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HUMAN PHYSIOLOGY 
 
ELEMENTS 
 
 OF 
 
 HUMAN PHYSIOLOGY 
 
 BY 
 
 D. L. HERMANN 
 
 PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF ZURICH 
 
 TRANSLATED FROM THE FIFTH EDITION 
 
 ARTHUR GAMGEE, M.D., F.R.S. 
 
 BRACKENBURY PROFESSOR OF PHYSIOLOGY AND HISTOLOGY IN THE OWENS COLLEGE, 
 MANCHESTER ; EXAMINER IN PHYSIOLOGY IN THE UNIVERSITY OF EDINBURGH 
 
 L I B R A R Y 
 
 j| UNIVERSITY OF ij 
 
 CALIFORNIA. J 
 
 LONDON 
 SMITH, ELDER, & CO., 15 WATERLOO PLACE 
 
 1875 
 
 lAll rights reserved] 
 
BIOLOGY 
 
 " r 
 
 6 
 
 / 2. 
 
TRANSLATOR'S PREFACE. 
 
 WHEN, now two years ago, at the solicitation of several 
 friends, I undertook the translation of Professor Hermann's 
 ' Elements of Physiology/ I was actuated by the convic- 
 tion, shared in by nearly all teachers, that an urgent need 
 existed for an English text-book which should represent 
 the actual state of the science. It appeared to me, at the 
 same time, that no text-book on Physiology existed in 
 any European language at once so concise, comprehensive, 
 and philosophical as the work which I now introduce to 
 the English reader, and I therefore undertook its transla- 
 tion. 
 
 During the progress of my task, which a multiplicity 
 of occupations caused to be a more protracted one than 
 I had anticipated, my early convictions as to the excel- 
 lence of the work have steadily deepened. 
 
 The very condensed style of the whole work, the 
 immense number of facts brought together under every 
 section, and the constant assumption on the part of the 
 Author that the reader is possessed of varied and accurate 
 knowledge of the sciences upon which Physiology is 
 based, may tend to dismay the student who brings to its 
 
ri TRANSLATORS PREFACE. 
 
 study but a scanty preliminary education or a lukewarm 
 zeal, but this is a result which cannot be avoided by any 
 author who treats his subject in a thorough manner. 
 The conviction is, fortunately, growing every day that a 
 thorough knowledge of Physiology is of primary import- 
 ance to the medical man, and the science is now being 
 earnestly studied, for its own sake, by many who are not 
 connected with the practice of medicine. 
 
 With the increased facilities which are now afforded 
 in our laboratories and lecture-rooms of studying phy- 
 siology as every experimental science should be studied, 
 a more thorough theoretical treatment of the subject than 
 nas usually been attempted in our text-books becomes 
 desirable and expedient, and therefore I believe that 
 by students the present work will be received as favourably 
 as it has been by those teachers who have long known 
 it in its original German dress. 
 
 After much hesitation and many doubts I decided 
 not to annotate the text, for had explanatory notes, of the 
 nature of commentaries with illustrations, been added to- 
 rt, as I once intended, its appearance would have been still 
 longer delayed, and the work would have been materially 
 altered in character it would have ceased to be Her- 
 mann's Physiology. 
 
 It will be obvious to the critical reader that in the 
 execution of such a work a great responsibility rests with 
 the translator, who in dealing with some subjects which 
 have never been fully treated of in his own language is 
 necessarily compelled to introduce new expressions, which 
 thenceforward will probably find a place in the scientific 
 nomenclature of the language. 
 
 It would occupy too much space to enter into the 
 
TRANSLATOR'S PREFACE. vii 
 
 philological or scientific grounds for the English equiva- 
 lents which I have employed in the translation of certain 
 little-used or even new words which occur in the 
 German text, or of common words which acquire a special 
 meaning from the context ; to a few of these I shall, how- 
 ever, refer. 
 
 6 Auslosende Kraft,' the term employed by Professor 
 Hermann to express a force which removes any hindrance 
 or impediment to the conversion of potential into kinetic 
 energy, has been translated ' liberating-force,' and con- 
 sistently ' Auslosung ' has been rendered by the word 
 4 liberation.' My friend Professor Burd on Sanderson, F.E.S., 
 strongly advised me, though after the first sheets of the 
 work had passed through the press, to adopt the term 
 ' discharging-force ' as the equivalent of the German ex- 
 pression, and chiefly for the reason that the term ' dis- 
 charging ' is used in English in an analogous sense, in 
 many cases where a conversion of potential into kinetin 
 energy is effected, as when we speak of the discharge of 
 a gun, the discharge of a Ley den jar, &c. 
 
 c Vorstellung ' has been generally rendered by the 
 English equivalent c consciousness,' or ' states of conscious- 
 ness.' ' Seele ' has been translated by' mind.' 
 
 The word ' Leistung ' has received several different 
 meanings according to the context, being rendered by 
 * function,' * act,' ' activity,' or ' energy. ' This latter meaning 
 has actually been applied to the title of Part II. of the 
 work, where ' Die Leistungen des Organismus ' has been 
 paraphrased, ' The Activities or Energies of the Body.' I 
 feel confident that the scientific reader will acknowledge 
 this to be the most intelligent equivalent for the title of 
 that division of the work which deals with those processes 
 
viii TRANSLATOR'S PREFACE. 
 
 in which potential is converted into kinetic energy, and in 
 which their conversion is the most prominent phenomenon. 
 In the exposition of Fechner's psycho-physical law I 
 have adopted as the equivalent of the German ' Schwel- 
 lenwerth,' the term ' liminal intensity,' which was suggested 
 to me by Dr. Sanderson, and which appeared to me a 
 more literal and more happy rendering than ' initial 
 intensity,' which I had adopted. 
 
 In the sections on voice and on hearing the nomen- 
 clature used is that adopted by Mr. Ellis in his translation 
 of Professor Helmholtz's work, ' On the Sensations of 
 Tone.' 
 
 In the accomplishment of my task I liave been greatly 
 aided by several friends, some of whom have contributed 
 translations of portions of the book, whilst others have 
 given me the benefit of their advice. I have, in the first 
 place, to express my obligations to my friend and pupil, 
 Mr. John Priestley, Platt Physiological Scholar in Owens 
 College, for very great help in the actual translation and 
 revision of many important sections. I have to make the 
 same acknowledgment to my friend Dr. Julius Dreschfeld, 
 Lecturer on Pathology in Owens College, and to Professor 
 Burdon Sanderson, F.E.S., the latter of whom has contri- 
 buted the whole of the physiological division of the section 
 on the Organ of Hearing, in Chapter X. 
 
 To Mr. Liebreich I am indebted for having revised 
 that section of the physiology of Vision which deals with 
 the Horopter. Lastly, I have to thank my friend Dr. 
 Klein, F.E.S., for having made several important sugges- 
 tions in the translations of the sections on Development, 
 in Chapter XII. 
 
 Although I have endeavoured to perform my task as 
 
TRANSLATOR'S PREFACE. ix 
 
 carefully as lay in my power, I am aware that numerous 
 errors must of necessity be found in the translation of a 
 work which deals in so technical a manner with the details 
 of many sciences, and which in a short compass embraces 
 many facts and quotes many authorities. For these 
 errors I have to crave the indulgence of the reader. 
 
 AETHUE GAMGEE. 
 
 THE OWENS COLLEGE, MANCHESTER: 
 October, 1875. 
 
CONTENTS. 
 
 PACK 
 
 INTRODUCTION 1 
 
 PART I. 
 THE EXCHANGES OF THE MATTER OF THE ORGANISM. 
 
 Introduction Chemical constituents of the human body . .' . 9 1 
 
 Elements ;" ' . . ' . .' . . , . " .. . J) 
 Chemical compounds . . . . .. . . . .10 
 
 L Water . . . ... . . . . 12 
 
 2. Acids and salts . * . . . ..-..' . 12 
 
 3. Alcohols . ...;,...; .. . . . '. . . . . M 
 
 4. Ethers and anhydrides . 18 
 
 5. Ammonia and ammoniacal derivatives ... ..' . . 20 
 
 6. Complex bodies of unknown constitution . . 30 
 
 CHAPTER I. 
 
 The blood and its circulation . .... . . . . 88 
 
 X The blood . . . . . . - . . . " . 31) 
 
 II. The circulation of the blood . . . . ., . . 54 
 
 The movements of the heart .. ,'. . . . .. 50 
 Movement of the blood in the vessels . . .'-.. GO 
 . . Influence, of the nervous system on the circulation of the 
 
 blood . . . . .'.. .'.. ., ; . ; ,. .72 
 Frequency of the pulse . , 81) 
 
 Appendix. Exit of blood from uninjured vessels . . . .81 
 
-xii CONTENTS. 
 
 CHAPTER II. 
 
 PAGE 
 
 Sources of loss to the blood. Secretion . . . . . . . 83 
 
 I. Secretion in general 84 
 
 II. Individual secretions ......... 8U 
 
 A. Parenchymatoiis tissues and their secretions ... 89 
 
 B. Fluids of cavities . . . . . . . . 91 
 
 C. Glandular secretions .... 92 
 
 CHAPTER III. 
 
 Reception of material into the blood (absorption) . .... 127 
 
 Preparation of food for absorption (digestion) . . . . . 136 
 
 I. The chemistry of digestion . . . . . . . 137 
 
 II. The mechanism of the digestive apparatus .... 142 
 
 CHAPTER IV. 
 
 Gaseous interchanges (income and expenditure) of the blood. Respi- 
 ration 149 
 
 I. Chemistry of respiration 150 
 
 II. The mechanism of respiration 158 
 
 Appendix. Consequences of a deficiency of oxygen . . . .171 
 
 Respiration of foreign gases . . . . . . . 174 
 
 CHAPTER V. 
 
 The exchanges of the matter of the blood 177 
 
 Changes having their seat in the blood-corpuscles . . . 177 
 
 Exchanges of the chemical constituents . . . 182 
 
 Constancy of the amount of blood in the body . . . . 185 
 
 Appendix. Formation of Glycogen and sugar in the tissues . . 186 
 
 CHAPTER VI. 
 
 The exchanges of the matter of the body as a whole . . 190 
 
 I. Income 190 
 
 II. Expenditure 198 
 
 III. Quantitative relationship between the income, expenditure, 
 
 and stock of the body 199 
 
 1. The necessary losses of the body and their reparation by 
 
 means of food 202 
 
 2. Insufficient ingestion of food . . . . . . 206 
 
 3. Superabundant ingestion of food ..... 210 
 
CONTENTS. xiii 
 
 PART II. 
 THE ACTIVITIES OR ENERGIES OF THE BODY. 
 
 PAGF, 
 
 Introduction . 215 
 
 Introduction of potential energy into the body . . . . 216 
 
 Origin of the kinetic energy of the body .... 217 
 
 Expenditure of energy ........ 220 
 
 Comparison between the income and expenditure of energy . 221 
 Influence of the conversion of energy on the exchanges of 
 
 matter 222 
 
 CHAPTER VII. 
 
 On the development of heat and on the temperature of the body . 226 
 
 I. Development of heat 226 
 
 II. Temperature of the body 228 
 
 CHAPTER VIII. 
 
 The energy of mechanical work (movements of the body) . . . 236 
 
 I. The muscles 237 
 
 A. Striated muscles 237 
 
 a. Muscle in a state of rest . . . . . . 242 
 
 b. Muscle in rigor . 244 
 
 c. Muscle in a state of activity 247 
 
 d. Thermic and electrical phenomena of muscle . . 268 
 
 e. Interdependence of the phenomena of muscle, and 
 
 theories of muscular activity 278 
 
 B. Smooth muscles 281 
 
 II. Contractile cells ; protoplasmic movements . . . . 283 
 
 III. Ciliated cells and spermatozoids 285 
 
 Appendix. The uses of muscles 286 
 
 Mechanism of the skeleton 289 
 
 Conditions of equilibrium and of active locomotion of 
 
 the whole body 295 
 
 Voice 302 
 
 Speech 311 
 
xiv CONTENTS. 
 
 PART III. 
 THE LIBERATING APPARATUS; THE NERVOUS SYSTEM. 
 
 CHAPTER IX. 
 
 PAGE 
 
 The conducting apparatus (nerves) . . . . . . . 321 
 
 A. General physiology of nerves . . . . . 321 
 
 Nerves in a state of rest . . . . , . . 322 
 
 Nerves in a state of death . . . ... 323 
 
 Nerves in a state of activity . . . ... 323 
 
 Electrical phenomena of nerves . . . ; . 337 
 
 Theories concerning the nature of nervous activity 342 
 
 The function and classification of nerve-fibres 343 
 
 B. Special physiology of nerves 346 
 
 I. Cranial nerves ....... 347 
 
 II. Spinal nerves 353 
 
 III. Sympathetic nerves ...... 354 
 
 CHAPTER X. 
 
 The peripheral end-organs of nerves . .... . . . 355 
 
 I. The organ of sight 355 
 
 Vision ........... 385 
 
 Movements of the eye 403 
 
 Binocular vision . . . . . . . . 410 
 
 The organs which protect the eye 426 
 
 Appendix. Facetted eyes 428 
 
 II. The organ of hearing ........ 429 
 
 Hearing . . . . . . . . . . . 437 
 
 Hearing with both ears 449 
 
 The organs which protect the ear . . . . . . 450 
 
 Appendix 450 
 
 III. The olfactory organ 451 
 
 IV. The organ of taste ........ 454 
 
 V. The remaining sense-organs 57 
 
CONTENTS. xv 
 
 CHAPTER XI. 
 
 PACK 
 
 The centra] end-organs of nerves (central nervous organs) . . . 467 
 
 A. General considerations 467 
 
 B. Special physiology of the central nervous organs . . 475 
 
 1. Spinal cord 475 
 
 2. Encephalon 491 
 
 A. Medulla oblongata . . . . . . . 497 
 
 B. Ganglia at the base of the brain, and white sub- 
 
 stance of the brain . . . . . 504 
 
 C. Cerebellum . . 509 
 
 3. Sympathetic centres and nerves .... 521 
 
 PAET IV. 
 ORIGIN, DEVELOPMENT, AND DEATH OF THE ORGANISM. 
 
 CHAPTER XII. 
 
 A. General observations 527 
 
 Sexual reproduction . . . . . . . . 532 
 
 Development of the impregnated egg .... 534 
 
 B. Reproduction in man 537 
 
 C. Development of the ovum in mammalia and man . . 547 
 
 D. Extra-uterine development 567 
 
 E. Death 569 
 
 Addendum . .... 573 
 
 Notes by the Author 575 
 
 Index . . 577 
 
I, I ii U A U Y 
 
 UNIVERSITY OF 
 
 CALIFORNIA.^ 
 
 INTKODUCTION. 
 
 PHYSIOLOGY is the science which treats of the normal processes 
 which have their seat in the living bodies or organisms of plants 
 and animals. The processes which are characteristic of living 
 beings, and whose sum constitutes life, may be classified as 
 orderly changes of (1) their chemical constituents; (2) the 
 forces which work within them; and (3) their form. For- 
 merly an attempt was made to explain the peculiar processes 
 which have their seat in the animal organism, by supposing it 
 to be endowed with properties special to it, and heritable, 
 depending on a supposed ' vital force? This vague conception 
 has, however, been abandoned since the laws of inorganic nature 
 have been discovered to preside over the most thoroughly in- 
 vestigated processes of life, and especially since the application 
 to the organic world of a great principle of modern science has 
 taught us the relations which exist between the changes in the 
 matter and the forces of organised beings. Eelying upon this 
 knowledge, we believe that the forces of living are the same as 
 those of inanimate bodies, and that they obey the same laws, 
 and, consequently, that it will ultimately be possible to explain 
 the hitherto incomprehensible phenomena of living beings, 
 particularly their morphological processes, by physical and 
 chemical laws. This conception possesses, quite apart from its 
 probability, the great merit of introducing into the study of 
 organic nature more precise views and more accurate research, 
 and, although it has not been rigidly proved, will, in the present 
 work, tacitly underlie the exposition of the processes of the 
 human organism. 
 
 The human body, like that of every other animal, is an 
 organism in which, by the chemical changes of its constituent 
 parts, potential is converted into kinetic energy. 
 
 B 
 
 t, 
 
2 INTRODUCTION. 
 
 These chemical changes depend on the presence, within the 
 organism, of energy-yielding substances. 
 
 The greater number of the chemical operations which occur 
 in the living body, and which are accompanied with the mani- 
 festation of kinetic energy, are oxidations, or decompositions 
 which depend on oxidation; nevertheless, there are, in all 
 probability, other processes which are so accompanied. The 
 energy-yielding material of the organism is chiefly represented, 
 on the one hand, by oxidizable (organic) combinations ; on the 
 other by free oxygen. 
 
 The following is an instance of a simple oxidation : 
 
 2C 5 H 4 N 4 2 + Q 2 = 2C 5 H 4 N 4 S 
 
 Xanthine Oxygen Uric acid 
 
 An example of a decomposition depending on oxidation is : 
 C 4 H 8 2 + 80 a = C 2 H 4 2 + 2C0 2 + 2 H 2 O 
 
 Butyric acid Oxygen Acetic acid Carbonic acid Water 
 
 The following may be adduced as examples of other decompositions 
 occurring in the body, and which are associated with a manifestation of 
 kinetic energy : 
 
 a. Simple decompositions, e.y. 
 
 (1) C 6 H 12 6 = 2C 3 H 6 3 
 
 Sugar Lactic acid 
 
 (2) C 6 H 12 6 = 2C 2 H 6 + 2C0 2 
 
 Sugar Alcohol Carbonic acid 
 
 b. Hydrolytic decompositions, in which a body splits up after combining 
 with the elements of water : 
 
 C 57 H 110 6 + 3 H 2 = 3 C 18 H 36 2 + C 3 H 8 3 
 
 Stearin Water Stearic acid Glycerin 
 
 Every act of the organism must diminish, to a corresponding 
 extent, the energy-yielding store which it contains. As the 
 products of the chemical changes, even when they, in the first 
 place, have definite purposes to fulfil in the body, are ultimately 
 thrown off from it ; and, moreover, as the reconversion of these 
 products into the substances from which they were originally 
 derived would require the expenditure of as much energy as is 
 generated during the process of decomposition, it follows that 
 a restitution of energy-yielding substances can only take place 
 from without. It is, therefore, essential, in order that the or- 
 ganism should continue to exist, that it be continuously supplied 
 with free oxygen and oxidizable substances. The latter are 
 called the organic constituents of food. 
 
INTRODUCTION. 3 
 
 In addition to its energy-yielding constituents, the organism 
 possesses other (inorganic) substances, which do not furnish it 
 with energy. Their uses are only imperfectly ascertained, 
 though they appear, in great part, to be mechanical. Some 
 serve as solvents for organic bodies, some play an important 
 part in the formation of the solid parts of the body, whilst 
 others are in complex combination with essential organic con- 
 stituents. Even the inorganic substances are continually being 
 thrown out of the body in certain quantities, serving, in part, 
 as solvents for the products of decomposition which have to be 
 eliminated. The inorganic substances of the body, therefore, 
 like the organic, have to be continually replaced by others 
 taken from without, which constitute the inorganic consti- 
 tuents of food. 
 
 It follows from what has been said that the existence of the 
 organism is associated with a continual movement of matter 
 into and out of it, which constitutes what may be termed the 
 circulation of the matter, or the material exchanges of the 
 organism (Stoffwechsel des Organismus). 
 
 The plant takes the products of the chemical operations of the animal 
 body (carbonic acid, water, ammoniacal salts) and reduces them j it arranges 
 their radicals (carbon, hydrogen, nitrogen, &c.) side by side, combines them 
 with oxygen, and, storing them up within itself as organic compounds, it 
 restores the greater part of the liberated oxygen to the atmosphere. In the 
 separation of the once combined molecules, a certain amount of kinetic 
 energy is expended, which is exactly equal to the amount of potential energy 
 remaining in the separated elements ; we may, therefore, say that in the 
 process of reduction kinetic is converted into potential energy. The kinetic 
 energy which the plant receives is apparently yielded to it, first by conducted 
 heat (plants cool the bodies in their vicinity), secondly by radiated heat, 
 thirdly by absorbed light (chemical rays). The potential energy into which 
 these forms of kinetic energy are converted is associated with the liberated 
 oxygen and the oxidizable organic compounds stored up in the plant. (We 
 must not forget, however, that even in plants there occur processes which are 
 similar in nature to those which are characteristic of the animal body; 
 thus many of the parts of plants generate heat. Further, the processes of 
 development in the plant, as in the animal, require kinetic energy.) From 
 what has been stated there follows the most weighty conclusion, viz. that 
 the vegetable and animal kingdoms are mutually dependent on one another. 
 The plant, acting as a reducing agent, converts kinetic into potential energy ; 
 the animal, acting as an oxidizing agent, converts potential into kinetic 
 energy. The plant uses the oxidation-products of the animal, C0 2 , H 2 O, 
 &c. ; the animal uses the reduction products of the plant 0, on the one 
 hand, and the organic compounds of 0, H, N, 0, &c., on the other. These 
 
 B 2 
 
4 INTRODUCTION. 
 
 organic compounds built up by the plant, if we except inorganic matters, 
 constitute the only nourishment of animals, for even carnivorous animals, 
 merely consume the elements of vegetable food which have been modified 
 and stored up for a time in the tissues of the creatures upon which they 
 feed. 
 
 The amount of kinetic energy developed in the chemical 
 processes of the organism is entirely determined (in any case) 
 by the nature of the process and the amount of the constituents 
 which take part in it. The modes of motion, however, in 
 which the kinetic energy manifests itself, the activities of the 
 body, which result from the chemical changes, depend upon 
 conditions with which we are unacquainted. We merely know 
 that certain results are associated with specific apparatuses of 
 the body, which we term organs, and which are distinguished 
 from one another, not only by the substances which they contain 
 (their chemical composition), but also by their peculiar structure. 
 The most general forms of motion which result from chemical 
 changes are heat, and changes in the state of aggregation and 
 in form. These changes may either proceed with imperceptible 
 slowness in the smallest parts, and are then designated growth, 
 division, &c., or they manifest themselves on a larger scale as 
 the visible motion of masses (mechanical worlt\ Electricity is 
 also one of the forms of energy which result from chemical 
 changes ; in many animals there is also an evolution of light. 
 
 The same organ can, either simultaneously or at different 
 times, give rise to different manifestations of energy. 
 
 There exist well-known (equivalent) quantitative relations between the 
 various forms of motion. A decomposition which, if leading to the formation 
 of heat, develops one heat-unit, will, if it accomplishes mechanical work, 
 perform 424 grammetres of work ; one unit of heat can therefore be con- 
 verted into 424 grammetres of work, and conversely. 
 
 The chemical changes, and consequently the activities of the 
 body, are, in great part, if not altogether, subjected to a certaiu 
 regulating influence, which proceeds from a peculiar apparatus 
 which we denominate the nervous system. This influence, 
 naturally, affects not only the amount and nature of the products 
 of chemical change, but also the amount of energy which becomes 
 kinetic, i.e. it affects the acts performed by the body. Accord- 
 ing to our views of the functions of an organ do we place this 
 or that effect of the influence in the foreground. Thus in 
 the case of a muscle we regard the influence of a nerve on its 
 
INTRODUCTION. 5 
 
 motion, and therefore on the work which it can accomplish, as the 
 essential effect ; whilst we habitually overlook the simultaneous 
 influence which it exerts on the quantity of the chemical 
 products which are generated in the muscle. In glands, on the 
 contrary, the influence of the nerves supplying them on their 
 chemical products, viz. on the specific constituents of their secre- 
 tions, appears to be the essential result, whilst the contempora- 
 neous influence on the production of heat, i.e. on the evolution 
 of kinetic energy, is usually neglected. 
 
 The mode in which this influence of the nervous system is 
 exerted is as yet quite unknown to us. From a mechanical 
 point of view, this influence may be regarded as a liberating 
 force, i.e. as a force which leads to a conversion of a certain 
 amount of potential into kinetic energy. 
 
 It is well known that an infinitely small liberating force may 
 liberate large quantities of kinetic energy, and it is exceedingly 
 probable that even the liberating forces of the nervous system, 
 if measured as forces, would be very small in amount, and con- 
 sequently that the chemical changes necessary to their evolu- 
 tion, as to that of all the other forces of the organism, are but 
 of small magnitude. 
 
 A second, even more obscure, influence of the nervous system 
 is that which relates to the kind of bodily acts by which the 
 liberated energy manifests itself; this qualitative influence 
 of the nervous system appears to be closely associated with its 
 influence on the quantity of the energy transformed. 
 
 The following remarks may render more easy the conception of a 
 1 liberating force.' A liberating force is one which removes any hindrance 
 or impediment to the conversion of potential into kinetic energy. A clock 
 wound up, but prevented from going by a catch, represents a certain amount 
 of potential energy ; the position of its weights or of its spring cannot then 
 be converted into motion. So soon, however, as the catch is withdrawn, the 
 potential energy becomes kinetic, the weight falls or the spring approaches 
 its original form, and the clock goes. The force which removes the catch, 
 which therefore liberates the clock, and liberates its potential energy, may 
 be called l the liberating force.' Its magnitude often bears no proportion to 
 that of the energy set free ; the same force which withdraws the catch 
 which impeded the motion of a clock driven by a gramme weight, might 
 also liberate a clock driven by a hundred weight. 
 
 Other examples of such liberations are : 
 
 A spark which inflames a mass of gunpowder, and consequently sets free 
 enormous quantities of energy, or a slight movement which closes the circuit 
 of a powerful battery. There occur, however, cases of liberation in which 
 
C INTRODUCTION. 
 
 the liberating force does not, as in the cases cited above, instantly set free 
 the whole store of energy, but only a portion, which bears a definite, though 
 it may be a complicated, relation to its own magnitude. Let us take the 
 case of a head of water confined by a sluice with a rectangular door. The 
 quantity of water which will flow out, and the kinetic energy represented 
 by its fall, will depend upon the height to which the sluice-door has been, 
 raised, and upon the force here acting as a liberating force expended in 
 raising it. 
 
 All the phenomena of liberation which occur in the body appear to bear 
 some resemblance to the last case which has been cited. 
 
 A closer survey of the nervous system reveals the fact that 
 not only does it exert a liberating influence on the organs of 
 work of the body, but that its own constituent parts exert a 
 similar action one upon the other. By organs of work we may 
 shortly designate those organs, such as muscles and glands, in 
 which considerable amounts of energy become kinetic and appa- 
 rent to us in the form of mechanical work, heat, &c. 
 
 A portion of the nervous system that engaged in con- 
 ducting may be looked upon as consisting of series of 
 elementary parts, of which each one possesses a certain amount 
 of potential energy, and which are so closely connected together 
 that the energy which has been liberated in one part serves to 
 liberate the energy of the adjoining elementary parts ; thus, a 
 liberating force which acts on the first of these elementary 
 parts produces a series of liberations, until at last the energy 
 set free in the ultimate particles situated in some other organ 
 (as an organ of work) brings about the liberation of forces 
 within that organ. \Ye distinguish two kinds of liberating- 
 chains, possessing distinct origins and terminations. The one 
 kind proceeds from the so-called organs of the senses, i.e. from 
 organs on which an external influence (as pressure, heat, sound, 
 light, &c.) acts as a liberating-agent, and terminates in the so- 
 called central organs of the nervous system ; to which we give 
 the name of centripetal chains, or centripetal nerves. The 
 second kind (the centrifugal chains), on the other hand, proceeds 
 from the central organs of the nervous system, and terminates 
 in the organs of work. 
 
 The central organs of the nervous system may, consequently, 
 be looked upon as the points of departure and of entrance of 
 liberating-chains. We are, however, unacquainted with the 
 nature of the processes which, in the case of centrifugal chains, 
 
INTRODUCTION 7 
 
 act as liberating causes, or in the case of centripetal chains 
 are the result of the influences which travel to the centre. 
 In reference to these questions, we merely possess hypotheses 
 which will be discussed in the section which treats of the 
 central organs of the nervous system. Here, it may however 
 be merely mentioned, that there are many cases in which the 
 question appears to be easily solved, viz. cases in which a cen- 
 tripetal chain, acting through a central organ, immediately 
 liberates a centrifugal chain, so that essentially there exists 
 only a single chain commencing in a sense-organ and ter- 
 minating in a work-organ (reflex action). 
 
 Finally, we must mention that in a part of the central 
 organs certain material processes amongst others such as are 
 capable of liberating centrifugal chains and such as are the 
 results of centripetal liberations are accompanied, in an inex- 
 plicable manner, with wholly undefinable phenomena, which 
 characterize what we term consciousness. The term mind may 
 be applied to the combination of all the actual and possible 
 states of consciousness of the organism. 
 
 It is the province of Physiology to investigate the mole- 
 cular processes of the organism, and to connect with these all 
 its functions. The means of treating in a scientific manner the 
 phenomena of mind are completely wanting, inasmuch as these 
 phenomena cannot be brought into relation with any of our 
 scientific conceptions. Physiology must here, therefore, provi- 
 sionally limit herself to the investigation of the organs with 
 which they are connected. Even of the remaining tasks of the 
 science, whose solution we may venture to designate as possible, 
 but a few have been really accomplished. 
 
 It is difficult to follow a strictly logical course in the ex- 
 position of the facts which have been already discovered. 
 Seeing that our knowledge of the relation between the chemical 
 processes and the forces of the organism is so limited that it is 
 nearly all included . under the general observations which have 
 already been made, it would be in vain to attempt to expound 
 them in their natural and close mutual relations. It is more 
 
8 INTRODUCTION. 
 
 convenient, therefore, to consider in two distinct parts of this 
 work the Material exchanges and the Transformations of 
 Energy of the organism. But here a fresh difficulty arises out 
 of the mutual relations of the organic processes. The forces of 
 the organism are often employed in directing its matter, so that 
 a knowledge of these forces is requisite, in the first place, for 
 the proper understanding of the material circulation. Hence 
 it happens that even in the first part of this book, which treats 
 of the Exchanges of Matter, reference is often made to move- 
 ments, therefore to potential energy which has become kinetic, 
 though, naturally, no reference is made to its origin. Con- 
 versely, our knowledge of the characteristic changes in the 
 matter of some organs of work is so limited, that, for many 
 reasons, it is more convenient to state what has been discovered 
 concerning it in the second part, when treating of the Organs 
 of Work (e.g. the muscles). 
 
 The Third Part of this book treats of the Physiology of the 
 Liberating Organs -i.e. of the Nervous System. The Fourth 
 Part discusses the origin, development, the periodic changes, 
 and the death of the organism. 
 
LIB Li A liY 
 
 i 
 
 UNIVERSITY OF 
 
 CALIFORNIA. 
 
 PART I. 
 
 THE EXCHANGES OF THE MAT TEH OF THE 
 ORGANISM. 
 
 INTRODUCTION CHEMICAL CONSTITUENTS OF THE HUMAN BODY. 
 
 Elements. 
 
 THE following elements enter into the composition of the human 
 body : oxygen, hydrogen, carbon, nitrogen, sulphur, phosphorus, 
 chlorine, fluorine, silicon ; potasssium, sodium, calcium, rrfag- 
 nesium, iron, manganese. 
 
 Copper and lead are found as occasional and, very probably, unimportant 
 constituents. (The supposed discovery of the former metal has probably 
 been owing to the use of reagents containing copper, Lessen). Probably 
 other universally diffused metals, as lithium, are present, in minute quan- 
 tities, in the body. 
 
 Only a few of the above-mentioned elements occur in a free 
 condition * in the body, namely : 
 
 1. Oxygen 2 0=0, enters the body in a free state, and 
 serves to oxidize (or burn) the substances which enter into its 
 composition. For reasons which will be subsequently given, 
 some surmise that it is in its condition of ozone, 3 o o o 
 
 
 or /\ , that oxygen is able to effect these oxidations without 
 
 the aid of a high temperature. Oxygen is found in all the 
 fluids of the body, either in a state of simple solution, or loosely 
 combined. 
 
 1 It must be remembered that even elements in a so-called free condition are 
 combinations of several atoms, e.g. Oxygen, 2 ; Ozone, 3 ; Nitrogen, N 2 . 
 
10 CHEMICAL COMPOUNDS. 
 
 The existence of a third modification of oxygen, ' antozone/ concerning 
 whose properties statements differ, is now denied, and the phenomena 
 ascribed to it are explained by the presence of hydric peroxide. 
 
 2. Nitrogen N 2 N==N is absorbed from the atmosphere in a 
 free condition, and is consequently found dissolved in the fluids 
 of the body. In addition, it is probably set free in the oxida- 
 tion of nitrogenous organic compounds, and eliminated in this 
 condition. 
 
 Even Hydrogen, H 2 , occurs in the alimentary canal as a product of de- 
 composition j probably it originates in the butyric acid fermentation. 
 
 Chemical Compounds. 
 
 The formation of chemical compounds from their elements 
 or from more simple compounds, by so-called synthetic pro- 
 cesses, has hitherto only been discovered to occur in the body to 
 a very slight extent. The more accurately known chemical pro- 
 cesses of the body consist, on the contrary, chiefly in the falling 
 to pieces of complicated compounds, whose composition is only 
 partially known, and whose constitution is entirely unknown to 
 us ; these bodies contain carbon, hydrogen, and oxygen ; many 
 contain, in addition, nitrogen ; some also sulphur, phosphorus, 
 and iron. The most important agent in bringing about this 
 falling to pieces is the oxygen which enters the body in respi- 
 ration, under whose influence complicated split up into more 
 simple bodies, which contain more oxygen, and which are called 
 oxidation-products. The simplest products which arise in this 
 way are carbonic acid, sulphuric acid, phosphoric acid, and 
 water; when these substances are formed, the individual ele- 
 ments combine with as much oxygen as they can in general 
 take up. Nitrogen never separates in combination with 
 oxygen, but it either isolates itself entirely and is then ex- 
 creted in a gaseous form an occurrence which has not been 
 absolutely proved or it leaves the body in simple combinations, 
 e.g. as ammonia, or as ammoniacal compounds (ammonias 
 whose hydrogen is replaced by other atomic combinations) like 
 urea. 
 
 Between these simple combinations which the organism 
 throws off, and the complex bodies which it receives, there 
 exist a very large number of intermediate substances, which 
 form the principal constituents of the body. 
 
CHEMICAL COMPOUNDS. 11 
 
 The most thoroughly known of these substances are those 
 whose chemical constitution is most simple; in other words, 
 which are soonest to be eliminated. In the latter we can with 
 tolerable accuracy follow the course of the oxidation and the 
 gradual simplification of the combinations ; many of these com- 
 pounds can be obtained by the oxidation of the substances 
 which precede them, and conversely many of the more simple 
 compounds can be synthetically obtained from their elements. 
 The origin of the more complicated and little known compounds 
 cannot, however, with equal certainty, be referred to oxidation, 
 and it is possible (nay, to a certain extent, probable) that in 
 their production synthetic processes come into play. 
 
 A number of substances which enter the body do not 
 undergo such changes as have been alluded to, but pass through 
 it without any change taking place in the grouping of the 
 atoms which compose them. These so-called inorganic matters, 
 play a part in the body which is not yet thoroughly known. 
 The chief of these, water, serves in the body as the general 
 solvent : it forms, in so far as regards bulk, the chief constituent 
 of all the organs but the bones, and it is received into, and 
 separated from, the body in large quantities, a small quantity 
 being formed in the body. 
 
 The other inorganic matters are the so-called inorganic 
 salts. They also occur in all parts of the body, but (except in 
 the bones, which are composed mainly of salts) only in small 
 quantity ; when the tissues of the body are burned these salts 
 remain as ' ashes.' Their importance in the organism is only 
 imperfectly understood. In great part they appear to be not 
 merely simply dissolved, but to exist in the form of unknown 
 chemical compounds with the more complex (organic) consti- 
 tuents of the body. We can only thus explain the constant 
 relation which they bear to other substances (e.g. in the bones) 
 and the fact that the solubility and 'behaviour of certain bodies 
 (e.g. the albuminous bodies) depend -very much upon the salts 
 which are present with them. Our knowledge of the salts which 
 are really present in the organism is, moreover, still very in- 
 complete, seeing that chemical analysis of the ashes only 
 acquaints us with the acids and metals, but not with the salts 
 which they contain ; and, further, a portion of the acids, which 
 
12 WATER. ACIDS AND SALTS. INORGANIC ACIDS. 
 
 occur in the ashes, are only formed in the process of combus- 
 tion (e.g. phosphoric, sulphuric, and carbonic acids). 
 
 Amongst the salts which are found in the excreta there are 
 some which have not entered the body in the food, but which 
 originate within it. This is the case with carbonates, sulphates, 
 and phosphates. 
 
 The following chemical compounds occur in the body : 
 1. Water H 2 H o H ? as has already been remarked, is a 
 general solvent, and one of the chief constituents of all the 
 juices and tissues of the body (it forms about 70 per cent, of the 
 whole body). It is continually being taken into the body in 
 large quantities with the food, and continually being excreted ; 
 small quantities are formed in the body by the oxidation of the 
 hydrogen of organic compounds. 
 
 Peroxide of Hydrogen, HO H or H 2 2 H 0-0 H, according to 
 some, occurs in the body and plays a part in the oxidation-processes which 
 go on within it. 
 
 2. Acids and Salts, 
 
 The following acids exist in part free, in part in salts, in 
 part as constituents of complex compounds to be afterwards 
 alluded to (ethers, amido-compounds). l 
 
 a. Inorganic Acids (i.e. containing no Carbon). 
 
 1. Hydrochloric Acid HC1 C I_H appears to exist in a free 
 state in the gastric juice (perhaps as a more complex acid 
 compound). (See Chap. II.) Its salts (chlorides) are widely 
 diffused throughout the body, e.g. sodium chloride, calcium 
 chloride, &c. 
 
 2. Sulphuric acid S"0 2 (OH) 2 
 
 o o 
 
 HO a o H 
 
 occurs in the body in salts (neutral sodium sulphate, calcium 
 sulphate), and in more complex compounds (see Taurine, 
 Albuminous Bodies). 
 
 The acid secretion of Dolium galea contains free sulphuric acid. 
 
 1 In the graphic formulse of acids which follow, those hydrogen atoms which 
 are replaceable by metals are indicated by an appended asterisk ; according to the 
 number of these asterisks the acid is mono-, di-, or polybasic. 
 
ORGANIC ACIDS: FATTY ACIDS. 
 
 13 
 
 3. Phosphoric acid (common, tribasic or c-phosphoric acid) 
 
 o 
 
 F"0 (OH) 3 
 
 H P H 
 O 
 
 j, 
 
 occurs in salts, as neutral and acid potassium and sodium phos- 
 phates, basic calcium phosphate, basic magnesium phosphate, 
 phosphate of magnesium and ammonium (P0 4 MgNH 4 ), and 
 frequently in more complex compounds (see below Grlycerin- 
 phosphoric Acid, Lecithin). 
 
 4. Silicic acid Si0 2 o=si=o has been found in some tissues of 
 the body, perhaps only as an accidental constituent, through the 
 inhalation of sand dust. 
 
 b. Organic Adds (i.e. containing Carbon). 
 
 5. Fatty acids (general formula GJI^^O (OH).) 
 
 The series of the fatty acids at present known includes : 
 
 Formic acid 
 Acetic acid 
 
 Propionic acid . 
 
 Butyric acid . 
 
 Valerianic acid 
 Caproic acid 
 Oenantbylic acid 
 Caprylic acid . 
 Pelargonic acid 
 Capric acid 
 Laurostearic acid 
 Myristic acid . 
 Palmitic acid . 
 Margaric acid . 
 Stearic acid 
 Aracbidic acid . 
 
 o 
 
 il 
 
 H C H 
 H O 
 
 H C C 1* 
 
 Jr 
 
 H H O 
 H C C C H 
 
 u 
 
 H H H 
 H C-C-C-C H 
 
 CHO(OH) 
 C 2 H 3 0(OH) 
 
 C 3 H 5 0(OII) 
 
 4 H 7 0(OH) 
 C 5 H 10 2 
 
 C^A 
 
 C 9 H 18 2 
 
 C 12 II 24 2 
 C 14 H 28 O 2 
 
 C 17 H 34 O 2 (probably a mixture of C 16 II 33 2 and 
 CisHsA C 18 H 36 2 ) 
 
 Co lI 40 2 
 
 These monobasic acids form a ' homologous ' series ; their 
 boiling point rises 1 9 C with every addition of CH 9 ; those which 
 contain less carbon are fluid and volatile, those which contain 
 
14 GLYCOLLIC ACIDS. 
 
 more carbon are solid and not volatile. The latter are ob- 
 tained from the former, by oxidation, CH 2 being removed (car- 
 bonic acid and water being formed). 
 
 C 4 H 8 2 + 30 = C 3 H 6 3 + C0 2 + H 2 
 
 Butyric acid Propionic acid 
 
 Free fatty acids are frequently found in the analysis of the 
 constituents of the body ; yet their presence during life has not 
 been positively determined. The solid fatty acids occur some- 
 times in a crystallized condition within cells which previously 
 contained fats. Alkaline salts of the fatty acids (soaps, so- 
 luble in water), further amido-compounds (see below Grlycine, 
 Leucine), and chiefly certain ethereal compounds of the fatty 
 acids (see below Neutral Fats) occur in many of the constituent 
 parts of the body. The fatty acids are in addition constituents 
 of still more complicated compounds (see Lecithin). 
 
 6. Glycollic Adds (general formula C n H 2n _ 2 0(OH) 2 ). 
 
 The glycollic acids are derived from the fatty acids by oxi- 
 dation, by the substitution of one H-atom by OH ; even the H 
 of the OH can be replaced by a metal, so that these acids are 
 dibasic. 
 
 From those fatty acids which contain more than two carbon 
 atoms (viz. from propionic acid upwards) several isomeric 
 glycollic acids can be obtained, according to the carbon atom to 
 which the second OH group adds itself ; thus arise, for instance, 
 the two isomeric lactic acids (oxypropionic acids), which differ 
 in their salts. 
 
 The following are the glycollic acids as yet known: 
 
 Carbonic acid (oxyformic acid) CO(OH) 2 
 Glycollic acid (oxyacetic acid) C 2 H 2 0(OH) 2 
 
 Lactic acid (oxypropionic acid) : C 3 H 4 0(OH) 2 
 
 Sarcolactic acid . . . H _ 
 
 Ordinary lactic acid 
 
 Butylactic acid (oxybutyric acid) C 4 H 8 3 
 Valerolactic acid (oxyvalerianic acid) C 5 H n O 3 
 Leucic acid (oxycaproic acid) C 6 H 12 S 
 
GLYCOLLIC ACIDS. OXALIC ACIDS. 15 
 
 Of these acids only carbonic and the two lactic acids occur 
 in the organism ; glycollic and leucic acids (oxyacetic and 
 oxycaproic acids) are obtained from glycine (amido-acetic acid) 
 and leucine (amido-caproic acid), by the action of nitrous acid 
 (see below). 
 
 Carbonic acid. Carbonic acid as it has been represented in 
 the above graphic formula does not exist in a free state ; we 
 are only acquainted with its anhydride C0 2 o=c=o. 
 
 Carbonic acid occurs either in the free state (as absorbed 
 gas), in the form of neutral and acid salts, or in amido-com- 
 pounds (as Urea), in nearly all the component parts of the 
 body, and is excreted in all these forms in large quantities as 
 the principal oxidation-compound of the body. The carbonates 
 which occur in the ash, are generally, in part, produced during 
 the process of ignition. The most important carbonates found 
 in the body are, sodium carbonate, acid sodium carbonate 
 (Na 2 C0 3 and NaHC0 3 ), calcium carbonate (CaC0 3 ), and mag- 
 nesium carbonate (MgC0 3 ). 
 
 Sarcolactic add is an important product of the chemi3al 
 changes which go on in muscle ; ordinary lactic acid is found in 
 various fluids of the body, being probably a product of the lactic 
 fermentation of sugar (see below.) 
 
 7. Oxalic Acids (general formula C n H 2n _ 4 2 (OH) 2 ). 
 
 These are dibasic acids obtained by the oxidation of the fatty 
 or glycollic acids (H 2 being removed). The members of the 
 series which have to be considered here are the following : 
 
 o o 
 Oxalic acid . . . C 3 2 (OH) 2 fi-o-c-c-o-H 
 
 OHO 
 
 Malonic acid . . C 3 H 2 O 2 (OH) 2 H-O-C C-C-O-H 
 
 Succinic acid . . . C 4 H 4 2 (OH) a 
 
 Of these, oxalic acid, and perhaps succinic acid (although 
 this has been lately disputed), occur in the organism in the form 
 of salts ; all three, however, occur in more complex compounds 
 (see below Urea, Uric Acid, &c.) 
 
16 OLEIC ACIDS. CHOLIC ACIDS. AROMATIC ACIDS. 
 
 8. Oleic Acids (general formula C n H 2n _ 3 0(OH).) 
 
 These monobasic acids may be represented as fatty acids, in 
 which two of the carbon affinities are not saturated (at least by 
 H). Some of the members of the series are : 
 
 H H o 
 
 Acrylic acid .... C 3 H 3 0(OH) H-C-C-C-O-H 
 Crotonic acid .... C 4 H.O(OH) I ' I 
 
 Angelic acid .* . C 5 H 7 O(OH) >r H H o 
 
 Oleic acid .... C 18 H 33 0(OH) H J C ^^ 
 
 Of these acids only oleic acid occurs in the body, and when 
 it does so it is in the same compounds as those of the fatty 
 acids (as a soap, as a neutral fat (olein), or in lecithin). 
 
 9. Cholic Acids. 
 
 The acids belonging to this group are of yet more unknown and at any 
 rate more complex constitution. They are insoluble in water, but form 
 easily soluble soap-like alkaline salts, and possess a common and charac- 
 teristic reaction (Pettenkofer's test). When they are heated with sugar and 
 concentrated sulphuric acid to 60 C a purple violet colouration is produced. 
 
 They occur in the bile and in the intestinal contents of all 
 animals, chiefly as complex compounds (conjugated bile-acids, 
 see below Glycine). 
 
 Those at present known are 
 
 % Cholic acid . . C 24 H 40 5 
 
 Anhydrides of this acid Choloidic acid . 84 TT 38 O 4 
 Dyslysin . . C 24 H 36 O 3 
 Hyocholic acid . . C 25 H 40 4 
 
 Hyodyslysin . . C 25 TI 38 O 3 
 Chenocholic acid . C^H^C^ 
 Guanogallic acid 
 Lithofellic acid . . C 20 H 36 4 
 
 10. Aromatic Acids. 
 
 These are acids which are derived from the atomic group benzol C G II C . 
 In this very stable group each H-atom can be replaced by a monatomic atom 
 or group of atoms ; amongst others the above-mentioned fatty acids. We 
 may explain the relations of benzol by saying that the monatomic group 
 phenyl C 6 H 5 ( = C 6 II 6 -H) can replace one atom of hydrogen in a large 
 number of combinations, e.g. 
 
ALCOHOLS CHOLESTERIN, SUGARS. 17 
 
 H H H H 
 
 C C C C O 
 
 / X ii * / \ ii * 
 
 H C C H H C-0 H H C C C H 
 
 \ / \ 
 
 C 6 H 8 CHJO, 
 
 Benzol Formic acid Phenyl-formic or Benzoic acid 
 
 The following are aromatic acids which possess some physiological 
 interest : 
 
 Benzoic acid (Phenyl- formic acid) . . . CH(C 6 H 5 )0, 
 Chlorobenzoic acid (Chlorophenyl-formicacid) CH(C 6 H 4 C1)0 2 
 Salicylic acid (Oxyphenyl-formic acid) . . CH(C 6 H 4 [OH])0 2 
 Anisic acid (Methoxyphenyl-formic acid) . CH(C 6 H 4 [O.CH 3 ])0 2 
 
 These acids do not occur as regular constituents of the body, yet they 
 pass through it, after having been introduced as constituents of vegetable 
 food, and in the body form peculiar compounds (see Hippuric Acid). 
 Possibly they also form part of more complex bodies, as of Tyrosine, which 
 is closely related to them, and which is a product of the decomposition of 
 the albuminous substances. 
 
 3. Alcohols, 
 
 Of undoubted alcohols only one occurs in the body, viz. 
 Cholesterin C 26 H 43 (OH). The constitution of this body is yet 
 unknown ; it is contained in the tissues composing the nervous 
 system, in bile, and in the blood corpuscles. 
 
 Cholesterin is insoluble in water, easily soluble in ether and hot alcohol ; 
 it crystallizes from its solutions in the latter in the form of rhombic tables, 
 which assume a blue colour when treated with sulphuric acid and iodine. 
 
 Glycerin, C 3 H 5 (OH) 3 , is a triatomic alcohol (see graphic 
 formula, page 19) ; it probably only occurs in the body in the 
 form of ethers. 
 
 To the group of alcohols probably belong the different 
 varieties of sugar (polyatomic alcohols), whose constitution is 
 unknown. 
 
 The different sugars are crystalline, soluble, bodies, possessed of a sweet 
 taste ; their solutions deviate the plane of polarised light, and in consequence 
 of the ease with which they are oxidised, they reduce many metallic oxides. 
 They split up, under the influence of certain organisms (yeast-cells) and 
 other so-called ferments, into simpler compounds (products of fermentation), 
 heat being evolved during the process. The following varieties of sugar 
 occur in the organism : 
 
 Grape sugar C 6 H 12 6 (Synonyms Starch sugar, Diabetic 
 
 c 
 
18 SUGARS, INOS1TE ETHERS AND ANHYDRIDES. 
 
 sugar, Liver sugar) occurs in minute quantities in the blood, 
 in the liver, in the muscles, and in the urine (?). In diseased 
 conditions it may occur in large quantities. 
 
 This group of atoms is besides contained in many of the 
 more complex constituents of the body (see below). It rotates 
 the plane of polarisation to the right. 
 
 Fermentations of sugar : a. Splitting up into alcohol and 
 carbonic acid (C 6 H 12 6 = 2 C 2 H 6 + 2 C0 2 ) under the in- 
 fluence of yeast ; 
 
 b. Splitting up into lactic acid (see page 14) (C 6 H 12 6 = 
 2 C 3 H 6 3 ), in the presence of decomposing albuminous bodies. 
 
 Sugar of Milk, C 12 H 22 1P is a constituent of milk, which 
 rotates the plane of polarised light to the right. This sugar 
 can directly only undergo the lactic acid fermentation, but 
 when boiled with dilute sulphuric acid it is converted into a 
 sugar (lactose) capable of undergoing the alcoholic fermen- 
 tation. 
 
 Inosite, C 6 H 12 6 , is a constituent of the muscles ; it does 
 not rotate the plane of polarisation ; it is susceptible of the 
 lactic acid fermentation. 
 
 The different sugars and their anhydrides are usually designated by the 
 term * carbohydrates,' which merely expresses that, in addition to carbon, 
 they contain hydrogen and oxygen in the proportion in which these ele- 
 ments are contained in water (H 2 O). 
 
 4. Ethers and Anhydrides, 
 
 When alcohol-radicals or acid-radicals, or both alcohol and acid-radicals 
 are held together by atoms of oxygen, ethers are formed ; when several 
 similar radicals are united together in this fashion, the compounds are 
 called anhydrides. 
 
 HHHH H H O H HO OH 
 
 I ! I I I I II I I II II | 
 
 H C C O C H H C C C C H H C C C C H 
 
 III! II I i I 
 
 HHHH HH H H H 
 
 C 2 H 5 .O.C 2 H 5 C 2 H 5 .O.C 2 H 3 C 2 H 3 O.O.C 2 H 3 
 
 Diethyl ether (common Acetyl-ethyl-ether Diacetyl oxide 
 
 ether or alcohol anhydride) (Acetic ether) (Acetic anhydride) 
 
 The ethers and anhydrides are formed from alcohols and acids by a 
 removal of H 2 O, and are reconverted into them when they combine with 
 H 3 0. The first process is a synthesis, the second a process of decomposi- 
 tion ; one may distinguish both these processes from other syntheses and 
 decompositions, by applying to them the term of hydrolytic. The part 
 which water plays in them is exhibited by the following diagram, which 
 
GLYCERIC ETHERS. 19 
 
 shows how the action of water leads to the splitting of acetic ether into 
 alcohol and acetic acid. 
 
 o H 
 
 H Acetic ether 
 
 H H Elements of water 
 
 Alcohol Acetic acid 
 
 Hydrolytic decompositions sometimes occur on mere contact with water, 
 at other times under the influence of boiling water (sometimes only at tem- 
 peratures above that of boiling water, ' superheating '), or under the influence 
 of boiling water and mineral acids ; lastly, they occur at moderate tem- 
 peratures under the influence of certain (' liydrolytic ') ferments (see p. 35). 
 The following ethers and anhydrides occur in the body : 
 
 1. Gly eerie ethers. a. The neutral fats (see their graphic 
 formulae) are ethers derived from the triatomic alcohol glycerin 
 (p. 17), the fatty acids (p. 13), and oleic acid (p. 16). 
 
 The animal fats are olein (more accurately triolein), which 
 is fluid, in contradistinction to those which follow, which are 
 solid, stearin, margarin (compare p. 13), and palmitin; in 
 addition, the following are present in milk, constituting the fat 
 of butter : myristin, caprinin, caprylin, capronin, butyrin. 
 
 The neutral fats are fluid Coils) or easily melted, insoluble in water, 
 easily soluble in ether and hot alcohol; when fluid, they render paper trans- 
 lucent (grease-spots) ; when mixed with colloid substances and water, they 
 admit of being broken up into fine drops, so that the fluid becomes white 
 and opaque (emulsion). Under the influence of hydrolytic ferments, or 
 when superheated with water (see above), they combine with the elements 
 of water, glycerin and free fatty acids being liberated ; the latter, if volatile, 
 are the cause of rancid smell. 
 
 These fats are likewise decomposed by alkalies, alkaline salts of the fatty 
 acids (soaps) being formed, which are soluble in water ; solutions of these 
 dissolve fats. 
 
 b. To the neutral fats is also connected another, but acid, glyceric ether, 
 viz., glycerinphosphoric acid, C 3 H 5 (OH) 2 O(PO[OH]) 2 , which is a combina- 
 tion of glycerin and phosphoric acid, minus a molecule of water. 
 
 HHH H H H. HHH 
 
 H C C C H H C - C -- C H H GC C H 
 
 I 
 
 o 
 
 - -- 
 
 II I I I III 
 
 oo o oo oo 
 
 III I I I III 
 
 HHH O=C O=G C=0 H P H 
 
 H-C-H H-C-H H-C-H H " O H 
 
 A i i 
 
 C S H 8 0, C 3 H 5 .0 3 (C 2 H 3 0),, CjHjPO, 
 
 Glycerin (see page 17) Triacetyl-glycerine ether Glycerinphosphoric acid 
 
 Triacetin (a neutral fat) 
 
 c2 
 
20 ANHYDRIDES OF SUGAR GLYCOGEN. 
 
 Glycerinphosplioric acid is a product of the decomposition of Lecithin 
 (p. 21). 
 
 2. In spermaceti (which is obtained from the cranial cavities of certain 
 whales) there occur some (nionatomic) ethers of the fatty acids with cetyl- 
 alcohol (ethal) C 16 H 33 .OH, viz., palmitic-cetyl-ether C 16 H 33 O.C 16 H 31 0. 
 
 3. Anhydrides of Sugar. Certain substances are very widely diffused 
 through the vegetable kingdom, which, when subjected to hydrolytic in- 
 fluences (see above : boiling with dilute acids, action of certain ferments), 
 combine with water and form, sugar, and are, therefore, to be considered 
 the anhydrides of sugar. 
 
 The most characteristic of these substances are the following : gum 
 C 12 H 22 O n , starch C 6 H 10 5 , cellulose, C 6 H 10 5 , and the substance inter- 
 mediate between starch and sugar, viz., dextrin, C 6 H 10 5 . 
 
 The formulae of these bodies, which appear to hold the same relation to 
 the sugars that the ethers bear to the alcohols, are probably multiples of the 
 above (starch being C 12 H 20 10 or C 18 H 30 15 ), their ' conversion ' into sugar 
 probably, in reality, being a process of decomposition. Probably milk sugar, 
 which, under hydrolytic influences, is changed into a variety of sugar 
 (lactose), allied to grape sugar, is an ether of lactose ; cane sugar apparently 
 behaves in the same way. 
 
 Other bodies which occur in plants, and which are termed glucosides 
 are ethers built out of sugar and other atomic groups, and split up under 
 hydrolytic influences into these and into grape sugar. 
 
 In the animal body the only anhydride of sugar which is present is 
 
 Glycogen C 6 H 10 5 (or a multiple of this formula). This 
 substance is a constituent of the liver, of the muscles, and, 
 it appears, of all embryonic organs; it is soluble in water, 
 yielding an opalescent solution. By the red colour which is 
 formed when it is treated with iodine, and in its power of devi- 
 ating the plane of polarisation to the right, it appears to approach 
 dextrin most closely. By the action of acids and ferments it 
 is easily transformed into (dextrin.? and) sugar. 
 
 In the brain there is also found a starch-like body, which is 
 coloured blue by iodine. 
 
 Some glucosides occur in the body (see Protagon, Chondrin). 
 
 5. Ammonia and Ammoniacal Derivatives. 
 
 1. Ammonia NH 3 and its salts, the so-called salts of Am- 
 monium, occur in traces in many of the constituents of the 
 body, e.g. in the blood. 
 
 Ammonia can take part in the formation of compounds either by the 
 monatomic group NH 2 , or the diatomic group BflT, replacing one or two 
 
AMMONIA AND AMMONIACAL DERIVATIVES : AMINES. 21 
 
 hydrogen atoms ; in other words, the hydrogen atoms in ammonia may be 
 replaced by monatomic or polyatomic molecules. 
 
 To the group of ammonia-derivatives belong nearly all the nitrogenous 
 substances of the body, with whose constitution we are well acquainted. 
 These nitrogenous bodies originate in the albuminous substances and their 
 derivatives ; in these the nitrogen is probably present in great part in the 
 form of ammonia, although a portion of it is contained as cyanogen, seeing 
 that some nitrogenous substances contain also cyanogen (e.g. uric acid). 
 The following bodies belonging to this class must be mentioned : 
 
 a. Amines, 
 
 which are compounds in which the H-atoms of ammonia, or of ammonium- 
 hydrate, are replaced by hydrocarbon groups, for example i 
 
 H 
 
 H 
 
 | | H H '9' H H | |- | 
 
 H- C-N H H c __ ^ _ c_ H H-N H H C N C H 
 
 it H H H/\ J H \/\ i 
 
 XH V X H \ 
 /\ 
 
 H 
 
 NH 3 NH 2 (CH 3 ) N(CH 3 ) 3 NH 4 OH N(CH 3 ) 3 (C 2 H 5 0)OH 
 
 Ammonia Methylamine Trimethy- Ammonium- Choline or Neurine 
 lamine hydrate 
 
 2. Methylamine, NH 2 (CH 3 ) and 
 
 3. Trimethylamine, N(CH 3 ) 3 , occur as products of the decomposition of 
 choline and creatine. 
 
 4. Choline or neurine, C 5 H 15 N0 2 , trimethyl-oxyethyl-ammonium- 
 hydrate, is one of the products of the decomposition of lecithin (see below). 
 It is obtained synthetically from glycocol and trimethylamine, as may be 
 easily understood by studying the graphic formula of choline ; for when we 
 unite the two groups which are joined to the nitrogen by means of the 
 oblique lines, we obtain the graphic formula which represents glycocol, while 
 trimethylamine remains. 
 
 As a salt of choline must be mentioned 
 
 Lecithin, C 44 H 90 NP0 9 . This body is a constituent of nerve 
 matter, of blood, of semen, of yolk of egg, &c., in which it 
 appears to be present in complex combinations (see Protagon, 
 Vitellin). 
 
 By boiling with baryta, lecithin yields stearic acid, glycerinphosphoric 
 acid, and choline : 
 
 C 44 H 90 NP0 9 + 3H 2 = 2<J ]8 H 36 2 + C 3 H 9 PO 6 + C 5 H 15 N0 2 
 
 Lecithin Stearic acid Glycerin- Choline 
 
 phosphoric acid 
 
 It is considered (Diaconow) as distearyl-glycerinphosphate of choline (in 
 
22 AMMONIACAL DERIVATIVES: AMIDES. 
 
 the radical or residue of glycerinphosphoric acid two H-atoms are re- 
 placed by the radical of stearic acid). According to this view, the (abbre- 
 viated) formula of lecithin would be 
 
 H H H 
 
 (C 18 H a4 0)-C C C-(C 18 H 3S 0) 
 HO O OH CH 3 . 
 
 HO P N<5 S 
 
 il | CH ' 
 
 O C Z H 5 
 
 In addition to distearin-leeithin, there appears to be also a diolein-leci- 
 thin, an oleo-palmitin-lecithin, &c. According to another view (Strecker), 
 lecithin is not a choline-salt of distearyl-glycerinphosphoric acid, but it is 
 an ether-like body combined with the C 2 H 5 O molecule of choline. 
 
 5. Guanidine, imido-carbodiamide, C(NH 2 ) 2 (NH) (or diamido-imido- 
 inethane) is a product of the decomposition of guanine. It is obtained syn- 
 thetically from chloropicrin C(N0 2 )C1 3 and ammonia: 
 
 CN0 2 C1 3 + 4 NH 3 = C(NH 2 ) 2 (NH) + N 2 + 2 H 2 + 3 HC1. 
 Guanidine is closely related to urea. 
 
 6. Methyluramine, methylated guanidine (guanidine, in which the group 
 CH 2 has entered, as in the groups of the homologous series of fatty acids, p. 
 13), or diamido-imido-ethane, C 2 H 2 (NH 2 ) 2 (NH), is a product of the de- 
 composition of creatine. 
 
 b. Amides, 
 
 are compounds in which the OH-group in acids is replaced by 
 NH 2 . 
 
 7. UKEA, carbamide, CO(!S T H 2 ) 2 
 
 HO H O H 
 
 * II * I I! * | I! I 
 
 H O C H H N C H H N C N H 
 
 CO(OH) ? CO(NH 2 )OH CO(NH a ) 
 
 Carbonic acid Monaxnide of carbonic acid Diamide of carbonic acid 
 
 (Carbamic acid) (Carbamide or Urea) 
 
 is one of the simplest amido-compounds, and is the chief pro- 
 duct of the oxidation of nitrogenous substances in the organism ; 
 it is excreted in large quantities in the urine. 
 
 Urea is crystalline, easily soluble in water and alcohol, forms a sparingly 
 soluble salt with nitric acid, and gives a white precipitate with solution 
 of mercuric nitrate. In the presence of decomposing substances, when boiled 
 with alkalies, and when superheated with water, it combines with 2 H 2 O, 
 and is converted into ammonium-carbonate : CO(NH 2 ) 2 + 2 H 2 = 
 CO(O.NH 4 ) 2 
 
 H H H H 
 
 H-N C N H H N 0-C-O N H 
 
 CO(NH 2 ), CO(O.NH 4 ) 2 
 
 Urea Ammonium carbonate 
 

 
 AMMONIACAL DERIVATIVES: AMIDES. 23 
 
 Urea was the first organic substance which was synthetically obtained 
 (Wohler) ; it can be made artificially by many processes, as by heating 
 ammonium cyanate, when a re-arrangement of atoms takes place 
 (CN(O.NH 4 ) = CO(NH 2 ) 2 ). 
 
 H U H H 
 
 * \/ i ii i 
 
 N=C H N=C N H N C N H 
 
 CN(OH) CN(O.NH 4 ) COfNH,)., 
 
 Cyanic acid Ammonium cyanate Urea 
 
 Urea can also be prepared from carbonyl chloride (phosgene gas) and 
 ammonia : 
 
 COC1 2 + 2 NH 3 = CO(NH 2 ) 3 + 2 HC1 
 
 H H H O H 
 
 H N H Cl C Cl H N H Cl H H N C N H H Cl 
 
 NH 3 COC1 2 NH 3 HC1 CO(NH 3 ) 3 HC1 
 
 Phosgene gas. Urea. 
 
 Urea differs from guanidine in that in the latter body the carbon atom 
 is joined to the diatomic molecule NH, instead of to an 0-atom. 
 
 In both the NH 2 -molecules in urea, the H-atoms admit of being replaced 
 by alcohol- or acid-radicals. Combinations of the latter kind, namely, 
 where 2H 3 are replaced by diatomic acid-radicals, are often obtained, in 
 addition to ordinary urea, in the artificial oxidation of uric acid (which is 
 itself a body of the same kind, only more complex). The radicals of the 
 oxalic acid series and their immediate derivatives are, indeed, such compound 
 ureas ; some of them are called acids, for the last H-atom of the amide 
 group, which is still present, can be replaced by a metal. Some of these 
 bodies are : Parabanic acid (oxalyl-urea) CO(NH) 2 (C 2 2 ), Barbituric acid 
 (malonyl-urea) CO(NH) 2 (C 2 H 2 2 ), Dialuric acid (tartronyl-urea) CO(NH) 2 
 (C 3 H 2 3 ), Alloxan (mesoxalyl-urea) CO(NH) 2 (C 3 3 ). 
 
 H 
 
 II || II I II II I II 
 
 c-c c-c c 
 
 OO OHO OOO OOO 
 
 - 
 f 
 
 o-o c c-c c-c c c c c 
 
 -/ VH H-/ H V-H H-/ H VH H-N-C-k 
 
 Parabanic acid Barbituric acid Dialuric acid Alloxan 
 
 When subjected to hydrolytic processes these ureas combine with one or 
 two molecules of H 2 ; in the first case the ring, as it were, opens, and an 
 acid is formed in which only one of the OH groups is replaced by urea ; if 
 two molecules, however, enter, urea entirely separates from the acid ; e.g., 
 in the case of parabanic acid, the first molecule of water yields oxaluric 
 
 acid. 
 
 H o H o o 
 
 i II i ;i II 
 
 H N C-N-C-C H 
 
 C 3 H 4 N 2 4 
 
 Oxaluric acid 
 
24 AMMONIACAL DERIVATIVES: AMIDO-ACIDS. 
 
 The second molecule of water leads to the formation of 
 
 H o H oo 
 
 I II I II II 
 
 H N C N H and H C C H 
 
 CO(NH 2 ) 2 C (yOH) a 
 
 Urea Oxalic acid 
 
 "When reduced, alloxan furnishes alloxantin (C 8 H 4 N 4 7 ). 
 2 C 4 H 2 N 2 4 + H 2 = C 8 H 4 N 4 7 + H 2 0. 
 
 Alloxantin is an ether-like combination of alloxan and dialuric acid (see 
 above), and on the addition of H 2 yields these two substances : 
 
 C 8 H 4 N 4 7 + H 2 = C 4 H 4 N 2 4 + C 4 H 2 N 2 O 4 
 
 Dialuric acid is obtained by the further reduction of alloxan or alloxantin : 
 
 C 4 H 2 N 2 4 + H 2 = C 4 H 4 N 2 4 
 C 8 H 4 N 4 7 + H 2 + H 2 = 2(C 4 H 4 N 2 4 ) 
 
 c. Amido-Acids 
 
 are acids in which hydrogen atoms of the acid radical are replaced by NH 2 , 
 for instance : 
 
 HO H H o 
 
 I II * ! I II * 
 
 H C C H H N C C H 
 
 I A ! 
 
 H H 
 
 C 2 H 3 0(HO) C 2 H 2 (NH 2 )0(OH) 
 
 Acetic acid Amidoacetic acid or glycocine 
 
 The amido-acids behave, on the one hand, as acids, on the other as bases, 
 inasmuch as their ammoniacal residue combines with acids, e.g. 
 
 H H o H H o 
 
 I I II I I II * 
 
 H N C C 0--Ag H N C C H 
 
 Glycocine-silver compound Glycocine hydrochlorate 
 
 Silver Amido- Acetate 
 
 When treated with nitrous acid the amido-acids yield oxy-acids ; thus the 
 amido-fatty acids yield the oxy-fatty acids (Gly collie Acids, p. 14), by the 
 replacement of the molecule NH 2 by the molecule OH. 
 
 8. Glycocine (glycocol, sugar of gelatin, amido-acetic acid), 
 C 2 H 2 (NH 2 )O.OH, does not occur, as such, in the body, but 
 forms part of so-called conjugate acids, and exists in complex 
 combinations in gelatin. 
 
 Glycocine when treated with nitrous acid yields oxy-acetic or gly collie 
 acid. It can be prepared synthetically from chloracetic acid and ammonia. 
 It unites with monobasic acids so as to form compounds, in which one H- 
 atom of the NH 2 is replaced by the acid radical (the OH-group and the H- 
 atom combining to form H 2 0), thus : 
 
AMMONIACAL DERIVATIVES: AMIDO-ACIDS. 25 
 
 H H H H 
 
 H H C C H H O C C 
 
 * ii I I * H / \ * H i i H y \ 
 
 C NH H 0-C C C H H-0 C N C C C-H 
 
 H O-C 
 
 i c= 
 
 W 
 
 Glycococine Benzole acid (p. 17) Hippuric acid 
 
 C 2 H 2 (NH 2 )0(OH) CH(C 6 H 5 )0 2 C 9 H 9 N0 3 
 
 The following are compounds which under hydrolytic influences combine 
 with H 2 and split up into glycocine and an acid: they are called conjugate 
 acids : 
 
 Glycocholic acid (see p. 16), C 26 H 43 N0 6 , is a constituent of 
 the bile. 
 
 Hippuric acid (Grlyco-benzoic acid), C 9 H 9 N0 3 , is a con- 
 stituent of the urine of the herbivora, but occurs in every 
 animal if benzoic or some other aromatic acids (cinnamic, 
 mandelic, and chinic acids) have been taken with the food. 
 
 Other, so-called substituted, aromatic acids do not form hippuric, but 
 corresponding acids. 
 
 9. Alanine, amido-propionic acid, C 3 H 4 (NH 2 )O.OH, does not occur in 
 the animal body. 
 
 10. Butalanine, amido-valerianic acid, C 5 H 8 (NH 2 ) O.OH, and 
 
 11. Leucine, amidocaproic acid, C 6 H 10 (NH 2 )O.OH, are found 
 in many constituents of the body, but, except in the pancreas, 
 they are probably products of decomposition. When treated 
 with nitrous acid, leucine yields oxycaproic acid or leucic acid 
 (p. 14). Leucine is an important ingredient of the albuminous 
 bodies. 
 
 12. Serine is probably amidolactic acid C 3 H 5 (NH 2 )0 S , and is obtained, 
 in addition to leucine and tyrosine, by boiling silk-gelatine with acids. 
 
 When treated with nitrous acid it yields oxylactic acid, viz., glyceric acid. 
 
 13. Cystine, C 3 H 7 NS0 2 , has been considered as serine, in 
 which one atom of oxygen has been replaced by S, and has pro- 
 bably the same constitution. 1 It is a constituent of the kidneys, 
 and is occasionally found in the urine and in urinary calculi. 
 
 14. Taurine, amido-ethyl-sulphonic acid, S0 2 (OH) 
 (C 2 H 4 .H 2 N) 
 
 00 OH H 0OH H H 
 
 H S H H 0-S-C C-H H S C C N H 
 
 S0 2 (OH), S0 2 (OH)(C 2 H 5 ) -, 4 
 
 Sulphuric acid Ethylsulphonic acid Amido-ethylsulphonic acid or Taurine 
 
 1 The formula of cystine is probably C 3 H 5 NS0 2 ; when decomposed by means 
 of nitrous acid it does not yield glyceric acid, as would almost certainly be the case 
 if it were derived from serine (Dewar and Gamgee). 
 
26 AMMONIACAL DERIVATIVES: AM1DO-ACIDS. 
 
 This body occurs in the bile as a compound of cholic acid, simi- 
 lar to that of glycocine, viz. as Taurocholic acid (C 26 H 45 NS0 7 ) ; 
 it is also present in a free condition in some glands. 
 
 15. Tyrosine, C 9 H n N0 3 , is an amido-acid, whose consti- 
 tution is not yet known, but which contains as its basis an 
 aromatic residue ; it is found in small quantities together with 
 leucine. Like leucine, it is an important constituent of the 
 albuminous bodies. 
 
 When heated with mercuric nitrate in presence of some nitrous acid, 
 tyrosine yields a red colouration. 
 
 d. Amido acids, in which the hydrogen of the ammoniacal 
 
 residue is itself substituted. 
 16. Sarcosine, methyl-amido-acetic acid or methyl-glycocine, 
 
 C 2 H 2 (NH[CH 3 ])O.OH, 
 
 is obtained when creatine is treated with alkalies, or synthetically by the 
 action of methylamine on chloracetic acid (refer to p. 24, for the synthesis of 
 Glycocine). It is an isomer of alanine. 
 H H H o 
 
 H N C C C H 
 
 C 3 H,N0 2 
 
 Alanine 
 
 17. Creatine, methyl-guanidine-acetic acid, C 4 H 9 N 3 2 , is a 
 constituent of the blood, the muscles, and the brain, &c. 
 
 H H 
 
 H N H H HNHHHO 
 
 i II I I I I! I I I II 
 
 H N C C N H H N C C N C C H 
 
 i i A 
 
 Methyl-guanidine Methyl-guanidine-acetic acid (Creatine) 
 
 Creatine is obtained synthetically from cyanamide (CN.NH 2 ), and sar- 
 cosine ; one can in the graphic formula of creatine easily recognise, on the 
 left, the residue of cyanamide, and, on the right, that of urea. 
 
 C 4 H 9 N 3 2 + H 2 = C 3 H 7 N0 2 + CH 4 N 2 0. 
 
 Actually, urea only differs from cyanamide in containing one molecule 
 more of H 2 0. 
 
 H H o H 
 
 HN C=N H N C N H 
 
 Cyanamide Urea 
 
 When oxidized (by means of mercuric oxide, peroxide of lead, &c.), 
 creatine yields methyl-guanidine and oxalic acid, a decomposition which is 
 intelligible enough when "we consider that both methyl-guanidine and acetic 
 
DERIVATIVES OF UNKNOWN CONSTITUTION. 27 
 
 acid occur in creatine, and that oxalic acid is a doubly oxidized acetic acid 
 (p. 15). 
 
 By other methods of oxidation, creatine yields methyl-parabanic acid, 
 which is also an intelligible enough reaction. 
 
 e. Ammoniacal Derivatives of unknown Constitution. 
 
 18. Uric acid, C 5 H 4 N 4 3 , is a constituent, and in some 
 classes of animals the principal constituent, of the urine. 
 
 The most probable view of the constitution of uric acid is, 
 that it is tartronylcyanamide. 
 
 H H H 
 
 000 HOOOH HOOOH 
 
 * II I I * I P I II I I II I II I 
 
 H C C C H H N C C C N H N=C N C C C N =CN 
 
 CjHjOjCOH),, C S H 4 O 3 (NH,),, C,H,0 3 (NH.CN)., 
 
 Tartronic (or oxymalonic Tartronylamide Tartronyl-cyanamide 
 
 acid) (uric acid) 
 
 Uric acid is bibasic, as in it, as in compound ureas (p. 23), both the 
 remaining H-atoms of the amide groups are replaceable by metals. Of the 
 salts, of which the acid ones are, like uric acid itself, very slightly soluble 
 in water, those of sodium and ammonium occur in man chiefly in patholo- 
 gical conditions. 
 
 By oxidation, uric acid yields: 
 
 a, in presence of acids, alloxan and urea : 
 
 C 5 H 4 N 4 3 + H 2 + = C 4 H 2 N 2 O 4 + CH 4 N 2 0. 
 
 (Alloxan yields on further oxidation carbonic acid and parabanic acid, 
 C 4 N 2 H 2 4 + = C0 2 + C 3 H 2 N 2 3 ). 
 
 b, in presence of alkalies, allantoin (C 4 H 6 N 4 3 ) and carbonic acid : 
 
 C 5 H 4 N 4 3 + H 2 + = C 4 H 6 N 4 3 + C0 2 . 
 
 c, when treated with nitric acid and evaporated to dryness, uric acid 
 yields a golden-red residue, which is coloured purple-red (murexide, pur- 
 purate of ammonia) by ammonia and blue by potash. 
 
 19. Xanthine, C 5 H 4 N 4 2 , occurs in traces in many organs of 
 the body and in the urine, and can artificially be obtained 
 from hypoxanthine. A body isomeric with it is obtained from 
 guanine. 
 
 20. Hypoxanthine or Sarcine, C 5 H 4 N 4 0, occurs together 
 with xanthine, into which it is converted by the action of oxi- 
 dizing agents. 
 
 21. Carnine, C 7 H 8 N 4 3 , occurs in small quantities in extract 
 of meat (Weidel) ; under the influence of bromine it is oxidized 
 to hypoxanthine : 
 
28 DERIVATIVES OF UNKNOWN CONSTITUTION. 
 C 7 H 8 N 4 3 + Br 2 = C 5 H 4 N 4 O.HBr + CH 3 Br + C0 2 
 
 Carnine Sarcine hydrobromite Methyl-bromide 
 
 22. Guanine, C 5 H 5 N 5 0, occurs in small quantities in the 
 pancreas and liver, as well as in guano and the excrements of 
 spiders. 
 
 When oxidized, guanine yields a body which is isomeric with xanthine 
 (isoxan thine), nitrogen beiDg evolved, 
 
 2 C 5 H 5 N 5 + 30-2 C 5 H 4 N 4 Q 2 + H 2 O + N 2 . 
 
 Other oxidizing agents split it up into carbonic acid, parabanic acid and 
 guanidine, 
 
 C B H 5 N 5 + H 2 + 3 = C0 2 + C 3 H 2 Ts T 2 3 + CH 5 N S . 
 
 23. Creatinine^ C 4 H 7 N 3 (>, is a constituent of urine. 
 
 Creatinine is a strongly alkaline substance ; it forms a characteristic 
 crystalline compound with chloride of zinc. It is an anhydride of creatine, 
 from which it is easily obtained, and into which it is easily reconverted. 
 The most probable view of the formation of this anhydride is shown in the 
 
 accompanying formula. 
 
 H 
 
 H H N H 
 
 i \/ \y 
 
 HNHHHO CC 
 
 H N C N C C O H H N=C H H C=0 
 
 A i V 
 
 
 
 C 4 H 9 N 3 Z C 4 H,N 3 
 
 Creatine Creatinine 
 
 24. Inosinic acid C 5 H 8 N 2 6 , a constituent of muscles. 
 
 25. Kynurenic add C 20 H 14 .N 2 O 6 , occurs in the urine of dogs. 
 
 26. Allantoin, C 4 H 6 N 4 3 , is a constituent of the urine of 
 the foetus and the sucking infant. It is obtained by the oxida- 
 tion of uric acid (see p. 27). Under hydrolytic influences allan- 
 toin splits into urea and allanturic acid (C 3 H 4 N 2 3 ) ; thus 
 
 4 H 6 N 4 3 + H 3 = CH 4 N 2 + C 3 H 4 N 2 S 
 
 27. Colouring matters. These substances, of which the 
 best known are connected with the derivatives of ammonia, 
 are in general crystallizable, and probably originate in one 
 substance, which contains iron, and is called hsematin. Some 
 of these colouring matters contain no iron; these being the 
 simpler, will be first treated of. 
 
 a. Bilirubin (biliphaein, cholepyrrhin, hsematoidin), 
 C 16 H 18 N 2 3 (Stadeler), the orange-red and crystallizable co- 
 
COLOURING MATTERS. 29 
 
 louring matter of the bile, is insoluble in water, soluble in 
 chloroform and in alkalies, with which it forms compounds, as 
 if it were a monobasic acid. When oxidized it passes into 
 biliverdin, and when more strongly oxidized into bilicyanin 
 and choletelin. That it originates in hsematin is proved by 
 the fact that it, or at any rate a body exceedingly like it, is 
 found in old extravasations of blood (hsematoidin crystals). 
 
 In contact with nitric aeid, which contains some nitrous acid, solutions 
 of bilirubin show at their margins rainbow colourations, which are produced 
 by the successive oxidations which take place. This (Gmelin's) test 
 enables the smallest quantities of bilirubin to be detected. 
 
 b. SiUverdin (C 16 H 20 N 2 5 = bilirubin + H 2 + O Stadeler; C 16 H 18 N 2 4 
 Maly) is formed when bilirubin is oxidized in air ; it does not appear to 
 occur in the organism ; when treated with sulphurous acid it appears to be 
 reconverted into bilirubin. 
 
 c. Bilifmdti C 16 H 20 N 2 0. (= bilirubin + H 2 0) and 
 
 d. Biliprasin C 16 H 22 N 2 O 6 ( = bilifuscin + H 2 + 0) have been found 
 in gall-stones in small quantities. 
 
 e. Bilicyanin (Heynsius and Campbell) is formed when any of the 
 above-mentioned colouring matters are strongly oxidized ; when present in 
 acid solution its spectrum possesses an absorption band close to F j it is 
 present in gall-stones. 
 
 /. Choletelin (Maly) is tire last oxidation product of all the bile colour- 
 ing matters. 
 
 ff. Urobilin (Jaffe) is probably identical with hydrobilirubin, C 32 H 40 N 4 7 
 (Maly), (a substance which can be obtained from bilirubin by reducing it in 
 alkaline solutions), and with stercobilin ("Vanlair and Masius), a constituent 
 of fsBces. This colouring matter occurs in urine, in bile, and in the intes- 
 tinal contents ; it possesses a broad absorption band in the green (at F), 
 and when existing in alkaline solution together with chloride of zinc, it is 
 strongly fluorescent. 
 
 h. Hcematin is a product of the decomposition of the normal 
 colouring matter of blood ; its composition and properties will 
 be described under Blood (Chap. I.). 
 
 i. Urinary colouring matters. In the urine, several 
 colouring matters have been found, of which some contain 
 iron, others contain none ; these substances do not crystallize, 
 and their composition is unknown. One of these, urobilin (see 
 above) occurs as a regular constituent in the bile and the intes- 
 tinal contents. Blue colouring matters, which appear to belong 
 to the indigo group, also occur in urine, but do not appear to 
 exist in it preformed (see Chapter II). 
 
 k. Melanin is a black or brown colouring matter, which 
 
 < THF"**** 
 
 'UNIVERSITY] 
 
30 BODIES OF UNKNOWN CONSTITUTION. 
 
 contains iron, and is little known ; it occurs in the lungs, the 
 bronchial glands, the rete malpighii, the hair, the choroid, &c. 
 
 6. Complex Bodies of unknown Constitution. 
 
 As was formerly mentioned, the bodies which we have 
 hitherto passed under review are to be considered as natural or 
 artificial products of the decomposition of other much more 
 complex bodies, in which the molecules of the simpler bodies, 
 as OH, CH 3 , NH 2 , C G H 5 , occur in the most varied and intricate 
 combinations. 
 
 Of these complex substances only a few can be obtained in 
 a pure condition ; the remainder cannot, either because they 
 are too unstable, or because they are not crystallizable ; with 
 regard to the majority we do not therefore know even their 
 composition by weight, much less their constitution. 
 
 The decomposition of these complex into more simple compounds is, 
 nearly always, easily effected under so-called hydrolytic influences. One 
 may (from the results of these decompositions) look upon them, either 
 wholly or in great part, (1) as anhydrides or ethereal compounds, viz. as 
 compounds of alcohol + alcohol water, or alcohol + acid water, or acid + 
 acid water, or (2) as amides, viz. acids + ammonia water, or (3) as com- 
 plex ureas, viz. as acids + urea water, &c. 
 
 Meanwhile the hydrolytic products of the decomposition of many of 
 these compounds are still too imperfectly known to allow of a complete in- 
 sight into their structure. Besides, even were we sufficiently acquainted 
 with these products, many difficulties would yet remain in the way of deter- 
 mining their constitution. We may illustrate these difficulties by referring 
 to the anhydrides of sugar ; if, for instance, we consider starch (C 6 H ]0 5 ) to 
 be derived from a single molecule of sugar, by the removal of one molecule 
 of H 2 0, there occur to us the most diverse possibilities as to the point in the 
 body whence the H 2 was removed ; the number of these possibilities in- 
 creases enormously, however, if we assume that starch is derived from two 
 molecules of sugar, 2H 2 O being separated. We can thus explain that in 
 the case of these more complex bodies there exist so many isomeric and 
 polymeric compounds, possessed of almost identical properties, and whose 
 true constitution is unknown. 
 
 The greater the number of atoms which combine to form a compound 
 the greater becomes the complexity of its composition, so that elementary 
 analyses are insufficient clearly to indicate its formula. The formulae of the 
 substances now to be treated of, are for this reason unknown to us. 
 
 We have to refer to the following groups of bodies : 
 
PEPTONES AND THEIR ANHYDRIDES. 31 
 
 Peptones and their Anhydrides (Albuminous Bodies 
 and Albuminoid Bodies). 
 
 The peptones are formed within the body, by the hydro- 
 lytic decomposition of their anhydrides (see Digestion, Chap. 
 III.), and apparently are soon reconverted into them. These 
 anhydrides, the albuminous and albuminoid bodies, are very 
 generally diffused throughout the body. 
 
 The hydrolytic products of decomposition of peptones are 
 chiefly amido-acids, especially glycocine, leucine, tyrosine (pp. 
 24, 25, and 26). These cannot, however, be the only products 
 of decomposition, for the majority of these peptones contain 
 sulphur. It is unknown in what molecular combination the 
 sulphur is contained, whether as sulphuric acid, as sulphuretted 
 hydrogen, or as carbon disulphide. Even the nitrogen appears 
 to be present in other states than in the amido-acids. 
 
 The various peptones differ in the relative quantities of the 
 three amido-acids which they yield. Whilst all peptones yield 
 leucine, gelatin-peptone furnishes only glycocine in addition ; 
 the remaining peptones, besides leucine, yield also tyrosine, in 
 different quantities. It addition to tyrosine, when hydrolytic 
 action is prolonged, other bodies possessed of a bad smell, and 
 belonging to the indigo group, are obtained. The anhydrides 
 yield, in the first place, peptones, and only afterwards the 
 further products of decomposition. 
 
 1. PEPTONES. The only peptone of which the percentage 
 composition is approximately known is that which is obtained 
 by the digestion of serum-albumin (C 51*37, H 7*25, N 16-18, 
 S 2-12, 23-11 percent.) 
 
 The peptones are soluble in water, and partially soluble in alcohol 
 (Briicke's ' Alkophyr ') ; they exert a left-handed rotation on the plane of 
 polarisation. They differ from solutions of albumin in not being precipitated 
 by heat, weak alcohol, dilute mineral acids, and divers metallic salts ; they 
 are, however, precipitated by corrosive sublimate, mercuric nitrate, silver 
 nitrate, and chlorine. They possess three reactions, which will be de- 
 scribed ' under Proteids. For the products of their hydrolytic decompo- 
 sition see above concerning their origin in the process of digestion see 
 Chap. III. 
 
 Proteids. 
 
 2. ALBUMINOUS BODIES (Protein bodies). These very numer- 
 ous peptone-anhydrides occur in almost all the tissues and fluids 
 
32 ANHYDRIDES OF PEPTONES: PROTEIDS. 
 
 of the body dissolved in water, or more frequently in a glutinous 
 (or swollen) state ; their solutions rotate the polarized plane to 
 the left. They are not crystallizable (all descriptions hitherto 
 given of albuminous crystals are uncertain), and consequently 
 cannot be obtained quite pure ; it is peculiarly difficult to free 
 them from inorganic matters, with which they appear, partly, 
 to exist in chemical combination. 
 
 By the action of heat and of mineral acids, and by the pro- 
 longed action of alcohol, they are converted into insoluble 
 modifications (coagulated). 
 
 Seeing that by hydrolytic treatment the coagulated modification is, first 
 of all, converted into the soluble, and that only then peptones are formed, 
 it would appear that the coagulated modification is a further anhydride of 
 the soluble. 
 
 The albuminous bodies form compounds with acids and 
 alkalies, of which the former (acid-albuminates, syntonin) are 
 precipitated by alkalies, the latter (alkali-albuminates, casein) 
 by acids. 
 
 Oxidizing and other reagents, which act energetically upon 
 the albuminous bodies, yield, by their action upon them, amido- 
 acids (see above): glyeocine, leucine, tyrosine; further, volatile 
 fatty acids, benzoic acid, hydrocyanic acid ; aldehydes of the 
 fatty acids, and of benzoic acid, &c., and it is even said urea. 
 They thus contain nitrogen in ammonia and cyanogen mole- 
 cules. 
 
 Nitric acid colours the albuminous bodies (and the peptones likewise) of 
 ' a yellow colour (xantho-proteie reaction), and the addition of alkali changes 
 the colour to red. Mercuric nitrate, in the presence of a little nitrous acid, 
 at 60 C., colours the albuminous bodies red (Millon's reaction). This re- 
 action, which agrees with that of tyrosine, probably depends upon an inter- 
 mediate formation of tyrosine. 
 
 With cupric sulphate and potassium hydrate the albuminous bodies yield 
 a violet solution. 
 
 All these three reactions may be employed in the detection of the albu- 
 minous bodies. 
 
 The origin of the albuminous bodies is not known with cer- 
 tainty ; but it is very probable that they may be regenerated 
 within the animal body, by synthetic processes, from peptones, 
 and perhaps even from the still simpler products of decompo- 
 sition formed during the digestion of the albuminous matters of 
 
ANHYDRIDES OF PEPTONES : ALBUMINOUS BODIES. 33 
 
 the food (Chap. III. and V.) The latter are derived in the first 
 instance from plants, which are the only constructors of albumin. 
 
 Equally little is known of the ultimate end of the albumi- 
 nous bodies in the organism. It would appear as if the so- 
 called albuminoid bodies were their closest derivatives. In 
 their more thorough decomposition in the organism, the 
 nitrogen probably passes into arnido-compounds, of which the 
 most completely oxidized, as urea, are excreted. It is, 
 however, very probable, from their composition, that fats, gly- 
 cogen, and sugars take their origin in the albuminous bodies, and 
 in support of this view there are weighty physiological facts. 
 Conversely, it appears that synthetic processes of a higher order 
 occur in the organism, whereby albuminous bodies form still 
 more complex compounds (see below, p. 36). 
 
 The various albuminous substances of the body possess nearly 
 the same percentage composition: C 52-7 54-5, H 6-9 7-3, 
 N 15-4 -16-5,80-8 -1-6, 020-9 23-5 per cent. Byhydrolytic 
 processes they yield to 2 per cent, of tyrosine and from 1 18 
 per cent, of leucine. They are chiefly distinguished from one 
 another by the circumstances of their precipitation and coagu- 
 lation. 
 
 The most important are : 
 
 a. ALBUMIN, which occurs in blood-serum, in white of egg 
 (somewhat modified), and in most tissue-juices. It coagulates 
 in neutral or acid solutions at temperatures varying from 
 6070 C. 
 
 The casein of milk is a potassium albuminate, but does not coagulate 
 when simply heated ; it does so only when an acid is added. It is precipitated 
 by most acids. 
 
 6. GLOBULIN is a constituent of the blood and of many 
 tissues ; it is precipitated from its solutions by acids, even by 
 carbonic acid, the precipitate being dissolved by the subsequent 
 passage of oxygen ; it is probably an albuminate of potassium. 
 Many different forms of this body exist, and these are, in part, 
 designated by the term * paraglobulin ' (Chap. I.) 
 
 c. FIBKIN, the stringy constituent of coagulated blood ; a 
 body which separates as the result of the inter-action of two 
 kinds of paraglobulin (the fibrinoplastic and fibrinogenous sub- 
 stances) (Chap. I.). When heated, fibrin assumes the characters, 
 of a coagulated albuminous body. 
 
34 ANHYDRIDES OF PEPTONES: ALBUMINOID BODIES. 
 
 d. MYOSIN, the coagulum of muscles which have sponta- 
 neously passed into the state of ' rigor ' (Chap. VIII.) 
 
 The syntonin of muscles is merely an acid albuminate which is produced 
 by acid which is formed in muscle or which has been employed in its extrac- 
 tion (p. 32). 
 
 3. ALBUMINOID BODIES. These substances, which occur as 
 the principal constituents of many tissues, and approach the 
 albuminous bodies in composition (although some of them 
 contain no sulphur), are looked upon as their nearest deriva- 
 tives. We do not know by what processes they arise from 
 them : whether by oxidation, or, on the contrary, by synthesis, or 
 in any other way. 
 
 They differ from one another much more than the albumi- 
 nous bodies, and, if we except their colloidal character, i.e. their 
 inability to crystallize and to form true solutions, they possess 
 no common character. Under hydrolytic influences they furnish 
 the same products as the albuminous bodies, viz. leucine and 
 tyrosine, in large quantities. One of these bodies, chondrin, 
 which is said to yield grape sugar when it is boiled with dilute 
 sulphuric acid, must be a glucoside, and should therefore be 
 separated from the other substances. 
 
 The most important albuminoid bodies are 
 
 a. Mucin, (C 52-2, H 7*0, N 12-6, 28-2 per cent.) forms a 
 viscid fluid with water (mucus), which is precipitated by a little 
 acetic acid, and by excess of alcohol. It occurs in mucous 
 secretions, and in gelatinous connective tissue (Wharton's jelly, 
 &c.) Besides leucine, it yields much tyrosine. 
 
 b. Glutin, gelatin (C 50-4, H 6-8, N18-3, S + 024-5) is 
 extracted from nearly all the connective tissues (bones, liga- 
 ments, skin) by boiling them with water. Grelatin swells in 
 cold water ; by boiling, a solution is obtained which again 
 gelatinizes on cooling. On prolonged boiling it splits up into 
 a non-gelatinizing peptone, which also is a product of digestion. 
 Hydrolytic treatment furnishes leucine, glycocine, and ammonia, 
 but no tyrosine. 
 
 c. Sericin, or silk-gelatine (C 15 H 25 N 5 8 ?) is a constituent of silk. 
 
 d. Keratin (C 50-3 -52-5, H6-4-7O, N16-2-17-7, SO-7 
 5'0, 20*7 25-0 per cent.) is the residue left when the so- 
 called horny tissues have been treated with ether, alcohol, water 
 and acids : it is a substance only soluble in hot alkalies, and 
 
FERMENTS. 35 
 
 which swells up in cold alkalies. It yields 10 per cent, of 
 leucine, and 3-6 per cent, of tyrosine. 
 
 e. Elastin (C 55-5, H 7-4, N 16-7, 20-5 per cent.) is the re- 
 sidue left after the removal of all soluble matters from connec- 
 tive tissue ; it is the characteristic substance of all elastic 
 tissues. It is insoluble in all agents which do not decompose it. 
 
 It yields much leucine (36 45 per cent.), but little tyrosine 
 ( per cent.) 
 
 /. Fibroin (0 48-6, H 6'5, N 17-3, 27*6 per cent.), is the chief consti- 
 tuent of silk, and is soluble in concentrated acids and alkalies. 
 
 g. HYDROLYTIC FERMENTS are bodies which, by an action 
 which is not yet understood, cause a decomposition of bodies 
 which are in proximity to them, without being themselves 
 consumed ; the bodies which are decomposed combine with the 
 elements of water. 
 
 Formerly these animal ferments were considered to belong 
 to the albuminous bodies ; the best known among them do 
 not, however, possess the characters of albuminous substances, 
 which, however, often adhere mechanically to them. 
 
 In order to separate many ferments in a pure condition we may avail 
 ourselves of their property of adhering to bulky precipitates, as to the pre- 
 cipitates which are produced when solutions of cholesterin or collodion are 
 added to fluids which contain them. 
 
 The animal body contains the following hydrolytic fer- 
 ments : 
 
 a. AMYLOLYTIC, OR SUGAR-FORMING FERMENTS, which convert 
 starch, glycogen, &c. into sugar, with absorption of water ; these 
 ferments are present in saliva, pancreatic juice, in the liver, and 
 many other organs. 
 
 @. FAT-DECOMPOSING FERMENTS, which cause fats to combine 
 with the elements of water and to decompose into fatty acids 
 and glycerin ; a ferment of this class appears to exist in the 
 pancreatic juice. 
 
 7. FERMENTS WHICH DECOMPOSE THE ALBUMINOUS BODIES : 
 these ferments which exist in the gastric juice (pepsin), and in 
 pancreatic and intestinal juices, convert soluble and coagulated al- 
 buminous bodies into peptones, and then in to leucine, tyrosine, &c. 
 
 No other but hydrolytic ferments have yet been discovered 
 in the body. 
 
 D 2 
 
36 COMPOUNDS OF PROTEIDSGLUCOSIDES. 
 
 2. BODIES MOKE COMPLEX THAN THE ALBUMINOUS SUBSTANCES. 
 We can only certainly assume the existence of bodies of this class 
 from the fact that when they are decomposed albuminous bodies 
 are liberated. To this group belong 
 
 1. Haemoglobin, the red crystalline colouring matter of 
 the blood corpuscles, which is likewise contained in small quan- 
 tities in serum and in the muscles. Its properties will be de- 
 scribed in the chapter on Blood. 
 
 2. Vitellin, a crystalline body which, when decomposed, yields 
 albumin and lecithin. It is a constituent of the yolk of eggs. 
 
 3. Ichthin, a body which apparently has a similar constitution to vitellin, 
 and which is found in the ova of fishes (ichthidin and emydin are bodies of 
 the same kind). 
 
 With the exception of the above, no other bodies having a 
 more complex constitution than the albuminous have yet been 
 demonstrated to exist. Nevertheless, it -appears in the highest 
 degree probable that such a body exists in the muscle, one of 
 whose products of decomposition is myosin. 
 
 3. GrLUCOSIDES WHICH CONTAIN NlTROGEN. The following 
 
 nitrogenous glucosides have been discovered in the human or- 
 ganism. 
 
 1. Protagon, which is a glucoside of lecithin, occurs as a 
 constituent of the brain, of the blood, and probably also of 
 other organs which contain lecithin. Under the action of 
 hydrolytic ferments, it yields grape sugar and the decomposition 
 products ,of lecithin (choline, glycerinphosphoric acid, &c.) ; 
 its formula has not been determined. 1 It is insoluble in water, 
 but swells into a viscid mass ; it is soluble in alcohol and warm 
 ether. 
 
 2. Chondrin (C 49-9, H 6-6, JST 14-5., SO-4, 28-6 per cent.), 
 is extracted from hyaline cartilage and the covering of the 
 holothuria by boiling with water.; in its external characters it 
 resembles gelatin. Under hydrolytic treatment it furnishes 
 leucine and grape sugar (the latter fact is disputed). 
 
 1 According to recent researches (Hoppe-Seyler and Diaconow) protagon appears 
 to be a mixture of lecithin and cerebrin. Cerebrin (W. Miiller), C 17 H 33 N0 3 (?), is 
 a glucoside, and possesses the property, ascribed to protagon, of swelling when 
 acted upon by water. "When decomposed by mineral acids it yields, in addition 
 to other bodies which have not yet been investigated, a sugar-like body which 
 rotates the plane of polarization to the left. 
 
PROGRESSIVE AND RETROGRADE METAMORPHOSIS. 37 
 
 3. Chitin, a nitrogenous glucoside, is contained in the shell 1 
 or exoskeleton of arthropoda. 
 
 4. Hyalin is a nitrogenous glucoside found in the cysts 
 of echinoeocci. 
 
 In the foregoing pages the chemical constituents of the 
 animal body have been classified according to their chemical 
 affinities. Other methods of classification are based on the 
 origin of these substances in the body, but they are necessarily 
 unsatisfactory, in consequence of the slight acquaintance which 
 we possess with the chemical processes of the organism. 
 
 The basis of the most commonly adopted arrangement is 
 the fact that from the albuminous bodies, the carbohydrates 
 and the fats, which form the chief organic food of the body, all 
 its constituents are derived. The changes which each substance 
 undergoes in its conversion into a formed element of the body 
 are included in the term assimilation, or 'progressive meta- 
 morphosis,' whilst the further changes which end in excretion 
 are included in the term 4 retrograde metamorphosis.' Processes 
 of oxidation and decomposition play the principal part in 
 bringing about the latter ; complicated breaking up into more 
 and more simple bodies, the chief representatives of which are 
 carbonic acid, water, urea, sulphuric and phosphoric acid. 
 
 The chemical processes which are concerned in the so-called 
 ' progressive metamorphosis,' and which lead to the formation 
 of albuminoid bodies, of haemoglobin, of protagon, &c., are 
 altogether unknown to us, although we may doubtless conclude 
 that in their production synthetic processes play some part. 
 
38 
 
 CHAPTER I. 
 THE BLOOD AND ITS CIRCULATION. 
 
 THE material interchanges which take place between the con- 
 stituents of the body and the external world, and between these 
 constituents themselves, occur through the medium of a fluid 
 which is in perpetual contact with the remotest parts of the 
 body, as well as with those apparatuses which are to be con- 
 sidered as the portals by which the body communicates with the 
 exterior ; that fluid is the blood. 
 
 The blood receives directly from the external world oxygen 
 and nutritive matters, and from it the individual tissues obtain 
 these substances. The latter, again, rarely give up their excre- 
 mentitious products directly to the external world, but pour 
 them, first of all, into the blood, which throws them out of the 
 body at certain destined places. The blood, moreover, is con- 
 tinually taking up substances which have undergone changes 
 in different localities, and deposits them, for further use, else- 
 where. 
 
 Every particle of the body which plays a part in its 
 chemical changes must therefore, repeatedly, presumably very 
 frequently, become the constituent of a very voluminous fluid 
 (the blood), in which it mixes with innumerable other sub- 
 stances, so that its further progress outwards depends upon 
 the accident of the place at which it again leaves the mass of 
 the blood. 
 
 It is therefore expedient, in the exposition of the chemical 
 changes which occur in the body, to consider the blood as its 
 natural centre, and to classify the various processes as sources 
 of expenditure or gain to the blood, before treating of the in- 
 terchanges between the matter of the whole organism and the 
 external world. 
 
THE BLOOD EED CORPUSCLES. 39 
 
 I. THE BLOOD. 
 
 Human blood is a red fluid, opaque even when in very thin 
 layers, and possessed of an alkaline reaction. It consists of a 
 yellow alkaline liquid (liquor, or plasma, sanguinis), and small 
 microscopic bodies, the blood corpuscles, which are suspended 
 in the fluid in large numbers (4 to 5*5 millions in one cubic 
 centimetre ; Welcker), and are in close contact with one another. 
 These are mostly red, but a small number (1 in 500 or 1 in 300, 
 Welcker in the splenic veins, however, 1 in 70, Hirt) of colour- 
 less corpuscles are mixed with them. 
 
 To test the alkaline reaction of blood the mere employment of litmus 
 paper is not sufficient ; either the colourless diffusate obtained by means of 
 a porous septum and distilled water is tested (Kiihne), or a drop of blood 
 is placed on litmus paper which has been previously moistened with a solution 
 of common salt (Zuntz). 
 
 Red Blood Corpuscles. 
 
 In man, the red blood corpuscles have the form of circular, 
 biconcave discs; their greatest diameter averages T ^mm. 
 They are uniformly coloured red. They, are very soft, ductile, 
 and elastic ; neither membrane nor nucleus can be detected, so 
 that they cannot be designated cells. 
 
 The blood corpuscles of mammalia, with the exception of the ellip- 
 tical ones of the camel, are similar to those of man ; in birds they are 
 elliptical and biconvex; in amphibia elliptical, flat, and very large (in 
 Proteus the diameter is actually jV ) ; in fishes they are mostly of a rounded 
 elliptical form. In birds, amphibia, and fishes, they have nuclei. In the 
 invertebrata red blood corpuscles are only present in a few classes. Almost 
 all invertebrata, and amongst vertebrata Amphioxus lanceolatus, have colour- 
 less or yellowish blood, with colourless corpuscles of various shapes ; a few, 
 however, have red blood with colouring matter similar to that of verte- 
 brata. 
 
 The specific gravity of blood corpuscles is somewhat greater 
 than that of the plasma ; for if not prevented (by coagulation, 
 &c.) they sink to the bottom of blood which is undisturbed. 
 When blood is at rest, the red corpuscles have a tendency to 
 aggregate into piles, like rouleaux of coins. The cause of this 
 phenomenon is unknown. 
 
 The presence of red corpuscles is the cause not only of the 
 red colour, but also of the opacity of the blood. By a variety of 
 means the red colouring matter can be extracted from the blood 
 
40 RED BLOOD CORPUSCLES. 
 
 corpuscles, when it dissolves in the plasma and colours it red ; 
 the blood becomes in consequence transparent when examined 
 in thin layers (' lake-coloured,' Eollett), but at the same time, 
 darker, owing to the absence of reflection from the concave red 
 disks. Conversely, the blood becomes of a brighter red when 
 the blood corpuscles are shrivelled up by the addition of salt, so 
 that the reflected light becomes more concentrated. The cor- 
 puscles in the process of decolourization swell up from their 
 margins (Hermann) and finally become globular; the de- 
 colourized and very pale residue of the corpuscles is called the 
 stroma (Eollett). 
 
 The means of discolourizing the blood corpuscles, previously referred to, 
 are : dilution of the blood with water : alternate freezing and thawing of 
 the blood (Rollett) : the transmission of electric shocks (RoJlett) : removal 
 of the gases of the blood (see below) : treatment with salts of the bile 
 acids (v. Dusch), ether (v. Wittich), chloroform (Bottcher), small quantities 
 of alcohol (Rollett), or carbon disulphide (Hermann). All these pro- 
 cesses, except the first named and the removal of the gases of the blood, 
 not only effect the discolourization of the corpuscles, but subsequently lead 
 to the solution of the stroma in the plasma, a glutinous nucleus being 
 sometimes left. 
 
 By the action of boracic acid on the nucleated corpuscles of amphibia, a 
 red mass containing the nucleus is separated from the residual colourless 
 stroma; we must therefore admit that the former contractile mass (the Zooid) 
 is infiltrated in the pores of the colourless stroma (the Oecoid; Briicke). 
 
 A similar deportment is observed in the case of the non-nucleated blood 
 corpuscles of mammalia (Roberts, Strieker). Some consider these separations 
 which are produced in numerous other ways, as the results of coagulation 
 (Rollett). 
 
 The chemical constituents of the red blood corpuscles are : 
 
 1. A red colouring matter containing iron, called Haemo- 
 globin (syn. hsematoglobulin, haematocrystallin), having ap- 
 proximately the following percentage composition : C 54'0, 
 H 7-25, N 16-25, Fe 0-42, S 0-63, 21-45. 
 
 It is slightly soluble in water, but much more readily 
 soluble in weak alkaline solutions. It is not known whether 
 hemoglobin impregnates the colourless residue of the zooid of 
 the blood corpuscles, or whether it exists in a state of chemical 
 combination with it. 
 
 Haemoglobin is a coloured albuminous compound, and 
 is therefore a body of most complex structure. It readily 
 splits up into an albuminous body, apparently closely connected 
 
It JED BLOOD CORPUSCLES. 41 
 
 to globulin (although, unlike the latter, it is not dissolved by 
 oxygen), and a colouring matter, hsematin. This decomposition 
 is effected by all agents capable of coagulating or precipitating 
 albumin (heat, alcohol, mineral acids), and, besides, by the 
 weakest acids (even by carbonic acid in the presence of much 
 water), and by strong alkalies. Different red-blooded animals 
 possess different kinds of haemoglobin, which have hitherto only 
 been found to differ in their crystallization. 
 
 Crystals of haemoglobin, the so-called blood-crystals, occur principally in 
 the form of rhombic prisms or tablets; rarely, as in the blood of the 
 guinea-pig, in the form of rhombic tetrahedra. These crystals may be 
 obtained by destroying the blood corpuscles (by means of water, ether, salts 
 of the bile acids), and evaporating or cooling the lake-coloured fluid which 
 results. Crystals are easily obtained from the blood of dogs, horses, guinea- 
 pigs, and birds ; with difficulty or not at all from that of oxen and pigs. 
 
 The coloured product of the decomposition of haemoglobin. 
 Hsematin (C 68 H 70 N 8 Fe 2 10 ? Hoppe-Seyler), which does not occur 
 uncombined in the body, is a crystalline colouring matter, which, 
 when dried, has a bluish-black colour and a metallic lustre ; it 
 is insoluble in water and alcohol, but soluble without decompo- 
 sition in aqueous or alcoholic solutions of acids and alkalies. 
 Its acid solutions are brown, its alkaline solutions are dichroic, 
 appearing green in thin, and red in thicker layers. 
 
 Solutions of haematin, when examined with the spectroscope, exhibit an 
 absorption band in the red, the position of which is different in acid and 
 alkaline solutions. When treated with reducing agents two new absorption 
 bands, situated close to each other in the yellow, make their appearance ; 
 these are not to be confounded with the two bands of O-hsemoglobin (see 
 below). Haematin crystallizes from solutions in glacial acetic acid in the 
 form of rhombic plates, which in the presence of chlorides are composed of 
 hydrochlorate of haematin (Hoppe-Seyler); these so-called haemin-crystals 
 may serve for the detection of blood (Teichmann). 
 
 By the action of concentrated mineral acids iron is separated from haematin ; 
 the resulting colouring matter bears the name of ' iron-free hsematin ' (Mulder 
 and von Goudoever), haematoporphyrin (C 6S H 74 N 8 12 ? Hoppe-Seyler), haa- 
 matoin (Preyer). 
 
 According to recent accounts (Hoppe-Seyler), when haemoglobin is de- 
 composed in the absence of air, a purple body, with four absorption bands, 
 ' hsemochromogen,' is formed ; the action of oxygen immediately converts 
 it into haematin. 
 
 In the organism haemoglobin gives rise \o coloured pro- 
 ducts other than the artificial ones, as haematoidin, bilirubin, 
 &c. (For these consult Chapter II. under the heads of Bile, 
 
42 COLOURLESS BLOOD CORPUSCLES BLOOD PLASMA. 
 
 Urine, &c.). For the deportment of haemoglobin towards gases, 
 and for its optical properties, see below. 
 
 2. An albuminous body precipitable by carbonic acid, but 
 soluble on the passage of air through the fluid, globulin. 
 
 The nuclei of the blood corpuscles consist of a substance containing 
 mucin (Brunton). 
 
 3. Small quantities of substances soluble in ether : fats, 
 soaps, cholesterin, protagon, and its products of decomposition 
 (lecithin, glycerin-phosphoric acid, &c.). 
 
 4. Salts, especially compounds of potassium, and of phosphoric 
 acid. 
 
 5. Water. 
 
 6. Gases. 
 
 Colourless Blood Corpuscles. 
 
 The colourless blood corpuscles (lymph corpuscles) are 
 globular, nucleated cells, with a somewhat granular, mulberry- 
 shaped surface ; they are larger than the red corpuscles, having 
 a diameter of about y-J-o mm . They show the greatest resem- 
 blance to the cells of the lymph, from which they are derived 
 (Chapter III.). At the temperature of the body these cells, 
 which are destitute of a cell wall, exhibit lively movements, 
 throwing out processes and drawing them in again, whereby 
 they can drag into their interior foreign particles (compare 
 Chapter VIII.) ; these cells also possess the power of subdi- 
 viding (Klein). Their chemical composition has not yet been 
 exactly determined ; it is probably very similar to that of the 
 red corpuscles without the pigment. There are grounds for 
 believing (Chapter V.) that the colourless blood corpuscles are 
 precursors of the red, as transition forms between white and red 
 corpuscles are found in certain situations (for example, in 
 the blood of the splenic veins ). 
 
 Blood Plasma or Liquor Sanguinis. 
 
 For the separation of the plasma of the blood see below 
 (under fc Dying of the Blood '). The reaction of blood plasma 
 is, like that of blood -itself, alkaline. The chemical constitu- 
 ents of the plasma are : 
 
 1. Water, about 90 per cent. 
 
BLOOD PLASMA THE GASES OF THE BLOOD. 43 
 
 2. Proteids, viz. : 
 
 a. Albumin (precipitated by heat). 
 
 P. Sodium albuminate (' berumcasein,' precipitated 
 by acids). 
 
 7. The substances which form fibrin during coagu- 
 lation of the blood (see below). 
 
 The greater portion of the albuminoid substances consists of 
 albumin : altogether they form from 8-10 per cent, of the plasma. 
 
 3. Creatine, hypoxanthine, and urea : also at times hippuric 
 and uric acids, in very small quantities. 
 
 4. Grape sugar, in small quantities, varying according to 
 the situation (see Chapter V.). 
 
 5. Fats, soaps, fatty acids, cholesterin, lecithin. The fat is 
 partly dissolved by the soaps, and partly exists as an emulsion, but 
 always in a small, though varying, quantity (0*1 0*2 per cent.). 
 
 6. An odoriferous principle peculiar to each kind of blood. 
 
 7. A yellow pigment. (The serum also often contains 
 haemoglobin, but this may be only an impurity, caused by 
 disintegrated blood corpuscles.) 
 
 8. Salts, with a preponderance of salts of sodium, chlorides, 
 and carbonates; therefore more especially common salt and 
 carbonate of sodium. 
 
 9. Gases (see below). 
 
 With the exception of the bodies included under 2, the above- 
 named constituents form also the constituents of the serum that 
 is, of the liquid obtained after the coagulation of the blood or 
 plasma (see below). 
 
 The Gases of the Blood, 
 
 The gases contained in blood are oxygen, carbonic acid, and 
 nitrogen which are partly absorbed, and partly in loose chemical 
 combinations (Magnus, Lothar Meyer, Ludwig). 
 
 The fundamental law of the absorption of gases by liquids (Henry's, 
 Dalton's, and Bunsen's law) may be expressed as follows : The unit of 
 volume of a liquid at a given temperature absorbs a definite volume of a 
 gas ; the latter is designated the coefficient of absorption of the liquid for the 
 gas. The coefficient of absorption decreases as the temperature increases, 
 according to a law which varies for each liquid and gas ; at the boiling 
 point of the liquid the coefficient of absorption is equal to 0. 
 
 The volume of gas taken up, therefore the absorption coefficient, is inde- 
 
44 THE GASES OF THE BLOOD. 
 
 pendent of the pressure, whilst the iveight of the gas taken up by a fluid 
 is directly proportional to it. 
 
 As different gases existing in a gaseous mixture exert no pressure upon 
 one another, we must in the preceding sentence understand pressure to 
 signify the partial pressure of the particular gas. Thus water absorbs only 
 as much oxygen from the atmosphere as corresponds to the' partial pressure 
 of the oxygen contained in it, viz. about -|- = 152 mm Hg. 
 
 Absorbed gases can therefore be expelled from a liquid, 1. By placing 
 it in a vacuum which is being continually renewed. 2. By placing it in a 
 space which is free from the gas to be expelled, and which is maintained 
 free. 3. By raising the temperature of the liquid to boiling point. 
 
 Certain gases form chemical compounds with certain bodies (in the 
 relations of their equivalents), which, however, undergo DISSOCIATION when 
 they are placed in a space where the partial pressure of the gas falls below 
 a certain limit. This minimum pressure, which is an essential condition to 
 the persistence of the combination, is, for each special case, a constant, which, 
 still, like the coefficient of absorption, decreases as the temperature in- 
 creases. From these loose chemical combinations the gas can, therefore, be 
 driven as from simple solutions (viz. by the vacuum, by foreign gases, or by 
 the action of heat). These loose compounds of gases are distinguished, 
 however, from simple solutions, in that by increasing the partial pressure 
 of the gas beyond a certain limit, the quantity taken up by the liquid 
 no longer increases. 
 
 There are some bodies which form loose chemical compounds with gases 
 dissolved in a liquid, so that the solution may contain a chemical compound 
 of the gas as well as a portion simply dissolved. In such a case the weight of 
 the gas dissolved is partly proportional to the pressure, and partly indepen- 
 dent of it. 
 
 The quantity of gas by weight taken up by a solution is dependent 
 on the partial pressure of that gas outside the fluid, because each gas which 
 is dissolved by a liquid possesses, at the surface of the latter, a tension, 
 in virtue of which it tends to escape. If this tension is equal to the partial 
 pressure of the gas in the space above the liquid, equilibrium is established ; 
 if it is greater or less, a passage of gas outwards or inwards occurs, until a 
 condition of equilibrium is attained. In the condition of equilibrium, which 
 is always established sooner or later, (and which is hastened by shaking to- 
 gether the liquid and gas) the partial pressure of each gas in the space sur- 
 rounding the liquid expresses directly the tension of the same gas in the 
 fluid. If we carry the idea of tension into the statement of the laws which 
 have been previously announced, these may be expressed as follows. 1. In 
 the case of purely physical absorption, the tension- of a dissolved gas is (a) 
 dependent upon the nature of the fluid and the gas, (6) proportional to the 
 amount, by weight, which has been taken up, (c) dependent upon the tem- 
 perature with which it, in general, increases. 2. If a fluid contain a body 
 which forms a loose chemical compound with a gas, the tension is not pro- 
 portional to the total quantity of gas taken up, but only to the excess above 
 the quantity which is required to saturate the combining body ; if the body, 
 on the other hand, is not saturated, fresh absorption of the gas leads to no 
 
THE GASES OF THE BLOOD. 45 
 
 increase of tension, but the latter remains equal to the above-mentioned 
 minimum pressure, which, however, varies with the temperature. 
 
 In order to separate, whether for qualitative or quantitative determina- 
 tion, the gases, contained in a fluid, e.g. in blood, one of the three above- 
 mentioned means may be employed, or a combination of several .(as boiling 
 in the vacuum of an air-pump or in the Toricellian vacuum). In conse- 
 quence of the consumption of oxygen which goes on in the blood imme- 
 diately after its withdrawal from the body (see below, under Dying 
 of the Blood), we must, if we wish to ascertain the real amount of its gases, 
 either separate these immediately after it has left the body, or we must 
 preserve the blood in ice until the time when the gases are separated. 
 
 In order to determine whether gases are in a state of simple solution or 
 of loose chemical combination in the blood, either absorption experiments 
 must be made under different pressures, with blood which has been freed 
 from gases, or we must make determinations of tension. The methods for 
 effecting the latter, which are of special importance in reference to the 
 chemistry of respiration, will be given in Chapter IV. 
 
 1. Oxygen gas is found in arterial blood (see below), on an 
 average, in the proportion of 16*9 volumes per cent, (the gas 
 being calculated under a pressure of 1 mtr. and C.), (Pfliiger): 
 the amount of oxygen in venous blood varies greatly (Chapter 
 IV.) ; in venous blood from muscles in a state of rest the amount 
 was found to be only 5-96 volumes per cent., taking an average 
 of 5 determinations. The deportment of blood, which has had 
 its gases removed, towards oxygen, shows that the latter is not 
 merely absorbed by the blood," but for the most part chemically 
 combined with it. The amount (by weight), of the oxygen taken 
 up by blood is almost entirely independent of pressure, and does 
 not therefore follow Dalton's law. But if the blood corpuscles are 
 removed, and simple blood plasma be taken, or (since the latter 
 is difficult to obtain, and immediately coagulates, whilst as re- 
 gards combination with the fibrin-formers may be considered 
 as unimportant), instead of plasma, plain serum (page 50), be 
 agitated with oxygen, the gas is merely absorbed (L. Meyer). 
 It follows from this that the oxygen of the blood is chemically 
 combined with a substance contained in the blood corpuscles, 
 but is only absorbed by the plasma or serum (that is, by the 
 water they contain, for serum absorbs just so much oxygen as 
 pure distilled water). 1 This proposition must likewise be ap- 
 plied to the oxygen normally present in the blood. 
 
 1 It has been stated (Fernet) that plain serum likewise takes up a certain 
 amount of oxygen, independently of pressure ; this result is probably owing to the 
 presence of a slight amount of haemoglobin in the serum. 
 
46 THE GASES OF THE BLOOD. 
 
 Haemoglobin is the substance which forms the loose chemical 
 compound with oxygen, and it likewise possesses the property 
 of combining with some other gases in constant proportions : 
 Ignn. O f haemoglobin combines with 1-2 -- 1-3 CC of 
 (measured at C and 1 meter pressure). The compound 
 which we may designate O-Haemoglobin is crystallizable and 
 somewhat less soluble than pure haemoglobin. Its solutions are 
 of a lighter red than those of the latter ; they are not dichroic, 
 whereas haemoglobin, which is free from gases, and which we may 
 term reduced haemoglobin, appears green when examined in thin 
 layers. Solutions of 0-Hsemoglobin exhibit, when examined 
 by means of the spectroscope, two absorption bands situated in 
 the green portion of the spectrum. Solutions of reduced 
 haemoglobin, on the other hand, exhibit a single, less denned, 
 band, which occupies the interval between the two first bands. 
 
 Oxygen can be removed from its combination with haemo- 
 globin not only by the means formerly referred to, but also 
 readily by the action of many reducing substances, as by ammo- 
 nium sulphide, by alkaline solutions of ferrous salts, by iron, by 
 nitric oxide. The minimum pressure required for the persist- 
 ence of the compound of + Haemoglobin, viz. the tension of 
 the oxygen of the blood, is dependent on the temperature, but 
 its absolute value is still unknown. 
 
 In addition to oxj'gen, haemoglobin can also combine chemically with 
 carbonic oxide (L. Meyer) and with nitric oxide (Hermann), in the same 
 proportions by volume, therefore in the same equivalent proportions. Of 
 these compounds, that with oxygen is the least stable, so that the oxygen 
 may be expelled from its combination with haemoglobin by carbonic oxide, 
 and the latter, in its turn, by nitric oxide. Even the two latter compounds 
 are to be designated as unstable, seeing that according to recent investiga- 
 tion (Bonders, Zuntz, Podolinski) they are also capable of decomposition 
 by physical means; the pressure at which they decompose is, however, 
 much lower than in the case of the oxygen compound. These CO- and 
 NO-com pounds are, like the 0-compound, not dichroic, and they possess 
 two absorption bands, which in the carbonic oxide compound are somewhat 
 differently situated from those in the other two analogous compounds. When 
 O-Heemoglobin is decomposed by means of acids, the oxygen is not liberated 
 and cannot be pumped out ; it must, therefore, enter into chemical combina- 
 tion with one of the products of decomposition (L. Meyer, Zuntz, Strassburg). 
 
 Seeing that the behaviour of the blood as a whole towards 
 oxygen (carbonic oxide, &c.), as well as its optical properties and 
 the dependence of these upon the gas contained in the blood, is 
 
THE GASES OF THE BLOOD. 47 
 
 exactly the same as that of a solution of haemoglobin, and, 
 further, as blood when saturated with oxygen takes up exactly 
 as much of that gas as corresponds to the amount which its 
 hsemoglobin can combine with, it follows that all the loosely 
 combined oxygen of the blood is linked to hsemoglobin. 
 
 The oxygen of the blood is given up so readily to oxidizable substances 
 that it has been thought to be present in the form of ' active oxygen ' or 
 * ozone/ 3 . The following properties of blood appear to favour this 
 view. 1. Both the blood-corpuscles and hemoglobin are so-called l ozone- 
 transferrers,' that is, they possess the power of immediately transferring 
 ozone from substances in which it is present (as turpentine which has be^n 
 kept for a long time) to readily oxidizable substances (ozone reagents, such 
 as tincture of guaiacmn, which becomes blue by oxidation, Schoenbein, 
 His) ; for this reaction the presence or absence of oxygen in the blood is of 
 no importance (for instance, it may be saturated with CO). 2. Blood and 
 haemoglobin can themselves ozonize oxygen, so that in presence of air they 
 can cause guaiacum tincture to become blue (A. Schmidt) ; if the blood 
 itself contains oxygen, the presence of air is not necessary ; it is necessary if 
 the blood has been saturated with CO (Kiihne and Scholz). On the activity 
 of its oxygen depends the decomposition of sulphuretted hydrogen by blood. 
 It is therefore very probable that the oxygen naturally contained in blood is 
 present in the form of ozone, or in some similar condition. 
 
 2. Carbonic acid is found in arterial blood on an average 
 in the proportion about 30 vols. per cent. : venous blood from 
 muscles at rest yields about 35 per cent. A portion of the car- 
 bonic acid can only be driven out by acids ; it is therefore in 
 stable chemical combination. The carbonic acid removable by 
 the pump may either be merely absorbed, or partly in very 
 weak chemical combination. A weak chemical combination may 
 take place either, with 1, the carbonate of sodium of the plasma, 
 2, the phosphate of sodium of the plasma (Fernet), 3, through 
 as yet unknown combinations in the blood corpuscles (Pfliiger and 
 Zuntz, Ludwig and A. Schmidt). Since solutions which contain 
 carbonic acid, either absorbed or in weak combinations, give an 
 acid reaction, the fact of the alkaline reaction of the blood would 
 appear opposed to the view of the carbonic acid being present in 
 other than a stable combination (Preyer), were it not that blood 
 still gives an alkaline reaction when saturated with carbonic 
 acid (Pfliiger and Zuntz). 
 
 Since the phosphate of sodium in blood ash is derived almost entirely 
 from burnt lecithin, the second combination referred to is probably only 
 very slightly operative (Hoppe-Seyler and Sertoli). Since, moreover, the 
 
48 DIFFERENT KINDS OF JBLOOD. 
 
 serum takes up carbonic acid independently of pressure, just like the blood 
 itself, a part, at least, of the chemically combined carbonic acid must be in 
 the serum (that is, in the plasma), probably in the form of bi-carbonate 
 (see above No. 1). That a part of the carbonic acid is combined in the 
 blood corpuscles (see No. 3) is shown by the fact, that blood contains 
 scarcely less carbonic acid than a similar volume of serum (Ludwig and 
 Schmidt), and moreover that the absorption of carbonic acid by blood and 
 by serum under increasing pressure obey different laws (Pfiiiger and Zuntz.) 
 Carbonate of sodium is changed by the addition of carbonic acid into the 
 bi-carbonate C0 3 Na 2 + C0 2 + H 2 = 2 C0 3 NaH ; the neutral salt is 
 again formed along with free carbonic acid by the employment of the means 
 used to drive out the gases. Neutral phosphate of sodium takes up carbonic 
 acid in a similar manner (one equivalent of acid to two equivalents of salt), 
 (Fernet), forming an acid phosphate and neutral carbonate : 2 P0 4 Na 2 H + 
 C0 2 + H 2 = 2 P0 4 NaH 2 + CO. 3 Na 2 (Hermann). The means used to 
 drive off the gases break up these combinations, giving off C0 2 and again 
 forming the neutral salt. 
 
 3. Blood contains from 1-2 vols. per cent, of Nitrogen. A 
 small portion of this gas also is probably chemically combined, 
 being most likely contained in the blood corpuscles (Fernet, 
 Setschenow). 
 
 When heated (Thiry) or merely allowed to stand (Briicke) the blood gives 
 off traces of ammonia, probably arising from the decomposition of some 
 ammoniacal salt contained in the blood (Kiihne and Strauch) ; no proof has, 
 however, yet been obtained of the presence of such a salt in the blood 
 (Briicke), The addition of oxygen favours the development of ammonia 
 (Exner). 
 
 Blood which has been deprived of its gases is very dark 
 (almost black), dichroic, and, in consequence of the destruction 
 of the blood-corpuscles, lake-coloured. 
 
 Different kinds of Blood. 
 
 The composition of the blood is not the same throughout 
 the whole body. The greatest difference is observed between 
 arterial blood (viz. that which is contained in the systemic 
 arteries, the left side of the heart, and the pulmonary veins), 
 and venous blood (viz., that of systemic veins, the right side of 
 the heart, and the pulmonary arteries), and consists principally 
 in the amount of gases contained, and in the colour. Arterial 
 blood contains more oxygen (on the other hand, less carbonic 
 acid) than venous, and has a brighter (scarlet) colour ; it does 
 not display the dichroism of the latter. This difference in colour 
 is closely connected with the difference in the amount of oxygen ; 
 
ARTERIAL AND VENOUS BLOOD QUANTITY OF BLOOD. 49 
 
 for on shaking up dark-coloured blood with oxygen (or with 
 atmospheric air), it becomes bright red, and bright red blood 
 becomes dark-coloured when shaken with other gases (except 
 carbonic oxide, page 46). 
 
