone with her babe. One morning, shortly after having 
 nursed it, she laid the infant in its cradle, asleep and apparently in perfect health ; her atten- 
 tion was shortly attracted to it by a noise; and, on going to the cradle, she found her infant 
 in a convulsion, which lasted for a few minutes, and then left it dead. Now, although the 
 influence of the mental emotion is less unequivocally displayed in this case than in the last, 
 it can scarcely be a matter of doubt ; since it is natural that no feeling should be stronger in 
 the mother's mind under such circumstances, than the fear that her own beloved child 
 should be taken from her, as that of her friend had been ; and it is probable that she had 
 been particularly dwelling on it, at the time of nursing the infant on that, morning. 
 
 c. Another instance, in which the maternal influence was less certain, but in which it was 
 not improbably the immediate cause of the fatal termination, occurred in a family nearly 
 related to the Author's. The mother had lost several children in early infancy, from a con- 
 vulsive disorder; one infant, however, survived the usually- fatal period; but whilst nursing 
 him, one morning, she had been strongly dwelling on the fear of losing him also, although 
 he appeared a very healthy child. In a few minutes after the infant had been transferred 
 into the arms of the nurse, and whilst she was urging her mistress to take a more cheerful 
 view, directing her attention to his thriving appearance, he was seized with a convulsion-fit 
 and died almost instantly. Now although there was here unquestionably a predisposing 
 cause, of which there is no evidence in the other cases, it can scarcely be doubted that the 
 exciting cause of the fatal disorder is to be referred to the mother's anxiety. This case offers 
 a valuable suggestion, which, indeed, would be afforded by other considerations, that an 
 infant, under such circumstances, should not be nursed by its mother, but by another woman 
 of placid temperament, who had reared healthy children of her own. 
 
 628. Other Secretions are in like manner vitiated by mental Emotions, al- 
 though the influence is not always so manifest. Thus, the halitus from the 
 lungs is sometimes almost instantaneously affected by bad news, so as to pro- 
 duce foetid breath. A copious secretion of foetid gas not unfrequently takes 
 place in the intestinal canal, under the influence of any disturbing emotion ; 
 or the usual fluid secretions from its walls are similarly disordered. The 
 tendency to defecation which is commonly excited under such circumstances, 
 is not, therefore, due simply to the relaxation of the sphincter ani (as com- 
 monly supposed) ; but is partly dependent on the unusually stimulating cha- 
 racter of the faeces themselves. The same may be said of the tendency to 
 micturition, which is experienced under similar conditions : the change in its 
 
 * Dr. Von Ammon, in his treatise " Die ersten Mutterpflichten und die erste Kindespflege," 
 quoted in Dr. Combe's excellent little work on the Management of Infancy. Similar facts 
 are recorded by other writers. Mr. Wardrop mentions (Lancet, No. 516), that having re- 
 moved a small tumour from behind the ear of a mother, all went well, until she fell into a 
 violent passion; and the child, being suckled soon afterwards, died in convulsions-. He was 
 sent for hastily, to see another child in convulsions, after taking the breast of a nurse who 
 had just been severely reprimanded; and he was informed by Sir Richard Croft, that he had 
 seen many similar instances. Three others are recorded by Burdach (Physiologic, 522) ; 
 in one of them, the infant was seized with convulsions on the right side, and hemiplegia on 
 the left, on sucking immediately after its mother had met with some distressing occurrence. 
 Another case was that of a puppy, which was seized with epilepsy, on sucking its mother 
 after a fit of rage. 
 
SOURCES OF DEMAND FOR ALIMENT. 477 
 
 character becomes perceptible enough among many animals, in which it ac- 
 quires a powerfully-disagreeable odour under the influence of fear; and thus 
 answers the purpose, which is effected in others by a peculiar secretion. It 
 is a prevalent, and perhaps not an ill-founded opinion, that melancholy and 
 jealousy have a tendency to increase the quantity, and to vitiate the quality, 
 of the biliary fluid ; perhaps the disorder of the organic function is more com- 
 monly the source of the former emotion, than its consequence ; but it is cer- 
 tain that the indulgence of these feelings has a decidedly morbific effect, by 
 disordering the digestive processes, and thus reacts upon the nervous system 
 by impairing its healthy nutrition. On the influence of mental emotion in 
 the Mother, on the Foetus in utero, some remarks will be offered hereafter 
 ( 938). 
 
 CHAPTER X. 
 
 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 1. Sources of the Demand for .Aliment. Hunger and Thirst. 
 
 629. THE dependence of all Organized beings upon a supply of aliment,- 
 in the first place for the development of their fabric, and in the second for the 
 maintenance of their activity, is a circumstance of such a familiar character, 
 that it might not seem worth while to dwell upon it. Nevertheless the in- 
 quiry into the purposes which the aliment serves in the economy, and into 
 the relative values of different articles of food, cannot be advantageously pro- 
 secuted, until we have first determined, with more precision, the causes 
 which occasion the demand to be set up. These will be now briefly enume- 
 rated. 
 
 630. In the first place, a due supply of aliment is required, for the first 
 development of the germ into the adult fabric. In all instances, the essen- 
 tial character of the act of Reproduction appears to be the liberation or setting- 
 free of a cell-germ ; which, according to the character of the being that gave 
 origin to it, may be destined to evolve, either a simple cell (as in the lowest 
 Cryptogamic Plants), a congeries of cells having a certain degree of variety 
 of form and of difference of function (as in the higher classes of the Vegetable 
 kingdom), or a complex fabric, composed of an immense variety of parts, 
 most of them departing widely, in appearance at least, from the original cellu- 
 lar type, and destined to perform a vast variety of actions, as we see in the 
 perfectly developed organism of the higher Animals. The materials which 
 are subservient to this evolution, are all derived from the external world ; 
 either immediately, or through the medium of the parent. The germs of the 
 lowly Cryptogamia are thrown at once upon the world (so to speak), to obtain 
 their own livelihood ; and they themselves occasion the combination of the 
 inorganic elements, which they there meet with, into the organic compounds, 
 which are to be applied to the development of their simple organisms. In 
 the Flowering Plants, on the other hand, the germ is at first supplied with a 
 store of nutriment, which has already undergone this preparation, by the 
 agency of the parent ; and this store, laid up in the s seed, is employed in the 
 development of the fabric of the young plant, until its organs are sufficiently 
 evolved to enable it to perform the same processes for itself. The same plan 
 
478 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 is invariably followed in the development of the Animal ; the nutriment stored 
 up in the ovum being usually sufficient for the evolution of the fabric, until it 
 acquires the power of ingesting food for itself ; and where this is not the 
 case (as in the Mammalia), a further provision being adopted, by which the 
 supply is continued during a lengthened period. Even when thrown upon 
 its own resources, the young Animal is often far from having attained even 
 the form of its parent; much less its size; and in the progress of its evolu- 
 tion, a greater or less degree of metamorphosis or change of form is observa- 
 ble. This is not usually so much' the case in the higher animals, as in the 
 lower; because the supply of nutriment is proportionally greater in the 
 former, and serves to carry on the development to a later period ; but the 
 changes of condition which their germinal structure undergoes within the 
 ovum, are really as remarkable as those which are presented in the early em- 
 bryos of the latter after their emersion from the egg. 
 
 a. The phenomena of metamorphosis are most familiarly known in the case of Insects, 
 and Frogs, which were formerly thought to be exceptions to all general rules ; the Insect 
 coming forth from the egg in the state of a Worm; and the Frog in the condition of a Fish. 
 But it is now known that changes of form, as complete as these, occur in a large proportion 
 of the lower tribes of Animals ; so that the absence of them is the exception. - The true 
 mode of viewing these early aspects of Animals of the inferior groups, seems to be to re- 
 gard them as foetal or embryonic ; thus, the Insect, in its larva state, is essentially a foetus, 
 as regards the grade of development of its several tissues and organs ; but it is a fostus 
 capable of obtaining its own nourishment. In this condition it attains its full growth as re- 
 gards size, though its form remains the same ; but it then, in passing into the Chrysalis state, 
 re-assumes (as it were) the condition of the embryo within the egg, the development of 
 various new parts takes place, at the expense of the nutriment stored up in its tissues, 
 and it comes forth in the state of the perfect Insect, which henceforth takes no more food 
 than is requisi4e for the maintenance of the fabric thus evolved, or for the preparation of the 
 stores to be imparted to the offspring. In many of the lower tribes, the animal quits the 
 egg at a still earlier period in comparison ; thus it has been lately shown by M. Milne Ed- 
 wards, that some of the long Marine Worms consist only of a single segment, forming a 
 kind of head, when they leave the egg ; and that the other segments, to the number it may 
 be of several hundred, are gradually developed from this ; the evolution continuing in some 
 instances during a considerable part of life. In some of the Radiated tribes, propagation 
 actually takes place whilst the animal is yet in its first or imperfect form ; thus the Medusae 
 begin life as Polypes, and in this condition they increase by germination or budding, in the 
 manner of the true or permanent Polypes. 
 
 631. It is desirable to bear in mind, that the function of the Germ is sim- 
 ply that of occasioning the combination of the materials supplied by the 
 external world, and of directing the appropriation of those materials. The 
 several parts of the complex fabric of the higher Animals, contain a great 
 variety of materials ; and it is therefore requisite for its development, that it 
 should be duly supplied with all these. The demand set up by the fabric, 
 whilst in course of development or evolution, for the materials of its growth, 
 constitutes, therefore, the primary source of the requirement of food ; and the 
 nature of this must be adapted to the wants of the being. Thus, the fabric 
 of Plants is essentially composed of Cellulose, a compound of Oxygen, Hy- 
 drogen, and Carbon ; and the materials required for the production of this are 
 simply Carbonic Acid and Water. But nearly all Plants form some azotized 
 compound in the interior of their cells ; for the production of which, Ammo- 
 nia also is required. And in those species, which, like the Cerealia, form a 
 large quantity of azotized compounds, and store them up in their seeds, a free 
 supply of Ammonia is requisite for the production of the greatest proportion 
 which they are capable of generating. In Animals, again, whose tissue chiefly 
 consists of these very azotized compounds, or of modifications of them, a 
 constant supply of such is required during the whole period of the develop- 
 ment of the fabric, as well as subsequently ; and if they be not afforded in 
 
SOURCES OF DEMAND FOR ALIMENT. 479 
 
 sufficient amount, the evolution of the organism is either retarded or checked 
 altogether.* But there is one tissue, namely, Fat, the peculiar characters of 
 which are derived from the presence of a non-azotized substance in its cells ; 
 and this cannot be developed, unless there be in the food either oily, saccha- 
 rine, or amylaceous matters, from any of which the fatty compounds may be 
 generated. 
 
 632. The full development of the Animal fabric, however, does not by any 
 means involve the cessation of the demand for food ; in fact, during the whole 
 period of that development, it may be observed that the amount of nutriment 
 ingested is far greater than that which is applied to the simple extension of 
 the structure ( 269). One source of this constant demand is to be found in 
 the continual waste or disintegration of the fabric, which goes on to a certain 
 extent under all circumstances, but which varies in degree according to cer- 
 tain conditions not difficult to be understood. All organized substances are 
 liable, from the peculiarity of their chemical composition, to interstitial de- 
 cay ; and this operates in the living organism, as much as in the dead body 
 ( 268). The difference is, that, in the living fabric, there is a provision for 
 at once removing the products of decay, so that they may be cast out of the 
 system as soon as possible ; whilst in the dead body they remain, and act as 
 ferments, accelerating the decomposition of other parts. Now the amount of 
 this interstitial decay varies with the temperature ; being increased by warmth, 
 and retarded by cold. It is consequently greatest in warm-blooded animals, 
 the temperature of whose bodies is constantly sustained at a high standard ; 
 it is reduced to its minimum in the torpid condition of cold-blooded animals, 
 which is brought on by the agency of cold ; and will be lowered to nearly 
 the same degree in the hybernating state of certain Mammalia. There is 
 another source of waste and decay, which is common to Animals, and all but 
 the simplest Plants ; this results from the limited duration of life in the indi- 
 vidual parts, which are most actively concerned in the Vegetative Functions. 
 We have seen that the essential instruments in the various functions of 
 Absorption, Assimilation, Respiration, Secretion, and Reproduction, are cells; 
 each of which goes through a certain series of processes and then dies and 
 decays, just as do the isolated cells, which compose the entire fabric of the 
 simplest Cryptogamic Plants. This is evidenced to us in the Vegetable king- 
 dom by the " fall of the leaf;" which is nothing else than the result of the 
 death and decay of the component cells of that organ, after having fulfilled 
 their peculiar functions ; these consisting in the preparation or elaboration of 
 the nutritious sap, from which the various tissues and secretions of the plant 
 are subsequently generated. The same process is continually taking place, 
 though in a less obvious manner, in the Animal body ; the rate of death and 
 renewal of each group of cells being greater, as the functions to which it 
 ministers are energetically performed ; whilst the energy of these operations 
 is mainly dependent upon the demand set up by the exercise of the Jlnimal 
 functions, for the reparation of the Nervous and Muscular tissues. 
 
 633. The great source of waste and decay in the Animal body, and con- 
 sequently the chief source of the demand for food, is the disintegration of the 
 Nervous and Muscular tissues, which has been shown to be a necessary con- 
 dition of their functional activity. Every manifestation of Nervous power, 
 of whatever kind, seems to require the combination of Oxygen with the ele- 
 ments of Nervous matter ; the normal composition of which is thus destroyed, 
 
 * The very curious discovery has lately been made, in regard to the integuments of the 
 Tunicated or Ascidian Mollusca (the lowest class of that sub-kingdom), that they contain a 
 considerable quantity of Cellulose ; a substance which had not been previously supposed to 
 be a normal constituent of the Animal Fabric. See Annales des Sciences Naturelles ; 3me 
 Serie, Zool., torn. v. p. 193 et seq. 
 
480 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 so that it ceases to be fit to form part of the body, and is cast out by the va- 
 rious processes of excretion. The same is the case in regard to the Muscu- 
 lar substance ; the waste of which is conformable to the use made of it. The 
 demand for the materials of reparation will follow the same proportion ; and 
 as the preparation of these materials can only be effected by the agency of 
 the Vegetative or nutritive functions, the rate at which these are performed 
 will be greatly influenced by the activity of the Animal functions. Hence 
 we see the necessity of regulating the supply of food, in accordance with the 
 state of the latter ; since a diet which would be superfluous and injurious to 
 an individual of inert habits, is suitable and beneficial to one who is leading a 
 life of continual exertion. This difference manifests itself remarkably in the 
 contrast between Animals of different tribes, whose natural instincts lead them 
 to different modes of life. The Birds of most active flight, and the Mammals 
 which are required to put forth the greatest efforts to obtain their food, need 
 the largest and most constant supplies of nutriment ; but even the least active 
 of these classes stand in remarkable contrast with the inert Reptiles, whose 
 slow and feeble movements are attended with so little waste, that they can 
 sustain life for weeks and even months, with little or no diminution of their 
 usual activity, without a fresh supply of food.* 
 
 634. Finally, there is a most important cause of demand for food, amongst 
 the higher Animals, which does not exist either amongst the lower Animals, or 
 in the Vegetable kingdom, at least to any great degree. In the classes of 
 Mammals and Birds, and in that of Insects also, we find a capability of sus- 
 taining the heat of the body at a fixed standard ; which is usually far above 
 that of the surrounding medium. This they are enabled to do, as will be 
 explained hereafter, by a process strictly analogous to ordinary combustion ; 
 the Carbon and Hydrogen, which are directly supplied by their food, or which 
 have been employed for a time in the composition of their living tissues and 
 then set free, being made to combine with Oxygen introduced by the respira- 
 tory process, and thus giving out the same heat, as if the same materials were 
 burned in a furnace. It will be hereafter shown that the immediate cause of 
 death in a warm-blooded animal, from which the food has been entirely with- 
 held, is the inability any longer to sustain the temperature which is requisite for 
 the performance of its vital operations (Chap. XVI., Sect. 2). Hence we see 
 the necessity for a constant supply of aliment, in the case of warm-blooded 
 animals, for this purpose alone ; and the demand will be regulated by the 
 external temperature. When the heat is rapidly carried off from the surface 
 by the chilling influence of the surrounding air or water, a much greater 
 amount of Carbon and Hydrogen must be consumed within the body, to main- 
 tain its proper heat, than when the medium is nearly as warm as the body 
 itself; so that a diet, which is appropriate in the former circumstances, is 
 superfluous and injurious in the latter; and the food which is amply sufficient 
 in a warm climate, is utterly destitute of pow r er to enable it to resist the influ- 
 ence of severe cold. Substances rich in carbon and hydrogen, and having 
 little or no oxygen, afford the most efficient heat-sustaining materials ; but it 
 is an essential condition of their due action, that they should be of a kind 
 that renders them capable of being reduced by the solvent action of the sto- 
 mach, and of being absorbed into the system. 
 
 635. The demand for food is -increased by any cause which creates an 
 unusual drain or waste in the system. Thus an extensive suppurating action 
 
 * The materials which are required for the reparation of the Muscular tissue, are chiefly 
 of a fibrinous nature ; those employed for the renovation of the Nervous substance, would 
 seem to be fatty matter with Phosphorus. But from the peculiar composition of the fatty 
 matters of the Nervous substance (especially the presence of Azote in them), it seems quite 
 uncertain from which of the constituents of the food they are really formed, 
 
DEMAND FOR ALIMENT. SENSE OF HUNGER. 481 
 
 can be sustained only by a large supply of highly nutritious food. The 
 mother who has to furnish the daily supply of milk, which constitutes the 
 sole support of her offspring, needs an unusual sustenance for this purpose. 
 And there are states of the system, in which the solid, tissues seem to possess 
 an unusual tendency to decomposition, and in which an increased supply of 
 aliment is therefore required. This is the case, for example, in Diabetes ; one 
 of the first symptoms of which disease is the craving appetite, that seems as 
 if it would be never satisfied. And there can be no doubt that, putting aside 
 all the other circumstances which have been alluded to, there is much differ- 
 ence amongst individuals, in regard to the rapidity of the changes which their 
 organism undergoes, and the amount of food consequently required for its 
 maintenance. 
 
 636. The want of solid aliment is indicated by the sensation of Hunger ; 
 and that of liquid by thirst. The former of these sensations is referred to 
 the stomach ; and the latter to the fauces : but although certain conditions of 
 these parts may be the immediate cause of the sensations in question, they 
 are really indicative of the requirements of the system at large. For the in- 
 tensity of the feelings bears no constant relation to the amount of solid or 
 liquid aliment in the stomach ; whilst, on the other hand, it does correspond 
 with the excess of demand in the system, over the supply afforded by the 
 blood; and it is caused to abate by the introduction of the requisite materials 
 into the circulating fluid, even though this be not accomplished in the usual 
 manner by the ingestion of food into the stomach. 
 
 637. That the sense of Hunger, however, is immediately dependent upon 
 some condition of the Stomach, seems to follow from the fact, that it is abated, 
 if not arrested, by section of the Par Vagum ( 412) ; and that it may be 
 temporarily alleviated, by introducing into the digestive cavity, matter which 
 is not alimentary. Of the precise nature of that condition, however, we have 
 no certain knowledge. It is easy to prove that many of the causes which 
 have been assigned for the sensation, are but little, if at all, concerned in pro- 
 ducing it. Thus, mere emptiness of the stomach cannot occasion it ; since, 
 if the previous meal have been ample, the food passes from its cavity some 
 time before a renewal of the uneasy feeling ; and this emptiness may continue 
 (in certain disordered states of the system) for many hours or even days, with- 
 out a return of desire for food. It cannot be due, as some have supposed, to 
 the action of the gastric fluid upon the coats of the stomach themselves ; since 
 this fluid is not poured into the Stomach, except when the production of it is 
 stimulated by the irritation of its secreting follicles. By Dr. Beaumont it is 
 thought, that the distension of these follicles with the secreted fluid is the 
 proximate cause of hunger; but there is no more reason to believe that the 
 secretion of Gastric fluid is accumulating during the intervals when it is not 
 required, than there is in regard to Saliva, the Lachrymal fluid, or any other 
 secretions, which are occasionally poured out in large quantities under the in- 
 fluence of a particular stimulus; and, moreover, it is difficult to imagine how 
 mental emotion, or any impression on the nervous system alone (which is 
 able, as is well known, to dissipate the keenest appetite in a moment), can re- 
 lieve such distension. It may, perhaps, be a more probable supposition, that 
 there is a certain condition of the Capillary circulation in the Stomach, which 
 is preparatory to the secretion, and which is excited by the influence of the 
 Sympathetic nerves, that communicate (as it were) the wants of the general 
 system. This condition may be easily imagined to be the proximate cause 
 of the sensation of hunger, by acting on the Par Vagum. When food is in- 
 troduced into the stomach, the act of secretion is directly excited ; the capil- 
 lary vessels are gradually unloaded ; and the immediate cause of the impres- 
 sion on the par vagum is withdrawn. By the conversion of the alimentary 
 
 41 
 
482 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 matter into materials fit for the nutrition of the system, the remote de- 
 mand also is satisfied; and thus it is that the condition of the stomach just 
 referred to, is permanently relieved by the ingestion of substances that can 
 serve as food. But if the ingested matter be not of a kind capable of solution 
 and assimilation, the feeling of hunger is only temporarily relieved, and soon 
 returns in greater force than before. The theory here given seems reconcile- 
 able with all that has been said of the conditions of the sense of hunger ; and 
 particularly with what is known of the effect produced upon it by nervous 
 impressions, which have a peculiar influence upon the capillary circulation. 
 It also corresponds exactly with what we know of the influence of the nerv- 
 ous system, and of mental impressions, upon other secretions ( 624). 
 
 638. The sense of Hunger, like other sensations, may not be taken cogni- 
 zance of by the Mind, if its attention be strongly directed towards other ob- 
 jects; of this fact, almost every one engaged in active occupations, whether 
 mental or bodily, is occasionally conscious. The nocturnal student, who takes 
 a light and early evening meal, and, after devoting himself to his pursuits for 
 several hours uninterruptedly, retires to rest with a wearied head and an empty 
 stomach, but without the least sensation of hunger, is frequently prevented 
 from sleeping by an indescribable feeling of restlessness and deficiency ; and 
 the introduction of a small quantity of food into the stomach will almost in- 
 stantaneously allay this, and procure comfortable rest. Many persons, again, 
 who desire to take active exercise before breakfast, are prevented from doing 
 so by the lassitude and even faintness which it induces, the bodily exercise 
 increasing the demand for food, whilst it draws off the attention from the sen- 
 sation of hunger. 
 
 a. The Author may be excused for mentioning the following circumstance, which some 
 years ago occurred to himself; and which seems to him a good illustration of the principle, 
 that the sense of hunger originates in the condition of the general system, and that its mani- 
 festation through a peculiar action in the stomach, is to be regarded as a secondary pheno- 
 menon, adapted, under ordinary circumstances, to arouse the mind to the actions necessary 
 for the supply of the physical wants, but capable of being overlooked if the attention of 
 the mind be otherwise directed. He was walking alone through a beautiful country, and 
 with much to occupy his mind ; and, having expected to meet with some opportunity of ob- 
 taining refreshment on his road, he had taken no food since his breakfast. This expectation, 
 however, was not fulfilled ; but, as he felt no hunger, he thought little of the disappointment. 
 It was evening before he approached the place of his destination, after having walked about 
 twenty miles, resting frequently by the way ; and he then began to feel a peculiar lassitude, 
 differing from ordinary fatigue, which rapidly increased, so that during the last mile he could 
 scarcely support himself. The " stimulus of necessity," however, kept him up ; but on ar- 
 riving at his temporary home, he immediately fainted. It is obvious that, in this case, the 
 occupation of the mind on the objects around, and on its own thoughts, had prevented the 
 usual warning- of hunger from being perceived ; and the effect which succeeded was ex- 
 actly what was to be anticipated, from the exhaustion of the supply of food occasioned by 
 the active and prolonged exertion. 
 
 639. The conditions of the sense of Thirst appear to be very analogous to 
 those of hunger. This sense is not referred, however, to the stomach, but to 
 the fauces. It is generally considered that it immediately results from an im- 
 pression on the nerves of the stomach ; since, if liquids are introduced into 
 the stomach through an oesophagus-tube, they are just as effectual in allaying 
 thirst, as if they are swallowed in the ordinary manner. It may, however, 
 be doubted, whether the sense of thirst is not even more immediately connect- 
 ed with the state of the general system, than that of hunger ; for the imme- 
 diate relief afforded by the introduction of liquid into the stomach, is fully ac- 
 counted for by the instantaneous absorption of the fluid into the veins, which 
 is known to take place when there is a demand for it, not only from Dr. Beau- 
 mont's observations, but from many experiments made with reference to this 
 particular question. This demand is increased with almost equal rapidity, 
 
NATURE AND DESTINATION OF FOOD. 483 
 
 by an excess in the amount of the fluid excretions ; and it may be satisfied 
 without the introduction of water into the stomach* ( 677). Thirst may also 
 be produced, however, by the impression made by peculiar kinds of food or 
 drink upon the walls of the alimentary canal ; thus salted or highly-spiced 
 meat, fermented liquors when too little diluted, and other similarly irritating 
 agents, excite thirst ; the purpose of which is obviously to cause ingestion of 
 fluid, by which they may be diluted. 
 
 2. Nature and Destination of the Food of Animals. 
 
 640. The substances which are required by Animals for the development 
 and maintenance of their fabric, are of two kinds ; the Organic and the In- 
 organic. The former alone are commonly reckoned as aliments ; but the lat- 
 ter are really not less requisite for the sustenance of the body, which speedily 
 disintegrates, if the attempt be made to support it upon any organic com- 
 pounds in a state of purity. In all ordinary articles of diet, however, the in- 
 organic matters are present in the requisite proportion ; and hence they have 
 very commonly escaped notice. The nature of these substances, and the 
 mode in which they are introduced into the body, will be considered here- 
 after ( 648). The Organic matters, used as food by Animals, are partly 
 derived from the Animal, and partly from the Vegetable kingdom ; and they 
 may be conveniently arranged under the four following heads:! 1. The 
 Saccharine group, including all those substances, derived from the Vegetable 
 kingdom, which are analogous in their composition to Sugar ; consisting of 
 oxygen, hydrogen,' arid carbon, alone \ and having the two first present in the 
 proportions to form water. To this group belong starch, gum, woody fibre, 
 and the various tissues of Plants ; which closely resemble each other in the 
 proportion of their elements, and which may be converted into Sugar by che- 
 mical processes of a simple kind. 2. The Oleaginous group, including oily 
 matters, whether derived from the Vegetable kingdom, or from the fatty por- 
 tions of Animal bodies. The characteristic of this class, is the great pre- 
 dominance of hydrogen and carbon, the small proportion of oxygen, and the 
 entire absence of nitrogen. 3. The Albuminous group, comprising all those 
 substances, whether derived from the Animal or Vegetable kingdom, which 
 are closely allied to Albumen, and therefore to the majority of the Animal 
 tissues, in their chemical composition. In this group, a large proportion of 
 azote is united with the oxygen, hydrogen, and carbon of the preceding. 
 4. The Gelatinous group, consisting of substances derived from Animal bodies 
 only, which are closely allied to Gelatine in their composition. These also 
 contain azote ; but the proportion of their components differs from that of the 
 preceding. 
 
 641. The compounds of the Saccharine group cannot, without undergoing 
 a metamorphosis, form part of any Animal tissue ; as there is none which 
 they resemble in composition. It will be shown, however, that they are con- 
 vertible, within the Animal body, into those of the Oleaginous group ; and, 
 like them, may be deposited in the form of Adipose matter. There is no 
 other tissue in the body, into which they can enter without considerable change ; 
 for all others are azotized; and it seems extremely improbable that non-azo- 
 tized compounds can, under any circumstances, be converted within the body 
 into compounds of the albuminous or gelatinous groups. 
 
 * This was among the remarkable results of the injection of fluid into the veins, in the 
 Asiatic Cholera. 
 
 t Dr. Prout's classification of alimentary substances is here adopted, with a slight modifi- 
 cation; not as being altogether unexceptionable, but as being, in the Author's opinion, the 
 most convenient hitherto proposed. 
 
484 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 642. The application of the substances forming the Albuminous group* to 
 the support of the Animal body, by affording the materials for the nutrition 
 and re-formation of its tissues, needs little explanation. The proportions of 
 the four ingredients of which they are all composed, are so nearly the same, 
 that no essential difference appears to exist among them ; and it is a matter of 
 little consequence, except as far as the gratification of the palate is concerned, 
 whether we feed upon the flesh of animals (fibrine), upon the white of egg 
 (albumen), the curd of milk (caseine), the grain of wheat (gluten), or the seed 
 of the pea (legumin). All these substances are reduced in the stomach to the 
 form of albumen; which resembles the gum of Plants, in being the raw ma- 
 terial, as it were, out of which the various fabrics of the body are constructed. 
 But the rule holds good, with regard to these also, that by being made to 
 feed constantly on the same substance, boiled white of egg, for instance, or 
 meat deprived of the principle (osmazome) that gives it flavour, an animal 
 may be effectually starved ; its disgust at the food being such, that even if it 
 be swallowed, it is not digested. It is very interesting to remark that, in the 
 only instance in which Nature has provided a single article of food for the 
 support of the animal body, she has mingled articles from the three first of 
 the preceding groups. This is the case in Milk, which contains a conside- 
 rable quantity of an albuminous substance, caseine, which forms its curd ; a 
 good deal of oily matter, the butter ; and no inconsiderable amount of sugar, 
 which is dissolved in the whey. The proportions of these vary in different 
 Mammalia ; and they depend in part upon the nature of the food supplied 
 to the Animal that forms the milk ; but the substances are thus combined in 
 every instance. Although the greater part of the organized tissue of Animals 
 is formed at the expense of the Albumen and Fibrine of their blood, yet 
 many of them also contain a large quantity of Gelatine. It seems certain 
 that this gelatine may be produced out of fibrine and albumen ; since in ani- 
 mals that are supported on these alone, the nutrition of the gelatinous tissues 
 does not seem to be impaired. But it also appears, that gelatine taken in as 
 food may be applied to this purpose; for ordinary experience shows, that be- 
 nefit is derived from jelly, soup, broth, &c. ; peculiarly by persons who have 
 been suffering under exhausting diseases, such as fevers. But it also ap- 
 pears certain, that it cannot be applied to the nutrition of the Albuminous 
 tissues. Some important experiments have been recently made in Paris on 
 this subject, with a view of determining how far the soup made from crushed 
 bones, which constituted a principal article of diet in the hospitals of Paris, 
 was adequate for the support of the patients. The result of these has been 
 quite confirmatory of previous conclusions, namely, that Gelatine may be 
 advantageously mixed with albumen, fibrine, gluten, &c., and those other in- 
 gredients which exist in meat-soup and bread ; but that, when taken alone, it 
 has little more power of sustaining life than sugar or starch possesses ; and 
 that, even when bread is united with gelatine-soup, it does not give it the re- 
 quisite power of nutrition. 
 
 643. If the non-azotized compounds which exist so largely in the food of 
 Herbivorous animals, be not destined to form part (in any considerable degree 
 at least) of their tissues, the question arises, what becomes of them? It is 
 not enough to say that they are deposited as Fat; since it is only when a large 
 quantity of them is taken in, that there is any increase in the quantity of fat 
 already in the body. We shall hereafter see, that they are used up in the 
 process of Respiration ; being burned-off within the body, for the purpose of 
 keeping up its temperature. The process will be hereafter considered more 
 in detail ; and at present we need only stop to remark upon the adaptation 
 between the food provided for animals in different climates, and the amount 
 of heat which it is necessary for them to produce. Thus the bears, and seals, 
 
NATURE AND DESTINATION OF FOOD. 485 
 
 and whales, from which the Esquimaux and the Greenlander derive their sup- 
 port, have an enormous quantity of fat in their massive bodies : this fat is as 
 much esteemed as an article of food among these people, as it would be thought 
 repulsive by the inhabitants of southern climates ; and by the large quantity of 
 it they consume, they are. able to support the bitterness of an Arctic winter, 
 without appearing to suffer more from the extreme cold, than do the residents 
 in more temperate climates during their winter. On the other hand, the ante- 
 lopes, deer, and wild cattle, which form a large proportion of the animal food 
 of savage or half-cultivated nations inhabiting temperate or tropical regions, pos- 
 sess very little fat; and the comparatively small supply of carbon and hydro- 
 gen, whose combustion is required to keep up the bodily temperature of the 
 inhabitants of those regions, is derived from the flesh of those animals, in the 
 manner that will be presently explained. Every one knows how much less 
 vigorous the appetite becomes, during the heat of summer, than it is during 
 the colder portion of the year; and this is a natural result of the diminished 
 demand for the fuel required to maintain the temperature. And one great 
 means of preserving the health, during a prolonged residence in a hot climate, 
 is to attend to the dictates of Nature, in regard to the quantity of food ingested ; 
 instead of endeavouring (as is the prevalent practice) to stimulate the appetite 
 by artificial provocatives. 
 
 644. The maintenance of the bodily temperature in Carnivorous animals, 
 appears to depend upon the combustion of the carbon and hydrogen set free 
 by the Disintegration of their Nervous and Muscular tissues: this disintegra- 
 tion taking place with much more rapidity, in consequence of their almost 
 unceasing activity, than it does in the Herbivorous animals, which lead com- 
 paratively inactive lives. Every one who has visited a menagerie, must have 
 noticed the continual restlessness of the Tigers, Leopards, Hyenas, &c., which 
 keep pacing from one end of their narrow cages to the other ; and it would 
 seem as if this restlessness were a natural instinct, impelling them to use mus- 
 cular exertion sufficient for the metamorphosis of an adequate amount of tissue, 
 that enough carbon and hydrogen may be set free for the support of the respi- 
 ratory process. And we see a corresponding activity in the Human hunters 
 of the swift-footed Antelope and agile Deer, which answers a similar purpose; 
 and which is remarkably contrasted with the stupid inertness of the inhabitants 
 of the frigid zone, which is only occasionally interrupted by the necessity of 
 securing the supplies of food afforded by the massive tenants of their seas. 
 The nutrition of the Carnivorous races may, then, be thus described. The 
 bodies of the animals upon which they feed contain flesh, fat, &c., in nearly 
 the same proportion as their own ; and all, or nearly all, the aliment they con- 
 sume, goes to supply the waste in the fabric of their own bodies, being con- 
 verted into its various forms of tissue. After having remained in this condition 
 for a certain time, varying according to the use that is made of them, these 
 tissues undergo another metamorphosis, which ends in restoring them to inor- 
 ganic matter ; and thus give back to the Mineral world the materials which 
 were drawn off from it by Plants. Of these Materials, part are burned off, as 
 it were, within the body, by union with the oxygen of the air, taken in through 
 the lungs ; and are discharged from these organs, in the form of carbonic acid 
 and water: the remainder are carried off in the liquid form by other channels. 
 Hence we may briefly express the destination of their food in the following 
 manner : 
 
 Food consisting oH ( T . . . . , ,. f Carbonic acid and Water 
 
 albumen, fibrine, I Convert- S lg . / An ' thrown off by respiration, 
 
 and other azotized f ed into ) Or 8 anized > metamor- Urea &nd bmary matter> &c > 
 compounds } \ thrown off by other excretions. 
 
 41* 
 
486 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 645. But in regard to the Herbivorous animals, the case is different. They 
 perspire much more abundantly, and their temperature is thus continually kept 
 down. They consequently require a more active combustion, to develope 
 sufficient bodily heat; and the materials for this are supplied, as we have 
 seen, by the non-azotized portions of their food, rather than by the metamor- 
 phosis of their own tissues, which takes place with much less rapidity than in 
 the Carnivorous tribes. Hence we may thus express the destination of this 
 part of their food ; that of the azotized matter, here much smaller in amount, 
 will be the same as in the preceding case : 
 
 Starch, toil, and } partly C . , . } but chiefly C Carbonic acid and Water, dis- 
 
 other non-azotized > converted ? . lpc J > thrown off < engaged by the respiratory 
 compounds ; into ( ) directly as ( process. 
 
 The proportion of the food deposited as fat, will depend in part upon the sur- 
 plus which remains, after the necessary supply of materials has been afforded 
 to the respiratory process. Hence, the same quantity of food being taken, the 
 quantity of fat will be increased by causes that check the perspiration, and 
 otherwise prevent the temperature of the body from being lowered, so that 
 there is need of less combustion within the body to keep up its heat. This is 
 consistent with the teachings of experience respecting the fattening of cattle ; 
 for it is well known that this may be accomplished much sooner, if the animals 
 are shut up in a warm dwelling and covered with cloths, than if they are freely 
 exposed in the open air. 
 
 646. Now the condition of Man may be regarded as intermediate between 
 these two extremes. The construction of his digestive apparatus, as well as 
 his own instinctive propensities, point to a mixed diet as that which is best 
 suited to his wants. It does not appear that a diet composed of ordinary 
 vegetables only, is favourable to the full development of either his bodily or 
 mental powers; but this cannot be said in regard to a diet of which bread is 
 the chief ingredient, since the gluten it contains appears to be as well adapted 
 for the nutrition of the animal tissues, as does the flesh of animals. On the 
 other hand, a diet composed of animal flesh alone is the least economical that 
 can be conceived ; for, since the greatest demand for food is created in him 
 (taking a man of average habits, in regard to activity and the climate he in- 
 habits), by the necessity for a supply of carbon and hydrogen to support his 
 respiration, this want may be most advantageously fulfilled by the employment 
 of a certain quantity of non-azotized food, in which these ingredients predomi- 
 nate. Thus it has been calculated, that, since fifteen pounds of flesh contain 
 no more carbon than four pounds of starch, a savage with one carcass and an 
 equal weight of starch, could support life for the same length of time, during 
 which another restricted to animal food would require five such carcasses, in 
 order to procure the carbon necessary for respiration. Hence we see the im- 
 mense advantage as to economy of food, which a fixed agricultural population 
 possesses over those wandering tribes of hunters, which still people a large 
 part both of the old and new continents. The mixture of the azotized and 
 non-azotized compounds (gluten and starch), that exists in wheat flour, seems 
 to be just that which is most useful to Man ; and hence we see the explanation 
 of the fact, that, from very early ages, bread has been regarded as the " staff 
 of life." In regard to the nutritious properties of different articles of vegetable 
 food, these may be generally estimated by the proportion of azote they con- 
 tain ; which is in almost every instance less than that existing in good wheat 
 flour. 
 
 647. The following table represents the relative quantity of Nitrogen in 
 different articles used as food ; and thus shows their relative applicability to 
 
NUTRITIVE POWER OF DIFFERENT KINDS OF FOOD. 
 
 487 
 
 the maintenance and reparation of the body.* Those which are poorest in 
 nitrogen, are richest in Carbon and Hydrogen ; and are, therefore, the best 
 adapted to serve as the pabulum for the heat-sustaining process. It is to be 
 borne in i^nd, however, that no table of this kind, founded simply upon the 
 Chemical composition of the various substances, can indicate their respective 
 fitness as articles of diet ; since this depends also upon the facility with which 
 they are reduced by the digestive process, and afterwards assimilated. Thus 
 an aliment, abounding in nutritive matter, may be inferior to one which really 
 contains a much smaller proportion, if only a part in the first case, and the 
 whole in the second, be readily taken up by the system. In the following 
 table, Human Milk is taken as the standard ; and the quantity of Nitrogen it 
 contains is expressed by 100. But it must be borne in mind that this sub- 
 stance is intended for the nourishment of a being that passes nearly the whole 
 of its time in a quiescent state ; and must not be supposed to be adapted for 
 the sole maintenance of the Human body in a state of activity. In fact, it is 
 inferior in its proportion of Caseine (the substance of which alone the azote 
 forms a part) to the milk of most, if not all, other Mammalia ; their young 
 bringing their animal functions into exercise at a much earlier period than the 
 Human infant. 
 
 Rice 
 Potatoes 
 Turnips 
 Rye . 
 Maize . 
 Barley 
 
 Human milk 
 
 Cow's milk . 
 
 Oyster 
 
 Yolk of eggs . 
 
 Cheese 
 
 Eel, raw 
 
 boiled 
 
 Liver of crab 
 Mussel, raw 
 
 boiled 
 
 Ox liver, Yaw 
 Pork-ham, raw 
 boiled 
 
 Vegetable. 
 
 . . 81 Oats . . . 138 
 
 . ^84 White bread . . . 142 
 
 . . 106 Wheat . . 119-144 
 . 106 Carrots . . . 150 
 
 100-125 Brown Bread . 166 
 
 . 125 Agaricus cantharellus 201 Beans 
 
 . 239 
 
 Agaricus russula . 264 
 Lentils . . .276 
 Haricot beans . . 283 
 Agaricus deliciosus 289 
 
 Animal. 
 
 . 100 
 
 Salmon, raw 
 
 . . 237 
 
 boiled 
 
 . 305 
 
 Liver of Pigeon 
 
 . . 305 
 
 Portable soup 
 
 331-447 
 
 White of Egg 
 
 . . 434 
 
 Crab, boiled . 
 
 . 428 
 
 Skate, raw 
 
 . . 471 
 
 boiled . 
 
 . 528 
 
 Herring, raw 
 
 . . 660 
 
 boiled 
 
 . 570 
 
 milt of 
 
 . . 539 
 
 Haddock, raw 
 
 . 807 
 
 boiled 
 
 776 
 610 
 742 
 764 
 845 
 859 
 859 
 956 
 910 
 808 
 924 
 920 
 816 
 
 Flounder, raw 
 
 boiled 
 
 Pigeon, raw 
 
 boiled 
 
 Lamb, raw 
 Mutton, raw . 
 
 boiled 
 
 Veal, raw 
 
 boiled 
 
 Beef, raw 
 
 boiled 
 
 Ox lung 
 
 . . 320 
 
 898 
 954 
 756 
 827 
 833 
 773 
 852 
 873 
 911 
 880 
 942 
 931 
 
 648. Besides these substances, there are certain Mineral ingredients, which 
 may be said to constitute part of the food of Animals ; being necessary to their 
 support, in the same manner as other mineral substances are necessary to the 
 support of Plants. Of this kind are common salt, and also phosphorus, sul- 
 phur, and lime, either in combination or separate. The uses of Salt are very 
 numerous and important. It consists of two substances of opposite qualities, 
 muriatic acid and soda ; and the former is the essential ingredient in the gastric 
 juice ; whilst the latter performs a very important part in the production of 
 bile. Phosphorus is chiefly required to be united with fatty matter, to serve 
 as the material of the nervous tissue; and to be combined with oxygen and 
 lime, to form the bone-earth, by which the bone is consolidated. Sulphur 
 exists in small quantities in several animal tissues ; but its part is by no 
 means so important, as that performed by phosphorus. Lime is required for 
 the consolidation of the bones ; and for the production of the shells and other 
 
 * Schlossberger and Kemp, in Philosophical Magazine. Nov. 1845. 
 
488 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 hard parts, that form the skeletons of the Invertebrata. To these ingredients 
 we may also add Iron, which is a very important element in the red blood of 
 Vertebrated animals. These substances are contained, more or less abund- 
 antly, in most articles generally used as food; and where they aft deficient, 
 the animal suffers in consequence, if they are not supplied in any other way. 
 Thus common Salt exists, in no inconsiderable quantity, in the flesh and 
 fluids of animals, in milk, and in the egg : it is not so abundant, however, in 
 plants ; and the deficiency is usually supplied to herbivorous animals by some 
 other means. Thus salt is purposely mingled with the food of domesticated 
 animals ; and in most parts of the world inhabited by wild cattle, there are spots 
 where it exists in the soil, and to which they resort to obtain it. Such are the 
 " buffalo licks" of North America. Phosphorus exists also in the yolk and white 
 of the Egg, and in Milk, the substances on which the young animal subsists 
 during the period of its most rapid growth ; and it abounds, not only in many 
 animal substances used as food, but also (in the state of phosphate of lime or 
 bone-earth) in the seeds of many plants, especially the grasses. In smaller 
 quantities it is found in the ashes of almost every plant. When flesh, bread, 
 fruit, and husks of grain, are used as the chief articles of food, more phosphorus 
 is taken into the body than it requires ; and the excess has to be carried out in 
 the excretions. Sulphur is derived alike from vegetable and animal substances. 
 It exists in flesh, eggs, and milk ; also in the azotized compounds of plants ; 
 and (in the form of sulphate of lime) in most of the river and spring-water that 
 we drink. Iron is found in the yolk of egg, and in milk, as well as in animal 
 flesh; it also exists in small quantities in most vegetable substances used as 
 food by Man, such as potatoes, cabbage, peas, cucumbers, mustard, &c. ; 
 and probably in most articles, from which other animals derive their support. 
 Lime is one of the most universally diffused of all mineral bodies ; for there 
 are very few animal or vegetable substances, in wfiich it does not exist. It 
 is most commonly taken in, among the higher animals, combined with Phos- 
 phoric acid ; and in this state it exists largely in the seeds of most grasses, 
 especially in wheat flour. If it were not for their deficiency in Phosphate 
 of lime, some of the Leguminous seeds would be more nutritious than wheaten 
 flour ; the proportion of azotized matter they contain being greater. A con- 
 siderable quantity of lime exists, in the state of carbonate and sulphate, in all 
 hard water. 
 
 649. The absolute quantity of food, required for the maintenance of the 
 Human body in health, varies so much with the age, sex, and constitution 
 of the individual, and with the circumstances in which he may be placed, 
 that it would be absurd to attempt to fix any standard which should apply to 
 every particular case. The appetite is the only sure guide for the supply of 
 the wants of each ; but its indications must not be misinterpreted. To eat 
 when we are hungry, is an evidently natural disposition ; but to eat as long 
 as we are hungry, may not always be prudent. Since the feeling of hunger 
 does not depend so much upon the state of fulness or emptiness of the sto- 
 mach, as upon the condition of the general system, it appears evident that the 
 ingestion of food cannot at once produce the effect of dissipating it, though 
 it will do so after a short time ; so that, if we eat with undue rapidity, we 
 may continue swallowing food long after we have taken as much as will really 
 be required for the wants of the system ; and every superfluous particle is 
 not merely useless, but injurious. Hence, besides its other important ends, 
 the process of thorough mastication is important, as prolonging the meal, 
 and giving time to the system to become acquainted (as it were) that the sup- 
 ply of its wants is in progress ; sovthat its demand may be abated in due time 
 to prevent the ingestion of more than is required. It is very justly remarked 
 by Dr. Beaumont, that the cessation of this demand, rather than the positive 
 
REQUISITE AMOUNT OF FOOD. 489 
 
 sense of satiety, is the proper guide. " There appears to be a sense of per- 
 fect intelligence conveyed to the encephalic centre, which, in health, invariably 
 dictates what quantity of aliment (responding to the sense of hunger and its 
 due satisfaction) is naturally required for the purposes of life ; and which, if 
 noticed and properly attended to, would prove the most salutary monitor of 
 health, and effectual preventive of disease. It is not the sense of satiety, 
 for this is beyond the point of healthful indulgence, and is Nature's earliest 
 indication of an abuse and overburden of her powers to replenish the system. 
 It occurs immediately previous to this ; and may be known by the pleasurable 
 sensations of perfect satisfaction, ease and quiescence of body and mind. It 
 is when the stomach says, enough ; and it is distinguished from satiety by 
 the difference of sensations, the latter saying too much" Every medical 
 man is well aware how generally this rule is transgressed ; some persons 
 making a regular practice of eating to repletion ; and others paying far too 
 little attention to the preliminary operations, and thus ingesting more than is 
 good for them, even though they may actually leave off with an appetite. 
 
 650. Although no universal law can be laid down for individuals, however, 
 it is a matter of much practical importance to be able to form a correct ave- 
 rage estimate. It is from the experience afforded by the usual consumption 
 of food by large bodies of men, that our data are obtained ; and these data 
 are sufficient to enable us to predict with tolerable accuracy what will be re- 
 quired by similar aggregations, though they can afford no guide to the con- 
 sumption of individuals. We shall first consider the quantity sufficient for 
 men in regular active exercise ; and then inquire how far that may be safely 
 reduced for those who lead a more sedentary life. The Diet-scale of the 
 British Navy may be advantageously taken as a specimen of what is required 
 for the first class. It is well known that an extraordinary improvement has 
 taken place in the health of seamen during the last 80 years ; so that three 
 ships can now be kept afloat with only the same number of men, which were 
 formerly required for two. This is due to the improvement in the quality of 
 the food, in combination with other prophylactic means. At present it may 
 safely be affirmed, that it would not be easy to conceive of any diet-scale 
 more adapted to answer the required purpose. The health of crews that 
 have been long afloat, and have been exposed to every variety of external 
 conditions, appears to be preserved (at least when they are under the direc- 
 tion of judicious officers), to the full as well as that of persons subject to 
 similar vicissitudes on shore ; and there can be no complaint of insufficiency 
 of food, although the allowance cannot be regarded as superfluous. It con- 
 sists of from 31 to 35| ounces of dry nutritious matter daily ; of this 26 oz. 
 are vegetable ; and the rest animal ; 9 t oz. of salt meat, or 4<| oz. fresh, 
 being the allowance of the latter. This is found to be amply sufficient 
 for the support of strength ; and considerable variety is produced, by ex- 
 changing various parts of the diet for other articles. This, however, is some- 
 times done erroneously ; thus 8 oz. of fresh vegetables, which contain only 
 1% oz. of solid nutriment, are exchanged for 12 oz. of flour, which is almost 
 all nutritious. Sugar and Cocoa are also allowed ; partly in exchange for a 
 portion of the Spirits formerly served out, the diminution of which, especially 
 in the case of boys, has been attended with great benefit. 
 
 651. A considerable reduction in this amount is of course admissible, 
 where little bodily exertion is required, and where there is less exposure to 
 low temperatures. In the case of Prisoners, the diet should of course be as 
 spare as possible, consistently with health ; but it should be carefully modi- 
 fied, in individual cases, according to several collateral circumstances, such 
 as depression of mind, compulsory labour, previous intemperate habits, and 
 . especially the length of confinement. It has been supposed by some, that 
 
490 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 prisoners require a fuller diet than persons at large ; this is probably erro- 
 neous ; but more variety is certainly desirable, to counteract, as far as possi- 
 ble, the depressing influence of their condition upon the digestive powers. 
 The circumstances which occurred at the Milbank Penitentiary in 1823, form 
 a lamentable warning against the reduction of the diet-scale to an insufficient 
 amount. The allowance to the prisoners had formerly been from 31 to 33 
 oz. of dry nutriment daily, and the prison was considered healthy ; but in 
 1822, it was reduced to 21 oz. The health of the prisoners continued un- 
 broken for nearly six months ; but scurvy then showed itself unequivocally, 
 and out of 860 prisoners, 437, or 52 per cent., were affected with it. The 
 effect of previous confinement here became remarkable ; for those were chiefly 
 attacked, who had been in the prison for two years, a' year, or six months. 
 Again, the prisoners employed in the kitchen, who had 8 oz. of bread addi- 
 tional per day, were not attacked, except three who had only been there a 
 few days. After the epidemic had spread to a great extent, it was found that 
 the addition of 8 oz. to the daily allowance of vegetable food, and | oz. to 
 the animal, facilitated the operation of the remedies which were used for the 
 restoration of the health of the prisoners. The effects of confinement have 
 been further shown in the experience of the Edinburgh House of Refuge, 
 which was first established in 1832, for the reception of beggars during the 
 cholera, and which has been continued to the present time. The diet was at 
 first a quart of oatmeal porridge for each person, morning and evening ; and 
 at dinner 1 oz. of meat, in broth, with 7 oz. of bread ; making altogether 
 about 23 oz. of solid food a day. During some months, this diet seemed to 
 answer very well ; the people went out fatter than they came in, owing to 
 the diet being better than that to which they had been accustomed ; but after- 
 wards a proneness to disease manifested itself in those who had been resi- 
 dents there for a considerable time, and the diet was therefore somewhat in- 
 creased, with good effect. The quantity of animal food was probably here 
 too small ; and the total weight might still have been sufficient, if it had 
 been differently apportioned. In a Convict-ship, which took out 433 prison- 
 ers to New Holland in 1802, the mortality was very trifling, and the general 
 health good ; although these prisoners were supported on 16 oz. of vegetable 
 food, and 7k oz. of animal food per day ; a quantity which was found to be 
 perfectly sufficient for them. The aged inmates of work-houses, especially 
 those who have been accustomed to poor food during their whole lives, re- 
 quire much less than this ; their vital functions being comparatively inactive, 
 and their amount of labour or exercise small. In the Edinburgh work-house, 
 of which the inmates usually have good health, they are fed upon oatmeal- 
 porridge morning and evening, with barley-broth at dinner ; the total allow- 
 ance of dry nutriment is about 17 oz. ; namely 13 oz. vegetable, and 4 oz. 
 animal. 
 
 652. It is a curious effect of insufficient nutriment, as shown by the recent 
 inquiries of Chossat,* that it produces an incapability of digesting even the 
 limited amount supplied. He found that, when turtle-doves were supplied 
 with limited quantities of corn, but with water at discretion, the whole amount 
 of food taken was scarcely ever actually digested ; a part of it being rejected by 
 vomiting, or passing off by diarrhea, or accumulating in the crops. It seems 
 as if the vital powers were not sufficient to furnish the requisite supply of 
 gastric fluid, when the body began to be enfeebled by insufficient nutrition ; 
 or perhaps we might well say, the materials of the gastric fluid were wanting. 
 Hence the loathing of food, which is often manifested by those who have 
 been subjected to the influence of an insufficient diet-scale in our prisons and 
 
 * Recherches Experimentales sur 1'Inanition, 1843. 
 
REQUISITE AMOUNT OF FOOD. 491 
 
 poor-houses, and which has been set down to caprice or obstinacy, and pun- 
 ished accordingly, may be actually a proof of the deficiency of the supply 
 which we might expect to have been voraciously devoured, if really less than 
 the wants of the system require. 
 
 653. The smallest quantity of food upon which life is known to have been 
 supported with vigour, during a prolonged period, is that on which Cornaro 
 states himself to have subsisted. This was no more than 12 oz. a day, 
 chiefly of vegetable matter, for a period of 58 years. There is only one in- 
 stance on record, in which his plan was followed ; and there are probably few 
 who could long persevere in it, at least among those whose avocations require 
 much mental or bodily exertion. It is certain, however, that life with a mode- 
 rate amount of vigour may be preserved for some time, with a very limited 
 amount of food ; this appears from the records of shipwreck and similar dis- 
 asters. In regard, however, to those who have been stated to fast for a period 
 of months or even years, taking no nutriment, but maintaining an active con- 
 dition, it may be safely asserted that they were impostors, probably possess- 
 ing unusual powers of abstinence, which they took care to magnify. The 
 instances in which the life of Man, or of other Mammalia, has been prolonged 
 to the greatest extent without water, are those in which, from the peculiarity 
 of the circumstances, the cutaneous exhalation must have been reduced to a 
 very small amount, or in which there may have been an actual absorption of 
 water by the skin and lungs. Thus, Fodere mentions that some workmen 
 were extricated alive, after fourteen days' confinement in a cold damp cavern, 
 in which they had been buried under a ruin. And there is a well-known case 
 of a Hog, which was buried in its sty for 160 days, under thirty feet of the 
 chalk of Dover cliff, and was dug out alive at the end of that time, reduced in 
 weight from 160 Ibs. to 40 Ibs. : here the temperature would be kept up by the 
 non-conducting power of the chalk around; and the air surrounding the ani- 
 mal would soon become sufficiently charged with fluid, to resist further evapo- 
 ration. The time during which life can be supported under total abstinence, 
 is usually stated to vary from 8 to 10 days : the period may be greatly 
 prolonged, however, by the occasional use of water, and still more by a very 
 small supply of food. In a case recorded by Dr. Willan, of a young gentle- 
 man who starved himself, under the influence of a religious delusion, life was 
 prolonged for 60 days ; during the whole of which time nothing else was 
 taken than a little orange-juice. In a somewhat similar case which occurred 
 under the Author's notice, in the person of a young French lady, more than 
 15 days elapsed between the time that she ceased to eat regularly, and 
 the time of her being compelled to take nourishment ; during this period she 
 took a great deal of exercise, and her strength seemed to suffer but little, al- 
 though she swallowed solid food only once, and then in small quantity. If 
 the cessation of muscular exertion be complete, it seems that life is usually 
 more prolonged than where exercise of any kind is performed ; and this is 
 what might naturally be expected. In certain states of the system commonly 
 known as Hysterical, there is frequently a very remarkable disposition for ab- 
 stinence, and power of sustaining it. In a case of this kind which occurred 
 under the Author's own notice, a young lady, who had suffered severely from 
 the tetanic form of Hysteria, was'unable to take food for three weeks. The 
 slightest attempt to introduce a mcfrspl of solid matter into the stomach, oc- 
 casioned very severe vomiting and retching ; and the only nourishment taken 
 during the period mentioned, was a cup of tea once or twice a day, on many 
 days not even this being swallowed. Yet the strength of the patient rather 
 increased than diminished, during this period ; her muscles became firmer, 
 and her voice more powerful. It may be well to remark that, under such 
 circumstances, the continual persuasions of anxious friends are very injurious 
 
492 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 to the patient ; whose return to her usual state will probably take place the 
 earlier, the more completely she is left to herself. 
 
 654. Of the quantity which can be devoured at a time, it is scarcely the 
 place to speak; since such feats of gluttony only demonstrate the extraordi- 
 nary capacity, which the stomach may be made to attain by continual practice. 
 Many amusing instances are related by Captain Parry in his Arctic Voyages ; 
 in one case, a young Esquimaux, to whom he had given (for the sake of cu- 
 riosity) his full tether, devoured in four-and-twenty hours, no less than 35lbs. 
 of various kinds of aliment, including tallow candles. A case has recently 
 been published of a Hindoo, who can eat a whole sheep at a time ; this pro- 
 bably surpasses any other instance on record. The half-breed voyageurs of 
 Canada, according to Captain Franklin, and the wandering Cossacks of Sibe- 
 ria, as testified by Capt. Cochrane, habitually devour a quantity of animal 
 food, which would be soon fatal to any one unused to it. The former are 
 spoken of as very discontented, when put on a short allowance of 81bs. of 
 meat a day; their usual consumption being from 12 to 20lbs. That a much 
 larger quantity of food than that formerly specified, may be taken, with per- 
 fect freedom from injurious consequences, under a particular system of exer- 
 cise, &c., appears from the experience of those who are trained for feats of 
 strength, pugilistic encounters, &c. The ordinary belief, that the Athletic 
 constitution cannot be long maintained, appears to have no real foundation ; 
 nor does it appear that any ultimate injury results from the system being per- 
 severed in for some time. That trained men often fall into bad health, on 
 the cessation of the plan, is probably owing in part to the intemperance and 
 other bad habits of persons of the class usually subjected to this discipline. 
 The effects of trainers' regimen are hardness and firmness of the muscles, 
 clearness of the skin, capability of bearing continued severe exercise, and a 
 feeling of freedom and lightness (or " corkiness") in the limbs. During the 
 continuance of the system, it is found that the body recovers with wonderful 
 facility from the effects of injuries ; wounds heal very rapidly ; cutaneous 
 eruptions usually disappear. Clearness and vigour of mind, also, are stated 
 to be results of this plan ; and it is probable that, where persevering attention 
 and intense application are necessary, a modification of this system, in which 
 due allowance should be made for the diminished quantity of exercise, would 
 be found advantageous.* 
 
 3. Of the Passage of Food along the Alimentary Canal. 
 
 655. The introduction of alimentary matter into the system, is accomplished 
 in Animals by the reception of the food into an internal cavity, where it is 
 subjected to a preparatory process, to which nothing analogous exists in Plants, 
 and which is termed Digestion. This process may be said to have three dif- 
 ferent purposes in view ; the reduction of the alimentary matter to a fluid 
 form, so that it may become capable of absorption ; the separation of that 
 
 * The method of training employed by Jackson (a celebrated trainer of prize-fighters in 
 modern times), as deduced from his answers to questions put to him by John Bell, was to 
 begin on a clear foundation, by an emetic and two or three purges. Beef and mutton, 
 the lean of fat meat being preferred, constituted the principal food ; veal, lamb, and pork 
 were said to be less digestible (" the last purges some men"). Fish was said to be a " wa- 
 tery kind of diet:" and is employed by jockeys who wish to reduce weight by sweating. 
 Stale bread was the only vegetable food allowed. The quantity of fluid permitted was 3 
 pints per diem ; but fermented liquors were strictly forbidden. Two full meals, with a light 
 supper, were usually taken. The quantity of exercise employed was very considerable, and 
 such as few men of ordinary strength could endure. This account corresponds very much 
 with that which Hunter gave of the North American Indians, when about to set out on a long 
 march. 
 
DIGESTIVE APPARATUS. 
 
 493 
 
 portion of it which is fit to be assimilated or converted into organized texture, 
 from that which cannot serve this purpose, and which is at once rejected ; 
 and the alteration (when required) of the chemical constitution of the former, 
 
 [Fig. 199. 
 
 
 A view of the Organs of Digestion, opened in nearly their whole length; a portion of the cesophagus 
 has been removed on account of want of space in the figure ; the arrows indicate the course of sub- 
 stances along the canal ; 1, the upper lip, turned off the mouth ; 2, its frasnum ; 3, the lower lip, turned 
 down; 4, its frsenum; 5, 5, inside of the cheeks, covered by the lining membrane of the mouth ; 6, points 
 to the opening of the duct of Steno ; 7, roof of the mouth; 8, lateral half arches ; 9, points to the tonsils; 
 10, velum pendulum palati ; 11, surface of the tongue ; 12, papillae near its point ; 13, a portion of the 
 trachea ; 14, the oesophagus ; 15, its internal surface ; 16, inside of the stomach; 17, its greater extremity 
 or great cul-de-sac ; 18, its lesser extremity or smaller cul-de-sac ; 19, its lesser curvature ; 20, its greater 
 curvature; 21, the cardiac orifice; 22, the pyloric orifice; 23, upper portion of duodenum; 24, 25, the 
 remainder of the duodenum ; 26, its valvulae conniventes ; 27, the gall bladder; 28, the cystic duct; 29, 
 division of hepatic ducts in the liver; 30, hepatic duct; 31, ductus communis choledochus ; 32, its open- 
 ing into the duodenum ; 33, ductus Wirsungii, or pancreatic duct ; 34, its opening into the duodenum J 
 35, upper part of jejunum ; 36, the ileum ; 37, some of the valvuloe conniventes ; 38, lower extremity 
 of the ileum ; 39, ileo-colic valve ; 40, 41, cfficum, or caput coli ; 42, appendicula vermiformis ; 43. 44, 
 ascending colon ; 45, transverse colon ; 46, 47, descending colon ; 48, sigmoid flexure of the colon ; 
 49, upper portion of the rectum ; 50, its lower extremity ; 51, portion of the levator-ani muscle ; 52, 
 the anus.] 
 
 42 
 
494 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 which prepares it for the important changes it is subsequently to undergo. 
 The simplest conditions requisite for the accomplishment of these purposes 
 are the following: a fluid capable of performing the solution and of effecting 
 the required chemical changes ; a fluid capable of separating the unorganiz- 
 able matter, by a process analogous to chemical precipitation ; and a cavity 
 or sac, in which these operations may be performed. In the lowest Animals, 
 we find this cavity formed on a very simple plan ; being evidently nothing 
 else than an inversion of the external integument, communicating with the 
 exterior by one orifice only, through which the food is drawn in and the ex- 
 crementitious matter rejected. The fluid necessary to dissolve the food, which 
 is known by the name of gastric fluid or juice, and that required to separate 
 the portion which is to be thrown off, which is known as the bile, are secreted 
 in the walls of the stomach. In the Sea-Anemone, which affords a very charac- 
 teristic example of this type of structure, it cannot be ascertained that the very 
 rapid solution of food, which takes place in the digestive cavity, is assisted 
 by any movement of its walls. In Polypes of a higher conformation, how- 
 ever, the digestive cavity is provided with a second orifice ; the stomach opens 
 into an intestinal tube, through which the excrement is rejected in little pellets ; 
 and the food, before entering the true digestive cavity, is submitted to a pow- 
 erful gizzard or triturating apparatus. Still, .the bile, like the gastric juice, is 
 secreted in the walls of the stomach; as may be distinctly perceived in many 
 of these animals, on account of their transparency, and the bright yellow co- 
 lour of the fluid. As we ascend the animal series, we find no essential change 
 in the character of the digestive apparatus. The biliary follicles are gradu- 
 ally collected into a glandular mass, which is altogether removed from the 
 walls of the stomach, and which pours its secretion into the intestinal tube, 
 at a short distance from its commencement; the gastric juice, however, is still 
 secreted in minute sacs imbedded in the substance of the membrane. Several 
 accessory glands are added, the uses of which are not accurately known; and 
 particular modifications of the apparatus are adapted to peculiarities in the 
 nature of the food, or in the mode of its ingestion. As a general rule it may 
 be stated, that the digestive apparatus is most simple in Carnivorous animals, 
 in which it has to effect little change upon the aliment except solution, in or- 
 der to bring it to the state fit for absorption ; whilst it is most complex in those 
 that feed upon Vegetable matter, Which needs to undergo a greater change, 
 both in its chemical composition and in the mechanical arrangement of its 
 components, before it can be rendered subservient to animal nutrition. 
 
 656. Mastication and Deglutition. The first step in the process of reduc- 
 tion, is the Mastication of the food, and the impregnation of its comminuted 
 particles with the Salivary secretion. Mastication is evidently of great im- 
 portance, in preparing the substances to be afterwards operated on, for the 
 action of their solvent; and it exactly corresponds with the trituration to 
 which the Chemist would submit any solid matter, that he might present it in 
 the most advantageous form to a digestive menstruum. The complete disin- 
 tegration of the alimentary matter, therefore, is of great consequence ; and, if 
 imperfectly effected, the subsequent processes are liable to derangement. This 
 derangement we continually meet with: for there is not, perhaps, a more fre- 
 quent source of Dyspepsia than imperfect mastication, whether resulting from 
 the haste with which the food is swallowed, or from the want of the proper 
 instruments. The disintegration of the food by mechanical reduction, is mani- 
 festly aided by Insalivation: and the admixture of Saliva appears further to 
 have the effect of commencing the transformation of the amylaceous or starchy- 
 particles into sugar. From recent experiments it would seem that Saliva, if 
 acidulated, possesses the same power of acting on azotized compounds, as that 
 which characterizes the gastric juice; and consequently, when introduced into 
 
MASTICATION AND DEGLUTITION. 
 
 495 
 
 the stomach, the Saliva may afford important aid in the digestive process. 
 (See 668 and 863.) When the reduction of the food in the mouth has 
 been sufficiently accomplished, it is carried into the oesophagus by the action 
 of Deglutition. The share which the nervous system has in this action has 
 been already stated ( 382) ; and it here only remains to define more pre 
 cisely the different movements which are concerned in it. These were first 
 described in detail by Magendie; but his account requires some modification, 
 through the more recent observations of DzondL* The^rsJ stage in the pro- 
 cess is the carrying back of the food, until it has passed the anterior palatine 
 arch ; this, which is effected by the approximation of the tongue and the 
 
 [Fig. 200. 
 
 A view of the Muscles of the Tongue, Palate, Larynx and Pharynx as well as the position of the 
 upper portion of the CEsophagus, as shown by a vertical section of the head; 1, 1. the vertical section of 
 the head ; 2, points to the spinal canal ; 3, section of the hard palate ; 4, inferior spongy bone ; 5. middle 
 spongy bone ; 6, orifice of the right nostril ; 7, section of the inferior maxilla ; 8, section of the os hyoides ; 
 9, section of the epiglottis; 10, section of the cricoid cartilage; 11, the trachea, covered by its lining mem- 
 brane; 12, section of sternum; 13, inside of the upper portion of the thorax; 14, genio-hyo-glossus muscle; 
 15, its origin ; 16, 17, the fan-like expansion of the fibres of this muscle ; 18, superficial linguae muscle ; 
 19, verticales linguse muscle; 20, genio-hyoideus muscle; 21, mylo-hyoideus muscle; 22, anterior belly 
 of digastricus ; 23, section of platysmamyoides; 24, levator menti ; 25, orbicularis oris; 26, orifice of Eus- 
 tachian tube ; 27, levator palati ; 28, internal pterygoid ; 29, section of velum pendulum palati, and azy- 
 gos uvulae muscle; 30, sty lo-pharyngeus ; 31, constrictor pharyngis superior ; 32. constrictor pharyngis 
 medius> 33, insertion stylo-pharyngeus; 34, constrictor pharyngis inferior ; 35, 36, 37, muscular coat of 
 ossophagus; 38, thyreo-arytenoid muscle and ligaments, and above is the ventricle of Galen: 39, section 
 of arytenoid cartilage ; 40, border of sterno-hyoideus.] 
 
 palate, is a purely voluntary movement. In the second stage, the tongue is 
 carried still further backwards, and the larynx is drawn forwards under its 
 root, so that the epiglottis is depressed down over the rima glottidis. The 
 muscles of the anterior palatine arch contract after the morsel has passed it, 
 and assist its passage backwards; these, with the tongue, cut off completely 
 the communication between the fauces and the mouth. At the same time, the 
 muscles of the posterior palatine arch contract in such a manner, as to cause 
 
 * Muller's Physiology, p. 501. 
 
496 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 the sides of the arch to approach each other like a pair of curtains ; so that 
 the passage from the fauces into the posterior nares is nearly closed by them ; 
 and to the cleft between the approximated sides, the uvula is applied like a 
 valve. A sort of inclined plane, directed obliquely downwards and backwards, 
 is thus formed; and the morsel slides along it into the pharynx, which is 
 brought up to receive it. Some of these acts may be performed voluntarily; 
 but the combination of the whole is automatic. The third stage of the pro- 
 cess, the propulsion of the food down the oesophagus, then commences. 
 This is accomplished in the upper part by means of the constrictors of the 
 pharynx; and in the lower by the muscular coat of the oesophagus itself. 
 When the morsels are small, and are mixed with much fluid, the undulating 
 movements from above downwards succeed each other very rapidly; this 
 may be well observed in Horses whilst drinking; large morsels, however, are 
 frequently some time in making their way down. Each portion of food and 
 drink is included in the contractile walls, which are closely applied to it during 
 the whole of its transit. The gurgling sound, which is observed when drink 
 is poured down the throat of a person in articulo mortis, is due to the want 
 of this contraction. The whole of the third stage is completely involuntary. 
 At the point where the oesophagus enters the stomach, the cardiac orifice of 
 the latter, there is a sort of sphincter, which is usually closed. This opens 
 when there is a sufficient pressure on it, made by accumulated food; and after- 
 wards closes, so as to retain the food in the stomach. The opening of the 
 cardiac is one of the first acts which takes place in vomiting. When the 
 sphincter is paralyzed by division of the pneumogastric nerve, the food regur- 
 gitates into the oesophagus. 
 
 657. Action of the Stomach. A remarkable opportunity of ascertaining the 
 condition of the Stomach during Digestion, presented itself, some time since, 
 in a case in which a large fistulous aperture remained after a wound that laid 
 open the cavity, but in which the general health was completely recovered; 
 so that the process may be considered as having been normally performed.* 
 " The inner coat of the stomach, in its natural and healthy state, is of a light 
 or pale pink colour, varying in its hues, according to its full or empty state. 
 It is of a soft or velvet-like appearance, and is constantly covered with a very 
 thin, transparent, viscid mucus, lining the whole interior of the organ. By 
 applying aliment or other irritants, to the internal coat of the stomach, and 
 observing the effect through a magnifying glass, innumerable lucid points, and 
 very fine nervous or vascular papillae, can be seen arising from the villous 
 membrane, and protruding through the mucous coat, from which distils a pure, 
 limpid, colourless, slightly viscid fluid. The fluid thus excited is invariably 
 distinctly acid. The mucus of the stomach is less fluid, more viscid or albu- 
 minous, semi-opaque, sometimes a little saltish, and does not possess the slight- 
 est character of acidity. The gastric fluid never appears to be accumulated in 
 the cavity of the stomach while fasting; and is seldom, if ever, discharged 
 from its proper secerning vessels, except when excited by the natural stimulus 
 of aliment, mechanical irritation of tubes, or other excitants. When aliment 
 is received, the juice is given out in exact proportion to its requirements for 
 solution, except when more food has been taken than is necessary for the 
 wants of the system." That the quantity of the Gastric Juice secreted from 
 
 * See the case of Alexis St. Martin, with the observations and experiments of Dr. Beau- 
 mont, republished in this country by Dr. A. Combe. [A very extended examination of the 
 phenomena of gastric digestion has been made by M. Blondlot. The chief subject of ex- 
 periment was a dog, in which he maintained, without affecting the health, a fistulous opening 
 into the stomach for more than two years. His examinations have furnished many new 
 and important facts, and have confirmed those of Dr. Beaumont made on Alexis St. Martin 
 in nearly every point. Traite Analytique de la Digestion, Paris, 1844. M. C.] 
 
ACTION OF THE TOMACH. 497 
 
 the walls of the stomach depends rather upon the general requirements of the 
 system, than upon the quantity of food introduced into the digestive cavity, is 
 a principle of the highest practical importance, and cannot be too steadily kept 
 in view in Dietetics. A definite proportion only of aliment can be perfectly 
 digested in a given quantity of the fluid; the action of which, like that of 
 other chemical operations, ceases after having been exercised on a fixed and 
 definite amount of matter. " When the juice has become saturated, it refuses 
 to dissolve more ; and, if an excess of food has been taken, the residue remains 
 in the stomach, or passes into the bowels in a crude state, and becomes n. 
 source of nervous irritation, pain, and disease, for a long time." The unfa- 
 vourable effect of an undue burthen of food upon the stomach itself, interferes 
 with its healthy action ; and thus the quantity really appropriate is not dis- 
 solved. The febrile disturbance is thus increased; and the mucous membrane 
 of the stomach exhibits evident indications of its morbid condition. The de- 
 scription of these indications, given by Dr. Beaumont, is peculiarly graphic, 
 as well as Hygienically important. 
 
 658. "In disease, or partial derangement of the healthy function, the mu- 
 cous membrane presents various and essentially-different appearances. In 
 febrile conditions of the system, occasioned by whatever cause, obstructed 
 perspiration, undue excitement by stimulating liquors, overloading the sto- 
 mach with food; fear, anger, or whatever depresses or disturbs the nervous 
 system, the villous coat becomes sometimes red and dry, at other times pale 
 and moist, and loses its smooth and healthy appearance ; the secretions be- 
 come vitiated, greatly diminished, or even suppressed ; the coat of mucus 
 scarcely perceptible, the follicles flat and flaccid, with secretions insufficient 
 to prevent the papillae from irritation. There are sometimes found, on the 
 internal coat of the stomach, eruptions of deep-red pimples, not numerous, 
 but distributed here and there upon the villous membrane, rising above the 
 surface of the mucous coat. These are at first sharp-pointed, and red, but 
 frequently become filled with white purulent matter. At other times, irre- 
 gular, circumscribed red patches, varying in size and extent from half an inch 
 to an inch and a half in circumference, are found on the internal coat. 
 These appear to be the effects of congestion in the minute blood-vessels of the 
 stomach. There are also seen at times small aphthous crusts, in connection 
 with these red patches. Abrasion of the lining membrane, like the rolling up 
 of the mucous coat into small shreds or strings, leaving the papillae bare for 
 an indefinite space, is not an uncommon appearance. These diseased appear- 
 ances, when very slight, do not always affect essentially the gastric apparatus. 
 When considerable, and particularly when there are corresponding symptoms 
 of disease, as dryness of the mouth, thirst, accelerated pulse, &c. no gas- 
 tric juice can be extracted by the alimentary stimulus. Drinks are imme- 
 diately absorbed or otherwise disposed of; but food taken in this condition of 
 the stomach remains undigested for twenty-four or forty-eight hours, or more, 
 increasing the derangement of the alimentary canal, and aggravating the gene- 
 ral symptoms of disease. After excessive eating or drinking, chymification is 
 retarded ; and, though the appetite be not always impaired at first, the fluids 
 become acrid and sharp, excoriating the edges of the aperture, and almost 
 invariably producing aphthous patches and the other indications of a diseased 
 state of the internal membrane. Vitiated bile is also found in the stomach 
 under these circumstances, and flocculi of mucus are more abundant than in 
 health. Whenever this morbid condition of the stomach occurs, with the 
 usual accompanying symptoms of disease, there is generally a corresponding 
 appearance of the tongue. When a healthy state of the stomach is restored, 
 the tongue invariably becomes clean." 
 
 42* 
 
498 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 a. Dr. A. Combe's commentary on the above passage is too apposite to be omitted. 
 " Many persons who obviously live too freely, protest against the fact, because they feel no 
 immediate inconvenience, either from the quantity of food, or the stimulants in which they 
 habitually indulge ; or, in other words, because they experience no pain, sickness, or head- 
 ache^ nothing, perhaps, except slight fulness and oppression, which soon go off. Observa- 
 tion extended over a sufficient length of time, however, shows that the conclusion drawn is 
 entirely fallacious, and that the real amount of injury is not felt at the moment, merely be- 
 cause, for a wise purpose, nature has deprived us of any consciousness of either the exist- 
 ence or the state of the stomach during health. In accordance with this, Dr. Beaumont's 
 experiments prove, that extensive erythematic inflammation of the mucous coat of the sto- 
 mach was of frequent occurrence in St. Martin after excesses in eating, and especially in 
 drinking, even when no marked general symptom was present to indicate its existence. 
 Occasionally, febrile heat, nausea, headache, and thirst were complained of, but not always. 
 Had St. Martin's stomach, and its inflamed patches, not been visible to the eye, he too might 
 have been pleased that his temporary excesses did him no harm; but, when they presented 
 themselves in such legible characters, that Dr. Beaumont could not miss seeing them, argu- 
 ment and supposition were at an end, and the broad fact could not be denied." 
 
 b. The observations of Dr. Beaumont have been confirmed by those of M. Blondlot (Traite 
 Analytique de la Digestion), and of M. Ch. Bernard (Archiv. d'Anat. Gen. et de Physiol., 
 Jan. 1846); which were made upon Dogs, in whose stomachs fistulous openings were main- 
 tained for a length of time. They found that, although a slight mechanical irritation, applied 
 directly to the mucous surface of the stomach, excites at once an abundant flow of gastric 
 fluid, yet if this irritation be carried beyond certain limits, so as to produce pain, the secre- 
 tion, instead of being more abundant, diminishes or ceases entirely; whilst a ropy mucus is 
 poured out instead, and the movements of the stomach are considerably increased. The 
 animal at the same time appears ill at ease, is agitated, has nausea, and, if the irritation be 
 continued, actual vomiting; and bile has been observed to flow into the stomach, and es- 
 cape by the fistulous opening. Similar disorders of the functions of the stomach result from 
 violent pain in other parts of the body ; the process of digestion in such cases being sus- 
 pended, and sometimes vomiting excited. When accidulated substances, as food rendered 
 acid by the addition of a little vinegar, were introduced into the stomach, the quantity of 
 gastric fluid poured out was much smaller, and the digestive process consequently slower, 
 than when similar food, rendered alkaline by a weak solution of carbonate of soda, was in- 
 troduced. If, however, instead of a weak solution, carbonate of soda, in crystal or in pow- 
 der, was introduced into the stomach, a large quantity of mucus and bile, instead of gastric 
 fluid, flowed into the stomach ; and vomiting and purging very often followed. When very 
 cold water, or small pieces of ice, were introduced into the stomach, the mucous membrane 
 was at first rendered very pallid ; but soon a kind of reaction followed, the membrane be- 
 came turgid with blood, and a large quantity of gastric fluid was secreted. If, however, too 
 much ice was employed, the animal appeared ill, and shivered ; and digestion, instead of 
 being rendered more active, was retarded. Moderate heat, applied to the mucous surface of 
 the stomach, appeared to have no particular action on digestion; but a high degree of heat 
 produced most serious consequences. Thus, the introduction of a little boiling water threw 
 the animal at once into a kind of adynamic state, which was followed by death in three or 
 four hours ; the mucous membrane of the stomach was found red and swollen, whilst an 
 abundant exudation of blackish blood had taken place into the cavity of the organ. Similar 
 injurious effects resulted in a greater or less degree, from the introduction of other irritants, 
 such as nitrate of silver or ammonia ; the digestive functions being at once abolished, and 
 the mucous surface of the organ rendered highly sensitive. 
 
 659. The food which is propelled along the resophagus, enters the Stomach 
 through its cardiac orifice, in successive waves ; and it is immediately sub- 
 jected to a peculiar peristaltic movement, which has for its object to produce 
 the thorough intermixture of the gastric fluid with the alimentary mass, and 
 also to aid the solution of the latter by the gentle trituration to which it is thus 
 subjected. The fasciculi composing the muscular wall of the human stomach, 
 are so disposed as to shorten its diameter in every direction ; and by the al- 
 ternate contraction and relaxation of these bands, a great variety of motion is 
 induced in this organ, sometimes transversely, and at other times longitudi- 
 nally. " These motions," Dr. Beaumont remarks, " not only produce a con- 
 stant disturbance or churning of the contents of the stomach, but they compel 
 them, at the same time, to revolve about the interior from point to point, and 
 from one extremity to the other." In addition to these movements, there is 
 
ACTION OF THE STOMACH. 
 
 499 
 
 A front view of the Stomach, distended by flatus, with the Peritoneal Coat turned off; 1, anterior face 
 of the cesophagus ; 2, the cul-de-sac, or greater extremity ; 3, the lesser or pyloric extremity ; 4, the duo- 
 denum ; 5, 5, a portion of the peritoneal coat turned back ; 6, a portion of the longitudinal fibres of the 
 muscular coat ; 7, the circular fibres of the muscular coat; 8, the oblique muscular fibres, or muscle of 
 Gavard ; 9. a portion of the muscular coat of the duodenum, where its peritoneal coat has been removed.] 
 
 A view of the interior of the Stomach, as given by the removal of its anterior parietes ; 1, oesophagus ; 
 2, cardiac orifice of the stomach ; 3, its greater extremity, or cul-de-sac ; 4, the greater curvature , 5, line 
 of the attachment of the omentum majus; 6, the muscular coat ; 7, the anterior cut edge of the mucous 
 coat ; 8, the rugae of the mucous coat; 9, the lesser curvature ; 10, the beginning of the duodenum ; 11, 
 pyloric orifice, or valve ; 12, the first turn of the duodenum downwards.] 
 
 a constant agitation of the stomach, produced by the respiratory muscles. 
 The motions of the stomach itself are not performed on any very exact plan, 
 and are much influenced by the character of the ingesta, the state of the 
 general system, and by other circumstances. The following is the ordinary 
 course, however, of the revolutions of the food. " After passing the oesopha- 
 geal ring, it moves from right to left, along the small arch ; thence, through the 
 large curvature, from left to right. The bolus, as it enters the cardia, turns to 
 the left, passes the aperture,* descends into the splenic extremity, and follows 
 the great curvature towards the pyloric end. It then returns, in the course of 
 the smaller curvature, makes its appearance again at the aperture in its descent 
 
 * The fistulous orifice in St. Martin's stomach, through which these observations were 
 made. 
 
500 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 [Fig. 203. 
 
 A view of the interior of the Stomach and Duodenum in situ, the inferior portion of each having been 
 removed; 1, 1, the under side of the liver; 2, the gall bladder; 3, 3, the lesser curvature and anterior 
 faces, as seen from below ; 4, the rugae, about the cardiac orifice; 5, the pyloric orifice ; 6, the rugae, and 
 thickness of this orifice ; 7, 7, the duodenum ; 8, lower end of the right kidney.] 
 
 into the great curvature, to perform similar revolutions. These revolutions 
 are completed in from one to three minutes. They are probably induced in 
 a great measure, by the circular or transverse muscles of the stomach. They 
 are slower at first, than after chymification has considerably advanced ;" at 
 which time also there is an increased impulse towards the pylorus. It is 
 probable that, from the very commencement of chymification, until the organ 
 becomes empty, portions of chyme are continually passing into the duode- 
 num ; for the bulk of the alimentary mass progressively diminishes, and this 
 the more rapidly as the process is nearer its completion. The accelerated 
 expulsion appears to be effected by a peculiar action of the transverse mus- 
 cles ; and especially of that portion of them which surrounds the stomach at 
 about four inches from its pyloric extremity. This band is so forcibly con- 
 tracted in the latter part of the digestive process, that it almost separates the 
 two portions of the stomach, into a sort of hour-glass form ; and Dr. B. states 
 that, when he attempted to introduce a long thermometer tube into the pyloric 
 portion of the stomach, the bulb was at first gently resisted, then allowed to 
 pass, and then grasped by the rriuscular parietes beyond, so as to be drawn 
 in : whence it is evident that the contraction has for its object, to resist the 
 passage of solid bodies into the pyloric extremity of the stomach, at this stage 
 of digestion ; whilst the matter which has been reduced to the fluid form is 
 pumped away (as it were) by the action of that portion of the viscus. These 
 peculiar motions continue, until the stomach is perfectly empty, and not a par- 
 ticle of food or chyme remains. Of the degree in which they are dependent 
 upon the influence of the Nervous System, some idea has been already given 
 ( 387) ; there is yet much to be learned, however, especially in regard to the 
 degree in which the movements may be checked or altered, by impressions 
 transmitted through the nervous system. It is stated by Brachetthat, in some 
 of his experiments upon the Par Vagum some hours after section of the nerve 
 on both sides, the surface only of the alimentary mass was found to have un- 
 dergone solution, the remainder of the mass remaining in the condition in 
 which it was at first ingested ; and if this statement can be relied on, it would 
 appear that the movements of the stomach, like those of the heart, can be 
 readily affected by a strong nervous impression. It may be partly in this 
 manner, therefore, and not by acting upon the secretions alone, that strong 
 Emotions influence the digestive process, as they are well known to do. On 
 the other hand, the moderate excitement of pleasurable emotions may be fa- 
 

 ACTION OF THE INTESTINAL TUBE. 501 
 
 vourable to the operation ; not only by giving firmness and regularity to the 
 action of the heart, and thence promoting the circulation of the blood, and the 
 increase of the gastric secretion ; but also in imparting firmness and regularity 
 to the muscular contractions of the stomach. 
 
 660. Action of the Intestinal Tube. The pulpy substance to which the 
 aliment is reduced, by the mechanical reduction and chemical solution it has 
 undergone in the mouth and stomach, is termed chyme. The consistence of 
 this will of course vary in some degree with the quantity of fluid ingested ; 
 in general it is greyish, semifluid, and homogeneous ; and possesses a slightly 
 acid taste, but is otherwise insipid. Dr. Beaumont describes it as varying in 
 its aspect, from that of cream, which it presents when the food has been of 
 a rich character, to that of gruel, which it possesses when the diet has been 
 farinaceous. The passage of the chyme through the pyloric orifice is at first 
 slow ; but when the digestive process is nearly completed, it is transmitted in 
 much larger quantities. From the time that the ingested matter enters the 
 intestinal canal, it is propelled by the simple peristaltic action of its muscular 
 coat, which is directly excited by the contact either of this matter, or of the 
 secretions which are mingled with it ;* and all that is not absorbed is thus 
 conducted to the rectum, its expulsion from which is due to an action of a 
 distinctly reflex kind, excited through the nervous centres ( 391). During 
 its progress through the intestinal tube, the product of the gastric operation 
 undergoes very important changes. The chyme is mingled in the duodenum 
 with the biliary and pancreatic secretions, which effect an immediate altera- 
 tion both in its sensible and chemical properties. The nature of this altera- 
 tion can be best estimated, by mingling bile with chyme removed from the 
 body. This has been done by several experimenters on the lower animals ; 
 and by Dr. Beaumont in the case already referred to, which afforded him the 
 means of obtaining not only chyme, but bile and pancreatic fluid. The effect 
 of this admixture was to separate the chyme into three distinct parts, a red- 
 dish brown sediment at the bottom, a whey-coloured fluid in the centre, 
 and a creamy pellicle at the top. The central portion, with the creamy pelli- 
 cle, seems to constitute the chyle absorbed by the lacteals ; the creamy matter 
 being chiefly composed of oily particles ; and the wheyey fluid having pro- 
 teine-compounds, saccharine and saline matters, in solution : the sediment, 
 partly consisting of the insoluble portion of the food, and partly of the biliary 
 matter itself, is evidently excrementitious. It is not until the food has passed 
 the orifice of the Ductus Choledochus, that the absorption of chyle begins, 
 the lacteals not being distributed upon the Stomach, or the higher part of the 
 Duodenum. 
 
 661. By4he gradual withdrawal of their fluid portion, the contents of the 
 alimentary canal are converted into a mass of greater consistence ; and this, 
 as it advances through the small intestines, assumes more and more of a faecal 
 character. A part of the faeces, however, may be derived from the secretions 
 of the enteritic mucous membrane, and of its glandulae ; the surface of the for- 
 mer, with its simple follicles, probably secretes nothing else than mucus ; but 
 the glandulsSj with which it is so thickly studded, appear to serve as the 
 channel for the elimination of putrescent matter from the blood. There can 
 be no doubt, that a large quantity of fluid is poured out by these glandulae, 
 when they are in a state of irritation from disease, or from the stimulus of a 
 purgative medicine; since the amount of water discharged from the bowels is 
 
 * The bile seems to have an important share in producing this effect; since, when the 
 ductus choledochus is tied, constipation always occurs. The action of mercury as a purgative 
 appears to take place through the increase of the hepatic and other secretions which it in- 
 duces. 
 
502 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 often much greater than that which has heen ingested, and must be derived 
 from the blood. The secretion of the caecum has been ascertained to be, in 
 herbivorous animals, distinctly acid during digestion ; and there is reason to 
 believe, that the food there undergoes a second process, analogous to that to 
 which it has been submitted in the stomach, and fitted to extract from it what- 
 ever undissolved alimentary matter it may still contain. There is no evi- 
 dence, however, that this is the case in Man, whose co3cum (commonly termed 
 the appendix coeci vermiformis) is very small, compared to that of most her- 
 bivorous animals. 
 
 662. The act of Defecation having been already sufficiently considered 
 ( 391), it only remains to notice the composition of the Faeces. These are 
 made up of certain parts of the food, which have not been reduced and ab- 
 sorbed ; together with that portion of the secretions poured into the aliment- 
 ary canal between the mouth and the anus, which has not been taken back 
 again into the system. Of the former portion, the constituents may be in 
 great part determined by the Microscope. Thus the cell-walls of the Vegeta- 
 ble tissues whose contents have be.en extracted, the entire woody fibres (on 
 which the digestive process has no influence), the granules of starch, when 
 they have undergone no preparation before being swallowed, portions of 
 tendon, ligament, adipose tissue, and even of muscular fibre, with other 
 substances constituting the undigested residue of the food, may be readily 
 detected. Besides these, the microscope enables us to recognize the brown 
 colouring-matter of the bile, epithelium-cells and mucus-corpuscles, and various 
 saline particles, especially those of the ammoniaco-magnesian phosphate, whose 
 crystals are well-defined ; most of which .are derived from the secretions. 
 The following is the result of the proximate analysis of the faeces of an in- 
 dividual in good health, who had taken the ordinary diet of this country, as 
 given by Dr. Percy : 
 
 Substances soluble in ether (brownish yellow fat) . . . 11-95 
 
 " alcohol of -830 . . . . . 10-74 
 
 " " water (brown resinoid matter) . . . 31-61 ' 
 
 Organic matter insoluble in the above menstrua .... 49 33 
 
 Salts soluble in water . . . . . . 4 - 76 
 
 Salts insoluble in water ., . . . . . .11*61 
 
 Ultimate analysis of the same faeces gave the following as the proportion of 
 the components of the Organic constituents ; Carbon 46*20, Hydrogen 6*72, 
 Nitrogen and Oxygen 30*71. The mineral ash of faecal matter has been ex- 
 amined by Enderlin ; who has given the following as the proportion of its 
 ingredients : 
 
 Chloride of sodium and alkaline sulphates . 1*3677 
 
 Bibasic phosphate of soda . . . 2-633 5 
 
 Phosphates of lime and magnesia . . 80-372 "j 
 
 Phosphate of iron .... . 2-090 i 
 
 Sulphate of lime 
 Silica 
 
 4-530 f 
 7-940 J 
 
 Soluble in water. 
 
 Insoluble in water. 
 
 It further appears from the inquiries of Enderlin, that a portion of the or- 
 ganic matter taken up by alcohol, sometimes (but not constantly) consists of 
 Choleate of soda, the characteristic ingredient of bile ; and he thinks that this 
 is more likely to be present, when the faeces have remained for only a short 
 period in the large intestine, and when there has been less time for its re- 
 absorption. In the faecal discharges which result from the action of mercu- 
 rials, large quantities of biliary matter may be detected, very little changed. 
 

 NATURE OF CHYMIFICATION. 503 
 
 4. Nature of Chymification and Chylificdtion. 
 
 663. The causes of the reduction of the food in the Stomach, have long 
 been a fruitful source of discussion amongst physiologists ; and various hy- 
 potheses have been devised to account for it. Some have compared the Sto- 
 mach of Man to the Gizzard of a fowl, and have supposed that the trituration 
 of the food between its walls was the essential element in the process ; but 
 this doctrine is completely incompatible with the fact, that digestible substances, 
 inclosed in metallic balls with perforations in their sides, are still dissolved by 
 the power of the gastric fluid, though the walls of the stomach do not come 
 in contact with them. Others, again, have imagined that the process of di- 
 gestion is one of putrefaction; but this idea, putting aside its inherent ab- 
 surdity, is proved to be incorrect by the fact that the gastric juice has a de- 
 cidedly antiseptic quality. Others, in despair of obtaining any other solution, 
 have attributed the operation to the direct agency^of the vital principle ; for- 
 getting that, as long as the aliment remains within the stomach and intestinal 
 canal, it can no more be the subject of any peculiarly vital process, than if it 
 were in contact with the skin, of which the mucous membranels but an inter- 
 nal reflexion. The theory of chemical solution, which was at first regarded 
 by many as quite untenable, has been of late years so much strengthened by 
 new facts arid arguments, that there now appears no valid reason for with- 
 holding our assent from it; even though it cannot yet give a complete expla- 
 nation of the complex phenomena in question. The chief opposition to this 
 theory has arisen from the difficulty of imagining, that any simply-chemical 
 solvent should have the power of acting on so great a variety of substances, 
 and of reducing them to a state so homogeneous. This difficulty, however, 
 seems now in a great degree removed, by the discovery of the close Chemical 
 relation that subsists, between the various substances of each of the groups 
 already enumerated ( 639) ; which renders it easy to conceive, that the 
 changes involved in their reduction may be of a very simple character. 
 
 664. The first series offsets which will be here adduced, as throwing light 
 on the process of Chymification, is that which has been obtained by the ex- 
 periments of Dr. Beaumont upon the individual already alluded to ( 658.) 
 By introducing a tube of India-rubber into the empty stomach, he was able 
 to obtain a supply of Gastric Juice whenever he desired it ; for the tube 
 served the purpose of stimulating the follicles to pour forth their secretion, 
 and at the same time conveyed it away. This fluid, of which the existence 
 has been denied by some physiologists, is not very unlike saliva in its appear- 
 ance ; it is, however, distinctly acid to the taste ; and chemical analysis shows 
 that it contains a considerable proportion of free muriatic acid, and also some 
 acetic acid. The former must evidently be derived from the decomposition 
 of the muriate of soda contained in the blood, the remote source of which is 
 the salt ingested with the food. The latter is an organic compound, probably 
 formed at the expense of some of the saccharine matter of the previous ali- 
 ment. Of equal importance with the free acids, is an animal matter, soluble 
 in cold water, but insoluble in hot, bearing considerable resemblance to albu- 
 men. Of this more will be said hereafter. Besides these principal ingre- 
 dients, the gastric fluid contains muriates and phosphates of potass, soda, 
 magnesia, and lime. It possesses the power of coagulating albumen in an 
 eminent degree ; it is powerfully antiseptic, checking the putrefaction of meat ; 
 and it is effectually restorative of healthy action, when applied to old fetid 
 sores and foul ulcerating surfaces. It may be kept for many months, if ex- 
 cluded from the air without becoming foetid. 
 
 a. The Chemistry of the Gastric Juice has been greatly unsettled by the results of recent 
 
504 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 inquiries; which seem inconsistent with the statement just given, especially in regard to the 
 presence of free muriatic acid. It may be well, in the first instance, to quote Professor 
 Dunglison's account of the analysis of the gastric fluid drawn from the stomach of Alexis 
 St. Martin, and supplied to him by Dr. Beaumont. " The quantity of free hydrochloric add 
 was surprising ; on distilling the gastric fluid, the acids passed over, the salts and animal mat- 
 ter remaining in the retort ; the amount of chloride of silver thrown down, on the addition 
 of nitrate of silver to the distilled fluid, was astonishing. The author had many opportu- 
 nities of examining the gastric secretion obtained from the case in question. At all times, 
 when pure or unmixed, except with a portion of the mucus of the lining membrane of the 
 digestive tube, it was a transparent fluid, having a marked smell of hydrochloric add ; and of 
 a slightly salt, and very perceptibly acid, taste." (Human Physiology, Sixth Edition, Vol. I., 
 p. 546.) 
 
 b. From the experiments of MM. Blondlot, Bernard, and Barreswill, and Dr. R. D. Thom- 
 son, on the other hand, it would seem that no free hydrochloric acid is present in the gastric 
 fluid; since the fluid which comes over, on distillation at a low temperature, contains none; 
 whilst the matter remaining in the retort becomes more and more acid with the progress of 
 the distillation, and may be subjected to a high temperature (300) without giving off acid 
 fumes. It is difficult to account for the discrepancy between these carefully conducted ex- 
 periments, and the positive statement of Professor Dunglison. otherwise than by supposing 
 that the Human gastric fluid differs from that of the Dog and the Pig, which were employed 
 in the analyses last quoted. The acid reaction was referred by Blondlot to the presence of 
 super-phosphate of lime ; but this seems incorrect. Professor Thomson agrees with MM. 
 Bernard and Barreswill in attributing it chiefly to Lactic acid ; which, contrary to previous 
 opinions, they regard as generally if not universally present in the stomach during healthy 
 digestion, and it would seem that this acid may partially decompose the phosphates and 
 muriates, which are contained in the secretion : and may thus occasion the phosphoric 'and 
 muriatic acids to be set free. The presence of a small quantity of free Acetic acid, also, 
 seems to have been recognized by them. 
 
 665. The Gastric Juice obtained from the stomach, was found by Dr. 
 Beaumont to possess the power of dissolving various kinds of alimentary sub- 
 stances, when these were submitted to its action at a constant temperature of 
 100, (which is about that of the stomach,) and were frequently agitated. 
 The solution appeared to be in all respects as perfect as that which naturally 
 takes place in the stomach ; but required a longer time. This is readily ac- 
 counted for when we remember, that no ordinary agitation can produce the 
 same effect with the curious movements of the stomach ; and that the conti- 
 nual removal from its cavity, of the matter which has been already dissolved, 
 must aid the operation of the solvent on the remainder. The following is 
 one out of many experiments detailed by Dr. Beaumont. "At ll o'clock, 
 A. M., after having kept the lad fasting for 17 hours, I introduced a gum-elastic 
 tube, and drew off one ounce of pure gastric liquor, unmixed with any other 
 matter, except a small proportion of mucus, into a three-ounce vial. I then 
 took a solid piece of boiled recently-salted beef, weighing three drachms, and 
 put it into the liquor in the vial ; corked the vial tight, and placed it in a 
 saucepan filled with water, raised to the temperature of 100, and kept at that 
 point on a nicely-regulated sand-bath. In forty minutes, digestion had dis- 
 tinctly commenced over the surface of the meat. In fifty minutes, the fluid 
 had become quite opaque and cloudy ; the external texture began to separate 
 and become loose. In sixty minutes, chyme began to form. At 1 o'clock, 
 P.M., (digestion having progressed with the same regularity as in the last half- 
 hour), the cellular texture seemed to be entirely destroyed, leaving the mus- 
 cular fibres loose and unconnected, floating about in fine small shreds, very 
 tender and soft. At 3 o'clock, the muscular fibres had diminished one-half, 
 since the last examination. At 5 o'clock, they were nearly all digested ; a 
 few fibres only remaining. At 7 o'clock, the muscular texture was completely 
 broken down, and only a few of the small fibres could be seen floating in the 
 fluid. At 9 o'clock, every part of the meat was completely digested. The 
 gastric juice, when taken from the stomach, was as clear and transparent as 
 water. The mixture in the vial was now about the colour of whey. After 
 
NATURE OF CHYMIFICATION. 505 
 
 standing at rest a few minutes, a fine sediment, of the colour of the meat, sub- 
 sided to the bottom of the vial. A piece of beef, exactly similar to that placed 
 in the vial, was introduced into the stomach, through the aperture, at the same 
 time. At 12 o'clock it was withdrawn, and found to be as little affected by 
 digestion as that in the vial ; there was little or no difference in their appear- 
 ance. It was returned to the stomach ; and, on the string being drawn out at 
 1 o'clock P.M., the meat was found to be all completely digested and gone. 
 The effect of the gastric juice on the piece of meat suspended in the stomach, 
 was exactly similar to ihat in the vial, only more rapid after the first half 
 hour, and sooner completed. Digestion commenced on, and was confined to, 
 the surface entirely in both situations. Agitation accelerated the solution in the 
 vial, by removing the coat that was digested on the surface, enveloping the 
 remainder of the meat in the gastric fluid, and giving this fluid access to the 
 undigested portions."* Many variations were made in other experiments ; 
 some of which strikingly displayed the effects of thorough mastication, in 
 aiding both natural and artificial digestion. 
 
 666. The attempt was made by Dr. Beaumont, to determine the relative 
 digestibility of different articles of diet, by observing the length of time re- 
 quisite for their solution. But, as he himself points out, the rapidity of diges- 
 tion varies so greatly, according to the quantity eaten, the nature and amount 
 of the previous exercise, the interval since the preceding meal, the state of 
 health, the condition of the mind, and the nature of the weather, that a much 
 more extended inquiry would be necessary to arrive at results to be depended 
 on. Some important inferences of a general character, however, may be 
 drawn from his inquiries. It seems to be a general rule, that the flesh of 
 wild animals is more easy of digestion than that of the domesticated races 
 which approach them most nearly. This may, perhaps, be partly attributed 
 to the small quantity of fatty matter that is mixed up with the flesh of the 
 former, whilst that of the latter is largely pervaded by it. For it appears from 
 Dr. B.'s experiments, that the presence in the stomach of any substance which 
 is difficult of digestion, interferes with the solution of food that would other- 
 wise be soon reduced. It seems that, on the whole, Beef is more speedily 
 reduced than Mutton, and Mutton sooner than either Veal or Pork. Fowls 
 are far from possessing the digestibility that is ordinarily imputed to them ; 
 but Turkey is, of all kinds of flesh except Venison, he most soluble. Dr. 
 B.'s experiments further show, that bulk is as necessary for healthy digestion, 
 as the presence of the nutrient principle itself. JMiis fact has been long known 
 by experience to uncivilized nations. The Kamschatdales, for example, are 
 in the habit of mixing earth or saw-dust with the train-oil, on which alone 
 they are frequently reduced to live. The Veddahs or wild hunters of Ceylon, 
 on the same principle, mingled the pounded fibres of soft and decayed wood 
 with the honey, on which they feed when meat is not to be had ; and on one 
 of them being asked the reason of the practice, he replied, " I cannot tell you, 
 but I know that the belly must be filled." It is further shown by Dr. B., 
 that soups and fluid diet are not more readily chymified than solid aliment, 
 and are not alone fit for the support of the system ; and this, also, is conform- 
 able to the well-known results of experience ; fpr a dyspeptic patient will 
 frequently reject chicken-broth, when he can retain solid food or a richer 
 soup. Perhaps, as Dr. A. Combe remarks, the little support gained from 
 fluid diet, is due to the rapid absorption of the watery part of it ; so that the 
 really nutritious portion is left in too soft and concentrated a state, to excite 
 the healthy action of the stomach. Dr. Beaumont also ascertained that 
 moderate exercise facilitates digestion, though severe and fatiguing exercise 
 
 * Experiments 2 and 3 of First Series. 
 43 
 
506 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 retards it. If even moderate exercise be taken immediately after a full meal, 
 however, it is probably rather injurious than beneficial ; but if an hour be per- 
 mitted to elapse, or if the quantity of food taken have been small, it is of de- 
 cided benefit. The influence of temperature on the process of solution, is 
 remarkably shown in some of Dr. B.'s experiments. He found that the gas- 
 tric juice had scarcely any influence on the food submitted to it, when the 
 bottle was exposed to the cold air, instead of being kept at a temperature of 
 100. He observed on one occasion, that the injection of a single gill of 
 water at 50 into the stomach, sufficed to lower its temperature upwards of 
 30 ; and that its natural heat was not restored for more than half an hour. 
 Hence the practice of eating ice after dinner, or even of drinking largely of 
 cold fluids, is very prejudicial to digestion. 
 
 667. From the foregoing statements we may conclude, that the process by 
 which the food is dissolved in the Gastric fluid is of a purely Chemical na- 
 ture, since it takes place out of the living body as well as in it, allowance 
 being made for the difference in its physical condifoon. That the natural pro- 
 cess of digestion is imitated, when the food is submitted to the action of the 
 gastric juice in a vial, not only in regard to the disintegration of its particles, 
 but as to the change of character which they are made to undergo, is proved 
 by the fact, that the artificial chyme thus formed exhibits the same changes as 
 the real chyme, when submitted to the action of the bile ( 658). The pro- 
 cess of digestion, however, may be freely conceded to be vital, in so far as it 
 is dependent upon the agency of a secreted product, which vitality alone (so 
 far at least as we at present know) can elaborate ; and all for which it is here 
 contended is, that, when this product is once formed, it has an agency upon 
 the alimentary matter, which, though not yet fully understood, is conformable, 
 in all that is known of its operation, to the ordinary laws of chemistry. Thus, 
 Digestion is conformable to Chemical solution, -first, in the assistance which 
 both derive from the minute division of the solids submitted to it ; secondly, 
 in the assistance which both derive from the successive addition of small por- 
 tions of the comminuted solid to the solvent fluid, and from the thorough in- 
 termixture of the two by continual agitation ; thirdly, in the limitation of the 
 quantity of food on whic'h a given amount of gastric juice can operate, which 
 is precisely the case with chemical solvents ; -fourthly, in the assistance which 
 both derive from an elevation of temperature, the beneficial influence of heat 
 being only limited, in the case of digestion, by its tendency to produce decom- 
 position of the gastric fluid ; -fifthly, in the different action of the same solvent 
 upon the various solids submitted to it. 
 
 668. It may be considered a well-established fact, that diluted acids alone 
 have no power of chymifying alimentary substances, although capable of 
 partially dissolving some of them ; but that their presence in the gastric fluid 
 is essential to its effectual action. The active agent in the process appears to 
 be an Organic compound, to which the name of pepsin has been given. The 
 properties of this have been investigated by Wasmann, who first succeeded in 
 obtaining it in an isolated state ; his observations were made upon the mucous 
 membrane of the stomach of the Pig, which greatly resembles that of Man. 
 
 a. When this membrane is digested in a large quantity of water at from 85 to 95, many 
 other matters are removed from it besides pepsin ; but if this water be removed, and the 
 digestion be continued with fresh water in the cold, very little but pepsin is then taken up. 
 Pepsin appears to be but sparingly soluble in water ; when its solution is evaporated to dry- 
 ness, there remains a brown, grayish, viscid mass, with the odour of glue, and having the 
 appearance of an extract. The solution of this in water is turbid, and still possesses a por- 
 tion of the characteristic power of pepsin, but greatly reduced. When strong alcohol is added 
 to a fresh solution of pepsin, the latter is precipitated in white flocks, which may be collected 
 on a filter, and produce a grey compact mass when dried. Pepsin enters into chemical com- 
 
NATURE OF CHYMIFICATION PEPSIN. 507 
 
 bination with many acids, forming compounds which still redden litmus paper ; and it is 
 when thus united with acetic and muriatic acids, that its solvent powers are the greatest. 
 
 b. "In regard to the solvent power of pepsin for coagulated albumen, it was observed by 
 M. Wasmann that a liquid which contains 17-lO,OOOths of acetate of pepsia, and 6 drops 
 of hydrochloric acid per ounce, possesses a very sensible solvent power, so that it will dis- 
 solve a thin slice of coagulated albumen in the course of 6 or 8 hours' digestion. With 12 
 drops of hydrochloric acid per ounce, the white of egg is dissolved in 2 hours. A liquid 
 which contains ^ gr. of acetate of pepsin, and to which hydrochloric acid and white of egg 
 are alternately added, so long as the latter dissolves, is capable of raking up 210 grains of 
 coagulated white of egg at a temperature between 95 and 104. It would appear, from 
 such experiments, that the hydrochloric acid is the true solvent, and that the action of the 
 pepsin is limited to that of disposing the white of egg to dissolve in hydrochloric acid. The 
 acid when alone dissolves white of egg by ebullition, just as it does under the influence of 
 pepsin; from which it follows that pepsin replaces the effect of a high temperature, which 
 is not possible in the stomach. The same acid with pepsin dissolved blood, fibrine, meat 
 and cheese; while the isolated acid dissolved only an insignificant quantity at the same 
 temperature; but when raised to the boiling point, it dissolved nearly as much, and the part 
 dissolved appeared to be of the same nature. The epidermis, horn, the elastic tissue (such 
 as the fibrous membrane of arteries) do not dissolve in a dilute acid containing pepsin. M . 
 Wasmann has remarked that the pepsin of the stomach of the pig is entirely destitute of the 
 power to coagulate milk, although the pepsin of the stomach of the calf possesses it in a very 
 high degree ; from which he is led to suppose, that the power of the latter depends upon a 
 particular modification of pepsin, or perhaps upon another substance accompanying it, which 
 ceases to be formed when the young animal is no longer nourished by the milk of its mother."* 
 
 669. It is considered by Liebig, however, that Pepsin has no proper ex- 
 istence as such ; and that it is nothing else than a proteine-compound in a 
 state of change, being, when obtained after the method of Wasmann, the 
 result of the partial decomposition of the membrane of the stomach, which 
 has been induced in it by exposure to air. This view accords well with the 
 fact, recently ascertained by MM. Bernard and Barreswill, that the Saliva and 
 Pancreatic fluid have an equal solvent power when acidulated. In their alka- 
 line condition, their action appears limited to starchy matters ; of which they 
 effect the conversion into sugar. In their acid state, they act, like the gastric 
 fluid, upon azotized matters ; and, in common with it, they are destitute of 
 power to act upon starch. We are further led, by this remarkable fact (the 
 knowledge of which enables us to harmonize many previous results, which 
 were apparently discordant), to a better understanding of the nature of the 
 action of this Organic compound in the Digestive process. Its operation on 
 starch is precisely that of the substance termed Diastase, which is found in 
 Plants, and which is the agent employed for the conversion of starch into 
 sugar, in various processes of the Vegetable economy. In so doing, it acts as 
 a sort of ferment ; having the power of exciting a change in another substance, 
 in which it does not itself participate. This appears to be precisely the 
 nature of its operation upon azotized matters ; in which it produces an in- 
 cipient change, that so alters their condition, as to dispose them to solution in 
 hydrochloric and acetic acids, 'with which they form definite chemical com- 
 pounds. The analogy of the action of Pepsin to that of a ferment, is further 
 shown in the power possessed by a very small quantity of it, to excite the 
 required change in an almost unlimited amount of alimentary matters ; whilst 
 only a definite quantity of these matters, when thus prepared, can be dissolved 
 in a limited amount of dilute acid; which is precisely analogous to the pro- 
 cess of chemical solution. The agency of Pepsin, in preparing them for that 
 process, resembles that of Heat ; by which it may be replaced, the dilute 
 acids alone, at a high temperature, having the power of dissolving azotized 
 compounds. 
 
 670. We have, in the last place, to consider the changes which are effected 
 
 * Graham's Elements of Chemistry, [Am. ed. p. 695.] 
 
508 OF FOOD, AND THE DIGESTIVE PROCESS. 
 
 in the nutritive materials, by the admixture of the biliary and pancreatic secre- 
 tions ; and to inquire into the form in which they are received into the absorb- 
 ent vessels. The substances of the first or saccharine group consist chiefly 
 of Sugar and Starch. It appears from the late researches of MM. Bouchardat 
 and Sandras, that Sugar is gradually converted, during its passage along the 
 alimentary canal, into lactic acid ; and that it is absorbed in this form alone, 
 unless it have been administered in considerable quantity or for a long period. 
 The conversion of sugar into lactic acid, appears to be preliminary to the 
 elimination of that substance by the respiratory process. The particles of 
 Starch, as already mentioned, are but very little acted on by the digestive pro- 
 cess, at least in Man and the Mammalia, unless their envelopes have been 
 previously ruptured by heat or chemical agents ; but the triturating power of 
 the gizzard in granivorous Birds, aided by the high temperature and the more 
 alkaline character of the secretions, enables them to act with more energy upon 
 amylaceous substances. The products of the digestive action upon starch, 
 are dextrine and grape-sugar; and this is gradually converted into lactic acid, 
 in which state it is absorbed. If sugar be introduced into the blood-vessels 
 unchanged, it is drawn off by the urine ; and its heat-sustaining agency, there- 
 fore, is not exerted. It is probably to avoid its too rapid introduction that 
 the conversion of amylaceous into saccharine matter is so slowly effected in 
 the alimentary canal ; this conversion seems to begin in the mouth, to cease 
 in the stomach during the operation of the acid solvent, and to recommence 
 after the neutralization of the acid by the biliary and pancreatic fluids, sub- 
 sequently continuing during nearly the whole of the passage of the alimentary 
 matter along the intestinal tube. It is now quite certain, that the substances 
 of this class may be converted, in the living body, into oleaginous matter. Of 
 the mode and the situation in which this conversion takes place, nothing 
 whatever is certainly known ; but a clue to an acquaintance with the former 
 seems to be given by the recently-discovered fact, that the continued contact 
 of bile with saccharine matter occasions the conversion of a portion of the 
 sugar into an adipose compound ( 835). 
 
 671. The substances forming the Oleaginous class do not seem to undergo 
 any change, except minute division of their particles, until the Chyme is min- 
 gled with bile; which substance acts as a soap, and renders the oily matters 
 soluble, or at any rate reduces them to a condition in which they can be ab- 
 sorbed by the lacteals. This, indeed, seems to be the main purpose of that 
 admixture of the bile with the mass in process of digestion, which experiments 
 and pathological observation abundantly prove, to be requisite for the due per- 
 formance of that function. Thus, it has been shown by the experiments of 
 Schwann, that, if the bile-duct be divided, and be made to discharge its con- 
 tents externally through a fistulous orifice in the walls of the abdomen, instead 
 of into the intestinal canal, those animals which survive the immediate effects 
 of the operation, subsequently die from inanition, almost as soon as if they 
 had been entirely deprived of food. In like manner, if the flow of the biliary 
 secretion into the intestine be prevented by disease, such as obstruction of 
 the gall-duct, the digestive function is evidently disordered, the peristaltic 
 action of the intestine is not duly performed, the faeces are white and clayey ; 
 and there is an obvious insufficiency in the supply of nutriment prepared for 
 the absorbent vessels. This deficiency seems partly due to the want of power 
 to absorb the oleaginous particles of the food, which is the result of the non- 
 intermixture of the bile with the chyme; and partly to the suspension of the 
 supply of combustible matter, that is afforded by certain constituents of the 
 bile itself, which are destined, not to be carried out of the system, but to be 
 re-absorbed. The presence of bile in the stomach has the effect of suspend- 
 
ABSORPTION FROM THE DIGESTIVE CAVITY. 509 
 
 ing the solution of the various azotized principles, and in regard to them, 
 therefore, it is injurious; but it seems, from the observations of Dr. Beaumont, 
 to be a spontaneous occurrence, whenever the diet has been for a long time, 
 and in great part, of an oleaginous nature ; and it then appears destined to aid 
 in the reducing process, which is the proper function of the stomach. It is 
 suggested by Dr. A. Combe, whether the peculiar digestibility of a piece of 
 fat bacon, in certain forms of Dyspepsia, may not be due to the abnormal 
 presence of bile in the stomach. The power of precipitating the proteine- 
 compounds from their acid solutions, which has been shown, by the recent 
 experiments of Platner, to belong to the peculiar principles of bile, fully ex- 
 plains its injurious effects upon the solvent processes, which normally take 
 place in the stomach. In regard to the Albuminous and Gelatinous articles 
 of food, there is no evidence that any other change is effected in them, than 
 one of simple solution ; and they appear to be absorbed in the same condition 
 as that to which they are reduced by the action of the stomach. 
 
 CHAPTER XI. 
 
 OF ABSORPTION AND SANGUIFICATION. 
 
 1. Absorption from the Digestive Cavity. 
 
 672. So long as the Alimentary matter is contained in the digestive cavity, 
 it is as far from being conducive to the nutrition of the system, as if it were in 
 contact with the external surface. It is only when absorbed into the vessels, 
 and carried by the circulating current into the remote portions of the body, 
 that it becomes capable of being appropriated by its various tissues and organs. 
 Among the Invertebrata, we find the reception of alimentary matter into the 
 Circulating system to be entirely accomplished through the medium of the 
 blood-vessels," which are distributed upon the walls of the digestive cavity. 
 But in the Vertebrata, we find an additional set of vessels interposed between 
 the walls of the intestine and the sanguiferous system ; for the purpose, as it 
 would seem, of taking up that portion of the nutritive matter which is not in 
 a state of perfect solution, and of preparing it for being introduced into the 
 current of the blood. These are the lacteals, or absorbents of the intestinal 
 walls. That their special office is to take up the product of the admixture of 
 the chyme with the biliary and pancreatic fluids, appears from the fact, that 
 they are not distributed at all upon the walls of the stomach, nor upon those of 
 the duodenum above the point of entrance of the hepatic and pancreatic ducts; 
 but that they are copiously distributed upon the walls of the remainder of the 
 small intestine, and more sparingly upon those of the large. Each lacteal 
 tube originates in the interior of one of the villous processes of the mucous 
 membrane lining the intestinal tube. The accompanying figure represents the 
 appearance offered by the incipient lacteals, in a villus of the jejunum of a 
 young man, who had been hung soon after taking a full meal of farinaceous 
 food. The trunk that issues from the villus is formed by the confluence of 
 
 43* 
 
510 OF ABSORPTION AND SANGUIFICATION. 
 
 Pig. 204. several smaller branches, whose origin it is difficult to 
 
 trace ; but it is probable that they form loops by anasto- 
 mosis with each other, so that there is no proper free 
 extremity in any case. It is quite certain that the lac- 
 teals never open by free orifices upon the surface of the 
 intestine, as was formerly imagined. From the researches 
 of Mr. J. Goodsir, already referred to ( 181), it appears 
 that these loops are imbedded in a mass of cells, which 
 are the real agents in the selection of the materials that 
 are destined to be conveyed into the lacteals. When 
 these cells have distended themselves, by their inherent 
 one of the intestinal viiii, POWCT of growth, with the materials which are adapted 
 with the commencement of to tnelr selecting function, and have reached their full 
 a lacteal. term of maturity, they appear to yield their contents to 
 
 the absorbent vessels, either by bursting or by deli- 
 quescence. It is thought by Prof. E. Weber, that the epithelial cells, which 
 cover the villus, perform a preliminary office; the nutrient matter being first 
 absorbed and partially prepared by them ; and then being drawn, through the 
 basement membrane of the villus, into the special absorbent cells which form 
 part of its substance. This seems the more likely, as we shall hereafter 
 find that the epithelial cells of the placental tufts appear to perform a like 
 function. 
 
 673. The villi are also furnished with a minute plexus of blood-vessels ; 
 of which the larger branches may be seen with the naked eye, when they are 
 distended with blood, or with coloured injection (Figs. 205, 206). 'The par- 
 ticular arrangement of the capillaries of which the plexus is formed, varies in 
 different animals; but in all they seem to be most copiously distributed upon 
 the surface of the villus. The purpose of these may be partly to afford some 
 of the materials for the development of the absorbent cells ; and this would 
 seem probable from the recent experiments of Mr. Fenwick,* which show 
 that the lacteals will not absorb alimentary matter from any part of the intes- 
 tinal canal, in which the blood is not circulating. But there can be no reason- 
 able doubt, that the blood-vessels of the mucous membrane lining the digestive 
 cavity, and especially those of the villi, perform an important part in the func- 
 tion of Absorption. This is established by the fact, that soluble substances 
 introduced into the stomach, and prevented from passing beyond its pyloric 
 orifice, are absorbed from its walls. 
 
 674. In regard to the degree in which the function of Nutritive Absorp- 
 tion is performed by the Lacteals, and by the Sanguiferous System, respect- 
 ively, considerable difference of opinion has prevailed. When the Absorbent 
 vessels were first discovered, and their functional importance perceived, it 
 was imagined that the introduction of alimentary fluid into the vascular sys- 
 tem took place by them alone. A slight knowledge of Comparative Anatomy, 
 however, might have sufficed to correct this error; since no lacteals exist in 
 the Invertebrated animals, the function of Absorption being performed by the 
 Mesenteric blood-vessels only ; from which it is evident, that these do pos- 
 sess the power of absorption : and it is scarcely to be supposed that they 
 should not exercise this power in Vertebrated animals also, since their dis- 
 position on the walls of the intestinal cavity is evidently favourable to it. On 
 the other hand, the introduction of a new and distinct system of vessels would 
 seem to indicate, that they must have some special purpose ; and there can 
 be no doubt that the absorption of certain kinds of nutritive matter is that 
 for which they are peculiarly designed. The fluid found in the lacteals is 
 
 * Lancet, Jan. and Feb. 1845. 
 
ABSORPTION BY BLOOD-VESSELS OF VILLI. 
 
 Fig. 205. 
 
 511 
 
 Vessels of an intestinal villus 
 of a Hare, from a dry prepara- 
 tion by DSHinger; 1, 1, veins 
 rilled with white injection ; 2, 2, 
 arteries injected red. Magnified 
 about 45 diameters. 
 
 A, apex of intestinal vil- 
 lus from the duodenum of 
 Human female ; B, a mesh of 
 the vascular net-work, 1, 1, 
 filled up with delicate cellu- 
 lar tissue, 2, magnified about 
 45 diameters. 
 
 almost invariably the same; being that to which the name chyle has been 
 applied. It appears from the uniformity of its composition, which forms a 
 striking contrast with the diversity of the food from which it is obtained, that 
 the lacteals (or rather the absorbent cells, amongst which they originate) have 
 in some degree the power of selecting the particles of which it is composed ; 
 and that, whilst they take up such a proportion of each class of alimentary 
 materials as will rightly blend with the rest in the nutritious fluid, they reject 
 not only the remainder, but also (for the most part at least) any other ingre- 
 dients which may be contained in the fluid of the intestines. Such may be 
 stated as the general result of the experiments that have been made to de- 
 termine their function ; though it is unquestionable that extraneous substances, 
 especially of a saline nature, occasionally find their way into this system of 
 vessels. This may not improbably be due to a correspondence in the size 
 and form of the ultimate particles of such substances, with those of the mate- 
 rials normally absorbed by the lacteals.* 
 
 675. On the other hand, the Blood-vessels seem to be less concerned in 
 nutritive absorption, but take up from the alimentary canal a portion of almost 
 any fluid matters which it may contain. This seems to have been established 
 by the carefully-conducted experiments of MM. Tiedemann and Gmelin, who 
 
 * Experiments upon the function of Absorption in Plants, whose radical vessels have a 
 corresponding power of selection, appear likely to assist in elucidating this interesting subject. 
 By the experiments of Dr. Daubeny it has been ascertained, that if a plant absorb any par- 
 ticular saline compound, it can also be made to absorb those which are isomorphous with it, 
 though it will reject most others. See Princ. of Gen. and Comp. Phys. , 294. 
 
512 OF ABSORPTION AND SANGUIFICATION. 
 
 mingled with the food of animals various substances, which, by their colour, 
 odour, or chemical properties, might be easily detected in the fluids of the 
 body. After some time the animal was examined ; and the result was, that 
 unequivocal traces of the substances were not unfrequently detected in the 
 venous blood and in the urine ; whilst it was only in a very few instances, 
 that any indication of them could be discovered in the chyle. The colouring 
 matters employed were various vegetable substances ; such as gamboge, mad- 
 der, and rhubarb : the odorous substances were camphor, musk, assafostida, 
 &c. ; while, in other cases, various saline bodies, such as muriate of barytes, 
 acetate of lead and of mercury, and some of the prussiates, which might easily 
 be detected by chemical tests, were mixed with the food. The colouring 
 matters, for the most part, were carried out of the system, without being re- 
 ceived either into the veins or lacteals ; the odorous substances were gene- 
 rally detected in the venous blood and in the urine, but not in the chyle ; 
 whilst of the saline substances, many were found in the blood and in the 
 urine, and a very few only in the chyle. A similar conclusion might be 
 drawn from the numerous instances in which various substances introduced 
 into the intestines have been detected in the blood, although the thoracic duct 
 had been tied ; but these results are less satisfactory, because even if there is 
 no direct communication (as maintained by many) between the lacteals and 
 the veins in the mesenteric glands, the partitions which separate their respect- 
 ive contents are evidently so thin, that transudation may readily take place 
 through them. It would seem probable, that substances perfectly dissolved 
 in the fluids of the stomach, are taken into the blood-vessels so copiously dis- 
 tributed on, its walls, by the simple and necessary process of Endosmose ; in 
 this manner we may account for the fact, that saline substances are for the 
 most part readily absorbed into the blood ; and there seems reason to believe 
 that the Albuminous portion of the chyme, together with the Saccharine prin- 
 ciples or the products of their transformation, may thus be introduced directly 
 into the circulating current, without passing through the lacteals. On this 
 subject there is much need of further information. 
 
 2. Absorption from the Body in general. 
 
 676. The Mucous Membrane of the alimentary canal is by no means the 
 only channel, through which nutritive or other substances may be introduced 
 into the circulating apparatus. The Lymphatic system is present in all animals 
 which have a lacteal system ; and the two evidently constitute one set of ves- 
 sels. The lymphatics, however, instead of commencing on the intestinal 
 walls, are distributed through the greater part of the body, especially on the 
 Skin ; their origins cannot be clearly traced ; but they seern in general to form 
 a plexus in the substance of the tissues, from which the convergent trunks 
 arise. After passing, like the lacteals, through a series of glandular bodies 
 (the precise nature of which will be presently considered, 682), they empty 
 their contents into the same receptacle with the lacteals; and the mingled 
 products of both pass into the Sanguiferous system. We find in the Skin, 
 also, a most copious distribution of capillary blood-vessels, the arrangement of 
 which is by no means unlike that of the blood-vessels of the alimentary canal ; 
 and its surface is further extended by the elevations that form the sensory 
 papillae, which are in many points comparable to the intestinal villi, although 
 their special function is so different. In the lowest tribes of animals, and in 
 the earliest condition of the higher, it would seem as if Absorption by the ex- 
 ternal surface is almost equally important to the maintenance of life, with 
 that which takes place through the internal reflexion of it forming the walls 
 of the Digestive cavity. In the adult condition of the higher animals, how- 
 
ABSORPTION THROUGH THE CUTANEOUS SURFACE. 513 
 
 ever, the special function of the latter is so much exalted, that itusually super- 
 sedes the necessity of any other supply ; and the function of the cutaneous 
 and pulmonary surfaces may be considered as rather that of exhalation, than 
 of absorption. But there are peculiar conditions of the system, in which the 
 imbibition of fluid through these surfaces is performed with great' activity, 
 supplying what would otherwise be a most important deficiency. It may 
 take place either through the direct application of fluid to the surface, or even 
 through the medium of the atmosphere, in which a greater or less proportion 
 of watery vapour is usually dissolved. This absorption occurs most vigour- 
 ously, when the system has been drained of its fluid, either by an excess of 
 the excretions, or by a diminution of the regular supply. 
 
 677. It may be desirable to adduce some individual cases, which will set 
 this function in a striking point of view; and those may be first noticed, in 
 which the absorption took place, through the contact of liquids with the skin. 
 It is well known that shipwrecked sailors, and others, who are suffering from 
 thirst, owing to the want of fresh water, find it greatly alleviated, or altogether 
 relieved, by dipping their clothes into the sea, and putting them on whilst still 
 wet, or by frequently immersing their own bodies. Dr. Currie relates the 
 case of a patient labouring under dysphagia in its most advanced stage; the 
 introduction of any nutriment, whether solid or fluid into the stomach', having 
 become perfectly impracticable. Under these melancholy circumstances, an 
 attempt was made to prolong his existence, by the exhibition of nutritive ene- 
 mata, and by immersion of the body, night and morning, in a bath of milk and 
 water. During the continuance of this plan, his weight, which had previously 
 been rapidly diminishing, remained stationary, although the quantity of the 
 excretions was increased. How much of the absorption, which must have 
 been effected to replace the amount of excreted fluid, is to be attributed to the 
 baths, and how much to the enemata, it is not easy to say ; but it is important 
 to remark that " the thirst, which was troublesome during the first days of the 
 patient's abstinence, was abated, and, as he declared, removed by the tepid 
 bath, in which he had the most grateful sensations." "It cannot be doubted," 
 Dr. Currie observes, "that the discharge by stool and perspiration exceeded 
 the weight of the clysters ;" and the loss by the urinary excretion, which in- 
 creased from 24 oz. to 36 oz. under this system, is only to be accounted for 
 by the cutaneous absorption. Dr. S. Smith mentions that a man, who had 
 lost nearly 3 Ibs. by perspiration, during an hour and a quarter's labour in a 
 very hot atmosphere, regained 8 oz. by immersion in a warm bath at 95, for 
 half an hour. The experiments of Dr. Madden* show that a positive increase 
 usually takes place in the weight of the body, during immersion in the warm 
 bath, even though there is at the same time a continual loss of weight by pul- 
 monary exhalation, and by transudationt from the skin. This increase was, 
 in some instances, as much as 5 drachms in half an hour ; whilst the loss of 
 weight during the previous half hour had been 65 drachms : so that, if the 
 same rate of loss were continued in the bath, the real gain by absorption must 
 have been nearly an ounce and a half. Why this gain was much less than 
 in the cases just alluded to, is at once accounted for by the fact that there was 
 no deficiency, in the latter case, of the fluids naturally present in the body. 
 
 678. The quantity of water which may be imbibed from the vapour of the 
 atmosphere, would exceed belief, were not the facts on which the assertion 
 rests, beyond all question. Dr. Dill relates the case of a diabetic patient, 
 
 * Prize Essay on Cutaneous Absorption, pp. 59 63. 
 
 t That part of the function of cutaneous transpiration, which consists in simple exhalation , 
 is of course completely checked by such immersion ; but that which is the result of an actual 
 secreting process in the cutaneous glands (CHAP, xv., Sect. 8) is increased by heat, even 
 though this be accompanied with moisture, 
 
514 OF ABSORPTION AND SANGUIFICATION. 
 
 who for five weeks passed 24 Ibs. of urine every twenty-four hours ; his in- 
 gesta during- the same period amounted to 22 Ibs. At the commencement of 
 the disease he weighed 145 Ibs. ; and when he died, 27 Ibs. of loss had been 
 sustained. The daily excess of the excretions over the ingesta could not have 
 been less* than 4 Ibs. ; making 140 Ibs. for the thirty-five days during which 
 the complaint lasted. If from this we deduct the amount of diminution which 
 the weight of the body sustained during the time, we shall still have 113 Ibs. 
 to be accounted for, which can only have entered the body from the atmo- 
 sphere. A case of ovarian dropsy has been recorded, in which it was ob- 
 served that the patient, during eighteen days, drank 692 oz. or 43 pints of 
 fluid, and that she discharged by urine and by paracentesis, 1298 oz. or 91 
 pints, which leaves a balance of 606 oz. or 38 pints, to be similarly accounted 
 for.* The following remarkable fact is mentioned by Dr. Watson in his Che- 
 mical Essays. " A lad at Newmarket, having been almost starved, in order 
 that he might be reduced to a proper weight for riding a match, was weighed 
 at 9 A. M., and again at 10 A. M. ; and he was found to have gained nearly 30 
 oz. in weight in the course of this hour, though he had only drunk half a 
 glass of wine in the interim." A parallel instance was related to the Author 
 by the late Sir G. Hill, then Governor of St. Vincent. A jockey had been 
 for some time in training for a r.ace, in which that gentleman was much inte- 
 rested ; and had been reduced to the proper weight. On the morning of the 
 trial, being much oppressed with thirst, he took one cup of tea ; and shortly 
 afterwards his weight was found to have increased 6 Ibs. ; so that he was in- 
 capacitated for riding. Nearly the whole of the increase in the former case, 
 and at least three-fourths of it in the latter, must be attributed to cutaneous 
 absorption ; which function was probably stimulated by the wine that was 
 taken in the one case, and by the tea in the other. 
 
 679. Not only water, but substances dissolved in it, may be thus introduced. 
 It has been found that, after bathing in infusions of madder, rhubarb, and tur- 
 meric, the urine was tinged with these substances; and that a garlic plaster 
 affected the breath, when every care was taken, by breathing through a tube 
 connected with the exterior of the apartment, that the odour should not be re- 
 ceived into the lungs.t Gallic acid has been found in the urine, after the ex- 
 ternal application of a decoction of a bark containing it; and the soothing influ- 
 ence in cases of neuralgic pain, of the external application of cherry-laurel 
 water, is well known. Many saline substances are absorbed by the skin, 
 when applied to it in solution ; and it is interesting to remark, that, contrary 
 to what happens in regard to the absorption of these from the alimentary ca- 
 nal, they are for the most part more readily discoverable in the absorbents 
 than in the veins. This is probably due to the fact, that the imbibition of 
 them is governed entirely by physical laws ; in obedience to -which, they pass 
 most readily into the vessels which present the thinnest walls and the largest 
 surface. In the intestines, the vascular plexus on each villus is far more ex- 
 tensive than the ramifying lacteal which originates in it; and as the walls of 
 the veins are thin, there is considerable facility for the entrance of saline and 
 other substances into the general current of the circulation ; but in the skin, 
 the lymphatics are distributed much more minutely and extensively than the 
 veins ; and soluble matters, therefore, enter them in preference to the veins. 
 The absorbent power of the Lymphatics of the Skin is well shown by the 
 following experiment. A bandage having been tied by Schreger round the 
 hind-leg of a Puppy, the limb was kept for twenty-four hours in tepid milk ; 
 
 * Madden, loc. cit. In this case, however, something is to be allowed for the quantity of 
 water contained in the solid food ingested. 
 
 t Dunglison'g Physiology, [Gth. ed., vol. i. p. 647.] 
 
ABSORPTION FROM THE BODY IN GENERAL. 515 
 
 fct the expiration of this period, the lymphatics were found full of milk, whilst 
 the veins contained none. In repeating this experiment upon a young man, 
 no milk could be detected in the blood drawn from a vein. It has been shown 
 by Miiller that, when the posterior extremities of a Frog were kept for two 
 hours in a solution of prtissiate of potass, the salt had freely penetrated the 
 lymphatics, but had not entered the veins. It does not follow, however, from 
 these and similar experiments, that in all tissues the lymphatics absorb more 
 readily than the veins ; for as the capillary blood-vessels in the lungs are much 
 more freely exposed to the surface of the air-cells, than are the lymphatics, 
 we should, on the principles just now stated, expect the former to absorb more 
 readily. This appears from experiment to be the fact ; for when a solution 
 of prussiate of potass was injected by Mayer into the lungs, the salt could be 
 detected in the serum of the blood much sooner than in the lymph, and in 
 the blood of the left cavities of the heart, before it had reached that of the 
 right. 
 
 680. Our inferences with regard to the ordinary functions of the Lymphatic 
 system, however, must be rather drawn from the nature of the fluid which it 
 contains, and from the uses subsequently made of it, than from experiments 
 such as the preceding. We shall presently see, that there is a close corre- 
 spondence in composition between the Chyle of the Lacteals, and the Lymph 
 of the Lymphatics ; the chief difference being the presence in the former, of 
 a considerable quantity of fatty matter, and of a larger proportion of the as- 
 similable substances (albumen and fibrine) which are equally characteristic of 
 both ( 691). This evident conformity in the nature of the fluid which these 
 two sets of vessels transmit, joined to the fact of the fluid Lymph, like the 
 Chyle, being conveyed into the general current f of the circulation, just before 
 the blood is again transmitted to the system at large, almost inevitably leads 
 to the inference, that the lymph is, like the chyle, a nutritious fluid, and is. not 
 of an excrementitious character, as formerly supposed. On the other hand, 
 the close resemblance between the contents of the Lymphatics, and diluted 
 Liquor Sanguinis, seems to indicate that 'the former are partly derived from 
 the fluid portion of the Blood, which has transuded through the walls of the 
 Capillary vessels ; and we shall presently see reason to believe that this 
 transudation is for the purpose of subjecting certain crude materials, that have 
 been taken up direct into the blood-vessels, to an elaborating or preparatory 
 agency, which it seems to be the especial object of the Absorbent system to 
 exert upon certain of the nutritive components of the circulating fluid. 
 
 681. But it seems not improbable that there may be another source for the 
 contents of the Lymphatics. We have already had to allude, on several oc- 
 casions, to the disintegration which is continually taking place within the living 
 body; whether as a result of the limited duration of the life of its component 
 parts, or as a consequence of the decomposing action of Oxygen. Now the 
 death of the tissues by no means involves their immediate and complete de- 
 struction ; and there seems no more reason why an animal should not derive 
 support from its own dead parts than from the dead body of another indi- 
 vidual. Whilst, therefore, the matter, which has undergone too complete a 
 disintegration to be again employed as nutrient material, is carried off by the 
 excreting processes that portion which is capable of being again assimilated, 
 may be taken up by the Lymphatic system. If this be the case, we may say, 
 with Dr. Prout, that " a sort of digestion is carried on in all parts of the body." 
 It may be stated, then, as a general proposition, that the function of the Ab- 
 sorbent System is to take up, and to convey into the Circulating apparatus, 
 such substances as are capable of appropriation to the nutritive process ; 
 whether these substances be directly furnished by the external world, or be 
 derived from the disintegration of the organism itself. We have seen that, 
 
516 OF ABSORPTION AND SANGUIFICATION. 
 
 in the Lacteals,the selecting power is such, that these vessels are not disposed 
 to convey into the systejn any substances but such as are destined for this 
 purpose ; and that extraneous matters are absorbed in preference by the Me- 
 senteric Blood-vessels. The case is different, however, with regard to the 
 Lymphatics ; for there is reason to believe, that they are more disposed than 
 the veins to the absorption of other soluble matters ; especially when these 
 are brought into relation with the skin, through which the lymphatic vessels 
 are very profusely distributed. 
 
 a. Since the time of Hunter, who first brought prominently forward the doctrine alluded 
 to, it has been commonly supposed that the function of the Lymphatics is to remove, by in- 
 terstitial absorption, the effete matter, which is destined to be carried out of the system ; and 
 any undue activity in this process (such as exists in ulceration), or any deficiency in its 
 energy (such as gives rise to dropsical effusions, and other collections of the same kind), 
 have been attributed to excess or diminution in the normal operation of the Absorbent Sys- 
 tem. From what has been stated, however, it appears that the special function of the 
 Lymphatics, like that of the Lacteals, is 'nutritive absorption;* and that the reception of any 
 other substances into their interior, must be looked upon as resulting simply from the per- 
 meability of their walls. This statement applies to the not unfrequent occurrence of the 
 absorption of bile, and other fluids, from the walls of the cavities in which they were col- 
 lected: with regard to the absorption of pus, however, which has been occasionally noticed 
 to take place, both from internal collections, and from open ulcers, it may be remarked, that 
 the lymphatic vessels were not improbably laid open by ulceration ; since in no other way 
 can be understood the entrance of globules so large as those of pus, into their interior. 
 
 b. If this view of the function of the Lymphatics be correct, it follows that we must at- 
 tribute to the Blood-vessels the absorption of the truly effete particles ; and in this there 
 would seem no improbability. We know that Venous blood contains the elements of two 
 important excretions, that of the lungs and that of the bile, in a far higher amount than does 
 arterial blood ; and we shall hereafter see, that there is a certain portion of the fluid, which 
 consists of " ill defined animal principles" that seem ready to be thus thrown off. 
 
 c. It may be further remarked, that the reciprocal part which Hunter imagined the Ar- 
 
 * The Author, at the time of the publication of the First Edition of this work, believed 
 this view to be altogether novel ; he has since learned, however, that a similar doctrine had 
 been put forward by Dr. Moultrie, of South Carolina, in the American Journal of the Medi- 
 cal Sciences, for the year 1827. 
 
 [In the American Journal of the Medical Sciences, for 1827, Dr. James Moultrie pub- 
 lished an essay on the " Uses of the Lymph," in which, amongst other things attempted to 
 be sustained, will be found the following views. 
 
