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THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 MRS. PRUDENCE W. KOFOID 
 
ELEMENTS 
 
 PHYSIOLOGY; 
 
 AN ACCOUNT OF THE LAWS AND PRINCIPLES 
 OF THE ANIMAL ECONOMY, 
 
 ESPECIALLY IN REFERENCE TO THE 
 
 CONSTITUTION OF MAN. 
 
 THOMAS JOHNSTONS AITKIN, M.D., F.R.C.S.E. 
 
 LECTURER ON PHYSIOLOGY AND ON MATERIA MEDICA 5 MEMBER OF THE MED1CO- 
 
 CHIRURGICAL SOCIETY ; EXTRAORDINARY MEMBER OF THE ROYAL 
 
 MEDICAL SOCIETY ; FORMERLY PRESIDENT OF 
 
 THE ROYAL PHYSICAL SOCIETY, 
 
 &C. &C. &C. 
 
 Shall the work say of him that made it, He made me not ?" 
 
 LONDON : 
 PRINTED FOR SCOTT, WEBSTER, AND GEARY, 
 
 36 CHARTERHOUSE SQUARE. 
 
 1838. 
 
EDINBURGH : 
 PRINTED BY W, BURNBSS. 
 
As 
 
 PREFACE. 
 
 A KNOWLEDGE of the structure of the human body 
 cannot but be considered by every cultivated, intel- 
 ligent, and inquiring mind, as a most desirable ac- 
 quisition. In tracing the many curious contrivances 
 which are exhibited in its organization, in perceiving 
 the admirable adaptation of its parts to the perfor- 
 mance of their varied offices, and in viewing the 
 whole series of its organs in their mutual relation 
 and subserviency, one exercises the highest faculties 
 of his mind, and acquires information that may be 
 useful in life. Indeed, so obvious is the importance 
 of an acquaintance with the mechanism of our bodily 
 frame, that one, viewing the subject in a general 
 sense, might naturally wonder why Anatomy and 
 Physiology are not considered as indispensable ele- 
 ments of education. 
 
 The object of the present work is to give such 
 an account of the structure of the animal body, and 
 
IV PREFACE. 
 
 especially of that of man, as well as of the man- 
 ner in which the various parts of the machinery 
 operate, as may be readily understood hy those who 
 may not previously have directed their attention to 
 investigations of this kind. Science is enriched with 
 several works of great merit on these subjects ; but 
 they either are exclusively intended to exhibit a 
 minute and detailed description of the organization, 
 in order to adapt them to the use of persons who, 
 from their profession, necessarily require an intimate 
 knowledge of the size, proportion, and relative situ- 
 ation of the different parts of the body ; or else they 
 treat of the functions in such a manner as can only 
 be properly understood by those who have previously 
 obtained considerable acquaintance with the struc- 
 ture. The descriptions, moreover, although suffi- 
 ciently clear and explicit to those who are familiar 
 with such subjects, are generally loaded with techni- 
 calities, and the allusions and illustrations, though 
 readily understood and appreciated by the initiated, 
 are but little adapted to interest or instruct the gene- 
 ral inquirer. 
 
 Nothing so much distinguishes the present age as 
 the eager desire evinced by all classes of society for 
 acquiring scientific knowledge : the crowds attend- 
 ing public lectures, the number and character of 
 the works on various departments of science that 
 
PREFACE. V 
 
 daily issue from the press, and even the tone of ge- 
 neral conversation, sufficiently shew how anxiously 
 information of this kind is sought after. It has been 
 from the conviction that a work like the present is 
 needed, and not from any belief that I am especially 
 qualified for the task, that I have been induced to 
 undertake it. I have, however, endeavoured to the 
 utmost of my power to fulfil the objects in view, to 
 afford such a description of the various structures of 
 the body as may serve to convey a correct idea of 
 their organization, and to give such an account of 
 their mode of action as appears best to accord with 
 experience and observation. 
 
 The professional reader will readily perceive that 
 the descriptions are drawn directly from the objects de- 
 scribed. Indeed, that I might do justice to the sub- 
 ject, this was the only method that was left me, in 
 attempting to give to the general reader an account of 
 the intricate construction of many parts of the animal 
 machinery. It was impossible to refer to the various 
 sources of information respecting the uses and applica- 
 tions of the different parts ; since, though many of the 
 discoverers of physiological truths be well known, ap- 
 preciated, and justly venerated by the professional 
 student, still their authority and names can have but 
 little comparative interest or weight with those whose 
 attention is less directed to such inquiries. Neither 
 
VI PREFACE. 
 
 has it been deemed necessary to cite the different 
 views taken as to the use and modes of action of the 
 various organs, nor particularly to insist upon the 
 reason why the opinion adopted has been preferred. 
 
 Were mankind a little better informed than they 
 generally are of the constitution of their own bodies, 
 and knew how fearfully and wonderfully they are 
 made, they would be more careful in avoiding causes 
 that tend to disturb and derange the functions; that 
 induce painful and incurable maladies ; that contri- 
 bute to shorten the limited period of human life : and 
 we should have fewer miserable and deluded dupes 
 of ignorant pretension and impudent quackery. 
 
CONTENTS. 
 
 INTRODUCTION. 
 
 General Observations Classification of Functions Conservative 
 Functions Circulation of the Blood Respiration Digestion 
 Nature and Constitution of the Blood Absorption Secretion 
 Functions of Relation Nervous System The External 
 Senses Foetal Life Concluding Remarks xv xxiv 
 
 CHAPTER I. CIRCULATION. 
 
 General View of Circulation Opinion of Hippocrates Theory 
 of Harvey Discovery of the Absorbents Structure of the 
 Heart Condition at the point of death Structure and Action 
 of the Arteries Of the Capillaries Of the Veins Operation 
 of Transfusion Heart an involuntary Organ Heart insensible 
 Effects of the Passions of the Mind Size of the Heart in 
 proportion to the other Organs Mechanical conditions of the 
 BloodVessels Circulation influenced by Respiration through 
 the Brain in the Abdomen 143 
 
Vlii CONTENTS. 
 
 CHAPTER II. RESPIRATION. 
 
 Organs of Inspiration Expiration Passages through the Dia- 
 phragm Incidental Respiration Respiration in Birds in 
 Reptiles Opinions of the Ancients as to the use of Respiration 
 Atmosphere Its Height Weight Humidity Tempera- 
 ture Composition Changes produced on the Air by breathing 
 Quantity of Water thrown off in the Breath Diminution of 
 Oxygen Increase of Carbonic Acid State of Nitrogen 
 Changes upon the Blood In Colour Density Chemical 
 Constitution Temperature and Animal Heat Source and 
 Distribution of How regulated when the Body is exposed to 
 High and to Low Temperatures Progressive Development 
 of Animal Heat in the New-born Adaptation to the Tem- 
 perature of different Climates Hybernation Voice and Speech 
 --Respiration of different Gases Asphyxia Means for restoring 
 the Functions in Suspended Animation 44115 
 
 CHAPTER III. DIGESTION. 
 
 A General Account of the Changes which the food undergoes in 
 the Digestive Organs Man a Cooking Animal Food assimi- 
 lated to the Temperature of the Body in the Mouth Teeth, 
 their Structure and Use in various Animals The Teeth of 
 Man, their Form, Number, and Structure Why there are two 
 Sets Motions of the Jaw Saliva, Composition and Use of 
 Deglutition General View of the Alimentary Canal Stomach 
 Duodenum Small Intestine Large Intestine Liver 
 Spleen Pancreas Organs of Digestion in Carnivorous Ani- 
 mals in Ruminants in Birds Digestive Apparatus of Man 
 adapted to a greater variety of Food than that of any other 
 Animal Animal Food, and its proximate principles Veget- 
 able Food, and its proximate principles One or other most 
 suitable to different climates Concentration, Variety, Con- 
 sistence, and Quantity influence the Digestibility of Food 
 
CONTENTS. IX 
 
 Condiments, Salt, Acids, Bitters, Astringents, Aromatics 
 Hunger and Thirst Chymification Gastric Juice Its pecu- 
 liar powers Chylification Biliary, Pancreatic, and Intestinal 
 Secretions Chyle absorbed, and conveyed through intricate 
 channels, becomes gradually assimilated to, and converted into 
 perfect Blood Last efforts for the Abstraction of Nourishment 
 Drinks Several substances introduced into the Circulation 
 from the Alimentary Canal without being changed . . 116185 
 
 CHAPTER IY. THE BLOOD. 
 
 Blood Physical Properties of Colour The Red Globules 
 Their Form and Constitution Smaller and more numerous iu 
 Mammalia Odour Characteristic of the Animal to which it 
 belongs Consistence Temperature Specific Gravity- -Quan- 
 tity of in the Body Coagulation Relative Proportion of Se- 
 rum and Clot Serum Fibrin Oil of the Blood Table of 
 Analysis of Vital Properties 186-201 
 
 CHAPTER V. ABSORPTION. 
 
 Purposes served by the function of Absorption Absorption from 
 the Skin From Mucous Membranes From Serous Mem- 
 branes From Cellular Tissue From the Surfaces of the Joints 
 Interstitial Absorption Its importance in carrying off the 
 old worn-out particles, and consequent subservience to the 
 renewal of the different parts of the body Special Organs of 
 Absorption Discovery of Controversies respecting Lacteals 
 and Lymphatics Their excessive number Lymphatic Glands 
 Their Office Case of puncture from Dissection Endosmose 
 and Exosmose Venous Absorption Causes influencing Ab- 
 sorption Causes which tend to increase or diminish the risk 
 from exposure to contagious Diseases 202232 
 
CONTENTS. 
 
 CHAPTER VI. SECRETION. 
 
 Preliminary Observations Classification of Secretions Matter 
 of Perspiration Scarf-skin serves as a barrier between the 
 Body and the External World The vast extent of the two 
 general Mucous Membranes Only one Mucous Membrane in 
 Animals below the class of Mammalia Gaseous Exhalations 
 Follicular Secretions Unctuous Secretion of the Skin 
 Necessity of Personal Cleanliness Liquor of the Eyelids 
 Wax of the Ears Musk, and other Odorous Secretions of 
 Animals Glandular Secretions Arrangement of the Glands 
 Tears Effects of the passions and emotions of the Mind upon 
 Lachrymal Glands Why Women and Children shed Tears 
 easily Secretions connected with Digestion adverted to 
 Structure and Use of the Kidneys The very compound nature 
 of the Urine Urine carries off the superfluous, useless, and 
 worn-out particles from the System The quantity of Urine 
 regulates the balance of Fluids in the Body Sugar in the 
 Urine Urinary Concretions Urinary Bladder its Structure 
 and Use Partly under the Control of the Will Glandular 
 Bodies, whose use has not been ascertained Interstitial Se- 
 cretion Nutrition, Growth, and Renewal of the various Tex- 
 tures of the Body 233264 
 
 CHAPTER VII. NERVOUS SYSTEM. 
 
 Introductory Remarks Hairy Scalp Skull formed of separate 
 Bones Advantages of this Construction Consists of two 
 Plates Advantages of Membranes of the Brain, and the 
 Purposes they serve Divisions of the Brain Presents one 
 Continuous Surface, without the slightest trace of Division 
 Dr Spurzheim's Demonstration of Enormous Quantity of 
 Water collected in Microscopic Observations of Bauer Of 
 Ehrenberg Structure described Evolution of the Nervous 
 System in size and complexity accompanied with Parallel 
 
CONTEXTS. XI 
 
 Advances in the Higher Instincts and Sagacity Development 
 of the Brain in the Foetus keeps pace with that of the System 
 in general Weight of the Brain in proportion to that of the 
 Body Size in proportion to the rest of the Nervous System 
 Brain the Seat of the Mind Results of Experiments on 
 Spinal Marrow, its Structure and Development Views and 
 Experiments of Sir Charles Bell Classification of the Nerves 
 Nerves of the Specific Senses Announce the properties of Ex- 
 ternal Bodies Motiferous Nerves Convey the Commands 
 of the Will Respiratory Nerves Indicate the Instinctive 
 Feelings, Passions, and Emotions of the Mind Their Uni- 
 versal Distribution Regular Double -rooted Nerves One 
 Root transmits the Mandates of the Will The other commu- 
 nicates Impressions received Ganglionic Nerves Immediate 
 Seat of Individual Vitality of the different Organs of the Body 
 Their General Connexions Universal Distribution Four great 
 Ganglionic Nervous Centres 265-339 
 
 CHAPTER VIII. SIGHT. 
 
 Arrangement of the different parts of the Apparatus of Sight 
 Appendages of the Eye The Orbit The Eyebrows The 
 Eyelashes The Eyelids and their Motions Lachrymal Ap- 
 paratus Motions of the Eyeball The Globe of the Eye cap- 
 able of Motion in every direction The Muscles by which the 
 Movements of the Eye are effected, as under the command of 
 the Will, and by Instinctive Feelings How we see an object 
 single with two Eyes Regulation of the Sphere of Vision 
 Compound Eyes of Insects Some species of Butterflies fur- 
 nished with 34,650 Eyes Squinting Various Causes of The 
 Globe of the Eye Sclerotic Coat gives protection, and affords 
 insertion to other parts Choroid Coat Furnished with a 
 Dark Secretion to absorb Light Its intimate Connexion with 
 the Retina The Iris, or Variegated Curtain The Hole in its 
 centre, the Pupil Regulates the quantity of Light admitted 
 in the Postei'ior Chamber A single object held close to one 
 Eye, several Images produced, and the object appears multi- 
 
Xll CONTENT'S. 
 
 plied Transparent parts of the Eye Aqueous Humour very 
 rapidly renewed Adaptation of the Eye to near and distant, 
 to large and minute objects Crystalline Lens Its beautiful 
 Organization Vitreous Humour The Retina the immediate 
 Organ of Sight Manner in which the Retina may see its own 
 Blood-vessels Insensibility to light at the entrance of the 
 Optic Nerve Seat of distinct Vision Curious effects from 
 indirect Vision Continuance of the Impression of Light 
 Cause of the appearance of Light when the eye is struck Re- 
 fraction of Light Short-sightedness Long-sightedness 
 Sun-beam decomposed into seven coloured rays Means by 
 which we estimate the size and distance of objects, by the 
 Visual Angle, the Intensity of Light, Shade, and Colour, and 
 by contrast with other known objects 340398 
 
 CHAPTER IX. HEARING. 
 
 Of the Nature of Sound Grave and Acute Tones Number of 
 Vibrations appreciable by the Human Ear Transmission of 
 Sounds Velocity of Sound Stethoscope Echo External 
 Ear adapted for collecting Vibrations Middle Ear or Drum 
 constructed for the Transmission and Modification of the 
 Vibrations Different Apparatus of- Internal Ear or Labyrinth 
 the immediate seat of the Sense of Hearing Construction and 
 Apparatus of General Inferences deduced from the Examina- 
 tion of the Structure as a whole .... . . 399421 
 
 CHAPTER X TOUCH. 
 
 General Observations on Touch Its universal diffusion over the 
 surface of the Body External Integument? The Scarf-skin, 
 forming the barrier between the living and the dead The 
 Mucous Web the especial seat of Colour Albinos Remark- 
 able case of a dark Hindoo becoming fair True skin, that of 
 which leather is made Its External Surface the immediate seat 
 of the Sense of Touch Tact and Touch All parts not equally 
 
CONTENTS. X1H 
 
 susceptible to the impressions of Touch Informs us of the 
 condition and properties of External Objects The most im- 
 portant Guardian of the Body Less liable to be imposed upon, 
 and to bear false witness, than the other Senses The confi- 
 dence placed in it The superiority enjoyed by Man in the 
 excellency of this Sense Case of J. Mitchell, born Blind and 
 Deaf . . . . 422-437 
 
 CHAPTER XI. SMELL AND TASTE. 
 
 Intimate connexion between Smell and Taste Not of much im- 
 portance as Intellectual Channels. SM ELL. The Nostrils 
 Confidence reposed in Smell by several of the Lower Animals 
 Its excellence in the Dog Smell in Vultures In the Raven 
 In Fishes Odours Gratification derived from Odours influ- 
 enced by Constitution, Habit, &c. Classification of Perman- 
 ence, Extent, and Divisibility of Morbid Conditions TASTE. 
 Seat of Papillae of the Tongue Savours Classification of 
 Influence of Habit Acquired Tastes Affected by the State 
 of the Stomach Morbid Conditions Gustatory Organs in dif- 
 ferent Classes of Animals The Condition of Matter necessary 
 to excite Taste . . . . 438463 
 
 CHAPTER XII. MOTION. 
 
 Organs of Motion consist of the Passive and the Active Bones 
 Their textures and various Forms Their Chemical consti- 
 tution Adaptation to the purposes they subserve Variety of 
 Connexion Gristle -Its peculiar Organization Its great elas- 
 ticity Forms the Principal Springs of the Animal Machine- 
 Subservient to Mechanical Movements Elastic Cushions 
 Ligament Its Structure A very Common Tissue in Animal 
 Bodies Presents great varieties, and subservient to many pur- 
 poses Elastic Ligamentous Tissue a substitute for Muscular 
 Power Continues its Action in the Dead Body Tendon 
 Varieties in the Form of Bears concentrated Muscular Force 
 
XIV CONTENTS. 
 
 Transfers Muscular Power Muscular Fibre Characteristic 
 Property Vital Organization Chemical Constitution Mus- 
 cular Action Changes in the State of Action and Repose 
 Exciting causes of Muscular Action The Will Instinct and 
 Sympathy Involuntary Muscular Motion Influence of Dis- 
 ease Mechanical and Chemical Excitants Remarkable Effects 
 of Galvanism on the Body of an Executed Criminal Various 
 Modifications of the Actions of Muscles in the Preservation of 
 the Attitudes, and in Performance of Motion Force of Muscles 
 How modified Muscular Vigour in Different Races 
 Duration of Action Velocity of Motion In Man In Ani- 
 mals Mutual adaptation of Structure and Function in Ani- 
 mal Bodies. .. ..464-494 
 
 CHAPTER XIIL FCETAL LIFE. 
 
 General Observations Progress of the formation of the Egg in 
 the Common Hen The Molecule All the other parts subser- 
 vient to it Incubation Formation of the Chick in the differ- 
 ent stages Membranes surrounding it in the egg Table of 
 periods of Gestation in several Mammalia The Vesicle Its 
 Passage Arrival in the Uterus Changes it undergoes through 
 the various periods of Gestation, and the Functions succes- 
 sively called into Action Respiration in the Foetus Regu- 
 lation of Temperature Secretions poured into the Alimentary 
 Canal Circulation of the Blood of the Foetus Milk Prin- 
 cipal Constituents of Proportion of these in different Animals 
 Conclusion 495514 
 
INTRODUCTION. 
 
 General Observations Classification of Functions Conservative Functions Cir- 
 culation of the Blood Respiration Digestion Nature and Constitution of the 
 Blood Absorption Secretion Functions of Relation Nervous System Ex- 
 ternal Senses Foetal Life Concluding Remarks. 
 
 THE material world around us comprises two great divi- 
 sions the organic and inorganic kingdoms of nature. 
 The latter consists of bodies whose elements are influenced 
 by the laws of attraction, repulsion, gravity, electricity, 
 and other powers, the investigation of which constitutes 
 the provinces of the chemist and natural philosopher. 
 Organic bodies, on the other hand, are endowed with 
 certain powers, in virtue of which they are enabled to re- 
 sist the influences to which mere dead matter is subject, 
 and to a certain extent to modify and control the proper- 
 ties of matter, so as to render them subservient to their 
 own preservation and development. These controlling 
 powers, laws, or properties, as they have been termed, 
 are called vital, and enable living bodies to resist the 
 mechanical and chemical tendencies of the materials of 
 their composition that, left to themselves, would subvert 
 and destroy the necessary arrangement of their organi- 
 zation. 
 
 The living organized kingdom of nature comprehends 
 two grand divisions, the animal and the vegetable ; and 
 although at the first glance there seems nothing in com- 
 mon between lordly man and the humble zoophyte, scarcely 
 distinguishable from the rock on which it is fixed, or the 
 simple lichen that clothes the aged tree, yet, on a more 
 close and patient examination, we shall find them per- 
 
XVI INTRODUCTION. 
 
 forming functions in several respects analogous to each 
 other. 
 
 The organs and functions of living bodies may be ar- 
 ranged under the four following heads : First, Those 
 that contribute to the support and preservation of the 
 individual, which may be termed the Conservative. 
 Secondly, Those whereby living bodies become affected 
 by the external objects around them; namely, of ap- 
 propriate instruments, the organs of sense, by means of 
 which they are enabled to take cognizance of the im- 
 pressions received, and the agents of locomotion, com- 
 prising together what have been called the Organs of 
 Relation. By a third set of organs, the most effectual 
 measures are provided for the permanent continuation of 
 the race. Lastly, man is possessed of faculties that en- 
 able him to trace effects to their causes, to distinguish 
 between virtue and vice, to reflect upon events that have 
 passed, to anticipate the issues of the future ; and, above 
 all, to raise his mind to the Supreme Intelligence, the 
 Cause of causes, to whom all nature owes her existence, 
 and to whom, with more or less clearness of conviction, 
 he feels conscious of responsibility. 
 
 On the present occasion our attention will be exclu- 
 sively directed to the consideration of the first two classes 
 of functions, and the machinery engaged in their perform- 
 ance, namely, the conservative, and those of relation. 
 
 In the first place, we shall examine into the distribu- 
 tion of the fluids through the different parts of the system, 
 or the Circulation of the Blood. 
 
 In considering this function, and the apparatus by which 
 it is exercised, we shall find in man, and in those animals 
 most closely allied to him in their organization, that the 
 heart is one of the most efficient agents for this purpose ; 
 that it forms, as it were, the fountain-head from which 
 issue forth the vital streams to distribute themselves 
 throughout the whole body, and to which they are again 
 returned. We shall find that by the action of one of its 
 cavities the blood is propelled into a large tubo opening 
 
INTRODUCTION. XVII 
 
 into it ; that this tube, by its divisions and subdivisions, 
 conveys the blood to every organ and every tissue, in the 
 requisite quantity, and with the due degree of force; 
 that part of the blood is deposited to effect growth and 
 renewal of their textures, part separated in the form of 
 secretions necessary for different purposes, and a third 
 portion thrown off as superfluous or deleterious, thereby 
 purifying the body. 
 
 Having been subservient to these and various other 
 functions in the system, the blood will be perceived to 
 have undergone an alteration in appearance and proper- 
 ties : from a bright vermilion hue it becomes changed to 
 a dark purple, and is rendered inadequate to the due per- 
 formance of the purposes it subserves. It is therefore re- 
 turned from all parts of the system by another set of 
 vessels, that form reiterated unions with each other, and 
 ultimately terminate by three trunks in another cavity of 
 the heart. Thus, we have two currents of blood in op- 
 posite directions, the one proceeding from the heart to 
 every part of the system, the other from all parts of the 
 system towards the heart. 
 
 In the next place, by the action of the heart it is forced 
 through the innumerable ramifications of an appropriate 
 tube through the minute tissue of the lungs, where, from 
 the influence of the atmospheric air, and by the ex- 
 trication of noxious vapours, it becomes purified, and 
 again changed in colour and properties from the dark pur- 
 ple to the vermilion red. Being thus once more prepared 
 for the various uses to which it is applied, it is conveyed 
 to the heart to be propelled to the system. 
 
 Such is the incessant course of the blood through the 
 body, from the commencement of life till its termination. 
 'Respiration is the next conservative function to which 
 we shall direct our attention. It is in a great measure 
 subservient to circulation, its chief final purpose being to 
 perfect the blood, to afford an opportunity for the escape 
 of noxious vapours from it, and to impart a portion of 
 atmospheric air necessary to its healthy constitution. 
 
XV111 INTRODUCTION. 
 
 The lungs, the organs directly subservient to this func- 
 tion, are placed without the xiavity of the chest. They 
 are of a light and spongy texture, and consist principally 
 of the ramifications of blood-vessels, along with number- 
 less air-tubes that terminate in minute cells. By the 
 alternate enlargement and diminution of the chest, the 
 air in these cells is constantly renewed, receiving from 
 the blood those vapours that are to be carried off by the 
 breath, and imparting to it those elements of its constitu- 
 tion that may be required. The chemical changes that 
 the air suffers in breathing, and the alterations the blood 
 undergoes by exposure to it in the lungs, enable us to 
 appreciate the effects that take place; while the alteration 
 produced upon the blood in the lungs, and the converse 
 change occurring in the system, furnish an explanation of 
 the curious and interesting phenomena connected with the 
 production and regulation of animal temperature. 
 
 In the alternate movements that take place in breath- 
 ing, various interesting muscular actions are called into 
 play, and numerous secondary effects result from the ex- 
 ercise of this important function. Among these the con- 
 version of air into Sound and Articulate Speech is not 
 the least curious in the contrivances by which it is ef- 
 fected. At the upper part of the windpipe is placed the 
 apparatus of voice an apparatus, as we shall find, con- 
 structed upon the principles both of the wind and of the 
 stringed instrument, while by the management of the 
 tongue, lips, and other parts, the voice is converted into 
 articulate language. 
 
 Our attention will next be directed to the function of 
 Digestion, by which food is converted into blood, in order 
 to compensate for the constant expenditure that takes 
 place. Here we shall trace the progress of the food, and 
 the various changes to which it is subjected, from its first 
 introduction into the mouth till it be converted into ar- 
 terial blood. 
 
 In the first place, we find that in the mouth it is re- 
 duced by the action of the teeth to a minute state of me- 
 
INTRODUCTION. XIX 
 
 chanical division, thoroughly intermixed and combined 
 with the salivary secretions. 
 
 It is then transferred to the stomach, where it meets 
 with a peculiar secretion termed the gastric juice, and 
 where it remains for some time, becoming converted into 
 a pultaceous mass named chyme. From the stomach the 
 chyme passes into the intestinal canal, where it is joined 
 by several fluids, such as the bile and other juices, and 
 where a nutritious fluid capable of being received into the 
 system is formed, named chyle. 
 
 The chyle is drunk up from the intestinal canal by 
 numerous minute tubes, which convey it through certain 
 bodies, termed lymphatic glands, and afterwards pour it 
 into the veins passing to the heart, in which it becomes 
 mingled with the general mass of blood ; and after trans- 
 mission to the lungs, and exposure to the air, its conver- 
 sion into arterial blood is completed. Drink?, which un- 
 dergo no change or decomposition, are introduced in a 
 more direct manner. They are immediately absorbed by 
 the veins, and thus enter at once the general mass of cir- 
 culating fluids. Various other materials, such as colour- 
 ing matter, odorjus principles, and chemical substances, 
 that resist the influence of the digestive apparatus, are 
 likewise taken up by veins, and carried through the liver, 
 so that while they are filtered through that organ, an op- 
 portunity is afforded for their partly be ng cast out along 
 with the secretion of bile. At all events, they here be- 
 come subject to intermixture with the blood, and undergo 
 modifications before their introduction into the system 
 at large. 
 
 Having taken under consideration the means by which 
 the Blood is circulated through the body, the alterations 
 it is subjected to, the manner of its purification, and the 
 mode of its formation and renewal, we shall be prepared 
 to enter upon the examination of its constitution. As 
 might be anticipated, we shall find it a very peculiar and 
 compound fluid, containing, if not all the principles, at 
 least all the elements that go to the formation of the va- 
 
XX INTRODUCTION. 
 
 rious textures of the body. That besides certain charac- 
 teristic physical properties, it displays others that neither 
 chemical nor mechanical laws can adequately account 
 for, and which it is conceived must depend upon its 
 vitality. We shall then advert to the function of Ab- 
 sorption, and endeavour to point out the means whereby 
 not only fresh materials are introduced, but also how the 
 various worn-out and decayed parts are taken up from 
 the different parts of the system. 
 
 Here we shall have to examine a subordinate set of 
 vessels that arise from every organ, and every tissue of 
 the body, of a peculiar structure, exceedingly numerous, 
 freely communicating with each other, and ultimately 
 terminating in the red veins, before these reach the heart. 
 By the action of these vessels, the Absorbents, and by 
 other means, the superfluous and decayed parts are carried 
 off, subsequently either to be renovated, or to be altoge- 
 ther rejected and cast out of the body. 
 
 The last of the conservative series of functions is Secre- 
 tion. Under this head we shall direct our attention to the 
 various fluids elaborated from the blood, and the charac- 
 ter and mode of action of the instruments by which they 
 are furnished, as well as the purposes they serve, either 
 in freeing the system from superfluous or noxious mat- 
 ters, or as they contribute to other useful ends. Some of 
 these fluids are to be considered chiefly, if not entirely, as 
 excrementitious, their evacuation being subservient to the 
 purification of the body by the removal of the decayed 
 and redundant parts. Of this kind are the vapours ex- 
 tricated from the breath, the matter of perspiration from 
 the external surface, several of the secretions poured into 
 the intestinal canal, and the urine derived from the ac- 
 tion of the kidneys. Others, again, are furnished for par- 
 ticular purposes, as the tears to moisten the eyes ; the 
 saliva to mix with the food ; the gastric juice, an impor- 
 tant agent in digestion ; the bile, to excite the intestines, 
 and to aid in the elaboration of the chyle ; and several 
 others, regarding which it is necessary not only to consider 
 
INTRODUCTION. XXI 
 
 how the secretion is furnished, and the nature of its consti- 
 tution, but likewise its application to other operations. 
 
 Lastly, since from the commencement of life to its ter- 
 mination, the component parts of the body are never the 
 same, but constantly receiving fresh accessions of matter, 
 and rejecting the old and decayed particles, numerous 
 vessels are incessantly engaged in the secretion of the 
 various textures composing the different organs of the body. 
 Thus, in bone the osseous tissue is secreted; in muscle 
 the muscular fibre; in glands their peculiar tissues, and 
 so forth. In every individual part the vessels furnish the 
 characteristic matter required in due quantity, and with 
 the necessary quickness of renewal. After examining 
 the various conservative organs and functions, we shall 
 next turn our attention to those of relation. 
 
 The Nervous System will first be taken into consi- 
 deration. In the brain we shall find the organ in which 
 mind -and matter become more immediately associated 
 with each other the especial seat of perception the 
 source from whence spring the purposes of the will the 
 throne of the intellectual powers, such as judgment, me- 
 mory, and reflection. 
 
 The nerves will be found to be subservient to various 
 purposes ; some of them belonging to the special organs 
 of sense, as sight, hearing, and smell ; others conveying 
 the commands of the will in order to bring into action 
 the muscles that obey its influence ; others transmiting to 
 the seat of perception the impressions made upon the dif- 
 ferent parts of the body; while some are connected with 
 instinctive movements ; and others, again, appear to be 
 more immediately subservient to organic life. 
 
 The knowledge we possess of the mode of action of the 
 different parts of the nervous system is less clear and de- 
 termined than of most other parts of the body. Yet 
 the functions to which they evidently contribute are of 
 such high and paramount importance :*-they are so es- 
 sential to the exercise of other organs, contribute so much 
 
XX11 INTRODUCTION. 
 
 to the combination of the different parts of the system 
 into one harmonious whole, and are so characteristic of 
 the higher organized animals, that their structure and 
 uses cannot fail to excite interest. Although, therefore, 
 we may be unable to point out the uses of the various 
 parts, we shall endeavour to give such an account of their 
 structure and distribution as may convey to the general 
 reader a correct view of the whole. At the same time 
 we shall be cautious in entering upon the merits of the 
 various discordant opinions that have been and are at 
 present entertained respecting this interesting portion of 
 the animal frame. 
 
 The organs of the five external Senses will in the next 
 place occupy our attention. The construction of these 
 instruments is so admirable, the uses of many of their parts 
 so obvious, and the beauty of the mechanism so striking, 
 that they have attracted the attention of the most super- 
 ficial observer. In tracing the connexion between the 
 mechanism and the result of its action, it will be a pleasing 
 task to point out the many evidences of design afforded, 
 the excellency of the contrivances, and how much these 
 senses contribute to the preservation, enjoyment, and 
 welfare of the animal. 
 
 The means by which animals are enabled to re-act upon 
 the external world, to perform the various motions so 
 essential to the exercise of various other functions, to 
 avail themselves of the power of locomotion, to fix their 
 attitudes, and to vary their postures and gestures, de- 
 pend upon the Muscular System ; in connexion with 
 which we shall consider the bones, the manner in which 
 they are bound together by ligaments, and several other 
 structures that contribute to these purposes. 
 
 Before leaving the animal mechanism, we shall direct 
 our attention to the various steps of its Formation and 
 Development, from its first rudimentary state, while it is 
 still connected with the parent, till its final separation 
 from the principle of life in old age, and when in death 
 
INTRODUCTION. XX111 
 
 the body is yielded up to mechanical and chemical in- 
 fluences and laws. 
 
 Many of the functions of the human body would have 
 been still unknown and unappreciated, had it not been 
 from observations made on the structures and uses of the 
 different parts in the lower animals : indeed these yet 
 afford the principal sources from whence the facts are de- 
 rived, not only for confirming what has been already 
 ascertained, but for affording the means for extending 
 physiological knowledge. The functions in the human 
 body have long ceased before we can presume to examine 
 them. But in the lower animals it is different : we are 
 able to examine them even in the living state ; we can 
 place them in various conditions best calculated to ex- 
 hibit them in action ; and, moreover, we obtain valuable 
 information from the various modifications of structures 
 as to size, proportion, and relation in the different classes, 
 orders, and families of animals. Accordingly, we shall 
 avail ourselves of these rich sources of physiological truth, 
 and advert to the numerous interesting and curious con- 
 trivances displayed in these structures, wherever they 
 seem calculated to throw light on corresponding organs 
 and functions in the human subject. 
 
 The study of no department of science affords so many 
 clear, striking, and irresistible proofs of the attributes of 
 the deity, as that which has for its object the considera- 
 tion of the animal structure, and the mode in which its 
 functions are carried on. Take, for example, any single 
 organ of the animal machinery the eye, or the ear, or the 
 organ of voice examine its mechanism, study its adap- 
 tation to the office it has to perform, observe it in opera- 
 tion ; and where can there be found more direct, more 
 explicit, and more irrefragable evidence of foresight in 
 the design, benevolence in the purpose, and wisdom in 
 the contrivance ? It is said to have been in consequence 
 of such studies that the celebrated Grecian physician and 
 philosopher Galen breaks forth in the following beautiful 
 
XXIV INTRODUCTION. 
 
 apostrophe " In explaining these things," he says, " I 
 esteem myself as composing a solemn hymn to the author 
 of our bodily frame, and in this I think there is more true 
 piety than in sacrificing to him hecatombs of oxen and 
 burnt-offerings of the most costly perfumes ; for I first 
 endeavour to know him myself, and afterwards to show 
 him to others, to inform them how great is his power, his 
 wisdom, his goodness." 
 
 However worthily Galen thus expresses himself when 
 contemplating the Great Author of all, and however far 
 in this respect he surpasses the most distinguished of his 
 heathen predecessors in a rational view of the character 
 and proper worship of the Deity, it is not to be forgotten 
 that though educated amidst the darkness of idolatry, 
 and although there be no reason to believe that he ever 
 laid aside its delusions, yet he was born in A. D. 131, at 
 Pergamos, where was established one of the seven churches 
 of Asia, and where the gospel had already widely spread. 
 It is impossible to conceive of a man of his acute, inquisi- 
 tive, and penetrating mind, with such a thirst as he dis- 
 played for the acquisition of truth, that he could have 
 overlooked, or have been altogether ignorant of the light 
 which had already begun to shine forth around him, and 
 which was to dissipate the darkness and gloom that had so 
 long overwhelmed the intellect of man, as if to show that 
 however great the original talents and endowments, how- 
 ever vast the acquirements, or however penetrating the 
 judgment, these of themselves could never have attained 
 to a just conception of the condition of man, and the true 
 character of the Creator and Preserver of the universe. 
 
 But when a knowledge of God has been obtained from 
 higher sources, how much does the contemplation of his 
 works, as displayed in the animal economy, contribute to 
 confirm the truth that is revealed ! how numerous are the 
 instances afforded of superintending providence, of infi- 
 nite power, of universal beneficence, wisdom, and fore- 
 sight! 
 
CHAPTER I. 
 
 CIRCULATION. 
 
 General View of Circulation Opinion of Hippocrates Theory of Harvey Dis- 
 covery of the Absorbents Structure of the Heart Condition at the point of 
 death Structure and Action of the Arteries Of the Capillaries Of the Veins 
 Operation of Transfusion Heart an involuntary organ Heart insensible 
 Effects of the Passions of the Mind Size of the Heart in proportion to the 
 other Organs Mechanical conditions of the Blood Vessels Circulation influ- 
 enced by Respiration through the Brain in the Abdomen. 
 
 IN all animals the blood is subjected to motion, more or 
 less rapid in each after its own kind; the agents by which 
 the motion is produced, and the channels through which 
 the blood is conveyed, being most perfectly adequate to the 
 purposes intended, and these purposes admirably adapted 
 to the circumstances under which the animal is destined 
 to be placed. In the more highly organized beings, such 
 as man, mammalia, and birds, from birth throughout 
 life, the agents which put th blood in motion are con- 
 structed upon the same general plan, and produce results 
 similar in all. An acquaintance, therefore, with the 
 structure in one species will enable us to acquire a correct 
 general notion of what obtains in the whole. The de- 
 scription we have now to submit will have especial re- 
 ference to the organs of the circulation of the blood in 
 man. These instruments are the heart, arteries, capil- 
 laries, and veins. A general view of these in the first 
 
 B 
 
2 GENERAL VIEW OF THE CIRCULATION. 
 
 place, will enable the reader fully to understand the more 
 detailed account, which it will be necessary subsequently 
 to present. 
 
 The heart is composed of four cavities or pouches, which 
 alternately receive and propel the blood. The walls form- 
 ing these pouches are composed of fleshy fibres curiously 
 interwoven. Two of the cavities are termed auricles, 
 the other two ventricles. An auricle and a ventricle 
 being placed towards the right, therefore are named the 
 right auricle and ventricle ; while the others, being placed 
 on the opposite side, are called the left. It is ascertained 
 that the blood from all parts of the body is conveyed to 
 the heart by the veins, which pour it into the right auricle. 
 The auricle throws it into the right ventricle, by which it is 
 propelled to the lungs through an artery. In consequence 
 of this artery, by its thousands of branches conveying it 
 to the lungs, it is called pulmonary. Having been ex- 
 posed to the air in the lungs, and after undergoing im- 
 portant changes, it is received by another set of vessels, the 
 pulmonary veins, which pour it into the left auricle by 
 four trunks ; the auricle then delivers it to the left ven- 
 tricle, by which it is forced into the aorta, the great 
 artery of the system, to be distributed to every part of 
 the body, there to furnish new materials to compensate 
 for that which becomes worn out to sustain the vital 
 action of the different organs of the body to supply the 
 various secretions, and maintain the vital heat. Having 
 performed these and other important purposes, it undergoes 
 a change the reverse to that which took place in the lungs. 
 While passing through the lungs one of the most evi- 
 dent changes effected upon it is from the dark purple to 
 the vermilion red, while here the converse takes place, 
 from the vermilion red to the dark purple ; after which it 
 is taken up 'by the veins to be conveyed to the right side 
 of the heart, from whence we started. This course of the 
 blood, of which the above is a general outline, is termed 
 the circulation, in which we see it flowing from all parts of 
 
GENERAL VIEW OF THE CIRCULATION. 6 
 
 the system to the right side of the heart, to be sent to the 
 lungs, and flowing from the lungs to the left side of the 
 heart, to be sent to the system, constituting what is 
 termed the complete circulation. But the lesser and 
 greater circulations are also often spoken of, the former 
 being applied to its transmission from the right to the 
 left side of the heart, through the lungs, the latter to its 
 course from the left through the 
 system to the right side again. 
 The circulation, as described, has 
 been compared to the figure of 
 eight ; the upper smaller division 
 representing the lesser, the lower 
 the greater circulation. The double 
 lines, a a, to the right, will repre- 
 sent the extent of the scarlet or 
 vermilion-coloured, and the dark FIG. i. 
 
 line, b b, the purple-coloured blood. Such is a general 
 sketch of the circulation of the blood in the most perfect 
 animals, as first ascertained and demonstrated by our 
 countryman the immortal Harvey, as he has been justly 
 termed. 
 
 That we may adequately appreciate the importance of 
 Harvey's discovery, it is necessary to consider the state of 
 knowledge previous to his time, and the important re- 
 sults which subsequently accrued to all departments of 
 the healing art. In the repugnance which every one feels 
 to the handling of the dead body, especially that of a 
 human being, there exists a powerful natural obstruction 
 to the study of the architecture of our frame, and the 
 manner in which its many curious functions are per- 
 formed a repugnance so strong that with most men it re- 
 quires no small effort of reason to overcome it, while with 
 others even the experience of years cannot entirely subdue 
 it. If to this be added religious prejudices and supersti- 
 tious fears, not altogether overcome even in these days of 
 boasted enlightenment, we shall not be surprised that the 
 
HARVEIAN THEORY OF THE CIRCULATION. 
 
 ancients knew so little, but rather that they acquired so 
 much knowledge of the structure of the body, when we 
 recollect the opinions, convictions, and practices which 
 obtained among the nations by whom the sciences were 
 first cultivated. The embalming of the dead among the 
 Egyptians, the killing of animals for food and for sacri- 
 fice, as well as the practice of auguring, in order to fore- 
 tel future events, by the inspection of the viscera of 
 animals, and sometimes it is said even of human victims, 
 have all been brought forward as means whereby a 
 knowledge of the structure was acquired. The hurried 
 manner, however, in which such investigations were ne- 
 cessarily conducted, precluded a sufficiently minute exa- 
 mination, and the w r armth of the climate presented an- 
 other difficulty. When we inquire of those among our- 
 selves who slaughter animals for our food, we find that 
 they are in reality as ignorant of the beautiful contri- 
 vances that are daily before their eyes as the mower is 
 of the structure of the grass which he cuts down, or the 
 miner of the wreck of former worlds that may lie scat- 
 tered at his feet. Need we wonder then that Hippocrates, 
 the father of medicine, who flourished in Greece about 
 four hundred years before the Christian era, believed that 
 the left side of the heart and the arteries contained air ? 
 This opinion arose from the circumstance that they are 
 found empty after death, for a reason which will after- 
 wards appear. 
 
 The celebrated Galen, who flourished about A. D. 130, 
 and who seems to have been deeply embued with the pro- 
 per spirit of philosophical investigation, though not the 
 first to suggest, was the first fully to establish the fact, 
 that the left side of the heart and the arteries contain 
 blood in the living body ; but he believed that the blood 
 flowed backwards and forwards in the same vessels, like 
 the tide upward and downward in a river. We need not 
 here advert to the torpid state of the human mind in what 
 are termed the dark ages. 
 
HARVEIAN THEORY OF THE CIRCULATION. 5 
 
 On the revival of learning, in the fifteenth century, we 
 find the learned chiefly engaged in commenting upon, 
 and blindly adopting the errors as well as the truths 
 of the Grecian sages. Bolder spirits soon began to 
 observe and think for themselves. In 1572, Fabricius, 
 then professor of anatomy at Padua, at that time the 
 most celebrated school of medicine in Europe, taught 
 the structure of the valves in the veins. Harvey, who 
 resorted to Padua for the study of medicine, was dissatisfied 
 with the explanation given of the function of these valves 
 by Fabricius. On his return to England, where he dili- 
 gently prosecuted his inquiries, being countenanced by 
 Charles the First, and allowed deer from the royal park 
 for the purposes of his investigations, he soon satisfied 
 himself respecting the course of the blood, and in 1628 
 publicly announced his great discovery. It is to be ob- 
 served that Harvey detected no new part : all the organs 
 had been named and described, most of them two thousand 
 years and all of them before he was born. The mate- 
 rials had all been collected, but hitherto no architect had 
 appeared to arrange them in order. Deductions certainly 
 had been drawn, and conclusions had been arrived at. 
 These were handed down from teacher to pupil, without 
 question or examination, till our illustrious countryman 
 burst the barriers of prejudice and dogmatism, first drew 
 the legitimate inferences, and by a strength of argument 
 and clearness of evidence which have never been surpassed, 
 established the truth of his doctrine. 
 
 It may be scarcely necessary to state that this great dis- 
 covery, this true explanation of the manner in which the 
 blood flows through every organ of our body, produced a 
 great change, nay, a complete revolution in medical opi- 
 nions and practices. But this did not occur at once : pre- 
 conceived opinions, envy, and ignorance had to be over- 
 come. He afterwards, in the language of complaint, states 
 that his discovery prejudiced him in his private interests, 
 and in the eyes of his professional brethren, none of whom 
 
6 ABSORBENTS. 
 
 above thirty-six years of age could be induced to believe in 
 the truth of the doctrine. That we may have some idea of 
 the debt of gratitude due to Harvey by posterity, it may be 
 sufficient to refer to the great changes that have taken 
 place in the performance of surgical operations, in conse- 
 quence of which much human suffering has been allevi- 
 ated, and many useful lives prolonged. 
 
 In order to avoid the mention of too many objects at 
 once, we have as yet taken no notice of a set of vessels 
 termed absorbents, of the existence of which Harvey 
 was ignorant. Indeed, he himself furnishes us with 
 a notable example of how slowly we adopt new views 
 in advanced life, and how unwilling we become of hav- 
 ing our long-cherished opinions overturned, and new 
 ones substituted in their place. In the daily waste to 
 which our bodies are subjected, there arises the necessity 
 for the introduction of new materials, which are furnished 
 by the food and drink. These, after undergoing the ne- 
 cessary processes of preparation by the digestive organs, 
 are taken up and conveyed into the general mass of cir- 
 culating fluids. Again, all the organs in our body, even 
 the hardest bones, are constantly undergoing change ; the 
 older materials are removed, and fresh ones are deposited 
 in their stead ; so that in the course of time, with perhaps 
 the single exception of the enamel of the teeth, not one 
 atom or smallest particle of matter which composed our 
 bodies a few years ago now remains in us. These old 
 worn-out particles are taken iip by appropriate vessels, 
 carried into the general circulating mass, and subsequently 
 cast out through the proper channels. Both of these of- 
 fices, that is, the introduction of new, and the removal of 
 old materials, were believed to be performed by the veins, 
 till an Italian anatomist, Acelli, on opening a live dog, 
 observed numerous small tubes conveying a whitish fluid 
 of a sw^eet taste from the intestinal tube. This was the chyle 
 or new fluid furnished by the organs of digestion, and which, 
 from its resemblance to milk, was called the lacteal fluid, 
 
STRUCTURE OF THE HEART. 7 
 
 while the vessels transmitting it were named the lacteals. 
 This discovery was announced by Acelli in the year 1 622. 
 Yet Harvey could not be induced to believe in their ge- 
 neral existence in the animal system, but continued to 
 hold by the old doctrine of venous absorption. Subse- 
 quently another set of absorbents, which, from the extreme 
 thinness and transparency of their coats, had escaped 
 notice, were discovered to arise from almost every part of 
 the body, and believed to exist universally. As they ge- 
 nerally convey a colourless fluid or lymph, they are named 
 the lymphatic absorbents. Both sets of absorbents ter- 
 minate in the veins before these pour their contents into 
 the right side of the heart. Their use and mode of 
 action will be hereafter considered under the head of ab- 
 sorption. It is necessary at present to advert to them, 
 in order that the reader may be able to understand allu- 
 sions which may be made in reference to them. 
 
 In warm-blooded animals, as man, mammalia, and 
 birds, the heart may be considered as double, the right 
 heart receiving the blood from the system at large, and 
 transmitting it to the lungs, while the left receives it 
 from the lungs, and transmits it to the system. During 
 each complete circulation, the whole mass of blood is ex- 
 posed to the influence of the air in the lungs. In cold- 
 blooded air-breathing animals, or reptiles, such as tor- 
 toises, turtles, frogs, lizards, serpents, the heart is single, 
 that is, has only one auricle and one ventricle, the auricle 
 receiving the blood both from the lungs and from the sys- 
 tem, and delivering it to the ventricle, which propels part 
 to the lungs and part to the system, so that a portion 
 only of the blood is exposed to the influence of the air. 
 A third modification is found in fishes : In them the heart 
 is single, as in the amphibia, but the auricle receives the 
 blood from the system only, and delivers it to the ventricle, 
 which propels it to the gills, or organs analogous to the lungs 
 of air-breathing animals. While filtered through the mi- 
 nute ramifications of the artery by which it is dispersed 
 
8 STRUCTURE OP THE HEART. 
 
 through the gills, it becomes exposed to the water, hold- 
 ing a portion of air in solution. From the gills it is col- 
 lected by numerous small vessels. These terminate in a 
 common trunk, which proceeds to transmit the blood to 
 all parts of the system, without the intervention of either 
 an auricle or a ventricle. The whole mass of blood, there- 
 fore, in each complete circulation becomes exposed to the 
 influence of the aerated water. We thus find that the 
 single heart of amphibia performs the office of both the 
 right and left heart of warm-blooded animals by a com- 
 bined action, while the single heart of fishes performs 
 that of the right only. The importance of these modifica- 
 tions will be hereafter better understood, when we come 
 to discuss the nature of the changes which the blood un- 
 dergoes in the lungs and in the system respectively, the 
 sources of animal temperature, and the rank each class 
 holds in the scale of intelligence, 
 
 As has been mentioned, the canals by which the blood 
 flows, and the direct agents of its circulation, are the 
 heart, arteries, capillaries, and veins. We shall now 
 proceed to examine each of these separately, after which 
 we shall be prepared to consider their combined opera- 
 tion. The heart is situated nearly in the centre of the 
 chest ; it is somewhat pear-shaped, with it& base or 
 broader part upwards, inclining backwards, and to the 
 right, its apex er point being forwards, and to the left. 
 In consequence of the apex being more superficial, and 
 less covered by the lungs, its beating is found under the 
 fifth left rib, hence the popular opinion that it is placed 
 in the left side. It is a powerful and very peculiarly 
 constructed muscle, or rather a combination of muscles, 
 the fibres of which are intricately interwoven with each 
 other. Externally, it is covered by a dense membrane, 
 which firmly adheres to the substance of the heart, 
 and is reflected, so as to form a capsule or bag. The inter- 
 nal surface of this capsule constantly exhales a thin watery 
 vapour, which preserves the surfaces moist and slippery, 
 
STRUCTURE OF THE HEART. 9 
 
 whereby the incessant motions of the heart are facilitated, 
 and the effects of friction obviated. The internal cavities 
 of the heart, and indeed the internal surfaces of all the 
 blood-vessels, are similarly dense and smooth, and in a 
 like manner bedewed with moisture, so that the blood 
 glides along, meeting with the least possible resistance. 
 The right auricle, which receives the blood brought by 
 the veins from all parts of the system, is placed on the 
 upper and right side' of the heart. On slitting it open 
 tlie termination of the two great veins of the body are 
 readily perceived. They are termed the superior and in- 
 ferior cavae, or great hollow veins. The former returns 
 the blood from the head, superior extremities, .and chest ; 
 the latter from the lower parts of the body. A third pours 
 in the blood which had circulated through the substance 
 of the heart itself, this being the only one of the three 
 furnished with a valve for the prevention of the return 
 of the blood when the auricle exerts its expulsive force. 
 A fourth wide orifice communicates with the right ven- 
 tricle, named the right auriculo-ventricular opening. 
 
 Let us now consider what occurs in the action of these in 
 the living state. The three veins just mentioned pour the 
 blood into the auricle until it has reached that degree of 
 distension at which contractile or expulsive power is ex- 
 cited. On . this being exerted, at first sight there is no- 
 thing to prevent the blood from being thrown back again 
 into the veins, excepting in that from the heart, which pos- 
 sesses a valve. The constant current of blood in the 
 cavae, however, will oppose this return ; and what is 
 more, there is no impediment to its passage into the right 
 ventricle, but rather it is solicited or drawn into the ven- 
 tricle by a power which must here be explained, a 
 power which furnishes us with one of the innumerable 
 striking examples of the vast superiority of living me- 
 chanism over any thing that the ingenuity and patient 
 industry of men can accomplish. The cavities of the 
 heart are not only endowed with the property of con- 
 
 B2 
 
10 STRUCTURE OF THE HEART. 
 
 traction, so as to expel their contents like a forcing 
 pump, but likewise with the property of dilatation, so as 
 to a certain extent to draw the blood into them like a 
 sucking pump. It must be borne in recollection that the 
 expansion of these cavities is not passive, but active ; 
 that is, they are not expanded in consequence of the blood 
 poured into them, but they dilate that they may receive 
 the blood. Hence it follows that while the right auricle 
 is contracting so as to force out the blood, the right ven- 
 tricle is dilating in order to receive it. We may have a 
 good example of this active power of dilatation in cold- 
 blooded animals, such as a turtle or shark, where, on the 
 removal of their heart immediately on capture, it con- 
 tinues to dilate and contract for many hours after, even 
 when thus detached, and altogether empty ; and if we 
 grasp it with our hand, we shall experience convincing 
 proof that it is by no means passive during dilatation. 
 Were it not that the different parts of the heart thus 
 beautifully co-operate to bring about the same end, the 
 languid current of blood in the veins might not be able 
 to overcome the passive contracted state of the auricle, 
 nor the comparatively weak contractile power of the auri- 
 cle to force it into the more muscular ventricle. But no 
 such want of adjustment exists in this machinery, for all 
 its parts harmoniously work together for the intended 
 purposes. 
 
 The right ventricle, which receives the blood de- 
 livered over to it by the auricle, is placed on the right, 
 inclining forwards. On opening it a very beautiful val- 
 vular apparatus will be found, named tricuspid, command- 
 ing the auriculo-ventricular opening : it is composed of 
 a fold of the dense lining membrane. Into the margin of 
 this fold are fixed several threadlike cords or tendons, 
 which proceed from fleshy bundles connected with the 
 walls of the ventricle. Behind this valve, leading up- 
 wards, is placed the orifice of the pulmonary artery, 
 which distributes the blood to the lungs. Here and there, 
 
STRUCTURE OF THE HEART. 11 
 
 crossing from one part of the ventricle to another, tendin- 
 ous cords may be observed, which tend to prevent over- 
 distension, and also small transverse fleshy bundles, which 
 aid in the contraction of the ventricle. The observer will 
 remark that the walls of the ventricle are thicker, and al- 
 together more powerful than those of the auricle; and 
 the reason of this is obvious, for whereas the auricle has 
 merely to deliver the blood to the ventricle, the ventricle 
 has to force it through the numerous divisions and subdivi- 
 sions of the pulmonary artery. On the contraction of 
 the ventricle the fleshy parts of the valvular apparatus, 
 which are connected with, and indeed form a part of its 
 walls, are simultaneously thrown into action, so that 
 by means of the little cords the valve is so placed as 
 completely to shut the auriculo-ventricular opening, and 
 thus effectually prevent any return of the blood into the 
 auricle ; at the same time the orifice of the pulmonary 
 artery offers no obstruction, and into it the blood is pro- 
 pelled. 
 
 Now, arteries are tubes possessed of very consider- 
 able elasticity, whereby, on a fluid being thus impelled 
 into them, they admit of expansion. By the same elastic 
 power, independently of any other contractile power 
 they may possess, they act upon the column of blood 
 forced into them ; consequently, on cessation of the con- 
 traction of the right ventricle, the blood would be thrown 
 back upon it, were it not that at the orifice of the pul- 
 monary artery are placed three little valves of excellent 
 mechanical contrivance. They are of a scmilunar shape, 
 and are so named. They are lodged in slight depressions, 
 their free edges being along the sides of the artery, and 
 in the centre of the margin of each there is a small lenti- 
 cular piece of cartilage, which prevents the too close ap- 
 plication to the surface of the artery, so as to admit of 
 the entrance of the blood behind them, when it is requi- 
 site they should be raised in order to perform their office. 
 They offer no resistance to the course of the blood from 
 
12 PULMONARY ARTERIES. 
 
 the ventricle into the artery, but on the reaction of the 
 artery on the column of blood, part of the blood gets be- 
 hind these valves, and raises them, whereby a complete 
 barrier is formed, to the return of the blood into the ven- 
 tricle ; it must therefore keep its onward course through 
 the lungs. These valves act altogether mechanically, and 
 consequently act efficiently even in the dead body. If a 
 tube be put into the artery, and an attempt made to inject 
 the ventricle from it, the valves will be found immediately 
 to be raised, and thus prevent one drop from entering 
 the ventricle. There is a marked difference between the 
 semilunar and tricuspid valves ; the latter, being thrown 
 into action by its appropriate muscular fibres, does not 
 act in the dead body, but performs its office only as a 
 vital agent, and, intimately connected as it is with the 
 walls of the ventricle, it co-operates with it. On the 
 other hand, the semilunar valves arc called upon to pre< 
 vent the action of the artery from being exerted upon 
 the blood in one direction, which action is principally, if 
 not entirely, the result of mechanical elasticity. 
 
 Soon after the pulmonic artery leaves the heart it divides 
 into two, the one proceeding to the right, the other to the 
 left lung. On entering the substance of the lungs they 
 begin to send off branches, until by reiterated subdivisions 
 they ultimately become as minute as the hairs of the head, 
 and are therefore termed capillary. These capillaries either 
 communicate with the capillaries of the pulmonary, or con- 
 tinuously become the venous capillaries. It is while the 
 blood is filtered through these minute tubes, and exposed to 
 the air in the lungs, that it undergoes the important changes 
 to which we have alluded : it is here its purple colour 
 becomes scarlet, and other changes occur, which can 
 only be understood when we come to discuss respiration. 
 In the meantime, it may be mentioned that notwithstand- 
 ing the great body of blood passing through the lungs in 
 the pulmonary artery and veins for especial purposes, 
 that blood does not appear to be fitted for general 
 
LEFT SIDE OF THE HEART. 13 
 
 purposes, such as nutrition and secretion, consequently 
 other arteries and veins are distributed through the 
 lungs, to which the name bronchial is applied. After the 
 blood undergoes the change, the venous capillaries unite 
 into branches, and these into Others, until by successive 
 unions the blood is collected into four trunks, two from 
 each lung. These pour it into the left auricle, which 
 delivers it to the left ventricle, from thence to be pro- 
 pelled into the aorta, the great arterial trunk of the 
 system, by the divisions and subdivisions of which the 
 vital stream penetrates every organ and every tissue of 
 our bodies, to sustain their life, their energies, and their 
 vital warmth. It would be an unnecessary repetition 
 minutely to describe the left side of the heart, since both 
 are constructed upon the same general plan. The same 
 relation subsists between the auricle and the veins and 
 between the auricle and ventricle. A similar valvular 
 apparatus commands the left auriculo- ventricular opening 
 as on the right side. From a fanciful resemblance to a 
 bishop's mitre, it is named the mitral valve. So also are 
 there three valves to guard the entrance of the aorta, like 
 to those of the pulmonary artery these six constituting 
 all the valves belonging to the arterial system. There is 
 one circumstance which the observer will not fail to no- 
 tice, that is, how much stronger the left side of the heart 
 is than the right, especially the ventricle : its walls are 
 much thicker, their texture more dense and compact, and 
 evidently capable of a much greater degree of exertion. 
 Nor will this excite surprise, when it is recollected that 
 the right ventricle has merely to propel the blood to the 
 -lungs by tubes similar in their mode of distribution, 
 penetrating an uniform structure which performs one 
 function, and that little liable to disturbance from exter- 
 nal causes ; while the left ventricle has to force the blood 
 to the furthest extremities of the body, through every 
 variety of vascular distribution, into organs of every 
 variety of texture, where very different functions are car- 
 
14 CIRCULATION AT THE POINT OF DEATH. 
 
 ried on, and to parts where the circulation is exposed to 
 numerous external disturbing causes. Here, then, as 
 everywhere else, are the means adapted to the ends. 
 
 It has been stated that the ancients believed that the left 
 side of the heart and the arteries contained air, and that 
 this opinion arose from the circumstance of their being 
 found empty after death, while those of the right are 
 generally gorged with blood. The cavities of the left side 
 will also be found smaller than those of the right. These 
 differences appear to be best accounted for by the occur- 
 rences which take place at the point of death. Death 
 seldom occurs throughout the whole of our organs si- 
 multaneously, but one link of the chain which con- 
 nects us with life is broken after the other ; nor are the 
 approaches of death made always in the same direction, 
 sometimes one and sometimes another of the functions 
 on which life more immediately depends ceasing to per- 
 form its office before the rest, and thus commencing the 
 first part of the last inevitable scene which closes our con- 
 nexion with this world. The cessation of the blood's 
 motion is generally the last to take place, nor does it 
 occur at the same instant through the whole series of the 
 agents by which it is put in motion. Here, too, one part 
 ceases to act before another. The left side of the heart 
 and the arteries appear to be endowed with a greater de- 
 gree of vital energy and tenacity of life, for as they are 
 among the first, if not the first, to be called into opera- 
 tion at the commencement of life, so are they among the 
 last to cease action at its close. They continue to force 
 onward the blood into the passive veins, where part stag- 
 nates, and part reaches the right side. At the same time 
 the powers by which the movements essential to breathing 
 are produced begin to fail. There is now an obstruction to 
 the passage of the blood through the lungs ; it accumu- 
 lates therefore in the right side of the heart, which 
 thus dies in a state of distension, while the left ceases 
 to act in the state of contraction. In order to reverse 
 
THE AORTA. 15 
 
 these conditions in a live dog, the veins entering the 
 right auricle were tied, so as to prevent the entrance 
 of blood into the right side ; and at the same time the 
 aorta was tied, so as to prevent its escape from the left. 
 The animal thus died with the right empty, and in a state 
 of contraction, while the left was gorged, and in a state 
 of dilatation. The very reverse was now found in the 
 relative size of the two sides, the right was the smallest 
 and the left the largest. The inference therefore is, that 
 in a living healthy state both ventricles are of the same 
 capacity, and indeed this is nothing more than what 
 might have been expected ; for had it been otherwise, a 
 want of proper adjustment between the two would have 
 been the consequence. The limits of the ventricles are 
 accurately defined by the valves ; but the limits of the 
 auricles are not so well marked : they are however of at 
 least equal capacity with the ventricles. With regard to 
 the order in which they respectively contract and dilate, 
 the two auricles simultaneously perform these functions, 
 as do also the ventricles, for it will be obvious that the 
 auricle and ventricle of the same side could not well con- 
 tract or dilate at the same instant without disturbance, 
 while both auricles and both ventricles may. 
 
 Without at present entering upon other points relative to 
 the heart, we shall now follow the blood through the larger 
 circulation, so as to complete its course. The aorta arising 
 from the base of the left ventricle, ascends, inclining to the 
 right, till it reaches the upper part of the breast-bone, 
 where it makes a remarkable turn towards the left, till it 
 rests upon the third vertebra of the back. This is termed 
 its arch. It then descends through the chest, enters the 
 abdomen, continues to rest on the vertebral column, till it 
 reaches the fourth vertebra of the loins, where it divides 
 into two, a right and a left branch. The first branches 
 it gives off are two for the supply of the heart itself. 
 From the arch are given off those which proceed to supply 
 the head and upper extremities, while in its descent in the 
 
1 6 ARTERIES, 
 
 chest it gives off its streams to the walls of the chest 
 and remaining viscera. Within the abdomen, before its 
 division, it furnishes the branches which supply the 
 walls ---and viscera of that cavity ; and lastly, its divisions 
 are distributed to the contents of the lower abdomen and 
 inferior extremities. All these branches which this main 
 trunk gives off, with their numerous subdivisions, in some 
 instances even to the fifth, sixth, seventh,, and eighth divi- 
 sions, are accurately traced and named, either singly or 
 in groups, till they amount to several hundreds; and not 
 only this, but their relative position with respect to other 
 organs, the varieties in size, or mode of distribution to 
 which they are subjected, are treasured in the memory of 
 every properly-educated and accomplished professional 
 man. But the millions and millions of smaller divisions 
 which we know must exist, are far beyond the grasp 
 of our finite minds to comprehend. We know that 
 there is not a point of the various surfaces of our bodies 
 that the point of the smallest needle can penetrate with- 
 out wounding thousands of these minute tubes, and that 
 a single grain of sand is considered equal to cover millions 
 of their ultimate extremities. Need we, then, look to mi- 
 croscopic objects alone for evidence of the apparent infinite 
 minuteness of creative power ? Is there not indeed in 
 every fibre, in every tube, and in every globule of which 
 our bodies are composed, an equal evidence of the same 
 truth furnished to us ? 
 
 Arteries do not always take the most direct course to 
 their destination, but always the safest, and where they 
 are least liable to be interfered with in their office. It 
 would be difficult, if not impossible, to shew any course 
 that the aorta could have pursued, possessed of so many 
 advantages as may be shewn to result from the very 
 course which it takes, and whatever modifications and 
 deviations it may present in other animals, they will 
 always be found to be made for the best possible reasons, 
 and followed by the best possible results. In crossing 
 
STRUCTURE OF THE ARTERIES. 17 
 
 joints, the main trunk is found in the flexures, where it is 
 more safely lodged, and less liable to injury than it could 
 have been anywhere else. Of such designs the main artery 
 of the thigh may be taken as an example. Immediately 
 on escaping from the cavity of the lower abdomen it is 
 found in the front of the groin ; as it proceeds downwards 
 (where, if it continued in the same direction it would be 
 much exposed to injury), it sinks deeper, and runs in- 
 wards, so that before it reaches the knee it is found 
 behind, securely lodged in the flexure of that joint, pro- 
 tected by the projections of the bones and the hamstrings. 
 
 The arteries are not composed of one substance, but of 
 three different tissues, in concentrate layers ox coats, as 
 they are termed : the internal is smooth and lubricated 
 with thin secretion; the external is constituted of the 
 cellular or interlaced tissue, chiefly for the purpose of 
 imparting strength, and connecting them with neigh- 
 bouring parts ; the middle layer, which is the thickest, 
 is cream-coloured, disposed in fibres, and highly elastic. 
 It is upon this coat that the effect the arteries have upon 
 the motion of the blood depends. Contrary to what 
 might have at first been expected, its thickness, elas- 
 ticity, and contractile power is not in proportion to the 
 size of the artery, but it is proportionally thinner, less 
 elastic, and contractile in the larger than in the smaller. 
 
 From the properties possessed by the middle coat, 
 the blood-vessels are enabled to accommodate them- 
 selves to many varying circumstances. If we bleed an 
 animal to death, as the quantity of blood diminishes, 
 so do the arteries contract and exert a certain degree of 
 tension upon the blood they contain, and the slower the 
 blood is withdrawn, the more completely will they adapt 
 themselves to the diminished quantity, and more effec- 
 tually exert their tension upon it. Accordingly, as it is 
 frequently the object with the medical practitioner to di- 
 minish this tension in disease, he bleeds his patient from 
 a large orifice, .and sometimes opens two veins at once. 
 
18 STRUCTURE OF THE ARTERIES. 
 
 that he may gain the relaxation he desires with the 
 smallest expenditure of blood, knowing that it is not 
 so much by the quantity of blood shed, as by the effect 
 produced on the organs of circulation that advantage ac- 
 crues, and that the speedier the blood is withdrawn the 
 more certain will be the effect. When a limb is ampu- 
 tated, the thigh for example, the surgeon does not find it 
 necessary to tie many arteries : the principal branches 
 only require to b secured, the others by their contractile 
 power or tonicity, as it is called, close their cut extremi- 
 ties, and arrest the haemorrhage. In the same way, daily 
 experience teaches us that the bleeding from slight wounds 
 soon stops ; but were it not that the arteries are endowed 
 with this property, the merest scratch might prove fatal, 
 for where the vessel is so situated as that it is prevented 
 from exerting this power of contraction, alarming and even 
 fatal haemorrhage may occur from a very small twig. Thus, 
 in the extraction of a tooth the bleeding is occasionally 
 suppressed with great difficulty ; and if the tonicity be im- 
 paired, of originally deficient, patients have been known 
 to bleed to death from very slight wounds, strongly im- 
 pressing upon us how much we are indebted to this con- 
 servative power of the blood vessels. After amputation 
 all the vessels shrink to a size sufficient to exert the ne- 
 cessary tension upon the diminished quantity of blood 
 required by the stump. 
 
 Another example of adaptation to circumstances is fur- 
 nished in the operation for the disease named Aneurism, 
 in which a tumour is formed in the course of an artery, 
 and which, if left to itself, might burst and prove fatal. 
 Here the surgeon cuts down on the main artery, and 
 applies to it a ligature, so as to cut off the supply to 
 the tumour. At the place where it is tied, the vessel 
 is finally obliterated, and the tumour gradually disap- 
 pears. But how, it may be asked, is the limb below 
 the part where the main channel was closed now sup- 
 plied ? The answer is, there are numerous communica- 
 
ACTION OF THE ARTERIES. 19 
 
 tions between tlie smaller branches of arteries, so that a 
 connexion is established among them, and where the 
 principal stream is arrested, as in the instance cited, the 
 collateral branches above the stoppage enlarge, and trans- 
 mit an increased quantity, most of which passes by the 
 communicating channels into the branches beneath, which 
 also enlarge, so as soon to re-establish a sufficient supply to 
 the limb below, and this is effected in a short time. Im- 
 mediately after the operation, the limb becomes cold and 
 benumbed, but in a few days the circulation is again fully 
 established by the new course just mentioned. 
 
 So also do we perceive that the blood-vessels accommo^ 
 date themselves, one would almost think instinctively, to 
 varying circumstances. Consider how the vessels of an 
 impregnated womb not only adapt themselves to the in- 
 creased wants of the enlarged womb itself, but furnish ma- 
 terials for the developement of the young that it bears. 
 Observe how in due season the blood is determined to 
 the breasts in increased quantity, and the vessels take on 
 a new action, so as to furnish an abundant supply of rich 
 and nutritious fluid, admirably adapted to the digestive 
 powers of the new-born offspring. The annual and rapid 
 developement of the stag's horns is another striking ex- 
 ample that the blood-vessels are not passive tubes ; and, 
 in like manner, might be brought forward abundant evi- 
 dence from comparative anatomy, from various diseased 
 conditions, and from the modifications which the circu- 
 lation undergoes, so as to be suited to each part of the 
 body, according to the tissue of which it is composed, and 
 the office which it has to perform. 
 
 When, by the contraction of the left ventricle, the 
 blood is injected into the aorta, the three semilunar valves 
 are immediately raised, so as completely to resist its re- 
 turn. Besides the impetus communicated to it by the 
 force of the left ventricle, it is exposed to the grasp of 
 the arterial tension : it therefore rushes forwards along 
 the arteries. In an instant a new wave succeeds, for 
 
20 CAPILLARIES. 
 
 ventricles propel the blood from sixty to eighty times in 
 a minute. In a healthy adult wave thus succeeds wave 
 from the centre to the furthest extremities, and only be- 
 comes exhausted in the ultimate capillary branches. 
 
 It has been stated that the smaller arterial divisions 
 possess a thicker, more elastic, and contractile middle 
 coat than the larger trunks ; they are also furnished more 
 abundantly with blood, for it is to be observed that al- 
 though the blood-vessels are the channels of the blood, 
 yet they themselves require to have still smaller branches 
 distributed upon their coats. Although even the larger 
 trunks are not perhaps altogether passive agents, exert- 
 ing merely a mechanical effect upon the blood, in virtue 
 of their elasticity, yet they are not endowed with the 
 same degree of irritability and vital contractility that the 
 capillaries possess. The reason of this is partly that 
 while the trunks are subservient to the general distribu- 
 tion, the smaller branches^ and more particularly the capil- 
 laries, have to adapt themselves to the peculiar exigencies 
 and conditions of the parts to which they more immedi- 
 ately dispense it. 
 
 It has been stated that it is only the larger trunks 
 which require to be secured in a surgical operation ; 
 that the smaller branches so contract as to prevent 
 the escape of the blood. This does not arise from the 
 circumstance of the smaller column of blood which they 
 transmit, for the tension will be in the same propor- 
 tion on all the columns, of whatever size, but from the 
 circumstance of their having proportionally a greater con- 
 tractile power. Thus endowed, they readily adapt them- 
 selves to the conditions of the various parts of the system ; 
 a muscle in action requires a greater quantity of blood, 
 and receives it ; a gland is excited, and the materials are 
 at hand from which its secretion is derived ; an increased 
 quantity of blood flows to one organ, the capillaries 
 adapt themselves to the increase, as they do in other parts 
 to the diminution necessarily occurring from such deter- 
 
STRUCTURE OF THE VEINS. 21 
 
 mination. It is in the capillaries that all the phenomena 
 of growth and nutrition take place, all the secretions are 
 elaborated, and all the various tissues formed. To ven- 
 ture upon a rude comparison, the heart and larger vessels 
 are no further concerned in the various actions of the 
 capillaries than the reservoir and hydraulic apparatus of 
 a water company in a large city are with the water they 
 transmit to the manufactories, shops, and domestic abodes 
 of the consumers. 
 
 The arterial capillaries having supplied the various de- 
 mands made upon the blood, form connexions with the 
 venous capillaries, and transfer to them their contents. 
 Here the opposite change to that which is effected in 
 pulmonic capillaries takes place, and the blood changes 
 from bright scarlet to dark purple. We have seen that 
 after the blood leaves the left ventricle, it flows in the 
 arteries^from trunks to branches ; but at this point, that 
 is, at the commencement of the veins, it begins to flow 
 from branches to trunks, and continues to do so till it 
 again reaches the heart. The veins have the same num- 
 ber of coats as the arteries, but their walls are much 
 thinner, their middle coat in particular ; hence they are 
 less elastic, possess little contractility, and a subordinate 
 degree of vitality. They are larger, more numerous, 
 and collectively of much greater capacity than the ar- 
 teries. Excepting in the cavities and parts beyond the 
 control of the will, they are furnished with valves, 
 which are formed by a doubling of the inner coat, pro- 
 ducing a little pouch. Sometimes the valves are single, 
 but generally in pairs, and rarely treble ; they readily per- 
 mit the blood to flow towards the heart, but effectually 
 prevent its retrograde course. In their substance and 
 mode of action, they are similar to those of the pul- 
 monary artery and aorta, already described. They may 
 readily be seen in the arm of the living body, provided 
 it be not loaded with too much fat. When a ribbon is 
 tied round the arm, as is done in bloodletting, the veins 
 
22 VEINS. 
 
 swell, and become gorged with blood. On attempting to 
 force the blood back towards the hand, little knots are 
 seen to rise here and there, which resist its returning. 
 These are the valves. But stroke the arm upwards, and the 
 blood will flow without impediment. It was mentioned 
 that the semilunar valves of the arteries act in the dead 
 body : so do the valves of the veins ; for, like them, their 
 action depends entirely on their mechanical contrivance. 
 For this reason, the anatomist, when he wishes to fill the 
 veins with an injection, so that he may more readily trace 
 them, and obtain a preparation worthy of a place in his 
 museum, has to seek out the distant branches, and direct 
 his injection towards the heart. If it be an arm or 
 a leg that he wishes to prepare, he must find some vein 
 on the hand or foot into which he may introduce his 
 pipe, so as to throw his injection upwards. This is the 
 reason why, in anatomical collections, the veins of those 
 parts of the body furnished with valves are never minutely 
 injected. The veins of the organs contained in the cavities, 
 over the actions of which we possess no voluntary power, 
 do not require valves, and consequently have none, the 
 circulation in them proceeding in an uniform and re- 
 gular manner, and subject to no impediment or interrup- 
 tion. But in those parts which are placed under the 
 control of our will, and which we employ in so many 
 different ways, and place in such a variety of conditions 
 which impede the regular course of the blood through 
 them, and would soon render them unfit for our use, 
 they are furnished with these little valves, in number 
 and proportion suited to the occasion. 
 
 The limbs are furnished with two sets of veins, one 
 set lying immediately under the skin, the other deep 
 seated, and accompanying the arteries. In the exer- 
 cise of these organs, and consequently when the mus- 
 cles are called into action, the circulation is carried on 
 with greater vivacity. When the limbs are benumbed 
 with cold, we have recourse to exercise to excite the Ian-. 
 
PROOFS OF CIRCULATION. 23 
 
 guid circulation ; the veins, however, not possessing the 
 same irritability and vital contractility as the arteries, are 
 not so readily roused; the blood would not therefore be car- 
 ried off sufficiently rapidly were they not more numerous, 
 and of greater capacity than the arteries. Further, dur- 
 ing the exercise of our limbs, the blood does not so readily 
 flow in the deep seated parts, for the play of the muscles 
 interferes with the current ; but then there are superficial 
 channels along which it can pass with less impediment. 
 Hence the surgeon, in bleeding a patient, directs him to 
 move his fingers and grasp some object, that the blood 
 may be driven along the superficial channel from whence 
 the blood is flowing. It is chiefly the smaller arteries 
 which establish connexions with each other, but the 
 veins have free and numerous communications even in 
 their larger trunks, as may readily be seen on the back 
 of the hand, or on the fore-arm. Since veins are much 
 more liable to have their currents interrupted, when one 
 course is obstructed, another is thus ready to transmit 
 the blood onwards. 
 
 At length the blood, collected from every part of 
 the body, and conveyed by the veins, is poured into 
 the right auricle of the heart, from whence we started 
 with our description ; and from the facts which have 
 come under our consideration, can we arrive at any 
 other conclusion than Harvey did, shall we not admit 
 that such must be the circulation of the blood? The 
 two auriculo-vcntricular valves, and the perfect and prompt 
 effect of the valves of the pulmonary artery, aorta, 
 and veins, even in the dead body, permit us to arrive at 
 no other conclusion. If such as we have described be the 
 true course which the blood pursues, then must every 
 circumstance which tends to interfere with that course 
 furnish a more or less clear evidence of its truth. It is 
 unnecessary, then, to multiply evidence, by referring to 
 the different effects produced by tying arteries and 
 veins, the former swelling between the heart and the 
 
24 TRANSFUSION. 
 
 ligature, and the latter beyond the ligature ; or to wounds 
 of an artery, or of a vein, where the former is observed 
 to bleed from the orifice next to the heart, the latter 
 from that farthest from it. Nor need we advert to what 
 has been noticed under the microscope on opening live 
 animals, nor to the results of disease, since no indubi- 
 table fact has been brought to witness against the Har- 
 veian doctrine. There is, however, an operation which 
 is sometimes brought forward as a proof, which may be 
 here adverted to, on account of the curious circumstances 
 connected with it, and the wild and absurd expectations 
 that were entertained when it was first promulgated, 
 namely, the operation of transfusion, in which the blood is 
 taken from the vessels of one animal and transferred to 
 those of another. It was suggested about the middle of the 
 seventeenth century, when hopes were not entirely abolished 
 respecting the elixir vitae, which was to cure all diseases, 
 and lengthen life to an indefinite extent, and when, too, it 
 was the prevailing doctrine in the schools of medicine, that 
 disease chiefly depended on morbid conditions of the 
 blood and humours. The idea of changing the blood 
 was therefore greedily seized upon. The diseased blood 
 was to be withdrawn, and healthy blood substituted 
 in its place. That of the young and vigorous w r as to fill 
 the vessels of the old and decrepit; the peccant hu- 
 mours were to be withdrawn ; such as gave origin to 
 jaundiced jealousy, ill-natured spleen, and moping melan- 
 choly, were to be replaced by blood which might furnish 
 more laudable secretions. So far did they carry their ex- 
 travagances, that they transfused into human veins the 
 blood of calves and sheep. As might have been expected, 
 their hopes and expectations were disappointed, and not a 
 few fatal results were the consequence. But, after all, 
 were they a whit more extravagant, credulous, or stupid 
 than those of our own day, who entrust their health and 
 their lives to the St. John Longs, the homceopathists, 
 and the advertising quacks who flourish among us. Ak 
 
HEART NOT UNDER CONTROL OF THE WILL. 25 
 
 though an operation which, from the way in which it was 
 abused on its introduction at first, can only fill our minds 
 with horror, contempt, and disgust, yet in later times, 
 in the hands of the scientific, it has furnished curious 
 illustrations of some of the vital functions, and has even 
 preserved life when aid could be obtained from no other 
 source. It has been ascertained that blood may be con- 
 veyed from one animal into the vessels of those of another 
 of the same species, as from one dog into another dog, 
 without proving fatal to that into which it is transfused, 
 and thus place it in a condition of complete plethora 
 throughout the whole vascular system, therefore furnish- 
 ing an evidence for the truth of the circulation ; but if 
 the blood of an animal of a different species be intro- 
 duced, it acts as a poison, shewing that the blood varies 
 according to the animal. As a remedial measure, it has 
 preserved life when endangered from haemorrhage ; and 
 lately, when the devastating cholera was with us, warm 
 water, with the salts found in the blood dissolved in it, 
 was injected into the blood-vessels to the extent of pints 
 in quantity, in order to compensate for the inordinate 
 evacuation of the thinner part of the blood, and frequently 
 with surprising temporary beneficial results ; but expe- 
 rience soon shewed that little permanent benefit was to 
 be expected. 
 
 The heart is one of those muscles over which we pos- 
 sess no immediate control. It is only part of our frame 
 which is entrusted to our voluntary use. Whatever or- 
 gans contribute more immediately to life, and the suspen- 
 sion of whose functions, even for an instant, would put 
 a stop to the working of the machinery of our bodies, 
 and ultimately destroy animation altogether, have been 
 gifted by the benevolent Creator, with the power of 
 continuing their action during the whole course of our 
 corporeal existence. The nerves which are distributed 
 to the organs which circulate the blood belong to a 
 peculiar class, to which our Attention will be directed in 
 
EFFECTS OF THE PASSIONS OF THE MIND. 
 
 the proper place. Were we to estimate the value and 
 importance of objects by their bulk, we should be inclined 
 to suppose that the nerves of the heart are very insignifi- 
 cant. They are exceedingly minute, and can only be 
 traced by the patient perseverance of those who are dex- 
 terous in such pursuits. Yet it is through these delicate 
 hair-like threads that this organ is brought into associa- 
 tion with many others with which it is known so directly 
 to sympathize. 
 
 Whatever may be our particular views, it is admitted 
 that the brain is the more immediate link between our 
 corporeal frame and our intellectual conceptions, emo- 
 tions, and passions ; and how directly the heart sympa- 
 thizes with the brain under these conditions is known 
 to every one. It is chiefly when under the influence of 
 the passions and emotions of the mind that we feel we 
 have a heart. Under the influence of the more stormy 
 passions, it is roused to violent exertion, so as to propel 
 the blood into the sanguiferous tubes with redoubled 
 force, while under those of a depressing kind its contrac- 
 tions become vacillating, feeble, and trembling. In the 
 former instance, the blood rushes to the brain ; and add- 
 ing fuel to the flame, it infuses energy into the muscles ; 
 deeds of daring are done, and feats of strength accom- 
 plished, which, in cooler moments, could neither have 
 been contemplated nor accomplished. In the latter case, 
 from the irregular supply .of blood, the mind becomes 
 wavering and irresolute, and the muscles weak and de- 
 bilitated, making a coward of one capable of the boldest 
 determination, and a trembling poltroon of another with the 
 limbs and sinews of a Hercules. From this we may learn 
 how important, even for the sake of our bodies, it is that 
 our passions should be kept in proper subjection, and 
 how a well-regulated mind conduces to health and long 
 life. 
 
 With the lungs, the organs of digestion, and indeed 
 all the important organs o the system, the heart is 
 
HEART INSENSIBLE. 27 
 
 intimately associated by sympathy. Then, in disease 
 how many sympathies are developed, which in health 
 are overlooked. It is well known that a change upon 
 the organs of circulation is one of the most frequent 
 concomitants* of disease; so much so, that the medical 
 practitioner, perhaps more intent upon matters of impor- 
 tance than routine, would be considered as careless and 
 inattentive were he to neglect to feel the pulse, no matter 
 what disease the patient was labouring under. 
 
 Though the heart is thus easily roused by the various 
 sympathetic cords with which it is connected, yet, in the 
 healthy state, it is possessed of little or no feeling, inso- 
 much that it may be touched without any sensation 
 being communicated to the individual to whom it be- 
 longs. A patient of the great Harvey had the heart ex- 
 posed by a wound in the chest, so that it could be touch- 
 ed, and yet the patient was unaware of its being so, un- 
 less he kept his eye upon him who tried the experiment. 
 The fact coming to the knowledge of Charles I, he ac- 
 companied Harvey, that he might have personal evidence 
 of the fact. 
 
 The blood propelled from the left side of the heart does 
 not return to the right in equal periods of time, for the 
 extent of the circuits which it makes are as various as 
 are the distances to which it is sent. The first arteries 
 given off from the aorta, it has been mentioned, distribute 
 their blood to the substance of the heart itself, which is 
 soon returned to the right auricle by the vein, while the 
 vessels which transmit and return the blood to the ex- 
 tremities of the body have an extended course before 
 they complete the circuit. The nearer, therefore, any 
 organ is to the heart, and the more immediately it re- 
 ceives its blood from it, the more is it under its control 
 and influence, and the greater energy does it possess. In 
 old age, or at the point of death, when the powers of the 
 system are impaired and almost exhausted, the extremities 
 of the body are the first to suffer, and thus become cold 
 
28 QUANTITY OF BLOOD IN THE HEART* 
 
 and benumbed. In the living body the circulation already 
 begun has only to be continued. The blood-vessels are 
 already full, all the communications are open, the blood 
 is flowing in its customary channels. In these circum- 
 stances, the heart meets with comparatively little resist- 
 ance, and hence the impulse which it gives to the blood 
 is instantly felt through all the larger arterial ramifica- 
 tions, and even extends to their ultimate subdivisions, 
 though the force of the impulse in the smaller branches 
 is so much diffused, and the effects so minute, as to elude 
 the touch or the eye ; but in cases of morbid sensibility, 
 as in toothache or a whitlow, by an internal feeling we 
 are made as conscious of it as by feeling the pulse at the 
 wrist. 
 
 The quantity of blood propelled into the aorta at each 
 contraction of the left ventricle is estimated to be about 
 two ounces, and as the auricles are filled when the 
 ventricles are emptied, and conversely, four ounces will be 
 the quantity in the heart at any given time, a very small 
 portion of the whole blood in the system. The diameter 
 of the aorta is much smaller than the arterial branches 
 collectively, and the whole arterial system is of much 
 narrower capacity than that of the venous. The blood, 
 therefore, from the time it leaves the left ventricle of the 
 heart till it reaches the veins, is flowing from narrower 
 into wider channels, and consequently its velocity and 
 force will be diminished. As the veins begin to col- 
 lect themselves into trunks of smaller diameter than 
 the branches collectively, so will the current be again 
 increased as it approaches the heart, though not to any 
 considerable extent, from the free entrance it meets with 
 into the right auricle. The heart, in proportion to the 
 rest of the sanguiferous system and the body in general, 
 varies in different animals. It is larger and more power- 
 ful in courageous animals than in the timid, in those that 
 are prompt and agile in their movements than in those 
 that are slow and torpid. It varies also in the propor- 
 
PROPORTIONAL SIZE OP THE HEART. 29 
 
 tion of its size and strength in different individuals of the 
 same species ; but in man, so many moral principles, 
 from prejudice, education, and other causes, modify its 
 action, that it would be as safe a rule to draw conclu- 
 sions from the size and vigour of the limbs as to the 
 courage or cowardice of an individual, as it would be 
 from the relative size of the heart. 
 
 In youth the heart and arteries possess and exert a 
 preponderating influence over the venous system. The 
 earlier in life, the greater is this preponderance, so that 
 the growth of the body at first is rapid, and gradually 
 becomes slower, until it has reached its full develope- 
 ment. During maturity a balance is established between 
 the two systems ; whereas there is a preponderance of 
 the one or the other at the beginning or at the close. 
 In old age the power of the heart is much dimi- 
 nished, the arteries become more rigid, many of the 
 smaller tubes are obliterated, and the blood is no longer 
 propelled with that vigorous impulse which duly sus- 
 tained its course through the capillaries. The body be- 
 gins to waste, the skin becomes dry and relaxed, the 
 hair is whitened or falls off, the eyes become hollow 
 and dim, the limbs tremble, and the secretions are di- 
 minished. At the same time, blood accumulates in the 
 venous system, and slowly and languidly returns to the 
 heart ; so that through the very means by which the 
 body was built up in youth, and sustained with vigour in 
 middle life, does it become decrepit and exhausted in old 
 age, declaring to us, in language that cannot be mistaken, 
 that here we have no abiding place, that sooner or later 
 this body must crumble into dust, and be resolved into 
 the elements from which it is formed. 
 
 The quantity of blood transmitted to an organ varies 
 according to the tissue of which it is composed, and the 
 function which it has to perform. The glands which have 
 to furnish the secretions and muscles by which the vari- 
 ous motions are effected, require an abundant supply, 
 
30 MECHANISM OF THE ARTERIES. 
 
 while bones, cartilages, tendons, and ligaments receive only 
 a small quantity, and that by vessels so minute that they 
 exclude the red colouring-matter of the blood. 
 
 Besides the modifications to which the circulation of 
 blood through an organ is subjected by the number 
 and size of the vessels distributed through it, there are 
 other circumstances deserving attention, which, by their 
 mechanical contrivance, are calculated to influence the 
 force and velocity of the blood in a part. There are, 
 we conceive, five modifications of arterial distribution 
 worthy of particular notice : namely, the angle at which a 
 branch arises from the trunk ; the length and subdivision 
 of the artery ; its direction ; its union ; and lastly, the 
 formation of a net-work. We shall make a few observa- 
 tions with respect to each of these. 
 
 1st, As to the angle. It will readily be seen, on exa- 
 mining our cut, that the branches b , arising from the 
 trunk a a, pass off at an acute angle, c c at a right angle, 
 and d d at an obtuse angle. The blood, to pass into b b 
 must make a very considerable turn, and thus have its mo- 
 mentum diminished ; in c c the turn is less, and still less 
 in dd\ so that if these vessels are of the same size, and 
 distributed upon parts of the same structure and function, 
 those supplied from b b will receive it with a smaller force 
 and velocity than those supplied by d d. The conditions 
 
MECHANISM OP THE ARTERIES. 
 
 31 
 
 under Avhich they act are therefore not equal. There is a 
 beautiful example of this kind of distribution in the vessels 
 given off from the aorta to supply the walls of the chest. 
 At the commencement of the aorta the blood rushes along 
 with the full impulse communicated by the heart ; but 
 that impulse is gradually diminished. Now, if we ex- 
 amine the arteries named intercostal, which supply the 
 spaces between the ribs, particularly in an animal with 
 a long back, such as the tiger, we shall find that the first 
 arise by an acute, the middle by a right, and the lower 
 ones by an obtuse angle, so that the angle may compen- 
 sate for the difference of velocity and force, according to 
 the part from which it takes its origin. By this beau- 
 tiful contrivance the blood is distributed uniformly to all 
 those parts which have the same office to execute. 
 As to its 
 
 FIG. 3. 
 
 length and subdi- 
 vision of the ar- 
 tery. Suppose, as 
 represented in the 
 cut, #, , and c are 
 three vessels of e- 
 qual capacity, and 
 the blood propel- 
 led into them with 
 equal force, a runs 
 a short course, and divides into branches, which soon reach 
 their destination ; b is of great length before it divides, but 
 its branches soon reach their destination ; while c soon 
 divides into branches, which, however, have to run far 
 before they reach their destination. As the momentum of 
 the blood is diminished by the friction on the sides of the 
 vessels, it will be evident that in a it will be exposed 
 to less diminution than in b, and in b than in c, so that 
 the circulation will be much more retarded in c than in 
 a, for two reasons, the length of course, and the sub- 
 divisions. Animals capable of rapid motions have a rapid 
 
32 MECHANISM OF THE ARTERIES. 
 
 circulation, and the arteries are so distributed as to insure 
 it, as in a ; while animals slow in their movements have 
 the arteries which are distributed upon the muscles of 
 this slow contraction, with a distribution after the man- 
 ner of c. In the sloth, the main artery does not run 
 down the extremities in one trunk, as it generally does, 
 but is subdivided into numerous long branches. In the 
 he,dgehog the vessels which supply the muscles command- 
 ing the movements of its spine-armed skin are exceedingly 
 long. They are also very long in the intestines of the 
 pig. Now, in all these instances, the slow motions are 
 confined to the parts which have this peculiarity of dis- 
 tribution. Though the sloth moves its limbs slowly, 
 and with apparent pain and difficulty, the motions of its 
 neck and jaws are rapid and prompt. There is another 
 circumstance deserving notice, where muscular movements 
 are very rapid, they quickly alternate with relaxation, 
 and cannot continue in the state of contraction for any 
 length of time ; while in the instances referred to, they 
 are capable of remaining in that state for a very con- 
 siderable period, so that nothing could have been so well 
 adapted to the conditions of the animals referred to. 
 
 3dly, Direction. It 
 is evident if a and b are 
 of equal diameter and 
 length, and if a fluid 
 were propelled into both 
 with the same force, in 
 consequence of the ser- 
 pentine course of #, it FlG< 4 * 
 will meet with a much greater degree of resistance, and 
 have its force diminished accordingly. Now, arteries 
 are frequently thus serpentine, and even an artery nearly 
 straight will become serpentine, if forcibly injected, pre- 
 senting a beautiful provision in order to diminish force 
 under particular and accidental circumstances. This ser- 
 pentine course obtains in the arteries which enter the skull 
 
MECHANISM OP THE ARTERIES. 
 
 33 
 
 FIG. 5. 
 
 for the supply of the brain. In the horse it is more con- 
 torted than in the human subject, and he requires it to be 
 so, particularly when feeding in the fields with his head 
 in the dependent posture. Many other examples might 
 be cited, but the effect and the advantages of such a dis- 
 tribution must be sufficiently obvious. 
 
 4^, Union. The cut represents two bran- 
 ches, a a, uniting to form a third, somewhat 
 larger than either. Of this we have an ex- 
 ample in two of the vessels which enter to 
 supply the brain. If the trunk be of greater 
 capacity than the separate branches, then the 
 velocity will be diminished; but if the con- 
 verse, it will be accelerated. Another effect 
 will be produced, the pulsative motion in 
 the direction of the dotted arrows a , when the streams 
 meet, will be reduced to continuous motion in the direc- 
 tion of the arrow b. By a similar contrivance, the in- 
 terrupted impulse with which the water is forced in the 
 working of the fire-engine, issues as a continued stream 
 from the pipe with which the water is played. 
 
 Lastly, Net- work. There are several examples of this 
 kind of modification in different animals, where an artery 
 is broken up into a great many branches which form numer- 
 ous communications with 
 each other, so as to consti- 
 tute an exceedingly in- 
 volved and intricate net- 
 work. There are two 
 modifications; 1st, where, 
 as in Fig. 6, the artery, 
 , is broken up to form 
 the net-work 5, the bran- 
 ches of which are reunit- 
 ed into one trunk, c. 
 2dly, as in Fig. 7, where the vessels of the net-work, 
 1^ instead of uniting to re-form one trunk, form se- 
 
 c2 
 
 FIG. 6. 
 
 FIG. 7. 
 
34 CIRCULATION ADAPTED TO THE ORGAN. 
 
 veral, cccc. Now, it will be evident that when the main 
 stream is thus broken up, the force must be very much dif- 
 fused and diminished, and the pulsative jet must also be even 
 more effectually destroyed than in the fourth modification 
 of union. There is a net-work in the principal artery 
 which supplies the brain, as in Fig. 6, in ruminating ani- 
 mals., which, in browsing, are able to keep their heads for a 
 long time in the dependent posture without sanguineous 
 congestion, or any risk of apoplexy. Here we have even 
 a more perfect preventive of the evils which might 
 otherwise have arisen from the head being long kept in 
 the dependent position than in the horse already alluded 
 to in the third modification. The formation of the plexus, 
 according to Fig. 7> is found in the arteries of the intes- 
 tines of the pig, and the inferences which may be drawn 
 from it will be considered when we treat of the peculiari- 
 ties of circulation in the abdomen. Such are among the 
 more striking mechanical modifications to which the cir- 
 culation is subjected, modifications which we conceive 
 have not as yet received that attention to which they are 
 entitled. 
 
 Besides the general laws which affect the distribution 
 of the blood through the body, every different organ may 
 be said to have a peculiar circulation of its own, either in 
 respect to quantity, velocity, or other circumstances which 
 adjust it to its own particular conditions. It would be 
 out of place here to enter at any length into these con- 
 siderations ; but there are three situations in which the 
 peculiarities are so striking and important, that they must 
 not be overlooked. These are in the head, chest, and 
 abdomen. In bringing these under discussion, we shall 
 first treat of those of the chest. 
 
 Although the alternate contraction and expansion of 
 the chest during breathing be chiefly intended for the 
 functions exercised by the lungs, yet these two condi- 
 tions affect, to no trifling extent, both the lesser and the 
 larger circulation. With respect to the effects produced 
 
EFFECTS OF RESPIRATION. 35 
 
 upon the circulation through the lungs by the increased 
 quantity of air in the tubes and cells, the whole volume 
 of the lungs is increased ; the circulation through them is 
 promoted ; the right ventricle has less resistance to over- 
 come in propelling the blood into the pulmonary artery ; 
 it flows with greater freedom through the arterial and ven- 
 ous capillaries, and returns more readily to the left ventricle. 
 Thus, at the time when the greatest quantity of air is in 
 the lungs, at that very time the greatest quantity of 
 blood passes through them. In the opposite condition, 
 when the lungs and other viscera sustain a certain degree 
 of compression from the diminution of the capacity of the 
 chest, the passage of the blood through the lungs is im- 
 peded. There is also not the same free entrance for it 
 into the chest by the great veins, and a retardation of it 
 in the whole venous system is the consequence. During 
 ordinary respiration these effects are but momentary, and 
 so slight as to escape notice, yet they may be beneficial 
 by the alternate acceleration and retardation of the tide 
 of blood through the body, inducing a certain degree of 
 action and repose in the whole sanguiferous system. 
 
 In extraordinary cases, however, where respiration is 
 impeded, interrupted, or imperfect, the effects become pro- 
 minent, and the consequences important. Let any one 
 take in a full breath and hold it, he will in a short time 
 experience an uneasy sensation in the chest, the face will 
 become suffused, and a painful feeling of distension will 
 be experienced in the head, so as to compel him to put a 
 stop to the experiment. Again, lot him expel as much 
 air as he can from the chest, and then hold the breath, 
 he will find that in one half the time the uneasy sensa- 
 tion will be experienced, more particularly in the suffusion 
 of the face, and the feeling of distension in the head. 
 Thus it will be perceived that there is a freer passage of 
 blood into the chest, and also through the lungs, in the 
 former than in the latter condition ; for these effects arise 
 from the impediment to the blood in its return from the 
 
36 CIRCULATION THROUGH THE BRAIN. 
 
 head and face, and to its transmission through the lungs. 
 In straining, where the breath is retained after a full in- 
 spiration, and the muscles powerfully thrown into ac- 
 tion, the organs in the chest are forcibly compressed, and 
 the blood is impelled with increased force from that ca- 
 vity. The same happens when we make any violent 
 effort, as lifting a heavy load, where we take a full 
 breath, and retain it, so as to increase the power of the 
 muscles. In these cases wounds sometimes break out 
 afresh, and vessels are occasionally ruptured. This may 
 happen in the vessels of the brain, and the person fall 
 down in a fatal apoplexy. In loud and forcible speak- 
 ing, or in singing, as on the stage, there is for similar 
 reasons an impediment to the return of the blood into 
 the chest; the face becomes suffused, and the veins in 
 the neck and throat swell. In asthma, hooping-cough, 
 croup, &c. the influence of the respiratory movements 
 on the circulation of the blood is strongly displayed; 
 and at the point of death, when the breathing becomes 
 weak and interrupted, the veins of the neck will be 
 observed to swell and subside in accordance with the 
 movements of the chest to subside during inspiration, 
 and swell during expiration. In all these instances the 
 influence is extended to the circulation through the skull, 
 and will be better understood when we have explained the 
 peculiarities of the distribution of blood through that 
 cavity. 
 
 In the care bestowed for the protection of the brain 
 from external injury, by the curiously constructed case 
 in which it is contained, we have an evidence of its 
 importance in the animal economy. Soft and delicate 
 in its texture easily deranged in function requiring a 
 large supply, but impatient of superfluous accumulation 
 of blood, there are many curious contrivances to insure 
 the necessary quantity without endangering its structure 
 or disturbing its function. There are four arteries which 
 transmit blood to the brain : the two larger internal caro- 
 
CIRCULATION THROUGH THE BRAIN. 37 
 
 tids, and the two smaller vertebrals. It is returned by 
 two veins : the internal jugulars. It has been stated that 
 the arteries, on entering the skull, make a tortuous and 
 indirect entrance, so as to diminish the impetus of the 
 blood ; and that this is more particularly the case in some 
 of the lower animals, as the horse. In man, from the 
 usual position of the body when awake and in a state of 
 activity, the blood has to be propelled upwards, contrary 
 to the influence of gravity, and therefore the serpentine 
 direction to an equal extent is not required in him. The 
 effect of position upon the circulation through the head 
 must be well known to every one who has laboured under 
 headache, who will recollect how much the pain is aggra- 
 vated by stooping. This may, however, partly arise from 
 obstruction to the return by the veins, as well as from the 
 increased flow by the arteries. 
 
 In entering the skull, the carotids pass close to the 
 internal ear, so that on increased sensibility of that or- 
 gan, or inordinate excitement of the arterial pulsation, 
 their throbbing can be distinctly heard. So soon as the 
 four arteries have entered, the two vertebrals are formed 
 into one, as has been mentioned; besides, there is a 
 free communication established with each other by all 
 the four. They then begin to divide into branches, 
 which do not however enter immediately into the deli- 
 cate nervous substance of the brain, but are first minutely 
 subdivided upon a membrane which closely embraces its 
 surface, and enters between its folds. So minutely are 
 these vessels ramified before they penetrate into the ner- 
 vous matter, that few are capable of transmitting the red 
 globules of the blood ; though the larger branches freely 
 communicate before they subdivide, yet they appear to 
 form few connections in their smaller branches. If any of 
 the four trunks be obstructed, or if one of them be tied, as 
 is sometimes the case, by the surgeon, in consequence of the 
 connection among them, the blood is not cut off from the 
 branches of that which is obstructed. There is another 
 
38 CIRCULATION THROUGH THE BRAIN. 
 
 circumstance which characterizes the arteries of the brain : 
 their coats are much thinner and more delicate than in 
 any other organ, for the strength and thickness of the 
 coats of arteries vary very much in different parts ; 
 those of the lower extremity, for example, are much 
 thicker and tougher than in most other parts ; but here 
 they are more tender than any where else. Hence 
 they are more apt to give way, producing a fatal effu- 
 sion of blood. 
 
 The brain in the living body, and after death, so 
 long as it retains its vital warmth, is much softer than 
 when it becomes cold. It undergoes a kind of coagu- 
 lation after death, whereby it becomes firmer, until 
 decomposition commences. In the living state it may 
 be said to be semifluid, and hence probably the neces- 
 sity for the delicacy of the coats of its blood vessels. The 
 veins returning the blood are at first distributed also 
 upon the membrane. They never accumulate into large 
 branches, but instead of doing so, they pour their con- 
 tents into receptacles for the purpose, termed sinuses, 
 to which we shall immediately refer. In most parts of 
 the body the larger veins accompany the larger arteries, 
 but here that is not the case ; for whereas the arteries 
 divide from the base towards the vertex, the veins collect 
 their branches from the base, and form larger at the ver- 
 tex, where they enter the sinuses. Another circumstance 
 influencing the circulation in the brain is the effect of 
 the strong unyielding vault of the skull in which it is 
 contained, whereby the absolute quantity of blood is at 
 all times the same, the atmospheric pressure supporting it, 
 even independently of the vascular action on the one 
 hand, and the vault of the skull preventing the vicissi- 
 tudes of atmospheric pressure on the other. It has been 
 ascertained that if an animal be bled to death, there will 
 yet remain as much blood in the skull as if it had been 
 killed without shedding a drop of blood. But if a por- 
 .tion of the skull be sawn out, and an opening made 
 
CIRCULATION THROUGH THE BRAIN. 39 
 
 through the dense membrane which lines it, and the 
 mal then bled to death, the vessels of the brain will in this 
 case be found as much blanched as those of any other part 
 of the body, in consequence of the atmospheric pressure 
 having now had an opportunity of exerting its influence 
 upon them* 
 
 Although, then, we may diminish the force and the 
 velocity with which the blood circulates through the 
 brain, we cannot diminish the quantity, we mean in 
 the whole cavity. That there may be a loss of balance is 
 true : that is to say, it may be determined to, or con- 
 gested in particular parts. Veins are liable to accumula- 
 tion of blood from the nature of their coats. Such 
 accumulations are, however, incompatible with the office 
 and safety of the brain, and therefore, to prevent the risk 
 of such an occurrence, the veins of the brain are not suf- 
 fered to collect themselves into trunks, but pour their 
 contents into the sinuses. These are placed in the folds 
 of the dense unyielding membrane which lines the skull or 
 dura mater, so that the venous blood in any consider- 
 able quantity can only accumulate in these receptacles, 
 which, from their strength, resist distension, and have, even 
 in their interior, transverse bands, named Willis' cords, 
 which further act towards the same end. The manner in 
 which the veins enter is also 
 worthy of remark. The cur- 
 rent of the blood in the sinus 
 is in the direction of the 
 arrows a a, that is, from 
 before backwards, while in 
 the veins it is in the direc- FlG - * 
 
 tion of the arrows, d d d, from behind forwards. The 
 reason is this : It has been already mentioned that when 
 the chest is enlarged, as in inspiration, there is a freer 
 passage for the blood into it, but that when it is con- 
 tracted in expelling the air, there is an impediment to 
 its entrance; that, therefore, the veins are seen occa- 
 
40 CIRCULATION THROUGH THE BRAIN. 
 
 sionally to swell. From the right auricle, along the de- 
 scending cava and internal jugular vein, up to the sinus, 
 there are frequently no valves, so that any impediment to 
 the entrance of the blood into the chest or auricle causes a 
 rise, while its free entrance produces a subsidence through- 
 out the whole extent, or a flux and reflux, which is some- 
 times called venous pulsation. In laborious breathing, 
 especially, this takes place. Now, if the reflux extended 
 to the veins of the brain, it might, and most probably 
 would, prove fatal ; but as the reflux in the sinus will be 
 in the direction of the arrows b b, coincident with the 
 current in the veins, and of the arrows d d d^ the obli - 
 quity of the entrance will therefore prevent the blood 
 from re-entering the veins, though there will be an ob- 
 struction to their emptying themselves into the sinus, 
 which explains what occurs under such circumstances as 
 the following. When the brain is compressed, as from 
 a fracture of the skull, and the depression of the frac- 
 tured portion, the breathing becomes affected, it takes 
 place at intervals, or is rendered stertorous. In the per- 
 formance of the surgical operation required in such cases, 
 the brain is seen to rise and fall to rise during ex- 
 piration, and subside during inspiration : that is, 
 during expiration there is an impediment to the en- 
 trance of the blood into the sinus from the veins ; it 
 consequently accumulates in them, and the brain swells, 
 but in inspiration the current of the blood becomes free, 
 and the brain subsides. Thus we see in the transmission, 
 in the distribution, in the collection and return of the 
 blood to and from that noble and delicate organ the 
 brain, everything is foreseen and provided for, nothing 
 left to chance, overlooked, or omitted. 
 
 We have next to turn our attention to the peculiarities 
 to be found in the circulation of the blood through the 
 abdomen. That cavity is chiefly occupied by the organs 
 which are either directly or indirectly engaged in the 
 preparation of the food for its entrance into the living 
 
CIRCULATION" IN THE ABDOMEN. 
 
 41 
 
 vessels, and for the introduction of fluids to compensate 
 for the loss every moment sustained by the general cir- 
 culating mass. 
 
 The motion to which the viscera of the abdomen are 
 constantly exposed, in consequence of the respiratory 
 movements, undoubtedly has an effect in promoting the 
 circulation through them. The stomach and intestinal 
 canal have a muscular coat which produces a peculiar 
 motion hereafter to be described. This is altogether 
 independent of the will, and in a state of health we 
 are unconscious of its existence. This motion is slow 
 and uniform, varying in these respects according to the 
 habit of the individual, and other circumstances. The 
 circulation through the stomach, intestinal tube, spleen, 
 pancreas, and certain folds of the lining membrane of the 
 abdomen, is different from that of any other part of 
 the body. The blood is, as elsewhere, transmitted by 
 arteries ; as elsewhere, it is collected by veins ; but in- 
 stead of directly conveying it to the heart, these collect 
 themselves into one trunk, which proceeds to the liver ; 
 there it again divides through the substance of that 
 organ, after the manner of an artery, that is, distributing 
 the blood from trunks to branches. Again it is taken 
 
 FIG. 9. 
 
 up by veins, which are collected into one or more 
 trunks ; and these pour into it the ascending cava to be 
 
42 CIRCULATION IN THE ABDOMEN". 
 
 carried into the right auricle. Thus we have it, 1st. 
 from trunks to branches of the artery ; 2^y, from the 
 branches to the trunk of a vein ; 3dly, from the trunk 
 of that vein, by its branches sent to the liver; and, 
 lastly, taken up by veins, and conveyed to the cava. 
 Our cut will illustrate this, where a is intended for 
 the mesenteric artery, b the porta of the abdomen col- 
 lecting the blood from the viscera, c the porta of the 
 liver distributing it through that viscus, d the cava of 
 the liver conveying it into' the ascending cava e. In this 
 way the course of the blood is much lengthened, and 
 from the greater portion being in veins, it must be com- 
 paratively sluggish. The first and second set of veins 
 are collectively termed the porta or vena portse, or the 
 vein of the gate, a name given by the ancients from its 
 entering under a portion of the liver which they called 
 the gate. That portion which takes up the blood from 
 the extremities of the arteries is termed the porta of the 
 abdomen ; the other, which transmits it through the 
 liver, is called the porta of the liver, and the vein by 
 which it is collected from the liver is called the cava of 
 the liver. 
 
 The mode of ramification of the arteries of the in- 
 testinal canal deserves notice. In the human subject 
 it divides into primary branches, which establish very 
 free communications with each other, forming what are 
 termed arches ; from the convexities of these arches other 
 secondary branches are sent off, which in a similar man- 
 ner form arches, and so on till they reach the intestine, 
 forming generally three or four series of arches before 
 they do so, and constituting the best example we have 
 in the human body of the net-work, which was stated as 
 being calculated to diminish the force and velocity of the 
 blood, and also take off the pulsative movement. Thus 
 the blood will flow to the intestines in a tranquil uniform 
 stream, adapted to the slow continuous motion of the in- 
 testine. Moreover, had the blood been propelled rapidly 
 
CIRCULATION IN THE ABDOMEN. 43 
 
 along these arteries, how could such rapid movement 
 accord with what must necessarily be a very slow, languid, 
 and sluggish stream in the venous system beyond ? In car- 
 nivorous animals, which have quick digestion, the arches 
 are not so numerous, nor the communications so free ; 
 while in herbivorous animals they are more frequent 
 than in the human species. In the pig both arteries and 
 veins present a very remarkable distribution : they are 
 closely and most intricately interwoven, so as to present 
 one of the most remarkable examples of vascular arrange- 
 ment in the whole animal kingdom. The adjustment of 
 this peculiar abdominal circulation to the condition of 
 the different organs will be further considered when we 
 come to digestion. 
 
 Having now brought under our consideration the gene- 
 ral structure and mode of action of the different organs 
 engaged in the distribution of the blood through the 
 body ; having adverted to certain mechanical conditions 
 to which they are subjected, and the principal modifica- 
 tions they undergo, so as to adapt them to particular 
 organs and conditions, our attention is next to be directed 
 to the function of respiration, which, in one point of view, 
 may be considered as subsidiary to circulation, in so far 
 as one of its most important offices is to prepare the blood 
 while passing through the lesser circulation for its subse- 
 quent course through the greater. 
 
44 
 
 CHAPTER II. 
 
 RESPIRATION. 
 
 Organs of Inspiration Expiration Passages through the Diaphragm Incidental 
 Respiration Respiration in Birds in Reptiles Opinions of the Ancients as 
 to the use of Respiration Atmosphere Its Height Weight Humidity 
 Temperature Composition Changes produced on the Air by breathing 
 Quantity of Water thrown off in the Breath Diminution of Oxygen Increase 
 of Carbonic Acid State of Nitrogen Changes upon the Blood- In Colour 
 Density Chemical Constitution Temperature and Animal Heat Source and 
 Distribution of How regulated when the Body is exposed to High and to Low 
 Temperatures Progressive Developement of Animal Heat in the New-born- 
 Adaptation to the Temperature of different Climates Hybernation Voice and 
 Speech Respiration of different Gases Asphyxia Means for restoring the 
 Functions in Suspended Animation. 
 
 RESPIRATION is that function in living bodies by which 
 the circulating fluids are brought under the influence of 
 the atmospheric air, during which the fluid exposed to 
 the air, and the air itself, mutually act on each other. The 
 organs engaged in this function present great diversities, 
 according to the rank the individual holds in the organic 
 kingdom. In man, mammalia, and birds, respiration is 
 performed by the lungs, and the alternate enlargement 
 and diminution of the cavity in which they are contained. 
 In reptiles the air is forced down, not drawn into the 
 lungs. In fishes the gills perform this oince. Animals 
 still lower in the scale present various modes in which it 
 is performed ; and in plants the leaves are its principal 
 agents. We shall chiefly confine ourselves to the con- 
 sideration of this function as it obtains in man, though 
 
ORGANS OF RESPIRATION. 45 
 
 for the purpose of illustration other animals will be oc- 
 casionally referred to. 
 
 The organs engaged in respiration are the direct and 
 the accessary ; the lungs being the former, the organs by 
 which the air is introduced into the lungs constituting 
 the latter. The chest or thorax is of the form of a cone, 
 with the apex cut off, approaching in the human subject, 
 and particularly in the male, to a quadrangular pyramid. 
 The skeleton of its walls is composed of twelve vertebras, 
 twelve ribs on each side, with their cartilages, and the 
 breast-bone in front. It is separated from the cavity of 
 the abdomen by a muscular partition called the diaphragm. 
 The vertebrce are termed dorsal, to distinguish them from 
 seven of the neck and five of the loins, which together 
 form the flexible spine. These dorsal vertebras are so 
 united or hinged together as to permit of a less degree of 
 motion than those of either the neck or loins. The ribs 
 are of an arched form, the first forming the segment of 
 the smallest circle, the circle gradually enlarging down- 
 wards. Their upper margin is rounded, and has an incli- 
 nation inwards ; the lower is sharp, and inclines outwards. 
 At their attachment behind to the vertebrae they incline 
 from above downwards and forwards. From these cir- 
 cumstances, when they are raised, the chest is enlarged. 
 Excepting the two last, they have two points of connec- 
 tion with the vertebras behind. When they come for- 
 wards, they terminate in cartilages or gristle, by which 
 they are connected to the breast-bone or to each other, 
 excepting the last two, which float loosely. Anteriorly, 
 from the first downwards, the cartilages become gradu- 
 ally longer, more slender, and flexible. From the con- 
 nection behind, and from the termination in front, the 
 upper rib is always more fixed than that immediately 
 beneath it. These points, along with the segment of the 
 circle which they form enlarging downwards, we shall 
 find have a considerable influence on their office. 
 
 There are two conditions of respiration which are ne- 
 
46 MOTIONS OF THE RIBS. 
 
 cessary to be considered ordinary and incidental. Or- 
 dinary respiration commences at birth, and must be 
 carried on to the last ; it is conducted whether we are 
 asleep or awake. In so far, therefore, it is like the 
 function of circulation, an involuntary act. But we pos- 
 sess a direct power over breathing which we have not 
 over circulation. To a certain extent we can hurry or 
 retard, or suspend it for some time, either when the chest 
 is expanded or contracted, or expel the air with different 
 degrees of force. This extraordinary or incidental respi- 
 ration is employed in speaking, singing, laughing, crying, 
 coughing, straining, &c. In both conditions respiration 
 consists of two acts : inspiration, during which the chest 
 is enlarged, and an additional portion of air drawn in ; 
 and expiration, when the chest is contracted and a por- 
 tion of air expelled. 
 
 The chest is enlarged by the elevation of the ribs and 
 descent of the diaphragm. By the former it is enlarged 
 from before backwards, and from right to left ; and by 
 the latter from above downwards, so that it is thus 
 enlarged in all its diameters. When the ribs are ele- 
 vated, their points of connection behind are not so, and 
 the seven superior, from being fixed anteriorly to the 
 breast-bone, are elevated at neither extremity. From 
 the form and position of the ribs, it is by the change 
 of the plane of their inclination, when they are de- 
 pressed or elevated, that they produce a difference in 
 the capacity of the chest. In ordinary inspiration a 
 set of muscles termed intercostals are the only ones re- 
 quired for the elevation of the ribs. These muscles 
 present us with a very beautiful example of design and 
 contrivance. They consist of two layers, lying one upon 
 the other, their fibres running in different directions. The 
 external layer begins behind at the vertebrge, and runs 
 downwards and forwards from the inferior margin of the 
 upper to the superior margin of the lower rib. This layer 
 is not continued the whole length of the ribs, but ceases 
 
MOTIONS OP THE RIBS. 47 
 
 near the cartilages. The internal layer commences at the 
 breast-bone, is attached as the last, but runs from above 
 downwards and backwards, and ceases before it reaches 
 the vertebrae. 
 
 To understand the manner in which these muscles act, 
 it is necessary to bear in mind that the motions of the 
 ribs are upwards and downwards on an axis, extending 
 from the vertebral attachment behind to their attachment 
 in front to the breast-bone ; that at these points of attach- 
 ment they are not elevated or depressed, but roll in the 
 socket ; as the rib immediately above is the segment of a 
 smaller circle than that immediately below, a motive 
 power extended between them has a greater purchase 
 upon the lower than the upper. 'Zdly, As already stated, 
 the superior rib is more fixed than the inferior ; and, 3dly, 
 we shall find that by the direction of the fibres of the 
 intercostals, they possess a longer lever upon the rib 
 below than on the rib above, and consequently, other 
 things being equal, they move the lower to the upper 
 faster than the upper to the lower; and as this takes 
 place throughout the whole series, the general result is 
 the elevation of the whole. This last position may be 
 a, I 
 
 V 
 
 FIG. 10. 
 
 illustrated by reference to the figure. Suppose A B, C D, 
 and E F, represent ribs moveable upon their two extre- 
 mities, and ACE the posterior or vertebral extremities, 
 and B D F the anterior : let a a and b b represent the muscular 
 fibres of the external layer of the intercostals, it is evident 
 that a a has a longer lever upon C D than A B ; but if 
 continued on to b 5, the reverse would happen ; b b 
 would have a longer lever on A B than C D ; but wher*. 
 
48 
 
 DIAPHRAGM. 
 
 ever this would take place, there the external intercostals 
 cease. This also applies to the internal layer, which com- 
 mences at the breast-bone in front, and terminates some 
 space before it reaches the vertebrae ; and for similar rea- 
 sons as above, as will be seen by looking at the figure, 
 where c c has a longer lever upon E F than C D, but 
 would have the reverse were it continued on as at d d, 
 which it is not, but ceases before it comes to have any 
 such superior power over the rib above. Therefore, from 
 the difference of the size of the circles of which the ribs 
 form segments, from the greater mobility of the lower 
 ribs, and from the fibres of both layers having a longer 
 lever upon the rib below than the rib above, they elevate 
 the ribs. 
 
 The transverse partition dividing the thorax from the 
 abdomen, named the diaphragm, is usually described as 
 composed of two portions ; the fibres of the larger pro- 
 ceeding from their attachments to the cartilages of the 
 lower ribs to a central heart-shaped or cordiform ten- 
 don. The lesser arises by two fleshy columns from the 
 vertebrae of the loins to be inserted also into the tendin- 
 ous centre ; so that the diaphragm forms a dome, convex 
 above, and concave below, with a central tendon ; this 
 tendon is attached to the capsule of the heart at its upper 
 surface, whereby it is rendered more fixed than the fleshy 
 circumference. 
 