 Moreover, arterial blood contains more water, fibrin, salts, sugar, and 
 extractive matter than venous, but on the other hand fewer blood corpuscles 
 and less urea. Its temperature is on an average 1 C. lower (Chap. VII.) 
 The changes effected by gases in the colour of the blood probably depend, on 
 the one hand, on an alteration in the shape of the blood corpuscles, which 
 shrink and become more concave in appearance on combination with oxygen, 
 swelling out, on the other hand, on the removal of the oxygen (by the passage 
 through it of carbonic acid, &c.) (Harless). In the first case, the blood cor- 
 puscles, acting as more powerful concave mirrors, would reflect light in a more 
 concentrated form, whilst in the latter they would tend more to disperse it. 
 At all events, it is in this manner that the addition of salts to the blood 
 renders it brighter. The addition of water, on the other hand, darkens 
 it. Gases, however, exert an action on the pigment which is quite indepen- 
 dent of any alteration which they may bring about in the shape of the cor- 
 puscles an action which may be observed after these bodies have been 
 broken up by the addition of water ; in lake-coloured blood, however, the 
 colour being darker of itself, the action of oxygen is less easily seen. 
 
 The peculiar composition of particular kinds of blood (the 
 blood of the portal, hepatic, and splenic veins), as well as the 
 influence on the blood of d/gestion, respiration, etc., will form 
 the subject of later chapters. 
 
 The changes taking place in the physical and chemical 
 constituents of the blood, its waste and reparation, form the 
 subject of the sixth chapter. 
 
 The Quantity of Blood in the Body. Its Quantitative 
 Composition. 
 
 The quantity of blood contained in the human body is not 
 accurately known: it amounts to about -^ (Bischoff) of the 
 whole weight of the adult body ; to about -^ (Welcker) of its 
 weight at birth. 
 
 The following are the best known methods for determining the quantity 
 of the blood : 1. By ascertaining the dilution of the blood caused by the injec- 
 tion of a known quantity of water ; the degree of dilution is determined by 
 comparing the amount of water contained in two samples of the blood taken, 
 the one immediately before, the other a short time after, the injection of the 
 water (Valentin). [This gives too high a result, both because the water does 
 not become equally mixed with the whole of the blood, and also because the 
 
 E 
 
50 DYING OF THE BLOOD: COAGULATION. 
 
 diluted blood commences at once to diffuse throughout the tissues, giving off 
 water (mainly through the kidneys) and taking up solid matter], 2. By 
 bleeding freely (by beheading) and washing out the blood still left in the 
 vessels with water (until the latter becomes no longer coloured), the amount 
 of the solids contained in the whole of the blood is determined ; the 
 quantity of blood can then be ascertained, by comparing these solids with 
 the amount of solids contained in an undiluted sample of blood (Ed. Weber). 
 [Inaccurate, both because all the blood is never washed out of the vessels, 
 and also because the water flowing through the vessels takes up substances, 
 by diffusion, from the parenchyma.]. 3. The blood remaining in the vessels 
 after decapitation is diluted with water until it is identical in colour (when 
 layers of equal thickness are compared), with a measured sample of blood pre- 
 viously obtained, and diluted with a known quantity of water; the quantity 
 of blood is then easily calculated from the amount of water required for 
 dilution (Welcker, Heidenhain). The amount of haemoglobin contained in the 
 muscles (Chap. VIII.) must be allowed for. It is advantageous to saturate the 
 blood with carbonic oxide (see above), so as to avoid variations in colour, 
 due to unequal saturation with oxygen (v. Bezold & Gscheidlen). 
 
 Note. The following may serve as an example of the quantitative com- 
 position of the blood. Venous blood of the horse (Hoppe-Seyler) consists of 
 67*4 per cent, plasma, and 32-6 corpuscles. The plasma itself consists of 90-8 
 per cent, water, 1-0 fibrin, 7-8 albumin, O'l fats, 0'4 extractive matters, O6 
 soluble salts, 0*2 insoluble salts. The corpuscles contain 56-5 per cent, of 
 water, and 43-5 per cent, solid matter; the organic constituents of the 
 corpuscles in the human subject are (Jiidell) from 12-2-5-1 per cent, albu- 
 minoid matter, 86'8-94'3 haemoglobin, 0-7-0-3 lecithin, 0'25 choiesterin. 
 
 Death of the Blood, and the Changes which accompany it. 
 
 So soon as blood or liquor sanguinis is withdrawn from the 
 influence of the walls of living vessels, it quickly runs through 
 a series of changes, which may be said to attend the death of the 
 blood. They are as follows : 
 
 1. Coagulation, that is, the separation of a solid albuminous 
 body, ' Fibrin.' The liquid blood is thus changed in the first 
 place into a soft red mass ; in a few hours, however, the 
 solid portion contracts, pressing out a yellow fluid -the blood 
 serum ; the solid portion retains, however, the shape of the 
 vessel containing it, but on a smaller scale. The firm red mass, 
 the blood clot (placenta sanguinis), now floating in the serum, 
 consists of matted filaments of fibrin, and the blood corpuscles 
 imprisoned within them, together with some occluded serum. 
 The fibrin is separated essentially from the plasma and not 
 from the blood corpuscles ; for the former, which may be 
 obtained either by allowing the corpuscles in uncoagulated 
 
DEATH OF THE BLOOD: ACIDIFICATION. 51 
 
 blood to sink to the bottom, or by filtering blood containing 
 large corpuscles (frog's blood diluted with sugared water, J. 
 Miiller), undergoes coagulation, forming a white cake which 
 consists solely of fibrin. The serum consequently contains the 
 same component parts as the plasma, with the exception of 
 fibrin. If before coagulation the blood corpuscles have time 
 to sink (as is usually the case with the blood of the horFe), the 
 upper layer of the blood clot consists solely of fibrin, without 
 corpuscles, and is therefore white and of closer texture than the 
 red portion ; this is called the ' Buffy Coat ' (also 6 crusta phlo- 
 gistica,' from its occurrence in blood obtained by bleeding 
 animals affected with inflammatory diseases). Fibrin may also 
 be obtained by whipping recently drawn and yet uncoagulated 
 blood with twigs, or stirring it with a stick ; the fibrin adheres 
 to the twigs or to the stick, in white filaments. The red un- 
 coagulable fluid remaining defibrinated blood consists of the 
 serum and corpuscles. 
 
 The process of coagulation is made- plain by the following Table : 
 
 Undisturbed coagulation- : When beaten : 
 
 Blrod Blood 
 
 Plasma Corpuscles Plasma Corpuscles 
 
 Serum Fibrin Fibrin Serum 
 
 Blood clat Defibrinated blood 
 
 The amount of fibsin is very small, in spite of the large 
 space it takes up during coagulation, especially at first ; it is 
 also exceedingly variable, even in different samples of the same 
 blood (S. Mayer) j on an average it forms about 0*2 per cent, 
 of the blood. 
 
 It has been recently stated that even washed blood corpuscles yield 
 fibrin (Heynsius). Embryonal blood is not at first coagulable (Boll). 
 
 2. Acidification. From the time it is drawn until coagu- 
 lation, the alkaline reaction of the blood steadily diminishes 
 (Pfliiger and Zu'ntz). This depends most probably on the for- 
 mation of an acid, the nature of which is yet unknown. 
 
 3. Deoxygenation. Immediately after it is drawn the 
 amount of oxygen contained in the blood becomes somewhat 
 diminished ; the amount of C0 2 , on the other hand, being 
 increased (Pfliiger, A. Schmidt). As this consumption of oxygen 
 takes place during life, the blood always containing oxydizable 
 
 E 2 
 
52 DEATH OF THE BLOOD: CALORIFICATION. 
 
 substances (compare Chap. IV.), it probably does not properly 
 belong to the death-phenomena, but is merely synchronous with 
 them. 
 
 4. Calorification.- -During coagulation a slight rise, per- 
 ceptible by means of the thermometer, takes place in the tem- 
 perature of the blood (Schiffer). 
 
 An evolution of electricity likewise probably takes place, under certain 
 circumstances, during the dying of the blood. On making a cross section 
 of fresh organs (as glands) a weak negative current is developed, as 
 opposed to the natural surface (Matteucci), This current is, however, only 
 apparent in organs containing blood (Hermann), and is usually absent in the 
 organs of warm-blooded animals (Du Bois-Reymond). Most probably it 
 arises from an evolution of electricity caused by the contact of the decom- 
 posing blood (at the incision) with the still unchanged blood in the vessels, 
 the former becoming negative (Hermann). Since, throughout the whole 
 ramification of vessels, the blood forms one continuous mass, the oppo- 
 sition between the section and the surface must depend on the difference 
 in the speed with which the blood decomposes in each case. At the section, 
 the blood in all cases at once dies; at the surface, owing to the protection 
 of the tissues, it dies but slowly in cold-blooded animals, although quickly, in 
 spite of this, in warm-blooded ; thus are explained the above-mentioned 
 facts. 
 
 The above-described phenomena show that during the pro- 
 cess of dying the blood undergoes complex chemical changes. 
 The most striking of these, the coagulation of fibrin, was for- 
 merly considered to be a spontaneous coagulation of an albu- 
 minous substance dissolved in the plasma. We now know that 
 the fibrin, as such, does not exist in the blood, but originates 
 in the process of dying. According to the ideas most generally 
 received (A* Schmidt), it arises from the chemical combination 
 of two albuminous substances, separate, although existing side 
 by side, in the blood ' fibrinogen ' and the ' fibrinoplastic sub- 
 stance. ' This combination is brought about by a ferment, which 
 is only developed during the death of blood. Both the fibrin 
 generators are contained in the plasma. 
 
 The fibrin generators are also contained in many other normal and patho- 
 logical fluids, e.g. in lymph and chyle, in pericardia! and hydrocele fluids, &c. 
 The former of these fluids also generate the ferment, and therefore coagulate 
 spon taneously,although more slowly than the blood; the others do not gene- 
 rate the ferment, and, therefore, coagulate only after the addition of ferment or 
 of blood. Fibrinogen and the fibrinoplastic substance are most closely related 
 to globulin. They can be obtained from their natural solutions in blood- 
 
DEATH OF THE BLOOD. 53 
 
 plasma by the addition of water and the subsequent passage of carbonic acid ; 
 the fibrinoplastic substance is first precipitated and carries down with it, 
 mechanically, the ferment. Both the fibrin generators are soluble in alkalies 
 and acids and in solutions of common salt ; they are soluble in water if a 
 stream of oxygen be passed through it. 
 
 The ferment is obtained by adding alcohol to blood, and extracting the 
 thoroughly dried and filtered residue with water. Blood allowed to flow 
 directly from an artery into alcohol yields no ferment. 
 
 On mixing solutions of fibrinogen and the fibrinoplastic substance in the 
 presence of the ferment, fibrin separates first as a gelatinous substance, which 
 afterwards contracts ; the quantity of the two substances determines the 
 amount of fibrin, to form which they appear to combine, although in pro- 
 portions which are not constant. The amount of ferment present merely 
 influences the rapidity of the separation of fibrin. Serum contains an excess 
 of fibrinoplastic substance (that of ox's blood contains 0*7 -0 - 8, of the horse 
 0-3-0-6 per cent). Presence of non-crystallisable haemoglobin, of carbon, 
 platinum, &c. hastens the formation of fibrin, when all other conditions are 
 present. If solutions of the fibrin generators and of the ferment are de- 
 prived of oxygen, by passing hydrogen through them, before they are mixed, 
 no fibrin is formed (A. Schmidt). 
 
 The connection between the above and the other phenomena 
 accompanying the death of the blood, particularly acidification, 
 is unknown. Blood which has undergone these changes, if kept 
 longer, particularly if defibrinated, gradually loses the whole 
 of its oxygen,, carbonic acid taking its place : at the same time 
 putrefaction sets in. 
 
 The phenomena accompanying its death are the result of the 
 cessation of an influence exercised constantly upon the blood 
 during life, by the living walls of the vessels (Briicke). The 
 blood does not coagulate as long as it circulates in the vessels, 
 so that every portion of it constantly comes in contact with their 
 living walls ; nor does it coagulate if, after being drawn, it 
 is in contact with a living vessel (as, for instance, when frog's 
 blood is placed, over mercury, in contact with a pulsating frog's 
 heart, Briicke). On the other hand, it coagulates after it has 
 been drawn from the vessels, or in the vessels, after their 
 death, or even in living vessels, if at any point stagnation of 
 the blood occurs, so that the central layers are removed from 
 the influence of the walls. 
 
 Many precise accounts concerning the causes of the process of coagulation 
 are here passed over, because they have not been verified. .According to our 
 present views of fibrin formation, Briicke's law would be expressed as 
 follows : the influence of the living vascular wall is to hinder the forma- 
 tion of the fibrin ferment, or to destroy it continuously as soon as it is formed. 
 
54 THE CIRCULATION OF THE BLOOD. 
 
 All the phenomena which characterize the dying of the 
 blood are hastened by high temperatures, and by the contact 
 of the blood with foreign bodies (as by stirring), also by air 
 (blood coagulates more quickly in open vessels than over mer- 
 cury). Coagulation may be checked by the addition of alkalies 
 or alkaline salts, or by precipitating the fibrinoplastic substance 
 by means of carbonic acid or other weak acids. 
 
 II. THE CIRCULATION OF THE BLOOD. 
 
 The blood circulates continually, and with great speed, 
 throughout all parts of the body, in the paths prescribed for it 
 by the vascular system, which, under normal circumstances, 
 it never leaves. All the matters given up by the blood have, 
 therefore, to pass through the closed vascular wall, and with 
 few exceptions (passage of lymph into the blood), this is the 
 case with the matters absorbed into the blood. Only the 
 thinnest portions of the vascular system, viz. the capillaries, 
 permit of this exchange taking place. 
 
 Seeing that the vascular system is completely closed and 
 that the movement of the blood is always in the same direction, 
 it is clear that that movement must be of the nature of a cir- 
 culation. 
 
 The vascular system may therefore be pictured as a system 
 of continuous closed tubes, with many branches ; the finest 
 ramifications of this system correspond to the capillaries. Only 
 in two places is the system perfectly simple ; these are the 
 aorta and the pulmonary artery, each with its appended half 
 of the heart. From each of these places the blood can only reach 
 the other through a capillary system : there are, therefore, two 
 principal capillary systems, through both of which every particle 
 of blood must pass once at each circulation the pulmonic 
 capillary system, and the systemic capillary system. The func- 
 tional difference between these capillary systems depends on 
 the character of the changes which the blood which they contain 
 undergoes (see Chapter V.) : in the pulmonic capillaries the 
 blood takes up oxygen, and gives off carbonic acid ; the reverse 
 takes place in the systemic capillaries. Throughout the whole 
 of the passage, therefore, from the pulmonic capillaries to the 
 systemic, the blood is rich in oxygen, and consequently bright 
 
SCHEMA OF THE BLOOD VASCULAR SYSTEM. 55 
 
 red or arterial ; on the other hand, during its passage from 
 the systemic to the pulmonic capillaries it is poor in oxygen, 
 but rich in carbonic acid, and therefore dark red or venous. 
 The whole circulation, therefore, naturally divides itself into 
 two halves, an arterial and a venous. 
 
 At the commencement of each of the trunks of the vas- 
 cular system (the one the arterial, the other the venous) is. 
 placed the principal motor apparatus, in the form of two con- 
 tractile pouches, supplied with valves the two halves of the 
 heart the left being on the arterial side of the circulation 
 (commencement of the aorta), the right on the venous (com- 
 mencement of the pulmonary artery). Reckoning from the 
 heart forwards, all those vessels which carry blood to a capillary 
 system are called arteries, whilst those carrying the blood /rom 
 a capillary system, are called veins. There are therefore two 
 arterial and two venous systems. The systemic arterial system 
 (the aortic system) carries arterial blood from the left side of 
 the heart into the systemic capillaries ; the systemic venous 
 system carries this blood, now become venous, into the right 
 side of the heart, from which the pulmonary arterial system 
 carries the venous blood into the pulmonary capillaries, and 
 the pulmonic venous system returns this blood, again become 
 arterial, into the left side of the heart. 
 
 Although the complete circulation forms one single circuit, the course of 
 the blood from the left side of the heart through the systemic capillaries to 
 the right side of the heart is often erroneously described as the greater or 
 systemic circulation, the other as the lesser or pulmonary circulation. One 
 portion of the systemic venous blood, viz. that coming from the capillaries 
 of the intestines and spleen, unites to form one vein (the portal vein), which 
 does not proceed directly to the right side of the heart, but branches out, like 
 an artery, into a second capillary system in the liver, whence it passes into 
 veins leadjjpg direct to the heart. This section of the vascular system is 
 erroneously called the portal circulation. 
 
 Since the sum of the diameters of the branches of an artery 
 almost always exceeds the diameter of the trunk, the sum of the 
 diameters of the vascular system must in general increase 
 with its ramifications, and consequently is smallest in the two 
 trunks (the aorta and pulmonary artery), and greatest in the 
 capillaries. The vessels, especially the arteries, are very elastic. 
 
 Amongst the motive powers producing the circulation of 
 the blood the movements of the heart occupy the first place. 
 
56 THE MOVEMENTS OF THE HEART. 
 
 The description of the circulation as a whole will therefore be 
 preceded by an account of the most essential facts relating to 
 the heart. 
 
 The Movements of the Heart. 
 
 The heart consists of two hollow muscular organs, com- 
 pletely divided, though of similar construction ; each of these 
 transmits its contents in a definite direction by means of rhyth- 
 mical contractions and valvular arrangements. The right half of 
 the heart is connected with the venous, the left with the arterial 
 half of the circulation ; the former therefore contains only dark 
 red, the latter only bright red blood (p. 48) ; the former 
 transmits, through the pulmonary artery, the blood pouring 
 into it through the venae cavae, the latter transmits through 
 the aorta the blood brought back from the lungs by the 
 pulmonary veins. Each half of the heart consists of a thin- 
 walled antechamber (auricle, atrium), which first receives the 
 entering blood, and a thick-walled chamber (ventricle), which 
 forces it into the artery. 
 
 Although entirely removed from the control of the will, the muscular fibres 
 which form the greater portion of the walls of the heart, are transversely 
 striated; they differ however from almost all other transversely striated 
 muscular fibres, as they ramify and join together. They form numerous 
 layers diversely arranged partially in spirals. Those of the ventricles 
 spring from the fibre-cartilaginous rings at the margins of the auriculo- 
 ventricular openings, and, in part, return to be inserted in the same, while, 
 in part, they are inserted in the chordae tendineaB, after forming the musculi 
 papillares. The muscles of the auricles are entirely distinct from those 
 of the ventricles, but many fibres pass from the right side of the heart 
 to the left. This arrangement of the muscles explains why both auricles or 
 both ventricles always contract simultaneously, whilst the movements of 
 the auricles and ventricles are independent of each other. 
 
 The heart in mammals and birds resembles the human Jieart. In 
 scaly amphibia the two ventricles communicate ; in the naked amphibia only 
 one is usually present. In the former the aorta and pulmonary artery originate 
 from the common ventricular cavity, in the latter only one vessel leaves the 
 ventricle, supplying blood both to the body and the lungs. In fishes and in 
 undeveloped batrachians the heart usually corresponds to the right half only 
 of the human heart (one ventricle and one auricle) ; no heart is inserted in 
 the arterial half of the circulation, so that the branchial veins open directly 
 into the aorta. In invertebrata, which usually possess no closed vascular 
 system, a real heart with auricles and ventricles exists only in a few orders ; 
 in some there exists merely an open bag provided with valves (as the dorsal 
 vessel of insects) j others have no such apparatus. 
 
THE MOVEMENTS OF THE HEART. 57 
 
 The rhythmical movements of the heart consist of an alternate 
 contraction of the auricles and ventricles. The two halves of 
 the heart work in all respects correspondingly and simultane- 
 ously. During the contraction (systole) of the two auricles, the 
 dilatation (diastole) of the ventricles takes place, and conversely. 
 The systole of the ventricles directly follows that of the auricles ; 
 on the other hand, a slight pause occurs after the systole of the 
 ventricles before the following systole of the auricles ; the 
 systole of the auricles, moreover, lasts a shorter time than that 
 of the ventricles. 
 
 The systole of the ventricles takes up about two-fifths, their diastole 
 about three-fifths of a complete cardiac revolution (Valentin, Landois). This, 
 however, is only when the pulse is of normal frequency, since any chang r e 
 in its rate only varies the duration of the diastole, whilst that of the systole 
 remains constant (Donders). 
 
 The heart and large vessels lie within the thorax, in a 
 spacious, closed chamber, which, together with the lungs, they 
 tend to fill ; in doing so they are dilated beyond their natural 
 volume (see Chapter IV.); they are, therefore, under negative 
 pressure, i.e. their walls (more especially those of the auricles 
 and of the large veins which are most yielding) are drawn 
 apart. The relaxed heart, therefore, tends to distend itself by 
 sucking blood out of the veins. Owing to a special contrivance, 
 the aspiration of blood through the veins is not even inter- 
 rupted during the contraction of the ventricle which must be 
 looked upon as the heart-pump proper but proceeds con- 
 tinuously. 
 
 As the large veins open into the contractile auricles they 
 possess a varying capacity. During the ventricular systole the 
 auricles are relaxed, and are therefore in a position to receive 
 the blood which is, in the meantime, sucked up into the 
 thorax. During the diastole of the ventricles, on the other 
 hand, blood flows into them from the then contracting auricles, 
 without the passage of blood through the veins into the auricles 
 being interrupted. The auricle must therefore not be considered 
 as a preliminary suction- and force-pump, whose action is fol- 
 lowed by that of a second pump, the ventricle, but is to be 
 looked upon merely as a reservoir which regulates the pressure 
 of blood in the venous system. Each lateral half of the heart, 
 therefore, being a simple suction- and force-pump, merely 
 
58 THE MOVEMENTS OF THE HEART. 
 
 requires a valvular arrangement at its orifice of entrance and 
 exit ; the first is formed by the auriculo-ventricular, the second 
 by the semilunar valves. During the systole of the auricles the 
 blood is sucked into the synchronously relaxed ventricle by the 
 aspiration of the thorax (aided, perhaps, by the active power of 
 aspiration exerted by the ventricle in its diastole, and to which 
 we shall afterwards refer), so that no valves are required to 
 prevent its reflux into the venous trunks. It is only the 
 coronary veins which -empty themselves into the right auricle, 
 and whose contents being regulated, not by atmospheric, but by 
 intra-thoracic pressure, require a valvular arrangement, and 
 this is provided for by the so-called valvula Thebesii. 
 
 The auricular cavities are never completely obliterated 
 during contraction, though this appears to be the case with the 
 auricular appendages. 
 
 The action of the heart as a pump commences with the 
 systole of the ventricles, which changes the negative pressure 
 of the contents into a positive pressure, and causes the 
 auriculo-ventricular valves to close. The closure of the valves 
 is furthered by the simultaneous contraction of the musculi 
 papillares, whilst the contraction of the ventricles forces 
 their whole contents, with great energy, into the arteries 
 (aorta and pulmonary artery). As soon as the systole ceases, 
 the high pressure of the blood in the large arteries closes the 
 semilunar valves, so that a reflux of blood into the relaxed ven- 
 tricle is impossible. After a short pause, during which, as was 
 previously mentioned, the ventricles receive blood from the 
 previously filled auricles, the action recommences with the 
 auricular systole. 
 
 The auriculc-ventricular valves, viz., the tricuspid on the right and the 
 mitral on the left side of the heart, consist respectively of three and two 
 segments, which are connected by a broad basis to the walls of the auriculo- 
 ventricular openings, whilst their free margins are connected to the musculi 
 paptilares by means of the chorda tendinece. When not in action these 
 valves hang slackly in the ventricles. As soon as the pressure within the 
 ventricle surpasses that in the auricle, the back current drives them up, 
 causes them to unfold, and as they are prevented by the chordce tendinece 
 from passing into the auricle, their inner borders are pressed together, so 
 that a complete closure is effected. 
 
 The semilunar valves are formed by three pocket-like membranes situ- 
 ated at the commencement of the aorta and pulmonary artery. These pouches 
 oppose no obstacle to the passage of blood into the arteries, but so soon as the 
 
THE MOVEMENTS OF THE HEART APEX BEAT. 50 
 
 pressure in the latter becomes greater than that in the ventricles, they fall 
 together, and by their edges press against one another. Their edges then 
 form a three-pointed star. In this position the semilunar valves form a 
 strong barrier between the ventricle and artery. 
 
 The position of the semilunar valves during systole, and their relation to 
 the coronary arteries, which take their origin in the sinuses of Valsalva, at the 
 commencement of the aorta, are subjects of dispute. Some (Scaramuzzi, 
 Thebesius, Briicke) suppose that during systole the valves lie close to the 
 arterial wall, in such a manner as to close the openings of the coronary 
 arteries, so that the latter are only supplied with blood during diastole. 
 The result of this would be a more easy entrance of blood into the substance 
 of the heart during its relaxation, and a .distension of the ventricle in diastole, 
 due to a turgescence of its walls, whereby an active aspiration of the blood 
 streaming out of the auricle would be effected (' Selbststeuerung des Herzens' 
 of Briicke.) 
 
 Others (Hamberger, Hyrtl, Riidinger, Oehl, Ceradini) raise the follow- 
 ing objections to this view. (1.) The valves are not pressed against the 
 wall during systole, but are stretched across and away from the sinuses. 
 (2.) When the coronary arteries are cut across, blood flows from them, 
 specially during systole, and from their central ends too. (3.) Blood meets 
 with less resistance in flowing through the capillaries of muscles during 
 contraction than relaxation (compare Chapter VI II.). (4.) The capacity 
 of the cavities of the heart is not only not increased by injection of the 
 coronary arteries, but diminished. According to the most recent researches 
 (Ceradioi), the diastolic closure of the semilunar valves is not brought 
 about by a regurgitation of blood, but by the elastic rebound of the aortic 
 walls at the time when the systolic stream through the axis of the aorta 
 is interrupted ; for, during the passage of blood through the aorta, the 
 pressure of blood at the sides of the aorta is greater than in the rapidly 
 moving axial layers. 
 
 The shape of the relaxed heart, or more accurately, of the 
 two ventricles, is that of an oblique cone, whose base (a section 
 through the auricular ventricular openings) is an ellipse. By the 
 systole of the ventricles the shape of the heart is altered ha such a 
 manner that the base becomes rounded, and the formerly oblique 
 axis vertical, so that an upright cone is formed. The change 
 in form is accompanied by a rotation of the axis, and, (owing to the 
 position of the heart in the thorax,) a tilting up of its apex, 
 which, in consequence, strikes against the wall of the chest 
 (Ludwig). The striking of the cardiac apex against the 
 thoracic wall may also be caused by the so-called recoil which is 
 communicated in a reverse direction to every moveable body 
 out of which a fluid is pouring (Grutbrod, Skoda). Both causes 
 have been supposed to account for the cardiac impulse or apex 
 beat, which may be seen and felt between the fifth and sixth left 
 
60 SOUNDS OF THE HEART. 
 
 ribs, a little to the inside of a vertical line drawn through 
 the nipple. When the heart strikes exactly on a rib only a 
 slight quivering is noticed. 
 
 Over the exposed heart, or when the ear is applied directly, 
 or with a stethoscope, to the prgecordial region, two sounds may- 
 be heard, following in quick succession the heart sounds. 
 The first (systolic) is a dull sound, loudest in the vicinity of the 
 ventricles, and lasts as long as their systole continues. Some 
 attribute this sound to the vibration of the tense membranous 
 auriculo- ventricular valves, whilst others suppose it to be the 
 muscular noise of the contracting heart (Chap. VIII)* 
 
 That the noise of muscular contraction takes a part in the 
 production of the first sound is known by the fact that it may 
 be heard in a heart which has been eut out and is empty of 
 blood (Ludwig and Dogiel). 
 
 The second, diastolic, sound follows immediately, and there- 
 fore occurs at the commencement of the ventricular diastole. 
 It is shorter and clearer than the first sound, and is caused 
 by the sudden closure of the semi-lunar valves, the cowipetence 
 of which is necessary to its production (Williams). 
 
 The cardiac impulse may be made to register directly the 
 movements of the heart. For this purpose an air-tight drum is 
 placed against the chest wall and the vibrations of the air con- 
 tained in it are propagated by a suitable arrangement to a 
 writing lever, which registers them upon a travelling band of 
 paper (' Cardiograph ' of Marey). The arterial pulse serves for 
 the indirect registration of the heart's action (see, below, Kymo- 
 graph, Sphygmograph). 
 
 Movement of the Blood in the Vessels. 
 
 Causes. 
 
 If we imagine the vascular system filled with blood, but with 
 every impulse to motion absent, the blood will stand every- 
 where within it under equal pressure, which, however, is greater 
 than would be caused by its own weight a proof that the 
 volume of the blood is greater than the natural capacity of 
 the vascular system (Brunner). If in such a system the pres- 
 sure be suddenly made unequal in two places, a current will be 
 immediately set up from the point of greater to that of less 
 
WEBEKS SCHEMA OF THE CIRCULATION. 61 
 
 pressure. The less the opposition to this adjustment of pres- 
 sure the more rapidly does it take place, and the greater, con- 
 sequently, the speed of the current. At any given moment 
 during this process of adjustment the difference of pressure 
 still remaining must be greater the greater the resistance. It 
 is moreover easy to see that, other things being equal, the 
 speed of the current will increase with the difference in pres- 
 sure. A constant inequality of pressure is caused in the 
 different portions of the vascular system by the movements of 
 the heart, which thus produce the circulation of the blood. 
 
 Imagining the system to have been at rest, the first systole 
 would press a certain quantity of blood (the contents of the 
 left ventricle, see below), just removed from the venous system, 1 
 into the elastic arterial system, thus raising the pressure in the 
 same. This increased pressure would immediately equalise 
 itself, through the capillaries, with the diminished pressure in 
 the venous system, if the blood did not meet with sensible 
 resistance by friction 2 against the walls of the smaller vessels, 
 particularly of the capillaries ; this so delays the passage through 
 the capillaries that the second systole follows before the ad- 
 justment is completed, causing an increased pressure in the 
 arterial system. The same occurs at each succeeding systole, 
 the repletion of the arterial system, and, at the same time, the 
 pressure of the blood from the dilatation of the elastic arteiial 
 walls, thus becoming greater and greater. The increasing dif- 
 ference of pressure, however, tends to drive the blood more and 
 more quickly through the capillaries, and it becomes at last so 
 
 1 For the purposes of the following explanation, the right auricle is con- 
 sidered as opening into the left ventricle, the pulmonary circulation, including the 
 right ventricle and left auricle, being left out of the question. 
 
 2 The resistance to a fluid running through a tube, provided that, like 
 water or blood, it adheres to (wets) the wall, is not caused by the friction 
 against the wall, but by the so-called 'internal friction.' The outer layer of 
 such a fluid remains entirely without motion. If we imagine the whole mass 
 to consist of very thin concentric layers, that layer which is next to the im- 
 movable one must rub against it, and so the others, each against the one 
 immediately outside. Every such contact causes resistance by friction ('in- 
 ternal friction'), and thus consumes a portion of the motive power that is, con- 
 verts it into heat ; each layer is consequently delayed in its course, and the outer 
 ones must naturally be the most delayed, the inner, therefore, the least : conse- 
 quently the speed is greatest at the axis. It follows that the delay of the axial 
 layer will be greater in narrow than in wide tubes. 
 
62 CONTENTS OF THE LEFT VENTRICLE. 
 
 great that as much blood is pressed through the capillaries 
 during the period between two systoles as each systole pours 
 into the arterial system. Under these circumstances no increase 
 of pressure can take place ; the difference in pressure now 
 existing between the arterial and venous systems is a constant 
 one ; it causes a continuous stream through the capillaries, carry- 
 ing through them just so much blood as the heart rhythmically 
 empties into the arteries. The rhythmic transfer from the 
 venous into the arterial system is thus converted into a con- 
 tinuous current from the arterial into the venous system, through 
 the capillaries (E. IL Weber). 
 
 The contents of the left ventricle, that is, the quantity of blood pumped 
 out during one systole has been calculated variously at from 150 to 190 
 grammes. The following are the principal methods : 1. (Legallois, Colin.) 
 The content of the veiitricle may be directly measured by filling the ven- 
 tricle, before rigor mortis sets in. with a fluid of known specific gravity, and 
 weighing before and after: in this case, as it is impossible to imitate the 
 normal pressure of the heart, the result is valueless. 2. (Volkmann.) The 
 diameter of the aorta, and the speed of the current of blood within it, are 
 used to calculate how high a column of blood the heart expels during a 
 unit of time ; knowing the frequency of the pulse, the quantity emptied 
 during each systole is found to be about ^ of the weight of the body ; that 
 is, in a body weighing 75 kgrms. = 187-5 grins. 3. (Vierordt.) Given the 
 speed of the blood in any section of the arterial system, the area of that 
 section, and also the area of the aorta, the mean speed in the latter 
 can be calculated, and also the quantity of blood discharged from the left 
 ventricle during a unit of time, since the speed in any two sections is in 
 inverse relation to their contents. The quantity of blood which the right 
 ventricle drives into the pulmonary arterial system must be very nearly 
 the same as that expelled by the left, because the same quantity of blood 
 flows through every section of the vascular system during the same time 
 (see below), and both sides of the heart contract synchronously. 
 
 The distension of the arteries and the slackness of the 
 veins show in the simplest manner how much higher is the 
 tension (blood pressure) in the arterial than in the venous 
 system ; this is also shown by the height of the jet of blood 
 issuing from an open vessel ; from a vein this is seldom of a 
 notable height, whilst the blood from an artery, on the other 
 hand, spurts to the height of several feet. 
 
 Absolute determinations of the pressure of the blood may 
 be made by connecting the vessel, laterally, with a manometer : 
 or the blood itself may be employed as the manometric fluid, 
 
TENSION OF VASCULAR SYSTEM: BLOOD PRESSURE. 63 
 
 by letting it rise in a vertical tube, and measuring the 
 height of the column (Hales). It is much more advantageous, 
 however, to use the mercurial manometer (Poiseuille) as an 
 6 haematodynamometer,' placing a solution of sodium bicar- 
 bonate between the blood and the mercury to prevent coagu- 
 lation. A priori, it follows that the blood pressure (that is, 
 the mean pressure, apart from the fluctuations of the pulse 
 wave) at one and the same spot of the arterial system will 
 increase: 1. With the fulness of the vascular system, that 
 is, with the quantity of blood. 2. With the frequency and 
 force of the contractions of the heart, for the greater the 
 quantity of blood pumped by the heart from the veins into the 
 arteries, the greater as is shown above will be the constant 
 difference in tension between the venous and the arterial sys- 
 tems. The tension, moreover, must vary in different parts of 
 the arterial system. Since any opposition hinders the equal- 
 ising of the difference in tension, the resistance offered in 
 any one portion of artery by the friction against its walls has 
 an influence on the tension of that particular portion of the 
 arterial system, similar to that of the capillaries on the general 
 tension of the arterial and venous systems. The tension must 
 always be greater before any point of opposition than behind. 
 It follows, therefore, that the blood pressure in the arterial 
 system gradually diminishes from the left ventricle to the 
 capillaries : that the diminution is most rapid where there is the 
 greatest resistance, that is, where contractions occur and where 
 branches are given off from the trunk, especially if at con- 
 siderable angles ; and that, lastly, the pressure in the principal 
 arterial trunks, on account of their size and the small number 
 of their branches, remains very nearly identical with that of 
 the bulbus aortse, whilst it diminishes in the smaller arteries 
 (H, Jacobson). Finally, on account of the less resistance offered 
 by the capillaries of the lungs as compared with the capillaries 
 of the body, the difference in tension between the pulmonary 
 arteries and veins will be less, and the pressure in the pulmo- 
 nary arteries will therefore also be less, than in the systemic 
 arteries, since the quantity of blood rhythmically pumped 
 over is the same in each. In the human aorta the blood 
 pressure has been estimated at 250 mm Hg. ; in the brachial 
 artery it has been directly determined at from 110-120 mm 
 
64 WORK OF THE HEART THE PULSE. 
 
 (Faivre). In the pulmonary artery it is said to be about one- 
 third as high as in the larger systemic arteries (Beutner). 
 
 The work done by the right ventricle (i.e. the product of the mass of 
 blood raised into the height to which it is raised) is (three times) less, 
 and its muscular coat therefore thinner, than that of the left. The work of 
 one systole of the latter, reckoning the quantity of blood at 175 grins., 
 and the aortic pressure at 250 mm Hg. ( = 3 mtr. of blood) may be reckoned at 
 0-525 of a kilogranirnetre, and the work of twenty-four hours (seventy-five 
 systoles in the minute) at 56,700 kilogrammetres. The work of the whole 
 heart, therefore, amounts to about 75,600 kilogrammetres. Since therefore 
 the weight of the heart is 292 grms., it would rai*e its own weight 10,788 
 mtrs. in one hour. As already shown, the whole of this work is converted 
 into heat, by friction in the vessels. Concerning the means which exist for 
 preserving a constant pressure of blood see below. 
 
 The continuous stream of blood through the capillaries 
 presupposes an almost constant tension of the arteries leading 
 immediately into them, so that in these the increase of pressure 
 corresponding to the systole can be scarcely appreciable. Fol- 
 lowing the arterial system, however, backwards to the heart, we 
 find in every portion of it a regular fluctuation in pressure, that 
 is, an increase of pressure corresponding to the systole, and a 
 diminution answering to the diastole. This fluctuation of pres- 
 sure, which can be easily demonstrated in any artery, is the more 
 considerable the nearer it is to the heart, and therefore, is greatest 
 at the commencement of the aorta (and pulmonary artery), and 
 least, almost unnoticeable, in the terminal arteries ; this fluctu- 
 ation of pressure is called the pulse. It does not occur syn- 
 chronously throughout the whole arterial system, but each 
 phase of it (for instance, its maximum) shows itself first nearest 
 the heart ; that is, the fluctuation in pressure travels, in the 
 form of a wave, from the heart to the capillaries through the 
 arteries, losing constantly in intensity. For the blood, pressed 
 during systole into the commencement of the arterial system, 
 at first increases the tension in that part alone ; the next 
 moment, however, this portion of artery, distended beyond its 
 diastolic volume, tends to relieve itself of its excess by its 
 elasticity : the return of the blood is prevented by the closure 
 of the semilunar valves ; the surplus is therefore forced forwards, 
 and, as in any elastic tube, the distension travels on towards the 
 capillaries. If the arterial system ended in closed tubes, it is 
 plain that the wave would run to the end in undiminished size, 
 
METHODS OF DETERMINING BLOOD PRESSURE. 65 
 
 and be then reflected hack again. But since the continual drain 
 through the capillaries constantly diminishes the systolic excess 
 in the arterial system, so that, according to Weber's theory, it 
 entirely disappears before the following systole, the wave, during 
 its course, becomes gradually smaller, until, at the end of its 
 journey, it disappears. In certain cases, however, the pulse 
 wave passes into the capillaries, and, through these, even into 
 the veins ; that is, in other words, in certain cases the plan 
 'described above is not carried out perfectly : the stream through 
 the capillaries becomes no longer continuous, but the cardiac 
 rhythm rules even in them : this takes place when the resist- 
 ance of an artery is diminished by its sudden enlargement, so 
 that the balance hitherto existing between the resistance and 
 the difference in tension of the arterial and venous systems 
 becomes locally disturbed, as, for instance, by the division of the 
 vaso-motor nerves (Bernard). 
 
 The speed of transmission of the pulse wave (not to be 
 confounded with the speed of the blood current, to be afterwards 
 considered) may be measured with a watch, by comparing the 
 moment of passage of the wave in a distant artery with the 
 moment of systole, or with the moment of the pulse in an artery 
 near the heart. On an average, it travels 28'5 feet per second 
 (E. H. Weber). 
 
 In investigating the pulse, both the rise in the pressure of the blood and 
 the increase in size (perceptible to both sight and touch), which take place 
 in every artery during the passage of the pulse wave, are made use of. The 
 former causes regular movements of the mercury in a manometer con- 
 nected laterally with an artery. In order to show these plainly, a float is 
 placed on the mercury in the open limb, and this, by means of a brush, 
 traces them on a drum, regularly rotating (by clock-work) on a vertical axis 
 (Ludwig's Kymographion). The up and down movements of the mercury 
 then form wave-like curves. These, however, give no exact indication of the 
 actual extent of the fluctuations in pressure, because the mercury, on account 
 of its inertia, soon sets up oscillations of its own, which, although of the 
 same duration as the pressure fluctuations, do not run the same course, In 
 order to ascertain the course of the fluctuation in pressure, other manometers 
 are used ; for instance, a bent elastic tube filled with fluid, which is expanded 
 by pressure on its contents (Bourdon's manometer, Fick's kymographion) ; 
 or an elastic bag filled with fluid, and placed in a closed tube containing air, 
 its changes in volume being transmitted by the air (Marey's kymograph) ; 
 or the dilatation of the artery is used directly, and for this sphygmographs are 
 employed. These instruments are applicable even to the human subject; 
 over the artery is placed a small plate, which, following its dilatation and 
 
66 CIRCULATION THROUGH CAPILLARIES AND VEINS. 
 
 contraction, moves a sensitive lever : the latter is made to write either on a 
 rotating drum (Vierordt), or on a travelling tablet (Marey). The best results 
 are given by Marey's instrument, because in it the oscillations originating 
 in the lever itself are prevented, as far as possible, by diminishing its size, 
 and counteracted, as far as practicable, by means of springs. 
 
 Under normal conditions the pulse in most arteries has a double (dicrotic) 
 or even triple (tricrotic) beat. The second and third beats, however, can 
 only be observed with fine instruments (with Marey's sphygmograph for 
 instance) as small eminences on the descending portion of the pulse wave 
 (Marey, Wolff, Rive). They are caused partly by the reflection of the wave 
 from the end of the artery, partly by the back current on the closing of the 
 aortic valves. For the respiratory fluctuations of pressure in the arteries 
 see p. 67. for an active motive power of the same see p. 68. 
 
 The pressure of the blood in the capillaries cannot be 
 measured ; its changes, however, can be estimated from their 
 size and from the amount of fluid which filters through them 
 (Chapter II.). According to the scheme of the circulation 
 previously described it must be constant, except when, as in the 
 above-cited cases, the pulse wave is transmitted to the capillaries. 
 Any diminution in the resistance of the vessels leading from 
 the capillaries will increase it. It rises and falls, moreover, with 
 the general pressure of the blood. 
 
 In the veins the blood pressure, appreciable with a mano- 
 meter, is extremely low, being slightly negative in the large 
 venous trunks, and increasing towards the periphery. Just as 
 each rhythmic injection of blood into the arteries produces a 
 rising wave in them, so each rhythmic removal of blood from the 
 venous system would cause a falling wave passing from the 
 capillaries, if this were not prevented by the auricles. 
 
 There are two other circumstances of such importance in 
 the circulation of the blood, that they may be classed along with 
 the contraction of the heart as causes of the circulation : they 
 are the aspiration of the thorax, and the adventitious compres- 
 sion of the veins. 
 
 The Aspiration of the Thorax. Owing to their position in 
 a large cavity, which they (together with the lungs) must 
 assist in filling, the heart and the large vascular trunks are 
 dilated beyond their natural volume, and are consequently more 
 completely filled with blood than they would be under other 
 circumstances. This especially affects the more yielding- 
 portions that is, the venous trunks and the auricles. As 
 already mentioned when speaking of the heart, the aspira- 
 
THE ASPIRATION OF THE THORAX. 67 
 
 tion of the thorax causes the blood, flowing through the venous 
 trunks opening into the heart, to be immediately replaced by 
 the flowing in of fresh blood from veins situated outside the 
 thorax, and this essentially aids the circulation. Each inspira- 
 tion, by its consequent enlargement of the cavity of the chest, 
 further increases the negative pressure, and thereby causes 
 over the whole mass of blood an aspiration in the direction 
 of the thorax ; but this aspiration will mainly affect the 
 venous system. In the arteries it causes merely a slight 
 decrease of tension ; on the other hand, it draws the venous 
 blood powerfully towards? the heart.. An ordinary expiration 
 merely removes the inspiratory increase of the negative 
 pressure ; on the other hand, a powerful expiration, caused by 
 muscular exertion, especially if an obstacle be opposed to the 
 exit of the air by closure of the glottis (as in coughing), changes 
 the negative pressure in the thorax into a positive one, com- 
 pressing the heart and vessels (in particular the veins), and 
 causes in the veins a serious stagnation, and in the arteries a 
 less important increase in pressure. In consequence of this, the 
 central end of a divided vein sucks in air during inspiration, 
 and this may lead to fatal consequences by leading to embolism 
 of the pulmonary capillaries : on the other hand, the veins 
 swell considerably during a powerful expiration, particularly 
 during coughing. If after a deep inspiration the glottis is 
 closed, and a powerful attempt made at expiration, the positive 
 pressure in the thorax becomes so great, that the venous trunks 
 are almost closed, less and less blood pours into the heart, and 
 at last the circulation is entirely stopped (E. Weber). The 
 action of these thoracic conditions on, the arteries shows itself 
 likewise in a regular fluctuation of the blood pressure (increase 
 during expiration, decrease during inspiration), which is syn- 
 chronous with the movements, not of the heart, but of breath- 
 ing, and is therefore four times as slow as the pulse. 
 
 On account of this the pulse waves of the kymographion curve appear to be 
 made up of a second (respiratory) system. If, by interposing a narrow tube 
 between the artery and the manometer, the pulse waves be prevented from 
 affecting the manometer, the respiratory waves are obtained alone (Setche- 
 now). 
 
 Transient, adventitious, compression of the veins by the con* 
 traction of neighbouring muscles. Any such compression of a 
 
 F 2 
 
68 CIRCULATION OF THE BLOOD THROUGH THE VEINS. 
 
 portion of a vein must press its contents in a direction towards 
 the heart) since the passage in the opposite direction is stopped 
 by the self-closing venous valves. This compressing apparatus 
 is in some places joined to an aspirating arrangement; thus 
 the portion of the femoral vein lying under Poupart's ligament 
 sucks in the blood from the periphery at each turn in an 
 outward direction of the upper part of the thigh, and empties 
 it into the vena cava on each turn in an inward direction, or on 
 flexion (Braune). 
 
 The movement of the blood in the veins consequently is as 
 follows : .when the blood has flowed through the capillary system, 
 its speed, according to the above scheme, almost = 0, because 
 the tension in the arterial system is only sufficient to drive the 
 necessary amount of blood (about 175 grms. in--Jj minute) 
 through the capillaries. The force of the heart therefore, being 
 entirely expended in overcoming this resistance, (being con- 
 verted into heat,) has no influence on the flow of blood in 
 the veins. 1 On the other hand the following forces come into 
 action: 1. Gravity: this can only aid the circulation in the 
 descending veins (as, e.g.., those of the head when upright), 
 while on the other hand it checks it in ascending veins : the 
 veins of the foot for instance, under the pressure of their high 
 column of blood, would be so enormously dilated and stretched, 
 and the resistance caused would be so great, that the whole move- 
 ment of the blood in the lower extremities would be stopped. 
 The other forces, therefore, which co-operate in the maintenance 
 of the venous circulation are of the greatest importance, viz. 
 2. The aspiration of the thorax, particularly during inspira- 
 tion, and 3. The muscular movements of the body. From 
 what has been stated it follows that the venous circulation goes 
 on very irregularly. 
 
 The movement of the blood in the capillaries, which may 
 be observed under the microscope in transparent parts (for 
 instance in the web and mesentery of the frog, in the omentum 
 
 1 This does not hold good in its entirety : the real conditions are more com- 
 plicated than the theoretical (Weber's) statement given here, for in many cases 
 the local tension of the artery exceeds this limit, and the blood enters the veins 
 with perceptible velocity, frequently under such pressure that, if cut, the veins spurt. 
 "We therefore usually find included amongst the forces causing the venous flow 
 the residue ' of the motive power of the arterial system (' vis-a-tergo, vis inertise,' 
 &c.)- 
 
VELOCITY OF THE CIRCULATION. 09 
 
 of the guinea-pig, in the latter case on a hot stage, Strieker), 
 frequently changes its direction in the branchings of their 
 fine network. At the same time the movements of the blood 
 corpuscles give one the opportunity of observing the unequal 
 speed of the different layers of blood previously alluded to ; 
 those floating in the axis having the greatest, those next to 
 the walls a far lower, rate of speed. In the finest capillaries, 
 through which only one row of red blood corpuscles can force 
 themselves at a time, the latter may frequently be seen to ac- 
 commodate their shape to their surroundings, they become 
 lengthened, bent, and curved, and pressed together until all 
 shape is lost, and then again assume their natural form. 
 For the emigration of the blood corpuscles, see the Appendix to 
 this Chapter. 
 
 Velocity of the Circulation. 
 
 If a fluid be circulating through a system of tubes, the same 
 quantity of fluid must flow through any collective cross-section 
 of the system during a given time. Whenever, on account of 
 some obstacle, this condition is not fulfilled, if the system is 
 dilatable, the section must become proportionately enlarged in 
 front of the obstacle, and a repletion of vessels takes place. 
 Thus for example the resistance of the capillaries causes the 
 constant repletion of the arterial system. If, however, the 
 circulation is in undisturbed progress, the same quantity of 
 blood must flow through any collective cross section of the vas- 
 cular system during a unit of time. It follows, moreover, from 
 this, that the speed of the current in the various collective cross 
 sections is inversely proportional to the area of the cross section : 
 it is, therefore, greatest in the commencement of the aorta and 
 the pulmonary artery, least (about 400 times less than in the 
 aorta) in the capillaries. Similar conditions control the speed 
 in the total cross sections of a single branched or unbranched 
 vascular segment : thus, the blood flows at the same speed 
 throughout the whole length of an unbranched vessel of uniform 
 size. 
 
 But the quantity of blood which flows through any cross 
 section of the vascular system during a unit of time, naturally 
 depends on the number and strength of the contractions of the 
 
70 VELOCITY' OF THE CIRCULATION. 
 
 heart. Let n be the number of systoles during the unit of 
 time, a the amount of blood contained in a ventricle ; then the 
 amount of blood m flowing in a unit of time through each sec- 
 tion is represented by m = n a, that is, in the human subject 
 about 218 grms. per second. 
 
 The rate of flow through the individual vessels, which make 
 up a collective section of the system, will, it is clear, depend 
 principally on the resistance which they offer, for the speed 
 will be the less, the greater the resistance, e.g. in narrow vessels, 
 which give off branches at large angles. That the speed more- 
 over varies ^greatly in -the different layers of a vessel has been 
 already shown. 
 
 Eegular fluctuations of speed only take place when the plan 
 of a continuous stream is not perfectly carried out, as is the case 
 in arteries, through, the influence of the pulse wave, and similarly 
 in the capillaries and veins when the pulse wave, as will ex- 
 ceptionally occur, reaches them (p. 65). That the passage of 
 the pulse wave must cause a momentary acceleration in each 
 portion of the -artery, follows from what has been before stated, 
 for the wave crest increases tension at a particular place, while 
 the tension is still of the diastolic height in -neighbouring 
 parts, and the speed increases with the difference in tension. 
 In the capillaries and veins, leaving out of the question the cases 
 of exceptional presence of pulse, the speed would be constant, 
 were it not that, in the latter, there are many influences at work 
 producing great irregularities. The stream of blood through 
 a vein may frequently be completely stopped ; this may, how- 
 ever, be unproductive of harm, since most sets of capillaries have 
 several efferent veins, so that if the stream of blood is ob- 
 structed or arrested in one, the blood flows more quickly 
 through the others. 
 
 The following methods are employed to measure the speed of the current 
 in the arteries : 1. Volkmann's hsemodromometer is a glass tube of known 
 volume, filled with water, which can suddenly he inserted into the stream of 
 the artery. The time that the hlood takes to run through the tube and 
 displace all the water is measured with a watch. A modification of this is 
 Ludwig's i Stromuhr ; ' it consists of two (spherical) droniometers, which 
 are alternately filled, the fluid (oil) being driven each time from one to 
 the other. 2. The tachometer (employed by Vierordt) is a tube inserted in 
 the artery ; the tube contains a light pendulum. The movements, which may 
 be observed externally, stand in a previously determined relation to the 
 
DISTRIBUTION OF BLOOD IN THE BODY. 71 
 
 velocity of the stream, which acts on the pendulum. If the latter is joined 
 to a sensitive lever, outside the tube, curves may be obtained, whose ordi- 
 nates will give the speed of the current (' dromograph,' Chauveau and Lortet). 
 3. The determination of the amount of blood flowing from an open artery, the 
 tension being maintained pretty constant by regulating the size of the open- 
 ing (Vierordt). Such determinations have naturally not been made in the 
 human subject. (In the carotid of dogs the speed varies from 200 to 700 mm 
 per second). In animals the speed in the capillaries is determined by direct 
 microscopic measurement of the course a blood corpuscle runs over in a given 
 time (E. H. Weber) ; in the human subject, by personal observation of the 
 entoptic visible movements of the blood corpuscles in the vessels of the retina 
 (Ludwig) ; by the latter method Vierordt found them in himself = 0'6-0'9 mm 
 in a second (compare Chap. X.) The speed in the veins may be measured 
 with the ' Stromuhr ' (Cyon & Steinmann). 
 
 In order to measure the time in which a portion of blood travels through 
 a given portion of the vascular system, or indeed through the whole round 
 of the circulation, an easily recognisable salt (ferrocyanide of potassium) is 
 injected into the central (cardiac) end of a vein, and the time noted at which 
 it is detected (by chloride of iron), in samples of blood taken at short 
 intervals from the peripheral end of the same vein (Hering). The first 
 discovered traces of the salt must have traversed the right side of the heart, 
 the capillaries of the lungs, the left side of the heart, and the capillary terri- 
 tory corresponding to the vein which is experimented upon, before reaching 
 the place where they are found. According to such experiments a complete 
 circulation occupies 15-2 seconds in dogs, and about 23 seconds in the human 
 subject. 
 
 Distribution of the Blood in the Body. 
 
 The quantity of blood contained in any portion of the body 
 in a given time depends : 1. On the number and size of the 
 afferent arteries. 2. On the speed of the current within them. 
 The latter, as stated above, depends on many circumstances, 
 particularly on their greater or less distance from the heart, 
 on the number and angles of their branches, &c. For the 
 changes in the size of an artery, see below under ' Innervation 
 of Vessels,' where further particulars will also be found concern- 
 ing the distribution of the blood in the body. 
 
 The distribution of blood in the individual parts of the body 
 may be determined in the dead subject by the same methods as 
 serve to ascertain the total amount of blood in the whole body 
 (p. 49). The individual parts of the body to be experimented 
 upon must, of course, be separated when they are in a frozen state 
 (v. Bezold and Grscheidlen). 
 
72 INNERVATION OF THE HEART. 
 
 Influence of the Nervous System on the Circulation of the 
 
 Blood. 1 
 
 The nervous system has a direct influence on the movements 
 of the blood, 1, by its control of the movements of the 
 heart ; 2, by its control of the calibre of the vessels, particu- 
 larly of the smaller arteries, for the latter are supplied with 
 muscles, on whose state of contraction their size depends. Not 
 only is the supply of blood to individual organs regulated by 
 changes in the capacity of a vessel, but change in the capa- 
 city of a large number of arteries, and the consequent change 
 in the contents of the whole arterial vascular system, has a 
 great influence on the activity of the heart. 
 
 1. Innervation of the Heart. 
 
 a. Intracardiac Centres. 
 
 The heart, removed from the body, or separated from 
 all the nerves supplied to it, still beats for some time ; in 
 cold-blooded animals for days, in warm-blooded animals so 
 long as a supply of oxygenized blood is provided. Its move- 
 ments must, therefore, at least in part, be caused by a 
 mechanism situated within itself, and the latter is supposed, 
 with the greatest probability, to reside in the ganglionic 
 cells (connected together by nerve fibres), which are lodged 
 in the muscular substance of the heart, particularly in the 
 septum between the auricles, and at the junction of the auricles 
 and ventricles (Eemak). At least a portion of these ganglia must 
 cause the automatic rhythmical contractions of the heart, and 
 indeed the whole process of contraction (from the auricles to 
 the ventricles) must be regulated and combined by them. In 
 a heart which is at rest, but still excitable, one or more regu- 
 lar contractions of its various divisions may be produced, by 
 reflex action, on applying different stimuli (mechanical, thermal, 
 chemical, or electrical) to the substance of the heart : greater 
 effect is obtained by stimulation of the inner than of the outer 
 surface of the heart. 
 
 1 It is advantageous to refer to the influence of the nerves when considering the 
 principal processes of molecular change, although by such anticipation many ideas 
 are introduced, which are only explained in the Third Part of this work. 
 
INHIBITORY NERVES OF THE HEART. 73 
 
 Portions of the muscular substance of the heart which contain no gan- 
 glia may, like all other portions of muscles, be thrown into simple contrac- 
 tion by direct irritation. 
 
 In the frog's heart the principal ganglionic masses (Remak's ganglia) lie 
 in the wall of the sinus venosus. After the separation of the latter, the heart 
 ceases to contract, whilst the sinus itself continues to pulsate (Stannius). 
 Other injuries which merely affect the sinus cause the heart to stand still 
 (v. Bezold). A second ganglion (Bidder's ganglion) lies near the junction of 
 the auricles with the ventricle ; if the heart which has been separated from 
 the sinus venosus, and which is not pulsating, be divided in this region, 
 that portion again commences to pulsate rhythmically in which the ganglion 
 has been left; usually the ventricles, sometimes the auricles, or both 
 auricles and ventricles. These pulsations are, however, temporary, and 
 appear to depend upon mechanical irritation of Bidder's ganglion, which 
 usually is not in a state of activity. (Even when this separation of auricles 
 and ventricles is not effected, the heart which has been separated from the 
 sinus, and which is motionless, may be made to pulsate for a time by a puncture 
 into the line of junction of auricles and ventricles, H. Munk). Some attri- 
 bute the arrest of the heart which follows its separation from the sinus 
 venosus, to irritation, caused by the section of the fibres of the vagus 
 (Heidenhain). The hypothesis that inhibitory centres exist which have 
 their seat in the auricles, and which are unable to control the combined 
 motor powers of the sinus and the ventricle, whilst they can control the 
 latter by itself, although capable of accounting for the phenomena to 
 which reference has been made, is unnecessary. 
 
 b. Inhibitory Nerves. 
 
 Even the nerves which enter the heart from the cardiac 
 plexuses, and which are derived partly from the pneumogastric, 
 partly from the sympathetic, exert an influence upon the move r 
 ments of the heart. The fibres contained in the vagus possess 
 the power, when they are continuously irritated by mechanical, 
 chemical, or electric means, of slowing, or weakening (Ludwig 
 and Coats) the contractions of the heart, and when subjected to 
 a more powerful irritation, of bringing the whole heart to a 
 stand-still in diastole (Ed. Weber, Budge). In mammalia, and 
 especially in man, such an excitation, originating in the origin 
 of the vagus in the medulla oblongata, is kept up throughout 
 the whole of life, so that section of the vagi suddenly in- 
 creases the frequency of the pulse. 
 
 The vagus contains, in addition to inhibitory fibres, others which accele- 
 rate the heart. Very slight excitations of the vagus occasionally cause an in- 
 crease in the number of heart-beats (SchifT, Giannuzzi). 
 
74 ACCELERATING NERVES OF THE HEART. 
 
 In relation to the heart, the vagus belongs to the group of * reyulating 
 nerves ' (consult on this subject Chapters IX. and XL). 
 
 In man the vagus can be occasionally irritated by mechanical means, as 
 by pressure (Czermak, Concato). 
 
 When both vagi are subjected to the same degree of irritation, it is found 
 that the right vagus possesses, in the lower animals, a more powerful in- 
 hibitory action on the heart than the left (Masoin, Arloin, and Tripier). A 
 short interval elapses between the time of commencement of the irritation of 
 the vagus and that of the display of its inhibitory action (' Latent period,' 
 Bonders and Prahl). The irritation of the vagus need not necessarily be 
 the same as that required to induce tetanus generally, in order to induce 
 the inhibitory influence, but it suffices if it consists of separate irritations 
 following one another rhythmically with moderate rapidity (v. Bezold). 
 During the arrest of the heart brought about by irritation of the vagus, any 
 immediate excitation of the organ gives rise to a single and regular contrac- 
 tion. 
 
 In the heart of the frog, the phenomena due to irritation of the vagi 
 may be induced by exciting the sinus venosus, to which the fibres of the 
 vagus run. Poisoning with curare, as well as powerful cooling, paralyses 
 the terminations of the vagus in the heart. 
 
 c. Accelerating Nerves. 
 
 Irritation of the medulla oblongata causes an acceleration 
 of the heart, provided that the communication with the heart 
 through the spinal cord, the rami communicantes which pro- 
 ceed from it to the sympathetic cord, the first thoracic ganglion 
 (ganglion stellatum\ and the sympathetic cord itself, be all 
 uninjured. 
 
 This acceleration is a complex phenomenon, inasmuch as 
 excitation of the medulla oblongata produces simultaneously 
 a contraction of the arterial system, which increases the fre- 
 quency of the pulse (Ludwig and Thiry). As, however, the 
 quickening of the pulse occurs even when the influence of 
 the vaso-motor nerves is withdrawn (by division of the chief 
 vaso-motor nerves, as, e.g., the splanchnic nerves), and as this 
 quickening occurs more rapidly when the nerves going to the 
 heart are preserved than when their influence is removed (in 
 which case increase in the frequency of the pulse could only 
 be brought about indirectly), we must conclude that there does 
 exist a system of fibres which accelerate the heart's action, 
 and which pass to the heart through the above-mentioned 
 channels. The centre whence these fibres proceed appears to 
 
1NNERVATION OF BLOOD VESSELS. 75 
 
 exist in the medulla oblongata. This centre is not continuously 
 in action, seeing that after division of the splanchnics section 
 of the spinal cord induces no diminution in the number of heart 
 beats (the brothers Cyon). According to some authors (SchifT), 
 the vagus contains, in addition to the inhibitory, also accelerator 
 fibres. Schmiedeberg has proved this to be the case in the 
 frog. 
 
 As the great majority of the vaso-motor nerves leave the spinal cord 
 below the second dorsal vertebra, whilst the accelerating nerves of the heart 
 are given off above, and as irritation of the cervical portion of the spinal cord, 
 after section at that vertebra, induces quickening of the heart without any 
 increase in the blood pressure, a further proof is afforded of the existence 
 of accelerating nerves (v. Bezold). The accelerating nerves belong to the 
 group of regulating nerves. 
 
 2. Innervatien of Blood Vessels. 
 
 The calibre of the arteries varies, quite independently of 
 their elasticity, with the degree of contraction of the smooth 
 muscular fibres which are contained in their coats. The latter 
 are influenced by a variety of circumstances ; thus, contraction 
 of arteries is increased by cold, and diminished by heat. Even 
 the blood pressure and the quantity of gases which the circu- 
 lating blood contains appear to exert an influence on the con- 
 traction of arteries (Ludwig and Sadler, Ludwig and Hafiz) ; 
 chiefly, however, the calibre of the arteries depends upon the 
 state of irritation of the nerves which govern the muscular 
 structures of the vessels, the vaso-motor nerves (Bernard). In 
 the case of the majority of these a continuous ' tonic' state of 
 excitation has been proved to exist, so that their section leads 
 to a paralysis of the muscular fibres of vessels, to a dilatation of 
 the artery, to an increased flow of blood through the organ 
 concerned, and, consequently, to its becoming red, to its tem- 
 perature becoming higher, and to an increased transudation 
 through its capillaries. The flow of blood may, under these 
 circumstances, increase so much, that the blood may pass into 
 the veins without having lost its arterial colour, and the pulse 
 waves may be propagated even to the veins (Bernard). The 
 irritation of the peripheral end of vaso-motor nerves must, 
 conversely, lead to a narrowing of arteries, and to a diminution 
 of the flow of blood, even to its complete stoppage, so that the 
 
76 THE VASO-MOTOR NERVES AND VASO-MOTOR CENTRE. 
 
 parts of the body concerned necessarily become pale, cold, and 
 the seat of scantier transudation from the blood. 
 
 A peristaltic contraction of the arteries, passing from the main trunks 
 towards the capillaries, would drive the blood actively into the capillaries, 
 and thus aid in the circulation. That this takes place during life is not 
 positive. After destruction of the motor power of the heart, however, an 
 active emptying of the arteries into the veins is brought about by stimula- 
 tion of the vaso-motor centres, (Goltz, Thiry, v. Bezold,) and it is probable 
 that the emptiness of the arteries after death is to be attributed to the 
 persistent activity of the same centre. 
 
 Blushing and erection of the penis are the best known phenomena pro- 
 duced by the action of nerves on the local movements of the blood. The 
 vaso-motor nerves run partly in spinal, partly in sympathetic trunks ; for 
 instance, in the cervical portion of the sympathetic for the scalp, conjunctiva 
 und salivary glands (Bernard) ; in the anterior roots of the spinal nerves 
 for the lower extremities (Pfliiger), first, however, joining the rami commu- 
 nicantes of the sympathetic (Bernard). The vaso-motor nerves of the upper 
 extremities proceed from the middle dorsal roots to the sympathetic chain, 
 thence to the first thoracic ganglion, and thence through the rami com- 
 municantes to the plexus brachialis (F. Cyon). The capacious vascular 
 system of the viscera l receives its fibres from the splanchnics, which are, con- 
 sequently, the most influential of the vaso-motor nerves (v. Bezold, Cyon 
 and Ludwig). Vascular nerves, possessing direct powers of dilatation, are 
 also asserted to exist (Bernard, Schiff), but whether the surmise is correct 
 has not yet been decided ; at all events, their action is as yet obscure. 
 Stimulation of the nervi erigentes causes relaxation of the arteries of the 
 penis (Loven) ; the same effect is produced in the salivary glands (compare 
 Chapter II.) by stimulating the cerebro-spinal fibres (Bernard). By 
 stimulation of the spinal cord, the muscular arteries are not contracted, 
 like others, but enlarged (Ludwig and Hafiz). For reflex enlargement of 
 the arteries see below. 
 
 A common central organ for the vaso-motor nerves is 
 situated in the medulla oblongata, by stimulating which, the 
 spinal cord and sympathetic being uninjured, contraction of 
 all the small arteries is produced, and, as a consequence, in- 
 crease of the blood pressure in the arterial trunks, and tur- 
 gescence of the heart (Ludwig and Thiry); for a description 
 of this see Chapter XI. This central organ is constantly in 
 action, and this explains the tone of the vaso-motor nerves. 
 Division of the spinal cord in its cervical portion abolishes this 
 
 1 This vascular division is so large, that it can contain almost the whole of 
 the blood of the body : on tying the portal vein, for instance, animals subjected 
 to the operation die of anaemia, because the whole of the blood remains in the 
 visceral vessels (Ludwig and Thiry). 
 
INNERVATION OF THE HEART AND BLOOD VESSELS. 77 
 
 tone, thus causing dilatation of all the arteries. Numerous 
 researches, particularly on inflamed tissues, as well as those 
 previously referred to on the direct influence of temperature, 
 point to the existence of ganglia in the vicinity of vessels, 
 the function of which is to rule over their calibre. 
 
 3. Origin of the Excitation of the Nerve Centres which preside 
 over the Heart and Blood Vessels. 
 
 The cause of the continuous rhythmical contraction of the 
 intracardiac nerve centres is wholly unknown to us. We, 
 however, know that the presence of oxygen (Ludwig, Volkmann, 
 Groltz) and a temperature not far removed from that of the 
 animal's blood are necessary conditions of its occurrence. A 
 rise of the blood pressure within the heart (induced, for instance, 
 by tying the aorta, or by causing the smaller arteries to contract 
 by irritating either the vaso-motor centre, or the more im- 
 portant vaso-motor nerves themselves, as the splanchnic) leads 
 to a quickening of the heart beats, which is probably due to a 
 direct irritation of the powerfully distended cardiac walls. 
 Conversely, when the blood pressure falls (as when the spinal 
 cord or the splanchnic nerves are divided) there is a slowing of 
 the heart (Ludwig and Thiry), 
 
 The increased frequency of the heart's action, which has been referred to, 
 and which is occasioned by a rise in the blood pressure, appears so to augment 
 the amount of work performed by the heart as more than to compensate for the 
 increased resistance which it has to overcome ; for in warm-blooded animals 
 when the smaller arteries are made to contract (by irritation of the medulla 
 oblongata, &c.), the velocity of the blood current through the arterial branches 
 increases (Heidenhain). 
 
 Temperatures from 4 C. to C., and above 30-40, arrest the contrac- 
 tion of the heart of the frog (Schelske, E. Cyon). The frequency of the 
 heart beats increases with rise in temperature until the superior limit is 
 nearly reached. The intensity and steadiness of the contractions is greatest 
 at low or medium temperatures. Between 30 C. and 40 C. they diminish. 
 The sudden action of high temperatures leads to the same eifectsas irritation 
 of the vagus. If, however, the heart has been previously strongly cooled, 
 rapidly succeeding beats, and ultimately tetanus of the heart, follow the 
 application of heat. When the heart has ceased to beat in consequence 
 of a high temperature, irritation of the sinus venosus (which previously 
 leads to stoppage of the heart through irritation of the vagus) causes a 
 tetanic contraction of the ventricle (E. Cyon). Even in warm-blooded 
 
78 INNERVATION OF THE HEART AND BLOOD VESSELS. 
 
 animals the frequency of the pulse increases, iu general, with the tempera- 
 ture of the body. 
 
 Tetanising currents acting upon the heart abolish the rhythmical activity 
 of its nerve centres, and occasion merely ineffectual spasmodic movements, 
 which are accompanied by a marked fall in the blood pressure (S. Mayer). 
 The same action is exerted by strong constant currents. Weak constant 
 currents conducted from the base of the h^art to its apex occasion rhythmical 
 contractions in the heart whjch has been separated from its sinus. With a 
 reversed direction of the current, the contractions commence in an abnormal 
 manner in the ventricle (Bernstein), a phenomenon which has not yet 
 received a satisfactory interpretation. 
 
 The Inhibitory Centre in the medulla oblongata, which 
 appears to be constantly in action (i.e. excited) in warm-blooded 
 animals, like the respiratory centre in its vicinity, is under the 
 influence of numerous centripetal nerves, whose irritation slows 
 the heart, so long as the vagus is uninjured. To this class of 
 nerves belong the different sensory nerves (Loven, Kratschmer), 
 the vagus itself (v. Bezold, Bonders, Aubert and Eoever ; one 
 vagus being excited whilst the other is intact), the- cervical and 
 abdominal cords of the sympathetic, and the splanchnic 
 (Bernstein) ; mechanical irritation (by blows) of the abdominal 
 viscera similarly slows the pulse by acting in a reflex manner 
 on the vagi (Groltz). Conversely, the excitation of the inhibitory 
 centre is diminished by inflation of the lungs (Hering). In 
 addition, the excitation of this centre is increased, like that of 
 respiration, by an asphyxiated state of the blood ; it may, 
 indeed, under these circumstances, assume a rhythmical action 
 similar to that of the respiratory centre (this occurs when the 
 lungs ar% filled with air containing much carbonic acid) ; even 
 under normal circumstances there appears to be an increased 
 excitation of the vagus centre corresponding to each inspiration 
 (Bonders). 
 
 A rise in the arterial pressure in the brain increases the ac- 
 tivity of the inhibitory centre. 
 
 Division of the above-mentioned sympathetic nerves is said to diminish 
 the tonic excitation of the vagus, which must therefore only be of a reflex 
 nature (Bernstein). 
 
 The reflex actions likewise referred to in the preceding paragraph, like 
 many others, are prevented by the powerful irritation of sensory nerves. 
 
 Nothing is known concerning the circumstances which in- 
 fluence the activity of the centre of the accelerating nerves. 
 
INNERVATION OF THE HEART AND BLOOD VESSELS. 79 
 
 The activity of the vaso-motor centre depends upon con- 
 ditions which are very similar to those which affect the inhibi- 
 tory centre for the heart. Centripetal nerve fibres which 
 intensify the tonic excitation of the centre (so-called 'pressor' 
 fibres) are contained in the vagus, specially in its superior 
 laryngeal branch, and even more abundantly in the cervical 
 sympathetic (Aubert and Eoever) ; further, every excitation of 
 a sensory nerve leads to a general contraction of blood vessels 
 (Loven). 
 
 Certain centripetal (depressor) fibres contained in the 
 vagus, which in some animals are contained in a separate 
 branch which arises from the heart, the ramus depressor (Cyon 
 and Ludwig), diminish the vascular tone. 
 
 The centripetal irritation of many sensory nerves causes di- 
 lation of the vessels distributed to the part supplied by the 
 nerve (Loven). 
 
 The tone of the vaso-motor centre is, further, dependent 
 upon the gases contained in the blood. When the quantity 
 of carbonic acid increases (in asphyxia, when an atmosphere con- 
 taining much carbonic acid is inhaled) the smaller arteries 
 generally contract with an increase of the intracardiac pressure 
 and a distension of the heart (Thiry) ; this contraction inter- 
 mits, however, in a regular rhythmical manner (Traube) and the 
 rhythm coincides with the respiratory excitations (Hering). 
 These phenomena occur even when the carotids have been oc- 
 cluded, whereby the blood which is stagnant in the brain 
 becomes fitted to induce dyspnoea (Nawalichin ; qompare 
 Chap. IV.). 
 
 The inhalation of irritating vapours through the nostrils exerts a pressor- ' 
 influence through the medium of the trigeminus (5th) nerve. Similarly 
 acts mechanical irritation of the stomach, and especially of its serous coat. 
 The pressor action of sensory nerves is only present as long as the brain is 
 intact (E. Cyon). The respiratory variations in the blood pressure which 
 were previously alluded to, appear in part to be in relation with the 
 rhythmical activity of the vaso-motor centre (Schiff). 
 
 Many of the facts which have been adduced point to the exis- 
 tence of a complex regulating system, by which the velocity and 
 the pressure of the blood flowing into the capillaries are main- 
 tained constant or within the limits necessary to the functional 
 activity of the organs. It is specially to be noticed that a high 
 
 - v, 
 
80 FREQUENCY OF THE PULSE. 
 
 pressure in the arterial system, and in the heart, on the one 
 hand, increases the activity of the heart, on the other (through 
 the nervi depressores), diminishes the resistance which it has to 
 overcome, by causing a relaxation of the peripheral arteries. 
 Our knowledge is as yet far too incomplete, to permit of our 
 understanding the complete mechanism. (For the regulation 
 of the blood pressure in the brain consult Chap. XL). 
 
 Frequency of the Pulse. 
 
 From the facts which have been adduced, it follows that the 
 frequency of the pulse, the height of the blood pressure, and the 
 velocity of the circulation depend upon very numerous in- 
 fluences. The mean frequency of the pulse amounts to seventy- 
 two beats in the minute ; in the foetus, however, it is much 
 greater ( 1 84) ; the pulse falls to the twenty-first year. In old 
 age the frequency again appears to increase. 
 
 The frequency of the pulse is very liable to vary ; thus 
 strong mental emotions exert a powerful action upon it, probably 
 through the vagi. The following are the influences which 
 chiefly affect the pulse rate. Temperature : heat increases, cold 
 diminishes the frequency of the pulse (either by a direct action, 
 or more probably in a reflex manner). Movement increases the 
 frequency. Position of the body : when the body is vertical, 
 though the muscles be at rest, the frequency of the pulse is 
 greater than when it is horizontal. Respiration : during inspi- 
 ration the pulse is slower than during expiration : further, the 
 frequency of the pulse is greater during digestion than during 
 the intervals between meals, and it is finally greater in persons 
 of the female sex and of small stature than in those of the male 
 sex and of large stature. 
 
 Numerous medicinal substances and poisons exert an action on the 
 frequency of the pulse, as soon as they enter the blood. They do so partly 
 by a direct action on the cardiac ganglia, partly by exciting or paralysing 
 the vagus-centre, or the fibres of the vagus, especially its terminations in the 
 heart, and they possibly even act on the accelerating system. The above- 
 mentioned influences on the pulse may also be due to an action exerted on 
 the vaso-motor apparatus. 
 
81 
 
 L i B R A R ^^ 
 
 APPENDIX. CAIJPOR\1A 
 
 EXIT OF BLOOD COEPUSCLES FEOM UNINJURED t VESSELS. 
 
 Emigration. Diapedesis. 
 
 UNDER abnormal conditions both red and colourless blood 
 corpuscles may leave vessels without rupture of their walls 
 (' Diapedesis '). The escape of the red corpuscles occurs during 
 stoppage of the venous current. In consequence of the high 
 pressure thus resulting, first the plasma is pressed out, and then 
 the blood corpuscles ; these, after being squeezed until all shape 
 is lost, are pressed out like a fluid mass ; afterwards, they resume 
 their original form (Cohnheim). The same thing also occurs 
 under other influences which are not mechanical, for instance, 
 by the action of salts on exposed vessels (Prussak, denied 
 by Cohnheim). Colourless corpuscles leave the vessels during 
 inflammation either alone or together with a few red ones. 
 After an enlargement of the small arteries and veins has been 
 caused in a manner which is not yet understood by inflamma- 
 tory action, and the speed of the current within them has been 
 considerably lessened, a separation takes place of the colourless 
 elements, which move slowly along close to the vascular walls, 
 and at last become stationary, whilst the red ones flow on in the 
 axis of the vessels. In the veins and capillaries the colourless cor- 
 puscles are then seen to pass through the vascular walls, dis- 
 playing amoeboid movements, and to appear outside as ' pus cor- 
 puscles ' (Cohnheim). The formation of the above marginal 
 layer may be explained either by the unequal speed of the 
 various layers of blood, which would cause the spherical colour- 
 less corpuscles to roll gradually to the periphery, especially 
 when the blood stream has become sufficiently slow (Bonders, 
 Cohnheim), or by a peculiar adhesiveness of the colourless cor- 
 puscles, which causes them, when the current is sufficiently slow, 
 and they have accidentally fallen against the vascular wall, to 
 
 a 
 
82 EMIGRATION OF BLOOD CORPUSCLES. 
 
 adhere to it (Hering). Whether the passage of the corpuscles 
 outwards happens in consequence of active amoeboid movements 
 (Cohnheim) or by a kind of filtration (Hering, Samuel), further, 
 whether the passage takes place through openings (stomata), 
 which exist preformed in the wall of the vessel, between the 
 epithelial cells, is as yet unknown. 
 
83 
 
 CHAPTEK II. 
 
 SOURCES OF LOSS TO THE BLOOD. 
 
 Secretion. 
 
 THE term ' secretion ' in its widest sense denotes all those pro- 
 cesses in which substances quit the blood in an altered or 
 unaltered condition. The products of such processes are called 
 6 secretions,' and may be regarded as of two sorts, viz : 
 
 1. Those liquids or gases 1 derived from the blood, which 
 exude from the internal or external surfaces of the body. Those 
 yielded by internal surfaces (in cavities or canals) called ' se- 
 cretions ' in the restricted sense are destined for particular 
 uses (e.g. in digestion), and are for the most part again taken 
 up by the blood after undergoing a certain amount of change. 
 Those yielded by external surfaces called ' excretions ' are, 
 on the contrary, lost to the body, although certain of them (e.g. 
 the sebaceous and sudoriparous excretions) have certain 
 functions in connection with the surfaces where they appear. 
 
 It will be seen that in their origin there is no difference between secretions 
 and excretions j certainly the fact of their being liberated at internal and 
 external surfaces respectively does not create a fundamental distinction. If 
 we must keep them separate it will be best to regard those substances as 
 excretions which are incapable of further use in the organism and whose 
 retention by it would be harmful. To this class belong certain ultimate 
 results of oxidation carbonic acid, urea, &c. ; and the respiratory and 
 urinary products would, therefore, be the chief excretions. Frequently all 
 the substances given off by the body, irrespective of their origin, are called 
 excretions. If this definition be adopted, we must add to those just men- 
 tioned the following, the essential constituents of which are not at all, or 
 only indirectly, derived from the blood : 1. The faeces, i.e. the indigestible 
 parts of food mixed with those constituents of the alimentary secretions 
 which are not reabsorbed by the blood-vessels. 2. Epithelial exuviations 
 (i.e. the cast-off portions of epidermis, hair and nails). 3. Ova and semen. 
 
 1 Gaseous secretions are treated of in Chapter IV. 
 G 2 
 
84 SECRETIONS. SECRETORY FORCES FILTRATION. 
 
 2. Those liquids derived from the blood which bathe the 
 tissues of the body, parenchymatous juices, muscle juice, the 
 fluid moistening connective-tissues, &c. 
 
 Inasmuch as the solid portions of the tissues (cells, fibres, &c.) derive 
 the material of which they are composed from the various parenchymatous 
 iuices, and therefore immediately from the blood, every constituent of the 
 body may be looked upon as a secretion. This process is, however, so im- 
 perfectly understood that we cannot pause to discuss it now. For the same 
 reason we can here only refer, in general, to the secretion of the parenchyma- 
 tous j uices. 
 
 I. SECEETION IN GENERAL. 
 
 % 
 Physical Processes. 
 
 All fluids separated from the blood must pass through the 
 walls of closed capillary vessels. It would seem that the only 
 Instance, during health, of a fluid passing through ruptured 
 vessels is the menstrual flux : and even this may turn out to be 
 a case of diapedesis. (See p. 81.) 
 
 The physical forces which bring about the passage of fluids 
 through membranes are filtration and diffusion. 
 
 By filtration we understand the passage of a liquid under the influence 
 of pressure through the pores (not the physical, interrnolecular spaces, but 
 the coarser, mechanical interstices) of a body such as a membrane. 
 Just as in the ordinary process of filtering the weight of the substance to be 
 filtered forces the liquid through the filter, so the tension of the blood- 
 vessels forces out some or all of the fluid constituents of the blood ; for the 
 pressure of the fluids surrounding the capillaries (parenchymatous juices) is 
 generally less than the pressure of the blood in the vessels. 
 
 The amount of the filtered fluid increases with the difference between 
 these two pressures. This difference is made more marked, 1, by relieving 
 tiie tension in the neighbourhood of the capillaries, as in the withdrawal of 
 the parenchymatous fiuids or the reduction of the atmospheric pressure by 
 cupping, &c. ; 2, by increasing the tension of the capillary walls, which 
 may be brought about (as was mentioned previously) : , by increasing the 
 blood-pressure all over the body; b, by widening the arteries conducting 
 blood to the part, e.y. by relaxing the normal contraction of their circular 
 muscles by the application of heat, or by cutting off" the influence of vase- 
 motor nerves. The converse operations, viz. diminution of blood-pressure, 
 application of cold, and abnormal irritation of vaso-motor nerves will diminish, 
 the amount of the filtered fluid. This partly explains the influence of the 
 nervous system upon secretion (see below). Filtration is affected also by 
 the nature of the filtering fluid. True solutions pass through the medium 
 
FIL TBATIOX DIFFUSION. &5 
 
 unchanged. Viscid fluids, such as solutions of albumin, starch and gum, 
 filter less perfectly, a portion only of their contained substances, in amount 
 varying with the pressure, being able to percolate. If indeed the pressure is 
 very slight, the whole is retained on the filter. Under slight pressure, there- 
 fore, the blood loses by filtration water, ealts, sugar, &c., which form true solu- 
 tions j while under a greater pressure it is deprived of more or less of its 
 albumin, h'brinogen, &c. 
 
 Diffusion (or osmose) is the intermixing of fluids through a mem- 
 brane, independently of any difference of pressure on the two sides, often 
 even in opposition to hydrostatic pressure. For this purpose it is not neces- 
 sary that the membrane should be porous, the essential molecular interspaces 
 of a homogeneous membrane being all that are required. (The most homo- 
 geneous membranes known are the so-called 'precipitation-membranes' 
 which are formed at the surface of contact when one of two solutions capable 
 of producing a precipitate is allowed cautiously to flow over the other, M. 
 Traube). In diffusion two liquids are required, while in filtration it is only 
 necessary to have a liquid on one side of the membrane, the other being pre- 
 sented to the air or to a vacuous space. Diffusion, moreover, can only take place 
 between liquids of different kinds, while filtration may occur between those of 
 the same kind, provided that each is subjected to a different pressure. The 
 essential condition of diffusion is that the membrane should be saturated 
 simultaneously by both liquids j the object of the process is the complete 
 chemical equalisation of the fluids on the opposite sides of the membrane. 
 According to the latest researches the passage of a substance through a 
 membrane (Endosmose) takes place, if there is on the other side of the 
 membrane a liquid capable of dissolving the substance and having an affinity 
 for it j and if the molecules of the body are somewhat less than the molecular 
 interstices of the membrane. Endosmose takes place more quickly, the 
 greater this affinity (' Endosmotic force '), the smaller the molecules of the 
 substance, and the larger the interstices (M. Traube). Endosmotic force is 
 very great in the case of strongly hygroscopic substances. Certain complex 
 bodies of great molecular weight (p. 30 et. seq.) are incapable of diffusing 
 through most membranes on account of the large size of their molecules. 
 Such substances are albumin, hemoglobin, 1 gum, &c., which have been de- 
 nominated ' colloids ' by Graham, on account of their non-existence in a crys- 
 tallised form, in contra-distinction to { crystalloids/ or substances which 
 admit of crystallisation. Other writers (Vierordt, Jolly) consider the 
 essential element in the process of diffusion to be the interchange between 
 a portion of the diffusing substance, and an amount of the solvent liquid 
 on the other side of the membrane : and the quantity of the solvent liquid 
 which passes through for every unit of weight of the substance they call its 
 ' endosmotic equivalent.' 
 
 As the blood is everywhere surrounded by fluids of a differ- 
 
 1 Although haemoglobin is crystalline, it cannot be said to belong to the 
 crystalloid group, as it does not diffuse ; without doubt, had Graham been ac- 
 quainted with this, the only known crystallisable, yet indiffusible body, he would 
 have chosen a more appropriate name for the group. 
 
86 CHEMICAL PROCESSES OF SECRETION. 
 
 ent chemical composition, and under a lower pressure than 
 itself, it is plain that in nearly all cases of secretion both filtra- 
 tion and diffusion must play a part. 
 
 The purely physical processes of filtration and diffusion can 
 only yield fluids containing the constituents of liquor sanguinis 
 in various proportions. It has not been ascertained with cer- 
 tainty whether such simple separations occur. The nearest ap- 
 proach to them are the so-called transudation fluids, viz. the 
 fluids found normally in the various cavities of the body 
 (e.g. in the pericardial, peritoneal and pleural sacs, in the 
 cerebral ventricles, &c.) ; and the pathological fluids of drop- 
 sical cavities and cedematous tissues. Their principal con- 
 stituents are water, salts, sugar, urea, varying amounts of 
 albumin, fibrinogen, and sometimes also fibrinoplastin. The 
 presence of fibrinogen may be demonstrated by the setting-in 
 of coagulation on the addition of fibrinoplastin and the fibrin- 
 ferment (e.g. in the form of a well-squeezed blood-clot. If 
 the transudation-fluid contains at the same time fibrinoplastin, 
 coagulation occurs spontaneously on withdrawal from the body ; 
 but, as a rule, only slowly, on account of the fibrinoplastin 
 being present in such small quantities. 
 
 It has lately appeared very probable that the fluids found in the various 
 cavities above mentioned should, in part at least, be regarded as lymph 
 (Chapter III.) ; for not only have lymph-corpuscles been seen floating in 
 them, but direct communications have been traced between the cavities 
 containing them and the lymphatic vessels (von Recklinghausen). 
 
 Chemical Processes. 
 
 Most secretions contain, in addition to the substances which 
 are common to them and the blood, certain specific constituents, 
 for the production of which the above-mentioned physical pro- 
 cesses cannot alone account. It is necessary, therefore, to 
 assume that certain chemical changes take place in the tran- 
 suded fluids, the seat of which, or at least the impulse to 
 which, must most probably be sought for in the cells with 
 which the various secretions come into contact. Such cells are, 
 in the case of parenchymatous juices, the cells or corpuscles 
 of the tissues in which they arise ; in the case of free secre- 
 tions, the gland-cells. 
 
 The only difference therefore between parenchymatous 
 
ORGANS OF SECRETION. 87 
 
 and free secretions appears to be that the former remain en- 
 closed in a fine cellular network, while the latter pass through 
 a thin layer of cells (in the glands) and so quit their place of 
 origin. 
 
 As the specific constituents of the various secretions belong, 
 for the most part, to a class of bodies whose nature and origin are 
 unknown, nothing can with certainty be said about the nature of 
 the chemical processes supposed to take place in the cells of the 
 various tissues and glands. Certain of these specific substances 
 are, however, undoubtedly the result of the oxidation of some 
 of the constituents of blood : and, as secretion is accompanied 
 by a manifestation of energy, viz., as Ludwig has directly 
 proved in the case of the salivary glands, by an evolution of 
 heat, it is probable that all the chemical processes of secretion 
 are merely processes of oxidation. This is further supported by 
 the facts that, during the production of a secretion rich in its 
 characteristic elements, more of the oxygen conveyed through 
 the arteries to the gland is used up, as is indicated by the darker 
 colour of the venous blood ; and that secretion becomes im- 
 possible as soon as the supply of arterial blood is prevented, 
 notwithstanding that, the other necessary conditions are fulfilled. 
 (Consult the section on Saliva). 
 
 In certain secretions the specific constituents are derived 
 from the disintegration of cells. This is known to be the case 
 with milk and the mucous, salivary and sebaceous secretions ; 
 and it is probably also the case with others. 
 
 Organs of Secretion. 
 
 Free secretions are generated in special organs. The 
 simplest form of secreting organ is a membrane provided with 
 blood-capillaries on the one side and a layer of epithelium cells 
 on the other ; it has, moreover, nerves, the terminations of which 
 are probably in direct connection with secreting cells. Such a 
 form of glandular apparatus is that which serves for the secre- 
 tion of the fluids filling the serous and synovial sacs, bursse and 
 sheaths. Most secretions, however, require a larger surface 
 than a simple smooth membrane can afford. To supply this 
 the membrane presents a single or branched, tubular or saccu- 
 late involution of its surface, upon which the secretion is poured 
 
88 GLANDS. INFLUENCE OF NERVES ON SECRETION. 
 
 out (mucous membrane, skin). Every layer of the originally 
 smooth membrane follows the course of the sacculations ; an 
 examination of any part, therefore, would show, externally, a 
 supporting stroma of connective tissue containing blood-vessels, 
 and often also muscular fibres ; and internally an epithelium, 
 the cells of which often become modified in form at the bottom 
 of an involution, passing there into special secreting cells. 
 Such an involuted secreting surface is called a gland. All 
 transudations through the sides of the blood-vessels must, there- 
 fore, pass through the layer of cells before occupying the hollow 
 of the gland as a secretion, or reaching the surface, the saccu- 
 lation of which forms the gland. There is another way in 
 which the secreting surface may be increased, viz., by processes 
 (villi), or projections such as are seen in synovial membranes. 
 
 If the involutions of the glandular surface are branched, the gland is 
 said to be ' compound ; ' if they, or their branches, are like tubes or cylin- 
 ders, the gland is called ' tubular ' (sweat glands and gastric follicles, 
 kidneys, testicles, &c.) ; if like sacs, ' racemose ' (mucous, sebaceous, and 
 salivary glands, &c.). In the case of compound glands, the tubular struc- 
 ture which leads into the gland, and into which the gland-products are 
 emptied, is called the f excretory duct.' This is frequently provided with 
 an enlargement which serves as a reservoir (urinary bladder, vesiculae 
 seminales) ; or it may be connected with such a reservoir by means of 
 another duct (gall-bladder). The so-called ( ductless' glands (spleen, 
 lymphatic glands, follicles, suprarenal capsules, thymus, thyroid) are really 
 not glands ; they will be discussed in Chapters IV. and VI. 
 
 Influence of Nerves on Secretion. 
 
 In every act of secretion there is probably a nervous in- 
 fluence at work. This has been distinctly proved in many 
 cases. It may assume the form of a first impulse to the act ; 
 or it may be evidenced by a quantitative or a qualitative 
 alteration of the products, brought about by nervous excitation. 
 
 As in several glands (e.g. in the salivary glands, Bernard) 
 the influence of the nervous system on secretion is connected 
 with that on the blood-circulation through the gland, we might 
 be inclined to explain the former as dependent upon the latter. 
 The nervous system may influence secretion by its action on the 
 circulation, which, leading to dilatation or narrowing of the 
 arteries, may bring about, 1, changes of pressure in the gland 
 capillaries, and, therefore, filtration-changes ; 2, changes in the 
 
INFLUENCE OF NERVES ON SECRETION. 89 
 
 chemical processes dependent on the greater or less quantity of 
 oxygen brought to the gland. Inasmuch as nervous influence 
 may bring about a secretion which is in abeyance (in glands 
 cut out of the body, Ludwig), even when the circulation is sus- 
 pended, and as secretion may proceed when nitration is im- 
 possible, we must conclude that the influence of the nervous 
 system upon secretion cannot be explained by its mere action 
 upon the circulation. (By preventing the escape of a secretion 
 the pressure in the excretory duct of a gland may, under nerve- 
 stimulation, be raised above that in the arterial branches 
 supplying the gland, and yet secretion proceed, Ludwig). 
 Recently, anatomical changes have been discovered to occur in 
 the glandular substance under the influence of nerve irritation 
 (Heidenhain ; see Saliva). It must be assumed, therefore, 
 that, besides the vaso-motor, there are other specific c secretory ' 
 nerve fibres, which have a direct, but as yet unintelligible, in- 
 fluence on the processes of secretion. 
 
 The influence of the vaso-motor nerves, apart from that of the proper 
 secretory fibres, is conclusively proved (Bernard) by the coincidence of 
 secretion- and circulation-changes, which has already been pointed out. Prom 
 the nature of the case their influence is principally upon the process of 
 transudation ; and they, therefore, affect the quantity and state of concen- 
 tration of the secretion. The influence of the nervous system upon the 
 chemical processes of glands, due to its power of modifying the supply of 
 oxygenated blood to them, is uncertain, although we know that a supply of 
 such blood is necessary for continuous secretion. (A gland cut out from 
 the body, when its nerves are stimulated, yields its secretion only at first, 
 even though by the production of artificial oedema a rich supply of fluid 
 has been stored up within). 
 
 An attempt has in recent times been made to prove anatomically the 
 existence of secretory nerves. The statement upon which this attempt is 
 founded, that a direct communication exists between nerve-fibres and 
 secreting cells (Pfliiger), has, however, been often contradicted. 
 
 II. INDIVIDUAL SECRETIONS. 
 
 A. Parenchymatous Tissues and their Secretions. 
 
 The methods hitherto used of obtaining the fluid secreted 
 by parenchymatous tissues have failed to yield it pure enough, 
 or in sufficient quantities, for the purposes of examination. 
 They consist either in expressing the juices from tissues which 
 
90 PARENCHYMATOUS JUICES AND TISSUES. 
 
 have been deprived, as far as possible, of their blood, or in ex- 
 tracting the constituents of those juices one by one by means 
 of various solvents (ether, alcohol, water, acids). Our know- 
 ledge of the composition and formation of the parenchymatous 
 secretions is, therefore, extremely scanty. It is often even 
 doubtful whether the substances thus obtained from a tissue 
 should be referred to its fluid or its structural elements. We 
 can only suppose in reference to their origin that their peculiar 
 constituents (gelatin, fat, colouring matters, &c.) are formed 
 from the fluids which transude from the blood-vessels by the in- 
 fluence of the cells of the tissues, and probably under the 
 control of special (trophic) nerves (Chapter IX.). It is further 
 assumed that the transuded fluids are yielded in excess, which 
 excess is returned to the blood by the lymphatics which absorb 
 it (Chapter III.). The specific substances which are formed 
 are in part insoluble, and become the structural elements of 
 the tissues. Hence it follows that a purely chemical consider- 
 ation of the fluid and formed constituents of parenchymatous 
 tissue is not yet possible, and that the whole history of the 
 development of the tissues can only be treated of from a mor- 
 phological point of view. It will only be necessary, therefore, 
 in this place, to state briefly, without any attempt at classifi- 
 cation, the facts which have been ascertained respecting the 
 chemical composition of the various parenchymatous tissues. 
 
 1. Osseous Tissue. Pure osseous tissue (after the removal 
 of the periosteum, marrow, &c.) contains a great excess of 
 inorganic salts. Perfectly dried bones (bones contain about 
 2 per cent, of water) exhibit a very constant composition, which 
 is different for different kinds of animals. In man there are 
 68 parts per cent, of salts, and 32 per cent, of organic matter 
 (Zalesky). The salts are, 84 per cent, of tribasic calcium 
 phosphate (Ca 3 2(P0 4 )), 1 per cent, of tribasic magnesium phos- 
 phate (Mg 3 2(P0 4 )), 7-6 per cent, of other salts of calcium 
 (CaC0 3 , CaCl 2 , CaFl 2 ), and 7 '4 per cent, of alkaline salts 
 (NaCl, &c.). 
 
 The organic portion consists almost entirely of a gelati- 
 genous substance, which yields gelatin on boiling, especially 
 after the addition of acids. 
 
 The osseous tissue of compact and spongy bones presents the same com- 
 position. This constancy of composition has led to the assumption that the 
 
FLUIDS OF CAVITIES. 91 
 
 organic portion is not merely mechanically impregnated by the mineral, but 
 that the two are chemically combined (Milne-Edwards jun., Zalesky). 
 
 Dilute acids deprive bone of its salts, and leave behind the animal por- 
 tion, which is soft and resembles cartilage. Subjection to heat, on the con- 
 trary, destroys the animal matter, leaving a white, porous, inorganic mass 
 (calcined bone). In both cases the bone retains its original external shape. 
 
 Connected with bone are the other calcareous tissues, e.g. teeth. Enamel, 
 which contains very little water, possesses only 4 per cent, of organic matter, 
 and is analogous to bone in its composition. 
 
 Nothing is known about the formation and regeneration of 
 bone-tissue, except the morphological appearances presented in 
 the various stages. 
 
 2. Cartilaginous Tissue. Besides water and the consti- 
 tuents of the corpuscles, cartilage contains chiefly chondrogenous 
 substance (p. 36), elastin (p. 35), and small quantities of inor- 
 ganic salts. 
 
 Nearest to cartilage stands the tissue of the cornea, which on boiling 
 yields a body resembling chondrin : it contains, in addition, much fibrino- 
 plastic substance. 
 
 3. Connective Tissue. In connective tissue the following 
 elements have been recognised (Kiihne): (1.) The substance 
 of the fibrillse, a gelatigenous substance. (2.) An interfibrillar 
 cementing substance, which can be extracted by lime-water or 
 baryta-water (Eollett), the extract containing mucin. (3.) 
 elastin. (4.) Corpuscles, composed mainly of albuminous 
 elements, and frequently containing fat. In fcetal and some 
 other tissues the gelatigenous substance is replaced by a mucin- 
 yielding substance. 
 
 4. Muscular Tissue. See Chapter VIII. 
 
 5. Nervous Tissue. See Chapter IX. 
 
 B. Fluids of Cavities. 
 
 These fluids are not secreted by glands, but by the epitheli- 
 ated membrane ( c serous membranes,' &c.) lining the cavities 
 where they are formed. From their composition they are re- 
 garded as simple transudations, the essential constituents of 
 which have already been enumerated (p. 86). Their quanti- 
 tative relations are extremely various and cannot be referred 
 to here. 'The following fluids may be regarded as simple 
 transudations : the cerebro-spinal fluid, the aqueous humour. 
 
92 MUCUS. 
 
 and perhaps also the amniotic and allantoic fluids. The peri- 
 cardia!, pleural, and peritoneal fluids were formerly placed 
 in the same category; but since they communicate directly 
 through apertures with the lymphatic vessels (von Reckling- 
 hausen, Oedmansson, Ludwig and Dybkowsky), they must be 
 considered as lymph (Chapter III.). 
 
 The following fluids of cavities have special constituents : 
 
 1. Synovia contains, in addition to the products of transu- 
 dation, mucin (0-2 to 0-6 per cent.) and fat (0-06 to 0-08 per 
 cent.). Numerous exuviated epithelial cells are also present. 
 
 2. The fluids of bursse mucosse and synovial sheaths contain 
 a gelatinous material which has not yet been investigated. 
 
 The way in which the secretions of this class are used up 
 and replaced is not understood. 
 
 C. Glandular Secretions. 
 I. ALIMENTARY SECRETIONS. 
 
 1. Mucus. 
 
 The mucus of the alimentary canal is secreted by glands 
 which are lined by an epithelium resembling that of the region 
 in which they are situated. In the mouth, pharynx, and 
 oesophagus, the glands are small and racemose, and contain 
 scaly epithelium ; in the stomach (especially in the neighbour- 
 hood of the pylorus) and in the intestine, they are simple, or 
 slightly compound and tubular, and the epithelium is cylin- 
 drical. Mucus is a clear, slimy, ropy, alkaline fluid, consisting 
 essentially of a solution of mucin, and also sometimes of albumin, 
 in which the normal salts of the blood, especially NaCl, are dis- 
 solved. The mucus of the intestine contains, in addition, certain 
 ferments which confer upon it special properties, and is, there- 
 fore, considered separately under the name of intestinal juice 
 (see below). As a rule, mucus contains morphological elements 
 in the form of (1) small, round, nucleated cells, resembling 
 the colourless blood-corpuscles the so-called mucous corpuscles 
 which are considered to be the young cells of the mucous 
 glands ; (2) fragmentary or entire cells of scaly epithelium from 
 the mucous membrane, frequently adhering together by their 
 
SALIVA. 93 
 
 edges as in their natural condition. The slimy nature of mucus 
 fits it admirably for the purpose of lessening the friction between 
 the walls of the alimentary canal and their contents. 
 
 Pure mucus maybe obtained from the mouths of animals after ligaturing 
 the ducts of all the salivary glands. It may be inferred from the morpho- 
 logical elements of mucus that mucin arises only through the disintegration 
 of gland-cells (compare the salivary, sebaceous, and milky secretions). The 
 influence which nerves exert upon the secretion is yet unknown. 
 
 As mucin does not appear to be capable of reabsorption, it 
 most likely all passes out of the body in the faeces, while some 
 of the remaining constituents of mucus probably find their way 
 back into, the blood. 
 
 2. Saliva. 
 
 The three different kinds of saliva from the parotid, 
 submaxillary, and sublingual glands are very watery, colourless 
 alkaline secretions of low specific gravity (1-004 1-009). 
 Besides the usual products of transudation (among which are 
 found very small quantities of albuminous bodies, albumin and 
 globulin), they contain, as specific constituents, (<x,) mucin, of 
 which the sublingual saliva possesses the most, the submaxillary 
 less, and the parotid least ; (6,) a hydrolytic ferment, ptyalin, 
 which converts starch into dextrin and sugar, this conversion 
 taking place rapidly if the starch is in the form of a paste, 
 and still more rapidly if it is subjected to the temperature of the 
 body; (c,) sulpho cyanides (potassium-sulphocyanide). More- 
 over, saliva, and especially, as it would seem, sublingual saliva 
 (Bonders), contains morphological elements salivary bodies 
 resembling closely mucous corpuscles ; these 6 salivary cells ' en- 
 close granules which exhibit active molecular movements. 
 Mixed saliva contains also mucus and exuviated squamous 
 epithelial cells from the cavity of the mouth. 
 
 In order to obtain the various kinds of saliva separately, use is made, in 
 man, of pathological salivary fistulse ; except in the case of the parotid gland, 
 where the saliva may be collected through a fine tube introduced into Steno's 
 duct, which opens in the side of the cheek opposite the second or third upper 
 molar tooth. In the lower animals artificial fistulao may be established. 
 Ptyalin may be thrown down mechanically (p. 35) by causing a precipita- 
 tion of calcium phosphate insaliva; it may then be extracted from the 
 precipitate by water, and re-precipitated from the watery solution by alcohol. 
 It is not an albuminous body (Cohuheim). The power of converting starch 
 into sugar belongs to each of the three kinds of human saliva; but it is best 
 
94 SALIVA. 
 
 shown in mixed saliva formed in the cavity of the mouth by the admixture 
 of saliva from all the glands with mucus. In the lower animals, however, 
 the three kinds do not all possess this power ; for, in general, the three kinds 
 of saliva are secreted in individual animals in proportions regulated by the 
 food they usually take. The conversion into sugar takes place very rapidly, 
 and is not prevented by the presence of a moderate amount of acid a circum- 
 stance which is of importance in digestion. A given quantity of saliva 
 cannot convert an indefinite quantity of starch into sugar (Paschutin). 
 Potassium sulpho-cyanide, CN.KS, the presence of which may be demon- 
 strated by the blood-red colouration which occurs on the addition of ferric- 
 chloride, is not a constant constituent of saliva, and is found most frequently 
 in mixed saliva from the mouth, especially if the teeth are decaying. 
 
 As an example of the quantitative composition of saliva, the following 
 analysis of human mixed saliva may serve (Bidder & Schmidt). In 1,000 
 parts water 995*16, solid constituents 4*84, containing epithelium 1'62, 
 soluble organic matters 1-34, inorganic matters 1-82, almost one half of the 
 last being alkaline chlorides. 
 
 Secretion. 
 
 The secretion of saliva is, as may be demonstrated, under 
 the influence of the nervous system, which influence has been 
 more fully investigated in this case than in that of any other 
 secretion in the body. Without the operation of this influence 
 secretion is completely inactive (C. GK Mitscherlich, Ludwig). 
 During life, the excitation of secretory nerves would seem to 
 take place always in one of two ways : either, in a reflex manner, 
 on irritation (1) of the sensory and gustatory nerves of the 
 mouth, (2) of the vagus, probably of those fibres proceeding from 
 the digestive apparatus (Oehl, though this is doubted by von 
 "Wittich, Nawrocki) ; or on (voluntary) stimulation of the 
 nerves to the masticatory muscles. Saliva is therefore se- 
 creted (a) on irritation of the cavity of the mouth by sapid 
 substances or mechanical, chemical, thermal, or electrical 
 stimuli, (6) in certain conditions of the stomach (nausea), and (c) 
 during the movements of mastication. The centripetal fibres, 
 which, on irritation, lead reflexly to secretion, run in the course 
 of the trigeminus, the glosso-pharyngeus, and the vagus. The 
 secretory fibres run in the course of the facialis, the trigeminus, 
 and the sympathetic. 
 
 Irritation of sensory nerves far removed from the glands (e.g. of the 
 central end of the ischiatic nerve) may also cause, by reflection, the secretion 
 of saliva (Owsjannikow & Tschiriew). 
 
SALIVA. 95 
 
 Among the secretory nerves we must distinguish two 
 species (Bernard, Eekhard, von Wittich) which, on irritation, 
 produce differences, not only in the character of the secretion, 
 but also in the vaso-motor phenomena : nevertheless, as was 
 pointed out on p. 89, we are not entitled to explain the former 
 as dependent upon the latter. Irritation of fibres of the first 
 kind induces narrowing of the arteries supplying the gland, the 
 blood reaching the veins in small quantities and very dark in 
 colour ; at the same time it yields small amounts of an extremely 
 tough and often gelatinous saliva, very rich in its specific con- 
 stituents, and especially in mucus. The second species of 
 nerve-fibres appears to cause widening of the vessels proceeding 
 to the gland, for, when irritated, the blood flows in such quantity 
 into the veins that they pulsate, and it is of a colour 
 almost as bright-red as that in the arteries ; the saliva secreted 
 under these circumstances is copious, and, as it contains but 
 small quantities of specific constituents, very fluid. The fibres 
 of the first kind run, to all the glands, in nerves of the sym- 
 pathetic system. Those of the second kind arise in the facialis 
 and afterwards pass into the course of the trigeminus ; viz., in the 
 case of the parotid gland, through the nervus petrosus super- 
 ficialis minor (of the facial), to the otic ganglion, and thence to 
 the aurieulo-temporal branch of the trigeminus (Bernard, 
 Nawrocki); and, in the case of the submaxillary and sub- 
 lingual glands, through the chorda tympani (of the facial) to 
 the lingual branch of the trigeminus, whence, after a brief 
 course, they pass, some directly, others through the submaxillary 
 ganglion, to the gland (Bernard). 
 
 Even if it be assumed that the copious trigenrinal-saliva secreted under 
 great pressure deprives the gland of the same quantity of specific con- 
 stituents in a unit of time as the scantier sympathetic -saliva (Bernard), 
 the vaso-motor effect would yet be insufficient to explain secretion j for the 
 pressure in the glandular ducts may rise higher than that in the blood-vessels 
 (p. 89), and secretion may be brought about, under nerve-stimulation, 
 after the cessation of the blood-stream through the gland (Ludwig, 
 Giannuzzi). Some other mechanism, therefore, as yet unknown, must lie 
 at the root of the process ; and here the reader may be reminded of the 
 assumed connection (according to Pfliiger) of nerve-fibres with glandular 
 cells. The following appearances (Heidenhain) indicate yet more clearly a 
 specific effect of secreting nerves : in the acini of those salivary glands, the 
 secretion of which contains mucin, two species of cells are to be found : (1) 
 nucleated, wall-less, ' protoplasm-cells/ containing much albumin, but no 
 
96 SALIVA. 
 
 mucus. In many glands they lie thickly scattered about; in the submax- 
 illary of the dog they form a crescent-shaped series on one side of the acinus, 
 while in the cat they occupy the whole circumference. (2) Shining ' mucus- 
 cells,' containing mucus enclosed in a cell-wall. After continued irritation 
 of the secreting nerves, especially of those of the cerebro-spinal series, pro- 
 toplasm-cells alone are found, undergoing rapid multiplication, while the 
 remains of mucus-cells are recognisable in the secretion. It is evident, there- 
 fore, that, during secretion, a conversion of protoplasm-cells into mucus- 
 cells through the ( mucin-metamorphosis ' of their contents has taken place ; 
 the protoplasm-cells are replaced by the fission of those left, and the mucus- 
 cells disintegrate. The cell-contents of the acini are, therefore, constantly 
 in course of renovation, and a continuously stimulated gland resembles in 
 appearance that of a recently-born animal. Some of the young protoplasm- 
 cells appear to mingle with the secretion as salivary corpuscles (p. 93). In 
 the submaxillary gland of the rabbit, which yields a secretion containing 
 no mucus, protoplasm-cells only are found. The buccal mucous glands (p. 
 92) resemble in their relations the mucus-yielding salivary glands. Ac- 
 cording to a later theory (Ewald) regeneration of the glandular contents 
 does not consist in destruction of the mucus-cells and their reformation out 
 of protoplasm-cells, but simply in the liberation of the mucus contained in 
 the former, whereby they again take on the appearance of protoplasm-cells. 
 The temperature of salivary glands may be raised 1'5 C. during secretion 
 (Ludwig). 
 
 As there exist poisons which paralyse the secretory fibres of the chorda 
 tympani without interfering -with those which cause vascular dilatation, e.g. 
 atropia (Heidenhain), it is probable that the former are not identical with 
 the latter. The salivary glands, therefore, possibly receive four different 
 Tarieties of centrifugal nerve fibres capable of influencing the secretion, viz. 
 separate vaso-motor and separate secretory fibres in each of the two classes 
 of nerves (cerebro-spinal and sympathetic) going to them. 
 
 Salivary secretion brought about by reflex irritation of 
 nerves yields constantly a very fluid (trigeminal) saliva. In 
 the case of the submaxillary gland the centre for this reflex 
 action, when stimulation proceeds from the nerves of taste 
 or from the stomach, is probably in the brain the medulla 
 oblongata as irritation of that organ produces a secretion 
 of saliva so long as the glandular nerves are intact (Eckhard). 
 In the case of stimulations other than gustatory applied to 
 the mucous membrane of the mouth the centre of reflection is 
 the submaxillary ganglion. This is proved by the fact that, 
 after section of the truncus tympanico-lingualis, stimulations of 
 the former kind no longer produce any effect, while those of 
 the latter kind operate as usual (Bernard). We must suppose, 
 therefore, that the submaxillary ganglion is a centre pre- 
 siding over secretion, which may be stimulated to reflex activity 
 
GASTRIC JUICE. 97 
 
 through certain fibres running from the tongue in the course of 
 the lingualis, a.nd leaving that nerve finally to reach the 
 ganglion. On the contrary the fibres coming from the brain, 
 and conducting reflected impressions which originated in the 
 gustatory nerves, reach the ganglion by way of the facialis, 
 chorda tympani and tympanico-lingualis, and probably simply 
 traverse it (Bernard). 
 
 It is, moreover, worthy of remark that, on cutting away the submaxillary 
 ganglion, with the exception of the fibres passing through it from the 
 tympanico-lingualis, or on poisoning the blood flowing through the gland 
 with curare, a continual secretion is induced, which can only be increased 
 by the stimulation of sapid substances (Bernard). This 'paralytic' secretion 
 appears also in the gland of the opposite side (Heidenhain). A continuous 
 secretion, moreover, occurs if the tympanico-lingual trunk has been cut 
 through for a long time ; in which case the sympathetic fibres alone are 
 able (in the manner before indicated) to modify the secretion. An explana- 
 tion of this paralytic secretion has been sought partly in the supposed exis- 
 tence of inhibitory nerves, and partly (Heidehain) in some effect of the 
 stagnating secretion. The paralytic secretion soon ceases, in consequence of 
 the degeneration of the glands. 
 
 The amount of saliva secreted in twenty-four hours has been 
 variously estimated at from ^ to 2 kilog. The fluid constituents 
 of saliva, with the exception of the mucin, are probably for the 
 most part reabsorbed in the alimentary canal (Chap. III). 
 
 3. Gastric Juice. 
 
 Grastric juice is the secretion of the tubular glands, which, 
 closely packed and swollen inferiorly, crowd the gastric mucous 
 membrane. Grastric juice is a thin, clear, colourless, acid 
 fluid which is mixed in the stomach with gastric mucus. 
 Its specific constituents are: (a) free hydrochloric acid; this 5 
 may, without prejudice to the effect of the gastric juice, be 
 replaced by lactic acid, which is generally formed in the 
 stomach during digestion (Chap. III.) : (6) a hydrolytic 
 ferment pepsin capable of splitting up albuminous bodies. 
 Pepsin has the property in acid solutions of quickly dis- 
 solving coagulated albuminous substances at the temperature 
 of the body. Solution, preceded by swelling up of the albu- 
 min, takes place most rapidly under that degree of acidity 
 which can produce the quickest swelling up (e.g., for the fibrin 
 of ox, 0*8 to 1 grm. HC1 per litre, Briicke). With the same 
 
 H 
 
 
98 GASTRIC JUICE. 
 
 quantity of acid, however, it takes place more quickly the more 
 pepsin there is in the solution, until a maximum is reached, 
 beyond which the solution cannot be hastened. A certain 
 quantity of pepsin has the power of dissolving fresh amounts 
 of albumin, if the acid used up be continually replaced. The 
 changes which albuminous bodies undergo during solution are 
 as yet little understood. At first they appear to retain their 
 original properties. They are precipitable by heat (provided 
 that, before being subjected to the action of the gastric juice, 
 they had not been coagulated by heat, in which case the 
 swelling up and solution generally take a longer time), and also, 
 for some time, by neutralization with alkalies. They are there- 
 fore at this stage converted into syntonin. After a longer 
 period they lose the power of being precipitated by heat, 
 alcohol, mineral acids and certain metallic salts, and are called 
 in this condition peptones. Peptones have, moreover, a far 
 / greater power of diffusion (p. .85) than ordinary albuminous 
 solutions (Funke). Dissolved albuminous bodies undergo the 
 same transformation under the influence of the gastric juice. 
 Gelatin is, by the action of gastric juice, converted into an 
 ungelatinizable modification. All these changes must, most 
 probably, be regarded as hydrolytic decompositions. As a 
 smaller amount of peptones is obtained, during continued 
 pepsin-digestion, than corresponds to the albumin used, it 
 would seem that peptones are capable of still further decom- 
 position, the products of which are, however, yet unknown 
 (Kiihne). Under the action of the gastric juice, even when 
 neutralised, milk is firstly curdled and the precipitate of 
 casein afterwards digested. It is supposed that pepsin quickly 
 converts milk sugar into lactic acid ; milk, however, coagulates 
 even when the gastric juice is alkaline. Processes of fermen- 
 tation and putrefaction are generally hindered by the gastric 
 juice. 
 
 The active properties of the gastric juice are suspended by 
 the same influences as deprive ferments of their activity 
 (boiling, concentrated acids, many metallic salts, strong alcohol, 
 &c.) Concentrated salt-solutions delay the solution of the 
 albuminous bodies, as they hinder their swelling up. In the 
 same manner solution is delayed if the swelling up be prevented 
 by tying thread tightly round the pieces of coagulated albumin. 
 
GASTRIC JUICE, 99 
 
 Bile also retards solution, not only by neutralising the acid, 
 but also by hindering the swelling up (Briicke), and precipitat- 
 ing the peptones (Bernard). 
 
 It has been sought to explain the interference of bile with gastric diges- 
 tion (Burkart) in the fact that a precipitation of glycocholic acid occurs on 
 the addition of bile to acid gastric juice, the pepsin being supposed to be 
 carried down mechanically in the process (p. 35). It is urged, on the contrary 
 (Hammarsten), that bile which contains only taurocholic acid also destroys 
 gastric digestion ; that, further, non-albuminous gastric juice is not precipi- 
 ated on the addition of bile, and yet loses its digestive properties on admix- 
 ture with that body. Pepsin is not destroyed in the process, but can 
 lie again isolated in an active condition. The power which bile possesses 
 of preventing digestion depends principally upon the fact that it hinders 
 the swelling up of the albuminous bodies ; it precipitates the peptones 
 already formed, even when the fluid is decidedly acid (Briicke, Scliiff). The 
 prevention of the process of swelling up is said to depend upon the combina- 
 tion of the bile-acids with albumin (Hammarsten). Glycocholic acid does, 
 however, possess the power (Burkart) of precipitating pepsin. The secretion 
 of Brunner's glands also renders the gastric juice inoperative (Schiff). 
 
 Natural gastric juice is obtained from pathological, or (in the case of the 
 lower animals) artificial gastric fistulas ; and also by causing sponges at- 
 tached to a string to be swallowed and, after a time, withdrawn from the 
 stomach. Artificial gastric juice is prepared by infusing fresh or dry gastric 
 mucous membranes with water or (von Wittich) glycerin, and then adding 
 hydrochloric acid (0-1 p. c.) j or, also, by dissolving pure pepsin, prepared 
 according to the method on p. 35 in water and acid. Hydrochloric acid may 
 be replaced by lactic acid (which in equal amounts is less effective), or by 
 oxalic, phosphoric, or acetic acids, but the activity of the gastric j uice is 
 thereby diminished. 
 
 The gastric juice of the dog, free from saliva, contains, as the mean of a 
 number of experiments, in 1,000 parts : Water 973-1, pepsin (and peptone) 
 17-1, free hydrochloric acid 3'0, salts 6'8 (Bidder and Schmidt). 
 
 Secretion. 
 
 The following has recently been made out with regard to 
 the structure of the gastric glands (Heidenhain, Rollett). The 
 glands contain two sorts of round cells : ( 1 ) the smaller, so- 
 called ' Hauptzellen ' (Heidenhain), or ' adelomorphous cells ' 
 (Rollett), which fill the greater part of all the glands, and are 
 alone found in certain glands, occurring especially in the pyloric 
 region (the 'gastric mucous glands' of earlier authors); (2) 
 the larger, so-called ' Belegzellen ' (Heidenhain), or ' delomor- 
 phous cells ' (Rollett), which occur, almost without exception, 
 only near the bottom of the glands at the sides. During secre- 
 
 H 2 
 
100 GASTRIC JUICE. 
 
 tion (in the process of digestion) the glands, and especially the 
 smaller cells previously referred to, at first swell up strongly, 
 and afterwards return to their former size (Heidenhain). 
 Pepsin is formed in the gastric glands, whence it can be ob- 
 tained by water in the form of a neutral solution, or, more 
 easily, by the action of dilute hydrochloric acid. It is probable 
 that, during life also, it is extracted from the cells by some acid 
 fluid. Nevertheless the glands themselves very seldom exhibit 
 an acid reaction, while the surface of the gastric mucous mem- 
 brane is covered with a strongly acid gastric juice. The acid 
 is, however, formed in the glands ; for, if the surface of the 
 mucous membrane is neutralised by means of calcined magnesia, 
 then washed with water and allowed to stand, an acid reaction 
 again appears after some time (Briicke). It must be sup- 
 posed, therefore, that the gastric glands form pepsin and an 
 acid, but get rid of the latter (charged with pepsin) at once at 
 the surface. The forces which effect these operations are not 
 understood ; nor is the origin of the free hydrochloric acid ; for 
 we can scarcely suppose that it results from the decomposition 
 of some salt (perhaps calcium chloride, Smith) by lactic acid. 
 Probably the simultaneous alkaline formation in the pancreatic se- 
 cretion is closely connected with this acid formation (Meissner). 
 What part each of the two kinds of glandular cells takes in 
 the formation of pepsin and acid is yet in dispute. While the 
 origination of pepsin used to be ascribed to the larger glan- 
 dular cells, it has recently been maintained that the smaller 
 variety are the pepsin-formers, because the latter more easily 
 disintegrate under the influence of hydrochloric acid when 
 warm than the former, and snippings from the surface of the 
 gastric mucous membrane digest the more quickly the greater 
 the number of the smaller kind of cells they contain (Heiden- 
 liain, Ebstein and Griitzner). Others., on the contrary, hold to 
 the former opinion, chiefly because the glands in the pyloric 
 end of the stomach, which contain the smaller cells only, do 
 not yield an infusion capable of digesting foods, if the secretion 
 of the larger cells is absent (Friedinger, von Wittich, Wolf- 
 hiigel). 
 
 Secretion of gastric juice appears to occur only under the 
 influence of the nervous system exerted in a reflex manner (see 
 Saliva). It ceases when the stomach becomes empty ; but re- 
 
BILE. 101 
 
 commences when it is filled with substances (food) which 
 mechanically irritate it ; and, probably also, on irritation of 
 the mucous membrane of the mouth. The saliva which is 
 swallowed seems to be concerned in this stimulation (Rollett). 
 Secretion appears to be independent of the integrity of the 
 nerves (vagi, &c.) running to the stomach ; the central organs, 
 therefore, of a portion of the secretory nerves must be sought 
 for in the walls of the stomach itself (Briicke, Ravitsch). 
 During secretion a reddening of the mucous membrane occurs, 
 and probably, therefore, a dilatation of the glandular vessels, 
 similar to that which takes place in the secretion of saliva. 
 
 The secreted gastric juice is, probably, for the most part, re- 
 absorbed in the intestines (Chap. III.). Small amounts of 
 pepsin are, therefore, found in various fluids of the body, e.g. 
 in the parenchymatous juices of the muscles, in urine (Briicke). 
 The acid of the gastric juice is neutralised by the alkaline in- 
 testinal secretion. No serviceable determination or estimation 
 exists of the amount of gastric juice secreted. 
 
 4. Bile. 
 
 Bile is a neutral or weakly alkaline, mostly viscid, bitter 
 fluid, varying in colour from yellow, brown, or green to black. 
 Its specific constituents (apart from the mucus which origi- 
 nates in the gall-bladder and ducts) are: (1) the sodium 
 salts of two conjugate acids (so-called ' bile-acids '), viz. glyco- 
 cholic acid (called also cholic acid) and taurocholic acid (called 
 also choleic acid). The former is compounded of nitrogenous 
 glycocine (p. 24) and non-nitrogenous cholic acid (p. 16), the 
 latter of taurine (which contains nitrogen and sulphur) (p. 25) 
 and cholic acid; (2) cholesterin (p. 17), held in solution by 
 the salts of the bile-acids ; (3) products of decomposition of 
 lecithin, viz. choline or neurine (p. 21), glycerin-phosphoric 
 acid (p. 19); (4) urea (Popp) ; (5) colouring matters, es- 
 pecially one of a reddish-yellow colour, bilirubin (cholepyrrhin, 
 bilifulvin) ; another of a green colour, biliverdin (p. 29) 
 perhaps only a derivative of the former, and one called urobilin 
 (p. 29) ; (6) small quantities of fats and soaps ; (7) a sugar- 
 forming ferment (J. Jacobson, von Wittich). 
 
 Bile may be obtained from the gall-bladder after death j and, during life, 
 
102 BILE. 
 
 in the lower animals by means of artificial biliary fistulse, which may, afc 
 the same time, be used to determine the amount secreted in a given time. 
 The colour of bile varies much under different physiological, and, still more,, 
 under different pathological, conditions, and in different classes of animals. 
 In the air yellow bile becomes green through the oxidation of bilirubin to- 
 biliverdin. The bile of vegetable-feeding animals is green while in the 
 gall-bladder. The salts of the bile-acids may be easily obtained by evapor- 
 ating bile, extracting with alcohol, decolourising the extract by means of 
 animal charcoal, and adding ether. When prepared in this manner, they 
 are obtained in the form of a resinous precipitate, which becomes crystalline 
 on being kept in a mixture of alcohol and ether (' crystallised bile'). The 
 two bile-acids are present in various proportions ; in man, amphibia, and 
 fishes, taurocholic acid predominates, as also in many mammals and birds : 
 in others (e.g. in pigs, kangaroos),- it is the glycocholic acid which predomi- 
 nates. The cholic acid contained in the bile-acids is replaced in various 
 animals, by other, allied acids (p. 16), e.g. in the goose by chenocholic 
 acid, in the pig by hyocholic acid, in guano by guanogallic acid j and the 
 bile-acids bear different names accordingly (taurochenocholic acid, hyogly- 
 cocholic acid). The bile-acids rotate the plane of polarisation to the right, 
 cholesterin to the left (Hoppe-Seyler). 
 
 Human bile contains in one thousand parts, water 822-7-908-1 ; salts of 
 the bile-acids 107-9-56-5 ; fat and cholesterin 47-3-30-9 ; mucin and colour- 
 ing matters 23-9-14-5 ; ash 10-8-6-3 (von Gorup-Besanez). 
 
 Secretion, 
 
 The formation of bile takes place in the so-called lobules 
 (acini) of the liver. Each acinus contains, like the whole liver, 
 arterial blood, which is brought by the hepatic artery, and venous 
 blood, which is conducted through the portal vein from the ca- 
 pillaries of the stomach, intestine, pancreas and spleen ; and 
 each furnishes venous blood to the hepatic vein. 
 
 The terminal branches of the portal vein (interlobulur veins), and of the 
 hepatic artery, which lie at the periphery of the lobule, are connected with 
 the initial branches of the hepatic vein (intralobular veins), which start 
 from the centre by a close, interlacing capillary network, whose meshes 
 are crowded by the large, round, glandular cells of the liver. These liver- 
 cells are so arranged (Hering) that they form the wall of the finest gall- 
 passages, often as few as two only occurring in a transverse section. These 
 passages open into an interlobular network surrounding the acini, whence 
 springs the ductus hepaticus, which, after giving oft' a lateral branch, the 
 ductus cysticus, to a reservoir, the gall-bladder, opens into the duodenum as 
 the ductus choledocJius. The blood of the portal vein, which has previously 
 traversed one capillary system, and which is now for the second time dis- 
 tributed over an enormous vascular area, must flow extremely slowly in the 
 capillaries of the liver. 
 