 1. The lacteals and lymphatics do not constitute, as they are supposed to do, the absorbent 
 system of the animal economy; they do not, as the absorbent theory supposes, remove from 
 the organs the "cast off molecules" of which they are composed, or carry/out of the body 
 the " effete" particles disintegrated by the act of the assimilative function. The one is en- 
 gaged in the preparation and introduction of chyle, and chyle only into the blood ; the other 
 in elaborating an organizable product a recrementitious secretion destined to unite with it 
 for objects of a common and nutritious nature. 2. The primary object of the lymph, and 
 that for which it is made to commingle with the chyle in the thoracic duct, is the vitalization 
 of the latter fluid. 3. The truly "effete" matter of the body is the carbonaceous element 
 of the venous blood, to which may be added the urea or azotic element of the urine. Than 
 these, we know of nothing to which that term can be applied. 4. The venous and not the 
 lacteal or lymphatic system, therefore, is the "absorbent system," in any disintegratory or 
 effete sense of the phrase. 5. Nature, in effecting the elimination of excrementitious mat- 
 ter from the constituency of the solid or fluid parts, appears to aim at restoring to the physi- 
 cal universe, the matter temporarily borrowed for subsistence, in a state of elementary sim- 
 plicity, or an approximation thereto; that is, the carbon as carbon, the azote as azote, and 
 hydrogen and oxygen as hydrogen and oxygen. The lungs she uses as one medium of es- 
 cape ; the kidneys as a second ; and the skin as a third, &c. Hence, the carbonic acid gas 
 of respiration ; the urea of the kidneys, and the aqueous exhalations of the skin, pulmonary 
 transpiration and urine. 
 
 These doctrines have been regularly taught by Dr. M., in his course of lectures on physi- 
 ology, delivered in the Medical College of the State of South Carolina, since the establish- 
 ment of the College in 1833. They have also been recently enforced in a brochure published 
 by Dr. M., in which he asserts and vindicates his claim to their paternity. On the Organic 
 Functions of Jlnimals. By JAMES MOVLTBIE, M.D., etc., Charleston, S. C. 1844. M. C.] 
 
STRUCTURE OF ABSORBENT GLANDULE. 
 
 517 
 
 teries and Lymphatics to perform in the function of Nutrition, is quite inconsistent with 
 what is now known of the nature of that process: for, as will subsequently appear, it en- 
 tirely consists in a reaction between the tissues and the nutritious fluid, in which the vessels 
 have no share save as the channels of supply. When these channels are obstructed, or the 
 supply of new matter is cut off in any other way, the removal of the old by interstitial ab- 
 sorption becomes evident; and that this is accomplished at least as much by the veins as by 
 the lymphatics, appears from the fact that in some tissues, in which it may take place with, 
 rapidity, lymphatics do not exist. 
 
 3. Of the Elaboration of the Nutrient Materials. 
 
 682. The alimentary substances, taken up by the Absorbent vessels, seem 
 very far from being capable of immediate application to the nutrition of the 
 body; for we find that they are not conveyed by any means directly into the 
 Circulating current, but that they first traverse a long series of tubes, convo- 
 luted at intervals into ganglia or knots ;* and that, in the course of this pas- 
 sage, they undergo considerable changes, which tend to bring the fluid into 
 closer relationship with the Blood. It seems probable that the materials, 
 which are directly received into the Blood-vessels, are equally far from being 
 immediately applicable to the Nutritive processes ; for we find, in connection 
 with the vascular system, certain bodies having the essential structure of 
 glands, but destitute of efferent ducts ; which must restore to the circulating 
 current any substances which they withdraw from it; and which there are 
 various reasons (as will presently appear) for placing in the same category 
 with the glandulae of the Absorbent system. The Absorbent Glandulae, whe- 
 ther placed upon the Lacteals in the Mesentery, or upon the Lymphatics in 
 various parts of the body, have the same general structure. They are made 
 up of convoluted knots of absorbent vessels, the simple cylindrical canals of 
 which, however, are usually dilated into larger .cavities, or cells; and amongst 
 these, capillary blood-vessels are minutely distributed. These blood-vessels 
 have no direct communication with the interior of the absorbents and the 
 cavities of the glandulae, being separated from them by the membranous walls 
 of both sets of tubes ; but there can be no doubt that transudation readily 
 takes place from one set of canals to the other. The epithelium, which 
 lines the absorbent vessel, undergoes a marked change where the vessel en- 
 ters the gland ; and becomes more like that of the proper glandular follicles 
 in its character. Instead of being flat and scale-like, and forming a single 
 layer in close apposition with the basement-membrane, as it does in the ab- 
 sorbents previous to their entrance into the gland and after their emergence 
 from it, we find it cornj)osed of numerous layers of spherical nucleated cells, 
 of which the superficial ones are easily detached, and appear to be identical 
 
 Fig. 207. 
 
 Fig. 208. 
 
 < 
 
 Diagram of a lymphatic gland, showing the 
 intra-glandular network, and the transition 
 from the scale-like epithelia of the extra-glan- 
 dular lymphatics, to the nucleated cells of the 
 intra-glandular. 
 
 Portion of intra-glandular lymphatic, 
 showing along the lower edge the thick- 
 ness of the germinal membrane, and upon, 
 it, the thick layer of glandular epithelial 
 cells. 
 
 * In Reptiles, in which there are no glands or ganglia in the Absorbent system, the tubes 
 are immensely extended in length. 
 44 
 
518 OF ABSORPTION AND SANGUIFICATION. 
 
 with the cells found floating in the Chyle.* Their purpose will be considered 
 hereafter. 
 
 683. To the class of Vascular Glands belong the Spleen, the Thymns 
 and Thyroid Glands, and the supra-Renal Capsules. With the exception of 
 the first, they all have their origin (as recently ascertained by Mr. J. Good- 
 sirt) in involuted portions of the Germinal membrane ; and, at an early period 
 of embryonic life, they are in actual continuity with each other. Their'original 
 identity of function, therefore, cannot be doubted ; and the probability of the 
 inference, which rests on other grounds, that this function is to assimilate or 
 elaborate the nutrient materials (in the manner in which the cells of the 
 leaves of Plants prepare their elaborated sap), is strengthened by its exact 
 conformity with the original function of the Germinal membrane. But there 
 is no improbability that they may severally have some subsidiary or supple- 
 mentary function to perform ; varying according to their respective structure, 
 position, and connections. This seems peculiarly the case in regard to the 
 Spleen; the origin of which body is not the same with that of the other three. 
 
 a. According to the account of Dr. Julian Evans, whose researches appear to have been 
 more successful than those of any other Anatomist, the Spleen essentially consists of a fibrous 
 membrane, which constitutes its exterior envelope, and which sends prolongations in all 
 directions across its interior, so as to divide it into a number of minute cavities or lacunas 
 of irregular form. These Splenic lacunae, communicate freely with each other, and with 
 the Splenic vein ; and they are lined by a continuation of the lining membrane of the latter, 
 which is so reflected upon itself, as to leave oval or circular foramina, by which each lacuna 
 opens into others, or into the splenic vein. The lacunae, whose usual diameter is estimated 
 by Dr. Evans at from half to one-third of a line, are generally traversed by filaments of 
 elastic tissue, imbedded in which a small artery and vein may be frequently observed ; over 
 these filaments, the lining membrane is reflected in folds ; and in this manner each lacuna 
 is incompletely divided into two or more smaller compartments. There is no direct com- 
 munication between the splenic artery and the interior of the lacunae ; but its branches are 
 distributed through the intercellular parenchyma (which will be presently described); and 
 the small veins, which collect the blood from the capillaries of the organ, convey it into 
 these cavities, from which it is conveyed away by the splenic vein. The lacunae may be 
 readily injected from the splenic vein with either air or liquid, provided they are not filled 
 with coagulated blood ; and they are so distensible, that the organ may be made to dilate to 
 many times its original size, with very little force. This is especially the case in the Spleen 
 of the Herbivora; lor the Spleen of a Sheep, weighing 4 ounces, may be easily made to con- 
 tain 30 ounces of water. That of Man, however, is less capable of this kind of enlargement. 
 According to Dr. Evans, the lacunae of the spleen never contain anything but blood ; and 
 he notices that a frequent condition of the Human Spleen after death, which is sometimes 
 described as morbid appearance, consists in the filling of the lacunae with firmly-coagulated 
 blood, which gives a granular appearance to the organ. 
 
 b. The partitions between the lacunae are formed, not only by the membranes already 
 mentioned, but by the peculiar parenchyma of the Spleen; which constitutes a larger part 
 of the organ in Man than in the Herbivorous Mammalia. It presents a half fluid appear- 
 ance to the eye; but when an attempt is made to tear it, considerable resistance is expe- 
 rienced in consequence of its being intersected by what appear to be minute fibres. When 
 a small portion of it is pressed, a liquid is separated; which is that commonly known as the 
 Liquor Lienis, or Splenic blood; and which is usually described (but erroneously, according 
 to Dr. E.) as filling the lacunae of the Spleen This liquid, when diluted with serum and 
 examined under the Microscope, is found to contain two kinds of corpuscles, one sort being 
 apparently identical with ordinary blood-corpuscles and the other with the globules cha- 
 
 * See Mr. J. Good sir's Anatomical and Pathological Researches, p. 46. 
 
 t Proceedings of the Royal Society, 1846. 
 
 J Lancet, April 6, 1 844. 
 
 "It differs in no respect from venous blood taken out of any' other part of the portal 
 system. I have found it fluid or coagulated, as in other parts of the venous system ; and I 
 have frequently pulled out from the splenic vein colourless coagula. Occasionally a number 
 of globules may be distinguished in it, resembling those found in the parenchyma; but in 
 these cases the organ appears to have suffered injury, and these matters appear to have got 
 into the cells and vein in consequence." Loc. cit. 
 
STRUCTURE AND FUNCTIONS OF THE SPLEEN. 519 
 
 racteristic of the lymph and abundant in the lymphatic glands. The remaining fibrous 
 substance consists entirely of capillary blood-vessels and lymphatics, with minute corpuscles, 
 much smaller than blood-corpuscles, varying in size from about 1-GOOOth to l-7000th of an 
 inch, of spherical form, and usually corrugated on the surface. These lie in great numbers 
 in the meshes of the sanguiferous capillaries; and the minute lymphatics are described by 
 Dr. E. as connected with the splenic corpuscles, and apparently arising from them. Lying 
 in the midst of the parenchyma are found a large number of bodies, of about a third of a line 
 in diameter, which are evidently in close connection with the vascular system : these have 
 long been known as the Malpighian bodies of the spleen, after the name of their discoverer; 
 but since his time, their existence has been denied, or other appearances have been mistaken 
 for them. According to Dr. E., they in all respects resemble the mesenteric or lymphatic 
 glands in miniature, consisting as they do of convoluted masses of blood-vessels and lym- 
 phatics, united together by elastic tissue, so as to possess considerable firmness : and they 
 further correspond with them in this, that the lymph they contain, which was quite trans- 
 parent in their afferent lymphatics, now becomes somewhat milky, from containing a large 
 number of Lymph-globules. 
 
 684. In regard to the functions of the Spleen, great uncertainty exists. It 
 appears from the foregoing account of its structure, that it may be regarded 
 as an organ of duplex character, and probably of double function. The eel- 
 lated structure maybe considered as a multilocular reservoir, capable of great 
 distention, and lined with a continuation of the inner membrane of the veinj 
 receiving blood, on the one hand, from the veins of the interior of the organ, 
 and transmitting it onward to the Vena Porire ; and on the other hand, acting 
 as a reservoir for the venous blood of the abdomen, when, from any cause, 
 its passage into the Vena Cava is obstructed. The splenic parenchyma, on 
 the other hand, must be regarded as a complex Lymphatic tissue, essentially 
 resembling that of the lymphatic glands, but differently arranged. In those 
 animals in which it predominates, as in Man, the artery is large ; on the other 
 hand, where the cellated structure is most developed, as in the Herbivora, the 
 Vein is very large, and the artery comparatively small. Nothing completely 
 analogous to a Spleen is found in Invertebrated animals ; and from the absence 
 of the Lymphatic system in them, it is evident that the parenchymatous por- 
 tion can have no existence as such. Something analogous to the cellated por- 
 tion of the Spleen, however, exists in the venous system of many Cephalopoda: 
 and this circumstance is an additional proof of the duplicity of the character 
 of this remarkable organ. 
 
 685. Out of the numberless theories of its operation, which have been at 
 different times brought forwards, the one which seems best to account for its 
 cellated structure, is that which regards it as a sort of diverticulum or reser- 
 voir; which may serve to relieve the Portal Venous system from undue dis- 
 tention, under a great variety of circumstances. This system is well known 
 to be destitute of valves ; so that the Splenic vein has free communication 
 with the whole of it. Hence the Spleen will be a ready diverticulum for the 
 venous blood, when the secreting action of the Liver is feeble, so that the 
 Portal circulation receives a partial check ( 832). That any cause of con- 
 gestion of the Portal system peculiarly affects the Spleen, has been proved by 
 experiment ; for after the Portal Vein has been tied, the Spleen of an animal, 
 which previously weighed only 2 ounces, has been found to weigh a pound 
 and a quarter, or ten times as much. Now it is evident that congestion of 
 the Portal system is liable to occur, when the alimentary canal is distended 
 with food ; and this from two causes, the pressure on the Intestinal veins, 
 and the quantity of fluid absorbed by these veins. Hence it may be conceived, 
 thaf the Spleen, by affording a reservoir into which the superfluous Venous 
 blood may be directed, serves an important purpose in preventing congestion 
 of other organs. From the observations of Mr. Dobson,* it appears that the 
 
 * London Med. and Phys. Journal, Oct. 1820. 
 
520 OF ABSORPTION AND SANGUIFICATION. 
 
 Spleen has its maximum volume, at the time when the process of chymifica- 
 tion is at an end, namely, about five hours after food is taken ; and that it 
 is small and contains little blood seven hours later, when no food has been 
 taken in the interval. Hence he inferred, that this organ is the receptacle for 
 the increased quantity of Blood, which the system acquires from the food, and 
 which cannot, without danger, be admitted into the blood-vessels generally ; 
 and that it regains its previous dimensions, after the volume of the circulat- 
 ing fluid has been reduced by secretion. This view is confirmed by the fact 
 noticed by several observers, that the Spleen rapidly increases in bulk after 
 the ingestion of a large quantity of fluid, which is absorbed rather by the 
 Veins than by the Lacteals. It has been further stated in support of this 
 theory, that animals from which the Spleen has been removed, are very lia- 
 ble to die of apoplexy, if they take a large quantity of food at a time ; but 
 that, if they eat moderately and frequently, they do not suffer in this manner. 
 The use of the Spleen as a diverticulum for the internal Venous circulation, 
 is further borne out by its liability to become enlarged in consequence of in- 
 termittent fever ; during the cold stage of which, a great quantity of blood is 
 driven from the surface towards the internal organs ; and it may be easily 
 imagined that, if there were no such reservoir, the congestions in these would 
 be much more dangerous than those which actually do occur. The perma- 
 nent enlargement of the organ is of course, on this idea of its use, a result of 
 its frequent distention. But besides this safety-valve function, there can be 
 little doubt that the Spleen performs another, in virtue of the parenchymatous 
 portion of its structure ; and that this function corresponds with that of the 
 Absorbent Glands in general. The identity in structure between its Malpi- 
 ghian bodies and the ordinary Lymphatic glands, is such as clearly points to 
 this inference ; which is confirmed by the remarkable fact, determined by the 
 recent experiments of Prof. Mayer, that, after the Spleen has been extirpated, 
 the lymphatic glands of the neighbourhood increase in size, and cluster toge- 
 ther as they enlarge, so as to form an organ which at least equals the original 
 spleen in volume.* This circumstance explains the reason of the almost in- 
 variable negative result of the extirpation of the Spleen ; for although the 
 operation has been frequently practised, with the view of determining the 
 functions of the organ by the symptoms presented by animals after its removal, 
 no decided change in the ordinary course of their vital phenomena has ever 
 been observed ; and the health, if at all disturbed for a time, is afterwards re- 
 gained. Now if the functions of the Spleen, putting aside the safety-valve 
 action of its distensible cavities, be the same with that of the Lymphatic 
 Glands in general, it is easy to understand, how its loss may be at once com- 
 pensated by an increased action on their part, and how it may be permanently 
 replaced by an increased development of some of those bodies. Thus, then, 
 we may fairly regard the Spleen as concurring in function with the glands of 
 the Absorbent system, in the Assimilating process, by which the crude nutri- 
 tive materials are rendered fit to circulate through the system ; the difference 
 between them appearing to be chiefly this, that, whilst the latter operate upon 
 the nutritive substances taken up by the Lacteals, the Spleen exerts its influ- 
 ence upon those which have been received into the Veins ; separating them 
 from the mass of the blood, and delivering them to the lymphatic system to 
 be further elaborated. 
 
 686. The Suprarenal Capsules seem to correspond with the Spleen in 
 their general structure, and in their connection with the Lymphatic system; 
 whilst, in the arrangement of their component parts, they bear more resem- 
 blance to the Kidney. 
 
 * Medical Times, March 29, 1845. 
 
SUPRA-RENAL CAPSULES. THYMUS GLAND. 
 
 521 
 
 a. In the Supra-Renal Capsules, as in the Kidneys, there is an obvious difference between 
 the cortical and the medullary substances. The former is of a yellowish colour ; and presents 
 an appearance, when cut into, as if it were. made up of straight parallel fibres, arranged side 
 by side. Of these straight fibres, however, a part are branches of arteries, which enter this 
 body at every point of its exterior, from a capillary network covering its surface; and others 
 are corresponding branches of veins, that receive the blood from these arteries, and convey 
 it into a venous plexus which forms the centre of the organ. Between the radiating blood- 
 vessels, there are found lying, in the cortical substance, numerous parallel cylinders or elongat- 
 ed cones, formed by closed sacs of basement-membrane, including nuclei and cells in various 
 stages of development, with fat-cells. The medullary substance is partly wiade up of the ve- 
 nous plexus, dilated into a sort of cavernous texture, together with empty cavities or lacunae, 
 that seem destitute of a lining membrane, and contain only a thick grayish-white fluid ; and 
 partly of an intervening parenchyma, consisting of cells in various stages of development. 
 In the Human adult, there is a great predominance of nuclei, which seem as if they did not 
 attain their full development ; but in Ruminant animals, and in the Human subject in early 
 life, the cells are more or less developed, and then resemble the ordinary lymph-corpuscles 
 in size and appearance. The Lymphatics are of large size, like those of the Spleen ; and 
 probably convey away the matter which has been elaborated by these organs, that it may be 
 mingled with that which is being taken up and prepared by other parts of the Absorbent 
 system. The Supra-Renal capsules attain a very large size early in fcetal life, surpassing 
 the true Kidneys in dimension, up to the tenth or twelfth week : but they afterwards dimi- 
 nish relatively to the latter, and are evidently subordinate organs during the whole remainder 
 of life. 
 
 It does not seem unlikely that these bodies, like the Spleen, have a double 
 function ; and that, besides participating in the general actions of the Absorb- 
 ent glandulse, they may serve as a diverticulum for the Renal circulation, when 
 from any cause the secreting function of the Kidneys is retarded or checked, 
 and the movement of bloocj through them is stagnated. 
 
 687. The Thymus Gland is another body which seems referrible to the 
 same group ; having all the essential characters of a true gland, save an excre- 
 tory duct ; and its function being evidently connected, during the early period 
 of life at least, with the elaboration of nutritive matter, which is to be re- 
 introduced into the circulating current. 
 
 a. Its elementary structure may be best understood from the simple form it presents when 
 it is first capable of being distinguished in the embryo. It then consists of a single tube, 
 closed at both ends, and filled with granular matter j and its subsequent development consists 
 
 [Fig. 209. 
 
 A section of the Thymus gland at the eighth month, showing its anatomy ; from a preparation of 
 Sir A. Cooper's ; 1, the cervical portions of the gland; the independence of the two lateral glands is 
 well marked ; 2, secretory follicles seen upon the surface of the section ; these are observed in all 
 parts of the section ; 3, 3, the pores or openings of the secretory follicles and pouches ; they are seen 
 covering the whole internal surface of the great central cavity or reservoir. The continuity of the 
 reservoir in the lower or thoracic portion of the gland with the cervical portion, is seen in the figure.] 
 
 44* 
 
522 , OF ABSORPTION AND SANGUIFICATION. 
 
 in the lateral growth of branching off-shoots from this central tubular axis. In its mature 
 state, therefore, it consists of an assemblage of glandular follicles, which are surrounded by 
 a plexus of blood-vessels; and these follicles all communicate with the central reservoir, from 
 which, however, there is no outlet. The Lymphatics are large, and communicate directly 
 with the Vena Cava ; but their immediate connection with the cavity of the Thymus body 
 has not yet been demonstrated. The cavities of the follicles contain a fluid in which a 
 number of corpuscles are found, giving it a granular appearance. These corpuscles are, for 
 the most part, in the condition of nuclei; but fully developed cells are found among them, at 
 the period when the function of this body seems most active. The chemical nature of the 
 .contents at this period, closely resembles that of the ordinary proteine-compounds. It has 
 been commonly stated, that the Thymus attains its greatest development, in relation to the 
 rest of the body, during the latter part of foetal life ; and it has been considered as an organ 
 peculiarly connected with the embryonic condition. But this is a mistake ; for the greatest 
 activity in the growth of this organ manifests itself in the Human infant, soon after birth; 
 and it is then, too, that its functional energy seems the greatest. This rapid state of growth, 
 however, soon subsides into one of less activity, which merely serves to keep up its propor- 
 tion to the rest of the body : and its increase usually ceases altogether at the age of about 
 two years. From that time, during a variable number of years, it remains stationary in 
 point of size ; but, if the individual be adequately nourished, it gradually assumes the cha- 
 racter of a mass of fat, by the development of the corpuscles of its interior into fat-cells, which 
 secrete adip'ose matter from the blood. This change in its function is most remarkable in 
 hybernating Mammals ; in which the development of the organ continues, even in an in- 
 creasing ratio, until the animal reaches adult age, when it includes a large quantity of fatty 
 matter. The same is the case, generally speaking, among Reptiles. It is an important fact 
 in the history of this organ, that it is not to be detected in Fishes ; and does not appear to 
 exist, either in the tadpole state of the Batrachian reptiles, or in the Perennibranchiate group ; 
 so that we may regard it as essentially connected with pulmonic respiration.* 
 
 688. Various facts lead to the conclusion, that the function of the Thymus, 
 at the period of its highest development, is that of elaborating and storing up 
 nutritive materials, to supply the demand which is peculiarly active during the 
 early period of extra-uterine life. The elaborating action probably corresponds 
 with that which is exerted by the glands of the Absorbent system ; and the 
 product, as in the preceding cases, seems to be conveyed away by the lymph- 
 atics. The provision of a store of nutritive matter seems a most valuable one, 
 under the circumstances in which it is met with ; the waste being more rapid 
 and variable than in adults, and the supply not constant. Thus it has been 
 noticed that, in over-driven lambs, the thymus soon shrinks remarkably ; but 
 that it becomes as quickly distended again, during rest and plentiful nourish- 
 ment. As the demand becomes less energetic, and as the supplies furnished 
 by other organs become more adequate to meet it, 4 the Thymus diminishes in 
 size, and no longer performs the same function. It then obviously serves to 
 provide a store of material, not for the nutrition of the body, but for the re- 
 spiratory process, when this has to be carried on for long periods as in hy- 
 bernating Mammals and in Reptiles without a fresh supply of food. It is 
 possible, that the Thymus gland may further stand in the same relation to the 
 Lungs, as the Spleen to the Liver, and the Supra-Renal capsules to the Kid- 
 neys ; that is, as a diverticulum for the blood transmitted through the bron- 
 chial arteries (which are the nutritive vessels of the Lungs), before the Lungs 
 acquire their full development in comparison with other organs, or when any 
 cause subsequently obstructs the circulation through their capillaries. 
 
 689. The Thyroid Gland bears a general analogy to the Thymus ; but its 
 vesicles are distinct from each other, and do not communicate with any com- 
 mon reservoir. They are surrounded, like the vesicles of the true glands, 
 with a minute capillary plexus ; and in the fluid they contain, numerous cor- 
 puscles are found suspended, which appear to be cell-nuclei, in a state of 
 more or less advanced development. This body is supplied with arteries of 
 considerable size ; and with peculiarly large lymphatics. Though propor- 
 
 * See Mr. Simon's admirable Prize Essay on the Thymus Gland. 
 
THYROID GLAND. ASSIMILATING GLANDS IN GENERAL. 523 
 
 tionably larger in the foetus than in the adult, it remains of considerable size 
 during the whole of life. It appears, from the recent inquiries of Mr. Simon,* 
 that a Thyroid gland, or some organ representing it in place and office, exists 
 in all Vertebrated animals. It presents its simplest form in the class of Fishes ; 
 in some of which it appears to consist merely of a plexus of capillary ves- 
 sels, connected with the origin of the cerebral vessels, and capable, by its dis- 
 tensibility, of relieving the latter, in case of any obstruction to the proper 
 movement of blood through them. In the higher forms of this organ, the 
 glandular structure, consisting of closed vesicles over which the capillary 
 plexus is distributed, and of their cellular contents, is superadded ; and the 
 organ then appears, like the Spleen, to be destined for two different uses ; 
 namely, to serve as a diverticulum to the Cerebral circulation ; and to aid in 
 the elaboration of nutritive matter, which is taken up by the Absorbent sys- 
 tem, and which is again poured by it into the general current of the circula- 
 tion. 
 
 690. Thus the Spleen, the Supra-Renal Capsules, the Thymus Gland, and 
 the Thyroid Gland, all seem to share in the preparation of the nutritive ma- 
 terials of the blood, along with the ordinary glandulae of the Absorbent system. 
 In fact, we may regard them all as together constituting an apparatus, which 
 is precisely analogous to that of the ordinary glands, but of which the element- 
 ary parts are scattered through the body, instead of being collected into one 
 compact structure. Thus if we could imagine any tubular gland, such as the 
 Kidney or the Testis, to be unravelled, and its convoluted tubuli to be spread 
 through the system, yet all discharging their contents by a common outlet, we 
 should have no unapt representation of the Lymphatic portion of the Absorb- 
 ent system. Its function appears to be, .to separate the crude Albuminous 
 matter from the blood, to subject it to an elaborating action performed by the 
 epithelium-cells lining the tubes, and then to pour forth this elaborated pro- 
 duct, not as an excretion to be carried out of the body, but (in conjunction 
 with that, which has been newly taken in by the Lacteal portion of the sys- 
 tem, and which has undergone elaboration by its glandulae), into the blood- 
 vessels, which are to convey it to the different parts of the body where it is 
 to be appropriated. The four bodies we have been just considering, appear 
 to be, so far as their glandular function is concerned, appendages to this sys- 
 tem. Their uses as diverticula to the circulation through other organs, render 
 them liable to occasional distention with blood ; and it seems determined that 
 this blood shall not lie useless, but shall be subservient to the action in ques~ 
 tion ; the gland-cells that line the cavities of the organ withdrawing certain 
 constituents of the blood, to restore them, through the Lymphatic system, in 
 a state of more complete preparation for the operations of Nutrition. Their 
 function is very probably vicarious; that is, the determination of blood is 
 greatest (through the state of the other organs) at one time to one of these bodies, 
 and at another time to another. Hence the effects of the loss of any one of 
 them are not serious ; as the others are enabled in great degree to discharge 
 its duty. 
 
 4. Composition and Properties of the Chyle and Lymph. 
 
 691. The chief chemical difference between the Chyle and the Lymph, 
 consists in the much smaller proportion of solid matter in the latter, and in the 
 almost entire absence of fat, which is an important constituent of the former. 
 This is well shown in the following comparative analyses, performed by Dr. 
 G. 0. Rees, of the fluids obtained from the lacteal and lymphatic vessels of a 
 
 * Philosophical Transactions, 1844. 
 
524 OF ABSORPTION AND SANGUIFICATION. 
 
 donkey, previously to their entrance into the thoracic duct: the animal having 
 had a full meal seven hours before its death. 
 
 CHYLE. LYMPH. 
 
 Water . 90-237 95-536 
 
 Albuminous matter (coagulable by heat) . . . 3-516 1*200 
 
 Fibrinous matter (spontaneously coagulable) . . . 0-370 0-120 
 
 Animal extractive matter, soluble in water and alcohol . 0-332 0*240 
 
 Animal extractive matter, soluble in water only . . 1-233 1.319 
 
 Fatty matter 3-601 a trace. 
 
 Salts; Alkaline chloride, sulphate and carbonate, with traces of 
 
 alkaline phosphate, oxide of iron .... 0-711 0*585 
 
 100-000 100-000 
 
 The Lymph obtained from the neck of a horse has been recently analyzed by 
 Nasse, with nearly the same result. He found it to contain 95 per cent, of 
 water; and the 5 per cent, of solid matter was chiefly composed of albumen 
 and fibrine, with watery extractive, scarcely a trace of fat being to be found. 
 The proportions of saline matter were found to be remarkably coincident with 
 those which exist in the serum of the blood; as might be expected from the 
 fact, that the fluid portion of the lymph must have its origin in that which has 
 transuded through the blood-vessels : the absolute quantity, however, is rather 
 less. A similar analysis of the Chyle of a cat by Nasse, has given results 
 very closely correspondent with that of Dr. Rees; for the proportion of water 
 was 90'5 per cent. ; and of the 9*5 parts of solid matter, the albumen, fibrine, 
 and extractive amounted to more than 5, and the fat to more than 3 parts. 
 Dr. Rees has also analyzed the fluid of the Thoracic duct of Man; and found 
 it to consist of 90*48 per cent, of water, 7'08 parts of albumen and fibrine, 
 1*08 parts of aqueous and alcoholic extractive, and 0*92 of fatty matter, with 
 0*44 per cent, of salines. Thus the composition of this fluid would seem to 
 resemble that of the Lymph, rather than that of the Chyle ; the proportion of 
 the fatty to that of the albuminous matter being very small. This, however, 
 might have been very probably due to the circumstance, that the subject from 
 which the fluid was obtained (an executed criminal) had eaten but little for 
 some hours before his death. 
 
 692. The characters of the Chyle drawn from the larger absorbent trunks, 
 near their entrance into the Receptaculum Chyli, are very different, however, 
 from those of the fluid as first absorbed into the Lacteals ; for during its 
 passage through these vessels, and their ganglia or glands, it undergoes 
 important alterations, which gradually assimilate it to Blood. The chyle 
 drawn from the lacteals that traverse the intestinal walls, contains Albumen in 
 a state of complete solution; but it is generally destitute of the power of co- 
 agulation, no Fibrine being present in it. The Salts, also, are completely 
 dissolved ; but the Oily matter presents itself in the form of globules of varia- 
 ble size.* It is generally supposed, that the milky colour of the chyle is 
 owing to these ; but Mr. Gulliver has recently pointed outt that it is really due 
 to an immense multitude of far more minute particles, which he describes as 
 forming the molecular base of the chyle. These molecules are most abundant 
 in rich, milky, opaque chyle ; and in poorer chyle, which is semi-transparent 
 or opaline, the particles float thinly or separately in the transparent fluid, and 
 often exhibit the vivid motions common to the most minute molecules of vari- 
 ous substances. Such is their minuteness, that, even with the best instru- 
 
 * These oily globules are more abundant in the Chyle of Man and of the Carnivora, than 
 in that of the Herbivora : their diameter has been observed to vary from l-25,000th to l-2000th 
 of an inch. 
 
 f Dublin Medical Press, Jan. 1, 1840, and Gerber's General Anatomy, Appendix, p. 88. 
 
CHARACTERS AND COMPOSITION OF CHYLE. 525 
 
 ments, it is impossible to form an exact appreciation either of their form or 
 their dimensions. They seem, however, to be generally spherical ; and their 
 diameter may be estimated at between l-36,000th and l-24,000th of an inch. 
 Their chemical nature is as yet uncertain : they are remarkable for their un- 
 changeableness, when subjected to the action of numerous re-agents; which 
 quickly affect the proper Chyle-corpuscles; and they are readily soluble in 
 Ether, the addition of which causes the whole molecular base instantly to dis- 
 appear, not a particle of it remaining; whence it may be inferred that they 
 consist of oily or fatty matter. The milky colour, which the serum of blood 
 sometimes exhibits, is due to an admixture of this, molecular base with the 
 circulating fluid ; it is most common in young animals that are suckling ; but 
 it is not uncommon in adults, and is not to be attributed to an absorption of 
 milk into the chyle, as the physical properties of the two are quite different. 
 (See 697, e.) 
 
 693. During the passage of the Chyle through the absorbents on the intes- 
 tinal edge of the Mesentery, towards the Mesenteric Glands, its character 
 changes in several important particulars. The presence of Fibrine begins to 
 manifest itself, by the slight coagulability of the fluid when withdrawn from 
 the vessels ; and while this ingredient increases, the Albumen and the Oil- 
 globules gradually diminish in amount. The Chyle drawn from the neigh- 
 bourhood of the mesenteric glands exhibits the Corpuscles regarded as cha- 
 racteristic of that fluid ; these are peculiarly abundant in the fluid drawn from 
 the glands themselves ; and they are constantly found in it, through its whole 
 subsequent course. The Chyle-corpuscles are much larger than the mole- 
 cules just described, and an examination of their character presents no diffi- 
 culty. Their diameter varies from 1-7 11 Oth to l-2600th of an inch ; the 
 average being about l-4600th. They are usually minutely granulated on the 
 surface, seldom exhibiting any nuclei, even when treated with acetic acid ; but 
 sometimes three or four central particles may be distinguished within them. 
 During the passage of the Chyle through the mesenteric glands, a further 
 increase in the proportion of Fibrine takes place ; and the resemblance of 
 the fluid to Blood becomes more apparent. The Chyle drawn from the vessels 
 intermediate between these and the central duct, possesses a pale reddish- 
 yellow colour; and, when allowed to stand for a time, undergoes a regular 
 coagulation, separating into clot and serum. The former is a consistent gela- 
 tinous mass, which, when examined with the microscope, is found to include 
 the Chyle-corpuscles, each of them being surrounded by a delicate film of 
 oil: the Fibrine of which it is principally composed, differs remarkably from 
 that of the blood, in its inferior tendency to putrefaction ; whence it may be 
 inferred that it has not yet undergone its complete vitalization. The serum 
 contains the Albumen and Salts in solution, and a proportion of the Chyle- 
 corpuscles suspended in it. It is curious, however, that considerable differ- 
 ences in the perfection of the coagulation, and in its duration, should present 
 themselves in different experiments. Sometimes the chyle sets into a jelly- 
 like mass, which, without any separation into coagulum and serum, liquefies 
 again at the end of half an hour, and remains in this state. This change takes 
 place in the true coagulum also, if it be kept moist for a sufficient length of 
 time. The Chyle from the Receptacnlum and Thoracic J)uct coagulates 
 quickly, often almost instantaneously; and few or none of the corpuscles re- 
 main in the serum. It is to be remembered that the Lacteals are the Lym- 
 phatics of the intestinal walls and mesentery ; performing that function of 
 Interstitial Absorption which is elsewhere accomplished by vessels that are 
 not concerned in the introduction of alimentary substances from without. 
 During the intervals of digestion, they contain a fluid which is in all respects 
 conformable to the. Lymph of the Lymphatic trunks. 
 
526 OF ABSORPTION AND SANGUIFICATION. 
 
 a. The fluid drawn from the Thoracic Duct, and from the Absorbent vessels which empty 
 their contents into it, is frequently observed to present a decided red tinge, which increases 
 on exposure to the air. This tinge is due to the presence of true Blood-corpuscles; but 
 these are somewhat modified in form and size, being a little smaller than the ordinary Blood- 
 discs, and frequently angular, granulated, or indented at the edges. By Mr. Lane* it is stated 
 that this intermixture is accidental ; and that it results from the absorption of Blood-particles 
 into the Lymphatics, at the points where the latter are divided, in making the sections ne- 
 cessary to expose the centres of the Absorbent system; and he mentions a striking- fact in 
 illustration of his view. He considers that the alteration in the character of the corpuscles 
 is due to the action of the Chyle on the Blood, since many other fluids will produce analogous 
 effects; and he states that, shortly after a flow of chyle into the blood, a large number of such 
 altered discs may be seen in the circulating fluid. On the other hand, Mr. Gulliver and 
 several eminent observers, regard these blood-discs as true constituents of the fluid of the 
 absorbents ; and suppose that they are in process of formation. Reasons have been given, 
 however, for the belief, that the red Blood-discs are not formed from the Chyle-corpuscles; 
 so that Mr. Lane's view is probably the correct one. Even if the Blood-discs are not intro- 
 duced into the Lymphatics during the operation of exposing the Thoracic Duct, it may not 
 be considered as improbable that, in those animals in which the Lymphatics have several 
 communications with the veins, they should naturally obtain an entrance in various parts of 
 the system. Such communications, -according to Gerber, decidedly exist in the Horse ; and 
 it is in the Chyle of that animal, that the rosy tint, and the Blood-corpuscles which occasion 
 it, have been chiefly observed. The following table, slightly modified from that of Gerber, 
 presents in a concise form, a view. of the relative proportions of the three chief ingredients 
 in the Chyle, in different parts of the absorbent system, and thus gives an idea of its advance 
 in the process of assimilation. 
 
 In the afferent or peripheral f Fat, in maximum quantity (numerous fat or oil globules). 
 Lacteals (from the Intes- J Albumen in minimum quantity, 
 tines to the Mesenteric j Few or no Chyle-corpuscles, 
 glands). (Fibrine almost entire wanting. 
 
 In the efferent or central ["Fat, in medium quantity (fewer oil globules). 
 Lacteals (from the Mesen- j Albumen, in maximum quantity. 
 
 teric glands to the Thoracic j Chyle-corpuscles very numerous, but imperfectly developed. 
 Duct). (Fibrine in medium quantity. 
 
 (Tat, in minimum quantity (fewer or no oil-globules). 
 T ti Ti T J Albumen, in medium quantity. 
 
 1 Chyle-corpuscles numerous, and more distinctly cellular. 
 (Fibrine in maximum quantity. 
 
 694. The aspect of the Lymph greatly differs from that of the Chyle, the 
 former being nearly transparent, whilst the latter is opaque or opalescent; and 
 this difference is readily accounted for, when the assistance of the microscope 
 is sought, by the entire absence from the Lymph of that molecular base 
 which is so abundant in the Chyle. A considerable number of corpuscles 
 are generally present in it; and these seem to correspond in all respects with 
 the white or colourless corpuscles of the Blood ( 151). Their amount, 
 however, is extremely variable ; as is also that of the oil-globules, which 
 sometimes occur, whilst in other instances none can be discovered. Lymph 
 coagulates like chyle; a colourless clot being formed, which incloses the 
 greater part of the corpuscles. 
 
 695. The fluid drawn from the Thoracic Duct, consisting as it does of an 
 admixture of Chyle and Lymph, will probably vary in its character and com- 
 position, according to the predominance of the former, or of the latter, of these 
 fluids. It may be noticed, however, that the floating corpuscles have a more 
 distinctly cellular character than have those of the chyle and lymph ; and 
 that they are of larger size, their diameter usually ranging from about 1 -2600th 
 to l-2900th of an inch. In these particulars, they correspond with the Colour- 
 less corpuscles of the Blood; as also in the change they exhibit on the action 
 of acetic acid, which brings into view three or four large central particles. 
 Some observations have been recently made by Bidder, on the amount of 
 
 * Cyclopaedia of Anatomy and Physiology, vol. iii. p. 220. 
 
PHYSICAL AND VITAL PROPERTIES OF THE BLOOD. 527 
 
 Jiquid which flows through the Thoracic duct into the venous system ; and if 
 any inference can be fairly drawn from the measurement of the quantity de- 
 livered in the course of a few minutes, it would appear that the total amount 
 thus transmitted in one day is nearly or quite equal to the entire mass of the 
 blood. At any rate, it so far exceeds the amount of liquid ingested, that we 
 must believe a large portion of it to be derived from the circulating current, 
 having been withdrawn from it for a time, to be again delivered into its stream, 
 after having undergone the requisite elaboration. 
 
 5. Physical and Vital Properties of the Blood. 
 
 696. Having now traced the steps, by which' the Blood is elaborated and 
 prepared for circulation through the body, and having formerly inquired into 
 the characters of its chief constituents (Chap, in.), we have now to consider 
 the fluid as a whole, to study the usual proportions of these constituents, and 
 the properties which they impart to it. The Blood, whilst circulating in the 
 living vessels, may be seen to consist of a transparent, nearly colourless, 
 liquid, termed Liquor sanguinis ; in which the Red Corpuscles, from which 
 the Blood of Vertebrated animals derives its peculiar hue, as well as the White 
 or Colourless corpuscles, are freely suspended and carried along by the cur- 
 rent. On the other hand, when the Blood has been drawn from the body, 
 and is allowed to remain at rest, a spontaneous coagulation takes place, sepa- 
 rating it into Crassamenlum and Serum. The Crassamentum or Clot is 
 composed of a network of Fibrine, in the meshes of which the Corpuscles, 
 both red and colourless, are involved, together with a certain amount of serous 
 fluid. The Serum, which is the same with the Liquor Sanguinis deprived of 
 its Fibrine, coagulates by heat, and is therefore known to contain Albumen ; 
 and if it be exposed to a high temperature, sufficient to decompose the animal 
 matter, a considerable amount of earthy and alkaline Salts remains. Thus 
 we have four principal components in the Blood; namely, Fibrine, Mbumen, 
 Corpuscles, and Saline matter. In the circulating blood, they are thus com- 
 bined : 
 
 Fibrine } 
 
 Albumen > In solution, forming Liquor Sanguinis. 
 
 Salts ) 
 
 Corpuscles, suspended in Liquor Sanguinis. 
 
 But in coagulated blood, they are combined as follows: 
 
 Fibrine ) 
 Corpuscles $ 
 
 c - > Remaining in solution, forming Serum. 
 
 In the blood of Man and the higher Vertebrata, the Colourless Corpuscles 
 usually bear so small a proportion to the Red, that they have until recently 
 escaped notice. In Reptiles, however, they attract attention, from their 
 marked difference in size and form, even whilst the blood is moving through 
 the capillaries ; and they are the more easily watched, owing to the compara- 
 tively small number of the Red Corpuscles in those animals. The blood of 
 the Invertebrata is usually pale, and contains very few red corpuscles; indeed 
 they would seem to be absent altogether in the lower Articulata and Mollusca. 
 On the other hand, the colourless corpuscles are frequently very numerous, 
 especially during the periods of most active growth. The blood of these 
 animals may be likened, therefore, in many respects to the Lymph and Chyle 
 of the Vertebrata ; and the resemblance is the more close, as there is no 
 
528 
 
 OF ABSORPTION AND SANGUIFICATION. 
 
 distinction among the Invertebrata between the absorbent and sanguiferoits 
 vessels. 
 
 697. The proportion of the several components of Blood is subject to con- 
 siderable variations, within the limits of health. Some of these variations 
 may be habitual, depending upon the constitution of the individual, his diet, 
 mode of life, &c.; whilst others are probably referrible to the period at which 
 the last meal was taken, and the amount of bodily exertion made within a 
 short time previous to the analysis. 
 
 a. The discordance in the results obtained by different experimenters is doubtless owing 
 in part to the diversity in their methods of analysis;* but even where the same method is 
 employed, a wide diversity is apparent ; as in the analysis of MM. Becquerel and Rodier. 
 As there is a tolerably constant difference between the Male and the Female, it will be de- 
 sirable to class them separately ; and the results of some of the most recent and trustworthy 
 analyses of each will be brought together for the sake of comparison. The analyses of M. 
 Lecanu were made on the blood of two stout and healthy men ; whilst those of MM. Bec- 
 querel and Rodier give the maximum, minimum, and mean amount, of each ingredient in 
 the blood of eleven healthy men, between the ages of 21 and 66 years. 
 
 Lecanu. 
 
 Water . . . . 
 
 Fibrine . . . 
 
 Corpuscles . . 
 
 Albumen . . 
 
 Extractive mat- 
 ters, Salts, and 
 loss 
 
 Fatty matters . . 
 
 I. 
 
 780-2 
 
 2-1 
 
 133-0 
 
 66-3 
 
 14-6 
 3-8' 
 
 ii. 
 
 785-6 
 
 3-6 
 
 119-6 
 
 71-5 
 
 13-1 
 66 
 
 MM. Eecquerel and Rodier. 
 
 Mean. 
 
 Maxima. 
 
 Minima. 
 
 779-0 
 
 8(5b-0 
 
 760-0 
 
 2-2 
 
 3-5 
 
 1-5 
 
 141-1 
 
 152-0 
 
 131-0 
 
 69-4 
 
 73-0 
 
 62-0 
 
 6-8 
 
 8-0 
 
 5-0 
 
 1-5 
 
 3-2 
 
 1-6 
 
 Simon. Nasse. 
 
 791-9 
 
 2-0 
 
 114-3 
 
 75-6 
 
 14-2 
 2-0 
 
 798-4 
 
 2-3 
 
 116-5 
 
 74-2 
 
 6-6 
 2-0 
 
 1000-0 1000-0 1000.0 
 
 1000-0 1000-0 
 
 The following table gives the results of similar analyses on the blood of Females; those 
 of MM. Becquerel and Rodier being made upon eight healthy subjects between the ages of 
 22 and 58 years. 
 
 MM. Becquerel and Rodier. Simon. 
 Mean. Maxima. Minima. 
 
 Water 
 
 Fibrine .... 
 
 Corpuscles . . . 
 Albumen .... 
 Extractive matters and Salts 
 Fatty matters 
 
 791-1 
 
 813-0 
 
 773'0 
 
 801-4 
 
 2-2 
 
 2-5 
 
 1-8 
 
 2-2 
 
 127-2 
 
 137-5 
 
 113-0 
 
 106.1 
 
 70-5 
 
 75-5 
 
 65-0 
 
 77-6 
 
 7-4 
 
 8-5 
 
 6.2 
 
 100 
 
 1-6 
 
 2-9 
 
 1-0 
 
 2-7 
 
 1000-0 
 
 1000-0 
 
 b. Of the Fatty matters of the Blood, a portion seems to correspond with the constituents 
 of ordinary Fat; another portion seems identical with the Cholesterine, or Biliary Fat; whilst 
 another contains Phosphorus, and seems allied to the fatty acids of Nervous matter ( 249). 
 
 c. Of the nature of the substances classed under the head of Extractive, very little is 
 known. It has been lately asserted, that a portion of them consists of binoxide of proteine 
 ( 116, a) ; but as to the actual existence of this substance, there is still much doubt Under 
 the general designation of extractive are arranged the " ill-defined animal principles," which 
 may include various substances in a state of change or disintegration, that are being elimi- 
 nated from the blood by the processes of Excretion. 
 
 d. The Saline constituents of the Blood, obtained by drying and incinerating the whole 
 mass, usually amount to between 6 and 7 parts in 1000. More than half their total quan- 
 tity is composed of the Chlorides of Sodium and Potassium ; and the remainder is made up 
 of the tribasic Phosphate of Soda, the Phosphates of Lime and Magnesia, Sulphate of Soda, 
 
 * Thus the small amount of Salts, in the analysis of Nasse and of MM. Becquerel and 
 Rodier, as compared with those of MM. Lecanu and Simon, appears due to the fact that the 
 former express only the free salts, whilst the latter include those which are in combination 
 with the organic constituents. 
 
USES OF THE SEVERAL CONSTITUENTS OF THE BLOOD. 529 
 
 and a little Phosphate and Oxide of Iron. Of these, the chief part are dissolved in the 
 Serum ; but the Earthy Phosphates, which are insoluble by themselves, are probably com- 
 bined with the Proteine-compounds ( 113); and the iron is contained, chiefly or entirely, 
 in the red corpuscles. It is difficult to speak with certainty, from the examination of the 
 ashes of the blood, as to the state of the Saline constituents of the circulating fluid. Thus 
 the Serum has an alkaline reaction ; and this has been supposed to be due to the presence 
 of alkaline Carbonates. Moreover the presence of the Lactates of potass and soda has been 
 usually asserted. On the other hand, the recent analyses of Enderlin, which have been con- 
 firmed by Liebig, would indicate that the alkaline reaction is entirely due to the presence of 
 the tribasic Phosphate of soda ; and that no alkaline carbonates or lactates exist in the blood. 
 This discrepancy seems partly due to the mode of analysis employed; for it has been lately 
 pointed out by Dr. G. O. Rees,* that although the ashes of the entire mass of blood do not 
 effervesce on the addition of an acid, effervescence takes place when acid is added to the 
 ashes of the serum, showing the existence in it, either of alkaline Carbonates, or of Lactates, 
 which have been reduced to the state of Carbonates by incineration. It appears that, when 
 the entire mass of blood is incinerated, enough phosphoric acid is produced from the phos- 
 phorized fats, to neutralize the alkaline carbonates, and thus to prevent their presence from 
 being recognized. There can be no doubt, however, that the tribasic Phosphate of Soda 
 exists as such in the blood, and contributes to its alkaline reaction ; and it appears to confer 
 upon the liquid a special power of absorbing Carbonic Acid. 
 
 e. Some very interesting observations upon the state of the blood soon after a meal, have 
 been recently made by Drs. Buchanan and R. D. Thompson. They are confirmatory of the 
 belief generally entertained, that the milky appearance, sometimes presented by the Serum, 
 is due to the admixture of Chyle. When a full meal containing oily matter is taken after 
 a long fast, and a small quantity of blood is drawn previously to the meal and at intervals 
 subsequently, the Serum, though quite Jimpid in the blood first drawn, shows an incipient 
 turbidity about half an hour afterwards ; this turbidity increases for about six hours subse- 
 quently, after which it usually begins to disappear. The period at which the discoloration 
 is the greatest, however, and the length of time during which it continues, vary according 
 to the kind and quality of the food, and the state of the digestive functions. Neither starch, 
 nor sugar, nor proteine-compounds, alone or combined, occasion this opacity in the chyle ; 
 but it seems entirely dependent upon an admixture of oleaginous matter with the food. 
 There are few ordinary meals, however, from which such matter is altogether excluded. 
 When such milky serum is examined with the Microscope, the opacity is found to be due 
 to the presence of an immense number of exceedingly minute granules, resembling in ap- 
 pearance those which form the " molecular base" of the chyle. They seem to be composed 
 of two chemically-distinct substances; for when the milky serum is agitated with ether, a 
 part is dissolved, whilst another portion remains suspended ; and this latter is soluble in 
 caustic potass. The former, therefore, appears to be identical with the " molecular base" of 
 the Chyle, and to be of an oily or fatty nature ; whilst the latter belongs to the proteine- 
 compounds. The Crassarnentum of such blood often exhibits a pellucid fibrinous crust, 
 sometimes interspersed with white dots ; and this seems to consist of an imperfectly-assi- 
 milated proteine-compound, analogous to that found in the serum. The quantity of this varies 
 according to the amount of the proteine-compounds present in the food ."f" It is evident from 
 these experiments, that the assimilating process is by no means completed, at the time of 
 the passage of the Chyle into the Blood ; and it would seem that the return of the trans- 
 parency of the serum is due to the gradual removal of the superfluous fatty matter through 
 the respiratory process, whilst the proteine-compound, of which part of the granules are 
 composed, is gradually reduced to a state of perfect solution. 
 
 /. The occasional presence of Sugar, even in healthy blood, when a large quantity of 
 saccharine matter exists in the food, appears to be now well established. But it seems to 
 be commonly transformed, either into lactic acid, or into fatty matter, previously to its recep- 
 tion into the circulating current, This last transformation is partly effected through the 
 agency of the Bile ; as will be shown hereafter ( 835). 
 
 698. It cannot be doubted that, upon the due admixture in the Blood of all 
 these elements, the regular performance of its actions is dependent. In regard 
 to its physical properties merely, it is easily shown that a slight alteration may 
 produce the most injurious consequences; for a certain degree of viscidity has 
 been found (by the experiments of Poisseuille) to favour the passage of fluid 
 through capillary tubes ; and thus, if the viscidity of the blood be diminished 
 by a loss of part of its fibrine, stagnation of the current, and extravasation of a 
 
 * On the Analysis of the Blood and Urine, p. 30. 
 | Medical Gazette, Oct. 10, 1845. 
 45 
 
530 OF ABSORPTION AND SANGUIFICATION. 
 
 portion of the contents of the vessels, will be the result. This has been fully 
 proved by the numerous experiments of Magendie ; and the fact-is one of very 
 important Pathological applications ( 707, b}. But the vital properties of the 
 fluid are still more immediately dependent upon the Fibrine it contains; since, 
 as we have seen reason to believe, it is the material which is most completely 
 prepared for organization, and which supplies what is requisite for the nutri- 
 tion of the larger proportion of the solid tissues of the body. It is, therefore, 
 continually being withdrawn from the blood by the nutritive operations; and 
 the demand appears to be supplied, in part by the influx of Fibrine that has 
 been prepared in the Absorbent system, and in part by the continued trans- 
 formation of Albumen, which takes place during the circulation of the Blood, 
 and of which we have seen reason to believe that the Colourless Corpuscles 
 are the instruments ( 153 159). The Albumen of the Blood is the raw 
 material, at the expense of which not only the Fibrine, but many other sub- 
 stances, are generated during the nutritive process. All the Albuminous com- 
 pounds of the Secretions, the Horny matter of the Epidermic tissues, the 
 Gelatine of the simple Fibrous tissues, and the Haematine of the Red Cor- 
 puscles, may be regarded as almost certainly produced by the transformation 
 of the Albumen of the Blood ; and a continual supply of this from the food 
 is therefore requisite to preserve the due proportion in the circulating fluid. 
 The Red Corpuscles appear to be more connected with the function of Respira- 
 tion than with that of Nutrition ( 150) ; and the stimulating action of Arterial 
 blood, especially upon the Nervous and Muscular tissues, appears to depend 
 upon their presence. It is by no means impossible that their peculiar con- 
 nection with the activity of the latter may be dependent upon an actual 
 Chemical relation between their contents and the red matter of the Ganglionic 
 corpuscles ( 245) ; and that a part of their function may be, to prepare the 
 substance which is afterwards to be appropriated as a peculiar nutritive prin- 
 ciple, by the active instruments of Nervous operations. It appears from the 
 experiments of Dieff'enbach on transfusion, that the Red Corpuscles are more 
 effectual as stimuli to the Heart's action, than is any other constituent of the 
 blood. The rapidity with which they may be decomposed and reconstituted, 
 is made remarkably evident by the experiments of Magendie; who found that, 
 when the Blood of one animal was injected into the veins of another having 
 discs of very different size and form (care being taken to prevent the coagula- 
 tion of the Fibrine during the operation), the original Red particles soon dis- 
 appeared, and were replaced by those characteristic of the species, in whose 
 veins the fluid was circulating. The use of the Saline matter is evidently in 
 part to supply the mineral materials, requisite for the generation of the tissues, 
 and for the production of the various secretions. It is by the Saline and 
 Albuminous matters in conjunction, that the specific gravity of the Liquor 
 Sanguinis is kept up to the point, at which it is equivalent to that of the con- 
 tents of the Red corpuscles; and it is only in this condition that the latter 
 present their proper characters. Thus it has been shown by Dr. G. O. Rees, 
 that when the quantity of water in the Liquor Sanguinis has been reduced by 
 copious perspirations or other similar causes, the corpuscles are thin, and very 
 like those whose contents have exuded by exosmose into a denser liquid 
 around ( 143). On the other hand, if the Liquor Sanguinis be diluted by the 
 withdrawal of blood and the injection of an equivalent quantity of water, the 
 serum speedily becomes tinged with the colouring matter of the corpuscles ; 
 apparently in consequence of a rupture of some of the cells, by endosmose 
 from the circumambient liquid, now reduced to a lower specific gravity than 
 that of their contents. The Fatty matters of the Blood are evidently derived 
 from the food, either directly, or by the transformation of its farinaceous in- 
 gredients ; and they are chiefly appropriated to the maintenance of the com- 
 
COAGULATION OF THE BLOOD. 531 
 
 bustive process. That which may be superfluous, is either deposited in the 
 cells of Adipose tissue, or it is eliminated by the Liver, the Sebaceous follicles 
 of the Skin, and (in the nursing female) by the Mammary glands. How the 
 peculiar Phosphorized Fats of the Blood are formed, whether by the con- 
 tinuation of the azotized and phosphorized materials with ordinary fat, or 
 by the metamorphosis of albuminous matter, cannot be said to be yet de- 
 termined. 
 
 699. When the Blood is drawn from the body, and left to itself, its organic 
 elements speedily undergo a new arrangement. The Fibrine coagulates, and 
 separates itself from the fluid in which it was previously dissolved ; and during 
 its coagulation it attracts the Red particles ; these are included in areolae or 
 meshes of the Clot, the substance of which has a tendency to assume a fibrous 
 arrangement ( 118) ; and they usually group themselves together in columnar 
 masses, resembling piles of money. ' The Coagulum or clot becomes dense, 
 in proportion to the amount of the Fibrine it contains ; and the Albuminous and 
 Saline matter still dissolved in the water are separated from it, constituting the 
 Serum. This separation will not occur, however, if the coagulation take 
 place in a shallow vessel ; nor if the amount of Fibrine should be small, or 
 its vitality low. A homogeneous mass, deficient in firmness, presents itself 
 under such circumstances ; though the solid part of this may pass into a state 
 of more complete condensation, after the lapse of a certain time. That the 
 coagulation is due to the Fibrine, and that the Red particles are merely passive 
 in the process, appears from several considerations. A microscopical exami- 
 nation of the Clot shows, that it has the same texture with Fibrine, when 
 coagulating by itself; the Corpuscles clustering together in the interspaces of 
 the network, and not being uniformly diffused through the whole mass. Their 
 Specific Gravity being greater than that of the Fibrine, they are usually most 
 abundant at the lower part of the clot ; and the upper surface is sometimes 
 nearly colourless, especially when the coagulation has taken place slowly ; yet 
 this upper part is much firmer than the under, showing that the Fibrine alone 
 is the consolidating agent. This has been proved to demonstration by an 
 experiment of Miiller's. He placed the blood of a Frog, diluted with water 
 (or still better with a very thin syrup) on a paper filter, of sufficiently fine 
 texture to keep back the Corpuscles ; and the Liquor Sanguinis, having passed 
 through the filter completely unmixed with them, presented a distinct coagu- 
 lum, although from the diluted state of the fluid, this did not possess much 
 consistency. Owing to the more minute size of the Blood-discs of warm- 
 blooded animals, this experiment cannot be so readily performed with their 
 blood. The sole agency of the Fibrine in coagulation is very easily proved 
 in another way. If fresh drawn blood be continually stirred with a stick, the 
 Fribrine will adhere to it in strings during its coagulation ; and the Red parti- 
 cles will be left suspended in the serum, without the slightest tendency to 
 coagulate. Moreover, if a solution of any salt, that has the property of re- 
 tarding the coagulation (such as carbonate of potash or sulphate of soda), be 
 added to the blood, the Corpuscles will have time to sink to the lower stratum 
 of the fluid, before the clot is formed ; the greater part of the Coagulum is 
 then entirely colourless, and is found by the microscope to contain few or no 
 red particles. 
 
 700. That the Coagulation of the Blood is not, as some have supposed, a 
 proof of its death, but is rather an act of vitality, appears evident from what 
 has been already stated ( 118) of the incipient organization which may be 
 detected even in an ordinary clot ; and still more from the fact that, if the 
 effusion of Fibrine take place upon a living surface, its coagulation is the first 
 act of its conversion into solid tissues possessing a high degree of vitality. It 
 is absurd to suppose that the Blood dies, in order to assume a higher form. 
 
532 
 
 OF ABSORPTION AND SANGUIFICATION. 
 
 A complete demonstration of the truth of the Hunterian doctrine, that the 
 Blood might become organized, like plastic exudations of " coagulable lymph," 
 has been lately afforded by the researches of Dr. Zwicky, on the changes 
 occurring in the clots of blood which form in blood-vessels, above the points 
 where they have been tied. He has traced the successive stages of the meta- 
 morphosis of the coagulum into fibro-cellular tissue, and the formation of ves- 
 sels in its substance ; the whole process taking place exactly as in an inflam- 
 matory exudation, and the blood-corpuscles exerting no other influence upon 
 it, than that of slightly retarding it. 
 
 701. When the Blood is withdrawn from the body, however, its Coagula- 
 tion is the last act of its life ; for, if not within the influence of a living sur- 
 face, it soon passes into decomposition. Instances occasionally present 
 themselves, in which the Blood does not coagulate after death ; and in most 
 of these, there has been some sudden and violent shock to the Nervous sys- 
 tem, which has destroyed the vitality of solids and fluids alike. This is 
 generally the case in men and animals killed by lightning, or by strong elec- 
 tric shocks ; and in those poisoned by prnssic acid, or whose life has been 
 destroyed by a blow on the epigastrium. It has also been observed in some 
 instances of rupture of the heart, or of a large aneurism near it ; and a very 
 interesting phenomenon then not unfrequently presents itself, the coagulation 
 of the Blood which has been effused into the pericardium (the effusion having 
 taken place during the last moments of life), whilst that in the vessels has re- 
 mained fluid. In several of the instances in which the blood has been found 
 uncoagulated in the vessels, many hours after death, a portion withdrawn from 
 the body has clotted; and Dr. Polli asserts that the complete absence of 
 coagulability is a phenomenon which has no real occurrence. During a long 
 course of researches on this subject, he has never yet met with an instance, 
 in which the blood, when left to itself, and duly protected from external 
 destructive influences, did not coagulate before becoming putrid. He has 
 even more than once caused blood to coagulate, which had been taken in a 
 fluid state from the veins, thirty-six or forty-eight hours after death.* It ap- 
 pears that simple arrestment of Nervous influence favours the coagulation of 
 the blood in the vessels ; clots being found in their trunks, within a few 
 minutes after the Brain and Spinal marrow have been broken down. 
 
 702. The length of time which elapses before Coagulation, and the degree 
 in which the clot solidifies, vary considerably ; in general, they are in the 
 inverse proportion to each other. Thus, if a large quantity of blood be with- 
 drawn from the vessels of an animal at the same time, or within short inter- 
 vals, the portions that last flow coagulate much more rapidly, but much less 
 firmly, than those first obtained. In blood drawn during Inflammatory states, 
 again, the coagulation is usually slow, but the clot is preternaturally firm ; espe- 
 cially at its upper part, where the Buffy coat ( 704) or colourless stratum 
 of Fibrine, gradually contracts, and produces the cup, which is usually re- 
 garded as indicative of a high degree of Inflammation. Except under the 
 peculiar circumstances just stated, the Blood withdrawn from the body always 
 coagulates ;t whether it be kept at rest or in motion ; whether its temperature 
 be high or low ; and whether it be excluded from the air, or be admitted to 
 free contact with the atmosphere. The Coagulation may be accelerated or 
 retarded, however, by variation in these conditions. Thus, if the blood be 
 continually agitated in a bottle, its coagulation is delayed, though it will at last 
 
 * Banking's Half- Yearly Abstract, vol. ii. p. 337. 
 
 f Some diseases may perhaps be an exception ; non-coagulation of the Blood is said to be 
 characteristic of the Scurvy, but this is erroneous. In very severe forms of Typhus, the same 
 has been stated to occur. 
 
COAGULATION OF THE BLOOD. BUFFY COAT. 533 
 
 take place in shreds or insulated portions ; but that rest is not the cause of its 
 coagulation (as some have supposed), is proved by the fact that, if a portion 
 of blood be included between two ligatures in a living vessel, it will remain 
 fluid for a long time. Again, the coagulation is accelerated by moderate heat, 
 and retarded by cold; but it is not prevented by even extreme cold; for, if 
 blood be frozen immediately that it is drawn, it will coagulate on being thawed. 
 Moreover it is accelerated by exposure to air, but it is not prevented by com- 
 plete exclusion from it, as is proved by its taking place in a vacuum, or in a 
 shut sac within the dead body : complete exclusion from the air, however, 
 retards the change ; as has been shown by causing Blood to flow into a ves- 
 sel containing oil, which will form an impervious coating on its surface, and 
 will occasion the coagulation to take place so slowly, that the Red particles 
 have time to subside, and the upper stratum of the clot is colourless.* A re- 
 markable case has been put on record by Dr. Polli, in which complete coagu- 
 lation of the blood did not take place until fifteen days after it had been with- 
 drawn from the body ; and fifteen days more elapsed before putrefaction 
 commenced. The upper four-fifths of the clot were colourless; the red cor- 
 puscles occupying only the lowest fifth. It is additionally remarkable, that 
 the patient (who was suffering under acute pneumonia) being bled very fre- 
 quently during the succeeding week, the blood gradually lost its indisposition 
 to coagulate.! An extrication of Carbonic acid usually takes place to a slight 
 degree during coagulation ; but this is not a constant occurrence ; and the 
 process is not prevented, even by agitating Carbonic acid with the Blood. 
 
 703. The proportions of Serum and Clot which present themselves after 
 coagulation, are liable to great variation, independently of the amount of the 
 several ingredients characteristic of each ; for the Coagulum may include not 
 only the Fibrine and Red particles, but also a large proportion of the Serum, 
 entangled as it were in its substance. This is particularly the case when the 
 coagulation is rapid ; and the clot then expels little or none of it by subse- 
 quent contraction. On the other hand, if the coagulation be slow, the parti- 
 cles of Fibrine seem to become more completely aggregated, the coagulum is 
 denser at first, and its density is greatly increased by subsequent contraction. 
 When a firm fresh clot is removed from the fluid in which it is immersed, its 
 concretion is found to continue for 24 or even 48 hours, serum being squeezed 
 out in drops upon its surface; and in order, therefore, to form a proper esti- 
 mate of the relative proportions of Crassamentum and Serum, the former 
 should be cut into slices, and laid upon bibulous paper, that the latter may be 
 pressed from it as completely as possible. According to the experiments of 
 Mr. Thrackrah, Coagulation takes place sooner in metallic vessels than in 
 those of glass or earthenware, and the quantity of Serum separated is much 
 less ; in one instance, the proportion of Serum to Clot was as 10 to 24, 
 when the blood coagulated in a glass vessel ; whilst a portion of the same 
 Blood, coagulating in a pewter vessel, gave only 10 of Serum to 175 of Clot. 
 The Specific Gravity of Blood is no measure of its coagulating power ; for a 
 high specific gravity may be due to an excess in the amount of globules, 
 which form the heaviest part of the blood ; and may be accompanied by a 
 diminution in the quantity of fibrine, which is the coagulating element. 
 
 704. The Crassamentum not unfrequently exhibits, in certain disordered 
 conditions of the Blood, a layer of Fibrine nearly free from colour; and this is 
 known as the Bvffy Coat. The presence of this has been frequently re- 
 garded as a sign of the existence of Inflammation, occasioning an undue pre- 
 dominance of Fibrine ; but this idea is far from being correct, since, as will pre- 
 
 * Babington in Medico-Chirurgicnl Transactions, vol. xvi. 
 f Mr. Paget's Report, in Brit, and For. Med. Rev., xix.p. 252. 
 
 45* 
 
534 
 
 OF ABSORPTION AND SANGUIFICATION. 
 
 Fig. 210. 
 
 sently appear ( 705), it may result from a very opposite condition of the 
 Blood. A similar colourless layer of Fibrine is always observable, when the 
 Coagulation of the blood is retarded by the addition of agents that have the 
 power of delaying it ( 699) ; and since, in Inflammatory states of the system, 
 the blood is generally long in coagulating, it has been supposed that the sepa- 
 ration of the red particles is due to this cause alone. Dr. Alison,* however, 
 maintains that there must be an absolute tendency to separation between the 
 two components of the clot, in order to account for the phenomena sometimes 
 presented by it; and he adduces the two following reasons in support of this 
 view. " 1. The formation of the Buffy coat, though no doubt favoured or 
 rendered more complete by slow coagulation, is often observed in cases where 
 the coagulation is more rapid than usual; and the colouring matter is usually 
 observed to retire from the surface of the fluid in such cases, before any 
 coagulation has commenced. 2. The separation of the Fibrine from the 
 colouring matter in such cases takes place in films of blood, so thin as not to 
 admit of a stratum of the one being laid above the other; they separate from 
 each other laterally, and the films acquire a speckled or mottled appearance, 
 equally characteristic of the state of the blood with the buffy coat itself." 
 It appears from the observations of Mr. Wharton Jones, that the red corpus- 
 
 cles of Inflammatory Blood have an 
 unusual attraction for each other, which 
 occasions their coalescence in piles and 
 masses; so that by this character, the 
 state of the Blood may be detected, 
 from the examination of no more than 
 a single drop of the fluid. Now if we 
 consider, in connection with this in- 
 crease in the mutual attraction of the 
 Blood-discs, the increase in the mutual 
 attraction of the particles of Fibrine 
 (which causes the coagulum of Inflam- 
 matory blood to be so much firmer and 
 more decidedly fibrous than that of the 
 healthy fluid), we have a cause suffi- 
 cient to explain the phenomena noticed 
 by Dr. Alison; without the necessity 
 of resorting to the idea of an absolute 
 repulsion being present between the two 
 constituents. It is in the Buffy Coat 
 of Inflammatory Blood, that we see 
 the clearest indications of organization 
 ever presented by the circulating fluid. 
 The fibrous network is frequently extremely distinct ; and it commonly in- 
 cludes a large number of White Corpuscles in its meshes. Sometimes, 
 indeed, according to the observations of Mr. Addison, it almost entirely con- 
 sists of these bodies. In its Chemical Composition, the buffy coat of Inflam- 
 matory blood appears to be peculiar ; containing a larger or smaller amount 
 of the substance, readily soluble in boiling water, which is considered by 
 Mulder to be the Tritoxide of Proteine ( 116, a). 
 
 705. When the Buff arises from other causes, however, its appearance is 
 less characteristic. It appears from the researches of Andral, that the usual 
 condition of its production is an increase in the quantity of Fibrine in propor- 
 tion to the Red Corpuscles; and not a simple increase of Fibrine. When the 
 
 The microscopic appearance of a drop of blood 
 in the inflammatory condition. The red corpus- 
 cles lose their circular form and adhere together ; 
 the white corpuscles remain apart, and are more 
 abundant than usual. 
 
 * Outlines of Physiology, 3d edition, p. S9. 
 
BUFFY COAT. PATHOLOGICAL CHANGES IN THE BLOOD. 535 
 
 Blood contains an excessive quantityofFibrine.it coagulates slowly; thus 
 the blood of a patient labouring under Rheumatism coagulates more slowly 
 than that of one affected with Typhoid fever. The increase may occur in. 
 two ways ; either by an absolute increase in the Fibrine, the amount of the 
 corpuscles remaining unchanged, or not being augmented in the same pro- 
 portion ; or by a diminution of the Corpuscles, the quantity of Fibrine re- 
 maining the same, or not diminishing in the same proportion. Hence in 
 severe Chlorosis, in which the latter condition is strongly developed, the buffy 
 coat may be as well marked, as in the severest Inflammation. Unless the 
 composition of the blood be altered in one of these two ways, it is stated by 
 Andral that the buffy coat is never formed ; the influence of circumstances 
 which favour it, not being sufficient to produce it when acting alone. The 
 absence of these circumstances may prevent it, however, when it would other- 
 wise have been formed ; thus, when the Blood flows slowly, the buff is not 
 properly produced; because the slow discharge gives one portion time to 
 coagulate before another; and only the blood last drawn furnishes the Fibrine 
 at the upper part of the vessel. Again, in a deep narrow vessel, the buff will 
 form much more decidedly than in a broad shallow one ; because the thick- 
 ness of the Fibrinous crust will be greater. 
 
 6. Pathological Changes in the Blood. 
 
 706. From the part which the Blood performs in the ordinary processes of 
 Nutrition, it cannot be doubted that it undergoes important alterations, when 
 these processes take place in an abnormal manner. These alterations must 
 be sometimes the causes, and sometimes the effects, of the morbid phenomena, 
 which constitute what we term the Disease. Thus, when some local cause, 
 affecting the solid tissues of a certain part of the body, produces Inflammation 
 in them, their normal relation to the blood is altered ; the consequence is, that 
 the Blood, in passing through them, undergoes a different set of changes from 
 those for which it is originally adapted ; and thus its own character under- 
 goes an alteration, which soon becomes evident throughout the whole mass of 
 the circulating fluid, and is, in its turn, the cause of morbid phenomena in 
 remote parts of the system. On the other hand, the strong analogy between 
 many Constitutional diseases, and the effects of poisonous agents introduced 
 into the Blood, appears clearly to point to the inference, that these diseases 
 are due to the action of some morbific matter, which has been directly intro- 
 duced into the current of the circulating fluid, and which has affected both its 
 physical and its vital properties.* Here, then, is a wide field for investiga- 
 tion, of which the surface can scarcely be said to be yet broken up, and 
 which must yield an abundant harvest to those who shall cultivate it with in- 
 telligence and zeal. The first and most complete series of connected re- 
 searches, which have been yet published, on the changes which the blood un- 
 dergoes in disease, are those of MM. Andral and Gavarret ;t these are confined 
 
 * This doctrine has been brought prominently forward, in a paper on Symmetrical Dis- 
 eases, read by Dr. William Budd before the Medico-Chirurgical Society, Dec. 16, 1841. The 
 Author ingeniously proves, that the symmetry of many diseases (such as certain forms of 
 cutaneous eruptions, rheumatism, &c.) which do not immediately depend upon external 
 causes, necessarily involves the idea of the conveyance of the morbific agent in the circulating 
 fluid; the palsy produced by lead is a very interesting example, in which the agent is known 
 to be mingled with the blood, and to be deposited in the parts affected, which are generally, 
 if not always, symmetrical. 
 
 t An account of these inquiries will be found in the Provincial Medical and Surgical 
 Journal for May, June, and July 1841; in the Annales des Sciences Naturelles, Dec. 1840, 
 and March 1841; and in the Ann. de Chimie, torn. Ixxv. They have since been published 
 
536 OF ABSORPTION AND SANGUIFICATION. 
 
 to the alterations which take place in the proportions of the Organic elements 
 of the fluid. Another series of researches of great value, and in almost every 
 point confirmatory of the preceding, has been since made by MM. Becquerel 
 and Rodier ;* and another by Dr. Karl Popp.t Numerous other less systematic 
 analyses have been made by various Chemists and Pathologists. The follow- 
 ing outline contains the general results of these. It is, of course, necessary to 
 determine, in the first instance, what are the usual or normal proportions; and 
 the following may be estimated as the ordinary quantity of each element, in 
 1000 parts of healthy Blood: 
 
 Fibrine from 2 to 3 
 
 Corpuscles " 110 " 100 
 
 Solid matter of Serum . . . . " 72 " 85 
 
 707. Before entering upon the consideration of the alterations in the Blood, - 
 which are effected by particular morbid states, it is requisite to notice the 
 results of two extraneous causes, usually operating in disease, which may affect 
 the proportions of its components. These are, Abstinence from food, and 
 Loss of Blood, as by Hemorrhage or Venesection. It has been commonly 
 supposed, that these causes have a tendency to diminish the proportion of all 
 the solid elements of the blood; but this is not the case; for they affect the 
 Corpuscles, chiefly or exclusively, the quantity of Fibrine and of the solids of 
 the Serum remaining nearly the same, unless the abstinence has been pro- 
 longed, or the loss of blood very considerable. It is probably to the effects 
 of abstinence, that we are to attribute the general diminution of the solids of 
 the blood, which presents itself in most acute diseases; thus, on the average 
 of 120 cases, MM. Becquerel and Rodier found the average Specific Gravity 
 of defibrinated blood reduced from 1060 (in Men) and 1057*5 (in Women), to 
 1056 (in Men), and 1055 (in Women). The diminution, in the proportion of 
 Corpuscles was well marked; that of the Albumen was much slighter; there 
 was on the whole a slight augmentation of Cholesterine and Phosphorized 
 Fat; and a marked increase in the Phosphates. The increase or diminution 
 of the Fibrine is entirely dependent (as we shall presently see) on the nature 
 of the disease. The influence of Venesection in impoverishing the blood is 
 well shown in the following table of the mean composition of the fluid, at three 
 successive Venesections in ten persons : 
 
 First Second Third 
 
 Bleeding. Bleeding. Bleeding. 
 Specific Gravity of defibrinated 
 
 Blood 1056 1053 1049-6 
 
 Water 793 807-7 823-1 
 
 Fibrine 3-5 3-8 3-4 
 
 Corpuscles 129'2 116-3 99-2 
 
 Albumen .... 65-0 63-7 64-6 
 Extractive, free salts, and fatty 
 
 matters 9'4 8'5 9'5 
 
 Thus we see that repeated venesections render the blood more watery; but 
 this, chiefly by the diminution they produce in the amount of Corpuscles. 
 They slightly diminish the albumen and fatty matters ; but they exert no per- 
 ceptible influence on the amount of Fibrine; a point of the highest practical 
 importance. 
 
 a. The most important fact substantiated by Andral, is one that had been previously sus- 
 pected, the invariable increase in the quantity of Fibrine during acute Inflammatory affec- 
 tions ; the increase being strictly proportional to the intensity of the Inflammation, and to the 
 
 in a separate form, under the title of " Essai d'Hematologie Pathologique.-' [See Transla- 
 tion by Drs. Meigs and Stille, Phil. 1844.] 
 
 * Gazette Medicale, 1844, Nos. 47 57. f Banking's Abstract, vol. iii. p. 306. 
 
PATHOLOGICAL CHANGES IN THE BLOOD. 537 
 
 degree of symptomatic Fever accompanying it. "The augmentation of the quantity of 
 Fibrine is so certain a sign of Inflammation, that, if we find more than 5 parts of fibrine in. 
 1000, in the course of any disease, we may positively affirm that some local inflammation 
 exists." Several cases are mentioned, in which an increase to 7 or 7^ parts took place, 
 without any apparent cause; but.in which it afterwards proved that severe local inflamma- 
 tion was present; and thus we are furnished with a pathognomonic sign of great importance. 
 The average proportion of Fibrine in Inflammation may be estimated at 7; the minimum 
 at 5; the maximum at 13*3. The greatest augmentation is seen in Pneumonia and Acute 
 Rheumatism. It does not appear that in robust athletic persons, the proportion of Fibrine is 
 greater than in those of feeble constit\ition ; in the latter it is the Corpuscles that are deficient; 
 and it is rather from this disproportion, than from an absolute excess of Fibrine, that their 
 greater liability to Inflammatory affections arises. Diseases which commence at the same 
 time as the Inflammation, or co-exist with it, do not prevent the characteristic increase of the 
 Fibrine; thus in Chlorotic females, the proportion rises to 6 or 7, under this influence. The 
 augmentation is observed at the very outset of the affection ; the quantity increases with its 
 progress; and a decrease shows itself when the disease begins to abate.* When the dis- 
 ease presents alternations of increase and decline, these are marked by precisely correspond- 
 ing changes in the quantity of Fibrine. It is a curious fact, that an augmentation is commonly 
 observable during the advanced stage of Phthisis, in spite of the deterioration which the 
 blood must then have undergone; this is probably dependent upon the development of local 
 inflammation around the tubercular deposits. In one of Popp's observations, the proportion 
 of Fibrine in the blood of a Phthisical patient was not less than 10-7. Some experiments 
 performed by M. Andral on the blood of pregnant women, seem to lead to the conclusion 
 that, during the first six months, the Fibrine is below the normal standard ; and that it sub- 
 sequently varies, usually undergoing an augmentation between the sixth and seventh, and 
 the eighth and ninth months. There is also a diminution in the Corpuscles; and these circum- 
 stances combined favour the production of the buffy coat ( 704). These observations are 
 confirmed by those of MM. Becquerel and Rodier. 
 
 b. It appears obvious, from what has been just stated, that the increase in the quantity of 
 Fibrine is not dependent upon the febrile condition, which is secondary to the local inflamma- 
 tion, but upon the Inflammation itself. This conclusion is confirmed by the interesting fact 
 that, in idiopathic Fever, the proportion of Fibrine is diminished, instead of undergoing an 
 increase. This diminution was constantly observed by Andral in the premonitory stage of 
 Continued Fever; in some instances the amount was no more than T6 parts in 1000. The 
 proportion of Corpuscles was found to have usually, but not constantly, undergone an increase ; 
 as had also that of the solid parts of the Serum. In ordinary Continued Fever, in which 
 there was no evident complication from local disease, the quantity of Fibrin varied from 4-2 
 to 2-2; that of the Corpuscles from 185-1 to 103-6 (excluding a case in which their amount 
 was only 82-5, which was that of a Chlorotic female); that of the solid matter of the Serum, 
 from 98-7 to 90'9; and that of the Water from 725-6 to 851-9. Hence the quantity of solid 
 matter appears to be usually increased ; but the peculiar condition of the disease may proba- 
 bly be stated to be, an increase in the proportion of the Corpuscles to the Fibrine. When, 
 however, a local Inflammatory affection developes itself during the course of the Fever, the 
 amount of Fibrine increases; but its augmentation seems to be kept down by the febrile 
 condition. In Typhoid Fever,"}" the decrease in the proportion of Fibrine is much more de- 
 cidedly marked; this does not depend upon abstinence; for it ceases as soon as a favourable 
 change occurs in the disease, long before the effect of food could show itself. In the various 
 cases examined by Andral, the blood furnished a maximum of 3-7 of Fibrine, and a minimum 
 of 0'9; in this last case, the Typhoid condition existed in extreme intensity, yet the patient 
 recovered. The proportion of Corpuscles varies considerably; in an early stage of the disease 
 it is usually found to be absolutely high ; and it always remains high relatively to the amount 
 of Fibrine. In Typhoid fever, then, the abnormal condition of the Blood, in regard to the 
 
 * By experiments on animals, M. Andral has ascertained that no circumstance of pre- 
 vious debility or privation prevents this characteristic change. Having ascertained the 
 amount of Fibrine in the blood of three dogs to be 2-3, 2'2, and 1-8 (the natural range for 
 these animals), he deprived them, completely or partially, of food. On the fourteenth day, 
 the proportion of fibrine had risen, in the first to 4-5 : and in the second, to 4 : these animals 
 had no food. In the third dog, which was supplied with a very small quantity of food 
 daily, the same condition developed itself at a later period ; the blood on the fourteenth day 
 exhibiting only 1'8 parts of fibrine: but on the twenty-second day presenting 3-3 parts -In 
 all these instances, the elevation in the proportion of Fibrine was coincident with Inflamma- 
 tory changes in the stomach. 
 
 f M. Andral confines this term to the species characterized by ulceration of the mucous 
 follicles of the intestinal canal. 
 
538 OF ABSORPTION AND SANGUIFICATION. 
 
 disproportion between the Corpuscles and the Fibrine, is more strongly marked than in ordi- 
 nary Continued Fever : yet the usual augmentation of Fibrine will take place, if a local in- 
 flammation developes itself. In the Eruptive Fevers, it does not appear that the proportion 
 between the Fibrine and the Corpuscles undergoes so striking a change, as in ordinary Con- 
 tinued Fever; but the number of cases examined was too-small to admit of decided conclu- 
 sions. It was evident, however, that the specific Inflammations proper to, and characteristic 
 of, these Fevers, have not the same effect in occasioning an increase of the Fibrine, as an 
 intercurrent Inflammation of an extraneous character. By the experiments of Magendie it 
 has been ascertained that one of the effects of a diminution in the proportion of Fibrine, is a 
 tendency to the occurrence of Hemorrhage or of Congestion, either in the parenchymatous 
 tissue, or on the surface of membranes : these conditions are well known to be of frequent 
 occurrence, as complications of febrile disorders. A marked diminution of Fibrine was 
 noticed also in many cases of the disorder termed Cerebral Congestion, which commences 
 with headache, vertigo, and tendency to epistaxis, and not unfrequently passes into coma 
 and apoplexy. In Apoplexy, the diminution of Fibrine was still more striking ; and in gene- 
 ral, there was found to be an increase of the Corpuscles. In one instance, the quantity of 
 Fibrine on the second day of the attack was found to have fallen to 1-9, whilst that of the 
 Corpuscles had risen to 175'5; but on the third day, when the patient's consciousness began 
 to return the quantity of Fibrine was 3'5, whilst that of the Corpuscles had fallen to ] 37 7. 
 It would seem from the great change in the character of the Blood, which was noticed in 
 this and in other instances, that the want of due proportion between the Fibrine and the 
 Corpuscles was the cause, rather than the effect, of the Apoplectic attack. 
 
 c. The amount of Red Corpuscles seems to be subject to greater variation within the limits 
 of ordinary health, than is that of Fibrine. In the condition which is ordinarily termed a 
 highly sanguineous temperament, or Plethora, it is chiefly the entire mass of the blood that 
 undergoes an increase ; but whatever excess there may be in the proportion of its solid con- 
 stituents, affects the Corpuscles rather than the Fibrine. Plethoric persons are not more 
 prone to Inflammation, than are those of weaker constitution ; but they are liable to Conges- 
 tion, especially of the brain, and to Apoplexy or other Hemorrhage. The effect of Bleeding 
 in diminishing this tendency is now intelligible; since we know that loss of blood reduces 
 the proportion of Corpuscles. On the other hand, in that temperament,* which, when ex- 
 aggerated, becomes Anaemia, there is a marked diminution of the Corpuscles; this tempera- 
 ment may lead to two different conditions of the system. In Chlorosis, the Red Corpuscles 
 are diminished, whilst the Fibrine remains the same; so that the clot, though small, is firm, 
 and not unfrequently exhibits the bufty coat; in some extreme cases of this disease, the Cor- 
 puscles have been found as low as 27. The influence of the remedial administration of 
 Iron, in increasing the quantity of Corpuscles, was rendered extremely perceptible by An- 
 dral's analyses; in one instance, after iron had been taken for a short time, the proportion 
 of Corpuscles was found to have risen from 49-7 to 64'3 ; whilst in another, in which it had 
 been longer continued, it had risen from 46'6 to 95*7. On the other hand, Bleeding reduced 
 still lower the proportion of Corpuscles ; thus in one instance, their amount was found, on a 
 second bleeding, to have sunk from 62*8 to 49. The full proportion of Fibrine in the blood 
 of Chlorotic patients accounts for the infrequency of Hemorrhage in them ; whilst it also 
 leads us to perceive that they may be, equally with others, the subjects of acute Inflamma- 
 tion, which we know to be the fact. A diminution of Corpuscles may also co-exist with a 
 diminution in the amount, or in the degree of elaboration, of the Fibrine; and this condition 
 seems to be characteristic of Scrofula. Andral has noticed a diminution in the proportion of 
 Corpuscles in other Cachectic states, resulting from the influence of various depressing causes 
 on the nutritive powers ; as in the case of Diabetes Mellitus, in which the patient was much 
 exhausted; a case of Aneurismal dilatation of the Heart inducing Dropsy; and in several 
 cases of Cachexia Saturnina. The increase in the proportion of Colourless Corpuscles, in 
 Inflammatory affections, has been particularly noticed by Popp ; he has found them espe- 
 cially abundant in Pneumonia and in Phthisis, in the former of which diseases the Fibrine 
 is invariably, and in the latter generally, increased. 
 
 d. The chief class of cases, in which any marked change has been observed in the 
 amount of solid matter in the Serum, is that of Albuminuria, or Bright's disease of the Kid- 
 ney. The diminished Specific Gravity of the Serum was long ago pointed out by Dr. Christi- 
 son; but Andral remarks that this is not an accurate criterion, since, if there be a diminished 
 amount of Corpuscles (as is not unfrequently the case in this disease), the proportion of 
 water in the whole will be increased, and the specific gravity of the serum thus lowered, 
 without any alteration in its proper quantity of solid matter. According to Andral, the 
 diminution in the amount of Albumen in the Serum is exactly proportional to the quantity 
 
 * The term lymphatic has been applied to this temperament; by which term was meant 
 a predominance of lymph in the absorbent vessels. 
 
PATHOLOGICAL CHANGES IN THE BLOOD. 539 
 
 contained in the urine. A case is related by him, under this head, which affords an interest- 
 ing exemplification of the general facts that have been already attained by his investigations. 
 A woman who had been suffering from Erysipelas of the face, and who had lost blood both 
 by venesection and by leeches, became the subject of Albuminuria. The blood drawn at 
 this time exhibited a considerable diminution in the proportion of Corpuscles, as well as of 
 Albumen, a fact which the previous loss of blood fully accounted for. After a short period, 
 during which she had been allowed a fuller diet, another experimental bleeding exhibited 
 an increase in the proportion of Corpuscles. Some time afterwards, when the Albumen had 
 disappeared from the Urine, some more blood was drawn ; and it was then observed that 
 the Albumen of the Serum had returned to its due proportion, but that the Corpuscles had 
 again diminished, whilst there was a marked increase in the quantity of Fibrine. This altera- 
 tion was fully accounted for by the fact, that, in the interval, several Lymphatic ganglia in 
 the neck had been inflamed and had suppurated; and that the patient had been again placed: 
 on very low diet. "Thus," observes Andral, "we were enabled to give a complete explana- 
 tion of the remarkable oscillations which were presented, in the proportion of the different 
 elements of the blood drawn at three different times from the same individual; and thus it 
 is that, the more extended are our inquiries, the more easy does it become to refer to general 
 principles the causes of all those changes in the composition of the blood, which, from the 
 frequency and rapidity with which they occur, seem at first sight to baffle all rules, and to 
 take place, as it were, at random. In the midst of this apparent disorder, there is but the 
 fulfilment of laws ; and in order to obtain these, it is only necessary to strip the phenomena 
 of their complications, and to reduce them to their simplest form." 
 
 708. That the Blood is subject to a great variety of other morbid altera- 
 tions, which are sometimes the causes, and sometimes the results, of Disease, 
 cannot be for a moment doubted. But our knowledge of the nature of these 
 changes is as yet very insufficient. The great amount of attention which is 
 being directed by Chemical Pathologists to the subject, however, will doubt- 
 less ere long produce some important results. Among the most frequent 
 causes of depravation in the character of this fluid, we must undoubtedly rank 
 the retention, in the Circulating current, of matters which ought to be re- 
 moved by the Excreting processes. We shall presently see, that a total 
 interruption to the excretion of Carbonic Acid by the lungs, will occasion 
 death in the course of a very few minutes ; and even when only a slight im- 
 pediment is offered it, so that the quantity of Carbonic Acid always contained 
 in arterial blood is augmented to. but a small degree, a feeling of discomfort 
 and oppression, increasing with the duration of the interruption, is speedily 
 produced. The results of the retention of the materials of the Biliary and 
 Urinary excretions will be hereafter considered (Chap, xv.) ; and at present 
 it will be only remarked, that such retention is a most fertile source of slight 
 disorders of the system, that it is largely concerned in producing many severe 
 diseases, and that if complete it will most certainly and rapidly produce a 
 fatal result. The most remarkable cases of depravation of the Blood, by the 
 introduction of matters from without, are those in which these substances act 
 as ferments? exciting such Chemical changes in the constitution of the fluid, 
 that its whole character is speedily changed, and its vital properties are alto- 
 gether destroyed. Of such an occurrence, we have characteristic examples in 
 the severe forms of Typhoid fever, commonly termed malignant; in Plague, 
 Glanders, Pustule Maligne, and several other diseases; in some of uijhich we 
 can trace the direct introduction of the poison into the blood, whilst in others 
 we must infer from the similarity of result) that it has been introduced through 
 some obscure channel, probably the lungs. The final symptoms which are 
 common to all these diseases have been well described by Dr. Williams,* 
 under the title of Necrcemia, or Death by depravation of the blood. " Almost 
 simultaneously, the heart loses its power, the pulse becomes very weak, 
 frequent, and unsteady : the vessels lose their tone, especially the capil- 
 laries of the most vascular organs, and congestions occur to a great amount; 
 
 * Principles of Medicine, [Am. Ed. by Dr. Clymer, p. 373.] 
 
540 OF THE CIRCULATION OF BLOOD. 
 
 the brain becomes inactive, and stupor ensues ; the medulla is torpid, and the 
 powers of respiration and excretion are imperfect: voluntary motion is almost 
 suspended ; secretions fail ; molecular nutrition ceases ; and at a rate much 
 more early than in other modes of death, molecular death follows close on 
 somatic death, that is, structures die and begin to run into decomposition as 
 soon as the pulse and breath have ceased ; nay, a partial change of this kind 
 may even precede the death of the whole body ; and parts running into gan- 
 grene, as in the carbuncle of plague, the sphacelous throat of malignant scarla- 
 tina, and the sloughy sores of the worst forms of typhus, pr the putrid odour 
 exhaled even before death by the bodies of those who are the victims of simi- 
 lar pestilential disease, are so many proofs of the early triumph of dead over 
 vital chemistry." "The appearance of petechiae and vibices on the external 
 surface, the occurrence of more extensive hemorrhage in internal parts, the 
 general fluidity of the blood, and frequently its unusually dark or otherwise 
 altered aspect, its poisonous properties as exhibited in its deleterious operation 
 on other animals, and its proneness to pass into decomposition, point out the 
 Blood as the first seat of disorder; and by the failure of its natural properties 
 and offices as the vivifier of all structure and function, it is plainly the medium 
 by which death begins in the body." 
 
 CHAPTER XII. 
 
 OF THE CIRCULATION OF BLOOD. 
 
 1. Of the Circulation in General. 
 
 709. THE Circulation of nutritive fluid through the body has for its object, 
 on the one part, to convey to every portion of the organism the materials for 
 its growth and renovation, together with the supply of Oxygen which is re- 
 quisite for its vital actions, especially those of the Muscular and Nervous 
 systems ; and at the same time to carry off the particles, which are set free by 
 the disintegration or waste of the tissues, and which are to be removed from 
 the body by the Excreting processes. Of these processes, the one most con- 
 stantly in operation, as well as most necessary for the maintenance of the 
 purity of the blood, is the extrication of Carbonic acid, through the Respira- 
 tory organs; and this is made subservient to the introduction of Oxygen into 
 the system. The extent, therefore, to which a Circulating apparatus is de- 
 veloped in the Animal kingdom, is partly dependent upon the degree in which 
 the function of nutritive Absorption is limited to one part of the body; and 
 partly upon the arrangement of the Excreting surfaces, and especially of the 
 Respiratory apparatus. Where the Digestive cavity extends itself through 
 the whole system, so that every part can absorb at once from its parietes, 
 and where the whole external surface is adapted, by its softness and permeability, 
 to expose the fluids of the body to the aerating medium around, there is no 
 necessity for any transmission of fluid from one part to another ; and accord- 
 ingly, in the lowest animals, which are thus formed, no true Circulation exists. 
 Again, in the Insect tribes, in whose bodies the absorption of fluids can only 
 take place at fixed points, there is a Circulation, for the purpose of transmit- 
 ting the absorbed matter to the remote portions of the body ; but as every part 
 of the interior is permeated by air, the second of the above-named purposes 
 
OF THE CIRCULATION IN GENERAL. 
 
 541 
 
 is already answered ; and the circuit of the blood through the vessels, there- 
 fore, is not accomplished with the energy and activity which, from the vigor- 
 ous movements performed by these little beings, might have been supposed 
 necessary. On the other hand, among the Mollusca, in which the absorption 
 of fluid and the respiratory action are alike limited, we find the circulating 
 apparatus almost as extensive, and the movement of blood as vigorous, as it is 
 in the lower Vertebrata. It is in those animals, in which there is the greatest 
 activity in the other functions,- which live, in fact, the fastest, that the Cir- 
 culation is most energetic ; thus the rapid and energetic movement of the 
 blood in Birds contrasts most strongly with its slow and feeble propulsion in 
 Reptiles. The movement may vary considerably, however, in the same ani- 
 mal at different times, according to its state of repose or activity ; and in dif- 
 ferent organs of the same animal, according to the energy with which their 
 functions are being respectively performed. 
 
 710. In Man, as in other Vertebrated animals, there is a regular and con- 
 tinuous movement of the nutritive fluid through the vascular system ; and upon 
 the maintenance of this, the activity of all parts of the organism is dependent. 
 The course of the Blood may be likened to the figure 8 ; for there are two 
 distinct circles of vessels, through which it is transmitted ; and the Heart is 
 placed at the junction of these. The Systemic and Pulmonary circulations 
 are entirely separate, and might be said to have distinct hearts ; for the left 
 and right sides of the heart, which are respectively appropriated to these, 
 have no direct communication with each other (in the perfect adult condition, 
 at least), and are merely brought together for economy of material. At an 
 early period of foetal life, as in the permanent state of the Dugong, the heart is 
 so deeply cleft, from the apex towards the base, as almost to give the idea of 
 two separate organs. Each system has its own set of Arteries or efferent 
 vessels, and Veins or afferent trunks ; these communicate at their central ex- 
 tremity by the Heart ; and at their peripheral extremity by the Capillary ves- 
 sels, which are nothing else than the minutest ramifications of the two systems, 
 inosculating into a plexus ( 219). 
 
 Fig. 211. 
 
 Web of Frog's foot, stretching between two toes, magnified 3 diam. ; showing the blood-vessels, and 
 their anastomoses : 1, 1, veins; 2, 2, 2, arteries. 
 
 46 
 
542 
 
 OF THE CIRCULATION OF BLOOD. 
 
 a. Although the diameters of the branches, at each subdivision, together exceed that of 
 the trunk, yet there is but little real difference in their size. For, according to a well-known 
 geometrical law, the areas of circles are as the squares of their diameters ; and, as the calibre 
 of a tube is estimated by its area, not by its diameter, it follows that, in comparing the size 
 of a trunk with that of its branches, we are to square the diameter of the former, and com- 
 pare the result with the sum of the squares of the diameters of the branches. When this is 
 done, there is found to be a very close correspondence. The following table gives the re- 
 sult of eight measurements, taken with a view to determine the question. The first three 
 were taken from the mesenteric artery of a Sheep 5 the next three from the aorta and iliac 
 arteries : the last two from the Horse.* 
 
 
 TRUNK. 
 
 
 DIAMETER. 
 
 I. 
 
 9 
 
 II. 
 
 7.2 
 
 III. 
 
 3.5 
 
 IV. 
 
 7.0 
 
 V. 
 
 17 
 
 VI. 
 
 10 
 
 VII. 
 
 4.5 
 
 VIII. 
 
 8 
 
 sq.tr ARE. 
 
 81 
 
 51.64 
 12.25 
 
 49 
 289 
 100 
 20.25 
 
 64 
 
 BRANCHES. 
 
 DIAMETERS. 
 7.5+5 
 
 6+4 
 3+2 
 5+5 
 
 10+10+9.5 
 
 7+7+2 
 
 3.5+3 
 
 4+7 
 
 SUM OF SQ.tr ARES. 
 
 81.25 
 
 52 
 
 13 
 
 50 
 290.25 
 
 102 
 21.25 
 
 65 
 
 The discrepancy between the two results must be considered extremely small, when it is 
 stated that the unit, in the above measurements, is no more than one-fortieth of an inch; 
 and when it is remembered that any error in the measurement is greatly increased in the 
 calculation. 
 
 b. From Mr. Paget's observations, however, it appears that there is seldom an exact 
 equality between the area of the trunk and that of its branches, but the area sometimes in- 
 creases, and sometimes diminishes; the former being the general rule for the subdivision 
 of the aorta and its principal branches in the upper extremities; the latter in the lower. 
 The following Table shows the relative areas of several arterial trunks, and of the branches 
 proceeding from them. 
 
 Arch of Aorta .... 
 Innominata ..... 
 Common carotid, .... 
 External carotid .... 
 
 Subclavian 
 
 Abdominal Aorta, to last lumbar art. 
 
 , just before dividing 
 
 Common Iliac 
 
 External Iliac 
 
 TRUNK. 
 1 
 1 
 
 1 
 1 
 1 
 1 
 1 
 1 
 1 
 
 BRANCHES. 
 
 1-055 
 
 1-147 
 
 1-013 
 
 1-190 
 
 1-055 
 
 1-183 
 
 893 
 
 982 
 
 1-150 
 
 711. That the movement of the Blood through the Arterial trunks and the 
 Capillary tubes is, in Man, and in other warm-blooded animals, chiefly de- 
 pendent upon the action of the Heart there can be no doubt whatever. It can 
 be easily shown by experiment, that, if the Arterial current be checked, the 
 Capillaries will immediately cease almost entirely to deliver the blood into 
 the veins, and the Venous circulation will be instantaneously arrested. And 
 it has also been proved, that the usual force of the Heart is sufficient to propel 
 the blood, not only through the Arterial tubes, but through the Capillaries, 
 into the Veins ; since even a less force will serve to propel warm water through 
 the vessels of an animal recently dead.t But there are certain "residual phe- 
 nomena" even in Man, which clearly indicate that this is not the whole truth ; 
 and that forces existing in the Blood-vessels have a considerable influence, in 
 producing both local and general modifications of the effects of the Heart's 
 action. There are also indications of the nature of an influence, in which the 
 blood-vessels do not partake, arising from those changes occurring between 
 the Blood and the Tissues, that constitue the processes of Nutrition, Secretion, 
 
 * Ferneley in Medical Gazette, Dec. 7, 1839. 
 
 | See Dr. Williams' Principles of Medicine, p. 143, note. 
 

 MOTION OF THE BLOOD IN THE VESSELS. 543 
 
 <fcc. Such, for instance, would appear to be the interpretation of the fact, 
 that whilst any variations in the action of the Heart affect the whole system 
 alike, there are many variations in the Circulation, which, being very limited 
 in their extent, cannot be attributed to such central disturbances, and must 
 therefore be dependent on causes purely local. Of the nature of these in- 
 fluences, and of the mode of their operation, we shall probably arrive at a 
 more correct knowledge, if we examine the phenomena of the Circulation in 
 those beings, in which the moving power is less concentrated than it is in the 
 higher Animals ; for just as we find in the latter, that the development of 
 special absorbent vessels does not exclude the function of absorption from 
 being still performed by the general vascular system ( 675), so may we here 
 be led to perceive, that there is a generally-diffused force, to which alone the 
 Circulation of the nutritious fluid in the lowest organisms is due, and which 
 is not altogether replaced by the special organ of impulsion, that is developed 
 in the centre of the system in the higher. 
 
 712. The ascent of the sap in Vegetables is probably to be regarded as due, 
 in part, to the vis a tergo occasioned by the action of Endosmose at the 
 roots; and in part, to the demand for fluid, occasioned by the vital processes 
 taking place in the leaves. For if the stem of the Vine, in which the sap is 
 rising, be cut across, the sap will continue to flow for some time from the top 
 of the lower portion ; and its force of ascent may be shown to be very con- 
 siderable, by tying over the cut surface a piece of bladder, which will be 
 speedily burst, or by affixing to it a bent tube, containing a column of mer- 
 cury, which will be raised to the height of forty inches or more. On the 
 other hand, the attractive force of the leaves is shown by the fact, that if the 
 lower end of the upper division be put into water, it will continue to absorb, 
 as long as the vital actions of the leaves are being performed with vigour; 
 but, if the branch be carried into a dark room, the exhalation from the leaves 
 is immediately checked, and absorption is checked also. The influence of 
 the actions at the periphery of the circulating system, in maintaining the flow 
 of fluid towards the part, is further shown by the fact, that, if a shoot of an 
 evergreen species be grafted on a stock of one with deciduous leaves, a con- 
 tinual and unwonted ascent of sap will be kept up in the latter through the 
 winter; this being evidently due to the demand occasioned at its summit. 
 Again, the recommencement of the annual flow of sap in an ordinary tree, has 
 been found to take place in the first instance, not at its roots, but in the 
 neighbourhood of the buds ; for their expansion, under the influence of the 
 returning warmth, exhausts the fluid from the vessels of their neighbourhood; 
 this, again, occasions a demand from below; and thus the motion is gradually 
 propagated to the roots. Now it has been experimentally ascertained, that if 
 a branch of a vine growing in the open air be trained into a hot-house, it may 
 be made to vegetate during the winter, and to draw up fluid through the 
 stems and roots, whose condition has not been changed. It is evident, then, 
 that in Plants, the demand for fluid, in the organs to which it is distributed by 
 the vascular system, is one of the chief forces by which the supply is obtained. 
 
 713. This is still more evidently the case, in regard to the Circulation of 
 nutritious or elaborated sap, which takes place in the under surface of the 
 leaves and in the bark. The object of this movement is not to convey the 
 fluid in a direct line from one point to another (as in the case with the 
 ascending current), but to supply every part with materials for its growth, or 
 for the production of its peculiar secretions. Hence the vessels in which it 
 takes place, form a minutely-anastomosing net-work, instead of consisting of a 
 system of straight and distinct tubes. Through this net-work, the latex or 
 elaborated sap is seen to move, exactly as does the blood through the capil- 
 lary vessels of animals. The movement takes place, under favourable circum- 
 
544 OF THE CIRCULATION OF BLOOD. 
 
 stances, with considerable rapidity ; it is accelerated by heat, and retarded by 
 cold; and it is subject to all those minor irregularities (such as the cessation 
 of movement, or change in the direction of the current, in a particular chan- 
 nel), which are so constantly to be noticed by any one who attentively watches 
 the capillary circulation of Animals, and which clearly prove the operation of 
 some causes independent of the heart's action ( 734). The general direction 
 of the elaborated sap, through this capillary system, is downwards ; but that 
 the force of gravity cannot have much to do with the movement, is shown by 
 the fact that, in dependent branches, it has to ascend towards the stem, which 
 it will do without interruption from this cause. Moreover it may be noticed 
 that this circulation takes place most actively, in parts which are undergoing a 
 rapid developement; and that its energy corresponds with the vitality of the 
 part. Further ; it may be observed to continue for some time in parts that 
 have been completely detached from the rest; and on which neither vis a 
 tergo, nor vis a fronte, can have any influence. It is evident, then, that the 
 force, whatever be its nature, by which this continued movement is kept 
 up, must be developed by the processes to which that movement is subserv- 
 ient ; in other words, that the changes involved in the acts of nutrition and 
 secretion are the real source of the motor power. The manner in which they 
 become so, is the next object of our inquiry: and on this subject, some new 
 views have recently been put forth by Prof. Draper,* which seem to account 
 well for the phenomena. 
 
 a. It is capable of being shown, by experiments on inorganic bodies, that, if two liquids 
 communicate with each other through a capillary tube, for the walls of which they both 
 have an affinity, and if this affinity is stronger in the one liquid than in the other, a 
 movement will ensue; the liquid which has the greatest affinity being absorbed most ener- 
 getically into the tube, and driving the other before it. The same result occurs when the 
 lluid is drawn, not into a single tube, but into a net-work of tubes, permeating a solid 
 structure; for if this porous structure be previously saturated with the fluid, for which it has 
 the less degree of attraction, this will be driven out and replaced by that for which it has 
 the greater affinity, when the latter is permitted to enter it. Now if, in its passage through 
 the porous solid, the liquid undergo such a change, that its affinity be diminished, it is ob- 
 vious that, according to the principle just explained, it must be driven out by a fresh supply 
 of the original liquid; and that thus a continual movement in the same direction would be 
 produced. 
 
 b. Now this is precisely that which seems to take place in the organized tissue, per- 
 meated by nutritious fluid. The particles of this fluid, and the solid matter through which 
 it is distributed, have a certain affinity for each other ; which is exercised in the nutritive 
 changes, to which the fluid becomes subservient during the course of its circulation. Cer- 
 tain matters are drawn from it, in one part, for the support and increase of the woody tis- 
 sue ; in another part, the secreting cells demand the materials which are requisite for their 
 growth, as starch, oil, resin, &c.; and thus in every portion that is traversed by the vessels, 
 there are certain affinities between the solids and the fluids, which are continually being 
 newly developed by acts of growth, as fast as those which previously existed are satisfied 
 or neutralized by the changes that have already occurred. Thus in the circulation of the 
 elaborated sap, there is a constant attraction of its particles towards the walls of the vessels, 
 and a continual series of changes produced in the fluid as the result of that attraction. The 
 fluid, which has given up to a certain tissue some of its materials, no longer has the same 
 attraction for that tissue; and it is consequently driven from it by the superior attraction then 
 possessed by the tissue for another portion of the fluid, which is ready to undergo the same 
 changes, to be in its turn rejected for a fresh supply. Thus in a growing part, there is a 
 constantly-renewed attraction for the nutritive fluid, which has not yet traversed it ; whilst 
 on the other hand, there is a diminished attraction for the fluid, which has yielded up the 
 nutritive materials required by the particular tissues of the part ; and thus the former is con- 
 tinually driving the latter before it. 
 
 c. But the fluid, which is thus repelled from one part, may still be attracted towards ano- 
 ther ; because that portion of its contents, which the latter requires, may not yet have been 
 removed from it. And in this manner, it would seem that the flow of sap is maintained 
 
 * On the Forces which produce the Organization of Plants, Chap. in. 
 
MOTION OF THE BLOOD IN THE VESSELS. 545 
 
 through the whole capillary net-work, untili t is altogether exhausted of its nutritive matter. 
 The source of the movement is thus entirely to be looked for in the changes which take place 
 in the act of growth; and the influence of heat, cold, and other agents, upon the movement 
 is exercised through their power of accelerating or retarding those changes. 
 
 714. The fluid which thus descends through the stem and roots, seems to 
 be at last almost entirely exhausted ; a portion of it appears to find its way 
 into the ascending current, and to be mingled with it ; but all the rest seems 
 to have been entirely appropriated by the different tissues, through which it 
 has circulated. Thus there is no need of any general receptacle, into which 
 it may be collected, and from which it may take a fresh departure ; such as 
 is afforded by the heart of the higher animals. And as the purpose of this 
 circulation is only to supply the nutritive materials, and not to convey oxy- 
 gen, this element being but little required in the vegetative processes, and 
 being supplied by other means, the same energy and rapidity are not re- 
 quired in it, as need to be provided for in the higher animals. 
 
 715. In the lowest Animals, the movement of the circulating fluid seems 
 as independent of any central organ of impulsion, as it has been shown to be 
 in Plants. Thus, in the living Sponge, a current of water is continually 
 flowing through the tubes and channels, by which its substance is traversed, 
 the fluid being taken in by the small orifices, and ejected in powerful streams 
 from the large ones; and yet the most attentive examination has not revealed 
 any mechanical cause for this movement. In some of the compound Polypi- 
 fera, a similar current may be seen ; and it is curious that, in many species, 
 its direction undergoes a periodical change ; being reversed at intervals of a 
 certain number of seconds. In the Star-Fish and Sea-Urchin tribe, a com- 
 plex circulation of blood takes place, through regular vessels ; and here we 
 find some indication of a contractile cavity, by the power of which it may be, 
 in some degree, kept up ; but its feeble pulsations can scarcely be regarded, 
 as having any great share in the movement of the fluid which passes through 
 it. In the Articulated series, there is, with a few exceptions, an absence of 
 any central organ of impulsion, possessed of power sufficient to carry the 
 blood through the vascular system, by its contractions alone. In many of the 
 aquatic worms and larvae, the movement of the blood, and the pulsations of 
 the dorsal vessel, may be distinctly seen : and the thinness of the walls of the 
 latter, and the character of its movements, seem clearly to show, that these 
 can scarcely be regarded as propulsive, but that they merely result from the 
 variations in the current which passes through it, the sides flapping together 
 when there is an outward flow, and bulging out when there is an influx. It 
 is in these Articulata, in which there is a provision for respiration throughout 
 the whole structure, as is especially the case in Insects, that the absence of 
 any central impulsive power is most remarkable. In the Crustacea, and in 
 the Mollusca in general, the respiration is aquatic, and is restricted to a par- 
 ticular organ ; and in these, the heart is found to be more muscular, and the 
 circulation to be more under its control. It is curious to remark, however, 
 that, in som'e of the lower Mollusca, which exhibit a tendency to aggregation 
 into compound structures, like those of the Polypifera, there is the same want 
 of definiteness in the course of the circulation, as has been just stated to exist 
 in the latter group; the flow of blood, through their complex apparatus of 
 nutritive organs, being arrested at regular intervals, and then recommencing 
 in the reverse direction. 
 
 716. Even in Vertebrated animals, we find indications of the same defi- 
 ciency of central power, over the peripheral circulation. When we look at 
 the simple, thin-walled heart of Fishes, for example, it seems impossible that 
 it should have much power over the current of blood flowing back to it by 
 the veins ; for of this blood, a considerable portion has to pass through three 
 
 46* 
 
546 OF THE CIRCULATION OF BLOOD. 
 
 sets of capillaries, between its ejection from the heart, and its return to it. It 
 is first transmitted through the respiratory capillaries, for the purpose of aera- 
 tion ; the confluent vessels, which collect the arterial blood from these, ter- 
 minate in the general systemic trunk or Aorta, in which, as in the veins of 
 Man, there is an absence of pulsation, and by these, it is distributed to the 
 systemic capillaries ; and the blood which, after passing through these, re- 
 turns from the posterior part of the body, and from the viscera, passes through 
 another set of capillaries, those of the liver and kidneys, before it returns to 
 the heart. Even in the warm-blooded Vertebrata, in which the respiratory 
 circulation is separately performed, the blood which is returned from the in- 
 testines, passes into a trunk, the Vena Portse, which again subdivides into 
 capillary ramifications, being transmitted over the plexus of biliary ducts, of 
 which the liver is chiefly composed ; and thus the Vena Portae, as Hunter 
 justly observed, should be considered rather in the light of an artery,* re- 
 sembling as it does the aorta of Fishes. Considering the small amount of 
 pressure which is exerted by the blood, upon the sides of the vessels that are 
 formed by the reunion of capillaries, it seems impossible to imagine that the 
 vis a tergo derived from the impulsive action of the Heart, can be alone suf- 
 ficient to maintain the portal circulation. 
 
 2. .fiction of the Heart. 
 
 717. The Heart is endowed in an eminent degree with the property of 
 irritability ; by which is meant, the capability of being easily excited to 
 movements of contraction alternating with relaxation ( 574). Thus, after 
 the Heart has been removed from the body, and has ceased to contract, a 
 slight irritation M r ill cause it to execute, not one movement only, but a series 
 of alternate contractions and dilatations, gradually diminishing in vigour until 
 they cease. The contraction begins in the part irritated, and then extends to 
 the rest. It appears from Mr. Paget's experiments,! that it is necessary for 
 the propagation of this irritation, that the parts should be connected by mus- 
 cular tissue, of which a very narrow isthmus will suffice ; and that the pro- 
 pagation will not take place, if the connecting isthmus be composed of ten- 
 don, even though this be a portion of the auriculo-ventricular ring, which has 
 been supposed by some to be peculiarly efficacious in this conduction. That 
 the irritability of the heart is not dependent upon the Cerebro-spinal system, 
 appears not merely from the manifestation of it, when the organ is altogether 
 removed from the body, but also from the fact, that if the flood of blood 
 through the lungs be kept up by artificial respiration, the heart's action will 
 continue for a lengthened period, even after the Brain and Spinal Cord have 
 been removed, and when animal life is, therefore, completely extinct. Hence 
 we see that the Irritability of this organ must be an endowment properly be- 
 longing to it, and not derived from that portion of the Nervous System. Like 
 the contractility of other muscles, it can only be sustained for any great length 
 of time, by a supply of Arterial blood to its own tissue ( 584). It is much 
 less speedily lost in cold-blooded animals, however, than in warm-blooded ; 
 the heart of the Frog, for example, will go on pulsating for many hours after 
 its removal from the body ; and it is stated by Dr. MitchellJ that the heart of 
 a Sturgeon, which he had inflated with air, continued to beat, until the auricle 
 
 * That it conveys venous blood, is no reason to the contrary ; since this is the case with 
 the pulmonary artery. The character of an artery is derived from the division of its current 
 into several divergent streams. 
 
 f Brit, and For. Med. Review, vol. xxi. p. 551. 
 
 J American Journal of the Medical Sciences, vol. vii. p. 58. 
 
ACTION OF THE HEART. 547 
 
 had absolutely become so dry, as to rustle during its movements. It has 
 lately been shown by Mr. Todd, that the irritability of the heart is of long 
 duration after death in very young animals : which, as long since demonstrated 
 by Dr. Edwards, agree with the cold-blooded Vertebrata in their power of 
 sustaining life, for a lengthened period, without oxygen. It is difficult to ac- 
 count for the long continuance of the alternate contractions and relaxations of 
 the muscular parietes of the heart, after all evident stimuli have ceased to act 
 upon it; and many theories have been offered on the subject, none of which 
 afford an adequate explanation. The extraordinary tendency to rhythmical 
 action, which distinguishes the heart from all other muscles, is shown by the 
 fact that not only do the entire hearts of cold-blooded animals continue to act, 
 long after their removal from the body, but even separated portions of them 
 will contract and relax with great regularity for a long time. Thus the auri- 
 cles will persist in their rhythmical action, when cut off above the auriculo- 
 ventricular rings ; and the apex of the heart will do the same, when separated 
 from the rest of the ventricle. The stimulus of the contact of blood with the 
 lining membrane of the heart, to which its regular actions have been com- 
 monly referred, can have no influence in producing these movements ; nor 
 does it appear that the contact of air can take its place ; since, as Dr. J. Reid 
 has shown, the rhythmical contractions of the heart of a frog will continue 
 in vacua. Nor is there any evidence that the flow of blood through the 
 cavities has the effect of securing the regularity of their successive contrac- 
 tions in the living body ; for this regularity is equally marked in the contrac- 
 tions of the excised heart, when perfectly emptied of blood, so long as its 
 movements continue vigorous. But when its irritability is nearly exhausted, 
 the usual rhythm is often a good deal disturbed, so that the contractions of 
 the auricles and ventricles do not regularly alternate with each other ; and one 
 set frequently ceases before the other. 
 
 a. It was formerly supposed, that the movements of the Heart were dependent upon its 
 connection with the centres of the Cerebro-Spinal nervous system ; and the experiments of 
 Lcgallois and others, who found that they were arrested by crushing, or otherwise suddenly 
 destroying, large portions of these centres, appeared to favour the supposition. But it has 
 been shown by Dr. Wilson Philip and his successors in the same inquiry, that the whole 
 Cerebro-Spinal axis might be gradually removed, without any such consequence ; which 
 fact harmonizes perfectly with the "experiments prepared for us by Nature," in the pro- 
 duction of monsters destitute of these centres, which nevertheless possessed a regularly- 
 pulsating heart. As already mentioned ( 416), it is difficult to obtain any distinct evidence, 
 that the actions of the heart are affected by any ordinary irritation of the Par Vagum ; but 
 the recent experiments of MM. Weber have shown that its movements may be immediately 
 arrested, by the transmission of the electric current from a rotating magnet, either through 
 the Spinal Cord, or through the Vagi nerves divided at their origin. The same irritation, 
 however, applied to a single one of the Vagi, produced no effect.* 
 
 b. It has latterly been the fashion with many, however, to attribute the action of the Heart 
 to the Sympathetic system ; but of this there is no sufficient evidence. The possibility of 
 exciting the action of the heart through the Sympathetic nerve ( 576), shows that this may 
 have an influence on its movements; whilst the great difficulty with which any evidence 
 to this effect can be procured, seems a sufficient proof, as in the case of the Muscular coat of 
 the intestines ( 388), that this influence cannot be nearly adequate to the constant main- 
 tenance of a function so energetic. Some have more recently maintained, that the move- 
 ments are of a strictly reflex nature, and that they are effected through the agency of certain 
 minute ganglia, belonging to the Sympathetic system, and scattered through the substance of 
 the heart ; in this way endeavouring to account for the persistence of the motions of the 
 organ after its complete removal from the body, and under circumstances which suspend all 
 reflex movements that have their centre in the cerebro-spirial system. But this attempt at 
 explanation affords no aid in the solution of the cause of the continued rhythmical move- 
 ments of the organ, or of its separated portions, after the withdrawal of all stimuli that can 
 be supposed to operate in exciting them; and the phenomena are just as fully explained by 
 
 * Archives d'Anat. Gener. et de Physiol., Janv. 1846. 
 
548 OF THE CIRCULATION OF BLOOD. 
 
 attributing them to the independent irritability of the muscular fibre, as by supposing the 
 nervous system to be concerned in them. 
 
 c. It would appear, however, that changes in the Ganglionic nerves, like strong impres- 
 sions upon the Cerebro-spinal system ( 580), may have the effect of impeding or even 
 checking the Heart's action ; for a case has lately been recorded, in which the movements 
 were occasionally checked for an interval of from 4 to 6 beats, its cessation of action giving 
 rise to the most fearful sensations of anxiety, and to acute pain passing up to the head from 
 both sides of the chest, these symptoms being connected, as it proved on a post-mortem 
 examination, with the pressure of an enlarged bronchial gland upon the great cardiac nerve.* 
 It may be surmised, that in many cases of angina pectoris, in which no lesion sufficient to 
 account for death could be discovered, some affection of the cardiac plexus might have been 
 traced on a more careful examination. 
 
 718. When the Heart is exposed in a living animal, and its movements are 
 attentively watched, they are seen to follow each other with great regularity. 
 In an active and vigorous state of the circulation, however, they are so linked 
 together, that it is not easy to distinguish them into periods. A case has 
 fallen under the notice of Prof. Cruveilhier, in which the heart was exterior 
 to the chest, having escaped from it by a perforation in the superior part of 
 the sternum ; and his observations upon it may be perhaps regarded as more 
 satisfactory than such as are made after the very severe operation required for 
 the artificial exposure of the organ ; although they are liable to some excep- 
 tion, from the very early age of the subject of them, which had only been 
 born nine hours. His conclusions will be here adopted ; with such addi- 
 tional remarks as are suggested by the experimental researches of others, 
 who have made this question a subject of special attention.! It is universally 
 admitted, that both Auricles contract, and also dilate simultaneously ; and that 
 both Ventricles do the same : also that the systole or contraction of the ven- 
 tricles corresponds with the projection of blood into the arteries, causing the 
 pulse ; whilst the diastole or dilatation of the ventricles coincides with the 
 collapse of the arteries. It is further admitted, that the contraction of the 
 Ventricles, and that of the Auricles, alternate with one another ; each taking 
 place (for the most part, at least), during the dilatation of the other. But it 
 is a question whether there is any interval between them. In the case just 
 alluded to, the contraction of the Ventricles is stated to have been precisely 
 synchronous with the dilatation of the Auricles ; and the dilatation of the 
 Ventricles to have been performed at the same time with the contraction of 
 the Auricles, no period of repose intervening between the two sets of actions. 
 It appears, however, from the concurrent testimony of numerous experiment- 
 ers, that, whilst the contraction of the Ventricle immediately succeeds that of 
 the Auricle, an interval, which is usually, however, extremely brief, may elapse 
 between the partial dilatation of the Ventricles and the succeeding systole of 
 the Auricles. The Ventricular dyastole may be distinguished into two stages, 
 of which the first immediately succeeds its systole, and manifests itself in the 
 recession of the Heart's apex from the front of the chest ; whilst the second 
 is attended with an enlargement of the heart in all its dimensions, and is 
 synchronous with the Auricular contraction. It is between these two, that 
 the interval of repose occurs, where it can be observed. The following 
 tabular view will, perhaps, make this account more intelligible ; it is framed 
 in such a manner as to commence with the Auricular contraction ; but, when 
 considering the Sounds of the heart, it will be necessary to commence with 
 the Ventricular systole. 
 
 * Muller's Archiv. 1841, heft iii.; and Brit, and For. Med. Rev., Oct. 1841. 
 f- See also another case, recently observed by M. Monod, in Bullet, de 1'Acad. de Med., 
 Fevr. 1843 ; and Edinb. Med. and Surg. Journ., July 1843. 
 
ACTION OF THE HEART. 549 
 
 Auricles. Ventricles. 
 
 Contraction. 2d stage of dilatation. 
 
 Dilatation. Contraction. Pulse. 
 
 1st stage of dilatation. 
 Brief interval of Repose. 
 Contraction. 2d stage of dilatation. 
 
 Dilatation. Contraction. Pulse. 
 
 719. The duration of the Contraction of the Ventricles is, according to 
 Cruveilhier, double that of their Dilatation ; and the same holds good of the 
 Auricles. In the Systole of the Ventricles, their surface becomes rugous ; the 
 superficial veins swell ; the carneae columnar of the left ventricle are delineated ; 
 and the curved fibres of the conical termination of the left ventricle, which 
 alone constitutes the apex of the heart, become more manifest. During their 
 contraction, every diameter of the Ventricles is lessened ; their shortening is 
 the most sensible change ; but this is owing to the vertical diameter being the 
 greatest. The lower extremity of the left ventricle, or, in other words, the 
 apex of the heart, describes a spiral movement from right to left, and from be- 
 hind forwards. It is to this slow, gradual, and as it were successive spiral 
 contraction, that the forward movement of the apex of the heart is owing, and 
 its consequent percussion against the thoracic parietes. The ventricular sys- 
 tole is not accompanied by a projection of the entire heart forwards (as some 
 have maintained) ; for it is exclusively the spiral contraction, which determines 
 the approach of the apex of the heart to the thoracic parietes. The Diastole 
 of the heart, according to Cruveilhier, has the rapidity and energy of an active 
 movement: triumphing over pressure exercised upon the organ, so that the 
 hand closed upon it is opened with violence. This is an observation of great 
 importance ; but of the cause to which this active dilatation is due, no definite 
 account can be given. It may partly be explained, perhaps, by the elasticity 
 of the tissue, interwoven with muscular fibre in the substance of the heart; 
 and this may be the cause of the first Ventricular dilatation, the second being 
 produced by the ingress of blood occasioned by the auricular systole. But 
 the dilatation of the Auricles appears to be much greater than can be accounted 
 for by any vis a tergo (which, as will hereafter appear, is extremely small in 
 the venous system), or by the elasticity of its substance ; for it was observed 
 in this case to be so great, that the right auricle seemed ready to burst, so great 
 was its distension, and so thin were its walls. Moreover, the large Veins 
 near the heart contract simultaneously with the auricular Systole, and not with 
 its Diastole ; so that they can have no influence in causing its dilatation. The 
 Ventricular diastole is accompanied with a projection of the heart downwards ; 
 this motion was at its maximum when the child was placed vertically, and 
 was very strongly marked. 
 
 720. When the ear is applied over the cardiac region, during the natural 
 movements of the Heart, two successive sounds are heard; each pair of which 
 corresponds with one pulsation. The whole interval between one beat of the 
 the Heart, and the next, may be divided into four parts ; of which the two 
 first are occupied by what is commonly known as the first sound ; the third, 
 by the second sound ; whilst the fourth is a period of repose. The first sound 
 is dull and prolonged ; it is evidently synchronous with the impulse of the 
 Heart against the parietes of the chest, and also with the pulse, as felt near 
 the heart ; it must, therefore, be produced during the Ventricular Systole. 
 The second sound follows so immediately upon the conclusion of the first, 
 that it can scarcely be imagined to take place during the auricular systole as 
 some have supposed, but must be assigned to the period of the first stage of 
 the Ventricular Diastole. This, indeed, may now be regarded as clearly esta- 
 blished; for it has been fully demonstrated, that the second sound is due to 
 
550 OF THE CIRCULATION OF BLOOD. 
 
 the sudden filling-out of the Semilunar valves of the aorta and pulmonary 
 artery, with blood ; when the outward current through them has ceased, and 
 the incipient dilatation of the ventricles occasions a vacuum behind them. If 
 one of these valves be hooked back by a curved needle against the side of the 
 artery, so that a reflux of blood is permitted, the sound is entirely suppressed. 
 The first sound cannot be so readily or satisfactorily accounted for. That it 
 is partly due to the Impulse of the apex of the Heart, seems proved by the 
 fact, that, when this impulse is prevented, the sound is much diminished in 
 intensity ; and also by the circumstance that, when the Ventricles contract 
 with vigour, the greatest intensity of the sound is over the point of percussion. 
 But that it is not entirely due to this cause is also evident from the fact, that 
 a sound may still be heard, when the Heart is contracting out of the body; as 
 in the case observed by Prof. Cruveilhier. This sound has been attributed, 
 by some experimenters, to the flapping-back of the auriculo-ventricular valves ; 
 by others to the muscular contraction of the walls of the ventricles ; by others 
 again to the rush of blood along the irregular walls of the ventricles, and 
 through the comparatively narrow orifices of the aorta and pulmonary artery. 
 This last is probably the most consistent with truth ; as would appear from 
 the following interesting observations made by Cruveilhier. By applying the 
 finger to the origin of the pulmonary artery (which is situated in front of the 
 aorta, and completely conceals it), a perfectly distinct vibratory fremissement 
 corresponding with the ventricular diastole, was perceived; but no such vibra- 
 tory thrill could be felt by the finger, when applied to any part of the base of 
 the ventricles : whence it was evident, that no action takes place in the mitral 
 and tricuspid valves, which can give rise to the same palpable effects, as those 
 produced by the semilunar valves. The same was ascertained regarding the 
 valvular sound, which could be distinctly heard, by laying the finger against 
 the origin of the pulmonary artery, and applying the ear to it as to a stetho- 
 scope : whilst nothing of the kind could be perceived in the region of the 
 auriculo-ventricular valves. Hence it seems quite certain, that the natural first 
 sound cannot be dependent in any way upon the action of the mitral and tri- 
 cuspid valves. It appeared, on the contrary, that the maximum intensity of 
 ihe first sound was in precisely the same situation as the maximum intensity 
 of the second, namely, at the origin of the large arteries ; and that it dimin- 
 ished, as the ear was carried from the base, towards the apex of the heart. 
 Moreover, the first sound was observed to be of exactly the same character 
 with the second (the complicating effect of the impulse being here withdrawn) ; 
 except as to its intensity, which was less, and its duration, which was greater. 
 721. Hence, although these observations do not entitle us to deny the par- 
 ticipation of the muscular contraction, and of the movement of the blood over 
 the ventricular walls, in the production of the first sound, they establish (if 
 correct), that the principal cause of it exists at the entrances to the arterial 
 trunks ; and it does not seem that any other reason can be assigned for it, than 
 the prolonged rush of blood through their orifices, and the throwing back of the 
 Semilunar valves ; which, in suddenly flapping down again, produce the second 
 sound. That an exaggeration of the first sound, not essentially differing from 
 it in character, is often produced by disease of the sigmoid valves, which 
 causes an obstruction of their orifice, has long been known ; and in such 
 cases, the character of the second sound is also changed. Indeed, M. Cru- 
 veilhier states it as, in his opinion, an uniform occurrence, that disease of the 
 Semilunar valves alters both sounds. When this disease is such as to prevent 
 the valves from effectually closing, a reflux of blood takes place into the ven- 
 tricle at the time of its diastole; causing a rushing sound, more or less pro- 
 longed, to be heard in the intervals of the pulse, instead of with it. These 
 considerations appear to prove almost incontestably, that the cause of the first 
 
ACTION OF THE HEART. 
 
 551 
 
 sound, and that of the second, are very closely allied ; and this view, which if 
 correct is of great importance in the explanation of numerous morbid phe- 
 nomena, harmonizes well with the known effect of a slight obstruction in a 
 tube, through which fluid is being rapidly forced, in producing a prolonged 
 sound, very analogous to the first sound of the heart. The following table 
 may assist the student in connecting the sounds of the Heart with its move- 
 ments. 
 
 FIRST SOUWD. Ventricular Systole, and Auricular Diastole. Impulse of apex against 
 
 parietes of chest. Pulsation in arteries. 
 SECOND SOUND. First stage of Ventricular Diastole. 
 INTERVAL Short repose ; then Auricular Systole, and second stage of Ventricular 
 
 Diastole. 
 
 722. The course of the circulating fluid through the Heart, and the action 
 of its different valves, will now be briefly described. The Venous blood, 
 which is returned by the ascending and descending Vepa Cava, enters the 
 right Auricle during its diastole ; and, when it contracts, is forced between 
 the Tricuspid valves, into the Ventricle. The reflux of blood into the veins, 
 during the auricular systole, is prevented by the valves with which they are 
 furnished ; but these valves are so formed, as not to close accurately, espe- 
 
 [Fig. 212. 
 
 The Anatomy of the Heart; 1, the right auricle; 2, the entrance of the superior venacava; 3, the 
 entrance of the inferior cava ; 4, the opening of the coronary vein, half closed by the coronary valve ; 
 5, the Eustachian valve ; 6, the fossa ovalis, surrounded by the annulis ovalis ; 7, the tuberculum Low- 
 eri ; 8, the musculi pectinati in the appendix auriculae; 9, the auriculo-ventricular opening; 10, the 
 cavity of the right ventricle; 11, the tricuspid valve, attached by the chordae tendinece to the carneae 
 columnse (12); 13, the pulmonary artery, guarded at its commencement by three semilunar valves; 14, 
 the right pulmonary artery, passing beneath the arch and behind the ascending aorta; 15, the left pulmo- 
 nary artery, crossing in front of the descending aorta; *, the remains of the ductus arteriosus, acting as 
 a ligament between the pulmonary artery and arch of the aorta; the arrows mark the course of the 
 venous blood through the right side of the heart; entering the auricle by the superior and inferior cava, 
 it passes through the auriculo-ventricular opening into the ventricle, and thence through the pulmonary 
 artery to the lungs ; 16, the left auricle ; 17, the openings of the four pulmonary veins ; 18, the auriculo- 
 ventricular opening ; 19, the left ventricle ; 20, the mitral valve, attached by its chordae tendineae to two 
 large columnse carneee, which project from the walls of the ventricle ; 21, the commencement and course 
 of the ascending aorta behind the pulmonary artery, marked by an arrow; the entrance of the vessel 
 is guarded by three semilunar valves ; 22, the arch of the aorta. The comparative thickness of ihe two 
 ventricles is shown in the diagram. The course of the arterial blood through the left side of the heart 
 is marked by arrows. The blood is brought from the lungs by the four pulmonary veins into the left 
 auricle, and passes through the auriculo-ventricular opening into the left ventricle, whence it is con- 
 veyed by the aorta to every part of the body.] 
 
552 OF THE CIRCULATION OF BLOOD. 
 
 cially, when the tubes are distended ; so that a small amount of reflux usually 
 takes place, and this is much increased when there is any obstruction to the 
 pulmonary circulation. Whilst the right Ventricle is contracting upon the 
 blood that has entered it, the carnese columns, which contract simultaneously 
 with its proper walls, put the chordae tendinese upon the stretch ; and these 
 draw the flaps of the Tricuspid valve into the auriculo-ventricular axis. The 
 blood then getting behind them, and being compressed by the contraction of 
 the ventricle, forces the flaps together in such a manner as to close the orifice ; 
 but they do not fall suddenly against each other, as is the case with the semi- 
 lunar valves, since they are restrained by the chordae tendine.se. ; whence it is, 
 that no sound is produced by their closure. The blood is expelled by the 
 ventricular systole into the Pulmonary Artery, which it distends, passing 
 freely through the Semilunar valves ; but as soon as the vis d tergo ceases, 
 and reflux might take place by the contraction of the arterial walls, the valves 
 are filled out by the backward tendency of the blood, and completely check 
 the return of any portion of it into the ventricle. The blood, after having cir- 
 culated through the lungs, returns as Arterial blood, by the Pulmonary Veins, 
 to the left Auricle ; whence it passes through the mitral valves into the left 
 Ventricle, and thence into the Aorta, in the same manner with that on the 
 other side, as just described. 
 
 723. There are, however, some important differences in the structure and 
 functional actions of the two divisions of the Heart, which should be here 
 adverted to. 
 
 a. The walls of the left Ventricle are considerably thicker than those of the right; and 
 its force of contraction is much greater. The following are the comparative results of M. 
 Bizot's recent measurements, taking the average of males from 16 to 89 years. 
 
 BASE. MIDDLE. APEX. 
 
 Left Ventricle 4 lines 5 lines 3| lines 
 
 Right Ventricle Ijf lines 1| lines 1^ lines 
 
 In the female, the average thickness is somewhat less. It will be seen that the point of 
 greatest thickness in the left Ventricle is near its middle ; while in the right, it is nearer the 
 base. The thickness of the former goes on increasing during all periods of life, from youth 
 to advanced age ; whilst that of the right is nearly stationary. The left Auricle is somewhat 
 thicker than the right ; the average thickness of the former being, according to Bouillaud, 
 a Jine and a half; whilst that of the latter is only a line. In regard to the refttive capaci- 
 ties of the right and left cavities, much difference of opinion has prevailed. The right Au- 
 ricle is generally allowed to be more capacious than the left ; and the same is commonly- 
 taught of the right Ventricle. So much fallacy may arise, however, from the peculiar condi- 
 tion of the animal at the moment of death, that this is not easily proved, and is, indeed, by 
 no means certain. 
 
 b. Many eminent Anatomists maintain, that the two cavities are equal. The capacity of 
 each of the cavities may be estimated, in the full-sized Heart, at about two ounces ; that of 
 the Auricles being probably a little less ; and that of the Ventricles a little greater. That 
 the Ventricles receive more blood from the Auricles, than the latter could transmit to them 
 by simply emptying themselves once, seems, therefore, probable ; and may be accounted for 
 by the fact already stated, regarding the slight intermission in the Ventricular Diastole, during 
 which more blood may enter the Auricle from the veins. 
 
 c. There is a well-known anatomical difference between the Auriculo- Ventricular valves, 
 on the two sides, which has given rise to the diversity of name. This seems, from the re- 
 searches of Mr. King,* to be connected with an important functional difference. The Mitral 
 valve closes much more perfectly than the Tricuspid : and the latter is so constructed, as to 
 allow of considerable reflux, when the cavities are greatly distended. Many occasional 
 causes tend to produce an accumulation of blood in the venous system, and in the right side 
 of the Heart; thus, any obstruction to the pulmonary circulation, cold, compression of the 
 venous system by muscular action. &c., are known to favour such a condition. This is a 
 state of peculiar danger, from the liability which over-distension of the Ventricular cavity 
 has, to produce a state of muscular paralysis ; and in the structure of the Heart itself, there 
 seems to be a provision against it. For, when the ventricle is thus distended, the Tricuspid 
 
 * Guy's Hospital Reports, vol. ii. 
 
ACTION OF THE HEART. 553 
 
 valves do not close properly; and a reflux of blood is permitted, not only into the Auricle, 
 but also (through the imperfect closure of their valves under the same circumstances), into 
 the large veins. This is proved by the fact, several times observed by Dr. J. Reid, in his 
 experiments upon Asphyxia, &c., that, when the action of the Right Ventricle had ceased 
 from over-distension, he could frequently re-excite it, not merely by puncturing its walls, but 
 by making an opening in the jugular vein. This fact evidently affords an indication of great 
 importance in the treatment of Asphyxia ; and it explains the reflux of blood, or venous 
 pulse, which is frequently observed in cases of pulmonary disease, and which, according to 
 Mr. King, always exists, though in a less striking degree. 
 
 724. It is not quite certain whether the Ventricles empty themselves com- 
 pletely .at each contraction ; but it seems probable that the blood which they 
 contain, is not entirely forced into the arteries. The quantity which is pro- 
 pelled by each Ventricle, at every stroke, maybe estimated, therefore, at from 
 l oz. to 2 oz. If we adopt the lower of these numbers, we shall find that, 
 reckoning 75 pulsations of the Heart to a minute, 112 oz., or 7 Ibs., of blood 
 pass through each ventricle in that time; and, on the higher estimate, 150 
 oz., or 9 Ibs. 6 oz., would pass through in the same period. Now the whole 
 quantity of blood contained in the human body, according to the estimate of 
 Haller (which is considered by Dr. Allen Thomson to be near the truth), is 
 about one-fifth of the weight of the body, or 28 Ibs. in a person weighing 
 140 Ibs.* This quantity would pass through the Heart, therefore, in four 
 minutes, on the lower of the two preceding estimates, or in three minutes on 
 the higher; and would circulate afresh, fifteen or twenty times in an hour. It 
 would appear, however, that this estimate of the rapidity of the circulation is 
 very far from the truth ; for recent experiments have shown, that substances 
 introduced into the Venous circulation, may be detected in the remotest parts 
 of the Arterial circulation, even in animals larger than Man, in less than half' 
 a minute. The earliest of such experiments were those of Hering,t who en- 
 deavoured to ascertain the rapidity of the circulation, by introducing Prussiate 
 of Potash into one part of the system, and drawing blood from another. He 
 states that he detected this salt, in blood drawn from one of the Jugular veins 
 of the Horse, within 20 or 30 seconds after it had been introduced into the 
 other ; in which brief space the blood must have been received by the Heart, 
 must have been transmitted through the Lungs, have returned to the Heart 
 again, have been sent through the Carotid artery, and have traversed its ca- 
 pillaries. From experiments of a similar nature upon other veins, he states 
 that the salt passed from the Jugular vein into the Saphena in 20 seconds ; 
 into the Masseteric artery in from 15 to 20 seconds ; into the External Max- 
 illary artery in from 10 to 25 seconds ; and into the Metatarsal artery in from 
 20 to 40 seconds. An attempt has been made to invalidate the inference 
 which seems inevitably to flow from these experiments, in regard to the rate 
 of the circulation, by attributing the transmission of the salt to the permea- 
 bility of the animal tissues ;J but it has never been shown, that even Prussiate 
 of Potash (which is probably more transmissible through this channel than 
 any other salt), can be carried from one part to another, with a rapidity at all 
 proportional to this. The only mode in which this property can be con- 
 ceived materially to facilitate the transmission of the salt through the vascular 
 system, would be by allowing it to pass through the septum of the auricles, 
 and thus to make its way from the right to the left side of the heart, without 
 passing through the pulmonary circulation ; and this it could scarcely do, to 
 the large amount which is evidently transmitted, in so short a time. 
 