 When the diaphragm is thrown into action, the fleshy 
 fibres contract, push downwards the viscera of the abdo- 
 men, and enlarge the chest in the diameter from above 
 downwards, and, along with the muscles of the walls of 
 the abdomen, produce that alternate motion upwards 
 and downwards, in accordance with respiratory move- 
 ments observed in that cavity. 
 
 The curious and beautiful contrivance of the openings 
 for the transmission of organs through this partition may 
 be here adverted to, and particularly those for the aorta, 
 the ascending cava, and the gullet. The inferior cava, 
 
PASSAGES THROUGH THE DIAPHRAGM. 49 
 
 in its ascent in the abdomen, as it approaches the liver, 
 leaves the vertebral column, and is lodged in a depression 
 of the liver, so as to be able to penetrate the diaphragm 
 near its centre, towards the right of the tendon. On 
 entering the chest, it immediately pours its blood into 
 the right auricle. The veins collecting the blood from 
 the walls of the abdomen could not, from this course of 
 the cava, have reached it without being exposed to inter- 
 ruption. Instead of doing so, however, they form a vein 
 which lies close upon the vertebrae, entering the chest by 
 another opening, through which the aorta passes into the 
 abdomen. This vein proceeds upwards on the right of 
 the aorta, collecting the branches from the walls of the 
 chest, and joins the descending cava. As it is a single 
 vein, or without a fellow, it is called the azygos. The 
 main trunk of the absorbents also passes through the 
 opening for the aorta. 
 
 We have therefore to consider two passages in the dia- 
 
 A O 
 
 phragm for blood-vessels the anterior for the vena cava, 
 the posterior for the aorta, vena azygos, and thoracic duct. 
 In the different states of action and repose of the diaphragm, 
 these might have been exposed to impediment, but this is 
 completely obviated by the following contrivances. Ten- 
 dons are not contractile, but are to be considered merely as 
 mechanical cords regulated and moved by the fleshy fibres. 
 The cordiform tendon of the diaphragm is formed by the 
 crossing and curious interlacing of the tendinous fibres ; 
 and they are so arranged as to form an opening for the 
 cava, which, in no state of the diaphragm is liable to be 
 affected in any way, the interlacement of the tendinous 
 fibres being such as to preserve the passage patent in 
 every condition. The aortal opening is somewhat diffe- 
 rently constructed, but the result is as complete. It is 
 situated between the two columns of the diaphragm, 
 which take tendinous origins from the vertebrae, some 
 of the fibres of which cross and are interlaced, so as to 
 form an arch over the passage. Both of these con- 
 
 D 
 
50 PASSAGES THROUGH THE DIAPHRAGM. 
 
 formations are perfectly adapted to the conditions re- 
 quired, that of a free passage at all times, whether the 
 diaphragm be in a state of contraction or relaxation. 
 The passage for the gullet, on the other hand, is through 
 the fleshy portion of the diaphragm, consequently it 
 becomes subject to obstruction in certain conditions of 
 that muscle, as in hiccough, where a difficulty of deglu- 
 tition is experienced. As deglutition, however, is only 
 an occasional act, the diaphragm in ordinary cases offers 
 no resistance to the transmission of the food, but rather 
 co-operates with the gullet. 
 
 If a person attends for a little to what takes place in 
 his own breathing, he will become conscious that inspira- 
 tion is that which principally requires an effort in ordi- 
 nary cases, and that the walls of the chest return to the 
 state of expiration of their own accord, as if it were their 
 more natural condition. Indeed, in healthy tranquil re- 
 spiration, such is the mode in which the ribs are hinged 
 to the vertebrae behind, and also the elasticity of their 
 cartilages in front, that by these mechanical conditions 
 alone the chest returns to the state of expiration, without 
 the necessity of muscular intervention. Accordingly, when 
 death takes place, this is the condition in which it is 
 left. Hence the occurrence of death is announced by say- 
 ing, that the person has expired. During sleep, or while 
 we are at rest, this important function requires merely that 
 the diaphragm, and two layers of intercostals be called into 
 action sufficiently, so that the chest may be enlarged to 
 the necessary extent ; and to this extent their involuntary 
 or instinctive contraction enables them uniformly to carry 
 it, without weariness or fatigue, from the first inspiration 
 at birth to the last expiration, when the breath of life is 
 finally yielded up, however long may be the interval 
 between. 
 
 Besides the above means for the constant, ordinary, or 
 involuntary enlargement and diminution of the chest, so 
 as to carry on the function of respiration, under vari- 
 
MUSCLES OF EXPIRATION. 
 
 51 
 
 ous circumstances, the apparatus engaged in these offices 
 are called into action at the command of the will, as in 
 blowing, singing, &c. ; or we instinctively employ them, 
 as in laughing, crying, sighing, yawning, &c. ; and be- 
 sides, other muscles powerfully co-operate with the ordi- 
 nary means in these and in other certain cases, so as to 
 enlarge and diminish the cavity of the chest to the utter- 
 most, as in coughing, speaking, straining ; in all of which 
 instances, many advantages result from the full exercise 
 of this function, and without it indeed they could not 
 have been performed. 
 
 "When we take in a full breath, we elevate the shoul- 
 ders by means of muscles extending from the head and 
 neck, and become conscious of the exertion of an effort. 
 In consequence of this elevation and fixation of the 
 shoulders, several powerful muscles attached to the 
 shoulder-blade and arm, connected with the ribs, ob- 
 tain a fixed point of action, and have their levers also 
 vastly increased. Five pairs of muscles are employed 
 in elevating and fixing the shoulders, and unless they 
 are called into play, those extending from the ribs to 
 the shoulders would act under much disadvantage. We 
 have only to try forcibly to draw in our breath with- 
 out raising the shoulders, and then do so, at the sametime 
 elevating them, to be convinced how much more air we 
 can draw in, and how much more easily we effect it 
 in the latter than in the former condition. For we hereby 
 obtain the aid of at least four pairs of powerful muscles, 
 which, as they cannot now pull down the shoulders, raise 
 the ribs to them. In an instant, then, whether from the 
 exertion of our will, or from an incidental occurrence call- 
 ing forth the instinctive employment of the respiratory 
 apparatus, these extraordinary means start into action in 
 aid of the ordinary instruments engaged. There is no 
 need on our part to consider the number that may be 
 selected ; no need for selection ; no necessity for calcu- 
 lating the force, velocity, or extent to which it will be 
 
52 STRUCTURE OF THE LUNGS. 
 
 requisite to employ them. In the proper number, with 
 adequate power, and in the necessary order of succession, 
 are they ready to obey the behests of a Carib or a Hotten- 
 tot as well as those of a Harvey or a Hunter. 
 
 It has been stated that the mechanical contrivance of 
 the chest is such that little or no muscular interference is 
 required for the expulsion of the proper quantity of air 
 in ordinary respiration. But in other cases, muscular 
 exertion becomes absolutely necessary, so as to expel it 
 with different degrees of force, and otherwise to regulate 
 it. Thus, in straining, the chest is filled, and its contents 
 powerfully compressed. In singing, it is filled, and the 
 air forced along the windpipe, through the organs of voice ; 
 its quantity, velocity, and force being adjusted with the 
 greatest nicety, in accordance with the sound required to 
 be produced. 
 
 There are four pairs of muscles which extend from the 
 bones of the pelvis to the ribs and breast-bone, forming 
 the anterior and lateral walls of the abdomen, constructed 
 upon the most curious and admirable principles, which, 
 however, we need not at present enter upon. These 
 muscles, by their joint action, pull down the ribs ; at the 
 same time they press upwards, and somewhat backwards, 
 the viscera against the relaxed diaphragm. Therefore, in 
 consequence of the action of these muscles, the ribs and 
 sternum are depressed, the diaphragm is pushed up, and 
 the chest diminished in all its diameters, and this they 
 are able to effect with the greatest nicety, to the neces- 
 sary extent, or with the necessary velocity and force. 
 
 We have now to consider the structure of the lungs. 
 We have already found that during each complete cir- 
 culation, the whole mass of blood is transmitted through 
 these organs by the ramifications of the pulmonary arteries 
 and veins. Between the meshes of these vessels we 
 have air tubes every where penetrating and conveying 
 the atmospheric air. The windpipe will afterwards come 
 more particularly under our consideration as an instru- 
 
STRUCTURE OF THE LUNGS. 53 
 
 rnent of voice. At present it may be sufficient to state 
 that at its upper part in the throat there is a compli- 
 cated apparatus connected with it, termed the larynx, 
 by which the entrance and exit of the air are regulated. 
 The windpipe itself is composed of about eighteen carti- 
 laginous rings, which are incomplete posteriorly, where 
 it is in contact with the gullet. It thus forms a rigid 
 tube, capable of resisting the pressure of the external air 
 when that which it contains becomes rarefied. Had it 
 not been capable of bearing a certain degree of pressure 
 from the external air, its sides would have been liable to 
 be compressed, and thus suffocation must have been the. 
 result. Thus we find in birds, where the air suffers a 
 greater degree of rarefaction, and is also in greater pro- 
 portional quantity in the body of the animal, the rings 
 composing the windpipe are much firmer, indeed almost 
 bony, and are complete round the whole circumference ; 
 while in reptiles, where the air is propelled downwards 
 by a force from above, it is more yielding than even in 
 man and mammalia. 
 
 On the entrance of the windpipe into the chest, it di- 
 vides into two trunks, one proceeding to each side. These 
 penetrate into the substance of the lungs, and immediately 
 begin to give off branches, which, by reiterated subdivi- 
 sions, become exceedingly minute, and permeate their 
 whole substance, the ultimate extremities of these tubes 
 terminating in very small cells. The smaller divisions 
 of the air-tubes are devoid of cartilage, as, beyond the 
 secondary branches of the windpipe, that substance be- 
 comes unnecessary. Throughout the whole extent of the 
 air-passages they are lined by a mucous membrane, con- 
 tinuous with the lining membrane of the mouth, nostrils, 
 and throat. 
 
 The essential substance or tissue of the lungs maybe con- 
 sidered as consisting in a congeries of blood-vessels and air- 
 vessels, the pulmonary arteries bringing to them the dark 
 purple, and the pulmonary veins carrying off the bright 
 
54 STRUCTURE OF THE LUNGS. 
 
 scarlet-coloured blood, while the reciprocal action of the air 
 and the blood on each other is the efficient agent of 
 this change. A subordinate set of blood-vessels, termed 
 bronchials, furnish them with nourishment and with 
 blood for the mucus of the air-passages. The nerves are 
 numerous, and belong to a particular class, to which we 
 shall afterwards direct our attention. The substance of 
 the lungs is light and spongy ; from our first inspiration 
 at the moment of birth, it contains always more or less 
 aerial fluid, and is never exhausted by any expiration 
 that afterwards succeeds. Surrounding the lungs there 
 -is a membrane covering the whole surface, and reflected 
 upon the walls of the chest, so as to form a shut sac, 
 into which a thin watery vapour is constantly exhaled to 
 preserve the surfaces moist and slippery. To this the 
 name of pleura is given : it constitutes the seat of the 
 disease termed pleurisy. 
 
 A correct general notion of the lungs may be easily ob- 
 tained by examining them in the sheep, rabbit, or other 
 quadruped. In common language they are known by the 
 name of lights. In mammalia they are generally divided 
 into a greater or less number of lobes. In animals with a 
 very flexible spine, as in the cat tribe, such as the tiger and 
 leopard, the lobes are more numerous, and the divisions more 
 complete than in those animals in which the spine is more 
 rigid, so that the lungs may more readily adapt them- 
 selves to the various postures of the animals. The chest 
 is divided into three principal compartments ; the middle 
 containing the heart, the two lateral the lungs. Be- 
 tween these there is no communication, so that if we throw 
 air or any other fluid into one of these compartments, it does 
 not find its way into the others. The lungs belong to 
 the double organs of the body, like the eyes, the ears, &c., 
 the windpipe and its appendages being common to both. 
 Accordingly, one lung may be, and often is diseased, 
 while the other remains healthy, and may alone carry on 
 the function for many years. 
 
INSPIRATION. 55 
 
 We shall now proceed to consider the effect of the re- 
 spiratory movements. 
 
 As the chest becomes enlarged, the pressure upon the 
 viscera, and particularly upon the lungs, is diminished. 
 The residual air left after the preceding expiration expands 
 and dilates the cells and tubes, and thereby the whole 
 volume of the lungs, so that they are always in contact 
 with the inner surface of the walls of the chest. In con- 
 sequence of the air having a constant tendency to keep 
 up the equilibrium of pressure, where it becomes rarefied 
 from any cause, the surrounding atmosphere rushes towards 
 that part, in order to restore the equilibrium. If we 
 exhaust the receiver of the air-pump, and then open the 
 valve, the air will rush in, or if we heat our apartment, 
 so as to rarefy its atmosphere, a draught will take place ; 
 or if we enlarge the receptacle in which air may be con- 
 tained, so as to cause expansion, fresh air enters to keep 
 up the balance, as in the common bellows. 
 
 The tubes and cells of the lungs being dilated, the 
 external air enters by the windpipe in a quantity com- 
 mensurate with the expansion. There is not at first a 
 rarefaction to the full extent, and then a sudden admis- 
 sion of air, so as to produce anything like a rush ; but as 
 it becomes more and more rarefied, so does the external 
 air enter coincident with the expansion. Although rare- 
 faction of the air in the lungs be the efficient cause of 
 fresh portions entering, yet so admirable is the adjust- 
 ment, that the rarefaction is never suffered to take place 
 to any appreciable extent. The reason is obvious : The 
 air cells are formed of an exceedingly delicate membrane, 
 incapable of bearing anything like sudden distension or 
 pressure. The extreme branches of the blood vessels, too, 
 distributed around the cells, would have been liable to 
 rupture, so that the very first inspiration might have 
 proved fatal. By the dilatation of the lungs, and the 
 entrance of fresh air, the muscles are enabled to enlarge the 
 chest to the full extent. Without this it is impossible 
 
56 RESPIRATION IN DIFFERENT ANIMALS. 
 
 to do so ; for powerful as the muscles may be which are 
 employed in inspiration, the most vigorous effort they 
 are capable of exerting is totally inadequate to lift the 
 ribs against the atmospheric pressure, if air be prevented 
 from entering the chest. If any one try complete ex- 
 piration, then hold the breath, and endeavour to elevate 
 the ribs, he will find that it is impossible to do so to any 
 extent. 
 
 In the act of inspiration, then, the following is the suc- 
 cession of the phenomena which occur : enlargement of 
 the chest by means of the muscles ; rarefaction of the 
 residual air, and consequent expansion of the cells ; 
 entrance of a fresh portion of air to preserve the balance. 
 As the chest contracts during expiration, the lungs now 
 become subject to pressure, so that a portion of the con- 
 tents of the cells is forced along the tubes, and expelled 
 through the windpipe. So far as the entrance and exit of 
 the air are concerned, the lungs, from the above descrip- 
 tion, are altogether passive ; but the agents employed are 
 fully adequate to the effect required, so that a sufficient 
 renewal of air is at all times perfectly insured. 
 
 In man and mammalia the windpipe, as we have stated, 
 is divided into numerous branches, which become more 
 and more minute, and ultimately terminate in very small 
 cells. The surface with which the air comes in contact is 
 thus vastly extended, and has been estimated by the cele- 
 brated Haller as equal to fifteen times that of the whole 
 external surface of the body. The blood being also ex- 
 posed to this surface, the reciprocal changes of the air 
 and blood, therefore, arc rapidly effected, rendering fre- 
 quent renewals of air necessary. 
 
 In birds the structure and offices of the lungs are 
 similar to those in mammalia, but, in addition, the air 
 is also necessary in them, to render the body buoyant, 
 that they may wing their way through the atmosphere. 
 For this purpose .a number of the air-tubes, instead of 
 terminating in the pulmonary tissue, open into large 
 
RESPIRATION IN DIFFERENT ANIMALS. 57 
 
 sacs, situated both in the thorax and abdomen, for the 
 reception of air, and likewise extend into several of the 
 bones, which are hollow and filled with air, thus com- 
 bining strength and lightness. These reservoirs regulate 
 the specific gravity of the bird, as the swimming bladder 
 does in the fish ; in fact, they are so many internal bal- 
 loons. An excellent example of modification to circum- 
 stances is found in auks and guillemots, so abundant on 
 our shores. These birds, in diving either in quest of their 
 food or to escape danger, use their wings in the same way 
 as in the air ; in fact, they fly through the water. To 
 enable them to adjust their weight in order to fly in 
 water, their muscles of expiration are very powerful, so 
 that they may adequately embrace the reservoirs, and 
 thus expel the necessary quantity of air when the bird 
 dives. A sufficient quantity, however, for the changes 
 of the blood still remains, enabling the bird to continue 
 in the water for a considerable time. As soon as it 
 reaches the surface, the reservoirs are again filled, so that 
 the body is lightened, and the bird may now mount into 
 the atmosphere. 
 
 In reptiles, a portion only of whose blood is exposed 
 to the air in each complete circulation, and in which the 
 changes consequent to its exposure to air are not so 
 unremitting, the proper pulmonary tissue is much more 
 limited. The cells in several, as the turtle tribe, are very 
 large, accompanied consequently with a diminution of air 
 surface ; while others have large reservoirs appended, as 
 in birds, but for a different reason. In birds the reser- 
 voirs are for the purpose of adapting the specific gravity 
 in order to enable them to ascend in the atmosphere, 
 while in serpents they render frequent renewals unneces- 
 sary. Serpents swallow their prey whole, and as they 
 generally feed on animals whose diameter is greater than 
 their own, the act of deglutition may not be completely 
 effected for days, during which, from the mouth remain- 
 ing open, the windpipe compressed, &c., no fresh air can 
 
 D2 
 
58 OPINIONS ON RESPIRATION. 
 
 be obtained. Those internal receptacles, along with the 
 action of the skin, however, furnish all that is required 
 for producing the necessary influence upon the blood. 
 
 In mammalia and birds the means by which the air 
 is drawn in and expelled is essentially the same as we 
 have described it to be in man; but in reptiles the 
 manner in which it is introduced is very different. Seve- 
 ral of this class of animals, from the structure of their 
 bodies, cannot have the chambers in which the lungs are 
 contained enlarged and diminished, for example, the tur- 
 tles and tortoises ; while others have no ribs to be subser- 
 vient for any such purpose, as frogs and toads. An- 
 other plan is consequently adopted by the action of the 
 parts surrounding the orifice of the windpipe : the air is 
 forced down into the lungs and cells. If a frog be watch- 
 ed, it will be perceived that the animal keeps the mouth 
 shut, and that beneath the lower jaw the throat is in con- 
 stant motion. The air being received by the nostrils, and 
 prevented from again escaping by a valve, it is then by 
 the action of the throat pumped down into the lungs. If 
 the frog's mouth, therefore, be kept open, the animal will 
 be as certainly suffocated as the dog is by tying a rope 
 round his neck. 
 
 We are told, " And the Lord God formed man of the 
 dust of the ground, and breathed into his nostrils the 
 breath of life, and man became a living soul." From the 
 beginning, therefore, the importance and absolute neces- 
 sity of this function to life must have been acknowledged. 
 But the manner in which it acts has been little under- 
 stood. 
 
 The ancients believed that breathing was necessary in 
 order to keep up the internal fire which they supposed 
 was situated in the left ventricle of the heart a fire which 
 they stated was not of the gross nature of common fire, 
 which destroys, but a living fire of the essence of the 
 stars, which sustains life, and supports and cherishes the 
 whole system. When this fire was discovered to have no 
 
WEIGHT OF THE ATMOSPHERE. 59 
 
 other existence than in the imagination, and it was found 
 that a very large quantity of blood was sent to the lungs, 
 it came to be supposed that the air had some influence 
 upon the blood. 
 
 When mechanical laws were had recourse to in order 
 to explain almost all the phenomena of life, by some it 
 was stated that the blood was rarefied from exposure to 
 air, and by others that it was condensed. 
 
 Chemistry was next brought forward, in order to ex- 
 plain the manner in which the air and the blood mutually 
 affect each other ; but even the chemists are not agreed as 
 to the precise manner in which the changes which take 
 place are brought about. It is not our business here to 
 enter upon the merits of the various opinions that have 
 been and are even now subjects which have excited keen 
 discussion, and called forth the powers of the most dis- 
 tinguished of those who have exerted their talents in this 
 department of human knowledge. It will be sufficient to 
 state what appears to us best to accord with the facts 
 which have been ascertained. We shall find that it is 
 not by confining our attention to one train of facts merely 
 that we can arrive at a satisfactory solution ; that it is 
 not merely sufficient to take under consideration the 
 nerves or the blood-vessels, or the changes produced upon 
 the blood and upon the air, in order to enable us to under- 
 stand what actually takes place ; that we must rather 
 reflect upon the joint co-operation of the whole, before 
 we can arrive at a just appreciation of the subject. 
 
 The atmospheric ocean, for existing in which we are 
 constructed, is estimated by natural philosophers to be 
 about 45 miles in height. Whether it be subject to 
 regular periodical motions, such as the tides of the ocean 
 of waters, has not been fully ascertained. From its being 
 a gaseous fluid, it is exceedingly susceptible of motion ; 
 it is therefore seldom still, but more or less agitated, 
 from the softest breeze to the most boisterous and destruc- 
 tive tornado. This incessant motion has the most bene- 
 
60 WEIGHT OF THE ATMOSPHERE. 
 
 ficial effect upon its salubrity, and produces important 
 results to the whole animated kingdom. It presses at the 
 level of the sea with the weight of about fifteen pounds to 
 the square inch. This weight, however, is liable to be 
 increased or diminished by a variety of circumstances 
 by temperature, electric condition, and the quantity of 
 moisture it may hold in solution. As we ascend in the 
 atmosphere, and consequently diminish its depth, the 
 pressure is diminished. The inhabitant of the plains of 
 Mexico or Quito in South America sustains a much less 
 degree of atmospheric pressure than the native of the 
 sea-beach, the air in these high regions being more rare, 
 and an equal quantity occupying a greater bulk. It is 
 therefore observed that in the inhabitants of these moun- 
 tainous regions the chest is more expanded, from the 
 habitual necessity they are under of dilating it to the ut- 
 most to obtain the necessary quantity ; and that when 
 they descend to the low country, an uneasy sensation 
 is experienced in the chest, from the same cause which 
 produces the distress of breathing in descending in the 
 diving-bell that is, from the exposure to unwonted at- 
 mospheric pressure or weight. On the other hand, the 
 native of a low country, on climbing a mountain, feels, as 
 he ascends, an uneasiness about the chest, and an inde- 
 scribable feeling in respiration, accompanied with general 
 languor and inaptitude to muscular exertion. It is from 
 the diminution of weight according to the diminished 
 depth of the atmosphere that the height of mountains or 
 the ascent in a balloon is ascertained by the barometer, 
 and that water boils at a lower temperature at the sur- 
 face of the sea than at the top of a high mountain ; so 
 that if we could ascend high enough, boiling water would 
 not cook an egg. 
 
 From the manner in which inspiration and expiration 
 are carried on, it will be evident that without this pressure 
 they could not have been performed ; and that, in fact, 
 the instruments by which they are effected are as much 
 
WATER IN THE ATMOSPHERE. 61 
 
 made for the conditions of the atmosphere as the atmos- 
 phere is for them. We are too apt to think that when 
 we find external objects so admirably adapted to us and 
 all our wants, that they have been merely created for 
 our gratification and necessities ; whereas it will not di- 
 minish the gratitude we ought to feel to the beneficent 
 Author of both to know that they are and were created in 
 the most perfect adjustment and accordance with each 
 other. 
 
 The weight of the atmosphere is also influenced by the 
 quantity of moisture it contains, and the quantity of 
 water which it is capable of holding in solution varies 
 according to the temperature and electric condition. 
 Watery vapour is lighter than the same bulk of atmos- 
 pheric air at the same temperature. The greater the 
 quantity of water therefore in the air, other things being 
 considered, the lighter will be the mixture, and the less 
 the pressure upon the surface of the earth. Hence the 
 barometer is employed as a hygrometer to measure the 
 quantity of water the air may hold in solution, and is 
 the most popular weather-glass. When the air is light 
 and the mercury falls, rain is anticipated. When it rises, 
 fair weather is prognosticated. The temperature of the 
 air influences to a very important extent its power of 
 dissolving and holding water in solution. Hence, in hot 
 climates, although there is actually a much greater quan- 
 tity of watery vapour in the atmosphere than in cold, so 
 perfect is the solution that the air is clear and transparent. 
 Its weight, however, is not so different as might have 
 been anticipated ; for another agent comes into opera- 
 tion. The heat causes expansion of the air, so that the 
 atmospheric ocean is much deeper at the equator than at 
 the poles, and what weight is lost by temperature and 
 moisture held in solution is gained by the height to which 
 the atmosphere reaches. Perfectly dry air has so strong 
 an attraction for water, that it greedily seizes upon it 
 from substances containing moisture, with which it comes 
 
62 CHEMICAL CONSTITUTION OF THE AIR. 
 
 in contact. This avidity is vastly increased by a high 
 temperature. Our bodies, composed as they are to a very 
 considerable extent of fluids, cannot be exposed with 
 impunity to such an atmosphere. Hence the deadly 
 effects of the simoom of Africa, and the burning pungent 
 thirst of the deserts of Arabia, which in our climate 
 can only be conceived in imagination. 
 
 The electric fluid, whether contemplated in the tran< 
 quil movements of the needle of the mariner, as bursting 
 forth from the thunder-cloud, or controlled and di- 
 rected by the electric eel or torpedo, is universally dif- 
 fused; and undoubtedly, though we are yet unable to 
 show how or in what way it may constantly be exerting 
 its influence upon our own bodies, its effects must be 
 neither very limited nor unimportant, particularly in such 
 a function as respiration, where a fluid like the air, so 
 much under its influence, is altered, and the evident 
 chemical changes which take place in the blood, are pro- 
 duced. "We have thought it necessary to advert to elec- 
 tricity, in relation to respiration, not that it has hitherto 
 explained to us any of the functions more immediately 
 connected with breathing, but because, as our knowledge 
 increases with respect to it, we may expect that electric 
 action will clear up much that is now obscure and unde- 
 termined ; and therefore, in the consideration of the opera- 
 tions which are carried on in living bodies, it ought not 
 to be entirely neglected. In considering facts which have 
 been already ascertained, we should not think that other 
 agencies may not come into operation, although, in the 
 present state of our knowledge, we may not be able fully 
 to appreciate them. 
 
 The atmospheric air, like other gaseous substances, is a 
 bad conductor of heat, yet, from the facility with which 
 the different particles of air are moved and intermingled 
 with each other, a rapid diffusion of heat takes place, so 
 as soon to establish nearly an uniformity of temperature 
 under the same climate and other circumstances. The 
 
CHEMICAL CONSTITUTION OF THE AIR. 63 
 
 temperature of the atmosphere is affected by a great va- 
 riety of causes by winds and currents of air, by the tides 
 of the ocean, by the evaporation of water, and, above all, 
 by the influence of the sun. In the torrid zone the air 
 is generally nearly of the same temperature as that of the 
 blood of man, and frequently above it ; while about the 
 frigid poles it occasionally falls, as ascertained by Captain 
 Back, to 60 below zero of Fahrenheit's scale ; and yet in 
 these two extremes man is capable of existing, for by the 
 combined exercise of his intellectual and corporeal endow- 
 ments in defending himself, he can defy the burning rays 
 of India or the freezing blasts of Greenland. 
 
 The constitution of the air has been found on chemical 
 examination to consist of oxygen, nitrogen, and car- 
 bonic acid gas. Oxygen is that principle to which the 
 air has been considered chiefly to be indebted for its 
 power of sustaining animal life, and therefore it has been 
 called vital air. When, however, an animal is forced to 
 breathe pure unmixed oxygen, it becomes diseased, and 
 sooner or later life is destroyed. The proportion in which 
 the three gases mentioned enter into the composition of 
 the air is as follows : oxygen constitutes one-fifth, nitro- 
 gen the other four-fifths, and carbonic acid only about 
 one two thousandth part. Nitrogen was at one time 
 termed azote, from its being found that when animals were 
 plunged into it they soon died. It was therefore suppos- 
 ed to be essentially inimical to life. It is now ascer- 
 tained that, if not necessary, which it most probably is, 
 it is by no means directly injurious to life. Whether 
 carbonic acid, in the quantity in which it is found at all 
 heights of the atmosphere which have hitherto been exa- 
 mined, be of any utility in the function of respiration in 
 animals or not, it is well ascertained that it executes a 
 very important office in the vegetable kingdom. Oxygen 
 and nitrogen have hitherto resisted all means which have 
 been used in order to decompose them, and are therefore 
 held as being simple bodies ; while carbonic acid is ascer- 
 
64 BREATHING A COOLING PROCESS. 
 
 tained to be a compound of one equivalent of oxygen and 
 two of carbon. 
 
 Examining the changes produced upon the air, we shall 
 find it affected in its rarefaction, temperature, moisture, 
 and chemical constitution. 
 
 In considering the respiratory movements, we have 
 already shewn that rarefaction of the air takes place 
 during inspiration, and that it is one of the necessary 
 steps in the performance of that function. With respect 
 to temperature, from the law by which heat has a ten- 
 dency uniformly to diffuse itself, and bring neighbouring 
 bodies into a state of equilibrium in this respect, the air 
 and the interior of the body into which it is received soon 
 become of the same temperature. The temperature of 
 the air we breathe being generally lower than that of the 
 body, particularly in cold climates, it soon becomes assi- 
 milated to the heat of the body. The breath expelled is 
 therefore warmer than the surrounding atmosphere, and 
 thus a considerable quantity of heat is constantly carried 
 off. Thus, when we are unusually heated, either from 
 exercise or disease, or from the state of the weather, we 
 breathe more frequently; we pant and draw in large 
 breaths, and rapidly renew them, so as to get quit of a 
 quantity of the heat which oppresses us; and this we do, 
 not from any knowledge we have that by such means 
 we shall relieve ourselves, but instinctively; and there- 
 fore we see that the dog and the horse use exactly the 
 same means for the same ends. So evident is this cool- 
 ing effect of respiration, that it w r as at one time consider- 
 ed as the only purpose which it served; while of late 
 respiration has been held as the only source of the heat 
 which animals are capable of generating. The connexion, 
 however, between respiration and the generation of ani- 
 mal heat, will be postponed till we have reviewed tho 
 chemical changes which the air and the blood undergo. 
 
 The most superficial observer must be aware that watery 
 vapour is exhaled with the breath. If we breathe upon 
 
 
VAPOUR OF THE BREATH. 65 
 
 the surface of a mirror, or on a plate of burnished metal, 
 we perceive it deposited, and rendering the surface dim ; 
 or on a frosty day, from its sudden condensation, it be- 
 comes a visible vapour. In the arctic regions, when the 
 whale comes to the surface to breathe, the vapour in the 
 expired air being suddenly condensed, forms a cloud 
 which may, in a cold clear day, be seen at the distance 
 of upwards of a mile, warm air having a greater capacity 
 and attraction for water than cold. The air inspired 
 having its temperature augmented, has consequently its 
 capacity and attraction for moisture at the same time 
 increased. It is now well ascertained that animal mem- 
 branes, thicker and of a much denser texture than that 
 which separates the blood and the air from each other in 
 the lungs, readily admit of the transmission of gases, 
 vapours, and fluids, and that such transmission takes 
 place even more rapidly through living than dead mem- 
 branes. It is thus easy to conceive how the water may pass 
 from the blood to the air, and be carried off in the breath. 
 With respect to the quantity thus removed, it must be 
 evident that it will vary according to different circum- 
 stances. When the circulation through the lungs becomes 
 hurried, and the respirations full and frequent, as from 
 exercise, a greater quantity is carried off, as may be 
 noticed in stage horses in a clear frosty day. A dry at- 
 mosphere, from the greater appetite it has for moisture, 
 will more readily absorb a larger quantity. Though, 
 from its more perfect solution in such air, it does not be- 
 come sensible in the breath. There being an intimate 
 sympathy between the skin and the lining membrane of 
 the air-passages, they become reciprocally affected by 
 various influencing causes. Thus, if the perspiration 
 from the external surface of the body be suddenly checked, 
 the balance of the circulation becomes affected ; the 
 blood is impelled to the internal parts, and pulmonary 
 transpiration may be increased, so as in some measure to 
 compensate for the check that of the skin has sustained. 
 
66 VAPOUR OF THE BREATH. 
 
 On the contrary, an indolent and inactive life, a moist 
 atmosphere, and a free and copious perspiration, will 
 tend to diminish the quantity carried off in breathing. 
 Various other causes, from the state of the constitution in 
 health and disease, particular kinds of food, regimen, and 
 medicines, will tend to affect the quantity of the thinner 
 part of the blood removed from the lungs. Any attempt 
 to estimate the quantity daily exhaled in this way must 
 necessarily be beset with many difficulties, and an ap- 
 proximation only to the truth can be arrived at. Ac- 
 cording to good authorities, the amount is rather more 
 than a pint of fluid in twenty- four hours in an adult 
 man under ordinary circumstances. 
 
 When a fluid passes to the aeriform state, a large 
 quantity of heat is absorbed, and becomes latent. If the 
 hand be moistened with spirit or ether, and freely ex- 
 posed to the air, evaporation rapidly takes place, produc- 
 ing cold in consequence of the heat necessary to the condi- 
 tion of vapour being abstracted from the hand. If a pint 
 of fluid be carried off in the breath every twenty-four 
 hours, a considerable quantity of heat must in this way be 
 daily expended. Consequently, in this respect, respira- 
 tion becomes a cooling process. From the exercise of 
 the function of respiration, therefore, heat is expended 
 in two ways, 1st, by the temperature of the air inhaled 
 becoming raised to that of the body ; and 2dly, from the 
 caloric necessary to the constitution of the vapour of the 
 breath. 
 
 The fluid of the pulmonary transpiration is not to be con- 
 founded with the thick viscid secretion which we cough up, 
 and which forms the matter of expectoration, a secretion 
 furnished by numerous little follicles scattered over the sur- 
 face of the air-passages, and which is deposited upon the lin- 
 ing membrane for its defence ; while the pulmonary trans- 
 piration is derived from the thinner and more watery part 
 of the blood, by the removal of which the blood becomes 
 condensed in passing through the lungs, in proportion to 
 
VAPOUR OF THE BREATH. 67 
 
 the quantity of the water thus removed. With respect 
 to the source of this vapour, it has been supposed that 
 the water was formed in the lungs by the direct union of 
 its elements ; that the hydrogen of the blood combined 
 with the oxygen of the air, and that during the union a 
 considerable quantity of caloric was extricated. This 
 opinion is, however, now set aside, and the vapour is 
 held as being entirely derived from the serous part of the 
 blood. When we consider that the air drawn into the 
 lungs comes in contact with an extensive surface of moist 
 membrane, and that the serum of the blood can easily 
 permeate the membrane ; and further, that the extreme 
 vessels, in their state of vital activity, may exhale more or 
 less freely according to different circumstances, it is not 
 difficult to understand the source from whence it is de- 
 rived. We know that other matters besides the thinner 
 part of the blood are carried off in this way. Hence, when 
 a person has partaken of a dish seasoned with onions or 
 garlic, or after he has swallowed ardent spirits, these sub- 
 stances are shortly after detected in the breath ; and hence, 
 too, in a contagious disease like typhus, the breath of the 
 patient becomes loaded with the poisonous miasmata, and 
 may thus communicate the disease to a person in health. 
 Hence the precaution which ought to be used in attend- 
 ing upon the sick under such circumstances, in order 
 to avoid receiving immediately their breath into our own 
 lungs. The breath may also be vitiated from a depraved 
 state of digestion, when, instead of a sweet and nutritious 
 chyle being produced, a crude and ill-digested matter is 
 introduced into the system, tainting the breath, as well 
 as disordering the general constitution. 
 
 The atmosphere, consisting as it does of oxygen, nitro- 
 gen, and carbonic acid, is changed by respiration : the 
 oxygen is diminished, the nitrogen remains much the 
 same, and the carbonic acid is increased. If an animal 
 be confined in a given quantity of air, it soon dies, even 
 when means are taken to remove the carbonic acid which 
 
O CHANGES ON THE AIR. 
 
 is exhaled; and if such air be tested, it will be found 
 that the oxygen has been much diminished, but that 
 the nitrogen remains as before. In all circumstances, 
 and in all animals, a quantity of oxygen thus disap- 
 pears, though the amount varies much in different ani- 
 mals, and in the same animal in different states of health 
 and other circumstances. Quadrupeds and birds expend 
 a much greater quantity than animals lower in the scale. 
 Although the nitrogen in general be but little affected, 
 still occasionally it has been found either increased or 
 lessened, most probably according to the wants of the 
 system at the time. Oxygen, nitrogen, carbon, and hy- 
 drogen, are the chief elements of which the body is com- 
 posed. Of these are formed the muscles, the tendons, 
 ligaments, and membranes ; the nerves, blood-vessels, 
 glands, and the blood itself; as well as the various secre- 
 tions which are elaborated from it. Though there are 
 other elementary bodies, still they are confined to parti- 
 cular tissues, or are found only in very small quantities, 
 as the lime of the bones, the iron of the blood, and the 
 sulphur of some secretions. All these elements must be 
 derived from without, for we can scarcely admit of a crea- 
 tive power even in living animals. The most that can be 
 ascribed to them is the power of appropriating arid com- 
 bining the elements of which they are composed, according 
 to their exigencies. Now, many animals subsist upon 
 food which contains little or no nitrogen, though it be 
 found abundantly in their structures. There is no other 
 source by which they can so readily obtain it as from the 
 air by respiration. On the other hand, if an excess of 
 nitrogen at any time exist in the system, the superfluous 
 part may be carried off by the lungs as well as by other 
 channels, and thus account for the increase or diminution 
 of the nitrogen which has been observed. 
 
 That carbonic acid gas is given off in the breath may 
 easily be proved, and no way more readily than by breath- 
 ing into lime-water, when it will combine with lime held 
 
CHANGES ON THE AIR. 69 
 
 in solution, and form with it a sparingly soluble com- 
 pound, which is thrown down, rendering the solution 
 turbid. 
 
 Different opinions are entertained as to the source of 
 this carbonic acid. Some believe that the oxygen of the 
 air is attracted by the venous blood, and combines with 
 its carbon, forming carbonic acid ; others that the carbon 
 passes from the venous blood to unite with the oxygen in 
 the cells of the lungs. According to these two opinions, 
 the carbonic acid is considered as formed in the lungs, and 
 carbon is extracted from the blood ; the difference between 
 them being, whether the oxygen be attracted by the blood 
 in the vessels, or the carbon be secreted by the vessels, so 
 as to combine with the oxygen of the air. In either case, 
 supposing no water is formed by the union of oxygen with 
 hydrogen from the blood, the quantity of carbonic acid 
 exhaled ought always to account for the quantity of oxygen 
 which disappears, knowing as we do the amount of oxygen 
 in a given bulk of carbonic acid gas. But it has been 
 found that we cannot always thus account for the oxygen 
 which disappears during respiration ; for sometimes there 
 is more carbonic acid given off, and sometimes less, than is 
 indicated by the expenditure of oxygen. Another view- 
 has consequently been taken, ascribing the loss of oxygen 
 which the air sustains to the blood, in its passage from the 
 arterial into the venous pulmonary capillaries, attracting 
 and combining with it during the change from the dark 
 purple to the florid red ; that is, when it undergoes its 
 specific change in the lungs. It is believed that the 
 oxygen which thus enters the blood gradually unites with 
 carbon, more especially in the capillaries between the 
 arteries and veins of the system, where" the converse 
 change to that which is effected in the lungs takes place, 
 and that the venous blood, on being transmitted to the 
 lungs through the ramifications of the pulmonary artery, 
 secretes or exhales carbonic acid. According to this 
 view, the blood, during its passage through the lungs, 
 
70 CHANGES ON THE AIR. 
 
 throws off the carbonic acid which is formed in its circu- 
 lation through the system, and absorbs oxygen to unite 
 with carbon in the system. A modification of this theory 
 is entertained, that it is not the oxygen alone which is 
 absorbed by the blood in the lungs, but a portion of the 
 entire air is taken up, and the quantity of oxygen and of 
 nitrogen retained, according to the wants of the system ; 
 so that if nitrogen be not required, an equal bulk of it is 
 exhaled as absorbed ; and thus we account for its being 
 generally apparently unaffected by respiration ; while, if 
 necessary, a portion may be retained or thrown off as re- 
 quisite, accounting for its diminution in some cases and its 
 increase in others : Further, that the quantity of carbonic 
 acid given off also varies according to the state of the sys- 
 tem in general, without any direct reference to the oxygen 
 taken up. 
 
 The quantity of carbonic acid given off has been found 
 to vary according to different circumstances. As its gene- 
 ration seems connected with and dependent upon some of 
 the most important of the vital functions of animals, we 
 may advert, for the sake of illustration, to some of the con- 
 ditions on which the variations seem to depend. It has 
 been observed to be affected by the time of the day, the 
 period of the year, the age of the animal, the nature of the 
 food, &c. We are indebted to Dr Prout for the first 
 notice as to the variation of the quantity according to 
 the hour of the day. He ascertained that the greatest 
 quantity is given off about noon, or between eleven 
 o'clock A. M. and one o'clock p. M. ; that the quantity 
 diminishes till about eight in the evening, when it re- 
 mains nearly stationary at the minimum till the fol- 
 lowing morning between three and four o'clock, when it 
 begins to increase, till it again reaches the maximum 
 about noon. There are so many changes to which our 
 bodies are subject, both in health and disease, dependent 
 upon causes which have hitherto eluded the most careful 
 researches, that on the announcement of a new and inte- 
 
CHANGES ON THE AIR. 
 
 71 
 
 resting fact like this, we become anxious to inquire whe- 
 ther we can from thence obtain any elucidation of phe- 
 nomena with the existence of which we are sufficiently 
 familiar, but as to the causes on which they depend we 
 are in profound ignorance. Among these phenomena, 
 the causes of which we are ignorant, may be mention- 
 ed the exacerbations and remissions which appear in 
 regular succession in agues and other diseases, which it is 
 possible may have some connection with the same causes 
 that originate the differences as to the amount of car- 
 bonic acid at different periods of the day. 
 
 The season of the year has also been found to influence 
 the generation of the carbonic acid ; in winter a greater 
 quantity being expelled from the lungs than in the sum- 
 mer. Young animals generate less carbonic acid than adults. 
 The nature of the food and drink has also a considerable 
 effect. Vegetable diet lessens the quantity, as also do 
 ardent spirits, violent exercise carried to fatigue, sleep, 
 and the depressing passions and emotions of the mind. 
 
 It appears that the causes which tend to diminish its 
 production are more various^than such as have an opposite 
 tendency. Generous diet, moderate exercise, and a cheer- 
 ful state of mind, promote its formation. Or, in other 
 words, whatever tends to keep up a vigorous and healthy 
 state of the body, increases it, and when the functions 
 are carried on with due alacrity and ease, it is more 
 readily formed. On the other hand, all those causes 
 which diminish the vital powers, and depress the energies 
 of the system, have a contrary tendency. 
 
 The condition of the skin has likewise a considerable 
 influence. For, in this respect, besides others, there is a 
 reciprocal connexion between the skin and the lungs, 
 which ought not to be overlooked. The skin produces 
 upon the air similar changes to those which result from 
 the action of the lungs. In some animals, as in toads 
 and frogs, the skin may effect the necessary changes 
 where the function of the lungs is altogether arrested. 
 
72 CHANGES ON THE AIR. 
 
 In some experiments, where a toad was surrounded by a 
 thick coating of Paris plaster, it continued to live for 
 some time, the air which penetrated the pores of the 
 plaster being sufficient to prevent the extinction of life. 
 We are in this way enabled to understand how that 
 animal has been found alive, imbedded in a sandstone 
 rock, belonging, as it does, to a class of animals which 
 require a less supply of air, and moreover being fur- 
 nished with external integuments capable of effecting the 
 changes upon the blood through the medium of the air 
 in contact with them. In so confined a situation, where 
 many of the functions are suspended, as muscular motion, 
 life remains, though of course in a very dormant and in- 
 active state. Even in man the skin produces the same 
 changes upon the air as are produced by respiration. The 
 extent of the effect upon the air, and the quantity of car- 
 bonic acid formed, will vary with the health and consti- 
 tution of the individual, and also according to the climate. 
 Dr. Copeland mentions, that in a series of experiments 
 performed by him on his own person, and on a negro, 
 whose chest was about the same capacity as his own, 
 he, Dr C., produced a larger quantity of carbonic acid 
 from the lungs ; but that the negro exhaled more from 
 the surface of the body, in the proportion of three to 
 two. This fact is interesting, in reference to the adapta- 
 tion of negro constitution to a hot climate. We shall 
 again have occasion to refer to this subject when we come 
 to treat of the production and regulation of animal tem- 
 perature. 
 
 The alimentary canal, too, lined as it is throughout by 
 a membrane similar in structure, and in some respect ana- 
 logous in function to that which covers the air-tubes, is 
 known to produce upon air effects identical with those effect- 
 ed by breathing. From the examination of the air found 
 in the stomach and different parts of the intestinal tubes, 
 it has been found that while in the stomach it is similar to 
 the external atmosphere, while in the intestine beyond, the 
 
CHANGES ON THE AIR. 73 
 
 oxygen entirely disappears, and is replaced by carbonic 
 acid ; and there is little doubt that the inner membrane 
 of the alimentary tube performs this office to no small 
 extent in many of the inferior tribes of animals. It may 
 be observed with respect to the beautiful gold fishes so 
 often kept in vases as pets, that when, from neglect, the 
 water has not been duly changed, and when therefore it 
 has become vitiated, the little creatures often come to 
 the surface for the purpose of obtaining a mouthful of air, 
 which they swallow. The lining membrane of the sto- 
 mach then takes on vicariously the office of the gills. 
 After the air has been changed, they may be observed to 
 reject it again by a kind of eruction; so that in this 
 way they are enabled in some measure to obviate the 
 evil consequences which result from the unhealthy state of 
 their surrounding medium. 
 
 It has been said that art requires to be abundant in 
 causes which produce but few effects, while nature is 
 sparing in causes, but abundant in effects. It may be 
 true that the operations of nature may be traced up to a 
 few leading general laws, or secondary causes; but in 
 each individual example of the functions of living ani- 
 mals, such an infinite number of subordinate causes are 
 brought into play, that even reversing the above rule 
 would come as near the truth. In a vague and super- 
 ficial manner it may be said that the blood is circulated 
 by the heart and blood-vessels ; that the function of re- 
 spiration is performed by the lungs, and that the food 
 is digested by the stomach ; but when we come to study 
 more closely any one of these functions, we soon find 
 such a vast number of modifying causes, that the mind 
 is at first apt to get bewildered ; or we may fall into the 
 error of attributing too much to one of the causes which 
 we find in operation, and neglect others which may ex- 
 ert a very important influence over the proper perform- 
 ance of the function under our consideration. When 
 we state that oxygen is abstracted from the air, and that 
 
 E 
 
74 CHANGES ON THE BLOOD. 
 
 carbonic acid is exhaled by respiration, we state the 
 truth, but not the whole truth, for we find that the 
 same is done by the skin and by the alimentary canal, 
 though in a subordinate degree. 
 
 Changes upon the Blood. From what has just been 
 stated respecting the changes which the air undergoes 
 in respiration, it is obvious that the blood, being subser- 
 vient to them, must itself become altered. The altera- 
 tions effected upon it may be considered in respect to its 
 colour and density, its chemical constitution and tem- 
 perature, and its vital properties. 
 
 Colour and Condensation. When a vein is opened, 
 the blood which flows is of a dark purple colour. On 
 exposure for a little time to the air, it assumes a bright 
 scarlet hue ; nor is immediate contact with the air abso- 
 lutely necessary to produce this effect, for, if received into 
 bladders much thicker than the delicate membranes which 
 separate the air from the blood in the cells of the lungs, 
 a similar change will take place. The blood, on exposure 
 to the air in the cells of the lungs, is seen to change from 
 purple to florid red. 
 
 It has already been stated, that every day upwards of 
 a pint of the watery part of the blood is carried off in the 
 breath, in a man of common size, under ordinary circum- 
 stances. The blood flowing to the left side of the heart 
 will be thereby so far condensed. 
 
 Chemical Constitution and Temperature. As has al- 
 ready been shewn, during respiration the air evolved con- 
 tains less oxygen and more carbonic acid than that which 
 is inhaled : in so far does the blood become chemically 
 changed, that it now will contain more oxygen and less 
 carbonic acid. Other alterations in the chemical condi- 
 tion between the venous and arterial blood are without 
 doubt effected, but elude the means we at present possess 
 of satisfactorily estimating them. A slight difference has 
 been observed to take place in the heat of the blood, there 
 being a temperature about one degree higher in the scarlet 
 than in the purple. 
 
 
ANIMAL HEAT. 75 
 
 The blood in the living body is not to be considered 
 merely a very compound mixture of water, colouring 
 matter, albumen, fibrin, with several salts, &c., but a 
 living substance, endowed with the peculiar vital proper- 
 ties of the system to which it pertains. These properties 
 are different in the two kinds of blood. Arterial blood 
 is necessary to the due contractility of the muscles, to the 
 all-important functions of the brain, to the formation of 
 the secretions, and even in an important degree to the 
 office of the lungs themselves. In becoming arterialized 
 by the function of respiration, therefore, the blood obtains 
 renewed vital energies. 
 
 In connexion with the function of respiration, we shall 
 consider animal temperature, voice, the effects of different 
 gases, and lastly, the phenomena resulting from the sus- 
 pension of breathing. 
 
 Animal Heat. The term caloric has been applied to 
 the cause which produces the sensation of heat. It is 
 necessary to have recourse to some such specific name ; 
 for if we were to depend on our sensation as to heat, our 
 conceptions would be vague, indefinite, and often errone- 
 ous. Let two persons enter a room in which the tem- 
 perature is, say 45 ; the one coming from a highly heat- 
 ed apartment, the other after having been for some time 
 exposed to the external air in a frosty night. To the 
 first the room will appear intolerably chill, to the latter 
 comfortably warm. Or let a person put for some time 
 one hand into a basin of water as warm as he can bear 
 it, his other into a basin containing ice-cold water ; then 
 let both waters be poured into one vessel, and let him 
 plunge both hands into the mixture ; now he will find 
 that to the one hand the water appears cold, and to the 
 other warm. Further, in a calm frosty day we may walk 
 abroad without experiencing the necessity of additional 
 clothing ; but if a breeze spring up, even though the tem- 
 perature become considerably elevated, we immediately 
 become sensible of the want of protection ; so that wero 
 
76 ANIMAL HEAT. 
 
 we to trust to our feelings in these cases, we should often 
 be misled. 
 
 Similar quantities of different bodies at the same tem- 
 perature do not contain the same quantity of caloric, or 
 matter of heat. Thus, a pint of water at any given tem- 
 perature contains twice the quantity of caloric that a pint 
 of olive oil does. This difference in bodies is termed their 
 capacity for caloric. Water, therefore, has twice the ca- 
 pacity for heat that olive oil has. The same body in dif- 
 ferent conditions has its capacity for caloric changed and 
 adapted to each state. When -ice is converted into water, 
 the capacity for heat in the fluid water is much greater 
 than in the solid ice ; and when water is converted into 
 vapour, the capacity is vastly increased ; so that the same 
 substance in these three conditions possesses very different 
 capacities for heat. 
 
 When two bodies enter into combination with each 
 other, the product of their union having a less capacity 
 for caloric than the two constituents, heat is given off. 
 Hence, under whatever circumstances oxygen and carbon 
 unite, there is an extrication of caloric. We have an 
 example of this in the common fire, where the carbon of 
 the fuel unites with the oxygen of the air in the chamber, 
 forming carbonic acid, the union being accompanied with 
 evolution of heat and light. Fermentation furnishes an- 
 other example. In living animals a combination takes 
 place between oxygen and carbon ; here, therefore, there 
 must be a liberation of caloric. 
 
 Caloric has a tendency to diffuse itself, so as to bring 
 contiguous bodies to an uniform temperature. When a 
 warm body is placed in a cold medium, caloric is carried 
 off, and the heat reduced in two ways ; first, by contact 
 with the colder body, when it is said to be removed by 
 conduction. 
 
 Different substances vary very much as to their power 
 of conducting caloric. If iron, glass, and fur, at the freez- 
 ing point, be brought in contact with the body, although 
 
ANIMAL HEAT. 77 
 
 the three be of exactly the same temperature, yet very 
 different sensations will be experienced. The iron will 
 feel intolerably cold, the glass less so, and the fur will 
 scarcely appear to be different from the warm hand. This 
 arises from the difference of their conducting power ; the 
 iron is an excellent conductor, the glass much inferior to 
 it, and the fur one of the worst conductors known. 
 
 2^/y, Heat is reduced in warm bodies by what is term- 
 ed radiation. If a red-hot ball of metal be suspended in 
 a room, caloric darts off from its surface in all directions, 
 until its temperature is brought into equilibrium with 
 surrounding bodies. Radiation of caloric, like conduc- 
 tion, varies very much in different substances. Dark rough 
 surfaces radiate much faster than bright polished surfaces. 
 Colour has a considerable influence on radiation, black 
 producing the greatest and white the smallest effect. 
 
 Lastly, bodies differ from each other in their power of 
 absorbing caloric ; this, however, is always in proportion 
 to the radiating power, those bodies which radiate caloric 
 readily being active in absorbing it, while slow radiators 
 are slow in absorbing. It is necessary to bear these facts 
 in our mind when we enter upon the consideration of the 
 manner in which organized bodies regulate their tempera- 
 ture. Among other properties of living beings, the regu - 
 lation of the heat of their bodies, so as to adapt it to their 
 individual constitutions and habits, and to the circum- 
 stances in which they are placed, is one of their most 
 general characteristics, most necessary to their well-being, 
 and indeed to their very existence in a living state. 
 Where the medium in which they exist is such as is sub- 
 ject to but slight variations of temperature, and these 
 brought slowly and gradually about, as in water, the tem- 
 perature in general differs but little from that medium. It 
 was not necessary, therefore, that the inhabitants of the 
 waters should be furnished either with the means of gene- 
 rating much heat, or with clothing for its preservation. 
 
 Water, being an excellent conductor of caloric when 
 
78 ANIMAL HEAT. 
 
 compared with air, rapidly abstracts heat. Accordingly, 
 we find that such inhabitants of the waters as sustain 
 any considerable temperature above it, are furnished with 
 admirable means for its preservation. The whale tribes 
 have smooth and polished skins, which do not readily 
 throw off the heat, underneath which there is a large 
 depositation of oily fat, a very bad conductor of caloric. 
 They are thus clothed in the best manner possible for the 
 retention of their internal heat. Seals and walruses have 
 clothing fashioned on the same principle. 
 
 On the other hand, such living bodies as inhabit the 
 air, exposed as it is to so many vicissitudes of tempera- 
 ture, require not only the power of generating heat, but 
 also the means for its regulation, according to varying cir- 
 cumstances. The average temperature of man in a state 
 of health is about 97 or 98 of Fahrenheit's scale. In 
 quadrupeds it reaches in some as high as 100, and in 
 birds to 107 or 108. 
 
 We shall, first, inquire into its source and distribution 
 through the body ; and, 2dl^ into the manner in which 
 it is regulated when the body is exposed either to very 
 high or very low temperatures. 
 
 No sooner had Black discovered the nature and com- 
 position of carbonic acid, and the large quantity which 
 was given off by animals during respiration, than it struck 
 him that here might be found an explanation of animal 
 heat, which, notwithstanding some vague suggestions of 
 Mayow, was previously very conveniently stated to be 
 an innate property of living bodies, a satisfactory mode of 
 getting quit of all such difficulties at once, without any 
 farther trouble ! Black's idea, although shewn to be un- 
 tenable, roused inquiry, and laid the foundation of all the 
 subsequent discoveries and acquirements which have since 
 been made. It would be out of place here to enter into 
 the various steps in the progress of our knowledge respect- 
 ing this subject. 
 
 It has been stated that more carbonic acid and less oxy- 
 
ANIMAL HEAT. 79 
 
 gen are thrown off by the breath than are inhaled by it. 
 An union of oxygen with carbon, to form the carbonic 
 acid, must therefore be effected in the body, and conse- 
 quently an extrication of heat. It has also been stated 
 that when substances pass from one condition to another, 
 their capacity for heat is changed. Accordingly, when 
 venous blood is converted into arterial, an alteration in 
 this respect is effected ; as also when it is again changed 
 from arterial to venous. 
 
 A question which has been much discussed is, where 
 does the union of the oxygen with the carbon take place ? 
 Is it in the lungs ? Or is it in the system ? Those who 
 hold that the union is effected in the lungs account for 
 the temperature of these organs remaining the same as in 
 the neighbouring viscera, notwithstanding the extrication 
 of caloric which necessarily takes place, by assuming that 
 this caloric immediately enters into the arterialized blood, 
 the capacity of which has been increased on its conversion 
 from the venous state. The arterial blood propelled by 
 the left ventricle of the heart penetrates through the arte- 
 ries into every tissue of the body. In the extreme branches 
 of the arteries it is again venalized, in which state the 
 blood has a less capacity for caloric. The caloric is con- 
 sequently set free, and supports the temperature. 
 
 Those again who contend that a portion of the entire 
 air enters into combination with the blood, account for the 
 phenomena in the following way : They assert that the 
 union between the oxygen and the carbon does not take 
 place particularly in the lungs, but in the extreme arterial 
 capillaries of the whole system, where the blood is changed 
 from arterial to venous, and that at the same time the 
 caloric is set at liberty to support the animal heat. 
 
 It thus appears that both agree that the immediate source 
 of animal heat is in the union of oxygen with carbon ; 
 both agree that the liberation of the caloric occurs where 
 the blood becomes venalized, the difference between the 
 parties being as to the place where the union is effected, 
 
80 ANIMAL HEAT. 
 
 a difference which the student of general physiology may 
 safely leave them to settle between themselves, at the same 
 time thanking them for the patience, diligence, and suc- 
 cess with which they have established the two important 
 positions on which they are agreed, and which probably 
 would not have been placed on so satisfactory a basis had 
 no rivalship taken place between them. 
 
 It would thus appear that the source and distribution 
 of animal heat is in the mutual exercise of the functions- 
 of respiration and circulation. Others, however, have at- 
 tempted to overthrow these views as to animal heat by 
 mutilating animals in various ways, justly considering 
 that it is both a more easy and successful plan, in order to 
 gain notoriety, to endeavour by ingenious objections to 
 upset a generally received doctrine, than to establish one 
 equally good in its place. 
 
 It is by no means here intended in the slightest degree 
 to condemn the performance of experiments on living 
 animals in order to advance knowledge and establish 
 truth. He must be very ignorant indeed who is not 
 aware of the many valuable facts which have been ascer- 
 tained in this way, which otherwise must have been 
 still unknown, and by which much suffering has been ob- 
 viated, and many a valuable life preserved. But cruel 
 mutilations of living animals, either in order to discover 
 something at haphazard, or to give a show of support 
 to the crude fancies of a loose imagination, ought, to 
 say the least, to be met with the contempt and neglect 
 they so richly deserve. Not so where the experiments are 
 such as necessarily deprive the animal of feeling, or where 
 - steps have previously been taken to effect the same pur- 
 pose : then no objection can be started on the score of 
 humanity ; but in all such cases it is to be recollected that 
 they are mutilations at best. Where, therefore, the ner- 
 vous system has been destroyed to such an extent as it 
 sometimes has been, in order to shew that such destruc- 
 tion was accompanied with loss of power in the produc- 
 
ANIMAL HEAT. 
 
 81 
 
 tion of heat ; instead of agreeing that animal heat con- 
 sequently results from the nervous system, it is much 
 more reasonable to believe that the result arises from the 
 stop that is put to the due performance of those functions 
 on which its production more immediately depends. 
 
 That the source and diffusion of heat through the body 
 depend on the combined action of the functions of respi- 
 ration and circulation, is supported by a great number of 
 phenomena both of health and disease. To some of these 
 we may now advert. Whatever tends to increase these 
 functions increases the temperature, and conversely, what- 
 ever lessens them produces a diminution of heat. Exer- 
 cise being accompanied with an exhilaration both of cir- 
 culation and respiration, produces, in the coldest weather, 
 a glow of heat over the whole body. When the hands 
 become benumbed with cold, friction, by increasing the 
 circulation, soon restores the warmth. For the same 
 reason, where exposure to cold has induced dangerous 
 symptoms, one of the first circumstances to be attended to 
 is the restoration of the circulation. At the same time, it is 
 necessary to do this with the utmost caution. Warmth, 
 friction, and other means ought to be gradually exhibited. 
 Violent applications at first are likely to be followed by 
 the worst effects. Experience has pointed out to the 
 Greenland sailor that the best mode of restoring the frost- 
 bitten extremities is to rub them with snow, and that 
 the sudden approach to a fire would probably produce the 
 death of the part, at any rate, violent and protracted in- 
 flammation and its consequences. He is at the same time 
 totally ignorant of the principles on which this judicious 
 practice is founded ; consequently, upon any unusual oc- 
 currence, cannot avail himself of it* A few years ago a 
 very fine healthy young man fell overboard from an open 
 boat, at some distance from his ship in Greenland, the 
 temperature at the time being considerably below zero. 
 Before he could be got on board of the ship, his clothes 
 were completely frozen, his extremities benumbed, and 
 
82 ANIMAL HEAT. 
 
 he was incapable of voluntary motion in his limbs. Still, 
 however, respiration was carried on, also circulation in 
 the central parts, and his mind remained unaffected. He 
 was carried down into the heated cabin, his clothes were 
 cut from him, and on being wrapt in warm blankets, he 
 was laid before the fire, when hot brandy and water was 
 administered to him. In a short time the benumbed 
 limbs were tortured by the most agonizing darting pains, 
 and in two hours he was dead. 
 
 When any organ is brought into a state of inordinate 
 action, and consequently has an increased quantity of 
 blood passing through it, the temperature is elevated. 
 Dr Granville mentions a case (Phil. Trans., 1825) where, 
 during the violent action of the womb in parturition, 
 he noticed the temperature rise as high as 120, by 
 much the highest animal heat recorded. In local inflam- 
 mations, as in whitlow, the temperature of the part af- 
 fected is raised above that of the surrounding parts. In 
 inflammatory fevers, both respiration and circulation being 
 increased, especially the latter, the burning heat forms 
 one of the most distressing concomitants. In ague, dur- 
 ing the cold stage, the circulation is retarded, the blood 
 leaves the surface, and accumulates in the cavities. The 
 surface becomes cold and chilly, accompanied with shiver- 
 ings. As soon as re-action takes place, the blood is pro- 
 pelled to the surface in an increased quantity, and the 
 temperature soon mounts above the natural standard. 
 On the other hand, during the paroxysm of asthma, where 
 both respiration and circulation arc involved, the tem- 
 perature falls sometimes to 82. 
 
 Small quadrupeds breathe quicker, their motions are 
 performed with greater quickness and vivacity, and they 
 support a higher temperature, than man. Birds inhale a 
 much greater quantity of air than other animals ; but, as 
 has been already stated, this is not merely for the pur- 
 pose of respiration, but to fill the air-bladders by which 
 their bodies are rendered buoyant. Still they breathe 
 
ANIMAL HEAT. 83 
 
 very quick, their circulation is very rapid, and all their 
 motions are performed with great force and velocity. 
 The temperature which they sustain is higher than in 
 other animals, their natural standard being the high 
 fever heat of man, 107 or 108. Reptiles, whose respira- 
 tion is slow and performed at distant intervals, a portion 
 only of their blood passing through the lungs at each 
 complete circulation, and whose blood is transmitted 
 slowly and sluggishly, have a temperature much lower 
 than man, and therefore are termed cold-blooded. Insects, 
 from the smallness of their size, and the peculiarities of 
 their respiratory and circulating systems, are not easily 
 examined as to the heat they may individually produce ; 
 yet collectively this is more easily effected. The bee- 
 hive, when the community are in a state of full activity, 
 has been observed to stand at 100. 
 
 Regulation of Temperature. This may be considered 
 under two points of view ; ls, When the body is ex- 
 posed to a high degree of heat, how does it preserve its 
 usual standard ? '"Zdly, By what means is vital warmth 
 preserved when the body is exposed to very low tempera- 
 tures ? These two questions might be considered to- 
 gether ; but there will be an advantage in examining 
 them, in the first place, separately. 
 
 The celebrated Boerhaave believed that the use of re- 
 spiration was to cool the blood, and that a higher tem- 
 perature than that of the body was incompatible with 
 life. Some experiments, undertaken at his suggestion by 
 Fahrenheit, appeared to confirm this hypothesis. But the 
 thermometer enabling travellers in tropical climates to 
 make accurate observations, it was found that in these 
 regions the heat of the air often rises considerably above 
 that of the blood, and which shewed the fallacy of his 
 opinion. Experiments were instituted to ascertain to 
 what extent the heat might be tolerated. A baker's 
 daughter in France was seen to enter an oven heated 
 to 260, and remain for twelve minutes without ex- 
 
84 ANIMAL HEAT, 
 
 periencing much inconvenience. Public exhibitors (term- 
 ing themselves fire-proof) often enter prepared chambers 
 where the temperature is raised to a height sufficient to 
 cook meat, and remain till it is sufficiently cooked. It 
 may be well to notice the effects of heated dry air, vapour 
 bath, and hot water bath. When animals are placed in a 
 small apartment, with dry air heated to 112, in about 
 half an hour the respirations are quickened, and after- 
 wards become more easy. After remaining for about an 
 hour and a half, on being removed, they gradually recover. 
 In some of the experiments performed on man, different 
 individuals have remained from seven to eight minutes 
 in a chamber heated to 230, 240, and 260. The 
 pulse of a young man, which beat commonly 75, was 
 raised to 164 per minute. Persons unaccustomed to the 
 use of the vapour bath cannot tolerate it much above 100 ; 
 but in Russia and Finland, where it is in common use, 
 individuals habituated to it can remain for half an hour 
 with the temperature raised to 160 and 165. Few per- 
 sons can remain in the hot bath for many minutes when 
 the temperature is that of the blood. 
 
 When the body is exposed to high temperatures, the 
 respirations become quicker and fuller ; the blood is pro- 
 pelled by frequent and powerful pulsations, and is deter- 
 mined especially to the surface ; and the heat of the body is 
 in a slight degree augmented, but by no means to any 
 thing like the extent that might have been anticipated. 
 In the cases of exposure to high degrees of heat, it was 
 never found to reach what it is observed to do occasion- 
 ally in inflammatory fever. We have therefore to inquire 
 by what means the living system is capable of resisting 
 these high temperatures, so as to preserve its own uni- 
 formity. 
 
 Where the heat of the atmosphere is below that of the 
 body, the air, on being inhaled, is soon assimilated to the 
 temperature of the body, and in this way a quantity of 
 heat is carried off. 
 
ANIMAL HEAT. 85 
 
 When fluids pass into the state of vapour, a very large 
 quantity of heat is necessary to them in that condition, 
 which does not raise their temperature. As has been 
 already mentioned, a considerable quantity of watery 
 vapour is exhaled by the breath. Hence in this way a 
 quantity of heat will be removed. 
 
 As, however, animal heat is evolved where the arterial 
 blood is changed into venous ; and since the effect of 
 heat is to increase the circulation and determine it to the 
 surface, so we find that the uniformity of animal tem- 
 perature is preserved chiefly in consequence of what takes 
 place on the surface of the body. At all times a quantity 
 of the thinner part of the blood is carried off from the 
 skin, generally in a state of invisible vapour, while in some 
 conditions it is deposited upon it in a fluid form, or sweat. 
 When it passes off in vapour, it is termed invisible trans- 
 piration, and when deposited in a sensible state, visible 
 transpiration. The quantity of fluid thus removed from 
 the body varies exceedingly, according to a great many 
 circumstances. The function of transpiration is at all 
 times of the greatest importance to the health and com- 
 fort of the individual. It has been estimated that an 
 ordinary-sized man, under ordinary circumstances, loses 
 about two pints of fluid in this way in the twenty-four 
 hours. Heat is one of the chief causes of its increase. 
 By the exercise of this function, a very great quantity of 
 heat must be daily expended. To have some idea of this 
 quantity, we have merely to consider how much heat 
 would be necessary to convert two pints of water to the 
 state of vapour, which is only the average quantity of 
 fluid daily transpired. 
 
 The conditions of the air have much influence upon 
 transpiration. The chief are the temperature of the air ; 
 dryness and humidity ; rest and motion. The higher 
 the temperature, the greater the quantity of water the 
 air is capable of holding in solution ; and the drier it is, 
 the greater is its attraction for moisture. We feel much 
 
ANIMAL HEAT. 
 
 less oppressed by a hot and dry atmosphere than by one 
 of inferior temperature saturated with moisture ; for, in the 
 first instance, the fluid of perspiration is instantly absorbed 
 and carried off by the air. Though the skin remains dry, 
 yet at the same time a free and copious perspiration is 
 carried on, and in this way removes a great quantity of 
 heat. In consequence of the loss of fluid which thus 
 takes place, thirst is excited, warning us to have recourse 
 to drinks, that compensation for the expenditure may be 
 effected. But in an atmosphere already loaded with 
 moisture, the matter of perspiration is not so readily re- 
 moved ; it forms a layer of moisture on the skin, or ac- 
 cumulates in drops, constituting sweat ; and although 
 thus rendered cognizable to the senses, yet, in reality, a 
 much smaller quantity may be passing off; consequently 
 we find in a warm moist day that we are much less ca- 
 pable of action ; we feel languid, easily fatigued, and, on 
 moderate exertion, become bedewed with sweat. 
 
 Air is comparatively a bad conductor of heat, so that 
 in a still atmosphere the body is not cooled so fast as 
 where fresh portions of air come in contact with it in 
 succession, each carrying along with it a certain quantity 
 of the heat. This is well illustrated by what Sir Edward 
 Parry states in his voyage to the arctic regions in 1820 : 
 February 15th, he remarks, " From 4 p. M. on the 14th 
 till half-past seven on the following morning, being 
 an interval of fifteen hours and a half, during which time 
 the weather was clear, and nearly a calm, a thermometer, 
 fixed on a pole between the ships and the shore, never 
 rose above 54, and was once during the interval, namely, 
 at six in the morning, as low as 55. This low temperature 
 might perhaps have continued much longer, but for a 
 breeze which sprung up from the northward, immediately 
 on which the thermometer rose to 49, and continued still 
 to rise, till, at midnight, it had reached 34. During the 
 lowest temperature above mentioned, which was the 
 most intense degree of cold marked by the spirit-thermo- 
 
ANIMAL HEAT. 87 
 
 meter during our stay in winter harbour, not the slight- 
 est inconvenience was suffered from exposure to the 
 open air by a person well clothed, as long as the weather 
 was perfectly calm ; but in walking against a very light 
 air or wind, a smarting sensation was experienced all 
 over the face, accompanied with a pain in the middle of 
 the forehead, which soon became rather severe. We 
 amused ourselves in freezing some mercury during the 
 continuance of the cold weather, and by beating it out 
 on an anvil, previously reduced to the temperature of the 
 atmosphere. It did not appear to be very malleable when 
 in this state, usually breaking after two or three blows 
 of the hammer." 
 
 It has been found that the power of generating heat 
 varies according to the season, animals possessing a 
 greater power of producing heat in the winter than in the 
 summer. It has also been ascertained that the quantity of 
 carbonic acid formed varies at different periods of the 
 day, a greater portion being given off during the day. 
 Fatigue, depressing passions of the mind, and what- 
 ever tends to impair the energies of the system, cause a 
 diminution of the carbonic acid generated, and conse- 
 quently of one of the principal sources of animal heat. 
 With respect to the causes which tend to the preserva- 
 tion of the uniformity of animal heat on exposure to low 
 temperatures, it is to be observed that it is not meant here 
 to refer to those degrees of cold which are incompatible 
 with the due exercise of the functions of life. Heat 
 causes a determination of blood to the surface, relaxes 
 the skin, and increases transpiration. Cold, on the other 
 hand, repels the blood from the surface, braces and as- 
 tringes the integuments, and lessens the transpiration. The 
 thinner and superfluous quantity of the circulating fluid 
 is no longer thrown from the surface, but is drained off 
 in the fluid state, principally through the kidneys, and 
 thus all the heat which would have been requisite for its 
 conversion into vapour, is preserved. It may be ob- 
 
00 ANIMAL HEAT. 
 
 served that persons will continue for hours in a warm 
 room, drinking abundantly, without experiencing disten- 
 sion of the urinary bladder ; but when they reach the cool 
 air, the bladder soon becomes distended, and gives warn- 
 ing accordingly. In winter, the superfluous fluids are 
 carried off chiefly by the kidneys, while in summer the 
 skin in a great degree performs this office. There is in- 
 deed an admirable balance between these two organs, 
 which is constantly tending either to the one or to the 
 other,, according to circumstances. When the heat of the 
 body is elevated, the blood flows towards the surface, and 
 the thinner part is dissipated in vapour, so as to carry off 
 the superfluous heat. When the body is exposed to cold, 
 the tide sets towards the central parts, and the excess of 
 fluids is filtered through the kidneys, to be discharged in 
 the liquid state. 
 
 Moderate cold acts as a stimulant to the system. The 
 powers of the digestive organs are exerted with greater 
 energy. They both crave, and are capable of assimilating, 
 a larger quantity of food, and thus furnish to the system 
 the additional fuel which becomes necessary. 
 
 Such are the most important facts to which it has been 
 deemed necessary here to advert, with respect to the 
 origin, distribution, and regulation of animal temperature. 
 In the view we have taken, chemical principles have 
 chiefly guided us ; but it is to be recollected that these 
 chemical principles are under the control and direction of 
 a living principle, which forces them to act according to 
 its behests, so as to produce results that the chemist in 
 his laboratory in vain attempts to imitate, when mani- 
 pulating upon dead matter through the medium of dead 
 apparatus, however high may be the genius, intelligence, 
 and dexterity of the director. 
 
 From no function are there so many, and so striking 
 allusions to, and images of life and death, as are derived 
 from animal heat. We speak of life's warm stream, the 
 glow of health, &c. ; and on the other hand, Byron writes : 
 
ANIMAL HEAT. 89 
 
 " And there lay the steed with his nostril all wide, 
 But through it there roll'd not the breath of his pride ; 
 And the foam of his gasping lay white on the turf, 
 And cold as the spray of the rock -beating surf." 
 
 Progressive Development of Animal Heat. Previous 
 to birth, the animal shares the heat of the mother; 
 but when born, it becomes subject to a new order of 
 things. Respiration starts into action for the first 
 time, and the young animal must now, to a certain 
 extent, call upon its own resources to supply the 
 vital warmth. None of the functions of life, how- 
 ever, at their first commencement, are capable of being 
 exerted to their full extent : they acquire their powers 
 gradually, requiring, as it were, to pass through a kind of 
 education before they are fully developed. At birth, the 
 power of producing heat is at the minimum, and in this 
 respect animals differ very much from each other, those 
 which are brought forth in the least perfect condition pos- 
 sessing the lowest power of generating heat, such as pup- 
 pies, kittens, and young rabbits. Here we have several at 
 a, birth, born in a state of less complete development. 
 The calf, the lamb, and the foal are born in a more 
 advanced stage, and they possess within themselves the 
 power of producing a sufficient degree of heat. The for- 
 mer require the cherishing care of the parent, and to re- 
 ceive a portion of her vital warmth, till their own powers 
 are sufficiently expanded to render them independent in 
 this respect. The latter are already prepared by the 
 progress of the organization to sustain, under ordinary 
 circumstances, the heat of their bodies. Some birds be- 
 stow much care and labour in the construction of their 
 nests, lining it with the warmest substances they can 
 procure, and selecting places for its construction, not 
 merely for the purpose of seclusion, but also for shelter, 
 while others are negligent in these respects. Birds, like 
 quadrupeds, are produced with very different powers as 
 to the production of animal heat, The young of the 
 
90 ANIMAL HEAT. 
 
 gallinaceous birds are capable of running about as soon 
 as they leave the shell, and only occasionally require 
 to place themselves under the sheltering wings of the 
 mother, to receive from her heat and protection, while 
 the callow brood of the pigeons and warblers require the 
 fostering care of the parent, in order to receive the warmth 
 they themselves are for some time incapable of generating 
 in sufficient quantity, however warm the nest may be, 
 or however sheltered the spot. These do not produce, 
 but retain the heat, thereby enabling the parent to leave 
 her nestlings for a little on necessary occasions. 
 
 The intelligence of man in most cases raises him 
 above his mere instinctive feelings and propensities. By 
 his reasoning powers he is enabled to control and di- 
 rect them. Still, however, he is endowed with instincts 
 in common with his fellow creatures. The mother 
 instinctively folds her infant in her bosom, not only be- 
 cause there is placed the fountain from which it derives 
 its nourishment, but because from thence also it obtains 
 that vital warmth which its new-born faculties are yet 
 incapable sufficiently to impart. The infant may be 
 WTapt in the most fleecy swaddlings, the most costly furs, 
 and the softest eider down may be had recourse to ; but 
 these cannot communicate heat ; they merely retard its 
 escape. Wherever there is a deficiency, heat must be 
 imparted from some source in which it is generated, and 
 no source can equal that which nature points out the 
 mother. Fashion and philosophy sometimes most mis- 
 chievously interfere with matters which they but little 
 understand. Infants are sometimes exposed to cold, in 
 order to render them hardy. They are lightly clothed, 
 or daily plunged in a frigid bath, for this purpose. It is 
 true that the more robust may escape without injury, but 
 it is because they are hardy : the more weakly perish. 
 "We see few decrepit, feeble, or maimed among savage 
 tribes, because they perish for the want of things ne- 
 cessary to their condition, those only of iron consti- 
 
ANIMAL HEAT. 91 
 
 tution reaching an age of maturity. A melancholy ex- 
 ample of physiological principles misunderstood and mis- 
 applied, may be here mentioned. A physician wishing 
 to invigorate the constitutions of his children, directed 
 that from within a day or two of their birth, they should 
 be every morning and evening plunged into cold water, 
 at all seasons of the year. The screams of the little suf- 
 ferers, and the horror that the very sight of the tub, at 
 all times, even when empty, excited, when they had no 
 other means of communicating the cruelty of the practice, 
 might, one would have thought, have led the fond parent 
 to reflect upon the soundness of his views. But he had 
 no doubts upon the subject. The consequence was, he 
 was deprived of three by consumption at an unusually early 
 period of infancy. Two only escaped, which they did 
 from occurrences in the family taking place so as to cause 
 the neglect of the practice, which, there can be no doubt, 
 led to the fatal event in the other three. 
 
 Gradually the functions on which animal heat depends, 
 are developed : the chest expands ; the respiration is fully 
 established; circulation is vigorously carried on, not merely 
 for the building up and enlarging the different parts of 
 the body, but also for enabling the muscles, with full effect, 
 to exert themselves in the various motions which from day 
 to day are called forth. 
 
 Adaptation to Temperature. Animals, even in the 
 adult state, present great differences in the power of 
 adapting their constitutions to different climates. Some 
 are limited to a single spot, removed from which they 
 languish and die. The reindeer and the polar bear 
 affect the low temperature v/ithin the arctic circle, while 
 the camel pines beyond the limits of the burning desert. 
 Others again more readily accommodate themselves to dif- 
 ferent climates, and are widely spread over the surface of 
 the globe. Man, by his constitution, has been intended to 
 inhabit every country and every clime ; and this he is ena- 
 bled to do, not only by having recourse to such measures as 
 
92 ANIMAL HEAT. 
 
 his reason and experience point out as the best means for 
 his protection, but also because his bodily frame possesses 
 a pliability which adapts itself to the circumstances in 
 which it may be placed. At the same time, by the exer- 
 cise of his intelligence, he is enabled not only to furnish 
 himself with such clothing as best suits his condition, but 
 likewise to make for himself an artificial temperature. 
 Here we have a striking example of the excellence of 
 reason. Instinct may direct one animal in the formation 
 of a warm nest, or another in the construction of a bur- 
 row, which moderate natural temperatures, and econo- 
 mize the natural expenditure of heat ; but these are only 
 conservative, not productive measures. Man alone has 
 recourse to artificial heat. By observation and expe- 
 rience he constructs his dwelling, and surrounds himself 
 with an atmosphere in the depth of winter which best 
 suits his feelings, and thus bids defiance to the howling 
 blast, and repels the approach of the severest frost. 
 
 At the first glance man might appear the most de- 
 fenceless of all animals, not only in respect to attacks 
 from his fellow creatures, but also against the elements. 
 But it is clear he never was intended to be a savage. He 
 is gifted with intellect that he may use it, and, by its di- 
 rection, bring the world under subjection. For him the 
 worm weaves its silken cone ; to him the sheep yields 
 its fleecy coat, the ermine its fur, the eider duck its 
 down ; the flax presents its pliant fibre, and the cotton 
 tree makes an offering of the coverings of its seed. The 
 shaggy coat protects the bear through the rigours of the 
 arctic winter ; but he cannot cast it from him in the warm 
 summer of more temperate climes. The thin- clad mon- 
 key may gambol under the burning sun in the forests of 
 the tropics, but he has no protection against the climates 
 of less ardent regions. 
 
 Hibernation. Hybernating animals present some curi- 
 ous phenomena in connexion with the vital functions in 
 a state of torpidity. Birds, possessing, as they do, excel- 
 
HYBERNATION. 93 
 
 lent powers of locomotion, can easily pass from one 
 country to another. Where, therefore, the supplies of 
 food become deficient, and the temperature unsuitable to 
 them, either from deficiency or excess of heat, they are 
 enabled to migrate to countries where subsistence can 
 more easily be procured, and where the temperature is 
 more congenial to them. Quadrupeds being more limited 
 in their locomotive power, are not capable of availing 
 themselves of change of place with the same facility, or 
 to an equal extent. Several, however, do shift their posi- 
 tions according to the seasons, as the reindeer and musk 
 ox of the northern regions. Others are obliged to remain 
 in the same country throughout the year. 
 
 Cold-blooded animals, such as frogs, serpents, and 
 lizards, need not here be adverted to, as sufficient exam- 
 ples are furnished from mammalia for the present purpose. 
 The food on which a great number of animals subsist 
 during summer is not to be obtained in the winter. They 
 must therefore seek it elsewhere, or change their diet. 
 Migrating birds have recourse to the former measure, 
 while many which remain with us throughout the year 
 have recourse to the latter. Of our wild quadrupeds, 
 some continue in a state of activity during the winter, 
 searching after food where it is to be had, and sustaining 
 their vital warmth in the depth of winter. Others, im- 
 pelled by a remarkable instinct, collect food when it can 
 be obtained in abundance at the end of autumn, and 
 store it up in magazines, which are generally deep bur- 
 rows in the ground, beyond the reach of frost, and lined 
 with substances fitted for the retention of heat. Others, 
 again, living on food which cannot be stored up, as the 
 bat, or not being endowed by any such instinct, as the 
 hamster, possess an organization which in a wonderful 
 manner accommodates itself to the circumstances. On 
 the approach of winter they seek out some convenient 
 retreat, where they are not likely to be disturbed in 
 their defenceless state. Their functions become gradually 
 
94 HYBERNATION. 
 
 benumbed, and are carried on merely to a sufficient extent 
 to preserve life in its most subdued state. 
 
 In hybernating animals voluntary motion is altogether 
 suspended, so also is the process of digestion ; several of 
 the secretions are suppressed, as the saliva, gastric juice, 
 and urine ; the senses are likewise sealed up ; and the cir- 
 culation is diminished. The hamster, in which the pulse 
 beats 150 per minute, in a state of activity, has it reduced 
 to 15 in its torpid condition. The dormouse, whose pulse 
 is so rapid as scarcely to be counted when in its ordinary 
 state, has it reduced to the same low standard when torpid. 
 
 Respiration is also affected in a remarkable degree, 
 not only in the number, but in the fulness and regularity 
 of recurrence. Marmots, in a state of health and activity, 
 perform about 500 respirations in an hour, but in the 
 torpid state these occur only 14 times during the same 
 period, and are performed at intervals of four or five mi- 
 nutes of absolute rest ; neither is the chest enlarged to 
 any considerable extent. 
 
 Irritability is much diminished ; parts of their limbs 
 may be cut off without the animal shewing any signs of 
 feeling. When the hamster is dissected in this condition, 
 the intestines discover not the smallest signs of irritabi- 
 lity on the application of stimulants. During the opera- 
 tion, the animal occasionally opens its mouth, as if it 
 wanted to respire, but the lethargy is too deep to admit 
 its being roused. Those functions on which animal heat 
 more immediately depends, namely, the circulation of the 
 blood ; those changes which effect its conversion from 
 arterial to venous, and the process of breathing, are car- 
 ried on in a very subdued manner ; the resulting tempera- 
 ture is accordingly low. The summer temperature of the 
 hedgehog is 100 ; in the state of torpidity it is only about 
 44. But it is to be observed that it is always from 3 to 
 4 degrees higher in the central parts than at the surface. 
 The ordinary heat of the marmot is 102; during hyber- 
 nation 43. Hybernating animals thus present to us a 
 
VOICE AND SPEECH. 95 
 
 very remarkable modification of organization; at one 
 season, when in a state of full activity, supporting animal 
 heat at its highest point ; but being incapable of sus- 
 taining the vital warmth, in opposition to low external 
 temperature, they are thrown into a peculiar condition, 
 in which life however is not extinguished, but remains 
 dormant in many instances for months. 
 
 At the end of autumn, from the abundant supply of 
 food which most of them are able to procure, they retire 
 to their winter retreats loaded with fat. This serves as 
 a reservoir of nourishment sufficiently adequate to the 
 supply of the small expenditure that takes place during 
 their torpid state. On the return of genial spring they 
 are roused from their lethargy, the fat being generally 
 wholly expended. We thus perceive that every fact 
 with respect to the source, distribution, and adaptation 
 of animal heat in these hybernating animals, fully accords 
 with the principles which have been adverted to as the 
 causes of these in animals which support a temperature 
 nearly uniform at all seasons. 
 
 Voice and Speech. The inhalation and exhalation of air 
 may be so modified as to cause vibrations, and thus be 
 productive of sound. Birds, which take a large quantity 
 of air into their capacious receptacles, are remarkable for 
 the strength and copiousness of the sounds they produce. 
 Mammalia present great varieties in the compass of their 
 voice, from the roaring of the lion to the mere blowing 
 of the whale. Even reptiles possess a kind of voice, as 
 is exemplified in the croaking of the frog, and the hiss- 
 ing of .the serpent. 
 
 In the exercise of no function is the superiority of man 
 more strikingly displayed than in the admirable manner in 
 w T hich he uses his organs of voice in the production of vocal 
 and articulate sounds. We shall first examine the mechani- 
 cal construction of the instruments employed, and then 
 consider the result of their action. It is principally during 
 expiration that sound is produced. In the lungs we have 
 
96 VOICE AND SPEECH. 
 
 reservoirs of air, capable of receiving a larger or smaller 
 quantity, according to circumstances, and from which it 
 can be propelled by the action of the muscles of expira- 
 tion with an adequate force. The air is impelled along the 
 tube named the trachea or windpipe, at the top of which 
 there is placed a complicated apparatus called the larynx, 
 where it is modulated into sound. The sound is then 
 sent through the mouth, and by the tongue, the palate, the 
 teeth, the lips, &c., it is converted into articulate speech, 
 or it is directed through the nostrils, when a peculiar 
 modification is effected. 
 
 The windpipe is composed of from 18 to 20 elastic 
 cartilaginous rings. For about a fourth of the circumference 
 it is deficient of cartilage posteriorly, where it is in con- 
 tact with the gullet. These rings are connected with each 
 other by dense, somewhat elastic membranes, and lined 
 internally with soft mucous membrane, continuous with 
 the lining membrane of the mouth and nostrils. This 
 tube admits of being lengthened and shortened. One set 
 of muscles extended from the chest to the larynx shorten 
 it ; another set between the lower jaw and larynx lengthen 
 it. There are also transverse muscular fibres, which 
 stretch across from tip to tip of the cartilaginous rings, 
 whereby the diameter of the tube is diminished on the 
 cessation of the action in the fibres ; it is restored to its 
 former state by elasticity. Had the rings been formed 
 of cartilage round the whole circumference, no such varia- 
 tion of diameter could have been effected. 
 
 By the movements of the head and neck the length 
 of the trachea is also varied. Singers may be observed 
 to elevate the neck, and carry the head backwards, so as 
 to stretch the windpipe, or incline the head and neck 
 forwards, for the purpose of shortening it, according to the 
 pitch of voice they wish to produce. 
 
 It will thus appear that the trachea possesses the pro- 
 perties of the long and short, the wide and narrow tubes 
 of such a wind instrument as the organ. The larynx, to 
 
ORGANS OF VOICE. 97 
 
 the influence of which the air is next subjected, is composed 
 of five cartilages, three single, and a pair. The largest in 
 the adult male, unless overloaded with fat, forms a conspi- 
 cuous projection at the upper part of the neck. The apple is 
 fancifully said to have stuck in Adam's throat opposite its 
 most projecting portion, which is therefore called Pomum 
 Adami. The form of this cartilage suggesting the idea 
 of a shield, it is termed thyroid. The next in size has 
 been compared to a ring, and therefore called cricoid. A 
 pair of small cartilages form together a resemblance to 
 the spout of a pitcher ; hence the name arytenoid has 
 been applied to them. Over the glottis, or narrow orifice 
 through which the sound issues, the fifth cartilage is 
 placed, which, from its situation, is named epiglottis. 
 
 The thyroid cartilage consists of a projection in front, 
 and two sides, terminating superiorly in two processes, 
 by which it is connected to the bone of the tongue : infe- 
 riorly, it is articulated by two processes with the cricoid. 
 As its name implies, it serves as a shield to the parts 
 placed behind it. At the same time several muscles are 
 attached to it, to which we shall have occasion to refer. 
 The cricoid is narrow in front, but becomes much en- 
 larged posteriorly ; it forms a complete ring, the only 
 part of the air passages which is thus completely sur- 
 rounded ; it serves as a fixed point both for the larynx 
 and windpipe, and as an insertion to several important 
 muscles. The arytenoids are two small triangular pyra- 
 mids articulated with the base of the cricoid by an uni- 
 versal joint. The surface of the joint in the arytenoid 
 is a shallow concavity resting upon a small corresponding 
 convexity of the cricoid, so as to admit of motion in every 
 direction. Stretching from the base of each to the thyroid 
 cartilage, are two ligamentous strings, named vocal cords, 
 the attachment to the thyroid being the fixed point ; be- 
 tween them is the chink termed the glottis, where the air is 
 converted into sound. A little above the cords there are 
 two folds of the lining membrane, termed the false vocal 
 
 F 
 
yo ORGANS OF VOICE. 
 
 cords, with a small lenticular pit interposed, termed the 
 ventricle of the larynx. In apes, monkeys, and baboons 
 these ventricles are exceedingly large, which has been 
 given as the reason why they cannot speak, a reason 
 probably as true as that given by the negroes, who be- 
 lieve that they will not speak lest they be forced to work. 
 By the movements of the arytenoid cartilages the cords 
 are rendered tense or relaxed, and the glottis is widened 
 or narrowed. 
 
 The muscles which command these movements are 
 the following: Two pairs arise from the cricoid, to be 
 inserted into the base of each arytenoid ; a third .pair 
 stretches from the thyroid to be fixed also to their 
 base ; and a single muscle crosses from the one arytenoid 
 cartilage to the other. One pair of crico-arytenoid 
 muscles, from their position, are named posterior ; the 
 other lateral. The posterior are comparatively large and 
 powerful muscles ; by their action they pull back the 
 arytenoid cartilages, and separate them from each other, 
 whereby the cords are put on the stretch, and the vocal 
 aperture or glottis is widened. The lateral draw them 
 aside and forwards, so that the glottis is widened as be- 
 fore, but the cords are relaxed. The thyro-arytenoid 
 muscles cause the arytenoid cartilages to approximate 
 each other, and draw them forwards, whereby the glottis 
 is narrowed, and the cords relaxed. And lastly, the fibres 
 which stretch from one arytenoid cartilage to the other 
 consist of transverse and oblique filaments, so that their mo- 
 tions are performed with greater steadiness and precision 
 than if they had all been parallel to each other. These 
 fibres constitute the arytenoid muscle, which by its action 
 brings the two little cartilages together, and closes the 
 glottis. 
 
 We thus perceive that by the action of these seven 
 muscles the vocal cords can be tuned to the proper pitch 
 by different degrees of tension, and the vocal orifice en- 
 larged or diminished, so as to admit also of proper tun- 
 
ORGANS OF VOICE. 99 
 
 ing. Here we see combined the properties of both the 
 stringed and wind instrument. To a person unaccus- 
 tomed to reflect upon the nicety, ease, and precision of 
 muscular action, it may appear strange that these seven 
 little bundles of flesh should be capable of producing such 
 wonderful results, in effecting the almost infinite tones of 
 voice, not only under the command of the will, but like- 
 wise in accordance with the feelings and passions of the 
 mind. It will be less strange when it is considered that 
 they are capable of acting with different degrees of force, 
 with different degrees of velocity, and to different degrees 
 of extent ; for they may contract to the tenth, the hun- 
 dredth, or the thousandth part of an inch, or they may 
 act together in various combinations. For instance, let 
 us take three, the two posterior crico-arytenoid and the 
 arytenoid : the pair will draw the two ary tenoid carti- 
 lages backwards, and stretch the cords, but they will be 
 prevented from separating them, by the arytenoid muscle 
 being at the same time in action, so that the cords will 
 be rendered tense, and the orifice kept narrow. Even 
 each muscle of a pair may act alternately with its fellow, 
 so as to keep one string in a greater degree of tension 
 than the other. Seeing, then, the innumerable powers 
 and capabilities of these organs, the wonder is lessened, 
 but the admiration is increased, that a little instrument 
 like this should be adequate to all the tones of every 
 language, and of every shade of passion ; should furnish 
 such an inconceivable variety, so that every individual of 
 the human race can easily be distinguished by the tone of 
 his voice. 
 
 The epiglottis is of a parabolic form, its base fixed to the 
 root of the tongue ; it is of softer cartilage than the others, 
 mixed with dense fibres, and has great elasticity. It is some- 
 what convex above and concave below. By its own elasti- 
 city and the elasticity of its attachments in a state of rest, 
 it is constantly raised, so as to preserve a free passage for 
 the air. It may be considered as the watchful guardian 
 
100 ORGANS OF VOICE. 
 
 of the passage to the lungs. It is covered, like the neigh- 
 bouring parts, with the common mucous membrane, but 
 here supplied with nerves which impart to it great sensi- 
 tiveness ; so that on the contact of any solid, fluid, or gase- 
 ous substance which ought not to enter the air-tube, the 
 alarm is instantly sounded, and the sympathetic action of 
 several neighbouring organs are called into play; the 
 tongue recedes backwards, the larynx is elevated, and the 
 entrance to the air-passage completely closed, so that the 
 contraband article is effectually excluded. If the finger 
 be placed upon Adam's apple, and an effort made to swal- 
 low, the larynx will be found instantly to start upwards ; 
 the tongue will also be found to press backwards, in order 
 to produce this effect. Occasionally, however, it is taken 
 off its guard, and a drop of fluid or a crumb of bread 
 slips past it, and then gets into what is called the wrong 
 throat. The alarm is now extended to the muscles of 
 expiration ; they are powerfully thrown into action ; the 
 air is expelled from the lungs by a succession of explosive 
 discharges, constituting coughing, till the intruder is dis- 
 lodged. By its elasticity, and by regulating the size of 
 the orifice, it is capable of modifying the sound already 
 formed by the glottis. 
 
 Let us now glance at the apparatus by which the 
 sound is converted into articulate speech. It may es- 
 cape either through the mouth or by the nostrils. On 
 looking into the mouth, the opening will be seen into 
 the fauces or throat, which is a kind of common vesti- 
 bule, from w r hence there are two openings downwards, 
 the anterior to the windpipe, the posterior to the gul- 
 let; two lateral openings leading to the drums of the 
 ears; two upwards and forwards to the nostrils, and 
 one forwards to the mouth. Over the opening to the 
 mouth, a fleshy curtain will be seen to hang down, named 
 the soft palate, from the centre of which is appended the 
 pap of the throat. By appropriate muscles this curtain is 
 capable of being raised, so as to close the posterior or in- 
 
ORGANS OF SPEECH. 
 
 101 
 
 ternal orifices of the nose, or it may be brought down, 
 and, along with the root of the tongue, shut the mouth at 
 the back part. These passages may thus be more or less 
 partially or completely closed, as may be required. 
 
 The tongue is a curiously constructed instrument. As 
 every one knows, it is principally composed of fleshy or 
 muscular fibres, which run in almost every direction. 
 At its root it is attached to a bone, having some resem- 
 blance to the Greek letter v, therefore. called the hyoid 
 bone. This bone is connected with the thyroid carti- 
 lage, and on each side with one of the bones of the 
 skull. It not only affords insertion to several muscles, 
 but gives a greater degree of firmness and stability to the 
 tongue, from the great number of muscles connected with 
 the tongue and hyoid bone. The tongue may be altered 
 in its length, breadth, and thickness ; it may be vari- 
 ously folded, coiled, and inflected ; and, in the twinkling 
 of an eye, it may be carried upwards or downwards, for- 
 wards or backwards, or to either side. The apex may be 
 darted out of the mouth with more rapidity than the 
 sight can follow it, and then, with the same rapidity, 
 drawn back in a straight line, or coiled or variously fold- 
 ed. By the same powers the whole tongue may be made 
 elastic, and, when put in motion by the air from the lungs, 
 may be made to vibrate. The varieties in force, velocity, 
 extent, and combinations of the motions of the tongue, 
 owing to the power possessed of distributing to the whole 
 or any given part nervous energy in various degrees of 
 quantity, intensity, rapidity, and duration, render its mo- 
 tions truly astonishing ; and yet, independently of all these 
 motions, by which it assists in sucking, deglutition, masti- 
 cation, and speech, its structure is such as to admit of the 
 distribution of glands and nervous papillae, so as to render 
 it subservient to secretion, to constitute it a delicate or- 
 gan of touch, and the principal organ of taste. By the 
 various forms which the tongue assumes, it modulates 
 the sound as it passes along ; or it changes the sound still 
 
102 ORGANS OF SPEECH. 
 
 further by more or less obstructing and retarding it ; or 
 by striking the back part of the palate with its root, or 
 the anterior part of the palate or teeth with its tip, it 
 altogether arrests the sound, and thus produces different 
 forms of articulate speech ; and, lastly , when the sound is 
 about to issue forth, it again becomes subject to the influ- 
 ence of the lips, which, under the control of all the com- 
 binations and modifications of no less than twenty-three 
 different muscles, assume an incalculable variety of forms, 
 and combining their effects with those preceding, furnish 
 means of expression next to inexhaustible. 
 
 But the sound, instead of being sent through the mouth, 
 may be transmitted through the nostrils, and thus become 
 subjected to the influences of the soft palate which com- 
 mands and regulates the posterior orifices of the nose, or, 
 by the movements produced by the muscles of the exter- 
 nal orifices, be subjected to other modifications before it 
 finally makes its escape. 
 
 All the surfaces along which the sound is transmited 
 are moistened with secretions, which aid and modify it 
 to a certain extent ; for, if they are deficient in quantity, 
 or vitiated in quality, the voice is affected, as in a common 
 catarrh. All these parts of this admirable instrument of 
 vocal and articulate sound are brought into co-operation 
 and attuned with just concordance through the medium 
 of the nerves, under the control and direction of the mind. 
 
 It is, indeed, an admirable piece of machinery, possessing 
 all the powers and properties both of the wind and stringed 
 instrument, far surpassing in compass, flexibility, and ex- 
 pression, every musical instrument of human invention, 
 even when played upon by another masterly instrument, 
 the human hand, under the direction of the human mind, 
 however excellent the original taste, or however high the 
 cultivation of that mind may be. 
 
 Every perfect human being at birth is capable of acquir- 
 ing every tone and modification of expression of every lan- 
 guage that ever has existed, now does, or ever can exist upon 
 
ORGANS OF SPEECH. 103 
 
 the face of the earth, with all their various inflections and ac- 
 cents. Nay, so infinitely various are these original capabili- 
 ties, that of the many millions of millions of the human race, 
 probably no two individuals have ever happened to employ 
 them exactly alike, even in the use of the same language; so 
 that every individual of mankind is characterized by his 
 voice. In the course of time, the different parts fall into 
 certain habits of action, so that the original capabilities 
 are in a great measure lost, the organs becoming limited 
 to the expression of the language in which they have been 
 educated, so that many of the sounds and inflections of 
 other languages in advanced life become difficult and 
 almost impossible to be acquired. There are certain 
 tones of the voice which are indicative of the feelings and 
 of the passions and emotions of the mind, as those of plea- 
 sure and pain, of joy and grief, of satisfaction and resent- 
 ment, which are instinctive, and universally understood 
 by the savage and the civilized. While the acquired 
 sounds express the conceptions of the mind, they are often 
 tinged by the emotions and passions. 
 
 The most excellent musical performers with the voice must 
 combine both the power of conceiving the music (possess 
 the ear), and the most complete control and command of the 
 instruments (have the voice), so as to execute the perform- 
 ance. However perfect the instrument may be, with- 
 out the mind to play upon it, it is useless as an organ of 
 music and as an organ of speech. The examination of 
 the organs of voice will not teach us whether they had 
 been employed in expressing the language of the civilized 
 European or savage New Hollander. It is therefore 
 useless to inquire why the lower animals cannot speak as 
 man does, notwithstanding their organs approach those of 
 man closely in conformation j yet the sounds which they 
 utter adequately express their conceptions and feelings, 
 and are sufficiently well understood by each other. 
 
 Respiration of different Gases. On the discovery of 
 the different gases, their effects were tried upon respira- 
 
104 RESPIRATION OF GASES. 
 
 tion. The greater number of the gaseous substances 
 known cannot be inhaled in their pure unmixed state ; 
 others are capable of being so. Gases are therefore di- 
 vided into respirable and irrespirable. 
 
 The respirable gases are nitrogen, hydrogen, oxygen, 
 nitrous oxide, and carburetted hydrogen. The two first 
 appear to be negative in action, the effects appearing to re- 
 sult merely from the exclusion of atmospheric air. As the 
 respiratory movements, however, and the distension of the 
 cells of the lungs, even with these gases, will favour the 
 transmission of blood through the lungs, where, at the same 
 time, it cannot undergo the necessary conversion from ve- 
 nous to arterial, and consequently the dark-coloured blood 
 being sent in greater quantity to the brain and the rest of 
 the system, death will sooner take place than in mere sus- 
 pension of respiration. When animals are made to breathe 
 pure oxygen, care being taken at the same time to with- 
 draw any carbonic acid which may be formed, at first 
 they appear but little affected, biit in time they become 
 uneasy, symptoms of distress are shewn, and finally life is 
 destroyed. On examination after death, there are found 
 evidences of inflammation of the lungs having been ex- 
 cited ; so that although this gas in a pure state may be 
 respired longer than any other, yet ultimately it proves 
 fatal. The most interesting account we have of the effects 
 from the respiration of nitrous oxide is given by Sir H. 
 Davy, who was the first to shew that it was by no means 
 so deleterious as had been previously believed, since he 
 proved that it might be inhaled with safety, and that 
 the respiration of it produced very striking and remark- 
 able effects. It has frequently been breathed since, and 
 now affords one of the most common displays in a popular 
 course of lectures. The following striking account of the 
 effects of this gas is given by Sir H. Davy : 
 
 " On December 26th I was inclosed in an air-tight 
 breathing-box, of the capacity of about nine cubic feet 
 and half, in the presence of Dr Kinglake. 
 
RESPIRATION OF NITROUS OXIDE. 105 
 
 " After I had taken a situation in which I could, by 
 means of a curved thermometer inserted under the arm, 
 and a stop-watch, ascertain the alterations in my pulse 
 and animal heat, 20 quarts of nitrous oxide were thrown 
 into the box. 
 
 " For three minutes I experienced no alteration in my 
 sensations, though immediately after the introduction of 
 the nitrous oxide the smell and taste of it were very 
 evident.* 
 
 " In four minutes I began to feel a slight glow in the 
 cheeks, and a generally diffused warmth over the chest, 
 though the temperature of the box was not quite 50. 
 I had neglected to feel my pulse before I went in ; at 
 this time it was 104, and hard; the animal heat was 98. 
 In ten minutes the animal heat was near 99 ; in a quar- 
 ter of an hour 99.5, when the pulse was 102, and fuller 
 than before. 
 
 " At this period 20 quarts more of nitrous oxide were 
 thrown into the box, and well-mingled with the mass of 
 air by agitation. 
 
 " In twenty-five minutes the animal heat was 100, 
 pulse 124. In thirty minutes 20 quarts more of gas 
 were introduced. 
 
 " My sensations were now pleasant ; I had a generally 
 diffused warmth, without the slightest moisture of the 
 skin, a sense of exhilaration similar to that produced by 
 a small dose of wine, and a disposition to muscular mo- 
 tion and to merriment. 
 
 " In three quarters of an hour the pulse was 104, and 
 animal heat not 99.5 ; the temperature of the chamber 
 was 64. The pleasurable feelings continued to increase, 
 the pulse became fuller and slower, till in about an hour 
 it was 88, when the animal heat was 99. 
 
 " 20 quarts more of air were admitted. I had now a 
 
 * The nitrous oxide was too diluted to act much ; it was mingled 
 with near 32 times its bulk of atmospheric air. 
 
 F2 
 
106 RESPIRATION OF NITROUS OXIDE. 
 
 great disposition to laugh ; luminous points seemed fre- 
 quently to pass before my eyes ; my hearing was certainly 
 more acute, and I felt a pleasant lightness and power of 
 exertion in my muscles. In a short time the symptoms 
 became stationary ; breathing was rather oppressed, and, 
 on account of the great desire of action, rest was painful. 
 
 " I now came out of the box, having been in precisely 
 an hour and quarter. 
 
 " The moment after, I began to respire 20 quarts of 
 unmingled nitrous oxide. A thrilling, extending from 
 the chest to the extremities, was almost immediately pro- 
 duced. I felt a sense of tangible extension highly plea- 
 surable in every limb ; my visible impressions were daz- 
 zling, and apparently magnified ; I heard distinctly every 
 sound in the room, and was perfectly aware of my situa- 
 tion.* By degrees, as the pleasurable sensations in- 
 creased, I lost all connexion with external things ; trains 
 of vivid visible images rapidly passed through my mind, 
 and were connected with words in such a manner as to 
 produce perceptions perfectly novel. I existed in a world 
 of newly connected and newly modified ideas. I theo- 
 rised ; I imagined that I made discoveries. "When I was 
 awakened from this semi-delirious trance by Dr. King- 
 lake, who took the bag from my mouth, indignation and 
 pride were the first feelings produced by the sight of the 
 persons about me. My emotions were enthusiastic and 
 sublime ; and for a minute I walked round the room 
 perfectly regardless of what was said to me. As I re- 
 covered my former state of mind, I felt an inclination to 
 communicate the discoveries I had made during the ex- 
 periment. I endeavoured to recall the ideas ; they were 
 feeble and indistinct. One collection of terms, however, 
 presented itself; and with the most intense belief and 
 prophetic manner, I exclaimed to Dr Kinglake, " Noth- 
 
 * In all these experiments, after the first minute, my cheeks 
 became purple. 
 
RESPIRATION OF NITROUS OXIDE. 107 
 
 ing exists but thoughts ! the universe is composed of im- 
 pressions, ideas, pleasures, and pains !" 
 
 " About three minutes and a half only had elapsed 
 during this experiment, though the time, as measured by 
 the relative vividness of the recollected ideas, appeared 
 to me much longer. 
 
 " Not more than half of the nitrous oxide was con- 
 sumed. After a minute, before the thrilling of the ex- 
 tremities had disappeared, I breathed the remainder. 
 Similar sensations were again produced ; I was quickly 
 thrown into the pleasurable trance, and continued in it 
 longer than before. For many minutes after the experi- 
 ment I experienced the thrilling in the extremities ; the 
 exhilaration continued nearly two hours. For a much 
 longer time I experienced the mild enjoyment before 
 described connected with indolence ; no depression or 
 feebleness followed. I ate my dinner with great appetite, 
 and found myself lively and disposed to action immedi- 
 ately after. I passed the evening in executing experi- 
 ments. At night I found myself unusually cheerful and 
 active ; and the hours between eleven and two were spent 
 in copying the foregoing detail from the common-place 
 book, and in arranging the experiments. In bed I en- 
 joyed profound repose. When I awoke in the morning, 
 it was with consciousness of pleasurable existence, and 
 this consciousness more or less continued through the 
 day." 
 
 He tried it on other occasions with similar results. It 
 was also breathed by several other persons under his 
 superintendence ; and though generally found to produce 
 pleasurable excitement and hilarity, without being fol- 
 lowed by subsequent depression, yet in some instances, 
 especially in females, disagreeable effects were experi- 
 enced, such as a tendency to fainting and hysterical 
 affections. The excitement from nitrous oxide displays 
 itself differently in different persons : Some are thrown 
 into a state of immoderate laughter, which to the spec- 
 
108 RESPIRATION OF CARBURETTED HYDROGEN. 
 
 tators is the more absurd, as there is no apparent cause 
 for it. Very often the bystanders sympathize, and the 
 laughter becomes universal. In other instances most 
 vigorous and active dancing is had recourse to ; while in 
 others no small degree of pugnacity is displayed. From 
 experiments performed upon the lower animals, it appears 
 that life is prolonged by the respiration of it longer than 
 where they breathe pure hydrogen or nitrogen, which 
 apparently act by excluding oxygen. Still, in a short 
 time life is destroyed by it, circulation and respiration 
 being thrown into the most tumultuous action previous to 
 death. Carburetted hydrogen having been found to be 
 destructive of animal life, its effects were also tried for 
 the first time, on his o\vn person, by Sir Humphry Davy. 
 These will be best shown by his own statement : 
 
 " Emboldened by this trial, in which the feelings were 
 not unlike those I experienced in the first experiments 
 on nitrous oxide, I resolved to breathe pure hydrocar- 
 bonate. 
 
 " For this purpose I introduced into a silk bag four 
 quarts of gas nearly pure, which was carefully produced 
 from the decomposition of water by charcoal an hour 
 before, and which had a very strong and disagreeable 
 smell. 
 
 " My friend, Mr James Tobin jun., being present, after 
 a forced exhaustion of my lungs, the nose being accurately 
 closed, I made three inspirations and expirations of the 
 hydrocarbonate. The first inspiration produced a sort of 
 numbness and loss of feeling in the chest and about the 
 pectoral muscles. After the second inspiration, I lost all 
 power of perceiving external things, and had no distinct 
 sensation except a terrible oppression on the chest. Dur- 
 ing the third expiration, this feeling disappeared, I seemed 
 sinking into annihilation, and had just power enough to 
 drop the mouth-piece from my unclosed lips. A short 
 interval must have passed, during which I respired com- 
 mon air, before the objects about me were distinguish- 
 
RESPIRATION OF CARBURETTED HYDROGEN. 109 
 
 able. On recollecting myself, I faintly articulated, " / 
 do not think I shall die" Putting my finger on the 
 wrist, I found my pulse thread-like, and beating with 
 excessive quickness. 
 
 " In less than a minute I was able to walk, and the 
 painful oppression on the chest directed me to the open 
 air. 
 
 " After making a few steps, which carried me to the 
 garden, my head became giddy, my knees trembled, and 
 I had just sufficient voluntary power to throw myself on 
 the grass. Here the painful feeling of the chest increased 
 with such violence as to threaten suffocation. At this 
 moment I asked for some nitrous oxide. Mr Dwyer 
 brought me a mixture of oxygen and nitrous oxide. I 
 breathed this for a minute, and believed myself relieved. 
 In five minutes the painful feelings began gradually to 
 diminish. In an hour they had nearly disappeared, and 
 I felt only excessive weakness and a slight swimming of 
 the head. My voice was very feeble and indistinct. 
 This was at two o'clock in the afternoon. 
 
 " I afterwards walked slowly for about half an hour 
 with Mr Tobin jun., and on my return was so much 
 stronger and better as to believe that the effects of the 
 gas had disappeared, though my pulse was 120, and very 
 feeble. I continued without pain for near three quarters 
 of an hour, when the giddiness returned with such vio- 
 lence as to oblige me to lie on the bed ; it was accom- 
 panied with nausea, loss of memory, and deficient sensa- 
 tion. In about an hour and half the giddiness went off, 
 and was succeeded by an excruciating pain in the fore- 
 head and between the eyes, with transient pains in the 
 chest and extremities. 
 
 " Towards night these affections gradually diminished. 
 At ten* no disagreeable feeling except weakness re- 
 
 * I ought to observe, that between eight and ten I took, by the 
 advice of Dr Beddoes, two or three doses of diluted nitric acid. 
 
110 ASPHYXIA. 
 
 mained. I slept sound, and awoke in the morning very 
 feeble and very hungry. No recurrence of the symptoms 
 took place, and I had nearly recovered my strength by 
 the evening-." 
 
 Thus, of the five gases which can be received into the lungs 
 in an unmixed fonn, two, nitrogen and hydrogen, act by 
 excluding oxygen. Pure oxygen can be respired longer 
 than any other, but ultimately induces fatal derangement. 
 Nitrous oxide causes a high state of excitement, and if per- 
 sisted in, soon causes death, apparently from over excite- 
 ment ; and carburetted hydrogen is one of the most direct 
 sedatives to which the body can be exposed. These gases, 
 when presented to the extensive surface of the air pas- 
 sages, where absorption is readily effected, are taken up 
 and carried along with the blood to every part of the 
 body, and speedily exert their influence upon the brain 
 and nervous system. All other gases in an undiluted 
 state cause such a degree of irritation as to produce spas- 
 modic closure of the glottis, and death follows from suf- 
 focation ; but when mingled with atmospheric air, they 
 may be received along with it, and display their peculiar 
 effects on the system with greater or less intensity, accord- 
 ing to their nature and degree of dilution. Thus, carbonic 
 acid, in the small quantity in which it is found in the 
 atmosphere, has no perceptible effect ; but when in 
 greater proportion to the air, it displays peculiar poisonous 
 properties; while pure and unmixed it cannot be inhaled. 
 
 Asphyxia. The term asphyxia is applied to that state 
 of apparent death arising from suspension of respiration, 
 and furnishes many facts which shew the absolute neces- 
 sity of that function. It differs from real death, in there 
 being a possibility of restoring life ; but the body can 
 only remain in this state for a very short time, as it soon 
 terminates in actual death. Suffocation may arise from 
 a number of different causes. The respiratory movements 
 of the chest may be prevented by mechanical causes ; 
 fluids may accumulate in the chest, so as to prevent the 
 
ASPHYXIA. 
 
 Ill 
 
 expansion of the lungs ; tumours may press on the air 
 passages ; or foreign bodies may be lodged at the orifice of 
 the windpipe, so as to obstruct breathing; and in the 
 same way does hanging produce its effects. It has been 
 stated that the entrance to the windpipe is endowed with 
 a remarkable irritability, whereby, on the contact of all 
 solids and fluids, and of gaseous substances, with the few 
 exceptions mentioned, it is instantly closed. Immersion 
 in any fluid, as in water, destroys life, by inducing this 
 spasmodic closure. Carbonic acid and other irritating 
 causes act in the same way. Asphyxia may also be pro- 
 duced by the condition of the brain and nervous system 
 being such as to put a stop to muscular movements neces- 
 sary for carrying on the process of breathing. Thus, 
 apoplexy, or injuries of the brain from falls, blows, &c., 
 may cause it. Various poisons operate by their direct 
 effect upon the brain and nerves, implicating and suspend- 
 ing the respiratory movements. In all these instances 
 the train of phenomena which takes place is similar, 
 the residual air in the lungs being soon exhausted. The 
 dark-coloured blood sent by the right ventricle of the 
 heart to the lungs does not undergo the necessary changes, 
 it paralyzes the capillary vessels. A less quantity is 
 transmitted to the left ventricle, and that too the dark 
 venous blood, which being propelled to the different parts 
 of the system, is incapable of supporting the functions, 
 and especially deadens the brain and nervous system, first 
 producing giddiness, and confusion of thought ; insensi- 
 bility follows, and the scene is generally closed in con- 
 vulsions. From respiration being stopped, the blood does 
 not obtain a ready entrance into the chest. It accumu- 
 lates in the veins, producing lividity of the face, and pro- 
 trusion of the eyeballs. In suffocation the lungs are the 
 first which die ; next the brain ; and last of all the heart. 
 The function of breathing cannot be suspended more 
 than four or five minutes with any chance of restoring life. 
 There are, however, instances where criminals have been 
 
112 
 
 ASPHYXIA. 
 
 hung for the legal period, which at one time was limited 
 in Scotland to an hour, and the functions again restored. 
 Several years ago a woman underwent her sentence in 
 Edinburgh. Her body was delivered to her friends, and 
 placed in a cart, in order to be conveyed to some distance 
 in the country. On the road the friends entered a public- 
 house for refreshment. On coming again to the cart, to 
 their astonishment they found their executed relation 
 restored to life. She afterwards for many years sold salt 
 through the streets of Edinburgh, under the name of 
 " half-hanged Maggie Dickson." 
 
 In fainting, where the circulation is suspended, there 
 is apparent death, as in asphyxia, but the dark-coloured 
 blood does not circulate so as to act as a poison. It 
 may continue so long that preparations have been 
 made for the burial of the body, and yet resuscita- 
 tion take place. It has even been stated, and is a 
 matter of general popular belief, that interment has been 
 carried into effect on persons in this state, affording 
 foundation for the concocters of stories of the horrible 
 and awful. Now, in the above case of " half-hanged 
 Maggie," it is most probable that when she was about 
 to be cast off, she fainted, and that therefore excitability 
 remained. It is also probable that the jolting of the 
 cart conduced to her restoration. Drowning produces 
 death by the water causing a spasmodic closure of the 
 glottis, so that there is little or no hope of restoring the 
 functions after a few minutes immersion. But there are 
 instances where persons have been under water for a much 
 longer period, and yet revived. These admit of the same 
 explanation as similar cases from hanging, for fainting 
 has occurred at the moment of immersion. 
 
 Carbonic acid being a product of many operations carried 
 on in nature, and in the arts, frequently produces fatal effects 
 by either of its modes of action, that is, by causing suffoca- 
 tion, or acting as a narcotic poison. Being heavier than 
 atmospheric air, it occupies the lowest situation. It some- 
 
MEANS OF RESTORING ANIMATION. 113 
 
 times accumulates in old wells and mines, and is known to 
 the miner under the expressive name of choke-damp. It 
 is also found in caves, as in the Grotto del Cane in Italy. 
 The celebrated valley of the Upas tree in Java is de- 
 structive of animal life from containing this gas. It 
 is given off during fermentation ; hence the danger of en- 
 tering a brewer's vat immediately after the liquor is 
 drawn off, as the vessel remains for sometime filled with 
 it. As has been shewn, it is discharged from the breath 
 during respiration. In crowded and ill- ventilated apart- 
 ments it sometimes accumulates in a quantity to prove 
 noxious, causing drowsiness and averseness to action. 
 The victims in the black hole of Calcutta seem to have 
 been destroyed by it. It is generated during combustion ; 
 hence the danger of leaving charcoal or cinders unex- 
 tinguished in sleeping chambers or ill ventilated rooms, 
 the neglect of which has not unfrequently produced fatal 
 consequences. Narcotic poisons, such as opium, ardent 
 spirits, &c., act by deadening the sensibility of the brain 
 and nerves : the muscular movements essential to breath- 
 ing are slowly and imperfectly performed ; the necessary 
 salutary changes are not produced on the blood ; it mounts 
 to the brain, and the evil is aggravated so as soon to 
 place the patient beyond the possibility of recovery. 
 