BILE. 103 
 
 Bile-formation takes place continually. It would seem 
 that, during the intervals between periods of digestion, the se- 
 cretion is conveyed through the cystic duct to the gall-bladder, 
 and there stored up ; but that, during digestion, it is poured, both 
 directly from the liver, and also from the gall-bladder, into the 
 intestine. The formation of the specific constituents takes place 
 in the liver- cells. That these constituents are not simply sepa- 
 rated from the blood, is shown by the fact that, neither under 
 ordinary circumstances, nor when secretion is prevented (by ex- 
 tirpation of the liver) can they be detected in the blood flo wing- 
 to the liver. 
 
 On the contrary, they rapidly appear in the blood if the outflow of the 
 bile from the liver is prevented by the stoppage of the excretory duct, and 
 the pressure in the gall-passages by this means raised ; a very slight pres- 
 sure is all that is required to effect this return into the blood; biliary 
 colouring matters, cholic, glycocholic, and taurocholic acids, may then be 
 detected in the urine (Hoppe-Seyler), and the first colours the urine brown, 
 and the skin and mucous membranes yellow Jaundice. Other colouring 
 matters also, which appear in the gall-passages under pressure, are re- 
 absorbed and colour the mucous membranes, &c. The acini themselves do 
 not become coloured under these circumstances ; nor is the bile coloured, 
 which is secreted by them at the same time j absorption in the liver does 
 not, therefore, take place in the acini, but in the coarser gall-passages 
 (Heidenhain). 
 
 It is uncertain from which of the two kinds of blood flow- 
 ing into the liver the materials for the preparation of bile 
 are chiefly derived. According to some investigators (Ore, 
 Frerichs, and others), ligature or obliteration (Kottmeyer) of 
 the hepatic artery suspends the secretion of bile, while that of 
 the portal vein has no such result. Other researches (Schiff) 
 have led to exactly opposite results. Natural injection of the 
 portal vein with colouring matters colours the periphery 
 only of the lobules, injection of the hepatic artery only the 
 centre ; it is, therefore, probable that both sets of vessels are 
 concerned in secretion (Chrzonszczewsky and Kiihne). Com- 
 parative examinations of blood flowing into and out of the 
 liver have merely approximately disclosed the nature of the 
 substances which are retained in the liver and there converted 
 into the constituents of bile. Analysis of blood from the portal 
 and hepatic veins shows that, apart from the appearance of sugar 
 in the latter (Chap. V.), hepatic venous blood contains less 
 water, albumin, fibrin, fats, blood-colouring matter and salts, 
 
104 BILE. 
 
 but more blood corpuscles (Chap. V.) than portal blood, which, 
 especially after digestion, is very rich in fats (Lehmann, C. 
 Schmidt). The high temperature of the gland and of he- 
 patic venous blood shows that active oxidation goes on during 
 secretion. 
 
 Of the more special chemical changes which take place during secretion, 
 the most probable is the formation of the biliary colouring matters from 
 blood-colouring matter, which is based upon the identity (Virchow, Va- 
 lentin, Jaffe), or at least the strong resemblance (Stadeler and Holm) of 
 bilirubin and hsematoidin (p. 28). Some maintain, also, the origin of cholic 
 acid and sugar from fats, the glycerin, according to various hypotheses, 
 yielding sugar, and the fatty acids, cholic acid ; but the existence of such 
 processes is as yet unsupported by facts. The processes of decomposition 
 which take place during digestion may possibly account for the origin of 
 glycocine and taurine ; and the further syntheses in which they take part 
 may have their seat in the liver. The glycocine of the liver may be conjugated 
 with other acids than cholic acid, e.g. with benzoic acid, to form hippuric 
 acid (see under Urine). 
 
 The amount of bile secreted, which it is impossible to esti- 
 mate exactly, varies between about 160 and 1,200 grms. in 
 twenty-four hours (as Ludwig has estimated from the data of 
 others). It depends to a large extent upon the food taken. 
 It is increased by ingestion of water (in which case the bile is 
 more watery), by an animal diet, and, to a less extent, by a 
 vegetable diet also. Fatty foods do not at all increase the 
 amount secreted ; and starvation diminishes it considerably. The 
 maximum of secretion is reached several hours after the ingestion 
 of food, and it occurs the later the more plentiful the rneal 
 has been (Bechamp). What influence the nervous system may 
 have upon the formation of bile is not yet known ; from several 
 experiments it would seem that irritation of the vaso-motor 
 nerves of the liver diminishes secretion (Heidenhain). 
 
 Other substances may be found abnormally in the bile, which have been 
 taken into the body along with the food, and are being voided by this way. 
 Heavy metals, especially, are said to find their way into the liver and the 
 bile. Copper and lead occur somewhat regularly in the liver. 
 
 Concerning other functions of the liver, see Chapter V. 
 
 Separation. 
 
 The out-flow from the liver of the bile already formed is oc- 
 casioned probably by the mechanical pressure exerted by the 
 
BILE. 105 
 
 secretion, assisted by the compression of the liver during in- 
 spiration. The amount of bile collected from fistulse is, there- 
 fore, diminished during the slow respiration after section of 
 the vagi (Heidenhain). The evacuation of the gall-bladder and 
 the larger gall-passages, however, is probably brought about by 
 the contraction of their smooth muscular fibres, which takes place 
 simultaneously with the movements of the intestine. By irrita- 
 tion of the spinal cord this evacuation can be artificially induced 
 (Heidenhain). 
 
 As animals with biliary fistulse quickly grow lean, provided 
 they are prevented from devouring the bile which escapes, it 
 is supposed that the greater portion of the bile is reabsorbed 
 in the intestines. The ultimate destination of the reabsorbed 
 biliary matters is, however, not known ; nor have the other 
 circumstances, which help to explain the starvation of the ani- 
 mals from which the biliary secretion is removed, been com- 
 pletely eliminated from the question. Moreover, in the normal 
 condition, all the biliary substances are found in the faeces in 
 considerable quantities the colouring matters which colour the 
 faeces, bile-acids, mucus, cholesterin, &c. The bile-acids, es- 
 pecially taurocholic acid, undergo in the lower part of the in- 
 testinal tube a hydrolytic decomposition (Chap. III.) ; there 
 being found in the faeces, therefore, glycocholic acid, cholic acid, 
 and their anhydrides, choloidic acid and dyslysin (Hoppe- 
 Seyler). The reabsorption of the specific constituents of bile 
 is, therefore, yet doubtful. 
 
 Unlike all the other secretions connected with the digestive 
 apparatus, bile is probably of no importance in digestion 
 proper (i.e. in the preparation of food for absorption). The one 
 property it possesses, which is of value for that purpose, viz. 
 that of emulsionising fats, is shared by it with other secretions 
 which possess it in a far higher degree (pancreatic juice, and, 
 perhaps, intestinal juice). Solutions of peptones are precipitated 
 by bile (p. 99) ; a circumstance the importance of which will be 
 spoken of in the next chapter. The importance of bile physio- I 
 logically appears to be chiefly in regard to the absorption of I 
 fats (Chap. III.). Bile (and the salts of the bile-acids), for 
 instance, renders possible both filtration of fats through mem- 
 branes under slight pressure, and diffusion between fats and 
 watery solutions (von Wistinghausen), probably because it oc- 
 
106 PANCREATIC JUICE. 
 
 casions the simultaneous imbibition of both (a condition of dif- 
 fusion, p. 85) in the form of soapy solutions. It renders 
 easier, also, the passage of fats through narrow (capillary) 
 tubes. Bile is also said to induce contraction of the muscular 
 fibres of the villi (Chap. III.) (Schiff), and thus, again, to assist 
 in the absorption of fats. It appears moreover to prevent putre- 
 factive decomposition of the contents of the intestine. 
 
 In accordance with what has been said above, when bile is suffered 
 to escape through a fistula, there occurs no essential disturbance of the di- 
 gestive processes, but only (1) prevention of the absorption of fats (as indi- 
 cated by the fat contained in the faeces, and the absence of fat in the chyle) ; 
 (2) colourless, ill-odoured, hard faeces ; (3) at the same time excessive 
 hunger on the part of the animal ; (4) the endeavour on the part of the 
 animal to make up for the deficient absorption of fat by increased consump- 
 tion of hydro-carbonaceous foods (Chapter VI.). 
 
 5. Pancreatic Juice. 
 
 The pancreatic juice secreted in the racemose pancreas, 
 whose structure resembles closely that of the salivary glands, 
 is a strongly alkaline, clear, very tough, colourless fluid, co- 
 agulable by heat. Its specific constituents are ( 1 ) several al- 
 buminous bodies coagulable by heat, which are scarcely dis- 
 tinguishable from albumin itself, and to which many observers 
 ascribe the fermenting properties of the secretion (pancreatin). 
 According to others (Danilewsky) the ferments of the pancreatic 
 secretion are special bodies. (2.) Several hydrolytic ferments 
 (see below) capable of separation one from another. (3.) 
 Leucine and other products of decomposition of albuminous 
 bodies. 
 
 Pancreatic juice may be obtained by means of artificial fistulas ; and an 
 artificial juice may be made by infusing the glandular substance in water. 
 
 The pancreatic juice has, by virtue of the ferments it 
 contains, three well-marked properties which render it very im- 
 portant in digestion : (1.) It converts starch-mucilage into 
 dextrin and sugar more powerfully than saliva from the mouth 
 (Bernard). (2.) It decomposes neutral fats very quickly, in 
 such a manner that, in the presence of water, glycerin and free 
 fatty acids are formed (p. 19); the latter then partly com- 
 bine with the alkali of the pancreatic juice to form soaps, 
 while the excess causes an acid reaction. With the decom- 
 
PANCREATIC JUICE. 107 
 
 position is connected an emulsionisation of the fats (Bernard), 
 which is probably brought about by the products of decom- 
 position themselves (Briicke). (3.) Coagulated albuminous 
 bodies are dissolved by the pancreatic juice, as also is gelatin 
 (Corvisart). This solution takes place only when the fluid is 
 alkaline (compare, on the contrary, the effect of gastric juice), 
 and is not preceded (as in gastric juice) by a swelling- 
 up, which even hinders the process (Danilewsky). The so- 
 lution agrees in its properties with peptone-solutions (Kiihne). 
 After some time, however, the peptone is further split up with 
 the production of leucine, tyrosine, and unknown extractives, 
 of which one is coloured violet on the addition of chlorine, and 
 another indol possesses a disagreeable fsecal odour (Kuhne). 
 These processes are not of the nature of putrefaction. 
 
 The leucine contained in the pancreatic juice is the result of the action 
 of the juice upon its own albumin, as is also the substance which produces 
 the red colouration of the pancreas when treated with chlorine (Tiedemann 
 and Gmelin). Alkaline albuminate is digested by the pancreatic juice, 
 though more slowly than fibrin (Senator) ; so also are gelatin and the gela- 
 tigenous tissues. It is remarkable that all the results of pancreatic diges- 
 tion are such as may be produced by boiling with mineral acids (see p. 19). 
 By injecting melted paraffin into the excretory duct the cooperation of the 
 pancreas in digestion can be prevented, without the latter process being 
 essentially disturbed (Schiff). 
 
 The pancreatic juice of the dog contains 91 per cent, of water, 8-2 per 
 cent, of organic matter, O8 per cent, of ash (Bernard). 
 
 Secretion. 
 
 The secretion of pancreatic juice probably never takes 
 place without nervous stimulation (as in that of saliva). It is 
 usually very slight, but increases much during digestion. That 
 the specific constituents of the secretion are formed in the 
 glandular cells, is proved by (1) the activity of an infusion of 
 the glandular substance, and (2) the presence of cell-fragments 
 in the secretion (Bonders).' It may be assumed, therefore, that 
 the constituents become free in this case also by the disintegra- 
 tion of the cells. Increased secretion is constantly accompanied 
 by increased circulation, and reddening of the gland (Bernard). 
 We may, therefore, suppose some vaso-motor effect of the 
 nerves, as is the case with the salivary glands. 
 
'' 
 
 108 INTESTINAL JUICE. 
 
 The nerves affecting this secretion are unknown; they appear to be 
 called into action reflexly by stimulation of the gastric mucous membrane, just 
 as are those of the salivary glands on stimulation of the mucous membrane 
 of the mouth (Ludwig) : hence the secretion of the gastric and pancreatic 
 juices occurs simultaneously (Bidder and Schmidt). Irritation of the 
 medulla oblongata increases the flow, probably only by inducing contraction 
 of the duct (Landau). Irritation of the central end of the vagus stops the 
 secretion (N. 0. Bernstein) ; the same stoppage occurs during vomiting (Wein- 
 mann, Bernard). The relative amount of solid constituents is inversely pro- 
 portional to the rapidity of secretion (Weinmann) ; that of salts, however, is 
 pretty constant, and is the same as in blood-serum (N. 0. Bernstein). 
 
 The quantity of pancreatic juice secreted cannot be accu- 
 rately estimated by means of fistulse, because the pancreas has 
 two anastomosing excretory ducts. The ultimate destination 
 of the secretion is probably the same as that of saliva and gastric 
 juice. 
 
 6. Intestinal Juice. 
 
 Intestinal juice (Succus entericus) is the secretion poured 
 out by the tubular glands of Lieberkiihn, which are present in 
 all parts of the intestine. (The racemose glands of Brunner in 
 the duodenum resemble in construction the pancreas ; their se- 
 cretion is, according to recent observations, most like mucus). 
 It was not possible until quite recently to obtain pure intes- 
 tinal juice. The method now adopted is as follows (Thiry) : 
 An animal is taken and a portion of the intestine, still connected 
 with the mesentery, is separated from the rest. The two ends 
 of the remaining portion are made to unite, the animal con- 
 tinuing to live, but with an intestine somewhat shortened. The 
 portion separated from the rest is closed at one extremity, while 
 the other is stitched to the sides of the wound in the abdomen. 
 As the nutrition of the piece of intestine has not been inter- 
 fered with, secretion will take place as usual, and the intestinal 
 juice will be poured out at the open end. 
 
 The juice so obtained is a thin, bright yellow, strongly 
 alkaline, albuminous fluid. It acts as a ferment only on fibrin, 
 which it quickly dissolves (it does not dissolve other coagulated 
 albuminous bodies, Thiry). Nothing is certainly known con- 
 cerning the chemical constituents. 
 
 Under ordinary circumstances secretion is almost quiescent ; 
 but under the stimulation of mechanical irritation or weak acids, 
 
RESPIRATORY SECRETIONS. URINE. 109 
 
 it may be largely increased (13 to 18 grms. hourly from a surface 
 of 100 sq. cm.) 
 
 Formerly an impure intestinal juice was obtained through intestinal 
 fistulas by the removal of the food, or by introducing sponges into the intes- 
 tine, or by preventing the admixture of the other secretions which are 
 poured into the intestine. According to an older view, which has been 
 supported in part in recent times, intestinal juice acts upon starch (Schiff, 
 Quincke), and upon fats (Schiff), like the pancreatic secretion, but some- 
 what more slowly. The ferments extracted from the intestinal mucous 
 membrane by means of glycerin do not possess the power of digesting 
 albumin, although they can convert starch into sugar. The glands of the 
 large intestine are unable to bring about the latter operation (Eichhorst, 
 Costa). 
 
 The intestinal juice of the dog contains 97*6 per cent, of water, 0*8 per 
 cent, of albumin, 07 per cent, of other organic matters, 0-9 per cent, of ash 
 (Thiry). 
 
 2. RESPIRATORY SECRETIONS. 
 
 The lungs may be regarded in structure and function as a 
 racemose gland with a gaseous secretion, the excretory duct of 
 which is the trachea. As will be explained in Chap. IV., the 
 forces which effect the separation of carbonic acid at the lungs 
 are by no means thoroughly understood. 
 
 The numerous mucous glands which are scattered about the 
 air passages, from the nasal opening in the face to the smaller 
 bronchial tubes, yield a fluid mucus. The glands are race- 
 mose and possess pavement-epithelium ; the smallest of them 
 are, however, more tubular, and are provided with cylindrical 
 epithelium. The same remarks apply to this secretion as 
 to that of the mucous glands of the alimentary apparatus 
 (p. 92). The mucus is apparently secreted only in small 
 quantities, and the excess is removed from the body by an 
 arrangement which will be spoken of hereafter (Chap. IV.) 
 
 3. URINARY SECRETION. 
 
 The urine secreted in the kidneys is a true excretion, the 
 removal of which from the organism is necessary, as it is of 
 no further use (p. 83, ' Excretions'). It serves to carry out of 
 the body certain ultimate products of the oxidation of nitro- 
 genous substances, as well as the excess of water. The products 
 of oxidation are separated along with salts in the form of watery 
 solutions. 
 
110 URINE. 
 
 The long-pending question as to whether these ultimate results of oxi- 
 dation exist as such in the blood and are merely separated in the kidneys ; or 
 whether some of them remain until they reach the kidneys in a partially 
 incomplete form, and ought, therefore, to be considered in the light of ' spe- 
 cific constituents ' of the urinary secretion j has not yet been decided (see 
 below). 
 
 Urine is a clear, transparent, amber-coloured and slightly 
 acid fluid, with a bitter saline taste and an aromatic odour 
 (specific gravity 1-005 1*030). A little mucus from the 
 mucous glands of the excretory ducts (especially of the bladder) 
 is usually mixed with it. Its specific constituents l are: 1. 
 Urea, the chief ultimate product of the oxidation of nitrogenous 
 bodies, part of which is pre-formed in the blood, but some of 
 which does not, in all probability, appear until the kidney is 
 reached. 2. Uric acid, a less oxidized product, existing in the 
 form of neutral urates of the alkalies. 3. A series of still less 
 oxidized bodies, which occur for the most part in small quantities, 
 and some (those marked with an asterisk) only occasionally : 
 * Allantoine, xanthine, hypoxanthine (sarcine), creatinine, gly- 
 cocine (only, however, conjugated with benzoic acid in the form 
 of hippuric acid), *taurine, *cystine, *leucine, *tyrosine, am- 
 monia, both free and in the form of salts (amongst others, in 
 the form of ammonium oxalurate (p. 23), Neubauer). 4. One 
 or more colouring matters (urobilin, urohsematin, &c., see p. 29), 
 besides indican. 5. Certain unknown bodies, so-called extrac- 
 tives (e.g. that which occasions the odour). The remaining con- 
 stituents of urine are: 1. Water. 2. Salts (the usual blood- 
 salts ; but, in addition, some which are also probably oxidation- 
 products, e.g. oxalates and sulphates produced possibly by the 
 oxidation of bodies, especially taurine, containing sulphur). 
 3. Small quantities of sugar (Briicke). 4. Grases : oxygen, 
 nitrogen (a remarkably large amount, Morin, Pfliiger), carbonic 
 acid. 
 
 The colour of urine varies with its state of concentration : it is darkest 
 in the concentrated morning-urine (' urina sanguinis '), and lightest in that 
 passed after the plentiful ingestion of fluids (' urina potus.') The acid reac- 
 tion results for the most part from the contained acid sodium phosphate 
 (Liebig). That urine contains no free acid is proved by the fact that it 
 gives no precipitate on the addition of sodium hyposulphite (Huppert). 
 Sometimes normal urine is alkaline, namely, after caustic alkalis, or alkaline 
 
 1 Note what was said in the paragraph above. 
 
URINE. Ill 
 
 carbonates, or salts of vegetable acids have been taken into the stomach. 
 (The latter, viz. the salts of the vegetable acids, having undergone oxidation, 
 appear in the urine as carbonates, which have an alkaline reaction, 
 Wohler). 
 
 On standing, urine forms gradually a precipitate of acid urates or free 
 uric acid. Simple cooling cannot be the cause of this, for, on again heating 
 to the temperature of the body, the sediment is not completely redissolved. 
 We must, therefore, suppose an acid-formation to take place, by a species of 
 fermentation, due probably to the influence of the mucus which is present 
 ('acid fermentation,' Scherer). After some time (which is shorter the 
 higher the temperature) decomposition sets in, owing to the organic germs 
 which the urine receives from the atmosphere; in this process urea is 
 converted into ammonium carbonate, the reaction becomes alkaline (' alka- 
 line fermentation '), a putrefactive odour appears, and precipitates of am- 
 monium urate, amrnonio-magnesium phosphate, &c., are formed, with the 
 development of fungi and infusorians. 
 
 Which of the above-mentioned specific constituents of urine are most 
 extensively represented seems to depend upon the kind of food taken. 
 In flesh-eating mammalia, such as man, urea is present in largest amount ; 
 very little uric acid and hippuric acid are found. In the urine of vege- 
 table-feeders, but little urea and no uric acid are present, while hippuric 
 acid abounds. Dietary changes effect variations in the urine. Among the 
 exceptional bodies found in urine are hyposulphurous acid (Schmiedeberg) in 
 the urine of animal-feeders, and carbolic acid (Stadeler) in that of vegetable- 
 feeders. The latter in all probability results from the action of acids upon 
 some complex aromatic body (perhaps indican or hippuric acid)(Hoppe-Seyler 
 and Buliginski) . Succinic acid, which was described (Meissner) as a consti- 
 tuent of the urine of men and animals, is at any rate not found constantly 
 (Salkowski). Human urine also varies with the food ingested (see below), 
 hippuric acid, especially, increasing with the increase of vegetable food 
 taken, and disappearing when animal food alone is eaten. The urine of birds, 
 scaled amphibia, insects, &c., which becomes solid immediately after evacua- 
 tion, contains, on the contrary, an excess of uric acid or urates j that of birds 
 contains also urea, creatine, albumin, &c. (Meissner). 
 
 Numerous substances taken into the body as foods or medicines re- 
 appear partly unaltered in the urine, e.g. most metallic salts, alkaloids, 
 colouring matters, alcohols. Other bodies appear in a more oxidized form. 
 Especially is this the case with the alkaline salts of many organic acids 
 (lactic, succinic, acetic, citric, and malic acids), which appear as alkaline 
 carbonates and render the urine alkaline (Wohler) ; and with benzol, which 
 is found again in the form of carbolic acid (Sclmltzen and Naunyn). Sub- 
 stances capable of complete combustion, such as glycerin, do not cause the 
 appearance of special constituents in the urine. Many conjugate bodies suffer 
 partial combustion ; tannic acid, for example (the glucoside of gallic acid), 
 yields gallic acid. Benzoic acid and several allied bodies, essential oil of 
 bitter almonds, cinnamic acid, and chinovic acid yield by conjugation with 
 glycocine, hippuric acid (Wohler) ; similarly some substitution-derivatives of 
 benzoic acid (chloro-benzoic acid, nitro-benzoic, salicylic, and anisic acids), 
 
112 URINE. 
 
 coupling themselves with glycocine, give rise to corresponding hippuric 
 acids. 
 
 The simpler amido-acids, glycocine and leucine, reappear as urea in urine 
 (Schultzen and Nencki). Sarcosine, on the contrary (p. 26), unites with 
 carbarnic acid (p. 22), water being eliminated, and appears as sarcosine-car- 
 bamic acid (C 4 H 8 N 2 3 ) in the urine (Schultzen) ; a part unites in a similar 
 manner with sulphamic acid (NH 2 -S0 2 'OH), and appears as sarcosine-sul- 
 phamic acid (C 3 H 8 N 2 S0 4 ). In like manner, taurine appears in the urine 
 united with carbamic acid, as taurine-carbamic acid (C 8 H 8 N 2 S0 4 ) (Sal- 
 kowski). 
 
 H 2 N-CO-OH H 2 N-CO-N<3_ CQ _ OH 
 
 Carbamic acid Sarcosine-carbamic acid 
 
 Sarcosine-sulpharaic acid 
 
 The hippuric acid in the urine of vegetable-feeders is formed most pro- 
 bably out of some vegetable substance resembling benzoic acid taken into 
 the body as food ; the glycocine necessary for its formation is derived from 
 the liver (Kiihne and Hallwachs). The vegetable substance is probably 
 the cuticular substance of plants which appears most to resemble chinovic 
 acid in composition (Meissner and Shepard) ; for those portions of plants 
 which possess no cuticular substance (e.g. underground portions, huskless 
 grains of corn), yield no hippuric acid. It is, however, possible that other 
 similarly occurring substances, which are allied to benzol, are the source of 
 the hippuric acid (Nencki). 
 
 The following numbers represent the average composition of urine, which, 
 however, is very variable. In 1,000 parts : Water 960, urea 23'3, uric acid 
 0-5, sodium chloride 11 '0, phosphoric acid 2-3, sulphuric acid 1-3, ammonia 
 0-4 (Vogel). 
 
 Secretion. 
 
 The secreting apparatus of the kidneys (for a more detailed 
 account of the structure of which refer to Manuals of Histology) 
 consists of the tubuli uriniferi and the vessels connected with 
 them. Every uriniferous tube ends in the cortical portion 
 of the kidney in a globular dilatation called a capsule or Mai- 
 pighian body, containing a glomerulus. The glomerulus is a 
 small coil of vessels, produced by the branching and re-uniting 
 of the finest twigs of the renal artery (vas afferens). The 
 vessel formed by the reunion of the branches of the glomerulus 
 (vas efferens), on emerging from the Malpighian body, again 
 divides up into true capillaries, which intertwine with the 
 tubuli uriniferi, especially with their convoluted commence- 
 ments, and finally unite with the initial branches of the renal 
 vein. 
 
URINE. 113 
 
 As the blood in the glomeruli is subjected to a high pres- 
 sure on account of the resistance of the second capillary system 
 in front, a free filtration into the capsule must take place. 
 Water and those constituents of the blood which form true 
 solutions (salts, urea, sugar, &c.) will, therefore, pass into the 
 tubuli uriniferi. Albumin, &c., which do not form true solu- 
 tions, do not filter through except under an abnormally increased 
 pressure (p. 85). The very dilute solution thus formed now 
 comes into proximity, at the walls of the tubuli uriniferi, with 
 the blood which it has just left, and which is in a concentrated 
 state owing to the loss of water ; diffusion must result (Ludwig), 
 leading to a return of water into the blood, and to a consequent 
 concentration of the urine. Besides these physical processes, 
 other causes seem to co-operate in the formation of urine. 
 Many circumstances lead us to suppose that the glandular cells 
 (epithelium) especially assist ; pathological degeneration of the 
 epithelial cells, for example, interferes with secretion ; and, in 
 birds, uric acid deposits are seen to originate within the cells, 
 the disintegration of which seems necessary before the deposits 
 can become free (von Wittich, Meissner). 
 
 As the branches of the vas afferenslie at the periphery of the glonierulus, 
 while the vas efferens proceeds from its centre, the flow of blood from the 
 former into the latter is rendered easy. Any tendency to a return of the 
 blood would, however, be hindered ; for an increase of pressure in the 
 branches of the vas efferens must force the branches of the vas afferens 
 against the walls of the capsule and close them (Ludwig). 
 
 The part played by the kidney-substance in the formation of urine is 
 regarded by some authors simply as a peculiar attraction exerted by its cells 
 for the small quantities of urea or uric acid of the blood (Bowman). Many 
 do not consider the small amounts of these bodies contained in the blood to 
 be any objection to this, purely physical, theory of secretion; for (they urge) 
 the swiftness of the blood-stream through the kidneys is sufficient to 
 account for the amounts secreted. Other observers, on the contrary, suppose 
 that the formation of urea, uric acid, &c., from less oxidized bodies, takes 
 place within the kidneys (Hoppe-Seyler and Oppler, Hoppe-Seyler and 
 Zalesky). The facts, however, upon which this theory is based, are doubted 
 or otherwise explained by others (Meissner, Voit). 
 
 The following are the points which are chiefly contested: (1.) The 
 simple question whether the blood of the renal artery contains more urea 
 than that of the renal vein (Picard), appears to have been recently settled 
 in the affirmative (Grehant) ; this difference disappears after ligaturing the 
 ureters. (2.) According to some observers (Bernard and Barreswil, Oppler, 
 Zalesky), after extirpation of the kidneys or ligature of the renal vessels, 
 
 I 
 
114 URINE. 
 
 no accumulation of urea takes place in the blood ; while others (Meissner, 
 Voit, Grehant), maintain that such an accumulation may be detected, some 
 even affirming that it varies in amount according to the time (Grehant). 
 If the former account be correct, it is still no proof of the formation of urea 
 in the kidneys ; for, after the operation, fluids containing urea and ammonia 
 are vicariously secreted by the stomach and intestine, and are got rid of by 
 vomiting (Bernard and Barreswil). Moreover the animals die for the most part 
 so quickly (of so-called ' ursemia,' whatever that may be whether the reten- 
 tion in the body of some poisonous substance, or simply of water), that no 
 considerable accumulation of urea is possible, such, e.g. as that which fol- 
 lows simple ligature of the ureters. Extirpation of one kidney does not 
 diminish the amount of urea excreted (Rosenstein). (3.) The presence in 
 the kidneys of characteristic bodies which do not pass into the urine (e.g. 
 cystine, taurine), certainly indicates the occurrence of processes of change 
 in the kidneys ; but it does not directly prove the formation of urea or uric 
 acid there. (4.) The accumulation of creatine, creatinine, &c., in many 
 organs (in blood, muscles), after extirpation of the kidneys (Oppler, 
 Zalesky)j is explained by the supposition that urea is normally derived from 
 them in the kidneys. Creatine, again, is said to undergo conversion into 
 urea on digestion with triturated kidney substance (Ssubotin). As, how- 
 ever, creatine and creatinine, when administered, reappear, as a rule, in 
 the urine, unaltered, and not as urea (Meissner, Voit), it would seem, that 
 these substances are not in general the source of the urea. In the present 
 state of our knowledge, therefore, we must incline to the belief that urea 
 and uric acid are separated from the blood and not formed in the kidneys. 
 
 In birds and serpents, ligature of the ureters is followed by an evident 
 accumulation of uric acid all over the body. After extirpation of the 
 kidneys in serpents, 1 there is simply a diminution in the amount of uric acid 
 excreted (Zalesky), which produces no decided effect. 
 
 If we then assume that the two essential constituents of urine reach the 
 kidneys already formed, the liver may possibly be one of the principal situ- 
 ations for their production ; for, of all organs, it contains most urea, or (in 
 the case of birds) uric acid (Heynsius, Stokvis, Meissner) : and it yields 
 urea to blood which is passed through its vessels (Cyon, Gscheidlen). 
 
 Besides the above-mentioned circumstances affecting the 
 secretion of urine, the following conditions influence the amount 
 secreted in a given time, and the substances contained : 1. 
 The quantity of urine depends (a) upon the intensity of the 
 blood-pressure in the glomeruli ; (6) upon the amount of mate- 
 rials of an easily diffusible nature (water, salts, &c.) contained 
 in the blood. This is evident, for the greater the blood-pres- 
 sure the larger will be the amount filtered in a unit of time, 
 and the greater the amount of water, salt, &c. in the blood 
 
 1 In birds, in consequence of the situation of the kidneys, they cannot be extir- 
 pated without killing the animal. 
 
URINE. llo 
 
 the less will be the amount of the filtered substances which will 
 re-diffuse into the blood-vessels from the tubuli uriniferi ; and, 
 therefore, the greater will be in both cases the quantity of urine 
 secreted. Among the circumstances which raise the blood- 
 pressure in the glomeruli must be reckoned : 1 . Rise of blood- 
 pressure all over the body, as when the distension of the vas- 
 cular system is increased (e.g. by a free ingestion of water, 
 which is quickly absorbed) ; 2. Increased tension of the arterial 
 system alone, produced by excessive activity of the heart ; 3. 
 Increased tension in the renal arteries produced, for example, 
 by ligaturing other great arteries ; or simply in the glomeruli 
 owing to a vaso -motor dilatation of the vasa afferentia ; 4. Pre- 
 vention of the free outflow of blood from the glomeruli through 
 the veins (e.g. by the morbid contraction of the capillaries, or 
 the ligature of the renal veins). Any very decided increase of 
 pressure, especially when produced by the 4th of the above 
 methods, causes, in addition, a nitration of the less diffusible 
 portions of the blood albumin, fibrinogen into the urine ; 
 and an increase above a certain limit leads to the appearance 
 in it of blood (blood-corpuscles), owing to the rupture of the 
 vessels, or, perhaps, to diapedesis (p. 81). Circumstances of 
 a nature opposite to those we have mentioned above especially, 
 therefore, diminished tension of the arterial system, occasioned, 
 for example, by diminished cardiac activity (heart-diseases) 
 must cause the amount of urine secreted to diminish. Among 
 the substances of an easily diffusible nature referred to above, 
 the water contained in the blood will have the greatest influence 
 upon the amount of the urinary secretion : as a fact, the quan- 
 tity secreted depends chiefly upon it, and therefore, as is ex- 
 plained above, upon the water ingested. The amount of each 
 individual constituent of the urine depends (a) upon the amount 
 of it previously contained in the blood and possibly also (6) 
 upon the oxidizing power of the kidneys. The following may 
 be increased: 1. The water by ingestion (drinking), and by 
 diminishing secretion in other ways, as by perspiring and 
 expiring under a low temperature. 2. The salts, by an in- 
 creased use of salts in food (certain salts which are formed in 
 the body by oxidation, of course, increase with the extent of 
 oxidation). 3. The sugar, by an increased formation of sugar 
 in the liver, or by a diminished destruction of what is formed 
 
 i 2 
 
116 URINE. 
 
 (Chapter V.). 4. The products of the oxidation of nitrogenous 
 bodies (considered as a whole and not as individual bodies 
 urea, uric acid, creatinine, &c.),by an increase in the amount of 
 the nitrogenous foods, such as flesh, eggs, &c., which are 
 assimilated ; and also by an increased destruction of substances 
 in the body containing nitrogen (as in excessive nervous activity, 
 abnormally high temperatures, fever, &c., Chapter VI.). 5. 
 The carbonic acid, by an increase in the number of operations, 
 especially of muscular movements (Morin), which generate car- 
 bonic acid in the body. 
 
 From what lias been said above it is easy to collect and mention all the 
 circumstances which increase the quantity of urea excreted in a given time. 
 They are (1) general increase in the urinary secretion, from whatever cause 
 resulting; (2) free ingestion of animal food ; (3) increased consumption in 
 the body of nitrogenous material (see Chapter VII. and Chapter VIII.) ; and 
 (which is doubtful) (4) increased power of oxidation on the part of the 
 kidneys. 
 
 Besides the substances we have mentioned, there may be detected in the 
 urine, after certain foreign bodies have been taken into the system, either 
 those bodies themselves or some oxidized modification of them. The urinary 
 secretion brings about a constant elimination of them from the body. In 
 the case of poisonous substances, if elimination takes place as quickly as 
 introduction into the blood, e.g. when absorption is taking place from the 
 stomach, a complete immunity from danger may result. Certain easily 
 diffusible poisons, therefore, such as curare, are harmless when taken into 
 the stomach during a constant secretion of urine. When injected directly 
 into the blood, or when quickly absorbed (as in subcutaneous injections), 
 or if the activity of the kidneys is interfered with by ligature of the renal 
 vessels (Bernard, Hermann), they act at once as poisons. As it is possible 
 that we frequently take into the body along with food many harmful 
 substances of this nature, their elimination at the kidneys is a further 
 important function of those organs. 
 
 The quantity of urine excreted in twenty-four hours varies 
 in adults (chiefly on account of the fluid ingested), between 
 1000 and 2000 grammes ; the amount of urea is on the average 
 30 grammes, of uric acid 1 gramme, and of hippuric acid 1-2 
 grammes. 
 
 That the nervous system has some influence upon the secre- 
 tion of the kidneys, is proved by the changes which take place 
 in the urine referable to emotions and to nervous diseases. 
 From the statements we possess respecting the nature of thds 
 influence, but which are not very exact (Bernard, Eckhard, 
 
URINE. 117 
 
 Knoll, Ustimowitsch), it would seem to be chiefly vaso-motor. 
 Section of the nerves accompanying the renal vessels, as also 
 of the splanchnics and of the cord, as well as lesion of a certain 
 portion of the fourth ventricle of the brain, increase the secre- 
 tion as a rule. At the same time the renal veins pulsate, the 
 blood in them usually becoming bright carmine-red in colour, 
 on account of the rapid flow from the arteries. Irritation of 
 the splanchnics diminishes the secretion and the rapidity of the 
 blood-stream through the kidneys. 
 
 Irritation of the vagus, on the other hand, is said to have an opposite 
 effect, viz., to increase the secretion and the rapidity of the blood-stream 
 (Bernard) ; and therefore, like the fibres of the facialis to the salivary glands 
 (p. 95), to dilate the arteries. The result of section of vaso-motor nerves 
 is the less certain the greater the number of fibres severed. If, for ex- 
 ample, the splanchnics or the upper part of the spinal cord be cut through, 
 the general arterial pressure sinks to such an extent that the dilatation 
 of the renal arteries is more than balanced. After section of the renal 
 nerves the gland undergoes change, and the urine secreted becomes 
 albuminous (Krimer, Brachet, Miiller, and Peipers). 
 
 Separation. 
 
 The urine after secretion passes out of the convoluted into 
 the straight uriniferous tubes, which unite several times at 
 acute angles one with another, and open, at the surface of the 
 renal papillae, into the calyx or pelvis of the kidney. In all 
 these situations urine is constantly found ; a return of the secre- 
 tion from the pelvis into the tubuli is impossible, as any in- 
 crease of pressure in the former closes the openings of the latter. 
 From the pelves of the two kidneys the urine passes through 
 the ureters (one to each kidney) into a reservoir the urinary 
 bladder. The passage through the ureters may be accounted for 
 by (1) the pressure exerted by the continually secreted urine; 
 
 (2) the weight of the contained secretion (for the bladder is, 
 in almost every position of the body, lower than the kidneys) ; 
 
 (3) peristaltic contraction of the muscles of the ureters, which, 
 it would seem, propels every drop of the fluid reaching the 
 ureters by continually closing the lumen of the tube behind it. 
 
 The urine collects in the bladder (which, when empty, is 
 collapsed infolds), until it completely fills out the walls of that 
 organ ; every further addition then causes an abnormal dis- 
 tention. The return of the urine into the ureters is prevented 
 
118 HEINE. 
 
 by the peculiar arrangement of their openings, which traverse 
 the walls of the bladder very obliquely, in such a manner that 
 pressure from within closes the channel entirely. The passage 
 of the stored-up secretion into the urethra is controlled by a 
 ring of elastic fibres ; and, in males, by the elasticity of the 
 prostate also. As soon as the pressure of the urine overcomes 
 the elasticity of those structures, and a drop of urine trickles into 
 the urethra, an impulse to micturition is felt ; whereupon either 
 the closure of the neck of the bladder is rendered firmer by 
 the voluntary contraction of the urethral muscles (Budge), or 
 a voluntary evacuation of the contents of the bladder is com- 
 menced. The latter is accomplished by the contraction of the 
 muscular walls of the bladder which proceeds gradually until the 
 lumen of the bladder is completely obliterated, and the whole 
 of the contents are expelled. The urethra itself is next emptied 
 by means of the muscles surrounding it (especially by the 
 bulbo-cavernous muscle). The evacuation of the contents of the 
 bladder is assisted by abdominal pressure (Chapter IV.). 
 
 During its stay in the bladder the urine is said by some to lose a portion 
 of its water by absorption (Kaupp) ; while others, on the contrary, maintain 
 that it receives a further addition of water from the blood, at the same time 
 yielding up to the latter some of its urea (Treskin) ; and a third set of 
 observers deny that any diffusion whatever takes place, as the bladder is 
 unable to absorb solutions of salts so long as its epithelium is intact (Kiiss, 
 Susini). Mucus from the numerous mucous glands is mixed with the urine 
 both in the bladder and in the urethra. 
 
 The peristaltic movements of the ureter are reflex in their character, as 
 they only occur on stimulation of the ureter by the urine forced into it, or 
 on artificial irritation : they proceed in the direction of the bladder with a 
 rapidity in rabbits of 20 to SO 01 " 1 per second (Engelmann). Each individual 
 irritation of the ureter produces a wave of contraction on both sides of the 
 point of irritation : as this may take place in portions of the ureter containing 
 no ganglia or nerves, the wave of movement would seem to be continued 
 by simple muscular conduction. The spontaneous movement of the ureter 
 has been recently regarded as a case of automatic contraction of muscle 
 (Chapter VIII.) (Engelmann). 
 
 The above theory of the closure of the bladder is disputed by some, who 
 suppose that it is produced by a sphincter, kept constantly in a condition of 
 contraction (tonus) by the nervous system (Heidenhain and Colberg, Sauer, 
 Kosenplatner, Kupressow). The presence of this sphincter in man is 
 denied by some (Barkow), but maintained by others (Heidenhain) ; while 
 the existence of a constant tonus has been contested on experimental 
 grounds (L. Rosenthal and von Wittich). 
 
 The nerves of the muscles of the bladder, according to some, may be 
 
SWEAT. 119 
 
 traced into the cord (lower portion, Budge), and even into the brain (Kilian, 
 Valentin). They can be brought into reflex action very easily by stimu- 
 lations originating in the mucous membrane of the bladder, and in the 
 bulbus urethras. Over-distension of the bladder, therefore, causes involun- 
 tary evacuation of its contents. 
 
 Retention of urine produced by paralysis of the muscular walls of the 
 bladder frequently follows degeneration of the spinal cord (Chapter XI. 
 Spinal Cord). 
 
 4. CUTANEOUS SECRETIONS. 
 Concerning the respiratory secretion of the skin, see Chapter IV. 
 
 1. Sweat. 
 
 Sweat is the secretion of the numerous tubular sweat- 
 glands of the skin, the inner, blind, extremities of which are 
 coiled up, and lie for the most part in the corium, but some- 
 times in the subcutaneous layer of connective tissue, while their 
 outer, free, extremities open at the surface as the ' pores ' of the 
 skin. 
 
 The sudoriparous secretion conveys out of the body the same excretory 
 matters, generally speaking, as the urine, from which it is chiefly distin- 
 guished. by the facts that it is not constantly secreted, and that it is poured 
 out over the whole skin, and is of further use to the organism as a regu- 
 lator of temperature. [The sweat-glands, therefore, bear the same morpho- 
 logical relationship to the kidneys as the mucous glands to the salivary 
 glands, the glands of Brunner to the pancreas, or the sebaceous glands to 
 the milk-glands.] 
 
 Sweat in large quantities may be obtained by supporting the body on 
 an inclined grooved plate of metal and submitting it to a vapour bath j or 
 by covering portions of the body with air-tight bags connected with a re- 
 ceiver. Sweat so obtained is almost always rendered impure by the pre- 
 sence of sebaceous secretion and epithelium-scales. 
 
 Sweat is apparently a colourless, clear, acid fluid of variable 
 odour according to the part of the skin whence it was taken. 
 The constituents of sweat are: 1. Water; 2. The usual salts; 
 3. Urea (and perhaps other products of the oxidation of nitro- 
 genous bodies Favre, for instance, mentioning an acid con- 
 taining nitrogen, hidrotic acid) ; 4. Traces of a colouring 
 matter (Schottin); 5. Fats; 6. Various volatile fatty acids 
 (formic, acetic, butyric, propionic acids, &c.). 
 
 Fats predominate in the secretion of the sweat-glands of the external 
 ear (ceruminous glands) to such an extent that it resembles rather a 
 
120 SWEAT. 
 
 * 
 
 sebaceous than a sudoriparous secretion. Sweat is easily decomposed ; and 
 decomposition may chiefly affect its fatty portions, in which case the odour 
 of the volatile acids and the acid reaction increase ; or it may chiefly affect 
 its nitrogenous portions, when ammonia appears and the secretion takes an 
 alkaline reaction. 
 
 The quantitative composition of sweat is about the following (in 1,000 
 parts) : water 995 '6, urea 0*04, fats 0-01, other organic matters 1-88, inor- 
 ganic matters, 2-5 (Favre). 
 
 Secretion. 
 
 The secretion of sweat only takes place under certain con- 
 ditions. It consists most probably in part of a process of 
 transudation, and in part of a peculiar activity of glandular 
 cells. The fat at least, contained in the secretion, originates 
 in the cells ; for the latter contain fat-globules, and in greater 
 quantity the richer the secretion is in fats or fatty acids. 
 Secretion is promoted by various circumstances : 1. By what- 
 ever raises the blood-pressure in the capillaries of the sweat- 
 glands as, a, general rise of blood-pressure (e.g. after free 
 ingestion of water) ; 6, increase in the temperature of the 
 body, or in the vicinity of the body, which causes dilatation 
 of the afferent arteries (possibly by relaxing their muscles). 
 In such circumstances the secretion of sweat is of special im- 
 portance ; for the evaporation of the secretion extracts heat 
 from the body and cools it (Chapter VII.). 2. By increase in 
 the quantity of the various constituents of sweat contained in 
 the blood, and especially of water. Liberal ingestion of warm 
 fluids, therefore, increases perspiration for several reasons. To 
 what extent the above-mentioned influences must operate in 
 order to induce ordinary secretion is unknown. The quantity 
 secreted, of course, varies very much. Frequently no perspira- 
 tion takes place for months ; while, at other times, as much as 
 16 00 grammes and more are yielded in an hour (Favre). Those 
 portions of the skin (the forehead, the axillge, the soles of the 
 feet, and the palms of the hand, &c. ) which are provided with 
 many large sweat-glands, yield the richest supply of secretion. 
 The value of the sweat to the whole organism is discussed in 
 Chapters V. and VII. 
 
 It is probable that the nervous system has some influence upon the forma- 
 tion of sweat from the known effect which the emotions exert upon it. 
 Nothing is, however, known of the way in which it operates ; nor indeed, 
 
SEBACEOUS SECRETION. MILK. 121 
 
 have nerves been traced to the glands. We "can, therefore, at present only 
 admit the existence of vaso-motor influences. As is the case with the urine, 
 substances taken into the bcdy as food may pass into the sudoriparous secre- 
 tion unchanged or oxidized. Hippuric acid is said to appear in the sweat, 
 as well as in the urine, after ingestion of benzoic acid (Meissner). Indican 
 also was once detected in sweat (Bizio). 
 
 2. Sebaceous Secretion. 
 
 The small, racemose, sebaceous glands of the skin open nearly 
 always into hair-follicles ; but the follicles are in many places 
 so small as to appear to be simply lateral involutions of the 
 excretory duct of the gland. The chief constituents of the 
 sebaceous secretion are various fats, normally fluid at the tem- 
 perature of the body, and cholesterin ; in addition, there are 
 found small quantities of the usual results of transudation (water, 
 salts), and an albuminous body. It is supposed that in secre- 
 tion the specific constituents (fats) arise within the gland-cells, 
 and become free by the disintegration of the latter. Possibly 
 the liberation of the fat- globules is due to a process of contrac- 
 tion similar to that which takes place in milk. The cells of the 
 mora superficial layers in the gland-cavity may be seen to con- 
 tain increasing quantities of fat (' fatty degeneration '), the most . 
 superficial being completely filled. The latter then disinteg- 
 rate ; and hence the secretion contains fragments of cells. An 
 influence of the nervous system upon this secretion has not been 
 demonstrated. The secretion lubricates the hair and also the 
 skin, giving them a shiny appearance, and preventing the 
 entrance of fluids. 
 
 Exact experiments with this secretion, especially of a quantitative de- 
 scription, are wanting, as there are no means of procuring large amounts 
 of it except in the case of that covering the skin of new-born animals (vernix 
 caseosa). The secretion of the Meibomian glands of the eyelids probably 
 resembles the sebaceous secretion. Cerumen, on the contrary, is a secretion 
 of sweat-glands, although there are sebaceous glands in the hair follicles 
 of the external meatus. 
 
 The sebaceous secretion is closely allied to the following 
 secretion milk. 
 
 5. SECRETION OF MILK. 
 
 The milk-glands may be regarded as greatly enlarged and 
 aggregated sebaceous glands, and the milk which they secrete 
 
122 MILK. 
 
 as a sebaceous secretion containing a greater quantity than 
 usual of the results of transudation. 
 
 Each gland consists of 1524 incompletely separated race- 
 mose glands, every one of which is provided with an excretory 
 duct, which, after dilating into a longish reservoir, opens upon 
 the nipple. These glands are only fully developed in the 
 female during the period of possible fertility, and they are only 
 active from about the period of delivery until the recurrence of 
 menstruation. 
 
 A secretion of milk takes place in new-born children, from the fourth to 
 the eighth day j and also occasionally in males. 
 
 Milk is an opaque, white fluid, generally weakly alkaline, 
 but frequently neutral or slightly acid (according to Soxlet 
 the normal reaction is amphichromatic). It has a sweetish 
 taste and a characteristic odour. It is an emulsion of very 
 small fat-globules (milk-corpuscles) in a clear fluid. Its specific 
 gravity is 1-008-1-014. 
 
 Casein also (see below) seems to belong to the list of formed elements of 
 milk, as it does not appear in the clear filtrate obtained by filtering milk 
 through clay by means of the air-pump (Zahn, Kehrer). It is probably con- 
 tained in the fragments of cells present in the secretion (Kehrer). Many 
 observers believe that the fat-globules possess an envelope of casein. 
 
 The constituents of milk are : 1. Water, in the proportion 
 on an average of about 89 percent. 2. Salts, especially com- 
 pounds of potassium, calcium, and phosphoric acid, and also of 
 iron and manganese, the combination of the saline constituents 
 showing a striking resemblance to that in the blood-corpuscles. 
 3. Milk-sugar. 4. Albuminous matters, especially casein, but 
 also a small amount of albumin ; that is to say, albuminous 
 matters, only a small portion of which is precipitable by heat, 
 the greater part being thrown down only on the addition of an 
 acid. 5. Fats, viz. the glyceric ethers of palmitic, stearic and 
 oleic acids, and in small quantities also of butyric, capronic, 
 caprinic, caprylic and myristic acids. 6. Lecithin or protagon 
 (Tolmatscheff). 7. Various c extractives,' among others urea 
 (Lefort). 8. Oases (C0 2 ,0,N). 
 
 Human milk contains in 1,000 parts (Th. Brunner) : water 900-0, casein 
 together with albumin (traces) G'3, fats 17*3, milk-sugar 62 '3, salts and 
 
MILK. 123 
 
 extractives 14 g l. The milk of the cow contains (Kiihn) : water 885'3, casein 
 and albumin 28-5, fats 31-2, milk-sugar 45-6, salts and extractives 9'8. 
 Older analyses differ considerably from those here given. 
 
 Secretion. 
 
 The secretion of milk consists probably in the formation 
 within the glandular cells of the specific constituents (milk- 
 sugar, casein, and fat) out of the materials transuded through 
 the walls of the blood-vessels, and the liberation of those 
 constituents by the disintegration, or some similar process, of 
 the cell-walls. In the case of the fat, this has been directly 
 shown to occur, the innermost layers of cells having been ob- 
 served to become more and more nearly filled with fat, in the 
 same manner as in the sebaceous secretion. These fat-laden 
 cells then either disintegrate, or, more probably (Strieker, 
 Schwarz), get rid of their fat-globules by contracting, like 
 colostrum-corpuscles to be described below. The globules thus 
 set free become emulsionized in the fluid. The milk-corpuscles, 
 as is generally the case with fat-globules found in albuminous 
 fluids, become coated over with a thin pellicle of some alkali- 
 albuminate (possibly casein). At the commencement of the 
 period of lactation, in the so-called colostrum, or milk first 
 secreted after delivery, certain round, unbroken, fat-laden cells 
 (colostrum-corpuscles) present themselves. At first they are the 
 only bodies present ; but after a time they are replaced to a 
 greater and greater extent, though never entirely, by the ordi- 
 nary milk-corpuscles. It has been observed that the colostrum- 
 corpuscles are contractile (Strieker, Schwarz), and force out 
 their contained fat-globules ; it may, therefore, be assumed that 
 the subsequent formation of milk-corpuscles happens in like 
 manner ; and that it is only at first that the parent-cells of 
 the milk-corpuscles themselves become free and pass into the 
 milk. From which of the substances composing the transuded 
 fluid the various specific constituents of milk are derived is still 
 a matter of supposition. Casein undoubtedly originates in the 
 albumin of the blood, as a ferment has recently been discovered 
 in the milk-gland, which is capable of converting a mixture of 
 albumin and an alkali into an alkali-albuminate (Dahnhardt). 
 Milk-sugar is derived in all probability from the grape-sugar 
 of the blood, as it is increased in quantity by the ingestion of 
 
124 MILK. 
 
 carbo-hydrates as food ; there are, however, other possible sources 
 (Chapter VI.). 
 
 The origin of the fat is as doubtful as the method of the 
 formation of fat generally (consult Chapter VI., where this ques- 
 tion is discussed) ; some have supposed it to be derived from 
 alkali-albuminates such as casein (Hoppe). The process of 
 secretion is, therefore, as yet quite uncertain ; even the amount 
 of salts contained in the milk cannot be accounted for on mere 
 physical grounds. An influence of the nervous system, such 
 as may and doubtless does exist, does not however seem 
 indispensable for simple secretion, which continues after section 
 of the cerebro-spinal nerves (in man the 4th to 6th intercostal 
 nerves) and also of the nerves (sympathetic ?) which accompany 
 the vessels in the gland (Eckhard). 
 
 Of the special circumstances affecting the secretion, those of 
 diet are best understood. The amount of casein and fat present 
 during an animal diet is greater than during a vegetable diet. A 
 liberal supply of food generally causes increase in the amount of 
 fat, while carbo-hydrates cause increase in the amount of sugar. 
 Fatty foods do not increase the quantity of fat. The composi- 
 tion varies also with the time during which active secretion has 
 proceeded, and with other circumstances attendant upon child- 
 bearing. 
 
 As was the case with urine, milk may contain foreign bodies (in a changed 
 or unchanged condition) which have been previously taken into the system. 
 
 As milk contains several easily alterable constituents, and, in all proba- 
 bility, some ferments also, it rapidly undergoes certain changes after its 
 secretion, which may in part be artificially induced and utilised. The fer- 
 ments may be partly separated by causing milk to transude through a mem- 
 brane, when they are left behind (F. Hoppe). Certain of these changes 
 may be proved to be processes of oxidation, and are accompanied by the 
 disappearance of oxygen and the formation of carbonic acid (Hoppe). In 
 the first place the milk-corpuscles, which are lighter on account of the fat 
 they contain, rise to the surface of the milk on standing, constituting the 
 1 cream.' By means of shaking (churning), the envelopes or pellicles of the 
 milk-corpuscles, become ruptured, and in consequence the fat contained in 
 them, runs together, the fatty part of milk being thus obtained almost 
 pure in the form of 'butter.' The remaining solution of casein, sugar, 
 and salts, constitutes f butter-milk ' : as a rule, butter is manufactured by 
 churning cream alone. Among the chemical changes occurring in milk the 
 chief are those affecting the milk-sugar and the fats. The former gradu- 
 ally undergoes lactic acid fermentation, especially if the temperature be some- 
 what high, the milk becomes acid, and the free lactic acid precipitates 
 
MILK. TEARS. lf>o 
 
 the dissolved casein, causing flocculence, just like any other free acid or 
 like the gastric juice. This coagulum, 'cheese,' includes also other of 
 the constituents of milk, especially the milk-corpuscles. The remaining 
 solution of sugar and salts is called 'whey.' A formation of lactic acid 
 frequently takes place while the milk is still within the gland, the secre- 
 tion having an acid reaction as soon as it is withdrawn. No oxygen is 
 needed in the formation of lactic acid (Hoppe). On the addition of yeast, 
 milk may, under certain circumstances (probably such as cause the conversion 
 of the milk-sugar into lactose), undergo alcoholic fermentation j such an 
 alcoholic preparation of milk is the i kumiss ' of the Tartars. The fats also 
 decompose, if milk or butter be allowed to stand, into glycerin and fatty 
 acids (caprylic, caprinic, capronic, butyric acids). Moreover, milk on stand- 
 ing exposed to the air, exhibits a diminution in the quantity of casein, and 
 an increase in the amount of the substances capable of being extracted by 
 means of alcohol and ether. This is accompanied by absorption of oxygen 
 and liberation of carbonic acid, and is an eifect (Kemmerich) of ferments 
 of a foreign nature. In all probability this is a case of the origin of fat by 
 the oxidation and splitting up of albuminous bodies (Hoppe). Finally, the 
 amount of casein increases at the expense of the albumin without the addi- 
 tion of air or a ferment (Kemmerich). 
 
 During the period of lactation the amount of milk secreted 
 at both breasts in twenty-four hours amounts to about 1350 
 grammes. 
 
 Separation. 
 
 The withdrawal of the milk out of the flask-shaped reser- 
 voirs of the milk-ducts is brought about, as a rule, by the suck- 
 ing of the young animal for whose nourishment the secretion 
 serves, i.e. by atmospheric pressure. The smooth muscular 
 fibres, which surround the whole gland, probably assist. A 
 portion of the muscles further subserves the purpose of the 
 erection of the nipple, which has as yet been insufficiently in- 
 vestigated, and which ceases to occur after section of the 
 cerebro-spinal nerves of the mammary gland (Eckard). 
 
 6. SECRETIONS FOR THE SENSE ORGANS. 
 
 We have here to do almost entirely with the secretion of 
 mucous glands, for which the same description will serve as 
 was given in the section on Alimentary Secretions. In addi- 
 tion there are the cerumen of the ear (p. 119), and the se- 
 cretion of the Meibomian glands (p. 121), which have been 
 already mentioned. It only remains, therefore, to describe the 
 secretion of tears. 
 
126 TEARS. 
 
 Tears. 
 
 Tears are secreted by the racemose lachrymal gland, which 
 is exactly similar in construction to the glands secreting mucus. 
 The secretion itself may also be regarded as a very watery 
 mucus (or saliva) : it consists of a large proportion of tran- 
 suded material, together with small amounts of mucin and 
 albumin. It is clear, colourless, alkaline, and of a saline taste. 
 
 Tears contain 99 per cent, of water, 0*1 per cent, of albumin, 0*8 per 
 cent, of salts, O'l per cent, of epithelium (Frerichs). 
 
 Tears are continually secreted in small quantities (Chapter 
 X.). Their secretion is, however, considerably increased by cer- 
 tain kinds of psychical stimuli, or, in a reflex manner, on irrita- 
 tion of the nasal mucous membrane, the conjunctiva, or the retina. 
 The impulse to secretion occasioned by irritation of the nasal 
 mucous membrane only extends to the gland of the side stimu- 
 lated (Herzenstein). The nerves, irritation of which increases 
 secretion, and which therefore contain the secretory fibres, are 
 the lachrymal branch of the trigeminal, the subcutaneous malar 
 branch of the same nerve, and the cervical sympathetic. Eeflex 
 stimulation proceeding from the nose may occur after section 
 of the lachrymal nerve (Herzenstein). 
 
 The tears reach the conjunctival sac by several excretory ducts. Con- 
 cerning their further application and destination, consult Chapter X. 
 
 The specific secretions of the generative organs, in which 
 morphological structures are the essential constituents, are 
 treated of in the fourth Section of this book. 
 
127 
 
 CHAPTEE III. 
 
 RECEPTION OF MATERIAL INTO THE BLOOD. 
 ABSORPTION. 
 
 The Materials Absorbed. 
 
 THE substances which are taken up (absorbed) into the blood 
 are : 
 
 1. The oxidizing body, oxygen, absorbed in the process of 
 respiration (Chapter IV.). 
 
 2. The food or material destined for the repair of the 
 tissues, or for the replacement of those portions of the body 
 which are separated and cast out unchanged. Certain pre- 
 paratory processes have to be passed through before absorption 
 is possible ; such processes are denominated digestion. 
 
 3. The products of the chemical changes of substances 
 which, having been absorbed by the blood and carried to the 
 various organs of the body, have there undergone oxidation. 
 The bodies thus formed are either gaseous (carbonic acid being 
 the only instance) or liquid. They are, moreover, either the 
 ultimate products of oxidation which the blood takes up simply 
 in order to convey them to situations specially appropriated 
 to their excretion (carbonic acid, urea, &c.) ; or they are com- 
 pounds which are not made use of at any particular spot, but are 
 further decomposed either in the blood itself, or after their re- 
 secretion in some other situation. To this class belong most 
 of the so-called ' specific constituents ' of the various secretions, 
 whether parenchymatous juices, the fluids of cavities, or free 
 secretions, the only difference being that in the first case the 
 constituents are re-absorbed by the blood in the place where 
 they were secreted, while in the case of the free secretions they 
 undergo reabsorption in other situations after they have 
 
128 ABSORPTION. 
 
 traversed for a longer or shorter distance the channels or canals 
 of the body. 
 
 4. Finally, a considerable amount of the materials separated 
 from the blood in the course of secretion are reabsorbed un- 
 changed, either elsewhere, or, if the physical conditions have in 
 the meantime become altered, in the very place of their secre- 
 tion ; such substances are water, salts, albumin, called collectively 
 6 transuded materials.' 
 
 Further explanation of the substances included in the third class will 
 be given on p. 138. The fourth class includes the unaltered constituents of 
 the parenchymatous juices and fluids of cavities, as well as of pathological 
 transudations (oedematous fluids, serous effusions). Their re-absorption into 
 the same vessels and under the same conditions as obtained during secretion 
 would, of course, be impossible. The conditions therefore must be changed 
 (e.g. the filtration-pressure of the blood, which is continually altering, 
 must diminish), or absorption must take place by another way (e.g. through 
 the lymphatic system). The unaltered constituents of true secretions are 
 reabsorbed elsewhere than at the place of secretion. 
 
 Methods of Absorption. 
 
 Absorption of material into the blood takes place in part 
 directly into the blood-capillaries, and in part indirectly 
 through the lymphatic vessels which constitute an appendage 
 to the blood- vascular system. The capillaries of blood-vessels 
 and lymph-vessels lie everywhere together. The lymphatic 
 vessels proceeding from the alimentary apparatus, and especially 
 from the intestine, are called lacteals. 
 
 The lymphatics and the lacteals form a simple, branched, vascular tree 
 (comparable with that of the veins), which opens into the jugular veins at 
 their bases by two inconsiderable trunks, viz., the thoracic duct and the 
 right lymphatic duct. The latter receives lymph only from the vessels of 
 the right upper portion of the body and the right half of the thorax, while 
 the thoracic duct collects the lymph from all the remaining vessels, including 
 the lacteals. But few accurate observations have as yet been made con- 
 cerning the origin of the lymphatic vessels in the various organs. Some 
 regard the closed network of capillaries (which are somewhat wider than 
 blood capillaries) as the commencement, while others suppose this network 
 to originate in the fine, wall-less, spaces of the tissues. In many compound 
 tissues, especially in glands, the lymphatic vessels commence in fissure- 
 like spaces between the blood-vessels and the other components of the tissue, 
 e.g. the glandular canals or ducts (Ludwig, Tomsa, Zawarykin, Mac- 
 Gillavry). In the spinal cord these spaces surround the blood-vessels as 
 perivascular spaces (His). These lymph-spaces appear to be lined by epi- 
 
LYMPHATICS. LACTEALS. 129 
 
 theiiura. The so-called serous sacs (pleura, peritoneum, &c.), and the sub- 
 cutaneous lymph-sacs of the frog, constitute similar but much larger lym- 
 phatic spaces. They are lined by epithelium and filled with lymph (p. 92) ; 
 and they communicate, by means of small openings (' stomata ') occurring 
 between the epithelium cells, with the lymphatic capillaries of the neigh- 
 bouring tissue, e.g. with those of the centrum tendiueum of the diaphragm 
 (von Recklinghausen, Ludwig and Dybkowsky, Schweigger-Seidel and 
 Dogiel, Oedmannson), and especially with those of tendons and fasciae 
 (Genersich). 
 
 The origin of the lymphatic vessels within the elementary tissues them- 
 selves must most probably be sought (Virchow) in the retiform canalicular 
 systems, which, according to Virchow's theory, are formed by the anasto- 
 mosing cells of those tissues (connective tissue proper, bone, &c.); or which, 
 according to von Recklinghausen, are systems of tubes bearing at their 
 nodal points the protoplasmic masses characteristic of the tissues in which 
 they occur. It is possible that this system of canaliculi stands, on the other 
 hand, in direct communication with blood-capillaries, in which many observers 
 suppose inter-epithelial openings stomata to occur. 
 
 The same uncertainty is felt regarding the origin of the lacteals in the 
 villi of the small intestine. The villi are small, closely-packed processes of 
 the mucous membrane, of various shapes, but mostly conical, which give the 
 inner surface of the small intestine the appearance of velvet. They are 
 covered with the columnar epithelium of the intestinal mucous membrane, 
 and possess smooth, longitudinal, muscular fibres, which produce in them 
 a shortening and a spiral twisting on contraction (Briicke). Each contains, 
 besides a net-work of capillary blood-vessels, the disputed commencement 
 of the lacteal, which leaves the villus as one, or sometimes several, small 
 vessels. These lacteals originate in some way in the epithelial cells cover- 
 ing the villi j for all bodies which reach the chyle-vessels from the intestine 
 must first pass through them, as may be demonstrated in the case of fat- 
 globules. Some suppose a direct union of epithelium cells, through the 
 canalicular system of the connective tissue of the villi, with the lacteal 
 vascular system, which communicates, by means of processes, with the united 
 bases of the epithelium cells (Heidenhaiu, Eitner, von ThanhofFer). Others 
 suppose a capillary system of lacteal vessels to exist within the villi, which 
 is, however, closed, and can only communicate by diffusion with the cells 
 of the epithelium (E. H. Weber). A third set of observers deny the 
 presence of such capillaries (Funke, Kolliker), and even of the central lac- 
 teal (Briicke, Basch); and think that the substances absorbed from the 
 intestine pass through wall-less spaces, through the meshes of the tissue 
 composing the villi, or through fissures between the blood-vessels and the 
 surrounding tissue (Basch). The same views, therefore, are held respecting 
 the origin of lacteals as of lymphatics. The nature of the epithelium cells 
 themselves is as much disputed as that of the origin of the lacteals. The 
 fact that they are capable of taking up bodies from the intestine (fat- 
 globules, pigment-granules, blood-corpuscles, &c.) has led to the supposi- 
 tion of openings. Each cell presents to the interior of the intestine a 
 thickened striated end where, if at all, the disputed openings must exist. 
 
 K 
 
130 LYMPHATICS. LACTEALS. 
 
 According to some this end consists simply of a stopper of mucus, the cells 
 themselves being, therefore, open. Others regard the striated appearance as 
 indication cf the existence of tine perforations (Kolliker, Welcker), or of 
 a closely-packed bundle of rods filling up the orifice, and reminding one of 
 cilia (Funke, Brettauer and Steinach, Heidenhain, Lipsky), the interspaces 
 of which would therefore correspond to the perforations of the preceding 
 observers. Others, again, think that the ends are quite imperforate. A 
 theory propounded by Letzerich differs from all those just mentioned in 
 supposing the particles which have succeeded in reaching the lacteal vessels 
 to have traversed certain goblet-shaped structures, situated between the 
 epithelium cells, which anastomose below with the canalicular network. 
 These goblet-cells are thought by some (Eimer, F. E. Schultze) to be es- 
 sentially secretory in function. Others regard them as simply the results of 
 the method of treatment (Ddnitz, Lipsky, Erdmann, Sachs), or as meta- 
 morphosed epithelial cells (Armstein, Oeffinger, Heidenhain). The glandular 
 organs connected with the lymphatic and lacteal systems of vessels will be 
 described below. 
 
 Forces concerned in Absorption. 
 
 The physical forces which are able to bring about an absorp- 
 tion of fluids into the blood (excluding those concerned in the 
 absorption of gases, which are treated of in Chapter IV.), are, in 
 the cases where it occurs through closed capillary walls, nitra- 
 tion and diffusion. The former in all probability only acts ex- 
 ceptionally, as it appears to be quite abnormal for the pressure 
 without the vessels to exceed that of the blood within them. 
 
 Absorption into the lymphatic and lacteal vessels, the 
 nature of the commencement of which is, as has been said, yet 
 doubtful, is probably assisted by additional forces ; such as, for 
 instance, capillary attraction, in the case of open tubes. Fil- 
 tration also may play a more prominent part here, as the pres- 
 sure in the lymphatic vessels is considerably less than in the 
 blood-vessels (Noll). It is impossible to say what substances 
 are absorbed directly into the blood, and what through the 
 lymphatics. As, however, from the uncertainty shrouding the 
 lymphatic and lacteal systems, we are allowed to theorise more 
 freely with respect to the forces concerned in absorption, we 
 may suppose that substances which do not diffuse at all, or only 
 with great difficulty in short, whose absorption by the blood- 
 vessels is to all appearance difficult or impossible are taken 
 up by the lymphatics or the lacteals. To this class of bodies 
 belong especially solutions of albumin and fats, as well as finely 
 
ABSORPTION FROM THE ALIMENTARY CANAL. 131 
 
 divided solids (colouring matters). Water and true solutions 
 (including peptones) are most probably taken up by both 
 systems of vessels. The absorption of fats, also, does not 
 appear to be confined entirely to the lymphatics, as is indicated 
 by the greater amount of fat in the blood of the portal vein, 
 which receives the venous blood from the intestines, as compared 
 with what is found in the blood from other vessels (Chapter V.\ 
 
 An immigration of cellular structures into the blood-vessels, corre- 
 sponding- to their emigration described on p. 81, has been recently observed 
 (von Recklinghausen, Saviotti). If those cells should contain in their interior 
 finely divided colouring matters, fats, &c., a species of direct absorption of 
 undissolved substances would thus be accomplished. 
 
 In frogs whose hearts have been destroyed, fluids are still capable of 
 absorption from the lymph-sacs, so long as brain and spinal cord are intact 
 (Goltz). It seems as if absorption ceases in vessels whose tonus is com- 
 pletely destroyed, as soon as they have become filled ; while those, the 
 nerves of which are active, are able again and again to expel their contents, 
 thus permitting absorption to recommence (Bernstein, Heubel). 
 
 Seats of Absorption. 
 
 One of the chief seats of absorption, which must now be con- 
 sidered separately, is the alimentary canal. The constituents 
 of food are here partially taken up, after having undergone the 
 changes necessary to prepare them for absorption, viz. digestion. 
 At the same, time an absorption takes place of the various 
 alimentary secretions (mucus, saliva, gastric-juice, pancreatic- 
 juice, bile, intestinal juice), probably in a partially altered con- 
 dition, after they have performed their several functions : certain 
 of their constituents (mucin, the specific constituents of bile) 
 are however not absorbed, being passed out of the system in 
 the faeces. The changes brought about in digestion, which will 
 be more fully described below, consist in the conversion of 
 materials, such as starch, albuminous bodies and gelatin, which 
 are unfitted for absorption, into modifications which are easily 
 diffusible, viz. sugar, solutions of peptones and of gelatin. A 
 small portion also of the fat is converted into easily absorbable 
 soap (p. 106), the rest being emulsionized. Altogether, there- 
 fore, in the alimentary canal there are the following substances 
 which undergo absorption : 
 
 1. Water derived partly from the food and partly from the 
 alimentary secretions. 2. Soluble salts, also in part derived 
 
 K 2 
 
132 ABSORPTION FROM THE ALIMENTARY CANAL. 
 
 from the insoluble salts, or the free acids and bases, taken in 
 with the food. 3. Different kinds of sugar, all of which are 
 derived from the food, grape sugar being, in addition, present as 
 the result of the conversion of starch. 4. Other soluble consti- 
 tuents of food or of the alimentary secretions (pepsin, etc.). 
 5. Soaps formed from the fatty materials of the food. 6. 
 Soluble albumin and the alkali-albuminate formed during 
 digestion. 7. Peptones derived from the soluble and insoluble 
 albuminous constituents of food. 8. Solutions of gelatin 
 derived from the gelatin and gelatigenous elements of food. 
 9. Emulsionized fat (fat in fine globules) from food. Of the 
 above substances those included in the first eight classes would 
 appear, on account of their diffusibility, to be absorbed both by 
 blood-vessels and by lacteals. All the true solutions (those men- 
 tioned in classes 1-4) are probably chiefly absorbed by the blood- 
 vessels, or, perhaps, equally by them and the lacteals ; but the 
 remaining substances are for the most part taken up by the 
 latter. The absorption of fat, on the contrary, seems to be con- 
 fined almost entirely to the lacteals. 
 
 The way in which fat reaches the lacteals is, according to 
 the various views stated on p. 129, either through complete 
 canals (openings in the epithelium of the villi, communicating, 
 through the canalicular system of the connective tissue, with the 
 central lacteal of the villus, Heidenhain) ; or along paths which 
 the fat-globules find out for themselves. 
 
 In either case, the action of bile in facilitating the filtration 
 of fat (p. 106) is most important. The forces, however, which 
 bring about absorption are still doubtful ; the most probable is 
 that of filtration under the somewhat high pressure in the in- 
 testines, since the pressure in the lymphatic system is slight. 
 Contraction of the muscles of the villi can only force the 
 contents of the lacteals within the villi towards the larger 
 vessels of the system, rendering no assistance whatever in the 
 absorption of fat from the interior of the inte tine. This con- 
 traction is said to be facilitated by the action of the bile 
 (Schiff). 
 
 The absorption of fat by the lacteals is well shown by the white, milky 
 contents of those vessels after the ingestion of fatty foods ; and the favour- 
 able action of the bile in promoting it is proved by the diminution in the 
 contents which occurs if the admixture of bile be prevented by closure of the 
 ductus choledochus, or the formation of a biliary fistula. 
 
ABSORPTION FROM THE SKIN. 133 
 
 A second seat of absorption is the external skin, which, 
 although only exceptionally active, is so often spoken of in con- 
 nection with absorption that mention will be made of it here. 
 All substances absorbed at the skin must first pass through the 
 epidermis. The permeability of this structure appears to be 
 usually very slight ; but it may be much increased by various 
 means (warm baths, etc.). The power of absorption possessed 
 by the skin is proved by well-established facts. 
 
 The absorption of parenchymatous juices is still a matter of 
 which little is known. It would appear that, apart from the 
 absorption of those products of oxidation which are really 
 soluble, the unaltered, albuminous constituents of transudation- 
 fluids are constantly, or under certain circumstances, taken up 
 by the lymphatics, and the more quickly according to the 
 rapidity with which transudation takes place, i.e. according as 
 the pressure of the parenchymatous fluids in the tissues is greater. 
 Lymph, at least, will flow from an open lymphatic vessel the 
 more quickly according as transudation is increased either by 
 dilatation of the arteries proceeding to the part (by section 
 or paralysis of vaso-motor nerves), or by prevention of the escape 
 of blood (by ligature of the veins, or compression of them by 
 muscular contractions), (Ludwig, Schwanda). The lymphatics, 
 therefore, may possibly have to be regarded as regulators of 
 turgescence. The condition in which there is increased pressure 
 of the parenchymatous fluids, and which is remedied by in- 
 creased activity of the absorbents, is called oedema. We may 
 say that a system of drainage is continually in operation in 
 the tissues, in which fluids are poured out of the blood-vessels 
 by transudation, percolate the surrounding cellular tissues, and 
 finally flow away through the lymphatics. The commencements 
 of the lymphatic vessels are, as a rule, removed as far as possible 
 from the blood-vessels (von Eecklinghausen). Absorption from 
 parenchymatous tissue appears to be promoted by pressure such 
 as that exerted by the contraction of neighbouring muscles 
 (Grenersich). Increase of arterial blood-pressure has no influence 
 upon the formation of lymph (Paschutin). 
 
134 CHYLE AND LYMPH. 
 
 Destination of the absorbed Materials. 
 
 The substances absorbed directly into the blood at once 
 form part of the plasma, from which they are in part excreted, 
 and in part secreted, in other organs. 
 
 It remains now to follow in their course to the blood the 
 substances which are indirectly absorbed through the lacteals 
 and lymphatics. During this course they do not remain un- 
 altered. Their composition is materially modified after passage 
 through certain organs, the lymphatic glands, which form part 
 of the lymphatic and lacteal systems of vessels. They are 
 converted into a fluid which resembles in many respects the 
 blood into which it is about to be poured, and is, as it were, a 
 preparatory stage of it. As these organs are not only found in 
 the course of the larger lymphatic vessels (as ordinary lymphatic 
 glands), but also at the very commencement of the lymphatic 
 and lacteal systems (as the so-called follicles), it is not possible 
 to procure the original fluid as it exists immediately after ab- 
 sorption. The names chyle and lymph are, therefore, used to 
 denote the modified contents of the absorbent vessels, which 
 have already traversed glands. 
 
 The follicles, which have recently come to be regarded as the simplest 
 form of lymphatic gland, are found in great numbers at the commencement 
 of the lacteal and lymphatic vessels. Those connected with the former set 
 of vessels, the lacteals, are buried in the intestinal mucous membrane, either 
 singly (/ solitary glands,' in the whole intestine), or in numbers together 
 (' Peyer's patches,' ' agminated glands,' in the lower part of the small intes- 
 tine). Those connected with the lymphatics are discovered in various parts 
 of the body, especially in the mucous membranes of the mouth, the 
 pharynx (the tonsils, also, are simply collections of follicles), the stomach, 
 and the conjunctiva, in the lungs (described for a long time as small lymphatic 
 glands), the spleen (Malpighian bodies), and probably also in many other 
 situations. For a description of the intimate structure of the follicles and 
 lymphatic glands, the student must refer to the Manuals of Histology ; 
 but the following account seems to embody all that is essential in their 
 formation : Collides contain one, and lymphatic glands many, cavities 
 (alveoli, lymphatic spaces), bounded by a network of connective tissue, and 
 traversed by a delicate reticulum of fibres and blood-capillaries ; the meshes 
 of this reticulum are closely packed with colourless, round, nucleated cells 
 (lymph-cells). These cell-filled spaces appear to be nothing but an ex- 
 tended canalicular system of connective tissue, the ground-substance of 
 which has shrunk into the fine network or reticulum of fibres. Into these 
 
CHYLE AND LYMPH. 135 
 
 spaces open either the usual connective-tissue canaliculi, or, in the case of 
 lymphatic glands proper, the branches of the lymph-vessels proceeding to 
 them which surround the alveoli as fissures (lymph-sinuses) lined with 
 epithelium. From the alveoli pass out the efferent lymphatic vessels. All 
 fluids, therefore, traversing the lymphatic system of vessels must pass 
 through these alveoli and find their way between the cells, in which case 
 they are brought into a relationship with the blood in the capillaries 
 which is favourable to osmosis. 
 
 Lymph is a colourless or whitish-yellow fluid which is 
 separable under the microscope into a colourless plasma and cer- 
 tain nucleated contractile cells (lymph-corpuscles), fat-globules 
 and free nuclei suspended in it. Lymph-corpuscles resemble 
 very closely the cells contained in the alveoli of the follicles 
 and lymphatic glands, and, undoubtedly, for the most part, 
 originate from them. Before passing through the larger 
 lymphatic-glands, lymph contains very few of these corpuscles, 
 which it obtained from the follicles, or from the connective- 
 tissue canaliculi (p. 129) and probably also from the blood- 
 vessels (p. 81). They completely resemble the white corpuscles 
 of the blood. When removed from the living body, lymph 
 coagulates like blood, only more slowly, a lymph-clot being 
 formed while a lymph-serum is squeezed out by its contraction. 
 It therefore contains fibrin-formers, and generates the ferment 
 (p. 52), but not to the same extent as blood, hence the addi- 
 tion of blood hastens coagulation. The remaining constituents 
 of lymph are exactly similar to those of blood, with the ex- 
 ception of the colouring matter, which is wanting, viz. water, 
 salts, alkali-albuminate, protagon, fats, sugar, urea, extractives 
 and gases (almost entirely composed of carbonic acid, Hammar- 
 sten). Chyle is difficult to obtain pure, as it is constantly 
 mingled with lymph in the receptaculum chyli and thoracic duct. 
 It is distinguished from the latter fluid by the greater quantity 
 of fat it contains during digestion, which gives to the vessels 
 containing it a milk-white appearance. The fat forms single 
 or united globules, larger than those of lymph. It is, moreover, 
 taken up by the contractile lymph-corpuscles. 
 
 The motion of the lymphatic fluids towards the blood takes 
 place under a slight pressure (^Noll) and very slowly, chiefly on 
 account of the considerable resistance which the lymphatic 
 glands must offer. The forces which sustain this motion can 
 only be guessed at: they are probably: 1. Those forces which 
 
136 THE MOVEMENTS OF LYMPH. 
 
 bring about absorption of the contents into the initial branches 
 of the system, and which, as was explained previously, are yet 
 unknown : their effect must be to cause a gradual progression 
 of the lymph or chyle. 2. The contraction of the various 
 muscles surrounding the lymph-vessels, which, on account of 
 the numerous valves existing in those vessels, forces the lymph 
 towards the larger trunks, just as is the case in veins (p. 67). 
 3. The aspiration of the thorax (p. 66) ; for the openings of the 
 principal trunks, and the greater part of the thoracic duct 
 also, lie within the thoracic cavity. 
 
 In amphibia and certain birds (Ratitse), the movement of the lymph 
 is assisted by the rhythmical pulsation of lymph-hearts, of which four exist 
 in the frog, two in other amphibia, and one in the ostrich. The central 
 nervous organ connected with this rhythmical motion is said by some to 
 be in the spinal cord, and by others in the hearts themselves. In guinea- 
 pigs a rhythmical contraction has recently been observed (A. Heller) in 
 the lymphatics of the mesentery. As this proceeds along those portions of 
 the vessel between the valves with a regular progression towards the larger 
 trunks, it must be regarded as a species of cardiac mechanism. 
 
 When the lymph has reached the blood vessels it mingles 
 with the blood. What further use is made of it, and how it is 
 transformed, will be described in Chap. V. 
 
 Preparation of Food for Absorption. 
 
 Digestion. 
 
 In the alimentary canal, which stretches from the mouth 
 to the anus, the food, which has been taken into the body in 
 a solid or liquid form, is in part directly absorbed through the 
 walls, thus coming to mix with the juices of the tissues. The 
 greater portion, however, has first to undergo a certain mechanical 
 and chemical preparation. Those constituents of the food which 
 are incapable of absorption either directly or after having passed 
 through the various stages of digestion the indigestible consti- 
 tuents pass out of the body per anum, in company with certain 
 portions of the alimentary secretions, as faeces. 
 
 LIBRARY 
 
 UNIVERSITY OF 
 CALIFORNIA. 
 
THE CHEMISTRY OF DIGESTION. 137 
 
 I. THE CHEMISTRY OF DIGESTION. 
 
 The secretion and properties of the alimentary juices have been described 
 in the preceding chapter. 
 
 Water, the inorganic constituents of food, and, for the 
 most part, the soluble organic constituents also, undergo no 
 essential chemical alteration in the alimentary canal. If they 
 are already dissolved, or are soluble in the secretions of the 
 canal, they are absorbed unchanged whenever they reach the 
 situations where absorption is possible ; while, if they are in the 
 form of free acids and bases, they are firstly combined. Certain 
 substances upon which the alimentary juices are unable to act, 
 and which are insoluble, also remain unchanged : to this class 
 belong especially cellulose, and horny and elastic tissues. Such, 
 moreover, is the fate of that portion of the soluble substances 
 which escapes solution owing to the superabundance of the 
 quantity ingested or to the closeness of texture of the body. 
 All such materials disappear from the body per anum, 
 together with certain portions of the digestive juices. The air 
 which happens to be swallowed with the food yields up its oxygen 
 in the alimentary canal and receives in its place carbonic acid 
 (Chap. IV.) ; hence, in the large intestine, it is chiefly nitrogen 
 and carbonic acid which are found. The essential chemical 
 changes of digestion chiefly concern certain insoluble, or dis- 
 solved but hardly diffusible, organic bodies, which rank 
 among the most important elements of food ; viz. carbohydrates 
 (especially starch); albumins (albumen, fibrin, the substance 
 of muscle, casein, etc.), both soluble and insoluble modifications; 
 gelatin ; and fats. These substances must be converted into 
 some form which admits of absorption. 
 
 Herbivores appear to possess some arrangement for the digestion of 
 cellulose, probably for its conversion into sugar. We are led to the supposi- 
 tion of a digestion of cellulose in such cases by a consideration of the large 
 amount of it contained in vegetable foods, and the almost complete absence 
 of it from other nutrient substances which seem nearly incapable of support- 
 ing life in those animals. In man, also, it has recently been observed that the 
 cellulose taken into the body along with food cannot be completely re- 
 covered from the faeces (Henneberg and Stohmann, Weiske). It is not 
 known which secretion acts upon it. The cuticular substances, also, which 
 
138 THE CHEMISTRY OF DIGESTION, 
 
 are said to contribute to the building up of hippuric acid, must undergo diges- 
 tion in the alimentary canal of herbivores, while to carnivores they are 
 indigestible. 
 
 In the cavity of the mouth food is saturated with the 
 alkaline fluid resulting from the mixture of saliva from the 
 parotid, submaxillary and sublingual glands with mucus from 
 the mouth. This saturation affords opportunity (1) for the 
 solution of soluble, but as yet undissolved, portions of food (e.g. 
 salts, sugar), and (2) for the conversion of the starch contained in 
 the food into dextrin and grape-sugar. This conversion begins 
 while the food is yet in the mouth and is continued in the 
 stomach if the quantity of acid there is not sufficient to retard it 
 (p. 94). 
 
 In the stomach the following operations take place : (1) An 
 intimate mingling of all portions of the food with one another 
 and with the secretion of the gastric glands, viz. mucus and 
 gastric juice. As the latter has an acid reaction the previously 
 alkaline mixture becomes for the most part neutralized or 
 acidified. Many constituents of it, which were before un- 
 dissolved, undergo solution in the stomach, especially such salts 
 as are only soluble in the presence of an acid, as, for instance, 
 the carbonates and phosphates of the alkaline earths. (2.) The 
 conversion of starch-mucilage into sugar by means of the 
 swallowed saliva, which continues as long as the acid reaction 
 
 I is not too strong. (3.) The modification of albuminous bodies, 
 which is the chief change effected in the stomach. Fibrin, and 
 the substance of muscle, reach the stomach almost always in an 
 insoluble form ; albumin is sometimes soluble and sometimes 
 insoluble (e.g. boiled white of egg), as also is casein which is dis- 
 solved in milk, and undissolved in cheese. Dissolved casein 
 is, however, precipitated by the gastric juice immediately on 
 its entrance into the stomach. As a rule, therefore, both 
 soluble and insoluble modifications of albumin are submitted to 
 the action of the gastric juice. Under the influence of the acid 
 of the gastric juice undissolved albumins swell up in the 
 stomach, and thereupon become dissolved by means of the 
 pepsin and converted for the most part into peptones (p. 31 ). 
 Soluble and insoluble albuminous substances are equally well 
 digested (Fick). Grelatin, also, and gelatigenous tissues (con- 
 nective tissue, the stroma of bone) are converted in the stomach 
 
THE CHEMISTRY OF DIGESTION. 139 
 
 into an ungelatinizable solution. It is not certain whether the 
 time during which food remains in the stomach is sufficient 
 for the completion of the above-mentioned changes ; but, after a 
 liberal allowance of food has been taken, quantities of un- I 
 altered starch and undissolved albuminous substances pass into / 
 the intestine. The contents of the stomach after passing into j 
 the intestine form a pulp, for the most part acid, which is ' 
 called chyme. 
 
 Natural digestion in the stomach has been observed, in man, through 
 gastric fistulae which have been the result of accident (Beaumont, Bidder 
 and Schmidt), and, in- the lower animals, through fistulse which have been 
 made artificially. Observations have also been made upon food which had 
 been enclosed in network bags and swallowed, and, after having remained in 
 the stomach for a certain time, withdrawn by means of an attached string. 
 From experiments with natural or artificial gastric juice at the tempferature 
 of the body (artificial digestion), many confirmations of the processes which 
 go on in the stomach have been obtained. 
 
 In the intestine the acid chyme comeg into contact with 
 secretions which are entirely alkaline, viz. with bile and pan- \ 
 creatic juice in the duodenum, and with intestinal juice in the 
 whole intestine. This must bring about, in the first place, a 
 change in the reaction, which occurs earlier in those portions 
 of the contents of the intestine touching the walls than in 
 those which are nearer the centre. Towards the middle of the 
 small intestine the change is complete, and the reaction is, 
 therefore, at that point alkaline. Although the properties of 
 each of the alimentary secretions are separately known (as was 
 seen in the preceding chapter), little has been discovered con- 
 cerning their action when mixed together in their normal con- 
 dition. It has been shown that intestinal digestion, so far as 
 it concerns the chemical changes of the contents of the intes-/ 
 tines, and not their absorption, produces the same effect on the 
 yet unaltered starch and undissolved albuminous and gelatinous 
 portions of the chyme as digestion in the preceding parts of 
 the alimentary canal. The starch, therefore, is converted into 
 sugar, and the albuminous substances and gelatin into soluble 
 peptones. It is also known that the fats, which have hitherto 
 remained unaltered, are here prepared for absorption. The 
 formation of sugar out of starch must be ascribed to the pan- 
 creatic juice, as the saliva from the mouth can no longer with 
 
140 THE CHEMISTRY OF DIGESTION. 
 
 certainty be shown to be present. Solution of the albuminous 
 bodies is effected most probably by the pancreatic and intes- 
 tinal juices, as the activity of the gastric juice which reaches 
 the intestine is destroyed by the bile (p. 99). Peptones are 
 in part further decomposed in the intestine (p. 107), for which 
 purpose their precipitation by the bile (p. 105) appears to be of 
 importance, as they would be otherwise too quickly absorbed. 
 As the result of this further decomposition leucine and tyrosine 
 are formed, and, since they cannot be discovered in the faeces, 
 are probably soon afterwards absorbed. Other products of the 
 decomposition help to form the faeces. Finally, fats are con- 
 verted into a very fine emulsion by the pancreatic juice (and 
 probably also by bile and intestinal juice), in which form they 
 are fitted for absorption. A portion of the fats* is decomposed 
 by the pancreatic juice into fatty acids and glycerin, which are 
 also soluble and capable of absorption. The last-named effect 
 of pancreatic juice does not appear to occur until the contents 
 of the intestine have assumed an alkaline reaction, i.e. until 
 the lower half of the small intestine has been reached. The 
 fatty acids resulting from the decomposition combine with 
 alkalies to form soaps, which, in their turn, aid in the emulsioniza- 
 tion of the remaining portion of the fats (Briicke). 
 
 Besides the above decompositions, which are of the highest importance 
 for absorption, others occur which are of no moment apparently in the 
 promotion of that process. Thus, cane-sugar, when taken into the body, is 
 converted into grape-sugar owing (according to Paschutin) to a peculiar fer- 
 ment of the intestinal juice. Grape-sugar, both when taken as food and 
 when formed in the course of digestion, as well as milk-sugar, are in part 
 changed into lactic acid prior to absorption, this change taking place while 
 they are yet in the stomach. Alcoholic and butyric acid fermentations also 
 occur, but probably only under abnormal conditions. The gases which are 
 yielded in these fermentations are principally carbonic acid and hydrogen, 
 but sometimes also light carburetted hydrogen (marsh gas). The intestinal 
 gases, therefore, consist chiefly of carbonic acid, nitrogen and hydrogen 
 (Chapter IV.). Salts of the organic acids, moreover, are said to become 
 entirely or in part converted into, carbonates while yet in the intestine 
 (Magawly). The fatty acids resulting from the decomposition of fats are 
 further split up, yielding gases and volatile products, which, together with 
 the ill-odoured bodies formed during pancreatic digestion (p. 107), endow 
 the otherwise almost odourless contents of the small intestine with their 
 characteristic faecal smell. The conjugate bile-acids undergo a hydrolytic 
 decomposition in the small intestine, probably under the influence of the 
 
THE CHEMISTRY OF DIGESTION. 141 
 
 pancreatic juice ; glycocine or taurine, as ^the case may be, and cholic acid, 
 are the products, and the latter passes into the faeces partly in the form of its 
 anhydrides, choloidic acid and dyslysin. 
 
 In consequence of the chemical changes which have just 
 been described, and of the succeeding absorption of fats and all 
 those constituents which were soluble or had been rendered 
 soluble, the contents of the small intestine become considerably 
 altered in composition as they pass along the alimentary 
 canal. Starch and the insoluble albuminous bodies which were 
 still present at the commencement of the intestine gradually 
 disappear, and instead of them we meet with sugar, lactic acid, 
 peptones, leucine and tyrosine. The larger globules and 
 masses of fat, also, which at first were mingled with the other sub- 
 stances, are no longer found, having formed an emulsion. The 
 colour is yellow or yellowish brown, owing to the admixture of 
 biliary colouring matters. Finally, all the dissolved dif- 
 fusible matters and fats disappear entirely from the mass, and 
 the amount of water present becomes continually less and less, 
 until at the extremity of the small intestine nothing is found 
 but the constituents of the faeces already possessing the 
 characteristic odour on account of the above-mentioned decom- 
 positions and fermentations. 
 
 In the large intestine the digestive processes (i.e. the 
 preparation for absorption) become less and less apparent. No 
 new secretions are added, except the intestinal juice, which is 
 formed here also, and absorption is restricted to water, the 
 result being a concentration of the contents. The latter, con- 
 sisting of faeces and gases, have already been described. 
 
 The faeces often exhibit an acid reaction, which is due to the presence of 
 free fatty acids. The amount of the faeces as compared with the amount of 
 the food taken depends, of course, upon the quantity of indigestible materials 
 contained in the latter. 
 
 The chemical processes of digestion have throughout the 
 character of hydrolytic decompositions (Hermann), as a com- 
 parison of the results of digestion with the bodies submitted 
 to that process will show. These decompositions not only 
 appear to be favourable to absorption, inasmuch as their pro- 
 ducts are for the most part more diffusible than the original 
 substances ; but they seem to have far more important func- 
 
142 THE MECHANISM OF DIGESTION. 
 
 tions in ' assimilation ' or the construction of the constituent 
 parts of the body out of the nutritive materials. (Concerning 
 this matter consult Chapters V. and VI.) 
 
 II. THE MECHANISM OF THE DIGESTIVE 
 APPARATUS. 
 
 The mechanical operations of the digestive apparatus com- 
 prehend : 1. The introduction of the food into the mouth, its 
 propulsion along the alimentary canal, and the evacuation of 
 the faeces. 2. The mechanical preparation for absorption, viz. 
 the breaking-down of solid foods and their intimate mixture 
 with the various fluids destined to effect their chemical prepara- 
 tion (mastication, insalivation, etc.). These processes go on side 
 by side. 
 
 The introduction of food is accomplished, in the case of 
 fluid substances, by a combination of the acts of pouring into 
 the mouth and sucking up by means of it (drinking) ; and in 
 the case of solid substances by placing small pieces behind the 
 lips and teeth, or by cutting or biting off small pieces from a 
 larger piece by means of the incisors. 
 
 Mastication, or the breaking down of the firmer portions, 
 begins immediately after the introduction of a piece of solid 
 food into the mouth. It commences with a division of the 
 food, by means of the knife-like incisor teeth, into small pieces, 
 which are thereafter ground down between the irregular sur- 
 faces of the molar teeth at the back of the mouth. The opera- 
 tion of cutting is effected by an up and down movement of the 
 lower jaw, i.e. by a rotation of it about a horizontal axis passing 
 through its two articulations. The upward movement is pro- 
 duced by the masseter, temporal and internal pterygoid mus- 
 cles, and the downward movement by the weight of the lower 
 jaw, and by the action of the digastric, mylo-hyoid and genio- 
 hyoid muscles, the hyoid bone being kept firm by the omo-hyoid, 
 sterno-hyoid, thyro-hyoid, and sterno-thyroid muscles. The 
 grinding is produced by a motion of the articular heads of 
 the inferior maxillary bone in their sockets in such a manner 
 that the lower jaw is displaced with respect to the upper jaw 
 in an anterior, posterior and lateral direction. This is accom- 
 plished in particular by the two pterygoid muscles. The morsels 
 
SWALLOWING. 143 
 
 of food are continually pushed between the teeth by the 
 muscles of the cheeks and lips, especially by the buccinator on 
 the outside, and by the tongue within. The latter, moreover, 
 has the power of crushing down softer portions of food by pres- 
 sing and rubbing them against the hard palate. During 
 digestion the food is intimately mixed with the fluids of the 
 mouth (saliva and mucus) and forms a plastic pulp. 
 
 The nerves which control these actions are, for the proper masticatory 
 muscles, the inferior maxillary branch of the trigeminal (particularly its 
 superior division) and for the tongue and a portion of the abductors of the 
 lower jaw, the hypoglossal. The centre for the co-ordinated masticatory 
 movements is situated in the medulla obloagata (Schroder van der Kolk). 
 In many animals the action of the saliva, and, in part also, the breaking down 
 of the food, are continued in certain apparatus connected with the stomach ; 
 as, for example, in the first three stomachs of ruminants (rumen, reticulurn, 
 and psalterium), from the first two of which the imperfectly masticated 
 food passes into the mouth before being transferred to the third ; in the 
 crop and gizzard of many birds ; in the masticatory stomach of beetles j in 
 the toothed stomach of crabs ; &c. 
 
 The propulsion of solids and fluids along the alimentary 
 canal is effected by the contraction of the circular and longitu- 
 dinal muscles of its walls, which takes place in such a manner 
 that the diminution or closure of the lumen of the canal drives 
 the contents before it in a direction from the mouth to the 
 anus. These propulsive contractions are called peristaltic 
 movements ; or, when occurring in the first portion of the 
 alimentary canal from the mouth to the oesophagus in which 
 case they are effected by voluntary muscles swallowing. In the 
 act of swallowing two stages are distinguished : 1. The bolus 
 of food situated on the anterior part of the tongue, which forms 
 a groove with concavity upward, is pushed along towards the 
 anterior arch of the fauces by the progressive application of the 
 tongue to the hard palate from before backwards. 2. a. The 
 anterior pillars of the fauces close-to by the contraction of the 
 palato-glossal muscles, and, at the same time, the root of the 
 tongue approaches the velum palati. 6. The posterior pillars 
 of the fauces, also, with the aid of the uvula, close-to and block 
 up the passage between them, and the whole velum is then 
 drawn upwards and backwards and apposed to the posterior wall 
 of the pharynx by means of the pharyngo-palati and the levator 
 and circumflexus palati. c. The hyoid bone and the larynx 
 
144 SWALLOWING. 
 
 are approximated by the action of the thyro-hyoidei, and drawn 
 strongly forwards and upwards by the genio-hyoidei, mylo- 
 hyoidei, and the anterior bellies of the digastric muscles, the 
 lower jaw, which is kept apposed to the upper by the muscles of 
 mastication, being the fixed point. By this means the root of 
 the tongue is bent backwards and pressed, together with the 
 epiglottis, upon the opening of the larynx. By the actions given 
 under a, a return of the food into the cavity of the mouth is 
 prevented, by those under 6, its passage into the pharyngeal 
 cavity and the nose, and by those under c, its passage into the 
 larynx. The morsel, therefore, propelled by the progressive 
 contraction of the constrictors of the pharynx and the stylo- 
 and salpingo-pharyngei, has no way left for it except into the 
 oesophagus. While in the neighbourhood of the tonsils, which 
 are rich in mucous glands, it becomes slimed over with mucus, 
 and its further movement is thereby facilitated. 
 
 Even in the absence of the epiglottis, the closure of the opening into the 
 larynx can be effected, but less securely, by the root of the tongue. The 
 recess or pouch between the root of the tongue and the epiglottis is so com- 
 pletely closed during the act of swallowing, that no portion of the fluids 
 swallowed is able to enter it, as may be proved by the absence from it of any 
 colouration after coloured liquids have been drunk. 
 
 The tongue as a whole is drawn downwards and somewhat forwards by 
 the genio-glossal, downwards and backwards by the hyo-glossal, and up wards 
 and backwards by the palato-glossal and stylo-glossal, muscles. All these 
 muscles, as well as the lingualis, traverse the substance of the tongue in a 
 vertical, transverse, or longitudinal direction. By their contraction in 
 various combinations, the tongue is able to assume the most diverse 
 forms; thus, flattening is produced by contraction of the vertical fibres; ex- 
 tension and thickening by contraction of the vertical and transverse fibres ; 
 shortening by con ti action of the longitudinal fibres; channelling of the 
 upper surface by contraction of the transverse and the inner set of the 
 vertical fibres ; arching of the upper surface by contraction of the inferior 
 transverse fibres ; lateral flexion of the tip by contraction of the longitu- 
 dinal fibres of one side ; &c. 
 
 In the oesophagus the morsel of food, well covered and 
 rendered slimy by mucus, is driven downwards into the stomach, 
 partly by its own weight, but chiefly by the peristaltic move- 
 ments of the walls, which are occasioned in the lower two-thirds 
 by the contraction of unstriped muscular fibres only. 
 
 In the stomach the larger portions of food remain for a 
 longer time. The movements which take place there are not as 
 
MOVEMENT OF INTESTINAL CONTENTS. 145 
 
 yet well understood. This much may however be said : on the 
 one hand the various parts of the contents of the viscus must be 
 kneaded together and intermixed, and the internal portions 
 thus made to come into contact with its walls ; and, on the 
 other, the food must be driven along the stomach and finally 
 through the pylorus. The latter result is effected by the peri- 
 stalsis, which occurs in every part of the alimentary canal. 
 How these two varieties of movement are produced, and how 
 they change one into the other, is almost unknown. In all 
 probability the gastric walls are usually contracted closely upon 
 their contents. The muscular fibres, which are present in 
 greater numbers around the cardia and pylorus, ordinarily 
 keep those orifices closed. The constant closure of the former 
 has, however, been recently disputed (Griannuzzi). The closure 
 of the pylorus is firmest at the commencement of digestion, 
 relaxing gradually as it proceeds, so as to allow the passage into 
 the intestine, first of fluids, then of chyme-pulp, and finally even 
 of solid material. The stomach, in course of becoming filled, 
 rotates about a horizontal axis passing through the cardiac and 
 pyloric openings, in such a manner that the great curvature, 
 which usually hangs down, is turned forwards. This is not pro- 
 duced by any muscular action, but is a purely mechanical effect. 
 Gases, which are swallowed with the food or are evolved in the 
 stomach, pass out for the most part through the cardiac opening, 
 which lies highest. The movements of the stomach are said to 
 cease during sleep (Busch). 
 
 Peristaltie movement is most marked in the small intestine. 
 It is associated with a varying disposition of the coils of the 
 whole intestine, except the closely confined duodenum, and is 
 constantly directed towards the anus. It gradually propels the 
 somewhat fluid contents, as well as the enclosed gases, until they 
 pass into the caecum. Movement in an opposite direction is 
 hindered by the valvular folds of the intestinal mucous mem- 
 brane, and a return into the small intestine from the caecum 
 (the special object of which is unknown) is prevented by the 
 ileo-csecai valve, a fold of the intestinal wall. 
 
 In the large intestine peristalsis takes place very slowly, the 
 contents being therefore able to remain in the sinus-like dilata- 
 tions of the colon for a longer time. After continuing there/ 
 until, by the loss of their fluid constituents, they have assumed 
 
 L 
 
146 LIBERATION OF INTESTINAL MOVEMENTS. 
 
 the characters of faeces, the contents reach the sigmoid flexure, 
 and finally the rectum. 
 
 Evacuation of the faeces from the rectum takes place, as a 
 rule, at intervals of twenty-four hours. Besides the peristaltic 
 movement of the intestinal tube, the pressure of the abdominal 
 muscles plays an important part in the operation, not indeed 
 by acting directly upon the rectum, which lies secure in the 
 bony pelvis, but probably by forcing the faeces from the upper 
 parts of the canal. (The mechanism of this pressure of the 
 abdominal muscles will be discussed in Chap. IV.) The 
 sphincters of the rectum are, as a rule, closed. Their contrac- 
 tion, and, when that is removed, their elasticity, is overcome by 
 the pressure of the faeces driven downwards by the forces 
 above mentioned. The levator ani prevents the protrusion of 
 the rectum, and, by shortening it, facilitates the liberation of 
 the contained mass of faeces. 
 
 Liberation of the Movements of the Digestive Apparatus. 
 
 The propulsive movements of the alimentary canal are oc- 
 casioned only by the stimulus of its contents. They appear 
 therefore to be induced in a reflex manner. The movements 
 of swallowing, for example, only occur but then always when 
 a foreign body is placed behind the soft palate. They take 
 place, therefore, whenever the posterior surface of the velum 
 palati, the epiglottis, &c. are touched. Hence the simple act 
 of swallowing can only be voluntarily performed, in the absence 
 of other stimuli, by bringing some saliva behind the soft palate ; 
 and this explains why it is only possible ' to swallow nothing ' a 
 few times in succession, viz. only as long as there is any saliva 
 in the mouth. 
 
 The nervous centres for the striated muscles concerned in 
 the movements of the upper part of the alimentary canal lie 
 in the medulla oblongata, and in man, in the olivary bodies 
 (Schroder v. d. Kolk). The nerves thence proceeding which 
 regulate the act of swallowing are : the facialis for the lips ; the 
 nerves of mastication (see above) for the jaws ; the hypoglossal 
 nerve for the tongue ; and the plexus pharyngeus (formed from 
 the glosso-pharyngeal, vagus-accessorius and sympathetic 
 nerves) for the pharynx. The tensor palati and the mylo- 
 
LIBERATION OF INTESTINAL MOVEMENTS. 147 
 
 hyoideus are provided for, in addition, by the trigeminal 
 nerve. The sensory fibres, irritation of which induces swallow- 
 ing, lie in the palatal branch of the trigeminal nerve (Schroder v. 
 d. Kolk). The peristaltic movements of the remaining portions 
 of the canal probably have their central organs in the ganglia 
 of the walls, some of which are known to exist, while the 
 rest must be assumed (Eemak, Meissner, Manz, Billroth, 
 Auerbach, Krause). The presence of ganglia explains the 
 movements of excised portions of intestine. Direct stimulation 
 brings about local contraction which sometimes, but by no 
 means constantly, continues as peristalsis. All parts of the intes- 
 tine are, however, provided with extrinsic nerves, derived espe- 
 cially from the vagus ^plexus oesophageus, rami gastrici) and from 
 the sympathetic (splanchnics, cosliac, mesenteric and hypogastric 
 plexuses). These are undoubtedly in part concerned in the 
 movements. All that has as yet been clearly demonstrated, 
 however, is (1) that irritation of the vagus is able to produce 
 contractions of the oesophagus and stomach ; (2) that section 
 of the vagi prejudices to an important extent the passage of 
 food out of the stomach ; and (3) that irritation of the splanch- 
 nics inhibits the peristaltic movements of the small intestine 
 (Pfliiger) ; the latter may therefore be included among the 
 class of ' inhibitory ' nerves (Chap. X). In the evacuation of 
 feces the nerves of the expiratory muscles, as well as of the 
 levatores ani and other muscles, are also concerned. 
 
 The movements of swallowing can also be induced by stimulation of the 
 larynx ; as also on irritation of the superior laryngeal nerve (Waller and 
 Prevost). 
 
 In the frog the movements of the throat and stomach become very 
 active after section of the vagi, or destruction of the cerebro-spinal organs ; 
 it has therefore been supposed (Goltz) that the vagi exert an inhibitory 
 influence upon them. 
 
 The movements of the intestine cease in warm-blooded animals if the 
 temperature sink below 19 0. : they become more active as the tempera- 
 ture increases ; interruption of the flow of blood to the organ stops them 
 (Horwath). As in the ureter, the transmission of peristalsis in the intestine.8 
 is considered to be due to direct muscular conduction (Engelmann and van 
 Brakel). The circumstance of transmission taking place in one direction only 
 is, however, opposed to this. 
 
 The movements of the intestine are stopped by saturating the blood with 
 oxygen, and increased during suffocation. They are, for this reason, probably 
 very active immediately after death. It would seem that the stimulus leading 
 
 L 2 
 
148 VOMITING. 
 
 to the liberation of the intestinal movements, analogous to that causing the 
 movements of respiration, is dependent upon the venous state of the blood 
 in the intestinal vessels (S. Mayer and von Basch). 
 
 The splanchnics are, at the same time, the vaso-motor nerves of the 
 intestine; irritation of them, therefore, occasions a diminution in the 
 amount of blood flowing to the viscera. This may possibly explain the in- 
 hibition of peristalsis, which it also produces. For the rest, if the intestinal 
 vessels are emptied, e.g. by compressing the aorta, increased movement 
 results, which ceases on again injecting the vessels with some fluid (O. 
 Nasse). After death, or, more exactly, at a time when the vessels are 
 paralysed, and the capillaries contain venous blood (Mayer and von Basch), 
 irritation of the splanchnics and irritation of the vagi both produce intes- 
 tinal movements. The effects of irritation of vagi are contested, or ascribed 
 to the contraction of the stomach, which drives the contents into the intes- 
 tine (van Braam, Houckgeest). 
 
 The occurrence of anti-peristaltic movements of the intestine, although 
 frequently maintained, is not yet proved. Vomiting, i.e. the evacuation of 
 the contents of the stomach through the mouth, consists, not in an active 
 contraction of the stomach, but in the compression of it by the contraction 
 of the diaphragm and the abdominal muscles (Magendie). This is shown 
 by the fact that vomiting is still possible after the substitution of a bladder 
 in place of the stomach (Magendie). It is, however, necessary for the 
 success of this experiment to remove the cardia and the lowest portion of 
 the oesophagus along with the stomach (Fantini, Schiff). Vomiting, more- 
 over, can no longer take place after poisoning by curare, which paralyses 
 voluntary motion, while it leaves intact the nerves going to the stomach 
 (Giannuzzi). Active movements of the stomach, consisting especially of 
 an active opening of the cardiac orifice (Schiff), may be observed in an 
 exposed stomach during the then unsuccessful attempts at vomiting. This 
 opening of the cardiac orifice is necessary before vomiting can occur. The 
 central nervous organ for the act of vomiting is closely allied to the respi- 
 ratory centre. Emetics prevent the occurrence of apnoea (Chap. IV.) ; and 
 strong artificial respiration prevents vomiting. It would seem, therefore, 
 as if emetics had the power of strongly irritating the respiratory centre 
 (Grimm). This irritation also results, from an action of centripetal nerves, on 
 injection of the emetic into the blood (Kleimann and Simonowitsch). 
 
 Purgatives act, according to some (Moreau), by increasing the secretion 
 of the fluids of the intestine, and according to others (Thiry, Kadziejewski) 
 by quickening the peristaltic movements. Saline purgatives, the activity of 
 which depends upon their endosmotic equivalent (Buchheim), and which 
 when injected into the blood-vessels produce costiveness (Aubert), act 
 chiefly by causing the retention of water in the intestine (Buchheim). 
 
149 
 
 CHAPTER IV. 
 
 GASEOUS INTERCHANGES (INCOME AND EXPENDITURE) OF THE BLOOD. 
 
 Respiration. 
 
 BY the term Respiration we designate those chemical processes 
 of the animal body which are concerned in the distribution of 
 gaseous substances, i.e., essentially those concerned in supplying 
 oxygen to the constituents of the body, and in separating the 
 gaseous product of oxidation carbonic acid. 
 
 This process, like all others connected with the interchange of 
 matter between the animal body and the outer world, is carried 
 on through the agency of the blood. This fluid comes into 
 contact, on the one hand, with the medium in which the animal 
 lives (atmospheric air or water), abstracting from it oxygen and 
 giving up to it carbonic acid (external respiration ) ; on the 
 other hand, with the animal tissues, to which it furnishes 
 oxygen and from which it abstracts carbonic acid (internal res- 
 piration). External respiration, which is briefly denominated 
 Respiration, takes place wherever the blood comes into suf- 
 ficiently close contact with the respiratory medium, but chiefly 
 in the organs specially devoted to the gaseous interchanges, and 
 which are denominated The Organs of Respiration. 
 
 Atmospheric air is a mixture composed of about one-fifth (0-208) by 
 volume of oxygen, and four-fifths (0-792) by volume of nitrogen, together 
 with a very small and fluctuating quantity (from 0*0003 to 0'0005 by volume) 
 of carbonic acid, and a similarly fluctuating quantity of aqueous vapour, the 
 maximum amount of which depends upon the temperature. This mixture, 
 at the level of the sea, is under a pressure of about 760 millimetres of mercury. 
 
 The water, which serves as the respiratory medium for many organisms, 
 contains in solution, besides some nitrogen and carbonic acid, oxygen, which 
 at a temperature of 15 C. and 760 millimetres pressure, amounts, at the 
 most, to one-twelfth (0'084) part of its volume. Corresponding to this 
 small amount of oxygen, animals living in water require proportionally little 
 of that element. 
 
150 CHEMISTRY OF RESPIRATION. 
 
 I. CHEMISTRY OF KESPIRATION. 
 
 External Respiration. 
 
 Kespiration, properly so called, which consists in the in- 
 terchange which takes place between the gases of the blood and 
 those of atmospheric air, has its seat wherever the blood- 
 capillaries are in intimate contact with the latter medium. 
 This occurs especially at the external surfaces of the ' Organs 
 of Kespiration,' which will be discussed below, and, in addition, 
 at the skin and in the alimentary canal which always contains 
 air, though in both these cases the process goes on with feeble 
 intensity. 
 
 In some animals, however, e.g. in frogs, cutaneous respira- 
 tion (perspiration) is of such importance that, after the lungs 
 have been removed, it suffices by itself to supply the small 
 quantity of oxygen which the animal requires. 
 
 Intestinal respiration, in consequence of the slight supply of 
 gas, is insignificant in man ; still all the oxygen contained in 
 the alimentary canal is consumed and replaced by carbonic acid, 
 so that in the large intestine carbonic acid and nitrogen are the 
 principal gases. 
 
 In many animals (e.g. in an air-swallowing fish, cobitis fossilis), intestinal 
 respiration appears to be important. 
 
 Cutaneous respiration was formerly supposed to be of great importance, 
 even in the case of warm-blooded animals, as its suspension, brought about 
 by varnishing the shaven skin, causes a rapid fall of temperature and death 
 (Bernard). According to recent researches (Rosenthal and Laschkewitsch), 
 there always occurs in such cases a dilatation of vessels over the varnished 
 area, which, when it extends to the whole body, occasions such a loss of 
 heat as to prove fatal. This paralysis of vessels, according to others, 
 likewise occurs in internal organs, the morbid processes in which (as in the 
 kidneys and spinal cord) play a part in inducing the symptoms (Feinberg, 
 Socoloff). 
 
 Further, there are some who attribute the injurious consequences of 
 varnishing the skin to the retention in the body of a deleterious excremen- 
 titious substance (' perspirabile retentum ') ; this appears to consist of a 
 volatile nitrogenous compound. From portions of the skin which have been 
 left uncovered by the varnish, an elimination of a volatile alkali (ammonia ?) 
 may be discovered by means of haematoxylon paper. Subsequently an 
 inflammatory oedema occurs in the portions of skin which have been long 
 kept covered with varnish, and in the serum, crystals of phosphate of mag- 
 
EXTERNAL RESPIRATION. 151 
 
 cesium and ammonium can be found (Edenbuizen) ; possibly tbe retained 
 substance is urea, which is decomposed and generates ammonia (Lang). 
 
 External respiration consists in a passage of oxygen from 
 the air into the blood, and of carbonic acid, aqueous vapour 
 and heat from the blood into the air. Eespired air, there- 
 fore, leaves the body poorer in oxygen, but hotter and richer 
 in carbonic acid and water, being almost saturated with the 
 vapour of the latter. Corresponding to the changes in the air, 
 the blood which leaves the lungs, in the. pulmonary veins, is 
 richer in oxygen, cooler (?), and poorer in carbonic acid and 
 water, than the blood of the pulmonary artery. It is, conse- 
 quently, of a more florid (arterial) colour. Only a small portion 
 however of the loss of heat and of water which takes place is 
 suffered by the blood in the lungs, as all parts of the respiratory 
 passages give up heat and aqueous vapour to the inspired air. 
 
 Traces of ammonia are also excreted in the process of respiration (Thiry), 
 but apparently in pulmonary respiration only (Schenk), so that the am- 
 moniacal compounds which are observed when the skin has been varnished 
 would appear to be abnormal products. 
 
 In spite of the loss of heat which the blood must undergo in the lungs, 
 the blood of the left side of the heart, according to recent observations 
 (Colin, Jacobson, and Bernhardt), is not cooler, but warmer than that of the 
 right ; possibly because a production of heat takes place in the lungs, owing 
 to its combining with oxygen (Colin). This statement is denied by others 
 (Heidenhain and Korner). (Consult Chap. VII.) 
 
 The cause of external respiration is, in great part, if not 
 entirely, the difference between the tension of the gases in the 
 blood and in the external atmosphere, respiration consisting 
 in the equalization of those tensions. 
 
 The tension of the oxygen in venous blood, i.e. in blood which 
 is to be subjected to the respiratory process, is smaller than 
 the tension of the oxygen in the atmosphere, while the tension 
 of the carbonic acid in the former is, on the other hand, greater 
 than that in the latter, This is true not only of pure atmo- 
 spheric air, but also of the air which is contained in the pul- 
 monary alveoli, and which is much poorer in oxygen and richer 
 in carbonic acid. In virtue of the very low tension of the 
 oxygen of its blood, an animal placed in a confined space can 
 consume almost the whole of the oxygen which it contains, 
 whilst the evolution of carbonic is very soon stopped by an 
 equalization of the tensions taking place (Wilh.^iiller). 
 
 'UNIVERSITY 
 
152 EXTERNAL RESPIRATION. 
 
 To determine the tensions of the gases of any specimen of blood, it must 
 be agitated with a limited volume of the gases ; the tensions of the com- 
 ponents of the latter after agitation (ascertained by determining the compo- 
 sition and the total pressure), are a direct measure of the tension of the 
 gases of the blood (Ludwig). 
 
 Strictly, such an experiment merely teaches the tension of the gases in 
 the blood after agitation. Hence the result is more correct, the smaller the 
 difference in the gaseous tension of the blood before and after agitation, 
 i.e, when the quantity of blood experimented upon is relatively large, the 
 volume of the gases used small, and when the tension of those gases repre- 
 sents closely the previous gaseous tension of the blood under investigation. 
 In order to obtain the most correct results, the blood is simultaneously but 
 separately agitated with two volumes of gas, of which the one possesses a 
 somewhat higher, and the other a somewhat lower tension than the gases 
 of the blood subjected to investigation ; the true gas-tension of the blood 
 is then found by taking the mean of the tensions of the two samples of 
 gas which have been in contact with it (' Aerotonometer ' is the name given 
 to an apparatus devised for this purpose by Pfliiger and Strassburg). 
 
 The tension of the oxygen of the blood is, in consequence of 
 the affinity of haemoglobin for it, very low ; but it becomes higher 
 when the blood is heated (Worm Miiller). In the arterial 
 blood of the dog it amounts on an average to 22 millimetres 
 of mercury (i.e. it corresponds to the tension of the oxygen of an 
 atmosphere which contains 2-9 per cent, of oxygen) ; in venous 
 blood it amounts to 29'6 mm (3-9 per cent.). The tension of the 
 carbonic acid is, in arterial blood, on an average 21 mm (2*8 
 per cent.), in venous blood 41 mm (5*4 per cent.) (Strassburg). 
 
 The tension of the oxygen in the external atmosphere 
 amounts on an average to 158 mm (2O8 per cent.), the tension 
 of carbonic acid to 0-38 mm (0-05 per cent.). 
 
 The tension of the carbonic acid in the air contained in the 
 pulmonary alveoli is so high that it may appear doubtful 
 whether it does not exceed the tension of the carbonic acid 
 in ordinary venous blood. Were such the case, one would have 
 to suppose that certain influences were in operation in the lungs, 
 capable of driving off the carbonic acid, i.e. of increasing the 
 tension of the carbonic acid of the blood entering the lungs. 
 Such influences have, indeed, been sought for partly in the ab- 
 sorption of oxygen, and partly in the action exerted by the lung 
 tissue itself. To determine this point, the tension of the carbonic 
 acid of the blood contained in the lung capillaries is directly 
 ascertained by shaking the blood with a known quantity of the 
 
EXTERNAL RESPIRATION. 153 
 
 air removed from the lungs, and analysing the air before and after 
 the process (Becher). As, however, when the breath is held, the 
 tension of the gases of the blood is very much altered, and as the 
 air which is removed from the lungs has not equally taken part 
 in the equalisation of tension, it is a better plan to remove, for 
 this purpose, by means of a lung-catheter, only the air from a 
 single* portion of the lung of an animal (Pfliiger and Wolff berg). 
 
 From such experiments it results that the tension of the 
 carbonic acid of the blood of the pulmonary capillaries of the 
 dog is about equal to that of the venous blood of the heart 
 (Wolffberg), so that external respiration is to be looked upon 
 as consisting essentially of a simple equalisation of the tensions 
 between venous blood and the air contained in the lungs. The 
 rapidity of gaseous diffusion in the lungs is such that even 
 when the respiration is free and quiet, the expired air of the 
 dog possesses a carbonic acid tension which is nearly equal to 
 that of venous blood (on an average 2-8 per cent C0 2 and 16'6 
 per cent, of 0, Wolffberg). 
 
 Nevertheless, it is possible that the simultaneous absorption 
 of oxygen in the lungs helps to drive off the carbonic acid, 
 though to what extent is unknown. The tension of the carbonic 
 acid of the blood is found to be greater when the blood is 
 agitated with a gas containing oxygen than with one containing 
 no oxygen, or than when the blood is placed in an empty 
 receiver (Ludwig and Holmgren ; Wolffberg). 
 
 Oxygen, therefore, increases the tension of the carbonic acid 
 of the blood, by exerting a chemical action which serves to expel 
 carbonic acid. Further, it is found (Ludwig and Schoffer, 
 Sczelkow, Prey er) that arterial blood is not only poorer than venous 
 blood in carbonic acid which may be pumped out of it, but also 
 in carbonic acid existing in more stable salt-like combinations. 
 Lastly, the carbonic acid tension of serum is much lower than 
 that of the blood as a whole, and is increased by the addition of 
 blood, though not by merely passing oxygen through it. From 
 these facts we should conclude that the blood corpuscles which 
 contain oxygen exert a chemical action, by which carbonic acid, 
 especially that existing in the serum, is liberated from stable 
 compounds, in a form capable of being pumped out of the blood. 
 
 According to J. J. Miiller, when blood is made to flow 
 through the blood-vessels of a luog inflated with nitrogen, it 
 
154 EXTERNAL RESPIRATION. 
 
 gives up more carbonic acid than when it is placed in a simple 
 chamber containing nitrogen. These researches, which ascribe 
 some share to the lung-tissue in causing the expulsion of 
 carbonic acid, have recently been disputed (Pfliiger and Wolff- 
 berg). 
 
 The action of the blood corpuscles referred to in the previous paragraph, 
 and which apparently can only depend upon the formation of an acid, may 
 be imagined to take place in various manners : 1. Oxy-hsemoglobin, which has 
 an acid reaction (Preyer), might itself possess the power of expelling C0 2 
 (Preyer) ; in support of this hypothesis, amongst other facts, may be men- 
 tioned, that passing oxygen through blood furthers the crystallisation of 
 haemoglobin, just as does diminishing the alkaline reaction of the blood by 
 the addition of acids (Kiihne). 
 
 2. Oxygen might bring about a decomposition of haemoglobin, leading to 
 the formation of an acid (in certain decompositions of haemoglobin, volatile 
 fatty acids are generated, Hoppe-Seyler). When the gases of the blood are 
 pumped out under such circumstances that evaporation goes on to a great 
 extent, the strongly combined carbonic acid of blood, even, for instance, that 
 derived from carbonates added to the fluid, is expelled (Pfliiger) ; it is con- 
 ceivable that in this case acids are generated by the decomposition of 
 haemoglobin. 
 
 3. The acid might originate in other constituents of the blood-cor- 
 puscles, e.g. in lecithin. 
 
 4. If carbonic acid contained in the blood corpuscles were in a state of 
 combination, say with haemoglobin, it is possible that oxygen might expel it 
 directly. Even in lung-tissue, whose influence in aiding the elimination of 
 carbonic acid was suspected, an acid occurs, to which the power of expelling 
 C0 2 was formerly ascribed, viz. taurine. (Cloetta ; formerly this body was 
 described under the name of pulmonic acid by Verdeil). As certain albumi- 
 nous compounds (globulin) liberate carbonic acid from carbonates in vacua, 
 an attempt has been made to make use of this fact in the explanation of the 
 respiratory process (HoDpe-Seyler and Sertoli) ; this explanation does not, 
 however, agree with the fact that oxygen has a more powerful action in ex- 
 pelling the carbonic acid of the blood than a vacuum. 
 
 Seeing that respiration proper consists in an equalisation of 
 the tensions of the gases existing in the blood and in the air 
 of the pulmonary alveoli, it follows that the blood in the lungs 
 is the richer in oxygen and the poorer in carbonic acid, the 
 closer the air of the alveoli approaches in composition to 
 atmospheric air. And this will depend upon the energy of the 
 respiratory process, that is to say, upon the frequency and 
 depth of the respiratory movements which influence in an im- 
 portant manner the gaseous constituents of the blood, and so 
 indirectly exert an influence upon the gaseous interchanges 
 
INTERNAL RESPIRATION. 155 
 
 of the whole organism. It is only by comparing the air 
 inspired and expired during long periods of time that we can 
 form a correct estimate of the gaseous exchanges of the body. 
 
 Respiration of the Tissues. 
 
 The question as to the seat of the respiration of the tissues 
 is the same as that of the seat of the oxidation-processes which 
 go on in the animal body. The ancient view (Lavoisier) that 
 carbonic acid was generated in the lung itself is disposed of 
 by the fact that the venous blood which goes to that organ 
 contains large quantities of carbonic acid. 
 
 The increase in the quantity of carbonic acid has to be 
 traced back to the capillaries. And it must be either within 
 these vessels, or in the tissues outside of them, that the con- 
 sumption of oxygen and the formation of carbonic acid 
 proceed. The first of these two views, viz. that which places 
 the seat of oxidation within the capillaries, is improbable, 
 because oxidation-processes are so closely linked to the functions 
 of organs that they must occur within them. The question 
 would be most easily solved if we could compare the tension of 
 the gases contained in the tissues with the tension of the gases 
 of the blood. In general, such a comparison is impossible. The 
 tension of carbonic acid in cavities and in fluids of the body 
 which are surrounded on all sides by healthy tissues (as, e.gr., in 
 intestinal loops and in the contents of the gall and urinary 
 bladder) is decidedly greater even than in venous blood, pointing 
 to the fact that the tissues give up carbonic acid to the blood ; 
 but to the place where carbonic acid originates, oxygen too 
 must wander (Pfluger and Strassburg). 
 
 Another method of determining indirectly the tension of the gases of the 
 tissues, would be to investigate the tension of the gases of the lymph 
 (Ludwig and Hammarsten). In this fluid the tension of the carbonic acid 
 is lower than in venous blood, though higher than in arterial blood. We 
 must not from this fact conclude that carbonic acid does not originate in the 
 tissues, seeing that the lymph experimented upon has had the opportunity, 
 both in the connective tissue and in the lymphatic vessels, of modifying the 
 tension of its gases J>y close contact with arterial blood. 
 
 One, though by itself a very insufficient, ground, for placing the seat 
 of oxidation-processes within the vessels, appeared to be the occurrence of 
 easily oxidisable substances (reducing substances) within the blood, especially 
 in the blood of asphyxiated animals (A. Schmidt). The source of the latter 
 
156 MAGNITUDE OF THE GASEOUS EXCHANGES. 
 
 substances, which are contained in the blood corpuscles and not in the plasma 
 (Afonassieff), may lie in the blood itself j lymph contains none of these 
 substances (Hammarsten). The oxygen tension of many tissues appears to 
 be almost equal to nothing, so that they must eagerly absorb oxygen. Muscle, 
 for instance, contains no oxygen capable of b^ing pumped out of it (Her- 
 mann, Chap. VIII.). 
 
 The energy of internal respiration naturally varies in the 
 case of different organs, and in each organ it varies with the 
 time, according to the energy of the processes of oxidation which 
 go on within it. A comparison of the gases and of the colour of 
 the blood of the arteries and veins of an organ supplies a 
 measure of this energy. The blood of the renal veins is almost 
 arterial in colour, whilst that of muscles is very dark. In the 
 latter it appears to be more florid during activity, probably 
 because the greater gaseous exchanges are more than compen- 
 sated for by the increased flow of blood through them (Chap. 
 VIIL). 
 