 725. The experiments of Hering have been recently fully confirmed by 
 
 * Valentin's estimate, founded upon different data, closely corresponds with this, 
 t Tiedemann's Zeitschrift, vol. iii. p. 85. 
 j See Dr. Allen Thomson, loc. tit. 
 
 47 
 
554 OF THE CIRCULATION OF BLOOD. 
 
 those of Mr. Blake;* who varied them by employing different substances, 
 and took other precautions against sources of fallacy. Ten seconds after 
 having injected a solution of Nitrate of Baryta into the Jugular vein Of ahorse, 
 he drew blood from the Carotid artery of the opposite side ; after allowing 
 this to flow for five seconds, he substituted another vessel, which received the 
 blood that flowed during the five ensuing seconds ; and the blood that flowed 
 after the twentieth second, by which time the action of the Heart had stopped, 
 was received into a third vessel. These different specimens were carefully 
 analyzed. No trace of Baryta could be detected in the blood, which had 
 escaped from the artery between the tenth and fifteenth second after the in- 
 jection of the poison ; but in that which was drawn between the fifteenth and 
 the twentieth second, the salt was found to be present, and in greater abun- 
 dance than in the blood which had subsequently flowed. Moreover, the 
 coincidence between the cessation of the Heart's action, and the diffusion of 
 the salt through the arterial blood, bear a striking correspondence ; and it may 
 be hence inferred, that the arrestment of its muscular movement is due to the 
 effect of this agent upon its tissue, when immediately operating upon it, 
 through the capillaries of the coronary artery. This conclusion is borne out 
 by a variety of other experiments ; which show that the time of the agency 
 of other poisons, that suddenly check the Heart's action (which is the espe- 
 cial property of mineral poisons), nearly coincides, in different animals, with 
 that which is required to convey them into the Arterial capillaries. And it 
 seems to derive full confirmation from the fact, that poisons, which act locally 
 on other parts, give the first indications of their operation, in the same period 
 after they have been introduced into the Venous circulation. Thus, in the 
 Horse, the time that is required for the blood to pass from the Jugular vein 
 into the capillary terminations of the Coronary arteries, is 16 seconds ; as is 
 shown by the power of Nitrate of Potass to arrest the Heart's action within 
 that time : and Nitrate of Strychnia, injected into a vein, gave the first mani- 
 festation of its action on the Spinal Cord, in precisely the same number of 
 seconds. In the Dog, the Heart's action was arrested by the Nitrate of Potass 
 in 11 or 12 seconds; and the tetanic convulsions occasioned by Strychnia, 
 also commenced in 12 seconds. In the Fowl, the former period was 6 
 seconds, and the latter 65 ; in the Rabbit, the first was 4, and the other 4 
 seconds. From these experiments, it seems difficult to resist the conclusion, 
 that the rapidity of the Circulation is very much underrated, in any estimate 
 that we found upon the capacity of the Heart, and its number of pulsations in 
 a given time ; and that some other force, than its contractions, must have a 
 share in producing the movement of the blood through the vessels. 
 
 726. The force with which the Heart propels the Blood, may be estimated 
 in two ways; either by ascertaining the height of the column of that fluid, 
 which its contractile action will support ; or by causing the blood to act 
 upon a shorter column of mercury. The former method was the one adopted 
 by Hales, who introduced a long pipe into the Carotid artery of a Horse, and 
 found that the blood would sometimes rise in it to the height of 10 feet. From 
 parallel experiments upon Sheep, Oxen, Dogs, and other animals, and by 
 comparing the calibre of their respective vessels with that of the Human aorta, 
 Hales concluded, that the usual force of the Heart in Man would sustain a 
 column of blood 7 feet high, the weight of which would be about 4 Ibs. 6 
 oz. The second method is that more recently adopted by Poisseuille ; and 
 the instrument which he contrived for carrying it into practice (termed by him 
 the Haemadynamometer) has been the means of aiding many valuable inqui- 
 ries on the physiology of the Circulation. The result of his experiments is 
 
 * Edinb. Med. and Surg. Journal, Oct. 1841. 
 
ACTION OF THE HEART. 
 
 555 
 
 very nearly the same as that of Hales ; his estimate of the force, with which 
 the blood is propelled into the Aorta, being 4 
 
 Ibs. 3 oz. The backward pressure upon the 
 walls of the Heart, or in other words the 
 force which they have to overcome in pro- 
 pelling the blood, is properly estimated, by 
 multiplying the pressure of blood in the aorta, 
 into the surface of a plane passing through 
 the base and apex of the left ventricle ; by 
 which calculation it is found to be about 13 
 Ibs.* The pressure appears, from the experi- 
 ments of Poisseuille, to be very nearly equal 
 for equal surfaces, throughout the larger arte- 
 rial branches ; since it diminishes regularly 
 in proportion to their calibre; in the radial 
 artery at the wrist, it was estimated by him 
 at 4 drachms. 
 
 727. The number of contractions of the 
 Heart in a given time, is liable to great varia- 
 tion, within the limits of ordinary health, 
 from several causes ; the chief of these are, 
 diversities of Age, of Sex, of Muscular exer- 
 tion, of the condition of the Mind, of the state 
 of the Digestive system, and of the Period of 
 the day. 
 
 a. Putting aside the other causes of uncertainty, the 
 following table may be regarded as an approximation 
 to the average frequency of the Pulse, at the several 
 ages specified in it. 
 
 [Fig. 213. 
 
 In the foetus in utero 
 Newly -born infant 
 During the First year 
 During the Second year 
 During the Third year , 
 About the Seventh year 
 Age of Puberty 
 Manhood . 
 
 BEATS PER MINUTE. 
 
 . 140 150 
 
 . . 130 140 
 
 . 115130 
 
 . . 100 115 
 
 90 100 
 
 . ' . 8590 
 
 80 85 
 
 . . 7080 
 
 50 65 
 
 Hsemadynamometer of Poisseuille. A 
 bent glass tube, filled with mercury in 
 the lower part, a d e. The horizontal 
 part 6, is provided with a brass head, 
 which fits into the artery. A small 
 quantity of a solution of the carbonate 
 of soda is interposed between the mer- 
 cury and the blood, to prevent its coagu- 
 lation. When the blood presses on the 
 fluid in the horizontal limb, the rise of 
 the mercury towards e, measured from 
 the level to which it has fallen towards 
 a, gives the pressure under which the 
 blood moves.] 
 
 Old age .... 
 
 b. The difference caused by sex is very considerable, 
 especially in adult age; it appears from the inquiries 
 of Dr. Guy,t that the pulse of the adult Female ex- 
 ceeds in frequency the pulse of the adult Male, at the 
 same mean age, by from 10 to 14 beats in a minute. 
 
 c. The effect of muscular exertion in raising the pulse is well known ; as is also the fact, 
 which is one exemplification of it, that the pulse varies considerably with the posture of the 
 body. The amount of this variation has been made the subject of extensive inquiry by Dr. 
 Guy ; and the following are his results. In 100 healthy Males, of the mean age of 27 years, 
 in a state of rest, the average frequency of the pulse was, when standing, 79, when sitting, 
 70, and when lying, 67 per minute. Several exceptions occurred, however, to the general 
 law; and when these were excluded, the average numbers were, standing, 81, sitting, 
 71, and lying', 66; so that the difference between standing and sitting was 10 beats, or 
 l-8th of the whole; the difference between sitting and lying was 5 beats, or 1-1 3th of the 
 whole; and the difference between standing and lying was 15 beats, or l-5th of the whole. 
 In 50 healthy Females, of the same mean age, the average pulse, when standing, was 89, 
 
 * The extreme latitude of the estimates which have been made of this force, has been a 
 subject of not undeserved ridicule. Borelli imagined it to be 180,000 Ibs.; whilst by Keill it 
 was supposed to be no more than from 5 to 8 ounces. 
 
 f Guy's Hospital Reports, vol. iii. p. 312. 
 
556 OF THE CIRCULATION OF BLOOD. 
 
 when sitting, 81, and when lying, 80. When the exceptions (which were more numerous 
 in proportion than in males) were excluded, the averages were, standing, 91, sitting, 84, 
 lying, 79; the difference between standing and sitting was thus 7 beats, or 1-1 3th of the 
 whole; that between sitting and lying was 4, or 1-2 1st of the whole; and that between 
 standing and lying was 11, or 1 -8th of the whole. In both sexes, the effect produced by 
 change of posture increases with the usual frequency of the pulse; whilst the exceptions to 
 the general rule are more numerous, as the pulse is less frequent. The variation is tem- 
 porarily increased by the muscular effort, involved in the absolute change of the posture ; 
 and it is only by the use of a revolving board, by which the position of the body can be 
 altered, without any exertion on the part of the subject of the observation, that correct results 
 can be obtained. That the difference between standing and sitting should be greater than 
 that between sitting and lying, is just what we should expect ; when we compare the 
 amount of muscular effort required in the maintenance of the two former positions respect- 
 ively. 
 
 d. The Pulse is well known to be much accelerated by Mental excitement, especially by 
 that of the Emotions; it is also quicker during Digestion; but on neither of these points can 
 any exact numerical statement be given. 
 
 e. The diurnal variation of the pulse, however, has been made the subject of observation 
 by Dr. Guy ;* and, as the results of his inquiries have much interest, although (from having 
 been made only on his own person) they may ultimately require some modification, they 
 will be here stated. " 1 . The pulse of a healthy male in a state of rest, unexcited either by 
 food or exercise, is most frequent in the morning, and gradually diminishes as the day ad- 
 vances. 2. The pulse diminishes in frequency more rapidly in the evening, than in the 
 morning. 3. The diminution in the frequency of the pulse (after excitement) is more regu- 
 lar and progressive in the evening than in the morning. 4. The effect of food is greater 
 and more lasting in the morning, than in the evening ; and in some instances, the same food, 
 which in the morning produces an effect considerable both in amount and duration, has no 
 effect whatever in the evening." It may be hoped that, ere long, this interesting and im- 
 portant subject will receive further elucidation. 
 
 [/. Dr. Valleix has recently published a series of interesting observations on the fre- 
 quency of the pulse in newly-born infants, and in children aged from seven months to six 
 years. He obtained the following results: 1. At birth the pulse is less frequent than at six 
 months; the number of beats in a minute may be stated with considerable exactness to be 
 between 90 and 100. 2. Increase of temperature, even in the slightest degree, invariably 
 produces a notable acceleration of the pulse. The exact ratio between the degree of eleva- 
 tion of temperature and the increase in the frequency of the pulse, is not yet accurately 
 ascertained. 3. Although the observations of Dr. Valleix show a progressive diurnal diminu- 
 tion in the frequency of the pulse, still, he thinks, it would be premature to conclude that 
 these facts support those of Dr. Guy. Dr. Valleix examined his patients in the morning 
 after they had been eating, and to this fact, he thinks, should be attributed the acceleration 
 of the pulse in the early part of the day, and its subsequent diminution towards evening. 
 4. The slightest muscular effort in children is sufficient to augment considerably the number 
 of pulsations. The same is true of any moral emotion. 5. The influence of sex on the 
 pulse is very marked in young children. The pulse is much more frequent in young girls 
 than in boys of the same age. 6. During sleep there is a decided diminution in the number 
 of beats. 7. Between 7 and 27 months there is no sensible change in the frequency of the 
 pulse. Its mean may be stated at 126 beats in the minute, without distinction of sex. If 
 sex be considered, it would be 121 for males and 128 for females. These numbers express 
 the frequency of the pulse at this age under ordinary circumstances, but if a state of perfect 
 calm is supposed, the numbers would be 119 for the males, and 124 for females. 8. After 
 some observations, not very numerous, however, the pulse would appear to range a little 
 above 100 till six years of age. 9. The mean number of inspirations in a minute in chil- 
 dren aged from 7 months to two years and a half, is between 30 and 32, and is to number 
 of pulsations : : 1 : 4. M. C.J 
 
 3. Movement of the Blood in the Arteries and Capillaries. 
 
 728. We have next to consider the influence of the Arterial tubes on the 
 flow of Blood through them. This influence is exerted by the middle or 
 fibrous coat, which alone is possessed of contractile properties. We find in 
 this coat, a layer of annular fibres, possessing no small resemblance to that 
 of which the muscular coat of the alimentary canal is composed. On the out- 
 
 * Op. cit, vol. iv. p. 69. 
 
MOTION OF THE BLOOD IN THE ARTERIES. 557 
 
 side of this, is a layer of yellow elastic tissue, which is much thicker in the 
 larger arteries, in proportion to their size, than in the smaller. To this last 
 tissue is due the simple elasticity of the arterial walls, which is a physical 
 property that persists after death, until a serious change takes place in their 
 composition : whilst to the one first mentioned, we are to attribute the property 
 which they unquestionably possess in common with proper muscular tissue, 
 of contracting on the application of a stimulus, so long as their vitality re- 
 mains. These two endowments exist, in various proportional degrees, in the 
 different parts of the Arterial system. Thus it was justly remarked by Hun- 
 ter, that elasticity, being the property by which the interrupted force of the 
 Heart is made equable and continuous, is most seen in the large vessels more 
 immediately connected with that organ. On the other hand, the contractility 
 is most observable in the smaller vessels, where it is more required for regu- 
 lating the flow of blood towards particular organs. 
 
 729. It is easily shown that the action of the Elasticity of the Arterial 
 tubes, is one of a purely physical character; and that its purpose is to con- 
 vert the intermitting impulses, which the fluid receives from the heart, into a 
 continuous current. The former are very evident in the larger trunks ; but 
 they diminish with the subdivision of these, until they entirely disappear in 
 the capillaries, in which the stream is usually equable or nearly so. We may 
 imagine a powerful forcing-pump injecting water, by successive strokes, into 
 a system of tubes with unyielding walls ; the flow of fluid at the farther ex- 
 tremities of these tubes, would be as much interrupted as its entrance into 
 them. But if an air-vessel (like that of a fire-engine) were placed at their 
 commencement, the flow would be in a great degree equalized; since a part 
 of the force of each stroke would be spent upon the compression of the air 
 included in it; and this force would be restored by the elasticity of the air, 
 during the interval, which would propel the stream, until directly renewed by 
 the next impulse. A much closer imitation of the natural apparatus would 
 be afforded, by a pipe which had elastic walls of its own ; if water were 
 forced by a syringe into a long tube of caoutchouc, for example, the stream 
 would be equalized before it had proceeded far. This effect is found to be 
 accomplished, at any point of the Arterial circulation, in a degree proportionate 
 to its distance from the Heart; and it is another effect of the same cause, that 
 the pressure of the blood upon the wall of the arteries (as shown by the ex- 
 periments of Poisseuille) is nearly the same all over the system. It is to the 
 distension of the arterial tubes, both in their length and calibre, that their 
 pulsation is due. Their elongation is the more considerable of the two effects ; 
 and it causes the artery to be lifted from its seat and to become curved. The 
 transverse dilatation has been denied by some physiologists ; but it has been 
 recently proved to take place, by an ingenious experiment of Poisseuille's. 
 The increase of capacity, however, is not more than l-10th ; so that the in- 
 crease of diameter will not be so much as l-20th, a quantity scarcely per- 
 ceptible to ordinary measurement. The transmission of the pulse-wave 
 through the whole system is not instantaneous, but takes place in an appre- 
 ciable time. The pulsation of the large arteries near the Heart, is synchron- 
 ous with the Ventricular systole ; but that of other arteries is somewhat later, 
 the difference varying with their distance, and amounting in some instances 
 to between l-6th and l-7th of a second. 
 
 730. It has been denied by many Physiologists, that the middle coat of the 
 Arteries possesses any property which can be likened to Muscular Contrac- 
 tility; and it will therefore be desirable to enter somewhat in detail into the 
 question. That it cannot be readily stimulated to contraction, through the 
 medium of its nerves, is universally admitted ; but the same is the case in 
 regard to the Muscular coat of the alimentary canal, which contracts most 
 
 47* 
 
558 OF THE CIRCULATION OF BLOOD. 
 
 vigorously on the direct application of stimuli to itself; and Valentin and 
 others have recently succeeded in producing evident contractions in the Aorta, 
 by irritation of the Sympathetic nerve, and of certain roots of the Spinal 
 nerves. Further, although many experiments have failed in producing con- 
 tractions of this tissue, by stimuli directly applied to itself, yet others have 
 distinctly witnessed them; and, in any question of this kind, the positive 
 evidence must be held to outweigh the negative. Thus Verschuir states, that 
 he has seen arteries contract, when stimulated by the mineral acids, by elec- 
 tricity, and by the application of the point of a scalpel. Dr. Thomson also 
 saw them contract, on the application of ammonia, and when punctured with 
 the point of a fine needle, in the living body. It has been ascertained by the 
 direct and careful experiments of Poisseuille, that, when the artery is dilated 
 by the blood injected into it from the heart, it reacts with a force superior to 
 the impressing impulse ; and he has also shown that, if a portion of an artery 
 from an animal recently dead (in which the vital contractility seems to be 
 preserved), and one from an animal that has been dead some days (in which 
 nothing but the elasticity remains), be distended with an equal force, the for- 
 mer becomes much more contracted than the latter, after the distending force 
 is removed. 
 
 731. Several experiments also indicate the existence of that power of slow 
 contraction in the arteries, which has been distinguished by the appellation 
 Tonicity ; but which does not seem anything else than a particular manifesta- 
 tion of the general property of vital contractility, and is certainly of a nature 
 quite distinct from ordinary elasticity. Thus, when a ligature is placed upon 
 an artery in a living animal, the part of the artery beyond the ligature becomes 
 gradually smaller, and is emptied to a certain degree, if not completely, of the 
 blood it contained. Again, when part of an artery in a living animal is isolated 
 by means of two ligatures, and is punctured, the blood issues from the orifice, 
 and the inclosed portion of the artery is almost completely emptied of its 
 contents. The exposure of arteries to the air was found by Hunter to occa- 
 sion their contraction, to such an extent, that obliteration of their tube was 
 the result ; and this statement has been subsequently confirmed. Further, 
 every Surgeon knows, that the contraction of divided arteries is an efficient 
 means of the arrest of hemorrhage from them, especially when they are of 
 small calibre ; so that, in the case of the temporal artery, for example, the 
 complete division of the tube is often the readiest means of checking the flow 
 of blood from it, when it has been once wounded. This contraction is much 
 greater than could be accounted for by the simple elasticity of the tissue ; and 
 is more decided in small, than in large vessels. The empty condition of the 
 arteries, generally found within a short time after death, seems to be in part 
 due to the same cause ; since their calibre is usually much diminished, and is 
 sometimes completely obliterated. A remarkable example of the same slow 
 contraction, is that which takes place in the end of the upper portion of an 
 arterial trunk, when the passage of blood through it is interrupted by a liga- 
 ture ; for the current of blood then passes off by the nearest large lateral 
 branch ; and the tube of the artery shrivels, and soon becomes impervious, 
 from the point at which the ligature is applied, back to the origin of that 
 branch. This last fact is important, as proving how little influence the vis a 
 tergo possesses over the calibre of arterial tubes ; since, without any interrup- 
 tion to the pressure of blood occasioned by it, the tube becomes impervious. 
 It is to the moderate action of the Tonicity of arteries, that their contraction 
 upon the stream of blood passing through them (which serves to keep the 
 tubes always full) is due. If the tonicity be excessive, the pulse is hard and 
 wiry ; but if it be deficient, the pulse is very compressible, though bounding, 
 and the flow of blood through the arteries is retarded. Dr. Williams has 
 
MOTION OF THE BLOOD IN THE ARTERIES. 559 
 
 performed some ingenious experiments, which prove that the force required 
 to propel fluid through a tube, whose sides are yielding, is very much greater 
 than that which will carry it through a tube of even smaller size, with rigid 
 parietes ; consequently, a loss of tonicity in the blood-vessels retards the flow 
 of blood through them ; whilst an increase hastens it. The Tonicity of the 
 arteries differs from their ordinary Contractility, in being augmented by cold, 
 and diminished by warmth. Hence cold and heat are two most valuable 
 remedial agents, when this property is deficient or in excess. 
 
 732. It is still to be inquired, in what manner the Contractility of the Arte- 
 ries is to be regarded as influencing the flow of Blood through them. It is at 
 once evident, that any general contraction of the arterial tubes would have 
 rather the effect of opposing, than of assisting the flow ; but if the fibrous 
 coat of the Arteries is in some degree disposed to the alternate contraction and 
 relaxation, which are so remarkable in the Heart, they may exert a force which 
 shall be supplementary to that of the Heart's impulse, relaxing to receive 
 the blood from it, and contracting upon their contents, with a power superior 
 to that by which they were distended. It is difficult to say whether or not 
 this be the case ; though there would certainly appear some evidence in favour 
 of the supposition. The loss of the Heart's power over the currents of blood, 
 in proportion to their degree of subdivision, occasioned by the increased fric- 
 tion to which they will be subjected, would seem to require some compensat- 
 ing power, in order that the perfect equality of pressure may be obtained 
 which has been spoken of as existing in all parts of the arterial system. In 
 no other way than this can the fibrous coat of the Arteries be regarded as 
 having any propulsive power over their contents ; except by a peristaltic or 
 vermicular movement, resembling that which takes place in the alimentary 
 canal ; and of such there is no evidence whatever. A very important use 
 may be assigned to this muscular coat, which has been generally overlooked 
 by Physiologists, that of regulating the diameter of the tubes, in accord- 
 ance with the quantity of blood to be conducted through them to any part ; 
 which will depend upon its peculiar circumstances at the time. Such local 
 changes are continually to be observed, in the various phases of normal life, 
 as well as in diseased states ; and they will be found to be constantly in har- 
 mony with the particular condition of the processes of Nutrition, Secretion, 
 &c., to which the Capillary circulation ministers. Of this kind are the en- 
 largement of the trunks of the Uterine and Mammary arteries, at the epochs 
 of pregnancy and lactation ; the enlargement and strongly-increased pulsa- 
 tion of the Radial artery, when there is any active inflammation in the thumb ; 
 the enormous diameter which the Spermatic artery will attain, when the 
 testicle is greatly increased in size by diseased action ; and many other simi- 
 lar phenomena. In such cases, it cannot be the action of the Heart that in- 
 creases the calibre of the vessels ; since this is commonly unaltered, and is 
 itself unable, as we have just seen, even to maintain their permeability. It 
 must, therefore, be by a power inherent in themselves, that their dilatation is 
 effected. The minute distribution of the Sympathetic nerve upon the walls 
 of the arteries, the known power which this has of producing contractions, 
 alike in their fibrous coat, and in the muscular tunic of the intestinal canal, 
 and various phenomena, which indicate the power of certain states of mind 
 over the dimensions of the arteries, in particular parts of the body at least, 
 render it highly probable that the calibre of the arteries is regulated in no in- 
 considerable degree through its intervention.* The permanent dilatation, 
 however, which is seen in the arteries supplying parts that are undergoing 
 
 * For Anatomical evidence to this effect, see Henle on the Contractility of the Blood- 
 vessels, in Casper's Wochenschrift, May 1840, and Brit, and For. Med. Rev., vol. x. p. 551. 
 
560 OF THE CIRCULATION OF BLOOD. 
 
 enlargement, must be due, not to simple dilatation merely, but to increased 
 nutrition ; since we find that their walls are thickened as well as extended. 
 And, on the other side, when slow contraction occurs in these tubes, as a 
 consequence of disease, it must be in part occasioned by atrophy; since 
 their nutrition is so much diminished, that in time they almost entirely disap- 
 pear, a portion of a large artery occasionally shriveling into a ligamentous 
 band. 
 
 733. We now come to the last head of the inquiry into the powers which 
 convey the blood through the capillary system ; that, namely, which con- 
 cerns the agencies existing in the Capillaries themselves. Many discussions 
 on this subject may be found in Physiological writings ; and it has so imme- 
 diate a bearing on one of the most important questions in Pathology, the 
 nature of Inflammation, that it deserves the fullest attention. The chief 
 question in debate, is the degree in which the Capillary circulation is influ- 
 enced by any other agency than the contractile power of the Heart and Arte- 
 rial system ; some Physiologists maintaining that this alone is sufficient 
 to account for all the phenomena of the Capillary circulation; and others 
 asserting that it is necessary to admit some supplementary force, which may 
 be exerted either to assist, retard, or regulate the flow of blood from the Arte- 
 ries into the Veins. We shall first consider what evidence there is of the 
 existence of any such force; and, when led to an affirmative conclusion, we 
 shall examine into its nature. No physiological fact is more clearly proved 
 than the existence, in the lower classes of Animals, as well as in Plants, of 
 some power independent of a vis a tergo, by which the circulating fluid is 
 caused to move through their vessels ( 712 716). This power seems to 
 originate in themselves, and to be closely connected with the state of the 
 Nutritive and Secreting processes : since anything which stimulates these to 
 increased energy, accelerates the circulation ; whilst any check to them occa- 
 sions a corresponding stagnation. It may be convenient to designate this 
 motor force by the name of capillary power; it being clearly understood, 
 however, that no mechanical propulsion is thence implied. On ascending the 
 Animal scale, we find the power which, in the lower organisms, is diffused 
 through the whole system, gradually concentrated in a single part ; a new 
 force, that of the Heart, being brought into operation, and the Circulation 
 placed, in a greater or less degree, under its control. Still there is evidence, 
 that the movement of blood through the capillaries is not entirely due to this ; 
 since it may continue after the cessation of the Heart's action, may itself 
 cease in particular organs when the Heart is still acting vigorously, and is 
 constantly being affected in amount and rapidity, by causes originating in the 
 part itself, and in no way affecting the Heart. The chief proofs of these 
 statements will now be adverted to. 
 
 734. When the flow of blood through the Capillaries of a transparent part, 
 such as the web of a Frog's foot, is observed with the Microscope, it appears 
 at first to take place with great evenness and regularity. But on watching the 
 movement for some time, various changes may be observed, which cannot be 
 attributed to the Heart's influence, and which show that a certain regulating 
 or distributive power exists in the walls of the capillaries, or in the tissues 
 which they traverse. Some of these changes, involving variations in the size 
 of the Capillary tubes, have been already referred to ( 219). Others, how- 
 ever, are manifested in great and sudden alterations in the velocity of the cur- 
 rent ; which cause a marked difference in the rates of the movement of the 
 blood through the several parts of the area under observation. Sometimes 
 this variation extends even to the entire reversion, for a time, of the direction 
 of the movement, in certain of the transverse or communicating branches ; the 
 flow always taking place, of course, from the stronger towards the weaker cur- 
 
MOTION OF THE BLOOD IN THE ARTERIES. 561 
 
 rent. Not unfrequently an entire stagnation of the current, in some particular 
 tube, precedes this reversal of its direction. Irregularities of this kind, how- 
 ever, are more frequent when the Heart's action is partially interrupted ; as 
 it usually is by the pressure, to which the Tadpole or other animal must be 
 subjected, in order to allow microscopic observations to be made upon its cir- 
 culation. Under such circumstances, the varieties in the capillary circulation, 
 induced by causes purely local, become very conspicuous ; for when the 
 whole current has nearly stagnated, and a fresh impulse from the heart re- 
 news it, the movement is not by any means uniform (as it might have been 
 expected to be) through the whole plexus supplied by one arterial trunk, but 
 is much greater in some of the tubes than it is in others ; the variation being 
 in no degree connected with their size, and being very different at short in- 
 tervals. 
 
 735. The movement of the blood in the Capillaries of cold-blooded ani- 
 mals, after complete excision of the Heart, has been repeatedly witnessed. 
 In warm-blooded animals, this cannot be satisfactorily established by experi- 
 ment, since the shock occasioned by so severe an operation much sooner de- 
 stroys the general vitality of the system ; but it may be proved^in other ways 
 to take place. After most kinds of natural death, the arterial system is 
 found, subsequently to the lapse of a few hours, almost or completely emptied 
 of blood ; this is partly, no doubt, the effect of the tonic contraction of the 
 tubes themselves ; but the emptying is commonly more complete than could be 
 thus accounted for, and must, therefore, be partly due to the continuance of 
 the capillary circulation. Moreover, when death has taken place suddenly 
 from some cause (as, for instance, a violent electric shock), that destroys the 
 vitality of the whole system at once, the arterial tubes are found to contain 
 their due proportion of blood. Further, it has been well ascertained that a 
 real process of secretion not unfrequently continues after general or somatic 
 death ; urine has been poured out by the ureters, sweat excluded from the 
 skin, and other peculiar secretions formed by their glands; and these changes 
 could not have taken place unless the capillary circulation were still continu- 
 ing. In the early embryonic condition of the highest animals, the movement 
 of blood seems to be unquestionably due to some diffused power, independent 
 of any central impulsion ; for it may be seen to commence in the Vascular 
 Area, before the development of the Heart. The first movement is towards 
 instead of from, the centre ; and even for some time after the circulation is 
 fairly established, the walls of the Heart consist merely of cells loosely at- 
 tached together, and can hardly be supposed to have any great contractile 
 power. 
 
 736. The last of these facts may be said not to have any direct bearing on 
 the question, whether the Capillary power has any existence in the adult con- 
 dition ; but the phenomena occasionally presented by the Foetus, at a later 
 stage, appear decisive. Cases are of no very unfrequent occurrence, in which 
 the heart is absent during the whole of embryonic life, and yet the greater part 
 of the organs are well developed. In most or all of these cases, however, a 
 perfect twin foetus exists ; of which the placenta is in some degree united with 
 that of the imperfect one ; and it has been customary to attribute the circula- 
 tion in the latter, to the influence of the heart of the former, propagated 
 through the placental vessels. This supposition has not been disproved 
 (however improbable it might seem) until recently; when a case of this 
 kind occurred, which was submitted to the most careful examination by an 
 accomplished anatomist ;* and this decisive result was obtained, that it seemed 
 
 * See Dr. Houston in the Dublin Medical Journal, 1837. An attempt has been recently 
 made by Dr. M. Hall (Edinb. Monthly Journal, 1843) to disprove Dr. Houston's inferences; 
 
562 OF THE CIRCULATION OF BLOOD. 
 
 impossible for the heart of the twin foetus to have occasioned the movement 
 of blood in the imperfect one ; and that some cause present in the latter, must 
 have been sufficient for the propulsion of blood through its vessels. It was 
 a very curious anomaly in this case, that the usual functions of the Arteries 
 and Veins must have been reversed; for the Vena Cava, receiving its blood 
 from the Umbilical Vein nearly as usual, had no communication with the 
 Arterial system (the Heart being absent), except through the Systemic Capil- 
 laries ; to which, therefore, the blood must have next proceeded, returning to 
 the placenta by the Umbilical Artery. This view of the course of the blood 
 was confirmed by the fact, that the veins were everywhere destitute of valves. 
 It is evident, that a single case of this kind, if unequivocally demonstrated, 
 furnishes all the proof that can be needed, of the existence, even in the high- 
 est animals, of a capillary power; which, though usually subordinate to the 
 Heart's action, is sufficiently strong to maintain the circulation by itself, when 
 the power of the central organ is diminished. In this, as in many other cases, 
 we may observe a remarkable power in the living system, to adapt itself to 
 exigencies. In the acardiac Foetus, the capillary power supplies the place 
 of the Heart, up to the period of birth ; after which, of course, the circula- 
 tion ceases, for want of due aeration of the blood. It has occasionally been 
 noticed, that a gradual degeneration in the structure of the Heart has taken 
 place during life, to such an extent that scarcely any muscular tissue could at 
 last be detected in it ; without any such interruption to the circulation, as 
 must have been anticipated, if it furnished the sole impelling force. 
 
 737. Further, it is a general principle, unquestioned by any Physiologist, 
 and embodied in the ancient aphorism Ubi stimulus, ibi fluxus, that, when 
 there is any local excitement to the processes of Nutrition, Secretion, &c., a 
 determination of blood towards the part speedily takes place, and the motion 
 of blood through it is increased in rapidity; and although it might be urged, 
 that this increased determination may not be the effect, but the cause, of the 
 increased local action, such an opinion could not be sustained, without many 
 inconsistencies with positive facts. For it is known that such local determi- 
 nations may take place, not only as a part of the regular phenomena of growth 
 and development (as in the case of the entire genital system at the time of 
 puberty and of periodical heat, the uterus after conception, and the mammae 
 after parturition), but also as a consequence of a strictly local cause. Thus, 
 the student is well aware that, after several hours' close application, there is 
 commonly an increased determination of blood to the brain, causing a sense 
 of oppression, a feeling of heat, and frequently a diminished action in other 
 parts ; and, again, when the capillary circulation is being examined under the 
 microscope, it is seen to be quickened by moderate stimuli, and equally re- 
 tarded by depressing agents. All these facts harmonize completely with the 
 phenomena, which are yet more striking in the lower classes of organized 
 beings, and which are evidently the results of the same laws. 
 
 738. It is equally capable of proof, on the other hand, that an influence 
 generated in the Capillaries may afford a complete check to the circulation 
 in the part ; even when the Heart's action is unimpaired, and no mechanical 
 impediment exists to the transmission of blood. Thus, cases of spontaneous 
 gangrene of the lower extremities are of no unfrequent occurrence, in which 
 the death of the solid tissues is clearly connected with a local decline of the 
 circulation ; and in which it has been shown, by examination of the limb after 
 its removal, that both the larger tubes and the capillaries were completely 
 
 but a most satisfactory reply has been made by Dr. Houston, at the Meeting of the British 
 Association, August 1843, and published in the Dublin Journal, Jan. 1844. See also Edinb. 
 Med. and Surg. Journ. July 1844. 
 
MOTION OF THE BLOOD IN THE CAPILLARIES. 563 
 
 pervious ; so that the cessation of the flow of blood could not be attributed to 
 any impediment, except that arising from the cessation of some power which 
 exists in the capillaries, and which is necessary for the maintenance of the 
 current through them. The influence of the prolonged application of Cold 
 to a part, may be quoted in support of the same general proposition ; for, al- 
 though the calibre of the vessels may be diminished by this agent, yet their 
 contraction is not sufficient to account for that complete cessation of the flow 
 of blood through them which is well known to occur, and to terminate in the 
 loss of their vitality. The most remarkable evidence on this point, however, 
 is derived from the phenomena of Asphyxia, which will be more fully ex- 
 plained in the succeeding Chapter. At present it may be stated as a fact, 
 which has now been very satisfactorily ascertained, that, if admission of air 
 into the lungs be prevented, the circulation through them will be brought to a 
 stand, as soon as the air which they contain has been to a great degree de- 
 prived of its oxygen, or rather has become loaded with carbonic acid; and 
 this stagnation will, of course, be communicated to all the rest of the system. 
 Yet, if it have not continued sufficiently long, to cause the loss of vitality in 
 the nervous centres, the movement may be renewed by the admission of air 
 into the lungs. Now, although it has been asserted that the stagnation is due 
 to a mechanical impediment, resulting from the contracted state of the lungs in 
 such cases, this has been clearly proved not to be the fact, by causing animals 
 to breathe a gas destitute of oxygen, so as to produce Asphyxia in a different 
 manner; the same stagnation results as in the other case. 
 
 739. If the phenomena which have been here brought together, be con- 
 sidered as establishing the existence, in all classes of beings possessing a cir- 
 culating apparatus, of a Capillary power, which affords a necessary condition 
 for the movement of the nutritious fluid, through those parts in which it comes 
 .into more immediate relation with the solids, the question still remains 
 open, as to its nature. That the Capillaries possess a contractile power, far 
 higher in degree than that of the large Arteries, and more easily excited than 
 that of the smaller, appears scarcely to admit of doubt; though to what it is 
 due, may be reasonably questioned. It has been recently asserted by 
 Schwann, that they possess the same kind of fibrous tissue in their walls, as 
 do the large vessels : and this cannot be regarded as improbable. It is not 
 possible, however, that their contractility could have any influence in aiding 
 the continuous motion of blood through them ; unless it were exercised in a 
 very different manner from that of which observation affords us evidence. 
 For, when we are microscopically examining the Capillary circulation of any 
 part, it is at once seen, that the vessels present no obvious movement ; and 
 that the stream, now rendered continuous by the elasticity of the arteries, 
 passes through them, as through unelastic tubes. The only method, in which 
 the contractility of the Capillaries could produce a regular influence on the 
 current of blood, would be an alternate contraction and dilatation, or a peri- 
 staltic movement ; and of neither of these can the least traces be discerned. 
 Hence we should altogether dismiss from our minds the idea of any mechani- 
 cal assistance, afforded by the action of the Capillaries, to the movement of 
 the blood. That^the contractile coat of the Capillaries has for its office, to 
 regulate the calibre of the vessels, can scarcely be doubted ; but any general 
 permanent contraction would only occasion an obstacle to the circulation, 
 as is shown by the effects of stimulating injections, which, if thrown into the 
 vessels before their vitality has been lost, will not pass through the capillaries. 
 It would appear, therefore, to be through their action on this coat, that local 
 stimuli occasion a contraction of the capillaries ; their effect, however, is dif- 
 ferent from what might have been anticipated ; for, instead of the capillary 
 circulation being retarded, it is accelerated, at least until an abnormal condition 
 
564 OF THE CIRCULATION OF BLOOD. 
 
 results from their continued operation. Here, again, is another evidence, that 
 something different from mechanical power must be the agent, that operates 
 in all the foregoing cases. 
 
 740. It appears, from the preceding facts, that the conditions, under which 
 the power in question uniformly operates, may be thus simply and definitely 
 expressed: Whilst the injection of blood into the Capillary vessels of every 
 part of the system, is due to the action of the Heart, its rate of passage 
 through those vessels is greatly modified by the degree of activity in the pro- 
 cesses, to which it should normally be subservient in them ; the current 
 being rendered more rapid by an increase in their activity, and being stagnated 
 by their depression or total cessation. Thus it seems that " the capillaries 
 possess a distributive power over the blood, regulating the local circulation, 
 independently of the central organ, in obedience to the necessities of each 
 part." If this be true, it is evident that the dilatation or contraction of the 
 Capillaries will only have a secondary influence on the movement of the blood 
 through them. The former condition is usually an indication of diminished 
 vital energy ; and when it is observed, it is almost invariably accompanied by 
 a retardation or partial stagnation of the current ; on the other hand, the ap- 
 plication of a moderate stimulus, which excites the contractility, accelerates 
 for a time the motion of the blood, by rendering more energetic that reaction 
 between the fluids and the surrounding tissues, which is the condition that 
 really has the most influence over the current. That alterations in the chemi- 
 cal state of the blood (involving, of course, important changes in its vital pro- 
 perties) are capable of exercising a most important effect on the Capillary cir- 
 culation, is shown, not merely by the stagnation of the Pulmonary Circulation 
 in Asphyxia ( 780), but by the curious fact ascertained by Dr. J*. Reid, that 
 the blood, when imperfectly arterialized, is retarded in the systemic capilla- 
 ries, causing an increased pressure on the walls of the arteries.' He found that, 
 when the ingress of air through the trachea of a Dog was prevented, and the 
 Asphyxia was proceeding to the stage of insensibility, the attemps at inspi- 
 ration being few and laboured, and the blood in an exposed artery being quite 
 venous in its character, the pressure upon the Arterial walls, as indicated by 
 the haemadynamometer applied to the Femoral artery, was much greater than 
 usual. Upon applying a similar test to a Vein, however, it was found that 
 the pressure was proportionably diminished ; whence it became apparent, that 
 there was an unusual obstruction to the passage of venous blood through the 
 systemic capillaries. After this period, however, the mercury in the haema- 
 dynamometer applied to the artery began to fall steadily, and at last rapidly, 
 in consequence of the diminished force of the heart, and the retardation of the 
 blood in the pulmonic capillaries ; but, if atmospheric air was admitted, the 
 mercury rose very speedily, showing that the renewal of the proper chemical 
 state of the blood, restored the condition necessary for its circulation through 
 the Capillaries. 
 
 741. The principles already noticed ( 713) as put forth by Prof. Draper, 
 seem fully adequate to explain these phenomena. 
 
 a. The arterial blood, containing oxygen with which it is ready to part, and being pre- 
 pared to receive in exchange the carbonic acid which the tissues set free, must obviously 
 have a greater affinity for the tissues, than venous blood; in which both these changes have 
 already been effected. Consequently upon mere physical principles, the arterial blood which 
 enters the systemic Capillaries on one side, must drive before it, and expel on the other side 
 of the net-work, the blood which has become venous whilst traversing it. But if the blood 
 which enters the Capillaries have no such affinity, no such motor power can be developed. 
 
 b. On the other hand, in the Capillaries of the lungs the opposite affinities prevail. The 
 venous blood and the air in the pulmonary cells have a mutual attraction, which is satisfied 
 by the exchange of oxygen and carbonic acid that takes place through the walls of the capil- 
 laries; and when the blood has become arterialized, it no longer has any attraction for the 
 
MOTION OF THE BLOOD IN THE CAPILLARIES. 565 
 
 air. Upon the very same principle, therefore, the venous blood will drive the arterial before 
 it, in the pulmonary capillaries, whilst respiration is properly going on : but if the supply of 
 oxygen be interrupted, so that the blood is no longer aerated, no change in the affinities takes 
 place whilst it traverses the capillary net-work; the blood continuing venous, still retains its 
 need of a change, and its attraction for the walls of the capillaries ; and its egress into the 
 pulmonary veins is thus resisted, rather than aided, by the force generated in the lungs. 
 
 c. The change in the condition of the blood, in regard to the relative proportions of its 
 oxygen and carbonic acid, is the only one to which the Pulmonary Circulation is subservient; 
 but in the Systemic Circulation, the changes are of a much more complex nature ; every 
 distinct organ attracting to itself the peculiar substances which it requires as the materials 
 of its own nutrition ; and the nature of the affinities thus generated being consequently differ- 
 ent in each case. But the same law holds good in all instances. Thus the blood conveyed 
 to the liver by the portal vein, contains the materials at the expense of which the bile-secret- 
 ing cells are developed; consequently the tissue of the liver, which is principally made up 
 of these cells, possesses a certain degree of affinity or attraction for blood containing these 
 materials ; and this is diminished, so soon as they have been drawn from it into the cells 
 around. Consequently the blood of the portal vein will drive before it, into the hepatic vein, 
 the blood which has traversed the capillaries of the portal system, and which has given up, 
 in doing so, the elements of bile to the solid tissues of the liver. The same principle holds 
 good in every other case. 
 
 742. It can be scarcely doubted, that it is by some influence exercised over 
 the molecular actions, to which the Blood is subject in the Capillaries, that 
 the Nervous system can operate on the functions of Nutrition, Secretion, &c. 
 in the manner already alluded to (Chap, vii.) ; and this influence may be not 
 improperly termed vital, if by so designating it we merely imply that its 
 nature and mode of operation are unknown, but that it is closely connected 
 with those actions which are altogether peculiar to living beings. The follow- 
 ing experiment, made by Dr. Wilson Philip, exhibits in a convincing manner 
 the possibility of such an influence. " The web of one of the hind legs of a 
 frog was brought before the microscope ; and while Dr. Hastings observed the 
 circulation, which was vigorous, the brain was crushed by the blow of a ham- 
 mer. The vessels of the web instantly lost their power, the circulation ceas- 
 ing ; an effect which cannot arise, as we have seen, from the ceasing of the 
 action of the heart. [Dr. P. here refers to experiments, by which it was ascer- 
 tained, that the circulation in the capillary vessels of the frog will continue for 
 several minutes, after the interruption of the heart's action.] In a short time 
 the blood again began to move, but with less force. This experiment was 
 repeated, with the same result. If the brain is not completely crushed, although 
 the animal is killed, the blow, instead of destroying the circulation, increases 
 its rapidity."* We are not hence to conclude, however, that the Nervous 
 system supplies any influence, which is essential to the continuance of the 
 Circulation ; since it is only by such sudden and severe injuries to the nervous 
 centres, as instantaneously destroy the vitality of the whole system ( 735), 
 that the movement of the blood is arrested. The experiments of Muller and 
 others satisfactorily prove, that mere action of the Nerves does not produce 
 any direct effect upon the Capillary circulation; and this corresponds with the 
 well-known fact, that the Nutritive processes may continue as usual, after this 
 action has been suspended. All the facts, which bear upon the question of 
 the connection between Nervous agency and the forces maintaining the 
 Capillary Circulation, have an equal relation to the functions of Nutrition and 
 Secretion in general; and as already shown, the Nervous System also influ- 
 ences these, by the control it exerts over the diameter of the blood-vessels 
 ( 730). 
 
 * Experimental Inquiry into the Laws of the Vital Functions, 4th edition, p. 52. 
 48 
 
566 OF THE CIRCULATION OF BLOOD. 
 
 4. Of the Venous Circulation. 
 
 743. The Venous system takes its origin in the small trunks that are 
 formed by the re-union of the Capillaries; and it returns the blood from these 
 to the Heart. The structure of the Veins is essentially the same with that of 
 the Arteries ; but the fibrous tissue, of which their middle coat is made up, 
 bears more resemblance to the areolar tissue of the skin, than it does either 
 to muscular fibre, or to the true elastic tissue. The Elasticity of the Veins, 
 however, is shown by the jet of blood, which at first spouts out in ordinary 
 venesection; when, by means of the ligature, a distension has been occasioned 
 in the tubes below it. A slight Contractility on the application of stimuli, 
 and on irritation of the Sympathetic nervous fibres, has been observed ; but 
 this is not so decided as in the Arteries. The whole capacity of the Venous 
 system is considerably greater than that of the Arterial ; the former is usually 
 estimated to contain from 2 or 3 times as much blood as the latter, in the 
 ordinary condition of the circulation ; and when we consider the great pro- 
 portion, which the Veins in almost every part of the body bear to the arteries, 
 we shall scarcely regard even the larger of these ratios as exaggerated. Of 
 course the rapidity of the movement of the blood in the two systems, will 
 bear an inverse ratio to their respective capacities ; thus if, in a given length, 
 the Veins contain three times as much blood as the Arteries, the fluid will 
 move with only one-third of the velocity. Even at their origins in the 
 Capillary plexus, the Veins are larger than the Arteries which terminate in 
 the same plexus ; so that, wherever the arterial and venous net-works form 
 distinct strata, they are readily distinguished from each other. The Veins 
 are remarkable for the number of valves which they contain, formed of dupli- 
 catures or loose folds of the internal tunic, between the component laminae of 
 which, contractile fibres are interposed ; and also for the dilatations behind 
 these, which, when distended, give them a varicose appearance. The valves 
 are single in the small veins, the free edge of the flap closing against the 
 opposite wall of the vein ; in the larger trunks they are double ; and in a 
 few instances they are composed of three flaps. The object of these valves 
 is evidently to prevent the reflux of blood ; and we shall presently see that 
 they are of important use in assisting in the maintenance of the venous circu- 
 lation. They are most numerous in those Veins which run among parts 
 affected by muscular movement ; and they are not found in the veins of the 
 lungs of the abdominal viscera or of the brain. 
 
 744. The movement of the blood through the Veins is, without doubt, 
 chiefly effected by the vis a tergo or propulsive force ; which results from 
 the action of the Heart and Arteries, and from the additional power generated 
 in the Capillary vessels. This is shown by the immediate arrestment of it, 
 which takes place when these forces are suspended. There are some con- 
 current causes, however, which are supposed by some to have much influence 
 upon it, and of which the consideration must not be neglected. 
 
 a: One of these is the suction-power attributed to the Heart ; acting as a vis a fronte, in 
 drawing the blood towards it. It is very doubtful how far the Auricles have such a power 
 of active dilatation, as that which would be required for this purpose; and no sufficient 
 evidence has been given, that the current of blood at any distance from the Heart is affected 
 by it. Indeed, for a reason to be presently stated, this may be regarded as impossible. 
 
 b. Another important agency has been found by some Physiologists in the Inspiratory 
 movement; this is supposed to draw the blood of the Veins into the chest, in order to sup- 
 ply the vacuum which is created there, at the moment of the descent of the Diaphragm. 
 That the movement in question has some influence on the flow of Venous blood into the 
 chest, is evident from the occurrence of the respiratory pulse, long ago described by Haller ; 
 which may be seen in the veins of the neck and shoulder in thin persons, and in those 
 especially who are suffering from pulmonary diseases. During Inspiration, the Veins are 
 
VENOUS CIRCULATION. 567 
 
 seen to be partially emptied ; whilst during Expiration they become turgid, partly in con- 
 sequence of the accumulation from behind, and of the check in front ; and partly (it may 
 be) in some cases, through an absolute reflux from the veins within the chest ( 723, c). 
 The fact that, in the immediate neighbourhood of the chest, the flow of blood towards the 
 heart is aided by Inspiration and impeded by Expiration, is further proved by Sir D. Barry s 
 experiment, which consisted in introducing one extremity of a tube into the Jugular vein of 
 a Horse, and the other into water, which exhibited an alternate elevation and depression 
 with inspiration and expiration ; this has been repeated and confirmed by several Physiolo- 
 gists. On the other hand, the expiratory movement, while it directly causes accumulation 
 in the Veins, will assist the Heart in propelling the blood into the Arteries ; and by the com- 
 bined action of these two causes are produced, among other effects, the rising and sinking of 
 the Brain, synchronously with expiration and inspiration, which are observed when a por- 
 tion of the cranium is removed. Several considerations, however, agree in pointing to the 
 conclusion, that no great efficacy can be rightly attributed to the Respiratory movements, as 
 exerting any general influence over the Venous circulation. The Pulmonary circulation, 
 being entirely within the chest, cannot be affected by variations in atmospheric pressure ; 
 and it may be further remarked, that the whole mechanism of respiration is so different in 
 Birds, from that which exists in Mammalia, that no vacuum can ever be said to exist in 
 their chests, although the venous circulation is performed as actively as usual. The Venous 
 circulation of the foetus, also, is independent of any such agency. Again, it has been shown 
 experimentally by Dr. Arnott and others, that no suction-power exerted at the farther end 
 of a long tube, whose walls are so deficient in firmness as are those of the Veins, can oc- 
 casion any acceleration in a current of fluid transmitted through it; for the effect of the 
 suction is destroyed, at no great distance from the point at which it is applied, by the flap- 
 ping together of the sides of the vessel. 
 
 c. One of the most powerful of the general causes which influence the Venous circula- 
 tion, is doubtless the frequently-recurring action of the Muscles upon their trunks. In every 
 instance that Muscular movement takes place, a portion of the Veins of the part will undergo 
 compression ; and as the blood is prevented, by the valves in the veins, from being driven 
 back into the small vessels, it is necessarily forced on towards the Heart. As each set of 
 muscles is relaxed, the Veins compressed by it fill out again, to be again compressed by 
 the renewal of the force. That the general Muscular movement is an important agent in 
 maintaining the Circulation, at a point above that, at which it would be kept by the action 
 of the Heart and Capillaries alone, appears from several considerations. The pulsations 
 are diminished in frequency by rest, accelerated by exertion, and very much quickened by 
 violent effort. In all kinds of exercise, and in almost every sort of effort, there is that 
 alternate contraction and relaxation of particular groups of Muscles, which has been just 
 mentioned, as effecting the flow of blood through the Veins; and there can be little doubt, 
 that the increased rapidity of the return of blood' ; through them, is of itself a sufficient cause 
 for the accelerated movements of the Heart. When a large number of Muscles are put in 
 action after repose, as is the case when we rise up from a recumbent or a sitting posture, 
 the blood is driven to the Heart with a very strong impetus ; and if that organ should be 
 diseased, it may arrive there in a quantity larger than can be disposed of; so that sudden 
 death may be the result. Hence the necessity for the avoidance of all sudden and violent 
 movements, on the part of those who labour under either a functional or structural disease of 
 the centre of the circulation. 
 
 745. The Venous circulation is much more liable than the Arterial, to be 
 influenced by the force of Gravity ; and this influence is particularly notice- 
 able, when the tonicity of the vessels is deficient. 
 
 a. The following experiments performed by Dr. Williams, to elucidate the influence of 
 deficient firmness in the walls of the vessels, and of gravitation, over the movement of fluids 
 through tubes, throw great light on the causes of Venous Congestion. A tube with two 
 equal arms having been fitted to a syringe, a brass tube two feet long, having several right 
 angles in its course, was adapted to one of them, whilst to the other was tied a portion of a 
 rabbit's intestine four feet long, and of calibre double that of the brass tube, this being 
 arranged in curves and coils, but without angles and crossings. When the two tubes were 
 raised to the same height, the small metal tube discharged from two to five times the quan- 
 tity of water discharged in a given time by the larger but membranous tube; the difference 
 being greatest, when the strokes of the piston were most forcible and sudden, by which the 
 intestine was much dilated at its syringe end, but conveyed very little more water. When 
 the discharging ends were raised a few inches higher, the difference increased considerably, 
 the amount of fluid discharged by the gut being much diminished ; and when the ends were 
 raised to the height of eight or ten inches, the gut ceased to discharge, each stroke only 
 moving the column of water in it, and this subsiding again, without rising high enough to 
 
568 OF THE CIRCULATION OF BLOOD. 
 
 overflow. When the force of the stroke increased, the part of the intestine nearest the 
 syringe burst. 
 
 b. From these experiments it is easy to understand, how any deficiency of tone in the 
 Venous System will tend to prevent the "ascent of the blood from the depending parts of the 
 body, and will consequently occasion an increased pressure on the walls of the vessels, and 
 an augmentation in the quantity of blood they contain. All these conditions are peculiarly 
 favourable to the escape of the watery part of the blood from the small vessels; and this 
 may either infiltrate into the areolar tissue, or it may be poured into some neighbouring 
 serous cavity, producing dropsy. Thus it happens, that such effusions may often be traced, 
 to that state of deficient vigour of the system, which peculiarly manifests itself in want of 
 tone of the blood-vessels ; and that it is relieved by remedies which restore this. In many 
 young females of leuco-phlegmatic temperament, for example, there is a tendency to swell- 
 ing of the feet, by cedematous effusion into the areolar tissue, in consequence of the depend- 
 ing position of the limbs; the oedema disappears during the night, but returns during the day, 
 and is at its maximum in the evening. And the congestion which frequently manifests 
 itself in the posterior parts of the body, towards the close of exhausting diseases, in which 
 the patient has lain much upon his back, is attributable to a similar cause; of such conges- 
 tion, effusions into the various serous cavities are frequent results ; and such effusions, taking 
 place during the last hours of life, are often erroneously regarded as the cause of death. To 
 the same cause we are to attribute the varicose state of the veins of the leg, which is so 
 common amongst persons of relaxed fibre, and especially in those whose habits require 
 them to be much in the erect posture ; and this distension occasionally proceeds to complete 
 rupture, the causes of which are fully elucidated by the experiments just cited. 
 
 5. Peculiarities of the Circulation in different Parts. 
 
 746. In several portions of the Human body, there are certain varieties in 
 the distribution and in the functional actions of the Blood- Vessels, which 
 should not be omitted in a general account of the Circulation. Of these, we 
 have in the first place to notice the apparatus for the Pulmonary circulation ; 
 the chief peculiarity of which is, that venous blood is sent from the heart, 
 through a tube which is Arterial in its structure, whilst arterial blood is re- 
 turned to the heart, through a vessel whose entire character is that of a Vein. 
 The movement of the blood through these is considerably affected by the 
 physical state of the Lungs themselves ; being retarded by any causes, which 
 can occasion pressure on the vessels (sach as over-distension of the cells with 
 air, obstruction of their cavity by solid or fluid depositions, or by foreign sub- 
 stances injected into them, &c.); and proceeding with the greatest energy and 
 regularity, when the respiratory movements are freely performed. The Por- 
 tal circulation, again, is peculiar, in being a kind of offset from the general or 
 systemic circulation ; and also in being destitute of valves ; and it may be 
 surmised with much probability, that the purpose of their absence is, to allow 
 of an unusually free passage of blood from one part of that system to another, 
 during the very varying conditions to which it is subjected ( 685). 
 
 747. Another very important modification of the Circulating system, is that 
 which presents itself within the Cranium. From the circumstance of the 
 cranium being a closed cavity, which must be always filled with the same 
 total amount of contents, the flow of blood through its vessels is attended with 
 some peculiarities. The pressure of the atmosphere is here exerted, rather 
 to keep the blood in the head, than to force it out ; and it might accordingly 
 be inferred that, whilst the quantity of cerebral matter remains the same, the 
 amount of blood in the cranial vessels must also be invariable. This infer- 
 ence appeared to derive support from the experiments of Dr. Kellie.* On 
 bleeding animals to death, he found that, whilst the remainder of the body was 
 completely exsanguine, the usual quantity of blood remained in the arteries 
 and veins of the cranium ; but that, if an opening was made in the skull, these 
 vessels were then as completely emptied as the rest. It is not to be hence 
 
 * Edinburgh Medico-Chirurgical Transactions, vol. i. 
 
PECULIARITIES OF CIRCULATION. 569 
 
 i 
 
 inferred, however, that the absolute quantity of blood within the cranium is 
 not subject to variation; and that in the states of inflammation, congestion, or 
 other morbid affections, there is only a disturbance of the usual balance of 
 the arterial and venous circulation. The fact in all probability is rather, that 
 the softness of the Cerebral tissue, and its varying functional activity, render 
 it peculiarly liable to undergo alterations in bulk ; and that the amount of the 
 cerebro-spinal fluid varies considerably at different times ( 476) ; so that the 
 quantity of blood may thus, even in the healthy condition, be continually 
 changing. Moreover, in disordered states of the circulation, the quantity of 
 blood in the vessels of the cranium may be for a time diminished by a sudden . 
 extravasation, either of blood or serum, into the cerebral substance; and the 
 amount of interior pressure upon the walls of the vessels may also be con- 
 siderably altered, even when there is no difference in the quantity of fluid 
 contained in them.* 
 
 748. The Erectile tissues constitute another curious modification of the 
 ordinary vascular apparatus. The chief of these are the Corpora Cavernosa 
 in the penis of the male, and in the clitoris of the female ; the collection of 
 similar tissues round the vagina, and in the nymphae, of the female ; and the 
 nipple in both sexes. In all these situations, erection may be produced by 
 local irritation ; or it may take place as a result of certain emotional conditions 
 of the mind ; the influence of which is probably transmitted through the 
 Sympathetic nerve, as it may be experienced even in cases of paraplegia. 
 The erectile tissue appears essentially to consist of a plexus of varicose Veins, 
 inclosed in a fibrous envelope. According to Gerber,t this plexus is traversed 
 by numerous contractile fibres, which are analogous to those that form the 
 dartos ; and to the contraction of these is probably to be attributed that ob- 
 struction to the return of blood by the Veins, which is the occasion of the 
 turgescence. The proximate cause of the erection of the Penis, has been 
 stated by some to be the action of the Ischio-Cavernosi muscles ; and by others 
 it has been attributed to the compression of the Vena dorsalis penis against 
 the Symphysis pubis. But it is obvious that nothing analogous to this can 
 apply to the other erectile organs, especially to the Nipple. In the Penis, 
 according to Muller, there are two sets of arteries ; of which one, destined for 
 the nutrition of the tissues, communicates with the veins in the usual way, 
 through a capillary net-work ; whilst the others pass off as large branches, and 
 penetrate the cavernous substance in a helicine manner, communicating ab- 
 ruptly with the venous cells. It would seem not improbable, that these last 
 are not ordinarily pervious to blood ; but that the same change in the contrac- 
 tile fibres, which impedes the return of the blood by the veins, may also 
 permit it to enter more freely from the helicine arteries. This double com- 
 munication, however, is denied by Valentin, who gives a different explanation 
 of the appearances described by Muller. The arteries are protected in such 
 a manner, that, even when the veins are most compressed, and the erection 
 most complete, they are still quite pervious. 
 
 * The results of the more recent experiments of Dr. G. Burrows (Med. Gaz., April and 
 May, 1843) fully confirm the views stated above, 
 f General Anatomy, p. 298. 
 
 48* 
 
570 OF RESPIRATION. 
 
 CHAPTER XIII. 
 
 OF RESPIRATION. 
 
 1. Nature of the Function: and Provisions for its Performance. 
 
 749. IT is obvious that the Nutritive fluid, in its circulation through the 
 capillaries of the system, must undergo great alterations, both in its physical 
 constitution, and its vital properties. It gives up to the tissues with which it 
 is brought into contact, some of its most important elements ; and, at the same 
 time, it is made the vehicle of the removal, from these tissues, of ingredients 
 which are no longer in the state of combination, that fits them for their offices 
 in the Animal Economy. To separate these ingredients from the general cur- 
 rent of the circulation, and to carry them out of the system, is the great object 
 of the Excretory organs ; and it is very evident that the importance of the 
 respective functions of these will vary with the amount of the ingredient 
 which they have to separate, and with the deleterious influence which its re- 
 tention would exert on the welfare of the system at large. Of all these injuri- 
 ous ingredients, Carbonic Acid is without doubt the one most abundantly 
 introduced into the nutritive fluid ; and it is also most deleterious in its effects 
 on the system, if allowed to accumulate. We find, accordingly, that the pro- 
 vision for the removal of Carbonic Acid from the Blood, is one of peculiar 
 extent and importance, especially in the higher forms of Animals ; and further, 
 that instead of being effected by an operation peculiarly vital (like other acts 
 of Excretion), its performance is secured by being made to depend upon simple 
 physical laws, and is not nearly so susceptible of derangement from disorder 
 of other processes, as it would be if its conditions were less simple. All that 
 is requisite for it, as we shall presently see, is the exposure of the Blood to 
 the influence of the Atmospheric air, or of Air dissolved in water, through the 
 medium of a membrane that shall permit the diffusion of gases; and an inter- 
 change then takes place between the gaseous matters on the two sides, Car- 
 bonic acid being exhaled from the Blood, and being replaced by Oxygen. 
 Thus the extrication of Carbonic acid is effected in a manner, that renders it 
 subservient to the introduction of the element which is required for all the 
 most active manifestations of vital power ; and it is in these two processes 
 conjointly, not in either alone, that the function of Respiration essentially con- 
 sists. We shall now inquire into the sources from which Carbonic acid is 
 produced in the living body; and the causes of the demand for Oxygen. 
 
 750. All organized bodies, as already explained, are liable to continual 
 decay, even whilst they are most actively engaged in performing the actions 
 of Life ; and one of the chief products of that decay is Carbonic Acid. A 
 large quantity of this gas is set free, during the decomposition of almost every 
 kind of organized matter; the Carbon of the substance being united with the 
 oxygen supplied by the air. Hence we find, that the formation and liberation 
 of carbonic Acid go on with great rapidity after death, both in the Plant and 
 in the Animal ; and that they take place, also, to a very great extent, in the 
 period that often precedes the death of the body, during which a general de- 
 composition of the tissues is occurring. Thus in Plants, as soon as they 
 become unhealthy, the extrication of carbon in the form of carbonic acid takes 
 
SOURCES OF CARBONIC ACID. 571 
 
 I 
 
 place in greater amount than its fixation from the carbonic acid of the atmo- 
 sphere ; and the same change normally occurs during the period that immedi- 
 ately precedes the annual fall of the leaves, their tissue being no longer able 
 to perform its proper functions, and giving rise, by its incipient decay, to a 
 large increase in the quantity of carbonic acid set free. The same thing 
 happens in the Animal body, during the progress of many diseases which are 
 attended with an unusual tendency to decomposition in the solids and fluids, 
 such as eruptive fevers ; the quantity of carbonic acid set free in Respira- 
 tion is greatly increased, although the body remains completely at rest ; and 
 notwithstanding this, the blood frequently exhibits a very dark hue, indicating 
 that it has not been freed from the unusual amount of that substance which 
 it has received from the tissues. Hence the first object of the Respiratory 
 process, which is common to all forms of organized being, is to extricate from 
 the body the carbonic acid, which is one of the products of the continual de- 
 composition of its tissues. The softness of many of the tissues of Animals, 
 and the large quantity of fluid contained in their bodies, render them more 
 prone than Plants to this kind of decomposition; and in warm-blooded animals, 
 the high temperature at which the fabric is usually maintained, adds con- 
 siderably to the degree of this tendency, so that the waste of their tissues, 
 from this cause alone, is as much greater than that of cold-blooded animals, 
 as the latter is than that of Plants. But when the temperature of the Reptile 
 is raised by external heat to the level of that of the Mammal, its need for 
 respiration increases, owing to the augmented waste of its tissues. When, on 
 the other hand, the warm-blooded Mammal is reduced, in the state of hyber- 
 nation, to the level of the cold-blooded Reptile, the waste of its tissues dimin- 
 ishes to such an extent, as to require but a very small exertion of the respira- 
 tory process to get rid of the carbonic acid, which is one of its chief products. 
 And in those animals which are capable of retaining their vitality, when they 
 are frozen, or when their tissues are completely dried up, the decomposition 
 is for the time entirely suspended, and consequently there is no carbonic acid 
 to be set free. 
 
 751. But another source of Carbonic acid to be set free by the Respiratory 
 process, and one which is peculiar to animals, consists in the rapid changes 
 which take place in the Muscular and Nervous tissues, during the period of 
 their activity. It has been already shown ( 586), that there is strong reason 
 to believe the waste or decomposition of the muscular tissue to be in exact 
 proportion to the degree in which it is exerted ; every development of muscu- 
 lar force being accompanied by a change in the condition of a certain amount 
 of tissue. In order that this change may take place, the presence of Oxygen 
 is essential; and one of the products of the union of oxygen with the elements 
 of muscular fibre is carbonic acid. The same may probably be said of the 
 Nervous tissue ( 292). Hence it may be stated as a general principle, that 
 the peculiar waste of the Muscular and Nervous substances, which is a con- 
 dition of their functional activity, and which is altogether distinct from the 
 general slow decay that is common to these tissues with others, is another 
 source of the carbonic acid which is set free from the animal body ; and that 
 the amount thus generated will consequently depend upon the degree in which 
 these tissues are exercised. In animals which are chiefly made up of the 
 organs of vegetative life, in whose bodies the nervous and muscular tissues 
 form but a very small part, and in whose tranquil plant-like existence there is 
 but very little demand upon the exercise of these structures, the quantity of 
 carbonic acid thus liberated will be extremely small. On the other hand, in 
 animals, whose bodies are chiefly composed of muscle, and whose life is an 
 almost ceaseless round of exertion, the quantity of carbonic acid thus liberated 
 is very considerable. 
 
572 OF RESPIRATION. 
 
 752. Besides these sources of Carbonic acid, which are common to all 
 Animals, there is another, which appears to be peculiar to the two highest 
 classes, Birds and Mammals. These are capable of maintaining a constantly 
 elevated temperature, so long as they are supplied with a proper amount of 
 appropriate food; and their power of doing so appears to depend upon the 
 direct combination of certain elements of the food, with the oxygen of the air, 
 by a process analogous to combustion ; these elements having been introduced 
 into the blood for that purpose, but not having formed a part of any of the 
 solid tissues of the body, unless they have been deposited in the form of fat. 
 The nature of these substances has been already noticed ( 641). It is quite 
 clear that they cannot be applied in their original form, to the nutrition of the 
 tissues that originate in proteine compounds; and it is tolerably certain that, 
 in the ordinary condition of the body, they undergo no such conversion, as 
 would adapt them to that purpose. The Liver seems to afford a channel, by 
 which some of the fatty matters are drawn off from the blood ; but even these 
 seem, in part at least, to be reabsorbed ( 671), and to be thrown off by the 
 respiratory process. 
 
 753. The quantity of carbonic acid, that is generated directly from the 
 elements of the food, seems to vary considerably in different animals, and in 
 different states of the same individual. In the Carnivorous tribes, which spend 
 the greater part of their time in a state of activity, it is probable that the quan- 
 tity which is generated by the waste or metamorphosis of the tissues is suffi- 
 cient for the maintenance of the required temperature, and that little or none 
 of the carbonic acid set free in respiration is derived from the direct combus- 
 tion of the materials of the food. But in Herbivorous animals of comparatively 
 inert habits, the amount of metamorphosis of the tissues is far from being suf- 
 ficient; and a large part of the food, consisting as it does of substances that 
 cannot be applied to the nutrition of the tissues, is made to enter into direct 
 combination with the .oxygen of the air, and thus to compensate for the de- 
 ficiency. In Man and other animals, which can sustain considerable variations 
 of climate, and can adapt themselves to a great diversity of habits, the quantity 
 of carbonic acid formed by the direct combination of the elements of the food 
 with the oxygen of the air, will differ extremely under different circumstances. 
 It will serve as the complement of that which is formed in other ways ; so 
 that it will diminish with the increase, and will increase with the diminution 
 of muscular activity. On the other hand it will vary, in accordance with the 
 external temperature; increasing with its diminution, as more heat must then 
 be generated ; and diminishing with its increase. In all cases, if a sufficient 
 supply of food be not furnished, the store of fat is drawn upon : and if this be 
 exhausted, the animal dies of cold ( 896). 
 
 754. To recapitulate, then, the sources of Carbonic Acid in the animal body 
 are threefold. I. The continual decay of the tissues; which is common to 
 all organized bodies ; which is diminished by cold and dryness, and increased 
 by warmth and moisture ; which takes place with increased rapidity at the 
 approach of death, whether this affect the body at large, or only an individual 
 part; and which goes on unchecked when the actions of nutrition have ceased 
 altogether. n. The Metamorphosis, which is peculiar to the Nervous and 
 Muscular tissues ; which is the very condition of their activity, and which 
 therefore bears a direct relation to the degree in which they are exerted. in. 
 The direct conversion of the carbon of the food into carbonic acid; which is 
 peculiar to warm-blooded animals ; and which seems to vary in quantity, in 
 accordance with the amount of heat to be generated. We shall now examine 
 into the manner in which this compound is set free, in the principal groups of 
 the Animal kingdom. 
 
 755. Notwithstanding their diversity in external form, {he organs of Re- 
 
GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 573 
 
 spiration are always formed upon the same general plan ; being essentially 
 composed of a membranous prolongation of the external surface, adapted, by 
 its vascularity and permeability, to bring the blood into close relation with the 
 surrounding medium. But as this medium may be either air or water, we 
 find two principal forms of the apparatus; one of them adapted for each kind 
 of respiration. In aquatic animals, the membrane is usually prolonged ex- 
 ternally into tufts or fringes, which are so arranged as to expose the greatest 
 amount of surface to the water ; each filament of which these are composed, 
 includes an afferent and efferent capillary vessel ; and it is whilst the fluid is 
 passing through them, that its aeration is accomplished. The collection of 
 tufts or fringes constitutes what are known as gills; 
 and though their arrangement varies considerably, their Fig. 214. 
 
 essential character is but little different, throughout the 
 classes of animals that possess them. On the other 
 hand, in air-breathing Animals, the aerating surface 
 is reflected inwardly, forming passages or chambers 
 into which the air is received, and on the walls of 
 which the blood is distributed in a minute capillary 
 net-work. Such a conformation is found even among 
 some of the lower Articulata, which have a series of 
 air-sacs disposed along each side of the body, one for 
 every segment. In Insects we find, instead of the 
 sacs, a system of prolonged tubes, ramifying through 
 the body, and carrying air into its minutest por- 
 tions. Even in Some Mollusca, such as the Snail One of the arborescent pro- 
 , , i /-M f i cesses, forming the gills of 
 
 and other terrestrial Gasteropods, we rind a provision Doris j h ns torii, separated 
 for aerial respiration ; a large cavity being formed in and enlarged. 
 the back, communicating with the air, and having a 
 
 beautifully-reticulated plexus of blood-vessels on its walls. In none of 
 the Invertebrata, however, does the respiratory apparatus communicate with 
 the mouth; which is an organ solely appropriated, in them, to the ingestion 
 of food. In the Mollusca, indeed, the channel through which the water, 
 that has passed over the aerating surface, leaves the chamber (formed by 
 a fold of the mantle or general envelope) which contains the gills, is the 
 same as that through which the excrementitious matter is discharged from 
 the intestine ; and the gills themselves are very commonly situated in the 
 neighbourhood of the anal orifice. This fact is interesting in regard to the 
 character of the temporary respiratory apparatus of the Human embryo. In 
 Fishes and the Iarva3 of Batrachia, which are the highest animals that breathe 
 by gills, these organs are so disposed in connecting with the cavity of the 
 mouth, that fresh currents of water are continually being forced over them by 
 its muscles ; and thus the energy of their action is greatly increased. More- 
 over the whole blood, which is propelled from the heart, proceeds first to the 
 respiratory organs ; instead of passing through them on its return from the 
 systemic circulation, as in most of the aquatic Invertebrata. Still, as the 
 quantity of oxygen which the blood can obtain in this manner is very small, 
 being limited to that contained in the atmospheric air dissolved in the water, 
 the amount of aeration must be considered as low. 
 
 756. In the lowest Vertebrata that possess anything like a pulmonary cavity, 
 this has a structure as simple as that of the air-sac of the Snail. This is the 
 case in many Fishes, where it is known as the air-bladder ; it is frequently 
 single in this class, and communicates with the intestinal canal near the sto- 
 mach, or is altogether destitute of outlet. In others, however, it is double, 
 and its duct opens into the oasophagus near the mouth ; so that its analogy to 
 the lungs of higher animals is very evident. The Batrachia begin life as 
 
574 
 
 OF RESPIRATION. 
 
 Fishes, breathing by gills during their tadpole state ; but at the time that the 
 legs are developed and the tail has decreased, the pulmonary organs also are 
 evolved, and the course of the blood is altered, so that it is no longer trans- 
 mitted through the gills, which speedily shrivel and disappear ( 31). There 
 are some species, however, whose metamorphosis is checked, so that in their 
 permanent condition both lungs and gills are present ; but the former are then 
 present in a very rudimentary form, not being more developed than the air- 
 sacs of many Fishes. The lungs of Reptiles are, for the most part, simple 
 sacs ; into which the bronchial tubes open freely ; and on the walls of which, 
 the pulmonary vessels are distributed. The extent of surface is considerably 
 increased, however, by the formation of a number of little pits or sacculi on 
 the inner wall of the cavity, especially at its upper part; and between these, 
 we observe a sort of cartilaginous frame-work, which is continuous with the 
 cartilage of the bronchus on either side. The Turtles and their allies are the 
 only Reptiles, in which the cavity of the lung is itself divided by membranous 
 partitions ; and thus it happens that, excepting in these, the net- work of pul- 
 monary capillaries, in the class of Reptiles, is exposed only on one side to 
 the influence of the air. The general distribution of these vessels is shown 
 in the accompanying figures. It will be seen that the trunk of the pulmonary 
 artery runs along one side of the sac, and that of the pulmonary vein along 
 the other (Fig. 215) ; and that numerous branches arise from the former, 
 which subdivide into capillaries that ramify over the whole surface, and then 
 reunite into small veins which terminate in the latter. The islets of paren- 
 chyma left between the capillary vessels, are seen to be much smaller than 
 those which are usually to be observed in the systemic circulation (Figs. 
 216, 217); so that the membrane is more copiously traversed by vessels, than 
 
 Fig. 215. 
 
 [Fig. 216. 
 
 Lung of Triton cristatus, magnified 
 about 3 diameters ; a, pulmonary artery; 
 b, pulmonary vein. 
 
 Portion of the lung of the same animal, 
 more highly magnified ; the vessels, finely- 
 injected with size and vermilion, form a 
 net-work so minute, that the parenchyma is 
 only seen in small islets in its interstices. 
 
GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 575 
 
 any other that is known. The walls of the capillaries, moreover, are much 
 less distinct than those of the systemic circulation. These two conditions 
 are obviously favourable to the exposure of the largest possible quantity of 
 blood to the influence of the air ; but as the surface is not an extensive one, 
 the amount which can be thus exposed at any one time is very limited ; and 
 the pulmonary artery is in fact one of the smaller branches of the aorta, which 
 conveys a mixed fluid to the system at large. 
 
 Fig. 217. 
 
 Portion of the lung of a living Triton, as seen under the microscope with the power of 150 diam. ; a, 
 b, pulmonary vein, receiving blood from the large trunk c, and a smaller vessel d, 
 
 757. In the warm-blooded Vertebrata, which have a complete double cir- 
 culation, namely, Birds and Mammalia, a much larger extent of surface is 
 provided for the aeration of the blood ; the whole current of which is trans- 
 mitted to the lungs, before circulating again through the system. This in- 
 crease is provided in Birds, partly by the greater extension of surface in the 
 lungs themselves, these cavities being subdivided by partitions into numerous 
 smaller chambers, each having pitted walls, and resembling the entire lung of 
 a Reptile ; and partly by the addition of a number of large air-sacs, which 
 are disposed in various parts of the body, and even in the interior of the long 
 bones. Hence it happens, that the amount of Respiration is greater in this 
 class than in any other ; although the form of the apparatus is not nearly so 
 concentrated as in the Mammalia ; nor is the mechanism of the chest so well 
 adapted to a constant exchange of the air contained in its cavities ( 37). In 
 Mammalia the lungs are proportionally smaller ; and the whole respiratory 
 
576 
 
 OF RESPIRATION. 
 
 apparatus is restricted to the thorax : but the minute subdivision of their cavity, 
 and the mechanism by which a continual interchange of air is provided for, 
 render them very efficient for their designed purpose. The following, accord- 
 ing to the latest researches, especially those of Mr. Rainey,* appears to be 
 the nature of the ultimate structure of the lungs in Man and the Mammalia 
 in general. The bronchial tubes divide and subdivide, like the branches of a 
 tree, still retaining their ordinary characters, until they are no more than from 
 l-50th to l-30th of an inch in diameter ; and in these the longitudinal and 
 annular fibres, together with the ciliated epithelium, come to an abrupt ter- 
 mination. Beyond this boundary, the tubular form of the air-passages con- 
 tinued from the bronchi is retained for some distance ; but it is gradually 
 changed by the irregular branching of the passages, and by the increase of 
 the number of apertures in their walls, which lead to the air-cells. Thus, at 
 last, each minute division of the air-passages becomes quite irregular in form ; 
 air-cells opening into every part of itj and almost constituting its walls ; until 
 it terminates, almost without dilatation, in an air-cell. This terminal portion 
 of the air-passage, with its surrounding cluster of air-cells, may be regarded 
 as forming a sort of lobule, and as representing the entire lung of a Frog or 
 
 [Fig. 218. 
 
 The Larynx, Trachea and Bronchia?, deprived of their fibrous covering, and with the outline of the 
 Lungs ; 1, 1, outline of the upper lobes of the lungs ; 2, outline of the middle lobe of the right lung ; 3, 3, 
 outline of the inferior lobes of both lungs ; 4, outline of the ninth dorsal vertebra, showing its relation to 
 the lungs and the vertebral column ; 5, thyroid cartilage ; 6, cricoid cartilage ; 7, trachea; 8, right bron- 
 chus ; 9, left bronchus ; 10, crico-thyroid ligament; 11, 12, rings of the trachea; 13, first ring of the tra- 
 chea ; 14, last ring of the trachea, which is corset-shaped ; 15, 16, a complete bronchial cartilaginous 
 ring ; 17, one which is bifurcated ; 18, double bifurcated bronchial rings ; 19, 19, smaller bronchial rings ; 
 20, depressions for the course of the large blood-vessels.] 
 
 * Medico-Chirurgical Transactions, vol. xxviii. 
 
STRUCTURE AND DEVELOPMENT OF HUMAN LUNG. 577 
 
 [Fig. 219. 
 
 A view of the Bronchise and Blood-Vessels of the Lungs as shown by dissection, as well as the rela- 
 tive position of the Lungs to the Heart ; 1, end of the left auricle of the heart ; 2. the right auricle ; 3, 
 the left ventricle with its vessels ; 4, the right ventricle with its vessels; 5, the pulmonary artery ; 6, 
 arch of the aorta ; 7, superior vena cava ; 8, arteria innominata ; 9, left primitive carotid artery ; 10, left 
 subclavian artery ; 11, the trachea ; 12, the larynx ; 13, upper lobe of the right lung ; 14, upper lobe of the 
 left lung; 15, trunk of the right pulmonary artery ; 16, lower lobes of the lungs. The distribution of the 
 bronchia and of the arteries and veins, as well as some of the air-cells of the lungs, is also shown in 
 this dissection.] 
 
 other Reptile ; the whole lung of the Mammal being made up of a multitude 
 of such lobules, which are almost exact repetitions of each other. There is, 
 however, this difference ; that the air-cells in the lung of the Reptile are mere 
 sacculated depressions in the walls of the cavity, opening very freely into it ; 
 whilst the air-cells of each lobule of the lung of the Mammal are arranged 
 around the central passage in such numbers, that the outer ones can only 
 communicate with this passage through the medium of those which are nearer 
 the middle of the cluster. Those cells which communicate directly with the 
 bronchial tubes and intercellular passages, open into them by large circular 
 apertures ; and they are themselves similarly opened into by other cells, which 
 again communicate with others beyond them ; so that each of the openings 
 in the air-passage leads to a series of air-cells, extending from it to the surface 
 of the lobule. These cells have also lateral communications with each other. 
 The walls of the air-cells are formed of a very thin and transparent mem- 
 brane, which is folded sharply at the orifices of communication, so as to 
 form a very definite border to them; and the capillary plexus is so placed 
 between the two layers, which form the walls of two adjacent air-cells, as to 
 expose one of its surfaces each ; by which provision, the full influence of the 
 air upon it is secured. 
 49 
 
578 OF RESPIRATION. 
 
 a. It appears from the researches of M. Bourgery,* that the development of the air-cells 
 continues in the human subject up to the age of thirty, at which time the capacity for re- 
 spiration is the greatest; it subsequently decreases, especially in persons who suffer from 
 cough, the violence of which expiratory effort frequently causes rupture of the air-cells, 
 and thus gradually produces that emphysematous state of the lungs, which is so common in 
 elderly persons. The power of increasing the volume of air taken in, by a forced inspira- 
 tion, is much less in the old person than in the child, though the average amount of air in- 
 spired may be the same; hence the young person possesses a greater capacity of respiration, 
 as it were, in reserve ; whilst the old man has little, and is, therefore, unfit for great exer- 
 tion. 
 
 b. The Lungs are developed, in the first instance, as diverticula from the oesophageal tube. 
 In the Chick, about the fourth day, a little sacculus is described as shooting forth at its pos- 
 terior and inferior part; and this soon subdivides at its lower part into two; at the same 
 time becoming more separated from the tube, by a constriction around the neck, which soon 
 elongates so as to form the trachea. On the fifth or sixth day, the lung of one side is com- 
 pletely distinct from that of the other, and each 
 
 Fi\ 220. i Attached to the common pedicle by a pecu- 
 
 liar branch, the future bronchus. The upper 
 portion has much thicker walls than the lower ; 
 and these appear to contain a large quantity 
 of vesicular parenchyma, in which the rami- 
 fications of the bronchial tubes subsequently 
 extend themselves. About the tenth or ele- 
 venth day of incubation, these ramifications 
 possess nearly their permanent character and 
 situation. The first trace of the Glottis ap- 
 First appearance of the lungs ; a, in a Fowl at pears about the fifth day; it is then a mere, 
 four days ; 6, in a Fowl at six days ; c, terrnina- s lit in the walls of the oesophagus, resembling 
 lion of bronchus in a very young Pig, that by which the ductus pneumaticus of some 
 
 Fishes, opens into the alimentary canal. The 
 
 formation of the cartilaginous rings of the trachea does not commence until after the twelfth 
 day, when they first appear as transverse striae on the median line of the front only ; they 
 gradually become solid, and extend themselves on either side, until they nearly meet at last 
 on the median line on the back or vertebral side of the tube. 
 
 c. The history of the process in the Human embryo, appears to be very nearly the same. 
 The first appearance of the Lungs takes place about the sixth week, at which time they are 
 simple vesicular prolongations of the cesophageal membrane. Their surface, however, soon 
 becomes studded with numerous little wart-like projections; and these are caused by the 
 formation of corresponding enlargements of their cavity. These enlargements soon become 
 prolonged, and develope corresponding bud-like enlargements from their sides ; and in this 
 manner, the form of the organs is gradually changed, a progressive increase in their bulk 
 taking place from above downwards, in consequence of the extension of the bronchial ra- 
 mifications from the single tube at the apex. At the same time, however, a corresponding 
 increase in the amount of the parenchymatous tissue of the lung is taking place ; for this is 
 deposited in all the interstices between the bronchial ramifications, and might be compared 
 with the soil filling up the spaces amongst the roots of a tree. It is in this parenchyma that 
 the pulmonary vessels are distributed ; and the portion of it which extends beyond the ter- 
 minations of the bronchial tubes, seems to act as the nidus for their further extension. It 
 can be easily shown that, up to a late period of the development of the lungs, the dilated 
 terminations of the bronchi constitute the only air-cells (Fig. 220, c) : but, as already men- 
 tioned, the parenchyma subsequently has additional cavities formed within it. It is a fact 
 of some interest, as an example of the tendency of certain diseased conditions to produce a 
 return to forms which are natural to the fcetal organism, or which present themselves in other 
 animals, that up to a late period in the development of the Human embryo, the lungs do 
 not nearly fill the cavity of the chest, and the pleura of each side contains a good deal of 
 serous fluid. 
 
 758. The network of vessels on the walls of the air-cells is so minute, that 
 the diameter of the meshes is scarcely so great as that of the capillary ves- 
 sels which inclose them. According to Mr. Addison, the capillaries in the 
 lung of a Toad admit, in their natural state, no more than one, or at most two 
 rows of blood-corpuscles ; and the islets of tissue between them are compa- 
 
 * Archives Generates de Medecine, Mars 1843. 
 
STRUCTURE AND DEVELOPMENT OF HUMAN LUNG. 
 
 579 
 
 Arrangement of the Capillaries of the air-cells of 
 the Human Lung. 
 
 ratively large ; whilst, if the lung Fig. 221. 
 
 be congested or inflamed, five or 
 six rows of corpuscles are seen in 
 the vessels ; and the islets of tissue 
 are almost entirely obliterated. 
 The diameter of the Human air- 
 cells is about twenty times greater 
 than that of the capillaries which 
 are distributed upon their parietes ; 
 varying (according to the measure- 
 ment of Weber) from the l-200th 
 to the l-70th of an inch. It has 
 been calculated by M.Rochoux, that 
 as many as 17,790 air-cells are 
 grouped around each terminal bron- 
 chus ; and that their total number 
 amounts to no less than 600 mil- 
 lions. 
 
 759. The fibrous coat of the bronchial tubes possesses a considerable amount 
 of contractility, which can scarcely be regarded as otherwise than muscular. 
 From the experiments of Dr. C. B. Williams,* it appears that all the air- 
 tubes are endowed with a considerable amount of contractility, which may 
 be excited by electrical, chemical, or mechanical stimuli, applied to them- 
 selves ; but this is not so readily excitable through their nerves, although the 
 experiments of Volkmann and Longet have clearly shown the possibility of 
 thus calling -it into action ( 410). This contractility resembles that of the 
 intestines or arteries, more than that of the voluntary muscles or heart ; the 
 contraction and relaxation being more gradual than that of the latter, though 
 less tardy than that of the former. It is chiefly manifested in the smaller 
 bronchial tubes ; since, in the trachea and the larger bronchi, the cartilaginous 
 rings prevent any decided diminution in the calibre of the tube. Wedemeyer 
 did not succeed in producing any distinct contraction of the fibres of the tra- 
 chea and larger bronchi ; but he states that tubes of less than a Ime in dia- 
 meter could be perceived to contract gradually under the stimulus of galva- 
 nism, until their cavity was nearly obliterated. It is remarked by Dr. Williams, 
 that the contractility of the bronchial muscles is soon exhausted by the action 
 of a stimulus ; but that it may in some degree be restored by rest, even when 
 the lung is removed from the body. When the stimulation is long continued, 
 however, as by intense irritation of the mucous membrane during life, the 
 contractile tissue passes into a state which resembles that of the tonic con- 
 traction of muscular fibre ( 593). The contractility is greatly affected by 
 the mode of death, and is remarkably diminished by the action of vegetable 
 narcotics, particularly stramonium and belladonna ; whilst it seems to be scarcely 
 at all affected by hydrocyanic acid. These facts are very important, as 
 throwing light upon certain diseased conditions. It has long been suspected, 
 that the dyspnoea of Spasmodic Asthma depends upon a constricted state of 
 the smaller bronchial tubes, excited through the nervous system, frequently 
 by a stimulating cause at some distance ; and there can now be little doubt 
 that this is the case. The peculiar influence of stramonium and belladonna, 
 in diminishing the contractility of these fibres, harmonizes remarkably with 
 the well-known fact of the relief frequently afforded by them in this distress- 
 ing malady. 
 
 760. The Lungs themselves are to be regarded as quite passive in the 
 
 * Athenaeum Report of the Meeting of the British Association, 1840, p. 802. 
 
580 OF RESPIRATION. 
 
 movements of respiration ; the renewal of their contained air being accom- 
 plished by the action of the muscles external to the thorax, or partly forming 
 its parietes. The lung completely fills the cavity of the pleura, in the healthy 
 state at least; so that, when this is enlarged, a vacuum is produced, which 
 can only be filled by a corresponding enlargement of the lung ; and to pro- 
 duce this, the air rushes down the trachea, and passes to the remotest air-cells. 
 
 a. The distension of the whole tissue of the lung, which is effected in this manner, is 
 much more complete than that, which could be occasioned by simple insufflation from the 
 trachea ; a fact of which it has been proposed to take advantage in juridical inquiries in 
 regard to suspected cases of Infanticide, where the lungs are found to float, and the defence 
 is set up that the child was still-born, and that air was blown into the chest for the purpose 
 of resuscitating it. It has been ascertained by the experiments of Mr. Jennings,* that if a 
 piece of lung, which has been filled with air by insufflation, be exposed to great pressure, 
 the air may be expelled from it sufficiently to cause it to sink in water; but that no pressure 
 can produce the same effect upon that which has been filled by a natural inspiratory effort. 
 It is a serious objection to the use of this test of juridical investigations, however, that the 
 early inspiratory efforts of the infant are often so feeble, as to produce but a very imperfect 
 dilatation of the air-cells; so that the lung of an infant which has naturally inspired cannot, 
 by such means, be distinguished from one that has been artificially inflated. The fact ascer- 
 tained by Mr. J., however, is one of much physiological interest. Owing to the freedom 
 with which the air enters the lungs, when there is no abnormal obstruction, the external 
 surface is always in contact with the walls of the chest, so that the pulmonary and costal 
 pleurae glide over one another with every inspiration and expiration. The smooth and 
 moistened character of their surface prevents the movement from producing any sound; but 
 it becomes evident when the friction is increased, either by the dryness that is commonly 
 one of the early changes produced by inflammation, or by the rough deposit that subsequently 
 appears. 
 
 b. The complete dependence of the expansion of the Lungs upon the production of a 
 vacuum in the chest, is well shown by the effect of admission of air into the pleural cavity. 
 When an aperture is made on either side, so that the air rushes in at each inspiratory 
 movement, the expansion of the lung on that side is diminished, or entirely prevented, in 
 proportion to the size of the aperture. If air can enter through it more readily than through 
 the trachea, an entire collapse of the lung takes place; and by making such an aperture on 
 each side, complete asphyxia is produced. But if it be too small to admit the very ready 
 passage of air, the vacuumi produced by the inspiratory movement is more easily filled by the 
 distension of the lungs, than by the rush of air into the pleural cavity ; so that a sufficient 
 amount of change takes place for the maintenance of life. This is frequently observed in 
 the case of penetrating wounds of the thorax, in the surgical treatment of which, it is of 
 great importance to close the aperture as completely as possible ; when this has been accom- 
 plished, the air that had found its way into the cavity is soon absorbed, and the lung re- 
 sumes its full play. When one lung is obstructed by tubercular deposit, or is prevented in 
 any other way from rightly discharging its function, an opening that freely admits air into 
 the pleural cavity of the other side, is necessarily attended with an immediately fatal result; 
 and in this manner it not unfrequently happens, that chronic pulmonary diseases suddenly 
 terminate in Asphyxia, a communication being opened by ulceration between a bronchial 
 tube and the cavity of the thorax. 
 
 761. The dilatation of the chest during Inspiration, is chiefly accomplished 
 by the contraction of the Diaphragm, which, from the high arch that it pre- 
 viously formed, becomes nearly plane; in this change of figure, it presses on 
 the abdominal viscera, so as to cause them to protrude, which they are ena- 
 bled to do by the relaxation of the abdominal muscles. In ordinary tranquil 
 breathing, the action of the diaphragm is alone nearly sufficient to produce 
 the necessary exchange of air; but, when a full inspiration is required, the 
 cavity of the chest is dilated laterally, as well as inferiorly. This is accom- 
 plished by the Intercostal muscles, the Scaleni, Serrati, and others ; which, 
 by elevating the ribs, bring them and their cartilages more nearly into the 
 same direction, and thus separate them more widely from the median line. 
 Expiration is chiefly effected by the contraction of the abdominal muscles, 
 which at the same time force up the diaphragm by their pressure on the vis- 
 
 * Transactions of the Provincial Medical and Surgical Association, vol. ii. 
 
ACTION OF THE LUNGS IN RESPIRATION. 581 
 
 cera, and depress the ribs ; in the latter movement they are aided by the 
 Longissimus Dorsi, Sacrolumbalis, &c., and also by the elasticity of the car- 
 tilages of the ribs, with that of the air-cells and air-tubes themselves. 
 
 762. It is difficult to form an estimate by observations on one's self, of the 
 usual number and degree of the respiratory movements; since the direction of 
 the attention to them is certain to increase their frequency and amount. In 
 general it may be stated, that from 14 to 18 alternations usually occur in a 
 minute; of these the ordinary inspirations involve but little movement of the 
 thorax ; but a greater exertion is made at about every fifth recurrence. The 
 average numerical proportion of the respiratory movements, to the pulsations 
 of the heart, is about 1 to 5 or 4| ; and when this proportion is widely de- 
 parted from, there is reason to suspect some obstruction to the aeration of the 
 blood, or some disorder of the nervous system. Thus in Pneumonia, in which 
 a greater or less amount of the lung is unfit for its office, the number of respira- 
 tions increases in a more rapid proportion than the acceleration of the pulse ; 
 so that the ratio becomes as 1 to 3, or even 1 to 2, in accordance with the de- 
 gree of engorgement.* In Hysterical patients, however, a similar increase, 
 or even a greater one, may take place without any serious cause; thus Dr. 
 Elliotsont mentions a case, in which the respiratory movements of a young 
 female, through nervous affection, were 98 or even 106, whilst the pulse was 
 104. On the other hand, the respirations in certain typhoid conditions and 
 in narcotic poisoning become abnormally slow, owing to the torpid condition of 
 the nervous centres, the proportion being 1 to 6, or even 1 to 8 ; and in such 
 cases, the lungs not unfrequently become cedematous, from the cause formerly 
 mentioned ( 411). 
 
 763. The amount, also, of the Respiratory Movements is affected by vari- 
 ous morbid conditions ; thus when dislocation of the spine takes place above 
 the origin of the intercostal nerves, but below that of the phrenic, so that the 
 former are paralyzed, the respiratory movement is confined to the diaphragm ; 
 and as this is insufficient, serum is effused into the lungs, and a slow Asphyxia 
 supervenes, which usually proves fatal in from three to seven days. Even 
 where the muscles and nerves are all capable of action, the full performance 
 of the inspiratory movements is prevented, by the solidification or engorge- 
 ment of any par.t of the lung, which interferes with its free distension ; or by 
 adhesions between the pleural surfaces, which offer a still more direct impedi- 
 ment. When these adhesions are of long standing, they are commonly stretched 
 into bands, by the continual tension to which they are subjected. If the 
 impeding cause affect both sides, the movements of both will be alike inter- 
 fered with; but if one side only is affected, its movements will be diminished, 
 whilst those of the other remain natural ; and the physician hence frequently 
 derives an indication of great value, in regard to the degree in which the lung 
 is incapable of performing its functions. It is to be remembered, however, 
 that the action both of the diaphragm and of the elevators of the ribs may be 
 prevented, by pain either in the muscles themselves or in the parts which they 
 move ; thus the descent of the diaphragm is checked by inflammation of the 
 abdominal viscera or of the peritoneum ; and that of the intercostals by rheu- 
 matism, pleuritis, pericarditis, or other painful disorders of the parts forming 
 the parietes of the thorax ( 431). 
 
 764. The capacity of the Lungs for air varies considerably in different in- 
 dividuals ; and as the most complete expiration does not by any means empty 
 
 * See a Paper by Dr. Hooker, on the Relation between the Respiratory and Circulating 
 Functions, in the Boston (N. E.) Medical and Surgical Journal ; an abstract of which will be 
 found in British and Foreign Medical Review, vol. vi. p. 263. 
 
 t Physiology, p. 215. note. 
 
 49* 
 
582 OF RESPIRATION. 
 
 them, it is not possible to ascertain it with accuracy. But the amount which 
 can be expelled by a forcible expiration, after a full inspiration, may be taken 
 as a measure of the comparative " capacity of respiration" in different indi- 
 viduals ; and the researches of Mr. Hutchinson have shown that, in the state 
 of health, this bears a very constant proportion to the height. Thus he found 
 that the average capacity of men of 5 ft. 7 in. is about 224 cubic inches, whilst 
 that of men of 5 ft. 2 in. is about 173 cubic inches, and that of men of 6 feet, 
 about 255 cubic inches. The size of the chest affords no good indication of 
 the capacity of expiration. The results of such examinations are so nearly 
 uniform, that disease may be suspected in any man, who cannot blow out 
 nearly so many cubic inches as the average of those of the same height ; the 
 only exceptions among healthy subjects, being in the case of fat men, whose 
 capacity is always low. It is obvious from these facts, that the amount of air 
 ordinarily respired will vary greatly in different individuals ; and this is doubt- 
 less one source of the discrepancy of the results of the various experiments, 
 which have been made to determine this point. Some of the most recent ex- 
 periments on the subject are those of Mr. Coathupe,* in which the Author has 
 much reason to feel confidence. According to his estimate, about 266 cubic 
 feet, or 460,224 cubic inches of air, pass through the lungs of a middle-sized 
 man in 24 hours; reckoning the average number of inspirations at 16 per 
 minute, this would give 20 cubic inches as the amount inhaled at each. 
 
 2. Effects of Respiration on the Mr. 
 
 765. We naturally pass from the foregoing inquiries, to those that relate to 
 the alterations in the Air, which are effected by Respiration. These mainly 
 consist in the removal of a portion of the Oxygen, and the substitution of a 
 quantity of Carbonic Acid, rather less in bulk than the Oxygen which has 
 disappeared. The proportion of the air thus changed appears to vary accord- 
 ing to the frequency of the respirations. Thus Vierordt found that, if he only 
 respired six times in a minute, the quantity of Carbonic acid was 5*5 per 
 cent, of the whole air exhaled ; with twelve respirations, it was 4*2 ; with 
 twenty-four, it was 3*3 ; with forty-eight, it was 3*0 ; and with ninety-six, it 
 was 2*6 per cent. In some of the experiments of Messrs. Allen and Pepys, 
 it was as much as 8 per cent. Probably about 4 per cent, may be taken as 
 the average, at the ordinary rate of respiration. It appears, however, from the 
 researches of the last-named experimenters, that if the air be already charged 
 in some degree with Carbonic acid, the quantity exhaled is much less ; for 
 when 300 cubic inches of air were respired for three minutes, only 28 cubic 
 inches (9 per cent.) of Carbonic acid were found in it; although the previous 
 rate of its production, when fresh air was taken in at every respiration, was 
 32 cubic inches in a minute. Knowing, then, the necessity of a free excre- 
 tion of carbonic acid, we are led by this fact to perceive the high importance 
 of ventilation ; for it is not sufficient for health, that a room should contain the 
 quantity of air requisite for the support of its inhabitants during a given time ; 
 since after they have remained in it but a part of that time, the quantity of 
 carbonic acid which its atmosphere will contain, will be large enough to inter- 
 fere greatly with the due aeration of their blood, and will thus cause oppres- 
 sion of the brain and the other morbid affections that result from the accumu- 
 lation of carbonic acid in the circulating fluid. On the other hand, it has been 
 ascertained by the recent experiments of Dr. Boswell Reid that, if the carbonic 
 acid be removed as fast as it is formed, an animal may remain in a limited 
 quantity of air, without much inconvenience, until nearly the whole of its 
 
 * Athenaeum Report of Meeting of the British Association, 1839; p. 707. 
 
EXCHANGE OF OXYGEN AND CARBONIC ACID. 583 
 
 oxygen is exhausted ; thus showing that the respirability of air does not de- 
 pend so much upon the proportion of oxygen it contains, as upon its freedom 
 from contamination with carbonic acid or other poisonous gases. 
 
 766. The reaction which thus takes place between the Air and the Blood, 
 is easily explained upon physical principles. If the Blood come to the Lungs 
 charged with Carbonic acid, and is exposed in their cells to the influence of 
 atmospheric air, which is a mixture of Oxygen and Nitrogen, an endosmose 
 and exosmose of gases will take place, according to certain fixed laws.* The 
 Carbonic acid of the blood will pass out, to be replaced by Oxygen and Ni- 
 trogen ; and the quantity of the former which enters will be much greater than 
 that of the latter, on account of the superior facility with which oxygen passes 
 through porous membranes. If the venous blood also contain Nitrogen as 
 well as carbonic acid, this also will pass out, to be replaced by the Oxygen of 
 the air. Thus, there will be a continual Exosmose of Carbonic acid and Ni- 
 trogen, and a continual Endosmose of Oxygen and Nitrogen. The exhalation 
 and absorption of Nitrogen appear usually to balance each other; so that the 
 amount of this gas in the respired air undergoes little or no change. But the 
 case is different in regard to the exchange of Carbonic acid and Oxygen. 
 According to the law of mutual diffusion of gases, the volume of Oxygen that 
 is taken in, should exceed that of the Carbonic acid which passes out, in the 
 proportion of 1174 to 1000. This calculation, deduced from the relative 
 densities of the two gases, corresponds so closely with the actual results of 
 experiments upon the respiration of Man, that the interchange may be regarded 
 as always taking place in accordance with the law of mutual diffusion ; so 
 that, from the amount of Carbonic acid exhaled, the quantity of Oxygen ab- 
 sorbed may be readily calculated.! Now as Carbonic acid contains its own 
 bulk of Oxygen, it follows that the amount of Oxygen absorbed exceeds that 
 which is given off, by 174 parts in every 1000 ; so that a quantity of oxygen, 
 equal to more than one-sixth of that which is converted into Carbonic acid, is 
 employed in the system for other purposes. It appears probable that a part 
 of this additional Oxygen is made to combine with Hydrogen furnished by the 
 food or by the disintegration of the tissues ; and that the water thus generated 
 forms part of that exhaled from the lungs ; whilst another part will be applied 
 to the oxidation of the Sulphur and Phosphorus, which are taken in as such 
 in the food, and which, after forming part of the solid tissues, are excreted in 
 the condition of Sulphuric and Phosphoric acids, chiefly through the kidneys. 
 
 767. The absolute quantity of Carbonic Acid exhaled from the Lungs is 
 liable to variation from so many sources, that no fixed standard can be 
 assigned for it. The mean of a great number of observations, however, 
 made in different modes, and under different circumstances, would give about 
 160 grains of Carbon per hour as the amount set free by a well-grown adult 
 man, under ordinary circumstances. Taking this as the average of the 
 twenty-four hours, the total quantity of Carbon thus daily expired from the 
 Lungs would be 3840 grains, or 8 oz. Troy. The chief causes of variation 
 are, the Temperature of the surrounding medium, Age, Sex, Development 
 of the body, state of Health or Disease, Muscular Exertion or Repose, Sleep 
 or Watchfulness, Period of the Day, and state of the . Digestive process. 
 These will now be considered in detail. 
 
 a. Temperature of surrounding Medium. The amount of Carbonic Acid exhaled by 
 warm-blooded animals is greatly increased by external Cold, and diminished by Heat; as is 
 shown by the following results of comparative experiments upon the quantity set free by 
 the same animals, at low, medium, and high temperatures, in periods of an hour (Letellier). 
 
 * See Principles of General and Comparative Physiology, 437 9. 
 j" Valentin's Lehrbuch der Physiologic, vol. i., pp. 507-SSO. 
 
584 OF RESPIRATION. 
 
 Temp, about 32. Temp. 59 68. Temp. 86 106. 
 
 Grammes. Grammes. Grammes. 
 
 A Canary - -. - 0-325 0-250 0-129 
 
 A Turtle-Dove - - 0-974 0*684 0-336 
 
 Two Mice - - - 0-531 0-498 0-268 
 
 A Guinea-Pig - - 3'006 2-080 1-453 
 
 From this table it appears that the quantity of carbonic acid exhaled by Mammals between 
 86 and 106 is less than half that set free near the freezing-point; whilst that which is 
 exhaled between 59 and 68 is but little more than two-thirds of the same amount. The 
 diminution occasioned by heat is still more remarkable in Birds; which exhaled at the 
 highest temperature scarcely more than one-third of that set free at the lowest. The ob- 
 servations of Vierordt upon himself show that the same is true of the Human subject ; a 
 difference of 10 Fahr., according to him, producing a variation of rather more than two 
 cubic inches in the amount of Carbonic Acid hourly expired. 
 
 b. Age. The amount of Carbonic Acid exhaled increases in both sexes up to about the 
 thirtieth year; it remains stationary until about the forty-fifth ; and then diminishes. The 
 following are the comparative results of experiments upon males of different ages, and of a 
 moderate degree of muscular development (Andral and Gavarret). 
 
 Carbon exhaled Carbon exhaled 
 
 Age. per hour. Age. per hour. 
 
 8 years - - 77-0 grains 37 years - - 164-7 grains. 
 
 12 " - - 113-9 " 48 " - - 161-7 " 
 14 - - 126-2 " 59 " - - 154-0 
 
 ' 20 " - - 166-3 " 68 " - - 147-8 " 
 
 26 " - - 169-4 " 76 " - - 92-4 " 
 
 c. Sex. At all ages beyond eight years, the exhalation is greater in Males than in Fe- 
 males. Nearly the same proportionate increase takes place, however, in females, up to the 
 time of puberty; when the quantity abruptly ceases to increase, and remains stationary so 
 long as they continue to menstruate. When, however, menstruation has ceased, the exhala- 
 tion of carbonic acid begins again to augment; and then again diminishes, with the advance 
 of years, as in men. Should menstruation temporarily cease at any time, the exhalation of 
 carbonic acid immediately undergoes an increase, precisely as at the final cessation of the 
 function. And during pregnancy, the exhalation increases in like manner. The following 
 table of the comparative respiration of females at different ages, will serve at the same 
 time for comparison with the preceding, so as to exhibit the general difference between the 
 two sexes, at ages nearly corresponding ; and also to indicate the peculiar modifications 
 induced by the operations of the genital system (Andral and Gavarret). 
 
 Carbon exhaled After Cessation of Catamenia. 
 
 Age. per hour. Carbon exhaled 
 
 10 years - - 92-4 grains Age. per hour. 
 
 13 - - 97-0 " 38 years - - 120-3 grains. 
 During Menstrual life. 49 - - 113-9 " 
 
 15^ years - - 97-0 grains. 52 - - 115-5 " 
 
 26 " - 97-0 " 56 " - - 119-3 " 
 
 32 " - - 95-4 66 - - 104-7 " 
 
 45 " - - 95-4 76 " - - 101-4 " 
 
 During Pregnancy. 82 - - 92-4 " 
 
 22 years - - 129-3 grains. 
 
 32 " - - 126-7 
 
 42 " - - 120-3 " 
 
 d. Development of the Body. The more robust the individual, cateris paribus, the more 
 Carbonic Acid is exhaled ; and the variation is much more influenced by the development 
 of the muscular system, than by the height, or weight, capacity of the chest, &c. Thus, a 
 very strong man of twenty-six years of age exhaled at the rate of 217-1 grains per hour; 
 when a man of moderate muscular power set free but 169-4 grains in the same time. An- 
 other robust man of sixty years of age exhaled at the rate of 209-4 per hour; another of 
 similar constitution, and sixty-three years of age, at the rate of 190-9 grains per hour ; and 
 an old man of 92 years, who still preserved an uncommon degree of energy, and who in 
 his younger days had boasted of extraordinary muscular powers, exhaled at the rate of 135-5 
 grains per hour. So also, a remarkably vigorous young woman of nineteen years exhaled 
 at the rate of 107-8 grains per hour ; another of twenty-two years, rather less powerful, at 
 the rate of 103*1 grains; and a strong woman of forty-four years (who had ceased to men- 
 struate) 152-4 grains. On the other hand, a slender man of forty-five years, in the enjoy- 
 
AMOUNT OF CARBONIC ACID EXHALED. 585 
 
 merit of good health, only exhaled at the rate of 132-4 grains per hour (Andral and Ga- 
 varret). 
 
 e. State of Health or Disease. Upon this very important cause <?f variation, few accurate 
 researches have yet been made. The per centage of carbonic acid in the expired air has 
 been found to be unusually great in the Exanthemata, and in chronic skin diseases (Mac- 
 gregor) ; and it has been stated to be diminished in typhus (Malcolm). Thus, the average 
 proportion in health being about 3 f 96 per cent. (Prout), it has been seen at 8 per cent, in 
 confluent small-pox, at 5 per cent, in measles, and at 7-2 per cent, in a severe case of icthyosis 
 which terminated fatally; whilst in Typhus the per centage has been found to range from 
 1*18 to 2-50. / But these statements do not indicate the total quantity exhaled in each case. 
 The remarkable increase of the exhalation in cases of Chlorosis, has been already noticed; 
 in four cases recorded by Hannover, the hourly expiration was 123'6, 118-6, 116-9, and 106-3 
 grains, the absolute quantity diminishing as the respirations increased in rapidity. In chronic 
 diseases of the respiratory organs, as might be anticipated, the amount of Carbonic acid ex- 
 haled undergoes a sensible diminution (Nysten and Hannover). Further researches are 
 much needed on this subject; but, for obvious reasons, they cannot be readily made in severe 
 forms of disease. 
 
 /. Muscular Exertion or Repose. The effect of bodily exercise, in moderation, is to produce 
 a considerable increase in the amount of carbonic acid exhaled, both during its continuance, 
 and for some little time subsequently to its cessation. According to the observations of Vie- 
 rordt, the increase amounts to one-third of the quantity exhaled during rest ; and it lasts for 
 more than an hour afterwards, being manifested in the greater quantity of air respired, and 
 in the larger per centage of carbonic acid contained in it. If the exercise be prolonged, 
 however, so as to occasion fatigue, it is succeeded by a diminished exhalation. The connec- 
 tion between muscular exertion and the exhalation of carbonic acid, is most remarkably 
 shown in Insects ; in which animals we may witness the rapid transition between the op- 
 posite conditions of extreme muscular exertion, and tranquil repose ; and in which the effects 
 of these upon the respiratory process are not masked by that exhalation of carbonic acid, 
 which is required in warm-blooded animals simply for the maintenance of a fixed tempera- 
 ture. Thus a Humble-Bee has been found to produce one-third of a cubic inch of carbonic 
 acid, in the course of a single hour, during which its whole body was in a state of constant 
 movement, from the excitement resulting from its capture ; and yet, during the whole twenty- 
 four hours of the succeeding day, which it passed in a state of comparative rest, the quantity 
 of carbonic acid generated by it was absolutely less. 
 
 g. Sleep or Watchfulness. The amount of carbonic acid exhaled during sleep is considera- 
 bly less than that set free in the waking state. This is particularly shown by the experi- 
 ments of Scharling; who confined the subjects of them in an air-tight chamber, within 
 which they could sleep, take their meals, &c. Thus in one case, the hourly exhalation sank 
 from 160 to 100, in another from 194*7 to 122-3, and in another from 99 to 75-1. The cause 
 of this result is partly to be sought in the cessation of all muscular exertion (save that con- 
 cerned in the maintenance of the respiration) ; and partly in the diminution in the dissipa- 
 tion of the heat of the body itself. 
 
 h. State of the Digestive Process. It is well established, that the exhalation of carbonic acid 
 is greatly increased by eating, and that it is diminished by fasting. Thus Prof. Scharling 
 states the hourly exhalation to have increased in one instance from 145 to 190, after break- 
 fast and a walk ; in another from 140 to 177 after breakfast alone ; and in another from 1 1 1'9 
 to 188'9, after dinner. It is remarkable that alcoholic drinks have a tendency to diminish the 
 exhalation of carbonic acid, especially when taken into an empty stomach; and strong tea is 
 said to have the same effect (Prout, Vierordt). The quantity is also increased by exhilarating 
 emotions, and decreased by depressing affections of the mind (Prout). 
 
 t. Period of the Day. Independently of these variations, which have their source in the 
 condition of the individual, there appears to be a slight tendency to increase in the quantity 
 of carbonic acid exhaled during the early part of the day, and a steady decrease during the 
 afternoon; so that, in the evening the quantity is decidedly less than in the morning. It is 
 very difficult to separate the effects of this influence, however, from those of the causes pre- 
 viously adverted to. 
 
 768. The aeration of the blood may take place, not only by means of the 
 Lungs, but also through the medium of the Cutaneous surface. In some of 
 the lower tribes of animals, indeed, this is a very important part of their 
 respiratory process : and even in some Vertebrata, the cutaneous respiration 
 is capable of supporting life for a considerable time. This is especially the 
 case in the Batrachia, whose skin is soft, thin, and moist ; and the effect is 
 here the greater, since the blood which circulates through the system is, from 
 
586 OF RESPIRATION. 
 
 \ 
 
 the small proportion of it that has passed through the lungs, very imperfectly 
 arterialized. By the experiments of Bischoff it was ascertained that, even 
 after the lungs of a Frog had been removed, a quarter of a cubic inch of car- 
 bonic acid was exhaled from the skin, during eight hours. Experiments which 
 have been made on the Human subject leave no room for doubt, that a similar 
 process is effected through the medium of his general surface ; for, when a 
 limb has been inclosed for some hours in an air-tight vessel containing atmo- 
 spheric air freed from carbonic acid, a sensible amount of this gas has been 
 found to be generated. Moreover, it has been observed not unfrequently, that 
 the livid tint of the skin which supervenes in Asphyxia, owing to the non- 
 arterialization of the blood in the lungs, has given place after death to the 
 fresh hue of health, owing to the reddening of the blood in the cutaneous 
 capillaries by the action of the atmosphere upon them. We have no means 
 of ascertaining the usual amount of carbonic acid excreted through the Skin, 
 except by determining the whole quantity disengaged from the body, and sub- 
 tracting the portion exhaled from the lungs ; and no sufficiently precise experi- 
 ments upon this subject have yet been made. The only way to separate the 
 results of the pulmonary and cutaneous exhalation of carbonic acid, would be 
 to confine the body in a close chamber, into which the product of the cutaneous 
 respiration might freely pass ; whilst the pulmonary respiration during the 
 same period should be measured by a distinct apparatus. It is not improbable 
 that, in cases of obstruction to the due action of the lungs, the exhalation of 
 carbonic acid through the skin may undergo a considerable increase ; for we 
 find a similar disposition to vicarious action in other parts of the excreting 
 apparatus. Moreover, there is evidence, that the interchange of gases between 
 the air and the blood, through the skin, has an important share in keeping up 
 the temperature of the body (Chap, xvi., Sect. 2) ; and we find the tempera- 
 ture of the surface much elevated in many cases of pneumonia, phthisis, &c., 
 in which the lungs seem to perform their function very insufficiently. 
 
 3. Effects of Respiration on the Blood. 
 
 769. That an important change is effected in the character of the Blood, by 
 exposure to Atmospheric air in the lungs, has been known, from the time 
 when it was first ascertained that it is regularly transmitted to those organs. 
 The most obvious part of this change is the alteration in its colour, from the 
 dark purple of the venous fluid, to the rich crimson of the arterial. But this 
 alteration is only the index of changes far more important, which occur in its 
 chemical constitution. Respecting the nature of these changes, there has 
 been, as formerly stated, much difference of opinion ; some maintaining that 
 the carbonic acid exhaled is formed in the lungs ; and others, that it is con- 
 tained in the venous blood, and is truly excreted from it. The latter opinion, 
 which was long since brought forward by La Grange and Hassenfratz, has 
 recently obtained such full confirmation, from the experiments of Spallanzani, 
 Edwards, Miiller, Bischoff, Magnus, and others, as to have a full claim for 
 adoption as a physiological truth. These experiments are of two kinds ; first, 
 those which show that an exhalation of carbonic acid may continue for a long 
 time, when the animal is breathing an atmosphere in which no oxygen exists ; 
 and, secondly, those which prove that much more carbonic acid exists in an 
 uncombined state in venous blood than in arterial, whilst more oxygen exists 
 in a similar condition in arterial blood than in venous. The results of these 
 will now be briefly stated. It was shown by Spallanzani, that Snails might 
 be kept for a long period in Hydrogen, without apparent injury to them ; and 
 that during this period they disengaged a considerable amount of Carbonic 
 acid. Dr. Edwards subsequently ascertained that, when Frogs were kept in 
 
EFFECTS OF RESPIRATION ON THE BLOOD. 587 
 
 hydrogen for several hours, the quantity of carbonic acid exhaled was fully as 
 great as it would have been in atmospheric air, or even greater ; this latter fact, 
 if correct, may be accounted for, by the superior displacing power, which (on 
 the laws of the diffusion of gases) hydrogen possesses for carbonic acid. 
 Collard de Martigny repealed this experiment in nitrogen, with the same re- 
 sults. In both sets of experiments, the precaution was used of compressing 
 the flanks of the animal, previously to immersing it in the gas, so as to expel 
 from the lungs whatever mixture of oxygen they might contain. These ex- 
 periments have been since repeated by Miiller and Bergemann, who took the 
 additional precaution of removing, by means of the air-pump, all the atmo- 
 spheric air that the lungs of the frog might previously contain, together with the 
 carbonic acid that might exist in the alimentary canal. They found in one of 
 their experiments, that the quantity of carbonic acid exhaled in hydrogen was 
 nearly a cubic inch in 65 hours ; and in another, that nearly the same amount 
 was given off in nitrogen ; but this required rather a longer period. It appears 
 from the table of their results,* that the amount was not ordinarily greater in 
 the experiments which were prolonged for twelve or fourteen hours, than in 
 those which were terminated in half the time ; hence it may be inferred, that the 
 quantity which the blood is itself capable of disengaging is limited, and that 
 the absorption of oxygen is necessary to enable carbon to be set free from the 
 tissues. It is impossible, however, for an adult Bird or Mammal to sustain 
 life for any considerable time, in an atmosphere deprived of oxygen; since the 
 greatly-increased rapidity and energy of all their vital operations, necessitate 
 a much more constant supply of this vivifying agent, than is needed by the 
 inferior tribes ; and, as we shall presently see, the capillary action necessary 
 for the passage of the blood through the lungs will not take place without it. 
 But Dr. Edwards has shown, that young Mammalia can sustain life in an 
 atmosphere of hydrogen or nitrogen, for a sufficient length of time to exhale a 
 sensible amount of carbonic acid ; so that the character of the process is clearly 
 proved to be the same in them, as in Reptiles and Invertebrata. 
 
 770. That the changes which Venous Blood undergoes in the lungs, are to 
 be explained upon principles of a purely chemical and physical nature, is evi- 
 dent from the fact, that the same changes will take place when it is exposed 
 to the air out of the body, even through the medium of a thick membrane, such 
 as a bladder. Such changes, however, only affect the surface of the fluid; but 
 this is exactly what we should expect, since the air has no access to the part 
 beneath. The Blood, whilst circulating through the capillaries of the Lungs, 
 is divided into an innumerable multitude of minute streamlets, each so small 
 as to admit but a single layer of its corpuscles; and in these, therefore, the 
 surface which is placed in contact with the air is so enormously extended, as 
 to be almost beyond calculation. Hence, then, we can at once understand 
 how such a change may be instantaneously effected in it, as would occupy 
 several hours, when the blood is less advantageously exposed to the influence 
 of oxygen. In studying the nature of these alterations, it is very necessary 
 to ascertain whether Oxygen and Carbonic Acid exist in a free state in the 
 Blood; and to what extent their proportions differ in Venous and Arterial 
 blood. The late researches of Professor Magnus have shown that Blood 
 possesses a very remarkable absorbing power for these gases, especially for 
 Carbonic acid. By freely exposing it to the latter gas, it was found that it 
 could take up as much as 1^ times its bulk; and that after all its Oxygen and 
 Nitrogen had been thus displaced, it could still absorb as much as 16 per 
 cent, of its volume of Oxygen, and 6*3 of Nitrogen, on being exposed to those 
 gases respectively. The usual quantity of Oxygen present in arterial blood 
 
 * Miiller's Physiology, p. 341. 
 
588 OF RESPIRATION. 
 
 is, according to the experiments of Magnus, about 10 per cent.; but while 
 passing through the systemic capillaries, this is diminished about one-half, so 
 that Venous blood does not contain more than 5 per cent, of its volume of 
 Oxygen. On the other hand, the Carbonic acid of Arterial blood is about 20 
 per cent, of its volume ; and this proportion is increased in Venous blood to 
 nearly 25 per cent. The amount of Nitrogen varies considerably, being some- 
 times as little as 1'7 per cent, of the volume of the blood, and sometimes 
 nearly double that proportion ; it does not appear to differ, according to any 
 constant law, in arterial and venous blood.* 
 
 771. There can be little doubt, then, that the changes which the function 
 of Respiration effects in the Blood have reference in great part to the relative 
 proportions of the different gases, which it holds in solution. And although 
 it might appear that the change of colour, which the Red Corpuscles undergo, 
 is a proof of a change of composition in the Haematine which they contain, 
 yet such a supposition is not borne out by experiment ; for no difference of 
 composition has been detected, between the Haematine of Venous and that of 
 Arterial blood ; and it appears from the researches of Peligot on the action of 
 the protoxide of nitrogen upon solutions of the salts of the protoxide of iron, 
 that liquids may have their colour changed by the absorption of gases, which 
 form no chemical union with them. There seems reason to conclude, how- 
 ever, from the statements formerly quoted ( 115) in regard to the difference 
 between the Fibrine of Venous and that of Arterial blood, that Oxygen derived 
 from the inspired air enters into actual combination with this element ; and 
 the same may very probably be true of other constituents of the blood : so 
 that we are to regard the influence of Respiration as partly exerted in modify- 
 ing the proportions of the gases dissolved in the blood, substituting Oxygen 
 for a portion of its Carbonic Acid ; and partly in enabling the ingredients of 
 the liquid to enter into new combinations with the Oxygen of the air. For 
 the reasons formerly stated ( 150) it appears probable that, whether or not 
 their Haematine be chemically affected by the change, the Red Corpuscles are 
 the chief carriers of the two gases to be interchanged, between the pulmonary 
 and systemic capillaries. 
 
 772. Although the alteration in the relative proportions of Oxygen and Car- 
 bonic acid which it contains, is doubtless the essential change effected in the 
 Blood by the Respiratory process, the alteration in its colour is the most ob- 
 vious ; and this is, under ordinary circumstances, an indication that the other 
 change has taken place. Thus, if Arterial blood be exposed, out of the body, 
 to carbonic acid, it will acquire the dark hue of venous blood; and Venous 
 blood exposed to it becomes darker still. On the other hand, if Venous 
 blood be exposed to Oxygen, it acquires the Arterial hue. The presence of a 
 certain amount of saline matter appears, from the experiments of Dr. Stevens 
 and others, to be a condition necessary for the due influence of oxygen upon 
 the colour of the blood; since, if it be deficient, the contact of oxygen will not 
 produce its usual effect. On the other hand, the addition of saline matter 
 (especially nitre) will occasion a decided change of hue in venous blood, with- 
 out any extrication of carbonic acid or absorption of oxygen. 
 
 * For the latest researches of Prof. Magnus, which have had their origin in the objections 
 of M. Gay Lussac to those previously published by him, see the Annalen der Physik und 
 Chemie, vol. Ixvi., p. 177, and an Abstract in the Philosophical Magazine, Dec. 1845, Suppl. 
 In these researches, far greater success was obtained in removing the gases from the blood, 
 than in any previous experiments ; and the account of their proportions, therefore, is more 
 satisfactory. It is extremely difficult to avoid all sources of error, in such researches ; but 
 the constancy of the results obtained by Magnus indicates that we may place much confidence 
 in them. 
 
ABSORPTION THROUGH THE LUNGS. 589 
 
 a. It has recently been attempted, by Mulder and others, to account for the change of hue 
 under the influence of carbonic acid, oxygen, and saline matter, by a change of form in the 
 red corpuscles ; which are supposed to be bi-concave and reflecting in bright coloured blood, 
 and bi-convex and refracting in blood presenting the venous tint. But the supposition is not 
 borne out by minute and careful observations on the forms of the corpuscles, nor by varied 
 experiments on the effects of re-agents. As Dr. G. 0. Rees has shown, the blood-corpuscles 
 may be changed in form, without any consequent change of colour ; whilst, on the other 
 hand, the blood is reddened by saline solutions, whether they produce endosmose or exos- 
 mose in the red corpuscles, thus either filling or emptying them, and rendering them either 
 bi-convex or bi-concave. 
 
 773. Exhalation and Absorption by the Lungs. The alteration in the 
 proportions of its usual gaseous ingredients, is by no means the only change 
 which the Blood undergoes in the Lungs. It parts also, with a considerable 
 amount of water, in the form of vapour; this usually contains a certain pro- 
 portion of animal matter; and it is sometimes charged with volatile substances, 
 which have been elsewhere introduced into the blood, or which have been 
 formed during its assimilation. It may also absorb from the atmosphere vola- 
 tile matter diffused through it. Both these changes are probably to be ex- 
 plained upon simple physical principles ; being dependent on the exposure of 
 the blood to the atmosphere, over a very extensive surface, and through a 
 membrane of great permeability. Of the fluid ordinarily exhaled with the 
 breath, a part doubtless proceeds from the moist lining of the nostrils, fauces, 
 &c. ; but it is indisputable that the greater proportion of it comes from the 
 lungs, since, when the respiration is entirely performed through a canula intro- 
 duced into the trachea, the amount of watery vapour which the breath contains, 
 is still very considerable. The quantity which thus passes off is by no means 
 trifling; probably between 16 and 20 ounces in the twenty-four hours. It is 
 not so liable to variation under the influence of temperature, the movement of 
 the surrounding air, and other similar causes, as is the cutaneous transpira- 
 tion ; for air, which has found its way into the air-cells of the lungs, is, 
 under almost all circumstances, nearly the same in regard to such conditions, 
 and becomes charged with that amount of watery vapour which saturates it at 
 the temperature of the body. It is considered by Dr. Prout, that the principal 
 source of this vapour is not the blood properly so called, but the chyle and 
 lymph which have just been introduced into it from the thoracic duct; a loss 
 of a portion of their fluid being required, to give them sufficient concentration. 
 A process very analogous takes place in Plants ; for a very large proportion of 
 the water taken up in the crude sap, is parted with in the leaves. But it is 
 probable that a part, at least, of the water thrown off by the lungs is generated 
 by the union of Oxygen and Hydrogen during the course of the Circulation. 
 
 774. The fluid thrown off from the Lungs is not pure water. It holds in 
 solution, as might have been expected, a considerable amount of carbonic acid, 
 and also some animal matter; the exact nature of the latter, which, according 
 to Collard de Martigny, constitutes about 3 parts in 1000, has not been ascer- 
 tained. If the fluid be kept in a closed vessel, and be exposed to an elevated 
 temperature, a very evident putrid odour is exhaled by it. Every one knows 
 that the breath itself has, occasionally in some persons, and constantly in 
 others, a fetid taint; when this does not proceed from carious teeth, ulcerations 
 in the air-passages, disease in the lungs, or other similar causes, it must result 
 from the excretion of the odorous matter, in combination with watery vapour, 
 from the pulmonary surface. That this is the true account of it seems evident, 
 from the analogous phenomenon of the excretion of turpentine, camphor, alco- 
 hol, and other odorous substances, which have been introduced into the venous 
 system, either by natural absorption, or by direct injection; and also from the 
 suddenness with which it manifests itself, when the digestive apparatus is 
 slightly disordered. 
 
 50 
 
590 OF RESPIRATION. 
 
 775. The Lungs are capable, under peculiar circumstances, of absorbing 
 fluid from the atmosphere. Thus Dr. Madden* has shown that, if the vapour 
 of hot water be inhaled for some time together, the loss by exhalation is found 
 to be so much less than usual, as to indicate that the cutaneous transpiration 
 is partly counterbalanced by pulmonary absorption; the pulmonary exhalation 
 being at the same time entirely checked. It is probable that, if the quantity 
 of fluid in the blood had been previously diminished by excessive sweating, 
 or by other copious fluid secretions, the pulmonary absorption would have 
 been much greater. Still in the cases formerly mentioned ( 678), in which 
 a large increase in weight could only be accounted for on the supposition of 
 absorption of water from the atmosphere, it seems probable that the cutaneous 
 surface was chiefly concerned : for it can only be when the air introduced into 
 the lungs is saturated with watery vapour, that the usual exhalation will be 
 checked, or that any absorption can take place. 
 
 776. That absorption of other volatile matters diffused through the air is, 
 however, continually taking place by the lungs, is easily demonstrated. A 
 familiar example, is the effect of the inhalation of the vapour of Turpentine 
 upon the urinary excretion. It can only be in this manner that those gases 
 act upon the system, which have a noxious or poisonous effect, when min- 
 gled in small quantities in the atmosphere. Of these, Sulphuretted Hydrogen 
 is one of the most powerful in its action ; for it has been found that air im- 
 pregnated with l-1500th part of it, will kill a bird in a very short time ; and 
 that a quantity but little more than double, namely l-800th part, will soon kill 
 a dog. This gas is exhaled in large quantities from many forms of decom- 
 posing animal and vegetable matter; and it has recently been shown (by Pro- 
 fessor Daniell) to be absorbed by the water of the estuaries of those African 
 rivers, whose mouths are regarded as among the most pestilential spots upon 
 the surface of the globe. Carburetted hydrogen is another gas whose effects 
 are similar ; but a larger proportion is required to destroy life. Carbonic 
 acid gas, also, appears to be absorbed by the lungs, when a large proportion 
 of it is contained in the atmosphere. The accumulation of this gas in the 
 blood, when the respired air is charged with it even to a moderate amount, 
 might be attributed to the impediments thus offered to its ordinary exhalation : 
 but the following experiment appears to prove, that it may be actually absorbed 
 into the blood ; and that it will thus exert a real poisonous influence, and not 
 merely produce an asphyxiating effect. It was found by Rolando, that the 
 air-tube of one lung of the land-tortoise may be tied, without apparently 
 doing any material injury to the animal, as the respiration performed by the 
 other is sufficient to maintain life for some time ; but, having contrived to make 
 a tortoise inhale carbonic acid by one lung, whilst it breathed air by the other, 
 he found that the animal died in a few hours.t Cyanogen is another gas 
 which has an actively-poisonous influence upon animals, when absorbed into 
 the lungs ; its agency, also, is of a narcotic character. 
 
 777. It is singular that the effects of the respiration of pure Oxygen should 
 not be dissimilar. At first, the rapidity of the pulse and the number of the 
 respirations are increased, and the animal appears to suffer little or no incon- 
 venience for an hour; but symptoms of coma then gradually develop them- 
 selves, and death ensues in six, ten, or twelve hours. If the animals are 
 
 * Prize Essay on Cutaneous Absorption, p. 55. 
 
 j- The fatal result of breathing the fumes of charcoal is, therefore, riot simple asphyxia, 
 such as would result from breathing hydrogen or nitrogen. Other volatile products are set 
 free in the combustion of charcoal, besides carbonic acid. Mr. Coathupe (loc. cit.) states 
 these to be Carbonate, Muriate and Sulphate of Ammonia, Carbonic Oxide, Oxygen, Nitro- 
 gen, Watery vapour, and Einpyreumatic Oil : to these Sulphurous acid may appear to be 
 properly added. 
 
EFFECTS OF SUSPENSION OF RESPIRATION. 591 
 
 removed into the air before the insensibility is considerable, they then quickly 
 recover. When the body is examined, the heart is seen beating strongly 
 while the diaphragm is motionless ; the whole blood in the veins, as well as 
 in the arteries, is of a bright scarlet colour; and several of the membranous 
 surfaces have the same tint. The blood is observed to coagulate with re- 
 markable rapidity ; and it is to the alteration in its properties, occasioned by 
 the hyper-arterialization, and indicated by this condition, that we are proba- 
 bly to attribute the fatal result. There can be no doubt that in this instance 
 an undue amount of oxygen is absorbed ; and it does not seem unlikely that 
 one cause of the fatal result, is a stagnation of the blood in the systemic capil- 
 laries, consequent upon the want of sufficient change in its condition. When 
 Nitrogen or Hydrogen is breathed, for any length of time, death results from 
 the deprivation of Oxygen, rather than from any deleterious influence which 
 these gases themselves exert. Death is also caused by the inhalation of 
 several gases of an irritant character, such as Sulphurous, Nitrous, and Muria- 
 tic acids : but it is doubtful how far they are absorbed ; or how far their 
 injurious effects are due to the abnormal action, which they excite in the 
 lining membrane of the air-cells and tubes. It cannot be doubted, that mias- 
 mata and other morbific agents diffused through the atmosphere, are more 
 readily introduced into the system through the pulmonary surface than by 
 any other ; and our aim should therefore be directed to the discovery of some 
 counteracting agents, which can be introduced in the same manner. The 
 pulmonary surface affords a channel for the introduction of certain medicines 
 that can be raised in vapour, when it is desired to affect the system with them 
 speedily and powerfully ; such are iodine, mercury, tobacco, stramonium, &c. 
 
 4. Effects of Suspension of Respiration. 
 
 778. We have now to consider the results of the cessation of the Respira- 
 tory function, and the consequent retention of carbonic acid in the blood. If 
 this be sufficiently prolonged, a condition ensues, to which the name of 
 Asphyxia has been given ; the essential character of which is the cessation 
 of muscular movement, and shortly afterwards of the circulation ; with an 
 accumulation of blood in the venous system. The time which is necessary 
 for life to be destroyed by asphyxia varies much, not only in different animals, 
 but in different states of the same. Thus Warm-blooded animals are much 
 sooner asphyxiated than Reptiles or Invertebrata; on the other hand, a hyber- 
 nating Mammal supports life for many months, with a respiration sufficiently 
 low to produce speedy asphyxia if it were in a state of activity. And among 
 Mammalia and Birds, there are many species which are adapted, by peculiari- 
 ties of conformation, to sustain a deprivation of air for much more than the 
 average period.* Excluding these, it may be stated as a general fact, that, if 
 a warm-blooded animal in a state of activity be deprived of respiratory power, 
 its muscular movements (with the exception of the contraction of the heart) 
 will cease within five minutes, often within three ; and that the circulation 
 generally fails within ten minutes. Many persons, however, are capable of 
 sustaining a deprivation of air for three, four, or even five minutes, without 
 insensibility or any other injury ; but this power, which seems possessed to 
 
 * Thus, the Cetacea contain far more blood in their vessels, than do any other Mamma- 
 lia ; and these vessels are so arranged that both arteries and veins are in connection with 
 large reservoirs or diverticula. The reservoirs belonging to the former are usually full ; but 
 when the Whale remains long under water, the blood which they contain is gradually in- 
 troduced into the circulation, and, after becoming venous, accumulates in the reservoirs con- 
 nected with the venous system. By means of this provision, the Whale can remain under 
 water for more than an hour. 
 
592 OF RESPIRATION. 
 
 the greatest degree by the divers of Ceylon, can only be acquired by habit. 
 The period during which remedial means may be successful in restoring the 
 activity of the vital and animal functions, is not, however, restricted to this. 
 Cases are not unfrequent, of the revival of drowned persons after a submer- 
 sion of half an hour; and more than one has been credibly recorded, in which 
 above three-quarters of an hour had elapsed. It is not improbable, however, 
 that in some of these cases a state of Syncope had come on at the moment 
 of immersion, through the influence of fear or other mental emotion, concus- 
 sion of the brain, <fcc. ; so that, when the circulation was thus enfeebled, the 
 deprivation of air would not have the same injurious effect, as when this 
 function was in full activity. The case would then closely resemble that of 
 a hybernating animal ; for in both instances the being might be said to live 
 very slowly, and would therefore not require the usual amount of vital stimuli. 
 The condition of the still-born infant is in some respects the same ; and re- 
 animation has been successfully attempted, when nearly half an hour had 
 intervened between birth and the employment of resuscitating means, and when 
 probably a much longer time had elapsed from the period of the suspension 
 of the circulation. 
 
 779. It has now been sufficiently proved, both by experiment and by pa- 
 thological observation, that the first effect of the non-arterialization of the 
 blood in the lungs, is the retardation of the fluid in their capillaries ( 738) ; 
 of which the accumulation in the venous system, and the deficient supply to 
 the arterial, are the necessary consequences. It is some time, however, be- 
 fore a complete stagnation takes place from this cause : since, as long as the 
 proportion of oxygen which remains in the air in the lungs is considerable, 
 and that of the carbonic acid is small, so long will some imperfectly-arte- 
 rialized blood find its way back to the heart, and be transmitted to the system. 
 This blood will have a depressing influence upon the functions of the brain 
 and of the muscular system ; which influence is aided by the diminution that 
 gradually takes place, in the quantity of blood propelled through the aorta ; 
 and the actions of the respiratory muscles and of the heart will therefore 
 soon become enfeebled. The cessation of the heart's contraction is due to 
 two distinct causes, acting on the two sides ; for on the right side it is the 
 result of the over-distension of the walls of the ventricle, owing to the accu- 
 mulation of venous blood ; and on the left to deficiency of the stimulus ne- 
 cessary to excite the movement. The property of contractility is not finally 
 lost, nearly as soon as the movements cease; for the action of the right ven- 
 tricle may be renewed, for some time after it has ceased, by withdrawing a 
 portion of its contents, either through the pulmonary artery, their natural 
 channel, or, more directly, by an opening made in its own parietes, in the 
 auricle, or in the jugular vein ( 723, c). On the other hand, the left ventricle 
 may be again set in action, by renewing its appropriate stimulus of arterial 
 blood. Hence, if the stoppage of the circulation have not been of too long 
 continuance, it may be renewed by artifical respiration ; for the replacement 
 of the carbonic acid by oxygen in the air-cells of the lungs, restores the cir- 
 culation through the pulmonary capillaries ; and thus at the same time relieves 
 the distension of the right ventricle and conveys to the left the due stimulus to 
 its actions. 
 
 780. Of the mode in which the pulmonary circulation is stagnated by the 
 want of oxygen, and renewed by its ingress into the lungs, no other explana- 
 tion can be given, than that which has been heretofore offered of the capillary 
 circulation in general; namely, that the performance of the normal reaction 
 between the blood and the surrounding medium (whether this be air, water, 
 or solid organized tissue) is a condition necessary to the regular movement 
 
GENERAL VIEW OF THE PROCESS OF NUTRITION. 
 
 593 
 
 of the blood through the extreme vessels.* This view has recently obtained 
 additional support from the experiments of Dr. J. Reid on the Respiration of 
 Azote.t He found that, when the ordinary respiration of an animal is inter- 
 rupted, and the Asphyxia is proceeding to the stage of insensibility, the first 
 effect upon the arterial system is an increased distension (as indicated by the 
 hffimadynamometer), even although the blood is at that time nearly venous in 
 its character ; this indicates that the fluid, now so perverted, is unable to pass 
 with facility through the systemic capillaries, in consequence of its not being 
 in a state fit for the performance of its normal actions. As the stagnation in 
 the pulmonary capillaries becomes more complete, however, less and less 
 blood is returned from the lungs to the heart; and, the systemic arteries 
 being gradually unloaded without being refilled, the pressure of the blood 
 upon their walls diminishes, and is at last no longer experienced. Its dimi- 
 nution is not arrested by causing the animal to breathe nitrogen, although the 
 respiratory movements are renewed, thus proving that the stagnation of the 
 blood in the capillaries of the lungs is not due (as some have supposed) to a 
 mechanical impediment: but the pressure is immediately increased by the 
 admission of atmospheric air, which occasions the renewal of the pulmonary 
 circulation, and the consequent increase in the supply of aerated blood to the 
 systemic arteries. It has been shown by Mr. Wharton Jones,:}: that the ca- 
 pillary circulation in a frog's foot is retarded or even checked, by the direc- 
 tion of a stream of carbonic acid gas against the membrane ; and he attributes 
 this stagnation to the disposition thus produced in the red corpuscles, to ag- 
 gregate together and to adhere to the walls of the vessel, so as to choke up 
 its calibre. 
 
 CHAPTER XIV. 
 
 OF NUTRITION. 
 