 Means of restoring Animation. From what has just 
 been stated, not a moment ought to be lost in having re- 
 course to proper measures with the view of restoring ani- 
 mation. In hanging, death may be caused in two ways. 
 The bones of the neck may be dislocated^ when death in- 
 stantly and inevitably takes place ; or suffocation is pro- 
 duced, inducing asphyxia. In drowning, apparent death 
 may arise from two causes, \st, the person may be sub- 
 mersed in the water while respiration is going on ; or 
 2dly, fainting may occur previous to immersion. The 
 chance of recovery is very different in these two condi- 
 tions, and therefore it is very important to distinguish 
 between them when a person is taken out of the water. 
 
114 MEANS OP RESTORING ANIMATION. 
 
 In the former case, the face appears swollen and livid, 
 especially the lips and ears. There is usually frothy mu- 
 cus about the mouth and nostrils, and the rest of the 
 body is generally pale. In the latter condition, there is 
 paleness of the face, without marks of struggle in the 
 features or in the neck, and the countenance appears 
 tranquil, as in a deep sleep. The first circumstance to 
 be attended to is to place the body in as favourable a 
 posture for the process of breathing as possible. With 
 this view, it is to be placed with the head and upper part 
 somewhat elevated. The neck is instantly to be laid bare, 
 and all bandages surrounding the chest immediately cut. 
 As the glottis is most likely still in a state of spasm, the 
 larynx must be drawn downwards ; at the sametime the 
 shoulders, ribs, and breastbone must be elevated, that the 
 residual air in the lungs may dilate, and a fresh portion be 
 drawn in ; the respiratory movements of the chest are as 
 far as possible to be imitated. 
 
 If these fail, the lungs should be inflated, either with 
 bellows or by blowing air with the mouth through 
 the nostrils or mouth, care being taken to keep the 
 larynx drawn down, that the glottis be kept open, 
 and also gently pressed upon the gullet, that air may 
 be prevented from passing into the stomach. Dur- 
 ing inflation means ought to be adopted for simulta- 
 neously enlarging the chest, for if this be neglected, and 
 the air be forced into the cells while the lungs are com- 
 pressed by the walls of the chest, the delicate air tubes 
 may be ruptured, and the patient placed beyond the pos- 
 sibility of recovery. 
 
 From the important relations between the skin and 
 the lungs, the body being stripped, which it ought 
 to be as soon as possible, it is to be rubbed with 
 hot flannels, and the palms of the hands and the 
 soles of the feet diligently brushed. In order to arouse 
 irritability, stimulating vapours may be applied to the 
 nostrils ; and, with the view of relieving the brain, the 
 
MEANS OF RESTORING ANIMATION. 115 
 
 jugular vein may be opened. If the temperature be re- 
 duced, means must be had recourse to for imparting heat. 
 Bags filled with warm sand, salt, sawdust, &c., or bottles 
 filled with hot water, wrapt up in cloth, may be applied 
 to the soles of the feet, pit of the stomach, &c. Frictions 
 with hot flannel are at the same time to be persisted in. 
 The warm bath, on physiological principles, to say the 
 least, is of very doubtful efficacy ; for though in this way 
 heat be readily imparted, still the beneficial influence of the 
 air upon the skin is lost, and other important means for 
 resuscitation cannot be so well applied at the same time 
 with it. If by these means we happily succeed in the 
 re- establishment of respiration, we must not intermit our 
 attentions. For the first blood transmitted by the heart 
 being only imperfectly purified, may paralyze the brain, 
 induce stupor, and endanger life. The patient must be 
 kept roused, a moderate bleeding may be useful, and 
 he must be assisted and kept walking about till the vital 
 functions are again fairly established. When asphyxia 
 has been produced by causes which do not at the same 
 time carry off the heat of the body, as from exposure 
 to carbonic acid, dashing cold water upon the face may 
 be of advantage. Where dangerous symptoms arise from 
 poisons, such as from opium and other narcotics, there is 
 generally time for procuring professional assistance, when 
 measures will be adopted which can only be properly car- 
 ried into effect by professional hands, or had recourse to - 
 under the immediate superintendence of the professionally 
 instructed. 
 
116 
 
 CHAPTER III. 
 
 DIGESTION. 
 
 A General Account of the Changes which the Food undergoes in the Digestive Or- 
 gans Man a Cooking Animal Food assimilated to the Temperature of the Body 
 in the Mouth Teeth, their Structure and Use in various Animals The Teeth 
 of Man, their Form, Number, and Structure Why there are two Sets Motions 
 of the Jaw Saliva, Composition and Use of Deglutition General view of 
 the Alimentary Canal Stomach Duodenum Small Intestine Large Intes- 
 tine Liver Spleen Pancreas Organs of Digestion in Carnivorous Animals 
 in Ruminants in Birds Digestive apparatus of Man adapted to a greater va- 
 riety of Food than that of any other Animal Animal Food, and its proxi- 
 mate principles Vegetable Food, and its proximate principles One or other 
 most suitable to different climates Concentration, Variety, Consistence, and 
 Quantity influence the Digestibility of Food Condiments, Salt, Acids, Bit- 
 ters, Astringents, Aromatics Hunger and Thirst Chymification Gastric 
 Juice Its peculiar powers Chylification Biliary, Pancreatic, and Intestinal 
 Secretions Chyle absorbed, and conveyed through intricate channels, becomes 
 gradually assimilated to, and converted into perfect Blood Last efforts for the 
 Abstraction of Nourishment Drinks Several substances introduced into the 
 Circulation fiom the Alimentary Canal without being changed. 
 
 THE continual expenditure which goes on in the body, 
 from the fluids dissipated on the surface of the skin and 
 in the breath, the discharges that take place in urine, 
 and other secretions, and the constant changes occurring 
 in the materials of every part of the body, demand fresh 
 matter to compensate for the loss. During the whole 
 existence of all living bodies, a perpetual succession of 
 matter occurs ; the old is discharged, and new taken up 
 in its place. Plants being fixed to a single spot, imme- 
 diately receive into their systems the materials on which 
 they subsist, as it is presented to them, without its being 
 previously subjected to alteration ; while animals, on the 
 
GENERAL VIEW OF DIGESTION. 117 
 
 other hand, are furnished with apparatus more or less 
 complicated, whereby their aliment is acted upon so as 
 to fit it for being conveyed into their systems. The or- 
 gans which effect these changes, and which adapt it to 
 the constitution of the animal, are the organs of diges- 
 tion. 
 
 No organs in the body more distinctly shew the ad- 
 mirable adaptation of structure to circumstances, according 
 to the rank of the animal, the nature of its food and ha- 
 bits. For example, carnivorous animals, subsisting upon 
 aliment highly nutritious in proportion to the bulk, and 
 of easy conversion into an appropriate animal fluid, pos- 
 sess a simple apparatus, and of comparatively small size ; 
 while in herbivorous animals, living on food which yields 
 no great quantity of nourishment, and that distinct from 
 animal substance, it requires to be exposed for a consider- 
 able length of time to the influence of capacious and com- 
 plicated machinery, in order to become animalized. The 
 cavity of the abdomen, or belly, which is occupied chiefly 
 by the digestive organs, is accordingly large in the lat- 
 ter, but much smaller in the former. 
 
 In the view which we shall take of the process of di- 
 gestion, wte shall follow the successive changes which take 
 place, and the manner in which they are brought about, 
 from the first introduction of food into the mouth, till it 
 is converted into arterial blood in the lungs. 
 
 In the mouth the food is subjected to the mechanical 
 action of the teeth, and is mixed with the secretions of se- 
 veral neighbouring glands. It is then transferred to the 
 stomach, along the gullet. In the stomach it remains 
 for some time, where it is subjected to the action of the 
 fluids of that organ, and converted into a pultaceous 
 mass, termed chyme. This gradually passes into a cy- 
 lindrical canal, the intestine, in the first portion of 
 which it meets with the bile from the liver, and with a 
 fluid furnished by another large gland called the pancreas. 
 After this, a white milky-like fluid, the chyle, is sepa- 
 
118 GENERAL VIEW OF DIGESTION. 
 
 rated from the general mass, and is drunk up by the 
 innumerable vessels which open on the surface of the in- 
 testine as it passes along. Having traversed the long 
 winding canal, the smaller intestine, and the nutritious par- 
 ticles having been absorbed, the mass is next transferred to 
 the large intestine, termed the colon, where the last efforts 
 are made to abstract nourishment from it ; and lastly, the 
 remainder, when time and opportunity are convenient, is 
 rejected. The chyle, on being taken up by the absor- 
 bent vessels, opening on the internal surface of the intes- 
 tinal canal, is conveyed by these vessels through a 
 number of small glands, after which it is collected into a 
 receptacle, from which it is conveyed by a tube through 
 the chest, and poured into the great veins, as they are 
 proceeding to the right side of the heart. From the com- 
 motion to which it is exposed by the concussion of the 
 right side of the heart, it is intermixed thoroughly with 
 the venous blood, and propelled to the lungs, where it is 
 perfected into arterial blood. 
 
 From the examination of the organs of digestion of 
 man, attempts have been made by some to prove that he 
 was intended to be carnivorous ; others contend for his 
 being frugivorous ; while numerous facts may be brought 
 forward from the same source to shew that he was in- 
 tended to be a cooking animal. It is very evident, that 
 the great Author of his being intended that this function 
 should be exercised to a certain extent, in connexion with 
 his intelligence as a rational creature. It is not only a 
 superficial and partial view, but unfair and untrue, to con- 
 sider man's character as dependent upon his mere mate- 
 rial organization. He has been blessed, it is true, with 
 an admirable material structure, but with a structure 
 associated with a rational spirit. While life exists, the re- 
 lations between them are most close and intimate, and 
 must continue to be so till dissolved by the hand of 
 death. They mutually act and react upon each other ; 
 whatever affects the one makes a greater or less impres- 
 
GENERAL VIEW OF DIGESTION. 119 
 
 sion on the other. As they are thus mutually dependent, 
 so do we find them beautifully co-operating together. 
 The history of mankind tends to prove, that wherever 
 man is found in a low and savage state, traces appear of his 
 having fallen from a more civilized condition ; and how- 
 ever degraded his savage condition may be, there is no 
 instance of his confining himself in his food entirely to 
 the state in which it is furnished by the hand of nature. 
 He subjects it to processes of preparation before he intro- 
 duces it into his organs of digestion. If man were not 
 a cooking animal ; did he not exercise his intelligence in 
 the preparation as well as in the selection of his food, 
 most of the fairest parts of this earth would be to him 
 totally uninhabitable for by far the greater part of the 
 year, and others constantly so throughout the whole year. 
 Many substances, which are altogether unfit as articles 
 of food, nay, even highly poisonous, are rendered grateful 
 and nutritious by preparation. The raw potato may 
 serve as an example, or the root of the deadly poisonous 
 plant Jatropha Manihot, which, on being exposed to 
 heat, has the poison dissipated, or by preparation fur- 
 nishes the Tapioca or Cassava of commerce, frequently 
 employed for the diet of invalids. 
 
 To nothing is man so much indebted for his comforts, 
 his luxuries, and even his very subsistence, as to the mas- 
 tery he has obtained over heat. It not only furnishes 
 him with the gigantic power of the steam-engine, reduces 
 metals to his subjection, supplies him with the most deadly 
 weapons of offence and defence, and in a thousand other 
 ways contributes to supply his wants and necessities, but 
 it also prepares an endless variety of food for him, which 
 without its aid would be altogether unfit as such ; while 
 it alters other substances, so that they are rendered both 
 more nutritious and more easily acted upon by his organs 
 of digestion. 
 
 Man, in proportion to his size, has the smallest mouth 
 of any animal : in every respect it is beautifully and sym- 
 
1 20 TRITURATION. 
 
 metrically formed. In the mouth the food is subject to 
 the following changes : it is assimilated to the tempera- 
 ture of the body; the teeth, by trituration, reduce it to a 
 minute state of mechanical division, and when it consists 
 of different substances intermix them together ; and by 
 insalivation it is mixed with fluids, which at the time 
 are poured abundantly into the mouth. 
 
 Assimilation of Temperature. The mouth possesses 
 great sensibility to temperature, much greater than the 
 stomach, whereby it is enabled to judge of the proper 
 temperature of substances before they are transmitted to 
 that organ. Had the reverse been the case, materials 
 might have been transferred to the stomach while scald- 
 ing hot. But as it is, a person, for example, eating hot 
 soup, will sometimes prefer hurrying it over into the 
 stomach, rather than do anything so unseemly as reject it 
 out of the mouth, knowing that its high temperature will 
 be more tolerable there. If the temperature of the morsel 
 of food be below that of the body, it gradually obtains 
 heat, so as to be assimilated to it. 
 
 Trituration. The teeth present great diversities in 
 form, number, situation, and the purposes to which they 
 are subservient in the different tribes of animals, so much 
 so, that naturalists have selected them to furnish characters 
 for the distribution of mammalia into orders and families. 
 Some of the mammalia are without teeth, as the ant-eaters 
 and armadilloes. In some of the whale tribe, they consist 
 of a series of horny plates proceeding from the upper jaw, 
 well known under the name of whalebone. These plates 
 are placed vertically, present sharp edges externally, which 
 overlap each other like tiles, their internal edges being 
 furnished with long hairlike fringes, which serve as sieves 
 whereby they entangle the food on w T hich they subsist. 
 
 The whole class of birds are devoid of teeth. Their 
 bills are variously modified for seizing or tearing their 
 food ; but where it is necessary that it should be subjected 
 to trituration, their stomach or gizzard is furnished with 
 
TEETH. 
 
 121 
 
 powerful muscular apparatus, lined with a hard insensible 
 horny covering ; and in order to aid in the reduction of 
 the food, they instinctively swallow pieces of quartz, and 
 other hard substances. 
 
 The teeth of venomous serpents present the most deadly 
 weapons with which animals are furnished. The poison- 
 fangs are of a curved form. When the animal is tranquil, 
 they are retracted by an elastic ligament, like the claws 
 of a cat ; but when it is about to. inflict a wound, they 
 are erected by a muscle ; they are also provided with a 
 tube, opening by a fissure, through which the poison, 
 secreted by a peculiar gland, is injected into the wound. 
 
 Teeth in carnivorous animals, such as the lion, tiger, 
 &c. are dreadful weapons : so are they in the wild boar. 
 The elephant employs them as means of defence. In the 
 narwhal or unicorn, a single tooth only is in general de- 
 veloped, its fellow being rudimental ; it is remarkable 
 for its length and spiral form, and has been conjectured 
 to serve as a weapon. These powerful tusks in the ele- 
 phant, narwhal, and walrus, are only fully developed in 
 the male, the female having them in a rudimentary state. 
 These animals are all gregarious, and the defence of the 
 herd falls principally upon the males, which are thus 
 armed accordingly. 
 
 In carnivorous animals, their food not requiring tritura- 
 tion, the teeth are adapted for seizing their prey, for 
 lacerating and tearing it to pieces ; they are conical and 
 pointed, and lock into each other, so that their points do 
 not come in contact, and thus preserve their sharpness. 
 In the squirrel, the beaver, rats, mice, &c., there are two 
 long cutting teeth in each jaw, furnished with a thick 
 deposit of enamel anteriorly, but devoid of it posteriorly, 
 the bony portion behind being more easily worn down 
 than the anterior enamel. The edge is preserved in the 
 proper degree of sharpness ; they exactly resemble chisels, 
 and although they may be employed for years in gnawing 
 very hard substances, in opening nuts, or in felling forest 
 
 G 
 
122 TEETH. 
 
 trees, yet they never become blunted. Besides these 
 chisels, animals of this order are furnished -with grinding 
 teeth for properly reducing their food. Granivorous and 
 herbivorous animals are supplied with cutting teeth in 
 both jaws, as in the horse, or they are confined to the 
 lower jaw, as in oxen, sheep, and deer. . The former seize 
 upon their food as with two rows of nippers, the latter with 
 the aid of the lips, tongue, and dense gum of the upper 
 jaw, cut the grass close to the ground while browsing in 
 the fields. They possess, besides, a series of excellent 
 grinders, whereby they reduce their food to a minute 
 state of mechanical division, and thus prepare it for being 
 more readily acted upon by the organs to which it has 
 subsequently to be presented. 
 
 Man, in proportion to his size, has the smallest teeth 
 of any of the mammalia. In him they form two rows, 
 each tooth being in contact with, and supporting its 
 neighbours ; they are also nearly on the same level, 
 circumstances which distinguish him from those animals, 
 such as the orang outang, w T hich approach nearest him 
 in bodily conformation. In the adult, each jaw contains 
 four cutting teeth in front, next to which are a pair of 
 conical teeth, named the eye or corner teeth, or, from their 
 being conspicuous in the dog, they are called canine, be- 
 hind w T hich are placed on each side five grinders, the two 
 anterior of which have two points, the three posterior 
 with broad upper surfaces, and more than two points, 
 which lock into corresponding depressions in their fellows 
 of the opposite jaw. There are thus sixteen teeth in 
 each jaw, when complete in both, forming a case of 
 thirty-two beautiful little instruments. 
 
 At birth, the teeth have not made their appearance. 
 The mouth is small, but admirably fitted for seizing the 
 nipple, and serving as a sucking instrument ; and how 
 well does it perform this duty, without previous tuition ! 
 affording one of the many thousand examples in the ani- 
 raal machine, that nothing is left to chance, nothing un- 
 
TEETH. 
 
 123 
 
 foreseen or unprovided for by its Author. "Wherever cir- 
 cumstances occur involving new conditions, whenever the 
 necessity arrives, means are at hand ready to start into 
 action to execute the duty, and without previous educa- 
 tion, perform the task with that perfectness and precision 
 which characterize all the works of the Creator. As the 
 organs of digestion in the infant gain strength, and be- 
 come prepared for an alteration of diet, the teeth begin 
 to appear, which they do in succession, commencing with 
 the central incisors of the upper jaw. 
 
 Teeth being formed of a substance which does not 
 admit of growth in accordance with the gradual enlarge- 
 ment of the jaw, a principle which nowhere else ex- 
 ists in the body is adopted. Two sets of teeth are fur- 
 nished, differing in size, number, and some of them in 
 form. The first set consists of four incisors, two canine, 
 and four grinders in each jaw. During the continu- 
 ance of the first, the second set are in the progress of 
 development. As they enlarge, they press upon the roots 
 of the first, and deprive them of nourishment, so as to 
 cause absorption of the roots. The former, therefore, are 
 shed without the roots. At birth, the bones of the face 
 bear a smaller proportional size to those of the skull than 
 they do subsequently. They rapidly outstrip in growth 
 the bones of the skull, particularly after the seventh year, 
 and continue to increase to the eighteenth or twentieth 
 year. About the seventh year, the second set of teeth, 
 which are larger, begin to supplant the first, and appear in 
 the same order of succession. The two pairs of grinders 
 in each jaw next the canine have no representatives in 
 the first. They are much longer in making up the 
 number, this not being completed till the eighteenth or 
 twentieth year, when the posterior pair of grinders make 
 their appearance, at a time when the owner, if he has not, 
 ought to have arrived at the years of discretion ; hence 
 they are termed the wisdom teeth. Some jaws are so 
 small, however, that they cannot contain the full num- 
 
124 TEETH. 
 
 ber. Some of the teeth, therefore, remain in the jaw, 
 which, when the others drop out, may make their ap- 
 pearance even in a very advanced period of life, nattering 
 the deluded individual that a renewal of his age is taking 
 place. 
 
 The earliest period from which the rudiments of the 
 teeth can be traced is about the fourth month of foetal 
 life. If examined some time after this, when they can 
 be observed with greater facility, they appear like small 
 sacs, abundantly supplied with blood-vessels and nerves. 
 The inner surface of the little vesicles secretes a peculiar 
 substance, the enamel, which is arranged in a crystallized 
 form, and constitutes the external crust of all that part of 
 the tooth which has to be exposed above the jaw. The 
 cavity within the crust is filled with a pulp composed of 
 blood-vessels and nerves, from which an exceedingly hard 
 bone is formed, so as to fill up the crust ; in order to give 
 it support, the fang or root is gradually added. When 
 the tooth bursts through the sac, the remains of the sac 
 are removed by absorption, so that the vessels which 
 formed the enamel are destroyed, consequently there can 
 be no renewal of it, though, according to some, the gum 
 subsequently takes upon it the office of nourishing the 
 enamel. 
 
 The bony part of the tooth, composing its centre and 
 root, continues to live and to be supplied with blood and 
 nervous energy. The blood-vessels and nerve in the full- 
 grown tooth are exceedingly minute. They enter by a 
 sm all hole in the root. The passage becomes enlarged 
 inwards, so as to form a small cavity where the process 
 of nutrition goes on : the nervous twigs are derived from 
 one of the most sensitive nerves of the whole body, the 
 fifth pair; so that when inflammation takes place, swelling- 
 being prevented, it is accompanied with such exquisite 
 anguish as no one can form an idea of who has not ex- 
 perienced tooth-ache. 
 
 The enamel is an insensible crust, covering the hard 
 
TEETH. 125 
 
 but living bone which composes the rest of the teeth. 
 Though insensible itself, it does not prevent the trans- 
 mission of sensation ; for, when the teeth are set on edge, 
 or when they are exposed to cold, they feel, notwithstand- 
 ing this covering ; just as the insensible scarf skin, the 
 nails, or even the hoofs of animals, do not destroy the 
 transmission of sensations, or rather the causes which ex- 
 cite sensations, in the subjacent parts. The crystalline 
 structure is beautifully arranged, in order to resist the 
 friction to which it is exposed. The crystals are longest 
 or the deposit is thickest where most exposed to attrition. 
 This will be best understood by the accom- 
 a panying wood-cut. In the cutting and ca- 
 nine teeth the crystals are longer at the points 
 and the outer surface , than on the inner 
 surface 6, while in the grinders they are long- 
 est upon their upper surface. The bony part 
 of the tooth is composed of a greater propor- 
 tional quantity of earthy matter than the 
 other bones of the body ; and the enamel, 
 FIG. 11. besides differing from bone, in being supplied 
 neither with blood-vessels nor nerves, and in being formed 
 of crystals, differs from bone in composition, by having 
 no cartilage in its constitution. 
 
 With respect to external characters, a tooth is divided 
 into the crown, or all that part which is externally ex- 
 posed ; the neck, which is immediately embraced by the 
 gum ; and the root or fang, which is inserted into the 
 socket. The incisors, acting like scissors, those of the 
 upper jaw generally overlapping those of the lower, have 
 small roots. The canine, employed in tearing, have large 
 and strong roots : the two first pairs of grinders have two 
 roots agglutinated into one, and the other grinders have 
 from three to four roots. 
 
 The manner in which the teeth are supported by the 
 gum, and fixed in the socket, is also deserving attention. 
 The gums not only serve as firm elastic cushions, whereby 
 
126 TEETH. 
 
 they rapidly diffuse the force, and powerfully support the 
 teeth when forcibly employed, but by the vascular con- 
 nexion between them, in part supply them with nourish- 
 ment. In old age, when the different parts of the body 
 begin to shrink, the gums recede from the teeth, whereby 
 they frequently become loose and drop out, though per- 
 & fectly sound. By the man- 
 
 ner in which the teeth are 
 implanted in the sockets, 
 they are afforded an ex- 
 tensive surface of support. 
 The force is not concen- 
 trated at the point, as in 
 the case of a nail thrust 
 FIG. 12.. into a board, but is uni- 
 
 formly diffused over the whole surface of the fang, as 
 may be seen in the annexed cut, where the fangs of the 
 middle tooth press on a surface, a a a, equal to four times 
 that of the crown, b ; so that supposing the pressure on. 
 the crown to be equal to four pounds, being extended 
 over the surface of the fangs, it is reduced to one pound 
 on any given point of the root, and with a similar force 
 upon the sockets. 
 
 In mammalia, the lower jaw alone is moveable. In 
 birds, the upper jaw is moveable in different degrees in 
 different families. In some reptiles, as in the crocodile, 
 both jaws are moveable, the upper moving on the first ver- 
 tebra of the neck, whereby the mouth can be opened to a 
 great extent. In serpents, the jaws may be opened so 
 as to take in prey of greater diameter than that of their 
 own body. In mammalia which grind their food, the 
 jaw, besides possessing motion upwards and downwards, 
 has also a lateral motion ; while in carnivorous animals 
 the hinge motion upwards and downwards alone exists. 
 
 Man is distinguished more by the variety than the ex- 
 tent of the motions of his jaw. These consist of six pri- 
 mary movements, viz. upwards and downwards, by which 
 
MUSCLES OF THE JAW. 
 
 127 
 
 the mouth is opened and shut ; lateral motion, from side 
 to side ; and motion forwards, whereby the teeth of the 
 lower jaw are carried before those of the upper, and 
 backwards, whereby the jaw is retracted. In' order to 
 facilitate the mobility of the jaw, the joint by which it is 
 connected with the skull is double, there being a move- 
 able cartilage interposed between two capsules. As the 
 principal force is required in shutting the jaw, the muscles 
 employed for this purpose are large and powerful. One 
 arises from the temple on each side, and from its situation 
 is named the temporal ; it may be seen in action during 
 mastication. Another proceeds from the cheekbone, and 
 runs down towards the angle of the jaw ; it may be felt 
 in action by placing the finger a little above the angle of 
 the jaw, and pressing the teeth together. Another is 
 placed opposite to it internally. The fourth, also placed 
 internally, is chiefly employed in the motion forwards. 
 The antagonists to these consist of a pair which extend 
 from the base of the skull to the chin, and of three pairs 
 between the hyoid bone and chin. Though physically 
 weaker than those which shut the jaw, they possess the 
 advantage of a longer lever ; still they are not required 
 to exert the same force as those which move it upwards. 
 It is to be recollected that the jaw rarely moves in the 
 direction of the fibres of any of the above muscles, but 
 generally in the diagonal between their different forces, 
 whereby the movements are performed with greater 
 steadiness than they otherwise would be. 
 
 The muscles which shut the jaw are supplied from the 
 fifth pair of nerves, already alluded to as supplying the 
 teeth. This may probably be the reason why these mus- 
 cles are so liable to spasmodic action, which is not un- 
 frequently produced by irritation of distant parts, as from 
 punctured wounds of the thumb and great toe, when lock- 
 jaw takes place. There have been instances where these 
 muscles have acted with such prodigious force as to crush 
 the teeth, notwithstanding the admirable manner in which 
 
128 SALIVA. 
 
 they are planted in their sockets. By the movements of 
 the cheeks, the lips and the tongue, the food is brought 
 in succession under the action of the teeth, which are put 
 in motion by the action of the muscles of the jaw, till it 
 is sufficiently triturated. 
 
 Insalivation. During mastication, an abundant quantity 
 of saliva flows into the mouth, and is thoroughly intermixed 
 with the food. The saliva is furnished by three glands on 
 each side. The largest is placed before and below the ear, in 
 the depression between the jaw and skull ; from its situa- 
 tion it is called parotid. The next in size lies under the 
 angle of the jaw, and the smallest more anteriorly, under 
 the tongue ; the former, from its situation, is termed sub- 
 maxillary, the latter sub-lingual. These glands are abun- 
 dantly supplied with blood, and derive their nerves from 
 the same source which imparts sensibility to the mouth 
 and tongue. Being brought also into connexion with the 
 nerves of the gullet and stomach, they sympathize with 
 these parts in various conditions. Stimulating substances 
 applied to the mouth, and particularly piquant and sa- 
 voury food, excite in them a more abundant flow of the 
 saliva. The quantity poured into the mouth at each 
 meal amounts to six or eight ounces, or about half a pint. 
 The ducts of the parotid open opposite the second grinder 
 of the upper jaw, and those of the other two glands under 
 the tongue, by the side of its frenulum or bridle. 
 
 The substances which enter into the composition of 
 saliva are various, consisting of mucus, osmazome, and 
 a peculiar animal matter, salivin, with six soluble, and 
 three sparingly soluble salts ; the soluble are compounds 
 of acetic, carbonic, muriatic, sulphuric, phosphoric, and 
 sulpho-cyanic acids, with potash in the human sub- 
 ject ; but in other animals, as in the sheep, it is soda. 
 The quantity of carbonate of soda in the sheep is so 
 considerable, that their saliva effervesces on the addi- 
 tion of a stronger acid. The sparingly soluble salts are 
 the phosphate and carbonate of lime and magnesia. 
 
SALIVA. 129 
 
 These are sometimes deposited on the teeth, forming 
 what is termed the tartar, which, insinuating itself be- 
 tween the gum and the tooth, is not only unseemly but 
 injurious. 
 
 Although chemical analysis thus shews that the saliva 
 is a very compound fluid, yet it is necessary to be very 
 chary in drawing inferences from chemical properties and 
 composition, as to the action of animal fluids in the living 
 body. No one, from chemical analysis, has hitherto suc- 
 ceeded in shewing the cause of the deadly effect of the 
 poison of the serpent, or of the not less dreaded saliva of 
 the mad dog ; and indeed the effects of all substances upon 
 the living system are only to be ascertained by observa- 
 tion and experience ; little or nothing can be gained by 
 anticipation. 
 
 From the quantity of saliva mixed with the food dur- 
 ing mastication, it has been supposed merely to reduce 
 the food to a soft pulpy mass, and to fit it for being swal- 
 lowed, and for being more readily acted upon by the sto- 
 mach. There is every reason, however, to believe, that 
 it produces other more important than these merely me- 
 chanical effects. It acts as a stimulant, and is by no 
 means an inert application to foul ulcers. The dog in- 
 stinctively licks wounds, w r hereby they take on a dispo- 
 sition to heal. It has a great attraction for oxygen ; 
 hence metals are more readily oxidized when rubbed with 
 it. Saliva may thus act as a stimulant to the coats of 
 the stomach, and, by disposing affinity, induce import- 
 ant changes in the mass of food. At the same time, it 
 is to be recollected, that it is a fluid immediately poured 
 from the living blood ; so that insalivation may be consi- 
 dered as the first step of assimilation of the food to the 
 constitution of the animal. 
 
 The food having been assimilated in temperature, and 
 reduced by trituratioii and insalivation to a pulpy mass, is 
 gathered together by the motions of the cheeks, lips, and 
 
 G2 
 
130 ABDOMEN. 
 
 tongue into a convenient form to be delivered to the or- 
 gans of deglutition. During swallowing, the soft palate 
 is raised in order to shut the posterior nostrils, the tongue 
 is carried . backwards, and the larynx ascends, so that the 
 glottis is closed. By the combined action of these dif- 
 ferent parts it is conveyed to the pharynx, which is a 
 muscular funnel at the top of the gullet, placed behind the 
 larynx, composed of muscular fibres arising from the 
 base of the skull, root of the tongue, hyoid bone, and 
 larynx. The mass of food is not only besmeared with 
 the mucus of the mouth, but just as it enters the pharynx 
 is plentifully lubricated with the viscid secretion fur- 
 nished by the almonds of the ear, situated at the back 
 part of the mouth, whereby deglutition is facilitated. 
 The pharynx having received the food, propels it into 
 the gullet, by which it is conveyed to the stomach. All 
 these actions take place during deglutition ; they do not 
 occur in succession, but simultaneously, so that they appear 
 to be only one act. Beyond the limits of the pharynx dis- 
 tinct sensation and voluntary motion does not extend. 
 The food is now subjected to organs which in the healthy 
 state carry on their action without our consciousness, and 
 over which we possess no direct control. 
 
 The Abdomen or belly, which is chiefly filled with the 
 digestive apparatus, is larger then either of the other two 
 large cavities, the head and thorax; the contents of the head 
 not admitting of the enlargement and diminution of the 
 cavity ; while the heart and lungs, which occupy the largest 
 portion of the chest, perform offices which are incompatible 
 with the expansion and contraction of that cavity be- 
 yond certain limits within which the enlargement and 
 diminution are confined, and which regularly take place 
 in accordance with their functions, as has been al- 
 ready explained. The abdomen, on the other hand, ad- 
 mits of great variation in capacity, not only where 
 ehanges in that respect take place slowly and gradually^. 
 
ABDOMEN. 131 
 
 as in dropsy, and during gestation, but likewise where 
 they occur more suddenly, as after a full meal, or where 
 large quantities of gases are generated. 
 
 The abdomen is bounded anteriorly and laterally by 
 inusculo-membranous walls, superiorly by the diaphragm, 
 posteriorly by the vertebral column and muscles of the loins, 
 and inferiorly by the pelvis or basin. It is lined through- 
 out by a thin membrane, which, from extending over the 
 different parts, is termed peritoneum. The peritoneum 
 not only lines the walls of the abdomen, but covers al- 
 most all its contents, and presents an exceedingly smooth 
 moist surface, thereby facilitating the motions of the 
 different parts upon each other. It likewise serves to 
 bind down and to connect the viscera ; and by its nume- 
 rous and extensive folds, the surface, from which a watery 
 vapour constantly exhales, is much extended. This 
 vapour, insinuating itself everywhere, not only lubricates 
 the surfaces, but also serves as excellent packing, so as to 
 support the different parts, and nowhere could a more 
 admirable instance of packing be found than the abdo- 
 men affords. 
 
 The contents of the abdomen, excepting such as are 
 fixed down to the back posteriorly, are subjected to con- 
 stant motion, in accordance with the respiratory move- 
 ments, whereby they are excited and aided in their 
 functions, and hence partly the advantage obtained from 
 exercise ; hence also one of the many evils which arise 
 from lacing the body with bandages or stays, where these 
 motions are interfered with. 
 
 The digestive organs, which we have now to consider, 
 consist of the direct and accessary ; the direct being the 
 gullet, stomach, and intestinal canal ; the accessary com- 
 prising the liver, pancreas, and spleen. If we examine 
 the alimentary tube from the gullet to the farthest extre- 
 mity of the intestine, we shall find it composed of three 
 layers or coats, as they are termed, viz. the mucous, the sub- 
 
132 ALIMENTARY CANAL. 
 
 mucous, and the muscular. In the abdomen, the peritoneum 
 furnishes a fourth, the serous coat, which in some parts 
 is only a partial covering. The mucous coat lines the 
 whole internal surface, and is that with which matters 
 traversing the tube come immediately in contact. 
 Throughout its whole extent it is studded with nume- 
 rous glands, furnishing a viscid fluid or mucus, which 
 serves as a protection to the very sensitive surface, and 
 at the same time facilitates the passage of substances- 
 along it, by rendering it smooth and slippery. These 
 glands are like little bottles with short necks. They are 
 furnished with a muscular power, by which they expel 
 their secretions, and also with another set of muscular 
 fibres, which form a fillet round their mouth, by which 
 their contents are retained until their mouths are excited, 
 so as to call forth their action, and cause them to evacuate 
 themselves. They vary in size : In some places they are 
 small, and collected in clusters ; while in others they are 
 larger, and more scattered. Besides the mucus which 
 lubricates the surface, there is constantly exhaled a thin 
 watery fluid, which is derived immediately from the ves- 
 sels terminating upon it, without the intervention of 
 glands. This fluid intermixes with the aliment as it 
 passes along, dilutes it, and effects important changes in 
 it, as in the stomach, where it is called the gastric juice. 
 It is not always produced in equal quantities, but the 
 quantity varies according to different causes, as the pre- 
 sence of the aliment, or stimulating substances, such as 
 medicinal agents of various kinds. Gases are also secreted 
 from it, sometimes in great quantity, producing flatu- 
 lency. These gases vary, being of different kinds, and 
 in different states and situations. 
 
 The mucous lining is by far the most extensive of the 
 coats of the intestine, being formed into numerous folds, 
 so as to present an extensive surface both for secretion 
 and absorption. In the stomach the folds are irregular 
 
ALIMENTARY CANAL. 133 
 
 in their direction, though generally longitudinal, while 
 in the intestine they are transverse, forming a series of 
 segments of circles, lying one upon another like tiles. 
 
 Beneath the mucous coat is a layer of condensed cellular 
 membrane, that universal animal tissue which is diffused 
 over the whole body, affording coverings for the different 
 organs and parts of organs, and insinuating itself every 
 where. It imparts strength to the tube, and the mucous 
 follicles or glands are inserted upon it. 
 
 The muscular layer consists of two sets of fibres, the 
 external or longitudinal running lengthways, the in- 
 ternal transversely. The longitudinal are strongest and 
 most conspicuous in the gullet and the extremity of the 
 gut. They tend to diminish, the length of the tube when 
 in action, and are more powerful in the parts mentioned, 
 being there partly under the command of the will, and 
 employed in propelling more solid matters than in the 
 rest of the canal. The transverse fibres do not form rings, 
 but segments of rings, whereby the centres of contrac- 
 tion are increased, and the resulting effect greater. They 
 diminish the transverse diameter of the tube. Thus, the 
 combined action of both sets will be to contract the tube 
 in all its diameters. The following is the mode of their 
 action : Supposing a portion of alimentary matter is 
 sent into the first portion of the intestine, its presence 
 excites the action of the muscular coat, whereby the con- 
 tents are embraced and pushed forwards into the next 
 part beyond, which at the time is empty, and ready to 
 receive ; but the contraction of the first does not imme- 
 diately relax on having expelled the matter : it continues 
 for some time, in order to prevent the return of the ali- 
 ment on the action of the second, so that it is forced into 
 a third portion, which in its turn becoming excited, forces 
 it onwards. In this way, a slow undulating motion is 
 produced, whereby the contents of the intestinal tube are 
 gradually and slowly carried along, yet not with the 
 
134 ALIMENTARY CANAL. 
 
 same degree of motion in every part, being retarded in 
 some parts, in order to become subjected to changes, while 
 it is accelerated in others. 
 
 The Gullet is a cylindrical tube by which the aliment 
 is conveyed from the pharynx down the neck and through 
 the back part of the chest into the abdomen, where its 
 coats are expanded to form the stomach. 
 
 The Stomach is a large pouch or bag situated at the 
 upper part of the abdomen, lying under the left short ribs, 
 extending across what is called the pit of the stomach, at 
 the end of the breast bone towards the right side. In shape 
 it resembles the bag of the bag-pipe. In fact, it is not un- 
 likely that the first kind of bag for that instrument was 
 the stomach of some animal. The left portion of the sto- 
 mach, in which the gullet terminates, is the largest. From 
 its proximity to the heart it is termed the cardiac extrem- 
 ity. As it approaches the right side, it becomes contracted, 
 and terminates in the intestine, where there is placed a val- 
 vular apparatus, by which the entrance into the intestine 
 is guarded, and which is therefore named the pyloric valve. 
 Hence too the name pyloric extremity of the stomach. 
 The cardiac portion serves principally as a receptacle, 
 while in the pyloric portion the peculiar changes produced 
 upon the food are chiefly effected. The stomach is com- 
 posed of the number of coats mentioned, which are abun- 
 dantly supplied with blood and nerves, the latter being 
 received more directly from the brain than the portions 
 of the alimentary canal beyond it. 
 
 The Duodenum, so termed from being about twelve 
 inches in length, is the first portion of intestine beyond 
 the stomach. By its turns it very nearly forms three sides 
 of a square ; it is more capacious than the rest of the 
 smaller intestine, is fixed in its position, and has the ducts 
 from the liver and pancreas opening into it. 
 
 The next portion of intestine is of the greatest length, is 
 somewhat more contracted, and variously coiled, especially 
 
LIVER. 135 
 
 towards the left side and middle of the abdomen, and 
 terminates on the inside of the right haunch-bone, in the 
 great gut or colon. At its termination there is a valve, 
 whereby any substance is prevented from returning into 
 it after it has entered the colon. 
 
 The Colon, or great gut, is, as its name indicates, capa- 
 cious. It is furnished with three bands of ligamento- 
 muscular tissue, which run along it longitudinally ; they 
 contract the length of the gut so as to form it into cells. 
 At its commencement the colon forms a shut sac, which 
 is abundantly supplied with mucous glands ; it then pro- 
 ceeds upwards towards the liver, crosses under the sto- 
 mach to the left side, down which it descends, where it is 
 much twisted, and finally enters the basin, where it is 
 called rectum, from the bowel being here straighter than 
 in any other part. 
 
 The Rectum is furnished with more powerful longitu- 
 dinal muscular fibres than any other portion of the intes- 
 tine. At its extremity it is guarded by a muscle which 
 closes it like the mouth of a purse. These muscles, be- 
 sides being supplied with nerves in common with the rest 
 of the intestine, receive filaments from the extremity of 
 the spinal cord, whereby a certain degree of voluntary 
 power is possessed over this part, so as to retain or expel 
 the contents under the command of the will. 
 
 A general view may now be taken of the accessary 
 digestive organs, namely, the liver, pancreas, and spleen. 
 
 The Liver is the largest gland in the body, weighing 
 about four pounds. It occupies the right superior region 
 of the abdomen, in contact with the diaphragm, to which 
 it adheres. It is divided into lobes by fissures, which are 
 more or less deep in different animals, being more com- 
 pletely divided in those which have a flexible spine, so as to 
 admit of ready adaptation to various postures of the body. 
 Its structure is composed of an infinite number of minute 
 granules, connected with each other by cellular tissue. 
 The circulation through the liver, as has been already 
 
136 BILE. 
 
 mentioned in the chapter on circulation, is peculiar, the ar- 
 tery being comparatively small, as conveying arterial blood 
 merely for its nourishment, while the venous blood from 
 the stomach, intestinal canal, spleen, pancreas, and folds of 
 the peritoneum, is brought to the liver by the vein termed 
 porta, by which it is minutely distributed through this 
 gland, and from it the bile is elaborated. The very languid 
 circulation of blood in the porta admits of the slow and 
 gradual formation of bile, a fluid composed of substances 
 very distinct from the constituents of the blood. Being 
 abundant in carbon and hydrogen, the venous blood, con- 
 taining a great proportional quantity of these elements, 
 becomes better fitted for furnishing materials for the biliary 
 secretion. The bile transudes through minute pores, and 
 is immediately drunk up by small tubes, which, by re- 
 iterated unions, form one bile duct, which proceeds to- 
 wards the first portion of the intestine. In its course 
 there branches off from it a duct, which terminates in a 
 sac, the gall-bladder, where the bile accumulates till re- 
 quired, where bitterness is imparted to it, and where also 
 the thinner parts are reabsorbed, so that the remainder 
 is thickened. In some animals, as the horse, there is 
 no gall-bladder, in which case the bile is immediately 
 conveyed into the intestine. 
 
 The bile is a greenish-yellow fluid, with a peculiar 
 heavy odour, and a taste at first sweetish, followed by 
 an exceedingly nauseous bitter. It is a very compound 
 fluid, and chemists disagree as to its constituents. It 
 is extremely difficult to obtain uniform and satisfactory 
 results from the chemical examination of organised sub- 
 stances, and very difficult to distinguish between their 
 constituents and such as are the products of the processes 
 to which they may have been subjected. Fluids, such as 
 the bile, when removed from the living body, are imme- 
 diately brought under the full influence of the general laws 
 affecting dead matter : spontaneous changes commence, a 
 separation of the different parts takes place, and the 
 
PANCREAS. 137 
 
 temperature is no longer the same as in the living body. 
 The bile may be stated to be a fluid containing water, 
 with salts in solution, some common animal principles, 
 and others peculiar to itself. The salts are compounds of 
 the following acids: colic acid, peculiar to the bile; 
 margaric, oleic, acetic, carbonic, sulphuric, muriatic, and 
 phosphoric, combined with soda ; the last is also united 
 with a little lime. To the carbonate of soda the bile owes 
 its alkaline property, and hence it is sometimes used for the 
 purpose of cleansing. The common animal principles are 
 mucus derived from the lining membrane of the gall ducts, 
 a modification of albumen, and osmazome. The peculiar 
 principles are a yellow colouring matter, resin, and a 
 substance, the taste of which is first sweet and then bitter, 
 hence named picromel ; but, when pure, it is sweet with- 
 out bitterness, the latter quality being owing to the bile 
 which it holds in solution, and for which it serves as a 
 solvent. Besides, in the human bile another peculiar 
 substance has been detected. From its forming the basis 
 of, and giving consistence to, gall-stones, it is called 
 cholesterine ; in external appearance it very much resem- 
 bles spermaceti. 
 
 The Pancreas, or sweetbread, is an elongated gland, 
 about five or six ounces in weight, lying in the curvatures 
 of the duodenum, and presenting a structure very much 
 resembling the salivary glands, whence it was inferred 
 that it furnished a secretion similar to the saliva. Later 
 examinations have shewn that the pancreatic fluid differs 
 from that secretion in containing a considerable quantity 
 of albumen, a curdy substance, and in the absence of 
 sulpho-cyanic acid ; the fluid secreted by the pancreas 
 is collected by the branches of its duct, which terminates 
 generally, in common with the bile duct, in the duodenum. 
 
 The Spleen is a dark purple or livid-coloured body, 
 weighing about eight ounces, situated in the left side, and 
 attached to the stomach and some neighbouring parts. It 
 is of a loose, spongy, and exceedingly soft texture, very 
 
138 
 
 SPLEEN. 
 
 abundantly supplied with blood-vessels, but has no ducts; 
 nor does it appear to elaborate any peculiar secretion 
 from the blood. The purpose it serves will hereafter be 
 examined. 
 
 I 
 
 FIG. 13. 
 
 The above engraving will give an idea of the general 
 form and relative position of the different organs engaged 
 in digestion : a is the gullet ; , the stomach ; c, the 
 duodenum ; d^ the convolutions of the small intestine ; <?, 
 the coscum ; /, the appendix of the ccecum ; g, the 
 ascending colon ; A, the transverse arch of the colon ; i, 
 the descending colon ; j, the rectum ; &, the liver ; /, the 
 gall-bladder ; m, the pancreas, the greater part of which 
 is covered by the stomach ; <?, the spleen. In the en- 
 
RUMINANTS. 139 
 
 graving the liver is elevated, and the transverse arch of 
 the colon drawn down, in order to shew parts which they 
 cover in their natural position. 
 
 When we consider the infinite variety of food on 
 which animals subsist, we will be prepared to expect 
 great diversities in the construction of the digestive 
 organs. Yet it will be found that they are all formed 
 upon the same general plan, from the highest to the 
 lowest, though variously modified, so as to adapt them to 
 the condition of each. It may be useful to advert to 
 some of these modifications before entering upon the con- 
 sideration of the action of the digestive apparatus, and the 
 results of that action in the human subject. 
 
 In those animals of the class mammalia which subsist 
 upon flesh, such as the lion, the tiger, and the cat, the sto- 
 mach is simple in its structure, the intestinal canal com- 
 paratively short, and the motions quick. The vascular dis- 
 tribution is also such as to admit of ready entrance of the 
 new matter into the general system. On the other hand, 
 in those which live upon crude vegetable food, such as 
 grass, the digestive organs are complicated. 
 
 In ruminating animals, as in the ox, sheep, deer, &c. 
 there are four stomachs. The animal transmits the food 
 into the first stomach without subjecting it to mastica- 
 tion in the first instance. This capacious cavity, known 
 by the name of paunch, is of a somewhat globular form, 
 lined internally with a dense insensible scarf skin, studded 
 with numerous papillae, and usually divided into distinct 
 pouches by strong muscular bands. It exerts a rotatory 
 motion, whereby, when indigestible substances, such as 
 hair, are introduced, they are formed into round balls, as 
 often occurs in oxen, from their licking their hides. It 
 always contains a portion of the previous meals, for when 
 the animal is even starved to death, a portion of food 
 is still found in the paunch. This may be considered 
 as a kind of cooking vessel ; the food, on being introduced 
 into it, is subjected to the internal heat of the animal, is 
 
140 RUMINANTS. 
 
 brought in contact with that which for sometime has been 
 under action, and kept in motion by the muscular power 
 of this stomach. 
 
 The second stomach is much smaller, and appears as 
 an appendage to the first. It too is lined with insensible 
 cuticle, and divided into numerous cells, generally of a 
 hexagonal shape. It is termed the honeycomb, or king's 
 hood. It appears chiefly to serve as a reservoir for fluids. 
 In the camel and dromedary there are several pouches 
 connected with this cavity, each capable of containing a 
 considerable quantity of w r ater. Their orifices are com- 
 manded by a sphincter muscle, whereby the water is re- 
 tained without being contaminated with the adjacent 
 food. These animals drink seldom, but take a large 
 quantity at once, which is stored up for many days 
 without undergoing change, remaining perfectly sweet 
 and clean. We thus see how admirably they are con- 
 structed for traversing the arid deserts in which they are 
 placed. The life of the traveller is occasionally preserved 
 by his sacrificing that of his camel in order to procure 
 the water contained in the cells of the honeycomb. 
 
 The ruminant possesses a voluntary power over these 
 two stomachs. When he chews the cud, a portion of 
 food is detached from the general mass, probably a part 
 of that which has been for the longest time lodged. As it 
 passes the second stomach it receives a quantity of mois- 
 ture, and is returned to the mouth, where it is subjected 
 to* trituration and insalivation. 
 
 On being swallowed for the second time, by a curious 
 power possessed over the gul]et, it is transferred to the third 
 cavity, which is the smallest of the four. Like the two 
 former it is lined with cuticle, which is folded into broad 
 plaits, from which circumstance it has obtained the name 
 of many-plies. It has not been clearly ascertained what 
 action the many-plies has upon the food ; but that a cer- 
 tain chemical effect is produced, appears from the fact that 
 here hydrogen gas is disengaged in considerable quantity. 
 
RUMINANTS. 141 
 
 The fourth stomach is to be considered as the proper 
 digestive organ ; it is named the rennet. Internally the 
 rennet is covered by a soft delicate mucous membrane, 
 formed into longitudinal folds, and gastric juice is secret- 
 ed in this compartment. In the suckling, the milk does 
 not enter any of the three first, but, by a peculiar manage- 
 ment of the gullet, it is immediately transferred into the 
 fourth stomach, where it is curdled by the gastric juice, 
 this being the first change to which it is subjected. This 
 power of coagulating milk possessed by the gastric juice 
 is one of its most striking and remarkable properties. 
 The rennet, even after being salted and dried, retains the 
 power of imparting to water, on being infused in it, this 
 quality ; and accordingly that of the calf is prepared and 
 preserved for this purpose in dairies. 
 
 The three first stomachs in ruminating animals may be 
 held as merely subsidiary to the first, where the crude 
 vegetable matter undergoes a process of preparation which 
 may be compared to the effects of cooking, so as to render 
 it more susceptible to the action of the proper stomach. 
 Where, however, such influence is unnecessary, as in the 
 case of milk, the food is not introduced into them, but 
 directly conveyed into the fourth. 
 
 Notwithstanding the length of time, and the extent 
 and complexity of apparatus to w T hich crude vegetable 
 food is exposed in these animals, it is calculated to yield 
 but a sparing quantity of nourishment. Accordingly, the 
 intestinal canal is long and capacious, so as to afford 
 both time and surface, that the whole of the nutritious por- 
 tion may be taken up, and that every particle capable of 
 furnishing nutriment may be abstracted. 
 
 In monogastrics that is, animals with a single stomach 
 which subsist on vegetable food various modifications of 
 the digestive organs, so as to adapt them to their office, 
 may be observed. The stomach is divided into two por- 
 tions, especially during the process of digestion, the left 
 extremity serving as a capacious reservoir where the food 
 
142 HERBIVOROUS MONOGASTRICS. 
 
 is lodged and prepared previous to its being brought un- 
 der the action of the right portion, in which the proper 
 conversion into chyme is effected. In the horse, the left 
 portion is lined with dense insensible cuticle, as in the 
 three first stomachs of ruminants. The length and capa- 
 ciousness of the intestinal canal, especially of the colon 
 and its appendage the coecum, in monogastric herbivorous 
 animals, compensate for the less elaborate construction of 
 the stomach. In the horse the colon is very large : so it 
 is in the hare and the rabbit. The food, therefore, after 
 having been subjected to the action of the stomach, and 
 the chyme there produced being changed into chyle, which 
 is absorbed in the smaller intestines, the residue is trans- 
 ferred into the larger intestine, where it is lodged for some 
 time, and there intermixed with new juices, having been 
 previously softened and otherwise altered in its passage 
 along the superior organs. The last efforts are now made 
 to abstract nourishment from it, after which the effete 
 residuum is ejected. 
 
 The circulation of the blood is in perfect accordance 
 with the various conditions of the organs of digestion in 
 different animals. Where the quantity of chyle is abun- 
 dant and rapidly produced, as in the carnivorous animals, 
 the circulation is rapid ; while in the herbivorous animals, 
 where the production of chyle is more gradual, the circu- 
 lation is correspondently slow. In the pig, the mesenteric 
 arteries, which supply the intestinal canal, have their pri- 
 mary divisions formed into bundles of very intricate net- 
 work, from which the vessels immediately distributed 
 upon t-he bowel are given off. The veins also present the 
 same distribution, and are curiously interwoven with those 
 of the arteries. This kind of circulation must be neces- 
 sarily sluggish, but gentle and uniform, affording ample 
 time for complete absorption of the ^nutritious chyle. 
 
 In birds, numerous modifications in the digestive organs 
 obtain, adapted, as in the mammalia, to the nature of their 
 food. My friend Mr Macgillivray has lately, in his excel- 
 
DIGESTIVE ORGANS OF BIRDS. 143 
 
 lent work on British birds, with great success adopted the 
 digestive organs as the basis of his arrangement. 
 
 In birds the gullet is capacious. At its lower extrem- 
 ity it is dilated into what is termed the proventriculus, 
 the internal surface of which is studded with numerous 
 mucous glandules, frequently symmetrically arranged. 
 In the proventriculus, the proper gastric juice is also se- 
 creted, for in many birds the stomach is lined with a hard 
 and dry membrane altogether unfit for the office of secre- 
 tion. The stomach in carnivorous birds, as in falcons, is 
 simple and membranous. The intestinal canal is not so 
 definitely divided into distinct portions, that is, into small- 
 er and larger, as it is found to be in mammalia. Towards 
 its extremity there are two blind guts or cceca, and the 
 extremity or rectum terminates in what is called the 
 cloaca, being the common termination of the intestine, 
 urinary, and genital organs. In granivorous birds, the 
 gullet is dilated into a remarkable pouch, named crop, 
 which serves as a reservoir for the food, where it also un- 
 dergoes slight preparatory changes, analogous to those 
 in the first stomachs of ruminants, and in the left portion 
 of monogastric herbivorous quadrupeds. In some, in- 
 stead of a distinct crop, the capaciousness of the gullet 
 serves the same purpose. In the proventriculus, the ne- 
 cessary fluids are furnished for the process of digestion. 
 The food is then transferred to the proper stomach, which 
 in those that live on flesh and on fish is simply mem- 
 branous, in accordance with the nature of the food, which 
 is easily and rapidly changed into chyme. But in grani- 
 vorous and insectivorous birds, the stomach is more com- 
 plicated in its structure ; its internal lining becomes hard, 
 dry, and insensible, and almost of horny consistence ; the 
 muscular coat is largely developed, and formed into dis- 
 tinct and powerful muscles, by the contraction of which 
 the contents of the stomach or gizzard (as it is named when 
 of this construction) are crushed and reduced to a minute 
 state of mechanical division. The action of the gizzard 
 
144 ANIMAL PRINCIPLES. 
 
 is aided in reducing the food by quartz and other hard 
 angular stones, which the bird instinctively swallows. 
 The length and capacity of the intestine varies much. 
 In gallinaceous birds, in particular, as the domestic fowl, 
 the cosca are very capacious, affording the best oppor- 
 tunity for the abstraction of nourishment like the largely 
 developed coecum and colon of herbivorous quadrupeds ; 
 while in most carnivorous birds the cceca are merely ru- 
 dimentary. 
 
 The stomach in man is intermediate between that of 
 the carnivorous and monogastric herbivorous quadrupeds, 
 being more developed in the former, and less so in the 
 latter. The intestinal canal is longer, and more capa- 
 cious than in animals which live entirely on flesh. But 
 though the colon is large, it is not of the same propor- 
 tional size as in those which are confined to vegetable 
 food. 
 
 FOOD is derived either from the animal or vegetable 
 kingdom, and has consequently been previously organized. 
 By digestion, the aliment is reduced to a new condition, 
 and by admixture with the fluids with which it meets, 
 becomes assimilated to the constitution of the animal. 
 
 THE PROXIMATE ANIMAL PRINCIPLES, as food, are 
 fibrin, albumen, gelatin, osmazome, and fat : they are com- 
 pounds of four elementary principles, carbon, oxygen, 
 hydrogen, and nitrogen, with the exception of fat, which 
 is deficient in nitrogen. 
 
 Fibrin is a white translucent elastic substance, in- 
 soluble in water, but softened by immersion in it. It 
 is the chief constituent of the flesh of mammalia and 
 birds, and of the coagulum of the blood. The flesh of 
 adult animals contains a greater proportional quantity of 
 it, and is also firmer and more easily digested than that 
 of the young. Thus beef and mutton are both more nu- 
 tritious and more easily digested than veal and lamb ; the 
 flesh of animals that are at liberty, and able to take 
 healthy exercise, than that of those which are kept in 
 confinement. 
 
VEGETABLE PRINCIPLES. 145 
 
 Gelatin, when pure, is colourless, semi-transparent, and 
 tasteless. It is obtained chiefly from the skins of ani- 
 mals, cartilages, the animal part of bones, and the sounds of 
 fishes. It is also found in considerable quantity in the 
 flesh of young animals. Gelatin is softened by cold wa- 
 ter, and dissolved in hot. Its solution concretes, on 
 cooling, into a tremulous mass called jelly. 
 
 Albumen is the most generally diffused of the proxi- 
 mate animal principles. It is found in two conditions ; 
 in solution in the blood and various secretions, and in 
 the solid form in flesh, tendons, ligaments, cartilage, horns, 
 hoofs, and membranous parts. The white of an egg con- 
 sists of albumen nearly pure. It is soluble in cold water, 
 and coagulated by heat. Albumen, along with a little 
 oil in the yolk, is the nutritive substance in eggs ; as also 
 of fish, combined with gelatin, and in some with oil. 
 
 Osm.azome is so named from having the smell of broth, 
 to which it gives the characteristic odour and taste. It 
 is of a brownish colour, soluble both in cold and hot 
 water. 
 
 Fat is a well-known substance, similar to the fixed oils 
 of vegetables. It is composed of two principles, stearine, 
 a white concrete substance resembling wax, and ela'ine, 
 a limpid fluid. The relative proportion of these two de- 
 termines the consistency of fat. Although subservient 
 to several secondary purposes, fat can scarcely be consi- 
 dered as an essential animal constituent. It appears ra- 
 ther to be a superaddition to the system, when the nou- 
 rishment exceeds the current expenditure, and serves as 
 a magazine from which the system may draw, under 
 particular circumstances. 
 
 PROXIMATE VEGETABLE PRINCIPLES. The following 
 are the chief nutritive vegetable principles : Gluten, ve- 
 getable albumen, starch, sugar, vegetable jelly, gum, and 
 fixed oils. With the exception of the two first, which 
 contain nitrogen, they are all ternary compounds, con- 
 sisting of carbon, oxygen, and hydrogen. 
 
146 VEGETABLE PRINCIPLES. 
 
 Gluten is a grey, viscid, elastic, and very adhesive sub- 
 stance, very sparingly soluble in water. It is obtained 
 from the cultivated grains, especially from wheat, the su- 
 periority of which for food has been attributed to the 
 quantity of gluten it contains. It is also found in the 
 pulse tribe, and in almonds, chesnuts, &c. The cow- 
 tree, which flourishes in the mountains of Quito in South 
 America, furnishes an abundant quantity of sap, having 
 the exact appearance and taste of milk, and used as a 
 substitute for that fluid by the natives, contains a modifi- 
 cation of gluten. When wheaten flour is put into a coarse 
 canvas bag, then washed and kneaded in water, the mu- 
 cilaginous part is dissolved and removed, the starch is sus- 
 pended in the water, and the grey tenacious mass which 
 remains consists of gluten and vegetable albumen. By 
 acting upon this mass with boiling alcohol, the gluten 
 is dissolved, and the albumen remains. From the close 
 resemblance which gluten has to animal principles, it 
 has been held to possess superior nutritive properties. 
 But the influence it exerts in fermentation, in which it 
 is an important agent, and its tenacity, also contribute to 
 its importance. During fermentation in making bread, 
 carbonic acid is disengaged, but prevented from escap- 
 ing by the adhesive quality of the gluten whereby it is 
 rendered light and spongy. The flour of barley and oats, 
 having less gluten, do not form sponge, as it is called by 
 bakers. 
 
 Vegetable albumen remains after gluten has been re- 
 moved by alcohol from the glutinous residue of wheat 
 flour. On drying, it becomes brittle and pulverulent. It 
 is sparingly soluble in cold water, and, like animal albu- 
 men, is coagulated by heat. It is found in mushrooms, 
 and in different other species of fungi. Almonds af- 
 ford about thirty per cent of a substance resembling 
 coagulated albumen. The juice of the fruit of the ochra, 
 according to Dr. Clarke, contains a liquid albumen in 
 such quantities that it is used in Dominica as a substi- 
 
VEGETABLE PRINCIPLES. 
 
 147 
 
 tute for the white of eggs in clarifying the juice of the 
 sugar cane. Vegetable albumen differs little in its essen- 
 tial properties from gluten. 
 
 Starch, or fecula, is a white tasteless and inodorous sub- 
 stance, insoluble in cold water, but readily dissolved in 
 water at a temperature between 160 and 180. If the 
 temperature be raised above 180, it coagulates into a 
 thick tenacious transparent jelly. When heated till it 
 becomes brown, it is changed into a substance resembling 
 gum, soluble in cold water, giving a mucilaginous solu- 
 tion. It exists in seeds, particularly of gramineous plants, 
 and in tuberous roots. It is procured by pounding, grat- 
 ing, and washing with cold water. In this way it is ob- 
 tained from wheat, or from potatoes. Sago is extracted from 
 the pithy substance of palms of the genus Sagus. Tapioca 
 and cassava are got from the South American plant Jatro- 
 pha Manihot, the juice of which is so virulent that the In- 
 dians employ it for poisoning their arrows. The poisonous 
 principle is, however, removed by washing, or it may be 
 dissipated by heat. The Maranta arundinacea furnishes 
 Indian arrow root ; and different species of the beautiful 
 genus Orchis, particularly the Orchis mascula, afford salop. 
 Most lichens contain a species of starch. Thus the Iceland 
 moss is employed by the natives of that country as an 
 article of food, and is, as well as other lichens, occasionally 
 prescribed for the sick. Starch is yielded by the roots of 
 a great variety of other plants. Frequently it is associ- 
 ated with bitter, resinous, acrid, and poisonous principles. 
 For example, in gentian root it is combined with a pure 
 bitter; in jalap, with a resinous purgative; inipecacuan, 
 with an emetic principle; and in Jatropha Manihot, 
 with a penetrating subtle poison. In this way, the mild 
 nutritious starch is protected from the attack of grubs, 
 &c. to which it would otherwise have been much exposed. 
 
 When gluten is present, as in the seeds of plants, 
 starch is converted into sugar, on being exposed to a pro- 
 per temperature, air, and moisture. When gluten is ab- 
 
1 48 VEGETABLE PRINCIPLES. 
 
 sent, the change takes place very slowly. This conver- 
 sion of starch into sugar occurs during germination of 
 seeds. In the process of malting, the grain is steeped in 
 water, then made up into a heap. When germination com- 
 mences oxygen is absorbed, and carbonic acid evolved, 
 and the temperature is elevated. At the proper point 
 the fermentation is checked by exposure to heat in a kiln, 
 when the malt is perfected, the starch being now changed 
 into sugar. The stage of germination is critical in the 
 growth of cultivated plants, especially of wheat ; for the 
 sugar invites the attack of grubs and insects, whereby 
 extensive depredations are frequently committed. Starch 
 is also converted into sugar by the agency of some acids, 
 such as sulphuric, nitric, muriatic, and oxalic ; and the 
 actual sugar thus obtained exceeds, by about one-tenth, 
 the original weight of the starch. Dr. Prout considers 
 wheat starch as the most perfect, and arrow- root as the 
 lowest of the varieties, the former by an easy transition 
 passing into sugar. 
 
 Sugar is well known for its sweet taste. It is soluble 
 in its own weight of cold water, and in a very small 
 quantity of hot water. From recent researches it appears 
 that there are several varieties of saccharine matter. In 
 its most perfect form it crystallizes into white semi-trans- 
 parent six-sided prisms. Another variety is uncrystal- 
 lizable, charged with a considerable quantity of colouring 
 matter, familiarly known under the name of treacle. 
 Sugar may be obtained from a number of vegetables, and 
 is contained in all those which have a sweet taste : it is 
 commonly procured from the sugar-cane. In North 
 America an inferior kind of sugar is obtained from the 
 juice of a species of maple growing wild in the woods. 
 A tree of average size will yield 50 quarts in 24 hours, 
 containing 5 per cent of sugar. The sap continues 
 to flow for five or six weeks. Sugar exists in all 
 sweet fruits : grapes, in good seasons^ yield from the 
 expressed juice nearly from 30 to 40 per cent of solid 
 
VEGETABLE PRINCIPLES. 149 
 
 matter, the greater part of which is sugar. The roots of 
 many plants afford it, such as beet-root, parsnips, and 
 carrots. In France, the beet is extensively cultivated 
 for sugar : 100 Ibs. of the root furnish from 4 to 5 Ibs. 
 of purified white sugar, besides a quantity of syrup, at 
 an average expense in that country of between 3d. and 
 4d. a pound. 
 
 Mannite, or manna sugar, is a species of sugar most 
 abundant in manna, a sweet juice which exudes from 
 several species of ash: four-fifths of the best manna 
 consists of this variety of sugar. It is also contained 
 in the sap of some of the pine tribe, and onions, celery, 
 asparagus, and other sweet plants. 
 
 Honey, secreted by flowers, and collected by bees, con- 
 tains two kinds of sugar, the one crystallizable, the other 
 not so, combined with wax, gum, colouring matter, and 
 principles which impart taste and smell, according to 
 the nature of the plants from which it is gathered. In 
 some instances it proves poisonous, from being collected 
 from plants possessed of deleterious qualities. 
 
 Milk furnishes a species of sugar : in Switzerland it is 
 an article of commerce. It is slowly soluble in three parts 
 of hot and six of cold water. In certain diseased states 
 of the human body, as in diabetes mellites, the urine 
 yields by evaporation a considerable quantity of saccharine 
 matter, similar in properties to common sugar. It has been 
 already stated that starch is converted into sugar by se- 
 veral of the acids ; and by the agency of sulphuric acid, 
 linen rags, saw-dust, and other substances, have been 
 changed into more than their own weight of crystallizable 
 sugar. 
 
 Sugar is pre-eminently nutritious. Although it soon 
 cloys the appetite, it is readily digested by the young, and 
 again it is relished in decrepit old age. During the sugar 
 harvest, the West Indian negro has more continued and 
 laborious exertion than at any other period of the year ; 
 yet notwithstanding he generally becomes fat and in good 
 
150 VEGETABLE PRINCIPLES. 
 
 condition, which is attributed to the quantity of cane juice 
 which he devours at pleasure. Dr Copland gives an inte- 
 resting case, illustrative of the nutritive properties of sugar. 
 He says, " A case which fully exemplifies the nutritious 
 quality of sugar, lately came under our observation in a 
 lady about the middle age, who consulted us respecting 
 great and increasing corpulency. Her countenance was 
 full, clear, and florid ; her pulse strong ; her health excel- 
 lent ; her strength very considerable. She partook of ani- 
 mal food only once in a day, and then in a very small 
 quantity. She never took suppers, and was very mode- 
 rate in the use of fluids. She had always taken consider- 
 able exercise on foot ; and even up to the period at which 
 we saw her, she resorted to it as much as the great bulk 
 of her body could permit. The secret, however, of her 
 obesity was disclosed, when she mentioned her insatiable 
 desire for refined sugar, which she almost hourly made 
 use of, frequently to the extent of one pound weight daily. 
 She considered it her chief article of diet. She reckoned 
 the average quantity she used at about three-fourths of a 
 pound in the day. Tea or coffee was taken by her sweet- 
 ened in the usual way. She ate the sugar in the solid 
 state, and unaccompanied with any other article of diet : 
 the finest sort- only was relished. Her digestive functions 
 were in a perfect condition ; neither cardialgia, acidity, 
 nor flatulence, were complained of. Her teeth were sound. 
 She found her corpulence supervene to a spare habit of 
 body, some time after the practice of eating sugar was 
 acquired. She thought that the obesity increased with 
 the increased quantity of sugar which she consumed. 
 The habit had become so confirmed at the time when we 
 saw her, that she conceived it to be quite impossible to 
 relinquish it/' 
 
 Vegetable jelly is obtained from various acid fruits, as 
 currants, gooseberries, raspberries, cherries, &c. by boiling 
 the recently expressed juice so as to dissipate the water. 
 It is sparingly soluble in cold, but abundantly dissolved 
 
VEGETABLE PRINCIPLES. 151 
 
 in hot water. As the solution cools, it again assumes a 
 gelatinous form. By protracted boiling it loses the pro- 
 perty of coagulating. It is supposed that vegetable jelly 
 is merely gum in combination with an acid. 
 
 Gum is a brittle, transparent, colourless, inodorous, and 
 tasteless substance. In its purest form it is known under 
 the name of gum arabic. It is soluble both in cold and 
 hot water ; its solution is called mucilage. Gum appears 
 to be the first transition that the sap of plants undergoes. 
 It is found in greater or less quantity in all young plants, 
 and exists in every part of vegetables : it is so abundant 
 in some that it exudes spontaneously, while from others 
 it is procured by incisions made in the bark. As obtained 
 from different plants, it varies in its properties : a variety 
 exudes from the cherry-tree, whence named cerasin, which 
 differs from gum arabic in many respects. When cold 
 water is added to it, it swells considerably, and is softened 
 but not dissolved. It is sparingly soluble in hot water. 
 Gum tragacanth is a variety of this. Between the very 
 soluble gum arabic and the nearly insoluble tragacanth 
 there are many shades of varieties procured from different 
 plants, as from the decoction of linseed, marshmallow, 
 onions, and other bulbous roots, fuci, lichens, and many 
 others. By the action of sulphuric acid on vegetable fibre, 
 gum is formed artificially. Starch, when heated till it be- 
 comes brown, is converted into a gummy matter used by 
 calico-printers under the name of British gum. Again, by 
 the action of alkalies, sugar is changed into a kind of gum. 
 The Arabs who collect the gum arabic in the forests of 
 Senegal, subsist upon it during the gum harvest, and 
 the subsequent journey across the desert. Hasselquist 
 mentions in his voyages, that a caravan of Abyssinians, 
 consisting of 1000 persons, must have been starved to 
 death, had it not been from their having a parcel of gum, 
 on which they subsisted for two months. 
 
 Fixed or fat oils, of which there is a great variety, are 
 viscid, nearly insipid, with little smell, and when pure, 
 
152 ADAPTATION OF FOOD TO CLIMATE. 
 
 semi-transparent. They are all lighter than water, and 
 insoluble in it. They consist of the same constituents as 
 animal fat, viz. of ela'ine and stearine. At the ordinary tem- 
 perature of the atmosphere, the greater number are liquid, 
 but solidify before they are reduced to the freezing point 
 of water. A few of them, as palm oil, the oil of nutmeg 
 and of cocoa nut, are solid at ordinary temperatures, when 
 they are called vegetable butters. Fixed oil is generally 
 obtained from the seeds of plants by compression, or 
 occasionally by boiling. Olive oil is extracted from the 
 fleshy part of the fruit of the olive. The roots and bark 
 of some vegetables afford fixed oil. As an article of diet, 
 fixed vegetable oil has been known from the earliest 
 periods of history, and is in extensive use at the pre- 
 sent day, being generally preferred in warm countries to 
 animal fats, which are more commonly employed by the 
 inhabitants of colder climates. 
 
 The five animal principles now mentioned, viz. fibrin, 
 gelatin, albumen, osmazome, and fat, with the seven vege- 
 table principles, gluten, vegetable albumen, starch, sugar, 
 vegetable jelly, gum, and fixed oil, comprise nutritive mat- 
 ter in all its shades and diversities, obtained from organized 
 nature. None of these principles are alone well calculated 
 for the proper sustenance of the more perfect animals. 
 For although life may be sustained for a considerable time 
 by the exclusive use of one, such instances are to be con- 
 sidered as exceptions to the general rule. It has been 
 found, by experiments both on man and the lower ani- 
 mals, that health declines when the food is restricted to 
 one article, such as sugar. Habit exerts a powerful influ- 
 ence in this respect. Climate likewise produces a con- 
 siderable effect. "When we extend our inquiries over the 
 globe, we shall find that the majority of the human race 
 subsist chiefly on vegetable food, and that principally 
 derived from gramineous seeds. Thus the millions of 
 China and Hindostan live almost exclusively on rice ; 
 wheat, barley, rye, and oats, furnish subsistence to another 
 
ADAPTATION OP FOOD TO CLIMATE. 153 
 
 large class of mankind ; maize supplies another ; while 
 others derive their aliment from roots and herbs. On 
 the other hand, the shepherds in the province of Caraccas, 
 in South America, live entirely on mutton ; some tribes 
 of Tartars on horse flesh ; the natives of Kamtschatka 
 scarcely on anything but fish ; and the Esquimaux devour 
 enormous quantities of raw blubber. 
 
 The inhabitants of warm climates generally prefer a 
 vegetable diet, not merely because nature furnishes a 
 great abundance and variety of this kind of food, but 
 from choice. Vegetables are productive of less heat and 
 irritation, and therefore much better adapted for aliment 
 in hot climates. Confinement to vegetable diet and 
 abstemiousness constitute, in such countries, an easy 
 virtue. " Religious sects," says Richerand, " by which 
 abstinence from animal food was considered a meritorious 
 act, were all instituted in warm climates. The school of 
 Pythagoras flourished in Greece ; and the anchorets who 
 in the beginning of the Christian religion peopled the 
 solitudes of Thebais, could not have endured such long 
 fastings, or supported themselves on dates and water, in a 
 more severe climate. Thus, the most austere were induced 
 to add to vegetables, which formed the base of their food, 
 eggs, butter, fish, and even water-fowl. In books of 
 casuistry it may be seen on what ridiculous grounds 
 there was granted a dispensation in favour of plovers, of 
 water-hens, wild-ducks, snipes, and scoters, birds whose 
 brown flesh, more animalized and more heating, ought to 
 have been proscribed from the kitchens of monasteries 
 much more strictly than that of common poultry." The 
 inhabitants of cold regions prefer animal food, not merely 
 from vegetables being scanty, ill adapted for nourish- 
 ment, or altogether wanting, but because they instinc- 
 tively make choice of animal diet, in order to enable 
 them to brave the rigours of the climate they inhabit. 
 
 Food is required not only to build up the growing 
 frame in childhood, or sustain the constant renewal of 
 
 H2 
 
154 FOOD. 
 
 parts in maturity, but also to compensate for the con- 
 stant expenditure which occurs from the functions which 
 are carried on, without intermission, in the living body. 
 It has been already observed, when treating of the regu- 
 lation of animal heat, that in hot climates there is a de- 
 termination of blood to the surface, and a large portion 
 of the thinner part discharged by sensible and insensible 
 perspiration, whereby the heat of the body is reduced. 
 In order to make up for this loss in the watery part of 
 the blood, fluids are craved, and fruits and vegetable diet 
 had recourse to. It has also been stated that animal 
 temperature is sustained by chemical changes which take 
 place in the constitution of the blood, especially in the 
 production of carbonic acid ; that the quantity of carbonic- 
 acid generated has a relation to the temperature of the 
 animal ; that a greater quantity is given off in winter 
 than summer ; and that vegetable diet produces less than 
 animal food. Blood derived from animal food being 
 better calculated to sustain the expenditure of heat, and 
 invigorate the system, is not only taken with impunity 
 in cold climates, but with the greatest advantage, in large 
 quantities, and sometimes even in an advanced state of 
 decomposition, which in a hot country would inevitably 
 produce fevers of the most malignant character. 
 
 It is not by the quantity or quality of the food taken 
 into the stomach, but by what is digested, that the body 
 is nourished. The digestibility of the aliment is therefore 
 of much importance. For, if it be not converted into pro- 
 per chyme and chyle, a crude mass remains, which is 
 often productive of serious consequences. The fault, in 
 such instances, may either be in the food or the state of 
 the stomach. 
 
 Highly concentrated aliment is not of easy digestion. 
 Thus the portable soup prepared for the voyagers of the 
 polar expeditions was not fit for nourishment till ade- 
 quately diluted, notwithstanding the energies of the 
 stomach were fully called into action by the rigour of the 
 
FOOD. 155 
 
 climate, and the laborious employments the adventurers 
 were engaged in. Is it to be wondered at that digestion 
 fails where the indolent inactive citizen loads his stomach 
 with rich gravies and concentrated soups, however the 
 flagging appetite may be spurred on by piquant sauces, 
 and all the arts of cookery. 
 
 It has been stated that single chemical principles are 
 not adequate for proper nourishment ; that when animals 
 are thus fed they become incapable of digesting a suffi- 
 cient quantity to support the wants of the system, and 
 that consequently health and strength rapidly decline. 
 A mixture or variety of food, whether vegetable or ani- 
 mal, becomes therefore requisite. In the same way occa- 
 sional variation of diet is beneficial. Both mixture and 
 change of food require, however, to be had recourse to 
 with discretion. At a feast where all sorts of aliment, in 
 every variety of preparation which the ingenuity, science, 
 and experience of the cook can supply, are introduced in- 
 to the stomach, it is impossible that such a complicated 
 mixture can be converted into sweet and healthy chyme, 
 however energetic the action of the digestive apparatus 
 may be. Much less can the proper conversion be effected 
 where the tone of the stomach has been impaired and its 
 vigour shaken. So also the sudden transition from one 
 kind of diet to another cannot be otherwise than preju- 
 dicial. 
 
 The consistency of aliments has a very considerable in* 
 fluence on their digestibility. Dry and hard food, such 
 as hung and salted meats, hard boiled eggs, &c. are di- 
 gested with difficulty. Soups and other liquid aliments 
 are also not easily acted on. A medium state of density 
 and coherence is favourable to the digestion of food. Nor 
 is it difficult to understand the reason of this. Dense 
 and hard matter resists the solvent power of the gastric 
 juice, and requires a long time before it is reduced to a 
 proper state of softness and liquidity, while soups elude 
 the grasp of the muscular action of the stomach, and are 
 
156 POOD. 
 
 not digested till the fluid part is drunk up, when the 
 more consistent residue is brought under the influence of 
 the digestive agents. 
 
 The texture and cohesion, and consequently the diges- 
 tibility of food, depends much upon the state in which it 
 is taken. The nature of the animal, its age, sex, and 
 condition, the manner of its death, and the length of time 
 the flesh has been kept, have an important influence ; and 
 the different processes of cookery produce great changes 
 in these respects, by the various forms of boiling, roasting, 
 broiling, frying, and baking. 
 
 Quantity also operates : unless a certain bulk be in- 
 troduced, the action of the stomach is not fully brought 
 into play. To a considerable extent this depends upon 
 habit. A curious instance of this was afforded by a 
 highland regiment. The men in their native hills had 
 been accustomed to fill their stomachs with a large quan- 
 tity of food, possessing comparatively slight nutritive 
 qualities, but which called forth the full exercise of their 
 stomachs, whereby they were adequately nourished. 
 Being transferred to one of the midland counties of 
 England, they had distributed to them beef and wheaten 
 bread, instead of oatmeal porridge and cabbage broth, 
 when they declared themselves to be starved under the 
 latter diet, though it was furnished to them in quantities 
 quite sufficient to satisfy the appetites of Englishmen. 
 
 The most judicious selection and careful preparation 
 of food are unavailing, if the stomach be not prepared to 
 perform its duty. Age, state of health, and custom, have 
 a powerful influence on the action of the stomach. Milk is 
 furnished by the hand of nature expressly for the diet of the 
 young of mammalia. Derived from such a source, we can 
 have no hesitation in acknowledging that it must be not 
 only the best, but also the only nourishment they can 
 properly digest. In adult age, however, milk is by no 
 means of easy digestion, unless custom has long habitu- 
 ated the stomach to it. Many substances are digested 
 
DRINK. 157 
 
 with facility in robust health, which the digestive powers 
 of the valetudinarian are totally unable to cope with ; 
 while in some diseased conditions, large quantities of 
 food are rapidly acted on, and substances chymified which 
 in ordinary health altogether resist the agency of the 
 stomach. No organs of the body so readily and so com- 
 pletely adapt themselves to varying circumstances as the 
 digesti ve apparatus. Notwithstanding this accommodating 
 facility, habit exerts a powerful effect. To the Greenlander 
 train oil affords a delicious repast ; while he neither re- 
 lishes, nor readily digests biscuit. Again, the Hindoo 
 easily disposes of his mea^of rice, while his stomach 
 would turn with loathing from food highly prized by the 
 Esquimaux or the Russian boor. 
 
 Drink. Food comprises all those substances which are 
 altered, reduced, and assimilated to the constitution of the 
 animal by the digestive organs, for the formation of the 
 more consistent materials of the system. Water, either in 
 combination or in mixture, enters into the formation of 
 every tissue of the body. As a constituent, it may be consi- 
 dered of the nature of food. So far as it is in mere mix- 
 ture, it is to be held as a simple diluent. The fluids of 
 the body being exposed to continual expenditure from the 
 tears, the saliva, the secretions poured into the alimentary 
 canal, from the vapour of the breath, the exhalations of 
 the skin, from the urinary and other secretions, the de- 
 mand for drink becomes even more urgent than for 
 food. That this is the case, we know from accounts fur- 
 nished, detailing the horrible sufferings not unfrequently 
 experienced by mariners, as well as from cases recorded 
 of persons who have voluntarily starved themselves to 
 death. Simple water is the only essential drink ; all other 
 fluids employed as drinks have, along with water, their 
 chief constituent, substances which may be classified into 
 two orders ; the one containing digestible matter, the other 
 incapable of affording nourishment, but which promote 
 the digestion of others, or correct deleterious qualities 
 
158 
 
 CONDIMENTS. 
 
 they may possess. To the former belong mucilaginous, 
 saccharine, and gelatinous fluids; the latter we shall con- 
 sider along with other condiments. 
 
 Condiments. In a state of health and vigour, simple 
 food and water are all that are required, without the ne- 
 cessity for substances to promote the process of digestion. 
 But where the energy of the organs is impaired, they 
 must be coaxed to perform their duty, or roused into ac- 
 tion by appropriate stimulants ; or the food may be of 
 such a nature as to require a corrective, in order to effect 
 its proper elaboration ; and lastly, the glutton may re- 
 quire stimulants for the purpose of exciting and spurring 
 up his overloaded organs of digestion, so that they may 
 in some way or other dispose of the burden he has im- 
 posed upon them. These substances, when introduced 
 into the stomach, are not acted upon ; they either tra- 
 verse the alimentary canal, and are subsequently ejected, 
 or they are taken up without change, and carried into 
 the general system, to be in the course of time removed. 
 Indeed, all substances introduced into the stomach may 
 be reduced to two kinds, the one comprising such ar- 
 ticles as are decomposed and digested, the other includ- 
 ing all such as resist the action of digestion. The latter 
 may either be inert or active. If they facilitate and pro- 
 mote digestion, or correct injurious qualities of food, they 
 are termed condiments. 
 
 Common salt is the only condiment obtained from the 
 inorganic kingdom. It is more universally employed for 
 this purpose than any other substance. Animals take it 
 greedily. In due quantity it conduces to their health, and 
 promotes their being brought into good condition. Wild 
 animals instinctively seek it with great avidity ; those of 
 the continents of Africa and America are known to tra- 
 verse immense tracts of country, overcome vast difficulties, 
 and undergo great fatigue, in order to procure it at the 
 sea-shore. In America there are salt springs, to which 
 great varieties of wild animals resort to obtain it. That 
 
CONDIMENTS. 159 
 
 these springs attracted animals now extinct, for the purpose 
 of licking salt, appears from the numerous remains of their 
 skeletons around them ; hence the name given to these 
 springs, Great Bone Licks. 
 
 The utility of salt is proved by a number of facts. An 
 ancient punishment existed in Holland, which consisted 
 in feeding the convicts upon unsalted bread and water 
 alone. The consequences are said to have been so hor- 
 rible that it was abandoned, the wretched criminals being 
 devoured by worms generated in their own bodies. When 
 the heavy excise duty was imposed on salt, the poor in 
 Ireland, not being able to procure it as a condiment for 
 their miserable fare, an epidemic fever appeared among 
 them, for which common salt was accidentally discovered 
 to act as a certain specific ; it was therefore inferred that 
 the disease arose from deficiency of it in their provisions. 
 Why salt should be so necessary appears to be accounted 
 for by the observations of Dr Prout, who has shewn that 
 chlorine, one of the constituents of salt, and a powerful 
 and energetic elementary principle, is essential to the con- 
 stitution of healthy gastric juice. Soda, another of its 
 constituents, found abundantly in the blood and the va- 
 rious secretions, is derived in all probability from the same 
 source. 
 
 Vinous or alcoholic fluids have, from the remotest ages, 
 been used by man in every stage of civilization, with very 
 few exceptions. Their stimulating effects depend on al- 
 cohol, though their action is modified by various substances 
 they may have in combination, as well as by the quantity 
 of alcohol they may contain. Pure alcohol is a limpid 
 colourless fluid, with an agreeable smell and strong pene- 
 trating flavour. It operates upon the animal body in 
 three different ways \flrst, by exciting the part with which 
 it comes immediately in contact ; secondly, by its influence 
 being transmitted along the nerves ; and lastly, by its be- 
 ing absorbed and carried along with the circulating fluids, 
 as is shewn by its appearing in the breath soon after being 
 swallowed. 
 
160 CONDIMENTS. 
 
 Wines, beer, and other fermented liquors, and the 
 various distilled spirits, are distinguished from each other 
 by substances which they contain, and to which they owe 
 their specific properties. Some of them hold nutrient 
 matter in solution, such as sugar, gluten, and starch ; or 
 they may have in combination acids, bitter and astringent 
 principles, and volatile oils, by which their properties are 
 modified and determined. 
 
 A healthy stomach certainly requires no prompting, 
 there being no necessity for the use of what Dr Kitchener 
 has called peptic persuaders. The peasantry of Scotland, 
 than whom more robust, vigorous, and active rustics, both 
 in mind and body, do not exist on the face of the globe, 
 employ habitually no other condiment than salt. In fact, 
 every thing else is not only superfluous, but directly inju- 
 rious. In an artificial state of society, however, it is dif- 
 ferent. Sedentary employment, protracted and harass- 
 ing mental or corporeal labour without healthy exercise, 
 impair the tone of the digestive organs. The moderate 
 and judicious use of vinous liquors is in such cases de- 
 cidedly beneficial, by enabling the organs to perform their 
 duty. When taken so as to produce intoxication, they are 
 poisons; where they are employed to urge the digestion of 
 more food than the body requires, they are prejudicial; and 
 they prove injurious to some constitutions in every quantity 
 and in every form. The condiments derived from the 
 vegetable kingdom are very various ; they may be classi- 
 fied as acid, bitter, astringent, and aromatic volatile prin- 
 ciples. 
 
 The acids used as condiments are acetic acid, or vine- 
 gar, citric acid from lemons, and the malic acid from 
 apples. They aid the digestion of crude vegetable food, 
 and rich and oily animal substances are more easily di- 
 gested by being taken along with these acids. Thus we 
 employ apple sauce with pork and goose, lemon with 
 wild fowl, and vinegar with salmon. Though vinegar 
 occasionally promotes digestion, in excess it destroys the 
 tone of the stomach. Young ladies anxious to be fashion. 
 
CONDIMENTS. 161 
 
 ably pale, and afraid of becoming too stout and robust, 
 have frequently taken vinegar in such quantities as to in- 
 duce even fatal consequences. 
 
 Vegetable bitters support the tone of the digestive 
 organs. The infusion of bitter herbs in wine was a very 
 common practice with the ancients. The wholesome 
 quality of malt liquors is in a great degree owing to the 
 bitters employed in their preparation. It has been as- 
 certained that cattle thrive better on pastures where there 
 is a due proportion of bitter herbs. Indeed nature 
 furnishes in the bile a bitter, which from this quality is 
 conducive to the process of digestion. 
 
 Astringent substances prove beneficial, where, from con- 
 curring causes, such as a warm and moist climate, or the 
 nature of the food, the organs of digestion become unu- 
 sually relaxed. Hence the natives of India and other 
 warm climates are in the habit of chewing astringent 
 vegetable substances, such as the betel leaves, whereby 
 the debilitating and relaxing tendency of the climate and 
 food is obviated. 
 
 The aromatic spices and pungent stimulants employ- 
 ed for the purpose of rousing the action of the stomach 
 and bowels, are exceedingly numerous. The different 
 peppers, cloves, nutmeg, ginger, &c. ; the onion tribe, 
 horse-radish, mustard, mint, sage, &c. ; to which may be 
 added tea and coffee. Some of these, as onions and nut- 
 meg, have the stimulating principle associated with nutri- 
 tious matter, but they are chiefly useful in promoting diges- 
 tion by the excitement which they produce. In hot coun- 
 tries they are required to rouse the nagging appetite, or 
 enable the stomach to digest vegetable diet, which with- 
 out their aid it might not be fully able to accomplish. 
 In a healthy and vigorous stomach, and with easily di- 
 gested food, they are worse than useless, by hurrying the 
 process of digestion, and exhausting the tone and excit- 
 ability of the stomach. 
 
 Hunger and thirst are sensations which are excited in 
 
162 HUNGER AND THIRST. 
 
 animals to warn them when it becomes necessary to take 
 into the system food and drink. The purpose which 
 they serve is consequently sufficiently obvious. Every 
 one must have personal knowledge as to the feelings 
 which characterize hunger and thirst, and from experi- 
 ence possess a more just idea of their nature than words 
 can convey. Numerous conjectures have been hazarded 
 in order to account for the physical cause of these sensa- 
 tions. 
 
 Hunger has been attributed to certain mechanical 
 conditions of the empty stomach, as to the friction of the 
 internal folds upon each other, to the pressure of the 
 neighbouring viscera, and to the congestion of blood in 
 its vessels. The form of the stomach is however such 
 that the surfaces cannot rub against each other ; and when 
 called into action by the introduction of solid food, were 
 friction the cause, instead of being subdued, it ought to 
 be increased, from the surfaces rubbing against the con- 
 tents, and from the increased muscular action called 
 forth. Pressure, too, instead of increasing the sensation, 
 allays it. For this purpose the wandering Tartar, when 
 pressed by hunger, places a board over the region of the 
 stomach, and secures it with a belt, which he tightens 
 when necessary, whereby the cravings are diminished. 
 Animals, and even man, when urged by hunger, occa- 
 sionally swallow substances which are wholly indigestible, 
 for the purpose of appeasing the appetite. 
 
 Further, the empty stomach, instead of having a larger 
 quantity of blood in its vessels, has less than when dis- 
 tended with food, and when exerting its full energy 
 during digestion. 
 
 Again, it has been attempted to account for hun- 
 ger by ascribing it to the action of the gastric juice 
 upon the internal surface ; but it has been ascertained 
 that gastric juice is not secreted, excepting during 
 the process of digestion ; and even if it were, it has 
 no power over living matter. Thus, worms are often 
 
HUNGER AND THIRST. 163 
 
 found in the stomachs of man and animals, without being 
 acted upon by the juices; whereas, when deprived of 
 life, they would be digested in an hour or two. 
 
 Lastly, hunger and thirst have been ascribed to the 
 condition of the nerves. That the nerves are the channels 
 by which these sensations are transmitted to the seat of per- 
 ception, is true ; and therefore if the nerve proceeding from 
 the brain to the stomach be cut, or tied, so as to interrupt 
 the communication between them, there remains no means 
 by which the conditions giving origin to these sensations 
 can be announced. In a dog, which had been starved so 
 as to render it ravenously hungry, the nerves proceeding 
 to the stomach were cut; instantly the dog displayed 
 perfect indifference to food ; and when presented with it, 
 continued to eat till the stomach was enormously dis- 
 tended. The stomach having been paralyzed, neither the 
 necessity for food, iu the first place, nor when a sufficiency 
 had been taken, in the second place, could be announced. 
 
 The condition of the mind also affects these sensations. 
 Let a person ready to partake of a favourite meal with the 
 keenest appetite, the result of fasting and exercise, be sud- 
 denly informed of some calamity that has occurred, in which 
 he is deeply interested, and in a moment all feeling of hun- 
 ger vanishes. Increased thirst, on the other hand, is a fre- 
 quent consequence of impressions made on the mind, 
 operating on the body. Diseases, and several medicinal 
 substances, such as narcotics, destroy the appetite ; and 
 therefore the sensation of hunger is not experienced ; 
 while, on the other hand, that of thirst is generally much 
 increased. This affords one of the examples so abun- 
 dantly furnished by the animal body, of adaptation to 
 circumstances. In such a disease as fever, the digestive 
 organs are not adequate to their duty. If food be intro- 
 duced, it cannot be acted on in a proper manner, but 
 is hurried into decomposition, and produces a corrupted 
 mass, which tends to keep up and aggravate the disease. 
 From fluids being taken up immediately, without the ne- 
 
164 ACTION OF THE STOMACH. 
 
 cessity of undergoing change by the action of the stomach, 
 they are craved and are taken not only with impunity 
 but with advantage, in order to preserve the blood suffi- 
 ciently diluted, and supply the loss sustained by the se- 
 cretions. The aversion to food therefore, and the loath- 
 ing which its very appearance excites, while there is an 
 increased desire for drinks, are wise and beneficent provi- 
 sions. 
 
 On the whole, the explanations as to the proxi- 
 mate cause of hunger and thirst which have been sug- 
 gested, are by no means satisfactory. They evidently 
 belong to that class of impressions imposed on organized 
 bodies by the Creator, which conduce to important and 
 useful purposes. 
 
 The fibres of the muscular coat of the stomach are ar- 
 ranged in longitudinal, transverse, and oblique directions, 
 whereby the contents are completely embraced. The 
 blood-vessels are large and numerous, and are so dis- 
 tributed as to admit of great variations in the quantity of 
 blood they transmit. Besides being supplied with nerves 
 from the same source with the other portions of the ele- 
 mentary canal, the stomach receives two nerves, by 
 which it is brought into more immediate connexion with 
 the brain. 
 
 We have already considered the changes the food is 
 subjected to previous to its introduction into the stomach, 
 and therefore have now to examine the effects produced 
 by the agency of this organ. These effects result from the 
 temperature to which the mass is exposed, the motion to 
 which it is subjected, and the changes produced upon it 
 by the gastric juice, whereby it is converted into a pecu- 
 liar substance, termed chyme. Chymification, which is 
 the result of the changes the food undergoes, is only one 
 step, though an important one, in the process of digestion. 
 The popular notion that digestion begins, and that it is 
 completed in the stomach, is far from being correct : the 
 process as a whole commences on its first introduction 
 
GASTRIC JUICE. 
 
 165 
 
 into the mouth, and is not perfected till the new matter 
 is converted into arterial blood in the lungs. Chyme is 
 a soft pulp, of an acid quality, which is owing to the 
 presence of free muriatic acid, generally of a grey or ash 
 colour, somewhat sweet, though frequently insipid, and 
 without any peculiar smell. Its properties, however, 
 vary according to the nature of the food from which it 
 has been derived. 
 
 Digestion in the stomach has been ascribed to tritura- 
 tion, to a concoction analogous to cooking meat by stewing, 
 to fermentation, and to solution. It is very true that the 
 food does undergo changes which are somewhat like these 
 mechanical and chemical processes, but by no means iden- 
 tical with them. On the introduction of a meal into the 
 stomach, its presence calls forth the action of that organ, 
 an increased determination of blood takes place towards it, 
 the gastric fluids are poured in more abundantly, and the 
 muscular action is roused. 
 
 The length of time required for chymification varies 
 much according to the state of the individual, and the 
 nature of the food. About four hours is considered the aver- 
 age time required for digesting a full meal. The food is 
 exposed in the stomach to the action of a secretion which 
 has been ascertained to be furnished only during the pro- 
 cess of digestion, to which the term gastric juice is espe- 
 cially restricted. This liquor is not the product of glan- 
 dular organs, but is poured out immediately from the 
 blood-vessels. The gastric juice, according to the dis- 
 covery of Dr. Prout, confirmed by others, contains a por- 
 tion of the elementary body chlorine, so termed from its 
 greenish-yellow colour. Chlorine is a gaseous substance 
 of energetic action, having a considerable affinity for 
 water ; with hydrogen it forms muriatic acid, or the spirit 
 of salt : hence the source of the muriatic acid found in 
 the gastric juice, and hence, too, the acidity of healthy 
 chyme. Excepting from the existence of chlorine, the 
 gastric juice would not appear to differ much from the 
 
166 GASTRIC JUICE. 
 
 saliva. But when we examine its properties, and the 
 results of its action, we must acknowledge it to be by no 
 means an inert substance. When it is recollected that " a 
 little leaven leaveneth the whole mass," we may easily 
 conceive how the gastric juice may be the cause of com- 
 mencing important changes in the food. 
 
 Its power of coagulating milk and albuminous sub- 
 stances is another of its striking properties ; and so effi- 
 cient is it in this way, that it has been ascertained that 
 six or seven grains of the rennet of a calf, dissolved in 
 water, will coagulate upwards of a hundred ounces of 
 milk ; and afterwards, by its solvent power, it again dis- 
 solves the coagulum, which peculiarly distinguishes it 
 from other substances possessing the property of produc- 
 ing coagulation. 
 
 Digestion was at one time compared to putrefaction, 
 but by the term putrefaction must have been understood 
 something very different from what it implies now, for 
 the gastric juice is not only a powerful antiseptic, but 
 even renders substances sweet which have partly under- 
 gone this kind of decomposition. Spallanzani found that 
 the gastric juice of a dog will preserve veal and mutton 
 perfectly sweet, and without loss of weight, thirty-seven 
 days in winter, whilst the same meats immersed in water 
 emit a foetid smell as early as the seventh day, and by 
 the thirtieth are resolved into a state of offensive putri- 
 dity. It has been ascertained that the most offensive 
 meats that dogs can be induced to swallow, are in a short 
 time rendered perfectly, free from putridity. Among 
 mankind meats are often kept till they become highly 
 offensive to the sense of smell, in order to render them 
 tender, mellow, and of easier digestion. Various kinds 
 of game and venison, for example, are often presented at 
 table in a condition which nothing but fashion and cus- 
 tom could tolerate, and yet almost instantly the putrid 
 mass is sweetened by the contact of the gastric juice. 
 
 Various fluids possess different solvent powers. Thus, 
 
GASTRIC JUICE. 167 
 
 water dissolves gum, but not resin, while alcohol will dis- 
 solve the latter, but not the former. In like manner, the 
 gastric juice possesses proper solvent power over sub- 
 stances, independently of their texture and density. It 
 exerts no action on living matter, and therefore worms 
 exist in different parts throughout the whole extent of 
 the alimentary canal, and seeds traverse it, without 
 having the germinating property injured, but rather 
 quickened, as occurs with corn when taken into the 
 stomach of the horse without having been bruised and 
 killed previous to introduction : it springs up rapidly on 
 the dunghill. In the same way the seeds of many plants 
 pass through the bowels of frugivorous animals, with ad- 
 vantage to their subsequent germination. In a similar 
 manner it has been conjectured that the eggs of fish may 
 be transported by birds, whereby new made ponds be- 
 come stocked with them. If gastric juice be present in 
 the stomach when death takes place, it then acts upon 
 the coats, so that the stomach is digested by the liquor 
 furnished by itself. This takes place when an animal is 
 killed after a meal, while the process of digestion is going 
 on. It has frequently been observed in criminals, where 
 they have taken food immediately previous to execution, 
 and has been noticed where sudden death has occurred 
 from accident during digestion. In the great majority of 
 cases, death takes place when the stomach is free from 
 gastric juice, as in natural death, where the function of 
 digestion is abolished sometime before decease. 
 
 The above coagulating, antiseptic, and special solvent 
 powers peculiarly distinguish the gastric juice ; but be- 
 sides, it is found to vary, not only in different animals, 
 but in different individuals, and in the same individual 
 at different times, under various conditions of health and 
 other circumstances. The gastric juice of a carnivorous 
 animal readily acts on flesh, but produces little or no 
 impression upon vegetable matter ; while in herbivorous 
 and granivorous animals, it dissolves the latter, but re- 
 
1 68 CHYME. 
 
 fuses to act on the former. In a suckling, milk is imme- 
 diately coagulated, and speedily re-dissolved, which does 
 not occur readily in the adult. In the same way are to 
 be accounted for variations depending on the habit and 
 custom, the peculiar constitution and state of health of 
 individuals. 
 
 From the gentle undulatory motion produced by the 
 muscular coat, the mass of food is kept in motion. It is, 
 however, not of that violent kind which has been com- 
 pared to churning, for by such agitation a portion would 
 be brought in contact with the surface of the stomach for 
 an instant, and again removed. Neither is the food dis- 
 posed in the stomach in an indiscriminate mass, nor in the 
 order in which it may have been swallowed. On opening 
 the stomach of one w r ho has died from repletion after a 
 gluttonous feast, the soups, the fish, the various stews 
 and roasts, with the puddings, tarts, and other articles in- 
 numerable, are not found layer upon layer as they were 
 devoured. The most easily digested occupies the surface, 
 in immediate contact with the inner coat of the stomach, 
 and thus becomes bedewed with the gastric juice, and 
 converted into chyme. The more intractable part is 
 placed in the centre, and thus is longest exposed to pre- 
 paratory influences, so that when presented at last, it 
 yields to the action of the solvent liquor, and, in its turn, 
 is chymified. Digestion, therefore, does not take place si- 
 multaneously throughout the whole mass, but is only 
 perfected in that which is in immediate contact with the 
 stomach. If fresh food be introduced into the stomach 
 before the previous meal has been digested, it becomes 
 coated over with that which has been for sometime lodged, 
 so that the recent portion is placed in the centre, like the 
 least digestible parts of a single meal. 
 
 It is by the action of the muscular coat that the food 
 is disposed in regular order, and brought in succession 
 under the power of the gastric juice. By the same mus- 
 cular action the chyme is carried onwards to the pylorus. 
 
CHANGES IN THE INTESTINES. lOy 
 
 where, if found properly elaborated, it is permitted to 
 enter the intestine ; if not, the pylorus is irritated, con- 
 tracts, and shuts the passage into the bowels. Muscular 
 action at the sametime is called into play, so as to throw 
 the food back again by what is termed antiperistaltic mo- 
 tion ; and this may occur again and again, till the valve 
 of the pylorus is satisfied. The irritation of the pylorus 
 may be so great, the call on the muscular coat so urgent, 
 and the sympathies brought into action so extensive and 
 violent, that the offensive matter is ejected altogether 
 from the body by vomiting. Here we have a beautiful 
 and striking instance of design for the most important 
 ends, which nothing but supreme knowledge and power 
 could have foreseen and provided for. By the peculiar 
 tact and sensibility with which the pylorus has been en- 
 dowed, it is enabled to judge when the matter is fitted 
 for entrance into the intestine, preparatory to its intro- 
 duction into the general system. It acts as a watchful 
 guardian ; and if not satisfied, rejects the matter pre- 
 sented to it, and causes it to be thrown back, that it may 
 be properly prepared ; or if it be of a highly offensive 
 nature, calls forth powers by which it is entirely ejected. 
 Insoluble and inert substances it however suffers to pass 
 the barrier. Thus the seeds of plants, metallic and other 
 indigestible matters, are permitted to enter, to be subse- 
 quently thrown out. Even by frequent application, it 
 at last yields to other substances, such as medicines, &c. 
 which are thus allowed to get into the bowels. 
 
 The following, then, are the occurrences which take 
 place in the stomach : Aided by the temperature, the 
 gastric juice dissolves the food, that which is most easily 
 affected being first acted on. The pulpy chyme, of the 
 consistence of thin gruel, is then, by the muscular coat, 
 carried and presented to the pyloric orifice, through 
 which it passes into the intestine, where it is subjected 
 to further change. 
 
 The first portion of the intestinal canal, as has been 
 
 I 
 
170 CHANGES IN THE INTESTINES. 
 
 already mentioned, is termed duodenum, beyond which 
 the smaller intestine is divided by anatomists into two 
 portions, the first named jejunum, the second ilium an 
 unnecessary division so far as their structure and func- 
 tions are concerned, for in these respects there is no dis- 
 tinction between them. From the pylorus of the stomach 
 onward to the ccecum, which forms the commencement 
 of the great gut, the canal becomes gradually contracted ; 
 the lining membrane, or internal mucous coat, is folded into 
 transverse plaits, which are larger and much more nume- 
 rous in the upper than in the lower portion. It presents 
 a villous or shaggy surface, like the nap of velvet, formed by 
 the termination and commencement of blood-vessels ; and 
 over its whole extent there are numerous glandular crypts, 
 either scattered singly or disposed in groups, which pour 
 out sufficient mucus to preserve the surfaces smooth and 
 slippery. There is also a fluid exhaled immediately from 
 the arteries, named intestinal juice, which, so far as has 
 been examined, appears to possess properties similar to 
 the gastric secretion. 
 
 The duodenum is the most capacious portion of the 
 smaller intestine. In proportion to its length, the mucous 
 folds are numerous and large. It is only covered by the 
 peritoneum anteriorly, and connected to the vertebral 
 column behind by loose cellular membrane. It is ex- 
 ceedingly dilatable. 
 
 The chyme does not flow into the duodenum in a con- 
 tinuous stream, but at intervals, being introduced by the 
 slow undulatory motions of the stomach, and carried on- 
 wards by similar motions in the duodenum. These move- 
 ments do not uniformly take place in the same direction, 
 but slight retrograde motions also occur, so that the same 
 portion of pulp is repeatedly presented to the same sur- 
 face, which is thus gently rubbed over it. 
 
 It has been already mentioned, that the duct from the 
 liver conveying the bile, and the duct of the pancreas, 
 terminate in the duodenum. The presence of the chyme 
 
CHANGES IN THE INTESTINES. 
 
 induces a flow of these secretions, just as sapid substances 
 in the mouth cause the saliva to be copiously poured out, 
 At the same time, the secretion from the surface of the 
 duodenum itself exudes more abundantly. The chyme, 
 therefore, comes in contact with three different fluids. 
 The alkaline bile neutralizes the acid chyme ; it also ap- 
 pears to combine with the more oily portion of the chyme. 
 The pancreatic fluid, as far as it has been examined, 
 abounds in an albuminous fluid, which is supposed to be 
 of essential importance in animalizing the chyme derived 
 from vegetable food in particular. The part performed 
 by the intestinal juice in the changes which take place in 
 the chyme in the duodenum, has not been ascertained ; 
 but the important results effected through the action of 
 the gastric juice prepare us to admit, that most probably 
 they are neither small nor unimportant. 
 
 The result of the changes effected in the duodenum is 
 the evolution of two products, the chyle and the re- 
 crementitious part. The chyle is a coloured fluid hav- 
 ing a considerable resemblance to cream; it has a 
 sweet and somewhat saline taste, and begins to shew an 
 analogy to perfect blood. Like blood, it separates into 
 a coagulum or clot, and a colourless serum. It differs 
 from blood in the albuminous matter being as yet im- 
 perfect, in the presence of oil or fatty substance, and in 
 the absence of fibrin and proper colouring matter. The 
 chyle is taken up by the absorbents, which commence on 
 the surface of the intestine : from conveying this milk-like 
 fluid, they are termed the lacteal absorbents. The lacteals 
 are more numerous in the duodenum and upper portion of 
 the smaller intestine, and become fewer at the lower part 
 of the gut, in accordance with the less extensive surface 
 from which they arise, and the diminution of the nutri- 
 tious fluid which they have to take up. Before the 
 contents of the bowels reach the coscum, the whole 
 of the chyle has disappeared, none being ever seen be- 
 yond the small intestines, excepting where the matter 
 
172 CHANGES IN THE INTESTINES. 
 
 has been preternaturally hurried through, either from 
 the exhibition of medicine, or from diseased condition of 
 the canal. 
 
 The bile attaches itself more especially to the recre- 
 mentitious portion, and gradually becomes mixed up 
 with it, imparting its colour and bitter taste. The bile, 
 besides being subservient to the changes which occur in 
 the duodenum, serves as a stimulus to the bowels, exciting 
 the peristaltic movements, and promoting the progress of 
 the contents. Where an excessive secretion of bile takes 
 place, a purgative effect results ; whilst its deficiency or 
 obstruction is followed by a torpid and constipated state 
 of the bowels. 
 
 When the recrementitious matter reaches the ccecum 
 it meets with new secretions, and is subjected to farther 
 changes. The caput coecum, the blind or shut head of 
 the great gut, is fixed down in its situation. The small 
 intestine which terminates here protrudes in such a 
 manner as to form a valve, named the iliac valve, by 
 which, in the perfect state, any return of matter is effec- 
 tually prevented. Attached to the coecum there is a 
 small vermicular appendage, which is abundantly sup- 
 plied with secretions. It has been ascertained that here 
 the residual matter again becomes acid ; besides, a peculiar 
 volatile principle is poured out, which imparts the cha- 
 racteristic odour to the contents of the great gut. It is 
 in the coecum that the last effort of digestion takes place, 
 and the first step of fecation commences. It has been 
 stated, that in several herbivorous animals the coecum 
 and colon are more capacious than the whole of the rest 
 of the alimentary canal. Whatever matter remains ca- 
 pable of furnishing nourishment after traversing the upper 
 portions, and being mingled and acted upon by the dif- 
 ferent secretions, is now subjected to the action of these 
 parts, and the secretions which are poured into them ; a 
 second chymification occurs, and a separation is effected be- 
 tween what may be taken up with advantage to the sys- 
 
ENTRANCE OF THE CHYLE. 173 
 
 tern, and that which is excrementitious, to be subse- 
 quently discharged, along with the excretions of the ali- 
 mentary canal. 
 
 The matter poured into the coscum is of a soft pulta- 
 ceous consistence. The colon is so contracted by three 
 longitudinal musculo-membranous bands, as to form cells. 
 In these cells the contents are lodged till the more fluid 
 and nutritious parts are absorbed, and the consistent ex- 
 crementitious matter alone remains. By the action of 
 the muscular coat, powerfully aided by the longitudinal 
 bands, the consistent residue is pushed onward, and 
 finally discharged by the rectum. 
 
 The chyle being absorbed by the lacteals, is conveyed 
 by them through a series of small lenticular-shaped bodies, 
 varying in size from a pin's head to that of half a cherry. 
 These bodies are termed the mesenteric glands. They 
 differ from the glands which separate from the blood 
 peculiar fluids, by having no excretory ducts. They are 
 abundantly supplied with blood-vessels, which are curi- 
 ously convoluted and interlaced with each other, so as to 
 admit of considerable congestion. As the lacteals ap- 
 proach one of these glands, they divide into numerous 
 branches, which enter it, and are there interwoven with 
 each other, and with the blood-vessels. Again, a num- 
 ber of small vessels proceed from the opposite margin, 
 unite to form larger, and convey the chyle out of the 
 gland ; and this may be repeated through three or four 
 of these glandular bodies, till at last the chyle brought 
 by these various intricate channels is poured into one 
 common tube, the commencement of which is swelled out 
 into what is termed the receptacle of the chyle. This re- 
 ceptacle lies in the front, and somewhat to the right of 
 the aorta, at the upper part of the cavity of the abdomen. 
 Becoming contracted into a cylindrical tube, named thora- 
 cic duct, it enters the chest, proceeds upwards, and crosses 
 to the left side, where it pours its contents into the stream 
 of venous blood proceeding to the heart, where the inter- 
 
174 
 
 ENTRANCE OF TIIE CHYLE. 
 
 nal jugular vein from the head and main vein of the arm 
 meet under the collar bone, to form the left branch of the 
 descending cava. 
 
 i f 
 
 FIG. 14. 
 
 In the engraving a represents a portion of intestine ; 
 &, the mesentery ; c, a lacteal arising from the intestine ; 
 d y mesenteric glands ; 0, a lacteal, after having passed 
 through two glands ; /, thoracic duct ; g, the receptacle 
 of the chyle ; /*, lymphatic absorbents, proceeding up- 
 wards to pour their contents also into the receptacle ; , 
 the aorta. 
 
 The chyle in the receptacle and thoracic duct is found 
 to approach still more closely to perfect blood than when 
 first taken up by the lacteals. The albumen is more 
 complete, fibrin appears, and small coloured globules of a 
 light pink colour are seen in it. These changes have 
 been effected in its transmission through the glands, and 
 from the slow progress through them, in consequence of 
 
ENTRANCE OF THE CHYLE. 
 
 the intricacy of the vascular distribution, there is time 
 afforded for its more complete elaboration, and for ad- 
 mixture with fluids from the blood-vessels. All the 
 lacteals do not however terminate in the receptacle and 
 thoracic duct ; some of them join branches of the vena 
 portae, either in the glands, or after having passed through 
 them, whereby they are carried to the liver. 
 
 "When the chyle mixes with the red blood, we soon 
 lose all trace of it. It has been noticed as far as the 
 right auricle of the heart, but the agitation to which it 
 is exposed along with the blood in the right side of the 
 heart, produces more complete intermixture. And lastly, 
 on being transmitted to the lungs, it undergoes its final 
 completion : by the exhalation of superfluous water, the 
 discharge of carbonic acid, and the attraction of what is 
 necessary from the atmosphere, it now becomes perfectly 
 arterialized blood. 
 
 When we take a general view of the function of diges- 
 tion, we find that it consists of a number of distinct acts, 
 each of which are necessary to the perfection of the pro- 
 cess, and failing any one of them, the necessary change 
 on the aliment is incomplete. We have seen, from 
 the first introduction of food into the mouth till the pro- 
 cess is perfected, that various secretions immediately pour- 
 ed out from the blood-vessels are added to the new matter, 
 so as to form a mixture between new and as yet crude 
 materials, and fluids assimilated to the constitution of 
 the individual, indeed forming a part of his body. We 
 have seen that at each stage there results from the 
 union a third matter, which product is not a mere solu- 
 tion in the fluid, as where salt is dissolved in water, nor 
 a mere mixture where the constituents may be again sepa- 
 rated, and presented in their original form, but a new for- 
 mation, modified, it is true, by the nature of the food, 
 and the character and condition of the secretions which 
 are added. 
 
 Of these processes the first that came under our notice 
 
176 ENTRANCE OF DRINKS, ETC. 
 
 were the changes effected in the mouth, consisting of assi- 
 milation of temperature, trituration, and insalivation. 
 The second occurred in the stomach, where the food re- 
 mains for a sufficient time, in order to undergo the process 
 of chymification. The third took place in the duodenum, 
 where chyle is elicited. In the fourth the chyle is 
 taken up by the lacteals, transmitted through the mesen- 
 teric glands, and conveyed into the thoracic duct, where 
 it presents characters similar to those of the blood. In 
 the fifth and last stage, it is mixed with the red blood, 
 and along with it sent by the right heart to the lungs, 
 where it is perfected into arterial blood. 
 
 In all these processes, vital agents are called into action, 
 the effect of which is the production of a vital fluid 
 adapted to the various purposes for which it is required 
 in the system. But even in our artificial processes many 
 striking alterations are effected, and remarkable products 
 obtained : for instance, in the successive changes which 
 occur in the conversion of the mild nutritious starch into 
 the pungent stimulating ether. Here we find, in the 
 first place, on the addition of a little ferment, with expo- 
 sure to a proper temperature, air, and moisture, that the 
 starch is changed into sugar ; secondly, by further ma- 
 nagement and regulation of heat, the sugar is converted 
 into alcohol ; and lastly, by adding an acid, aided by 
 heat, the alcohol in its turn is formed into ether. 
 
 Hitherto we have followed those materials which are 
 actually digested, and so altered that their original pro- 
 perties entirely disappear, to be replaced by new qualities 
 and characters of the product. But drinks, with several 
 substances taken along with the food, as well as medi- 
 cinal agents, gain entrance into the system without suf- 
 fering decomposition, and without having their physical 
 properties affected. We now proceed to consider by 
 what channels these are introduced. 
 
 Drinks, from being taken more rapidly than solid food, 
 and immediately transmitted to the stomach, have their 
 
ENTRANCE OF DRINKS, ETC. 177 
 
 temperature assimilated chiefly in that organ. Cold 
 fluids may therefore be the means of reducing the in- 
 ternal temperature, whilst hot drinks impart heat to the 
 body. Water being absolutely necessary to preserve the 
 blood in a proper state of dilution, in consequence of the 
 incessant loss it is exposed to from transpiration, in- 
 ternal exhalation, and secretion, it is consequently ur- 
 gently demanded, and we are informed when it becomes 
 necessary to introduce it by the sensation of thirst. Soon 
 after reaching the stomach it gradually disappears, even 
 when prevented from passing into the intestine by secur- 
 ing the pylorus with a ligature. 
 
 Although the absorbents arising from the stomach and 
 intestinal canal are exceedingly numerous, it is now as- 
 certained that they do not form the only channels by which 
 nutritious matters enter the system, nor do all the absor- 
 bents from these parts terminate in the thoracic duct, 
 several of them pouring their contents into the branches 
 of the vena portse. The veins collecting the blood from 
 the alimentary passages, not only return the blood con- 
 veyed to these parts by the arteries, but also perform the 
 office of absorbents, and carry off especially such sub- 
 stances as are not altered by the powers of digestion, and 
 converted into chyle. The lacteal absorbents appear to 
 be endowed with the power of selection, taking up chyle, 
 but refusing to receive other matters ; whilst the veins are 
 less particular as to the nature or qualities of the ma- 
 terials they drink up. There are accordingly two sets 
 of agents employed in receiving and conveying sub- 
 stances from the alimentary canal. First, the absorbents, 
 which either transmit their contents through the mesen- 
 teric fluids into the receptacle of the chyle and thoracic 
 duct, or join veins without entering glands, or while they 
 are distributed through the glands, and lastly after they 
 have again emerged from them. The branches of the 
 vena portae of the abdomen constitute the other set by 
 which absorption is performed. As has been stated in the 
 
 i 2 
 
178 ENTRANCE OP DRINKS, ETC.* 
 
 chapter on circulation, these veins unite and form one 
 trunk, which proceeds to the liver, where it divides and 
 transmits its blood through that viscus, after the manner 
 of an artery, that is from trunks to branches. 
 
 Drinks not being subject to alteration, either before or 
 subsequently to their absorption, are immediately intro- 
 duced into the sanguiferous system. If they contain 
 nutritious matter, it remains in the stomach while the 
 fluid part is removed, in order that it may be digested ; 
 so that, as has been already stated, soups and other nu- 
 tritious liquids have their fluid parts removed before they 
 are acted upon. In the same way the drinks we take 
 along with our meals are carried off before digestion is 
 commenced, or at least before it is completed. 
 
 The body is not constituted so as to admit with perfect 
 impunity sudden or instant change, but if time be af- 
 forded it possesses admirable powers of adaptation, so as to 
 suit varying circumstances. A comparatively small quan- 
 tity of blood taken from a large orifice in a blood-vessel 
 may produce fainting, whilst a large portion may be 
 withdrawn without such effect, if the blood-vessels have 
 time to accommodate themselves to the diminished quan- 
 tity in the system. Many causes tend to subvert the 
 balance between the blood of the internal cavities and 
 that of the external surface and extremities. Cold im- 
 pels the blood to the internal parts, while it astringes 
 the vessels of the surface. Heat, on the other hand, pro- 
 duces a relaxation of the integuments, and promotes the 
 flow of the blood from the deep-seated organs. Disease 
 affords numerous examples of subversion of balance, 
 where local congestion takes place in some parts, and de- 
 ficiency in others. Ague affords a striking instance of 
 this : in the cold stage the blood leaves the surface, the 
 skin shrinks, the countenance becomes pale, and the ex- 
 tremities cold, but in the hot stage the face becomes suf- 
 fused, and the whole surface hot and turgid. 
 . Now, when a large quantity of drink has been taken, 
 
ENTRANCE OF DRINKS, ETC. 17 
 
 and rapidly carried off from the stomach, the minute, con*- 
 voluted, and tortuous absorbents are not calculated to af- 
 ford a sufficiently capacious and ready entrance, while the 
 veins are adequately voluminous for this purpose. Yet 
 the veins from the stomach and intestinal canal, though 
 sufficient for the conveyance, cannot contain any consi- 
 derable quantity of fluid, or admit of much accumulation ; 
 and further, the vena portse distributed through the dense 
 substance of the liver, is both incapable of much disten- 
 sion or of rapid transmission. 
 