 The nature of the oxidation-processes which go on in the tissues strictly 
 do not belong to the study of respiration ; yet they must be briefly alluded 
 to in this place. 
 
 In muscles, which are the organs in which they have been chiefly 
 studied, oxidation does not go on directly, for the processes of absorption 
 of oxygen and formation of carbonic acid do not occur simultaneously. (On 
 this subject further information will be found in Chap. VIIL). On that 
 account the theories which connect the oxidation-processes of the body 
 with a process of ozonizing of the oxygen, or with a formation of peroxide 
 of hydrogen, are improbable. 
 
 Magnitude of the Gaseous Exchanges. 
 
 The magnitude of the gaseous exchanges of the body, 
 leaving aside the variations occasioned by the movements of 
 respiration, is chiefly dependent upon the amount of oxygen 
 which the organism requires (for this requirement see Part II.). 
 The more the blood is charged with carbonic acid produced in 
 the processes of oxidation of the body, the larger the quantity 
 of carbonic acid which is given up. Amongst the circumstances 
 which increase either the individual or combined processes 
 of oxidation, the following are specially to be emphasized : 
 muscular work ; a low temperature of the medium surrounding 
 the body (which increases the production of heat in the body, so 
 as to maintain the normal temperature, Chap. VII.) ; the process 
 of digestion (which is connected with the increase of many secre- 
 
DETERMINATION OF GASEOUS EXCHANGES. 157 
 
 tions) ; great energy of all the vital processes (as in persons of 
 the male sex, of strong constitution, in the prime of life, &c., and 
 in cold-blooded animals during a rise in temperature). All these 
 circumstances increase the evolution of carbonic acid, for in all 
 oxidation-processes of the body carbon is oxidized. Those 
 processes increase the excretion of carbonic acid the most 
 which are connected with the combustion of highly carbonaceous 
 substances, as, for instance, the consumption of a diet rich in 
 carbo-hydrates, which, in part, appear to be directly burned. 
 The consumption of oxygen need not necessarily proceed 
 exactly simultaneously with the evolution of carbonic acid, even 
 when all the carbonic acid which is formed is immediately 
 excreted : for, on the one hand, a formation of carbonic acid is 
 conceivable without oxygen being needed (the carbonic acid 
 being one of the products of a process of decomposition), and, 
 on the other hand, oxygen may, in some way, be stored up, and 
 not be used at once. (Further information in reference to this 
 process may be obtained in Chap. VIII.) 
 
 From what has been stated it follows that the numbers given below, 
 which express the average magnitude of the gaseous exchanges, possess 
 comparatively, little value : 
 
 An adult man requires in 24 hours about 746 grammes (520 litres) of 
 oxygen, and expires about 867 grammes (443 litres) of carbonic acid 
 (Vierordt). 
 
 If all the oxygen were employed in the oxidation of carbon, and all the 
 carbonic acid formed were expired, the volume of the latter would, over 
 considerable periods of time, be equal to the volume of oxygen, seeing that 
 a molecule of C0 2 and a molecule of oxygen (0 2 ) occupy the same volume. 
 As, however, other oxidation-processes occur (lending to the formation of 
 H 2 0, &c.), and as a portion of the carbonic acid formed is excreted in the 
 urine, &c., it follows that the carbonic acid formed must occupy less space 
 than the oxygen consumed, so that when an animal breathes in a confined 
 space, a rarefaction of the air takes place. (The latter circumstance is ex- 
 plained also by the fact that the consumption of oxygen proceeds until the 
 supply is exhausted, whilst the separation of carbonic acid soon diminishes 
 and ultimately ceases. 
 
 By the influence of work the consumption of oxygen per hour may increase 
 from 31 grammes (see above) to about five times this amount (156 grammes. 
 Him). 
 
 In man the interchange of gases through the skin, as compared with that 
 at the lungs, is almost imperceptible. The carbonic acid excreted in 24 
 hours varies between 2'3 and 6-3 grammes, being on an average 3-87 
 grammes ; its amount increases with the temperature (Aubert). 
 
 The daily experience that exhaled air is warmer and moister than the at- 
 
158 MECHANISM OF RESPIRATION. 
 
 mosphere, and the simple experiment of breathing through a tube which dips 
 into lime- or baryta- water, which becomes turbid in consequence, suffice to 
 show qualitatively the differences between inspired and expired air. 
 
 In quantitative comparison, as the composition of the air inspired is 
 known, it suffices to investigate the air expired, which for this purpose is 
 collected in a mercurial gasometer (Allen and Pepys). The air which is 
 breathed is freed from carbonic acid and water by passing it through caustic 
 potash and sulphuric acid. 
 
 In order to determine the total gas-exchanges which go on during long 
 periods of time, the expired air may be allowed to pass through an apparatus 
 in which the carbonic acid and water formed are absorbed, so that they may 
 both be weighed. For this purpose appliances for aspirating are required, 
 e.g. a vacuum (Andral and Gavarret), a vessel containing water, which is 
 allowed to run out (Scharling), or an air-pump (Pettenkofer). If the research 
 has to be carried out on a large scale (as in Pettenkofer's apparatus, the 
 air-space of which can conveniently supply a man for some time), it suffices 
 to allow only a measured fraction of the in-going and out-going air to pass 
 through the absorbing fluids, provided that the total volumes of the gases 
 are continually measured (by means of gas-meters). 
 
 According to another method, respiration is carried on in a completely 
 confined space, which is in communication only with an oxygen reservoir ; 
 the carbonic acid formed is continually being absorbed by a connected appa- 
 ratus containing solution of caustic potash ; in consequence of the diminu- 
 tion of pressure which results from the absorption, oxygen is continually 
 being sucked from the reservoir. At the end of the experiment the amount 
 of carbonic acid absorbed by the caustic potash is determined, as well as the 
 nitrogen which was originally present in the chamber ; the oxygen which 
 has been used, is found by ascertaining the diminution which the store of 
 this gas originally present in the chamber and the connected reservoir 
 has undergone (Regnault and Eeiset). Similar, though simpler, apparatuses 
 have lately been constructed (Ludwig and Kowalewski, Ludwig and Sanders- 
 Ezn). 
 
 When the gaseous exchanges dependent upon the whole external re- 
 spiration have to be determined, the respiratory space surrounding the whole 
 body must be investigated. If only the respiration of the skin is to be 
 investigated, the mouth and nose are made to communicate with the ex- 
 terior by means of a tube ; finally, if only the pulmonary respiration be the 
 object of research, the respiratory chamber is in communication by an air- 
 tight mask with the mouth and nose. 
 
 II. THE MECHANISM OF KESPIKATION. 
 
 In the lowest organisms, the bodies of which are but small, the mere 
 bathing of the body in the medium to be breathed (water) is sufficient to keep 
 up the interchange of gases by diffusion ; more highly developed animals of 
 larger size require a larger surface for the proper interchange between the 
 juices of the body on the one hand and the medium on the other. In animals 
 

 THORAX AND LUNGS. 159 
 
 in which the blood-vascular system is either in a rudimentary state or alto- 
 gether wanting, the medium must be introduced into and distributed over 
 all parts of the body in order to be everywhere brought into contact with 
 the juices; but where the blood-vascular system is fully developed, the mass 
 of the blood can be passed into an organ of large surface, where it can meet 
 the medium to be breathed, and wh^re, thus, on large surfaces the blood can 
 enter with it into the process of diffusion. 
 
 The arrangement in the first class consists of a system of branched tubes, 
 as in the water-vascular system of echinodermata and scolecida, and the tra- 
 cheal system of arthropoda : while in the latter class we have an eversion 
 of the body surface if water is breathed, as in the gills of mollusca, fishes, 
 asid the larvae of batrachia; or an involution if air is breathed, as in the lungs 
 of amphibia, birds, mammals, and man. As a separate respiratory medium 
 for the fetus of mammals and of man, we have the oxygenated maternal 
 blood, which meets the blood of the foetus in the placenta (fcetalis and 
 uterina), where through the walls of the capillaries the gaseous exchange 
 takes place (Chap. XII.). 
 
 The human respiratory organs, 1 the lungs, represent two 
 elastic bags, containing a branched system of tubes with terminal 
 vesicles (alveoli), and the surface in each alveolus being further 
 extended by the presence of prominent ridges in its walls. The 
 cavity of each lung communicates by means of the trachea, 
 larynx, pharynx, and the nasal or oral cavity, with the external 
 air. 
 
 The lungs left to themselves contain no air : they are dialec- 
 tic^ like the lungs of the foetus before it has c breathed,' i.e. 
 the walls of its tubes and of its alveoli lie in apposition by 
 virtue of their elasticity. In the human body, however, the 
 lungs are so fitted into an unyielding reservoir (the thorax) 
 that no air can pass between their external surface and the 
 internal surface of this reservoir (more accurately, between 
 the pleural surface of the lungs and the lining of the thorax). 
 The pressure of the atmospheric air entering the lungs must 
 necessarily therefore expand them against their own elasticity 
 to more than their normal volume : they closely apply them- 
 selves to the thoracic walls, and are therefore during life always 
 found filled with air. Should, however, through any opening, 
 air pass into the space between the lungs and the thoracic walls, 
 then the lungs by virtue of their elasticity collapse to their 
 natural (atalectic) volume (Pneumothorax). 
 
 1 The cutaneous and intestinal respiration (p. 150), not possessing a separate 
 mechanism, are not considered here ; their importance in man is but small. 
 
160 
 
 THORAX. 
 
 Not only the lungs, but the heart and vessels also, contribute towards the 
 filling up of the thoracic cavity. The pressure of the air acts upon the inner 
 surface of all these organs ; it acts directly (through the trachea) on the 
 lungs; it acts indirectly on the heart, for the whole body, and therefore all the 
 vessels situated outside the thorax, and communicating with the interior of 
 the heart, are under atmospheric pressure. The same pressure then tending to 
 enlarge all the hollow organs within the thorax, these organs will expand ac- 
 cording to their degree of expansibility, and hence the most expansible organs, 
 the lungs, will contribute most towards the filling up of the thorax (they 
 will be dilated the most beyond their original volume), the thick-walled 
 ventricles the least, while the thin-walled auricles and the venous trunks 
 (p. 5) will be perceptibly dilated. The atmospheric pressure acting equally 
 upon the external surface of the thoracic walls, their more yielding parts 
 will likewise contribute towards the filling up, or rather the diminution 
 of the thorax : hence the diaphragm and the intercostal spaces will arch in 
 towards the thorax. 
 
 The following model illustrates these relations. A bottle provided with a 
 stopcock, o, contains two elastic bags, represented in fig. 1 in their natural 
 
 configuration ; the one, hourglass-shaped, with a thin- walled and thick-walled 
 division, v and K, is filled with a fluid and communicates with an open 
 vessel containing water j this double bag represents the heart (v = auricle, 
 K = ventricle), the other bag, Z, filled with air and communicating through 
 t ( = trachea) with the atmosphere, represents the lung. The membrane ^ 
 represents the soft parts of an intercostal space. Fig. 2 shows the apparatus 
 after the air has been exhausted, through o, from the bottle. Both bags, on 
 
RESPIRATORY MOVEMENTS. 161 
 
 the inner walls of which the atmospheric pressure acts (indirectly on y K), 
 are seen expanded, filling up completely the interior of the bottle ; I is most 
 expanded, v much less, and K the least j t is also seen to be somewhat vaulted 
 in. If now through o air is again allowed to enter, we get again the same 
 condition of things as in fig. 1, which corresponds to the condition of 
 pneumothorax. 
 
 Each of the two bags in fig. 2 tends to contract at the expense of the 
 other, i.e. to extend the other. The figure represents the state of equilibrium. 
 Hence in the usual representation of the relations in the thorax, lungs ex- 
 panded above their normal volume are made to exercise a pull (' negative 
 pressure ') on the heart and the soft parts of the thoracic walls (represented 
 by arrows in fig. 2), but we have also to consider that the heart, &c. acts 
 in the same way on the lungs. 
 
 We are able to measure manometrically the elastic force with which the 
 lung, when expanded to the size it has in the passive thorax, tends to con- 
 tract (or in other words, its negative pressure when the thorax is at rest), by 
 fixing a manometer air-tight into the divided trachea of a dead body and 
 then opening the thorax ; this elastic force is about 6 mm. of mercury 
 ( Donders). The elastic force of the expanded lung may be further assisted 
 by the non-striped muscles surrounding the bronchial tubes, for by their con- 
 traction the bronchial tubes would be narrowed, and therefore the negative 
 pressure in the thorax increased, whereby a greater expansion of the other 
 organs would be effected. We know, however, nothing definite either about 
 the time and mode of this contraction or about the innervation of the muscles. 
 Irritation of the pneumogastric diminishes slightly the volume of the lung, 
 when the latter is cut out and ligatured (Schiff). 
 
 The Respiratory Movements. 
 
 The air contained in the alveoli of the lungs enters into 
 relations with the gases of the blood circulating in the capil- 
 laries surrounding the alveoli. These relations, as already 
 stated, consist, on the part of the air contained in the alveoli, in 
 a loss of oxygen and a gain of carbonic acid, whereby this air is 
 soon rendered unfit for any further gaseous exchanges. Owing 
 to the diffusion of gases, however, an exchange between the gases 
 contained in the alveoli and the separate layers of the super- 
 imposed air is possible, and this exchange will eventually reach 
 the external air ; but as it will only take place in layer after 
 layer, it will be too slow to effect a thorough removal of the 
 gases of the blood : it will be necessary therefore that the air 
 in the alveoli be repeatedly and mechanically renewed, and 
 this is effected by a regularly alternating expansion and con- 
 traction of the thorax (inspiration and expiration), which the 
 lungs of necessity must follow. 
 
 M 
 
162 
 
 INSPIRATION. 
 
 The expansion of the thorax, Inspiration, is always pro- 
 duced by muscular action. The regularly acting inspira- 
 tory muscles are : the Diaphragm, the Scaleni and Intercostal 
 muscles, particularly the external intercostals. In deep or (on 
 account of obstacles) laboured inspiration, other accessory in- 
 spiratory muscles are called into play, namely, the Serrati 
 postici and the Levatores costarum ; and, when there is great 
 difficulty of breathing, the Sterno-cleido-mastoidei, the 
 Pectorales and the Serrati antici, &c. 
 
 The expansion of the thorax is chiefly effected by the dia- 
 phragm, the muscular portion of which, in contracting, becomes 
 less convex, while its borders recede from the thoracic walls, to 
 which they are apposed when at rest. Nearly all the other muscles 
 act on the ribs : they generally run forward and downward, and, 
 their upper ends, which are attached to the vertebral column or 
 (Pectorales, Serrati antici) to fixed points of the upper extre- 
 mities, forming the fulcrum, they draw the ribs outwards and 
 upwards, whereby the thorax is expanded. 
 
 Each rib, having one of its two joints attached to the body of a vertebra, 
 and the other to the transverse process, is movable round an inclined axis ; 
 each upward rotation round this axis will make the inclined plane pass- 
 ing through the curvature of the rib more horizontal, and will therefore 
 widen the diameter of the thorax. The rotation of the ribs round this axis 
 
 FIG. 3. 
 
 R 
 
 a' 
 
 b' 
 
 is, however, kept within narrow limits by the costal cartilages (though they 
 are elastic and somewhat yielding) which fasten the ribs to the sternum. 
 The action of the muscles which elevate the ribs is therefore easily under- 
 stood. How far the intercostals also are elevators of the ribs will be evident 
 from the following consideration (Hamburger). 
 
EXPIRATION. 163 
 
 In the accompanying figure RR' and rr' represent the posterior portions 
 (passing forward and downward) of two consecutive ribs during rest ; RR" 
 and rr" the same during inspiration ; ab represents a fibre of an intercostalis 
 internus, cd a fibre of an intercostalis exteraus. It will be seen at a glance 
 that the distance ab is less in the elevated position ('&'), while cd is less in 
 the lowered position. 1 
 
 From this it follows inversely that the shortening of ab will elevate, the 
 shortening of cd will lower, both ribs. Now, as the direction of the fibres is 
 exactly the reverse in the anterior portion of the ribs (between the angle of 
 the ribs and the sternum), the interni will here act as inspiratory, the 
 externi as expiratory muscles; or, in other words, those externi attached 
 to the bony parts of the ribs and those interni attached to the cartilaginous 
 portions will act as inspiratory muscles ; and as this corresponds nearly accu- 
 rately to the chief seats of distribution of the two kinds of fibres, we may 
 therefore consider the intercostals as inspiratory muscles. Experimentally, 
 however, the action of the intercostals has not yet been definitely deter- 
 mined. 
 
 While the elevators of the ribs increase the transverse diameter of the 
 thorax, the contraction of the diaphragm causes an increase of the longitu- 
 dinal diameter. According as the movements of the ribs or of the diaphragm 
 preponderate, do we distinguish between costal respiration and abdominal re- 
 spiration (the latter name being derived from the fact that with the descent 
 of the arch of the diaphragm, the contents of the abdomen are pushed down- 
 wards, in consequence of which there is protrusion of the abdominal walls). 
 Costal respiration is chiefly observed in the female, abdominal respi- 
 ration in the male, sex. 
 
 The diminution of the capacity of the thorax, Expiration, 
 is brought about by the weight and the elasticity of the thoracic 
 walls, by virtue of which they return to their position of equili- 
 brium after the inspiratory forces which have forced them from 
 this position have ceased to act. The weight of the ribs draws 
 them down, the elasticity of the lungs draws the diaphragm up- 
 wards, and the thoracic walls inwards ; the elasticity of the 
 costal cartilages, which have undergone torsion, brings the ribs 
 back again to their normal position. In forced and obstructed 
 expiration, muscular force will also enter into play, the direc- 
 tion of the expiratory muscles "being forwards and upwards. 
 The principal expiratory muscles are : the abdominal muscles, 
 the quadrati lumborum, the serrati postici inferiores, and the 
 
 1 Supposing the angle r&b = x, we have : 
 
 ab- = Rr- + (ra R&) 2 + 2Rr (ra nb) cos x 
 cd z = Rr 2 + (s-d rc} z 2Rr (R^ re) cos x ; 
 
 . * . ab will be the greater the smaller x is, while cd will be the greater the larger a? 
 is (the cosine increasing with the decreasing angle). 
 
 M 2 
 
164 EXPIRATION. 
 
 intercostales interni. The abdominal muscles compress by their 
 contraction the contents of the abdomen they therefore push 
 the diaphragm up and draw the ribs down ; the quadrati lum- 
 borum and the serrati postici inferiores do the same, as do also 
 the intercostals, as far as they run along the bony parts of 
 the ribs. How the lowering of the ribs contracts the thorax 
 will be evident from what has been said before. 
 
 The different apparatus which conduct the air to the lungs also take part 
 in the respiratory movements : the rima ylottidis dilates in inspiration, and in 
 forced inspiration the nostrils are dilated by the levatores alee nasi, thus facili- 
 tating the entrance of air to the lungs. 
 
 The lungs, as already stated, must of necessity follow every 
 movement of the thoracic walls, and every inspiration will there- 
 fore cause an increase of capacity of the lungs, both in the 
 transverse and vertical diameters. The parts of the lung close 
 to the chest- wall will also participate in this movement, for the 
 borders of the diaphragm recede with each contraction from the 
 chest-wall. Every inspiration is naturally associated with a 
 descent of the lung in the chest ; and this of itself would cause, 
 even without any increase of the transverse diameter of the 
 thorax, an increase in the transverse diameter of the lungs ; 
 for the thorax is of a conical form, and by the descent every 
 section of lung would be received into a deeper and therefore 
 wider section of the thorax. The descent of the lung causes 
 in its turn a lowering of the trachea and larynx, which is visible 
 from without. 
 
 The expansion of the lungs with inspiration, which affects all 
 their cavities, but particularly the more easily yielding alveoli, 
 causes an increase in the volume of air they contain. This 
 increase in calm breathing amounts to about 6 per cent, of the 
 total volume ; deep inspiration causes, however, a much greater 
 change. We have a measure for the limit of this possible 
 change of air in the 6 vital capacity ' of the lungs, by which we 
 mean the difference between the volumes of air in the lungs 
 when these are expanded and contracted to the fullest possible 
 extent, or in other words the quantity of air whieh is expelled 
 after the deepest possible inspiration by the deepest possible 
 expiration (Hutchinson). This quantity is in nearly constant 
 proportion to the size of the individual ; it varies, however, with 
 
AIR IN THE LUNGS. 165 
 
 the occupation and the sex (being larger in men, Arnold). 
 In grown-up persons its medium value is 3770 Cc. 
 
 To measure the vital capacity we use the c spirometer ' (Hutchinson), 
 which consists in a gasometer, the receiver of which is kept in equilibrium 
 by weights ; into this gasometer we expire (through an india-rubber tube 
 connected with it) after a deep inspiration ; the volumes of air are measured 
 by the proportional heights to which the cylindrical receiver is raised. Gas- 
 meters may also be used for this purpose. 
 
 Other measurements to be considered are : a. The quantity of air con- 
 tained in the lung after the strongest possible expiration ('residual air/ 
 Hutchinson). This quantity may be determined by breathing hydrogen from 
 a closed receiver till there is no longer any alteration in the composition of 
 the gas, at which point the hydrogen will be uniformly mixed with the air in 
 the lungs: by now expiring to the deepest possible extent, the amount of gas 
 still contained in the lungs may be calculated from the composition of the 
 expired gas mixture and the quantity of hydrogen which is missing ( H. Davy, 
 Grehant). b. The quantity of air contained in the lungs at ordinary ex- 
 piration (which is determined in the same way as above). The difference 
 between these two quantities, or the quantity of air which after an ordinary 
 expiration can still be expired, is called the * reserve air/ or ' supplementary 
 air : ' in like manner the difference between the quantities of air at the ordinary 
 and at the deepest possible inspiration is called the ' complementary air/ 
 while the difference between the quantities of air at ordinary in- and ex- 
 piration is called the ' respiratory air.' If we call the residual air a, the sup- 
 plementary air 6, the respiratory air c, and the complementary air d, then 
 a + 6 + c + disthe vital capacity. 
 
 As regards the chemical renewal of the gases in the lungs, it has been 
 found (by inhaling hydrogen, Grehant) that if a quantity, c, of a gas be in- 
 haled between any two expirations, a certain quantity, a. <?, of this gas remains 
 in the lungs and is equally diffused (if c = 500 c.c., o. c = 330). At ordinary 
 
 inspiration, therefore, ,- represents the volume of new air (in the 
 a + b + c 
 
 chemical sense) which the unit-volume of the lung-cavity receives at each 
 inspiration ; this quantity (which, for instance, if c - 500 and a + b + c = 
 
 2930, is -?5_ = 0-113) is called the < coefficient of ventilation.' It has 
 2930 
 
 further been found (by a single inspiration of hydrogen, followed by ordinary 
 respiration in air) that when the quantity of gas inspired is 500 c.c., it is only 
 after the sixth to the tenth respiration that it has all left the lung (Gre- 
 hant). 
 
 To determine the movements of the thorax the ' thoracometer ' is used 
 (Sibson), which measures the alterations in the horizontal median diameter 
 of the chest. The anterior chest-wall pushes a small rod before it which by 
 means of a spring moves an index : the axis of the index is fastened by a sup- 
 port to a board on which the body rests in a horizontal position. Similar 
 apparatus (Ransome) measure at the same time the excursions in several 
 diameters ; they can also be so modified as to give graphic representations 
 
160 RHYTHM OF RESPIRATION. 
 
 (Riegel). The 'pneumograph ' or ' atrnograph ' (Marey) is a belt, of which 
 an elastic hollow cylinder, the lumen of which is extended by every inspiration, 
 forms part. The pressure of the air in the cylinder is graphically registered. 
 The variation in the diameter can be registered in the same manner as the 
 variation in the circumference, by pressure transmitted through a column of air 
 (Fick). In animals the movements of the diaphragm can be measured by 
 means of a needle inserted into it, or by means of a lever pushed against 
 the diaphragm from the side of the abdomen, which registers its movements 
 graphically in curves on a paper passed before it (' phrenograph,' Rosen- 
 thai). 
 
 As the thorax expands with every inspiration, the hollow organs situated 
 within it will also become expanded above the natural volume which they 
 possess when at rest. Hence, amongst other results, ' the negative pressure ' 
 under which the heart and great vessels exist will increase, thus causing the 
 aspiration exerted by them to increase also. 
 
 On the other hand, the negative pressure may be entirely removed, or 
 even converted into a positive pressure by expiration, though ordinarily the 
 latter merely restores the conditions existing before inspiration. This will 
 occur when during active expiratory effort the air is prevented from 
 escaping from the thorax by closure of the rima glottidis. 
 
 The effects of the aspiration of the thorax on the circulation in the lungs 
 are according to some accelerating (Haller, Quincke, Pfeiffer), according to 
 others retarding (Poiseuille, J. J. Miiller). The pressure of the air in the 
 respiratory passages (which during rest is equal to the atmospheric pressure) 
 also undergoes slight variations, owing to the narrowness of the entrance 
 (nostrils, rima glottidis), being about 1 mm. at inspiration, and 2-3 mm. at 
 .expiration. These variations can be determined, in animals by a manometer 
 connected laterally with the trachea, and in man by a manometer which is 
 attached to one nostril, the individual expiring through the other nostril, 
 while he keeps his mouth closed. 
 
 The friction against the walls of the larynx and the system of tubes through 
 which the current of air passes during each inspiration gives rise to murmurs 
 audible by the ear applied to the chest-wall. In the unyielding parts 
 (larynx, trachea, and larger bronchi) this murmur has a more whiffing, 
 breezy character ( = h or cA, ' bronchial murmur ') ; in the smallest 
 bronchi, where the air has to force its way through narrow channels, it is 
 more of a sipping, hissing, or whizzing nature ( = v or/, ' vesicular mur- 
 mur '). In the superficial respiration (of grown-up men) the character of the 
 murmur becomes indeterminate 5 in like manner regular expiration 
 produces an indistinct weak murmur. 
 
 Rhythm and Liberation of the Respiratory Movements. 
 
 The movements of inspiration and expiration can be pro- 
 duced at will. Ordinarily, however, they are involuntary, and 
 have a certain rhythm and a certain intensity or depth. 
 
LIBERATION OF RESPIRATORY MOVEMENTS. 167 
 
 We are able at will to vary both, in any manner we like ; 
 but total cessation is only possible for a very brief period of 
 time. The medium frequence of respiration in an adult is 18 
 per minute. 
 
 The respiratory movements are increased in frequency in the very young 
 and the very old, in the female, at high temperatures, during muscular effort, 
 during digestion, with emotions, and after a temporary suppression of respira- 
 tion, these agencies being the same as cause an increased frequency of pulse. 
 In general we have in every condition one respiration to four heart's contrac- 
 tions. The influence of the passions affects not only the frequency but also 
 the depth and the form of the respiratory movements ; the latter producing 
 thereby sometimes characteristic sounds or murmurs in the tubes which con- 
 duct the air to the lungs. To this category of characteristic sounds belong : 
 sobbing, when the inspirations succeed each other quickly ; sighing, when a 
 deep inspiration is followed by a forced expiration ; yawning, when there is 
 slow and prolonged inspiration while the mouth is kept spasmodically 
 opened ; laughing, where there is a jerking, interrupted expiration; &c. 
 
 The impulse to the involuntary rhythmical respiratory move- 
 ments proceeds from a circumscribed spot of the medulla 
 oblongata, which is situated at the place of origin of the 
 pneumogastric and spinal accessory nerves (Chap. XI.) : the de- 
 struction of this spot suppresses at once all respiration, and is 
 therefore fatal (' No&ud vital,' Flourens). From this spot the 
 diaphragm is acted upon through the phrenic nerves, and the 
 other inspiratory muscles through the external thoracic nerves ; 
 expiration also, as far as muscular forces are concerned in 
 it, is under its influence. The rhythm of the excitations of the 
 respiratory centre is influenced by certain fibres which run in the 
 course of the pneumogastric, and which are in a constant state 
 of irritation. There are two kinds of these fibres : the one kind 
 are accelerating ; the other, which the pneumogastric receives 
 from the Ramus laryngeus superior (Rosenthal), or according 
 to other authors (Pfliiger and Burkart, Hering and Breuer) 
 from other nerves, particularly the Eamus laryngeus inferior, 
 are retarding or inhibitory. Ordinarily the excitation of the 
 former (the accelerating) fibres predominates ; for after division 
 of one or both vagi (in the neck) the respiratory rhythm 
 becomes slower (Traube) : on artificial irritation also of the 
 central end of the divided vagi, the excitation of accelerating 
 fibres usually overbalances the other (the inhibitory), respiration 
 in consequence becoming quicker : if the irritation is stronger 
 
103 LIBERATION OF RESPIRATORY MOVEMENTS 
 
 still, it becomes tetanic, i.e., the diaphragm remains in a 
 state of contraction inspiration (Traube). At times, however, 
 we have the opposite effect on strong irritation, namely, the 
 arrest of the diaphragm in a state of relaxation expiration : 
 this is particularly the case on the fatigue of the nerves the 
 result being due to the fact that the inhibitory fibres do not so 
 quickly become exhausted (Burkart). On excitation of the 
 regulator-fibres the respiratory movements become deeper or 
 more superficial in the same ratio as they become slower or 
 quicker, so that the activity of the medulla oblongata remains 
 nearly the same, though it is differently distributed; after section 
 of the vagi, at least, the inspired quantities of gas are on the 
 whole not less (Eosenthal), and the gaseous exchange, at all 
 events at the commencement, is not altered (Voit and Rauber). 
 The inspiratory muscles not in action before irritation of tjjie 
 accelerating fibres, are not affected by the irritation, which 
 suspends also the action of those expiratory muscles which 
 happened to be in action before. On the other hand, with the 
 increasing irritation of the inhibitory fibres, the expiratory 
 muscles will at last come into play (Rosenthal), after the in- 
 spiratory movements have ceased. 
 
 The accelerating and inhibitory fibres belong to the class of regulator- 
 nerves (for details see Chap. XI.). Different views have already been ex- 
 pressed about the mode in which this regulation is set in motion peripher- 
 ally during life (Rosenthal, Sklarek, Hering and Breuer). The state of 
 distension of the lungs seems to act mechanically as an excitant of these 
 fibres (Rosenthal), expansion, on the one hand, exciting the inhibitory 
 fibres, which act as expiratory fibres; and contraction, on the other, excit- 
 ing the accelerating, which act as inspiratory, fibres ; in this way there would 
 be a sort of self-regulating mechanism presiding over the movements of res- 
 piration (Hering and Breuer) : the presence of regulator-fibres in the 
 laryngeal nerves also shows that the larynx takes part in this regulation 
 (Sklarek). 
 
 Irritation of the mucous membrane of the nose causes for some time 
 an arrest of respiration during expiration ; this eiFect is brought about 
 not by the olfactory nerve, but by the trigeminus (Hering and Kratschmer). 
 A similar arrest in expiration follows the irritation of many cutaneous 
 nerves, as, for example, the irritation of the cutaneous nerves of the chest on 
 plunging into water (Schift) Falk). 
 
 The exciting cause of the respiratory movements, of which 
 more will be said further on, may either act directly on the 
 medulla oblongata (Rosenthal) or on the terminations of the 
 
LIBERATION OF RESPIRATORY MOVEMENTS. 169 
 
 centripetal nerves going to the medulla oblongata (Each, v. 
 Wittich), in which latter case respiration would be a Reflex act. 
 The decisive experiment, namely, to determine whether all 
 respiratory movements cease after the separation of the medulla 
 oblongata from all its 'centripetal fibres, has been repeated by 
 both sides with different results. It is, therefore, not possible 
 to come to a decision on this point, as the other experiments 
 carried out to support these two views do not agree among 
 themselves. 
 
 The exciting cause itself consists in the presence of a certain 
 amount of oxygen and carbonic acid in the blood. The follow- 
 ing facts prove that this condition of the blood causes the 
 respiratory movements : 1. The respiratory movements can be 
 totally arrested ('Apncea') if, either by a forced artificial 
 respiration (by blowing air into the lung) or by voluntary 
 forced breathing, the blood becomes saturated with oxygen and 
 poor in carbonic acid. 2. Respiration becomes stronger, and 
 the more accessory muscles take part in it ( ; Dyspnoea : ' see 
 Appendix), the poorer in oxygen and the richer in carbonic 
 acid the blood is : as e.g. on the entrance of air or fluid into the 
 pleural cavities, causing a collapse of the lungs, or when 
 by inflammation, &c. the lungs are made unfit for respiration. 
 The first respiratory movement in the foetus is in like manner 
 caused by interruption of the respiration carried on through 
 the placenta, which causes a sudden deficiency of the oxygen in 
 the blood, while the carbonic acid accumulates (Schwartz). 
 3. The same effect will be produced if this alteration in the com- 
 position of the blood takes place only locally in the vessels of 
 the medulla oblongata ; l this happens, e.g., on stagnation of the 
 blood in these vessels, as after ligature of all arteries going to 
 the brain (Kussmaul and Tenner, Rosenthal) or on preventing the 
 return of venous blood from the brain (Hermann and Escher), 
 whereby the blood becomes poorer in oxygen and richer in 
 carbonic acid. 
 
 A very great deficiency of oxygen destroys the excitability 
 of the medulla oblongata, and no irritation whatever, not even 
 
 1 This, however, is no criterion for the determination of the question whether 
 the respiratory movements are a reflex act or not ; for the advocates of the first 
 view will explain these results by holding the blood of the medulla oblongata to 
 exert an influence in the production of the reflex action. 
 
170 LIBERATION OF RESPIRATOR Y MOVEMENTS. 
 
 a large surcharge of carbonic acid, will again start respiration. 
 This condition is called 'Asphyxia ' (see Appendix). 
 
 As almost all the conditions which increase the amount of carbonic acid 
 in the blood are associated with a decrease in the quantity of oxygen, it is 
 difficult to decide whether the want of oxygen or the accumulation of the 
 carbonic acid forms the real ' liberating agent ' for the respiratory move- 
 ments. For the present it will be best to look upon both conditions as 
 constituting the ' increased venosity ' or ( dyspnoeic quality ' of the blood 
 (Hering). It is proved that respiration and dyspnoea may be caused by both a 
 deficiency of oxygen without accumulation of carbonic acid (as in the respira- 
 tion or artificial inflation of the lungs by indifferent gases free from oxygen, 
 H, N, N 2 0) (Rosenthal), and also by an accumulation of C0 2 without any 
 deficiency of the (as in the respiration of air which is rich in C0 2 without 
 being poor in 0) (Traube). The argument that in the first case also there 
 is in reality an accumulation of C0 2 , because the indifferent gases cannot 
 expel the C0 2 from the blood as completely as O does (compare p. 153), 
 and that therefore in both these cases the CO 2 is really the excitant (Thiry), 
 is refuted by the consideration that the respiration of nitrogen causes no 
 accumulation of C0 2 in the blood (Pfliiger). We must therefore conclude 
 (Dohmen, Pfliiger) either that a deficiency of oxygen by itself, and likewise an 
 accumulation of carbonic acid by itself, may excite the respiratory centre, or 
 (Hermann) that if the C0 2 is alone the exciting cause, its action is the less 
 powerful the larger the amount of present, just as the action of strychnia, 
 for example, is prevented when the blood is saturated with oxygen : see 
 Chap. XI. 
 
 In apncea the amount of presented is increased in arterial and diminished 
 in venous blood (Ewald) j the latter condition is probably produced by a 
 diminution in the velocity of the blood-current in consequence of the great 
 decrease of the arterial blood-pressure (Pfliiger). 
 
 The phenomenon of Cheyne and Stokes is a peculiar case of abnormal 
 regulation of the respiratory movements : In patients suffering from cerebral 
 and cardiac affections there occurs sometimes an intermittence of respiration ; 
 after each pause the respiration increases till dyspnoea is produced, when it 
 gradually sinks again till the next pause. As an explanation it is stated 
 (Traube) that when the excitability of the respiratory centre is diminished, 
 a considerable increase in the venous state of the blood is required each time 
 n order to excite it ; the powerful respirations which eventually appear 
 will, however, again considerably diminish the venous state. 
 
DEFICIENCY OF OXYGEN. 171 
 
 APPENDIX TO CHAPTEE IV. 
 
 CONSEQUENCES OF A DEFICIENCY OF OXYGEN. 
 
 IF by any means the access of oxygen to the blood be pre- 
 vented altogether, or the quantity entering be diminished in an 
 important manner ; or if the oxygen which already exists in 
 the blood be expelled from it or removed in any other way ; a 
 group of phenomena can be observed, which ultimately end in 
 death (asphyxia, suffocation). 
 
 The oxygen which exists in chemical combination in the 
 blood can be expelled from it by the inhalation of carbonic 
 oxide (p. 46) ; further, the oxygen of the blood can be re- 
 moved by substances which unite with it, as, e.g., sulphuretted 
 hydrogen. The circumstances which, according as they are in 
 full or partial operation, check or altogether put a stop to the 
 oxygenation of the blood, are the following : 1. A want of oxygen 
 in the medium breathed (e.g., prolonged respiration in a limited 
 space of air, respiration in a vacuum or under water). 2. In 
 the foetus, the separation of the placenta or closure of the 
 umbilical vessels before birth. 3. Interruption to the cutaneous 
 or pulmonary respiration, the former by varnish being applied 
 to the skin (p. 150), the latter by closure of the air-conducting 
 passages. The closure may be due to external causes, as when 
 pressure is applied from without, in strangulation, or to internal 
 causes, such as the following : spasmodic closure of the glottis ; 
 obstruction caused by foreign bodies or tumours ; accumulation 
 of morbid products, as mucus, in the bronchi ; collapse of the 
 lungs by the entrance of air or water into the pleural cavities 
 (pneumothorax, pleuritic exudations) ; partial destruction of the 
 lungs (as in phthisis) ; cessation of the respiratory movements ; 
 and, lastly, embolism of the pulmonary artery. 
 
 When placed in a chamber in which the air is rarefied, warm- 
 blooded animals die before the whole of the oxygen has been 
 consumed, in consequence of the evolution of gas within the 
 blood, which leads to disturbance of the circulation (Hoppe- 
 
172 DYSPNCEA. 
 
 Seyler). In compressed air death ensues in consequence of 
 the elimination of carbonic acid being hindered (Bert). 
 
 With the impoverishment in oxygen which the blood under- 
 goes under the above-mentioned circumstances, there is gene- 
 rally also an increase in the carbonic acid of that fluid, and 
 these changes in the gases of the blood, as before said, at 
 once cause the respiratory movements to become slower and 
 deeper, under the influence of the accessory muscles of respira- 
 tion (p. 162); this change in the respiratory movements con- 
 stitutes dyspnoea. Dyspnoea is a regulating act, for in the 
 majority of cases (unless when there is a complete absence of 
 oxygen in the respiratory medium, or when the passage of 
 oxygen to the alveoli is quite impossible) it leads to an increase 
 in the quantity of oxygen contained in the blood, and then it- 
 self ceases. 
 
 If the impoverishment in oxygen proceeds further, general 
 spasms of all the muscles of the body set in (clojiic convul- 
 sions) ; the centre which presides over these is situated in the 
 medulla oblongata, so that we must suppose that the stimulus 
 which leads to normal respiration, if it be increased beyond a 
 certain degree, exerts its action not only on the respiratory, but 
 on neighbouring centres which were normally less irritable. 
 Later on a contraction of the muscular coats of blood-vessels 
 occurs which exerts an action upon the heart (see p. 77). 
 This spasm of blood-vessels is an intermitting one (Traube), 
 and follows the same rhythm as governs the rudimentary 
 spasms of respiration, which are perceptible even at this 
 stage. (Hering : compare Chapter XI. ) 
 
 The spasms also occur when the flow of blood to the head 
 is cut off, by ligaturing the carotid and vertebral arteries, and 
 also when an animal loses large quantities of blood (Kussmaul 
 and Tenner) ; when produced in these ways the spasms have 
 been designated ' anaemic : ' their true cause is, however, in all 
 cases, the presence of stagnating blood in the capillaries of the 
 brain that is to say, of blood which is poor in oxygen and rich 
 in carbonic acid and they can therefore be produced by pre- 
 venting the return of venous blood from the brain (Hermann 
 and Escher). Even in the experiment of Kussmaul and Tenner, 
 dyspnoea precedes the spasms (Eosenthal). After haemorrhage 
 we can readily conceive how stagnation ot blood in the vessels 
 
ASPHYXIA. 173 
 
 of the brain may result in consequence of insufficiency of the 
 propulsive power : it would, however, in this case, be just as easy 
 to suppose that either the want of oxygen or the increase in the 
 quantity of carbonic acid might act as excitants of the substance 
 of the brain. 
 
 If the want of oxygen proceeds still further, the irritability 
 of the nerve-centres, which requires for its maintenance a cer- 
 tain supply of oxygen, ceases, and the strongest irritants cannot 
 occasion either movements of respiration or spasms, which, 
 therefore, are in complete abeyance : this condition, which 
 must not be confounded with 'Apnoea' (p. 169), is called 
 c Asphyxia.' When it has set in, the heart very soon ceases to 
 beat, and death (by suffocation) occurs. 
 
 In the state of asphyxia, so long as the heart continues to beat, recovery 
 is still possible (except in cases where the blood has been saturated with 
 carbonic oxide) by distending the lungs with oxygen (artificial respiration). 
 The phenomena which were previously referred to as occurring necessarily 
 during the production of asphyxia then recur, but in inverse order, viz. first 
 of all spasms, then dyspnoea, then normal respiration, and lastly, if air be 
 very energetically introduced, apnoea. 
 
 In the dead bodies of asphyxiated animals no difference 
 exists between arterial and venous blood. All the blood of the 
 body is of a dark red colour (this is not the case when death 
 has resulted by the action of carbonic oxide) ; no oxygen 
 capable of being removed by the usual means is present, and 
 the blood exhibits, when it is examined with the aid of the 
 spectroscope, the absorption band of reduced haemoglobin (p. 
 46) ; the quantity of carbonic acid is, on the other hand, 
 increased, although not to such an extent as would correspond 
 with the diminution in the quantity of oxygen. The quantity 
 of combined carbonic acid and of nitrogen remain unchanged 
 (Setschenow). 
 
 If the blood of asphyxiated animals be shaken with oxygen, a portion of 
 the latter is at once consumed, carbonic acid being formed, apparently in 
 consequence of the presence of easily-oxidized (reducing) substances. 
 
 When the deficiency of oxygen persists for a long period, 
 but in a moderate degree, e.g., in cases of partial destruction of 
 lung, in one-sided pneumothorax, the requirement of oxygen 
 and its supply become adjusted : in consequence, those functions 
 of the body which are associated with oxidation become corre- 
 
174 FOREIGN GASES. 
 
 spondingly diminished, and the body becomes cooler, more flaccid, 
 the respiratory movements become more rapid. Continuous 
 deficiency of oxygen makes itself perceived by the darker colour 
 of the blood, which, aided by a relaxation of the smaller arteries, 
 causes the blue tint presented by the lips, and other mucous 
 membranes (Cyanosis). 
 
 Respiration of Foreign Gases. 
 
 In warm-blooded animals the supply of oxygen cannot, con- 
 sistently with the preservation of life, be dispensed with even 
 for the shortest time ; still the oxygen may be mixed with other 
 innocuous gases (hydrogen, nitrogen), as in the atmosphere. 
 
 The statement that nitrous oxide (laughing gas) could 
 replace oxygen for considerable lengths of time (H. Davy) has 
 not been confirmed ; pure N 2 causes dyspnoea and asphyxia to 
 occur at once in warm-blooded animals ; but in man the former is 
 not perceived, owing to the intoxication it produces (Hermann). 
 
 The other gases may be classified, in so far as their action 
 on living beings is concerned, in the following manner : 
 
 A. Indifferent Gases. These can, when mixed with oxygen, 
 be respired for an indefinite time without injurious conse- 
 quences. 1. Nitrogen; 2. Hydrogen; 3. Marsh gas. If in- 
 haled alone, they occasion dyspnoea, spasms, and asphyxia. 
 
 B. Irrespirable Gases. These can only be respired when 
 very small quantities of them are mixed with other gases, 
 because in more concentrated states they induce, by reflex ac- 
 tion, spasm of the glottis. To this group belong : 
 
 a. Gaseous acids. 1. Carbonic acid, which being the 
 weakest acid is in the least degree irrespirable, and can 
 therefore be respired in a tolerably concentrated form ; when it 
 is respired through tracheal fistulse it exerts a poisonous action 
 (it therefore has a place under Group C). 2. Hydrochloric acid ; 
 3. Hydrofluoric acid ; 4. Hyponitric acid ; 5. Sulphurous acid, 
 &c. 
 
 b. Gases which form acids : 1. Nitric oxide (NO), when 
 mixed with oxygen at once forms hyponitric acid (NO + = N0 2 ), 
 and would prove poisonous could it reach the blood (consult 
 Grroup C). 2. Phosgene gas (chloro-carbonic oxide), COC1 2 
 ^p. 23) when it comes in contact with water at once splits into 
 carbonic acid and hydrochloric acid (COC1 2 4- H 2 = CO, + 2HC1). 
 
FOREIGN GASES. 175 
 
 3. Chloride of boron (BC1 3 ) in contact with water gives boracic 
 and hydrochloric acids. 4. Fluoride of boron (B F1 3 ) in con- 
 tact wi|;h water gives boracic acid and hydroborofluoric acid. 
 5. Fluoride of silicon (SiFl 4 ) under similar circumstances gives 
 silicic acid and hydrofluosilicic acid, &c. 
 
 c. Alkaline gases. 1. Ammonia; 2. Substitution deriva- 
 tives of ammonia, as methylanium, &c. 
 
 d. Gases capable of forming substitution compounds or of 
 exerting an oxidizing action. 1. Chlorine ; 2. Fluorine (?) ; 
 3. Ozone. 
 
 Irrespirable gases can be introduced, through tracheal 
 fistulas, into the lungs of the lower animals; they generally 
 exert a strongly destructive action upon these organs. Spasm 
 of the glottis is therefore a protective act, and it ceases after 
 the vagi had been divided. 
 
 C. Poisonous Gases. These can be respired, but being 
 taken into the blood they lead to injurious or fatal conse- 
 quences. 
 
 This group can be subdivided as follows : 
 
 a. Reducing Gases. These become oxidized at the expense 
 of the blood, the oxygen of which they remove ; in this manner 
 they lead to the phenomena which are caused by a deficiency of 
 oxygen (p. 171), dyspnosa, convulsions, and asphyxia. 1. Sul- 
 phuretted hydrogen, H 2 S, is oxidized in the blood, H 2 and S 
 being formed. As soon as the blood has been freed from oxygen, 
 its haemoglobin is decomposed, with the formation at first of a 
 body like hsematin, then of a green substance: these actions do 
 not really go on in warm-blooded animals ; for before time for 
 their production has elapsed, death results in consequence of the 
 removal of oxygen (Hoppe-Seyler, Kaufmann and Eosenthal). 
 2. Phosphuretted hydrogen (PH 3 ) is oxidized in the blood, phos- 
 phoric acid and water being formed (Dybkowski). 3. Arseni- 
 uretted hydrogen, AsH 3 , and 4. Antimoniuretted hydrogen, 
 SbH 3 , appear to exert a similar action to the preceding. 5. 
 Nitric oxide gas, NO, appears at first to act as a reducing agent 
 (Hermann) : it is, however, irrespirable. 6. Cyanogen, C 2 N 2 , 
 also exerts a reducing action on blood, soon, however, leading to 
 further changes (Eosenthal and Laschkewitsch). 
 
 b. Gases which expel Oxygen.' These expel the oxygen from 
 its combination with haemoglobin, and then form a more stable 
 
176 FOREIGN GASES. 
 
 and a brighter coloured red compound ; they also occasion the 
 phenomena which are characteristic of a deficiency of oxygen. 
 
 1. Carbonic oxide gas, CO (compare p. 46). If the blood 
 be not completely saturated with CO, recovery is possible, for 
 the oxygen yet present in blood can oxidize the CO and produce 
 C0 2 (Pokrowsky). 
 
 2. Nitric oxide likewise forms a stable compound with 
 haemoglobin (Hermann) : in consequence of its irrespirable 
 nature, it cannot in reality exert this action. 
 
 c. Intoxicating gases, which, when inhaled with oxygen, 
 occasion loss of consciousness and anaesthesia : 
 
 1. Nitrous oxide gas, N 2 (H. Davy) ; 
 
 2. Chloride of Methyl, CH 3 C1 (Hermann); 
 
 3. Carbonic acid, C0 2 , leads to a series of complicated 
 phenomena, of which some have already been referred to at 
 pp. 79, 170, and 174 ; it further induces a kind of stupor 
 (Narcosis); the cause of these phenomena is not yet fully un- 
 derstood. 
 
 d. Poisonous Gases, the mode of action of which is not 
 known. To this class belong the majority of the remaining 
 gases, which have as yet been very slightly investigated. 
 
177 
 
 lj i i> It A It JL 
 
 I UNIVERSITY OF | 
 
 CALIF [A'. 
 
 " 
 
 CHAPTER V. 
 THE EXCHANGES OF THE MATTER OF THE BLOOD. 
 
 THE causes of loss and of gain to the blood (expenditure and 
 income) having been considered in the three preceding chapters, 
 the means by which the blood and its constituents remain 
 absolutely and relatively constant must now be discussed. 
 
 That under normal conditions of life the income and expen- 
 diture of the blood almost exactly balance is proved by the very 
 constant amount (tension) and composition of the blood. Slight 
 fluctuations occur, it is true, even in the normal state, but 
 these "are only temporary ; an example of such occurs during 
 the time of digestion, when the income decidedly preponder- 
 ates in amount over the expenditure. It is not yet possible to 
 strike a balance between the income and expenditure of the 
 blood, seeing that as yet it is impossible, even approximately, to 
 ascertain the exact amount of either. 
 
 Changes having their seat w, the Blood Corpuscles. 
 
 It is possible to conceive of changes in the chemical consti- 
 tuents of the blood corpuscles occurring without any simul- 
 taneous morphological change. Many facts, however, which 
 will be subsequently referred to, indicate that continually red 
 blood corpuscles are being destroyed, whilst new ones originate. 
 Other facts indicate that the new red corpuscles take their 
 origin in colourless ones. 
 
 Tolerably accurate facts are forthcoming in reference to the 
 origin of the latter (the colourless) ; but far less is known of the 
 place and nature of the transition of colourless into red cor- 
 puscles, or at least as to the exact mode of transition. 
 
 1. The colourless blood corpuscles are identical with the 
 lymph cells, but probably originate in new-born animals 
 
 N 
 
178 THYMUS, THYROID, ETC. 
 
 almost entirely in the lymphatic glands and follicles (as well as 
 in some apparently similarly constructed organs, as the thymus 
 and thyroid glands), in the spleen and the marrow of bones 
 (Neumann). The cells which are formed in the first-named 
 organs are poured into the blood with the lymph ; those which 
 originate in the spleen and the marrow of bones, on the other 
 hand (with the exception of those from the splenic follicles, 
 which appear to belong to the lymphatic system), are directly 
 mixed with the blood, in part after being already converted into 
 red corpuscles. 
 
 The lymphatic glands and follicles have already been alluded to. 
 
 The thymus gland, an embryonic thoracic organ which grows very 
 slowly after birth, and which later in life completely disappears, consists, 
 according to the most recent researches, of alveoli, which correspond com- 
 pletely to the lymphatic alveoli and follicles : it also contains products of 
 degeneration (fat cells, amyloid bodies, &c.). Its structure, and the abun- 
 dant lymphatic vessels supplied to it, lead one to look upon the thymus as 
 an organ similar to the lymphatic glands. In the thyroid body also, ac- 
 cording to some (Jendrassik and, in the case of the frog, Toldt), lym- 
 phatic alveoli occur as normal constituents. The cysts which are found in 
 the thyroid filled with colloid masses and crystals of unknown nature, are 
 looked upon as due to a degeneration, whilst other vesicles, filled with fluid 
 and lined with epithelium, are looked upon as the normal constituents. 
 
 The supra-renal capsules belong to a class of organs of like structure ; 
 the areolar tissue of these organs is filled with cells which, by some, are 
 considered identical, or almost identical, with nerve-cells. Concerning their 
 function nothing is known. In consequence of their richness in nerve-fibres 
 and in the above-mentioned cells, some look upon them as a variety of sympa- 
 thetic ganglia. Others consider them to be connected with the formation 
 of pigmentary matters. In a certain anomalous pigmented condition of 
 the skin (bronzed skin) the supra-renal capsules are diseased (Addison), and 
 a violet substance can be extracted from them (Holm). 
 
 The structure of the spleen is similarly involved in obscurity (on this 
 subject consult histological text-books). According to the now most 
 generally received conception, the following propositions may be stated : 
 
 1. The Malpiyhian vesicles, which are situated on the sides of the finer 
 arterial twigs, are to be considered as lymph follicles (Gerlach) ; these 
 form circumscribed thickenings of the arterial wall, and may be considered 
 as simple deposits of colourless (lymph) cells between the separated layers 
 of the adventitia; in many animals this alveolar thickening is not circum- 
 scribed, but is more uniformly distributed over the arterial wall (W. 
 Miiller). 
 
 2. The splenic pulp consists, according to some (W. Miiller, Frey), of 
 spaces which are quite similar to the alveoli of the lymphatic glands, except 
 that in the splenic pulp the blood-vessels play the same part as the lym- 
 phatics in the glands, i.e. the capillaries open into the alveoli, which are 
 
ORIGIN OF COLOURLESS BLOOD CORPUSCLES. 179 
 
 filled with lymph cells, and from the alveoli originate the veins. The con- 
 stituents of the blood thus become mixed with the lymph corpuscles which 
 are there. Besides the red and colourless cells, numerous transition forms 
 between the colourless and coloured blood corpuscles occur in these spaces, 
 and in addition coloured cells and nuclei, which are held to be red blood 
 corpuscles undergoing retrograde changes ; these nuclei are in part free, in 
 part enclosed in cell-like masses. Others (Billroth, Kolliker, Kyber, Wedl) 
 look upon the blood-vessels as forming a system of perfectly closed paths, 
 and explain the apparent admixture as artificial. The splenic pulp has an 
 acid . reaction, and, in addition to all the blood constituents, it contains 
 numerous products of oxidation : uric acid, hypoxanthine, xanthine, leucine, 
 tyrosine, inosite, volatile fatty acids (formic, acetic, butyric acids), and lactic 
 acid. It contains, in addition, numerous pigments, an albuminous substance 
 containing iron, and (a fact most worthy of notice) many compounds of 
 iron. The venous blood of the spleen contains an extraordinary number 
 of colourless cells (1 to 70 red, Hirt), and the coloured cells found in it 
 are distinguished from others by their small ness, by their being only 
 slightly flat, by their great resistance to the action of water and by their 
 not having a tendency to arrange themselves into rouleaux : these characters 
 are considered to be evidences of their recent formation. In addition, the 
 venous blood of the spleen, like the splenic pulp, contains many transitional 
 forms. 
 
 Extirpation of the spleen does not necessarily cause death. The function 
 of this organ appears to be capable of being replaced by other lymphatic 
 organs (lymphatic glands, marrow of bones), which enlarge under the cir- 
 cumstances. 
 
 The marroiv of bones contains, in an areolar network, which is quite 
 similar to that of the lymphatic glands, numerous colourless contractile 
 cells, which entirely agree in characters with lymph cells, and, in addition, 
 also transitional forms between these and red blood corpuscles (Neumann, 
 Bizzozero). The way in which these cells pass into the blood-vessels is 
 not yet ascertained. 
 
 The formation of lymph cells in all these organs is, according 
 to the more recent investigations, a process which in its nature 
 agrees with the origin of connective tissue corpuscles. 
 
 The analogous colourless contractile corpuscles, which are 
 able to wander actively from place to place, and are found in 
 the canal-system of the connective tissue, in the lumen of the 
 lymphatic vessels which originate from this tissue, in the 
 expanded canalicular system of the lymphatic glands and 
 follicles, and, lastly, in the analogous spaces in the spleen, are, 
 we must surmise, constantly being propagated (by a process of 
 fission), so as continually to replace those which pass into the 
 blood (Virchow, v. Recklinghausen). 
 
 N 2 
 
180 ORIGIN OF RED BLOOD CORPUSCLES. 
 
 These views are supported by numerous facts, and, amongst others, by 
 the following : the presence of lymph cells in lymph which has not yet 
 passed through any lymphatic gland or follicle ; further, the pathological 
 formation of lymph cells from undoubted connective tissue cells in leuk- 
 aemia, a disease in which also the formation of lymph cells in the lymphatic 
 glands or in the spleen (sometimes also in the medulla ossium), is morbidly 
 increased; lastly, according to some writers, the formation of pus cells 
 exactly similar to lymph cells by a multiplication of connective tissue cells 
 (Virchow, 0. 0. Weber, Rindfleisch, Strieker) ; this is, however, denied by 
 others (Cohnheim). 
 
 The new formation of colourless blood cells appears to be 
 thus shared by several formative organs, so that one can replace 
 or supplement the other. This conclusion is drawn from the fact 
 that extirpation of any of these organs (spleen, thymus, 
 lymphatic glands, &c.) is followed by no bad consequences to 
 the body, but is compensated for by a vicarious enlargement of 
 the remainder. When, however, several of these organs are 
 extirpated at the same time, life is endangered. 
 
 The formation of blood corpuscles in the embryo is quite different from 
 the process which goes on during extra-uterine life. The first blood cells 
 originate with the blood-vessels, inasmuch as the innermost layers of the 
 rows of cells which form the latter are directly converted into blood cells 
 and by fission give rise to new ones (Remak, Kolliker). Later on, as soon 
 as the liver is formed, the formation of blood corpuscles is transferred to 
 this organ (E. H. Weber, Kolliker) ; nevertheless, the process is not clear, 
 nor is the fact itself altogether certain. 
 
 Some (Lehmann, Funke) attribute to the liver, during the whole course 
 of life, the function of forming new blood cells, relying chiefly on the rich- 
 ness of the blood of the hepatic veins in colourless cells and in newly formed 
 red corpuscles (similar to those of the splenic blood) ; nevertheless these 
 observations permit of being otherwise interpreted (see below), and hitherto 
 no follicle-like organs have been detected in the liver. 
 
 2. The conversion of colourless into red blood corpuscles 
 appears to occur generally throughout the blood, although it 
 has only been directly demonstrated in the spleen, the venous 
 blood of which contains numerous transitional forms, and in the 
 marrow of bones. The chemical transformation upon which it 
 depends, viz. the origin of haemoglobin, is unknown ; it is affirmed 
 that this substance crystallises with peculiar readiness in the 
 newly formed red corpuscles (Funke). Haemoglobin appears to 
 originate under the influence of oxygen, inasmuch as lymph and 
 organs containing lymph are seen to assume a red tint on 
 exposure to air (Virchow, Friedreich). The morphological 
 
DESTRUCTION OF RED BLOOD CORPUSCLES. 181 
 
 change consists, according to the received view, in a disappear- 
 ance of the nucleus, which is followed by a general flattening of 
 the cell, which becomes red ; at the same time the corpuscle 
 appears to permit of diffusion taking place into it more and 
 more readily. The young cells, which have just become red, as 
 they are found in splenic and hepatic venous blood, swell but 
 slightly in water and are not as decidedly flattened as the 
 ordinary, older, blood corpuscles, which are easily destroyed by 
 water, are disk-shaped, and -are also larger. 
 
 In the frog the passage of colourless into red blood corpuscles can be 
 directly observed to occur in blood which has been drawn from the body 
 (v. Recklinghausen). The transitional forms which originate in this pro- 
 cess are also observed in the circulating blood. 
 
 A portion of the colourless cells may possibly not be converted into red, 
 but be destroyed by a process of fatty degeneration (Virchow). 
 
 3. Little is yet known in reference to the destruction of the 
 red corpuscles. It may be suspected to occur wherever colour- 
 ing matters originate, as it is probable that these all are derived 
 from blood colouring matter which has been liberated, therefore 
 especially in the spleen, the liver, the kidney, &c. 
 
 Most probably a considerable destruction of red blood corpuscles takes 
 place in the spleen and liver. 
 
 In the spleen, if actually the blood is (according to the previously enun- 
 ciated views) obliged to filter between the colourless cells of the alveoli, 
 many of the cells which penetrate therein with the arterial blood, are pro- 
 bably retained. The actual occurrence of such a retention is rendered pro- 
 bable by the following facts : the traces of substances which are due to the 
 destruction of coloured cells j the shrivelled cells caught in the act of retro- 
 grade metamorphosis; the pigmentary matters and ferruginous compounds 
 and perhaps also the oxidation products ; further, the circumstance that the 
 venous blood of the spleen contains only colourless and young red blood cor- 
 puscles. The cells which appear to contain blood corpuscles seem to originate 
 by colourless contractile cells taking into themselves red blood corpuscles. 
 
 A destruction of red blood corpuscles in the liver appears probable from 
 the fact that the salts of the bile acids possess the power of dissolving the 
 red corpuscles, as well as from the fact that bile pigment is formed; further, 
 from the extremely slow flow of blood through the liver, and lastly from 
 the poverty of the blood of the hepatic veins in the older red corpuscles. 
 The latter, like the splenic venous blood, contains, as has been already men- 
 tioned, only young coloured, and many colourless, cells (Lehmann) j from 
 this we may in nowise conclude that a new formation of blood corpuscles 
 takes place in the liver, for the new cells of the splenic vein are conducted 
 to the liver by the portal vein. If we suppose that the 'old' red cells 
 carried by the other radicles of the portal vein are in part or wholly 
 
182 EXCHANGES OF CHEMICAL CONSTITUENTS. 
 
 destroyed in the liver, the blood of the hepatic veins must naturally contain 
 a greater number of new elements than the portal bloqd. 
 
 Consequently it appears that a fractional portion of the blood contained 
 in the coeliac and mesenteric arteries loses its red corpuscles, in part directly 
 in the spleen and liver (hepatic artery), in part in the liver (portal vein) 
 only after the stomach and intestines have been supplied. Even in the 
 marrow of bones where pigment and cells containing blood corpuscles are 
 found (Bizzozero ; according to Neumann only in pathological conditions) 
 a destruction of red blood corpuscles must occur (Bizzozero). 
 
 Exchanges of the Chemical Constituents. 
 
 Even less is certainly known in reference to the exchanges of 
 the chemical than of the morphological constituents of the 
 blood. We are acquainted, it is true, in a general manner, as 
 has been explained in the last three chapters, with the consti- 
 tuents which the blood receives and excretes, but we only know 
 approximately the magnitude of this exchange, nor do we know 
 in what manner it is distributed over the various seats of ex- 
 change. Further, we know almost nothing on the question as 
 to whether chemical changes of its constituents go on within 
 the blood itself. 
 
 The fact that in fresh blood, which contains oxygen, but which 
 is free from carbonic acid, either no carbonic acid or only a 
 mere trace of it is formed, is opposed to the view that oxida- 
 tion takes place within the blood. On the other hand, it is usu- 
 ally assumed that the fibrinogenous substance originates either 
 within the blood or in the lymph, from other albuminous sub- 
 stances ; but even this is no certain fact, for it is possible that it 
 may be taken up, already formed, from some organ. It is further 
 ascertained that certain easily oxidisable substances, as lactate 
 or caprate of sodium, and glycerin (on the contrary not sugar, 
 or formiate, acetate or benzoate of sodium), when injected into 
 the blood are readily burned, and also when they are made to 
 pass, mixed with blood alone, through any organ ; it is, never- 
 theless, not known whether this process of combustion occurs 
 in the blood itself (Ludwig and Scheremetjewsky). 
 
 The exchanges amongst the chemical constituents of the blood 
 which take place during secretion and absorption may shortly 
 be summed up as follows. 
 
 1. The gaseous exchanges of the blood have already been 
 systematically discussed in Chap. IV. 
 
EXCHANGES OF CHEMICAL CONSTITUENTS. 183 
 
 2. The inorganic constituents are continually being absorbed 
 in large quantities from the digestive apparatus and from paren- 
 chymatous juices, and similarly are being given out to paren- 
 chymatous juices and secretions, water besides passing in the 
 process of cutaneous or pulmonary respiration, directly into the 
 atmosphere. 
 
 The constancy in the proportion of the inorganic constituents 
 of the blood is maintained by the following arrangements. 
 
 A. Water. A diminution of the water of the blood must so 
 influence the exchanges due to diffusion, that, on the one hand, 
 less water is given up by the concentrated plasma to the paren- 
 chymatous juices and secretions^, whilst on the other hand more 
 water is absorbed. Further, every diminution in the amount of 
 water of the blood is accompanied by a diminution of the volume 
 of that fluid, and therefore by a diminution of the pressure of 
 blood in the vessels, so that less, water is given up even in pro- 
 cesses of filtration. This effect is most marked in the diminu- 
 tion of the water contained in (and therefore in the amount of) 
 those secretions which are poured outside the body, such as the 
 urine and sweat. In the tissues themselves this effect of a 
 diminished blood pressure is noticeable only in their diminished 
 turgescence. 
 
 Finally, local deficiencies in the amount of water in certain 
 tissues give rise to specific sensations, which lead to an increased 
 quantity of water being taken with the food (Thirst, Chap. 
 VI). Conversely, an excess of water in the blood naturally leads 
 to increased excretion by filtration! and diffusion, which again is 
 manifested by an increase in the quantity of urine and sweat, and 
 by a cessation of thirst. 
 
 Concerning the distribution of water in the body, see 
 Chap. VI. 
 
 B. Salts. Even changes in the saline constituents of the 
 blood must modify, as is easily intelligible, the diffusion-ex- 
 changes of the blood in such a manner as to lead to an approxi- 
 mate constancy in its saline composition as a whole. We do 
 not, however, know by what means the amounts of the individual 
 salts are maintained constant, or whether a mutual replacement 
 occurs. 
 
 3. Organic constituents. As the forces in virtue of which or- 
 ganic substances pass into and out of the blood are as yet quite 
 
184 EXCHANGES OF ORGANIC CONSTITUENTS. 
 
 unknown to us, we cannot surmise the nature of the mechanism, 
 analogous to that alluded to in discussing the inorganic constitu- 
 ents, which maintains them in an approximately constant quan- 
 tity. We merely know that a continual introduction of organic 
 alimentary substances takes place in consequence of certain 
 mysterious sensations (hunger and thirst), the intensity of which 
 varies with the wants of the system. 
 
 The receipt of organic substances into the blood occurs in 
 part without any further change, when they are absorbed from 
 the food without having undergone chemical changes ; this is 
 the case with many of the soluble organic constituents of food, 
 with a portion of the soluble albumin, and, lastly, with a por- 
 tion of the fat, which is absorbed into the blood in a state 
 of simple emulsion. 
 
 The greater number of the alimentary constituents undergo, 
 however, chemical changes in the process of digestion (Chap. 
 III.), and the products of these which are absorbed, appear (after 
 absorption) to undergo farther changes before they are converted 
 into constituents of the Hood. These changes, which are in 
 great part tmknown, are 'expressed by the term 'assimilation. 
 The following processes of assimilation have been as yet approxi- 
 mately discovered : 
 
 1. Albuminous bodies, gelatin and allied substances are in 
 part converted into peptones before absorption, and in part 
 they are still further decomposed. Inasmuch as peptones can- 
 not be detected in the juices or tissues (Lehmann, Hoppe- 
 Seyler and De Bary) and do not pass into the urine (Fede), 
 they must rapidly be converted into other bodies, presumably 
 into albuminous bodies. 
 
 2. A portion of the fatty matters undergoes decomposition in 
 the intestine, and being saponified, absorption of soaps occurs. 
 Seeing that from soaps taken as food the corresponding fats are 
 formed in the animal body, it is probable that the soaps which 
 are formed in the intestine can, after absorption, be reconverted 
 into fats (Radziejewsky). 
 
 3. Sugar, ingested as such or formed in the process of diges- 
 tion out of starchy constituents of food, is, after absorption, 
 converted into a starch-like substance (glycogen) in the liver 
 (see the Appendix to this chapter). 
 
ASSIMILA TION SYNTHESIS. 185 
 
 Seeing that a portion of the albuminous bodies undergoes absorption with- 
 out a previous conversion into peptones, some suppose that peptones are not 
 reconverted into albumin, but, being burned up so as to furnish urea, are 
 excreted. 
 
 The seat of these processes of assimilation is as yet un- 
 known. Many suppose them to occur in the liver, in which organ 
 especially the processes referred to under ( 3) are to be localised. 
 These processes are, as a whole, synthetic, in opposition to the 
 hydrolytic processes of decomposition which occur during di- 
 gestion, and of which they are the exact reversals (another syn- 
 thesis which goes on in the body, that of hippuric acid from gly- 
 cocine and ingested benzoic acid, apparently occurs in the liver, 
 Ku'hne and Hallwachs). The process by which the alimentary 
 principles are split up in the intestine (the products of decom- 
 position being, after absorption, employed in synthetic pro- 
 cesses, partly in the re-formation of the original substances), is 
 of use from two points of view (Hermann) ; in the first place, 
 the products of decomposition are in general, on account of 
 their smaller molecules, more easily absorbed than the original 
 substances ; in the second place, the products of decomposition 
 furnish a more simple formative material, which alone renders 
 possible the synthesis of the numerous substances which the 
 body requires. 
 
 The majority of the complex substances which the body requires must 
 necessarily first arise within it by synthetic processes. As the introduction, 
 with the food, of ready-made haemoglobin, of undecomposed muscular sub- 
 stance, &c., is impossible, because these bodies are partly decomposed 
 spontaneously, and partly in the alimentary apparatus, it follows that 
 assimilation must consist of syntheses (Hermann). 
 
 In reference to haemoglobin it has been ascertained that its quantity in 
 the blood is increased by an albuminous diet (Subbotin). 
 
 As little is known of the nature of the processes which are 
 concerned in the supply of organic constituents from the blood 
 to the tissues, as of those concerned in the introduction of 
 organic constituents into the blood. 
 
 Constancy of the Amount of Blood in the Body. 
 
 The constancy in the amount of the blood in the body 
 naturally depends upon the constancy of the different consti- 
 tuents of the blood. As water is by far the principal ingredient 
 
186 CONSTANCY OF THE AMOUNT OF BLOOD. 
 
 of the blood (forming about 80 per cent, of its weight), and as 
 the volume of blood is almost equal to that of the water which 
 it contains, it follows that in the preservation of the constancy 
 of the volume of blood, the constancy in the quantity of water 
 is of greatest importance ; the mechanism concerned in the 
 preservation of the latter has been already discussed. Actually, 
 after great losses of blood, its volume is very soon restored, for, 
 under the diminished blood-pressure, less water is given up to 
 the tissues and to the secretions and more is absorbed, whilst, 
 in addition, increased thirst leads to increased introduction of 
 fluids. 
 
 APPENDIX TO CHAPTER V. 
 
 FORMATION OF GLYCOGEN AND SUGAR IN THE TISSUES. 
 
 IN many cf the animal tissues there occurs a starch-like, or, 
 more correctly, a dextrin-like substance, named glycogen^ which 
 is very easily converted into sugar by the same means as effect 
 the conversion of starch. This substance occurs principally in 
 the liver (Bernard, Hensen), in muscles (Macdonell, 0. Nasse), 
 in nearly all the tissues of the embryo and of its appendages 
 (Bernard), as well as in the tissues of young animals, and in 
 newly-formed pathological formations (Kuhne). 
 
 Qlycogen appears to occur frequently in small organisms, e.g. it is found 
 in the Ascaris lumbricoides, and principally in its muscles (Foster). Sugar- 
 forming (glycogenic) substances, which more or less closely resemble the 
 glycogen of the liver, occur also in the brain (Jaffe), in the muscles (dextrin, 
 Limpricht), in many glands (Kuhne, Briicke), in blood (Briicke), &c. 
 
 Glycogen is obtained from liver by pounding the perfectly fresh organ 
 in sand and water at 100 C., acidulating the fluid so as to completely de- 
 compose the alkaline albuminates, filtering and boiling the residue with 
 fresh portions of water until the filtrate is no longer opalescent. The united 
 precipitates are evaporated to half their bulk and precipitated with alcohol, 
 by which the glycogen, mixed with some glutin, is precipitated in white 
 flakes ; from the latter it is purified by boiling with caustic potash, neutral- 
 ising and precipitating with alcohol. 
 
 It is more easily obtained free from nitrogenous contaminations by pre- 
 
FORMATION OF SUGAR. 187 
 
 cipitating the aqueous extract of liver by means of a solution of iodide of 
 mercury in iodide of potassium previous to throwing dowii the glycogen by 
 means of alcohol (Briicke). 
 
 Ferments which are capable of converting glycogen into 
 sugar, are not only contained in the sugar-forming secretions 
 (saliva, pancreatic juice) but also in the liver (Bernard), in the 
 blood, and in almost all the tissues (v. Wittich, Lepine). The 
 liver when removed from the body contains large quantities of 
 sugar, which go on increasing as long as glycogen is present. 
 
 A question which has not yet been decided is whether the 
 liver contains sugar during life. A perfectly fresh liver taken 
 from an animal immediately after it has been killed contains, 
 according to some (Bernard, Kiihne), small but yet perceptible 
 quantities of sugar, according to others (Pavy, Bitter, Schiff, 
 Eulenburg), not a trace. A formation of sugar in the liver 
 during life is further rendered probable by the fact that the 
 hepatic venous blood of animals fed upon a diet containing 
 neither starches nor sugars, is richer in sugar than the blood 
 of the portal vein (Bernard, Tieffenbach) ; this continuous pas- 
 sage of sugar has been found to be associated with the presence 
 of only a very small quantity of, or even with no sugar in 
 the liver, whilst the very presence of sugar in the liver, and 
 specially its presence in the blood of the hepatic veins, has 
 been denied (Pavy, Ritter, Schiff). 
 
 Those who suppose that no sugar is formed in the liver during 
 life, argue either for the presence of a sugar-forming ferment 
 which is only formed after death or in pathological conditions 
 (Diabetes) (Schiff), or suppose that the ferment being present is 
 restrained from exerting its action by a kind of inhibitory 
 influence of the nervous system (Pavy). 
 
 The pre-existence of such a ferment in the blood and tissues 
 has lately been contradicted (Lepine, Plosz, Tiegel). 
 
 Blood exerts no action on glycogen unless its corpuscles 
 have been destroyed (by the action of water, ether, &c.) so that 
 probably the blood corpuscles generate the ferment at the 
 very moment of their destruction (Plosz, Tiegel). It is worthy 
 of observation in reference to this matter that probably a 
 destruction of blood corpuscles is continually taking place in 
 the liver. 
 
 The presence of glycogen in the liver depends very much 
 
188 FORMATION OF SUGAR. 
 
 upon the food. Its amount is large in proportion as the latter 
 is rich in carbo-hydrates (Pavy, TscherinofF). 
 
 In warm-blooded animals which are starved glycogen disap- 
 pears in the course of a few days, and reappears in large quan- 
 tities after the injection of sugar into the intestine (Dock). 
 The same result is produced by injections of glycerin (Weiss). 
 Hence we must conclude that glycogen is derived in the liver 
 from sugar, by the formation of an anhydride. 
 
 Another supposition, which has been investigated, considers 
 other substances (proteids) to be the source of glycogen ; gly- 
 cogen is, however, easily further oxidized, if other easily-oxi- 
 dized substances, such as sugar, are not present to keep oxygen 
 from attacking it. In support of this is adduced the fact 
 that even injections of glycerin into the intestine cause the liver 
 to contain glycogen. In opposition to it, recent researches 
 would show that sugar is not an easily oxidized substance 
 (Scheremetjewsky) ; further, some other easily oxidized sub- 
 stances, e. g. sodium lactate, bring about no increase in the 
 quantity of glycogen, and glycerin does so only when it is 
 injected into the intestines, and not when it is subcutaneously 
 injected (Luchsinger). Other kinds of sugar, as milk-sugar 
 and levulose, furnish normal glycogen (Luchsinger). 
 
 The different kinds of sugar, and glycerin, which is closely 
 allied to them, appear to be converted into glycogen when they 
 are carried to the liver in the blood of the portal vein. In sup- 
 port of this it may be stated that sugar when injected into the 
 portal vein does not appear in the urine, whilst it does so when 
 it is injected into other veins (SchopfTer). 
 
 The destination of the glycogen of the liver is not accurately 
 known. Those who believe that a formation of sugar takes 
 place during life suppose that glycogen is converted into sugar, 
 which is partly excreted and partly burned. Other possible 
 hypotheses as to its destination are the following : that it is 
 carried to other organs which contain glycogen (the muscles, 
 the testicles) and is there consumed; further, that it is con- 
 verted into other substances, e. g. into fats, &c. 
 
 Under certain circumstances an abundant excretion of sugar 
 takes place through the urine diabetes. 
 
 These circumstances are : 1. Pathological alterations the 
 seat and nature of which are unknown to us (pathological 
 
DIABETES. 189 
 
 diabetes). 2. Injury of a limited space in the medulla oblongata, 
 in the floor of the fourth ventricle (traumatic diabetes, Ber- / 
 nard). 3. The action of certain poisons, especially of curare. 
 4. The injection of very dilute salt solutions into the blood- 
 vessels (Bock and Hoffmann). The cause of diabetes may be 
 sought for : a. in a conversion (or increased conversion) of the 
 glycogen of the liver or of other organs into sugar ; b. in a 
 diminished conversion of ingested sugar into glycogen ; c. in 
 a diminished destruction of sugar normally originating in the 
 glycogen of the liver. 
 
 In pathological diabetes the sugar disappears, almost if not entirely, 
 from the urine, when no carbo-hydrates are taken as food. Even puncturing 
 the floor of .the fourth ventricle (der Zuckerstich) induces no diabetes if the 
 animals have, in consequence of starvation, livers free from glycogen (Dock). 
 
 In animals in which diabetes has artificially been induced, feeding with 7 
 sugar does not, as it normally does, cause the liver to contain glycogen. Jj ** 
 Hence it follows that traumatic, and probably also pathological, diabetes ' 
 de L end upon the incapability of the liver to arrest "the "sugar which is " 
 brought to it, and convert it into glycogen, so that sugar passes unchanged 
 into the urine, or accumulates in other organs. On the contrary, starved 
 animals become diabetic under the influence of curare, even when no sugar 
 is furnished to them (Dock) ; probably in this case the sugar is derived "j 
 from a store of glycogen (possibly contained in muscles) which is converted 3 "*" 
 into sugar. 
 
 The proximate cause of traumatic diabetes has lately been sought for in 
 a paralysis of the blood-vessels of the liver (Schiff, Cyon and Aladoff). 
 
 The spot on the fourth ventricle the puncture of which occasions diabetes 
 is possibly a portion of the vasomotor centre (Chap. XI.) 
 
 Even other injuries affecting the vasomotor supply of the liver, e.g. injury 
 of the inferior cervical ganglion or of the nerves which proceed from it to 
 the ganglion stellatum, occasion diabetes. On the contrary section of the 
 splanchnic nerves, which probably lowers the blood pressure too much, 
 does not induce diabetes (Cyon and Aladoff). It is indeed asserted that 
 irritation of the splanchnic nerves causes diabetes (Grafe). Even diabetes 
 induced by curare may possibly be referred to a vasomotor paralysis. 
 
 From what has been previously stated vasomotor paralysis should, on I 
 the one hand, hinder the formation of glycogen from sugar, or should 
 convert the glycogen (whether stored up in the tissues or newly formed) 
 into sugar, by exciting a hitherto unexplained influence upon the develop- 
 ment of the amylolytic ferment. When diabetes follows the injection of dilute 
 saline solutions, the destruction of blood corpuscles may take a part in the 
 formation of the ferment ; in these cases the ferment passes into the urine 
 (Plosz and Tiegel). 
 
190 
 
 CHAPTEK VI. 
 
 EXCHANGES OF THE MATTER OF THE BODY, AS A WHOLE. 
 
 I. INCOME. 
 
 As has already repeatedly been said, the organism receives 
 regularly from without : 
 
 1. Food, i.e. material for the repair of that which has been 
 excreted either after undergoing oxidation, or in an unoxidized, 
 unaltered condition. 
 
 2. Oxygen, for the oxidation of those constituents of the 
 body capable of it. All that is to be said concerning the 
 introduction of oxygen will be found in Chap. IV. Food, on the 
 other hand, here requires a closer consideration. 
 
 Food, 
 
 The elements of food must in general be the same as those 
 of the body, if they are to serve for the repair of the losses of 
 the latter. Their introduction into the body in an isolated 
 condition is, however, of no value for the purposes of nutrition, 
 because in the case of some of them absorption into the blood 
 is impossible, and in the case of others which are capable of 
 absorption their elaboration into the chemical compounds which 
 they are to repair is not practicable within the body. As a 
 rule, therefore, chemical compounds alone are capable of use as 
 food, and only in so far as they satisfy the following conditions : 
 
 1. The compound must be fit for absorption into the blood 
 or chyle, either directly or after preparation by the processes of 
 digestion (i. e. it must be 6 digestible '). 
 
 2. It must replace directly some inorganic or organic consti- 
 tuent of the body ; or it must undergo conversion into such a 
 constituent while in the body ; or it must serve as an ingredient 
 
FOODS. 191 
 
 in the construction of such a constituent. Neither itself nor 
 any of the possible products of its decomposition must be detri- 
 mental to the structure or activities of any of the organs of the 
 body (such detrimental bodies are called ' poisons '). 
 
 Scarcely a single nutritious substance is taken into the body 
 by itself, almost all being ingested, when mixed together in 
 certain proportions found in nature and called ' Foods,' which 
 are for the most part vegetable or animal tissues or portions of 
 such tissues. These also are generally further mingled together 
 by artificial means and prepared in various ways, partly to 
 facilitate digestion and partly to render them more palatable. 
 
 In the preparation of nutritious material as foods, the most essential 
 process is the addition of so-called ' spices/ that is to say, of substances 
 possessed of such stimulating qualities as render them peculiarly fitted for 
 inducing in a reflex manner the secretion of the alimentary juices (saliva, 
 gastric juice, &c.). The commonest seasoning is salt, which, however, is, in 
 addition, a nutritious body (see below). The preparation of food by boiling, 
 roasting, baking, &c., has for its special object to assist the processes of 
 digestion by anticipating certain of its stages, e.g. by dissolving what is 
 soluble, by rendering capable of solution what is insoluble, by loosening 
 the compacter portions, by breaking indigestible skins or husks, &c. 
 
 In consequence of what has been said above, all nutritious 
 substances fall into two natural classes, both of which ought to 
 be represented in the food. The first class, which serves for 
 the repair of the unoxidizable constituents of the body, consists 
 of the inorganic elements of food, essentially water and salts ; 
 the second, destined to replace the oxidizable portions which 
 are lost, and including therefore bodies which are themselves 
 oxidizable, consists of the organic elements of food. The latter 
 in common with all organic substances are derived immediately 
 or mediately from plants ; for even the organic constituents of 
 the animal body (forming ' animal food ') can be traced back to 
 the vegetable kingdom, as carnivorous animals feed directly or 
 at least in the last instance upon herbivorous animals. 
 
 Only a very small proportion of the various organic com- 
 pounds of C, H, N, 0, S, etc., which are formed in plants, really 
 rank as nutritious substances, as many do not fulfil the pre- 
 viously mentioned conditions. The animal substances result- 
 ing from the assimilation of such of them as are reallv 
 nutritious must plainly be capable for the most part of again 
 serving as nutriment; they are the more worthless in this 
 
192 ORGANIC CONSTITUENTS OF FOOD. 
 
 respect the higher the degree of oxidation to which they have 
 attained. That is to say, the value of a nutritious substance 
 is chiefly determinable by the amount of potential energy 
 associated with it; i.e. by the quantity of kinetic energy or 
 work which may result from its combustion. The more highly 
 oxidized the nutritious substances, the less is the amount of 
 oxygen which they are in a condition to combine with, and the 
 more incapable are they of furnishing energy to the body. Thus 
 urea has no value as a food, creatine very little, while, on the 
 contrary, albumin and sugar are of the highest importance. 
 
 The substances which form the essential organic food of the 
 body would be indicated by considering all the regular con- 
 stituents of the body (pp. 12 et sg.), as indispensable to it, and 
 inquiring whether > they were capable of formation out of any 
 other substance contained in the animal body ; those which were 
 not would of necessity have to be taken into the organism along 
 with the food. 
 
 It must, however, here be remembered that in the first place 
 all the substances occurring in the body cannot be regarded as 
 indispensable to it. There is a danger therefore in following the 
 method just given of considering too many nutritious substances 
 as necessary ; and a reservation would have to be made on this 
 account. Moreover it must not be forgotten that a certain 
 number of the constituents of the body cannot be replaced by 
 the introduction of a fresh supply along with the food, either 
 because they are incapable of absorption and indigestible (e.g. 
 mucin, keratin, cholic acid); or because they unavoidably 
 decompose before they are ingested (e.g. muscle-substance in 
 the act of rigor), or are decomposed in the alimentary canal 
 (e.g. hsemoglobin by the acid of the gastric juice) ; or because 
 they would become rapidly changed oxidized after absorp- 
 tion, before they could reach their proper situation. Such 
 substances, therefore, are only produced within the organism. 
 
 Our efforts to discover, by the above method, the essential 
 constituents of food are chiefly frustrated by our ignorance of 
 the synthetic powers of the organism. In the preceding chapter 
 it was said that, most probably, in the course of assimilation, 
 albuminous bodies were formed from peptones, fats from soaps 
 (and glycerin), and glycogen from sugar. It is, however, yet 
 unknown whether, for example, the results of the further de- 
 
ORGANIC CONSTITUENTS OF FOOD. 193 
 
 composition of albuminous bodies (leucine, tyrosine, &c.), are 
 capable of synthetic regeneration into albumin. If the organism 
 possessed in general the power of uniting substances syntheti- 
 cally, with the elimination of water, we might briefly indicate 
 the following as necessary organic nutritious substances : viz., 
 the products of the hydrolytic decomposition of all the essential 
 constituents of the body, i.e. of the albuminous bodies and their 
 compounds, of the glucosides, of the lecithin-bodies, of fats, &c. 
 These decomposition-products might be contained in food 
 either in an isolated form or already combined into some 
 group, which would in that case be again split up in the course 
 of digestion. The above-mentioned bodies, which have been 
 taken as examples, might therefore be represented in the food 
 in the following ways : (a) fatty acids (soaps), glycerin, phos- 
 phoric acid, sugar (starch), peptones ; (6) fats, phosphoric acid, 
 sugar (starch), albumin; (c) lecithin, sugar (starch), albumin; 
 or (d) protagon, albumin, &c. 
 
 The question is still further complicated by the circumstance 
 that we do not know whether, in addition to hydrolytic de- 
 compositions, other prof o under chemical changes (apart from 
 oxidations) do not take place in the body. Fats especially seem 
 to be capable of originating from other bodies than fats and 
 lecithin, for the animal body may contain a large quantity of 
 fat even when the food contains none. Fats might be derived 
 in the organism from the following sources besides those already 
 mentioned : 
 
 1. From albuminous bodies, as is indicated (a) by the ap- 
 pearance of a fatty body (adipocere) in the albuminous tissues of 
 dead bodies ; (6) by the formation of fat out of casein in stand- 
 ing milk ; (c) by a similar process in the ' ripening ' of cheese ; 
 (d) by the appearance of stearin in the body, when, in addition 
 to albumin, a kind of fat (palm oil) containing no stearin is 
 taken with the food (Subbotin). Other phenomena which are 
 cited to prove the formation of fat from albuminous bodies, 
 etc., e.g. the ' fatty degeneration ' of organs rich in nitrogen, 
 cannot be regarded as giving any support to the theory, as 
 they simply show that at one part of the organism, which is 
 in connection with every other part by the continual inter- 
 change of material, one body is deposited, instead of another, 
 and this cannot, of course, be taken to prove that the cne is 
 
 o 
 
194 ORGANIC CONSTITUENTS OF FOOD. 
 
 derived from the other. In like manner, some time since, it was 
 customary to mention among the proofs of the formation of fat 
 from albuminous bodies the fact that the crystalline lens and 
 other nitrogenous bodies destitute of fat when placed in the 
 abdominal cavity of a living mammal became after some time 
 very fatty having lost some of their nitrogen. But all the ex- 
 periments devised to control this result, in which indifferent 
 porous materials, such as wood, elder-pith, &c., were substituted 
 for the fatless nitrogenous body, have shown that these bodies 
 also become impregnated with fat. 
 
 2. From carbo-hydrates. Although the transformation of 
 carbo-hydrates into fats would have to be regarded as a process 
 of reduction unless indeed we suppose the former to yield only 
 the glycerin necessary for the latter the following circum- 
 stances seem to indicate some such operation : (a) Bees fed on 
 sugar alone yield a fatty body, wax ; (b) Food containing a large 
 quantity of carbo-hydrates tends to fatten the body (' Fatten- 
 ing,' see below), an accumulation of fat taking place imme- 
 diately, in such cases, in the liver (Tscherinoff). The last- 
 mentioned circumstances admit of another explanation, viz. that 
 the oxidation of the easily combustible carbo-hydrates renders 
 unnecessary the combustion of fat or fat- forming bodies (e.g. 
 albuminous bodies); but of this more will be said hereafter. 
 The fact that fats are formed in some fruits (olives) out of 
 carbo-hydrates (mannite) cannot be taken to support the theory 
 that a similar process occurs in animals. 
 
 It is now considered that albumin is the only source of the fat in the 
 body, except that which is derived from the fat directly eaten ; for in all cases, 
 even in the enormous formation of fat which takes place in milch-cows, the 
 fatty and albuminous materials of the food are sufficient to account for the 
 fat in the milk yielded. Moreover, the production of wax by bees fed 
 entirely on sugar is explicable by the theory oi its formation from the albu- 
 min stored up ; and the fattening of cattle on hydro-carbons is only success- 
 ful when albuminous food is at the same time taken (Voit). 
 
 We are, therefore, guided in the choice of alimentary sub- 
 stances solely by experience, which teaches us that, after water 
 and salts (of which chlorides and phosphates are the chief), 
 albuminous bodies are most indispensable. To what extent true 
 albuminous bodies may be replaced by digestible albuminoids 
 gelatin and gelatigenous tissues we shall have occasion to 
 discuss in the third division of the present chapter. It would 
 
CHIEF ARTICLES OF DIET. 195 
 
 seem, moreover, that fats (stearin, palmitin, olein, etc.) may 
 only be omitted from the food when the albuminous bodies are 
 present in it in large excess or when the fats are represented by 
 carbo-hydrates. It is probable, however, that we are not at 
 present acquainted with all the indispensable- alimentary sub- 
 stances. 
 
 The following are among the more important articles of 
 food: 
 
 1. Flesh (muscle) contains, besides water and salts (especially of potas- 
 sium) amongst the more essential nutritious elements (Chap. VIII.), 
 several albuminous bodies (myo&in, albumin), gelatigenous tissues, small 
 quantities of lecithin (possibly derived from the intra-muscular nerves), fats 
 and certain ' extractive matters/ some of which are agreeable to the taste 
 C osmazome '), while others seem to have weakly stimulating properties 
 (creatine, c.). It is ingested raw, boiled with water, or roasted. After 
 boiling, the extract broth of meat contains chiefly the gelatin, the ex- 
 tractive matters, the salts (which on account of the potassium they contain 
 cause concentrated broths to have an important effect upon the heart, 
 Kemmerich), and some of the fat floating on the surface. The albuminous 
 bodies are insoluble in hot water, and remain behind in meat which is 
 immersed at once into hot water ; if cold water be used, the albumin passes 
 into the water, coagulates as the latter becomes heated, and is removed with 
 the ' scum.' The flesh which remains behind after the removal of the broth 
 still retains most of the nutritious constituents (myosin and the gelati- 
 genous tissues, and albumin if the water used were hot to commence with), 
 but has lost its salts and those bodies which gave it an agreeable flavour. 
 Meat which has been roasted, i.e. strongly heated with the addition of little 
 or no fluid substance (water or fat), retains all its constituents ;. and certain 
 brown, empyreumatic bodies possessed of an agreeable taste and smell are 
 formed in it, especially at the surface. 
 
 2. Milk contains albuminous bodies (albumin, casein), fats (butter), 
 and probably lecithin, besides carbo-hydrates (milk-sugar), water, and 
 a considerable quantity of salts. It may be ingested fresh or sour : or 
 the butter alone may be taken ; or the cheese alone. Cheese, however, or 
 the casein precipitated on the acidification of milk, whether occurring spon- 
 taneously or on the addition of -rennet' (the mucous membrane of the 
 calf's true stomach), includes a considerable amount of the fat. On stand- 
 ing, cheese undergoes a change similar to that of digestion, becoming soft 
 and translucent owing to the formation of peptones and the further decom- 
 position of casein. This is called ' ripening,' in the course of which fat 
 is said to be formed out of casein and leucine and tyrosine to appear. 
 Concerning whey and kumiss, see p. 125. 
 
 3. Eggs. The white of egg contains a concentrated solution of albumin, 
 while in the yolk are found albuminous bodies, much lecithin, cholesterin 
 and fats, and sugar. On heating, the white coagulates firmly, the yellow 
 into a mass which readily crumbles. 
 
 o 2 
 
196 CHIEF ARTICLES OF DIET. 
 
 4. Cereals (wheat, rye, maize, barley, rice, oats, &c.) contain an albu- 
 minous body (gluten, vegetable fibrin, which are insoluble in water), an 
 albuminoid (vegetable gelatin), lecithin (Hoppe-Seyler), traces of fat, 
 starch in large amount, and, especially at the time of germination, an amy- 
 loid ferment (diastase). Grain which has been ground and freed from the 
 husks (bran) is called flour or meal, and is used chiefly in the preparation 
 of bread. On mixing flour with water a tenacious mass, dough, is formed 
 by the action of the latter on the gluten. This dough must be then loosened 
 or rendered spongy, and afterwards heated strongly. The loosening is 
 effected by the evolution in the dough of carbonic acid gas, produced by the 
 conversion of part of its starch, by means of the diastase, into dextrin and 
 sugar, and the fermentation (alcoholic) of the latter on the addition of barm 
 or yeast. The dough thus caused to l rise ' is then heated to about 200 C., 
 which serves to drive off the alcohol at once. The plan of introducing arti- 
 ficially prepared carbonic acid into the dough instead of evolving it by 
 means of fermentation has recently been adopted (aerated bread). Another 
 substance derived from cereals is beer, a watery decoction of grain (malt) 
 which is germinating, and therefore rich in dextrin and sugar. Yeast is 
 added to the decoction, which thereupon undergoes alcoholic fermentation. 
 Beer contains chiefly dextrin, alcohol, bitter substances which are added to 
 it, and absorbed carbonic acid. Of all intoxicating liquors it is the one 
 which contains least alcohol (2-8 p.c.). On distillation, beer and similar 
 fermented liquids prepared from malt (or potatoes) yield a beverage (brandy) 
 very rich in alcohol. 
 
 5. Leguminous fruits (peas, beans, lentils, &c.) contain a great quantity 
 of an albuminous body (legumin), besides lecithin and starch. They are 
 eaten for the most part after having been boiled in water, the starch being 
 therefore in the form of a paste. It is not possible to use them in the pre- 
 paration of bread, as they do not form a dough on account of the absence of 
 gluten. 
 
 6. Potatoes chiefly contain starch, in addition to a small quantity of 
 albumin. 
 
 7. Fruits which are sweet contain various kinds of sugar, dextrin, 
 vegetable gelatin, very little albumin, and organic acids (tartaric acid, malic 
 acid, citric acid, &c.) Many species, especially grapes, furnish alcoholic 
 beverages wines on fermentation of their juices. 
 
 8. The green parts of plants (leaves, stalks, &c.), and roots, contain 
 chiefly starch, dextrin, sugar, and albuminous bodies in small amount. 
 
 All vegetable alimentary substances contain, as their chief constituent, 
 cellulose, which is almost or entirely incapable of digestion by man and 
 carnivorous animals, but which is. probably of great nutritive value to 
 herbivorous animals. 
 
 Ingestion of Food. 
 
 The ingestion of food takes place voluntarily, at intervals 
 which are, for the most part, of such short duration that diges- 
 tion and absorption are scarcely interrupted, at least during the 
 
THIRST. HUNGER. 197 
 
 day. It receives its stimulus in certain sensations, hunger and 
 thirst, which have not hitherto been satisfactorily explained, 
 but which indicate the lack of nourishment on the part of the 
 organism. The sense-organs in which this necessity of the 
 whole body makes itself felt as a sensation are certain parts of 
 the alimentary apparatus. Thirst alone takes the form of a 
 localised sensation, a feeling of dryness and burning in the 
 throat, occasioned by deficiency of water in the mucous mem- 
 brane of the palate and pharynx. This deficiency of water is 
 usually but the local manifestation of the general state of the 
 tissues of the organism. It may, however, be produced by 
 drying the mucous membrane of the throat (by blowing dry 
 air over the part), or by withdrawing the water in some other 
 way (by the application of hygroscopic salts). The feeling of 
 thirst may be allayed as a rule by the local application of water 
 to the parts concerned ; and, as this is accomplished most fre- 
 quently by drinking, the whole body is at the same time supplied 
 with water. Other methods of introducing water into the 
 system, e. g. its injection into veins, also allay it, as would be 
 expected from the circumstance that it results from the general 
 deficiency of water in the tissues (Chap. X., Sec. v.). Hunger, on 
 the contrary, which is a pressing, gnawing sensation in the 
 stomach, and, in its later stages, in the intestine also, cannot be 
 regarded as the local expression of a general lack of nutriment 
 occasioned by deficiency of material in the neighbourhood of 
 the gastric and intestinal membranes. It is, as it seems, a 
 sensation of emptiness in the digestive organs, the conditions 
 of which are yet quite unknown ; for it may be assuaged by 
 filling the stomach, even though it be with indigestible matter. 
 In such a case, of course, a sensation of general lack of nourish- 
 ment supervenes after a time, which differs from the usual 
 feeling of hunger, but the nature of which is as little under- 
 stood. 
 
 The nerves which minister to the sensation of thirst are probably some 
 or all of those of the palate and pharynx (trigeminal, vagus, and glosso- 
 pharyngeal). Those concerned in hunger are yet quite unknown. Section 
 of the vagi and of the splanchnics does not diminish the desire for food in 
 animals. 
 
198 EXPENDITURE OF THE ORGANISM. 
 
 II. EXPENDITUKE. 
 
 The substances which the body is continually giving up as 
 of no further use to it are : 
 
 1. Substances which are quite incapable of taking part in 
 the exchanges of matter, viz. the indigestible portions of food. 
 
 2. Those results of the oxidations occurring in the body 
 which are incapable of any further oxidation while within the 
 body, viz. carbonic acid, water, urea, and uric acid. 
 
 3. Certain secreted materials which have been poured out 
 on the internal or external surfaces of the body in order to be 
 utilised there, and which, on account of some property, are 
 incapable of reabsorption, e.g. the insoluble constituents of 
 bile, the mucus of the alimentary secretions, the fats of the 
 tegumentary secretion, horny substance, &c. 
 
 4. A portion of the unoxidizable constituents of the body, 
 water and salts which are continually excreted, owing to 
 their physical deportment towards other bodies ; for exEimple, 
 water is excreted for the most part as the solvent of other 
 excretory substances. 
 
 The above-mentioned substances may be got rid of in the 
 form of gaseous, liquid, or solid excretions. The most im- 
 portant are : 
 
 1. The respiratory excretion from the lungs, skin, and in- 
 testine (carbonic acid and water). 
 
 2. The urine (water, salts, urea, uric acid, &c.). 
 
 3. The fluid tegumentary excretions, viz. sweat (water, 
 salts, urea, fatty acids, &c.\ and the sebaceous excretion (fats, 
 water, salts, albumin). 
 
 4. The faeces (the indigestible portions of food and of the 
 alimentary secretions). 
 
 5. The exuviation of epithelium (the shedding of epidermis, 
 hair and nails). 
 
 In addition to the above-mentioned excretions, which con- 
 tain for the most part true excrementitious substances, the 
 body yields up periodically certain of its constituents which 
 are so little oxidized as to be capable of further use in the 
 formation or nourishment of other organisms. They are : 
 1, Milk; 2, Ova; 3, Semen; which are excretions rich in 
 
EXPENDITURE OF THE ORGANISM, 199 
 
 albumin, carbo-hydrates, and fat. Menstrual blood may also 
 be included in the list. 
 
 Most of the excretions above referred to are direct secretions 
 from the blood, and, as such, have been already described. 
 Thus urine, the sudoriparous and sebaceous excretions, and 
 milk, are treated of in Chapter II., and the respiratory excre- 
 tion in Chapter IV. Faeces, or the mixture formed in the 
 alimentary canal during digestion, have been mentioned in the 
 description of that process in Chapter III. The remaining 
 excretions, viz. those of epithelium, ova, and semen, consist 
 essentially in the separation of cells or portions of cells. The 
 last two are discussed in the Fourth Section of the book. The 
 exuviation of epithelium takes place in the following manner : 
 Those internal and external surfaces which are covered with 
 scaly epithelium, viz. the epidermis, the mucous membrane of 
 mouth and pharynx, portions of the urinary and genital organs, 
 and the conj unctiva, lose continually their upper layers of cells 
 after the latter have undergone a peculiar process of shrinking 
 and conversion into a horny material. The horny cells of the 
 external skin, i.e. the most external layers of the epidermis, 
 together with the corresponding portion of nails and hair, are 
 simply rubbed off by use ; those of the mucous membranes 
 mingle in the secretions which bathe them (saliva, mucus, urine, 
 tears), and are conveyed out of the body in the faeces or 
 urine as the case may be. This desquamation of epithelial 
 cells is the cause of no inconsiderable loss of nitrogen and 
 sulphur to the body. 
 
 III. QUANTITATIVE KELATIONSHIP BETWEEN THE 
 INCOME, EXPENDITUKE, AND STOCK OF THE 
 BODY. 
 
 At the commencement of this chapter it was stated that 
 the object of the ingestion of food was to repair the losses 
 which the body sustained through the excretion of its inorganic, 
 and the oxidation of its organic, constituents. The simplest 
 relationship which can exist between the food taken and the 
 body is, therefore, when the former is just sufficient to cover 
 the expenditure of the latter, and so to maintain it at its usual 
 standard of weight. In this case it is not, of course, sufficient 
 
200 THE ECONOMY OF THE ORGANISM. 
 
 that the total gains of the body equal the total losses. If the 
 chemical composition of the body is to remain unchanged, the 
 amount of the individual chemical constituents of the former 
 must also be equal to the corresponding constituents of the 
 latter. Moreover, the amount of the food taken into the body 
 and of the individual constituents must constantly adapt itself 
 to the variations in the losses produced by the changes in the 
 extent of the decompositions in the organism dependent on the 
 work done. 
 
 The ingestion of food, however, takes place for the most 
 part voluntarily, and is not regulated by any exact knowledge 
 of the needs of the organism. The sensations of hunger and 
 thirst which give indications of the necessity for food only 
 prompt as a rule to its ingestion, and not to its ingestion in 
 definite quantity ; and, indeed, food is very frequently taken 
 without any such prompting. The ingestion, therefore, of 
 superfluous or insufficient amounts of food occurs very often. 
 In the former case we may suppose one of the following sets of 
 circumstances to take place: 1. The losses of the body may 
 remain the same while the body-weight increases, the amount 
 of potential energy in the body becoming increased and stored 
 up. 2. The superfluity of nutriment may remain unabsorbed 
 and pass unchanged out of the body in the faeces. This only 
 occurs when the superfluity is excessive. The maximum power 
 of absorption, in the case of the more easily absorbable ali- 
 mentary substances, is first attained in the case of salts, 1 then 
 in the case of fats, and finally in the case of water. 3. The 
 superabundant alimentary substances may be absorbed and im- 
 mediately re-secreted without any further change. This only 
 occurs in the case of water and salts, the excretion of which 
 proceeds until the body possesses its normal quantity (p. 183). 
 Unoxidized organic bodies are never found under normal cir- 
 cumstances in any excretions except milk, ova, and semen. 4. 
 Such an excess in the amount of the food taken may be fol- 
 lowed by increase of the decompositions and oxidations occur- 
 ring within the body and of the work done, the losses of the 
 
 1 The absorption of the easily soluble salts, which usually takes place rapidly, 
 is interfered with, when they are ingested in larger quantities, by the circumstance 
 that they render the contents of the intestine fluid by their attraction for water, 
 and so cause their rapid excretion (diarrhcsa) before absorption can occur. 
 
THE ECONOMY OF THE ORGANISM. 201 
 
 organism increasing while the body-weight remains unchanged. 
 5. It is conceivable that even without any marked increase of 
 the oxidation-processes going on in the body, its weight may be 
 maintained nearly constant, e.g. by the decomposition of the 
 constituents of the body, which are in excess of the immediate 
 wants of the organism, into substances rich, and into substances 
 poor in energy, of which the former may be retained in the 
 body, whilst the latter are excreted. In this manner the 
 energy contained in the ingesta would, as it were, be concen- 
 trated, i.e. associated with a lesser weight of matter, so that 
 there might be an increase in the stock of potential energy at 
 the disposal of the body, unaccompanied by any appreciable 
 increase of its weight. 
 
 In the contrary case, when an insufficient amount of food is 
 ingested, one of the following results may occur : 1 . The work 
 done by the body and the various losses to which it is subject 
 may remain as before while its weight decreases. 2. The 
 body-weight may be unaltered while the expenditure or losses 
 of the body diminish. As, however, the second of these 
 possibilities is limited by the circumstance that a certain 
 amount .of work, accompanied by the using up and loss of a cer- 
 tain amount of material, is indispensably necessary to the 
 maintenance of the body, the diminution in the amount of 
 food taken must sooner or later reach a point after which the 
 weight of the body must decrease until life is no longer possible. 
 
 To test experimentally the accuracy of the theories here 
 laid down is the aim of the department of physiology now 
 being considered. By a long series of experiments on man and 
 the lower animals, in which the conditions of excess, sufficiency, 
 or insufficiency of food were artificially arranged, and the 
 amounts of the gains and losses of the body individually and 
 collectively estimated, it has been sought to discover (1) which 
 elements of the body are excreted under normal circumstances, 
 when no increase by special activity occurs in the materials used 
 up ; and hence the quantity and composition of the food neces- 
 sary to repair the losses thus sustained ; (2) how the material 
 exchange varies when repair is insufficient ; and (3) how it varies 
 when an excess of alimentary substances is administered. The 
 results of these experiments will now be given in order. 
 
202 MINIMUM EXCHANGE OF MATTER. 
 
 1 . The necessary Losses of the Body and their Reparation 
 by means of Food. 
 
 In order to decide what losses sustained by the body are 
 indispensable, and what amount of food is therefore necessary 
 for their repair, two methods are possible, neither of which 
 leads, however, to absolutely correct results. The first consists 
 in giving a man or an animal the smallest amount of food 
 requisite for the maintenance of the weight of the body, and in 
 analysing the excreted substances under these conditions, the 
 elements of which should correspond quantitatively with those 
 of the food : the second, in depriving an animal of all food, in 
 which case we may be certain that no material is unnecessarily 
 excreted, and then determining the necessary elements of food 
 by analysis of the excreta. 
 
 The first method possesses the following sources of error : 1. The 
 process itself is a working in the dark, and leads with difficulty to an 
 exact result. 2. The difficulty of excluding all unnecessary use of material 
 such as would be occasioned by movements, &c. 3. The uncertainty 
 whether the amount of food which is just sufficient to maintain the weight 
 of the body at its normal, would not be found to be less if its composi- 
 tion were more judiciously arranged; or, in other words, whether certain of 
 the constituents of the excreta are not due to an excess of the materials 
 ingested. 4. The difficulty in estimating the elements of the faeces. The 
 fasces contain (Chap. III.) not only the results of material exchanges 
 (portions of the alimentary secretions), but also the indigestible parts of food, 
 which must by no means be reckoned among the losses of the body due to 
 the repair of its tissues, but are to be attributed to the accidental composi- 
 tion of the food itself. The faeces of herbivorous animals, for example, form 
 almost the half of the total excretions of the body (in horses 40 to 50 per 
 cent., Valentin, Boussingault ; in cows, 34-4 per cent., Boussingault) on ac- 
 count of the considerable quantity of indigestible material contained in vege- 
 table food. In carnivorous animals, on the contrary, the proportion is very 
 unimportant (in cats 1 per cent., Bidder and Schmidt). In omnivores it is 
 intermediate (being in men 4 to 8 per cent., Valentin, Barral, Hildesheim ; 
 and in pigs 19-9 per cent. Boussingault), and varies from time to time with 
 the kind of food. In order to eliminate this very varying and unnecessary 
 factor in the calculation of the losses of the body, we must either dis- 
 regard the faeces altogether in doing which another error is introduced by 
 overlooking the real elements of loss which they may happen to contain or 
 we must choose alimentary substances which contain no indigestible portions 
 an experiment which has not yet been tried. 
 
 In the second method a great error is introduced by the circumstance 
 that in famished animals the various functions quickly become languid; and, 
 
DISTRIBUTION OF EXCRETA. 203 
 
 in consequence, the use of material and the losses of the body less than when 
 a sufficiency of food is taken. 
 
 Of the results yielded by the above methods of experiment, 
 those relating to the relative quantities of the excreta are the 
 most certain and important, as they teach at the same time by 
 what channels the various elements of the body are separated. 
 
 1. The total losses of the body, after subtracting the faeces 
 which are most variable in quantity, are referable in about an 
 equal extent to the urine on the one hand, and to the sudori- 
 parous and respiratory secretions on the other. In this division 
 the following are neglected : the true elements of loss contained 
 in the faeces (constituents of bile, &c.), the sebaceous secretion, 
 and the exuviated epithelial cells, concerning which no deter- 
 minations have as yet been made. In carnivorous animals the 
 urinary secretion is for the most part somewhat in excess of 
 all the others, including the faeces. In herbivorous animals, on 
 the contrary, it only amounts to one- eighth or one-third of the 
 other secretions. The cause of this lies chiefly in the greater 
 amount of faeces excreted by the latter. 
 
 2. The elements which compose the inorganic constituents 
 of the body (water and salts), and which are excreted and res- 
 tored in similar combinations, are the following : 
 
 a. Water. The proportionate amounts of water separated 
 by the various excretions, if we except that separated in the 
 faeces, which is generally of small amount, depend chiefly upon 
 the temperature and the hygrometric state of the atmosphere. 
 The loss of water from the lungs is almost constant, as there the 
 same extent of surface moistened to the same degree constantly 
 comes into contact with the atmosphere by means of a stratum 
 of air which is continually in motion. Moreover, the loss of 
 water by cutaneous respiration cannot be distinguished from 
 that which occurs in the secretion of sweat ; hence, both may 
 be taken together. Therefore, it may be said that the chief 
 loss of water is referable to the lungs, skin, and kidneys. For 
 reasons which are very apparent, it will be seen that with a 
 dry, warm atmosphere, the loss of water from the skin will be 
 greater than that from the kidneys, while with a moist, cold 
 atmosphere, the reverse will obtain. That the total amount of 
 the excreted water depends upon the amount ingested has 
 
204 DISTRIBUTION OF EXCRETA. 
 
 already (p'. 115) been indicated; and more will be said below 
 in reference to this matter in speaking of the ingestion of 
 excessive amounts of food. In carnivores almost the whole of 
 the water (as much as 90 per cent.) is got rid of from the kidneys ; 
 while in herbivores as much as 60 per cent, passes away in the 
 faeces. 
 
 b. Salts are chiefly excreted in the urine ; some, however, 
 appear in the sweat, while a few (mostly those of potassium 
 and the indigestible salts) pass out of the body in the faeces, 
 together with any superfluity of salts which may have been 
 ingested. 
 
 3. The elements of the (oxidized) organic compounds of 
 the body are excreted for the most part in the form of inorganic 
 products of oxidation, and less frequently as organic products 
 of oxidation or decomposition. They are : 
 
 a. Carbon, by far the largest portion (more than 90 per 
 cent.) being excreted in the form of carbonic acid in the pro- 
 cess of respiration. A smaller amount is separated in the form 
 of less highly oxidized products during the other processes of 
 secretion (in urea, uiic acid, &c. ; in the horny substance of 
 epithelium, the sebaceous secretion, the constituents of the 
 secretions contained in the faeces, &c.). 
 
 b. Hydrogen (i.e. that derived from the organic constituents 
 of the body) is separated for the most part in the form of 
 water, together with the water which previously existed as such 
 in the body. A small portion quits the organism in the organic 
 compounds mentioned under a. 
 
 c. Oxygen (i.e. that derived from the organic compounds of 
 the body) is excreted together with that taken into the system 
 for the purposes of oxidation, the amount of the latter kind 
 being from three to ten times as great as that of the former. 
 By far the greater proportion is separated in the highest forms 
 of oxidation, viz. as carbonic acid and water, only a small amount 
 being excreted in the lower forms as urea, &c. 
 
 d. Nitrogen is excreted entirely in the form of decomposi- 
 tion-products, for the most part as urea in urine and sweat, but 
 also as uric acid, urinary colouring matter, horny substance, 
 biliary constituents, and possibly in small amounts, as ammonia 
 and pure nitrogen. 
 
MINIMUM EXCHANGE OF MATTER. 205 
 
 The old question whether, when the body-weight remains the same, all 
 the nitrogen taken into the system reappears in the visible excretions 
 (especially in urine and faeces), or whether a part only is so excreted a 
 circumstance which would compel the admission of a separation of nitrogen 
 in the lungs seems now to have been settled in favour of the former 
 alternative (Voit, Siewert, Schulze and Marcker [Henneberg], Stohmann : 
 this view is, however, opposed by Seegen). In the special case where the 
 food happens to be very albuminous, it is still maintained by Stohmann 
 that the amount of nitrogen recoverable from the visible excretions is less 
 than that ingested. When cutaneous perspiration takes place such a com- 
 parative deficiency of nitrogen is observable owing to the excretion of that 
 body in the sweat (Leube). 
 
 e. Sulphur (derived especially from the alkaline albuminates 
 of the body) leaves the organism, about half of it in the form 
 of sulphates in the urine, and the rest, combined in various 
 organic compounds, in epithelial exuviations and in the faeces 
 (keratin, taurine). 
 
 The data for the determination of the absolute amount of 
 the minimum excretion of the body, and of the minimum quan- 
 tity of food necessary to repair the losses occasioned by that ex- 
 cretion, are still less definite, more especially because of the un- 
 certainty before mentioned attaching to the methods of investi- 
 gation (p. 202). The following is an epitome of the results 
 which have been obtained : 
 
 1. The minimum excretion (or ingestion) is larger the 
 smaller the animal observed. For the purposes of comparison, 
 the material .exchange, in twenty-four hours, per kilogramme 
 of the weight of the animal, is determined. It is thus found 
 that in pigeons a far larger exchange of material occurs for 
 every kilogramme than in dogs ; while in the latter it is far 
 greater than in man. This is explained by the greater activity 
 of the vital processes in smaller organisms : small animals, for 
 example, on account of the comparatively larger extent of 
 surface which they expose, must generate more heat than large 
 ones, in order to maintain their temperature (Chapter VII.). 
 
 2. The minimum amount of food necessary is lowest when 
 the elements of the food are mingled together in a definite 
 manner. Such a perfect mixture of the elements of food 
 contains proteids, fats or carbo-hydrates, possibly also lecithin, 
 water and salts in certain proportions, the salts being present 
 in smallest amount, and water in greatest. 
 
 3. The most favourable relationship of these elements one to 
 
206 STARVATION. 
 
 another, i.e. the proportion that must exist among them so 
 that the smallest amounts may be able to maintain the normal 
 weight of the body, varies in the varying conditions of age, 
 sex, and mode of life. 
 
 4. Up to a certain point the amount of albumin usually 
 considered necessary in the food may be decidedly diminished 
 by increasing the amount of fats or carbo-hydrates : possibly, 
 as Hoppe and Voit suggest, because every body which oxidizes 
 more easily than albumin prevents the action of oxygen on that 
 body by attracting it to itself. 
 
 5. The minimum amount of food necessary is greater ac- 
 cording as the organism is already fattened by excessive feeding. 
 
 The absolute numbers obtained by the methods before mentioned are, on 
 account of the sources of error to which those methods are open, only of value 
 when all the experimental conditions are exactly carried out. They will 
 therefore not be given here. It should also be mentioned that circumstances, 
 such, for instance, as temperature, have an influence upon the utilization of 
 material in the body. ' 
 
 2. Insufficient Ingestion of Food. 
 
 It has already been said (p. 201) that if the food ad- 
 ministered be insufficient in amount, a time must of necessity 
 come after which the body-weight will steadily decrease. In 
 the case of starvation, when there is a complete deprivation 
 of food, this diminution in body-weight commences at once ; 
 and sooner or later, according to the condition of the animal 
 at the commencement, a period arrives at which the functions 
 of the body, as well as its losses, begin to diminish ; this dimi- 
 nution continues until death. The material exchanges which 
 occur in fasting animals merely consist in the combustion of the 
 constituents of the body by means of the oxygen continually 
 inspired, and the excretion of the products of that combustion, 
 and of the incombustible constituents, water and salts. The 
 organism, as a whole, undergoes in the meantime no repair ; 
 but, in all probability, certain portions of it are restored at the 
 expense of others by the action of the blood, which transfers 
 to the former the energy-yielding materials which the latter 
 may contain in superabundance. 
 
 Observations o the material exchanges of fasting animals (Experiments 
 on Inanition) extending over considerable periods have only been made on 
 
STARVATION. 207 
 
 the lower animals, chiefly on pigeons (Chossat), dogs (Bischoff and Voit), 
 and cats (Bidder and Schmidt). 
 
 The following generalisations have been made from ex- 
 periments on fasting animals : 
 
 1. At the beginning of the process of starvation the body- 
 weight, the activities and the losses of the body all decrease. 
 The diminution in the losses of the body naturally causes the 
 decrease in its weight to become less from day to day ; for the 
 sum of the losses or excretions, after subtracting the amount 
 of the oxygen taken into the body, expresses directly the loss 
 of the body in weight (see Fig. 4). The diminution in the 
 bodily energies or activities, which is intimately connected 
 with the decrease in the losses, is indicated especially by a 
 low temperature and an infrequent pulse and respiration, the 
 diminished income of oxygen thus brought about occasioning a 
 diminution in the processes of oxidation. 
 
 2. The diminution in the excreta does not affect all their 
 elements equally. Herbivores exhibit the most considerable 
 alteration in the composition of their excreta ; for all fasting 
 animals may be regarded as carnivores, since they subsist on 
 nothing but the constituents of their own bodies. Thus, in the 
 case of fasting herbivores, the amount of urea in the excretions 
 at first increases (p. 111). As a rule, however, the amount of 
 urea in the excretions diminishes as the time during which no 
 food has been taken extends a proof that the decrease in the 
 processes of oxidation in the organism concerns also the oxida- 
 tion of the nitrogenous (albuminous) constituents of the body. 
 The diminution in the amount of urea excreted is at first abrupt, 
 and the more so the larger the amounts which were normally 
 excreted before starvation commenced ; later on, the excretion 
 of urea diminishes slowly and regularly. While, therefore, in 
 the later periods of starvation, a certain proportion of the 
 albumin of the body (organic albumin) is regularly used up, at 
 the commencement it is the stored-up albumin derived from 
 the food last ingested which is expended (Voit). 
 
 3. After the animal has lost a certain fraction of its weight, 
 death by starvation supervenes, the interval preceding it from 
 the commencement of starvation varying in different individuals. 
 The length of the interval, and the amount of the loss which 
 the animal is able to sustain before death, depend upon the 
 
208 STARVATION. 
 
 condition of the animal previously. Animals which have been 
 fattened require a certain time longer to allow of their weight 
 attaining its normal condition ; for not until this has been ac- 
 complished does any diminution in the losses and activities of 
 the body occur, and starvation, therefore, really commence. 
 Thus, young and poorly-fed pigeons die in three days after losing 
 one-fourth of their weight, while old and well-fed birds will live 
 for thirteen days, until they have lost nearly the half of their 
 former weight (Chossat). 
 
 4. The amount of loss in weight differs much in various 
 parts of the body. The oleaginous contents of the fatty tissues 
 ( or, briefly, the fat) diminish most, the whole tissue losing from 
 VI to 93 per cent., i.e. the connective-tissue alone remains. 
 The abdominal viscera and muscles lose less weight than the fat. 
 The brain and spinal cord lose extremely little ; the former, 
 however, somewhat less than the latter. The blood, it may 
 be noted, especially in the amount of its haemoglobin, main- 
 tains approximately its relationship to the whole weight of the 
 body. This inequality of loss in the various parts of the body 
 is brought about by the power before referred to which the blood 
 has of conveying material from one organ to another, and thus 
 securing as perfectly as possible the nourishment of the organs 
 most frequently used. This is indicated not only by the fact 
 of the slight loss of weight of the brain, the activity of which 
 continues undiminished until death, but also by the smallness of 
 the loss sustained by those muscles which are continually in use, 
 as compared with the loss sustained by those which are less active. 
 As fat and muscle are the chief elements in the losses of animals 
 when fasting, it is generally stated that animals in such a con- 
 dition live upon their own fatty and muscular tissues. Certain 
 investigators (Schmidt, Bischoff and Voit) have even calculated 
 from the nitrogenous elements of the excreta the quantity of 
 such muscular substance used, and have considered all the re- 
 maining elements which are referable to the organic constitu- 
 ents of the body (calculated from the carbonic acid excreted) 
 as effete fatty material. 
 
 In addition to the case of total deprivation of food, we must 
 consider that in which food is administered in insufficient 
 quantity. This insufficiency may be quantitative or qualita- 
 tive, i.e. the food taken may contain all the necessary elements 
 
INSUFFICIENCY OF FOOD. 209 
 
 of food, but in insufficient quantities, or it may not contain all 
 the essential elements. Quantitative insufficiency induces all 
 the symptoms of complete starvation, but much more slowly. 
 Qualitative insufficiency in most cases terminates in death as 
 quickly as complete starvation, but with a less diminution 
 in the body-weight. During complete deprivation of water ] 
 (Schuchardt) animals very quickly cease to take solid food ; 
 and, on the contrary, during complete deprivation of the solid 
 constituents of food (Bischoff and Voit, Chossat), they very 
 soon refuse to take water : each, therefore, may lead to starva- 
 tion. In most combinations of the alimentary elements in 
 food, the observations are interfered with, either by the fact 
 that the maximum absorption becomes so slight that it is im- 
 possible to study the effects of large amounts, or by the ap- 
 pearance of morbid symptoms, e.g. of diarrhoea when the 
 combination consists of sugar and water. Those experiments 
 are of most importance in which one of the two chief organic 
 alimentary substances, albuminous bodies or fats (carbo- 
 hydrates), is withheld from an animal. In such cases the 
 general loss to the body is considerably less than in fasting 
 animals ; each of these elements of food, therefore, can replace 
 the other to some extent. On withholding the albuminous ele- 
 ments (as by feeding on fat and water, or on fat, carbo- 
 hydrates and water) the excretion of urea becomes considerably 
 decreased, while the weight of the body undergoes a certain 
 but not excessive diminution, indicating that the oxidation of 
 nitrogenous bodies is proceeding less rapidly than usual within 
 the organism. On withholding fats, no marked alteration in the 
 material exchanges of the body occurs if the food contain 
 instead carbo-hydrates. If the latter are also withheld, a very 
 decided increase occurs in the excretion of urea, indicating an 
 increased oxidation of nitrogenous materials, and necessitating 
 an increased ingestion of nitrogenous food in order that life 
 may be maintained. No essential disturbance in the body is 
 occasioned on the removal of sodium chloride from the food ; 
 and on deprivation of phosphoric acid the bones retain for u 
 long time the phosphates they happen to possess (Weiske). 
 
 1 That is to say, of that also which is contained in the organic alimentary 
 substancey ; for many animals (e.g. cats, Bidder and Schmidt) can do very well 
 without actually drinking water. 
 
210 SUPERABUNDANT INGESTION OF FOOD. 
 
 Albumin may for certain purposes be replaced by gelatin ; for the ad- 
 dition of gelatin renders unnecessary the use of so much albumin as before, 
 as is proved by the body-weight maintaining its normal standard under such 
 circumstances. As, however, the weight of the body rapidly falls when 
 gelatin is the only nitrogenous element in the food, it is evident that the 
 necessity of the tissues for albumin cannot be met entirely by that substance 
 (Voit). 
 
 3. Superabundant Ingestion of Food. 
 
 As has already been mentioned, the income of the body is very 
 often greater than is necessary to cover the (minimum) expen- 
 diture, and to maintain the body-weight at its normal weight ; 
 and this excess may affect some or all of the essential elements 
 of the food. We have now to determine which of the possible 
 methods mentioned on pp. 199 et sqq. is adopted for the disposal 
 of the excess. The question is simplified by excluding: (1) 
 All excess of alimentary substance taken into the body over 
 the amount which is capable of absorption (as determined by 
 the maximum absorptive power of the body for the particular 
 substance, p. 200). (2) All increased ingestion of food ren- 
 dered necessary by the increased activities of the body (forma- 
 tion of heat, mechanical work see the second Section of this 
 book). Moreover, any excess of inorganic elements of food 
 water and salts may be left out of the question ; for, as 
 already mentioned, the body gets rid of any superfluity of 
 those bodies by direct excretion from the blood the water 
 through the skin and kidneys and the salts through the 
 kidneys. 
 
 There remains, therefore, the case where an excess of organic 
 alimentary substances has been ingested. For its disposal three 
 courses are possible: 1. It may be simply retained in the 
 organism. 2. It may be quickly oxidized and excreted. 3. It 
 may be decomposed, and a part oxidized and excreted, while 
 the rest, which is capable of yielding energy, is retained (p. 201). 
 In the first case, the weight of the body would increase while 
 the losses remained constant ; in the second, the losses would 
 increase while the body-weight was unchanged; and in the 
 third both would increase. Experience has shown that if an 
 excess of food be ingested, the body increases in weight ; that 
 the excretion of the products of oxidation is also increased, 
 especially (C. Gr. Lehmann, Bidder and Schmidt) in the case 
 
FATTENING. 211 
 
 of urea, when the excess consists of nitrogenous food ; and, 
 finally, that the materials never make their appearance in the 
 excreta in an unoxidized form. The first of the above-men- 
 tioned courses is, therefore, excluded by the circumstance that 
 the excretions always increase. The second, besides that it 
 does not tally with the experimental fact of an increase of 
 weight in over-fed animals, would necessitate a corresponding 
 increase in the amount of oxygen taken into the body, and 
 in the bodily energies or activities, in consequence of the in- 
 creased extent of oxidation. In a reposing body this increase 
 in the bodily energies could only manifest itself by an in- 
 creased formation of heat (Chapter VII.). Such an increased 
 formation of heat does, in fact, occur ; the augmented diges- 
 tive activity requiring a greater consumption of material and 
 yielding more heat in the processes of secretion and movement ; 
 but the amount is too slight to satisfy the second theory. The 
 following facts support the third of the above methods of 
 disposal. 
 