 1. General Considerations. Selective Power of Individual Parts. 
 
 781. THE function of Nutrition, considered in the widest acceptation of the 
 term, includes the whole series of processes, by which the fluid alimentary 
 materials, prepared by the Digestive process, introduced into the system by 
 Absorption, and carried into its penetralia by the Circulation, are converted 
 into Organized tissue; by which conversion it is caused to manifest a set of 
 properties altogether new, which, being neither Physical nor Chemical, are 
 termed Vital. Thus Albumen, which is a perfectly dead or inert substance, 
 and of which the distinguishing properties are entirely attributable to its pecu- 
 liar composition, is transformed by the Nutritive process into Muscular Fibre, 
 possessed of the remarkable Vital property of Contractility. But this process 
 of conversion commences in the nutritive materials whilst they are still in a 
 fluid condition, and are moving through the vessels ; for we have seen that, at 
 this stage of the operation, the unorganizable Albumen is transformed into 
 
 * For a fuller discussion of the Pathology of Asphyxia, see the Author's essay on the sub- 
 ject in the Library of Practical Medicine, vol. iii. 
 f Edinb. Med. and Surg. Journal, April 1841* 
 j British and Foreign Medical Review, vol. xiv., p. 600, 
 
 50* 
 
594 OF NUTRITION. 
 
 Fibrine, a substance which possesses a tendency to spontaneous organization, 
 and which must be regarded as endowed with Vital properties. It is convenient 
 to speak of it, therefore, under a distinct designation ; and the term Assimilation 
 has been applied to it. In its more restricted sense, the term Nutrition is 
 applied to the growth of the various tissues of the body, at the expense of the 
 materials prepared by the Assimilating process, and supplied by the Circu- 
 lating current. 
 
 782. It appears evident, from what has been formerly stated (Chap, in.), 
 that the process of Nutrition mainly consists in the growth of the individual 
 cells composing the fabric; and that these derive their support from the 
 organic compounds with which they are supplied by the blood, just as the 
 cells composing the simplest Plants derive theirs from the inorganic elements 
 which surround them. And as different species of the latter select and com- 
 bine these in such modes and proportions as to give rise to organisms of 
 very diversified forms and properties, so is it easily intelligible that the dif- 
 ferent parts of the fabric of the highest Animals should exercise a similar 
 selective power, in regard to the materials with which the blood supplies 
 them. The structure composing every separate portion of the body has 
 (what may be termed) an elective affinity for some particular constituents of 
 the blood ;. causing it to abstract from that fluid, and to convert into its own 
 substance, certain of its elements. The property by which the cells of the 
 Animal or Vegetable structure are enabled to perform it, is one of which we 
 are not likely soon to know more. It will probably long remain an ultimate 
 fact in Physiology, that cells have the power of growing from germs, of under- 
 going certain transformations, and of producing germs that will develope other 
 cells similar to themselves ; just as it is an ultimate fact in Physics, that 
 masses of matter attract each other ; or in Chemistry, that the molecules of 
 different substances have a tendency to unite, so as to form a compound dif- 
 ferent from either of the elements. It is of such ultimate facts as these, that 
 the science of Vitality essentially consists : since the Physical and Chemical 
 phenomena which occur in living bodies, are not strictly removable from the 
 laws of Inorganic Nature. The conditions under which this appropriating 
 power operates, however, are freely open to our investigation ; and it is a 
 great step in the progress of the inquiry, to become aware that these are so 
 closely conformable, throughout the organized world, as they have been 
 shown to be. It may be stated, as a general fact, that in assimilating, or con- 
 verting into its own substance, matter which was previously unable to exhibit 
 any of the manifestations of life, every cell thereby participates in the process 
 of organization and vitalization; for, by the new circumstances in which the 
 matter is placed, its properties undergo a change, or, to speak more correctly, 
 properties which were previously dormant are caused to manifest themselves. 
 No matter, that is not in a state of Organization, can exhibit those properties, 
 which, from their being peculiar to living bodies, and altogether different from 
 Physical and Chemical, are termed Vital; and it may also be asserted that 
 no matter, which exhibits perfect organization, is destitute of the peculiar 
 vital properties belonging to its kind of structure.* As a corollary to this 
 general fact, it may be stated, that no organism can be produced by any 
 fortuitous combination of inorganic matter; since, even for the generation of 
 the simplest cell, there is required a cell previously existing, to furnish the 
 germ. 
 
 * For a fuller consideration of this question, and the grounds upon which this view is 
 supported, the reader is referred to the Article Life in the Cyclopedia of Anatomy and Phy- 
 siology; and to the Chapter on the "Nature and Causes of Vital Actions," in his Principles of 
 General and Comparative Physiology. 
 
SELECTIVE POWER OF INDIVIDUAL PARTS. 595 
 
 783. We have seen that, in some cases, the germs are prepared by pre- 
 viously-existing cells of the same kind; thus the Red and colourless corpuscles 
 of the Blood, the Cartilage-cells, the cells of Vesicular Nervous matter, and 
 those of many other tissues, appear to be the offspring of parents exactly 
 similar to themselves. In other cases, however, the germs seem to be fur- 
 nished by certain " nutritive centres," which appear to be constantly engaged 
 in the preparation of them, deriving their materials from the blood".* Thus 
 the Epidermic and Epithelial cells are produced, not from preceding cells of 
 a similar character (for these are thrown off without performing any such 
 reproductive act), but from germs derived from the basement or primary mem- 
 brane beneath; and, in like manner, the minute cells, of which the ultimate 
 Jibrillse of Muscle are composed, appear to originate in nuclei or germinal 
 centres, belonging to the tubular Myolemma. But even these germinal centres 
 may probably be considered as nothing else than the nuclei of certain parent- 
 cells, which, instead of producing their like, give origin to a new generation 
 having different properties. Thus, the basement or primary-membrane has 
 been already stated ( 135) to exhibit not unfrequently the indications of a 
 cellular constitution ; the germinal centres which it contains being the nuclei 
 of its component cells : and its character is particularly well seen where it is 
 inverted so as to form secreting follicles ; for, as we have seen ( 174), each 
 of these follicles may be regarded as a single parent-cell, which opens at the 
 extremity farthest from the nucleus, and continues to discharge from its orifice 
 successive generations of cells, having their origin in its nucleus, which thus 
 acts as a permanent " germinal centre." And in like manner, the germinal 
 centres of Muscular Fibre may be regarded as the nuclei of the cells, of which 
 it was originally composed. 
 
 784. The Selecting power, which is possessed by the germs of each kind 
 of tissue, and which enables them to draw from the Blood the materials which 
 they severally require for their development, manifests itself also in the mode 
 in which substances, that are abnormally present in the Blood, affect the con- 
 dition and development of the solid tissues. Thus we find that the presence 
 of a certain quantity of Arsenic in the Blood, will produce a state of irritation 
 of all the Mucous membranes in the body. The continued introduction of 
 Lead into the circulating system, occasions a modification in the nutrition of 
 the extensor muscles of the forearm, producing the form of partial paralysis 
 commonly termed wrist-drop; and the existence of this modification is shown 
 by the fact (disclosed by Chemical analysis) of the actual presence of lead in 
 the palsied muscles. Here we have to remark the Symmetrical nature of the 
 affection, consequent upon the occurrence of the same disorder in the corre- 
 sponding parts of the two sides of the body ; for these muscles appear to have 
 the same kind of tendency to attract Lead from the circulating current, in a 
 degree that is equal on the two sides, as they have to draw from the blood 
 the materials of their regular growth, and to develope themselves in an exactly 
 similar manner. In like manner, the cutaneous eruptions, which are occa- 
 sionally produced by the internal exhibition of iodide of potassium, are found 
 to be almost precisely symmetrical; the presence of the medicine in the blood 
 being the occasion of a disordered nutrition of certain parts of the skin ; and 
 the selecting power of particular spots being evinced by the exact correspond- 
 ence of the parts affected on the two sides. 
 
 785. The same appears to be the case with regard to substances, whose 
 presence in the blood is rather the result of a disordered condition of the 
 digestive and assimilating processes, than of their direct introduction from 
 without. Thus in Lepra and Psoriasis, chronic diseases of the Skin, which 
 
 * See Goodsir's Anatomical and Pathological Observations, Chap. i. 
 
596 OF NUTRITION. 
 
 seem to have their origin in a disordered state of the Blood, rather than in the 
 solid tissues affected, we find a remarkable tendency to the repetition of the 
 patches, on the two sides of the body, or on the corresponding parts of the 
 limbs ; and this we must attribute, to the peculiar attraction subsisting between 
 the solid tissues of those parts, and the morbid matter circulating through 
 them. So in those chronic forms of Gout and Rheumatism, which modify 
 the nutrition of the joints, producing a deposit of "chalk stones," or perma- 
 nent distortion and stiffening from an alteration of the tissues, of the joint, we 
 almost invariably find the corresponding joints of the two sides affected. 
 The chief exceptions to the general principle, that the presence of morbid or 
 extraneous matters in the blood affects all parts alike, are found to occur 
 where there is much febrile disturbance, or where local causes produce a 
 peculiar tendency to disorder of a single part. The nearer the approach 
 presented by the morbid process, in point of rate and character, to the ordi- 
 nary nutritive operations of the part, the more does it tend to approach these, 
 in the symmetry with which it developes itself.* 
 
 2. Varying Activity of the Nutritive Processes. Separative Operations. 
 
 786. Without any change in the character of the Nutritive processes, there 
 may be considerable variations in their degree of activity ; and this, either as 
 regards the entire organism, or individual parts, though most commonly the 
 latter. These variations may be so considerable as to constitute Disease ; 
 though there are some which take place as part of the regular series of Phy- 
 siological phenomena. Thus, the Nutritive processes should have a degree 
 of activity more than sufficient to supply the Waste of the body during the 
 whole period of infancy, childhood and adolescence, until, in fact, its full 
 dimensions are obtained ; whilst, on the other hand, they are usually less 
 rapid than the disintegrating processes in old age, so that the bulk of the body 
 diminishes. Now as the Waste of the body, so far from being more rapid in 
 old age than in childhood, is much less so, it follows that the difference in 
 the activity of the Nutritive processes in these two states must be very con- 
 siderable ; and this is manifested, not only in the greater demand for food 
 which exists in the child (relatively to the bulk of its body), but also in the 
 greater quickness and facility with which injuries are repaired. Local varia- 
 tions may also occur, as part of the regular train of vital actions in the adult; 
 thus we perceive an enormous increase in the amount of tissue contained in 
 the Uterus and Mammary glands during pregnancy, and a decrease in the 
 bulk of the Thymus gland after the period of infancy. Now in these cases 
 we see, that increased Nutrition is invariably connected with increased Func- 
 tional activity; and diminished nutrition with diminished functional activity: 
 and this we shall find to be the constant rule, in regard also to those variations 
 which must be considered as abnormal. 
 
 787. Increased Nutrition, or Hypertrophy, is never known to affect the 
 whole body, to a degree sufficient to constitute disease. It cannot be pro- 
 duced as a consequence of the ingestion of an undue supply of food : for this 
 does not increase the formative activity of the tissues, but merely renders the 
 blood richer in nutritive materials; a part of which the excreting organs are 
 called on to be continually removing, without its being rendered subservient to 
 the wants of the body ( 819); whilst another part may be employed in the 
 nutrition of one particular tissue, the Adipose, which has a tendency to in- 
 crease with the superfluity of non-azotized food, provided that the requi- 
 
 * See Dr. W. Budd's valuable paper on the " Symmetry of Disease," in vol. xxv. of the 
 Medico-Chirurgical Transactions. 
 
VARYING ACTIVITY OF THE NUTRITIVE PROCESSES. 597 
 
 site amount of cellular tissue be generated to hold the fatty matter ( 184). 
 But examples of Hypertrophy of particular tissues or organs are very com- 
 mon. Thus any particular set of Muscles, which is subjected to frequent and 
 energetic use, acquires a great increase in bulk ; as we see in the arms of a 
 Blacksmith or Waterman, the legs of an Opera-dancer, &c. The hypertrophy 
 of these muscles is a consequence of their increased functional activity ; which, 
 being produced by an exertion of the will, and unaccompanied with any in- 
 jurious effects on the system, can scarcely be regarded as morbid. But there 
 are many instances, in which the involuntary muscles acquire a greatly- 
 increased strength, in consequence of an obstruction to their action, which 
 results from disease. Thus we see the right ventricle of the Heart become 
 hypertrophied (and dilated at the same time), where chronic pulmonary dis- 
 ease produces a difficulty in the propulsion of the blood through the vessels 
 of the lungs ; the muscular fibres of the Bladder become enormously hyper- 
 trophied, when stricture, diseased prostate, or other causes produce a demand 
 for increased expulsive force on the part of that organ ; and those of the 
 Stomach also become so, in cases of stricture of the pylorus. As an instance 
 of hypertrophy of a Secreting organ in consequence of an undue excitement 
 of its function, we may notice the enlargement which usually takes place in 
 the Kidney, when its fellow is incapacitated by disease. And the Nervous 
 system presents us with a very remarkable case of hypertrophy of a part, 
 resulting from over-excitement of its function; for if young persons, who 
 naturally show precocity of intellect, are encouraged rather than checked in 
 the use of their brain, the increased nutrition of the organ (which grows faster 
 than its bony case) occasions pressure upon its vessels, it becomes indurated 
 and inactive, and fatuity and coma are the result. 
 
 788. Local hypertrophy may be induced also by local congestions ; but in 
 such cases it will usually be found, that the form of tissue produced is of the 
 lowest kind, unless the functional activity of the part be increased by the 
 congestion. Thus, when disease of the Heart produces long-continued con- 
 gestion of the Lungs, Liver, Spleen, &c., the bulk of these organs increases ; 
 but chiefly by the production of an additional amount of interstitial Areolar 
 tissue, which may result (as we have seen) from the simple consolidation of 
 Fibrine ; and partly also (in the case of the spleen especially) by the gorging 
 of their distensible veins with blood. One of the least explicable cases of 
 Hypertrophy, is that which takes place in the Thyroid gland, causing Bron- 
 chocele. So little is known of the normal office of this organ, that it cannot 
 be determined, whether its increased size be due to an increased activity of 
 its functional operations, or to an unusual formative activity in its tissue, 
 depending on some hidden cause. The connection of this disorder with 
 causes which affect the whole constitution rather than individual parts, would 
 seem to indicate the former. 
 
 789. When the Waste of the Tissues is more rapid than their replacement 
 by Nutrition, Atrophy is said to take place ; and this may affect either the 
 whole body, or individual parts. General Atrophy, Marasmus, or emaciation, 
 may result from an insufficient supply of plastic matter, from want of forma- 
 tive power in the tissues themselves, or from their too rapid disintegration. 
 The insufficiency of the supply of nutritive matter may depend either on de- 
 ficiency in the azotized substances ingested as food, or on imperfect perform- 
 ance of those processes by which they are converted into the plastic ele- 
 ment, Fibrine. Hence, even when there is an ample supply of food, 
 atrophy may take place to a very severe extent, in consequence of disordered 
 digestion, or a want of vital power in the fibrine-elaborating cells. Again, we 
 have reason to believe that the formative power in the tissues themselves may 
 be diminished, so as to check the process of Nutrition, even when the plastic 
 
598 OF NUTRITION. 
 
 material is supplied ; thus there seems to be a complete stoppage of this action 
 in Fever, and a diminution of it in that irritable state of the system, which 
 results from excessive and prolonged bodily exertion or anxiety of mind, es- 
 pecially when accompanied by want of sleep. It is difficult to separate this 
 cause, however, from mal-assimilation on the one hand, or from too rapid 
 decay of the tissues on the other : for we know that, in such states, there is a 
 tendency to imperfect elaboration of the Fibrinous element, and at the same 
 time an unusually rapid disintegration, as manifested by the increased amount 
 of Urea in the urine. The influence of excessive waste in causing Atrophy 
 of the body, is well shown in the cases of Diabetes mellitus and colliquative 
 Diarrhoea ; in both these, the increase and depravation of the secretions are 
 undoubtedly to be regarded as the effects, and not the causes, of the textural 
 changes with which they are associated. Colliquative Diarrhoea is a constant 
 occurrence on the last day or two of life, in animals reduced by Starvation ; 
 and is accompanied by that foetid odour of the body, which indicates that 
 decomposition is already going on throughout the system. The same thing 
 occurs as the ordinary termination to many diseases of exhaustion ; in which 
 Inanition is unquestionably the immediate cause of death. 
 
 790. Partial Atrophy may occur in consequence of disuse of the organ 
 affected, occasioning inactivity in its formative processes ; or as a result of a 
 deficiency of nutriment, occasioned by an obstruction to the circulation. Of 
 the operation of the former cause, we have many examples in the ordinary 
 processes of the economy. Thus the Uterus is atrophied, relatively to its 
 previous condition, as soon as parturition has taken place ; and the Mammary 
 glands, when lactation has been discontinued. It is probably in part to this 
 cause, and in part to the diversion of the blood into other channels, that we 
 are to attribute the atrophy of many parts, as the development of the system 
 advances, which at an earlier period were of large comparative size, such as 
 the Corpora Wolffiana, the Suprarenal capsules, and the Thymus gland. 
 Many instances might be adverted to, of the influence of suspension of func- 
 tional activity, as a result of disease or injury, in producing local atrophy. 
 One of the most common cases, is the atrophy of Muscles which is conse- 
 quent upon their disuse. This disuse will produce the same effect, whether 
 it be occasioned by paralysis, which prevents the nervous centres from excit- 
 ing the muscles to contraction; or by anchylosis, which interposes a mechani- 
 cal impediment to their use ; or by fractures or other accidents, the reparation 
 of which requires the limb to be kept at rest. Or even if, without having 
 suffered from any injury, a limb be fixed during some time in one posture, its 
 muscles will become atrophied, as is seen in the case of the Indian Fakirs. 
 (See 588). Similar facts may be adduced, in regard to Atrophy of Nerves, 
 from interruption of their normal function. Thus when the Cornea has been 
 rendered so opaque by accident or disease, that no light can penetrate to the 
 interior of the eye, the Retina and the Optic nerve lose, after a time, their 
 characteristic structure ; so that scarcely a trace of the peculiar globules of the 
 former, or of the nerve-tubes of the latter, can be found in them. These and 
 similar facts are readily understood, when connected by the general principle 
 formerly laid down, that every proper vital operation involves an act of 
 nutrition ; in such a manner that, whilst the vital properties of any part are 
 dependent upon its due nutrition, the amount of its nutrition will in return 
 depend upon the degree in which these properties are exercised. 
 
 791. Partial Atrophy may depend, however, upon causes of a purely me- 
 chanical nature ; such, for example, as produce an interruption of the current 
 of Blood through the part. This may result from changes in the Arteries 
 supplying it ; such as ossification, or other forms of obstruction. Or it may 
 be consequent upon disease in the part itself ; as when the deposits produced 
 
VARYING ACTIVITY OF THE NUTRITIVE PROCESSES. 5&9 
 
 by Inflammation tend to contract, and thus to press upon the vascular struc- 
 ture, which frequently happens in the lungs, liver, and kidneys; or when the 
 inflammation occurs in the vessels themselves, causing adhesion of their walls, 
 and obliteration of their tubes ; or when a new growth absorbs into itself all 
 the nutritive materials which the Blood supplies.* 
 
 792. The nutritive operations take place, with extraordinary energy and 
 rapidity, in the process of Reparation; by which losses of substance, occa- 
 sioned by injury or disease, are made good. In its most perfect form, this 
 process is exactly analogous to that of the first development of the correspond- 
 ing parts ; and its results are as complete in the one case as in the other. In 
 fact, among the lowest tribes of Animals, we find these two conditions 
 blended, as it were, together; for the process of reparation may be carried in 
 them to such an extent, as to regenerate the whole organism from a very small 
 portion of it. In the Hydra, or Fresh-water Polype, there would seem to be 
 scarcely any limit to this power; for, if the body of the animal be minced 
 into the smallest possible fragments, every one of these can produce a new 
 and perfect being. In this manner no less than forty have been artificially 
 generated from a single individual. In ascending the Animal scale, we find 
 this reparative power less conspicuous, because exercised with regard to 
 smaller parts only of the body ; but the greater complexity of the changes 
 involved in the process, renders it in reality not less considerable than in the 
 lower classes. Thus, the restoration of a Bone destroyed by Necrosis is a 
 much more extraordinary operation, than the growth of an entire Polype from 
 a single fragment: since it involves a far greater amount and variety of 
 actions. Numerous and well-authenticated instances are on record, of the 
 reunion of parts that had been entirely separated from the body, and of the 
 restoration of all their vital properties : and this could only take place, through 
 the perfect reproduction of a large number of very different structures. The 
 reappearance of Fungous growths, whose organization is of a low character, 
 is a fact with which every surgeon is familiar ; and cases occasionally, though 
 rarely, present themselves, in which reproduction of a whole member takes 
 place even in the Human subject.t 
 
 793. [t is the general opinion among British surgeons (founded upon what 
 they believe, but erroneously, to have been the doctrine of Hunter), that In- 
 flammation is essential to the process of Reparation. There is no doubt that, 
 as usually conducted, the healing of wounds is attendee^ by a greater or less 
 degree of Inflammation ; but it does not thence follow that this morbid con- 
 dition is essential to the renewal of the healthy state; and in fact it can be 
 shown that, in the majority of cases, the Inflammation is injurious rather than 
 beneficial. The following important conclusions are drawn by Dr. Macart- 
 ney:}: from a very philosophical comparative survey of .the operations of Re- 
 paration and Inflammation, as performed in the different classes of animals : 
 " That the powers of Reparation and Reproduction are in proportion to the 
 indisposition or incapacity for Inflammation ; that Inflammation is so far 
 from being necessary to the Reparation of parts, that, in proportion as it exists, 
 the latter is impeded, retarded, or prevented; that, when Inflammation does 
 not exist, the Reparative power is equal to the original tendency to produce 
 and maintain organic form and structure ; and that it then becomes a natural 
 function, like the growth of the individual, or the reproduction of the species." 
 
 794. Guided chiefly by Dr. Macartney's views, which have derived im- 
 
 * See on this subject Dr. Williams' Elements of Medicine, chap. iv. ; to which the Author 
 is partly indebted for the preceding paragraphs. 
 
 f See, on the whole of the subject of the comparative powers of Reparation in the Ani- 
 mal series, the Author's Principles of Gen. and Comp. Physiol. 586, 587. 
 
 J Treatise on Inflammation, p. 7. 
 
600 OF NUTRITION. 
 
 portant confirmation from recent observations, we shall treat of the reparative 
 processes under three distinct heads : First, the adhesion of the sides of a 
 wound by a medium of coagulable lymph, or of a clot of blood. Second, 
 reparation without any medium of lymph or granulations, the cavity of the 
 wound being filled by a natural process of growth from its walls. Third, 
 reparation by means of a new, vascular, and organized substance, termed ' 
 Granulations. The first of these modes of Reparation, is that which is ordi- 
 narily termed union by the first intention; of this kind of adhesion, the heal- 
 ing of the incision made in venesection, which usually takes place almost 
 without consciousness on the part of the patient, and with scarcely any In- 
 flammation, is a characteristic example: the white line of cicatrix which is 
 left, marks the formation of new substance ; and is the result of the want of 
 that perfect approximation of the lips of the wound, which may frequently be 
 obtained in parts, where pressure can be more firmly applied, and where the 
 space to be filled up is proportionably thinner. This mode of union is ordi- 
 narily considered by British Surgeons to be the result of an adhesive inflam- 
 mation. In so regarding it, they conceive that they are following out the 
 views of Hunter ; but he expressly states that wounds may heal without any 
 pain or constitutional disturbance, the reunion proceeding "as if nothing had 
 happened ;" so that he in effect admits, that reparation of this kind may take 
 place without Inflammation. It is well known that if a slight wound, which 
 is thus healing, be provoked to an increased degree of Inflammation, its pro- 
 gress is interrupted ; and all the means which the Surgeon employs to pro- 
 mote union, are such as tend to prevent the accession of this state. The 
 doctrine that the effusion of Lymph for the Reparation of the tissues, is not 
 to be regarded as necessarily a result of the Inflammatory process, is not so 
 novel as its opponents have regarded it; since it has been maintained by many 
 eminent observers, even from the earliest times. The only case in which 
 the occurrence of Inflammation can be regarded as salutary, is that in which 
 there is a deficiency of Fibrine in the blood, causing a deficient organiza- 
 bility of the lymph. It has been seen that the amount of Fibrine is rapidly 
 increased by inflammation ; and the Surgeon well knows that a wound with 
 pale flabby edges, in a depressed state of the system, will not heal, until some 
 degree of Inflammation has commenced. 
 
 795. When the Liquor Sanguinis of the Blood, known as Coagulable 
 Lymph, is effused between the two edges of a wound, or upon the surface of 
 a membrane lining a closed sac, the following appears to be the history of its 
 organization. The new matter, which is poured out in a fluid state, and 
 which seems to have been subjected to the peculiar influence of the Colour- 
 less Corpuscles that rapidly collect in large numbers at the injured spot, un- 
 dergoes a Coagulation resembling that of Blood; the Serum, being set free 
 by the concretion of the Fibrine, is absorbed; and the fibrinous coagulum 
 speedily attains an almost membranous density. If examined with a Micro- 
 scope at the commencement of the process of organization, it is seen to con- 
 tain a large number of cells, which sometimes closely resemble the Colourless 
 Corpuscles of the Blood; and in other instances (especially where there has 
 been active Inflammation) present greater similarity to Pus-corpuscles ; these 
 cells, which are known as exudation-corpuscles, probably originate in granules 
 set free from the Colourless Corpuscles of the circulating blood, and exuded 
 with the Liquor Sanguinis. In a short time, these corpuscles present the 
 appearance of regular cells, disposed in layers, and adhering together^ by an 
 intermediate unorganized substance ; bearing, in fact, a strong resemblance to 
 the cells of tesselated epithelium. Some hours later, the mass exhibits an 
 evidently-fibrous character ; which is probably due to the further elaboration 
 of the plastic material, by the cells just mentioned. Between the fibres, a 
 
REPARATIVE PROCESSES. 601 
 
 considerable amount of unorganized substance yet remains ; and they may be 
 readily separated, or torn in any direction. A vascular rete next makes its 
 appearance, in connection with the vessels of the subjacent surface; the first 
 appearance of this network is in the form of transparent arborescent streaks, 
 which push out extensions on all sides ; these encounter one another, and 
 form a complete series of capillary reticulations, the distribution of which very 
 nearly resembles that which has been seen in the villi of the intestines (Fig. 
 204). From the observations of Mr. Travers* it appears, that isolated glob- 
 ules enter these capillary tubes, and perform an oscillatory motion in them 
 for some hours, before any series of them passes into it ; so that we cannot 
 regard the new channel as burrowed out by a string or file of red corpuscles, 
 pushed out from the nearest capillary by vis a tergo,zs some have maintained. 
 And he has further established two important facts, in the history of the Re- 
 paration of Tissues, which correspond with the observation just cited: 1. 
 That the Liquor Sanguinis first effused is not sufficiently organizable to be- 
 come an entirely new and permanent tissue ; although adequate both to afford 
 nutrition to the old, and to form a new tissue of temporary character : and, 
 2. That the generation of the new tissues is preceded by the collection of a 
 large number of white corpuscles, in a nearly stationary condition, in the 
 blood-vessels immediately subjacent ; and by the appearance of a large number 
 of similar cells in the newly-forming tissue ; the two together constituting 
 what Mr. T. has aptly called " the new lymph-bed of organization." The 
 views formerly advanced ( 154-159) respecting the function of the Colour- 
 less Corpuscles, are thus strikingly confirmed. This process of Reparation 
 appears to be conformable, in all essential particulars, with that which has 
 been observed in the first Development of new parts, such as the toes of the 
 larva of the Water-Newt. 
 
 796. Although many have doubted whether effusions of Blood could thus 
 become organized, there seems no valid reason to think that its Fibrine would 
 comport itself in any other way, when Red particles are included in its coa- 
 gulum, than when they are absent. That large masses of extravasated Blood 
 should exhibit little or no tendency to organization, will not be considered 
 surprising; when it is remembered that only their surface can be in that re- 
 lation with a living membrane, which has been stated to be essential to the 
 further vitalization of the effused Fibrine (119). It has been proved in many 
 instances, however, that Coagula of Blood completely inclosed within the body 
 possess an incipient vascularity, being capable of injection from the surface 
 beneath ( 700) ;t and there is no valid reason to deny that the thin layer of 
 Blood which remains between the lips of an incised wound, when these are 
 closely brought together, is the medium of their reunion. It is unquestionable, 
 however, that the Fibrine of an ordinary Blood-clot is less highly-elaborated, 
 and consequently less susceptible of organization, than that of the Liquor 
 Sanguinis, which is poured forth after an injury, and which has been subjected 
 to the local action that is its immediate result. 
 
 797. To the second mode of Reparation, attention has recently been strongly 
 directed by Dr. Macartney ; and as this, too, is a strictly Physiological action, 
 and is one which the Surgeon should aim at producing, it will be here dis- 
 cussed somewhat in detail. The Surgeon has, until recently, regarded the 
 processes of Granulation and Suppuration, which are attended with much 
 local Inflammation, and with a considerable amount of Constitutional disturb- 
 ance when the surface is large, as the only means by which an open wound 
 
 * Physiology of Inflammation and the Healing Process. 
 
 j" For well-established cases of this sort, see communications by Mr. Dalrymple in the 
 Medico-Chirurgical Transactions, vol. xxiii.; and in Lancet, March 23, 1844. 
 51 
 
602 OF NUTRITION. 
 
 can be filled up. Occasional instances, however, have not heen wanting, in 
 which large open wounds have closed up under the dry clot of blood, by which 
 they were at first covered over, without any suppuration, or other symptom 
 of inflammation ; and in these it has been found, that the new surface much 
 more nearly resembles the ordinary one, than does the Cicatrix which follows 
 granulation. To Dr. Macartney, however, is due the merit of explaining the 
 rationale of this action ; which is precisely analogous to that which is con- 
 cerned in the ordinary processes of growth, and to that reproduction of whole 
 parts which takes place in the lower animals without Inflammation. It is 
 termed by him the modelling process ; and he remarks as characteristic of it 
 that, when it goes on perfectly, and without Inflammation, the patients are so 
 completely free from uneasy sensations, as only to be aware of the extent of the 
 injury by their own examination. In this process, the surfaces of the wound 
 do not unite by vascular connection, even when they lie in contact; nor is the 
 space between them filled up with coagulable lymph ; but they are smooth 
 and red, moistened with a fluid, and presenting the appearance of one of the 
 natural mucous membranes. " It might be anticipated that, as this mode of 
 reparation bears so strong a resemblance to the natural formation and develop- 
 ment of parts, it is the slowest mode ; but this is of little account, when com- 
 pared with its great advantages in being unattended with pain, inflammation, 
 and constitutional sympathy, and leaving behind it the best description of 
 cicatrix." In the case of large burns on the trunk in children, the difference 
 between the two modes of Reparation will frequently be that of life and death; 
 for it often happens that the patient sinks under the great constitutional dis- 
 turbance occasioned by a large Suppurating surface, although he has survived 
 the immediate shock of the injury. 
 
 798. The most effectual means of promoting this kind of Reparative pro- 
 cess, and of preventing the interference of Inflammation, vary according to 
 the nature of the injury. The exclusion of air from the surface, and the 
 regulation of the temperature, appear the two points of chief importance. By 
 Dr. Macartney, the constant application of moisture is also insisted on.* He 
 states that the immediate effects of injuries, especially of such as act severely 
 upon the sentient extremities of the nerves, are best abated by the action of 
 "steam at a high but comfortable temperature, the influence of which is 
 gently stimulant, and at the same time extremely soothing. After the pain 
 and sense of injury have passed away, the steam, at a lower temperature, 
 may be continued; and, according to Dr. M., no local application can com- 
 pete with this, when the Inflammation is of an active character. For subse- 
 quently restraining this, however, so as to promote the simple Reparative 
 process. Water-dressing will, he considers, answer sufficiently well; its prin- 
 cipal object being the constant production of a moderate degree of Cold, 
 which diminishes, whilst it does not extinguish, sensibility and vascular 
 action, and allows the Reparative process to be carried on as in the inferior 
 tribes of animals. The reduction of the heat in an extreme degree, as by 
 the application of ice or iced water, is not here called for, and would be 
 positively injurious; since it not only renders the existence of Inflammation 
 in the part impossible, but, being a direct sedative to all vital actions, suspends 
 also the process of restoration. The efficacy of Water-dressing in injuries 
 of the severest character, and in those which are most likely to be attended 
 with violent Inflammation (especially wounds of the large joints) has now 
 been established beyond all question; and its employment is continually 
 becoming more general.! Other plans have been proposed, however, which 
 
 * Treatise on Inflammation, p. 178. 
 
 j- See an account of the results of this treatment by Dr. Gilchrist, in Brit, and For. Med. 
 Rev., July 1846, p. 242. 
 
ORIGIN OF THE SOLID TISSUES. 603 
 
 seem in particular cases to be equally effectual. To Dr. Greenhow, of New- 
 castle, for instance, it was accidentally suggested, a few years since,* to cover 
 the surface of recent burns with a liquefied resinous ointment; and he states 
 that in this manner Suppuration may be prevented, even where large sloughs 
 are formed; the hollow being gradually filled up by new tissue, which is so 
 like that which has been destroyed, that no change in the surface manifests 
 itself, and none of that contraction, which ordinarily occurs even under the 
 best management, subsequently takes place. A plan has, moreover, been 
 proposed for preventing suppuration, and promoting reparation by the model- 
 ling process, which consists in the application of warm dry air to the wounded 
 surface. The experiments made on this have not been entirely satisfactory, 
 but they seem to show that, though the process of healing is much slower 
 under treatment of this kind, it is attended with less constitutional disturb- 
 ance than is unavoidable in the ordinary method; and it may, therefore, be 
 advantageously put in practice in those cases in which the condition of the 
 patient requires every precaution against such an additional burthen, as after 
 amputation in a strumous subject. But of the superiority of this treatment 
 to the water-dressing, no evidence has yet been adduced. 
 
 799. The third method of Reparation, that by Granulation appears to 
 be a means employed by Nature for the purpose, under the unfavourable cir- 
 cumstances of Irritation or a continuance of Inflammation ; proving that parts 
 previously in a healthy state, are disposed to heal, in despite of many impe- 
 diments thrown in their way. The Granulation-structure is a special one, 
 formed for a temporary purpose. It is endowed with higher vascularity and 
 a more rapid power of growth, than is possessed by any modification of 
 ordinary tissue; but it is very easily destroyed by injury, or by a higher 
 degree of inflammation. The existence of Granulations has been supposed 
 to be necessary to fill up deficiencies; this, however, is not altogether true; 
 as we occasionally find very considerable vacancies filled with lymph, which 
 gradually becomes organized, without being converted into granulations; and 
 the void may be also supplied by the process of natural growth just described. 
 Moreover, it is only in the beginning that granulations take the place of the 
 natural structure; for the approximation of the edges of a wound filled with 
 them, requires that they should be removed by interstitial absorption ; so that 
 wounds healed* by this process do not exhibit any remains of the new me- 
 dium. This approximation somewhat resembles that which occurs in open 
 wounds that have never inflamed, being the result of the natural processes of 
 growth; and it does not take place until the Inflammation has in great degree 
 subsided : but it differs from the modelling processes in this, that, as the wound 
 is occupied by granulations, its closure takes place prematurely, as it were ; 
 so that, when the granulations are subsequently absorbed altogether, a con- 
 tracted cicatrix is the result. It will be presently seen that the formation of 
 the Granulation-structure is intimately connected with the elaboration of Pus ; 
 and this process, accompanied as it is with such great constitutional disturb- 
 ance, and involving such a loss of nutritious material, cannot but be regarded 
 as an action to be altogether avoided, if possible. 
 
 800. We shall now consider, more in detail, the nature of the process of 
 Granulation, and of the Suppuration which usually accompanies it. Its com- 
 mencement is exactly conformable to the first stage of ordinary reunion by the 
 first intention ; for Liquor Sanguinis is thrown out, in which Exudation-cor- 
 puscles present themselves in large numbers. According to Gerber, the trans- 
 formation of these into a sort of imperfect Epithelium may be seen to take 
 place within half an hour. New layers are in the mean time developed ; and 
 
 * Medical Gazette, Oct. 13, 1838. 
 
004 OF NUTRITION. 
 
 the most superficial of the Exudation-corpuscles, which are exposed to the 
 contact of air, change their character (in the mode to be presently described, 
 
 5 805), and become Pus-Globules ; whilst those in close contact with the sub- 
 jacent surface take a share in the process of reparation. A new layer of 
 exudation-corpuscles is next deposited over this : of which the outer portion 
 degenerates as before into pus-globules, whilst the inner part gives origin to 
 a kind of areolar tissue, forming Granulations. These Granulations are them- 
 selves extremely vascular ; and, as recently shown by Mr. Listen,* the ves- 
 sels of the subjacent tissue are much enlarged, and assume a varicose charac- 
 ter. The bright red colour of the Granulations, however, does not depend 
 on their vascularity alone ; for the cells themselves, especially those most 
 recently evolved, are of nearly as deep a colour as the blood-globules ; and 
 the superficial bleeding which follows even the slightest touch of the granu- 
 lating surface, does not proceed from blood shed from the newly-formed vessels 
 only ; for the red fluid shed in this manner contains, besides blood-discs, 
 newly-developed red cells, ruddy cytoblasts, pale granules and reddish serum. 
 It is a common property of animal cytoblasts, that they present a red colour 
 on their first formation, when in contact with oxygen ; but this hue they 
 lose again, whether they advance to perfect development and become integral 
 parts of a living tissue, or die and degenerate. 
 
 801. The process of Granulation and Suppuration appears to differ from 
 that of simple Reparation (the modelling process of Dr. Macartney) in this, 
 that a large part of the Exudation-corpuscles deposited on the wounded 
 surface degenerate into Pus in the former case, whilst none are thus wasted 
 in the latter ; but that the existence of Inflammation occasions a more co- 
 pious supply of Fibrine in the former case, and increases its tendency to be- 
 come organized ; the filling-up of a wound with Granulations being thus a 
 much more rapid process than that renewal of the completely-formed Tissues, 
 which may take place in the absence of Inflammation. The imperfect cha- 
 racter of the Granulation-structure is shown, by the almost complete disap- 
 pearance of it after the wound has closed over. The portion of it in immediate 
 contact with the subjacent tissue, however, appears to undergo a higher organi- 
 zation ; for it becomes the medium by which the Cicatrix is made to adhere 
 to the bottom of the wound. It is very liable to undergo changes which 
 end in its disintegration ; as is evident from the known tendency to re-open- 
 ing, in wounds that have been closed in this manner. 
 
 3. Abnormal Forms of the Nutritive Process. 
 
 802. Under the preceding head, we have considered the chief variations 
 in the degree of activity, that are witnessed in the ordinary or normal condi- 
 tions of the Nutritive process, that is, those conditions in which the pro- 
 ducts are adapted, by their similarity of character, to replace those which 
 have been removed by disintegration. But we have now to consider those 
 forms of this process, in which the products are abnormal, being different 
 from the tissues they ought to replace. We shall confine ourselves to a brief 
 examination of the two most important of these states ; that which is termed 
 Inflammation ; and that which gives rise to Tubercular deposit. The 
 former results from an excess of the plastic element in the blood ; the latter 
 from a depraved condition of it, whereby its plasticity is impaired or destroy- 
 ed. Notwithstanding all the attention which has been given to the state of 
 the vessels in Inflammation, a careful consideration of its phenomena, with the 
 light which recent investigations have thrown upon these, leads us to attach 
 
 * Medicc-Chirurgical Transactions, vol. xxiii. 
 
ABNORMAL FORMS OF THE NUTRITIVE PROCESS. 605 
 
 comparatively little importance to this, and to seek for the essential character of 
 the process elsewhere. The researches of Addison, Williams, Barry, Gulli- 
 ver, Andral, and others, all seem to point to the following conclusions : 1. 
 That there is a peculiar afflux or determination of the White Corpuscles of 
 the Blood towards the inflamed part. 2. That the total amount of these cor- 
 puscles in the circulating blood undergoes a great increase. 3. That the 
 quantity of Fibrine in the Blood augments, in proportion to the extent and 
 intensity of the Inflammation ; and this, even when it was previously, from 
 the influence of some other morbid condition, below the usual standard. 
 With its quantity, its plasticity, or tendency to organization, also increases in 
 a healthy subject. Now when these facts are compared together, and are 
 connected with those formerly adduced, in regard to the probable function 
 of the White Corpuscles of the blood, they lead almost irresistibly to the con- 
 clusion, that the process of Inflammation essentially consists in an undue 
 stagnation of these corpuscles in the vessels of the part, an excessive multi- 
 plication of them by the ordinary process of generation, and a consequent 
 over production of Fibrine. By these changes, and by the results which fol- 
 low them, Inflammation may be distinguished from the various forms of Hy- 
 peraemia and Congestion. To the results, then, we shall next direct our at- 
 tention. 
 
 803. It may be inferred from various phenomena, that whilst the forma- 
 tive power of the Blood is increased in Inflammation, that of the Tissues is 
 diminished. Certainly this is the case in regard to the system at large, when 
 febrile irritation has been established; for, notwithstanding the increased Plas- 
 ticity of the Blood, we see the body wasting, instead of increasing in vigour. 
 'And it may be inferred also, in regard to the tissues of the part aflfected, 
 from the tendency to Atrophy and' Disintegration which they exhibit; and 
 which is greater (leading even to the death of whole parts) in proportion as 
 the inflammation is more intense, and as the tendency to the deposit of new 
 products is the more decided. That a Stagnation of Blood takes place in 
 the vessels of the inflamed part, is another general fact, which throws some 
 light upon the nature of the process ; for this stagnation is obviously favour- 
 able to the transudation of the fluid Plasma of the blood, through the walls 
 of the vessels, into the surrounding tissue, or upon a neighbouring surface. 
 This deposition of the Fibrinous element, possessing a high degree of plasti- 
 city, and capable of spontaneously passing into simple forms of tissue (which 
 may be gradually replaced by higher forms, when penetrated by vessels from 
 the surrounding parts), may be regarded as the first characteristic result of 
 Inflammation. It is by the deposition, and subsequent organization, of plas- 
 tic matter in the substance of organs, that their tissues become consolidated ; 
 and by its deposition and subsequent organization upon their free surfaces, 
 that false membranes and adhesions are formed. It appears probable, from 
 the recent inquiries of Mr. Robinson,* that this deposition may be attributed 
 to physical causes. It is well known, that simple Congestion will occasion 
 transudation of the serous portion of the Blood ; and if the return of the 
 Blood by the veins of a part be completely prevented, a greater or less pro- 
 portion of fibrine also may be poured forth. Now when the quantity of Fi- 
 brine in the blood is greatly augmented, and the firmness of the walls of the 
 vessels in the inflamed part is diminished by the alterations taking place iri 
 their tissue, it is easy to understand that the disposition to the effusion of Fi- 
 brine will be much increased. Sometimes the Fibrine is diluted with a large 
 quantity of Serum ; and is poured into a cavity (as that of a serous sac) in 
 the form of a liquid, which afterwards separates into clot and serum. 
 
 * Medico-Chirurgical Transactions, vol. xxvi. p. 51. 
 51* 
 
606 OF NUTRITION. 
 
 804. Should the Inflammation increase in intensity, a complete stagnation 
 of blood in the tissue most affected, or even in an entire organ, will be the 
 result; and this will occasion its death. If a large part be thus entirely de- 
 stroyed at once, the process is termed Gangrene; and it separates from the 
 living part, at a line where the Inflammation is less intense, and where there 
 is a deposit of Fibrine, which serves the important purpose of closing the 
 mouths of the blood-vessels that are laid open by the process. If the destruc- 
 tion of tissue, however, be interstitial, the dead parts are not thus thrown off, 
 but are taken up by the absorbent process ; and thus the cavity of an Jlbscess, 
 or of an Ulcer is formed. This cavity is usually bounded by tissue, that has 
 been consolidated by the effusion of Fibrine ; a fact readily accounted for on 
 the principles just stated. For the death and removal of tissue take place, 
 where the Inflammation has been most intense and the stagnation most com- 
 plete, which is in the centre of the inflamed spot; and the fibrinous effusion, 
 the result of moderate inflammation, is poured into the surrounding tissue. 
 The elements of Liquor Sanguinis are poured into the central, as well as the 
 peripheral, portion of the inflamed tissue ; but they assume a different form 
 that of Pus. It would appear as if the influence of the surrounding death and 
 decay produces a degradation of their character; so that they become entirely 
 aplastic or unorganizable, although immediately derived from Blood highly 
 charged with Fibrine. 
 
 805. Between Coagulable Lymph and Purulent effusions, there are many 
 degrees of transition ; the very same deposit being frequently organizable at 
 one part, presenting the character of a tough fibrous membrane, interspersed 
 with corpuscles, whilst it is friable in another, from want of complete fibril- 
 lation in the fluid portion of th effusion, and is entirely destitute of tenacity 
 in a third portion, especially the superficial part, or free surface, of the deposit. 
 When examined by the Microscope, Pus is found to be characterized by the 
 presence of a number of cells of a peculiar aspect, having a very tuberculated 
 or mulberry surface ; these are seen floating in a fluid, termed liquor puris,, 
 which is of an albuminous or low fibrinous character, being entirely destitute 
 of organizability. Now the production of Pus in an inflamed part, or in other 
 words, the act of Suppuration, may be due to one of three causes, viz. the 
 intensity of the inflammation ; the presence of air, which becomes a source of 
 irritation ; and a previously vitiated state of the blood. Various attempts 
 have been made to show that the Pus-globule is a degenerated red or white 
 corpuscle of the Blood ; it seems more probable, however, that it does not 
 escape from the vessels as a complete cell, but as a cell-germ, which may 
 have had its origin in a white corpuscle of the blood ; and which, under 
 favourable circumstances, might have produced an Exudation-corpuscle ( 800). 
 At any rate, it must be regarded as a degenerated form of cell ; and the liquor 
 puris must be considered as analogous to the plasma of the Blood in a de- 
 generated state. 
 
 806. In what manner the Inflammatory process determines the formation 
 of the Pus-cell, and the consequent degradation of the product, we are at 
 present unable to state ; but that the degree of irritation in the part has an 
 influence upon it, is evident from the effects of the contact of air upon inflamed 
 surfaces, causing those elements to take the form of Pus, which would other- 
 wise have been thrown out as a plastic deposit. This circumstance would 
 seem to indicate, beyond all doubt, that the Exudation and Pus-corpuscles, 
 the plastic Lymph and the aplastic Liquor puris have the same origin ; but 
 that their character is determined by local circumstances. There is great 
 reason to believe, that when Pus is introduced into the Blood, it may induce 
 such a change in the character of the fluid, as speedily to impair its vital pro- 
 perties ; so that the Pus-corpuscles will rapidly propagate themselves in the 
 
ABNORMAL FORMS OF THE NUTRITIVE PROCESS. 607 
 
 Blood, and the plasticity of the Liquor Sanguinis will be diminished. In this 
 manner the whole system will be seriously affected, and there will be a tend- 
 ency to deposits of Pus in various organs especially in those which, like the 
 Lungs and Liver, serve as emunctories to the system without any previous 
 inflammatory changes in these parts. It has been ascertained by Mr. Addi- 
 son, that if a drop of Pus be treated with Liquor Potassa?, it entirely loses its 
 opaque character, and becomes clear and transparent, like Mucus, with whose 
 tenacity and elasticity also it becomes endowed. If it be then treated with 
 acetic acid, it recovers somewhat of its former opacity ; and, when pressed 
 into a thin film, exhibits a distinct fibrillation. 
 
 807. In persons of that peculiar constitution, which is te*rmed Scrofulous 
 or Strumous, we find an imperfectly-organizable or Caco-plastic deposit, or 
 even an altogether aplastic product, known by the designation of Tuberculcft 
 matter, frequently taking the place of the normal elements of Tissue ; both 
 in the ordinary process of Nutrition, and still more when Inflammation is set 
 up. From an examination of the Blood of Tuberculous subjects it appears, 
 that the Fibrinous element is not deficient in amount, but that it is not duly 
 elaborated ; so that the coagulum is loose, and the red corpuscles are found 
 to bear an abnormally low proportion to it. We can understand, therefore, 
 that such a constant deficiency in Plasticity must affect the ordinary nutritive 
 process ; and that there will be a liability to the deposit of cacoplastic pro- 
 ducts, without Inflammation, instead of the normal elements of tissue. Such 
 appears to be the history of the formation of Tubercles in the lungs and other 
 organs, when it occurs as a kind of metamorphosis of the ordinary Nutritive 
 process ; and in this manner it may proceed insidiously for a long period, so 
 that a large part of the tissue of the lungs shall be replaced by an amorphous 
 deposit, without any other ostensible sign than an increasing difficulty of 
 respiration. It is in the different forms of Tubercular deposit, that we see 
 the gradation most strikingly displayed between the plastic and the aplastic 
 formations. In the semi-transparent, miliary, gray, and tough yellow forms 
 of Tubercle, we find traces of organization in the form of cells and fibres, 
 more or less obvious ; these being sometimes almost as perfectly formed as 
 those of Plastic Lymph, at least on the superficial part of the deposit, which 
 is in immediate relation with the living structures around ; and sometimes so 
 degenerated, as scarcely to be distinguishable. In no instances do such de- 
 posits ever undergo further organization; and therefore they must be regarded 
 as caco-plastic. But in the opaque, crude, or yellow Tubercle, we do not 
 find even these traces of definite structure; for the matter of which it con- 
 sists is altogether granular, more resembling that which we find in an albu- 
 minous coagulum. The larger the proportion of this kind of matter in a 
 tubercular deposit, the more is it prone to soften, whilst the semi-organized 
 tubercle has more tendency to contraction. This is entirely aplastic. 
 
 808. Now although Tubercular matter may be slowly and insidiously de- 
 posited, by a kind of degradation of the ordinary Nutritive process, yet it can- 
 not be doubted that Inflammation has a great tendency to favour it ; so that a 
 larger quantity may be produced in the lungs, after a* Pneumonia has existed 
 for a day or two, than it would have required years to generate in the pre- 
 vious mode. But the character of the deposit still remains the same ; and its 
 relation to the plastic element of the blood is shown by the interesting fact, of 
 no unfrequent occurrence, that, in a Pneumonia affecting a Tuberculous 
 subject, Plastic Lymph is thrown out in one part, whilst Tubercular matter is 
 deposited in another. Now Inflammation, producing a rapid deposition of 
 Tubercular matter, is peculiarly liable to arise in organs, which have been 
 previously affected with chronic Tubercular deposits, by an impairment of 
 the process of textural Nutrition ; for these deposits, acting like foreign bodies, 
 
608 OF NUTRITION. 
 
 may of themselves become sources of irritation ; and the perversion of the 
 structure and functions of the part renders it peculiarly susceptible of the 
 influence of external morbific causes. These views, at which several recent 
 Physiologists and Pathologists have arrived on independent grounds, seem to 
 reconcile or supersede all the discordant opinions which have been upheld at 
 different times regarding the nature of Tubercle ; and lead to the soundest 
 views with respect to the treatment of the Diathesis. 
 
 809. We frequently meet with abnormal growths of a Fatty, Cartilaginous, 
 Fibrous, or even Bony structure; which result from the development of these 
 tissues in unusual situations, and appear to originate in some perverted action 
 of the parts themselves. But there is another remarkable form of disordered 
 Nutrition, which is concerned in producing what have been termed hetero- 
 togous growths, that is, masses of tissue, differing in character from any 
 which is normally present in the body. Most of these are included under 
 the general designation of Cancerous or Fungous structures ; and it has been 
 shown by Miiller and others, that the new growth consists of a mass of cells; 
 which, like the Vegetable Fungi, develope themselves with great rapidity ; and 
 which destroy the surrounding tissues by their pressure, as well as by ab- 
 stracting from the Blood the nourishment which was destined for them. 
 These parasitic masses have a completely independent power of growth and 
 reproduction ; and it seems difficult to refuse them the character of distinct 
 existences. They can be propagated by inoculation, which conveys into the 
 tissues of the animal operated on, the germs of the peculiar cells that consti- 
 tute the morbid growth ; and these soon develope themselves into a new 
 mass. It seems to be by the diffusion of the germs produced in one part, 
 through the whole fabric, by the circulating current, that the tendency to re- 
 appearance (which is one great feature in the malignant character of these 
 diseases) is occasioned. Yet there is no evidence, that the first production 
 of a Cancerous growth is due to germs introduced from without; in fact, as 
 it appears to the Author, the history of its origin, as well as the analogy of 
 similar cases, makes it far more probable, that the Cancer-cell is but an abnor- 
 mal form of the ordinary tissue-cells of the body, being, in fact, a cell which 
 possesses to an unusual degree the power of reproduction, instead of under- 
 going those transformations by which it would be converted into other 
 kinds of tissue. 
 
 a. Several instances have been recently published, of the occurrence of Vegetable organ- 
 isms as parasites upon the Animal body. That in some of these a true Plant, possessing a 
 regular apparatus of nutrition and reproduction, has arisen from a germ introduced from 
 without, there can be little question ; but in other instances (as in the case of the crusts of 
 Porrigo favosa), it has been assumed that the organization is Vegetable, merely because it 
 consists of a mass of cells capable of extending themselves by the ordinary process of mul- 
 tiplication. But it must be remembered, that the cellular organization is common to Ani- 
 mals as well as to Plants ; being the only form that manifests itself at an early period of 
 development in either kingdom, and remaining throughout life in those parts which have 
 not undergone a metamorphosis for special purposes. Hence to speak of Porrigo favosa, or 
 any similar disease, as produced by the growth of a Plant within the Animal body, appears 
 to the Author a very arbitrary assumption ; the simple fact being, in regard to this and many 
 other structures of a low type, that they present the simplest or most general kind of organ- 
 ization. Their nature must be decided by their Chemical constitution ; and this, in the case 
 of the Porrigo favosa, appears to be unquestionably Animal. 
 
 b. There seems a strong probability in the idea, that the propagation of many diseases by 
 inoculation, essentially consists in the transplanting of cell-germs from the body of one ani- 
 mal to that of another. Thus the Vaccine Vesicle appears to be made up of an aggregation 
 of distinct cells, to which we may very fairly attribute an origin of this kind. But this seems 
 rather true of diseases which manifest themselves by a local development of cellular struc- 
 tures, such as Cancer and Cow-pox, than of such as Hydrophobia, Plague, Poisoning by 
 Serpents, &c., in which the symptoms are referrible, more or less clearly, to an alteration in 
 the character of the Blood, by the introduction of a substance acting as a ferment ( 708). 
 

 VARYING DURATION OF CELL-LIFE. 609 
 
 4. Varying duration of different parts of the Organism. 
 
 810. From the foregoing details the obvious inference results, that each 
 part of the organism has an individual Life of its own, whilst contributing to 
 uphold the general Life of the entire being. This Life, or state of Vital 
 Action, depends upon the due performance of the functions of all the subordi- 
 nate parts, which are closely connected together. The lowest classes of or- 
 ganized beings are made up of repetitions of the same elements; and each 
 part, therefore, can perform its functions in great degree independently of the 
 rest. But, in ascending the scale, we find that the lives of the individual parts 
 become gradually merged (so to speak) in the general life of the structure ; 
 for these parts gradually become more and more different in function, and 
 therefore more and more dependent on each other for their means of support ; 
 so that the activity of all is necessary for the maintenance of any one. 
 
 811. The doctrine of Development from Cells gives us a clearer idea of the 
 nature of the continual process of decay and renewal, which take place in the 
 Animal body. Every Cell has, to a certain degree, an individual life of its 
 own. This individuality is much more decided in the lower forms of organ- 
 ized being, where each cell can maintain an independent existence, than ifcis 
 in the higher, in whose fabric a large number having different functions are 
 united into one structure, the combined activity of the whole of which is 
 necessary to the life of any one. But, even in the highest, it is evident that 
 each cell will possess a certain duration of its own ; and that, from its first 
 period of development, all the changes which it undergoes are governed by 
 laws peculiar to it. In the various parts of the Vegetable, as in those of the 
 Animal, we find a great difference in the duration of the existence of the cells 
 composing them. These differences may be reduced to five heads. 
 
 i. Cells may be generated, which have a very transient existence, and 
 "which disappear again, without undergoing any transformation. This may be 
 seen in the Vegetable ovule, and in the Germinal Vesicle of the Animal Ovum ; 
 as well as in many other parts. Thus we have Absorbent Cells ( 181), 
 Secreting Cells ( 179), and probably Assimilating or Fibrine-elaborating 
 Cells ( 154); all of which originate in pre-existing germs, attain their full 
 development (in the course of which they perform their allotted function), 
 and then disappear by rupture or liquefaction. In such instances it is obvious 
 that, from their first origin, the cells are subject to a law of limited duration, 
 and that their death and decay are as much- the result of their inherent consti- 
 tution, as are those of each entire Animal or Vegetable organism. 
 
 ii. The contrary extreme to this may be found in those Cells, of which the 
 function, instead of being transient, is to be indefinitely prolonged ; such are 
 those of which the organs of mechanical support are usually formed. Here 
 the cell, instead of changing its form, or of giving origin to new cells within 
 itself, becomes the subject of an internal deposit of hard matter, which lines 
 its walls, and cuts it off, more or less completely, from the general course of 
 Vital Action. When this is the case, and the hard matter is not itself liable 
 to decomposition, the duration of the cell-walls, which are protected by their 
 peculiar aggregation from exposure to decomposing agents, may undergo little 
 or no change for an almost indefinite period. Thus the heart-wood of Plants, 
 the Bones of Animals, and still more their Hair, Hoofs, Horns, &c., may re- 
 main unaltered through a long series of years. Of some of these parts it can 
 scarcely be said that they are less alive, when removed from the organism to 
 which they belonged, than when included in it. In the heart-wood of a Plant, 
 for example, no vital change takes place, from the time that the woody tubes 
 and cells are once consolidated by internal deposition ; it may decay, whilst 
 
610 OF NUTRITION. 
 
 still forming part of the stem, without interfering with the nutritive operations 
 of the tree ; and if we could possibly remove it entirely, without doing injury 
 by the operation to the rest of the structure, its absence would be productive 
 of no other evil consequences than those which would necessarily result 
 from the withdrawal of the mechanical support afforded by it. The same 
 may be said of the Epidermic Appendages of Animals, and of the External 
 Skeletons of many Invertebrata ; which remain equally unchanged from the 
 time of their first formation. Now as long as these structures hold together, 
 it is evident that the organized part of them must have undergone little change 
 from the condition in which it existed in the living fabric ; and that their 
 death takes place, in reality, only when the structures decay, this decay 
 being, in fact, the consequence of it. The law of existence of such cells, 
 therefore, is that of indefinitely -prolonged duration ; this law must have been 
 impressed upon them from their origin; and the power by which their walls 
 secrete and deposit the consolidating materials, appears to be the chief means 
 of keeping it in operation. 
 
 in. In all the higher forms of Animal structure, the Cells originally com- 
 posing it are only the means of generating tissues of other kinds, in which 
 the Cellular character is less obvious. Thus the Muscular and Nervous tis- 
 s*fes have their origin in cells, which at first appear in no respect different 
 from others, but which subsequently undergo a peculiar metamorphosis, and 
 themselves no longer exist as such. Upon all these primordial cells, there- 
 fore, a law of transformation is impressed, from the time of their first pro- 
 duction. In their original aspect, they cannot be distinguished from the cells 
 which are not destined to undergo any such metamorphosis; but, just as the 
 first cell of the embryo, from which Man is produced, must have some real 
 though not apparent difference from that in which the Polype originates, so 
 must the cell which is afterwards developed into Muscular Fibre, be inherently 
 different from that which is subsequently converted into Nervous tissue. 
 
 iv. The tissues, thus formed by the transforming processes to which certain 
 Cells are subject, are evidently governed by the same laws of Nutrition as 
 those which regulate ordinary Cell-growth ; these are modified in their action, 
 however, by the conditions in which they are placed, in regard to the activity 
 of the function which the Tissue is called upon to perform. In all instances, 
 however, these Tissues have a limited period of existence. They are gene- 
 rated, they grow from the alimentary materials with which they are supplied, 
 they arrive at maturity, they decline, they die, and they decay; just as do the 
 isolated vesicles constituting the humblest forms of vegetation. For all of 
 them there is an appointed duration of life, just as there is for the entire Man. 
 Now on this view we can explain many physiological phenomena, which 
 cannot otherwise be very satisfactorily accounted for. It is owing to the con- 
 tinual death and decay of its component cells, that the process of decomposition 
 goes on with such constancy and uniformity in the living body; whilst, on the 
 other hand, it is by the continual reproduction of new cells, in the place of 
 those which have disappeared, that the normal organization is maintained. 
 The limited duration of the life of the cells composing the various tissues is 
 further made evident, by the rapid disappearance of the normal organization, 
 and by the loss of the functional power of those tissues, when the cessation 
 of their activity prevents the development of the new cells, by which alone 
 their character can be maintained. Of the change of structure and loss of 
 power which result from disuse and consequent want of nutrition in Muscular 
 and Nervous tissues, instances have already been given ( 588 and 790). 
 The ordinary processes of Decomposition and Interstitial Absorption are pro- 
 bably less rapid than usual under such circumstances ; so that the length of 
 time required for the disappearance of the characteristic structure, and the 
 
VARYING DURATION OF DIFFERENT PARTS. Oil 
 
 consequent loss of functional power, affords us some idea of the limit to the 
 duration of the life of the tissue. It may be stated, then, as a general pro- 
 position, that the interstitial change, which the whole structure of the body is 
 continually undergoing, in its normal or physiological condition, is due to the 
 regularly-occurring death and reproduction of its component cells, of which 
 every one has its own limit of duration. We uniformly find that those 
 Tissues, in which the most active vital changes are going on (such as the 
 Nervous and Muscular), are those in which the duration of the individual 
 component portions is the least; as is shown by the rapidity of the changes 
 of removal and reposition, which are continually taking place in them. The 
 converse holds good also. Further it may be remarked, and this is a matter 
 of much practical importance, that anything which increases the functional 
 activity of any particular tissue, thus causing it to live faster, diminishes the 
 duration of its life ; as is shown in the increased rapidity of disintegration, 
 which results from the continued exercise of the Muscular and Nervous 
 systems. 
 
 v. There is yet another phase, under which Cellular life presents itself as 
 a natural condition in the lower organisms, and in the early condition of the 
 higher ; but which constitutes a morbid state in the adult condition of the 
 latter. This is when cells reproduce themselves with extreme rapidity, 
 neither the primary nor secondary cells undergoing any further transforma- 
 tion, and the duration of each individual being limited by the development 
 of its progeny within it, causing its own distension and final rupture or dis- 
 appearance. The growth of the lower Fungi offers a striking example of this 
 in the Vegetable kingdom ; and the early processes of development in the 
 Ovum of the highest Animals, exhibit the same character. Every cell, as it 
 is generated, proceeds at once to the work of multiplication, for which it 
 seems specially destined; and thus it is subject from the first to the law of 
 Reproduction. It is this which distinguishes the Fungoid diseases ; which 
 derive the character designated by the Surgeon as malignancy, simply from 
 their tendency to propagation, and his want of power to control it. It seems 
 probable that many other changes of structure are due to a corresponding 
 cause. 
 
 812. The duration of the existence of the individual Cells in corresponding 
 parts, is further subject to variation, in accordance with the period of life of 
 the entire organism. Thus all the tissues, even those most consolidated, are 
 undergoing continual changes in the young animal, in which the processes of 
 decay and renewal go on much faster than in the adult ; and in the adult, than 
 in the aged person. Even the cells of the Bony structure, which in the adult 
 are almost permanent, and in the aged person are subject to extremely little 
 change, are liable in the infant to an early decomposition ; their places being 
 filled up by others, of which the form adapts itself to the growth of the struc- 
 ture. This may be partly accounted for by the imperfect degree, in which, 
 so long as the entire organism is undergoing rapid increase, the normal struc- 
 ture is developed in any one portion of it; for the degree of consolidation 
 being less, the tendency to decay will naturally be greater. But this explana- 
 tion is not in itself sufficient ; and we must be content for the present to 
 regard it as a general law (which may ultimately prove to be but a result of 
 some more general principle) that the duration of the existence of individual 
 cells increases, cseteris paribus, with the advance of life. At the same time, 
 their functional activity diminishes. They may be said to live more slowly. 
 The dull perceptions, and slow and feeble movements, of the aged man, form 
 a striking contrast with the acute sensibility, and the rapid and vigorous mus- 
 cular actions, of the child ; and the same change may be noticed in the organic 
 functions. Hence it may be stated as a general law, that the vital activity of 
 
612 OF NUTRITION. 
 
 the Cells (and of the tissues produced by their transformation) diminishes in 
 proportion to the prolongation of the general life of the system ; and this law 
 exactly corresponds with what has just been observed, as to the comparison 
 of the tissues of different kinds, which are present in the same body. 
 
 5. Of Death, or Cessation of Nutrition. 
 
 813. It is a necessary consequence of that intimate mutual dependence of 
 the several operations, which is characteristic of the higher organisms, that 
 the interruption of the function of any one important part is followed by the 
 Death of the whole structure; because it interferes with the elaboration, cir- 
 culation, or depuration of that nutritive fluid, which supplies the pabulum for 
 the growth and reproduction of each portion of the system. But the lives 
 of individual parts may be prolonged for a greater or less duration, after the 
 suspension of the regular series of their combined operations; hence it is 
 that Molecular Death is not always an immediate result of Somatic Death. 
 But, on the other hand, if the function of the part have no immediate relation 
 to the indispensable actions just alluded to, it may cease without affecting 
 them; so that Molecular death may take place to a considerable extent (as in 
 entire limbs, or in the muscles and integuments of the head and trunk) with- 
 out Somatic death necessarily resulting. 
 
 814. The permanent and complete cessation of the Circulating current, is 
 that which essentially constitutes Somatic Death; and this may be traced to 
 several distinct causes. In i\\e first place, it may be due to failure in the pro- 
 pulsive power of the Heart, which constitutes Syncope; and this may result 
 from a variety of causes, which cannot be here particularized. Secondly, it 
 may be occasioned by an obstruction to the flow of blood through the capil- 
 laries of the lungs, constituting Asphyxia; and this, as we have seen, may 
 be consequent upon disordered states of the lungs themselves, or upon sus- 
 pension of the respiratory movements, through affections of the Nervous 
 centres. It is in this mode that most fatal disorders of the Nervous System 
 produce death; except when a sudden and violent impression (as from con- 
 cussion of the brain, or a blow on the epigastrium) occasions a cessation of 
 the heart's power. Thus in Apoplexy, Narcotic Poisoning, &c., death results 
 from the paralyzed condition of the Medulla Oblongata ; whilst in the con- 
 vulsive diseases, the fatal result ensues upon a spasmodic fixation of the 
 respiratory muscles. Thirdly, Somatic death may be occasioned by a dis- 
 ordered condition of the Blood itself, which at the same time weakens the 
 power of the Heart, impairs the activity of the Nervous system, and prevents 
 the performance of those changes in the systemic capillaries, which afford a 
 powerful auxiliary to the circulation. This is Death by Necrsemia. Fourthly, 
 Somatic death may result directly from the agency of Cold, which stagnates 
 all the vital operations of the system. Where the cooling is due to the agency 
 of an extremely low external temperature, which acts first upon the super- 
 ficial parts, there is reason to think that the congestion of the internal vessels 
 thereby induced, occasions a torpid condition of the nervous centres, and that 
 the cessation of the Circulation is immediately due to Asphyxia. But when 
 the cooling is gradual, and the loss of heat is nearly equally rapid throughout, 
 it is obvious that the stagnation will be universal, and that no cessation of 
 activity in any one part is the occasion of the stagnation in the functions of 
 the remainder. It is in this manner that death results from Starvation ; and 
 not by the weakening of the heart's action, as commonly supposed. The 
 proofs of this will be stated hereafter ( 896). 
 
 815. That Molecular death should speedily follow Somatic death, is not 
 surprising; when it is borne in mind how constant is the dependence of all 
 
OF DEATH, OR CESSATION OF NUTRITION. 613 
 
 those functional operations, in which vital activity consists, upon the due 
 supply of the circulating fluid. And as a general rule we find, that the more 
 active the changes which normally take place in any tissue during life, the 
 more speedily is its complete loss of activity, or Death, when the requisite 
 conditions of its vital action are no longer supplied to it. We may observe 
 that, in Cold-blooded animals, the supervention of Molecular upon Somatic 
 death is much less speedy than it is in Birds and Mammals. This seems 
 due to two causes. In the first place, the tissues of the former, being at all 
 times possessed of a lower degree of vital activity than those of the latter, 
 are disposed to retain it for a longer time ; according to the principle already 
 laid down. And, secondly, as the maintenance of a high temperature is an 
 essential condition of the vital activity of the tissues of warm-blooded ani- 
 mals, the rapid cooling of the body after Somatic death is calculated to extin- 
 guish it speedily; and that this cause has a real operation, is evinced by the 
 influence of artificial warmth in sustaining the vital properties of separated 
 parts. The rapidity with which Molecular death follows the cessation of the 
 general circulation, will be influenced by a variety of causes ; but especially 
 by the degree in which the condition of the solids and fluids of the body has 
 been impaired by the mode of death. Thus in Necraemia, and in death by 
 gradual -cooling, Molecular and Somatic death may be said to be simultane- 
 ous ; and the same appears to be true of death by sudden and violent impres- 
 sions on the Nervous System. But in many cases of death by causes, which 
 suddenly operate in producing Syncope or Asphyxia, the tissues and blood 
 having been previously in a healthy condition, Molecular death may be long 
 postponed. We cannot be quite certain that it has supervened, until signs of 
 actual decomposition present themselves. 
 
 816. When Molecular death takes place in an isolated part, it must result 
 from some condition peculiar to that part, and not primarily affecting the 
 body in general. Thus we may have Gangrene or Mortification of a limb as 
 a direct result of the application of severe cold, or of an agent capable of 
 producing chemical changes in its substance, or of violent contusions occa- 
 sioning mechanical injury; or, again, from an interruption to the current of 
 nutritive fluid; or, further, from some ill-understood stagnation of the nutri- 
 tive process, which manifests itself in the spontaneous death of the tissues 
 without any assignable cause, as in some cases of Senile Gangrene. Some- 
 times we are enabled to trace this stagnation to some disordered condition of 
 the circulating fluid; as in the Gangrene resulting from the continued use of 
 the Ergot of Rye or Wheat; but we can give no other account of the almost 
 invariable commencement of such gangrene in the extremities, than we can 
 of the selection of Lead, introduced into the blood, by the extensors of the 
 fore-arm. When Mortification or Molecular Death is once established in any 
 part, it tends to spread, both to contiguous and to distant portions of the body. 
 Thus we have continually to witness the extension of Gangrene of the 
 lower extremities, resulting from severe injury or from the use of the Ergot, 
 from the small part first affected, until the whole limb is involved ; and this 
 extension is easily accounted for by our knowledge of the tendency of organic 
 substances in the act of decomposition, to produce a similar change in other 
 organic substances subjected to their influence. And the propagation of the 
 Gangrenous tendency to other parts, is obviously due to the perversion of the 
 qualities of the Blood, which results from a similar cause. It is not, how- 
 ever, until some organ is affected, whose action is essential to the due main- 
 tenance of the Vegetative functions, that Molecular death becomes a cause of 
 Somatic death ; and very extensive ravages may thus take place without the 
 extinction of the sufferer's life. 
 52 
 
614 OF SECRETION. 
 
 CHAPTER XV. 
 
 OF SECRETION. 
 
 1. Of Secretion in General. 
 
 817. The literal meaning of the term Secretion is separation; and this is 
 nearly its true acceptation in Physiology. We have seen that the Nutritive 
 materials, which are received into the living body, are combined in a certain 
 proportion in the circulating fluid; and that they are carried in its current to 
 every part of the structure. Of the elements of the Blood, some are being 
 continually separated from it, to be introduced into the solid textures, of which 
 they become constituents ; forming, as it were, the organized frame-work, in 
 the interstices of which various other matters (also separated from the blood) 
 are deposited in an inorganic condition. This separation, the object of which 
 is to build up a living fabric, has been already considered under the head of 
 Nutrition; but it may be here remarked, that the deposition of Calcareous 
 matter in the Bones and Teeth, of Chondrine and Gelatine in the Bones and 
 Cartilages, and of Horny matter in the cells of the Epithelium and its ap- 
 pendages (Hair, Nails, Hoofs, &c.), is accomplished by a process analogous 
 in all respects to that concerned in the separation of those other products 
 which are ordinarily considered as Secretions. The same may be said of the 
 Serous fluid, which distends the interspaces of Areolar tissue, the Oily matter 
 contained in the Fat-cells, the Albuminous fluid of the Humours of the Eye, 
 and other analogous constituents of the living fabric. 
 
 818. But we have chiefly to consider under the present head, the nature 
 and origin of those products which are continually being cast forth from the 
 living body ; the amount of which is usually equal, in the .adult animal, to 
 that of the solids and fluids ingested, after allowance has been made for the 
 portion rejected, in the form of faeces, as indigestible. The experiments of 
 Dr. Dalton* on his own person, give the following as the proportional quan- 
 tities discharged through the principal channels of excretion. The mean 
 quantity of solid and liquid Aliment taken into the system daily (during 14 
 days in spring) being 91 oz., or about 5| Ibs., the average amount of Faeces 
 (including part of the solid matter of the bile) was 5 oz. ; the average amount 
 of Urine was 48 oz. daily ; and, as the total weight of the body remained 
 the same, the quantity of fluid and solid matter excreted by the Skin and the 
 Lungs must have been 37k oz. At other periods of the year, a variation was 
 observed ; especially in the relative amount of fluid passing off by the Urine, 
 and by Cutaneous exhalation. 
 
 819. It can scarcely be questioned, that the chief source of the Excretions 
 is to be found in the continued Decomposition of the various tissues of the 
 body, which has been several times alluded to ( 275 and 811) ; and it is pro- 
 bable, from considerations heretofore adduced, that they are derived, not so 
 much from the fluid returned into the blood by the Lymphatics (as formerly 
 supposed), as from the Blood itself ( 680). It has been pointed out by Lie- 
 big, that there is a remarkable correspondence between the elements of the 
 Blood, and those of the Bile and Urine taken together ; so that the Tissues, 
 
 * Edinburgh New Philosophical Journal, 1832, 1833. 
 
OF SECRETION IN GENERAL. 615 
 
 which are all formed from the nutritive fluid, may be regarded as resolving 
 themselves, by their ultimate decomposition, into these two excretions. 
 Moreover, the* Blood, during its circulation, gives up one portion of its con- 
 stituents in one part of the body -another at a different situation, and so on. 
 Thus, the elaboration of Gelatine, which is deposited so largely in the solid 
 tissues, must occasion a considerable alteration in the blood : since, in its pro- 
 duction from Albumen, a certain residuum must be left ( 141, 6, c). This 
 residuum is probably another important source of the products of Excretion. 
 The same may be remarked in regard to the Nutrition of the Nervous Sys- 
 tem ( 249). In several other instances, peculiarities of action in different 
 parts will deprive the Blood that passes through them, of its due proportion 
 of certain of its constituents ; these are partly restored by its admixture in 
 the Heart, with the Blood that has returned from other parts ; but still a gene- 
 ral alteration in the character of the Blood is the result of its Circulation ; and 
 for this alteration, it is the province of the Excretory function to compensate. 
 A striking illustration may be found, in the change of the colour, and of the 
 proportional amount of free Oxygen and Carbonic Acid, which takes place 
 in the Systemic capillaries, and which is reversed in the passage of the Blood 
 through the Lungs ( 766). Moreover it appears that two, at least, of the 
 Excreting organs have for their function to prevent the accumulation, in the 
 Blood, of matters which have been taken in as food, but for which there is 
 no demand in the economy. Thus the Liver appears to be the peculiar 
 channel for the elimination of superfluous non-azotized matter ( 833) ; and 
 the Kidney of these azotized compounds, which cannot be worked up (so 
 to speak) into tissue ( 842). Particular sources for the respective contents 
 of other Excretions will be pointed out, when they are considered in detail. 
 
 820. A distinction has already been drawn ( 278) between the proper 
 Excretions, the retention of which in the Blood would be positively injurious, 
 and those Secretions which are destined for particular purposes within ihe 
 system, and the cessation of which has no immediate influence on any but the 
 function to which they are destined. This distinction is one of great import- 
 ance, especially when it is considered with reference to the Chemical Elements, 
 that are found in the two classes of fluids respectively. The solid matter dis- 
 solved in those of the latter class, is little else than a portion of the constitu- 
 ents of the Blood, either pure, or but slightly altered ; thus, in the Lachrymal 
 fluid, the Saliva, the Pancreatic juice, the Serous fluid of areolar tissue and 
 of serous and synovial membranes, we find little else than Albuminous and 
 Saline matter, derived at once from the blood. The Caseine, which is the 
 most characteristic ingredient of Milk ( 854 6), is but a slightly-altered form 
 of Albumen; and some curious evidence has recently been obtained, that this 
 alteration commences in the Blood, and goes on during pregnancy as a pre- 
 paration for lactation.* On the other hand, the characteristic ingredients of the 
 Excretions are very different in character from the normal elements of the 
 Blood. They are all of them completely unorganizable; and they possess, 
 for the most part, a simple atomic constitution. Some of them also, have a 
 tendency to assume a crystalline form ; which is considered by Dr. Prout to 
 indicate their unfitness to enter into the composition of organized tissues. 
 With regard to some of the chief of these, there is sufficient evidence of their 
 existence, in small quantity, in the circulating Blood; but it is also clear, that 
 they exist there as products of decomposition, and that they are destined to 
 be separated from it as speedily as possible. If their separation be prevented, 
 they accumulate, and communicate to the circulating fluid a positively delete- 
 rious character. Of this, we have already seen a striking example in the 
 
 * See Dr. G. Bird, in Guy's Hospital Reports, vol. v. 
 
616 OF SECRETION. 
 
 case of Asphyxia ( 779) ; and the history of the other two principal Excre- 
 tions, the Bile and Urine, will furnish evidence to the same effect. As a 
 general fact, then, it may be stated, that the materials of the Secretions pre- 
 exist in the Blood, in a state nearly resembling that in which they are thrown 
 off by the secreting organs : but that the materials of those secretions, which 
 are only destined to perform some particular function in the economy, are 
 derived from the substances which are appropriated to its general purposes ; 
 whilst those of the excretions are the result of the changes that have taken 
 place in the system, and cannot be retained in it without injury. 
 
 821. Of the reason why certain compounds forming part of the circulating 
 Blood, are separated from it by one organ, and others by a different one, no 
 other account can be given, than that which refers them to the special endow- 
 ments of the ce//5, which are the real instruments of the process. When the 
 ultimate structure of Glands is considered, it is found to be neither more nor 
 less than a vascular membrane, covered with epithelium-cells, and made up 
 into various forms for convenience of packing. Of such a membrane, in its 
 most expanded state, that which composes the walls of the Serous cavities, or 
 of the Synovial capsules, affords a good example. Of Mucous membrane 
 ( 178), the structure is in some instances almost equally simple ; but in gene- 
 ral the secreting surface is extended, by the inversion of the membrane, into 
 a large number of little open sacs or follicles (Fig. 45), which are lined with 
 epithelium-cells, and copiously supplied with blood-vessels, and which are 
 equally" concerned with the external superficies, in the elaboration of the pro- 
 tective secretion that covers these membranes. In the most complex form of 
 gland, we find nothing but a very obvious modification of this structure. 
 Either the sacs are prolonged into coeca or blind tubes, as is the case in the 
 Human Kidney or Testis ; or they are very greatly multiplied, and are clus- 
 tered together (just like currants upon a stalk) upon efferent ducts common to 
 several of them, as is seen in the Parotid. Now, that the particular modifica- 
 tion of structure, which the Gland may present, has no essential connection 
 with the character of the Secretion it is destined to form, is evident from this 
 circumstance, that almost every gland may be found under a variety of .forms, 
 in different parts of the Animal series. The Secreting system, like every 
 other, is far simpler in the lower classes of Animals than in the higher; the 
 number of effete compounds, to be excreted from the circulating fluid, is much 
 smaller; and the variety of purposes, for which special secretions are required, 
 is much less. Hence, for almost every Gland, there is a part of the Animal 
 scale below which it does not exist ; and when it makes its first appearance, 
 it almost invariably presents a character nearly as simple, as that of the least 
 complex glanular structures in the higher animals. Thus the Pancreas in 
 Fishes (Fig. 257), the Mammary Gland in the Ornithorhyncus (Fig. 222), the 
 
 Salivary glands in the Echinodermata, 
 
 Fig. 222. and the Urinary organs of Insects, are 
 
 nothing more than follicles more or less 
 extended, and having separate orifices. 
 Again, in Insects, we find that all the 
 glands, the Liver and Salivary glands, 
 as well as the Kidneys and Testes, 
 have the form of prolonged tubes ; 
 
 whilst in Mollusca, all the secret- 
 Mammary Gland of Ornithorhyncus, ing organs, the Urinary and Genital, 
 
 as well as the Biliary and Salivary, 
 
 consist of multiplied vesicles connected with a ramifying duct. Moreover, it 
 is a well-ascertained fact that, even in the highest organisms, the functions of 
 Glandular structures (especially of those concerned in Excretion) are to a 
 
OF SECRETION IN GENERAL. 617 
 
 certain degree vicarious with each other ; so that, when the secretion from one 
 of them is checked, the system makes an effort to throw off, by another chan- 
 nel, the injurious products that would otherwise accumulate in the Blood. 
 What is the nature of the change in any secreting organ, that causes it thus to 
 take upon itself a new function, is a question upon which we can at present 
 only speculate ; we have no more certain knowledge of it, than we have of 
 the cause which occasions their normal actions. 
 
 822. It has been recently proved, beyond all reasonable doubt, that in all 
 secreting organs, the Cells which cover the membranous surfaces, and line the 
 follicles and tubes, constitute the really operative part. The simplest condi- 
 tion of a Secreting Cell, in the Animal Body, is that in which it exists in Adi- 
 pose tissue ; every cell of which possesses the power of secreting or separat- 
 ing Fatty matter from the Blood. In this case, the secreted product remains 
 stored up in the cavity of the cell, as it usually does in the Cellular tissue of 
 Plants ; not being poured forth, as it generally is elsewhere, by the subse- 
 quent bursting or liquefaction of the cell. But when the Secreting Cells are 
 disposed on the surface of a membrane, instead of being aggregated in a mass, 
 it is obvious that, if they burst or dissolve away, their contents will be poured 
 into the cavity bounded by that membrane ; and this is the case in the ordinary 
 Secreting processes. Thus the Mucus, which covers the surface of the Mu- 
 cous membranes, and which is being continually renewed, is the product of 
 the elaboration performed by the Epithelium-cells, which cover their -free sur- 
 faces, and line their follicles. These cells are being continually cast off, and 
 replaced by a fresh growth, which has its origin in germs supplied by the 
 subjacent membrane ; and thus it is by the act of Cell-growth, that the Secret- 
 ing process is accomplished. For just as the cells at the extremities of the 
 Intestinal Villi select, from the contents of the alimentary tube, the nutritious 
 portion which is to be introduced into the absorbent vessels, so do the cells 
 of the Secreting Tubuli or Follicles select from the Blood those effete particles 
 which it is their peculiar province to assimilate, and then discharge them into 
 the canals by which they will be carried out of the system.* Hence, as Mr. 
 Goodsir justly remarks, " there are not, as has been hitherto supposed, two 
 vital processes going on at the same time, viz., growth and secretion; but 
 only one, viz., growth. The only difference between this kind of growth, 
 and that which occurs in other organs is, that a portion of the product is, from 
 the anatomical condition of the part, thrown out of the system." 
 
 823. From the study of the changes which take place in the Glandular 
 organs, during their first development and their continued activity, Mr. Good- 
 sir has arrived at the conclusion, that the follicles may be considered as pa- 
 rent-cells ; and that the secreting cells in their interior may be regarded as a 
 second generation, developed from the nuclei or germinal spots on the walls 
 of the first. Now the successive production and development of the latter, 
 in which the process of secretion essentially consists, may take place on two 
 different plans. 
 
 a. In one class of Glands, the parent-cell, having begun to develope new cells in its inte- 
 rior, gives way at one point, and bursts into the excretory duct, so as to become an open fol- 
 licle, instead of a closed cell; its contained or secondary cells, in the progress of their own 
 growth, draw into themselves the matters to be eliminated from the blood, and, having at- 
 tained their full term of life, burst or liquefy, so as to discharge their contents into the cavity 
 of the follicle, whence they pass by its open orifice into the excretory duct; and a continual 
 new production of secondary cells takes place from the germinal spot or nucleus at the ex- 
 tremity of the follicle, which is here a permanent structure. In this form of gland, we may 
 frequently observe the secreting cells existing in various stages of development, within a 
 
 * We shall hereafter meet with an instance ( 829) in which, from the position of the 
 cells secreting it, Adipose matter is discharged from the body as an Excretion. 
 
 52* 
 
618 OF SECRETION. 
 
 single follicle ; their size increasing, and the character of their contents becoming more dis- 
 tinct, in proportion to their distance from the germinal spot (which is at the blind termina- 
 tion of the follicle), and their consequent proximity to the outlet (Fig. 41). In some varieties 
 < >f such glands, however, especially when the follicles are extended into prolonged tubes, the 
 production of new cells does not take place from a single germinal spot at the extremity of 
 tfye follicle, but from a number of points scattered through its entire length. 
 
 b. In the second type of Glandular structures, the parent-cell does not remain as a perma- 
 nent follicle; but, having come to maturity, and formed a connection with the excretory 
 duct, it discharges its entire contents into the latter, and then shrivels up and disappears, to 
 be replaced by newly-developed follicles. In each parent-cell of a gland formed upon this 
 type, we shall find all its secondary or secreting cells at nearly the same grade of develop- 
 ment ; but the several parent-cells, of which the parenchyma of the gland is composed, are 
 in very different stages of growth at any one period some having discharged their contents, 
 and being in progress of disappearance, whilst others are just arriving at maturity, and con- 
 necting themselves with the excretory duct; others exhibiting an earlier degree of develop- 
 ment in the secondary cells ; others presenting the latter in their incipient condition ; whilst 
 others are themselves just starting into existence, and as yet exhibit no traces of the second 
 generation, which they are destined subsequently to develope. 
 
 c. The former of these seems to be the usual type of the ordinary glands; the latter is 
 chiefly, if not entirely, to be met with among the Spermatic Glands.* 
 
 824. It is important to bear in mind, that an essential difference exists be- 
 tween the vital power concerned in the true Secreting process, and the phy- 
 sical property which occasions fluid Exhalation or Transudation. This dif- 
 ference is precisely the same as that which exists between the vital act of 
 Selective Absorption, and the physical operation of Endosmose or Imbibition. 
 By Imbibition and Transudation, certain fluids may pass through organic 
 membranes, in the dead as well as in the living body; and this passage de- 
 pends merely upon the physical condition of the part, in regard to the amount 
 and the nature of the fluid it contains, and the permeability of its tissues. 
 Not only does water thus transude, but various substances that are held in 
 complete solution in it, especially albumen and saline matter : it is in this 
 manner that the Blood absorbs fluids from the digestive cavity ( 675), and 
 pours out the serous fluid which occupies the interspaces of the areolar tissue 
 and the serous cavities. The transudation of the watery portion of the blood 
 is much increased by any impediment to its flow through the vessels, as in 
 Congestion and Inflammation; and also by any causes that produce a dimi- 
 nished resistance in their walls. We shall hereafter see, in examining the 
 Physiology of the Urinary secretion, a very striking example of the contrast 
 between physical Transudation and vital Secretion ( 840). 
 
 2. The Liver. Secretion of Bile. 
 
 825. The Liver is probably more universally found, throughout the Ani- 
 mal scale, than any other gland. Its form varies so greatly, however, in dif- 
 ferent tribes, that, without a knowledge of its essential structure, we should be 
 disposed to question whether any identity of character exists amongst the 
 several organs which we include under this designation. 
 
 a. In the higher Polypes, for example, we find it to consist of a number of distinct folli- 
 cles, lodged within the walls of the stomach, and pouring their secretion into its cavity by 
 as many separate orifices ; and it is more by the peculiar character of their secretion, than 
 by any other distinction, that these follicles are recognized as Hepatic. In the lower Articu- 
 late, a very similar conformation is met with ; but in the higher classes of this series, such 
 as Insects, the follicles are prolonged into tubes of considerable extent. It is very curious 
 to observe, in animals of such complex structure, that a few long tubes, closed at one end, 
 and opening at the other into the alimentary canal, are all which they have to represent a 
 Liver ; but the wonder is readily accounted for by keeping in view the extremely active 
 
 * See Goodsir's Anatomical and Pathological Researches, Chap. v. 
 
THE LIVER SECRETION OF BILE. 619 
 
 Respiration of these beings, which renders unnecessary any other complex apparatus for ela- 
 borating carbon from the system. 
 
 6. On the other hand, among the Mollusca, the Liver attains a much greater development. 
 Instead of the follicles being prolonged into tubes (which is the usual form of the glandular 
 system in Insects), they are very much increased in number, and arranged on the sides of 
 canals or efferent ducts, which either separately pour their fluid into the intestine, or partially 
 unite with each other before doing so. The Liver thus acquires a lobulated character, each 
 lobe consisting of a duct with its branching follicles ; and the whole organ forms a consider- 
 able proportion of the mass of the viscera, and is evidently of great importance in the 
 economy of the animal. It as interesting to compare this complex structure with the very 
 simple condition presented by the Liver in insects ; arid, when we keep in view the relative 
 amount of Respiration in the two groups of animals, we are at once struck with the fact, 
 that the development of the Liver bears an inverse proportion to the opportunity afforded 
 by the Respiratory organs for the aeration of the blood; it being peculiarly extended, when 
 these, either from their small size, or from their employment in an aquatic medium, cannot 
 perform their function with great activity. This conclusion is confirmed in an interesting 
 manner by the fact, that the Crustacea, which have the general organization of Insects, but 
 which inhabit the water and breathe by gills instead of by a complex system of air-tubes, 
 
 Fig. 223. Fig. 224. 
 
 Lobule of Liver of Squilla Mantis ; exterior. Lobule of Liver of Squilla Mantis cut open. 
 
 possess a Liver corresponding in form and in degree of development with that of the 
 Mollusca. 4| 
 
 c. In the Vertebrated Sub-kingdom, we may trace the operation of the same principle; 
 but the internal structure of the Liver, in the adult condition at least, is less easily demon- 
 strated, than it is in the lower classes ; owing to its increased complexity of structure, and 
 the closer union between its different parts. In Fishes and Reptiles, the Liver is of consider- 
 able size, and seems to perform a very important part in the decarbonization of the blood : 
 its form is adapted to that of the cavity in which it is lodged, sometimes one lobe only being 
 developed. In Birds, on the other hand, whose respiration is so much more active, it is much 
 smaller, but is placed on the median line, in conformity with the general symmetry of their 
 internal as well as external organs ( 40). In Mammalia, also, it is comparatively small ; 
 but, though reduced in proportional size, it is at the same time much more compact and 
 firm than in the lower Vertebrata. 
 
 rf. The Liver of Man is much less developed than that of many other Mammalia; and 
 presents, as rudimentary indications, certain organs which are elsewhere fully developed. 
 The whole mass, which we are accustomed to describe as consisting of a right and left lobe, 
 does in reality form but one (there being no real division between its two portions), which 
 must be regarded as the Central lobe ; the Lobulus Spigelii is the rudiment of a second or 
 right lobe, and the Lobulus Caudatus is a Lobule developed from it. In the Carnivora and 
 Rodentia, which present the most complex form of Liver that we meet with among Mam- 
 malia, there are five distinct parts ; a central or principal lobe, corresponding with the 
 principal part of the liver of Man; a right lateral lobe with a lobular appendage, correspond- 
 ing to the Lobulus Spigelii and Lobulus Caudatus ; and a similar lobe and lobule on the left 
 side. 
 
 e. The Gall-bladder is an appendage to the Liver, of which we find no traces in the 
 Invertebrata. It may be regarded as simply a dilatation of the efferent duct, more or less 
 prolonged from it, adapted to store up the hepatic-secretion against the time when it may be 
 required. In Fishes it frequently, but by no means constantly, presents itself; in Reptiles, 
 on the other hand, it invariably exists. In Birds it is occasionally absent, even in species 
 
620 
 
 OF SECRETION. 
 
 [Fig. 225. 
 
 The inferior or concave surface of the Liver, showing its subdivisions into lobes ; 1, centre of the right 
 lobe ; 2, centre of the left lobe ; 3, its anterior, inferior or thin margin ; 4, its posterior, thick or diaphragm- 
 atic portion ; 5, the right extremity ; 6, the left extremity ; 7, the notch in the anterior margin ; 8, the 
 umbilical or longitudinal fissure ; 9, the round ligament or remains of the umbilical vein ; 10, the portion 
 of the suspensory ligament in connection with the round ligament ; 11, pons hepatis, or band of liver 
 across the umbilical fissure ; 12, posterior end of longitudinal fissure ; 13, 14, attachment of the obliterated 
 ductus venosus to the ascending vena cava ; 15, transverse fissure ; 16, section of the hepatic duct; 17, 
 hepatic artery; 18, its branches ; 19, venaportarum ; 20, its sinus, or division into right and left branches ; 
 21, fibrous remains of the ductus venosus ; 22, gall-bladder ; 23, its neck ; 24, lobulus quartus ; 25, lobulus 
 spigelii; 26, lobulus caudatus ; 27, inferior vena cava ; 28, curvature of liver to fit the ascending colon; 
 29, depression to fit the right kidney ; 30, upper portion of its right concave surface over the renal cap- 
 sule ; 31, portion of liver uncovered by the peritoneum ; 32, inferior edge of the coronary ligament in the 
 liver; 33, depression made by the vertebral column.] 
 
 closely allied to others that possess it, and without any marked difference in the food, habits, 
 &c. of the two. In Mammalia, again, it is frequently absent, especially among herbivorous 
 animals; sometimes, on the other hand, two are present, a second or accessory gall-bladder 
 
 being formed upon the Ductus com- 
 
 [Fig. 226. munis choledochus, which else- 
 
 where not unfrequently presents a 
 dilatation in the same situation. In 
 the first Giraffe dissected by Mr. 
 Owen, no gall-bladder was found ; 
 in the second there were two. 
 
 /. In the Human species the gall- 
 bladder is rarely absent, except in 
 cases of malformation depending 
 upon general arrest of development, 
 in which several organs are in- 
 volved. The Excretory Ducts of 
 the Liver and Gall-bladder have 
 three coats, an internal or mucous, 
 a middle or fibrous, and an external 
 or areolar. The internal coat is con- 
 tinuous with the Mucous membrane 
 of the intestinal tube, into which it 
 opens; and the whole glandular 
 structure may indeed be considered 
 as a complex prolongation of this, 
 copiously supplied with blood-ves- 
 sels, and -packed into the smallest 
 possible compass. The middle or 
 Shows the three coats of the Gall-Bladder separated from fibrous coat bears a considerable 
 each other ; 1, the external or peritoneal coat; 2, the cellular resemblance in aspect to that of the 
 coat with its vessels injected ; 3, the mucous coat covered Arteries ; in its properties, however, 
 with wrinkles ; 4, 4, valves formed by this coat in the neck of it is still more nearly allied to true 
 the gall-bladder; 5,5, orifices of the mucous follicles at this muscle, being capable of exhibiting 
 point.] contraction on the application of 
 
THE LIVER SECRETION OF BILE. 
 
 621 
 
 stimuli to the Sympathetic nerves 
 supplying it j and in some instances 
 of obstruction, it has presented an 
 appearance very closely resembling 
 that of the muscular coat .of the 
 alimentary canal.* Dr. Davy has 
 pointed out, that the mucous coat of 
 the Ductus communis is disposed in 
 valve-like folds ; in such a manner, 
 as to prevent the reflux of the bile, 
 or of the contents of the intestine. 
 
 826. The Liver may be re- 
 garded as essentially consist- A view f the Gall - Bladd " distended with air, and with its 
 
 mff of a mass of cells in con- vessels injected; x ' C y 9tic arterv ' 2 > the branches of it which 
 iiass 01 us, in cor gupply the peritonea i coat of the liver . 3) the branch of the 
 
 nection With the ramifications hepatic artery which goes to the gall-bladder j 4, the lymphatics 
 
 of the Hepatic Duct : and these O f the gall-bladder.] 
 are in close relation with the 
 
 ramifications of the Portal Vein and Hepatic Artery, that serve to con- 
 vey blood to the minutest parts of this organ ; and with those of the 
 Hepatic Vein, which return it to the heart, after it has been subservient to 
 the Nutrition of the structure and to the elaboration of the Secretion. Be- 
 sides these, the Liver contains Lymphatics and Nerves ; the latter are chiefly 
 derived from the Sympathetic system, and are distributed on the walls of the 
 vessels and ducts. These various portions of the structure are connected 
 together by a fibrous tissue, to which the name of Glisson's Capsule has been 
 given. For our present knowledge of their ultimate arrangement, we are 
 almost entirely indebted to Mr. Kiernan,t whose account of them will be here 
 followed, his researches having been confirmed, in all essential particulars, 
 by other Anatomists. 
 
 a. When a Liver is closely examined with the naked eye, it is seen to be made up of a 
 great number of small granular bodies, about the size of a millet seed, of an irregular form, 
 and presenting a mjjnber of rounded projecting 
 
 processes upon their surfaces. These are com- 
 monly termed lobules, although by some Anatomists 
 they are spoken of as acini. When divided longi- 
 tudinally, they have a somewhat foliated appear- 
 ance (Fig. 229), arising from the distribution of 
 the Hepatic Vein ; which, passing into the centre 
 of each division, is termed the mfra-lobular vein. 
 The exterior of each Lobule is covered by a pro- 
 cess of the capsule of Glisson ; which is very dense 
 in the Pig and other animals ; but which is so thin 
 as to be almost undistinguishable in the Human 
 liver- Its substance is composed of the minute 
 ramifications of the before-mentioned vessels, arranged in the manner presently to be de- 
 scribed ; the spaces between which are filled up with a parenchyma, composed of nucleated 
 cells, like those shown in Fig. 232. The structure of each lobule, then, gives us the essential 
 characters of the whole gland. 
 
 b. The Lobules, when transversely divided, are usually found to present somewhat of a 
 pentagonal or a hexagonal shape ; the angles being generally somewhat rounded, so as to 
 form a series' of passages, or tnter-lobular spaces: in these lie the branches of the Vena Portae^ 
 and of the Hepatic Artery and Duct, from which are derived the plexuses that compose the 
 lobules. Each Lobule, when examined with the microscope, is found to be apparently com- 
 posed of numerous minute bodies of yellowish colour, and of various forms, connected to- 
 gether by vessels , to these the name of acini was given by Malpighi; and to these, if they 
 deserve a name, it ought to be restricted. They will be presently shown, however, to be 
 nothing else than the irregular islets, left between the meshes of the plexus formed by the 
 
 f ultimate ramifications of the Portal Vein. The Vena Portae, it will be recollected, is formed 
 
 [Fig. 228. 
 
 1, Nucleated cells composing the parenchy- 
 ma of the gland; 2, lobules of human liver 
 with ramifications of the hepatic vein.] 
 
 * In the Horse and Dog this coat is clearly muscular. 
 t Philosophical Transactions, 1833. 
 
622 
 
 OF SECRETION. 
 
 by the convergence of the veins, which return the blood from the chylopoietic viscera; and 
 there is reason to believe that it also receives the blood, which is conveyed to the Liver for 
 
 Fig. 229. * 
 
 Fig. 230. 
 
 Connection of the lobules of the liver with 
 the hepatic vein; 1, a trunk of the vein; 2, 2, 
 lobules depending from its branches, like 
 leaves on a tree; the centre of each being 
 occupied by a venous twig, the Intra-lobu- 
 lar Vein. 
 
 Horizontal section of three superficial lobule.?, 
 showing the two principal systems of Blood- Ves- 
 sels; 1, 1, t'nJra-lobular veins, proceeding from the 
 Hepatic veins; 2, 2, inter-lobular plexus, formed 
 by branches of the Portal veins. 
 
 the purposes of Nutrition, by the Hepatic Artery. As it is an afferent, not an efferent ves- 
 sel, it has a strong claim to the character of an Artery; even although it conveys Venous 
 blood. Like an artery, it gradually subdivides into smaller and yet smaller branches ; and 
 at last forms a plexus of vessels, which lie in the inter-lobular spaces, and spread with the 
 freest inosculation, throughout the entire Liver. To these vessels, the name of inier-lobular 
 Veins is given by Mr. Kiernan. They ramify in the capsules of the lobules, covering with 
 their ramifications the whole external surface of these; and then enter their substance. 
 When they enter the Lobules, they are termed lobular veins ; and the plexus formed by their 
 convergence, from the circumference of each lobule towards its centre (where their ultimate 
 ramifications terminate in those of the intra-lobular or hepatic vein), is designated as the 
 Lobular Venous plexus. In the islets of this plexus (the acini of Malpighi) the ramifications 
 of the hepatic duct are distributed in the manner next to be described. 
 
 c. The Hepatic duct forms, by its subdivision and ramification, an Interlobular plexus of a 
 very similar character ; but the anastomosis between the branches going to the different lobules 
 
 is less intimate than that of the inter- 
 Fig. 231. lobular veins, and cannot be directly 
 demonstrated; although Mr. Kiernan 
 thinks that his experiments leave but 
 little doubt of its existence, a com- 
 munication (which cannot be seen to be 
 established by any nearer channel) be- 
 ing proved to exist between the right 
 and left primary subdivisions of the 
 duct. The Interlobular Ducts ramify 
 upon the capsular surface tff the lobules, 
 with the branches of the Portal Vein 
 and Hepatic Artery ; they then enter its 
 substance, and subdivide into minute 
 branches, which anastomose with each 
 other, and form a reticulated plexus, 
 termed by Mr. K., the Lobular Biliary 
 plexus. This plexus constitutes the prin- 
 cipal part of the substance of the lobule ; 
 and when seen through the meshes of 
 the Portal plexus, gives rise to the ap- 
 
 Horizontal section of two superficial Lobules, show- 
 ing the interlobular plexus of biliary ducts; 1,1, intra- 
 lobular veins ; 2, 2, trunks of biliary ducts, proceeding 
 from the plexus which traverses the lobules ; 3, inter- 
 lobular tissue ; 4, parenchyma of the lobules. 
 
THE LIVER SECRETION OF BILE. 623 
 
 pearance of ccecal terminations of ducts. The ultimate terminations of these ducts have 
 not, however, been traced in the adult Liver of any of the higher animals, although they are 
 sufficiently evident in the embryonic condition. From the analogy of other organs, there 
 would seem good reason to believe, that the ultimate ramifications of the hepatic ducts 
 anastomose freely together, and that they form a network, in which their terminations are 
 lost, as it were, without forming true caeca. This view of the matter finds confirmation in 
 the curious fact pointed out by Mr. Kiernan, that, in the kft lateral ligament, the essential 
 parts of a lobe are found in the simplest form and arrangement. From the edge of the liver 
 next to the ligament, numerous Ducts emerge, which ramify between the two layers of peri- 
 toneum of which the ligament is composed. They are accompanied by branches of the Portal 
 and Hepatic Veins, and of the Hepatic Artery; which also ramify in this ligament, especially 
 around the parietes of the ducts. These Ducts, of which some are occasionally of considera- 
 ble size, divide, subdivide, and anastomose with each other; and the meshes formed by the 
 network of larger or excreting Ducts, are occupied by minute plexuses of their ultimate 
 ramifications or secreting Ducts. 
 
 d. The Hepatic Artery sends branches to every part of the Liver, supplying the walls of 
 the Portal and Hepatic Veins, and of the Hepatic Ducts, as well as Glisson's capsule. The 
 principal distribution of its branches, however, is to the Lobules, which they reach, in the 
 same manner with the Portal vessels and Biliary Ducts, by spreading themselves through the 
 interlobular spaces. There they ramify upon the interlobular ducts, and upon the capsular 
 surface of the lobules, which they then penetrate; their minuteness prevents their distribu- 
 tion within the lobules from being clearly demonstrable ; but, as they enter along with the 
 biliary ducts, there can be little doubt that, here as elsewhere, they are. principally distributed 
 upon the walls of these. As to the ultimate termination of the capillaries of the Hepatic 
 Artery, whether they enter the Portal plexus, or the Hepatic Vein, there is a difference 
 of opinion amongst anatomists ; the former view being upheld by Kiernan, the latter by 
 Muller. The question is a very interesting one in a physiological point of view ; since, if 
 the former aqcount be the true one, the Blood which is brought to the Liver by the Hepatic 
 Artery becomes subservient to the secretion of Bile, only by passing into the Portal plexus; 
 whilst, if the latter be the correct statement, either the arterial Blood is not at all subservient 
 to the formation of Bile, or the secretion can be elaborated from the arterial capillaries. The 
 experiments of Mr. Kiernan have satisfactorily proved, that the Intralobular or Hepatic Veins 
 cannot be filled by injection from the Hepatic Artery, though they maybe readily filled from 
 the Portal plexus ; whilst, on the other hand, there is reason to believe, that a very fine in- 
 jection into the Hepatic arteries, will find its way into the Portal plexus.* It is certain that 
 all the branches of the Hepatic artery, of which the termination can be ascertained, end in 
 the Vena Portaej a free capillary communication existing between their two systems of 
 branches, on the walls of the larger blood-vessels and. ducts. According to Muller, there is 
 an ultimate plexus of capillary vessels, with which all the three systems freely communicate ; 
 but for this idea there is no adequate foundation; and it is inconsistent with the fact just stated, 
 that injection into the Hepatic Artery does not return by the Hepatic vein. And the views 
 of Mr. Kiernan have lately received important confirmation from the researches of Mr. 
 Bowman on the circulation in the Kidney ( 841). 
 
 e. It now only remains to describe the Hepatic Veins, the branches of which occupy the 
 interior of the Lobules, and are termed wrtra-lobular veins (1, 1, Figs. 230 and 231). On 
 making a transverse section of a lobule, it is seen that the central vessel is formed by the 
 convergence of from four to six or eight minute venules, which arise from the processes 
 upon the surface of the lobule. In the superficial lobules, (by which term are designated 
 those lobules which lie upon the exterior of the glandular substance, not only upon the sur- 
 face of the Liver, but also against the walls of the larger vessels, ducts, &c.,) the Intralobular 
 Veins commence directly from their surface; and the minute venules of which each is com- 
 posed may be seen in an ordinary injection, converging from the circumference towards 
 the centre, as in the transverse section of other lobules. The Intralobular Veins terminate in 
 the larger trunks, which pass along the bases of the lobules, collecting from them their 
 venous blood ; these are called by Mr. Kiernan sublobular veins. The main trunk of the 
 Hepatic Vein terminates in the ascending Vena Cava. 
 
 /. In regard to the mode in which the nucleated Cells, that are the real agents in the 
 Secreting process, are arranged in the Liver of Man and the higher animals, there is much 
 uncertainty; owing especially to our want of acquaintance with the mode in which 
 the Hepatic Ducts terminate. They would seem to form the greatest part of the Paren- 
 chyma, which fills up the interstices between the reticulations of the Blood-vessels 
 and Ducts ; but it is obvious, from their functional operation, that they must have a more 
 
 * This is stated to have been the case in the injections of Lieberkuhn, although Mr. Kier- 
 nan has not succeeded in effecting it. 
 
624 
 
 OF SECRETION. 
 
 Glandular cells of 
 Liver ; a, nucleus ; 6, 
 nucleolus (?); c, adi- 
 pose particles. 
 
 Fig. 233. 
 
 Fig. 232. close relation to the latter than to the former. Their diameter 
 
 is usually from 1-1 500th to l-2000th of an inch; and they are conse- 
 quently easily recognized, whenever a portion of the substance of 
 the Liver is torn up and examined with the higher powers of the 
 Microscope. Their shape is usually spheroidal. They have a distinct 
 biliary tinge ; and contain a, granular amorphous matter, with a few 
 small adipose globules. 
 
 g. In regard to the Embryonic Development of the Human Liver, 
 a considerable part of our information must necessarily be derived 
 from the study of that of other animals ; and this not so much from 
 Mammalia, as from Birds ; since the development of this organ com- 
 mences so early in the former, its phases are so rapidly hurried 
 through, and its evolution is so soon completed, that the process cannot 
 
 be continuously watched. In the Chick, the rudiments of the Liver are found at the commence- 
 ment of the third day of incubation, in the 
 form of two ccecal pouches, which are pro- 
 longed from the Intestinal tube ; these carry 
 before them a fold of the vascular layer, from 
 which the blood-vessels subsequently origin- 
 ate ; and they soon begin to ramify in this, 
 sending off branches, of which the coecal ex- 
 tremities are still evident. At the end of the 
 fourth day, the tubuli and their ramifications 
 have attained a considerable size ; and they 
 approach each other and coalesce at the base, 
 entering the intestine by an orifice common 
 to the two. In this process, it is easy to re* 
 cognize the analogy to the succession of 
 forms, which we encounter in ascending the 
 animal scale. The size and density of the 
 organ are gradually increased ; but it is not 
 until several days afterwards, that the gall- 
 bladder is developed. In the Human Em- 
 bryo, the formation of the Liver begins at 
 about the third week of intra-uterine existence ; the organ is from the first of very large 
 size, when compared with that of the body; and between the third and the fifth week, it is 
 one-half the weight of the entire embryo. It is at that period divided into several lobes. 
 By the third lunar month, the liver extends nearly to the pelvis, and almost fills the abdo- 
 men ; the right side now begins to gain upon the left ; the gall-bladder begins to appear at 
 this time. The subsequent changes chiefly consist in the consolidation of the viscus, and the 
 diminution of its proportional size. Up to the period of birth, however, the bulk of the 
 Liver, relatively to that of the entire body, is much greater than in the adult ; the proportion 
 being as 1 to 18 or 20 in the new-born child, whilst it is about 1 to 36 in the adult: and 
 the difference between the right and left sides is still inconsiderable. During the first year of 
 extra-uterine life, however, a great change takes place ; the right lobe increases a little or re- 
 mains stationary, whilst the left lobe undergoes an absolute diminution, being reduced nearly 
 one-half; and as, during the same period, the bulk of the rest of the body has been rapidly 
 increasing, the proportion is much more reduced during that period, than in any subsequent 
 one of the same length. According to Meckel, the liver of the newly-born infant weighs 
 one-fourth heavier than that of a child of eight or ten months old ; and as the weight of the 
 whole body is more than doubled, during the same time, it is obvious that the change in the 
 proportion of the two must be principally effected at this epoch. 
 
 827. The knowledge of the distribution of the Biliary ducts, and of the two 
 chief systems of Blood-vessels, in the Lobules of the Liver, has enabled Mr. 
 Kiernan to give a most satisfactory explanation of appearances, by which 
 Pathological anatomists had been previously much perplexed. When the 
 Liver is in a state of Anaemia (which rarely happens as a natural condition, 
 although it may be induced by bleeding an animal to death), the whole sub- 
 stance of the lobules is pale, as represented in Fig. 234. In general, how- 
 ever, the Liver is more or less congested at the moment of death; and this 
 congestion may manifest itself in several ways. The whole substance may 
 be congested ; in which case the lobules present a nearly uniform dark colour 
 throughout their substance, their centres being usually more deeply-coloured 
 
 Origin of the Liver from the intestinal wall, in 
 the embryo of the Fowl, on the fourth day of incu- 
 bation ; a, heart ; 6, intestines ; c, everted portion 
 giving origin to the liver ; d, liver ; e, portion of 
 yolk-bag. 
 
SECRETION OF BILE. 
 
 625 
 
 Fig. 235. 
 
 1, angular lobules in a state of Ansemia, as 
 they appear on the external surface of the liver ; 
 2, interlobular spaces ; 3, interlobular fissures ; 
 4, interlobular veins, occupying the centres of 
 the lobules ; 5, smaller veins, terminating in the 
 central veins. 
 
 1, rounded lobules infirjst stage of Hepatic Ve- 
 nous congestion, as they appear on the surface 
 of the liver; 2, interlobular spaces and fissures. 
 
 than the margins. An appearance more frequently offered after death, how- 
 ever, is that represented at Fig. 235, and termed by Mr.Kiernan the first stage 
 of Hepatic Venous congestion. In this, the isolated centres of the Lobules alone 
 present the colour of sanguineous congestion; and the surrounding substance 
 varies from a yellowish-white, yellow, or greenish colour, according to the 
 quantity and quality of the Bile which it contains. This accumulation of the 
 blood in the Hepatic Veins, and the emptiness of the Portal plexus, seem due 
 to the continuance of capillary action after the general circulation has ceased ; 
 a circumstance to which we find an exact parallel, in the emptiness of the 
 systemic arteries, and the fulness of the veins, after most kinds of death. In 
 the second stage of Hepatic Venous congestion, the accumulation of blood is 
 found not only in the Intralobular Veins, but even in parts of the Portal or 
 Lobular Venous plexus. The parts which are freest from it are those sur- 
 
 Fig. 236. 
 
 A, lobules in the second stage of Hepatic Venous 
 congestion ; B, and c, interlobular spaces ; u, con- 
 gested intralobular veins ; E, congested patches, 
 extending to the circumference of the lobules ; 
 F, non-congested portions of lobules. 
 
 53 
 
 A, lobules as they appear on the surface in a 
 state of Portal Venous congestion ; B, interlo 
 bular spaces and fissures; c, intralobular hepatic 
 veins, containing no blood; D, the central por- 
 tions in a state of anaemia; E. the marginal por- 
 tions in a congested state. 
 
626 OF SECRETION. 
 
 rounding the interlobular spaces ; so that the non-congested substance here 
 appears in the form of circular or irregular patches, in the midst of which the 
 spaces and fissures are seen (Fig. 236).* Although the Portal as well as the 
 Hepatic venous system is thus involved in this form of congestion, yet, as 
 the obstruction evidently originates in the latter, the term given by Mr. Kier- 
 nan is, still applicable ; and it is important to distinguish this appearance from 
 that next to be described. The second stage of Hepatic venous congestion very 
 commonly attends disease of the heart, and other disorders in which there is 
 an impediment to the venous circulation ; and in combination with accumu- 
 lation in the biliary ducts, it gives rise to those various appearances, which 
 are known under the name of dram-drinkers' or nutmeg liver. The other 
 form of partial congestion arises from an accumulation of blood in the Portal 
 veins, with a reverse condition of the Hepatic or intralobular veins ; in this 
 condition, which Mr. K. designates as portal venous congestion, the marginal 
 portions of the lobules are of deeper colour than usual, and form a continuous 
 network, the isolated spaces between which are occupied by the non-congested 
 portions (Fig. 237). This is a very rare occurrence ; having been seen by Mr. 
 K. in children only. These differences fully explain the diversity of the state- 
 ments of different anatomists, as to the relative position of the so-called red 
 and yellow substances ; for it now appears, that the red substance is the con- 
 gested portion of the lobules, which may be either interior or exterior, or 
 irregularly disposed; whilst the yellow is the non-congested part, in which 
 the Biliary plexus shows itself more or less distinctly. 
 
 828. Another very interesting form of Pathological change in the aspect of 
 the Liver, which the knowledge of the structure of the Lobules enables us to 
 comprehend, is that to which the name of Cirrhosis has been given. This 
 has been erroneously attributed to the presence of a new deposit, analogous to 
 that of Tubercular matter ; but it is really due to Atrophy and partial Con- 
 gestion in the Liver itself. It is described by Laennec as usually presenting 
 itself in small masses, varying in size from a cherry-stone to a millet-seed, 
 and scattered through the substance of the Liver. When these are minute, 
 and closely set, they impart what appears at first to be a uniform brownish- 
 yellow tint to the divided surface of the Liver ; but when the tissue is more 
 attentively examined, their separation becomes evident. These small masses 
 are not distinct lobules in a variable state of hypertrophy (as supposed by 
 Cruveilhier) ; but small uncongested patches, composed of parts of several 
 adjoining lobules, and having one or more interlobular spaces for a centre ; 
 and the biliary plexuses of these, being filled with bile, give them their yellow 
 colour. On the other hand, there is an atrophy, more or less complete, of 
 the portions of the substance of the liver intervening between them ; so that 
 the bulk of the whole organ is much diminished, very commonly to one-half, 
 and sometimes to one-third, of its original size. 
 
 829. The application of the Microscope to the Hepatic Cells, in various states 
 of disease, has afforded many facts of great interest. The fatty liver, which 
 is often found in the bodies of persons who have died from diseases obstructing 
 the pulmonary circulation, has been shown by Mr. Bowrnant to depend 
 upon the presence of a large quantity of fatty matter in the interior of the 
 cells ; which frequently appear as if gorged with it. This would seem to 
 be occasioned by the want of elimination of the fatty matter through the 
 respiratory process ; and the consequent accumulation of it in the Blood, by 
 
 * This very common aspect of the Liver, which presents numerous modifications, has been 
 a source of great perplexity to those who have studied the minute anatomy of this organ, and 
 has even led Anatomists of. the highest eminence into serious errors. See Cyclop, of Anat. 
 and Physiol., vol. iii. pp. 185, 186. 
 
 t Medical Gazette, January 1842. 
 
SECRETION OF BILE. 627 
 
 which the burden of separating it is thrown upon the Liver. Dr. Williams* 
 mentions, that, in a case of obstruction of the ductus 
 choledochus by malignant disease, which occasioned com- Fig. 238. 
 plete interruption to the passage of bile, and consequent 
 jaundice, scarcely an entire nucleated cell could be dis- 
 covered by attentive examination of a large part of the organ. 
 Nothing more than minute free particles of fat, and free float- 
 ing amorphous granular matter, could be detected. He further 
 states that, in a case of fever, the hepatic cells were found to Hepatic Ceils 
 be almost entirely destitute of fatty particles; and that in gorged with Fat: 
 what is known as " granular liver," the granules (which have 3J^ 
 much the appearance of tubercles) consist of cells, which globules.' 
 strongly resemble the ordinary cells of the parenchyma of the 
 Liver in every respect, except that they are almost or completely destitute of 
 yellow contents. Similar observations have been also recorded by Dr. G. 
 Budd. In two cases of jaundice examined by Mr. Gulliver, the hepatic cells 
 were gorged with biliary matter; some of them to such an extent, that they 
 had become nearly opaqu. Perhaps if this condition had continued, these 
 cells would have been all ruptured, and the state of the organ would have 
 resembled that described by Dr. Williams. 
 
 830. Previously to birth, the Liver is the only decarbonizing organ in the 
 system, the Lungs being at that time inert ; but as soon as the latter come 
 into play, they separate from the Venous blood a large proportion of the car- 
 bon with which it is charged, and less blood is transmitted to the Liver for 
 this purpose. The diminution in the quantity of the BloOd circulating through 
 this organ, is extremely rapid ; and it is usually very evident within a short 
 time after birth, in the comparative paleness of the substance of the gland. It 
 has been proposed to give this fact a practical bearing, in those judicial in- 
 quiries which are directed to the determination of the question, whether or 
 not an Infant has respired after birth ; it having been conceived, that the 
 diversion of the current of the Blood from the Liver to the Lungs, consequent 
 upon the first inspiration, would be sufficient to make a certain difference in 
 their relative weights, if that inspiration had taken place. More careful and 
 extended observations, however, have satisfactorily proved that, although an 
 increase in the weight of the Lungs, and a diminution of that of the Liver, are 
 generally found to exist after respiration has been fully established, they are 
 not by any means constantly produced when the inspirations have been feeble, 
 as they frequently are for some hours or days after birth ; whilst, on the other 
 hand, it is not uncommon to meet, in infants that have not breathed, with Lungs 
 as heavy, and Livers as light, as in the average of those which have respired.f 
 
 831. We have now to consider the conditions, under which the secretion 
 of Bile takes place ; and one of the most important of these, is the character 
 of the Blood with which the organ is supplied. We have seen that there is 
 anatomical reason for the belief, that the blood supplied by the Hepatic Artery 
 is not directly concerned in the Secretion ; but that it first serves for the 
 Nutrition of the organ, and then, passing into the Portal system (in the same 
 manner as does the blood of the mesenteric and other arteries), forms part of 
 the mass of Venous Blood, from which the secreting cells elaborate their pro- 
 duct. This view is borne out by the results of Experiment, and of Patholo- 
 gical observation. Thus, if the Vena Portae be tied, the secretion of bile still 
 continues, though in diminished quantity^ and several cases are on record, in 
 which, through a malformation, the Vena Portae terminated in the Vena Cava 
 
 * Guy's Hospital Reports^ 1843. 
 
 j" See Dr. Guy, in Edinb. Med. and Surg. Journal, vols. Ivi. and Ivii. 
 
628 OF SECRETION. 
 
 without ramifying through the liver, and in which secretion of Bile took 
 place, evidently from the blood of the Hepatic Artery, which had become 
 venous by circulating through the substance of the Liver; and this blood 
 appears* to have passed into the ramifications of the Umbilical Vein, which 
 formed a plexus in the lobules, exactly resembling the ordinary portal plexus. 
 It must be remembered, however, that in all these instances, the arterial 
 Blood will become abnormally charged with the elements of Bile ; since the 
 blood of the chylopoietic viscera, from which it ought to have been separated, 
 returns to the heart without undergoing any such purification : and the secre- 
 tion of Bile from the blood supplied by the Hepatic Artery under such circum- 
 stances cannot, therefore, be considered as proving that the arterial blood is 
 ordinarily concerned in the secretion to the same degree. 
 
 832. That the proximate elements of the Bile accumulate in the Blood, 
 when from any cause the secretion is suspended, is a fact now well ascer- 
 tained ; and this satisfactorily accounts for the disturbance of the other func- 
 tions, especially those of the Nervous system, which then ensues. When 
 the suppression is complete, the patient suddenly becomes jaundiced, the 
 powers of that system are speedily lowered (almost as by a narcotic poison), 
 and death rapidly supervenes.! When the secretion is diminished, but not 
 suspended, the same symptoms present themselves in a less aggravated form. 
 It is probable that much of the disorder in the functions of the Brain, which 
 so constantly accompanies deranged action of the Digestive system, is due to 
 the less severe operation of the same cause, the partial retention within the 
 Blood, of certain constituents of the Bile, which should have been eliminated 
 from the circulating fluid. In such a condition, we derive great benefit from 
 the use of mercurial medicines ; which, by stimulating the Liver to increased 
 action, cause the removal of the morbific agent from the blood. Deficient 
 secretion of the Liver may be recognized as the cause of this and of other 
 diseases, by the paleness of the alvine evacuations, the diffused yellowness of 
 the surface of the body, the yellowish-brown fur upon the tongue, and the 
 congestion of the portal system ; this last results from the same cause, as that 
 which stagnates the blood in the Lungs when there is deficient Respiration 
 ( 738), and frequently occasions Aseites, and other disorders of the contents 
 of the abdomen. An abnormal accumulation of the elements of the Bile in 
 the Blood, is habittiaLin some persons; and it produces a degree of indisposi- 
 tion to bodily or mental exertion, which it is difficult to counteract. It may 
 often be recognized by the accumulation of dark mucus having distinctly the 
 taste of bile, on the surface of the tongue, especially during the night; this 
 secretion being apparently eliminated by the mucous membrane of the tongue, 
 when the function of the liver is not duly performed. 
 
 833. Much discussion has taken place among Chemists, in regard to the 
 proximate principles of the Biliary secretion ; a large number of analyses hav- 
 ing been made, amongst the results of which there is great want of conformity. 
 The discrepancies principally arise from this source, that the secretion is 
 acted on with great facility by chemical reagents ; so that many of the com- 
 ponent parts which have been enumerated, are not true educts ; but are pro- 
 ducts of the operations, to which the fluid has been subjected. The propor- 
 tion of solid matter is usually from 9 to 12 per cent,; and nearly the whole of 
 this consists of substances peculiar to Bile. 
 
 a. The following are the general results of the analyses made by Berzelius, of Human 
 Bile, and of that of the Ox: 
 
 * This, at least, was found to be the case, in the only instance in which the liver was 
 examined with sufficient care. 
 
 | See Dr. Alison in Edinburgh Medical and Surgical Journal, vol. xliv. p 287. 
 
SECRETION OF BILE. 629 
 
 MAN. Ox. 
 
 Water . .. . . . . 90-44 92-84 
 
 Biliary matter ...... 8-00- 5'00 
 
 Mucus . . . . . -30 -23 
 
 Alkali (in combination with fatty acids) . . '41 
 
 Chloride of sodium, and extractive . . . -74 1'50 
 
 Phosphates and sulphates of soda and lime . . '11 '43 
 
 100-00 100-00 
 
 In the Biliary matter, we are to distinguish at least three distinct substances ; Cholesterine, 
 Bilic acid, and Colouring matter. In healthy bile, the proportion of Cholesterine appears to 
 be very small; but in many disordered states of the secretion, and especially in disease of 
 the Gall-bladder, this substance is present in much larger amount; and it usually forms the 
 principal, if not the sole, ingredient in biliary concretions. It is a white crystallizable fatty 
 matter, somewhat resembling Spermaceti; free 'from taste and odour; not soluble in water, 
 but dissolving freely in alcohol, from which it is deposited on cooling in pearly scales. It 
 is almost entirely composed of Carbon, and Hydrogen; its constitution being 36 Carbon, 32 
 Hydrogen, 1 Oxygen. It may be obtained by a chemical process of no great complexity, 
 from the Serum of the BJood; and it is not unfrequently deposited as a result of diseased ac- 
 tion in other parts of the body, especially in the fluids of local Dropsies, as hydrocele, ovarian 
 dropsy. &c. % , 
 
 b. The principal constituent of Bile is a compound of soda with a peculiar organic body ; 
 which is now generally regarded in the light of a fatty acid, and named Bilic add. Accord- 
 ing to Platner, this bilic acid and the bibilate of soda may be obtained in a pure crystalline 
 state from fresh bile ; a yellowish-brown syrup being left, which seems principally to consist 
 of colouring matter diffused through the water. No analysis has yet been made of bilic acid 
 thus purified ; that of Dr. Kemp, rnade upon an impure bilic acid, gives as its ultimate com- 
 position 48 Carbon, 42 Hydrogen, 13 Oxygen, and 1 Nitrdgen. This is the substance described 
 by different Chemists (doubtless under various modifications, according to the process used 
 to obtain it), as Choleic acid, Bilin, Picromel, &c. It is very readily altered by reagents, espe- 
 cially by acids; and a great variety of products may be formed by its decomposition. Some 
 of these appear to present themselves in the living body, as results of disordered condition^ 
 of the secreting process. 
 
 c. The colouring matter of the bile is now termed Eiliverdin. That of the Ox contains no 
 azote ; and appears to be identical with the Chlorophyl of plants. That of Man, however, 
 contains about 7 per cent, of Azote, with 68 parts of Carbon, 7 of Hydrogen, and 17^ of 
 Oxygen; and it cannot be derived so directly from the food. When exposed to the air, it 
 becomes of a deep green absorbing oxygen ; and the same change is produced by nitric acid, 
 the liquor soon passing, however, to a red hue.. This frequently takes place within the 
 body, in cases of Jaundice; but more especially in the urine. Though the colouring matter 
 is usually present but in small quantity during health, it sometimes accumulates in disease, 
 so as to produce solid masses, which include little else. 
 
 834. The amount of the secretion of Bile appears to bear some proportion 
 to that of the Food digested. That its formation is continually going on to a 
 certain degree appears unquestionable ; but that its quantity is greatly increased 
 during the solution of food in the stomach, appears also to be well established. 
 In those animals which are most constantly ingesting food, we find no Gall- 
 bladder : for in them, the Bile may be poured into the Intestine as fast as it is 
 formed. In those which only take food occasionally, on the other hand, and 
 which are provided with a Gall-bladder, the Bile, when not required in the 
 Intestine, flows back into that reservoir. This reflex would appear due to the 
 valve-like termination of the Ductus Choledochus in the walls of the Intestine ; 
 by which a certain resistance is offered to the entrance of the fluid, unless it 
 be propelled by some decided force. The flow of Bile into the Intestinal tube, 
 when its action is needed there, is commonly imputed to the pressure of the 
 distended Duodenum against the Gall-bladder; it may be doubted, however, 
 whether the contractile power of the Duct itself does not afford important aid 
 in the process ; and it is easy to understand, from the known influence of the 
 Sympathetic system of nerves upon it ( 825,/), that peristaltic movements 
 may be thus excited at the time when they are needed. It is an interesting 
 fact, proving how completely the passage of Bile into the Intestine is depend- 
 
 53* 
 
630 OF SECRETION. 
 
 ent upon the presence of aliment in the latter, that the Gall-bladder is almost 
 invariably found turgid in persons who have died of starvation ; the secretion 
 formed at the ordinary slow rate having gradually accumulated, for want of 
 demand. This fact is important in juridical inquiries. 
 
 835. The Bile, as already shown ( 660), has an important operation to 
 effect in the Digestive process ; that of reducing the oily matter of the food 
 to a state in which it may be taken up by the Absorbent vessels. This it 
 effects by means of its soapy character ; which, notwithstanding the doubts 
 of Chemists, seems to be proved by familiar facts. Thus, Ox-Gall is com- 
 monly employed to remove grease spots ; and the bile of the Sea-Wolf (Anar- 
 rhicas lupus) is ordinarily used as soap by the Icelanders. Moreover, the 
 small quantity of Cholesterine contained in healthy Bile, is certainly in a state 
 of complete solution; the biliary soap having the same action upon it, as 
 upon the oleaginous constituents of the chyme. From the recent experiments 
 of H. Meckel, however, it appears that the Bile may perform another very 
 important office, the transformation of sugar into fatty matter. He found 
 that, when bile was mingled with grape-sugar, and allowed to remain in con- 
 tact with it for some time, a much larger quantity of fatty matter existed in 
 the mixture, than could have been present in the bile ; and that the transfor- 
 mation is much aided by heat. Thus, the amount of fat, contained in an equal 
 amount of the bile employed, having been ascertained from parallel experi- 
 ments to be from '48 to '54 grammes, the amount obtained from the mixture 
 of bile and grape-sugar, after five hours' exposure to the warmth of an incu- 
 bating machine, was *87 grammes ; and after twenty-four hours' exposure, 1*84 
 grammes.* It seems probable that this transformation may take place in the 
 Liver itself; for in animals fed upon grape-sugar, this substance has been de- 
 tected in the blood of the portal vein, but not in that of the hepatic vein. It 
 will take effect, not merely upon the Sugar introduced as such in the food, 
 but also upon the amylaceous substances, which have been converted into 
 sugar by the action of the Salivary and Pancreatic fluids ( 670). 
 
 836. There can be no doubt, however, that the Bile is partly an excremen- 
 titious fluid ; a portion of it being destined to be at once carried out of the 
 system, by the intestinal canal, although another portion is destined to be re- 
 absorbed, for the purpose (as it would seem) of being ultimately carried off 
 by the respiratory process. The former part probably includes the whole of 
 the colouring matter ; the presence of which in the faeces is sufficiently ob- 
 vious. The latter seems usually to comprise the fatty or soapy portion ; no 
 distinct indications of which can be generally found in the faeces, unless they 
 have rapidly passed through the alimentary canal ( 662). But in particular 
 states of the system, the freces may contain a very large quantity of bile ; the 
 presence of which almost unchanged, may be recognized in the evacuations 
 in bilious diarrhoea, and in the stools which follow mercurial purgatives. 
 Hence the Bile may be a completely excrementitious product; and the idea 
 of the action of the Liver, as one of the great purifiers of the body from the 
 results of its decay, is not at all invalidated by the observation, that a large 
 part of its secretion is ordinarily destined for immediate re-absorption. The 
 composition of the secretion clearly indicates, that it is especially intended to 
 eliminate from the blood its superfluous Hydro-Carbon, whether this have 
 been absorbed as such from the aliment, or have been taken up by the Blood 
 as effete matter, during the course of the circulation. 
 
 a. If more non-azotized food be taken into the system, than can be got rid of by the 
 Respiratory process, and if there be not a sufficiently rapid production of Adipose tissue to 
 admit of its being deposited as Fat, it would accumulate in the Blood, unless separated by 
 
 * Mr. Pagefs Report, in Brit, and For. Med. Rev., July 1846, p. 261. 
 
SECRETION OF BILE. 631 
 
 the Liver. If too much work be thrown upon this organ, its function becomes disordered, 
 from its inability to separate from the Blood, all that it should draw off: the injurious sub- 
 stances accumulate in the Blood, therefore, producing various symptoms that are known un- 
 der the general term of bilious. This is particularly liable to happen in warm climates, in 
 consequence of the diminished excretion through the Lungs, occasioned by the warmth of 
 the surrounding air, and the small quantity of exercise usually taken.' To remove these 
 symptoms, medicines are required, which shall stimulate the liver to increased action. The 
 constant use of such, however, has a very pernicious effect upon the constitution ; and care- 
 ful attention to the regulation of the diet, especially the avoidance of a superfluity of oily 
 or farinaceous matter, together with the employment of an increased amount of exercise, 
 will probably answer the same end in a much better manner. 
 
 Besides the source of Biliary matter already pointed out in the decompo- 
 sition of the Fibrinous tissues ( 819), it seems probable that there is another 
 very important one in the continual waste of Nervous matter, which more 
 nearly approaches Bile in composition ( 249); especially if, as asserted by 
 Fremy, the peculiar acids of the Brain may be detected in the Liver. In 
 cases of slow Asphyxia, the amount of the Biliary secretion is much increased; 
 as might be expected, from what has just been stated of its purpose. 
 
 837. It would not seem improbable, that the Liver acts towards the ab- 
 sorbed matters which enter the blood by the Mesenteric Veins, the same part 
 which the Lungs perform for those which are introduced through the Lymph- 
 atic system ; namely, the affording an opportunity for the excretion of super- 
 fluous or injurious substances contained in the absorbed fluid, before it 
 enters the general current of the Circulation. There is every reason to be- 
 lieve, that the conversion of Chyle into Blood is a slow process, requiring the 
 prolonged influence of the latter fluid upon the former; during this influence 
 many chemical changes take place, which are almost certain to be attended 
 with an extrication of Carbon and Hydrogen, these being the ingredients of 
 which the Chyle contains most when compared with blood ; and for the extrica- 
 tion of these, the Lungs and Liver afford ready means. Hence we see why the 
 Lacteal system should terminate in a Venous trunk near the Heart, so that the 
 fluid discharged by it will proceed at once to the Lungs ; and why the Liver, 
 wherever it has a distinct circulation, should receive the blood from the walls 
 of the Intestines. Among the Mollusca, in which the chyle is absorbed by 
 the mesenteric veins, (there being no separate lacteal system,) these veins, in- 
 stead of returning to the heart through the liver, terminate in the branchial 
 vessels ; and the process of depuration is effected by the gills. Their liver 
 is supplied only by the hepatic artery. 
 
 a. This view derives interesting confirmation from the experiments of Cruveilhier, on 
 the artificial production of purulent deposits by injection of Mercury into the veins. He found 
 that, when the mercury was introduced into any part of the general venous system, abscesses 
 in the Lungs were induced ; each inclosing a globule, the irritation occasioned by which 
 was the cause of the purulent deposit. When the mercury was introduced into one of the 
 Intestinal veins, on the other hand, similar purulent deposits occurred in the Liver. It is 
 well known that abscesses in the Lungs aiid Liver are very common sequelae of wounds of 
 the head, and of surgical operations, especially those in volving bones ; and there seems good 
 reason to believe, that in such cases PUS (or some of its elements, which may act the part of 
 a ferment in exciting suppuration elsewhere) . is actually carried along with the current of blood 
 in the Lungs and Liver; and that, like the globules of mercury, not being susceptible of elimi- 
 nation by these two great emunctories, it acts as a disturbing cause, and occasions disease of 
 their tissue. The fact that a considerable amount of Copper may be detected in the substance 
 of the Liver, after the prolonged introduction of its salts into the system, seems to add weight 
 to this view of its function. It is yet to be ascertained, however, why some substances should 
 be arrested in this organ, whilst others are allowed to pass. 
 
632 
 
 OF SECRETION. 
 
 3. The Kidneys Secretion of Urine. 
 
 838. The Kidneys cannot be regarded as inferior in importance to the 
 Liver, when considered merely as excreting organs ; but their function only 
 consists in separating from the blood certain effete substances, which are to 
 be thrown off from it; and has no direct connection with any of the nutritive 
 operations, concerned in the introduction of aliment into the system. Organs 
 destined to the elaboration of a Urinary secretion may be traced very low 
 down in the Animal scale. Among many of the Mollusca we find a small 
 sac, filled with a semi-fluid secretion which has been shown to contain uric 
 acid, opening into the intestine, near its anal orifice. In Insects, we often 
 meet with prolonged tubes, resembling the biliary vessels in form, but termi- 
 nating in a lower part of the intestinal tube ; hi some species these are dilated 
 near their extremity into a receptacle for their secretion, or a urinary bladder. 
 Throughout the Vertebra ted classes, they exist in a still more evident form. 
 They are uniformly composed of a congeries of prolonged tubes, subdividing 
 and ramifying more or less ; which spring from the ureter or efferent duct, 
 and terminate either in blind extremities, or in a plexus formed by their inos- 
 culation. There are considerable variations in the arrangement of these tubes, 
 however, in different tribes of animals. In Fishes, the Kidneys very com- 
 monly extend the whole length of the abdomen ; and they consist of tufts of 
 uniform-sized tubules, which shoot out transversely at intervals from the long 
 ureter. These tubes frequently divicle into pairs, but without any great alte- 
 ration in their diameter. They appear to terminate in ccecal extremities, with- 
 out any inosculation; the number of bifurcations, and the degree of convolu- 
 
 [Fig. 240. 
 
 A view of the Right Kidney with its Renal 
 Capsule ; 1, anterior face of the kidney ; 2, exter- 
 nal or convex edge ; 3, its internal edge ; 4, hilum 
 renale ; 5, inferior extremity of the kidney; 6, pel- 
 vis of the ureter ; 7, ureter ; 8, 9, superior and in- 
 ferior branches of the emulgent artery ; 10, 11, 12, 
 the three branches of the emulgent vein ; 13, an- 
 terior face of the renal capsule ; 14, its superior 
 edge ; 15, its external edge ; 16, its internal ex- 
 tremity; 17, the fissure on the anterior face of the 
 capsule.] 
 
 A section of the Kidney, surmounted by the 
 Supra-Renal Capsule ; 1, the supra-renal cap- 
 sule ; 2, the vascular portion ; 3, 3, its tubular 
 portion, consisting of cones ; 4, 4, two of the 
 calices receiving the apex of their correspond- 
 ing cones ; 5, 5, 5, the three infundibula ; 6, the 
 pelvis ; 7, the ureter.] 
 
THE KIDNEYS SECRETION OF URINE. 
 
 633 
 
 [Fig. 241. 
 
 Represents the half of a Kidney di- 
 vided vertically, and with its arteries 
 injected ; the matter has also passed 
 into the excretory ducts; 1, 2, branches 
 of the emulgent artery ; 3, 3, hilum re- 
 nale ; 4, 4, cprtical substance, as essen- 
 tially formed by the capillary termina- 
 tions of the vessels of the kidney ; 5, 
 medullary or tubular portion.] 
 
 A view of half a Kidney divided vertically from its con- 
 vex to its concave edge ; one of its extremities is perfect; 
 1, 1, the lobes which form the kidney ; 2, 2, the lines of se- 
 paration of these lobes ; 3, the cortical substance ; 4, 5, the 
 pyramids of Malpighi; 6, the hilum renale split up and 
 cleared of its vessels ; 7, 7, poilits to the tubes of Bellini ; 
 8, one of the papillae ; 9, 10, two other papillae, uncut, but 
 deprived of the calicesthat surrounded them; 11, one of the 
 foveolae in the papilla ; 12, 12, the vascular circle sur- 
 rounding the papillae ; 13, circumference of the tubular 
 portion ; 14, external surface of the kidney ; 15, the por- 
 tion of its external surface on a line with its fissure.] 
 
 tion, vary greatly in different species. The uriniferous tubes are connected 
 together by a very loose areolar web. The structure of the gland in Reptiles 
 appears to be essentially the same ; its form, however, varies considerably 
 in the different tribes, being greatly prolonged in the Serpents, and abbreviated 
 in the Tortoises. In the Crocodile, the distinction between the cortical and 
 medullary portion begins to show itself; the tubes being nearly straight where 
 they issue from the ureter, and being convoluted near the surface only of the 
 lobes. The Corpora Malpighiana ( 839, 6), however, where they exist in this 
 class, are scattered through the whole substance ; not being confined, as in 
 higher animals, to the cortical portion. In Birds, the urinary tubes, forming 
 the several clusters, are more closely united together; they frequently ramify 
 to a considerable degree. In the Mammalia, as in Man, there is an evident 
 distinction between the straight and the convoluted portions of the system of 
 tubes ; the former character is seen in the medullary substance ; the latter in 
 the cortical. In nearly all below the Mammalia, the kidneys present exter- 
 nally a tabulated aspect ; resulting from the want of union between the differ- 
 ent bundles of tubes, which arise from separate parts of the ureter. In the 
 kidney of the Mammalia, however, the ureter dilates into a capacious recep- 
 tacle, towards which the several bundles of uriniferous tubes converge, so 
 that they open into it in close proximity with each other ; and the lobules 
 formed by these bundles are so closely brought together, that no appearance 
 of a division presents itself, until a section of the gland is made. Among 
 some Mammalia, however, the lower form is still retained ; and it is presented 
 in the Human species also, at an early period of its festal development. 
 