 The spleen is now generally admitted to be the organ 
 which serves as a reservoir of fluids, till they can be con- 
 veniently introduced into the system. In proportion to 
 its bulk, it is the most vascular organ in the body ; its 
 artery is very large, and the veins numerous and capa- 
 cious ; the absorbents also are abundant. Indeed, it may 
 be considered as a congeries of blood-vessels, with little 
 or no intervening tissue. That these different vessels 
 freely communicate with each other is proved from the 
 facility with which injections flow from the artery into 
 the veins, and also into the absorbents. It has been as- 
 certained that coloured fluids and odorous substances 
 have found their way into the vessels of the spleen, when 
 introduced into the stomach, without having passed into 
 the intestinal canal, and that during digestion, especially 
 where much fluid has been taken, the spleen is swelled. 
 During the cold fit of an ague the spleen is found to be 
 enlarged, from distension of its vessels, and when a patient- 
 has long laboured under that disease, a permanent en- 
 largement of this viscus takes place. 
 
 It is therefore concluded, in the first place, that the 
 spleen serves as a reservoir, in which fluids may accumu- 
 late till they be carried off by the returning vessels, the 
 veins carrying them towards the liver on the one hand, 
 the absorbents conveying them to the thoracic duct on 
 the other, so that they are thus more or less rapidly in- 
 troduced into the general circulating mass according to the. 
 
180 ENTRANCE OF DRINKS, ETC. 
 
 wants of the system. Secondly, when the blood is im- 
 pelled from the surface towards the central parts, as on 
 exposure to cold, or during the cold stage of an intermit- 
 tent, the construction of the spleen readily permits ac- 
 cumulation of blood to take place in it without incon- 
 venience, and in this way prevents other organs from 
 being oppressed by congestion, which neither their struc- 
 ture nor function can bear with impunity. The spleen in 
 this manner seems as >a kind of safety valve to the san- 
 guiferous system, to divert the fluids of the body under 
 particular circumstances, and therefore must be considered 
 as an important conservative organ. Notwithstanding 
 the useful purposes to which it may conduce, it does not 
 appear to be absolutely essential to life, or rather its func- 
 tions may be vicariously performed by others, for it has 
 frequently been removed from the lower animals by way 
 of experiment, and after recovery from the operation, the 
 system, as far as has been observed, does not appear in 
 any respect to suffer. 
 
 The spleen being classed along with the glands, and as 
 the term gland is apt to suggest the idea of an organ 
 subservient to the separation of a peculiar fluid from the 
 blood, innumerable attempts have been made by dissec- 
 tion, experiment, and conjecture, to ascertain what it 
 secretes. The most careful search has failed in detecting 
 any thing like an excretory duct, such as we find the 
 salivary glands, the pancreas, liver, &c., to be supplied 
 with ; but it is to be recollected that all those organs 
 furnished with ducts separate from the blood fluids 
 which are not intended to be reintroduced into the sys- 
 tem, and several of them are altogether excrementitious. 
 From the free communication which is established be- 
 tween the arteries, veins, and absorbents of the spleen, 
 an interchange of fluids may be readily effected, and the 
 drinks be thus partly assimilated before further intro- 
 duction into the body. The numerous absorbents pro- 
 ceeding from the spleen to the thoracic duct are found to 
 
ENTRANCE OF DRINKS, ETC. 181 
 
 convey a fluid of a reddish colour, and coagulable, which 
 mixes with the contents of the thoracic duct. A change 
 analogous to that which the chyle undergoes in passing 
 through the mesenteric glands, appears thus to be ef- 
 fected upon the fluids transmitted through the spleen. 
 Upon the whole, we are warranted in concluding that the 
 spleen serves as a reservoir for drinks till they can be op- 
 portunely introduced into the system, and also allows 
 a congestion of blood under peculiar circumstances, so as 
 to admit of alteration in the balance between the quan- 
 tity of blood on the surface and in the internal organs ; 
 and further, that while these fluids remain in this viscus, 
 or during their transmission through it, they are so 
 elaborated as to be prepared for reception into the general 
 circulating mass. As has been stated, these purposes are 
 not absolutely essential, or other organs may vicariously 
 perform them, since the spleen may be extirpated without 
 much apparent inconvenience to the animal. 
 
 Colouring bodies, odorous substances, various medi- 
 cinal and chemical agents, pass along the stomach and 
 intestinal canal, and are received into the general cir- 
 culation without suffering change, or with only slight 
 alteration of properties. When animals are fed on food 
 mixed with madder, the bones, cartilages, and membranes 
 become of a pink colour ; the colouring matter of that 
 root entering capillaries which are too minute to admit 
 the red particles of the blood. Soon after rhubarb pow- 
 der has been swallowed, the urine becomes tinged with 
 yellow from that substance, which has thus passed 
 from the stomach to the kidneys without change. 
 Various bodies, characterized by their peculiar odour, 
 enter the system, and that too in a very short time 
 after being swallowed. Thus, garlic, onions, and spiri- 
 tuous liquors, are soon detected in the breath, having 
 passed from the digestive organs without alteration. The 
 oil of turpentine, a few minutes after it has been taken, 
 imparts to the urine the exact smell of sweet violets. 
 
182 ENTRANCE CF DRINKS, ETC. 
 
 Medicinal articles are generally exhibited by the mouth 
 in this way ; their subsequent action depends upon their 
 immediate effect upon the mucous membrane lining the 
 stomach and intestinal tube, or on the action being trans- 
 ferred to distant parts, or to the whole system, through 
 the medium of the nerves ; and lastly, they may be taken 
 up and introduced into the blood, and subsequently make 
 their appearance in one or other of the secretions. For 
 example, many find their way to the kidneys, and pro- 
 duce an increased flow of urine ; some are determined to 
 the skin, promoting transpiration and inducing sweat; 
 others direct their action to the lining membrane of the 
 air-passages, and facilitate expectoration, while others 
 exert an influence more or less marked upon the body at 
 large. Sulphur, when taken internally, shortly discovers 
 itself by the odour it imparts to the breath and emana- 
 tions of the skin. When mercury has been exhibited for 
 some time in any quantity, it displays its action on vari- 
 ous secreting organs, and exerts an influence directly or 
 indirectly on every organ and tissue in the body ; in some 
 instances it has shewn itself by silvering coins, or the 
 watch in the pocket, or rings and other ornaments worn 
 by a person undergoing what used to be called a course 
 of mercury. In these instances it unites with the other 
 metals, as gold and silver, forming what is termed an 
 amalgam. In other cases it has been observed deposited 
 in its metallic state, even when taken in another form, 
 shewing that it had suffered reduction in the system. 
 Several salts pass from the stomach into the circulation, 
 and are again expelled without suffering decomposition 
 or change. This is the case with saltpetre or nitrate of 
 potash, for on evaporating the urine of an individual who 
 has previously taken doses of this salt, it is found in a 
 proportional quantity in the residue. Several other saline 
 substances may be shewn to pass by the same channel, 
 and with similar integrity, as proved by their appropriate 
 tests 'and reagents; others again are altered or decom- 
 
ENTRANCE OF DRINKS, ETC." 183 
 
 posed either while in the stomach or intestines, or after 
 they have been absorbed. The salts of iron, from the 
 facility with which they are decomposed by tannin, the 
 astringent and tanning principle of most vegetables, are 
 often reduced to the tan-gallate of iron, the colouring 
 matter of ink. "When exhibited as medicine, and when 
 they meet with tannin and gallic acid in their course, 
 either from the food or other medicines which may have 
 been taken during their employment, the discharges 
 become of a black inky colour, frequently to the no 
 small alarm and consternation of the patient and his 
 friends. Calomel, which is composed of chlorine and 
 mercury, is also liable to be changed in the bowels, 
 by meeting with substances capable of acting upon 
 it. Of these sulphuretted hydrogen is one, a gas which, 
 in some diseased states of the intestine, especially of 
 the colon, is generated in considerable quantity. When 
 calomel is exposed to this gas, it is converted into a black 
 substance, which imparts a dark colour to the alvine dis- 
 charges. Some physicians, ignorant of this fact, have 
 recommended that the calomel should be continued as 
 long as dark-coloured discharges are produced. Now, 
 in such cases sulphuret of mercury is the cause of that 
 colour, and as long as the cause continues, so long will the 
 effect. Various alkaline salts, formed with the vegetable 
 acids, are liable to decomposition, the alkali and the acid 
 being separated either in the first passages or in the 
 course through the circulation, or lastly, while being ex- 
 creted from glands, especially the kidneys. This is apt 
 to occur where potash or soda is combined with carbonic, 
 acetic, citric, and tartaric acids. 
 
 We have already shewn that chyle is taken up from 
 the intestinal canal by the lacteal absorbents, and con- 
 veyed to the thoracic duct, but that occasionally a little 
 of it may find its way to the liver, either in consequence 
 of some of the lacteals having joined branches of the vena 
 portse, or from these veins themselves acting as absorbents ; 
 
184 ENTRANCE OF DRINKS, ETC. 
 
 for, as we have stated, the lacteals appear to exercise the 
 power of selection or choice with respect to what they 
 receive. The veins, on the other hand, are much more 
 indiscriminate in what they take up. Now there is a 
 wise provision in this ; for whatever the absorbents re- 
 ceive, they must convey into the general mass of cir- 
 culating fluids, although it may be retarded or modified 
 in its course ; but when any substance has been absorbed 
 by the branches of the vena portee, there is a subsequent 
 opportunity for its being cast out, while the contents of 
 the porta are filtered through the liver. In this way the 
 liver acts as an important organ in connexion with diges- 
 tion and sanguification, and thus not only is the bile 
 secreted in order to be subservient to chylification, and to 
 stimulate the peristaltic motion of the bowels, but the 
 liver acting as a strainer in the formation of bile, drains 
 off from the venous blood what might have proved highly 
 noxious ; and hence the total suppression of the action of 
 the liver speedily proves fatal. 
 
 It has been stated that drinks are rapidly taken up 
 after their introduction, that they are not subjected to 
 alteration previous to absorption, and that the veins from 
 the stomach and intestines appear to be the chief agents 
 of their removal. They are in this way mixed with the 
 venous blood, instead of being immediately taken into 
 the absorbents. It has been farther stated that the spleen 
 is calculated to admit of considerable accumulation of 
 fluids, that a very large quantity of blood circulates through 
 it, that after a meal it swells, and that the numerous ab- 
 sorbents arising from it, and terminating in the receptacle 
 of the chyle and the thoracic duct, convey a coloured fluid, 
 displaying several of the characters of more perfect blood. 
 Fluids, therefore, enter the circulation from the alimen- 
 tary canal, pursuing three different routes in their pas- 
 sage ; first, directly to the liver, through the veins, mixing 
 immediately with the contents of the veins ; secondly, 
 they may be arrested for some time in the spleen, where 
 
ENTRANCE OF DRINKS, ETC. 185 
 
 certain changes may be effected upon them. Besides,, their 
 slow introduction being partly insured in this way, it 
 becomes more in accordance with the gradual changes 
 which occur in organized bodies in general. From the 
 spleen one portion flows by the absorbents to the thoracic 
 duct, the other is conveyed by the porta, and filtered 
 through the liver. It may be observed that as the porta 
 is the only vein which appears expressly intended to con- 
 vey new materials into the general system, so is it the 
 only one which discharges from its blood a secretion 
 whereby an opportunity is afforded of throwing off what 
 might have been superfluous or noxious ; and, as just 
 now observed, the bile may thus far be considered as 
 excrementitious. 
 
 Colouring, odorous, medicinal, and chemical substances, 
 such as have been adverted to, though occasionally ob- 
 served in the absorbents, are principally carried off by the 
 veins through the liver. The speedy appearance which 
 some of them make, as garlic and alcohol, in the breath, 
 and turpentine and prussiate of potash in the urine, has led 
 to the inference that such matters may enter the circula- 
 tion, and be conveyed more directly to those parts than 
 by the more circuitous course through the heart and 
 arteries. The observations, however, are as yet too few 
 and indefinite to warrant any certain conclusions from 
 them. 
 
 To recapitulate, the chyle enters by the lacteal ab- 
 sorbents, to be carried into the thoracic duct, and by the 
 veins to be conveyed into the system chiefly through 
 the spleen ; and all those substances which find their 
 way into the circulation without change, and which are 
 characterized by their peculiar qualities, such as their 
 colour, odour, chemical properties, or the effects they 
 produce upon the body, being taken up by the veins, 
 are introduced principally through the liver. 
 
186 
 
 CHAPTER IV. 
 
 THE BLOOD. 
 
 Blood Physical Properties of Colour The Red Globules Their Form and 
 Constitution Smaller and more numerous in Mammalia Odour Characteris- 
 tic of the Animal to which it belongs Consistence Temperature Specific 
 Gravity Quantity of in the Body Coagulation Relative Proportion of Serum 
 and Clot Serum Fibrin Oil of the Blood Table of Analysis of Vital Pro- 
 perties. 
 
 ONE of the most characteristic properties of organized 
 bodies is the power which they possess of appropriating to 
 themselves foreign matter, and so altering it as to adapt it to 
 their various necessities in the growth and nourishment 
 of their own individual structures, and for the continuance 
 of their race. 
 
 In the last chapter we have treated of the various suc- 
 cessive steps which occur in the conversion of food into 
 a fluid in its most perfect state of adaptation to the 
 highest organized beings. The name blood is applied to 
 this elaborated fluid in animals, the term sap being em- 
 ployed to designate the corresponding fluid in plants. 
 We have noticed what a multiplicity of organs and 
 complexity of apparatus are engaged in forming and 
 perfecting the arterial blood, the characters of which 
 we have now to inquire into. 
 
 The examination of this interesting and important fluid 
 may be conveniently conducted under the following heads : 
 first) its physical properties ; secondly ', its chemical con- 
 stitution ; and thirdly, its vital characters. 
 
 The physical properties may be considered in respect 
 
RED GLOBULES. 
 
 187 
 
 to its colour, odour, consistency, temperature and specific 
 gravity. 
 
 Colour. The blood of vertebrated animals contains 
 particles termed the red globules, to which its colour is 
 owing. These globules have excited much interest, and 
 great attention has been paid to them, with the view of 
 ascertaining their nature and constitution. Nevertheless 
 much discrepancy of opinion exists as to their real charac- 
 ter. They are said to consist of a central nucleus, with a 
 thin vesicular covering. In the human subject, when 
 examined under the microscope, according to some they 
 are spherical ; by others they are held to be oval or ellip- 
 tical : some describe them as being flat, like a shilling, 
 or of this form with a hole in the middle : others, again, 
 represent them as of no determinate shape. The greater 
 number, however, describe them as being spherical in 
 man, and elliptical in the lower animals. Equally dis- 
 cordant are the accounts furnished by different observers 
 as to their size the statements varying from the T T L Q n th 
 to the so^o^ 1 of an inch in diameter. It is said that 
 they are smaller in birds, and larger in fishes than in mam- 
 malia. They are certainly larger than the particles of 
 colouring matter in a number of vegetable substances ; 
 for when animals are fed with food intermixed with 
 madder, their bones, membranes, and cartilages become 
 tinged with the colour imparted by that root, shewing 
 that it enters the vessels of these tissues, which exclude 
 the red globules of the blood. Individually, they are co- 
 lourless, reflecting colour only when in the aggregate. 
 This is, however, the case with most, if not every kind 
 of matter, a single insulated particle being colourless, 
 while in the mass the appropriate colour is displayed. 
 The size of the globules excludes them from the minute 
 capillary vessels, which are of such a diameter as to admit 
 the transmission of merely the transparent and colourless 
 part of the blood. Or perhaps it may be stated more 
 correctly, that in the healthy condition a single globule 
 
188 RED GLOBULES. 
 
 alone can pass from the arterial to the venous capillaries, 
 so that during the passage of the blood through these 
 minute tubes, its colour disappears, and again becomes 
 evident in vessels of such a diameter as admit of a suffi- 
 cient accumulation of the globules. 
 
 In diseased states many vessels become capable of 
 transmitting red blood, which, in their healthy condition, 
 they exclude. For example, the white of the eye speedily 
 becomes bloodshot from injury, and numerous vessels ap- 
 pear in a very short time to start into existence. This 
 change with respect to the blood-vessels is one of the 
 most usual and characteristic concomitants of inflamma- 
 tion; many organs which are white and colourless in 
 health becoming red when affected with it. There 
 are organs, however, the vessels of which are so ex- 
 ceedingly minute that they exclude the red particles at 
 all times, even when they have for some time been sub- 
 jected to inflammation, as is the case with the transparent 
 parts of the eye, and some delicate internal membranes, 
 where a loss of transparency is the only change they un- 
 dergo. 
 
 The quantity of colouring matter in proportion to the 
 whole mass of blood varies in different classes of animals. 
 In mammalia and birds it bears the greatest proportion, 
 a smaller in reptiles, and still less in fishes. In the two 
 last classes, namely, reptiles and fishes, the red blood is 
 chiefly confined to a few internal organs, as the heart, 
 liver, kidneys, lungs, and gills. If the statement be cor- 
 rect, which there appears to be no reason to doubt, the 
 larger size of the globules will partly account for this. 
 Their flesh is consequently white, and apparently blood- 
 less. In mammalia and birds great differences in this 
 respect arise from a variety of circumstances. The flesh 
 of wild animals is generally of a darker colour than that 
 of the domesticated. Animals of the chase, after a long 
 run, bleed sparingly, the blood having been impelled into 
 the minute capillaries. It is said that butchers occasion- 
 
RED GLOBULES. 
 
 189 
 
 ally have recourse to the practice of driving their cattle 
 furiously, and running them for some time before killing 
 them, in order to increase the weight of the carcass, expe- 
 rience having taught them that this takes place; in 
 such cases a much less quantity of blood is drawn, and 
 the flesh presents a dark and somewhat carrion- like ap- 
 pearance. It may be noticed, that in moor game the 
 large mass of flesh upon the breast, forming the powerful 
 muscle so vigorously brought into action in striking the 
 wings against the air during their flight, is of a dark 
 colour approaching to brown, while the deep-seated layer 
 is pale, having merely to raise up the wing against a less 
 degree of resistance. The quantity of colouring matter 
 also varies, not only in different individuals, but also in 
 the same individual at different times, according to age, 
 health, and other circumstances. 
 
 During every moment of our existence the globules are 
 incessantly undergoing changes in the two sets of capil- 
 laries respectively. When treating of the effects of re- 
 spiration on the blood, it was mentioned that one of the 
 most marked of these is the change of colour in the pass- 
 age of the blood through the lungs, from deep purple 
 to scarlet, while the opposite change occurs in the capil- 
 laries of the system, from scarlet to purple ; so that we 
 have thus a reduction, and again a recomposition, as often 
 as the one passes into the other. 
 
 The colouring matter of the blood is considered as a 
 peculiar animal principle, to which the name Hsematosin 
 has been given. Various alkaline, acid, and saline solu- 
 tions have been tried, which produce marked effects upon 
 its colour ; alkaline and acid substances darken it, while 
 neutral saline solutions produce a florid tint. It has, 
 therefore, been inferred that the changes which the blood 
 undergoes in colour in the lungs and in the system re- 
 spectively depend upon these causes ; carbonic acid in the 
 system darkening the heematosin, while its escape from 
 the lungs enables the salts of the blood to restore the ver- 
 
190 ODOUR. 
 
 milion hue. This account of the colour of the blood 
 in the venous and arterial conditions appears sufficiently 
 simple, but unfortunately the theory is not altogether 
 consistent with other well established facts ; for example, 
 carbonic acid does not exist as such in any greater appre- 
 ciable quantity in venous than arterial blood, and the salts 
 in the blood are not altogether neutral. 
 
 The colouring principle of the blood has also been con- 
 sidered to be iron, according to some, in the state of an 
 oxide; according to others, combined with phosphoric 
 acid. That iron exists in the blood is fully established ; 
 but in what particular state, or whether it be essential to 
 the colour of the blood, further observation is necessary to 
 determine. 
 
 Odour. Newly drawn blood has a peculiar odour, 
 which is more distinctly perceptible in the arterial than 
 in the venous. It appears to be a peculiar volatile prin- 
 ciple, imparting not only to different species, but also to 
 each individual of the same species, their characteristic 
 odour. This peculiar principle may be discharged from 
 the blood by adding strong oil of vitriol, when it is freely 
 liberated; so that one may know, by the odour thus 
 evolved, the animal from which the blood had been drawn. 
 The odour is similar to that of the perspiration belonging to 
 each, as of man, the horse, the ox, the sheep, the pig, the rat, 
 &c. ; and so also the peculiar odour of different species of 
 birds, of reptiles, and of fishes may be elicited. Further, it 
 is said to be more penetrating in the male than in the fe- 
 male. It is well known that the different races of mankind 
 are easily distinguishable by their perspiration. Savages 
 can detect their friends and foes by the scent, and the 
 dealers in hair can ascertain by the smell the nation to 
 which the hair belongs. That each individual leaves a 
 trace of his odour, by which his dog can distinguish his 
 course through the streets of a city, may be observed 
 every day, when the dog that has lost his master traces 
 him by scent, and is thus enabled to discover him, al- 
 
CONSISTENCE. ] 91 
 
 although many other persons may have passed in the 
 same direction. 
 
 The colour and odour of the blood may be employed 
 with advantage in the detection of crime, and in cases of 
 criminal prosecution, in establishing the innocence or the 
 guilt of the accused. In this view we have offered to us 
 several points of interest, it being now sufficiently estab- 
 lished that every new fact in science, however apparently 
 insignificant at first, may afterwards lead to the most 
 important results in regard to the safety, comfort, and well- 
 being of the human race. 
 
 Consistence. The blood cannot with propriety be con- 
 sidered as a fluid ; for we have seen that it contains 
 numerous globules, which in the living vessels are never 
 aggregated together in a mass, but have been observed 
 to possess motion among each other, and from the ef- 
 fects of stimulants and poisons, this motion appears to 
 depend upon vital properties, for they are inexplicable 
 upon known chemical and mechanical principles. The 
 fibrin likewise would appear to be diffused through the 
 fluid part, and not dissolved in it. In consequence of 
 the peculiar consistency of the blood, it has an unctuous 
 or somewhat soapy feel, and a certain degree of tenacity. 
 
 The venous blood poured into the right auricle of the 
 heart is a very heterogeneous mixture, being composed of 
 arterial blood, changed into venous in the capillaries of 
 the system, of lymph absorbed from the various surfaces 
 of the body, and of every constituent of the body, solid 
 and fluid, taken up by the absorbents, and sooner or later 
 poured into the red veins, and lastly, of new matter 
 from the digestive organs ; so that venous blood varies 
 according as it is taken from different veins, not only 
 from the materials which may have been poured into the 
 veins, but likewise from what the arterial blood may 
 have given off in the various secretions, and in the 
 nourishment of the different tissues of the body. Thus 
 blood returned from the kidneys is different, from the 
 
192 TEMPERATURE AND SPECIFIC GRAVITY. 
 
 urine having been separated ; that from the liver from the 
 separation of the bile, and so also from the other secreting 
 organs. The blood therefore returning from every in- 
 dividual organ of the body is in some degree to be 
 held as peculiar, and different from that of every other 
 organ. The arterial blood, on the other hand, having been 
 formed in the lungs, and flowing to the left heart, to be 
 propelled to the system at large, is identical, from what- 
 ever vessel it may be drawn. 
 
 Temperature and Specific Gravity. From what has 
 been already stated when discussing animal heat, it is 
 unnecessary at present to treat of the temperature of the 
 blood. It was there shewn that it differs in different 
 animals, and in the same individual in various circum- 
 stances and conditions, that in man the ordinary tem- 
 perature is about 98 of Fahrenheit, and that it is 
 somewhat higher in the arterial than the venous blood. 
 
 Various substances possess different weights, and even 
 the same body differs in its weight at different tempera- 
 tures. In order to obtain the relative weights of liquids, 
 it is merely necessary to procure equal bulks, and weigh 
 them at the same temperature. For this purpose, we 
 take a phial and place it on an accurate balance. Hav- 
 ing got an equipoise, the phial is to be filled with dis- 
 tilled water, at the temperature of 60. Supposing it 
 to weigh 1000 grains, we have now got a standard by 
 which we may estimate the weight of other bodies by 
 the rule of proportion. Suppose the phial be filled with 
 mercury, and found to hold 13,500 grains; or oil of vitriol, 
 weighing 1845 grains; or oil of turpentine, weighing 
 872 grains, these will give respectively the specific gravi- 
 ties of water, mercury, oil of vitriol, and oil of turpen- 
 tine. The blood varies in its specific gravity in diffe- 
 rent individuals, and in the same individual in different 
 conditions, the extremes being 1022 and 1125, the me- 
 dium about 1050. Arterial blood has a specific gravity 
 somewhat less than venous ; and the blood of the lower 
 
CHEMICAL CONSTITUTION. 193 
 
 animals is generally less than that of man. Calculations 
 have been made as to the total quantity of blood in the 
 body at any one time ; as it necessarily varies, however, 
 according to a great variety of causes, an approximation to 
 the truth is all that can be arrived at. The estimate of 
 Haller may be taken as coming near the average quantity ; 
 he supposes that the blood constitutes about one-fifth of 
 the whole weight of the body, the relative proportion being 
 greater in youth, and less in advanced life. A body 
 weighing one hundred and fifty pounds will therefore 
 contain thirty pounds of blood : of these one-fifth, or six 
 pounds, is estimated as arterial, the other twenty-four 
 pounds being venous, the relative quantity of arterial 
 being less in the male and aged than in the female and 
 young. 
 
 Chemical Constitution. No department of chemistry 
 is beset with so many difficulties as that which has for 
 its object the investigation of the chemical constitution of 
 organized matter. The chemical actions which are effected 
 in living bodies take place between quantities so ex- 
 tremely minute, through instruments so complicated in 
 their construction, and liable to influences so various, 
 that it becomes exceedingly difficult, if not impossible, 
 accurately to estimate the influence of each. The in- 
 fluence of quantity in conducting chemical processes is 
 well known ; many substances affording results, when 
 operated upon in minute proportions, which they do not 
 yield on a greater scale, and conversely, products are ob- 
 tained by processes conducted upon large masses, pos- 
 sessing peculiar defects or excellencies. The distillation 
 of spirits, the fermentation of malt liquors, and the mak- 
 ing of bread, afford examples where the product obtained 
 varies in quality according to the quantity operated upon. 
 
 But what is of still greater importance, the moment an 
 animal fluid or solid is separated from the body to which 
 it belonged, it is severed from vital influence, and imme- 
 diately the reign of chemical and mechanical laws com- 
 ic 
 
194 CHEMICAL CONSTITUTION. 
 
 mences. The change must be as instantaneous as the 
 electric shock, although the effects are not at once per- 
 ceptible to the senses. The results of our most minute 
 and searching examination cannot indicate the precise 
 chemical condition of any substance, when that substance 
 constituted a portion of a living organized structure, no 
 more than when shewn a piece of coagulated albumen, 
 we can tell whether it had been coagulated by heat, elec- 
 tricity, alcohol, or other influences which are known to 
 produce that effect. Moreover, the condition in which 
 the solid or fluid, as well as of the organism in general 
 existed at the instant of separation, will to a very consi- 
 derable extent determine the results ; and accordingly 
 various states of health and disease, as well as the man- 
 ner of death, exert an important influence upon the blood, 
 as shewn in its coagulation, and on the constitution of 
 different secretions, furnishing matter of the deepest in- 
 terest to the medical inquirer. Further, it is exceedingly 
 difficult to determine whether the results obtained in ope- 
 rating upon organized matter, or substances produced by 
 organized matter, be or be not products of the processes 
 to which they have been subjected ; or, in other words, 
 in these cases there is a risk of considering as a consti- 
 tuent or property of a substance thus acted on, what may 
 be merely the consequence of the action to which it had 
 been exposed. It is to be recollected, then, that what is 
 known of the chemical constitution of the blood, has been 
 ascertained from the examination of, and observation 
 upon it as a dead, and not as a living fluid. Though the 
 condition in which it existed as a constituent of the living 
 body influences and determines to a considerable extent 
 the occurrences which take place after its separation, so 
 far, indeed, that it has been considered by some that these 
 are to be held as arising from its retaining its vitality, as, 
 for example, the phenomenon of its coagulation, which, 
 however, indicates nothing more than the state in which 
 it existed while tinder vital influence, and is rather an in- 
 
COAGULATION. 195 
 
 dication that death has taken place than that life con- 
 tinues. 
 
 Generally, in about two or three minutes after emission, 
 the blood begins to separate into a thin watery portion 
 termed serum, and a thickish consistent clot or crassa- 
 mentum. All that can be said is, that coagulation is one 
 of the properties of the blood, as to the efficient cause of 
 which we are ignorant. There are, indeed, not wanting 
 many hypotheses sufficiently inconsistent with each other, 
 which from time to time have been promulgated in order 
 to account for it. Into the consideration of the merits of 
 these, it would be here out of place to enter, nor would 
 the discussion unfold much either of interest or import- 
 ance. It is observed to take place more speedily in ve- 
 nous than arterial blood; and in that which is last 
 drawn from an animal bled to death, and in those in a 
 weakened, fainting, and dying condition. It is also pro- 
 moted by rest, by a temperature somewhat less than that 
 of the body, by exposure to air, and when abundant 
 in serum. It is retarded by agitation, dilution with 
 water, and by the addition of saline solutions, though 
 not entirely prevented by them. It takes place when 
 extravasated in the living body, and even within the 
 vessels themselves, when a portion of an artery or vein is 
 included between two ligatures. In aneurism, where a 
 large tumour filled with blood, and having communica- 
 tion with an artery constitutes the disease, the blood 
 coagulates, and after death the cavities of the heart, and 
 the great vessels leading from it, are frequently filled 
 with coagulated blood, forming moulds of the vessels. In 
 these instances, the blood appears to have coagulated at 
 the point of death, and a separation between the consti- 
 tuents of the clot to have been effected. These moulded 
 pieces of clotted blood receive the name of polypi ; they 
 have given rise to idle stories of large worms being found 
 in the heart, and the ignorant have considered them to 
 have been the cause, not the consequence of death. 
 
196 COAGULATION. 
 
 One of the most evident and important final purposes 
 arising from the coagulation of the blood is the stoppage 
 of haemorrhage, for although the contraction of the coats 
 of the blood-vessels be conducive to this end, yet the 
 blood becoming thick and consistent, constitutes an effi- 
 cient agent in arresting the bleeding in cases of wounds, 
 by plugging up the vessels, and forming an adhesive 
 sheath over their cut extremities ; as likewise in aneurism, 
 it occasionally happens that by the gradual accumulation 
 of coagulated blood the tumour is filled up, and the channel 
 of the vessel obliterated, thus effecting what is termed 
 a spontaneous cure of an extremely dangerous disease, 
 which generally requires a surgical operation, in some 
 situations forming the most difficult and hazardous prac- 
 tised in the art. 
 
 Many circumstances modify the coagulation of blood 
 besides those now adverted to, such as age, sex, and 
 temperament : in fact, the blood participates in every 
 state of the constitution, both in health and disease, inso- 
 much that for a long time every diseased condition was 
 attributed to changes in the blood, and still constitutes a 
 considerable part of the popular notions entertained re- 
 specting the nature and cause of disease. In some cases, 
 the constituents of the clot, namely, the fibrin and red 
 particles, separate from each other, leaving the fibrin 
 upon the surface, forming what is called the buffy coat, 
 as observed in different inflammations. This does not 
 appear to arise from the coagulation taking place more 
 slowly than usual, for even when it has occurred slowly 
 no such appearances are presented ; but seems rather to 
 depend on a state in which the red globules and those of 
 the fibrin are in a state of repulsion to each other, for it 
 occasionally happens where the coagulation is unusually 
 rapid. The clot is much firmer and consistent in 
 some instances, as if the attraction between the parti- 
 cles was stronger than usual. On the other hand, the 
 coagulum sometimes forms a soft spongy mass, a condi- 
 
COAGULATION. 1 97 
 
 tion which is observed after violent muscular exertion ; in 
 typhus and other putrid fevers, in erysipelas, and the 
 dreadful disease which originates from wounds got in the 
 examination of a body, in which death has occurred in 
 particular states. Further, in other cases the attraction 
 between the globules seems entirely destroyed, or rather 
 the blood is in such a condition that attraction is never es- 
 tablished, the blood remaining permanently fluid, as when 
 death has taken place suddenly, from a blow on the 
 stomach, from hanging, lightning, violent mental emo- 
 tion, cholera, and the worst forms of fevers. Some poi- 
 sons, especially prussic acid and the venom of serpents, 
 also produce the same effect. In these cases, the body 
 hastens rapidly into decomposition, so that the more solid 
 parts, as well as the blood, indicate the peculiar state of 
 the body previous to death, and also the kind of the 
 death itself. 
 
 The proportion of coagulum varies much in different 
 animals, and in the same animal in different states, the 
 average proportion being about one-third of clot. The 
 extremes furnish equal parts of serum and clot, on the 
 one hand, and one-fourth only of clot on the other : these 
 extremes, however, are rare. Even in the same bleed- 
 ing the proportions differ, the first cupful having a 
 greater, and the last a less quantity of the more consis- 
 tent part. 
 
 The serum is a pale straw-coloured greenish liquid of 
 a specific gravity from 1025 to 1030. It contains a 
 considerable quantity of albumen, so that on exposure 
 to the temperature of 160 it is coagulated into a whitish 
 somewhat translucent mass like the white of an egg. 
 We have already, when treating of the proximate animal 
 principles, had occasion to advert to the general pro- 
 perties of albumen, so that it is unnecessary to repeat 
 what has been stated. If the coagulated serum be al- 
 lowed to drain, particularly after being broken up and 
 cut into small pieces, a watery fluid filters from it, termed 
 
198 COAGULATION. 
 
 the serosity of the blood, just as we observe the curd of 
 milk separating into the more consistent curdy part, and 
 the more fluid portion, the whey. Besides holding in so- 
 lution the different salts of the blood, the serosity con- 
 tains a peculiar animal matter which is not coagulable, 
 and when obtained in the dry state by evaporation, is 
 again dissolved, both by water and alcohol. At one time 
 it was considered to be gelatin, but it is not acted upon 
 by the characteristic tests of that substance, so that at 
 present gelatin does not rank among the constituents of 
 the blood. 
 
 The coagulum consists of fibrin and red globules merely 
 in a state of mechanical mixture. The fibrin is not held 
 in solution in living blood, but appears to be formed of 
 colourless particles, between which in the living state 
 there exists repulsion, but on the occurrence of death 
 attraction is established between them, so as to produce 
 coagulation. As has just been stated, however, this at- 
 traction is variously modified, or altogether prevented by 
 various causes. When the mass is examined by the aid 
 of the microscope, it presents a fibrous and cellular ap- 
 pearance, which has been compared to the reticulated 
 texture of the leaves of plants. When blood is stirred 
 with a bunch of twigs, the fibrin adheres to the twigs, 
 and may thus be obtained separate from the albumen. 
 If too forcibly agitated, coagulation is prevented, whether 
 we stir the blood or agitate it in a bottle. By washing 
 the clot with water, the colouring matter is removed, when 
 the fibrin remains nearly colourless, presenting a fibrous 
 structure, from which it has derived its name. The cha- 
 racters and properties of fibrin and the red globules hav- 
 ing been already adverted to, they need not be further 
 noticed in this place. 
 
 The blood contains a small quantity of oleaginous 
 matter, which may be procured separately by agitating 
 it with ether. In some instances it is so abundant that 
 the serum has the appearance of whey, milk, or cream, 
 according to the proportion of fatty matter. 
 
VITAL PROPERTIES. 199 
 
 The following are the results of two analyses of the 
 blood by Le Cann. 
 
 Water 780.145 785.590 
 
 Fibrin 2.100 3.565 
 
 Colouring matter 133.000 119.626 
 
 Albumen 65.090 69.415 
 
 Fat (crystalline) 2.430 4.300 
 
 Ditto (oily) 1.310 2.270 
 
 Extractive, soluble in water and alcohol 1 .790 1 .920 
 
 Albumen united to soda 1.265 2.010 
 
 Chlorides of sodium and potassium 
 Carbonates -I 
 
 Phosphates Vof soda and potassa 
 Sulphates J 
 
 Carbonate of lime and magnesia 
 
 Phosphate of lime, magnesia, and iron }~ 2.100 1.414 
 
 Peroxide of iron. . . - , 
 
 Loss .. 2.400 2.586 
 
 1000.000 1000.000 
 
 Vital Properties. Since the blood is endowed with 
 many properties which cannot be explained either on 
 mechanical or chemical principles, we are entitled to at- 
 tribute them to its vitality. Its vitality has been dis- 
 puted on the ground of its being a fluid ; but even to 
 admit (which is by no means necessary) that life is incon- 
 sistent with mere fluidity, we have seen that the blood can- 
 not properly be termed a perfect fluid, as it contains nume- 
 rous globules which are curiously organized, and displays 
 properties different from those which result from physical 
 agencies, and which cease on its being separated from the 
 living organism, or on the supervention of death. Much 
 depends upon the ideas attached to the terms life and 
 vitality, and the keen discussions which have so often 
 taken place originate in most cases from different accep- 
 
200 VITAL PROPERTIES. 
 
 tations of terms, or from the various points from which a 
 subject may be viewed. While some have denied that the 
 blood possesses vitality, others have gone to the opposite 
 extreme, and considered it as the especial seat of life ; 
 and as if the writings of Moses had ever been intended for 
 the teaching of physiology, they have appealed to such 
 texts as the following : Genesis, ix. 4. " But the flesh, with 
 the life thereof, which is the blood thereof, shall ye not 
 eat." Leviticus, xvii. 11-14. " And whatsoever man 
 there be of the house of Israel, or of the strangers that 
 sojourn among you, that eateth any manner of blood ; I 
 will even set my face against that soul that eateth blood, 
 and will cut him off from among his people. For the 
 life of the flesh is in the blood ; and I have given it 
 to you upon the altar, to make an atonement for your 
 souls : for it is the blood that maketh an atonement for 
 the soul. Therefore I said unto the children of Israel, 
 No soul of you shall eat blood, neither shall any stranger 
 that sojourneth among you eat blood. And whatsoever 
 man there be of the children of Israel, or of the strangers 
 that sojourn among you, which hunteth and catcheth any 
 beast or fowl that may be eaten ; he shall even pour out 
 the blood thereof, and cover it with dust. For it is the life 
 of all flesh ; the blood of it is for the life thereof : therefore 
 I said unto the children of Israel, Ye shall eat the blood 
 of no manner of flesh : for the life of all flesh is the blood 
 thereof j whosoever eateth it shall be cut off." Some com- 
 mentators understand these injunctions as intended to 
 preclude such a horrid mode of using animal food as 
 practised by the Abyssinians, who, on certain occasions, 
 cut from the living animal flesh, and devour it, still 
 quivering with life, and reeking in blood, at the same 
 time taking care to avoid vital parts, that the life of the 
 poor mangled animal may not be destroyed. Bicherand 
 thus adverts to the effects of animal diet : " Savages, who 
 live by hunting, and who feed on raw, bloody, and pal- 
 pitating flesh, are the most ferocious of men ; and in our 
 
VITAL PROPERTIES. 201 
 
 own country, in the midst of those scenes of horror which 
 we have witnessed, and from which we have suffered, it 
 was observed that butchers were foremost in the mas- 
 sacres, and in all the acts of atrocity and barbarity. I 
 know this fact, which was uniformly noticed, has been 
 explained by saying, that the habit of slaying animals 
 had familiarised them to shed human blood. But though 
 I do not deny the existence of this moral cause, which 
 certainly operates, I think I may add to it, as a physical 
 cause, the daily and plentiful use of animal food, and the 
 breathing of an air filled with emanations of the same 
 kind, which contributes to their embonpoint, which is some- 
 times excessive." Animal food is not well adapted for 
 a warm climate, such as Palestine is for the greater part 
 of the year, in which the Hebrews were destined to be 
 placed. These appear to be sufficient reasons why the 
 great Lawgiver imposed such injunctions and restrictions 
 on that people, prone as they were to adopt the customs 
 and follow the practices of their neighbours, who were 
 sunk in the most base and degrading superstitions, ac- 
 companied with the most abominable and demoralising 
 rites and usages. 
 
202 
 
 CHAPTER V. 
 
 ABSORPTION. 
 
 Purposes served by the function of Absorption Absorption from the Skin From 
 Mucous Membranes From Serous Membranes From Cellular Tissue From 
 the Surfaces of the Joints Interstitial Absorption Its importance in carrying 
 off the old worn-out particles, and consequent subservience to the renewal of the 
 different parts of the Body Special Organs of Absorption Discovery of Con- 
 troversies respecting Lacteals and Lymphatics Their excessive number Lym- 
 phatic Glands Their Office Case of puncture from Dissection Endosmose 
 and Exosmose Venous Absorption Causes influencing Absorption Causes 
 which tend to increase or diminish the risk from exposure to contagious Diseases. 
 
 ABSORPTION is that function of living organized bodies 
 by which new matter is taken up from without and in- 
 troduced into their own systems, and by which also the 
 different constituent parts of the body itself are removed, 
 in order to give place to others in the renewal and de- 
 velopment of the different parts of the frame. Every 
 organ, and every constituent particle of an organ, is sub- 
 ject to absorption, with the exception of the enamel of 
 the teeth, the hair, the scarf skin, and the nails. 
 
 We may consider this function, in the first place, as it 
 is carried on, either upon the external surface, or on sur- 
 faces having communication with it ; secondly, as it occurs 
 in shut cavities ; and thirdly, where it takes place in 
 the integral parts of the body. 
 
 First, Numerous facts prove that absorption from the 
 skin takes place to no inconsiderable extent, though the 
 scarf-skin, forming, as it does, a barrier between all that 
 
ABSORPTION. 203 
 
 it covers and the external world around it, offers an im- 
 pediment in a certain degree to the introduction of foreign 
 matter. After bathing, or being exposed to a moist atmos- 
 phere subsequently to exercise, the body has been found to 
 gain considerably in weight. Yarious medicinal agents also 
 are introduced by cuticular absorption, which is much pro- 
 moted when the skin is relaxed by warmth and mois- 
 ture, or the function is excited by means of friction, 
 whereby substances are insinuated between the scales 
 of the cuticle. Exposed, as we frequently are, to noxious 
 vapours of various kinds, and to different substances, 
 which, if readily admitted through the skin, would be 
 productive of most injurious consequences, the protec- 
 tion afforded by the scarf-skin is most important; its 
 removal, on the other hand, is had recourse to with good 
 effects where medicinal agents are required to be intro- 
 duced into the body, in cases either where it is desirable 
 to bring the system speedily under their action, or where 
 we wish to avoid their direct action upon the digestive 
 organs ; and lastly, where their exposure to the digestive 
 apparatus, and the fluids which they meet with in their 
 course, might effect changes upon them, and thus alter 
 their properties, and frustrate the intention with which 
 they are exhibited. Accordingly, blisters are applied for 
 the removal of the cuticle, when the medicine being placed 
 upon the skin denuded of its natural defence, becomes 
 very rapidly absorbed. Mercury, sulphur, and iodine are 
 thus frequently introduced by the skin. Opium, and 
 other narcotics and purgatives, such as croton oil, may 
 obtain entrance in this way ; no doubt these also affect 
 the system from the impression they produce upon the 
 extremities of the nerves distributed on the surface of the 
 body. From the extensive surface of the air-passages, 
 absorption is very readily effected on exposure to the 
 vapour of turpentine : the presence of that substance will 
 in a few minutes be indicated in the urine. The breath- 
 ing of an atmosphere loaded with alcoholic spirits soon 
 
204 . ABSORPTION. 
 
 produces intoxication; and a person entering a snuff- 
 manufactory, even although in the habit of using tobacco, is 
 so powerfully impressed that in a few seconds he experiences 
 great prostration of strength, and sickness and vomiting 
 are apt to supervene. The poisonous miasmata emanating 
 from those labouring under contagious diseases are most 
 readily received by the breath ; indeed, it is chiefly by 
 cuticular and pulmonic absorption that they are propa- 
 gated. The noxious exhalations from stagnant marshes 
 and other unhealthy situations are introduced in the same 
 manner. Medicated vapours are inhaled frequently with 
 greater advantage than can be derived from the use of 
 these agents in any other way, particularly in diseases of 
 the lungs, where they operate not only by their direct 
 effect upon the extremities of the nerves, but also in con- 
 sequence of their being immediately taken up by the 
 vessels of the lungs. 
 
 We have already had occasion to advert to absorp- 
 tion from the alimentary canal. Throughout its whole 
 extent this function is carried on with more or less 
 rapidity, according to a variety of circumstances; and, 
 as we have seen, it is from this surface that new mat- 
 ter is derived, to compensate for the losses to which the 
 system is constantly exposed. Medicines are much 
 more commonly exhibited by the mouth than in any 
 other way, whether they produce their effects in con- 
 sequence of their impression upon the nerves distributed 
 on these parts, or are taken up and carried into the 
 general circulating mass, and subsequently induce their 
 specific effects upon distant organs, on which their action 
 is expended. The facility and the rapidity with which 
 substances are carried off from the alimentary canal is 
 surprising. Various colouring and odorous principles, 
 such as rhubarb and garlic, are in a very few minutes 
 detected in the breath or in the urine. The extent of 
 this surface for absorption is not limited to the alimentary 
 canal, but is extended to the internal surface of all the 
 
ABSORPTION PROM SEROUS MEMBRANES. 205 
 
 excretory ducts which terminate in it. The salivary, bili- 
 ary, and pancreatic ducts must be included : where these 
 are obstructed, the secretions which they convey are again 
 taken up and carried into the system. Thus in jaundice 
 the whole surface of the body is rendered yellowy from the 
 bile being conveyed into the general circulation. In the 
 same manner does absorption occur from the other sur- 
 faces continuous with the external integuments, and hav- 
 ing communication with them, as the lining membranes 
 of the nose, eyes, ears, &c. 
 
 Secondly, There are several shut sacs in the body termed 
 serous membranes ; others belong to the joints, and are named 
 synovial membranes : and analogous to these in several re- 
 pects is the cellular membrane. A few observations respect- 
 ing each of these may be here advantageously introduced. 
 The serous membranes are thin, transparent, or semi-trans- 
 parent webs, extended over the contents of the different 
 cavities, and reflected upon the walls of these cavities so 
 as to form shut sacs. They have been rudely compared 
 to a double night-cap, the layer immediately in contact 
 with the head being analogous, to the portion of serous 
 membrane immediately investing the viscera, while the 
 external layer is likened to the part reflected upon the 
 walls of the cavity, the space between them being the un- 
 adherent, free, secreting, and absorbing surface. One of 
 these belongs to the brain and spinal cord ; from its thin- 
 ness and delicacy it has been compared to the spider's 
 web, and therefore named the arachnoid membrane. It 
 covers the different surfaces within the skull and spinal ca- 
 nal. There constantly exhales from it a thin vapour, which 
 preserves the different parts moist, enabling them to glide 
 easily upon one another in the slight movements which 
 take place between them. In the chest there are three of 
 these membranes : one investing the heart, and from that 
 circumstance named the pericardium ; the others termed 
 pleura. The two pleurae adhere to the external surface 
 of the lungs, and are reflected upon the inner side of the 
 
206 ABSORPTION FROM SEROUS MEMBRANES. 
 
 walls of the chest. They divide the thorax into two late- 
 ral cavities. In these bags a vapour exhales to preserve 
 the surfaces moist and slippery. The most extensive of 
 all the serous membranes is situated in the abdomen ; it 
 not only furnishes a covering to the contents and walls of 
 the belly, but by its numerous and extensive folds its 
 surface is still farther extended, so as to form one of the 
 most expanded in the body. One of the most remarkable 
 of these folds proceeds from the inferior convexity of the 
 stomach, over the transverse portion of the colon, below 
 which it is doubled upon itself. This is known under the 
 name of omentum or apron. It affords occasionally lodge- 
 ment for a considerable quantity of fat, and extends over 
 the front of the bowels between them and the parietes. 
 Besides increasing the surface for absorption and secretion, 
 it serves the purpose of a roller in machinery, being a 
 moveable body interposed between two other moveable 
 bodies, by which motion is facilitated and friction dimi- 
 nished ; but its vast superiority over similar mechanical 
 contrivances of art is displayed, not only in its delicacy 
 and pliability, but in furnishing a lubricating fluid in a 
 quantity commensurate with the expenditure. There is 
 a membrane within the eye secreting the aqueous hu- 
 mour, and another in the internal ear, which are similar 
 to the more extensive serous membranes of the cavities. 
 
 The fluid exhaled from these membranes is analogous 
 to the serum of the blood, but it differs somewhat as deri- 
 ved from each. That of the arachnoid contains very little 
 albumen, probably from the extreme minuteness of the 
 vessels which discharge it ; for even after being long sub- 
 jected to inflammation, no red vessels can be observed 
 upon that membrane, the loss of transparency, and a cer- 
 tain degree of thickness, being the only change it appears to 
 have undergone, while the thicker and more dense pericar- 
 dium, pleura, and peritoneum discharge a fluid more close- 
 ly resembling the serum. When affected with inflamma- 
 tion, a large quantity of albumen is secreted, which occa- 
 
ABSORPTION FROM JOINTS. 207 
 
 sionally coagulates so as to glue the different parts to each 
 other ; sometimes the serum is even bloody, and in other 
 cases its character is changed into a pus-like fluid. In 
 the healthy state an accurate balance is preserved be- 
 tween exhalation and absorption in these bags; but if 
 this balance be subverted, either from the increase of se- 
 cretion, or from the diminution and obstruction of absorp- 
 tion, then an accumulation takes place constituting a dropsy. 
 Such accumulation cannot take place within the skull 
 and spinal canal to any considerable extent, unless they 
 yield to the internal pressure, as they occasionally do in 
 infancy and childhood before the bones are firmly united. 
 Thus, water in the head may collect to a very great ex- 
 tent. In one instance where the patient laboured under 
 the disease for twenty-one years, we took from the skull 
 ten pints and a quarter of limpid fluid; and even lar- 
 ger quantities have been observed. Similar collections take 
 place in one or other or both of the two pleurae, which are 
 accompanied with considerable embarrassment of the 
 function of respiration, and may prove fatal from the 
 mechanical pressure on the lungs preventing them from 
 duly performing their office. So likewise dropsy occurs 
 in the pericardium when the movements of the heart are 
 impeded and disturbed. From the construction of the 
 walls of the chest dropsies within that cavity are necessa- 
 rily attended with a comparatively small quantity of water; 
 whereas in the abdomen, surrounded with walls which 
 admit of great distension, the accumulations which some- 
 times take place are amazing, several gallons being in some 
 instances drawn off by the surgeon at one tapping, and 
 that repeatedly from the same person. In all these cases 
 the water is merely to be considered as the consequence 
 of disease, not the disease itself, though it may by me- 
 chanical pressure be productive of serious results. 
 
 Now when we reflect that in all these cavities, during 
 the whole course of our existence, watery fluid is con- 
 stantly poured out, and therefore requires to be as con- 
 
208 ABSORPTION FROM JOINTS. 
 
 stantly removed, we perceive how accurately the balance 
 between the two functions must be preserved. The 
 slightest deviation from the natural state must be follow- 
 ed by consequences incompatible with the health, and 
 even the life of the individual. But so admirably are 
 these functions adjusted that accumulations of serum are 
 of rare occurrence, when the number of causes which tend 
 to produce them are taken into account, or they arise from 
 such slight and temporary causes that the parts are easily 
 and speedily again rendered conformable to their wonted 
 healthy action. The rapidity with which these collec- 
 tions occasionally disappear sufficiently indicates how very 
 actively absorption may take place in these serous mem- 
 branes. Besides, experiments have been performed on 
 living animals, in which large quantities of fluids having 
 been thrown into these sacs, have been found to be car- 
 ried off in the course of an hour or two. 
 
 The joints are furnished with membranes which cover 
 the articular surfaces, and pour out the synovial fluid. 
 In their structure and general appearance they very 
 much resemble the serous membranes ; they are, how- 
 ever, more dense and less elastic, and the fluid which 
 they secrete differs somewhat from that of the serous 
 sacs, being viscid and tenacious, from the presence of 
 a principle resembling mucilage. Besides the capsules 
 of the joints, there are in various parts of the body 
 little synovial pouches like air cushions, placed be- 
 tween muscles and the asperities of bones, and likewise 
 interposed between muscles themselves, where they would 
 otherwise be liable to pressure on each other : they are 
 like the Macintosh air cushions, but of a more excellent 
 construction, for they accurately adapt themselves to the 
 varying forms and positions of the different parts, and 
 the quantity and quality of synovia furnished by these 
 capsules and pouches correspond to the extent and con- 
 tinuance of the motion to which they are exposed. 
 When they have been excited for some time in an inordi- 
 
ABSORPTION FROM CELLULAR MEMBRANE. 209 
 
 nate degree, as from a long journey, after a little rest the 
 secretion becomes deficient, and the joints and limbs stiff, 
 but on being roused again into action by exercise, they 
 pour out a due quantity, and the stiffness disappears. 
 Absorption from these surfaces must be commensurate 
 with secretion, otherwise an accumulation takes place, as 
 sometimes happens, forming dropsy of the joints, which 
 may be discussed by promoting absorption by means of 
 friction, liniments, blisters, &c. 
 
 The cellular membrane is the most universally diffused 
 of all the tissues of the body. It forms a constituent of 
 almost every organ, and serves to separate the different 
 parts from each other, and to constitute .the general bond 
 of connexion between them. It is formed of an infinite 
 number of small thin membranous plates, forming cells of 
 an irregular shape, and strengthened by filaments crossing 
 in different directions. These cells communicate with each 
 other. They vary in the size and strength of their walls in 
 different situations. From the surface of the plates form- 
 ing the cells a serosity is exhaled, which preserves them 
 moist and lubricated. This does not appear to differ 
 from that furnished by the serous sacs. Dispersed 
 through the cellular tissue of several parts of the body, 
 there are other cells, in which fat accumulates, distinct 
 apparently from those which secrete serum, and which 
 do not communicate with each other. The fat cells vary 
 much in size and shape in different parts of the body. 
 They are large, and of an irregular shape in the orbit 
 of the eye, and around the kidneys, small and of 
 a spherical form in the scalp. Some parts always con- 
 tain fat, as the orbits, the soles of the feet, and the extre- 
 mities of the fingers and toes; others generally have 
 more or less, as immediately under the skin, around the 
 heart, in the folds of the peritoneum, and around the kid- 
 neys ; while with the functions of others its presence is 
 incompatible, as the eyelids, the brain, &c. 
 
 The quantity of fat in the body, even in a perfect state 
 
210 INTERSTITIAL ABSORPTION. 
 
 of health, varies prodigiously, from scarcely an -ounce or 
 two in some living skeletons, as they are termed, to 
 the monstrous accumulations of several hundred pounds. 
 Both the serosity of the cellular membrane and the fat 
 may be deposited in greater quantity by the secernants 
 than the absorbents may be able to remove. In some 
 cases of great laxity and debility, the serosity accumulates 
 in the depending parts of the body, and thus the feet and 
 ancles may swell during the day, and again the swelling 
 entirely disappear, after the horizontal posture in bed, in 
 the morning, the fluid having been carried off during the 
 night by absorption. From the obstruction offered by 
 the enlarged womb in the latter stages of pregnancy to 
 the return of fluids, the lower limbs frequently swell, es- 
 pecially towards evening. In diseased states, the quan- 
 tity of serum collected in the cellular membrane is fre- 
 quently very great in this form of dropsy ; and when a 
 favourable change is effected, it is as rapidly removed by 
 the absorbents. 
 
 Lastly, The fluids are not the only parts of the organ- 
 ism of living beings which are subject to constant removal 
 and replacement, but every tissue, and every particle of 
 which that tissue is composed, sooner or later become unfit 
 for the situation in which they are placed, and requires, 
 therefore, to be removed, in order to be replaced by an- 
 other better suited to the purpose. The animal body 
 does not grow by additions, like a crystal, nor by simple 
 dilatation and distension of the individual parts, which 
 neither their texture nor organization admit of; but every 
 old particle is removed, and a fresh one deposited in its 
 stead ; or if growth and enlargement be going on, there 
 is not only depositation in proportion to the expenditure, 
 but an increase in the number of the materials of which the 
 organ is composed. The bones of the child are very dif- 
 ferent in density, form, and texture from those of the 
 adult, and so it is also with the other solid parts of 
 the body. We perceive, likewise, tumours are frequently 
 
INTERSTITIAL ABSORPTION. 211 
 
 developed from diseased action, and again removed by 
 absorption. In short, from the first dawn of our exist- 
 ence till life is closed, there is a perpetual and unceasing 
 contention between the vessels which deposit new matter, 
 and those which remove the old, the result of the actions 
 of both constituting nutrition. 
 
 At the commencement of life, the preponderance is in 
 favour of the depositing or secreting vessels. From day 
 to day the framework is enlarged, and the different or- 
 gans in succession gradually unfolded, till they reach their 
 full development. For a time the two functions are 
 equipoised, and the body appears to suffer little or no 
 perceptible change ; but as age advances, many of the 
 secreting vessels are obliterated ; the organs shrink one 
 after another, at last become unfit for carrying on the 
 operations of the machinery, and the scene closes. 
 
 When the balance is subverted between the two 
 functions, either accumulation or diminution must be 
 the result, producing growth or decrease, according to 
 the activity of the one or of the other. The term inter- 
 stitial absorption is applied to the function, as thus exer- 
 cised upon each individual tissue of the body. 
 
 The absorbents appear to have less vitality and irrita- 
 bility, and to participate less in the various conditions of 
 the system in health and disease, than the secreting ves- 
 sels ; and therefore when the action of the latter is dimi- 
 nished or suspended, that of the former continues, conse- 
 quently its effects become more perceptible, and it seems 
 to be increased ; whereas it may not in such cases have 
 undergone any augmentation, but even suffered decrease, 
 though not to the same extent with its antagonist. In 
 fevers and other acute diseases, where the digestive func- 
 tion is stopped, and the expenditure of materials still goes 
 on, emaciation is the consequence ; and the same occurs 
 from starvation and other causes of inanition, shewing 
 that the absorbents continue to perform their office. When 
 a morbid growth has taken place, the object of the medi- 
 
212 ABSORBENT SYSTEM. 
 
 cal practitioner is to endeavour to diminish the action of 
 the vessels which nourish it, and thereby produce a pre- 
 ponderance in favour of absorption ; or he determines the 
 force of the circulation to some other part, as the kidneys 
 or skin, so as to procure copious evacuations. 
 
 When the depositing vessels are interrupted, as from 
 pressure of a tumour or other causes, absorption will still 
 go on, so as to remove the parts thus deprived of their due 
 quantity of nourishment. If the pressure be upon a bone, 
 the earthy part is first removed ; or if on a muscle, the 
 fibrin is that which is first carried off, leaving the cartilage 
 of the one and the cellular substance of both to be the last 
 for removal. Now, this apparent selection of earthy mat- 
 ter and fibrin arises, not from any preference the absor- 
 bents have for either, or from their being more easily ab- 
 sorbed, but from there being no fresh depositation of them 
 to compensate for what is removed by absorption. 
 
 When blood or any other fluid is extravasated, as from 
 blows or bruises, these substances being placed out of the 
 sphere of vitality, and in every respect become dead 
 foreign matter, the absorbents nevertheless continue to 
 act upon them, and in time carry them off altogether. 
 In the same way, when a bone or any part has been de- 
 prived of life, the absorbents operate upon them so as 
 to cause their removal, while the secernants may at the 
 same time be engaged in the production of new ones in 
 their stead. From these circumstances the absorbents 
 have been termed the scavengers of the body, as they are 
 constantly engaged in removing old worn-out and super- 
 fluous matter from every part of the system. 
 
 Absorbent System. The term absorbent system is here 
 meant to be confined to those organs which are chiefly 
 engaged in taking up and conveying from the different 
 parts of the body the various materials of which it is com- 
 posed, although they do not exclusively perform this office. 
 The absorbents have been described by some as a subor- 
 dinate set of veins, differing from the red veins, in trans- 
 
ABSORBENT SYSTEM. 213 
 
 mitting colourless instead of red blood, but terminating 
 in the veins before they reach the heart. In their struc- 
 ture, however, as well as in their office, there exist cha- 
 racters which sufficiently entitle them to rank as separate 
 organs. 
 
 The ancients and earlier modern anatomists appear oc- 
 casionally to have noticed these vessels, but they had no 
 correct notion of their use. Aselli, an Italian, seems to 
 have been the first who observed the lacteals, which he 
 did on opening a living dog in the year 1622, and ascer- 
 tained their office, but believed that they conveyed their 
 contents to the liver. Pecquet, in 1657, discovered the 
 absorbent trunk in which they terminate, now known 
 under the name of the thoracic duct. Much about the 
 same time similar vessels were noticed to arise from dif- 
 ferent parts of the body, containing a colourless fluid or 
 lymph, hence named the lymphatic absorbents, which led 
 to an acrimonious dispute as to the priority of discovery 
 between Jolliffe, an Englishman, Rudbeck, a Swede, and 
 Bartholin, a Dane, into the merits of which it is unneces- 
 sary for us to enter. During the last century, by the 
 labours of the Hunters, Hewson, Cruikshank, Mascagni, 
 and the second Monro, they were observed proceeding 
 from every part of the body, with perhaps the exception 
 of the brain and spinal marrow, though Mascagni has 
 figured some small lymphatics from the brain, which he 
 succeeded in detecting and injecting. Their existence 
 has been disputed in these parts, as well as in the inte- 
 rior of the eye, for no other reason than that they have 
 not been seen by those who have looked for them. Mas- 
 cagni devoted great attention to the investigation of the 
 absorbent system, and his experience enabled him to inject 
 these vessels with greater success than any other person. 
 Besides the general difficulties in the way of preserving 
 such preparations, he had to contend against the warmth 
 of the climate of Italy ; and therefore contented himself, 
 after a successful preparation of the parts, with an accu- 
 
214 ABSORBENT SYSTEM. 
 
 rate representation of them, and there appears to be no 
 reason to doubt his integrity. 
 
 It requires no small experience and dexterity to trace 
 and properly display the minute parts of organized struc- 
 tures, and he who is deficient in the necessary tact and 
 experience has no right to dispute the existence of ar- 
 rangements which he finds himself incapable of unfold- 
 ing. No one dreamt of the stars, and systems of stars, 
 which the telescope has declared in the hands of a Kepler, 
 a Newton, and a Herschel ; nor imagined the structures 
 which have been unfolded by a Hooke, a Lewenhoek, 
 and a Bauer, by means of the microscope. There can 
 be no doubt that the function of absorption is carried on 
 in these parts, as well as in the rest of the body. The 
 fact that the lymphatic glands of the neck have been ob- 
 served to be affected in diseases of the brain, tends to prove 
 the existence of absorbents in that organ. Many as have 
 been and still are the disputes as to the merits due to differ- 
 ent individuals, with respect to discoveries made in anatomy 
 and physiology, and as to the respective credit belonging 
 to each one who may have contributed to the establish- 
 ment of a popular and generally received doctrine, the 
 absorbent system has furnished an arena in which contro- 
 versies with regard to these points have been carried on 
 with greater keenness and acrimony than in any other 
 department of these sciences. 
 
 The absorbents have a greater resemblance to veins in 
 their structure and functions than to arteries. They consist 
 of two layers or coats : the external is cellular, the inter- 
 nal thinner, and similar to the lining membrane of the 
 other blood-vessels, being smooth and slippery, and be- 
 dewed with an exhalation from the extreme arteries sup- 
 plying those coats. The extreme thinness and trans- 
 parency of their coats, along with the colourless nature 
 of the fluids which they generally convey, was the reason 
 of their existence being so long unknown, and the diffi- 
 culty which exists in tracing them. Notwithstanding the 
 
ABSORBENT SYSTEM. 215 
 
 thinness of their coats, they possess considerable strength, 
 so as to support a higher column of mercury than arteries 
 or veins of the same diameter. The internal coat is folded, 
 so as to form little semilunar valves, generally in pairs, 
 which, like the corresponding valves of the veins, prevent 
 the retrograde movement of their contents, and force it 
 to pursue the course towards the heart. These valves 
 are exceedingly numerous, so that when injected they 
 present the appearance of a string of beads. 
 
 We noticed, when treating of the veins, in the chapter 
 on circulation, that it is only in the veins of those parts 
 of the body which are subject to voluntary motion, that 
 valves exist, and that there are no valves in the veins 
 of the viscera. The absorbents are different in this re- 
 spect, being furnished with valves equally in every part, 
 whether superficial or deep-seated, whether subjected 
 to the will or beyond its control. These valves must 
 therefore be more essential to the action of the absorbents 
 than that of the veins. The veins being principally en- 
 gaged in returning the blood from the various organs of 
 the body, and the blood being impelled along them from 
 the force communicated from the arteries behind, it flows 
 through these vessels, even independently of the action 
 of the veins themselves, while the fluids in the absorbents 
 are not influenced by any such impelling power. From 
 absorbents possessing less irritability and vital con- 
 tractility than other vessels, and their contents being 
 transmitted chiefly by their mechanical elasticity, possibly 
 aided however by a proper vital contractile power, there 
 arises the necessity for mechanical contrivance to insure 
 the flow in the proper direction of the fluids they trans- 
 mit ; hence the number and universal distribution of the 
 valves. These valves offer a great impediment to the 
 successful injection of the absorbents, since it is necessary 
 to introduce the instruments into their minute further 
 extremities, whereby it becomes exceedingly difficult to 
 trace them with any degree of success. 
 
216 ABSORBENT SYSTEM. 
 
 The absorbents are much more numerous than either 
 of the other two sets of blood-vessels. Though they do 
 not form any considerable trunks, they establish frequent 
 and reiterated unions with each other, so that if one is 
 obstructed, the contents can easily pass along another 
 channel. Like the veins in the limbs and external parts, 
 they are divided into two sets, the superficial and deep- 
 seated, probably for the same reason which we had oc- 
 casion to suggest was the purpose served by a similar 
 arrangement of veins, and they generally pursue the 
 course of the venous trunks, just because that is either 
 the most direct or the most secure. 
 
 Although the thoracic duct be often described as the 
 common trunk of the absorbent system, from its being 
 larger and more regular than any of the other absor- 
 bents, it does not appear to deserve that distinction, for 
 many of the absorbents terminate in the veins, especially 
 in the right subclavian, without joining it, and several 
 terminate in veins at a considerably greater distance from 
 the heart. Indeed, the absorbents from the lower limbs, 
 abdomen, and chest, could have in no other direction pur- 
 sued so safe a course as that along the vertebral column, 
 just as we perceive the veins from the upper part of the 
 walls of the abdomen and chest unite in the formation of 
 the vena azygos. The final termination, then, of all the 
 absorbents, is in the veins, generally the two large veins 
 under the collar bones, named the subclavians. Al- 
 though the absorbents do not unite so as to form vessels 
 of any considerable size, they are exceedingly numer- 
 ous, and constitute bundles of net-work in almost every 
 part, especially on the inner side of the arms, legs, and 
 thighs, on each side of the neck, and along the vertebral 
 column. Their valves preventing successful injection, 
 they require great care and expertness in order to trace 
 them. On one occasion, in the class-room of the distin- 
 guished teacher of anatomy in Edinburgh, the late Dr 
 
LYMPHATIC GLANDS. 217 
 
 Barclay, the thoracic duct, as usual, was filled with quick- 
 silver, for the purpose of demonstration to the class, when 
 the injection flowed from the duct to the absorbents of 
 the lungs, diaphragm, and walls of the chest, and that too 
 so exceedingly minutely and generally, that they formed a 
 most splendid appearance of lace-work of silver tissue, 
 leaving not a space on these surfaces into which the point 
 of the smallest needle could be inserted without wound- 
 ing several of the vessels of which it was composed. This 
 appearance was altogether unprecedented, and left an im- 
 pression on the minds of those who had the good fortune 
 to witness it, which can never be obliterated, and which 
 conveyed an idea of the excessive number and universal 
 distribution of these vessels which no description can con- 
 vey. In this instance, either the valves did not exist, or 
 they acted imperfectly. No anticipation having been en- 
 tertained of such an occurrence, the body had been dis- 
 sected in such a manner that the quicksilver so rapidly 
 made its escape that in less than an hour scarcely a trace 
 was left of this interesting appearance, except on the 
 memory of those who saw it. 
 
 A circumstance which distinguishes the absorbents in 
 an especial manner, is their passing through certain bodies 
 termed glands in their course. These are fleshy bodies of 
 a lenticular or globular form, abundantly supplied with 
 blood, varying in size from that of a filbert to the smallest 
 grain of sand ; so minute are several of them that they are 
 invisible, excepting when they become enlarged by dis- 
 eased action, without which their existence could not be 
 suspected. They are numerous, and collected into clus- 
 ters in some situations, as along the sides of the neck, in 
 the arm-pits, groins, at the bifurcation of the windpipe, 
 and in the abdomen, between the layers of the mesentery. 
 When an absorbent approaches one of these bodies, it 
 begins to divide into numerous twigs which enter the 
 gland, in the substance of which the different branches of 
 these vessels freely communicate with each other, and also 
 
218 
 
 LYMPHATIC GLANDS. 
 
 establish connections with veins ; so that injections pass 
 from the one into the other. The number and size of the 
 arteries, also, are much greater than is merely requisite 
 for their nourishment ; hence the probability that the arte- 
 rial blood is subservient to the function carried on in these 
 organs. The absorbents passing out of the glands again 
 unite into larger branches, and in the same way they may 
 enter and pass out of these bodies several times before they 
 ultimately pour their contents into the veins. The an- 
 nexed figure, formerly introduced, shewing the passage 
 of the lacteals through the glands of the mesentery, will 
 illustrate these points. 
 
 FIG. 15. 
 
 We have already had occasion, when treating of the 
 passage of chyle, to state, that a change is effected upon 
 that fluid during its passage through these bodies, whereby 
 
LYMPHATIC GLANDS. 219 
 
 it becomes more elaborated, and approaches more closely 
 to the constitution of blood. It is not unlikely that a 
 mutual interchange is effected between the three fluids 
 namely, those of the artery, the vein, and the absorbents. 
 The fluid conveyed from every part of the body ought not 
 to be considered as merely old worn-out and useless matter, 
 otherwise why is it again introduced into the general circu- 
 lating mass ; if only for the purpose of its subsequent dis- 
 charge, we should have expected a more direct course to the 
 organ by which it should be evacuated. This not being the 
 case, it is fair to infer that it serves some useful purpose in the 
 animal economy. It may be stated, that the blood in 
 the veins, the lymph in the lymphatics, and a great part 
 of the chyle in the lacteals being derived from arterial 
 blood, so do these again unite to be reformed into arte- 
 rial blood in the lungs, and thus a circle of decomposi- 
 tion and rccom position of the one and of the other, is 
 continually taking place in the lungs, and in the system 
 at large, a change being perceptible in the chyle, which 
 we are more easily enabled to detect, from its colour and 
 constitution, as well as from its quantity, when proper 
 advantage is taken after a meal for procuring it. An 
 analogous change may be inferred to be effected on the 
 lymph in its passage through the lymphatic glands. The 
 materials which the absorbents take up and convey being 
 as various as the tissues of which the body is composed, the 
 heterogeneous matters, in filtering through these glands, 
 and on being subjected to their action, are both thoroughly 
 mechanically intermixed, while they are converted into a 
 fluid of a more homogeneous nature, and qualities which 
 they might possess previous to entering them, may be so 
 modified and altered as to adapt them to their introduc- 
 tion into the general circulation, whereas, had they been 
 introduced without undergoing such change, their pre- 
 sence might be highly prejudicial. It is well established 
 that many substances act with much greater intensity 
 when immediately injected into the blood, than when 
 
220 LYMPHATIC GLANDS. 
 
 they are conveyed into the system through the circui- 
 tous and intricate channels of absorption. The deadly 
 poison of the rattlesnake, or of the cobra-de-capello, may 
 be swallowed with impunity, while the introduction of 
 the most minute quantity by a wound inevitably causes 
 death, in some instances in a few minutes. In the former 
 case the poison is digested, and its composition and pro- 
 perties altered and destroyed : in the latter it acts on 
 the body in its state of unchanged integrity. 
 
 But the glands, besides acting as vital agents in al- 
 tering and elaborating the fluids transmitted through 
 them, offer a mechanical obstruction to the too rapid in- 
 troduction of matter into the general system. It is well 
 known that the animal frame will bear the introduction 
 of foreign matter with impunity, when it enters in detail, 
 which it is incapable of resisting when rapidly applied 
 in the mass ; the system having time either to accom- 
 modate itself to the circumstances, or expel the inju- 
 rious matter through the excretory organs in the for- 
 mer case, while in the latter there is neither time to 
 guard against its influence, or for its expulsion. We can 
 often trace the course of an absorbent which has conveyed 
 acrid or poisonous matter, by its becoming inflamed ; red 
 streaks being observed from the point where the substance 
 was absorbed, along the course of the absorbents, up to 
 the next lymphatic gland, in which its progress is ar- 
 rested. The gland becoming irritated from the presence 
 of the poison, inflames and swells, and frequently sup- 
 purates, establishing a new secretion. In many cases, no 
 trace of the poison can be detected till it reaches the 
 gland, which becomes hard, painful, and swollen. There 
 can be no doubt that this arrestment of the poison in its 
 progress tends to the preservation of the system, so 
 much so, that I believe that I owe the preservation of my 
 own life to this conservative arrangement of the absorb- 
 ing system, as the following account will show, and 
 which is here introduced by way of illustration. 
 
DISEASE FROM PUNCTURE. 221 
 
 Eight years ago, a patient of mine died under circum- 
 stances which rendered me suspicious that the fluids were 
 in such a condition as was likely to be productive of the 
 worst effects, if introduced into a healthy person, either 
 by puncture, scratch, or other kind of wounds inducing 
 that peculiar and often fatal disease characterized among 
 other symptoms by a diffuse inflammation of the cellu- 
 lar membrane. My attention having been particularly 
 directed to the nature and treatment of this affection, 
 from eminent professional men having been cut off by it, 
 from having witnessed the agonies and death of some of 
 my own friends and fellow-students, and from my occu- 
 pations at the time, I chose this subject for my proba- 
 tionary essay submitted to the Royal College of Surgeons 
 of Edinburgh, when I joined that body. 
 
 I was not in the least deterred from requesting the ex- 
 amination of the body of my patient, there having been 
 symptoms present which made investigation desirable. 
 From the suspicions excited in my mind with respect to 
 the state of the body, I would not permit my pupils who 
 accompanied me in any respect to interfere with the opera- 
 tion, as I considered that my experience rendered me more 
 expert in the use of the instruments. Having employed 
 every precaution, the operation was conducted in the usual 
 way, and I left the house to attend to my duties, without 
 the slightest suspicion or apprehension, having similarly 
 examined some hundred bodies before. After noting 
 down the appearances observed, the subject was entirely 
 dismissed from my mind. I was in as excellent a state 
 of health as I had ever been in my life, and enjoyed per- 
 fect elasticity both of mind and body. 
 
 Next morning at breakfast I felt somewhat chilly, and 
 did not enjoy my meal with my usual appetite. After 
 breakfast I called upon a patient at some distance, when 
 I suddenly became affected with great prostration of 
 strength, sickness, and shiverings, and for the first time 
 
222 DISEASE FROM PUNCTURE. 
 
 became alarmed from a stiffness and pain in the armpit. 
 On narrowly inspecting my hand I found that a small 
 piece of scarf skin had been abraded from the back of 
 the ring finger of the right hand, which was a little red, 
 but without pain or swelling, and not the slightest trace 
 of an inflamed absorbent could be noticed. 
 
 In the evening the nature and character of the disease 
 were fully established. From having made the affection 
 the subject of careful study and observation, and having 
 had some experience of its treatment, I did not feel the 
 slightest apprehension as to the issue. 
 
 I passed the night in great pain and distress, and on 
 the following day the arm was swelled from the wrist 
 upwards ; the swelling also extended to the chest as far as 
 the breast bone in front to the spine posteriorly on the 
 right side, arid also up the neck to the ear. The late dis- 
 tinguished Professor Duncan junior and other profes- 
 sional friends saw me. The pain was most excruciating, 
 rendering motion impossible; but the mind was un- 
 affected, either with apprehension or otherwise, except 
 with the fear that delirium might supervene, and render 
 me unfit to conduct the treatment, or judge of the sug- 
 gestions of my friends. 
 
 The night was again passed without sleep, and the 
 symptoms became more and more aggravated. About 
 noon of the third clay I experienced for the first time a 
 perfect indifference to life. Though suffering great agony, 
 there was no desire for death, but as I repeat, a perfect 
 indifference as to the result. Nor was I at the time con- 
 scious, nor am I yet convinced, that my mind was other- 
 wise unhinged. 
 
 Besides leeching, the principal reliance was placed on 
 the blue pill, which from the first time the disease un- 
 equivocally displayed itself was regularly taken every 
 two hours, in the dose of two of the ordinary pills, 
 its action on the bowels being restrained by the use of 
 kino. 
 
DISEASE FROM PUNCTURE. 223 
 
 After the twenty-sixth dose indications of the medi- 
 cine having made its impression presented themselves. 
 About three o'clock in the morning of the fourth day, for 
 the first time, I fell asleep, and awakened at half-past 
 seven completely drenched in most profuse perspiration. 
 At the same time the love of life was completely restored, 
 and although I was fully aware that the crisis had passed 
 favourably, for the first time I became exceedingly 
 anxious, as, in the state of helpless debility and exhaus- 
 tion to which I w T as reduced, I well knew that the 
 slightest relapse would most probably have a fatal termi- 
 nation. Indeed it is impossible for me to describe the 
 very great and remarkable mental change which a few 
 hours had brought about. In the evening an opening was 
 made in the armpit, from which about a pint of pus was 
 discharged, and from this time I slowly and progres- 
 sively recovered. It was not, however, for more than 
 twelve months that the discharge entirely ceased, dur- 
 ing which I conceive my constitution underwent a 
 greater change than in seven years of my life. 
 
 The absorbent system, then, consists of vessels and 
 glands. The vessels are extremely numerous, arising from 
 every part of the body, never collected into trunks of 
 any considerable size, having their transparent but dense 
 and tough coats freely communicating with each other, 
 abundantly furnished with valves, and finally terminating 
 in the veins. The glands are firm fleshy bodies copious- 
 ly supplied with blood, varying in size, frequently col- 
 lected into clusters, through which the absorbents pass 
 once or several times in their course to the centre of cir- 
 culation, in which they are variously coiled and inter- 
 laced with each other, and with the arteries and veins, 
 establishing frequent communications with each other, 
 and with the veins, and where their contents are for 
 sometime arrested, and subjected to a certain degree of 
 alteration. 
 
224 ACTION OP ABSORBENTS. 
 
 This system is usually divided into the lacteal and 
 lymphatic absorbents, not from any difference which can 
 be observed either in their structure or the function which 
 they perform. This distinction between lacteals and lym- 
 phatics is to be rejected, as it is apt to mislead and pro- 
 duce an erroneous notion with respect to them, since 
 the lymphatics do not always convey a colourless fluid 
 or lymph, nor do the lacteals always transmit chyle, 
 the former frequently containing fluid of a reddish tint, 
 and the latter occasionally transparent lymph. 
 
 Mode of Action. The extremities of the absorbents are 
 frequently described as important agents in the function 
 of absorption, under the name of mouths of the lacteals 
 and lymphatics, and the action of these mouths described 
 in such a manner as would lead to the supposition that 
 they are easily observed, and their office, and mode in 
 which they perform it, fully ascertained. This is, how- 
 ever, by no means the case, the greater part of what has 
 been written. on this subject being more a matter of con- 
 jecture than observation ; and when the extreme minute- 
 ness of these extremities is considered, when we reflect 
 that Leuwenhoek estimates that a single grain of sand 
 could cover some millions of them, we will be less dis- 
 posed to place implicit reliance upon detailed descriptions 
 respecting them. The sum of our knowledge with regard 
 to this point is, that we know that fluids from the surfaces, 
 and the materials from every part of the body, do enter 
 the absorbents ; but whether that entrance be effected in 
 consequence of a mechanical structure such as is observed in 
 the capillary tubes, and therefore named capillary attrac- 
 tion, or by a proper vital action analogous to the vital con- 
 tractile power with which the extremities of the arteries are 
 especially endowed, cannot be determined, though it is 
 probable that both are to a certain degree instrumental in 
 the performance of the duty. 
 
 It has been ascertained that substances readily permeate 
 
ACTION OF ABSORBENTS. 
 
 225 
 
 organic tissues, without any special reference to the tex- 
 ture of these tissues, but rather according to the laws of 
 attraction and repulsion, which may operate on the fluids 
 which these tissues separate from each other. 
 
 If w r e take an in- 
 strument such as re- 
 presented in Fig. 16, 
 resembling a bottom- 
 less phial, , with a 
 long stem like the 
 tube of a thermome- 
 ter, &, and cover its 
 lower orifice with a 
 piece of animal mem- 
 brane, as in Fig. 17, 
 at b, and fill the phial 
 half full with syrup, 
 mucilage, or milk, 
 
 FIG. 16. 
 
 FIG. 17- 
 
 and then place it 
 in the cup c, half filled with water, we shall find that 
 the water passes through the membrane into the syrup, 
 and that the fluid will ascend to any height in the stem, as 
 to d. On reversing the experiment, by filling the phial 
 and its tube quite full of water, and putting it in the cup, 
 having such fluids as mentioned placed in it, we shall now 
 find that the water passes out of the phial into the cup to 
 join the syrup or mucilage, and a descent will take place 
 in the stem to any extent, as to e. If a bladder be filled 
 with pure hydrogen gas and exposed to the air, in a short 
 time the bladder will be found to contain atmospheric air 
 alone ; in this instance the hydrogen lias passed out of the 
 bladder, and the atmospheric air entered into it, and both 
 changes have been effected simultaneously. 
 
 The roots of plants terminate in exceedingly minute 
 radicles, frequently, however, bulging out into small bul- 
 bous bodies, which have been termed spongiols. These 
 extremities are composed of a very delicate tissue without 
 
226 
 
 ACTION OF ABSORBENTS. 
 
 any cuticular covering, and very actively perform the office 
 of absorption by a kind of imbibition, or endosmose as it 
 has been called. They also give off fluids to the soil in 
 which they are planted, thereby imparting peculiar pro- 
 perties to it by exudation or exosmose. 
 
 When it is recollected that the internal surface of the 
 absorbents, however minute, is a secreting surface from 
 which an exhalation is poured out from the arteries dis- 
 tributed upon it, we can readily comprehend how these 
 vessels may be filled with fluids from the arterial blood, 
 and endowed with peculiar properties whereby they may 
 exert attraction for substances exterior to their coats ; and 
 when we know, as we do, that fluids easily penetrate 
 much thicker and even more dense membranes and other 
 tissues than the exceedingly thin and delicate coats of the 
 absorbents, we can have no difficulty in understanding the 
 manner in which they may pass into the absorbents. Fur- 
 ther, since gases, fluids, and even solids exert different 
 degrees of attraction and repulsion towards each other, 
 and since we observe that materials are taken up from 
 the alimentary canal, for example, by some vessels, and 
 rejected by others, it is quite possible to explain these 
 apparent selections and rejections on the above principles 
 without having recourse to any peculiar vital property 
 with which the absorbents or their minute extremities or 
 mouths may be endowed. 
 
 At the same time, there is every reason to believe that 
 the absorbents are not merely passive tubes : we have had 
 occasion, when treating of the arteries, to observe that 
 their minute capillary extremities possess considerable 
 irritability, and exert considerable influence on the circu- 
 lation, both in states of health and disease. That they 
 derive their nervous energy from a peculiar class of nerves 
 is sufficiently established : that the veins participate in 
 these properties and nervous influence, though in a minor 
 degree, is also evident. If irritability and vital action be 
 conceded to the capillaries of the arteries and veins, there 
 
ACTION OF ABSORBENTS. 227 
 
 appears to be no good reason for withholding them from 
 the absorbents, although, from the greater density of their 
 coats, it is probable that they possess a much inferior 
 degree of irritability than even the veins, and are less 
 under the influence of those causes which tend to inter- 
 fere especially with the action of arteries : hence circum- 
 stances which interrupt or totally destroy depositation or 
 secretion, as in the death of any particular organ, as a 
 bone or a morbid growth, produce little effect on the ab- 
 sorbents, which continue to carry on their action till the 
 part affected is entirely removed. 
 
 That the absorbents exert a certain degree of pressure, 
 is shewn by their expelling their contents with a consider- 
 able force when punctured ; but whether this depends upon 
 their being furnished with a muscular contractile power, 
 or upon mere mechanical elasticity, is also a question 
 which it is difficult to determine. The most careful and 
 close inspection has failed in detecting more than an ex- 
 ternal cellular coat, and an internal serous one. The mid- 
 dle, corresponding with the muscular coat of the arteries, 
 is universally omitted by anatomists in their descriptions ; 
 but though, from the minuteness of these vessels, we may 
 fail to observe muscular fibres, even when aided by the 
 microscope, its non-existence is inferred entirely upon 
 negative grounds, and, reasoning from analogy, a mus- 
 cular coat should be admitted in the absorbents. At all 
 events, the fluids, which are poured into them by the 
 arteries, being under the influence of the agencies to which 
 secreting vessels are subjected, and as the nature of the 
 fluids contained in them will regulate the attraction and 
 repulsion between them and substances exterior to their 
 coats, even on these grounds the introduction of ma- 
 terials into the absorbents cannot altogether be held as 
 arising from mere mechanical laws. 
 
 The pressure which the absorbents exert upon their 
 contents will impel them towards the heart, for the num- 
 ber of valves with which they are furnished will permit 
 
228 VENOUS ABSORPTION. 
 
 the fluids they convey to pursue no other course. There- 
 fore, admitting that they have no muscular coat, their elas- 
 ticity will be sufficient to explain the motion of their 
 contents without the aid of capillary attraction. The 
 movements in surrounding parts, such as muscular con- 
 tractions, will also operate to a certain extent, and even 
 the motions of the vessels which they accompany \vdll in 
 some measure contribute to the same effect ; the dif- 
 ferences also produced on the atmospheric pressure within 
 the chest, and on the surface of the body, already alluded 
 to, as an agent subservient to the circulation of the blood, 
 will exert its influence in promoting the current in the 
 absorbents, which, as just now observed, can take place 
 only in one direction. 
 
 Venous Absorption. Previous to the discovery of the 
 lymphatics, absorption, as far as it was understood, was 
 supposed to be carried on entirely by veins. As the exist- 
 ence, structure, and use of the lacteals and lymphatics 
 became gradually unfolded, the opinion that these vessels 
 exclusively executed the office of absorption became gene- 
 rally and almost universally entertained. Farther observa- 
 tion and experiment have shewn that this duty is shared 
 by the veins, and that also to no inconsiderable extent. 
 
 Several lacteals and lymphatics are observed to pour 
 their contents into veins in the immediate neighbourhood 
 of the seat of their origin, and such connexions more espe- 
 cially occur in the lymphatic glands ; still, independently 
 of the communication thus established between these ves- 
 sels, the veins have been shewn to perform the function 
 of absorption by their own proper action. When we 
 considered the removal of substances from the alimentary 
 canal, we had occasion to state that the lacteals are the 
 chief instruments by which the chyle is carried off; but 
 that water, chemical substances, various colouring and 
 odorous principles, found entrance by the branches of the 
 vena portae, whereby they were carried through the liver 
 before they were introduced into the general mass of blood. 
 
CAUSES INFLUENCING ABSORPTION. 229 
 
 In the same way, substances which can be identified by 
 their odour, colour, or chemical properties, have been in- 
 jected in the intestinal canal into the serous sacs, as into 
 the cavity of the peritoneum, into the windpipe, and into 
 the subcutaneous membrane. In all of these instances 
 they were found either exclusively, or more abundantly 
 in the \ r eins than absorbents, and in several cases they 
 could be detected in the former before any trace of them 
 could be ascertained in the latter. 
 
 Indeed there is nothing with regard to the functions 
 which the veins exercise incompatible with absorption, 
 the most important and well-marked difference between 
 the two sets of vessels consisting in the existence of the 
 fleshy bodies termed glands in the course of the lacteals 
 and lymphatics, the office of which appears to be to pro- 
 duce a certain degree of alteration and assimilation of the 
 matters they transmit previous to their introduction into 
 the general system. In the distribution and filtration of 
 the blood of the vena portas through the liver, a vein 
 which, arising as it does from the alimentary canal, and 
 therefore having presented to its radicles new and foreign 
 matter, an arrangement exists whereby similar effects can 
 be brought about ; and still further, in the secretion of 
 the bile from the blood of the vein in question, an oppor- 
 tunity is afforded for the removal of substances, the intro- 
 duction of which into the general circulation might prove 
 prejudicial. 
 
 Causes influencing Absorption. Several circumstances 
 tend either to accelerate or retard the function of ab- 
 sorption, and exert an important influence in many con- 
 ditions of health and disease. It has been shewn that 
 the states of repletion and inanition especially have great 
 influence in respect to the rapidity or slowness with which 
 materials are taken up, whether foreign to the body or 
 forming part of its constituents. 
 
 Experiments performed by M. Magendie, in illustra- 
 tion of this, may be here introduced. 
 
230 CAUSES INFLUENCING ABSORPTION. 
 
 " In a public lecture upon the operations of medicines, 
 I showed upon the living animal what are the effects of 
 an introduction of a certain quantity of water at 104 
 Fahrenheit, into the veins. In making this experiment, it 
 occurred to me to see what might be the influence of the 
 artificial plethora which I produced, upon the phenomena 
 of absorption. In consequence, after having injected al- 
 most two pints of water into the veins of a dog of ordi- 
 nary size, I introduced into his pleura a small dose of a 
 substance, with the effects of which I was familiar. I 
 was surprised to see these effects only take place seve- 
 ral minutes after the period at which they usually shew 
 themselves. I immediately repeated the experiment upon 
 another animal, and obtained a similar result. 
 
 " In another experiment, wherein I had introduced as 
 much water (about four pints) as the animal could sup- 
 port without ceasing to live, the effects did not shew 
 themselves at all; absorption had probably been pre- 
 vented. 
 
 " I might also make the opposite experiment ; namely, 
 to diminish the quantity of blood, and observe whether 
 absorption would then be more rapid : the event was 
 exactly what I had foreseen. An animal was bled, and 
 also deprived of about half a pound of blood ; the effects, 
 which should not have happened before the end of the se- 
 cond minute, shewed themselves distinctly before the 
 thirtieth second." 
 
 These experiments of M. Magendie illustrate the im- 
 portant effects which the different states of repletion and 
 inanition produce on the system, accounting for its greater 
 or less susceptibility to the impression of external agents 
 upon it, and enabling us to understand how various con- 
 ditions in these respects operate in modifying the function 
 of absorption. 
 
 After long fasting, the quantity of fluids being dimi- 
 nished in the body, absorption is effected with greater fa- 
 cility, and substances are rapidly taken up and introduced 
 
CAUSES INFLUENCING ABSORPTION. 231 
 
 into the system. Hence the greater risk of entering, 
 when fasting, apartments occupied by persons labouring 
 under contagious diseases, in consequence of the miasms 
 emanating from them being more easily introduced under 
 such circumstances. 
 
 All kinds of evacuents indirectly promote absorption, 
 such as blood-letting, purgatives, medicines which aug- 
 ment the discharge of urine, and those which increase per- 
 spiration : they are therefore had recourse to by the medi- 
 cal practitioner in diseases where his object is to effect 
 the removal of dropsical effusions, or morbid growths, and 
 this they are calculated to produce by their double effect 
 in diminishing the action of the arterial capillaries, and 
 favouring the function of absorption. 
 
 Whatever tends to relax arterial tension, and to lessen 
 the strength and tone of the system, is found to promote 
 absorption, and conversely, whatever excites the action 
 of the heart and arteries diminishes it. In this way nau- 
 seating emetics, exhibited with the view of causing vo- 
 miting when poisons have been received into the stomach, 
 increase the danger, by favouring their introduction into 
 the circulation, so that even if vomiting be excited, it may 
 be too late, a sufficient quantity of poison to effect a 
 fatal termination having been already introduced. 
 
 Mental causes operate in a similar manner ; hence de- 
 pressing feelings of the mind, such as fear, anxiety, and 
 despair, favour the propagation of contagious disease, 
 while confidence and hope act as conservative principles. 
 It has therefore been observed that a dog is in much less 
 danger from the bite of a viper when suddenly bitten, 
 than when he has been for some time gazing at the reptile, 
 and thereby more or less terrified by the sight. 
 
 From the consideration of facts like these, we may per- 
 ceive the important results arising from the relative condi- 
 tions of the different sets of vessels of the body, and mark 
 the connection which subsists between these conditions 
 and the functions to which the A T essels are subservient. 
 
232 CAUSES INFLUENCING ABSORPTION. 
 
 On these grounds we can also partly understand how, on 
 the exposure of two individuals to the same source of 
 contagion, the one may escape while the other is affected, 
 and likewise how the same individual may at one time 
 resist the causes of infection, while at another he becomes 
 subject to it, although under exactly the same external 
 conditions of exposure. 
 
233 
 
 CHAPTER VI. 
 
 SECRETION. 
 
 Preliminary Observations Classification of Secretions Matter of Perspiration 
 Scarf-skin serves as a barrier between the Body and the External World The 
 vast extent of the two general Mucous Membranes Only one Mucous Mem- 
 brane in Animals below the class of Mammalia Gaseous Exhalations Follicular 
 Secretions Unctuous Secretion of the Skin Necessity of Personal Cleanliness 
 Liquor of the Eye-lids Wax of the Ears Musk, and other odorous Secretions 
 of Animals Glandular Secretions Arrangement of the Glands Tears Effects 
 of the passions and emotions of the Mind upon Lachrymal Glands Why Women 
 and Children shed Tears easily Secretions connected with Digestion adverted 
 to Structure and use of the Kidneys The very compound nature of the Urine 
 Urine carries off the superfluous, useless, and worn-out particles from the System 
 The quantity of Urine regulates the balance of Fluids in the Body Sugar in 
 the Urine Urinary Concretions Urinary Bladder its Structure and Use 
 Partly under the control of the Will Glandular Bodies, whose use has not been 
 ascertained Interstitial Secretion Nutrition, Growth, and Renewal of the 
 various Textures of the Body. 
 
 HAVING considered the agents by which the blood is 
 distributed to the various parts of the body, the changes 
 it is subjected to in its circulation through the lungs and 
 system at large, the means of compensation for its expen- 
 diture, its character and constitution, and the manner in 
 which both the old and new materials are taken up and 
 introduced, we may now direct our attention to the nature 
 and source of the different substances elaborated from it 
 by the function of secretion. 
 
 No physical laws, either mechanical or chemical, as 
 hitherto ascertained, will enable us to explain the mode 
 of formation from the same fluid of the various gaseous, 
 fluid, and solid substances of which living bodies consist, 
 these products materially differing, as they do, not only 
 from each other, but likewise from that from which they 
 
234 GENERAL REMARKS. 
 
 are derived. In the sap taken up by different plants, 
 and in which, from whatever plant derived, chemists can 
 detect not the slightest shade of difference, we see nar- 
 cotic opium formed by the seed capsules of the poppy, 
 the poisonous prussic acid by the leaves of the cherry- 
 laurel, an emetic principle by the root of ipecacuan, a 
 pure bitter in the strobiles of the hop. Acids are obtained 
 from some, alkalies from others, sweet juices, nutritious 
 fecula, and fixed or volatile oils from others. Even 
 different parts of the same plants furnish peculiar secre- 
 tions : the fleshy part of the fruit of the olive abounds 
 with a bland oil, no trace of which can be detected in the 
 sap of the vessels proceeding to the part in which it is 
 formed, and the most minute examination of the tissue 
 in which it is prepared has failed to furnish an explana- 
 tion of the manner of its production. So likewise in 
 animals we cannot tell how the nutritious milk is se- 
 creted in one organ, the bitter bile in another, the acrid 
 urine in a third, and from others an offspring endowed with 
 independent life for the continuance of the race ; nor can we 
 tell how the same individual, under the influence of dis- 
 ease, has established new secretions possessed of properties 
 whereby they become capable of propagating themselves 
 to an indefinite extent, such as from small pox, measles, 
 and contagious fevers. The most careful and elaborate 
 examination of the blood, from which these secretions are 
 formed, throws no light on the processes by which they 
 are effected, nor will the most delicate and searching 
 analysis explain the origin of their essential qualities. 
 
 We say that the ultimate elements of animal bodies 
 are chiefly hydrogen, carbon, oxygen, and nitrogen : they 
 are termed elements because they have resisted all the 
 means hitherto had recourse to for decomposing them ; 
 we are therefore entitled to hold them as elementary un- 
 til they be shewn to be compound. Yet for any thing 
 that is known they may in reality be composed of still 
 more subtile principles, and regulated by laws of which 
 
CLASSIFICATION OF SECRETIONS. 235 
 
 at present we can entertain no conception. The com- 
 pound nature of such as water and atmospheric air, not 
 long ago considered as elements ; the still more recent 
 decomposition of the fixed alkalies and earths, as well as 
 the simple constitution of others, such as chlorine, till 
 lately esteemed compound; the powers possessed by 
 electricity, as modified by friction, chemical action, mag- 
 netism, heat, and organic life ; and the effects which 
 heat and light are capable of producing, the investiga- 
 tion of which adds every day to our acquirements, all 
 tend to show the uncertainty of human knowledge, and 
 teach a lesson of humility in estimating the stability of 
 the most universally received and generally established 
 doctrines respecting the laws and operations of nature. 
 
 Although the means by which living organs effect these 
 transmutations, and the immediate source of these seem- 
 ingly creative powers baffle every attempt to unravel 
 them ; although the proximate causes of the peculiar 
 qualities of their products, and in what these essejitiaUy 
 consist, be entirely unknown ; admitting that these are 
 provinces which cannot be cultivated with any prospect 
 of success, that they are secrets which man cannot pene- 
 trate, mysteries which for the present at least are hid 
 from his eyes, still the examination of the construction 
 of the machinery by which they are produced, and the 
 investigation of the properties characterizing them, are 
 both legitimate and interesting fields of inquiry, and well 
 repay the labour bestowed on their cultivation. 
 
 For the present we shall confine ourselves to the ex- 
 amination of those secretions which contribute to the 
 preservation and wants of the individual, leaving for a 
 future occasion the consideration of such as are subser- 
 vient to the continuance of the race. Secretions may be 
 arranged under four general divisions : first, exhalations 
 where the thinner part of the blood is discharged from 
 extended surfaces, including those from the skin, mucous, 
 synovial, serous, and cellular membranes ; second, follicu- 
 
236 EXHALATIONS. 
 
 lar secretions from small crypts dispersed on the skin, 
 and mucous membranes ; third, glandular secretions, com- 
 prising the tears, saliva, pancreatic juice, bile, and urine ; 
 and, fourth, interstitial secretions, such as constitute the 
 peculiar matter to each tissue, as that of bone, cartilage, 
 ligament, muscle, nerve, &c. 
 
 Exhalations. We have already had occasion to state 
 (p. 85) that a large quantity of the watery part of the 
 blood is daily discharged from the skin, forming the mat- 
 ter of sensible and insensible perspiration, and that it is 
 of great importance in the regulation of animal heat. 
 This discharge may depend on two causes mechanical 
 transudation, or exosmose, and vital action of the vessels, 
 whereby a portion of the serous part of the blood escapes 
 in quantity varying according to the state of the system 
 and condition of the atmosphere. The cuticle or scarf-skin, 
 spreading over the whole external surface of the body, 
 affords a covering of greater or less porousness and density 
 in different situations, forms a barrier between all that 
 belongs to the body of the individual and the external 
 world around him, and regulates to a certain extent per- 
 spiration. It is devoid both of blood-vessels and nerves, 
 and is the product of the subjacent vessels ; it forms nu- 
 merous branched and reticulated lines or ridges, some- 
 times symmetrically arranged, as at the points of the 
 fingers, and having intermediate fissures conspicuous in 
 the palms of the hands. It is pierced with an infinite 
 number of exceedingly minute perforations, termed pores, 
 some of which give exit to the hair, through which the 
 vapour exhales ; but even independently of these pores, 
 as shewn by the phenomena of endosmose and exosmose, 
 membranes do not offer a complete obstruction to the 
 passage of fluids. Being extravascular, its influence is 
 entirely mechanical, and continues to operate even in the 
 dead body. In temperate climates, it lessens evaporation 
 from the dead body, and to a certain extent retards de- 
 composition ; but so rapidly does evaporation take place 
 
EXHALATIONS. 237 
 
 in the arid deserts of Africa and Arabia, that when the 
 devoted caravan has been overtaken and destroyed by the 
 blast of the burning simoom, the fluids are so instantly 
 drunk up that the light and parched mummy which re- 
 mains may continue for years without undergoing further 
 change. 
 
 The true skin, which lies immediately under the cuticle, 
 is highly vascular, and possessed of acute sensibility, and 
 although defended by its covering, still it is not beyond 
 the influence of external agents which come in contact 
 with the external surface of the body, and which affect 
 the condition of its vessels; for, on the application of 
 several substances, these become excited, and exhale a 
 greater quantity than usual of the serous part of the 
 blood. Thus heat, friction, and various other stimulants, 
 promote this discharge, and the quantity poured out may 
 be so abundant that it cannot obtain a sufficiently ready 
 escape through the scarf-skin, and therefore accumulates 
 beneath it, raising blisters which may appear in a few 
 seconds, as from the application of boiling water. The 
 action of the vessels distributed on the surface of the true 
 skin is also affected by the state of the system, in all its 
 various conditions of health and disease, or as under the 
 influence of medicinal and other agents. The quantity 
 and quality of the blood likewise have their effect. Some 
 parts of the body also perspire more freely than others, 
 as the palms of the hands, and the soles of the feet. Thus 
 we perceive that perspiration, whether sensible or insen- 
 sible, is regulated by the condition of the atmosphere, 
 the state of the cuticle, of the true skin, and system at 
 large. So far as it depends on the two last, it may be con- 
 sidered as more affected by vital than mechanical agency. 
 
 The vessels of the skin likewise secrete carbonic acid, 
 as proved by keeping the arm in a jar, so managed as to 
 prevent the renewal of air in the jar ; v after some time an 
 additional quantity of carbonic acid will be found to have 
 made its appearance. This secretion of carbonic acid, and 
 
238 EXHALATIONS. 
 
 also the absorption of oxygen, are still more striking in 
 reptiles, such as the toad, so that this animal will live 
 longer under the suspension of the function of the lungs 
 than of that of the skin. Odorous principles are also ex- 
 haled from the skin, to which we shall again refer. 
 
 The mucous membrane is by much the most extensive 
 in the whole body. It covers all those orifices which com- 
 municate with the external integuments, and is continuous 
 with them. In mammalia it forms two distinct expan- 
 sions, the gastro-pulmonary and genito-urinal mucous 
 membranes. 
 
 The gastro-pulmonary commences externally at the 
 mouth, nostrils, and external covering of the eyes. The 
 portions from the eyes are continued along the channels 
 by which the tears are conveyed to the nostrils, there 
 meeting with a similar lining, and behind the soft palate 
 the mucous membrane from the mouth and nostrils be- 
 comes continuous. At the sides of the throat a tube 
 opens which extends to the drum of the ear of the cor- 
 responding side, which is lined with an extension of the 
 same mucous membrane, and from the throat downwards 
 it proceeds in two divisions, the one to cover the air tubes, 
 the other to line the whole of the alimentary passages. 
 Further, this membrane is not only extended over all 
 these surfaces, but also furnishes a lining to all the ducts 
 which open upon them, as the lachrymal ducts in the 
 eyes, the salivary ducts in the mouth, and the pancreatic 
 and biliary ducts in the intestinal canal. Ilaller esti- 
 mated that the portion belonging to the air passages was 
 equal to fifteen times the extent of the whole external 
 surface of the body, and when we add to this the pro- 
 longations to the eyes, nostrils, ears, the whole of the 
 alimentary canal, and of all the tubes that terminate upon 
 these, we may have some general conception of the very 
 great extent of the gastro-pulmonary membrane. 
 
 Being identical in structure and function throughout 
 the whole, every part of it sympathizes more or less with 
 
EXHALATIONS. 239 
 
 every other. We cannot irritate any point of its delicate 
 expansion, over the white of the eye for example, without 
 the sympathy of that in the more immediate vicinity 
 being called forth. When the irritation of any part is 
 violent, the alarm extends to the whole, even to the most 
 distant. Thus inflammation of the eye may produce dis- 
 turbance in the stomach and bowels, while conversely a 
 deranged state of these may cause inflammation of the 
 eye ; and worms at the extremity of the gut may pro- 
 duce a foul tongue, grinding of the teeth, itching of the 
 nostrils, a dulness in the eye, and a heavy disagreeable 
 odour in the breath. 
 
 The genito-urinal mucous membrane is also extensive, 
 but not so much so as the other. The internal lining 
 of the bladder, with its evacuant tube, the canals which 
 convey the urine from the kidneys, and the ducts of 
 these glands, constitute the anterior portion of this di- 
 vision of this mucous membrane, the posterior lines the 
 organs of reproduction, being extended over the whole 
 of the secreting surfaces, which furnish the prolific fluid 
 in the male, and those which cherish and bring to ma- 
 turity the offspring in the female. 
 
 In the female of mammalia, and even in the male, in 
 a rudimentary state, there are two additional mucous 
 membranes covering the surfaces, which furnish, retain, 
 and transmit the milk, the extent of which varies accord- 
 ing to circumstances, but in some instances its whole 
 amount is very considerable, as shewn in the cow, for 
 example, in the quantity of milk her receptacles are 
 capable of containing. In all the other classes of ani- 
 mals there is only one mucous membrane, common to all 
 the organs opening upon the external surface. The 
 mucous membrane at the exterior orifices is continuous 
 with the common integuments. They imperceptibly pass 
 into each other, as at the lips and nostrils. The cuticle 
 is prolonged over the mucous membrane for some extent 
 from the orifices, as from the mouth along the gullet, 
 
240 EXHALATIONS. 
 
 where it is lost at the cardiac opening of the stomach ; 
 while in some animals, as in the horse, it may be traced 
 over the cardiac portion of that organ. It lines the three 
 first stomachs of ruminants, and the gizzard of birds. 
 
 In some situations the mucous membrane is thicker than 
 in others, for example, in the nostrils, where it is soft and 
 exceedingly vascular. In other parts it is folded so as to 
 extend the surface still further, as in the intestinal canal ; 
 and in the smaller intestine it is furnished with downy 
 nap, whereby the contents are retarded, and the surface 
 of absorption and secretion much extended. 
 
 Throughout the whole extent of the mucous membrane 
 watery exhalation is constantly carried on, so as to pre- 
 serve the surface moist. The amount of watery fluid 
 extricated in breathing, and the purposes to which it is 
 subservient, we have already had occasion to examine, 
 when treating of respiration. 
 
 The carbonic acid from the lungs is strictly to be con- 
 sidered as a secretion, and in the same light the discharge 
 of various accidental substances, w^hich emanate from the 
 air passages, according to the matters taken into the sto- 
 mach, imparting to the breath their characteristic odour, 
 or, in disease, where the air of expiration becomes loaded 
 with tainted and infectious vapours. 
 
 In like manner, the arteries of other mucous mem- 
 branes pour out a thin secretion, so as to preserve them 
 moist, as is more especially observed in the stomach and 
 intestinal tube. In the former, as has been already shewn, 
 it .is possessed of remarkable and peculiar properties, 
 whereby it performs an important part in the office of 
 digestion, under the name of gastric juice ; and in the 
 latter there is reason to infer that it serves an essential 
 purpose, as secreted from the different parts of the intes- 
 tines. In the stomach and bowels it is liable to be in- 
 creased or diminished in quantity, or vitiated in quality, 
 by various causes. 
 
 Along the course of the alimentary canal various gase- 
 
FOLLICULAR SECRETIONS. 241 
 
 ous exhalations are given off, especially in deranged con- 
 ditions. Of these gases, carbonic acid is evolved princi- 
 pally in the stomach and small intestine, and its discharge 
 is considerable in the lower tribes of animals, whereby 
 the office of the lungs or gills is vicariously performed. 
 In the lower bowels the gases disengaged are chiefly car- 
 buretted and sulphuretted hydrogen. 
 
 An analogy of structure and function is thus observed 
 to obtain between the skin and the whole extended sur- 
 face of mucous membranes, accounting not only for the 
 close sympathy which subsists between them in a state 
 of health, but likewise for the connections established 
 among them in a deranged state, and the similarity in 
 the characters of the diseases to which they are liable. 
 
 The serous sacs, synovial and cellular membranes, 
 having been generally described in the last chapter, the 
 properties which characterize them, and the balance which 
 subsists between their secreting and absorbing functions 
 pointed out, it is unnecessary further to treat of them at 
 present. 
 
 Follicular Secretions are of two kinds : first, an oily or 
 sebaceous matter poured out upon the surface of the body 
 for the purpose of preserving it soft and pliant, and de- 
 fending it from moisture ; secondly, the fluid furnished by 
 the mucous glandules dispersed over the mucous sur- 
 faces. The sebaceous secretion is formed in small glan- 
 dular bodies implanted in the skin, and having a resem- 
 blance to little globular bottles with short necks, the latter 
 serving the office of excretory ducts, while in the former 
 the secretion is prepared and retained till required. Some- 
 times it accumulates till it becomes so thick and consis- 
 tent that it cannot be readily expelled ; it then produces 
 irritation and inflammation, and a pimple is the conse- 
 quence. At the sides of the nose and other parts of the 
 face, sebaceous crypts are easily seen. The matter they 
 contain occasionally becomes blackened where it comes in 
 contact with the air ; and when squeezed out, presents the 
 
 M 
 
242 FOLLICULAR SECRETIONS. 
 
 appearance of a small white worm with a black head. 
 Generally the hairs traverse the cavity of a follicle in 
 their direction outwards ; and when the beard begins to 
 sprout, the stripling's face often becomes disfigured with 
 pimples, caused by the irritation and swelling of these 
 crypts. Errors of diet and various deranged conditions 
 of the system produce a similar effect. 
 
 The sebaceous follicles furnish likewise a volatile odour, 
 or rather perhaps the sebaceous secretion is itself partly 
 odorous and volatile, becoming thickened and having its 
 scent diminished by evaporation ; in the flexures of joints, 
 especially in the arm-pits, groins, and other parts, the 
 crypts are large and numerous, and emit a peculiarly cha- 
 racteristic odour. The quantity and character of the seba- 
 ceous secretion vary much in different individuals, and in 
 the same individual in different conditions of health. The 
 different varieties of mankind are distinguished by their 
 peculiar odour, and the activity of these small glandules 
 is much greater in some cases than in others. Heat pro- 
 motes the secretion of sebaceous matter ; accordingly the 
 inhabitants of hot climates produce a greater quantity of 
 it than those of cold and temperate regions. 
 
 This oily or unctuous substance performs an important 
 purpose in preserving the skin in a proper condition for 
 the performance of its functions, and defending it espe- 
 cially from the effects of moisture. It is apt, however, 
 to accumulate on the surface, and likewise to cause the 
 adhesion of particles of dust, producing a sordid condi- 
 tion of the skin, and of the clothing immediately in con- 
 tact with it. Hence the absolute necessity not only of 
 properly washing the body itself, but likewise of a fre- 
 quent change of the inner clothing. From the unctu- 
 ous nature of this secretion, water alone is not sufficient 
 for its removal ; therefore soap becomes requisite, although 
 detergents of this nature, from their effects upon the skin, 
 ought to be used sparingly, and only in their mildest 
 forms. 
 
FOLLICULAR SECRETIONS. 243 
 
 Along the margin of each eye-lid there is a row of 
 crypts like a string of beads, larger and more numerous 
 in the upper than in the under eyelid. They belong to 
 the follicular glands, and furnish a thick viscid fluid for 
 keeping the eyelids sufficiently slippery and smooth, 
 and preventing the tears from trickling over the mar- 
 gin. Occasionally one of these little bottles becomes 
 inflamed, producing the affection known by the name of 
 Stye, which is generally accompanied with greater pain 
 and constitutional disturbance than might be expected 
 from a cause apparently so slight. The acuteness of the 
 inflammation, however, and the exquisite sensibility of 
 the part, sufficiently explain this. Sometimes the stye 
 becomes indolent, and remains a very long time, per- 
 manently disfiguring one of the most beautiful features of 
 the countenance, shewing that even a trifle like this should 
 not be neglected. 
 
 The external passages to the ears present us with ano- 
 ther variety of follicular crypts for the secretion of the 
 wax. They form a cluster of small glandular bodies, 
 occupying about one-half the length of the canal. The 
 secretion they furnish, termed the wax of the ear, is of a 
 resinous nature, and yellowish colour, with a heavy dis- 
 agreeable odour and nauseous bitter taste. Its resinous 
 
 O 
 
 character facilitates the transmission of sound, while an 
 oily or mucilaginous fluid would have diminished the 
 vibrations, so that it serves the purpose that the rosin 
 does to the bow of the violin ; at the same time it repels 
 moisture, and, from its odour and taste, prevents the en- 
 trance of insects. 
 
 In several of the lower animals, certain follicular glands 
 are found, which, instead of being solitary, are formed 
 into compound glands, as in the beaver, musk-deer, and 
 civet. The secretions furnished by these compound folli- 
 cular glands are of a volatile and resinous nature. Gene- 
 rally they have an exceedingly penetrating smell ; some 
 of them being grateful, are employed as perfumes, for 
 
244 FOLLICULAR SECRETIONS. 
 
 which purpose musk is highly prized ; others are so abo- 
 minably disgusting that they constitute the principal 
 means of defence of the animal, as in the skunk of North 
 America, which when pursued emits a discharge upon 
 the enemy which at once disarms him. Clothes on 
 which they have been ejected can never be thoroughly 
 cleansed, and are therefore rendered utterly useless. 
 
 The second class of follicular glands are those belonging 
 to mucous membranes. In their structure they resemble 
 the sebaceous crypts. They are found every where scatter- 
 ed over the surface of mucous membranes, either singly or 
 in groups, varying in their size in different situations. 
 In some places they are collected into one bundle, thus 
 forming a compound gland, as in the almonds of the throat. 
 The fluids to which we have already had occasion to refer, 
 as poured out from the mucous surfaces, so far as their che- 
 mical constitution shews, differ but little from the serum 
 of the blood, and appear to be derived immediately from 
 the vessels, without the intervention of any peculiar struc- 
 ture; while the thick viscid tenacious matter which is 
 spread over the mucous membrane owes its distinguish- 
 ing character to a peculiar substance not recognised in 
 the blood, and elaborated from appropriate organs : to 
 this the term mucus is strictly applied. 
 
 The following are the most important properties of 
 mucus according to Berzelius. It swells and acquires 
 apparent fluidity in water, without being actually dissolv- 
 ed, but gives a ropiness to it when present to a less amount 
 than one per cent. With pure water at the temperature 
 of 95 this appearance ensues in a few hours ; but if the 
 apparent solution is filtered, the mucus remains upon the 
 paper, and gradually thickens. It may be repeatedly 
 dried and moistened without material change of proper- 
 ties ; it however becomes less transparent, yellow, and at 
 length has a purulent appearance. When boiled in water 
 it does not harden and shrink, but becomes tough, and 
 on cooling is found to retain its former characters. When 
 
GLANDULAR SECRETIONS. 245 
 
 dried it is yellow and translucent ; and subjected to dis- 
 tillation it yields carbonate of ammonia and empyreu- 
 matic oil; and phosphate and carbonate of lime and a 
 trace of carbonate of soda are found in the residuary ash. 
 
 Mucous secretion, besides containing mucus, holds va- 
 rious salts in solution, and there are also found in it traces 
 of albumen and osmazome. The serous exhalations, like 
 the serum of the blood, display alkaline properties, while 
 the mucous secretions are either neutral or acid. 
 
 Mucus serves as a defence to the surfaces which it covers, 
 and is variously subservient to the functions performed 
 by the different parts on which it is poured out. It 
 facilitates the motions of the eyelids, and of the contents 
 of the alimentary canal ; it aids in the exercise of the 
 smell and taste ; it defends the gall-bladder and urinary 
 passages from the acrimony of their contents, and in va- 
 rious other ways contributes to the functions carried on 
 in the animal machinery. 
 
 Glandular Secretions. Glands are organs composed 
 chiefly of the ramifications of blood-vessels. The mode 
 of distribution of the vessels not only varies in different 
 glands, but in the same gland in different animals. They 
 are surrounded with a covering of condensed cellular 
 membrane, which constitutes their proper coat. Where 
 the gland separates from the blood a fluid which is to be 
 conveyed off, it is furnished with tubes for this purpose, 
 termed excretory ducts. These are distributed through 
 the glands variously according to the nature of each. The 
 glands, which are thus supplied with excretory ducts, 
 and which demand our attention for the present, are the 
 lachrymal glands in the orbits of the eyes, those which 
 have their secretions transmitted into the alimentary 
 canal, and those subservient to the secretion of urine. 
 
 In each orbit above the external angle of the eye the 
 lachrymal gland is situated in a slight depression. It is 
 about the size of a small filbert, and composed of a num- 
 ber of granules connected with each other through the 
 
246 GLANDULAR SECRETIONS. 
 
 medium of cellular membrane ; from these granules pro- 
 ceed little tubes for carrying off the tears as formed in 
 the gland, and terminating by six or seven ducts, about 
 two or three lines from the margin of the upper eyelid 
 towards the temple. By the movements of the eyelid 
 the tears are diffused over the anterior surface of the eye, 
 so as to preserve it sufficiently moist for the due per- 
 formance of its office, and also to wash away any light 
 particles of dust that may fall upon it. When the two 
 eyelids come in contact they do so only at their outer 
 edges, there being left a little gutter posteriorly, along 
 which the tears flow towards the internal angle, where 
 there is placed in each eyelid a small pore, which can 
 easily be seen by drawing down the lower lid, and look- 
 ing at its margin close to the termination next the 
 nose. These lachrymal pores are the orifices of two chan- 
 nels which convey the tears into a small sac, from 
 which they are transmitted by a duct to the nose, where 
 by the current of air they are soon evaporated, after hav- 
 ing moistened the nasal membrane. All these parts de- 
 rive their sensibility from the same nerve; according- 
 ly we observe how intimately they sympathize with one 
 another. On the application of any irritating cause to 
 the surface of the eye, the lachrymal glands are ex- 
 cited, and the tears are more abundantly secreted. Pun- 
 gent substances exciting the lining of the nostrils call 
 forth the sympathy of the organs, and the tears flow co- 
 piously. When we are asleep, the eyes being closed, 
 evaporation is prevented, and the lachrymal glands have 
 rest, but no sooner do we open our eyes than, stimulated 
 by the air and light, they are again roused into action. 
 
 No organs of the body so clearly and strikingly dis- 
 play the effects of the passions and emotions of the 
 mind upon the corporeal frame as the lachrymal ap- 
 paratus. A moderate degree either of the joyful or 
 depressing emotions is accompanied with the copious 
 shedding of tears ; while either joy or overwhelming grief 
 
GLANDULAR SECRETIONS. 247 
 
 produce their suppression, and we know that relief is 
 come, that sorrow is abated, when the tears begin to flow. 
 During infancy and childhood tears are shed more readi- 
 ly, both from the greater abundance of fluids, and from 
 the greater susceptibility of the young. For the same 
 reasons too the female weeps from slighter causes than 
 the more arid and impenetrable male : his manly pride 
 and more determined character also operate in suppress- 
 ing such external marks of emotion and feeling. 
 