 As in the case of an insufficient allowance of food, so here 
 also where the food is administered in excess, the expenditure 
 of the body accommodates itself to a certain extent to the 
 income. This accommodation has been most exactly made out 
 in the case of the albuminous elements (Bischoff, Voit). When- 
 ever an animal is fed for a long time abundantly with albumin, 
 a condition of equilibrium supervenes, after a short time, be- 
 tween the nitrogen in the food and that in the excreta ; and 
 this equilibrium is connected with a definite weight of body, 
 which is meanwhile maintained. If the amount of food is 
 suddenly increased, and maintained at the increased rate, the 
 equilibrium is again established, after a certain time, with an 
 increased body-weight. Until this state of equilibrium is 
 reached the excreta are somewhat less than the ingesta, and 
 albumin is stored up in the body, the animal being said ' to 
 make flesh.' If, on the contrary, the amount of albuminous 
 food is diminished, the excreta continue to be somewhat greater 
 than the ingesta in the interval preceding the readjustment of 
 equilibrium with a diminished body-weight; and the animal 
 ' loses flesh.' The organism can, therefore, within certain 
 limits, ' readjust itself,' for every alteration in the amount ol 
 the food ingested, its constitution undergoing a change in the 
 
 p 2 
 
212 
 
 THE STORING OF FAT. 
 
 process. If the amount of food ingested is diminished below 
 a certain point, the condition of hunger supervenes, the laws of 
 which are similar to those above given. 
 
 The following figure serves to illustrate diagrammatically what has been 
 said. The abscissa-line AA/ indicates the time, the ordinates of the thick curve 
 the weight of the body, or its albuminous constituents, those of the thin curve 
 the amount of the daily excreta, and those of the dotted one the amount of 
 the daily ingesta. The ingesta are suddenly increased in amount at , and 
 at c suddenly diminished, and are at e nothing. A, be, cle, indicate the 
 periods of states of equilibrium between ingesta and excreta ; ab, the period 
 during which readjustment is in progress when the excreta and the body- 
 weight are both increasing ; cd, the period during which readjustment is 
 taking place when the excreta and the body-weight are both diminishing ; eh.' 
 the period of hunger, also characterized by the decrease of both body-weight 
 and excreta. The alterations in the weight of the body on each day are 
 of course determined by the difference between ingesta and excreta. 
 
 FIG. 4. 
 
 f. 
 
 A- 
 
 a 
 
 a 
 
 According to recent investigations (Pettenkofer and Voit), 
 it would seem that a similar relationship between income, ex- 
 penditure, and stock exists in the case of fat as in the case of 
 albumin. The amount of fat stored up in the body is, how- 
 ever, also dependent upon the albuminous ingesta. When, 
 therefore, the latter are increased in amount, there occurs not 
 only an accumulation of albumin, but. also of fat. Fat is pro- 
 bably formed (p. 194) during the decomposition of albumin under 
 certain circumstances ; a decomposition, attended with ex- 
 cretion of urea and retention in the body of certain energy- 
 yielding complex molecules, such as is contemplated in the 
 third of the three possible courses mentioned above. What 
 the circumstances are which are favourable to this formation 
 of fat, and whether they are connected with the excessive 
 
COMBUSTION OF ALBUMIN. 213 
 
 ingestion of food, cannot yet be exactly stated. On the other 
 hand, the expenditure of albumin is diminished by the simul- 
 taneous ingestion of fats or carbo-hydrates, of which fact no 
 explanation has hitherto been given. The very general state- 
 ment that fats and carbo-hydrates, being easily combustible 
 substances, attract to themselves the oxygen, and in that 
 manner save the albumin, is not very well founded. That the 
 addition of a fatty element to an albuminous diet leads to 
 the accumulation of fat in the body is most probably to be 
 explained by the direct accumulation of the fat ingested, or 
 the diminished use of that already present. The statement that 
 carbo-hydrates have the same effect as fat in this case is dis- 
 puted ; it certainly remains at present quite unexplained. 
 
 The increased expenditure of albumin when it is ingested 
 in greater quantity is connected with an increase in the amount 
 of oxygen used (Pettenkofer and Voit) ; and the decompositions 
 which take place are, therefore, concluded to be oxidations. 
 In the attempt to calculate the amount of albumin consumed 
 from the nitrogen eliminated, it is found that only a portion 
 of the carbon is present in the excretions a proof that, in the 
 decomposition, some constituent rich in carbon is retained in the 
 body (Pettenkofer and Voit). The seat of these processes is 
 entirely unknown. It used formerly to be stated that the super- 
 abundance of ingested albumin was simply burnt up in the 
 blood without first forming part of any organ (' Luxus-consump- 
 tion'). It is, however, now considered much more probable, 
 especially as no one has ever succeeded in demonstrating the 
 existence of true processes of oxidation in the blood, that all 
 decompositions are accomplished in the cells of the organs, 
 and are only influenced in some unknown manner by the 
 extent to which blood is present. The formation of fat is 
 always brought about by means of cells, as may be demon- 
 strated. Adipose tissues, especially of the mesentery, are to 
 be regarded according to modern research (Toldt, Rollett), 
 not as simple connective-tissue, the cells of which are filled 
 with fat (Virchow), but as glandular organs with special vessels, 
 which in man are early surrounded by a growth of connective- 
 tissue. 
 
 The decomposition of a portion of the albumin in the intestines into 
 leuciue, tyrosine, &c. (p. 107) has recently been regarded as a case of ' luxus- 
 
214 GROWTH. 
 
 consumption.' Many observers consider even peptones as albumin set apart 
 for direct combustion (p. 185). 
 
 The consumption of albumin, besides being dependent on 
 the addition of albumin, fats and carbo-hydrates present in food, 
 is determined to a certain extent by the salts ingested. A 
 moderate ingestion of sodium chloride especially is said to 
 diminish the expenditure of albumin (Klein and Verson), while 
 an excess increases it (Voit). The addition of water also has 
 an influence ; free ingestion of water increases the excretion of 
 urea, which must be attributed to an influence upon the decom- 
 position of albumin, as mere physical conditions cannot effect 
 any increase in the amount of the urea. Increase in tempera- 
 ture causes an increased consumption of albumin. For the influ- 
 ence of muscular activity see the following Section of the book. 
 
 The reason why food is generally ingested in superabund- 
 ance is because the weight (and dimensions) of the organism 
 increase continually from birth to maturity, this increase being 
 called growth ; and also because, thereafter, certain regular 
 excretions of unoxidized materials occur both in males and in 
 females, viz. in the former semen, and in the latter menstrual 
 blood and the excretions destined for the use of the developing 
 ovum, and at a subsequent period milk for the nourishment 
 of the child. This matter is treated in Section IV. of the 
 
215 
 
 PART II. 
 
 THE ACTIVITIES OR ENERGIES OF THE BODY. 
 
 INTRODUCTION. 
 
 IN the general Introduction to this work it is stated that the 
 animal body is the seat of transformations of potential into 
 kinetic energy. 
 
 It may be stated generally that the potential energy of the 
 body is associated with two kinds of matter, widely separated 
 from one another, viz. atmospheric oxygen on the one hand, 
 and the. oxidizable constituents of the body, which enter it as 
 food, on the other. Energy-yielding substances are, therefore, 
 being continuously introduced into the body. It has, further, 
 already been stated, that the products of the combination of 
 the above-mentioned different kinds of matter, i.e. oxidation- 
 products, are continually being thrown out of the body. 
 
 Similarly, it has now to be stated that the energy which 
 has become kinetic in the animal body is continually being- 
 transferred from it to bodies existing in the medium outside 
 and independent of it. Just as, however, the expenditure of 
 the matter of the body is always a little below its income (and 
 this difference is necessary to the existence and persistence of 
 the body), so also the expenditure of energy is always below its 
 income, for the organism always contains a certain store of 
 energy, part of which is potential in its yet unoxidized con- 
 stituents, part of wh? ;h is kinetic its heat. 
 
 The transformations of the energy of the body run side by 
 side with the exchanges of its matter. As in the preceding 
 chapter, the income and expenditure of the matter of the body 
 have been discussed and compared, the same task must now be 
 
216 INTRODUCTION OF POTENTIAL ENERGY. 
 
 undertaken in reference to its energies, whilst these must, as 
 far as possible, be brought into relation with the exchanges 
 of matter. The scanty knowledge yet possessed on this subject 
 merely permits of the discussion of some of its salient points. 
 
 Introduction of Potential Energy into the Body. 
 
 Although the potential energy which has here to be con- 
 sidered is associated, not only with the matters to be oxi- 
 dized, but also with oxygen, we usually only speak of the 
 energy of the alimentary substances of the food, whilst we 
 tacitly and correctly assume the presence of the quantity of 
 oxygen required to oxidize them. The potential energy of the 
 oxidizable (organic) alimentary constituents is usually expressed 
 as heat, i.e. the total kinetic energy which can be developed 
 by the oxidation is represented as heat, although, as can be 
 proved, forms of energy other than heat arise from them. 
 
 This simplification possesses great advantages for quanti- 
 tative determinations. 
 
 The determination of the heats of combustion of the ali- 
 mentary substances is easily effected by burning them in a calori- 
 meter, i.e. a chamber surrounded on all sides by some liquid, 
 generally water. The temperature of the liquid, the amount 
 of which is known, is determined before and after the combus- 
 tion. The result, which is the amount of heat produced, is 
 expressed in 'units of heat' (see page 5), and furnishes a 
 measure of the heat of combustion. The difficulties which 
 attend this experimental determination are, however, great in 
 the case of many of the alimentary substances, so that the 
 heat of combustion of many is not accurately known. 
 
 Although, in the animal body, the combustion of the 
 alimentary substances (or of the constituents of the body which 
 originate from them) does not take place suddenly, as is the 
 case in artificial combustion, but gradually, yet the results of 
 calorimetrical determinations do afford a measure of the heat 
 developed in the slower oxidations ; for the sum of all the heats 
 developed in the individual successive oxidations, or decom- 
 positions of any other kind, which a body undergoes before it 
 is completely burned (so as to yield carbonic acid, water, sul- 
 phuric acid, &c.) is equal to the heat which is directly developed 
 by perfect combustion. 
 
HEATS OF COMBUSTION KINETIC ENERGY. 217 
 
 A method of very simply determining the heats of combustion which 
 has been adopted by some scientific men is not trustworthy, and leads to 
 false results. They have, namely, attempted to calculate the heat of com- 
 bustion of a compound from the known heats of combustion of its elements; 
 to do this they suppose the oxygen which exists in the compound itself to 
 be already combined, partly with hydrogen or carbon ; it appears, however, 
 firstly, that the basis for such a hypothesis is wanting ; and secondly, that 
 the other elements of a compound are bound together with a certain amount 
 of energy, so that to separate them one from the other, a portion of the 
 kinetic energy developed in the combustion must be consumed : the results 
 obtained by such a method must therefore differ from the results of direct 
 experiment by an amount which corresponds to the energy used up in the 
 dissociation process just referred to. 
 
 In, the case of chemical compounds of known constitution (and few of the 
 alimentary substances can as yet be classed under this category) the heats 
 of combustion can be calculated according to simple rules (Hermann). 
 
 From experimental determinations it has been made out that in com- 
 plete combustion 1 gramme of albumin generates 4998 heat units, 1 gramme 
 of beef (freed from fat) 5103 heat units, 1 gramme of beef fat 9069 heat units. 
 "When oxidized so as to yield urea, albumin is calculated to furnish 4263, 
 and beef 4368 units of heat (Frankland). By calculation it is found that 
 1 gramme of stearin develops 9036, 1 gramme of palmatin 8883, 1 gramme 
 of olein 8958, 1 gramme of glycerin 4179, 1 gramme of leucine 6141, and 
 1 gramme of creatine 4118 units of heat (Hermann). 
 
 Origin of the Kinetic Energy of the Body. 
 
 (The Energies of the Body.) 
 
 Oxidation (as has already been repeatedly stated) is the^ 
 process which, far more frequently than all others, leads to the 
 transformation of potential into kinetic energy. We cannot, 
 nevertheless, forget that oxidation is not the only process 
 associated with the liberation of energy, but that it is only one-' 
 of the processes, though certainly by far the most frequent, 
 which prove the general law that in every chemical process, \ 
 in which stronger affinities are saturated than were saturated ) 
 before its occurrence, potential energy becomes kinetic. 
 
 An example of a process not dependent upon oxidation in which, how- 
 ever, heat is generated is afforded by the alcoholic fermentation of sugar. 
 
 HHHH HH O HH 
 
 H_C C C C C C H II C C H C H C C H 
 I I I I I I II II II | | 
 
 OOOOOO OH O OH 
 
 UUU J, i 
 
 C 6 H 12 O e splits up into C 2 H 6 + C0 2 + C0 2 + C a H 6 
 
218 FORMS OF ENERGY IN THE BODY. 
 
 As the above graphic formulae indicate, carbon atoms, which in sugar 
 are linked either to carbon or hydrogen atoms, are, after the decomposition, 
 linked to oxygen atoms. As, however, the attraction of carbon for oxygen 
 is greater than it is for carbon or for hydrogen, this change in the position of 
 atoms must be associated with the liberation of energy. As these groups of 
 atoms which result from such a process of decomposition are bound together 
 by stronger affinities than those which existed before, the new compounds 
 are more stable ; and it may be stated as a general proposition that in 
 operations attended by the formation of chemical compounds, or of more 
 stable compounds than existed before, potential energy becomes kinetic. 
 Under this general law are included the ordinary processes of oxidation, as 
 well as others which are analogous to the fermentation of sugar. 
 
 The forms of energy in which the kinetic energy developed 
 
 in the body from the potential energy introduced into it may 
 
 ^ manifest itself are, so far as we know, heat, electricity, and 
 
 ^ mechanical work. When the animal body is in a state of rest, 
 
 viz. when all kinds of work which are not absolutely essential 
 
 to the continuance of life are avoided, it may be stated that all 
 
 these forms of energy are almost entirely transformed into a 
 
 single form heat. 
 
 The form which energy (see the Introduction) may assume is, as we 
 know, very variable ; heat is easily converted into motion (as in the steam- 
 engine), motion into heat (by friction) ; both heat and motion into 
 electricity (frictional- and thermo-electricity) ; and electricity into heat (as 
 evidenced in the heating of wires along which a current of electricity is 
 passing) and into motion (electro-magnetism). 
 
 Nevertheless the amount of kinetic energy always remains constant, 
 though such transformations occur, for they always proceed in definite pro- 
 portions (equivalents). The most important of these equivalents is 
 the ' Mechanical Equivalent of Heat,' i.e. the mechanical work into which 
 a certain amount of heat may be converted, or conversely. 
 
 The formation of heat goes on directly in all organs of the 
 body in %hich processes of oxidation occur, i.e. in all, except 
 the horny, tissues. 
 
 Electricity r , so far as we yet know, is only developed in the 
 muscular and nervous systems (Chapters VIII. and IX.). 
 
 Movements occur with perceptible rapidity, 1 . in the striped 
 and smooth muscular fibres ; 2. in contractile cells ; 3, in 
 . ciliated cells ; 4. in spermatozoids ; whilst other movements 
 take place with such slowness in all organic forms that they 
 cannot be perceived ; such occur during growth, in the fission 
 of cells, &c. 
 
THE BODY AT REST AND AT WORK. 219 
 
 The proof that, in the body when in a state of rest, all 
 forms of energy are converted into heat, and are in this form / 
 transferred from it to the external world, rests upon the fol- 5 
 lowing facts : 
 
 1 . Movements which occur in the body when at rest do not, 
 as such, exert any action upon the medium outside of it, but dis- 
 appear within the body itself. This disappearance is brought 
 about chiefly by friction : thus, the whole of the kinetic energy 
 of a cardiac contraction expended on the mass of the blood im- 
 parts to it motion ; in the course of the circulation this*motion, 
 by friction against the walls of the blood-vessels, and especially 
 of the capillaries, ceases to exist. This same disappearance of 
 motion is observed in the case of the alimentary apparatus, 
 where it occurs partly in consequence of friction against the 
 contents and against the structures which surround it. 
 
 As no other mode of motion (e.g. electricity) is known to 
 result from this friction, we are led to suppose that, everywhere, 
 a quantity of heat is generated which is equivalent to the 
 motion, i.e. mechanical work, which disappears. 
 
 2. Even the small quantities of electricity developed in the 
 nervous and muscular systems appear, in great part, to be con- 
 verted into heat (Chapter VIII.). 
 
 Exceptions which, judged of quantitatively, are of very small importance 
 must be made to the general statement previously enunciated, that in the 
 body at rest, the only form of kinetic energy imparted to the medium 
 around it is heat : thus, (1) the movements of respiration, of the heart, of 
 the pulse may be communicated to bodies outside the organism; and (2) 
 electric currents may be conducted away from the surface of the body to 
 surrounding objects by the interposition of condueting media (Chapter 
 VIII. ). 
 
 In the animal body when at work there originates an in- 
 creased quantity of kinetic energy, in addition to that which is 
 being produced during rest. This energy, which is developed 
 within the muscles, takes the form of heat and mechanical 
 work. Of this mechanical work a great part is converted, 
 within the organism itself, into heat by the friction of the 
 muscles and tendons within their sheaths, and by the move- 
 ment of bones in their articulations. The remainder of the 
 mechanical work is employed, partly in effecting the movement 
 of the various parts of the body in reference to one another, 
 partly in moving the body as a whole through the medium 
 
220 EXPENDITURE OF ENERGY. 
 
 which it inhabits, and partly in effecting the movements of 
 bodies which exist in that medium. 
 
 Seeing that even the last-named portion of the energy of the 
 body (viz. that expended on the bodies of the external world) is 
 easily converted into heat, and may be expressed in units of 
 heat, it is evident that the natural measure of the whole of the 
 energies of the body is the amount of heat corresponding to 
 them. 
 
 One might, naturally, just as well express the whole energy according to 
 its mechanical equivalent, i.e. in units of work instead of units of heat (as 
 kilogrammetres, foot-pounds, &c.). 
 
 The numbers of heat units which express the kinetic energy of the 
 organism are enormously great, amounting to several millions per diem. Some 
 employ in their calculations an unit of heat which is a thousand times greater 
 than that usually employed, defining the unit of heat to be that quantity of 
 heat which will raise one kilogramme of water from C. to 1 C. ; the 
 mechanical equivalent of this unit is then = 424 kilogrammetres. 
 
 Expenditure of Energy. 
 
 'With the exception of the small quantity of energy which 
 the organism loses in its imperfectly oxidized organic excreta 
 (urea, uric acid, milk, &c.), all the potential energy of its food 
 passes as kinetic energy to the outer world. From what has 
 been previously stated, this energy escapes from the body at rest 
 only in the form of heat, whilst in the case of the body which is 
 doing external work in the form of heat and mechanical work. 
 The modes in which heat is given out to the bodies of the outer 
 world will be treated of in the following chapter ; the transfer 
 of mechanical work needs no further discussion. 
 
 The direct measurement of this expenditure of energy 
 (heat) is effected, in the case of the body at rest, by placing 
 the man or the animal, exactly as a burning body, into a 
 calorimetrical chamber adapted to the purpose. In the case 
 of the body engaged in performing external work an arrange- 
 ment is provided within the chamber which permits of the 
 work done being measured ; such, for example, as a treadmill 
 which is connected with a steam-engine, and which the man 
 under observation ascends or descends, so as to perform an 
 amount of work (either in accelerating or retarding the move- 
 ment of the wheel) which permits of being estimated (Hirn). 
 From the quantity of mechanical work thus estimated the 
 
INCOME AND EXPENDITURE OF ENERGY COMPARED. 221 
 
 equivalent number of units of heat may be calculated and 
 added to the expenditure of heat as found by the direct method. 
 (For the magnitude of the expenditure of heat and of the 
 mechanical work done as well as for their relations, consult the 
 two following chapters.) 
 
 Comparison betiueen the Income and Expenditure of Energy. 
 
 The object of attempting a comparison between the energy 
 which enters and leaves the body is, firstly, to confirm the 
 theoretical conceptions which we have formed, and secondly, to 
 check the separate determinations of income and expenditure. 
 
 As has been previously mentioned, the amount of energy 
 received into the body can be determined if we know the 
 amount of the organic constituents of the food and the heat 
 which they develop on combustion ; and at the same time it 
 has been stated that for only a few of the alimentary substances 
 has this heat of combustion been accurately determined. We 
 must therefore rest satisfied with estimating the kinetic energy 
 corresponding in a given time to the potential energy at the 
 disposal of the body, and comparing it with the actual amount 
 of energy given out. 
 
 The former of these data is estimated according to the 
 following principle : every manifestation of energy is neces- 
 sarily associated with a corresponding consumption of oxygen, 
 and the consumption of oxygen is, if estimated for long periods 
 of time, equal to the oxygen received into the body (see p. 157). 
 From the oxygen received we might calculate the amount of 
 energy which becomes kinetic, if the whole of the oxygen were 
 used up in the oxidation of one and the same body, whose heat 
 of combustion were exactly known. 
 
 Since different compounds of unequal heats of combus- 
 tion are oxidized, the knowledge of the amount of oxygen re- 
 ceived cannot be utilised. But from the oxidation-products 
 which are excreted in a given time we can, at any rate approxi- 
 mately, determine the elements which are oxidized, as for in- 
 stance, the carbon from the carbonic acid, and the hydrogen from 
 the water, produced in the course of oxidation. The amount of 
 water which is formed in the body can, however, scarcely be 
 estimated, and we are therefore compelled to subtract the amount 
 of oxygen which corresponds to the carbon (i.e. required to oxidize 
 
222 INCOME AND EXPENDITURE OF ENERGY COMPARED. 
 
 the carbon to form C0 2 ), and assume that all the remaining 
 oxygen is employed in the oxidation of hydrogen. The error 
 doubtless arising from this dogmatic assumption becomes in- 
 significant when compared with the much larger one, due to 
 our determining the heat of combustion of the carbon and 
 hydrogen found, as equal to the heat which is developed by the 
 combustion of their organic combinations. 
 
 As we should expect from these considerations, such re- 
 searches (as those of Dulong and Despretz) have led to no 
 agreement between the expenditure of heat as calculated and as 
 directly measured. 
 
 An attempt has been made to determine, in the case of the 
 energy of the body as in that of its matter, by what channels 
 its distribution is effected. The numbers which have been 
 obtained by calculation, being affected by numerous errors, 
 which have in part been already mentioned, need not be quoted ; 
 the results of these calculations possess therefore only the value 
 which attaches to an approximate estimate. According to 
 Barral's calculations the expenditure of the energy of the body 
 is distributed as follows : from 1 to 2 per cent, is lost in heating 
 the excreta (urine and faeces), 4 to 8 per cent, is lost as heat 
 in the respiratory processes, from 20 to 30 per cent, is used up 
 in the evaporation of water ; the greatest part (60 to 75 per 
 cent.) leaves the body either as heat conducted or radiated from 
 its surface, or is converted into external mechanical work. (Con- 
 cerning the importance of this question consult the succeeding 
 section.) 
 
 Influence of the Conversion of Energy on the Exchanges 
 of Matter. 
 
 In the preceding chapter it has been shortly stated that 
 the oxidation-processes of the body must necessarily reach a 
 certain amount in order that the organism may continue to 
 exist, and that this amount constitutes the ' minimum exchange 
 of its matter.' A closer investigation into the causes which 
 render this minimum exchange necessary reveals at once that 
 the necessary oxidation-processes are required for the supply of 
 the energies of the body, viz. for the development of heat, for 
 the performance of certain kinds of mechanical work (as for the 
 movement of the heart, the movements of respiration, of the 
 
EXCHANGES OF ENERGY AND OF MATTER. 223 
 
 alimentary canal, &c.\ The minimum exchange of matter is, 
 therefore, so to speak, conditioned by the minimum exchanges 
 of energy required. 
 
 The oxidation-processes which go on in glands appear to constitute an 
 apparent exception to this statement ; here, at first sight (see the Introduc- 
 tion), the formation of oxidation-products (the specific constituents of the 
 secretion) would appear to be more important than the evolution of kinetic 
 energy (development of heat) which is associated with it, but there are no 
 proper grounds for such speculations as to uses. For the requirements of 
 the body, not merely the liberated energy, but likewise the chemical pro- 
 ducts which are the results of the activity of glands, are of use : that which is 
 true of glands is true of the tissues generally, the oxidation-products of which 
 (specific constituents of the tissues) as woll as their energies, are utilised. 
 
 An increase in the activity of one of these processes must 
 necessarily lead to an increase in the other. It has been already 
 mentioned that an increase of the luxus-consumption increases 
 the kinetic energy of the body, and the case has now to be 
 considered in which an increased expenditure of energy renders 
 an increased consumption of food necessary. 
 
 We know by experience that the mechanical work of the 
 muscles, which we shortly designate work, is that act of the 
 body associated with transformation of energy, which is most 
 frequently, and to the greatest extent, influenced by the will, 
 by reflex action, by cramps or convulsions due to disease, &c. 
 
 An increase in the amount of this work is associated with 
 increased exchanges of matter, and consequently leads to an 
 increase in the excretions, especially to an increased excretion 
 of carbonic acid, and necessitates, if the weight of the body is 
 to remain constant, an increased consumption of food ( 6 Arbeits- 
 Consumption ') ; at the same time, the sensation which in- 
 dicates the want of food, viz. hunger, is increased. 
 
 It is yet disputed whether, under certain circumstances, 
 especially as a consequence of losses of heat, an increased pro- 
 duction of heat takes place in the body, quite independently of 
 muscular movements, but in accordance with certain fixed 
 laws. On this subject the reader must consult the following 
 chapter. 
 
 As will afterwards be stated in detail, the different mani- 
 festations of energy in the body are associated with the oxidation 
 of specific constituents. In order to form a judgment as to 
 the article of diet which would best supply the increased con- 
 
224 EXCHANGES OF ENERGY AND OF MATTER. 
 
 sumption due to any given act, we should require to know the 
 constituent which principally undergoes oxidation during that 
 act. The most direct way to acquire this knowledge would 
 appear to be to study the organs, as e.g. the muscles, in which 
 the various manifestations of energy are observed, and in which 
 the oxidations proceed. As, however, this department of phy- 
 siology is yet but little developed, we must satisfy ourselves 
 with a study of the changes in the excretions, which correspond 
 to increased evolution of kinetic energy. 
 
 Especially has the amount of urea to be studied as evidence 
 of the oxidation of nitrogenous bodies, and the amount of 
 carbonic acid as expressing the oxidation-processes of the body 
 in general. 
 
 In consequence of doubtful statements (especially one which 
 asserted that muscular activity increased the excretion of urea) 
 the view was, for a long time, promulgated that only those 
 nitrogenous constituents of the body which enter into the com- 
 position of the tissues, are made use of in the production of 
 mechanical work. It was supposed that no heat was developed 
 from these nitrogenous constituents until by processes of de- 
 composition they had furnished non-nitrogenous substances. 
 The non-nitrogenous constituents, on the other hand, were 
 supposed to be simply employed in the production of heat. 
 
 Upon these hypotheses was based a classification of foods, 
 according to their uses. The nitrogenous constituents were, 
 because of their relation to the tissues, called 6 plastic ' (or 
 4 flesh-formers'); the non-nitrogenous, on the other hand, were 
 called ' respiratory ' constituents ; or, the former were desig- 
 nated as the sole generators of movements, ' dynamogenous,' or 
 ' kinesogenous,' whilst the latter, as the sole generators of heat, 
 were spoken of as ' thermogenous ' (Bischoff and Voit). Since 
 it has been ascertained, however, that the excretion of urea is 
 not increased during mechanical work, this hypothesis has. 
 fallen to the ground ; and the importance of the numerous con- 
 siderations opposed to it is now fully recognised. 
 
 Amongst these the following must be mentioned (M. Traube) : 
 1. That even with a food which is very poor in nitrogen (vege- 
 table food) a considerable amount of mechanical work can be 
 performed (the majority of beasts of burden are herbivorous, 
 and bees, though fed merely on honey, are continually in 
 
ATTEMPTED CLASSIFICATION OF FOODS. 225 
 
 motion). Such facts as these could only be brought into 
 harmony with the old theory, by supposing that the mechanical 
 work of the body, even when it attains a high magnitude, is 
 insignificant in amount when compared to the heat formed 
 a view which has already been combated. 2. That cold- 
 blooded animals, and even animals and men inhabiting hot 
 zones, and whose heat-production can only be very small, yet 
 live, in great part, on a vegetable diet containing but little 
 nitrogen. 3. That carnivorous animals, in spite of the small 
 quantity of non-nitrogenous food which they consume, have 
 sufficient heat generated within them, even when they do not 
 perform much mechanical work. 4. It has lastly been directly 
 ascertained that the albuminous bodies which are consumed 
 in a given time (calculated from the amount of urea excreted) 
 are not by any means capable of accounting for the work done 
 during the same time, even when the heat of combustion of 
 those bodies was calculated extravagantly high (Fick and 
 Wislicenus). With this fact the circumstance is in harmony 
 that the inhabitants of mountainous districts prefer to take 
 fat and sugar as provisions when they have arduous journeys 
 to perform. 
 
 We cannot, therefore, point out any act accompanied with 
 the evolution of kinetic energy, for which the consumption of 
 a particular kind of food (nitrogenous food) is absolutely neces- 
 sary. 
 
226 
 
 CHAPTEE VII. 
 
 ON THE DEVELOPMENT OF THE HEAT AND ON THE TEMPERATURE 
 OF THE BODY. 
 
 I. DEVELOPMENT OF HEAT. 
 
 BUT little remains to be said concerning the origin of the heat 
 of the animal body. It has been repeatedly stated, that in all 
 organs in which processes of oxidation occur, either the whole 
 of the energy which becomes kinetic, or, at least, a consider- 
 able fraction of it, takes the form of heat. The other forms 
 of energy (mechanical work, electricity) are only generated in 
 certain organs, and then only in addition to heat. 
 
 According to recent investigations even the lungs belong to the group of 
 heat-generating organs ; in the lungs the combination of oxygen with 
 haemoglobin is a source of heat. 
 
 The absolute amount of heat generated in the unit of 
 time, by the unit of weight of any organ, is as yet undeter- 
 mined; it varies greatly, however, in the case of different 
 organs. The glands, for example, generate far more heat than 
 the parenchymatous tissues, because the oxidation-products of 
 the former (the specific constituents of the secretion) are con- 
 tinually being removed and replaced by newly-formed sub- 
 stances. The oxidation-products of the latter, on the other 
 hand, i.e. the specific constituents of the parenchymatous 
 juices, remain very long in the place where they originate ; 
 oxidation is therefore far more active in glands. Even in 
 one and the same organ the development of heat varies very 
 materially at different times, and, as is readily conceivable, 
 with the energy of the oxidation-processes, or, which is the 
 same thing, with the amount of oxygen which is consumed. 
 
 The increased generation of heat dependent on the energy 
 
DEVELOPMENT OF HEAT. 227 
 
 of the oxidation-processes is particularly remarkable in the 
 case of glands, the temperature of which notably increases as the 
 secretion becomes more active. Even in muscles an increased 
 development of heat is observed during" activity. (Consult the 
 following chapter.) 
 
 No heat is generated in the horny tissues of the body, in which, it 
 would appear, no oxidation-processes occur. Whether heat is generated in 
 the blood can only be determined by answering the question as to whether 
 oxidation goes on in that fluid. 
 
 In addition to the direct sources of heat which have just 
 been referred to, there are also others which have been pre- 
 viously treated of. It has, namely (p. 219), been ascertained 
 that in the body when it is at rest, other forms of kinetic 
 energy, particularly mechanical work, are almost entirely con- 
 verted into heat. This conversion into heat occurs partly 
 through the friction of the actively moving organs (muscles) 
 against the tissues with which they are in contact, and partly 
 by the friction and dragging of passive organs (tendons, bones, 
 blood in the vessels, &c.) brought about by those which are in 
 active motion. Thus, in the body which is doing work, a great 
 part of the mechanical work is, by friction, converted into heat. 
 
 Muscular work consequently increases the production of heat in the 
 body, in a twofold manner : 1. By increasing that production of heat in 
 muscle which is connected with muscular activity. 2. By the friction of 
 the muscle and of the structures moved by it against the surrounding 
 parts. 
 
 It is yet undecided whether the production of heat in the 
 parenchymatous tissues (considered apart from glands and 
 muscles) is directly under the control of special nerves. The 
 majority of the changes in temperature which follow the section 
 or the irritation of nerves can be explained by the influence 
 exerted upon the distribution of heat through the vaso-motor 
 nerves (see below). Still, some recent observations appear to 
 point to a direct influence exerted by the nervous system upon 
 the production of heat. 
 
 Under certain circumstances, after traumatic lesions which 
 interrupt the continuity of the spinal cord, or after its division 
 (Brodie, Billroth, Quincke), a rise in the temperature of the 
 body occurs. Seeing that division of the spinal cord would by 
 its influence on the vaso-motofr nerves cause a lowering of the 
 
 Q 2 
 
228 EQUALIZATION OF TEMPERATURE. 
 
 temperature, the rise which occurs under such circumstances 
 has led to the supposition that certain fibres exist in the spinal 
 cord which have a direct influence on the production of heat, 
 being capable of inhibiting it. The inhibitory centre presiding 
 over these nerves would, according to this theory, have to be 
 sought for in the brain (Naunyn and Quincke). In order that 
 rise in temperature may occur after division of the spinal cord, 
 the counterbalancing influence exerted by the vaso-motor nerves 
 must be prevented, by hindering the external loss of heat. 
 Some have failed to observe any rise of temperature as a con- 
 sequence of division of the cord (Kosenthal). 
 
 Even when the medulla oblongata is separated from the 
 pons Varolii, and when both the portions of the brain are 
 injured, rises in temperature occur (Tscheschichin, Bruck, and 
 Griinther) which cannot yet be adequately explained. 
 
 II. TEMPEKATUEE OF THE BODY. 
 
 The different organs of the animal body are in relation 
 with one another, in part by actual contact, and in part through 
 the circulating blood, which acts as a conductor or distributor 
 of heat. Through its agency, the heat generated in the different 
 parts of the economy is distributed pretty uniformly throughout 
 the body, and even to those parts of it which do not themselves 
 generate heat. The result of this equalisation, as well as of 
 the losses of heat about to be discussed, is an approximately 
 constant temperature of the whole body, which in the human 
 subject varies between 36 C. and 38 C. The temperature is 
 nearly the same in other mammals ; it is higher in birds. Or- 
 ganisms which possess a constant temperature are called warm- 
 blooded or homo-thermous. In other animals the energy of 
 the oxidation-processes, and consequently the heat generated, 
 is so small in amount, that there is no constant body-temper- 
 ature, which merely rises a few degrees above that of the 
 surrounding medium (air or water). Such animals are called 
 cold-blooded or, more appropriately, poikilothermous (of variable 
 temperature). 
 
 Losses of Heat. 
 
 The animal body, being almost always surrounded by media 
 which are colder than itself, is constantly giving out heat to 
 
LOCAL TEMPERATURES. 229 
 
 them. This loss of heat occurs in the following manners : 
 1. By radiation from the free surfaces of the body. 2. By 
 conduction, a. To those bodies which are in contact with 
 the surface and are colder than the body, especially air and 
 clothing. 6. To the bodies taken into the organism, air and 
 food, which are colder than it. The last-named loss of heat is 
 frequently expressed by saying, that the body gives up heat 
 with its excreta (expired air, sweat, urine, faeces), which pos- 
 sess, in general, the temperature of the body. Obviously 
 these are two ways of expressing the same facts, assuming, as 
 is generally the case, that the matters taken into and excreted 
 from the body are equal in quantity and possess the same 
 specific heat. c. To excreta, especially sweat, which have to 
 be evaporated, and which, during evaporation, remain in 
 contact with the surface of the body ; the heat thus given up 
 becomes forthwith latent. It is usual to express this loss of 
 heat as ' heat lost by the evaporation of water.' 
 
 As the loss of heat takes place principally from the surface of the body, 
 its amount depends upon the extent of that surface ; and it is therefore clear 
 that small individuals, the external surface of whose body, as compared 
 with their body-weight, is more extensive, give up relatively more heat 
 to the medium which surrounds them than do larger ones. 
 
 Many of the losses of heat here referred to are of very 
 variable nature ; and their variability is utilised in maintain- 
 ing the constancy of the temperature of the body. 
 
 Local Temperatures. 
 
 For reasons which are easily intelligible, the above-men- 
 tioned equalisation between the temperatures of the different 
 parts of the body cannot be complete, so that certain differences 
 in temperature constantly exist. These differences, which, 
 without any further explanation, may be surmised from the 
 relations of the body already alluded to, have by experiment 
 been fully determined to exist ; they are principally the fol- 
 lowing : 1. The greater the amount of heat which any part of 
 the body generates, the warmer it is (cceteris paribus). Glands 
 are, therefore, hottest during secretion, and muscles during 
 work (and during rigor mortis) ; the horny (epithelial) tissues 
 are the coldest. 2. The greater the amount of heat which any 
 
230 LOCAL TEMPERATURES. 
 
 organ must lose by radiation or conduction, in consequence of 
 its situation or of other relations, the colder it is. Hence the 
 following structures are the coolest : the skin, particularly when 
 it is covered with sweat ; the lungs ; the first portions of the 
 alimentary canal ; &c. 3. Amongst these parts of the body, 
 those are coldest which are most exposed, those warmest which 
 are most protected (&(} the axilla, the cavity of the mouth, 
 &c.). As the blood is the most important agent in the equalisa- 
 tion of the temperature of the different parts of the body, its 
 temperature might be taken as representing the mean tempera- 
 ture of the body ; as a fact, the numbers which have been 
 given at page 228 are deduced from observations of the heat 
 of the blood. From the facts stated we may further conclude : 
 a. In organs which generate much heat, and whose tempe- 
 rature therefore exceeds that of the blood (glands, muscles 
 during work), the venous blood which flows out of them is 
 warmer than the arterial blood which flows into them; the 
 opposite is the case with organs which produce little heat or 
 which give up heat to the external medium ; thus, for example, 
 the venous blood of the skin is cooler than the arterial. Ac- 
 cording to some observers (Colin, Jacobson, and Bernhardt), 
 the heat which the blood in the lungs loses to the air is more 
 than compensated for by the combination with oxygen, so that 
 the blood of the pulmonary veins and of the left side of the 
 heart is hotter than that of the right side of the heart. Ac- 
 cording to others, however (Gr. Liebig, Bernard, Heidenhain 
 and Korner), the opposite is the case ; a fact to be explained, 
 according to Korner, not by the small losses of heat sustained 
 in the lungs (p. 151), but by the fact of the thin-walled right 
 side of the heart lying near the warm abdominal viscera in its 
 vicinity. 6. An organ whose temperature is below that -of the 
 blood becomes warmer in proportion as the amount of blood 
 flowing into it in the unit of time increases. The temperature 
 of such organs (as the skin) increases under the following 
 circumstances : when the blood-pressure of the whole body is 
 raised ; when the activity of the heart is increased ; and par- 
 ticularly when the arteries supplying them are dilated (as when 
 their vaso-motor nerves are divided). On the other hand, under 
 opposite circumstances, the temperature falls. Hence, redness 
 
REGULATION OF TEMPERATURE. 231 
 
 of any portion of the skin is, as a rule, accompanied by heat, 
 paleness by cold. 
 
 Even the heat of inflamed parts merely depends upon a more 
 active supply of blood to them, and not upon an ncreased local 
 production of heat, as it is constantly lower than the normal 
 temperature of the internal organs (Hunter, Jacobson and 
 Bernhardt, Schneider). 
 
 Tliese relations must always be kept in mind in determinations of the 
 temperature of the body as a whole. As it is only in the case of the lower 
 animals that the temperature of the blood can be directly determined by 
 placing thermometers in the vessels, in man those parts are chosen for 
 observation of temperature which are least exposed to loss of heat; the 
 thermometer is therefore placed in the cavity of the mouth, in the rectum, 
 in the vagina, or in the axilla, and is allowed to remain there as long as 
 possible. It must here be mentioned that a high temperature of the exter- 
 nal zone of the body, by increasing the loss of heat, leads to a cooling of 
 the interior. Conclusions cannot, therefore, be safely drawn from determina- 
 tions of the temperature of the external zone as to the temperature of the 
 interior of the body j the latter can be determined by placing the thermo- 
 meter deeply into the rectum. Absolute determinations of temperature are 
 always made with the (mercurial) thermometer. Comparisons of the 
 temperature of two parts of the body, or of the temperature of the same 
 part at different times and under different conditions, &c., are conducted 
 either with the aid of the thermometer, or better still, by thfermo-electric 
 methods (Chapter VIII.). 
 
 Maintenance of the Mean Temperature in Warm-blooded 
 Animals. 
 
 The mean temperature which has been stated to exist in 
 man and warm-blooded animals appears to be an absolutely 
 necessary condition for the most important vital processes. 
 
 This conclusion is arrived at by a consideration of the fact 
 that even small deviations of the temperature of the body n 
 beyond the stated limits (36 C. to 38 C.) are accompanied 
 by important dangers. The numerous processes which go on 
 in the body, and which are akin to fermentation, explain these 
 dangers ; at a temperature of 42-6 C. coagulation within the 7) 
 blood-vessels commences (Weikart), and at 49 C. heat-rigor " 
 commences in the muscles (Chapter VIII.). Accordingly the 
 organism possesses numerous contrivances for maintaining its 
 temperature within certain limits. 
 
 The most important of these are the following: 
 
232 REGULATION OF TEMPERATURE. 
 
 1. Such arrangements as act by regulating the amount of 
 heat eliminated : a. The sensation of a diminished or increased 
 temperature (sensation of cold or heat, Chap. X.) leads man in 
 the first case to surround himself with bad conductors of heat 
 (thick clothes, wool, silk), and in the second with good con- 
 ductors (thin clothes, linen), or even to use extraneous means 
 (cold baths), to get rid of some of the body heat. 6. In- 
 creased temperature increases the activity of the heart (p. 80) 
 and of respiration (p. 167); the former leads to an increased 
 fulness of the capillaries, amongst others of those of the skin, 
 and consequently to a rise in the temperature of the latter 
 organ, and to an increased loss of heat by conduction and 
 radiation. Thus, when the heat of the body increases, the skin 
 becomes turgid, warm, and moist ; when the temperature falls, 
 on the other hand, the skin shrinks, and becomes cold and dry. 
 Increased respiratory activity augments the loss of water from 
 
 !,' the respiratory passages. 1 The secretion of sweat is, moreover, 
 either occasioned or increased in quantity by an increased fulness 
 
 1 of the vessels of the skin, and the rapidly evaporated sweat con- 
 sumes an extraordinary amount of heat. In summer, when the 
 surrounding air is of nearly the same temperature as the body, 
 this is almost the only way in which the heat of the body is 
 lost. c. Cold causes contraction, and heat causes dilatation 
 of the small arteries (p. 75), especially of the skin. This 
 must exert the same regulating action as the phenomena 
 referred to under b. 
 
 2. Such arrangements as exert their action in regulating the 
 production of heat : a. An involuntary and direct increase in 
 the amount of heat produced on exposure to cold, which takes 
 place in a manner yet unknown, has been suspected to occur 
 by some (Hoppe, Liebermeister, Eohrig and Zuntz), especially 
 because under the influence of the cold bath the temperature 
 of the axilla at first rises, whilst the excretion of carbonic 
 acid is increased ; others, however (Senator, Winternitz), sup- 
 pose the first phenomenon to be due to an arrested loss of heat 
 owing to the contraction of the blood-vessels of the skin, whilst 
 the increase of tissue-change, evidenced by the increase in the 
 
 1 The possible generation of heat in the lungs cannot be materially increased by 
 increased respiration without a corresponding increase in the quantity of oxygen 
 used. 
 
VARIATIONS IN TEMPERATURE. 233 
 
 excretion of carbonic acid, is not a constant phenomenon, and 
 may be replaced by a decrease ; in any case it need not be asso- 
 ciated with an increased production of heat. 6. A diminution 
 of temperature (cold) increases the feeling of hunger, and in- 
 creased consumption of food augments the production of heat. 
 c. When the body is exposed to cold the need for muscular 
 exertion is felt, such as walking backwards and forwards, 
 work and this raises the temperature in a twofold manner 
 (p. 227); further, there occur certain (presumably reflex) 
 involuntary muscular movements (shivering, chattering of the 
 teeth), both of which actions can be executed voluntarily with 
 the object of generating heat. 
 
 Small individuals, whose losses of heat are constantly greater than those 
 of larger individuals, eat more and move more actively. 
 
 The efficiency of the regulating arrangements in providing against loss of 
 heat, especially in the case of man, is but small, so that clothing, fuel, and 
 movements of the body are the most efficacious protection which he possesses 
 against the cold. 
 
 Fluctuations in the Mean Temperature. 
 
 It yet remains to be stated that fluctuations of the mean 
 body temperature (blood-heat) occur within the normal limits, 
 i.e., within such limits as not to call into action the regulatirjg 
 apparatus of the body ; and further, to point out what relation 
 these fluctuations bear to the functions of the body and the mode 
 of living. As the heat-producing processes, as a whole, yield \ 
 carbonic acid nearly in proportion to the heat generated, the I 
 fluctuations of heat coincide very nearly with the fluctuations 
 in the carbonic acid excreted. 
 
 The following circumstances cause a high temperature : 
 muscular movements ; abundant glandular secretion, especially 
 of bile (hence the calorific value of digestion) ; great energy 
 of the whole material exchanges of the body, as in persons of 
 the male sex, of strong constitution, of adult age, &c. ; morbidly 
 increased material exchanges, such as probably exist in fever 
 (the excretion of urea is here increased, and before the rise in 
 temperature occurs, so that the former phenomenon cannot 
 (p. 214) be explained by the latter, Naunyn). Circumstances 
 of an opposite nature to the above often cause low temperatures, 
 as do also diseased conditions, which restrain the consumption of 
 oxygen (such as some diseases of the lungs, starvation, p. 207), &c. 
 
234 VARIATIONS IN TEMPERATURE. 
 
 Further, a diurnal fluctuation of the temperature of the body 
 occurs, independently of the digestive process, which appears to 
 be due to variations in the energy of the oxidation-processes 
 connected with particular periods of the day. 
 
 Not only can the mean temperature of the body be affected 
 in a lasting manner by the processes which generate heat, but 
 likewise by those concerned in its dissipation from the body : 
 thus, e.g..) the body- temperature is very much influenced by the 
 state of contraction of the blood-vessels of the skin, and there- 
 fore by the state of excitation of the vaso-motor centre ; as the 
 latter is increased in fever, the high* temperatures of fever 
 may in part be thus explained ( L. Traube). 
 
 The heat of the blood diminishes when sensory nerves are 
 irritated (Mantegazza, Heidenhain), apparently through the 
 agency of the medulla oblongata ; for when the medulla is excited 
 directly the same results follow. This effect is due to an accele- 
 ration of the blood current and a consequently increased loss of 
 heat (Heidenhain). 
 
 From tlie facts which have been stated it is easy to explain the increase 
 of temperature which follows irritation of the spinal cord (Tscheschichin), 
 and the decrease caused by division of the spinal cord, as well as by 
 paralysis of the vaso-motor nerves brought about by poisons (nicotine, curare). 
 We conclude that an increased elimination of heat does take place in the 
 latter circumstances from the fact that when the animals subjected to ex- 
 periment are placed in a warm medium, section of the spinal cord (accord- 
 ing to some authors, p. 227 etseq.} leads to a rise in temperature. 
 
 Hybernating animals possess during the period of hyberna- 
 tion a very low temperature. In them the production of heat, 
 as well as the loss of heat, is reduced to a minimum, by an 
 extraordinary slowing of the circulation. 
 
 Ordinary warm-blooded animals die when exposed to cold, so soon as 
 their temperature has sunk below a certain limit. Previous to death in them, 
 asinhybernating animals, the frequency of the pulse and the movements of 
 the alimentary canal undergo an enormous diminution, and the central ner- 
 vous organs become incapable of performing many actions, as e.g. of bringing 
 about the convulsions of asphyxia (Horwath). If the temperature of the 
 body does not fall below the limit indicated above, the animal may by 
 warmth be awakened from the soporific state into which it has fallen, and 
 which corresponds to the winter-sleep of hybernating animals. If the 
 cooling does not cause the body-temperature to fall below 20 or 18, the 
 animals possess the means of warming themselves again, as soon as they are 
 brought from the cold into a mean temperature. Even when the diminution 
 of temperature has exceeded these limits, the body can of itself become 
 
FATAL COOLING. 235 
 
 warm again, if artificial respiration be carried on ("Walther; Horwath 
 succeeded in reviving animals, whose bodies had been cooled to 5 0., by 
 merely warming them). 
 
 APPENDIX. 
 
 Immediately after death a temporary rise of temperature is frequently 
 observed (post-mortem rise in temperature). According to some this rise is 
 due to the formation of heat which attends rigor mortis, whilst others ac- 
 count for it by supposing that when the circulation ceases, whilst the loss of 
 heat is very materially delayed, the production of heat in the different 
 organs continues for some time after death (Beidenhain). 
 
236 
 
 CHAPTER VIII. 
 
 THE ENEKGY OF MECHANICAL WORK (MOVEMENTS OF 
 THE BODY). 
 
 THE liberation of energy in the form of motion is far less fre- 
 quent in the animal body than the formation of heat, and is con- 
 nected with certain definite apparatuses. These apparatuses are, 
 wherever found, simple or metamorphosed cells, or constituents 
 of cells. The phenomena of motion have been proved to occur 
 in the following situations in the human body : 1. In muscular 
 fibres, striated and smooth. 2. In lymph-corpuscles and the 
 corpuscles resembling them (colourless blood-corpuscles, connec- 
 tive-tissue corpuscles, mucus-corpuscles, pus-corpuscles, etc.). 
 3. In ciliated cells. 4. In spermatozoa. 5. In cells exhibiting 
 molecular movements. To these must be added the contractile 
 masses of many simple organisms. Finally, the processes 
 of formation, growth, division, etc., may be regarded as move- 
 ments. The movements previously mentioned are, however, 
 contrasted with those just given by their much greater rapidity, 
 which renders their direct observation possible ; whereas the 
 processes of growth take place so slowly as to be only recognis- 
 able, after considerable intervals, in their effects. The former, 
 also, cause only transitory changes of place and form, after 
 which the parts set in motion return approximately to their 
 previous condition ; while the latter lead to permanent altera- 
 tions. The latter are referred to in the fourth Section of the 
 work. 
 
 The above-mentioned organs, some of which are entirely, and others in 
 part, contractile, have, as far as they have been investigated, certain charac- 
 teristics in common, apart from the contractility itself, which point to an 
 essential substance present in all. This substance appears throughout the 
 animal kingdom, and in many vegetable organisms. It was formerly termed 
 ' sarcode ; ' but now in general it is called ' protoplasm.' It may, therefore, 
 be stated as a general law, that active movements only occur where proto- 
 
STRUCTURE OF MUSCLES. 237 
 
 plasm is found. The properties of protoplasm will be most fittingly de- 
 scribed in connection with the physiology of the most important and most 
 thoroughly investigated of the motor apparatuses of the body, viz. the 
 muscles, which will now be considered. 
 
 I. THE MUSCLES. 
 
 Muscles are essentially distinguished from almost all other 
 motor-structures by the fact that in them motion only occurs 
 after the operation of a liberating force, the existence of which 
 may be demonstrated. This liberation originates, as a rule, in 
 the nervous system. 
 
 The existence of automatic muscular movements has been recently main- 
 tained (Engelmann : see Smooth Muscle). 
 
 Two kinds of muscles are distinguished, chiefly from the 
 arrangement of their histological elements, viz., the striated and 
 the smooth. The physiological properties of both are, as the 
 following consideration will show, essentially the same, although 
 many distinctions appear in the details. 
 
 A. Striated Muscles. 
 
 Transversely striated muscles are placed wherever ener- 
 getic movements occur. With few exceptions all such move- 
 ments, and consequently the activity of all transversely striated 
 muscles, are dependent upon the will. Striated muscles 
 are therefore also called voluntary muscles. The heart, whose 
 striated fibres differ in other respects also from those of 
 ordinary voluntary muscle, forms the chief of the exceptions 
 (p. 56). 
 
 Striated muscles form for the most part long roundish cords, 
 or sometimes flat expansions, of a reddish-brown colour, which 
 exhibit a coarse longitudinal fibrillation. They are attached to 
 the parts to be moved (bone, cartilage, etc.) either directly or 
 by means of bundles of connective-tissue (tendons). They are 
 surrounded by strong sheaths of connective-tissue (fasciae) ; and 
 internally they are divided up into numerous longitudinal 
 bundles by septa of a finer connective-tissue (perimysia). A 
 piece of muscle may without difficulty be teased and separated 
 in a longitudinal direction into smaller and smaller bundles of 
 
238 STRUCTURE OF MUSCLE-TUBES. 
 
 fibres, until what is called the 'primitive bundle ' is reached, 
 after which separation by tearing is impossible. This ' primitive 
 bundle ' is really no bundle at all, but a tube filled with an 
 apparently fluid mass the proper muscular substance. The 
 wall of this tube (the muscle-fibre or muscle-tube) consists of a 
 very elastic, completely closed membrane the sarcolemma. 
 The contents exhibit under the microscope fine, regular trans- 
 verse strice, caused by rows of little bodies possessing more 
 strongly refractile properties than the ground-substance. These 
 little bodies are doubly refractive (Briicke). The distance be- 
 tween the transverse striae, while the muscle is at rest, is very 
 regular, and differs little in the various classes of animals 
 (0-0020 to 0-0028 mm ) (Hensen). The majority of the muscle- 
 tubes run the whole length of the muscle, and are attached 
 directly to the tendon, bone, etc.; some, however, end in 
 pointed extremities in the interior of the muscle (Rollett). 
 
 It is concluded that the contents of the muscle-tubes are fluid from the 
 fact that, under certain circumstances, waves of motion are seen travelling 
 along them ; and especially from the appearance here, as in other fluids, of 
 Porret's phenomena (Kiihne), i.e. the flow of the contents towards the nega- 
 tive pole on the transmission of an electric current through a muscle-tube. 
 One observer (Kiihne) has, moreover, seen in a recently prepared specimen 
 of frog-muscle an included uematode worm move about evidently without 
 any mechanical resistance. Under the influence of various reagents, the 
 contents of the muscle-tubes solidify (as will be described more fully 
 hereafter) and fall to pieces in various directions : a. in the direction of the 
 transverse striae, into round thin plates (' discs,' Bowman) ; b. in a longitudinal 
 direction, into fine longitudinal fibres which exhibit slight varicose swellings 
 at distances corresponding with the intervals of the strioe in the fresh 
 condition of the muscle, constituting, therefore, an indication of the 
 earlier striated condition (muscular fibrillae, Kolliker) ; c. in both directions 
 at once, into small prismatic bodies which may be regarded as due to the 
 breaking up of the fibrillae in a transverse direction, or of the discs in a lon- 
 gitudinal direction (' sarcous elements,' Bowman ; * muscle-prisms,' Kiihne). 
 All these structures formed by the splitting up of the 'primitive bundle ' or 
 * muscle-tube ' have, at one time or another, been regarded as pre-formed 
 '-muscular elements. Now that a more accurate knowledge of facts has 
 rendered it possible to regard the sarcous elements of living muscle (especially 
 of the muscles of insects) as bodies suspended in the fluid contents of the 
 muscle-tube, we must consider the sarcous bodies as pre-formed ele- 
 ments, the tibrillse as a row of those elements superimposed, and the discs as 
 made up of a number placed side by side in one plane. In most muscles 
 the sarcous elements have the property, on coagulating, of separating in such 
 a manner as to form fibrillee ; and many reagents have the power of splitting 
 muscle-tubes into discs. The sarcous elements exhibit for the most part on 
 
STRUCTURE OF MUSCLE-TUBES. 239 
 
 section from three to five sides, and they are so closely apposed that there 
 exists but a small space between them for the fluid ground-substance (Cohn- 
 heiin). 
 
 When examined with polarised light, the sarcous elements appear 
 doubly refractive (and coloured, with crossed Nichol's prisms), while the 
 ground substance refracts light simply. As they change their form during 
 contraction, becoming shorter and thicker, they cannot be regarded as simple 
 doubly-refractive structures, like crystals, but must be supposed to consist of 
 groups of numerous small doubly-refractive elements (' disdiaclasts '), which 
 are arranged differently in sarcous elements at rest and in contraction 
 (Briicke). 
 
 According to more recent views (Krause, Hensen, Flogel, Merkel, 
 Eugelmann, and others), over the details of which there is, however, yet 
 much dispute, the structure of muscular tissue is much more complicated 
 than that which has just been given. The transverse striation is the optical 
 effect of the alternation of light and dark layers ; in the middle of the bright 
 striae a fine line is seen, which is taken to indicate the existence of a transverse 
 membrane (Krause). In the dark layers also a (bright) transverse line is 
 described. New schemes of construction have been built upon these dis- 
 coveries, into the consideration of which we cannot enter here, as it is very 
 difficult to exclude the differentiating effects of post-mortem coagulation. 
 Krause's scheme is the most complicated, in which the sarcolemma is di- 
 vided up, by means of transverse and longitudinal septa, into a system of 
 f muscle-cells,' each of which contains a sarcous element forming part of the 
 dark transverse line existing between the two brighter, fluid layers which 
 are in contact with the transverse septa. 
 
 In addition to the above, muscle-tubes contain the following morpholo- 
 gical elements : 
 
 1. Nuclei. These are cellular, with nucleoli surrounded by a shapeless 
 mass of granular matter (which is regarded by some as protoplasm) ; they 
 lie in the neighbourhood of the sarcolemma, but in many animals they are 
 scattered regularly throughout the contents of the muscle-tubes. 
 
 2. Nerve-terminations (Kiihne). The branched primitive nerve-fibres 
 enter the muscle-tubes, the ueurilemina becoming continuous with the 
 sarcolemma; the white substance of Schwann ceases immediately after 
 entrance, and the axis-cylinder passes into a prominence, or mass of matter, 
 lying immediately upon the transversely striated substance of the muscle-tube 
 and called the terminal nervous prominence, or prominence of Doyere the 
 sarcolemma being bulged outwards at that point. The substance composing 
 this prominence of Doyere is homogeneous, finely granulated and provided 
 with large nuclei in which lies a forked expansion (terminal plate), 
 the proper termination of the axis-cylinder. For every nerve-fibre which 
 enters a muscle there are, in the muscles of the eye, one to ten muscular 
 fibres, and in other muscles far more, as many as twenty to eighty (Tergast). 
 
 Muscles have, in addition to muscle-tubes and the septal system of the 
 perimysium, an abundant supply of connective-tissue connected with the 
 latter, as well as blood- and lymph-vessels, and a network of nerves. 
 
240 CHEMICAL CONSTITUENTS. 
 
 The Chemical Constituents of Muscle. 
 
 The reaction of fresh muscle in a state of repose is neutral, 
 or, owing to its being moistened with alkaline juices (lymph), 
 slightly alkaline (du Bois-Reymond). 
 
 As muscle is chemically a very unstable substance, the 
 determination of certain of its constituents requires special pre- 
 cautions, and is not yet complete. Such are, in particular, the 
 albuminous constituents. The contents of the muscle-tubes 
 may be obtained as pure as it is possible to obtain them by the 
 following methods (Kuhne) : 1. By expressing the juice from 
 the muscles of cold-blooded animals after first removing the 
 blood by washing out the vessels with some indifferent fluid 
 (5 to 1 per cent, solution of Nad). 2. By freezing bloodless 
 muscles, separating them into small fragments by means of 
 cooled instruments, and allowing them to filter at a temperature 
 slightly above C., the latter operation being assisted by the 
 previous addition of cooled NaCl solution. The ' muscle- 
 plasma ' so obtained is a turbid, neutral or slightly alkaline 
 fluid. It undergoes change more or less rapidly according as 
 the temperature is higher or lower. It coagulates, firstly form- 
 ing a homogeneous gelatinous mass, coagulation being recog- 
 nisable only by the fact that the plasma becomes tougher and 
 cannot be poured from the containing vessel ; but afterwards 
 the coagulum contracts into flocculi, in the course of which 
 it becomes very turbid and liberates an acid fluid, ' muscle- 
 serum? 
 
 The body thus separated in the process of coagulation is an 
 albuminous body, myosin. It is soluble in concentrated NaCl- 
 solution, and is precipitable from such solutions by the addition 
 of more water or more salt. Dilute acids also easily dissolve 
 myosin, and, in doing so, convert it into syntonin (p. 32). 
 
 Spontaneous separation of myosin takes place most rapidly, 
 indeed instantaneously, at a temperature of 40 C. for cold- 
 blooded animals, and (5f 48-50 C. for warm-blooded animals. 
 It may also be induced at once by means of distilled water and 
 acids. 
 
 The muscle-serum contains the remainder of the constituents, 
 viz.: 1. A number of albuminous bodies which coagulate at 
 various temperatures from 45 to 70 C., that coagulating at about 
 
CHEMICAL CONSTITUENTS. 241 
 
 60 or 70 being ordinary albumin. 2. Various carbo-hydrates : 
 viz. (a) glycogen (Nasse), which is present in especially large 
 quantities in embryos and young animals (Mac-Donnell) ; (6) the 
 products of the decomposition of glycogen dextrin (Limpricht), 
 and grape-sugar (Meissner), which are said by Nasse only to 
 appear post mortem ; (c) inosite, in large amount. 3. Lecithin 
 in all probability, on account of the presence in muscles of the 
 terminations of nerves ; this has not, however, been directly 
 proved. 4. Fats in small amounts. .5. Free acids, especially 
 sarcolactic acid, in addition to certain volatile fatty acids 
 formic, acetic. 6. Various amides : viz., creatine (and, according 
 to some, creatinine also, though others incline to the belief that 
 the latter is derived directly from the former), carnine (p. 27), 
 hypoxanthine (sarcine), xanthine, inosinic acid, and sometimes 
 uric acid, though this is doubtful. 7. A red colouring matter, 
 in most muscles haemoglobin (Kiihne). 8. Salts, especially salts 
 of potassium. 9. Water. 10. Gases, chiefly carbonic acid. 
 
 The above-named constituents are those of the contents of 
 muscle-tubes which have already undergone coagulation. As the 
 latter process, as well as contraction (see below), is connected 
 with certain chemical changes in the muscle which are as yet im- 
 perfectly understood, and as the investigation of uncoagulated 
 muscle or muscle-plasma cannot be carried on without the 
 occurrence of this process, the substances just mentioned 
 are not to be regarded as the constituents of unaltered living 
 muscle. All that has been discovered or surmised with respect 
 to them will be stated in the proper place. 
 
 In muscle as a whole there are found, in addition, the constituents of the 
 other bodies which help to make up the structure (connective-tissue, vessels, 
 blood, nerves, &c.). Gelatigenous substance, elastin, &c., must, therefore, 
 be added to the above list. The sarcolemma appears to consist of an elastic 
 substance. 
 
 The quantitative composition of coagulated beef-muscle is as follows 
 (Lehmann) : in 100 parts water, 70-80 ; solids, 26-20; insoluble albumi- 
 nous bodies (among them myosin, the sarcolemma, &c.), 15-4-17-7 ; soluble 
 albuminous bodies, and alkaline albuminate of potassium, 2'2-3-0; gelatin, 
 0-6-1-9; creatine, 0-07-0-14 ; fat, 1-5-2-3; lactic acid, 1-5-2-3; phosphoric 
 acid. 0-66-0-7; potassium, 0-5-0-54; the remainder of the ash, 0-17-0-26. 
 Carnine has hitherto only been found in the extract of beef (1 p.c. in 
 Liebig's extract, Weidel). 
 
242 MUSCLE AT REST. ELASTICITY. 
 
 Conditions of Muscle. 
 
 The usual condition of living muscle is one of rest; the 
 processes taking place in muscle in such a state are impercep- 
 tible except by the aid of delicate instruments. Out of this 
 state of rest muscle may pass, under certain conditions, into 
 other states: 1. Into a state of activity, during which a visible 
 shortening of the muscle occurs. 2. Into a state of rigor, 
 which is induced by certain chemical changes connected with 
 the cessation of life (coagulation), and which, also, is accom- 
 panied by a diminution in length. 
 
 a. Muscle in a State of Rest. 
 Mechanical Properties of Muscle in a State of Rest. 
 
 For the sake of simplicity we shall regard all muscles here 
 as spindle-shaped, and extended in the direction of their length 
 a form which the majority of muscles have in fact. A muscle 
 is a structure of slight but very perfect elasticity, i.e. it is very 
 extensile, slight weights producing a considerable elongation ; 
 but it has the power of returning, immediately on the removal 
 of the extending force, to its original length. During elonga- 
 tion there is, of course, a diminution in thickness, but the 
 volume remains about the same (it is said to be slightly dimin- 
 ished Schmulewitsch). Unlike inorganic bodies, and re- 
 sembling in this respect all other organic structures, muscle 
 does not elongate proportionately to the extending force ; but 
 equal increments of extending force produce a less amount of 
 elongation the greater the degree of tension of the muscle at 
 the time (Ed. Weber). The curve of extension got by taking 
 the weights as abscissae and the degree to which they extend 
 the muscle as ordinates is, therefore, not a straight line as in 
 the case of inorganic bodies, but approaches an hyperbola 
 (Wertheim). In the living body the muscles are constantly 
 stretched a little beyond their natural length, as is shown by 
 their retraction from their point of attachment when the fibres 
 are cut across. The value of this lies in the fact that, on 
 contraction, the points of attachment and insertion are ap- 
 proximated immediately without any loss of time or energy in 
 
MATERIAL EXCHANGES OF MUSCLE AT REST. 243 
 
 gathering up, or rendering taut, the relaxed muscle. In 
 muscles separated from their attachments the muscle-tubes 
 are not usually found extended in straight lines, but in. curves 
 and zigzags. 
 
 Exchanges of Matter in Muscle in a State of Rest. 
 
 Very little has yet been discovered respecting the chemical 
 processes taking place in resting muscle. As muscular tissue 
 continually effects the conversion into venous blood of the 
 arterial blood flowing to it, chemical processes must occur in 
 it, in which oxygen is used and carbonic acid formed. Certain 
 observations which will be detailed afterwards render it pro- 
 bable that these processes (viz. the use of oxygen and the 
 formation of carbonic acid) are not identical, but only take 
 place side by side. 
 
 In excised muscles (and here it is best to use those of cold-blooded 
 animals, as they retain for a long time the properties of normal living 
 muscle) an absorption of oxygen and an excretion of carbonic acid may be 
 detected (du Bois-Reymond, G. Liebig) ; as also in muscles which have 
 been deprived of blood (p. 240). These operations cannot therefore be as- 
 cribed to the blood in the blood-vessels of the muscle, but to the muscular 
 substance itelf. As the same gaseous exchanges are exhibited by muscle 
 in a state of rigor as by living muscle (Hermann), they cannot, at least 
 in by far the majority of cases, be considered as the result of functional 
 processes, but must be regarded as due to putrefactive changes which occur 
 especially at the surface of the muscle and at the exposed transverse 
 sections. The amount of such gaseous exchanges is in accordance with 
 this theory, being greater the larger the surface of the muscle exposed, and 
 the nearer it is to absolute putrefaction. 
 
 As, however, excised muscles retain their vitality under certain circum- 
 stances somewhat longer in air or oxygen than in hydrogen or other in- 
 different gases which contain no oxygen (Humboldt, G. Liebig, Hermann), 
 it must be admitted that some slight absorption of oxygen connected with 
 the functions of the muscle does take place, which is, nevertheless, too small 
 to account for the gaseous exchanges above mentioned. That the physiolo- 
 gical absorption of oxygen in muscles through which blood is passing is much 
 greater than in those which are excised, and so removed from the circulation, 
 may be accounted for by the following circumstances : 1. That, in the former 
 case, a much greater extent of surface is exposed to the operation of the 
 oxygen-carrier, viz. the blood, than in the latter, where the oxygen-carrier 
 is the atmosphere and the surface exposed the external superficies. 2. That 
 the oxygen of the blood, which is combined with haemoglobin, may possibly 
 have special properties more favourable to its transference to the muscular 
 . substance than those of the free atmospheric oxygen (p. 47). 3. That, in 
 
 a 2 
 
244 RIGOR OF MUSCLE. 
 
 the process of combining oxygen with the muscle-substance, other bodies 
 are needed which are not found in muscle itself, but are conveyed to it by 
 the blood. 
 
 Nothing further has been directly made out concerning the 
 chemical processes of resting muscle ; but certain conclusions 
 may be drawn from the appearances of muscle during contrac- 
 tion and rigor; reference will, therefore, be presently made 
 to this matter. 
 
 6. Muscle in Rigor. 
 
 If a muscle is removed from the blood-current, or excised 
 from the body altogether, it passes in warm-blooded animals 
 quickly, in cold-blooded animals much more slowly into a 
 state which is called death-rigor. In this condition it is devoid 
 of irritability, it is strongly contracted in the direction of its 
 length, it is less elastic, it has a whitish curdled appearance, and 
 an acid reaction (du Bois-Reymond) ; and its volume is slightly 
 diminished (Schmulewitsch, Walker). Under the microscope 
 the previously transparent muscle-tubes appear opaque and 
 flocculent, and their contents solid (Kiihne). The force exerted 
 in the contraction of rigor will be spoken of in considering 
 Irritability. 
 
 The appearance of c spontaneous ' rigor is hastened by 
 previous continued activity of the muscle; and by heat, a 
 temperature of 40 C. for cold-blooded animals, or of 48 to 
 50 C. for warm-blooded animals, inducing it instantly (heat- 
 rigor). In the cold the occurrence of rigor is much delayed, 
 not taking place for several days at a temperature of C. 
 It is induced, moreover, by distilled water (water-rig or\ by 
 acids, even the weaker kinds, such as carbonic acid (acid- 
 rigor}^ by various chemical bodies, and by first freezing and 
 then thawing the muscle. 
 
 The action of many of the above-mentioned agents in in- 
 ducing rigor may take place even when the circulation through 
 the muscle is intact; but a longer-continued and intenser 
 operation is necessary. The effect of the circulation of blood 
 through the muscle is to retard the occurrence of rigor (Her- 
 mann). 
 
 Cessation of the blood-circulation causes rigor in muscle by 
 depriving it of oxygen ; for rigor may be postponed for a con- 
 
RIGOR OF MUSCLE. 245 
 
 siderable time in excised muscles by injecting into their vessels 
 oxygenated blood a result which does not follow if the blood 
 injected contain no oxygen (Ludwig and A. Schmidt). More- 
 over, excised muscles through which no blood is passed lose 
 their irritability less quickly in air or oxygen than in gases 
 containing no oxygen (von Humboldt, Gr. Liebig) ; but here 
 the difference is extremely small, probably because the oxygen 
 comes into contact only with the external surface of the muscle. 
 
 The essential process in rigor is a coagulation of the con- 
 tents of the muscle-tubes, whereby they become solid (Briicke, 
 Kiihne). The coagulated body, the spontaneous separation of 
 which from muscle-plasma takes place at once at a higher tem- 
 perature, is an albuminous substance, myosin. From the 
 observations upon muscle-plasma we must suppose that the 
 contents of the muscle-tubes become first viscid and then gela- 
 tinous ; and that at last the coagulum, like the coagulum 
 of fibrin in a blood-clot, contracts, thus shortening the muscle, 
 which becomes opaque and yields a juice, the muscle-serum 
 (p. 240). It appears, therefore, that various stages are to be 
 distinguished in the occurrence of rigor, only the last of which 
 are visible to the eye, viz. the opacity and the diminution in 
 length. 
 
 Besides the separation of myosin other processes occur, 
 viz. : 1. The already-mentioned acidification, which is the 
 result of the formation of an acid or of an acid salt. The acid 
 may be sarco-lactic acid (p. 15 et sq.); but glycerin-phosphoric 
 acid is also said to be present (Diaconow). The amount of 
 acid which results from the occurrence of rigor in a muscle is 
 the same whether the latter take place slowly (spontaneous rigor) 
 or quickly (heat-rigor) ( J. Eanke). 2. An excretion of carbonic 
 acid which depends upon the formation of free carbonic acid. 
 Here again the amount is independent of the method by which 
 rigor is induced. The carbonic acid formed during the oc- 
 currence of rigor is, moreover, less the greater the amount the 
 muscle has generated previously by contracting (Hermann). 
 3. A diminution in the amount of glycogen present, which 
 is also independent of the manner in which rigor takes place : it 
 has not been discovered what becomes of the glycogen (0. Nasse). 
 
 Of the first, imperceptible, stage in the separation of myosin, 
 it may be said that, in all probability, in the case of cold- 
 

 
 246 RIGOR OF MUSCLE. 
 
 blooded animals, it takes place very gradually, since a muscle 
 from the moment of its excision, after a very transitory period 
 of exalted irritability, steadily loses its power of responding to 
 stimulation : it may therefore be said that excised muscle 
 commences at once to pass slowly into a condition of rigor, 
 i.e. myosin is separated in a gelatinous form, carbonic acid is 
 generated, glycogen is used up, and an acid appears which 
 gradually changes the reaction of the muscle to test paper. 
 The second stage, however, does not occur until after some 
 time, and consists in the contraction of the coagulum and the 
 shortening of the muscle, thus completing rigor. When rigor 
 has become complete the muscle begins to putrefy, in the 
 course of which vibriones are formed, the acid reaction gives 
 place gradually to an alkaline one owing to the formation of 
 ammonia, and ill-odoured gases are given off. Putrefying 
 muscle evolves, even in a vacuum, chiefly carbonic acid, ni- 
 trogen, and a little sulphuretted hydrogen. Long before the 
 excised muscle is in rigor in every part, similar, though slighter, 
 putrefactive changes have commenced on its external surface. 
 
 A muscle may be reclaimed from the first stage of rigor by 
 allowing blood to flow through its vessels, but not from the 
 second, i.e. after the contraction of the coagulum of myosin 
 (Kiihne, Hermann). The second stage of rigor may be rapidly 
 induced in the muscle of a warm-blooded animal by ligaturing 
 the arteries conveying blood to it (Stenson), and from this 
 stage it cannot recover by the mere renewal of the interrupted 
 blood-current. More will be said hereafter concerning the 
 nature of this recovery. 
 
 By suddenly heating a muscle strongly (as by throwing it into boiling 
 water scalding) it loses its power of entering into rigor : it neither be- 
 comes acid in its reaction under such circumstances (du Bois-Keymond) nor 
 forms carbonic acid (Hermann). Mineral acids have the same effect ; and 
 we must therefore distinguish acid-rigor from that which usually occurs 
 (Hermann). 
 
 If the muscles remain in their natural position in the body 
 after death, their contraction on entering into rigor produces 
 a stiffness of all the limbs death-rigor which does not dis- 
 appear until the occurrence of putrefaction, after which they 
 again become lax. From this rigor, or stiffening, of the corpse, 
 the term as applied to muscles is derived. 
 
IRRITABILITY. 247 
 
 The position of the limbs in the stiffened corpse is chiefly the result of 
 the tension of the muscles and the weight of the limbs. In some cases, 
 when rigor has occurred very suddenly, the limbs have been fixed in the 
 positions they occupied owing to the contraction of their muscles at the 
 moment of death (Rossbach). 
 
 c. Muscle in a State of Activity, 
 
 That change of state in muscles which is most important, 
 physiologically speaking, is the passage into the active con- 
 dition, i.e. into a condition in which the material exchanges 
 increase, and the muscle takes upon itself a new form. 
 
 Liberation of Muscular Activity. 
 
 The influences which call forth this change of condition are 
 called stimuli ; the conversion of the muscle from one state to 
 the other, excitation ; and the capability of excitation by means 
 of stimuli, which characterizes muscle, its irritability. Inasmuch 
 as the stimidi induce the conversion of potential into kinetic 
 energy, they have the relationship to the latter of liberating 
 forces (p. 6), and we may, therefore, speak of the liberation of 
 muscular activity by means of stimuli. The normal stimulus 
 for muscle proceeds from the motor nerves which are scattered 
 throughout its substance ; its nature is little understood, and 
 will be discussed in the next chapter. There are, however, 
 numerous other muscular stimuli, some of which are the result 
 of morbid conditions, while others may be employed artificially. 
 
 For a long time it was thought that muscles were incapable of direct ex- 
 citation, i.e. that all stimuli applied directly and with effect to muscle only act 
 upon the muscles through the nerve-terminations contained in them. The 
 following circumstances have, however, decided the matter in favour of the 
 independent excitability of muscle. 1. Portions of muscle containing no nerve- 
 endings, e.g., the extremity of the sartorius of the frog, are capable of ex- 
 citation by means of the direct application of stimuli (Kuhne). 2. Certain 
 chemical stimuli are incapable of exciting nerves (Kuhne); while, on the 
 contrary, certain electrical stimuli which act upon nerves have no effect upon 
 muscle itself (Briicke: Chapter IX.) 3. Substances which have the 
 property of rendering nerves, and especially intramuscular nerve-endings, 
 inactive, do not deprive muscle of its capability of direct excitation (e.g. 
 the Indian arrow-poison curare, Kolliker). Moreover, other influences 
 (e.y. excessive cold, interruption of blood-current) induce a transitory 
 state in which intramuscular nerve-terminations are paralysed while the 
 
248 STIMULI FOR MUSCLE. 
 
 possibility of direct excitation remains to the muscles. 4. In certain con- 
 ditions (exhaustion of muscle) local irritation induces contraction only in 
 the immediate neighbourhood of the point of application of the stimulus, 
 without respect to the distribution of the nerves near the spot (Schiff, Kiihne). 
 5. The lower contractile organisms, which agree in the nature of their es- 
 sential substance with muscle, are quite destitute of nerves. 6. It is, more- 
 over, said that automatic movements occur in the muscles of the more 
 highly organised animals. (Consult the section on Smooth Muscles). 
 
 The muscular stimuli with which we are already acquainted 
 are: 1. The normal nervous stimulus, which proceeds to the 
 muscle either from the central nervous organ in the production 
 of voluntary, automatic, or reflex movements, or from some 
 point in the course of the nerve supplying the muscle, at which 
 irritation has been applied. 2. Electrical stimuli, which will 
 be more fittingly discussed in the chapter on Nerves (Chapter 
 IX.), as their laws of action upon muscle and nerve are similar. 
 3. Chemical stimuli, among which must be regarded in general 
 all those substances which rapidly induce changes in the 
 chemical constitution of the contents of the muscle-tubes. At 
 the point of application they cause rigor as well as contraction. 
 The majority of them act even when in a very diluted con- 
 dition ; especially is this the case (Kiihne) with mineral acids 
 (HC1 in solutions of 0-1 per cent.), solutions of metallic salts, 
 lactic acid, diluted glycerin, and ammonia even when present 
 in traces in the atmosphere. To the list of chemical stimuli 
 belongs also distilled water, especially when injected into the 
 vessels of muscles. The greater number of these substances 
 have no stimulating action upon the nerves (e.g. ammonia), or 
 only when very concentrated. 4. Thermal stimuli, i.e. tempe- 
 ratures above 40 C., strongly heated bodies inducing contrac- 
 tions very readily on coming into contact with muscle. 5. 
 Mechanical stimuli, i.e. some sudden and marked change 
 of form occurring at any point, induced, for example, by 
 pressure, torsion, tearing, extension, &c. The method of 
 operation of these stimuli is as yet quite unknown. 
 
 The same intensity of stimulus does not always produce in 
 the same muscle the same effects it may liberate at different 
 times dissimilar quantities of energy ; that is to say, the irri- 
 tability of a muscle is not always constant. It depends, as far 
 as has yet been discovered, upon the following circumstances : 
 1. It is greatest in any organism under a certain medium tern- 
 
IRRITABILITY. 249 
 
 perature, and diminishes as the temperature rises or falls above 
 that mean. 2. It is diminished for a time by previous activity : 
 this diminution is called ' exhaustion ' of the muscle, and it may 
 owe its origin to the following circumstances : (a.) The accu- 
 mulation in the muscle of certain products which are formed 
 in quantity while the muscle is acting, and which are probably 
 not absorbed with sufficient rapidity. These must be supposed 
 to have some prejudicial influence upon activity a supposition 
 which has recently been confirmed (J. Eanke). The products 
 are carbonic acid and the acid of the muscle, whether it be a 
 free acid or form part of an acid salt. (6.) The deficiency of 
 the special constituents upon the consumption of which mus- 
 cular activity depends, and which cannot be remedied quickly 
 enough during the active condition. In all probability both 
 causes are concerned in the production of exhaustion. 3. In 
 muscles which are removed from the body, or which are deprived 
 of oxygen by ligaturing their arteries ( Stenson), as well as in those 
 of the dead body, irritability diminishes after a slight period 
 of exaltation, but more quickly in warm- than in cold-blooded 
 animals. The diminution in irritability occurs pari passu with 
 the development of rigor, is accelerated by the same circum- 
 stances (p. 244), and has entirely disappeared by the time that 
 rigor is complete. 4. All influences which essentially modify 
 the normal composition of muscle-substance in the living body 
 diminish and tend to destroy irritability. 5. If irritability has 
 been much diminished by any of the above means except the 
 last, and rigor has not yet occurred, it may in a certain sense 
 be recovered by passing for a long time a strong and constant 
 galvanic current through the muscle in the direction of its 
 length (Heidenhain), the probable explanation of which will 
 be given in Chapter IX. when speaking of the modifications of 
 nervous irritability. 6. Another means of restoring irritability 
 when it has been diminished by ligaturing the arteries supply- 
 ing a muscle, is by renewing the circulation, which, however, 
 only operates so long as rigor is incomplete. 
 
 As the majority of solutions, and even distilled water, have a stimulating 
 and destructive action upon muscle, there are but few indifferent liquids in 
 which it undergoes no change. Such are dilute solutions of NaCl (0'6 per 
 cent, being the most favourable, O. Nasse), or of other sodium salts, the 
 per-centage strength which is most favourable being- determined by the mole- 
 cular weight of the salt (Nasse). Less favourable than these, but less 
 
250 MATERIAL EXCHANGES OF ACTIVE MUSCLE. 
 
 destructive than distilled water, are solutions of boracic acid (1-5-2 per 
 cent.), and of arsenious acid (Briicke). 
 
 Exchanges of Matter of Muscle in a State of Activity. 
 
 The following chemical processes have been shown to occur 
 in active muscle : 
 
 1. Carbonic acid is formed and given up to the blood, or in 
 the case of excised muscles, to the air. This excretion of car- 
 bonic acid is considerably greater during states of activity than 
 of rest. It occurs in excised muscles (Matteucci, Valentin) as 
 well as in those of a living animal or in those through which 
 a stream of blood is artificially maintained ; in the latter case 
 the venous blood yields more carbonic acid while the muscle is 
 active than while it is at rest (Ludwig and Sczelkow, Ludwig 
 and Schmidt). The whole body excretes more carbonic acid 
 during periods of activity than when in repose (Regnault and 
 Keiset, p. 156). 
 
 2. Muscles in the body, and muscles through which blood 
 is artificially forced, consume more oxygen during activity than 
 during rest, as is proved by the fact that venous blood contains 
 less oxygen in the former case than in the latter (Ludwig and 
 Sczelkow, Ludwig and Schmidt). The whole organism, also, 
 requires more oxygen during exertion than at other times 
 (Eegnault and Reiset) ; but the difference is much less than 
 that between the amounts of carbonic acid excreted under the 
 same circumstances (Pettenkofer and Voit). 
 
 An increased consumption of oxygen in the case of excised muscles 
 while in action cannot be detected by direct measurements (Hermann). 
 
 The absorption of oxygen is not immediately demanded 
 for the purposes of contraction, as muscles are capable of con- 
 tinued exertion in a vacuum or in an atmosphere containing 
 no oxygen. Muscles, moreover, contain no store of oxygen 
 which is capable of removal by exposure to a vacuum (Her- 
 mann). 
 
 3. During a period of activity muscle becomes acid (du 
 Bois-Reymond), just as in rigor ; probably the acid is the same 
 in both cases. 
 
 4. The composition of muscle alters during activity in such 
 a manner that the constituents which are soluble in water 
 
MATERIAL EXCHANGES OF ACTIVE MUSCLE. 251 
 
 decrease in quantity, while those soluble in alcohol increase 
 (Helmholtz). 
 
 The above are the only processes which are certainly known to take 
 place in contracting muscle. Others have, in addition, been mentioned, 
 some of which have been the result of faulty methods of observation, 
 while others have been disproved, or rendered doubtful, by the occurrence 
 of opposite results. The two chief methods of investigation employed are 
 the following : 1. The comparison of the excreta of the organism during 
 rest and exertion ; from the list of substances excreted in greater quantity 
 during exertion, conclusions may be drawn as to the substances used. 2. 
 The comparison of the chemical composition of muscles (preferably of the 
 same animal) after periods of repose and of continued exertion. In these 
 experiments muscular exertion may be undergone either (a) by muscles 
 in the living animal (as, e.g. by inducing the tetanic convulsions of strychnia- 
 poisoning, one limb being kept at rest by the previous division of its nerves), 
 or (/3) by excised muscles. 
 
 There exists, however, in the second method of investigation a source of 
 error which renders useless the majority of the experiments. It will appear 
 from what is said hereafter that the chemical processes occurring during 
 contraction and rigor are identical in nature ; indeed, two similar, excised 
 muscles, after having undergone rigor, have exactly the same composition 
 (except as regards the amounts of carbonic acid excreted), whether one 
 has previously been in a state of activity or not. As, now, the requirements 
 of chemical analysis are almost always such as to induce immediate rigor in 
 the muscles under experiment (they have to be at once ' scalded '), we cannot 
 expect to find any difference in composition in the case (/3) when excised 
 muscles are used ; and if differences do appear, no certain meaning can be 
 attached to them. In the case (a), on the other hand, where the exertion is 
 undergone by the living animal, the blood-current continually removes the 
 products of the material exchanges occurring during the periods of activity, 
 in consequence of which the muscles which have been contracting contain, 
 after rigor, less of those products than those which have been at rest. If, 
 now, we regard as the products of activity those substances only which we 
 can find in increased amount in the muscles which have been active, we shall 
 commit an error (if the occurrence of rigor is not prevented) which will lead 
 us to conclusions exactly the reverse of true. The following are the chief 
 theories of the material exchanges occurring in active muscle: 
 
 1. That muscles in contracting consume (oxidize) albuminous bodies. 
 This theory rests upon (a) a supposed increase in the amount of urea ex- 
 creted during muscular exertion, which, however, does not really occur 
 (Voit); (b) a supposed diminution in the albumin contained in muscles 
 during their activity (J. Ranke) a diminution which, according to others 
 (Nawrocld), is slight enough to be set down to the unavoidable errors of ex- 
 periment apart from the consideration of the important error above mentioned; 
 (c) a supposed accumulation in active muscles of nitrogenous products of oxi- 
 dation, viz., of creatine (J. Liebig, Sorokin, Sczelkow the presence of which 
 was not confirmed by the researches of Nawrocki), hypoxanthine, etc. 
 
252 MATERIAL EXCHANGES OF ACTIVE MUSCLE. 
 
 (Scherer) : such an accumulation appears to occur under certain circum- 
 stances, but not as the immediate result of muscular exertion. 
 
 2. That muscles produce, during activity, grape sugar ( J. Ranke) : the 
 supposed increase is, however, so extremely slight (0-005 per cent.), that, 
 apart from what has been said above, it cannot form the basis for any con- 
 clusions. 
 
 3. That muscles produce, during activity ', fats (J. Ranke) : this statement 
 is useless as long as the intramuscular nerves, a great part of which is 
 soluble in ether, are not excluded. 
 
 4. That muscles during contraction oxidize volatile fatty acids (Sczel- 
 kow) : for the reasons before mentioned the experiments cannot be regarded 
 as affording conclusive proof. 
 
 On the whole, therefore, we must reject Ranke's theories, based upon 
 the data given above, that active muscle consumes albumin and forms 
 creatine, sugar (lactic acid), fats and carbonic acid. In their stead the 
 following may be stated as to the nature of the chemical processes of mus- 
 cular contraction. 
 
 The chemical actions which take place during contraction 
 and rigor of muscles are most probably identical (Hermann). 
 This conclusion is drawn from the facts: 1. That an excised 
 muscle yields the same amount of carbonic acid whether it 
 enters at once into rigor or has previously generated carbonic 
 acid by contraction: therefore, the more carbonic acid there is 
 produced by contraction, the less does the muscle evolve on 
 entering afterwards into rigor (Hermann), the original compo- 
 sition being supposed the same in all cases. 2. That the same 
 relationship seems to exist in the case of the lactic acid 
 at least, a muscle which has been active in the body, on 
 entering into rigor after excision, produces less acid than one 
 which has remained at rest (J. Eanke). 3. That both the 
 processes are independent of the absorption of oxygen, muscles 
 being able to contract and to enter into rigor in a vacuum or an 
 atmosphere of some indifferent gas. They are, therefore, pro- 
 cesses not of oxidation, but of decomposition, in which stronger 
 affinities are saturated or satisfied, and energy in consequence 
 liberated, as was explained on p. 217. 4. That recovery is 
 possible to muscles in states of exhaustion after continued 
 activity, as well as in states of incomplete rigor, by means of 
 the circulation of blood through them. 5. That muscles can 
 pass immediately from a condition of activity into one of com- 
 plete rigor (rigor of the second stage). 
 
 It is now only necessary, for the two processes of contrac- 
 tion and rigor to be exactly comparable, that there should occur 
 
THEORY OF MUSCULAR ACTIVITY. 253 
 
 a separation of myosin in the gelatinous modification, in which, 
 as was said before, no change in optical appearance is effected. 
 Such a separation is rendered most probable by the circumstance, 
 just alluded to, that muscles may pass at once from a condition 
 of activity into one of complete rigor ; for, as the second stage 
 in the coagulation of myosin of necessity implies the occurrence 
 of the first, it follows, in the case before us, that the first stage 
 must have occurred during activity. 
 
 The following may in all probability be regarded as the simplest theory 
 of the chemical processes occurring during- contraction and rigor : Muscle 
 contains at any moment a store of a complicated nitrogenous substance dis- 
 solved in the contents of the muscle tubes and in the muscle-plasma, 
 which may be described, for the sake of brevity, as the ' energy-gene- 
 rating,' or ' inogene, substance.' This l inogene substance ' is capable of 
 undergoing a decomposition in which energy is evolved, and the following 
 products yielded, viz. carbonic acid, sarco-lactic acid, probably glycerin- 
 phosphoric acid (p. 245) and a gelatinous body, myosin, of an albuminous 
 nature, which separates spontaneously, and afterwards contracts firmly, 
 becoming probably concentrated. This decomposition occurs spontaneously, 
 but slowly, while the muscle is at rest, the rapidity of its occurrence being 
 determined by the height of the temperature. It takes place instantaneously 
 at the temperature of heat-rigor. It is, moreover, at once accelerated by 
 stimulation ; and this acceleration is essentially what occurs during the 
 active condition. When the substance is entirely used up ; muscular activity 
 is no longer possible. 
 
 The ' inogene substance ' has not hitherto been isolated, as in everv method 
 of chemical investigation yet devised the characteristic decomposition occurs. 
 The latter may, indeed, be prevented by subjecting the muscle suddenly to 
 a strong heat (scalding) or to the action of mineral acids, but both these 
 methods destroy the substance. As regards its composition, it would seem 
 to resemble haemoglobin (p. 36), as both yield an albuminous body on de- 
 composition. On account of the analogy between the chemical processes of 
 muscular activity and of rigor we must suppose an expenditure of glycogen 
 (0. Nasse) to occur during the former as during the latter. 
 
 As the essential energy-yielding substance is used up during 
 muscular exertion, a continual renewal of it is necessary in 
 order that a muscle may retain its active properties. This is 
 effected, as already mentioned, both after contraction and rigor, 
 by the blood. The blood effects the recovery of the muscle, 
 not only by the production or renewal of the ' inogene sub- 
 stance,' but also by the removal of the products of decomposition 
 themselves which are harmful to the muscle. Blood removes 
 from muscle carbonic acid and, most probably, also sarco-lactic 
 acid (du. Bois-Keymond), both deleterious substances; and it 
 
254 SYNTHETIC RESTITUTION. 
 
 gives up to that tissue oxygen. It is, however, evident that 
 oxygen alone cannot repair all the losses sustained by muscle, 
 as carbon and hydrogen are continually leaving it in the form 
 of carbonic and lactic acids. The blood must, therefore, supply 
 to it, besides oxygen, organic materials containing carbon and 
 hydrogen. 
 
 The whole of the products of the decomposition of ' inogene substance ' 
 do not leave the muscle ; for, as the excretion of nitrogenous material is not 
 increased by muscular exertion, it must be concluded that the myosin 
 remains within the muscle. In consequence of this, and of the fact that it 
 is not the prepared substance, but only the materials necessary to form it, 
 which are conveyed to the muscle by the blood, it is most probable that the 
 recovery of muscle after exhaustion, apart from the mere removal of the 
 effete materials, consists in a synthesis of the ' inogene substance/ in which 
 myosin plays a part, and for which the blood supplies oxygen and some 
 non-nitrogenous organic body hitherto undiscovered (Hermann). Myosin, 
 therefore, according to this theory, undergoes in muscle a complete cycle of 
 chemical changes. 
 
 The following conditions are necessary for the restoration of muscle : 
 1. The addition of oxygen, which may take place, though to a limited extent, 
 in excised muscles. 2. The addition of the yet unknown organic body 
 referred to above, of which it is possible that excised muscles may contain 
 a slight store. The latter supposition may at least be taken to explain the 
 facts that restoration is, to a certain extent, possible by simple exposure to 
 the air, and that irritability is retained for a longer time when the sur- 
 rounding atmosphere contains oxygen. 3. The presence of myosin capable 
 of being used, i.e. which has not passed into the firmly-contracted condition. 
 A consideration of this third condition will explain why the restoration of 
 muscular tissue by means of the circulation is limited. The synthesis of the 
 ' inogene substance ' in which oxidation is one of the processes seems to be 
 analogous to the synthesis of haemoglobin, in which also oxygen plays a 
 part (p. 180). 
 
 The chemical process, which forms the basis of muscular 
 activity, and the process of restoration, occur without any 
 essential dependence one upon the other : it follows, therefore, 
 that the excretion of carbonic acid by the muscles and by the 
 whole organism, which is characteristic of the former process, 
 and the absorption of oxygen, muscular and general, which is 
 an important feature in the latter, are equally independent 
 (p. 157). It must, however, not be forgotten, that whenever 
 the decomposition of 6 inogene substance ' is accelerated, as 
 during muscular activity, the processes of restoration and 
 repair are also increased, i.e. that muscle takes up more oxygen 
 from the blood during activity than during repose ; for it is in 
 
MATERIAL EXCHANGES OF ACTIVE MUSCLE. 2">5 
 
 this way that the danger of exhaustion is diminished. This 
 regulating action is explained chiefly by the fact that the circu- 
 lation is accelerated in a muscle by its contraction (Ludwig 
 and Sczelkow). If the exertion is excessive, the repair of the 
 ' inogene substance ' cannot keep pace with its expenditure, 
 and the muscle becomes for the time acid, and can only be 
 stimulated to contraction with difficulty. This condition is 
 called exhaustion, and resembles the state of approaching 
 rigor, such as is induced by subjecting muscle to heat. 
 
 Certain circumstances render it probable that individual fibres of a 
 muscle may pass into a condition of complete rigor, especially if the pre- 
 vious exertion of the muscle have been excessive. In such cases the 
 myosin is no longer capable of use in the synthetic process of restoration ; 
 and the loss thus occasioned must be repaired by the formation of ' inogene 
 substance ' in some other manner. There must therefore occur, in addition 
 to the above-mentioned regular functional exchange of matter, another 
 process which may be described as the material exchange due to wear and 
 tear. We have only now to suppose that the myosin of the completely 
 coagulated fibres decomposes further with the formation of creatine, the 
 separation of which would serve to increase the amount of urea ex- 
 creted ; and perhaps also of fat, as fibres which have undergone fatty de- 
 generation are found in every muscle. This theory would serve well to 
 explain the statements of the occurrence of increased nitrogenous excretions, 
 &c., after muscular activity. Under such circumstances other albuminous 
 bodies resembling myosin, which are held stored up in the muscle, would 
 be used instead of the latter in the synthesis of 'inogene substance.' Such 
 albuminous components of muscle are those which coagulate between 40 
 and 60 C. 
 
 According to the theory which has just been propounded, only non- 
 nitrogenous substances are really used up. This is supported by the obser- 
 vation that the excretion of urea is not increased by muscular exertion 
 (Voit). Attempts have been made to reconcile this observation with the 
 consumption of nitrogenous material j firstly, by the supposition that the 
 consumption of material by muscle was not in general increased during 
 activity, and that therefore the same amount of energy was liberated as when 
 the muscle was at rest, but in another form (Voit) ; and, secondly, by the 
 theory that the increase in the extent of the material exchanges produced 
 by exertion was counteracted by a corresponding diminution immediately 
 afterwards (J. Ranke). That neither explanation is correct is shown by the 
 fact of the increase in the excretion of CO 2 both at the very time of muscular 
 exertion, and during longer periods of work alternated with rest. Since it 
 was first stated that non-nitrogenous substances only were used up during 
 muscular exertion (M. Traube), it has been directly shown that the quan- 
 tity of albuminous materials used up during the time of exertion, calculated 
 from the urea excreted, is not tufucient, even when an excessive heat of com- 
 
256 MATERIAL EXCHANGES OF ACTIVE MUSCLE. 
 
 bustion is assigned, to account for the work done (expressed in heat-units) 
 (Fick and Wislicenus, Frankland). 
 
 It has been sought to explain the circumstance that muscular tissue 
 takes up oxygen without immediately utilising it in the formation of carbonic 
 acid, by the hypothesis (M. Traube) that the gas is first taken up by a 
 ferment, which retains it until the moment of contraction, when it gives it 
 up to the non-nitrogenous substances to be oxidized. This view agrees 
 essentially with the theory of muscular activity given above : the ferment 
 is myosin, which does not, indeed, store up oxygen until the periods of 
 activity return, but which unites with that gas and some non-nitrogenous 
 complex body to form a compound which decomposes during contraction, 
 and thus sets the myosin free to be used again in the same manner. 
 
 It has, further, been supposed, in order to account for the fact that the 
 quantitative ratio between absorbed oxygen and excreted carbonic acid 
 is different during exertion and during rest, that in the former condition other 
 substances are oxidized in muscle than in the latter (Ludwig and Sczelkow). 
 This supposition is unnecessary, owing to the independence, which was 
 above referred to, of the processes in which, respectively, oxygen is used 
 (synthesis of ' inogene substance ') and carbonic acid formed (decomposition 
 of l inogene substance '). 
 
 Among the effects of muscular exertion upon the constitution of the 
 excretions, it has been mentioned that the degree of acidity of the urine is 
 increased during muscular exertion (Kliipfel) ; but this is denied by others 
 (Sawicki). 
 
 Changes in the Form of Contracting Muscles. 
 
 The chief and most manifest result of the evolution of 
 energy in active muscle, and which may be especially described 
 as the work done by muscle, takes the form of mechanical 
 work movement. This movement consists in an alteration 
 in the form of the muscle, viz. a diminution in length, affecting 
 the primitive fibres, and an increase in thickness. The altera- 
 tion is effected with such energy as to overcome even considerable 
 resistances opposed to it. In the majority of cases the re- 
 sistances are opposed to the diminution in length, and consist 
 of forces which tend to separate the extremities of the muscle ; 
 the most frequent example, and the one to which all others are 
 referred, being that of a muscle fixed at one extremity and 
 supporting a weight attached to it at the other. By contraction 
 of the muscle the weight is raised, and the mechanical work 
 thus accomplished is expressed by the product of the weight 
 into the height through which it is raised. 
 
 The diminution in length and increase in thickness of a 
 
MUSCULAR CONTRACTION. 257 
 
 muscle on contracting are connected with a diminution in 
 volume a species of condensation. This may be proved by 
 suspending a muscle in a vessel, provided with a narrow, up- 
 right tube protruding through the cork, the whole of which is 
 accurately filled with a fluid. When the muscle is stimulated 
 to contraction the fluid sinks in the narrow tube (Erman, 
 Valentin). Muscle when contracted is also less elastic, and 
 therefore more extensible, than when at rest (Ed. Weber). 
 
 After each simple stimulation directly applied, a single and 
 rapid alteration in form occurs in the muscle, and is called 
 a contraction. The diminution in length does not take place 
 immediately on the application of the stimulus, but is post- 
 poned for the space of about y^-oth of a second, during which 
 time the muscle is, to all appearance, still at rest : this is 
 called the ' period of latent excitation ' (Helmholtz). At the 
 end of that time active contraction commences, at first with 
 increasing, but afterwards with diminishing rapidity, and con- 
 tinues until a maximum is attained. The contracting forces then 
 cease gradually to act upon the muscle, which is thereupon ex- 
 tended by means of the attached weight, at first quickly, but 
 afterwards more slowly, to its previous length. If the muscle is 
 not acted on by any weight, not even its own (as, for example, 
 when it rests upon a surface of mercury), it retains approxi- 
 mately the form it had at the instant of maximum contraction 
 (Kiihne) ; and, if the weight is but slight, it does not com- 
 pletely attain its original length (Hermann). If we imagine 
 the upper extremity of a vertically suspended muscle to be 
 fixed, and an upright plate to travel quickly and regularly in 
 a horizontal direction in front of the lower, a curve would be 
 described upon the plate during the contraction of the muscle, 
 the abscissae of which would represent the times, and the ordi- 
 nates the degree of contraction. Such a curve presents the fol- 
 lowing points of interest : From the instant of stimulation it 
 runs at first for some distance upon the abscissa-line (latent 
 period period of latent excitation); it then rises, being at 
 first convex, but afterwards concave towards the abscissa- 
 line, until it reaches a maximum, after which, if the weight have 
 been sufficiently large, it gradually falls again to the abscissa- 
 line (Helmholtz). 
 
258 
 
 MUSCULAR CONTRACTION. 
 
 The time occupied in the evolution of energy in a muscle after stimula- 
 tion may be discovered in two ways (Helmholtz) : 
 
 1. A muscle to which a slight weight is attached is allowed to contract 
 freely, in which case the distance through which the attached weight is 
 lifted increases and diminishes in the same ratio as the contracting force. 
 The muscle is suspended vertically, and its lower extremity is attached to 
 a lever provided with a pen arranged in such a manner as to mark, when 
 the muscle contracts, upon a surface moving with uniform velocity in a 
 horizontal direction in front of it. This moving surface is either in the form 
 of a cylinder rotating evenly about a vertical axis, as in Helmholtz's myo- 
 graph, or of a smooth plate tixed to the extremity of a long pendulum, as 
 in that of Fick. A curve is in this manner produced, of which the abscissfe 
 represent the time, and the ordinates the degree or extent of contraction. 
 As the latent period occupies an appreciable portion of the line traced by 
 these means, the instant of stimulation must be indicated on the recording 
 surface by some mark. This is most easily done by causing the moving 
 surface itself in passing some point in its course to effect the stimulation, 
 say by closing a current. 
 
 2. Contraction is not allowed to occur, but is hindered by means 
 of weights placed in a scale-pan attached to the lever do (Fig. 5), 
 
 FIG. 5. 
 
 which is supported in such a manner that the weight cannot act 
 upon the muscle while it is at rest, but only when it tends to con- 
 tract. Each weight placed in the scale-pan ('overload') keeps the 
 muscle in the position it occupies when at rest, until the contracting force 
 (energy) attains an intensity equal to that of the overload. As the con- 
 tracting force is evolved gradually after stimulation, the time intervening 
 between stimulation and the lifting of the weight from its support, 
 i.e. the breaking of contact at c, is greater the heavier the weight. If the 
 muscle is not overloaded, the time from the application of the stimulus to 
 the raising of the lever corresponds to the latent period. A degree of over- 
 loading is at last attained, which prevents any movement of the lever by the 
 muscle, and therefore represents the limit to the evolution of the contracting 
 
MUSCULAR CONTRACTION. 259 
 
 force. The measurement of the time from the moment of stimulation to 
 the raising of the weight (i.e. to the breaking of contact at e) is effected by 
 the method of Pouillet, according to which it is registered by the deflection 
 of the needle of a galvanometer G, the current of which is made at the 
 instant of stimulation, and broken at c when the weight is raised. The 
 coincidence of closure of the galvanometer-current and the stimulation of 
 the muscle is accomplished by pressing the point of the wire against the 
 plate e of the commutator w, whereby the current from the battery K is 
 closed, while that from the battery K' connected with the primary coil p 
 is broken at /, in consequence of which an opening induction shock is trans- 
 mitted by the wires from the secondary coil s to the muscle. 
 
 If the times registered by the above method be taken as abscissae, and 
 the corresponding weights as ordinafces, a curve representing energy is ob- 
 tained, which agrees with the ascending portion of the ordinary muscular 
 curve, got by means of the myograph. The latter, however, deviates 
 slightly from the former, on account of the weight suspended to the muscle 
 in myograph-experiments in order to keep it extended (Kliinder). The 
 curve representing energy may also, by proper arrangements, be obtained 
 directly (Pick). 
 
 Instead of making use of the shortening of muscle for the production of 
 a curve, the thickening which it undergoes on contraction may, by a suit- 
 able apparatus, be registered in the form of a curve, which, as might be ex- 
 pected, agrees with that produced in the above manner (Aeby, Marcy). 
 This method is applicable to the muscles of a living man. 
 
 Certain muscles have the characteristic that their con- 
 traction proceeds very slowly, and, in consequence, gives rise 
 to a very extended muscle-curve : such, for example, are the 
 muscles of the tortoise and of the heart (Marey), the latter form- 
 ing the transition in rapidity of contraction between striped 
 and unstriped muscles (see below). Cold, exhaustion, &c., 
 hinder the progress of contraction (Valentin, Kliinder) and 
 diminish its extent (Volkmann). 
 
 The greatest degree of force which a muscle is capable of exerting, as 
 measured by the weight which is just able to keep the muscle extended in 
 the position of rest, as described in the second of the above experiments, is 
 called the ' absolute power ' of the muscle. If an unweighted muscle be 
 allowed to contract, and in the midst of contraction brought to a standstill 
 suddenly by means of a weight, it will be found that a smaller weight is 
 required to effect this according to the extent to which contraction of the 
 muscle has already gone. The force of a muscle, therefore, diminishes during 
 contraction, and is equal to nothing at the end of it. In order to show this, 
 the weighted lever is so arranged by placing it nearer to the fixed extremity 
 of the muscle, that a certain extent of contraction must have taken place 
 before the muscle begins to act upon it (Schwann). 
 
 If two stimuli follow one upon the other so quickly that 
 
 s 2 
 
260 TETANUS. MUSCULAR SOUND. 
 
 the contraction induced by the first, although it has got past 
 the latent period, has not reached its maximum before the 
 second commences to operate, their united result is to produce 
 a stronger contraction. That is to say, the second stimulus 
 operates just as if the contracted form which the muscle had 
 when it began to act were the natural form of the muscle 
 (Helmholtz). From this it is evident that the maximum of 
 contraction under the most favourable circumstances may be 
 doubled, viz. when the difference in time between the two 
 stimulations equals the duration of a single contraction from its 
 commencement to its maximum. 
 
 Further, if a series of stimulations are brought to bear upon 
 a muscle at very short intervals of time, no opportunity is 
 afforded to the muscle of regaining its normal extension between 
 any two of them ; and, in consequence, it retains its contracted 
 form during the whole series : this condition is called c tetanus.' 
 All continued muscular contraction, of which the body presents 
 so many examples, must be regarded as tetanic, i.e. as being 
 produced by a series of stimuli following closely one upon 
 another (Ed. Weber). That such continued contraction is to 
 be looked upon as the result of a series of single contractions, 
 appears evident ; firstly, because of the phenomenon of ' secon- 
 dary tetanus j' to be described afterwards (du Bois-Reymond); 
 and, secondly, from the evolution of the * muscular murmur.' 
 The latter may be heard by applying the ear or stethoscope to 
 the tetanised muscle of a man (e.g. one that is kept under 
 voluntary contraction) ; it appears to be a weak murmur in 
 which a distinct note predominates the muscular murmur or 
 note (Wollaston). The vibrations of this muscular murmur, 
 when the muscle is tetanised by an induction current, corre- 
 spond per second with the number of stimuli applied (Helm- 
 holtz). As voluntarily tetanised muscles generally emit a dis- 
 tinct sound (of 19-5 vibrations per second), the number of 
 stimuli proceeding from the motor central nervous organs during 
 tetanus by the will must be 19-5 per second (Helmholtz). 
 
 If stimuli of a certain strength follow one another very 
 quickly (e.g. if more than from 224 to 360 occur per sec.), no 
 tetanus results (Harless, Heidenhain), and only the first pro- 
 duces a contraction (initial contraction, Bernstein). If the 
 strength of the stimuli be increased, tetanus follows. 
 
MUSCULAR SOUND. PROGRESS OF CONTRACTION. 261 
 
 The best means of tetanising muscle is by using as stimuli a series of 
 frequent electric shocks ; such a series, for instance, as is produced by the 
 continual opening and closing of an electric current. In order to study 
 those characters of active muscle for the development of which a single 
 contraction is too fleeting, e.g., the chemical changes during activity, the 
 evolution of heat, the negative variation of the muscle current, which the 
 galvanometer, on account of the inertia of the needle, does not show in the 
 case of a single contraction, it is best to tetanise the muscle experimented 
 upon. 
 
 The first sound of the heart is most probably an instance of a muscular 
 murmur of the usual pitch (Natanson, Haughton, p. 60) ; ventricular 
 systole must therefore be a tetanic contraction. The muscular murmur 
 may be heard, preferably at night, by stopping the ears with wax, 
 and contracting the muscles of mastication. The depth of the muscular 
 note was formerly given at from 36-40 vibrations per second (Natanson, 
 Haughton, Helmholtz). When it became possible to determine it more 
 exactly by the method given below, it was fixed at 19 vibrations per second 
 the audible tone is therefore the first harmonic of the primary note in the 
 muscular sound (Helmholtz). The dependence of the note upon the number 
 of stimuli applied per second becomes evident to any one who tetanises his 
 own masseter muscle by means of an induction apparatus, the coils of which 
 are placed in a distant room, the note being the same as that emitted by the 
 interrupter of the machine used (Helmholtz). The fact that a muscle when 
 tetanised by stimuli proceeding from the central nervous organs has a tone 
 with an independent and characteristic number of vibrations was first noticed 
 in the case of an animal, the muscles of which were thrown into tetanus by 
 stimulating the spinal cord, and which then emitted the deep murmur of 
 contracting muscle (du Bois-Reymond) . In such a case the note is inde- 
 pendent of that caused by the vibrations of the interrupter of the apparatus 
 used. The muscular murmur may also be heard by fixing a frog-muscle, 
 properly weighted, to one end of a short staff', the other end of which is in- 
 serted into the ear, and tetanising it by means of electricity. The vibra- 
 tions may be rendered visible by imparting them, by resonance, to a strip of 
 flexible metal or paper (Helmholtz). 
 
 If a muscle or a muscular fibre be stimulated to contraction 
 at any one point, the remainder takes up and continues the 
 condition of activity (Kuhne). The rapidity with which the 
 contraction is propagated along the muscle is equal to about 
 0'8 1*2 metres per second (Aeby, von Bezold), or, according 
 to recent statements, probably a little more (3 metres, Bern- 
 stein); and it decreases with the temperature. Under the 
 microscope contraction passes like a wave over the fluid con- 
 tents of the muscle-tubes (Kuhne); the transverse striae ap- 
 proximate each other (Ed. Weber), and become smaller, while 
 the doubly-refractive sarcous elements diminish in the direction 
 
262 WEBER S THEORY OF CONTRACTION. 
 
 of their long axes (Briicke), The curved or zigzag position of 
 the fibres while at rest (p. 243) disappears during activity (Ed. 
 Weber). If the muscular fibres have lost their irritability, as, 
 for example, through exhaustion, stimulation produces only 
 local contraction, and puffy protuberances (Kiihne) are formed, 
 especially with powerful mechanical stimuli, by the local 
 contraction and thickening. These were formerly called 4 idio- 
 muscular contractions,' a name which can on theoretical grounds 
 no longer be retained (Schiff). 
 
 On powerful local stimulations of a mechanical nature these puffy appear- 
 ances may occur, even in muscles which are perfectly irritable, together with 
 the general but weaker contraction of the whole length of the fibre. This may 
 result, for example, from a powerful blow on the muscles of the upper arm. 
 
 In accordance with the recent statements concerning the minute structure 
 of striated muscles, numerous theories have been devised respecting the 
 alterations which take place on contraction ; but they are too diverse to be 
 inserted here. 
 
 On the Amount of Work done by the Contracting Muscle. 
 
 1. WHEN THE TRANSFORMATION OF ENERGY WITHIN THE MUSCLE 
 IS AT ITS MAXIMUM. 
 
 In the first place the most simple case will be considered, 
 that, namely, in which, by as powerful an irritation as possible, 
 as much energy becomes kinetic within the muscle as it is 
 capable of yielding. 
 
 An idea may be formed of the mechanical changes which 
 occur in a muscle when it contracts (Ed. Weber) if we imagine 
 that, under the influence of an excitant, and in consequence of 
 the chemical processes which result from its action, the muscle 
 AB (Fig. 6) suddenly assumes a new natural form Ab, which 
 differs from the first in being shorter, thicker, and less elastic 
 (p. 256), and which tends to return to its original shape. 
 When the muscle passes from the first into the second, or 
 contracted, form, it behaves exactly as if it had been stretched 
 beyond its natural length, and in virtue of its elasticity had 
 tended to assume the new form. The same happens if the 
 muscle when at rest be extended by a weight, only that in this 
 case the length attained is greater than if the same muscle were 
 stretched while contracted. The difference between these two 
 lengths is, of course, the height through which the weight is 
 
WEBER'S THEORY OF CONTRACTION. 
 
 263 
 
 lifted (Hubhohe), which, for the sake of brevity, we may term 
 the lift. The product of the weight raised into the height 
 through which it is raised, i.e. the product of load into lift, ex- 
 presses the work done by the muscle. 
 
 A moment's consideration, assisted by a glance at Fig. 6, 
 serves to show that when the extensibility of the contracted 
 muscle becomes considerably greater than that of the muscle at 
 rest, the lift of the muscle will diminish as the load increases, 
 being with a certain load nothing, and finally becoming nega- 
 tive. That is to say, when the load attains a certain amount, it 
 will no longer be raised on the application of a stimulus to the 
 muscle ; and also, as it increases still more, stimulation will 
 
 FIG. 6. 
 
 JL :&* ja^a 
 
 cause elongation of the muscle, instead of contraction. Let 
 AB, in Fig. 6, be the natural length of the uncontracted 
 muscle ; moreover, suppose loads of various sizes to form 
 abscissse on the axis BD, and the extensions corresponding to 
 them to be carried down as ordinates ; then BC is the curve 
 of extension of resting muscle, and A^, A 2 B 2 , A 3 B 3 , etc., are 
 the lengths of the muscle corresponding to the loads BC I? BcZ 2 , 
 BrZ 3 , etc. Again, let A& be the natural length of the contracted 
 muscle (for a given stimulus) ; as, now, its elasticity is to a 
 certain extent less than that of the muscle at rest, the curve of 
 extension, be, obtained in the above manner, will fall more 
 
264 WEBER'S THEORY OF CONTRACTION. 
 
 abruptly than BC, and cut it in a point B 4 . As A ,6^ A 2 6 2 , A 3 fr 3 , 
 A 4 6 4 , etc., are the lengths of the contracted muscle under the 
 different loads, the lines B^, B 2 6 2 , etc., between BC and 6c, are 
 the lifts of the muscle on stimulation. It is seen at once that 
 they become smaller and smaller, being at B 4 = 0, and after 
 that point (B 5 6 5 ) negative. That is to say, elongation takes 
 the place of contraction on the application of a stimulus, A 5 B 5 
 extending to A 5 6 5 . The work done by the muscle when carrying 
 the various loads is found by multiplying the abscissae (Bc/ 15 
 Bc2 2 , etc.) into the corresponding lifts. It is at once seen that 
 this product =0 at two points, viz., at B and at B 4 ; that it is 
 greatest a little before the middle position between those two 
 points is reached ; and that, on the other side of B 4 , it is a 
 negative quantity. The variations in the work done may be 
 represented by the curve RUS. 
 
 Many facts agree with this view, as, for instance, the easily 
 observed diminution of the height through which a weight is 
 lifted as the weight increases, the elongation of the muscle when 
 made to contract whilst bearing very heavy loads (Weber), 1 and 
 some other phenomena to be afterwards mentioned. 
 
 The relations of muscles of the same kind (from the same 
 animal), but of different size, are very simple. The activity of 
 contraction being at its maximum, the weight which a 
 muscle can lift to a given height will increase as its transverse 
 section becomes larger, and, the weight being constant, it will 
 be lifted higher the longer the muscle. The demonstration of 
 this is easy. Let us imagine n similar muscles to be suspended 
 close together in parallel lines ; suppose each of the muscles to 
 have attached to its free extremity a unit-weight, which it is 
 capable of raising to a unit-height ; a muscular system is thus 
 arranged which has n times the extent of transverse section of 
 one muscle, and which can raise n units of weight through a unit 
 of height. On the other hand, if the n muscles be connected 
 together end to end, and the system suspended by one extremity 
 while a unit-weight is attached to the other, a muscular arrange- 
 ment is produced which is n times as long as in the preceding 
 case, and which can raise a unit-weight through n units of height. 
 
 1 According to Fick, no amount of weighting produces elongation during 
 contraction (or 'negative ' Hubhbhe) : he supposes therefore that the two curves bo 
 and BC do not cut, but are asymptotes one to the other. 
 
MAXIMUM ENERGY. ABSOLUTE FORCE. 265 
 
 We may render these laws evident by diagrams similar to the 
 one represented in Fig. 6 , if we hold in view the fact that the 
 extensibility of a muscle is directly proportional to its length 
 and inversely proportional to its cross section. 
 
 The amount of work which is done under the influence of 
 the most powerful excitant 'would appear to be the natural 
 measure of the maximum amount of energy which can become 
 kinetic in a muscle, when its irritability is greatest. The 
 amount of work done is, however, very variable. It depends, 
 for example, upon the weight, as was shown above. Moreover, 
 it follows from Weber's theory, that it is greater if the load be 
 continually diminished as it is being raised (Fick) ; and, as a 
 fact, many muscles in the body act on levers in such a manner 
 that the moment of the load about the point of support dimi- 
 nishes as contraction proceeds. The maximum amount of work 
 which 1 grm. of frog's muscle can perform varies between 3324 
 and 5760 grammeters (Fick). 
 
 Commonly the functional activity of a muscle is determined 
 by ascertaining the maximum power of shortening which it dis- 
 plays on the application of the strongest excitation. The 
 magnitude of this so-called ' absolute muscular force ' expressed 
 in units of weight, is dependent upon the area of its cross 
 section, and is therefore expressed in relation to the unit-area 
 of the section. A square centimeter of frog muscle corresponds 
 to between 2800 and 3000 grammes (Eosenthal), and a square 
 centimeter of human muscle to between 6000 and 8000 grms. 
 (Henke and Knorz, Koster). 
 
 In a muscle separated from the body, the so-called ( absolute force ' is 
 determined by the method of ' overloading ' which has been described at p. 
 258. Other methods depend upon the fact that the weight which represents 
 this absolute muscular force is, according to Weber's theory, the same as would 
 be capable of stretching the unloaded and contracted muscle to the length 
 occupied by it when unloaded and at rest (i.e., in Fig. 6, the weight cor- 
 responding to the abscissa Bd 2 ) ; and, in addition, the same as would be 
 necessary for loading the muscle in order that, on contraction, it should 
 regain the length it occupies when uncontracted and not loaded. The de- 
 termination of this force in man is effected amongst others in the following 
 ways (Weber) : When we stand on tiptoe, or, more correctly, when we 
 rest our weight on the heads of the metatarsal bones, tne gastrocnemii 
 muscles, through their insertion into the os calcis, exert an action upon a 
 lever of the second kind, the fulcrum of which is situated at the point of 
 junction of the metatarsal bones to the ground; the weight (of the body) 
 
2(36 EXHAUSTION. WORK DURING TETANUS. 
 
 acts upon the point of the foot, through which the line of direction of the 
 centre of gravity passes. If the body be now laden with weights until it is 
 impossible to raise the heel from the ground, then the absolute force of the 
 gastrocnemii is equal to the moment of the weight (body + weights) into its 
 arm, divided by the length of the arm acted upon by the muscles 5 this 
 value, when found, has only to be reduced in terms of the cross section. 
 The mean cross section of a muscle is determined by dividing its volume 
 (which is equal to its absolute weight divided by its specific weight) by its 
 length. 
 
 The method of Schwann (p. 259) measures as it were the absolute 
 force of a muscle in the different conditions of its shortening, when possess- 
 ing the different lengths between A B and A b (Fig. 6) : as, however, in the 
 case of the length A 1 6 1 , the force found is equal to the weight which can 
 stretch the active muscle A & to the length AJ b lf it is represented by the 
 abscissa nd v Schwann's experiments afford a means of determining the 
 curve which represents the extensibility of active (i.e. contracted) muscle, 
 at least of the portion 6 6 2 (Hermann). 
 
 In the condition of muscular fatigue (p. 249) the absolute force of a 
 muscle diminishes, as well as its power of shortening. When the stimulus 
 is at its maximum, and the load borne by the muscle remains constant, the 
 lift diminishes by an equal amount with every successive muscular contrac- 
 tion, providing that the time which intervenes between successive con- 
 tractions is always the same. The longer the interval between successive 
 stimulations, the smaller the diminution in the lift. The influence of the 
 time which intervenes between the contractions is most marked when the 
 muscle is in a state of fatigue. The times between the contractions remain- 
 ing constant, the differences in the contractions become less perceptible as 
 soon as the muscle no longer contracts so as to have the length which it 
 possessed when at rest and unweighted ; the curve which represents the 
 magnitude of the muscular contractions, which up to this point is rectilinear, 
 now becomes a hyperbola, which is asymptotical to the curve which indicates 
 the extensibility of the uncontracted muscle. 
 
 During tetanus a muscle executes no external mechanical 
 work, as no weight is lifted by it ; the weight already lifted to 
 a certain height being merely maintained at that height. As 
 the chemical changes which go on in a muscle which is in a 
 state of tetanus are greater in amount than in a muscle at rest, 
 we must assume that a tetanised muscle actually does perform 
 work, the muscle losing and immediately thereafter regaining 
 the whole of its tension during the extremely short interval be- 
 tween two successive stimulations ; this sudden regain of tension 
 mut, whenever it occurs, lead to a development of heat. One 
 must seek for the equivalent of the tissue-changes which go on 
 in the tetanised muscle, in the heat which is generated. The 
 continually recurring changes in the tension of a muscle are 
 
STRENGTH OF STIMULI AND MUSCULAR ACTIVITY. 267 
 
 probably the cause of the ' bruit musculairej or muscular noise, 
 to which reference was previously made. It has not hitherto 
 been possible, even with the help of the most delicate 
 arrangements, to demonstrate that at the time of the production 
 of the muscular noise the load borne by a muscle is slightly 
 lifted up and down. 
 
 2. WHEN THE ACTIVITY OF THE MUSCLE IS NOT AT ITS MAXIMUM. 
 
 The lift and the work done by a muscle, when the stimulus 
 applied to it is constant, but of moderate intensity, appear to 
 follow the same laws as hold in the case of the muscle excited 
 by an intense stimulus. 
 
 If the strength of the stimulus varies, the degree of 
 muscular activity varies also ; the new form which the muscle 
 tends to assume, under the influence of the stimulus, differs, 
 both in elasticity and in length, less from that which the muscle 
 possessed when at rest, the weaker the stimulus. It has not 
 yet been determined according to what law the strength of the 
 stimulus affects the intensity of the active condition of a 
 muscle. It is asserted that as the strength of the stimulus 
 increases the active condition increases, although not with the 
 same rapidity (Hermann) ; but it is also asserted that the active 
 condition increases at equal rate from up to a certain point, 
 but that after a certain strength of stimulus has been attained 
 it remains constant (A. Fick). 
 
 The methods which are adopted in making such determinations are the 
 following : 
 
 1. The strength of the stimulus is determined which must be applied to 
 the muscle in order that it should perform a definite task, such as the 
 slightest possible movement of an excessive load (p. 258). 
 
 2. The load remaining constant, the lift is determined for stimuli of 
 varying strengths (Fick). 
 
 If the changes in the elasticity of the muscle which corre- 
 spond with every change in its form were known, one might, as 
 in Fig. 6, construct, for every case, the extension curve of the 
 active muscle, and so determine the height to which a weight 
 would be lifted for every weight and for every degree of muscular 
 activity. The relation between changes in elasticity and in form 
 is, however, unknown, and determinations of the height to which 
 
268 STRENGTH OF STIMULI AND MUSCULAR ACTIVITY. 
 
 a known load is lifted permit of no conclusion being arrived at as 
 to the natural form of the unloaded muscle (for the same degree 
 of activity). Although the extension curves of the contracted 
 muscle cannot be constructed a priori, yet Fig. 6 shows us that 
 the line be approaches more closely to BC and is proportionately 
 less inclined to BC the smaller the activity of the muscle, and 
 the weaker the stimulus. Hence the differences between the 
 heights to which different weights are lifted must diminish as 
 the strength of the stimulus diminishes, and the weakest 
 stimulus capable of exerting an action must therefore lift to a 
 slight extent as well the smallest as the heaviest weight in 
 other words, in order to produce the minimum lifting of 
 1 gramme or 100 grammes, the same strength of stimulus is 
 required ; experiment confirms this conclusion (Hermann). 
 
 From what has been stated it follows that a certain stimulus 
 leads to the performance of very varying amounts of work in 
 muscles which are differently weighted : this is explained by 
 the supposition that the effect of weighting a muscle is to con- 
 vert it into a new body, possessed of more potential energy than 
 before. 
 
 The influence of the' weight borne by the muscle must be 
 even greater than the preceding statement implies, as it exerts 
 an influence on the material exchanges which go on in the 
 muscle. 
 
 Even in the case of the shortening which occurs during rigor (p. 244), 
 the heights to which different weights are lifted, and the absolute muscular 
 power, may be determined. These heights are, in the case of light weights, 
 greater, in the case of heavy weights smaller, than when the living muscle 
 is excited by the strongest possible stimulus : the natural form of 'the 
 muscle in a state of rigor is therefore, according to Weber's theory, shorter, 
 but its extensibility is greater, than that of the active (contracted) muscle ; 
 the absolute muscular power is, in the case of the rigid muscle, smaller 
 than in that of the contracted muscle (Walker). 
 
 d. Thermic and Electrical Phenomena of Muscle. 
 
 Thermic Phenomena. . 
 
 Muscles removed from the body, as well as muscles which 
 retain their connection with it, are hotter during contrac- 
 tion (Helmholtz, Beclard) and during rigor (v. Walther, 
 Huppert, Fick and Dybkowsky, Schiffer) than when in a state 
 
FORMATION OF HEAT IN MUSCLE. 269 
 
 of rest. Both conditions lead, therefore, to a development of 
 heat i n other words, the generation of heat which goes on in 
 the muscle which is inactive, increases when it becomes active, 
 or passes into a state of rigor. 
 
 The production of heat which is observed in rigor occurs 
 simultaneously with the shortening of the muscle (Fick and 
 Dybkowsky). 
 
 That heat is developed in muscle during contraction was formerly only 
 proved in the case of tetanus ; lately, however, it has been shown even in 
 the case of individual muscular contractions (Heidenhain). 
 
 The determination is made by placing one thermo-electric junction, or 
 one series of such junctions, in contact with the muscle, which is made to 
 contract, whilst another junction or series of junctions is maintained at a 
 constant temperature. (This is most easily effected by placing the second 
 junctions in contact with a second corresponding muscle, which is kept at 
 rest.) In the earlier experiments, needle-shaped . thermo-elements were 
 employed, which were either thrust into or passed through the muscle 
 experimented upon, so that the junction was in contact with the muscular 
 substance. In the more recent researches, thermo-piles, composed of a 
 combination of many bismuth and antimony junctions, have been employed, 
 one set of junctions being placed closely in contact with the muscle 
 (Heidenhain). 
 