 839. The following is an account of the structure of the Kidney, according 
 to the most recent investigations.* 
 
 * See Bowman in Philosophical Transactions, 1842; afso Gerlach, in Miiller's Archiv., 
 Heft 4, 1845, and in Banking's Abstract, vol. iii. p. 307. 
 
634 
 
 OF SECRETION. 
 
 a. The distinction between the cortical and medullary parts of the Kidney essentially con- 
 sists in this, that the former is by far the most vascular, and the plexus formed by the 
 tubuli uriniferi seems to come into the closest relation with that of the sanguiferous capil- 
 laries, so that it is probably the seat of the greater part of the process of secretion; whilst 
 the latter is principally composed of tubes, passing in a straight line from the former towards 
 their point of entrance into the ureter. In this respect there is a .considerable analogy of 
 structure and comparative function, between the two parts of the kidney and the two parts 
 of the brain. The adjoined figure represents the appearances presented by a portion of an 
 
 Fig. 243. 
 
 Fig. 244. 
 
 Portion of the Kidney of a new-born infant ; A, natural 
 size; 1, 1, corpora Alalpighiana, as dispersed points in the 
 cortical substance ; 2, 2, papilla ; B, a smaller part magni- 
 fied j 1, 1, corpora Malpighiana ; 2, 2, tubuli uriniferi. 
 
 Portion of one of the tubuli uriniferi, 
 from th* kidney of an adult; showing 
 its tesselated epithelium. Magnified 
 250 diameters. 
 
 injected kidney, as seen by the naked eye, and under a low magnifying power. The tubuli 
 uriniferi, in passing outwards from the calices, increase in number by divarication, -to a con- 
 siderable extent, as shown in Fig. 246; but their diameter remains the same. When they 
 arrive in the cortical substance, their previously straight direction is departed from, and they 
 become much convoluted. The "closeness of the texture formed by their interlacement with 
 the blood-vessels, renders it difficult to obtain a clear view of their mode of termination. 
 They seem to inosculate with each other, forming a plexus, with a free extremity, or more 
 probably a loop, here and there (Fig. 246); the number of these free extremities, however, 
 does not appear to be nearly equal to that of the uriniferous tubes themselves. 
 
 b. Scattered through the plexus formed by the blood-vessels and uriniferous tubes, a num- 
 ber of little dark points may be seen with the naked eye, to which the designation of Cor- 
 pora Malpighiana has been given, after the name of their discoverer. Each one of these, 
 when examined with a high magnifying power, is found to consist of a mass of minute 
 blood-vessels (Fig. 246, 7) ; somewhat resembling those convoluted masses of Absorbents, 
 termed Lymphatic Glands. Each of these is included in an offshoot from one of the tubuli 
 uriniferi, which swells into a flask-like dilatation to receive it (Fig. 247) ; and every tube 
 may have several such lateral offshoots. The Epithelium which elsewhere lines the tube 
 (whose usual character is shown in Fig. 244) is altered in appearance, where the tube is 
 continuous with this capsular dilatation (Fig. 247, 2') ; being there more transparent, and 
 furnished with cilia (as shown at 2"), which in the Frog may be seen, for many hours after 
 death, in very active motion, directing a current down the tube. Further within the capsule, 
 the Epithelium is excessively delicate ; but it may be clearly seen to cover the convoluted 
 knot of vessels, which constitutes the Malpighian body.* The Renal Artery, on entering 
 the Kidney, divides itself into minute twigs, which are the afferent vessels of the Malpighian 
 tufts (Fig. 248, a/). After it has pierced the capsule, the twig dilates ; and suddenly divides 
 and subdivides itself into several minute branches, terminating in convoluted capillaries, 
 which are collected in the form of a ball (m, m} ; and from the interior of the ball, the soli- 
 tary efferent vessel, ef, arises, which passes out of the capsule by the side of the single affe- 
 rent vessel. This ball seems to lie loose and bare in the capsule, being attached to it only 
 by its afferent and efferent vessels (Fig. 248, m) ; but it appears in reality to be enveloped 
 in a reflexion of the membrane that forms the capsule; and from this are probably generated, 
 the epithelium-cells, by which it is covered. The efferent vessels, on leaving the Malpighian 
 bodies, separately enter the plexus of capillaries, p, surrounding the tubuli uriniferi, st, and 
 supply that plexus with blood : from this plexus the Renal vein arises. In Mr. Bowman's 
 
 * On this point, which is one of difference between Mr. Bowman and Dr. Gerlach, the, 
 Author's own observations lead him unhesitatingly to concur with the latter. 
 
SECRETION OF URINE, 
 
 [Fig. 245. 
 
 635 
 
 A section of one of the Pyramids of Malpighi, and of its corresponding cortical substance, as seen 
 under the microscope ; 1, portion of the surface of the kidney ; 2, from this figure up to 1, is the cortical 
 substance of the kidney ; 3, from 2 to this number is the tubular portion ; 4, the foveola ; 6, 6, arteries 
 and veins ramifying through the kidney ; 7, arteries to the acina of the kidney ; 8, capillary extremities 
 of veins anastomosing with corresponding arterioles; 9, tortuous extremities of the arteries directed 
 into the interior of the gland ; 10, bases of the cones of the cortical and pyramidal substance of the kid- 
 ney ; from 10 to 4 is a collection of these cones ; 11, the envelop of the cortical layer; 12, prolongations 
 of the tubular portion ; 13, tortuous tubes, or those of Ferrien ; 14, straight tubes, or those of Bellini ; 15, 
 vessels which wind between them ; 16, course of the uriniferous tubes in the tubular portion ; 17, the 
 matter between these tubes ; 18, bifurcation of the straight tubes ; 19, sections of these tubes ; 20, their 
 orifices.] 
 
 opinion, all the free extremities of the tubuli uriniferi thus include Corpora Malpighiana ; 
 and the appearance of coacal terminations, such as those represented at a and c, Fig. 246, he 
 regards as an optical illusion, caused by a change in the direction of the tubuli, which occa- 
 sions them to dip away suddenly from the observer. 
 
636 
 
 OF SECRETION. 
 
 Fig. 246. 
 
 7 2 3 
 
 I 
 
 A small portion of the Kidney, magnified about 60 times; 1, supposed C03cal extremity of a tubulus 
 uriniferus ; 3, 3, recurrent loops of tubuli ; 5, 5, bifurcations of tubuli ; 4, 5, 6, tubuli converging towards 
 the papilla ; 7, 7, 7, Corpora Malpighiana, seen to consist of plexuses of blood-vessels, connected with a 
 capillary net- work ; 8, arterial trunk. 
 
 c. The Embryological Development of the Urinary organs in Vertebrated animals is a 
 subject of peculiar interest; owing to the correspondence which may be traced between the 
 transitory forms they present in the higher classes, and their permanent condition in the 
 lower. In this respect there is an evident analogy with the Respiratory system. The first 
 
THE KIDNEYS SECRETION OF URINE. 
 
 637 
 
 appearance of anything resembling a Urinary apparatus in the Chick, is seen on the second 
 half of the third day. The form at the time presented by it is that of a long canal, extend- 
 ing on each side of the Spinal Column, from the region of the heart, towards the Allantois ; 
 and the sides of this present a series of elevations and depressions, indicative of the com- 
 mencing development of coeca. On the fourth day, the Corpora Wolffiana, as they then are 
 termed, are distinctly recognized, as composed of a series of coecal appendages, which are 
 attached along the whole course of the first-mentioned canal, opening into its outer side. On 
 the fifth day these appendages are convoluted; and the body which they form acquires 
 increased breadth and thickness. They evidently then possess a secreting function ; and the 
 fluid which they separate is poured by the long straight canal into the cloaca. Between 
 their component shut sacs, numbers of small points appear, which consist of little clusters 
 of convoluted vessels, exactly analogous to the Corpora Malpighiana of the kidney. The 
 
 Fig. 247. 
 
 Fig. 248. 
 
 Fig. 249. 
 
 .../f 
 
 Uriniferous Tube, Malpighian 
 Tuft, and Capsule, from Kidney 
 of Frog : a, cavity of the tube ; 
 fc, epithelium of the tube; &', 
 ciliated epithelium of the neck 
 of the capsule; 6", detached 
 epithelium scale; c, basement 
 membrane of tube ; c', basement 
 membrane of capsule. Magnified 
 about 320 diam. 
 
 Distribution of the Renal ves- 
 sels ; from Kidney of Horse ; a, 
 branch of Renal artery; of, 
 afferent vessel; m, m, Malpig- 
 hian tufts; e/", ef, efferent ves- 
 sels; p, vascular plexus sur- 
 rounding the tubes ; s, straight 
 tube ; ct, convoluted tube. Mag- 
 nified about 30 diam. 
 
 Corpora Wolffiana, with kid- 
 ney and testes, from embryo of 
 Bird; 1, kidney; 2,2, ureters; 3, 
 corpus Wolffianum ; 4, its ex- 
 cretory duct; 5, 5, testicles; at 
 the summit are seen the supra- 
 renal capsules. 
 
 Corpora Wolffiana, however, have only a temporary existence in the higher Veftebrata; 
 although it seems that, in Fishes, they constitute the permanent kidney.* The development 
 of the true Kidneys commences in the Chick about the fifth day. They are seen on the 
 sixth, as tabulated grayish masses, which sprout from the outer edges of the Wolffian bodies ; 
 and they gradually increase, the temporary organs diminishing in the same proportion. The 
 sexual organs, as will be hereafter explained ( 866, 6), also originate in the Wolffian bodies; 
 and at the end of foetal life, the only vestige of 'the latter is to be found as a shrunk rudi- 
 ment situated near the testes of the male. The progress of development in the Human 
 embryo seems closely conformable to the foregoing account. The Wolffian bodies begin to 
 appear towards the end of the first month; and it is in the course of the seventh week, 
 that the true Kidneys first present themselves. From the beginning of the third month the 
 diminution in the size of the Wolffian bodies goes onparipassu With the increase of the Kidneys; 
 and at the time of birth scarcely any traces of them can be found. At the end of the third 
 
 54 
 
 See Principles of General and Comparative Physiology, 659. 
 
638 OF SECRETION. 
 
 month, the kidneys consist of seven or eight lobes, the future pyramids; their excretory 
 ducts still terminate in the same canal, which receives those of the Wolffian bodies and of 
 the sexual organs; and this opens, with the rectum, into a sort of cloaca, or sinus urogeni- 
 talis, analogous to that which is permanent in the oviparous Vertebrata. The Kidneys are 
 at this time covered by the Supra-Renal Capsules, which are very large ; about the sixth 
 month, however, these have decreased, whilst the kidneys have increased, so that their pro- 
 portional weight is as 1 to 4. At birth the weight of the Kidneys is about three times 
 that of the Supra-Renal Capsules; and they bear to the whole body the proportion. of 1 to 
 SO; in the adult, however, they are no more than 1 to 240. The Corpora Wolffiana are, 
 when at their greatest development, the most vascular parts of the body next to the liver; 
 four or five branches from the" aorta are distributed to each, and two veins are returned from 
 each to the vena cava. The upper veins and their corresponding arteries are converted 
 into the Renal or emulgent vessels; and the lower into Spermatic vessels. The lobulated 
 appearance of the kidney gradually disappears ; partly in consequence of the condensation 
 of the areolar tissue, which connects the different parts; and partly through the develop- 
 ment of additional tubuli in the interstices. The Urinary Bladder is formed quite inde- 
 pendently of the secreting apparatus, being a part of the allantois, which is first developed 
 as a large coscum or diverticulum from the lower extremity of the alimentary canal (Chap. 
 XYII.). The part of the tube below this forms the Cloaca, or common termination of the 
 intestinal and vesical apparatus. The sides of this cloaca, however, gradually approach 
 one another, so as to form a transverse partition, which separates the Rectum from the 
 Genito-urinary canal ; and the urethra of the female is afterwards separated from the Vagina 
 by a similar process. 
 
 840. The researches of Mr. Bowman on the structure of the Malpighian 
 bodies, and on the vascular apparatus of the Kidney, have thrown great light 
 upon the mode in which the Urinary secretion is elaborated. One of the 
 most remarkable circumstances attending this excretion, in the Mammalia 
 particularly, is the large but variable quantity of water, which i thus got rid 
 of, the amount of which bears no constant proportion to that of the solid 
 matter dissolved in it. The Kidneys, in fact, seem to form a kind of regu- 
 lating valve, by which the quantity of water in the system is kept to its proper 
 amount. The Exhalation from the Skin, which is the other principal means 
 of removing the superfluous liquid from the blood, is liable to great variations, 
 from the temperature of the air around ( 870) : hence, if there were not some 
 other means of adjusting the quantity of fluid in the Blood-vessels, it would 
 be liable to continual and very injurious variation. This important function 
 is performed by the Kidneys ; which allow such a quantity of water to pass 
 into the urinary tubes, as may keep the pressure within the vessels nearly at 
 a uniform standard. The quantity of water which is passed off by the kid- 
 neys, therefore, will depend in part upon that exhaled by the Skin; being 
 greatest when this is least, and vice versa: but the quantity of solid matter to 
 be. conveyed away in the secretion has little to do with this ; being dependent 
 upon the amount of waste in the system, and upon the quantity of surplus 
 azotized aliment which has to be discharged through the channel. The Kid- 
 ney contains two very distinct provisions for these purposes. The cells lining 
 the Tubuli Uriniferi are probably here, as elsewhere, the instruments by which 
 the solid matter of the secretion is elaborated ; whilst it can scarcely be doubted 
 that the office of the Corpora Malpighiana is to allow the transudation of the 
 superfluous fluid through the thin-walled and naked capillaries of which they 
 are composed. "It would, indeed," Mr. Bowman remarks, " be difficult to 
 conceive a disposition of parts more calculated to favour the escape of water 
 from the blood, than that of the Malpighian body. A large artery breaks up 
 in a very direct manner into a number of minute branches; each of which 
 suddenly opens into an assemblage of vessels of far greater aggregate capacity 
 than itself, and from which there is but one narrow exit. Hence must arise 
 a very abrupt retardation in the velocity of the current of blood. The vessels 
 in which this delay occurs are uncovered by any structure. They lie bare in 
 a cell, from which there is but one outlet, the orifice of the tube. This orifice 
 
THE KIDNEYS SECRETION OF URINE. 639 
 
 is encircled by cilia, in active motion, directing a current towards the tube. 
 These exquisite organs must not only serve to carry forward the fluid which 
 is already in the cell, and in which the vascular tuft is bathed; but must tend 
 to remove pressure from the free surface of the vessels, and so to encourage 
 the escape of their more fluid contents." 
 
 841. There is a striking analogy between the mode in which the Tubuli 
 Uriniferi are supplied with Blood, for the purpose of elaborating their secre- 
 tion, and the plan on which the Hepatic circulation is carried on. The 
 secretion of the Liver is formed from blood conveyed to it by one large vessel, 
 the Vena Portae, which has collected it from the Venous capillaries of the 
 ehylopoietic viscera, and which subdivides again to distribute it through the 
 liver. The secretion of the Kidney, in like manner, is elaborated from blood 
 which has already passed through one set of capillary vessels, those of the 
 Malpighian tufts ; this blood is collected and conveyed to the proper secreting 
 surface, not by one large trunk (which would have been a very inconvenient 
 arrangement), but by a multitude of small ones, the efferent vessels of the 
 Malpighian bodies, which may be regarded as collectively representing the 
 Vena Portae, since they convey the blood from the systemic to the secreting 
 capillaries. Hence the Kidney may be said to have a portal system within 
 itself. This ingenious view of Mr. Bowman's finds support from jthe fact, 
 that in Reptiles (in which, as in Fishes, the Portal trunk receives the blood 
 from the whole posterior part. of the body, and supplies the Kidneys as well 
 as the Liver), the efferent vessels of the Malpighian bodies which receive 
 their blood, as elsewhere, from the Renal Artery unite with the branches 
 of the Portal vein, to form the secreting plexus around the Tubuli Uriniferi. 
 Here, therefore, the blood of the secreting plexus has a double source; the 
 vessels which supply it receiving their blood in part from the capillaries of the 
 organ itself, and in part from those of viscera external to it; just as, in the 
 Liver, the secreting plexus is supplied in part by the blood conveyed from the 
 chylopoietic viscera through the Vena Portae, and in part by the nutritive 
 capillaries of the organ itself, which receive their blood from the Hepatic 
 Artery. 
 
 842. The nature and purposes of the Urinary secretion, and the alterations 
 which it is liable to undergo in various conditions of the system, are much 
 better understood than are those of the Bile ; this is owing, in great part, to 
 the circumstance, that it may be readily collected in a state of purity ; and 
 that its ingredients are of such a nature, as to be easily and definitely sepa- 
 rated from each other by simple chemical means. There can be no doubt 
 that the chief purpose of this excretion, is to remove from the system the effete 
 azotized matters which the blood takes up in the course of the circulation, or 
 which may have been produced' by changes occurring in itself. This is evi- 
 dent from -the large proportion of Nitrogen which is contained in the solid 
 matter dissolved in it ; and from the crystalline form presented by this solid 
 matter when separated, a form which indicates that its state of combination 
 is such, as to prevent it from conducing to the nutrition of the system. The 
 injurious effects of the retention in the Blood, of the components of the Uri- 
 nary secretion, are fully demonstrated by the results of its cessation ; whether 
 this be made to take place experimentally (as by tying the renal artery), or be 
 the consequence of a disordered condition of the kidney. Symptoms of great 
 disorder of the nervous centres, analogous to those produced by many narcotic 
 poisons, soon exhibit themselves ; and the patient dies comatose, if the secre- 
 tion be not restored. In such cases, Urea (the characteristic ingredient of the 
 urine) is found to have accumulated in the Blood ; and it may even be detected 
 by the smell, in the fluid effused into the Ventricles of the Brain. The con- 
 clusion which may be drawn from this circumstance, regarding the pre-exist- 
 
640 OF SECRETION. 
 
 ence of the components of the secretion in the Blood, is strengthened by the 
 fact that, even in the healthy state, Urea may be detected in the blood ; it only 
 exists there normally, however, in very small quantity ; but,- when there is 
 any impediment to its excretion, it goes on accumulating, and produces conse- 
 quences more or less serious in proportion to its amount. It is not improba- 
 ble that, as in the case of the retention of Bile in the Blood ( 832), many of 
 the minor as well as of the severer forms of sympathetic disturbance, connected 
 with disordered secretion from the Kidney, are due to the directly poisonous 
 operation of the elements of the Urine, upon the several organs whose func- 
 tion is disturbed ; and that many complaints, in which no such agency has 
 been until recently suspected, especially Convulsive affections arising from 
 a disordered action of the Nervous centres, are due to the insufficient elimi- 
 nation of Urea from the Blood. 
 
 843. In order to form a correct opinion of the state of the Urinary secretion 
 in morbid conditions of the system, it is desirable to be acquainted with every 
 leading particular regarding its healthy characters. The average Quantity, 
 during 24 hours, has been variously estimated : it differs, of course, with the 
 amount of fluid ingested, and it is influenced also by the external temperature, 
 a much smaller amount of the superfluous fluid of the body being set free 
 from the skin in winter than in summer, and a larger proportion being carried 
 off by the kidneys. Probably we shall be pretty near the truth, in estimating 
 the amount at from about 30 oz. in sunimer, to 40 oz. in winter, for a person 
 who does not drink more than the simple wants of nature require. The 
 Specific Gravity comes to be a very important character, in various morbid 
 conditions of the urine : and it is therefore desirable to estimate it correctly. 
 This also is, of course, liable to the same causes of variation ; since, when 
 the same amount of solid matter is dissolved in a larger or smaller quantity of 
 water, the specific gravity will be proportionably lower OF higher. The 
 average, according to Dr. Prout, in a healthy person, taking the whole year 
 round, is about 1020; the standard rising in summer (on account of the greater 
 discharge of fluid by perspiration) to 1025 ; and being lowered in winter to 
 1015. Simon, however, states the average specific gravity at no more than 
 1012. It will depend, in each individual case, upon the amount of fluid habitu- 
 ally ingested, as compared with that dissipated by cutaneous exhalation; and 
 it will also vary with the period that has elapsed since the last introduction of 
 liquid into the stomach. From these and other causes, the proportion of solid 
 matter in 1000 parts of Urine may vary from 20 to 70. The following table 
 expresses the relative amounts of the different components, in every 100 parts 
 of this solid matter; according to the analyses of different Chemists. 
 
 Berzelius. Lehmann. Simon. Marchand. 
 
 Urea . . 45-10 49'68 33-80 48-91 
 
 Uric Acid 1-50 1'61 1-40 1'59 
 
 Extractive matter, Ammonia-salts, ) 36 . 3Q 2g . 95 - 42W 32<49 
 
 and Chloride of sodium $ 
 
 Alkaline Sulphates . . . . . 10-30 11-58 8-14 10-18 
 
 Alkaline Phosphates . . . . . 6'88 f 5-96 6-50 . 4-57 
 
 Phosphates of Lime and Magnesia . . . 1'50 1-97 1-59 1-81 
 
 We shall presently find the causes of some of these variations in the nature 
 of the ingesta, and in the amount of exercise taken by the individual. The 
 Urine in health usually exhibits an acid reaction; this depends, however, 
 upon certain conditions furnished by the aliment; and may be altered (as will 
 presently appear) by a change in the ingesta. 
 
 844. The most important of the above ingredients (constituting from one- 
 third to one-half of the whole solid matters of the Urine) is evidently that 
 \vhich, from its being the principal cause of the characteristic properties of the 
 
SECRETION OF URINE. 
 
 641 
 
 secretion, is termed Urea. This maybe readily separated from Urine, in the 
 form of transparent colourless crystals ; which have a faint and peculiar, but 
 not urinous odour: and, as already mentioned, it is distinctly traceable in the 
 Blood, where it rapidly accumulates, if its continual elimination be in any way 
 interfered with. It is very soluble in water, and combines with acids without 
 neutralizing them. In its chemical composition, it is identical with cyanate 
 of ammonia; this composition being 2 Carbon, 4 Hydrogen, 2 Nitrogen, and 
 2 Oxygen, a formula much more simple than that of almost any other 
 organic substance. The amount of Urea excreted in twenty-four hours has 
 been made the subject of examination by Lecanu ;* and the following are his 
 results, as deduced from a series of 120 analyses : 
 
 
 Minimum. 
 . 357-51 grs 
 
 By women '. . .... 
 By old men (84 to 86 years) 
 By children of eight years 
 By children of four years . 
 
 . . 153-25 
 
 61-08 
 . . 161-78 
 . 57-28 
 
 Mean. 
 
 433-13 grs. 
 295-15 
 125-22 
 207-99 
 
 69-55 
 
 Maximum. 
 510-36 grs. 
 437-06 
 295-15 
 254-20 
 81-83 
 
 It is very interesting to perceive, in this table, how large an amount of Urea 
 is excreted by children ; and how small a quantity, in proportion to their bulk, 
 by old men. This corresponds precisely with the rapidity of interstitial 
 change at different periods of life. (See 812.) Moreover, as this continual 
 disintegration is very much accelerated by increased vital activity of the Tis- 
 sues, the amount of Urea undergoes a like augmentation ; so that other cir- 
 cumstances being equal the amount of Urea excreted may fairly serve as a 
 measure of the waste of the tissues, and consequently of the degree in which 
 they have been exercised. This will be especially the case in regard to the 
 Muscular Tissue ; which constitutes so large a part of the fabric. In some 
 experiments recently made on the influence of various causes upon the con- 
 stitution of Urine, Dr. Lehmann found that, by the substitution of violent for 
 moderate exercise, the quantity of Urea was raised from 32s to 45 parts ; 
 and Simon found that, by two hours' violent exercise, the proportion of the 
 urea in the urine passed half an hour subsequently was double that contained 
 in the morning urine. If such increased waste be not compensated by in- 
 creased nutrition, a diminution in the bulk of the body is the necessary con- 
 sequence. 
 
 845. The next important ingredient, Uric or Lithic Acid, exists much 
 more largely in the Urine of the lower Vertebrata, than in that of Mammalia; 
 thus the nearly solid urinary excretion of Serpents, and the semi-fluid urine 
 of Birds, is almost entirely composed of this acid, in combination with Am- 
 monia. Its presence has not yet been detected in healthy blood; but when 
 it is imperfectly eliminated, we are assured of its accumulation in the circu- 
 lating fluid, by its deposition, in combination with Soda, in the neighbourhood 
 of the joints, formingfGrouty concretions, or Chalk-stones. Pure Lithic acid 
 crystallizes in fine scales of a brilliant white colour, and silky lustre ; it is 
 tasteless and inodorous, and is so sparingly soluble in water, that at least 
 10,000 times its own weight is required to dissolve it. As it exists in a state 
 of perfect solution in healthy Urine, it must be in combination with some 
 base; and that this is the case, is at once proved by the fact, that it is precipi- 
 tated immediately on the addition of a small quantity of any acid, even the 
 Carbonic. It is generally believed, that the base is Ammonia ; but it has 
 recently been affirmed by Liebig,t that the Uric acid (with the Hippuric) is 
 held in solution by the Phosphate of Soda, which, from being bibasic or 
 alkaline, is rendered acid, by yielding up a part of its soda to these organic 
 
 Journal de Pharmacie, torn. xxv. 
 
 f Lancet, June 8, 1844. 
 
 54* 
 
642 OF SECRETION. 
 
 acids, which are thereby rendered soluble. It is in this manner that he partly 
 explains, the usually acid reaction of healthy urine ; the other causes of which 
 will be presently noticed. If there be an undue proportion of Lithic acid in 
 the urine, it will be precipitated on cooling ; because it is less soluble in a 
 cold than in a warm solution of phosphate of soda ; and the same result will 
 happen, if there be a predominance of other acids in the urine, which will 
 seize upon its base, as soon as its own affinity for it is diminished by the 
 lowering of its temperature. By Dr. Prout it is believed that Lactic acid, ex- 
 isting in the Blood or in the Urine in excess, is an ordinary source of this 
 deposit ; but the presence of this acid is altogether denied by Liebig ( 846). 
 The composition of Lithic Acid is as follows: 10 Carbon, 4 Hydrogen, 
 4 Nitrogen, 6 Oxygen. The amount of it usually excreted in the Urine of 
 Man is but very small; it is occasionally, however, considerably increased; 
 but the circumstances under which this increase takes place have not yet been 
 exactly determined. 
 
 a. Uric acid is replaced in the Herbivorous animals by the Hippuric ; the composition and 
 properties of which are very different from those presented by that substance. When pure, 
 it forms long transparent four-sided prisms; it is soluble in 400 parts of cold water, and dis- 
 solves readily at a boiling heat ; and it has a strong acid reaction, and bitterish taste. Its 
 formula is 18 Carbon, 8 Hydrogen, 1 Nitrogen, and 5 Oxygen, with 1 equiv. of Water. It 
 has very curious relations with Benzoic acid ; which it yields, together with Benzoate of 
 Ammonia, when acted upon by a high temperature, or during the putrefaction of the urine 
 of which it forms a part. According to Liebig, the Hippuric acid in the urine of the Horse 
 and Ox is replaced by Benzoic acid, when the animal is subjected to hard labour. It appears 
 from his recent experiments,* that we are to regard Hippuric acid as a normal element of 
 Human urine; for he has detected Benzoic acid among the products of its putrefaction; and 
 as we know that the latter does not exist in the Urine of Man, and as there is no other sub- 
 stance at the expense of which it can be formed during the putrefactive process, we can 
 scarcely hesitate to admit that such must be the case. It is a very curious fact, that the intro- 
 duction of Benzoic acid into the system causes a large increase in the amount of Hippuric 
 acid in the Urine ; and if this be formed at the expense of the elements, which would other- 
 wise have produced Uric acid, an easy method is pointed out for the elimination of the latter 
 substance from the blood, when it has accumulated there,- the salts of Hippuric acid being 
 so much more soluble than those of the Uric. According to Keller,")" whose experiments 
 were made upon himself, both Urea and Uric acid existed in normal quantity in his urine, 
 though a large quantity of Hippuric acid was being excreted ; whilst Mr. Alexander Ure 
 states,J that he has succeeded, by the administration of Benzoic acid, in preventing the de- 
 position of Gouty concretipns, and even in removing them when they had been formed. 
 
 b. Many remarkable changes are effected in Lithic acid, by the operation of other chemi- 
 cal agents ; and these changes are very important, in their bearing on pathological conditions 
 of the Urine. When Uric acid is subjected to the action of Oxygen, it is first resolved into 
 Urea and a compound termed JLlloxan. Now this Alloxan, when acted on by a new supply 
 of Oxygen, is resolved into Urea and Oxalic acid ; or, with a still further amount of Oxygen, 
 into Urea and Carbonic acid : a fact, which has a very important bearing on the production 
 of Calculi composed of Uric and Oxalic acids, and which explains the remarkable alterna- 
 tions which are often observed in the layers of these concretions. It is affirmed by Liebig, 
 that the calculi which are composed of Urate of Ammonia, or of Oxalate of Lime, occur in 
 persons, in whom, from want of exercise, or from other causes, Ae quantity of Oxygen intro- 
 duced into the system is beneath what it ought to be. When patients suffering under Uric 
 acid Calculi take more exercise, the Urates are replaced by Oxalates, in consequence of the 
 larger amount of Oxygen introduced into the system ; and if the oxygenation could be carried 
 still further, the latter would cease to be deposited, their elements passing off in the form of 
 Urea and Carbonic acid. These views are borne out by the results of Lehmann's experi- 
 ments upon himself; for he found that the violent exercise, which raised the proportion of 
 Urea in the urine by more than one-third ( 844) brought down the amount of Uric acid 
 from 1-18 to -642, or nearly one-half. 
 
 c. Another change is that which gives rise to the peculiar compound termed Attantoin; 
 which naturally exists in the fluid of the Allantois of the fetal calf. This may be formed 
 artificially by boiling Uric acid with peroxide of lead ; from which process there result an 
 
 * Loc. cit. f Liebig's Animal Chemistry, p. 327. 
 
 J Medico-Chirurgical Transactions, vol. xxiv. 
 
SECRETION OF URINE. 643 
 
 Oxalate of the protoxide of lead, Urea and Allantoin ; the composition of which last substance 
 is very different from that of urea or uric acid, being 8 Carbon, 5 Hydrogen, 4 Nitrogen, and 
 5 Oxygen. 
 
 d. By the operation of Nitric Acid upon Uric acid, several new products are generated, 
 some of which are of much practical interest. To one of these the name of Murexid has 
 been given, on account of its reddish purple colour (resembling that of the Tyrian dye which 
 was obtained from a species of Murex) ; this is a crystalline substance, sparingly soluble in 
 cold water, but copiously soluble in warm, imparting to it its vivid colour. By Dr. Prout it 
 was long since described as consisting of a peculiar acid, the Purpuric, in combination with 
 Ammonia; this view of its composition is not generally received by German Chemists ; but 
 it has lately been supported by Fritzche, who has shown the real existence of the acid, by 
 obtaining Purpurates of other bases. This substance is one source of the colours of the 
 pink and lateritious sediments which so often present themselves in the Urine ; these hues 
 partly depend, however, on the influence of nitric acid upon the peculiar Colouring princi- 
 ples of the urine, the nature of which principles is not yet fully understood. 
 
 846. It was supposed until recently, that Lactic acid is a normal constitu- 
 ent of Human Urine. It appears to have been demonstrated by the experi- 
 ments of Liebig, however, that this is not the case ; and that another organic 
 substance, which forms a crystalline compound with zinc, very similar to the 
 lactate, has been mistaken for it. The composition of this substance, which 
 usually forms about one part in 200 of Urine, has been recently determined 
 to be 8 Carbon, 8 Hydrogen, 3 Nitrogen, and 3 Oxygen. It thus differs from 
 Lactic acid in containing Nitrogen ; as well as in proportion of its other com- 
 ponents. 
 
 847. It has been shown ( 843), that the Urine contains a considerable 
 amount of Saline matter; the excretion of which from the system appears to 
 be one of the principal offices of the Kidney. Various saline compounds, 
 and the bases of others, are being continually introduced with the food ( 648) ; 
 and these, after performing their part in the organism, must be eliminated from 
 the circulating fluid, in order to prevent injurious accumulation. Of these 
 we shall now examine the chief sources. The mode in which the Muriates 
 find their way into the Urine is easily understood. Of the Common Salt in- 
 gested, a considerable part is decomposed into Muriatic Acid and Soda ; the 
 former being found uncombined in the Gastric juice ; and the latter in the Bile. 
 By the mixture of the Bile with the Chyme, a re-union of these two consti- 
 tuents takes place ; and Salt is again formed, which is received into the Cir- 
 culation that it may be eliminated (its part in the economy having been now per- 
 formed) by the Kidney. The quantity of the Sulphates present in the Urine, 
 appears to have no relation with that of the amount of Sulphuric acid ingested ; 
 for it much surpasses what could be thus accounted for, being often consi- 
 derable, when no Sulphate whatever can be detected in the food. But most 
 of the azotized compounds employed as food have Sulphur in combination 
 with them ; and there can be no doubt, that this undergoes oxidation within 
 the system, and thus generates Sulphuric acid, which unites with any free 
 or weakly-combined bases it may meet with, to form the Sulphates present in 
 the Urine. The Phosphates are probably derived in part from the Phos- 
 phates taken in with the food, and in part from the free Phosphorus, which 
 its elements contain. Of the latter, great use is made in the production of 
 Nervous matter (249) ; the continual waste of which must set it free again. 
 When thus set free, there is obviously no channel for its elimination, save by 
 its conversion into Phosphoric acid, and its union with an alkaline base.* 
 That this is really the case, would appear from the fact noticed by Dr. Prout, 
 and confirmed by many others, that mental or bodily labour which involves 
 
 * This circumstance has been entirely overlooked by Liebig, in his late discussion (he. 
 cit.) of the Constitution of the Urine; the Phosphates being regarded by him as having their 
 sole origin in the Phosphates of the ingesta. 
 
644 OF SECRETION. 
 
 much waste of the Nervous System, is followed by an increase in the quan- 
 tity of the alkaline Phosphates in the Urine ( 295). This increase cannot 
 proceed from the waste of the Muscular system ; for this would set free 
 Phosphate of Lime, which chiefly passes off by the faeces. 
 
 848. The alkaline or acid reaction of the Urine, therefore, will not only 
 depend upon the quantity of alkaline Phosphates converted into acid Phos- 
 phates by the Uric and Hippuric acids ( 845) ; but also upon the amount of 
 the bases in the ingesta, compared with that of the permanent Acids intro- 
 duced into the system or generated within it. The Urine of animals which 
 live chiefly or entirely upon Vegetable food, is almost invariably alkaline; 
 because this food contains a large quantity of alkaline bases, in combination 
 with Citric, Tartaric, Oxalic, and other acids, which are decomposed within 
 the system ; and the amount of Sulphuric and Phosphoric acids produced is 
 not sufficient to neutralize them. On the other hand, the food of Carnivo- 
 rous animals contains no free or weakly-combined bases ; and as its Sulphur 
 and Phosphorus, when oxidized in the system, produce a considerable quan- 
 tity of free acids, which share the bases with the Muriatic acid already there, 
 the Urine must necessarily have an acid reaction. The character of the 
 Urine of Man, in this respect, is considered by Liebig to depend entirely upon 
 that of the food ingested. 
 
 a." Proceeding upon his determination that no Lactic acid is ever present in the Urine, he 
 remarks : " The acid, neutral, or alkaline reaction of Urine of healthy individuals, does not 
 depend on any difference in the processes of digestion, respiration, or secretion,, in the va- 
 rious classes of animals, but upon the constitution of the aliments, and upon the alkaline 
 bases which enter the organism through the medium of these aliments. If the amount of 
 these bases is sufficiently large to neutralize the acids formed in the organism, or supplied 
 by the aliments, the urine is neutral ; whilst it manifests an alkaline reaction, when the 
 amount of alkaline bases thus supplied to the organism is more than sufficient to neu- 
 tralize the acids; but in all these cases, the urine accords with the nature of the aliments 
 taken." The varying amount of Uric Acid, which, on Prof. Xiebig's own showing, is very 
 much influenced by the respiration, is altogether left out of consideration in this sweeping 
 generalization. 
 
 849. The amount of Azotized matter in the Urine, also, is greatly influ- 
 enced by the nature of the food ingested, whilst the constitution of the Ani- 
 mal frame remains nearly the same ; hence it appears, that a certain portion 
 of it must be derived from the unassimilated materials which have been taken 
 into the blood, and which, being superfluous, are injurious. It is well known 
 that the ingestion of an over-supply of azotized matter does not occasion an 
 increased production of the fibrinous or gelatinous tissues ; and it may be 
 hence inferred that, as there is no means by which the superfluous amount 
 can be stored up in the system (in the mode that non-azotized matter is stored 
 up as Fat), it must be continually eliminated from the Blood. And there can 
 be no doubt that the Kidneys are the principal channel by which this is ef- 
 fected ; the amount of azote thrown off in a given time, in the various com- 
 pounds which they excrete, being equal to 10-llths of the whole quantity 
 ingested. The following are the results of the most satisfactory inquiries 
 that have yet been made, in regard to the influence of various kinds of Ali- 
 ment upon the amount of the solid matters in the Urine. These experiments 
 were performed by Dr. Lehmann of Leipsig, upon himself. In the first series, 
 Dr. L. adopted an ordinary mixed diet ; but he took no more solid or liquid 
 aliment than was needed to appease hunger or thirst, and abstained from fer- 
 mented drinks. Every two hours he took exercise in the open air, but he 
 avoided immoderate exertion of every kind. The average result of the exa- 
 mination of the Urine passed under these circumstances, for fifteen days, is 
 given in the first line of the subsequent Table. In a second series of experi- 
 ments, Dr. L. lived for twelve days on an exclusively Animal diet ; and for 
 
SECRETION OF URINE. 645 
 
 the last six of these, it consisted solely of eggs. He took 32 eggs daily ; 
 which contained 189*7 grammes of dry albumen, and 157*48 of fatty matters; 
 or about 228*75 grammes of carbon, and 30*16 of azote. The amount of 
 Urea is shown, in the second line of the Table, to have undergone a very 
 large increase ; and it contained more than five-sixths of the whole azote in- 
 gested. In a third series of experiments, Dr. L. lived for twelve days on a 
 Vegetable diet ; and its effect upon the solid matter of the Urine is shown in 
 the third line of the Table. -In a fourth, he lived for two days upon pure 
 farinaceous and oleaginous substances, without azotized food of any kind ; 
 and the azotized matter of the Urine must, therefore, have been solely the 
 result of the disintegration of the tissues. It is seen to undergo a very marked 
 diminution under this regimen, as is shown in the fourth line of the Table. 
 His health was so seriously affected, however, by this diet, that he was una- 
 ble to continue it longer. 
 
 Lactic Acid (?) Extractive 
 Solid Matters. Urea. Uric Acid, and Lactates. Matters. 
 
 I. Mixed diet . . . 67-82 32-498 1-183 2*257 10-480 
 
 II. Animal diet . . . 87-44 53-198 1-478 2-167 5-145 
 
 III. Vegetable diet . . . 59-24 22-481 1-021 2-669 16-499 
 
 IV. Non-Azotized diet . . 41-68 15-408 0-735 5-276 ,11-854 
 
 850. The following inferences are drawn by Dr. Lehmann, from these 
 experiments: " 1. Animal articles of diet augment the solid matters of the 
 Urine. Vegetable substances, and still more such as are deprived of azote, 
 on the contrary, diminish it. 2. Although Azote be a product of decomposi- 
 tion of the organism, yet its proportions in the urine depend also on the food, 
 for we find a richly-azotized diet augment considerably the quantity of Urea. 
 In the above experiments, the proportion of the Urea to the other solid mat- 
 ters was as 100 to 116 in a mixed diet; as 100 to 63 in an animal diet; as 
 100 to 156 in a vegetable diet; and as 100 to 170 in a non-azotized diet. 3. 
 The quantity of Uric Acid depends less on the nature of the diet, than on 
 other circumstances ; the differences observed in it being too slight to warrant 
 us in ascribing them to the former cause. 4. The combinations of Proteine, 
 and consequently the azote of the food, are absorbed in the intestinal canal ; 
 and what is not employed in the formation of the tissues, is thrown off by 
 the Kidneys in the form of Urea or Uric acid, these organs being the chief 
 if not the sole, channel through which the system frees itself of its excess of 
 azote. 5. The urine contains quantities of Sulphates and Phosphates pro- 
 portional to the azotized matters which have been absorbed ; and the propor- 
 tion of these salts is sensibly increased under the use of a large amount of 
 those. 6. In the same circumstances, the Extractive matters diminish, while 
 their quantity is increased by the use of vegetable diet, a fact which proves 
 the influence of vegetable aliment over the production of these matters in the 
 urine. 7. Under an animal diet, the quantity of Lactic acid diminishes ; but 
 the greater part of this acid is free. It is the reverse under a vegetable diet ; 
 there is more lactic acid, but it is united to bases. The largest production of 
 lactic acid is under a non-azotized diet ; and most of it is then combined with 
 ammonia. Therefore the lactic acid eliminated with the urine, is in great part 
 the product of non-azotized substances not entirely assimilated; but it results 
 also in part from the decomposition of the azotized substances entering into 
 the composition of the body and the food. 8. The Kidneys not only sepa- 
 rate certain constituent parts of the organs, which have become inadequate for 
 the maintenance of life, but they also expel the superfluous nutritive matters 
 that may have been absorbed."* It must be remarked, with regard to these 
 
 * L'Experience, Dec. 7, 1843; andEdinb. Monthly Journal, March, 1844. 
 
646 OF SECRETION. 
 
 inferences, that the statements concerning the amount of Lactic acid and the 
 Lactates, must be considered as invalidated by the discoveries of Liebig al- 
 ready referred to ( 846). The most unequivocal facts determined by Dr. 
 Lehmann's inquiries, are those which relate to the influence of Diet on the 
 amount of Urea excreted. The experiments upon a purely non-azotized 
 diet were not continued long enough for a satisfactory result to be obtained ; 
 but it is evident that, so long as the ingesta contain no azote, the whole of 
 that element in the Urine must be attributed to the disintegration or waste of 
 the tissues, and may be fairly taken as a measure of its amount. 
 
 851. The fact of the pre-existence of the chief constituents of Urine in the 
 Blood, is important as explaining the facility with which the secreting function 
 appears to be transferred to other membranes, in some of the cases in which 
 the Kidney does not perform its function. Doubtless there has been much 
 error on this subject, arising out of deceptions practised by impostors ; but a 
 sufficient number of indubitably genuine cases are on record, to put it beyond 
 doubt that such transferences have taken place, urinous fluid being secreted 
 from the stomach, mammae, umbilicus, nose, &c.* On the other hand, the 
 Kidney may serve as the channel for the elimination of substances which 
 are usually drawn off by other organs. Thus, when the secreting action of 
 the Liver has been gradually impaired by structural disease, the Kidneys ap- 
 pear to have performed its function, in separating some (at least) of the ele- 
 ments of Bile. And a case has recently been mentioned, in which the urine 
 of a parturient female, who did not suckle her infant, was found to contain a 
 considerable amount of Butyric acid, during several days. The elimination 
 of Kiesteine by the Kidney during pregnancy will be presently noticed ( 859). 
 
 852. The facility with which substances taken into the current of the 
 Circulation pass into the Urinary secretion, varies extremely ; and no general 
 law can be stated in regard to it. It appears from Wohler's elaborate re- 
 searches on this subject, that the salts which are most readily excreted are 
 those which excite the action of the kidneys.t The rapidity with which 
 absorption and elimination take place is often extremely remarkable; Frus- 
 siate of Potash having been detected in the urine, within two minutes after it 
 had been introduced into the stomach. The variations in this respect would 
 appear to depend chiefly on the degree of concentration of the saline solution, 
 which will affect the rapidity of its absorption, according to the laws of En- 
 dosmose ; its reception into the blood being more rapid, in proportion as its 
 density is lower, in comparison with that of the circulating fluid. Pure water, 
 or water containing but a small admixture of saline matter, is readily absorbed 
 into the blood-vessels of the Intestinal villi ; but it is as readily drawn off 
 through the Kidneys (by the agency, as it would seem, of the Malpighian 
 bodies, 840) ; and consequently a large amount may be ingested in a short 
 time. But if the water contain an amount of saline matter equal to that of 
 the Serum, no absorption of it takes place ; it remains in the intestinal tube ; 
 and it is voided by the rectum. Further, if the quantity of saline matter in 
 the solution be greater than that of the Serum, not only will no absorption 
 take place, but there will be an endosmose of the water of the blood towards 
 the solution ; so that a large quantity of fluid is discharged by the Intestinal 
 canal. This simple 'explanation, first offered by Liebig4 accounts well for 
 the diuretic effect of most weak saline solutions, and the purgative qualities of 
 stronger ones. For the transit of the peculiar principles of Vegetables, how- 
 ever, it appears that from one to two hours are usually required. The effect 
 
 * For a scientific explanation of this fact, see Princ. of Gen. and Comp. Phys., 539. 
 See Muller's Physiology, p. 589. 
 Chemistry applied to Agriculture and Physiology, Part ii. 
 
MAMMARY GLANDS SECRETION OF MILK. 
 
 647 
 
 of Oil of Turpentine, and probably of other volatile agents, is produced much 
 more rapidly; the characteristic odour of violets being perceptible in the 
 Urine passed but a few minutes after the vapour of the oil had been received 
 into the lungs. 
 
 4. Mammary Glands. Secretion of Milk. 
 
 853. We now come to those Glands, whose action is rather to elaborate 
 from the Blood certain products, which are destined for special uses in the 
 economy, than to eliminate matters, whose retention in the circulating current 
 would be injurious. Pre-eminent amongst these in size and importance, at 
 least during their period of activity, are the Mammary Glands; which are 
 found only in the animals of the Class Mammalia, and which present them- 
 selves in an almost rudimentary state in some of the non-placental subdivisions 
 of the class (44). 
 
 a. The structure of the Human Mammary Gland, which has been recently investigated 
 fully by Sir A. Cooper, is very simple, and easily described. It consists of a series of ducts 
 passing inwards from their termination in the nipple, and then ramifying like the roots of a 
 tree, their ultimate subdivisions terminating in minute follicles. The mamillary tubes are 
 usually about ten or twelve in number; they are straight ducts, of somewhat variable size; 
 and their orifices, which are situated in the centre of the nipple, and are usually concealed 
 by the overlapping of its sides, are narrower than the tubes themselves. At the base of the 
 nipple, these tubes dilate into reservoirs, which extend beneath the areola and to some dis- 
 tance into the gland, when the breast is in a state of lactation. These are much larger in 
 many of the lower Mammalia than they afe in the Human female; their use is to supply 
 the immediate wants of the child when it is first applied to the breast, so that it shall not 
 be disappointed, but shall be induced to proceed with sucking until the draught be occasioned 
 ( 626). From each of these reservoirs commence five or six main branches of the lacti- 
 ferous tubes, each of which speedily subdivides into smaller ones; and these again divari- 
 cate, until their size is very much reduced, and their extent greatly increased. The propor- 
 tional size of the trunk and of its branches, appears to follow the same law which governs 
 that of the blood-vessels. The breast is not formed into regular lobes by the ramifications 
 of the ducts; because they ramify between, and intermix with each other so as to destroy 
 
 [Fig. 250. 
 
 [Fig. 251. 
 
 The Mammary Gland after -the removal of the 
 skin, as taken from the subject three days after 
 delivery ; 1, the surface of the chest ; 2, subcuta- 
 neous fat ; 3, the skin covering the gland ; 4, cir- 
 cumference of the gland; 5, its lobules separated 
 by fat; 6, the lactiferous ducts converging to unite 
 in the nipple ; 7, the nipple slightly raised and 
 showing the openings of the tubes at its extremity.] 
 
 A vertical section of the Mammary Gland, 
 showing its thickness and the origins oHfce lacti- 
 ferous ducts ; 1, 2, 3, its pectoral surface ; 4, section 
 of the skin on the surface of the gland ; 5, the thin 
 skin covering the nipple ; 6, the lobules and lobes 
 composing the gland ; 7, the lactiferous tubes com- 
 ing from the lobules; 8, the same tubes collected 
 in the nipple.] 
 
648 
 
 OF SECRETION. 
 
 Fig. 252. 
 
 Distribution of the milk-ducts in the Mamma of the Human female, during lactation; the ducts 
 
 injected with wax. 
 
 the simplicity and uniformity of their divisions. It is- very rarely, however, that they inos- 
 culate. The mammary ducts are composed of a fibrous coat lined by a mucous membrane ; 
 the latter is highly vascular, and forms a secretion of its own, which sometimes collects in 
 considerable quantity when the milk ceases to be produced. 
 
 b. The gland itself is composed of the union of a. number of glandules, which are con- 
 nected by means of the fibrous or fascial tissue of the gland ; it is between these, that the 
 mammary tubes may be observed to ramify; and from them their branches spring. When 
 the glandules are filled with injection, and for a long time macerated in water and un- 
 ravelled, they are found to be disposed in lobuli ; and when a branch of mammary tube is 
 separated, with the glandules attached, the part appears like a bunch of fruit hanging by its 
 stalk. When the lactiferous tube proceeding from a glandule is minutely injected, the latter 
 will be found to be composed of numerous follicles, in which the ultimate ramifications of 
 the former terminate, or rather originate. Their size, in full lactation, is that of a hole 
 
 Fig. 253. 
 
 Fig. 254. 
 
 Termination of portion of milk- 
 duct in a cluster of follicles ; from 
 a mercurial injection; enlarged 
 four times. 
 
 Ultimate follicles of Mammary 
 gland, with their secreting cells, 
 o, o/ 6, 6, the nuclei. 
 
MAMMARY GLANDS SECRETION OF MILK. 649 
 
 pricked in paper by the point of a very fine pin ; so that the follicles are, when distended 
 . with quicksilver or milk, just visible to the naked eye. At other times, however, the follicles 
 do not admit of being injected, though the lactiferous tubes may have been completely filled. 
 They are lined by a continuation of the same membrane, with that which lines the ducts ; 
 and this possesses a high vascularity. The arteries which supply the glandules with blood, 
 become very large during lactation; and their divisions spread themselves minutely on the 
 follicles. From the blood which they convey, the milk is secreted and poured into the 
 follicles, whence it flows into the ducts. From the researches of Mr. Goodsir it appears, 
 that, in common with other glandular structures, the inner surface of the milk-follicles is 
 covered with a layer of epithelium-cells; which, being seen to contain milk-globules, may 
 be without doubt regarded as the real agents in the secreting process. Absorbent vessels 
 are seen to arise in large numbers in the neighbourhood of the follicles; their function ap- 
 pears to be, to absorb the more watery part of the milk contained in the follicles and tubes, 
 so as to render it more nutrient than it is as first secreted; and also to relieve the distention 
 which would occur, during the absence of the child, from the continuance of the secreting 
 process. 
 
 c. The Mammary gland may be detected at an early period of fetal existence ; being 
 easily distinguishable from the surrounding parts, by the redness of its colour and its high 
 vascularity, especially when the whole is injected. At this period it presents no difference 
 in the male and female; and it is not until near the period of puberty, that any striking 
 change manifests itself, the gland continuing to grow, in each sex, in proportion to the 
 body at large. About the age of thirteen, however, the enlargement of the gland com- 
 mences in the Female ; and by sixteen years, it is greatly evolved, and some of the lactife- 
 rous tubes can be injected. At about the age of twenty, the gland attains its full size 
 previous to lactation ; but the milk follicles cannot even then be injected from the tubes. 
 During pregnancy, the mammae receive a greatly-increased quantity of blood. This deter- 
 mination often commences very early, and produces a feeling of tenderness and distention, 
 which is a valuable sign (where it exists in connection with others) of the commencement 
 of gestation. The Areola at this time becomes darker in its colour, and thicker in sub- 
 stance, and more extended ; its papillae become 'more developed, and the secretion from its 
 follicles increased. The vascularity of the gland continues to increase during pregnancy; 
 and at the time of parturition, its tabulated character can be distinctly felt. The follicles 
 are not, however, developed sufficiently for injection, until lactation has commenced. After 
 the cessation of the catamenia from age, so that pregnancy is no longer possible, the lactife- 
 rous ducts continue open, but the milk follicles are incapable of receiving injection. The 
 substance of the glandules gradually disappears, so that in old age only portions of the ducts 
 remain, which are usually loaded with mucus; but the place of the glandules is commonly 
 filled up by adipose tissue, so that the form of the breast is preserved. Sir A. Cooper 
 notices a curious change, which he states to be almost invariable with age, namely, the 
 ossification of the arteries of the breast, the large trunks as well as the branches ; so that 
 their calibre is greatly diminished, or even obliterated. 
 
 d. The Mammary gland of the Male is a sort of miniature picture of that of the female. 
 It varies extremely in its magnitude, being in some persons of the size of a large pea ; 
 whilst in others it is an inch, or even two inches in diameter. In its structure it corre- 
 sponds exactly with that of the female, but is altogether on a smaller scale. It is composed 
 of lobules containing follicles, from which ducts arise ; and these follicles and ducts are not 
 too minute to be injected, although with difficulty. The evolution of the gland goes on pari 
 passu with that of the body, not undergoing an increase at any particular period ; it is some- 
 times of considerable size in old age. A fluid, which is probably mucus, may be pressed 
 from the nipple in many persons; and this in the dead body, with even more facility than in 
 the living. That the essential character of the gland is the same in the male as in the female, 
 is shown by the instances, of which there are now several on record, in which infants have 
 been suckled by men. The following is given by Dr. Dunglison.* " Professor Hall, of the 
 University of Maryland, exhibited to his Obstetrical class, in the year 1837, a coloured man, 
 fifty-five years of age, who had large, soft, well-formed mammae, rather more conical than 
 those of the female, and projecting fully seven inches from the chest; with perfect and large 
 nipples. The glandular structure seemed to the touch to be exactly like that of the female. 
 This man had officiated as wet-nurse, for several years, in the family of his mistress ; and 
 he represented that the secretion of milk was induced by applying the children entrusted to 
 his care to the breasts during the night. When the milk was no longer required, great dif- 
 
 * Dunglison's Physiology, [sixth ed., vol. ii. p. 480.] See also the case described by the. 
 Bishop of Cork, in the Philosophical Transactions, vol. xli. p. 813: one mentioned by Cap- 
 tain Franklin (Narrative of a Journey to the Polar Sea, p. 157); and one which fell under 
 the notice of the celebrated traveller Humboldt (Personal Narrative, vol. iii. p. 58). 
 55 
 
650 OF SECRETION. 
 
 ficulty was experienced in arresting the secretion. His genital organs were fully deve 
 loped." Corresponding facts are also recorded of the male of several of the lower animals 
 
 854. The secretion of Milk consists of Water holding in solution Sugar, 
 various Saline ingredients, and a peculiar albuminous substance termed 
 Caseine; and having Oleaginous particles suspended in it. The constitution 
 of this fluid is made evident by the ordinary processes, to which it is sub- 
 jected in domestic economy. If it be allowed to stand for some time, exposed 
 to the air, a large part of the oleaginous globules come to the surface, being 
 of less specific gravity than the fluid through which they are diffused. At 
 the same time there is reason to believe that they undergo a change which 
 will be presently described. The cream thus formed does not, however, con- 
 sist of oily particles alone ; but includes a considerable amount of caseine, 
 with the sugar and salts of the milk. These are further separated by the 
 continued agitation of the cream ; which, by rupturing the envelopes of the 
 oil-globules, separates it into butter, formed by their aggregation, and butter- 
 milk, containing the caseine, sugar, &c. A considerable quantity of caseine, 
 however, is entangled with the oleaginous matter ; and this has a tendency to 
 decompose, so as to render the butter rancid. It may be separated by melting 
 the butter at the temperature of 180 ; when the caseine will fall to the bot- 
 tom, leaving the butter pure, and much less liable to change. The milk, after 
 the cream has been removed, still contains the greatest part of its caseine and 
 sugar. If it be kept long enough, spontaneous change takes place in its com- 
 position ; the sugar is converted into lactic acid, and this coagulates the caseine, 
 precipitating it in small flakes. The same precipitation may be accomplished 
 at any time, by the addition of an acid; all the acids, however, which act 
 upon albumen, do not precipitate caseine, as will presently be pointed out in 
 detail ; the most effectual is that contained in the dried stomach of a calf, 
 known as rennet. This exerts so powerful an influence over it, that, accord- 
 ing to the experiments of Berzelius, a piece of the membrane coagulated the 
 caseine of 1800 times its weight of milk, with the loss of only l*17th part of 
 its own weight; so that the active principle, dissolved from the rennet, must 
 have collected the caseine of about 30,000 times its weight of milk. The 
 whey left after the curd has been separated, contains a large proportion of the 
 saccharine and saline matter, entering into the original composition of the 
 milk. This may be readily separated by evaporation.* 
 
 a. When Milk is examined with the Microscope, it is seen to contain a large number of 
 particles of irregular size and form, suspended in a somewhat turbid fluid; these particles 
 (according to the measurement of Donnef) vary in size from about the l-12,700th to the 
 l-3040th of an inch; and they are termed milk-globules. They are not affected by the mere 
 contact of ether or alkalies ; but if these reagents are shaken with them, an immediate solu- 
 tion is the result. The same effect happens, if they are first treated with acetic acid. 
 Hence it is evident, that the globules consist of oily matter, inclosed in an envelope of some 
 kind; and an extremely delicate pellicle may, in fact, be distinguished after the removal of 
 the oily matter by ether; or, after the globules have been ruptured, and their contents.pressed 
 out, by rubbing a drop of milk between two plates of glass. No proof of the organization 
 of this pellicle has, however, been detected ; and it is probably to be regarded as the simple 
 result of the contact of oil with albuminous matter, which is known to give rise to a mem- 
 branous film. Besides these milk-globules, other globules of much smaller size are seen in 
 milk ; and these present the peculiar movement, which is exhibited by molecules in gene- 
 ral. Most of them seem to consist of oily matter, not inclosed in an envelope, as they are 
 at once dissolved, when the fluid is treated with ether; but, according to the statements of 
 Donne, it would seem that a portion of them are composed of caseine, suspended, not dis- 
 solved, in the fluid. It may be reasonably doubted, however, whether these were not in 
 
 * A considerable quantity is thus obtained for household purposes in Switzerland, 
 j- Cours de Microscopie, Douzieme Legon. 
 
MAMMARY GLANDS SECRETION OF MILK. 651 
 
 a state of change ; whether from their own decomposition, or from incipient coagulation ; 
 either of which might have taken place during the processes of filtration, &c., that were 
 required to determine their nature. In addition to the foregoing particles, there are found in 
 the Colostrum, or milk first secreted after delivery, large yellow granulated corpuscles, which 
 are described by Donne as composed of a multitude of small grains aggregated together, and 
 frequently including a true globule of milk in their centre : these are for the most part solu- 
 ble in ether; but traces of some adhesive matter, probably mucus, holding together the par- 
 ticles, are then seen. They are considered by some as exudation-corpuscles; to which they 
 certainly bear a close resemblance. Lamellae of epithelium are also found in the milk. 
 All the larger globules may be removed by repeated filtration; and the fluid is then nearly 
 transparent. This, in fact, is the simplest way of separating the oleaginous from the other 
 constituents of the milk ; as little caseine then adlieres to the former. That the transparent 
 fluid which has passed through the filter contains nearly the whole amount of the caseine 
 of the milk, appears a sufficient proof that this is, for the most part, truly dissolved in the 
 fluid. 
 
 b. We shall now consider the chemical characters of each of the foregoing ingredients. 
 The Oleaginous matter of milk principally consists, like fatty matter in general, of the two 
 substances, elaine and stearine; which are converted in the process of saponification into 
 the elaic, stearic, and margaric acids : but it also contains another substance peculiar to it, 
 which yields in saponification three volatile acids, of strong animal odour, to which Chev- 
 reul has given the names of butyric, caproic, and capric acids ; whilst the fatty substance 
 itself, to which the peculiar smell and taste of butter are due, is designated as butyrine. The 
 peculiar acids are not only formed when the butyrine is treated with alkalies; but are pro- 
 duced by the ordinary decomposition of this principle, which is favoured by time and mode- 
 rate warmth. The Caseine or cheesy matter of milk,, which is obtained with some slight 
 admixture of fatty matter in the production of cheese from skimmed milk, is chiefly distin- 
 guished from Albumen, by the peculiar readiness with which it is precipitated by feeble 
 organic acids, such as the lactic and acetic ; and by its non-coagulability by heat alone. The 
 Caseine of Human milk, however, is much less precipitable by acids, than is that of the 
 Cow; very commonly resisting the action of the mineral acids, and even that of the acetic; 
 but being always coagulated by rennet, though the curd is long in collecting. It is remarked 
 by Dr. G. O. Rees,* that the caseine of human milk thus bears somewhat the same relation 
 to that of the cow, that the albumen of chyle bears to that of the blood. The Sugar of milk, 
 which may be obtained by evaporating whey to the consistence of a syrup and then setting 
 it aside to crystallize, contains a large proportion (12 per cent.) of water, so that it may be 
 considered as really a hydrate of sugar; it is nearly identical in its composition with starch, 
 and may, like it, be converted into true sugar by the action of sulphuric acid ; and when in 
 contact with a ferment, or decomposing azotized compound, it is extremely prone to be con- 
 verted into lactic acid, by appropriating to itself the elements of water. It is, in fact, through 
 this process, that the coagulation of the caseine is effected, by means of rennet; for as soon 
 as a very minute quantity of lactic acid is generated, it withdraws from the caseine the free 
 alkali which kept it in solution, and the caseine is consequently precipitated. The same 
 effect will be produced by incipient decomposition of the caseine itself; which will soon 
 occasion lactic acid to be generated from the sugar, in sufficient quantity to give to the milk 
 a distinctly acid reaction. The Saline matter contained in milk, appears to be nearly iden- 
 tical with that of the blood; with a larger proportion of the phosphates of lime and mag- 
 nesia, which amount to 2 or 2^ parts in 1000. These phosphates are held in solution chiefly 
 by the Caseine; which seems to have a power of combining with them, even greater than 
 that of Albumen : the presence of a minute proportion of free alkali, also, assists their solu- 
 tion. A small portion of iron in the state of phosphate, together with the chlorides of 
 potassium and sodium, may also be detected in milk.-f- 
 
 855. The proportion of these different constituents is liable to great varia- 
 tion, from several causes. Thus, the whole amount of the solid constituents 
 may vary from 86 to 138*6 parts in 1000; the difference being partly due to 
 individual constitution, but in great part, also, to the amount and character 
 of the ingesta. The average seems to be between 100 and 120 parts. The 
 following are the results of the analyses of Simon; the first column being 
 the average of fourteen observations upon the same woman ; the second giv- 
 ing the maximum of each ingredient; and the third the minimum: 
 
 * Art. MILK, in the Cyclopaedia of Anatomy and Physiology, 
 f Haidlen, in Annalen der Chemie und Pharmacie, xlv. p. 263. 
 
652 OF SECRETION. 
 
 I- II. III. 
 
 Water 883*6 914-0 861-4 
 
 Butter 25-3 54'0 8-0 
 
 Caseine . . . . . . 34'3 45'2 19'6 
 
 Sugar of Milk and Extractive Matters 48-2 62*4 39-2 
 
 Fixed salts 2-3 .2-7 1-6 
 
 It also appears from the analyses of Simon, that the proportion of the differ- 
 ent ingredients is liable to variation, according to the time which has elapsed 
 since parturition. The quantity of Caseine is at its minimum at the com- 
 mencement of lactation, and then gradually rises until it attains a nearly fixed 
 proportion. The quantity of Sugar, on the contrary, is at its maximum at 
 first, and gradually diminishes. The amount of Butter (as appears from the 
 wide extremes shown in the above tables) is more variable than that of any 
 other constituent .That some of the variations are due, moreover, to the 
 character of the ingesta, and others to the external temperature, amount of 
 exercise, and other circumstances affecting the individual, is proved by the 
 recent inquiries of Dr. Playfair upon the Milk of the Cow. He has shown 
 that the amount of butter depends in part upon the quantity of oily matter in 
 the food ; and in part upon the amount of exercise which the animal takes, 
 and the warmth of the atmosphere in which it is kept. Exercise and cold, 
 by increasing the respiration, eliminate part of the oily matter in the form of 
 carbonic acid and water; whilst rest and warmth, by diminishing this drain, 
 favour its passage into the milk. The proportion of Caseine, on the other 
 hand, is increased by exercise ; which would seem to show that this ingre- 
 dient is derived from the disintegration of Muscular tissue, and thus adds 
 strength to the Author's view ( 681) that of the matter thus set free, a part 
 only is destined to immediate excretion, and that a part may again be 
 subservient to the operations of Nutrition. Dr. Playfair's experience on this 
 head seems to correspond with the results of common observation in Swit- 
 zerland, where they pasture cattle in very exposed situations, and are obliged 
 to use a great deal of muscular exertion. The quantity of Butter yielded by 
 them is very small; whilst the Cheese is in unusually large proportion. But 
 these very cattle, when stall-fed, give a large quantity of Butter and very little 
 Cheese. 
 
 856. The change which naturally takes place, from the condition of Co- 
 lostrum to that of true Milk, during the first week of lactation, is a very im- 
 portant one. The Colostrum has a purgative effect upon the child, which is 
 very useful in clearing its bowels of the meconium that loads them at birth ; 
 and thus the necessity of any other purgative is generally superseded. Oc- 
 casionally, however, the colostric character is retained by the milk, during 
 an abnormally long period; and the health of the infant is then severely af- 
 fected. It is important to know that this may occur, even though the rnilk 
 may present all the usual appearances of the healthy secretion ; but the mi- 
 croscope at once detects the difference.* The return to the character of the 
 early milk, which has been stated to take place after the expiration of about 
 twelve months, seems to indicate that Nature designs the secretion no longer 
 to be encouraged. The mother's milk cannot then be so nutritious to the 
 child as other food;t and every medical man is familiar with the injurious 
 consequences, to which she renders herself liable by unduly prolonging lac- 
 tation.J 
 
 * See Donne, "Du Lait, et en particulier celui des Nourrices;" and Brit, and For. Med. 
 Review, vol. vi. p. 181. 
 
 f On the whole subject of Infant Nutrition, the Author would strongly recommend the 
 excellent little work of Dr. A. Combe, formerly referred to. 
 
 One of these, which has particularly fallen under the Author's notice, is debility of the 
 
MAMMARY GLANDS SECRETION OF MILK. 653 
 
 857. It is very interesting to observe that Milk contains the three classes 
 of principles which are required for human food, the Albuminous, Oleagi- 
 nous, and Saccharine ; and it is the only secreted fluid, in which these all 
 exist in any considerable amount. It is, therefore, the food most perfectly 
 adapted for the young animal ; and is the only single article supplied by na- 
 ture, in which such a combination exists. Our artificial combinations will be 
 suitable to replace it, just in proportion as they imitate its character; but in 
 none of them can we advantageously dispense with milk, under some form 
 or other. It should be remembered that the saline ingredients of Milk, espe- 
 cially the phosphates of lime, magnesia, and iron, have a very important 
 function in the nutrition of the infant, affording the material for the consoli- 
 dation of its bones, and for the production of its red blood-corpuscles ; and 
 any fluid substituted for milk, which does not contain these, is deficient in 
 essential constituents. It is very justly remarked by Dr. Rees, that of all 
 the secreted fluids, Milk is most nearly allied in its composition to blood. 
 
 858. The proportion of the different ingredients in the Milk of different 
 animals, is subject to considerable variation : and this fact is of much practi- 
 cal importance in guiding our selection, when good Human milk cannot be 
 conveniently obtained for the nourishment of an infant. The first point to 
 be inquired into, is the quantity of solid matter contained in each kind ; this 
 may be determined either by evaporation, or by the specific gravity of the 
 fluid. The Specific Gravity of Human milk is stated by Dr. Rees to vary 
 between 1030 and 1035; others, however, have estimated it much lower. 
 That of the Cow appears to be usually about the same ; that of the cream, 
 however, being 1024, and that of the skimmed milk about 1035. The varia- 
 tion will in part depend (as in the case of the urine) upon the quantity of fluid 
 ingested, and in part, it is probable, upon the manner in which the milk is 
 drawn ; for it is well known to milkers, that the last milk they obtain is much 
 richer than that with which the udder is distended at the commencement. 
 The quantity of solid matter, obtainable from Human and from Cow's Milk 
 by evaporation, seems, like the specific gravities of the fluids, to be nearly the 
 same. In the relative proportion of the ingredients, however, there is a con- 
 siderable difference ; there being much more sugar, and less caseine in Human 
 Milk than in that of the Cow. The following table exhibits the relative pro- 
 portion of the different ingredients, in the Milk of various animals, from which 
 it is commonly obtained: 
 
 Cow. Goat. Sheep. Ass. Mare. 
 
 Water 861-0 868-0 856-2 907-0 896-3 
 
 Butter . . . . . 38-0 33-2 42-0 12-10 traces 
 
 Caseine 68-0 40-2 45-0 16-74 162 
 
 Sugar of Milk and Extractive Matters . 29-0 52-8 50-0 ) R9 . qi R7 . 
 
 Fixed Salts .... 6-1 5-8 6-8 \ 
 
 It appears from this, that, whilst the milk of the Cow, Goat, and Sheep do 
 not differ from each other in any very prominent degree, that of the Ass and 
 Mare is a fluid of very dissimilar character, containing a comparatively small 
 proportion of caseine and butter, and abounding in sugar. Hence it is, that 
 it is much more disposed to ferment than other milk ; indeed the sugar of 
 Mare's milk is so abundant, that the Tartars prepare from it a spirituous 
 liquor, to which they give the name of koumiss. It appears from these de- 
 tails that no milk more nearly approaches that of the Human female, than 
 that of the Sheep and Goat ; these both possess, however, a larger proportion 
 of caseine, which forms a peculiarly dense curd ; and the milk of the Goat 
 
 retina, sometimes proceeding to complete amaurosis; this, if treated in time, is most commonly 
 relieved by discontinuance of lactation, generous diet, and quinine. 
 
 55* 
 
654 OF SECRETION. 
 
 is tainted with the peculiar odour of the animal, which is more intense if the 
 individual be dark-coloured. The milk of the Cow will usually answer very 
 well for the food of the infant ; care being taken to dilute it properly, accord- 
 ing to the age of the child, and to add a little sugar. It is an interesting cir- 
 cumstance, lately ascertained, that the milk of Carnivorous Mammals, fed ex- 
 clusively on animal diet, contains scarcely a trace of sugar, whilst the caseine 
 and butter are abundant. 
 
 859. From what has been stated of the close correspondence between the 
 elements of the Blood and those of the Milk, it is evident that we can scarcely 
 expect to trace the existence of the latter, as such, in the circulating fluid. 
 To what degree the change, in which their elaboration consists, is accom- 
 plished in the Mammary gland, or during the course of the circulation, there 
 is no certain means of ascertaining. The recent discovery of the usual pre- 
 sence of the organic compound named kiesteine (which is nearly related to 
 caseine), in the urine of pregnant women, seems to indicate that the conversion 
 of albumen into caseine takes place in the blood, this curious excretion being 
 the means of preventing its accumulation in the circulating fluid, previously 
 to the time when it is secreted by the mamma?.* It is evident that this secre- 
 tion cannot serve as the channel for the deportation of any element, the accu- 
 mulation of which would be injurious to the system; since it does not occur 
 in the male at all ; and is present in the female at particular times only. Yet 
 there is reason to believe that if, whilst the process is going on, it be suddenly 
 checked, the retention of the material in the blood, or the reabsorption of the 
 secreted fluid, is attended with injurious consequences. Thus if, when the 
 milk is first secreted, the child be not put to the breast, an accumulation takes 
 place, which, if not relieved, occasions great general disturbance of the system. 
 The narrowness of the orifice of the milk-tubes obstructs the spontaneous exit 
 of the fluid, especially in primiparx; the reservoirs and ducts become loaded; 
 further secretion is prevented ; and a state of congestion of the vessels of the 
 gland, tending to inflammation, is induced. The accompanying fever is partly 
 due, no doubt, to the local disturbance ; but in part also, there seems reason 
 to believe, to the reabsorption of the milk into the blood; this cannot but be 
 injurious, since, although but little altered, the constitution of milk is essen- 
 tially different, especially in regard to the quantity of crystallizable matter 
 (sugar) which it contains. The instances of the vicarious secretion of milk 
 are not numerous ; and in no instance is there any proof that the elements of 
 the fluid were pre-existent in the blood. Some of the most curious are those 
 in which it has been poured out from a gland in the groin ; but it is probable 
 that this was in consequence of the existence of a real repetition, in that 
 place, of the true mammary structure, this being the situation of the mamma? 
 of many of the inferior animals, of which the analogues in Man are usually 
 undeveloped. 
 
 a. The following is a more unequivocal case of vicarious secretion ; and it is peculiarly 
 interesting as exhibiting the injurious effects of the re-absorption of the secretion, and the 
 relief which the system experienced when it was separated from the blood by the new 
 channel. " A lady of delicate constitution (with a predisposition to pneumonia) was pre- 
 vented from suckling her child, as she desired, by the following circumstance. Soon after 
 her delivery she had a severe fever, during which her breasts became very large and hard; 
 the nipples were swollen and firm; and there was evidently an abundant secretion of 
 milk ; but neither the sucking of the infant, nor any artificial means, could draw a single 
 drop of fluid from the swollen glands. It was clear that the milk-tubes were closed; and as 
 the breasts continued to grow larger and more painful, purgatives and other means were 
 employed to check the secretion of milk. After three days the fever somewhat diminished, 
 and was replaced by a constant cough, which was at first dry, but soon after was followed 
 
 See Dr. Golding Bird, in Guy's Hosp. Rep., vol. v. 
 
SALIVARY GLANDS AND PANCREAS. 655 
 
 by the expectoration of simple mucus. After this, the cough diminished in severity, and the 
 expectoration became easy ; but the sputa were no longer mucous, but were composed of a 
 liquid, which had all the physical characters of genuine milk. This continued for fifteen 
 days; the quantity of milk expectorated amounting to three ounces or more in the twenty- 
 four hours. The breasts gradually diminished hi size : and by the time that the expectoration 
 ceased, they had regained their natural dimensions. The same complete obstacle to the 
 flow of milk from the nipples recurred after the births of four children successively, with 
 the same sequelse. After the sixth, she had the same symptoms of fever, but this time 
 they were not followed by bronchitis or the expectoration of milk ; she had in their stead 
 copious sweatings, which, with other severe symptoms, reduced her to a cachectic state, and 
 terminated fatally in a fortnight."* 
 
 860. Of the quantity of Milk ordinarily secreted by a good Nurse, it is 
 impossible to gain any definite idea ; as the amount which can be artificially 
 drawn, affords no criterion of that which is secreted at the time of the draught 
 ( 626). The quantity which can be squeezed from either breast at any one 
 time, and which, therefore, must have been contained in its tubes and reser- 
 voirs, is about two ounces. The amount secreted is greatly influenced by 
 the mental and physical condition of the female, and also by the quantity and 
 character of the ingesta. In regard to the influence of the mental state upon 
 this secretion, a^nple details have already been given (Chap. ix.). With 
 respect to the physical state most favourable to the production of an ample 
 supply of this important fluid, it may be stated generally, that sound health, 
 a vigorous but not plethoric constitution, regular habits, moderate but not 
 fatiguing exercise, and an adequate but not excessive amount of nutritious 
 food, furnish the conditions most required. It is seldom that stimulating 
 liquors, which are so commonly indulged in, are anything but prejudicial ; but 
 the unmeasured condemnation of them in which some writers have indulged, 
 is certainly injudicious ; as experience amply demonstrates the improvement 
 in the condition both of mother and infant, which occasionally results from the 
 moderate employment of them. 
 
 861. The influence of various Medicines upon the Milk, is another im- 
 portant question, which has not yet been sufficiently investigated. As a 
 general rule, it appears that the most soluble saline compounds pass into the 
 milk as into other secretions ; but there are many exceptions. Common salt, 
 the sesqui-carbonate of soda, sulphate of soda, iodide of potassium, oxide of 
 zinc, tris-nitrate of bismuth, and sesqui-oxide of iron, have been readily de- 
 tected in the milk, when these substances were experimentally administered 
 to an a'ss; and ordinary experience shows, that the human infant is affected 
 by many of these, when they are administered to the mother. The influence 
 of mercurial medicines taken by the mother, in removing from the infant a 
 syphilitic taint possessed by both, is also well known. The vegetable purga- 
 tives, especially castor oil, senna, and colocynth, have little effect upon the 
 milk ; hence they are to be preferred to the saline aperients, when it is not 
 desired to act upon the bowels of the child. 
 
 5. Salivary Glands and Pancreas. 
 
 862. The structure of the Salivary Glands and Pancreas in Man, bears 
 considerable resemblance to that of the Mammary glands. In some of the 
 lower tribes, however, they are much simpler. Thus, in the Echinodermata 
 and in Insects, the Salivary glands have the character of prolonged coeca, 
 more or less convoluted ; and the Pancreas of Fishes presents itself in the 
 form of a cluster of short cceca round the pyloric extremity of the stomach, 
 and opening into it by distinct orifices. The accompanying figure will give 
 
 * Bulletino delle Scienze Mediche, Apr. 1839; and Brit, and For. Med. Review, Jan. 
 1840. 
 
656 
 
 OF SECRETION. 
 
 Fig. 255. 
 
 Fig. 256. 
 
 Lobule of Parotid gland of a new-born infant 
 injected with mercury. Magnified 50 diam. 
 
 Distribution of Capillaries around the 
 follicles of Parotid Gland. 
 
 Fig. 257. 
 
 a sufficient idea of the structure of these glands in Man ; the follicles are 
 
 very minute, having a diameter only about 
 three times greater than that of the capillary 
 blood-vessels. Their development commences 
 from a simple canal, sending off bud-like pro- 
 cesses, which opens from the mouth, and lies 
 amidst a cellular blastema. As development 
 proceeds, the canal becomes more and more 
 ramified, and communicates with the enlarged 
 parent-cells of the blastema, which remain as 
 the terminal follicles of the branches of the 
 gland-duct ( 823). 
 
 863. The Salivary secretion is by no means 
 necessarily constant; being almost or com- 
 pletely suspended by cessation of the move- 
 ment of the masticator muscles and tongue, if 
 unexcited by any nervous stimulus. Hence 
 it is, that the secretion is checked during sleep ; 
 so that, if the mouth be kept open, its surface 
 is almost dried up by the atmosphere. The 
 mode in which the secretion is excited through 
 
 the influence of the nervous system has already been considered ( 625, 626). 
 The quantity of Saliva formed during the twenty-four hours has been estimated 
 at about 15 or 20 ounces ; but on this point it is evidently impossible to speak 
 with certainty. The fluid obtained from the mouth is of a more viscous cha- 
 racter than the true saliva secreted by the glands ; being mingled with mucus. 
 The salivary fluid varies as to its chemical reaction ; being sometimes slightly 
 acid, and sometimes slightly alkaline ; but it is seldom precisely neutral. 
 According to Huenefeld, it will at the same time strike a blue colour with 
 reddened litmus-paper ; and turn blue litmus-paper red ; but the saliva ex- 
 amined directly before, and during, the act of eating, is always alkaline. It 
 seems probable that the acid reaction is due to the mucus of the mouth ; 
 which, at times when only a small amount of saliva is excreted, is not neu- 
 tralized by its alkali. The specific gravity of Saliva varies from T006 to 
 1*009. It contains a small number of corpuscles, which seem to be partly 
 epithelium-cells from the mucous surface of the mouth, and partly the secret- 
 ing cells of the salivary vesicles. The solid matter contained in Saliva 
 amounts to from 10 to 13 parts in 1000. The animal principles of which 
 
 Rudimentary Pancreas from Cod : 
 a, pyloric extremity of stomach; b, in- 
 testine. 
 
LACHRYMAL GLAND THE TESTIS. 657 
 
 this is composed are Albumen, Mucus, and a peculiar substance termed Ptya- 
 lin, which is soluble in Water, insoluble in alcohol, and yet is different either 
 from albumen or gelatin. A considerable proportion of saline and earthy 
 matter exists in the solid residue of saliva ; this is nearly of the same cha- 
 racter as that which the blood contains, being chiefly composed of the phos- 
 phate of lime and soda, the chlorides of sodium and potassium, and the lac- 
 tates of soda and potash. One remarkable property of the salivary secretion, 
 is its formation of a rust-red precipitate when mixed with a solution of per- 
 salt of iron. This is supposed to be due to the presence in it of the prin- 
 ciple termed sulpho-cyanogen. The tartar which collects on the human teeth 
 consists principally of the earthy phosphates, the particles of which are held 
 together by about 20 per cent, of animal matter ; and nearly the same may 
 be said of the salivary concretions which occasionally obstruct the ducts. It 
 appears from various recent experiments, that the peculiar animal matter of 
 the Saliva has a decided effect in metamorphosing certain alimentary sub- 
 stances, and thus performs the first part of the digestive process. Starch may 
 be converted into sugar, and sugar into lactic acid, by its agency ; and if acidu- 
 lated, it has a solvent power for caseine, animal flesh, and other albuminous 
 substances ( 669). 
 
 864. The Pancreatic Secretion of Man cannot, of course, be readily ob- 
 tained for analysis ; that which is procured from the lower animals, however, 
 probably gives a sufficiently correct idea of its character. It seems to be of 
 a nearly similar nature with saliva, but usually contains a much larger propor- 
 tion of solid matter; in that of the Dog as much as 87 parts in 1000 have 
 been found ; and in that of the Sheep, 40 parts. The probable offices of this 
 secretion in the digestive process, have been already noticed ( 669, 670). 
 
 6. Lachrymal Gland. 
 
 865. The Lachrymal glands and their secretion may be next mentioned ; 
 but neither require any lengthened description. The gland in Man is formed 
 very much on the plan of the Parotid, being composed of branched canals 
 terminating in follicles, the ultimate ramifications of the several branches 
 forming lobules or divisions of the glands. The lachrymal fluid has not re- 
 cently undergone any accurate analysis ; and all that can be stated respecting 
 it is the general fact, that the quantity of solid matter in it is extremely small, 
 and that this consists chiefly of saline, and either mucous or albuminous 
 compounds. It seems probable that the secretion of the lachrymal gland 
 itself is very little else than the serum of the blood, deprived of a great part 
 of its albumen ; and that the mucus of the tears is secreted from the surface 
 of the conjunctival membrane. This secretion has a slightly alkaline reac- 
 tion. It is being constantly formed in moderate amount, for the purpose of 
 cleansing the surface of the eye from the impurities which would otherwise 
 rest upon it ; and it is then absorbed by the open orifices of the nasal duct, 
 and carried into the nose, as fast as it is poured out. The cause of this ab- 
 sorption does not seem very clear. Capillary attraction is probably in part 
 concerned ; and it has been thought that the momentary partial vacuum, oc- 
 casioned by the inspiratory effort in all the air-passages, will cause the empty- 
 ing of the nasal duct below, and a consequent in-draught above. The influ- 
 ence of the nervous system upon this secretion has been already adverted to 
 ( 625, 626). 
 
 7. The Testis. Spermatic Fluid. 
 
 866. In the Testes we return to the tubular form of glandular structure, 
 which so remarkably distinguishes the Kidney from all the other glands 
 
658 
 
 OF SECRETION. 
 
 hitherto mentioned. The external forms presented by these glands through- 
 out the Animal kingdom, are extremely various ; but their composition is for 
 the most part very uniform. The object is sometimes attained by a simple 
 but much elongated canal ; sometimes by shorter branched tubes ; and in 
 other instances, again, by numerous aggregated co3ca, which are often rounded 
 into cells. In regard to this, as to many other glands, it may be stated that, 
 whilst its general form in Insects is that of prolonged tubes, the required ex- 
 tension of surface is given in the Mollusca by the multiplication of cells, so 
 that the structure has a compact spongy character. It is interesting to remark 
 that, in some of the lowest Fishes, this organ consists of a mass of vesicles 
 which have no efferent duct; and that the secretion formed within these 
 escapes by the rupture of the vesicles, allowing it to escape into the abdomi- 
 nal cavity, whence it passes by openings that lead directly to the exterior. 
 In these Fishes, the ova are discharged from the ovarium in a very similar man- 
 ner ; a modification of which plan is followed in all the higher Vertebrata, 
 the ovum being in them also discharged, by the rupture of its containing vesi- 
 cle or ovisac, into the abdominal cavity, but being immediately received and 
 conveyed away by the funnel-shaped internal prolongation of the external ori- 
 fice, which is known as the fimbriated extremity of the Fallopian tube.* 
 
 a. The Testis in Man has in every respect, however, a distinctly glandular character. It 
 consists of several lobules, which are separated from each other by processes of the tunica 
 albuginea that pass down between them, and also by an extremely delicate membrane (de- 
 scribed by Sir A. Cooper under the name of tunica vasculosa) consisting of minute ramifica- 
 tions of the spermatic vessels united by areolar tissue. Each lobule is composed of a mass 
 of convoluted Tubuli Seminiferi, throughout which blood-vessels are minutely distributed. 
 
 [Fig. 258. 
 
 [Fig. 259. 
 
 The Testicle injected with mercury; 1, tunica 
 albuginea ; 2, seminiferous tubes; 3, the rete vas- 
 culosum testis ; 4, a globule of mercury which has 
 ruptured the tubes ; 5, the vasa efierentia which 
 form the coni vasculosi; 6, coni vasculosi forming 
 the head of the epididymis; 7, epididymis ; 8, glo- 
 bus minor of the epididymis ; 9, vas deferens.] 
 
 A view of the minute structure of the Testis ; 
 1,1, tunica albuginea; 2, 2, corpus highmorianum; 
 3, 3, tubuli seminiferi convoluted into lobules ; 4, 
 vasa recta ; 5, rete testis ; 6, vasa efferentia ; 7, 
 coni vasculosi constituting the globus major of 
 the epididymis ; 8, body of the epididymis ; 9, its 
 globus minor; 10, vas deferens 11, vasculum 
 aberrans or blind duct.] 
 
 See Principles of General and Comparative Physiology, 641. 
 
THE TESTIS SPERMATIC FLUID. 
 
 659 
 
 The lobules differ greatly in size, some containing one, and others many of the tubuli ; the 
 total number of the lobules is estimated at about 450 in each testis, and that of the tubuli at 
 840. The convolutions of the tubuli are so arranged, that each lobule forms a sort of cone, 
 the apex of which is directed towards the Rete Testis. It is difficult to trace the free ex- 
 tremities of the Seminiferous tubes, owing to the frequency of their anastomoses with each 
 other; in this respect, therefore, the structure of the testis accords closely with that of the 
 
 Fig. 260. 
 
 Human Testis, injected with mercury as completely as possible; 1, 1, lobules formed of the semini- 
 ferous tubes; 2, rete testis ; 3, vasa efferentia; 4, flexures of the efferent vessels passing into the head, 
 5, 5, of the epididymis ; 6, body of the epididymis; 7, appendix ; 8, cauda ; 9, vas deferens. 
 
 Fig. 261. 
 
 Plan of the structure of the Testis and Epididymis; a, a, seminiferous tubes; a*, a*, their anasto- 
 moses ; the other references as in the last figure. 
 
660 OF SECRETION. 
 
 Kidney. The diameter of the Tubuli is for the most part very uniform; in the natural con- 
 dition they seem to vary from about the l-195th to the l-10th of an inch; but when injected 
 with mercury they are distended to a size nearly double the smaller of these dimensions. 
 When they have reached to within a line or two of the Rete Testis, they cease to be con- 
 voluted, several unite together into tubes of larger diameter, and these enter the rete testis 
 under the name of tubuli recti. The rete teslis consists of from seven to thirteen vessels, 
 which run in a waving course, anastomose with each other, and again divide, being all 
 connected together. The vasa efferentia which pass to the head of the epididymis are at 
 first straight, but soon become convoluted, each forming a sort of cone, of which the apex is 
 directed towards the rete testis, the base to the head of the epididymis. The number of 
 these is stated to vary from nine to thirty ; and their length to be about eight inches. The 
 epididymis itself consists of a very convoluted canal, the length of which is about twenty-one 
 feet. Into its lower extremity, that is, the angle which it makes where it terminates in the 
 vas deferens, is poured the secretion of the vasculum aberrans or appendix ; which seems 
 like a testis in miniature, closely resembling a single lobule in its structure. Its special func- 
 tion is unknown. 
 
 6. The Testicles originate, in the Embryo, from the lower part of the Corpora Wolffiana 
 ( 839, c) ; arising from their lower and inner sides, whilst the Kidneys spring from their 
 upper and outer parts. They make their first appearance in the Chick about the fourth day, 
 as delicate striae on the Wolffian bodies ; and at this period no difference can be detected be- 
 tween the Testes and the Ovaria, which originate in precisely the same manner. Like 
 the kidneys, the germ-preparing organs increase in proportion with the diminution in the 
 temporary structures , at first their efferent ducts open into those of the Wolffian bodies, but 
 they are subsequently separated by the formation of a partition, like that which separates 
 the rectum from the cloaca. In the Human embryo, the rudiments of the sexual organs, 
 whether testes or ovaria, first present themselves soon after the kidneys make their appear- 
 ance, that is, towards the end of the seventh week. They are at first much prolonged, and 
 seem to consist of a kind of soft, homogeneous blastema, in which the tubular structure subse- 
 quently developes itself. The Ovary at that period has the same aspect and texture ; but its 
 subsequent course of development is different. The Testis gradually assumes its permanent 
 form ; the epididymis appears in the tenth week ; and the gubernaculum, (a membranous 
 process from the filamentous tissue of the scrotum, analogous to the round ligament arising 
 from the labium, and attached to the ovary, of the female,) which is originally attached to 
 the vas deferens, gradually fixes itself to the lower end of the testis or epididymis. The 
 Testes begin to descend at about the middle period of pregnancy ; at the seventh month 
 they reach the inner ring ; in the eighth they enter the passage ; and in the ninth they usually 
 descend into the scrotum. The cause of this descent is not very clear. It can scarcely be 
 due merely, as some have supposed, to the contraction of the gubernaculum ; since that does 
 not contain any fibrous structure, until after the lowering of the testes has commenced. It 
 is well known that the testes are not always found in the scrotum at the time of birth, even 
 at the full period. Upon an examination of 97 new-born infants, Wrisberg found both testes 
 in the scrotum in 67, one or both in the canal in 17, in 8 one testis in the abdomen, and 
 in 3 both testes within the cavity. Sometimes one or both testes remain in the abdomen 
 during the whole of life ; but this circumstance does not seem to impair their function. This 
 condition is natural, indeed, in the Ram. 
 
 867. The fluid secreted by the Testes is thick, tenacious, and of a greyish 
 or yellowish colour. It is mingled, during or before emission, with fluid 
 secreted by the Prostate, Cowper's glands, &c. ; and it cannot, therefore, be 
 obtained pure, but by drawing it from the testicle itself; hence no accurate 
 analysis can be made of it in the Human subject. The so-called Spermatozoa 
 and Seminal Granules, which form the most important and characteristic parts 
 of the Semen, are so intimately connected with the Reproductive Function, 
 that they will be more appropriately described under that head. It may be here 
 remarked, however, that they correspond most exactly with other Secretions, 
 in their mode of production ; for, as will be shown hereafter, they are elaborated 
 by cells, which lie within the tubuli, and which rupture so as to set them free, 
 when they are mature ( 902). The peculiar odour which the Semen pos- 
 sesses, does not appear to belong to the proper spermatic fluid ; but is probably 
 derived from one or other of the secretions with which it is mingled. The 
 chemical analyses which have been made of this fluid are all defective, inas- 
 much as they do not distinguish the real secretion of the testes from the mucus, 
 prostatic fluid, &c., with which it is mingled. It may be stated, however, that 
 
CUTANEOUS AND MUCOUS FOLLICLES. 
 
 661 
 
 it has an alkaline reaction, and contains albumen, with a peculiar animal prin- 
 ciple termed Spermatine ; and also saline matter, consisting chiefly of muriates 
 and phosphates, especially the latter, which form crystals when the fluid has 
 stood for some little time. 
 
 8. Cutaneous and Mucous Follicles. 
 
 868. Having now described the structure 
 and functions of the principal Glands, which 
 are composed of aggregated masses of secret- 
 ing cells or tubes, we may proceed to those in 
 which the glandulx are more scattered, but 
 are still, in their aggregate amount, of sufficient 
 importance to claim particular notice. This 
 is especially the case in the Skin, and its in- 
 ternal prolongations, forming Mucous Mem- 
 branes. The Skin is the seat of various secre- 
 tions ; for each of which it is provided with 
 special organs. Of these the most important 
 is the Perspiration; which is formed in small 
 glandular organs seated just beneath the cutis, 
 and diffused over the whole surface of the 
 body. The efferent ducts of these Glandulae 
 open by minute pores in the Epidermis, which 
 are seen in elevated lines on the skin of the 
 palm of the hand and the sole of the foot ; they 
 penetrate the epidermis rather obliquely, so 
 that a sort of little valve is formed by it, which 
 is lifted up by the excreted fluid as it issues. 
 The ducts pass through the Epidermis and 
 Cutis in a spiral direction; and then enter the 
 glands, which consist of the convolutions of 
 the ducts, more or less subdivided, on which 
 blood-vessels are distributed. Where the 
 Epidermis is thin, the canal is straighter.* On 
 the palm of the hand, the sole of the foot, and 
 the extremities of the fingers, the apertures of 
 the perspiratory ducts are visible to the naked 
 eye ; being situated at regular distances along 
 the little ridges of sensory papillae, and giving 
 to the latter the appearance of being crossed 
 by transverse lines. According to Mr. Eras- 
 mus Wilson,* as many as 3528 of these 
 fflandulae exist in a square inch of surface on 
 
 1 f* 1 1 -I i -1 OUUUI IlCH-fU.0 V-i 10.1HJ. iiwm 1.1^ ^i*..." ~ 
 
 the palm of the hand ; and as every tube, when the hand> magnified 40 diameters ; i, i, 
 
 straightened out, is about a quarter of an inch contorted tubes, composing the gland, 
 
 in length, it follows that, in a square inch of and uniting into two excretory ducts, a, 
 
 skin from the palm of the hand, there exists a 2, which unite into one spiral canal, that 
 
 T , c i i , ooo i *oi c i perforates the epidermis at 3, and opens 
 
 length Of tube equal tO 883 inches, or 73 feet, ^n its surface at 4; the gland is imbedded 
 The number of glandulcB in Other parts of the i n fat-vesicles, which are seen at 5, 5. 
 
 skin, is sometimes greater, but generally less 
 
 than this ; and according to Mr. Wilson, about 2800 may be taken as the 
 
 average number of pores in each square inch throughout the body. Now the 
 
 Sudoriferous Gland from the palm of 
 
 Practical Treatise on Healthy Skin, p. 42. 
 
 56 
 
662 
 
 OF SECRETION. 
 
 [Fig. 263. 
 
 [Fig. 265. 
 
 Vertical section of the skin 
 and sweat-glands of the axilla ; 
 a. Layer of glands with their 
 ducts traversing ft, the cutis and 
 cuticle, c. Small hair, d, d. 
 Portions of larger hairs. 
 Magn. one and a half diam.] 
 
 [Fig. 264, 
 
 Sweat-gland and the commencement of its 
 duct : a. Venous radicles on the wall of the 
 cell in which the gland rests. This vein anas- 
 tomoses with others in the vicinity, b. Capilla- 
 ries of the gland separately represented, arising 
 trom their arteries, which also anastomose. 
 The blood-vessels are all situated on the outside 
 or deep surface of the tube, in contact with the 
 basement-membrane. Magn. 35 diam.] 
 
 a. Vertical section of the cuticle from the heel, 
 detached by maceration. The epithelium of the 
 sweat-duct, continuous with the cuticle, has been 
 drawn out of the tube of basement-membrane, as 
 far as the gland, where it begins to be contorted. 
 The cavity of the duct is seen dilating as it enters 
 the cuticle, and then stretching up to the surface 
 through the epidermic laminae. The deep surface 
 of the duct is continuous with the surface of the 
 cavities in which the papillae are lodged. Magn. 
 35 diameters. 
 
 6. Duct at its entrance into the cuticle. More 
 highly magnified.] 
 
 number of square inches of surface, in a man of ordinary stature, is about 
 '2500 ; the total number of pores, therefore, may be about seven millions ; 
 and the length of the perspiratory tubing would thus be 1,750,000 inches, or 
 145,833 feet, or 48,611 yards ; or nearly 28 miles. 
 
 869. The Secretion of fluid by these Glands is continually taking place ; 
 but this fluid, being usually carried off in the form of vapour "as fast as it is 
 separated, does not accumulate and become sensible. If, however, from the 
 increased amount of the secretion, or from the condition of the surrounding 
 air, the whole fluid thus poured out should not evaporate, it accumulates in 
 
CUTANEOUS AND MUCOUS FOLLICLES. 663 
 
 minute drops upon the surface of the skin. Thus the Sudoriferous excretion 
 may take the form either of sensible or insensible transpiration ; the latter 
 bemg constant, the former occasional. It is difficult to obtain enough of this 
 secretion for analysis, free from the sebaceous and other matters which accu- 
 mulate on the surface of the skin ; and its character can only, therefore, be 
 stated approximately. It has usually an -acid reaction, which seems due to 
 the presence of acetic acid ; and to this, or to lactic acid, we are probably to 
 attribute the sour smell which it has, especially in some disordered states of 
 the system. The proportion of solid matter, according to Anselmino, varies 
 between 5 and 12*5 parts in 1000. The greatest part of it consists of animal 
 matter, wKl6his.agpaj;ently a proteine-compound in a state of incipient decom- 
 position. The remaTMer. consists 'of saline compounds ; of which the chlorides 
 of potassium and sodium appear to be pretty constantly present ; whilst the 
 muriate of ammonia, free acetic acid, and acetate of soda, have also been said 
 to occur in it. The proportion of these ingredients would probably be found 
 larger in the fluid of the Sudoriferous glands, if we had the means of collecting 
 it separately ; for of the whole fluid which passes off from the surface of the 
 skin, only a small proportion can be properly said to be secreted by the Sudo- 
 riferous glands ; the greater part, under ordinary circumstances, being the 
 product of simple Evaporation, by which, of course, nothing but pure watery 
 vapour is dissipated. 
 
 870. The entire amount of fluid which is insensibly lost from the Cutaneous 
 and Pulmonary surfaces, is estimated by Seguin at 18 grains per minute ; of 
 which 11 grains pass off by the skin, and 7 by the lungs. The maximum 
 loss by Exhalation, cutaneous and pulmonary, during twenty-four hours, (ex- 
 cept under very peculiar circumstances,) is 5 Ibs. ; the minimum If Ib. It 
 varies greatly, according to the condition of the atmosphere, and that of the 
 body itself. The manner and degree in which it is influenced by atmospheric 
 conditions, will be better discussed under the head of Animal Heat ( 897) ; 
 since this influence has a most important effect in the regulation of the tem- 
 perature of the body. As already pointed out, the Urinary excretion is in 
 great degree vicarious with it, in regard to the amount of fluid discharged, 
 the urine being more watery in proportion as the Cutaneous Exhalation is 
 diminished in amount, and vice versa ( 840). But we are also to look at 
 these two excretions as vicarious, in regard to the deportation (or getting rid) 
 of the products of the waste of the system. The share which the Skin has 
 in this office has probably been generally under-rated. There is reason to 
 believe that at least 100 grains of azotized matter are excreted from it daily; 
 and any cause which checks this excretion, must throw additional labour on 
 the kidneys, and will be likely to produce disorders of their function. 
 
 871. The Exhalant action of the Skin is influenced by general conditions of 
 the vascular and nervous systems ; which are as yet ill understood. It is quite 
 certain, however, that through the influence of the latter the secretion may 
 be excited or suspended ; this is seen on the one hand in the state of syncope, 
 and the effects of depressing emotions, especially fear, and its more aggravated 
 condition, terror ; and on the other in the dry condition of the skin during 
 states of high nervous excitement. It is very probable that, in many forms of 
 fever, the suppression of the perspiration is a cause, rather than an effect, of 
 disordered vascular action ; for there are several morbid conditions of large 
 parts of the surface, in which the suppression of the transpiration appears to 
 be one of the chief sources of danger, having a tendency to produce congestion 
 and inflammation of internal organs. From the recent experiments of Dr. 
 Fourcault,* it appears that complete suppression of the Perspiration in animals, 
 
 * Comptes Rendus de 1' Academic, May, 1844; and Lancet, June 8, 1844. 
 
664 
 
 OF SECRETION. 
 
 by means of a varnish applied over the skin, gives rise to a state termed by 
 him Cutaneous Asphyxia ; which is marked by imperfect arterialization of the 
 blood, and considerable fall of temperature ( 768, 891); and which, as- it 
 produces death in the lower animals, would probably do the same in Man. 
 A partial suppression by the same means gives rise to Febrile symptoms, and 
 to Albuminuria. 
 
 872. The Skin is likewise furnished with numerous Sebaceous glands, also 
 distributed more or less closely throughout the whole surface of the body. By 
 these an Adipose secretion is poured forth, which keeps the skin from being 
 dried and cracked by the action of the sun and air. It is especially abundant 
 in the races which are formed to inhabit warm climates. Some of these glan- 
 
 [Fig. 266. 
 
 Sebaceous glands, showing their size and relation to the hair- follicles : 4. and B from the nose ; c from 
 
 the beard. In the latter the cutis sends down an investment of the hair-follicle. Magn. IS diam.] 
 
 \ 
 
 dulae are simple follicles lined with secreting cells, and contained in the sub- 
 stance of the Skin itself; whilst others are formed out of similar follicles, more 
 or less branched, elongated, and convoluted ; and others, again, seem to con- 
 sist of little else than clusters of Fat cells, from one part of which an excretory 
 duct arises: these last commonly open into the passage, by which the Hair 
 makes its way outwards. Besides these there are other glands situated in 
 particular parts of the body, and having special functions. Such are the Ceru- 
 minous glands situated beneath the skin of the auditory meatus ; these are 
 closely analogous in form to the sudoriferous glands, as the accompanying 
 figure shows ; but their secretion is very different, being nearly solid, and 
 having somewhat of a resinous character. A peculiar series of glandulae, 
 bearing a general resemblance to the sudoriferous glands, but of larger size, 
 have lately been discovered by Prof. Homer* and M. Robin to exist in the 
 human axillae ; where they probably serve to secrete the peculiar odorous 
 matter, characteristic of that part. In many of the lower animals, such glands 
 maybe detected, having a structure of considerable complexity. The odorous 
 secretion would appear to be elaborated from the blood by a simple chemical 
 change; for it may be made evident even in blood that has been dried up, by 
 
 * [Am. Journ. Med. Science, Jan. 1846, p. 13.] 
 
CUTANEOUS AND MUCOUS FOLLICLES. 
 
 Fig. 267. 
 
 665 
 
 Cutaneous glands of external meatus auditorius. 1. Section of the skin, magnified three diameters ; 
 2, 2, hairs ; 3, 3, superficial sebaceous glands ; 1, 1, larger and deeper-seated glands, by which the ceru- 
 men is secreted. 2. A hair, perforating the epidermis at 3 ; 1, 1, sebaceous glands, with their excretory 
 ducts 2,2; 4, base of the hair, in its double follicle 5,5. 3. Cerumen-gland, formed by the contorted 
 tube, 1, 1, of the excretory duct, 2; 3, vascular trunk and ramifications. The last two figures highly 
 magnified. 
 
 [Fig. 268. 
 
 Cutaneous Follicles or Glands of the Axilla, magnified one-third. (Homer.)] 
 
 treating it with sulphuric acid. This aromatic principle differs sufficiently m 
 the blood of different animals, to enable a person with a delicate sense of 
 smell to determine from what animal any specimen has been procured ; and 
 this fact has been applied with success to juridical investigations. It has even 
 
 56* 
 
666 
 
 OF SECRETION. 
 
 been stated that the blood of the human Male may be distinguished from that 
 of the Female, by its more powerful odour; but this does not appear- to be 
 the case. at least with sufficient certainty for medico-legal inquiries.* 
 
 873. Besides the crypts or follicles, which have been spoken of as gene- 
 rally existing in Mucous Membranes ( 178), there exist, in that of the Intes- 
 tinal Canal, numerous glandulae in various parts, for the elaboration of par- 
 ticular secretions. In the Stomach, for example, a large number of these 
 secreting organs, some of them possessing rather a complex structure, are 
 included in the thickness of its walls, composing, indeed, the greater part of 
 the mucous membrane. If this be divided by a section perpendicular to its 
 surface, it is seen to be made up of a number of tubuli closely applied to each 
 other, their blind extremities being in contact with the submucous tissue, and 
 their open ends being directed towards the cavity of the stomach. In some 
 situations, these tubuli are short and straight ; in other parts they are longer, 
 and present an appearance of irregular dilatation or partial convolution. This, 
 indeed, is their usual character, especially towards the cardiac orifice of the 
 
 Fig. 269. 
 
 Section of the coats of 
 the stomach, near the py- 
 lorus, showing the gastric 
 glands, 1, magnified three 
 times. 2, magnified twenty 
 times. 
 
 [Fig. 270. 
 
 A. Horizontal section of a stomach-cell, a 
 little way within its orifice, a. Basement- 
 membrane, b. Columnar epithelium. All 
 but the centre of the cavity of the cell is oc- 
 cupied by transparent mucus, which seems 
 to have oozed from the open extremities of 
 the epithelial particles, c. Fibrous matrix 
 surrounding and supporting the basement- 
 membrane, d. Small blood-vessel. 
 
 B. Horizontal section of a set of stomach 
 tubes proceeding from a single cell. The 
 letters refer to corresponding- parts. The 
 epithelium is glandular; the nuclei very 
 delicate ; the cavity of the tubes very small, 
 and in some cases not visible. 
 
 From the dog, after twelve hours' fasting. 
 Magnified 200 diameters.] 
 
 * See Annales d'Hygiene, vol. j. pp. 267 and 548; vol. ii. p. 217; vol. x. p. 160, &c. 
 
CUTANEOUS AND MUCOUS FOLLICLES. 
 
 667 
 
 stomach. On the other hand, towards the pyloric extremity, they have a 
 much more complex structure. Betweeen the tubuli, blood-vessels pass up 
 from the sub-mucous tissue, and form a vascular net-work on its surface. 
 From the examination of these horizontal sections of the mucous membrane 
 at various depths, Dr. Todd* has ascertained that the tubuli are arranged in 
 bundles or groups, surrounded and bound together by a fine areOlar mem- 
 brane ; the size of the bundles, and the number of tubules contained in them, 
 vary considerably. The tubes do not, in general, open directly upon the 
 surface, but into the bottom of small depressions or pits, which may be seen 
 to cover the membrane. These pits are more or less circular in form, and 
 are separated from one another by partition-like elevations of the membrane, 
 which vary in depth ; and sometimes even by pointed processes, that have 
 been mistaken by some anatomists for villi. The diameter of these pits 
 varies from about l-100th to l-250th of an inch; it is always greatest near 
 
 [Fig. 271. 
 
 Fig. 272. 
 
 [Fig. 273. 
 
 Portion of the mucous 
 
 membrane of the stomach, 
 
 showing entrances to the 
 
 A secreting tubes, in pits 
 
 upon its surface. 
 
 A. Inner surface of the stomach, showing 
 the cells after the mucus has been washed 
 out. Magnified 25 diameters. 
 
 B. Columnar epithelium of the inner sur- 
 face and cells of the stomach: a. Free 
 ends of the epithelial particles, seen on 
 looking down upon the membrane, b. Nu- 
 clei visible at a deeper level, c. The free 
 ends seen obliquely, d. Deep or attached 
 ends of the same. The oval nuclei are seen 
 near the deeper ends. 
 
 From the dog. Magnified 300 diameters.] 
 
 * Gulstonian Lectures <*n the Physiology of the Stomach, in Medical Gazette, 1839. 
 See also Dr. Sprott Boyd's Inaugural Dissertation on the Mucous Membrane of the Stpmach, 
 in Edinb. Med. and Surg. Journal, vol. xlvi. 
 
 Vertical section of a stomach cell, with its 
 tubes : A in the middle region, B in the pyloric 
 region, a a. Orifices of the cells on the inner 
 surface of the stomach. 6 6. Different depths at 
 which the columnar epithelium is exchanged 
 for glandular, c. Pyloric tube, or prolonged 
 stomach cell. d. Pyloric tubes, terminating 
 variously, and lined to their extremities with 
 sub-columnar epithelium. 
 
 From the dog, after twelve hours' fasting. 
 Magnified 200 diameters.] 
 
668 
 
 OF SECRETION. 
 
 [Fig. 274. 
 
 the pylorus. When the surface of the membrane, cleansed from mucus and 
 epithelium-scales, is examined with a sufficient magnifying power, it is seen 
 that from three to five perforations exist in the bottom of each pit ; and these 
 are the openings of the secreting tubes. The Gastric fluid, elaborated by this 
 apparatus, having been already made a subject of special consideration ( 664) 
 need not be here described. 
 
 874. The whole Mucous sur- 
 face of the Intestinal canal is fur- 
 nished with glandular follicles of 
 a very similar character; of which 
 some approach those of the sto- 
 mach in complexity of structure ; 
 whilst others evidently corre- 
 spond with the crypts of ordinary 
 Mucous Membrane. An innu- 
 merable multitude of pores are 
 easily seen, by the aid of a sim- 
 ple lens, to cover the whole in- 
 ternal. surface of the large Intes- 
 tine ; and these are the entrances 
 to tubular follicles, closely resem- 
 bling those of the stomach, but 
 more simple in structure. Their 
 coecal extremities abut against the 
 sub-mucous tissue : towards the 
 end of the Rectum, however, 
 they are much prolonged, and 
 constitute a peculiar layer be- 
 tween the mucous and muscular 
 coats; the tubes which are there 
 visible to the naked eye, being 
 erect, parallel, and densely crowd- 
 ed. These glands probably form 
 the peculiarly thick and tenacious 
 mucus of the large intestine. In 
 the small intestine, on the other 
 hand, the coeca are less deep and 
 their apertures are smaller. These 
 apertures are, for the most part, 
 situated around the bases of the 
 villi : in the fo3tus and newly-born child, they are so abundant as to be almost 
 
 A section of the Ileum, inverted so as to show the ap- 
 pearance and arrangement of the villi on an extended 
 surface, as well as the follicles of Lieberkiihn ; the whole 
 seen under the microscope. A close examination of this 
 cut will show a great number of black points in the 
 spaces between the projections of villi : these are the 
 follicles of Lieberkiihn.] 
 
 Fig. 275. 
 
 Fig. 276. 
 
 One of the glandulae majores sim- 
 plices. viewed from above at A, and 
 seen in section at B ; from the large 
 intestine. 
 
 Mucous coat of small intestines as 
 altered in fver ; the follicles of Lie- 
 berkiihn filled with tenacious white 
 secretion. 
 
CUTANEOUS AND MUCOUS FOLLICLES. 
 
 669 
 
 [Fig. 277. 
 
 in contact ; but in the adult, the intervals increase, so as to occupy more 
 space than the apertures. The glandulae of the small intestines have long 
 been known under the name of the follicles of Lieberkiihn ; they become 
 particularly evident (Fig. 275) when the mucous membrane is inflamed, being 
 then filled with an opaque whitish secre- 
 tion, which is absent in the healthy state. 
 Besides the foregoing descriptions of 
 solitary glandulae, the Ccecum and the 
 lower part of the Rectum contain a num- 
 ber of simple and large follicles, which 
 produce slight rounded elevations on the 
 surface of the mucous membrane ; the 
 centre of each of these elevations is per- 
 forated by an aperture of the follicle ; and 
 around this are seen the orifices of the 
 tubular coeca, which closely envelope 
 the globular follicle (Fig. 270). These 
 seem most abundant where the largest 
 quantity of mucus is required. They 
 have been confounded with the glands of 
 Brunner ; but are rather analogous to the 
 solitary Peyerian glands, presently to be 
 noticed. 
 
 875. The true glands Of Brunner are A section of the small Intestine containing 
 
 chiefly situated in the Duodenum ; and some of the e lands of Pe y er > as shown und r 
 
 the 
 
 
 Fig. 278. 
 
 they lie not in the mucous but in 
 
 Sub-mUCOUS tiSSUe, where they form a cording to Boehm, a white, milky and rather 
 
 Continuous layer of white bodies Stir- thick fluid, with numerous round corpuscles of 
 
 rounding the whole intestine. Their various sizes, but mostly smaller than blood- 
 
 size, unless diseased, is scarcely that of globules. The meshes seen in the cut are the 
 
 a hemp-seed; each consists of nmne- 
 
 rous minute lobules, of which the ducts 
 
 open into a common excretory tube ; 
 
 and in the lobules may be distinguished the minute ramifications of these 
 
 ducts, with clusters of follicles forming acini, of which about six hundred 
 
 are computed to exist in each. Hence these glands 
 
 are of complex structure, much resembling that of the 
 
 Salivary glands and Pancreas, and entirely differing 
 
 from all the other glandulae of the walls of the ali- 
 
 mentary canal. Of the peculiar nature of their secre- 
 
 tion nothing is known. 
 
 876. The so called Peyerian glands constitute, 
 when aggregated together, large patches on the mucous 
 membrane of the small intestine, where they are 
 known as the glandulsc agminatx ; and it is to 
 these alone that Peyer's name is usually applied. 
 Similar bodies, however, known as the glandulse 
 solitarise, exist separately in the lower part of the 
 small intestines ; where they have been confounded with the glands of Brun- 
 ner, which do not extend beyond the commencement of the Jejunum. The 
 glands of Peyer, when examined in a healthy mucous membrane, present the 
 appearance of circular white slightly-raised spots, about a line in diameter, 
 over which the membrane is usually less set with villi, and very often entirely 
 free from them. Each of these white spots, of which a large number are 
 contained in the agminated glands, is surrounded by a zone of openings like 
 
 Conglomerate gland of 
 Brunner, from commence- 
 ment of duodenum; mag- 
 nified a hundred limes. 
 
670 
 
 OF SECRETION. 
 
 Fig. 279. 
 
 Portion of one of the patches of Peyer's glands, 
 from the end of the Ileum, highly magnified ; the villi 
 are also displayed. 
 
 those of the follicles of Lieberkuhn, which lead (as do those) into tubular 
 cceca. On rupturing the surface of one of the white bodies, there is found a 
 
 cavity, corresponding in extent with 
 the spot, and of considerable extent; 
 but this cavity has usually no ex- 
 cretory opening, and the tubular fol- 
 licles by which it is surrounded, 
 have no connection with it. In its 
 interior is found a grayish-white 
 mucous matter, interspersed with 
 cells in various stages of develop- 
 ment. There is reason to 1 believe 
 that, at a certain period of the ex- 
 istence of each of these glandulae, 
 an excretory orifice is formed, by a 
 sort of dehiscence in the wall of the 
 cavity ; and' that, through this, the 
 product secreted by the contained 
 cells may be poured forth. Each 
 of them may be compared, on this 
 view, to one of the ultimate folli- 
 cles, which constitutes the secreting 
 portion of any one of the larger 
 glands ( 823) ; the only difference being, that the latter are situated at the 
 extremities of the ramifying ducts, by which their product is collected and 
 conveyed away; whilst the former pour their secretion at once into the 
 cavity of the intestine. The membrane which covers in the cavity is ex- 
 tremely thin, and is very liable to be destroyed by ulceration ; hence it is, that, 
 after inflammation of the enteritic mucous membrane, the patches of Peyer 
 are often to be seen as a congeries of shallow open cells or follicles. 
 
 877. Although the particular use of each variety of the Intestinal glandulae 
 cannot yet be determined, there seems little doubt that their general function 
 is, to eliminate from the Blood those putrescent matters which would other- 
 wise accumulate in it; whether as one of the results of the normal waste of 
 the system, 'or as produced by various morbific causes, which act as ferments, 
 and thus occasion an unusual tendency to decomposition in the solids and 
 fluids of the body. That the putrescent elements of the faeces are not imme- 
 diately derived from the food taken in, so much as from the excreting action 
 of the Intestinal .Glandulae, appears from this consideration, among others ; 
 that faecal matter is still discharged, even in considerable quantities, long after 
 the intestinal tube has been completely emptied of its alimentary contents. 
 We see this in the course of many diseases, when food is not taken for many 
 days, during which time the bowels have been completely emptied of their 
 previous contents by repeated evacuations ; and whatever then passes, in ad- 
 dition to the biliary and pancreatic fluids, must be derived from the intestinal 
 walls themselves. Sometimes a copious flux of putrescent matter continues 
 to take place spontaneously ; whilst it is often produced by the agency of 
 purgative medicine. The "colliquative diarrhea," which frequently comes 
 on at the close of exhausting diseases, and which usually precedes death by 
 starvation, appears to depend, not so much upon a disordered state of the 
 intestinal glandulae themselves, as upon the general disintegration of the solids 
 of the body, which calls them into extraordinary activity for the purpose of 
 separating the decomposing matter. 
 
GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 671 
 
 CHAPTER XVI. 
 
 * 
 
 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. ANIMAL HEAT. 
 
 \.~Review of the Nutritive Processes, with Practical Applications. 
 
 878. THE detailed survey which has been now taken, of the different 
 Functional operations concerned in maintaining the life of the individual, 
 may suggest to us some general views that have important practical applica- 
 tions. In the first place, it has been shown, that the province of the Animal 
 is not to combine Inorganic elements into Organic compounds, fit to be ap- 
 plied to the purposes of Nutrition ; but to use those which are prepared for 
 it by the Plant. The nutritive materials thus obtained may be divided into 
 two great classes, the azotized and the non-azotized. The former have been 
 shown ( 642) to be so nearly identical in composition with the proximate 
 principles of which the Animal body is composed, that no great amount of 
 chemical transformation can be required to prepare them for being appropri- 
 ated by it. The latter are altogether different in character; and whether or 
 not they can, by any process of transformation, be made subservient to the 
 nutrition of the Azotized tissues, it is unquestionable that their ordinary use 
 is to serve as the materials for the Respiratory process, and for the mainte- 
 nance of Animal heat. The demand for these several articles in the system 
 will depend, in regard to the former, upon the amount of Tissue which has 
 been disintegrated and needs repair; and with respect to the latter, upon the 
 amount of Heat which it is necessary to generate, to keep up the tempera- 
 ture of the body to its regular standard. Hence a highly-azotized diet is 
 most required when the greatest amount of muscular exertion is being used ; 
 whilst a diet, in which non-azotized substances are predominant, will serve 
 to sustain the Animal Heat in a cold atmosphere. The adjustment of the 
 diet to the wants of the system, is a matter of the greatest importance for 
 the preservation of health. If too great an amount of azotized food be in- 
 gested, and the superfluity be thrown upon the Kidneys to eliminate ( 850), 
 disorder of the Urinary Secretion is almost certain, sooner or later, to mani- 
 fest itself. The quantity of Lithic Acid, in particular, undergoes considerable 
 increase; and, by the removal of its bases through the increased production 
 of other acids, it is very likely to pass out in an insoluble state, giving rise to 
 Gravelly deposits. Or it may accumulate in the Blood, and there combine 
 with Soda; forming a salt which is deposited in various parts (especially in 
 the neighbourhood of the smaller joints), forming concretions, which are com- 
 monly known tinder the name of "chalk-stones." These deposits usually 
 take place, however, after severe attacks of a peculiar Inflammation, known 
 as Gout; and this inflammation seems to be connected with the accumulation 
 of Lithate of Soda in the Blood. Over this disease a careful regulation of 
 the diet exercises a powerful control. A patient affected with the " Lithic 
 Acid diathesis," may palliate, if not altogether cure his disorder, by rigorously 
 abstaining from the use of any superfluous amount of azotized compounds 
 as food ; and by subsisting as much as possible upon those belonging to the 
 Farinaceous group. It is by no means every case, however, that is capable 
 of alleviation by treatment of this sort ; in fact, it can seldom be rigorously 
 
672 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 
 
 enforced, except in early life, or at any rate when the constitution is unbroken 
 by disease or intemperance. Not unfrequently it will be found, that the per- 
 sistence in a diet of this kind, occasions so much disorder of the stomach, as 
 to be quite out of the question. On the other hand, in the " Strumous dia- 
 thesis," there would seem to be a low condition of those vital powers, which 
 are concerned in the conversion of the Albuminous materials prepared by 
 the Digestive process, into the Fibrinous matter which is ready for assimila- 
 tion ; so that, by a perversion of the ordinary nutrient actions, Albuminous 
 Tubercle is deposited in the interstices of the tissues, instead of these tissues 
 being themselves regenerated by Organizable Fibrine ; and the same may 
 take place in a more rapid manner, in consequence of that disturbance of the 
 nutrient processes, which is known in healthy constitutions as Inflammation 
 ( 802). It is obvious, then, that the treatment of the Strumous Diathesis 
 should be directed towards the invigoration of the general powers of the sys- 
 tem ; and although, when disease of the Chest has once established itself, a 
 warm moist atmosphere may be necessary as a preventive of inflammatory 
 affections, it is a great mistake to imagine that such a plan is applicable to 
 those in whom there is merely a Strumous predisposition ; for this should be 
 combated by such means as are calculated rather to brace than to relax the 
 system, especially out-door exercise, a nutritious diet in which easily-digested 
 proteine-compounds should predominate, and a dry and well-ventilated habi- 
 tation. There can be no doubt that the Tuberculous Cachexia is encouraged, 
 and developed, by injudicious management during the early ages of life, in 
 many cases where it might have been avoided.* 
 
 879. Equally important is the regulation of the diet, in regard to its non- 
 azotized constituents. If these are in excess, the elimination of them from 
 the Blood falls especially upon the Liver ( 836) ; and a continued excess 
 gives rise to disorders in its function, which a diminution in the quantity of 
 Farinaceous or Oleaginous matter ingested would prevent or cure. This is 
 especially liable to happen to Europeans proceeding to warm climates ; who 
 are not warned by their decrease of appetite, that there is no longer a necessity 
 for the same supply ; but force themselves to eat much more than they have 
 any real occasion for. There is a very remarkable condition of the system, 
 in which there is a tendency to the presence of a large amount of Sugar within 
 the vessels ; either through the absence of power to convert that which has 
 been taken in ; or through the actual production of that compound, as a result 
 of the waste of the system. We have seen that Sugar may be detected in 
 the Serum of healthy blood, drawn soon after a meal; but that it soon becomes 
 untraceable, probably in consequence of its being carried off by the respi- 
 ratory process ( 697). In the disease termed Diabetes, or the " saccharine 
 diathesis," there is a much larger amount of Sugar in the Blood: and this 
 appears to be constantly present, as if, from some cause, its elimination by 
 the usual channel were retarded. The Sugar makes its appearance, also, in 
 the Urine ; the Kidneys taking-on the unusual office of separating this com- 
 pound, that it may not accumulate in the Blood. Some late researches on 
 the exclusive employment of azotized principles as articles of diet, in the 
 treatment of the Saccharine diathesis, have given very favourable results. The 
 plan was long since proposed by Dr. Rollo ; and when the diseased condition 
 has been uncomplicated by other maladies (as is not unfrequently the case), 
 the rigorous enforcement of such a diet has been attended with success in 
 numerous instances. One of the greatest difficulties in the application of the 
 system, however, has arisen from the longing which the patients experience 
 
 * See the excellent works of Sir James Clark, in which the tVnportance of Hygienic treat- 
 ment is strongly insisted on. 
 
GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 673 
 
 for Vegetable food ; since this tempts them to gratify their appetites, to the 
 complete prejudice of the remedial system, a very small amount of farina- 
 ceous matter being sufficient to cause the re-appearance of the Sugar, after it 
 had seemed to be entirely got rid of. It has been proposed, however, by M. 
 Bouchardat to gratify this longing to a certain degree, by allowing the use of 
 bread made of wheaten flower, from which nearly all the Fecula has been 
 separated, the Gluten only being left, with such a small amount of Fecula 
 as may serve to make it rise in fermentation ; so that it is as free from un- 
 azotized constituents, as the average of animal substances. This plan has 
 been very successfully practiced; having frequently kept the disease in com- 
 plete check, where, from the advanced period of life, the duration of the 
 morbid state, and other circumstances, a perfect cure could not be reasonably 
 expected. 
 
 880. From what has been stated in Chap, xn* respecting the nature of the 
 Function of Circulation, it is evident that primary disorders of that function 
 are not nearly so frequent as they are ordinarily supposed to be ; and that 
 the proximate cause of morbid phenomena is seldom to be found in them. 
 By the action of the Heart and Blood-vessels, the nutrient fluid, which has 
 been prepared from the atooientary materials submitted to the digestive appara- 
 tus, is conveyed to the tismies which it is to nourish ; but the true process of 
 Nutrition is independent of this, and may take place after the motion of the 
 fluid has ceased, just as it commences before any movement shows itself. 
 For the tissue which exists in the Embryo during the early period of its de- 
 velopment, and also in any newly-forming part, is destitute of vessels, consist- 
 ing only of cells ; and these grow and reproduce themselves at the expense 
 of the nutritive materials supplied to them from without, just as does the 
 whole mass of a Cellular Plant. Moreover it has been shown ( 740), that 
 the activity of the nutrient processes has much to do with the movement of 
 the fluid through the smaller vessels, and is a cause rather than a consequence 
 of it. If the action of the Heart cease, the whole circulation must obviously 
 come to a stand ere long; but in many animals the Capillary movement may 
 continue for some time after the general circulation has been checked; and, 
 so long as blood is supplied to the parts, so long may their nutrition continue, 
 provided other circumstances be favourable. It is unquestionably true, that 
 the cessation of the Circulation is usually the immediate cause of Death ; and 
 that, when the suspension is permanent, the loss of the vitality of the system, 
 considered both as a whole, and as made up of distinct parts, is a necessary 
 consequence. But still, we find that the cause of this cessation seldom origi- 
 nates in the Circulating apparatus itself; and in general, a disturbed state of 
 the Circulation is to be looked upon rather as a result, than as a cause, of 
 diseased action. An extreme case of such a disturbance, which, when suffi- 
 ciently prolonged, is attended with fatal results, is to be found in Asphyxia ; 
 in which the cessation of the action of the Lungs induces a stagnation of the 
 Blood in their capillaries ; and as, in warm-blooded animals, the whole cur- 
 rent of Blood has to pass through the Lungs, before proceeding again to the 
 system, a total suspension of the Circulation necessarily results from this inter- 
 ruption ( 738 and 779). Now if we take this (which it appears reasonable 
 to do) as a type of a great number of morbid conditions of different organs, 
 we are led to see why a serious disturbance of the movement in any one part 
 should affect the entire circulating apparatus, and should thus influence its 
 flow through almost every other organ. There are no other organs, however, 
 in which a stagnation can be so serious as in the Lungs ; since there are none 
 through which the whole current flows. The Liver ranks next in importance, 
 since all the venous blood collected from the Chylopoietic viscera passes 
 through it ; and every practical man is aware how frequently derangement of 
 57 
 
674 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 
 
 the circulation through the Liver, originating in an unhealthy state of the gland 
 itself, is a cause of serious disorders in the abdominal viscera. Minor irregu- 
 larities in the Circulation, in various parts, not unfrequently become causes of 
 serious inconvenience. Thus, few conditions are more common, especially 
 amongst persons of active minds but inert habits, than undue determination of 
 blood to the Head, conjoined with torpor of the circulation through the Skin, 
 especially that of the extremities, which are ordinarily cold. The obvious 
 indication here is, to endeavour to restore the balance of the Circulation ; and 
 excitement of the flow of blood through the Skin, by frictions, moderately- 
 stimulating applications, exercise, &c., will commonly prove of great utility. 
 
 881. There are many disorders commonly regarded as affections of the 
 Circulation, which evidently consist in reality of a morbid alteration in the 
 Nutritive, processes : among these there can be little doubt that w r e are to rank 
 local Determinations and Congestions, which result from an exalted or dimi- 
 nished activity of the formative actions ; and Inflammation, in which these 
 actions are perverted. Much has been said and written, to very little purpose, 
 respecting the essential nature of this process ; it has been attributed by some 
 to disordered action of the vessels, and by others to an injurious impression 
 on the nerves, the fact, that Inflammation may occur in tissues which con- 
 tain neither vessels nor nerves, having been entirety overlooked. The only 
 view of the character of Inflammation that seems likely to account for its 
 phenomena, is that which regards it as essentially consisting in a disturbance 
 of the due relation between the living Tissue and the nutrient materials 
 contained in the Blood ; in other words, as an abnormal form of the ordinary 
 nutritive process ( 802 806). A similar remark may be made, in regard 
 to those productions formerly termed " Heterologous transformations" of 
 tissue ; which are rather to be regarded as new growths, that have appro- 
 priated the nutriment designed for the support of the proper tissues, and have 
 therefore become developed at the expense of these. It is quite as absurd 
 to attempt to account for the growth of Scirrhus, Carcinoma, &c., by any 
 peculiar action of the vessels of the part, as it would be to attribute the secre- 
 tion of fatty matter by the cells of one tissue, or of phosphate of lime by 
 those of another, to the peculiar distribution of their vessels. The progress 
 of research obviously leads to the conclusion, that in every part of the living 
 body there is an inherent and independent vitality, which enables it to grow 
 and maintain its normal structure and constitution, so long as it is supplied 
 with the requisite materials ; and that changes in the character of the tissue 
 can be referred to nothing else than to alterations in its properties, resulting 
 from external agencies, or to alterations in the materials supplied for its 
 renewal. Of these two morbific causes, the latter is undoubtedly the most 
 frequent ; and the tendency which is now gaining ground, to seek in the Blood 
 for indications of pathological changes, when there is no obvious general dis- 
 turbance of the system, will probably lead to a greatly-increased knowledge 
 of the real nature of diseased states ; in spite of the opposition which any 
 return to the Humoral Pathology is sure to excite, in the minds of those who 
 regard it as an exploded and pernicious system. 
 
 882. The Sympathy between different parts of the system, which espe- 
 cially manifests itself in the tendency to simultaneous affection with the same 
 Disease, affords an excellent illustration of this principle. Of those Sympa- 
 thetic actions, which result from the Nervous connections of the various 
 organs, this is not the place to speak ; since we are at present concerned 
 with those perversions of the Nutritive processes, which give rise to Inflam- 
 matory and other diseases. Where a certain tissue, throughout the body, is 
 similarly affected, there is strong reason to presume that the morbific cause 
 is conveyed to it in the Blood ; this is the case, for example, with regard to 
 
GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 675 
 
 the Mucous membranes, which all manifest a tendency to Inflammation, when 
 Arsenic has been received into the system : and certain forms of the disease 
 commonly termed Influenza, are marked by a similar disposition. The same 
 may be said in regard to Inflammation of the Fibrous membranes, Areolar 
 tissue, Serous membranes, and other structures. It has been considered a 
 sufficient account of these consentaneous affections, to say that they result 
 from Sympathy, a mere verbal quibble, which explains nothing. If, on the 
 other hand, we regard the disease as a perversion of the ordinary processes 
 of Nutrition, Secretion, &c., and as dependent upon an abnormal condition of 
 the Blood (such as is induced by the introduction of a poison into it), the 
 rationale of the sympathetic disturbance becomes apparent; since all the 
 tissues of the same kind will of necessity be similarly affected, although some 
 local cause may occasion one to suffer more severely than another. In the 
 ingenious paper by Dr. W. Budd, already referred to ( 785), the perfect cor- 
 respondence, which not unfrequently manifests itself between the diseased 
 actions on the two sides of the body, is Adduced in support of the same view, 
 to which it is made to afford very striking confirmation. The fact that this 
 kind of Sympathy not unfrequently manifests itself between tissues having 
 an analogous structure, but very different function, is another argument in 
 favour of the same view ; of this fact, the sympathy of which every practical 
 man is aware, between the Skin and Mucous Membranes, is a very good 
 example. The sympathy of the different tissues forming any individual organ, 
 by which disease in one becomes a cause of disorder in the rest, is, however, 
 to be very differently explained. We have examples of this in Inflammatory 
 affections of the Mucous membranes, which usually extend themselves to the 
 remaining constituents of the organs of which they form a part; and in those 
 of the Serous membranes, which almost always follow inflammation of the 
 organs they invest. Here the local disturbance of one part appears sufficient 
 to account for the extension of it to another, that is closely connected with it 
 by vessels and nerves; this has been termed the Sympathy of Contiguity. 
 The Fibrous membranes are less liable to be affected in this manner, than are 
 most other tissues ; and the reason appears simply this, that there is usually 
 less vascular connection between them and the adjacent parts, than there is 
 in the case of the Serous membranes. Hence the Fibrous membranes fre- 
 quently act as insulators, preventing the spread of disease to adjacent parts. 
 883. The general characters of the processes of Nutrition and Secretion 
 are so nearly allied, that what has been stated of the Pathological states of the 
 former, is nearly as applicable to those of the latter. Although it is unques- 
 tionable that disordered Secretion may result from a purely local cause, acting 
 on the solid tissue of the part affected, yet there is also increasing reason to 
 believe, that in a large number of cases, the abnormal character of the pro- 
 duct is in reality a result of the abnormal state of the Blood from which it 
 is separated ; and that the organ itself is still performing a healthy function, 
 in separating from the blood that which would be injurious to it. This 
 leads us to refer such disorders to causes much more remote than those 
 which were formerly supposed to operate ; but they are undoubtedly nearer 
 the true ones. Such a view has been prosecuted by Dr. Prout in regard to 
 the abnormal conditions of the Urine, with great success ; and there can be 
 little doubt that it is also applicable to the Biliary secretion, on the true 
 chemical nature of which there is scarcely yet an agreement among Chemists, 
 and whose pathological conditions, therefore, are, and must long remain, 
 comparatively obscure. It is obvious that, if the Assimilation of Nutritive 
 matter be in any respect wrongly performed, the products of the Decomposi- 
 tion of the Tissues (in which these excretions probably originate, 819), must 
 also be different; and our remedial measures must often be directed, therefore, 
 not so much to the Secreting organ, as towards the previous operations. 
 
676 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 
 
 884. These considerations are of the highest importance in the treatment 
 of Disease ; the success of which will greatly depend upon the degree in 
 which the Physician follows the indications of Nature, instead of putting him- 
 self in antagonism to her course of operation. If we pay but a slight attention 
 to those ^phenomena which result from the introduction of poisons into the 
 system, we perceive that there is almost invariably an increased excretion of 
 some kind, which tends to eliminate them from the blood. Even where there 
 is no other obvious means for their removal, we can have little doubt that the 
 Respiratory function gives important aid in their separation ; when we keep 
 in view that from five to eight ounces of solid carbon, to say nothing of the 
 hydrogen, are thrown off from the lungs in the course of every twenty-four 
 hours. It is important to bear this circumstance in mind ; since it enables us 
 to understand how, if time be given, the system frees itself from such noxious 
 substances; and it points out the duty of the medical attendant to be rather 
 that of supporting the powers of the body by judiciously-devised means, and 
 of aiding in the elimination of the noxious matter by a copious supply of pure 
 air, than of interfering more actively to promote that which Nature is already 
 effecting in the most advantageous manner. We see the results of this ope- 
 ration in the case of Narcotic poisoning ; in which, if the Respiratory process 
 can be artificially kept up for a sufficient length of time, the powers of the 
 nervous system are gradually restored, even after what seemed to be their 
 complete and final cessation. There can be no doubt that, in like manner, 
 the system makes an effort to rid itself of other noxious substances, the pre- 
 sence of which in the blood results from morbid processes going on in the 
 body itself, and which, if retained, would produce the most serious conse- 
 quences. Thus a copious discharge of Lithic acid by the Urine will frequently 
 avert or curtail an attack of Gout. The copious acid perspirations, which 
 occur in certain forms of Rheumatism, are the means by which the Lactic acid 
 (which seems to be the materies morbi of this disease) is separated from the 
 blood. And there can be no doubt that an attack of Diarrhoea often prevents 
 more serious disease, by removing an unusual accumulation of the elements 
 of bile, or by eliminating an undue amount of putrescent matter, the continued 
 presence of which in the circulating fluid would induce the most serious dis- 
 orders in the nervous system. There can be no doubt that a due regulation 
 of the Excreting processes is one of the most important means, by which the 
 Physician can counteract the results of disordered actions in the system. They 
 may frequently require to be gently stimulated, in order to remove some mor- 
 bific elements from the blood. But it will be seldom that it will be desirable 
 to check them, even when apparently excessive, unless there be strong reason 
 to believe, that the excess proceeds from a disordered state of the organ itself, 
 produced by local causes only. 
 
 2. Minimal Heat. 
 
 885. All the vital actions that have been considered in the preceding pages, 
 require a certain amount of Heat as a condition of their performance ; and in 
 the more elevated tribes of animals, in which (for the very purposes of their 
 creation) a high degree of constancy and regularity is required in these actions, 
 there is a provision within themselves for the maintenance of their temperature 
 at a certain standard. We shall inquire, in the first place, into the amount of 
 Heat thus generated by Man ; and then into the sources of its production. 
 
 886. Our present knowledge of the Temperature of the Human body under 
 different circumstances, is chiefly due to the investigations of Dr. J. Davy. 
 Much additional information may be expected, however, from inquiries which 
 
ANIMAL HEAT. 677 
 
 are at present in progress. Dr. Davy's observations* have included 114 in- 
 dividuals of both sexes, of different ages, and among various races, in different 
 latitudes, and under various temperatures; the external temperature, however, 
 was in no instance very low, and the variations were by no means extreme. 
 The mean of the ages of all the individuals was 27 years. The following is 
 a general statement of the results, the temperature of the body being ascer- 
 tained by a thermometer placed under the tongue. 
 
 Temperature of the air 60 Average temperature of the body 91-28 
 
 69 " 98-15 
 
 78 " 98-85 
 
 79.50 99 . 21 o 
 
 80 " 99-67 
 
 82 " " " " 99-9 
 
 Mean of all the experiments 74 Mean of all the experiments 100 
 
 Highest temperature of air 82 Highest temperature of body 102 
 
 Lowest temperature of air 60 Lowest temperature of body 96-5 
 
 From this we see that the variations noted by Dr. Davy, which were evidently 
 in part the consequence of variations in external temperature, but which were 
 also partly attributable to individual peculiarities, amounted to 5| degrees ; the 
 lower extreme would probably undergo still further depression, if the inquiries 
 were carried on in very cold climates. The Temperature of the body may 
 be affected by internal as well as by external causes ; thus in diseases which 
 involve an accelerated pulse and an augmented respiration, the temperature is 
 generally higher than usual, even though a large portion of the lung may be 
 unfit for its function. This is often remarkably seen in the last stages of 
 Phthisis, when the inspirations are extremely rapid, and the pulse so quick as 
 scarcely to admit of being counted ; the skin, in such cases, often becomes 
 alm,ost painfully hot. On the other hand, in diseases of the contrary character, 
 such as Asthma and the Asiatic Cholera, the temperature of the body falls, 
 sometimes, to the extent of 20 degrees. The following observations have been 
 made on this subject by M. Donne ;t it is much to be desired, however, that 
 fuller data could be collected on the subject. In a case of Puerperal Fever, 
 the pulse being 168, and the respiration 48 per minute, the temperature was 
 104. In a case of Hypertrophy of the Heart, the pulse being 150 and the 
 respirations 34, the temperature was 103< In a case of Typhoid Fever, the 
 pulse being 136, and the respirations 50, the temperature was 104. And in 
 a case of Phthisis, the pulse being 140, and the respirations 62, the tempera- 
 ture was 102. On the other hand, in a case of Jaundice, in which the pulse 
 was but 52, the temperature was only 96*40 ; but the same temperature was 
 observed in a case of Diabetes, in which the pulse was 84. The limited re- 
 sults of Mons. D.'s experiments, whilst they clearly indicate that a general 
 relation exists between the temperature of the body and the rapidity of the 
 pulse, also show that this relation is by no means invariable, but that it is 
 liable to be affected by several causes, of which our knowledge is as yet very 
 limited. Dr. Dunglison speaks of having frequently seen the thermometer at 
 106 in Scarlatina and Typhus ; and Dr. Edwards mentions a case of Tetanus, 
 in which it rose to 11014 
 
 * Phil. Trans., 1814; republished in Anatomical and Physiological Researches. 
 
 f Archives Generates, Oct. 1835 ; and Brit, and For. Med. Rev., vol. ii. p. 248. 
 