 Having, in the chapter on digestion, considered the va- 
 rious fluids which are poured into the intestinal canal, it is 
 unnecessary for us again particularly to advert to them. 
 We have seen that three pairs of glands furnish the saliva to 
 be mixed with the food in the mouth ; that the pancreas 
 transmits its secretion by a duct into the duodenum ; 
 that the bile secreted from the blood of the vena portae, 
 in its transmission through the liver, affords the only ex- 
 ample in the human body of a secretion from venous 
 blood ; that in the gall bladder the bile undergoes cer- 
 tain changes, and has added to it a secretion from the 
 arteries of that sac, according to some it being here that 
 the bile derives its bitterness, which must therefore be 
 considered as obtained from arterial and not from venous 
 blood ; we have observed further that the biliary duct ter- 
 minates like the pancreatic in the duodenum, to meet 
 with the chyme from the stomach ; and that all these 
 glands are excited by their appropriate stimulants, so as 
 to be roused into action at the proper time, and to the 
 necessary extent. 
 
 The kidneys, by which the urine is secreted, are 
 situated in the loins, at the posterior part of the cavity of 
 the abdomen, by the sides of the vertebral column, and 
 surrounded with a loose cellular membrane, usually 
 loaded with a considerable quantity of fat, the right be- 
 ing placed somewhat lower than its fellow of the oppo- 
 site side. The kidney is of a somewhat ovoid form, a 
 little compressed posteriorly, and more convex anteriorly, 
 with its outer border convexly rounded, and the inner 
 
248 GLANDULAR SECRETIONS. 
 
 presenting a fissure for the entrance and exit of the 
 vessels and nerves. On making a horizontal section of 
 the kidney we perceive it to be constituted of two por- 
 tions. The external, superficial, or cortical substance is of 
 a dark purple colour, and composed of an infinite num- 
 ber of ramifications of 
 blood vessels. The 
 central or medullary 
 part is formed of nu- 
 merous straight tubes, 
 \ which are collected 
 S into conical bundles 
 or nipples. The num- 
 ber of these nipples 
 corresponds with the 
 number of glands of 
 which the kidney ori- 
 ginally consisted, for 
 
 in the foetus the kidney is divided into a number of distinct 
 lobes, usually from twelve to fifteen in the human sub- 
 ject. The lobulated structure continues throughout life 
 in some animals, as in the ox. In others, as in the whale 
 tribe, seals and bears, when divested of the loose exter- 
 nal covering, the kidney presents a striking resemblance 
 to a bunch of grapes. The blood-vessels of the kidney 
 are very large in proportion to its size, its artery being 
 one-eighth of the calibre of the aorta. From its short course, 
 and the peculiar distribution of its branches, it is well 
 adapted for quick and copious secretion, readily account- 
 ing for the great abundance of fluid which it so speedily 
 separates from the blood. The extreme arterial divi- 
 sions are tortuous, and freely communicate with the ac- 
 companying venous twigs, so that injections readily pass 
 from the one into the other. They open freely into the 
 excretory duct, so that on introducing a pipe into the 
 artery of the kidney, and injecting it with water, we 
 find the latter flowing copiously into the vein on the one 
 hand, and through the ducts on the other. 
 
GLANDULAR SECRETIONS. 249 
 
 The conical nipples, formed by a collection of tubes, 
 are each surrounded by a little cup, into which the urine 
 trickles from the tubes. Several cups again form larger 
 ones, termed funnels, which are united into one general re- 
 servoir, called the basin, from which the urine is conveyed 
 by a duct, named ureter, into the appropriate receptacle, the 
 urinary bladder. 
 
 In the engraving, a represents the cortical portion ; b, 
 the nipples ; c, funnels ; </, the basin ; and 0, the ureter. 
 
 The urine is by far the most compound of the fluids 
 separated from the blood, draining off as it does particles 
 of every tissue which the absorbents take up from all 
 parts of the body, as worn out, redundant, and useless. 
 The kidneys also afford the most ready passage for the 
 evacuation of various substances introduced into the sys- 
 tem in food, drink, and as medicines, which may easily 
 be detected by their colour, odour, or appropriate chemi- 
 cal tests. Thus, in a very short time after being swallowed, 
 rhubarb, logwood, madder, cochineal, litmus, soon dis- 
 play themselves by the tints they impart to the urine. 
 Camphor, ether, and musk are detected by their odour. 
 Oil of turpentine gives the smell of sweet violets, and by 
 the use of asparagus a peculiarly disagreeable odour is given 
 off from the urine. Nitre, prussiate of potash, iodine, mer- 
 cury, and various other chemical substances, are ascertain- 
 ed with facility by having recourse to their proper tests. 
 Mr Brande gives the following list of substances as being 
 found in healthy urine : 
 
 1. Water. 
 
 2. Carbonic acid. 
 
 3. Phosphoric acid, or su- 
 
 per-phosphate of lime. 
 
 4. Uric acid, or super-urate 
 
 of ammonia. 
 
 5. Phosphate of lime. 
 
 6. Phosphate of ammonia. 
 
 7. Phosphate of soda. 
 
 8. Phosphate of magnesia. 
 
 9. Common salt. 
 
 10. Sulphate of soda. 
 
 11. Albumen. 
 
 12. Urea. 
 
 To which he adds, 
 
 M2 
 
250 GLANDULAR SECRETIONS. 
 
 13. Fluoric acid. 
 
 14. Benzoic acid. 
 
 15. Acetic or lactic acid. 
 
 16. Gelatin. 
 
 17. Lactate or acetate of 
 
 ammonia. 
 
 18. Sulphate of potassa. 
 
 19. Fluate of lime. 
 
 20. Muriate of ammonia. 
 
 21. Sulphur. 
 
 22. Silica. 
 
 23. Mucus. 
 
 24. Colouring and odorous 
 
 matter. 
 
 In operating chemically upon so complicated a fluid as 
 the urine, it is extremely difficult to distinguish between 
 what may merely be the result of the processes to which 
 we subject it, and those substances which really form a 
 part of its constitution. It is also very difficult, with 
 any degree of accuracy, to ascertain the relative propor- 
 tions of the different ingredients. Indeed these vary 
 according to such a variety of circumstances, that the 
 results of no two operations are found to furnish more 
 than an approximation to each other. The following table 
 given by Berzelius will serve as an example of the result 
 of one such examination. 
 
 Water 933.00 
 
 Urea 30.10 
 
 Sulphate of potassa 3.71 
 
 Sulphate of soda 3.16 
 
 Phosphate of soda 2.94 
 
 Muriate of soda 4.45 
 
 Phosphate of ammonia 1.50 
 
 Free lactic acid (acetic) \ 
 
 Lactate of ammonia (acetate) I 1714 
 
 Animal matter soluble in alcohol I ^ 
 
 Urea, not separable from the preceding " 
 
 Earthy phosphates, with a trace of the fluate of 
 
 lime 1.00 
 
 Uric acid '. 1.00 
 
 Mucus of the bladder 0.32 
 
 Silica 0.03 
 
 1000. 
 
GLANDULAR SECRETIONS. 251 
 
 Of the articles in the above list, urea is that which 
 imparts to the urine its principal peculiarities. When 
 obtained perfectly pure it is transparent and colourless, 
 with a peculiar cooling taste, and a faint but not urinous 
 smell ; it is soluble in about its own weight of water at 
 60 ; it displays neither alkaline nor acid effects upon vege- 
 table colours, but unites with some of the acids, such as 
 the nitric and oxalic. Urea is a proximate animal prin- 
 ciple, composed of four elementary bodies, viz. carbon, 
 hydrogen, oxygen, and nitrogen. The last of these con- 
 stitutes nearly one-half of its weight. The present ad- 
 vanced state of chemical science, and the philosophic views 
 which now direct chemical operations, are strikingly dis- 
 played in the artificial preparation of urea, by acting on 
 cyanate of silver or of lead with ammonia, affording the 
 first instance in which success has crowned the various 
 attempts which have been from time to time made in 
 order to imitate by art the products of nature. 
 
 Uric acid is another of the ingredients deserving parti- 
 cular notice. It is composed of the same elements as 
 urea, though in different proportions ; it is nearly inso- 
 luble in water ; when perfectly pure it forms a white, 
 tasteless, inodorous substance. In combination with va- 
 rious bases, especially with ammonia, it is found in the 
 urine of all animals, but more abundantly in the carnivo- 
 rous than herbivorous. In serpents, as in the boa con- 
 strictor, the secretion from the kidneys is voided in the 
 solid form, and consists chiefly of uric acid. 
 
 The kidneys, constituting as they do important emunc- 
 tories or channels by which superfluous and hurtful mat- 
 ters are discharged from the blood, it is necessary that 
 their function should be carried on without intermission, 
 as is found to be the case during health. We have seen 
 that the system is freed from excess of carbon by the se- 
 cretion of carbonic acid from the lungs. The discharge 
 of bile likewise tends to the purification of the blood ; 
 and we now find that through the kidneys, in the secre- 
 
252 GLANDULAR SECRETIONS. 
 
 tion of urea and uric acid, any redundancy of nitrogen is 
 readily got quit of, the constant depositation of new, and 
 absorption of the old materials (for our body is not the 
 same for two consecutive days, nay hours, or even mi- 
 nutes), demands the unceasing evacuation of these old 
 worn-out particles from the general mass of circulating 
 fluids, although, for the comfort and convenience of the 
 animal, means are adopted to obviate the necessity of 
 constant discharge from the body by the provision of an 
 urinary reservoir, in which it may be lodged and accu- 
 mulated till a fitting opportunity offer for its expulsion. 
 
 The purposes served by several secretions render their 
 constant production unnecessary, as the tears, the saliva, 
 and the gastric juice ; while the secretion of carbonic acid 
 from the lungs cannot be suspended for a minute or two 
 during the continuance of our existence after birth with- 
 out the most imminent danger to life. Neither can the 
 function of the kidneys be suspended for any length of 
 time without injury. Although during sleep, from the 
 discharge by the skin being more copious, there is a less 
 quantity of urine secreted, yet it will be found to contain 
 a greater proportional quantity of the salts and animal 
 matters by the discharge of which the purity of the blood 
 is preserved, than that which formed during the day, thus 
 preserving an uniformity in this respect. Where the 
 function of the kidneys is suppressed by disease, or where 
 they have been extirpated by way of experiment in the 
 lower animals, the formation of urea and of uric acid does 
 not become altogether suspended, for in such cases they 
 have been detected in the blood shewing that though the 
 kidneys constitute the proper channels for their discharge, 
 still they are not absolutely essential to their preparation. 
 Of all the substances formed in the animal body, 
 none are so liable to decomposition as urea -, and of all 
 the fluids, the urine is that which hastens most speedily 
 into a state of putridity. When its secretion is suspend- 
 ed, or when its evacuation is obstructed, great distress is 
 
GLANDULAR SECRETIONS. 253 
 
 soon experienced in the whole system ; symptoms of de- 
 composition commence before the extinction of life ; and 
 when death takes place, the body rapidly passes into a 
 state of offensive putrefaction indicating how important 
 to the health and well-being of the whole frame the due 
 performance of the function of the kidneys necessarily is. 
 
 By the tables which we have introduced, it will be seen 
 that saline and other matters discharged by the urine are 
 very various. The quantity of solid contents which are 
 discharged in this way amounts to about fifteen drams in 
 the twenty-four hours. The average specific gravity of 
 healthy urine is about 1020 to 1025; in some instances it is 
 little more than that of simple water, while in certain dis- 
 eased states it rises to 1030, and occasionally even to 1040. 
 
 The function exercised by the kidneys is one of the 
 most important of the compensating functions ; or, in 
 other words, the urinary secretion is of great use in pre- 
 serving a proper balance in the system, and enabling it 
 readily to accommodate itself to the great variety of cir- 
 cumstances to which it is exposed. We have had occa- 
 sion to advert to the connection which subsists between 
 the state of the skin and the quantity of urine discharged. 
 In dry warm weather and in hot climates the fluids are 
 determined to the surface, where they are discharged in 
 the state of vapour, thereby reducing the temperature of 
 the body. In winter, on the other hand, and also in a 
 damp atmosphere, the cuticular discharge is diminished, 
 while that of the urine is augmented. In cold damp 
 climates the kidneys are therefore the most active, while 
 in tropical countries the skin is most excited ; and it is 
 interesting to observe that in the former, diseases of the 
 urinary organs predominate, while in the latter derange- 
 ments of the skin chiefly prevail. The quantity of urine 
 is materially affected by the quantity of food, and espe- 
 cially of drinks, so that a due proportion of fluids in the 
 body is thus regulated. Where there is great expendi- 
 ture in other directions, or increased evacuations by other 
 
254 GLANDULAR SECRETIONS. 
 
 channels, this secretion is diminished, and conversely, when 
 discharges from other parts become lessened, an increase 
 of urine takes place. Various substances possessing the 
 property of exciting the action of the kidneys and promot- 
 ing the secretion of urine, are therefore termed diuretics, 
 and are of essential use to the physician in the treat- 
 ment of several diseases. 
 
 In the healthy state, the urine, when first evacuated, 
 possesses acid properties; but on standing, in a very 
 short time chemical changes are effected, whereby it is 
 rendered alkaline. The alkali elicited is the volatile, 
 or ammonia. From its alkaline quality, stale urine is 
 employed in manufactures as a detergent, especially in 
 cleansing woollen cloth. The urine of cattle forms an 
 excellent top-dressing for meadows ; that of birds, voided 
 along with their excrement, contains a considerable quan- 
 tity of the carbonate of lime, and forms the best manure 
 for the cultivation of several vegetables. Mr Morier ob- 
 serves, " The dung of doves is the dearest manure which 
 the Persians use ; and as they apply it almost entirely to 
 the rearing of melons, it is probably on that account that 
 the melons of Ispahan are so much finer than those of 
 other cities. The revenue of the pigeon-house is about a 
 hundred tomauns per annum ; and the great value of the 
 dung, which rears a fruit which is indispensable to the 
 existence of the natives during the great heats of summer, 
 will probably throw some light on that passage of Scrip- 
 ture, where, in the famine of Samaria, the fourth part of 
 a cab of dove's dung was sold for five pieces of silver." 
 
 As the urine carries off from the system the debris of 
 the body, so does it vary in different states of the consti- 
 tution. In children and in nurses, the phosphate of lime, 
 which constitutes the earthy matter of bones, scarcely 
 appears in this secretion, being determined to the forma- 
 tion of bone in the one and milk in the other, while in 
 old age this earth becomes abundant, from its excess in 
 the body at large. In gome morbid conditions the phos- 
 
GLANDULAR SECRETIONS. 255 
 
 phate of lime, instead of being deposited in the formation 
 of bone, is discharged by the urine, whereby the bones 
 become flexible, and incapable of supporting the weight 
 of the body : hence distortions of various parts, particu- 
 larly of the spine, pelvis, and lower limbs, as in rickets. 
 
 In some cases new formations appear which do not 
 exist in healthy urine. Of these sugar forms one of the 
 most remarkable ; it occurs in one of the forms of the 
 disease called diabetes, in which there is a prodigious 
 quantity of urine secreted, accompanied with an insatiable 
 thirst, and most voracious appetite ; and although these 
 may be freely indulged, still the body rapidly wastes, 
 from the inordinate expenditure to which it is subjected. 
 Diabetic sugar is granular, resembling grape sugar in its 
 appearance, composition, and properties. In another 
 form of diabetes, the urine is equally excessive, but with- 
 out the presence of sugar, and the formation, of urea is 
 suspended. The leanness and dryness of the whole body 
 in these diseases, where the fluids are drained off in this 
 way, is the opposite of what takes place where the action 
 of the kidneys is diminished or suppressed, where effu- 
 sions take place in the shut sacs, and in the cellular mem- 
 brane, forming the different varieties of dropsy, according 
 to their situation. 
 
 Another occasional formation in the urine is oxalic 
 acid, so named from its existence in the wood-sorrel. It 
 may be got from several other plants ; but for the various 
 purposes of art, it is found more economical to form it ar- 
 tificially than to elicit it from those combinations in 
 which it is produced by nature ; it is therefore procured 
 by the action of nitric acid on sugar. This conversion of 
 sugar into oxalic acid, and the occasional appearance of 
 sugar in the urine, throws some light on the probable oc- 
 currences which give rise to oxalic acid in the urine. 
 From the great affinity which exists between oxalic acid 
 and lime, it attracts the lime in the urine, and an inso- 
 luble compound is formed, producing one of the forms of 
 
256 GLANDULAR SECRETIONS. 
 
 urinary concretions, or calculi, as they are termed. From 
 the rough and dark-brown appearance which it usually 
 presents it is called the mulberry calculus. 
 
 The great quantity and variety of saline and crystal- 
 lizable ingredients in the urine account for the frequency 
 of urinary concretions, giving rise to sabulous or gritty 
 deposits, gravel or calculi. These deposits are frequently 
 temporary only, and may be produced by a variety of 
 accidental causes which influence the secretion of urine ; 
 but when they are more or less constant, or arise from 
 apparently trifling causes, they then require the utmost 
 attention, as being the frequent forerunners of stone. The 
 tendency to the depositation of gravel is generally first ob- 
 served in the urine as it cools, but it afterwards increases 
 to such an extent that the urine is voided more or less 
 turbid. The composition of urinary concretions is very 
 various, as might be expected from the great diversities 
 which obtain in the condition of the urine, according to 
 different states of the system. Of these uric acid is by 
 far the most common : generally it is in combination with 
 ammonia, producing a brick-coloured deposit or red sand, 
 or agglutinated into masses of variable sizes, forming gravel 
 or stone. The next most common are those composed of 
 phosphoric acid in union with lime, ammonia, or magnesia, 
 either as binary, ternary, or quaternary compounds. They 
 produce a white sabulous deposit from the urine or white 
 sand. The oxalate of lime, carbonate of lime, and several 
 others, occasionally present themselves. 
 
 These distressing affections are more liable to occur at 
 the commencement and towards the decline of life than 
 during middle age. In childhood the rapid renewal of 
 parts in the growth of the body, and the consequent re- 
 moval of old materials, the activity of the digestive func- 
 tion producing an accumulation of matters in excess, call 
 upon the kidneys for the full exercise of their action. 
 "While in old age an excessive formation of bone-earth 
 takes place, as is shewn by the tendency to its depositation 
 
GLANDULAR SECRETIONS. 257 
 
 in cartilages, blood-vessels, and membranes. The cuticular 
 action is also diminished, so that the kidneys require again 
 to exert their function to the utmost. Cold damp climates 
 also predispose to the formation of urinary calculi, by 
 checking the action of the skin, and thus throwing a 
 greater burden upon the kidneys. We therefore find that 
 they are extremely prevalent in Britain and Holland. In 
 the latter country a surgeon of the name of Raw is said 
 to have cut for the stone fifteen hundred patients success- 
 fully. 
 
 The urine presents great varieties in colour, consis- 
 tency, and quantity in different diseases. Albumen is a 
 common ingredient in healthy urine, but always in a 
 very small relative proportion ; in some cases of disease 
 it is so abundant as to coagulate by heat, or even some- 
 times spontaneously within the bladder; it is also re- 
 cognised by the precipitate it affords by proper tests ; 
 but in applying those tests, and indeed generally in judg- 
 ing of the state of the urine of any individual, it should, 
 if possible, be previously ascertained that it is not na- 
 turally subject (which is at times the case) to excess or 
 deficiency of this or other of its components. In some 
 forms of dropsy, especially where there is disease of the 
 kidneys, excess of albumen is often observed; in these 
 instances the urine is scanty, and its specific gravity be- 
 low the usual average, in consequence of deficiency of 
 urea and saline matter. 
 
 As the constant discharge of the urine from the body 
 would be both inconvenient and offensive, a reservoir is 
 provided for its reception in the urinary bladder, which is 
 situated in the pelvis, in front of the rectum. In its 
 form it is somewhat of a compressed oval, though its 
 shape varies in different ages and sexes. It receives a 
 partial investment of peritoneum at its upper part. It is 
 essentially composed of a muscular layer externally, and 
 an internal mucous covering, with the interposition of 
 cellular membrane. The muscular fibres are curiously 
 
258 
 
 GLANDULAR SECRETIONS. 
 
 interwoven with each other. The general direction of 
 the external fibres are from below upwards, others are 
 oblique, while the internal pursue a transverse or circular 
 direction. At its lower part these fibres are more 
 numerous, especially the circular, so as to form a sphincter 
 for the retention of the urine. The mucous lining when 
 the bladder is empty is folded into ridges, but these dis- 
 appear when it is distended. It is supplied with blood 
 from the neighbouring vessels, and its nerves are derived 
 from two sources., being twigs from the great sympathetic 
 connected with its organic life, and others from the extre- 
 mity of the spinal cord, by which we possess voluntary 
 power over the bladder in the retention and expulsion 
 of the urine. As the urine is secreted in the kidneys it 
 is conveyed by the tubes named ureters into the blad- 
 der. The ureters are endowed with a certain degree of 
 contractility, though little contraction is necessary for the 
 transmission of the urine in ordinary cases. They proceed 
 to the lower part of the bladder near its neck, and pene- 
 trate its coats obliquely, this obli- 
 quity of entrance serving the pur- 
 ~ a pose of a valve, so as effectually 
 to prevent the return of urine from 
 the bladder. Even in the dead 
 state, when the bladder is fully 
 TJ distended with air, none of it can 
 escape by the ureters, so complete- 
 ly does this valvular contrivance 
 operate. 
 
 In the engraving, a represents a 
 kidney; >, an ureter; and c, its 
 termination near the neck of the 
 c bladder. 
 
 In the whale tribe the urinary 
 FIG. 19. bladder is comparatively small. In 
 
 a porpoise, ten feet in length, the bladder was not larger 
 than that of a rabbit. The element in which these animals 
 
GLANDULAR SECRETIONS. [259 
 
 exist probably renders the frequent evacuation of urine 
 less inconvenient. The urinary bladder is confined to the 
 class of mammalia. In birds, reptiles, and fishes, the ure- 
 ters terminate in a reservoir common to them, the rec- 
 tum and genital organs, and known under the name of 
 cloaca. The urine of birds is voided along with the feculent 
 matter of the intestines, and is generally of a whitish co- 
 lour, from the abundance of carbonate of lime it contains. 
 
 By the gradual accumulation of urine, the bladder is 
 distended, when its sensibility becoming excited, we 
 are warned to relieve it. Being accustomed to the pre- 
 sence of the urine, and also being protected by the 
 mucus from the internal coat, it suffers it to collect to a 
 certain extent, but when the urine is unusually acrid 
 from the exhibition of medicines or other causes, or where 
 the sensibility of the bladder is preternaturally acute, the 
 calls become more frequent and urgent. On the other 
 hand, when its sensibility is impaired, as often happens 
 in old age, the urine sometimes accumulates to such an 
 extent as to paralyze the muscular coat, and the most 
 powerful straining of the muscular walls of the abdomen 
 are inadequate to afford relief though they co-operate 
 efficiently in the healthy condition of the parts. 
 
 Before leaving the glands some notice may here be 
 taken of certain bodies which are usually classed along 
 with them, but of the functions of which we are igno- 
 rant. These are the pineal and pituitary glands within 
 the skull, the thyroid body on the anterior part of the 
 windpipe, the thymus gland in the chest, and the supra- 
 renal capsules in the abdomen. 
 
 Those glands which are destined for the formation and 
 separation of matters from the blood being furnished 
 with excretory ducts and other appendages, we can 
 readily avail ourselves of opportunities for collecting the 
 fluids which they elaborate. We can examine the phy- 
 sical properties of these fluids, and subject them to various 
 chemical and mechanical processes, by which we become 
 acquainted with their distinguishing characters. We are 
 
260 GLANDULAR SECRETIONS. 
 
 enabled to pursue them to their destination, and draw 
 conclusions as to the final purposes to which they may be 
 subservient. But in the investigation of the use of such 
 glandular bodies as do not separate any fluid from the 
 blood, the difficulties met with have been hitherto insu- 
 perable. Late observations on the glands in the course 
 of the absorbents, and on the spleen, have tended to 
 throw some light on their uses, to which w r e have had 
 occasion already to direct our attention. 
 
 The Pineal Gland is a small conical-shaped body, from 
 which circumstance it has derived its name, from its form 
 resembling the cone of a pine. It is of a dark grey colour, 
 and situated towards the base of the brain. The cele- 
 brated Descartes conjectured, it being a single organ 
 attached by nervous cords, and placed nearly in the 
 centre of the brain, that it formed the peculiar seat of the 
 soul. The conjecture appeared supported by the fact, that 
 in the brains of certain idiots a quantity of earthy matter 
 was found, which was supposed to interfere with the 
 manifestation of the mental faculties ; but when it was 
 ascertained that in almost every pineal gland, whether 
 belonging to the idiotic or the most intelligent, such con- 
 cretions may very frequently be found without the slight- 
 est trace of connection with deranged action, the doc- 
 trine of this being the peculiar seat of the soul was aban- 
 doned, and we still remain ignorant of its use. 
 
 The Pituitary Gland is situated in a depression on the 
 internal surface of the base of the skull, lying between the 
 dense lining of the bone and the serous membrane called 
 the arachnoid. At one time it was believed to serve as a 
 sewer to the brain, discharging its excretions through the 
 nostrils, from which conjecture it derives its name. It is 
 still a vulgar belief that there is a direct connection be- 
 tween the nose and the brain, and that discharges take 
 place in this way to the relief of the latter ; so true it is 
 that popular notions are generally nothing more than the 
 cast-off opinions of former philosophers. 
 
 The Thyroid Gland is situated in the front and by the 
 
INTERSTITIAL SECRETION. 261 
 
 sides of the windpipe, immediately below the larynx, and 
 is abundantly supplied with blood. Strictly there are 
 two thyroid glands, though their close approximation 
 gives frequently the appearance of a single body. This 
 body is the seat of the disease known in this country 
 under the name of Derbyshire neck. It is not unfrequent 
 in the valleys of the Alps, where it is termed goitre : it 
 is also endemic in other mountainous regions. 
 
 The Thymus Gland is placed in the anterior part of 
 the chest, immediately behind the breast-bone. It is not 
 only proportionally but absolutely larger at birth than in 
 the adult, and even entirely disappears in advanced life. 
 It is therefore justly inferred that it performs some office in 
 the foetus which is either not necessary after birth, or that 
 it is subservient to some temporary vicarious function, but 
 what that may be does not yet appear. We dissected a 
 marmot some years ago, in which the thymus was ex- 
 ceedingly large and fully organized, although the animal 
 was of adult age. We should therefore suppose that in- 
 vestigations as to its use might be pursued with greater 
 chance of success in that animal than in any other. 
 
 The Suprarenal Capsules are bodies so named from 
 their situation above the kidneys. Like the thymus they 
 are large and of a granulated texture in the fcetus, while 
 in the adult their size is considerably diminished and their 
 texture altered, becoming cellular, and containing a dark- 
 coloured fluid. When humoral doctrines were in vogue- 
 when it was believed that the temperament of the consti- 
 tution, the character of disease, and the mental condition 
 depended on the state of the fluids a gloomy desponding 
 state of the mind was ascribed to a black bile which was 
 supposed to be furnished by these glands : hence our word 
 melancholy, from ^aiXa;, black, and xoXs, bile ; and for 
 this reason also these bodies were termed atrabiliary 
 glands. 
 
 Interstitial Secretion. In the extreme capillary vessels 
 of every tissue of the body there is deposited the peculiar 
 
262 INTERSTITIAL SECRETION. 
 
 matter belonging to each. Thus in bones the osseous sub- 
 stance is elaborated, in cartilage cartilaginous matter, in 
 muscle muscular fibre, and so on with every organ in 
 the body, as the nervous system, the glandular, the mem- 
 branous, and the cuticular. Every tissue of the body 
 has the blood distributed to it in a manner adapted to its 
 organization and to the function it has to exercise, so as 
 to supply it with a greater or less quantity, with different 
 degrees of velocity and with different degrees of force. 
 While it passes through these exceedingly minute tubes, 
 which are invisible to the naked eye, the matter belong- 
 ing to each is separated, just as we find the bile separated 
 from the blood of the vena portse in the liver, the urine 
 from the vessels of the kidneys, or the saliva from the 
 salivary glands. The blood containing, already formed, a 
 great number of the materials which compose the majo- 
 rity of the tissues, such as fibrin, albumen, muco-extractive 
 phosphates of lime and magnesia, and various other salts, 
 it may be supposed that simple separation alone takes 
 place. This indeed may be the case to a certain extent, 
 but it will not explain, after all, how the vessels are en- 
 dowed with the power whereby they are enabled to select 
 from the general mass of blood that particular matter 
 which is required. On the other hand, several substan- 
 ces are found in the animal textures which cannot be re- 
 cognised in the blood, as gelatin, the nervous matter, 
 and even fat; for the oil found in the blood is probably 
 derived by absorption from the adipose cells. It must 
 therefore be admitted that the vessels of those tex- 
 tures which contain substances not recognisable in the 
 blood possess the power of forming them. At the same 
 time we cannot acknowledge them to be endowed with 
 any thing like creative power. The elements of which 
 these animal products are formed must exist in the mate- 
 rials from which they are prepared, and must ultimately 
 be derived from without. In whichever way the proxi- 
 mate principles of the different tissues are derived, whe- 
 
INTERSTITIAL SECRETION. 263 
 
 ther by the separation of matter already in the blood, or 
 by the formation from it of the elements of which they are 
 composed, we have afforded us in the admirable perfec- 
 tion with which the processes are conducted, and their 
 excellent adaptation to each individual organ and condi- 
 tion of that organ, proof of the supreme power, wis- 
 dom, and prescience, which have arranged and contrived 
 them. 
 
 The separation and depositation of the peculiar matter 
 belonging to each individual tissue has been termed 
 nutrition, instead of secretion. The term nutrition has 
 been applied to the separation of solid matter from the 
 blood, while secretion is applied to that of fluids, and in 
 a still more restricted sense to the separation of fluids by 
 glands. It appears to us that there is not only no ad- 
 vantage, but even a disadvantage, in using different terms 
 to indicate the states in which the different substances 
 derived from the blood may be separated from it, for it 
 is allowed that the earthy matter of bones is as distinctly 
 a secretion as when it is deposited on parts which in their 
 healthy condition are free from it. The nutrition or nou- 
 rishment of the different organs of the body depends as 
 much upon the exercise of the function of absorption as 
 upon secretion ; that is to say, it is as necessary that the 
 old be removed as that fresh materials be deposited; and 
 since the term interstitial absorption has been applied to 
 the removal of the textures, in like manner we apply the 
 term interstitial secretion to the depositation of new matter 
 in these textures; and by the term nutrition we under- 
 stand the result of the action of both. 
 
 From the first rudimental state in the womb till life is 
 extinguished in old age, the weight and bulk of the body 
 is continually changing ; its organs undergo alterations in 
 consistence, colour, elasticity, and even chemical consti- 
 tution. The materials which compose the body of the 
 adult man did not enter into the construction of the in- 
 fant ; nor do the materials of the robust man continue to 
 
264 INTERSTITIAL SECRETION. 
 
 extreme old age. The matter which forms the body 
 which we place in the grave did not constitute the same 
 body a few years antecedently. We are constantly throw- 
 ing off old particles and adopting new ; and many of those 
 which enter into the composition of our frame to-day will 
 not belong to us to-morrow. We cannot even be placed 
 in the same room with other individuals for any length of 
 time without mutually interchanging particles with each 
 other. The emanations from one body are absorbed and 
 adopted by another : and in like manner, of those parti- 
 cles which are thrown off one person, some are taken up 
 by another, and become a part of his constitution. 
 
 The rapidity with which these changes are effected 
 depends on a great variety of causes : on age, consti- 
 tution, the state of health, and the texture of the indivi- 
 dual parts. In the earlier periods of life nutrition goes 
 on rapidly, speedily producing a complete renewal of 
 parts ; but as life advances the changes occur more slowly. 
 To fix the limits within which complete alteration is effect- 
 ed in every part is therefore impossible. "With those who 
 have attempted it, the period of seven years is a favourite 
 one, very likely in part from some mysterious attachment to 
 the number seven. The soft parts, and those organs in 
 which depositation and absorption are carried on with great 
 activity, will be completely renewed several times for 
 once of those parts which are denser in their texture, and 
 in which the circulation is more subdued. Sailors, sol- 
 diers, and several savage tribes, are in the habit of im- 
 pressing the skin with figures, in which they trace and 
 insert colouring matters, which remain during their lives ; 
 and by the use of the nitrate of silver the skin has been 
 rendered permanently blue, which would appear to dis- 
 prove the renewal of the skin ; but it is possible that the 
 absorbents refuse the colouring matter employed in tat- 
 tooing ; and as to the colour produced by the internal use 
 of the nitrate of silver, it has frequently completely dis- 
 appeared after having remained for some years. 
 
265 
 
 CHAPTER VII. 
 
 NERVOUS SYSTEM. 
 
 Introductory Remarks Hairy Scalp Skull formed of separate Bones Advan- 
 tages of this Construction Consists of two Plates Advantages of Membranes 
 of the Brain, and the Purposes they serve Divisions of the Brain Presents 
 one Continuous Surface, without the slightest trace of Division Dr Spurz- 
 heim's Demonstraiion of Enormous Quantity of Water collected in Micros- 
 copic Observations of Bauer Of Ehrenberg Structure described Evolution 
 of the Nervous System in size and complexity, accompanied with Parallel 
 Advances in the Higher Instincts and Sagacity Development of the Brain in 
 the Foetus keeps pace with that of the System in general Weight of the Brain 
 in proportion to that of the Body Size in proportion to the rest of the Nervous 
 System Brain the Seat of the Mind Results of Experiments on Spinal Mar- 
 row, its Structure and Development Views and Experiments of Sir Charles 
 Bell Classification of the Nerves Nerves of the Specific Senses Announce 
 the properties of External Bodies Motiferous Nerves Convey the Commands 
 of the Will Respiratory Nerves Indicate the Instinctive Feelings, Passions , 
 and Emotions of the Mind Their Universal Distribution Regular Double- 
 rooted Nerves One Root transmits the Mandates of the Will The other com- 
 municates Impressions received Ganglionic Nerves Immediate Seat of Indi- 
 vidual Vitality of the different Organs of the Body Their General Connec- 
 tionsUniversal Distribution Four great Gangliouic Nervous Centres. 
 
 THE nervous system, to which our attention is now to 
 be directed, furnishes the material instrument of thought, 
 the means by which we become acquainted with the ex- 
 ternal world around us, the channels by which the com- 
 mands of the will, the impressions of instinct and of pas- 
 sion, are conveyed to the instruments by which they are 
 displayed, and the cords of connection which associate the 
 various organs of the body into one harmonious whole. 
 Forming as it does the bond of union between the intel- 
 lectual and physical conditions of the constitution of man, 
 
 N 
 
266 HAIRY SCALP. 
 
 it is equally interesting and important whether we espe- 
 cially devote our attention to sciences which have for their 
 consideration the one or other of these two states of human 
 existence. 
 
 Neither the limits nor object of the present work per- 
 mit us to enter upon the examination of many subjects 
 of the utmost importance connected with the nervous 
 system ; others involve so much controversy and contra- 
 riety of opinion, that to embark in them we should be 
 necessarily led far beyond the boundaries within which 
 we at present wish to confine ourselves. In treating of 
 this department of our subject, we shall therefore alto- 
 gether avoid metaphysical disquisition, and as much as 
 possible controverted points, but shall endeavour to give 
 as clear and complete, at the same time as concise an 
 account of the nervous system as we can, taking care to 
 advert to the functions dependent upon it. 
 
 We shall consider this system under the following divi- 
 sions, and in the following order : 1st, The brain, com- 
 prising the cerebrum, cerebellum, and medulla oblongata. 
 2d%, The spinal cord ; and 3^/y, The nerves. The last we 
 shall classify under five orders: 1. Nerves of special 
 sense. 2. Nerves of simple voluntary motion. 3. Nerves 
 of respiratory or instinctive movements. 4. The regular 
 or double-rooted nerves. And 5. The ganglionic nerves. 
 
 The Brain, constituting the most important organ in 
 the whole body, and being, from the delicacy of its tex- 
 ture, incapable of resisting external influence, is carefully 
 and admirably protected. The coverings of the brain are 
 the scalp, the skull, and certain membranes. 
 
 The hair of the head, furnishing as it were a covering 
 of felt, serves as a protection, by deadening blows, and 
 preventing injury from pressure. Besides, being a bad 
 conductor of heat, it preserves an uniformity of tem- 
 perature ; by favouring exhalation, it contributes to the 
 same effect ; and being impregnated with an oily matter 
 from the sebaceous follicles, it is enabled to resist moisture. 
 
THE SKULL. 
 
 267 
 
 The fat in the cells of the scalp is less liable to variation 
 in quantity than in most other parts of the body, and 
 never accumulates to any considerable extent. 
 
 Beneath the common integuments of the head there is 
 situated a muscle extended by a broad tendinous sheath 
 from the occiput to the forehead, hence called occipito-fron- 
 talis. By means of this muscle, some individuals are able 
 to move the hairy scalp freely backwards and forwards, but 
 in most persons its movements are limited. It elevates and 
 wrinkles the skin of the forehead. Immediately invest- 
 ing the skull, there is a dense fibrous membrane, similar 
 to the membranes covering other bones, here termed peri- 
 cranium, upon which the vessels entering the bone are 
 distributed. 
 
 The skull is divided by anatomists into the bones of 
 the cranium and those of the face. Of the former there 
 are eight, and of the latter fourteen. Nothing could 
 more beautifully illustrate the principles and advantages 
 of the arched form, than the construction of the skull, 
 by which lightness and strength are combined. Where 
 the bone is thin, it is so formed as rapidly to diffuse a 
 blow in different directions. Sometimes the force thus 
 diffused is concentrated again on the opposite side of the 
 skull to that to which the blow was applied ; but, pro- 
 ceeding from the concave instead of the convex surface 
 of the arch, a piece is thus apt to be driven out. Where 
 the bone is so situated as to be liable to a concentration 
 of force, it is there increased in thickness and strength. 
 
 The skull is much more capable of resisting external 
 force, from being composed of separate bones, and at their 
 junctures a freer vascular communication exists between 
 the external and internal surfaces. At birth, the bones 
 of the cranium, at the upper part, are not even in contact 
 with each other. When the head is compressed, they 
 may be made to overlap, whereby birth is more easily 
 accomplished, and subsequently they yield to the growth 
 of the brain. When the brain arrives at its full size, 
 
268 THE SKULL. 
 
 the bones become more completely united, and do not 
 readily yield, and in advanced life their joinings or 
 sutures, as they are called, are often entirely obliterated. 
 The facility with which the sutures give way in child- 
 hood to pressure from within, is the reason why water 
 can accumulate without proving immediately fatal. In 
 such cases the head occasionally becomes enormously 
 enlarged, so as to be capable of containing several pints 
 of fluid; while in a more advanced period of life, the 
 bones being more firmly united, such collections cannot 
 take place, consequently the diseases in which fluids are 
 effused become more rapidly fatal. Some of the bones 
 at the sutures overlap each other like the scales of a fish ; 
 some are dove-tailed, the projections of the one being re- 
 ceived into corresponding depressions of the other ; some 
 are inserted like the panels of a door, while others meet 
 by plain edges. Every one of these instances may easily 
 be shown to be the best possible, as adapted to the cir- 
 cumstances of each individual case. For example, the 
 outer table of the skull is tough and fibrous, like a board 
 of wood. Here dove-tailing is employed, but the inner 
 table is brittle, requiring to be joined by even surfaces, 
 like two pieces of glass, which method is accordingly 
 adopted. 
 
 The skull is formed of two layers or tables, as they are 
 termed, the outer of which is nourished by the peri- 
 cranium, while the internal is supplied with blood by the 
 vessels of the lining membrane. The two tables differ 
 from each other in their density, as has just been stated ; 
 between them there is interposed a spongy substance 
 termed diplb'e, in which the bone is very cellular in its 
 texture. This serves the same purpose as deadening in 
 flooring, whereby concussions are lessened in their pas- 
 sage from the external to the internal table ; the latter 
 being much less capable of resisting their effects, the 
 danger to the brain is in this way also much diminished. 
 
 The bones of the cranium are proportionally large, 
 
THE SKULL. 269 
 
 compared with those of the face, in infancy and child- 
 hood. But afterwards those of the face outstrip in their 
 growth the bones of the cranium. The bones of the 
 cranium, which are in connexion with those of the face, 
 require therefore to increase proportionally in their 
 growth, so as to keep pace with the face, and preserve 
 the symmetry of the parts. This they do, however, only 
 in their external table, the internal remaining to preserve 
 the symmetry with the bones of the cranium. From this 
 inequality of development spaces are left between the 
 two tables, termed sinuses. In the forehead immediately 
 under the eyebrows, there are two such, named frontal 
 sinuses. It sometimes happens that the brain shrinks 
 from disease : this occasionally occurs in idiocy, suc- 
 ceeding insanity. In such instances the internal table fol- 
 lows the diminished brain, when the distance between 
 the two tables is increased, the intervening space being 
 either filled with diploe or remaining empty, forming 
 sinuses. The skulls of the insane are thus frequently 
 very thick. In the elephant the space between the two 
 tables is in some parts to the extent of a foot, the size 
 of the head of that animal giving no idea of the size of 
 the brain, though it imparts to him an air of great sa- 
 gacity. 
 
 Lining the internal table of the skull there is a firm 
 dense membrane named dura mater, from the older ana- 
 tomists considering it as the origin or mother of the hard 
 firm membranes of the body, just as they held the deli- 
 cate vascular web which is in immediate contact with the 
 substance of the brain, to be the mother of the tender 
 membranes, and called it the pia mater. Interposed be- 
 tween these two is the arachnoid, as fine and fragile as a 
 spider's web, from which circumstance it derives its name. 
 The dura mater is a strong fibrous membrane, serving as 
 an internal periosteum. It adheres to the internal surface, 
 and especially at the sutures, by means of the blood- 
 vessels, which pass between it and the bone: at the base 
 
270 MEMBRANES OF THE BRAIN. 
 
 it still more firmly adheres, partly on account of sending 
 processes through the holes at which the blood-vessels 
 and nerves pass at certain parts. It is separated into two 
 layers, the internal of which is doubled on itself, so 
 as to form two remarkable processes, the one termed 
 falciform process, from the resemblance of its shape to a 
 sickle, the other, from being extended over the cerebellum, 
 is called tentorium cerebelli. The falciform process is 
 interposed between the two hemispheres of the brain, so 
 that when we lie upon one side the hemisphere which is 
 placed uppermost is prevented from pressing upon the 
 lower one. In the same way the pressure of the cerebrum 
 upon the cerebellum is obviated by the tentorium, which 
 otherwise would have happened when the head is in the 
 erect position. Between the layers of the dura mater 
 are situated those sinuses to which we had occasion to 
 refer when treating of the peculiarity of the circulation 
 through the brain, wherein the blood is safely lodged 
 without the risk of pressure on the susceptible cerebral 
 contents. A tubular prolongation of the dura mater is 
 extended along the vertebral canal, so as to serve as a pro- 
 tection to the spinal cord, but it does not come in con- 
 tact with the bones of the canal. 
 
 The arachnoid membrane, as we have seen, belongs to 
 the class of serous membrane, and is the most delicate of 
 the order. It covers the internal surface of the dura 
 mater, whence the latter is sometimes described as being 
 nbro-serous : it is extended along the spinal cord, and re- 
 flected over the surface of the brain externally as well as 
 internally. 
 
 The pia mater has a closer analogy to cellular mem- 
 brane than to any other class : it is peculiarly distinguish- 
 ed by having the cerebral blood-vessels minutely subdi- 
 vided upon it before they enter the substance of the brain 
 itself: it is closely attached to the surface of the brain, 
 following all its convolutions, entering into its cavities, 
 and is prolonged down the spinal canal, investing thu 
 
THE BRAIN. 271 
 
 cord ; it also affords a covering to the nerves, forming 
 what is termed their neurilema, or immediate investment ; 
 so that in this way it extends to every part to which 
 nerves are distributed, and thus constitutes one of the 
 most extensive as well as important membranes in the 
 body, intimately connected as it is with the paramount 
 constituent of the animal organism, the nervous system. 
 
 Cerebrum or Brain proper. The whole nervous sys- 
 tem is double, or composed of two symmetrical halves, a 
 right and a left; these have connexions established between 
 them by transverse bands termed commissures, by which 
 they are brought into accordance and co-operation with 
 each other, and on which the individuality of the animal 
 essentially depends. The two halves of the cerebrum 
 are called hemispheres, each of which is divided by ana- 
 tomists into three lobes, the anterior occupying the fore- 
 head, the middle placed by the temples, and towards the 
 base of the skull, and the posterior situated at the back 
 part of the head. 
 
 The nervous tissue is composed of two substances., dif- 
 fering in colour and consistence. The one is of a grey, 
 or rather cineritious or pale ash colour, of a softer texture, 
 and more abundantly supplied with blood. The other 
 is white, of a firmer consistence. The former, from its 
 colour, is called cineritious, or sometimes from its occu- 
 pying the surface of the brain it is termed cortical ; the 
 latter, from being placed chiefly in the central parts of 
 the brain, receives the name of medullary. Their rela- 
 tive position, however, is in several parts reversed, as in 
 the spinal cord. 
 
 The surface of the cerebrum is divided into a great num- 
 ber of waving eminences termed con volutions, by which the 
 surface is greatly extended. The convolutions are con- 
 fined to the class of mammalia ; but they are not found in 
 the whole of this class, for the order of rodentia or gnaw- 
 ers, such as rats, mice, and squirrels, are destitute of them. 
 Each convolution consists of a layer of cineritious matter 
 
272 THE BRAIN. 
 
 on the surface, with a layer of medullary matter in the 
 centre. Dr Spurzheim was the first to show that these 
 convolutions may be unfolded so as to present one uni- 
 form surface of cineritious substance externally, with a 
 corresponding extension of medullary matter beneath. 
 They are occasionally unfolded ir> cases where a large 
 quantity of water is collected within the brain. 
 
 On Dr Spurzheim's first visit to Edinburgh, we en- 
 joyed the advantage of hearing his lucid demonstrations 
 on the structure of the brain and nervous system, and of 
 witnessing several of his private dissections. The ac- 
 count he gave of the manner in which the convolutions 
 of the brain are occasionally unfolded, in cases of water in' 
 the head, excited in us great interest. Sometime after- 
 wards a case fell under our own observation, which may 
 be here adverted to, where we had an opportunity, under 
 the most favourable circumstances, of observing the 
 changes which had been effected from the accumulation 
 of a large quantity of water in the ventricles of the 
 brain. 
 
 A female child, about four months after birth, was 
 noticed to have an unusually large head. Till the fourth 
 year, however, it did not excite much attention, and 
 the mental powers up to this period seemed to be de^- 
 veloped in the ordinary degree. At this period, however, 
 the head began rapidly to enlarge, and the mind became 
 more and more obscured, till complete idiocy supervened, 
 and continued till her death, which occurred in her 
 twenty-second year. We had several opportunities of 
 seeing her some years before her death. The head wa& 
 too large to admit of being supported by the puny mus- 
 cles of the neck ; she therefore constantly lay on a pallet 
 by the side of the fire. The body was small, and de- 
 formed. She appeared to have some slight glimmerings 
 of mind, was readily amused, like a young child, with 
 noise and brilliant objects, shewed some attachment to 
 her parents, and for years kept rubbing a penny piece in 
 
THE BRAIX. 27$ 
 
 her hands, which she would not for a moment part with 
 day or night. When we first saw her it was reduced to 
 the thinness of a wafer. 
 
 Twenty-four hours after her death, permission having 
 been obtained to examine her body, the following mea- 
 surements of the skull, on the removal of the scalp, were 
 made : From the great occipital hole, over the crown, to 
 the space between the eyes, 24f inches ; from one auditory 
 passage over the crown to the other, 21-g- inches ; circum- 
 ference 29 inches. On carefully removing the skull-cap, 
 and exposing the brain, the hemispheres appeared like a 
 large bag filled with water. On the upper surface and 
 sides no trace of convolution could be noticed, but they 
 were not completely unfolded on the base. Upon pimc- 
 turing the bag, ten pints and a quarter of water escaped ; 
 and on examining the interior it presented a vast dome, 
 consisting of a thin layer of cineritious matter on the ex- 
 ternal surface, and a layer of medullary internally. The 
 fibrous arrangement was beautifully displayed : the cere- 
 bral ganglions and tubercles lay at the base, of the usual 
 size. The cerebral contents of the skull weighed two 
 pounds eleven ounces. 
 
 The convolutions are more numerous and extensive in 
 man than in any other animal. The depressions between 
 them are also much deeper in him. If the convolutions 
 of the human brain were all completely unfolded, a sur- 
 face would be presented much more extensive than in 
 any other animal. We may have some idea of the 
 manner in which these convolutions are formed by taking 
 two pieces of cloth of different colours, laying the one 
 upon the other, and collecting them up in folds into a 
 globular shape, so as rudely to represent the brain with 
 its various convolutions. By this arrangement a much 
 greater surface of cerebral matter is packed up in the 
 space occupied by the brain than could have been ef- 
 fected in any other way. It is also to be remarked that 
 
 N 
 
274 THE BRAIJST. 
 
 there is not the slightest line of demarcation between one 
 part of this extended surface and another : it is not like 
 the skin, which varies in different situations, different as 
 it is in appearance, and modified in structure when ex- 
 tended over the cheeks, the body, the limbs, the palms of 
 the hands, and points of the fingers, while the surface 
 of the brain presents one uniform unvaried continuous 
 surface, without the smallest change of appearance in 
 colour, consistence, or texture, however eagerly it may be 
 sought after. 
 
 According to the estimate of Baron Haller, a fifth part 
 of the whole blood of the body in man is sent to the 
 brain. The vessels are first divided and subdivided into 
 exceedingly minute tubes before they penetrate the sub- 
 stance of the nervous matter, and are more abundantly 
 distributed upon the cineritious substance ; so much so 
 that when minutely injected that matter appears to be 
 entirely composed of blood-vessels. Microscopic obser- 
 vations have shewn that the nervous matter is composed 
 of globules. According to Mr. Bauer, the dimensions of 
 these globules vary from ^oW to -g-/^ part of an inch 
 in diameter ; some few being ^oW? or > according to his 
 measurement, of the same size with the globules of the 
 blood, when divested of their coloured investment. With 
 it he estimates the size of the blood globules as TTO-Q- P ar t 
 of an inch in diameter. We thus perceive that the ner- 
 vous globules are much smaller than those of the blood. 
 As a standard for comparison, it may be stated that the 
 human hair varies from T ~ to T ~ part of an inch 
 in diameter. These globules are disposed in rows like a 
 string of beads, and it is this arrangement which gives 
 to the nervous system its fibrous appearance. He no- 
 ticed a transparent tenacious jelly-like semi-fluid matter. 
 Besides this jelly-like fluid, there exudes a colourless 
 aqueous fluid, which evaporates on exposure to the air. 
 Of these three namely, the globules, the elastic jelly, 
 
THE BRAIN. 275 
 
 and the colourless watery fluid the nervous matter es- 
 sentially consists. 
 
 According to the observations of Professor Ehrenberg, 
 the nervous system consists of the three following forms 
 of organic structure. 1. Minute tubes resembling hol- 
 low strings of pearls, the pearls of which are not in con- 
 tact, which gives them a knotted, jointed, or articulated 
 appearance. They contain a tough transparent fluid, to 
 which he restricts the name nervous fluid. These tubules 
 run in straight parallel lines, giving the fibrous character 
 to the medullary matter, converging from the convoluted 
 surface of the brain towards the base. They sometimes 
 cross each other, occasionally ramify, but are never seen 
 to anastomose. They form the principal 
 constituent of the brain, spinal cord, and 
 of the optic, auditory, and olfactory nerves. 
 Fig. 20 shews the appearance which this 
 structure presents under the microscope. 
 2. Simple cylindrical unjointed nervous 
 tubes like the last, running parallel, and 
 never anastomosing, about T 4o- part of a 
 line in thickness, and united into bundle*, 
 which again form larger bundles denomi- 
 nated the nervous cords. These bundles 
 FIG. 20. an( j cor <j Sj b u t no t the individual tubes, 
 are surrounded with a ligamentous vascular covering, or 
 neurilema. The cylindrical tubes are larger than the 
 jointed, and contain a viscid, whitish, less transparent 
 matter, which he calls medullary. Ehrenberg has traced 
 these medullary tubes along the motiferous nerves back 
 to their emergence from the spinal marrow, and finds 
 them to be continuous with the jointed that is, the small 
 jointed tubes containing the transparent liquid enlarge 
 and become cylindrical tubes filled with medullary mat- 
 ter, forming the nerves, with the exception of the three 
 special nerves of the senses of sight, hearing, and smell, 
 
276 
 
 THE BRAIN. 
 
 in which no such conversion takes place. The tubes, as well 
 as the fluids, appear in this way gradually to pass into each 
 other, and to form merely modi- 
 fications of the same structure. 
 Fig. 21 shews the appearance of 
 these cylindrical tubes, some of 
 which have been emptied of the 
 jelly-like milk-coloured medullary 
 fluid. 
 
 3. On the convoluted cineritious 
 matter of the brain he observed a 
 very fine-grained soft substance, in 
 which here and there are scattered 
 larger grains. The large grains are 
 FIG. 21. free, and consist of small granules, 
 
 which appear to be connected in rows by means of slen- 
 der threads to the very fine small grains of the sub- 
 r: vf; ; ;;p ?s , r? ^ 7/ .,. stance. Fig. 22 represents the termi- 
 f nation of the optic nerve in the retina 
 of the eye, where the grains are seen 
 of the size of T ~ part of an inch, ly- 
 ing upon the jointed tubes of which 
 the retina is chiefly composed, their 
 diameters being -g-oW P art of an mcn > 
 and the nuclei of the grains are of 
 The globules of nervous matter being 
 arranged in rows, forming the tubular structure of Ehren- 
 berg, produce the fibrous appearance presented in the 
 brain, so that when we speak of the direction of the fibres, 
 we in other words indicate the direction pursued by the 
 rows of globules or jointed tubes. 
 
 From the circumference of the brain the fibres proceed 
 in two directions : the one set concentrate like rays to- 
 wards the middle line, and meet their fellows of the oppo- 
 site side, forming commissures whereby a consent and 
 identity of action is established between the two sides of 
 
 
 FIG. 22. 
 
 the same size. 
 
THE BRAIN. 277 
 
 the brain. Between the two hemispheres there is situ- 
 ated the great commissure of the cerebrum, composed of 
 parts formed of medullary matter, which are termed the 
 corpus callosum, septum lucidum, and/0mi#. Towards 
 the base there are two other medullary bands, named an- 
 terior and posterior commissures, and a fourth of cineri- 
 tious substance is called the soft commissure. The me- 
 dullary commissures constitute the converging fibres of 
 Drs Gall and Spurzheim. 
 
 Another set of fibres like the last commence at the con- 
 volutions, and concentrate towards the base, where they 
 form the crura of the cerebrum, and become continuous 
 with the medulla oblongata and spinal cord. Gall and 
 Spurzheim having traced these fibres from the spinal cord 
 and crura upwards to the convolutions, have called them 
 the diverging fibres, while the converging fibres of these 
 authors constitute those which form the commissures. 
 
 Towards the centre and base of the cerebrum, the sur- 
 face is inflected inwards, so as to form an intricate internal 
 cavity, the several compartments of which are known 
 under the name of ventricles. Of these there are the two 
 lateral ; the third and fourth are situated between the 
 cerebellum and the medulla oblongata. They are all co- 
 vered with pia mater and arachnoid, which are extended 
 into them. They communicate with each other, and serve 
 to increase the cerebral surface. The two lateral ventricles 
 are the largest, and each contains a fold of the pia mater 
 invested with arachnoid, in which there are numerous 
 blood-vessels, chiefly veins, which form what is termed 
 the choroid plexus. It is principally in the ventricles that 
 collections of serous fluid take place in cases of water in 
 the head. In the healthy condition of the brain they can 
 scarcely be considered as cavities, but rather as means 
 whereby the surface of the brain is still further extended. 
 Like the external surface, it is constantly bedewed with 
 moisture exhaled from the serous membrane covering it, 
 
278 THE BRAIN. 
 
 and which only accumulates in quantities when the ba- 
 lance between secretion and absorption is subverted. 
 
 Along the floor of the lateral ventricles there are situa- 
 ted two swellings, sometimes named the anterior cerebral 
 ganglions. From streaks of white matter being seen pass- 
 ing through the cineritious substance of which they are 
 principally composed, they are more commonly known 
 under the name of the striated bodies, and are connected 
 with each other by the anterior commissure. Immediately 
 behind them are placed two other swellings, or posterior 
 cerebral ganglions, which, from the circumstance of the 
 optic nerves resting upon them for some length of their 
 course, are termed the optic thalami. They are united be- 
 hind by the posterior commissure, and in the middle by 
 a quantity of grey matter forming the soft commissure. 
 
 Still further back, just before the prolongations from 
 the cerebrum and cerebellum unite to form the medulla 
 oblongata, we have four rounded tubercles or ganglions, 
 disposed in pairs, suggesting the idea of twins : hence 
 they are named the four twins, or tubercula quadrige- 
 mina. 
 
 The pineal gland is placed between the anterior tuber- 
 cles and the posterior cerebral ganglions, with the latter 
 of which it is connected by bands of medullary fibres. 
 
 We have thus four pairs of ganglions near to the base 
 of the brain, the anterior of which is the largest, each pair 
 becoming smaller as we count backwards, and in the 
 middle of them the pineal gland is placed in a situation 
 which once gained for it the pre-eminence of being con- 
 sidered the especial seat of the soul. 
 
 The Cerebellum, or little brain, is about one-eighth of 
 the size of the cerebrum. It is situated at the back part of 
 the head, and divided into two lateral lobes. It is com- 
 posed of cineritious and medullary matter like that of the 
 cerebrum. Instead of waving convolutions, its surface pre- 
 sents from sixty to seventy nearly horizontal plaits, with 
 
THE BRAIN. 
 
 smaller ones interposed between them, by which arrange- 
 ment its surface is vastly extended. 
 
 The fibres of the cerebellum, like those of the cerebrum, 
 proceed in two sets. The one set pass obliquely down- 
 wards, and become continuous with the medulla oblon- 
 gata and spinal cord : the other incline forwards, and form 
 what is called the pons or bridge of Varolius, bearing the 
 same relation to the cerebellum that the great commissure 
 does to the cerebrum. The former constitute the diverg- 
 ing, and the latter the converging fibres of the cerebellum, 
 according to Gall and Spurzheim. On each side a fasci- 
 culus or bundle of medullary fibres also proceed upwards 
 to the posterior pair of the tubercula quadrigemina, in 
 which they terminate. They are united by a semitrans- 
 parent medullary web, which serves as a commissure, 
 though it gets the name of a valve. 
 
 If a vertical section be made of one of the lobes of the 
 cerebellum, a peculiar appearance is presented, resembling 
 the stem and branches of a tree, and therefore called arbor 
 vitce. 
 
 From the above description it will appear that the 
 cerebrum and cerebellum are each composed of two sets 
 of fibres, which, commencing at the surface, run in two 
 directions, the one proceeding to become continuous with 
 the columns of the spinal cord, the other running towards 
 the middle line to meet with their fellows of the opposite 
 side, so as to establish an unity and sympathy of action 
 between the right and the left. 
 
 The Medulla Ollongata may be considered as the com- 
 mon centre of the cerebro-spinal portion of the nervous 
 system, or where the influences of intellect, passion, in- 
 stinct, sensation, and motion meet and associate, and as 
 that part on which life more immediately depends. Those 
 parts of the nervous system with which intellect, passion, 
 and instinct are especially connected, may be destroyed 
 without the immediate extinction of life. The nerves on 
 which sensation or voluntary and instinctive motion are 
 
280 
 
 THE BRAIX. 
 
 dependent may be cut by way of experiment, or rendered 
 wholly incapable of performing their function by disease ; 
 nevertheless death does not necessarily follow, but the 
 instant that the medulla oblongata is touched, in the 
 same moment life is extinguished. For this reason sports- 
 men sometimes terminate the sufferings of their game by 
 introducing an instrument so as to destroy this part ; and 
 in some countries it is the practice with butchers to spine, 
 or pith as it is called, the cattle which they kill. It may 
 also be observed, that many animals of prey, especially 
 birds, strike their victims on the back of the head, or at 
 the top of the neck, so as instantly to deprive them of 
 vitality. 
 
 The medulla oblongata is formed of six columns, or 
 three pairs. The two anterior are continuous with fibres 
 both from the cerebrum and cerebellum. Those from the 
 surface of the crura of the cerebrum pass under the pons, 
 and descend along the whole length of the spinal cord. 
 Immediately under the pons they are of a pyramidal 
 shape, and there known by the name of the pyramidal 
 bodies or eminences. About an inch below the pons, some 
 of the fibres of the pyramids decussate ; those of the right 
 side crossing to the left, and those of the left to the right, 
 and this they do either in one bundle or in several divi- 
 sions, differing in this respect in different individuals. 
 This decussation of the pyramidal bodies enables us to 
 explain how injuries of the brain on one side are followed 
 by loss of power or paralysis of the opposite side of the body. 
 The posterior pair of columns are termed the posterior 
 pyramids or restiform bodies. They are continuous with 
 the diverging fibres of the cerebellum, and with others 
 from the cerebrum, and are prolonged downwards along 
 the spinal cord. 
 
 Between the anterior and posterior pyramids, two mid- 
 dle or lateral bodies are placed. From their resem- 
 blance to the fruit of the olive, they are called the olivary. 
 Fibres proceeding from them may be traced upwards 
 
THE BRAIN. 281 
 
 under the pons to the crtira and cerebral hemispheres, and 
 also downwards along the side of the spinal cord, but 
 very faintly on the cord. 
 
 A narrow line of white matter lies upon the olivary 
 bodies, between them and the posterior pyramids. This 
 line is most distinct at the upper part of the medulla ob- 
 longata. The fibres of which it is composed may be 
 traced upwards to the inferior of the tubercles, but not to 
 the hemispheres. Downwards, they terminate opposite 
 to the fourth vertebra of the neck. From this track the 
 nerves of respiratory or instinctive motion have their ori- 
 gin. It has been already mentioned, that the pons is 
 formed by the converging fibres of the cerebellum, which 
 cross the sides of the medulla oblongata, and meet their 
 fellows of the opposite side, so as to form the commissure 
 of the cerebellum. 
 
 Nothing can be more striking than the difference be- 
 tween the remarkable simplicity of the structure of the ner- 
 vous system, and the multiplicity and intricacy of the func- 
 tions to which it is subservient. Nevertheless, the con- 
 dition in which it is found in the various classes and 
 tribes of animals, as well as its successive evolution in the 
 human subject, from its primary rudimental state to its 
 complete development, shew us that some portions per- 
 form much higher functions in the animal economy than 
 others. Just as we find gradual and almost imperceptible 
 steps of progressive improvement, from the most simply 
 organized zoophyte up to man, in the mechanism of the 
 organism, correspondent with the scope, variety, and ex- 
 tent of the function exercised, so do we find different 
 parts of the nervous system gradually unfolded, coinci- 
 dent with the development and manifestation of the or- 
 gans and faculties. 
 
 In zoophytes, the nervous globules are disseminated 
 through the general mass of which their bodies consist, 
 without being concentrated into any given point. In 
 the more perfect invertebrate animals, as the structure 
 
282 THE BRAIN. 
 
 becomes more complicated, the nervous matter assumes a 
 distinct arrangement, so as to form one or more swellings 
 or ganglions connected with each other by intermediate 
 nervous threads, the number of the ganglions, and the in- 
 tricay of the communications corresponding with the de- 
 velopment of the organs. As we ascend in the scale of 
 animal existence, and examine the lowest class of verte- 
 brated animals, fish, we find superadded to the ganglionic 
 system, a spinal marrow, with nerves of voluntary motion 
 and sensation, of instinctive movement, of peculiar sense ; 
 but the brain is merely in a rudimentary state. As we 
 proceed through the other three vertebrated classes, rep- 
 tiles, birds, and mammalia, we find a successive evolution 
 in the size and complexity, especially of the brain, and 
 nerves more immediately connected with it, and observe 
 that these increments are accompanied with parallel ad- 
 vances in the manifestation of the higher instincts, saga- 
 city and intelligence, till we reach man, the most saga- 
 cious and most intelligent of all animals, and who feels 
 himself a moral and responsible creature. 
 
 The foetus is found to pass through several successive 
 stages of organization, or it undergoes a variety of meta- 
 morphoses, commencing with the more simple forms in 
 the structure of the organs connected with the different 
 functions, becoming more elaborate and complicated at 
 the different periods of its growth and development. Of 
 the nervous system, the ganglionic portion is that which 
 is first established, to which the spinal cord, and nerves 
 in connexion with it, next succeed, and lastly, the brain ; 
 the hemispheres being the last to be completely unfolded, 
 for even at birth the convolutions are scarcely established. 
 The medullary matter, at least so far as the brain is con- 
 cerned, takes precedence of the cineritious. 
 
 The weight of the brain, in proportion to that of the 
 rest of the body, varies in different animals, as will be 
 seen from the following table of instances selected from 
 Blumenbach's Comparative Anatomy ; 
 
THE BRAIN. 283 
 
 Man ................................ J t jV 3 T o yj 
 
 Qrang Outangs. 
 Gibbon .......................................... ^s 
 
 Sapajous (American Apes.} 
 
 Samiiri ................................... 
 
 Sai...... 
 
 Ouistiti 
 Coa'ita 
 
 African and Indian Apes. 
 
 Malbrouk 
 
 The Monk Ape 
 
 Mammalia. 
 
 D g ....................... IT 5 
 
 Fox 
 
 Paf 111 
 
 ^ at .................................... ^? 54 I5 
 
 Beaver ........................................ 2 J 
 
 Hare 
 
 Bat ............................................. ,V 
 
 Mouse ........................................ 4^ 
 
 Elephant ..................................... ^J 
 
 "Wild boar ............ , . ...................... B 7 ^ 
 
 Chinese hog ................................... 4 1 T 
 
 Roebuck ...................................... ?% 
 
 Stag 
 
 Ox ......... 
 
 Calf 
 
 Horse ........................... . 
 
 ^ SS .............. ............................... 254 
 
 Porpoise ....................................... ^ 
 
 Dolphin ........................... ^ ^ ^ Tusf 
 
 Common whale .............................. 3 ^o o 
 
 Canary bird .................................... { 
 
 Goose ........................................... 
 
284 THE BRAIN. 
 
 Turtle ! 
 
 Fishes. 
 
 Carp jj, 
 
 Shark : ! 
 
 It will be perceived from the inspection of the above 
 table that no inference of the slightest importance can be 
 deduced from the weight of the brain compared with that 
 of the rest of the body : that the proportion varies exceed- 
 ingly in different individuals of the same species, and in- 
 deed in the same individual at different times, for the 
 brain does not alter with the increase and diminution of 
 weight to which the body is so liable in various condi- 
 tions of health and disease. Thus an animal may become 
 enormously fat when the weight of the brain will bear a 
 smaller, or if emaciated, a larger relative weight to the 
 whole bulk of the body. 
 
 When we compare the size of the brain with that of 
 the spinal marrow and nerves arising from it, we find that 
 the proportion they bear to each other has a connection 
 with the rank the animal may hold in the scale of intelli- 
 gence, and also with its tenacity of life. Of all ani- 
 mals the brain of man has the greatest development, not 
 only in the size, but also in the intricacy of the structure 
 and extent of its surface in proportion to the spinal mar- 
 row and nerves ; while in animals lower in the scale, as 
 reptiles and fishes, the brain presents merely a delicate 
 anterior termination of the spinal cord, not much larger 
 in its diameter, and differing from the rest of the cord 
 chiefly in presenting a more complicated organization, in 
 which we have the more important parts of the brain ex- 
 hibited in a rudimental state; and in being connected with 
 a greater variety of nerves, both as to their number, and 
 the functions with which they are associated. In these 
 
THE BRAIN. 285 
 
 animals the instincts are limited, and the displays of saga- 
 city extremely obscure, while they possess great tenacity 
 of life ; and their different systems of organs seem less in- 
 timately connected and more independent of each other. 
 Frogs still continue to jump about for some time after their 
 heart has been torn out ; and the heart of the shark will 
 palpitate for several hours after it has been removed from 
 the body. In one instance we saw the heart of a large 
 skate distinctly display contractions on being pricked 
 with a needle thirty hours after removal. Turtles have 
 continued to live for months after the whole brain has 
 been scooped out. 
 
 In some of the lower tribes of invertebrate animals, the 
 independent existence of the different parts is still more 
 strikingly displayed ; for on dividing their bodies, pro- 
 vided each piece retains a nervous ganglion, it will be- 
 come a separate individual, adequate to the exercise of all 
 the functions performed by the entire animal, and repro- 
 ducing at each extremity new portions, which likewise 
 become endowed with distinct vitality ; and when we 
 descend to zoophytes, we find that on cutting them into 
 shreds, however minute or irregular, each piece retains 
 life and continues to grow, division forming in them one 
 of the means of rapid multiplication. 
 
 Numerous experiments and observations on different 
 animals, and on man in different conditions, tend to es- 
 tablish the conclusion that the cerebrum is entitled to be 
 considered as the special organ through which are dis- 
 played the passions, the emotions, the intellectual powers, 
 and the moral affections of the mind ; that it is the 
 throne from which the behests of the will are issued forth 
 to the various parts of the body under its control, and to 
 which the various impressions received by the organs of 
 sense are finally communicated. 
 
 From the earliest times the brain has been generally 
 understood as the established seat of the mind. Thus, 
 according to ancient mythology, Minerva, the goddess of 
 
286 THE BRAIN. 
 
 wisdom, sprang ready armed from the head of Jupiter; and 
 the " king of gods and men" is uniformly represented with 
 an enormous head ; while in athletes and heroes gifted with 
 muscular strength, the head is very small in proportion to 
 the rest of the body. It is certainly reasonable to suppose 
 that the size, and the more or less elaborate construction 
 of that organ from which the conceptions of the mind are 
 issued, and through which the impressions from external 
 agencies are appreciated, should exhibit proportional re- 
 lations to the instinct, sagacity, and intelligence of the 
 animal ; so we find comparative anatomy, as well as the 
 gradual evolution of the nervous system in the foetus, 
 support this view. 
 
 Notwithstanding the innumerable observations and ex- 
 periments which have so long engaged the attention 
 of the most distinguished physiologists of past times, 
 and more especially of the present age, the precise 
 share which the different parts of the brain exercise in 
 the various functions with which it is confessedly con- 
 nected, has been by no means ascertained. It is, however, 
 sufficiently established by experiment, that although the 
 cerebrum, either conjointly with, or independently of, the 
 cerebellum, be the instrument which takes cognizance 
 of sensation, and the source from which the motives 
 spring which call forth voluntary and instinctive mo- 
 tions, yet it may be sliced off in successive layers with- 
 out the animal showing the slightest marks of suffering, 
 and that neither indication of pain nor excitement of 
 movement occur till the turbercles are reached, when 
 violent convulsive movements are produced, accompanied 
 with expressions of intense suffering. The hemispheres, 
 the commissures, the anterior and posterior cerebral 
 ganglions, may be thus removed layer after layer, with- 
 out exciting pain or motion. The senses, however, no 
 longer produce perception. Memory, intelligence, and 
 judgment are abolished, and the animal appears to be re- 
 duced to a kind of automaton, deprived of desires, ap- 
 prehensions, and judgment. 
 
SPINAL MARROW. 287 
 
 Similar sections have been performed on the cere- 
 bellum, with results shewing that it is equally insensible 
 and incapable of exciting motion as the cerebrum ; that 
 when it is extirpated, feeling, volition, and percep- 
 tion are retained, while the animal is no longer ca- 
 pable of regulating its movements ; if it attempts to 
 walk, it staggers about without the power of com- 
 manding the necessary co-operation of the muscles, 
 or infusing the precise degree of energy necessary for the 
 due performance of the task. The distinguished experi- 
 menter, M. Fleurens, observes, " In depriving the animal 
 of the cerebrum, it was thrown into a state resembling 
 sleep ; in removing the cerebellum, it was brought to a 
 state resembling intoxication." 
 
 Through the medulla oblongata the influence of the 
 cerebrum and cerebellum is transmitted to the nerves, 
 which obey the will ; it serves also as a channel for con- 
 veying to those parts the impressions received by the 
 nerves of sense and general sensation. Besides these 
 offices it would appear that it is endowed with the power 
 of instituting motions, and that it forms the general 
 centre and great bond of connexion between the different 
 portions of the nervous system. 
 
 Spinal Cord. Between the medulla oblongata and 
 spinal cord there is no distinct line of demarcation. They 
 are therefore held by several anatomists as one organ, and 
 as such described. The medulla oblongata, however, 
 consisting of six columns, giving rise to several nerves 
 of distinct function, being the point at which excitement 
 to motion commences, and sensation terminates, and pos- 
 sessing the power of originating motion in itself, seems 
 from these circumstances entitled to a separate considera- 
 tion. Mere continuity of structure and identity of texture 
 might equally be brought forward as a reason for regard- 
 ing the cerebrum and cerebellum also as merely portions 
 of the same organ, as indeed in many respects they are. 
 
 For these reasons it apj ears more advantageous to se- 
 
288 SPINAL MARROW. 
 
 parate the spinal cord from the medulla oblongata, 
 though it is by no means easy to fix upon a point at 
 which the one terminates and the other commences, 
 they slide so imperceptibly into each other. The old 
 anatomical line of separation may therefore be adopted, 
 that is, where the medulla escapes from the foramen 
 magnum, or great hole in the base of the skull. 
 
 Leaving the foramen magnum, the spinal cord pro- 
 ceeds down the canal of the vertebrae, till it reaches the 
 first or second vertebra of the loins, where it generally 
 terminates in a spindle-shaped extremity. In the foetus 
 it is prolonged through the whole extent of the canal, as 
 it is in animals with a tail. In the earlier periods of 
 foetal life, the human subject is furnished with a caudal 
 appendage, which gradually disappears as the system be- 
 comes unfolded, though some monsters have been born 
 with a tail. Indeed a great number of monstrosities 
 arise from the circumstance of the evolution of the 
 organ affected having been arrested in some of the stages 
 through which it passes, from its first rudimentary state 
 to complete development. The ascent of the spinal cord 
 in the canal is to be attributed partly to the extension of 
 the lower limbs, and enlargement of the pelvis, so that it 
 is as much merely apparent as real. 
 
 Besides the strong and admirably constructed case 
 of bone in which the cord is lodged, it is surrounded 
 by a tubular prolongation of the dura mater, which docs 
 not adhere immediately to the bone as it does within the 
 skull. It is also supplied with extensions of the arach- 
 noid and pi a mater, which closely invest it. Between 
 the arachnoid and pia mater there is a quantity of thin 
 serous fluid, varying from two to six ounces. The cord 
 is thus surrounded by a fluid medium, and is kept 
 steady in this fluid by little ties or stays, which stretch 
 from the dura to the pia mater. They are attached along 
 the sides of the cord, between the anterior and posterior 
 roots of the nerves, having the appearance of the teeth of 
 
CLASSIFICATION OP NERVES. 289 
 
 a saw, and are therefore termed the dentated processes. 
 A similar fluid to that in the canal is effused between the 
 arachnoid and pia mater throughout their whole extent, 
 over the internal and external surfaces of the brain. Be- 
 sides imparting a certain degree of support by its pressure, 
 it is admirably adapted to obviate the effects of concus- 
 sion, so as to prevent injuries from jars which these organs 
 are so impatient of, and by which they are so liable to 
 be injured. 
 
 The general form of the spinal cord is cylindrical, 
 though somewhat greater in its transverse diameter, so 
 that it presents a flattened appearance. It is not uniform 
 in thickness throughout its whole extent, but is enlarged 
 at the lower part of the neck, where the nerves of the 
 arms have their origin, and again at the lower part of the 
 back, from whence spring t he nerves of the legs. The 
 substance of which it is composed is similar to that of 
 the brain, consisting of cineritious and medullary matter, 
 the latter being disposed in a thin layer upon the surface, 
 while the former constitutes its central nucleus, so that we 
 have here the relative position of the two reversed from 
 what occurs in the cerebrum and cerebellum. This disposi- 
 tion, however, also obtains in the medulla oblongata, and 
 in the central parts of the cerebrum and cerebellum. 
 
 The cord is divided into two lateral halves by a groove 
 in front, and a similar groove behind. On each side 
 there are also two lateral grooves faintly marked, from 
 which the anterior and posterior nerves have their origin. 
 Each lateral half is composed of two columns, so that the 
 cord consists of four columns ; from the two anterior the 
 nerves of motion spring, and from the two posterior those 
 of sensation. 
 
 Of no part of the nervous system has the function been 
 more satisfactorily determined. For the discovery and 
 complete establishment of this important truth, as 
 well as for a more philosophical arrangement of the 
 nerves in general, we are indebted to Sir Charles 
 
290 CLASSIFICATION OF NERVES. 
 
 Bell. The inextricable confusion in which the nervous 
 system was involved, as taught by the most distinguished 
 teachers, from which the genius of Bell has done so much 
 to emancipate us, must be within the recollection of many ; 
 and although the structure which he has erected may not 
 be complete in all its details, yet he has laid a firm foun- 
 dation, and pointed out the way by which we may hope 
 ultimately to arrive at a more just appreciation of this 
 most interesting and most mysterious portion of our ma- 
 terial constitution. 
 
 Thirty pairs of nerves spring from the spinal marrow ; 
 eight from the region of the neck, twelve from that of 
 the back, five from the loins, and five from the pelvis. 
 All these nerves arise by two roots, the one root from the 
 anterior, and the other from the posterior column. The 
 fibres from the posterior root swell into a ganglion before 
 they unite with the anterior, in constituting the nerves 
 which are distributed on the parts under the control of 
 the will, and from which common sensation is derived. 
 Sir Charles Bell ascertained, by laying open the spinal 
 canal in a living animal, and dividing the posterior roots 
 of the nerves, that the parts to which they are distri- 
 buted are deprived entirely of feeling. The limb may 
 be cut, pricked, or lacerated in any way, without the 
 animal shewing the slightest indication of suffering : at 
 the same time it retains the power of motion. In another 
 experiment, he first stunned the animal, then exposed the 
 spinal marrow, and pricked the posterior roots, without 
 the slightest indication of irritation in the muscles with 
 which they were connected being induced. But on 
 grasping the anterior roots with the forceps, contraction 
 of the muscles supplied by the nerve accompanied each 
 touch of the instrument. 
 
 These experiments have been repeated by M. Magendie, 
 and others, and varied in different ways, completely esta- 
 blishing the fact, that the anterior roots are subservient 
 to motion, and the posterior to sensation; that one or 
 
CLASSIFICATION OF NERVES. 291 
 
 other of these functions may be destroyed at pleasure, by 
 cutting the roots with which either is immediately con- 
 nected, and that on dividing the two roots, complete para- 
 lysis, both as to motion and sensation, ensues. One of 
 Magendie's experiments is interesting. It is well known 
 that the introduction of mix vomica into the animal 
 economy produces violent spasmodic contraction, tremors, 
 and rigidity of the muscles. This property was made 
 available as a test of the distinct function of the two se- 
 ries of nervous roots. It was found that while all the 
 muscles whose nerves remained entire were thrown into 
 a state of the greatest agitation, those supplied with 
 nerves, the anterior roots of which had been divided, re- 
 mained relaxed and unaffected. 
 
 This discovery of the separate office performed by each 
 set of fibres, explains what sometimes happens in disease, 
 where a part of the body is deprived of motion, retain- 
 ing sensation; or, conversely, sensation may be abolished, 
 while motion remains, complete paralysis occurring where 
 both roots are involved. 
 
 From the statements now made, it will appear that the 
 impressions upon the surface of the body, and on all those 
 parts endowed with common feeling, are conveyed by a 
 peculiar set of nerves connected with the posterior co- 
 lumns, which serve as conductors upwards to the brain ; 
 that through perception exercised by the brain, these im- 
 pressions are taken cognizance of, and the mind is enabled 
 to appreciate them. If the result of the mental determina- 
 tion is such as to require the exercise of muscular action, 
 the command is transmitted along the anterior column to 
 the motific nerve, distributed to the muscle required to 
 be employed, and instantly the muscle obeys. We have 
 thus two streams of nervous influence : by the one intel- 
 ligence is announced to the mind ; by the other the pur- 
 poses and resolutions of the will are communicated to the 
 muscles necessary to carry these into effect. The cir- 
 cuitous course forms no objection, since we know, for ex- 
 
292 CLASSIFICATION OF NERVES. 
 
 ample, that the galvanic shock is transmitted from one 
 extremity to another of a wire miles in length without 
 the smallest perceptible interval of time. The velocity of 
 light affords another instance of rapid transmission, for 
 astronomers have shewn that light reaches us from the 
 sun in eight minutes and a quarter, or at the rate of 
 192,500 miles in a second of time; or we may say its 
 velocity is such that it would traverse a space equal to 
 eight times the circumference of the earth while the pulse 
 makes a single beat. So the impression may be made at 
 the point of the finger, the sensation communicated to the 
 mind, the resolution formed, the command issued, trans- 
 mitted and complied with, in an instant of time, so as to 
 appear merely as one act, though in reality consisting of 
 a succession of several. 
 
 If the chain of connection be interrupted, no command 
 can be conveyed in the one direction, nor sensation in the 
 other. Thus, when a double-rooted nerve is divided, the 
 control of the will over the muscles on which it is rami- 
 fied is lost ; but by irritating the extremity of the divided 
 nerve next to the muscles, the communication being un- 
 broken, they are thrown into action. Again, when the 
 limb is pricked or lacerated beyond the division, no sen- 
 sation is experienced ; but if the cut extremity nearest the 
 brain be irritated, then is the pain felt, there being no 
 interruption between the point of injury and the seat of 
 perception. Thus we find that individuals who have had 
 their limbs amputated frequently complain of pain as it 
 were in the fingers or toes, of which they may have been 
 deprived for years, because the stumps of the nerves that 
 formerly supplied the amputated parts are affected. 
 
 The double-rooted nerves constitute an order, the func- 
 tion of which appears to be fully ascertained. Their dis- 
 tribution seems more uniform than that of some others : 
 hence they have been called the regular or symmetrical. 
 They all arise from the spinal cord. One pair of nerves 
 from the skull, distributed to the face and other parts, 
 
CLASSIFICATION OF NERVES. 293 
 
 resembles them in its double origin, in the anterior root 
 swelling into a ganglion, and in its twofold function of 
 sensation and motion. According to the numerical names 
 which have been given to the cranial or those nerves which 
 pass out of the skull, it is the fifth, so that, including this 
 nerve, we have thirty-one pairs of regular nerves. 
 
 The nerves contributing to the senses of sight, hearing, 
 and smell, are so obviously essential to the respective 
 functions with which they are connected, that there can 
 be no question as to the propriety of classifying them as 
 a distinct order. Their numerical names are the first, 
 second, and soft portion of the seventh. 
 
 There remain for consideration other cranial nerves, 
 having only a single origin. Three of them arise from 
 the anterior columns of the medulla oblongata, one pair 
 springing from above, the other two from below the pons. 
 These three pairs have consequently an origin correspond- 
 ing with the anterior roots of the regular nerves, and like 
 them contribute exclusively to motion. They are the 
 third, sixth, and ninth. . 
 
 Besides these three we have five pairs also taking their 
 rise by single roots from the same line or tract. This 
 tract is different from that to which the motiferous 
 nerves are attached. It forms a slip of fibres, lying be- 
 tween the middle and posterior columns of the medulla 
 oblongata, and may be traced downwards till it becomes 
 gradually lost opposite the fourth vertebra of the neck j it 
 is continued under the pons upwards to the inferior 
 tubercle of its own side. The nerves proceeding from 
 this tract, form an order to which Sir Charles Bell has 
 applied the terms respiratory, or irregular. They con- 
 stitute a division of his classification which is the least 
 satisfactorily established, has excited the greatest con- 
 troversy, and called forth the keenest opposition to the 
 views he has taken. The names he has chosen seem 
 likewise unfortunate, requiring an explanation of the 
 sense in which they are applied. "VYe need not, however, 
 
294 NERVES OF SPECIFIC SENSE. 
 
 here enter upon these controversies, for although they 
 may not deserve altogether to be considered as a distinct 
 order of nerves, in so far as their function is essentially 
 concerned, still their mode of origin, their manner of 
 distribution, their character in different classes of animals, 
 and their especial connexions with instinctive motions, all 
 seem to entitle them to a separate examination. They 
 comprehend the fourth dense portion of the seventh and 
 eighth cranial nerves, and two from the neck, the phrenic 
 and external respiratory. 
 
 The following is the arrangement we shall adopt in 
 treating of the nerves : First, nerves of special sense, in- 
 cluding the first, second, and soft portion of the seventh. 
 Second, Motific nerves, the third, sixth, and ninth. 
 Third, The respiratory, the fourth dense portion of the 
 seventh, eighth, phrenic and external respiratory. Fourth, 
 The regular nerves, comprising the fifth, cranial, and the 
 thirty spinal nerves ; and, lastly, we shall conclude with 
 an account of the ganglionic nerves. 
 
 FIRST ORDER. Nerves of Specific Sense. The nerves 
 of this order are, according to Ehrenberg, composed 
 of jointed tubules like the substance of the brain and 
 spinal cord. They are incapable of transmitting to the 
 mind any other impression than such as belong to the 
 respective senses with which they are connected. Thus, 
 the olfactory can communicate only ideas of odours, the 
 optic of colours, the auditory of vibrations, by whatever 
 kind of stimulants they are excited. Electricity applied 
 to the eye excites the impression of vivid light ; to the 
 nose, a peculiar odour ; to the ear, sound. In the same 
 way mechanical irritants produce on these nerves only 
 appropriate impressions. When the expansion of the 
 optic nerves is pierced by the needle of the surgeon, a 
 flash of light is perceived. A blow produces the same 
 effect, and the eyes are said to strike fire. Pressure 
 upon the ball of the eye causes the appearance of a beau- 
 
NERVES OF SPECIFIC SENSE. 295 
 
 tiful zone of light : not that light in any of these in- 
 stances is produced, but because the optic nerve being 
 irritated, announces to the mind its being affected in the 
 only manner of which it is capable. These nerves are all 
 connected with an apparatus admirably constructed for 
 their individual functions, as we shall have occasion to 
 shew. As they transmit their impressions from the organs 
 to the seat of perception, they may be said to have their 
 origin at the extremity unfolded in the organ, and their 
 termination in the brain. For the sake of uniformity, 
 however, it is as well to follow the general practice of 
 considering the cerebral extremity as the origin, and the 
 organic as the termination. 
 
 First, or Olfactory the latter term being applied 
 from their office. They are the softest nerves in the body, 
 and are more closely connected with the hemispheres of 
 the brain than any other. They are composed of three 
 sets of fibres, two of them of medullary, and the third 
 of cineritious matter. They maybe traced backward to the 
 anterior cerebral ganglions, and are seen lying under the 
 anterior lobes of the brain. Proceeding forward, they 
 swell into a bulb, from which numerous fibres issue, and 
 pass into the nose through a plate of one of the bones of 
 the skull. This plate is perforated by so many holes for 
 the transmission of the twigs of the nerve, that it has the 
 appearance of a sieve, a circumstance from which the 
 bone obtains the name of ethmoid. 
 
 The olfactory nerve is ultimately distributed upon the 
 lining membrane of the nose with which it is inextrica- 
 bly incorporated : it terminates upon the surface, and is 
 merely defended by a layer of mucus, thus becoming the 
 most exposed nerve in the body, for it is necessary that 
 it should reach the surface, in order to come in contact 
 with the vapours inhaled by the nostrils. The olfactory 
 nerves are very large in some animals, particularly in 
 ruminants, in which they are tubular. On the other hand, 
 they are wanting in the whale tribe, which, if suscep- 
 
296 NERVES OF SPECIFIC SENSE. 
 
 tible of odorous emanations, must therefore become cog- 
 nizant of them through the medium of other nerves than 
 these ; and probably the fifth pair may perform to a 
 certain extent this duty, as it seems in several tribes to 
 be capable of fulfilling vicariously the office of other 
 nerves. In fishes the bulb of the olfactory is placed im- 
 mediately under the cup-like nostril. From the bulb 
 the nerve runs backwards along a canal filled with trans- 
 parent fluid, enters the skull, and joins the brain. In 
 the cod-fish it tapers as it proceeds backwards, and ter- 
 minates in the brain in a minute pencil of fibres. 
 
 The Second, or Optic, are the largest of the cerebral 
 nerves, with perhaps the exception of the fifth. They can 
 be traced as far back as the tubercles, and therefore arise 
 from the upper part of the medulla oblongata. They 
 pass along the base of the brain, and before they enter 
 the orbits, unite with each other. 
 
 This commissure of the optic nerves has attracted a 
 good deal of attention, and been the cause of consider- 
 able discrepancy of opinion. Some have held that they 
 merely come in contact, others that they completely de- 
 cussate, and a third party contend for semi-decussation 
 that is, they allege that one-half of the right optic nerve, for 
 example, crosses to the opposite side, and joins a half of 
 the left nerve to proceed to the left eye. The complete de- 
 cussation without union which occurs in fishes supports the 
 view of total crossing ; so also in some experiments where 
 the eye on one side has been destroyed, and time afforded 
 for an alteration in the nerve to be effected, it has been 
 found changed on the same side as far back as the junc- 
 tion, but on the opposite side beyond. Similar observa- 
 tions have been made in the human subject, where one 
 eye has been lost. On the other hand, the destruction 
 has been found to affect the optic nerve of the same side 
 throughout its whole extent. It would appear from care- 
 ful dissection that semi-decussation is what actually takes 
 place ; nor are the facts just stated inconsistent with it. 
 
MOTIFEROUS NERVES. 297 
 
 Each eye, therefore, receives its optic nerve from both 
 sides of the brain the right supplying the right side of 
 both eyes, as the left does its corresponding side of both. 
 
 The optic nerve, on entering the orbit, proceeds for- 
 ward to the ball of the eye, and penetrates the coats of 
 that organ a little towards the nasal side, and in the 
 centre ; it then expands into a very delicate web or ner- 
 vous network called the retina, which serves as a screen 
 for the reception of the image falling upon it. 
 
 The Auditory, for some extent in its course, runs along 
 with another nerve, the two together being known as the 
 seventh, of which the auditory forms the soft portion, or 
 portio mollis. It arises in the bottom of the fourth ven- 
 tricle from the posterior columns of the medulla oblongata. 
 Coming in contact with the portio dura, they proceed to- 
 gether to the internal auditory passage, which they enter. 
 Within this passage the portio mollis divides into a great 
 many minute branches, which are distributed to the several 
 compartments of the labyrinth of the ear, where their ex- 
 tremities float in the water contained in that cavity, from 
 which they receive vibrations productive of the impres- 
 sions of sound. 
 
 SECOND ORDER. Motif erous Nerves. Tn this order we 
 have three nerves, characterized by their origins from the 
 anterior columns, in the same line with each other, a line 
 which corresponds with that from which spring the moti- 
 ferous roots of the regular nerves, with which they agree 
 in function. The separation of the fibrils of motion from 
 those of sensation in this instance takes place however 
 only at the cerebral extremities, for they are associated 
 together at their further extremities. The greater por- 
 tion of the fifth pair of nerves we shall find is sensiferous, 
 and distributed to the parts on which the nerves of this 
 order are ramified, thereby imparting to them sensation. 
 The third, sixth, and ninth, with the fifth, may conse- 
 quently be considered, in a physiological point of view, 
 
 o2 
 
298 MOTIFEROUS NERVES. 
 
 as analogous to one of the double-rooted nerves from the 
 spinal marrow, and even others belonging to the respira- 
 tory order may likewise be included. 
 
 The, Third Pair spring from the crura of the cerebrum 
 above the pons. They may be traced into the substance 
 of the anterior columns, where they are found to be con- 
 nected with the grey substance of their centre. From 
 their origin they pass forward to a hole in the bottom of 
 the orbit, through which they enter that cavity, and sup- 
 ply four of the six muscles which move the eye, and like- 
 wise the muscle which raises the upper eyelid. Besides 
 communicating to these muscles the commands of the 
 will, a small twig of this nerve is joined by another from 
 the fifth pair. Previous to the union the branch of the 
 fifth swells into a small ganglion, from its shape named 
 lenticular ; so that we here observe the general law kept 
 up of the formation of a ganglion in the sensific nerve 
 before it becomes intimately associated with the filaments 
 of motion. These twigs penetrate the coats of the eye, 
 to which they impart sensibility. Being chiefly expended 
 upon the iris, they become connected with its movements. 
 
 The Sixth Pair arise from the pyramidal bodies close 
 to the pons. They soon pierce the dura mater, carrying 
 along with them a tubular prolongation of that membrane. 
 In their course they mount over a sharp ridge of the 
 temporal bone ; and run through one of the venous sinuses, 
 named cavernous, from the blood of which they are sepa- 
 rated by the lining membrane. Here communications are 
 established between it and the great ganglionic nerve. It 
 enters the orbit, and is entirely expended upon the muscle 
 which turns the eye towards the temple. The length, of 
 course, between the dura mater and the bone, and its 
 passage over the sharp ridge of the temporal is probably 
 the reason why this nerve is more liable to injury from 
 concussion than any of the others ; for we find that blows 
 or falls are sometimes followed by no further mischief 
 than the paralysis of the abductor muscle of the eye, 
 
RESPIRATORY NERVES. 299 
 
 whereby its antagonist keeps the eye permanently turned 
 inwards to the nose, rendering the eye nearly useless, as 
 its motions cannot properly be brought parallel with 
 those of its fellow. 
 
 The Ninth Pair take their origin from the lower part 
 of the pyramidal bodies. They pass through holes of the 
 occipital bone. They proceed forward towards the angle 
 of the jaw, where there is given off from each a branch 
 which passes downwards in the neck to supply some of 
 the superficial muscles anteriorly. The trunk of the nerve 
 runs from the angle of the jaw, by the side of the hyoid 
 bone of the tongue, and becomes ultimately distributed 
 upon the muscles between the lower jaw, hyoid bone, 
 and tongue, the motions of which it regulates. 
 
 THIRD ORDER. Respiratory Nerves. It has been al- 
 ready stated, that there exists a greater discrepancy of 
 opinion with respect to this than any of the other divi- 
 sions of the nerves. We shall postpone our general re- 
 marks upon the order till we have had under review their 
 course, distribution, and the functions of the parts on 
 which they are expended, whereby the observations which 
 may be submitted will be better understood, and the reasons 
 which induce us to agree in some measure with those who 
 hold them as entitled to be considered as a distinct class, 
 directly connected with the expression of the sympathetic 
 motions, and those which contribute to the expression of 
 the passions and emotions of the mind, will be more 
 readily appreciated. They arise from the same tract, 
 and in the same line, with the exception of the fourth 
 pair, which spring from below the inferior tubercles, from 
 the valvular commissure crossing the fourth ventricle. 
 This distinct origin is, however, more apparent than real, 
 for the fibres from which the fourth originate, are conti- 
 nuous w T ith the respiratory tract. The nerves belonging 
 to this order arc the fourth, the portio dura of the seventh, 
 from its distribution on the face named facial, the 
 
300 RESPIRATORY NERVES. 
 
 eighth, consisting of the divisions, the phrenic, and the 
 external respiratory. 
 
 Fourth Pair. These nerves are the smallest of the 
 cerebral, and arise by several minute filaments from the 
 valvular commissure, close to the inferior tubercles. They 
 run forwards, and enter the orbit at the same passage 
 with the third and sixth, to be expended upon a single 
 muscle of the eye, named the superior oblique, and com- 
 municating with the fifth. This muscle is curious in its 
 construction, and interesting in the motions which it pro- 
 duces. It arises from the bottom of the orbit, lies along 
 the roof of that cavity till it comes close to its brim, where 
 it terminates in a small tendon, w T hich passes through a 
 loop or pulley, then proceeds backwards, and towards the 
 temple. Its passage through this pulley changes the di- 
 rection of its action, so that it carries the eye forward, 
 and rolls it inwards to the nose, thereby giving to the 
 eye a peculiar expression, as in ogling.. As the eyes of 
 lovers are said frequently to take this expression, the 
 nerve has long been known under the name of the amatory. 
 It is not merely, however, under the passion of love 
 that this nerve declares, through the superior oblique, the 
 sentiments of the mind, but it also becomes affected under 
 other emotions and feelings ; and hence it is called the 
 pathetic nerve. 
 
 Whenever the will ceases to control the movements of 
 the eye, that organ comes under the action of the supe- 
 rior oblique. When the mind is occupied and absorbed 
 by emotion, we see the eye rolled by it ; therefore paint- 
 ers give this position to the eye when they wish to 
 depict intense mental feeling, such as deep devotion. 
 Where the eyes are of unequal power, the person so af- 
 fected habitually employs the stronger, leaving its weaker 
 fellow to the action of the superior oblique, and squinting 
 is the consequence. So accustomed are we to associate 
 with this position mental feeling in the individual in 
 whom it takes place, that squinting eyes are frequently 
 
RESPIRATORY NERVES. 301 
 
 supposed to express sentiments which may be far from 
 being entertained by the owner at the time. Squinting, 
 arising from unequal power of the eyes, has occasionally 
 been cured by shading the stronger eye, so as to lay it up 
 in ordinary, as it were, and bring its weaker companion 
 into action, that it may be invigorated, while the other, 
 from want of use, has its power diminished, and an equa- 
 lity is thus obtained between them. During acute bodily 
 suffering, the eye is thrown into the same position, the 
 will having in consequence withdrawn from regulating 
 its movements. At the point of death, the voluntary 
 muscles having lost their power, the eye is left to the 
 operation of this muscle, and the bystanders suppose 
 that the dying person experiences great agony, while in 
 fact, pain and suffering have in all probability ceased for 
 ever. So, likewise, we observe, on lifting the eyelid of 
 the sleeper, that the eye is turned in this direction, as oc- 
 curs, too, in fainting, and other conditions of suspended 
 animation. 
 
 We perceive, then, that the fourth pair are nerves capable 
 of acting independently of the will, whereby they are dis- 
 tinguished from those whose action entirely depends upon 
 it. At the same time, the will is capable of exerting a 
 certain degree of influence upon them ; but they do not 
 obey its injunctions so promptly as those of instinct and 
 feeling. Ogling may be imitated, but it is only an imi- 
 tation at best, and often a failure. 
 
 Facial. The seventh nerve, according to the numeri- 
 cal arrangement, consists of two portions, or rather two 
 distinct nerves, differing in texture, origin, distribution, 
 and function. The auditory has been already described. 
 The portion we have now to examine receives the name 
 of facial, from its extensive ramification on the face. It 
 arises between the olivary and restiform bodies, that is, 
 between the anterior rnd posterior columns, close to the 
 pons. Looking at this part of the medulla oblongata, wo 
 perceive an excellent example of the relative position, as 
 
302 RESPIRATORY NERVES. 
 
 to the origin of the three orders of motific, respiratory, 
 and sensific nerves. The sixth, a motific, proceeds from the 
 anterior columns ; the facial, a respiratory, from between 
 the middle and posterior; and the auditory, a sensific, from 
 the back part of the posterior columns, all springing from 
 nearly the same horizontal plane. The facial nerve, al- 
 though it emerges at the point mentioned, is formed of 
 a number of filaments, some of which are connected with 
 the anterior, others with the posterior, while the remain- 
 der spring from the respiratory tract, so that its origin is 
 complicated, in accordance with the variety of uses to 
 which it is applicable, for it cannot be considered as per- 
 forming exclusively any one function in particular, but 
 may rather be held as representing the combined charac- 
 ter of a regular nerve, and of one of instinctive motion. 
 From the medulla it passes forward, accompanied by the 
 auditory, and along with that nerve enters the internal 
 auditory passage. It traverses a canal of the temporal 
 bone, in which it is associated with a branch of the fifth. 
 Emerging from this canal, it forms connexions with the 
 great sympathetic, and then penetrates the parotid gland, 
 in the substance of which it divides into branches, which, 
 escaping from the gland, are spread out upon the head, 
 face, and side of the neck. This expansion of the facial 
 nerve has been compared to a goose's foot ; one division 
 proceeds upwards to the temple, to distribute its filaments 
 to the scalp, the forehead, and upper eyelid, establishing 
 connexions with the occipital nerve, and with the frontal 
 branch of the fifth ; another crosses the face, sending nu- 
 merous branches to the cheek, upper lip, nose, and lower 
 eyelid, where it is interlaced with the facial branch of 
 the fifth ; a third plexus passes down to the chin and 
 lower lip, where it meets with a branch of the third of 
 the fifth ; and lastly, some of its branches proceeding 
 dow r nwards to the neck, to form connexions with the 
 eighth and ninth cerebral, and with some of the inferior 
 cervical nerves. 
 
RESPIRATORY NERVES. 303 
 
 The extensive distribution and numerous connexions 
 of this nerve have gained for it the name of the smaller 
 sympathetic. It is to be observed that it nowhere sends 
 branches to parts which do not besides derive nerves from 
 other sources. It is therefore reasonable to suppose that 
 the two sets of nerves transmitted to such parts have dif- 
 ferent offices to perform. 
 
 Man is pre-eminently distinguished by the vast scope 
 of his intelligence ; and the numerous relationships of fa- 
 mily alliance, of friendship, and of other social ties, call 
 forth and exercise the affections of his heart, and the emo- 
 tions of his soul. These mental conceptions excite his 
 corporeal frame, which, on its part, is admirably fitted 
 for declaring the state of the feelings within. How ex- 
 pressive is the face of man ! How clearly it announces the 
 thoughts and sentiments of the mind ! How well depicted 
 are the passions on his countenance ! tumultuous rage, 
 abject fear, devoted love, envy, hatred, grief, and every 
 other emotion, in all their shades and diversities, are im- 
 printed there in characters so clear that he that runs may 
 read ! How difficult, nay how impossible is it to hide or 
 falsify the expressions which indicate the internal feelings ! 
 Thus conscious guilt shrinks from detection, innocence de- 
 clares its confidence, and hope anticipates with bright ex- 
 pectation. 
 
 We admire the actor in proportion to the success with 
 which he imitates the expression of the passions and feel- 
 ings ; indeed the great difficulties which he has to con- 
 tend with are sufficiently manifest, from the rarity with 
 which success crowns the efforts of the artist in pourtray- 
 ing the effects even of one class of passions on the body, 
 for tragedy and comedy each essentially consist in dis- 
 playing the impressions of the respective passions and emo- 
 tions which they are calculated to illustrate. The incidents 
 of the plot, and the sentiments to be conveyed, are all 
 furnished to the performer constructed with the most re- 
 fined skill, and clothed with the most glowing and appro- 
 
304 RESPIRATORY NERVES. 
 
 priate language, so as to produce the clearest conception 
 of the meaning which is to be developed ; yet, however 
 accurately the actor may judge of the intention of the 
 author, howsoever justly he may appreciate the character 
 he has to perform, and however anxiously he endeavours 
 thoroughly to imbue his mind with the sentiments which 
 are supposed to have actuated the hero he represents, the 
 great difficulty is to embody these conceptions, to exhibit 
 the corresponding expressions in the countenance, the at- 
 titudes, and the tones and inflexions of the voice ; art- 
 fully to combine and associate the proper muscles, to call 
 them into action to the necessary extent, with due force and 
 velocity, to vary them in accordance with circumstances, 
 and in no instance to outstep the modesty of nature ; to 
 do all this effectually requires an original combination of 
 talent which falls to the lot of few, and a laborious 
 study as unremitted and intense as is required by any 
 profession whatever. 
 
 On the other hand, let the most simple and least re- 
 fined individual labour under revenge, jealousy, or grief, 
 or let him be actuated with joy, satisfaction, or mirth, 
 and immediately he expresses the feeling in his coun- 
 tenance in language which cannot be mistaken, not in 
 imitation, but in reality ; and yet we admire the imita- 
 tion more than the reality, because we seldom reflect on 
 the wonderful perfection of the machinery by which these 
 expressions are effected, looking upon it merely as a 
 matter of course, just as we admire an excellent picture, 
 while the landscape it depicts may not gain from us 
 even a moment's attention, from being commonplace, and 
 every day before our eyes. 
 
 By cultivation the intelligence of the mind is ex- 
 panded, the passions regulated and controlled, and the 
 sentiments and feelings unfolded. All the original and 
 acquired modifications variously affect the expression of 
 the countenance, so ihat in time it receives a stamp and 
 impress according to the predominating character of the in- 
 
RESPIRATORY NERVES. 305 
 
 dividual. We thus unconsciously draw an inference as to 
 the disposition of a person we see for the first time; from 
 the expression of the face, we either feel that there is some- 
 thing repulsive in his look, or else something amiable 
 and attractive, which leads us to desire a further ac- 
 quaintance with him. It is on facts like these that phy- 
 siognomy rests; but however correct physiognomy may 
 be in theory, so many controlling and modifying influ- 
 ences operate, according to an infinite number of different 
 circumstances, that in practice it must totally fail, as ex- 
 perience shews. 
 
 The fifth nerve is distributed to the same parts on 
 which the facial is ramified on the face, and the respec- 
 tive purposes to which they are subservient have been 
 established from a great variety of experiments per- 
 formed upon the lower animals, and from observations 
 made on man. When the facial nerve is divided, or its 
 functions suspended by disease or accident, the side af- 
 fected loses all power of expression, although sensation 
 remains unimpaired, while by division of the branches of 
 the fifth pair sensation is entirely, or at least in a very 
 great degree, abolished. The motions of the face there- 
 fore undoubtedly depend upon this nerve, and that the 
 influences it transmits are of a mixed character, appears 
 also sufficiently established. We have had occasion to 
 remark that the determinations of the will are commu- 
 nicated to the muscles brought into action, by being 
 transmitted in the course of certain fibres; that from 
 these fibres spring the nerves, which convey the com- 
 mands to the muscles, constituting the nerves of volun- 
 tary motion. Such motions are at first imperfectly per- 
 formed, for the muscles require to be educated and drilled 
 before they are taught properly to co-operate with each 
 other. Thus, they must undergo education before they 
 can be effectually employed in walking ; but having mas- 
 tered the task, they continue to perform it so promptly 
 and readily that no effort of the will is apparently re- 
 
306 RESPIRATORY NERVES. 
 
 quired, and the necessity for its interference and superin- 
 tendence is only discovered when, from poisons, disease, 
 or other causes, the nerves are injured, or the will be- 
 comes dormant or inadequate. 
 
 All the motions performed by the purely voluntary 
 muscles are at first executed awkwardly, but by prac- 
 tice are rendered easy. In the various movements per- 
 formed in different arts with the utmost nicety, we see 
 the muscles employed in the most complicated move- 
 ments without the slightest apparent effort. The experi- 
 enced performer on the piano runs over the keys of the 
 instrument with the greatest precision, as it were intui- 
 tively, however awkward her first performance may have 
 been. 
 
 There are, on the other hand, various motions in the 
 animal body, which are perfectly executed from the first 
 without previous practice, and in which the different 
 muscles combine with the utmost accuracy, as necessity, 
 passion, or feeling may dictate. Such are the motions 
 essential to breathing, deglutition, and expression in the 
 features of the countenance. These motions are per- 
 formed independently of the will, and its interference 
 rather tends to disturb and derange than to perfect them. 
 The facial nerve communicates the purposes of the will 
 to the muscles of the face ; at the same time it is capable 
 of calling them into action under the influence of in- 
 stinct and sympathy. Many examples might be quoted 
 illustrative of the dependence of these instinctive move- 
 ments upon the facial nerve : the following case, which 
 has come under our own observation, may however suffice. 
 
 A youth fell from a wall ten feet high 011 a hard foot- 
 path, and was taken up insensible. Half an hour after 
 he was found in the same condition ; blood flowed from 
 the left ear, behind which, from external marks, it was 
 evident the head had been struck. After the adoption 
 of the necessary measures the more urgent symptoms 
 were overcome ; still, notwithstanding close attention and 
 
RESPIRATORY NERVES. 307 
 
 prompt treatment, he made but a slow recovery, nor have 
 the effects even now, nine years after the injury, been en- 
 tirely removed. "While he lay in a state of insensibility, with 
 laborious breathing, the difference between the right and 
 left side of the face was most striking: the right was 
 thrown into a state of great agitation, and frequently 
 affected with convulsive twitches, the eyelids contracted, 
 the nostril dilated, and the angle of the mouth drawn 
 up spasmodically on every inspiration. On the con- 
 trary, the left side remained in a state of perfect placidity. 
 After his recovery from the more dangerous conse- 
 quences it was ascertained that the left side of the face 
 had sustained permanent injury, which no means that 
 were had recourse to had the effect of removing, though 
 they were neither few nor impotent. His speech was also 
 affected, having become hesitating and stammering. The 
 unusual expression of his face and impediment of speech 
 attracting the attention and ridicule of his thoughtless 
 associates, he became morose in his temper, and unsocial 
 in his habits. 
 
 He is now a very athletic young man, but still prefers 
 solitude with his books, and is keenly alive to the pecu- 
 liarities of his features and speech. Among those with 
 whom he is in habits of intimacy, and when he is off his 
 guard, it is extremely curious to watch the changes of 
 his countenance. If he laughs it is only with one side of his 
 face ; when he frowns the left side remains in a state of placid 
 indifference, as is the case whatever mental excitement 
 he may be under at the time. He possesses voluntary 
 power over the muscles affected as completely as ever, 
 and the sensibility has never in the slightest degree been 
 impaired. Sensation depending on the fifth pair, and that 
 nerve having escaped injury in this instance, feeling remains 
 entire. The commands of the will continue to be com- 
 municated to the muscles through the facial nerve, which 
 received the shock, while the impulses of sympathy are 
 no longer transmitted by it. 
 
308 BESPIRATORY NERVES. 
 
 Eighth Pair. These nerves consist of three distinct 
 portions, different in their course and distribution, though 
 they arise from the same tract. The first has its origin 
 between the olivary and restiform bodies ; the second 
 springs by several filaments in the same line immediately 
 below the first; and the third portion arises as low 
 down from the spinal marrow as opposite to the fourth 
 vertebra of the neck, ascending along the spinal canal, 
 and entering the skull to join the other two; still, how- 
 ever, proceeding from the same tract, and lying between 
 the anterior and posterior roots of the cervical nerves. 
 The three divisions, besides their distinct origin from the 
 respiratory tract, have also connexions with the anterior 
 columns of the spinal cord, and consequently, like the 
 facial, combine the three functions of sensation, of vol- 
 untary and of instinctive motion. 
 
 The first portion being distributed to the tongue and 
 throat is named glosso-pharyngeal ; the second, from its 
 extensive distribution, is aptly termed the wandering 
 nerve, or vagans ; and the third, from appearing like an 
 accession from the spinal marrow to the cerebral nerves, 
 is called the accessory. It seems advisable to treat of 
 each of these separately, for they only come in contact as 
 they are about to escape from the cranium, which they do 
 along with the internal jugular vein, far back in the base 
 of the skull : immediately on their exit they establish con- 
 nexions with the great sympathetic. 
 
 The Glosso-Pharyngeal passes forwards, and in its 
 course forms connexions with the facial. It sends off 
 branches, which form a plexus or network round the 
 pharynx, distributing its ultimate ramifications to the 
 root of the tongue, the almonds of the throat, and the 
 mucous follicles towards the base of the tongue. We 
 have found that the ninth pair is ramified upon the 
 muscles of the tongue, in connexion with the voluntary 
 movements of that organ ; but the tongue being an 
 instrument employed in many instinctive movements, 
 
RESPIRATORY NERVES. 309 
 
 requires the influence of appropriate nerves, that it 
 may be ready immediately to perform any task which 
 may be imposed upon it, without previous tuition, 
 such as it requires to exert immediately after birth in 
 sucking. The instinctive movements connected with 
 deglutition, and the regulation of the entrance to the air- 
 passages, equally demand nerves from the same source. 
 The contributions of this nerve to the almonds of the 
 throat and the mucous follicles shew that it is not merely 
 to be considered as a motific nerve, for in these instances 
 it is connected with secretion. Indeed, mistakes are very 
 apt to be committed in limiting too much the function of 
 nerves. It ought constantly to be borne in recollection 
 that the function of the nerve becomes modified by the 
 organ on which it is distributed, that the actions which 
 we see executed in the living body are not the result of 
 one or two parts of the machinery employed, but of the 
 joint co-operation of the whole. At the same time, fixing 
 upon some leading character in the nerves, serves the use- 
 ful purpose of enabling us to classify and arrange them, 
 that the mind may more easily recognise and retain them 
 in the memory. 
 
 Vagans. On leaving the skull, the vagans sends off 
 two branches ; the one passes to the pharynx and upper 
 part of the gullet ; the other is distributed to the larynx, 
 and commands the muscles which close the air passage, 
 and supplies the mucous membrane covering it. The 
 trunk of the vagans descends along the side of the neck, 
 included in the same sheath with the carotid artery and 
 internal jugular vein, and enters the chest under the col- 
 lar bone, between the subclavian ajtery and vein on the 
 right, and between the left subclavian vein and arch of 
 the aorta. Here a branch is given off, which loops round 
 the subclavian artery on the one side, and arch of the 
 aorta on the other, to return upwards to the larynx, and 
 therefore named the recurrent. The recurrent ascends 
 between the windpipe and gullet, to which it furnishes 
 
3JO RESPIRATORY NERVES. 
 
 twigs, and is ultimately ramified on tlie larynx, commu- 
 nicating with the superior laryngeal, and supplying the 
 muscles which open the air-passage. Where the vagans 
 enters the chest, besides giving off the recurrent, it sends 
 branches, which are accompanied by others from the great 
 sympathetic, forming together a network of nerves, 
 which surrounds the divisions of the windpipe, to accom- 
 pany them in all their ramifications through the tissue 
 of the lungs. Other minute twigs, also associated with 
 filaments from the sympathetic, descend along the aorta 
 and pulmonary arteries to the heart, and along the course 
 of these arteries respectively, through all their divisions 
 and subdivisions, on the one hand to the lungs, and on 
 the other to the whole system, accompanying the blood- 
 vessels throughout their entire distributions. Having 
 given off these important branches, the vagans with its 
 fellow surrounds the gullet, and enters along with it into 
 the cavity of the abdomen, first distributing freely ramifica- 
 tions to the stomach, and ultimately furnishing branches 
 which combine with the great sympathetic in the forma- 
 tion of the great central ganglion of the abdomen, from 
 whence all the viscera of that cavity are supplied with 
 nervous energy. 
 
 The functions exercised, and the sympathetic connexions 
 established by this nerve are of the utmost importance and 
 interest. It is very evident that it is not confined to mo- 
 tion, nor yet entirely to sensation ; but that it superin- 
 tends also the secretion from the different surfaces on 
 which it is distributed. 
 
 Let us consider, in the first place, the relations esta- 
 blished through the medium of this nerve, between the 
 different organs of digestion and secretion. At the upper 
 part of the throat it forms connexions with the nerves of 
 the mouth and nostrils. Throughout the whole extent 
 of the gullet it is plentifully distributed, as it is also upon 
 the stomach ; then, along with the great sympathetic, its 
 filaments are extended throughout the whole of the intes- 
 
RESPIRATORY NERVES. 311 
 
 tinal tube, to the liver, pancreas, and spleen, and to the 
 urinary and reproductive organs. 
 
 It is well known how directly the state of the secre- 
 tions in one part of the alimentary canal indicates their 
 condition throughout. The physician looks at the tongue 
 of his patient, not that it is the seat of complaint, but be- 
 cause its appearance announces to him the condition of 
 organs which he cannot see ; and he is thereby enabled to 
 draw an inference as to the nature and extent of the de- 
 rangement under which they may be labouring. The irri- 
 tation of the throat also is frequently had recourse to in 
 order to excite vomiting, the connexion between the sto- 
 mach and that part being so direct through the medium 
 of this nerve ; and, conversely, nauseous substances in the 
 stomach produce convulsive movements and a disagree- 
 able sensation in the throat. In fact, the whole train of 
 phenomena connected with nausea and vomiting are ex- 
 plicable from the ramifications of the vagans. The prompt 
 and perfect co-operation, too, of the various muscles en- 
 gaged in deglutition is to be explained in the same 
 way. 
 
 We have already seen how admirable is the consent, 
 and how delicate the tact of the various portions of the 
 stomach and intestinal tube, how opportunely the bile 
 flows into the duodenum at the time it is required there, 
 and how the gastric, pancreatic, and intestinal juices are 
 adapted in quantity, and varied in quality in the different 
 conditions of action and repose. A rupture, in which a 
 portion of the intestine is protruded and pinched, causes 
 sickness and vomiting ; the passage of an urinary concre- 
 tion along the ureter produces the same effect. Derange- 
 ments of the womb are accompanied with an uneasy sen- 
 sation at the pit of the stomach, and the feeling of the 
 ascent of a ball to the throat, with the impression of im- 
 mediate suffocation. And in the same way we might 
 mention an almost infinite number of other examples of 
 the intimate connexions established between the various 
 
312 RESPIRATORY NERVES. 
 
 viscera and the sympathies they display, both in healthy 
 and deranged conditions, which are brought about through 
 distributions of the vagans. 
 
 Again, if we turn our attention to the respiratory 
 system we shall equally find evidence of the important 
 part played, and the associations formed through the 
 ramifications of this nerve in the wonderful adaptation 
 and co-operation of the organs of voice and articulate 
 speech, in the secretion of watery exhalation, mucus, 
 and carbonic acid from the lungs, and in the superin- 
 tendence of the other important functions carried on in 
 respiration. 
 
 Lastly, when we consider that the vagans, along with 
 the great sympathetic, supplies the heart, and accom- 
 panies all the ramifications of the blood-vessels, the ques- 
 tion comes to be, not on what parts is the vagans ramified? 
 but where, throughout the whole system of the body, are 
 its filaments not to be found ? In fact, when we reflect 
 that these two nerves are distributed on the circulating 
 organs at large, we perceive that their presence must 
 be universal ; that they form the cords through which 
 the sympathies thrill, and the most distant and ap- 
 parently least connected parts are bound together, and 
 associated into one harmonious unity. 
 
 Accessory. The three portions of the eighth, on their 
 escape from the skull, form connexions with each other, 
 with the ninth facial, with several of the cervical nerves, 
 and likewise with the great sympathetic. The acces- 
 sory on parting from the rest passes through the sub- 
 stance of a powerful muscle, named from its attachments 
 sterno-mastoid, which lies superficially by the side of 
 the neck, and which will be readily seen thrown into 
 action on the head being turned from side to side. 
 The accessory supplies this muscle, and then proceeds 
 backwards, forming connexions with the cervical nerves. 
 Ultimately it distributes its branches to a large muscle, 
 which, with its fellow on the opposite side, covers 
 
RESPIRATORY NERVES. 313 
 
 the back part of the neck and shoulders like a cowl, 
 hence named cucularis, and to a third muscle which 
 raises the shoulder blade, the levator scapulae. These 
 three muscles elevate the- shoulders, and render them 
 fixed, whereby the muscles extending between the ribs 
 and the shoulders obtain both a fixed point and the ad- 
 vantage of a longer lever, in consequence of which they 
 are enabled efficiently to raise the ribs, and thereby 
 powerfully to co-operate with the muscles of inspiration. 
 