 In frog muscles the heat generated during individual muscular contrac- 
 tions amounts to between 0t 001-0 0l 005 C. : during tetanus it may be as 
 great as 0-15 C. It is yet unknown at what state of a muscular contraction 
 the development of heat occurs. 
 
 The heat developed during rigor is likewise ascertained by thermo- 
 electric methods; one set of junctions being maintained at a constant tem- 
 perature (Schiffer). Another method consists in placing the bulbs of two 
 similar mercurial thermometers into two muscles, of which the one is yet 
 living, the other is in a state of rigor. These muscles are dipped in an 
 indifferent fluid, which is then warmed ; when the temperature which pro- 
 duces heat-rigor is attained, the thermometer which was placed in the yet 
 living muscle indicates a sudden rise in temperature (Fick and Dybkowsky). 
 That heat is developed during rigor mortis is proved, in the case of the 
 uninjured dead body, by the fact that after death the body takes a longer 
 time to cool than the body which is artificially heated after cadaveric 
 rigidity has set in (Huppert). The development of heat during rigor mortis 
 explains post-mortem rises in temperature ; and indeed the occurrence of 
 the latter (in certain cases) first led to the supposition that an evolution of 
 heat is associated with rigor (Walther). 
 
 Even when a muscle is stretched, a very slight evolution of heat occurs 
 (Schniulewitsch, Westermann). 
 
 Concerning the proximate causes of these evolutions of heat 
 we possess mere assumptions, which will be noticed in the 
 sequel. 
 
270 MUSCLE-CURRENTS. 
 
 Electrical Phenomena. 
 
 If a muscle be cut so as to present a transverse section, and 
 if the two ends of a galvanoscopic circuit, especially one which 
 contains a delicate multiplier or mirror-galvanometer, be applied 
 to a muscle in such a manner that one end is in contact with 
 the transverse section and the other with a point of the longi- 
 tudinal surface, the galvanometer will indicate the existence of 
 a current (Nobili, Matteucci, du Bois-Keymond). This cur- 
 rent passes through the galvanometer in a direction from the 
 longitudinal to the transverse section, and therefore, in the 
 muscle, in a direction from the transverse to the longitudinal 
 section. This, which is called the muscle-current, is also ob- 
 tained if any strip of muscular tissue, however small, obtained 
 by longitudinal division of a muscle, be substituted for the whole 
 muscle in the above experiment, provided that the strip is 
 bounded by a transverse section to which one electrode of the 
 galvanometer is applied, and that the other electrode is applied 
 to the longitudinal surface (' artificial longitudinal section '). 
 In this case the artificial longitudinal section bears the same 
 relation to the transverse section as did the natural longitudinal 
 surface (' natural longitudinal section ') in the former case. It 
 seems evident that an individual muscular fibre would also 
 exhibit a muscle-current. 
 
 If a living muscle or a bundle of muscular fibres be taken, 
 and the vitality of the tissue be destroyed over a limited length 
 of the muscle or muscular bundle by caustics, by crushing, or 
 by the application of heat, the muscle or muscular bundle will 
 be divided into living portions, which are separated from one 
 another by a dead portion, which is inserted between the 
 former as an indifferent conductor of electricity might be. In 
 this case every point in the cross line of demarcation between 
 the living and dead muscle, and in general every point in the 
 area of dead muscle, behaves, in reference to the longitudinal 
 surface, as the cross section in the experiments previously 
 alluded to. If such an artificial limitation of the living muscular 
 fibres be also called an artificial cross section, we may state 
 that generally, in whatever way it is made, the artificial cross 
 section of a muscle is negative in respect to the natural or 
 

 DEMONSTRATION OF MUSCLE-CURRENTS. 271 
 
 artificial longitudinal section. The nearer the two poles of 
 the galvanometer are to the centre of the longitudinal and 
 cross sections respectively, the greater the intensity of the cur- 
 rent which it indicates. 
 
 Amongst the many necessary precautions which must be taken in con- 
 ducting these researches, we can only mention here that the animal tissues 
 which are the subject of experiment must not be brought directly into con- 
 tact with the metallic ends of the galvanometer, or of the wires connected 
 with these ; for it is well known that two apparently perfectly similar 
 pieces of metal (e.g. two copper wires) when brought into contact with a 
 moist conductor and all the animal tissues may be considered as such 
 form a galvanic chain, the current of which must cause a deviation of the 
 needle of the galvanometer. 
 
 Pieces of zinc which have been amalgamated do not, however, give 
 rise to a current when they are connected by means of a solution of zinc 
 sulphate ; the two pieces of metal behave under these circumstances as if 
 they were ' absolutely similar.' Relying upon this property, the two poles 
 of the galvanometer are connected (in all researches in animal electricity) 
 with two amalgamated pieces of zinc; each of these pieces dips into a 
 vessel containing solution of sulphate of zinc, and from each of these vessels 
 there projects a pad of filtering paper soaked with the same solution. The 
 animal tissue the electro-motive properties of which are to be investigated is 
 now so arranged that it completes the circuit between the two pads, bridging 
 over from one to the other. 
 
 The animal structure is protected from the injurious effect which the 
 solution of zinc sulphate would exert upon it by the interposition of an in- 
 nocuous conductor; this consists of sculptor's clay which, having been dried, 
 is made into a paste of suitable consistence by means of a 1 per cent, solu- 
 tion of common salt. 
 
 The employment of these zinc electrodes possesses the additional advan- 
 tage of preventing the return of the needle after its first deviation, which, 
 if any other method were adopted, would occur in consequence of the polari- 
 zation of the electrodes. Electrodes made of amalgamated zinc plunged into 
 solutions of zinc sulphate are non-polarizable. 
 
 The muscular current may be demonstrated by methods other than the 
 galvanometric. (1.) By the electro-chemical method, viz. by causing the 
 muscular current to decompose a mixture of iodide of potassium and starch 
 paste ; in this case iodine separates at the positive pole and colours the starch 
 blue. (2.) The muscular current may be employed to stimulate nerves, as e.g. 
 to stimulate the very nerve supplying the muscle (' physiological rheo- 
 scope '). In this case it is necessary, as is mentioned in Chapter IX., to 
 allow the current suddenly to break into the nerves. This is effected by 
 suddenly completing a circuit, in the course of which is the nerve of a pre- 
 pared frog's leg, by interposing the longitudinal and transverse sections of a 
 muscle ; at the moment of closure of the circuit, a contraction of the leg 
 takes placer 
 
 When experimenting with a single muscle the arrangement is as follows. 
 
272 
 
 MUSCLE-CURRENTS. 
 
 The nerve belonging to the muscle (which we must imagine to be in contact 
 with the natural longitudinal sections of all the muscular fibres) is suddenly 
 allowed to fall upon the cross section of the muscle ; a muscular contraction 
 ensues. (These contractions, without the interposition of metals, were known 
 before the muscular current was discovered.) 
 
 Not only are currents observed when the longitudinal and cross sections of 
 a muscle are connected, but also when the electrodes are made to touch two 
 points of one and the same section. A circle embracing a muscle and dividing 
 it into two halves may be called the equator of the muscle. Now if in any 
 longitudinal section, natural or artificial, two points be taken for investiga- 
 tion, of which one lies nearer to the equator than the other, it will be found 
 that the former is positive in relation to the latter (which is nearer to the 
 cross section). Similarly, if any two points of a cross section of a muscle be 
 investigated, which are unequally distant from the axis, it will be found 
 that the point which is near the axis is negative in reference to the point 
 which is further away from it (and which therefore is nearer the longitu- 
 dinal surface). 
 
 No currents are observed when the electrodes touch two points which 
 are equidistant from the equator of a longitudinal section, or two points 
 equidistant from the axis of a cross section. 
 
 All these laws apply not merely to points on the same cross section, but 
 also to points on different cross sections, and similarly to points on different 
 longitudinal sections. Naturally, the two terminal points of the axis, and 
 any two points on the equator of a muscle, when connected, do not cause a 
 deflection of the galvanometer. 
 
 The currents which are obtained by connecting any two points on a lon- 
 gitudinal section, or any two points on a transverse section, are always very 
 much weaker than those obtained when a point on a longitudinal is con- 
 nected with a point on a transverse section, and they increase in strength as 
 the difference in the position of the electrodes, in reference to the equator 
 and axis, increases. The currents obtained by connecting two points on the 
 same section are termed weak currents, as distinguished from the strong 
 currents which pass between a longitudinal and transverse section. 
 
 In Fig. 7 the rectangular figure represents a piece of muscle : L L are its 
 longitudinal surfaces, Q Q its cross sections, a b its equator. The thin lines 
 
 FIG. 7. 
 
 show combinations of points (on the same kind of surface) which give rise 
 to weak currents j the thick lines illustrate the production of strong cur- 
 
CURRENTS OF INCLINATION. 273 
 
 rents ; the dotted lines show how different parts of a muscle may be arranged 
 in reference to the electrodes, so as to exhibit no electric current. 
 
 If an oblique section be made through a muscle, or a vertical section be 
 so altered by pulling as to furnish such a section, a departure is observed 
 from the previously mentioned behaviour, inasmuch as the most negative 
 point of the oblique section does not lie in the middle of it, but is in proximity 
 to its sharp edge ; similarly, the most positive points on the longitudinal 
 section do not lie any longer in the equator, but nearer to the blunt edge of 
 the section. In such a muscular rhomb a point in proximity to the latter is 
 positive in relation to a point near the former, in spite of the two points 
 being equally distant from the middle. In rhombic pieces of muscle currents 
 must therefore pass from the acute to the obtuse edges which are super- 
 added to the usual muscular current. Such currents are denominated cur- 
 rents of inclination. 
 
 All the phenomena which have yet been referred to may be explained by 
 the law, that each individual muscular fibre exhibits the same (electrical) 
 relations as the entire muscle, viz. that a transverse section through any 
 part of it whatever is negative in relation to the longitudinal surface or sec- 
 tion. By this hypothesis the ' strong ' currents between the longitudinal 
 and cross sections are explicable. The * weak ' currents are explicable simply 
 by the hypothesis that when a portion of muscle presents cut surfaces, the 
 latter rapidly die down to a certain depth, and are converted by this process 
 of death into indifferent conductors j in this indifferent layer, the muscular 
 current adjusts itself partly, and the electrical tension is not so distributed 
 on the surface that the greatest positive tension is in the middle (equator) of 
 the longitudinal section, the greatest negative tension in the middle of the 
 cross section. The phenomena which were described at p. 272 are explained 
 by the fact that a point possessing weak positive tension behaves negatively 
 towards a point of stronger positive tension, and similarly a weakly negative 
 point is positive in relation to a more intensely negative point ; lastly, two 
 points which possess the same amount and the same kind of electrical ten- 
 sion do not, when connected, give a current. In an oblique section the 
 successively projecting active cross sections of the muscular fibres form a. 
 kind of battery, whose positive pole is near the obtuse, and whose negative 
 pole is near the acute, edges ; the current which is formed in this battery 
 adds itself algebraically to the prdinary muscular current. In this way 
 may be explained the phenomena of the ( currents of inclination.' 
 
 The electro-motive force of the current between the longitudinal and! 
 transverse sections of a muscle amounts, in the case of a frog, to as much as- 
 0*08 of a Daniell j the electro-motive force of ' currents of inclination ' may 
 exceed 0-1 of a Daniell (du Bois-Reymond). All circumstances which 
 produce muscular exhaustion diminish the intensity of the muscular current 
 (Roeber). 
 
 In uninjured muscles separated from the body, currents 
 pass from different points on the surfaces, which are of varying 
 intensity and direction. Frequently tendons, i.e., the indif- 
 ferent conductors which are applied to the natural terminations 
 
 T 
 
274 BEHAVIOUR OF UNINJURED MUSCLES. 
 
 of the muscular fibres, are negative in relation to the longi- 
 tudinal section of the former, yet not so powerfully negative as 
 an artificial cross section. 
 
 In frogs which have been thrown into a kind of hybernating 
 state by the action of cold, the tendons are frequently electri- 
 cally neutral, or positive in relation to the longitudinal section 
 of muscle (du Bois-Reymond). In a perfectly uninjured, 
 unsJcinned animal, the muscles which are in a state of rest 
 are entirely free from electrical currents (Hermann); the 
 currents originate during the preparation of the muscle, in 
 consequence of injurious influences acting upon their sur- 
 faces. In frogs, for instance, amongst other such influences, 
 is to be mentioned the action of traces of the caustic secretion 
 of the skin. 
 
 The more these injurious influences are avoided, the greater 
 the freedom of the muscle from electrical currents. In muscles 
 which are at rest there are, therefore, no currents except those 
 which are brought about by the negative electric tension of the 
 artificial cross section in reference to the longitudinal section 
 (Hermann). 
 
 In order to investigate the electrical currents of the muscles of unskinne'd 
 frogs it is not sufficient to bring the electrodes, which are connected with 
 the galvanometer, in contact with two points on the surface of the skin, as 
 the skin at a-n_y point perpendicular to its surface, from without inwards, 
 possesses electro-motive properties (du Bois-Reymond). These cutaneous 
 currents, which are rapidly destroyed by the action of caustic alkalies, must 
 be first eliminated (du Bois : Reymond). If this be done in such a way as 
 to obviate the downward passage of the caustic to the muscle, at any rate 
 up to the time when the experiment is made, the muscles are found to be 
 entirely free from electrical currents (Hermann). Injuries which affect the 
 whole muscular surface always cause the tendons to become negative in 
 relation to the longitudinal surface of the muscle connected with them, for 
 the fibres of the muscle die throughout their whole length, and therefore pos- 
 sess no current of their own, whilst under the tendon are placed the artificial 
 transverse sections of many yet living muscular fibres ; this is especially the 
 case when the tendons present merely a thin aponeurotic membrane (as in 
 the case of the gastrocnemius). The different deportment of the muscles of 
 hybernating animals is most probably to be explained by a certain in- 
 difference which they present to slight transient injuries, which entirely 
 agrees with their well-known sluggishness when stimulated. 
 
 feWhen electrodes are placed in contact with two points on the surface of 
 the limbs of skinned animals, or on two points of the surface of the body 
 generally, currents are observed which are the resultants of the numerous 
 individual muscular currents. 
 
BEHAVIOUR OF ACTING MUSCLE. 275 
 
 Muscles, or muscular fibres, which are entirely rigid, or 
 which have been killed without rigor mortis occurring, exhibit 
 no muscular current. 
 
 When a piece of muscle which is limited by a longitudinal and cross 
 section is heated to a temperature which does not exceed that required to 
 bring on heat rigor, the strength of the muscular current is increased. 
 Cooling the muscle on the other hand diminishes the strength of the 
 current. Warm places in a fibre behave positively in reference to cooler 
 ones. 
 
 The strength of the current which passes between two points of a 
 muscular fibre is not influenced by the temperature of those portions of the 
 fibre which lie between them. The changes in the electro-motive pro- 
 perties of muscle which are brought about by heat 'and cold disappear when 
 the original temperature is restored (Hermann). 
 
 When the whole of a muscle whose external surface and 
 artificial cross section are connected with the galvanometer is 
 thrown into contraction, there is a cessation of the muscular 
 current, a 'negative deflection' (du Bois-Reymond). A single 
 muscular contraction is not sufficient to overcome the inertia 
 of the needle of the galvanometer, and to bring about the 
 change in its motion which corresponds to the negative vari- 
 ation : the muscle must therefore be tetanised. Making use of 
 the physiological rheoscope (p. 271), the negative variation can 
 nevertheless be proved, in the case of a single muscular contrac- 
 tion, by causing the change in the intensity of the current to 
 act as a stimulus to the nerves of a second muscle. (The nerve 
 of the second muscle is brought in contact with the longitudinal 
 and transverse sections of the first.) For every contraction of 
 the first there is a contraction of the second muscle ( ; secon- 
 dary contraction'). If the first muscle be tetanised, the second 
 one also becomes tetanic (secondary tetanus), a fact which 
 proves that in tetanus there are series of fluctuations in the in- 
 tensity of the muscular current (p. 260). The ' negative deflec- 
 tion ' at the most amounts to a cessation of the current, there 
 never being a reversal of its direction (Bernstein). 
 
 If the electrodes in contact with a muscle are so situated 
 that, during rest, there is only a weak current, or an absence of 
 current, it is observed that the corresponding variation in the 
 intensity of the current, brought about by the contraction of 
 the muscle, is in the first case very small, and that in the second 
 there is no change (du Bois-Eeymond). 
 
 T 2 
 
276 BEHAVIOUR OF ACTING MUSCLE. 
 
 When the nerves going to a muscle which is uninjured and, 
 either approximately or entirely, free from electric currents, are 
 excited, contraction leads to certain electro-motive manifesta- 
 tions, for which no general law has been yet found ; the gastro- 
 cnemius, for instance, becomes the seat of a descending current 
 which passes between the upper and lower tendons ; similarly, 
 during contraction, a descending current is observed in the 
 unskinned lower extremity of the frog. During the volun- 
 tary tetanic contractions of the muscles of the human arm there 
 is an ascending current, whilst a similar contraction of the leg 
 is accompanied by a descending current (du Bois-Eeymond). 
 If muscular currents be present in the limbs whilst at rest, they 
 add themselves algebraically to those just referred to as produced 
 during contraction. 
 
 If a bundle of fibres is excited near one of its terminations, 
 so that a wave of contraction runs along it (p. 261), it is noticed 
 that the different spots in succession on the longitudinal surface 
 become negative in reference to other spots, there being a 
 negative wave, as it were, which travels along with the same 
 rate as the wave of contraction, viz. about 3 metres per second 
 (Bernstein). At each point the negative state, which first in- 
 creases and then decreases, lasts about -^-oth of a second ; it is 
 entirely gone by the end of the c latent period,' which lasts 
 -j-i-^th of a second. Every point in a fibre must therefore first 
 of all undergo electrical changes before contracting (Helmholtz, 
 Holmgren) ; or, in other words, the wave of muscular contrac- 
 tion is immediately preceded by a negative wave. This wave 
 of negative tension diminishes in intensity as it runs along* 
 (Bernstein). 
 
 For the methods by which these results were obtained, consult Chapter 
 IX. 
 
 The magnitude of the fluctuations in the intensity of the muscular 
 current depends precisely upon the same conditions as the magnitude of the- 
 excitation. 
 
 The two following opposed hypotheses serve to explain the 
 electro-motive phenomena of muscle. 
 
 According to some (du Bois-Reymond), every muscular 
 fibre contains in its interior electro-motive molecules, which are 
 suspended in regular order in a conducting fluid. As these 
 molecules altogether present positive surfaces towards the 
 
ELECTROMOTIVE PROPERTIES OF MUSCLE. 277 
 
 longitudinal sections, and negative surfaces towards the trans- 
 verse sections of a muscle, the former possess positive and the 
 latter negative electrical tension. Every cross section, or the 
 action of caustics, &c., lays bare new negative surfaces. During 
 contraction or, rather, during the latent stage which pre- 
 cedes it, the electric-potential of these molecules diminishes, 
 so that during the complete contraction of a muscle its current 
 diminishes as a whole, whilst during partial contraction the 
 tract of the muscle which is involved in contraction resembles 
 in its behaviour an indifferent conductor, which now, in virtue 
 of the negative elements of the portion of fibre at rest which 
 are contiguous to it, comports itself negatively in reference to 
 the remaining portion of the fibre. In order to explain how it 
 is that the natural terminations of the muscular fibres do not 
 behave (as they ought to do if the above-mentioned scheme 
 held in its entirety) exactly like an artificial cross section, it is 
 assumed that in contact with the ends there is a layer of abnor- 
 mally arranged (' parelectronomic ') elements, which present 
 positive, and not negative, surfaces towards the natural cross 
 section ; the greater the number of these elements present the 
 more free is the muscle from electrical currents, or the directior 
 of the current may even be reversed. The development of par- 
 electronomic elements, which, however, are never entirely want- 
 ing, is, as must be assumed, promoted by the action of cold, &c. 
 In order to explain the deportment of uninjured muscles which 
 are thrown into contraction, it is assumed that the parelec- 
 tronomic elements of a muscle are not influenced by activity in 
 the same manner as the other elements. 
 
 The other hypothesis (Hermann) refers all the phenomena 
 to the effects of contact. There are two sets of circumstances 
 under which muscular tissue comports itself as electrically 
 negative with respect to living, inactive muscle, viz. : (1) when 
 it is dying (entering into rigor), and (2) when it is in activity, 
 or, more exactly, during the latent period preceding contrac- 
 tion. 
 
 The former case is taken to explain the negative state of 
 every artificial cross section of a living, inactive, muscular fibre 
 with respect to its exterior, for, at every artificial cross section 
 between the already dead, and therefore indifferent, portions of 
 the muscular fibre and those which are still living, there is 
 
278 ELECTROMOTIVE PROPERTIES OF MUSCLE. 
 
 found a layer just in the act of passing into rigor. Hence, all 
 the phenomena of the currents of muscle at rest (p. 272) are 
 explicable. The latter case is cited to explain all the pheno- 
 mena of muscle after stimulation, especially the diminution of 
 the muscle-current on irritation of the injured fibre in toto, and 
 the negative condition of the wave of contraction with respect 
 to the rest of the muscle-tube. The fact that muscles destitute 
 of currents, when acted on by stimuli proceeding from nerves, 
 exhibit currents of definite direction between two electrodes, 
 may be due to the circumstance that the waves of contraction 
 running through the fibre from the point of entrance of the 
 nerve reach the two points with different intensities, due, for 
 example, to the different distances they are from the point of 
 entrance of the nerve. In such a case the point where the 
 wave was more intense would be negative to the other. 
 
 The two hypotheses above enunciated agree equally well with the facts. 
 The second theory, in addition to its simplicity (it "being necessary in the 
 first (du Bois-Reymond's) to make at least four entirely independent as- 
 sumptions), has in its favour that it brings into complete analogy the 
 processes of rigor and activity, of which more will be said hereafter; 
 and that the electrical currents exhibited by glands containing blood (p. 
 52) as well as by sections of plants, are capable of explanation in exactly the 
 same way. 
 
 The above-mentioned influence of temperature, according to the first 
 hypothesis, would have to be enunciated thus : That heat increases and cold 
 diminishes the energy of the molecules. According to the second hypothesis 
 it would, on the other hand, be necessary to assume that electricity was 
 developed by the contact of warm and cold muscular substance, in which, 
 development the colder became negative. 
 
 Concerning the effects of electrical currents upon muscles reference 
 should be made to the chapter on Nerves (Chapter IX.) 
 
 e. Interdependence of the Phenomena of Muscle, and Theories 
 of Muscular Activity. 
 
 No satisfactory explanation of all the phenomena exhibited 
 by muscle as yet exists. The most enigmatical of these pheno- 
 mena, the diminution in length after stimulation, has hitherto 
 been regarded by most thinkers as a sudden approximation of the 
 smallest particles of the muscle in a longitudinal direction, the 
 ultimate cause of which is a suddenly increased combustion. 
 Many have, moreover, supposed quantitative relations to exist 
 
THEORIES OF MUSCULAR ACTIVITY. 279 
 
 between the three forms in which kinetic energy may manifest 
 itself in muscle, viz. mechanical work, heat, and electricity, of 
 such a nature that (1) the sum total of these manifestations is 
 greater during states of activity than during states of rest (during 
 which, as a rule, none of the three forms appears to exist) ; that 
 (2) any increase in one of the modes of manifestation is always 
 correlated with a diminution in another. 
 
 None of these suppositions has, as yet, a basis in fact. It is especially 
 doubtful whether, with equal stimulation, an increase in the amount of me- 
 chanical work done is accompanied by a diminution in the formation of 
 heat. If the work done be varied by altering the weight to be lifted, the 
 chemical processes which occur on contraction are also altered in extent, 
 the amount of acid and substances soluble in alcohol, for example, increas- 
 ing with the load (Heidenhain, Niegetiet and Heppner) a circumstance 
 which certainly does not agree with the supposition above named : the 
 amount of heat generated plus the amount of work done (corresponding to the 
 exchange of matter) vary with the load. Again, stimulus and load remaining 
 the same, the work done may be varied in one of the following ways : 
 Firstly, the weight may be allowed to fall freely to its former position after 
 each lift has been accomplished, so that no available work is done, while the 
 muscle is heated by the stretching due to the sudden fall of the weight. 
 Secondly, the contracting muscle may be allowed to raise the weight higher 
 and higher, by means of a wheel and axle arrangement, the weight being 
 held by a catch during the intervals between contraction, real work being in 
 this way effected (Pick). In the former case the muscle is certainly warmer 
 than in the second j but it may be objected (Heidenhain) that the chemical 
 processes of contraction do not terminate with the lift, but rather continue 
 during the succeeding extension of the muscle, and are then, as during con- 
 traction, influenced by the tension. It is a fact that the muscle generates 
 less acid in the former case than in the latter (Landau and Pakully). Thus, 
 again, the conditions of experiment determine the interchange of material, 
 and therefore the sum of the work done plus the heat generated. It is, of 
 course, undoubted, according to the principle of the conservation of energy, 
 that the sum of the forces set free in muscle is, in every case, equivalent to 
 that of the chemical decompositions which occur. 
 
 The analogy, which is now complete, between the pheno- 
 mena of rigor and of activity warrants the proposition of a 
 new theory of muscular contraction (Hermann) which differs 
 from the views previously held. The points of analogy be- 
 tween rigor and the active state are the following: 1. The 
 chemical process, so far as is known, is the same in both con- 
 ditions (p. 252 et sq.). 2. In both acts the muscle shortens 
 and thickens, its volume diminishing, and its electrical pheno- 
 mena becoming less marked (pp. 244, 256), 3. In both acts 
 
280 THEORIES OF MUSCULAR ACTIVITY. 
 
 heat is generated (p. 268). 4. In both acts the contents of the 
 muscle-tubes comport themselves electrically negatively towards 
 unaltered (living and resting) muscle (p. 277). In muscle, 
 which is entering into rigor, contraction of length is attributed 
 to the coagulation of myosin, since it is well known that every 
 albuminous tissue, e.g. a tendon, contracts strongly in the direc- 
 tion of its fibrillation on coagulation such as occurs on the ap- 
 plication of heat. As now the supposition that contraction in 
 a living muscle is accompanied by a sudden and transitory 
 coagulation is not contrary to any of the known facts, we may 
 assume such a coagulation to take place on the grounds of the 
 analogy between rigor and contraction. Moreover, the follow- 
 ing circumstances seem to favour such an assumption. There 
 are no grounds for supposing that any conversion takes place in 
 muscle of heat into motion (as in a steam-engine), or of electri- 
 city into motion (as in an electro-magnetic machine). There 
 remains, therefore, only one possibility, viz. that of a direct origin 
 of motion from the chemical decompositions which occur in 
 muscular tissue. We can only imagine such a process to take 
 the form of the production in consequence of chemical change 
 of a new body, whicji endeavours, like the gases evolved on the 
 ignition of gunpowder, to fill by elasticity a definite volume. 
 That such is the case in muscle is already affirmed by Weber's 
 theory (p. 262), and we may very well suppose the new body to 
 be due to a sudden coagulation of albuminous substance, the 
 explanation of details being as easy in this case as in that of 
 contraction of tendon on boiling. The heat and electricity 
 generated in muscle, from the quantities in which they occur, 
 are at all events by-products. It is not yet decided whether 
 they are dependent upon the processes of chemical decomposi- 
 tion, or upon physical changes of aggregation. 
 
 If contraction really depends upon a coagulation of the muscular con- 
 tents, the coagulum formed must be capable of immediate disappearance, 
 and in tetanus, of an alternate disappearance and reappearance several hundred 
 times in a second. The above-mentioned process of synthetic restitution 
 (p. 254 et sq.) is insufficient to account for this, as muscle, even during com- 
 plete deprivation of oxygen, becomes again lax after each contraction. More- 
 over, that process does not' affect firmly coagulated myosin at all. We may 
 imagine that under stimulation the process of decomposition referred to on 
 page 253 is suddenly very much accelerated, and that the myosin is gene- 
 rated with such rapidity that it has not time to pass at once into the state of 
 
THEORIES OF MUSCULAR ACTIVITY. 281 
 
 gelatinous solution, but enters for a moment into the undissolved condition 
 which does not appear, under slower decomposition (nV/or), until after con- 
 siderable concentration. The fact that only very sudden stimuli are able to 
 produce irritation in muscle seems to favour this view. 
 
 Although the view of muscular contraction just enunciated leaves much 
 to be desired (the significance of the muscle-prisms or sarcous elements, for 
 example, being provisionally quite unexplained), it seems to be a closer ap- 
 proximation to the true state of things than any of the older, purely 
 physical, theories. 
 
 The production of heat does not probably depend entirely upon the pro- 
 cesses of decomposition, but is, in part, a result of the synthetic processes of 
 oxidation. These processes must be accompanied by manifestations of 
 energy, and as they proceed during states of repose as well as during ac- 
 tivity, being, however, increased in the latter condition, everything seems 
 to imply that they are characterized by a development of heat. Muscle at 
 rest may therefore be one of the chief seats of heat-formation. Finally the 
 relative amount of heat produced in muscles cut out of the body renders it 
 impossible that these processes of oxidation which then occur in traces 
 should alone be the source of the greater part of the heat formed. 
 
 The uses of voluntary muscles in the body will be de- 
 scribed in the Appendix to this chapter. 
 
 The sensory powers of muscle are discussed in Chapter X. 
 
 b. Smooth Muscles. 
 
 The ' smooth ' or ' organic ' muscles occasion the less ener- 
 getic and slower movements of those organs, especially the ali- 
 mentary viscera, which are not subjected to the influence of 
 the will. They form, for the most part, membraniform ex- 
 pansions of varying thickness (tunicce musculosce\ which are 
 always fibrillated in a definite direction, and often so as to be 
 divisible into layers. These expansions consist of long, spindle- 
 shaped elements, which lie with their longitudinal axes in the 
 direction of the fibrillation. The spindle-shaped elements do 
 not, like the elements of transversely striated muscle, each run 
 the whole length of the fibrillated tract, but they are arranged 
 in rows, end to end. They are regarded as elongated cells 
 which are not known certainly to possess a membrane (sarco- 
 lemma), but which contain a somewhat long nucleus. The 
 latter is said by some observers (Frankenhauser) to be at the 
 same time a nervous end-organ, though others (Schwalbe, 
 Arnold, Hertz) deny this. The cells never exhibit any trace of 
 
282 SMOOTH MUSCLES. 
 
 transverse striation, but there is sometimes an indication of a 
 striation in a longitudinal direction. They are called ' smooth 
 muscular fibres ' or ' contractile fibre-cells.' 
 
 An examination in polarized light shows that smooth muscular fibres 
 also contain doubly refractive bodies (disdiaclasts), which are not, however, 
 arranged so regularly as in transversely striated muscle, but are scattered 
 throughout the whole mass, so as to give the whole fibre the appearance of 
 being doubly refractive (Briicke). According to more recent theories 
 (Engelmann) the division of the masses of smooth muscle into spindle- 
 shaped elements is considered to be a phenomenon of death, and not to be 
 pre-existent. 
 
 The chemical constituents of smooth muscular fibres are 
 apparently the same as those of transversely striated muscle. 
 The existence of a spontaneously coagulable substance may be 
 assumed from the circumstance of the occurrence of death-rigor. 
 As their reaction is constantly neutral or alkaline (du Bois- 
 Keymond), it cannot be decided whether rigor in this case is 
 accompanied by the formation of an acid ; since an acid might 
 "be generated in quantity insufficient to overcome the alkali 
 present. The muscles of the contracted uterus are acid to test 
 paper (Siegmund). 
 
 The properties of the two classes of muscles are, as far as 
 they have been investigated, almost identical ; but the re- 
 spiration, the chemical changes due to activity, the electrical 
 conditions, the formation of heat, &c. of smooth muscles 
 have not yet been made out. The activity of smooth muscle 
 manifests itself mechanically in the form of a diminution 
 in length, which proceeds according to the same laws as in 
 the case of transversely striated muscle (p. 256), but at a much 
 slower rate so much slower that the individual phases (latent 
 period, gradual shortening and re-extending) may be perceived 
 without any assistance ; that is to say, after stimulation a con- 
 siderable time elapses prior to contraction, which takes place 
 very slowly, is maintained for some time at its maximum, and 
 afterwards gradually disappears. Where muscular bands exist 
 (as in the ureter and intestine) contraction caused at one point 
 may be seen to travel like a wave with a velocity of 20-30 mm 
 per second, owing, apparently, to the direct conduction of 
 irritation (Engelmann). Automatic contractions have recently 
 been stated to take place in the smooth muscles of the ureter 
 (Engelmann). 
 
PROTOPLASMIC MOVEMENTS. 283- 
 
 Investigations of smooth muscles are very difficult, inasmuch as it is 
 only possible to obtain sufficient material from warm-blooded animals, in 
 which case it quickly loses its irritability. 
 
 II. CONTKACTILE CELLS. PROTOPLASMIC 
 MOVEMENTS. 
 
 The contractile substance, protoplasm (p. 237), occurs in- 
 closed in tubular sheaths (in muscle) and also in free, wall-less 
 conglomerations, forming finely granular, and for the most 
 part, microscopic masses of very variable form, and including 
 nuclei. Such contractile masses form the whole substance of 
 the body of many of the lower forms of animal life (Amoebea y 
 &c.), or the soft portions of such animals (Ehizopoda); 
 colourless blood-corpuscles, and the analogous corpuscles 
 of connective-tissue, lymph, spleen, mucus, and pus in the 
 higher animals (pp. 42, 81, 179) ; and the contents of many 
 elementary parts of vegetables (cell-capsules). 
 
 All these protoplasmic masses are capable of general and 
 partial contractions. The former follow on stimulation by 
 means of induction-currents. The mass, takes on the globular 
 form where it is possible, and where it is not (e.cj. when the 
 mass is enclosed in a tube), approximates to that form as far 
 as practicable by shortening and thickening (Kuhne). 
 
 Partial contractions are, however, far commoner, and con- 
 stitute, perhaps, the only kind which ever occurs in a normal con- 
 dition. They may produce most manifold changes of form, such, 
 for example, as the protrusion and retraction of processes 1 
 whereby foreign granules may be dragged into the midst of the 
 mass ; movements of the whole structure from place to place 
 effected by means of the processes (pseudopods) ; movements 
 of the granules, &c. in the interior of the mass ; dancing move- 
 ments (molecular movements) ; the excavation in the interior 
 of the mass of spaces (vacuoles) which become filled with fluid. 
 All these forms of movement have been frequently observed 
 (M. Schultze, Briicke, Hakel, Kuhne, von Eecklinghausen). 
 
 1 The protrusion of a process can only be explained Ly supposing contraction 
 to be exerted along the direction of a chord, whereby a segment is pressed' out- 
 wards. The process becomes long and thin in consequence of the repetition of the 
 contraction along the various chords in the same segment one after another. 
 
284 PROTOPLASMIC MOVEMENTS. 
 
 Molecular movement has been more exactly studied (Briicke) in the 
 granules of the following 1 cells : colourless blood-corpuscles, pus-corpuscles, 
 mucous and salivary cells, cartilage cells, and pigment cells of the frog. 
 This form of movement is very generally found. Inasmuch as molecular 
 movement is prevented by many influences which prejudice the life of the 
 cells in which it occurs, and as it always disappears at death, it is clear that 
 this phenomenon is not the same as the molecular movement of inorganic 
 precipitates. The ' cells ' above mentioned are not structures possessed of 
 cell-wall and fluid contents, but consist of a tough mass in which, according 
 to certain indications, we must suppose a complicated system of excavations 
 or canals to exist. The matter of the corpuscles when at rest is chiefly 
 aggregated about their nuclei and frequently forms radiating processes 
 towards the periphery. Induction shocks cause the cessation of motion, and 
 .afterwards a sudden diminution in the size of the cell with expulsion of gran- 
 ules. Molecular movement is, therefore, a complicated phenomenon, closely 
 connected with the remaining appearances of vitality. 
 
 The stimuli by means of which these structures may be in- 
 duced to activity are the same as in the case of muscle, as are 
 -also the conditions of irritability and death (Kiihne). At a 
 temperature of 40 C. a species of rigor occurs ; a temperature 
 of 36 C. acts as a stimulus producing tetanus (and the globular 
 shape). Deficiency of oxygen destroys the irritability of proto- 
 plasmic masses. This circumstance, which is not in agreement 
 with the slight influence which oxygen has on muscles removed 
 from the body, is explained by the relatively greater surface 
 exposed in the case of the small masses. 
 
 All protoplasmic structures appear, therefore, to contain the same essen- 
 tial substance as muscle. Its decomposition takes place during conditions of 
 activity, and slowly during repose, until rigor intervenes. Its regeneration 
 as accompanied by an absorption of oxygen at the surface. The weakest acids 
 even carbonic acid have a most important prejudicial effect upon all pro- 
 toplasmic movements. 
 
 Certain protoplasmic structures which do not migrate, e.g. 
 & portion of the connective-tissue corpuscles of the cornea, are 
 connected with nerve fibres, irritation of which leads to con- 
 traction (Kiihne, Lipmann, though others doubt it). The 
 great majority are, however, totally independent of the nervous 
 system ; and the stimulus which causes the movements is still 
 unknown. These movements may be considered as automatic. 
 
CILIATED CELLS AND SPERMATOZOA. 285 
 
 III. CILIATED CELLS AND SPERMATOZOA. 
 
 The superficial cells of the cylindrical epithelium which 
 covers certain surfaces of the body in single or stratified layers 
 are provided at their free ends with fine, structureless hairs or 
 6 cilia ' which are constantly in motion. Such surfaces of the 
 body are : the respiratory tract, from the entrance of the nose to* 
 the alveoli of the lungs : the female generative organs from 
 the opening of the Fallopian tubes to the os uteri externum : 
 the cerebral ventricles with their communications. In the case 
 of these cilia, no liberation of energy by means of the nervous- 
 system takes place so far as is known. Their movements con- 
 sist for the most part in an alternate bending and straighten- 
 ing ; but pendulous, conical, and other forms of motion are- 
 said to occur. 
 
 Spermatozoa may be regarded as vibratory structures pro- 
 vided with one cilium. The head corresponds to the ciliated 
 cell, and the tail is the cilium. The movement is a lashing to* 
 and fro. 
 
 If .movable particles appear on ^such a vibratile surface^ 
 they are gradually pushed forward in a definite direction. This 
 direction proceeds, in the case of the respiratory and genital 
 apparatus, outwards. In order to explain it we must suppose 
 that the movement of the cilia in one direction takes place 
 more rapidly than in the other, so that one forward push 
 follows another, otherwise the particles would have regained 
 their old position after each forward and backward swing. The 
 application of this vibratile motion in respiration has been 
 noticed ; for its use in the movements of the ovum consult the 
 fourth Section of the book. Small bodies provided with 
 vibratile cilia, such as many infusorians and spermatozoa, are* 
 able to propel themselves actively by means of them through 
 fluids in which they may be placed. 
 
 The circumstances which influence the movements of ciliated 
 cells and spermatozoa are exactly the same as in the case of pro- 
 toplasm (Roth, Kiihne, Engelmann). The conditions necessary 
 to its occurrence are : the maintenance of the state of concen- 
 tration of the fluid bathing them ; the presence of oxygen 
 (Kiihne, according to Engelmann they can do without oxygea 
 
286 THE USES OF MUSCLES. 
 
 for long periods of time) ; and a medium temperature. Increase 
 of temperature accelerates their motion (Calliburces), as also 
 do variations in electrical currents (Kistiakowsky). Very low 
 or very high temperatures cause a stand-still (cold- and heat- 
 tetanus) which gives place to movement on a return to the 
 normal temperature (Roth). At a temperature of 45 C. a per- 
 manent stand-still, rigor, is produced, with acidification. Rigor 
 occurs spontaneously after removal from the body. The action 
 of acids is very prejudicial to ciliary movement as well as to 
 the movements of protoplasm. The effect of alkalies in restor- 
 ing the power of vibration to cilia in which it has spontaneously 
 disappeared (Virchow) merely consists, therefore, in all pro- 
 bability in the neutralisation of prejudicial acids (Roth). Other 
 observers, however, ascribe similar reviving powers to acids, 
 alcohol, ether, &c. (Engelmann). 
 
 The vibratile movements of ciliated cells and spermatozoa 
 are therefore, most probably, but a special modification of the 
 movements of protoplasmic masses. It is not yet decidedly 
 known whether the cilia are passive and merely moved by the 
 protoplasm of the cell, or whether they also, being themselves 
 of a protoplasmic nature, actively assist. 
 
 APPENDIX TO CHAPTER VIII. 
 
 THE USES OF MUSCLES. 
 
 THE property of muscles to shorten or contract is made use of in 
 the most varied manner in order to bring movable parts towards 
 each other, out of their position of equilibrium, so as to produce 
 changes in the form of the body. The position of equilibrium 
 of the parts of the body is dependent on various mechanical 
 causes, chiefly gravity and tension (elasticity). Changes of 
 form either take place for purposes subject to the will (voluntary 
 movements), or they are brought about by certain mechanisms, 
 which have their seat in the central organs of the nervous 
 
THE USES OF MUSCLES. 287 
 
 system (involuntary movements). The form-change caused by 
 the shortening of a muscle (or of a single muscular fibre, which 
 may be taken as a type of the entire muscle) may be determined 
 in every case, if the position of equilibrium and the degree of 
 mobility of the parts to be moved, and the position of the 
 muscle itself, are known. We have here to consider chiefly two 
 forms of muscular effort. 1. The two terminal points of a 
 niuscle a,re connected together and therefore not movable towards 
 ach other. Here a shortening of the muscle can only take place 
 when the muscle does not stretch in a straight line, but between 
 its two points forms a curve. This is the case with the hollow 
 muscular organs, where the muscular fibres run along on a 
 cylindrical, spherical, or otherwise curved surface, either with 
 their ends joined (directly, or by the juxtaposition of many 
 fibres), or with their ends acting on a body which may be con- 
 sidered fixed (intestine, heart, uterus, bladder, &c.). In this 
 case a tendency to approach a straight line is manifested during 
 the muscular contraction, and hence the surface on contracting 
 exerts a pressure on the fluids which may be contained in these 
 hollow organs. 2. The end-points are movable in reference to 
 one another, being either both movable or (as is commonly the 
 case) one movable and one fixed. In this case the contraction of 
 the muscle, supposing it to be stretched between its two terminal 
 points, causes these end-points and all the parts to which they 
 are fixed to approach each other. In the case in which one of 
 the two points is fixed the other alone will move ; if, however, 
 both are movable, then the changes are inversely proportional 
 to the resistances acting in opposition to the movement. The 
 direction of the movement does by no means always lie in the 
 straight line joining the two points. Deviations from this 
 direction are caused: a, when the course of the (stretched) 
 muscle or its prolongations (tendons) is not straight, but either 
 curved or bent (when, for instance, the muscle or tendon runs 
 over a pulley-like projection) ; 6, when the two fixed points 
 cannot move towards each other in a straight line, their extent 
 of motion being limited by some mechanism or other. In 
 the latter case the whole of the kinetic energy of muscular action 
 (which is determined by the length, section, and degree of ac- 
 tivity of the muscle) is not employed in bringing about changes 
 of position, but a part of dt is, by the resistance of the me- 
 
288 THE USES OF MUSCLES. 
 
 chanism, converted into heat. The part used in changing the 
 form is easily determined by the parallelogram of forces, ac- 
 cording to which it is split up into two component parts, the 
 one in the direction of the absolute resistance, the other in 
 the direction of the absolute mobility ; the latter of the two 
 components represents the amount of form-change. 
 
 Let ac and Ic be two bones which are connected by a hinge-joint c, and 
 movable towards each other by the muscle de ; ac being considered fixed, 
 cp then the point d can only be moved in the direction 
 dg. vertical to be (the tangent of the arc di). The 
 force of muscular contraction is therefore to be re- 
 solved into the two components dg (the moving por- 
 tion, or the form-changing portion) and dh (the direc- 
 tion of the absolute resistance, or the portion which 
 represents the pressure on the joint). It will be 
 seen at once that as the contraction increases the 
 moving portion, d^g^ increases, while the other por- 
 tion, rfjAj, diminishes. If now we call K the force 
 of traction of the muscle, then that portion of K which is effective 
 = K sin cde, and the moment in relation to the lever-arm cd = K. cd. sin cde ; 
 
 but cd = - ; the moment therefore = K.C/C .; i.e. the muscle acts at 
 sin cde 
 
 every instant as if it acted with its full power on the arm of a lever, the 
 length of which is equal to the shortest distance of the joint from the muscle 
 (Henke). 
 
 The conversion into heat of that portion of the work done by the muscle 
 which exerts pressure on the joint is to be taken in the sense, that the 
 pressure on the joint increases the friction, whereby the evolution of heat 
 normally due to this cause is increased. 
 
 Those muscles which act on rigid parts of the body (bones, 
 cartilage) act almost always as on levers, since the rigid parts 
 are nearly all arranged so as to be movable around a point ; 
 hence also the constitution of the momentum of the muscular 
 action as regards weight and velocity will become variously 
 modified. Most of these levers belonging to the second and 
 third kinds, i.e. the point of traction of the muscle (power) and 
 the resistance (weight) are on one and the same side of the ful- 
 crum ; levers of the first kind are, however, also found, as, for 
 instance, in the forearm, where the triceps acts on the olecra- 
 non. The point of traction of the muscle|(the power) is gene- 
 rally situated near the fulcrum, and the power-arm is thus 
 much smaller than the weight-arm, and hence^only small 
 weights (considered to act at their natural point of application) 
 
CONNECTIONS OF BONES. 289 
 
 can be moved, but with great velocity. This arrangement 
 enables us to perform the different movements of the body 
 with great rapidity, and obviates also the clumsy form which 
 our body, particularly the extremities, would have to take under 
 the opposite arrangement, as will be easily understood on 
 reflection. 
 
 Where more than one muscle act in different directions on 
 the same part, or where only one muscle acts, the fibres of 
 which, however, have different directions, the resultant can 
 always be easily found by the parallelogram of forces. When 
 different muscles acting on the same part are so arranged that 
 the resulting motion due to the simultaneous action of all 
 becomes = 0, that is, the part acted upon remains at rest, then 
 each of these muscles is called the antagonising muscle of the 
 rest. The position of equilibrium of any part of the body acted 
 upon by antagonising muscles is, apart from the effect of 
 gravity, that position in which the elastic forces of all muscles 
 balance each other. 
 
 We have already spoken of some of the special uses to 
 which muscles are applied in the first Section, particularly when 
 considering circulation, digestion, and respiration. In this 
 chapter we shall consider in a general way the movements of 
 the rigid parts of the body, bones and cartilage, which are so 
 connected with each other as to admit of motion, and then 
 study separately two important groups of motion, namely, 
 1, the locomotion of the entire body, and, 2, those movements 
 in the passage of entrance to the respiratory apparatus, which 
 serve for the formation of voice and speech. 
 
 Mechanism of the Skeleton. 
 
 The elements of the skeleton the bones are for the most 
 part movably joined to each other. An exception to this is seen 
 in the connection of the bones by sutures, such as are feund in 
 the cranial bones, which render the bones absolutely immovable 
 for all such forces as do not endanger the existence of the 
 organism ; such bones are then to be considered as forming an 
 immovable mass. Amongst the movable connections of bones 
 we distinguish two kinds : the first of these the synchondroses 
 and symphyses allows but a very slight movement, yet fairly 
 
290 SYNCHOXDROSES. JOINTS. 
 
 unlimited as regards direction; the combination resulting 
 from this junction is of stable form, to disturb which requires 
 a very strong* force and into which the bones, as soon as that 
 force ceases to act, spring back by virtue of their elasticity. 
 The second kind the movable joints allows of a free move- 
 ment without any material resistance, a movement which is, 
 however, limited as regards direction ; this form, therefore, has 
 no definite position of equilibrium. 
 
 Synchondroses. 
 
 The synchondrosis is formed by the connection of two 
 opposed, generally congruent, bony surfaces by means of an 
 intermediate more or less solid connecting substance, mostly 
 hyaline or nbro-cartilaginous. Ligamentous sheaths at the 
 place of junction prevent the lateral displacement of this 
 connecting substance. The degree of mobility of this joint 
 depends (1) on the absolute strength of the connection; (2) on 
 its dimensions, for the mobility is (independently of the liga- 
 mentous sheath) directly proportional to the thickness of the 
 connection, i.e. the distance of the two bone surfaces from each 
 other, and inversely proportional to the transverse diameter of 
 the connection, i.e. the size of the two opposing bone surfaces ; 
 (3) on the rigidity of the surrounding ligamentous band. The 
 mobility of these joints is in all cases very small and muscular 
 traction has therefore scarcely any effect on them ; their elas- 
 ticity is, however, of great importance ; especially is this the 
 case with the spinal column, in which we have a series of syn- 
 chondroses (the intervertebral cartilages) in virtue of which 
 this curved column is endowed with a certain amount of flexi- 
 bility and great elasticity. 
 
 Movable Joints. 
 
 In these joints the causes opposed to motion are reduced to 
 a minimum ; the direction of the movements is, however, by 
 the form of the joint, limited in various ways. The two bones 
 entering into a joint oppose to each other smooth surfaces, 
 covered with cartilage (the articular surfaces), which are con- 
 stantly kept in apposition with each other, over as wide an 
 area as possible, by certain means which will be described pre- 
 
FORMS OF JOINTS. 291 
 
 sently. The one of the two articular surfaces is always larger 
 than the other. 
 
 The most simple joints are those in which the smaller 
 articular surface is always everywhere in contact with the 
 larger. Where this contact is permanent, there can be no 
 other but a gliding movement of the smaller articular surface 
 on the larger ; the relative movement of the two bones then 
 depends entirely on the form of the articular surface (as one 
 surface covers the other, the one is the exact cast of the other). 
 In general only certain surfaces of regular form will allow such 
 a gliding movement, and these surfaces are : 1. Plane surfaces 
 (joints of this kind seem not to occur, but the movements 
 which they would allow are: a. Eotation of each of the two 
 bones round axes which are perpendicular to the plane of the 
 joint, b. Movement of the axis of each bone parallel to itself). 
 2. Parts of surfaces of rotation, i.e. surfaces which may be con- 
 ceived to have been formed by the rotation of a straight line 
 or of a line of single curvature round an axis lying in the same 
 plane. In this manner, if the rotating line be a straight line 
 parallel to the axis the articular surface is a cylinder ; if it is a 
 straight line, but not parallel to the axis, a cone ; if it is a 
 semicircle and the axis its diameter, a sphere ; if it is a seg- 
 ment of a circle and the axis on its convex side, it is a surface 
 of saddle-form ; if the axis is on the concave side forming a 
 chord, a cycloid; if it is an ellipse and the axis one of its 
 geometrical axes, an ellipsoid, &c. ; lastly, if it is any other 
 curved line, the articular surface is that of some pillar-like, 
 turned, body, &c. All joints of this description allow of a 
 rotation of both bones round a common axis, the geometrical 
 axis of the articular surface; they are called uniaxial or 
 hinge-joints (Ginglymi). An exception to this, however, is 
 presented by those joints whose articular surfaces are parts of 
 a sphere ; they allow a rotation around any diameter of the 
 sphere, or, as it is said, round a point, namely, the centre of 
 the sphere ; these joints are called multiaxial or ball-and- 
 eocket joints (Enarthrodia). In the screw-joints we have a 
 uniaxial joint of peculiar construction. Here the articular 
 surface may be thought to have been formed by the rotating 
 line (which is here a curved line) advancing in the direction of 
 the axis, during the rotation, with a velocity which is propor- 
 
 v 2 
 
292 JOINTS. 
 
 tional to the velocity of rotation. Joints of this description 
 cause an opposite movement of the two articular surfaces 
 around the axis (analogous to the movement of the screw 
 turning within the nut). 
 
 The conditions which have just been the subject of con- 
 sideration are only found in some of the joints of the body, and 
 not even there with mathematical precision. In a great many 
 of the joints the surfaces are not congruent, and a perfect con- 
 tact of all the points of the smaller of the two articulating 
 surfaces is therefore impossible. Again in some of the forms 
 spoken of we notice positions in which the apposition of the 
 surfaces is imperfect ; such a condition of things, for instance, 
 enables joints with saddle-shaped or cycloid surfaces to admit of 
 rotation round two axes ; to wit, round the axis of rotation, and 
 round a second axis which passes through the geometrical centre 
 of the rotating arc and is vertical to the axis of rotation, pro- 
 vided always that the one surface covers only a small part of 
 the other. Wherever the two articulating surfaces are not in 
 
 O 
 
 contact the spaces are filled up by soft parts or fluids (see 
 below.) 
 
 Wherever a perfect congruence of the articulating surfaces 
 is not required, the variety of joints and the movements of 
 which they are capable increase beyond measure. It is there- 
 fore impossible to draw any conclusions from the mere shape 
 of the two articular surfaces, as to the degree of movement 
 allowed ; for the limitation of movements will chiefly depend 
 on the other factors. A general consideration of these irre- 
 gular joints, whose surfaces are not those of rotation, is there- 
 fore impossible; but to consider each one separately would 
 lead us too far. 
 
 Mechanism, for Maintaining Contact. 
 
 The constant and close contact of the two articular surfaces 
 is effected by the following means. 1. The space between the 
 two surfaces is closed, for the ends of both bones are connected by 
 a short tube (the synovial capsule), which is attached round the 
 articular head of each of the two bones ; the cavity which is thus 
 formed has only a capillary lumen and is filled with a tenacious 
 lubricating fluid (Synovia). The two articulating surfaces can 
 separate no further from each other than the small quantity of 
 
CHECK MECHANISMS. 293 
 
 synovial fluid will allow, and every further separation is pre- 
 vented by atmospheric pressure, which presses with a force 
 equal to the product of the surface-capacity of the smaller 
 articular surface and the barometric pressure for the surface- 
 unit. This mode of contact is of importance in joints with 
 large surfaces, especially in the ball and socket joints, where 
 any other mode of attachment would restrict the free mobility 
 in all directions. In the hip-joint, the largest ball-and-socket 
 joint of the body, the smaller articular surface (that of the 
 acetabulum) is of such a size, that the atmospheric pressure 
 balances the weight of the whole lower extremity, so that even 
 after all the soft parts surrounding the joint are separated and 
 the synovial capsule cut through, the lower extremity does not 
 drop out of the socket (the brothers Weber) ; the surface of 
 the acetabulum is further increased and the closure of the joint 
 ensured by a thin-edged elastic cartilaginous ring (Labrum car- 
 tilaginium) which surrounds everywhere the free margin of the 
 acetabulum and attaches itself closely to the head of the femur 
 in all movements. Where the articular surfaces cover each 
 other but very imperfectly and the joint-cavity is thus con- 
 siderably increased, we have the greater part of this cavity filled, 
 not by synovia, but by movable cartilage, masses of fat and 
 ligaments which pass through the joint ; the best example of 
 this form is the knee-joint. 2. In nearly all joints ligamentous 
 masses serve to fix the joint; these masses consist either of 
 stretched bands, which run from one bone to the other (in most 
 cases attached to the capsule) or in stretched parts of the cap- 
 sule itself. As these fixing bands have always to be in a state 
 of tension, they must be so placed as not to hinder movement ; 
 with hinge-joints they are therefore always found at both ends 
 of the axis of rotation. In most joints where the surfaces are 
 incongruent (i.e. do not ^over each other) the axis of rotation 
 is only determined by the insertion of the fixing ligaments. 
 3. The tension of the surrounding muscles plays an important 
 part in holding the articular ends in apposition. 
 
 Check Mechanisms. 
 
 The appliances which determine, not the direction, but the 
 extent of articular movements, are these : 1. A particular con- 
 
294 CHECK MECHANISMS. 
 
 figuration of the bone ; thus, for instance, the abutting of the 
 olecranon against the sinus maximus of the humerus restricts 
 the extension of the forearm. 2. So-called check-ligaments, 
 i.e. ligaments which become stretched in extreme positions of 
 the joints by being so attached that the distance between their 
 two extremes increases to a maximum with the movement of 
 the joint (in joints also where bones restrict the extreme move- 
 ments we have often ligaments which limit the movement still 
 more). One form in which ligaments which maintain contact 
 act as check ligaments occurs in so-called spiral joints, of 
 which the knee-joint forms a good instance. A horizontal section 
 through the articular end of the femur shows as external limit 
 a spiral, the centre of which is situated posteriorly, while its 
 vectors increase in length as they proceed from behind forward. 
 The upper ends of both lateral ligaments are attached to the 
 terminal points of an axis passing transversely across the centre 
 of the spiral (tuberositas condyli interni and externi femoris) ; 
 the lower end of the internal ligament is attached to the con- 
 dylus internus tibiae, that of the external to the head of the 
 fibula. These two ligaments make the knee-joint an imperfect 
 hinge-joint, but inasmuch as with flexion of the knee the 
 smallest vectors of the spiral, and with progressive extension, 
 progressively larger vectors, are moved in the direction of the 
 ligaments, so the distance of their points of insertion, and 
 therefore also their tension, increases as the knee passes from 
 flexion into extension, the tension reaching a maximum, beyond 
 which further extension is impossible. This arrangement it is 
 which renders possible the rotation of the fore-leg round its 
 vertical axis independently of the thigh only during flexion of 
 the knee, and not when the lower extremity is extended, in 
 which case the thigh and fore-leg being wedged in at the joint 
 form but one piece. 3. The soft parts also (muscles, tendons, 
 and skin) surrounding the joints assist by their tension to 
 limit the movements in a manner similar to that of the check- 
 ligaments. 
 
 It happens occasionally that when a muscle runs over two joints, the 
 flexion or extension of one of these joints stretches the muscle in such a way 
 as to make it a sort of check ligament for the other joint : this is called 
 t passive insufficiency/ in contradistinction to ' active insufficiency/ by which 
 is meant the opposite condition, in which flexion or extension of the one 
 
THE ERECT POSTURE. 295 
 
 joint slackens the muscle in such way as to make its contraction have no 
 effect (C. Hiiter, Henke). 
 
 Conditions of Equilibrium and of active Locomotion of the whole 
 
 Body. 
 
 It will be found convenient for the relations which are to be 
 considered under this head to look upon the body as a chain, 
 with many links and various branches, the joints of which are 
 to be looked for where two bones are movably connected. 
 Such a chain can only be in a stable equilibrium when each 
 joint is sufficiently supported. This will be effected in different 
 ways in the different positions of the body (lying, sitting, etc.). 
 The positions which will be considered here are the erect 
 posture and the sitting posture. 
 
 The Erect Posture. 
 
 By the free erect posture we mean that position of equili- 
 brium in which the whole body rests entirely supported by the 
 two feet touching the ground. If now the body were a rigid, 
 unjointed pillar, the only condition to be fulfilled would be that 
 the centre of gravity should be supported by the basis or surface 
 of support (which is given by the points of contact between the 
 soles of the feet and the floor), or, in other words, that the line 
 of direction of the centre of gravity should meet the floor 
 within the basis of support. The human body can only be 
 made into such a rigid pillar by having all the movable articu- 
 lations immovably fixed. In the natural erect posture this 
 is effected almost without any muscular effort, the muscles 
 coming in use only to supplement the somewhat unstable equi- 
 librium. 
 
 The articulations to be considered here are the tarsal and 
 tarso-metatarsal joints, the ankle-joint, the knee-joint, the hip- 
 joint, the articulations of the vertebrae (the symphyses of the 
 pelvic bones may be considered as absolutely fixed) and the 
 articulation between the head and the uppermost cervical verte- 
 brae. The other articulations (those of thorax, upper extremity 
 and jaw) do not enter into consideration here, for the bones to 
 which they belong are merely appended to, without in any way 
 serving for the support of, the other bones. 
 
296 THE ERECT POSTURE. 
 
 1. The joint between the head and the uppermost cervical 
 vertebrae. The two surfaces of the atlas which articulate with 
 the occipital bone form parts of one curved surface with con- 
 cavity upwards, the curvature of which is slighter antero- 
 posteriorly than laterally. The joint is, therefore, biaxial, i.e. 
 the sagittal axis of rotation is situated higher in the head than 
 the frontal, and the greatest amount of motion takes place 
 about the latter. The joint allows also a rotation of the head 
 on the atlas during forward flexion. The most important rota- 
 tion of the head, however, occurs at the odontoid articulation 
 between atlas and axis. In this joint the odontoid process of 
 the latter vertebra forms a vertical axis of rotation for the atlas 
 and skull. The articular surfaces of the superior oblique pro- 
 cesses of the axis are seen, in a sagittal section through atlas 
 and axis, to be convex towards their articular cavities. There- 
 fore, in the mean symmetrical position, the head must be 
 highest, and must glide somewhat downwards, on lateral rota- 
 tion, like a screw. This arrangement probably guards against 
 torsion of the cord when the head is rotated from side to side. 
 While, in the joints about to be considered, every care seems 
 to be taken to expend as little muscular energy as possible, 
 and to gain the required objects by mechanical means, the 
 great freedom of the axial, atlantic, and occipital articulations 
 requires that the position of the head should be determined by 
 the muscular effort of the numerous muscles attached to it. If 
 this effort is wanting (as, for instance, during sleep), then the 
 head in the erect posture inclines forward and rests with the 
 chin on the chest, for its centre of gravity is in front of its 
 point of support. 
 
 2. The vertebral column. The vertebral articulations are 
 chiefly synchondroses ; the vertebral column forms therefore a 
 rigid, somewhat flexible and exceedingly elastic rod, variously 
 curved (with the convexity in front in the cervical and lumbar 
 regions, and with the concavity in front in the dorsal and sacral 
 regions). The mobility of the vertebral column, which is quite 
 wanting in the sacral region, increases from below upwards, 
 owing less to the diminished transverse section of the inter- 
 vertebral cartilages for this circumstance, otherwise of advan- 
 tage for movement, is neutralised in its effects by the simul- 
 taneous diminution in the thickness of the cartilages than to 
 
THE ERECT POSTURE. 297 
 
 the constitution of the true joints between the oblique (articular) 
 processes. In the lumbar region these articular surfaces are 
 nearly vertical, sagittal, and almost parallel (being slightly 
 convergent forwards), so that each upper vertebra is locked in 
 the one below ; rotation about a longitudinal axis is, therefore, 
 quite prevented, while flexion, antero-posterior, or lateral,, is 
 possible only in the slightest degree. In the dorsal region the 
 surfaces of articulation of the articular processes are more 
 antero-posterior in aspect, converging posteriorly, and per- 
 mitting, therefore, a lateral rotation ; lateral flexion, also, is 
 not entirely prevented, but antero-posterior movement is quite 
 impossible without a disengagement of articulating surfaces. 
 In the cervical region the articular surfaces become more 
 and more horizontal, and allow of movement in all three 
 directions. 
 
 3. The hip-joint. a. The centre of gravity of that portion 
 of the body which is to be supported by this joint (head and 
 trunk) is situated near the vertebral column (in front of the 
 tenth dorsal vertebra), in a horizontal plane passing through 
 the xyphoid process (Weber) ; it will of course vary somewhat 
 with the degree of distension of the digestive canal. A plumb- 
 line let fall from this point (the line of gravity) passes behind 
 the line of junction of the hip-joints, and the trunk would 
 therefore in the erect position fall backwards, but for its 
 attachment anteriorly by the ilio-femoral ligament to the femur 
 (linea intertrochanterica anterior). This balancing of the 
 trunk on the heads of the thigh bones might thus be compared 
 to the position of a gun obliquely supported over the shoulder, 
 where the grasp of the butt end by the hand prevents its fall- 
 ing over. The action of the anterior part of the tense fascia 
 lata (Lig. ilio-tibiale) and of the stretched m. extensor quad- 
 riceps is similar to that of the ilio-femoral ligaments, only 
 with this difference, that they are attached to the leg. b. The 
 trunk has also to be fixed in a vertical plane to prevent it fall- 
 ing either to the right or left ; for as the two feet are not fixed 
 to the floor, a falling over to one side, i.e. the rotation of the 
 trunk around the head of the femur laterally, would be pos- 
 sible; this is, however, prevented by the ligamentum teres, 
 which checks the adduction of the extended thigh beyond the 
 middle line, and without such adduction, the lateral rotation of 
 
298 THE ERECT POSTURE. 
 
 the trunk spoken of cannot take place ; this is particularly the 
 case in the erect posture, where the ligamentum teres is already 
 stretched by the eversion of the thigh and leg (this rotation 
 outwards is due to the action of the gluteus maximus) ; the 
 external tense sheath of the fascia lata is another accessory to 
 check adduction, c. It is unnecessary, as long as the body 
 rests on the two feet, to provide against the rotation of the 
 trunk on the head of the femur ; this can, however, be effec- 
 tually done by the glutei and the ligaments. 
 
 4. The knee-joint. a. The common centre of gravity of head 
 and trunk and thighs is situated somewhat lower than, but not 
 much anteriorly to, the centre of gravity of head and trunk. 
 The line of gravity will therefore here also pass behind the 
 point of support of the knee-joint, but the difference is so slight 
 that no great force is required to prevent falling over (flexion 
 of the knee). The agents are the lig. ilio-tibiale (see above), 
 the slight tension and contraction of the extensor quadriceps 
 and the lig. ilio-femorale, for in order to flex the knee while 
 the fore-leg is fixed the femur has to rotate outwards, which is 
 prevented by the lig. ilio-femorale. 6. There is no need of fixing 
 the knee-joint laterally, as this is sufficiently insured by the 
 hingelike nature of the joint (lig. lateralia). c. Eotation on the 
 fore-leg during extension is prevented by the crucial ligaments, 
 as described before, p. 294. 
 
 5. The ankle-joint. The centre of gravity of the whole 
 body (neglecting the feet) lies approximately in the promontory 
 of the sacrum ; the line of gravity will therefore pass a little in 
 front of the line connecting the axes of both ankle-joints, and 
 hence the falling forward of the body has to be provided 
 against. This can be done, a, by the axes of the two ankle-joints 
 forming an angle with each other, so that the simultaneous rota- 
 tion round both is impossible without a change of position (sepa- 
 ration) of the lower extremities ; 6, by the posterior and smaller 
 part of the pulley-like articulating surface of the astragalus 
 becoming wedged into the fork-like surface formed by the two 
 malleoli, which, when the leg is extended, is so narrow as not to 
 be able to receive the anterior and wider part of the trochlear 
 surface of the astragalus (which would be necessary for the 
 falling forward) ; this wedging in between the malleoli is 
 brought about by a rotation of the tibia round the fibula, which 
 
THE SITTING POSTURE. 290 
 
 accompanies the final act of every extension of the leg, 1 whereby 
 the fork-like cavity on the articular surface of tibia and fibula is 
 so turned as to grasp the trochlear surface of the astragalus 
 obliquely, c. By the contraction and tension of the flexors of 
 the foot (in the anatomical sense), the muscles attached to- 
 the tendo Achillis, tibialis post., peronei post,, etc. 
 
 6. The small joints of the foot. The tarsal and metatarsal 
 bones form an arch, on the highest point (caput astragali) of 
 which the weight of the body acts, and which rests with three- 
 points on the floor, viz. with the tuber calcanei (heel) and with 
 the capitula of the first and fifth metatarsal bones (the ball of 
 the big and of the little toe). This arch, which the weight of 
 the body tends to flatten, is chiefly maintained by the tension of 
 the ligaments on the plantar side of the foot ; only when these 
 ligaments are rendered pathologically lax, does the arch yield 
 (flat foot). 
 
 The toes do not serve any purposes for support in the erect 
 posture, but are of use in maintaining the balance, particularly 
 in walking. ' Standing on tip-toe ' is likewise only the balancing 
 of the body on the capitula of the metatarsal bones, while the 
 ankle-joint is extended (in the vulgar sense) and the trunk so- 
 much arched forward, that its line of gravity falls within the 
 line of support. 
 
 The Sitting Posture. 
 
 In sitting, the trunk rests on the two tubera ischii like on 
 the rockers of a rocking-horse (H. Meyer), and it can therefore 
 swing forward and backward ; we thus distinguish between 
 an anterior and posterior sitting posture, according as the line 
 of gravity falls either in front of or behind the line connecting the 
 two resting points of the tubera ischii. In the anterior sitting 
 posture the trunk is prevented from falling forward, a, by 
 supporting it (resting the elbows on the table, etc.) ; b, by fixing: 
 it against the lower extremities, by putting the feet on the 
 ground or supporting the thigh on the anterior border of the 
 chair ; the fixing is chiefly carried out by the extensors of the 
 thigh. In the posterior sitting posture the trunk must rest 
 
 1 This rotation is due to the form of the knee-joint, for with every extension 
 the two condyles of the femur roll forward on the articular surface of the tibia 
 in the manner of a wheel, though not to the same extent. 
 
300 WALKING. RUNNING. 
 
 against a posterior support, either with the back (high-backed 
 chair) or with the lumbo-sacral region (low-backed chair), but 
 the equilibrium can also be sustained without a support, in 
 which case the point of the sacrum forms the third point of 
 support. Lastly, by stretching the legs forward and fixing the 
 trunk against them by muscular exertion, a position may be 
 found, in which the centre of gravity of the whole is moved 
 forward to such an extent that the feet form the third point of 
 .support ; when, in this position, the trunk is moved slightly 
 backward, the feet will leave the floor. 
 
 Walking. Running. 
 
 In walking, the pelvis (and with it the trunk) is rhythmically 
 and alternately supported by one of the two legs (the active 
 leg) and dragged forward a certain distance (the length of 
 step), while the other (the passive) leg merely hangs on the 
 pelvis. At the commencement of a step the leg which is to be 
 the active leg during this step is placed vertically (slightly 
 flexed, see below), and forms one of the two sides of a rectan- 
 gular triangle, the hypothenuse of which is formed by the pas- 
 sive leg, stretched out behind and touching the floor only with 
 the toes, while the line joining the feet on the floor forms the 
 third side. The active leg now passes forward carrying the 
 pelvis with it from its vertical position into an oblique (hypo- 
 thenuse) position, but as the pelvis is to be moved horizon- 
 tally forward, the active leg must necessarily be lengthened, 
 and this is brought about by the extension of the leg (which 
 we saw at the beginning was slightly flexed) in all its joints : 
 the extension of the foot causes the heel to be lifted from the 
 floor, whereby the point of support also moves to the capitula 
 of the metatarsal bones, but these also are in their turn lifted 
 from the floor, so that the leg only touches the floor with the 
 extremity of the big toe ; the foot is thus as it were raised 
 from the floor like a chain, its separate joints being succes- 
 sively lifted from the floor. The active leg now occupies the 
 same position in relation to the trunk as the passive leg did at 
 the commencement of the step. Now the passive leg, which 
 of course was the active leg of the step immediately preceding, 
 leaves the floor at the commencement of the step and describes a 
 
WALKING. RUNNING. 301 
 
 pendulum oscillation forward around its pelvic point of suspension, 
 which brings the foot of the passive leg just as far in advance 
 of the active leg as it was behind it at the commencement of 
 the step (namely, the length of a step) ; the foot is now put 
 down and comes to be just vertically under the pelvis, which in 
 the meantime has been carried horizontally forward by the 
 active leg, as we saw. (In order not to touch the floor while 
 swinging forward, the passive leg is somewhat shortened by 
 being flexed.) During the step the active leg has thus passed 
 from its original position (that of one of the two sides) to the 
 position of the hypothenuse of the rectangular triangle, the 
 passive has moved from the hypothenuse position into that of 
 one of the two sides of the triangle ; the triangle is moved for- 
 ward the length of one step ; the passive leg has swung forward 
 the length of the step, while the active leg has kept its position ; 
 both legs now change their c part,' that leg which had been the- 
 active becomes the passive leg and commences its oscillations^ 
 while the passive leg, after being put down on the floor, com- 
 mences its series of extensions, etc. 
 
 The rapidity of walking will therefore depend : 1, on the 
 length of the step ; 2, on the duration of the step, which is 
 composed of the duration of the pendulum oscillation and the- 
 interval between its termination and the commencement of the- 
 next, or, in other words, the length of time during which both 
 feet rest on the floor. 1. The length of step, considered as one 
 of the two sides of the rectangular triangle, is the greater, the- 
 greater the difference between the hypothenuse and the other 
 of the two sides of the triangle ; therefore, a, the smaller, i.e. 
 the more flexed the active leg is at the commencement of the- 
 step, or the lower the pelvis is carried ; 6, the greater is the dif- 
 ference in length between the leg totally stretched (or totally 
 lifted from the floor) (passive leg) and the leg planted vertically, 
 or, in other words, the longer are the leg and foot long persons 
 therefore take longer steps than short persons : 2. a. The pen- 
 dulum oscillation is, according to known laws, the quicker the 
 shorter the swinging leg is ; the elongation (length of step) is. 
 likewise to be taken into account, for the angle of elongation 
 here is relatively large. 6. The interval of time during which 
 both feet rest on the floor, can be shortened at will, and in very 
 quick walking is = ; the extended foot therefore leaves the floor 
 
302 VOICE. 
 
 exactly at the moment in which the other after being swung for- 
 ward touches it. 
 
 A still greater velocity is obtained in the act of running, 
 where there is an interval in the period of the step during 
 which both feet are off the ground the one (the extended) 
 leg has already begun to swing forward before the other has 
 finished its oscillation. The only thing essential here is that the 
 pelvis should swing forward with sufficient velocity, so as to be 
 prevented from falling during the time it is suspended in the 
 4iir ; this is effected by having the active leg at the commence- 
 ment of the step strongly flexed, and stretching it with great, 
 as it were, jerking velocity. 
 
 We cannot consider here the different varieties of walking and running 
 .and the necessary phenomena thereby observed (W. and E. Weber, II. 
 Meyer), part of which are deducible from what is stated above. 
 
 Voice and Speech. 
 
 The stream of air which passes through the larynx and the 
 cavities of the pharynx, mouth, and nose during expiration (and 
 in exceptional cases during inspiration also), is made use of in 
 order to throw into vibration portions of those organs and so to 
 produce sounds and noises. To the sounds thus produced the 
 term ' voice ' is applied ; and both sounds and noises when 
 used as signs for intercommunication are called ' speech.' 
 
 1. Voice. 
 
 The sounds of the voice are produced by the vibration of 
 the lower vocal cords of the larynx, which are stretched out 
 after the fashion of a membranous tongue in the laryngeal tube. 
 The stream of expired air is projected upon them from below ; 
 and the tube into which the vocal cords are fixed formed 
 below ( c windpipe ') by the bronchial tubes, trachea, and larynx, 
 and above (' sounding pipe ') by the larynx, pharynx, buccal and 
 nasal cavities serves, as is the case in reed instruments, partly 
 to modify the sounds and partly to intensify them. 
 
 A compound tone (Klang} has recently been defined by Helmholtz as 
 any auditory sensation produced by periodically regular vibrations. If the 
 vibrations of the air are simple, like those of a pendulum, a ' tone ' is the 
 result. The vibrations producing any complicated regular sound may be 
 resolved by a well-known mathematical law into a number of simple, pen- 
 dular vibrations, having the ratios one to another of 1 : 2 : 3, &c. (Fourier). 
 
VOICE. 303 
 
 This resolution of a sound into its elements may be brought about not only 
 mathematically, but also to a certain extent mechanically, in a manner 
 which will presently be described. Every compound tone may therefore be 
 considered to be an aggregate of simple tones, the numbers of whose vibrations 
 are in the ratio of 1 : 2 : 3, &c. The deepest of these tones is called the 
 1 prime tone,' and the rest ' harmonics.' If the number of vibrations of the 
 prime tone is n, those corresponding with the harmonics are 2n (the octave 
 of the prime tone), 3n (the twelfth of the prime tone), 4ra (the second 
 octave), 5/i (the compound), &c. The number of the partial tones of a tone, 
 and their relative intensity, vary much in different musical sounds, as, e.g., 
 in the sounds produced by different instruments. It often happens that 
 certain of the harmonics are wanting altogether. A musical sound is named 
 after its most prominent partial tone. If any given tone, say A, occurs as the 
 principal tone in different sounds, the latter are described as A accompanied 
 by differences in f timbre ' or ' quality' (Ktanfffarbe). If the vibration of a 
 compound tone be represented by a curve, the latter will be found to differ 
 considerably in form from that of a simple tone; though it frequently approxi- 
 mates in shape to the wave of its prime tone. Hence it used to be said 
 that two ' tones of different timbre,' of equal pitch and intensity, differed 
 from one another in the characters of their representative curves or waves, 
 which were, of course, of the same height and length in each case. 
 
 The resolution of a compound tone into its partial tones is most easily 
 effected by means of resonators (Helmholtz). A simple tone is able to 
 throw into sympathetic vibration almost all bodies which have the power 
 of vibrating an equal number of times per second. Hence, any compound 
 tone is capable of calling into vibration neighbouring bodies whose vibra- 
 tory powers correspond with those of its partial tones; and, moreover, of 
 causing them to vibrate with the relative intensity corresponding to the 
 individual tones into which (according to Fourier's law) the sound may be 
 decomposed. If, therefore, a sound with A as the prime tone were produced 
 in the neighbourhood of a series of such resonators or bodies the vibratory 
 powers of which correspond with the harmonics of the tone A, some of the 
 resonators of the series would resound with varying intensities, while others 
 would not sound at all. The simplest resonators are glass or metal globes 
 of a certain pitch, provided with two openings, one of whicli communicates 
 with one ear of the investigator, while the other ear is stopped. Whenever 
 the tone to which the resonance-globe answers occurs in a sound, it is heard 
 quite loudly by the person whose ear communicates with the globe, while he 
 cannot hear the other partial tones. Just as a compound tone can be 
 analysed into its partial tones, it is possible in a similar manner to build 
 up a sound from its component parts. The methods of producing and com- 
 bining simple tones will be explained in the section on speech. 
 
 In like manner the sounds produced by the larynx and analogous reed- 
 pipes consist of prime tones and harmonics. The former are very marked, 
 but as many as six or eight harmonics may be detected by the above method 
 of analysis. In the following section, whenever the tones of the larynx and 
 their pitch are spoken of, it must be understood that the prime tones are 
 referred to. 
 
304 REEDS AND REED-PIPES. 
 
 Sounds of Reeds and Reed-pipes. 
 
 The -word ( tongue ' or 'reed ' is used in acoustics to denote an elastic 
 plate which, when at rest, nearly closes an opening, but which is so ar- 
 ranged that every excursion from the position of rest tends to increase the 
 space between its edge and that of the opening. If a sufficiently powerful 
 blast of air be blown upon the opening, the ' tongue ' or ' reed,' as is easily 
 seen, is thrown into vibration. That is to say, the space between the 
 border of the opening and the edge of the plate, while the latter is at rest, is 
 so narrow, that the stream of air is not able to pass through it in that con- 
 dition, but experiences an obstruction. In consequence of this, the air accu- 
 mulates behind the tongue, and presses upon it with a force which gradually 
 increases, until a point is reached at which the elastic plate is forced out of 
 position. This gives a passage to the accumulated air, which rushes through: 
 violently, and so reduces the pressure behind the tongue that the latter falls 
 back into its former position j whereupon the whole action is repeated. By 
 this means a continuous stream of air is converted into an intermittent or 
 rather a varying current, and the tongue thrown into vibrations. The 
 sound resulting is really produced by the vibrations of the air (as in the 
 instrument called the Siren) and not by those of the tongue (Helmholtz). 
 The tongue may consist either of a firm elastic plate fixed at one side, as is 
 the case in many musical reed instruments, or of an elastic membrane (mem- 
 branous tongue) stretched over the opening. If of the latter kind, the mem- 
 brane may be so fixed as to leave spaces at both sides, or it may completely 
 cover the opening, with the exception of a slit in the centre. The larynx, 
 with its vocal cords and glottis, answers to the last-mentioned description. 
 
 The pitch of the note given out by a tongue vibrating under the in- 
 fluence of a current of air (i.e. the number of vibrations per second necessary to 
 produce it) depends upon the time of vibration of the plate itself, as by 
 that is determined the frequency of the impact of the air. The time of 
 vibration of the plate varies inversely as its length and directly as the 
 square root of its elasticity, and therefore, in the case of stretched mem- 
 branes, directly as the square root of the extending force, just as in the case 
 of an extended string. In the case of membranous tongues, a third in- 
 fluence must be added, viz. that of the violence of the impinging blast of 
 air, which has no effect upon the pitch of notes caused by the vibration of 
 the usual firm tongue. The note is not simply intensified by increasing the 
 strength of the blast, but its pitch is raised (J. Miiller). This is explained 
 by the consideration that the tension of the membrane is also at the same 
 time increased ; for the middle position about which the tongue vibrates 
 deviates further from the position of rest with a strong than with a weak 
 blast; and this greater deviation increases the tension of membranous 
 tongues, as is evident, while it does not affect the elasticity of firm plates, 
 in so far as that property is concerned in the vibrations. The law of this 
 increase in pitch as the blast becomes stronger has not yet been determined. 
 The form and size of the slit only affects the note to the extent that, with 
 the same expenditure of energy, the narrower the slit the greater the accu- 
 
LARYNX. 305 
 
 mulation of air behind the tongue, the greater the pressure upon the 
 latter, and, in consequence, the stronger the blast it is possible to obtain. 
 
 If the tongue is fixed into a pipe (reed-pipe) that portion of it which 
 conveys air to the tongue is called the wind-pipe, while that which is beyond 
 the tongue is called the sound-pipe. In general the effect of the sound-pipe 
 may be said to be to add its own proper tone to the sound produced by the 
 vibrating tongue, and to intensify certain of the component tones of the 
 latter. By intensifying one of the harmonics the pitch of the resulting 
 sound is apparently raised, as the intensified tone becomes prominent as the 
 principal tone. On the contrary, if the primary tone of the sound-pipe is 
 deeper than that produced by the tongue, an apparent diminution of pitch 
 may result. The sound~pipe of the vocal organ has this effect only to a 
 slight extent, the timbre, or sound-colour, of the voice being but slightly, 
 though clearly, modified by it (see below, Vowels), and the principal tone of 
 the sound produced in the larynx remaining the same. 
 
 The Larynx. 
 
 In the larynx the membranous tongue is formed by two 
 horizontal membranous plates, the inferior vocal cords, which 
 extend between the inner surface of the thyroid cartilage 
 and the anterior and external surfaces of the arytsenoid carti- 
 lages, and are covered by the laryngeal mucous membrane, 
 which is here provided with pavement epithelium. The 
 slit between them (glottis vocalis) is continuous posteriorly 
 with the interspace between the interior surfaces of the two 
 arytsenoid cartilages (glottis respiratoria). The thyroid and 
 arytsenoid cartilages are so fixed to the cricoid cartilage as to 
 admit of a certain degree of movement. The former, the 
 thyroid cartilage, turns about a horizontal transverse axis in 
 such a manner that its anterior portion approaches or recedes 
 from the anterior portion of the cricoid. The effect of this 
 movement is to increase or diminish the angle of inclination of 
 the thyroid with the vertical, and, in consequence, to move its 
 superior portion, to which the vocal cords are affixed, forwards or 
 backwards. The arytsenoid cartilages turn principally about 
 their long vertical axes, the effect of which is, as they are 
 pyramids with triangular bases, to cause their edges to occupy 
 different positions, and thus to alter the shape of the slit. 
 From what has been just said it is clear that the thyroid carti- 
 lage influences, especially by its position, the length and tension 
 of the vocal cords. The thyroid cartilage may therefore, with 
 regard to the vocal cords, be fitly styled the 4 cartilage of ex- 
 
 x 
 
306 LARYNGEAL MUSCLES. 
 
 tension,' the cricoid the c basement cartilage,' and the arytsenoid 
 the 'cartilage of position ' (Ludwig). 
 
 The following are the muscles which govern the relative 
 positions of those cartilages with which the vocal cords are con- 
 nected : 
 
 1. The crico-thyroidei approximate the thyroid to the 
 cricoid cartilage, rotating the former about its axis in a forward 
 and downward direction, and thus pulling the upper portion of 
 the cartilage forward, and extending the vocal cords when the 
 arytsenoid cartilages are firmly fixed. 
 
 2. The thyro-arytcenoidei, which run for the most part 
 within the vocal cords, rotate the thyroid cartilage in a direc- 
 tion upwards and backwards towards the arytsenoid cartilages, 
 and therefore render less tense the vocal cords. Some of their 
 fibres arise from points of the vocal cords themselves, and must 
 therefore, on contraction, confer different degrees of tension 
 upon different parts of the vocal cord ; for only that portion 
 will be rendered lax in which the contracting fibres run, while 
 the rest will be kept tense. As, moreover, a portion of the 
 fibres are attached about the external edge of the arytsenoid 
 cartilage, the effect of contraction must be to press together the 
 anterior internal edges (processus vocales) of the opposing carti- 
 lages, and to separate their posterior internal edges, the result 
 being that the glottis vocalis is narrowed to a small slit, while 
 the glottis respiratoria is increased to a triangular space. 
 
 3. The crico-arytcenoidei postici drag the external edges of 
 the arytsenoid cartilages, to the lower extremities of which 
 (processus musculares) they are attached, backwards and down- 
 wards, thus at the same time rotating outwards the anterior 
 internal edges (processus vocales), separating them slightly 
 above, and approximating the posterior edges. The effect of 
 this movement is to convert both the glottis vocalis and the 
 glottis respiratoria into triangular spaces, which together form 
 a wide rhombic aperture. 
 
 4. The crico-arytcenoidei laterales drag the muscular pro- 
 cesses of the arytsenoid cartilages downwards, forwards, and 
 outwards, whereby the apices of the two pyramids are somewhat 
 separated one from the other, while the bodies of the latter are 
 so rotated as to occupy the position they take up on contrac- 
 tion of the thyro-arytsenoidei muscles, with the exception that 
 
VOICE. 307 
 
 the processus vocales are not so closely applied one to the 
 other. 
 
 5. Arytcenoidei proprii (inter-arytgenoidei, transversus et 
 obliqui) approximate the apices of the pyramids and their pos- 
 terior edges one to the other. If they act in concert with the 
 thyro-arytsenoid muscles, both glottis vocalis and glottis re- 
 spiratoria are closed, and respiration completely interrupted, as, 
 e.g. immediately before coughing. 
 
 The ventricles of Morgagni give the vocal cords free space in which to 
 vibrate, a provision especially necessary when the vocal cords are much 
 arched by the strength of the impinging blast of air. The superior vocal 
 cords do not appear to play any part in the production of voice. It has cer- 
 tainty been observed that a diminution in the calibre of the sound-pipe above 
 the tongue of a reed instrument raises the pitch of the note produced (J. 
 Miiller) ; but experiment has shown that the excised lar} r nx constantly gives 
 the same note whether the upper vocal cords be present or not. In birds 
 the vocal cords are not, as a rule, concerned in the production of notes, the 
 latter being the function of the ( inferior larynx/ a characteristic organ 
 situated in the majority of cases at the point of division of the trachea. 
 
 The larynx receives its supply of motor nerves from the inferior laryn- 
 geal branch of the vagus, paralysis of which occasions loss of voice. The 
 superior laryngeal branch of the vagus is considered to supply the crico- 
 thyroid muscle only; but this is denied by some authorities (Nawratil). 
 
 Sounds produced by the Vocal Organs. 
 
 The general conditions necessary for the production and 
 alteration of sounds will easily be perceived from what has 
 already been said concerning reeds and reed-pipes. In general 
 there is necessary a blast of air of a certain strength, the pro- 
 duction of which requires the closure of the glottis respiratoria 
 and the narrowing of the glottis vocalis. These actions are 
 effected by the contraction of the crico-arytsenoidei laterales or 
 of the thyro-arytsenoidei. During the contraction of the crico- 
 arytsenoidei postici the production of voice is impossible. 
 From what has been said above, it is moreover evident that the 
 pitch of the note sounded depends upon the length and tension 
 of the vocal cords, and upon the strength of the blast. It 
 is, on the contrary, independent of the shape of the glottis, 
 which only varies in accordance with the strength of the blast, 
 being narrower in the production of a stronger blast. The pitch 
 is also independent of the form and length of the wind-pipe 
 and sound-pipe in the case of the larynx. It may therefore be 
 
 x 2 
 
308 VOICE. 
 
 stated that the pitch of the note rises: 1. With increasing- 
 tension of the vocal cords, which is induced (a) by the contrac- 
 tion of the crico-thyroidei (perceptible externally to the touch); 
 (6) by the relaxation of the whole of the thyro-arytsenoidei ; 
 (c) by increased violence of blast (p. 304) of which use i& 
 chiefly made in the production of the highest notes, which can 
 therefore only be rendered forte and not piano. In order to 
 produce the strongest blast of air through the larynx, the glottis 
 vocalis must be made as narrow as possible, and the glottis re- 
 spiratoria completely closed, the latter action being effected by 
 the arytaenoidei proprii. On the contrary, the tenser the vocal 
 cords the stronger must be the blast of air necessary to cause 
 them to vibrate ; and, in consequence, the greater must be the 
 atmospheric pressure in the trachea, as may be proved by 
 means of a manometer fixed into a tracheal fistula (Cagniard- 
 Latour). The pitch of the note also rises (2) according as the 
 length of the portion of the vocal cord set vibrating diminishes. 
 The latter is brought about without at the same time disturb- 
 ing the tension, (a) by partial contraction of the thyro-arytse- 
 noidei (p. 306); (fr) by the close apposition of the processus 
 vocales of the arytsenoid cartilages, whereby the portions of the 
 vocal cords in which the cartilages are placed are prevented 
 from vibrating ; (c) in larynges of small dimensions, especially 
 in those of women and children, the general range of pitch is 
 higher on account of the shortness of the cords. All the above 
 statements are based upon observations which have, in addition^ 
 taught us that as the pitch of the note increases the superior 
 vocal cords approach nearer and nearer to one another without 
 ever completely closing the orifice between them, and that the 
 epiglottis falls more and more over the opening into the larynx 
 (Garcia). Moreover, as the pitch increases the larynx rises, 
 owing partly to the contraction of the elevators of the larynx, 
 and partly, in all probability, to the extension of the trachea 
 under the increasing pressure of the air within. In spite of 
 the apparent simplicity of the arrangements, the process of the 
 production of voice must be extremely complicated. For ex- 
 ample, with a given arrangement of the vocal cords any increase 
 in the force of the blast not only intensifies the note, but also 
 raises it ; as, however, we may require to sustain the same note 
 with a varying intensity (piano sand forte), in order to do so a- 
 
VOICE. 309 
 
 continual process of compensation must be J kept up by the 
 muscles. 
 
 In conducting observations on the production of voice in the larynx the 
 following methods are practicable : 1. Palpation and auscultation of the 
 larynx from without. 2. Direct observation of the interior of the larynx by 
 means of a laryngoscope (Garcia, Czermak, Tiirck). The latter instrument 
 consists of a small mirror, \vhich is held, by means of a handle, at an angle of 
 45, over the opening of the larynx and in front of the velum palati, having 
 been previously warmed to prevent the condensation of vapour upon it. 
 Concentrated light is thrown upon this small mirror by means of another 
 concave mirror provided with an aperture to which the eye of the observer 
 is applied. The mouth of the patient is opened wide and the tongue pulled 
 forward. By the arrangement of mirrors the top of the larynx is seen 
 strongly illuminated. 3. Observation of the larynx of a living animal exposed 
 from above. 4. Experiments with the excised larynges of human bodies 
 (J. Miiller). The action of the muscles is imitated by passing threads to 
 which weights are hung over pulleys, and attaching them to the points of 
 insertion of the muscles they are to represent, pulleys and larynx being 
 fixed to a stand. The blast of air is transmitted through a tube fastened 
 into the trachea either from the lungs of the experimenter or from a pair of 
 bellows. In order to measure the pressure of the air in the trachea, a mano- 
 meter is connected laterally with the tube, which is continuous with the 
 trachea. To study the effect of the sound-pipe, the larynx is left attached to 
 the head. Experiments with the larynges of dead subjects have led to 
 many results inconsistent with the appearances of the living larynx, some of 
 which are still unexplained, and which indicate our lack of knowledge re- 
 specting the actions of the latter. 5. Experiments with artificial larjnges 
 (J. Miiller) ; to this class of experiments belong, generally, all experiments 
 with reed-pipes. 
 
 A greater height of pitch than can be attained by the 
 ordinary method of production of voice is possible by means of 
 the so-called ' falsetto voice.' This is another register, another 
 method of producing voice, which is specially suitable for the 
 higher notes, and which differs from the usual method in a 
 manner which is not yet thoroughly understood. Besides the 
 superior pitch of the ' falsetto notes,' they differ essentially in 
 timbre or tone-colour from those ordinarily produced. It has 
 been observed that the glottis vocalis during the emission of 
 falsetto notes is wider than in the formation of the ordinary 
 voice ; and that the superior vocal cords are also farther apart. 
 It is further maintained that the true vocal cords do not 
 vibrate in such an extent of their breadth (in fact only at their 
 edges) in the former case as in the latter (J. Miiller, Lehfeldt), 
 
310 VOICE. 
 
 owing, according to Mandl, to the partial imposition upon 
 them of the superior vocal cords. Others state exactly the 
 reverse of this, viz. that a greater breadth of the vocal cords is 
 in vibration during the utterance of falsetto notes (Garcia), 
 It is, finally, probable that an extreme tension of the vocal 
 cords is necessary for their production, as is indicated by the 
 sense of exertion in the larynx under those circumstances. 
 Owing to the greater width of the glottis vocalis during the 
 use of falsetto, the air in the lungs is quickly exhausted, in 
 consequence of which it is impossible to sustain a falsetto 
 note as long as an ordinary one. Another distinction between 
 notes of the two registers, and one which depends upon the 
 circumstance last mentioned, originates in the resonance of 
 the wind-pipe and sound-pipe in the two cases; this will be 
 referred to below. 
 
 As was said previously, the form and length of the wind- 
 and sound-pipes have no influence in the case of the larynx 
 upon the pitch of the notes. They serve, however, to intensify 
 them, and also to modify them, inasmuch as the tones to 
 which they gave origin intensify certain of the harmonics 
 of the voice, and so regulate the timbre, which forms such 
 an essential distinction in the voices of different individuals. 
 By means of voluntary alterations in the form of the sound-pipe 
 the latter may be made to give rise to special tones and noises 
 which are essential to speech (see below). Owing to the ac- 
 cumulation of mucus, &c. in various parts of the windpipe, or 
 about the vocal cords themselves, other noises may be pro- 
 duced, which are unnecessary, or even detrimental to perfect 
 speech. In the production of ordinary voice, resonance is 
 strongest in the windpipe, as it contains the air which is being 
 compressed through the narrow slit of the glottis vocalis. The 
 bronchial tubes and the parietes of the chest therefore enter 
 strongly into resonance, and give rise to a trembling motion 
 (fremitus pectoralis). Hence, ordinary full and powerful voice 
 is called ' chest-voice.' In the production of falsetto notes, on 
 the contrary, no resonance of the chest takes place, owing to 
 the greater width of the glottis vocalis, the sound-pipe, and 
 the cavities of the nose and mouth being the chief seats of 
 resonance. 
 
 The compass of the chest-voice when the vocal organs are 
 
VOICE. SPEECH. 311 
 
 fully developed, ranges from about two to two and a half 
 octaves ; but the limits vary with the size of the larynx. The 
 general range of voice is lowest in men and highest in women 
 and children. Thus the bass as a rule extends from E (80 
 vibrations per second) to f (342); the tenor from c (128) to 
 c" (512) ; the alto from/ (171) to /" (684) ; and the soprano 
 from c' (256) to c" f (1024). The complete compass, therefore, 
 of the human voice ranges from about E (80 vibrations per 
 second) to c'" (1024 vibrations per second), nearly four 
 octaves. The range from c' (256) to f (342) is common to all 
 voices ; but the character of the notes varies in different in- 
 dividuals, according to the timbre or 'colour' they acquire 
 from the larynx. In many cases the limits here set down are 
 exceeded. 
 
 The development of the larynx bears a definite relationship to that of 
 the sexual powers. At the commencement of puberty there is a sudden in- 
 crease in its size, and the alto or soprano (treble-voice) of the boy changes into 
 the bass or tenor of the man. This is what is commonly known as the 
 ' breaking ' of the voice. In castrated individuals, and in cases of hypo- 
 spadias, &c., the voice remains abnormally high, higher even than the 
 soprano of women. 
 
 2. Speech. 
 
 Speech consists of certain tones and sounds which the ex- 
 pired air produces in the cavities above the larynx, and which 
 are used for the purposes of speech, either alone as in whis- 
 pering or in conjunction with the sounds of the voice as in 
 speaking aloud. 
 
 The elements, the sequent arrangement of which consti- 
 tutes speech, are called articulate sounds, and are divided into 
 vowels and consonants. The distinction, which was formerly 
 described as existing between these two classes, viz. that the 
 consonants are those articulate sounds which cannot be uttered 
 without the aid of vowels, cannot now be held. Both conso- 
 nants and vowels are now regarded as being capable of utter- 
 ance alone, if we except that certain of the former lose some- 
 what of their characteristics (see below). The true distinction 
 between them is, that the consonants are indefinable sounds, 
 while vowels have rather the character of tones. That is 
 to say, when whispered, the latter are sounds produced in the 
 
312 SPEECH. VOICE. 
 
 cavity of the mouth, in which a tone predominates whose 
 pitch may be determined, and when spoken aloud they are 
 modifications of the voice caused by the intensification of in- 
 dividual harmonics by the c proper ' tone of the buccal cavity 
 at the time. 
 
 Vowels. 
 
 1. In whispering, vowels are produced by expelling a 
 current of air through the cavity of the mouth, the shape of 
 the latter being different for each vowel. Sounds are thus pro- 
 duced in which, by a careful examination, and especially on 
 comparing the various vowels, tones of definite pitch may be 
 distinguished. For the same vowels the same tones are found 
 to be remarkably constant in persons of varying age and sex ; 
 and they may be determined by means of the piano (Bonders). 
 These tones are the characteristic tones of the cavity through 
 which the current of air passes. They may be still better 
 determined by means of resonators in the following manner. 
 Tuning-forks are set vibrating, and successively placed in 
 front of the mouth, which is arranged as if for the production 
 of a certain vowel ; as soon as a tuning-fork is thus placed, the 
 prime tone of which is in unison with that of he buccal 
 cavity, the tone emitted is intensified by resonance, and ren- 
 dered more audible (Helmholtz). The form of the cavity of 
 the mouth during the production of the vowel sounds U 1 and 
 0, is that of a globular flask with a short neck ; during the 
 production of A, that of a funnel with the wide extremity di- 
 rected forward ; of E and I, that of a globular flask with a 
 long narrow neck, &c. Corresponding with the characteristic 
 tones of such bodies, the tones of the cavity of the mouth are : 
 
 for U / 
 
 0-6' 
 
 A ft" 
 
 E -f and V" \ one tone for the body of the 
 
 !_/ (?) and d"" J flask, the other for the neck 
 
 1 The vowel-sounds referred to here are those of the German language : 
 
 a like a in father 
 e ,, e ,, hen 
 i i fish 
 o o open 
 u oo ooze 
 
PRODUCTION OF VOWEL-SOUNDS. 313 
 
 (Helmholtz). Slight modifications of pronunciation materially 
 affect the tone. The constant occurrence of the same charac- 
 teristic tone for the same vowel in buccal cavities of different 
 sizes is accounted for by the proportionate alteration in the 
 orifice of the mouth* 
 
 According to more recent researches (Konig) the characteristic tones of 
 the various vowels are : 
 
 for U 6 
 
 A-ft" 
 E V" 
 n !_&"" 
 
 The various forms of the buccal cavity are brought about in 
 the following manner. In the production of all the vowels, if 
 the buccal cavity alone is to be used the passage of the current 
 of air to the nasal cavities is prevented by the raising of the 
 soft palate. If this is not done the vowels have, when spoken 
 aloud, a ' nasal ' character. This elevation of the soft palate 
 is least complete during the production of A, becoming more 
 and more so in the case of the other vowels in the following 
 order: E, 0, U, I. The various flask-like arrangements of 
 the mouth are thus produced : in A the cavity of the mouth is 
 largest, owing to the position of the tongue along the floor, the 
 mouth being wide-open (funnel-shaped). In and U the glo- 
 bular flask is produced by the elevation of the root of the 
 tongue, and the contraction of the aperture of the mouth into 
 a round opening which is narrower in the case of U than of 0. 
 In E, I, the long neck of the flask is produced by approximat- 
 ing the tongue to the hard palate, &c. In sounding all the 
 vowels except U the larynx moves upwards somewhat, least of 
 all in the case of 0, and more so in the cases of the others in 
 the following order, A, E, I. 
 
 2. In speaking aloud, vowels result from the intensification 
 of various of the harmonics of the voice by means of the reson- 
 ance of the buccal cavity (Wheatstone, Helmholtz). Hence it 
 follows that vowels may be best sung with those notes which 
 have a prominent harmonic agreeing with the ' proper ' tone 
 of the cavity of the mouth ; further, that the individual 
 vowel-sounds are not distinguished by the peculiar arrangement 
 of the intensified harmonics, but by their absolute height. 
 
314 ANALYSIS OF VOWEL-SOUNDS. CONSONANTS. 
 
 The vowel-sounds may easily be analysed by means of the resonance^- 
 apparatus mentioned on p. 303. The analysis is more exact if made by 
 means of a phonautograph (Bonders), in which a tense membrane is allowed 
 to take up the vibrations of a particular vowel-sound and to trace them upon 
 a rotating cylinder. In order to reproduce a vowel-sound synthetically, all 
 that is necessary is to raise the clamper from the strings of a piano and to 
 sing the vowel in a clear, loud voice in front of the instrument. Under 
 such circumstances all the strings the tones of which exist in the vowel- 
 sound as harmonics, are called into vibration (p. 302), and to a degree of 
 intensity corresponding with the intensity of the harmonics. The vowel, 
 therefore, resounds from the instrument, not simply as a tone, but as a vowel 
 (Helmholtz). The direct synthesis out of simple tones is still more instruc- 
 tive. A number of tuning-forks corresponding in pitch with the various 
 harmonics of a primary tone (e.g. B, 6, /, V, d",f, as", I", d'", *"',/", V") 
 are set vibrating by means of electro-magnets, which are so arranged that 
 the current passing round them is opened and closed by the vibrations of a 
 special tuning-fork fitted up on the principle of Wagner's hammer. The 
 tones of the tuning-forks are rendered inaudible by placing them upon 
 caoutchouc. Before each fork, however, stands a resonance-tube tuned 
 to the prime tone of the fork. When the tube is open, it renders audible 
 the prime tone of the tuning-fork a simple tone, therefore. With this 
 apparatus it is possible, by opening the resonance tube more or less perfectly 
 by means of keys, to sound and combine at will strong or weak individual 
 tones. In this way not only vowels, but also the characteristic sounds of 
 various instruments, may be synthetically represented. The same result may 
 more simply be effected by means of reed-pipes, which yield simple tones 
 (Helmholtz). 
 
 Diphthongs are produced during the transition from the 
 form of mouth necessary for the one vowel to that necessary for 
 the other. They consist of two sounds following quickly one 
 upon the other. 
 
 Consonants. 
 
 The articulate sounds called consonants are sounds produced 
 by the vibrations of certain easily movable portions of the 
 throat and mouth ; and they have a different sound according 
 as they are accompanied by voice or not. The pharyngo- 
 buccal canal is capable of constriction or interruption at three 
 places, at each of which vibrations may be produced ; these are : 
 1. At the lips, the constriction being formed by the two lips, 
 or by the upper (or lower) lip with the lower (or upper) row of 
 teeth. 2. Between the tongue and the palate, the constriction 
 being brought about by the apposition of the tip of the tongue 
 to the anterior portion of the hard palate, or the posterior sur- 
 
CLASSIFICATION OF CONSONANTS. 315 
 
 face of the upper row of teeth. 3. At the fauces, the constric- 
 tion being due to the approximation of the root of the tongue 
 and the soft palate. Sounds may originate at each of these 
 places of interruption ; and hence consonants may be classified 
 into three series, viz. labial, dental, and guttural consonants. 
 
 The sounds which may be formed at each of the places of 
 interruption are (Briicke) : 
 
 1. EXPLOSIVES. These are produced by suddenly opening or 
 closing the passage at one of the points mentioned during the 
 expulsion of air : a, without the aid of voice, P, T, K ; 6, with 
 the aid of voice, B, D, Gr. 
 
 Opening of the passage is necessary for the formation of one of these- 
 consonants when it begins a syllable ; closure when it ends one (e.g. pa, p)- 
 As P, T, and Kare distinguishable from B, D, and G respectively only by the 
 absence or presence of the voice, no sharp distinction is possible between 
 them during whispering. 
 
 2. ASPIKATES. The passage is constricted at one of the 
 above-mentioned points to a small slit through which the cur- 
 rent of expired (or inspired) air can rush. Hence arise the 
 following consonants : a, without the aid of voice, F, S (sharp), 
 Oh (guttural) ; 6, with the aid of voice, V, Z, J (as in the 
 German ja, &c.). At the constriction between the tongue and 
 the palate a second aspirate may be formed, in addition to the 
 sharp S, viz. L, by completely closing the passage in front and 
 allowing the air to escape only at the sides between the molar 
 teeth. By forcing air through two narrow spaces situated one 
 behind the other, viz. that between the tip of the tongue and 
 the hard palate, and that between the two rows of teeth, two 
 other sounds may be produced : a, without the aid of the 
 voice, Sh ; 6, with the aid of the voice, Zh. If a space be left 
 between the tip of the tongue and both rows of teeth, the 
 following consonant-sounds are produced : a, without the aid 
 of the voice, Th (hard) as in than ; with the aid of the voice, 
 Th (soft) as in thunder. The guttural Ch may be produced 
 near the front of the mouth as in the German word, ich ; or near 
 the back, as in ach. 
 
 F and V, &c. are distinguished in the same way as P and B, &c. 
 
 3. KESONANTS. The current of air no longer passes through 
 the usual opening, which is closed, but through the nose, which 
 
310 
 
 CLASSIFICATION OF CONSONANTS. 
 
 is left open by the depending soft palate. The aid of the voice 
 is necessary. The consonants thus produced are M, N. 
 
 4. VIBRATORY SOUNDS. There are three varieties of the 
 vibratory K which differ in their place of origin. The first is 
 the labial K, produced by the vibration of the lips, which does 
 not occur as an articulate sound in any European language ; 
 the second is that produced by the vibration of the tip of the 
 tongue in the constricted portion of the buccal cavity formed 
 by the tongue and the teeth ; and the third is the guttural R. 
 In order to produce them the pharyngo-buccal cavity is con- 
 stricted at the necessary point, but not firmly ; and the margins 
 are then set vibrating by the expiration of air. The vibrations 
 are, however, too slow to give forth a definite note. 
 
 The consonants may therefore be grouped in the following- 
 manner : 
 
 
 Labials 
 
 Dentals 
 
 Gutturals 
 
 1. Explosives: 
 
 
 
 
 a. Without the J 
 
 P 
 
 T 
 
 K 
 
 voice . \ 
 
 
 
 
 b. With the voice 
 
 B 
 
 D 
 
 G- 
 
 2. Aspirates: 
 
 
 
 
 a. Without the ) 
 voice . ) 
 
 F 
 
 S (hard), L,Sh,Th (hard) 
 
 Ch (in ' ich ' and ' ach ') 
 
 b. With the voice 
 
 V 
 
 Z, L, Zh, Th (soft) 
 
 J(in'ja') 
 
 3. Resonants 
 
 M 
 
 N 
 
 N (nasal) 
 
 4. Vibratory^ 
 sounds \ 
 
 Labial K 
 
 Lingual R 
 
 Guttural R 
 
 H is the sound produced in the larynx by the quick rushing 
 of the current of air through the widely-opened glottis. 
 
 Compound consonants are produced by suddenly opening 
 the air-passage previously closed for the utterance of P, T, or 
 K, as the case might be, and allowing the current of air to rush 
 through the second of the before-mentioned places of constric- 
 tion narrowed as if for the utterance of S (hard) : thus are pro- 
 duced Ps (Greek ), Ts (German Z), and Ks (X). Other com- 
 pound consonants are formed by the rapid transition from the 
 position of mouth necessary to produce one consonant to that 
 necessary to produce the other. 
 
 Observations upon the movements which take place during the formation 
 of speech are made partly by direct inspection of the cavity of the mouth 
 while the latter is open, and partly by palpation by means of the fingers 
 
OBSERVATIONS ON SPEECH. 
 
 317" 
 
 introduced into the mouth. In order to decide whether the posterior nares 
 are opened or closed at any particular time, a candle-flame, or a bright, cold 
 mirror may be placed in front of the nasal openings on the face. Finally, 
 many of the conditions of speech have been determined by noticing the- 
 mode of utterance in persons suffering from pathological malformations of 
 the vocal organs ; such as absence, or adhesions of the soft palate, &c. 
 
PAET III. 
 
 THE LIBERATING APPARATUS. 
 
 The Nervous System. 
 
 WE have already broadly described in the Introduction (p. 5 
 et seq.~) the arrangement of the liberating apparatus (the nervous 
 system), and its relationships, on the one hand, to the external 
 world, and on the other, to the c organs of work.' From what 
 was there said, it will be seen that the following five groups 
 of organs are to be distinguished in the nervous system : 
 1. Organs by means of which energy is set free in the organs of 
 
 work viz. the nervous end-organs in parenchymatous 
 
 tissues, glands and muscles. 
 *2. Organs which transmit the process of liberation from the 
 
 central nervous organs to those included under group 1 
 
 viz. the centrifugal conducting apparatus. 
 
 3. Central nervous organs. 
 
 4. Organs which transmit the process of liberation originat- 
 
 ing from the external medium, to the central nervous 
 organs viz. the centripetal conducting apparatus. 
 
 5. Organs upon which the movements of the external medium 
 
 first act in order to set in action the processes of liberation 
 which it is the function of the fourth group of organs to 
 transmit viz. the organs of sense. 
 
 For physiological purposes, however, this fivefold division 
 of the nervous system is unnecessary. The centrifugal and 
 centripetal conducting apparatus are un distinguishable one from 
 the other in their characters, and differ only in being connected 
 peripherally with organs which are different (see groups 1 and 5). 
 
320 THE NERVOUS SYSTEM. 
 
 We must therefore distinguish : apparatus for conduction ; 
 central-organs ; sense-organs ; and end-organs situated in the 
 organs of work. The two last-mentioned sets of apparatus may, 
 also, both be regarded as peripheral end-organs of the conduct- 
 ing apparatus, as is done in Chap. X. 
 
321 
 
 CHAPTER IX. 
 THE CONDUCTING APPARATUS (NERVES). 
 
 A. GENERAL PHYSIOLOGY OF NERVES. 
 
 THE elements of a nervous cord are thin, longitudinally striated, 
 fibres, which are arranged side by side into round or flattened 
 bundles (nerves}, and bound together, like the c muscle tubes' 
 of muscle, by means of interspersed connective tissue which ex- 
 tends over the exterior of the bundle as a firm fibrous sheath 
 (perineurium). Each nerve-fibre is a tube filled with partly 
 fluid contents. The thin walls of the tube (the primitive 
 sheath, neurilemmd) consist, as in the sarcolemma of muscles, 
 of an elastic membrane, and are provided with large nuclei. 
 The contents of the tubes are divided into a thin cord running 
 in the axis the axis-cylinder and a shining mass surrounding 
 it the medulla or medullary sheath composed of a substance 
 which easily breaks up. 
 
 The fine nerve-fibres of a certain class do not possess a 
 medullary sheath, and consist simply of an axis- cylinder and a 
 sheath (non-n/iedullated nerve-fibres). A third class of nerve- 
 fibres is characterized by the regular varicose arrangement of 
 the axis-cylinder, and the absence of all signs of a sheath (gray 
 or varicose fibres ; fibres of Remak). 
 
 The distribution of the various classes of nerve-fibres will be 
 discussed in Chap. XI. 
 
 The axis-cylinder is especially well seen after the death of the nerve ; 
 and it has therefore heen considered by many to be a post-mortem contracted 
 coagulum. The greater number of observers, however, regard it as existing 
 during life ; and, indeed, it must be considered to be the most important 
 element of the nerve-tube, as it is connected directly with the essential 
 portions of the central and peripheral nervous end-organs, unless we are pre- 
 pared to regard the latter also as the appearances of coagulation. Many 
 
 T 
 
322 CHEMICAL CONSTITUENTS OF NERVES. 
 
 axis-cylinders, if not all, consist of a bundle of very fine ' nervous fibriHae ' 
 (Max Schultze). An especially delicate species of axis-cylinders (simple 
 nerve-fibrillee, Max Schultze) is discovered in the central nervous organs, 
 forming there intercentral connections between the ganglion-cells (Chap. 
 XI.) ; the thickness of a nerve-fibre depends essentially upon the greater or 
 less thickness of the medullary sheath, which seems to serve the purpose of 
 nourishing the axis-cylinder. Under certain methods of treatment medul- 
 lated nerve-fibres exhibit at definite distances apart annular constrictions at 
 which the medullary sheath is said to be interrupted. As a nucleus of the 
 neurilemma is constantly found between two such constrictions, it would 
 seem as if the appearances were indications of the original formation of a 
 nerve-fibre out of a row of cells, the constrictions corresponding with the 
 divisions between the primitive cells (Ranvier). 
 
 Chemical Constituents of Nerves. 
 
 Scarcely anything is known about the chemical constitution 
 of nerves. The axis-cylinder seems to be related in its characters 
 to the albuminous bodies. The medullary sheath, whose appear- 
 ance and behaviour towards solvents indicate a fatty nature, 
 possibly contains no proper fat, but only lecithin and protagon 
 (pp. 21 and 36). These, however, have only been prepared 
 hitherto from brain-substance, &c., and not from nerve-fibres 
 themselves. Nerve-fibres contain in addition cholestrin and 
 creatine. 
 
 The reaction of fresh nerve in a state of rest is neutral 
 (Funke). The reaction and composition of brain-substance will 
 be discussed in Chap. XI. 
 
 The Various Conditions under which Nerves exist. 
 
 Nerves, like muscles, may exist in three conditions : 1 . The 
 usual condition of Eest. 2. The condition of Death. 3. The 
 condition of Activity. The three conditions cannot, however, 
 in the case of nerves, be distinguished by mere inspection, as 
 the physical properties of the nerves undergo no alteration. 
 
 The mere mechanical properties of nerves have, as a rule, no interest 
 physiologically speaking. Flaccid nerves have a tendency to form fine 
 transverse folds the transverse striae of Fontana. 
 
 Nerves in a State of Rest. 
 
 A certain amount of material exchange occurs in nerves in 
 a state of repose, just as was seen to be the case in muscles, 
 although hitherto neither absorption of oxygen nor formation 
 
DIFFERENT CONDITIONS OF NERVES. IRRITABILITY. 323 
 
 of carbonic acid has been proved to take place. The existence 
 of such processes may, however, be inferred from the fact that 
 nerves contain specific tissue-elements which differ from the 
 constituents of the blood. The extent of the material exchanges 
 occurring in nerves must be very slight, as nerves are almost 
 destitute of blood-vessels ; but nothing more particular is known 
 about them. 
 
 Nerves in a State of Death. 
 
 The death of nerve-tissue is not marked, like that of muscle, 
 by any evident process of coagulation j it is only recognized by 
 the loss of irritability (see below), the appearance of an acid 
 reaction (Funke), and the electro-motor phenomena which will 
 be described hereafter. Dead nerve-tissue undergoes putrefac- 
 tion, just like dead muscle^ if not prevented from doing so by 
 a process of drying. 
 
 Nerves in a State of Activity, 
 
 The active condition is induced in nerves by the same 
 means as in muscles, viz. by some liberating force some 
 stimulus ; and the term ' irritability ' is applied to nerves as 
 to muscles, to indicate this property of being called into 
 activity by the application of a stimulus 
 
 The conditions of irritability and the stimuli, in the case 
 of nerves, agree in many particulars with those of muscles. 
 The irritability of nerves is greater than that of muscles ; that 
 is to say, stimuli which are physically equal (ejj. equal degrees 
 of variation in electric currents which are of the same inten- 
 sity), have a more powerful stimulating: effect when acting 
 upon muscle through; a nerve, than when acting directly upon 
 a muscle deprived of its nervous connections by the action of 
 curare (Kosenthal), > , 
 
 jj 
 
 * ; 
 Irritability* 
 
 Irritability is connected' with the normal constitution of 
 nerves. As, however, our knowledge of the latter is very 
 superficial, it must suffice to establish empirically the condi- 
 tions which increase, diminish, or destroy irritability. In the 
 
 Y 2 
 
324 CONDITIONS AFFECTING NER VO US IRRITABILITY. 
 
 majority of cases the rationale is unknown. The following are 
 the facts connected with this question : 
 
 1. When a nerve ceases to be connected with a living central 
 
 organ, owing, for example, to section of the nerve or 
 death of the central organ, its irritability increases con- 
 siderably at first, but afterwards diminishes and finally 
 disappears. Transverse section of the nerve hastens the 
 process (Rosenthal); which, moreover, takes place more 
 quickly in the central portions of the nerve than in those 
 nearer the periphery (Ritter and Valli's law). A nerve 
 separated from its central organ, but still allowed to 
 remain in the body, subsequently undergoes certain 
 chemical and morphological changes, denominated ' fatty 
 degeneration.' If, however, the cut ends be kept in 
 apposition, they grow together after some time. The 
 presence of oxygen is as little necessary to the mainten- 
 ance of irritability in the case of excised nerves as in that 
 of muscles (Pfliiger and Ewald, p. 243). 
 
 2. Continued repose of a nerve diminishes and destroys its 
 
 irritability, and leads at last to fatty degeneration. 
 Sensory nerves, when cut across, undergo degeneration in 
 both their central and peripheral portions in the former 
 because they can no longer be irritated, in the latter 
 because they are separated from the central nervous organ. 
 
 3. Continued activity of a nerve diminishes its irritability in 
 
 proportion to the time, and may destroy it altogether 
 (Exhaustion). In the former case rest restores the nerve 
 to its original condition. The alterations which take 
 place in nerves during exhaustion have not yet been 
 made out. 
 
 4. Any decided mechanical alteration in the condition of a 
 
 nerve, such as tearing or twisting, destroys its irritability. 
 
 5. Any decided disturbance of chemical composition, such as 
 
 desiccation, treatment with strong alkalies or acids, etc., 
 has the same effect. 
 
 6. The effects of temperature, hitherto studied only on frogs, 
 
 are the following. Temperatures above 45 C. destroy 
 irritability, the more rapidly the higher they are, the de- 
 struction being instantaneous at 70. If the temperature 
 to which the nerve has been subjected have not exceeded 
 
CONDITIONS AFFECTING NER VO US IRRITABILITY. 325 
 
 50, irritability may be restored on cooling (Rosenthal). 
 Below 45, a rise in temperature at first increases, but 
 afterwards diminishes, irritability, the increase being 
 greater and the diminution more rapid according as the 
 temperature is higher. Rise in temperature, therefore, 
 diminishes the duration, while it increases the intensity, 
 of irritability (Afanasieff). A sudden rise of temperature 
 to 35 45 acts as a stimulus (see below). 
 
 7. The effects of electrical currents through nerves appear to 
 be especially important. If a constant galvanic current 
 be passed through a portion of a nerve, its whole length 
 enters into an altered condition (du Bois-Reymond), in 
 which, among other circumstances, its power of being 
 stimulated is modified (Eckhard, Pfliiger). This is called 
 the ' electrotonic ' condition, or ' electrotonus ' (du Bois- 
 Reymond). The condition which obtains in the region 
 of the positive electrode (the Anode) is called ' anelectro- 
 tonus,' and that in the region of the negative electrode 
 (the Cathode), ' catelectrotonus ' (Pfliiger). The constant 
 current which causes this change of condition is called 
 the c polarising ' or ' electrotonising ' current. The 
 boundary between the anelectrotonic and catelectrotonic 
 states, called the c indifferent point ' of the ' intrapolar 
 region,' is situated near to the anode when the polarising 
 current is weak, and moves towards the cathode as the 
 polarising current increases in strength. The influence 
 of electrotonus is strongest in the neighbourhood of the 
 pole. Irritability is increased in the catelectrotonie area 
 and diminished in the anelectrotonic area. Immediately 
 after the cessation of the polarising current the conditions 
 of irritability become reversed in the different regions 
 (irritability being increased near the anode and diminished 
 near the cathode) ; but afterwards they gradually regain 
 the normal (Pfliiger). At the instant of closure of the 
 current, irritability is said to be increased in the whole 
 nerve (Wundt). (Reference should be made in this con- 
 nection to what is said below about Stimuli and the 
 Electrical Phenomena of Nerves.) 
 
 The variations of irritability may be explained, for the sake of illustra- 
 tion, by supposing for the moment that the particles of nerve-matter in 
 
326 STIMULI, ELECTRICAL. 
 
 the anelectrotonic area have a diminished, while those in the catelectrotonic 
 area have an increased, degree of mobility. Variations in irritability are 
 measured either by differences in the degree of contraction produced by 
 stimuli which should be weak; or by variations in the strength of the 
 stimulus, which is just sufficient to induce the slightest contraction. The 
 results so obtained admit of an explanation, to be mentioned below, which 
 does not require the assumption of variation in the degree of irritability. 
 
 The electrotonic variations of irritability may be demonstrated in the 
 case of man also by the application of a constant current (Eulenburg, Erb). 
 To prevent disappointment, however, the test-stimulus must be applied at 
 the points where the current is most dense, as it is only in the immediate 
 neighbourhood of the electrodes that the current passed through the nerve 
 is dense enough to induce the phenomena of electrotonus ; and hence it 
 is that it appears as if there were an anode on each side of the cathode, and a 
 cathode on each side of the anode (Erb). 
 
 Stimuli. 
 
 The stimuli which are able to call a nerve into activity are 
 the following : 
 
 1. Variations in an electrical current. A completely con- 
 stant current flowing through a nerve does not appear to be 
 essentially capable of stimulating the nerve to activity even 
 if apparently so. Every variation, on the contrary, in the 
 intensity of the current (or, more exactly, in the density 1 df 
 the current) produces irritation in the nerve, which is more 
 powerful the more quickly or suddenly the variation occurs 
 (du Bois-Reymond). The variation which is most frequently 
 used as a stimulus is that produced on making or breaking a 
 current through the nerve : i.e. the passage of the intensity from 
 nothing to the full strength of which, the current is capable, 
 or the reverse. Any other variation, however, acts as a 
 stimulus ; e.g. the sudden increase or diminution in strength 
 of a current already passing through the nerve ; or the mere 
 alteration of the density of the current in a nerve, the intensity 
 of the whole current remaining unaltered. 2 
 
 1 By the density of a current is understood the intensity of the current divided 
 by the area of transverse section of the body through which it is flowing in this 
 case, of the nerve. The value is clearly relative, for the same intensity of current 
 must have more marked effects the thinner the nerve. 
 
 2 The latter is effected by suddenly laying over the nerve, through which a 
 current is passing, a moist conductor. The current which had previously to 
 traverse the nerve alone in order to complete its circuit, now passes through both 
 conductors, the effect of which is to diminish suddenly the density of the current 
 in the nerve. 
 
ELECTROTONUS. PFLUGEKS LAW. 327 
 
 If the time occupied by one complete variation be supposed to be divided 
 up into fractions, and these fractions taken as abscissae ; and if the density of 
 current corresponding with each of those fractions of time be regarded as 
 ordinates ; a curve will be obtained which will represent the course of the 
 variation according to time. From the law just enunciated of the stimulation 
 of nerves by currents, it follows that the value of a given variation as a 
 stimulus is greater the more sudden the ascent or descent of this curve; but 
 the more exact conditions of this relation are at present unknown. From 
 the same law we gather that a nerve may be very powerfully stimu- 
 lated by means of a very weak current, if only the rapidity with which it 
 is allowed to break into or out of the nerve be sufficiently great. Hence 
 the shocks of frictional electricity have a very powerful stimulating effect ; 
 for although the amount of electricity really present is very small, the 
 currents it forms are extremely rapid in their appearance and disappearance. 
 For similar reasons, the rapid currents of the induction coil are generally used 
 for the purposes of stimulation. On the other hand, it is evident that a very 
 strong current may be made to pass through a nerve without inducing irri- 
 tation, if care be taken to do it extremely gradually. 
 
 The above-mentioned stimulation by constant currents is evidenced in the 
 case of motor nerves by the induction of tetanus in the muscle with which 
 they are connected, and in the case of sensory nerves by sensations (pain, 
 &c.), which continue during the passage of the current. The appearances in 
 the former case are more marked with ascending than with descending 
 currents. They are present in the case of very weak currents, and become 
 more and more decided as the current increases in strength, until a certain 
 limit is reached, above which the electrotonic modifications of the con- 
 ditions of irritability again render the results less marked (Pfliiger). 
 
 The stimulating effect of a current operates, on closing 
 (and, in general, on any positive variation), at the cathode onlj ; 
 and, on opening (negative variation), at the anode only. In 
 other words, a portion of nerve is stimulated by a current, 
 when the latter causes in it the appearance- (or increase) of 
 catelectrotonus, or the disappearance (or diminution) ofanelec- 
 trotonus (Pfliiger). The stimulation of the other portions of 
 the nerve is only a consequence of the transmission of irritation 
 (see below). 
 
 Expressed in the hypothetical manner made use of on p. 325, Pfl iiger's law 
 of stimulation would run thus : The passage of the molecules of nerve-matter 
 from the usual into the mobile (catelectrotonic) condition ; or from the 
 hardly mobile (anelectro tonic) into the usual condition, acts as a stimulus. 
 On the contrary, the passage from the usual into the hardly mobile (an- 
 electrotonic) condition j or from the easily mobile (catelectrotonic) into the 
 usual condition, does not act as a stimulus. In this form the law is some- 
 what more intelligible, on account of the rationale supplied. 
 
 The experiments from which this law has been deduced are rather compli- 
 
328 
 
 ELECTROTONUS. PFLUGEES LAW, 
 
 cated. As they have been for the most part made upon motor nerves, the law 
 is also called the 'Law of Contraction.' If the stimulating current be allowed 
 to pass through a given (central) portion of the nerve, the whole of the 
 latter is divided into two parts, in which opposite conditions obtain, in one 
 the anelectrotonic, in the other the catekctrotonic. The above law affirms 
 that, on closing the stimulating current, it is the catelectrotonic area only, 
 while, on opening, it is the anelectrotonic area only, which suffers stimula- 
 tion. Hence we may, if we like, express the law as follows : Stimulation 
 proceeds from the cathode on closing, and from the anode on opening, the 
 stimulating current. If the stimulating current has an ascending direction 
 (i.e. if the positive electrode is nearer the muscle) it is evident that the 
 upper portion of the nerve will be stimulated during closure, and the lower 
 during opening, of the stimulating current : and the contrary results will 
 obtain if the current is descending. It may now be asked, which regions of 
 the nerve, on stimulation, call the connected muscle into activity, i.e. induce 
 contraction ; and the answer will be found to depend upon the strength cf 
 the current used in stimulation. Thus, when the current is strong, the 
 anelectrotonic area loses its powers of conductivity (see below), in con- 
 sequence of which only the stimuli operating in the portion of nerve between 
 it and the muscle can possibly produce a contraction. In the case of strong 
 currents, therefore, the descending current can only act effectively on closing 
 and the ascending only on opening. With currents of medium strength 
 both areas or regions have the power of inducing stimulation and causing 
 contraction of the connected muscle, as the conductivity of the whole nerve 
 is nowhere interrupted. In this case, therefore, whatever the direction of 
 the current, contraction will follow on both opening and closing. With 
 currents of the weakest sort, that area only will act as a stimulus in inducing 
 contraction which is most favourably situated for the purposes of stimula- 
 tion j that is to say, cesteris paribus, that area which is most removed from 
 the muscle (see under Conductivity). When, therefore, the current is very 
 weak, closing the ascending, and opening the descending, current should in- 
 duce contraction. But, as the appearance of catelectrotonus is a stronger 
 stimulus than the disappearance of anelectrotonus, the latter operation, viz. 
 epening the descending current, gives place to closure of the same as a more 
 powerful means of stimulation ; and, in consequence, the weakest descend- 
 ing currents do not give opening but closing contractions. The law of 
 contraction may be formulated thus : 
 
 (R = Rest, C = Contraction). 
 