 J [An extensive series of observations has been made by M. Roger* on the temperature 
 of children in health and various diseases. 
 
 In nine examinations of infants from one to twenty minutes after birth, the temperature' 
 (observed in these and in all the other cases, in the axilla), was from 99'95 to 95-45. Im- 
 
 Arch. Gen. de Medecine, Juillet, Aout, &c., 1344. 
 
 57* 
 
678 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 
 
 887. Although there appears to be, for all species of animals, a distinct 
 limit to the variations of bodily temperature, under which their vital opera- 
 tions can be carried on, this limitation does not prevent animals from existing 
 in the midst of great diversities of external conditions ; since they have within 
 themselves the power of compensating for these, in a very extraordinary de- 
 gree. This power seems to exist in Man to a higher amount than in most 
 other animals; since he can not only support, but enjoy, life under extremes, 
 either of which would be fatal to many. In many parts of the tropical zone, 
 the thermometer rises every day through a large portion of the year to 110; 
 and in British India it is said to be seen occasionally at 130. On the other 
 hand, the degree of cold frequently sustained by Arctic voyagers, and quite 
 endurable under proper precautions, appears much more astonishing ; by 
 Capt. Parry, the thermometer has been seen as low as 55, or 87 below 
 the freezing point; by Capt. Franklin at 58, or 90 below the freezing 
 point ; and by Capt. Back at 70, or 102 below the freezing point. In both 
 cases, the effect of the atmospheric temperature on the body is greatly influ- 
 enced by the condition of the air as to motion or rest; thus, every one has 
 heard of the almost unbearable oppressiveness of the sirocco or hot wind of 
 Sicily and Italy, the actual temperature of which is not higher than has often 
 been experienced without any great discomfort, when the air is calm : and, on 
 the other side, it may be mentioned that, in the experience of many Arctic voya- 
 gers, a temperature of 50 may be sustained, when the air is perfectly still, 
 with less inconvenience than is caused by air in motion at a temperature fifty 
 degrees higher. This is quite conformable to what might be anticipated on 
 physical principles. 
 
 888. Again, the degree of moisture contained in a heated atmosphere, makes 
 a great difference in the degree of elevation of temperature, which may be sus- 
 
 mediately after birth the temperature was at the highest; but it quickly fell to near the 
 lowest of those above stated ; but, by the next day, it was again completely or nearly what 
 it was before. The rapidity of the pulse and of respiration appeared to have no certain re- 
 lation to the temperature. 
 
 In thirty-three infants of from one to seven days old, the most frequent temperature was 
 98-6; the average was 98-75; the maximum (in one case only) 102-2; the minimum (also 
 observed only once) 96- 8. All the infants were healthy. The frequency of respiration 
 had no evident or constant relation to tlie temperature. A few of the infants were of a 
 weakly habit; their average was 97-7: the others were strong, and their average tempera- 
 ture was 99-534. The age of the infant (in this short period) had no influence on its 
 temperature ; neither had its sex, nor its state of sleep or waking, nor the period after 
 suckling. 
 
 In twenty-four children, chiefly boys, from four months to fourteen years old, the most fre- 
 quent temperature was above 98 0> 6 ; the average was 98 0> 978, the minimum was 98 0> 15; 
 the maximum 99-95. The average temperature of those six years old or under, was 
 98-798; of those above six years old, 99-158. The average number of pulsations in the 
 minute was in those under six years old 102 ; in those above that age 77 ; yet the tempera- 
 ture of the latter was higher than that of the former, or of younger infants. There was no 
 evident relation between the temperature and the frequency of respiration ; nor in a few 
 examinations, was the temperature affected in a regular way, by active exercise for a short 
 time, or by the stage of digestion. 
 
 As already said, in all the examinations from which these results were obtained, the 
 thermometer was held in the axilla; comparative examinations proved that the tempera- 
 ture of the axilla (though lower than that of internal organs), was higher than that of any 
 other part of the surface of the skin. Of the other parts examined, the warmest was the 
 abdomen, then in succession, the cavity of the mouth, the bend of the arm, the hands, the 
 feet ; of which last, the average temperature, in four examinations, was only 87-35. (These 
 results correspond sufficiently with those obtained by Dr. John Davy.) 
 
 In diseased states, (to the illustration of which the greater part of the memoir is devoted,) 
 the temperature of the skin in children may descend to 74-3, and may ascend to 108-5. 
 Its range of variation is therefore much greater than in adults, in whom M. Andral found it 
 to vary in different diseases not more than from 95 to 107-6. M. C.] 
 
ANIMAL HEAT. 679 
 
 tained without inconvenience. Many instances are on record, of a heat of 
 from 250 to 280 being endured in dry air for a considerable length of time, 
 even by persons unaccustomed to a particularly high temperature ; and per- 
 sons whose occupations are such as to require it, can sustain a much higher 
 degree of heat, though not perhaps for any long period. The workmen of 
 the late Sir F. Chantrey have been accustomed to enter a furnace in which 
 his moulds were dried, whilst the floor was red-hot, and a thermometer in the 
 air stood at 350 ; and Chabert, the " Fire-king," was in the habit of entering 
 an oven, whose temperature was from 400 to 600. It is possible that these 
 feats might be easily matched by many workmen who are habitually exposed 
 to high temperatures; such as those employed in Iron -foundries, Glass- 
 houses, and Gas-works. In all these instances, the dryness of the air facili- 
 tates the rapidity of the vaporization of the fluid, of which the heat occasions 
 the secretion by the Cutaneous glands; and the large amount of caloric which 
 becomes latent in the process, is for the most part withdrawn from the body, 
 the temperature of which is thus kept down. Exposure to a very elevated 
 temperature, however, if continued for a sufficient length of time, does pro- 
 duce a certain elevation of that of the body ; as might be expected from the 
 statements already made in regard to the variation in the heat of the body 
 with changes in atmospheric temperature ( 886). In the experiments of 
 MM. Berger and Delaroche, it was found that, after the body had been ex- 
 posed to air of 120 during 17 minutes, a thermometer placed in the mouth 
 rose nearly 6 degrees above the ordinary temperature; it may be remarked, 
 however, that as the body was immersed in a close box, from which the head 
 projected (in order to avoid the direct influence of the heated air on the tem- 
 perature of the mouth), the air had probably become charged with the vapour 
 exhaled from the surface, and had therefore somewhat of the effects of a moist 
 atmosphere. At any rate, the temperature of the body does not appear to 
 rise, under any circumstances, to a degree very much greater than this. In 
 one of the experiments of Drs. Fordyce and Blagden, the temperature of a 
 Dog, that had been shut up for half-an-hour in a chamber of which the tem- 
 perature was between 220 and 236, was found to have risen from 101 to 
 about 108. MM. Delaroche and Berger tried several experiments on differ- 
 ent species of animals, in order to ascertain the highest temperature to which 
 the body could be raised without the destruction of life, by inclosing them in 
 air heated from 122 to 201, until they died: the result was very uniform, 
 the temperature of the body at the end of the experiment only varying 
 in the different species between 11 and 13 above their natural standard: 
 whence it may be inferred, that an elevation to this degree must be fatal. 
 This elevation would be attained comparatively soon in a moist atmo- 
 sphere ; partly because of the greater conducting power of the medium ; 
 but principally on account of the check which is put upon the vapor- 
 ization of the fluid secreted by the skin. Even here, however, custom 
 and acquired constitution have a very striking influence ; for whilst the in- 
 habitants of this country are unable to sustain, during more than 10 or 12 
 minutes, immersion in a vapour-bath of the temperature of 110 or 120, the 
 Finnish peasantry remain for half-an-hour or more in a vapour-bath, the tem- 
 perature of which finally rises even to 158 or 167. Accurate experiments 
 are yet wanting, to determine the influence of humidity on the effects of cold 
 air. From experiments on young Birds incapable of maintaining their own 
 temperature, of which some were placed in cold dry air, and others in cold air 
 charged with moisture, it was found by Dr. Edwards that the loss of heat was 
 in both instances the same; the effect of the evaporation from the surface in 
 the former case, being counter-balanced in the latter by the depressing influ- 
 ence of the cold moisture. This influence, the existence of which is a mat- 
 
680 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 
 
 ter of ordinary experience, is probably exerted directly upon the nervous 
 system. 
 
 889. Having thus considered the general facts which indicate the faculty 
 possessed by the living system, in the higher Animals, of keeping up its tem- 
 perature to an elevated standard, and of preventing it from being raised much 
 beyond it by any degree of external heat, we have next to inquire to what 
 this faculty is due. We shall be more likely to arrive at accurate results in 
 such an inquiry, the more comprehensive is our survey of the phenomena to 
 which it relates.* 
 
 a. The most recent experiments on the temperature of Plants (those made by MM. Bec- 
 querel and Breschet with the thermo-multiplier) have demonstrated, that in those parts in 
 which the vital processes are taking place with activity, a sensible amount of caloric is being 
 constantly evolved. The amount of this evolution of heat is generally very low, not more, 
 in fact, than a single degree (Fahr.) ; and as it does not more than counterbalance the effect 
 of the evaporation, which is continually taking place from the surface, there is no sensible 
 difference between the temperature of the plant and that of the surrounding air. At the 
 time of Flowering, however, a much greater degree of heat is generated in many plants, 
 especially in those in which a large number of flowers are crowded together, as in the case 
 of the Arum tribe: thus a thermometer placed in the midst of twelve spadixes has been 
 seen to rise to 121, whilst the temperature of the air was only 66. During the Germina- 
 tion of seeds, again, a considerable development of heat takes place; this, which is soon 
 carried off from a single seed, becomes very sensible when a large number are heaped toge- 
 ther, as in malting ; the thermometer plunged into a heap of germinating barley having been 
 seen to rise to 110. 
 
 b. These facts are of more importance than might appear at first sight ; for they indicate 
 unequivocally, that the source of the heat is to be looked for in the Organic functions, not in 
 those of Animal life. The evolution of Caloric has been attributed by many physiologists 
 to the Nervous system ; the influence which this system evidently possesses over the func- 
 tion, being mistaken for the efficient cause of it. As has been remarked on several former 
 occasions, however, the fact that any change takes place in Vegetables, to the same degree 
 (under certain conditions,) with that in which it ever presents itself in Animals, is a suffi- 
 cient proof that it cannot be dependent upon nervous agency, although it may be influenced by 
 it. Moreover, it may be remarked that the production of Heat is an operation of an entirely 
 physical character, and that it may be referred to physical causes ; whilst the operations in 
 which the Nervous system is concerned, are such as we cannot liken in any degree to physical 
 phenomena, and are of a purely vital character. In our inquiry into the sources of the Heat 
 evolved by living beings, we are limited, therefore, to those which can operate in the Vege- 
 table kingdom ; and on examining into the phenomena which present any relation to this, 
 we are at once struck with the fact, that an absorption of Oxygen from the air, with an ex- 
 trication of Carbonic acid, is continually taking place (constituting the true Respiratory pro- 
 cess of Plants, 750); and that these changes occur with excessive activity, at the very 
 periods at which the evolution of Heat is tnost remarkable, those, namely, of germination 
 and flowering. The quantity of Oxygen consumed by flowers is enormous those of the 
 Arum Italicum having been found to convert 40 times their own bulk of that gas into Carbonic 
 acid, between the periods of their first appearance and their final decay ; and of this, the far 
 larger proportion is consumed by the sexual apparatus, which has been found to consume 132 
 times its own bulk of Oxygen in 24 hours. That this change is a condition necessary for the 
 production of Heat, is fully proved by the fact, that no caloric is evolved when the flowers 
 are excluded from the contact of Oxygen ; whilst the substitution of pure oxygen for atmo- 
 spheric air occasions the elevation of temperature to be more rapid and considerable than 
 usual-t The same may be said of the heat liberated by seeds in the act of Germination : a 
 large amount of oxygen is absorbed, and of carbonic acid given out, during this process ; and 
 the evolution of Heat may be easily shown to be as dependent upon this change, as in the 
 instance just quoted. 
 
 c. When the phenomena of Calorification in Animals are carefully examined, they are 
 found to harmonize completely with this view. Throughout the whole kingdom, an exact 
 conformity may be perceived between the amount of Oxygen consumed and of Carbonic 
 acid given off, and the degree of Heat liberated. In the cold-blooded animals, whose tem- 
 
 * This subject is more fully treated in the Author's Principles of General and Compara- 
 tive Physiology, 548567. 
 
 j" See the very interesting experiments of MM. Vrolik and Vriese, in the Ann. des Sci. 
 Nat., N. S. Botan., torn, xi., p. 551. 
 
DEVELOPMENT OF HEAT. 681 
 
 perature is almost entirely dependent upon that of the surrounding element, the respiration 
 is feeble, being carried on, for the most part, through the medium of water. In the warm- 
 blooded Vertebrata, however, which have the power of keeping up the heat of their bodies to 
 an elevated standard, even when that of the surrounding air is far beneath it, the quantity of 
 oxygen consumed is very large ; and that required by Birds is more, in proportion to their size, 
 than that employed by Mammalia ; as we should expect from the more elevated tempera- 
 ture of the former. In the class of Insects, we have a very remarkable illustration of the 
 same general fact. It appears, from the researches of Mr. Newport, that Insects, during 
 their larva and pupa states, and even in their perfect condition when at rest, are to be re- 
 garded as truly cold-blooded, animals ; their temperature rising arid falling with that of the 
 surrounding medium, and being at no time more than a degree or two above it. In a state 
 of activity, however, the temperature of the body attains a considerable elevation, fre- 
 quently as much as 10 or 15 above that of the air. It must be remembered that, owing 
 to their larger extent of surface in proportion to their bulk, small animals are cooled much 
 more rapidly than large ones ; and the temperature of Insects would probably rise much 
 higher, if it were not for the loss they are thus continually experiencing, which is greatly 
 increased by the action of the wings. In one of Mr. N.'s experiments, a single Humble-bee, 
 in a state of violent excitement, communicated to three cubic inches of air as much as 4 
 of heat within five minutes; its own temperature being raised 7 in the same time. When 
 several individuals in a state of excitement, however, are clustered together, so that the loss 
 of heat is prevented, the elevation of temperature is much more considerable; thus a ther- 
 mometer introduced among seven "Nursing-Bees" stood at 92^, whilst the external air 
 was only 70; and the temperature of a hive was raised by disturbing it, during winter, 
 from 4S^ to 102, the temperature of the air being only 34 at the time ! In all these 
 instances, the amount of Oxygen consumed bears an exact proportion to that of the Heat 
 evolved. 
 
 890. In the higher animals, as in the lower, exercise has a considerable 
 effect in producing an elevation of temperature ; and, that this is not merely 
 due to the acceleration of the circulation, is shown by the very curious fact, 
 that the exercise of a particular muscle will cause an increase in the heat 
 liberated from it, as shown by needles plunged in its substance, and connected 
 with the thermo-multiplier.* It may, indeed, be stated as a general proposi- 
 tion, applicable as well to different parts of the same being, as to different 
 individuals, that the development of Heat is proportional to the activity of the 
 molecular processes which constitute the functions of Nutrition, Secretion, 
 &c. ; increasing with their activity, and diminishing with their torpor. It is 
 very easy to explain, on this principle, the known influence of the Nervous 
 system on the calorific function : since, although the molecular changes in the 
 organized fabric are not dependent upon the agency of that system, they are 
 very much influenced by it; and thus we can readily understand how a state 
 of nervous excitement may produce an elevation of temperature, whilst a de- 
 pression of nervous power occasions a cooling of the body. The experi- 
 ments of Sir B. Brodie, Chossat, and others, in which a greater or less 
 portion of the nervous centres was removed, and the animal cooled notwith- 
 standing the maintenance of the circulation, by no means prove that the 
 Nervous system is directly concerned in the production of heat; since in all 
 such experiments, there is a gradual loss of those other vital powers, which 
 are concerned in the function of calorification. From the experiments of Dr. 
 W. Philip and Dr. Hastings, it appears that an animal whose nervous centres 
 have been removed, cools much faster when left to itself, than when Artifi- 
 cial Respiration is practised; and that, if the cooling have made much pro- 
 gress before the artificial respiration is caused to commence, the temperature 
 may be raised; and this, too, in spite of the very imperfect manner in which 
 natural Respiration is replaced by movements artificially effected. 
 
 891. That the maintenance of Animal Heat is due in part to those molecu- 
 lar changes, to which the Cutaneous Respiration is subservient, appears from 
 
 * See the experiments of MM. Becquerel and Breschet, in Ann. des Sci. Nat. N. S. Zool., 
 torn. vi. 
 
682 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 
 
 the following experiments recently performed by MM. Becquerel and Bres- 
 chet. The hair of Rabbits was shaved off, and a composition of glue, suet, 
 and resin, forming a coating through which air could not pass, was applied 
 over the whole surface. It might seem natural to suppose that, by preventing 
 the evaporation of the sweat, the temperature of the tissues would be very 
 sensibly increased ; and that, by this increase of the temperature of the whole 
 body, a high state of fever would be engendered, with the symptoms of which 
 the animal would at last die. But the contrary occurred. In the first Rabbit, 
 which had a temperature of 100 before being shaved and plastered, it had 
 fallen to 891 by the time the material spread over him was dry. An hour 
 after, the thermometer placed in the same parts (the muscles of the thigh and 
 chest) had descended to 76. In another Rabbit, prepared with more care, 
 by the time that the plaster was dry, the temperature of the body was not 
 more than 51 above that of the surrounding medium, which was at that time 
 69s; and in an hour after this, the animal died. These experiments place 
 in a very striking point of view the importance of the Cutaneous surface as a 
 respiratory organ, even in the higher animals: and they enable us to under- 
 stand how, when the secreting power of the Lungs is nearly destroyed by 
 disease, the heat of the body is kept up to its natural standard by the action 
 of the Skin. A valuable therapeutic indication, also, is derivable from the 
 knowledge which we thus gain, of the importance of the Cutaneous Respira- 
 tion ; for it leads us to perceive the desirableness of keeping the skin moist, 
 in those febrile diseases in which there are great heat and dryness of the sur- 
 face, since secretion cannot properly take place through a dry membrane. Of 
 the relief afforded by cold or tepid sponging in such cases, experience has 
 given ample evidence. 
 
 892. All the foregoing facts point to the formation of Carbonic Acid, by the 
 union of the Oxygen absorbed from the air with Carbon set free from the 
 body, as the main source of the evolution of Heat within the Animal sys- 
 tem. The precise mode in which this union is accomplished, is not yet 
 known; but it is certain that, in whatever manner the combination may take 
 place, a certain measure of caloric must be generated. The combustion of 
 from 5 to 10 oz. of Carbon per day, however, would be by no means suffi- 
 cient to keep up the temperature of the Human body to its proper standard ; 
 for it has been experimentally ascertained, that the amount of Caloric set free 
 by a warm-blooded animal in a given time is more than can be thus accounted 
 for. It does not hence follow, however, that we are to look to any other than 
 Chemical processes, for the explanation of this most important function; since 
 there can be no doubt that there are many other changes of composition, con- 
 tinually taking place in the living body, which have their share in the pro- 
 duction of the effect. These take place, for the most part, at the expense of 
 the surplus of Oxygen absorbed over that which is given out in the form of 
 Carbonic Acid; this surplus amounting to as much as 15 per cent, of the 
 whole ( 766). Of the manner in which this surplus is employed, no precise 
 account can be given ; but there can be little doubt that part of it is expended 
 in uniting with Hydrogen, to form a portion of the watery vapour which is 
 exhaled from the lungs; and that another part unites with the Phosphorus 
 and Sulphur which are taken in as food (forming part of the proteine-com- 
 pounds ( 114), to be excreted as Phosphates and Sulphates ( 847). These 
 and other changes, in which the absorbed Oxygen participates, will be attended 
 with the evolution of Caloric ; and thus we are probably to account for the 
 excess of Heat generated by a warm-blooded animal in a given time, above 
 that which would be produced by the combustion of the amount of Carbon 
 exhaled by it during the same period; as shown in the experiments of Dulong 
 
DEVELOPMENT OF HEAT. 683 
 
 and Despretz.* Although, therefore, the Chemical doctrine of Calorification 
 cannot be regarded as yet perfected as to its details, there can be no reasonable 
 doubt that it is altogether sufficient to account for the phenomena in question. 
 And it may be stated as a general fact, that the production of Animal Heat is 
 due to the various changes in Chemical composition, that are continually 
 taking place within the system ; of which changes, the absorption of Oxygen, 
 and the disengagement of Carbonic Acid, are the two chief external manifesta- 
 tions: and that the degree of Caloric liberated bears a close relation to the 
 activity of these changes, either in regard to the body at large, or to any 
 portion of it. 
 
 893. The researches of Dr. Edwards upon Animal Heat have brought to 
 light some very interesting facts, regarding the diversity which exists as to 
 the power of generating heat, in the same species of animal, at different ages, 
 and at different periods of the year. 
 
 a. It appears to be a general fact, that the younger the animal, the less is its independent 
 calorifying power. The development of the embryo of oviparous animals is entirely de- 
 pendent upon the amount of external warmth supplied to it; and there are many kinds of 
 Birds, which, at the time they issue from the egg, are so deficient in the power of generating 
 heat, that their temperature rapidly falls, when they are removed from the nest and placed 
 in a cold atmosphere. It was shown by collateral experiments, that the loss of heat was 
 not to be attributed to the absence of feathers, nor to 'the extent of surface exposed in com- 
 parison with the bulk of the body; and that nothing but an absolute deficiency in the power 
 of generating it, would account for the fall of temperature. This is quite conformable to 
 facts well ascertained in regard to Mammalia. The fcetus, during intra-uterine life, has 
 little power of keeping up its own temperature; and in many cases it is much dependent 
 on external warmth, for some time after birth. The degree of this dependence, however, 
 differs greatly in the various species of Mammalia, as among Birds: being less, in propor- 
 tion as the general development is advanced. Thus, young Guinea pigs, which can run 
 about and pick up food for themselves almost as soon as they are born, are from the first 
 independent of parental warmth ; whilst, on the other hand, the young of Dogs, Cats, Rab- 
 bits, &c., which are born blind, and which do not, for a fortnight or more, acquire the same 
 development with the preceding, rapidly lose their heat when withdrawn from contact with 
 jhe body of the mother. 
 
 b. In the Human species it is well known, that external warmth is necessary for the 
 Infant; but the fact is too often neglected (under the erroneous idea of hardening the con- 
 stitution) during the early years of childhood. It is to be carefully remembered, that the 
 development of Man is slower than that of any other animal; and that his calorifying 
 power is closely connected with his general bodily vigour. In the case of children born 
 very prematurely, the greatest attention must be given to the sustenance of the heat of the 
 body ( 932) ; and though the infant becomes more independent of it as development 
 advances, it is many years before the standard can be maintained without assistance, 
 throughout the ordinary vicissitudes . of external temperature. The calorifying power, 
 which is fully possessed by adults, decreases again in advanced age. Old people complain 
 that their " blood is chill;" and they suffer greatly from exposure to cold, the temperature of 
 their whole body being lowered by it. 
 
 c. These facts have a very interesting connection with the results of statistical inquiries, 
 as to the average number of deaths at different seasons, recorded by M. Queteletf 
 
 * It has been recently shown by Liebig, that the discrepancy between the actual amount 
 of heat generated, and the amount which was calculated to have been produced by the 
 union of Carbon and Hydrogen with Oxygen, to form the Carbonic Acid and Water exhaled, 
 in these experiments, may be nearly reconciled by adopting a more correct estimate of the 
 heat generated by combustion of given quantities of Carbon and Hydrogen respectively. But 
 all these calculations proceed upon the supposition, that the whole amount of Oxygen ab- 
 sorbed, which is not exhaled as Carbonic acid, is exhaled in combination with Hydrogen, as 
 Water ; and thus no account is taken of other combustion-processes going on in the body, by 
 which a greater amount of heat may be generated, than by the combustion of Hydrogen. 
 We have no means whatever of ascertaining how much of the watery vapour thrown off 
 by the lungs and skin is actually formed within the body, and how much is the mere super- 
 fluity of the liquid ingested. 
 
 | Essai de Physique Sociale, torn. i. p. 197. 
 
684 
 
 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 
 
 
 First 
 Month. 
 
 23 
 Years. 
 
 812 
 Years. 
 
 2530 
 Years. 
 
 5065 
 Years. 
 
 90 Years 
 and above. 
 
 January 
 
 1-39 
 
 1-22 
 
 1-08 
 
 1-05 
 
 1-30 
 
 1-58 
 
 February 
 
 1-28 
 
 1-13 
 
 1-06 
 
 1-04 
 
 122 
 
 1-48 
 
 March 
 
 1-21 
 
 1-30 
 
 1-27 
 
 1-11 
 
 1-11 
 
 1-25 
 
 April 
 
 1-02 
 
 1-27 
 
 1-34 
 
 1-06 
 
 1-02 
 
 0-96 
 
 May 
 
 0-93 
 
 1-12 
 
 1-21 
 
 1-02 
 
 0-93 
 
 0-84 
 
 June 
 
 .0-83 
 
 0-94 
 
 0-99 
 
 1-02 
 
 0-85 
 
 0-75 
 
 July 
 
 0-78 
 
 0-82 
 
 0-88 
 
 0-91 
 
 0-77 
 
 0-64 
 
 August 
 
 0-79 . 
 
 0-73 
 
 0-82 
 
 0-96 
 
 0'85 
 
 0-66 
 
 September 
 
 0-86 
 
 0-76 
 
 0-81 
 
 0-95 
 
 0-89 
 
 0-76 
 
 October 
 
 0-91 
 
 0-78 
 
 0-76 
 
 093 
 
 0-90 
 
 0-74 
 
 November 
 
 O93 
 
 091 
 
 0-80 
 
 0-97 
 
 1-00 
 
 1-03 
 
 December 
 
 107 
 
 1-01 
 
 0-96 
 
 0-97 
 
 1-15 
 
 1-29 
 
 We see from this table that, during the first month of infant life, the external temperature 
 has a very marked influence; for the average mortality during each of the three summer 
 months being 80, that of January is nearly 140, and the average of February and March is 
 125. This is confirmed by the result obtained by MM. Villerme and Milne-Edwards, in 
 their researches on the mortality of the children conveyed to the Foundling Hospitals in 
 the different towns in France ; for they not only ascertained that the mortality is much the 
 greatest during the first three months in the year, but also that it varies in different parts of 
 the kingdom, according to the relative severity of the winter. As childhood advances, how- 
 ever, the winter mortality diminishes, whilst that of the spring undergoes an increase ; this 
 is probably due to the greater prevalence of certain epidemics at the latter season ; for the 
 same condition is observed, in a still more remarkable degree, between the ages of 8 and 12 
 years, the time when children are most severely affected by such epidemics. As the con- 
 stitution acquires greater vigour, and the bodily structure attains its full development, the 
 influence of the season upon mortality becomes less apparent; so that at the age of from 
 25 to 30 years, the difference between the summer and winter mortality is very slight. This 
 difference reappears, however, in a very marked degree, at a later period, when the general 
 vigour, and the calorifying powejs undergo a gradual diminution. Between the ages of 50 
 and 65 it is nearly as great as in early infancy ; and it gradually becomes more striking, 
 until, at the age of 90 and upwards, the deaths in January are 158, for every 64 in July (a 
 proportion of 2^ to ] ) ; and the average of the three winter months is 145, whilst that of 
 the three summer months is only 68, or less than one-half. 
 
 894. Not only does the same individual possess different degrees of calori- 
 fying power, at different periods of his life, but also at different seasons of 
 the year. 
 
 a. Dr. Edwards found that Sparrows, when exposed for some time to a temperature of 
 32 during the summer, rapidly lost heat, the refrigeration during 3 hours being from 6 to 
 21 degrees ; but that, when they were placed in the same circumstances during winter (after 
 having been accustomed to a warm temperature) the refrigeration was much less, not being 
 in any instance more than 2 in 3 hours. Although it would be difficult to prove the fact 
 experimentally in regard to Man, there can be little doubt that he shares with the other 
 Mammalia in this variation. It is well known that the general vigour of the system is less 
 in summer than in winter; in hot climates than in moderately cold. Moreover, we con- 
 tinually experience the great discomforts of a cold day in summer; when, our system not 
 being prepared for it, we can less readily maintain our temperature at its normal standard. 
 The practical inference, that we should be much on our guard against exposure to low 
 temperatures during summer, is one of much importance ; and its value has been fully 
 confirmed by experience. The same principle may also be applied to the explanation of 
 the well-known fact, that those who have been long resident in warm climates feel the cold 
 acutely ; whilst those who have been inured to cold are able to resist it much better, than 
 those who are exposed to it for the first time. The former have a continued summer con- 
 stitution ; and their system not being called upon by its external conditions to produce much 
 heat, the power is after a time partially lost. On the other hand, those who live in cold 
 climates have a perpetual winter constitution (as it were) established; and the amount of 
 heat generated by them is much greater. It will be obvious that this must be the case, if 
 Man's capability of living under the greatest varieties of climate be sufficiently considered. 
 From Dr. E.'s experiments it appears, that every month makes an evident difference in the 
 
DEVELOPMENT OF HEAT. 685 
 
 seasonal degree; the heat lost by Sparrows in August being miuh less than that lost by 
 birds of the same species in July. 
 
 895. Our knowledge of the dependence of all the vital processes in warm- 
 blooded animals, upon the Heat of their bodies, and of the dependence of 
 their Calorifying power upon the due supply of material for the Chemical 
 changes which generate Heat, has lately received some very remarkable 
 additions from the experiments of M. Chossat.* He found that Birds, when 
 totally deprived of food and drink, suffered a progressive, though slight, daily 
 diminution of temperature. This diminution was not so much shown by a 
 fall of their maximum heat, as by an increase in the diurnal variation, which 
 he ascertained to occur even in the normal state. The amount of this varia- 
 tion, in Birds properly supplied with food, is about 1 Fahr. daily; the 
 maximum being about noon, and the minimum at midnight. In the in- 
 anitiated state, however, the average variation was about 6, gradually 
 increasing as the animal became weaker: moreover, the gradual rise of tem- 
 perature, which should have taken place between midnight and noon, was 
 retarded; whilst the fall subsequently to noon commenced much earlier than 
 .in the healthy state; so that the average of the whole day was lowered by 
 about 4| between ihe first and the penultimate days of this condition. On 
 the last day, the production of Heat diminished very rapidly, and the ther- 
 mometer fell from hour to hour, until death supervened; the whole loss on 
 that day being about 25 Fahr., making the total depression about 295. 
 This depression appears, from the considerations to be presently stated, to be 
 the immediate cause of Death. On examining the amount of loss sustained 
 by the different organs of the body, it was found that 93 per cent, of the Fat 
 had disappeared, all, in fact, which could be removed; whilst the Nervous 
 Centres scarcely exhibited any diminution in weight. The loss of weight of 
 the whole body averaged about 40 per cent. ; and that of the various other 
 component tissues was very much what might have been anticipated. From 
 the constant coincidence between the entire consumption of the Fat, and the 
 depression of Temperature, joined to the fact that the duration of life under 
 the inanitiating process evidently varied (other things being equal) with the 
 amount of Fat previously accumulated in the body, the inference seems 
 irresistible, that the Calorifying power depended chiefly, if not entirely, on 
 the materials supplied by this substance. The maintenance of the normal 
 amount of matter in the Nervous centres, is a very remarkable fact; and 
 seems to countenance the idea, that the substances peculiar to Nervous tissue 
 may be formed from Fatty matter, rather than from a Proteine-compound 
 ( 249). 
 
 896. Whenever, therefore, the store of combustible matter in the system was 
 exhausted, whether by the Respiratory process alone, or by this in conjunc- 
 tion with the conversion of Adipose matter into the. materials for the Nervous 
 or other tissues, the inanitiated animals died, by the cooling of their bodies 
 consequent upon the loss of Calorifying power. That this is the real expla- 
 nation of the fact, is shown by the results of a series of very remarkable ex- 
 periments performed by M. Chossat, with a view of testing the correctness 
 of this view. When inanitialed animals whose death seemed impending (in 
 several instances death actually took place, whilst the preliminary processes 
 of weighing, the application of the thermometer, &c., were being performed), 
 were subjected to artificial heat, they were almost uniformly restored from a 
 state of insensibility and want of muscular power to a condition of compara- 
 tive activity; their temperature rose, their muscular power returned, they flew 
 
 * Recherches Experimentales sur 1'Inanition, Paris, 1843. See, also, the Brit, and For. 
 Med. Rev. for April, 1844. 
 
 58 
 
686 GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 
 
 about the room and took food when it was presented to them ; and, if the ar- 
 tificial assistance was sufficiently prolonged, and they were not again subjected 
 to the starving process, most of them recovered. If they were left to them- 
 selves too early, however, the digestive process was not performed, and they 
 ultimately died. Up to the time when they began to take food, their weight 
 continued to diminish ; the secretions being renewed, under the influence of 
 artificial heat, sometimes to a considerable amount. It was not until Diges- 
 tion had actually taken place (which, owing to the weakened functional power, 
 was commonly many hours subsequently to the ingestion of the food), that 
 the animal regained its power of generating heat ; so that, if the external 
 source of heat was withdrawn, the body at once cooled : and it was not until 
 the quantity of food actually digested was sufficient to support the wants of 
 the body, that its independent power of Calorification returned. It is to be 
 remembered that, in such cases, the resources of the body are on the point of 
 being completely exhausted, when the attempt at re-animation is made ; con- 
 sequently it has nothing whatever to fall back upon ; and the leaving it to itself 
 at any time until fresh resources have been provided for it, is consequently 
 as certain a cause of death, as it would have been in the first instance. It 
 can scarcely be questioned, from the similarity of the phenomena, that Inani- 
 tion, with its consequent depression of temperature, is the immediate cause 
 of death in various Diseases of Exhaustion ; and it seems probable that there 
 are many cases, in which the depressing cause is of a temporary nature, and 
 in which a judicious and timely application of artificial Heat might prolong 
 life until it has passed off, just as artificial Respiration is serviceable in cases 
 of Narcotic Poisoning ( 885). It is especially, perhaps, in those forms of 
 Febrile disease, in which no decided lesion can be discovered after death, that 
 this view has the strongest claim to reception ; but many other cases will 
 occur to the intelligent Practitioner.* 
 
 897. Having thus considered the means, by which the degree of Heat ne- 
 cessary for the performance of the functions of the Human system is gene- 
 rated, we have to inquire how its temperature is prevented from being raised 
 too high ; in other words, what Frigorifying means there are, to counter- 
 balance the influence of causes, which in excess would otherwise be fatal, by 
 raising the heat of the body to an undue degree. How is it, for example, 
 that, when a person enters a room whose atmosphere is heated to one or 
 two hundred degrees above his body, the latter does not partake of the eleva- 
 tion, even though exposed to the heat for some time ? Or, since the inhabitants 
 of a climate where the thermometer averages 100 for many weeks together, 
 are continually generating additional heat in their own bodies, how is it that 
 this does not accumulate, and raise them to an undue elevation ? The means 
 provided by Nature for cooling the body when necessary, are of the simplest 
 possible character. From the whole of its soft moist surface, simple Evapo- 
 ration will take place at all times, as from an inorganic body in the same cir- 
 cumstances ; and the amount of this will be regulated merely by the condi- 
 tion of the atmosphere as to warmth and dryness. The more readily watery 
 vapour can be dissolved in atmospheric air, the more will be lost from the 
 
 * The beneficial result of the administration of Alcohol in such conditions, and the large 
 amount in which it may be given with impunity, may probably be accounted for on this 
 principle. That it is a specific stimulus to the Nervous system, cannot be doubted from its 
 effects on the healthy body; but that it serves as a fuel to keep up the Calorifying. process, 
 appears equally certain. Now its great efficacy in such cases seems to depend upon the 
 readiness with which it will be taken into the Circulation, by a simple act of Endosmotic 
 Imbibition, when the special Absorbent process dependent upon the peculiar powers of the 
 cells of the villi ( 181 ), is in abeyance. There is no other combustible fluid, whose density, 
 relatively to that of the Blood, will permit of its rapid Absorption by the simple physical 
 process adverted to. 
 
OF REPRODUCTION. 687 
 
 surface of the body in this manner. In cold weather, very little is thus carried 
 off, even though the air be dry : and a warm atmosphere, already charged 
 with dampness, will be nearly as ineffectual. But simple evaporation is not 
 the chief means by which the temperature of the body is regulated. The 
 Skin, as already mentioned ( 868), contains a large number of glandulae, the 
 office of which is to secrete an aqueous fluid ; and the amount of this Exha- 
 lation appears to depend solely or chiefly upon the temperature of the sur- 
 rounding air. Thus, when the external heat is very great, a considerable 
 amount of fluid is transuded from the skin ; and this, in evaporating, converts 
 into latent heat a large quantity of the free caloric, which would otherwise 
 raise the temperature of the body. If the atmosphere be hot and dry, and 
 also be in motion, both Exhalation and Evaporation go on with great rapidity. 
 If it be cold, both are checked, the former almost entirely so ; but if it be 
 dry, some evaporation still continues. On the other hand, in a hot atmosphere, 
 saturated with moisture, Exhalation continues, though Evaporation is almost 
 entirely checked; and the fluid poured out by the exhalant glands accumulates 
 on the skin. There is reason to believe that the secretion continues, even 
 when the body is immersed in water, provided its temperature be high. We 
 learn from these facts the great importance of not suddenly checking Exhala- 
 tion, by exposure of the surface to cold, when the secretion is being actively 
 performed ; since a great disturbance of the circulation will be likely to ensue, 
 similar to that which has been already mentioned, as occurring when other 
 important secretions are suddenly suspended. 
 
 CHAPTER XVII. 
 
 OF REPRODUCTION. 
 
 1. General Character of the Function. 
 
 898. THE Function of Reproduction has been commonly regarded as so 
 entirely different in character from the ordinary Nutritive processes, that no 
 analogy can be drawn between them. The results of late inquiries, however, 
 leave nO doubt that the difference between them is extremely small, having, 
 in fact, a relation rather to the object of the action, than to the mode in which 
 it is performed. In the ordinary function of Nutrition, there is a continual 
 regeneration or reproduction of the tissues and organs of the body; but the 
 new parts are destined still to constitute the same whole. On the other hand, 
 in Reproduction, the newly-formed parts are destined from the first to be cast 
 off from the parent structure, and to become new individuals. Still, their ori- 
 gin is essentially the same in both instances ; as appears from the mode in 
 which the multiplication of the lower Plants and Animals takes place. Thus 
 in the simplest Cryptogamia, such as the Yeast Fungus,* every single cell 
 may be regarded as a distinct individual ; since it is capable of living by itself, 
 and of generating new cells ; and thus the production of a new cell, in con- 
 nfection with the original one, may be regarded as alike an act of Nutrition 
 and of Reproduction. So again, in the Hydra and other Polypes, the remark- 
 able power of reparation which is manifested in their Nutritive operations, 
 
 * See Principles of General and Comparative Physiology, 98. 
 
688 OF REPRODUCTION. 
 
 may be employed in generating new individuals ; since, when the body is 
 divided into numerous parts, each one of these has the power of developing 
 all the rest of the structure, and thus of becoming a complete animal ( 9). 
 Still we find in most Plants, and in all Animals, some portion of the structure 
 specially designed to form and to set free germs, which are destined to become 
 new individuals ; and it is in the liberation and development of these, that the 
 function of Reproduction essentially consists. 
 
 899. In Plants it is very evident that these germs differ but little from 
 those which elsewhere produce new cells ( 122) ; and that the first aspect 
 of the new being is neither more nor less than a single cell, in which all the 
 other cells of the structure subsequently originate. In the Cryptogamia, the 
 cell-germs are contained in what is termed the spore; and, when liberated 
 from the parent, they are developed into cells without any further assistance 
 than that which they derive from the air, moisture, &c., that surround them. 
 In Flowering Plants, on the other hand, the cell-germs are conveyed into a 
 new set of organs, in which they are supplied with nutriment previously ela- 
 borated for them by the parent ; and, in this manner, they are enabled to attain 
 an ultimate development which is much higher than that of the Cryptogamia. 
 It is now well established, that the pollen-grain of Phanerogamia is analogous 
 to the spore of Cryptogamia; since it-contains the reproductive granules, which 
 are the germs of the first cells of the new individual. When the pollen-grains 
 are cast upon the stigmatic surface, they project one or more long tubes, which 
 insinuate themselves down the soft loose tissue of the style, and reach the 
 ovarium. Into these tubes, the granules which the pollen-grain contained are 
 seen to pass ; and they are thus conveyed into the ovules, the foramina of 
 which are penetrated by the extremities of the pollen-tubes. The ovules 
 previously contained nothing but- starchy matter; but from the time that the 
 pollen-tubes have thus implanted (as it were) their contents in their cavity, 
 they may be considered as fecundated. The subsequent growth of the embryo 
 from the first-formed cells, takes place according to the principles already 
 stated, under the head of Nutrition; and thus it is seen, that the mysterious 
 process of Reproduction evidently consists, in Flowering Plants, of nothing 
 else than the implantation of a cell-germ prepared by the male organs, in a 
 nidus or receptacle adapted to aid its early development, which nidus consti- 
 tutes the essential part of the female system. 
 
 900. There is now good reason to believe that, in no Animals, is the Re- 
 productive apparatus less simple than it is in the higher Plants ; that is to 
 say, in every instance, two sets of organs, a germ-preparing, and a germ- 
 nourishing,, are present. These organs differ much in form and complexity 
 of structure in the various tribes of Animals ; but their essential function is 
 the same in all. Those which are termed Male organs prepare and set free 
 certain bodies, which, having an inherent power of motion, have been sup- 
 posed to be independent Animalcules, and have been termed Spermatozoa ; 
 there is but little reason, however, to regard them in this light, since ciliated 
 epithelium-cells may exhibit as much activity ; and there is no evidence that 
 their function is any higher than that of the pollen-tube of Plants, which con- 
 veys into the ovulum the germs of the first cells of the embryo. This view of 
 the character of the Spermatozoa rests alike upon the nature of their move- 
 ments, and the mode of their production.* Dr. Barry's observations on the 
 history of the Ovum, and on the nature of the act of Fecundation (which will 
 be presently given in some detail) have left scarcely any doubt, that this act 
 consists in the introduction of some new element into the Ovule, through the 
 medium of the Spermatozoa ; the arrival of which at the surface of the ovary 
 
 * See Principles of General and Comparative Physiology, 606. 
 
ACTION OF THE MALE. 
 
 had been more than once previously seen, and the penetration of which to the 
 Ovum there was good reason to suspect : and these have been confirmed by 
 the observations of Dr. A. Farre on the Ovum of the Earth-worm, which he 
 has distinctly seen to be penetrated by Spermatozoa. The act of Fecunda- 
 tion is evidently analogous, therefore, in Animals, to the process which has 
 been described as taking place in the Flowering Plants. In many of the 
 lower tribes of Animals, the spermatic fluid effused by an individual of one 
 sex, comes into direct contact with the ova previously deposited by the other ; 
 but in all the higher tribes, as in Man, the act of fecundation is performed be- 
 fore, or shortly after the ova quit the ovarium. With these general views, we 
 shall now be prepared to consider the share which each sex has in the Function 
 of Reproduction. 
 
 2. Action of the Male. 
 
 901. The Spermatic fluid secreted by the Testes of the Male ( 867), differs 
 from all other secretions, in containing a large number of very minute bodies, 
 only discernible with a high power of the Microscope ; and these, in ordinary 
 cases, remain in active motion for some time after they have quitted the living 
 body. The Human Spermatozoon (of which representations are given in 
 Plate I,, Fig. 18), consists of a little oval flattened body from the l-600th to 
 the 1 -800th of a line in length, from which proceeds a long filiform tail gradu- 
 ally tapering to the finest point, of l-50th or at most l-40th of a line in length. 
 The whole is perfectly transparent ; and nothing that can be termed structure 
 can be satisfactorily distinguished within it.* The movements are principally 
 executed by the tail, which has a kind of vibratile undulating motion. They 
 may continue for many hours after the emission of the fluid ; and they are not 
 checked by its admixture with other secretions, such as the urine and the 
 prostatic fluid. Thus, in cases of nocturnal emission, the Spermatozoa may 
 not unfrequently be found actively moving through the urine in the morning; 
 and those contained in the seminal fluid collected from females that have just 
 copulated, are frequently found to live many days. Their presence may be 
 readily detected by a Microscope of sufficient power, even when they have 
 long ceased to move, and are broken into fragments ; and the Physician and 
 the Medical Jurist will frequently derive much assistance from an examination 
 of this kind. Thus, cases are of no uncommon occurrence, especially among 
 those who have been too much addicted to sexual indulgence, in which seminal 
 emissions take place unconsciously and frequently, and produce great general 
 derangement of the health; and the true nature of the complaint is obscure, 
 until the fact has been detected by ocular examination. Again, in charges of 
 rape, in which evidence of actual emission is required, a microscopic exami- 
 nation of the stiffened spots left on the linen will seldom fail in obtaining proof, 
 if the act have been completed : in such cases, however, we must not expect 
 to meet with more than fragments of Spermatozoa; but these are so unlike 
 anything else, that little doubt need be entertained regarding them. It has 
 been proposed to employ the same test, in juridical inquiries respecting doubt- 
 ful cases of death by suspension : seminal emissions being not unfrequent 
 results of this kind of violence: but there are many obvious objections which 
 should prevent much confidence being placed in it.t 
 
 * It has been asserted that distinct oral and anal orifices, with appearances of internal 
 organs, have been seen in the Spermatozoa of certain Mammalia ; but these observations 
 have not been confirmed ; and they are not borne out by the attentive examination of the 
 larger Spermatozoa of other animals. 
 
 f See the Author's Article "Asphyxia," in the Library of Practical Medicine, and the 
 authorities there referred to. 
 
 58* 
 
690 OF REPRODUCTION. 
 
 902. The mode of Evolution of Spermatozoa, which has been recently 
 discovered by Wagner, is so different from the ordinary method of produc- 
 tion amongst Animalcules, as of itself to indicate that the former cannot be 
 referred to the same category with the latter. It may be best studied in those 
 animals which only have a periodical fertility ; and the Passerine Birds are 
 among the most convenient subjects for the purpose. During the winter, the 
 testes are small and almost bloodless, and no trace of Spermatozoa can be 
 detected within them ; on the return of spring, however, they undergo great 
 enlargement and become almost gorged with blood, and the gradual steps of 
 the evolution of the Spermatozoa may be easily observed. The fluid drawn 
 from them is first seen to contain a number of granular corpuscles, resembling 
 those known as the Seminal Granules in the human semen (delineated at , 
 Fig. 18, Plate I.); and in a short time there are seen, in addition to these, 
 numerous rounded transparent vesicles, at first having but one nucleus, and 
 afterwards presenting several. These nuclei bear a close resemblance to the 
 granular corpuscles just mentioned ; and it is probable that the former are to 
 be regarded as cytoblasts, from which the Spermatoferous cells (shown, as 
 existing in the human semen, in Fig. 19, Plate I.) are evolved. The nuclei 
 seem afterwards to resolve themselves into a fine granular matter, which is 
 diffused through the whole vesicle or "cyst of evolution ;" and in this, a linear 
 arrangement soon becomes perceptible. The lines become more and more 
 distinct, and are at last seen to be evidently produced by the arrangement of 
 the Spermatozoa, which lie side by side within the vesicle; and the form of 
 this changes from a sphere to a long oval. After a time they break forth, 
 but still adhere to each other for a short period, forming bundles, such as may 
 often be met with in the human semen, when taken directly from the testis 
 (Fig. 20, Plate I.).* That the Spermatozoa are the essential elements of the 
 spermatic fluid, has been reasonably inferred from several circumstances, such 
 as their absence or imperfect development in hybrid animals, which are nearly 
 or entirely sterile : and the fact that Fecundation essentially consists in the 
 direct communication of one of them with a certain point in the Ovum, ap- 
 pears too well established to admit of further doubt. Regarding the uses of 
 the other constituents of the Semen, no sufficient account can be given. 
 
 903. The power of procreation does not usually exist in the Human Male, 
 until the age of from 14 to 16 years; and it may be considered probable that 
 no Spermatozoa are produced until that period, although a fluid is secreted by 
 the testes. At this epoch, which is ordinarily designated as that of Puberty, a 
 considerable change takes place in the bodily constitution: the sexual organs 
 undergo a much-increased development; various parts of the surface, especially 
 the chin and the pubes, become covered with hair; the larynx enlarges, and 
 the voice becomes lower in pitch, as well as rougher and more powerful ; and 
 new feelings and desires are awakened in the mind. Instances, however, are 
 by no means rare, in which these changes take place at a much earlier 
 period; the full development of the generative organs, with manifestations of 
 the sexual passion, having been observed in children of but a few years old. 
 The procreative power may last, if not abused, during a very prolonged 
 period. Undoubted instances of virility at the age of more than 100 years 
 are on record; but in these cases, the general bodily vigour was preserved in 
 a very remarkable degree. The ordinary rule seems to be, that sexual power 
 is not retained by the male in any considerable degree, after the age of 60 or 
 65 years. To the use of the sexual organs for the continuance of his race, 
 
 * For a fuller account, with illustrations, of the development of the Spermatozoa, and its 
 analogy with the formation of other tissues, see Princ. of Gen. and Comp. Phys., 430 
 and 007. 
 
ACTION OF THE MALE. 691 
 
 Man is prompted by a powerful Instinctive desire, which he shares with the 
 lower animals. This Instinct, like the others formerly alluded to ( 428 
 430), is excited by sensations ; and these may either originate in the sexual 
 organs themselves, or may be excited through the organs of special sensation. 
 Thus in Man it is most powerfully aroused by impressions conveyed through 
 the sight or the touch : in many other animals, the auditory and olfactive organs 
 communicate impressions which have an equal power ; and it is not impro- 
 bable that, in certain morbidly-excited states of feeling, the same may be the 
 case in ourselves. That local impressions have also a very powerful effect in 
 exciting sexual desire, must have been within the experience of almost every 
 one ; the fact is most remarkable, however, in cases of Satyriasis, which dis- 
 ease is generally found to be connected with some obvious cause of irritation 
 of the generative system, such as pruritus, active congestion, &c. That some 
 part of the Encephalon is the seat of this, as of other instinctive propensities, 
 appears from the considerations formerly adduced ; but that the Cerebellum 
 is the part in which this function is specially located, cannot be regarded as 
 by any means sufficiently proved ( 466 470). The instinct, when once 
 aroused (even though very obscurely felt), acts upon the mental faculties and 
 moral feelings; and thus becomes the source, though almost unconsciously so 
 to the individual, of the tendency to form that kind of attachment towards one 
 of the opposite sex, which is known as love. This tendency cannot be re- 
 garded as a simple passion or emotion, since it is the result of the combined 
 operations of the reason, the imagination, and the moral feelings ; and it is in 
 the engraftment (so to speak) of the psychical attachment, upon the mere 
 corporeal instinct, that a difference exists between the sexual relations of Man 
 and those of the lower animals. In proportion as the Human being makes 
 the temporary gratification of the mere sexual appetite his chief object, and 
 overlooks the happiness arising from spiritual communion, which is not only 
 purer but more permanent, and of which a renewal may be anticipated in 
 another world, does he degrade himself to the level of the brutes that perish. 
 Yet how lamentably frequent is this degradation ! 
 
 1 904. When impelled by sexual excitement, the Male seeks intercourse with 
 the Female, the erectile tissue of the genital organs becomes turgid with blood 
 ( 748), and the surface acquires a much-increased sensibility ; this is espe- 
 cially acute in the Glans penis. By the friction of the Glans against the rugous 
 walls of the Vagina, the excitement is increased ; and the impression which 
 is thus produced at last becomes so strong, that it produces, through the 
 medium of the Spinal Cord, a reflex contraction of the muscles which sur- 
 round the Vesiculae Seminales ( 393). These receptacles discharge their 
 contents (partly consisting of semen and partly of a secretion of their own) 
 into the Urethra; and from this they are expelled with some degree offeree, 
 and with a kind of convulsive action, by its own Compressor muscles. Now 
 although the sensations concerned in this act are ordinarily most acutely plea- 
 surable, there appears sufficient evidence that they are by no means essential to 
 its performance; and that the impression which is conveyed to the Spinal Cord 
 need not give rise to a sensation, in order to produce the reflex contraction of 
 the Ejaculator muscles ( 372). The high degree of nervous excitement 
 which the act of coition involves, produces a subsequent depression of corre- 
 sponding amount ; and the too frequent repetition of it is productive of conse- 
 quences very injurious to the general health. This is still more the case with 
 the solitary indulgence, which (it is to be feared) is practised by too many 
 youths ; for this, substituting an unnatural degree of one kind of excitement, 
 for that which is wanting in another, cannot but be still more trying to the 
 bodily powers. The secretion of seminal fluid being, like other secretions, 
 very much under the control of the nervous system, will be increased by the 
 
692 OF REPRODUCTION. 
 
 continual direction of the mind towards objects which awaken the sexual pro- 
 pensity ( 626, note) ; and thus, if intercourse be very frequent, a much larger 
 quantity will altogether be produced, although the amount emitted at each 
 period will be less. The formation of the secretion seems of itself to be a 
 much greater tax upon the corporeal powers, than might have been supposed 
 a priori: and it is a well-known fact, that the highest degree of bodily vigour 
 is inconsistent with more than a very moderate indulgence in sexual inter- 
 course ; whilst nothing is more certain to reduce the powers, both of body 
 and mind, than excess in this respect. These principles, which are of great 
 importance in the regulation of the health, are but results of the general law, 
 which prevails equally in the Vegetable and Animal kingdoms, that the 
 Development of the Individual, and the Reproduction of the Species, stand 
 in an inverse ratio to each other. 
 
 3. Action of the Female. 
 
 905. The essential part of the Female Generative system is that in which 
 the Ova are prepared ; the other organs are merely accessory, and are not to 
 be found in a large proportion of the Animal kingdom. In many of the lower 
 animals, the Ovaria and Testes are so extremely like each other, that the dif- 
 ference between them can scarcely be distinguished ; and the same has already 
 been stated, regarding the condition of these organs in Man, at an early period 
 of development ( 866 6). The fact is one of no small interest. In the lower 
 animals, the Ovarium consists of a loose tissue containing many cells, in which 
 the Ova are formed, and from which they escape by the rupture of the cell- 
 walls ; in the higher animals, as in the Human female, the tissue of the Ova- 
 rium is more compact, forming what is known as the stroma; and the Ova, 
 except when they are approaching maturity, can only be distinguished in the 
 interstices of this, by- the aid of a high magnifying power. We owe to Dr. 
 Barry the discovery of the earliest stages in the production of the Ovum and 
 its accessory parts, in Mammalia and other Vertebrata. In order to under- 
 stand his account, however, it will be necessary that the parts of which the 
 ovum consists should be previously understood. Taking the Fowl's Egg as a 
 familiar illustration, it must be remarked, in the first place, that neither the 
 albumen which forms the white, nor the shell-membrane with its testaceous 
 covering, exist in the Ovarian Ovum ; these portions being added during its 
 passage along the oviduct. The parts which we have to analyze, are the 
 Yolk-membrane and its contents. Within the Yolk-membrane, we find in the 
 first place, the Yolk itself; a substance consisting in part of albuminous gran- 
 ules, and in part of oily globules. Towards the centre, the character of the 
 Yolk in some degree changes ; its colour being lighter, and the granules pre- 
 senting more the appearance of cells, with minuter globules in their interior. 
 The central portion is termed the discus vitellinus. Occupying the centre of 
 the yolk (in the immature ovulum) is a large cell, very distinct in aspect from 
 the rest, and having a well-marked nucleus upon its walls. This is termed 
 the germinal vesicle; and the nucleus, the germinal spot. The Mammalian 
 Ovum contains exactly the same parts ; but the yolk is much smaller in pro- 
 portion, and corresponds in character rather with the discus vitellinus, than 
 with the whole yoljt of the Bird's egg. The Ovum in all Vertebrated animals 
 is produced within a capsule or bag, the exterior of which is in contact with 
 the stroma of the ovarium ; this has been termed in Mammalia, the Graafian 
 follicle, after the name of its first discoverer ; but the more general and ap- 
 propriate designation of Ovisac has been given to it by Dr. Barry, who has 
 shown that it exists in other classes of Vertebrata. Between the Ovum and 
 the Ovisac, in Oviparous animals, there is scarcely any interval ; but in the 
 
ACTION OF THE FEMALE. 603 
 
 Mammalia, a large amount of granular matter is present ; and this arranges 
 itself into some peculiar structures discovered by Dr. Barry, and presently to 
 be described. The membrane which surrounds the yolk in Mammalia has 
 received, on account of its thickness and peculiar transparency, the designation 
 of zona pellucida. The several parts of the Ovum now described are shown 
 in Fig. 5, Plate I. 
 
 906. From the researches of Dr. Barry on the early development of the 
 Ovum, it appears that the Germinal Vesicle is the part which can first be 
 distinctly traced. In Fig. 1 (Plate I.) is seen a representation of one of its 
 incipient stages in the Rabbit; there is nothing here visible, but a collection 
 of very transparent vesicles, surrounded by a mass of dark granules. In the 
 succeeding stage, represented in Fig. 2, some of the vesicles have enlarged, 
 and the granules immediately surrounding them have become developed into 
 cells. A more advanced condition is represented (on a smaller scale) in Fig. 
 3 ; in which a distinct spot (b) is seen on the central vesicle (a), marking it as 
 the Germinal Vesicle ; whilst many of the granules surrounding it have be- 
 come cells, and have taken-on a very regular arrangement. After a time, a 
 membrane forms around each cluster of granules, separating it from the stroma 
 of the ovarium ; this is the Ovisac. At a later period, a separation takes place 
 between the inner and outer portions of the mass of granular matter, included 
 between the ovisac and the germinal vesicle ; and the separation is completed 
 by the development of a membrane, which envelopes the inner stratum. This 
 stratum becomes the Yolk, and includes most of the oil-particles which pre- 
 viously existed within the ovisac ; whilst the portion of the granular mass, 
 exterior to this, gives origin in Mammalia to certain structures of a very pe- 
 culiar character, which seem to be concerned in the liberation of the ovum 
 from the Graafian follicle or Ovisac. The appearance of the Human Ovisac 
 and its contents is seen in Fig. 4. The granules immediately surrounding 
 the Ovum assume the appearance of cells ; and these unite to form a sort of 
 membrane, to which the name of tunica granulosa has been given. This is 
 seen at t g (Fig. 7). The granules lining the Ovisac also combine themselves 
 into a membranous structure ; to which Dr. Barry has given the designation 
 of membrana granulosa (g g. Fig. 6). These are connected by four band- 
 like extensions of the same cellulo-membranous structure, which seem to sus- 
 pend the ovum in its place ; and these are called retinacula (r r, Figs. 6 and 
 7). The space between the Tunica Granulosa and the Membrana Granulosa, 
 which is not occupied by the Retinacula, is filled with fluid, in which few or 
 no cells can be seen. The uses of this structure, so far as they are apparent, 
 will be described, when the processes by which the Ovum escapes from the 
 Ovary are detailed. 
 
 907. The Ovisac does not form the entire structure which has been described 
 as the Graafian follicle ; for this consists of two layers, of which the inner 
 one is the true Ovisac, whilst the outer results from a thickening and conden- 
 sation of the surrounding layer of the Stroma of the Ovarium. It is the outer 
 layer only which is vascular ; the inner presents no trace of structure ; and 
 the increase of the ovum must take place by simple imbibition, through it, of 
 the supply of nutritive matter brought into contact with its exterior. The 
 Ovarium may be seen, even in the fetal animal, to contain immature Ova ; in 
 which the several parts can be clearly distinguished. At a later period, how- 
 ever, the number of Ova greatly increases ; and the development of some ad- 
 vances, whilst others degenerate. According to the recent valuable inquiries 
 of Dr. Ritchie,* it appears that, even during the period of childhood, there is a 
 continual rupture of Ovisacs, and discharge of Ova, at the surface of the 
 
 * London Medical Gazette, 1844. 
 
694 OF REPRODUCTION. 
 
 Ovarium. The Ovaria are studded with numerous minute copper-coloured 
 maculae ; and their surface presents delicate vesicular elevations, which are 
 occasioned by the most matured ovisacs : the dehiscence of these takes place 
 by minute punctiform openings in the peritoneal coat ; and no cicatrix is left. 
 At the period of puberty, the stroma of the ovarium is crowded with Ovisacs; 
 which are still so minute, that in the Ox (according to Dr. Barry's computa- 
 tion) a cubic inch would contain 200 millions of them. The greatest advance 
 is seen in those which are situated nearest the surface of the Ovarium; and 
 in these, the Graafian follicle with its two coats, may be distinctly traced. It 
 is curious that the outer wall (which is itself a part of the condensed stroma 
 of the ovarium) should contain an immense number of minute ovisacs ; so 
 that this, in the adult animal, is the most convenient situation in which to 
 view them: these ovisacs have been termed by Dr. Barry " parasitic ovisacs." 
 In those animals whose aptitude for conception is periodical, the development 
 of the Ova, to such a degree that they become prepared for fecundation, is 
 periodical also. This development becomes evident, when the parts are ex- 
 amined in an animal which is " in heat," by the projection of the Graafian 
 follicles from the surface ; and it consists not merely in an increase of size, 
 but in certain internal changes presently to be described. 
 
 908. In the Human female, the period of Puberty, or of commencing apti- 
 tude for procreation, is usually between the 13th and 16th year; it is earlier 
 in warm climates than in cold ;* and in densely-populated manufacturing towns, 
 than in thinly peopled agricultural districts. The mental and bodily habits 
 of the individual have also a considerable influence upon the time of its 
 occurrence ; girls brought up in the midst of luxury or sensual indulgence, 
 undergoing this change earlier than those reared in hardihood and self-denial. 
 The changes in which Puberty consists, are for the most part connected with 
 the Reproductive system. The external and internal organs of generation 
 
 [*It has been stated, by almost all physiological writers, that women reach maturity, and 
 that menstruation commences much earlier in hot climates, particularly between the tropics, 
 than in temperate and very cold countries. Haller states that in the warm regions of Asia, 
 the catamenia appear from the 8th to the 10th year; and in Switzerland, Britain, and other 
 temperate regions, at the age of 12 or 13, and later the farther we ascend towards the north. 
 The same view has been held by nearly all subsequent writers on the subject, and they infer 
 that animals, like plants, reach maturity sooner in hot than in cold climates. Dewees says 
 that menstruation occurs later in our northern than in our southern states. From many 
 elaborate and interesting papers which have been published within a few years, especially 
 from those of Mr. Roberton of Manchester, it would seem that the natural period of puberty 
 in women occurs in a much more extended range of agesy and is much more equally dis- 
 tributed through that range than others have alleged, and that, in other countries, the parallel 
 between plants and fruits does not hold good. 
 
 At Gottingen, Osiander ascertained the ages at which 1 37 women began to menstruate. 
 In 21 of these the catamenia appeared at 14; in 32 at 15; in 24 at 16; 9 at 12 ; and 1 not 
 before the 24th year. The Indian girls in Canada, and in our north-western states and ter- 
 ritories, begin to menstruate frequently at 12, 13 and 14. From the statement of Baron 
 Humboldt, the same is equally true of the Korriacs, and the tribes of northern Asia, where 
 girls of 10 years are sometimes found mothers. The notion that women in Lapland do not 
 menstruate till 20,vand then only during summer, is founded on a mistake in Linnaeus's 
 Flora Lapponica. Tooke states that the Sclavonian, or native Russians, reach puberty at an 
 early age ; and Dr. Robert Lee, who was in the Crimea, and all the Russian provinces along 
 the Black Sea, and in the Ukraine, and whose opportunities of observation were extensive, 
 says that his conviction is, that over the whole south of Russia the period of puberty is the 
 same as in Great Britain ; and that women cease to bear children at the same age. The 
 same would appear to hold good in Java, and in all the islands of the Indian Archipelago, and 
 in Sierra Leone; and the difference said to exist in Arabia in this respect is due to the 
 early marriages, and universal licentiousness and depravity of morals in that country. It 
 would appear from observations made in the West India Islands, that menstruation occurs 
 there about the same period, and that the alleged difference in this respect between the 
 negress and the white female does not exist. M. C.] 
 
ACTION OF THE FEMALE. 695 
 
 undergo a considerable increase of size ; the mammary glands enlarge ; and a 
 deposition of fat takes place in the mammae and on the pubes, as well as over 
 the wjiole surface of the body,- giving to the person that roundness and ful- 
 ness, which are so attractive to the opposite sex, at the period of commencing 
 Womanhood. The first appearance of the Catamenia usually occurs whilst 
 these changes are in progress, and is a decided indication of the arrival of the 
 period of Puberty; but it is not unfrequently delayed much longer; and its 
 absence is by no means to be regarded as a proof of the want of aptitude for 
 procreation, since many women have borne large families, without having ever 
 menstruated. The Catamenial discharge appears normally to consist of blood 
 deprived of its fibrine ; the fluid being composed of serum, in which red cor- 
 puscles are suspended, and being readily distinguishable from true blood by 
 its want of power to clot. When clots are found in it, therefore, a morbid 
 condition of the secreting surface must be inferred. The interval which usu- 
 ally elapses between the successive appearances of the secretion, is about four 
 weeks ; and the duration of the flow is from three to six days. There is, 
 however, great variety in this respect among the inhabitants of different cli- 
 mates, and among individuals ; in general, the appearance is more frequent, 
 and the duration of the flow greater, among the residents in warm countries, 
 and among individuals of luxurious habits and relaxed frame, than among the 
 inhabitants of colder climes, or among individuals inured to bodily exertion. 
 The first appearance of the discharge is usually preceded and accompanied by 
 considerable general disturbance of the system; especially pain in the loins 
 and a sense of fatigue in the lower extremities ; and its periodical return is 
 usually attended with the same symptoms, which are more or less severe in 
 different individuals. 
 
 909. Much discussion has taken place respecting the causes and purposes 
 of the Menstrual flow ; and recent inquiries have thrown much light upon 
 them. The state of the Female Generative system, during its continuance, 
 appears to be analogous to the heat of the lower animals ; many of which 
 have a sero-sanguinolent discharge at that period. There is good reason to 
 believe that in Women the sexual feeling becomes stronger at that epoch ; 
 and it is quite certain that there is a greater aptitude for Conception, imme- 
 diately before and after Menstruation, than there is at any intermediate period. 
 Observations to this effect were made by Hippocrates, and were confirmed by 
 Boerhaave and Haller ; indeed coitus immediately after menstruation appears 
 to have been frequently recommended as a cure for sterility, and to have 
 proved successful. It is well known that, among many of the lower animals, 
 the Ova are entirely extruded by the Female, before the Spermatic fluid of 
 the Male reaches them ; and that even in Birds, this occasionally takes place. 
 This question has been recently made the subject of special inquiry by M. 
 Raciborski ; who affirms that the exceptions to the rule that Conception 
 occurs immediately before or after, or during, Menstruation are not more 
 than 6 or 7 per cent. Indeed, in his latest work on this subject,* he gives the 
 details of 15 cases, in which the date of Conception could be accurately fixed, 
 and the time of the last appearance of the Catamenia was also known ; and in 
 all but one of them, the correspondence between the two periods was very 
 close. Even in the exceptional case, the Catamenia made their appearance 
 shortly after the Coitus ; which took place at about the middle of the interval 
 between the two regular periods. When Conception occurs immediately be- 
 fore the Menstrual period, the Catamenia sometimes appear, and sometimes 
 are absent ;0f they appear, their duration is generally less than usual, 
 fact that Conception often takes place immediately before the last appearance 
 
 * Sur la Ponte des Mammiferes. Paris, 1844. 
 
696 OF REPRODUCTION. 
 
 of the Catamenia (and not after it, as commonly imagined), is one well known 
 to practical men. Numerous cases have been collected by Mr. Girdwood, 
 Dr. Robert Lee, MM. Gendrin, Negrier, Raciborski, and others, in which the 
 Menstrual period was evidently connected with the maturation and discharge 
 of Ova ; but the most complete observations yet made upon this subject, are 
 those of Dr. Ritchie (loc.''cit.) He states that about the period of Puberty a 
 marked change usually takes place in the mode in which the Ovisacs discharge 
 their contents ; but that this change does not necessarily occur simultaneously 
 with the first appearance of the Catamenia ; as in some cases the conditions, 
 which obtain in the period before puberty, are extended into that of menstrua- 
 tion. The Ovaries now receive a much larger supply of blood; and the Ovi- 
 sacs show a great increase in bulk and vascularity ; so that, when they appear 
 at the surface of the ovary, they present themselves as pisiform turgid eleva- 
 tions ; and the discharge of their contents leaves a much larger cicatrix, and 
 is accompanied by an effusion of blood into their cavity, with other subsequent 
 changes, to be presently described. It would appear, however, that although 
 such a discharge takes place most frequently at the Menstrual period, yet that 
 the two occurrences are not necessarily co-existent; for menstruation may 
 take place without any such rupture ; whilst, on the other hand, the matura- 
 tion and discharge of mature ova may occur in the intervals of Menstruation, 
 and even at periods of life when that function is not taking place. The 
 essential condition of Menstruation itself would appear to be the increased 
 turgescence of the vessels of the Uterus ; and the appearance, on its internal 
 surface, of a meshwork of deciduous villous vessels, which may remain for at 
 least two weeks. It is evident that this is a preparation for the formation of 
 the Decidua ( 919). 
 
 910. The duration of the period of aptitude for procreation, as marked by 
 the persistence of the Catamenia, is more limited in Women than in Men; 
 usually terminating at about the 45th year; it is sometimes prolonged, how- 
 ever, for ten or even fifteen years longer ; but cases are rare in which women 
 above 50 years of age have borne children. There is usually no Menstrual 
 flow during Pregnancy and Lactation ; in fact, the cessation of the Catamenia 
 is generally one of the first signs, indicating that Conception has taken place. 
 But it is by no means uncommon for them to appear once or twice subse- 
 quently to Conception ; and in some women, there is a regular monthly dis- 
 charge, though probably not of the usual secretion, through the whole period. 
 Some very anomalous cases are recorded, in which the Catamenia never 
 appeared at any other time than during Pregnancy ; and were then regular. 
 The absence of the Catamenia during Lactation is by no means constant, 
 especially if the period be prolonged ; when the Menstrual discharge recurs, 
 it may be considered as indicating an aptitude for Conception ; and it is well 
 known that, although Pregnancy seldom recurs during the continuance of 
 Lactation, the rule is by no means invariable. 
 
 911. The function of the Female, during the coitus, is entirely of a passive 
 character. When the sexual feeling is strongly excited, there is a considera- 
 ble degree of turgescence in the erectile tissue surrounding the vagina, and 
 composing the greater part of the nymphae and the clitoris ; and there is also 
 an increased secretion from the mucous follicles.* But these changes are by 
 
 [* The glands of Duverney have been lately (1840) very accurately described by Profes- 
 sor Tiedemann, his attention having been directed to these organs by the late Dr. Fricke, of 
 Hamburg. These glands are situated at either side of the entrance of the ^agina, beneath 
 the integument covering the inferior part of the vagina, as well as the superficial perineal 
 fascia, and the constrictor vaginae muscle. The space they occupy lies between the lower 
 end of the vagina, the ascending ramus of the ischium, the crus clitoridis, and the erector 
 clitoridis muscle. Superiorly are the fibres of the levator ani which are attached to the 
 
ACTION OF THE FEMALE. 697 
 
 no means necessary for effectual coition ; since it is a fact well established, 
 that fruitful intercourse may take place, when the female is in a state of nar- 
 cotism, of somnambulism, or even of profound ordinary sleep. It has been 
 supposed by some, that the os uteri dilates, by a kind of reflex action, to re- 
 ceive the semen; but of this there is no evidence. The introduction of a 
 small quantity of the fluid just within the Vagina, appears to be all that is 
 absolutely necessary for conception; for there are many cases on record, in 
 which pregnancy has occurred, in spite of the closure of the entrance to the 
 vagina by a strong membrane, in which but a very small aperture existed. 
 That the Spermatozoa make their way towards the Ovarium, and fecundate 
 the Ovum either before it entirely quits the Ovisac or very shortly afterwards, 
 appears to be the general rule in regard to the Mammalia; and the question 
 naturally arises, by what means do they arrive there. It has been supposed 
 that the action of the cilia, which line the Fallopian tubes, might account for 
 their transit; but the direction of this is from the Ovaria towards the Uterus, 
 and would therefore be opposed to it. A peristaltic action of the Fallopian 
 tubes themselves may generally be noticed in animals killed soon after sexual 
 intercourse ; and in those which have a two-horned membranous Uterus, such 
 as is evidently but a dilatation of the Fallopian tube, this partakes of the same 
 movement, as may be well seen in the Rabbit : in animals, however, which 
 have a single Uterus with thicker walls (as in the Human female), it must 
 evidently be unavailable. Among the tribes whose Ova are fertilized out of 
 the body, the power of movement inherent in the Spermatozoa is obviously 
 the means by which they are brought in contact with the Ova : and it does 
 not seem unreasonable to suppose, that the same is the case in regard to the 
 higher classes ; and that the transit of these curious particles, from the Va- 
 gina to the Ovaries, is effected by the same kind of action as that which 
 causes them to traverse the field of the microscope. We shall now consider 
 the changes in the Ovum and its appendages, by which it is prepared for 
 fecundation. 
 
 912. Up to the period when the Ovum is nearly brought to maturity, it re- 
 mains in the centre of the Ovisac or inner layer of the Graafian follicle ; and 
 it is supported in its place by the Retinacula, which connect its Tunica 
 Granulosa with the Membrana Granulosa that lines the ovisac. (See Fig. 6, 
 
 ischiura, and behind these are the transversi-perinei muscles. They are surrounded by very 
 loose cellular tissue. They are rounded, but somewhat elongated, being flat and bean- 
 shaped. Their long diameter is from 5 to 10 lines ; their transverse diameter 2^ to 4 lines, 
 and they are from 2j to 3 lines thick. The excretory duct is at the anterior edge of the 
 superior part of the gland, and runs beneath the constrictor vaginae, horizontally forwards 
 and inwards, to the inner face of the nympha, opening in front of the carunculae myrtiformes, 
 in the midst of a number of small mucous follicles. These glands were first discov^ed by 
 Duverney in the cow, about the middle of the seventeenth century. Bartholinus subse- 
 quently found them in the human female, and his observations were confirmed by Duver- 
 ney, Morgagni, Santorini, Peyer, &c. Haller denied their existence; and such structure 
 seems to have been forgotten until they were again described by Mr. Taylor (Dublin 
 Journal, vol. xiii. 1838). They are analogous to Cowper's glands in the male, according to 
 Tiedemann, and like them are sometimes wanting, and differ in size. In advanced age 
 they are said to diminish in size, and even disappear. They are present in the females of 
 all animals, where Cowper's glands exist in the males. They secrete a thick, tenacious, 
 grayish- white fluid, which is emitted in large quantities, at the termination of the sexual act, 
 most likely from the spasmodic contraction of the constrictor vagina? muscle, under which 
 they lie. Its admixture with the male semen is supposed to probably have some connection 
 with impregnation, and it has been suggested that it may be the vehicle of the fecundating 
 principle of the semen. These glands were probably known to the ancients, and it is doubt- 
 less their secretion which Hippocrates and others describe as the female semen. (1843.) 
 These glands have lately been described by Huguier of Paris, in the Archives d^natomie. 
 His description corresponds in every respect with that given above. (1847.) M. C.] 
 59 
 
698 OF REPRODUCTION*. 
 
 Plate I.) The Ovum then begins to move towards the periphery of the 
 Graafian follicle; and always towards that point of it which is nearest the 
 surface of the Ovary. This movement appears to be due, in the first instance, 
 to the shortening of the Retinacula in that direction ; and whilst the Ovum 
 lies against the membrane of the Ovisac, a gradual thinning of the latter seems 
 to take place. At the same time an important change is occurring in the outer 
 wall of the Graafian follicle, especially at the part most deeply imbedded in 
 the Ovary; its vascularity is greatly increased, and its substance appears 
 thickened. This thickening is probably due to the deposition of blood in a 
 state ready to become more highly organized, upon the exterior of the Ovisac; 
 and the consequence of it is, that considerable pressure is made upon the con- 
 tents of the follicle, the effect of which is, of course, exerted most upon the 
 thinnest part of it. Thus, a sort of vis a tergo is exercised against the Ovum 
 and the Disc (consisting of the tunica granulosa and the central part of the 
 retinacula) in which it is imbedded ; and the whole is forced, by the rupture 
 of the Graafian follicle, into the funnel-shaped entrance of the Fallopian tube, 
 the Retinacula being gradually detached from the Membrana Granulosa, 
 which is left behind. This action is represented in Fig. 8, Plate I. What 
 becomes of the Ovisac is not certain. Dr. Barry affirms that he has some- 
 times known it to be subsequently expelled from the ovary ; but it appears 
 more commonly to coalesce with the surrounding envelope, and to constitute, 
 together with it, the lining of the cavity, which is usually found in the Corpus 
 Luteum. The substance known under this name is found in the Ovary, after 
 the Ovum has escaped from it ; and the importance of the question, how far 
 its presence may be regarded as an indication that Conception has taken 
 place, requires that we should have clear ideas respecting its nature. 
 
 913. The term Corpus Luteum has been usually applied to a reddish-yel- 
 low substance, glandular in aspect, friable in consistence, and very vascular ; 
 which occupies the part of the Ovary from which the germ has escaped, and 
 is larger or smaller according to the length of time that has elapsed since con- 
 ception. At first it is usually so large as to occasion a considerable projection 
 on the surface of the Ovary ; its form is oval, or resembles that of a bean. 
 When cut across, its dimensions are usually found to be from 4 to 5-8ths of 
 an inch in its long diameter, and from 3 to 4-8ths in its short ; and it thus 
 occupies from a fourth to a half of the whole area of the ovarium ; but these 
 dimensions are not unfrequently exceeded. The centre of this substance is 
 hollow ; and by a proper acquaintance with this character, the true Corpus 
 Luteum may be distinguished from substances, bearing a general resemblance 
 to it, but very different in their character. The following is Dr. Mont- 
 gomery's account of it. " Its centre exhibits either a cavity, or a radiated or 
 branching white line, according to the period at which the examination is 
 made. If within the first three or four months after conception, we shall, I 
 believe, always find the cavity still existing, and of such a size as to be capable 
 of containing a grain of wheat at least, and very often of much greater dimen- 
 sions ; this cavity is surrounded by a strong white cyst ; and as gestation 
 proceeds, the opposite parts of this cyst approximate, and at length close to- 
 gether, by which the cavity is completely obliterated, and in its place there 
 remains an irregular white line, whose form is best expressed by calling it 
 radiated or stelliform. This is visible as long as any distinct trace of the 
 Corpus Luteum remains."* The true Corpus Luteum is further distinguished 
 by its capability of being injected from the vessels of the Ovary ; which is 
 not the case with Tubercular deposits, or other substances which may stimu- 
 late it. After Delivery, the size of the Corpus Luteum rapidly diminishes ; 
 
 * Signs of Pregnancy, p. 226. 
 
ACTION OF THE FEMALE. 699 
 
 and in a few months it ceases to be recognizable as such. The cicatrix by 
 which the Ovum has escaped is visible for some time longer ; but this too, 
 according to the careful researches of Dr. Montgomery, cannot be distin- 
 guished at a subsequent period. Hence there is no correspondence between 
 the number of Corpora Lutea found in the ovaries of a woman, or of Cica- 
 trices on their surface, and the number of children she may have borne. The 
 number of Corpora Lutea must always be less, when there have been many 
 conceptions ; but the number of Cicatrices maybe greater; for several causes, 
 such as the escape of unimpregnated ova, or the bursting of little abscesses, 
 may give rise to such appearances. 
 
 914. Much discussion has taken place amongst Embryologists, as to 
 whether the substance of the Corpus Luteum is deposited within the Graafian 
 follicle, externally to it, or between its layers. The first is the opinion of 
 Baer, Bischoff, and others; who regarded it as a growth from the inner layer 
 of the Graafian follicle. The second is the opinion of Dr. R. Lee and Mr. 
 Wharton Jones. The third is the doctrine taught by Drs. Montgomery and 
 Barry ; the former regarding it, however, as deposited between the two layers, 
 of which the cellulo-vascular layer of the Graafian follicle (which are both 
 derived from the condensed stroma of the ovarium) consist ; whilst the latter 
 maintains that the deposit takes place between the true Ovisac and its Ovarian 
 envelopes. The recent inquiries of Dr. Ritchie* throw great light on this 
 question ; by showing that a great variety of changes may take place, after the 
 discharge of the Ovum from the Ovisac ; amongst which may be included all 
 the appearances described by the several writers just quoted. The following 
 is an abstract of the results of Dr. R.'s researches. 
 
 a. The appearances presented by the Ovaries, Graafian follicles, and by the blood which 
 is contained in the latter subsequent to their rupture, vary according to the time at which 
 they are examined, and the absorbing power of the individual. In cases of the recent dis- 
 charge of an Ovum, the Peritoneal coat of the Ovaiy is marked by a jagged slit or opening, 
 having a florid vascular areola ; in those of longer standing, the opening is covered over, 
 with the exception of a minute circular foramen in the centre, (or where the slit has been of 
 great length) of two such openings, with new tissue, surrounded by a claret-coloured mar- 
 gin ; and in those still more ancient, ihe whole is healed up into a cicatrix, which is more 
 or less superficial and free from discoloration, according to its age. 
 
 b. With respect to the Blood, which is generally contained in the ruptured follicles, it is 
 seen first as a florid coagulum ; next, having only its centre scarlet-coloured, and its peri- 
 phery more or less black, and perhaps furrowed ; frequently the clot has a gamboge colour 
 from the decomposition of its red corpuscles, or has become pale from their absorption; and 
 lastly, the clot is found in different stages of absorption. But it sometimes also happens, 
 and that indifferently in every variety of the uterine state, that the ruptured follicles are 
 found empty, or containing only an aqueous fluid. 
 
 c. The coats of the ruptured Follicles have been found in four different general condition?, 
 apparently dependent on their relative degree of organization ; and each class presenting, 
 also, modifications of their respective characteristics, proceeding in part from the same cause, 
 and in part also from changes connected with the period of their progress in which they 
 were examined. 
 
 i. The first class was distinguished by the attenuated state of the coats of the ruptured 
 Follicle; and by the total absence of any organic changes in these, different from their con- 
 dition previous to their discharge. The only alterations observable resulted from the me- 
 chanical dyeing of their coats of an inky-black, or of a yellow colour, proceeding from their 
 contact with decomposed blood. The first class of appearance was found indifferently in 
 all ages and states, subsequent to puberty. 
 
 ir. The second general class of ruptured Follicles was characterized, in addition to the 
 appearances just described, by organic changes in their coats ; consisting, progressively, of 
 an increased vascularity, a thickening, a whitening of the colour, and finally, a corrugation 
 of their tissue. The white bodies thus formed, to which Dr. R. has given the designation of 
 Corpora Jllbida, may exist under two distinct forms: 1. As soft bodies of a yellowish fatty 
 aspect, having the outer coat much thickened, whilst their inner remains as a delicate dia- 
 
 Medical Gazette, 1844. 
 
700 OF REPRODUCTION. 
 
 phanous pellicle ; these, after a lengthened period, present themselves as yellowish-white, 
 and generally globular bodies, more or less fissured from their contraction, and sometimes in 
 process of absorption, having a granular-looking structure, and seldom being divisible into 
 laminae by simple dissection: and 2. As dense bodies of a whitish, shining, firm structure, 
 their inner coat being the seat of these changes, and their outer adhering loosely as a 
 transparent peculiar layer; the inner layer presents itself as a thick, opaque, deeply- 
 wrinkled or corrugated, and rocky cyst, or is sometimes partially diaphanous, and of a shin- 
 ing pearly aspect, and very white colour; and it sometimes contains a yellow, greenish, 
 transparent fluid, or a clot of blood, either unchanged, or converted into a yellow or black 
 pigment. This second variety appears to be the Corpus Luteum of Baer. These white 
 bodies, or Corpora Albida, were found by Dr. R. in every variety of uterine condition, subse- 
 quent to the establishment of menstruation, but never before it ; and the dense kind, espe- 
 cially, were persistent for a long period. They had no necessary connection with the gravid 
 condition; but they were occasionally (especially the dense variety) the only specialty ob- 
 servable in the ovaries of the puerperal female, some time after delivery. 
 
 in. The third class was characterized by the presence of an organized yellow-coloured 
 brain-like, granular matter ; forming bodies to which Dr. R. has given the name of Corpora 
 Cephaloidea. These differed, according as the cerebriform matter was deposited between 
 the layers of ruptured Follicles, having transparent pellicular walls, as in Class i., or having 
 either their inner or outer coat thickened, as in Class u. ; or according as the cerebriform 
 matter was deposited externally to the two inner layers oflhe Follicle. The former of those 
 varieties was found by Dr. Ritchie in menstruating females ; also during the first months of 
 the gravid state ; and sometimes even in the period of lactation. In some instances, only 
 one or two of the cerebriform bodies were found ; but in others, five or six. Their struc- 
 ture, especially in the more perfectly-organized specimens, presented a striking resemblance 
 to the convoluted reddish-yellow surface of the brain, covered by its inner membranes, and 
 painted with its scarlet-coloured and dark vessels. These cephaloid bodies undergo diminu- 
 tion in proportion to their age, and the absorbing power of the female. In those possessed 
 of only thin coats, or having the outer layer as the seat of the thickening, the inner walls of 
 the cysts speedily contracted and coalesced; so that their centres exhibited a delicate opaque 
 streak: or, in those better developed, a serrated, curved, and well-marked white line, ac- 
 cording as the cyst was of elliptical or of a globular form. This variety of cerebriform cyst 
 was met with in a recent state as well in immediate connection with the existence of men- 
 struation, as during the first seven months of pregnancy ; and in this latter case, by under- 
 going a conversion in its form presently to be noticed (iv), they constituted the Corpora 
 Lutea of Dr. Montgomery. In the second variety of Cephaloid bodies, the two inner layers 
 of the Graafian Follicle were converted into a dense white body, surrounded by an envelope 
 of yellow matter. Such cysts (the Corpora Lutea of Dr. Lee) were never observed as an 
 effect of menstruation simply, but were met with exclusively in the gravid female ; although 
 two were seen (as were also the cephaloid bodies of the preceding order) to be present in 
 some cases of single conception. This form of Cephaloid bodies was generally distinguished 
 by large, persistent, white, glistening cavities. The granular cephaloid matter was some- 
 times found quite absorbed within a few days after parturition ; but in other instances it 
 underwent the metamorphosis characteristic of the next class. 
 
 iv. The fourth general state of the ruptured Graafian follicle was peculiar to the impreg- 
 nated and lactating female, in the period between the 8th and 13th months after concep- 
 tion ; and appeared to be a conversion of the Corpora Cephaloidea already described, arising 
 out of a higher and more perfect organization. Down to the 7th month of pregnancy, the 
 cysts contained in the Ovaries did not differ in any respect from the cerebriform bodies 
 found in the unimpregnated state; except that they were sometimes plumper, more vascu- 
 lar, better developed, and had their inner layer more frequently thickened. A change in 
 the hue of the granular matter then commences, which becomes more decided as time 
 elapses; so that by the end of the 1st month after delivery, it becomes of a decided rose 
 colour, changing to a still more florid hue on exposure to air. Its cavity also contracts, so as 
 to leave but a stellated point, or a curved groove : and a fibrous appearance (probably de- 
 pendent on the traction thus exercised) is seen in the surrounding substance. Although 
 these bodies, termed by Dr. Ritchie Corpora rubra, are found exclusively in the later months 
 of pregnancy, or in the puerperal state, yet they are not always present in those conditions. 
 
 The number of cases examined by Dr. Ritchie is not, perhaps, sufficient to 
 enable us to found any positive statements upon the results of his examina- 
 tion of them ; but the following inductions appear highly probable : 1. That 
 the presence of Corpora Rubra may be regarded as indicative, not only of 
 conception, but also of an advanced state of pregnancy, or of recent delivery; 
 but that their absence is not to be regarded as any proof to the contrary. 2. 
 
ACTION OF THE FEMALE. 701 
 
 That the presence of Corpora Cephaloidea of the second order is to be re- 
 garded as indicative of conception. 3. That the presence of the Corpora 
 Cephaloidea of the first order, or of Corpora Jllbida, cannot be regarded as 
 in the least degree indicative of Conception ; as they may result from the 
 simple discharge of an Ovum, in the ordinary course of those changes to 
 which the Ovarium is subject. The excess of Corpora Albida above every 
 other appearance is due, not merely to their being an ordinary result of the 
 discharge of unimpregnated Ova ; but also to the frequency of their produc- 
 tion as degenerated forms (so to speak) of the Corpora Cephaloidea and Cor- 
 pora Rubra of the gravid female ; and also to their occasional existence as, 
 from the first, the only Ovarian change following upon Conception. 
 
 915. The object of the changes which have been already described, is to 
 bring the Ovum within reach of the fecundating influence ; and to convey it 
 into the Uterus after it has been fertilized. We have now to consider the 
 changes in the Ovum itself, which take place during the same epoch. At 
 about the same period that the Ovum moves towards the periphery of the 
 Graafian follicle, the Germinal Vesicle moves towards the periphery of the 
 yolk-bag ; and it always takes up its position at the precise point of the Zona 
 Pellucida which is nearest the Ovisac, and which is closest, therefore, to the 
 surface of the Ovary. Moreover, the Germinal Spot is always on that part 
 of the Germinal Vesicle, which is in closest contact with the Zona Pellucida. 
 (See a, Figs. 9 and 10, Plate I.) Thus, the Germinal Spot is very near the 
 exterior of the Ovary; but is separated from it by the peritoneal coat of the 
 latter, by a thin layer of its stroma forming the external layer of the Graafian 
 follicle, by the ovisac forming its internal membrane, and by the zona pellu- 
 cida. We have already seen how the obstacle interposed by the three former 
 to the entrance of the Spermatozoon, is overcome ; we shall presently find 
 that the Zona Pellucida undergoes a similar change. 
 
 916. Whilst the Ovum is being prepared for fecundation, a series of very 
 important actions takes place in the Germinal Vesicle. The exterior or peri- 
 pheral portion of the Spot, which previously consisted of a collection of very 
 minute granules, begins to develope itself into a ring of new cells of extreme 
 delicacy (Fig. 9, ) ; these gradually enlarge, and a second ring of cells is 
 developed within it, pushing the first-formed cells further away from the cen- 
 tre. Many successive rings of cells are thus formed ; and at last the whole 
 Germinal Vesicle is filled with them, as shown at 6, Fig. 10. Still there 
 remains a pellucid space in the centre of the Germinal Spot (resembling that 
 seen at a, Fig. 12) ; in which no cells are developed. The first-formed cells 
 that have been pushed outwards, are so much compressed by those subse- 
 quently formed, as frequently to undergo liquefaction ; and during the time 
 that the Ova are being matured for fertilization, there is a continual new pro- 
 duction of cells at the centre, and a degeneration at the circumference. At 
 the same time, the Yolk undergoes changes somewhat analogous ; for it 
 ceases to contain separate oil-globules ; and large elliptical discs or cells are 
 seen in it, especially just beneath the Zona Pellucida (Fig. 9, c).* Here, too, 
 the formation of new cells takes place from the periphery towards the centre ; 
 the peripheral ones gradually undergo liquefaction, as is seen in the outer 
 layer of those in Fig. 10, which are becoming indistinct; and they are replaced 
 by a new layer pushed outwards from the centre. The same process sub- 
 sequently continues in the Yolk, for some time after fecundation ; and this 
 not only in regard to the yolk as a whole, but in respect to its individual cells, 
 
 * It is to be remembered that the observations of Dr. Barry, here quoted, were made on 
 the Rabbit : and are, therefore, probably applicable equally to other Mammalia, but not to 
 Oviparous Animals. 
 
 59* 
 
702 OF REPRODUCTION. 
 
 as is shown in Fig. 1 1 , where concentric rings of new cells are seen in each 
 of the parent vesicles. Even in the most advanced of these secondary cells, 
 another generation may be seen, and these are developed upon the same plan 
 with those of the Germinal Vesicle : thus in Fig. 12, the pellucid centre of 
 the original nucleus of the parent disc is seen at , and is surrounded by seve- 
 ral concentric rings of cells, increasing in size from within outwards ; and at 
 b is represented the condition of the outer and older cells, in which the same 
 process is undergoing repetition. (Although the figure only represents one 
 secondary cell as in the act of producing others, the others of the same age 
 are alike engaged in the process of multiplication.) The foregoing history is 
 equally applicable to the cells, from which the Embryo subsequently origi- 
 nates ; and it is probably the general mode in which the process takes place. 
 
 917. At the time when the interior of the Germinal Vesicle is being pre- 
 pared for the reception of the fecundating influence, the portion of the Zona 
 Pellucida against which it lies becomes attenuated; and a chink then forms in 
 it, just above what was the pellucid centre of the Germinal Spot. Through 
 this chink, the Spermatozoon can reach the Germinal Vesicle; and that it does 
 so, we are now entitled to affirm, not only from analogy, but also from actual 
 observation ( 900). What is the nature of the influence communicated by it 
 is less certain; but from the known character of the process of fecundation in 
 Plants, we shall have little difficulty in concluding, that it deposits in the 
 Germinal Vesicle the rudiments of the first cells, which are subsequently to 
 be developed into the Embryonic structure. It is certain that none of the 
 cells previously contained in the Germinal Vesicle subsequently form part of 
 it ; in fact, they all liquefy after a time, and disappear entirely. But in the 
 previously pellucid centre of what was the Germinal Spot, two new cells are 
 seen after fecundation; these enlarge at the expense of the rest; and from 
 them, all the permanent structures originate. This pair of cells is seen at , 
 Figs. 13 and 14; in the former some of the cells of the Germinal Vesicle are 
 still left ; in the latter, they have been all absorbed. The Germinal Vesicle 
 returns after fecundation to the centre of the Yolk, being at first entirely con- 
 cealed by its discs (Fig. 11); and the cleft in the Zona Pellucida soon closes, 
 so as to be no longer distinguishable. The two new cells and the other con- 
 tents of the Germinal Vesicle, undergo such a rapid increase in size, that they 
 soon fill the whole interior of the Zona Pellucida ; and the cells of the Yolk 
 being reduced by the pressure into a liquid form, their elements are absorbed 
 by the new cells of the Embryonic structure. This, at least, is the case in 
 the Mammalia ; among which the Yolk performs but a very subordinate part, 
 having only to serve for the development of the Embryo during a very brief 
 period. In each of the two primary Germ-cells (as they may be called) a 
 series of changes takes place, exactly conformable to that already described as 
 occurring in the Germinal Vesicle ; that is to say, a ring of new cells origi- 
 nates in the margin of its nucleus, this increases in size, and is pushed out- 
 wards by another ring nearer the centre, this again by another, and so on, 
 and at last, two cells appear in the pellucid central space, which are developed 
 at the expense of all the rest, and are to be regarded as the real permanent 
 offspring of the parent. These changes may be seen in progress in Figs. 13 
 and 14; in the former, the original cells of the Germinal Vesicle have not 
 quite disappeared, although their liquefaction is in progress ; in the latter, no 
 vestige of them is left, the whole cavity being occupied by the twin-cells. 
 
 918. These changes commence during the passage of the Ovum along the 
 Fallopian tube ; and during its transit to the Uterus, it acquires a sort of gela- 
 tinous envelope, which is inclosed in a membrane of fibrous texture, termed 
 the Chorion. The gelatinous envelope is probably of an albuminous nature 
 in reality, corresponding with the white of the Bird's egg ; whilst the fibrous 
 
ACTION OF THE FEMALE. 703 
 
 texture of Chorion seems to be produced, like the membranous basis of the 
 egg-shell of the Bird ( 118), by the exudation of Fibrine from the lining 
 membrane of the Fallopian tube or Oviduct. The outer layer of this en- 
 velope, in the egg of the Bird, is consolidated by the deposition of particles of 
 Carbonate of Lime in its areolae ; but it undergoes no higher organization. 
 The Chorion of the Mammal, on the other hand, subsequently undergoes 
 changes of a much higher order; which adapt it for participating, to a most 
 important degree, in the nutrition, of the included embryo. The first of these 
 changes consists in the extension of the surface of the membrane into a num- 
 ber of villous prolongations, which give it a spongy or shaggy appearance. 
 These serve as absorbing radicles, and form the channel through which the 
 embryo is nourished by the fluids of the parent, until a more perfect commu- 
 nication is formed, in the manner to be presently explained. 
 
 919. We have now to speak of the changes in the Uterus, which take 
 place in consequence of Conception, and which prepare it to receive the 
 Ovum. Of these the most important is the formation of the Membrana De~ 
 cidua, so called from its being cast off at each parturition. This membrane 
 has been usually supposed to be a new formation ; and has been described as 
 originating in coagulable lymph thrown out on the inner surface of the Uterus, 
 into which vessels ^are prolonged from the subjacent surface. It appears, 
 however, from the late researches of Dr. Sharpey and Prof. Weber,* that this 
 is not the true account of it; and that the Decidua is really composed of the 
 inner portion of the Mucous membrane itself, which undergoes a considerable 
 change in its character. The Mucous membrane of the Uterus had been ob- 
 served by Dr. J. Reid to possess, on its free surface, a tubular structure ; not 
 very unlike that which has been described as existing in the lining membrane 
 of the stomach ( 873 and Fig. 269). This tubular portion becomes thickened 
 and increased in vascularity, within a short time after conception ; and when 
 the inner surface of a newly-impregnated Uterus is examined with a low 
 magnifying power, the orifices of its tubes (Plate I., Fig. 17, b,b) are very 
 distinctly seen, being lined with a white epithelium. The blood-vessels (c, c) 
 form a very minute net-work, which extends in loops from the subjacent 
 portion of the membrane. According to the recent observations of Mr. J. 
 Goodsir,t the interfollicular spaces (, , ) also are crowded with nucleated 
 particles ; and it is to the development of this interfollicular substance, as well 
 as to the enlargement of the follicles themselves, and the copious development 
 of epithelial cells in their interior, that the mucous membrane in this condition 
 owes its increased thickness. At a later period, the Decidua may be found 
 to consist of two distinct layers; the Decidua vera, lining the uterus; and the 
 Decidua reflexa, covering the exterior of the ovum. It was formerly supposed 
 that the latter is a portion of the former, which has been pushed before the 
 ovum at its entrance into the uterus ; but the two layers are so different in 
 texture, that they cannot be supposed to have the same origin. The difficulty 
 appears to be solved by the observations of Mr. Goodsir. " From what has 
 now been stated," he remarks, " it appears that the Decidua consists of two 
 distinct elements; the mucous membrane of the uterus, thickened by a pecu- 
 liar development ; and a non-vascular cellular substance, the product of the 
 uterine follicles. The former constitutes, at a later period, the greater part of 
 the decidua vera ; the latter, the decidua reflefta. This view of the consti- 
 tution of the Decidua clears up the doubts which were entertained regarding 
 the arrangement of these membranes at the os uteri and entrances of the Fallo- 
 pian tubes. It is evident that these orifices will be open or closed, just as the 
 
 * Mullet's Physiology, pp. 1574-1580. 
 
 f Anatomical and Pathological Observations, Chap. ix. 
 
704 OF REPRODUCTION. 
 
 cellular secretion is more or less plentiful, or in a state of more or less vigor- 
 ous development."" When the ovum enters the cavity of the uterus, the 
 cellular decidua surrounds it, and becomes what has been named the decidua 
 reflexa, by a continuation of the same action, by which it had been increasing 
 in quantity before the arrival of the ovum. The cellular decidua grows around 
 the ovum by the formation of new cells, the product of those in whose vicinity 
 the ovum happens to be situated." 
 
 920. When the Ovum has arrived in the Uterus, therefore, and the villous 
 tufts of the Chorion are developed, these come into contact, in the first in- 
 stance, with the layer of cellular decidua, which intervenes between them 
 and the vascular decidua. Through this cellular membrane, therefore, the 
 ovum must derive its nutriment from the vascular surface; and it cannot.be 
 deemed improbable, that the office of its component cells is to draw from the 
 subjacent vessels the materials which are to serve for the nutrition of the 
 ovum, and to present it to the villous tufts of the chorion. Each of these is 
 composed (according to the observations of Mr. J. Goodsir) of an assemblage 
 of nucleated cells, which are found in various stages of development ; and 
 these are always inclosed within a layer of basement-membrane, which 
 seems to be itself composed of flattened cells united by their edges. At the 
 free extremity of each villus, is a bulbous expansion, the cells composing 
 which are arranged round a central spot ; and it is at this point that the most 
 active processes of growth take place, the villus elongating by the develop- 
 ment of new cells from its germinal spot, and (like the spongiole of the plant) 
 drawing in nutriment from the soil in which it is imbedded. In its earliest 
 grade of development, the chorion and its villi contain no vessels; and the 
 fluid drawn in by the tufts is communicated to the embryo, by the absorbing 
 powers of the germinal membrane of the latter. But when the tufts are pe- 
 netrated by blood-vessels, and their communication with the embryo becomes 
 more direct, the means by which they communicate with the parent are found 
 to be still essentially the same ; namely, a double layer of nucleated cells, 
 one layer belonging to the foetal tuft, an'd the other to the vascular maternal 
 surface. It is from these elements that the Placenta is formed, in the manner 
 next to be described. 
 
 921. The first stage in this process consists in the extension of the foetal 
 vessels into the villi of the Chorion over its entire surface, in the manner here- 
 after to be detailed ( 941) ; so that the nutriment which these villi imbibe, 
 instead of being merely added tb the albuminous fluid surrounding the yolk- 
 bag, is now conveyed directly to the embryo. This, the earliest and simplest 
 mode by which the Fretus effects a new connection with the parent, is the 
 only one in which it ever takes place in the lower Mammalia, which are hence 
 properly designated as " non-placental," rather than as ovo-viviparous ( 44). 
 In the higher Mammalia, however, there soon occurs a great extension of the 
 vascular tufts of the fetal Chorion, at certain points ; and a corresponding 
 adaptation, on the part of the Uterine structure, to afford them an increased 
 supply of nutritious fluid. These specially-prolonged portions are scattered, 
 in the Ruminantia and some other Mammalia, over the whole surface of the 
 Chorion, forming what are termed the Cotyledons ; but in the higher orders, 
 and in Man, they are concentrated in one spot, forming the Placenta. In 
 some of the lower tribes, the maternal and the fetal portions of the Placenta 
 may be very easily separated ; the former consisting of the thickened Decidua; 
 and the latter being composed of the prolonged and ramifying vascular tufts 
 of the Chorion, dipping down into it. But in the Human Placenta, the two 
 elements are mingled together through its whole substance. 
 
 922. On looking at the Foetal surface of the Human Placenta, we perceive 
 that the umbilical vessels diverge in every direction from the point at which 
 
ACTION OF THE FEMALE. 
 
 705 
 
 they enter it; and their subdivisions ramify very minutely, forming a large 
 part of its substance. The terminal ramifications are represented by Dr. J. 
 Reid* as having the digitated aspect represented in Fig. 23, (Plate I.) ; but 
 this is one of the more complex forms. In its simplest character, each 
 villus is cylindrical or nearly so ; and the digitated villi are only solitary villi 
 grouped together at the extremity of a primary branch. Each villus contains 
 a capillary vessel, which forms a series of loops, communicating with an 
 artery on one side and with a vein on the other; but the same capillary may 
 pass into several villi, before re-entering a larger vessel. The vessels of the 
 villi are covered, as in the Chorion, by a layer of cells (Fig. 280/), inclosed 
 
 Fig. 280. 
 
 Fig. 281. 
 
 Extremity of a placental villus : o, exter- Portion of the external membrane, 
 
 nal membrane of the villus, continuous with with the external cells, of a placental 
 
 the lining membrane of the vascular system villus: a. cells seen through the mem- 
 
 of the mother ; 6, external cells of the villus, brane ; b, cells seen from within the 
 
 belonging to the placental decidua ; c, c, ger- villus ; e, cells seen in profile along the 
 
 minal centres of the external cells ; d, the edge of the villus. 
 
 space between the maternal and foetal por- 
 tions of the villus; e, the internal membrane of 
 the villus, continuous with the external mem- 
 braneofthe chorion;/, the internal cellsof the 
 villus, belonging to the chorion ; g, the loop of 
 umbilical vessels. 
 
 in basement-membrane (e) ; but the foetal tuft thus formed is inclosed in a se- 
 cond series of envelopes (a, 6, c), derived from the maternal portion of the 
 Placenta, a space (d) being left, however, between the two, at the extremity 
 of the tuft. 
 
 923. Whilst the foetal portion of the Placenta is thus being generated by 
 the extension of the vascular tufts of the Chorion, the Maternal portion is 
 formed by the enlargement of the vessels of the decidua, between which they 
 dip down. " These vessels assume the character of sinuses ; and at last swell 
 out (so to speak) around and between the villi ; so that finally the villi are 
 completely bound up or covered by the membrane which constitutes the walls 
 of the vessels, this membrane following the contour of all the villi, and even 
 passing to a certain extent over the branches and stems of the tufts. Between 
 this membrane, or wall of the enlarged decidual vessels, and the internal mem- 
 brane of the villi, there still remains a layer of the cells of the decidua."t In 
 this manner is formed the Maternal portion of the Placenta, which may be re- 
 garded in its adult state (as was well pointed out by Dr. J. Reid) in the light 
 of a large sac formed by a prolongation of the inner coat of the Uterine vessels ; 
 against the foetal surface of which sac, the tufts just described may be said to 
 push themselves, so as to dip down into it, carrying before them a portion of 
 its thin wall, which constitutes a sheath to each tuft. Now as every extension 
 
 * Edinb. Med. and Surg. Journal, Jan. 1841. 
 
 j- Goodsir's Anatomical and Pathological Observations, p. 60. 
 
706 
 
 OF REPRODUCTION. 
 
 of the uterine vessels carries the decidua before it, every one of the vascular 
 tufts that dips down into it will be covered with a layer of the cellular struc- 
 ture of the latter ; and the foetal portion of each tuft will thus be inclosed in a 
 layer of maternal cells and basement-membrane (Fig. 280, , 6, c; and Fig. 
 
 281, , 6, e). In this manner, the whole interior of the placenta! cavity is in- 
 tersected by numerous tufts of foetal vessels, disposed in fringes, and bound 
 down by reflections of the delicate membrane that forms its proper wall ; just 
 as the intestines are held in their places by reflections of the peritoneum that 
 covers them. This view was suggested to Dr. R. by the very interesting fact, 
 that the tufts of fcetal vessels not unfrequently extend beyond the uterine sur- 
 face of the Placenta, and dip down into the uterine sinuses ; where they are 
 still covered, and held in their places, by reflections of the same membrane 
 (Plate I., Fig. 24). All the bands which connect and tie down the tufts (Fig. 
 
 282, g-), are formed of the same elements as the envelopes of the tufts them- 
 selves ; namely, a fold of the lining membrane of the decidual sinuses, and a 
 layer of the cellular decidua. 
 
 Fig. 282. 
 
 Diagram illustrating the arrangement of the placental decidua : a, decidua in contact with the interior 
 of the uterus ; 6, venous sinus passing obliquely through it by a valvular opening ; c, a curling artery 
 passing in the same direction ; d, the lining membrane of the maternal vascular system, passing in from 
 the artery and vein, lining the bag of the placenta, and covering e, e, the fcetal tufts, passing on to them 
 from their stems from the festal side of the cavity, also by the terminal decidual bars/./, from the uterine 
 side, and from one tuft to the other by the lateral bar, g ; h, h, separated fcetal tufts, showing the internal 
 membrane and cells, which, with the loops of umbilical vessels, constitute the true fcetal portion of the 
 tufts. 
 
 924. The blood is conveyed into the Placental cavity by the "curling 
 arteries" of the Uterus ; and is returned from it by the large veins, that are 
 commonly designated as sinuses. The fcetal vessels, being bathed in. this 
 blood, as the branchiae of aquatic animals are in the water that surrounds them, 
 not only enable the fetal blood to exchange its venous character for the arte- 
 rial, by parting with its carbonic acid to the maternal blood, and receiving 
 oxygen from it ; but they also serve as rootlets, by which certain nutritious 
 elements of the maternal blood (probably those composing the liquor sanguinis) 
 are taken into the system of the Foetus. In this they closely correspond with 
 the villi of the Intestinal canal; and there is this further very striking analogy, 
 
 that the nutrient material is selected and prepared by two sets of cells, one 
 
 of which (the maternal) transmits it to 'the other (the foetal), in the same man- 
 ner as the epithelial cells of the intestinal villi seem to take up and prepare 
 the nutrient matter, which is destined to be still further assimilated by the 
 special absorbing cells of their interior ( 672). There is no more direct 
 communication between the Mother and Foetus than this; all the observations 
 which have been supposed to prove the existence of real vascular continuity, 
 
ACTION OF THE FEMALE. 707 
 
 having been falsified by the extravasation of fluid, consequent upon the force 
 used in injecting the vessels. Moreover, the different size of the blood-corpus- 
 cles in the Foetus and in the Parent ( 149) shows the non-existence of any 
 such communication. 
 
 925. The formation of the Placenta, in the manner just described, com- 
 mences in the latter part of the second month ; during the third, it acquires 
 its proper character; and it subsequently goes on 'increasing, in accordance 
 with the growth of the ovum. Towards the end of the term of gestation, 
 however, it becomes more dense and less vascular ; owing, it would seem, to 
 the obliteration of several of the minuter vessels, which are converted into 
 hard fibrous filaments. The vessels of the Uterus undergo great enlargement 
 throughout, but especially at the part to which the Placenta is attached ; and 
 the blood in moving through them produces a peculiar murmur, which is 
 usually distinctly audible at an early period of Pregnancy, and may be regarded 
 (when due care is taken to avoid sources of fallacy), as one of its most unequi- 
 vocal positive signs. The Placental bruit is thus described by Dr. Mont- 
 gomery.* " The characters of this phenomenon are, a low murmuring or 
 somewhat cooing sound, resembling that made by bio wing- gently over the lip 
 of a wide-mouthed phial, and accompanied by a slight rushing noise, but with- 
 out any sensation of impulse. The sound is, in its return, exactly synchronous 
 with the pulse of the mother at the time of examination ; and varies in the 
 frequency of its repetitions, with any accidental variation which may occur 
 in the maternal circulation. Its situation does not vary during the course of 
 the same pregnancy; but in whatever region of the uterus it is first heard, it 
 will in future be found, if recognized at all, for it is liable to intermissions, 
 at least we shall occasionally be unable to hear it where we have already 
 heard it a short time before, and where we shall shortly again recognize it. 
 According to my experience, it will be most frequently heard about the situa- 
 tion of the Fallopian tube of the right side; but it may be detected in any of 
 the lateral or anterior parts of the uterus." That the cause of this, sound 
 exists in the Uterus itself, is distinctly proved by the fact, that it has been 
 heard when that organ was so completely anteverted, that the fundus hung 
 down between the patient's thighs. A sound so much resembling this, as to 
 be scarcely distinguishable from it, may be occasioned, however, by a cause 
 of a very different nature, namely, an abdominal tumour, pressing upon the 
 aorta, iliac arteries, or enlarged vessels of its own; and, in doubtful cases, it 
 is necessary to give full weight to the possibility of such an explanation. The 
 sound may be imitated at any time, by pressing the stethoscope on the iliac 
 arteries. The Placental bruit has been not unfrequently heard in the llth 
 week ; but it cannot generally be detected before the fourth month, when the 
 fundus uteri rises above the anterior wall of the pelvis. 
 
 92B. The amount of the peculiar tissue of the Uterus ( 234) greatly 
 increases during pregnancy. At the same time, the Mammary gland and its 
 appendages undergo a fuller development; and from this a valuable, but not 
 unequivocal, indication of pregnancy may be drawn. Occasional shooting 
 pains in the Mammae are not unfrequently experienced within a short period 
 after conception ; and more continued tenderness is also not unusual. A sense 
 of distension is very commonly experienced at about the end of the second 
 month ; and from that time a distinct " knottiness" usually begins to present 
 itself, increasing with the advance of Pregnancy. In many instances, how- 
 ever, these mammary sympathies are entirely absent; and they may be simu- 
 lated by changes that take place in consequence of various affections of the 
 Uterus. A change of colour in the areola is a very common, but not an 
 
 * Op. cit., p. 121. 
 
708 OF REPRODUCTION. 
 
 invariable, occurrence in the early months of pregnancy ; but another sign is 
 afforded by the areola and nipple, which is of more value because more con- 
 stant, namely, a puffy turgescence, and an increased development of the 
 little glandular follicles, or tubercles, which commonly secrete a dewy mois- 
 ture. The presence or absence of kiesteine in the Urine ( 859) also may 
 probably be regarded as a valuable diagnostic sign. This substance appears 
 on the surface of the fluid, after it has stood for two or three days, in the form 
 of a thin pellicle of a somewhat fatty aspect ; it is preceded by a sediment 
 which has very much the appearance of cotton wool; and it disappears when 
 the urine is decomposing, at the same time emitting an odour like that of 
 putrid cheese.* Many other changes in the constitution take place during 
 Pregnancy ; indicated by the buffiness of the blood, the irritability of the sto- 
 mach, and the increased excitability of the mind. All these, however, are 
 discussed with sufficient amplification, in works on Obstetric Medicine. 
 
 927. The act of Conception, being one of a purely organic nature, is not 
 attended with any consciousness on the part of the mother ; but there are 
 some women, in whom it is attended with certain sympathetic affections, such 
 as faintness, vertigo, &c., that enable them to fix upon the particular time at 
 which it has taken place. From that period, however, the Mother has no 
 direct consciousness of the change going on in the Uterus (save by the effects 
 of its increasing pressure on other parts), until the occurrence of what is 
 termed " Quickening." This is generally described as a kind of fluttering 
 movement, attended with some degree of syncope or vertigo. After it has 
 once occurred, and has strongly excited attention, it is occasionally renewed 
 once or twice, and then gives place to the ordinary movements of the foetus. 
 Not unfrequently, however, no movement whatever is felt, until near the end 
 of the term of gestation, or even through the whole of it. As to the cause of 
 the sensation, Obstetricians are much divided ; and no satisfactory account 
 has been given of it. It has been vulgarly supposed to be due to the first 
 movement of the Foetus, which was imagined then to become possessed of an 
 independent life : and the English law recognizes the truth of this doctrine, 
 in varying the punishment of an attempt to procure Abortion, according to 
 whether the woman be " quick with child" or not; and in delaying execution 
 when a woman can be proved to be so, though it is made to proceed if she is 
 not, even if she be unquestionably pregnant. Whether or not the first sensible 
 motions of the Foetus are the cause of the peculiar feeling in question, there 
 can be no doubt that the Embryo has as much independent vitality before, as 
 after, the quickening. From the time that the Ovum quits the Ovary, it ceases 
 to be a part of the Parent, and is dependent on it only for a due supply of 
 nourishment, which it converts, by its own inherent powers, into its proper 
 fabric. This dependence cannot be said to cease at the moment of quicken- 
 ing; for the connection must be prolonged during several weeks, before the 
 Foetus can be said to be capable of living without such assistance. The earliest 
 period at which this may occur, will be presently considered ( 932). 
 
 928. At the conclusion of about nine (solar) months from the period of con- 
 ception, the time of Parturition arrives. The Uterus, by its own efforts, and 
 by the assistance of the muscles of Expiration, expels its contents ; and the 
 membranes of the Ovum being usually ruptured before it is entirely dis- 
 charged, the Foetus comes at once into the world. Although there can be no 
 doubt that, as already stated ( 393), the contractile fibres of the Uterus may 
 be called into effectual action without Nervous influence, yet it is equally cer- 
 tain that Uterine contractions may be induced through the Spinal system of 
 
 * [See an excellent paper on this subject in Am. Journ. of Med. Sci., vol. iv., N. S., by 
 Elisha Kane, M. D. M. C.] 
 
ACTION OF THE FEMALE. 709 
 
 nerves. For in no other way can we account for many phenomena which 
 are obviously of a reflex character ; such as the sudden contraction of the Ute- 
 rus, previously distended and inactive, when cold is applied to the external 
 surface of the body, or when the child is applied to the nipple. In the first 
 stage of labour, the Uterine contractions appear to be alone concerned ; and 
 it is not until the head of the child is passing through the Os Uteri, and is 
 entering the Vagina, that the assistance of the Expiratory muscles is called 
 in. The excitor fibres, which convey to the Spinal Cord the stimulus that 
 calls them into action, must originate, therefore, rather in the Vagina than in 
 the Uterus itself. Whilst the fibres of the fundus and body of the Uterus are 
 in powerful contraction, those of the Cervix Uteri and Vagina must be in a 
 state of dilatation ; and this dilatation appears to be in some respects different 
 from the mere yielding to the pressure of the child's head. A slow contrac- 
 tion of the fibres of the fundus and body of the Uterus, and a yielding of 
 those of the cervix, usually take place during some days previous to Par- 
 turition ; so that the child lies lower, and the size of the abdomen diminishes.* 
 
 929. As to the reason why the period of Parturition should be just nine 
 months after that of Conception, we know nothing more than we do of that 
 of similar facts in the physical history of Man such as the periodical return 
 of the Catamenia, the renewal of the Teeth, the recurrence of the tend- 
 ency to Sleep, &c. That it is immediately dependent upon some state of the 
 constitution, rather than upon the condition of the Uterus, appears from the 
 fact that, in cases of Extra-uterine pregnancy, contractions resembling those 
 of labour take place in its walls. Moreover, various states of the constitu- 
 tion, especially that which is designated as irritability, may induce the occur- 
 rence of the parturient efforts at an earlier period ; and this constitutes Abor- 
 tion, or Premature delivery, according to the viability of the child. There 
 are some women, in whom this regularly happens at a certain month, so that it 
 seems to be an action natural to them ; but it is always to be prevented, if pos- 
 sible, being injurious alike to the mother and child ; and this prevention is to 
 be attempted by rest and tranquillity of mind and body, and by a careful avoid- 
 ance of all the exciting causes, which may produce Uterine contractions by 
 their operation on the Nervous system. For it is to be remembered that, 
 although the muscular fibres of the Uterus are capable, like those of the ali- 
 mentary canal, of an independent action, they are likely to be excited to ope- 
 ration through the Nervous system, and especially through the Sympathetic 
 ( 393). The same action which expels the Foetus, also detaches the Pla- 
 centa ; and if the Uterus contract with sufficient force after this has been 
 thrown off, the orifices of the vessels which communicated with it are so 
 effectually closed, that little or no hemorrhage takes place. If, however, the 
 Uterus does not contract, or relaxes after having contracted, a large amount 
 of blood may be lost in a short time from the open orifices. For some little 
 time after Parturition, a sero-sanguineous discharge, termed the Lochia, is 
 poured out from the Uterus ; and this commonly contains shreds of the De- 
 ciduous membrane, which had not been previously detached. Within a few 
 weeks after delivery, the Uterus regains (at least in a healthy subject) its pre- 
 vious condition; and it is probable that the portion of its mucous Membrane, 
 which had been thrown off as Decidua, is very early reproduced. 
 
 930. Although the duration of Pregnancy is commonly stated at nine 
 solar months, it would be more correct to fix the period at 40 weeks, or 280 
 days ; which exceeds nine months by from 5 to 7 days, according to the 
 months included. This, at least, is the average result of observation, in cases 
 
 * See some interesting Papers on the Physiology of Parturition, by Dr. W. Tyler Smith, 
 in the Lancet, July 6 and 13, 1844. 
 
 60 
 
710 OF REPRODUCTION. 
 
 in which the period of Conception could be fixed from peculiar circumstances, 
 with something like certainty. The mode of reckoning customary among 
 women, is to date from the middle of the month after the last appearance of 
 the Catamenia; but it is certain that Conception is much more likely to take 
 place soon after they have ceased to flow, or even before their access, than at 
 a later period ( 909) ; so that, in most instances, it would be most correct to 
 expect Labour at forty weeks and a few days after the last recurrence of the 
 Menses. The period of Quickening may be relied on in some women, in 
 whom it occurs with great regularity in a certain week of Pregnancy ; but 
 there is in general great latitude as to the time of its occurrence. The usual 
 or average time is probably about the 18th week. 
 
 931. The question of the extreme limits of Gestation, is one of great import- 
 ance both to the Practitioner and to the Medical Jurist ; but it is one which 
 cannot yet be regarded as satisfactorily decided. Many persons, whose expe- 
 rience should give much weight to their opinion, maintain that the regular 
 period of 40 weeks is never extended for more than two or three days ; whilst, 
 on the other hand, there are numerous cases on record, which, if testimony is 
 to be believed at all, (and in many of these, the character and circumstances 
 of the parties placed them above suspicion,) furnish ample evidence that Ges- 
 tation may be prolonged for at least three w r eeks beyond the regular term.* 
 The English law fixes no precise limit ; and the decisions which have been 
 given in our courts, when questions of this kind have been raised, have been 
 mostly formed upon the collateral circumstances. The law of France pro- 
 vides that the legitimacy of a child born within 300 days after the death or 
 departure of the husband, shall not be questioned ; and a child born after more 
 than 300 days is not declared a bastard, but its legitimacy may be contested. 
 By the Scotch law, a child is not declared a bastard, unless born after the 
 tenth month from the death or departure of the husband. 
 
 a. The analogical evidence drawn from observations on the lower animals is extremely 
 strong. The observations of Tessier, which were continued during a period of forty years, 
 with every precaution against inaccuracy, have furnished a body of results, which seems 
 quite decisive. In the Cow, the ordinary period of gestation is about the same as in the 
 Human female; but out of 577 individuals, no less than 20 calved beyond the 298th day, and 
 of these, some went on to the 321st, making an excess of nearly six weeks. Of 447 Mares, 
 whose natural period of gestation is about 335 days, 42 foaled between the 359th and the 419th 
 day, the greatest protraction being thus 84 days, or just one-fourth of the usual term. Of 912 
 Sheep, whose natural period is about 151 days, 96 yeaned beyond the 153d day; and of 
 these, 7 went on until the 157th day, making an excess of 6 days. Of 161 Rabbits, whose 
 natural period is about 30 days, no fewer than 25 littered between the 32d and 35th ; the 
 greatest protraction was here one-sixth of the whole period, and the proportion in which 
 there was a manifest prolongation was also nearly one-sixth of the total number of indi- 
 viduals. In the incubation of the common Hen, Tessier found that there was not unfre- 
 quently a prolongation to the amount of three days, or one-seventh of the whole period. 
 
 b. In regard to Cows, the observations of Tessier have been recently confirmed by those 
 of Earl Spencer, who has published! a table of the period of gestation as observed in 764 
 individuals; he considers the average period to be 284 or 285 days: but no fewer than 310 
 calved after the 285th day; and of these, 3 went on to the 306th day, and 1 to the 313th. 
 It is curious that, among the calves born between the 290th and 300th days, there was a 
 decided preponderance of males, these being 74, to 32 females ; whilst all of those born 
 after the 300th day were females. 
 
 c. It appears, however, from some recent statements published on the authority of Earl 
 Spencer, that the Male parent may exert an important influence on the period of gestation. 
 Of 75 Cows in calf by a particular bull, the average period was 288 days, or four days 
 more than the usual period. Of the 764 cows previously mentioned, 185 (nearly one-fourth) 
 went less than 281 days; whilst not one of the cows in calf to this bull did so. On the 
 
 * A good collection of such cases will be found in Dr. Montgomery's excellent work on 
 the Signs of Pregnancy. 
 
 f Journal of the English Agricultural Society, 1839. 
 
ACTION OF THE FEMALE. 711 
 
 other hand, of the 764 cows first mentioned, 111 (rather more than one-seventh) went above 
 289 days; while, of the cows in calf by this bull, 29 out of 75 (nearly two-fifths) went above 
 289 days * 
 
 d. Another series of observations has recently been published by Mr. C. N. Bement of 
 Albany, U. S.,f who has recorded the period of gestation of 62 Cows. The longest period 
 was 336 days; the shortest, 213 days. The average period for male calves was 288 days; 
 and for females, 282 days. 
 
 These variations are probably to be regarded as due, not so much to a pro- 
 longation of the period of tftero-gestation, as to various circumstances which 
 may have a retarding influence on the process of Fecundation, and on the 
 transmission of the Ovum through the Fallopian tube. These have been well 
 pointed out by Dr. Montgomery.^ It may be a'dded that, in Dr. Barry's ob- 
 servations on the early changes that take place in the Ovum of Rabbits, he 
 has noticed several irregularities of this description. On the whole, it may 
 be considered that, in regard to the Human female, the French law is a very 
 reasonable one. It is probable, from the circumstances alluded to in the pre- 
 ceding paragraph, that Gestation is protracted to the extent of a week, ten 
 days, or a fortnight, much more frequently than is commonly supposed. In 
 several of the cases in which the protraction appeared indubitable, the Infant 
 was unusually large and vigorous. 
 
 932. In regard to the shortest period at which Gestation may terminate, 
 consistently with the viability of the Child, there is a still greater degree of 
 uncertainty. Most practitioners are of opinion, that it is next to impossible 
 for a Child to live and grow to maturity, which has not nearly completed its 
 seventh month ; but it is almost unquestionable that Infants, which have been 
 born at a much earlier period, have lived for some months. It is rare in such 
 cases, however, that the date of Conception can be fixed with sufficient pre- 
 cision to enable a definite statement to be given. Of the importance of the 
 question, a case which recently occurred in Scotland affords sufficient proof. 
 A vast amount of contradictory evidence was adduced on this trial ; but, on 
 the general rule of accepting positive in preference to negative testimony, it 
 seems that we ought to consider it possible, that a child may live for some 
 months, which has been born at the conclusion of 24 weeks of. gestation. In 
 the case in question, the Presbytery decided in favour of the legitimacy of an 
 Infant born alive within 25 weeks after marriage. 
 
 a. A very interesting case is on record, || in which the mother (who had borne five chil- 
 dren) was confident that her period of gestation was less than 19 weeks; the facts stated 
 respecting the development of the child are necessarily very imperfect, as it was important 
 to avoid exposing his body, in order that his temperature might be kept up; but at the age 
 of three weeks, he was only 13 inches in length, and his weight was no more than 29 oz. 
 At that time, he might be regarded, according to the calculation of the mother, as correspond- 
 ing with an infant of 22 weeks or 5^ months; but the length and weight were greater than 
 is usual at that period, and he must have been probably born at about the 25th week. It is 
 an interesting feature in this case, that the calorific power of the Infant was so low, that 
 artificial heat was constantly needed to sustain it; but that, under the influence of the heat 
 of the fire, he evidently became weaker, whilst the warmth of a person in bed rendered 
 him lively and comparatively strong. During the first week, it was extremely difficult to 
 get him to swallow ; and it was nearly a month before he could suck. At the time of the 
 report, he was four months old, and his health appeared very good. 
 
 b. Another case of very early viability has been more recently put on record by Mr. 
 Dodd:1T in this, as in the former instance, the determination of the child's age rests chiefly 
 on the opinion of the mother ; but there appears no reason for suspecting any fallacy. The 
 
 * Dr. J. C. Hall, in Medical Gazette, May 6, 1842. 
 
 f American Journal of the Medical Sciences, October, 1845. J Op. cit, p. 272. 
 
 Report of Proceedings against the Rev. Fergus Jardine, Edin., 1839. 
 
 || Edinb. Med. and Surg. Journal, vol. xi. 
 
 IT Provincial Medical and Surgical Journal, vol. ii. p. 474. 
 
712 OF REPRODUCTION. 
 
 child seems to have been born at the 26th or 27th week of gestation ; and having been 
 placed under judicious management, it has thriven well. 
 
 c. One of the most satisfactory cases on record, is that detailed by Dr. Outrepont (Professor 
 of Obstetrics at Wurtzburgh), arfd stated by Dr. Christison in his evidence on the case just 
 alluded to. The evidence is as complete as it is possible to be in any case of the kind ; being 
 derived not only from the date assigned by the Mother to her Conception, but also from the 
 structure and history of the Child. The Gestation could have only lasted 27 weeks, and was 
 very probably less. The length of the child was 13^ inches, and its weight was 24 oz. Its 
 development was altogether slow; and at the age of eleven years, the child seemed no more 
 advanced in body or mind, than most other lads of seven years old. In this last point, there 
 is a very striking correspondence with the results of other observations upon very prema- 
 ture children, made at an earlier age : and these all harmonize with the general principle 
 already more than once alluded to, that the shorter the period during which the early de- 
 velopment of the embryo takes place at the expense of nourishment supplied by the parent, 
 the lower is the degree of development it will ultimately attain ( 45). 
 
 d. To these may be added another case of recent occurrence in America : in which a 
 woman, who believed herself to be in the sixth month of pregnancy, was prematurely de- 
 livered in consequence of a fall. The child seemed barely alive, showing scarcely any 
 motion, and being too feeble to cry. It had no nails on its hands or feet, nor hair on the scalp ; 
 and the cranium was imperfectly ossified. At the end of seven weeks it was weighed for 
 the first time, and found to weigh only 26 oz. When ten months old, it was playful, lively, 
 and healthy; and weighed 10 Ibs. The reporter of this case regrets that he did not take 
 more particular notice of the state of the Child at birth, which he was prevented from 
 doing by the daily expectation of its death.* 
 
 933. There is another question regarding the Function of the Female in 
 the Reproductive act, which is of great interest in a scientific point of view, 
 and which may become of importance in Juridical inquiries ; namely, the 
 possibility of ^uperfoetation^ that is, of two distinct conceptions at an interval 
 of greater or less duration ; so that two foetuses of different ages, the offspring 
 perhaps of different parents, may exist in the Uterus at the same time. The 
 simplest case of Superfretation, the frequent occurrence of which places it be- 
 yond reasonable doubt, is that in which a female has intercourse on the same 
 day with two Males of different complexions, and bears twins at the full time; 
 the two infants resembling the two parents respectively. Thus, in the slave- 
 states of America, it is not uncommon for a black woman to bear at the same 
 time a black and a mulatto child ; the former being the offspring of her black 
 husband, and the latter of her white paramour. The converse has occasionally 
 though less frequently, occurred ; a white woman bearing at the same time a 
 white and a mulatto child. There is no difficulty in accounting for such 
 facts, when it is remembered that nothing has occurred to prevent the Uterus 
 and Ovaria from being as ready for the second conception as for the first ; since 
 the orifice of the former is not yet closed up ; and, at the time when one ovum 
 is matured for fecundation, there are usually more in the same condition. 
 But it is not easy thus to account for the birth of two children, each appa- 
 rently mature, at an interval of five or six months ; since it might have been 
 supposed that the uterus was so completely occupied with the first Ovum, as 
 not to allow of the transmission of the seminal fluid, necessary for the fecun- 
 dation of the second. In cases where two children have been produced at 
 the same time, one of which was fully-formed, whilst the other was small and 
 seemingly premature, there is no occasion whatever to imagine that the two 
 were conceived at different periods ; since the smaller foetus may have been 
 " blighted," and its development retarded, as not unfrequently happens in other 
 cases. Nor is it necessary to infer the occurrence of Superfoetation in every 
 case, in which a living child has been produced a month or two after the birth 
 of another; since the latter may have been premature, whilst the former has 
 been carried to the full term. But such a difference can scarcely be, at the 
 
 * American Journal of the Medical Sciences, April 1843. 
 
DEVELOPMENT OF THE EMBRYO. 713 
 
 most, more than 2| or three months ; and there are several cases now on re- 
 cord, in which the interval was from 110 to 170 days, whilst neither of the 
 children was premature in appearance; so that the possibility of a second 
 Conception, when the Uterus already contains an Ovum of several months, 
 can scarcely be denied, however improbable it may seem. 
 
 4. Development of the Embryo. 
 
 934. Under this head it is intended to state, not so much the details of the 
 process of Development, as those leading facts, the knowledge of which is 
 desirable in itself, as well as essential to the due comprehension of the former. 
 It is difficult to see what practical benefit can result from a minute acquaint- 
 ance with all the steps of the evolution of the Embryo, however interesting 
 these may be in a scientific point of view ; and the time of the ordinary Stu- 
 dent, on which there are so many pressing calls, may be much better occupied 
 than in committing them to memory. In the following sketch, little will be 
 said respecting the latter stages of the process, or the development of particular 
 organs, since these have been already noticed under their severally distinct 
 heads. Our attention will first be given to the formation of the Embryonic 
 mass, and of the membranes surrounding the Yolk-bag; and then to the ori- 
 gin of the Vertebral column, Digestive organs, and Circulating apparatus. 
 
 935. The Ovum, when it quits the Ovarium, has been stated to contain 
 within the Germinal Vesicle, two cells which tlid not exist there previously 
 to fecundation ; and from each of these, two new cells are subsequently pro- 
 duced, which in their turn give birth to eight others ( 917). In this manner, 
 the number of vesicles originating in the twin-cells of the Germ is continually 
 increased, until at last they become too numerous to be counted, and form a 
 cluster resembling a Mulberry in appearance; this mulberry-like structure 
 maybe conveniently termed the Germinal Mass (Plate I., Fig. 15, a). In the 
 centre of this mass there is found a peculiar Cell, differing from the rest in its 
 greater size, and in possessing a very well-defined annular nucleus, with a 
 pellucid cavity in its centre (Fig. 16, a, 6). From this peculiar Cell, all the 
 parts which enter permanently into the composition of the Embryo are de- 
 veloped ; the vesicles forming the exterior of the germinal mass being sub- 
 servient to a merely temporary purpose. This central or Embryonic Cell is 
 gradually brought to the surface of the Germinal Mass, by the formation of a 
 cavity c in the interior of the latter; for the layer of cells within which this 
 cavity is formed, progressively extends itself, until it comes into contact with 
 the inner surface of the Yolk-bag, having absorbed the yolk into the hollow 
 thus left. Thus out of the periphery of the Mulberry-mass, appears to be 
 formed the exterior layer of what is termed the Germinal Membrane : this 
 membrane is first seen as an epithelium-like layer of cells, covering the Yolk ; 
 but beneath this layer, which is afterwards known as the serous lamina of the 
 Germinal membrane, two others are subsequently produced from the central 
 portion of the Germinal mass. Now it is highly interesting to observe, that 
 this Germinal Membrane, which in the higher animals is a mere temporary 
 structure, subservient only to a temporary function, forms, in the lower tribes, 
 the greater part of the permanent fabric of the body. Thus, in the Polypes, 
 the cavity in which the Yolk is inclosed becomes a Stomach ; the external 
 layer of the Germinal Membrane becomes the integument ; whilst the internal 
 forms the lining of the Digestive cavity, of which the mouth is formed by 
 absorption of its wall at one point. Here the Yolk is directly absorbed and 
 assimilated by the surrounding membrane. In the higher Oviparous animals, 
 the Germinal Membrane serves to absorb nutritious matter from the Yolk, 
 and to prepare it for the use of the Embryo itself, by converting it into "Blood 
 
 60* 
 
714 OF REPRODUCTION. 
 
 ( 938) ; but, after the Yolk has been exhausted, the Yolk-bag is taken into 
 the body, and is gradually removed by absorption. In Mammalia, these 
 structures are of less importance. The store of Yolk, laid up for the nutrition 
 of the Embryo, is comparatively inconsiderable ; being only destined to serve 
 for the short time that elapses, before the Ovum forms its new connection 
 with the Parent, through the medium of the Chorion ; and the Yolk-bag is 
 ultimately separated from the Embryo, and thrown off as useless. Still the 
 early processes are the same in Mammiferous, as they are in Oviparous ani- 
 mals ; and the Development of Man, of a Bird, of a Reptile, or of a Fish, 
 takes place, up to a certain point, upon the same general plan. 
 
 936. The Embryonic Cell, and the cluster of cells that surrounds it, hav- 
 ing arrived on the surface of the Yolk by the movement just described, con- 
 stitute what is known in the Bird's egg under the name of the Cicatricula. 
 This is a semi-opaque disc, composed of numerous flattened cells ; and in the 
 midst of it is seen a round transparent space, termed the Area Pellucida, 
 which is nothing else than the place occupied by the large Embryonic Cell, 
 now become flattened, and still retaining its clearness. In the centre of this 
 is seen a very faint line, which is termed the Primitive Trace; and this is 
 the large annular Nucleus (Plate L, Fig. 16, b) of the Embryonic Cell, now 
 become elongated, and itself beginning to be developed into cells. The same 
 process then takes place within the Embryonic Cell, which has been described 
 as occurring within the Germinal Vesicle ( 916); the granules forming the 
 periphery of the nucleus are first developed into cells, and these are pushed 
 outwards by a new series subsequently generated near the centre. From the 
 mass of cells thus formed, a hollow process passes down into the Yolk; and 
 this gradually extends itself in the same manner as did that formed from the 
 Mulberry-mass, until it includes the whole Yolk, and comes into contact with 
 the inner surface of the layer of cells already mentioned as forming the serous 
 or external lamina of the Germinal Membrane. This second layer of cells 
 is probably that which forms the vascular lamina of the Germinal Membrane. 
 A third process seems to be afterwards sent down, from a part of the nucleus 
 somewhat interior to that from which the last proceeded : and this becomes 
 the mucous or internal lamina of the Germinal Membrane. 
 
 937. The cell-germs forming the periphery of the Nucleus having been thus 
 developed, those nearer the centre then begin to exhibit a corresponding acti- 
 vity. Their evolution follows exactly the same plan as that which has been 
 described in regard to the contents of the Germinal Vesicle ( 916); with 
 the exception that these are arranged in an elongated and not in a circular 
 form. The shape of the nucleus at this time may be compared to that of a 
 pear; the large end marking the situation of the Head ; whilst the prolonged 
 portion is the rudiment of the body. On the median line is seen a groove, 
 occupying the situation in which the Nervous Centres are to be subsequently 
 evolved (Fig. 25, Plate II.). These, when first developed, are surrounded by 
 a tubular structure, which has but a temporary existence in the higher Verte- 
 brata, but which is permanent in the lower Fishes : this structure, termed the 
 Chorda Dorsalis, is found, wherever it exists, to be entirely composed of 
 nucleated cells. From the cells which are exterior to these, is produced the 
 Vertebral Column ; and the mode in which this originates is somewhat as 
 follows. The cells on either side of the central space (in which the elements 
 of the nervous system are not yet developed) rise up in a ridge, so that the 
 central space becomes a groove ; these two ridges gradually rise up and ap- 
 proach one another, and they are then observed to contain, in what subse- 
 quently becomes the thoracic region, a few pairs of small opaque plates. 
 The ridges (termed plicse dorsales,or dorsal laminae) continue inclining towards 
 each other, until they coalesce, so that a complete tube is formed ; and in this 
 
DEVELOPMENT OF THE EMBRYO. 715 
 
 tube an indication is soon perceived of a division into vertebrae, of which the 
 plates just mentioned are the incipient arches (Fig. 26, Plate II.). Towards 
 the anterior extremity, however, the dorsal laminae do not at once close in ; 
 and the large cells, in which the great divisions of the Encephalon originate 
 ( 358), may be seen between them. From the Dorsal Lamina on either side, 
 a prolongation passes outwards and then downwards, forming what is known 
 as the ventral lamina ; in this are developed the Ribs and the transverse pro- 
 cesses of the Vertebrae ; and the two have the same tendency to meet on the 
 median line, and thus to close in the abdominal cavity, which the dorsal 
 laminae have to inclose the spinal cord. At the same time the layers of the 
 Germinal Membrane, which lie beyond the extremities of the Embryo, are 
 folded in, so as to make a depression on the yolk ; and their folded margins 
 gradually approach one another under the abdomen. In these two modes, a 
 cavity is formed beneath the Embryonic mass, which is separated from the 
 general cavity of the Yolk by the folds just described; but these still leave a 
 passage which, in the Bird, remains of considerable size until a much later 
 period, but which, in the Mammiferous Ovum, is soon obliterated. For the 
 sac which contains the yolk, and from which the abdominal cavity is pinched 
 off (as it were) at a very early period, is destined, in the Mammiferous ani- 
 mal, to be entirely cast away ; the purpose which it has to serve being one of 
 a very temporary character. 
 
 938. Whilst these new structures are being produced, a very remarkable 
 change is taking place in that part of the Serous lamina, which surrounds the 
 Area Pellucida. This rises up on either side in two folds ; and these gradually 
 approach one another, at last meeting in the space between the general en- 
 velope and the embryo, and thus forming an additional investment to the 
 latter. As each fold contains two layers of membrane, a double envelope 
 is thus formed ; of this, the outer lamina adheres to the general envelope ; 
 whilst the inner remains as a distinct sac, to which the name of Jlmnion is 
 given. (See Figs. 284, 285, and 286.) This takes place during the third 
 day in the Chick ; the period at which it occurs in the Human Ovum is diffi- 
 cult to be ascertained, owing to the small number of normal specimens which 
 have come under observation at a sufficiently early stage. During the same 
 
 Fig. 283. Fig. 284. 
 