 When we take in a full breath we instinctively elevate 
 the shoulders for this purpose ; in asthma they are power- 
 fully called into action, and sometimes during the par- 
 oxysm the patient may be observed to place his hands 
 upon the table, the better to enable him to raise and fix 
 the shoulders, and in some measure to relieve these mus- 
 cles. In stage exhibitions, in painting, and statuary, in 
 which the passions are depicted, these muscles are dis- 
 played in full action. The elder Kean, especially in the 
 characters of the Jew and Richard, used to throw them 
 into the most vigorous exertion with a powerful effect. 
 The shrugging up of the shoulders is thus another of the 
 means by which the sentiments of the mind are indi- 
 cated by appropriate external signs. 
 
 Phrenic. This nerve gets its name from being distri- 
 buted on the diaphragm, which at one time was con- 
 sidered as the seat of the soul. The phrenic and exter- 
 nal respiratory are more directly connected with the an- 
 terior and posterior columns than the cranial respiratory 
 nerves which we have described, so much so that they 
 appear merely to be branches of the cervical nerves ; at the 
 same time, however, they receive some minute filaments 
 from the side of the spinal marrow, and therefore the ana- 
 logy is kept up, at least between them and the facial and 
 eighth pair ; for we have noticed that on carefully trac- 
 ing the filaments of the facial, and of the divisions of the 
 eighth, some can be followed to the anterior, others to 
 the posterior, while the greater number Spring from the 
 
314 RESPIRATORY NERVES. 
 
 middle tract. On the other hand, the filaments from tho 
 middle tract are few and minute compared with the an- 
 terior and posterior origins. As in the former instances, 
 we have the combined influence of sensific, motific, and 
 fibres of instinctive movement in the same nerve, the two 
 formej predominating over the last in the number and 
 size of the filaments. 
 
 The phrenic passes out of the vertebral canal, between 
 the second, third, fourth, and sometimes fifth cervical 
 vertebrae : it runs down the neck, and enters the chest 
 on the outer side of the internal jugular vein. In the chest 
 it passes down by the side of the capsule of the heart, and 
 distributes its branches to the diaphragm, at the same 
 time transmitting twigs which join the great abdominal 
 nervous centre. The phrenic nerves are not the only 
 nerves ramified on the diaphragm, for the lower intercos- 
 tals send also several branches to it. 
 
 External Respiratory. This nerve proceeds from be- 
 tween the third, fourth, and fifth vertebras of the neck ; 
 it passes under the collar bone, and runs down, crossing 
 the outer surfaces of the ribs about their middle, and dis- 
 tributes its branches to the intercostal muscles, and to 
 the powerful muscles which extend from the ribs to the 
 shoulders, which are occasionally called into action in 
 laborious breathing. 
 
 We now perceive in what manner the various organs 
 connected with the important function of respiration are 
 bound together. The eighth being distributed through- 
 out the whole extent of the air-passages, conveys the im- 
 pressions made upon that surface, and therefore is so far a 
 sensiferous nerve ; but the sensations it communicates 
 are of a peculiar kind, and expressly connected with the 
 peculiar functions of the parts, for it does not transmit 
 any idea of the qualities of substances, as hardness, soft- 
 ness, roughness, or smoothness, such as the nerves distri- 
 buted on the skin announce. Nor will the most inge- 
 nious experiments performed on the lower animals shew 
 
RESPIRATORY NERVES. 315 
 
 that they convey the sensation of pain, however nume- 
 rous the convulsive movements which may be called forth, 
 or however varied the writhings of the poor animal, with 
 which we generally associate agonizing pain, since they 
 have no means of declaring to us what in reality are their 
 sensations. We have little more right to suppose that 
 these are necessarily connected with suffering than we 
 have to believe that the horrible distortions displayed in 
 the countenance of an executed criminal, when the gal- 
 vanic shock is transmitted along the course of the nerves, 
 are proofs that the body feels, or that the mind is still 
 associated with it. 
 
 The ramification of this nerve on the muscles of voice, 
 and on those of the tongue and gullet, shew that it is a 
 motiferous nerve, but a motiferous nerve with peculiar 
 endowments ; it not only transmits the commands of the 
 will by which these parts are called into action, but with- 
 out the necessity of the will forming a determination, or 
 without any authority from the mind, brings them into 
 operation with the utmost promptitude, and combines 
 them with the greatest accuracy, according to the exi- 
 gencies of the moment. It is therefore not only a volun- 
 tary, but also an instinctive motiferous nerve. 
 
 The connexion which the eighth pair has with various 
 secreting organs farther shews that it is capable of regu- 
 lating their functions, and that it brings their action into 
 accordance with the state of the system, or of individual 
 parts ; so that the secretions are varied in quantity and 
 quality, as may be suited to the circumstances of the case. 
 
 Again, through the instrumentality of the accessory, 
 phrenic, and external respiratory, the muscles employed 
 in inspiration, either in ordinary breathing or when the 
 inhalations are full and laborious, are brought into ac- 
 tion, combined and directed with the proper degree of 
 force, velocity, and extent, without the necessity of inter- 
 ference of the mind. Though at the same time they are 
 ready, within certain limits, to obey the mandates of the 
 
316 RESPIRATORY NERVES. 
 
 will, still it is only in a secondary degree, the impulses 
 of instinct being ever held paramount to the commands 
 of the will. No one can suspend to an indefinite extent 
 the movements of respiration. In a short time, however 
 strong may be his determination, he is compelled to give 
 way to the irresistible mandates of instinctive feeling, 
 which requires not the aid of erring reason, nor will it 
 brook the capricious interference of the will, constituting, 
 as it does, the great conservative principle of the animal 
 organism, and endowed with powers which it has pleased 
 the Great Artificer to bestow upon it. Its behests are 
 issued forth along the appropriate channels, and implicitly 
 obeyed, without hesitation or delay. 
 
 Further, it may be noticed that the muscles w r hich ele- 
 vate the shoulders are frequently employed in connexion 
 with the passions and feelings of the mind, as in shrug- 
 ging up the shoulders, and the various positions the head 
 may be placed in by the muscles which derive nerves from 
 the same source. The extent and degree of action, as 
 well as the number of muscles employed for the purpose 
 of communicating the state of the feelings in ordinary 
 life, varies in different individuals. Some employ nume- 
 rous gesticulations and much grimace in their intercourse, 
 in expressing their internal conceptions, while others de- 
 liver an account of their feelings with an appearance 
 of the utmost indifference. In the majority of instances, 
 however, these are merely conventional modes of convey- 
 ing ideas, and accordingly vary in different countries and 
 states of society. But when once the passion or emotion 
 is felt in reality, then the display is the same in all, and 
 the agents selected similar. 
 
 Connected as this order of nerves is with the different 
 muscles which are engaged in variously depicting the pas- 
 sions, intimately associated as the nerves are which com- 
 pose it, and universal in their distribution, their arrange- 
 ment together is calculated to clear up much that would 
 otherwise be obscure, and to combine facts which would 
 
RESPIRATORY NERVES. 317 
 
 otherwise appear insulated and inexplicable. Although, 
 therefore, it has been considered as the weakest part of 
 the classification of Sir Charles Bell, we are inclined to 
 think it one of the most beautiful portions of the inte- 
 resting and philosophic theory he has erected. In fur- 
 ther illustration, the following striking description may 
 be introduced from Sir C. Bell's treatise on the nervous 
 system. 
 
 " In terror, we can readily conceive why a man stands 
 with his eyes intently fixed on the object of his fears, the 
 eyebrows elevated, and the eyeballs largely uncovered ; 
 or why, with hesitating and bewildered steps, his eyes 
 are rapidly and wildly in search of something. In this 
 way, we only perceive the intense application of his mind 
 to the objects of his apprehension, and its direct influence 
 on the outward organs. But when we observe him far- 
 ther, there is a spasm on his breast : he cannot breathe 
 freely : the chest remains elevated, and his respiration is 
 short and rapid : there is a gasping and convulsive mo- 
 tion of his lips, a tremor on his hollow cheeks, a gulping 
 and catching of his throat : his heart knocks at his ribs, 
 while yet there is no force in the circulation, the lips and 
 cheeks being ashy pale. 
 
 " It is obvious that there is here a reflected influence 
 in operation. The language and sentiments of every 
 people have pointed to the heart as the seat of passion, 
 and every individual must have felt its truth. For though 
 the heart be not in the proper sense the seat of passion, 
 it is influenced by the conditions of the mind, and from 
 thence its influence is extended through the respiratory 
 organs, so as to mount to the throat, lips, and cheeks, and 
 account for every movement in passion which is not ex- 
 plained by the direct influence of the mind on the fea- 
 tures. 
 
 " So we shall find, if we attend to the expressions of 
 grief, that the same phenomena are presented, and we 
 may catalogue them, as it were, anatomically. Imagine 
 
318 RESPIRATORY NERVES. 
 
 the overwhelming influence of grief : the object in the 
 rnind has absorbed the powers of the frame : the body is 
 no more regarded, the spirits have left it : it reclines, and 
 the limbs gravitate : the whole frame is nerveless and re- 
 laxed, and the person scarcely breathes : so far there is 
 no difficulty in comprehending the effect in the cause. 
 But why, at intervals, is there a long-drawn sigh ? why 
 are the neck and throat convulsed, and whence the qui- 
 vering and swelling of the lip? why the deadly paleness, 
 and the surface earthy cold ? or why does convulsion 
 spread over the frame like a paroxysm of suffocation ? 
 
 " To those I address, it is unnecessary to go farther than 
 to indicate that the nerves treated of in these papers are 
 the instruments of expression, from the smile upon the 
 infant's cheek to the last agony of life. It is when the 
 strong man is subdued by this mysterious influence of 
 soul on body, and when the passions may be truly said 
 to tear the breast, that we have the most afflicting pic- 
 ture of human frailty, and the most unequivocal proof, 
 that it is the order of functions we have been considering 
 that is then affected. In the first struggles of the infant 
 to draw breath, in the man recovering from a state of 
 suffocation, and in the agony of passion, when the breast 
 labours from the influence at the heart, the same system 
 of parts is affected, the same nerves, the same muscles, 
 and the symptoms or characters have a strict resem- 
 blance." 
 
 Comparative anatomy affords numerous facts corrobo- 
 rative of the purposes fulfilled by this order of nerves. 
 In fishes, as might have been expected, from the limited 
 number of their sympathies and instinctive notions, their 
 development is limited, and the eighth pair appears to 
 perform the office of the whole. It is of considerable 
 size, and distributed upon the gills and gill-covers, or the 
 organs of respiration, upon the organs of circulation, and 
 upon those of other functions immediately connected 
 with animal life. In the electric eel and torpedo, they 
 
RESPIRATORY NERVES. 319 
 
 are distributed upon the very curious electric apparatus 
 which these fishes employ with so much effect as weapons, 
 and the nerves are correspondently large. 
 
 In reptiles, we find the facial nerve added to the eighth ; 
 and wherever these animals display sympathetic action, 
 we observe the parts on which these nerves are ramified 
 become involved. The hissing of the serpent shows the 
 commotion into which the respiratory apparatus is thrown, 
 and the inflation of the neck of the hooded snake, while 
 under the influence of rage, affords a similar instance. The 
 croaking of the frog at certain seasons may also be cited 
 as an example. 
 
 When we ascend to birds, the number of the respiratory 
 nerves is limited as in reptiles. The distribution of the 
 facial in them is interesting. Instead of proceeding for- 
 ward to the hard and inexpressive bill, it is turned back 
 over their neck and shoulders, and is large in those which 
 display their passion by the bristling of the feathers of 
 the neck and back of the head. The vocal organs in 
 birds are well known as the instruments by which they 
 are enabled to communicate the feelings actuating them 
 to an infinite extent, and in every degree of modulation. 
 By means of the vocal organs the hen can sound the 
 alarm to her young brood on the approach of danger, 
 can announce to them the discovery of food, or encourage 
 them to take air and exercise ; and by the same means 
 she exultingly publishes the fact of her having been deli- 
 vered of an egg. Her pugnacious husband bids defiance 
 to his distant neighbour, who retorts by declaring his ac- 
 ceptance of the challenge in the vigorous use of his organs 
 of voice. 
 
 In mammalia the number of the respiratory nerves is 
 the same as in man, but not nearly so fully developed, 
 nor are the divisions, subdivisions, and interlacements so 
 various as they are in him. "We perceive in the different 
 orders of this class of animals great diversities, especially 
 in respect to the facial nerve. In the sheep it is small 
 
320 REGULAR NERVES. 
 
 and simple ; in its distribution it becomes larger in pro- 
 portion to the fifth, and more intricate in its distribution, 
 as we proceed from the graminivorous tribes through the 
 carnivorous, monkeys and apes, up to man, in whom it is 
 developed in the highest degree, in accordance with the 
 versatility and power of expression he possesses in the 
 features of his countenance. The division of the facial 
 nerve on one side of the face of a monkey destroys at 
 once the peculiar activity of its features on that side ; and 
 if it be cut on one side of a dog, the animal when under 
 excitement presents a ludicrous appearance one side of 
 the face remaining in a state of placidity and indiffe- 
 rence, while the other presents a condition of great agi- 
 tation. 
 
 FOURTH ORDER. Regular Nerves. When treating of 
 the spinal cord, it was mentioned that it has been com- 
 pletely established by the experiments and observations 
 of Sir Charles Bell, and confirmed by others, that the 
 nerves arising from the cord possess different powers in 
 the two roots from which they spring ; that the anterior 
 roots are subsidiary to motion, and transmit the mandates 
 of the will to the muscles, while the posterior are the 
 channels by which sensations are communicated to the 
 seat of perception ; that there are thirty pairs of spinal 
 nerves, and that the fifth cerebral in its structure and 
 function is analogous to these. We shall first treat of 
 the fifth, and afterwards classify the spinal nerves, so as 
 to furnish a general view of their distribution and use. 
 
 Fifth Nerve. This nerve arises by two distinct roots, 
 the posterior or sensiferous of which is by much the largest, 
 being as four to one. The filaments of the sensiferous portion 
 can be traced through the fibres of the pons till they become 
 continuous with the fibres of the posterior column or resti- 
 form body immediately below the pons. The anterior small- 
 er portion springs from the anterior column between the 
 olivary and pyramidal bodies. Piercing the dura mater, 
 
REGULAR NERVES. 321 
 
 or rather carrying forward a tubular prolongation of that 
 membrane, they reach the side of a depression in the base 
 of the skull, which has been likened to a Turkish saddle, 
 where the anterior swells out into a large knot or ganglion, 
 named after its discoverer the Gasserian ganglion ; after 
 which it divides into three divisions ; the first passing 
 into the orbit, from its connection with the eye termed 
 opthalmic ; the second, from its distribution being princi- 
 pally to the upper jaw, is called the superior maxillary ; 
 and the third sent to the lower jaw is named inferior 
 maxillary. The anterior root joins the third branch 
 alone, so that the two first are composed of filaments 
 solely from the anterior root, while the third is truly a 
 compound nerve like those which proceed from the spinal 
 marrow. We shall consider the three divisions of the 
 fifth separately. 
 
 Opthalmic Branch. This enters the orbit at the same 
 passage with the third, fourth, and sixth, when it imme- 
 diately divides into branches ; one proceeds forwards, and 
 is reflected on the forehead, where it establishes connec- 
 tions with the frontal plexus of the facial ; another re- 
 enters the skull, and accompanies the first pair of nerves 
 to the nose ; a third passes to the lachrymal gland. A 
 small twig runs along the optic nerve, to join others from 
 the third pair. Before they combine, a small ganglion 
 is formed on this twig, termed from its form lenticular ; 
 from these arise minute nerves, which pierce the coats of 
 the eye, to be ramified upon its interior. The mucous 
 membrane and other secreting organs are supplied from 
 the opthalmic branch, so that extensive connections are 
 established by it. 
 
 Superior Maxillary Branch. This passes through a 
 hole a little posterior to the first, and immediately begins 
 to divide into branches, some of which have ganglions 
 formed in their course. The principal branches are sent to 
 the back part of the nostrils, the pendulous curtain and al- 
 monds of the throat, where it forms connexions with the 
 
322 
 
 REGULAR NERVES. 
 
 eighth; to the palate, gums, and teeth of the upper jaw, and 
 externally to the cheek, upper lip, and nose, where it is in- 
 timately associated with the facial. A small twig re-en- 
 ters the skull, passing by the side of the carotid canal : it 
 sends filaments to unite with the sixth and great sympa- 
 thetic. It then enters a canal, and for a short space be- 
 
 FIG. 23. 
 
 comes associated with the trunk of the facial, from which 
 it derives some minute filaments, after which it runs 
 through the drum of the ear, and again emerging from the 
 skull, joins the branch of the fifth, which is distributed 
 upon the tongue, and finally it is expended in the neigh- 
 bourhood of the submaxillary gland. 
 
REGULAR NERVES. 323 
 
 Inferior Maxillary Branch, formed of a combina- 
 tion of the sensiferous and motiferous filaments of the 
 fifth. The latter are distributed to the muscles which 
 shut the jaw, and also on those which regulate the pos- 
 terior orifices of the nostrils; the former are ramified upon 
 the tongue, salivary glands, gums, and teeth of the lower 
 jaw, on the external ear, cheek, chin, and lower lip, 
 maintaining communications with the facial, the eighth 
 and ninth, and with the great sympathetic. 
 
 The engraving is here introduced to shew the distribu- 
 tion of the facial and fifth nerves on the face, and in 
 order to give an idea of the manner in which nerves are 
 ramified, d is the trunk of the facial, its branches radiat- 
 ing from this situation to the forehead, across the face to 
 the chin, down by the side of the neck ; they are seen to 
 communicate with each other, and to join twigs of the 
 three branches of the fifth ; a is the frontal branch of the 
 fifth ; b the facial of the same, and c its submaxillary 
 branch ; e are ramifications of the cervical and accessory 
 nerve, forming communications with the facial. 
 
 The fifth being profusely distributed upon the integu- 
 ments of the face, has been unequivocally demonstrated 
 to be the nerve by which feeling is transmitted. From 
 exposure probably to the vicissitudes of external tempera- 
 ture, it is liable to an exquisitely painful affection, named 
 tic douloureux, which is sometimes removed by cutting 
 the nerve affected, the patient preferring the loss of 
 sensibility to the agonizing pain w r hich accompanies the 
 disease. In the cat, the hare, and other animals with 
 large whiskers, the filaments of this nerve have been 
 traced to the bulbs of the hairs, accounting for the deli- 
 cate tact which these animals are endowed with, and 
 by means of which they are enabled to wind their way 
 in the dark through intricate passages with the greatest 
 facility. 
 
 It deserves attention, that the fifth is associated with 
 the organs of the senses of smell, sight, and hearing ; 
 
324 REGULAR NERVES. 
 
 that it exercises that of touch, especially on the lips and 
 tip of the tongue, and that it is the immediate instrument 
 of taste. From the general outline we have given of its dis- 
 tribution, it will be seen that both the first and second 
 branches contribute filaments to the nose, those from the 
 first accompanying the olfactory nerve. Magendie has at- 
 tempted to prove that these twigs constitute the proper 
 seat of smell, and that the first nerve has nothing to do 
 with that function, though he has seen reason somewhat 
 to modify his opinion. In this he has furnished a nota- 
 ble instance how torturing animals, by what are called 
 experiments, is as apt to mislead and bewilder as elicit 
 truth. It is a source of no small pleasure to know that 
 the conclusions which Sir Charles Bell has arrived at, 
 and the truths which he has succeeded in establishing, 
 were not the result of cruelties committed on our fellow- 
 creatures in the first instance, and that when it became 
 necessary to put them to the test upon living animals, 
 the experiments were previously well devised, and con- 
 ducted with every consideration of humanity the case 
 would admit of ; and in no instance does he have recourse 
 to unnecessary repetitions, furnishing a beautiful contrast 
 to that butcher-like indifference to animal suffering which 
 is so fashionable in the present day, and which is often 
 practised with so little appearance of design, aim, or pur- 
 pose, that it looks as if it sprung more from the gratifica- 
 tion of a depraved and cruel disposition than from the 
 desire for the advancement of science. 
 
 Magendie cut the first pair of nerves in dogs, and ap- 
 plied ammonia to the nostrils, when there appeared as 
 much sensibility as ever. He cut the nasal branches of 
 the fifth pair, and the animal no longer displayed evi- 
 dence of being affected, and therefore he inferred that 
 the fifth was the true nerve of smell. Now, in the first 
 place, ammonia has no odour ; it is a powerful stimulant, 
 but does not communicate to us any impression such as 
 the olfactory nerves convey ; as a powerful stimulant it is 
 
REGULAR NERVES. 325 
 
 calculated to rouse the common sensibility of the nostrils, 
 which depends upon the fifth. The other pungent stimu- 
 lants he employed with the view of upsetting long es- 
 tablished opinions, namely, the oils of lavender, of tur- 
 pentine, and so forth, not only impress the first pair with 
 their odour, but likewise rouse the sensitiveness of the 
 fifth. Then as to the fifth pair being necessary to the 
 exercise of the sense of smell, without having recourse to 
 mangling animals, there was little or no ground to doubt 
 that the destruction of the fifth pair would be attended 
 with derangement of the sense of smell, since the organ 
 by which it was exercised had lost its integrity. 
 
 From the distribution of the first branch of the fifth 
 pair upon the iris, the lachrymal organs, and nose, we have 
 an explanation of the connexion which subsists between 
 these parts, affording an example of sympathy, not of 
 that kind which calls forth motion, but sensation ; yet al- 
 though there appears to be a sufficient number of facts to 
 establish the existence of sympathy of sensation, some 
 contend for its being limited to the respiratory system of 
 nerves, and account for the -connexions which are dis- 
 played between such parts as those on which the first 
 branch of the fifth pair is ramified to the communications 
 with the pathetic and facial. But however that may be, it 
 is well known that pungent substances applied to the nose 
 produce a copious flow of tears ; the iris will also be found 
 to contract, and when the curtains are opened in the 
 morning, and a sudden glare of light is thrown upon the 
 eyes, sneezing is apt to follow from the transference of 
 excitement to the nose ; and from the connexion which 
 the branches of the fifth establish with the respiratory 
 nerves, the muscles of respiration are powerfully thrown 
 into action, and the air is forcibly expelled through the 
 nostrils. The gratification from snuff-taking does not arise 
 from its odour, but from the stimulus of the sensiferous 
 nerves. When a hearty pinch is taken, the eyes water, 
 the excitement extends to the forehead, the teeth tingle, 
 
326 
 
 REGULAR NERVES. 
 
 and the most distant parts are roused. In megrim, re- 
 lief is occasionally experienced from the application of 
 pungent substances to the nose; hence the use of cephalic 
 snuff. 
 
 The twig of the second branch, which we have de- 
 scribed as taking a very circuitous route through the drum 
 of the ear, associates this nerve with the organ of hear- 
 ing, whereby it becomes influenced by the vibrations 
 of sound, accounting for the teeth being set on edge by 
 grating sounds, such as the sharpening of a saw. 
 
 FIG. 24. 
 
 The lips are well known to be delicate instruments of 
 touch, deriving their sensibility from the second and third 
 branch, which are intimately associated with the facial, 
 and are the immediate seat of the gratification of kissing, 
 so far as that is merely a sensual act. 
 
 From various experiments it appears sufficiently esta- 
 
REGULAR NERVES. 327 
 
 blished that the fifth pair constitutes the more immediate 
 seat of taste, the second branch supplies the palate, and 
 a large portion of the third is distributed to the tongue. 
 We perceive, therefore, that the fifth is brought directly 
 into communication with all the senses ; that it confessedly 
 exercises the function of touch, and forms the essential 
 instrument of taste ; that it is affected by pungent odorous 
 substances, by light, and by sound. In the absence there- 
 fore of special organs of sense and of appropriate nerves, 
 this may convey impressions communicating to the ani- 
 mal some conception of these qualities of bodies. 
 
 As it is from the fifth that the teeth derive their nerves, 
 so we can comprehend how toothache should be accom- 
 panied with such exquisite pain ; why the salivary glands 
 pour out their fluids abundantly during the paroxysm ; 
 and the reason of the extension of pain to the ear, the 
 face, and head, when the dental nerves are exposed from 
 caries of the teeth. 
 
 The engraving is intended to exhibit the relative size 
 and situation of the most important parts of the cerebro- 
 spinal portion of the nervous system. A is the anterior 
 lobe of the cerebrum ; B the middle lobe ; and C the pos- 
 terior lobe ;/is the great commissure ; g the tubercles ; D 
 is the cerebellum ; h the arborescent appearance presented 
 by a vertical section of it ; E the spinal marrow, with the 
 regular double-rooted nerves arising from it ; 1 the first 
 pair, or olfactory nerves ; 2 the second, or optic ; 7 the au- 
 ditory portion of the seventh, forming the nerves of special 
 sense ; 3 the third ; 6 the sixth ; 9 the ninth, forming the 
 motiferous nerves ; 4 is the pathetic or fourth pair ; 7 ' the 
 facial of the seventh ; 8 the glosso-pharyngeal of the eighth; 
 8 ' the vagans ; and 8 ' ' the spino-accessory of the same, 
 forming three of the five respiratory nerves ; 5 is the 
 first, 5 ' the second, and 5 ' ' the third branches of the fifth 
 nerve, 
 
 Spinal Nerves. After what has been already stated, 
 it is unnecessary to enter at any length into the examina- 
 
328 SPINAL NERVES. 
 
 tion of the nerves arising from the spinal cord, since they 
 are all similar in their construction and in the functions 
 which they perform. On tracing the fibres proceeding from 
 the anterior column of the cord, we find that they swell in- 
 to a ganglion before they are joined by those from the ante- 
 rior column. Although both sets of filaments are wrapt 
 up in the same covering or neurilema, yet they never ac- 
 tually coalesce or anastomose, with each other, but each 
 filament remains separate, however intricately it may be 
 interwoven with others, from its origin to its ultimate 
 termination. 
 
 Our notions of sensibility are chiefly derived from our 
 experience of it on the surface of the body. According 
 to common belief, the deep-seated parts are possessed of 
 a more exquisite sensibility than the surface, but the very 
 reverse is actually the case. When the surgeon performs 
 an operation, he with truth assures the patient that when 
 he has cut through the external parts, the most painful 
 part of the operation is over ; and the patient bears up with 
 greater ease in the further steps of the operation, where 
 the knife is plied among the deep-seated parts. The bone 
 is sawn through, the muscles, tendons, and ligaments 
 cut and lacerated, and even burnt with a red-hot iron, 
 and yet the patient experiences little or no suffering ; 
 at least the pain he feels is derived from the wounded 
 and divided nerves which communicated with the integu- 
 ment. 
 
 This high degree of sensibility in the integuments of 
 the body is a wise and benevolent provision, whereby we 
 are warned to avoid not only what might injure the skin 
 itself, but also endanger internal parts. The skin, there- 
 fore, from being endowed with acute sensibility, becomes 
 an admirable protector to the whole body. The extremes 
 of heat and cold, which might prove injurious, produce 
 their painful impression ; mechanical causes rouse by their 
 sharpness, roughness, or hardness; acrid and corrosive 
 chemical agents induce uneasy sensation by all which 
 
SPINAL NERVES. 329 
 
 \ve are admonished to shun the cause producing such 
 disagreeable effects. 
 
 The sensibility varies much, not only in degree, but in 
 kind. The skin is sensible to variation of temperature, 
 but not to the uneasy sensation arising from over-exer- 
 tion ; while the muscle is liable to the sense of fatigue, 
 but not to the vicissitudes of temperature. In the same 
 way every other organ of the body is endowed with a 
 peculiar sensibility, which is best adapted to its structure 
 and the purposes of its existence : the eye is sensible to 
 light, the ear to vibrations of sound, the nose to odours, 
 and so forth. These sensations are conveyed from the 
 point on which the impression has been made, upwards 
 along the sensiferous filaments of the nerves to the seat 
 of perception, the brain. 
 
 The mind having determined a purpose, the mandate 
 is issued forth from the brain along the motiferous nerves, 
 and transferred to the muscles which are required to carry 
 it into effect. The filaments which communicate the sen- 
 sations in one direction are bound up in the same sheath 
 with those by which the command is transferred on the 
 other, so that they become thus associated with each other, 
 and in harmony carry on together their respective func- 
 tions, though the disorder or even the total destruction of 
 one is not necessarily followed with complete loss of 
 power in its companion. 
 
 The spinal nerves are generally classed by anatomists 
 according to the portions of the spinal column from 
 which they issue, as the neck, back, loins, and pelvis, 
 forming the cervical, dorsal, lumbar, and sacral nerves. 
 Of the first we have eight ; of the second twelve ; five of 
 the third; and five of the fourth. They all establish 
 connexions with the great sympathetic. On their escape 
 from the spinal canal, they divide into anterior and pos- 
 terior branches, the latter of which are small, and ramified 
 on the muscles and parts in their immediate neighbour- 
 hood. The former are more extensively distributed, espe- 
 
330 SPINAL NERVES. 
 
 cially those which supply the arms and legs. The cervi- 
 cal nerves form, by their anterior branches, direct con- 
 nexions with the fifth, facial, eighth, and ninth cranial 
 nerves, and with each other, so' as to form a plexus or 
 net-work. By their frequent interlacements, they are 
 more closely associated together. 
 
 The four lower cervical, and the first dorsal proceed to 
 the axilla or arm-pit, where they form an intricate net- 
 work, termed axillary plexus. It may be observed that 
 the intricacy of a plexus bears some relation to the varie- 
 ty of the movements performed by the parts on which 
 the nerves forming the plexus are distributed. Accord- 
 ingly, in the arm of man, where the variety, extent, 
 and complex combinations of the movements infinitely 
 surpass the simple and limited motions of the correspond- 
 ing limb of the horse, the ox, or the sheep, although the 
 number of the nerves is the same, they are not equal 
 in proportional size, and more especially are they dis- 
 tinguished in these animals by the simple construction of 
 the plexus. The same holds with respect to the leg, 
 where we also find a plexus at the commencement of the 
 nerves destined for it. Although in man this plexus is 
 less complicated than that of the arm, in accordance with 
 the less varied movements of the lower limb, it is still 
 more simple in such animals as are above referred to, 
 in which the motions are limited. 
 
 Some of the nerves from the axillary plexus are distri- 
 buted to the parts in the vicinity of the shoulder, others 
 extend to the muscles and integuments, as far as the 
 wrist, while others again proceed to the hand and points 
 of the fingers ; the last are composed chiefly, if not en- 
 tirely, of the filaments of sensation, and are delicate or- 
 gans of touch. 
 
 The dorsal nerves are characterized by their principal 
 branches, with the exception of that of the first, running 
 along the inferior margins of the ribs ; their posterior 
 branches supply the muscles and integuments of the 
 
GANGLIONIC NERVES. 331 
 
 back ; their anterior run forward to be distributed on 
 the intercostal muscles, and those of the chest. 
 
 The lumbar and sacral nerves are connected with each 
 other in the plexuses which they form, having supplied 
 the muscles of the loins and the walls of the abdomen. 
 Their principal branches proceed to the lower limb, some 
 being confined to the hip-joint, while others extend to the 
 extremities of the toes. It may be observed that the 
 same nerve is usually distributed on muscles which are 
 commonly associated with each other, as those which bend 
 or extend a joint, those employed in rolling it inwards 
 or outwards. The last of the spinal nerves send twigs 
 to the extremity of the intestinal canal and urinary blad- 
 der, whereby a certain degree of voluntary power is gained 
 over them, and they become endowed with common sen- 
 sation ; other branches are distributed to the external 
 organs of reproduction, imparting to them sensibility. 
 
 FIFTH ORDER. Ganglionic Nerves. The portion of the 
 nervous system we have had under consideration com- 
 prises what is termed the cerebro-spinal. We have seen 
 that it comprehends the material instrument of thought, 
 perception, and sensation that it is the source, and fur- 
 nishes the channels, of voluntary motion, and of instinc- 
 tive movements and sympathy. 
 
 We have now to direct our attention to another por- 
 tion, whose functions are independent of the cerebro-spinal 
 system, though intimately associated with it. None of 
 the names applied to this order are without objection, 
 when used in their strict signification. It was supposed, 
 from its extensive distribution, that it constituted, if not 
 the only, at least the principal channel by which sympa- 
 thies were transmitted. From this hypothesis it got the 
 name of great sympathetic conferred upon it. But sympa- 
 thy has been shewn to be independent of it, excepting in 
 so far as it receives filaments from the cerebro-spinal 
 nerves. In consequence of its numerous connexions with 
 
332 GANGLIOMC NERVES. 
 
 the spinal intercostals, it is called the great intercostal^ but 
 it is in no especial manner connected with the intercostals, 
 and exists in several animals which have no intercostals, 
 and in many which have no ribs. It may also be no- 
 ticed in passing, that the epithet great has been bestowed 
 upon it, not from its size, but from its real or supposed 
 importance. Indeed, were bulk a measure of the import- 
 ance of the different parts of the nervous system, the 
 great sympathetic must sink very low in estimation, for 
 one of its distinguishing characters is, that its filaments 
 are extremely minute. It is named ganglionic, from the 
 numerous ganglions established in various parts through- 
 out its distribution. But we have already seen that 
 ganglions are also found in the sensiferous nerves, and 
 therefore are not peculiar to the order in question. Still, 
 the employment of these names, merely in an arbitrary 
 sense, without reference to the circumstances from which 
 they have been applied, is attended with no incon- 
 venience or disadvantage. 
 
 Ganglions are masses of nervous substance, varying in 
 their size, shape, and in the connexions they form ; they 
 are composed of a mixture of cineritious and medullary 
 matter, inextricably incorporated together. Various opi- 
 nions have been entertained as to their use. The most 
 probable appears to be that which holds them as the cen- 
 tres of peculiar nervous power. It is generally close to, 
 or in the substance of, a ganglion, that the sympathetic 
 forms connexions with the cerebro-spinal system. 
 
 At one time the sympathetic was considered as a mere 
 offset or emanation of the cerebro-spinal, and as such de- 
 scribed as proceeding from the sixth, and second branch 
 of the fifth. By way of illustration, we may here advert 
 , to the mode of connexion with the sixth. The sixth, on 
 its passage through the cavernous sinus, has a communi- 
 cation established with the great sympathetic, by a twig 
 or twigs, which accompany the internal carotid artery 
 through the skull, in the course of which there is usually 
 
GANGLIONIC NERVES. 333 
 
 a ganglion, termed the cavernous. Now the question is, 
 whether does the sixth give off or receive this branch of 
 union ? If it gave it off, we should expect to see the sixth 
 diminished, which it is not, neither is it increased in pro- 
 portion to the twig of connexion. The inference, there- 
 fore, which may be drawn is, that there is a mutual inter- 
 change of filaments between the sixth and sympathetic, 
 that filaments pass from the former to the latter, and 
 again, that filaments from the sympathetic accompany 
 the ramifications of the sixth throughout its whole distri- 
 bution. 
 
 This may be taken as an example of the character of 
 the intercourse which subsists between the ganglionic and 
 cerebro-spinal systems, and such connexions being formed 
 with every cerebro-spinal nerve as concomitants, where- 
 ever there is a filament of the one, there also is there a 
 filament of the other ; and thus the distribution of both 
 is universal. 
 
 A plexus is, as we have already seen, an interlacement 
 of fibres, as in the axillary plexus. The commissure of 
 the optic nerves may also be cited as an example. A si- 
 milar interlacement of fibres exists in ganglions, so that 
 a ganglion is not only a mass composed of a mixture of 
 grey and white matter, but likewise a network, where 
 the nervous filaments are interwoven with each other. 
 The ganglionic system is not' only distinguished by the 
 number and variety of its ganglions, but also in the pre- 
 valence of plexuses. Accompanying, as they everywhere 
 do, the blood-vessels, they are found sheathing the larger 
 arteries with a covering of intricate network. 
 
 In a general and limited sketch such as the present, it 
 is impossible to advert to the many interesting physiolo- 
 gical bearings in which the ganglionic system may be 
 viewed, as well as its numerous and important relations, 
 both in respect to health and disease, even were the pre- 
 sent a proper occasion to enter at length upon such dis- 
 cussions. "We shall therefore content ourselves by taking 
 
334 GANGLIONIC NERVES. 
 
 an instance of its importance, which may afford a glimpse 
 of its proper use in the animal machinery. 
 
 We have seen that the function of the heart depends 
 on its contractility. There have been many instances of 
 foetuses born, some without a brain, and others destitute 
 both of brain and spinal marrow, and yet, throughout the 
 life of such monsters, the heart continued to circulate the 
 blood as completely as in the perfect foetus. We know 
 that the heart, when torn from the body, does not in- 
 stantly cease to contract ; that in some animals it con- 
 tinues to palpitate for hours after removal. The motions 
 of the heart appear therefore to be independent of the 
 cerebro-spinal system. We possess no direct power over 
 the heart's action : we can neither hasten nor retard, nor 
 can we increase or diminish the force of its pulsation. 
 But there is not a passion or emotion of the mind, or 
 disease in any other organ the most distant, with which 
 the heart does not sympathize, and in consequence be- 
 come affected, in the frequency, force, and regularity of 
 its action. These affections we are enabled to explain 
 by the filaments it derives from the respiratory vagans. 
 
 The heart, in its healthy condition, is destitute of sensa- 
 tion, at least in the common acceptation of that term. We 
 formerly alluded to the case of a youth of noble family 
 brought under the notice of the illustrious Harvey by the 
 direction of Charles the First, where an opportunity was 
 afforded for proving the absence of common feeling in 
 the heart. In this case, after a fall, an abscess had formed, 
 and burst externally. When the wound healed, an open- 
 ing was left by which the heart and lungs were exposed, 
 To use the words of Harvey, " When I paid my respects 
 to this young nobleman, and conveyed to him the king's 
 request, he made no concealment, but exposed the left side 
 of his breast, when I saw a cavity into which I could in- 
 troduce my fingers and thumb. Astonished with the 
 novelty, again and again I explored the wound, and first 
 marvelling at the extraordinary nature of the cure, I set 
 
GANGLIONIC NERVES. 335 
 
 about the examination of the heart. Taking it in one 
 hand, and placing the finger of the other on the pulse of 
 the wrist, I satisfied myself that it was indeed the heart 
 which I grasped. I then brought him to the king, that 
 he might behold and touch so extraordinary a thing, and 
 that he might perceive, as I did, that unless when we 
 touched the outer skin, or when he saw our fingers in 
 the cavity, this young nobleman knew not that we 
 touched the heart." 
 
 In inflammation, rheumatism, and other morbid affec- 
 tions, the heart becomes exquisitely sensible. The agony 
 it suffers is now announced to the seat of perception, and 
 this we can account for by the interchange of filaments 
 between the ganglionic and regular nerves. The sym- 
 pathetic movements, and the morbid sensibility of the 
 heart can therefore be explained as depending upon the 
 filaments which it receives from the cerebro- spinal sys- 
 tem. Still there remain to be accounted for its inde- 
 pendent contractility, its peculiar sensibility, or innate 
 vitality. 
 
 The facts derived from comparative anatomy and physi- 
 ology, and from the gradual development of the nervous 
 system in the higher tribes of animals, all furnish strong 
 evidence that the peculiar vitality of every organ in the 
 body directly depends upon the ganglionic nerves. The 
 structure of these nerves, formed as they are everywhere 
 of cineritious and medullary matter, their independence 
 of every other part of the nervous system, the indepen- 
 dence of the different portions, even without reference to 
 each other, and their universal distribution, all corrobo- 
 rate the opinion that they are capable of receiving im- 
 pressions, of instituting action, and communicating ex- 
 citement to the action of other tissues, such as that of mus- 
 cular contractility, of absorption, secretion, and so forth, 
 according to the structure and function of each organ ; and 
 that there nowhere exists a paramount centre of refe- 
 rence, such as the brain constitutes to the cerebro-spinal 
 
336 GANGLIONIC NERVES, 
 
 system, but that each part is independent of every other, 
 though all are linked together by filaments of connexion, 
 so that the different individual parts may be combined 
 into one confederate harmonious system. 
 
 The heart, therefore, contracts from being furnished 
 with muscular fibre, the proper office of which is con- 
 traction ; we infer that the contractility is put in action 
 by the muscular fibre being associated with nervous mat- 
 ter capable of furnishing the stimulus to contraction ; 
 that this power of instituting stimulus, as well as proper 
 sensibility of the heart, and of every other organ in the 
 body, is inherent in the ganglionic system of nerves. 
 
 The ganglionic nerves, properly speaking, cannot be 
 said to have any particular origin or course of distribu- 
 tion, every organ in the body possessing through them 
 its own independent seat of nervous energy, with which 
 its special function is more immediately connected. 
 Nevertheless, for the sake of description, it is necessary 
 to have recourse to certain starting points, from which 
 the various bearings may be taken, just as the geographer 
 employs the arbitrary lines of meridian and longitude on 
 a map. 
 
 There are four positions which may conveniently be 
 fixed on as central points at which the ganglionic nerves 
 establish numerous connexions with those of the cerebro- 
 spinal system, and with each other, composed of a ganglion 
 or ganglions with intricate interlacements, thus forming 
 gangliform plexuses. The first is situated on the fore 
 part of the two or three first vertebrae of the neck ; the 
 second at the lower part of the neck and upper part of 
 the chest ; the third at the upper part of the abdomen 
 behind the stomach ; the fourth in the pelvis at the ex- 
 tremity of the vertebral column. They may be termed 
 respectively the cervical, thoracic, abdominal, and pelvic 
 ganglionic centres. 
 
 Cervical Ganglionic Centre. The superior cervical gan- 
 glion lying on the front of the two or three first cervical 
 
GANGLIOMC NERVES. 337 
 
 vertebrae, generally of a fusiform shape, may be taken as 
 the focus of this gangiiform plexus. At this point the 
 great sympathetic establishes connexions with every one 
 of the cerebral nerves, by filaments which may be traced 
 to each, in several of which ganglions are formed, as the 
 lenticular in the orbit, the cavernous within the skull, 
 and the spheno-palatine, otic, and submaxillary connected 
 with the fifth. It anastomoses freely with the facial and 
 eighth, with the ninth, and with three or four of the supe- 
 rior cervical nerves. Reinforced by filaments from the facial 
 and vagans, its twigs extend along the ramifications of 
 the external and internal carotid artery, forming sheaths 
 which may be traced accompanying the larger divisions, 
 but becoming too minute for detection by the eye, even 
 when aided by the microscope, though there is no rea- 
 son to suppose that their distribution is limited to the 
 larger trunks. According to this view, therefore, their 
 distribution must be co-extensive with that of the arte- 
 ries ; and consequently the brain itself is supplied with 
 nerves, as are likewise the nerves themselves, just as 
 we have blood-vessels ramified upon the heart and coats 
 of the blood-vessels. From this nervous centre we there- 
 fore perceive connexions established and filaments ex- 
 tended to the brain, the organs of sense, and those of 
 the secretions connected with them, to the organ of voice 
 and deglutition, and the different muscles which put them 
 in motion, and to those subservient to the movements of 
 the neck. Lastly, a branch or branches run down behind 
 the sheath of the common carotid and internal jugular 
 vein, considered as the continuation of its trunk. 
 
 Thoracic Ganglionic Centre. 3U the lo\ver part of the 
 neck, opposite the fifth, sixth, and seventh cervical verte- 
 brae, are placed two or three ganglions, the superior termed 
 middle, and the lower inferior cervical ganglions. They 
 form numerous connexions with the vagans, phrenic, and 
 nerves of the axillary plexus. The frequent interlace- 
 ments surround the blood-vessels proceeding from and 
 
338 GANGLION 1C NERVES. 
 
 entering the chest. Nervous sheaths accompany the 
 common carotid artery upwards, to unite with those from 
 the superior ganglion, along the vertebral artery to the 
 spinal marrow and brain, and along the artery of the 
 arm throughout all its divisions and subdivisions to 
 their ultimate terminations. Others run along the air- 
 tubes to the lungs associated with the branches of the 
 vagans to the heart, and along the gullet ; so that from 
 this centre we have emanating the filaments which are 
 connected with the arm and upper part of the walls of 
 the chest, the organs of respiration, the organs of circula- 
 tion, and the gullet. The great sympathetic, proceeding 
 down the back part of the chest behind the investing 
 membrane, establishes connexions with the twelve intercos- 
 tal nerves, forming a ganglion opposite to each. Spring- 
 ing from four to seven branches, there are two nerves which 
 enter the abdomen through the diaphragm by separate 
 passages, named from their distribution on the viscera the 
 great and small splanchnic nerves. 
 
 Abdominal Ganglionic Centre. By the two splanch- 
 nics, reinforced by branches from the vagans and a few 
 filaments from the phrenic, an exceedingly intricate ner- 
 vous centre is formed of an assemblage of ganglions and 
 plexuses at the upper part of the abdomen, lying upon the 
 diaphragm behind the stomach. On each side there is a 
 ganglion larger than the rest, which has received the 
 name of semilunar, from the shape it usually presents. 
 Each semilunar ganglion forms connexions with its fel- 
 low of the opposite side, surrounding one of the principal 
 trunks from the aorta ; and as we have got two moon- 
 shaped ganglions, so Itave we here a solar plexus. The 
 nerves of the right and left form here, by numerous intri- 
 cate interlacements with an assemblage of ganglions, a 
 great, nervous centre, from which issue filaments that 
 sheath the arteries arising from the abdominal aorta, and 
 accompany them in their distribution to the stomach and 
 intestinal canal, to the spleen, pancreas, and liver, to the 
 
GANGLIONIC NERVES. 339 
 
 kidneys, to the organs of reproduction, and lastly, along 
 the bifurcations of the aorta to the lower limbs. 
 
 Pelvic Ganglionic Centre. Filaments of continuation 
 pass from the thorax into the abdomen behind the dia- 
 phragm, and run down by the side of the vertebrae of the 
 loins, sending filaments to the plexuses from the abdomi- 
 nal centre. Entering the pelvis, they pursue their course 
 in the front of the sacrum, at the extremity of which the 
 sympathetics of each side unite together in the formation 
 of a single ganglion, named ganglion impar. Through- 
 out the course of the filaments of continuation, connex- 
 ions are established and ganglions formed, as in the re- 
 gions of the neck and chest, with the spinal nerves. In 
 the pelvis, twigs are sent off to the extremity of the in- 
 testinal canal, to the urinary and reproductive organs, 
 along the arteries ramified within the pelvis, and to ac- 
 company those which pass out to be distributed extejs 
 nally. 
 
340 
 
 CHAPTER VIII. 
 
 SIGHT. 
 
 Arrangement cf the different parts of the Apparatus of Sight Appendages of 
 the Eye The Orbit The Eyebrows The Eyelashes The Eyelids and their 
 Motions Lachrymal Apparatus Motions of the Eyeball The Globe of the 
 Eye capable of Motion in every direction The Muscles by which the move- 
 ments of the Eye are effected, as under the command of the Will, and by In- 
 stinctive Feelings How we see an object single with two Eyes Regulation of 
 the Sphere of Vision Compound Eyes of Insects Some species of Butterflies 
 furnished with 34,650 Eyes Squinting Various Causes of The Globe of the 
 Eye Sclerotic Coat gives protection, and affords insertion to other parts 
 Choroid Coat Furnished with a Dark Secretion to absorb Light Its intimate 
 connexion with the Retina The Iris, or Variegated Curtain The hole in its 
 centre, the Pupil Regulates the quantity of Light admitted in the Posterior 
 Chamber A single object held close to one Eye, several Images produced, and 
 the object appears multiplied Transparent parts of the Eye Aqueous Humour 
 very rapidly renewed Adaptation of the Eye to near and distant, to large and 
 minuteobjects Crystalline Lens Its beautiful organization Vitreous Humour 
 The Retina the immediate Organ of Sight Manner in which the Retina may- 
 see its own Blood-vessels Insensibility to Light at the entrance of the Optic 
 Nerve Seat of distinct Vision Curious effects from indirect Vision Conti- 
 nuance of the Impression of Light Cause of the appearance of Light when the 
 Eye is struck Refraction of Light Short-sightedness Long-sightedness Sun- 
 beam decomposed into seven coloured rays Means by which we estimate the 
 size and distance of objects, by the Visual Angle, the Intensity of Light, Shade, 
 and Colour, and by contrast with other known objects. 
 
 LIGHT lias a considerable effect upon the whole of ani- 
 mated nature; it promotes the growth and vigour of 
 vegetables, and produces powerful and beneficial effects 
 on the health and comfort of animals, from the highest 
 to the lowest. The more perfect animals are furnished 
 with instruments by which they are enabled to appreciate 
 several of the properties of light, whereby they become 
 
EYEBROWS. 341 
 
 acquainted with near and distant objects, obtaining from 
 this source conceptions which vastly extend the sphere 
 of their knowledge, and contribute to their gratification 
 and delight. 
 
 The eyes are the material instruments by which we re- 
 ceive our impressions of the different modifications of light. 
 The brilliancy and beauty of these noble organs cannot 
 escape the attention of the most heedless, and their ad- 
 mirable adaptation to the purposes for which they have 
 been furnished us, must call forth the admiration and 
 gratitude of every one who gives the subject even a super- 
 ficial consideration. 
 
 The different parts of the apparatus of sight may be 
 conveniently considered under three divisions ; first, The 
 appendages of the eye, by which it is protected from ex- 
 ternal injury, preserved in a condition adequate for its 
 duties, and whereby its motions are effected; secondly, 
 The various coats, which perform different functions ac- 
 cording to the structure of each, and the humours through 
 which the rays of light pass to be pictured upon the im- 
 mediate seat of vision ; and thirdly, The nervous screen 
 which receives the image, and transmits the impression 
 to the seat of perception in the brain, where the mind 
 takes cognizance of it. 
 
 Appendages of the Eye. The orbit is a four-sided vault 
 of a pyramidal shape, composed of seven bones ; the mar- 
 gin is rounded, and projects at the upper part over the an- 
 terior surface of the eye, whereby that organ is protected 
 from blows or other external causes of injury. It is more 
 complete in man than in other mammalia. The axes of 
 the two orbits, if continued backwards, cross each other, 
 since they diverge somewhat towards the temples, but 
 the divergence is less in man than even in apes, which 
 approach him so nearly in their structure. 
 
 The Eyebrows are composed of loose cellular sub- 
 stance, covered with skin, from which spring short bristly 
 hairs, projecting outwards. Like all hairs, they penetrate 
 
342 EYEBROWS. 
 
 follicular crypts, and become besmeared with an oily se- 
 cretion, which preserves their glossiness, so that the drops 
 of sweat which may accumulate on the brow are pre- 
 vented from trickling over the eyelids, where they might 
 interfere with vision. 
 
 Attached to the eyebrows, we have the three follow- 
 ing muscles : Fibres extend from the occipito-frontalis, 
 which are inserted into them, whereby the brows are ele- 
 vated. Another muscle proceeds from the root of the 
 nose, its fibres spreading out like a fan upon the eyebrow 
 and skin of the lower part of the forehead ; this acts as 
 an antagonist to the last, knits the eyebrows, and cor- 
 rugates the skin of the forehead, hence named the cor- 
 rugator. The third is common to the brow and eyelid ; 
 it is formed of a series of fibres, which arise from a little 
 sinew or tendon at the inner angle of the eye, spreading 
 out upon the upper eyelid and brow, over the integu- 
 ments at the external angle; then it passes inwards, 
 across the under eyelid, to be again fixed to the tendon : 
 from its shape it is called orbicular. By this muscle the 
 eye is closed, and, when powerfully thrown into action, 
 it wrinkles the skin around the margin of the eyelids. 
 
 These muscles are regulated in their movements by 
 the facial nerve, or the nerve of expression of the face, and 
 it is well known that they are thrown into action by, 
 and become expressive of, the passions and emotions of 
 the mind. In advanced life, the integuments losing their 
 elasticity and becoming relaxed, the skin of the fore- 
 head, at the outer margin and on the eyelids, presents fur- 
 rows which mark the impress of years. Where the stormy 
 passions have frequently called these muscles into power- 
 ful action, the markings are deeper, and may leave their 
 traces even in early life ; hence the wrinkled forehead, 
 the lowering brows, and streaked eyelids, are equally 
 the result of mental perturbation and of age. 
 
 The Eyelashes form beautiful fringes to the margins 
 of the eyelids ; they consist of two or more rows of stiff 
 
EYELIDS. 343 
 
 bristly hairs, generally of the same colour with those of 
 the head and eyebrows, but sometimes of a different 
 shade ; those of the upper eyelid are longer than those of 
 the lower. They serve to ward off insects, and protect the 
 eye from particles floating in the air. When the eye- 
 lashes are humid, the litle drops of moisture decompose 
 the rays of light, and, even independently of humidity, 
 they partly resolve the light passing into the interior of 
 the eye, causing the appearance of a luminous zone around 
 the flame of a candle. 
 
 The Eyelids are formed externally of a very thin 
 skin, beneath which the cellular membrane, instead of 
 containing fat, has its cells occupied with a gelatinous 
 semir transparent fluid. The inner surface of the eyelid, 
 next to the ball, is a mucous membrane continuous with 
 the skin, and named conjunctiva. Immediately under the 
 skin the fibres of the orbicular muscle are situated, under 
 which, in each eyelid, there is placed a cartilaginous body, 
 which gives a sufficient degree of tension to the lid, at 
 the same time admitting of the necessary movements. 
 Anterior to each cartilage is situated a row of follicular 
 crypts, for the secretion of viscid fluid which collects on 
 the margins of the eyelids, and especially towards the 
 internal angle during the night, constituting the gummy 
 matter accumulated in the morning. Attached to the 
 cartilage of the upper eyelid there is a muscle, the leva- 
 tor, which arises from the bottom of the orbit, by means 
 of which the eye is kept open. It is entirely under the 
 command of the will, while the eye is shut by the orbi- 
 cular muscle, whose action does not necessarily require 
 a mandate from the will, in order to perform its function. 
 The advantage of this arrangement is obvious ; for had 
 it been otherwise, we might have gone to sleep forget- 
 ting to close the eyelid, from which great danger and 
 injury might have happened : but the closure of the eye 
 is not left to our discretion; no sooner do we become 
 drowsy than the eyes begin to close, and if we are desi- 
 
344 TEARS. 
 
 rous of keeping awake, we feel the necessity for exertion 
 to keep them open. The eyelids are not equal in size, 
 the upper being the largest, besides possessing the freest 
 and most extensive movements; it serves as a curtain 
 which covers the delicate organ when not in use, and by 
 its motions diffuses uniformly the tears and mucous se- 
 cretions over the surfaces. The winking or nictitation of 
 the upper eyelid is performed so rapidly that there is 
 no interruption to the continuance of vision; therefore, as 
 we shall find immediately, the closure and re-opening of 
 the eye must be effected in less than the eighth part of a 
 second ; so rapidly indeed are the two movements effected, 
 that the " twinkling of an eye" is used as expressive of the 
 least possible measure of time. The eyelids do not com- 
 pletely prevent the transmission of light when they are 
 closed ; for we then still continue capable of distinguishing 
 between light and darkness. "When the body has been 
 refreshed by sleep, and the susceptibility, which continued 
 action had impaired, is again restored by rest, on the light 
 falling upon the eyelids in the morning, a sufficient quan- 
 tity is transmitted to arouse sensibility, and we awake. 
 
 Birds are furnished with a third eyelid, formed of a du- 
 plicature of the conjunctiva, named the nictitating mem- 
 brane; it is commanded by two very peculiarly constructed 
 muscles, which, on exposure to a strong light, are able to 
 bring this semi-transparent fold over the eye, so as to 
 protect it, enabling the organ to bear with ease the 
 full glare of the meridian sun. They are thus supplied 
 with a veil or obscured medium, through which they can 
 look upon that glorious luminary with ease and im- 
 punity. It is also found in a rudimental state in some 
 mammalia. 
 
 Lachrymal Apparatus. The tears are secreted in the 
 little distilleries, the lachrymal glands, and poured out 
 upon the inner surface of the upper eyelid by seven or eight 
 tubes ; along with the mucus from the conjunctiva, they 
 are spread over the surface of the eye by the movements 
 
TEARS. 
 
 345 
 
 of the lids. The organs which furnish these secretions 
 sympathize with the conditions of the mind. Under ex- 
 citement, they are poured out more abundantly, and the 
 brilliancy of the eye is increased under some emotions ; 
 the eyelids are at the same time more fully open, the 
 tension of their different muscles is increased, the ball re- 
 mains fixed, or moves with the quickness of thought, pro- 
 ducing a combination which renders the eye one of the 
 most expressive features of the countenance, in connexion 
 with the feelings within. 
 
 The two eyelids, when closed, come only in contact 
 with each other at a fine line upon the external part of 
 the margin, leaving a triangular groove between them 
 and the anterior surface of the ball. This groove has an 
 inclination from the temporal angle, downwards and in- 
 wards to the nasal angle corresponding with the direction 
 of the level where the eyelids meet, consequently the 
 tears flow down this inclined channel to the inner angle, 
 where, in each lid, there is a small pore by which they 
 are absorbed and conveyed by little tubes into a recep- 
 tacle from which they are transmitted to the nose. At 
 the internal angle of the eye, a small reddish-coloured 
 body is placed, from its fleshy appearance named the 
 lachrymal carnucle. On minute inspection, a number of 
 short stiff hairs will be found springing from it. It is 
 composed of seven or eight follicles, arranged like a cres- 
 cent, with the concavity towards the eye. These folli- 
 cles correspond with those of the margins of the eyelids, 
 so that the series of little crypts is thus completed around 
 the whole circumference of the eye. The colour of the 
 carnucles affords a good index of the state of health : 
 when the general health is vigorous, they are .tense, 
 shining, and of a rose colour, while their laxity and pale- 
 ness indicate debility and disease, thus furnishing one of 
 the numerous tests of health to the physiological physi- 
 cian, whereby he is enabled to estimate the condition of 
 his patient, and detect attempts to impose upon him, 
 
346 WHITE OP THE EYE. 
 
 whether by the individual himself or by his friends ; and 
 to judge also of the condition of those w r ho are unable 
 to give an account of their sufferings and feelings, such 
 as infants, the idiotic, and the insane. 
 
 Birds have an abundant secretion of tears ; and in addi- 
 tion to the lachrymal glands and follicular crypts, have a 
 gland situated towards the internal angle, named the gland 
 of Harder, which furnishes a thick viscid secretion, poured 
 out by a single duct, opening upon the inner surface of 
 the nictitating membrane. The eye in most birds is 
 closed by the lower lid, which is furnished with a de- 
 pressor muscle, just as we find that in those animals 
 which possess the greatest mobility in the upper eyelid a 
 levator is supplied. The ostrich, parrot, owl, and goat- 
 sucker, afford examples in which the upper eyelid is the 
 largest and most moveable. 
 
 The conjunctiva forms the lining membrane of the eye- 
 lids. As we have already had occasion to mention, it 
 constitutes a part of the gastro-pulmonary mucous mem- 
 brane, and is continuous with the fine skin of the eyelid. 
 It proceeds backwards to about the middle of the globe, 
 where it is reflected forwards over the transparent ante- 
 rior surface. It adheres so firmly to the surface of the 
 cornea, that it has been contended by some that it termi- 
 nates at the margin of that body. But independently of 
 this forming an exception to the otherwise universal law 
 of the skin and mucous membrane, in their various diver- 
 sities and modifications, being the only tissues exposed 
 immediately to external objects, facts from comparative 
 anatomy do not bear out this opinion. In several rep- 
 tiles, as in serpents, the skin is continued over the ante- 
 rior surface of the eye ; and when they cast their skins, 
 which they generally do annually, they likewise throw 
 off that portion which covers the eyes. So likewise in 
 fishes the external integument may be observed to pass 
 over the eye, but at the same time it undergoes a modifi- 
 cation in its texture, becoming perfectly transparent, so 
 
MOTIONS OF THE EYE. 347 
 
 that it offers no impediment to the transmission of the 
 rays of light. The conjunctiva is highly sensitive, an 
 attribute which it owes to the fifth nerve. It manifests 
 irritation by the least contact of external bodies, even in 
 the form of vapour, so that on exposure to the volatile 
 principle, in onions for example, it is excited, and through 
 sympathy the lachrymal glands pour out an abundant flow 
 of tears, and the eyelids are pinched together, the former 
 to wash off, and the latter action to protect it from the 
 irritating cause. 
 
 Motions of the Eyeball. The globe of the eye is placed 
 in the orbit, where, with the exception of the external 
 surface, it is surrounded by fat. It is to be recollected 
 that the fat around the eyeball is contained in compara- 
 tively very large cells ; that it is of a more fluid nature 
 than that of fat in general ; that at the ordinary tempera- 
 ture of the animal this fat is in the fluid state ; and that 
 it is less liable to variation in quantity than the same 
 substance in any other part of the body, for we may 
 notice that the sinking of the eyes in their sockets affords 
 the last and most unequivocal evidence of extreme ema- 
 ciation. The eyeball therefore moves in a fluid medium, 
 fully adequate to give it every necessary support, and at the 
 same time offering the least possible degree of resistance. 
 
 The ball of the eye is capable of motion in every direc- 
 tion, though in some directions to a greater extent than 
 in others. Its movements are consequently universal, 
 but for the sake of description they may be resolved into 
 motions on four different axes, or in eight different direc- 
 tions, as the following : In a room we can move the eyes 
 up towards the ceiling or down towards the floor, the 
 eyeball moving on a horizontal axis from the temple to 
 the nose ; or we may turn them to the right hand or the 
 left on a vertical axis from above downwards, or on an 
 oblique axis from the inner to the outer angle ; and lastly, 
 we can carry them forward so as to cause them to pro- 
 ject, or retract them backwards towards the bottom of 
 
348 MOTIONS OF THE EYE. 
 
 the sockets. Movements may be effected in these va- 
 rious directions to different degrees of extent. Thus, 
 when we look upon a tall pillar, our eyes may be fixed 
 on the base, the middle, or the top ; or when we direct 
 them on a horizontal line, they may be fixed on the right 
 or left extreme, or on any intermediate point, and in 
 like manner upon the other two axes, forwards and back- 
 wards, or obliquely inwards and outwards. Moreover, 
 when we reflect that these various movements may be 
 performed with different degrees of velocity, with diffe- 
 rent degrees of force, and to various degrees of extent, 
 and in all these respects in an infinite degree of combina- 
 tion, we must perceive that the possible combinations and 
 variations of action of which the muscles of the eye are 
 capable, far surpass what the intellect of man "is able 
 to appreciate, producing an impression on the mind which 
 can only be indicated by such inter] ectional expressions 
 as the Psalmist has recourse to " How wonderful are 
 thy works, O Lord ! In wisdom hast thou made them 
 all !" 
 
 On reflecting upon all these varieties of movements, 
 and their infinite combinations, the mind is apt to con- 
 nect them with a complicated apparatus, and to associate 
 them with a multiplicity of machinery accessory to the 
 results. But when the question is put, how are all these 
 varieties of motion performed ? and how are these various 
 positions effected ? The answer must be, by six little 
 bundles of flesh ! 
 
 Four of the muscles of the eye arise from the bottom 
 of the orbit, proceed forwards, become tendinous, and 
 are inserted by broad thin tendons into the forepart of 
 the ball, a little posterior to the margin of the transparent 
 cornea, where they are covered merely by the thin mu- 
 cous membrane or conjunctiva. The white pearly ap- 
 pearance of the eye is caused by these tendons shining 
 through the conjunctiva, and the different tints of the 
 white of the eye depend on the greater or less transpa- 
 
MOTIONS OF THE EYE. 
 
 349 
 
 rency of the conjunctiva, or it may be tinged with colour- 
 ing matter deposited in it, as happens in jaundice, where 
 the bile produces a dingy yellow hue. 
 
 The muscles receive names according to their actions. 
 Thus, we have the levator, raising the eye upwards ; the 
 depressor, bringing it downwards ; the adductor, turning 
 it towards the nose ; and the abductor towards the tem- 
 ple. It is not to be supposed that one muscle alone is 
 engaged in performing any single movement ; for exam- 
 ple, when the eye is lifted upwards to the top of a pillar, 
 the levator is not the only one called into action ; the de- 
 pressor is at the same time required to moderate the force, 
 and to fix the extent to which the eye is earned. The 
 adductor and abductor also are employed to preserve the 
 motion steady, and prevent vacillation either to the right 
 or left, so that the eye is moved steadily in the required 
 direction with the utmost precision. The levator in this 
 instance merely takes the lead the other three being in 
 action, in a less degree, but still in action, and in an 
 instant ready to take the lead in any movement in the 
 direction of their individual forces. 
 
 By the admirable co-operation of the muscles of the eye, 
 that organ, like the needle of the mariner's compass point- 
 ing to the pole, preserves the same relative position with re- 
 spect to its object, whether the object be in motion or at 
 rest, or whether the body to which it belongs be in motion 
 or at rest. If we fix our eye upon any object, the head may 
 be moved upwards or downwards, to the right or left, the 
 eye all the time keeping perfectly steady. Here we have 
 the eyes fixed, and the orbits moving round them. On the 
 other hand, the head may be kept steady, and the eyes 
 rolled in their sockets in different directions. When the 
 eyes are directed to any object which happens to be mov- 
 ing from right to left, or from left to right, both steadily 
 follow the direction of the object ; but the correspondence 
 in the movements of the two eyes does not depend on 
 corresponding muscles, for when both are turned to the 
 
350 MOTIONS OF THE EYE. 
 
 right or left, the abductor of the one and the adductor of 
 the other is thrown especially into action. Nor does it 
 depend upon the rays of light falling on corresponding 
 points of the retina, for when the rays enter by the right 
 or left, they fall on those parts of the retina which are 
 respectively on the outer side of one eye, and on the 
 inner side of the other. Neither does it depend on their 
 receiving twigs from the same motor nerve, for the sixth 
 supplies the abductor, while the adductor receives its nerves 
 from the third ; it must depend on that power with which 
 the will is endowed, whereby it can command and con- 
 trol the various muscles which are placed under its 
 power, so as to bring them into just association with each 
 other, in order adequately to effect the intended purpose. 
 When the four straight muscles, as they are termed, are 
 simultaneously thrown into action with equal degrees of 
 force, then the eye is retracted backwards towards the 
 bottom of the orbit. 
 
 The two other muscles of the ball are called oblique, 
 in consequence of the direction in which they move the 
 eye ; and in respect to their relative position the one 
 is termed superior oblique, the other inferior oblique. 
 The superior oblique, like the four straight muscles, 
 arises from the bottom of the orbit. It proceeds forwards, 
 and becomes tendinous. In connexion with this muscle, 
 we have a very beautiful example of contrivance. Its 
 tendon, when it reaches near to the margin of the orbit, 
 is passed through a little cartilaginous pulley, by which 
 the direction of its action is changed exactly in the same 
 way as we see the direction of the action of a rope changed 
 in machinery, as in the rigging of a ship ; but, as may 
 well be supposed, the apparatus in this instance is of the 
 most perfect construction. The little ring of cartilage is 
 of the requisite density, smoothness, and elasticity, a 
 lubricating fluid is furnished to diminish friction, and 
 facilitate motion, and tough ligamentous filaments are 
 attached to regulate the extent of the movements. From 
 
MOTIONS OF THE EYE. 351 
 
 the pulley the tendon runs obliquely backwards and to- 
 wards the internal angle, to be inserted into the ball. 
 When this muscle is thrown into action, the eye is car- 
 ried in the direction of its tendon forwards, and rolled 
 inwards to the inner angle, a direction in which the eye 
 is moved when the mind is influenced by passions and 
 emotions ; wherefore the superior oblique becomes a 
 muscle of expression. 
 
 The inferior oblique arises from the inferior margin of 
 the orbit, external to the lachrymal sac. It proceeds 
 towards the bottom of the orbit, being under the ball, and 
 is inserted into the ball near the external angle. In 
 action it pulls the eyeball forwards, and rolls it obliquely 
 outwards to the temple. When the two oblique muscles 
 are thrown into action with equal degrees of force, the 
 eye is neither rolled inwards nor outwards, but is steadily 
 carried forwards. 
 
 From the above view of the motions of the eye, and of 
 the muscles by which they are effected, it appears that 
 the globe of the eye moves in eight cardinal directions : 
 by the four straight muscles it is moved upwards, down- 
 wards, to the right and to the left, each of these movements 
 being effected by an appropriate muscle ; that when these 
 four act together, it is drawn backwards towards the bot- 
 tom of the orbit, moving steadily in the diagonal between 
 their different forces ; that the eye is moved in the other 
 three directions by the two oblique muscles, each pro- 
 ducing a motion peculiar to itself, whereby the eyeball 
 is rolled obliquely inwards by the one, and outwards by 
 the other, while, by the combined action of both, it is 
 brought forwards. As far as the muscles of the eye are 
 voluntary, their action in the various movements neces- 
 sarily requires the exercise of volition, or in other words, 
 the mind must first determine on a purpose, and then 
 issue its command along the nerve to the muscle thereby 
 called into action. Accordingly, every movement of the 
 eye, however slight, must be preceded by an act of the 
 
352 MOTIONS OF THE EYE. 
 
 will, and accompanied with consciousness, although the 
 determination of the purpose, the conveyance of the com- 
 mand, and the completion of the motion, are performed 
 in succession, with such rapidity that they appear only as 
 one act. When an officer stands in the front of his regi- 
 ment drawn up in line, he partly becomes aware of the 
 relative position of each individual, in consequence of the 
 muscular feffort necessary to place the eye upon each ; 
 and when we look upon different heights of a tall pillar, 
 the eye requires to be shifted so as to be directed to every 
 point upon which it is fixed. In like manner, by the ad- 
 justment of the eye through the medium of the muscles do 
 we become in some measure aware of the relative distances 
 of different objects, by instituting a comparison between 
 them and the various intervening objects. In conse- 
 quence, therefore, of the voluntary effort required in 
 placing the eye in these different circumstances, we are 
 informed of the various relative positions and distances 
 of bodies, independently of the various intensities with 
 which they may be illuminated. 
 
 In man, apes, monkeys, and bats, among mammalia, 
 and in owls, in the class of birds, both eyes look forwards, 
 and are capable of being fixed upon, and of receiving im- 
 pressions from the same object simultaneously. In order 
 to effect this, it is necessary that the axes of both eyes be 
 brought parallel with each other, so that the rays coming 
 from the same points of an object may fall upon the cen- 
 tral point of each retina, the seat of distinct vision, where 
 these nervous membranes appear especially to sympathize 
 with each other. When the rays of light from any ob- 
 ject fall upon these corresponding points, the object is 
 seen single. Single vision with two eyes, therefore, re- 
 quires voluntary muscular action, in order to effect the 
 proper adjustment of the eyes, that the requisite degree 
 of convergence of their axes may be produced. Where 
 the object is near, as at the tip of the nose, this conver- 
 gence is very considerable, becoming less as the object 
 
MOTIONS OF THE EYE. 
 
 353 
 
 is removed to a greater distance. To bring the two eyes 
 into just accordance with each other, and to maintain the 
 proper degree of convergence, some experience is neces- 
 sary ; for if they are not accurately adjusted, the object 
 appears double. If an object is held up in one hand close 
 to the tip of the nose, and another object with the other 
 hand at the distance of ten or twelve inches in the same 
 line, on fixing both eyes upon the near object, the distant 
 one will appear double ; but if they are fixed upon the 
 distant object, then the near one appears double. 
 
 FIG. 25. 
 
 The annexed figure may illustrate this, and it will be 
 still better understood when the retina has been described. 
 There is a space at the bottom of the eye, which is the 
 centre of distinct vision, as at e e in the eyes A and B. 
 Thus the rays from ah object at C will fall upon the cen- 
 tre of distinct vision at e 0, and be distinctly seen. Un- 
 less the rays from any object fall upon this in both 
 
354 MOTIONS OF THE EYE. 
 
 eyes, it will appear double, so that when the attention 
 is fixed on the distant object, as at D, then the near 
 object at N is seen double, and conversely. Thus the eyes 
 require to be adjusted to each distance, that single vision 
 may be effected with two eyes. 
 
 There can be little doubt that the necessary dexterity in 
 the use of the muscles employed in these movements is 
 only acquired gradually by experience, in the same manner 
 as the requisite command and facility of using our other 
 voluntary muscles is only obtained by education, and 
 after repeated trials and failures, as the use of the limbs 
 in walking, the employment of the hands for the various 
 purposes of the arts, the exercise of the organs of speech, 
 and so forth. The vague and indefinite expression of the 
 eyes of infants is a proof of this. Any one carefully no- 
 ticing the eyes of a young infant, will perceive that they 
 are never fixed in such a manner as to effect the proper 
 convergence of their axes upon one object ; consequently 
 single vision with two eyes does not take place at this 
 period of life, nor until experience has given the necessary 
 dexterity. The drunkard loses the necessary control 
 over these muscles, and therefore sees double, just as he 
 stammers in his speech and staggers in his walk. Al- 
 though the adjustment of the two eyes be thus difficult, 
 in somewhat the same proportion is the accuracy obtained 
 as to the relative position of different objects ; hence the 
 greater facility of threading a needle, for example, with 
 both eyes than with one, and hence, too, the experienced 
 archer adjusts the direction of his arrow with both eyes, 
 while the inexperienced marksman conceives it better to 
 have recourse to one, and consequently the aim is not so 
 certain. In by far the greater number of mammalia, 
 birds, reptiles, and fishes, the eyes are so placed on each 
 side that they cannot be brought to bear upon the same 
 object at the same time ; their lateral position, however, 
 has the effect of vastly extending their sphere of vision, 
 and the precision with which several of them mark the 
 
MOTIONS OF THE EYE. 355 
 
 relative position of objects is sufficiently evinced by the 
 accuracy with which many birds will pounce upon their 
 prey from great heights in the air, notwithstanding their 
 knowledge of its position having been obtained from a 
 single eye. 
 
 Besides the six muscles by which the motions of the 
 eye are effected in man, the great majority of mammalia 
 and birds are furnished with a seventh, named the sus- 
 pensory. This muscle is situated at the back part of the 
 eyeball, arises from the bottom of the orbit surrounding the 
 optic nerve, and is implanted in the ball posterior to the 
 other muscles. It is composed of several bundles, so dis* 
 tinct that they may be considered as forming so many 
 distinct muscles, each capable of performing separate and 
 independent movements ; at the sametime none of these 
 bundles, either independently or conjointly, can place the 
 eye in any direction into which it may not be brought by 
 the straight muscles of the human eye, or of those animals 
 in which it is present. From the mode of its insertion the 
 extent of the motions effected by it must be more limited 
 than those which result from the action of the straight mus- 
 cles. The name, suspensory, would lead to the inference 
 that its use is to suspend the eye in its socket when the head 
 is in the dependent posture ; but a ligament would have 
 answered the intention much better, as it would have ac- 
 complished the end sufficiently, and at the same time 
 would not have been liable to the fatigue to which mus- 
 cular fibre is exposed. The action of this muscle, alter- 
 nating with that of the straight, may afford both muscles 
 an interval of rest, and by their combined action a more 
 just idea of the relative position of objects may be obtained, 
 whereby the same result may arise as from the exercise 
 of the muscles of two eyes. 
 
 In man, when the motions of the eyes are too limited 
 for the sphere of vision that may at the time be required, 
 it may be instantly extended by the motions of the 
 head, and if these are still too confined, the whole body 
 
356 MOTIONS OF THE EYE. 
 
 may be turned round on the heels, as on a pivot, so as 
 to bring the whole horizon in succession upon the field 
 of distinct vision ; thus by the motions of the eye, with 
 the co-operation of the motions of the head, neck, and 
 trunk in various directions, the canopy of the heavens 
 above, and the surface of the earth beneath, may be 
 viewed in a portion of time so minute, that what is suc- 
 cessive appears instantaneous. In the lower animals, 
 the lateral situation of the eyes effect the same purpose, 
 and in many of them, especially in birds, the flexibility 
 of the neck enables them to place the eye in the desired 
 position in an instant. The great majority of reptiles 
 are placed prone upon the surface of the ground, and 
 require their eyes to be directed upwards, so that 
 their position enables them at once to take in the ne- 
 cessary extent of the sphere of vision, without the in- 
 tervention of muscles. The eyes in these animals are 
 therefore fixed, and where an extension of the sphere be- 
 comes desirable, it is effected by the motions of the head. 
 The chameleon, which remains perfectly motionless, lest it 
 should alarm its prey before it comes within the reach of 
 its long prehensile tongue, has an eye supported on a pivot, 
 on which it turns in different directions. The whole 
 eye is covered with integument, of precisely the same 
 colour with the rest of the animal, w r ith the excep- 
 tion of the pupil, so that the motions can only be no- 
 ticed on the closest inspection, consequently no alarm is 
 given to the unwary insect till it comes within the reach 
 of its tongue, when it is too late, as that instrument is 
 darted out with a quickness which often escapes the eye 
 of the bystander, and he is aware of the insect being re- 
 moved only by its disappearance. In lobsters and crabs 
 the eye is placed at the extremity of a long tube, which 
 can be moved in various directions, extended or with- 
 drawn, w r hereby the inconvenience which might have 
 arisen from their rigid and inflexible bodies is obviated. 
 Spiders, like the chameleon, require patiently to wait and 
 
COMPOUND EYES. 
 
 357 
 
 seize their prey by stratagem. The slightest movement on 
 their part might give the alarm. They remain therefore 
 perfectly still and motionless, till the heedless fly is en- 
 tangled in their net, when they instantly issue forth and 
 destroy it. Although they appear in the midst of the 
 web inattentive, nevertheless, Argus-like, they have an 
 eye in every direction, for nature has furnished them with 
 from six to fourteen eyes, according to their tribes, that 
 they may have one on every point, and take in an ex- 
 tensive sphere of vision, without the necessity for motion, 
 which would have been incompatible with the means by 
 which they gain their subsistence. The greater number 
 of insects are furnished with two kinds of eyes, one of 
 which is termed compound, from being composed of 
 several hexagonal facets, each of which is a distinct eye 
 in itself. These facets vary in their size, and from their 
 position are enabled to receive the rays coming from dif- 
 ferent directions. Hooke, in his Micrographia, has the 
 following observations on the compound eyes of the grey 
 drone-fly : " These rows were so disposed that there 
 was no quarter visible from his head that there were not 
 some of these hemispheres directed against, so that a fly 
 may be truly said to have an eye every way, and to be 
 really circumspect. And it was further observable, that 
 that way where the trunk of his body did hinder his 
 prospect, these protuberances were elevated, as it were, 
 above the plane of his shoulders and back, so that he was 
 able to see "backwards also over his back. 
 
 " In living flies I have observed, that when any small 
 mote or dust which flies up and down the air chances to 
 light on any part of these knobs, as it is sure to stick 
 firmly to it and not fall, though through the microscope 
 it appears like a large stone or stick (which one would 
 admire, especially since it is noways probable that there 
 is any wet or glutinous matter upon these hemispheres, 
 but I hope I shall render the reason in another place), so 
 the fly presently makes use of its two fore-feet, instead 
 
358 COMPOUND EYES. 
 
 of eyelids, with which, as with two brooms or brushes, 
 they being all bestuck with bristles, he often sweeps or 
 brushes off whatever hinders the prospect of any of his 
 hemispheres, and then, to free his legs from that dirt, he 
 rubs them one against another ; does cleanse them in the 
 same manner I have observed those that card wool to 
 cleanse their cards, by placing their cards so as the teeth 
 of both look the same way, and then rubbing them one 
 against the other. In the very same manner do they 
 brush and cleanse their bodies and wings, as I shall by 
 and by shew. Other creatures have other contrivances for 
 the cleansing and clearing their eyes. 
 
 " The number of i\\Q pearls or hemispheres in the clusters 
 of this fly was near 14,000, which I judged by number- 
 ing certain rows of them several ways, and casting up the 
 whole contents, accounting each cluster to contain about 
 7000 pearls, 3000 of which were about a size, and con- 
 sequently the rows not so thick, and the 4000 I accounted 
 to be the number of the smaller pearls next the feet and 
 proboscis. Other animals I observed to have a greater 
 number, as the dragon-fly or adderbolt, and others to have 
 a much less company, as an^aal, &c., and several other 
 small flies and insects." 
 
 Some species of butterflies have facets amounting to 
 the number of 34,650. In these compound eyes each 
 facet consists of a hard transparent lenticular body, 
 through which the rays of light pass, to reach a corres- 
 ponding division of the optic nerve, so that each facet is 
 composed of a very dense cornea for collecting and 
 transmitting the rays, and a bundle of nervous matter 
 for receiving their impression, each facet thus form- 
 ing a complete eye in itself. Exposed as these animals 
 are to the atmosphere, fluids would soon have been dis- 
 sipated by evaporation. Their eyes are therefore con- 
 structed upon principles which do not require fluids, and 
 the various adaptations which result from the modifica- 
 tions the humours undergo in the higher tribes of ani- 
 
GLOBE OF THE EYE. 
 
 359 
 
 mals are compensated for by the number of eyes with 
 which they are furnished, each facet being fitted to see 
 objects at a certain distance ; and as the distances vary, a 
 facet is applied in accordance to it, being furnished with 
 a lens of the adequate size and convexity. The facets 
 being immoveable, their number also compensates for the 
 want of motion, so that they have an eye in most direc- 
 tions at once. The variety, extent, and combination of 
 the motions of the eye, as well as the facility with which 
 the humours accommodate themselves to varying circum- 
 stances in the higher classes of animals, produce an infi- 
 nitely greater number of adaptations to distances, posi- 
 tions, and degrees of illumination, than result from the 
 thousands of eyes with which these insects are furnished. 
 From what has now been mentioned, it appears that, with 
 respect to motion, situation, and number, the eyes have 
 reference to the form and structure of the animal, as these 
 again have a reference in their turn to various functions, 
 relations, and circumstances, which the animal more ac- 
 curately discovers by instinct than the physiologist by his 
 profound and laborious researches. 
 
 The peculiar defective state termed squinting arises 
 from several causes. A very common one is unequal 
 power in the eyes, which induces the individual to use the 
 stronger one, the weaker being left to wander irregularly 
 at random, though generally brought under the influence 
 of the superior oblique, whereby the countenance appears 
 to have an expression of feelings which the person by no 
 means entertains at the time. Occasionally the individual 
 is unconscious of this inequality, until it is pointed out to 
 him by desiring him to close the more perfect eye and 
 employ the weaker, so as to institute a comparison be- 
 tween them. One means whereby this deformity may 
 be obviated is by covering the stronger eye, and for some 
 time using the other, till their strength be reduced to an 
 equality, when the squinting disappears. In other cases 
 the distortion arises from loss of power in one or other of 
 
360 GLOBE OF THE EYE. 
 
 the muscles, and for the most part will be found irremedi- 
 able. When a person is in a deep reverie, where the 
 effort necessary to preserve the parallelism between the 
 two eyes is suspended, squinting takes place ; and when 
 he is roused from this state of mental rumination, the 
 eyes may be seen to start again into concordance. The 
 same occurs during sleep, when volition is entirely sus- 
 pended ; and it forms a symptom indicative of the condi- 
 tion to which the system is reduced by narcotic poisons. 
 Sometimes squinting depends on the condition of the 
 brain, and points out the state of the internal parts ; in 
 this way it frequently happens in water in the head, or 
 apoplectic diseases. 
 
 Globe of the Eye. The eyeball consists of a number 
 of membranes termed coats, enclosing certain humours, 
 through which the rays of light are transmitted and modi- 
 fied before they fall upon the nervous screen, on which 
 they make their impression. Each of these must be 
 studied individually before we are prepared fairly to esti- 
 mate the result of the action of the whole. 
 
 The Sclerotic Coat, so named from its firmness and den- 
 sity, constitutes about four-fifths of the globe of the eye, the 
 remaining fifth being formed of the transparent cornea. 
 It is composed of a number of fibres, intricately inter- 
 woven with each other ; between them are disposed several 
 irregular-shaped plates, which contribute to its consis- 
 tency. Its colour is bluish white ; anteriorly it is thicker 
 and denser where the tendons of the muscles are implant- 
 ed into it. Neither blood-vessels nor nerves can be traced 
 to their termination in it, though many of both perforate 
 it in their passage to the internal parts. Upon the whole, 
 it must be held as possessing only a low degree of vita- 
 lity, and therefore better fitted for the purposes of 
 defending the delicate internal parts, and affording a 
 fixed attachment to the muscles. In the whale tribe it 
 is upwards of an inch in thickness at the back part, yet 
 a whale seventy or eighty feet in length has an eye the 
 
COATS OF THE EYE. 
 
 361 
 
 interior of which is not more capacious than that of a 
 bullock. In birds, on the other hand, the anterior part 
 is much thicker and stronger, and in several composed of 
 a series of bony plates, forming a collar around the ante- 
 rior surface of the ball. The purposes served by these 
 modifications of structure have not been ascertained, 
 though no doubt they are the best fitted to the circum- 
 stances of the animals in which each obtains. 
 
 The Cornea is the term applied to the anterior trans- 
 parent portion of the ball. It is a segment of a smaller 
 sphere than that of the sclerotica. In the human subject 
 it is nearly circular ; its convexity varies in different indi- 
 viduals and in different ages. It is received into a cir- 
 cular groove in the anterior margin of the sclerotica, 
 in the same way as the watch-glass is inserted into the 
 case. The cornea is somewhat thicker than the scle- 
 rotica, and composed of six concentric plates, separable 
 from each other without much difficulty, after a little ma- 
 ceration. A small quantity of transparent fluid may be 
 squeezed out from between its plates; but its blood- 
 vessels are so exceedingly minute that they totally ex- 
 clude the colouring particles of the blood, so long as it 
 retains its organization. When affected with inflamma- 
 tion it loses its transparency, whereby more or less com- 
 plete blindness results from the obstruction to the pass- 
 age of light. 
 
 Between the sclerotic coat and cornea there is placed a 
 ring, circle, or ligament, generally known . by the name 
 of ciliary ligament; besides the cornea and sclerotica, 
 it is connected with the iris and choroid coat, especially 
 with the latter. It constitutes a good point of reference 
 w r hen speaking of the relative position of other parts. 
 
 The Choroid Coat is formed principally of a tissue of 
 blood-vessels and nerves, with a delicate cellular membrane 
 interlaced through them. Its great vascularity has caused 
 it to be likened to a vascular membrane, investing the 
 foetus in the womb, termed chorion ; hence the origin of 
 
 B 
 
362 COATS OF THE EYE. 
 
 its name. It lies immediately in contact with the inter- 
 nal surface of the sclerotica, commencing at the optic 
 nerve behind, for the passage of which there is a hole in 
 it. It proceeds forwards till it reaches the ciliary liga- 
 ment, where it is folded into a number of plaits like the 
 ruffle of a shirt ; these collectively form a zone or belt, 
 which is placed immediately behind the iris, surrounding 
 the margin of the crystalline lens like a collar, and fringed 
 with little projections or processes which float in the 
 watery humour. Its great vascularity, and the numerous 
 nerves distributed upon it, chiefly derived from the fifth 
 nerve, indicate its high sensibility; and from its close proxi- 
 mity to and intimate relation with the retina, it becomes 
 directly connected with sight. Although the nerves 
 distributed on the choroid are incapable of transmitting 
 such impressions as properly produce sight, yet they are 
 highly sensitive to the rays of light, and constitute the 
 channels by which painful sensations are conveyed to the 
 mind, from exposure of the eye to the intense light of the 
 meridian sun for example. In this view the choroid may 
 be considered as the sensitive guardian of the retina ; as 
 that nerve can only convey specific impressions, it was 
 necessary that it should be associated with a structure 
 which might give warning on the approach of danger. 
 
 The vessels of the choroid secrete a dark-coloured matter, 
 consisting of globules, and named black pigment. From 
 the external surface this pigment is easily brushed off, 
 though not so readily from the internal, where it is pro- 
 tected by a delicate membranous expansion. The dark 
 colouring matter is well fitted for absorbing the super- 
 fluous and scattered rays of light. In some animals a 
 portion of the internal surface of the choroid, instead of 
 being furnished with dark pigment, is supplied with 
 covering of a bright metallic lustre named tapetum. It 
 exists in the horse, dog, and many other animals ; and 
 when they are placed in an obscure light, produces 
 a reflection of light which gives their eyes that re- 
 
o 
 
 COATS OF THE EYE. 36' 
 
 markable brilliancy that makes many suppose that they 
 flash fire. 
 
 The number and size of the vessels of the choroid are 
 much greater than what would be requisite merely for the 
 nourishment of this membrane and the secretion of the dark 
 pigment. The arteries, by their frequent communications 
 with each other, present a beautiful appearance of net- 
 work, and the veins are so disposed as to form numerous 
 whorls. Both of these arrangements are well adapted for 
 admitting of congestion, and readily accommodate them- 
 selves to varying quantities of blood in each set of ves- 
 sels. Another circumstance affecting the circulation of 
 blood within the eye arises from the sclerotica and cornea 
 being of sufficient firmness and strength to enable them 
 to resist the influence of atmospheric pressure; conse- 
 quently the circulation in the interior of the eye is in 
 somewhat similar condition to that w r ithin the skull, the 
 quantity of blood in the vessels remaining the same un- 
 der every variety of atmospheric pressure. Neither can 
 it be diminished by blood-letting and other means of 
 depletion, although the force with which it is trans- 
 mitted may be lessened. Accordingly we find that in 
 inflammation of the interior of the eye, leeching, cup- 
 ping, and even general blood-letting, have not that im- 
 pression in subduing the symptoms that is usually pro- 
 duced by them. 
 
 The Iris. The colour of the eye depends upon that of a 
 curtain or partition which divides the interior of the eye 
 into two unequal portions, termed chambers. The colour 
 of this curtain varies in different individuals, being dark- 
 brown or black, light-grey, blue, and several shades and 
 combinations of these. The variety of colour is still 
 greater in the different species of the lower animals, and 
 particularly in birds, in which it exhibits hues as various 
 as the rainbow, whence in fact its name is derived. 
 In the centre of the iris a dark spot is observed, com- 
 monly called the star of the eye. This is a hole through 
 
364 THE PUPIL. 
 
 which the dark pigment of the choroid coat is seen. 
 If we look into the eye of another, or on our own re- 
 flected in a mirror, we shall perceive a little image of 
 our own face, like a very minute child or pupil, conse- 
 quently this hole has received the name of pupil. The 
 iris is attached at its greater circumference to the ciliary 
 ligament, the smaller forming the margin of the pupil. 
 The anterior surface presents two concentric bands ; the in- 
 terior surrounds the margin of the pupil, and is of a darker 
 colour than the exterior broader belt. Upon closely in- 
 specting the surface of the iris several undulations or 
 folds may be observed radiating from the ciliary ligament 
 towards the pupil, on approaching which they divide, and 
 are interwoven with each other. The lines marked upon 
 the iris have been imagined to represent letters and other 
 characters. A remarkable example of this occurred in 
 the south of Scotland a few years ago, where an illegiti- 
 mate child was born. The man who had been indicated 
 by the mother having denied the paternity, the charge 
 was brought home to him to the entire satisfaction of the 
 credulous and superstitious, by his name being written 
 upon the child's iris, with the year of its birth, 1819. It 
 was afterwards carried about for several years for public 
 exhibition, when we had an opportunity of examining 
 the eye, but failed in tracing the letters or figures on the 
 iris, which was of a light-blue. We have no doubt, 
 however, that by a little aid from creative fancy, they 
 might have been perceived, just as castles, towers, and 
 pinnacles are conjured up amidst the dying embers. 
 
 The posterior surface that looks towards the ciliary 
 folds is furnished with dark pigment, and this shining 
 through the iris imparts to it the colour characteristic of 
 the individual. In albinos of the human race, and in the 
 lower animals, the dark pigment is wanting both in the 
 choroid coat and this membrane, and these parts being 
 very vascular, the blood is seen imparting a red colour to 
 the eye, From the deficiency of the dark pigment, al- 
 
THE IRIS. 365 
 
 binos cannot tolerate a strong light, such as at noon-day, 
 while they are said to enjoy vision very perfectly during 
 the obscurity of night. Indeed, persons differ consider- 
 ably as to their powers of vision, in strong and obscure 
 light. Those possessing the power of seeing distinctly under 
 the former condition are said to have diurnal, and the lat- 
 ter nocturnal sight. According to the habits of various 
 animals, we perceive them enjoying different degrees of 
 these, as the falcon tribe on the one hand, and owls on 
 the other. 
 
 The iris consists of three layers, covered by a serous 
 membrane. The anterior layer is composed of circular 
 fibres, which contract so as to diminish the size of the 
 pupil. The posterior layer, on the other hand, is formed 
 of radiating fibres, arising from the ciliary ligament, and 
 running towards the margin of the pupil. These, when 
 thrown into action, enlarge the pupil. The middle layer is 
 composed of a net-work of blood-vessels, along with 
 which nervous twigs are plentifully distributed. It may 
 be mentioned, however, that the movements of the iris 
 are attributed by some to a greater or less accumulation 
 of blood in the vascular net- works, of which there are 
 two, of different diameters the larger around the mar- 
 gin of the ciliary ligament, the smaller surrounding the 
 margin of the pupil. This opinion has been taken up 
 from the impossibility of clearly demonstrating muscular 
 fibre in the tissue of this organ, though at the sametime 
 many motions are performed in animals by textures wide- 
 ly different from what is usually held as proper mus- 
 cular fibre, and their muscularity is not disputed. Those 
 who deny the muscularity of the iris cite the experiment 
 of transfixing it with a needle, when no motion can be 
 perceived ; but in this case both fibres must be irritated, 
 and their contractions consequently neutralize each other. 
 On the other hand, when the experiment is so conducted 
 as to irritate merely the anterior layer of circular fibres, 
 the contraction is distinctly perceptible. 
 
366 THE IRIS. 
 
 The iris by its movements regulates the quantity of 
 light passing through the pupil. During sleep, the pupil 
 will be found in an intermediate state, and when the per- 
 son is awakened in an obscure light, and begins to exer- 
 cise his sight, the pupil will be seen to contract. Again, 
 when a strong light is thrown upon the eye, it very dis- 
 tinctly contracts so as to diminish the quantity of light 
 admitted into the interior of the eye, the intercepted rays 
 being either absorbed by the pigment, or reflected back 
 again through the cornea ; those rays alone which pass 
 through the pupil contributing to vision by striking against 
 the retina. If a person hold a candle close to the eye of 
 another, the pupil will be observed much contracted, 
 and as the candle is withdrawn it will gradually dilate, 
 showing how admirably this little curtain is constructed 
 and endowed for the purposes of its creation. The an- 
 terior circular fibres which are chiefly to be engaged in 
 the regulation of the pupil in respect to light, are so situ- 
 ated as at once to receive their impression, while the 
 radial fibres are placed behind, being called into action 
 principally in accordance with the condition of the inte- 
 rior organs. 
 
 It also contributes to the adaptation of the eye to near 
 and distant, to large and minute objects. A curious 
 experiment may here be mentioned, that will serve to 
 illustrate this : If a small object, such as a hair or a 
 fine needle, be held before one eye, while the other 
 is closed, so that the bright light from the window, or 
 the flame of a candle, falls upon the object ; or if it be 
 a needle, the back of the person may be turned upon the 
 light, and the bright reflection received by the eye; 
 when the object is placed at the distance of fifteen or 
 eighteen inches, that is, at the point of distinct vision, it 
 will be seen single ; but when carried a little nearer it 
 will appear double, treble, or quadruple, and so on as the 
 distance is varied. The best way of performing the ex- 
 periment is to ta^c a parallel ruler and open it slightly, 
 
THE IRIS. 367 
 
 so as to afford a small linear aperture ; on holding it up 
 between the eye and the light, alternate bright and dark 
 lines will be seen according to the distance at which it is 
 held within the point of distinct vision. This curious mul- 
 tiplication of the image of an object has been accounted 
 for by what Newton has termed fits of easy refraction 
 and fits of easy reflection. Now, if the eye of the per- 
 son making the experiment be watched as he approxi- 
 mates the object to his eye, and is intensely engaged in 
 counting the number of images, the pupil will be seen 
 contracted to a minute point. Or if we hold up before a 
 person a sheet of white paper on which minute characters 
 are traced, first directing him to place his eyes fixedly on 
 the paper, then marking the condition of the pupil, we 
 next desire him to endeavour to make out the characters ; 
 when he attempts to do this, the pupil will be seen to 
 contract, in order to fit the eye for the examination of 
 minute objects. By this contraction of the pupil the 
 more divergent rays of light which pass through the 
 cornea are prevented from entering into the posterior cham- 
 ber, and consequently cannot pass through the margin 
 of the lens, where they could not have been brought to 
 a correct focus on the retina. In this way spherical aber- 
 ration is obviated. 
 
 The iris derives its nerves from the lenticular ganglion 
 of the fifth, from the third or motor nerve of the eye, and 
 filaments accompanying its numerous blood-vessels from 
 the sympathetic and respiratory nerves. Its being fur- 
 nished with twigs from the third is confirmatory of its 
 muscularity, and the filaments from the other sources ex- 
 plain its sensibility and the sympathy it displays with 
 the condition of other parts. Where blindness arises 
 from loss of power in the retina, occasionally the iris dis- 
 plays no mobility in accordance with different degrees of 
 light, while in other cases it is but little impaired. Irri- 
 tation of the nostrils causes contraction of the iris, which 
 is easily accounted for by the nervous connexions that 
 
368 THE IRIS. 
 
 have been already explained. The iris especially sympa- 
 thizes with the condition of the brain and nervous system 
 in general. Where susceptibility to impressions is im- 
 paired, either by narcotic poisons or by disease, the con- 
 dition of the pupil affords valuable information to the 
 medical practitioner as to the state of his patient, in the 
 various phases the disease may present during its progress. 
 The deadly nightshade has obtained the name of Bella- 
 dona^ or beautiful lady, from the paleness its use pro- 
 duces, and from causing a dilatation of the pupil, and 
 therefore a dark eye ; the names Atropa and deadly night- 
 shade are however the more applicable terms, from its 
 very dangerous qualities. 
 
 In the lower animals the iris presents great diversities, 
 not only in its colour, but in its mobility, and in the form 
 of its pupil. In birds, especially in owls, the motions 
 are free, conspicuous, and evidently voluntary ; the same 
 holds good in the cat tribe. In reptiles its motions are 
 obscure, and in fishes altogether imperceptible. In rumi- 
 nants, in the horse, the marmot, and in the whale tribe, 
 the pupil is elongated transversely, so that a greater num- 
 ber of the lateral rays receive entrance into the inner 
 chamber from the upper margin. In the horse a small 
 square curtain hangs down, which must intercept a great 
 part of the rays coming from above. It is also elongated 
 transversely in owls, the goose, and the dove among birds. 
 In the cat tribe, as in the domestic cat, the lion, the 
 tiger, leopard, and so forth, it is elongated vertically, as 
 it is also in the crocodile. These animals have, therefore, 
 EO far as the pupil is concerned, a more extensive sphere 
 of vision, and a greater number of rays admitted from 
 above downwards than in the lateral directions, and their 
 habits accord with this conformation in watching their 
 prey, which is very generally placed above them, and 
 more in front than to either side, while timid animals, 
 such as ruminants, have to guard against the insidious 
 approach of enemies while quietly browzing in the fields ; 
 
HUMOURS OF THE EYE. 369 
 
 their pupil accordingly admits freely of the rays coming 
 laterally. 
 
 In the fcetal state the pupil is closed by a membrane 
 till about the seventh month, when it disappears. In 
 those animals which are born blind, and continue so for 
 some time after birth, such as the dog, cat, and so forth, 
 the eyelids are united by the conjunctiva passing be- 
 tween them, so as to form a mucous sac, shut in all 
 directions excepting along the lachrymal canals towards 
 the nose, an arrangement which obtains through life 
 in reptiles. In these animals thus born blind, the 
 pupillary membrane remains till the eyes are opened. 
 It has been suggested that the use of the pupillary 
 membrane is for the purpose of keeping the pupil 
 open during the formation of the different parts an 
 explanation which is by no means satisfactory, as it 
 would imply imperfection and deficiency in resources, 
 neither of which ever exist in organized structures. 
 We may rest assured that all the various modifica- 
 tions of structures are the best possible in every 
 individual case, though we may fail in ascertaining 
 the manner in which they conduce to the purposes 
 intended, or even in comprehending the end of their 
 formation. It therefore better becomes us at once to 
 confess our ignorance, than idly to hazard an explana- 
 tion which may be far from the truth, and tend more to 
 the retardation than the advancement of sound know- 
 ledge. 
 
 We have next to consider the transparent parts of the 
 eye, through which the rays of light pass before they 
 reach the retina to depict the image, whereby the im- 
 pression of the external objects is received, subsequently 
 to be conveyed to the seat of perception, the brain. The 
 cornea, one of these, we have already described, leaving for 
 consideration three substances termed humours: One 
 of these, the aqueous humour^ differs little from transr 
 parent water, excepting in holding in solution some of 
 
 R2 
 
370 HUMOURS OF THE EYE. 
 
 the salts of the blood, and a trace of albumen. The se- 
 cond is curiously organized, of a lenticular shape, and, 
 from its resemblance to rock crystal, named the crystal- 
 line lens. The third, from presenting the appearance of 
 a mass of melted glass, has received the name of vitreous 
 humour. 
 
 The Aqueous Humour is furnished by a thin delicate 
 transparent web, covering the internal surface of the cornea, 
 and the anterior surface of the iris. From its structure 
 and use, this web ranks under the class of serous mem- 
 branes, having the peculiarity of being perforated at the 
 pupil. Although previous to the removal of the pupillary 
 membrane it constitutes a complete shut sac, the disap- 
 pearance of that partition leaves a hole in it. The 
 watery humour which it secretes fills not only the an- 
 terior chamber between the cornea and the iris, but also 
 the posterior chamber between the iris and the lens, and 
 is very rapidly renewed after being evacuated, as it oc- 
 casionally is in surgical operations. It is derived chiefly 
 from the exhalation of the vessels of the iris, and may 
 possibly contribute by its varying quantity to the adjust- 
 ment of the eye to different sizes and distances of objects, 
 which is probably a conjoint result of the action of 
 several parts of the complicated machinery of the eye, 
 and not merely dependent upon the condition of any 
 one part. This adjustment of the eye to near and 
 distant objects, to large and minute, can scarcely be al- 
 together the consequence of muscular movements, as it 
 requires some time to be adequately adapted to the dis- 
 tance, or to the size, which would at once have promptly 
 been effected had it depended on muscular contractility 
 alone, as we see to be the case in placing the eye in diffe- 
 rent positions. On fixing it on a distant object, as on a 
 ship far at sea, it takes some time before we can well make 
 it out, as it also does before we can satisfactorily ascertain 
 the texture or conformation of a very minute object. These 
 changes, necessary to the proper arrangement of the eye, 
 
CRYSTALLINE LENS. 371 
 
 in order to fit it to different purposes, appear to be in 
 accordance with the more gradual results of vascular al- 
 terations, although these may only constitute one part of 
 the requisite adjustment. The increase and diminution of 
 the aqueous humour are capable of affecting, to a certain 
 extent, the relative position of the lens. By the former 
 the lens may be pressed backwards near to the retina, 
 and by the latter again allowed to move forward nearer 
 the pupil. Where the accumulation of aqueous fluid is 
 considerable, it alters also the form and condition of the 
 cornea, rendering it more convex, while, if it take place 
 to any considerable extent, the pressure produces opacity 
 of the substance, thereby causing blindness. This some- 
 times occurs with horses that have been fed during the 
 winter in the stable on dry food, either placed on a level 
 with the head, or considerably above it. On turning 
 them out in spring to the green pasture, where there is 
 not only a change from dry to succulent diet, but also in 
 the position of the head in collecting the food, congestion 
 of aqueous humour is apt to occur to such an extent as 
 to produce temporary blindness. 
 
 The Crystalline Lens is placed immediately behind the 
 pupil, and is bathed anteriorly by the aqueous humour. 
 It constitutes a doubly convex lens, perfectly transparent. 
 The posterior surface is more convex than the anterior, and 
 it approaches nearer to a sphere in infancy than in adult 
 age. The lens is enclosed in a capsule, w r hich forms a shut 
 sac, firmer and denser anteriorly than posteriorly, and also 
 transparent. The capsule of the lens is itself invested 
 by an extension of the delicate web which surrounds the 
 vitreous humour, and known by the name of hyaloid 
 membrane. This membrane, on reaching the margin of 
 the lens, divides into two layers the one passing over 
 the front of the capsule, the other covering it posteriorly. 
 Where they separate, a small triangular canal is left, run- 
 ning round the circumference of the lens. 
 
 When the crystalline lens is first removed from its cap- 
 
372 CRYSTALLINE LENS. 
 
 sule, it appears like a mass of transparent crystal, without 
 trace of any special organization. Towards the surface 
 it is soft and pulpy, becoming more and more dense and 
 consistent towards the centre. Its density is also found 
 to be in the direct ratio of the age, it being soft in the 
 young, and firm and dense in the old. It consists prin- 
 cipally of albumen ; consequently, when exposed to heat, 
 as by putting it into boiling water, it is hardened, and be- 
 comes milk-white, or of an opal colour. Alcohol, acids, 
 and several metallic salts, produce a similar effect. When 
 examined in this state it will be found to be very curious- 
 ly organized, especially towards the centre, for the soft 
 surface, from its delicacy, does not display any particular 
 organic arrangement. The firmer central mass presents 
 a number of concentric plates or lamellae. Two thou- 
 sand of these have been counted, increasing in their den- 
 sity towards the centre. Each layer consists of an in- 
 finite number of exceedingly minute filaments, wound 
 round in different directions, from various centres. The 
 arrangement of these fibres 'differs in various animals, but 
 remains uniform in every individual of the same species. 
 
 In fishes the lens is almost completely spherical. It is 
 less so in reptiles, and becomes more flattened in birds 
 and mammalia. In those of the latter class, whose vision 
 is adapted both for air and water, as seals and whales, 
 the lens is of greater convexity than in those which em- 
 ploy their eyes in the former medium only. 
 
 The lens, or its capsule, or both at the same time, oc- 
 casionally become opaque, producing partial or complete 
 obstruction to the transmission of the rays of light, and 
 forming the disease named cataract. The removal of the 
 diseased lens from the sphere of vision frequently pro- 
 duces a cure of the accompanying blindness, when the 
 space occupied by the lens is filled up by aqueous humour. 
 
 The Vitreous Humour is a glairy transparent fluid, 
 contained in the cells of an equally transparent membrane, 
 named the hyaloid. This delicate web forms numerous 
 
THE RETINA. 373 
 
 cells, which communicate with each other, so that if we 
 puncture it, the somewhat viscid fluid with which they 
 are filled will in time escape, though "but slowly, from 
 the intricacy of the cellular structure. When first re- 
 moved from a fresh eye, the vitreous humour presents a 
 globular shape, with a depression in front, for the recep- 
 tion of the posterior hemisphere of the lens. At first 
 sight it appears to possess a consistency equal to the 
 white of an egg, but in reality it is much less so, the ap- 
 pearance arising from the fluid being retained in the cells 
 of the hyaloid. 
 
 This humour occupies two-thirds of the cavity of the 
 eyeball, and serves principally to afford a surface for the 
 extension of the expanded retina, to keep the lens at the 
 requisite distance, and to transmit the rays of light. 
 
 Retina. The retina is so named from presenting an 
 interlacement of tissue like a net-work. It consists of 
 two layers ; the one, embracing the vitreous humour, is 
 composed of a net-work of blood-vessels j the other, con- 
 tiguous to the choroid coat, consists of soft medullary 
 nervous matter. It is, however, not in immediate con- 
 tact with the choroid, for there is interposed between 
 them an exceedingly delicate film, corresponding to a 
 neurilema, named Jacob's membrane. In the living body 
 the retina is perfectly transparent, and remains so after 
 death, so long as the vital warmth continues, but after- 
 wards becomes of a pale milky colour, and rapidly hastens 
 into decomposition. If the blood-vessels be filled with 
 injection, and the retina macerated for a day or two, the 
 nervous layer may be removed with a gentle stream of 
 water, leaving the vascular layer behind. 
 
 The retina is continuous with the optic nerve, though 
 different from it in texture and consistence ; if, therefore, 
 it is held as an expansion of that nerve, it must be ad- 
 mitted at the same time that a considerable change in 
 structure takes place along with the expansion. It pro- 
 ceeds forwards, along the internal surface of the choroid, 
 
374 THE RETINA. 
 
 till it reaches the commencement of the ciliary folds, 
 where it forms a somewhat thickened ring, from which, 
 
 according to some, it is 
 extended as a very thin 
 nervous film over these 
 folds to the margin of 
 the lens, while others 
 contend for its termi- 
 nation at the rim. 
 
 The accompanying 
 engraving will convey 
 an idea of the parts 
 now described : mm are 
 
 FIG. 26. 
 
 reflections of the mu- 
 cous membrane, covering the front of the eye ; c o c o the 
 cornea ; * i the iris, with the hole, the pupil, in its centre, 
 marked p ; c p are the ciliary folds ; c r the crystalline 
 lens ; v the vitreous humour ; s s s the sclerotic coat ; 
 *' s the same turned back ; c c the choroid coat ; o n the 
 optic nerve ; and r r the retina. 
 
 From the transparency of the retina, the rays of light 
 must pass through it, and depict the image behind it on 
 the choroid. But, however that may be, this delicate web 
 is admitted to be most essential to vision, to which the 
 retina, indeed the whole of the rest of the apparatus, may 
 be considered as merely subsidiary. The nervous layer is 
 that which is directly connected with vision. By pro- 
 per management of the following experiment, the blood- 
 vessels of the vascular layer may be seen by the eye, or 
 rather nervous layer, to which they belong. Having 
 closed the left eye with the left hand, take a candle 
 in the right hand, and hold it about two or three inches 
 from the right temple, at the same time keeping the 
 eye of that side steadily looking forwards ; then move 
 the candle slowly upwards and downwards. In the course 
 of three or four movements the blood-vessels of the vas- 
 cular layer of the retina will come into view greatly en- 
 
POINT OF DISTINCT VISION. 3/5 
 
 larged, and presenting a beautiful example of vascular 
 distribution. 
 
 The optic nerve, on reaching the sclerotic coat, is con- 
 tracted ; it then penetrates that investment and the cho- 
 roid, and enters the interior of the eye, not in the centre 
 of the sphere, but about two lines from that centre, on 
 the side next the nose, a little below the transverse axis. 
 In the centre of this point an artery enters, which is pro- 
 bably the cause of the insensibility to the impression of 
 light at that spot, as may be shewn by the following ex- 
 periment. Place on a wall three pieces of paper, on a 
 horizontal line, parallel with the eyes, and about two feet 
 apart ; the middle piece may be placed half an inch below 
 the two lateral. Stand opposite the middle paper, three 
 feet from the wall, close the left eye, and fix the right on 
 the paper on the left, the three papers at this distance 
 will be seen. Now, retire slowly backwards, and at the 
 distance of eight or ten feet the middle paper will disap- 
 pear, as if suddenly removed, and the space it occupied 
 will seem of the same colour as the rest of the wall. On 
 retiring still further back, it will again come into view. 
 In this instance the rays of light from the middle paper, 
 at the distance where it vanishes, will be found to fall 
 exactly upon the centre of the optic nerve, where it en- 
 ters, that is, where the central artery of the retina is 
 placed. 
 
 Directly opposite the pupil, or in the exact axis of the 
 eye, may be observed a yellowish spot, with a small hole 
 in its centre ; by the removal of Jacob's membrane this 
 spot is more easily detected. It is by no means general 
 in the animal kingdom, having been as yet detected only 
 in man, apes, and a few reptiles : its use is altogether 
 unknown ; for though it exactly corresponds to the point 
 of the retina where the most distinct vision takes place, 
 still in those animals which enjoy sight even more per- 
 fectly than man does, it cannot be detected. 
 
 When we look upon an extensive landscape, a corres- 
 
376 INDIRECT VISION. 
 
 ponding picture is depicted on the retina, and the mind 
 receives a general impression of the scene. If any object 
 attracts particular attention, the eyes are especially direct- 
 ed to it, and the rays coming from that object now im- 
 pinge against the centre of the retina, on the point of 
 distinct vision, and a more clear and vivid perception is 
 obtained, constituting distinct or direct vision. 
 
 The rays falling upon the rest of the retina, although 
 they do not impart distinct vision, still make a suffi- 
 cient impression to communicate a general conception 
 of the relative situation, appearance and distance of ob- 
 jects, and the rapidity with which the eye moves from 
 one point to another of the landscape readily compensates 
 for any inconvenience which might arise from this source. 
 Sir David Brewster has the following remarks upon in- 
 direct vision, which are interesting : He says, " In mak- 
 ing some experiments on the indistinctness of vision at a 
 distance from the axis of the eye, I was led to observe a 
 very remarkable peculiarity of oblique vision. If we shut 
 one eye, and direct the other to any fixed point, such as 
 the head of a pin, we shall see indistinctly all other ob- 
 jects within the sphere of vision. Let one of these ob- 
 jects thus seen indistinctly be a stripe of white paper, or 
 a pen, lying upon a green cloth. Then after a short time 
 the stripe of paper, or the pen, will disappear altogether, 
 as if it were entirely removed; the impression of the 
 green cloth upon the surrounding parts of the eye ex- 
 tending itself over the part of the retina which the image 
 of the pen occupied. In a short time the vanished image 
 will re-appear, and again vanish. When both eyes are 
 open, the very same effect takes place, but not so readily 
 as with one eye. If the object seen indistinctly is a 
 black stripe on a white ground, it will vanish in a simi- 
 lar manner. When the object seen obliquely is luminous, 
 such as a candle, it will never vanish entirely, unless its 
 light is much weakened, by being placed at a great dis- 
 tance ; but it swells and contracts, and is encircled with a 
 
INDIRECT VISION. 377 
 
 nebulous halo, so that the luminous impressions must ex- 
 tend themselves to adjacent parts in the retina which are 
 not influenced by the light itself." 
 
 Indirect vision would thus appear not only to be less dis- 
 tinct than direct vision, but also to be incapable of sustain- 
 ing a continued impression, the sensation it communicates 
 being intermittent. Though thus inferior in vivacity and 
 permanence, astronomers have observed the curious fact, 
 that very small stars, invisible to direct, may be seen by 
 indirect vision. " In this way," say Messrs Herschel 
 and Louth, " a faint star in the neighbourhood of a large 
 one will often become very conspicuous, so as to bear a 
 certain illumination, which will yet totally disappear, as 
 if suddenly blotted out, when the eye is turned full upon 
 it, and so on, appearing and disappearing alternately as 
 often as you please." The intermittent impression re- 
 ceived by indirect vision appears to arise from the retina 
 beyond the axis alternately becoming sensible and insen- 
 sible to the rays of light falling upon it. If this be the 
 reason, it is very remarkable how soon, after a little re- 
 pose, it regains its sensibility. That it is so, how- 
 ever, appears from the circumstance, that when the ex- 
 periment is continued for some time, the periods of in- 
 sensibility are prolonged, and that at the moment when 
 it begins to be insensible the retina is instantly restored 
 to its susceptibility by a momentary closure of the eye- 
 lids. 
 
 In obscure light even direct vision becomes intermit- 
 tent, as may be found by attempting to read small print 
 or written characters by moonshine, or in twilight. If 
 we fix an eye on objects we experience the necessity 
 for a painful effort to enable us to distinguish them, 
 and after all they appear and disappear, from the faint 
 light with which they are illuminated not being suffi- 
 cient to produce an image strong enough to effect a con- 
 tinuous impression on the retina. 
 
 Sir David Brewster justly remarks, " These affections 
 
378 PHOSPHORESCENCE OF THE EYE. 
 
 are no doubt the source of many optical deceptions which 
 have been ascribed to a supernatural origin. In a dark 
 night, when objects are feebly illuminated, their disap- 
 pearance and re-appearance must seem very extraordinary 
 to a person whose fear or curiosity calls forth all his 
 powers of observation." The impression of light upon 
 the retina is not removed the instant the light is with- 
 drawn, but remains for sometime impressed. It has been 
 ascertained that the light of a live coal moving at the 
 distance of 165 feet maintains its impression on the retina 
 during the seventh part of a second. If, therefore, we 
 whirl a burning stick round in a circle seven times in a 
 minute or less, it will appear a continuous circle of fire. 
 In the same way meteors, such as falling stars, form a 
 line of light, and the electric spark darting across a dark 
 thundercloud, appears as a continuous flash of lightning. 
 For the same reason, when our eyes are fixed on objects, 
 as in reading, we never lose sight of them, notwith- 
 standing every now and then the upper eyelid moves 
 ovei the anterior surface of the eye, to diffuse over it the 
 tears ; but so quickly is this effected, that both the de- 
 pression and elevation which constitute the twinkling of 
 the eyelid are completed in at most the seventh part of 
 a second, and consequently no interruption takes place. 
 
 In his interesting work on Natural Magic, Sir David 
 Brew^ster states, " Another class of ocular deceptions have 
 their origin in a property of the eye which has been very 
 imperfectly examined. The fine nervous fabric which 
 constitutes the retina, and which extends to the brain, 
 has the singular property of being phosphorescent by pres- 
 sure. When we press the eyeball outwards by applying 
 the point of the finger between it and the nose, a circle 
 of light will be seen, which Sir Isaac Newton describes 
 as ' a circle of colours like those of a feather of a pea- 
 cock's tail.' If the eye and the finger remain quiet, 
 these colours vanish in a second of time; but if the 
 finger be moved with a quivering motion, they appear 
 
PHOSPHORESCENCE OF THE EYE. 379 
 
 again." After further statements Sir David Brew- 
 ster continues " We are led, therefore, to the important 
 conclusions, that when the retina is compressed in total 
 darkness, it gives out light ; that when it is compressed 
 when exposed to light, its sensibility to light is increas- 
 ed, and that when it is dilated under exposure to light, 
 it becomes absolutely blind, or insensible to all luminous 
 impressions. 
 
 " When the body is in a state of perfect health, this 
 phosphorescence of the eye shews itself on many occasions. 
 When the eye or the head receives a sudden blow, a bright 
 flash of light shoots from the eyeball. In the act of 
 sneezing, gleams of light are emitted from each eye, both 
 during the inhalation of the air, and during its subsequent 
 protrusion; and in blowing air violently through the nos- 
 trils, two particles of light appear above the axis of the 
 eye, and in front of it, while other two luminous spots 
 unite into one, and appear as it were about the point of the 
 nose, when the eyes are directed to it." He again says 
 " la a state of indisposition the phosphorescence of the 
 retina appears in new and more alarming forms. When 
 the stomach is under a temporary derangement, accom- 
 panied with headache, the pressure of the blood-vessels on 
 the retina shews itself in total darkness, by a faint blue 
 light floating before the eye, varying in its shape, and 
 passing away at one side. This blue light increases in 
 intensity, becomes green and then yellow^ and sometimes 
 rises to red, all these colours being frequently seen at 
 once, or the mass of light shades off into darkness. When 
 we consider the variety of distinct forms which, in a state 
 of perfect health, the imagination can conjure up when 
 looking into a burning fire, or upon an irregularly shaded 
 surface, it is easy to conceive how the masses of coloured 
 light which float before the eye may be moulded by the 
 same power into those fantastic and natural shapes which 
 so often haunt the couch of the invalid, even when the 
 mind retains its energy, and is conscious of the illusion 
 
380 REFRACTION OF LIGHT. 
 
 under which it labours. In other cases, temporary blind- 
 ness is produced by the pressure upon the optic nerve, or 
 upon the retina, under the excitation of fever or delirium. 
 When the physical cause which produces the spectral 
 forms is at its height, there is superadded a powerful in- 
 fluence of the mind, which imparts a new character to the 
 phantasms of the senses." 
 
 Now in all this Sir David Brewster considers light to 
 be absolutely present, and that the eye is a source of 
 light. A more correct view, however, is derived from 
 the fact, that a nerve of specific sense like the optic, can 
 convey to the mind no other impression, when irritated, 
 than such as corresponds with its individual function. 
 Thus the olfactory or auditory nerves can respectively, 
 when irritated, from whatever cause the irritation arises, 
 merely convey the impressions of smell or audition. So, 
 likewise, with the retina and optic nerve : when excited 
 in any way whatever, as from a blow, from pressure, or 
 from being transfixed by the instrument of the surgeon, 
 pain is not communicated by it, but an impression in ac- 
 cordance with the only sensation it is calculated to trans- 
 mit, and a flash of light is, as it were, perceived of greater 
 or less intensity according to the energy of the exciting 
 cause. 
 