 Strength of current 
 
 Ascending 
 
 Descending 
 
 On closing 
 
 On opening 
 
 On closing 
 
 On opening 
 
 Strong . 
 Moderate 
 Weak . 
 
 K 
 C 
 C 
 
 C 
 C 
 
 E 
 
 C 
 
 C 
 
 C 
 
 E 
 C 
 E 
 
MITTEtfS TETANUS. 329 
 
 Induction currents are currents which are called into existence very 
 suddenly and disappear somewhat more slowly. Of the two means of 
 stimulation which follow thus immediately one upon the other, the former, 
 according to the above-mentioned general law of stimulation, is the more 
 powerful. In the case of weak currents, indeed, it is the only one of the 
 two which is effectual ; so that weak induction currents act in stimulation 
 like the closure of a similarly directed constant current. With this un- 
 derstanding, the Law of Contraction holds for induction-currents also 
 (Rosenthal). 
 
 The effects of stimuli on the centripetal nerves of animals can only be 
 imperfectly investigated. The method adopted is to induce an extreme 
 reflex irritability by means of strychnia-poisoning, in order that peripheral 
 stimuli may readily induce tetanic muscular contractions (Chap. XL). 
 An analogous law of stimulation may be demonstrated in the case 
 of inhibitory nerves, as, for example, the inhibitory fibres of the vagus 
 (Bonders). 
 
 If the current used in stimulation is very strong, or has been kept closed 
 for some time, tetanus occurs on opening (tetanus of Hitter), instead of the 
 usual single contraction. This tetanus immediately disappears on reclosing 
 the same current, but is, on the contrary, intensified if the current is first re- 
 versed and then closed. As Hitter's tetanus results from the strong irri- 
 tating effect due to the disappearance of anelectrotonus, it ceases immediately 
 on separating the anelectrotonic area of the nerve from the muscle ; which 
 can only be done, for obvious reasons, in the case of descending currents-, 
 where section of the nerve at the ' indifferent point ' (p. 325) accomplishes 
 the purpose (Pfliiger). The condition of the nerves just referred to was 
 formerly considered to be a distinct modification of irritability, similar to 
 those described on p. 325 j and it used to be said that the constant current in- 
 creased the irritability of the nerve for the opening of a current in the same 
 and for the closure of a current in the contrary direction ; and vice versa 
 (Rosenthal). The phenomena described are, however, easily explicable by 
 Pfliiger's law of stimulation. If the stimulating current is too weak, or 
 has been closed for an insufficient time ; or if the irritability of the nerve 
 is diminishing on account of the approaching death of the latter ; a some- 
 what languid contraction takes place, followed finally by the usual opening 
 contraction, instead of the tetanus of Hitter. 
 
 The power of constant currents to restore irritability to exhausted 
 muscles, to which reference was made on p. 249, also belongs to this 
 category of phenomena ; for it must not be forgotten, that all the laws of 
 the electrical stimulation of nerves are equally applicable to muscles. In 
 the case of muscles also, for instance, stimulation only results on opening a 
 current in the same, or on closing a current in the contrary direction. 
 
 As stimulation, according to Pfliiger's law, depends upon 
 the appearance or disappearance of a different condition (elec- 
 trotonus) of the nerve, none can result from currents which are 
 
330 ELECTRICAL STIMULATION OF MUSCLES. 
 
 too transitory to allow of the completion of the electrotonic 
 state. Experiment confirms this statement ; as currents which 
 do not last more than O0015 of a second are incapable of stimu- 
 lating nerves (Konig). 
 
 Currents have the most powerfully stimulating effects when 
 they traverse the nerves in the direction of their length, being 
 indeed powerless in this respect when flowing transversely. 
 Currents in directions intermediate between these two extreme 
 positions have intermediate values as stimuli, the laws of which 
 have not yet been established. The length of the portion of 
 nerve traversed by the stimulating current, which was formerly 
 supposed to influence irritability favourably, is now known to 
 do so only in the case of descending currents, while in ascend- 
 ing currents the shorter the piece of nerve included between 
 the electrodes, the better appears to be the stimulating effect. 
 Stimulation, therefore, according to the law of electrotonus, is 
 more powerful the nearer the cathode to, and the farther the 
 anode from, the muscle (Willy). 
 
 In the electrical stimulation of muscles, the same laws hold 
 as in that of nerves (p. 248). Here, also, it is only varia- 
 tions in currents that produce stimulation, which, as before, 
 proceeds, on closing, from the cathode, and, on opening, from 
 the anode (von Bezold). As changes take place more slowly in 
 muscle than in nerve (as evidenced, for example, by the dif- 
 ferent degrees of rapidity with which they transmit impressions), 
 length of duration of the stimulating current is more necessary 
 in the former than in the latter for the production of stimula- 
 tion. Hence all induction-currents, and the more transitory 
 constant currents are unable to stimulate to contraction muscle 
 deprived of its nervous connections by curare, while they are 
 able to cause contractions in a muscle by acting upon its motor 
 nerves (Briicke). This fact was early known to be the case 
 with muscles, the nervous organs of which were rendered in- 
 capable of performing their functions by exhaustion, local 
 death, pathological paralysis, &c. (von Bezold, Fick, Neu- 
 mann ). 
 
 Pfliiger's law of stimulation may be demonstrated to hold in the case of 
 muscles in the following ways (Engelmann) : 
 
 1. A muscle A B (Fig. 9) is fixed by its middle portion c, care being 
 taken not to crush it, and the lower half is arranged so as to register its 
 
STIMULI OF NERVES, CHEMICAL. 
 
 331 
 
 contractions on a myographion. If the cathode be placed at A and the 
 anode at B, the latent period (p. 257) occurs sooner during a closing con- 
 traction than during an opening contraction, as in the former case the 
 stimulus proceeds from A and in the latter from B : and vice versa. 
 
 FIG. 9. 
 
 FIG. 10. 
 
 FIG. 11. 
 
 2. If the electrodes he placed at the thin edges of a piece of flat muscle, 
 split as in Fig. 10, contraction follows, on the passage of a moderate current, 
 in the strip next the cathode on closing, and in that next the anode on 
 opening; of course each fibre has its own cathode and anode, but the 
 density of the current is only sufficient to induce contraction in the neigh- 
 bourhood of the points where stimulation originates. If the muscle be not 
 split (Fig. 11) it bends, for the same reasons, on closure towards the cathode 
 (s) and on opening towards the anode (o). 
 
 2. Chemical stimuli. It may be stated in general' that 
 whatever effects in a nerve a change of chemical constitution of 
 a certain extent and with a certain degree of rapidity acts upon 
 it as a stimulus. Almost all chemical stimuli cause at the| 
 same time the death of the nerve to which they are applied, i.e. 
 they destroy its irritability. But the contrary of this cannot be 
 stated, viz., that all destructive substances act as stimuli ; for 
 some of them, as, for instance, ammonia and solutions of 
 metallic salts, produce death so rapidly as to prevent the deve- 
 lopment of the stimulating effect. Chemical stimuli must, as 
 a rule, be in a more concentrated state for nerves than for 
 muscles, as the substance of the former, especially the sheath, 
 permits but slow diffusion of liquids. The principal chemical 
 stimuli for nerves are the following (Eckhard, Kiihne) : con- 
 centrated solutions of the mineral acids, alkalies, alkaline salts, 
 concentrated lactic acid, concentrated glycerin, &c. Depriva- 
 tion of water (desiccation) also acts as a strong stimulus. 
 
332 THERMAL, MECHANICAL, AND NATURAL STIMULI. 
 
 3. Thermal stimuli.^A temperature of from 34 to 45C. 
 acts as a stimulus upon the motor nerves of the frog, without 
 producing serious consequences ; temperatures up to 40 causing 
 clonic, and temperatures above 40 tetanic, contractions of the 
 connected muscles. Higher temperatures (p. 324) kill the 
 nerve without acting as stimuli (Eosenthal, Afanasieff). 
 
 4. Mechanical stimuli. All mechanical impressions which 
 cause alterations of form in any portion of a nerve with a 
 certain degree of rapidity (e.g. blows, pressure, ligature, 
 section, &c.) act as stimuli while producing the change. If 
 the form of the nerve has been permanently injured, irritability 
 and conductivity are, as a rule, lost. 
 
 5. Natural stimuli originating in the end-organs ; that is 
 to say, the stimuli induced in the central nervous organs, or in 
 the special nervous terminations of the organs of sense by the 
 action of light, sound, heat, pressure, &c., which it is the 
 function of the nerves to conduct (consult the Introduction to 
 this Section ; and also Chaps. X. and XL). 
 
 Phenomena of the Active Condition. 
 
 Concerning the active condition of the nerve itself, very 
 little is as yet known. We know neither the nature of the 
 forces which become free during that condition nor the chemical 
 processes which form their basis. There is absolutely no 
 indication in the case of nerves such, for instance, as exists in 
 the shortening of muscle which serves to distinguish an active 
 from an inactive portion ; and the only chemical difference 
 which has been insisted upon between nerves which -have been 
 at rest and nerves which have been in activity, is (Funke, J. 
 Ranke), that the latter exhibit an acid reaction ; but even this 
 is denied by other observers (Liebreich, Heidenhain). As little 
 is known about the utilisation of oxygen by active nerves as by 
 inactive nerves. No generation of heat can be shown to take 
 place in active nerves (Helmholtz, Heidenhain). More will be 
 said concerning the electrical appearances and the temporary 
 duration of the activity of nerves when considering their 
 electromotor properties. 
 
A CTIVE CONDITION OF NER VES. COND UCTION. 333 
 
 Transmission of the State of Activity along the Nerve-fibres. 
 (Conduction.) 
 
 The state of activity in a nerve, which, as above mentioned, 
 is accompanied by no external manifestations, leads to change 
 in one of its two end-organs, the peripheral or the central. 
 Under ordinary circumstances, the stimulus, which throws the 
 nerve into the active state, is applied to one of these end- 
 organs, whereupon a certain change, which we are accustomed 
 briefly to call the ' result,' becomes evident in the other. If 
 this ' result ' occurs in the central end-organ after stimulation 
 applied to the peripheral, the process is called centripetal ; 
 and if the contrary, centrifugal. 
 
 As a rule, only one of these directions is possible in par- 
 ticular nerve fibres; hence a distinction is made between 
 centripetal and centrifugal nerves and nerve fibres. In addi- 
 tion to this natural method, in which the stimuli are applied 
 to the end-organs, nerves may be artificially stimulated at any 
 point in their course ; but in this case also the result takes 
 place in the same way as on natural stimulation, viz. in a 
 central organ in the case of a centripetal fibre, and in a 
 peripheral organ in the case of a centrifugal fibre. 
 
 The simplest explanation of this behaviour is that which 
 supposes that on normal stimulation of an end-organ the whole 
 course of the nerve is not thrown into the active condition at 
 once, but that the state of activity is transmitted from, one 
 cross section to the next, and so conducted through the whole 
 course of the nerve ; that, moreover, any stimulus applied at 
 any point in the course of a nerve-fibre induces the active con- 
 dition at that point only, whence it is transmitted to the next 
 point, and so on, just as in the case of normal stimulation. 
 This property which nerves have of transmitting the active 
 state from one point to the next until the end-organ is reached 
 is called their conductivity. The condition necessary for con- 
 duction is that, between the stimulated point and the end- 
 organ in which the result is to be manifest, the nerve be quite 
 intact. Lesion at any point in its course through section, 
 pressure (ligature), burning or chemical destruction (treatment 
 with caustics), interrupts conduction. In addition, the other 
 
334 PROPERTIES OF SENSORY AND MOTOR NERVES. 
 
 circumstances which diminish irritability act at the same time 
 prejudicially upon conductivity, as, for instance, the an electro- 
 tonic state. The passage of the active condition from one fibre 
 to another never occurs. 
 
 Such a passage seems to take place in the case when, on isolated 
 electrical stimulation of one branch of a nerve, contractions follow in a 
 muscle supplied by another branch. This so-called 'paradoxical con- 
 traction' will be discussed more at length in treating of the electrical 
 phenomena. 
 
 In order to explain the difference between a centripetal 
 and a centrifugal nerve-fibre, it was formerly supposed that 
 every nerve had the power of conducting in one direction only, 
 the former towards the central, the latter towards the peripheral, 
 nervous organs. Such a supposition is, however, unnecessary, 
 as every nerve is connected with one end-organ only which is 
 capable of exhibiting the results of conduction. For example, 
 no nerve exists which is at one end connected with sensory 
 ganglion-cells and at the other with a muscle, in which, there- 
 fore, conduction in both directions might be proved. Hence 
 there is no necessity of a specific distinction between centripetal 
 and centrifugal nerves ; and we may suppose that all nerves 
 can conduct in both directions, but that only one of the end- 
 organs of each is capable of indicating that conduction. That 
 such a conductivity in two directions does really exist seems to 
 be indicated by the following circumstances : 1. If a nerve be 
 stimulated at a given point, the electrical changes characteristic 
 of nervous activity appear, not on one, but on both sides of the 
 point of stimulation (du Bois-Eeymond). 2. If one terminal 
 twig of a forked motor nerve be stimulated, activity is induced 
 in the other terminal twig, provided the common trunk be 
 intact. The fibres of the former twig must, therefore, have 
 conducted in a centripetal, and not in their usual centifugal 
 direction (Kiihne). 3. No anatomical, chemical, or physio- 
 logical distinction has hitherto been made out between fibres 
 of the two classes. 4. The most direct proof, however, of this 
 power of nerves to conduct in opposite directions is an experi- 
 mental one. If the central portion of a severed sensory nerve be 
 caused to unite with the peripheral portion of a divided motor 
 nerve, an arrangement will have been created for indicating 
 conduction in two directions (Bidder). This experiment has 
 
RAPIDITY OF NERVOUS CONDUCTION. 335 
 
 been performed in the case of the peripheral part of the 
 hypoglossus and the central part of the lingualis ; and the 
 results were such as were anticipated (Philippeaux and Vulpian, 
 Rosenthal). 
 
 A physiological distinction between the two classes of nerve fibres has 
 been sought in the statement that certain poisons affect one kind only ; thus 
 it is said, for instance, that the arrow-poison, curare, paralyses motor nerves 
 alone (p. 247). It has, however, been shown that the action is one upon 
 peripheral end-organs, and therefore does not affect the properties of the 
 nerves themselves. 
 
 The active condition, therefore, induced first of all at the 
 spot where the stimulus was applied, is transmitted by conduc- 
 tion to the regions on both sides of the spot in the case of a 
 stimulus applied at an intermediate point of the nerve-fibre ; 
 or to the region on one side only in the case of a stimulus ap- 
 plied to an end-organ. By this means every portion of the 
 nerve passes successively into the state of activity. It has been 
 observed (Pfliiger) that the effect of stimulation, as manifested 
 in an end-organ (e.g. the contraction of a muscle on irritation 
 of a motor-nerve) is more marked the farther removed is the 
 point of stimulation from the end-organ. This is explained by 
 supposing that the condition of activity does not travel along a 
 nerve with unaltered force, but that it increases like the 
 momentum of a falling mass (< cascade-' or 'avalanche-effect'). 
 It is, however, more probable that this phenomenon depends 
 upon an increased irritability of the more distant portions of 
 the nerve due to artificial division where such has taken place, 
 or, perhaps, in other cases, to the proximity of the central organ 
 with which it is connected. 
 
 Rapidity of Conduction. 
 
 The processes of transmission, upon which conduction depends, 
 take up a definite time. Conduction therefore takes place with 
 a certain, and not very great, degree of rapidity. For the motor 
 nerves of the frog, this rapidity is about 26-27 metres per second 
 (Helmholtz). For the sensory nerves of man the determina- 
 tions vary. The following are some of the principal results of 
 experiments : 
 
336 RAPIDITY OF NERVOUS CONDUCTION. 
 
 94 metres per second . . . . (Kohlrausch) 
 
 60 (Helmholtz) 
 
 34 (Hirsch) 
 
 30 (Schelske) 
 
 26 (de Jaager) 
 
 41-3 (vonWittich) 
 
 For the motor nerves of man, the mean rapidity is about 
 33*9 metres per second (Helmholtz and Baxt), which is, doubt- 
 less, the correct rate for sensory nerves also. Eapidity of 
 conduction is modified by various influences, being diminished, 
 for instance, by cold (Helmholtz), and also by either phase of 
 the electrotonic condition (von Bezold). It is, moreover, probable 
 that rapidity of conduction is not uniform, but diminishes as 
 the distance from the place of origin of the stimulation in- 
 creases (H. Munke, Helmholtz and Baxt). 
 
 For the determination of the rapidity of conduction in the motor nerves 
 of the frog the same method is made use of as in the discovery of the time 
 taken up in muscular contraction (p. 258). That is to say, the same nerve 
 is successively stimulated at two different points in its course (a and b in 
 Fig. 5) ; on stimulation of a point nearer the muscle the period of latent con- 
 traction is of shorter duration than on stimulation of a point more distant, 
 in consequence of which contraction of the muscle occurs more quickly. 
 The duration of the latent period in each case may be registered either 
 by Pouillet's method or by means of the myographion ; and the difference 
 of duration taken in connection with the measured distance between the two 
 points of stimulation gives the data for determining the required rapidity of 
 conduction in the nerve (Helmholtz). 
 
 In the case of man, physiologists were formerly limited, in the deter- 
 mination of the rapidity of conduction, to sensory nerves. The general 
 method of procedure is as follows : The person experimented upon gave, on 
 perceiving a certain sensation, a preconcerted signal. The time intervening 
 between this signal and another connected with the stimulus which had 
 given rise to the sensation was measured by means of one of the numerous 
 instruments devised for such a purpose. Sometimes Pouillet's method 
 was made use of. Hipp's chronoscope (for an account of which, see the 
 Text-Books of Physics) was another instrument used; as was also Krille's 
 registering apparatus, in which marks were made upon a rotating cylinder, 
 while a pendulum was so arranged as to record seconds on the cylinder at 
 the same time. In Hankel's registering apparatus, which was also used 
 for this purpose, the marks coincident with stimulation and sensation were 
 made by the pressure of a pencil upon a surface of paraffin fixed at the 
 circumference of a quickly revolving wheel, while the rate of rotation of the 
 wheel was checked by means of Krille's instrument. Another instrument 
 was Konig's phonautograph, on the same principle as Krille's, except that a 
 vibrating tuning-fork recorded time instead of a pendulum ; the object of 
 
ELECTRICAL PHENOMENA. 337 
 
 this improvement being to register much smaller intervals than is possible 
 with a pendulum, a most important point when the rate of rotation varies. 
 The time so measured is divisible into three portions : a the time taken up 
 by the passage of the sensation to the brain; b the time occupied in the 
 perception of sensation and the origination of motor impulse ; c the time 
 which elapses from that origination to the occurrence of the pre-arranged 
 signal ; that is to say, T = a + b + c. If now the experiment be twice made, 
 once with a stimulus applied at a point near the brain, and once at a point 
 more remote (say at the neck and at the foot respectively), the difference be- 
 tween the two times T and T', considered in relation with the difference in 
 length of the nerve traversed, would give the desired rapidity of conduction ; 
 supposing always that the difference between T and T' consists of that be- 
 tween a and a' only, and that b and c remain the same in both experiments. 
 The latter supposition, however, with regard to b, cannot always be relied 
 upon as holding ; for it has been found that the kind of sensation, a previous 
 knowledge or ignorance of it, the expectation of it at a given time, the 
 character of the pre-arranged signals, &c., have the greatest influence upon 
 the time (Bonders and de Jaager). The great difference observable in the 
 determinations of various observers may, therefore, depend either upon the 
 inconstancy of the factor b or upon real individual differences of conductive 
 power. 
 
 The rate of conduction of motor nerves of man is determined by tracing 
 upon a myograph the curve of contraction of the muscles of the thumb by 
 means of their increase in thickness (p. 259). Two tracings must be taken, 
 one when the stimulus has been applied to the nerve at a point on the arm 
 near to the hand, and the other when it has been applied at a point more 
 remote from the hand, from which the determination is easily made 
 (Helmholtz). It may be mentioned, by the way, that weak stimuli were 
 found during these experiments to be conducted more slowly than strong 
 ones. 
 
 Electrical Phenomena of Nerves. 
 
 1. Action of Galvanic Currents upon Nerves. 
 
 The resistance of nerves to electrical conduction is about 
 five times as great in a direction across, as in the direction of, 
 the fibres : in dying, this difference is diminished by about one- 
 half. The cause of this condition is altogether or in part an 
 internal polarization, which appears at the border between the 
 sheath and contents of the nerve-tube. This polarization de- 
 velops instantly on closing, and vanishes as suddenly on open- 
 ing, the current in the course of which the nerve is placed. 
 Similar phenomena are noticed in the case of muscles in which 
 the resistance in a transverse direction is seven times as great 
 as that in a longitudinal direction (Hermann). 
 
 z 
 
338 ELECTRICAL PHENOMENA. 
 
 During electrotonus a current having the same direction 
 as the polarizing current is everywhere demonstrable in the 
 extra-polar region, and adds itself algebraically to the current 
 of repose, where such is present. This electrotonic current is 
 strongest in the region of the electrodes. It appears imme- 
 diately on closing, and is constantly diminishing on the side of 
 the cathode (du Bois-Beymond). 
 
 No current in the same direction as the polarizing current 
 is known to exist in the intra-polar region, in addition to the 
 polarizing current itself (Hermann). 
 
 The sudden appearance of the electrotonic current in the extra-polar 
 regions may act as a stimulus upon neighbouring nerves, thus causing 
 4 secondary contraction or secondary tetanus ' (p. 275) j of such a nature is 
 the 'paradoxical contraction/ already mentioned, which follows in a 
 muscle connected with one branch of a nerve after the electrical stimula- 
 tion of another branch of the same nerve : it is explained by supposing that 
 the contiguity of the fibres of the two branches gives opportunity for the 
 sudden appearance of the electrotonic current in the one to act as a stimulus 
 upon the other (du Bois-Beymond). 
 
 After breaking the polarizing current certain ( after-currents ' remain 
 (Fick) for a short time. In the intra-polar and anelectrotonised extra-polar 
 regions they have the opposite direction to the polarizing current ; but in 
 the catelectrotonised extra- polar region the ' after-current ' has the same 
 direction as the polarizing current (Hermann). 
 
 The electromotive force of electrotonic currents is very great. Some 
 electrotonic currents have been observed to possess electromotive force 
 equal to half that of a Darnell's element (du Bois-Beymond). 
 
 2. Essential Electrical Properties of Nerves. 
 
 In a portion of nerve bounded by two transverse sections, 
 the existence of currents is demonstrable which obey the same 
 laws as those of muscle (du Bois-Beymond, p. 270 et sq.). 
 
 No currents have with certainty been detected at any natural 
 cross-section of a nerve. 
 
 The electromotive force of the current passing from longitudinal to 
 transverse sections of a nerve is, as a rule, equal to about *02 of that of a 
 Darnell's element (du Bois-Beymond). 
 
 On stimulation of a nerve the electromotive force of the 
 essential nerve-current is diminished (du Bois-Beymond;. This 
 ' negative variation ' which, if the stimulus is strong enough, 
 may proceed to the reversal of the nerve-current, develops 
 
ELECTRICAL PHENOMENA. 339 
 
 more quickly than it disappears, and occupies altogether about 
 0007 of a second (Bernstein). In polarized nerves the extra- 
 polar electrotonic currents also exhibit a ' negative variation ' 
 on stimulation (Bernstein) ; in the intra-polar region stimula- 
 tion induces the appearance of an accessory current in the same 
 direction as the polarizing current (Hermann). 
 
 Stimulation applied to a nerve-trunk is evidenced by the negative varia- 
 tion of its proper current just as a stimulation of intramuscular nerve- 
 terminations is evidenced by muscular contraction. The same use may, 
 therefore, be made of negative variation, as of the contraction of muscle, for 
 the discovery of the laws of stimulation of nerves. Both, for example, are 
 diminished if the region of stimulation be already anelectronised, and in- 
 creased if it be catelectrotonised (Bernstein) 5 and the interval of time be- 
 tween stimulation and the occurrence of the negative variation may be used, 
 in the same way as the interval between stimulation and contraction, in 
 determining the rapidity of conduction (Bernstein). Since the difficulty is 
 great of arranging nerves (p. 334) so as that both ends shall be connected 
 with muscles, whilst it is easy to have a nerve with two artificial transverse 
 sections, negative variation affords the simplest means of proof of the power 
 of nerves to conduct in opposite directions (du Bois-Reymond). 
 
 It is, moreover, necessary, just as in the case of muscle (p. 275), to 
 app-y to nerves a considerable number of rapidly succeeding stimuli in order 
 to indicate the negative variation of their currents by the needle of a mul- 
 tiplier. It is not possible, as a rule, to get evidence of negative variation by 
 means of the physiological rheoscope, as 'secondary contraction and 
 secondary tetanus ' proceeding from nerves are not caused by the negative 
 variation of the proper currents of the latter, but by the currents due 
 to electrotonus. For example, ' secondary contraction ' does not follow 
 at all when the stimulus applied to the nerve is not electrical; and it 
 may be shown by means of the Law of Contraction that, under certain 
 circumstances, ' secondary contraction ' depends upon a stimulation of the 
 rheoscopic nerve due to a positive variation, such, e.g., as that caused by 
 the appearance or disappearance of electrotonus (du Bois-Reymond). The 
 following experiment serves for determining the length of time which 
 elapses between stimulation and the occurrence of negative variation 
 (Bernstein) : A quickly revolving wheel causes at each revolution, (1) the 
 electrical stimulation of a point, a, of the nerve, and immediately afterwards 
 (2). the transitory closure of a circuit which includes a galvanometer and a por- 
 tion of nerve 6, arranged as for the demonstration of its natural current. The 
 interval ef time between (1) and (2) can be varied at will ; and, by 
 gradually increasing it from 0, a point is at last reached at which closure of 
 the galvanometer-circuit exactly coincides with the commencement in the 
 region b of the negative variation due to the stimulation of a. The time thus 
 determined clearly indicates the period required for the irritation to travel from 
 a to b. This period is proportional to the length of nerve between a and h 
 (whence it immediately follows that the effect of stimulation commences 
 
 z 2 
 
340 ELECTRICAL PHENOMENA. 
 
 the moment it is applied) ; and from the data it has been calculated that 
 irritation travels at the rate of 28-718 metres per second. 
 
 If the time between (1) and (2) be so arranged that the nerve-current 
 in b shows, at the moment of closure of the galvanometer-circuit, not the be- 
 ginning but some other phase of the negative variation, say the maximum, or 
 the end, it is possible to determine from the time intervening between (1) 
 and (2) the duration and progress in time of the negative variation itself. 
 
 There are two theories regarding the currents of nerves as 
 of muscles (p. 276 etsq.). According to one (du Bois-Eeymond) 
 every nerve-fibre contains regularly arranged electromotive 
 molecules, which present their positive elements to a longi- 
 tudinal, and their negative elements to a transverse, section, 
 and whose activity diminishes on stimulation. Electrotonic 
 currents are explained, according to this hypothesis, by attribut- 
 ing to the polarizing current a directive action upon the movable 
 molecules, which are supposed to be so turned as to have the 
 same direction as the polarizer. In order that this should be 
 possible, each molecule must be supposed to be divided into 
 two bipolar halves, incapable of mechanical or chemical separa- 
 tion, each of which can, however, rotate about an axis of its own. 
 By this means an arrangement of the halved molecules end to 
 end is possible, which is most complete in the neighbourhood 
 of the polarizing electrodes, and which explains the electrotonic 
 current. 
 
 In opposition to this explanation of electrotonic currents may be cited 
 the condition of the intrapolar region. According to the above theory this 
 region should exhibit an extremely powerful accessory current in the 
 same direction as the polarizer, whereas there is no trace of such a current. 
 
 The other theory (Hermann) explains the natural current 
 of nerves, like that of muscles (p. 277), as the effect of contact : 
 the contents of nerve-tubes which are dying or in activity are 
 negative to the contents of nerve-tubes which are living and at 
 rest. The cause of the electrotonic phenomena is the polariza- 
 tion at the boundary between nerve-sheath and contents to which 
 reference has already been made. 
 
 If a current passes from one conductor to another, and if at the boundary 
 between them polarization, and, in consequence, resistance take place, both 
 current and state of polarization spread out over the region about the points of 
 entrance and exit. In consequence of this any pair of electrodes situ- 
 ated in an extra-polar region receives a branch of the current having the same 
 
ELECTRICAL PHENOMENA. 341 
 
 direction as the polarizing current. In the intra-polar region the branches of 
 the original current would be found, if it were possible to demonstrate them, to 
 have a direction opposite to that of the polarizer. This circumstance, which 
 was first shown to occur in the case of moist, covered wires (Matteucci), is 
 taken to explain electrotonus in nerves, as in the latter the necessary condi- 
 tions are present (Hermann). The polarization-currents remain a short time 
 after the polarizer is broken ; but in the anelectrotonic area the more power- 
 ful effect of the opening or breaking shock at the anode produces the ap- 
 pearance of reversal of the after-current, which flows in an opposite direc- 
 tion to the polarizer (see above). 
 
 If, as was supposed on page 332, conduction in a nerve is 
 nothing but the transmission of the condition of activity from 
 one portion to another, then both the above theories of the 
 nerve-current must require that, while a nerve is conducting, 
 the point of it at which the active condition for the moment 
 obtains must be negative towards every other point in the long 
 axis of the nerve. No direct indication of such a condition 
 has as yet been given. 
 
 The alterations of electrotonic currents effected by stimula- 
 tion may be explained by assuming that irritation in its course 
 through the polarized nerve varies in intensity, increasing when 
 it reaches a point which is more positive (i.e. which is more 
 strongly positively, or more weakly negatively, polarized), and 
 diminishing when it reaches a point which is more negative. 
 In this way are explained : 1. The positive increase of current 
 in the intra-polar region ; for irritation is more powerful as it 
 reaches the anode than as it reaches the cathode, and in conse- 
 quence the former becomes through irritation more strongly 
 negative than the latter. 2. Similarly the diminution in extra- 
 polar electrotonus. 3. The negative variation of the proper 
 nerve-current ; for the latter causes negative polarization in 
 the neighbourhood of the transverse section, in consequence 
 of which irritation is less powerful by the time it has reached 
 the transverse section, and every longitudinal sect^m there- 
 fore becomes on irritation more strongly negative than a 
 transverse section. It follows on the contrary from the same 
 supposition that any irritation arising in a positively polarized 
 (anelectrotonic) portion of nerve must diminish in its course 
 through the nerve, while any irritation arising in a negatively 
 polarized (catelectro tonic) portion must increase. Hence we 
 can see the cause of the apparent diminution of irritability 
 
342 ELECTRICAL PHENOMENA. 
 
 which occurs during anelectrotonus, and of the apparent increase 
 during catelectrotonus (and in the neighbourhood of the trans- 
 verse section). The phenomena described on page '625 may 
 also in this way be explained (Hermann). 
 
 Theories concerning the Nature of Nervous Activity. 
 
 Most thinkers on the subject assume the existence in nerves 
 of movable or alterable particles, so connected together that the 
 movement or alteration of any one leads to the movement or 
 alteration of those in its immediate neighbourhood. Many 
 identify these particles with those which are assumed for the 
 purpose of explaining the electromotive properties (p. 340) of 
 nerves. It is further supposed that the movement or alteration 
 of which the particles are capable, takes place in opposition to 
 resistances or inhibitions whose power is inversely proportional 
 to the irritability of the nerve. These inhibitions or resist- 
 ances are diminished in catelectrotonus and increased in 
 anelectro bonus. 
 
 The motion or alteration of one of the nerve-particles would, therefore, 
 act like a stimulus on the next, whereby it seems to be implied that con- 
 ductivity proceeds pan passu with irritability. The latter is not apparently 
 always the case. Thus, in the catelectrotonic condition, irritability is in- 
 creased while the rapidity of conduction diminishes (pp. 325 and 336) in the 
 spinal cord there are said to exist conducting fibres which are incapable of 
 direct stimulation (Chap. XT.) j and nerves poisoned by conine, curare, or 
 carbonic acid, as well as, occasionally, the nerves of paralysed parts, are 
 said to be still able to conduct irritations from the nervous centres, but are 
 incapable of direct stimulation (Schiff, Erb, Griinhagen). 
 
 There are various views as to the nature of the process of stimulation. 
 Some are inclined to imagine a real movement (rotation, deviation, &c.), 
 others a chemical change, a decomposition analogous to that which takes 
 place in muscle, and which sets free a similar process in neighbouring 
 particles somewhat as fire travels along a train of gunpowder. This 
 decomposition would occur slowly even during repose and would be 
 accelerated by death and the influences increasing irritability. Stimuli 
 (influences suddenly working) would cause great acceleration and the im- 
 pulse to decomposition would be imparted to the neighbouring particles 
 the more quickly according as the rapidity of the process was greater. 
 Death spreads slowly, and irritation quickly, through nerves, the latter the 
 more quickly according as it is stronger. 
 
 Polarization which occurs at the border between the sheath and contents 
 of a nerve-tube and upon which electrotonus depends (p. 340) possibly plays 
 an important role in the transmission of irritation. As, for instance, a stiinu- 
 
CLASSIFICATION OF NERVE FIBRES. 343 
 
 lated portion of the interior of a nerve is electrically negative to the sur- 
 rounding portions which have not heen stimulated, small currents arise 
 which tend to equalise through the sheathing substance. They have, how- 
 ever, the effect of producing anelectrotonus, and therefore of inhibiting 
 irritation at the point of stimulation, and of causing catelectrotonus, 
 with the accompanying irritation, in the surrounding non-stimulated 
 portions. 
 
 The Function and Classification of Nerve Fibres. 
 
 Although it is highly probable that all nerve-fibres are 
 alike (p. 334), some classification of them is expedient. The 
 usual division is founded upon the accidental function of the 
 fibres as indicated by the arrangement of their end-organs. 
 The function of a nerve thus determined is called its ' specific 
 energy.' All nerve-fibres, or, more exactly, all nerve-fibres 
 with their accompanying end-organs, may, therefore, be divided 
 into : 
 
 A. Centrifugally conducting fibres (p. 333) : 1. Motor 
 fibres, at the peripheral end of which is a muscular fibre or 
 another of the contractile elements mentioned in the preceding 
 Chapter ; 2. Secreting fibres, at the peripheral extremity of 
 which stands a glandular element, and whose specific energy 
 consists in stimulating increased secretion in glands, without 
 the aid of the vaso-motor apparatus, on reflex or central 
 excitation; 3. Trophic fibres, i.e. such as regulate the pro- 
 cesses of nutrition (oxidation) in the various parenchymata, and 
 therefore have the same relation to the parenchymatous 
 juices as secreting fibres to free secretions. Their existence, 
 although not improbable, has never yet been demonstrated. 
 Almost all the phenomena which have hitherto been cited to 
 prove their existence may be referred to the action of motor 
 (and especially vaso-motor), secreting and even sensory fibres, 
 as will be stated in describing the trigeminal nerve. The only 
 undoubted case of nervous influence on nutrition is that of the 
 influence on the nutrition of nerves themselves. It has been 
 previously stated that divided nerves undergo fatty degenera- 
 tion in their peripheral portions. 
 
 The secreting nerves, and the trophic nerves if they exist, 
 also influence the formation of heat (pp. 5 and 96), and might, 
 therefore, be described as thermal, just as muscular nerves are 
 described as motor. The influence of nerves upon local tern- 
 
344 SPECIFIC ENERGIES. 
 
 peratures appears, however, to be connected with the distribu- 
 tion of blood (vaso-motor nerves, compare p. 227 ). 
 
 B. Centripetally conducting fibres : 1. Sensory fibres, the 
 central end-organ of which is an organ of the mind, and the 
 result of irritation of which is a mental operation, viz. sensa- 
 tion ; their peripheral end-organs are organs of sense (Chap. 
 X.) ; 2. Reflex, or excito-motor, fibres, in the central end-organ 
 of which the irritation which has traversed the fibre to that 
 point is transferred to another fibre and finally to a centrifugal 
 system. 
 
 The central organs connected with the sensory fibres have 
 to do with various kinds of sensations, some with sensation of 
 sight, others with sensations of hearing, &c. The same sensory 
 fibre always calls into action the same portion of the mental 
 apparatus, and always therefore produces the same sort of sen- 
 sation, in whatever way it is stimulated. Hence, the 
 ' specific energy ' of the optic fibres is the transmission of 
 visual impressions, that of the acoustic fibres the transmission of 
 auditory impressions, &c. Further, it is necessary to ascribe to 
 the irritation of different fibres the different qualities of any 
 given sensation, e.g. the sensation of red and of blue light, or 
 of high and of low notes, and hence, to suppose that certain 
 fibres have, as their ' specific energy,' to aid in the perception 
 of the red rays, while that of others is to assist in the 
 perception of the blue. For, if it were not so, we should be 
 compelled to assume that one and the same nerve-fibre was 
 capable of states of irritation which were qualitatively different 
 an assumption hitherto entirely unsupported by facts. There 
 must, therefore, be at least as many sensory fibres as simple 
 qualities of sensation, and the student may be reminded that 
 the innumerable varieties and shades of sensation which are 
 actually experienced arise from the mingling in various ways of 
 a relatively small number of simpler qualities (Chap. X.). 
 Although this logical consequence of the principle of specific 
 energy (Young, Helmholtz) is a physiological postulate, it is as 
 yet only applicable to a few of the organs of sense. 
 
 This principle is apparently at variance with our experience that the 
 nerves of taste occasion different sensations, according as they are stimulated 
 by ascending or descending currents. The experiments in question, however, 
 admit of another explanation (Chap. X.). 
 
SENSATIONS REFERRED TO THE EXTERIOR. 345 
 
 The peripheral end-organ of every sensory nerve (organ 
 of sense), and such organ alone is capable of excitation not 
 only by the stimuli common to all nerves, but also by one 
 peculiar to itself, which constitutes its usual means of irritation. 
 Thus the end-organs of the optic fibres in the retina are 
 irritable by means of waves of light ; those of the acoustic fibres 
 by waves of sound; those of the olfactory fibres under the influ- 
 ence of odorous bodies, &c. 
 
 As the mind has no means of recognising the origin of any 
 given stimulation, it assumes that all sensations come from 
 their usual source. For example: (1.) It refers the origin of 
 every sensation which reaches it through a sensory fibre to the 
 end-organ of that fibre, even though stimulation has not been 
 applied in the usual manner but to the trunk of the nerve. 
 Thus, persons who have had a limb amputated feel sensations 
 caused by any irritation of the stump of the nerve as if they 
 arose in the amputated limb (eccentric reference of 
 sensations.) (2.) In the case of special sensations it assumes 
 the stimulus to have been that which usually causes the same 
 sensation (light, sound, &c.), notwithstanding that any of the 
 common nervous stimuli (mechanical, electrical, thermal or 
 chemical) may have originated it. Thus it considers every 
 visual sensation as occasioned by waves of light which have 
 impinged upon the retina, even though mechanical disturbance 
 of the retina, pressure on the optic nerve, &c. may have been 
 the cause. The conclusions arrived at by the mind concerning 
 the origin of stimulation go in many cases still further, as, for 
 example, when the stimulus proper to a given organ of sense 
 always takes the same path in order to reach it. Thus, it 
 supposes every wave of light impinging upon the retina, or 
 every wave of sound acting upon the acoustic nerve, to have 
 previously traversed the transparent media of the eye, or the 
 conductors of sound of the ear, as the case may be. Hence, it 
 refers the causes of all sensations of light or sound to without. 
 In the case of visual sensations the mind even forms a judg- 
 ment as to the position of the illuminating body, or at least 
 as to its direction. In the act of seeing, every illuminated 
 point of the retina may be connected with the point whence 
 the rays of light proceed by means of the axial ray of the 
 particular pencil illuminating that point (Chap. X.), and the 
 
346 SPECIAL PHYSIOLOGY OF NERVES. 
 
 cause of the visual sensation is referred to the external medium 
 in the direction of this ray even though that cause be subjec- 
 tive. 
 
 C. Intercentral fibres ; that is to say, such as unite two 
 central organs (ganglion-cells). Their number is enormous, 
 and their function, which is as yet only hypothetical, will be 
 discussed in Chapter XI. The following are included under 
 this head : the majority of the fibres of the brain and spinal 
 cord ; the chief portion of the sympathetic nerves ; the so- 
 called inhibitory nerves ; &c. 
 
 B. SPECIAL PHYSIOLOGY OF NERVES. 
 
 The various nervous fibres, motor, sensory, &c., are so 
 arranged as a rule that all those destined for the same region 
 of the body, of whatever sort they are, run together for a certain 
 distance in one ' mixed ' nerve-trunk, which gives off branches 
 composed of one kind of fibres only (' sensory nerves,' ' motor 
 nerves') when the locality about to be supplied by those 
 branches is almost reached. In the case of cranial nerves, the 
 whole course of which is short, this union is rarely if ever effected. 
 Cranial nerves are, therefore, from their origin for the most 
 part either purely motor or purely sensory. 
 
 The object of the special physiology of nerves is to determine 
 for each nerve-fibre its specific energy, which is called for the 
 sake of brevity its ' function.' This would be self-apparent in 
 the case of any fibre, if its two end-organs were anatomi- 
 cally known and their functions understood. Here the two 
 sciences of anatomy and physiology mutually supplement one 
 another. 
 
 In order to determine the special function of a nerve the following 
 methods are adopted : 
 
 1. A nerve is divided at any point. Stimulation applied to the nerve on 
 that side of the point of section remote from the organ in which the 
 results of excitation would follow norm ally no longer produces the customary 
 results. Thus, if it is a muscular nerve which has been divided, the muscles 
 connected with it remain inactive although the will, or a reflex or automatic 
 stimulus, or any other excitant applied to the nerve above the place of section, 
 are still operative, the muscle is ' paralysed ; ' while, if the nerve is centri- 
 petal, stimulation of the sense-organ, or excitation of the peripheral portion 
 of the nerve, no longer induces sensations, and blindness, deafness, in- 
 sensibility, &c. follow. 
 
CRANIAL NERVES. 347 
 
 2. The ends of the nerve on each side of the place of section are irritated 
 respectively, for the most part with tetanic stimuli, and the consequences 
 noticed. 
 
 Nerve-trunks are divided according to their origins (their 
 central ends) into Cranial, Spinal and Sympathetic Nerves. 
 
 I. Cranial Nerves. 
 
 For greater detail concerning the origin of the cranial nerves refer to 
 Chap XI. 
 
 First pair (Olfactory nerve). The fibres of this nerve have 
 the function of conducting every irritation, at whatever point of 
 their course it originates, to that portion of the brain concerned 
 in the sensation of smell, thereby giving rise to that sensation. 
 Irritation always takes place physiologically in the peripheral 
 end-organs situated in the olfactory membrane of the nose 
 (Chap. X.), by means of specific irritants, 'odorous bodies.' 
 Section of the olfactory bulb, which is practicable in the case 
 of young animals, destroys the sense of smell (Bifri). 
 
 The production of the sensation of smell on stimulation of the olfactory 
 nerves by means of ordinary nerve -stimulants, has not yet been directly 
 demonstrated. 
 
 Second pair (Optic nerve). All stimulations of this nerve 
 cause irritation of that portion of the brain concerned in the per- 
 ception of light, and, in consequence, produce the impression of 
 luminosity. Its normal stimulus proceeds from the peripheral 
 terminations of its fibres in the retina of the eye. It has, in 
 addition, the power of calling into reflex action the sphincter 
 of the iris through fibres of the motor oculi proceeding to that 
 muscle. The optic chiasma is discussed in Chap. X. 
 
 Third pair (Motores oculi). This nerve is the motor nerve 
 for most of the, orbital muscles, viz. for the rectus sup., rectus 
 inf., rectus int., obliquus inf., and levator palpebrae superioris ; 
 for the circular muscle of the pupil and the tensor choroidea3. 
 It may be called into activity by voluntary stimuli, or those 
 of its fibres destined for the iris may be excited in a reflex 
 manner by irritation of the optic nerve (Chap. X.). It is 
 maintained by some that it contains also sensory fibres ; but 
 it seems probable that it does not possess any until after its 
 
348 CRANIAL NERVES. 
 
 union with the trigeminal nerve ; this is, however, denied by 
 Adamiik. 
 
 Section and paralysis .of the motor oculi causes: 1. Drooping of the 
 upper eyelid ('ptosis'). 2. Rotation outwards of the eyeball, since the 
 muscles supplied by it can no longer balance those supplied by the fourth 
 (trochlearis) and sixth (abducens). 3. Dilatation and insensibility to light 
 of the pupil. 4. A constant state of accommodation for long distances. 
 
 In animals, the fibres for the pupil are said occasionally to run in the 
 abducens instead of in the niotorius oculi (Adamiik). In their course to the 
 iris they traverse the ciliary ganglion and nerves. 
 
 Fourth pair (Trochlear, or pathetic). This is the motor 
 nerve for the obliquus superior muscle of the eyeball. The exis- 
 tence of sensory fibres in this nerve is maintained by some 
 writers. 
 
 Fifth pair (Trigeminal). This is a mixed nerve, arising, 
 after the fashion of a spinal nerve, by two roots, a sensory (large) 
 and a motor (small), and soon afterwards splitting up again into 
 motor and sensory branches. The sensory root, like the sensory 
 root of a spinal nerve, possesses a ganglion the Grasserian or 
 semilunar ganglion. 
 
 Its sensory fibres confer sensibility on nearly the whole of 
 the head, and they serve the purposes of a large number of 
 reflex acts. The regions of the head not supplied by the 
 trigeminus are : portions of the pharynx, palate and root of 
 the tongue which receive branches from the vagus and glosso- 
 pharyngeus ; the Eustachian tubes, tympanic cavity, and a part 
 of the external auditory meatus and external ears which 
 receive branches from the auricular branch of the vagus ; and 
 finally a portion of the back of the head which is supplied by 
 the cervical spinal nerves. Some of the fibres of the trigeminus 
 appear to belong to the nerves of taste (Chap. X.). Its motor 
 fibres supply the muscles of mastication (temporal, masseter, 
 mylo-hyoid and both pterygoids), the tensor tympani, tensor 
 palati mollis, and probably also (Oehl) the dilatator iridis 
 (Chap. X.). In addition, there run in the trigeminus vaso- 
 motor fibres (probably of sympathetic origin) for the con- 
 junctiva and iris. Finally, it contains secreting fibres for the 
 lachrymal, parotid and submaxillary glands, concerning the 
 origin and course of which, and their connection with the 
 facialis, more is given on p. 96. 
 
 Some ascribe to the trigeminus fibres of a trophic character, destined 
 
CRANIAL NERVES. 349 
 
 especially for the eyeball, since section of the trigeminus in the skull causes 
 inflammation and degeneration of that organ. It is probable, however, that 
 this result is to be attributed merely to loss of sensation which interferes 
 with the protection of the eyeball from external influences ; for no inflam- 
 mation follows after section of the trigeminus, if a sensitive protective surface 
 be artificially placed before the eyeball, e.g. in rabbits by stitching in front of 
 it the ear which is supplied by the cervical nerves (Snellen). The latter ex- 
 planation has recently been doubted. In the first place, after paralysis of the 
 facialis, no inflammatory changes follow, notwithstanding that the animal 
 thus paralysed is no longer able to protect its eye by closing the lid 
 (Samuel). In the second place, after partial section of the trigeminal trunk 
 in which the innermost fibres have been left intact, no inflammation is 
 noticed, notwithstanding the complete sensory paralysis which occurs, and 
 that the eye remains unprotected by artificial means ; while, on the other 
 hand, the eye becomes inflamed very easily (if not artificially protected), if 
 in partial section the innermost fibres have been destroyed, notwithstanding 
 that sensation still remains (Meissner, Schiff). If, therefore, the preceding 
 isolated statements should be confirmed, and if the influence of vaso-motor 
 fibres can be excluded, it will be necessary to resume the supposition of 
 special ' trophic ' fibres which course along the inner border of the trunk. 
 The operation of these fibres is, as yet, quite unintelligible. The trigeminus 
 is, moreover, said to contain trophic fibres for the cavity of the mouth, since 
 section of that nerve occasions ulceration. The latter, however, depends 
 upon the distortion of the lower jaw due to unilateral paralysis of masti- 
 catory muscles, whereby the teeth no longer meet, but press upon the mucous 
 membrane opposite (Rollett). 
 
 Sixth pair (Abducens). This is the motor nerve for the 
 external rectus muscle of the eyeball (abducens). 
 
 The abducens receives, by anastomosis, fibres from the cervical portion 
 of the sympathetic, so that the external rectus received in addition fibres 
 from the ciliospinal region of the spinal cord (Chap. XL). 
 
 Seventh pair (Facial). This nerve contains almost exclu- 
 sively centrifugal (motor and secreting) fibres. Wherever it hap- 
 pens to possess sensory twigs it is due to the presence of fibres from 
 the trigeminus, and, since section of the trigeminus does not 
 cause complete loss of sensibility, to a slight extent from the 
 vagus also. The chorda tympani, according to more recent 
 theories, conveys gustatory fibres (Chap. X.). 
 
 Its motor fibres supply all the superficial muscles of the 
 head, the ' muscles of expression,' the muscles of the external 
 ear, the stylo-hyoid muscle, the levator palati, the posterior 
 belly of the digastric muscle, the stapedius, and finally the 
 platysma myoides. Its secreting fibres are connected with the 
 salivary glands. 
 
350 CRANIAL NERVES VAGUS. 
 
 Paralysis of the facialis of one side causes contraction of the face towards 
 the opposite side. This is due to the fact that, after contraction of the face, 
 the tension of the paralysed muscles is not sufficient to stretch out the 
 muscles of the opposite side to their previous length. 
 
 Eighth pair (Auditory nerve) (portio mollis of the seventh 
 cranial nerve of Willis). This is the only nerve connected 
 with the perception of sound. Every irritation of it calls forth 
 an auditory sensation, and section of it causes deafness. Con- 
 cerning a noteworthy relationship between the auditory nerve 
 and the position of the head, consult the Appendix to the 
 Section on the sense of Hearing (Chap. X.). 
 
 Ninth pair (Glosso-pharyngeal) (part of the eighth cranial 
 nerve of Willis). This is a mixed nerve, which, however, only 
 contains a few motor fibres for the following muscles : levator 
 palati, azygos uvulae, middle constrictor of the fauces, and stylo- 
 pharyngeus. The remaining fibres are centripetal, and minister 
 in part to the sense of touch, but chiefly to the sense of taste, 
 of the soft palate and the root of the tongue. 
 
 Tenth and eleventh pairs (Vagus or Pneumogastric and 
 Spinal Accessory of Willis). Both together form a mixed 
 nerve. It has been maintained (Longet) that these two nerves 
 are to be regarded as two roots, of which one (Vagus) contains 
 the centripetal, while the other (Accessorius), whose inner or 
 anterior branch unites with the Vagus of descriptive anatomy, 
 contains the centrifugal fibres. The vagus, however, at its 
 origin, contains motor-fibres for the larynx, pharynx, and oaso- 
 phagus (Van Kempen). 
 
 The centrifugal fibres, so far as is known, are the following: 
 
 a, Motor fibres. 1. For the muscles of the soft palate and 
 the pharynx. 2. For the muscles of the larynx, contained for 
 the most part, in the n. laryngeus inferior or recurrent laryngeal. 
 The n. laryngeus superior supplies a branch for the crico- thyroid 
 muscle : this statement has, however, been lately denied. 
 
 3. For the muscles of the bronchi : this is, however, doubtful. 
 
 4. For the oesophagus ; after Section of both vagi food which is 
 swallowed no longer enters the stomach, while after section of 
 the accessories no such result follows. 5. P'or the stomach (p. 
 101, 147). 6. According to some writers, for the small and large 
 intestine and for the uterus. 7. For the sterno-cleido-mastoid 
 and trapezius muscles, the fibres being situated in the outer or 
 posterior branch of the accessorius of descriptive anatomy. 
 
FUNCTIONS OF THE VAGUS. 351 
 
 b. Eegulating inhibitory fibres for the heart (Ed. Weber, 
 Budge). 
 
 c. Secretory fibres. 1. For the glands of the gastric mucous 
 membrane, &c. : this fact has not been conclusively proved, and 
 has lately been contested. 2. For the kidneys (Bernard), since 
 irritation of the vagus at the cardia is said to increase the 
 urinary secretion, producing simultaneously arterialization of 
 the venous blood (?). 
 
 d. Vaso-motor fibres for the vessels of the lungs (?). 
 The centripetal fibres are the following : 
 
 a. Sensory fibres supplying, in all probability: 1. The whole 
 respiratory apparatus. 2. The digestive apparatus from velum 
 palati to pylorus. 3. The heart. 
 
 b. Eegulating fibres: 1. Accelerating for the inspiratory 
 centre, arising probably in the lungs. 2. Inhibitory for the 
 same centre (Kosenthal). The distribution of these acceler- 
 ating and inhibitory fibres among the branches of the vagus 
 has been described on p. 167. 3. Stimulant for the cardiac 
 inhibitory centres (Bonders). 4. Stimulant for the vaso-motor 
 centre ('pressor fibres'), especially in the superior laryngeal 
 branch (Aubert and Eoever). 5. Inhibitory for the same centre, 
 which in many animals run in a special branch, the Eamus de- 
 pressor nervi vagi (Ludwig and Cyon). 6. Stimulant for the 
 salivary secretion, arising probably from the stomach (though 
 this is doubtful : consult p. 94 et sq.\ 7. Inhibitory for the 
 pancreatic secretion (Ludwig and N. 0. Bernstein). 8. Stimu- 
 lant for the sugar-formation in the liver, i.e. fibres, the centripetal 
 irritation of which calls into reflex activity the nerves which 
 lead to the formation of sugar; these fibres have their peri- 
 pheral terminations in the fchorax, possibly in the lungs (Bernard). 
 
 The results of experimental section and irritation of the vagus and acces- 
 sory, which have served to determine the various series of fibres contained 
 in those nerves will now be gathered into a resume. 
 
 1. Section of the spinal accessory above its point of union with the 
 vagus (or, as is the usual plan, removal of the accessorius-roots from the cord), 
 paralyses all the muscles dependent upon the vago-accessorius for their nerve- 
 supply : according to some, the laryngeal muscles (van Kempen, Navratil) are 
 not affected, and the power of swallowing is not entirely lost. In addition 
 section of the accessorius causes acceleration of the heart's action, while 
 stimulation produces slowing (Waller, Heidenhain). Unilateral paralysis 
 of the external portion of the accessorius causes a twisting of the head. 
 
 2. Irritation of the vagus above the point of union with the accessorius 
 
352 FUNCTIONS OF THE VAGUS. 
 
 causes, among other things, contractions in larynx, pharynx, and 
 oesophagus. 
 
 3. Section of the vagus-trunk in the neck causes (a) paralysis of laryn- 
 geal muscles and, in consequence, when both vagi are divided, inaction of 
 the vocal cords, loss of voice and passage of portions of food into the lungs, 
 whereby fatal pneumonia is induced ; (&) quickening of the heart's action ; 
 (c) slowing of the movements of inspiration ; (d) prevention of those reflex 
 acts which stimulations applied to larynx, pharynx, and stomach, normally 
 induce ; (e) prevention of the last act in the operation of swallowing, so that 
 the oesophagus becomes filled with food ; (/") interruption of the sugar- 
 formation in the liver (?). 
 
 4. Irritation of the peripheral portion of the divided vagus in the neck 
 causes () spasms of the glottis or contraction of the laryngeal muscles, 
 which is also induced by irritation of the peripheral end of the inferior laryn- 
 geal nerve ; (b) slowing of the heart's action, and finally stand-still of that 
 organ in diastole; (c) contraction (so it is said) of the smooth muscles of 
 the bronchi, thus narrowing their lumen somewhat ; this has, however, been 
 frequently denied, by Donders, Wintrich, Rosenthal and Rugenberg, but 
 has been again supported recently by Schiff ; (d) contraction of stomach, 
 intestine (?), uterus (?), &c. ; (e) increased renal secretion (?). 
 
 5. Irritation of the central portion of the divided vagus in the neck 
 causes () quickening of inspiratory movements which proceeds even to 
 inspiratory tetanus; occasionally, however, an opposite result follows (p. 
 168) ; (b) increased sugar-formation (?) ; (c) increased salivary secretion (?) ; 
 (d) diminished pancreatic secretion ; (e) diminished blood-pressure if stimu- 
 lation be applied above the point of union of depressor and vagus ; (f) 
 slowing of the heart's beat when the other vagus is intact. 
 
 6. Section or paralysis of the inferior laryngeal nerve paralyses the 
 laryngeal muscles, causing the same phenomena as section of the vagus in 
 the neck (see 3. ) ; aneurisms of the aortic arch sometimes pr^ss upon the 
 left inferior laryngeal nerve, thus producing paralysis of the left vocal cord. 
 
 7. Section of the superior laryngeal nerve causes a slight slowing of inspi- 
 ration (Sklarek), on account of the motor fibres for the larynx, and espe- 
 cially for the crico-thyroid muscle, which it contains, Nawratil has recently 
 denied that the crico-thyroid muscle receives motor supply from this nerve. 
 
 8. Irritation of the central portion of the divided superior laryngeal 
 nerve causes (a) slowing of inspiration which proceeds to complete cessation 
 of the respiratory movements (Rosenthal); (6) increased blood-pressure by 
 inducing contraction of the arteries. 
 
 9. Irritation of the central portion of the divided depressor branch of the 
 vagus causes dilatation of all the arteries and, in consequence, a fall of 
 blood-pressure (Cyon and Ludwig). 
 
 The irritability of the fibres of the vagus or, more correctly, of the end- 
 organs of the fibres, varies with the fibre. 
 
 On irritation of the peripheral portion of a divided vagus, a stronger 
 stimulus is needed to produce slowing of the heart than is necessary to pro- 
 duce contraction of the laryngeal muscles (Rutherford). During irritation 
 of the central portion the fibres which cause quickening of respiration are 
 
HYPOGLOSSUS SPINAL NERVES. 353 
 
 sooner exhausted than those which cause slowing (Burkart). The inhibi- 
 tory fibres for the heart are sometimes very unequally divided between the 
 two vagi (p. 74). 
 
 Twelfth pair (Hypoglossal). This nerve is the motor nerve 
 for all the muscles of the tongue, and, therefore, also the motor 
 nerve concerned in speech. In addition it supplies the muscles 
 connected with the os hyoides. It receives sensory fibres through 
 its ramus descendens from the first cervical nerve, in consequence 
 of which the tongue retains a certain amount of sensibility 
 even after section of the trigeminus. 
 
 II, Spinal Nerves. 
 
 The centric course and. origin of the spinal nerves is given in Chap. XL 
 
 All the nerves springing from the spinal cord are, in a great 
 part of their course, mixed. They are not so, however, at their 
 origin, each arising by two roots, an anterior, containing the 
 centrifugal, and a posterior, containing the centripetal, fibres 
 (Charles Bell). The former is called the motor, and the latter 
 the sensory, root ; the sensory root being provided with a gan- 
 glion. 
 
 If all the anterior roots of the nerves on one side be divided, the muscles 
 on the corresponding side of the body become completely paralysed : while 
 section of the posterior roots causes complete insensibility. If in an animal 
 a frog we divide on the one side (say the right) the posterior, and on the 
 other the anterior, roots of the lower spinal nerves, the following pheno- 
 mena may be induced. If the right leg be irritated, no movements what- 
 ever occur, since the frog feels no pain ; but if the left leg be irritated, 
 movements for the purpose of avoiding the irritant take place in the right 
 leg, since pain is felt in the left leg, while the right only is capable of 
 motion. Moreover, in leaping, the frog drags its right leg just as it would a 
 paralysed limb, because it no longer feels it. 
 
 The anterior roots are said sometimes to contain sensory fibres (Longet). 
 They are, however, only such as proceed in reality from the posterior root 
 and bend backwards into the anterior, after the roots have united to form 
 the common trunk. Hence, after section of such anterior roots, it is only 
 the peripheral portions which are sensitive, and sensibility is quite lost as 
 soon as the posterior roots are also divided (Magendie). 
 
 The centrifugal fibres of the spinal nerves (contained in the 
 anterior roots) are : 
 
 1. Motor fibres for all the transversely striated muscles of 
 the trunk and extremities, and, probably through the medium 
 
 A A 
 
354 SPINAL NERVES. 
 
 of the sympathetic, for certain smooth muscles of the abdominal 
 viscera also, as for example, for the muscular wall of the bladder. 
 2. Vaso-motor fibres for most of the arteries of the body ; they 
 however, in part, first pass into the sympathetic system of nerves 
 and then enter into other spinal roots (p. 76). 3. Possibly also 
 secreting and trophic fibres. The centripetal fibres are the 
 nerve-fibres of sensation for the whole surface of the body except- 
 ing the face and the forehead. 
 
 The distribution among the thirty-one pairs of spinal nerves 
 of the various motor and sensory nerves destined for the different 
 muscles and regions of surface falls under the province of 
 anatomy. 
 
 If the posterior roots of the spinal nerves be divided, the irritability of 
 the anterior roots suddenly sinks (Ludwig and Cyon ; the statement is, how- 
 ever, denied by Griinhagen and G. Heidehain). The former must, there- 
 fore, by a sort of reflex process, keep the irritability of the latter constantly 
 increased, or, as is more intelligible, keep the latter under constant but 
 weak stimulation (consult Chap. XI. on the tonus of muscle). If the last- 
 mentioned supposition be correct, on irritation of the anterior roots, the 
 stimulus' applied will simply serve to increase that constant weak stimulation. 
 
 III. Sympathetic Nerves. 
 
 The consideration of the sympathetic nerves cannot well be 
 separated from that of the sympathetic central organs, which 
 will be found in Chap. XI., where, also, the reasons for such 
 combined treatment are given at length. 
 
355 
 
 CHAPTEE X. 
 
 THE PERIPHERAL END-ORGANS OF NERVES. 
 
 IN discussing the organs engaged in secretion and motion 
 the little which is known concerning the peripheral termina- 
 tion of centrifugal nerves has been referred to. The peripheral 
 organs of centripetal nerves have in great part been accurately 
 investigated. Many of these are in connection with con- 
 trivances which serve to transmit in a suitable manner to the 
 end-organs the influences of the external medium, such as light, 
 sound, heat, pressure, &c., which are capable of exciting nerves. 
 For this purpose there exist organs which are composed both 
 of conducting arrangements and end-organs of nerves, and 
 which are called Organs of the Senses. 
 
 As the physiology of the conducting arrangements cannot 
 be separated from that of the end-organs, the whole of the 
 physiology of the Organs of the Senses will be here treated of. 
 
 I. THE OKG-AN OF SIGHT. 
 
 In the organ of sight, the eye, the end-organs of the nerves 
 terminate in a spherically curved membrane (the retina) ; the 
 luminous impressions capable of exciting the sense of sight fall 
 upon this surface. The rays of light which enter the eye are pro- 
 jected by means of a system of different refractive media upon 
 the retina, in such a manner that a diminished, inverted and 
 real image of the objects seen, is formed upon it, just as in a 
 camera obscura. 
 
 Schema of the Eye. 
 
 The refractive media of the eye in the order in which they 
 are traversed by the rays of light which fall upon them, are 
 
 A A 2 
 
356 SCHEMA OF THE EYE. 
 
 the following : 1 . The cornea. 2. The aqueous humor. 3. The 
 lens with its capsule. 4. The vitreous body. Four separating 
 surfaces (refracting surfaces) correspond to these media. 1. A 
 surface between the air and the substance of the cornea 
 (anterior surface of the cornea). 2. A surface between the 
 cornea and the aqueous humor (posterior surface of the cornea) 
 &c. In order to be able to follow the paths of luminous rays 
 which pass through the eye to the retina, the following data 
 must be known : 1. The refractive indices of all the media. 2. 
 The forms of all the refracting surfaces. 3. The distances of 
 these from one another and from the surface upon which the 
 image is projected (retina). 
 
 The crystalline lens is not a simple refracting medium ; 
 its consistence and its power of refraction increase from the 
 exterior to the interior, its solid nucleus, which is of very small 
 radius of curvature, refracting light most powerfully. 
 
 The annexed diagram, Fig. 12, which represents in a 
 simplified manner the structure of the lens, shows that it may 
 
 ^ looked upon as made up of a 
 powerful convex lens c and of two 
 concave lenses a and b. The latter 
 neutralize to a certain extent the 
 action of c, and they do so the less 
 the smaller their refractive index. 
 In as much 'as a and b -possess a 
 smaller index of refraction than c, 
 the action of the lens as a whole is greater than it would be if 
 they had the same index of refraction as c, i.e. it is greater 
 than would be the case were the lens composed of homogeneous 
 matter having the same index of refraction as the nucleus. 
 The focal distance of the lens being determined by experiment, 
 and its shape being known, the so-called total index of refrac- 
 tion of the lens may be calculated, i.e. the index of refraction 
 which the lens would possess, were it homogeneous. According 
 to what was said previously it follows that the index thus cal- 
 culated is greater than that of tire nucleus. 
 
 The optical problems connected with the eye are much 
 simplified by the fact that the cornea is a membrane the sur- 
 faces of which are parallel, and which limits anteriorly and pos- 
 teriorly fluids which possess approximately the same index of 
 
SCHEMA OF THE EYE. 357 
 
 refraction (in front is the lachrymal fluid which moistens it, 
 behind the aqueous humor) ; such a body (like a plate of glass 
 the surfaces of which are in contact with air, e.g. a window- 
 pane or a watch-glass) cannot give a new direction to a ray of 
 light which traverses it, but can only deviate it slightly in a 
 direction parallel to itself. The cornea itself may therefore be 
 entirely neglected, and we may reason as if the aqueous humour 
 extended to the anterior surface of the cornea. There re- 
 main, therefore, only three refracting media to be taken into 
 account, the aqueous humour, the lens, and the vitreous body, 
 in addition to three refracting surfaces, viz. the anterior surface 
 of the cornea and the anterior and posterior surfaces of the 
 crystalline lens. The centres of curvature of these three sur- 
 faces lie in one straight line the optic axis. 1 
 
 The following data apply to the eye when at rest (i.e. when 
 not accommodated for distance) (Listing). 
 
 (a.) The refracting surfaces are spherical surfaces the radii 
 of which have the following measurements : 
 
 1. The anterior surface of the cornea about 8 mm 
 
 2. The anterior surface of the lens 10 mm 
 
 3. The posterior surfaces of the lens 6 mm 
 
 (6.) The distances between these refracting surfaces are 
 
 from 1 to 2 . . . . about 4 mm 
 2 to 3 (' axis of the lens >) 4 mm 
 
 3 to the retina ... 13 mm 
 
 (c.) The indices of refraction are (that of air being taken 
 as 1 ) for the aqueous humour 
 
 for the lens (total) = 
 
 103 
 
 for the vitreous body = 
 
 The results of the most accurate of these determinations (Brewster, the 
 two Krauses, Helmholtz) cannot here find a place ; only the methods which 
 have been employed in making them can be shortly indicated. The re- 
 fractive indices of the fluid media have been determined in the media of eyes 
 removed from the body by well-known optical methods ; the total refractive 
 
 1 When examined under water the action of the anterior surface of the cornea 
 also ceases, so that the eye under tfiese circumstances possesses but two refracting 
 surfaces. The consequences of this will be seen further on. 
 
358 OPHTHALMOMETER FORMATION OF THE IMAGE. 
 
 index of the lens is calculated from its empirically determined focal distance 
 and from its external form. The determination of the radii of curvature 
 must when possible be determined in the living eye, as the forms undergo 
 various changes (see below). This determination is made by the following 
 very exact method, which is specially of importance in ascertaining exactly 
 the changes which occur during accommodation (Helmholtz). According 
 to simple geometrical principles the radius of a spherical surface may be 
 calculated by placing a body of linear form and of known length at a 
 measured distance from it, and measuring the image of the body reflected 
 at the spherical surface. These measurements are effected in the following 
 manner : the corneal image, which we shall suppose to be horizontal, is 
 observed through a thick glass plate. This plate is divided horizontally 
 into two halves, which are movable around a common vertical axis. So 
 long as the rays of light pass perpendicularly through the glass plate, the 
 reflected image appears unchanged ; if now the two glass plates are turned 
 around their axis, but from opposite sides (so that looked at from above 
 they appear crossed), each plate is struck obliquely by the rays, and in con- 
 sequence the image is displaced in a horizontal direction. The two plates 
 displace the image in opposite directions, and there appear two images ; if 
 now the plates have been turned to such an extent that the image seen through 
 each is displaced through a distance of one half of its length and that the op- 
 posite terminal points of the two images touch (one image appearing to be a 
 prolongation of the other), the length of the image may be calculated from 
 the angle which the two plates make one with the other, providing that 
 the thickness and refractive index of the plates be known. Such an ap- 
 paratus, so arranged that the angle between the plates may be read off, is 
 termed an l Ophthalmometer.' In reference to the distance between the re- 
 fracting surfaces, it may be said that the thickness of the lens (i.e. the 
 length of the axis of the lens) may be determined in lenses removed from 
 the eye. Yet it is better, on account of the changes which it undergoes 
 physiologically, to effect this measurement by means of the Ophthalmo- 
 meter, in the living eye, from the reflected images ; the same method is 
 followed in determining the distance between the anterior surface of the 
 cornea and the anterior surface of the crystalline lens. 
 
 Formation of the Image. 
 
 According to the statements which have been made, the eye 
 is a system composed of three concentric refracting surfaces. 
 The laws of refraction of such a system may be explained as 
 follows. 
 
 1. Let CD (Fig. 13) be a spherically curved refracting surface, K the 
 centre of curvature, and A B a straight line which passes through it, the axis. 
 Let c D separate two media, of which the one to the left (the anterior or 
 first) possesses the refractive index m t the other (the posterior or second) the 
 index n. 
 
 The luminous ray E G falling from the point E on the axis in the first 
 
REFRACTION AT SPHERICAL SURFACES. 359 
 
 medium upon the surface c D is refracted at G ; the perpendicular to the 
 tangent- plane at the point G is the radius K I, therefore E G I =p is the 
 angle of incidence, K G L = q is the angle of refraction. According to the 
 law of refraction EG, K I and G L lie in one plane, so that G L must like E G 
 cut the axis. Let the distance, E H, of the point E from the principal point 
 
 H, be equal to a lt and the distance of the point L from the principal point 
 H, L H, be equal to 2 . The relation of the distances a 1 and a z is then 
 obtained in the following manner (let the angle H E G = s, then the angle 
 HKG=P s, and the angle HL Q=p q s j lastly, let the radius K H 
 = KG = r). 
 
 According to the law of refraction 
 
 sin^? : smq = n : m ......... (1) 
 
 In the triangle E G z 
 
 a^ + r : r = sin (180-^) : sin s ...... (2) 
 
 And in the triangle GEL 
 
 2 r : r = sin q : sin (p q s) ...... (3) 
 
 If E and H are very distant from one another, or if G and H are very 
 close to one another, then the ray E G is only slightly bent from the direc- 
 tion of the axis, and if it falls upon the refracting surface near the axis, the 
 angles p, q, and s are so small that one may consider their sines to the arc 
 as equal. If one does this, and if one considers that sin (180 p) = sin p, 
 then 
 
 (1) becomes nq*>mp ........... (4) 
 
 (2) ..... pr = s(a 1 + r) ......... (5) 
 
 (3) ..... qr = (p-q-sXa z -r) ---- (6) 
 
 If in these three equations we eliminate q and s, p vanishes, and we 
 obtain the following simple relation between j and 2 : 
 
 a, 2 r 
 
 As this relation is independent of the angles p and s, all other rays fall- 
 ing from E upon c D (always assuming that the angles p and s are not too 
 large) must, after being refracted, pass through the point L. A ' homocen- 
 tric ' pencil of rays proceeding from E must, therefore, after refraction again 
 be homocentric; the point of intersection after refraction is termed the 
 image of the luminous spot E. 
 
360 REFRACTION AT SPHERICAL SURFACES. 
 
 2. If the point E be not situated in the axis, a straight line may always 
 be drawn through it and the nodal point K, and this line may be looked 
 upon as a new axis ; the image L then lies in this line. 
 
 3. The law of homocentric pencils of light applies wherever the point E 
 may be situated. A point of intersection of the rays proceeding from it cor- 
 responds to every luminous point, and this point of intersection always lies 
 in a straight line, joining the luminous point and the nodal point ; this line 
 is called the principal ray or line of direction. 
 
 The image is called real when the^rays, as in Fig. 14, pursuing their 
 proper direction, form it ; it is called virtual when it is not formed by the 
 rays, but is only obtained by prolonging them backwards. 
 
 4. If the positions are reversed and the refracted rays be regarded as the 
 incident rays (the real or the virtual point in the image becoming the real 
 or virtual point of exit of rays), these will again unite, as the most super- 
 ficial consideration teaches us, at the original luminous points. 
 
 The luminous point and the image have, therefore, a reciprocal relation- 
 ship, and they are, for this reason, more correctly designated { conjugate 
 foci/ and their respective distances from the principal point (a l and a 2 in 1), 
 as ' conjugate focal distances.' 
 
 5. If in Fig. 13 the incident ray E G be parallel to the axis, then E H = x 
 
 = oo , and in equation (7) = o, and consequently a 2 acquires the value 
 
 Conversely, if the ray L G coming from the second medium be parallel to 
 the axis, then 
 
 L H = a 2 = ao , and in equation (7), a l acquires the value 
 
 (9) 
 
 Thus all rays which are in the first instance parallel to the axis unite after 
 refraction at a point P a (Fig. 14) which may be termed the posterior or 
 second focal point, and the distance of which from the principal point 
 HF 2 =/ (equation 8) is termed the second focal distance. Similarly all 
 those rays which are parallel to the axis in the second medium, unite to form 
 the first or anterior focal point F 1 , the distance of which from the centre of 
 curvature, H F x = /j (equation 9), is termed the first focal distance. (Con- 
 
REFRACTION AT SPHERICAL SURFACES. 
 
 361 
 
 versely all rays which proceed from the focal points, become parallel after 
 refraction.) 
 
 6. From (8) and (9) it follows further that 
 
 /i'.'A -": (10) 
 
 A-A-' ( n ) 
 
 i.e. the first and the second focal distances are related to one another as the 
 indices of refraction of the first and second media, and the difference between 
 these focal distances is equal to the radius of curvature ; thus in Fig. 15, 
 HF I = KP a , i.e. the distance of the first or anterior focal point from the 
 principal point H is equal to the distance of the second focal point from the 
 nodal point. 
 
 7. The focal points can very usefully be employed in order to find geo- 
 metrically the image S 2 , which corresponds to a luminous point s r 
 
 In Fig. 15, let H again be the principal point, K the nodal point, F 1 and 
 F 2 the two focal points. The point of intersection of any two refracted 
 
 FIG. 15. 
 
 rays proceeding from s x must be the point of intersection of all other rays. 
 In order to find this point of intersection we may best make use of the 
 following rays : 1. The unrefracted principal ray, S 1 K S 2 ; 2. the ray, s t G, 
 which pursues a course parallel to the axis and passes after refraction 
 through the second focal point, viz., which pursues the course GF 2 s 2 ; 
 3. The ray S 1 F X I, which passes through the first (or anterior) focal point, 
 and which after refraction is parallel to the axis, pursuing the line I S 2 . 
 Any two of these rays suffice in order to find s a , and it is easy to prove 
 geometrically that they all pass through S 2 . 
 
 By the same construction we can further find that any luminous point T, 
 situated in the line s t TJ t perpendicular to the axis, will throw its image on 
 the perpendicular s 2 u 2 , at the point T 2 . All points lying in a plane per- 
 pendicular to the axis therefore form images on a plane which is also per- 
 pendicular to the axis. Every flat object which is perpendicular to the axis 
 furnishes therefore a flat image perpendicular to the axis, which really, as 
 can readily be proved by geometrical methods, resembles the object. 
 
 From 6 it follows that all luminous points situated at an infinite dis- 
 tance (from the refracting surface) throw their image on a plane which is 
 perpendicular to the axis at the focal point ; this plane is termed the focal 
 plane. Rays which are parallel to one another, therefore, always intersect 
 at one point of the focal plane. 
 
REFRACTION AT SPHERICAL SURFACES. 
 
 8. From the preceding there results a simple method of constructing 
 the course of the refracted ray G I, which corresponds to the incident ray 
 E G (Fig. 16). Let o P be the focal plane. A ray parallel to E G must in- 
 tersect the required (refracted) ray at some point (M), situated in the focal 
 plane. 
 
 FIG. 16. 
 
 -R 
 
 In order to find this point we may either make use of the unrefracted 
 principal ray N K M which is parallel to E G, or we may draw through the 
 ifocal point F l a parallel ray (F X L), parallel to E G, which will after refrac- 
 tion pursue a course parallel to the axis and will so lead to M. 
 
 9. If in Fig. 15 ( 7) we take H T^ = a t and H U 2 = 2 , further if the size 
 of the object T^ s^ / the size of its image U 2 S 2 = / 2 (it has a negative 
 sign as it lies below the axis) the following relations are found : 
 
 In the similar triangles s x T7 X ^ and I H F X 
 
 In the similar triangles S 2 TT 2 F 2 and G H F 2 
 
 From (12) it follows li = 1 - 
 
 Irt 
 
 From (13) 
 
 (14) 
 (15) 
 
 ?1 /2 f f 
 
 Lastly from (15) and (16) ^ / 2 + a^ = x 2 or -I* + - = 1 
 
 (16) 
 
 The equation (16) passes into equation (7) if we substitute for/ x and 
 / 2 the values furnished by equations (8) and (9). 
 
 10. If in equation (16), we give to a x all values between oo and 0, 2 ac- 
 quires the following values : 
 
 (1) when j = GO (the luminous point being infinitely distant) 2 =/ 2 
 
 (image situated at F 2 , see 5) 
 
 (2) j = /j (luminous point at FJ) 2 = oo (image infinitely 
 
 distant, see 5) 
 
 (3) Oj = (luminous point at H) 2 = (image coincides 
 
 with H) 
 
 (4) x = (/ 3 /j) x (luminous point at K) 2 =/ 2 / x (image 
 
 coincides with K). 
 
 1 rtj must always be reckoned as positive when it is on the left of H. negative 
 when it is on the right; a 2 , on the contrary, is reckoned positive when it is on 
 the right side. 
 
REFRACTION AT SPHERICAL SURFACES. 363 
 
 The principal point and the nodal point coincide with their own images. 
 
 11. Planes which intersect conjugate foci at right angles to the axis 
 may be called conjugate planes, for the images of objects on the one plane are 
 thrown upon the other. The relation between the size of these images is ex- 
 pressed by /! and / 2 (compare 9). Every point in one plane has therefore 
 an image which corresponds to it in the other, and the distances of these 
 points from the axis are as / x : / 2 . If, therefore, one knows the situation 
 and relation between the sizes of the images on two conjugate planes, we 
 may make use of any point for constructing the image j for every ray which 
 passes from this point in the anterior plane must after refraction pass 
 through a perfectly definite point of the posterior plane. If now in the con- 
 struction we select two rays which obey also the condition of passing through 
 the foci, they are ipso facto perfectly determined. It is naturally most con- 
 venient for the purpose of these constructions to select those conjugate planes, 
 the images in which are not merely similar, but of equal magnitude, and 
 which are called principal planes. 
 
 Their situation is found when in equations (15) and (16) ^ = l v It 
 follows then that a l = and 2 = 0, i.e. the two principal planes coincide not 
 only with one another but also with the refracting surface. 
 
 12. In the case of two spherically curved refracting surfaces, a straight 
 line which joins their centres of curvature constitutes their common axis. 
 As a homocentric pencil of rays falling upon the first surface (providing that 
 its rays do not form too great an angle with the axis) continues homocentric 
 even after refraction, and therefore falls homocentrically upon the second 
 surface, it follows that even after issuing from the second surface the rays 
 are homocentric. 
 
 13. Let the distance of the two refracting surfaces along the axis be e ; 
 further let/^/g be tne focal distances of the first and g lf # 2 those of the second 
 surface. Let now a l be the distance of an object from the first surface, 
 then the first surface casts an image at distance a 2 behind itself. 
 
 If this image be situated at the distance b l in front of the second refract- 
 ing surface, then the image cast by this is situated at a distance 6 2 behind. 
 The following relations are found to exist : 
 
 from (16) A + f* = 1 
 
 a, 2 
 
 from (16) l +_{* = ! 
 
 6j 6 2 
 
 lastly 2 + b l = e. 
 
 Hence 6 2 = fa-/i*-M)g ...... (17) 
 
 14. Further, if / be the size of the object, 1 2 that of its image after pass- 
 ing through the first refracting surface, w 2 the ultimate image after refrac- 
 tion by the second surface, it follows from 
 
 (14) that / = f* - . ^ 
 
 /i ~" a i 
 
 from (15) that m 2 = fc^g . / g 
 
 9% 
 
364 REFRACTION AT SPHERICAL SURFACES. 
 
 If for J 2 we substitute the value found by (17) we obtain : 
 
 15. If it be required to find the positions of the principal planes ( 11), 
 we must in (18) make w? 2 = ^ ; the distance of the first principal plane from 
 the first refracting surface is then found by the following equation : 
 
 (19) 
 
 The distance of the second principal plane from the second refracting 
 surface is found by substituting the value found by equation (19) for a i in 
 equation (17) : 
 
 The two principal planes do not therefore coincide, but are separated 
 from one another by 
 
 a \ + ^ + e. 
 
 16. The ultimate focal point of the rays which before passing through 
 the first refracting surface were parallel to the axis (i.e. the principal focal 
 point or focus} is formed by making a 1 =00 in equation (17) ; b% is then the 
 distance of the posterior principal focus from the second refracting surface, 
 and 
 
 B 2 = (-/)& ........ (21) 
 
 e -f*-ffi 
 
 Conversely the anterior principal focal point, corresponding to the rays, 
 which after the last refraction become parallel to the axis, is found by 
 equation (17), making 6 2 = GO ; x is then the distance of the anterior focal 
 point from the first refracting surface, and 
 
 A = (*-/i)/i . (22) 
 
 e-A-ffi 
 
 17. The distance of the first (anterior) principal focus from the first 
 principal point, i.e. the first anterior focal distance is Aj a l = r t , therefore 
 
 "< = ....... - (23) 
 
 Corresponding to this is the distance of the second (posterior) focal 
 point from the second principal point, i.e. the second chief focal distance 
 
 B 2 6 2 = F 2 , therefore 
 
 F 2 = & - ......... (24) 
 
 / 2 + ^i-e 
 
 From (23) and (24) we obtain 
 
 If now m be the refractive index of the first, n that of the second, o that 
 of the third medium, it results (from 10, 6) 
 
 /i : /a = m ' n 
 ' = n : o 
 
 = m : i therefore 
 
 = m : o ....... (26) 
 
REFRACTION AT SPHERICAL SURFACES. 
 
 365 
 
 i.e. the two principal focal distances bear the same relation to each other as the 
 indices of refraction of the first and last medium. 
 
 18, With the help of the two principal planes (h 1 h l and A 2 7* 2 in Fig. 17), 
 and of the two principal focal points FJ and F 2 , we can easily construct the 
 image S 2 , which corresponds to any given luminous object s x ; here again 
 two rays are made use of. The ray S 1 c 1 proceeding from the point S 1 in a 
 direction parallel to the axis, passes after refraction through C 2 , and F 2 , 
 
 Fm. 17. 
 
 and must therefore follow the path C 2 F 2 S 2 . The ray SjDj which passes from Sj 
 through F X must, after refraction, at first be parallel to the axis, then pass 
 through the point D X on the second refracting plane which corresponds to 
 the point D T on the first, and therefore it must pursue the path D 2 s 2 , and S 2 
 must therefore be the image sought for, which corresponds to s r 
 
 19. If now the lengths H I TJ I = A X and H 2 TJ 2 = A 2 , i.e. if the conjugate focal 
 distances be calculated from the principal points, we obtain from an exa- 
 mination of the similar triangles in Fig. 17, eq. (16), corresponding to an 
 equation 
 
 A^ + A^ =A 1 A 2 (27) 
 
 If in this equation A a = - A w we obtain 
 
 A,-*,-*! (28) 
 
 which is the distance of that point from the first principal plane, the image 
 of which lies just as far behind the second principal plane. 
 
 We have now two new conjugate foci, the two nodal points (KJ and K 2 
 in Fig. 17), which are distant from one another to the extent of the differ- 
 ence of both principal focal distances from the principal points. (In the 
 case of a simple refractive surface, there is but a single nodal point, 2). 
 As the two nodal points are conjugate points, each ray, which after the 
 first refraction is directed towards KJ, e.g. SjKj, i.e. each so-called principal 
 ray, must after the second refraction pass through K 2 , and must be parallel to 
 s 2 Kj, therefore fall on G 2 s 2 , because it has yet to satisfy the other condition, i.e. 
 to cut the second principal plane at the point G 2 , which corresponds to Q l 
 (see 18). It may be easily seen that, in the construction of the image of 
 Sj, instead of one of the two rays s^ or SjDj, the ray SjXj might also be 
 employed. (The two nodal points are hence axial points possessed of the 
 following characters j each ray which before refraction is directed to the 
 first point, passes after refraction through the second, in a direction parallel 
 
366 CARDINAL POINTS OF THE EYE. 
 
 to that of incidence. From this property, the position of the nodal points 
 may be directly determined.) 
 
 20. If to the previously considered system, composed of two refracting 
 surfaces, we add yet a third refracting surface, or a second system composed 
 of two refracting surfaces,the same simplification may as before be admitted, 
 as long as all the refracting surfaces have a common axis (are concentric), i.e. as 
 long as their centres of curvature lie in the same straight line (which could 
 naturally only be constantly the case with two surfaces) ; for only under these 
 circumstances will a homocentric bundle of rays, falling upon each succeed- 
 ing surface, make so small an angle with the axis as to continue homo- 
 centric. It is always possible then to give, in the case of the whole system, 
 the situation of the cardinal points, which serve in the construction of the 
 image, and which are, viz., the two principal points, the two focal points, and 
 the two nodal points. 
 
 If the focal distances of two systems have been found, and the distance 
 of their principal planes known, the cardinal points of the resulting system 
 can always be found by means of equations 19-24 and 28. 
 
 In order to find the cardinal points for the compound system 
 of the eye, the focal distances of each single refracting surface 
 must be ascertained. Equations (8) and (9) or (8) and (11) 
 are employed with this object. 
 
 1. Anterior surface of the cornea : r = 8 mm , m = 1, n = 
 
 103 
 17* 
 Therefore/! = 23-692 mm ,/ 2 = 31-692. 
 
 103 
 
 2. Anterior surface of the lens : r = 10, m = , n = 
 
 W 
 11' 
 
 Therefore/! = 11 4-444, / 2 = 124-444. 
 
 i f\ 
 
 3. Posterior surface of the lens : r = 6, m = , n = 
 
 103 
 77' 
 
 Therefore/! = 74-667, /, = 68-667. 
 
 If 2 and 3 be now combined so as to form one (optical) system, 
 i.e. if the cardinal points of the lens surrounded by the fluids 
 of the eye be wanted, e = 4 mm ,/i = 1 14-44, / 2 = 124-44, g l 
 = 74-667, g 2 = 68-667. Therefore : 
 
 the first principal point of the lens is situated behind the 
 anterior surface of the lens (according to 19) by 
 about - ! = 2-346 mm ; 
 
CARDINAL POINTS OF THE EYE. 367 
 
 the second principal point of the lens is situated in front 
 of the posterior surface of the lens (according to 20) 
 about 6 a = l^OS 1 * 1 ; 
 
 the two focal distances of the lens, which according to 26, 
 in consequence of the indices of refraction of the 
 aqueous and vitreous humour being equal, are equal, 
 are (according to 23 or 24) F t = F 2 = 43-797 mm . 
 
 If now, finally, the cornea is combined with the lens as in 
 the complete system of the eye, we have in this com- 
 bination : 
 
 /, = 23-692,/ 2 = 31-692,0! = 43-797, 
 <7 2 = 43-797, e = 4 + 2-346 = 6-346 mm . 
 In the case of the eye as a whole 
 
 the first principal point is situated (according to 19) at 
 
 ttj = 2-l74 mm behind the convexity of the cornea; 
 the second principal point is situated (according to 20) at 
 
 6 2 = 4-020 mm in front of the second principal 
 point of the lens, therefore 4-020-1- 1-408 = 5'428 mm 
 in front of the posterior surface of the lens, or 
 2-572 mm behind the convexity of the cornea ; 
 
 the two principal points are therefore distant from one another 
 by 0-398 mm . 
 
 The first principal focal distance is (by 23) F t = I5 f 007 wm 9 
 the first focal point is situated therefore 12-833 mm , 
 in front of the convexity of the cornea ; 
 the second principal focal distance is (by 24) F 2 = 20-074 mm , 
 the second focal point is situated therefoie 22-646 mm 
 behind the convexity of the cornea. 
 
 As the distance of the nodal points from the principal points 
 = F 2 -F, = 5-067 
 
 the first nodal point is situated 7-241 mm behind the con- 
 vexity of the cornea, and 
 the second nodal point is situated 7-639 mm behind the 
 
 convexity of the cornea. 
 
 The two principal points are therefore 0*398 mm from one 
 another, about the middle of the anterior chamber of the eye ; 
 the two nodal points lie similarly 0-398 mm from one another, in 
 the posterior part of the lens, the second focal point being either 
 close to or in the retina. 
 
 Figure 18 exhibits the schematic eye with its cardinal points. 
 
368 CARDINAL POINTS OF THE EYE. 
 
 The distance between the two nodal points is so small that 
 in drawings intended for purposes of demonstration they may, 
 without introducing any great error, be united at K ; similarly 
 the principal rays may be simply represented by straight lines. 
 (Likewise the two principal planes may be imagined united in 
 the spherical surface hh, which therefore represents the refract- 
 ing surface of the eye.) If we suppose that all points in the 
 image lie on the retina (on this subject refer to what is said on 
 Accommodation), we can for every point in the object easily find 
 the corresponding point in the image, by drawing from the former 
 a straight line passing through the nodal point and falling upon 
 the retina. 
 
 Such straight lines (e.g. o B in Fig 18) are called lines of 
 direction or visual rays, and the combined nodal points (K) are 
 
 FIG. 18. 
 
 LI BRAR i 
 
 S' IV KUSITY OF 
 
 IALIPOR 
 
 
 
 included under the terms point of intersection of lines of 
 direction] the angle which two visual rays make with one 
 another, is called the visual angle. If it be desired to ascertain 
 the direction in which lies the point of an object which corre- 
 sponds to any point in an image, it is only necessary to draw a 
 straight line (a visual ray) from the point on the image through 
 the combined nodal points, and to prolong it outwards. 
 
 Appendix on the Action of Lenses. 
 
 In the case of a lens, which is bounded on both sides by atmospheric 
 air, the two principal focal distances are (according to equation 26) equal ; 
 by (28), in consequence of this, the nodal points coincide with the principal 
 points. 
 
 In order to find the value of the focal distance, let the two radii of cur- 
 
ACTION OF LENSES. 369 
 
 vature of a biconvex lens be r t and r 8 , let w be the index of refraction 
 (the index of refraction of the atmosphere being 1) ; then the four focal 
 distances of the two surfaces are by 8 and 9 : 
 
 jf r \ f nr, nr r. 
 
 /* - ' /2 = " ' * = 
 
 It follows from (23) or (24), that if the thickness of the lens, e, be 
 
 neglected 
 
 If one of the surfaces be concave, its radius must be considered to be 
 negative. Biconcave and concavo-convex lenses (in which the concave 
 surface has the smaller radius) have, therefore, negative focal distances. 
 
 If two lenses, having the focal distances f and g, be placed so close one 
 behind the other that the distance between them, e, may be neglected, it 
 follows from (23), F being the focal distance of the combination, that 
 
 = f^ff r F = / * g ' ' (80) 
 
 Similarly for a combination of several lenses in proximity, 
 
 (31) 
 
 Let a l be the distance of an object from a lens, ^ its size, f the focal dis- 
 tance, and 2 and / 2 the distance and size of the image, it follows from (16), 
 
 - + - =\ ......... (32) 
 
 a i a z f 
 further from (14), 
 
 i - 1 - 5,', . ...... ... (33) 
 
 l z J 
 
 From the above the characters of the image formed by each kind of lens 
 ma) 7 be ascertained ; the most important are given below. a 1 and / x are 
 always assumed to be positive. 
 
 I. Convex lenses (/ being positive). 
 
 1. 2 is positive, i.e. the images are real, when a^ > /; 
 2 is negative, i.e. the images are virtual, when t < f. 
 
 2. / 2 is negative, i.e. the images are inverted, when a t > f; 
 / 2 is positive, i.e. the images are erect, when a^ < f, 
 
 3. 1 2 < /j, i.e. the images are diminished, when a l > 2f: 
 / a = - / when ^ = 2/; 
 
 / 2 > /j, i.e. the images are enlarged, when t < 2/. 
 
 Hence a convex lens gives, when a x > 2/, real, inverted, diminished images 
 (object-glasses of telescopes, opera-glasses, and camera obscurse) ; when 
 2f>a l >/. the images are real, inverted, and magnified (solar micro- 
 scope, object-glass of the compound microscope) ; lastly, when a v < /, the 
 images are virtual, erect, and magnified (simple magnifying glass, eye-piece 
 of astronomical telescopes and of compound microscope). 
 
 II. Concave lenses (/negative). 
 1. # 2 ^ s always negative, 
 
 B B 
 
370 ACTION OF LENSES. RETINAL IMAGES. 
 
 2. Z 2 is always positive, 
 
 3. L is always < l r 
 
 Concave lenses always furnish virtual, erect, and diminished images of objects. 
 
 If a convex lens be so placed that it furnishes a real, inverted image of 
 an object, and if a second lens be placed in the path of the refracted rays, 
 before they have united to form the image, the rays form the object for the 
 second lens j the distance of the former from the latter, a lt is, however, to be 
 considered as negative. 
 
 The action of the lens thus interposed is as follows : 
 
 I. When the interposed lenses are convex (/is positive). For every 
 negative value of a v 2 becomes positive, 2 < a lf / 2 has the same sign as, 
 but is less than l v i.e. the interposed convex lens furnishes a real inverted 
 image, but brings it closer to the first lens and diminishes its size. The col- 
 lecting lens of the compound microscope exerts this action. 
 
 II. When the interposed lenses are concave (/ is negative). 
 
 1. 2 is positive when a 1 < /, and negative when a l > f. 
 
 2. / 2 has the opposite sign to 7 X when a l < f } and the same sign 
 when !>/. 
 
 3. / 2 < /! when -r^ >2/; / 2 = / x when - a l = 2/j / 2 > / when 
 -i < 2/. 
 
 When a concave lens is interposed between a convex lens and a real 
 image, the latter continues to be real and inverted, providing that the lens is 
 situated at a distance from the image less than its focal distance ; on the 
 contrary, the image becomes virtual and erect if the concave lens is more 
 than its focal distance from the image formed by the first lens ; the eye-piece 
 lens of opera-glasses has this property. It does not alter the size of the 
 image, if it be at a distance from the object equal to twice its focal length. 
 
 On the Images formed on the Retina when the Eye is passive. 
 
 When luminous rays proceeding from any object fall into 
 the eye. a definite point in the image corresponds to every point 
 in the object. All the points of the image together furnish an 
 image which corresponds to the object; the image is, naturally, 
 an inverted one. In order to be distinctly perceived, this image 
 must fall exactly upon the surface of the retina. It is evident 
 that for any given eye remaining perfectly passivej there can 
 be only a single surface, the image of which can fall exactly on 
 the retina. The form and the distance of this surface may 
 be determined from the optical values of the eye. Each point 
 of the object which does not lie in this surface has its 
 corresponding point in the image lying, not in the retina, but 
 in a plane before or behind it. In both cases the retina cuts 
 the pencil of refracted rays proceeding from the object ; in the 
 first case after, in the second before, they have united to form 
 
CIRCLES OF DIFFUSION. SCHEINERS EXPERIMENT. 371 
 
 points in the image'; in both cases, instead of a luminous point 
 being formed on the retina, there ' is a circle of diffused light,' 
 i.e. a small circular area is lighted up ; this corresponds to a 
 section through the luminous cone. 
 
 In Fig 19, B represents the point of the image of the object 
 o, which falls upon the retina r r. If, however, the retina lies 
 
 FIG. 19. 
 
 in front of the point in the image (viz. at r' r'), or behind it 
 (e.g. at r" r"), circles of diffused light are formed, which have 
 the diameters of b' or a" b". 
 
 Hence it follows that, strictly, an immovable eye can only 
 distinctly see objects lying in one plane,, and at a perfectly 
 definite distance. All objects or portions of objects which lie 
 outside the plane, furnish indistinct, blurred, images, in which 
 circles of diffusion instead of points correspond to the luminous 
 points of the object. 
 
 The size of the circle of diffusion depends, cateris paribus, upon the 
 dimension of the cone of luminous rays which reaches the eve, and this 
 again depends upon the width of the pupil, the inner border of which limits the 
 luminous cone. If therefore the pupil contracts, or if it be replaced by a 
 small aperture placed in front of the eye, as e.g. by a hole made in a card, 
 then the circles of diffused light will, cceteribus paribus, become smaller, and 
 consequently the image will be sharper. In Fig. 19, if c d represents the 
 aperture of the contracted pupil, it can be easily seen how the contraction 
 diminishes the diameters of the circles of diffusion to c' d r and c" d" 
 respectively. 
 
 If the pupil be replaced by two small openings, if, e.g., a card which has 
 been perforated in two places by a pin, be placed in front of the eye, the 
 distance between the perforations being smaller than the diameter of the pupil, 
 two smaller luminous cones are as it were cut out of the larger one, and 
 instead of one ' circle of diffusion ' being formed upon the retina, there are 
 two smaller. 
 
 In Fig. 20 let e and/ be the holes in the card which replace the pupil 5 
 the two luminous cones reunite at B ; the retina, if it is not situated in the 
 plane r r, but in two planes r' / or r" r", receives, instead of the luminous 
 point B, two circles of diffused light e f and/" or e" and/" respectively. 
 
 B B 2 
 
372 
 
 A CCOMMODA TION. 
 
 All objects which are so placed in reference to the eye, as to throw a 
 diffused image upon the retina, would in the case just considered throw 
 two diffused images, and therefore be seen double (Schemer's experiment). 
 
 FIG. 20. 
 
 /' r 
 
 Accommodation, 
 
 Daily experience, however, teaches us that a normal eye is 
 capable of seeing objects distinctly which are placed at almost any 
 distance ; there must therefore exist an arrangement, capable 
 of altering the eye, and dependent upon the will. The changes 
 in the eye which occur as a result of this arrangement are 
 included under the term accommodation. It is not known with 
 certainty for what distance the eye is adjusted when it is not 
 actively accommodated. It was formerly supposed that the eye 
 when at rest was accommodated for a medium distance, and ac- 
 commodation was therefore supposed to occur in two directions, 
 in one direction for near objects (positive accommodation), and 
 in another for distant objects (negative accommodation). Now, 
 however, it is almost universally supposed that the normal eye 
 when at rest is adjusted for infinite distances, i.e. that the focal 
 point of the normal passive eye lies on the retina. It follows from 
 this that accommodation only occurs in one direction, i.e. for 
 near objects. 
 
 The principal grounds upon which this view is based are : 1. When tke 
 eyelids which have been long closed are suddenly opened, the eye is found to 
 be adjusted for distant objects (Volkmann). 2. The vision of distant objects, 
 unlike the vision of near objects, is not accompanied by a feeling of exertion. 
 (3) Atropia, which paralyses the apparatus concerned in accommodation, 
 causes an unchangeable adjustment for objects which are as distant as 
 possible from the eye ; if a negative apparatus for accommodation did exist, 
 one would have to make the improbable assumption that under these circum- 
 stances it was thrown into a state of tetanic activity at the same time that 
 paralysis of positive accommodation occurred (Donders). 4. Even in cases 
 of neurotic paralysis of the apparatus of accommodation (as when the third 
 nerve is paralysed) the eye is always accommodated for infinite distance, 
 
ACCOMMODATION. 373 
 
 whilst no paralytic condition is known in which the eye is accommodated 
 for near objects. 
 
 Accommodation might depend upon the following changes 
 occurring in the eye. 1. Changes in the indices of refraction of 
 the media of the eye. 2. Displacement of the surface of pro- 
 jection (retina), analogous to the artificial accommodation in the 
 camera obscura. 3. Alterations in the forms of the refracting 
 surfaces. It is self-evident that the first changes do not occur. 
 A displacement of the retina in the direction of the optic axis, 
 would be possible by a lateral compression of the eyeball 
 brought about by the recti muscles of the eye ; this influence, 
 which was formerly assumed in order to explain accommodation, 
 must be unimportant, seeing that even in eyes which have been 
 cut out of the body changes of accommodation can be occasioned. 
 Changes in the form of the refracting surfaces must, therefore, 
 be possible. These have actually been discovered, and they 
 have been found to occur in the crystalline lens. 
 
 When the eye is accommodated for near objects, the 
 anterior surface of the lens becomes more strongly curved, and 
 approaches closer to the cornea ; this is especially the case with 
 that portion which is not covered by the iris, and which arches 
 forwards through the pupil (Cramer). 
 
 These changes are proved by the following experiment : 
 
 If a lighted candle be placed at one aide of the eye, and if one looks into 
 the eye from the other side, three distinct little images of the flame are seen, 
 which are due to reflexion from the refracting surfaces of the eye : the first, erect 
 (virtual), is formed by the anterior surface of the cornea ; the second, which is 
 also erect, but much weaker, is formed by the anterior surface of the lens ; the 
 third is brilliant, inverted (real), and is formed by the posterior surface of the 
 lens. If the eye now looks fixedly at an object close to it, the second image 
 becomes perceptibly smaller, and approaches somewhat the first image, 
 affording a proof that the anterior surface of the lens becomes more strongly 
 convex and moves forwards. 
 
 Changes of an opposite character occur when the eye stares into infinite 
 distance (Purkinje and Sanson's experiment, Cramer). Instead of aflame it 
 is more convenient to employ one or two luminous points (holes in a screen) j 
 the distance between the reflected images of these points can then more 
 easily be measured by means of the ophthalmometer than the size of the 
 image of a flame (Helmholtz). 
 
 The protrusion of the iris, which is brought about by an increase in 
 the curvature of the anterior surface of the lens, may be shown in the 
 following way : the caustic line (due to refraction through the corneal 
 surface), which shows itself upon the opposite half of the iris when the eye is 
 
374 
 
 A CCOMMODA TION. 
 
 lightedup from the side, changes when the eye is accommodated for near 
 objects then approaching the margin (Helmholtz). 
 
 The following table (Helmholtz) exhibits the changes in the optical 
 constants of the eye which occur during accommodation ; the places are cal- 
 culated from the convexity of the cornea, and are reckoned from behind as 
 positive, from the front as negative. The numbers for the condition of rest 
 have been given at pages 357 and 366, slightly modified from those given by 
 Listing for the typical^eye. 
 
 
 E} r e at rest : 
 adjusted for 
 distant view 
 
 Eye accommo- 
 dated : adjusted 
 for near view 
 
 Kadius of curvature of the cornea 
 
 8 
 
 8 
 
 ., ,, anterior surface) 
 
 
 
 of the lens / 
 
 10 
 
 6 
 
 posterior surface") 
 of the lens / 
 
 6 
 
 5-5 
 
 Position of anterior surface of the lens 
 
 3-6 
 
 3-2 
 
 posterior ,, 
 first principal point 
 
 7-2 
 1-9403 
 
 7-2 
 2-0330 
 
 second 
 
 2-3563 
 
 2-4919 
 
 first nodal ,, 
 
 6-957 
 
 6-515 
 
 second ,, 
 
 7-373 
 
 6-974 
 
 first focal ,, 
 
 -12-918 
 
 -11-241 
 
 second ,, 
 
 22-231 
 
 20-248 
 
 First focal distance . 
 
 14-858 
 
 13-274 
 
 Second 
 
 19-875 
 
 17*756 
 
 
 
 
 Accommodation is chiefly effected by the ciliary muscle (M. 
 ciliaris, M. tensor choroideae, Briicke's muscle). This muscle is 
 composed of both radiating and circular fibres. The first, 
 which constitute the chief part of the muscle, arise from the 
 point of reflexion of the membrane of Descemet, where it 
 passes from the cornea to the iris (lig. iridis pectinatum), and 
 are inserted into the ciliary processes of the choroid ; the un- 
 important circular fibres, which are situated on the inner side 
 of the radiating fibres in the most anterior part of these 
 muscles, surround the border of the crystalline lens. The 
 radiating fibres pull forwards the anterior border of the 
 choroid coat, and so draw the choroid and the retina together like 
 a bag, around the vitreous body (whereby the latter presses the 
 lens forwards). The zonule of Zinn, the tension of which during 
 the state of rest draws the border of the lens backwards and out- 
 wards, and thus flattens the lens, becomes relaxed owing to its 
 posterior insertion being approximated to its anterior (the 
 border of the lens), and thus causes the lens to become thicker 
 (less flat). (Helmholtz.) 
 
ACCOMMODATION. 375 
 
 The circular fibres appear to co-operate by drawing the 
 ciliary processes inwards, and thus leading to a relaxation of 
 the zonule of Zinn (F. E. Schulze). 
 
 The iris also takes a part in the accommodation of the eye for 
 near vision. On the one hand, the part which it plays is 
 passive, in that it assumes a more arched form merely as a 
 result of the greater convexity of the anterior surface of the 
 lens, for the border of the pupil lies immediately in contact 
 with the capsule of the lens ; l on the other hand, it plays an 
 active part, by the contraction of the pupils. (For the movements 
 of the iris see below. ) The contraction of the pupil does not 
 appear to be indispensable to accommodation, seeing that the 
 latter is possible when the iris is wanting or imperfect. Its 
 significance in accommodation is probably to be sought for in 
 the fact that when a lens becomes more convex its spherical 
 aberration increases, and consequently a greater number of the 
 marginal rays require to be screened off. The independence of 
 contraction of the pupil and accommodation is also proved by the 
 fact that the latter precedes the former (Bonders). 
 
 The nerve fibres which are concerned in accommodation are 
 contained in the ciliary nerves ; when these are irritated the 
 eye is accommodated for near vision (Volckers and Hensen). 
 It is in the highest degree probable that these fibres are derived 
 from the third nerve (motor oculi). 
 
 Fig. 21 exhibits a section of the anterior segment of the eye ; n the left- 
 hand side the eye is shown adjusted for distant vision, on the right for near 
 T is ion (after Helmholtz). 
 
 Concordant data are yet wanting concerning the rate at which the act 
 of accommodation proceeds; the rate is, however, tolerably slow. The 
 change from the state of activity to that of rest occurs more rapidly than the 
 reverse (Hensen and Volckers). 
 
 There appears to exist a yet imperfectly investigated central connexion 
 between the nerves which are concerned in accommodation, and those which 
 supply the iris and the external muscles of the eyeball. In favour of such a 
 connexion the following facts may be cited : 1. The behaviour of the pupil in 
 accommodation (see above). 2. Rotation of the eyeball inwards is associated 
 with contraction of the pupil and involuntary accommodation for near vision 
 (Czermak). 3. Atropia, which dilates the pupil, paralyses at the same 
 
 1 The proof of this statement is afforded by the fact that no shadow of the 
 iris falls upon the lens (Helmholtz) ; nevertheless only the margins of the iris 
 are in contact with the lens, for between the other parts of the iris and the lens 
 there exists a posterior chamber filled with fluid (Hensen and Volckers). 
 
376 
 
 ANOMALIES OF REFRACTION. 
 
 time, as has been already stated, the accommodating mechanism ; conversely 
 Calabar bean occasions contraction of the pupil and tetanic accommodation 
 for near view. 
 
 According to some writers, the movements of accommodation 
 always follow a parallel course in the two eyes ; others dispute 
 this statement. 
 
 For every eye' there are definite limits of clear vision ; the 
 furthest point, the image of which can fall exactly upon the re- 
 tina, is called the ''far-point ' (punctum remotum) ; the nearest 
 point is called the ' near-point ; ' the distance between them 
 is called the region of distinct vision. In the case of normal 
 
 FIG. 22. 
 
 F 
 
 N 
 
 s s, canal of Schlemm ; a a b b, the folds of the zonule of Zinn, which are inter- 
 calated between the ciliary processes ; the latter are partly hidden and covered 
 by the former (the section is so arranged that a fold of the zonule lies in front 
 of the ciliary process). The radiating fibres of the ciliary muscle are seen 
 springing from s. 
 
 eyes the * far-point ' is infinitely distant ; the ' near-point,' 
 which is nearer the eye the more active the apparatus of accom- 
 modation, is at a distance of between 0*2 to O3 mm from the eye. 
 In many eyes which are otherwise normal, the focus during 
 rest does not, as usual (in the Emmetropic eye), fall upon the 
 retina, but in consequence of an abnormal length or shortness 
 of the optic axis, it either falls in front of the retina (Myopia) 
 or behind it (Hypermetropia). The distant point of myopic 
 eyes therefore lies abnormally near, the distant point of hyper- 
 metropic eyes, on the contrary, is more than infinitely distant 
 i.e. in order to perceive objects which are at an infinite dis- 
 tance the hypermetropic eye must perform movements of 
 accommodation. The activity of the accommodating mechanism 
 
OPT O METER. IRIS AXD PUPIL. 377 
 
 being the same, the near point of the myopic eye must be 
 abnormally near, that of the hypermetropic eye must be ab- 
 normally distant. Hence myopic eyes are ' short-sighted,' and 
 hypermetropic eyes 'long-sighted.' Other abnormalities depend 
 upon a small degree of activity of the accommodating mechanism; 
 these naturally only exert an influence upon the situation of 
 the point of near sight, not upon that of distant vision. 
 
 The defective or excessive refraction of abnormal eyes i.e., the relatively 
 too great or too small curvature of their lens, can be corrected by glasses 
 (spectacles) ; these must naturally, in the first case (in Myopia), be concave j 
 in the second (in Hypermetropia) be convex. 
 
 Even deficiency in the power of accommodation may be corrected by 
 artificial accommodation, by means of the temporary use of spectacles. The 
 simplest method of determining the situation of the near and distant 
 point is by ascertaining at what distances the eye can readily recognise 
 distinctly an object which is brought near to or which is removed from it, 
 as, e.g., at what distance letters can be read. This method is, nevertheless, in- 
 exact, because the diminution of the visual angle by distance makes the object 
 less easily recognisable. A much better method consists in determining at 
 what distance an object throws a clear, and at what distance a diffused, image 
 on the retina. For this purpose Scheiner's experiment (p. 371) affords the 
 best means of investigation. If ah object (e.g. a pin's head) be looked at 
 through two holes in a card placed close to one another, it appears single if 
 the eye be accurately adjusted, but under opposite circumstances it appears 
 double. If the object be brought closer to the eye, or, on the contrary, 
 removed from it, the space in which it is clearly seen is the field of distinct 
 vision. On this property are based various apparatuses which are used in 
 selecting spectacle-glassesso-called * optometers.' In the best known opto- 
 meter (Stampfer's) the object is an illuminated slit, the distance of which from 
 the eye can be altered and measured at the same time. As age increases, 
 even after the fifteenth year (MacGillavry), the capability of accommo- 
 dating for near objects diminishes, presumably in consequence of an indura- 
 tion of the lens (Bonders). 
 
 Iris and Pupil. 
 
 The iris with its central aperture, the pupil, serves at once 
 as a diaphragm to shut off the marginal rays (being thus 
 analogous to the diaphragms of optical instruments), as well 
 as to regulate the amount of light entering the eye, and as an 
 auxiliary to accommodation. The size of the pupil depends upon 
 the state of contraction of the two antagonistic sets of muscular 
 fibres in the iris, the sphincter and dilator fibres of the pupil. 
 The first form a circular layer around the pupil, the second 
 have a radiate arrangement; the first derive their nervous 
 
378 IRIS AND PUPIL. 
 
 supply from the motor oculi, the second from the sympathetic. 
 If both sets of fibres or their nerves are subjected to the same 
 stimulus, the sphincter fibres predominate and the pupil con- 
 tracts. Usually both nerves are in a certain state of excitation 
 (tonus), for when one is cut through, the muscle governed by 
 the other predominates. If the cervical sympathetic be divided 
 the pupil contracts ; if the third nerve be divided it dilates. 
 
 Eecently the existence of a dilator of the pupil has been denied in 
 mammals (Griinhagen, Hampeln). The older view is supported by nearly 
 all the statements of anatomists (lately Henle, Merkel, Dogiel and v. Hiitten- 
 brenner) ; by the dilatation of the pupil when the sympathetic is irritated 
 (those who deny the existence of dilating fibres maintain that this dilatation 
 is a vaso-motor effect) ; and, lastly, by the circumstance that direct excitation 
 of the border of the iris is able to cause local circumscribed dilatation 
 (B err. stein and Dogiel, Engelhardt). 
 
 The fibres of the motor oculi which cause contraction of 
 the pupil pass to the eye through the ciliary ganglion ; this 
 is, however, not the case with the fibres of the sympathetic 
 which cause dilatation of the pupil. The latter take their 
 origin first of all in the spinal cord, in the neighbourhood of 
 the lower cervical and superior dorsal vertebrae (cilio-spinal 
 centre of Budge). In pathological conditions, when this region 
 is irritated, the pupil dilates. The real centre for these fibres 
 is, however, situated in the higher regions of the cord, presum- 
 ably in the medulla oblongata (Salkowski). 
 
 In the head the fibres which dilate the pupil run in the course of the 
 trigeminus, the irritation of which occasions dilatation, and the section 
 of which prevents the effect which follows irritation of the sympathetic. 
 
 Seeing, however, that after division of the sympathetic the pupil 
 does not contract so powerfully as after the division of the fifth, we must 
 conclude that the fifth contains special fibres capable of dilating the pupil. 
 The origin of these fibres can, in frogs, be traced to the Gasserian ganglion 
 (Oehl, Rosenthal, Hirschmann, S. Guttmann). There exist, however, opposite 
 statements concerning the influence of the fifth pair on the pupil (Rogow). 
 
 Movements of the iris oceur principally under the following 
 circumstances : 
 
 1. Irritation of the optic nerve occasions contraction of the 
 pupil., by irritating in a reflex manner the motor oculi. The pupil 
 contracts, therefore, when light falls into the eye, and the more 
 strongly, the more powerful the light. In this way the amount 
 of light which reaches the retina is partly regulated. Con- 
 
IltIS AND PUPIL. 379 
 
 traction of the pupil also occurs when the trunk of the optic 
 nerve is irritated ^Mayo), and ceases after division of the motor 
 oculi. Irritation of one optic nerve is sufficient to cause con- 
 traction of both pupils. Generally both pupils are, under normal 
 circumstances, of the same size (Bonders). 
 
 2. When the eye is accommodated for near vision the pupil 
 contracts. Poisons which occasion tetanic accommodation 
 for near vision (Calabar bean) also cause contraction. This 
 contraction is caused by an excitation of the nerves which 
 contract the pupil, and is to be looked upon as a kind of ' as- 
 sociated ' movement (Chap. XI.). This contraction commences 
 later, and (in the toxic form) disappears earlier, than the affec 
 lion of accommodation, and is therefore only partly dependent 
 upon the latter. 
 
 The contraction of the pupil which is caused by light commences, on an 
 average, about 0-49 sec. (0-4 Listing) after the irritation, and the maximum 
 effect (contraction) occurs 0-58 sec. after the irritation. 
 
 The contraction connected with accommodation begins 0*41 sec., and 
 reaches its maximum 1-13 sec. after the cause which occasions it. The 
 dilatation which follows irritation of the sympathetic commences in rabbits 
 0-89 sec., and reaches its maximum 3 -40 sec. after the commencement of the 
 irritation (Arlt, jun.) 
 
 3. Rotation of the eyeball inwards occasions a contraction 
 of the pupil, as a kind of 'associated' movement, by irritation 
 of the motor oculi. 
 
 As the eyes are during sleep turned inwards and upwards, 
 the contraction of the pupils which is observed during sleep 
 can be explained. 
 
 4. During dyspnwa the pupils are dilated; this dilata- 
 tion ceases when asphyxia sets in. This dilatation depends 
 upon irritation of the centre which exists in the cord and which 
 presides over the pupil, for it does not occur if the sympathetics 
 have been previously divided. 
 
 5. Powerful irritation of sensory nerves causes, in a reflex 
 manner, dilatation of the pupil (Bernard, Westphal). 
 
 6. Violent muscular efforts (especially powerful inspiratory 
 and expiratory movements) are associated with dilatation of 
 the pupil (Romain-Vigouroux). 
 
 In addition, in the normal state, a very slight alteration of the pupil is 
 observed to occur with every beat of the pulse, as well as with every ex- 
 
380 CHROMATIC ABERRATION. 
 
 piration ; every flow of blood to the iris appears especially to occasion a con- 
 traction of the iris ; in this way may be explained the contraction of the pupil 
 which follows withdrawal of the aqueous humour (Hensen and Volckers). 
 
 7. Numerous poisons, either when introduced into the blood 
 or topically applied, induce changes in the size of the pupil. 
 Atropia, for example, dilates the pupil, by causing a paralysis of 
 the terminations of the third nerve in the circular fibres of the 
 iris. Nicotia, physostigma, morphia, &c. cause contraction of 
 the pupil (Myosis). This is due, according to some, to a 
 paralysis of the terminations of the sympathetic in the dilating 
 (radiating) fibres, but, according to others (Griinhagen), to irrita- 
 tion of the third nerve. Anaesthetic poisons (chloroform, alcohol, 
 &c.) occasion in the first place a contraction, and afterwards a 
 dilatation of the pupil. 
 
 The kind of action which these poisons exert is still matter for con- 
 troversy. Meanwhile the supposition that they all exert an action upon 
 the sphincter arrangement of the iris appears the most probable, seeing that 
 the poisons under dispute exert a simultaneous and corresponding action on 
 the apparatus engaged in accommodation. It is especially a matter of doubt 
 whether the poisons which induce contraction (Myotics) act by paralysing 
 the sympathetic ; in support of the latter view it is stated that irritation of 
 the sympathetic does not exert any action upon the pupil of animals under 
 the influence of such poisons ; this result might be due to the intensity of the 
 tetanic contraction of the sphincter fibres. 
 
 Further, the circumstance that the action of atropia manifests itself 
 even after division of the ciliary ganglion (Hensen and Volckers), and 
 that the action of these poisons occurs when they are dropped into the eye, 
 render it very probable that yet unknown ganglionic centres exist either in 
 the iris itself, or in its immediate proximity (v. Bezold). 
 
 When one pupil is dilated by atropia. the other contracts and remains 
 contracted in consequence of the large amount of light which falls into the 
 first eye. 
 
 Anomalies and Peculiarities of the Eye. 
 
 From what has been stated in the preceding pages it is seen that a 
 sharp, diminished, and inverted image of any object brought within the 
 field of distinct vision can be formed on the retina. Yet the absolutely 
 faultless production of such images is rendered impossible in consequence 
 of certain properties of the eye, which it shares with other optical instru- 
 ments : these are 
 
 1. Chromatic Aberration. White light, as is well known, is decomposed 
 by refraction into its coloured components, in consequence of the unequal 
 refrangibility of the latter. Consequently, if white light proceeds from a 
 point in an object, the latter, instead of having a single spot corresponding to 
 
SPHERICAL ABERRATION. 381 
 
 it in the image, must have a series of such points lying one hehind the other, 
 the most anterior point corresponding to the most refrangible (violet), and 
 the most posterior to the least refrangible (red) rays. The eye cannot 
 therefore be thoroughly accommodated for a white object: if, for instance, it 
 is so accommodated that the image of the violet rays falls upon the retina, 
 the remaining colours appear in concentric diffusion-rings, which are larger 
 the further the colour is separated from violet ; as, however, all the diffused 
 rings and the violet spot fall on the middle, there results a white spot with 
 coloured borders. Similarly every white object must appear white with 
 coloured borders as the coloured diffused images are superimposed as far as 
 the margins. 
 
 If the eye be accommodated for a colour which lies in the middle of the 
 spectrum, as for green, there result, naturally, two series of coloured diffused 
 images ; these cover one another to such an extent to the very borders that the 
 complementary colours (see below) fall upon one another, and the borders even 
 appear in great part to be white. The latter circumstance is one cause why 
 in ordinary vision we do not see the coloured borders of the objects which 
 are looked at; these coloured borders, moreover, in consequence of the 
 slight dispersive power of the media of the eye (the dispersive power of which 
 is nearly the same as that of distilled water), are very slight, and disappear 
 entirely when contrasted with the powerful white light which falls upon the 
 middle of the eye ; possibly, too, the combination of the different ocular 
 media tends to make the eye achromatic (the arrangement being analogous 
 to the combination of flint and crown-glass lenses in optical instruments). 
 In order clearly to perceive these coloured margins, the eye must be ac- 
 commodated, not for a colour in the middle of the spectrum, but for a colour 
 at the extreme end (red or violet) ; this is obviously best done by not 
 accommodating for the object. 
 
 White fields appear, when the eye is accommodated for too great a distance, 
 to possess a faint reddish yellow margin ; when the eye is accommodated for 
 too near a distance the margin is blue (Helmholtz) ; a luminous point seen 
 through a reddish-violet glass appears, when the eye is accommodated for 
 the red rays, to be red with a violet circle of diffusion ; in other cases the con- 
 verse occurs (Helmholtz). From what has been stated it also results that the 
 extent of the field of distinct vision is various for these different colours. 
 Naturally the point of near and distant vision for violet light must be 
 appreciably nearer than for red, a fact which can be proved by looking 
 through a telescope at equally distant spots of various colours, when the 
 glass must be adjusted differently in order that all the colours should be 
 seen with equal distinctness (Frauenhofer). 
 
 Red surfaces appear nearer than blue surfaces which are in the same 
 plane, because the eye has to be more strongly accommodated for the former, 
 and therefore judges the object to be nearer (Briicke). 
 
 2. Spherical (monochromatic) Aberration. As has been already frequently 
 stated, the rays which proceed from the point in an object can only join again 
 to form the point of an image when they fall upon the spherical refracting 
 surface within a very small distance of the axis. This condition is in part 
 satisfied by the iris when it cuts off a large number of the peripheral rays 
 
382 ASTIGMATISM. FLUORESCENCE. 
 
 which fall upon the eye. A further correction is effected by the form of some 
 of the refracting surfaces of the eye ; being ellipsoids, their curvature dimin- 
 ishes decidedly near the margins. Moreover, in the case of the lens, the rays 
 which pass through its borders only traverse the outer layers, which possess 
 smaller powers of refraction than the inner. This correction is, however, 
 never perfect, being sometimes not sufficient, sometimes too great, so that 
 nearly always, especially when the pupil is dilated, a certain amount of 
 aberration is present, which gives rise to circles of diffused light, and con- 
 sequently to indistinct images. 
 
 Sometimes a defective centering of the refracting surfaces of the eye 
 can be discovered (Briicke). 
 
 Some other forms of monochromatic aberration are the following : 
 Astigmatism (Helmholtz, Knapp, Bonders). a. So-called 'irregular 
 astigmatism ' depends upon various deviations in the curvatures of the 
 refracting surfaces, so that the union of a homocentric pencil of rays at one 
 point is hindered j each small segment of the surface has its special image, 
 so that an object such as a point throws a star-like (fixed star) image upon 
 the retina. The cornea, moreover, is subject to transitory inequalities of its 
 surface (tears, &c.). 6. ' Regular ' astigmatism depends upon a difference 
 of the curvature of the refracting surfaces in different meridians. The two 
 meridians which are furthest removed from one another are called principal 
 meridians. As a rule, the vertical meridian is more arc lied than the 
 horizontal. The two meridians, therefore, possess different focal distances, 
 so that the eye may be short-sighted in the vertical meridian, and long- 
 sighted in the horizontal. Generally, however, the difference is so slight 
 that it can only be discovered by looking at fine parallel lines from a 
 distance ; these can be seen from a greater distance, when vertical than 
 horizontal. When the degree of astigmatism is very great, it is corrected 
 by a glass which is stronger in one direction than the other, or, more simply, 
 which is only curved in one direction, which is, therefore, cylindrical. 
 
 3. Fluorescence. All the media of the eye are fluorescent ; the lens is 
 most so (Helmholtz, Setschenow, Regnauld). As the sensitiveness of the 
 retina is restricted so as to permit of its only appreciating waves of a 
 certain length, the fluorescent property of the media tends to increase the 
 range of perception for light of smallest wave-length (ultra-violet rays). 
 Of the true limits more will be said below. 
 
 4. Polarization. If polarized blue light, or light which contains blue, 
 falls on the eye (for example, if we look at the sky through a Nicol's prism, 
 or even with the naked eye, as the blue rays of the sky are already polarized), 
 a tuft-like image (Haidinger) is seen, which moves with the eye. The powers 
 of double refraction which the ocular nerves possess (Janin, Valentin) are 
 not sufficient to explain this phenomenon. It appears to depend upon the 
 (presumably doubly refracting) fibres of the yellow spot (see below), which 
 being struck by the polarized light at different angles, absorbs at one place 
 more, at another less, giving rise to the appearance above mentioned (Helm- 
 holtz). 
 
ILLUMINATION OF THE EYE. 383 
 
 On the behaviour of Light which penetrates the Eye. 
 
 The luminous rays after penetrating the eye are in part 
 absorbed and in part reflected, so that issuing from the eye they 
 follow the same course which they pursued on entering. Each 
 bundle of homocentric rays entering an eye which is perfectly 
 accommodated is, after refraction, brought to a focus on one 
 point in the transparent retina, presumably on its outer layer (of 
 rods and cones). Each rod ] is to be looked upon as a prism of 
 very high refractive power the base of which touches the choroid, 
 and which at its margin lies in contact with a feebly refracting 
 intermediate substance (Briicke). The rays which, after uniting 
 to form points in the image, again diverge, come in part in 
 direct contact with the choroid (axial rays) and in part strike 
 the sides of the rods, but at so oblique an angle, that instead of 
 being refracted by the intermediate substance, they undergo 
 total reflection. Ultimately all these rays must be thrown 
 upon the choroid. Here they are almost all absorbed by the 
 black pigment ; the unabsorbed rays, however, are reflected, in 
 part directly (axial rays), in part after reflection from the sides 
 of the rods. According to well-known optical principles, they 
 ultimately return again to the point in the object from which 
 they emanated. By this arrangement the passage of rays 
 from one part of the retina to the other (phenomena of 
 interference, &c.) is avoided, and clear vision is made possible. 
 Upon this arrangement, too, depends the fact that on looking 
 into the eye the fundus always appears dark. 
 
 In order to see the fundus of the eye illuminated, the 
 observer must make his own retina the point of departure of rays 
 which are perceived on their return from the observed eye. 
 This object is attained by the use of the ophthalmoscope. By 
 means of this instrument the light of a flame is thrown into 
 the eye as if it came from the eye of the observer. 
 