 Plan of early uterine Ovum. Within the Diagram of ovum at later stage; the digestive ca- 
 
 external ring, or zona pellucida, are the serous vity beginning to be separated from the yolk-sac, 
 
 lamina, a; the yolk, b; and the incipient em- and the amnion beginning to be formed; a, chorion; 
 
 bryo, c. 6, yolk-sac ; c, embryo ; d, and e, folds of the serous 
 
 layer rising up to form the Amnion. 
 
 period, a very important provision for the future support of the Embryo begins 
 to be made; by the development of Blood-vessels and the formation of Blood. 
 Hitherto, the Embryonic structure has been nourished by direct absorption of 
 
716 OF REPRODUCTION. 
 
 the alimentary materials supplied to it by the Yolk ; in the same manner as 
 the simplest Cellular plant is developed at the expense of the carbonic acid, 
 moisture, &c., which it obtains for itself from the surrounding elements. But 
 its increasing size, and the necessity for a more free communication between 
 its parts than any structure consisting of cells alone can permit, call for the 
 development of Vessels, through which the nutritious fluid may be conveyed. 
 These vessels are first seen in that part of the Vascular lamina of the Germinal 
 Membrane, which immediately surrounds the embryo ; and they form a net- 
 work, bounded by a circular channel, which is known under the name of the 
 Vascular <flrea (Fig. 27, Plate II.). This gradually extends itself, until the 
 vessels spread over the whole of the membrane containing the yolk. The 
 first blood-discs appear to be formed from the nuclei of the cells, whose 
 cavities have become continuous with each other to form the vessels ( 222) ; 
 and from these, all subsequent blood-discs are probably generated. This net- 
 work of blood-vessels serves the purposes of absorbing the nutritious matter 
 of the Yolk, and of conveying it towards the embryonic structures, which are 
 now in process of rapid development. The first movement of the fluid is 
 towards the embryo ; and this can be witnessed before any distinct heart is 
 evolved. The same process of absorption from the Yolk, and of conversion 
 into Blood, probably continues as long as there is any alimentary material left 
 in the sac. 
 
 939. The Yolk-sac is early separated in the Mammalia, by a constriction 
 of the portion which is continuous with the abdomen of the Embryo ; and it 
 is known from that time under the name of the Umbilical Vesicle. The com- 
 munication, however, remains open for a time through the constricted portion, 
 which is termed the Vitelline Duct ; and even after this has been cut off, the 
 trunks which connected the circulating system of the Embryo with that of the 
 Vascular Area, are still discernible; these are called Omphalo-Mesenteric, 
 Meseraic, or Vitelline vessels. It was formerly believed, that the nutrient 
 matter of the yolk passes directly through the Vitelline duct, into the (future) 
 digestive cavity of the Embryo, and is from it absorbed into its structure; but 
 there can now be little doubt, that the Vitelline vessels are the real agents of 
 its absorption, and that they convey it to the tissues in process of formation. 
 They do, in fact, correspond to the Mesenteric veins of Invertebrated animals, 
 which are the sole agents in the absorption of nutriment from their digestive 
 cavity ( 674) ; and the yolk-bag, as already remarked, is the temporary sto- 
 mach of the Embryo, remaining as the permanent stomach in the Radiated 
 tribes. Previously to the ninth day of incubation (in the Fowl's egg), a series 
 of folds are formed by the lining membrane of the yolk-bag, which project 
 into its cavity; these become gradually deeper and more crowded, as the bag 
 diminishes in size by the absorption of its contents. The Vitelline vessels, 
 that ramify upon the yolk-bag, send into these folds (or valvula? conniventes) 
 a series of inosculating loops, which immensely increase the extent of this 
 absorbing apparatus. But these minute vessels are not in immediate contact 
 with the yolk; for there intervenes between them a layer of nucleated cells, 
 which is easily washed away. It was from the colour of these, communicated 
 to the vessels beneath, that Haller termed the latter vasa lutea; when the 
 layer is removed, the vessels present their usual colour. There seems good 
 reason to believe, that these cells, like those of the Intestinal Villi in the adult 
 ( 672), are the real agents in the process of absorbing and assimilating the 
 nutritive matter of the yolk ; and that they deliver this up to the vessels, by 
 themselves undergoing rupture or dissolution, being replaced by new layers. 
 
 940. The formation of the Heart takes place in the Vascular layer, beneath 
 the upper part of the Spinal Column ; it at first appears as a mere cavity in its 
 substance, surrounded only by cells ; but its walls gradually acquire firmness 
 
DEVELOPMENT OF THE EMBRYO. 
 
 717 
 
 and distinctness, and become sufficiently powerful to propel the blood through 
 the vessels of the Embryo and those of the Vascular Area. The first ap- 
 pearance of the Heart in the Chick is at about the 27th hour ; the time of its 
 formation in Mammalia has not been distinctly ascertained. In its earliest 
 form, it has the same simple character, which is presented by the central im- 
 pelling cavity of the lower Invertebrata ; being a mere prolonged canal, which 
 at its posterior extremity receives the veins, and at its anterior sends forth the 
 arteries. After a short time, however, it becomes bent upon itself (Plate II., 
 Fig. 27, d) ; and it is soon subdivided into three cavities, which exist in all 
 Vertebrata, a simple auricle or receiving cavity, a simple ventricle or pro- 
 pelling cavity, and a bulbus arteriosus at the origin of the aorta. The circu- 
 lation is at first carried on exactly upon the plan, which is permanently 
 exhibited by Fishes. The Aorta subdivides into four or five arches on either 
 side of the neck ; and these are separated by slits or fissures, much resem- 
 bling those which form the entrances to the gill-cavities of Cartilaginous 
 Fishes. These arches reunite to form the descending aorta, which transmits 
 branches to all parts of the body. Such is the first phase or aspect of the 
 Circulating Apparatus, which is common to all Vertebrata during the earliest 
 period of their development, and which may, therefore, be considered as its 
 most general form. It remains permanent in the class of Fishes; and in them 
 the vascular system undergoes further development on the same type, a num- 
 ber of minute tufts being sent forth from each of the arches, which enter the 
 filaments of the gills, and serve for the aeration of the blood. In higher 
 Vertebrata, however, the plan of the circulation is afterwards entirely changed, 
 by the formation of new cavities in the heart, and by the production of new 
 vessels; these changes will be presently described. It is incorrect, therefore, 
 to speak of the vascular arches in their necks as branchial arches ; since no 
 branchiae or gills are ever developed from them. The clefts between them 
 may be very distinctly seen in the Human Foetus towards the end of the first 
 month ; during the second, they usually close up and disappear. 
 
 941. With the evolution of a Circulating apparatus, adapted to absorb 
 nourishment from the store prepared for the use of the Embryo, and to con- 
 vey it to its different tissues, it becomes necessary that a respiratory apparatus 
 
 Fig. 286. 
 
 The Amnion in process of formation, by the 
 arching over of the serous lamina; a, the 
 chorion ; b, the yolk-bag, surrounded by se- 
 rous and vascular laminae ; c, the embryo ; 
 d, e, and/, external and internal folds of the 
 serous layer, forming the amnion ; , incipi- 
 ent allantois. 
 
 a,/ 
 
 Diagram representing a Human Ovum in 
 second month ; a. 1, smooth portion of cho- 
 rion ; a. 2, villous portion of chorion ; k, k, 
 elongated villi, beginning to collect into Pla 
 centa ; 6, yolk-sac or umbilical vesicle ; c, em 
 bryo; /, amnion (inner layer); g, allantois; 
 A, outer layer of amnion, coalescing with 
 cborion. 
 
718 
 
 OF REPRODUCTION. 
 
 should also be provided, for unloading the blood of the carbonic acid with 
 which it becomes charged during the course of its circulation. The tempo- 
 rary Respiratory apparatus now to be described, bears a strong resemblance 
 in its own character, and especially in its vascular connections, with the gills 
 of the Mollusca; which are prolongations of the external surface (usually 
 near the termination of the intestinal canal), and which almost invariably 
 receive their vessels from that part of the system. This apparatus is termed 
 the Allantois. It consists at first of a kind of diverticulum or prolongation of 
 the lower part of the Digestive cavity, the formation of which has been already 
 described. This is at first seen as a single vesicle, of no great size (Fig. 
 285, g) ; and in the Fretus of Mammalia, which is soon provided with other 
 means of aerating its blood, it seldom attains any considerable dimensions. 
 In Birds, however, it becomes so large as to extend itself around the whole 
 Yolk-sac, intervening between it and the membrane of the shell ; and through 
 the latter it comes into relation with the external air. The preceding diagram 
 (Fig. 286) will serve to explain its origin and position in the Human ovum. 
 The chief office of the Allantois in Mammalia is to convey the vessels of the 
 
 Diagram of Human Ovum, at the time of formation of Placenta; a, muco-gelatinous substance, block- 
 ing up os uteri ; 6, 6, Fallopian tubes ; c, c, Decidua vera, prolonged at c 2, into Fallopian tube ; d, cavity 
 ofuterus, almost completely occupied by ovum; e, e, angles at which Decidua vera is reflected ; /, De- 
 cidua serotina ; g, allantois; h, umbilical vesicle ; i, amnion ; fc, chorion, lined with outer fold of serous 
 tunic. 
 
DEVELOPMENT OF THE EMBRYO. 719 
 
 embryo to the Chorion; and its extent bears a pretty close correspondence 
 with the extent of surface, through which the Chorion comes into vascular 
 connection with the Decidua. Thus, in the Carnivora, whose Placenta ex- 
 tends like a band around the whole Ovum, the Allantois also lines the whole 
 inner surface of the Chorion, except where the Umbilical Vesicle comes in 
 contact with it. On the other hand, in Man and the Quadrumana, whose 
 Placenta is restricted to one spot, the Allantois is small, and conveys the 
 foetal vessels to one portion only of the Chorion. When these vessels have 
 reached the Chorion, they ramify in its substance, and send filaments into its 
 villi; and in proportion as these villi form that connection with the uterine 
 structure, which has been already described, do the vessels increase in size. 
 They then pass directly from the Foetus to the Chorion; and the Allantois, 
 being no longer of any use, shrivels up, and remains as a minute vesicle, only 
 to be detected by careful examination. The same thing happens in regard to 
 the Umbilical vesicle, from which the entire contents have been by this time 
 exhausted; and from henceforth the Foetus is completely dependent for the 
 materials of its growth, upon the supply it receives through the Placenta, 
 which is conducted to it by the vessels of the Umbilical Cord. This state of 
 things is represented in the preceding diagram. The Allantois has a corre- 
 spondence in situation with the Urinary Bladder ; but it is only the lower 
 part of it, pinched off, as it were, from the rest, that remains as such. The 
 duct by which it is connected with the abdomen gradually shrivels; and a 
 vestige of this is permanent, forming the Urachus or suspensory ligament of 
 the Bladder, by which it is connected with the Umbilicus. Before this takes 
 place, however, the Allantois is the receptacle for the secretion of the Corpora 
 Wolffiana, and of the true Kidneys, when they are formed. 
 
 942. It will be seen from the preceding diagram, that the Umbilical Cord 
 receives an investment from the Amnion, which forms a kind of tubular 
 sheath around it ; it is continuous at the Umbilicus with the integument of 
 the foetus ; and at the point where the cord enters the Placenta, it is reflected 
 over its internal or foetal surface. The Amnion (which thus forms a shut 
 sac, like that of the Pleura, Arachnoid, &c.) contains a fluid known as the 
 liquor amnii; this consists of water holding in solution a small quantity of 
 albumen and saline matter, and resembling, therefore, very diluted serum. 
 During the first two months of gestation, the Amnion and the inner surface 
 of the Chorion (which is really the reflected layer of the Amnion, just as the 
 lining of the abdominal cavity is formed by the peritoneum) are separated by a 
 gelatinous-looking substance; which may perhaps be considered as represent- 
 ing the white of the egg in Birds ; and which probably aids in the nutrition 
 of the Embryo, previously to the formation of the Placenta ( 918). This 
 is absorbed during the second month; and the Amnion is then found imme- 
 diately beneath the Chorion. In the Umbilical Cord, when it is completely 
 formed, the following parts may be traced. 1. The tubular sheath afforded 
 by the Amnion. 2. The Umbilical Vesicle, with its pedicle, or Omphalo- 
 Enteric duct. 2. The Vasa Omphalo-Meseraica, or mesenteric vessels of 
 the Embryo, by which the Yolk was absorbed into the body of the Foetus; 
 these accompany the pedicle. 4. The Urachus, and remains of the Allantois. 
 5. The Vasa Umbilicalia, which, in the later period of gestation, constitute 
 the chief part of the Cord. These last vessels consist in Man of two Arte- 
 ries and one Vein. The Arteries are the main branches of the Hypogastric ; 
 and they convey to the Placenta the blood which has to be aerated and other- 
 wise revivified, by being brought into relation with that of the Mother. The 
 Vein returns this to the Foetus, and discharges a part of it into the Vena 
 Portaj, and a part directly through the Ductus Venosus into the Aorta. 
 
720 OF REPRODUCTION. 
 
 943. A change in the type of the Circulating system of the foetus, from 
 that at first presented by it ( 940), takes place at a very early period. At 
 about the 4th week, in the Human Embryo, a septum begins to be formed in 
 the Ventricle ; and by >the end of the 8th week it is complete. The Septum 
 Auriculorum is formed at a somewhat later period, and it remains incomplete 
 during the whole of foetal life ; it is partly closed by the valvular fold cover- 
 ing the Foramen Ovale, which fold is developed during the third month. 
 During the same period, a transformation takes place in the arrangement of 
 the large vessels proceeding from the Heart; which ends in their assumption 
 of the form they present until the end of Festal life; and this undergoes but 
 a slight alteration, when the plan of the circulation is changed at the moment 
 of the first inspiration. The number of Aortic arches on each side, which 
 was five at first, soon becomes reduced in the Mammalia to three, by the 
 obliteration of the two highest pairs. The Bulbus Arteriosus is subdivided, 
 by the adhesion of its walls at opposite points, into two tubes, of which one 
 becomes the Aorta and the other the Pulmonary Artery ; and of the three 
 pairs of (branchial) arches, the highest, being connected with the Aortic trunk, 
 contributes to the formation of the Subclavian and Carotid arteries ; whilst of 
 the middle pair, the arch on the right side is obliterated, the other becoming 
 the Arch of the Aorta. The lowest pair arises from the Pulmonary trunk, 
 and forms the Pulmonary artery on each side ; that on the left side, however, 
 goes on to join the descending Aorta as before, and thus constitutes the Ductus 
 Arteriosus. 
 
 944. The following is the course of the circulation of the blood in the 
 Foetus. The fluid brought from the Placenta by the Umbilical Vein is partly 
 conveyed at once to the Vena Cava ascendens, by means of the Ductus 
 Venosus, and partly flows through the Vena Portae into the Liver, whence it 
 reaches the ascending Cava by the Hepatic Vein. Having thus been trans- 
 mitted through the two great depurating organs, the Placenta and the foetal 
 Liver, it is in the condition of arterial blood ; but, being mixed in the vessels 
 with that which has been returned from the trunk and lower extremities, it 
 loses this character in some degree by the time that it arrives in the Heart. 
 In the right Auricle, which it then enters, it would be also mixed with the 
 venous blood conveyed by the descending Cava; were it not that a very curi- 
 ous provision exists, to prevent (in great degree, if not entirely) any such fur- 
 ther dilution-. The Eustachian valve has been found, by the experiments of 
 Dr. J. Reid,* to serve the purpose of directing the arterial blood, which flows 
 upwards from the ascending Cava, through the Foramen Ovale, into the left 
 Auricle, whence it passes into the Ventricle; whilst it also directs the Venous 
 blood, that has been returned by the descending Cava into the right Ven- 
 tricle. When the Ventricles contract, the Arterial blood which the left con- 
 tains is propelled into the ascending Aorta, and supplies the branches that 
 proceed to the head and upper extremities, before it undergoes any admix- 
 ture ; whilst the Venous blood, contained in the right Ventricle, is forced 
 through the Pulmonary artery and Ductus Arteriosus into the descending 
 Aorta, mingling with the arterial current which that vessel previously con- 
 veyed, and passing thus to the trunk and lower extremities. Hence the Head 
 and superior extremities, whose development is required to be in advance of 
 that of the lower, are supplied with blood nearly as pure as that which returns 
 from the Placenta : whilst the rest of the body receives a mixture of this, 
 with what has previously circulated through the system ; and of this mixture 
 a portion is transmitted to the Placenta, to be renovated by coming into rela- 
 tion with the maternal fluid. At birth, the course of the current is entirely 
 
 * Edinb. Med. and Surg. Journal, vol. xliii. 
 
DEVELOPMENT OF THE EMBRYO. 
 
 [Fig. 288. 
 
 O O 
 
 721 
 
 The Foetal Circulation; 1, the umbilical cord, consisting of the umbilical vein and two umbilical 
 arteries; proceeding from the placenta (2) ; 3, the umbilical vein dividing into three branches; two (4, 4) 
 to be distributed to the liver ; and one (5), the ductus venosus, which enters the inferior vena cava (6) ; 
 7, the portal vein, returning the blood from the intestines, and uniting with the right hepatic branch; 8, 
 the right auricle ; the course of the blood is denoted by the arrow, proceeding from 8 to 9, the left auricle ; 
 10, the left ventricle ; the blood following the arrow to the arch of the aorta (11), to be distributed through 
 the branches given off by the arch to the head and upper extremities. The arrows, 12 and 13, represent 
 the return of the blood from the head and upper extremities through the jugular and subclavian veins, 
 to the superior vena cava (14), to the right auricle (8), and in the course of the arrow through the right 
 ventricle (15), to the pulmonary artery (16) ; 17, the ductus arteriosus, which appears to be a proper con- 
 tinuation of the pulmonary artery the offsets at each side are the right and left pulmonary artery cut 
 off; these are of extremely small size as compared with the ductus arteriosus. The ductus arteriosus 
 joins the descending aorta (18, 18), which divides into the common iliacs, and these into the internal 
 iliacs, which become the umbilical arteries (19), and return the blood along the umbilical cord to the 
 placenta ; while the other divisions, the external iliacs (20), are continued into the lower extremities. 
 The arrows at the termination of these vessels mark the return of the venous blood by the veins to the 
 inferior cava.] 
 
 changed by its diversion into the Lungs ; which takes place immediately on 
 the first inspiration. The Ductus Venosus and Ductus Arteriosus soon shrivel 
 into ligaments ; the Foramen Ovale becomes closed by its valve ; and the 
 circulation, which was before carried on upon the plan of that of the higher 
 Reptiles, now becomes that of the complete Bird or Mammal. It is by no 
 means unfrequent, however, for some arrest of development to prevent the 
 61 
 
722 OF REPRODUCTION. 
 
 completion of these changes ; and various malformations, involving an imper- 
 fect discharge of the function, may hence result.* 
 
 945. The Alimentary Canal has been shown to have its origin in the Yolk- 
 sac or Umbilical Vesicle ; being a portion pinched off (as it were) from that 
 part of it, which is just beneath the Spinal Column of the Embryo ( 937). 
 At first it is merely a long narrow tube, nearly straight, and communicating 
 with the Umbilical Vesicle at about the middle of its length ; thus it may be 
 regarded as composed of the union of two, an upper and a lower division. 
 At first, neither Mouth nor Anus exists ; but these are formed early in the 
 second month, if not before. The tube gradually manifests a distinction into 
 its special parts, (Esophagus, Stomach, Small Intestine, and Large Intestine ; 
 and the first change in its position occurs in the Stomach, which, from being 
 disposed in the line of the body, takes an oblique direction. The curves of 
 the large and small intestines present themselves at a later period. It is at the 
 lower part of the small Intestine, near its termination in the large, that the 
 entrance of the Omphalo-Enteric duct exists ; and a remnant of this canal is 
 not unfrequently preserved throughout life, in the form of a small pouch or 
 diverticulum from that part of the intestine. The various Glandular structures 
 connected with the alimentary canal, originate in diverticula from its walls, in 
 the manner already described in regard to the Liver ( 826, g). The Lungs 
 and Respiratory apparatus are formed in like manner, as diverticula from the 
 (Esophagus ( 757, 6, c). 
 
 946. The mode in which the chief organs of the Human embryo originate 
 having been thus described, and sufficient particulars in regard to their subse- 
 quent development having been already given under distinct heads, it is un- 
 necessary here to add more on this very interesting but complex subject; be- 
 cause for practical purposes there is little or no advantage to be gained from 
 the most perfect aquaintance with it. The most important of all the facts that 
 have come under our review, is that which has been stated as in the highest 
 degree probable, if not yet absolutely proved, in regard to the relative offices 
 of the Male and Female in this hitherto mysterious process. According to 
 the view here given, the Male furnishes the germ; and the Female supplies 
 it with Nutriment, during the whole period of its early development. There 
 is no difficulty in reconciling such a doctrine with the well-known fact, that 
 the offspring commonly bears a resemblance to both parents (of which the 
 production of a hybrid between distinct species is the most striking example) ; 
 since numerous phenomena prove that, in this earliest and simplest condition 
 of the organism, the form it will ultimately assume very much depends upon 
 circumstances external to it; among which circumstances, the kind of nutri- 
 ment supplied will be one of the most important.t Upon the same principle 
 we may account for the influence of the mental condition of the Mother upon 
 1ier Offspring, during a later period of pregnancy. That such influence may 
 occur, there can be no reasonable doubt. " We have demonstrative evidence," 
 says Dr. A. Combe,^ " that a fit of passion in a nurse vitiates the quality of 
 the milk to such a degree, as to cause colic and indigestion [or even death] 
 in the suckling infant. If, in the child already born, and in so far independent 
 of its parent, the relation between the two is thus strong, is it unreasonable to 
 suppose that it should be yet stronger, when the infant lies in its mother's 
 womb, is nourished indirectly by its mother's blood, and is, to all intents and 
 purposes, a part of her own body? If a sudden and powerful emotion of her 
 own mind exerts such an influence upon her stomach as to excite immediate 
 
 * See Principles of General and Comparative Physiology, Chap. vi. 
 f See Principles of General and Comparative Physiology, 665. 
 J On the Management of Infancy, p. 76. 
 
DEVELOPMENT OF THE EMBRYO. 723 
 
 vomiting, and upon her heart as almost to arrest its motion and induce fainting, 
 can we believe that it will have no effect on her womb and the fragile being 
 contained within it ? Facts and reason, then, alike demonstrate the reality of 
 the influence: and much practical advantage would result to both parent and 
 child, were the conditions and extent of its operations better understood." 
 Among facts of this class, there is, perhaps, none more striking than that 
 quoted by the same Author from Baron Percy, as having occurred after the 
 siege of Landau in 1793. In addition to a violent cannonading, which kept 
 the women for some time in a constant state of alarm, the arsenal blew up 
 with a terrific explosion, which few could hear with unshaken nerves. Out 
 of 92 children born in that district within a few months afterwards, Baron 
 Percy states that 16 died at the instant of birth ; 33 languished for from 8 to 
 10 months, and then died ; 8 became idiotic, and died before the age of 5 years ; 
 and 2 came into the world with numerous fractures of the bones of the limbs, 
 caused by the cannonading and explosion. Here, then, is a total of 59 chil- 
 dren out of 92, or within a trifle of 2 out of every 3, actually killed through the 
 medium of the Mother's alarm and the natural consequences upon her own 
 organization, an experiment (for such it is to the Physiologist) upon too large 
 a scale for its results to be set down as mere " coincidences." No soundly- 
 judging Physiologist of the present day is likely to fall into the popular error, 
 of supposing that marks upon the Infant are to be referred to some transient 
 though strong impression upon the imagination of the Mother; but there ap- 
 pear to be a sufficient number of facts on record, to prove that habitual mental 
 conditions on the part of the Mother may have influence enough, at an early 
 period of gestation, to produce evident bodily deformity, or peculiar tendencies 
 of the mind. But whatever be the nature and degree of the influence thus 
 transmitted, it must be such as can act by modifying the character of the nu- 
 tritive materials supplied by the Mother to the Fretus ; since there is no other 
 channel by which any influence can be propagated. The absurdity of the 
 vulgar notion just alluded to, is sufficiently evident from this fact alone ; as it 
 is impossible to suppose that a sudden fright, speedily forgotten, can exert 
 such a continued influence on the nutrition of the Embryo, as to occasion any 
 personal peculiarity.* The view here stated is one which ought to have great 
 weight, in making manifest the importance of careful management of the health 
 of the Mother, both corporeal and mental, during the period of pregnancy ; 
 since the constitution of the offspring so much depends upon the impressions 
 then made upon its most impressible structure. 
 
 947. It is frequently of great importance, both to the Practitioner and to 
 the Medical Jurist, to be able to determine the age of a Foetus, from the physi- 
 cal characters which it presents ; and the following table has been framed by 
 Devergiet in order to facilitate such determination. It is to be remarked, how- 
 ever, that the absolute Length and Weight of the Embryo are much less safe 
 criteria, than its degree of Development, as indicated by the relative evolution 
 of the several parts, which make their appearance successively. Thus it is 
 very possible for one child, bom at the full time, to weigh less than another, 
 born at 8 or even at 7 months ; its length, too, may be no greater ; but the 
 position of the middle point of the body will usually afford sufficient ground 
 
 * For some valuable observations on this subject, see Montgomery on the Signs of Preg- 
 nancy. Numerous cases have been recorded, during the last few years (especially in tJ 
 Lancet and Provincial Medical Journal) in which malformations in the Infant appeared 
 distinctly traceable to strong impressions made on the mind of the Mother, some months 
 previously to parturition ; these impressions having been persistent during the remaining 
 period of pregnancy, and giving rise to a full expectation on the part of the Mother, that 
 child would be affected in the particular manner which actually occurred. 
 
 t Medecine Legale, vol. i. p. 495. 
 
724 OF REPRODUCTION. 
 
 for the determination ; since, during the two latter months of pregnancy, the 
 increasing development of the lower extremities throws it lower down. 
 
 Embryo 3 to 4 weeks.' It has the form of a serpent ; its length from three to five lines ; 
 its head indicated by a swelling ; its caudal extremity (in which is seen a white line, indi- 
 cating the continuation of the medulla spinalis), slender, and terminating in the umbilical 
 cord; the mouth indicated by a cleft; the eyes by two black points ; the members begin 
 to appear as nipple-like protuberances ; the liver occupies the whole abdomen ; the bladder 
 is very large. The chorion is villous, but its villosities are still diffused over the whole surface. 
 
 Embryo of 6 weeks. Its length from 7 to 10 lines; its weight from 40 to 75 grains; 
 face distinct from cranium; aperture of nose, mouth, eyes, and ears perceptible: head 
 distinct from thorax ; hands and fore-arms in the middle of the length, ringers distinct; 
 legs and fee,t situated near the anus ; clavicle and maxillary bone present a point of ossifi- 
 cation ; distinct umbilicus for attachment of cord, which at that time consists of the om- 
 phalo-meseraic vessels, of a portion of the urachus, of a part of the intestinal tube, and of 
 filaments which represent the umbilical vessels. The placenta begins to be formed ; the 
 chorion still separated from the amriion; the umbilical vesicle very large. 
 
 Embryo of 2 months. Length from 16 to 19 lines; weight from 150 to 300 grains; the 
 elbows and arms detached from the trunk ; heels and knees also isolated ; rudiments of 
 the nose and of the lips; palpebral circle beginning to show itself; clitoris or penis ap- 
 parent; anus marked by a dark spot; rudiments of lungs, spleen, and supra-renal capsules; 
 caecum placed behind the umbilicus ; digestive canal withdrawn into the abdomen ; 
 urachus visible ; osseous points in the frontal bone and in the ribs. Chorion commencing 
 to touch the amnion at the point opposite the insertion of the placenta; placenta begins to 
 assume its regular form ; umbilical vessels commence twisting. 
 
 Embryo of 3 months. Length from 2 to 2^ inches ; weight from 1 oz. to 1 \ oz. (Troy) ; 
 head voluminous; ^eyelids in contact by their free margin: membrana pupillaris visible ; 
 mouth closed; fingers completely separated; inferior extremities of greater length than 
 rudimentary tail ; clitoris and penis very long; thymus as well as supra-renal capsules 
 present ; caecum placed below the umbilicus ; cerebrum 5 lines, cerebellum 4 lines, me- 
 dulla oblongata 1^ line, and medulla spinalis of a line, in diameter; two ventricles of 
 heart distinct. The decidua reflexa and decidua uterina in contact: funis contains umbili- 
 cal vessels and a little of the gelatine of Warthon ; placenta completely isolated ; umbilical 
 vesicle, allantois, and omphalo-mesenteric vessels have disappeared. 
 
 Foetus of 4 months. Length 5 to 6 inches; weight 2^to3oz.; skin rosy, tolerably 
 dense; mouth very large and open; membrana pupillaris very evident; nails begin to 
 appear: genital organ and sex distinct ; caecum placed near the right kidney ; gall-bladder 
 appearing ; meconium in duodenum ; coecal valve visible ; umbilicus placed near pubis ; 
 ossicula auditoria ossified ; points of ossification in superior part of sacrum ; membrane 
 forming at point of insertion of placenta on uterus; complete contact of chorion with 
 amnion. 
 
 Fatus of 5 months. Length 6 to 7 inches ; weight 5 to 7 oz. ; volume of head still com- 
 paratively great; nails very distinct; hair beginning to appear; skin without sebaceous 
 covering; white substance in cerebellum; heart and kidneys very voluminous ; caecum 
 situated at inferior part of right kidney ; gall-bladder distinct ; germs of permanent teeth 
 appear ; points of ossification in pubis and calcaneum ; meconium has a yellowish-green 
 tint, and occupies commencement of large intestine. 
 
 Fcetus of 6 months. Length 9 to 10 inches: weight 1 Ib. ; skin presents some appear- 
 ance of fibrous structure ; eyelids still agglutinated, and membrana pupillaris remains ; 
 sacculi begin to appear in colon; funis inserted a little above pubis; face of a purplish 
 red; hair white or silvery; sebaceous covering begins to present itself; meconium in 
 large intestines; liver of dark red; gall-bladder contains serous fluid destitute of bitter- 
 ness- testes near kidneys ; points of ossification in four divisions of sternum ; middle 
 point at lower end of sternum. 
 
 Fastus of! months. Length 13 to 15 inches; weight 3 to 4 Ibs.; skin of rosy hue, thick, 
 and fibrous; sebaceous covering begins to appear; nails do not yet reach extremities of 
 fingers ; eyelids no longer adherent; membrana pupillaris disappearing; a point of ossi- 
 fication in the astragalus ; meconium occupies nearly the whole of large intestine ; valvulee 
 conniventes beginning to appear; caecum placed in right iliac fossa; left lobe of liver 
 almost as large as right ; gall-bladder contains bile ; brain possesses more consistency ; 
 testicles more distant from kidneys ; middle point at a little below end of sternum. 
 
 Fo3tus of 8 months. Length 14 to 16 inches; weight 4 or 5 Ibs. ; skin covered with 
 well-marked sebaceous envelope ; nails reach extremities of fingers ; membrana pupillaris 
 becomes invisible during this month : a point of ossification in last vertebra of sacrum ; 
 cartilage of inferior extremity of femur presents no centre of ossification ; brain has some 
 
PROPORTION OF SEXES. 725 
 
 indications of convolutions; testicles descend into internal ring; middle point nearer the 
 umbilicus than the sternum. 
 
 Fcetus of 9 months, the full term. Length from 17 to 21 inches: weight from 5 to 9 Ibs., 
 the average probably about 6 Ibs. ; head covered with hair in greater or less quantity, of 
 from 9 to 12 lines in length; skin covered with sebaceous matter, especially at bends of 
 joints ; membrana pupillaris no longer exists ; external auditory meatus still cartilaginous ; 
 four portions of occipital bone remain distinct; os hyoides not yet ossified; point of ossi- 
 fication in the centre of cartilage at lower extremity of femur ; white and grey substances 
 of brain become distinct; liver descends to umbilicus; testes have passed inguinal ring, 
 and are frequently found in scrotum; meconium at termination of large intestine; middle 
 point of body at umbilicus, or a little below it. 
 
 948. Even at Birth, there is a manifest difference in the physical conditions 
 of Infants of different sexes ; for, in the average of a large number, there is a 
 decided preponderance on the side of the Males, both as to the Length and 
 the Weight of the body. 
 
 a. The Length of the body in fifteen new-born infants of each sex, as ascertained by Que- 
 telet,* was as follows : 
 
 Males. Females. Total. 
 
 From 16 to 17 inchest (French) 2 4 6 
 
 17 to 18 8 19 27 
 
 - 18 to 19 28 18 46 
 
 19 to 20 ..... 12 8 20 
 
 - 20 to 21 1 1 
 
 From these observations, the mean and the extremes of the Lengths of the Male and Female 
 
 respectively, were calculated to be, 
 
 Males. Females. 
 
 Minimum . . 16 inches, 2 lines 16 inches, 2 lines 
 
 Mean 18 6 18 li 
 
 Maximum 19 8 20 6 
 
 Notwithstanding that the maximum is here on the side of the Female (this being an acci- 
 dental result, which would probably have been otherwise, had a larger number been ex- 
 amined), the average shows a difference of 4^ lines in favour of the Male. 
 
 b. The inequality in the Weight of the two is even more remarkable; the observations of 
 M. QueteletJ were made upon 63 male and 56 female infants. 
 
 Infants weighing from Males. Females. Total. 
 
 1 to 1$ kilog. ..... 1 1 
 1 to 2 1 1 
 
 2 to2i 3 7 10 
 
 2J to 3 13 14 27 
 
 3 to 3i ,28 23 51 
 
 3to4 14 7 21 
 
 4 to 4i ...... 5 3 8 
 
 The extremes and means were as follows : 
 
 Males. Females. 
 
 Minimum . . . 2-34 kilog. 1-12 
 
 Mean . . . . 3-20 2-91 
 
 Maximum . . , 4-50 4-25 
 
 c. The average weight of infants of both sexes, as determined by these inquiries, is 3-05 
 kilog. or 6-7 Ibs. ; and this corresponds almost exactly with the statement of Chaussier, whose 
 observations were made upon more than 20,000 infants. The mean obtained by him, with- 
 out reference to distinction of sex, was 6'75 Ibs. ; the maximum being 11'3 Ibs., and the mini- 
 mum 3-2 Ibs. || The average in this country is probably rather higher; according to Dr. 
 Joseph Clarke,1T whose inquiries were made on 60 males and 60 females, the average of 
 
 * Sur L'Homme. torn. ii. p. 8. 
 
 f The French inch is about one-fifteenth more than the English. 
 j Op. pit, torn. ii. p. 35. 
 
 The kilogramme is equal to 2 j Ibs. avoirdupois. 
 
 || These numbers have been erroneously stated in many Physiological works ; owing to 
 the difference between the French and English pound not having been allowed for. 
 IT Philosophical Transactions, vol. Ixxvi. 
 
 61* 
 
726 OF REPRODUCTION. 
 
 Male children is 7g- Ibs.: and that of Females 6$ Ibs. He adds that children which at the 
 full time weigh less than 5 Ibs. rarely thrive ; being generally feeble in their actions, and 
 dying within a short time. Several instances are on record, of infants whose weight at birth 
 exceeded 15 Ibs. It appears that healthy females, living in the country, and engaged in 
 active but not over-fatiguing occupations, have generally the largest children ; and this is 
 what might be expected a .priori from the superior activity of their nutritive functions. 
 
 949. Notwithstanding .that, in any ordinary population, there is a decided 
 preponderance in the number of Females, the number of Male births is con- 
 siderably greater than that of females. Taking the average of the whole of 
 Europe, the proportion is about 106 Males to 100 Females. It is curious, 
 however, that this proportion is considerably different for legitimate and for 
 illegitimate births ; the average of the latter being only 102 to 100, in the 
 places where that of the former was 105| to 100. This is probably to be 
 accounted for by the fact, which is one of the most remarkable contributions 
 that have yet been made by Statistics to Physiology, that the Sex of the off- 
 spring is influenced by the relative ages of the parents. The following table 
 expresses the average results obtained by M* Hofacker* in Germany, and by 
 Mr. Sadlert in Britain ; between which it will be seen that there is a manifest 
 correspondence, although both were drawn from a too.limited series of observa- 
 tions. The numbers indicate the proportion of Male births to 100 Females, 
 under the several conditions mentioned in the first column. 
 
 Hofacker. Sadler. 
 
 Father younger than Mother . . 9O6 Father younger than Mother . . 86-5 
 
 Father and Mother of equal age 
 Father older by 1 to 6 years 
 6 to 9 
 9 to 18 . 
 18 and more 
 
 90-0 Father and Mother of equal age . 94-8 
 
 103-4 Father older by 1, to 6 years . . 103-7 
 
 124-7 . . 6 to 11 . . . 126-7 
 
 143-7 . . 11 to 16 . . . 147-7 
 
 200-0 16 and more 163-2 
 
 From this it appears, that the more advanced age of the Male parent has a 
 very decided influence in occasioning a preponderance in the number of Male 
 infants ; and as the state of society generally involves a condition of this kind 
 in regard to marriages, whilst in the case of illegitimate children the same 
 does not hold good, the difference in the proportional number of male births 
 is accounted for. We are not likely to obtain data equally satisfactory in 
 regard to the influence of more advanced age on the part of the Female parent ; 
 as a difference of 10 or 15 years on that side is not so common. If it exist 
 to the same extent, it is probable that the same law would be found to prevail 
 in regard to Female children born under such circumstances, as has been 
 stated with respect to the Male ; namely, that the mortality is greater during 
 embryonic life and early infancy, so that the preponderance is reduced. 
 
 950. There appears to be, from the first, a difference in the viability (or 
 probability of life) of Male and Female children ; for, out of the total number 
 born dead, there are 3 Males to 2 Females : this proportion gradually lessens, 
 however, during early infancy ; being about 4 to 3 during the first two months, 
 and about 4 to 5 during the next three months ; after which time the deaths 
 are nearly in proportion to the numbers of the two sexes respectively, until 
 the age of puberty. The viability of the two sexes continues to increase 
 during childhood ; and attains its maximum between the 13th and 14th years. 
 For a short time after this epoch has been passed, the rate of mortality is 
 higher in Females than in Males; but from about the age of 18 to 28, the 
 mortality is much greater in Males, being at its maximum at 25, when the 
 viability is only half what it is at puberty. This fact is a very striking one ; 
 and shows most forcibly that the indulgence of the passions not only weakens 
 the health, but in a great number of instances is the cause of a very premature 
 
 * Annales d'Hygiene, Oct. 1S29. f Law of Population, vol. ii. p. 343. 
 
PROPORTION OF SEXES. 
 
 727 
 
 death. From the age of 28 to that of 50, the mortality is greater, and the 
 viability less, on the side of the Female ; this is what would be anticipated 
 from the increased risk, to which she is liable during the parturient period. 
 After the age of 50, the mortality is nearly the same for both. 
 
 a. These facts have been expressed by Quetelet in a form which brings them prominently 
 before the eye (Fig. 289). The relative viability of the Male at different ages is represented 
 by a curved line; the elevation of which indicates its degree, at the respective periods 
 marked -along the base line. The dotted line which follows a different curve, represents 
 the viability of the Female. Starting from a, the period of birth, we arrive at the maxi- 
 mum of viability for both at b ; from this point, the Female curve steadily descends towards 
 
 Fig. 289. 
 
 CL b 70 15 20 26 30 
 
 Diagram representing the comparative Viability of the Male and Female at different Ages. 
 
 M, at first very rapidly, but afterwards more gradually; whilst the Male curve does not de^ 
 scend quite so soon, but afterwards falls much lower, its minimum being c, which corresponds 
 with the age of 25 years. It afterwards ascends to rf, which is the maximum of viability 
 subsequently to the age of puberty; this point is attained at the age of 30 years, from which 
 period, up to 50, the probability of life is greater in the Male than in the Female. In the 
 decline of life there seems little difference for the two sexes. 
 
 951. Similar diagrams have been constructed by Quetelet, to indicate the 
 relative Heights and Weights of the two sexes (Fig. 290). 
 
 a. In regard to Height it may be observed, that the increase is most rapid in the first 
 year, and that it afterwards diminishes gradually; between the ages of 5 and 16 years, the 
 annual increase is very regular. The difference between the Height of the Male and I 
 male, which has been already stated to present itself at birth, continues to increase during 
 infancy and youth; it is not very decided, however, until about the 15th year, after which 
 the growth of the Female proceeds at a much diminished rate, whilst that of the Male con- 
 tinues in nearly the same degree, until about the age of 19 years. It appears, then, that the 
 Female comes to her full development in regard to Height, earlier than does the Male. J 
 seems probable, from the observations of Quetelet, that the full height of the Male is not 
 
728 
 
 OF REPRODUCTION. 
 
 generally attained until the age of 25 years. At about the age of 50, both Male and Female 
 undergo a diminution of their stature, which continues during the latter part of life. 
 
 6. The proportional Weight of the two sexes at different periods, corresponds pretty 
 closely with their height. Starting from birth, the predominance then exhibited by the Male 
 gradually increases during the first few years ; but towards the period of puberty, the pro- 
 portional weight of the Female increases ; and at the age of 12 years, there is no difference 
 between the two sexes in this respect. The weight of the Male, however, then increases 
 much more rapidly than that of the Female, especially between the ages of 15 and 20 
 years ; after the latter period, there is no considerable increase on the side of the Male, 
 though his maximum is not attained until the age of 40; and there is an absolute diminu- 
 tion on the part of the Female, whose weight remains less during nearly the whole period of 
 child-bearing. After the termination of the parturient period, the weight of the Female again 
 undergoes an increase, and its maximum is attained about 50. In old age, the weight of 
 both sexes undergoes a diminution in nearly the same degree. The average Weights of the 
 Male and Female, that have attained their full development, are twenty times those of the 
 new-born Infant of the two sexes respectively. The Height, on the other hand, is about Si- 
 times as much. 
 
 Fig. 290. 
 
 70 15 
 
 952. The chief differences in the Constitution of the two sexes manifest 
 themselves during the period, when the Generative function of each is in the 
 greatest vigour. Many of these distinctions have been already alluded to ; 
 but there are others of too great importance to be overlooked ; and these 
 chiefly relate to the Nervous System and its functions. There is no obvious 
 structural difference in the Nervous System of the two sexes (putting aside 
 the local peculiarities of its distribution to the organs of generation) ; save the 
 inferior size of the Cerebral Hemispheres in the Female. This difference, 
 which is not observed in other parts of the Encephalon, is readily accounted 
 for on the principles formerly stated ; when we compare the physical charac- 
 ter of Woman, with that of Man, For there can be no doubt that putting 
 aside the exceptional cases which now and then occur the intellectual pow- 
 ers of Woman are inferior to those of Man. Although her perceptive facul- 
 ties are more acute, her capability of sustained mental exertion is much less ; 
 and though her views are often peculiarly distinguished by clearness and deci- 
 sion, they are generally deficient in that comprehensiveness which is neces- 
 sary for their stability. With less of the volitional powers than Man pos- 
 sesses, she has the emotional and instinctive in a much stronger degree. The 
 emotions therefore predominate; and more frequently become the leading 
 
PROPORTION OF SEXES. 729 
 
 springs of action, than they are in Man. By their direct influence upon the 
 bodily frame, they produce changes in the organic functions, which far sur- 
 pass in degree anything of the same kind that we ordinarily witness in Man ; 
 and they thus not unfrequently occasion symptoms of an anomalous kind, 
 which are very perplexing to the Medical practitioner, but very interesting to 
 the Physiological observer. But they also act as powerful motives to the 
 Will ; and, when strongly called forth, produce a degree of vigour and deter- 
 mination, which is very surprising to those who have usually seen the indi- 
 vidual under a different aspect. But this vigour, being due to the strong 
 excitement of the Feelings, and not to any inherent strength of Intellect, is 
 only sustained during the persistence of the motive, and fails as soon as it 
 subsides. The feelings of Woman, being frequently called forth by the 
 occurrences she witnesses around her, are naturally more disinterested than 
 those of Man; his energy is more concentrated upon one object; and to this 
 his intellect is directed with an earnestness that too frequently either blunts 
 his feelings, or carries them along in the same channel, thus rendering them 
 selfish. The intuitive powers of Woman are certainly greater than those 
 of Man. Her perceptions are more acute, her apprehension quicker; and 
 she has a remarkable power of interpreting the feelings of others, which 
 gives to her, not only a much more ready sympathy with these, but that 
 power of guiding her actions so as to be in accordance with them, which we 
 call tact. This tact bears a close correspondence with the adaptiveness to 
 particular ends, which we see in Instinctive actions. In regard to the infe- 
 rior development of her Intellectual powers, therefore, and in the predomi- 
 nance of the Instinctive, Woman must be considered as ranking below Man ; 
 but in the superior purity and elevation of her Feelings, she is as highly 
 raised above him. Her whole character, Psychical as well as Corporeal, is 
 beautifully adapted to supply what is deficient in Man; and to elevate and 
 refine those powers, which might otherwise be directed to low and selfish 
 objects. 
 
APPENDIX. 
 
 I. ON PHRENOLOGY. 
 
 WITHOUT entering into a general discussion of the merits of the system of Phrenology at 
 present in vogue, which would be misplaced in a Treatise like the present, the Author feels 
 it desirable to express the opinion, which a recent careful examination of the chief questions 
 at issue between Phrenologists and their opponents have led him to entertain. 
 
 That the different portions of the Cerebral mass should have different parts to perform in 
 that wonderful series of operations, by which the Brain as a whole becomes the instrument 
 of the Mind, does not seem to him in the least improbable. Nor, if we duly consider the 
 general plan of construction of the nervous centres in Vertebrated animals, is it a legitimate 
 objection to such a view, that there is no mechanical distinction of " organs" either upon 
 the surface or in the interior of the Cerebrum ; for in the Spinal Cord and Medulla Oblon- 
 gata, there is a continuous tract of grey matter, which is really made up of an assemblage of 
 ganglia having dissimilar functions, although there are no external indications of the dis- 
 tinctness of these ganglia. Further, it appears to be quite legitimate to judge of the com- 
 parative powers of different parts of the Cerebrum, or of the same portions in different in- 
 dividuals, by their comparative sizes,- due allowance being made for other circumstances of 
 difference. And if the development of a particular part of the Cerebrum were constantly 
 found to be in harmony with the manifestation of a certain feature of psychical character, 
 there would be strong ground for regarding such a part as the instrument of the mental 
 operation in question. The attempt to establish a system of Cerebral Physiology by com- 
 parative observations of this nature, appears to the Author, therefore, a most legitimate one ; 
 and his objections to the present system of Phrenology are based only on the very imperfect 
 manner in which it has been constructed; the foundations on which it rests being (in his 
 opinion) of a very insecure character; and the superstructure having been built up of the 
 slightest possible materials. The following are the chief points on which he feels called 
 upon to express his dissent. 
 
 1. The present system of Phrenology is founded only on comparative observation of the 
 psychical character and cerebral conformation in different individuals of the Human species 
 alone; evidence derived from Comparative Anatomy being admitted only so far as it corre- 
 sponds with the system thus constructed. When the fundamental importance of the study 
 of Comparative Anatomy in the determination of the functions of all other organs, and of 
 other parts of the Nervous System itself, is duly considered, the Author cannot regard any 
 system of Cerebral Physiology as having a claim to a place in a scientific treatise, which is 
 not founded on this basis. 
 
 2. The present system of Phrenology is altogether inconsistent with well-ascertained facts, 
 regarding the Comparative Anatomy and Embryological Development of the Cerebrum. It 
 is clearly established by anatomical research, that the posterior lobes of the Cerebrum are 
 relatively much smaller in the Quadrumana than they are in Man, and that they disappear 
 altogether in the Carnivora, not a vestige of them being discoverable in any of the lower 
 Mammalia ; and that the middle lobes, though they may be traced in the lowest of the Mam- 
 malian Class, are altogether wanting in Birds, Reptiles, and Fishes. The Cerebrum of these 
 animals, therefore, is the rudiment of the anterior lobe only of that of Mammalia. Further, 
 it has been lately shown by Prof. Retzius (whose researches on this head are confirmatory 
 of those of Tiedemann, at the same time being more full and precise), that the development 
 of the Cerebrum of the Human Embryo takes place on the same plan. In the first period, 
 which corresponds with the second and third months, only the anterior lobes form; in the 
 second period which is comprised in the end of the third month, in the fourth, and in a 
 small portion of the fifth, the two middle lobes appear ; and it is not until the latter part of 
 the fifth month, that the development of the posterior lobes properly commences. They 
 sprout, as it were, from the posterior extremity of the middle lobes; from which they are 
 divided, on the brain of the mature foetus, as well as occasionally in that of adults, by a dis- 
 tinct furrow. The exact mutual confirmation afforded by these two sources of knowledge, 
 
732 APPENDIX. 
 
 proves the complete inadmissibility of the ordinary Phrenological interpretation of the in- 
 creased development of the posterior lobes in Man, namely, that they are present in all 
 Vertebrata, but that they are pushed backwards in the higher forms by the increased de- 
 velopment of the anterior portion of the Cerebrum. Now as the Instincts and Propensities 
 are located, according to the present system of Phrenology, in the posterior and middle lobes 
 of the Cerebrum, which are altogether wanting in the Oviparous Classes in which these In- 
 stincts and Propensities most strongly manifest themselves, it would appear that some funda- 
 mental error must exist in the allocation. 
 
 3. The present system of Phrenology takes no account whatever of the series of ganglionic 
 masses, which lie at the base of the Cerebrum in Man, and which are thrown into the shade 
 (as it were) by its excessive development; but which increase in relative size and import- 
 ance as we descend the scale, until, in the lower Fishes and Invertebrata generally, they 
 come to constitute the whole Brain. We have seen that, in the Cod, the rudiment of the 
 Cerebrum is much smaller than a single pair of these ganglia, the Optic ; and as this rudi- 
 ment does not possess a ventricle (which is present in the Sharks, &c., dividing the rudiment 
 of the hemisphere which arches over it, from the corpus striatum which lies at its base), it 
 is probably to be regarded as not really analogous to any part of the Cerebrum strictly so 
 called, but to the Corpus Striatum, which (with the Thalamus) constitutes an independent 
 organ. Thus we have the Cerebrum entirely disappearing in the Osseous Fishes ; and the 
 whole Brain made up of the Sensory Ganglia and the Cerebellum. In the Invertebrata, not 
 the rudiment of a Cerebrum can be discovered; the cephalic masses of nervous matter being 
 made up of ganglia in immediate connection with the organs of sense and motion. It is 
 obvious, therefore, that these organs must be of primary importance as centres of nervous 
 action ; and that the functions of the Cerebrum, whatever be their nature, must be of a super- 
 added^ and of a non-essential character. The view which the Author takes of these pheno- 
 mena will be found at large in the Text. He regards the Sensory Ganglia as the seat of 
 Sensation (each kind of sensation being communicated through its own ganglion) and of 
 the simple feelings of pleasure and pain connected with those sensations ; and also as the 
 instrument of those consensual movements, which follow immediately and necessarily upon 
 sensations. To this category he would refer the purely Instinctive actions, which are imme- 
 diately prompted by sensations, which seem to involve no idea of the purpose towards which 
 they are directed, and which cannot be said (the idea of the object being deficient) to spring 
 from a desire or propensity. Probably all or nearly all the actions of Invertebrata and of 
 the lower Fishes are of this class. The emotions and propensities of Man and of the higher 
 Mammalia, which form the chief springs of action in them, may be regarded as involving 
 the combined operation of the Sensory Ganglia and the Cerebrum ; the latter affording the 
 ideas,- whilst the former invest these ideas with the pleasure or pain, which gives them the 
 form of passions, desires, or propensities, and which causes them to become the moving 
 springs of a great part of the intellectual operations, which are purely Cerebral. The action 
 of the Cerebrum in the passions, emotions, &c., is limited, therefore, on this view of their 
 nature, to its instrumentality in furnishing the several classes of ideas to which those emotions 
 respectively relate. If the Phrenological system be thus modified, there will no longer be 
 the same difficulty in reconciling it with the facts of Comparative Anatomy ; since in those 
 animals which are unpossessed of the posterior lobes, the actions, which in Man and the 
 higher Mammalia result from desires or propensities involving a distinct idea or conception 
 of the object, may be purely instinctive, and may thus be performed through the medium of 
 the Sensory Ganglia alone, without the participation of the Cerebrum. 
 
 4. The present system of Phrenology leaves undetermined a very large proportion of the 
 Cerebral surface in Man, probably not less than one-half; namely the whole series of 
 convolutions covering the opposing median surfaces of the hemispheres, the convolutions of 
 nearly the whole of the base of the Cerebrum, and those of the fissure of Sylvius. Yet 
 not the slightest ground can be adduced for the supposition that these unappropriated por- 
 tions have any less participation in the operations of the intellect, the exercise of the moral 
 feelings, or the influence of the animal propensities, than have the external and superior 
 portions of the respective lobes. No admission of the imperfection of the present system 
 of Phrenology can be a sufficient explanation of this fact, which would seem to indicate 
 some fundamental error in the method employed ; since one of the great claims which is set 
 up in behalf of that system is the completeness of the system of Psychical philosophy which 
 it presents ; so that, if there were every facility for observing the relative development of the 
 parts of the Cerebral surface in question, there would seem to be no "organs" left to distri- 
 bute over it. 
 
 5. If it be urged, however, that none of these objections are sufficient to overthrow the 
 position, now established by a long course of observation, that a constant correspondence 
 exists in Man between the development of certain parts of the Cerebrum, and particular 
 Psychical characteristics, and that the present system must consequently be true, in spite of 
 its inconsistency with the facts of Comparative Anatomy, it becomes necessary to inquire in 
 
APPENDIX. 733 
 
 more detail into the character of the evidence adduced in its behalf. The following objec- 
 tions may be urged upon this subject. The greater part of the observations upon which the 
 present system of Phrenology rests, have been made upon crania alone, or upon casts of 
 crania; not upon the cerebrum itself. In this method of observation there are many falla- 
 cies; especially those arising from the indisputable fact, that the cerebrum may be moulded 
 in such a manner as to undergo considerable alteration in form, without any change in its 
 internal structure or in the relative development of its several parts. And an extensive 
 comparison of the crania of different nations shows that their differences of form have in 
 many instances no relation whatever to their psychical character. That the form of the cra- 
 nium is to a certain extent independent of that of the brain, and may impress itself upon its 
 contents, appears further from a comparison between the cerebral and cranial conformations 
 of different species of animals. It is found that, even when closely-allied species are torn- 
 pared together, similar projections of the cranium may cover different convolutions ; the 
 general form of the cranium being modified by its instrumentality in other functions, espe- 
 cially in mastication, and by its position upon the trunk and its mode of muscular connection 
 with it. There is a peculiar uncertainty attending all estimates of the comparative size of 
 the Cerebellum, from inspection of the exterior of the cranium ; for the observations of Prof. 
 Retzius upon the varieties of form which the cranium presents in different races, have in- 
 dicated this fact among others, that the position of the cerebellum may vary considerably, 
 being much more horizontal in one case and more vertical in another ; so that cerebella of 
 the same size may exist in crania having very different amounts of occipital protuberance; 
 and vice versa. Further, after dismissing the sources of error already mentioned, there yet 
 remain many, arising from want of precision in the cranioscopical observations, and want of 
 opportunity of forming a correct estimate of the characters of the individuals whose " deve- 
 lopments" have been examined. The difficulty of precisely estimating the relative sizes of 
 different organs by any system of measurement, which has been acknowledged and regretted 
 by candid phrenologists, often leads to the formation of very different inferences from the 
 same data, as the Author can vouch from his own knowledge. And when the estimate of 
 the character has been formed from craniological indications, there are many difficulties in 
 the way of a faithful comparison with the real character of the individual, of which the 
 manifestation in his ostensible conduct can generally reveal but a small part. Now there 
 can be little doubt, that the habit of attending-to and of recording coincidences between cere- 
 bral developments and psychical manifestations, without due regard to the cases in which 
 there is no coincidence, has been far too prevalent amongst professed phrenologists. Unless 
 the failures are duly chronicled with the successes, no value can be attached to any series 
 of observations, however numerous and satisfactory. Many such failures, upon points in 
 regard to which there could be no misapprehension or evasion, have come under the Author's 
 knowledge ; and have tended to prevent his reception of the present phrenological system ; 
 but they find no place in formal treatises on Phrenology, which lead their readers to suppose 
 that the coincidences are invariable. The connection of the Sexual propensity with the 
 Cerebellum has been usually regarded by Phrenologists as one of the best-ascertained of its 
 whole series of dogmata ; and yet we have seen how little this determination can stand the 
 test of a careful scrutiny. 
 
 Those who are desirous of studying the Phrenological system at present in vogue, as ex- 
 pounded by an intelligent and unfettered partisan, may be referred to Mr. Noble's recent 
 treatise, entitled "The Brain and its Physiology;" whilst the objections summed up in this 
 Appendix are stated more at large in a critique on that work in the British and Foreign Me- 
 dical Review, for October, 1846. 
 
 II. ON ARTIFICIAL SOMNAMBULISM AND MESMERISM. 
 
 It appears to the Author that the time has now come, when a tolerably definite opinion 
 may be formed regarding a large number of the phenomena commonly included in the term 
 "Mesmerism." Notwithstanding the exposures of various pretenders, which have taken 
 place from time to time, there remains a considerable mass of phenomena, which cannot 
 be so readily disposed of, and which appear to him to have as just a title to the attention of 
 the scientific Physiologist, as that which is possessed by any other class of well-ascertained 
 facts. 
 
 Passing over, for the present, the inquiry into the manner in which these effects may be 
 induced, the Author may briefly enumerate the principal phenomena which he regards as 
 having been veritably presented in a sufficient number of instances, to entitle them to be 
 considered as genuine and regular manifestations of the peculiar bodily and mental condition 
 under discussion. 
 
 1. A state of complete Coma or perfect insensibility, analogous in its mode of access and 
 departure to that which is known as the " Hysteric Coma," and (like it) usually distin- 
 62 
 
734 APPENDIX. 
 
 guishable from the Coma of Cerebral oppression by a constant twinkling movement of the 
 eyelids. In this condition, severe surgical operations may be performed, without any con- 
 sciousness on the part of the patient ; and it is not unfrequently found that the state of tor- 
 por extends from the Cerebrum and Sensory Ganglia to the Medulla Oblongata, so that the 
 respiratory movements become seriously interfered with, and a state of partial asphyxia 
 supervenes. 
 
 2. A state of Somnambulism or Sleep-waking, which may present all the varieties of the 
 natural Somnambulism, from a very limited awakening of the mental powers, to the state 
 of complete double Consciousness ( 500), in which the individual manifests all the ordi- 
 nary powers of his mind, but remembers nothing of what has passed when restored to his 
 natural waking state. This state of Somnambulism, in the form which it commonly takes, 
 is characterized by the facility with which the thoughts are directed into any channel which 
 the observer may desire, by the principle of " suggestion ;" and by the want of power, on 
 the part of the Somnambulist, to apply the teachings of ordinary experience to the correction 
 of the erroneous ideas which are thus made to occupy the mind. In these particulars, this 
 condition closely corresponds with that of Dreaming; and differs from it chiefly in the 
 readiness with which ideas are excited through the ordinary channels of sensation, and with 
 which the bodily powers are called into action to give effect to the ideas thus aroused. The 
 emotional states are more easily brought into play, than the purely intellectual operations. 
 It is a peculiar characteristic of this condition, that the whole attention maybe so completely 
 fixed upon one object, that there is an insensibility to all impressions unconnected with it, 
 although every thing which bears upon it is fully appreciated. In this respect there is a 
 complete correspondence with the phenomena of ordinary somnambulism ; but there is this 
 difference, that, from the greater subjection of the mind to external influences, it may be 
 more readily played upon (so to speak) by the observer, and may thus be exclusively fixed 
 upon any object which he may direct. In this manner, a state of insensibility to pain may 
 Le brought about, nearly as complete as that which occurs in the comatose state, by causing 
 the mind to be strongly and exclusively directed towards another object. This condition 
 finds its parallel in that of Reverie ; in which strong impressions upon the body may be 
 unfelt, so long as the mind is engrossed upon some different train of thought. 
 
 3. A frequent phenomenon of this condition, and one which has its parallel in Natural 
 Somnambulism, is a remarkable exaltation of one or more of the Senses, so that the indi- 
 vidual becomes susceptible of influences, which, in his natural condition, would not be in 
 the least perceived. The Author has referred to a case ( 532, note) in which such an 
 exaltation of the sense of Smell was manifested ; and in the same case, as in many others, 
 there was a similar exaltation of the sense of Temperature. The exaltation of the Muscular 
 Sense, by which various actions that ordinarily require the guidance of vision, are directed 
 independently of it, is a common phenomenon of the Mesmeric or Artificial, as of the 
 Natural, Somnambulism. 
 
 4. The Muscular system 'may also be excited to action in unusual modes, and with 
 unusual energy. Notwithstanding the fallacy of many of the cases of Cataleptic rigidity 
 which have been publicly exhibited, the Author is satisfied, from investigations privately 
 made, of the possibility of artificially inducing this condition. A slight irritation of the 
 muscles themselves, or of the skin which covers them, as by drawing the points of the 
 fingers over them, or even wafting currents of air over the surface, is sufficient to excite 
 the tonic muscular contraction, which may continue in sufficient force to suspend a con- 
 siderable weight, for a longer period than it could be kept up by any conceivable effort of 
 voluntary power. Further, by directing the attention exclusively to any set of muscles, and 
 by impressing the mind of the Somnambulist with the facility of the action to be performed, 
 a very extraordinary degree of muscular power may be called forth, even in very feeble 
 individuals. Thus the Author has seen a man of extremely low muscular development and 
 small stature, not only lift up a 28 Ib. weight upon his little finger, but even swing it round 
 his head with the greatest apparent facility, having been previously assured that it was as 
 light as a feather. Upon taking up the same weight upon their own little fingers, the 
 Author and his friends were very glad to lay it down after raising it a foot from the ground : 
 and the subject of the experiment (a respectable middle-aged man, who was not a regular 
 " exhibitor," and upon whom no suspicion of any kind rested) declined, when in his waking 
 state, even attempting to lift the weight, on the ground that it would strain him too much. 
 
 These are the principal phenomena of Artificial Somnambulism, in regard to which the 
 Author feels his mind made up. He does not see why any discredit should be attached to 
 them, since they correspond in all essential particulars with those of states, which naturally 
 or spontaneously occur in many individuals, and which he has had opportunities of per- 
 sonally observing, in cases in which the well-known characters of the parties placed them 
 above suspicion. When the facility with which the mind of the Somnambulist is played on 
 by suggestions conveyed either in language or by other sensations which excite associated 
 ideas, and the absence of the corrective power ordinarily supplied by past experience, are 
 
APPENDIX. 735 
 
 duly kept in view, many of the supposed " higher phenomena" of Mesmerism may be 
 accounted for, without regarding the patient on the one hand as possessed of extraordinary 
 powers of divination, or on the other as practising a deception. Thus, bearing in mind 
 that Somnambulism is an acted dream, the course of which is governed by external impres- 
 sions, it is easy to understand how the subject of it may be directed by leading questions to 
 enter buildings which he has never seen, and to describe scenes which he has never wit- 
 nessed, without any intentional deceit. The love of the marvellous so strongly possessed 
 by many of the witnesses of such exhibitions, prompts them to grasp at and to exaggerate 
 the coincidences in all such performances, and to neglect the failures ; and hence reports 
 are given to the public, which, when the real truth of them is known, prove to have been 
 the results of a series of guesses, the correctness of which is in direct relation to the amount 
 of guidance afforded by the questions themselves. In like manner the manifestations of the 
 excitement of the " phrenological organs" seem to depend upon the conveyance of a sug- 
 gestion to the patient, either through his knowledge of their supposed seat, or through' the 
 anticipations expressed by the by-standers. Many instances are recorded, in which the 
 intention has been stated of exciting one organ, whilst the finger has been placed upon or 
 pointed at another ; and the resulting manifestation has always been that which would flow 
 from the former. It does not hence follow that intentional deception is being practised by 
 the Somnambulist ; since the condition of mind already referred to, causes it to respond to 
 the suggestion which is most strongly conveyed to it. Many of the emotional states are 
 readily excitable, by placing the muscles in the position which naturally expresses them ; 
 thus the combative tendency may be called forth by gently flexing the fingers, so as to 
 double the fist ; a cheerful hilarious mood may be induced by drawing outwards the cor- 
 ners of the mouth as in laughter ; and this may be exchanged for the reverse state of gloom 
 and ill-temper, by drawing the eyebrows downwards and towards each other, as in frown- 
 ing. In like manner, on putting the hand upon the vertex, the Somnambulist draws him- 
 self up, and shows the manifestation of self-esteem ; whilst the depression of the head into 
 the position of humility calls forth the corresponding emotion. Those who have carefully 
 observed the habits of infants and young children, must perceive the accordance of these 
 phenomena with those which continually present themselves at that early period of life, 
 when the condition of the mind is so completely under the government of suggestions re- 
 ceived from without. 
 
 In regard to the alleged powers, which are said to be possessed by many Somnambulists, 
 of reading with the eyes completely covered, or of discerning words enclosed in opaque 
 boxes, the Author need only here express his complete conviction that no case of this de- 
 scription has ever stood the test of a searching investigation. 
 
 The modes in which the Artificial Somnambulism may be induced, are extremely vari- 
 ous. The experiments of Mr. Braid have shown, that one of the most effectual is the con- 
 tinued convergence of the eyes upon a bright object, held at a small distance above and in 
 front of them, and gradually approximated towards them. The mere steady direction of the 
 eyes towards a distant object, in persons who have often practised the former method, fre- 
 quently serves to induce the state. All the phenomena described in the preceding para- 
 graphs, have been witnessed by the Author in individuals thus " hypnotized ;" and he 
 considers that this curious class of observations cannot be better prosecuted than by the em- 
 ployment of that method. He is not yet satisfied that, in the ordinary " Mesmeric " process, 
 any other influence than this is really exerted; but the patient is sent to sleep with the 
 dominant idea that some special influence is exerted by the Mesmerizer, and this idea affects 
 all the subsequent phenomena, producing, for example, in some cases, insensibility to every- 
 thing but what is said by the mesmerizer or by an individual placed by him en rapport with 
 the Somnambulist. It will generally be found, that the degree of this supposed connection 
 depends upon the notions of it previously formed by the individual Mesmerized. In the 
 hypnotic state, there is an entire absence of any such peculiar influence ; the Somnambulist 
 being equally conscious of what is said or done by every bystander. 
 
 The Author may refer to an Article in the British and Foreign Medical Review for April, 
 1845, as on the whole expressing (although not written by himself) his opinions upon this 
 curious and interesting subject. 
 
INDEX. 
 
 The Numbers refer to the Paragraphs. 
 
 A. 
 
 ABEKRATION, spherical, 535; chromatic, 535 
 
 Abnormal forms of nutritive process, 802 809 
 
 Abortion, 929 
 
 Abscess, 804 
 
 Absorbent cells, 181, 182 
 
 vessels, see Lacteals, and Lympha- 
 tics 
 
 ABSORPTION 
 
 Nutritive, general account of, 107, 271 ; by 
 intestinal surface, 672 675; by lacteals, 
 672, 674; by blood-vessels, 673, 675; by 
 general surface, 676681 ; by skin, 676 
 679 ; by lungs, 678, 775, 776 
 Interstitial, by lymphatics, 680, 681 ; by veins, 
 
 681 & 
 Of gases and vapours by lungs, 775, 776 
 
 Abstinence, cases of, 653 
 
 Actinia, nervous system of, 312, 313 
 
 Activity, varying, of nutritive processes, 786 
 791 
 
 Adaptiveness of movements, no proof of sensa- 
 tion, 306 
 
 Addison, Mr., his observations on blood-cor- 
 puscles referred to, 151, 158, 159; on fibril- 
 lation of liquor sanguinis, 136 ; on blood-ves- 
 sels of lungs, 758 ; on pus, 806 
 
 Adhesion, 793, 794 
 
 Adipose tissue, see Fat-cells 
 
 Aeration, 107 ; see Respiration 
 
 Afferent nerves, 289, 344 
 
 Age, influence of, on pulse, 727 a ; on excretion 
 of carbonic acid, 767 b ; on excretion of urea, 
 844; on activity of nutritive processes, 786, 
 812 ; on power of calorification, 893 
 
 Air, influence of respiration on, 765 768 
 
 Air-cells of lungs, 757, 758 
 
 Albinoism. 80 
 
 Albumen, 112; composition of, 114; properties 
 of, 113 115 ; conversion of into fibrine, 114, 
 117, 153158; proportion of in blood, 697, 
 706; purposes of, 698; diminution of in blood, 
 707 d; predominance of in tubercular depo- 
 sits, 878 
 
 Albuminous principles of food, 640, 857 ; ap- 
 plication of in the animal body, 642 
 
 Albuminuria, 707 d 
 
 Alcock, Dr., his experiments on nerves of taste, 
 407 
 
 Alcohol, use of in supporting heat, 896 note 
 
 Alfourous, 105 
 
 Aliment, causes of demand for, 629635; see 
 Food 
 
 Alimentary materials, 640 ; see Food 
 
 Allantoin, 845 c 
 
 Allantois, origin and uses of, 839 c 
 
 Allen and Pepys, their researches on respira- 
 tion, 765 
 
 American nations, 101 
 
 Amphibia, 31 
 
 Amphioxus, 110, 180; nervous centres of, 425 
 
 Anaemia, 707 c 
 
 Andral, M., on amount of carbonic acid excret- 
 ed, 767; on pathological changes in blood, 
 706, 707 
 
 Animal Heat, see Heat 
 
 Animal kingdom, primary subdivisions of, 5 
 
 Animal magnetism, Appendix II. 
 
 Animals, distinguished from Plants, 1 4 
 
 early development of, 3 
 
 Anselmino, on solid matters of cutaneous ex- 
 halation, 869 
 
 Aplastic deposits, 804, 807 
 
 Aplysia, 12, 15; nervous system of, 321 
 
 Apoplexy, decrease of fibrine in, 707 c ; death 
 by, 814 
 
 Arabian nations, 94 
 
 Arciform fibres of medulla oblongata, 353 
 
 Area pellucida, 936 
 
 Areolar tissue, 138, 139 
 
 Areas, comparative, of arteries, 710 
 
 Arnott, Dr., on stammering, 619 ; on the ven- 
 ous circulation, 744 6 
 
 Arteries, distribution of, 710; area of, 710; 
 structure and properties of, 728 732 ; elas- 
 ticity of, 729 ; their contractility, proofs of, 
 730 ; its influence in regulating the circula- 
 tion, 732; their tonicity, 731; influence of 
 nerves upon, 623, 732 
 
 Articulata, 5, 16 19; segmental division of, 
 16 ; animal powers of, 17 ; nutrition of, 18 ; 
 bi-lateral sympathy of, 16; respiration and 
 heat of, 18; nervous system of, 324334 
 
 Articulate sounds, 612 619; vowels, 613 
 615; consonants, 616, 617 
 
 Articulation, movements of, guided by sensa- 
 tion, 611, 617 
 
 Asphyxia, nature of, 778; phenomena of, 779; 
 780 ; referred to, 738, 740, 814, 820 
 
 Assimilation in Plants, 107; in Animals, 271, 
 781 
 
 Asthma, spasmodic, 504, 759 
 
 Atrophy, 789791 
 
738 
 
 INDEX. 
 
 The Numbers refer to the Paragraphs. 
 
 Attention, effects of, on sensations, 519 521 
 Auditory ganglia, in Fishes, 357 ; in Man, 422 
 Auditory nerve, 446 ; terminations of, in ear, 
 
 559 
 Auricles of heart, action of, 718, 719 ; capacity 
 
 of, 723 b 
 
 Automatic actions, 438 a 
 Azote, absorption and exhalation of, 766 ; ex- 
 cretion of, in urine, 819, 842850; respira- 
 tion in, 769, 780 
 
 B. 
 
 BARRY, Dr. M., his researches on the blood- 
 corpuscles referred to, 148 ; his embryologi- 
 cal researches referred to, 130, 900918 
 
 Barry, Sir D., his experiments on the venous 
 circulation, 744 b 
 
 Basement-membrane, 135 
 
 Bat, peculiar sensibility of, 526 
 
 Batrachia, 31, 32; metamorphosis of, 32 
 
 Beaumont, Dr., his experiments and observa- 
 tions on digestion, 637, 649, 657660, 664 
 666 
 
 Becquerel on the heat of Plants, 889 a; on the 
 heat of Animals, 891 ; on the heat of Muscle, 
 890 
 
 Bee, perfection of instinct of, 336 ; construction 
 of hexagonal cell by, 336 note ; uneducability 
 of, 429 b ; temperature of, 889 c 
 
 Bell, Sir C., his discoveries referred to, 344, 
 349,351,376,377,433 
 
 Bell, Mr. T., on the development of the teeth, 
 217 i ; on secretion after death, 624 
 
 Bellingeri, on the Spinal Cord, -349 
 
 Berger and Delaroche, their experiments on 
 Animal Heat, 888 
 
 Berber race, 94 
 
 Bernard, M. Ch., his researches on digestion, 
 658 b, 664 i, 669 
 
 Bibra, Von, his analyses of Bone, 196 ; of Teeth, 
 212 
 
 Bile, secretion of, 831 837 ; composition of, 
 833 ; amount of, 834 ; formed from venous 
 blood, 831 ; partly an excrementitious fluid, 
 836; effects of non-elimination of, 836; 
 sources of, 836 ; purposes of, in digestive 
 process, 660, 670, 671, 835 
 
 Birds, 3341 ; skeleton of, 37, 38 ; respiration 
 and heat of, 33, 757, 889 c ; covering of, 36 ; 
 instinctive powers and intelligence of, 39, 
 479 , nutritive system in, 40; bi-lateral sym- 
 metry in, 40 ; development of young in, 41 ; 
 blood-corpuscles of, 146 b, 149 ; brain of, 361 
 
 Bischoff, his experiments on respiration, 768 
 
 Bladder, contraction of, 390 
 
 Blake, Mr., his experiments on the Circulation, 
 725 
 
 Blind persons, acuteness of touch in, 525 
 
 Blondlot, M., his researches on digestion, 658 
 6, 664 6 
 
 BLOOD, 
 
 Physical and vital properties of, 696708 ; 
 composed of liquor sanguinis and cor- 
 puscles, 696; proportion of components, 
 of, in health, 697 ; purposes of, 698 ; total 
 amount of in body, 724 
 Structure of Red Corpuscles, 143, 144; form 
 of corpuscles, 145, 146 ; size of corpuscles, 
 
 146; chemical constitution of corpuscles, 
 147 ; origin of, from each other, 148 ; first 
 production of, in embryo, 149; purposes 
 of, in animal economy, 150 
 Colourless corpuscles, 151, 152; their uses 
 
 in the economy, 153 159 
 Serum, composition of, 697 ; milky, 697 e 
 Coagulation of, 699705; due to fibrine 
 alone, 117, 118, 699; an act of vitality, 
 118, 700, 701 ; causes influencing, 701, 702; 
 proportions of serum and clot, 703 ; bufiy 
 coat, causes of, 704, 705 ; composition of, 
 1 1 6 a ; artificially producible, by retarding 
 coagulation, 699 
 
 Pathological changes in, 706 708 ; normal 
 proportion of chief constituents, 706 ; in- 
 fluence of abstinence and hemorrhage, 
 707 ; increase of fibrine in inflammation, 
 158, 707 a, 802; deficiency of fibrine in 
 fever and hemorrhagic diseases, 707 6 ; in- 
 crease of corpuscles in plethora, 707 c ; 
 diminution in chlorosis, anaemia, &c., 707 
 c ; decrease of albumen in Bright's disease, 
 707 d ; general depravation of, 708 ; imper- 
 fect elaboration of, in tuberculous cachexia, 
 807 
 
 Changes produced in, by respiration, 769 
 772; difference of arterial and venous 
 blood, 769; excretion of carbonic acid from, 
 769; absorption of oxygen by, 766 ; gases 
 extracted from, 770 ; change of colour, 
 causes of, 771, 772 ; aeration of, by gene- 
 ral surface, 768 
 Organization of, 118, 700, 796 
 Movement of through vessels, see Circulation 
 Blood-discs, see Corpuscles 
 Blood-vessels, see Arteries, Capillaries, and 
 
 Veins 
 
 Bone, 192207; structure of, 192 196; form- 
 ation of, in membrane, 197 ; in cartilage, 
 198200; chemical composition of, 196; 
 growth of, 201 203 ; regeneration of, 204 
 207 
 Bouchardat, M., his researches on digestion, 
 
 670 
 
 Bovista giganteum, 153 a 
 Bourgery, M., his observations on air-cells of 
 
 lungs, 757 a 
 
 Bowman, Mr., his observations on muscular 
 
 fibre, 226, 228, 231, 232, 590 a ; on mucous 
 
 membrane, 176; on structure of the kidney, 
 
 839 841 ; on fatty liver, 929 
 
 Brain, see Encephalon, Cerebrum, Cerebellum, 
 
 &c. 
 Brewster, Sir D., his law of visible direction, 
 
 543 
 
 Bright's disease of the Kidney, 707 d 
 Brodie, Sir B., his experiments on the Par Va- 
 
 gum, 414, a; on animal heat, 890 
 Bronchial tubes, contractility of, 410, 759 
 Brunner's glands, 875 
 
 Buchanan, Dr., his researches on the blood re- 
 ferred to, 697 e 
 
 Budd, Dr. W., his cases of reflex action re- 
 ferred to, 365 369 ; his observations on 
 symmetrical diseases referred to, 785, 882 
 Buffy coat, 704, 705 
 Bulbus arteriosus, 940, 943 
 Bushmen, 70 
 
INDEX. 
 
 739 
 
 The Numbers refer to the Paragraphs. 
 
 C. 
 
 CACOPLASTIC deposits, 807 
 Callus, formation of, 206 
 Cancer, 809, 881 
 Capacity of respiration, 764 
 Capillary vessels, distribution and size of, 219, 
 220 ; origin of, 221, 222 ; properties of their 
 walls, 739 ; absent in some tissues, 220 ; in- 
 dependent movement of blood in, 733 ; 
 proofs of, 734739 
 
 Capillary circulation, 733 742 ; phenomena 
 of, 734; continues after cessation of heart's 
 action, 735; in acardiac foetus, 736; stagna- 
 tion of, in Asphyxia, &c., 738 ; influence of 
 local excitement on, 737 ; laws regulating, 
 739 741 ; connection of, with nervous in- 
 fluence, 742 
 
 Carbonic acid, excretion of, 749; sources of, 
 750 754 ; amount of, 765 767 ; made sub- 
 servient to introduction of oxygen, 766 ; 
 effected through the skin, 768 ; contained 
 in venous blood, 770; expiration of, in hy- 
 drogen, 769 ; influence of on colour of blood, 
 771, 772; effects of its retention in the sys- 
 tem, 778 780 
 
 , absorption of, by lungs, 776 
 
 Carnivorous animals, nutrition of, 644 
 Cartilage, structure of, 187 191 ; composition 
 of, 177, a ; nutrition of, 188, 191 ; ulceration 
 and reparation of, 191 ; ossification of, 198 
 200 
 
 Catamenia, 908, 909 
 Caucasian race, 93 
 
 Cells, the types of Organization, 259 ; compose 
 bulk of fabric of Vegetables, 106 109 ; 
 origin of, 122 124; transformations of, 
 120, 121 
 
 Origin of animal structures in, 110; indi- 
 vidual growth of, in animals, 126, 127; 
 history of development of, 128131 ; 
 transformations of, 132, 133, 223 ; indi- 
 vidual life of, 126, 811; continual death 
 of, in living body, 108, 261, 811 ; varying 
 duration of, 811, 812 
 
 Functions of, general, 110, 126, 132,259; 
 in Absorption, 181, 182, 271, 672; in As- 
 similation, 153, 154, 271 ; in. Secretion, 
 174, 179, 278, 821823; in Reproduc- 
 tion, 174,281,902- 
 
 Persistence of, in animal tissues, 180 ; in 
 pigment, 163, 164; in fat, 184; in shell, 
 192 ; in epidermis and epithelium, 160 
 174 ; in cartilage, 187 ; in muscle, 230 ; 
 in nerve, 245 
 
 Replacement of by Fibres, 134, 136 
 Cellular Plants, 106 
 Cellular tissue, see Areolar tissue 
 Cellulose, Vegetable, 4, 111 
 Cementum of teeth, structure of, 208, 211; 
 
 composition of, 212; development of, 216 
 Centipede, nervous system and actions of, 326 
 
 329 
 
 Cerebellum, 340, 457470 ; of Fishes, 357 ; of 
 Reptiles, 360; of Birds, 361 ; of Mammalia, 
 362 ; of Human embryo, 358, 359, 361; re- 
 lative dimensions of, 457, 458, 461 ; experi- 
 ments on, 459, 460, 463; observations on 
 size of, in castrated animals, 468, 469 ; con- 
 nection of, with motor power, 459 465 ; 
 
 with sexual instinct, 466 470 ; pathological 
 changes in, 464, 465, 467; phrenological ac- 
 count of, 470 
 
 Cerebro-spinal fluid, 476, 477 
 Cerebrum, 340, 471 495; general structure 
 of, 472474 ; of Fishes, 357 ; of Reptiles, 
 360 ; of Birds, 361 ; of Mammalia, 362; of 
 Human embryo, 358, 359, 361 ; general 
 functions of, 478 480; relative dimensions 
 of, 481 484 ; experiments on, 485 ; patholo- 
 gical changes in, 486 ; connection of, with 
 intelligence, 485495 ; with the will, 487, 
 494 ; distinct functions of several parts of, 
 Appendix I. ; peculiar conditions of, in sleep, 
 somnambulism, &c., 499, 500, Appendix II. 
 Ceruminous glands, 872 
 Chaetodon rostratus, 490 
 Change, involved in idea of life, 254 
 Cheselden's case of cataract, 541 
 Chimpanzee, 51 59 
 Chlorosis, 707 c 
 Chondrine, composition and properties of, 141, 
 
 187 a 
 
 Chorda dorsalis, ISO, 937 
 Chordae vocales, 603, 605, 607 
 Chorea, 504 note 
 Chorion, production of, 918; subsequent changes 
 
 in, 918, 920923 
 Chossat,fiis experiments on inanition, 652, 895, 
 
 896 
 
 Chyle, 674 ; formation of, in intestines, 660 : ab- 
 sorption of, 181, 672 ; analysis of, 691; aspect 
 of, 692 ; changes of, in progress through 
 lacteals, 692, 693; globules contained in, 
 their nature and source, 155, 693 ; their 
 destination, 154 159, 693 ; chyle from tho- 
 racic duct, 693, 695; relative constitution 
 of, 691 
 
 Chyme, formed by digestive process, 657 660 
 Chymification, 663 669; a chemical action, 
 
 667 
 
 Cicatricula, 936 
 Cilia, 171173 
 Cineritious matter, 246 
 CIRCULATION 
 
 General account of, 272 ; objects of, 709 ; 
 course of, in Man, 710 ; arterial trunks, 
 710; capillaries, 219, 710; veins, 710 
 In Plants, 712714; in lower Animals, 715, 
 
 716 
 
 Action of Heart, 719 727; connection of, 
 with nervous system, 416, 576, 580, 
 717; rhythmical movements of, 717 719; 
 sounds of, 720, 721 ; course of blood in, 
 722; differences of two sides, 723 ; quan- 
 tity of blood impelled by, 724, 725; force 
 of contractions, 726 ; number of contrac- 
 tions, 727 
 
 Action of Arteries, 728732; their elas- 
 ticity and contractility, 728 ; influence of 
 their elasticity, 729 ; proofs of their con- 
 tractility, 730; their tonicity, 731 ; influ- 
 ence of their contractility, 732 
 Independent motion in capillaries, 733 
 742 ; proofs of, 734738 ; stagnation in, 
 738, 740 ; influence of capillaries in regu- 
 lating amount of flow, 740 ; contractility of 
 capillaries, 739; general principles of their 
 action, 751 ; influence of nerves on capil- 
 lary circulation, 742 
 
740 
 
 INDEX. 
 
 The Numbers refer to the Paragraphs. 
 
 Motion of Blood in Veins, 743 745 ; struc- 
 ture and properties of veins, 743 ; causes 
 of flow of blood through, 744; influence 
 of gravity upon, 745 
 
 Peculiarities of circulation, in lungs, 746 ; in 
 
 portal system, 685, 746 ; in cranium, 476, 
 747; in erectile tissue, 748; in fetus, 
 early state of, 938 940 ; subsequent con- 
 dition of, 943944 
 Disorders of circulation, 881 
 
 Civilization, influence of, on development of 
 human body, 8790 
 
 Clot, of Blood, see Crassamentum 
 
 , organization of, 118, 119, 700, 
 
 796 
 
 Coagulable lymph, see Liquor Sanguinis 
 
 Coagulation, of blood, 699705; due to fibrine 
 alone, 117, 118, 699; an act of vitality, 118, 
 700, 701 ; circumstances influencing, 701, 
 702; proportion of serum and clot, 703 ; of 
 chyle, 117, 693; of lymph, 694; of fibrine, 
 117119 
 
 Coathupe, Mr., his experiments on respiration, 
 764; on products of combustion of charcoal, 
 776 note 
 
 Coccochloris, 125 
 
 Cochlea, 566 
 
 Cockchafer, 19 
 
 Coecilia, 31 
 
 Coition, act of, in Male, 904 ; in Female, 911 
 
 Cold, degree of, endurable by Man, 987 ; death 
 by, 814, 895, 896 ; means of producing, in 
 the living body, 897 ; influence of, on young 
 animals, 893, 894 
 
 Collard de Martigny, his experiments on re- 
 spiration, 769, 774 
 
 Colostrum, 854 a, 856 
 
 Colour of Skin, 7981 (see Pigment-cells) 
 
 Colourless corpuscles in blood, 151158 
 
 Colours, impressions made by, 552 ; comple- 
 mentary, 552; deficiency of power of distin- 
 guishing, 553 
 
 Combe, Dr. A., quoted from, 658 a, 666, 671 
 
 Commissures of Brain, 474; deficiency of, 
 474 a 
 
 Complementary colours, 552 
 
 Conception, aptitude for, 909; act of, 911, 
 927 
 
 Conchifera, nervous system in, 317, 318 
 
 Concussion of brain, effects of, 580, 625 
 
 Consciousness, double, 500 
 
 Consensual movements, 335 ; of Articulata, 
 336; ofVertebrata, 337, 430 436; of Eye- 
 balls, 450456 
 
 Consonants, 616 
 
 Contractility of Muscle, 573; two forms of, 
 574 ; of arteries, 730, 731 ; of Capillaries, 
 739 ; of bronchial tubes, 410, 759 (see Irri- 
 tability) 
 
 Contraction of Muscle, mode of, 230, 575, 
 576; causes of, 575, 576; alternating with 
 relaxation, 575,577; after death, 578, 595 
 597 ; dependent on arterial blood, 583, 584 ; 
 power of, the same at different degrees of 
 extension, 592; energy of, in Man, 598; in 
 Insects, 599 ; rapidity of, 600 
 
 Convolutions of Brain, 472 
 
 Convulsive diseases, 502 504 
 
 Cooling power of cutaneous exhalation, 897 
 
 Cooper, Sir A., his experiments on circulation 
 
 through cranium, 290 ; his researches on 
 mammary gland and its secretion, 853 
 
 Coral, 6 
 
 Corallines, 4 
 
 Cornaro, his diet, 653 
 
 Cornea, structure and nutrition of, 189 
 Corpora Albida, 914 
 
 Cephaloidea, 914 
 
 Lutea, 912-914 
 
 Malpighiana, of Spleen, 683; of Kid- 
 ney, 839 b 
 
 Olivaria, 352, 353 
 
 Pyramidalia, 352, 353 
 
 Quadrigemina, 422, 436 
 
 Restiformia, 352, 353 
 
 Rubra, 914 
 
 Striata, 423, 424 
 
 Wolffiana, 26, 839 c 
 
 Corpus Callosum, 474 
 
 Corpuscles, Red, of Blood, 143 150; struc- 
 ture of, 143, 144; form of, 145, 146; size of, 
 in Mammalia, 146 a; in Birds, 1466; in Rep- 
 tiles, 146 c; in Fishes, 146 d; chemical con- 
 stitution of, 147; origin of, 148; production 
 of in embryo, 149; large in fetus, 149; uses 
 of, in animal economy, 150, 698; proportion 
 of in Blood, 697; increase of, in plethora, 
 707 c; diminution of, in chlorosis, 707 c 
 
 , Colourless, of Blood, 151159 ; 
 
 characters of, 151; movement of, 152; uses 
 of, 153159 
 
 of Chyle, 155 
 of Lymph, 155 
 of Spleen, 6846 
 of Supra-Renal Capsules, 686 
 Cortical Substance, of Brain, 472 
 
 , of Kidney, 839 a 
 
 Convulsive diseases, 501 504 
 
 Cotyledons of Ruminants, 921 
 
 Coughing, act of, 381 
 
 Cranium, circulation in, 476, 747; forms of in 
 different races of Men, 8187 
 
 Crassamentum of Blood, 696 
 
 Crowing inspiration of infants, 504 
 
 Crusta petrosa of teeth, 208, 211, 212, 216 
 
 Cruveilhier, M., his observations on heart, 718 
 722; on purulent deposits, 837 a 
 
 Crying, act of, 380 
 
 Cryptogamia, reproduction in, 899 
 
 Crystalline lens, 190 
 
 Currie, Dr., case of dysphagia related by, 677 
 
 Cutaneous follicles, perspiratory, 868 870; 
 sebaceous, 872 
 
 Cuttle-fish, nerves of arms in, 322, 323; ejec- 
 tion of ink by, 438 
 
 Cutis anserina, 234 
 
 Cyclostome Fishes, 22 
 
 Cylinder-epithelium, 170 
 
 D. 
 
 DARTOS, contractility of, 234 
 
 Davy, Dr. J., his researches on animal heat, 
 886 
 
 Death, somatic and molecular, 813 816,880; 
 death of individual cells, 811, 812 ; by as- 
 phyxia, 814; by cold, 814, 895 ; by syncope, 
 814; by necrsemia, 814; by retention of se- 
 cretions, 278, 832, 842 
 
INDEX. 
 
 741 
 
 The Numbers refer to the Paragraphs. 
 
 Decay, constant in Animal body, 268, 632, 633, 
 
 750 (see Disintegration) 
 Decidua, formation of, 919 
 Decomposition, continual, in living beings, 268, 
 
 632, 633 (see Disintegration) 
 Decussation, of optic nerves, 445 
 Defecation, movements concerned in, 391, 392 
 Degeneration, of nervous structure, 263, 292 
 296; of muscular fibre, 239, 263,586; of ele- 
 ments of blood into pus, 800, 805 ; into tu- 
 bercle, 807, 808 
 
 Deglutition, 382 386; a reflex action, 382, 
 383 ; nerves concerned in, 384, 385; actions 
 preceding, 386 a-c; in Polypes, 382 
 Delaroche and Berger, their experiments on 
 
 Animal Heat, 888 
 Dental groove, 217 
 Dentine, 208; structure of, 210; composition 
 
 of, 212 ; development of, 213, 214 
 Dermo-skeleton,20 
 Despretz, M., his researches on animal heat, 
 
 892 
 Devergie, M., his table of development of foetus 
 
 at different ages, 947 
 Diabetes, 879 
 
 Diaphragm, movements of, 761 
 Diathesis, gouty, 878, 884 ; saccharine, 879 ; 
 
 tubercular, 878 
 Diet-scale, see Food 
 DIGESTION, 
 
 General account of, 270 ; in lower Animals, 
 655; alimentary materials, 641 ; their re- 
 spective destinations, 642 647; inorganic 
 substances, 648; relative digestibility of 
 different kinds of food, 666; importance of 
 bulk, 666 
 
 Processes of, 656 662 ; mastication and 
 insalivation, 656 ; deglutition, 656 ; con- 
 dition of stomach in, during health, 657 ; 
 disorder of, 658 ; entrance of food into 
 stomach, 659 ; movements of stomach, 
 659; expulsion into duodenum, 660; pas- 
 sage along intestines, 661 ; discharge of 
 faeces, 662 
 
 Chemical phenomena of, 663 671 ; compo- 
 sition and properties of gastric juice, 664; 
 its chemical action, 665, 667 ; artificial so- 
 lution of food, 668 ; Wasmann's researches 
 on pepsin, 668 ; Bernard and Barreswill's 
 researches, 669 ; conversion of saccharine 
 and oleaginous principles, 670, 671 
 Influence of nerves upon, 387, 413 415 
 Interstitial, according to Dr. Prout, 681 
 Digestive cavity in lower animals, 655 ; origin 
 
 and formation of, 937, 945 
 Direction, law of visible, 543 
 Discs, of Blood, see Corpuscles 
 Disintegration of Muscular tissue, 239, 263, 
 
 586 ; of Nervous tissue, 263, 292296 
 Distance, adaptation of eye to, 536 ; estimate 
 
 of, 548 
 
 Diving animals, 778 
 Dobson, Mr., his experiments on the Spleen, 
 
 685 
 
 Domesticability of Animals, 39, 42 
 Donne, M., his observations on Milk, 854 a, 
 
 856 ; on temperature in disease, 886 
 Doris, gills of, 755 
 Dormant Vitality, 255 
 Dorsal vessel of Articulata, 18 
 
 Double consciousness, 500 
 
 Draper, Professor, on Capillary Circulation 713, 
 
 741 
 
 Dreaming, 499 
 Dugong, heart of, 710 
 Dulong, M., his researches on animal heat, 
 
 892 
 
 Dumas, his analysis of fibrine, 114 
 Duration of life in individual parts, 810 812 
 Dytiscus, experiments on, 328 
 Dzondi, on deglutition, 656 
 
 E. 
 
 EAR, general action of, 556; comparative struc- 
 ture of, 557, 558; distribution of auditory 
 nerve in, 559 ; uses of membrana tympani, 
 563; of tympanic cavity, 564; of labyrinth, 
 565, 566 ; of external ear and meatus, 567, 
 568 
 
 Echinodermata, 710; shell of, 192 
 
 Educability, of Birds, 39, 479 ; of Mammalia, 
 42, 480 ; of Man, 60 
 
 Edwards, Dr., his experiments on respiration, 
 769; on animal heat, 888, 893, 894 
 
 Efferent nerves, 289, 344 
 
 Egg, see Ovum 
 
 Egg-shell, Membrane of, 118 
 
 Ehrenberg, on limits of vision, 540 
 
 Eighth Pair of Nerves, see Glosso-pharyngeal, 
 Par Vagum, and Spinal Accessory 
 
 Ejaculatio seminis, 372, 393, 904 
 
 Elaboration of fibrine, 116, 154 159 
 
 Elasticity of arterial walls, 728, 729 
 
 Elastic tissues, 138, 139 
 
 Electricity, not identical with nervous power, 
 297 
 
 Embryo, early development of, 915917, 934 
 945 ; formation of germinal mass, 935 ; of 
 germinal membrane, 935, 936 ; of vertebral 
 column, 937 ; of amnion, 938 ; of vascular 
 area and umbilical vessels, 938, 939 ; of 
 heart and branchial arches, 940 ; of allan- 
 tois, 941; of umbilical cord, 941, 942; later 
 circulation in, 943, 944 ; influence of mo- 
 ther on, 946 ; table of development, 947 ; 
 size and weight of at birth, 948; proportion 
 of males and females, 949 ; relative viability 
 of, 950 
 
 Embryonic cell, 935, 936 
 
 Embryonic development, of brain, 358, 359, 
 361 ; of cephalic neryes, 420, 421 ; of Jungs, 
 757 6, c; of blood-corpuscles, 149 ; of liver, 
 826 g; of kidney, 839 c; of heart, 940; of 
 circulating apparatus, 940, 943, 944 ; of di- 
 gestive cavity, 945 
 
 Emissio seminis, 372, 393 
 
 Emotions, influence of on Intelligence and 
 Will, 440; on nutrition and secretion, 625 
 628 
 
 Emotional actions, 437 440 
 
 Enamel, 208; structure of, 209; composition 
 of, 212 ; development of, 215 
 
 Endosmose, 271, 675 
 
 Encephalon, 356 ; comparative anatomy of, 357 
 362; weight of, in proportion to entire 
 body, 475 ; proportions of different parts, 
 in Fishes, 357359 ; in Reptiles, 360 ; in 
 Birds, 361; in Mammalia, 362; in Human 
 
742 
 
 INDEX. 
 
 The Numbers refer to the Paragraphs. 
 
 embryo, 358, 359, 361 ; supply of blood to. 
 476, 477 
 
 Epidermic tissues, 160 174; epidermis, 161, 
 162; hair, 166 168; nails, 162,165; epithe- 
 lium, 169174; nutrition of, 135, 161, 174; 
 functions of, 162, 174 
 
 Epilepsy, 503 
 
 Epithelium, 169 174; the real secreting struc- 
 ture, 174; cylindrical, 170; tesselated, 170; 
 ciliated, 171173 
 
 Erect -vision, 543 
 
 Erectile tissue, 748 
 
 Ethiopian nations, 97 99 
 
 Eustachian tube, uses of, 564 
 
 Eustachian valve, uses of, 944 
 
 Evans, Dr. Julian on the structure of the Spleen, 
 683, 684 
 
 EXCRETION, 
 
 Objects of, 275; of carbon, 275, 833 ; of ni- 
 trogen, 276, 842; result of decomposition, 
 275, 81 9; elements of, previously in blood, 
 820, 832, 842 
 
 Excretions, outlets of, guarded by spinal cord, 
 
 O. ' 1 
 
 Exhalation, in Plants, 107; by lungs, 773, 774; 
 influenced by mental state, 774 ; from skin, 
 870, 871 
 
 Experiments on nerves, fallacies of, 302 306 
 
 Expiration, act of, 761 
 
 External Ear, uses of, 567 
 
 Exudation corpuscles, 800, 805 
 
 Eye, general action of, 536 ; an optical instru- 
 ment, 536; adaptation of, to distance, 536, 
 537 ; defects of, 538 ; optical powers of, 540; 
 consensual movements of, 450 456 
 
 F. 
 
 FACIAL nerve, 406 
 
 Faeces, composition of, 662 
 
 Fallopian tubes, passage of Spermatozoa 
 through, 911; passage of ova along, 911, 
 918; contractions of, produced by nervous 
 agency, 393 
 
 Falsetto notes, how produced, 609 
 
 Faraday, Mr., optical illusion discovered by, 
 551 
 
 Farre, Dr. A., discovery of Spermatozoa in 
 Ovum, 900 
 
 Fat-cells, 184; contents of, 185; uses of, 186; 
 formation of, 186 
 
 Fatty livers, 829 
 
 Feathers, 166 
 
 Fecundation in Plants, 899; in Animals, 900 
 
 Fever, state of blood in, 707 6 
 
 Fenestra ovalis, 557, 558 
 
 rotunda, 558 
 
 Fenwick, Mr., his experiments on absorption, 
 673 
 
 Ferments, action of, in digestion, 669 ; in 
 blood, 70S, 877 
 
 Ferneley, Mr., on areas of arteries, 710 a 
 
 Fibres, origin of, 118, 119, 136; white, 138, 
 140; yellow, 138, 142; mixture of in areolar 
 tissue, 138; in serous and synovial mem- 
 branes, 175; in mucous membrane and skin, 
 176, 177 
 
 of Muscle and Nerve, see Muscular 
 
 Fibre, and Nervous tissue 
 
 Fibrillae, ultimate of Muscle, cellular nature 
 of, 230 
 
 Fibrine, composition of, 114; properties of, 
 114, 115; coagulation of, 117 119; elabo- 
 ration of, 117, 158, 159; in chyle, 693; in 
 blood, 696 705; increase of, in inflamma- 
 tion, 158, 707 a, 802; diminution of, in fever 
 and hemorrhagic diseases, 707 6 ; imperfect 
 elaboration of, in strumous diathesis, 807, 
 878; formed at expense of albumen, 114 
 117; effusion of, 803; organization of, 119, 
 700, 795, 796 
 
 Fibro-cartilage, 187 
 
 Fibrous tissues, simple, 138142; origin of, 
 118,119,136 
 
 Fifth Pair of nerves, 403, 404 ; lingual branch 
 of, 404, 407; development of, 421; influ- 
 ence of, o'n organic processes, 625 
 
 Fishes, 26, 27; skeleton of, 26 ; respiration of, 
 27, 755; air-bladder of, 27, 755; kidneys 
 of, 838, 839 c; encephalon of, 357, 358; 
 circulation in, 27, 716: blood-corpuscles of, 
 146, d 
 
 Flourens, M., his experiments on the nervous 
 system, 432, 435, 436, 459 
 
 Fluids, absorption of, by intestinal surface, 
 674, 675 ; by general surface, 676, 677 ; by 
 veins, 675, 676; by lacteals, 674,675; by 
 lymphatics, 679 
 
 Fly-catcher, incubation of, 41 
 
 Foetus, table of development of, 947; circula- 
 tion in, 940, 943, 944; brain of, compared 
 with that of lower animals, 358, 359, 361 ; 
 see Embryo 
 
 Follicles of Lieberkuhn, 874 
 
 Food, causes of demand for, 629635 ; differ- 
 ent kinds of, 640, 648; relative amount of 
 azote in each, 647 ; destination of, 641 
 646 ; desire for, 636639 ; relative digesti- 
 bility of different kinds of, 666; mechanical 
 reduction of, 656; action of stomach upon, 
 657 659 ; passage of, into intestine, 660 ; 
 passage of, through intestinal canal, 661 ; 
 ejection of insoluble portion of, 662; mode 
 of solution of, 663671 ; smallest quantity 
 of, on which life can be supported, 653; 
 greatest quantity that can be devoured, 654; 
 supply of, required by Man, 650, 651 ; suf- 
 ficiency of, indicated by satiety, 649 ; allow- 
 ance of, in Navy, 650; in Milbank Peniten- 
 tiary, 651 ; in Edinburgh House of Refuge, 
 651 ; in Convict-ship, 651 ; effects of insuf- 
 ficient supply of, 651, 652 
 
 Form, mode of acquiring knowledge of, by 
 touch, 523 ; by sight, 541, 542, 546, 547 
 
 Fourth pair of nerves, 405 
 
 Fourth ventricle, 346, 355 
 
 Foville, Dr., his observations on brain, 486 
 
 Freckles, 164 
 
 Fremy, M., his analysis of Nervous matter, 
 249 
 
 Frog, metamorphoses of, 31; excitable state 
 of spinal cord in, 401 a 
 
 Functions, 260 ; division of, into organic and 
 animal, 261, 262; connection of, 263267; 
 of Animal life, 283288 ; of Organic life, 
 268282 
 
 Fungous growths, 809 
 
INDEX. 
 
 743 
 
 The Numbers refer to the Paragraphs. 
 
 G. 
 
 GALL, Dr., his statements respecting the Cere- 
 bellum, 468 
 
 Gall-bladder, 825 e,f 
 
 Ganglia, structure of, 252, 245 247 
 
 of Special sense in Vertebrata, 422 
 
 425 
 
 of Sympathetic, 314, 342 
 
 Gangrene, 804 
 
 Gases, contained in blood, 770; absorption of, 
 by lungs, 775777 
 
 Gasteropoda, Nervous System of, 319321 
 
 Gastric fluid, composition and properties of, 
 664; action of, 665; secretion of, propor- 
 tional to wants of the system, 657 ; not de- 
 pendent on nervous influence, 414, 415; but 
 affected by it, 626, 637 
 
 Gelatine, composition of, 141 
 
 , of cartilage, 187 a; of bone, 196 
 
 Gelatinous principles of food, 640; application 
 of, in the animal body, 642 
 
 Gerber, Prof., referred to, 693 a 
 
 Germinal mass, 935 
 
 membrane, 935; serous layer, 936; 
 
 mucous and vascular layers, 936 
 
 spot, 905, 915 
 
 vesicle, 905, 906, 915917 
 
 Gestation, signs of, 926; ordinary duration of, 
 928930; protracted, 931 ; shortest period 
 of, 932 
 
 Gills, respiration by, 755 
 
 Glands, general structure of, 821 823 
 
 , lymphatic, 682 
 
 , vascular, 683690 
 
 Globules, see Corpuscles 
 
 Globuline, composition of, 147 
 
 Glosso-pharyngeal nerve, functions of, 384, 
 407 ; development of, 420, 421 
 
 Glycerine, composition and properties of, 185 a 
 
 Glycicoll, 141 c 
 
 Goodsir, Mr., his observations on primary 
 membrane, 135; on the Teeth, 217; on 
 Bone, 194; on ulceration of Cartilage, 191 ; 
 on Absorption, 181, 672; on Vascular 
 Glands, 683; on Secretion, 822, 823; on 
 Milk-cells, 853 ft; on formation of Decidua, 
 919 ; on structure of Placenta, 921923 
 
 Gouty diathesis, 878, 884 
 
 Graafian follicle, 905, 912914 
 
 Grainger, Mr., referred to, 345, 367 
 
 Granulation, process of, 799801 
 
 Gravity, influence of on Circulation, 745 
 
 Greenhow, Dr., his plan of treating burns, 
 798 
 
 Grey matter of Nervous system, 245, 246; of 
 Brain, 472 
 
 Gryllotalpa, nervous system of, 332 
 
 Gulliver, Mr., his observations on blood-cor- 
 puscles referred to, 146, 149, 151, 156, 158; 
 on reparation of bone, 206 ; on chyle, 692 
 
 Guy, Dr., his researches on the Pulse, 727 
 
 H. 
 
 HABITUAL movements, 438 
 
 Haematine, 147 
 
 Haematococcus, 125 
 
 Hair, characters of, in different human races, 
 
 82; structure, growth, and composition of, 
 166-168 
 
 Hales, Dr., his experiments on the circulation, 
 726 
 
 Hall, Dr. M., his discoveries on the Nervous 
 system, 307, 345, 363, 365, 374, 375, 383, 
 386, 392, 394, 398, 400, 505 ; his views on 
 muscular irritability, 585, 589 6 
 
 Haller, his doctrine of muscular irritability, 
 591 
 
 Hastings, Dr., his experiments on capillary 
 circulation, 717 a; on animal heat, 890 
 
 Haversian canals, 193; formation of, 197, 199, 
 201 
 
 Hearing, sense of, 556 572 ; physical condi- 
 tions of, 557, 560 562; use of tympanum, 
 563 ; tympanic cavity and Eustachian tube, 
 564; chain of bones, 565; labyrinth, 566; 
 external ear, 567 ; auditory nerve, 559 ; 
 tones produced by succession of sounds, 
 569 ; estimate of degree, direction, and dis- 
 tance of sounds, 570; rapidity of perception 
 by, compared with sight, 571 ; uses of, in 
 regulating voice, 572, 611 
 
 Heart, 111; muscular fibre of, 234 ; inherent 
 contractility of, 717; rhythmical movements 
 of, 717 719; influence of nerves on, 416, 
 576,717 a-c; sounds of, 720, 721 ; course 
 of blood through, 722; differences of struc- 
 ture in two sides of, 723 ; difference of 
 valves, 723 c ; quantity of blood propelled 
 by, 724, 725 ; force of contraction of, 726 ; 
 number of contractions of, 727; various 
 causes influencing, 727 a-e ; origin of, 940 ; 
 subsequent development of, 943 
 
 Heat, Animal, amount of, developed by Man, 
 885, 886; in disease, 886; dependence of 
 on formation of carbonic acid, 889 892 ; 
 development of, in Plants, 889 a, 6; in 
 lower animals, 889, c; effect of exercise on, 
 890 ; partly maintained by artificial respira- 
 tion, 896; dependent in part on cutaneous 
 respiration, 891 ; chemical theory of, 892; 
 heat of young animals, 893 ; variations in 
 power of generating, at different seasons, 
 894; loss of, during inanition, 895, 896 ; pro- 
 visions against excess, 897 
 
 Heat, external, influence of, on incubation of 
 Birds, 41 ; influence of, on vital actions in 
 general, 885; extremes of, endurable by 
 Man, 887, 888; power of resisting, 887, 
 888, 897 
 
 Heat, sexual, 909 
 
 Helmholtz, his observations on composition of 
 muscle, 238 6, 586 
 
 Hemiopia, 545 note 
 
 Hepatic artery, 826 d 
 
 cells, 183, 826 / 
 
 duct, 826 c 
 
 vein, 826 a, e 
 
 Herbivorous animals, nutrition of, 645 
 
 Hering, experiments of, on circulation, 724 
 
 Heterologous growths, 809, 881 
 
 Hiccup, act of, 380. 
 
 Hippuric acid, 845 a 
 
 Holland, Dr., referred to, 521 
 
 Horny matter, composition of, 162 
 
 Horses, cerebella of, 468. 
 
 Hottentots, 100 
 
 Houston, Dr., on acardiac fetus, 736 
 
744 
 
 INDEX. 
 
 The Numbers refer to the Paragraphs. 
 
 Hunger, sense of, 412, 636638 
 
 Hunter, John, on muscular tonicity, 593, 594; 
 on functions of lymphatics, 681 a, c ; on con- 
 tractility of arteries, 731 ; on union by ad- 
 hesion, 794 
 
 Hutchison, Mr., on capacity of respiration, 764 
 
 Hydra, 9 ; movements of, 313 ; reproduction 
 of parts in, ft, 792 
 
 Hydrophobia, 502. 
 
 Hymenoptera, nerves of wings of, 298 ; in- 
 stincts of, 336, 429 
 
 Hypertrophy, 787, 788 
 
 Hypoglossal nerve, functions of, 418, 419 ; de- 
 velopment of, 420, 421 
 
 Hysteria, 503 ; remarkable abstinence in, 653 
 
 I. 
 
 IDEAS, formation of, 488. 
 
 Idiots, actions of, 428, 474, 478, 484 
 
 Improbability of Man, 60 
 
 Inanition, Chossat's experiments on, 895, 896 
 
 Incontinence of urine, 401, 504 
 
 Indo-European nations, 95 
 
 Indian nations, 95 
 
 Infants, inferior calorifying power of, 893, 932 a 
 
 Inflammation, increase of fibrine of blood in, 
 707 a, 802 ; diminished vitality of the- tissues 
 in, 803 ; results of, 804806 ; generally un- 
 favourable to reparation, 793, 799 801 ; 
 prevention of, after injuries, 798; how far 
 concerned in deposition of tubercle, 808 
 
 Ingestion of food, actions concerned in, 382, 
 656 
 
 Insalivation, 656 
 
 Insects, Muscular apparatus of, 19 ; strength of, 
 599; instincts of, 17, 429,479; heat deve- 
 loped by, 889 c ; nervous system of, 325 
 336 ; reflex actions of, 328, 329 ; consensual 
 actions of, 336; circulation in, 715; respira- 
 tion in, 755 
 
 Inspiration, act of, 761 
 
 Instinctive actions, characters of, 428 
 
 Instincts, of Articulata, 17, 336,429,479; of 
 Birds, 479 ; of Mammalia, 42, 480; of Man, 
 428, 437440, 484 ; of Cuttlefish, 438 ; of In- 
 fants and Idiots, 428, 484 
 
 Intelligence, of Vertebrata, 2.3, 482 ; of Birds, 
 479; of Mammalia, 480; of Man, 484; gene- 
 ral absence of, in Invertebrata, 429 ; seat of, 
 in the Cerebrum, 478 
 
 Intercellular passages, 218 
 
 Intervertebral nerves, 421 
 
 Intestines, peristaltic movements of, 388, 389; 
 passage of food through, 660, 661 ; glandulse 
 of, 661, 874876 ; secretions of, 66], 877 
 
 Intuitive perceptions, 490 
 
 Invertebrata, general absence of red corpus- 
 cles in, 150; character of blood of, 155 
 
 Iron, contained in food, 648 ; in blood-discs, 
 147; administration of, in chlorosis, 707 c 
 
 Irritability, of muscular fibre, see Muscle 
 
 lulus, nervous system and actions of, 326, 329 
 
 J. 
 
 JENNINGS, Mr., on artificial insufflation of lungs, 
 760 a 
 
 Jewish nation, 80, 94 
 
 Jones, Dr. Bence, his observations on phos- 
 phatic deposits, 295 note 
 
 Jones, Mr. Wharton, his observations on blood- 
 corpuscles, 152, 159 a ; on effects of inflam- 
 mation, 704 ; on capillary circulation, 780 
 
 K. 
 
 KELLIE, Dr., his experiments on circulation in 
 cranium, 747 
 
 Kidneys, general function of, 276, 819 ; struc- 
 ture of, 838, 839 ; cortical and medullary sub- 
 stances, 839 a ; tubuli uriniferi, 839 a ; Mal- 
 pighian bodies in, 839 6; circulation in, 840; 
 embryological development of, 839 c; see 
 Urine. 
 
 Kiernan, Mr., on the liver, 826, 827 
 
 Kiesteine, in urine of pregnant women, 859, 
 926 
 
 Knight, Mr., observation on incubation of Fly- 
 catcher, 41 
 
 Kronenberg,Dr., on roots of spinal nerves, 304. 
 344 
 
 L. 
 
 LACHRYMAL gland, 865 
 
 influence of nerv- 
 
 secretion, 865; 
 ous system on, 625, 626 ' 
 
 Lacteals, origin and distribution of, 672 ; func- 
 tions of, 674, 675 
 
 Lactic acid, present in stomach during diges- 
 tion, 664 b ; not a constituent of urine, 846 
 
 Lacunae of bone, 193, 194 
 
 Lamina spiralis, 559 
 
 Lamprey, 22 
 
 Lane, Mr., his investigations on chyle, 693 a 
 
 Language, indication of affinity of races, 95 a 
 
 Laryngeal nerves, 378 
 
 Larynx, structure of, 602604 ; action of, 604 
 611 ; muscles of, 604, 605 
 
 Laughing, act of, 380 
 
 Lecanu, M., his analysis of blood, 697 a; his 
 observations on urine, 844 
 
 Lehmann, his experiments on composition of 
 urine, 844, 849, 850 
 
 Letellier, M., his researches on respiration, 
 767 a 
 
 Leuret, M., his observations on Cerebellum, 
 468, 469 
 
 Liebig, Prof., on digestive process, 669 ; on 
 red corpuscles of blood, 150 a; on compo- 
 sition of urine, 845 848; on uric acid, 845 
 
 Life, idea of, involves change, 254, 255 ; dura- 
 tion of, in individual parts, 259, 810 812 
 
 Ligaments, structure of, 140; vocal, 140 
 
 Ligamentum nucha?, 140 
 
 Light, laws of refraction of, 533535 ; rapidity 
 of perception of, compared with sound, 571 ; 
 influence of, on metamorphosis, 32; effect 
 of, on pupil, 395, 443; influence of, on pig- 
 ment-cells, 164 
 
 Lime, an element of animal structures, 648 
 
 Lingual branch of fifth pair, 407 
 
 Lintott, Mr., his observations on the teeth, 
 217 c 
 
 Liquor sanguinis, 696 : organization of, 117 
 119,795,796 
 
INDEX. 
 
 745 
 
 The Numbers refer to the Paragraphs. 
 
 Liver, general function of, 275, 819 ; univer- 
 sally present in Animal Kingdom, 825; size 
 and form of, in Vertebrata, 825 c, d ; gene- 
 ral structure of, 826; component cells of, 
 183, 826 /; distribution of portal vessels, 
 826 6 ; of hepatic artery, 826 d ; of hepatic 
 vein, 826 a, e; of hepatic ducts, 826 c ; con- 
 gestion of, 827 ; cirrhosis of, 828 ; embryo- 
 nic development of, 826 g; proportional 
 size of, before and after birth, 826 g, 830 ; 
 secretion of bile by, 831836, see Bile; 
 other depurating actions of, 837 
 
 Lizards, 29 
 
 Locomotive actions, 397 
 
 Looped terminations of Nerves, 240, 248 
 
 Lungs, structure of, in lower Vertebrata, 756 ; 
 in Man, 737 ; development of, 757 a-c ; ac- 
 tion of, in respiration, 760 ; capacity of, 764; 
 chemical changes in, 765 767 ; exhalation 
 by, 773, 774 ; absorption by, 775, 776 
 
 Lymph, composition of, 691 ; elaboration of, 
 682 ; globules in, 155, 694 ; purposes of, 154 
 159 
 
 Lymph, coagulable, see Liquor Sanguinis 
 
 Lymphatic glands, structure of, 682 
 gLymphatics, distribution of, through the body, 
 676 ; function of, 679, 680 ; specially con- 
 cerned in nutritive absorption, 680, 681 
 
 M. 
 
 MACARTNEY, Dr., his views on the reparative 
 processes, 793801 
 
 Macleod, Dr., on first production of blood-cor- 
 puscles, 149 a 
 
 Madden, Dr., his experiments upon absorption, 
 677, 775 
 
 Madder, effect of, on bones, 202 ; on teeth, 210 
 
 Magnetism, Animal, Appendix II. 
 
 Magnus, his experiments on the blood, 770 
 
 Malayo-Polynesian race, 103 
 
 Malignant growths, 809, 881 
 
 Mammalia, 4250 ; sub-classes of, 44 ; skele- 
 ton of, 46 ; respiration and heat of, 47, 757 ; 
 subdivisions of, 48 ; brain of, 362 ; intelli- 
 gence of, 42, 485 ; blood-corpuscles of, 146 a 
 
 Mammary gland, 853; structure of glandulae, 
 853, a, 6 ; development of, 853, c ; structure 
 of in male, 853 d ; secretion of, 854861 ; 
 see Milk 
 
 Man, characteristics of, 5161 ; erect attitude 
 of, 5157 ; hand of, 57 ; other distinctive 
 characters of, 58 ; sensibility and locomotive 
 power of, 59 ; intelligence of, 60 ; soul of, 
 61; psychical operations in, 283 286; sub- 
 division of into races, 62, 63, 78 105; com- 
 mon origin of, 91 ; extremes of variation 
 amongst races of, 72 ; proper food of, 646 
 
 Mantis, nervous system of, 328 
 
 Margarine, composition and properties of, 185 a 
 
 Mastication, 656 
 
 Matteucci, his experiments on Electricity, 297 
 
 Mayer, Prof., his experiments on the Spleen, 
 685 
 
 Median nations, 95 
 
 Medulla Oblongata, 350 ; structure and connec- 
 tions of, 351 355 ; ganglionic character of, 
 355; general functions of, 370, 374, 384; 
 63 
 
 centre of respiratory movements, 374; cen- 
 tre of acts of deglutition, 384, 385 
 
 Medullary matter of nervous system, structure 
 of, 243, 246 ; functions of, 248 
 
 Melolontha vulgaris, 19 
 
 Membrana granulosa, 906, 912 
 
 Membrana tympani, uses of, 563 
 
 Membrane, basement or primary, 135 ; fibrous, 
 140; mucous, 176 179; serous and syno- 
 vial, 175 
 
 Membrane, development of bone in, 197 
 
 Memory, 491 
 
 Menstruation, 908, 909 
 
 Metamorphosis of Batrachia, &c., 32, 630 a 
 
 Milk, peculiarity of as alimentary substance, 
 642, 647 ; general composition of, 854, 857 ; 
 microscopic characters of, 854 a ; constitu- 
 ents of, 854 b ; proportion of constituents in 
 human milk, 855 ; in milk of different ani- 
 mals, 858 ; quantity of, 860 ; change in cha- 
 racter of, during nursing, 856 ; consequences 
 of retention of, 859 ; transference of secre- 
 tion, 859 a; foreign substances entering, 
 861 ; influence of emotions on, 627 j secre- 
 tion of, in male, 853 c 
 
 Milky aspect of Chyle, 692 
 
 serum, 697 e 
 
 Milbank Penitentiary, 651 
 
 Mind, elementary operations of, 487 495 ; in- 
 fluence of, on nutrition and secretion, 625 
 628 
 
 Mineral ingredients of Food, 648 
 
 Mitchell, James, case of, 532 
 
 Modelling process, 797, 798 
 
 Molecular base of Chyle, 692 
 
 Molecular death, 813, 815, 816 
 
 Mollusca, 5, 1 1 15 ; deficiency of symmetry 
 in, 11 13; organs of locomotion in, 13; 
 organs of nutrition in, 14 ; blood and respira- 
 tion of, 15 ; shells of, 192 ; nervous system 
 in, 315 322 ; circulation in, 715 ; respiration 
 in, 755 
 
 Mongolian nations, 96 
 
 Montgomery, Dr., on Corpus luteum, 913, 914; 
 on placental bruit, 925 
 
 Mother, influence of, on foetus, 946 
 
 Motions of Plants, 1, 230 
 
 Motor influence, laws of propagation of, 299 
 
 Motor linguae, 418, 419 
 
 oculi, 405 
 
 nerves, determination of, 300 303 
 
 tract of Sir C. Bell, 351 
 
 Mucous layer of germinal membrane, 936 
 
 Mucous Membrane, 176 179; of stomach, 
 appearance of, in health, 657; in disease, 
 658; intestinal, structure of, 661; glandulae 
 of, in stomach, 873 ; in intestines, 874 877 
 
 Mucus, properties of, 179 
 
 Mulder, his analysis of albumen and fibrine, 
 114; of proteine and its oxides, 116; of 
 gelatine, 141 a 
 
 Mu'ller, Prof., his researches on vision referred 
 to, 519,537,543, 552; on hearing, 561,562, 
 564; on blood, 699; on voice, 606610; on 
 respiration, 769; on cancer, 809 
 
 Muscular Fibre, 223240 ; chemical composi- 
 tion of, 238 
 
 Structure of, 224, 225; in muscles of Animal 
 life, 225233 ; arrangement of, in fasci- 
 
746 
 
 INDEX. 
 
 The Numbers refer to the Paragraphs. 
 
 culi, 226 ; composed of fibrillae, 226 ; en- 
 veloped in sheath, 227 ; form and com- 
 parative dimensions of, 228, 229 ; structure 
 of ultimate fTbrillse, 230 ; state of, in con- 
 traction, 231, 233; origin of, 235, 236; 
 reparation of, 237; supply of blood-vessels 
 to, 239; supply of nerves to, 240; struc- 
 ture of, in Muscles of Organic life, 234; 
 development of, 235, 236; disintegration 
 of, from use, 239, 263, 586 
 Contractility of, 573, 574 ; irritability of, 575 ; 
 contraction alternating with relaxation, 
 576, 577; persistence of after death, 578 ; 
 depressed by sedatives, 579; by violent 
 nervous impressions, 580, 581; increased 
 by stimuli, 582; dependent on arterialized 
 blood, 583 585; increased by habitual 
 employment of particular muscles, 587 ; 
 diminished by want of action, 588 ; in- 
 fluence of nerves on, 589 591 ; loss of, 
 from section of nerves, 589 6, c ; restored 
 after exhaustion, 589 d', an independent 
 endowment, 591 ; difference of, on two 
 sides of heart, 585} the same at different 
 degrees of contraction, 592; power gene- 
 rated by, in Man, 598 ; in Insects, 599 
 Tonicity of, 593 597 ; effect of heat and 
 
 cold upon, 593, 594 
 Contraction of, after death, 595597 
 
 Muscular Contraction, influence of, on Circu- 
 lation, 744 c 
 
 Muscular Sense, 433, 434 
 
 Tension, maintained through Spinal 
 
 Cord, 398, 399 
 
 Musk-deer, blood-corpuscles of, 146 a, 151 ; 
 hair of, 166 
 
 Myolemma, 227, 235 
 
 Myopia, 538 
 
 Myxinoid fishes, 180 
 
 Myriapoda, nervous system of, 326 ; develop- 
 ment of head of, 426 a 
 
 NAILS, 162, 165 
 
 Necraemia, 708 
 
 Negro races, 97 99 
 
 Nerves, origin of, in ganglia, 246,247; termi- 
 nations of, in muscles, 239 ; in skin and 
 sensory organs, 248 ; mode of determining 
 functions of, 300 306 
 
 Nervous agency, hypothesis on its nature, 297; 
 laws of its transmission, 298, 299 ; not es- 
 sential to Nutrition and Secretion, 620, 624 ; 
 influence of, on organic functions, 625 628 
 
 Nervous circle, 433 
 
 Nervous System, general functions of, 289, 307 ; 
 elementary structure of, 241 253 ; fibrous 
 matter of, 242 244 ; vesicular matter of, 245, 
 
 246 ; arrangement of fibres in ganglia, 246, 
 
 247 ; afferent and efferent fibres of, 289, 344 ; 
 use of plexuses in, 298; isolated course of 
 single fibres, 298 ; general purposes of, 307 
 309; dependence of its activity upon supply 
 of blood, 290, 291 ; functional activity of, in- 
 volves disintegration, 292 296; nature of 
 changes in, 297; existence of in lowest Ani- 
 mals, 311, 312; general recapitulation of 
 
 functions, 496 498; peculiar conditions of, 
 499 501 ; pathological states of, 501 505 
 Nervous system of Radiata, 313, 314; of Mol- 
 lusca, 315323; of Articulata, 324336; of 
 Vertebrata, 337362 
 
 Nervous tissue, 241 253; fibrous element of, 
 242244; cellular element of, 245, 246; re- 
 lation of two structures in, 246 248; com- 
 position of, 249; nutrition of, 250, 251; first 
 development of, 252; regeneration of, 253; 
 disintegration of, with use, 292 296; decay 
 of, when not employed, 442 
 Neuro-skeleton, 20 
 
 Newport, Mr., his observations on the blood- 
 corpuscles of Insects, 156; on their nervous 
 system, 325 330 ; on their temperature, 
 889 c; on development of head of Myria- 
 poda, 426 a 
 
 Nitrogen, proportion of, in different articles of 
 food, 647; exhalation and absorption of, 
 766; respiration in, 769, 780; amount of, in 
 blood, 770 
 Nostoc, 125 
 
 Nucleus, 124; its offices and metamorphosis, 
 in Plants, 124, 125; in Animals, 128133 
 Nucleus-filaments, 138 * 
 
 NUTRITION, 
 
 General account of, 273, 274, 781 ; connec- 
 tion of, with nervous system, 279; not de- 
 pendent upon nervous agency, 624; but 
 influenced by it, 624, 625 
 Essential nature of, 782; a continuous pro- 
 cess of cell development, 782, 783; select- 
 ing power of individual parts, 784, 785 
 Varying activity of, 786791 ; affected by 
 age, 786 ; hypertrophy, 787, 788 ; atrophy, 
 789791 
 
 Reparative processes, 792 801 ; reproduc- 
 tion of parts in lower Animals, 792; union 
 by first intention, 793, 794; organization 
 of liquor sanguinis, 119,795; organization 
 of blood, 700, 796; modelling process of 
 Dr. Macartney, 797 ; circumstances favour- 
 able to, 798 ; granulation, 799801 
 Abnormal forms of Nutritive processes, 802 
 809; inflammation, 802 804; suppura- 
 tion, 805, 806; tubercular deposit, 807, 
 808; cancerous growths, 809 
 Varying duration of different parts, 810 
 812; limited term of existence of cells, 
 811 ; variation of, with period of life, 812 
 Death, or Cessation of Nutrition, 813816; 
 somatic and molecular, 813 ; somatic, by 
 Syncope, 814 ; by Asphyxia, 814; by Cold, 
 814; Molecular, consequent upon somatic, 
 815; dependent on local change, 816 
 
 0. 
 
 OBLIQUE muscles of orbit, 451 
 Oceanic races, 102 
 Octopus, nerves of, 298 
 Odoriferous glandulae, 872 
 Odorous matter in blood, 872 
 Odours, sensibility to, 531, 532 
 (Esophagus, descent of food through, 386,656 
 Oleaginous principles of food, 640, 641 ; de- 
 stination of, in Animal body, 643 646, 671 
 
INDEX. 
 
 747 
 
 The Numbers refer to the Paragraphs. 
 
 Oleine, composition and properties of, 185 a 
 
 Olfactory lobes, in Fishes, 357359 ; in Rep- 
 tiles, 360; in Birds, 361; in Mammalia, 
 362; in Man, 422 
 
 Olfactive nerves, functions of, 331 
 
 Olivary bodies, 350354 
 
 Omphalo-Meseraic vessels, 939 
 
 Optic lobes, in Fishes, 357 359 ; in Reptiles, 
 360; in Birds, 361 ; in Mammalia, 362; in 
 Human embryo, 358, 359, 361; in Man, 
 422 ; functions of, 436 
 
 Optic Nerve, 442 445 ; an excitor of motion, 
 443; decussation of, 445; termination of, in 
 retina, 539 
 
 Optic Thalami, 423,424 
 
 Orang Outan compared with Man, 50 60 
 
 Orbicularis muscle, reflex action of, 394 
 
 Orbit, motor nerves of, 405; muscles of, 450, 
 451 
 
 Organic fibres of Nervous System, 244, 247, 
 341 
 
 Organization, connection of, with vital proper- 
 ties, 781 ; incipient in liquor sanguinis, 117 
 119 ; in coagulable lymph, 117, 795 
 
 Organs of Sense, their mode of operation, see 
 Ear, Eye, &c, 
 
 Ornithorrhyncus, 44; mammary gland of, 821 
 
 Ossification, in membrane, 197, 201 ; in carti- 
 lage, 198201 
 
 Ostrich, incubation of, 41 
 
 Otter-breed, origination of, 70 
 
 Ovarium, origin of ova in, 905 907 ; corpus 
 luteum in, 913, 914 
 
 Ovisac, 907, 908 
 
 Ovum, component parts of, 905 ; origin of, 906, 
 
 907; maturation of, 909 ; arrival of sperma- 
 
 , tozoa at, 900, 911 ; discharge of, from ovary, 
 
 912; first changes in, 915918; later 
 
 changes in, 934947 
 
 Owen, Mr., on blood-corpuscles of Siren, 145 
 note; on structure of dentine, 210 ; on forma- 
 tion of dentine, 213, 214; on formation of 
 enamel, 215; on formation of crusta petrosa, 
 216 
 
 Oxygen, introduction of, in respiration, 766; 
 presence of, in arterial blood, 770, 771 ; in- 
 fluence of, on colour of blood, 771, 772 ; 
 effect of respiration of, 777 
 
 P. 
 
 PAGET, Mr. J., on areas of arteries, 710 6 ; on 
 concentric hypertrophy of heart, 597 ; on 
 absence of corpus callosum, 474 a ; on ac- 
 tion of heart, 717 
 
 Pancreas, structure of, 862 ; secretion of, 669, 
 670, 863 
 
 Papillae, of skin, 522 ; of tongue, 527 
 
 Papuans, 104 
 
 Paralysis agitans, 381 note 
 
 Paraplegia, cases of, showing reflex action, 
 366369 
 
 Parturition, 393, 928, 929 
 
 Par Vagum, 408 ; the excitor of respiratory 
 movements, 374, 375; influence of, on pha> 
 rynx, 385 ; on oesophagus, 386 ; on stomach, 
 387 ; chief excitor of sense of hunger, 412, 
 
 637 ; effects of section of, on lungs, 409 
 411 ; on digestion, 412 415; on heart, 416 
 
 Pelagian-Negro races, 104 
 
 Pelvis, various forms of in different races of 
 Men, 88 
 
 Pepsin, 668, 669 
 
 Perception, 488490 
 
 Perenni-branchiate Batrachia, 32 
 
 Peristaltic movements of intestines, 388, 575, 
 660; independent of nervous agency, 388; 
 influenced by spinal cord through sympa- 
 thetic, 388, 389 
 
 Peyerian glands, 874, 876 
 
 Philip, Dr. Wilson, his experiments on the Par 
 Vagum, 414, 415; on connection of Nervous 
 System with heart, 717 a; with Capillaries, 
 742 ; on animal heat, 890 
 
 Phosphorus, an element of food, 648 ; in pro- 
 teine-compounds, 113, 114; oxidation of, in 
 system, 847 
 
 Photophobia, 431 
 
 Phrenological doctrines regarding Cerebellum, 
 466470 
 
 Phrenology, observations on, Appendix I. 
 
 Physiology, objects of the science, and mode 
 of pursuing it, Introduction. 
 
 Pigment-cells, 163, 164 
 
 Piementum nigrum, 164 
 
 Placenta, 44 ; formation and structure of, 920 
 924 
 
 Placental souffle, 925 
 
 Plants, see Vegetables 
 
 Playfair, Dr., his observations on Milk, 855 
 
 Plethora, increase of blood-corpuscles in, 
 708 c 
 
 Plexus of nerves, use of, 298 
 
 Plica Polonica, 168 
 
 Plicae dorsales, 937 
 
 Pneumogastric nerve, see Par Vagum 
 
 Poisseuille, M., his experiments on the circu- 
 lation, 726, 729, 730 
 
 Polli, Dr., his observations on blood, 701, 702 
 
 Polydesmus, nervous system of, 326 
 
 Polynesian races, 103 
 
 Polypes, 6 10 ; circulation in, 715 ; reproduc- 
 tion of parts in, 9, 792; movements of, 313 
 
 Porrigo favosa, 809 a 
 
 Portal circulation, 685, 746; in liver, 826, 
 827 ; in kidneys, 839 6 841 
 
 Portio dura, 406 
 
 Posterior roots of spinal nerves, 344 
 
 Pregnancy, signs of, 926 ; see Gestation 
 
 Presbyopia, 538 
 
 Prichard, Dr., his ethnographical researches 
 referred to, 63 note, 77, 92 
 
 Primitive trace, 936 
 
 Protecting agency of Spinal Cord, 394 396 
 
 Proteine, composition and properties of, 116 
 
 Proteus, 32; blood-corpuscles of, 146 c, 151 
 
 Prout, Dr., his classification of alimentary sub- 
 stances, 640 ; his observations on secondary 
 digestion, 681 ; on amount of carbonic acid 
 excreted, 767 ; on watery exhalation from 
 the lungs, 773; on urine, 845 rf; on general 
 disorders of secretion, 883 
 
 Puberty, in Male, 903; in Female, 908 
 
 Pulsation of heart, 717 
 
 r- of arteries, 729 
 
 Pulse, average frequency of, at different ages, 
 
748 
 
 INDEX. 
 
 The Numbers refer to the Paragraphs. 
 727; variations of, under different circum- 
 stance^ 727 a-e ; proportion of to respira- 
 tory movements, 762 
 
 Pulse, respiratory, 744 b 
 
 venous, 723 c 
 
 Pupil, action of, 395 
 
 Purkinje, optical experiment of, 555 
 
 Pus, production of of, 779, 800, 805, 806 
 
 Pyramids, anterior and posterior, 350 354 
 
 Q- 
 
 QUADRUMANA, 50 
 
 Quekett, Mr. J.,, his observations on bone re- 
 ferred to, 194 a 
 
 Quetelet, M., his researches on relative mor- 
 tality at different seasons, 699 c; on length 
 and weight of infants at birth, 948 ; on rela- 
 ( tive viability of males and females, 950 ; on 
 comparative heights of males and females, 
 951 . 
 
 Quickening, 927 
 
 R. 
 
 RACIBORSKI, fiis researches on Conception, 909 
 
 Radiata, 510; general structure of, 5; affi- 
 nity with vegetables, 6, 7 ; symmetry in, 8; 
 reproduction of parts in, 9; nutritive organs 
 in, 10 ; nervous system in, 311- 314 
 
 Rainey, Mr., his researches on structure of 
 lungs, 757 
 
 Recti muscles of orbit, 450 
 
 Red Corpuscles of Blood, see Corpuscles, Red 
 
 Reeds, vibrating, laws of, 606 c 
 
 Rees, Dr. G. O., his observations on blood-cor- 
 puscles referred to, 143, 144, 148; on com- 
 position of Chyle and Lymph, 691 ; on Saline 
 matter of Blood, 697 d 
 
 Reflex action, 313, 363 ; in Mollusca, 316, 317, 
 322,; in Articulata, 327329,335; in Ver- 
 tebrata, 337, 364373 
 
 , cases of in Man, without sensa- 
 tion, 365370 
 
 Regeneration of parts, in lower Animals, 9, 
 792; of bone, 204207, 792; of nervous 
 substance, 253 
 
 Reid, Dr. J., his researches on respiratory 
 movements, 374, 375; on movements of 
 deglutition, 384386 ; on movements of sto- 
 mach, 387; onglosso-pharyngeal nerve, 407; 
 on pneumogastric, 408 416 ; on laryngeal 
 nerves, 378, 379 ; on spinal accessory, 417; 
 on muscular contractility, 589; on irritabi- 
 lity of heart, 717 ; on Asphyxia, 723 c, 
 780; on capillary circulation, 740; on mu- 
 cous membrane of uterus, 919 ; on structure 
 of placenta, 922 
 Reid, Dr. D. B., his researches on respiration, 
 
 765 
 
 Reinforcement, fibres of, 326 
 Reparative processes, 792 801 ; Dr. Macart- 
 ney's views of, 793 801 ; union by first in- 
 tention, 794 ; process of organization of 
 liquor sanguinis, 119, 795; organization of 
 blood, 700, 796; modelling process, 797; 
 
 causes favourable to, 798; granulation, 799 
 
 801 
 
 Repetition of parts in Radiata, 6 9 ; in Ar- 
 ticulata, 324, 330 
 
 REPRODUCTION, - 
 
 General account of, 281, 282,898 ; in Plants, 
 
 109, 898, 899 ; in Animals, 900 
 History of, in Malej 901 904; spermatic 
 fluid, 867, 901 ; evolution of spermatozoa, 
 902 ; power of, 903 ; coitus, 904 
 History of, in Female, 905 933; general 
 account of ovum, 905; first development 
 of, 906, 907; menstruation, 908, 909; 
 aptitude for conception, 909, 910 ; coitus, 
 911; escape of ovum, 912; corpus luteum, 
 913, 914; first changes in ovum, 915 
 917; addition of chorion, 918; formation 
 of decidua, 919 ; formation and structure 
 of placenta, 920924 ; sound of, 925 ; in- 
 crease of tissue of uterus, 926; quicken- 
 ing, 927 ; parturition, 928, 929; ordinary 
 duration of gestation, 930; protracted ges- 
 - tation, 931 ; shortest term of gestation, 
 
 932 ; superfcetation, 933 
 Development of embryo, see Embryo 
 Reproduction of lost' parts, 9, 792 
 
 Reptiles, 28 32; respiration and circulation 
 in, 28, 756; different orders of, 29, 30 ; 
 connected with Fishes by Batrachia, 31, 
 32; brain of, 360; blood-corpuscles of, 
 145, 146 c; lungs of, 756 
 
 Resistance, sense of, 514 
 
 RESPIRATION, 
 
 General purposes of, 749 754; necessity 
 for, 749 ; in Plants, 750 ; in Animals, 
 generally> 751 ; in warm-blooded Verte- 
 brata, 752 ; variation in degree of, 753, 
 754 
 
 Structure and action of Respiratory organs, 
 in Invertebrata, 755 ; in lower Vertebrata, 
 756 ; structure and development of lungs 
 in Man, 757 ; arrangement of their blood- 
 vessels, 758; contractility of bronchial 
 tubes, 758 ; movements concerned in ex- 
 change of air, 760, 761 ; number and ex- 
 tent of, 762, 763 ; capacity of lungs, 764 
 Chemical phenomena, 765 768; carbonic 
 a,cid exhaled, 765 ; proportional amount 
 of oxygen absorbed, 766; absolute quan- 
 tity of carbon set free, 767; variations in, 
 767 a-i ; azote absorbed and exhaled, 
 766; cutaneous respiration, 768 
 Effects on the blood, 769 772; carbonic 
 acid in venous blood, 769, 770; exhala- 
 tion of, in hydrogen and azote, 769 ; com- 
 parative analysis of free gases in arterial 
 and venous blood, 770; causes of change 
 of colour, 771, 772 
 
 To be regarded as an Excretion, 275, 749 ; 
 consequences of retention of carbonic 
 acid, 778 780 ; phenomena of Asphyxia, 
 779 ; its immediate causes, 780 
 Movements of, 760 763 ; dependent on 
 Nervous agency, 374, 375 ; centre of, in 
 Medulla oblongata, 376; nerves concerned 
 in, 374376 ; independent of will and of 
 consciousness, 377 ; guard to entrances of 
 lungs, 378, 379; modifications of, 379 
 381 ; influence of pain on, 431, 763 ; num- 
 
INDEX. 
 