 Before adverting to other considerations with respect 
 to the action of this admirable organ, it will be necessary, 
 as far as our limits will permit, to direct our attention to 
 some of the properties of light, that we may be better 
 enabled to comprehend the exceeding beauty and excel- 
 lent adaptation of the organization. 
 
 Refraction of Light. When rays of light pass through 
 the same medium, they keep in perfectly straight lines; but 
 when they pass from one medium to another, they change 
 their direction, that is, their straight course is broken or re- 
 fracted. It is a general rule that rays passing from a dense 
 into a rare medium incline from the perpendicular, as from 
 water into air, and conversely when they pass from a rare 
 
REFRACTION OF LIGHT. 381 
 
 to a dense medium, they are bent towards the perpendicu- 
 lar, as from air into water. This may be illustrated by 
 taking an object such as a shilling, and fixing it at the 
 bottom of an empty basin, then retiring backwards until 
 & the brim of the basin hides it ; 
 now let water be poured into 
 the vessel, and the coin will 
 again come into light. Thus, 
 in Fig. 27, let a be the shil- 
 ling at the bottom of the 
 basin, and c the eye. While 
 the vessel is empty, the eye 
 cannot receive a ray nearer the 
 
 coin than d, but when water is poured in, the light from 
 the shilling proceeding through the water in the direction 
 a b, when it reaches the surface and passes into the air, 
 its direction is changed, and inclines from the perpendicu- 
 lar in the path b c. In this line it reaches the eye, and 
 the coin becomes visible. When the rays of light fall 
 perpendicularly on a surface, they suffer no refraction, but 
 continue in the same direct line. 
 
 When the rays passing through such a medium as the 
 air, fall upon a lens of greater refractive power than the 
 air, they are refracted towards the perpendicular, or con- 
 centrated into a smaller cone ; and the degree of concen- 
 tration is in proportion' to the convexity of the lens, so 
 that a lens of greater convexity will effect a greater con- 
 centration than one whose convexity is less. Rays from 
 a level surface, falling upon a sphere, reach it at differ- 
 ent angles, in consequence of the different distances of 
 the several radiating points from the several parts of the 
 sphere on which they are directed, and therefore (if the 
 refractive power of the sphere throughout be the same) 
 some of the rays will undergo a greater refraction than 
 others, according to their angle of incidence, and the 
 focus of all will not be the same. This is termed sphe- 
 rical aberration. 
 
382 REFRACTION OP LIGHT. 
 
 Now, a ray of light, in passing from the air in order to 
 reach the retina, has to traverse four transparent media 
 of different densities, of different sphericities, and of dif- 
 ferent refractive powers, viz. the cornea, the aqueous hu- 
 mour, the crystalline lens, and the vitreous humour. 
 According to Sir D. Brewster (Natural Philosophy), 
 the following are the refractive powers of the humours 
 of the eye : 
 
 Crystalline Lens. 
 
 Aqueous , * > Vitreous. 
 
 Humour. Surface. Centre. Mean. Humour. 
 
 1.336. 1.3767. 1.3990. 1.3839. 1.3394. 
 
 According to the same philosopher, the refractive power 
 of atmospheric air is 1.000294, and of water 1.336. 
 
 If we take a double convex lens, such as a common 
 magnifier, and hold it opposite a window in a room, and 
 place a sheet of paper behind it, at a proper distance, we 
 shall see depicted on the paper a perfect image of the 
 window diminished according to the convexity of the 
 glass. The greater the convexity, the image is so much * 
 the more diminished, and the closer must the glass 
 be held to the paper ; according to the distance also at 
 which the window is placed will be the size of the image. 
 We shall likewise perceive that the relative position of 
 the parts of the window are exactly inverted, the upper 
 sash being the lowest in the image, and the right side on 
 the left. Moreover, we shall find that when the glass is so 
 held as to make the central bars sharply defined, those at 
 the margin appear obscure, and conversely when the side 
 bars are brought out distinctly ; these differences being 
 occasioned by the different degrees of refraction that the 
 rays suffer at the centre and margin of the lens, produ- 
 cing spherical aberration. Upon these properties of the 
 lens depend the powers of optical instruments, such as 
 the telescope and microscope, which have contributed so 
 much to extend the sphere of human knowledge the 
 
FORMATION OF THE IMAGE. 383 
 
 one bringing within our reach stars and clusters of stars 
 placed at such vast distances that without its aid we 
 must for ever have remained ignorant of them, and the 
 other declaring to us objects so minute as altogether to 
 elude the naked eye. The camera obscura in its most 
 simple form is nothing more than a lens fixed in a hole 
 of a window-shutter, and all light excluded from the 
 room, excepting what is admitted through the lens. 
 
 On similar principles, though more complicated, yet 
 with the most perfect adjustment, is the eye constructed. 
 As in the camera obscura, the rays from the different ob- 
 jects within the sphere of vision are collected and con- 
 centrated, so as to be depicted on the retina in an image 
 of the utmost accuracy. Those rays which in passing 
 through the cornea and aqueous humour become subject 
 to the greatest degree of refraction, fall on those parts of 
 the lens which possess the least refractive power, and 
 conversely, so that spherical aberration is thus obviated. 
 x^^v The image on the 
 
 d /I A == ===; ^\ retina is reversed from 
 
 ^(Iz^^^^j^^^^^^^^^^l above to below, and 
 
 v^^x/ c from right to left. In 
 
 FIG. 28. Fig 28, the rays from 
 
 the arrow a c proceed in the directions a b and c d, and 
 produce on the retina the inverted image b d. That this 
 occurs in the eye may easily be seen by procuring the 
 fresh eye of a bullock, and shaving off with a sharp 
 knife the back part of the sclerotic coat till it becomes 
 translucent, when an inverted image will be seen on 
 the retina ; or a small portion of the coats of the eye 
 may be removed entirely in the axis of vision, and the 
 space covered with a piece of transparent oiled silk, 
 which will afford for a short time a most perfect, though 
 minute, camera obscura. 
 
 A great many theories have been started in order to 
 account for our being able to see objects in their proper 
 position., although their image must be inverted upon the 
 
384 SHORT-SIGHTEDNESS. 
 
 retina. All these theories attempt to explain the fact on 
 physical principles, which have perhaps little or nothing 
 to do with the matter. It is not the retina which per- 
 ceives or sees, but the mind. The eye is merely the in- 
 strument, and, without the mind to use it, would be as 
 inoperative and useless as the microscope is to an irrational 
 creature. 
 
 To examine the comparative . merits of the different 
 opinions which have been entertained appears superfluous, 
 although many of them proceed from interesting facts 
 connected with the organs of sight, and tend to elucidate 
 the perfection of the mechanism. With respect to 
 the action of mind on matter, and matter on mind, there 
 exists a barrier which man in his present state seems 
 never to be destined to pass, and even the very attempt 
 to do so appears worse than useless. 
 
 There are two states of the eye depending on the con- 
 dition of its refractive apparatus, that the laws of refrac- 
 tion satisfactorily explain. In the one, the refractive 
 power is too great, producing short-sightedness ; in the 
 other it is deficient, causing long-sightedness. 
 
 Short-sightedness arises from the rays of light being 
 brought to a focus before they reach the retina, and con- 
 sequently producing an 
 indistinct picture on the 
 retina, as seen in Fig. 
 29. Those who labour 
 under this defect re- 
 Fig. 29. quire to bring an object 
 close to the eye, in order to see it distinctly. They also 
 corrugate the eyebrows, and diminish the aperture between 
 the eyelids, so as to exclude as much as possible the more 
 oblique rays. Short-sightedness occurs most frequently in 
 early life, and may even be acquired by habit. Some em- 
 ployments tend to induce it, as the art of the engraver, and 
 that of the watchmaker. Wearing convex glasses is capable 
 of producing it. As it formed an adequate ground for ex- 
 
LONG-SIGHTEDNESS. 385 
 
 emption for persons who fell in the conscription list under 
 Napoleon, young lads took to the constant wearing of very 
 convex glasses, for the purpose of artificially inducing it 
 a practice by which they not unfrequently succeeded 
 in their object. The inconveniences arising from short- 
 sightedness are obviated by using doubly concave glasses, 
 thereby producing that degree of divergence in the rays 
 coming from distant objects which compensates for the 
 too great refractive power of the eye. 
 
 This defect of the eye may arise from several causes : 
 from too great a convexity either of the cornea or of the 
 lens from too great density of the humours, especially 
 the crystalline and from the space between the lens and 
 the retina being too short. Where it depends on too 
 much convexity, as age approaches it may disappear ; 
 but where too great density is the cause, age is apt rather 
 to aggravate than relieve it. For while in the young 
 the convexity both of the cornea and the lens is greater 
 than in advanced life, the less density of the humours 
 counterbalances it : and again, as life advances, the more 
 scanty supply of humours, along with the diminishing 
 convexity, are neutralized by the increasing density; there- 
 fore, if these keep pace with each other, the eye remains 
 till a very protracted period of life without the necessity 
 for artificial assistance. 
 
 Long-sightedness depends on the opposite causes which 
 produce the former condition, in consequence of which the 
 
 rays are not brought 
 to a focus sufficient- 
 ly soon, and the 
 image would fall 
 beyond the retina, 
 FIG. so. as in Fig. 30. .It 
 
 is obviated by the use of doubly convex glasses, adapted 
 to the extent of the deficiency. It generally appears 
 about middle age, and first displays itself by a difficulty 
 in making out small print, or of following the next line 
 
386 LONG-SIGHTEDNESS. 
 
 in the order of succession, especially in candle light. A 
 person labouring under this defect looks as if beholding ob- 
 jects at a distance, elevates the eyebrows, and opens widely 
 the eyelids. To effect this change, where it depends on 
 an alteration of the lens, it sometimes requires several 
 months before the change is uniformly completed. Sir D. 
 Brewster very justly observes, " If the human eye is not 
 managed with peculiar care at this period, the change in 
 the condition of the lens often runs into cataract, or ter- 
 minates in a derangement of fibres, which, though not 
 indicated by opacity, occasions imperfections of vision that 
 are often mistaken for amaurosis and other diseases. A 
 skilful oculist, who thoroughly understands the structure 
 of the eye, and all its optical functions, would have no 
 difficulty, by nice experiments, in detecting the very por- 
 tion of the lens where this change has taken place in 
 determining the nature and the magnitude of the change 
 which is going on in applying the proper remedies for 
 stopping its progress and in ascertaining whether it has 
 advanced to such a state that aid can be obtained from 
 convex or concave lenses. In such cases lenses are often 
 resorted to before the crystalline lens has suffered an uni- 
 form change of figure or of density, and the use of them 
 cannot fail to aggravate the very evils which they are in- 
 tended to remedy. In diseases of the lens, where the 
 separation of fibres is confined to small spots, and is yet 
 of such magnitude as to give separate coloured images of 
 a luminous object, or irregular halos of light, it is often 
 necessary to limit the aperture of the spectacles, so as to 
 allow the vision to be performed by the good part of the 
 crystalline lens." 
 
 In the above remarks on refraction, light has been re- 
 garded as a simple substance, and at first scarcely any- 
 thing, one should suppose, could be more simple in its 
 constitution than the light of the sunbeam. This, how- 
 ever, is not the case, for it has been satisfactorily shewn 
 that the pure w T hite light of the sun is in reality composed 
 
DECOMPOSITION OF WHITE LIGHT. 
 
 387 
 
 of rays possessed of different colours, each of which differs 
 in its refrangibility. 
 
 To the illustrious Sir Isaac Newton we are indebted for 
 the discovery of the compound nature of light. This he 
 effected in the following manner : In a darkened room, 
 having admitted through a small hole, H, in the window- 
 shutter, E F, a beam of sun light, S, he interposed a glass 
 prism, A B C, as in Fig. 31, through which the light was 
 
 XVhite 
 
 FIG. 31. 
 
 transmitted, when, instead of continuing in the straight 
 dotted line, S P, as white light, in passing through the 
 prism its direction was changed at g, and received on 
 the screen M N, producing the spectrum K O L, com- 
 posed of seven different colours, namely, red, orange, 
 yellow, green, Hue, indigo, and violet. The red, it will 
 be seen by examination of the figure, is that which de- 
 viates least from the original direction of the sunbeam, or 
 it is the least refrangible, while the violet is situated at 
 the opposite extremity, having been subjected to the great- 
 est degree of refraction, the others being intermediate in 
 various degrees. The image received on the screen is 
 termed the solar or prismatic spectrum., and the tints the 
 prismatic or primary colours, and their mixtures or com- 
 binations secondary. 
 
388 DECOMPOSITION OF WHITE LIGHT. 
 
 Light is likewise decomposed by transmission through 
 coloured media, during which some of the colours are re- 
 tained or absorbed, and others transmitted. When white 
 light is transmitted through blue glass, for example, the 
 glass absorbs the other colours, and transmits the blue, 
 and the recombination of the absorbed and transmitted 
 light would again form white light ; they are therefore 
 complements of each other, and hence called complemen- 
 tary. As they harmonize with one another in painting, 
 and produce a pleasing effect in relation to each other, they 
 are likewise termed harmonic. When a substance absorbs 
 all the rays, black is produced, and when it reflects or 
 transmits the whole, white light retains its integrity. 
 
 The different colours occupy different spaces on the 
 spectrum. They are not bounded by well defined lines, 
 but slide gradually into each other. From the most ac- 
 curate estimates Sir Isaac Newton could form of the ex- 
 tent of the respective spaces they occupy, he arrived at 
 the following results : Supposing the colours are arranged 
 9 in a circle, as in Fig. 32, of 
 
 the 360 degrees into which 
 Gxeen. the circle may be divided, red 
 
 ^x\"" ^""x W 'H occupy 45, orange 27, 
 
 yellow 48, green 60, blue 60, 
 indigo 40, and violet, 80. 
 
 The composition of light 
 , may be proved by synthesis 
 $ or combination, as well as by- 
 analysis or decomposition. If 
 we paint upon a circular board, 
 Fig. 32, the different colours, 
 as seen in the spectrum, then, 
 if the board be whirled quickly 
 
 round on its centre, the colours will be blended together 
 so as to appear nearly white ; and if the paints were of 
 sufficient purity and lustre, they would appear perfectly 
 white. 
 
ACCIDENTAL COLOURS. 389 
 
 When the eye has been for some time strongly im- 
 pressed with any particular colour, and then directed to 
 a sheet of white paper, the paper does not appear white, 
 nor of the colour impressed, but of a different colour, 
 varying according to that which had been impressed. 
 Thus, if we place a red wafer on a 'sheet of white paper, 
 and keep one eye for some time steadily fixed on a mark 
 in its centre, after some time, if the wafer be struck off, 
 and the eye kept fixed on the space it occupied, an image 
 of the same form as the wafer will remain, but of a blu- 
 ish green, or the same image will appear by moving the 
 eye from the wafer, after it has become sufficiently im- 
 pressed, to some other part of the white paper. The co- 
 lour which replaces that of the wafer is termed the acci- 
 dental, and is identical with the complementary. In 
 making the experiment, if the wafer is white, and placed 
 on a dark ground, the accidental colour will be black, or 
 if black on a white ground, and the wafer removed, the 
 spot it occupied appears whiter than the rest. The ac- 
 cidental colour is likewise called opposite, because, when 
 the prismatic spectrum is arranged in a circle, as in Fig. 32, 
 the primary and accidental colours are directly opposite 
 to each other, as in the following table : 
 
 Colour of Wafer. Accidental Colour, or of the Spectrum. 
 
 Red Bluish Green. 
 
 Orange Blue. 
 
 Yellow Indigo. 
 
 Green Violet Reddish. 
 
 Blue Orange Red. 
 
 Indigo Orange Yellow. 
 
 Violet Yellow Green. 
 
 Black White. 
 
 White Black. 
 
 The explanation which accidental colours admit of is 
 sufficiently simple : When the eye has, for example, been 
 
390 ACROMATIC INSTRUMENTS. 
 
 for a sufficient time impressed with the rays from the red 
 wafer, the spot on the retina upon which they fall be- 
 comes insensible to red light, and therefore, when the eye 
 is turned upon the white paper, the red rays of the white 
 light make no impression, being as it were blotted out 
 or withdrawn, leaving the other rays which make up the 
 complementary colour, or bluish green. And in the case 
 where a black wafer is placed on a white ground, a cor- 
 responding spot on the retina is protected from the white 
 light to which the surrounding parts of the nervous web 
 are exposed ; its sensibility is therefore increased, and 
 when the black wafer, acting as it were like a screen, is 
 withdrawn, its greater sensibility is displayed, and a 
 spot whiter than the rest of the field, of the same form as 
 the wafer, appears. Again, where a white wafer is used 
 on a black ground, on turning the eye on a sheet of white 
 paper, a black spectrum appears, partly from the increased 
 sensibility of the greater portion of the retina, and the 
 diminished sensibility of the part impressed with the 
 white light. 
 
 When white light undergoes refraction, it at the same 
 time suffers decomposition. In optical instruments of 
 great power, this produces confusion and indistinctness in 
 the image, an imperfection obviated by an ingenious 
 combination of substances possessed of different degrees 
 of refractive power, so that the combined result is a colour- 
 less spectrum. Instruments constructed on these princi- 
 ples are termed acromatic. 
 
 Although the different refractive powers of the humours 
 of the eye, and especially the different density of the lens 
 at its centre and circumference compensate for spherical 
 aberration, it does not appear to be constructed so as to 
 act as an acromatic instrument, for if a card be so placed 
 before the eye as to exclude the light from entering the 
 pupil, excepting at a small segment at its margin, a pris- 
 matic spectrum will be distinctly visible, which would not 
 have happened had it possessed the power of acromatic 
 
ESTIMATION OF SIZE AND DISTANCE. 391 
 
 adjustment. But such power has been shewn to be un- 
 necessary, for by calculation it appears that the deviation 
 of the different coloured rays in the eye is too small to pro- 
 duce indistinctness of vision. 
 
 Many curious instances have been recorded in which 
 individuals were totally insensible to certain prismatic 
 colours, although, in other respects, their eyes were capa- 
 ble of performing in a perfect manner the other functions 
 of vision. Some could only appreciate blue and yellow. 
 One was incapable of distinguishing the ripe Siberian 
 crab-apple, and another ripe cherries, from the leaves, ex- 
 cept by form and size. In one instance, a naval officer 
 purchased a blue uniform coat and waistcoat, with red 
 breeches to match the blue ; in another, a tailor patched 
 the elbow of a blue coat with a piece of crimson cloth, 
 considering them a proper match ; and in several such 
 instances the defect has been found to run in families. 
 
 Estimation of Magnitude and Distance. When treat- 
 ing of the motions of the eye, we shewed, that in order to 
 have single vision with two eyes, it is necessary that both 
 the eyes should converge to a greater or less extent, ac- 
 cording to the distance, so that the rays of light coming 
 from the same points of an object may fall on the point 
 of distinct vision in the centre of the retina of both. To 
 effect this, a voluntary muscular effort is required to pro- 
 duce the requisite degree of convergence of the axes of 
 the two eyes, a great degree being necessary for objects 
 placed close to the eye, and a small degree for those at a 
 distance. In consequence of this voluntary effort, an idea 
 is obtained of the relative situation and distance of objects. 
 
 Besides convergence of the axes, we are able to ascer- 
 tain the size and distance of an object by other means, 
 such as the visual angle, the intensity of light, shade, and 
 colour, and by contrasting it with known objects. 
 
 The visual angle is that formed by the rays proceeding 
 from the extremities of an object, and crossing the lens 
 previous to being depicted on the retina, so that the 
 
392 ESTIMATION OF SIZE AND DISTANCE. 
 
 visual angle subtended by the object a 5, Fig. 33, is equal to 
 that subtended by its image c d on the retina. It is evi- 
 dent that if all objects were at equal distances from the 
 eye, and of the same magnitude, they would subtend on 
 
 Fro. 33. 
 
 the retina at the same visual angle, and if not of the 
 same magnitude, the difference would be accurately indi- 
 cated by the difference of the angle subtended by them ; 
 thus the comparative size of the two crosses a b and c b, 
 is represented by their images on the retina, e d and ef. 
 But the cross g h, which is twice the size of c 6, subtends 
 at the same visual angle, and is represented on the retina 
 of the same size as ef. We thus perceive that the visual 
 angle does not give us a correct idea of the relative 
 magnitudes of bodies, unless at the same time we are ac- 
 quainted with their respective distances from the eye ; and 
 conversely, we cannot judge accurately of their distances 
 without being aware of their magnitudes. A man on 
 horseback, when near, is subtended at a certain visual angle, 
 which lessens with the increase of the distance, yet we 
 find no difficulty in accurately estimating the size from our 
 knowledge by previous experience ; but when objects are 
 at a great distance, when we have not the means of compar- 
 ing them with nearer objects, we are constantly liable to 
 fallacy, believing them to be much smaller than they really 
 are, as is the case for example with the heavenly bodies. 
 Thus, a sixpenny piece, held at some distance from the eye, 
 will shut out the sun, whose diameter is 888,000 miles. 
 The sun and moon, subtending at nearly the same visual 
 angle, appear to us of the same size, although we are 
 aware of the mathematical accuracy with which it has 
 
ESTIMATION OF SIZE AND DISTANCE. 
 
 393 
 
 been determined that the former is distant 96,000,000 of 
 miles, and the latter only 240,000. For the same reason, 
 when looking along a street or along an avenue of trees, 
 the houses or trees that are nearest to us on the foreground 
 appear largest, and the rest gradually diminish, according 
 to the distance, so that if we could imagine a line drawn 
 along the tops and bottoms of the objects, they would 
 appear to meet at a point, as in Fig. 34. 
 
 FIG. 34. 
 
 Objects of every figure, excepting that of a sphere, 
 vary in form according to the aspect in which they are pre- 
 sented to the eye. When an oval body, for example, is 
 situated so as to present one of its ends, its smallest dia- 
 meter only is seen, and it appears spherical ; but when so 
 placed as to present a greater diameter, the image is oval 
 or elliptical. If we take a rod, and hold it obliquely, its 
 length will appear more or less shortened according to the 
 angle at which it is held ; for the same reason the slope 
 of a rising ground would appear much greater if placed 
 perpendicularly. The appearance arising from the obli- 
 quity of position of an object is termed foreshortening ; 
 and the art which treats of the apparent size of an object, 
 according to the distance, and of foreshortening according 
 to position, is termed perspective an art of the utmost 
 importance in painting. The intensity of light and shade 
 in which an object is seen diminishes according to the 
 
 s2 
 
394 ESTIMATION OF SIZE AND DISTANCE. 
 
 square of the distance, being only one-fourth as powerful 
 at twice the distance, one-sixteenth at four times, and 
 so on, as indicated by the squares seen in the front of the 
 houses and trees seen in Fig. 34. By this law, we are 
 enabled to judge of the distance of bodies with considerable 
 accuracy. Notwithstanding, numerous optical illusions 
 spring from this source. Thus, distant hills appear nearer 
 in bright sunshine than in a cloudy day, their outlines 
 being more sharply defined. The sky appears less dis- 
 tant directly over the head than nearer the horizon, be- 
 cause the rays of light have to pass through a less quan- 
 tity of atmosphere, and for the same reason partly the 
 sun and moon appear larger in rising and setting than 
 when high in the zenith. 
 
 When we look at the revolving light of a light-house 
 it appears to approach as the intensity of the light in- 
 creases, and again to recede as it becomes dim. In 
 the same way a lamp in the street brighter than the 
 rest appears nearer. The old city of Edinburgh, viewed 
 from Prince's Street, in a dark evening, when the win- 
 dows and lamps are lighted up, presents a very remark- 
 able example of optical illusion, which even those long 
 familiar with the scene cannot altogether divest them- 
 selves of, and never fails to make on the mind of a stranger 
 a strong impression of romantic grandeur. The tall houses 
 rise one above another on the high precipitous ridge, of 
 every form and architecture used for these last two hundred 
 years, with windows of every variety of shape and size ; 
 those belonging to the more wealthy shops of the High 
 Street, being better lighted, appear nearer than the more 
 humble establishments at the base of the precipice, that 
 are closer to the spectator. The illusion is so complete 
 that it is impossible, as far as seeing can inform us, to 
 believe otherwise than that we are looking on a range 
 of fantastic buildings between thirty and forty storeys in 
 height. 
 
 The shade afforded by objects is in proportion to the 
 
ESTIMATION OF SIZE AND DISTANCE. 395 
 
 intensity of light. The shadow of the body in sunshine 
 is more strongly defined than by moonlight. In like 
 manner, it becomes less intense according to the distance, 
 until at length the shadows are so blended together that 
 the range of mountain and plain presents one uniform 
 undefined outline. 
 
 Without the alternation of light and shade, the only 
 means of distinguishing bodies would be by the difference 
 of colour. Unless from the prominences and depressions 
 brought out by light and shade, the landscape would pre- 
 sent one uniform unvaried aspect. The principles, there- 
 fore, which regulate light and shade are of the greatest 
 importance to the painter. By proper attention to them, 
 and a judicious combination with the laws of perspective, 
 he is enabled to produce the most perfect optical illusion, 
 representing, on a flat surface of canvas, an extensive scene 
 of mountain and plain, of woodland and lake, near and 
 distant objects, according to the impression he desires to 
 convey; the outline of objects on the foreground being 
 bold and sharply defined, while they are made gradually 
 to fade away in the distance. 
 
 The relative proportion which unknown objects bear 
 to those whose magnitude we are aware of from previous 
 experience, enable us to judge of their size and distance. 
 It is for want of subjects wherewith to institute compari- 
 sons that difficulty is experienced in estimating the ex- 
 tent of an unvaried plain, or the exact distance of objects 
 at sea, a difficulty which every landsman especially ex- 
 periences at sea when he endeavours to estimate the dis~ 
 tance of vessels, or that of the shore ; and consequently 
 he commits the greatest errors, according to the height of 
 the land, the degree of atmospheric clearness, and so 
 forth. Partly from the same cause the sun and moon 
 appear larger when nearer the earth. The intervention 
 of known objects, such as a tower, a city, or a mountain, 
 cause these heavenly bodies to appear much larger. Ar- 
 nott observes, " The sun and moon, in appearance from 
 
396 ESTIMATION OP SIZE AND DISTANCE. 
 
 the earth, are nearly of the same size, viz. always occu- 
 pying in the field of view about the half of a degree, or 
 as much as is occupied by a circle of a foot in diameter, 
 when held about 250 feet from the eye, which circle, 
 therefore, at that distance, would just hide either of them. 
 Now, when a man sees the rising moon apparently filling 
 up the end of a street, which he knows to be a hundred 
 feet wide, he very naturally believes that she then sub- 
 tends a greater angle than usual, until the reflection oc- 
 cur to him, which it rarely will of itself, that he is using, 
 as a measure of her size, a street known indeed to be a 
 hundred feet wide, but of which the part concerned, ow- 
 ing to the distance, appears to his eye exceedingly small. 
 The width of the street near him may occupy sixty de- 
 grees in his field of view, and he might see from between 
 the houses many broad constellations instead of the moon 
 only ; but the width of the street far off may not occupy, 
 in the same field of view, the twentieth part of a degree ; 
 and the moon, which always occupies half a degree, will 
 then appear comparatively large. The kind of illusion 
 now spoken of is still more remarkable when the moon 
 is seen rising near still larger known objects, for instance, 
 beyond a town, or a hill, which then appear within her 
 luminous circle." 
 
 Tall steeples appear much taller than they really are, 
 from being viewed without any object to compare them 
 with, and this effect is much increased by their being 
 surmounted by a cross or other object, which again, for 
 the same reason, appears much smaller than it actually is, 
 and thus tends still further to magnify the apparent 
 height of the steeple. The cross at the top of the dome 
 of St. Paul's is thirty feet from the ball to the summit, 
 yet, when viewed from the street, it does not appear to 
 be more than one-sixth of that height ; on this account, 
 too, statues placed on tall pillars require to be of colossal 
 size. In fact, the effect produced by architectural struc- 
 tures, like painting, in a great measure depends on opti- 
 
ESTIMATION OF SIZE AND DISTANCE. 397 
 
 cal illusion. From the principles of foreshortening like- 
 wise, objects seen from great heights, especially from high 
 precipices, appear much diminished. This effect is very 
 strikingly displayed in the Shetland island of Foula, the 
 celebrated Thule of the ancients, the favourite resort of 
 innumerable flocks of sea birds. Here there is a preci- 
 pice 1100 or 1200 feet perpendicular, affording to those 
 who have nerve enough to contemplate the scene beneath, 
 a spectacle more stupendous than the wildest fancy could 
 imagine. From this giddy height, the thousands of birds 
 beneath skimming through the air in varied circles, each 
 according to its kind, seem like so many moths and but- 
 terflies, and the green expanse of water beyond, with the 
 heaving and curling waves, appears like another sky 
 studded with fleecy clouds. 
 
 Habit tends in some measure to dissipate these optical 
 illusions, and persons who are accustomed to view objects 
 from different heights, and to compare them with neigh- 
 bouring and interposed known objects, are enabled readily 
 to allow for the effects of foreshortening, and obtain correct 
 notions respecting their magnitude and distance. The 
 tall houses and high precipices of Edinburgh and its vi- 
 cinity, are well fitted for imparting to its inhabitants this 
 kind of knowledge. Still, when a new object is present- 
 ed to the view, of unusual grandeur and magnitude, pre- 
 vious education fails in enabling the mind to obtain a 
 just conception. On this account, it is not till after some 
 time, and repeated observation and reflection, that the 
 stupendous magnificence of such structures as St. Paul's 
 is justly appreciated. I myself had a very forcible in- 
 stance of this on visiting St. Paul's last year for the 
 first time. On a very favourable day in August I as- 
 cended to the ball, and spent some hours in contempla- 
 ting the city from the lantern and outer galleries of the 
 dome. I did not, in the slightest degree, observe any di- 
 minution of the persons and other objects passing on the 
 streets, which so frequently strikes strangers from the 
 
398 ESTIMATION OF SIZE AND DISTANCE. 
 
 same situation. This I attributed to my being in the 
 habit of seeing objects from similar heights in and around 
 Edinburgh, as from the Castle, the Calton Hill, and Sa- 
 lisbury Crags, and therefore accustomed to estimate and 
 allow for the influence of relative situation. 
 
 Upon descending, however, to the whispering gallery, 
 and looking over upon the people walking on the marble 
 floor beneath, I was not a little surprised to notice that 
 their persons were reduced to the most dwarfish dimen- 
 sions. The choir also appeared very much smaller than 
 my recollection and judgment knew it to be, and by no 
 effort on my part could I dissipate the illusion. Inquir- 
 ing of the attendant if the persons beneath appeared to 
 him diminished, he assured me they did not. 
 
 Now this illusion on my part, and not on his, depended 
 upon the conceptions which at the time we respectively 
 entertained of the true relative size of that splendid struc- 
 ture, my untutored mind was incapable of grasping at 
 once its grandeur and real magnitude, and consequently 
 a reduced standard was employed when endeavouring to 
 comprehend it ; and by the same reduced standard, the 
 persons on the floor were examined, and therefore they 
 seemed dwarfish, while custom had habituated the eye, 
 or rather the mind of the attendant, to the estimation of 
 their just relative proportion. 
 
 The painter has recourse to contrast with the greatest 
 advantage. In order to convey an idea of the size and 
 distance of unknown objects, he brings upon the field 
 known objects to serve as a standard of comparison. Con- 
 trast therefore is one of the most efficient means by which 
 we judge of size and distance. 
 
399 
 
 CHAPTER IX. 
 
 HEARING. 
 
 Of the Nature of Sound Grave and Acute Tones Number of Vibrations appre- 
 ciable by the Human Ear Transmission of Sounds Velocity of Sound Ste- 
 thoscope Echo External Ear adapted for collecting Vibrations Middle Ear 
 or Drum constructed for the Transmission and Modification of the Vibrations 
 Different Apparatus of Internal Ear or Labyrinth the immediate seat of the 
 Sense of Hearing Construction and Apparatus of General Inferences deduced 
 from the Examination of the Structure as a whole. 
 
 SOUND has no existence as a distinct substance, but is 
 merely the result of certain conditions of bodies. When 
 a body is struck, its particles are thrown into a state of 
 motion which extends in every direction to a greater or 
 less distance, according to the intensity of the impulse. 
 Thus, if a pebble be cast upon the smooth and tranquil 
 surface of a pool of water, undulating circles are produced ; 
 these radiate from the point struck in every direction of 
 the surface, gradually diminishing, till they imperceptibly 
 subside altogether in the distance. The undulations or 
 oscillations in this instance are not confined to the sur- 
 face of the water, where they are visible, but extend to 
 the whole body of water, in every direction, and likewise 
 to the air in contact with it; consequently the point 
 where the water and pebble come in collision is the cen- 
 tre of a sphere from which the oscillations are commu- 
 nicated to a hemisphere of water in one direction, and to 
 a hemisphere of air in the other. "We may take another 
 example : If an elastic wire be fixed at one end, and the 
 other laid hold of and pulled to one side, when set free, 
 
400 SOUNDS. 
 
 it will move towards the point from whence it was with- 
 drawn, where, however, it will not stop, but proceed be- 
 yond it, and again return to the point where it was let 
 go, and thus it will continue to traverse the space, till 
 at last it comes to rest. During these movements it will 
 communicate to the air in contact with it similar vibra- 
 tions. These motions are similar to the oscillations of a 
 pendulum. They may be performed with such rapidity 
 that the eye cannot follow them, while in the measured 
 movements of the pendulum they are easily noted. 
 
 When the vibrations are slow or few in a given time, 
 the individual impulses may be counted ; but when the 
 motions are performed with rapidity, their individuality 
 is lost, and a continuous sound or tone is produced. When 
 the vibrations of a sonorous body are numerous in a given 
 time, or follow each other in quick succession, the sound 
 is acute or high ; and when fewer during the same pe- 
 riod, a grave or low sound is produced. The highest 
 tones appreciable by the human ear consist of 32,000 
 vibrations in a second, and the lowest 32. 
 
 On this point Dr Wollaston observes, {Phil. Trans. 
 1820), " In the natural healthy state of the human ear, 
 there does not seem to be any strict limit to our power of 
 discerning low sounds. In listening to those pulsatory 
 vibrations of air of which sound consists, if they become 
 less and less frequent, we may doubt at what point tones 
 suited to produce any musical effect terminate ; yet all 
 persons but those whose organs are palpably defective 
 continue sensible of vibratory motion, until it becomes a 
 mere tremor, which may be felt and even almost counted. 
 
 " On the contrary, if we turn our attention to the op- 
 posite extremity of the scale of audible sounds, and with 
 a series of pipes exceeding each other in sharpness, if we 
 examine the effects of them successively upon the ears of 
 any considerable number of persons, we shall find (even 
 within the range of those tones which are produced for 
 their musical effects) a very distinct and striking differ- 
 
SOUNDS. 401 
 
 ence between the powers of different individuals, whose 
 organs of hearing are in other respects perfect, and shall 
 have reason to infer that human hearing in general is 
 more confined than has been supposed with regard to its 
 perception of very acute sounds, and has, probably in 
 every instance, some definite limit, at no great distance 
 beyond the sounds ordinarily heard." 
 
 He states further, " The suddenness of transition from 
 perfect hearing to total want of perception, occasions a 
 degree of surprise, which renders an experiment on this 
 subject, with a series of small pipes, among several per- 
 sons, rather amusing. It is curious io observe the change 
 of feeling manifested by various individuals of the party 
 in succession, as the sounds approach and pas's the limits 
 of their hearing. Those who enjoy a temporary triumph, 
 are often compelled, in their turn, to acknowledge to how 
 short a distance their little superiority extends." 
 
 Dr Wollaston mentions, that a friend of his could im- 
 perfectly hear a note four octaves above the middle E of 
 the pianoforte, and that he could not hear the F next 
 above it, although his hearing in other respects was per- 
 fect, and his perception of musical pitch as correct as that 
 of any other person. He likewise gives instances where 
 the chirp of the grasshopper could not be heard ; and he 
 observes, that " inability to hear the piercing squeak of 
 the bat seems not very rare, as I have met with several 
 instances of persons not aware of such a sound." He 
 also cites the case of a gentleman who could never hear 
 the chirping of a house sparrow. 
 
 The number of vibrations which a string of a musical 
 instrument makes in a given time varies according to its 
 length^ tension, and thickness, consequently, according as 
 these conditions vary, so will the tones produced. If a 
 string vibrates a hundred times in a second, when shor- 
 tened by one-half its length it will vibrate two hundred 
 times, and give out a sound more acute, or higher, by one 
 octave, and so on according to its length. If a string 
 
402 SOUNDS. 
 
 stretched or rendered tense with a force equal to one 
 pound gives out a hundred vibrations, with a tension of 
 four pounds it will vibrate two hundred times, with nine 
 pounds three hundred times, with sixteen pounds four 
 hundred times, and so on, the number of the vibrations 
 being in proportion to the square roots of the forces with 
 which the string is stretched. A string reduced to one- 
 half its thickness, with the same length and tension, will 
 vibrate twice as fast, to one-third three times as fast, and 
 so on according to the quantity of matter put in motion. 
 These principles are fully illustrated by a stringed instru- 
 ment such as the violin or harp. 
 
 The extent of the vibrations, or the distance the elas- 
 tic body deviates from the point of rest, depends upon 
 the force applied. If the force with which it is struck be 
 small, the sound elicited will be weak, and will soon cease ; 
 but when a great force is used, the oscillations are corre- 
 spondently great, and a loud sound is produced, which will 
 be heard from afar, and continue for a great length of time. 
 
 Sound is transmitted or conducted by different bodies 
 with different degrees of velocity. In air it travels at the 
 rate of 1142 feet in a second ; in sulphurous acid gas it 
 moves only at the rate of 751 feet ; while in hydrogen it 
 passes at the velocity of 3000 feet in a second. Through 
 liquids its velocity is greater, moving in water at the rate 
 of 4708 feet in a second, and in solids it is greatly aug- 
 mented, passing through tin at the rate of 8175 feet, and 
 through iron, glass, and some kinds of wood, at the rate 
 of 18,530 feet in a second. 
 
 By these facts we are enabled to understand how, when 
 a gun is fired at a distance over the smooth expanse of a 
 frozen lake, two reports are heard after the flash, first a 
 sharp and loud one, transmitted by the solid ice, and then 
 a weaker and duller sound through the air. In pro- 
 portion to the conducting power of bodies, is the force 
 and distance to which sounds are transmitted ; accordingly 
 fluids transmit sounds further, and with greater force than 
 
SOUNDS. 403 
 
 aeriform bodies, and solids again very much surpass fluids 
 in these respects. A blow struck by the hammer of the 
 workman in the diving bell is distinctly heard several fa- 
 thoms above, and if the head be plunged into the water, 
 each stroke is heard with painful intensity. The scratch 
 of a pin at one end of a long log of wood is distinctly 
 heard by the ear applied to the other, although it is quite 
 inaudible through the air. The report of a cannon is 
 heard to a much greater distance over the frozen surface 
 of snow ; under such circumstances, the firing has been 
 heard at distances varying from one hundred to two 
 hundred miles. Approaching footsteps are distinctly 
 heard when the ear is applied to the surface of the ground, 
 long before they become audible through the air, a fact 
 of which savages avail themselves in listening to the foot- 
 steps of their enemy or their prey. In like manner, by 
 placing one end of a walking-stick to the ground, and the 
 other upon the ear, hearing is facilitated ; and if one end 
 of a poker be placed on the ear, and be slightly struck, 
 strong and clear sounds are perceived, an experiment 
 occasionally had recourse to in order to ascertain whether 
 water in a kettle boils. For these reasons watchmen now 
 strike the pavement to communicate with each other, 
 which they are thus able to do to a greater distance than 
 by the use of their old instrument, the rattle. A musical 
 box, when held on the hand, may give out scarcely 
 audible sounds, but when it is pressed upon the table, 
 and more especially when placed on a sounding-board, 
 its sounds become clear, and distinctly audible to a con- 
 siderable distance. 
 
 An instrument known by the name of stethoscope is 
 of the utmost practical importance to the physician, 
 especially for investigating the nature and extent of 
 diseases of the chest, whereby he is enabled with great 
 precision to ascertain the character and seat of affections 
 of the heart and lungs, from the sounds which they give 
 out, and to regulate his practice accordingly. 
 
404 
 
 SOUNDS. 
 
 Organized as we are for existence in an ocean of at- 
 mospheric air, we are much more familiar with, and bet- 
 ter able to appreciate vibrations communicated through 
 the air than other media, and circumstances which mo- 
 dify atmospheric sounds are not only detected with 
 greater facility, but are likewise more interesting and 
 important. The numerous changes to which the atmos- 
 phere is subjected from variations in temperature, quan- 
 tity of moisture, and motion, very materially affect the 
 transmission of sound through it. During the night, 
 when the air is still, and of uniform density and tem- 
 perature, sounds are heard to a great distance ; but when 
 the atmosphere is loaded with vapours, or in a fall of 
 snow or rain, and also when it is composed of strata dif- 
 fering from each other in conducting power, the sounds 
 are more limited, and rendered confused and indistinct. 
 The indistinctness arising from the transmission of sound 
 by media of different densities requires attention in the 
 use of the stethoscope. Where the object is to investigate 
 the sounds produced by the air in breathing, a hdllow 
 tube is the best adapted, as the ear receives the sounds by 
 the same medium as that in which they are produced. 
 On the other hand, when listening to the sounds produced 
 by the motions of the heart, a solid cylinder is to be pre- 
 ferred, as being more in accordance with the nature of the 
 organs which are the source of the sound. The intensity 
 of sounds, and the distances to which they are conveyed, 
 depend on the state of the air as to density. In a dry 
 cold atmosphere, at the level of the sea, they are transmit- 
 ted to vast distances with great sharpness and clearness, 
 while at the top of a high mountain, such as Mont Blanc, 
 the report of a pistol is not louder than that of an Indian 
 cracker. The velocity of sound, and the extent to which 
 it is conveyed, are affected by the wind, so that striking 
 effects are produced when it either retards or conveys the 
 distant report of artillery. 
 
 Sound, like light, is subject to reflection, and in this 
 
SOUNDS. 
 
 405 
 
 respect obeys similar laws, the angle of reflection being 
 equal to the angle of incidence. When a stone is cast 
 into a tranquil pool of water, the undulations which are 
 produced on meeting with an impediment, such as the 
 bank, or any other object, rebound, and the obstacle be- 
 comes the centre from which new waves proceed with an 
 intensity diminished in proportion to the distance from 
 the original centre. The reflected sound is termed an 
 echo ; and on meeting with a second impediment, it may 
 again be reflected, so as to give rise to a second echo, and 
 so on, according to the number of reflections, each be- 
 coming weaker than its predecessor, till they die away 
 altogether. The rolling of thunder depends partly upon 
 the sound being reflected from cloud to cloud, and through 
 strata of air of different densities, though it also arises 
 from the discharge of electricity taking place through a 
 volume of air, perhaps miles in extent ; consequently the 
 sound from the point nearest the hearer first reaches his 
 ear, while several seconds elapse before the arrival of the 
 more distant, hence giving origin to a prolonged peal. 
 As the passage of light for all distances on the surface of 
 the earth may be considered as instantaneous, and as 
 sound travels at the rate of about a mile in four seconds, 
 the pulse at the wrist, in a healthy person, may con- 
 veniently serve for measuring the time between the light- 
 ning and the thunder, each beat of the pulse being taken 
 as marking a second ; the number of beats between the 
 flash and report will enable us pretty accurately to esti- 
 mate the distance of the electric shock. 
 
 Sound, like light, decreases in intensity in the inverse 
 square of the distance, so that at double the distance it is 
 only one-fourth part as strong, and so on ; but when 
 sound is transmitted along a tube, so as to prevent its 
 spreading, the diminution is much less. In houses and 
 manufactories, pipes are frequently fitted up for communi- 
 cating verbal orders to distant apartments, attention 
 being attracted by ringing a bell. Sounds are likewise 
 
406 SOUNDS. 
 
 to a certain extent prevented from spreading along the 
 smooth surface of a lake, or along a level wall, and there- 
 fore conversation may be kept up at greater distances in 
 such situations. 
 
 The reflections of sounds may be collected into a focus, 
 so as to increase their intensity, and aid the organ of 
 hearing in appreciating them. Dr Arnott mentions a 
 remarkable instance of this concentration, where the sail of 
 a ship rendered concave by a gentle breeze caused the sound 
 to become audible at a great distance. He says, " It hap- 
 pened once on board-a ship sailing along the coast of Brazil, 
 a hundred miles from land, that the persons walking on 
 deck, when passing a particular spot, always heard very 
 distinctly the sound of bells, varying as in human rejoic- 
 ings. All on board came to listen, and were convinced, but 
 the phenomenon was mysterious and inexplicable. Months 
 afterwards it was ascertained, that at the time of observa- 
 tion the bells of the city of St Salvador, on the Brazilian 
 coast, had been ringing on the occasion of a festi\ 7 al. 
 Their sound, therefore, favoured by a gentle wind, had 
 travelled over a hundred miles of smooth water, and had 
 been brought to a focus by the sail in the particular situ- 
 ation on the deck where it was listened to. It appears 
 from this that a machine might be constructed having 
 the same relation to sound that a telescope has to sight." 
 
 Upon the law of reflection of sound the instruments 
 for assisting the sense of hearing are constructed. The 
 ear-trumpet, with its wide mouth, collects the vibrations, 
 and these being reflected several times as they pass along 
 the curvatures, are finally collected to a focus at the 
 smaller extremity, inserted into the passage of the ear, 
 thereby enabling a person whose hearing has been blunt- 
 ed, to enjoy the exercise of this sense much better than he 
 could otherwise do. The speaking-trumpet acts by re- 
 flecting the voice upon a particular point. To employ it 
 efficiently, it is necessary that the words should be dis- 
 tinctly articulated, otherwise a confused noise only is 
 
EXTERNAL EAR. 
 
 407 
 
 communicated. By means of this instrument the com- 
 mander at sea is enabled to transmit his orders aloft dur- 
 ing the hurricane, in the midst of the noise and uproar 
 of the wind and waves, or hail another vessel at a dis- 
 tance. 
 
 The Ear. The organ of hearing may conveniently be 
 divided into three portions -.first, the external ear, or 
 auricle, by which the vibrations are collected, concentrat- 
 ed, and transmitted ; second, the middle ear or drum, by 
 which they are conveyed and modified in their intensity ; 
 and, third, the internal ear or labyrinth, wherein is lodg- 
 ed the auditory nerve for the reception of the vibrations, 
 and by means of which the impressions are communicat- 
 ed to the brain, the seat of perception, where cognizance 
 is taken of them, forming the ultimate limit of physical 
 investigation. 
 
 The Auricle. The general conformation and shape 
 of the external ear must be sufficiently known to every 
 one. In man it consists of the pavilion and the lobe ; the 
 latter, forming an appendage to the former, especially 
 characterises this organ in the human subject. The pa- 
 vilion consists of a cartilage, formed into several eminen- 
 ces and depressions, so arranged as to collect and concen- 
 trate the vibrations of the air at the orifice of the auditory 
 passage, the elasticity of the cartilage well fitting it for 
 this office. The cartilage is covered with a layer of very 
 dense ligamentous fibre, which again is embraced with a 
 covering of thin integument. In this part no fat is de- 
 posited, excepting a small quantity in minute cells of the 
 lobe, and along the margin of the brim of the pavilion, as 
 that substance would have tended to deaden the vibra- 
 tions. The auricle is attached to the surrounding parts 
 by ligamentous bands and by muscles. One of the 
 muscles is composed of fibres proceeding from the pavilion 
 upwards and forwards, to be connected with the layer 
 which moves the hairy scalp ; by its action the auricle is 
 carried upwards and forwards. Another muscle arising 
 
408 EXTERNAL EAR. 
 
 from the skull behind the ear, is generally divided into 
 distinct slips, which carry it backwards and downwards. 
 Besides these there are several distinct slips of muscular 
 fibres belonging to different portions of the pavilion, by 
 which the tension of the different parts is regulated in 
 accordance with the tone and intensity of the vibrations. 
 In civilized life, where the comfort and safety of the in- 
 dividual is not so dependent on the acuteness of the ex- 
 ternal senses as they frequently are in the savage state, 
 their powers are not exercised, and consequently not so 
 perfectly developed as in the latter condition. Among 
 savages, motion in the auricle is not unfrequently possess- 
 ed to a considerable extent ; while among those who are 
 not so dependent upon the perfection of their external 
 senses, perceptible movements are comparatively rare. 
 
 The external ear, strictly speaking, is confined to ani- 
 mals of the class mammalia, nor is it universal among 
 them. The mole, the water shrew, and other diving 
 animals, seals, and whales, are destitute of it. With re- 
 spect to the mole, while burrowing through the soil, the 
 vibrations will be transmitted to its organ of hearing 
 with great intensity through the solid medium ; and 
 diving animals require an organization which may be 
 adapted to the difference of intensity in the vibrations in 
 water and in air, a difference that amounts to more than 
 four to one : in the same way as they have to adapt their 
 eye for seeing in the two media, so likewise is it neces- 
 sary to adapt the ear for hearing, though it would appear 
 that their sensibility to sonorous vibrations through air 
 is by no means acute, so that opportunities are afforded 
 to the whaler to approach unawares his huge but timid 
 prey, and plunge his harpoon into its carcass. In like 
 manner the seal and the walrus remain unconscious of 
 the footsteps of their foe, till it is too late for retreat. 
 Among land animals of this class, great diversities exist 
 in the development of the auricle; in timid creatures, 
 such as the hare and the rabbit, it is large, formed of se- 
 
EXTERNAL EAR. 
 
 409 
 
 veral distinct pieces, moulded into various shapes, and 
 endowed with great mobility, so as to be placed in the 
 direction from whence the sound proceeds, and thus be- 
 come capable of extensive adaptation to various intensities 
 and velocities. 
 
 In birds, the arrangement of the feathers encircling the 
 ear is in some degree calculated to fulfil the purposes of 
 the auricle; and besides this, in owls several folds of 
 integument, although destitute of cartilage, are evidently 
 constructed with this intention. 
 
 The sonorous oscillations being collected and concen- 
 trated by the auricle, are conveyed along the auditory 
 passage. This tube is about ten or eleven lines in depth, 
 forming a cul de sac ; its direction is somewhat winding, 
 passing inwards, a little forwards, and slightly down- 
 wards, and it is also to a certain degree contracted about 
 its middle. For about one-half its length it consists of a 
 prolongation of the cartilaginous and fibrous textures of 
 the auricle. The cartilage, however, does not complete 
 the whole circumference of the canal, but is interrupted 
 on one side, thereby admitting of variation in its diame- 
 ter. The other half is composed of bone, though in the 
 infant there is merely a ring on which the membrane of 
 the drum is stretched, the bony portion of the tube being 
 subsequently added in the progress of the growth of the 
 skull. The width as well as the tension of this tube are 
 effected by the motions of the jaw; by inserting the fin- 
 ger into its orifice, it will be found to be diminished by 
 shutting, and widened by opening the jaw. This is con- 
 sidered as the reason why the jaw is dropped when a per- 
 son listens attentively and anxiously, an act which is 
 almost invariably performed under such circumstances. 
 The external integument is prolonged, so as to line the 
 passage throughout, becoming exceedingly thin, and los- 
 ing its white colour; for about the external half it is 
 pierced by numerous pores, the excretory orifices of the 
 crypts which furnish the wax of the ear. This secretion 
 
 T 
 
410 DRUM. 
 
 is of an oleo-resinous nature, of a nauseous odour and taste ; 
 qualities admirably suited to the purposes it promotes, 
 those of excluding the entrance of insects, and preserving 
 the canal in a proper condition for the conveyance of vi- 
 brations. 
 
 Variations in the conditions of the wax may be pro- 
 ductive of more or less complete deafness. When defi- 
 cient, and the ear dry, the hearing becomes imperfect, 
 and still more so when it accumulates so as to plug up 
 the passage, a circumstance of no unusual occurrence, but 
 which admits of an easy remedy. A more serious altera- 
 tion arises from a change in the character of the secretion, 
 whereby it is rendered thin and purulent. Attempts on the 
 part of rash and ignorant persons suddenly to put a stop to 
 this vitiated secretion have not unfrequently been followed 
 by the most distressing and even fatal consequences. 
 
 The Drum. This is an irregular cylindrical cavity, 
 separated from the external passage by the membrane 
 of the drum. Anteriorly a canal leads from it for- 
 wards, and a little downwards, to the throat, named the 
 Eustachian tube. Posteriorly there are several openings 
 into osseous cells, situated between the two tables of 
 the temporal bone, where the skull bulges out imme- 
 diately behind the ear, termed mastoid cells, and, dividing 
 this cavity from the internal chamber or labyrinth, there 
 is a partition formed of another part of the temporal bone, 
 named the petrous portion. In this partition are placed 
 two holes, filled up with membranes, hence named fe- 
 nestrce or windows, and, stretching from the membrane of 
 the drum to the oval window, there is a chain of bones, 
 four in number, called the auditory ossicles. 
 
 Membrane of the Drum. This membrane is composed 
 of three layers. The external is continuous with the in- 
 tegument lining the auditory passage. The internal con- 
 stitutes a part of the mucous membrane extended from the 
 throat to the middle ear. Between these two is interposed 
 a fibrous layer, which is the vibratory membrane. Upon 
 
DRUM. 411 
 
 this membrane the vibrations conveyed along the auditory 
 passage strike, just as the tambourine is struck by the 
 fingers. By the parts attached to it, it is capable of 
 being rendered more or less tense, in accordance with 
 the strength of the vibrations, and consequently it is 
 calculated to moderate the intensity of the vibrations 
 transmitted to the immediate seat of hearing. The mem- 
 brane of the drum is however not absolutely essential to 
 the function of hearing, as it is not unfrequently broken 
 without any very material diminution of the function. 
 When this occurs, the individual is capable of blow- 
 ing through the ear, so as to affect the flame of a 
 candle. Still the perforation of it must render it less 
 capable of adaptation to different sounds. While this 
 membrane preserves its integrity, it is impossible for in- 
 sects, or other foreign bodies, to gain entrance into the 
 drum, shewing how unfounded must be many of the idle 
 stories respecting such accidents, and how groundless is 
 the apprehension of many respecting them. 
 
 Eustachian Tube. Vibratory oscillations* 1 cannot be 
 transmitted through a vacuum, as is sufficiently shewn 
 by the well-known experiment of exhausting the receiver 
 of an air-pump, when neither the ringing of a bell nor the 
 blow of a hammer can communicate sound. It was there- 
 fore necessary for an animal destined to hear in the atmos- 
 phere that air should be admitted, in order to communicate 
 the vibrations. Had the external air, however, been direct- 
 ly introduced, liable as it is to so many disturbing causes, 
 it might have been productive of much inconvenience, 
 and become the ready source of diseased action. To ob- 
 viate such disadvantages, the moist air coming up from 
 the lungs, and already assimilated to the temperature of 
 the body, is admitted into the drum by a tube extending 
 from the throat. This tube, first described by an anato- 
 mist of the name of Eustachius, from whom it derives 
 its name, proceeds from the forepart of the drum, where 
 it is formed of bone, but soon becomes cartilaginous, and 
 
412 DRUM. 
 
 is lined with a mucous membrane continuous with that 
 of the throat. It is about an inch and a half in length, 
 widening from the ear to the throat, like a trumpet. 
 By this passage the air obtains access to the drum, 
 and we are enabled, by holding the nostrils, and in- 
 flating forcibly the cheeks, to distend the drum with 
 air, and thus produce such a degree of tension of the 
 membranes as to render the ear insensible to certain 
 tones. By the closure of the mouth and nostrils, and 
 at the sametime making a powerful effort to inspire, 
 the elasticity of the air within the drum is diminished, 
 when the atmosphere causes external pressure, and very 
 low notes become inaudible, though high tones con- 
 tinue to make their impression. The complete obstruc- 
 tion of the Eustachian tube causes deafness ; and even a 
 diminution of its calibre, by the swelling of its lining 
 membrane from inflammation, may be productive of tem- 
 porary dulness of hearing. When deafness arises from 
 complete closure of this tube, hearing may be restored by 
 perforating the membrane of the drum. It is therefore 
 of importance to ascertain whether it proceeds from this 
 or other causes. This may to a certain degree be effected 
 by placing a watch between the teeth of the patient ; if 
 the oscillations from its movements are audible, we may 
 be assured that the essential organ of hearing is unaffected, 
 and that the imperfection of the sense depends upon some 
 part of the accessory apparatus. The Eustachian tubes 
 have been considered as subservient to the transmission 
 of sound ; but independently of their unfavourable posi- 
 tion for this purpose, it would appear from the fact that 
 when partial deafness depends on obstruction of the ex- 
 ternal passage, the patient hears no better w r hen the mouth 
 is open than when closed, they must act very imperfectly 
 in this way. 
 
 In the whale tribe, on the other hand, from the pecu- 
 liar construction of the blowing tube at the orifice of the 
 windpipe, from the length and narrowness of the auditory 
 
MASTOID CELLS. 413 
 
 passage through the mass of fat over the seat of hearing, 
 and from the great size and wide opening of these tubes 
 into the posterior nostrils of this order of animals, as well 
 as the peculiarities of their circumstances as to sound, 
 vibrations are probably transmitted by this channel. 
 
 Mastoid Cells.- The internal surface of the drum is 
 lined throughout with a very thin and delicate mucous 
 membrane, which is likewise extended into cavernous 
 cells placed between the two tables of a portion of the 
 temporal bone. The cavity for the reception of air is 
 thus greatly extended by being prolonged into these cells, 
 and a considerable portion of the internal ear becomes 
 surrounded with an internal atmosphere of its own. "We 
 have had occasion to mention that in the elephant the 
 two tables of the skull are separated from each other by 
 a bony cellular structure to the extent of upwards of a 
 foot. These cells have communication with the drums of 
 the ear, so that in this animal a volume of air surrounds 
 the whole head, thereby contributing to the perfection of 
 hearing for which the elephant is pre-eminently distin- 
 guished. In the cat tribe, in dogs, and in gnawing ani- 
 mals, there is attached to the drum a hollow sphere of 
 exceedingly hard bone, which, like a conch, is well adapt- 
 ed for reflecting the vibrations of sound, thereby increas- 
 ing their intensity. In the whale tribe a similar hard 
 conch is found connected with this cavity, very slightly 
 united to any other part of the skull. These various 
 modifications of structure, adapted for the extension of 
 the internal receptacles of air, are thus modified to the 
 circumstances of the animal, each modification undoubt- 
 edly being calculated to fulfil the purposes of the function 
 in the most perfect manner. In birds, as in the elephant, 
 the two tables of the skull are separated from each other 
 by air-cells, which not only contribute to the lightness of 
 the head, but also communicate with the drums, increas- 
 ing the volume of air for the reception of vibration. 
 
 Petrous Portion. It has been stated that hard elastic 
 
414 AUDITORY OSSICLES. 
 
 substances transmit the vibrations of sound with greater 
 velocity and with less diminution of intensity than matter 
 in any other condition. The temporal bone, in which are 
 lodged the principal parts of the apparatus of hearing, has 
 a portion of it composed of bone, of ivory hardness, form- 
 ing, with the exception of the enamel of the teeth, by far 
 the densest structure in the animal body ; from its hard 
 and stony character it obtains the name of petrous portion, 
 It is remarkable for its early development, for even in the 
 foetus its structure is unfolded to a greater extent than 
 that of other bones. The labyrinth, in which is situated 
 the auditory nerve, is completely invested with this pe- 
 trous bone ; it forms the partition between that chamber 
 and the drum, and contributes to the formation of a consi- 
 derable portion of the walls of the latter cavity. In whales 
 the skeleton is formed of loose spongy bones, with a con- 
 siderable quantity of oil collected in their cells. To 
 compensate for the softness and sponginess of the bones 
 in general, they have the extremely dense conch attached; 
 and in fishes the organ of hearing is furnished with seve- 
 ral small concretions of bone of a smooth and polished 
 appearance, and as hard and brittle as porcelain. These 
 may often be seen in the heads of fish brought to table, 
 their artificial appearance frequently exciting the atten- 
 tion of the curious. 
 
 In the partition between the labyrinth and drum, as 
 already mentioned, are two holes closed with membrane, 
 which has suggested the term window, or fenestra, applied 
 to them. The oval fenestra has resting upon it one of the 
 bones of the chain of connexion between its membrane and 
 that of the drum, whereby the vibrations are communi- 
 cated to the labyrinth. The round fenestra divides the 
 drum from another part of the labyrinth, and retains the 
 fluids of that cavity. 
 
 Auditory Ossicles. The engraving, representing an out- 
 line of the four small bones composing the chain from the 
 membrane of the drum to the oval fenestra, will give a 
 
AUDITORY OSSICLES. 415 
 
 better idea of the appearance of these curiously constructed 
 bodies than the most lengthened description, being here 
 figured of their natural size and rela- 
 tive proportions, a has been likened 
 to a mallet, I to an anvil, c, from its 
 shape, is termed the lenticular or orbi- 
 cular, and d is very appropriately de- 
 signated the stirrup. 
 
 As the office that these bones have to 
 execute is peculiar, they are constructed 
 accordingly. Their hardness and brittle- 
 ness equal those of the petrous portion. 
 The most close examination of their surfaces of connexion 
 fails in detecting, even when aided with magnifying 
 glasses, any thing resembling cartilage upon their articular 
 surfaces, such as in the joints of other bones affords 
 a covering that greatly contributes to lessen friction and 
 diminish the effects of collision. As such effects, how- 
 ever, in the present instance, would be attended with 
 disadvantage, by blunting the intensity of the vibra- 
 tions, no cartilage, ligament, or synovia enter into the 
 construction of the joints of these little bones, but the 
 dry and polished surfaces are accurately fitted to each 
 other, and the bones united together by an extension of 
 the common lining membrane of the drum, along with 
 the delicate and minute muscles required for their move- 
 ments. These bones at birth are as large and nearly as 
 dense as at any subsequent period. The mallet is at- 
 tached to the membrane of the drum by its handle, its 
 head resting on a corresponding depression of the second 
 bone or anvil. The anvil consists of a body and two 
 branches; to the longest of these branches the minute 
 lenticular bone is attached, serving as a small point inter- 
 posed between the anvil and the head of the fourth bone. 
 The fourth bone or stirrup presents a very exact resem- 
 blance to the object from which it derives its name : it 
 consists of a head, two branches, and a base the space 
 
416 ADAPTATION TO SOUND. 
 
 between the branches and the base, corresponding to the 
 space for the reception of the foot in a stirrup, is filled up 
 with a very thin and delicate membrane. The base rests 
 upon the membrane of the oval fenestra, to which it cor- 
 responds in size and shape. 
 
 Several little muscles are attached to these bones, which, 
 by appropriate movements, tend either to relax or tighten 
 the chain, and likewise to moderate the tension both of 
 the membrane of the drum and of the oval fenestra, so 
 that they may be accurately adjusted to the conditions 
 of the sounds they transmit, as the strings of a harp or 
 other stringed instrument are tuned to the required pitch. 
 We thus find in the means adopted for the regulation of 
 the tension of the osseous chain, and that of the two 
 membranes at its extremities, excellent provision for their 
 due adjustment to the various conditions of strength and 
 tone in the undulations of sound they transmit, and per- 
 ceive how it happens that time is requisite for their adap- 
 tation to these conditions, and that a painful and disagree- 
 able impression is produced by the sudden and violent 
 transition from one extremity of the gamut to the other, 
 or from very weak to very loud or strong vibrations. In 
 all this there is a striking analogy between the construc- 
 tion of the ear and the eye. In the last chapter we have 
 seen the means that regulate the quantity of the rays of 
 light permitted to enter the posterior chamber of the eye ; 
 and that the disadvantages resulting from the rapid transi- 
 tion from very strong to very weak light, or from very weak 
 to very strong, are so great, that time is required before the 
 eye can accommodate itself to the circumstances. So it 
 s with respect to the ear : the tension of those parts situ- 
 ated in the drum modify the rays of sound before they 
 enter the interior chamber of the organ of hearing, and 
 the sudden transition from very low to very high, or from 
 very weak to very strong vibrations, or conversely, is ac- 
 companied with a certain degree of insensibility to them. 
 Thus, a person whose ears have been stunned by the dis- 
 
LABYRINTH. 417 
 
 charge of cannon, remains for some time insensible to weak 
 sounds ; as the eye, exposed to strong light, becomes for 
 some time unsusceptible of the impressions of weak light. 
 
 According to what has now been stated, the course of 
 vibrations is from the external ear, along the auditory 
 passage to the membrane of the drum ; from thence along 
 the chain of bones to the membrane of the oval fenestra, 
 situated in the partition between the drum and the laby- 
 rinth, the latter being the peculiar seat of audition, as 
 the posterior chamber of the eye is the peculiar seat of 
 vision. Sounds, however, may reach the labyrinth by 
 other channels than this, the proper course ; and there- 
 fore complete deafness does not occur even when the 
 membrane of the drum and the ossicles are totally de- 
 stroyed, provided the membrane of the oval fenestra re 
 mains entire, so that it retains the contents of the laby- 
 rinth. Thus, vibrations communicated to the skull are 
 conveyed to the labyrinth directly. Whatever tends to 
 increase the impetus of the circulation may be accom- 
 panied with distinct perception of the pulsations of the 
 internal carotid artery, which enters the skull through a 
 canal in the petrous portion of the temporal bone ; and 
 when the sensibility of the ear is morbidly augmented, 
 each beat of this artery becomes distinctly audible. When 
 a watch is held in the mouth, without touching the teeth, 
 the ticking is indistinctly heard, but in contact with the 
 teeth it is rendered very perceptible. 
 
 The Labyrinth. This is the proper audience-cham- 
 ber of the ear. It is entirely surrounded with hard pe- 
 trous bone, and consists of several intricate winding gal- 
 leries, which have suggested the name applied to it. Our 
 engraving, representing a view of the labyrinth, magni- 
 fied, where the different passages are seen laid open, will 
 convey a better idea of the different parts than a detailed 
 description could do. The labyrinth consists of the vesti- 
 bule or lobby, marked a a a ; of three semicircular canals, 
 named, according to their 'relative position, the inferior, 
 
418 LABYKINTH. 
 
 tuperior, and posterior, the first marked b 6, the second 
 c c, and the third d d. Each limb of these canals opens 
 into the vestibule separately. These orifices are marked 
 1, 2, 3, and 4, excepting one limb of the superior, and 
 another of the posterior, which terminate in a common 
 canal, e, opening at 5. The third portion of the labyrinth 
 
 FIG. 36. 
 
 resembles in form the shell of a snail, from which circum- 
 stance it has obtained the name of cochlea. The cochlea 
 consists of two spiral canals, which wind round a central 
 pillar two times and a half. These canals are separated by 
 a spiral partition ; they communicate however at the sum- 
 mit, where they are covered by what is termed the cupola. 
 One of these canals or staircases commences in the vesti- 
 bule, and ascends spirally to the cupola, marked h h hhh. 
 The other, g ] g g g, may be considered as commencing at 
 the cupola, descending till it terminates at the round 
 fenestra of the drum, from which it is separated by the 
 membrane of that orifice. 
 
LABYRINTH. 
 
 This intricate and curiously constructed part of the 
 apparatus of hearing is lined throughout by a membrane 
 which secretes a somewhat viscid and limpid fluid, in 
 which terminate the delicate pulpy extreme divisions of 
 the auditory nerve, somewhat in the same manner as the 
 retina is spread out upon the choroid coat of the eye. 
 Besides, there are little vesicles filled with a transparent 
 fluid, much smaller in their diameters than the several 
 canals they occupy. These fill up the central spaces, and 
 may be compared to the vitreous humour of the eye, serv- 
 ing to support the delicate auditory nerve, as that sup- 
 ports the expanded retina. At the same time, they are 
 admirably fitted for receiving and communicating the 
 vibratory impressions to the nervous fringes. It has 
 been supposed that the use of that canal of the cochlea, 
 which terminates at the oval fenestra, is to admit of the 
 undulation of the fluid contents of the labyrinth, where 
 the vibrations communicated through the oval fenestra 
 circulate along the winding passages, pass up the spiral 
 staircase of the cochlea, leading from the vestibule to the 
 cupola, and from the cupola down the other staircase to 
 the round fenestra, the membrane of which yields to the 
 impulse, and again, by its elasticity, returns the vibration 
 in the opposite direction. 
 
 The fifth cranial nerve, associated with filaments from 
 the facial nerve, contribute the nervous twigs to the in- 
 ternal ear ; the former imparting common sensibility to 
 the different parts, as the filaments from the same nerve 
 send branches to the interior of the eye for a similar pur- 
 pose ; the latter commanding the movements of the mus- 
 cles of the chain, so as to bring them into action with 
 due force in the necessary state of combination, and like- 
 wise supplying the muscles of the auricle. Thus we find 
 the peculiar sensibility of the ear depends on the audi- 
 tory, the common sensibility on the fifth, and the volun- 
 tary and instinctive movements on the facial, nerve. 
 
 Fig. 37 is intended to convey a general idea of the 
 
420 
 
 COMBINED ACTION. 
 
 relative position of the different parts of this interesting 
 organ, which we have endeavoured to describe, a is the 
 pavilion of the external ear, b the lobe, c the external 
 auditory passage, d the membrane of the drum, e the 
 cavity of the drum, / the Eustachian tube, g the oval 
 fenestra, h the round fenestra, i the vestibule, k the cochlea, 
 / the auditory nerve, on its passage to the labyrinth, M 
 the semicircular canals. 
 
 I 
 
 FIG. 37. 
 
 From what has been stated, it will be perceived that 
 every part of this delicate instrument combines with every 
 other with the utmost nicety and accuracy ; that the pavi- 
 lion is constructed for the reception and transmission of 
 vibrations from without to the drum, where they are sub- 
 jected to various modulations, and subsequently convey- 
 ed to the labyrinth, the immediate seat of the auditory 
 nerve ; that from this chamber the impressions from the 
 vibrations are communicated backwards to the origin of 
 
COMBINED ACTION. 421 
 
 the auditory nerve, at the posterior surface of the medulla 
 oblongata, the centre of the cerebro-spinal portion of the 
 nervous system ; and lastly, that they become objects of 
 perception to the mind through the medium of the cere- 
 brum. But how they should impress the delicate extre- 
 mities of the auditory nerve, how they are conveyed by 
 it to the brain, or of what nature is the communication 
 between the matter of the brain and the mind, we are 
 entirely ignorant, and in all probability, in our present 
 state of existence, will ever remain so. 
 
 In vain also shall we attempt to account for the plea- 
 surable sensations derived from the various combinations 
 of sound which constitute music, music being one of 
 those combinations of material and mental conditions 
 from which we, in onr material and mental relations, 
 derive more or less gratification according to our indivi- 
 dual characters. It will be time enough for us to explain, 
 by material causes, how one person is - so sensibly affected 
 by music to which another, under the same apparent cir- 
 cumstances, seems to be altogether indifferent, when we 
 become able, on material principles, in a satisfactory man- 
 ner, to account for peculiarities which distinguish the in- 
 dividuals of the human race. It is sufficiently well 
 known that the gratification arising from music depends 
 to a very considerable extent upon association of ideas, 
 on education, and even npon transient, accidental, and 
 apparently trivial circumstances, the investigation of 
 which is more calculated to gratify the fancy than im- 
 prove the judgment. 
 
422 
 
 CHAPTER X. 
 
 TOUCH. 
 
 6eneral Observations on Touch Its Universal Diffusion over the surface of the 
 Body External Integuments The Scarf-skin, forming the barrier between 
 the living and the dead The Mucous Web, the especial seat of Colour Albinos 
 Remarkable case of a dark Hindoo becoming fair True Skin, that of which 
 Leather is made Its External Surface the immediate seat of the Sense of 
 Touch Tact and Touch All parts not equally susceptible to the impressions 
 of Touch Informs us of the condition and properties of External Objects 
 The most important Guardian of the Body Less liable to be imposed upon, and 
 to bear false witness, than the other Senses The confidence placed in it The 
 superiority enjoyed by Man in the excellency of this Sense Case of J. Mitchell, 
 born Blind and Deaf. 
 
 BY sight and hearing we become cognizant of the ex- 
 istence of distant objects, and we have seen how admira- 
 bly the instruments are constructed for affording us the 
 information they are destined to communicate, and how 
 accurately they accommodate themselves to the varying 
 conditions of the causes which excite these respective 
 sensations. By means of touch we are informed, in the 
 first place, of the form and size of objects, and of the resis- 
 tance they offer, thereby giving ideas of smoothness, 
 roughness, hardness, softness, and weight. In the ma- 
 jority of these instances, if not in all of them, the sensa- 
 tion communicated results from the combined impression 
 made on the surface of the organ brought in contact with 
 the object, and the degree of muscular effort necessary 
 to oppose or overcome the resistance presented. Secondly, 
 by the same sense we are able to judge of the differences 
 between the temperature of external objects and that of 
 
SCARF-SKIN. 
 
 42B 
 
 our bodies, which excite in us the feelings of heat and 
 cold. Self-preservation depending more immediately on 
 this than any other sense, the faculty is not limited to 
 any particular situation, as is the case with the other 
 senses, but it is diffused generally over every part exposed 
 to external influences. The skin, however, is especially- 
 endowed with the susceptibility to impressions which ori- 
 ginate the sensations of touch, and in this respect it 
 varies in different situations, some parts, from a favourable 
 combination of structure, being better adapted for re- 
 ceiving and transmitting accurate and definite sensations 
 than others. 
 
 We have already had occasion to take under our con- 
 sideration the external integuments, in so far as they 
 exercise the functions of secretion and absorption, and 
 have now to examine them in reference to the function of 
 touch. The external integuments consist of three layers, 
 which require special notice, namely, the cuticle, mucous 
 web, and true skin. 
 
 The Cuticle, or Scarf-skin, forms the external invest- 
 ment of the body, and varies in its texture and thick- 
 ness in different parts. It does not present any particu- 
 lar organization, nor have blood-vessels or nerves been 
 traced in its structure, but it appears to be the product 
 of the subjacent vessels. These vessels pour out an al- 
 buminous secretion, which, by the influence of the air, 
 becomes converted into the cuticle a change similar to 
 that which takes place in the coagulation of the white of 
 an egg. The cuticle then may be considered as an indu- 
 rated pellicle, serving as a barrier between the living parts 
 of the body and all that is external to it. It varies very 
 much in thickness and consistence in different parts, ac- 
 cording to the condition of the subjacent vessels from 
 which it is derived, and forms an exact mould of the sur- 
 face which it covers. From its being translucent, the 
 colour of the parts beneath shine through it, though from 
 its not being perfectly transparent, the tints are somewhat 
 
424 SCARF-SKIN. 
 
 modified by their transmission. When the surface of the 
 body is exposed to irritation, the vessels that pour out 
 the lymph, from which the cuticle is derived, have their 
 action increased, and the cuticle either becomes thickened, 
 as in the palms of the hands and soles of the feet, or the 
 effusion is so abundant as to cause a separation between 
 it and the true skin, producing blisters. The thickening 
 of the cuticle from pressure affords one of the innumerable 
 examples of design which the construction of the animal 
 body so admirably displays. Had this tissue been sub- 
 ject to the general law, in virtue of which pressure excites 
 absorption, as exemplified in the internal organs under 
 various diseased and other conditions, it should have been 
 rendered thinner, and consequently less capable of afford- 
 ing due protection under the very circumstances where 
 protection is most necessary ; but instead of this, pressure 
 causes the cuticle to become thicker and more dense, that 
 it may serve as a shield to the parts it covers. It is per- 
 forated by millions of minute pores, which allow of the 
 escape of the matter of transpiration, and of the sebaceous 
 secretion. It is constantly being renewed from the internal 
 surface, and as constantly peeling off from the external 
 surface, in a fine powder, or in thin scales. After some 
 diseases, as scarlet fever, and other affections in which the 
 integuments are much involved, it is often completely 
 renewed, the old scarf-skin being thrown off in large 
 patches. 
 
 The cuticle is present in all organized beings, plants as 
 \vell as animals, though it presents, as may be readily 
 supposed, great diversities in appearance and structure, 
 according to the rank of the object for which it serves as 
 a protection. In many reptiles and crustaceous animals 
 it is cast off at certain periods in one mass, when it pre- 
 sents an exact mould of their bodies, their scales and 
 other external parts being exactly represented. 
 
 The Mucous Wei. Immediately under the scarf-skin 
 is situated a soft pulpy network, exceedingly thin in 
 
MUCOUS WEB. 425 
 
 the fair European, but much more apparent in the dark- 
 coloured races, especially in the Negro. It appears to 
 consist chiefly of the shaggy extremities of blood-ves- 
 sels, interlaced and bound together by delicate filaments 
 of cellular membrane. This is the immediate seat of 
 colour, the colouring matter, consisting of minute globules, 
 varying in their tints in the different races ; even the 
 different nations of Europe are characterized by the co- 
 lour of their skin. It has been supposed that the colour 
 of the skin depends upon the intensity of heat and light 
 to which the body is exposed. It is true, that in tropical 
 countries, the colours of both plants and animals are more 
 intense and brilliant than in colder regions, and that ex- 
 clusion from light produces a pale blanched appearance, 
 while exposure to it has a contrary tendency ; but the 
 variations thus produced in the colour of the skin are 
 neither permanent nor do they descend to the offspring. 
 In every variety of the human race, as well as in the 
 lower animals, examples occasionally happen where the 
 mucous web is totally devoid of colour, such individuals 
 being termed Albinos. Their skin has a somewhat dis- 
 agreeable deadly white appearance ; their eyes are blood- 
 red, from the absence of colour in the iris and choroid 
 membranes, and their hair is also colourless. These acci- 
 dental occurrences are not easily accounted for, though 
 apparently they have a tendency to run in families ; and 
 it is possible, that by attention to breeding in and in, a 
 permanent variety might be established. At Lasswade, 
 a village five miles from Edinburgh, there is a family of 
 seven children, two of which are albinos, a male and a 
 female. The parents, and particularly the father, were 
 what would be termed swarthy; the other brothers 
 and sisters are also dark-complexioned. In every re- 
 spect they enjoy ordinary health and strength, but are 
 less able to tolerate strong light, though they do not see 
 better than others in obscure light. A few years ago, 
 there was a very remarkable instance in Edinburgh of a 
 
426 TRUE SKIN. 
 
 Hindoo, advanced in life, who came over to this country 
 when a boy. At an early period of manhood, white spots 
 began to appear on different parts of the skin, which, in 
 progress of time, gradually enlarged, so as ultimately to 
 spread over by far the greater part of his body, leaving 
 on the face a few black spots, as also a few patches on 
 the trunk and limbs. In this case, the colouring matter 
 of the mucous web was not entirely removed, but merely 
 replaced by globules of a whiter colour. I attended this 
 individual during his last illness, and afterwards examined 
 the body, whereby an opportunity was afforded for ob- 
 taining a portion of his spotted skin, which w r as carefully 
 examined, without being able to ascertain the cause of 
 this curious change. He was well known in Edinburgh, 
 and must still be in the recollection of many, as his case 
 excited some curiosity among medical men, as well as 
 others. The white portion of his skin was as fair as that 
 of the majority of Scotchmen, and the spots as dark as 
 the skin of the darkest of the Hindoo races. He was 
 married to a Scotchwoman, and had a family as fair as 
 their mother, but with the Hindoo features so well marked 
 as not to be mistaken. 
 
 The Dermis or True Skin. This is the thickest and 
 most important part of the external integuments. It is 
 composed of an infinite number of plates, consisting of 
 filaments inextricably interwoven together, and abun- 
 dantly furnished with blood-vessels and nerves. Exter- 
 nally, its texture is most dense, becoming softer and 
 looser, and gradually passing into the common cellular 
 tissue beneath. Its thickness varies in different parts of 
 the body, as also according to the age and sex of the in- 
 dividual. On the back it is nearly twice the thickness 
 that it is on the anterior surface of the body, and much 
 thicker on the outside of the limbs than on their inner 
 surfaces. It is chiefly composed of animal gelatin, and 
 by being combined with the vegetable principle named 
 tannin, becomes converted into leather. It is everywhere 
 
TRUE SKIN. 427 
 
 perforated by numerous pores, which give transmission to 
 the oily or sebaceous secretion, by which its softness, 
 smoothness, and flexibility are preserved. 
 
 Its external surface is everywhere studded by exceed- 
 ingly minute nipples or papillae. In several parts, as in 
 the palms of the hands, and extremities of the fingers, 
 these are disposed in regular symmetrical rows, forming 
 waving lines, and separated by small crevices that admit 
 of the flexions of the skin, and of its adaptation to the 
 surfaces of external objects. The papillae are plentifully 
 supplied with blood-vessels, which are so constructed as 
 to allow of a congestion or accumulation of blood in 
 them, whereby they swell and become erect, consequently 
 the nerves are rendered more susceptible to impressions. 
 The readiness with which the external surface of the skin 
 admits of an increased quantity of blood is strikingly dis- 
 played in the act of blushing, and in various other con- 
 ditions. 
 
 The immediate instruments of touch are the extremities 
 of the sensiferous nerves terminating in the papillae on 
 the surface of the body. The object, the properties of 
 which it is the office of these nerves to communicate to 
 the mind, does not come immediately in contact with 
 these ; both the cuticle and mucous web being interposed, 
 the removal of which, by blisters or otherwise, does not in- 
 crease the sense, but tends to destroy and disturb it. From 
 this arrangement, impressions are transmitted through 
 the insensible scarf-skin, by the hairs, and through the 
 nails. The whiskers of many animals, such as the cat 
 tribe, are subservient to touch, nerves being situated at 
 their roots that are highly susceptible of such impres- 
 sions. Even by the hard and insensible hoofs of animals, 
 sensations are communicated to the subjacent nerves, as 
 may be witnessed when the highland pony exercises his 
 sagacity in ascertaining the soundness of a moorland path 
 by beating it with his hoof before trusting his weight 
 upon it. 
 
428 TACT AND TOUCH. 
 
 Tact and Touch. This, as well as the other senses, 
 may be regarded under two conditions. In the one, 
 where the attention is especially directed to the impres- 
 sions received from the sense, and a voluntary effort made 
 to bring it into the most favourable state for the exercise 
 of its function ; in the other, the mind is not particularly 
 roused in order to receive distinct perceptions from the 
 sensations communicated from the seat of impression. 
 The former may be held as the active, and the latter as 
 the passive condition of the senses. Thus, with respect 
 to vision, when we call the eyes actively into operation 
 we look ; but in their passive condition we only see. As 
 also in audition, actively, we listen ; passively, we hear. 
 So likewise, in regard to taction, when we exercise it in 
 the active state, we touch ; while in its passive condition 
 we have merely tact. 
 
 All parts of the surface of the body are not equally 
 susceptible to the impressions of touch. The extremities 
 of the fingers and toes are admirably constructed for the 
 exercise of this sense. The nerves proceeding to these 
 parts are comparatively very large, and almost entirely 
 distributed upon the papillae. They are accompanied 
 with large blood-vessels, which readily admit of a vary- 
 ing quantity of blood, according to the conditions required 
 for the due exercise of the function. They are supported 
 upon cushions, which, by their fulness and elasticity, 
 adapt them to the form and consistence of objects brought 
 in contact with them, and they are protected by the 
 broad shield-like coverings, the nails. The lips and tongue 
 are likewise delicate instruments of touch, and ap- 
 pear to be the first employed for that purpose. The 
 infant probably first experiences sensations from this 
 sense on being applied to the breast, and there can be no 
 doubt that the gratification enjoyed by the mother and 
 her offspring is mutual, in giving and receiving that 
 bountiful provision destined by providence for the nourish- 
 ment of the new-born of the highest class of animals. 
 
SIXTH SENSE. 
 
 429 
 
 The infant having thus learned first to cultivate and re- 
 ceive impressions of touch in the lips and tongue, conti- 
 nues for some time to rely with greater confidence on the 
 evidence obtained from this than any other source, and 
 accordingly persists in carrying every object to the mouth, 
 in order to subject it to their scrutiny, till the hands and 
 fingers become sufficiently educated and manageable to 
 serve as substitutes for them. 
 
 Sir Charles Bell states, in his Bridgewater Treatise, that 
 the tongue is incapable of perceiving the pulsation of the 
 artery at the wrist. This may be the case with some in- 
 dividuals, but it is certainly not universally true, for I 
 myself can distinctly feel and count my own pulse at the 
 wrist by the tongue, though more perceptibly when it 
 rests upon the teeth. The pressure of the cushions on 
 the small bones at the extremities of the fingers, on 
 which they rest, contributes to the sense of touch. When 
 we examine solid bodies, the teeth are excellent instru- 
 ments for this purpose in the examination of very hard 
 substances. Liquids, on the other hand, are accurately 
 judged of by the soft and pliable tongue. 
 
 In the same treatise he contends for the existence of a 
 sixth sense, which he terms the muscular. It may be 
 doubted, however, whether his arguments are sufficient to 
 induce one to acquiesce in the propriety of considering 
 the muscles as endowed with a distinct sense, apart from 
 their peculiar sensibility ; and if the peculiar sensibility 
 which they undoubtedly possess be sufficient to be consi- 
 dered as a distinct sense, upon the same grounds there 
 would arise the necessity of still further multiplying the 
 number of senses ; for the lungs, alimentary canal, urinary 
 organs, and others, have each peculiar sensibilities and 
 endowments adapted to the functions they have to per- 
 form. Muscular action is necessary to the proper exer- 
 cise of the sense of touch, enabling us to estimate the 
 resistance which bodies offer, and thereby to judge of 
 their consistence and weight, their smoothness and rough- 
 
430 EXCELLENCE OF TOUCH IN MAN. 
 
 ness, and their size and form. By touch we also obtain 
 ideas of time, number, and space. 
 
 Constructed as we are for existence in an atmosphere 
 which is subject to constant and sudden variations of 
 temperature, and liable as we are to have heat either im- 
 parted or extracted from our bodies with such rapidity or 
 in such a quantity as to be inconsistent with our safety 
 and preservation, it became absolutely necessary that we 
 should be furnished with the means of being warned to 
 withdraw or protect ourselves from objects calculated to 
 affect us in a dangerous manner in these respects. No- 
 where could this safeguard be placed so conveniently and 
 so advantageously as in the integumentary coverings. 
 The special sensibility, therefore, resident in the skin, 
 not only furnishes us with a knowledge of the geometrical 
 characters of external substances, and the resistance they 
 offer, but likewise informs us of the presence of dangers 
 which may surround us ; and by the pain which may 
 be excited, forcibly admonishes us to avoid the causes 
 which originate it. 
 
 Man enjoys, in the exquisite sensibility of his skin, 
 a superiority in the sense of touch which he does 
 not possess in the other senses, many animals surpass- 
 ing him in one or other of the rest. In this, how- 
 ever, he stands unrivalled. His beautiful and admirable 
 instrument, the hand, is by him employed chiefly in con- 
 nexion with touch, and for this purpose it is altogether 
 unequalled in the whole of the animal creation. Even in 
 those animals which make the nearest approaches to him 
 in their organic structure, the corresponding organ is em- 
 ployed for locomotion. He alone reserves it for higher 
 and more delicate operations. So evident are the many 
 advantages derived from the hand, and so great the supe- 
 riority to which he is indebted to it, that some philoso- 
 phers have not hesitated to ascribe to this cause the pre- 
 eminence he has over his fellow-creatures, forgetting that 
 man's pre-eminence does not by any means altogether 
 
 
EXCELLENCE OF TOUCH IN MAN. 
 
 43J 
 
 spring from the construction of his body, admirable as 
 it is, but from that body being the associate of a rational 
 spirit, which discovers and exercises the capabilities and 
 powers of the instruments entrusted to its use. 
 
 Instead, then, of the delicacy and tenderness of the skin 
 of man being a disadvantage, it is the source of some of 
 his most exquisite physical enjoyments, and the means of 
 his obtaining accurate knowledge of the properties of the 
 external world around him. Sight, hearing, and touch, 
 are justly entitled to be considered as the intellectual 
 senses. They are the means through which we obtain 
 our most valuable information the witnesses that fur- 
 nish the evidence of the existence of external things. 
 Where they agree in the evidence they deliver, we can- 
 not for a moment doubt of the truth of their report. In- 
 dividually, however, they are liable to receive erroneous 
 impressions. Sight is liable to many illusions ; so like- 
 wise is hearing. Upon the whole, perhaps touch is the 
 least subject to deception ; accordingly we rely upon ita 
 testimony with greater confidence than on any of the 
 others. It is important to know that the fact of the 
 greatest and most paramount interest of all others to 
 mankind, the resurrection of the Saviour, is established 
 on the evidence of the three intellectual senses. That 
 such evidence was afforded we are assured on several 
 occasions, particularly on the following, recorded by St 
 John : " But Thomas, one of the twelve, called Didy- 
 mus, was not with them when Jesus came. The other 
 disciples therefore said unto him, We have seen the Lord. 
 But he said unto them, Except I shall see in his hands 
 the print of the nails, and put my finger into the print 
 of the nails, and thrust my hand into his side, I will not 
 believe. And after eight days again his disciples w T ere 
 within, and Thomas with them : then came Jesus, the 
 doors being shut, and stood in the midst, and said, Peace 
 be unto you. Then saith he to Thomas, Reach hither 
 thy finger, and behold my hands ; and reach hither thy 
 
432 EXCELLENCE OP TOUCH IN MAN. 
 
 hand, and thrust it into my side : and be not faithless, 
 but believing. And Thomas answered and said unto 
 him, My Lord and my God. Jesus saith unto him, Tho- 
 mas, because thou hast seen me, thou hast believed : 
 blessed are they that have not seen, and yet have believ- 
 ed." Thus the incredulity of the Apostle Thomas has 
 furnished to all succeeding ages a remarkable instance of 
 the graciousness of our Saviour, and of an opportunity 
 afforded to the sense of touch to bear testimony as to the 
 reality of the resurrection of his body. 
 
 The excellence of the sense of touch, has led some to 
 consider that the erroneous impressions to which the other 
 senses are liable are corrected by it. Strictly speaking, 
 however, the senses cannot correct each other, since the 
 sensations they communicate to the mind are of a different 
 character. The eye can convey no idea of sound, nor 
 the ear of colour, nor can the touch furnish impressions 
 of either the one or the other. It is true, that where ne- 
 cessity has called forth the pow r ers of the sense of touch, 
 as in the blind, the accuracy with which they are enabled 
 to judge of the properties of bodies is truly astonishing 
 to those who enjoy the use of all the senses, and can se- 
 lect one or another for obtaining information respecting 
 external objects, as may best suit their purpose. But 
 where the evidence is chiefly or entirely to be derived 
 from one sense, and where it is frequently called into 
 operation, and much attention paid to its reports, its ca- 
 pabilities become vastly increased. Dr Sanderson, Pro- 
 fessor of Mathematics at Cambridge, and who was blind 
 from the second year of his age, could distinguish false 
 from true medals. Rudolphi mentions the case of Baczko, 
 who could distinguish cloth of equal quality, but of 
 different colours: black appeared to him among the 
 roughest and hardest j to this succeeded dark blue and 
 dark brown, which he could not distinguish from each 
 other ; neither could he distinguish the colour of cotton 
 or silk stuffs. There are many other remarkable instan- 
 
CASE OF MITCHELL, BLIND AND DEAF. 433 
 
 ces of the wonderful delicacy reached by this sense from 
 its cultivation by the blind. But in all such cases there 
 merely exists a greater degree of perfection in the exer- 
 cise of its own powers, not an assumption of the pecu- 
 liar function belonging to the others. 
 
 Even the touch is liable to error in some instances. If 
 two fingers are crossed over each other, and a pea rolled 
 between them, we receive the impression of the presence 
 of two distinct objects, though we very well know that 
 there exists only one : nor 4oes sight in this instance re- 
 move the deception. However, in this case the organs 
 are placed in an unnatural position, and there is every 
 reason to believe, that by continuing the practice for a 
 length of time, the illusion would vanish. A fallacy to 
 which touch is much more subject, occurs with respect 
 to heat. Thus, if we place the hand in separate vessels, 
 the one containing warm, and the other very cold water, 
 and after some time withdraw the hands, and immediately 
 plunge them into the mixture of both waters, to the one 
 hand the mixture appears warm, and to the other cold. 
 Or, in a tropical country, if one person descends a high 
 mountain from the region of perpetual snow, and meets 
 at the middle of the descent another ascending from the 
 burning valley at its base, he who is descending may feel 
 oppressed with heat, while the other is shivering with 
 cold, though both sensations are produced by the same 
 temperature. Frozen mercury excites the same sensa- 
 tion, when touched by the finger, as is experienced from 
 the contact of red-hot iron. 
 
 It is almost impossible to conceive an individual totally 
 deprived of touch, though numerous cases daily occur of 
 individuals deprived of it in particular parts from para- 
 lysis. Numerous instances of deprivation of one of the 
 two other noble senses, sight and hearing, are constant- 
 ly presented to us. There are also melancholy exam- 
 ples recorded, where unhappy individuals have been des- 
 titute of both, but fortunately they are of rare occur- 
 
 u 
 
434 CASE OF MITCHELL, BLIND AND DEAF. 
 
 rence. A case of this kind which excited great interest 
 some years ago in the Royal Society of Edinburgh, is de- 
 tailed in the 7th and 8th Yols. of their Transactions. 
 The case is so well calculated to shew the vast superiority 
 of the intellect of man under peculiarly unfavourable cir- 
 cumstances, and to display the excellency of the imma- 
 terial part of his constitution, even when deprived of 
 information through some of the most essential mate- 
 rial channels, that we shall select a few of the instances 
 of the state of this individual. James Mitchell, the sub- 
 ject of the following account, was the son of a respectable 
 parish minister in the county of Elgin. He was blind 
 from birth, in consequence of opacity of the cornea, though 
 the iris displayed susceptibility to light. He was also 
 completely deaf, and consequently dumb. He had the 
 advantage of affectionate and intelligent parents, and was 
 happy in the possession of an amiable and judicious sis- 
 ter, to whom he appears to have been much indebted. 
 " His mother, who is an intelligent and sensible lady," 
 says the Rev. Professor Glennie, " very early discovered 
 his unfortunate situation ; she noticed that he was Hind, 
 from his discovering no desire to turn his eyes to the light, 
 or to any bright object ; and afterwards (in his early in- 
 fancy also) she ascertained his being deaf, from the circum- 
 stance that no noise, however loud, awakened him from 
 sleep. As he grew up, he discovered a most extraordi- 
 nary acuteness in the senses of touch and smell, being 
 very soon able by these to distinguish strangers from the 
 members of his own family, and any little article which 
 was appropriated to himself, from what belonged to others. 
 In childhood, the most noticeable circumstance relating 
 to him, was an eager desire to strike upon his fore-teeth : 
 this he would do for hours." * * * 
 
 " His countenance, notwithstanding his unfortunate 
 defects, does by no means indicate fatuity ; nay, the 
 lineaments (in church, for instance, and during the time 
 of family prayer) are perfectly composed and sedate ; 
 
CASE OF MITCHELL, BLIND AND DEAF. 435 
 
 when sensible of the presence of a stranger, or of any ob- 
 ject which awakens his curiosity, his face appears anima- 
 ted ; and when offended or enraged, he has a very marked 
 ferocity of look. He is (for his age) of an athletic form, 
 and has altogether a robust appearance. 
 
 " He behaves himself in company with much more 
 propriety than could be expected, a circumstance owing 
 undoubtedly to the great care of his parents, and of his 
 elder sister. He feeds himself. When a stranger ar- 
 rives, his smell immediately and invariably informs him 
 of the circumstance, and directs him to the place where 
 the stranger is, whom he proceeds to survey by the sense 
 of touch. In the remote situation where he resides, male 
 visitors are the most frequent, and, therefore, the first 
 thing he generally does, is to examine whether or not the 
 stranger wears boots ; if he does wear them, he imme- 
 diately quits the stranger, goes to the lobby, feels for, 
 and accurately examines his whip ; then proceeds to the 
 stable, and handles his horse with great care, and with 
 the utmost seeming attention. It has occasionally hap- 
 pened that visitors have arrived in a carriage, and on 
 such occasions he has never failed to go to the place 
 where the carriage stood, examined the whole of it with 
 much anxiety, and tried innumerable times the elasticity 
 of the springs. In all this he is undoubtedly guided by 
 the smell and touch only." * * * 
 
 " The feeling by which he appears to be most power- 
 fully actuated (at least to a stranger), is curiosity, or an 
 anxious desire to make himself acquainted with every thing 
 that is new to him. He appears to feel affection for his fa- 
 mily very strongly : discovered extreme sorrow on account 
 of his father's death. * * * He is likewise capable 
 of feeling mirth, and frequently laughs heartily. He is 
 highly gratified by getting new clothes ; and as tearing 
 his clothes is the most usual expression of his anger, so 
 the punishment he feels most is to be obliged to wear 
 them after he has torn them. He is subject to anger after 
 
436 CASE OF MITCHELL, BLIND AND DEAF. 
 
 being crossed in any of his desires, or when he finds any 
 of his clothes, or articles with which he amuses himself, 
 removed from the chest in which he keeps them." * * * 
 " When he is hungry he approaches his mother or sis- 
 ters, touches them in an expressive manner, and points 
 towards the apartment where the victuals are usually 
 kept. If he wants dry stockings, he points to his legs, 
 and in a similar way intimates his wishes upon other 
 occasions. A pair of shoes were lately brought to him, 
 and on putting them on he found them too small. His 
 mother then took them and put them into a small closet. 
 Soon after a thought seemed to strike him ; he contrived 
 to obtain the key of the closet, opened the door, took the 
 shoes, and put them on the feet of a young lad who at- 
 tends him, whom they suited exactly." * * * 
 
 " When he is sick and feverish, which sometimes hap- 
 pens, he points to his head, or takes his mother's hand and 
 places it opposite to his heart, seemingly with an inten- 
 tion that she may observe its beating more quickly than 
 usual. He never attempts to express his feelings by ut- 
 terance, except when angry, when he bellows in a most 
 uncouth manner. Satisfaction or complacency he ex- 
 presses by patting the person or object which excites that 
 feeling. His smell being wonderfully acute, he is fre- 
 quently offended through that sense, when other persons 
 near to him smelL nothing unpleasant ; he expresses his 
 dissatisfaction on such occasions by putting his hand to 
 his nose, and retreating rapidly. His taste seems also 
 to be exquisite, and he expresses much pleasure by laugh- 
 ing and smacking his lips when savoury victuals are laid 
 before him. 
 
 " His father, when alive, was at much pains in direct- 
 ing him, as his mother still is ; but his elder sister seems 
 to have a much greater ascendency over him, and more 
 power of managing him than any other person. Touch- 
 ing his head with her hand seems to be the principal 
 method she employs in signifying her wishes to him re- 
 
CASE OF MITCHELL, BLIND AND DEAF. 437 
 
 spec ting his conduct. This she does with various degrees 
 of force, and in different manners ; and he seems readily 
 to understand the intimation intended to be conveyed. 
 In short, by gratifying him when he acts properly, and 
 withholding from him the objects of his complacency 
 when he has done amiss, he has been taught a sense of 
 what is becoming in manners, and proper in conduct, 
 much stronger than it could be otherwise believed that 
 any person in his singularly unfortunate situation could 
 acquire." 
 
 Several further details are given of this interesting case 
 in the above transactions, by the late Professor D. Stew- 
 art, Dr Gordon, lecturer on physiology, Sir James Mack- 
 intosh, Miss Mitchell, and others. The extracts now 
 cited from Professor Glennie's account may, however, 
 suffice to shew the display of character evinced under 
 such remarkable and fortunately rare circumstances. 
 Another case is detailed in Hibbert's Description of Shet- 
 land, of a lad born blind and deaf, but he appears to have 
 been at the same time idiotic, so that the case is not cal- 
 culated to afford the same interest to the general reader. 
 
438 
 
 CHAPTER XI. 
 
 SMELL AND TASTE. 
 
 Intimate connexion between Smell and Taste Not of much importance as Intel- 
 lectual Channels. SMELL. The Nostrils Confidence reposed in Smell by 
 several of the Lower Animals Its excellence in the Dog Smell in Vultures 
 In the Raven In Fishes Odours Gratification derived from Odours influ- 
 enced by Constitution, Habit, &c. Classification of Permanence, Extent, and 
 Divisibility of Morbid Conditions. TASTE. Seat of Papillae of the Tongue 
 Savours Classification of Influence of Habit Acquired Tastes Affected by 
 the State of the Stomach Morbid Conditions Gustatory Organs in different 
 Classes of Animals The Condition of Matter necessary to excite Taste. 
 
 THE senses of smell and taste may, to a certain extent, 
 be considered in connexion. Their respective functions 
 have a reference to digestion, and are in some measure 
 subservient to it. They are more closely associated than 
 any of the other senses, and under some circumstances 
 their co-operation is essential to the due performance of 
 their office. Thus, when the nostrils are obstructed, taste 
 is considerably impaired, and pleasurable or disagreeable 
 sensations produced by many substances depend on a 
 combined result of the impressions on the organs of smell 
 and taste. Neither of them are of much importance as 
 intellectual organs in civilized life, therefore they are not 
 much cultivated ; indeed, much attention to their gratifi- 
 cation is held as being in an especial manner sensual, and 
 rather to be avoided than indulged in. This ought to re- 
 fer, however, only to their abuse, and not to their proper 
 and legitimate use. None of our faculties are to be de- 
 spised or neglected because they may be wrongfully em- 
 
ORGANS OF SMELL. 439 
 
 ployed, or rendered subservient to the degradation of 
 individuals. Smell is useful to the apothecary, the che- 
 mist, and the perfumer, and taste to the two former of 
 these, as well as to the wine-taster, the grocer, the tea- 
 taster, &c. 
 
 SMELL. 
 
 Of the fourteen bones which enter into the formation 
 of the face, only three are excluded from forming a part 
 of the cavities of the nostrils, namely, the two cheek bones 
 and the lower jaw. Three of the eight bones of the cranium 
 likewise constitute a part of the nose. Several of these are 
 extremely light and spongy in their texture, and are 
 curiously convoluted and laminated, so as to present a 
 very extensive surface, especially in animals remarkable 
 for the acuteness of their scent. In the seal, for example, 
 the external surface of the nose has been estimated as 
 equal to 240 cubic inches. The two bones of the upper 
 jaw form a considerable portion of the nose ; from each 
 a process projects upwards, and ascends to join the frontal 
 bone. Upon these processes rest two small bones, named 
 nasal, which are united with each other, and form the 
 bridge of the nose, the two upper jaw-bones serving as 
 abutments to the arch. The internal bones are extremely 
 delicate and spongy. Their laminated and convoluted 
 structure has suggested the idea of a Turkish turban : 
 hence they are termed turbinated bones. In connexion 
 with the nostrils, especially in the adult, there are several 
 cavities, as in the frontal and upper jaw-bones, that are 
 called sinuses. These sinuses considerably extend the 
 surface on which the lining membrane is expanded, and 
 contribute to the perfection of the function, by affording 
 capacious receptacles for air, loaded with odorous par- 
 ticles. The nose is divided by a central partition into 
 the two symmetrical organs, the nostrils, in the same 
 manner as are all the other organs in the body which are 
 placed in what has been named the median plane, as the 
 
440 ORGANS OP SMELL. 
 
 mouth, tongue, larynx, &c. Besides the bones, there are 
 cartilages which enter into the formation of the nostrils ; 
 one of these completes the central partition, two others 
 extend from the lower margin of the nasal bones, and 
 two lateral cartilages form the wings of the nostrils. 
 These elastic bodies readily admit of motion and modifica- 
 tion of shape in the nose ; at the same time they contribute 
 to its form and shape as characteristic of the individual, or 
 of the race. In some animals these cartilages are largely 
 developed, as in the elephant, in the formation of the pro- 
 boscis, an instrument of varied powers, and applicable, 
 under the control of the will, to a great variety of pur- 
 poses. Attached to the cartilages there are several mus- 
 cular fibres for the movement of the nostrils, for re- 
 gulating the external orifices in accordance with different 
 conditions of respiration, and for enabling us to exercise the 
 sense of smell with greater effect when we wish volun- 
 tarily to employ that function. 
 
 The lining membrane of the nose belongs to the class 
 of mucous membranes, and from the anatomist who first 
 gave a particular description of it, it is known by the name 
 of the Schneiderian. From being the source of the phlegm 
 or mucus of the nose, it is likewise termed pituitary mem- 
 brane. This membrane is prolonged into all the cavities 
 connected with the nostrils, and over the whole of the 
 laminated folds of the spongy bones. Externally it is 
 continuous with the common integuments, and posteriorly 
 with the lining membrane of the throat. It differs in its 
 appearance and thickness in different situations. Where 
 it constitutes the immediate seat of smell it is thicker, 
 more vascular, and of a redder colour than mucous mem- 
 brane in other situations ; but where it is extended into 
 the sinuses, it becomes thin, pale, and of a smooth sur- 
 face. The thick vascular portion is covered with a shaggy 
 filamentous nap, like the pile of velvet, amidst which there 
 are scattered numerous little mucous crypts that yield the 
 secretion with which it is chiefly moistened, though it 
 
ACUTENESS OF SMELL IN ANIMALS. 441 
 
 is also bathed with the tears that, after having washed the 
 external surface of the eye, are conveyed by the nasal 
 ducts to be diffused over the internal surface of the nose, 
 in order to dilute the thick viscid mucus. The blood- 
 vessels of this part are exceedingly numerous, and present 
 a very curious modification of distribution. The nerves, 
 as we have already seen, are derived from three sources. 
 The first pair, or olfactory, are limited to the thick vas- 
 cular portion, and constitute the immediate channels for 
 the transmission of odorous sensations to the brain. 
 Twigs from the first and second branches of the fifth are 
 plentifully ramified over the whole expanse of the pitui- 
 tary membrane, imparting to it common sensibility. 
 Lastly, there are branches from the facial, to regulate 
 the action of the muscles. 
 
 The apparatus of smell presents great diversities in 
 different tribes of animals, some of the class mammalia 
 placing more confidence in it than all their other senses 
 taken together. This is remarkably the case with rumi- 
 nants, as oxen, sheep, deer, and antelopes. The shepherd 
 occasionally avails himself of it, when a lamb has died, 
 and he wishes to put to the ewe another lamb that may 
 have lost its dam ; if she refuses to foster the stranger, 
 he is sure to succeed by stripping off the skin of her own 
 offspring and tying it on the back of the stranger, that 
 she may smell the skin ; she then entertains and treats it 
 as her own. In this case she neglects the sense of sight, 
 for nothing can be more uncouth than the new object of 
 her affections; neither does she attend to the evidence 
 afforded by hearing ; however unlike the bleating of the 
 foster lamb may be to that to which she was first accus- 
 tomed, her smelling is satisfied, and she is content. 
 The same practice succeeds with the cow. Such are 
 termed in Scotland tulchan lambs and tulchan calves. 
 When the lay nobility seized on the property and dues 
 of the church at the Reformation, and the people began to 
 demur paying tithes of many things previously paid to 
 
 u2 
 
442 ACUTENESS OF SMELL IN ANIMALS. 
 
 the clergy, they employed agents to enforce their collec- 
 tion : these agents the people nicknamed tulchan bishops, 
 thereby strongly indicating the estimation in which they 
 held them. 
 
 The final purpose why these animals should be endowed 
 with an acute and delicate smell is sufficiently obvious : 
 they have to select their food from amidst a variety of 
 plants, many of which are possessed of highly deleterious 
 properties, whereby they might readily be poisoned, were 
 they to take them along with their food. Accordingly, we 
 find their olfactory nerves are larger than any of the others 
 connected directly with the brain. The cavities of the 
 nose are very capacious, the surface of the pituitary mem- 
 brane vastly extended, and the orifices placed in the con- 
 venient vicinity of the mouth, that every thing may be 
 submitted to this highly developed sense before it is taken 
 up to be introduced to the organs of digestion. The ele- 
 phant, the tapir, and the hog, have an acuteness of scent 
 corresponding to the great extent of the apparatus. The 
 latter animal is employed in France to hunt for truffles, 
 a species of mushroom which vegetates at a considerable 
 depth under the surface, but not beyond the reach of the 
 sense of smell of the pig. When laid on upon ground 
 adapted for this kind of hunting, the pig soon ascertains 
 where the truffle is situated, and by his powerful snout 
 would soon unearth and devour it, if not restrained by the 
 sportsman, who immediately proceeds to dig for the 
 treasure, and appropriates it to himself. 
 
 In carnivorous quadrupeds the organ of smell is also 
 fully developed. Its accuracy and delicacy in the dog, 
 for example, are too well known to require any argument 
 to prove them. The certainty with which he detects the 
 footsteps of animals, long after they have been imprinted, 
 is truly astonishing ; as is the facility with which he traces 
 the progress of his master through crowded streets, dis- 
 tinguishing the emanations which his foot, defended by 
 stockings and shoes, has left on the surface, and recog- 
 
 
SMELL IN VULTURES. 
 
 443 
 
 nising them, moreover, amidst thousands of odorous par- 
 ticles, not only of different kinds, but of different in- 
 dividuals of the same species. In like manner he se- 
 lects, and pertinaciously pursues an individual from a 
 herd or from a flock, and however anxiously his prey 
 may seek protection amidst its fellows, he unhesita- 
 tingly continues to follow its track, guided by his 
 scent. Such acuteness and perfection in this sense, which 
 exists in man only comparatively in a very obtuse state, 
 is truly marvellous. 
 
 In the whale tribe, if the sense exists at all, it must 
 be exercised by some other nerve than that which is sub- 
 servient to this purpose in other animals in which it is 
 displayed in the greatest perfection, as they have no nerve 
 corresponding with the olfactory, nor do they present any 
 structure expressly adapted to the exercise of this function. 
 
 Birds are universally furnished with the instrument 
 of smell, though they present great diversities in the de- 
 velopment of the organs, and appear to be very differently 
 influenced by the sensations it communicates. In general, 
 it is more completely developed in rapacious and fish- 
 ing birds than in any others. Those birds that prefer 
 putrid animal remains and other garbage, are generally, 
 and perhaps justly, supposed to possess this sense in an 
 eminent degree. Vultures especially have been imagined 
 to be guided to their prey at immense distances, by their 
 scent : that the acuteness of their smell, however, has 
 been much exaggerated, seems to be fully proved by a 
 number of facts. The celebrated Audubon, in his splendid 
 work the Ornithological Biography, has the following 
 observations and experiments respecting the turkey buz- 
 zard of America : 
 
 " As soon as, like me, you shall have seen the turkey 
 buzzard follow, with arduous closeness of investigation, 
 the skirts of the forests, the meanders of creeks and rivers, 
 sweeping over the whole of extensive plains, glancing his 
 quick eye in all directions, with as much intentness as 
 
444 SMELL IN VULTURES. 
 
 ever did the noblest of falcons, to discover where below 
 him lies the suitable prey ; when, like me, you have re- 
 peatedly seen that bird pass over objects calculated to 
 glut his voracious appetite unnoticed, because unseen; 
 and when you have also observed the greedy vulture, 
 propelled by hunger, if not famine, moving like the wind 
 suddenly round his course as the carrion attracts his eye ; 
 then will you abandon the deeply-rooted notion, that this 
 bird possesses the faculty of discovering, by his sense of 
 smell, his prey at an immense distance. 
 
 " This power of smelling so acutely I adopted as a fact 
 from my youth. I had read of this when a child ; and 
 many of the theorists to whom I subsequently spoke of 
 it, repeated the same with enthusiasm, the more parti- 
 cularly as they considered it as an extraordinary gift of 
 nature. But I had already observed, that nature, although 
 wonderfully bountiful, had not granted more to any one 
 individual than was necessary, and that no one was 
 possessed of any two of the senses in a very high state of 
 perfection ; that if it had a good scent, it needed not so 
 much acuteness of sight, and vice versa. When I visited 
 the southern states, and had lived, as it were, amongst 
 these vultures for several years, and discovered, thousands 
 of times, that they did not smell me when I approached 
 them, covered by a tree, until within a few feet ; and that 
 when so near, or at a greater distance, I shewed myself 
 to them, they instantly flew away much frightened, the 
 idea evaporated, and I assiduously engaged in a series of 
 experiments, to prove, to myself at least, how far this 
 acuteness of smell existed, if it existed at all." 
 
 His first experiment was as follows : " I procured the 
 skin of our common deer, entire to the hoofs, and stuffed 
 it carefully with dried grass, until filled rather above the 
 natural size, suffered the whole to become perfectly dry, 
 and as hard as leather, took it to the middle of a large 
 open field, laid it down on its back, with the legs up 
 and apart, as if the animal was dead and putrid. I then 
 
SMELL IN VULTURES. 445 
 
 retired about a hundred yards, and on the lapse of some 
 minutes, a vulture, coursing round the field tolerably 
 high, espied the skin, sailed directly towards it, and 
 alighted within a few yards of it. I ran immediately, 
 covered by a large tree, until within about forty yards, 
 and from that place could spy the bird with ease. He 
 approached the skin, looked at it with apparent sus- 
 picion, jumped on it, raised his tail, and voided freely (as 
 you well know all birds of prey in a wild state generally do 
 before feeding), then approaching the eyes, that were 
 here solid globes of hard, dried, and painted clay, attack- 
 ed first the one and then the other, with, however, no 
 farther advantage than disarranging them. This part was 
 abandoned ; the bird walked to the other extremity of the 
 pretended animal, and there, with much exertion, tore 
 the stitches apart, until much fodder and hay was pulled 
 out ; but no flesh could the bird find or smell ; he was 
 intent on discovering some where none existed ; and after 
 reiterated efforts, all useless, he took flight, and coursed 
 about the field, when suddenly wheeling round and alight- 
 ing, I saw him kill a small garter snake, and swallow it 
 in an instant. The vulture rose again, sailed about, and 
 passed several times quite low over the stuffed deer-skin 
 as if loath to abandon so good-looking a prey. 
 
 " Judge of my feelings when I plainly saw that the 
 vulture, which could not discover, through its extraordi- 
 nary sense of smell, that no flesh, either fresh or putrid, 
 existed about the skin, could at a glance see a snake, 
 scarcely as thick as a man's finger, alive, and destitute of 
 odour, hundreds of yards distant. I concluded that, at 
 all events, his ocular powers were much better than his 
 sense of smell." 
 
 In another experiment he directed the carcass of a hog 
 to be put into a deep ravine, and completely covered over 
 with cane, so as effectually to exclude it from the eye, 
 when he saw from time to time many vultures, in search 
 of food, sail over the ravine in all directions, but none 
 
446 SMELL IN GULLS. 
 
 discovered the carcass, although several dogs had visited 
 it, and fed plentifully upon it. This took place in the 
 hottest season of the year, and the smell from the putrid 
 body was so insufferable, that it could not be approached 
 within thirty yards. 
 
 Audubon performed several experiments with similar 
 results, and fully satisfied himself that the turkey buzzard 
 is guided to his prey by sight, and not by smell. 
 
 In support of similar views, it may be mentioned, 
 that in Greenland, when a whale is captured, although at 
 the moment of capture scarcely a bird may be visible, 
 yet before the operation of flencing has been well com- 
 menced, dozens of fulmars and different species of gulls 
 are perceived hastening to the scene from every point 
 of the compass, from the windward as well as from the 
 leeward. In such cases it is impossible to conceive that 
 odorous emanation can extend in opposition to the direc- 
 tion of the wind, even for a few feet. Still, notwith- 
 standing a brisk breeze blowing at the time, birds are 
 seen flying in as great numbers from the windward as 
 from other directions. At the same time, it cannot be 
 disputed that the fulmar and gull tribe, and especially 
 the former, have the apparatus of smell highly developed, 
 and therefore the fair inference is, that they enjoy the 
 faculty in a corresponding degree, and that it is most pro- 
 bably highly useful to them in guiding them to food, 
 placed within the range of its action, though sight be 
 better calculated to detect it at great distances. 
 
 That excellent naturalist, my friend, Macgillivray, in 
 the first volume of his History of British Birds, has the 
 following remarks on the raven : " It has seemed to me 
 strange that in a country where, under ordinary circum- 
 stances, few ravens are seen, so many as from twenty to 
 two hundred or more should collect in a few days. In per- 
 ambulating these islands " (Outer Hebrides) " one scarcely 
 meets with more than a pair in the space of a mile or so ; 
 and in Harris, where their breeding-places were pretty 
 
SMELL IN THE RAVEN. 447 
 
 generally known to me, I could not count a dozen pairs 
 along a coast-line of as many miles. In Pabbay, as men- 
 tioned above, several hundreds had come together, so that 
 the people naturally marvelled whence they had arrived. 
 If, along a coast-line of ten miles, there are ten pairs of 
 ravens, with five young birds to each, or seventy in all, 
 on one of a hundred and forty, there might be nearly a 
 thousand. Pabbay is two miles distant from Berneray, 
 and six from Harris. Even should the wind blow in 
 the latter direction, it is not likely that a raven should 
 smell carrion six miles distant, and in Berneray, which 
 the effluvia might reach, there are not usually more than 
 three or four resident pairs. The birds of the west coast 
 of Lewis, South Uist, and Barra, could not be guided a 
 distance of fifty miles or more by the smell. How then 
 did they arrive in Pabbay ? It seems to me that the phe- 
 nomenon may be explained thus : 
 
 " The two pairs of ravens residing in Pabbay itself would, 
 with their broods, first perceive the carcasses. Those of 
 Berneray might stroll over, as they often do, or they 
 might see the prey, as might those on the Harris coast. 
 Ravens have character in their flight, as men have in 
 their walk. A poet sauntering by a river, a concholo- 
 gist or fish worn an looking for shells along the shore, a 
 sportsman searching the fields, a footman going on a mes- 
 sage, a lady running home from a shower, or a gentleman 
 retreating from a mad bull, move each in a different man- 
 ner, suiting the action to the occasion. Ravens do the 
 same, as well as other birds ; and so, those at the next 
 station, perhaps a mile distant, judging by the flight of 
 their neighbours that they had a prize in view, might 
 naturally follow. In this manner the intelligence might 
 be communicated over a large extent of country, and in 
 a single day a great number might assemble. We know 
 from observation that ravens can perceive an object at a 
 great distance, but that they can smell food a quarter of a 
 mile off we have no proof whatever ; and as we can ac- 
 
448 SMELL IN FISHES. 
 
 count for the phenomenon by their sight, it is unnecessary 
 to have recourse to their other faculties." 
 
 In reptiles the olfactory organs are not much developed. 
 In the turtle the pituitary membrane is of a very dark 
 colour ; the nerve is of considerable size, and its fibres 
 easily traced. In frogs the nostrils are little more than 
 two holes. They are more elongated in serpents, and still 
 more so in lizards, particularly in the crocodile. In none 
 of this class are there any cavities corresponding to the 
 sinuses, so that the air accumulated in the nostrils must 
 be comparatively trifling. 
 
 Some physiologists are inclined to limit the sense of 
 smell to such animals as respire air, and therefore deny 
 its existence in fishes, considering the corresponding or- 
 gans as instruments of taste and not of smell. They do 
 not pretend to deny that the inhabitants of the waters 
 are capable of perceiving very minute differences in the 
 condition of the water, from the presence of foreign bodies, 
 such as dead carcasses, baits impregnated with odorous 
 principles, and so forth ; but in all these cases they hold 
 that they are enabled to detect the existence of these 
 substances in water by taste. There is, however, so much 
 analogy between the two senses, that this appears rather to 
 be a dispute about words than about facts. Moreover, it is 
 quite impossible to arrive at any exact determination on 
 a point of this kind, since we can only imagine what per- 
 ception any animal obtains by the exercise of its or- 
 gans from the sensations excited in ourselves, and by ob- 
 serving the effects produced by similar objects on the 
 same organs in other animals. Fishes are furnished 
 with organs analogous to those of smell in the higher 
 classes of animals, though the cavities have no communi- 
 cation with the mouth or gullet. They are insulated 
 cavities, having valvular lids over their apertures. The 
 lining membrane is beautifully plaited, presenting an ap- 
 pearance that has a striking resemblance to the under 
 surface of several mushrooms, by which the surface is 
 
SMELL IN INSECTS. 
 
 449 
 
 greatly extended : it is abundantly covered with a viscid 
 mucus. The nerves proceed from the anterior ganglions 
 of the brain. In the cod fish they traverse in their course a 
 large cavity, more capacious than that in which the brain 
 itself is contained. This cavity is filled with transparent 
 fluid, and divided by a central partition. As the nerve 
 proceeds forwards it gradually becomes enlarged, and 
 upon the internal surface of the mucous membrane swells 
 into a ganglion, from which numerous soft filaments pene- 
 trate the membrane, apparently to be dissolved, or incor- 
 porated as it were, in the mucus. That the cod is guided 
 by smell in the selection of food must be well known to 
 every one who has taken it with bait in circumstances 
 where he could watch the conduct of the fish. If not 
 very hungry, it may frequently be observed to approach 
 the bait, apparently attracted by the sight, till, at a closer 
 distance, it seems distinctly to smell at it, and if not 
 satisfied, turns aside and neglects it. 
 
 It appears sufficiently established by numerous facts 
 that many insects are able to distinguish odorous princi- 
 ples even at considerable distances. By this sense the 
 common flesh fly is guided to putrid meat, on which she 
 deposits her eggs. In some instances her instinct is de- 
 ceived by the smell of a species of mushroom, which gives 
 off an odour exactly the same as that of putrid flesh. In 
 such a situation, however, the eggs, if hatched at all, 
 must produce maggots that immediately perish for want 
 of proper food. The organs by which insects exercise 
 this sense have not been satisfactorily ascertained. 
 
 In order that a substance produce an impression on the ol- 
 factory organs of animals which breathe air, it is necessary 
 that it be dissolved or suspended in the air ; or, more cor- 
 rectly speaking, it is requisite that the matter should be 
 in the gaseous form when presented to the pituitary sur- 
 face. Some vapours or gases, however, produce no im- 
 pression on the olfactory nerve, and are therefore termed 
 inodorous, such as the vapour of water ; others rouse the 
 
450 CLASSIFICATION OF ODOURS. 
 
 common sensibility of the nose, without affecting its spe- 
 cial sensibility, such as spirits of hartshorn. 
 
 Odours are nearly as various as the principles on which 
 they depend ; consequently all attempts to classify them 
 have completely failed. The division into agreeable and 
 disagreeable is quite inadequate, and its unsatisfactory na- 
 ture sufficiently obvious. It can be applicable only to one 
 species of animals, and even different individuals of the 
 same species are very differently affected by the same sub- 
 stance ; nay, the same individual often receives gratifica- 
 tion from the smell of a substance at one time, which at 
 another was wont to excite disgust ; so much depends on 
 constitution, habit, the state of health, and various other 
 circumstances that cannot be adequately estimated or ac- 
 counted for. The number of odours being so various, it 
 is impossible to designate them otherwise than by compar- 
 ing them with others that are common and well-known. 
 Thus we say the vapour of metallic arsenic has the odour 
 of garlic or an alliaceous smell : in like manner we speak 
 of the violet, rosaceous, musky odours, and so forth. The 
 celebrated Linnaeus, who seems to have had some super- 
 stitious reverence for the number seven, arrays odours into 
 the seven following classes : \st, ambrosiac, in which he 
 places the rose and musk ; ^d, fragrant, as the lily, saffron, 
 jasmine ; 3d, aromatic, such as the laurel, and various 
 spices ; 4tk, alliaceous, as that of garlic ; 5tk, fetid, as in the 
 valerian, and different species of fungi ; 6tk, virous or nar- 
 cotic, as in opium, henbane, &c. ; Jtk, nauseous, as that of 
 melons, cucumbers, and different species of the gourd tribe. 
 
 Odours differ very much as to the permanence of 
 the impression they produce. In some the scent re- 
 mains even for hours after the application of the sub- 
 stance, while others are exceedingly transient in their 
 effect. They differ also in the extent to which their in- 
 fluence extends, or in their diffusiveness ; the effluvia of 
 some being very limited, while others extend to vast dis- 
 tances. It has been stated, that the smell of cinnamon 
 
DIFFUSIBILITY OF ODOURS. 451 
 
 has been wafted on a gentle breeze, so as to be percepti- 
 ble twenty-five miles from the shores of Ceylon. Lord "Va- 
 lentia mentions, that he distinctly smelt it at the distance 
 of nine leagues. The quantity of matter capable of ex- 
 citing the sensation of smell, even in the human subject, 
 is inconceivably minute. Scales on which a few grains 
 of musk have been weighed, have been known to retain 
 the odour of that substance for upwards of twenty years. 
 The distinguished physiologist and excellent mathemati- 
 cian, Haller, kept some papers for more than forty years, 
 which had been perfumed with a single grain of amber ; 
 yet at the end of that time they did not appear to have 
 lost any of their odour. He calculated, that in this in- 
 stance, every inch of their surface had been impregnated 
 by v K s T o\ 4 o o o th of a grain of amber, and that they had 
 scented a stratum of air, at least a foot in thickness, for 
 14,600 days. A certain degree of moisture in the atmos- 
 phere is favourable to the diffusion of odours. The tem- 
 perature of the air has also a considerable effect ; warmth 
 promoting the conversion of the odorous particles into the 
 state of vapour. Hence the flower-garden is at no time 
 the source of greater enjoyment than in the morning, 
 when the dew is evaporating, or after a warm summer 
 shower. Some flowers, however, give off their scent only 
 at certain times, generally when they are fully expanded, 
 and their parts are in the greatest activity. 
 
 Like all the other senses, smell is greatly improved by 
 education. Savages, who are accustomed to pay minute 
 attention to the indications of their external senses, enjoy 
 this faculty in a pre-eminent degree. Humboldt affirms 
 that the Peruvian Indians, in the middle of the night, can 
 distinguish different races by their smell, whether they 
 are European, American, Indian, or Negro. In the case 
 of Mitchell, detailed in last chapter, we have seen that 
 his smell was exceedingly acute, as it is in general in the 
 blind. Sometimes it becomes morbidly sensitive. Thus 
 Cloquet refers to the case of an eminent physician in 
 
452 ORGANS OF TASTE. 
 
 Paris who was tormented with megrim, in the paroxysms 
 of which his smell became morbidly acute. On one oc- 
 casion he was very much annoyed with the smell of cop- 
 per : on a search being made, the source of his annoyance 
 was found in a small brass pin that had been dropt among 
 the bed-clothes. 
 
 TASTE. 
 
 THE seat of this sense is the general lining of the mouth 
 and upper part of the throat, though the superior surface 
 of the tongue is the part on which sapid bodies more com- 
 monly make their impressions. The tongue is chiefly 
 composed of muscular fibres, running in almost every di- 
 rection, and consequently it is possessed- of great versati- 
 lity of motion, and the capability of being moulded into 
 a great variety of shapes. It is formed of two symme- 
 trical halves, and therefore may be considered as a double 
 organ. A slight groove is observable over its upper sur- 
 face, dividing it into right and left. From this groove a 
 dense fibrous septum extends perpendicularly, terminating 
 in the bridle on the under surface. The tongue is very 
 abundantly supplied with blood, and its nerves we have 
 seen are derived from three sources. There has been con- 
 siderable discrepancy of opinion as to which of the three 
 nerves is to be held as the special nerve of taste ; the opi- 
 nion now generally acquiesced in, holds the fifth as the 
 proper nerve of taste, as well as of common sensibility ; 
 the ninth as that of voluntary motion ; and the eighth 
 as the means whereby the organ is brought into associa- 
 tion with the throat, gullet, larynx, and so forth. 
 
 Three varieties of papillae are seen on the tongue, dis- 
 tinguished by their forms. About a dozen comparatively 
 large ones are situated towards the root, and are named 
 from their shape lenticular. They belong to the class of 
 mucous follicles, several of which are disseminated over the 
 whole surface of the mouth, as on other mucous membranes, 
 to furnish their viscid secretion. Those at the root of the 
 
ORGANS OF TASTE. 453 
 
 tongue are, however, larger than usual, and, along with the 
 almonds of the throat, afford the mucus with which the 
 bolus of food becomes besmeared in the act of deglutition. 
 The other two sets of papillae are instruments of gustation : 
 one set consists of small rounded heads, supported on 
 short stalks ; their form having suggested the idea of a 
 mushroom, has obtained for them the name of fungiform. 
 The other, the most numerous and minute, impart to the 
 tongue its velvety appearance, and are termed the coni- 
 cal or filiform. These sensitive papillae are furnished 
 with numerous blood-vessels, and are capable of becoming 
 erected, thus adapting themselves to the active or passive 
 condition of the sense of taste. That these are the pecu- 
 liar seat of taste, appears from the application of sapid 
 bodies, for, by the aid of a magnifier, they may be seen 
 to dilate and erect themselves, when a camel's-hair pencil 
 moistened with vinegar, or any other sapid substance, is 
 brought in contact with them. 
 
 The tongue is not the only instrument of this sense. 
 The lips, gums, palate, and throat likewise participate. 
 Upon all of those parts the fifth nerve is distributed, be- 
 coming the channel for the transmission of the sensation to 
 the brain. None of them, however, are so well adapted 
 for being exercised actively, or for undergoing modifica- 
 tion, according to circumstances, as the tongue. 
 
 In order that the sense be fully exercised, it is necessary 
 that a due supply of moisture be furnished to the diffe- 
 rent surfaces. Thus the salivary glands are in some 
 measure requisite to the proper exercise of the function, 
 partly by preserving the parts in a proper condition for 
 their office, and partly by serving as a solvent for the sub- 
 stances which excite the sensation ; for it is necessary, in 
 order to affect the nerves, that the substance be in solu- 
 tion, otherwise no impression is produced. Insoluble 
 substances, therefore, are totally insipid. Several sub- 
 stances insoluble in water, or in the saliva, but soluble 
 in alcohol or other fluids, produce an intense sensation 
 
454 CLASSIFICATION OF SAVOURS. 
 
 in the latter case, while in the former they are quite in- 
 ert. The numerous salts entering into the composition 
 of the saliva no doubt are efficient agents in many cases 
 in reducing substances to a proper condition for making 
 an impression on the gustatory organs. Thus metals 
 impart a peculiar taste, though they are quite insoluble 
 in simple water. Metals applied to the organs of taste 
 in such a manner as to call forth electric action, power- 
 fully impress them. If a thin plate of one metal be placed 
 under the tongue, and another of a different kind on its 
 upper surface, on bringing the edges of the two in con- 
 tact at the tip, taste is powerfully excited. On touching 
 the surface of the tongue with the point of a wire con- 
 nected with the positive pole of an electric instrument, a 
 sour taste is experienced, while the negative pole excites 
 an alkaline taste. It does not follow from these experi- 
 ments that electricity has in itself any savour, but the 
 phenomenon probably arises from electricity disengag- 
 ing an acid in the one instance, and an alkali in the 
 other, either of which may readily be derived from the 
 saliva. Or the impression from electricity may depend 
 on the electric excitement calling forth the special sensi- 
 bility of the gustatory organs, in the same manner as 
 this agent rouses the special sensibility of the other senses. 
 Although solution be a necessary condition, so that bodies 
 may impress this sense, yet all liquids are not sapid, nor 
 is savour in proportion to the solubility of different sub- 
 stances : pure water, for instance, has no taste, and gum- 
 arabic, isinglass, &c., though abundantly soluble, have 
 very little. 
 
 Savours, like odours, are innumerable, and so various 
 that they do not admit of distinct and satisfactory classi- 
 fication ; though we readily comprehend the terms sweet, 
 bitter, sour, acrid, saline, &c., yet each of these differs 
 in intensity, as well as other shades of character, accord- 
 ing to the nature of the material which produces it; 
 and with respect to an infinite number of other savours, 
 
ACQUIRED TASTES. 
 
 455 
 
 we can only convey an idea of them by referring to the 
 individual substance which they may characterize. They 
 vary also according to the permanence or transientness 
 of their impression ; some being merely momentary, while 
 others remain fixed as it were for hours. The more per- 
 manent savours are sometimes advantageously employed 
 to forestall the sense of taste before the exhibition of 
 nauseous drugs. For this purpose, aromatics and bitters 
 are well adapted. This is further exemplified in the ex- 
 periment where a person blindfolded has given to him 
 in rapid succession brandy, rum, gin, or different kinds 
 of wines. After a few contacts, all distinction becomes 
 impossible, even by the. most experienced. It is neces- 
 sary that time be afforded for allowing the impression to 
 be made. Accordingly, tasters of wine, tea, and so forth, 
 take a small portion, and move it over the whole surface 
 of the mouth, so as to extend the sphere of its action ; 
 while medicinal draughts are generally gulped over as 
 speedily as possible. Different parts of the mouth pos- 
 sess different degrees of susceptibility for sapid bodies ; 
 some producing their impression chiefly on the tip, sides, 
 or base of the tongue ; others on the lips, gums, or palate ; 
 while others again impress principally the throat. Strong 
 savours impair the sensibility to others that are feeble, in 
 the same way that a strong light impairs vision, and a 
 loud noise audition. In like manner, the handling of 
 hard and rough substances diminishes the sense of touch 
 for judging of soft and delicate fabrics, and strong and 
 pungent odours deaden the olfactory organs. 
 
 No sense is more influenced by habit than taste. Many 
 substances that are exceedingly disgusting at first, be- 
 come not only less so, but even highly grateful by cus- 
 tom. Fashion or necessity may at first be the cause of 
 their being taken, but habit soon renders them eagerly 
 sought after. Of this we have innumerable instances in 
 every state of society, in every country, and in all ages, 
 such being known by the designation of acquired tastes. 
 
456 
 
 ACQUIRED TASTES. 
 
 Thus the most celebrated sauce of antiquity was prepared 
 from the half-putrid intestines of fish. Assafcetida is a 
 favourite condiment with some orientals, and a rotten 
 egg, especially if it contains a chick, is highly esteemed 
 by the Siamese. Fish in an advanced state of decompo- 
 sition is relished in the northern and western islands of 
 Scotland, under the name of sour-fish. Dried putrid mut- 
 ton is habitually eaten in Iceland and Faroe ; and, in like 
 manner, fully to enjoy high-seasoned game and venison, 
 adapted to the palate of the epicure, some degree of edu- 
 cation is necessary. Numerous other examples of acquired 
 taste might be cited that are sufficiently well known, such 
 as a relish for olives, garlic, parmesan cheese, and so forth. 
 The susceptibility of the organs of taste to pleasurable 
 sensations depends very much on the state of the stomach, 
 even in health. With whatever gout we enjoy a favou- 
 rite dish when we at first sit down with a good appetite, 
 as hunger becomes appeased the relish is diminished, suc- 
 ceeded by satiety ; and if, notwithstanding, eating be per- 
 sisted in, nausea and disgust at length supervene, and 
 the glutton is compelled to desist. This consent subsist- 
 ing between the stomach and the organ of taste is an im- 
 portant and wise provision, informing the animal when 
 a sufficiency of food has been taken. 
 
 In general, those articles that are agreeable to the 
 sense of taste are safe and nutritious ; but this is not in- 
 variably the case ; for one of the most deadly poisons 
 known, the prussic acid, has both an agreeable odour 
 and savour, on account of which it is occasionally used 
 to impart flavour to dishes and liqueurs, such as noyau. 
 Though they are thus rendered fascinating, they are not 
 without danger. Many substances which are at first 
 highly acceptable to taste become after some time, and 
 particularly if too freely indulged, disagreeable. On this 
 principle the grocer acts with a new apprentice, allowing 
 him unrestricted indulgence of his appetite for sweets, 
 till the appetite becomes cloyed, and all temptation dis- 
 
ACQUIRED AND MORBID TASTES. 
 
 457 
 
 appears: on the other hand, some substances become 
 highly .grateful by use, that at first are disrgreeable to 
 the palate. This is remarkably the case with bitters, 
 aromatic spices, and pungent stimulants. 
 
 The alteration which the constitution undergoes in the 
 progress of age produces striking changes in respect to 
 the relish for various articles of food and drink. Such 
 changes are still more remarkable as resulting from 
 different states of health, a morbid condition of this 
 sense being a frequent concomitant of disease. In jaun- 
 dice every thing appears bitter ; in other affections taste 
 is variously vitiated ; while in many conditions it is alto- 
 gether abolished. Frequently these symptoms depend on 
 the state of the stomach thus, the presence of acrid 
 matter gives rise to false appetite but in other cases 
 this may depend on derangement of other functions, or 
 on a peculiar state of the constitution at the time. Taste 
 frequently becomes remarkably depraved, so that chalk, 
 brick-dust, cinders, and the like, are greedily sought after. 
 We have frequently a forcible instance of this in the preg- 
 nant female, where the most out-of-the-way articles are 
 ardently longed for, though there is no reason to believe 
 that it ever extends in reality to articles of jewellery or 
 dress, as has been alleged. The most urgent desire is 
 often experienced in such cases for substances which were 
 perhaps previously repugnant to the individual ; and it 
 is apt likewise to occur capriciously at the most unseason- 
 able hours, as in the middle of the night. 
 
 The lower animals sometimes evince a similar appetite 
 in similar conditions. The settlers in some parts of New 
 South Wales have sustained serious losses from a propen- 
 sity shewn by breeding ewes for licking earth impreg- 
 nated with saline matter. A few extracts from Mr 
 Bennett's Wanderings in New South Wales, &c. will af- 
 ford evidence of this. He says, " On account of the 
 morbid appetite existing in the sheep, which I am about 
 to relate, their natural innocent dispositions are changed ; 
 
458 ACQUIRED A:N T D MORBID TASTES. 
 
 they become carnivorous and savage ; and it is difficult to 
 drive them away from the pits in which the earth impreg- 
 nated with the alkaline salts may be situated ; although, 
 when taken to afresh run, they proceed feeding as usual, 
 until this salt earth is again discovered, when they be- 
 come addicted to the unnatural custom of devouring their 
 lambs. On discovering one of the pits, they rush to it 
 with activity, licking and gnawing the earth with avi- 
 dity." 
 
 " Among the breeding ewes, eating earth was followed 
 by their devouring the progeny of the other ewes when 
 brought forth ; and on the shepherds endeavouring to save 
 from their voracity the lambs just born, they would rush 
 upon them, biting their trousers, and making strenuous 
 efforts to seize the lambs in the arms of the men." " After 
 eating the earth, they do not feed on the herbage in any 
 regular manner ; they are restless, picking a bit of grass 
 here and there, according to the statement of the shep- 
 herds, until, on approach of evening, they feed in a more 
 regular manner." 
 
 In a letter addressed to government on this subject 
 by a Mr Dutton, and quoted by Mr Bennett, the destruc- 
 tive effects produced among the flocks are clearly point- 
 ed out. He says, " The disadvantages which I have 
 thus to detail to you arise from the novel disease with 
 which the sheep are affected. It appeared after the first 
 lambing, and within four months from the time of my 
 occupation of the land in question. Its unaccountable 
 and destructive nature renders my selection utterly use- 
 less. The nature of the disease, as far as I have yet re- 
 marked, is as follows : The sheep, in the first place, de- 
 vour the earth ravenously, the pasture being at the same 
 time luxuriant, principally rib-grass, and other succulent 
 herbs; they become speedily emaciated from this unnatural 
 diet, more particularly as the lambing season advances ; 
 and when lambing commences, the other ewes surround the 
 one lambing, and devour the young as they emerge from 
 
ACQUIRED AND MORBID TASTES. 459 
 
 the mother. The lambs saved through the care of the 
 shepherds become poverty-stricken, from the low condition 
 of the mothers, and generally die before they become a 
 month old. Thus, instead of having twelve hundred 
 lambs this season, as my regular increase, I do not count 
 four hundred ; besides a very great decrease from mor- 
 tality in the maiden sheep, originally purchased at high 
 prices ; the number of shepherds required being at the 
 same time twice beyond the proportion usual in the co- 
 lony." 
 
 Mr Bennett observes, " Although the breeding ewes 
 suffer both in health and acquire the morbid appetite of 
 devouring the progeny of others, yet rams, wedders, and 
 ewes not breeding, fatten to an extraordinary degree upon 
 the same pasturage where breeding ewes had become 
 miserably lean, and died in numbers, from being in so low 
 a condition. On one of these spots I saw a wedder 
 killed from a flock, which was so fat as to render the 
 meat almost uneatable ; and Mr Manton, who, from the 
 cause before mentioned, had been obliged to remove all 
 his breeding ewes from his pastures about Morrumbidgee, 
 would, nevertheless, send his rams and wedders on the 
 luxuriant pasturage, as the best place to fatten them." 
 
 From what has been stated, it will be seen that the sense 
 of taste is not confined to the tongue in the human subject : 
 we are therefore not entitled to infer, because in some of 
 the lower animals the tongue is presented only in a rudi- 
 mentary state, and in others, from its being of dense tex- 
 ture, or covered with prickles or scales, that they are con- 
 sequently destitute of this sense. Even in man there 
 have been instances of individuals born without a tongue 
 possessing the faculty, or of others in whom the tongue 
 has been lost, and the sensation remained exercised by 
 other parts of the mouth. Blumenbach says, " I have 
 seen an adult, and, in other respects, well-formed man, 
 who was born without a tongue. He could distinguish, 
 nevertheless, very easily the tastes of salts, sugar, and 
 
460 THE TONGUE. 
 
 aloes, rubbed on his palate, and would express the taste 
 of each in writing." 
 
 None of the lower animals possess a tongue exactly 
 like that of man. Even in apes, that approach nearest in 
 their organization, it is comparatively much elongated. 
 In ruminants, the tongue is covered with a dense cuticle, 
 studded over with numerous pointed papillae, especially 
 towards the root. From the direction of these papillae 
 backwards, and from the waving ridges on their palates, 
 they must derive considerable advantage in collecting 
 and swallowing the tender and succulent herbage on 
 which they feed. In the cat tribe, the sharp horny 
 prickles situated on the tongue must enable them to take 
 a firm hold. In the lion and tiger, these prickles are 
 sufficient to tear off the skin even of large animals. Ant- 
 eaters are furnished with a very long and exceedingly 
 slender tongue, covered with a viscid adhesive secretion, 
 whereby they are enabled to seize on their prey, on thrust- 
 ing it into the ant-hill. Those whales which obtain their 
 food by filtering water containing it through the plates 
 of the peculiar substance termed whalebone, have an 
 enormous tongue, though it may be doubted whether it 
 be endowed with the sense of taste, as these animals re- 
 ceive indiscriminately all substances which are large 
 enough to pass between the plates. Their mode of feed- 
 ing is curious, and conducted in the following manner : 
 The arctic seas abound with several species of small me- 
 dusae or sea-blubber : so crowded are they, that when the 
 water is still, the surface smooth, and particularly when 
 seen between the observer and a large ice-berg deep in 
 the water, they present a striking resemblance to a thick 
 snowfall, when the flakes are large and the air is cairn. 
 This is the principal food of the common Greenland whale. 
 That huge animal has projecting downwards from the 
 upper jaw, a kind of palisade, formed of several hundred 
 plates of whalebone, the outer edges of which are sharp, 
 the inner fringed with long hair-like appendages, the 
 
THE TONGUE. 461 
 
 spaces between the plates being little more than half an 
 inch. The length of the plates sometimes exceeds twelve 
 feet, where the mouth opens widest that is, about the 
 middle. This palisade, when the mouth is closed, is 
 covered by the enormous fleshy lower-lip, but when open, 
 it presents a kind of grating, through which the water, 
 loaded with medusae and other small animals, flows. 
 The mouth is furnished with an immense mass of soft 
 spongy texture constituting the tongue, to all appearance 
 better adapted for licking the food from the hairy whale- 
 bone roof, and transferring it to the gullet, than to serve 
 as an instrument of taste. 
 
 In many birds, from the horny consistence of the 
 tongue, it cannot well be imagined to serve the purposes 
 of taste. In the toucan, it is several inches in length, 
 and extremely narrow, like a long stripe of whalebone. 
 Fixed to the tip of the tongue of the woodpecker, there 
 is a long sharp-pointed spear-like body with serrated 
 edges, for piercing and seizing on insects burrowing be- 
 neath the bark of trees. On the other hand, several 
 animals of this class have soft fleshy tongues, well adapted 
 to the exercise of taste, as in the parrot tribe. 
 
 Among reptiles, the tongue presents a great variety of 
 forms and applications. In the crocodile it is so small 
 and immoveable as to have led some naturalists to deny 
 its existence. In the serpent tribe it is forked, and pos- 
 sessed of considerable mobility. In the frog it is folded 
 back in the state of inactivity ; but when the animal is about 
 to seize an insect, it suddenly unfolds and projects it out 
 of the mouth. The tongue of the cameleon is contained 
 within a sheath, admits of being projected forth to the 
 extent of six inches, and is besmeared with glutinous se- 
 cretion. In the twinkling of an eye it is darted out to 
 catch its food, which chiefly consists of flies. 
 
 Fishes have the tongue merely in the rudimentary 
 state, and generally fixed near the throat. It is often 
 furnished with teeth. Whether it is subservient or not 
 
462 TASTE IN INSECTS, ETC. 
 
 to taste admits of doubt, as there are no means of deter- 
 mining the fact. Other parts of the mouth, however, 
 may act in this way, as the soft and irritable body on the 
 palate of the carp. 
 
 That many of the invertebrated animals are endowed 
 with taste, we have every reason to believe ; such as bees, 
 wasps, flies, and leeches. The organs subservient to this 
 purpose, however, have not as yet been satisfactorily as- 
 certained. The condition in which substances most readily 
 act upon the sense (if indeed it be not absolutely essential) 
 is the state of solution. Of the three conditions of matter, 
 then, touch judges most correctly of solids, taste appreciates 
 fluids, and smell takes cognisance of gaseous bodies. In 
 order to excite smell, it is necessary that the odorous par- 
 ticles be inhaled with the breath, and drawn with it through 
 the nostrils, where they come in contact with the imme- 
 diate seat of the sense. With respect to savours, it is 
 requisite that they be dissolved and brought in contact 
 with the papillae, in which twigs of the gustatory nerves 
 are incorporated, on which the impressions are made, sub- 
 quently to be transmitted to the seat of perception. 
 
 The intimate connexion subsisting between smell and 
 taste is sufficiently demonstrated in the closure of the 
 nostrils, when the latter becomes much blunted, and 
 almost abolished ; wherefore it is nearly impossible to dis- 
 tinguish between the tastes of different substances, as 
 between sweet and bitter, sour and alkaline, and so forth, 
 a circumstance that is occasionally taken advantage of 
 when nauseous medicines are to be administered, by shut- 
 ting the mouth when the draught is swallowed. 
 
 It has been already observed, that neither smell nor 
 taste rank high as channels of intellectual information, 
 although by cultivation their powers are much extended, 
 and their accuracy vastly improved. Dr Kitchener as- 
 serts that some epicures are actually able to tell from 
 what precise reach of the Thames a salmon had been 
 caught, when presented at table. But such refinement in 
 
USE OP TASTE. 463 
 
 either of these senses may truly be held as by no means 
 desirable, since they are liable to so many causes that 
 excite in them offence and annoyance, rather than grati- 
 fication and satisfaction. Yet in many of the lower 
 animals they are no doubt of the most essential import- 
 ance in enabling them to select that kind of food that is 
 proper for them, and in rejecting such as might prove 
 prejudicial. 
 
464 
 
 CHAPTER XII. 
 
 MOTION. 
 
 Organs of Motion consist of the Passive and the Active Bones Their Textures and 
 various Forms Their Chemical Constitution Adaptation to the purposes they 
 subserve Variety of Connexion Gristle Its peculiar Organization Its great 
 Elasticity Forms the Principal Springs of the Animal Machine Subservient 
 to Mechanical Movements Elastic Cushions Ligament Its Structure A very 
 Common Tissue in Animal Bodies Presents great varieties, and subservient to 
 many purposes Elastic Ligamentous Tissue a substitute for Muscular Power 
 . Continues its Action in the Dead Body Tendon Varieties in the Form of 
 Bears concentrated Muscular Force Transfers Muscular Power Muscular 
 Fibre Characteristic Property Vital Organization Chemical Constitution 
 Muscular Action Changes in the State of Action and Repose Exciting causes 
 of Muscular Action The Will Instinct and Sympathy Involuntary Muscu- 
 lar Motion Influence of Disease Mechanical and Chemical Excitants Re- 
 markable Effects of Galvanism on the Body of an Executed Criminal Various 
 Modifications of the Actions of Muscles in the Preservation of the Attitudes, 
 and in Performance of Motion Force of Muscles How modified Muscular 
 Vigour in Different Races Duration of Action Velocity of Motion In Man 
 In Animals Mutual adaptation of Structure and Function in Animal Bodies. 
 
 IN the last four chapters we have had tinder consideration 
 the instruments by which we become acquainted with the 
 external world around us. We have now to inquire into 
 the mechanical means whereby we are enabled to react on 
 surrounding objects, to change our positions, to fix our at- 
 titudes, and to exercise several of those functions to which 
 our attention has already been directed. For these pur- 
 poses the higher classes of animals are furnished with 
 several distinct organs, of various textures and adaptations, 
 differing in their forms, number, proportion and structures, 
 according to the rank and circumstances of the animal. 
 The organs subservient to the form, motions, stability. 
 
CONSTITUTION OP BONE* 465 
 
 and postures of the body, consist of two classes, the passive 
 and the active. To the former belong the bones, carti- 
 lages, ligaments, and tendons ; the latter comprises the 
 muscular fibre. A few general observations respecting 
 each of these tissues will be necessary. 
 
 Bone. The bones constitute the hardest and most 
 solid parts of the whole system, and are the principal 
 parts that give it form, stability, and posture, forming, as 
 it were, the frame-work of the animal machine. In man 
 and the higher order of animals, the skeleton, generally 
 speaking, is internal ; while in the lower tribes, as insects 
 and Crustacea, such as the lobster, crab and others, it is 
 placed externally. Including the teeth, the number in 
 the human adult amounts to about 245. They are usually 
 arranged in three classes, the long or cylindrical, such as 
 the bones of the arms and legs, the broad flat bones, as 
 the shoulder-blade, and the round or angular bones, as 
 those of the wrist and ankle. When the broken surface of 
 a bone is examined under a good microscope, it presents an 
 uniform surface, abundantly supplied with minute blood- 
 vessels, without any appearance of fibres or plates. The 
 different densities which bones present, arise from diffe- 
 rences in the 'mechanical arrangement of the particles com- 
 posing them. In the thigh-bone, for example, the ex- 
 tremities bulge out so as to afford a more extensive sur- 
 face for the insertion of muscles and ligaments, and to 
 increase their levers by throwing them further from the 
 centre of motion. In the shaft, where strength is chiefly 
 required, the surface is compact, either surrounding a 
 spongy, cellular, or cancellated structure, or forming a hol- 
 low tube filled with marrow, thus in the most perfect man- 
 ner combining the greatest degree of strength with the 
 least degree of weight and expense of material. It can 
 be mathematically demonstrated that the resistance of a 
 cylindrical body, such as a pillar or mast, to a force ap- 
 plied transversely, is increased in proportion to its dia- 
 meter. The same quantity of matter, therefore, placed 
 
 x 2 
 
466 CONSTITUTION OF BONE. 
 
 in the circumference of a circle, produces a stronger bone 
 than if united in the centre with proportionally dimi- 
 nished diameter. 
 
 The broad bones either offer an extensive surface of 
 defence, as in those of the skull, or afford an extended 
 surface for the origin and insertion of muscles, as the 
 shoulder blade. The rounded bones composing the spi- 
 nal column, and the angular bones of the wrist and ankle, 
 have the osseous matter extended over a considerable space, 
 in order in the most efficient manner to combine the pro- 
 perties of lightness and strength. ' 
 
 The bones are covered with sheathings of dense mem- 
 brane, with which they are closely united by means of 
 an infinite number of minute blood-vessels. Other blood- 
 vessels enter by appropriate holes in the shafts of the 
 long bones, while a considerable number enter at their ex- 
 tremities. They are thus plentifully supplied with blood. 
 Though many of the vessels are too minute to admit of the 
 free passage of the red particles, yet they readily transmit 
 the colouring matter of madder. Accordingly, when 
 animals are supplied with food mixed with that substance, 
 in a few days the bones are rendered red, or of a pinkish 
 colour, and on the discontinuance of it, in a short time 
 their natural colour is restored, shewing the rapidity with 
 which deposition and absorption is carried on even in the 
 healthy state. Of this we have numerous proofs afforded 
 by accident and disease. How soon, for instance, in 
 healthy vigorous persons are the fractured ends of a bone 
 again firmly united. 
 
 In the lattice work of the spongy bones, and the canals 
 of those of a cylindrical form, there is everywhere distri- 
 buted a delicate membranous web, in the cells of which 
 a modification of fat is secreted, well known under the 
 name of marrow. The purpose it serves, or whether it 
 be of any particular use further than as a reservoir of 
 nourishment, has not been satisfactorily ascertained. It 
 is found in greater quantity in the adult and aged than 
 
CONSTITUTION OF BONE. 467 
 
 in the young ; in the latter, indeed, its place is occupied 
 by a gelatinous fluid. 
 
 It is impossible, consistently with our limits and objects, 
 to advert to the infinite varieties of form, texture, and 
 densities that bones present, not only in different animals, 
 but in the same species, in different ages, sexes, and cir- 
 cumstances both of health and disease, all of which exert 
 a powerful influence on the form and development of this 
 part of the animal structure. 
 
 Chemical examination shews that bone consists of 
 earthy and animal matter, though chemists are not alto- 
 gether agreed as to the proportions of the materials, or 
 whether some of the products afforded are or are not to 
 be held as resulting from the processes to which they are 
 subjected. According to Berzelius, in 100 parts from 
 the thigh-bone of an adult, the following is the result of 
 analysis : 
 
 Gelatin 32.17 
 
 Blood-vessels 1.13 
 
 Phosphate of lime 51.04 
 
 Carbonate of lime 11.30 
 
 Fluate of lime 2.00 
 
 Phosphate of magnesia 1.16 
 
 Muriate of soda and water. . . 1.20 
 
 100.00 
 
 From the above it appears that about a third part of the 
 substance consists of animal, the remainder being earthy 
 matter. The most minute particle of bone that can be 
 examined yields a portion of animal and earthy sub- 
 stance. Both may be held, therefore, as essential to its 
 composition, and existing in a state of chemical union, 
 and not as a mere mechanical mixture. By subjecting 
 bones to chemical processes, we are enabled to separate 
 the respective constituents from each other. Thus, when 
 
468 CONSTITUTION OF BONE, 
 
 immersed for some time in water acidulated with nitric, 
 acetic, and especially with muriatic acids, though they 
 retain their size and form, their weight is considerably 
 diminished, and they are rendered soft, pliable, and elas- 
 tic. Again, if subjected to strong white heat, as in a 
 charcoal fire, and afterwards allowed gradually to cool, 
 they appear to have undergone no alteration in figure or 
 bulk, but they are rendered white as chalk ; their weight 
 is lessened, and they become extremely brittle. By the 
 former process, the earthy matter is removed through the 
 agency of the acid, leaving the animal matter unaltered ; 
 by the latter, the animal matter is dissipated by the heat, 
 and the earthy substance alone remains. 
 
 The gelatin appears to be in a peculiar state of mo- 
 dification; for although the bones of young animals 
 afford a portion of that substance, still it is only in 
 an inconsiderable quantity. That it exists, however, is 
 proved from their yielding it by long boiling in water, 
 especially in a proper apparatus, as in Pappin's digester, 
 where the heat can be employed considerably above the 
 ordinary boiling point ; and thus a portion of nourish- 
 ment may be abstracted from them. Lately in France 
 biscuits were prepared from bones for the supply of the 
 army of Algiers. Bones are likewise used in the manu- 
 facture of glue. The proportion between the animal and 
 earthy substances varies in different individuals, and in 
 the same individual at different periods of life, and under 
 various conditions of health. In youth the former pre- 
 dominates, while in old age the latter is in the greater 
 proportional quantity. Sometimes the earthy matter is 
 so deficient that the bones have not the necessary degree 
 of firmness and rigidity. The consequence is, that those 
 parts of the skeleton which have to support any conside- 
 rable weight bend under it, as the spine, the bones of the 
 pelvis, and of the lower limbs. Subsequently, on the de- 
 position of the earthy matter, they are rendered sufficient- 
 ly dense and compact ; but the distortion becomes fixed 
 
CONSTITUTION OF CARTILAGE. 469 
 
 and permanent. On the other hand, a deficiency of ani- 
 mal matter occasionally happens, whereby the proper de- 
 gree of tenacity is wanting, and they are more readily 
 broken by slight blows or falls. 
 
 Among the principal uses of bones are the following : 
 1st. They afford firm pillars of support, in the preserva- 
 tion of the attitudes and relative position, and furnish 
 attachments for the more flexible parts, ^dly. They serve 
 as levers and as fixed points of attachment for the muscles 
 by which the various movements are performed ; and, 
 3dly. They constitute the chief strength of the cavities 
 for containing the delicate and important organs so essen- 
 tial to the life and well-being of the animal, as the cavi- 
 ties of the skull and spinal canal, for the lodgment and 
 protection of the most important parts of the nervous 
 system ; the cavities of the orbits, ears, nostrils, and 
 mouth, for the delicate organs of the senses; those of 
 the chest, abdomen, and pelvis, for the principal organs of 
 circulation, respiration, digestion, &c. 
 
 The bones are variously connected with each other by 
 joints or articulations, which admit of different degrees of 
 motion, both in extent and variety. Some of these con- 
 nexions allow free, easy, and conspicuous motion, as the 
 shoulder and hip joints ; others of motion that is rather 
 obscure, as in the instep of the foot ; while in others, 
 again, the motion is next to imperceptible, as the bones 
 of the skull and face. 
 
 Cartilage is a peculiar animal tissue, well known under 
 the name of gristle, of a pearl colour, and possessing a 
 high degree of elasticity. When cut, it presents an uni- 
 form smooth surface, without any perceptible traces of 
 distinct organization, but has an appearance like firm 
 jelly. Neither blood-vessels nor nerves can be traced into 
 the substance of cartilage ; not that they do not exist, but 
 they are so minute as altogether to elude the most scru- 
 tinizing inspection. Where, however, it comes in contact 
 with the growing extremities of bones, blood-vessels can 
 
470 USE OF CARTILAGE. 
 
 readily be traced to its margin, and when divided in a 
 living animal with a sharp knife, the smooth surface is 
 speedily bedewed with a serous exudation. In jaundice, 
 too, it becomes tinged with the prevailing colour which 
 characterizes that disease \ thus proving the existence of 
 capillary circulation throughout its texture. 
 
 Cartilage furnishes a smooth elastic covering to the 
 articular surfaces of bones in the moveable joints. From 
 its smoothness, density, and elasticity, it is admirably 
 adapted for facilitating motion, and diminishing the ef- 
 fects of friction. By immersion for some little time in 
 nitric acid, and then in water, its intimate structure may 
 be unfolded, when it will be seen to consist of an infinite 
 number of minute fibres, arranged perpendicularly, like 
 the pile of velvet. We in this way perceive that in the 
 construction of the joints millions and millions of springs 
 of the most curious and excellent contrivance stand per- 
 pendicular to the direction of the force applied, bend to 
 pressure, and on its removal regain their form by their 
 elasticity. When we stand in the erect posture, the 
 number of minute but efficient springs on which the 
 weight of the body rests in the several joints of the back, 
 in the hip, knee, and ankle joints, infinitely surpasses the 
 powers of the human mind to calculate, or even to ima- 
 gine. 
 
 In those parts of the body which require a certain de- 
 gree of firmness and resistance, combined with flexibility 
 and alteration of figure and posture, cartilage enters into 
 their construction from combining these properties. When 
 treating formerly of the organs of voice, we have had oc- 
 casion to advert to the manner in which it contributes to 
 the formation of that apparatus. In the construction of the" 
 chest, too, cartilage is adopted for fixing the ribs to the 
 breast -bone, and for connecting them with each other ; 
 and we have seen that in tranquil breathing muscular 
 power is only required in the act of inspiration, the me- 
 chanical conformation of the chest, especially in the pre- 
 
FIBRO-CARTILAGE. 
 
 471 
 
 sence of the cartilages of the ribs, being sufficient to bring 
 it to the state of expiration to the necessary extent. 
 
 A modification of cartilage, termed fibro-cartilage, is 
 found in certain joints. It consists of a mixture of liga- 
 mentous fibre with cartilage, or rather it is cartilage in 
 a fibrous form, being in this condition better adapted to 
 the peculiar purposes required. In the articulation of 
 the lower jaw, in the joints between the collar and breast- 
 bones, at the wrist and knee joints, there are found move- 
 able bodies of this construction interposed between the 
 articular surface of the bones, thus separating them to a 
 certain extent from each other, and thereby rendering 
 the motions more free and extensive. They likewise 
 serve as cushions for the diminution of the jar to which 
 the ends of the bones are exposed. In another modi- 
 fication, somewhat similar to this, we see them inter- 
 posed between the vertebrae of the back, where the most 
 excellent example of cushions of this kind is presented. 
 The cartilaginous fibres of these intervertebral cushions 
 are intermingled with a liquor of a thick and viscid con- 
 sistence. This liquor is in the greatest proportion in 
 the centre, the number of the fibres increasing towards 
 the circumference. Thus most admirable cushions are 
 formed for the support of the weight of the body, and for 
 the admission of free and easy movement to the necessary 
 extent. 
 
 A combination of ligament and cartilage is interposed 
 between several bones that admit of scarcely perceptible 
 motion, as the collar-bone with the shoulder-blade, and 
 the different bones of the pelvis. Cartilage is also at- 
 tached to the margins of some of the broad flat bones, in 
 order to increase the extent of their surface. 
 
 Like the bones, cartilages receive dense membranous 
 sheathings closely attached by blood-vessels and tough 
 filamentous cords, whereby their strength and tenacity 
 is greatly increased. 
 
 Cartilage presents some of the properties of coagulated 
 
472 LIGAMENTOUS TISSUE. 
 
 albumen ; the stronger acids dissolve it, such as the nitric, 
 sulphuric, and muriatic ; but the weaker., such as vinegar, 
 have little effect, unless it be long macerated in them, 
 when it is rendered soluble in water, and appears to be 
 converted into a kind of jelly. Gelatin may likewise be 
 procured from it by long boiling. 
 
 'Ligament is one of the toughest and strongest tissues in 
 the animal body. It consists of strong bluish or grey fibres 
 of satiny lustre, intricately interwoven together in various 
 directions, so as not to admit of being unravelled. This 
 tissue enters very extensively into the construction of the 
 body, and presents great diversities in form, arrangement, 
 and texture, according to the purposes to which it is subser- 
 vient. All the moveable joints are furnished with liga- 
 ments. In some, as the shoulder-joint, there is merely 
 a cup-shaped sheath surrounding the articulation, of diffe- 
 rent degrees of strength, at various points of the circum- 
 ference, according as it is more or less supported by 
 muscles. This conformation admits of free and extensive 
 movement in every direction. In other joints, where the 
 motions are limited to certain directions, as in the elbow 
 and knee, besides the general capsular investment, there 
 are, in addition, round or flattened bundles of great strength, 
 which not only serve the purpose of binders, but like- 
 wise confine the movements to the required directions. 
 The internal surface of the ligamentous capsules, as well 
 as the cartilaginous coverings of the bones, have a delicate 
 expansion of secreting membrane for the supply of the 
 liquor of the joints, termed synovia, which lubricates the 
 surface, and serves the same purpose that oil does in a 
 piece of machinery. Every joint of the body has its liga- 
 ments accurately adjusted to its individual mechanism, 
 so that every one of them serves to illustrate the wisdom 
 of design, the excellence of the contrivance, and the 
 beauty of the workmanship in their machinery. 
 
 In other parts, ligaments pass from one point of a bone 
 to another, or fill up holes where from their toughness 
 
LIGAMENTOUS TISSUE. 473 
 
 they afford a surface for the attachment of muscles of 
 greater strength and lightness than bone could have fur- 
 nished. In some situations, again, they form strong 
 bandages, as at the wrist and ankle, and along the fingers 
 and toes, where they bind down muscles or their tendons, 
 and enable them to act with greater steadiness and preci- 
 sion than they could otherwise have done. Were it not 
 for the ligamentous bandages, the tendons would start up 
 from their situations on being pulled by the muscular 
 fibres connected with them. Their power would be thus 
 diminished, and the symmetry of the body greatly im- 
 paired. Occasionally they are sprained from over-exer- 
 tion or accident, when an artificial bandage becomes ne- 
 cessary, in some measure to supply their place, and then 
 is it known how superior they are to any artificial con- 
 trivance, however cunningly devised, or however dexter- 
 ously applied. 
 
 The ligamentous tissue is sometimes expanded into 
 broad sheets, under the name offascice., or when these ex- 
 pansions are connected with muscles, they are termed apo- 
 neuroses. They present great varieties in form, strength, 
 and arrangement. They furnish coverings which surround 
 not only the muscles and other structures in the various 
 regions of the body generally, but likewise the individual 
 parts, form partitions between them, and afford linings 
 for the separate portions composing them. In the loins, 
 and along the back there is a strong binder of this kind, 
 which greatly facilitates the motions of the body, and 
 powerfully contributes to the action of the muscles. 
 Where this is weak, a belt round the waist is of con- 
 siderable service ; but in a well-formed person it is 
 a clumsy substitute of art for nature, and ultimately 
 tends to weaken the back, for exercise strengthens and 
 invigorates all parts of the frame, while artificial sub- 
 stitutes invariably weaken the parts they are supposed to 
 strengthen. 
 
 The varieties of the ligamentous tissue adverted to are 
 
474 ELASTIC TISSUE. 
 
 chiefly characterized by their tenacity and intricate inter- 
 lacement of the threads composing them, toughness and 
 strength being the properties principally required in the 
 office they have to perform. 
 
 Allied to ligament in some respects, we have a pecu- 
 liar tissue, which has been ranked under a distinct order 
 in the classification of the animal textures. It is dis- 
 tinguished by its high degree of elasticity, its fibrous 
 structure, and yellow or tawny colour ; hence it has been 
 named the yellow fibrous or elastic tissue. It is known 
 by the Scotch wr&fixfax. It is by far the most elastic 
 substance in the animal body. This mechanical property 
 fits it for many purposes, and adapts it to several situ- 
 ations where the preservation of certain postures, attitudes, 
 or forms, with the capability of alteration in these re- 
 spects, is requisite. It is very conspicuous in the neck 
 of those animals which have to support a heavy load 
 horizontally at the extremity of a long neck, as in the 
 elephant, the deer, and our domestic cattle. Had their 
 heads been supported merely by muscular action, as that 
 is liable to fatigue, and requires intervals of rest, as well 
 as the exercise of volition, the postures could not have 
 been sustained for any length of time without pain and 
 exhaustion. This tissue, which is liable to none of these 
 objections, is accordingly substituted for muscular power, 
 in fixing the forms, preserving the attitudes, and contribut- 
 ing to motion. The strong fibrous band, stretching along 
 the back part of the neck to the head of these animals, 
 enables them with perfect ease to support the head. It 
 is also the cause of the head being bent back in dead 
 animals, as its power is entirely physical. In virtue of its 
 elasticity, it continues to exert its force after death, when 
 that of the muscles has altogether ceased. It is like- 
 wise adapted for retracting and retaining the sharp claws 
 of the cat tribe within their sheaths when not in use. 
 The wings of birds, also, in the state of rest, are retained 
 bent by a ligament of this tissue. Along the bellies of 
 
TENDON. 475 
 
 cattle, broad bands of the same structure are extended, 
 in order to support the contents of the abdomen. It is 
 not much employed in the preservation of the attitudes of 
 the human subject, though traces of it are met with along 
 the spinal column, where it contributes to the maintenance 
 of the erect posture. The elasticity observable in tubes, 
 such as the windpipe and its branches, blood-vessels, and 
 certain excretory ducts, is owing to the presence of this 
 particular tissue in their organization. 
 
 Ligament appears to be a combination of coagulated 
 albumen and gelatin, under a peculiar modification. 
 In the elastic tissue, traces of fibrin have also been de- 
 tected. Both structures forcibly resist chemical action 
 and decomposition. 
 
 Tendon or Sinew. This tissue must be well known 
 to every one, constituting, as it does, so common an 
 appendage to muscles. At the wrist, on the back of the 
 hand, at the heel, the sinews or tendinous cords are dis- 
 tinctly perceived in the living body. They have a white 
 satin-like glistening lustre, possess great physical strength, 
 but have little or no elasticity. They are composed of 
 filamentous threads, generally running parallel, but vari- 
 ously interlaced, and bound together by transverse threads. 
 They vary much in their figure and extent, being some- 
 times cylindrical, tapering to the point of their insertion, 
 and flattened where they spring from the muscular fibres. 
 In some situations they form broad expansions, under the 
 name of aponeuroses. Tendons are to be considered as 
 simply appendages to muscles. They receive merely 
 colourless blood, and in their healthy state are totally 
 insensible, so that the strongest and thickest tendon of 
 the body, that of the heel, known by the name of the 
 tendon of Achilles, may be (and it occasionally is) snapt 
 across, and yet the accident is accompanied with not the 
 slightest degree of pain, the sufferer conceiving, perhaps, 
 that a part of the floor has given way under him, or that 
 he has received a smart stroke from behind, Where the 
 
476 MUSCULAR FIBRE. 
 
 force of a muscle is concentrated, there it becomes ten- 
 dinous, since tendon, from its insensibility, is capable of 
 bearing such concentration without pain or fatigue. 
 Where it passes over joints, there also it becomes ten- 
 dinous. So likewise w T here the force is to be exerted 
 upon some distant part, it is transmitted along a tendon, 
 as forces in machinery are by ropes. In some instances, 
 where tendons cross over joints, a bone is formed where 
 they cross. Of this we have an example in the knee- 
 pan, which is nothing more than a round bullet-shaped 
 bone, formed in the course of a strong tendon, possess- 
 ing the advantage of throwing the force farther from the 
 centre of motion, thereby increasing the lever, and con- 
 sequently the effect. Similar bones in the course of ten- 
 dons are by no means rare in the animal body, particu- 
 larly in the tendons of the feet. 
 
 Muscular Fibre. This tissue must be familiar to every 
 one, under the name of flesh. Its most characteristic 
 property is essentially vital, consisting in the innate power 
 of contraction, a property which distinguishes it from 
 every other texture in the body. By the aid of the most 
 powerful microscope, it appears to consist of exceedingly 
 minute threads, so fine, according to estimate, as the 
 loJootii part of an inch in diameter. The ultimate 
 filaments are collected together, so as to form a fibre. 
 The fibres are easily perceived in boiled flesh, and the 
 number of ultimate filaments of which each is composed, 
 varies in different muscles, and in the same muscle in 
 different animals. Several fibres are again collected, so 
 as to constitute what is termed a fasciculus or bundle, 
 and according to the size of the bundles, the muscle appears 
 coarse or delicate. Thus a number of ultimate filaments 
 form a fibre ; a collection of fibres a bundle; and these 
 bundles collectively constitute a muscle. The fibrous 
 and fascicular arrangement appears to be chiefly confined 
 to muscles of voluntary action, being scarcely perceptible 
 in the heart, and not recognisable in the alimentary canal 
 
MUSCULAR FIBRE. 477 
 
 or urinary bladder. It is very distinct, however, in the 
 stomachs of very many birds, especially in hawks and 
 owls. 
 
 The muscular fibres are everywhere penetrated by cel- 
 lular tissue, and numerous blood-vessels and nerves. Ac- 
 cording to the quantity and quality of the blood, the 
 colour of the muscles varies. In adult and vigorous 
 animals of the class mammalia, it is of various shades of 
 red ; in young animals it approaches to a cream colour, 
 as in veal ; in birds it presents great diversities, not only 
 in different species, but in the different muscles of the 
 same individual, sometimes being very dark red, while 
 in others it is whitish ; in fishes it is bluish or white, and 
 of various other tints. 
 
 The direction of the fibres of muscles varies ; in some 
 they lie nearly parallel to each other, when the muscle is 
 said to be straight ; in others they radiate in different di- 
 rections ; in others they are disposed obliquely to the 
 general direction of the muscle, giving rise to their clas- 
 sification into penniform and semi-penniform ; others 
 again are circular ; not that we have in any case a fibre 
 continued round the whole circumference of a circle, but 
 in several instances a series of fibres, forming segments of 
 circles, complete the circumference, as in the intestinal 
 canal and in the muscles called sphincters. 
 
 As far as has been ascertained by chemical analysis, 
 muscular fibre consists of fibrin, albumen, osmazome, and 
 gelatin. It is not easy to determine in what particu- 
 lar condition or proportion each of these constituents 
 enter into the constitution of the tissue. It is well known, 
 however, that the proportions they yield vary according 
 to different conditions, as the species of animal, its age, 
 sex, state of health, and so forth. The flesh of young 
 animals, for example, affords a large proportion of gelatin, 
 while it is deficient in fibrin. In the adult animal, the 
 reverse occurs, fibrin predominates, and gelatin is de- 
 ficient. 
 
478 MUSCULAR ACTION. 
 
 Muscular Action. Contractility, the characteristic pro- 
 perty of muscular fibre, is essentially a vital property, 
 since it can be ascribed neither to chemical nor mechani- 
 cal laws ; its existence in and connexion with the muscu- 
 lar fibre is an ultimate physiological fact, which does not 
 admit of explanation. In this vital property we recog- 
 nise a source, and not a mere application of power. 
 
 The most evident alteration a muscle undergoes in a 
 state of action is a diminution of length, with a corre- 
 sponding increase in thickness. Both in the state of re- 
 laxation and contraction its actual bulk has been ascer- 
 tained to remain precisely the same. Very opposite opi- 
 nions have been and are still entertained with respect to 
 the efficient cause of muscular action. The opinion 
 which appears best to accord with the observed pheno- 
 mena is that which ascribes it to a change in the form of 
 the constituent fibre, becoming more or less bent in oppo- 
 site directions, so as to present zig-zag lines, the angles 
 formed being more or less acute, according to 
 the degree of contraction. Fig. 38 represents 
 a series of muscular fibres in a state of relaxa- 
 tion, with a nervous filament ramified through 
 them, as observed under the microscope. Fig. 
 FIG. se. 39 shews the change which takes place in the 
 state of contraction, where, instead of the fibres 
 lying parallel, or nearly so, as in the former 
 instance, they present zig-zag lines. 
 
 Various exciting causes call forth muscular 
 action. The principal stimulants are the vital, 
 FIG. 39. ^e morbid, and the mechanical and chemical. 
 The vital excitants are chiefly displayed through the 
 medium of the nerves, in the voluntary, instinctive, and 
 involuntary movements. 
 
 Volition enables us to exert the action of those muscles 
 placed under the control of the will, and, by means of 
 what is termed the muscular sense, we are enabled to ap- 
 portion the degree of contraction to the effect required. 
 
MUSCULAR ACTION. 
 
 479 
 
 We do not use the same effort in lifting one grain as we 
 do in raising a hundred-weight. The adaptation of the 
 effort to the effect was strikingly displayed by the ele- 
 phant Chuny a few years ago at Exeter Change. When 
 filberts were given him, he placed them under his ponder- 
 ous foot, and cracked the shell without bruising the ker- 
 nel, so accurately did he calculate the power to the de- 
 sired effect. Many muscular movements which have be- 
 come easy and familiar to us by habit and education, appear 
 to require no intervention of the will, because that power 
 may be transmitted along the nerves as quick as light- 
 ning, and as quick as lightning the muscle responds to 
 the call. The first attempts at writing, playing on mu- 
 sical instruments, and several mechanical arts, are awk- 
 ward and imperfect ; but how easy do they become, and 
 with what celerity are they performed, when practice has 
 made them familiar. Walking, running, dancing, and 
 many other motions, require education before they can 
 be executed with facility, quickness, or grace. Powerful 
 effects result from the condition of the mind. Many of 
 the more pleasurable mental feelings, as hope, confidence, 
 and joy, brace the muscles, increase their vigour, and 
 enable them to perform their function with alacrity and 
 ease. Joy displays its influence chiefly on the action of 
 the heart, which may be augmented to such a degree as 
 to induce palpitation. The consequences of this increased 
 action of the heart are the augmentation of the force and 
 velocity of the blood, fuller and more powerful inspira- 
 tions of air, a rapid circulation towards the surface, an 
 increased brilliancy of the eyes, and an augmentation of the 
 temperature of the body. The more stormy passions, as 
 anger, and particularly when accompanying delirium or 
 madness, produce astonishing effects ; the muscular con- 
 tractions are then performed with immeasurable, and al- 
 most uncontrollable force ; strong bonds are broken asun- 
 der ; and a thin, delicate female resists the efforts of several 
 strong men to subdue her during the paroxysm, while 
 
480 INSTINCTIVE MOVEMENTS. 
 
 after it is spent a child may bind her with a woollen 
 thread. On the contrary, the depressing emotions, such 
 as despondency, sorrow, and fear, paralyse, as it were, 
 the muscular power; the heart fails in propelling the 
 blood in due quantity to the surface ; the face becomes 
 blanched, and the limbs tremble. 
 
 When treating of the nervous system, we have seen 
 that the nerves from the cerebro-spinal portion of that 
 system, distributed on the muscles, perform separate offi- 
 ces; one set of nervous filaments conveying to the muscle 
 called into action the commands of the will, the other 
 set communicating to the mind the fact that the order has 
 been complied with. The issue of the command, and the 
 announcement of its performance, constitute the chain of 
 effects in purely voluntary muscular action ; if one be 
 deficient, then is the result imperfect. Thus, a person 
 paralytic as to feeling, with retention of the power of 
 throwing the muscles into action, may hold in his grasp 
 an object, so long as his attention is fixed upon that act ; 
 but the moment the attention is withdrawn, in the same 
 instant the object is dropt. For the performance of pure- 
 ly voluntary motion, more or less education is necessary, 
 according to the complexity of the operation required. 
 
 But the muscles which usually obey the will may like- 
 wise be called into action without any previously deter- 
 mined purpose, such as involves the exercise of volition ; 
 and still we may feel conscious of the muscular action 
 employed. Instinctive and sympathetic movements are 
 of this kind : the act of sucking in the new-born infant, 
 deglutition of food, winking the eyes from the apprehen- 
 sion of injury, throwing the arms forward when falling, 
 coughing from the irritation of the air- passages, sneezing 
 from the application of pungent substances to the nostrils, 
 and many other motions, which are performed from an 
 irresistible impulse, without the necessity of predetermi- 
 nation or volition, and even in many cases in spite of 
 them. In all these instances, motions are performed as 
 
EFFECTS OF GALVANISM. 481 
 
 perfectly the first time they are attempted as at any sub- 
 sequent period, however often they may be repeated ; 
 and whatever number of muscles are called into action, 
 they invariably operate with the precise degree of force, 
 velocity, and extent, and in the exact degree of combina- 
 tion and order of succession for the end required, without 
 previous education or training. 
 
 Involuntary movements are performed, not only in- 
 dependently of the will, but without our being conscious 
 of them. Of this kind are the motions of the heart, those 
 of the stomach and intestinal canal, the contraction of 
 the urinary bladder, the blood acting as a stimulus in 
 one case, the aliment in another, and the urine in a third. 
 Various diseased conditions induce muscular action in 
 different degrees of intensity and permanence, giving rise 
 to spasms, such as locked jaw, and convulsions of various 
 kinds. Mechanical and chemical stimulants produce mus- 
 cular contractions, not only in the living body, but even 
 after death has taken place. The facility with which they 
 may be excited after death depends much upon the state 
 of the body immediately preceding, on the nature of the 
 death, and the interval elapsed from its occurrence. When 
 an animal is killed, and when all motion has ceased, mo- 
 tion may be again excited by mechanical irritation of the 
 nerves supplying the muscles, as by scratching them with 
 a needle, or the heart may be roused to contraction by 
 pinching. But the most remarkable effects result from 
 the application of electricity : this agent is well known 
 as a powerful stimulus to muscular contraction in the 
 living body, and it is by far the most powerful that can 
 be applied in the dead. Dr Ure has given a most remark- 
 able instance of the effects of galvanism upon a human 
 subject which he operated upon a few years ago in Glas- 
 gow. It was the body of a murderer of the name of 
 Clydesdale, a powerful middle-sized man about thirty 
 years of age. After being suspended from the gallows 
 about an hour, having had no convulsive struggles when 
 
482 EFFECTS OF GALVANISM. 
 
 he dropped, he was carried to the anatomical theatre about 
 ten minutes after he was cut down. His face had a per- 
 fectly natural appearance, without lividity or swelling ; 
 neither had the neck been dislocated. 
 
 An incision was immediately made in the nape of the 
 neck, in order to expose the spinal marrow. The princi- 
 pal nerve of the thigh was laid bare on the left hip, and 
 a small cut was also made in the heel : from neither in- 
 cision did any blood flow. A pointed rod, connected 
 with one end of a powerful galvanic battery, was brought 
 in contact with the spinal marrow, while a similar rod, 
 connected with the other end of the battery, was applied 
 to the nerve at the hip. Every muscle of the body was 
 immediately agitated with convulsive movements, re- 
 sembling a violent shuddering from cold, the left side 
 being most powerfully affected. On removing the rod 
 from the hip to the heel, the knee being previously bent, 
 the leg was thrown out with such violence as nearly to 
 overturn one of the assistants, who in vain attempted to 
 prevent its extension. 
 
 In order to excite the movements of breathing, the 
 nerve of the diaphragm (the principal muscle of respira- 
 tion) was exposed in the neck, and one of the rods applied 
 to it, while the other was brought in contact with the 
 diaphragm through an incision made under the seventh 
 rib. On the circuit being completed, the diaphragm in- 
 stantly contracted, but with no great force. " Satisfied," 
 says Dr Ure, " from ample experience on the living body, 
 that more powerful effects can be produced in galvanic 
 excitation by leaving the extreme communicating rods 
 in close contact with the parts to be operated on, while 
 the electric chain or circuit is completed by running the 
 ends of the wires along the top of the plates in the last 
 trough of either pole, the other wire being steadily im- 
 mersed in the last cell of the opposite pole, I had im- 
 mediately recourse to this method. The success of it was 
 truly wonderful. Full, nay laborious breathing, instantly 
 
CO-OPERATION OF MUSCLES. 483 
 
 commenced. The chest heaved and fell, the belly was 
 protruded, and again collapsed, with the relaxing and re- 
 tiring diaphragm. The process was continued without 
 interruption as long as I continued the electric dis- 
 charges. 
 
 " In the judgment of many scientific gentlemen who 
 witnessed the scene, this respiratory experiment was per- 
 haps the most striking ever made with a philosophical 
 apparatus. Let it also be remembered, that for full half 
 an hour before this period, the body had been well nigh 
 drained of its blood, and the spinal marrow severely la- 
 cerated. No pulsation could be perceived meanwhile 
 at the heart or wrist ; but it may be supposed that but 
 for the evacuation of the blood, the essential stimulus of 
 that organ, this phenomenon might also have occurred." 
 
 In a third experiment, the nerve of the forehead was 
 exposed, and one of the rods applied to it, the other to 
 the heel. Dr Ure says, " Every muscle of the face was 
 thrown into fearful agitation. Rage, horror, despair, an- 
 guish, and ghastly smiles, united their hideous expres- 
 sions in the murderer's face, surpassing far the wildest re- 
 presentations of a Fuseli or a Kean. At this period se- 
 veral of the spectators were forced to leave the room from 
 terror or sickness, and one gentleman fainted." 
 
 The last experiment consisted in transmitting the elec- 
 tricity from the spinal marrow in the neck to one of the 
 principal nerves of the arm at the elbow, when the fin- 
 gers moved quickly like those of a violin player ; and an 
 assistant who tried to close the fist, found that the hand 
 was forcibly opened in spite of every effort to prevent it. 
 When the rod was applied to a slight cut on the tip of 
 the fore-finger, the fist being closed, the finger was in- 
 stantly extended, and from the convulsive movements of 
 the arm, he seemed to point to different spectators, some 
 of whom thought he had come to life. 
 
 Suppose a joint capable of motion in no less than four 
 cardinal directions, and its motions regulated not by four, 
 
484 CO-OPERATION OF MUSCLES. 
 
 but by six, eight, ten, or twelve different muscles, all of 
 them capable of varying the force, the extent, duration, 
 and order of succession of these actions, at the pleasure of 
 the will, the variety of effect must be almost incalculable. 
 In the regulation of these motions, a smaller number of 
 muscles than four can never be employed ; and even these 
 must be employed in different capacities to produce their 
 effects with steadiness and accuracy. Let us take the 
 motions of the head for example : Suppose we bend the 
 head forward, there must be muscles, not only to carry it 
 forward, but likewise others to prevent its inclination to 
 the right or left ; and as the head can also be moved in 
 the opposite direction backwards, there must also be mus- 
 cles to oppose or antagonize those that bend it forward. 
 The muscles in the direction of which the head is moved 
 are in this case termed motors, those that prevent its va- 
 cillation to either side directors, and those which anta- 
 gonize them moderators. 
 
 Further, these motions could scarcely be executed with 
 firmness and precision, unless the muscles producing them 
 have a fixed point of action. Winslow mentions the 
 case of a lady who was incapable of raising her head from 
 the pillow. Various painful applications, such as blisters, 
 &c. were applied without effect to the region of the neck. 
 No treatment produced the slightest beneficial result till 
 a physician, master of the motions of the body, was con- 
 sulted, when it was ascertained that when she attempted 
 to raise her head, and with this view threw the powerful 
 muscles arising from the breast and collar bones into ac- 
 tion, instead of the head being carried forward to the 
 breast, the breast was raised up towards the head. On 
 further examination, it was observed that the ribs and 
 breast-bone were unusually unsteady : this was found to 
 arise from a preternatural laxity in the muscles of the ab- 
 domen, by which they are drawn down and fixed. "When 
 this condition of matters was ascertained, a bandage was 
 applied round the waist, in order to fix the chest, and 
 
CO-OPERATION OF MUSCLES. 485 
 
 afford a fixed point of action to the muscles of the neck 
 employed in bending the head forward. The lady was 
 now desired to rise from the pillow, and to the astonish- 
 ment of herself and the bystanders, she got up with fa- 
 cility, the simple application of the bandage round the 
 waist having appeared to perform a miraculous cure. 
 Hence it appears that in changing the positions and at- 
 titudes, a number of muscles not employed as motors, di- 
 rectors, or moderators, are engaged &$Jixors. 
 
 Lastly, as all the motions that vary the positions of 
 the head, trunk, and limbs, must likewise vary the cen- 
 tre of gravity of the body, a number of muscles must be 
 thrown into action for the preservation of the equilibrium, 
 whether a person be sitting, standing, or moving from 
 one place to another. Muscles thus engaged in maintain- 
 ing the balance are termed Vibrators. In general, we are 
 unconscious of their action, unless they happen to be in a 
 state of morbid sensibility, or unless, in performing a mo- 
 tion we did not intend, we happen to stumble, or upon 
 suddenly changing the librators we experience a violent 
 jerk in the whole body ; then we are surprised how mus- 
 cles so distant, and in so great a number, "should be con- 
 cerned in merely changing the position of a part. 
 
 It is from the muscles being always ready to act on the 
 shortest notice in every emergency from their general 
 prompt co-operation in harmonizing the various motions 
 throughout the system from the yielding, yet steady 
 flexibility of the joints from the oblique opposition of 
 their surfaces from the angles, the curves, and the varied 
 direction of the bones united by articulation and from 
 the elastic substance interposed, that the body is enabled 
 to resist so successfully the violent jars to which it is ex- 
 posed in running, leaping, in stopping suddenly, or in 
 falling from a height. By such happy contrivances, for- 
 ces applied to the body are rapidly diffused throughout 
 every part, so that in ordinary cases, even the functions 
 of the most delicate are seldom impeded. To these, more 
 
486 CO-OPERATION OF MUSCLES/ 
 
 than the strength of the bones, the ligaments, and the 
 muscles, are we frequently indebted, in cases of concussion, 
 for the safety of the contents of the head, chest, and ab- 
 domen. This is obvious from the violent jerks to which 
 men in a state of intoxication are exposed, from inability 
 to regulate their equilibrium ; from the violent shocks 
 which we often receive in attempting to recover our ba- 
 lance ; from distortions of the joints in rheumatism and 
 paralysis ; and from the number of dislocations and frac- 
 tures arising from unequal action in the muscles, when 
 they happen to be taken off their guard. 
 
 In order to change and fix the attitudes with steadiness 
 and accuracy, it is necessary that numerous muscles be 
 called into action with various degrees of force, to diffe- 
 rent degrees of extent, and in various states of combina- 
 tion ; and not only this, but it is also necessary that all 
 the various forms of the joints should be mutually ac- 
 commodated to one another ; hence it is that the functions 
 of joints are not only closely and accurately connected, 
 but all the joints so adapted to the muscles, and all the 
 muscles so adapted to the joints, that amidst some mil- 
 lions of possible relations which they might have had, 
 the particular relations which they actually have are the 
 only relations, so far as we can judge, that could have 
 rendered them fit to co-operate ; and yet these relations, 
 numerous, and minute, and intricate as they are, are, 
 so far as essential, regularly preserved from birth to ma- 
 turity ; for as the bones grow in size and in strength, 
 so grow the muscles in their fleshy and tendinous fibres ; 
 in due measure is the blood transmitted, as to quantity^ 
 velocity, and force ; with the necessary adjustment are 
 the fibrous and cellular sheaths supplied, and the ner- 
 vous cords distributed ; so that, free from disease, and 
 free from the natural infirmities of age, the voluntary 
 muscles, when properly directed, are capable of perform- 
 ing their functions in all the different periods of life. 
 We speak of a muscle being in the state of contraction 
 
CO-OPERATION OF MUSCLES. 487 
 
 and in the state of relaxation, but it is to be recollected 
 that these are only relative terms : when we say that a 
 muscle is in a state of relaxation, it is still endowed with 
 energy, and only relaxed compared with some one or 
 other of its former conditions, or with the condition of 
 other living muscles, and never in that state of relaxa- 
 tion which a muscle exhibits in the dead body. Al- 
 though contraction be the most active condition of the 
 muscle, and that which usually gives rise to motion 
 in the healthy and vigorous state of the system, never- 
 theless motion may also result from the passive state 
 of relaxation, for motion results merely from a subver- 
 sion of the balance between the antagonist muscles of 
 a part, and may equally arise from the one losing or 
 withholding a certain degree of power, as from the other 
 exerting it. Thus the equilibrium of loaded scales will 
 be destroyed equally whether we withdraw a portion of 
 the weight from the one or add additional weight to the 
 other. For example, let us take the wrist-joint when 
 the hand is stretched out, so that the palm is parallel 
 with the fore-arm ; so long as it is kept steadily in this 
 position, the different muscles that tend to bend it for- 
 wards and backwards, inwards and outwards,, all perfectly 
 balance each other, from their acting with precisely the 
 same degree of force. But suppose the muscles which bend 
 the wrist forward relax in their action, then will it be 
 bent backwards, although the antagonists exert no more 
 force than before. Thus we perceive that relaxation may 
 be the cause of motion as well as contraction, and that it 
 is so is sufficiently well established. When a person be- 
 comes drowsy, the eyes are closed, and the head falls 
 forwards, not that the muscle which closes the eye in the 
 one case, or those that bend the head in the other, are in 
 a more active state, but because their antagonists become 
 comparatively relaxed. Numerous motions that occur, 
 especially in a state of debility, in various diseased con- 
 ditions, and at the approach of death, arise from this 
 
488 FORCE OF CONTRACTION. 
 
 cause, that is, from diminished, and not from increased 
 action. 
 
 Force of Muscular Action. The force which a muscle 
 exerts partly depends upon its vital energy, and partly on 
 its physical condition. As the principal power is de- 
 rived from a vital source, the change produced by death 
 is sudden and obvious. The muscles that when living 
 could have ruptured their tendons, dislocated the bones, 
 and broken them to pieces, when dead become soft and 
 flabby ; and were it not that they are held together by 
 their sheaths, cellular membrane, and blood-vessels that 
 every where penetrate them, and for some time hold them 
 together, they would scarcely be able to support their own 
 weight. A muscle composed of large firm fibres will con- 
 tract more forcibly than one with soft, delicate, loose 
 fibres. Like every part of the body, the muscular power 
 is greatly influenced by the state of health, and the effects 
 of a due degree of exercise is in no part of the animal frame 
 more strikingly displayed. Thus the legs of the pedestrian 
 become strong and vigorous, the arms of the blacksmith are 
 rendered powerful, and the shoulders and loins of the 
 porter are enabled to bear heavy loads with comparative 
 ease. When a muscle is in action, as already observed, it 
 swells and is shortened, the enlargement in diameter cor- 
 responding to the diminution in length, so that no change 
 of bulk occurs ; at the same time it is rendered harder 
 and firmer according to the degree of energy with which 
 it is endowed. The muscle which shuts the jaw, and 
 which is inserted into its angle, cannot shorten itself be- 
 yond a certain extent when the teeth are brought forcibly 
 together, but on placing the points of the fingers upon it 
 when it swells out the cheek, by its action, it will be 
 found to have different degrees of hardness according to 
 the energy of its contraction. In the condition of forcible 
 contraction, muscles become elastic, and are also sup- 
 posed to be in a state of vibratory oscillation, during 
 which they are capable of resisting sharp and heavy 
 
FORCE OF MUSCULAR ACTION. 489 
 
 blows with comparative impunity. It is in this way 
 that the common feat of bending a poker across the fore- 
 arm is explained. They likewise become less sensible to 
 punctured and incised wounds. In a surgical operation, 
 therefore, the muscles instinctively start into powerful 
 action to prepare for resistance. When strung to the ut- 
 most state of excitement, as in a pugilistic combat or in 
 the field of battle, they bear with impunity blows and 
 wounds that in their state of relaxation would greatly in- 
 jure them. In some cases of inordinate action the mus- 
 cles have been known to snap across the powerful tendon 
 of Achilles at the heel, and in other cases to fracture the 
 knee-pan, and even the thigh-bone. 
 
 Numerous instances of surprising strength have been 
 recorded. One of the most remarkable and best authen- 
 ticated is recorded by Sir David Brewster in his Letters 
 on Natural Magic. It is the case of Thomas Topham of 
 London. Dr Desaguliers saw him, with the strength of 
 his fingers, roll up a very thick and large pewter dish. 
 He lifted with his teeth a table six feet long, which had 
 half a hundred weight hanging at the end of it, and held 
 it in a horizontal position for a considerable time, the feet 
 of the table resting against his knees. He broke a rope 
 about two inches in circumference, which was in part 
 wound round a cylinder of four inches in diameter, having 
 fastened the other end of it to straps that went over his 
 shoulders. He lifted a rolling stone 800 Ibs. in weight 
 with his hands only, standing in a frame above it, and 
 taking hold of a chain that was fastened to it. 
 
 The mean effect of the labour of an active man, work- 
 ing to the greatest possible advantage, and without im- 
 pediment, is generally estimated to be sufficient to raise 
 ten pounds ten feet in a second, for ten hours in a day, 
 or to raise 100 pounds one foot in a second, or 36,000 
 feet in a day, or 3,600,000 pounds in a day. Dr Desa- 
 guliers affirms that the weakest men who are in health, 
 and not too fat, lift about 125 pounds, and the strongest 
 
 Y2 
 
490 DURATION OP MUSCULAR ACTION. 
 
 of ordinary men 400 pounds. Topham, we have observ- 
 ed, lifted 800. The daily work of a horse is estimated 
 to be equal to that of five or six men. 
 
 It would appear that civilization is favourable to mus- 
 cular strength, which has also some relation to the dif- 
 ferent races of mankind. Peron, in his voyage round the 
 world, took with him one of Regnier s dynamometers, 
 which measures the relative force of men and animals. 
 He directed his attention to the strength of the arms and 
 of the loins, making trials on several individuals of various 
 nations, viz. twelve natives of Van Diemen's Land, seven- 
 teen of New Holland, fifty-six of the island of Timor, 
 seventeen Frenchmen belonging to the expedition, and 
 fourteen Englishmen in the colony of New South Wales. 
 The results are stated in the following table. It may 
 be observed that the value of the kilogramme is about 
 two pounds avoirdupois, and that of the myriagramme 
 about twenty. 
 
 STRENGTH 
 
 Of the arms. Of the loins. 
 
 Kilogrammes. Myriagrammes. 
 
 1. Van Diemen's Land 50.6 
 
 2. New Holland 50.8 10.2 
 
 3. Timor 58.7 11.6 
 
 4. French , 69.2 15.2 
 
 5. English 71.4 16.3 
 
 The highest numbers in the first and second divisions 
 were respectively 60 and 62, the lowest in the fifth 63, 
 and the highest 83 for the strength of the arms. In the 
 power of the loins, the highest among the New Holland- 
 ers was 13, and the lowest of the English 12.7- 
 
 Duration of Muscular Action. It has been already 
 stated that the terms contraction and relaxation of living 
 muscles are only relative ; that a certain degree of contrac- 
 tion always exists, and that the degree of action depends 
 on the energy of the exciting cause, though influenced to 
 a certain extent by the physical condition of the muscle 
 
DURATION OF MUSCULAR ACTION. 491 
 
 engaged. Involuntary muscles are remarkable for the 
 very rapid and continued alternations of comparative ac- 
 tion and repose ; thus, from the first time the heart exer- 
 cises its function till it ceases to act at the moment of 
 death, it continues incessantly its oscillations of action, 
 though the period between may extend to seventy, eighty, 
 or a hundred years ; and that too whether we are asleep 
 or awake, by day and night, in health and disease. 
 
 The duration of voluntary motion depends in a great 
 degree on the determination of the will, and the influences 
 with which it may be actuated. In the East, fanatical 
 enthusiasts have been known to persevere in certain pos- 
 tures till they have become actually incapable of altering 
 them. It is impossible to conceive such endurance with- 
 out a certain degree of enthusiasm to keep it up. This 
 connexion between the condition of the mind and muscu- 
 lar contractility is similar to other extraordinary changes 
 which take place in the system of credulous persons, 
 whose fancies are under the impressions of witchcraft, in- 
 sanity, or animal magnetism, and accounts also for the 
 few real cures in the annals of modern empiricism that 
 are so ostentatiously blazoned forth when they happen to 
 occur. The same connexion likewise explains how our 
 muscular strength is varied by the states of sickness and 
 health, and how our exertions are more or less vigorous 
 and extensive, continued for a longer or a shorter period, 
 and attended with greater or less fatigue, in proportion 
 as the mind happens to be influenced by the exhilarating 
 or depressing passions. 
 
 The continuance of muscular action under the influence 
 of the will, in preserving a particular attitude, in bearing 
 a burden, and so forth, sooner or later induces exhaustion, 
 and the necessity for rest is experienced. But even dur- 
 ing the preservation of a fixed posture, the muscles en- 
 gaged experience certain intermissions or oscillations in 
 the intensity of their contraction, which in some measure 
 accounts for the length of time they may be persevered in. 
 
492 VELOCITY OF MUSCULAR ACTION. 
 
 Velocity of Muscular Action. The velocity with which 
 the voluntary muscles contract, depends in a great mea- 
 sure on the influence of the will, at the same time that 
 it is regulated to a certain extent by habit, those move- 
 ments to which we are accustomed being executed with 
 the greatest celerity and ease, while those that practice 
 has not rendered familiar are performed slowly and deli- 
 berately. The velocity of movement, as well as the in- 
 fluence of habit, are displayed by performers on musical 
 instruments, as the violin, flute, and piano-forte, in writ- 
 ing, speaking, running, and so forth. The celebrated 
 Haller states that he could articulate distinctly 1500 let- 
 ters in the space of a minute ; and as the relaxation of 
 a muscle occupies as much time as its contraction, each 
 change in the pronunciation of one of the letters in this 
 instance must have occupied not more than the three 
 thousandth part of a minute ; yet this is slow in com- 
 parison to the velocity with which changes take place in 
 drawing a straight line with the hand, where the line is 
 composed entirely of points belonging to the circumfer- 
 ence of as many circles, and where every point, of which 
 there may be thousands in a second of time, requires an 
 alteration in the condition of the muscles employed. Hal- 
 ler calculates that the rectus, one of the principal muscles 
 of the thigh for the extension of the knee, contracts three 
 inches in the twenty-eighth part of a second in the most 
 rapid motions of the leg. 
 
 Though the human body affords numerous instances of 
 quickness of motion almost inconceivable, yet the various 
 classes of animals present many examples of velocity far 
 surpassing any thing that occurs in the human subject. 
 Eclipse^ one of the fleetest race-horses on record, passed 
 over a mile in a minute and a half, and Childers ran 
 ninety feet in one second, which is at the rate of upwards 
 of a mile in a minute. Haller has calculated that a race 
 horse, at the height of his speed, must lift his leg in the 
 seventieth part of a second. Still this is far outstripped 
 
VELOCITY OF MUSCULAR ACTION. 493 
 
 by what may be observed in birds, many of which are 
 capable of wheeling round and round the most rapid 
 racer in circles of immense diameter. Montagu, the or- 
 nithologist, estimates the flight of several of the falcon 
 tribe as equal to 150 miles an hour. A falcon belonging 
 to Henry IV of France made its escape from Fontain- 
 bleau, and was caught twenty-four hours after at Malta, 
 a distance of not less than 1350 miles, being at the rate 
 of about fifty-seven miles an hour ; but as falcons do not 
 fly by night, nor is it likely that he was caught imme- 
 diately on landing at Malta, the flight must have been 
 at a much greater velocity. Many other instances are 
 afforded by birds, not merely of quickness of motion, but 
 of long continuance and great power, not only without 
 fatigue, but apparently with the greatest degree of en- 
 joyment. 
 
 In our most rapid movements in travelling, we are often 
 accompanied with insects making wide circuits round us, 
 and that too against the wind. How incalculable, then, 
 must be the celerity of motion in the muscles, that keep 
 their wings in action ! In force, how far comparatively 
 do the muscles of the grasshopper or common flea, in 
 making their leaps, surpass the gigantic strength of the 
 elephant, or the energy of muscular contraction in the 
 boa constrictor, when he crushes the bones of a large 
 animal like the stag in his dreadful coils ! What dura- 
 tion of action is displayed in the muscles of the limbs of 
 the sloth, which with ease clings to the highest branches 
 of the loftiest trees when they are lashed with the fury of 
 the hurricane ! and yet that animal has been made the 
 object of ignorant contempt and pity, as being doomed to 
 an imperfection in the very organization where peculiar 
 excellency of adaptation is displayed. 
 
 The different apparatus of motion are invariably adapted 
 in the most perfect manner to the habits and circumstances 
 of every animal, and the construction, adjustment, and 
 action in all their various forms and diversities equally 
 
494 ADAPTATION TO THE ANIMAL. 
 
 declare the wisdom, power, resources, and beneficent pro- 
 visions of the Divine Author of all, presenting to the in- 
 quiring and intelligent mind a subject for contemplation 
 and study that is quite inexhaustible. The organs of mo- 
 tion even in one animal, such as man, would require for 
 their elucidation volumes ; and as knowledge advances, 
 new and interesting views will present themselves in this 
 admirable mechanism. 
 
 In our examination of an animal structure, in no in- 
 stance do we find anything approaching to inconsistency 
 of structure with function, but in every case the very re- 
 verse. Invariably do we perceive the most happy adap- 
 tation to, and the most perfect accordance with each 
 other. It is only when we misconceive the purpose for 
 which the mechanism is intended, or when, in our ignor- 
 ance, we attribute to it purposes for which it never was 
 destined, that incongruity, error, and imperfection appear. 
 
495 
 
 CHAPTER XIII. 
 
 FCETAL LIFE. 
 
 General Observations Progress of the formation of the Egg in the Common en 
 The Molecule All the other parts subservient to it Incubation Formation 
 of the Chick in the different stages Membranes surrounding it in the egg 
 Table of periods of Gestation in several Mammalia The Vesicle Its Passage 
 Arrival in the Uterus Changes it undergoes through the various periods of 
 Gestation, and the Functions successively called into action Respiration in the 
 Foetus Regulation of Temperature Secretions poured into the Alimentary 
 Canal Circulation of the Blood of the Fcetus Milk Principal Constituents of 
 Proportion of these in different Animals Conclusion. 
 
 IN a work with the objects of the present, where the 
 various parts of the animal machinery are intended to be 
 described, it is necessary that some notice be taken of the 
 earlier stages in the growth and development of the 
 body, and of the various successive steps of its organiza- 
 tion, at least so far as these seem to have been satisfac- 
 torily ascertained. At the same time, it appears both 
 inexpedient and uncalled for that we should enter upon 
 the consideration of the phenomena connected with the 
 commencement of animal existence, still less to discuss the 
 numerous discordant opinions that have been entertained 
 respecting this subject; nor is it requisite to state the 
 reasons for avoiding such disquisitions on the present oc- 
 casion, since they must be obvious to every one. 
 
 The term embryo is applied to the new being before it 
 arrives at any considerable degree of development, for in- 
 stance, anterior to the fifth month in the human subject ; 
 
496 . FORMATION OF THE EGG. 
 
 that of fcetus, in the more strict acceptation of the word, 
 designating its subsequent condition, though both terms 
 are loosely and frequently indiscriminately used. 
 
 From the facility and accuracy with which observa- 
 tions can be made as to the progress of formation of the 
 chick in the egg at any period of incubation, our most 
 important knowledge respecting the development of the 
 new offspring has been chiefly derived from the exami- 
 nation of it at different periods. Similar observations, 
 made at different periods of gestation in mammalia, shew 
 that the character and succession of the phenomena are 
 in all the essential points identical. For this purpose the 
 egg of the common domestic fowl is that which for con- 
 venience is selected. In order, therefore, to convey some 
 notion of the manner in which the animal machinery is 
 unfolded, the history and structure of the egg, in the 
 first place, may be examined, that we may more readily 
 comprehend the various changes which take place in the 
 short period of twenty-one days, being that required 
 for the formation of a perfect chicken out of the mate- 
 rials that compose it, when it has been placed under 
 the necessary favourable circumstances. 
 
 Within the cavity of the abdomen of the common hen, 
 and attached to the middle of the back, a cluster of glo- 
 bular bodies is situated, these bodies varying in their 
 size from that of the head of the smallest pin to the full- 
 sized yelk. These are the first rudiments of the egg. 
 The smaller yelks are colourless and transparent, or 
 nearly so ; the larger have a more or less intense degree 
 of yellow tint according to their size. Upon the yelks, 
 even before they are detached from the cluster, there may 
 be perceived a minute spot of great importance, as being 
 the centre from which the formation of the chick sub- 
 sequently commences. It is known by the name of 
 molecule. The membrane of the ovary, as the cluster of 
 yelks is called, is abundantly supplied with blood. On the 
 larger yelks, numerous blood-vessels are seen distributed. 
 
CONSTITUTION OF THE EGG. 497 
 
 By some of these they are attached to the membrane as by 
 a stalk. But when the yelk has acquired its full develop- 
 ment, the vessels of attachment shrivel up, at the same 
 time the ovarian membrane at the opposite unattached 
 surface opens, and the yelk escapes, in the same manner 
 as when the pea in the cod has reached maturity, the 
 pedicle dries up, the pea is detached, and the cod opens 
 for its escape. On the escape of the yelk, it is received 
 by the orifice of a tube or canal, named oviduct. At the 
 upper part of the oviduct, the white is added ; in the mid- 
 dle portion the membranes of the shell and other parts 
 are supplied; in fact the egg is completed, excepting 
 the covering of calcareous matter which it receives to- 
 wards the extremity of this tube. Occasionally the egg 
 is laid without being furnished with the calcareous coat- 
 ing, when it is termed a rein d egg. 
 
 All the different parts of the egg are subservient to 
 the molecule, for this is the essential point from whence 
 life has to start, and, in fact, in which life is pecu- 
 liarly resident in the perfect egg. A little reflection 
 will shew that it would have been inconsistent with the 
 locomotive power of flying through the air for a mother 
 of the feathered tribe to have borne within her own body 
 her offspring till its parts were sufficiently developed for 
 its being placed in a new and more independent condi- 
 tion, were there no other reason ; but there are numerous 
 other circumstances which render the connexion unsuit- 
 able between the parent and offspring, especially in other 
 classes of animals, such as reptiles, fishes, &c. The sup- 
 ply of the materials, therefore, out of which the new in- 
 dividual is not merely to be formed, but from which it 
 has for some time to derive its nourishment, constitutes 
 the principal office of the parent, with the exception of 
 the highest class of organized beings, the mammalia. 
 
 On examining a new-laid egg, we observe it covered 
 with the porous calcareous shell, not so compact as to 
 exclude the transmission of air. It appears wonderful 
 
CONSTITUTION OF THE EGG. 
 
 that so curious a piece of mechanism as this should re- 
 quire no longer time than a few hours for its formation, 
 and that too without any apparent adequate means. But 
 although this is well deserving of our most sincere 
 admiration, still it is a very subordinate contrivance 
 amidst the innumerable, we may say miraculous, ex- 
 amples of conformation that organized structures every- 
 where display. Internally, the shell is lined by a mem- 
 brane capable of being separated into at least two dis- 
 tinct layers j between these, at the larger end, there is a 
 small quantity of air accumulated. This air varies in 
 quantity at different periods of incubation, and at the 
 earlier periods is the principal means of aerating the blood 
 of the chick. 
 
 "We next come to the white. This portion, it has been 
 observed, is furnished by the oviduct in the progress of 
 the egg along that canal. It consists of two strata, the 
 outer being thinner than the inner, and of a less degree 
 of consistency and viscidity. "When eggs are kept for 
 some time, the thinner part evaporates in a great mea- 
 sure through the shell, and the quantity of air is increased 
 to fill up the space it occupied. 
 
 The yelk occupies the centre, inclosed in two mem- 
 branes, an external common to it and the molecule, and 
 an internal or proper covering. It is balanced by two 
 bodies termed poles, attached opposite to each other to 
 the outer membrane, and terminating in flocculent ex- 
 tremities in the white in which they float. The yelk 
 furnishes materials for the growth of the embryo, which, as 
 it diminishes, receives also the white, until that is wholly 
 expended. Finally, what remains at the end of incu- 
 bation is conveyed into the intestinal canal of the chick 
 the day before it leaves the shell, to be digested, and to 
 supply nutriment, till the stomach is sufficiently vigor- 
 ous to perform that duty. Thus we perceive that the 
 young chick does not come into the world without pro- 
 vision for its nourishment, laid up for it by its parent 
 long before the time at which it is required. 
 
INCUBATION OF THE EGG, 499 
 
 As has been stated, the molecule is the essential part. 
 It is an exceedingly minute vesicle, containing a perfectly 
 transparent fluid, and surrounded by a kind of halo or 
 zone, more opaque than the surrounding parts, and termed 
 areola. By some means that have not been fully ascer- 
 tained, in whatever position the egg may be placed, the 
 yelk turns round like a globe and presents the molecule 
 uppermost, so that it is always situated nearest the breast 
 of the mother during incubation. This turning of the yelk 
 upon its axis, probably depends on the poles being attached 
 higher up on the hemisphere on which the molecule is 
 placed, and on the less specific gravity of the yelk at that 
 part, so that they may be considered as the balancers. 
 
 Incubation of the Egg. All that is necessary for hatch- 
 ing the chick in the egg is exposure to the necessary 
 degree of temperature, namely, that of the parent. Ac- 
 cordingly, this temperature is frequently applied artifici- 
 ally. In Egypt, from time immemorial, the practice of 
 hatching hundreds of eggs at once in properly constructed 
 stoves has been extensively followed. It is observed 
 that birds instinctively sit more or less closely during in- 
 cubation, according to the temperature of the atmosphere. 
 In cold climates they sit without intermission, and the 
 duty is shared, in many instances, between both parents. 
 While in hot countries, where the necessity does not 
 exist, a great degree of laxity and carelessness in this re- 
 spect appears to exist. 
 
 The immortal Harvey and John Hunter, both an- 
 xiously directed their attention to the formation of the 
 chick in the egg, and made important discoveries and ob- 
 servations. We owe a debt to the late Sir Everard Home, 
 for having induced that experienced, zealous, and accu- 
 rate microscopic observer, Mr Bauer, to undertake this 
 subject. No one could be better qualified for such a task. 
 A complete master of the necessary instruments an 
 acute and indefatigable investigator he started untram- 
 melled by preconceived opinions, and without any desire 
 
500 INCUBATION OF THE EGG. 
 
 to support previous doctrines, or to establish new ones, fur- 
 ther than the facts themselves would warrant. The fol- 
 lowing account is drawn up from what he observed, 
 according to the statement given by Sir E. Home in his 
 Lectures on Comparative Anatomy. 
 
 In four hours after incubation, the outer edge of the 
 areola had become enlarged, and that part of it next the 
 molecule appeared darker. One part of the molecule 
 appeared like a white line, the first rudiments of the 
 embryo. 
 
 In eight hours the white line was found to be extended, 
 and the rudiments of a brain and spinal marrow were 
 formed, surrounded by a membrane. 
 
 The areola had extended itself, and the surface beyond 
 the line which formed its boundary had acquired the con- 
 sistence of a membrane, and had also a distinct line by 
 which it was circumscribed. 
 
 In twelve hours the rudiments of the brain were more 
 distinct, as well as of the spinal marrow. 
 
 In sixteen hours there was a further advance in the 
 structure of all these parts. 
 
 In twenty -four hours a still greater increase. 
 
 In thirty-six hours the head was turned to the left side ; 
 the cerebrum and cerebellum appeared to be distinct 
 bodies ; the iris was seen through the pupil of the eye ; 
 the intervertebral nerves were nearly completely formed 
 those nearest the head the most distinct ; a portion of 
 the heart was seen. 
 
 At this period, apparently at the termination of the 
 spinal marrow, a vesicle had begun to protrude. In some 
 eggs it is seen earlier than in others, and has been ob- 
 served before the heart had become visible. 
 
 In two days and twelve hours the spinal marrow was 
 found to have its posterior part inclosed ; the auricles and 
 ventricles of the heart were seen the auricles filled with 
 red blood. An arterial trunk from the left ventricle gave 
 off two large vessels, the one to the right side of the em- 
 
INCUBATION OF THE EGG. 501 
 
 bryo, the other to the left, sending branches over the 
 whole of the areolar membrane, which was bounded on 
 each side by a large trunk carrying red blood ; but the 
 branches of the two trunks did not unite, there being a 
 small space on one side rendering the circle incomplete. 
 
 In three days the outer areola had extended itself over 
 one-third of the circumference of the yelk, carrying the 
 marginal arteries along with it to the outer edge, but di- 
 minished in size ; the brain was much enlarged, consist- 
 ing of four cavities containing a fluid the cerebellum still 
 the largest ; the spinal marrow and its nerves were more 
 perfectly formed; the eye appeared to want only the 
 nigrum pigmentum. 
 
 The right ventricle of the heart contained red blood ; 
 the arteries could be traced to the head; the rudiments 
 of the wings and legs were formed ; the vesicle was fur- 
 ther enlarged, but its vessels did not carry red blood. It 
 had forced its way out through the external covering of 
 the yelk, and opened a communication through this slit, 
 by which a part of the albumen was admitted to mix it- 
 self with the yelk, and gave it a more oval form. At 
 this period the embryo is generally found to have changed 
 its position, and to be wholly turned on the left side. 
 
 In four days the vesicle was more enlarged and very 
 vascular, its vessels containing red blood. 
 
 The optic nerve and nigrum pigmentum of the eye 
 were visible ; the other parts had become more perfectly 
 formed. 
 
 The outer areola had extended itself half over the yelk, 
 which had now become still more increased in size, a 
 greater proportion of the albumen having become mixed 
 with it. 
 
 In Jive days the membranous bag that formed the vesi- 
 cle had acquired a great size, and become exceedingly 
 vascular in its coats ; the yelk itself had become thinner 
 in its consistence, more of the albumen having been mixed 
 with it. 
 
502 INCUBATION OP THE EGG. 
 
 In six days the vascular membrane of the areola had 
 extended farther over the yelk. The vesicle at this time 
 had suddenly extended itself in the form of a double 
 night-cap over the yelk, and its coverings were beginning 
 to enclose the embryo. This change is so rapid as to be 
 with difficulty detected. The amnion contained a fluid in 
 which the embryo was suspended by the vessels of the 
 vesicular membrane. 
 
 The brain had become enlarged, so as to be equal in 
 size to the body of the embryo ; its vessels were distinct- 
 ly seen ; the two eyes equal in size to the whole brain. 
 
 The parietes of the thorax and abdomen had begun to 
 form ; the wings and legs were nearly completely formed, 
 as well as the bill. At this period muscular action was 
 first noticed. 
 
 In seven days the vesicle, having extended over the 
 embryo, had begun to enclose the areolar coverings of the 
 yelk, and a pulsation was distinctly seen in the trunk 
 that supplied the vesicular bag with blood. The pulsa- 
 tions were seventy-nine in a minute, while the embryo 
 was kept in a temperature of 105 ; but when the tem- 
 perature was diminished, they ceased ; when again raised 
 to the same point, the pulsation was re-produced. By 
 keeping it up, the pulsation continued thirty-six hours. 
 The muscles of the limbs now moved with vigour. 
 
 When the embryo was completely immersed in water 
 at 108, the pulsations immediately ceased. 
 
 In eight days the anastomosing branches of the vesicu- 
 lar circulation had strong pulsation in them. 
 
 In nine days the vesicle had nearly inclosed the yelk, 
 but not entirely ; for when the embryo was turned upon 
 its back, and the opposite surface examined, a portion of 
 the yelk was uninclosed ; and beyond it some of the albu- 
 men was met with not mixed with the yelk. 
 
 In ten days, divided the vesicle through both its mem- 
 branes, and turned aside one half. When the embryo 
 was taken out of the amnion, which had become full of 
 
IXCUBATION OF THE EGG. 503 
 
 water, the thorax was found completely formed, and the 
 roots of the feathers were very distinct. 
 
 The contents of the egg having been much diminished 
 during the formation of the embryo, the void space had 
 been gradually filled with a gas. This was examined by 
 Mr Hatchett, and found to be atmospheric air deposited 
 at the great end of the egg, between the layers of the 
 membrane lining the shell. 
 
 In fourteen days the yelk remained out of the body. 
 When the thorax and abdomen were opened, and the 
 heart as well as the lobes of the liver were turned aside, 
 the trunks of the blood-vessels were seen arising from 
 the heart ; but as the arteries immediately after death be- 
 come empty, and the veins continue full, the vesicular 
 vein terminating in the auricle, and the areolar vein ter- 
 minating in the porta of the liver, were alone conspi- 
 cuous. 
 
 In eighteen days the greater part of the yelk was drawn 
 into the body. 
 
 In twenty days the chicken was completely formed ; 
 the yelk was entirely drawn in, and only portions of the 
 membrane belonging to the vesicle were seen externally. 
 The yelk-bag had a narrow tube half an inch long con- 
 necting it to the intestines eight inches above the open- 
 ings of the coeca into the gut ; this tube entered the in- 
 testine in a direction obliquely downward. 
 
 Such is an account of the changes the egg undergoes, 
 and the various steps of development in the chick during 
 incubation, by one thoroughly qualified to make minute 
 observation, and on the accuracy of whose report the ut- 
 most confidence may be placed. 
 
 We thus perceive that the perfect egg possesses in it- 
 self a separate and independent life, and that the new 
 being is endowed with the power of forming its own 
 blood, and of evolving the organs necessary for the exer- 
 cise of its functions ; the accessary conditions required 
 being exposure to an adequate temperature, and the due 
 
504 APPENDAGES OF THE FOETUS. 
 
 supply of atmospheric air; for the functions on which the 
 production and regulation of animal heat depend are not 
 established in a manner to render it independent in this 
 respect. Some of the membranes mentioned in the fore- 
 going account deserve a little further notice. 
 
 Amnion. As early as the eighth hour we find imme- 
 diately in contact with the embryo a membrane to which 
 this name is applied. At a later period, when the parts 
 can be more distinctly observed, the amnion is the sac 
 in which the chick is contained ; it is a smooth secreting 
 membrane, continuous with the external integuments and 
 the mucous membranes of the various passages ; it fur- 
 nishes the fluid in which the new being swims, and is in 
 greater proportional quantity in the earlier than in the 
 latter periods. 
 
 The Areolar Membrane. This appears at the same 
 early period, the eighth hour, and corresponds with the 
 vascular membrane in mammalia termed chorion. The 
 blood-vessels first make their appearance upon this mem- 
 brane, though those of the embryo itself simultaneously 
 and independently begin to be formed. These vessels are 
 the channels for the conveyance of materials from the 
 yelk, according to the exigencies of the embryo. 
 
 Vesicular Membrane. At thirty-six hours a vesicle 
 begins to protrude from the lower extremity of the em- 
 bryo, seen earlier in some eggs than in others. On the 
 sixth day the membrane of this vesicle has extended itself 
 like a double night-cap over the yelk on the one hand, 
 and over the embryo on the other. Finally, it extends 
 over the whole contents of the egg and interior surface 
 of the shell, being abundantly supplied with blood. This 
 appears to be the proper respiratory instrument, its ex- 
 tension corresponding with the enlargement, and conse- 
 quently with the wants of the embryo. At first, the 
 small quantity of air placed between the layers of the lin- 
 ing membrane of the shell is fully adequate to the neces- 
 sities ; but on the further development, this membrane 
 
GESTATION. 505 
 
 lining the shell affords an expansion for the distribution 
 of the blood-vessels, where the air, passing through the 
 shell, may produce the required changes. 
 
 Parallel changes take place in the ovum of mammalia, 
 and the phenomena of development are in almost every 
 respect the same. The vesicle, however, is the only part 
 formed by the ovary in this class ; the materials of 
 growth required, and the functions performed, especially 
 as regards respiration, are furnished in a different man- 
 ner, and carried on by other contrivances during the pe- 
 riod of gestation, which corresponds with the period of 
 incubation of the egg. 
 
 We are totally ignorant of the causes that tend to limit 
 the periods of formation of the young animal, each ac- 
 cording to its kind being restricted to certain definite 
 circuits, within which the various organs reach their 
 proper development. It is as impossible to obtain any 
 explanation of the laws that regulate these periods as it 
 is to account for the extent of the life bestowed upon 
 each individual species. These are ultimate facts, the 
 final purposes of which are often sufficiently obvious, 
 while the efficient causes are, and probably ever will be, 
 beyond the reach of human discovery. All that can be 
 said then in respect to such matters is, that it has seemed 
 good to the Author of all to set established boundaries to 
 the continuance of their existence. 
 
 The periods of gestation vary much in different ani- 
 mals, as do also the number produced at a birth. In the 
 human subject, its continuance is from thirty-nine to 
 forty^ weeks, or from 270 to 280 days. The following 
 table from Dr Dunglison shews the periods of gestation, 
 and the number of young produced at a birth, in a num- 
 ber of animals in the class mammalia. 
 
506 
 
 GESTATION. 
 
 Animals. 
 
 Duration of 
 Gestation. 
 
 Number of 
 Young. 
 
 Ape 
 
 .About 9 months . 
 
 1 
 
 Bat 
 
 
 2 
 
 Rat 
 
 5 or 6 weeks 
 
 5 or 6 
 
 Mouse 
 
 
 6 to 10 
 
 Hare . . 
 
 30 days 
 
 4 or 5 
 
 Rabbit 
 
 30 days 
 
 4 or 5 
 
 Guinea-pig 
 
 
 5 to 12 
 
 
 6 weeks 
 
 4 or 5 
 
 Mole 
 
 
 4 or 5 
 
 Bear. 
 
 
 2 or 3 
 
 Otter 
 
 
 4 or 5 
 
 Bitch. . .. 
 
 
 4 to 10 
 
 Ferret 
 
 6 weeks 
 
 6 or 7 
 
 Wolf.. 
 
 
 5 to 9 
 
 Opossum 
 
 
 4 or 5 
 
 ICansfaroo 
 
 
 1 
 
 Jackall 
 
 
 6 to 8 
 
 Fox . . 
 
 10 weeks 
 
 4 or 5 
 
 Lioness 
 
 
 4 or 5 
 
 Tioress. . 
 
 
 4 or 5 
 
 Cat 
 
 8 weeks 
 
 4 or 5 
 
 Seal 
 
 
 2 
 
 Mare 
 
 (11 months andl 
 
 1 
 
 Ewe 
 
 \ some day ... / 
 5 months . . . 
 
 1 or 2 
 
 Goat. . . 
 
 
 1, 2, or 3 
 
 Cow . 
 
 9 months 
 
 1 or 2 
 
 Reindeer .... 
 
 8 months 
 
 2 
 
 Hind. . 
 
 
 1 or 2 
 
 Sow 
 
 4 months 
 
 6 to 10 or more 
 
 Camel 
 
 12 months 
 
 1 
 
 Walrus 
 
 9 months 
 
 1 
 
 Elephant . . 
 
 2 years 
 
 1 
 
 Whale 
 
 9 or 10 months..... 
 
 1 or 2 
 
 
 
 
PROGRESSIVE STAGES OF GESTATION. 507 
 
 When conception has taken place, a great alteration 
 occurs in the whole constitution of the female in general, 
 and in the uterus and its appendages in particular. Im- 
 mediately a determination of blood takes place to this or- 
 gan ; its internal surface has an inflammatory appearance ; 
 a quantity of gelatinous fluid plugs up its orifice, and 
 from its surface a membrane is formed. For the first two 
 or three months it undergoes little change in form or 
 bulk. About the fourth month it begins to ascend, and 
 to enlarge in its diameters. This it continues to do up 
 to the eighth month, when it is found to have reached 
 considerably above the navel ; it then fills the whole an- 
 terior part of the cavity of the abdomen, crowding the 
 viscera behind it, and in the flanks. During the ninth 
 month its base somewhat descends, and projects forwards. 
 In all this period of enlargement, a very great quantity of 
 blood circulates through its walls, and its muscular fibres 
 become more and more increased in number and strength, 
 that it may be prepared for the duty it has to perform in 
 the expulsion of its contents. 
 
 Even before the ovum reaches the womb, there is thus 
 prepared for it a proper receptacle, where it can be con- 
 veniently lodged, cherished, and brought to maturity, and 
 lastly, when it has arrived at full development, for power- 
 fully expelling it. 
 
 The ovum presents merely the appearance of a globu- 
 lar transparent vesicle filled with limpid fluid. It is sup- 
 posed to arrive at the uterus on the seventh or eighth day, 
 having traversed a canal extending from the uterus about 
 four or five inches in length, and terminating in a wide- 
 fringed mouth, which floats loosely in the cavity of the 
 abdomen. At first the ovum is without any adhesion to 
 the internal surface of the uterus. 
 
 Progress of Gestation. Up to the twenty-first day 
 little alteration can be observed in the ovum. About 
 this period the fluid it contains appears turbid, and in the 
 midst of it there is an opaque spot suspended ; the em- 
 
508 PROGRESSIVE STAGES OF GESTATION. 
 
 bryo, when immersed in spirits, becomes more percep- 
 tible, appears somewhat of the shape of an ant, and of 
 little more consistence than the surrounding fluid. 
 
 to 
 
 About the forty-fifth day the form of the embryo is 
 more determined ; the head is very large in proportion to 
 the rest of the body ; blackish points or lines indicate the 
 presence of the eyes, nostrils, and mouth ; the limbs ap- 
 pear like minute buds ; length about ten lines. 
 
 Second month. Eyes enlarged in every diameter ; the 
 eye-lids appear, and are transparent; the nose begins 
 to stand out ; the mouth increases and becomes open ; the 
 fingers and toes are distinct; the heart is largely developed. 
 
 Third month. The eye -lids developed and firmly closed; 
 the pavilion of the ear becomes perceptible ; the lips ap- 
 proximate, and close the mouth ; the brain and spinal 
 marrow pulpy, but considerably unfolded ; the heart beats 
 forcibly ; the liver very large, soft, and pulpy. 
 
 Fourth month. All parts acquire much development 
 and character, except the brain and liver, which do not 
 increase much in bulk but in consistence ; the muscular 
 system, begun to be developed in the third month, is now 
 distinct, and slight movements take place. 
 
 Fifth month. Increase in every part has advanced, par- 
 ticularly in the muscles, which produce distinct and un- 
 equivocal motions ; the eye-lids are glued together ; the 
 head is still very large in proportion to the rest of the 
 body, and covered with short silvery hairs. 
 
 Sixth month. The skin delicate, smooth, and of a purple 
 colour, cuticle distinguishable from the true skin ; the in- 
 teguments seem plaited, from the absence of subjacent 
 fat; the nails make their appearance, and towards the 
 close of the month are somewhat firm. Should the foetus 
 be born now, it may breathe and faintly cry, but it dies 
 in a few hours. 
 
 Seventh month. All the parts are better proportioned : 
 the eyelids begin to be opened, and the membrane which 
 previously closed the pupil begins to be absorbed ; fat is 
 
APPENDAGES OP THE FCETUS. 509 
 
 deposited more abundantly, and consequently the form is 
 more rounded ; the follicles of the skin secrete a fluid 
 which renders the waters turbid. If birth occurs at this 
 period, great care in nursing for the next two months will 
 be necessary for the preservation of life. 
 
 Eighth month. The increase is more in breadth than in 
 length, and all the parts attain firmness, consistency, and 
 strength. 
 
 Ninth month. The organs of the foetus acquire the ne- 
 cessary degree of development, in order to fit them for 
 entering upon a new state of existence. The weight of 
 the body is usually from six to seven pounds, and its 
 length from twelve to twenty inches. 
 
 The appendages of the foetus consist of two membranes, 
 the chorion and amnion, and of the umbilical or navel cord. 
 The chorion is the exterior membrane in contact with the 
 internal surface of the uterus. In the earlier stages, it is 
 furnished with a shaggy covering, which gradually disap- 
 pears. In further progress, numerous blood-vessels shoot 
 forth from the shaggy surface, and apply themselves to 
 the lining membrane of the uterus, and where they come 
 in contact with this membrane, vascular processes are 
 projected. Thus two sets of vessels are formed one set 
 belonging to the fetus, and the other to the mother ; these 
 interlace with each other, without, however, forming ac- 
 tual communications with one another; together they 
 form what is termed the placenta, an organ of the most 
 essential importance in the foetal economy, since it is the 
 means of intercourse with the mother. The placenta 
 makes its appearance towawls the end of the second 
 month. At this time it covers two thirds, or at least one 
 half of the ovum ; at the full period not more than one 
 fourth, The chorion can be traced along the cord as far 
 as the navel, where it is lost. Up to the end of the third 
 month, the two membranes are separated from each other 
 by a quantity of fluid, which then disappears, so that they 
 come in contact. 
 
 z2 
 
510 FCETAL RESPIRATION. 
 
 The amnion is the innermost of the two membranes. It 
 is somewhat elastic, and of a whitish colour, becoming 
 thicker and firmer as pregnancy advances. It is contin- 
 uous with the common integuments and mucous mem- 
 branes of the foetus. From its internal surface are derived 
 the waters surrounding the foetus. These waters are in 
 the inverse proportion to the advancement of gestation. 
 Calculated as they are to afford equable support in every ' 
 direction, to sustain the tender fabric in its first formation, 
 and to obviate the effects of concussion from without, we 
 perceive these waters are of essential importance. Accor- 
 dingly, at first, when all the parts are most delicate, so 
 are they in greatest quantity, in order to afford defence 
 and protection; but as the organs gain firmness and 
 strength, they proportionally diminish. 
 
 The umbilical cord consists of the blood-vessels passing 
 between the foetus and the placenta ; it varies greatly in 
 length in different cases ; in some instances it is not more 
 than a few inches, while in others it extends to five or 
 six feet. 
 
 In the higher classes of animals, before birth, the func- 
 tion of respiration does not exist in the same manner that 
 it is exercised after that event, but still an analogous 
 function is carried on, chiefly through the placenta, where 
 the blood in the mammalia becomes exposed to the aerated 
 blood of the mother ; in so far, therefore, being similar to 
 what takes place in fishes, where the blood is changed on 
 exposure to the aerated water while passing through the 
 gills. In birds, towards the latter period of incubation, 
 the fcetal blood is more directly exposed to the influence 
 of the air, where it is distributed upon the membrane ex- 
 tended over the internal surface of the shell, through the 
 pores of which noxious gases make their escape, and the 
 atmospheric air enters ; thus the function of breathing is 
 performed in a modified form, before the chick leaves the 
 shell, and at the commencement of the process, from the 
 air lodged between the layers of the membrane of the 
 shell placed at the larger end. 
 
FCETAL CIRCULATION. 511 
 
 Although the chemical changes that necessarily"occur 
 in the alteration the fluids undergo in the various pro- 
 cesses carried on in the foetal state, must involve the ex- 
 trication and absorption of caloric, and consequently to a 
 certain extent the temperature, yet they do not take 
 place in such a degree or manner as to sustain and 
 regulate the temperature requisite for the due exercise 
 'of the functions of life. Accordingly, in birds, heat 
 is imparted externally during the process of hatching, 
 and in mammalia the feet us participates of the heat of 
 the mother. 
 
 In birds, the materials for building up the different 
 parts of the frame are stored up in the egg, and even in 
 such quantity that when the perfect chicken is formed 
 a residue remains, which we have seen is conveyed into 
 the intestinal canal, where it becomes digested, and 
 forms the first food presented to the digestive appara- 
 tus. In mammalia, as the foetus is developed, mate- 
 rials are furnished in due quantity, and in the condition 
 suitable to its exigencies. Thus the function of digestion, 
 strictly speaking, does not commence till after birth ; a 
 considerable quantity of fluids, however, from various 
 sources, and especially from the liver, are poured into the 
 alimentary canal ; part of these may undergo a change 
 somewhat analogous to digestion, and be reintroduced 
 into the system, while the remainder accumulates in the 
 bowels, till they can be discharged after birth. 
 
 An idea of the condition of the foetus can be more easily 
 and more correctly obtained by studying the manner in 
 which the blood circulates in its system than in any other 
 way. Two kinds of circulation exist in the foetus the one 
 belonging to its own body in particular, the other carried 
 on through the placenta, for effecting the necessary changes 
 on the blood, and whereby fresh matter is introduced into 
 the system, derived from the mother. Beginning with 
 the course of the blood at the placenta, we find col- 
 lected from that body numerous veins, which unite into 
 
512 FOETAL CIRCULATION. 
 
 one trunk, named the umbilical vein. This vein pas- 
 ses along the cord, and enters the abdomen at the 
 navel; from thence it proceeds upwards to the liver, 
 where it is joined by the porta from the viscera ; the 
 greater portion of the blood circulates through the liver, 
 but part enters directly the ascending cava by a channel 
 peculiar to the foetus, and the portion that circulated 
 through the liver is likewise poured" into the same vessel, 
 to be conveyed into the right auricle of the heart. The 
 greater portion of the blood in this way is filtered through 
 the liver, which is correspondently,of a large proportional 
 size in the foetus. Here a considerable quantity of fluid 
 is separated from it in the earlier periods, free from any 
 bitterness ; but towards the full period it presents the 
 usual characters of bile. The bile may in this condition 
 be considered as an excretion for the purification of the 
 blood, though at the same time it may, when poured into 
 the intestine, serve for exercising the function of digestion 
 for the first time. 
 
 The foetal heart presents a peculiar organization ; the 
 right and left auricles freely communicate by an oval 
 aperture, whereby the blood of the ascending cava passes 
 directly to the left side, to be transmitted into the aorta,, 
 the great arterial trunk of the system. Into this oval 
 aperture the blood of the ascending cava is directed by a 
 valvular apparatus, while that of the descending cava,* 
 being the blood from the head and superior limbs, as 
 also the proper vein of the heart, pour their contents into 
 the right ventricle, to be propelled into the pulmonary 
 artery. This artery divides into three branches two 
 lateral ones for the lungs. The lungs are only developed 
 towards the latter period of gestation, as their function 
 is only called forth after birth. The arterial tubes they 
 receive are correspondent^ small, while the third branch 
 of the pulmonary artery, peculiar to the fretus, is large, 
 and joins the aorta after the arteries from the head and 
 superior parts of the body have been sent off. By this 
 
FOETAL CIRCULATION. 513 
 
 arrangement, the fresh blood from the placenta, brought 
 by the ascending cava, flows directly to the left side, and 
 that from the upper part of the body is carried into the 
 descending aorta, by which the greater part of the blood 
 is conveyed to the placenta. Moreover, we perceive that 
 both ventricles co-operate in propelling the blood into the 
 aorta, that it may be transmitted, not only to the system, 
 but along the cord, and subsequently through the pla- 
 centa. 
 
 The aorta appears to divide in the loins into two large 
 arteries, which, after giving off branches to the pelvis and 
 lower limbs, ascend by the side of the bladder to the 
 navel, pass along the cord, and distribute their blood to 
 the placenta. There is no direct vascular connexion be- 
 tween the mother and the foetus. Their circulations are 
 carried on independently of each other, the pulsations of 
 the fcetus being nearly double those of the mother ; and 
 if the mother be bled to death, the vessels of the fcetus 
 remain fully distended, suffering no loss. The mode of 
 connexion subsisting between them consists in the vessels 
 of the one, in the form of bundles or clusters, being re- 
 ceived into corresponding crevices of the other. A very 
 large quantity of blood circulates through that part of 
 the uterus to which the placenta is attached, affording to 
 the .foetal blood the means of effecting the necessary 
 changes, and presenting additional materials required 
 and taken up by the vessels of the fcetus. Along with 
 these fresh materials poisons and other matters gain en- 
 trance into the foetal system, by being absorbed from 
 the blood of the mother ; if she therefore labours under 
 an infectious disease, the same in this way may be im- 
 parted to the fcetus. Sftch facts show how important 
 must be the healthy condition of the mother, that proper 
 and healthy materials may be furnished to the offspring. 
 
 At last the period arrives when the body has reached 
 that degree of development that enables it to exercise the 
 functions in a new sphere of existence, and birth takes 
 
514 CONCLUSION. 
 
 place. In mammalia tliere is provided by the system of 
 the mother a nutritious fluid, expressly formed for the 
 young and delicate organs of digestion, containing the 
 elements of all that for some time is required for the 
 growth and enlargement of the different parts of the 
 frame. 
 
 This fluid, the milk, consists principally of a modifica- 
 tion of albumen termed cheese or caseum ; an oily mat- 
 ter, butter ; a peculiar form of sugar, along with a con- 
 siderable quantity of watery fluid termed whey or serum. 
 MM. Deyeux and Parmentier, after a great number of 
 experiments, give the following classification of six kinds 
 of milk in respect to the relative proportion of the chief 
 constituents in each : 
 
 Caseum. 
 
 Butter. 
 
 Sugar of Milk. 
 
 Scrum. 
 
 Goat 
 Sheep 
 Cow 
 
 Sheep 
 Cow 
 Goat 
 
 Woman 
 
 Ass 
 Mare 
 
 Ass 
 Woman 
 Mare 
 
 Ass 
 
 "Woman 
 
 Cow 
 
 Cow 
 
 Woman 
 
 Ass 
 
 Goat 
 
 Goat 
 
 Mare 
 
 Mare 
 
 Sheep 
 
 Sheep 
 
 From what we have now seen of the animal body, it 
 will be perceived that from its first appearance, like a 
 drop of limpid water, to the extreme of old age, the solids 
 gradually gain upon the fluids, until at last a stop is 
 put to the w r orking of the machinery ; the living prin- 
 ciple that hitherto protected the frame, yields it up to the 
 influences that regulate dead inert matter ; part flies off 
 in the gaseous form, part is resolved into fluids, and part 
 crumbles into dust ; while the immortal and responsible 
 spirit of man returns to Him who gave it. 
 
 W. BimNKSS, PRINTKR, KDINBdRGH. 
 
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