 749 
 
 The Numbers refer to the Paragraphs. 
 
 ber of, 762, 76.3; share of lungs and air- 
 passages in, 759, 760; various influences 
 affecting, 763 
 
 Respiratory Circulation, 710 ; peculiarity ^>f, 
 746 
 
 Respiratory pulse, 744 6 
 
 Restiform bodies, 350 354 
 
 Rete mucosum, 161 
 
 Retina, structure of, 539 ; the recipient of 
 visual impressions, 536 ; inversion of pic- 
 tures upon, 543; persistence of impressions 
 on, 551, 552 ; vanishing of images on, 554 ; 
 visual representation of, 555 
 
 Retinacula, 906, 912 
 
 Rigor Mortis, 232, 595 697 
 
 Ritchie, Dr., his researches on development 
 of ova, 907 ; on Menstruation, 909 ; on the 
 Corpus luteum, 914 
 
 Robinson, Mr., on effusion of fibrine, 803 
 
 8< 
 
 SACCHARINE principles of food, 640 ; destina- 
 tion of, 641, 643, 645, 670 
 
 Saliva, properties of, 656, 668, 863 ; incorpo- 
 ration of with food, 656 
 
 Salivary glands, structure of, 862 ; secretion 
 of, 863 ; influence of nervous system on, 
 625, 626 
 
 Saunders, Mr. .E., his researches upon the 
 teeth, 217 k-m 
 
 Savart, M., his researches upon sound, 469 a 
 
 Scharling, Prof., his researches on respiration, 
 767 
 
 Schleiden, his researches on the development 
 of cells in Plants, 124 
 
 Schwann, his experiments on muscular con- 
 traction, 592 ; his observations on cellular 
 origin of Animal structures, 135 
 
 Seasons, influence of on Calorification, 894 
 
 Sebaceous glands, 872 
 
 SECRETION, general nature of, 275 278, 817 ; 
 structures adapted for, 821823; essen- 
 tially composed of cells, 821 823 ; disor- 
 ders of, connected with nutritive processes, 
 882 ; not dependent on nervous agency, 620, 
 624 ; influence of nervous system on, 625 
 628 
 
 Secretions, amount of, 818; sources of, 819 ; 
 elements of, pre-existing in the blood, 820 ; 
 some of them used in the system, 820 ; see 
 Bile, Urine, Milk, &c. 
 
 Seguin, on cutaneous exhalation, 870 
 
 Selecting power, of individual parts, 782 785 
 
 Semicircular canals, 366 
 
 Seminal secretion, 867, 901, 904; influenced 
 by state of feeling, 626 note 
 
 SENSATION, 307, 308 ; characteristic of Ani- 
 mals, 283, 284; why associated with reflex 
 actions, 371, 372; dependent on Capillary 
 Circulation, 290, 507, 508 ; the originator o 
 consensual movements, 430 432 ; the. guide 
 of voluntary movements, 433 
 Sensations, nature of, 506 ; different kinds of 
 
 507 ; dependence of on supply df blood 
 
 508 ; pain or pleasure connected with, 509 
 influence of habit on, 510 513 ; special 
 
 514, 518 ; common, 514, 515 ; subjective 
 and objective, 516, 518, 521 ; transference 
 of, 517 ^ influence ofattention on, 519 521 ; 
 knowledge gained from, 487 490 
 
 Sense, Muscular, 433, 434 
 
 Sensibility in different parts, 507, 508 
 
 Sensitive Plant, movements of, 1 
 
 Sensorium, 435 
 
 Sensory ganglia, 422427 ; functions of, 428 
 440 
 
 nerves, 441 449 ; terminations of, 248 
 
 tract of Sir C. Bell, 351 
 
 Serous membranes, 175 
 
 Serpents, 29 
 
 Serres, his measurements of Cerebellum, 457 ; 
 of Cerebrum, 481 
 
 Serum of blood, 696 ; composition of, 697 ; 
 proportion of, to clot, 703; milky, 697 e 
 
 Seventh pair, portio mollis of^ 446 ; portio 
 dura of, 406 
 
 Sexual instinct, 903, 909 ; its supposed loca- 
 tion in the Cerebellum, 466470 
 
 Sharpey, Dr., his observations on development 
 of bone, 197 201 ; on muscular fibrillae, 
 230, note; on nerves of Cuttlefish, 322 ; on 
 decidua, 919 
 
 Shell, structure of, in Echinodennata, 192 ; in 
 Mollusca, 192 
 
 Siege of Landau, 946 
 
 Sighing, act of, 380 
 
 Sight, sense of, see Vision 
 
 Simon, Mr., on Thymus and Thyroid Glands, 
 687, 688 
 
 Single vision with two eyes, 545 547 
 
 Siren, 32 ; blood-corpuscles of, 145 note 
 
 Sixth pair of nerves, 405 
 
 Size, mode of estimating by vision, 549 
 
 Skin, structure of, 176, 177 ; contractility of, 
 234 ; absorbing power of, 676 679 ; respi- 
 ratory power, of, 768 ; exhaling apparatus 
 in, 868 ; transpiration from, 869871 ; seba- 
 ceous and ceruminous glands in, 872 ; exu- 
 dation from, increased by heat, 897 
 
 Skull, forms of, in different races of Men, 83 
 87 
 
 Sleep, 499 
 
 Smell, sense of, 531, 532 ; seat of, 531 ; con- 
 ditions of, 531; acuteness of, in some Ani- 
 mals and Men, 532 
 
 Sneezing, act of, 381, 531 
 
 Sobbing, act of, 380 
 
 Solen, nervous system of, 317, 318 
 
 Somatic death, 813, 814 
 
 Somnambulism, 500, Appendix 11. 
 
 Sound, laws of propagation of, 560 562; suc- 
 cessive pulses of, 569 ; mode of estimating 
 direction, distance, and intensity of, 570 ; 
 rapidity of perception of, compared with 
 that of light, 571 ; use of in regulating voice, 
 572, 611 
 
 Sounds, articulate, 612 619 
 
 , of heart, 720, 721 ; of placenta, 925 
 
 Spasmodic diseases, 501 504 
 
 Species, discrimination of, 64 67; variation 
 within limits of, 68 73 ; distinguished by 
 physiological and psychological characters, 
 7477 
 
 Spencer, Earl, on the duration of gestation in 
 Cattle, 931 
 
750 
 
 INDEX. 
 
 Spermatic fluid, 867 
 
 Spermatozoa, 900, 901 ; function o'f, 900, 911, 
 917; development of, 902 
 
 Sphincters, action of, 391, 392 
 
 Sphinx ligustri, Nervous system of, 325 
 
 Spinal accessory nerve, 4i7 
 
 Spinal Cord of Vertebrata, 346350 ; its com- 
 parative anatomy, 346; its divisions, 346, 
 347 ; its connections with the nerves, 347, 
 348 ; functions of several parts, of, 349, 350; 
 general functions of, 363 373 ; absence of 
 proper sensibility in, 365; protecting agency 
 of, 394 396; maintenance of muscular ten- 
 sion through, 398, 399 ; influence of, on 
 heart, 717 a ; power of sustaining locomo- 
 tive actions, 397 ; pathological conditions of, 
 400,401,501504 
 
 Spinal nerves, double roots of, 344 
 
 Spinal system, nerves of, 402421 
 
 Spleen, structure of, 683 ; functions of, 684, 
 685 
 
 Sponges, 1, 7 
 
 Spongioles of Plants, 107 
 
 Stammering, causes of, 617, 618 ; treatment 
 of, 619 
 
 Star-fish, structure of, 8 10 ; nervous system 
 of, 312, 314 
 
 Stark, Dr., his analysis of Bone, 196 & 
 
 Stearlne, composition and properties of, 185 a 
 
 Stereoscope, 546, 547 
 
 Stilling, Dr., his researches on the Spinal 
 Cord, 347 
 
 Stomach, presence of, characteristic of Ani- 
 mals, 2; general characters of, 655; state 
 of, in health, 657; in disease, 758 ; sense of 
 hunger referred to, 637 ; movements of, 387, 
 413, 659; influenced by nerves, 387, 413 ; 
 secretions of, 665, 873 ; influence of nerves 
 on, 414, 415 ; effects of blows or*, 580, 625 
 
 Stomato-gastric system, ofMollusca, 319, ^20; 
 of Articulata, 332334 
 
 Strabismus, 454 a-d 
 
 Strangury, 504 
 
 Strings, vibrating, laws of, 606 a 
 
 Strumous diathesis, 878 (see Tubercle) 
 
 Subjective sensations, 516, 518, 521 
 
 Suction, act of, 386 c 
 
 Sudoriferous glandulse, 868 ; their secretion, 
 869, 870 
 
 Sulphur, contained in food, 648 ; in proteine- 
 compounds, 113, 114; oxidation of, in sys- 
 tem, 847 ... 
 
 Superfo3tation, 933 
 
 Suppuration, 799801 
 
 Supra-renal capsules, 686 
 
 Swimming-bladder, 27 
 
 Symmetrical diseases, 784, 785 
 
 Symmetry, radiate, 8 ; bilateral, of Articulata, 
 18 ; of Vertebrata, 25 ; deficiency of, in 
 Mollusca, 12 
 
 Sympathetic System, peculiar fibres of, 244 ; 
 general structure of, 338, 341, 342; influ- 
 ence of, on movements of intestinal canal, 
 388, 389 ; on ureter and muscular coat of 
 bladder, 390 ; oh uterus and fallopian tubes 
 393; on heart and vessels, 416, 623, 717 6, 
 730, 732; on duetus choledochus, 825 /; 
 on processes of organic life, 620 628 
 
 Sympathies, motor, 620623 ; organic, 625 
 628 
 
 The Numbers refer to the Paragraphs. 
 
 Syncope, 580, 814 
 Synovial Membranes, 175 
 Syro-Arabian nations, 94 
 
 T. 
 
 TALIACOTIAN operation, 253 
 
 Taste, nerves of, 407, 447 
 
 Taste, sense of, 527 530; nerves concerned 
 in, 407, 447; conditions of, 528 : partly de- 
 pendent on smell, 529 ; educability of, 530 ; 
 purposes of, 529 
 
 Teeth, 208217; component tissues of, 208 
 216; development of, in Human infant, 
 217, a-i ; a test of age, 2"l7 k, I, m 
 
 Temperature, sense of, 514, 524 ; ordinary, of 
 the human body, 886 ; extremes of sustain- 
 able by Man, 887, 888 ; (see Heat) 
 
 Tendons, structure of, 140 ; attachment of to 
 muscle, 233 
 
 Tenesmus, 504 
 
 Tension of Muscles, 398, 399 
 
 Tetanus, 401, 502 
 
 Testis, structure of, 866 ; development of, 866 
 6 ; secretion of, 867 
 
 Tessier's experiments on duration of gestation, 
 931 
 
 Thackrah, Mr., his observations on coagula- 
 tion of blood, 703 
 
 Thalami Optici, 423, 424 
 
 Thaumalrope, 551 
 
 Third pair of Cranial Nerves^Oo 
 
 ventricle of Brain, 358, 359 
 
 Thirst, sense of, 639 
 
 Thorax, movements of, in respiration, 760, 
 761 
 
 Thymus gland, 687, 688 
 
 Thyroid gland, 689 
 
 Tiedemann, his researches on absorption, 675 
 
 Tissues, elementary, classification of, 187 
 
 Todd, Dr., on mucous membrane, 873 
 
 Tomes, Mr., his observations on bone referred 
 to, 196, 203, 207 
 
 Tongue, papilla of; 527; movements of, 418, 
 419 
 
 Tonicity of muscles, 593 597 ; of arteries, 
 731 ; effects of deficiency of, 745 
 
 Tortoises, 29 
 
 Touch, nerves of, 448 
 
 Touch, sense of, 522826 ; varying acuteness 
 of, in different parts, 522 ; ideas derived from, 
 514, 523; peculiarities of, 524 ; improvability 
 of, 525; modifications of, in different ani- 
 mals, 526 ; connection of, with vision, 541, 
 542 
 
 Toynbee, Mr., his researches on non-vascular 
 tissues, 187190 
 
 Trainers' diet, 654 
 
 Transudation, 824 
 
 Travers, Mr., his observations on formation of 
 new vessels, 222 ; on production of new tis- 
 sue, 795 
 
 Trifacial nerve, 403, 404 
 
 Tubercula Quadrigemina, 422, 436 
 
 Tubercular matter, 807, 
 system to deposit, 878 
 
 tendency in the 
 
 Tubular tissues, simple, 218222; compound, 
 223253 
 
INDEX. 
 
 The Numbers refer to the Paragraphs. 
 
 751 
 
 Tunica granulosa, 906, 912 
 
 Turkish race, 96 
 
 Tunicata, nervous system and actions of, 316 
 
 Tympanum, membrane of, 563 ; cavity of, 564 
 
 U. 
 
 UMBILICAL cord, 941, 942 
 
 vesicle, 939, 941 
 
 Unguiculated Mammalia, 48, 49 
 
 Ungulated Mammalia, 48, 49 
 
 Unity, specific, of human races, 91 
 
 Urea, composition of, 844 ; increase of by ex- 
 ercise, 844 
 
 Uric acid, composition of, 845 ; pathological 
 changes in, 845 a-d 
 
 Urine, nature and purposes of its secretion, 842 
 852; effects of its retention, 8,42; com- 
 position of, in health, 843; amount of area 
 contained in, 844; uric acid in, 845; hippu- 
 ric acid in, 845 a; no lactic acid in, 846; 
 
 saline compounds in, 847 ; alkaline' or acid 
 reaction of, 848 ; amount of azotized matter 
 in, 849 ; influence of diet on, 849, 850 ; trans- 
 ference of secretion, 851 ; excretion of saline 
 matter with, 852 
 
 Uterus, changes of, preparatory to gestation, 
 919; increase in substance during gestation, 
 926 ; contractions of, how far dependent on 
 nervous agency, 393, 928 
 
 V. 
 
 VAGUS nerve, see Par Vagum 
 
 Valentin, his researches on Spinal Cord, 349 ; 
 on movements of Stomach, 387 ; on the Sym- 
 pathetic, 388, 390, 393, 730 ; on Olfactory 
 nerve, 441 ; on Optic nerve, 442 ; on Portio 
 Dura, 406 ; ,on Par Vagum, 408, 416 ; on Spi- 
 nal Accessory, 417 ; on Hypoglossal, 418 ; 
 on quantity of blood in system, 724 
 
 Valves of heart, actions of, 722, 723 c ; sounds 
 produced by, 720, 721 
 
 Vapour, exhalation of, from lungs, 773, 774 
 
 Variation, extremes of in species, 6871 ; in 
 Man, 72, 73 
 
 Varicose nerve-tubes, 243 
 
 Vasa lutea, 939 
 
 Vascular area, 938 
 
 - lamina of Germinal Membrane, 936, 
 
 938,940 
 
 Vegetable proximate principles, 111 
 
 Vegetables, distinguished from Animals, 14; 
 food of, 2 ; movements of, 1, 283 ; early de- 
 velopment of, 3; formation of cells in, 106 
 109, 120125; general functions of, 107, 
 261; circulation in, 712 714; respiration 
 in, 750 ; reproduction in, 899 
 
 Veins, distribution of, 710; structure of, 743; 
 movement of blood in, 744; causes of con- 
 gestion in, 745; pulsation in, 723 c 
 
 Ventricles of heart, contraction of, 718721 ; 
 force of, 726 ; thickness of, 723 ; capacity of, 
 724 
 
 Ventricles of brain, third, 358: fourth. 346, 
 358 
 
 Vertebrae, 21 ; origin of, 937 
 
 Vertebral column in Fishes, 26 
 
 Vertebrata, 5, 2025 ; skeleton of, 21, 22; ex- 
 tremities of, 22; predominance of nervous 
 system in, 20, 23 ; organs of animal and vege- 
 tative life in, 25; symmetry in, 25; intelli- 
 gence of, 23 ; nervous system of, 339 362 
 
 Vesicles of Brain in Embryo, 358 
 
 Vessels, formation of, in Plants, 218; in Ani- 
 mals, 221, 222 
 
 Viability of Infant, earliest period of, 932 
 
 Vierordt, his researches on respiration, 765, 
 767 
 
 Villi of Mucous Membrane, 178, 472, 473 
 
 Visceral system of nerves, see Sympathetic ' 
 
 Visible direction, law of, 543 
 
 Vision, sense of, 533 555; optical conditions 
 of, 534537 ; defective, 538 ; limits of, 540; 
 mental conditions of, 541 ; connection of, 
 with touch, 541, 542; erect, 543; single, 544, 
 545 ; appreciation of form by, 546, 547 ; of 
 distance, 548 ; of size, 549; persistence of 
 impressions, 551 ; complementary colours, 
 552; want of power to distinguish colours, 
 553; vanishing of images, 554; visual per- 
 ception of retina, 555 
 
 Vital Action involves change, 254 " 
 
 dependence of, on external stimuli, 
 
 255, 258 
 
 Vital Actions, classifications of, into Functions, 
 260 . , 
 
 Vital forces, 256 
 
 Vitality, duration of in individual parts, 810 
 812; dormant, 255 
 
 .of general system, destroyed by sudden 
 
 shock, 580, 735, 742 
 
 Vital properties, 256, 258 ; retention of, 259 
 
 Vitelline vessels, 939 
 
 Vitreous humour, 190 
 
 Voice, 602619 ; conformation of larynx, 603 
 605.; sounds resembling produced by 
 strings, 606 a ; by flute-pipes, 606 b ; by reeds, 
 606 c; action t of chordae vocales, 607; arti- 
 ficial larynx, 607 ; pitch, how regulated, 608 ; 
 falsetto notes, how, produced, 609 ; influence 
 of air-passages on, 610 ; movements concern- 
 ed in, how directed, 611 
 
 Volkmann, his experiments on Muscular con- 
 traction, 576 
 
 Voluntary actions, distinguished from automa- 
 tic, 483 ; originate in Cerebrum, 483, 495 
 
 Vomiting, 505 
 
 Vowel sounds, 614, 615 
 
 W. 
 
 WAGNER, his observations on blood-corpuscles, 
 148, 155, 157, 159 a ; his account of develop- 
 ment of Spermatozoa, 902 
 Wasmann, his researches on pepsin 668 
 Waste of Animal tissues, see Decay, and Dis- 
 integration 
 
 Weber, Prof., his researches on sensation, 522 ; 
 on absorption, 672; on movements of heart, 
 717 a 
 
 Whale, Spermaceti, peculiar sensibility of, 526 
 Wheatstone, Prof., his Stereoscope, 546, 547 
 White corpuscles of blood, 151159 
 White fibrous tissue, 138141 
 
752 
 
 INDEX. 
 
 
 The ^Numbers refer to the Paragraphs. ( ' . , 
 
 White matter of nervous system, 242, 243 
 WiJliams, Dr., on contractility of bronchi, 759; 
 on Necrsemia, 708 ; on Inflammation, 158 ; 
 on causes of Venous Congestion, 745 
 Willis, Mr., his researches on the Voice, 604 
 
 608 
 Wilson. Mr. Erasmus, on cutaneous follicles, 
 
 868 
 
 Wings of Insects, interlacement of nerves sup- 
 of, 600 
 upon sound, 
 
 plying, 298; rapidity of motion of, 600 
 Wollaston, Dr., his observations upon 
 569 a ; upon hemiopia, 545 note 
 
 YAWNING, act of, 390 
 Yellow fibrous tissue, 138 142 
 Yolk, 905, 935, 939 , 
 Yolk-bag, 905, 935, 939 
 
 Young animals, low calorifyirig power of, 893, 
 932 a; influence of cold upon, 893 c 
 
 Z. 
 
 ZONA pellucida, 905, 917 
 
 Zwicky, Dr., on organization of thrombus, 700 
 
 
 v-. -' 
 
 -X- ' ' 
 
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LEA & BLANCHARD'S PUBLICATIONS. 
 
 NOW COMPLETE. 
 
 THE GREAT SURGICAL LIBRARY. 
 
 A SYSTEM "OF SURGERY, 
 
 BY J. M. CHELIUS, 
 
 Doctor in Medicine and Surgery, Public Professor of General and Ophthalmic Surgery, etc. etc. in the Uni- 
 versity of Heidelberg. 
 
 TRANSLATED FROM THE GERMAN, 
 
 AND ACCOMPANIED WITH ADDITIONAL NOTES AIND OBSERVATIONS, 
 BY JOHN F. SOUTH, 
 
 Surgeon to St. Thomas' Hospital. 
 
 EDITED, WITH REFERENCE TO AMERICAN AUTHORITIES, 
 BY GEORGE W. NORRIS, M. D. 
 
 Now complete in three large 8vo. volumes of nearly twenty-two hundred pages, or in 17 numbers, at 50 cents. 
 
 This work has been delayed beyond the time originally promised for its completion, by the very extensive 
 additions of the translator. In answer to numerous inquiries, the publishers now have the pleasure to pre- 
 sent it in a perfect state to the profession, forming three unusually large volumes, bound in the best manner, 
 and sold at a very low price. 
 
 This excellent work was originally published in Germany, under the unpretending title of "Handbook to 
 the Author's Lectures." In passing, however, through six successive editions, it has gradually increased 
 in extent and importance, until it now presents a complete view of European Surgery in general, but more 
 especially of English practice, and it is acknowledged to be well fitted to supply the admitted want of a com- 
 plete and extended system of Surgery in all its branches, comprehending both the principles and the prac- 
 tice of this important branch of the healing art. Since Benjamin Bell's great work, first published in 1783, 
 and now almost obsolete, no thorough and extended work has appeared in the English language, occupying 
 the ground which this is so well calculated to cover. 
 
 The fact of this work being carried to six editions in Germany, and translated into no less than eight Ian- 
 guages, is a sufficient evidence of the ability with which the author has carried out his arduous design. 
 
 This translation has been undertaken with the concurrence and sanction of Professor Chelius. The trans- 
 .ator, Mr. John F. South, appears to have devoted himself to it with singular industry and ardor, and to have 
 brought it up almost to the very hour of publication His notes and additions are very numerous, embodying 
 the results and opinions of all the distinguished surgeons of the day, Continental, English and American. 
 The leading opinions of John Hunter, on which Modern English Surgery has been raised, are set forth ; the 
 results of the recent microscopical discoveries, especially in reference to inflammation, will be found here, 
 together with many other practical observations, placing the work'on a level with the present state of Sur- 
 gery, and rendering it peculiarly useful, both to the student and practitioner. 
 
 The labors of the English translator have been so numerous and important, that there is but little which 
 remains to be supplied by the American editor. Dr. G. W. Norris has consented, however, to superintend 
 ihe passage of the workj through the press, and supply whatever may have been omitted in relation to the 
 Surgical Literature of this country. 
 
 The Medical Press and profession, both in England and in this country, have joined in 
 praise of this great work.as being more complete ihan any other, and as affording a complete 
 library of reference, equally suited to the praciitioner and to the student. 
 
 " We strongly recommend all surgical practitioners and students, who have not yet looked into this work, 
 to provide themselves with it without delay, and study its pages diligently and deliberately." The Edin- 
 burgh Medical and Surgical Journal. 
 
 'Judging from a single number only of this work, we have no hesitation in saying that, if the remaining 
 portions correspond at all with the first, it will be by far the most complete and scientific System of Surgery 
 in the English language. We have, indeed, seen no work which so nearly comes up to our idea of what 
 such a production should be, both as a practical guide and as a work of reference, as this ; and the fact that 
 it has passed through six editions in Germany, and been translated into seven languages, is sufficiently.con- 
 vincing proof of its value. It is methodical and concise, clear and accurate, omitting all minor details and 
 fruitless speculations, it gives us all the information we want in the shortest and simplest form." The New 
 York Journal of Medicine. 
 
 ' Nor do these parts, in any degree, fall short of their predecessors, in the copiousness and value of their 
 details. The work certainly fprms an almost unique curiosity in medical literature, in the fact that the 
 notes occupy a larger portion of the volume than the original matter, an arrangement which is constantly 
 appearing to render the text subsidiary to its illustrations. Still this singularity of manner does not at all 
 detract from the value of the matter thus disposed." The London Medical Gazette. 
 
 'This work has long been the chief text-book on Surgery in the principal schools of Germany, and the 
 publication of five editions of it in the original and of translations into no less than eight foreign languages, 
 shows the high estimation in which it is held. As a systematic work on Surgery it has merits of a high order. 
 It is methodical and concise and on the whole clear and accurate. The most necessary information is 
 conveyed in the shortest and simplest form. Minor details and fruitless speculations are avoided. It is in 
 fact, essentially a practical book. This work was first published nearly twenty years ago, and its solid and 
 permanent reputation has no doubt led Mr. South to undertake the present translation of the latest edition 
 of it, which, we are informed, is still passing through the press in Germany. We should have felt at a loss 
 to select any one better qualified for the task than the translator of Otto's Compendium of Human and Com- 
 parative Pathological Anatomy a surgeon to a large hospital whose industry and opportunities have 
 enabled him to keep pace wjih the improvements of his time." The Medico- Chirurgical Review. 
 
 ' Although Great Britain can boast of some of the most skillful surgeons, both among.her past and her present 
 professors of that branch of medical gcience.no work professing to be a complete system of Surgery has been 
 published in the British dominions since that of Benjamin Bell, now more than half a century old. 
 
 "This omission in English medical literature is fully and satisfactorily supplied by the translation of Profes- 
 sor Chelius's System of Surgery by agentleman excellently fitted for the task, both by his extensive reading, 
 and the opportunities of practical experience which he has enjoyed for years as surgeon to one of our largest 
 metropolitan hospitals. The fact of Professor Chelius's work having been translated into seven languages is 
 sufficient proof of the estimation in which it is held by our continental brethren, and the English Edition, 
 now in course of publication, loses none of the value of the original from the treatment received at the hands 
 of its translator. The notes and additions of Professor South are numerous, and contain the opinions result- 
 ing from his vast experience, and from that of his colleague." The Medical Times. 
 
 l lt ably maintains the character formerly given, of being the 'most learned and complete systematic 
 treatise now extant The descriptions of surgical diseases, and indeed the whole of the pathological depart- 
 ment, are most valuable." The Edinburgh Medical and Surgical Journal. 
 
 Op* Persons wishing this work sent to them by mail, in parts, can remit Ten Dollars, for 
 which a set will be sent by the publishers, free of postage, together with a copy of "The 
 
 Medical News and Library" for one year. 
 
 j 
 
LEA & BLANCHARD'S PUBLICATIONS. 
 
 GHELIUS'S SURGERY, CONTINUED. 
 
 The publishers annex a very condensed summary of the contents of Chelius's Surgery, showing 
 the complete and systematic manner in which the whole subject is divided and treated. 
 I. DIVISION. Qf Inflammation. 
 
 1. Of inflammation in general. 
 
 2. Qf some peculiar kinds of inflammation. 
 
 a. Of erysipelas ; 6. Of burns ; c. Of frost- 
 bite ; d. Of boils ; e. Of carbuncle. 
 
 3. Qf inflammation in some special organs. 
 
 a. Of inflammation of the tonsils ; b. Of the 
 
 parotid gland ; c. Of the breasts ; d. Of 
 
 the urethra ; e. Of the testicle ; /. Of the 
 
 muscles of the loins; g. Of the nail 
 
 joints ; h. Of the joints, viz. 
 a. Of the synovial membrane ; b. Of the car- 
 tilages ; c. Of the joint-ends of the bones, 
 
 viz., aa. in the hip-joint; 66. in the 
 
 shoulder-joint ; cc. in the knee-joint ; 
 
 and so on. 
 
 II. DIVISION. Diseases which consist in a dis- 
 
 turbance of physical connexion. 
 1. Fresh solutions of continuity. 
 A. Wounds ; B. Fractures. 
 n. Old solutions, 
 
 A. Which do not suppurate, viz. 
 
 a. False joints ; 6. Hare-lip ; c. Cleft in 
 the soft palate ; d. Old rupture of 
 the female perineum. 
 
 B. Which do suppurate, viz. 
 i. Ulcers. 
 
 1. In general. 
 
 2. In particular. 
 
 a. Atonic ; 6. Scorbutic ; c. Scrofulous ; 
 d. Gouty ; e. Impetiginous ;/. Vene- 
 real ; g. Bony ulcers or caries. 
 ii. Fistulas. 
 
 a. Salivary fistula ; 6. Biliary fistula ; c. Faecal 
 fistula and artificial anus ; d. Anal fistula ; 
 e. Urinary fistula. 
 m. Solutions of continuity by changed position of 
 
 parts. 
 1. Dislocations; 2. Ruptures; 3. Prolapses; 
 
 4. Distortions. 
 
 IV. Solutions of continuity by unnatural distention. 
 1. In the arteries, aneurisms ; 2. In the veins, 
 varices ; 3. In the capillary-vascular sys- 
 tem, teleangiectasis. 
 
 III. DIVISION. Diseases dependent on the unna- 
 
 tural adhesion of parts. 
 
 1. Anchylosis ofthe joint-ends of bones ; 2. Grow- 
 ing together and narrowing of the aperture 
 ofthe nostrils; 3. Unnatural adhesion of the 
 tongue ; 4. Adhesion of the gums to the 
 cheeks; 5. Narrowing ofthe oasophagus ; 6. 
 Closing and narrowing of the rectum ; 7. 
 Growing together and narrowing of the pre- 
 puce ; 8. Narrowing and closing of the ure- 
 thra; 9. Closing and narrowing of the vagina 
 and ofthe mouth ofthe womb. 
 
 IV. DIVISION. Foreign bodies. 
 
 1. Foreign bodies introduced externally into our 
 
 organism. 
 
 a. Into the nose ; 6. Into the mouth ; c. Into 
 the gullet and intestinal canal ; d. Into 
 the wind-pipe. 
 
 2. Foreign bodies formed in our organism by the 
 
 retention of natural products. 
 
 A. Retentions in their proper cavities and 
 
 receptacles. 
 
 a. Ranula ; 6. Retention of urine ; c. 
 Retention ofthe fetus in the womb 
 or in the cavity ofthe belly, (Caesa- 
 rean operation, section ofthe pubic 
 symphysis, section ofthe belly.) 
 
 B. Extravasation external to the proper cavi- 
 
 ties or receptacles. 
 
 a. Blood swellings on the heads of new- 
 born children ; 6. HaematoceJe ; c. 
 Collections of blood in joints. 
 
 3. Foreign bodies resulting from the accumulation 
 
 of unnatural secreted fluids. 
 a. Lymphatic swellings ; 6. Dropsy of joints ; 
 c. Dropsy ofthe bursae mucosse ; d. Wa- 
 ter in the head, spina bifida ; e. Water 
 in the chest and empyema; /. Dropsy 
 of the pericardium ; g. Dropsy of the 
 belly ; h. Dropsy of the ovary ; i. Hy- 
 drocele. 
 
 4. Foreign bodies produced from the concretion of 
 
 secreted fluids. 
 
 V. DIVISION. Diseases which consist in the de- 
 generation of organic parts, or in the produc- 
 tion of new structures. 
 
 1. Enlargement ofthe tongue; 2. Bronchocele ; 
 3. Enlarged clitoris; 4. Warts; 5. Bunions; 
 6. Horny growths ; 7. Bony growths ; 8. Fun- 
 gus of the dura mater; 9. Fatty swellings; 
 10. Encysted swellings; 11. Cartilaginous 
 bodies in joints ; 12. Sarcoma; 13. Medul- 
 lary fungus ; 14. Polypus ; 15. Cancer. 
 
 VI. DIVISION. Loss of organic parts. 
 
 1. Organic replacement of already lost parts, es- 
 
 pecially ofthe face, according to the Taglia- 
 cotian and Indian methods. 
 
 2. Mechanical replacement: Application of arti- 
 
 ficial limbs, and so on. 
 
 VII. DIVISION. Superfluity of organic parts. 
 VIII. DIVISION. Display of the elementary ma- 
 nagement, of surgical operations. 
 General surgical operations : Bleeding, cupping, 
 application of issues, introduction ofsetons, 
 amputations, resections, and so on. 
 .Jnd One Hundred and Seventy-five Pages 
 of Index. 
 
 DRUITT'S SURGERY, New Edition Now Ready, 1847, 
 
 THE PRINCIPLES AND PRACTICE OF MODERN SURGERY, 
 
 BY ROBERT DRUITT, SURGEON. 
 
 THIRD AMERICAN PROM THE THIRD LONDON EDITION 
 Illustrated with one hundred and fifty- three wood engravings. 
 
 WITH NOTES AND COMMENTS, 
 
 BY JOSHUA B. FLINT, M.D., M. M., S. S., &c. &c. 
 
 In One very neat Octavo Volume of about Five Hundred and Fifty Pages. 
 
 In presenting this work to the American profession for the third time, but little need be said to solicit for 
 it a continuation of the favor with which it has been received. The merits which have procured it this 
 favor, its clearness, conciseness, and its excellent arrangement, will continue to render it the favorite text- 
 book ofthe student who wishes in a moderate space a compend ofthe principles and practice of Surgery. 
 
 "This work merits our warmest commendations, and we strongly recommend it to youug surgeons as uu 
 admirable digest of the principles and practice of modern Surgery." Medical Gazette. 
 
LEA &, BLANCHARD'S PUBLICATIONS. 
 
 WOW READY. 
 
 KOTLE'S MATERIA MEDICA. 
 
 MATERIA MEDICA AND THERAPEUTICS; 
 
 INCLUDING THE PREPARATIONS OF THE PHARMACOPOEIAS OF LONDON, 
 EDINBURGH, DUBLIN, AND OF THE UNITED STATES. 
 
 WITH MANY NEW MEDICINES. 
 
 BY J. FORBES ROYLE, M.D, F. R. S. f 
 
 Late of the Medical Staff in the Bengal Army, Professor of Materia Medica and Therapeutics, King's Col- 
 lege. London, &c. &c. 
 
 EDITED BY JOSEPH CARSON, M.D., 
 
 Professor of Materia Medica in the Philadelphia College of Pharmacy, &c. &c. 
 
 WITH NINETY-EIGHT ILLUSTRATIONS. 
 |J" See Specimen of the Cuts, but not of the faper or Working; on next fag-t* 
 
 In one large octavo volume of about 700 pages. 
 Being* one of the most beautiful Medical works published in this Country* 
 
 The want has been felt and expressed for some time, of a text-book on Materia Medica, which 
 should occupy a place between the encyclopaedic works, such as Pereira, and the smaller treatises 
 which present but a meagre outline of the science. It has been the -aim of the author of the 
 present work to fill this vacancy, and by the use of method and condensation, he has been enabled 
 to present a volume to the student, which will be found to contain what is necessary in a complete 
 and thorough text-book of the science, encumbered with few unnecessary details. The editor, 
 Dr. Carson, has added whatever was wanted to adapt it to the Pharmacopeia of the United States, 
 and it is confidently recommended to the student and practitioner of medicine, as one of the best 
 text-books on the subject, now before the profession. Great care has been taken in its mechanical 
 execution. 
 
 " In regard to the yet more essential constituent, the literary portion of the work, no one who is 
 acquainted with the former productions of Dr. Royle, will doubt that the author has discharged his 
 duties with the same skill as the artist. The work is, indeed, a most valuable one, and will till up 
 an important gap that existed between Dr. Pereira's most learned and complete system of materia 
 medica, and the class of productions at the other extreme, which are necessarily imperfect from 
 their small extent. British and Foreign Medical Review. 
 
 Of the various works that have from time to time appeared on materia medica on the plan of the 
 one before us, there is none more deserving of commendation. From the examination which we 
 have given, accuracy and perspicuity seem to characterize it throughout, as a text book of refer- 
 ence to the student of medicine, and especially of pharmacy in its application to medicine, none 
 could be better. 
 
 We think that every one who can afford it should possess this excellent work, the value of which 
 has been greatly enhanced by the additions of Dr. Carson, than whom no one is more competent 
 to estimate it correctly, and to make such additions as may adapt it for American service. The 
 Medical Examiner. 
 
 BARTLETT ON FEVER New and much improved edition, now ready, 
 THE HISTORY, DIAGNOSIS AND TREATMENT 
 
 OF THE 
 
 FEVERS OF THE UNITED STATES. 
 
 BY ELISHA BARTLETT, M.D., 
 
 Professor of the Theory and Practice of Medicine in ihe Medical Departmentof Transylvania University. A.C. 
 
 In One Octavo Volume of Five Hundred and Fifty Pages, beautifully printed and strongly bound. 
 
 This is rather a new work, than a second edition of Dr. Bartlett's well known treatise on Fevers. 
 Besides numerous improvements in the portion devoted to Typhoid and Typhus Fevers, the whole 
 of that descriptive of Periodical and Yellow Fevers, amounting to about half the volume, is addi- 
 tional. The work is now what it purports to be, a systematic, complete and methodical treatise on 
 the Fevers of the United States. 
 
 NOW READY. 
 
 A MANUAL OF TOXICOLOGY. 
 
 BY ALFRED S. TAYLOR. 
 EDITED BY R. E. GRIFFITH, M. D., &c 
 
 Jn one octavo volume, to match the "Medical Jurisprudence" of the same author. 
 
SPECIMEN OF CUTS IN 
 
 xmw 
 
 Y L E ' S JT 3HT no 
 
 
 
 MATERIA MEDICA AND THERAPEUTICS 
 
 
 KtftS 
 
10 LEA & BLANCHARD'S PUBLICATIONS. 
 
 CHURCHILI/S MIDWIFERY. 
 
 ON THE THEORY AND "PRACTICE OF MIDWIFERY, 
 
 BY FLEETWOOD CHURCHILL, M. D., M.R.I. A., 
 
 Licentiate of the College of Physicians in Ireland ; Physician to the Western Lying- in- Hospital; Lecturer OB 
 
 Midwifery, &c., in the Richmond Hospital Medical School, &c. &c. 
 
 WITH NOTES AND ADDITIONS, 
 
 BY ROBERT HUSTON, M.D., 
 
 Professor of Materia Medica and General Therapeutics, arid formerly of Obstetrics and the Disease of Wo- 
 men and Children in the Jefferson Medical College of Philadelphia; President of the Philadelphia 
 
 Medical Society, &c. &c. 
 'SECOND AMERICAN EDITION. 
 
 WITH ONE HUNDRED AND TWENTY-EIGHT It LUSTRATIONS, 
 Engraved by Gilbert from Drawings by Bagg and others. 
 
 In one beautiful octavo volume. 
 
 In this age of books, when much is written in every department of the science of medicine, it is a matter of 
 lo small moment to the student, which of the many he shall choose for his study in pupilage, and guide in 
 practice. In no department is the choice more difficult than in that of midwifery ; many excellent and truly 
 valuable treatises in this department of medicine have, within a few years past, been written; of this character 
 are those of Dewees, Velpeau, Meigs and R'gby, with due respect to the authors of the works just cited, we are 
 compelled to admit, that to Mr. Churchill has been reserved the honorof presenting to the profession, one more 
 particularly adapted to the want and use of students, a work rich in statistics clear in practice and free in 
 style possessing no small claims to our confidence. The New York Journal of Medicine. 
 
 WILLIAMS' PATHOLOGY. 
 
 NEW AND IMPROVED EDITION, BROUGHT UP TO 1848, NEARLY READY. 
 
 PRINCIPLESHTF MEDICINE, 
 
 COMPRISIXS 
 
 GENERAL PATHOLOGY AND THERAPEUTICS, 
 
 AXD A GENERAL YIEW OF 
 
 ETIOLOGY, NOSOLOGY, SEMEIOLOGY, DIAGNOSIS AND PROGNOSIS. 
 BY CHARLES J. B. WILLIAMS, M.D., F.R.S., 
 
 Fd'ow of the Royal College of Physicians &c. 
 Second American, from the Second London Edition* 
 
 WITH NOTES AND ADDITIONS, BY MEREDITH OLYMER, M.D., Ac. 
 
 In one volume, octavo. 
 
 P E R E I R A'S MATERIA M E D I C A . 
 
 With nearly Three Hundred Engravings on Wood. 
 
 A NEW EDITION, LATELY PUBLISHED. 
 
 THE ELEMENTS OF 
 
 MATERIA MEDICA AND THERAPEUTICS, 
 
 COMPREHENDING 
 
 THE NATURAL HISTORY, PREPARATION, PROPERTIES, COMPO- 
 SITION, EFFECTS AND USES OF MEDICINES. 
 BY JONATHAN PEREIRA, M.D., F.R.S. AND L.S. 
 
 Member of the Society of Pharmacy of Paris; Examiner in Materia Medica and Pharmacy of the University 
 of London; Lecturer on Materia Medica at the London Hospital. &c &c. 
 Second American, from the last London Edition, enlarged and improved. 
 
 WITH NOTES AND ADDITIONS BY JOSEPH CARSON, M.D. 
 
 In two volumes, octavo, containing Fifteen Hundred very large pages, illustrated by Two Hundred and 
 
 Seventy-five Wood-cuts. 
 
 This encyclopaedia of materia mediea. for such it may justly be entitled, gives the fullest and most ample ex- 
 position of materia mediea and its associate branches of any work hitherto published in the English language, 
 it abounds in rest-arch and erudition: its statements of facts are clear and methodically arranged, while its 
 therapeutical explanations are philosophical, and in accordance with sound clinical experience. It is equally 
 adapted as a text-book for students, or a work of reference for the advanced practitioner, and no one can 
 Consult its pages without profit. The editor has performed his task with much ability and judgment. In thte 
 first American edition, he adopted the Pharmacopeia of the United States, and the formulas set forth in that 
 standard authority; in the present he has introduced an account of substances that have recently attracted at- 
 tention by their therapemic employment, together with the mode of forming the characters and uses of new 
 pharmaceutic preparations, and the details of more elaborate and particular chemical investigations, with 
 respect to the nature of previously known and already described elementary principles all the important 
 indigenous medicines of the United States heretofore known, are also described. The work, however, is too 
 well known to need any further remark. We have no doubt it will have a circulation commensurate wilh its 
 extraordinary merits. The New York Journal of Medicine. 
 
 ' An Encyclopaedia of knowledge in that department of medical science by the common consentofthe pro- 
 fession the most elaborate and scientific Treatise on Materia Medica in our language." Western Journal qf 
 Medicine and Surgery 
 
LEA & BLANCHARD'S PUBLICATIONS. 11 
 
 WILSON'S ANATOMY, New Edition Now Ready, 1847, 
 
 A SYSTEM OF HUMAN ANATOMY, 
 GENERAL AND SPECIAL, 
 
 BY ERASMUS WILSON, M.D., 
 
 Lecturer on Anatomy, London. 
 THIRD AMERICAN FROM THE LAST LONDON EDITION. 
 
 EDITED BY P. B. GODDARD, A. M., M.D., 
 
 Professor of Anatomy in the Franklin Medical College of Philadelphia. 
 
 WITH TWO HUNDRED AND THIRTY-FIVE ILLUSTRATIONS BY GILBERT. 
 In one beautiful octavo volume of over SIX HUJYltRED IJarg-e fag-e t 
 
 Strongly Bound and sold at a low price. 
 
 Since the publication of the second American edition of this work, the author has issued a new 
 edition in London, in which he has carefully brought up his work to a level with the most advanced 
 science of the day. All the elementary chapters have been re-written, and such alterations made 
 through the body of the work, by the introduction of all new facts of interest, illustrated by appro- 
 priate engravings, as much increase its value. The present edition is a careful and exact reprint 
 of the English volume, with the addition of such other illustrations as were deemed necessary to a 
 more complete elucidation of the text; and the insertion of such of the notes appended to the last 
 American edition as had not been adopted by the author and embodied in his text ; together with 
 such additional information as appeared calculated to enhance the value of the work. It may also 
 be stated that the utmost care has been taken in the revision of the letter-press, and in obtaining 
 clear and distinct impressions of the accompanying cuts. 
 
 It will thus be seen, that every effort has been used to render this text-book worthy of a con- 
 tinuance of the great favor with which it has been everywhere received. Professors desirous of 
 adopting it for their classes may rely on being always able to procure editions brought up to the 
 day. 
 
 This book is well known for the beauty and accuracy of its mechanical execution. The present 
 edition is an improvement over the last, both in the number and clearness of its embellishments ; 
 it is bound in the best manner in strong sheep, and is sold at a price which renders it accessible 
 to all. 
 
 CONDIE ON CHILDREN. New Edition, 1847. 
 
 A PRACTICAL~TKEATISE ON 
 THE DISEASES OF CHILDREN. 
 
 BY D. FRANCIS CONDIE, M. D , 
 
 Fellow of the College of Physicians, Member of the American Philosophical Society, &c. 
 In one large octavo volume. 
 
 Jj* The publishers would particularly call the attention of the profession to an examination of this book. 
 
 In the preparation of a new edition of the present treatise, every part of the work has been subjected to a 
 careful revision; several portions have been entirely rewritten; while, throughout, numerous additions 
 have been made, comprising all the more important facts, in reference to the nature, diagnosis, and treat- 
 ment of the diseases of infancy and childhood, that have been developed since the appearance of the first 
 edition. It is with some confidence that the author presents this edition as embracing a full and connected 
 view of the actual state of the pathology and therapeutics of those affections which most usually occur be- 
 tween birth and puberty. 
 
 Thla work is being introduced, as a text-book, very extensively throughout the Union. 
 
 CHURCHILL ON FEMALES. New Edition, 1847. Now Ready. 
 
 THE DISEASES~OF FEMALES, 
 
 INCLUDING THOSE OF 
 
 PREGNANCY AND CHILDBED. 
 
 BY FLEETWOOD CHURCHILL, M D., 
 
 Author of "Theory and Practice of Midwifery," &c. &c. 
 FOURTH AMERICAN, FROM THE SECOND LONDON EDITION, WITH ILLUSTRATIONS 
 
 EDITED, WITH NOTES, 
 BY ROBERT M. HUSTON, M.D., fcc.&o. 
 
 In one volume, 8vo. 
 
 The rapid sale of three editions of this valuable work, stamp it so emphatically with the approbation of the 
 profession of this country, that the publishers in presenting a fourth deem it merely necessary to observe, 
 that every care has been taken, by the editor, to supply any deficiencies which may have existed iu former 
 impressions, and to bring the work fully up to the date of publication. 
 
12 LEA & BLANCHARD'S PUBLICATIONS. 
 
 LIBRARY OF OPHTHALMIC MEDICINE AND SURGERY. 
 Brought up to 1847. 
 
 A TREATISE ON THE~DISEASES OF THE EYE, 
 
 BY W. LAWRENCE, F.R.S., 
 
 Surgeon Extraordinary to the Queen, Surgeon to St. Bartholomew's Hospital, &c. &c. 
 A NEW EDITION, 
 
 With many Modifications and Additions, and the Introduction of nearly two hundred Illustrations. 
 
 BY ISAAC HAYS, M. D., 
 
 Surgeon to Wills' Hospital, Physician to the Philadelphia Orphan Asylum, &c. Sec. . 
 
 In one very large octavo volume of near 900 pages, with twelve plates and numerous wood-cuts through 
 
 the text. 
 
 This is among the largest and most complete works on this interesting and difficult branch of Medica 
 Science. 
 
 The early call for a new edition of this work, confirms the opinion expressed by the editor of its great 
 value, and has stimulated him to renewed exertions to increase its usefulness to practitioners, by incorporat- 1 
 ing in it the recent improvements in Ophthalmic Practice. In availing himself, as he has freely done, of 
 the observations and discoveries of his fellow-laborers in the same field, the editor has endeavored to do so 
 with entire fairness, always awarding to others what justly belongs to them. Among the additions which 
 have been made, may be noticed, the description? of several affections not treated of in the original, an 
 account of the catoptric examination of the eye, and of its employment as a means of diagnosis. one hun- 
 dred and seventy -six illustrations, some of Hiem from original drawings, and a very full index. There have 
 also been introduced in ihe several chapters on the more important diseases, the results of the editor's ex- 
 perience in regard to their treatment, derived from more than a quarter of a century's devotion to the subject, 
 during all of which period he has been attached to some public institution for the treatment of diseases of the 
 eye. 
 
 " We think there are few medical works which could be so generally acceptable as this one will be to the 
 profession on this side of the Atlantic. The want of a scientific and comprehensive treatise on Diseases 
 of the Kye, has been much deplored That want is now well supplied. The reputation of Mr. Lawrence 
 as an Oculist has been long since fully established; his great merit consists in the clearness of his style 
 and the very practical tenor of his work. The value of the present beautiful edition is greatly enhanced, 
 by the important additions made by the editor. Dr. Hays has, for nearly a quarter of a century, been con- 
 nected with public institutions for the treatment of Diseases of the Eye. and few men have made better im- 
 provement than he has, of such extensive opportunities of acquiring a thorough knowledge of the subject. 
 The wood-cuts are executed with great accuracy and beauty, and no man, who pretends to treat disease* 
 of the eye, should be without this work." Lancet. 
 
 JONES ON THEJTYE, Now Ready, 
 
 THE PRINCIPLES~AND PRACTICE 
 OF OPHTHALMIC MEDICINE AND SURGERY. 
 
 BY T. WHARTON JONES, F.R.S., &c. &c. 
 
 "WITH ONE HUNDRED AND TEN ILLUSTRATIONS. 
 
 EDITED BY ISAAC HAYS, M.D. ; &c. 
 
 In One very neat Volume, large royal I2mo., with Four Plates, plain or colored, and Ninety- 
 eight well executed Wood-cuts. 
 
 This volume will be found to occupy a place hitherto unfilled in this department of medical science. 
 The aim of the author has been to produce a work which should, in a moderate compass, be suffi- 
 cient to serve both as a convenient text-book for students and as a book of reference for practitioners, 
 suitable for those who do not desire to possess the larger and encyclopaedic treatises, such as 
 Lawrence's. Thus, by great attention to conciseness of expression, a strict adherence to arrange- 
 ment, and the aid of numerous pictorial illustrations, he has been enabled to embody in it the prin- 
 ciples of ophthalmic medicine, and to point out their practical application more fully than has 
 been done in any other publication of the same size. The execution of the work will be found 
 to correspond with its merit. The illustrations have been engraved and printed with care, and the 
 whole is confidently presented as in every way worthy the attention of the profession. 
 
 a We are confident that the reader will find, on perusal, that the execution of the work amply fulfils the 
 promise of the preface, and sustains, in every point, the already high reputation of the author as an ophthal- 
 mic surgeon, as well as a physiologist and pathologist. The book is evidently the result of much labor and 
 research, and has been written with the greatest care and attention ; it possesses that best quality which a 
 general work, like a system, or manual, can show, viz: the quality of having all the materials whenceso- 
 ever derived, so thoroughly wrought up. and digested in the author's mind, as to come forth with the freshness 
 and impressiveness of an original production. We regret that we have received the book at so late a period 
 as precludes our giving more than a mere notice of it, as although essentially and necessarily a compilation, 
 it contains many things which we should be glad to reproduce in our pages, whether in the shape of new 
 pathological views, of old errors corrected, or of sound principles of practice in doubiful cases clearly laid 
 down. But we dare say most of our readers will shortly have an opportunity of seeing these in their original 
 locality, as we entertain little doubt that this book will become what its author hoped it might become, a 
 manual for daily reference and consultation by the student and the general practitioner. The work is 
 marked by thai correctness, clearness and precision of style which distinguish all the productions of the 
 learned author." The British and Foreign Medical Review. 
 
HI WniWUll! 3BT W 
 
 Q f * mL$A ; & BtLANCHARD'S PUBLICATIONS. -r T g r 13 
 NEW AND COMPLETE MEDICAL BOTANY. 
 
 N W READ Y. 
 
 MEDICAlTBOTANY, 
 
 OR, A DESCRIPTION OF ALL THE MORE IMPORTANT PLANTS USED IN 
 
 MEDICINE, AND OF THEIR PROPERTIES, USES AND 
 
 MODES OF ADMINISTRATION. 
 
 BY R. EGLESFELD GRIFFITH, M. D. &c. &c. 
 
 In one large octavo volume. 
 
 With about three hundred and fifty Illustrations on Wood. 
 Specimens of the Cuts are annexed, but not so well printed as in the work, rior on as good paper. 
 
 This work is intended to supply a want long felt in this country, of some treatise present- 
 ing correct systematic descriptions of medicinal plants, accompanied by representations of 
 the most important of them, and furnished at a price so moderate as to render it generally 
 accessible and useful. In the arrangement, the author has treated more fully of those 
 plants which are known to be of the greatest importance; and more especially of such as 
 are of native origin ; while others, rarely used, are briefly noticed, or mentioned only by 
 name. In all cases, the technical descriptions are drawn up in accordance with the existing 
 state of botanical knowledge, and in order that these maybe fully appreciated, even by those 
 not proficients in the science, an Introduction has been prepared, containing a concise view 
 of Vegetable Physiology, and the Anatomy and Chemistry of Plants. Besides this, a very 
 copious GLOSSARY of botanical terms has been appended, together with a most complete 
 INDEX, giving not only the scientific but also the common names of the species noticed in 
 it. It will thus be seen that the work presents a view not only of the properties and medical 
 virtues of the various species of the vegetable world, but also of their organization, compo- 
 sition and classification. 
 
 To the student, who is really anxious to study Botany for those great purposes which ren- 
 der it so necessary for the advancement of Medical Science, and who has been obliged to 
 rest satisfied with such imperfect knowledge as can be obtained from the different treatises 
 on the Materia Medica, the present work will be of great utility as a text-book and guide in 
 his researches, as it presents in a condensed form, all that is at present known respecting 
 those vegetable substances which are employed to alleviate suffering and to minister to the 
 wants of man. It will also be found extremely convenient to practitioners through the 
 country, who are anxious to obtain a knowledge of the medicinal plants occurring in their 
 vicinity, and who are unwilling to procure the scarce and high-priced works which are at 
 present the only ones accessible on this important branch of medical knowledge. 
 
 Great care has been taken to render the mechanical execution satisfactory. 
 
 NOW PREPARING, 
 AND TO BE READY AT AN EARLY DAY, 
 
 AN ANALYTICAL COMPEND OF THE VARIOUS BRANCHES OF 
 
 PRACTICAL MEDICINE, SURGERY, ANATOMY, 
 
 MIDWIFERY, DISEASES OF WOMEN AND CHILDREN, 
 Jfledica and Therapeutic^ Physiology, 
 
 oars 20 etna's' .A urn) ' 
 
 B JOHN NEILL, M D, 
 
 Demonstrator of Anatomy in the University of Pennsylvania, and 
 
 F. GURNEY SMITH, M.D., 
 Lecturer on Physiology in the Philadelphia Association for Medical Instruction. 
 
 To make one large royal Duodecimo volume, with numerous Illustrations on Wood. 
 It is the intention of the publishers to page this work in such a way, that it can be done up in 
 separate divisions, and in paper to go by mail; no one division will cost over 50 cents, thus pre- 
 senting separate MANUALS on the various branches of medicine, and at a very low price. 
 
 NEARLY READY. 
 
 BURROWS ON DISORDERS OF CEREBRAL CIRCULATION, 
 
 AND ON THE CONNECTION BETWEEN AFFECTIONS OF THE BRAIN AND 
 
 DISEASES OF THE HEART. 
 In one neat octavo volume, with six colored plates. 
 
SPECIMEN OF THE ILLUSTRATIONS HI 
 
 GRIFFITH'S MEDICAL BOTANY. 
 
LEA & BLANCHARD'S PUBLICATIONS. 15 
 
 THE GREAT MEDICAL LIBRARY, 
 THE CYCLOP/EDIA OF PRACTICAL MEDICINE ; 
 
 COMPRISING TREATISES ON THE 
 
 NATURE AND TREATMENT OF DISEASES, 
 
 MATERIA MEDICA AND THERAPEUTICS, 
 
 DISEASES OF WOMEN AND CHILDREN, 
 MEDICAL JURISPRUDENCE, &c. &c. 
 
 EDITED BT - 
 
 JOHN FORBES, M. D., F.R.S., 
 ALEXANDER TWEEDIE, M.D., F.R.S., 
 
 AND 
 
 JOHN CONOLLY, M.D. 
 
 REVISED, WITH ADDITIONS, 
 
 BY ROBLEY DUNGLISON, M. D. 
 
 THIS WORK IS NOW COMPLETE, AND FORMS 
 
 FOUR LARGE SUPER-ROYAL, OCTAVO VOLUMES. 
 
 CONTAINING THIRTY-TWO HUNDRED AND FIFTY-FOUR 
 
 UNUSUALLY LARGE PAGES IN DOUBLE COLUMNS, 
 
 PRINTED ON GOOD PAPER, WITH A NEW AND CLEAR TYPE. 
 
 THE WHOLE WELL AND STRONGLY BOUND, 
 WITH RAISED BANDS AND DOUBLE TITLES. 
 Or, to he had in twenty-four parts, at Fifty Cents each. 
 
 For a list of Articles and Authors, together with opinions of the press, see Supplement to the No- 
 vember number of the Medical News and Library for 1845. 
 
 This work having been completed and placed before the profession, has 
 been steadily advancing in favor with all classes of physicians. The nu- 
 merous advantages which it combines, beyond those of any other work ; the 
 weight which each article carries with it, as being the production of some 
 physician of acknowledged reputation who has devoted himself especially 
 to the subject confided to him; the great diversity of topics treated of; the 
 compendiousness with which everything of importance is digested into a 
 comparatively small space ; the manner in which it has been brought up 
 to the day, everything necessary to the American practitioner having been 
 added by Dr. Dunglison ; the neatness of its mechanical execution ; and 
 the extremely low price at which it is afforded, combine to render it one of 
 the most attractive works now before the profession. As a book for con- 
 stant and reliable reference, it presents advantages which are shared by no 
 other work of the kind. To country practitioners, especially, it is abso- 
 lutely invaluable, comprising in a moderate space, and trifling cost, the 
 matter for which they would have to accumulate libraries, when removed 
 from public collections. The steady and increasing demand with which 
 it has been favored since its completion, shows that its merits have been 
 appreciated, and that it is now universally considered as the 
 
 LIBRARY FOR CONSULTATION AND REFERENCE. 
 

 
 A 2MLA.GHM Uk'lCElMT ATfD CHEAP WORK. 
 
 SMITH & HORNER'S ANATOMICAL ATLAS, 
 
 Just Published, Price Five Dollars in Parts. 
 
 AN 
 
 ANATOMICAL ATLAS 
 ILLUSTRATIVE OF THE STRUCTURE OF THE HUMAN BODY. 
 
 BY HENRY H. SMITH, M.D., 
 
 uLlJ Fellow of the College of Physicians, <f-e. 
 
 UNDER THE SUPERVISION OF 
 
 WILLIAM E. HORNER, M.D., 
 
 Professor of Anatomy in the University of Pennsylvania. 
 In One large Volume, Imperial Octavo. 
 
 This work is but just completed, having been delayed over the time intended by the great difficulty in giving 
 to the illustrations the desired finish and perfection. It consists of five parts, whose contents are as follow*: 
 
 PART I. The Bones and Ligaments, with one hundred and thirty engravings. 
 
 PART II. The Muscular and Dermoid Systems, with ninety-one engravings. 
 
 PART III. The Organs of Digestion and Generation, with one hundred and ninety-one engravings. 
 
 PART IV. The Organs of Respiration and Circul-ation, with ninety-eight engravings. 
 
 PART V. The Nervous System and the Senses, with one hundred and twenty-six engravings. 
 Forming altogether a complete System of Anatomical Plates, of nearly 
 
 SIX HUNDRED AND FIFTY FIGURES, 
 
 executed in the best style of art, and making one iarge imperial octavo volume. Those who do not want it in 
 parts can have the work bound in extra cloth or sheep at an extra cost. 
 
 This work possesses novelty both in the design and the execution. It is the first attempt to apply engraving 
 on wood, on a large scale, to the illustration of human anatomy, and the beauty of the parts issued induces the 
 publishers to flatter themselves with the hope of the perfect success of their undertaking. The plan of the 
 work is at once novel and convenient. Each page is perfect in itself, the references being immediately under 
 the figures, so that the eye takes in the whole at a glance, and obviates the necessity of continual reference 
 backwards and forwards. The cut? are selected from the best and most accurate sources ; and, where neces- 
 sary, original drawings have been made from the admirable Anatomical Collection of the University of Penn 
 sylyania. It embraces all the late beautiful discoveries arising from the use of the microscope in the investi- 
 gation of tlie minute structure of the tissues. 
 
 In the getting up of this very complete work, the publishers have spared neither pains nor expense, and they 
 now present it to the profession, with the full confidence that it will be deemed all that is wanted in a scientific 
 and artistical point of view, while, at the same time, its very low price places it within the reach of all. 
 
 It is particularly adapted to supply the place of skeletons or subjects, as the profession will see by examining the list 
 f plates 
 
 "These figures are well selected, and present a complete and accurate representation of that wonderful fabric, 
 the human body. The plan of this Atlas, which renders it so peculiarly convenient for the student, and its 
 uperb artistical execution, have been already pointed out. We must congratulate the student upon the 
 completion of this atlas, as it is the most convenient work of the kind that lias yet appeared; and, we must 
 add, the very beautiful manner in which it is 'got up' is so creditable to the country as to be flattering to our 
 national pride." American Medical Journal. 
 
 "This is an exquisite volume, and a beautiful specimen of art. We have numerous Anatomical Atlases, 
 but we will venture to say that none equal it in cheapness, and none surpass it in faithfulness and spirit. We 
 strongly recommend to our friends, both urban and suburban, the purchase of this excellent work, for which 
 both editor and publisher deserve tfljb thanks of the profession." Medical Examiner. 
 
 "We would strongly recommend it, not only to the student, but also to the working practitioner, who, 
 although grown rusty in the toils of his harness still has the desire, and often the necessity, of refreshing his 
 knowledge in this fundamental part of the science of medicine." frew York Journal of Medicine and Surg. 
 
 " The plan of this Atlas is admirable, and its execution superior to any thing of the kind before published m 
 this country. It is a real labour-saving affair, and we regard its publication as the greatest boon that could be 
 conferred on the student of anatomy. It will be equally valuable to the practitioner, by affording him an easy 
 means of recalling the details learned in the dissecting room, and which are soon forgotten." American Medi- 
 cal Journal. 
 
 ' It is a beautiful as well as particularly useful design, which should be extensively patronized by physicians, 
 surgeons and medical students." Boston Med. and Surg. Journal. 
 
 "It has been the aim of the author of the Atlas to comprise in it the valuable points of all previous works, to 
 embrace the latest microscopical observations on the anatomy of the tissues, and by placing it at a moderate 
 price to enable all to acquire it who may need its assistance in the dissecting or operating room, or other field 
 of practice." Western Journal of Med. and Surgery. 
 
 ''These numbers complete the series of this beautiful work, which fully merits the praise bestowed upon the 
 earlier numbers. We regard all the engravings as possessing an accuracy only equalled by their beauty, 
 and cordially recommend the work to all engaged in the study of anatomy." New York Journal of Medicine 
 and Surgery. 
 
 "A more elegant work than the one before us could not easily be placed by a physician upon the table of 
 his student. 1 * Wetter* Journal of Medicine and Surgery. 
 
 ;f We were much pleased with Part I, but the Second Part gratifies us still more, both as regards the attract- 
 ive nature of the subject, (The Dennoid and Muscular Systems,) and the beautiful artistical execution of the 
 Jlustrations. We have here delineated the most accurate microscopic views of some of the tissues, as, for 
 instance, the cellular and adipose tissues, the epidermis, rete mucosum and cutis vera. the sebaceous and 
 r>f rspiraiory organs of the skin, the perspiratory glands and hairs of the skin, and the hair and nails. Then 
 fellows ilir- general anatomy of the muscles, and, lastly, their separate delineations. We would recommend 
 this Anatomical Atlas to our readers in the very strongest terms." Ntw York Journal of Medicine and Sur> 
 
LEA & BLANCHARD'S PUBLICATIONS. 17 
 
 HQRNER'S ANATOMY, 
 
 NEW EDITION. 
 
 SPECIAL ANATOMY AND HISTOLOGY. 
 
 BY WILLIAM E. HORNER, M.D., 
 
 PROFESSOR OF ANATOMY IW THE UNIVERSITY OF PENNSHVANIA, &C., &C. 
 
 Seventh edition. 
 
 With many improvements and additions. In two octavo volumes, with illustrations on 
 
 wood. 
 
 This standard work has been so long before the profession, and has been so extensively 
 used, that, in announcing thenewedition.it is only necessary to state, that it has under- 
 gone a most careful revision ; the author has introduced many illustrations relating to Mi- 
 croscopical Anatomy, and has added a large amount of text on those various points of 
 investigation that are rapidly advancing and attracting so much attention. This new edition 
 has been arranged to refer conveniently to the illustrations in Smith and Horner's Anato- 
 mical Atlas. 
 
 "The name of Professor Homer is a sufficient voucher for the fidelity and accuracy of 
 any work on anatomy, but if any further evidence could be required of the value of the pre- 
 sent publication, it is afforded by the fact of its having reached a seventh edition. It is 
 altogether unnecessary now to inquire into the particular merits of a work which has been 
 so long before the profession, and is so well known as the present one, but in announcing a 
 new edition, it is proper to state that it has undergone several modifications, and has been, 
 much extended, so as to place it on a level with the existing advanced state of anatomy. 
 The histological portion has been remodelled and rewritten since the last edition; numerous 
 wood cuts have been introduced, and specific references are made throughout the work to 
 the beautiful figures in the Anatomical Atlas, by Dr. H. H. Smith." The American Medical 
 Journal, for January, 1847. 
 
 HORNER'SJ3ISSSCTOR. 
 
 THE UNITED STATES DISSECTOR, 
 
 BEING A NEW EDITION, WITH EXTENSIVE MODIFICATIONS, 
 AND ALMOST REWRITTEN, OF 
 
 "BORJVJEIP& FKMCTICML, MAWTOMIW 
 
 IN ONE VERY NEAT VOLUME, ROYAL 12MO. 
 With many Illustrations on Wood. 
 
 The numerous alterations and additions which this work has undergone, the improve- 
 ments which have been made in it, and the numerous wood-cuts which have been intro- 
 duced, render it almost a new work. 
 
 It is the standard work for the Students in the University of Pennsylvania. 
 
 Some such guide-book as the above is indispensable to the student in the dissecting room, 
 and this, prepared by one of the most accurate of our anatomists, may claim to combine as 
 many advantages as any other extant. It has been so favorably received that the publish- 
 ers have issued the fourth edition, which comes forth embellished by various wood cuts. 
 The copy for which we are indebted to the publishers, although received by us a fortnight 
 since, gives proof in its appearance that it has already seen service at the dissecting table, 
 where students have found it a valuable guide. The Western Journal of Medicine and <Sur- 
 gery. 
 
 ., 
 
 HOPE ON THE HEART. NEW EDITION, JUST PUBLISHED. 
 
 A TREATISE ON THE DISEASES 
 
 OF THE HEART AND GREAT VESSELS, 
 
 AND ON THE AFFECTIONS WHICH MAY BE MISTAKEN FOR THEM. 
 
 Comprising the author's view of the Physiology of the Heart's Action and Sounds as demonstrated by his ex- 
 periments on the Motions and Sounds in 1830 and on the Sounds in 18345. 
 
 BY J. HOPE, M. D., F. R. S , &c. &c. 
 Second American from the third London edition. With Notes and a Detail of Recent Experiments. 
 
 BY C. W. PENNOCK, M. D., &c. 
 In one octavo volume of nearly six hundred pages with thographic plates. 
 
18 LEA & BLANCHARD'S PUBLICATIONS. 
 
 WORKS BY PROFESSOR W. P. DEWEES. 
 
 NEW EDITIONS. 
 
 DEWEES'S JPJWIFERY, 
 
 A COMPREHENSIVE SYSTEM OF MIDWIFERY. 
 
 CHIEFLY DESIGNED TO FACILITATE THE INQUIRIES OF THOSE WHO MAY BE PUR- 
 SUING THIS BRANCH OF STUDY. 
 
 ILLUSTRATED BY OCCASIONAL CASES AND MANY ENGRAVINGS. 
 Eleventh Edition, with the Author's last Improvements and Corrections. 
 
 BY WILLIAM P. DEWEES, M.D., 
 
 LATE PROFESSOR OF MIDWIFERY IN THE UNIVERSITY OF PENNSYLVANIA, ETC. 
 
 , In one volume, octavo. 
 
 * That this work, notwithstanding the length of time it has been before the profession, and the numerous treat- 
 ises that have appeared since it was written, should have still maintained its ground, and passed to edition after 
 edition, is sufficient proof that in it the practical talents of the author were fully placed before the profes- 
 sion. Of the book itself it would be superfluous to speak, having been so long and so favorably known through- 
 out the country as to have become identified with American Obstetrical Science. 
 
 DEWEES ON^ FEMALES. 
 
 A TREATISE ON THE DISEASES OF FEMALES, 
 
 BY WILLIAM P. DEWEES, M. D., &c., 
 
 LATE PROFESSOR OF MIDWIFERY IN THE UNIVERSITY OF PENNSYLVANIA, ETC. 
 
 NINTH EDITION, 
 With the Author's last Improvements and Corrections. 
 
 In one octavo volume, with plates. 
 
 DEWEES ON CHILDREN. 
 
 A TREATISE ON THE 
 
 PHYSICAL AND MEDICAL TREATMENT OF CHILDREN, 
 
 BY WILLIAM P. DEWEES, M.D., 
 
 LATE PROFESSOR OF MIDWIFERY IN THE UNIVERSITY OF PENNSYLVANIA, ETC. ETC. 
 
 NINTH EDITION. 
 
 In one volume octavo. 
 
 This edition embodies the notes and additions prepared by Dr. Dewees before his death, and will be found 
 much improved. 
 
 The objects of this work are, 1st, to teach those who have the charge of children, either as parent orguardian, 
 the most approved methods of securing and improving their physical powers. This is attempted by pointing 
 out the duties which the parent or the guardian owes for this purpose, to this interesting but helpless class of 
 beings, and the manner by which their duties shall be fulfilled. And 2d. to render available a long experience 
 to those objects of our affection when they become diseased. In attempting this, the author has avoided as 
 much as possible, "technicality," and has given, if he does not flatter himself. too much to each disease of 
 which he treats, its appropriate and designating characters, with a fidelity that will prevent any two being 
 confounded together, with the best ctode of treating them, that either his own experience or that of others has 
 suggested. 
 
 Physicians cannot too strongly recommend the use of thfs book in all families. 
 
 ASHWELL ON THE DISEASES OF FEMALES. 
 
 A PRACTICAL TREATISE ON THE 
 
 DISEASES PECULIAR TO WOMEN, 
 
 ILLUSTRATED BY CASES 
 DERIVED FROM HOSPITAL AND PRIVATE PRACTICE. 
 
 BY SAMUEL ASHWELL, M. D., 
 
 Member of the Royal College of Physicians; Obstetric Physician and Lecturer to Guy's Hospital, &c. 
 
 EDITED BY PAUL BECK GODDARD, M. D. 
 
 The whole complete in one large octavo volume. 
 
 " The most able, and certainly the most standard and practical work on female diseases that we 
 ba?e yet seen." Medico- Chirurgical Review. 
 
American practitioner, ro commend it still more strongly to the profession, the publishers 
 rreat expense in preparing this edition with larger type, finer paper, and stronger binding w 
 It is edited with reference particularly to American practice, by Dr. Condie; and with thes 
 provements, the price is still kept so low as to be within the reach of all, and to render it am< 
 
 LEA & BLANCHARD'S PUBLICATIONS. 19 
 
 WATSON'S PRACTICE OF PHYSIC. 
 
 NEW EDITION, BROUGHT UP TO SEPTEMBER 1847. 
 LECTURES ON THE 
 
 PRINCIPLES AND PRACTICE OF PHYSIC. 
 
 DELIVERED AT KING'S COLLEGE, LONDON, 
 
 BY THOMAS WATSON, M.D., &c. &c. 
 Third American, from the Last London Edition, 
 
 REVISED, WITH ADDITIONS, 
 
 BY D. FRANCIS CONDIE, M. D., 
 
 Author of a work on the "Diseases of Children," &c. 
 
 In One Octavo Volume 
 
 Of nearly ELEVEN HUNDRED LARGE PAGES, strongly bound with raised bands. 
 The rapid sale of two large editions of this work is an evidence of its merits, and of its general favor with the 
 American practitioner. To commend it still more strongly to the profession, the publishers have gone to a 
 
 e, finer paper, and stronger binding with raised bands, 
 ractice, by Dr. Condie; and with these numerous im- 
 the reach of all, and to render it among the cheapest 
 
 works offered.to the profession. It has been received with the utmost favor by the medical press, both of this 
 country and of England, a few of the notices of which, together with a letter from Professor Chapman, are 
 submitted. 
 
 Philadelphia, September 27th, 1844. 
 
 ^ Watson's Practice of Physic, in my opinion, is among the most comprehen- 
 sive works on the subject extant, replete with curious and important matter, and 
 written with great perspicuity and felicity of manner. As calculated to do much 
 good, I cordially recommend it to that portion of the profession in this country 
 who may be influenced by my judgment. 
 
 N. CHAPMAN, M.D., 
 
 Professor of the Practice and Theory of Medicine in the University of Pennsylvania. 
 
 "We know of no work better calculated for being placed in the hands of the student, and for a text-book, and 
 as such we are sure it will be very extensively adopted. On every important point the author seems to have 
 posted up his knowledge to the day." American MedicalJournal. 
 
 One of the most practically useful books that ever was presented to the student indeed a more admirable 
 rnmmary of general and special pathology, and of the application of therapeutics to diseases, we are free to 
 say has not appeared for very many years. The lecturer proceeds through the whole classification of human 
 ills, a capite ad calcem, showing at every step an extensive knowledge of his subject, with the ability of commu- 
 nicating his precise ideas in a style remarkable for its clearness and simplicity." N. Y. Journal of Medi- 
 cine and Surgery. 
 
 " We are free to state that a careful examination of this volume has satisfied us that it merits all the com- 
 mendation bestowed on it in this country and at home. It is a work adapted to the wants of young practi- 
 tioners, combining as it does, sound principles and substantial practice. It is not too much to say that it is a 
 representative of the actual state of medicine as taught and practised by the most eminent physicians of the 
 present day, and as such we would advise everyone about embarking in the praetice of physic to provide him- 
 self with a copy of It." Western Journal of Medicine and Surgery. 
 
 IVOCEL'S PATHOLOGICAL ANATOMY. 
 
 THE 
 
 PATHOLOGICAL ANATOMY OF THE HUMAN BODY. 
 
 BY JULIUS VOGEL, M.D., &c. 
 TRANSLATED FROM THE GERMAN, WITH ADDITIONS, 
 
 BY GEORGE E. DAY, M.D. ; &c. 
 
 KUustratetJ feg uptoartis of rte S^imtjreU $lafn anti Colored JSnjjrabfnas* 
 In One neat Octavo Volume. 
 
 In our last number we gave a pretty full analysis of the original of this very valuable work, to which w 
 must refer the reader. We have only to add here our opinion that the translator has performed his task in an 
 excellent manner, and has enriched the work with many valuable additions. The British and Foreign Meduai 
 Kevieiv. 
 
 It is decidedly the best work on the subject of which it treats in the English language, and Dr. Day, whose 
 translation is well executed, has enhanced its value by a judicious selection of the most important figures Iroa 
 the atlas, which are neatly engraved. The London Medical Gazette. 
 
20 LEA & BLANCHARD'S PUBLICATIONS. 
 
 A NEW EDITION OP THE GREAT 
 
 M E D I A L_L E X I H . 
 
 A Dictionary of 
 
 MEDICAL SCIENCE, 
 
 CONTAINING A CONCISE ACCOUNT OF THE VARIOUS SUBJECTS AND TERMS; WITH THE 
 FRENCH AND OTHER SYNONYMES: NOTICES OF CLIMATES AND OF CELE- 
 BRATED MINERAL WATERS; FORMULAE FOR VARIOUS OFFICINAL 
 AND EMPIRICAL PREPARATIONS, &c. 
 
 BY ROBLEY DUNGLISON, M. D., 
 
 PROFESSOR OF THE INSTITUTES OF MEDICINE, ETC. IN JEFFEKSON MEDICAL COLLEGE, PHILADELPHIA. 
 
 Sixth edition, revised and greatly enlarged. In one royal octavo volume of over 800 very large pages, 
 double columns. Strongly bound in the best leather, raised bands. 
 
 "The most complete medical dictionary in the English language." Western Lancet. 
 
 " We think that 'the author's anxious wish to render the work a satisfactory and desirable if not indispen- 
 sable Lexicon, m which the student may search without disappointment for every term that has been 
 legitimated in the nomenclature of the science,' has been fully accomplished. Such a work is much needed 
 by all medical students and young physicians, and will doubtless continue in extensive demand. It is a 
 lasting monument of the industry and literary attainments of the author, who has long occupied the highest 
 rank among the medical teachers of America " The New Orleans Medical and Surgical Journal. 
 
 "The simple announcement of the fact that Dr. Dunglison's Dictionary has reached a sixth edition, is almost 
 as high praise as could be bestowed upon it by an elaborate notice. It is one of those standard works that have 
 been ' weighed in the balance and (not) been found wauling ' It has stood the test of experience, and the fre- 
 quent calls for new editions, prove conclusively that it is held by the profession and by students in the highest 
 estimation. The present edition is not a mere reprint of former ones; the author has for some time been 
 laboriously engaged in revising and making such alterations and additions as are required by the rapid pro- 
 gress of our science, and the introduction of new terms into our vocabulary. In proof of this it is stated ' that 
 the present edition comprises nearly two thousand five hundred subjects and terms not contained in the last. 
 Many of these had been introduced into medical terminology in consequence of the progress of the science, 
 and others had escaped notice in previous revisions.' We think that the earnest wish of the author has been 
 accomplished ; and that he has succeeded in rendering the work 'a satisfactory and desirable if not indis- 
 pensable Lexicon, in which the student may search, without disappointment, for every term that has been 
 legitimated in the nomenclature of the science.' This desideratum he has been enabled to attempt in suc- 
 cessive editions, by reason of the work not being stereotyped ; and the present edition.certainly offers stronger 
 claims to the attention of the practitioner and student, than any of its predecessors. The work is got up in 
 the usual good taste of the publishers, and we recommend it in full confidence to all who have not yet supplied 
 themselves with so indispensable an addition to their libraries." The New York Journal of Medicine. 
 
 A NEW EDITION OF DUNGLISON'S HUMAN PHYSIOLOGY, 
 
 HUMAN PHYSIOLOGY, 
 
 WITH THREE HUNDRED AND SEVENTY ILLUSTRATIONS. 
 BY ROBLEY DUNGLISON, M.D., 
 
 PROFESSOR OF THE INSTITUTES OF MEDICINE IN THE JEFFERSON MEDICAL COLLEGE, PHILADELPHIA, ETC., ETC. 
 
 Sixth edition, greatly improved. In two large octavo volumes, containing nearly 1350 pages. 
 " It is but necessary for the Author to say, that all the cares that were bestowed on the preparation of the 
 fifth edition have been extended to the sixth, and even to a greater amount. Nothing of importance that has 
 been recorded since its publication, has, he believes, escaped his attention. Upwards of seventy illustrations 
 have been added; and many of the former cuts have been replaced by others. The work, he trusts, will be 
 found entirely on a level with the existing advanced stale of physiological science." 
 
 In mechanical and artistical execution, this edition is far in advance of any former one. 
 The illustrations have been subjected to a thorough revision, many have been rejected and 
 their places supplied with superior ones, while numerous new wood-cuts have been added 
 wherever perspicuity or novelty seemed to require them. 
 
 . "Those who have been accustomed to consult the former editions of this work, know with how much 
 care and accuracy every fact and opinion of weight, on the various subjects embraced in a treatise on 
 Physiology, are collected and arranged, so as to present the latest and best account of the science To suctt 
 we need hardly say, that, in this respect, the present edition is not less distinguished than those which have 
 preceded it. In the two years and a half which have elapsed since the last or fifth edition appeared, nothing 
 of consequence that has been recorded seems to have been omitted. Upwards of seventy illustrations have 
 been added, and many of the former cuts have been replaced by others of better execution. These mostly 
 represent the minute structures as seen through the microscope and are necessary for a proper comprehension 
 of the modern discoveries in this department " The Medical Examiner. 
 
 The " Human Physiology" of Professor Dunglison has long since taken rank as one of the medical classics 
 in our language. Edition after edition has been issued, each more perfect than the la>t, till now we have the 
 sixth, with upwards of seventy new illustrations. To say that it is by far the best text-book of physiology ever 
 published in this country, is but echoing the general voice of the profession. It is simple and concise in style, 
 clear in illustration, and altogether on a level with the existing advanced state of physiological science. The 
 additions to the present edition are extremely numerous and valuable; scarcely a fact worth naming which 
 has a bearing upon the subject seems to have been omitted. All t!ie recent writers on physiology, both in the 
 French. German and English languages, have been consulted and freely used, and the facts lately revealed 
 through the agency of organic chemistry and the microscope have received a due share of attention. As it is, 
 we cordially recommend the work as in the highest degree indispensable both to students and practitioners 
 of medicine. New York Journal of Medicine. 
 
 The most full and complete system of physiology in our language. Western Lancet. 
 
LEA & BLANCHARD'S PUBLICATIONS. 21 
 
 DUNGLISON'S. THERAPEUTICS. 
 
 NEW AND MUCH IMPROVED EDITION. 
 
 GENERAL THERAPEUTICS AND MATERIA MEDICA, 
 
 With One Hundred and Twenty Illustrations. 
 
 ADAPTED FOR A MEDICAL TEXT-BOOK. 
 
 BY ROBLEY DUNGLISON, M.D., 
 
 Professor of Institutes of Medicine, &c. in Jefferson Medical College; Late Professor of Materia Medica, &c. 
 in the Universities of Virginia and Maryland, arid in Jefierson Medical College. 
 
 Third Edition, Revised and Improved, in two octavo volumes, well bound. 
 
 In this edition much improvement will he found over the former ones The author has subjected it to a tho- 
 rough revision, and has endeavored to so modify the work as to make it a more complete and exact exponent 
 of the present state of knowledge on the imporiant subjects of which it treats. The favor with which the former 
 editions were received, demanded that the present should be rendered still more worthy of the patronage of the 
 profession, and this alteration will be found not only in the matter of the volumes, but also in the numerous 
 illustrations introduced and the general improvement in the appearance of the work. 
 
 ''This is a revised and improved edition of the author's celebrated book, entitled ' General Therapeutics;' an 
 account of the different articles of the Materia Medica having been incorporated with it. The work has, in 
 fact, been entirely remodelled, so that it is now the most complete and satisfactory exponent of the existing state 
 of Therapeutical Science, within the moderate limits of a text-book, of any hitherlo published What gives the 
 work a superior value, in our judgment, is the happy blending of Therapeutics and Materia Medica a^ they are, 
 or ought to be taught in all our medical schools; going no farther inio the nature and commercial hisiory of 
 drugs, than is indispensable for the medical student. This gives to the treatise a clinical and practical charac- 
 ter, calculated to benefit in the highest degree, both students and practitioners. We shall adopt it as a text- 
 book for our classes, while pursuing this branch of medicine, and shall be happy to learn that it has been 
 adopted as such, in all of our medical institutions ." The N. Y. Journal oj Medicine. 
 
 "Our junior brethren in America will find in these volumes of Professor Dunglison. a 'THESAURUS MBDICA- 
 MINUM,' more valuable than a large purse of gold." London Mrrlico-Chir'i./rgical Review. 
 
 DUNGLISON ON NEW REMEDIES. 
 
 NEW EDITION, BROUGHT UP TO OCTOBER 1846. 
 
 NEW REMEDIES. 
 
 BY ROBLEY DUNGLISON, M.D., &c. &c. 
 
 Fifth edition, with extensive additions. In one neat octavo volume. 
 
 The numerous valuable therapeutical agents which have of late years been introduced into the Materia 
 Medica. render it a difficult matter for the practitioner to keep up with the advancement of the science, espe- 
 cially as the descriptions of them are difficult of access, being scattered so widely thiougn transactions of 
 learned societies, journals, monographs. &c. &c. To obviate this difficulty, and to place within reach of the 
 profession this important information in a compendious form, is the object of the present volume, and the num- 
 ber of editions through which it has passed show that its utility has not been underrated. 
 
 The author has taken particular care that this edition shall be completely brought up to the present day. 
 The therapeutical agents added, which may be regarded as newly introduced into the Materia Medica. to- 
 gether with old agents brought forward with novel applications, and which may therefore be esteemed as 
 "New Remedies," are the following: Ben/oic Acid, Chromic Acid, Gallic Acid.'JNilric Acid. Phosphate of 
 Ammonia, Binelli Water, Brocchieri Water, Atropia Beerberia, Chloride of Carbon (Chloroform), Digitalia, 
 Electro-Magnetism, Ergotin, Ox-gall, Glycerin, Hsemospasy, Hcemostasis, Hagenia Abyssinica. Honey Bee, 
 Protochloride of Mercury and Quinia. lodoform, Carbonate of Lithia, Sulphate of Manganese, Matico, Double 
 Iodide of Mercury and Morphia, lodhydrate of Morphia, Iodide of lodhydrate of Morphia, Muriate of Mor- 
 phia and Codeia, Naphthalin, Piscidia Erythrina, Chloride of Lead. Nitrate of Potassa. Arseniateof Quinia, 
 Iodide of Quinia, Iodide of Cinchonia. Iodide of lodhydrate of Quinia, Lactate of Quinia, Pyroacetic Acid, 
 (Naphtha, Acetone) Hyposulphate of Soda. Phosphate of Soda, Iodide of lodhydrate of Strychnia, Double Iodide 
 of Zinc and Strychnia, Double Iodide of Zinc and Morphia, and Valerianate of Zinc. 
 
 : <k A work like this is obviously not suitable for either critical or analytical review. It is. so far as it goes, a 
 dispensatory, in which an account is given of the chemical and physical properties of all the articles recently 
 added to the Materia Medica and their preparations, witlia notice of the diseases for which they are prescribed, 
 the doses, mode of administration &c." The Medical Examiner. 
 
 THE MEDICAL STUDENT f 
 
 OR AIDS TO THE STUDY OF MEDICINE. 
 
 A REVISED AND MODIFIED EDITION. 
 
 BY ROBLEY DUNGLISON, M. D. 
 
 In one neat I2mo. volume. 
 
 HUMAN HEALTH: 
 
 OR, THE INFLUENCE OF ATMOSPHERE AND LOCALITY. CHANGE OF AIR AND CLIMATE, 
 
 SEASONS, FOOD. CLOTHING, BATHING AND MINERAL SPRINGS, EXERCISE, 
 
 SLEEP, CORPOREAL AND INTELLECTUAL PURSUITS, &c. &c., 
 
 ON HEALTHY MAN: CONSTITUTING 
 
 ELEMENTS OF HYGIENE. 
 
 BY ROBLEY DUNGLISON, M. D. 
 
 A New Edition with many Modifications and Additions. In one Volume, 8vo. 
 
LEA & BLANCHARD'S PUBLICATIONS. 
 
 AMEEICAN PRACTICE OF MEDICINE. 
 
 BY PROFESSOR DUNGLI8ON. 
 THIRD EDITION, MUCH IMPROVED, NOW READY, BROUGHT UP TO 184a 
 
 THE PRACTICETOF MEDICINE; 
 
 A TREATISE ON 
 
 SPECIAL PATHOLOGY AND THERAPEUTICS. 
 
 THIRD EDITION. 
 
 BY ROBLEY DUNGLISON, M. D. 
 
 Professor of the Institutes of Medicine in the Jefferson Medical College; Lecturer on Clinical Medicine, Sfe 
 
 In Two large Octavo Volumes of over Fourteen Hundred Pages. 
 
 Since the publication of the second edition of this work, short as the interval has been, so much 
 activity has prevailed in the advancement of medical knowledge, that a thorough revision of it 
 became necessary. Several pathological affections, too, had been omitted, which are now insert- 
 ed. The greatly enlarged dimensions of the work will sufficiently exhibit the amount of additions, 
 which might escape superficial observation. 
 
 In preparing the present edition, the author has carefully scanned the various monographs on 
 pathology and therapeutics, which have appeared alone or in different cyclopaediac and other works, 
 transactions of learned societies, and journals. He has also availed himself of the valuable matter 
 contained in recent treatises having a similar scope with his own, of which he may specify more 
 particularly those of Canstatt, Fuchs, and Wunderlich of Germany; Valliex and Grisolle of France; 
 and Dickson of this country. The Pathological Anatomy of Vogel, and the Animal Chemistry of 
 Simon, have also yielded him valuable assistance. Nothing of importance that has been recorded 
 since the publication of the last edition has, he believes, escaped his attention; and altogether he 
 trusts that the present edition will be regarded as an adequate exponent of the existing condition 
 of knowledge on the important departments of which it treats. 
 
 Notwithstanding the numerous and attractive works which have of late been issued on the Practice of 
 Physic, these volumes keep their place as a standard text-book for the student, and manual of reference for 
 the practitioner. The care with which the author embodies everything of value from all sources, the industry 
 with which all discoveries of interest or importance are summed up in succeeding editions, the excellent 
 order and system which is everywhere manifested, and the clear and intelligible style in which his thoughts 
 are presented, render his works universal favorites with the profession. 
 
 "In the volumes before us, Dr. Dunglison has proved that his acquaintance with the present facts and 
 doctrines, wheresoever originating, is most extensive and intimate, and the judgment, skill, and impartiality 
 with which the materials of the work have been collected, weighed, arranged, and exposed, are strikingly 
 manifested in every chapter. Great care is everywhere taken to indicate the source of information, and 
 under the head of treatment, formulae of the most appropriate remedies are every where introduced. In con- 
 clusion, we congratulate the students and junior practitioners of America on possessing in the present 
 volumes a work of standard merit, to which they may confidently refer in their doubts and difficulties." 
 Brit, and For. Med. Rev. 
 
 " Since the foregoing observations were written, we have received a second edition of Dunglison's work, 
 a sufficient indication of the high character it has already attained in America, and justly attained." Ibid. 
 
 "In the short space of two years, a second edition of Dr. Dunglison's Treatise on Special Pathology and 
 Therapeutics has been called for, and is now before the public in the neat and tasteful dress in which Lea 
 & Blanchard issue all their valuable publications. We do not notice the fact for the purpose of passing any 
 studied eulogy upon this work, which is now too well known to the profession to need the commendation of 
 the press. 
 
 " A cursory examination will satisfy any one, that great labor has been bestowed upon these volumes, 
 and on a careful perusal it will be seen that they exhibit the present state of our knowledge relative to 
 special pathology and therapeutics. The work is justly a great favorite with students of medicine, whose 
 exigencies the learned author seems especially to have consulted in its preparation." Western Jour, of 
 Med. and Surg. 
 
 " This is a work which must at once demand a respectful consideration from the profession, emanating as 
 it does from one of the most learned and indefatigable physicians of our country. 
 
 "This arrangement will recommend itself to the favorable consideration of all, for simplicity and com- 
 prehensiveness. We have no space to go into details, and, therefore, conclude by saying, that although 
 isolated defects might be pointed out, yet as a whole, we cheerfully recommend it to the profession, as 
 embracing much important matter which cannot easily be obtained from any other source." Western Lancet. 
 
 WILSON ON THE SKIN. 
 
 NEW AND IMPROVED EDITION, (1847.) 
 
 ON DISEASE8~OF THE SKIN. 
 
 BY ERASMUS WILSON, F.R.S., 
 
 AUTHOR OF "A SYSTEM OF HUMAN ANATOMY," ETC. 
 
 SECOND AMERICAN, FROM THE SECOND LONDON EDITION. 
 In one neat octavo volume, extra cloth, of Four Hundred and Forty Pages, with Eight Steel Plates. 
 
 accurately and beautifully colored. 
 
 Copies may be had with or without the plates, or the plates may be had separate, neatly and strongly 
 done up. 
 
 The increase of this work by nearly a hundred pages shows that this edition is much improved, and brought 
 up to the date of publication. 
 
LEA & BLANCHARD'S PUBLICATIONS. 23 
 
 BRODIE'S SURGICAL WORKS. 
 
 SELECT SURGICAL WORKS OF SIR BENJ'N BRODIE, BART., V. F. R. S. 
 
 CONTAINING HIS 
 
 CLINICAL LECTURES ON SURGERY, 
 LECTURES ON THE DISEASES OF THE URINARY ORGANS, 
 
 AND 
 
 OBSERVATIONS ON THE DISEASES OF THE JOINTS. 
 The whole in one neat octavo volume, strongly bound. 
 
 ALSO, 
 Eacli of the above works to be had separately, done up in cloth* 
 
 MULLER'S PHYSICS AND METEOROLOGY Nearly Ready, 
 
 PRINCIPLES OF PHYSICS AND METEOROLOGY. 
 BY J. MULLER, 
 
 PROFESSOR OF PHYSICS AT THE UNIVERSITY OF FREIBURG. 
 
 Illustrated with nearly Five Hundred and Fifty Engravings on Wood, and Two Colored Plates. 
 
 In One Octavo Volume. 
 
 "The Physics of Muller is a work superb, complete, unique; the greatest want known to English Science 
 eould not have been better supplied. The work is of surpassing interest. The value of this contribution to 
 the scientific records of this country may be duly estimated by the fact, that the cost of the original drawings 
 and engravings alone has exceeded the sum of 2000."- Lancet, March 1847. 
 
 SOLLY ON THE BRAIN Nearly Ready. 
 THE HUMAN BRAIN: ITS STRUCTURE, PHYSIOLOGY, AND DISEASES. 
 
 WITH 
 
 A DESCRIPTION OF THE TYPICAL FORMS OF BRAIN IN THE ANIMAL KINGDOM, 
 BY SAMUEL SOLLY, F.R.S., 
 
 Senior Assistant-Surgeon to St. Thomas' Hospital; and Lecturer on Clinical Surgery, &c. 
 
 SECOND EDITION, GREATLY ENLARGED. 
 
 One Octavo Volume, with 120 Cuts. 
 
 MILLER'S SURGICAL WORKS. 
 
 THE PRINCIPLES OF SURGERY. 
 
 BY JAMES MILLER, F.R.S.E., F.R.C.S.E., 
 
 Professor of Surgery in the University of Edinburg, &c. 
 In one neat octavo volume, to match the Author's volume on " Practice." 
 
 " We feel no hesitation in expressing our opinion that it presents the philosophy of the science 
 more fully and clearly than any other work in the language with which we are acquainted." Phi- 
 ladelphia Medical Examiner. 
 
 LATELY PUBLISHED. 
 
 THE PRACTICE OF SURGERY. 
 
 BY JAMES MILLER, 
 
 Professor of Surgery in the University of Edinburg. 
 
 In one neat octavo volume. 
 This work is printed and bound to match the " Principles of Surgery," by Professor Miller, lately 
 
 issued by L. & B. Either volume may be had separately. 
 
 " This work, with the preceding one, forms a complete text-book of surgery, and has been under- 
 taken by the author at the request of his pupils. Although as we are modestly informed in the 
 preface, it is not put forth in rivalry of the excellent works on practical surgery which already exist, 
 we think we may take upon ourselves to say,that it will form a very successful and formidable 
 rival to most of them. While it does not offer the same attractive illustrations, with which some of 
 our recent text-books have been embellished, and while it will not, as indeed is not its design, set 
 aside the more complete and elaborate works of reference which the profession is in possession of, 
 we have no hesitation in stating that the two volumes form, together, a more complete text-book 
 of surgery than any one that has been heretofore offered to the student." The Northern Journal 
 of Medicine. 
 
24 LEA & BLANCHARD'S PUBLICATIONS. 
 
 CARPENTER'S NEW WORK. 
 
 A MANUAL, OR ELEMENTS OF PHYSIOLOGY, 
 
 MJTCLVDIJrG PHYSIOLOGICAL AJTJLTOMY, 
 
 FOR THE USE OF THE MEDICAL STUDENT. 
 
 BY WILLIAM B. CARPENTER, M. D., F. R. S , 
 
 FTTLLEfclAN PROFESSOR OF PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN, ETC. 
 
 With one hundred and eighty illustrations. In one octavo volume of 566 pages. Elegantly printed to match 
 
 his " Principles of Human Physiology." 
 
 This work, though but a very short time published, has attracted much attention from all engaged in teach- 
 ing the science of medicine, and has been adopted as a text-book by many schools throughout the country. 
 The clearness and conciseness with which all the latest investigations are enunciated render it peculiarly 
 well suited for those commencing the study of medicine. It is profusely illustrated with beautiful wood en- 
 gravings, and is confidently presented as among the best elementary text-books on Physiology in the lan- 
 guage. 
 
 NEW AND MUCH IMPROVED EDITION. NOW READY. 
 
 CARPENTER'S HUMAN PHYSIOLOGY. 
 
 BROUGHT UP TO SEPTEMBER, 1847. 
 
 PRINCIPLES OF HUMAN PHYSIOLOGY, 
 
 WITH THEIR CHIEF APPLICATIONS TO 
 
 PATHOLOGY, HYGIENE, AND FORENSIC MEDICINE. 
 BY WILLIAM B. CARPENTER, M. D., F. R. S., &c. 
 
 Third American, from a New and Revised London Edition, 
 
 WITH NOTES AND ADDITIONS, 
 
 BY MEREDITH CLYMER, M. D., &c. 
 
 With Three Hundred and Seventeen Wood-cut and other Illustration*, 
 
 In one octavo volume, of over 750 closely and beautifully printed pages. 
 
 The character of the present work is too well known and established to need any commendation. Within 
 a period of four years, it has passed through three editions both in this country and Great Britain. It will be 
 seen, that the present edition has been essentially modified and improved; and, besides attentive revision, has 
 undergone material alteration in the arrangement. 
 
 Many of the Notes of the American Editor to former editions have been incorporated by the Author in the 
 text of the present; others remain; whilst such additions have been made, as the progress of the science 
 required. 
 
 Besides the additions of the Author, the Editor has been enabled to add numerous illustrations; which, 
 accompanied by copious references, will, he trusts, be found to enhance the value of this edition, and to 
 peculiarly adapt it to the Student of Physiology. There are one hundred and fifteen more wood-cuts in this 
 than in the third English edition, and one hundred and one more than in the last American. 
 
 SUPPLEMENT TO THE ENCYCLOPEDIA AMERICANA, IIP TO THE YEAR 1847. 
 
 ENCYCLOPEDIA AMERICANA-Supplementary Vol. 
 
 A POPULAR DICTIONARY 
 
 OF ARTS, SCIENCES, LITERATURE, HISTORY, POLITICS AND 
 
 BIOGRAPHY. 
 
 VOL. XIV. 
 
 EDITED BY HENRY VETHAKE, LL. D., 
 
 Vice-Provost and Professor of Mathematics in the University of Pennsylvania, Author of "A Treatise on Poli- 
 tical Economy." 
 
 In One large Octavo Volume of over Six Hundred and Fifty double columned pages. 
 
 The numerous subscribers who have been waiting the completion of this volume can now perfect 
 their sets, and all who want a Register of the Events of the last Fifteen Years, for the Whole 
 World, particularly embracing interesting scientific investigations and discoveries, can obtain this 
 volume separately, price Two Dollars uncut in cloth, or Two Dollars and Fifty Cents in leather, 
 to match the styles in which the publishers have been selling sets. 
 
 Subscribers in the large cities can be supplied on application at any of the principal bookstores ; 
 and persons residing in the country can have their sets matched by sending a volume in charge of 
 friends visiting the city. 
 
 Complete sets furnished at very low prices in various bindings. 
 
 "The Conversations Lexicon (Encyclopaedia Americana) has become a household book in all the intelli- 
 gent families in America, and is undoubtedly the best depository of biographical, historical, geographical and 
 political information of that kind which discriminating readers require. There is in the present vo!um much 
 matter purely scientific, which was all the more acceptable to us that it was unexpected." Sillimari's Journal. 
 
LEA & BLANCHARD'S PUBLICATIONS. 25 
 
 FOWJVES' CHEMISTRY FOR STUDENTS. 
 
 NEW AND IMPROVED EDITION, 1847. 
 
 ELEMENTARY CHEMISTRY. 
 
 THEORETICAL AND PRACTICAL. 
 
 BY GEORGE FOWNES, PH. D., 
 
 Chemical Lecturer in the Middlesex Hospital Medical School, &c. &c. 
 With Numerous Illustrations. Second American Kdition. Kdited, with Additions, 
 
 BY ROBERT BRIDGES, M.D., 
 
 Professor of General and Pharmaceutical Chemistry in the Philadelphia College of Pharmacy, &c. &c. 
 
 In one large duodecimo volume, sheep or extra cloth. 
 
 Though this work has been so recently published, it has already been adopted as a text-book by many of the 
 Medical Institutions throughout the country. As a work for the first cltlss student, and as an introduction to 
 the larger systems of Chemistry, such as Graham's, there has been but one opinion expressed concerning it, 
 and it may now be considered as 
 
 THE TEXT-BOOK FOR. THE CHEJfllCJtL, STUDEJTT. 
 
 " An admirable exposition of the present slate of chemical science, simply and clearly written, and display- 
 ing a thorough practical knowledge of its details, as well as a profound acquaintance with its principles. The 
 illustrations, and the whole getting-up of the book, merit our highest praise." British and Foreign Med. Rev, 
 
 " Remarkable for its clearness, and the most concise and perspicuous work of the kind we have seen, admi- 
 rably calculated to prepare the student for the more elaborate treatises." Pharmaceutical Journal. 
 
 This work of Fownes, while not enlarging on the subject as much as Graham, is far more lucid and expanded, 
 than the usual small introductory works. Persons using it may rely upon its being kept up to the day by fre- 
 quent revisions. 
 
 NEW EDITION OF GRAHAIVVS CHEMISTRY, PREPARING. 
 
 THE ELEMENTS OF CHEMISTRY. 
 
 INCLUDING THE APPLICATION OF THE SCIENCE TO THE ARTS. 
 With Numerous Illustrations. 
 
 BY THOMAS GRAHAM, F. R. S. L. and E. D., 
 
 Professor of Chemistry in University College, London, &c. &c. 
 
 SECOND AMERICAN. FROM THE SECOND ENGLISH EDITION. 
 
 WITH NOTES AND ADDITIONS BY ROBERT BRIDGES, M. D., &c. &c. 
 
 In one volume octavo. 
 
 SIMON'S CHEMM3TRY OF MAN. 
 
 ANIMAL CHEMISTRY, 
 
 WITH REFERENCE TO THE PHYSIOLOGY AND PATHOLOGY OF MAN. 
 BY DR. J. FRANZ SIMON. 
 
 TRANSLATED AND EDITED BY 
 
 GEORGE E. DAY, M. A. & L. M. CANTAB., &c. 
 
 With plates. In one octavo volume, of over seven hundred pages, sheep, or in two parts, boards. 
 
 This important work is now complete and may be had in one large octavo volume. Those who obtained the 
 first part can procure the second separate. 
 
 "No treatise on physiological chemistry approaches, in fulness and accuracy of detail, the work which 
 stands at the head of this article. It is the production of a man of true German assiduity, who has added to his 
 own researches the results of the labors of nearly every other inquirer in this interesting branch of science 
 The death of such a laborer, which is mentioned in the preface u> the work as haying occurred prematurely m 
 1842, is indeed a calamity to science. He had hardly reached the middle term of life, and yet had made himself 
 known all over Europe, and in our country, where his name has been familiar for several years as among the 
 
 most successful of the cultivators of the Chemistry of Man It is a vast repository of facts to which the 
 
 teacher and student may refer with equal satisfaction." The Western Journal of Medicine and Surgery. 
 
 "The merits of the work are so universally known and acknowledged, as to need no further commendation 
 at our hands." JV. Y. Journal of Medicine and Surgery. 
 
 THE CHEMISTRY OF THE FOUR SEASONS A NEW WORK. 
 THE CHEMISTRY OF THE FOUR SEASONS, 
 
 SPRING, SUMMER, AUTUMN AND WINTER. 
 
 AN F.SSAY PRINCIPALLY CONCERNING NATURAL PHENOMENA ADMITTING OF ILLUS- 
 TRATION BY CHEMICAL SCIENCR AND 1LLUSTR ATI NO-PASSAGES OF SCRIPTURE. 
 
 BY THOMAS GRIFFITHS, 
 
 Professor of Chemistry in the Medical College of St. Bartholomew's Hospital, &c. 
 
 In One very neat Volume, royal 12mo., of Four Hundred and Fifty large Pages, extra cloth, iMu* 
 trated urith numerous Wood-cuts. 
 
 ANSTED'S ANCIENT WORLD Just Issued. 
 
 THE ANCIENT WORLD; OR, PICTURESQUE SKETCHES OF CREATION. 
 
 BY T. D. ANSfED, M.A., F.R.S., F.G.S., &c. 
 
 PROFESSOR OF GEOLOGY IN KING'S COLLEGE, LONDON. 
 
 In One very neat volume, fine extra cloth, with about One Hundred and Fifty Illustrations. 
 The object of this work is to present to the general reader the chief results of Geological investigation in 
 simple and comprehensive manner. The author has avoided all minute details of geological formations 
 and particular observations, and has endeavored as far as possible to present striking views of the wonderl 
 results of the science, divested of its mere technicalities. The work is printed in a handsome manner, wita 
 numerous illustrations, and forms a neat volume for the centre-table. 
 
26 LEA & BLANCHARD'S PUBLICATIONS. 
 
 LECTURES ON THE OPERATIONS OF SURGERY, 
 
 AND ON 
 
 DISEASES AND ACCIDENTS REQUIRING OPERATIONS, 
 
 DELIVERED AT UNIVERSITY COLLEGE, LONDON. 
 BY ROBERT LISTON, ESQ., F. R. S., &c. 
 
 EDITED, WITH N U M E R O XI 8 ALTERATIONS AND ADDITIONS, 
 
 BY T. D. MUTTER, M.D., 
 
 Professor of Surgery in the Jefferson Medical College, Philadelphia. 
 
 In One Large and Beautifully Printed Octavo Volume* 
 
 WITH TWO HUNDRED AND SIXTEEN ILLUSTRATIONS ON WOOD. 
 
 More than one-third of this volume is by Professor Mutter, embodying elaborate treatises on 
 Plastic Operations, Staphyloraphy, Club-Foot, Diseases of the Eye, Deformities from Burns, ficc.&c. 
 
 A SYSTEM OF PRACTICAL STJRCrF*Y. 
 
 BY WILLIAM FERGUSSON, F. R. S. E. 
 
 SECOND AMERICAN EDITION, REVISED AND IMPROVED. 
 With Two Hundred and Fifty-two Illustrations from Drawings by Bagg, Engraved by Gilbert, 
 
 With Notes and Additional Illustrations, 
 
 BY GEORGE W. NORRIS.M. D., &c. 
 
 In one beautiful octavo volume of six hundred and forty large pages. 
 
 THE PRINCIPLES AND PRACTICE OP 
 
 OBSTETRIC MEDICINE AND SURGERY, 
 
 IN REFERENCE TO THE PROCESS! OF PARTURITION. 
 
 ILLUSTRATED BT 
 One hundred and forty-eight f/arg-e Figure* on 55 lithographic Plate** 
 
 BY FRANCIS H. RAMSBOTHAM, M. D., &c. 
 
 A NEW EDITION, FROM THE ENLARGED AND REVISED LONDON EDITION. 
 
 In one large imperial octavo volume, well bound. 
 
 Philadelphia, August 6th, 1845. 
 MESSRS. LEA. & BLA.NCHABD. 
 
 GENTLEMEN : I have looked over the proofs of Ramsbothara on Human Parturition, with its important im- 
 provements, from the new London edition. 
 
 This Work needs no commendation from me, receiving, as it does, the unanimous recommendation of the 
 British periodical press, as the standard work on Midwifery; "chaste in language, classical in composition, 
 happy in point of arrangement, and abounding in most interesting illustrations." 
 
 To the American public, therefore, it is most valuable from its intrinsic undoubted excellence, and as being 
 the best authorized exponent of British Midwifery. Its circulation will, I trust, be extensive throughout our 
 country. 
 
 There is, however, a portion of Obstetric Science to which sufficient attention, it appears to me, has not been 
 paid. Through you, I have promised to the public a work on this subject, and although the continued occupa- 
 tion of my time and thoughts in the duties of a teacher and practitioner have as yet prevented ihe fulfilment of 
 the promise, the day, I trust, is not distant, when, under the hope of being useful, I shall prepare an account of 
 the MECHANISM OF LABOR, illustrated by suitable engravings, which may be regarded as an addendum to the 
 standard works of Rams both am, and our own Dewees. 
 
 Very respectfully, yours, 
 
 HUGH L. HODGE, M.D., 
 Professor of Obstetrics, SfC. 8?c., in the University of Pennsylvania,. 
 
 PROFESSOR CHAPMAN'^' WORKS ON PRACTICE. 
 
 A COMPENDIUM ofLECTURES ON THE 
 
 THEORY AND PRACTICE OF MEDICINE. 
 
 DELIVERED BY PROFESSOR CHAPMAN IN THE UNIVERSITY OF PENNSYL- 
 VANIA. PREPARED, WITH PERMISSION, FROM DR. CHAPMAN'S MA- 
 
 NUSCRIPTS, AND PUBLISHED WITH HIS APPROBATION, 
 By N. D. BENEDICT, M. D. In one very neat octavo volume. 
 
 ftjT This work contains the diseases not treated of in ihe two following. 
 
 LECTURES ON THE MORE IMPORTANT DISEASES OF THE 
 
 THORACIC AND ABDOMINAL VISCERA. 
 
 Delivered in the University of Pennsylvania, by N. CHAPMAN, M. D., Professor of the Theory 
 and Practice of Medicine, &c. In one volume, octavo. 
 
 LECTURES ON THE MORE IMPORTANT 
 
 ERUPTIVE FEVERS, HEMORRHAGES AND DROPSIES, 
 
 AND ON GOUT AND RHEUMATISM, 
 
 Delivered in the University of Pennsylvania by N. CHAPMAN, M. D., Professor of the Theory 
 and Practice of Medicine, &c. &c. In one neat octavo volume. 
 
LEA & BLANCHARD'S PUBLICATIONS. 27 
 
 A NEW MEDICAL DICTIONARY. 
 In one Volume, large 12mo,, now ready, at a low price, 
 
 A DICTIONARY OF 
 
 THE TERMS USED IN MEDICINE 
 
 AND 
 
 THE COLLATERAL SCIENCES; 
 
 BY RICHARD D. HOBLYN, A. M., OXON. 
 FIRST AMERICAN, FROM THE SECOND LONDON EDITION. 
 
 REVISED, WITH NUMEROUS ADDITIONS, 
 
 BY ISAAC HAYS, M. D., 
 
 Editor of the American Journal of the Medical Sciences. 
 
 A NEW ANlHx)^^ FEVERS. 
 
 FEVERS; 
 
 THEIR DIAGNOSIS, PATHOLOGY AND TREATMENT. 
 
 PREPARED AND EDITED WITH LARGE ADDITIONS, 
 
 FROM THE ESSAYS ON FEVER IN 
 
 TWEEDIE'S LIBRARY OF PRACTICAL MEDICINE, 
 BY MEREDITH CLYMER, M. D., 
 
 Professor of the Principles and Practice of Medicine in Franklin Medical College, Philadelphia ; 
 
 Consulting Physician to the Philadelphia Hospital; Fellow of the College of Physicians , c. c. 
 
 In one octavo volume of 600 pages. 
 
 THE SURGICAL WORKS OF SIR ASTLEY COOPER. 
 
 THE ANATOMY AND SURGICAL TREATMENT OF 
 
 AIBBMHHAIL El IE IB M HA 
 
 B* SIR ASTLEY COOPER, BART. 
 
 Edited by C. ASTON KEY, Surgeon to Guy's Hospital, &c. 
 
 In one large imperial 8vo. volume, with over 130 Lithographic Figures. 
 
 ON THE STRUCTURE AND DISEASES OF THE TESTIS. 
 
 Illustrated by 120 Figures. From the Second London Edition. 
 
 BY BRANSBY B. COOPER, ESQ. 
 AND ALSO ON THE ANATOMY OF THE THYMUS GLAND. 
 
 Illustrated by fifty-seven Figures. 
 The two works together in one beautiful imperial octavo volume, illustrated with twenty-nine plates. 
 
 ANATOMY AND DISEASES OP THE BREAST, &c. 
 
 WJIS LARGE AND BEAUTIFUL VOLUME CONTAINS THE ANATOMY OF THE BREAST 
 THE COMPARATIVE ANATOMY OF THE MAMMARY GLANDS; ILLUSTRA- 
 TIONS OF THE DISEASES OF THE BREAST ; 
 
 And Twenty-five Miscellaneous Surgical Papers, now first published in a collected form. 
 
 BY SIR ASTLEY COOPER, BART., F. R. S., &c. 
 The whole in one large imperial octavo volume, illustrated with two hundred and fifty -two figures. ' 
 
 A TREATISE OS DISLOCATIONS AND FRACTURES OF THE JOINTS. 
 
 BY SIR ASTLEY COOPER, BART., F. R. S., Sergeant Surgeon to the King, &c. 
 
 A New Edition much enlarged ; 
 
 EDITED BY BRANSBY COOPER, F. R. S., Surgeon to Guy's Hospital. 
 With additional observations from Professor JOHN C. WARREN, of Boston. 
 
 Witfc numerous Engravings on Wood, after designs by Bagg, a Memoir and a splendid Portrait of Sir Astley 
 
 In one octavo volume. 
 
LEA & BLANCHARD'S PUBLICATIONS. 
 
 OTHER WORKS 
 
 VARIOUS DEPARTMENTS 
 MEDICINE AND SURGERY, . 
 
 PUBLISHED 
 
 BY LEA & BLANC HARD. 
 
 AMERICAN JOURNAL OF THE MEDICAL SCIENCES. Edited by Isaac Hays, M.D. 
 Published quarterly at $5 00 per annum. 
 
 ANDRAL ON THE BLOOD. Pathological Haematology ; an Essay on the Blood in Dis- 
 ease. Translated by J. F. Meigs and Alfred Stille. In one octavo volume, cloth. 
 
 ARNOTT'S PHYSICS. The Elements of Physics in plain or non-technical language. A 
 New Edition. Edited by Isaac Hays, M. D. In 1 vol. 8vo., sheep, with 176 wood-cuts. 
 
 ABERCROMBIE ON THE STOMACH. Pathological and Practical Researches on Dis- 
 eases of the Stomach, Intestinal Canal, &c. Fourth Edition. In 1 vol. 8vo., sheep. 
 
 ABERCROMBIE ON THE BRAIN. Pathological and Practical Researches on the Dis- 
 eases of the Brain and Spinal Cord. A New Edition. In one octavo volume, sheep. 
 
 ALISON'S PATHOLOGY. Outlines of Pathology and Practice of Medicine. In three 
 parts, containing Preliminary Observations, Inflammatory and Febrile Diseases, and 
 Chronic or Non-Febrile Diseases. In one neat octavo volume, sheep. 
 
 BENNET'S PRACTICAL TREATISE ON INFLAMMATION, ULCERATION AND 
 INDURATION OF THE NECK OF THE UTERUS. In one small 12mo. volume, 
 cloth. 
 
 BIRD ON URINARY DEPOSITS. Urinary Deposits, their Diagnosis, Pathology and The- 
 rapeutical Indications. In one neat octavo volume, cloth, with numerous wood-cuts. 
 
 BERZELIUS ON THE KIDNEYS AND URINE, in 1 vol. 8vo., cloth. 
 
 BUCKLAND'S GEOLOGY. Geology and Mineralogy, with reference to Natural Theology. 
 A Bridgewater Treatise. In two octavo volumes, with numerous maps, plates, &c. 
 
 BUDD ON DISEASES OF THE LIVER. In one octavo volume, sheep, with beautiful 
 colored plates and numerous woodcuts. 
 
 BRIDGEWATER TREATISES. The whole complete in 7 vols. 8vo., containing Roget's 
 Animal and Vegetable Physiology, in 2 vols., with many cuts; Kirby on the History, 
 Habits and Instinct of Animals, 1 vol. with plates ; Prouton Chemistry; Chalmers on the 
 Moral Condition of Man; Whewell on Astronomy ; Bell on the Hand; Kiddon the Phy- 
 sical Condition of Man; and Bnckland's Geology, 2 vols., with many plates and maps. 
 
 BARTLETT'S PHILOSOPHY OF MEDICINE. Essay on the Philosophy of Medical 
 Science. In two Parts. One neat octavo volume, extra cloth. 
 
 BRIGHAM ON MIND, &c. The Influence of Mental Excitement and Mental Cultivation, 
 on Health. In one neat 12mo. volume, extra cloth. 
 
 BILLING'S PRINCIPLES OF MEDICINE. The First Principles of Medicine. From the 
 Fourth London Edition. In one octavo volume, cloth. 
 
 CARPENTER'S VEGETABLE PHYSIOLOGY. A Popular Treatise on Vegetable Phy- 
 siology. With numerous wood-cuts. In one 12mo. volume, extra cloth. 
 
 CLATER'AND SKINNER'S FARRIER. Every Man his own Farrier. Containing the 
 Causes, Symptoms, and most approved Methods of Cure of the Diseases of Horses. 
 From the 28th London Edition. Edked by Skinner. In one 12mo. volume, cloth. 
 
 CLATER AND YOUATT'S CATTLE DOCTOR. Every Man his own Cattle Doctor. 
 Containing the Diseases of Oxen, Sheep, Swine, &c. Edited by Youatt, and revised by 
 Skinner. With Wood-cuts. In one volume, 12mo. 
 
 DURLACHER ON CORNS, BUNIONS, &c. A Treatise on Corns, Bunions, the Dis- 
 eases of Nails, and the General Management of the Feet. In one 12mo. volume, cloth. 
 
 ELLIOTSON'S MESMERIC .CASES. In one octavo pamphlet. 
 
 ELLIS' FORMULARY. The Medical Formulary, being a collection of Prescriptions de- 
 rived from the Writings and Practice of the most eminent Physicians of America and 
 Europe. To which is added an Appendix, containing the usual Dietetic Preparations 
 ' and Antidotes for Poisons. By Benjamin Ellis, M. D. Eighth Edition, with extensive 
 Alterations and Additions. By Samuel George Morton, M. D. In one neat 8vo. volume. 
 
 ESQUIROL ON INSANITY. Mental Maladies, Considered in Relation to Medicine, Hy- 
 giene and Medical Jurisprudence. Translated by E. K. Hunt, M.D. &c. In 1 vol.8vo. 
 
 GUTHRIE ON THE BLADDER, &c. The Anatomy of the Bladder and Urethra, and 
 the Treatment of the Obstructions to which those passages are liable. In 1 vol. 8vo. 
 
 HARRIS ON MAXILLARY SINUS. Dissertation on the Diseases of the Maxillary Sinus. 
 In one small octavo volume, cloth. 
 
 HARRISON ON THE NERVES. An Essay towards a correct Theory of the Nervous 
 System. In one octavo volume, sheep. 
 
 HUGHES ON THE LUNGS AND HEART. Clinical Introduction to the Practice of 
 
LEA & BLANCHARD'S PUBLICATIONS. 29 
 
 Auscultation, and other Modes of Physical Diagnosis, intended to simplify the study of 
 the Diseases of the Heart and Lungs. By H. M. Hughes, M.D., &c. "in one 12mo. 
 volume, with a plate. 
 
 BASSE'S PATHOLOGICAL ANATOMY. An Anatomical Description of the Diseases 
 of the Organs of Circulation and Respiration. Translated and Edited by Swaine. In 
 one octavo volume. 
 
 INTRODUCTION TO PRACTICAL ORGANIC CHEMISTRY; based on the Works of 
 Brande. Liebig and, others. In 1 volume, 18mo., paper, price 25 cents. 
 
 INTRODUCTION TO VEGETABLE PHYSIOLOGY. With reference to the Works of 
 De Candolle, Lindley, &c. In 1 volume, 18mo., paper, price 25 cents. 
 
 KIRBY ON ANIMALS. The History, Habits and Instinct of Animals. A Bridgewater 
 Treatise. In one large volume, 8vo., with plates. 
 
 KIRBY AND SPENCE'S ENTOMOLOGY. An Introduction to Entomology ; or Elements 
 of the Natural History of Insects; comprising an Account of Noxious and Useful 
 Insects, of their Metamorphosis, Food, Stratagems, Habitations, Societies, Motions, 
 Noises, Hybernation, Instinct, &c. &c. In one large octavo volume, neat extra cloth, 
 with plates, plain or beautifully colored. From the sixth London Edition. 
 
 LAWRENCE ON RUPTURES. A Treatise on Ruptures, from the fifth London Edition. 
 In one octavo volume, sheep. 
 
 MAN'S POWER OVER HIMSELF TO PREVENT OR CONTROL INSANITY. One 
 vol. 18mo., paper, price 25 cents. 
 
 MAURY'S DENTAL SURGERY. A Treatise on the Dental Art, Founded on Actual Ex- 
 perience. Illustrated by 241 Lithographic Figures and 54 Wood-cuts. Translated by 
 J. B. Savier. In 1 octavo volume, sheep. 
 
 MULLER'S PHYSIOLOGY. Elements of Physiology. Translated by Wm. Bayly, M. D., 
 and edited and arranged by John Bell, M. D. In one large octavo volume, sheep. 
 
 PRACTICAL ORGANIC CHEMISTRY. 18mo., sewed, price 25 cents. 
 
 PROUT ON THE STOMACH. On the Nature and Treatment of Stomach and Renal 
 Diseases. In 1 octavo volume, sheep, with colored Plates. 
 
 POPULAR MEDICINE, BY COATES. In one octavo volume, sheep, with Wood-cuts. 
 
 PHILIP ON INDIGESTION. A Treatise on Protracted Indigestion. In 1 vol., 8vo. 
 
 PHILLIPS' ON SCROFULA. Scrofula, its Nature, its Prevalence, its Causes, and the 
 Principles of its Treatment. In one neat octavo volume, cloth, with a Plate. 
 
 ROGET'S PHYSIOLOGY. A Treatise on Animal and Vegetable Physiology, with over 
 400 Illustrations on Wood. In two octavo volumes, cloth. A Bridgewater Treatise. 
 
 ROGET'S OUTLINES OF PHYSIOLOGY. Outlines of Physiology and Phrenology. la 
 one large octavo volume, cloth. 
 
 RIGBY'S MIDWIFERY. A System of Midwifery. With Wood-cuts. In 1 vol. 8vo. 
 
 RICORD ON VENEREAL. A Practical Treatise on Venereal Diseases; with a Thera- 
 peutical Summary, and a Special Formulary. In 1 vol. 8vo., cloth. 
 
 ROBERTSON ON TEETH. A Practical Treatise on the Human Teeth, with Plates. One 
 small volume, octavo, cloth. 
 
 TAYLOR'S MEDICAL JURISPRUDENCE. With numerous Notes and Additions, and 
 References to American Practice and Law. By R. E. Griffith, M. D. In 1 vol., 8vo. 
 
 THE CONNECTION BETWEEN PHYSIOLOGY AND INTELLECTUAL SCIENCE. 
 1 vol. 18mo., paper, price 25 cents. 
 
 THOMPSON'S SICK ROOM, Domestic Management of the Sick Room, Necessary in Aid 
 of Medical Treatment for the cure of Diseases. Edited by R. E. Griffith, in one large 
 royal 12mo. volume, extra cloth, with Wood-cuts. 
 
 TRAILL'S MEDICAL JURISPRUDENCE. Outlines of a Course of Lectures on Medical 
 Jurisprudence. Revised, with numerous Notes. In one octavo volume, cloth. 
 
 TRIMMER'S GEOLOGY. A Text Book of Practical Geology and Mineralogy. With In- 
 structions for the Qualitative Analysis of Minerals. In one handsome octavo volume, 
 extra cloth, with 212 Wood-cuts. 
 
 WALSHE ON THE LUNGS. Physical Diagnosis of the Diseases of the Lungs. In one 
 neat 12mo. volume, extra cloth. 
 
 WILLIAMS AND CLYMER ON THE CHEST. A Treatise on the Diseases of the Re- 
 spiratory Organs, including the Larynx, Trachea, Lungs and Pleura. With numerous 
 Additions and Notes, by Meredith Clymer, M. D. In one neat 8vo. volume, with cuts. 
 
 WILSON'S DISSECTOR. THE DISSECTOR, OR PRACTICAL AND SURGICAL 
 ANATOMY. With 106 Illustrations. Modified and re-arranged by Paul B. Goddard, 
 M. D., &c. In one large royal 12mo. volume, sheep. 
 
 YOU ATT ON THE HORSE. The Horse: containing a full account of the Diseases of 
 the Horse, with their Mode of Treatment; his Anatomy, and the usual Operations per- 
 formed on him ; his Breeding, Breaking and Management ; and Hints on his Soundness, 
 and Purchase and Sale. Together with a General History of the Horse ; a Dissertation 
 on the American Trotting Horse, how Trained and Jockeyed, an account of his remark- 
 able performances; and an Essay on the Ass and the Mule. By J. S. Skinner, Assist- 
 ant Postmaster-General, and Editor of the Turf Register. In one volume, octavo, wilh 
 numerous Cuts. 
 
30 LEA & BLANCHARD'S PUBLICATIONS. 
 
 A TREATISE ON THE DISEASES OF FEMALES," 
 
 AND ON THE SPECIAL HYGIENE OF THEIR SEX. 
 
 WITH NUMEROUS WOOD-CUTS. 
 BY COLOMBAT DE L'l 8 E R E, M. D., 
 
 Chevalier of the Legion of Honor ; late Surgeon to the Hospital of the Rue de Valois, devoted to the 
 
 Diseases of Females, fyc. SfC. 
 TRANSLATED, WITH MANY NOTES AND ADDITIONS, 
 
 BY C. D. MEIGS, M. D., 
 
 Professor of Obstetrics and Diseases of Women and Children in the Jefferson Medical College, $c. <J-e. 
 In one large volume, 8vo. 
 
 OJY THE BOG. 
 
 THE DOG. 
 
 BY WILLIAM YOUATT. 
 
 WITH NUMEROUS AND BEAUTIFUL ILLUSTRATIONS. 
 EDITED BY E. J. LEWIS, M. D., &c. &c. 
 
 In One beautifully printed Volume, Crown Octavo, with Twenty Jour Plates, done up in richi 
 
 son extra cloth. 
 
 " With this explanation of his connection with the work he leaves it, in the hope that it may 
 prove of value to the sportsman from its immediate relation to his stirring pursuits; to the general 
 reader from the large amount of curious information collected in its pages; and to the MEDICAL 
 STUDENT from the light it sheds on the PATHOLOGY AND DISEASES of the dog, by which he 
 will be surprised to learn how many ills that animal shares in common with the human race." 
 EDITOR'S PREFACE. 
 
 LANDRETH'S JOHNSON'S_GARDENERS' DICTIONARY. 
 
 JUST READY. 
 
 A DICTIONARY OF MODERN GARDENING. 
 
 BY GEORGE WILLIAM JOHNSON, Esa., 
 
 Fellow of the Horticultural Society of India, &c. &c. 
 
 With One Hundred and Eighty Wood-Cuts. 
 
 EDITED, WITH NUMEROUS ADDITIONS, 
 
 BY DAVID LANDRETH, OP PHILADELPHIA. 
 
 In the American edition, many modifications and additions have been made, so as to render the work a com- 
 plete and satisfactory book of reference upon every subject connected with modern gardening in its most ex- 
 tended sense ; while great care has been exercised in adapting it to the practice of every section of this country. 
 
 Numerous wood-cut illustrations have been added, and the publishers present a beautiful volume of near 
 650 pages, in a clear but small type, well done up in extra cloth, and at a very low price. Such a work has 
 long been needed by the many persons who cannot afford to purchase the large expensive work of Loudon. 
 
 Sold by all Booksellers, Nurserymen and Seedsmen in the United States. 
 CONTENTS OF THE 
 
 AMERICAN JOURNAL OF THE MEDICAL SCIENCES, 
 
 For *fprtf, 1847. 
 
 MEMOIRS AND CASES. Art. I. History of seven cases of Pseudo-membranous Laryngitis, or True Croup. 
 By J. F. Meigs, M. D. II. Poisonous Properties of the Sulphate of Quinine. By VVm. O.Baldwin, M. D. III. 
 Removal of the Superior Maxilla for a tumour of the antrum; Apparent cure. Return of the disease. Second 
 operation. Sequel. By J. Marion Sims, M. D. [With a wood-cut] IV. Laceration of the Perineum. By John 
 P. Mettauer, M. D. V. Report of Cases treated in Cincinnati Commercial Hospital. By John P. Harrison, 
 M. D. VI. Surgical Cases. By Geo. C. Blackman, M. D. [With a wood-cut.] VII. Cases of Paralysis 
 peculiar to the Insane. By Pliny Earle, M. D. VIII. Contributions to Pathology ; being a Report of Fatal 
 Cases taken from the records of the U. S. Naval Hospital, New York. By W. S. W. Ruschenberger, M. D. 
 IX. Case of Hydrops Pericardii suddenly formed, with Remarks. By S. Jackson, M. D. X. Case of Tuber- 
 cles in the pericardium, vena cava, columnse carnese, pleura, lungs, liver, &c., with Meningitis. By J. D. 
 Trask. M. D. XI. On letting Blood from the Jugular in the Diseases of Children. By Charles C. Hildreth, 
 M.D. 
 
 REVIEW. XII. Lectures on Subjects connected with Clinical Medicine ; comprising Diseases of ttee 
 Heart. By P. M. Latham, M. D. 
 
 BIBLIOGRAPHICAL NOTICES. XIII. Green on Diseases of the Air Passages. XIV. Condie on the Diseases of 
 Children. Second edition. XV. Royle's Materia Medica and Therapeutics. Edited by Carson. XVI. Vogel's 
 Pathological Anatomy of the Human Body. Translated, with additions, by George E. Day. XVII. Trans- 
 actions of the College of Physicians of Philadelphia. From September to November, 1846, inclusive. 
 XVIII. Wharton Jones on the Principles and Practice of Ophthalmic Medicine and Surgery. Edited by 
 Isaac Hays, M. D. XIX. Wood on the Practice of Medicine. XX. Wernher's Manual of General and 
 Special Surgery. XXI. Baumgarten's Surgical Almanac for the years 1&44 and 1845. XXII. Wilson's 
 System of Human Anatomy, General and Special. Third American from the third London edition. Edited 
 by Paul B Goddard, M. D. XXIII. Von Behr's Handbook of Human Anatomy, General, Special and 
 Topographical. Translated by John Birkett 
 
LEA & BLANCH ARD'S PUBLICATIONS. 31 
 
 Contents of the Medical Journal Continued. 
 QUARTERLY RETROSPECT, 
 
 A SUMMARY OF THE IMPROVEMENTS AND DISCOVERIES IN THE MEDICAL SCIENCES 
 
 FOREIGN INTELLIGENCE ANATOMY AND PHYSIOLOGY!. Quelcett on Intimate Structure of Bone. 2. Meckel 
 on Process of Secretion. 3. Blondloton the Properties of the Bile. 4. Bainbriggeon Supplementary Spleen, 
 death from the patient being placed in the supine position. 5. Robinson on the Nature and Source of the 
 contents of the Fcetal Stomach. 6. Prof. Bischoffon ihe Absorption of Narcotic Poisons by the Lymphatics. 
 
 MATERIA MEDICA AND PHARMACY. 7. Battley on Syrup of Iodide and Chloride of Iron. 8. Ricord on Bro- 
 mide of Potassium as a substitute for the Iodide. 9. Voillemier on Santonine. 10. Guibourt on the changes 
 of composition which the Tincture of Iodine undergoes in keeping. 11. Melion on the Action of the Acetate 
 of Morphia on Children. 
 
 MEDICAL PATHOLOGY AND THERAPEUTICS AND PRACTICAL MEDICINE. 12. Bennett on Anormal Nutrition 
 and Diseases of the Blood. 13. Rostan on Acute Spinal Myelitis. 14. Rostan on Curability of Hypertrophy 
 of the Heart. 15. CVisp on Rupture of the left Ventricle of the Heart. 16. Francis on Aneurism of the Basi- 
 lar Artery. 17. Lombard's Observations on Sudden deaths, probably dependent on Diseases of the Heart 
 and large Blood-vessels. 18. Carson on Obliteration of the Vena Cava Descendens. 19. Thompson on 
 Treatment of Chronic Bronchitis and Bronchial Asthma. 20. Miihlbauer's Microscopic Researches on the 
 Absorption of Pus. 21. Briquet on Mercurial Ointment in Variola. 22. Bell on Rupture of Lateral Sinus of 
 Dura Mater. 23. Watts on Tubercles in Bones. 24. Gendrin on Hysterical Affections. 25. Cottereau's 
 Remedy for Toothache. 26. Prof Trousseau on Anatomy of Pneumonia in Infants. 27. Volz on Hooping 
 Cough an Exanthemata. 28. Crisp on Infantile Pleurisy. 29. Youl on Abscess of the Brain in a Child. 30. 
 Trousseau on the Employment of Nux Vomica in the Treatment of St. Vitus' Dance. 
 
 SURGICAL PATHOLOGY AND THERAPEUTICS AND OPERATIVE SURGERY. 31. Prof. Syme on Amputation at 
 the Shoulder Joint for Axillary Aneurism. 32. Whipple on Amputation at the Hip Joint. 33. Prof. Ehr- 
 mann on Successful Extirpation of a Polypous Tumour of the Larynx. 34. Bellingham on Compression in 
 Aneurism. 35. Orr's Case of Tracheotomy. 36. Holmes Coote on Cancer of the Breast in the Male. 37. 
 Moore on Gunshot wound of the Lung, where the ball lodged fifty years. 38. On the Employment of Iodide 
 of Potassium in the Treatment of Syphilis. 39. Application ofice in the treatmentof injuries. 40. Lenoiron 
 Ununited Fracture successfully treated by Acupuncturation. 41. Prof. Syme on Amputation of the Thigh. 
 42. Curling's Case of Fatal Internal Strangulation caused by a cord prolonged from a Diverticulum of the 
 Ileum. 43. Golding Bird and John Hilton on Case of Internal Strangulation of Intestine relieved by Opera- 
 tion. 44. Fergussonon Strangulated Congenital Hernia in an infant seventeen days old, requiring opera- 
 tion. 45. Guersant, Jr., on Surgical Treatment of Croup. 46. Geoghegan on Partial Amputation of the Foot. 
 47. Report of a Committee of the Surgical Society of Ireland, relative to the use and effects of Sulphuric 
 Ether. 
 
 OPHTHALMOLOGY. 48. Prof. Jacob on Foreign Bodies in the Eye. 49. Dixon's Remarkable Case of Injury 
 of the Eye. 50. Szokahkion Obscurations of the Cornea in their Histological relations with reference to the 
 Practice of Ophthalmic Surgery. 51. Berncastle on Amauro sis from Hydatid Cyst in the Brain. 
 
 MIDWIFERY. 52. Robiguet on Remarkable case of spontaneous rupture of the Uterus during labour Re- 
 Chaptois* Case of Vaginal Entero-hysterocele reduced by taxis, and maintained in place 
 
 covery. 53. Le 
 
 by the introduction of sponges in the Vagina. 54. Kuhne on Rupture of the Uterus abdominal section 
 recovery. 55. Czajewski on Wound of the Gravid Uterus premature delivery peritonitis recovery. 56. 
 Bennett on Inflammatory Ulceration of the Cervix Uteri during Pregnancy, and on its Influence as a Cause 
 of Abortion. 57. Caesarian Operation performed by Mr. Skey, at St. Bartholomew's Hospital, the patient 
 being rendered insensible by ether. 58. Pochhammer on Congenital protrusion of the Liver through the 
 umbilical ring. 59. Caesarian Section. 60. Roux on Lacerated Perineum. 61. Depaul on Asphyxia neona- 
 toruin. 62. Klencke on Diet in Infancy. 
 
 MEDICAL JURISPRUDENCE AND TOXICOLOGY. 63. Taylor on Contested identity determined by the teeth. 
 64. Blake on Poisons. 65. Delirium Tremens in an Infant. 66. Hamilton on the Echites Suberecta. 67. 
 Dupasquier on Vapours of Phosphorus, Lucifer Matches. 68. Thompson on the mode of testing the presence 
 of minute quantities of Alcohol. 69. Invalidity of a Contract made by a Lunatic. 70. Procuring of Abortion. 
 71. Lepage's Case of Poisoning by Arsenic relieved by the use of Magnesia. 72. Sale of Poisonous Sub- 
 stances. 
 
 MEDICAL EDUCATION. 73. The Edinburgh Statutes regarding the Degree. 74. Medical Organization in 
 Spain. 
 
 FOREIGN CORRESPONDENCE. Letters to the Editor from London. Sulphuric Ether in Surgical Operations 
 at Vienna. 
 
 AMERICAN INTELLIGENCE ORIGINAL COMMUNICATIONS. Parfcmon's Anatomical Anomaly. Tyler" 1 * Ante- 
 version of the Womb with adhesion of Os Uteri to body of 4th Lumbar Vertebra, &c. 
 
 DOMESTIC SUMMARY Beck on Effects of Mercury on the Young Subject. Brainard on Amputation for 
 Scrofulous Diseases of the Joints. Baker on Case of Vicarious Menstruation from an Ulcer on the right 
 Mamma. Allen on Singular case of laceration of the Broad Ligaments. McLean on Blindness caused by 
 the use of Sulphate of Quinine. Harrison's Speculations on the Cause of Yellow Fever. Herrickon Foreign 
 Bodies in the Organs and Tissues of the Body. Swett on Case of Empyema in which the operation for Para- 
 centesis Thoracis failed from a cause not generally noticed. M'Pheeters on Rheumatism, with Hypertrophy 
 of both eyes. Draper on the Cause of the Circulation of the Blood. Little on Ischuria Renalis. Hogan on 
 Strychnine in Chorea. Deaderick on Excision of the Inferior Maxillary Bone for Osteo-Sarcoma. Cain on 
 Imperforate Prepuce. Couper on Medical Schools of the United States. Warren on Inhalation of Ether. 
 Burwell on Absence of one Kidney. Brainard on Dislocation of the Elbow. Gilman on Presentation of 
 the shoulder, prolapsed Cord, cord not pulsating, yet child born alive. National Medical Convention. 
 Delegates to National Medical Convention. Arrangements for the Meeting of the National Medical Con- 
 vention. Resignation of Professor Warren. New Medical Books. 
 
 LEA & BLANCHARD, Philadelphia. 
 
 THE TERMS ARE 
 
 For the Medical Journal and the Medical News, if paid for in advance, (owing to the time of 
 issuing this advertisement, this year, amounts remitted before the first of July will be con- 
 sidered in advance,) Five Dollars. 
 
 For the Journal only, when ordered without funds, or when paid for after the first of July, Five Dollars 
 For the Medical News only, to be paid for free of postage, and always in advance, - One Dollar 
 
 1C?" In no case can the N"ews be sent without pay in advance. _r"[j 
 
 Or, persons sending Ten Dollars, before next July, can have both the Journal and the News for 1847 and 
 1848, together with nine numbers of the News for 1846, containing the first 228 pages of Todd and Bow- 
 man's Physiology. 
 
 Philadelphia, May, 1847 
 

 33 LEA & BLANCHARD'S PUBLICATIONS. 
 
 Two Medical Periodicals for Five Dollars a Year, 
 
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 THE 
 
 AMERICAN JOURNAL OF THE MEDICAL SCIENCES, 
 
 EDITED BY ISAAC HAYS, M. D., 
 
 IS PUBLISHED QUARTERLY, ON THE FIRST OF JANUARY, APRIL, 
 JULY AND OCTOBER. 
 
 The number for January last contained over THREE HUNDRED large octavo pages, with two plates ; 
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 The Medical Journal is now in the twenty-ninth year of its existence, during the whole of which time it 
 has commanded the approbation of the profession at home and abroad. Appearing quarterly, its object is 
 to furnish its readers with a full and accurate resume" of all interesting investigations and discoveries made 
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 devoted to 
 
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 minent members of the profession for many years past; it then furnishes REVIEWS and BIBLIOGRA- 
 PHICAL NOTICES of all new works of interest; and lastly, it presents a very full and extended QUAR- 
 TERLY SUMMARY, consisting of a 
 
 RETROSPECT AND ABSTRACT 
 
 OF THE PROGRESS OF THE MEDICAL SCIENCES, 
 
 CAREFULLY COLLECTED FROM ALL THE 
 FOREIGN AND DOMESTIC JOURNALS. 
 
 This department is considered so practically useful, that no exertion is spared to render it as complete as 
 possible, so that both in extent and variety it may compare with any publications of a similar kind. The 
 shorter periods at which this journal appears, enables us to anticipate, by several months, from the original 
 sources, a large portion of the intelligence contained in the semi-annual publications of BR AITHWAITE 
 and RANKING, and the Annual Reports in the BRITISH AND FOREIGN MEDICAL REVIEW, DUB- 
 LIN MEDICAL JOURNAL, &c., and whateverof value is found in them, of which the original accounts 
 have not reached us, is at once taken and laid before our readers; besides much AMERICAN INTELLI- 
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 supply of this department, by purchase and exchange, are very extensive, embracing the principal Periodicals 
 of GREAT BRITAIN, FRANCE, GERMANY, DENMARK, ITALY, the EAST INDIES, &c., beside* 
 
 ALL THE AMERICAN JOURNALS: 
 
 And especial attention will be given to make it as complete a digest as possible, of all the 
 
 IMPROVEMENTS AND DISCOVERIES IN MEDICAL SCIENCE. 
 Besides this, subscribers have the advantage of 
 
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 PHYSIOLOGICAL ANATOMY AND PHYSIOLOGY OF MAN, 
 
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|C29c 
 1847 
 
 Carpenter, W.B. 65113 
 Principles of human 
 iology- 3d American- 
 ed.