 One of the simplest ophthalmoscopes 'Helmholtz's) consists 
 of an arrangement of glass plates, which serves at once as a mirror 
 and as a transparent medium. By means of this arrangement of 
 plates the luminous rays from a light placed at the side of the 
 observed eye are thrown into the latter. The rays which return 
 
 ' According to recent researches it is only the external segments of the rods or 
 of tr,e analogous cones which have this function. 
 
 
384 OPHTHALMOSCOPE. 
 
 after reflection from the fundus are only in part thrown back by 
 the plates to the source whence they first emanated (the light) ; 
 in part they traverse the plates and reach the eye of the observer. 
 The observed eye appears in this way to be diffusely illumi- 
 nated with a red light. 
 
 A clear image of the fundus of the eye may further be 
 obtained in the following manner. When the observed eye is 
 .placed at an infinite distance, the retina is somewhat behind 
 the focal point of the optical system, which, like the object- 
 glass of a microscope, throws a real, inverted, and enlarged 
 image of the retina in that plane to which the eye is turned. As 
 this image, in consequence of its large size (which only permits 
 of a small part of it falling at once upon the pupil of the 
 observer), and on account of its continually changing position, 
 cannot be observed, an auxiliary lens must be employed : this is 
 either a collecting convex lens, which makes the image smaller, 
 brighter, and brings it nearer to the observer, whilst it allows 
 it easily to be fixed in one place, or it is a concave lens, which 
 possesses similar properties, but which furnishes a distinct and 
 erect image. 
 
 The combination of glass plate in the instrument above referred to may 
 be replaced by a plane or concave mirror ; which, being furnished with a cen- 
 tral aperture, permits a portion of the rays returning from the fundus of the 
 observed to reach the observing eye ; upon this plan other ophthalmoscopes 
 bave been constructed (those of von Ruete and Coccius). Between the 
 source of light and the (plane) mirror, a convex lens may be placed with 
 the view of concentrating the rays. If it be desired merely to see the eye 
 diffusely lighted up, and not to obtain a sharp image of the retina, the 
 following procedure may be bad recourse to (Briicke). The eye which is 
 to be observed is fixed upon a near luminous object, but is accommodated 
 for distant vision. Instead of the rays of light then converging to points, 
 circles of diffused light are formed upon the retina. The reflected rays 
 which leave the eye under these circumstances do not again meet at the 
 points whence they emanated, but either far bebind them or they do not 
 meet at all (i.e. they are either parallel or divergent). If now the observer's 
 eye is placed in the path of the cone of the returning rays (being protected, 
 if needs be, from the direct influence of the flame by a screen), the observed 
 eye is seen to be illuminated, of a red tint. 
 
 The eyes of human and animal albinos exhibit, without any special 
 arrangement being required, an illuminated fundus, as light passes through 
 the sclerotic and choroid, and falls into the eye. The illumination of the 
 eye is especially brilliant in animals, in wbicb over a portion of the choroid 
 the black pigment is replaced by a bright, shining, strongly reflecting mem- 
 brane, the so-called tapetum (this is seen in the eyes of many of the mam- 
 mals, especially in beasts of prey, and cetacea, in fishes, &c.). 
 

 VISION RODS AND CONES. 385 
 
 Vision. 
 
 The rays which fall upon the retina lead to the perception 
 of light, in consequence of the vibrations of the ether affecting 
 in an unknown manner the terminations of the optic nerve in 
 the retina. 
 
 The only nerve terminations which are to be considered 
 sensitive to light are the rods and the cones. The proofs for 
 this statement are the following : 
 
 1. The point of entrance of the optic nerve, where the 
 retina consists of nerve fibres without either rods or cones, is 
 insensitive to light ; this is therefore called the blind spot (also 
 Mariotte's spot). If we look fixedly with the right eye at the 
 spot A (keeping the left eye closed), holding the paper at a 
 
 A B 
 
 
 
 distance from our eye four times as great as the distance of A 
 from B, the point B will not be seen. In this case, by looking at 
 A, its image falls upon the termination of the optic axis, and the 
 image of B falls upon the point of entrance of the optic nerve, 
 which is situated about 3-J mm on the inner side. Likewise A 
 disappears, if B be looked at fixedly with the left eye at the 
 same distance as in the previous experiment. The function of 
 the blind spot in the field of vision will be discussed below. 
 
 2. The fovea centralis retinae and the macula lutea which 
 surrounds it, which contain rods and cones, but no fibres of the 
 optic nerve, are fitted for the most acute vision (the fovea 
 centralis almost exactly coincides with the termination of the 
 optic axis) ; the image of any fixed object which is looked at 
 falls upon this part of the retina. As the fovea centralis only 
 contains cones, and the macula lutea cones in large numbers 
 (one cone being surrounded by a circle of rods), and as the re- 
 maining part of the retina contains only few cones (one cone 
 surrounded by many circles of rods), we are entitled to con- 
 clude that the cones are even more sensitive to light than the 
 rods. 
 
 3. When the eye is illuminated from without, the vessels of 
 the retina which are situated behind the layer of fibres," but 
 anterior to the layer of rods and cones, cast a shadow ; as this 
 
 c c 
 
386 RODS AND CONES OF RETINA. 
 
 shadow can be perceived ent optically, under certain circum- 
 stances which will have to be discussed (Purkinje's figures), it 
 is proved that the rods and cones are the structures which are 
 ''sensitive to light. By accurate measurement it has been 
 determined that the shadows which are perceived really are 
 shadows of the blood-vessels of the retina, and not of other 
 vessels situated in front. For example, by moving the source of 
 light, the position of the shadow changes, and as these changes 
 of position can be measured entoptically, the distance of the 
 bodies which cast the shadows from the sensitive surface can 
 easily be calculated. The distance agrees exactly with the 
 distance between the vessels of the retina and the rods, as ascer- 
 tained by direct measurement (H. Miiller). 
 
 The end-organs, the rods and the cones, are, therefore, the 
 only organs which are directly capable of being excited by the 
 vibrations of the ether ; this property not being shared by the 
 fibres of the optic nerve either in the retina or in the trunk of 
 the nerve. Irritation of the optic nerve, at any point in its 
 course or terminations, by any of the usual nerve excitants (me- 
 chanical, electrical, &c.) gives rise to the sensation of light, which, 
 therefore, constitutes the ' specific energy ' of the optic nerve. 
 
 Mechanical irritation, as contusion or section of the trunk of the optic 
 nerve, leads to a lightning-like illumination of the whole field of vision. 
 Pressure applied to the eye or to a limited part of the retina leads to circular 
 bright l pressure-figures/ 'phosphenes,' upon the corresponding (opposite) side 
 of the field of view ; in eyes which are morbidly excitable, the contact of the 
 circulating blood with the retina is sufficient to occasion manifestations of 
 light (sparks, images of the vessels) ; lastly, a sudden change in the accom- 
 modation of the eye in the dark, by causing a traction upon the anterior 
 margin of the retina, gives rise to the appearance of a bright fringe at the 
 border of the field of view (Purkinje, Czermak). Electrical irritation 
 (passage of a constant current through the eye, or variations in the intensity 
 of the current) also occasions peculiar appearances of light, different parts of 
 the retina being perceived (Ritter, Purkinje). For the influence of elec- 
 trical irritation upon the perception of colour, see below. 
 
 In order to bring about an excitation of the retina the 
 luminous impression need only act upon it for a very short 
 period (the time of duration of an electric spark suffices). 
 When light continues to act upon the retina for a long time, 
 the excitation becoming more intense, fatigue of the retina 
 results. These facts explain the following : 1. The appearance of 
 persistent ' negative images ' (see below). 2. The much greater 
 
RODS AND CONES OF RETINA. 387 
 
 sensitiveness of the retina after the eye has been in darkness 
 for considerable periods. 3. The greater effect produced by 
 intermittent luminous stimulations as compared with those 
 which are continuous. The effect of such intermittent stimu- 
 lations is most marked when they follow one another seventeen 
 or eighteen times in each second (Briicke), presumably because 
 then the new irritation exerts its influence at a time when the 
 eye has just recovered from the effect of the preceding; the 
 complementary after-images (see below) co-operate in bringing 
 about this effect (Briicke). 
 
 A much shorter time suffices for the perception of yellow than for that 
 of violet (Vierordt, Burckhardt and Faber) ; red requires the longest time 
 (Lamansky) ; the intensity of light required for perception is nearly the 
 same for all colours. 
 
 The brighter and larger the images which are formed on the retina, the 
 shorter is the time necessary for their perception, yet the time required only 
 diminishes in arithmetical, though the intensity of the illumination and the 
 size of the retinal image increase in geometrical, progression. The most 
 sensitive part of the retina lies further from the centre of the retina than that 
 part which perceives most rapidly the outlines of objects (Exner). The 
 curve which represents the excitation of the retina presents a rise and a fall, 
 so that when the illumination lasts a very short time, the full perception 
 of the luminous impression does not occur (Fick). When the eye is con- 
 tinuously illuminated, the falling part of the curve indicates exhaustion of 
 the retina. The absolute brightness of the light has no influence oil the 
 relative fatigue; the effect of this fatigue is the same as if the objective light 
 were diminished in intensity by a fraction of its whole amount (Helmholtz). 
 Fatigue increases most rapidly at first ; the loss of light due to fatigue 
 amounts in the first seconds, during which the luminous impression lasts, 
 to more than 7 per cent, of the total amount ; later, however, the loss is 
 relatively much less. The whole loss during exposure for a whole day 
 amounts to about 51 per cent., because the eye has continuous opportunities 
 for restoration. In the morning the influence of fatigue is greatest (Fick, 
 and C. F. Miiller). In the centre of the retina the influence of fatigue is 
 sooner developed than at the periphery (Aubert). 
 
 Quality of Luminous Impressions. 
 
 All the vibrations of the ether do not possess the power of 
 exciting the end-organs of the optic nerve. Those the wave- 
 length of which is greater than corresponds to Frauenhofer's line 
 A (ultra-red heat rays) are unable to excite them, and are, there- 
 fore, invisible ; those the wave-length of which is shorter than 
 corresponds to the line H (ultra-violet chemical rays) exert so 
 
388 LUMINOUS IMPRESSIONS. 
 
 feeble an action that peculiar arrangements are required in order 
 to make them manifest. 
 
 The invisible character of the ultra-red rays has led to the investigation 
 of the diathermancy of the media of the eye, and it results that the latter 
 absorbs above 90 per cent, of the heat rays (Briicke, Janssen). In relation 
 to the separate portions of the spectrum, the diathermancy of the media of 
 the eye behaves as that of water (Franz) ; they therefore allow a sufficient 
 number of the ultra-red rays to pass, to lead one to ascribe their not being per- 
 ceived to their incapability of exciting the retina. The ultra-violet rays, 
 which are seen with difficulty, appear of a lavender grey colour when they 
 have been rendered artificially visible by removing the remaining portions 
 of the spectrum (Helrnholtz) ; the most external rays of the very long 
 spectra of metals have no perceptible colour (Masoart). 
 
 The vibrations of the ether which are capable of exciting 
 the retina give rise to the sensation of light by being propa- 
 gated from the end-organs in the retina to the central organs 
 in connection with the optic nerve. 
 
 The intensity (height of wave) of the waves determines the 
 intensity of the luminous impression ; the length of the waves, 
 however, determines the specific peculiarities of the luminous 
 impressions, to which we give the name of colours. The solar 
 spectrum, which allows rays of all wave-lengths capable of 
 affecting the eye to reach it simultaneously, exhibits all colours 
 arranged side by side. In addition to these, which we 
 denominate * simple,' there are others which we term ' mixed ' 
 colours. The consciousness of the impression produced by a 
 mixed colour is the result either of the union of rays of different 
 wave-length (different simple colours), which have united so as 
 to form a resulting wave-system which strikes the retina ; or of 
 a simultaneous excitation of corresponding fibres of the optic 
 nerve by several rays of different colour. 
 
 In both cases the same simple colours give rise to the same 
 mixed colour. 
 
 The sensation produced by the absence of any luminous 
 impression upon a part of the retina which is sensitive to light 
 is called ' black.' 
 
 We may realise the two modes in which colours are mixed in the follow- 
 ing manner : 1. Formation of a system of waves of different wave-lengths. 
 a. The source of light itself furnishes such a system, which is decomposable 
 by a prism into simple colours. 6. The same effect results when luminous 
 rays proceeding from several points strike the eye so as to fall upon the 
 same spot in the retina. Simple means of effecting this are the following : 
 
PERCEPTION OF COLOURS. 389 
 
 a colour is looked at through an obliquely-placed glass plate, which at the 
 same time throws, by reflexion, another colour into the eye (Helinholtz), or, 
 in Scheiner's experiment, which was previously referred to, two differently 
 coloured glasses are placed in front of the two small apertures ; in this case 
 the two luminous cones are differently coloured. If the observing eye be 
 now so accommodated that the two circles of diffusion partly cover one 
 another, that part of the retina which is common to both is illuminated with 
 a mixed light (Czermak). 
 
 2. Excitation of the same or of corresponding elements of the retina by 
 different colours, a. The property which the retina possesses of retaining 
 for a time luminous impressions is made use of, and different colours are 
 allowed to fall into the eye in very rapid succession (the apparatus known 
 as Newton's disc is made use of in this experiment) ; in this way the effect 
 of the first excitation is still present, when the second commences to operate. 
 b. Different colours are allowed to fall upon two ( corresponding points ' in 
 the two eyes. 
 
 Experiments conducted upon the perception of colours and 
 upon mixed colours (Newton, Grrassmann, Helmholtz, Maxwell) 
 have led to the following laws : 1. The same impression of 
 colour may be produced by very different combinations of 
 colours ; the number of possible colour-perceptions is therefore 
 much smaller than that of the possible objective wave-forms. 
 
 2. Each colour appears whiter, the more intense the illumination, 
 and when the illumination is most intense it appears white ; of all 
 colours yellow is the one which most easily passes into a white. 
 
 3. A combination of two simple colours of the spectrum gives 
 rise to an impression, which can in every case be reproduced by 
 a colour lying between them in the spectrum, mixed with a 
 certain quantity of white (i.e. undecomposed sunlight), or it 
 may be reproduced by white alone (in the latter case the two 
 colours are called complementary colours); hence it follows 
 that even three or more colours of the spectrum when mixed 
 always produce an impression, which can be reproduced by one 
 of the colours of the spectrum mixed with white ; any luminous 
 impression whatever may therefore be produced by one of the 
 colours of the spectrum and white. 
 
 In order to make the third law universally applicable, we must consider 
 the spectrum to be in the form of a closed ring, a new colour being interposed 
 between the red and the violet ends, this being a compound colour, viz. 
 purple, resulting from the mixture of red and violet. If in the middle of 
 this closed field (Fig. 22) white be placed, and if the field be so coloured, 
 that every -vector contains the combinations of one of the spectral colours 
 with white in all proportions (so that the colour as it approaches the 
 
390 PERCEPTION OF COLOURS. 
 
 white always becomes whiter), a diagram is obtained, which immediately 
 tells us what impression will result when any given colours are mixed. 
 Let us, for example, imagine that at the points which correspond to the 
 coloured components masses are placed, the magnitude of which corresponds 
 to the intensity of the components, and let the centre of gravity of these 
 (which must naturally lie within the field) be found ; its situation will 
 
 FIG. 22. 
 
 represent the luminous impression sought for. It is then seen that the 
 coloured impression produced by the spectral colours corresponds to a spec- 
 tral colour which lies between the component (elementary) colours, mixed 
 with white ; further, that the mixture with white becomes more intense the 
 more diametrically opposed the two ingredients j lastly, that each shade of 
 white unites two complementary colours. 
 
 The form of the including curve and the situation of the white must 
 therefore be so chosen that the latter always lies in the line of union of two 
 complementary colours, and indeed always lies nearer to that colour which 
 must be represented relatively more intensely in order to form white with 
 its complementary colour. 
 
 If we supposed that every fibre of the optic nerve were 
 differently excited by different colours and so occasioned 
 different luminous impressions, not only would the principle of 
 'specific energies' (p. 344) be contradicted, but many of the 
 observations which have been referred to, especially the identity 
 of the impressions perceived when the same colours are mixed 
 objectively and subjectively, would be absolutely incomprehen- 
 sible. All difficulties, are, on the other hand, set aside by the 
 hypothesis of Thomas Young and Helmholtz, that each spot on 
 the retina contains a number of nerve-terminations, of which 
 each one is capable of being excited by one particular colour 
 and is able, by transmission through a nerve fibre in connection 
 with it, to occasion the consciousness of a particular coloured im- 
 
PERCEPTION OF COLOURS. 391 
 
 pression. A compound colour would then be decomposed (just as 
 a musical sound is decomposed by resonators, or like light by a 
 prism) into its components, which would excite the correspond- 
 ing fibres. Admitting this hypothesis, the same impression would 
 naturally result whether a compound colour, or each of its sepa- 
 rate components, fell upon the retina, or if the components fell 
 in rapid succession upon the retina, or even were distributed 
 upon corresponding points of the two retinae. According to this 
 hypothesis, white would be perceived when all the retinal ele- 
 ments were equally excited. 
 
 It is impossible to determine a priori how many of these 
 colour-perceiving retinal elements must be associated with 
 each spot on the retina ; the smallest number which can be 
 assumed is three (Young). For reasons which cannot here be 
 discussed, it is usually assumed that there must be present 
 elements capable of perceiving red, green, and violet. Probably 
 the number is actually much greater. 
 
 The most recent anatomical investigations have almost 
 certainly demonstrated, that the cones are the elements in 
 the retina which are concerned in the perception of colour 
 (M. Schultze). These cones must, however, be looked upon as 
 collections of nerve terminations ; they appear to be longitudi- 
 nally striated, and they pass into a thick fibre (cone-fibre), which 
 consists of a bundle of the finest axis cylinders, which separate in 
 the granular layers of the retina. The power of perceiving colours 
 possessed by different parts of the retina varies according 
 to the distribution of cones in them. The rods are in all 
 probability merely endowed with the power of determining the 
 quantity of light. They are connected with a single axis 
 cylinder, or at least with a far smaller number of axis cylinders 
 than the cones. 
 
 The hypothesis which has already been referred to in the 
 text, viz. that each of the fibres supposed by Young to exist, is 
 excited not merely by one, but by all colours, only in different 
 degrees, explains the observation referred to at p. 389 in dis- 
 cussing the second law. In Fig. 23 the ordinates of the curves 
 indicate the relative degree of stimulation which each of Young's 
 fibres undergoes under the influence of each of the primary 
 colours of the spectrum. 1 is the curve which represents the 
 excitability of the fibres which are specially sensitive to red 
 
92 PERCEPTION OF COLOURS. 
 
 rays ; 2, of those which are sensitive to green rays ; 3, of those 
 which are sensitive to violet rays. 
 
 As when the intensity of the illumination increases, the 
 stimulation must soon attain a maximum, it follows that an 
 intensely illuminated colour must excite all three fibres to a 
 maximum degree, therefore equally strongly, and that there- 
 fore a sensation of white must result. Yellow, which, as the 
 curves show, excites almost to an equal degree the three kinds 
 
 FIG. 23. 
 
 of fibres, must most easily pass into white. In the colour- 
 plane (Fig. 22) places must be given to coloured impressions 
 which correspond to the excitation of the individual fibres of 
 Young, outside of the coloured field, viz. at K, Gr and v ; then, 
 as Fig. 23 shows, no objective colour exists, which merely 
 stimulates a single fibre of Young. Naturally again white must 
 lie in the centre of gravity of three equal masses placed at R, 
 or and v. The triangle RGrv includes all imaginable 
 coloured impressions, but the inner field alone contains those 
 which are possible in the case of objective illumination ; the 
 remaining colours can only be developed subjectively. 
 
 The theory of Young, Helmholtz and Schultze is moreover 
 supported by the following facts in addition to those previously 
 referred to (viz. the results of mixing colours ; the form of the 
 fibres of the cones and rods) ; 1. In animals the habits of which 
 are nocturnal (owls, bats) the cones are wholly wanting, and rods 
 alone are present (M. Schultze) ; this fact agrees with their sup- 
 posed function of merely appreciating differences in the quantity 
 of light (light and darkness). 2. The power of descriminating 
 colours is, in the eye of man, most developed in the fovea cen- 
 tralis, where cones alone are present, and diminishes towards 
 
PERCEPTION OF COLOURS. 393 
 
 the periphery in proportion as rods occur, ceasing entirely at 
 the periphery, where the cones only occur in isolated situations 
 (Aubert, M. Schultze). Here a qualitative irregularity in the 
 perception of colours is discovered (see below). 3. Very fre- 
 quently there exists an abnormality of the eye, to which the name 
 of colour-blindness or blindness for red (Daltonism) is given. 
 This abnormality consists in this, that red appears black, and 
 that mixed colours which contain red appear as if the red 
 were absent (white for instance appears greenish-blue). This 
 condition cannot be explained otherwise than by supposing an 
 absence, or a functional incapacity, of the retinal elements 
 concerned in the perception of red. As some colour-blind 
 people do perceive very intense red, it follows that we must 
 assume not an absence, but an imperfection of these elements, 
 of which there may be many gradations. The peripheral parts 
 of the retina are normally to a certain extent colour-blind for 
 red, and are so, according to Woinow, for green also. White is 
 seen on those parts of the retina of a greenish tint. Moreover,, 
 when we try to ascertain the limits of the sensitiveness of 
 the eye to colour, as for example the power of perceiving a 
 very small coloured image or one imperfectly illuminated, 
 red appears to be the colour which is least easily perceived 
 (Aubert, Lamansky); it would thus appear that the cones 
 which are sensitive to red require a stronger stimulus than 
 the remaining cones, and further that in order that a coloui 
 be perceived, it is necessary that a certain number of cones be 
 excited ; these two suppositions are sufficient to explain all the 
 known phenomena (still even a green colour-blindness can exist, 
 Preyer). 
 
 When electrical currents are passed through the optic nerve, 
 weak luminous sensations result ; the field of vision ap- 
 pears of a violet colour with an ascending, and reddish-yellow 
 with a descending, current (Eitter). This action manifests itself 
 when coloured objects are looked at, by an addition of violet or 
 yellow to their proper colour. 
 
 The excitation of the fibres which are sensitive to violet 
 rays, appears therefore to be stronger with an ascending current, 
 and weaker with a descending current, whereas the fibres which 
 are sensitive to green or red are but slightly affected. 
 
 The yellow colouring matter of the macula lutea causes 
 
394 STRUCTURE OF RODS AND CONES. 
 
 the centre of the retina to be more sensitive for yellow and less 
 sensitive for violet, as many facts teach us (Maxwell, Preyer). 
 The yellow colour of the field of vision, which comes on in 
 cases of poisoning by santonin, has been explained by some 
 (M. Schultze) as due to an increase of the yellow pigment, 
 whilst others (Hiifner) imagine that it depends upon a paralysis 
 of the fibres which are sensitive to violet, especially because, as 
 a first effect, the field of vision is coloured violet a phenomenon 
 which is to be explained on the supposition that there is a 
 preliminary stage of irritation which precedes the stage of 
 paralysis of the fibres. 
 
 The manner in which light of different colours is decom- 
 posed in the cones cannot yet be understood (see below). 
 But birds are provided with an apparatus which throws some 
 light upon the function of the cones in the perception of 
 colours. The cones of the retina of birds are simple elements, 
 being only connected with a single, simple axis cylinder, and are 
 therefore, according to Schultze's theory, really rods : these rods 
 present, however, at the junction of their inner with their outer 
 segment (see below) a spherical fatty body, which in the case 
 of some is red, in that of others yellow, or even colourless. It 
 is conceivable that the rods of the first kind only transmit red, 
 those of the second yellow, those of the third perhaps white light. 
 The perception of colours appears therefore, even in this case, to 
 depend upon several rods, each kind being excited by light of 
 a particular colour ; this combination of rods corresponds to a 
 single cone of the human retina (M. Schultze). In the retina 
 of the owl the pigmented rods, above referred to, are absent, the 
 only ones present being colourless. 
 
 In both rods and cones two constituent parts (segments), an 
 inner and an outer, can easily be distinguished (M. Schultze). 
 The external segment is essentially the same in both rods and 
 cones, being merely longer in the former ; it is regularly rod- 
 like, it refracts light strongly, and is most strongly coloured 
 black by perosmic acid ; it constitutes a reflecting arrangement. 
 The internal segment differs in the rods and cones ; in the 
 former it possesses the same thickness as the external part, 
 in the latter it is fusiform and longitudinally striated ; it is 
 apparently of a purely nervous nature. The line of demarcation 
 between these two segments is sharp, and here the rays coming 
 
IMAGES. 395 
 
 from within must, in great part, be totally reflected. The light 
 which penetrates the external portion of the rods and cones is 
 either absorbed by the choroid coat or again reflected towards 
 the inner portions. Seeing that in the retina of birds the 
 pigmented granular bodies are situated at the point of junction 
 of the inner and outer segments of the rods and cones (while in 
 other animals also refracting apparatuses of elliptical or lenticular 
 form occur in the same situation), it is highly probable, that the 
 external segments are the specific light-perceiving organs. 
 These present in all animals a transverse cleavage into fine 
 plates, which are 0'0006 mm thick in doves, and 0-002 0*008 in 
 crabs (M. Schultzej. This peculiar structure has led to the 
 hypothesis that the external segments have the property of 
 changing by reflection against these plates the progressive light- 
 waves into stationary waves ; the latter would act in such a 
 way that the maximum point would not coincide in the case of 
 the different colours, but that individual colours would excite 
 different points of the organ, an effect similar to that required 
 by Young's theory. That stationary waves corresponding to 
 all the different wave-lengths may be generated appears possible 
 from the fact that not only the distance of the reflecting surfaces 
 (thickness of the plates), but also the refractive index of the 
 different plates in a rod, vary. 
 
 linages. 
 
 It has already been stated* that from every point in an 
 object the corresponding point in the image can be obtained 
 by drawing the visual ray which joins them. It is in this 
 direction too that consciousness refers to the exterior the 
 cause of every luminous impression which originates in conse- 
 quence of the irritation of a retinal element. It will be shown 
 subsequently to what distance on this line the point of the 
 object is referred. In the first place, let us now consider the 
 case in which the transfer is effected in such a manner that 
 all the points of the object appear to lie in a plane floating 
 before the eye. This plane is called the ' field of vision.' As 
 consciousness is continually forming a representation dependent 
 on the state of irritation of all the retinal elements according 
 to their real arrangement in space, it happens that a field of 
 
396 THE BLIND SPOT. 
 
 vision is always being seen ; this appears ' black,' as long as 
 every cause of irritation is wanting. To every excited retinal 
 element there corresponds a luminous point, and to every 
 unexcited element a black point, at diametrically opposite 
 points of the field of vision. The latter then is filled with 
 exactly the same, but inverted, images as are objectively present 
 on the retina. As the latter are, in relation to the objects seen, 
 inverted, the objects are seen erect in the field of view. 
 
 The blind spot does not occasion any perceptible gap in the 
 field of vision. The want of optical excitation (the conscious- 
 ness of which we designate by the term black) can only be 
 perceived where terminations of nerves sensitive to light are 
 present. But there are no such terminations in the blind spot. 
 The latter therefore behaves towards light as any spot on the 
 skin would do ; we do not experience with the hand any 
 sensation of black, although no luminous impression proceeds 
 from the hand. As the visual impressions of the contour of the 
 blind spot are by means of the visual rays localised in the field 
 of vision, consciousness must logically perceive the want of 
 intermediate luminous points, and appears to conceive them 
 according to the rules of probability (E. H. Weber). In this 
 way we may probably explain the experiment described at page 
 385 in which the place of the object which has disappeared is 
 taken by the colour of the ground and not by a black spot. 
 The white colour of the paper here fills up the gap as the most 
 probable substitute. 
 
 As every point in the retina merely contains a definite 
 number of terminations of the optic nerve (rods or cones), any 
 image can only consist of a limited number of luminous 
 impressions separated from one another in space and forming 
 a kind of mosaic or embroidery pattern. But the mosaic is so 
 fine that there may result an impression as of a continuous 
 drawing. The same object must appear sharper, the greater 
 the number of sensitive retinal elements over which its 
 image is distributed. Hence the sharpness with which a given 
 object is perceived depends (1) upon the magnitude of its 
 retinal image; the same object will therefore appear sharper when 
 near than when distant ; (2) upon the situation of the retinal 
 image, for the sensitive retinal elements are most thickly 
 pressed together in the fovea centralis and the macula lutea, 
 
VISION OF OBJECTS. 397 
 
 whilst they are most sparsely scattered near the borders of the 
 retina. An object, therefore, which is situated at the same 
 distance will be seen most sharply when its image falls upon 
 the centre of the retina ; nence when the eye looks most keenly 
 at (i.e. is fixed upon) an object, it is so turned that the latter 
 throws its image upon the middle of the retina, on the fovea 
 centralis. The visual ray which strikes the fovea centralis^ 
 viz. the axis of vision, does not absolutely coincide with the 
 optic axis of the eye ; but is bent backwards and a little outwards 
 and downwards from the latter. The two form an angle of 3*5 
 7 with one another. 
 
 This deviation of the two axes can be recognised and measured by causing 
 the centre of a horizontally placed measuring rod to be fixed by the eye 
 observed ; at one end of the rod is a light, at the other the eye of the 
 observer. The three luminous reflexions which were previously referred to 
 in. describing Mariotte's experiment do not then appear in symmetrically 
 similar order if the observer and the light change places ; the symmetry 
 is only restored when the observed eye is fixed, not upon the centre, but 
 on a point somewhat to the inner side of the centre, of the measuring rod. 
 The symmetry is even then not absolutely perfect, because the centering of 
 the three refracting surfaces of the eye is not absolutely true. 
 
 An .object will further not generally be recognisable, unless 
 its retinal image covers a sufficient number of sensitive retinal 
 elements, so that consciousness receives a number of impres- 
 sions separated from one another, sufficient to characterize the 
 form of the object. It has been found that two points of an 
 image must be at least O002 mm distant from one another when 
 falling upon the fovea centralis of the retina, in order to give 
 rise to two separate impressions. In other parts of the retina 
 the distance must be even greater. For these reasons neither 
 very minute nor very distant objects can be perceived by the 
 eye. 
 
 The size (diameter) of the retinal image is evidently always 
 determined by the size of the visual angle^ which the two 
 external lines of direction proceeding from an object form with 
 one another: we therefore usually say that objects are not 
 recognisable under a very small visual angle. In order to be 
 able to recognise such objects the visual angle must be arti- 
 ficially increased, and with this object we employ in the case of 
 small objects magnifying glasses and microscopes, in the 
 case of distant objects, telescopes. 
 
398 VISUAL ANGLE OPTICAL INSTRUMENTS. 
 
 The magnifying glass is a convex lens ; the object is placed within its 
 focal distance, and therefore furnishes a virtual, erect and magnified image 
 of itself (p. 369). 
 
 In the solar microscope the object lies outside the focal distance, near to the 
 focal point, and furnishes therefore a real, magnified, inverted image, which 
 is received on a screen. In the compound microscope the real image, which 
 is similarly obtained, is not seen, but by means of a convex (collecting) 
 lens it is brought somewhat nearer and diminished in size, and then is 
 observed by means of a magnifying glass (eyepiece lens); it therefore 
 remains inverted. In all dioptric telescopes a real, inverted image of 
 distant objects is thrown by the convex lens of the object-glass. In astro- 
 nomical telescopes this image is observed with the aid of a convex eyepiece 
 lens, and it remains inverted and becomes virtual. In terrestrial tele- 
 scopes, the real inverted image is looked at through a compound microscope 
 which forms the object glass, and is therefore again reversed, and therefore 
 seen erect ; in the Dutch telescope (opera-glasses) the real image thrown by 
 the objective becomes by means of an interposed concave lens (the eye- 
 piece) reversed and virtual, and therefore the object appears erect. 
 
 By the magnifying power of optical instruments we understand the in- 
 crease in the visual angle which is brought about by them. 
 
 In the case of instruments which furnish real images, as the solar micro- 
 scope, the magnifying power is found simply 
 
 In all instruments which furnish virtual images the focal distance of the 
 eye of the observer exerts an influence, for the virtual image to be distinctly 
 seen must lie at the distance at which the observer is accustomed to see 
 near objects clearly. If the eye of the observer is placed immediately 
 behind the magnifying glass or eyepiece lens respectively, for the latter 
 2 = s. The magnifying power v of an ordinary magnifying glass is 
 
 therefore = , or, as by (32) 
 a i 
 
 J_ _ JL = _L, it follows that 
 
 ......... (2) 
 
 The magnifying power of such a lens is therefore relatively less for short- 
 sighted people than for others. 
 
 In the compound microscope the object-glass by itself, when/! is the focal 
 distance, as in the case of the solar microscope, has a magnifying power 
 found by the following formula : 
 
 the eyepiece, of which let the focal distance be/ 2 , magnifies by itself ac- 
 cording to the following formula, V 2 = '* . 
 
 /2 
 
 The total magnifying power of the combination is therefore 
 
OPTICAL INSTRUMENTS. 399 
 
 The distance between the object-glass and the eyepiece, i.e. the length of 
 the microscope, must then be equal to the sum of the distances of the 
 images of the object-glass, and the focal distance of the eyepiece required 
 is therefore - 2 = s; both the quantities to be added are found by equation 
 (32), so that 
 
 i* -_ + lA ........ (4) 
 
 Generally in microscopes L is given as unchangeable, so that lt the distance 
 of the object from the object-glass, must be changed for every visual distance 
 s ; the magnifying power is obtained by eliminating a 1 from (3) and (4). 1 
 
 Even the influence of the collecting lens can easily be calculated, though. 
 its introduction here would lead us too far. 
 
 In the case of astronomical telescopes the magnifying power is 
 
 v = /i ( s + / 2 ) a i (5\ 
 
 The length has the same value as in 4 ; as in this case a l is given by 
 nature L must be changeable ; from (4) it follows that the telescope must 
 be drawn out the more, the smaller the magnitude of a l} and the larger that 
 
 of s. From (5) v = i and from (4), L = / t +/ 2 ; the length is there- 
 
 /2 
 
 fore the sum of the focal distances of the objective and eyepiece. In opera- 
 glasses it is, as can easily be seen, nearly equal to the difference of the 
 focal distances. 
 
 The smallest distance at which two points in a retinal image can be 
 separately seen is found by the following, amongst other, methods (Volk- 
 uiann). 
 
 1. Two fine threads or lines, which are at a constant distance from 
 the eye are approximated to one another until they can no longer be dis- 
 tinguished one from the other, and then the distance between their images 
 on the retina is calculated. Instead of approximating the objects to one 
 another, they can also be looked at with the aid of an apparatus for diminish- 
 ing the size of objects (macroscope). 
 
 2. A point very near to the centre of suspension of an oscillating pendulum 
 is looked at from different distances, until its movement is no longer 
 perceptible. In these experiments irradiation must be guarded against. In 
 the older determinations the smallest appreciable distance on the retina was 
 found to correspond with the then accepted diameter of the cones (O004 mm ). 
 New determinations have led to both the magnitudes being diminished, and 
 even now an agreement between the two may be affirmed to exist. 
 
 The cones of the fovea centralis have a diameter of about 0'002 mm , but 
 it appears that one ought to consider only the surface which bounds the 
 outer and inner segment, which has a diameter of O001 mm (M. Schultze). As 
 these surfaces naturally are at some distance one from the other, it may 
 
 1 As the magnifying power of a microscope differs for different eyes, opticians 
 base their statements as to magnifying power upon a conventional value of s 
 (generally making it O m> 25). 
 
400 SUBJECTIVE IMAGES. 
 
 possibly occur that in central sight minute points, as stars, form images 
 which fall in the space between the cones, and so disappear. This actually 
 does occur (Hensen). 
 
 For the perception of small images the mode of disposition of the mo- 
 saic of retinal elements is not without importance ; in the yellow spot it is 
 in the rhombic figures formed by the intersecting of neighbouring circles that 
 the cones are situated. 
 
 The details of an image are distinguished partly by the 
 difference in brightness, partly by the difference in colour. In 
 the latter case the delicacy of the power of perception does not 
 depend upon the number of the retinal elements, but upon the 
 number of the elements capable of appreciating colour which 
 are covered by the image. In the centre of the field of vision 
 the two circumstances co-exist, as in this situation cones only 
 exist ; towards the periphery, however, the power of distin- 
 guishing colours diminishes far more rapidly than the power of 
 discriminating differences in luminous intensity. 
 
 Subjective Images and Optical Illusions. 
 
 As nervous arrangements play a part in the perception of light, as of . all 
 other sensations, all the peculiarities of nervous excitability must be noted 
 in connection with them ; for example, lesions and illusions. 
 
 The same vibration of the ether will, for instance, give rise to a strong 
 or weak impression, according to the degree of excitability of the end- 
 organs of the optic nerve, or of its fibres, or even of the central organs con- 
 nected with them. Other circumstances lead to actual errors, to a percep- 
 tion of a luminous impression independent of rays of light, or to the per- 
 ception of other rays than those which are actually present (colour-illusions). 
 Such impressions we call ' subjective.' The most frequent are the follow- 
 ing : 
 
 1. Persistent or after-images. A fibre of the optic nerve having been ex- 
 cited, persists in its excited condition for some time after the exciting luminous 
 ray has ceased to act, and the continuance is long and intense in proportion 
 as the primary excitation was long and intense. In consequence of this, 
 after every luminous impression, the object which has been seen remains 
 visible for a very short time an after-image being seen. Upon the property 
 which has been alluded to depends the appearance of a fiery circle, which is 
 seen when a burning coal is swung in a circular path before the eyes. The 
 following instruments are based upon the existence of persistent images. 
 The Thauma^rope is a disk rotating in front of the eyes, near the circum- 
 ference of which a body which is continually moving is represented in the 
 different successive stages of its movement, so that each figure can be per- 
 ceived for a moment ; each impression then persists until the following one 1 
 succeeds it, and in this way the movement appears continuous. 
 
PERSISTENT IMAGES IRRADIATION. 401 
 
 The coloured rotatory disk (Newton's disk) is a disk turning- with rapidity 
 and divided into sectors of various colours ; the colour of one sector persists 
 during one whole rotation, so that a mixture of many colours is presented to 
 consciousness. If the original luminous impression is strong, the persistent 
 (or secondary) image is at times dark, i.e. the excitability of the fibres 
 has been for the moment diminished by fatigue, so that a dark place, having 
 the same situation as the bright object seen at first, appears ; this is called a 
 negative persistent image. At times positive and negative secondary images 
 alternate for a period, i.e. the momentarily abolished irritability returns for 
 an instant, so that the (positive) secondary image appears, to disappear 
 again, &c. The secondary images offer some peculiarities when the primary 
 impression has been due to an intense light or to a prolonged luminous im- 
 pression. These images do not then appear of the same positive colour, but 
 often of another contrasting colour, and often pass from one to the other 
 successively. The contrasting colour is always that one which, if added to 
 the primary colour, would give the tint of ordinary daylight (which is not 
 pure white, but a little red), and therefore the ' contrasting ' is very nearly 
 the same as the ' complementary ' colour (Briicke). 
 
 Even white light appears after a luminous impression, amongst the ' con- 
 trasting colours ; ' if, for instance, we place a coloured piece of paper on a 
 white surface, and stare fixedly at it for some time, and then look at the 
 white surface, there appears a secondary image possessing the form of the 
 coloured piece, but of the contrasting colour. The phenomena of contrast 
 may be explained by supposing the exhaustion of the retinal elements which 
 correspond to the primary colours. 
 
 Secondary coloured images appear also after impressions produced by 
 white light, when these have been very intense (after looking, for example, 
 at the sun) ; ordinarily a succession of divers colours appears, sometimes 
 positive and negative colours alternating. This phenomenon of successive 
 contrast of colours is probably explained by the excitation of the individual 
 colour-perceiving elements lasting for different periods of time after the 
 luminous impression has acted. In the peripheral parts of the retina these 
 contrast-phenomena are modified by the red-blindness (and green-blindness), 
 which are characteristic of these regions (Adamiik and Woinow). 
 
 2. Irradiation becomes perceptible when a bright object on a dark 
 ground is looked at ; the object then appears to be larger than it really is 
 conversely, a dark object on a bright ground appears smaller. This pheno- 
 menon results from defective accommodation, whereby the bright objects 
 furnish blurred images. 
 
 Consciousness, under these circumstances, is inclined to add to the pre- 
 dominating part of the image the half-illuminated fringe (which is equal in 
 width to the radius of the diffusion- circle) ; now, on the one side brightness 
 predominates over shade, and on the other the object over the ground be- 
 neath it. If the ground is black, and the object white, the latter appears 
 larger at the cost of the former j if, on the other hand, the object be black and 
 the ground white, the second influence can preponderate so much over the 
 first, that even black lines appear broader at the expense of the white ground 
 ( Volkmaun). 
 
 D D 
 
402 ENTOPTICAL PERCEPTIONS. 
 
 3. Simultaneous contrast includes a series of phenomena which depend 
 upon the comparison of two colours or tints bounding one another in the 
 field of vision, as well as the illusion which results therefrom. 
 
 A white field appears the brighter, the darker its immediate surround- 
 ings (a white trellis-work upon a dark ground exhibits at the points of 
 intersection apparently dark spots, for here the surroundings of the white 
 spots contain less black than the remaining parts of the trellis) ; similarly, a 
 colour appears the more intense, the more completely are its surroundings 
 destitute of it, i.e. the nearer the surrounding medium approaches a con- 
 trasting colour. Conversely on a (feebly illuminated) white surface those 
 components of white come out most strongly which are wanting in the 
 vicinity ; white thus appears in the contrasting colour of the vicinity (the 
 shadow of a rod illuminated by a candle appears in daylight not white or 
 grey, but is of the contrasting colour to the yellow candlelight, viz. blue). 
 
 The many examples of actions of simultaneous contrast which occur can- 
 not here be referred to. Phenomena of contrast do not appear upon wholly 
 unexcited places of the retina, so that the so-called associated- sensations are 
 in no way identical with them (Rollett). 
 
 4. Amongst subjective phenomena are further to be mentioned the illu- 
 sions as to colour which originate through the peripheral colour-blindness 
 and the unequal excitability of the organs engaged in the perception of 
 colours, e.g. very rapidly intermitting white light, as the luminous impres- 
 sion does not last long enough to excite the retinal elements which are sen- 
 sitive to red, appears greenish (Briicke). 
 
 5. Excitations of the light-perceiving retinal elements due to causes 
 which are purely internal, without external influence. To this class belong : 
 a. Mechanical irritation, brought about by the circulation, and which only 
 occurs where there is morbid irritability ; under these circumstances appear- 
 ances of sparks, lightning, &c. may be seen ; sometimes there appears, espe- 
 cially before sleep, a complete image of the retinal vessels, with their con- 
 tained blood-corpuscles, &c. 6. Central excitations of unknown origin and 
 manifesting themselves in the most diverse forms (< hallucinations/ l phan- 
 tasms ') ; these are seen especially in dreams, in the half-waking state, before 
 going to sleep, and in diseased conditions even during the waking state. 
 
 Entoptical Perceptions. 
 
 1 Entoptical ' phenomena are to be clearly distinguished from such as 
 are subjective. Entoptical phenomena are visual impressions of objects 
 which are present within the eye itself. The most important of such 
 phenomena are : 1. Perceptions of opacities and obscurations of the refract- 
 ing media of the eye. These are apparent when, by illuminating the eye, 
 their shadows fall upon the retina, and they are best seen when parallel 
 luminous rays traverse the eye. 
 
 They appear in the form of dark spots, balls, streaks, rows of pearls, &c. ; 
 in part, they are fixed, in part (those of the vitreous humour), they change 
 their position, especially during sudden movements of the eye or of the 
 head. 
 
MOVEMENTS OF THE EYE. 403 
 
 2. Perceptions of the retinal vessels, "brought about by their shadows 
 falling- upon the layer of rods. In order to bring out these shadows they 
 are directed upon the lateral parts of the retina, which are seldom lighted 
 up, by causing an intense light to fall upon the transparent sclerotic, or the 
 shadows are made to move by causing a luminous point to pass backwards 
 and forwards before the eye. Under these circumstances a dark delineation 
 of the vessels, on an illuminated field, is perceived; even the border of the 
 fovea centralis is recognisable by a shadow (Purkinje's figures). 
 
 3. The perception of the blood-corpuscles in the retinal capillaries, when 
 the eye is very feebly illuminated (as by a layer of snow, a lamp-globe, or 
 (Griinhagen) a dark blue glass held before the sun.) ; this phenomenon is ; 
 as yet, not fully explicable. 
 
 Movements of the Eye-. 
 
 The eye is capable of very extensive movements in the orbit, 
 and the absolute mobility of the organ of vision is considerably 
 increased by that of the head as a whole. Hence it is possible 
 in any position of the body to observe objects in all situations 
 of space, i.e. so to place the eye as to cause the retinal image of 
 any object to fall on the fovea centralis retinae. The great 
 mobility of the eyeball depends upon the mode of its attach- 
 ment to the orbit. It rests on the pad of fat of the orbit, as 
 the head of a bone in a ball and socket joint rests in the hoilow 
 cavity, and it can therefore rotate around innumerable axes. 
 These movements, which are effected by the muscles of the eye, 
 are held in check, firstly, by the points of attachment of 
 antagonizing muscles, and, secondly, by the attachment of the 
 optic nerve. In addition to the movements of rotation, changes 
 in the position of the globe as a whole can occur in consequence 
 of the yielding nature of the surroundings in this case ' the 
 joint-cavity is displaceable ' (Ludwig). 
 
 The point of rotation of the eyeball (in the sense referred 
 to at p. 291) does not lie, as was surmised a priori and as was 
 concluded from researches (Volkmann), in the middle of the 
 visual axis, but (Bonders and Doijer, Fick and Miiller) in the 
 case of normal eyes l-77 mm behind it. 
 
 It is to be noticed that when the eyelids are forcibly 
 opened, the eyeball protrudes somewhat from the orbit, 
 probably by the contraction of both the oblique muscles ; the 
 movement forwards is most marked when the eyes look horizon- 
 
 D D 2 
 
404 PRIMARY POSITION. 
 
 tally or downwards, and then it amounts to about l mm (Fick 
 and Miiller). 
 
 To understand the changes in the situation of the globe 
 and the arrangement and mode of action of its muscles, we 
 must assume the existence of certain fixed points and lines in 
 the eyeball, the changes in the situation of which furnish a 
 measure of the movements of the eye. One line in the eye is 
 given by its anatomical construction, viz. the visual axis, which 
 is the principal ray proceeding from a fixed point, the situation 
 of which in relation to the axis of the cornea has already been 
 referred to (p. 397). Starting from the fovea centralis, which 
 may be considered to be one pole of the eyeball, two meridians 
 at right angles to one another may be drawn on the retina. 
 Their position is determined by certain physiological properties 
 of the eye ; they divide the retina into four quadrants which 
 have in the two eyes certain reciprocal relations, and they are 
 called lines of separation (one of which is horizontal, the other 
 vertical). 
 
 If we now imagine a plane passing through the eye at the 
 centre of the visual axis and perpendicular to it, it will cut the 
 spherical surface in a great circle perpendicular to the meridians, 
 which we designate the equator of the eye, the plane being- 
 termed the 'equatorial plane*' We have then three great 
 circles perpendicular to one another (the equator and two 
 meridians); the planes corresponding to these circles intersect 
 one another in three diameters at right angles to one another ; 
 these are : one sagittal (the visual axis); another vertical, and a 
 third horizontal. These may be employed as a system of co-ordi- 
 nates movable with the eye and indicating its movements. A 
 second system of co-ordinates absolutely fixed in space, and 
 coinciding with the movable system when the eye is in its 
 position of rest, must also be assumed to exist. In any other 
 position of the eye two or three of the corresponding axes of the 
 two systems must form angles with one another. 
 
 The movements of the eye are especially of importance in 
 bringing about the combined positions of the eyes and are 
 limited by the latter. That position is assumed as the position 
 of rest, from which all movements may be supposed to start. 
 This so-called 'primary position ' is one in which all three axes 
 of one eye are parallel to those of the other, and the transverse 
 
SECONDARY AND TERTIARY POSITIONS. 405 
 
 axes lie in one straight line, the visual axes being therefore 
 antero-posterior (sagittal) from within outward^. 
 
 It is obvious that this position can be associated with a 
 voluntary inclination of the visual axes to the horizon. 
 Amongst all such possible positions there is one to be men- 
 tioned as a primary position, properly so called, namely, that 
 inclination in which convergent movements of the visual axes 
 may occur without the eyes requiring visibly to rotate 
 around their visual axes, as is the case in all other positions. 
 The determination of this inclination will be given below. It 
 has now been established (Listing, Meissner, Helmholtz) that 
 when the eye moves from the primary position, its movements 
 take place around axes situated in the equatorial plane (so that 
 the visual axis is always perpendicular to the axes of rotation 
 and that rotations never take place around the visual axis). 
 Amongst the innumerable axes which may be supposed to exist 
 in the equatorial plane, there are two which are first to be men- 
 tioned,, viz. those which are at the same time co-ordinate axes, 
 viz. the transverse axis and the vertical axis. Eotations around 
 these two axes lead to the ' secondary positions ' of the eye. 
 Rotation around the first merely occasions an alteration of the 
 inclination towards the horizon and the parallelism of the axes 
 continues ; rotation around the vertical axes produces a rota- 
 tion inwards or outwards, and consequently a convergence or 
 divergence of the visual axes, the inclination to the horizon 
 continuing the same. Thus in the first case the plane of ver- 
 tical separation, but not that of horizontal separation, coincides 
 with that which corresponds to it in the fixed system of co-or- 
 dinates ; in the second case the converse is true. 
 
 Rotations around other axes lying in the equatorial plane of 
 the eyeball lead to ' tertiary positions ' of the eye. As every 
 such rotation can resolve itself, according to simple rules, into a 
 rotation around the vertical axis and a movement around the 
 transverse axis, it follows, in the first place, that tertiary posi- 
 tions are as much associated with convergence of the visual axes 
 as with their change of inclination to the horizon, and, secondly, 
 that neither the vertical nor the horizontal plane of separation 
 coincide with the planes which correspond to them in the fixed 
 system of co-ordinates ; they are both inclined the one to the 
 other. The eyes have therefore undergone iii the tertiary posi- 
 
406 TERTIARY POSITIONS OF THE EYE. 
 
 tions an apparent rotation around their visual axes, in the same 
 direction as the hand of a watch moves, when directed to the 
 left looking upwards, when to the right downwards. Every 
 position of the visual axes is therefore associated with a certain 
 rotation of the eye, which can be deduced from Listing's law. 
 
 If a be the vertical and j3 the horizontal deviations of the visual axis 
 from the primary position, the angle of rotation (' Raddrehungswinkel ') is 
 found by the equation (Helmholtz) 
 
 - 
 
 cos a -t- cos |3 
 
 or ~ tang = tang tang ; 
 
 these equations show that when a = or /3 = (secondary positions) the 
 rotation is 0. 
 
 If we denominate the plane of both visual axes the visual plane, then the 
 horizontal meridian of the retina, either in the primary or secondary posi- 
 tion, coincides with the visual plane, but differs from it in tertiary positions ; 
 the angle which both planes form is the angle of circular rotation. With 
 the help of the visual plane the positions of the eye can also be defined as 
 follows. In the primary position the visual plane has a determined inclina- 
 tion ; the visual axes are parallel and perpendicular to the line which unites 
 the points of rotation of the two eyes. Secondary positions arise either when 
 the visual plane alters its inclination, the visual axes remaining fixed in it, 
 or when the visual plane remaining fixed, the visual axes change their posi- 
 tion in it. All other positions are tertiary positions. 
 
 The necessary result of Listing's law, according to which every deviation 
 of the visual axes from the primary position indicates the inclination of the 
 meridian of the retina to the visual plane, and therefore the position of the 
 whole eye, can be deduced from the ' principle of the easiest orientation ' 
 (Helmholtz). As, namely, the orientation in vision depends upon the 
 appreciation by our consciousness of the position of the visual axes in refe- 
 rence to the head, and upon our estimation of the ( angle of rotation/ we need 
 not calculate the latter. We learn by experience, or probably by an inherited 
 automatism which had its origin in experience (refer to the review of 
 Darwin's principle in Chap. XII.), to associate with every position of the 
 visual axes a definite 'angle of rotation.' 
 
 A further mathematical extension of the { principle of easiest orientation ' 
 teaches that the most convenient point of departure (primary position) is 
 that in which the visual axis is exactly in the centre of its field of move- 
 ment (i.e. in the centre of the cone of the orbit, and that it can only deviate 
 from this position by rotations of the bulb around the diameter of the equa- 
 torial plane (Listing's law). The primary position is in fact the median 
 position of the eye. 
 
 The newly discovered facts (Javal, Skrebitzky, Nagel) that when the 
 head is inclined to either side a true (compensating) circular rotation takes 
 
MUSCLES OF THE EYE. 
 
 407 
 
 . 24. 
 
 X 
 
 place, which appears to be immutably connected with the movement of the 
 head, in no way contradicts Listing's principle. 
 
 Let Fig. 24 represent a vertical plane placed before the eye at the (reduced) 
 distance A B, and let p be its point of intersection with the visual axis 
 in the primary position. If the eye 
 now looks at any other point of inter- 
 section of the figure, the lines (cor- 
 respondingly reduced) represent the 
 direction in which the planes of the 
 horizontal and vertical meridians 
 of the eyeball intersect the observed 
 plane. It can be seen that these 
 directions remain horizontal or verti- 
 cal in secondary positions, i.e. in posi- 
 tions within the lines h h and v v ; in 
 all other (tertiary) positions, however, 
 the circular rotation must deviate 
 from the horizontal or vertical direc- 
 tion. If in the primary position the 
 vertical strongly-marked cross at p 
 be looked at fixedly, so that a persis- 
 
 tent image is impressed upon the vertical and horizontal meridians, that 
 image remains unaltered in the secondary positions (*, * 1 ), but takes up in 
 the tertiary positions t and t l the situations given, appearing therefore oblique, 
 and at the same time no longer rectangular, corresponding to the lines of 
 intersection of the two meridian planes with the observed plane. If the 
 cross at p were placed like the dotted cross, so that one of its limbs fell on 
 the line p t, no distortion of the secondary image occurs at t. If the plane 
 which is looked at be provided with horizontal and vertical lines, Listing's 
 law may easily be proved and confirmed by means of the situation of the 
 secondary images (Helmholtz). 
 
 Jl 
 
 The Muscles of the Eye. 
 
 The mode of action of each individual muscle of the eye, i.e. 
 the position of the axis, around which, if it acted independently, 
 it would move the eye, can be calculated, provided that the 
 situation of its origin in the orbit and the position of its at- 
 tachment to the bulb be known. The situation of these points 
 is expressed by the length of the abscissae cut off by the per- 
 pendiculars drawn from them to the three fixed co-ordinate axes. 
 
 The situation of the axis is determined by the three angles 
 which it forms with the three co-ordinate axes of the eye in its 
 initial position. In this way the following positions of the axes 
 have been determined in the case of the six muscles of the eye 
 
408 
 
 MUSCLES OF THE EYE. 
 
 (Fick) ; the initial position coincided approximately with the 
 primary position. 
 
 
 Angle which the axis of rotation forms with the 
 
 
 Visual axis 
 
 Vertical axis 
 
 Horizontal axis 
 
 Kectus superior . 
 
 111 21' 
 
 108 22' 
 
 151 10' 
 
 ,, inferior . 
 
 63 37' 
 
 114 28' 
 
 37 49' 
 
 externus . 
 
 96 15' 
 
 9 15' 
 
 95 27' 
 
 ,, interims . 
 
 85 1' 
 
 173 13' 
 
 94 28' 
 
 Obliquus superior 
 
 150 16' 
 
 90 0' 
 
 60 16' 
 
 ., inferior 
 
 29 44' 
 
 90 0' 
 
 119 44' 
 
 For the chosen initial position there does not exist, as may 
 be seen, any axis of rotation in the equatorial plane of the eye, 
 otherwise it would form a right angle with the visual axis. 
 The axes of rotation of the internal and external recti are very 
 close to the vertical axis, so that actually they rotate the cornea 
 almost simply inwards or outwards. The axes of the two 
 oblique muscles, on the contrary, are situated exactly in the 
 horizontal plane, at each side of the visual axis, each being at 
 a distance of about 30 from it, so that the rectus superior 
 draws the cornea outwards and downwards, whilst the rectus 
 inferior draws it outwards and upwards. The axes of rotation 
 of the recti, superior and inferior, are considerably deviated 
 from the horizontal axis, so that the former rotates the cornea 
 upwards and inwards, the latter downwards and inwards. 
 From the angles we conclude that each of the three pairs of 
 muscles has approximately a single axis, and therefore acts 
 almost antagonistically to the others. 
 
 As all the real movements of rotation of the eye are effected 
 around the diameter of the equatorial plane, it follows that 
 several muscles must co-operate in the production of almost 
 any movement. This has actually been ascertained to be the 
 case with eyes which have been partially paralysed. 
 
 Fig. 25 exhibits a horizontal section of the left eye ; sSj is 
 the visual axis, and qq } the transverse axis. This plane con- 
 tains, according to what was previously stated, the axes of 
 rotation of the recti rr^ and of the oblique muscles oo r 
 
 If the moments of rotation be expressed by lines corre- 
 sponding to the axes of rotation, and drawn to the one side or 
 to the other of the point of rotation, these moments of rotation 
 
MUSCLES OF THE EYE. 409 
 
 may, in a manner quite analogous to the parallelogram of 
 forces, be combined into resultant moments of direction ; the 
 diagonal of the parallelogram gives by its direction the situation 
 of the resulting axis of rotation, FIG. 25. 
 
 and the direction of the rotation, 
 whilst its length furnishes the 
 magnitude of the resulting rota- 
 ting force. Conversely, rotations 
 can be decomposed according to 
 given axes. Thus the diagram 
 shows that to produce a rotation 
 of the bulb around the horizontal 
 axis to the extent c q, the rectus 
 superior and obliquus inferior 
 must act together, and in the relations indicated by c a and c b. 
 For an equal rotation c q, in the opposite direction, the obliquus 
 superior and the rectus inferior must co-operate in the relations 
 indicated by the lines c d and c e. 
 
 Further, the figure shows that the rectus inferior by itself 
 can bring about not merely a rotation around the horizontal 
 axis c g, but also one around the visual axis (c/). The 
 consideration and estimation of muscular action necessary to 
 produce any given movement are such very complex processes, 
 especially because as soon as the smallest changes in the position 
 of a muscle have set in its axis of rotation has become altered, 
 that the subject cannot here be pursued further. * 
 
 The nerves which preside over the movements of the eyeball 
 are, the oculomotor (3rd), the N. abducens (6th), and the 
 trochlear nerve (4th). These nerves, which contain a large 
 number of fibres, and the actions of which can be varied with great 
 rapidity, are united on the two sides of the brain by a certain 
 bond, which tends to limit the movements brought about under 
 their influence. This association leads, in the first place, to 
 only such movements happening, as result in both visual axes 
 being in the same plane (visual plane), so that when they are 
 not parallel, if prolonged, they meet and intersect at a point ; 
 they have, therefore, so long as the head is held erect, the same 
 inclination towards the horizon, for the two points of rotation 
 can be considered fixed. Further, their reciprocal inclination 
 is limited, so that they only diverge to a very slight extent 
 
410 BINOCULAR VISION CORRESPONDING POINTS. 
 
 anteriorly, whilst they can converge to any required extent in 
 so far as their position will admit of it. The mechanism by 
 which this association of movements is effected is altogether a 
 puzzle. Deviations from its normal condition constitute 
 squinting (strabismus). The central organ, which co-ordinates 
 the movements of the eye, is situated in the corpora quadri- 
 gemina. 
 
 Binocular Vision. 
 
 Normally the two eyes act together, and the advantages 
 which result from this association are the following : 1. Cor- 
 rection of the faults of the one eye by the other. 2. The 
 perception of space is more perfect, because when we look at an 
 object from two different points of view, instead of observing a 
 mere projection of it in a surface, its third dimension in space 
 is appreciated. 3. A more accurate estimate of the magnitude 
 and the relative distances of objects is formed. 
 
 Simple Vision. 
 
 Though we look at external objects with both eyes, these in 
 general are seen as single ; this can only depend upon the fact 
 that the excitation of certain associated spots on the two retinae 
 is referred by consciousness to the same point in space or, in 
 other words, that both eyes possess but a single, common, field 
 of vision, and that the luminous impression which originates 
 by the excitation of two associated points, appears at one point 
 in the field of vision. Such associated points are called corre- 
 sponding or identical points. An object which is seen single 
 by the two eyes, whatever their position, must therefore project 
 its image on the two retinae in such a manner that the two 
 points of the image which correspond to one point of the 
 object fall upon corresponding points on the retinae. If one of 
 the two eyes be deviated, to however small an extent, a double 
 image must at once originate. We shall subsequently refer 
 more in detail to the nature of ' Identity.' 
 
 Situation of Corresponding or Identical Points. 
 
 Concerning the relative positions of corresponding points, 
 the following laws are apparent : 
 
HOROPTER. 
 
 411 
 
 1. As an object c, which is looked at fixedly by both eyes, 
 and the images of which fall, consequently, upon the terminations 
 of the visual lines c and c 15 is seen single, the two terminations 
 of the visual axes c and c l must be corresponding points. 
 
 2. If the centre, c, of an object, which is seen single, be 
 looked at, it follows, as the simple construction of the figure 
 shows, that the identical points which correspond to all points 
 
 FIG. 27. 
 
 of the right half of the retina, lie on the right side of the other 
 retina also, and conversely. Further, that the upper half of 
 the retina of one eye corresponds to the upper half of the retina 
 of the other eye, and the lower half of the one to the lower half 
 of the other. 
 
 Let the circles L and n represent projections of the two 
 retinae, the similarly designated quadrants a, a 1? &c., are 
 corresponding. The two meridians which separate these identical 
 quadrants are called lines of separation (vertical and horizontal) 
 
 3. It follows, further, that corresponding points on the two 
 vertical lines of separation must be identical, and this is also 
 true of points on the horizontal lines. 
 
 If in a given position of the eye the visual rays belonging 
 to two corresponding points be drawn and prolonged beyond 
 the eye until they intersect, the points of intersection will 
 evidently be the points which in that position of the eyes ap- 
 pear single. The term horopter is given to the combination 
 of all those points in space which, for any one position of the 
 eyes, appear single. If the horopter had been perfectly deter- 
 mined for any position of the eyes, the relation in the position 
 of corresponding points would obviously be likewise determined, 
 and the horopter for any other position of the eyes might be 
 constructed. Conversely, when the relation of the situation of 
 
412 HOROPTER. 
 
 these points is known, the horopter for any position of the eye 
 can be deduced. In so far as the relative positions of the 
 points, the most simple statement is the following : If the two 
 retina?, with their corresponding lines of separation, be ima- 
 gined to be superposed, all the points which coincide, or touch, 
 are corresponding points. 
 
 This statement is not rigorously true, even if the form of the retina, 
 which is not perfectly spherical, be taken into account. The vertical 
 meridians are not perfectly identical, and the true vertical lines of separation 
 do not exactly coincide with them, above being inclined outwards, and below 
 being inclined inwards. The physiological vertical axis is therefore some- 
 what inclined to the geometrical axis. 
 
 With the help of the above data the horopter can be deter- 
 mined mathematically or geometrically. The results of calcu- 
 lations are confirmed by experiments, and the latter establish 
 the correctness of the relations in the position of corresponding 
 points on the retina?. 
 
 A general deduction relating to the horopter can be arrived 
 at by the following method (Helmholtz). Every point on the 
 retina may be considered as a point of intersection of a meridian 
 and of a ' parallel circle ' (parallel circles being such concentric 
 circles as pass around the fovea centralis, which is the pole of 
 the retinal sphere). It is possible to calculate, 1, the ' meri- 
 dian horopter,' i.e. the assemblage of lines of intersection of 
 two planes passing through identical meridians and the nodal 
 points ; 2, the ' circular horopter,' that is to say, the assem- 
 blage of the intersections of two conical surfaces passing through 
 identical parallel circles and the nodal points ; 3, the point- 
 horopter, i.e. the horopter of corresponding points, which ob- 
 viously is the intersection of the meridian and circular horopters. 
 
 A second method of deduction (Hering, Helmholtz) con- 
 siders the plane of the vertical meridian as rotating around the 
 vertical axis, and the plane of the horizontal as rotating round 
 the horizontal axis ; the sections of retina so obtained are termed 
 longitudinal and transverse sections. Longitudinal sections 
 which make the same angle with the plane of the vertical 
 meridian are identical. The lines of intersection of the planes 
 of corresponding longitudinal sections constitute together the 
 6 horopter of the longitudinal sections.' Similarly, the identical 
 transverse sections form a system of intersecting lines the 
 
HOROPTER. 413 
 
 loropter of the transverse section. The intersection of the 
 TVVO horopters is the point-horopter sought for. 
 
 Both methods must, if rightly carried out, furnish the same 
 results. Each method possesses special interest, for not only 
 :he point-horopter, but the line-horopter is of importance. 
 Fhis remark specially applies to the previously mentioned 
 neridian horopter. A straight line, which is fixed at one 
 point, naturally forms an image of itself in a meridian of the 
 :etina. If now a line throws an image upon two identical 
 meridians, it must appear single, even though its individual 
 points do not fall upon identical points, for the double images 
 then are superposed in the field of vision, as the lines A B and 
 :i b in Figure 28. The meridian horopter or the normal surface 
 
 FIG. 28. 
 
 [v. Recklinghausen) possesses the property that all straight lines 
 falling upon it appear single, though all the points lying in it 
 :lo not do so. 
 
 For practical purposes the second of the two methods pre- 
 viously referred to is more convenient, chiefly because it permits 
 of our taking into account the deviation of the physiological 
 vertical meridian. The results of the calculation cannot here 
 be discussed, as an exhaustive treatment of the difficult problem 
 Df horopters would not be consistent with the object of this 
 handbook, and instead of attempting it, those determinations 
 of horopters will be treated of which can be arrived at by 
 simple geometrical considerations. 
 
 1. In the primary position, and in secondary positions 
 when the visual axes are parallel and directed forwards, the 
 horopter is a plane parallel to the plane of vision passing 
 through the point of intersection of the vertical axes of the two 
 3yes. As it is the physiological vertical axes, however, which 
 ire here concerned, and as their point of intersection is situated 
 ibout five feet below the field of vision, it follows that the 
 plane of the horopter, which would otherwise be at an infinite 
 distance below, is only five feet below the visual plane. If 
 therefore we look horizontally into infinite distance, the ground 
 constitutes the horopter-surface a fact which is of great im- 
 portance for sight in this position (Helmholtz). 
 
414 HOROPTER. 
 
 2. In secondary symmetrical positions, when the visual 
 axes are convergent, the horopter is as follows : two lines in the 
 horopter must be determined, viz. one which corresponds to 
 the identical points in the horizontal lines of separation, and one 
 which corresponds to the identical points in the vertical lines 
 of separation (a transverse section of the horopter formed by the 
 plane of vision, and a median section of the horopter). 
 
 (a.) The transverse section of the horopter is a circle 
 (J. Miiller). In Fig. 29 the two transverse sections of the eyes 
 pass through the horizontal lines of separation. The transverse 
 section of the horopter must therefore be in the plane of the 
 paper (visual plane) ; c and c { are the extremities of the visual 
 axes, c is the fixed point. If now for two points, as a and b in 
 the horizontal line of separation, we seek the identical points 
 on the other side, the latter must evidently, 1, lie on the same 
 side of the termination of the visual axis ; 2, be equally distant 
 from the visual axis ; they lie therefore at a t and 6 r The 
 visual rays which belong to these inter- 
 sect at the points A and B, which are there- 
 fore points in the horopteric line sought 
 for. It is readily seen by looking at the 
 drawing of the angles at the nodal points 
 k and \ that the angles at A, B, and c 
 (7) are equal. As they all proceed from 
 the common points k and & 1? they must 
 be a ^ peripheral angles of a circle H H, 
 passing at once through k and k r But 
 as this is the transverse horopter-line sought for the visual rays 
 proceeding from all the other identical points on the lines of 
 horizontal separation must here intersect. 
 
 (b.) The median section of the horopter, on the other 
 hand, is a straight line, perpendicular to the visual plane, and 
 therefore inclined to the horizon the line in which the two 
 planes which, pass through the vertical lines of separation 
 intersect. This is most easily understood if Fig. 30 be drawn 
 upon a piece of paper, which is then cut through along the line 
 H H, so that the two sides can be made to converge. The two 
 sections of the eye pass through the vertical lines of separation 
 in such a manner that the two converging planes which cut at 
 H H are the planes of the vertical meridians. It can be seen 
 
HOROPTER. 
 
 415 
 
 at a glance that the visual rays of all the points in the lines of 
 separation which are equally distant from the terminal points 
 c and Cj of the visual axis, e.g. a and a 19 b and b l meet in points 
 on the intersecting line H H, and that the latter therefore 
 represents the median horopteric line. This horopter for the 
 converging secondary positions is limited by the two lines just 
 alluded to. 
 
 3. In (symmetrical) tertiary positions the vertical lines of 
 separation, as well as the horizontal lines of the two eyes, meet 
 
 FIG. 30. FIG. 31. 
 
 n H 
 
 M 
 
 at an angle. If now (a) a plane is made to pass through each 
 vertical line of separation, the two planes intersect in a straight 
 line, which is inclined to the visual plane (nearer to the eyes 
 superiorly in tertiary positions, with these eyes inclined upwards, 
 nearer to the eyes inferiorly in tertiary positions in which the 
 eyes are directed downwards). This inclined line, as well as 
 the inclined position of the vertical lines of separation, are 
 rendered evident by the annexed Figure 31, which like 30 
 should be drawn upon a piece of paper, and be split up along 
 H H. In the model c c c l is the visual plane, and H H is the 
 line of intersection of the two planes of separation, and which 
 is inclined as in Fig, 30. It is seen that the visual rays of all 
 the corresponding points situated in the vertical lines of 
 separation, for example a and o& 19 b and 6 19 intersect also in the 
 line H IT, and that this line represents in consequence the 
 horopter of the vertical lines of separation. 
 
 (6.) If planes are made to pass through the horizontal 
 lines of separation, these likewise cut in a line. The visual 
 
416 HOROPTER. 
 
 rays of identical points of the horizontal lines of separation, if 
 they do intersect, could therefore only do so in this line. But 
 if from any point in the latter two visual rays be drawn, these 
 rays meet, as can readily be seen, in symmetrical but not in 
 identical quadrants of the vertical circles of separation. Hence 
 it follows that the visual rays proceeding from identical points 
 of horizontal lines of separation do not in general intersect, in 
 tertiary positions, and that for these there is consequently no 
 horopter. In general, the horopter for tertiary positions, besides 
 the meridian line, only includes another curve of double 
 curvature passing through the fixed point;, and which cannot be 
 here considered. 
 
 Hitherto only symmetrical positions of the eyes have been 
 discussed. It is impossible here to examine in detail the 
 un symmetrical positions in which the fixed point is at unequal 
 distances from the nodal points. It is to be remarked, that 
 positions occur in which the fixed point alone forms the 
 horopter. 
 
 In addition to the horopter of points which has hitherto 
 been considered, the horopter of meridians or the normal surface, 
 whose properties have already been referred to at p. 413, is to 
 be mentioned. 
 
 This surface (v. Eecklinghausen) in secondary convergent 
 positions is a plane perpendicular to the visual plane in the 
 fixed point ; it is in tertiary symmetrical positions a double 
 oblique cone whose summit lies at the fixed point. From this 
 first .property this important consequence follows, that in every 
 plane inclined before the eye, assuming that it be considered in 
 a secondary position, as is ordinarily the case, every straight line 
 must appear simple, providing that one of its points strike the, 
 eye. Experiments have, however, revealed that all the straight 
 lines lying in the normal surface, and none but such lines, appear 
 perpendicular to the meridian plane, even in tertiary positions, 
 where their real direction is quite different. If, for example, 
 we look at a star formed of threads, whose rays lie in one plane, 
 and fix our eyes upon its middle point, it will appear plane only 
 in secondary positions, and curved in tertiary positions, and its 
 rays then are deviated from the plane surface apparently in a 
 direction opposed to that of the normal surface ; the star only 
 appears lying in a plane, in tertiary positions, providing an 
 
NATURE OF 'IDENTITY.' 417 
 
 artificial curvature corresponding to the normal surface be given 
 to it. Other researches show that every luminous point, whose 
 distance cannot be determined by other methods, is projected 
 in the line of direction into the normal surface. This surface 
 appears therefore to be familiar to our eyes, and very probably 
 it plays a very important part in stereoscopic vision, for the 
 position of every part which does not lie within it is deter- 
 mined in accordance with it. 
 
 In order to explain this relation of corresponding points, 
 one might surmise that the fibres of the optic nerve which 
 belong to them are connected in the central organ in a peculiar 
 manner so that their excitation only occasions one single act of 
 consciousness, or at least that the two impressions are trans- 
 ferred to one and the same place in space, viz. to the point 
 of intersection of their visual rays. Many interpret in this 
 fashion the relation of the fibres of the optic nerve in the 
 chiasma nervorum opticorum. It is highly probable that in 
 this situation a transfer of one half of the fibres from one side 
 to the other occurs, so that each optic nerve-trunk is composed, 
 half of fibres derived from the optic tract of one side, the other 
 half being made up of fibres of the optic tract of the other 
 side; each tract must furnish fibres to the two halves of the 
 retina which possess the same name, and which therefore are 
 corresponding, the halves being limited by the vertical lines 
 of separation. In support of this view, the occurrence of hemi- 
 opia, in which in both eyes the retinal sensibility of the same 
 half of the retina has been lost, may be adduced. In this case we 
 must suppose that the fibres of, and the nerve centres connected 
 with one of the optic tracts, are incapable of discharging their 
 function (v. Grraefe). In opposition to this view a complete 
 crossing of the fibres has lately again been stated to occur in the 
 chiasma (Mandelstamm). In this case hemiopia of both sides 
 would not be caused by an affection of one tract, but by an affec- 
 tion of the outer angles between the tract and nerve, whilst an 
 action upon the anterior angle of both nerves would lead to dis- 
 turbance of the inner portions of the retina, and one affecting 
 the posterior angle of both tracts would lead to disturbances 
 in the outer portions of the retina ; true hemiopia with exact 
 demarcations in the vertical meridian yet would remain without 
 explanation. 
 
 E E 
 
418 NON-PERCEPTION OF SECOND IMAGES. 
 
 The correctness of the view that a central anatomical union 
 of corresponding points exists is, however, still doubtful, because 
 the ' identity ' of such points is not to be taken in an absolute 
 sense (compare below under Stereoscopy), but should perhaps 
 be looked upon as a property acquired by habit. Further, in 
 no case can the anatomical union of the corresponding points 
 be such that the excitation of two points produces a single 
 sensation, for the phenomena of stereoscopic vision, when the 
 illumination is sudden, prove that stereoscopic vision depends 
 upon the fusion of two separate sensations. 
 
 Non-Perception of Second Images. 
 
 It results from what has been previously stated, that in 
 consequence of the limitation of the horopter in all positions of 
 the eyes, the majority of objects before the eye appear double, 
 and that, moreover, disorders and variations must be produced 
 in the field of vision of the two eyes, because the rays pro- 
 ceeding from different points of the object fall upon identical 
 points. If, in spite of this, we have in ge ^eral only the con- 
 sciousness of simple images, and fail to see any perturbations 
 in the field of vision, it is because the following circumstances 
 are probably in operation : 
 
 1. Objects which furnish images which fall on the centre 
 of the retina (fovea centralis 'and macula lutea) appear simple 
 under almost any circumstances, because the terminal points 
 of the visual axes are corresponding points, and these axes, if 
 prolonged, intersect at one point. Now as this is the seat of 
 the most acute vision, and as the attention is almost constantly 
 fixed upon it, the influence of the light falling upon it pre- 
 ponderates over the influence proceeding from the whole of the 
 rest of the field of vision. 
 
 2. Objects which appear simple (which lie in the horopter) 
 can impress consciousness with greatest intensity, seeing that 
 they excite with double energy the same part of the nerve 
 centres. 
 
 3. The eyes are always accommodated for those objects for 
 which their axes are suited, so that they appear more sharply 
 defined than those which are placed in front of or behind the 
 point of intersection of the axes, and which are therefore not 
 situated in the horopter. 
 
STEREOSCOPIC VISION. 419 
 
 This relation between the movements of the eyes and ac- 
 commodation is brought about at first by the will, afterwards 
 with the co-operation of a nervous mechanism (Czermak); in 
 fact, the slightest movement of rotation of the eye is accom- 
 panied by a change in its accommodation, e.g. when the eye is 
 rotated inwards it is accommodated for near objects. 
 
 4. Consciousness fuses, under certain circumstances, images 
 of points which do not really correspond (see under Stereoscopy). 
 
 Co-operation of the two Eyes in Vision. 
 
 The most obvious advantage of vision with two eyes is, that 
 portions of one retina which are incapable of discharging their 
 function, e.g. by disease (v. Graefe), or portions of the retina 
 which through opacities in the refracting media cannot receive 
 images, are compensated for by corresponding points in the 
 other retina. It is in consequence of this function of double 
 vision that the mutual replacement of the gap in the field of 
 vision due to the blind spot is filled up, for the corresponding 
 points to the blind spots are parts of the retina which are 
 sensitive to light (the blind spots are situated in retinal quad- 
 rants of different names, but symmetrical). 
 
 Stereoscopic Vision. 
 
 Stereoscopic vision, the perception of the third dimension 
 occupied by bodies in space, depends upon the circumstance, 
 that the two images of a material object or of a surface, which 
 do not coincide with the horopter, can never be completely 
 united (according to the theory of corresponding points) so as 
 to furnish one single visual impression. As the two eyes con- 
 template the object from two separate points of view, two 
 separate perspective images fall upon the two retinae. Now 
 only exactly corresponding retinal images can uniformly fall 
 upon corresponding points ; when the eyes remain immovable 
 only one part of a body can therefore appear single, the rest 
 appearing double. 
 
 If, e.g., L and R (Fig- 32) are the two perspective retinal 
 images of a truncated pyramid, the summit of which is directed 
 towards the eyes which contemplate it, it is seen that either 
 the images of the surfaces of the base, viz. abed and ^ b l c l d^ 
 or the images of the truncated surface efgh smd e l f l g l h l9 
 
 E E 2 
 
 . 
 
420 
 
 STEREOSCOPIC VISION. 
 
 can alone fall upon corresponding points of the retina ; in the 
 first case, the smaller (truncated) surface appears double, in 
 the second, the larger. Nevertheless, the two images are fused 
 into one, and convey the impression of a single body occupying 
 
 FIG. 32. 
 
 c d, 
 
 three dimensions. A simple explanation of this phenomenon 
 would appear to be the following (Briicke) : the two eyes are 
 continually in a state of motion ; their position of convergence 
 varies so far from one side to the other, that, one after the other, 
 the images of all sections of the pyramids fall upon corre- 
 sponding points of the retinae. 
 
 In Fig. 33, three of the fusion-impressions which occur in 
 two series of movements have been selected for examination. 
 In the first the images of the basal-surfaces, and in the third 
 those of the truncated surface, fall upon corresponding points ; 
 the image of a section of the pyramid situated between the 
 two first (i k I TI), and placed in the centre of the two first, is 
 
 FIG. 33. 
 
 c f,f 
 
 s---^ 
 
 d, 
 
 d d, 
 
 seen simply by the eyes. As now, in order that the impression 
 exhibited by Fig. 33, III., shall be perceived, the eyes must 
 converge more strongly than for the perception of I. ; and as 
 the convergence of the eyes affords a means of determining the 
 distance of objects from them (see below), the conclusion is 
 arrived at by consciousness, that the surfaces efgh, ikln, 
 and a b c d, lie one behind the other, and the conception of a 
 material object is arrived at, through the combination of all 
 the rapidly succeeding impressions. 
 
 But the fact that the exceedingly short space of time during 
 
STEREOSCOPIC VISION. 421 
 
 which an electric spark lasts suffices to fuse two simple stereo- 
 scopic images into one material impression, appears to afford an 
 argument in opposition to the explanation above given, for in 
 the moment of time during which the spark lasts no movements 
 of the eyeball could take place. 
 
 This observation compels us to modify somewhat the theory 
 of binocular vision. The identity of two corresponding retinal 
 points is, namely, not to be taken as absolute, presumably does 
 not depend upon a direct anatomical communication, but is 
 something which is acquired. 
 
 Corresponding points are therefore such points as furnish 
 images which, as experience teaches, are habitually combined or 
 fused. But as it appears necessary to effect these combinations 
 in order to obtain correct impressions of objects, we get into 
 the habit of fusing also the images of two not perfectly corre- 
 sponding points which under ordinary circumstances we should 
 perceive as double. It can easily be demonstrated that simul- 
 taneous images, which fall upon corresponding points, are not 
 united, although it is true that they do not form second 
 images. When the mind must unite images which do not fall 
 upon corresponding points, the process must be associated with 
 the conception that the corresponding points in the object 
 occupy the situation for which the eye would have to be 
 arranged, in order that the images should coincide. 
 
 We cannot here enter into an examination of the numerous 
 theories which have been advanced in explanation of the above- 
 mentioned facts. Moreover, Briicke's explanation of the stereo- 
 scopic fusion is not entirely refuted by the experiment of in- 
 stantaneous illumination which was previously adduced, as, for 
 the vision of complicated objects, such a movement of the eye 
 from side to side is, at any rate, very useful. For the vision of 
 such objects momentary illumination does not suffice. 
 
 Stereoscopic vision can be artificially imitated by placing 
 before each eye the drawing of a body executed from its own 
 point of view ; such drawings are shown in Fig. 32. The eyes 
 in this case bring either successively or at the same moment 
 the different parts of the drawing over corresponding points, and 
 so the impression of the shape of body is produced. This is the 
 basis of the stereoscope. Without further apparatus the images 
 B and L, which lie side by side, may combine, if we direct each 
 
422 
 
 THE STEREOSCOPE. 
 
 of the two optic axes to the corresponding image (Fig. 35). 
 But inasmuch as few persons can control their eyes for a suffi- 
 
 cient length of time, in order to fix 
 two separate points on a surface, in- 
 stead of allowing as usual the axes to 
 intersect at the surface which is looked 
 at, arrangements are provided whereby 
 this exertion is dispensed with, so that 
 with an ordinary position of the eyes 
 images are thrown upon corresponding 
 B L points. The two best known stereo- 
 
 scopes are those of Wheatstone (Fig. 35) and Brewster (Fig. 
 36), which are explained by the annexed figures. 
 
 In the first (Wheatstone's) stereoscope the images are super- 
 posed by two converging mirrors, in the second (Brewster's) by 
 two prismatic glasses g g (halves of lenses) upon a place R, to 
 which the optic axes are directed. 
 
 FIG. 35. FIG. 36. 
 
 B 
 
 If two perfectly similar drawings are placed in the stereo- 
 scope, they naturally furnish a single image. If they are, how- 
 ever, ever so little different, the difference even being limited 
 to the situation of certain parts, the eyes are compelled to make 
 movements in order to combine these parts, and they appear, 
 from what was previously stated, as removed from the surface, 
 being either in front or behind it. Hence the stereoscope may 
 be employed in order to distinguish between two similar objects 
 which differ only in small and limited points, as, for example, 
 between a real and a forged bank-note, as between two (diffe- 
 rent) impressions from the same mould, &c. (Dove). 
 
 If the relative positions of the stereoscopic image of a body 
 
THE PSEUDOSCOPE. 423 
 
 be changed, for example, those seen in Fig. 32, so that the one 
 intended for the right eye is brought before the left, or con- 
 versely, the body appears hollow and as if seen from within, the 
 smaller surface, efgh, .appearing to be placed behind the 
 larger. Actually the perspective views obtained by both eyes 
 from a hollow pyramid, seen from the interior, only differ from 
 those which are obtained on looking at a massive pyramid from 
 the outside, in the fact that in the first case the right eye 
 obtains the view which in the second case reaches the left eye. 
 
 On looking at an object from the outside, the right eye 
 catches more of the right side of the object than of the left (the 
 surface b l ^ / t g l (Fig. 32) is therefore larger than a T d l e l h^ ; 
 on looking into a hollow body matters are reversed (the right 
 eye then occupies the point of view L, 'and b cf g is smaller 
 than ad eh}. The fallacious impression obtained in such a 
 manner by exchanging two stereoscopic images is designated 
 ' pseudoscopic.' 
 
 The pseudoscope, Fig. 37, is an apparatus by which the two 
 eyes which are contemplating an object are subjected to a 
 pseudoscopic influence ; each eye receives, F 1G . 37. 
 
 namely, by reflexion from the hypothenu- 
 sal surfaces of a rectangular prism, the 
 impression which belongs to it, reversed, 
 so that one eye receives the form which 
 properly pertains to the other. The body 
 thus appears hollow and as if seen from 
 the inside, when, in reality, its external 
 surface is directed towards the eye, and 
 conversely. The apparatus, as may 
 readily be understood, can only be em- M N o 
 
 ployed in looking at bodies which are symmetrically formed. 
 
 Very distant objects, e.g. those parts of a landscape which 
 lie near the horizon, appear usually as if they were extended 
 upon a surface, as in a picture, because the two eyes are 
 situated too close to one another to obtain essentially different 
 views of objects in the distance. The telestereoscope of Helm- 
 fa oltz is an instrument which serves to magnify the distance be- 
 tween the points of view of the two eyes. It is a Wheatstone's 
 stereoscope, the two images of which, L and n, are received by 
 two mirrors turned towards the horizon and parallel to the in- 
 
424 STEREOSCOPIC BRILLIANCY. 
 
 ternal mirrors ; the two eyes thus obtain views as if they 
 occupied the positions of the external mirrors, and the horizon 
 appears, consequently, as if it had stood-out more ; ordinarily 
 the two internal mirrors are looked at through two telescopes. 
 
 When two stereoscopic representations of an object are 
 coloured of different intensity (e.g. one being black, another 
 white, or of a different colour) or if two surfaces possessing 
 different depths of the same colour, or coloured differently, be 
 brought before the eye, the object or the surface appears to 
 shine. The most probable explanation of this phenomenon is the 
 following : A surface which is looked at with one eye appears 
 shining, when ft reflects the light very uniformly ; even abso- 
 lutely plane or absolutely planely curved surfaces (if presenting 
 no unevennesses) therefore appear shining. 
 
 If this same surface be examined with the two eyes, it ap- 
 pears to each as possessing a different brilliancy and a different 
 depth of tint, because the reflected light falls into the two eyes 
 at a different angle. If now, conversely, the two eyes receive 
 two impressions which when seen alone are dull, but if they are 
 of different depth, consciousness pictures a regularly reflecting 
 (which consequently illuminates the two eyes differently) and 
 brilliant surface (Helmholtz). The two stereoscopic images of 
 a smooth ball, which exhibit the reflexion of light at different 
 places, give rise in the same way to the impression of a shining 
 ball. 
 
 It is not so easy to explain the cause of the brilliancy of 
 colours. The simplest explanation appears to be the following : 
 besides arising by simple regular reflexion, certain sorts of 
 brilliancy are generated by reflexion from multiple surfaces 
 placed one behind the other, even when these surfaces are dull. 
 Thus, for example, 'metallic lustre depends upon the fact that 
 a slightly transparent metal not only reflects light from its sur- 
 face, but also from its deeper layers (Briicke). As now for two 
 different colours at an equal distance, a somewhat different ac- 
 comodation of the eye is requisite, it appears as if one colour 
 lay a little behind the other, and so the body exhibits lustre 
 (Dove). Moreover, many persons fail to observe the binocular 
 combination of colours, both colours not uniting to form one 
 image, but they either appear alternately or are seen side by 
 side in the field of view (' Wettstreit der Sehfelder '). 
 
MAGNITUDE AND DISTANCE OF OBJECTS. 425 
 
 Estimation of Magnitude and Distance of Objects. 
 
 A third useful purpose subserved by binocular vision is the 
 aid which it affords in the determination of the magnitude and 
 distance of external objects. The starting-point for the de- 
 termination of magnitude is the size of the retinal image. 
 The greater the latter, the greater, cceteris paribus, does the 
 object appear. As, however, the magnitude of the retinal 
 image, or what is the same, the magnitude of the visual angle., 
 does not depend merely upon the magnitude, but also upon the 
 distance of the object from the eye (as the visual angle is in- 
 versely proportional to the distance), the determination of the 
 magnitude of objects is associated with a determination of their 
 distance. For the latter, the eye by itself possesses a method 
 of estimation, in the effort to accommodate, the magnitude 
 and direction of the effort being appreciated by the muscular 
 sensation in the muscle concerned. In vision with two eyes 
 there is added the important help afforded by the muscular 
 sense of the muscles which move the eyeball, and which inform 
 us to what degree the optic axes have converged. 
 
 An object of apparently equal magnitude appears the nearer, 
 1, the greater the retinal image which it furnishes; 2, the 
 stronger the positive accommodation ; 3, the stronger the con- 
 vergence of the optic axes. Further helps to the determination 
 of distance are, the intensity of the light, which in general de- 
 creases witn the distance. Further, the displacement of the ob- 
 ject in reference to others seen at the same time, which occurs 
 either when the object itself moves, or when the other objects 
 move, or when the organ of sight changes its place in consequence 
 of movements of the head or of the whole body. 
 
 The most direct proofs that the above are the three prin- 
 cipal means of estimating the distance or size of objects are the 
 following : 
 
 1. The influence of the retinal image scarcely requires proof; 
 such a proof is, however, that in defective accommodation (in 
 the circles of diffusion) an object seen appears larger than if the 
 accommodation be perfect and the object sharply defined. 
 
 2. The influence of the sensation produced by accommodation 
 is most apparent from the fact that a secondary image, however 
 
426 ORGANS OF PROTECTION OF THE EYE. 
 
 produced, changes in apparent magnitude when the accommoda- 
 tion changes ; and further, that if red and blue fields occupy 
 the same plane, the first appear nearer than the second 
 (Briicke). 
 
 3. The influence of the convergence of the axes is proved in 
 a striking manner by the so-called ' carpet-phenomenon.' If 
 whilst one is looking at any regular pattern (as a carpet) the 
 eye be fixed upon a point lying in front of or behind it, the 
 pattern soon appears to advance in the plane of the point 
 of convergence of the visual axes, and appears, consequently, 
 near or more distant, and in. the same manner smaller or 
 larger. 
 
 The explanation is easy. Under these circumstances an 
 irregular pattern would appear double ; even a regular pattern 
 will appear double ; but as in the two images situated one over 
 the other, equal parts of the pattern almost exactly cover one 
 another, the deception originates that both images with their 
 corresponding parts fall upon corresponding points,, and there- 
 fore the object lies at the distance of the point of intersection 
 of the visual axes (H. Meyer). Just as the images of the centres 
 of the two retinae are transferred to the point of intersection of 
 the visual axes, so the remaining images are transferred to the 
 surfaces, in which the identical meridians intersect, i.e. to the 
 normal surface. 
 
 The Organs which protect the Eye. 
 
 1. The eye, which is protected nearly on all sides by the 
 osseous orbit in which it is placed, can also be shut off anteriorly 
 by the closure of the cartilaginous eyelids. The closure is effected 
 by the contraction of the orbicularis palpebrarum muscle, 
 which receives its nervous supply from the facial nerve, and in 
 so far as the upper eyelid is concerned, it is brought about to 
 a certain extent by the mere action of its weight (gravity). 
 The lower eyelid is opened by the action of gravity, the upper 
 by the contraction of the levator palpebrae superioris, which 
 derives its nervous supply from the third (oculomotor) nerve, 
 whilst both are influenced by retractor involuntary muscular 
 fibres which are under the influence of the sympathetic (H. 
 Miiller, Sappey), Movements of opening and of closure are 
 frequently and alternately occurring (blinking, winking). 
 
LACHRYMAL APPARATUS. 427 
 
 The closure of the eyelids occurs, 1, voluntarily; 2, involun- 
 tarily and automatically, in sleep; 3, by reflex action, when 
 the eyeball is touched or the eyelashes which serve as touch- 
 hairs, or when the optic nerve is excited by intense light. The 
 narrowing of the space between the eyelids and the shade 
 thrown by the eyelashes co-operates with the contraction of 
 the pupil in protecting the eye when the light is intense. 
 
 The retractors of Miiller are situated in the posterior surface of the eye- 
 lids perpendicular to the opening between the lids. Another smooth muscle 
 bridges over the inferior orbital fissure and by its contraction somewhat 
 diminishes the capacity of the orbit, so that the eyeball somewhat projects. 
 Both muscles exist in a state of tonic contraction. When the sympathetic 
 is cut cross in the neck the space between the lids narrows and the eyeball 
 is somewhat retracted (H. Miiller). 
 
 2. The anterior surface of the eye is continually bathed in 
 lachrymal fluid, and by it maintained in a state of cleanliness 
 and preserved from desiccation. The tears reach it through 
 the fine excretory ducts of the glands situated in the upper and 
 external region of the conjunct! val sac. (The conjunctival sac 
 is, as is well known, a mucous sac, which by its free border is 
 attached along the edge of the lids, and which covers a part of 
 the eyeball ; it covers the posterior surface of the eyelids, then 
 is reflected over the eyeball, of which it covers the anterior 
 third. The eyelids being closely applied to the eyeball, the con- 
 junctival sac possesses only a capillary lumen. It only widens 
 near the line of contact of the closed lids, where it forms a 
 shallow three-sided canal, as the more slight curvature of the 
 lids does not here permit of their clasping the eyeball). The tears 
 are sucked into the capillary conjunctival space by capillary 
 attraction, and are prepsed towards the inner angle of the 
 eye. This movement is aided by the closure of the lids, which 
 presses them towards the inner angle of the eyes (inner can- 
 thus), which is the point of attachment of the orbicularis pal- 
 pebrarum. 
 
 The overflow of tears over the fine edge of the lids is pre- 
 vented, when the secretion is not exceedingly great (as in crying) 
 by the fatty secretion of the meibomian glands. At the inner 
 angle of the eye the tears accumulate into what may be called 
 a little tear-lake (' Thranensee'), where commence the two capil- 
 lary rigid lachrymal canals with their openings, the 'puncta 
 
428 FACETTED EYES OF INSECTS. 
 
 lachrymalia.' The nasal duct, into which the ducts lead, and 
 which is protected below in the nasal cavity by a valve open- 
 ing downwards, dilates superiorly at the time when the eyelids 
 are closed (because its posterior wall is connected with the bone, 
 and its anterior with the anterior palpebral ligament which 
 stretches when the lids are closed) ; by these arrangements it 
 sucks the tears from the little tear-lake. The same effect is 
 produced by the contraction of Horner's muscle, which also 
 enlarges the lachrymal sac. 
 
 The closure of the lids might also, when the lids are completely closed, 
 press the tears into the sac. This has actually been recorded to occur by 
 some (Rose, Stellwag, v. Carion). Experiments with coloured fluids, 
 which have been instituted to decide this question, have not furnished con- 
 cordant result (Stellwag, Arlt). 
 
 3. The eyebrows are supposed to protect the eye from the 
 sweat which may flow from the forehead. 
 
 Appendix. The facetted eyes of insects and Crustacea are 
 composed of conical segments arranged as the radii of a ball : 
 each of these segments consists of a dioptric apparatus which 
 acts as a convex lens, and of internal nervous structures which 
 are in connection with the terminal ends of the optic nerve in 
 the centre of the ball. Each of these radiating segments, 
 which by pigment and by total reflection (like the rods of the 
 retina) are optically distinct one from the other, most probably 
 only allows such light to be perceived as falls in the direction 
 of its axis, so that the creature possesses, especially for near 
 objects, as many fields of view as there are segments. The 
 adjustment of an optic-nerve element to a particular direction 
 is effected here also, as in the eyes of vertebrata, by other 
 means. In the latter, for instance, the complex dioptric ap- 
 paratus only allows such light to reach each individual retinal 
 element as follows a particular direction (viz. that of the cor- 
 responding visual ray); in the eye of insects, on the other 
 hand, each retinal element has a telescope arranged for one 
 particular direction. 
 
ORGAN OF HEARING. 429 
 
 II. THE ORGAN OF HEARING. 
 
 Schema of the Organ of Hearing. 
 
 The terminal organs of the auditory nerve are spread out like 
 those of the optic nerve on membraneous surfaces, which have, 
 however, an irregular form (ampullce, saccules of the vestibule, 
 and membraneous portion of the lamina spiralis). The 
 sonorous vibrations capable of exciting the auditory nerve are 
 transmitted to these terminal organs by a system of easily 
 vibrating bodies in contact with each other, the first of which, 
 situated most externally, vibrates in unison with the sounding 
 body ; the vibrations of the sonorous body are transmitted to it 
 directly or indirectly : in the latter case through an inter- 
 mediate body, such as air or water. 
 
 There are two such systems, and these have one part in 
 common, that adjacent to the end organs, viz. the fluid con- 
 tents of the labyrinth in which the terminal organs are bathed. 
 The labyrinth-fluid can be thrown into vibrations in two ways: 
 1, by the surrounding bones, the petrous portion of temporal 
 and all the other cranial bones. This mode of transmission 
 comes into play when the sonorous (solid) body is either in im- 
 mediate contact with the skull or is connected with it by a 
 chain of solid or fluid bodies, or when the medium immediately 
 surrounding the head is not gaseous, as, for instance, when the 
 sounding body is in contact with the teeth, or when the head is 
 immersed in water ; 2, by the membrane of the fenestra ovalis, 
 which separates the labyrinth-fluid from the air-containing 
 tympanic cavity. This membrane is thrown into vibrations by 
 the following chain of bodies (beginning from the fenestra 
 ovalis) : stapes, incus, malleus, membrana tympani, the air 
 and walls of the external meatus and auricle. This system 
 serves for the perception of those sonorous vibrations which are 
 transmitted to the ear by the air : it is therefore the common 
 form of conduction in man, and is found absent in aquatic 
 animals. 
 
430 AUDITORY PASSAGES. 
 
 Of the two systems just enumerated the latter alone requires 
 further consideration, for the first plays in the case of man only 
 a very infeiior part. 
 
 Conduction of Sound to the Tympanic Cavity. 
 
 It is chiefly at the surface of the membrana tympani, but 
 also at the walls of the auricle and external meatus, that the 
 transition of the sonorous vibrations from air to solids takes 
 place. The vibrations communicated to the auricle and 
 external meatus are for the most part conducted further to the 
 membrana tympani along its ring of attachment ; a portion of 
 these reaches the labyrinth through direct conduction by the 
 bones, together with all those vibrations which are imparted to 
 the head by the air. The walls of the external meatus, and 
 possibly also of the auricle, serve, however, a much more im- 
 portant service, by reflecting the sonorous waves on to the 
 membrana tympani, the waves being thrown from the auricle 
 into the auditory meatus and from the meatus on to the mem- 
 brana tympani. For the auricle, this function is far from 
 proved, and experiment throws great doubt upon it. 
 
 There is no form of solid body more adapted for the reception and 
 further transmission of vertically or obliquely impinging air-vibrations than 
 that of a stretched membrane or of rigid, elastic, thin plates. To the latter 
 description the cartilaginous auricle answers, whilst the membrana tympani 
 is of the first-described form. In both cases the body is so thin that the 
 waves of condensation and rarefaction of the air which fall on it are capable 
 of setting its total mass in vibration, in the direction of its transverse 
 diameter (transverse vibrations) ; otherwise the different layers of molecules 
 would vibrate successively and thus give rise to condensation and rarefaction 
 waves in the body itself (longitudinal vibrations) ; in the first case, where the 
 elasticity has only to be overcome, the resistance is much less and the elonga- 
 tion of the vibrations therefore much greater than in the latter case, where the 
 greater resistance is opposed to the mutual separation of the molecules. Such 
 bodies, however, are also capable of longitudinal vibrations, when vibrations 
 are communicated to them from the border, as e.g. the vibrations transmitted 
 to the membrana tympani by the external meatus. 
 
 The reflexion of sound by the walla of the external meatus requires 
 no further elucidation, for all vibrations which fall on the walls of a 
 cylindrical tube must reach, after being once or oftener reflected, the surface 
 which closes the tube (in the case of the ear, the membrana tympani, which 
 is placed obliquely to the axis of the tube, passing from below upwards, and 
 outwards). 
 
 "Reflexion of sound waves from the surfaces and promonotories of the 
 
TYMPANUM. 431 
 
 auricles on to the orifice of the auditory meatus may very well be thought 
 possible, especially as the auricle, both in toto as well as in its separate parts, is 
 movable by means of muscles ('which, however, owing to non-use, are often 
 but ill developed). Experiments, however, in which the whole auricle, with 
 the exception of the meatus (which was prolonged by means of a tube inserted 
 into it) was filled up with a soft material, showed no perceptible diminution 
 of the hearing, from which the function of the auricle as a reflector of sound 
 would seem improbable (Harless) ; others, however, have obtained opposite 
 results (Schneider). The absence of the auricle has not been known to 
 cause diminution of hearing. Artificial reflectors of considerable power 
 (for people affected with difficulty of hearing) are ear trumpets, which may 
 be considered to be cylindrical prolongations of the meatus, with a funnel- 
 shaped external termination. The stethoscope may be considered as a similar 
 prolongation of the meatus, the other end of which is in contact with the 
 sonorous body ; its action, however, depends, to a great extent, on the con- 
 duction of sound along its walls. 
 
 Stretched membranes, just like stretched strings, are, in 
 general, only thrown into vibration when the number of their 
 vibrations is the same as, or a multiple of, the number of vibra- 
 tions of the excited sound, and then they answer only in their 
 own pitch ; the membrana tympani, however, is set in vibration 
 by a sound of any pitch (within certain limits) and vibrates 
 exactly in the proportion of the number of vibrations of, and 
 with an intensity proportional to that of, the sound. Even very 
 complex sonorous waves compound tones throw the membrana 
 tympani into fully sympathetic vibration. This is proved by 
 the fact that (within a certain limit) we hear a sound of any 
 given pitch in its own specific timbre and that we are able to 
 judge of its intensity. It must, however, be observed that low 
 tones are heard less distinctly than very high tones of the same 
 objective intensity, showing that the membrana tympani does 
 not respond so well to deeper tones. The peculiarity of the 
 membrana tympani just spoken of is explained as follows : 1 , its 
 connection with the ossicles of the ear and the membrane of the 
 fenestra ovalis offers a pretty considerable resistance to its vibra- 
 tions (Seebeck). This diminishes considerably the intensity of 
 the vibrations of the tympanic membrane (the terminations of 
 the auditory nerve must therefore be very sensitive, Ludwig), 
 but as its mass (and therefore likewise the momentum of in- 
 ertia) is but small, the influence of its own vibrations is almost 
 entirely lost. 
 
 The same circumstance prevents also the continued or after- 
 
432 ACCOMMODATION OF THE TYMPANUM. 
 
 vibrations of the tympanic membrane, so that we hear the sound 
 no longer than it lasts ; 2, partially also because the state of 
 tension of the tympanic membrane can be altered by the m. 
 tensor tympani ; this can only make the tympanic membrane 
 answer better to certain tones, i.e. to very high or very low tones. 
 Tension of the membrane corresponds to accommodation for 
 high, relaxation of the membrane for low, sounds. A high 
 degree of tension reduces, moreover, the intensity of the vibra- 
 tions, that is, produces difficulty of hearing (J. Miiller), for the 
 resistances are thereby increased. 
 
 The stretching of the tympanic membrane by the m. tensor 
 tympani is effected in the following way : the manubrium of 
 the malleus is inserted between the lamellae of the membrane in 
 a radial direction passing from above downwards and terminating 
 a little below the centre of the membrane. The malleus 
 (together with the incus) is movable around an axis passing- 
 through its neck from before backwards (see below), and in its 
 position of equilibrium, owing to its connection with the other 
 ossicles and the elasticity of its supporting ligaments (see below), 
 the lower end of the manubrium points inwards ; this causes the 
 membrana tympani to be drawn inwards towards the tympanic 
 cavity in the form of a flattened cone or funnel, the meridians 
 of which, owing to the tension of the circular fibres, are not 
 straight, but somewhat curved, with the convexity outwards. 
 
 This form of the tympanic membrane has the advantage of 
 increasing the force of its vibrations at the expense of their ampli- 
 tude, for it can be proved both mathematically and experimentally 
 that the effect of the atmospheric pressure on the termination 
 (the umbilical central depression of the tympanic membrane) of 
 slightly arched meridians, is the same as if that termination were 
 the end of a very small lever arm, while the atmospheric 
 pressure acts on a very long lever (Helmholtz). 
 
 The tendon of the tensor tympani, which, after passing over 
 its pulley and running at right angles to the manubrium, inserts 
 itself into the point of rotation of the malleus, draws with every 
 contraction of its muscle the manubrium still more inwards, 
 and thus brings about a still further tension of the tympanic 
 membrane. The contraction (dependent on the fifth nerve) 
 can be produced by some persons voluntarily (J. Miiller); it is 
 observed in all persons as a co-ordinate movement in connection 
 
ACTION OF THE TENSOR TYMPANI. 433 
 
 with the forcible contraction of the muscles of mastication 
 (Fick). Opinion is as yet divided as to whether the contraction 
 is purely a voluntary one or a reflex action (to damp strong 
 impressions of sounds), dependent on the auditory nerve or the 
 sensory nerves of the external meatus. As soon as the contrac- 
 tion of the muscle ceases, the manubrium and, with it, the 
 tympanic membrane, return to their position of equilibrium by 
 help of the elasticity of the membrane, and the arrangement of 
 the ligamentous appendages of the malleus and the connection of 
 the different joints of the ossicles. It will be evident that 
 there is no necessity for a muscle acting as an antagonist to the 
 tensor tympani, and what has been described as such (laxator 
 tympani) is merely a ligamentous band. 
 
 Many persons can produce at will a crackling- noise in the ear, -which 
 formerly was thought to be connected with the contraction of the tensor 
 tympani (muscular sound or sudden stretching of the tympanic membrane). 
 This assumption is contradicted by the fact that the sound is not accompanied 
 by a drawing inward of the membrana tympani (this is ascertained by insert- 
 ing a manometer into the meatus, Politzer, Lowenberg). This sound is now 
 thought to be produced by the sudden opening (by the tensor palati) of the 
 Eustachian tube, which, according to some (Toynbee, Politzer, Moos) is con- 
 sidered to be quite closed while at rest, while according to others (Riidinger, 
 Lucae) it is said to have always a free lumen, which only closes during the 
 act of deglutition (Cleland). 
 
 The tympanic membrane can be more powerfully stretched 
 in another way, when, namely, to the already existing conditions 
 there is added a difference of the atmospheric pressure on the 
 two sides of the membrane (in the tympanic cavity and in the 
 external meatus). Ordinarily the atmospheric pressure is the 
 same on both sides, for the air in the tympanic cavity, which 
 is connected with the pharynx through the Eustachian tube, is 
 under atmospheric pressure. By a forcible expiration the oral 
 and nasal cavities being closed, air can be driven into the> 
 tympanic cavity, whilst by a forcible inspiration, under the same 
 conditions, air will be driven from that cavity (ValsalvaV 
 experiment). In the first case the tympanic membrane will be 
 driven outwards, in the latter case inwards, and in both cases 
 therefore it will be more stretched. The consequence of this 
 is, besides the accommodation for higher pitched sounds, a 
 momentary deafness. Permanent deafness is caused when by 
 
 F P 
 
434 CONDUCTION BY THE TYMPANIC CAVITY. 
 
 occlusion of the Eustachian tube, the atmospheric pressure in 
 the tympanic cavity is abnormal, a condition which can only be 
 remedied by making the tube permeable (introduction of a 
 catheter through the inferior nasal passage). 
 
 The lowest sounds which can still be perceived are said to be those of 
 40, the highest those of about 16,000 vibrations in the second ; it is how- 
 ever doubtful whether this limit is due to the tympanic membrane, or to the 
 perceptive power of the auditory nerve. The limits are different for 
 different persons : thus some persons can hear some high-pitched sounds and 
 yet not perceive still higher pitched sounds audible to others, as, e.g. the 
 chirping of the cricket. (Compare also what is said further on on the diffe- 
 rent forms of vibrations of the tympanic membrane.) 
 
 Conduction of Sound by the Tympanic Cavity. 
 
 The further conduction of the vibrations of the tympanic 
 membrane is affected by the chain of ear ossicles, which ap- 
 pear only to serve the purpose of transmitting the vibrations 
 of the tympanic membrane to the membrane of the fenestra 
 ovalis. 
 
 In birds, and in the scaly amphibia, they are therefore 
 represented by a single rod-like ossicle (columella) only. In 
 man the two opposed membranes are not connected by a single 
 rod, but by a compound lever composed of three bones, the 
 axis of rotation of which is the malleo-incus axis (a, in Fig. 38). 
 FIG. 38. The arrows in the figure indicate how the 
 
 membrane of the fenestra ovalis must always 
 vibrate in the same sense as the membrana tym- 
 pani. The connection of the lever with the 
 membrane of the fenestra ovalis is not brought 
 about, as in the case of the tympanic membrane, by a radially 
 inserted arm, but by a plate, which is attached centrally, the 
 base or foot of the stirrup. The joints between the separate 
 ossicles, which are so fixed by help of their own elasticity and 
 the contraction of the tensor tympani, that their system vibrates 
 as a whole with the tympanic membrane, serve most probably to 
 allow the mutual sliding of the ossicles in the different positions 
 of the membrana tympani, for which purpose also the stirrup is 
 attached by its base, so as to be able to vibrate only in the 
 direction of its slightly moveable longitudinal axis. The dimen- 
 sions of the ossicles and the amount of the fluid of the labyrinth 
 
OSSICULA AUDITUS. 435 
 
 which vibrates with them, are so small in comparison to the 
 wave length of the sound waves, that all these parts must always 
 be in the same phase of vibration. (E. Weber, Helmholtz.) 
 
 The malleus is supported by a ligamentous mass which is stretched 
 from before backwards through the tympanic cavity, forming at the same 
 time the axis of rotation (axial band, Helmholtz) ; this band consists of two 
 ligaments, which are inserted into the neck of the malleus, an anterior liga- 
 ment, attached to the spina tympanica anterior, and a posterior ligament, 
 which is only a prolongation of the anterior. The movements of the mem- 
 brana tympani being communicated to the manubrium of the malleus, the 
 latter, and with it the incus, rotate round the axis just described; the incus 
 is chiefly supported by the malleus, but it is so connected by its short process 
 to the posterior wall of the tympanic cavity, that it slightly modifies the 
 movements of the malleus (so that both might be considered as forming one 
 complex lever), and allows the umbilicus of the tympanic membrane to 
 move only in a direction vertical to the marginal plane of the membrane. 
 The long process of the incus, which articulates with the stapes, curves 
 round a little inwards from the manubrium of the malleus, remaining 
 throughout parallel to it. The articulation between malleus and incus is 
 saddle-shaped, the body of the incus surrounding the convexo-concave 
 articular surface found on the neck of the malleus. The articular surfaces 
 are provided with a kind of check tooth, so that only the rotations inwards of 
 the malleus are exactly communicated to the incus, but not the rotations 
 outwards ; from this it follows that the stapes cannot be torn away from the 
 fenestra ovalis by such outward movements of the tympanic membrane, 
 while the tension of the latter membrane provides against the forcing in of 
 the stapes (Helmholtz). The action of the stapedius muscle, which, passing 
 from behind and at right angles to, inserts itself into the constricted portion 
 of the neck of the stapes, seems to be that of altering the position of the foot 
 of the stapes in its relation to the membrane of the fenestra ovalis, the foot 
 being either pushed in by its posterior border or lifted out by its anterior 
 border ; both movements, it is presumed, diminish the amount of excursion of 
 the stapes : the stapedius muscle would thus act as a damper. Nothing 
 definite is known about its innervation (by the facial nerve). 
 
 The lever formed by the malleus and incus, the fulcrum of which is at 
 the end of the short process of the incus, transfers the vibrations of the 
 tympanic membrane to the stapes, diminished in extent in the ratio of 3 : 2, 
 but inversely increased in force, an arrangement which, considering the great 
 resistance to the stapes, can only be of advantage (Helmholtz). 
 
 Conduction through the Labyrinth. 
 
 The impulses of the base of the stapes produce progres- 
 sive waves in the labyrinth, i.e. the fluid contents of the laby- 
 rinth recede in toto with every impulse, thereby causing the 
 yielding part in the wall of the labyrinth, the fenestra rotunda, 
 
436 CONDUCTION THROUGH THE LABYRINTH. 
 
 to arch outwards towards tlie tympanic cavity. (If the laby- 
 rinth fluid were surrounded on all sides by rigid walls, each 
 impulse of the foot of the stapes would, to a large extent, be 
 reflected, and only an infinitesimal part of the kinetic energy 
 would be propagated through the nearly incompressible laby- 
 rinth fluid, in the form of waves of condensation and rarefac- 
 tion.) The further course of the wave produced by the impulse 
 of the base of the stapes in the labyrinth, and whether all parts 
 are equally set in motion and so on, can, in consequence of the 
 complicated form of the labyrinth, only be surmised. The last 
 part of the course, namely, that through the Cochlea, is best 
 known. The wave entering by the apertura scalce vestibuli runs 
 along the scala vestibuli to the cupola, passes thence into the 
 scala tympani, which it traverses to its end, viz. to the fenestra 
 rotunda ; it is, however, highly probable that already during 
 its course along the scala vestibuli a partial passage into -the 
 scala tympani takes place through the lamina spiralis mem- 
 branacea. Much more difficult to understand is the course of 
 the wave in the vestibule and the semicircular canals. It seems 
 most natural to assume that the wave, on entering the vestibule, 
 is split up, sending a branch into each semicircular canal, and 
 that all these waves again unite in the vestibule to be trans- 
 mitted to the cochlea. In its course along the vestibule the 
 wave would move the saccules, and in its course along the 
 semicircular canals, the ridges of the ampullae. The use of the 
 semicircular canals would then rest in this, that they enable 
 the ridges of the ampullse to be moved, for no to-and-fro wave 
 could enter a perfectly closed cavity. This explanation, how- 
 ever, is far from satisfactory (compare also the Appendix to the 
 Organ of Hearing). 
 
 From what has been said, the importance of the air-containing tympanic 
 cavity, namely to give free play both to the vibrations of the tympanic 
 membrane and ossicles and to the deviation of the membrane of the fenestra 
 rotunda, will be evident, the function of the Eustachian tubes being, as already 
 stated (page 433), the equilisation of the pressure in the tympanic cavity 
 with that of the air. The supposition that the tuba serves chiefly the purpose 
 of enabling one to hear one's own voice, is not very probable. 
 
 Just as normally the vibrations of the air are transmitted to the vibra- 
 ting parts of the organ of hearing by the membrana tympani, so the reverse 
 happens, when the organ of hearing is primarily (by conduction through 
 bone, as, e.g., in the case of one's own voice) set in vibration; this mode of 
 
NERVE-ENDINGS IN AMPULLAE, ETC. 437 
 
 conduction diminishes the vibrations of the ear (Mach). By preventing 1 
 the transmission of vibrations outwards (closing the meatus) the sound of 
 one's own voice, conducted by the bones, is increased (Weber). 
 
 Hearing. 
 
 Excitation of the Terminal Organs of the Auditory Nerve. 
 
 The movements of the liquid contents of the labyrinth, 
 which are communicated to the membranous labyrinth and the 
 membranous part of the lamina spiralis, give rise to auditory 
 sensations by exciting the terminations of the auditory nerve, 
 which are contained in it. 
 
 The present state of knowledge as to the terminal organs of the auditory 
 nerve may be stated as follows : 
 
 1. Nerve-Endings in the Ampulla and Vestibular Sacs (Saccuhis and 
 Utriculus). In - the ampulla the nerve-endings are contained in a 
 yellowish, semicircular, equatorial septum, which is a thickening of the 
 membranous labyrinth (Scarpa, Steifensarid, M. Schultze). Its structure, 
 particularly in the skate, as investigated by M. Schultze, may be thus 
 described. The simple epithelium of the ampulla? is raised on the septum 
 of hard connective tissue, so as to form a thick cushion consisting of several 
 layers, from which fine stiff bristles (the auditory cirrhi) project, of such 
 length as almost to reach the opposite wall of the ampulke. The nerves, 
 which suddenly part with their medullary sheaths at the border of the 
 connective tissue, are distributed in the epithelial mass, breaking up into 
 naked axis-cylinders of extreme fineness. 
 
 The cells of the epithelial layer are of the following kinds : 
 
 a. Several layers of cylindrical nucleated epithelial cells, of which the 
 deepest (called l Basal cells') are somewhat pyramidal and pointed. 
 I. Spindle-shaped cells, each of which has two long fine processes, one of 
 which is directed towards the surface where it seems to end, while the 
 other, which is frequently varicose (these varicosities being, according to 
 Schultze, artificial products), tends towards the base, its mode of termination 
 being uncertain. These spindle- shaped cells, with their fibres, are nervous 
 structures, and are supposed to constitute the ends of the fine axis-cylinders. 
 <?. Round or cylindrical cells in the superficial layer, each of which sends 
 out one of the auditory cirrhi or hairs already referred to. According to 
 some, these cirrhi spring out of the superficial processes of the nerve 
 cells. 
 
 In the vestibular sacs, as observed in fishes, the nerve-endings are in 
 like manner contained in a crescentic septum, which, however, is less 
 elevated. In this structure the same elements are found as in that of the 
 ampullae, with the exception of the cirrhi, the place of which is 
 taken by the otolith. This is accurately applied to that part of the inner 
 wall of the sacculus which bears the septum, for the reception of which it 
 is grooved. The otolith consists of a hard or pasty mass of minute prisms 
 
438 
 
 NERVE-ENDINGS IN THE COCHLEA. 
 
 of calcic carbonate in the form of arragonite, and is suspended without 
 attachment in the viscid fluid resembling vitreous humour (endolympJi) 
 which occupies the cavity (M. Schultze). Here and there short cirrhi are 
 to be seen where the otolith is not applied to the surface. 
 
 2. Nerve-Endings in the Cochlea (Organ of Corti). The special canal 
 which winds round the columella of the cochlea is divided into three 
 channels, viz. the Scala vestibuli (Sc. Ve. Fig. 39), the Scala tympani (Sc. 
 
 FIG. 39. 
 
 Ty.}, and the duct of the Cochlea (C.C.) which lies between them by the 
 bony part of the lamina spiralis (L.O.), and by the two membranes which 
 stretch across from this structure to the outer wall of the canal, namely, the- 
 membrana lasilaris (M. 6.) and the membrane of Reissner (M.R.). The 
 fibres of the cochlear nerve, which are contained in the columella, spread out 
 from it in the form of a fan, which winds spirally round it, entering the duct 
 of the cochlea by the radiating canaliculi of the lamina ossea (N.N.), in 
 order to reach the organ of Corti. This organ, according to the latest 
 researches (Kolliker, Bottcher, Waldeyer and Gottstein, v. Winiwarter), has 
 the following structure : The epithelial lining of the duct of the cochlea 
 assumes on the membrana basilaris a peculiar development. In every radial 
 section, two hardish elastic pillars (a and &) are seen, which articulate 
 with each other by their heads. These are called the l arches or pillars of 
 Corti. 9 On the inner side of each internal pillar, an * internal hair cell * (c) 
 is to be found, which is in connection with the nerve fibre. In like manner, on 
 the outer side of the outer pillar, there are a number of ' external hair cells y 
 (d}. These (which in mammalia generally are three in number, but in the 
 human cochlea four or five, while in birds and amphibia they are wanting) 
 are also provided with nerve fibres (c). The heads of the pillars of Corti 
 have each of them a process by which it contributes to the formation of a 
 supporting network (the lamina reticularis), the level of which coincides 
 with that of the epithelial border (lamina reticularis, /./.). In the rings of 
 this beautiful network, the heads of the hair cells fit in quincuncial 
 arrangement. The whole organ of Corti is covered by a soft membrane 
 (M. t.) } which springs from the lamina ossea, and floats by its free edge (g) 
 in the fluid of the cochlear duct. (The drawing is diagrammatic.) 
 
FUNCTIONS OF THE LABYRINTH. 439 
 
 In all the organs of the internal ear there are arrangements 
 in connection with the nerve-ending, of such a nature as to 
 favour their mechanical excitation. Thus, in the ampullse, and 
 in the organ of Corti, the cirrhi, thrown into motion by the 
 passing wave of liquid, may agitate the nerve cells; in the 
 vestibule the nerve-endings, to which the otoliths are most 
 accurately applied, must be tapped by them on. the slightest 
 agitation; while, finally, throughout the whole membrana 
 basilaris of the cochlea, the vibrations of the membranes and 
 pillars must exercise pressure on the nerve cells wedged in be- 
 tween them. Hence arises the notion that the excitation of the 
 auditory nerve-endings consists in their being mechanically 
 tetanized a notion which seems to be supported by the con- 
 stant occurrence of otoliths throughout the whole animal 
 kingdom. 
 
 At present we have only hypotheses as to the special functions of the 
 various terminal organs, and consequently of the various parts of the 
 labyrinth. The opinion formerly held, that the cochlea serves specially for 
 the perception of auditory impressions transmitted through bone, rested 
 on the mistaken assumption that the nerves of the cochlea ended directly in 
 the lamina ossea. Such a view is negatived by the existence of the organ 
 of Corti, and by the absence of the cochlea in animals which only hear by 
 conduction through bone, e.g. in fishes. Further information as to the 
 probable function of the cochlea will be given below. With reference to 
 the semicircular canals, see the Appendix to this Section. 
 
 Characteristics of the Sensation of Hearing. 
 
 The excitation of the terminal organs of the auditory nerve 
 by the vibrations of the liquid contents of the labyrinth, or 
 any other excitation of the auditory nerve fibres, causes an 
 auditory sensation. The ' height ' (elongation) of the waves 
 determines the intensity of the perception of sound, while the 
 6 length ' of the waves, or the number of the vibrations in a given 
 time, determines the pitch of the tone heard. 
 
 As regards pitch, the range within which sounds can be 
 distinguished is very considerable, and the limits given on 
 .p. 393 are probably determined, not by the excitability of the 
 auditory nerve, but by the vibratory capacity of the transmit- 
 ting organs, e.g. of the tympanum. 
 
 The interval between the lowest tone there given (40 vibra- 
 tions) and the highest (16,000 to 20,000) amounts to 8- 
 
440 SIMPLE AND COMPOUND TONES. 
 
 ; or 9 octaves, whereas the interval between the limits of visi- 
 bility of the red and violet rays reckoned in an analogous 
 manner does not reach one octave. 
 
 The subjects of auditory sensations are generally, however, 
 not simple tones, just as the colours we usually see are not the 
 simple colours of the spectrum, but mixed colours. Ordinary 
 sounds consist of musical tones, simple or compound, or of 
 noises. 
 
 The essence of a compound musical sound, and its analysis into simple 
 tones, lias been already discussed (p. 303). Simple tones can only be artifi- 
 cially produced by throwing a resonator into consonance with one of the 
 constituent or partial tones of a compound tone, with which tone it is in 
 tune. For such a purpose one of the resonators mentioned on p. 303, or 
 the resonance tubes (p. 314), may be employed ; or a monochord, along the 
 string of which a vibrating tuning-fork is made to slide until the string is of 
 such length that its ' proper tone ' is in unison with a constituent tone of 
 the compound sound produced by the tuning-fork (Helmholtz). 
 
 If two different simple tones of a given force are produced 
 simultaneously, mutual disturbances in their wave-systems be- 
 come perceptible, which give rise in sound-conducting media 
 e.g. the air to new vibrations. 
 
 These new vibrations are of two orders, in one of which the 
 vibration number is equal to the difference between the two 
 primary vibration numbers, and in the other to their sum. 
 Although in this case only one resulting wave-system reaches the 
 ear and is transmitted unchanged through the conducting media 
 to the nerve-endings, four separate single tones are heard at the 
 same time, provided the intensity is sufficient ; that is to say, 
 two primary and two combinational tones. Of these last, one is 
 the differential tone, the other the summationcd tone. 
 
 Whenever a compound tone is produced we recognise in it 
 its specific composition in other words, the musical colour 
 (Klangfarbe), timbre or ' quality,' which accompanies the funda- 
 mental tone. (See p. 302.) Besides this, each single constituent 
 tone of the compound tone may, without special practice, be 
 singled out from it by the ear, provided that immediately before 
 the production of the compound tone the single tone has been 
 heard. 
 
 Finally, the effect produced by the simultaneous sounding of 
 many compound tones is not, as one might expect from the com- 
 plexity of the resulting wave-systems which pass through the 
 
PERCEPTION OF SOUND. 441 
 
 ear, a mere noise, for each separate tone can be clearly dis- 
 tinguished. Indeed, in an orchestra, one instrument can be 
 singled out from the rest, and its sounds followed. 
 
 All these observations point to the conclusion that there is 
 in the organ of hearing an arrangement which resolves every 
 wave-system^ however complex, into simple pendulum vibra- 
 tions ; just as every compound tone may be resolved by reso- 
 nators into its constituent tones. They indicate further that 
 every simple partial vibration excites a particular nerve fibre, 
 and by doing so brings about the sensation of a simple tone. 
 This supposition, the only one which satisfies the principle of 
 specific energies (p. 343), is raised into a certainty by the 
 following observation (Helmholtz) : If several simple tones, 
 each beginning at a different time, in such a way that different 
 phases of their vibrations are coincident, are combined into one 
 compound tone, the most manifold variations of the combined 
 wave-system result. If the auditory nerves were excited to 
 different forms of functional activity by the wave-system as 
 such, then the impressions of musical sounds received would 
 vary in each experiment. But if the experiment is made with 
 the vowel apparatus mentioned on p. 314, it is found that in all 
 cases the same musical sound is heard ; the slightest difference 
 would manifest itself in a corresponding difference in the vowel 
 sound. 
 
 Every resonator answers, not only to its proper tone, but also to tones 
 which are very near it; the further, however, the two tones are apart, the 
 feebler is the resonance. 1 
 
 The difference as regards pitch, at which a resonator is capable of being 
 excited by a tone (called the range of sympathetic vibration) varies 
 proportionately to the completeness with which the resonator is damped. 
 The degree of damping is measured by the number of vibrations which 
 must occur before the intensity is reduced to a definite fraction say to one- 
 tenth of what it was at first. On the other hand, the extent of the sympa- 
 thetic vibration executed by any tone can be measured by the difference 
 between this tone and the proper tone of the resonator when the former 
 excites the resonator, as its proper tone does, but with a definite fraction, 
 say, one-tenth of its intensity. If this difference is known, the degree of 
 damping of the resonator can be calculated, and vice versa. The following- 
 Table shows the relation in which each stands to the other (Helmholtz) : 
 
 1 In point of fact, the strongest answering tone is somewhat different from the 
 proper tone of the resonator ; the two would only be absolutely identical, if 
 friction and resistance of the air were nil. 
 
442 RANGE OF SYMPATHETIC VIBRATION. 
 
 Number of vibrations which 
 
 Difference of pitch (the intensity of the occur before the intensity 
 
 sympathetic vibration being of the tone of the re- 
 
 reduced to one-tenth). senator is reduced to 
 
 one-tenth. 
 
 Eighth of a Tone 38-00 
 
 Fourth of a Tone 19'00 
 
 Semitone 9'50 
 
 Three-fourths of a Tone 6'33 
 
 Whole Tone 475 
 
 Five-fourths of a Tone 3*80 
 
 Tempered Minor Third (1-| Tone) 3-17 
 
 Seven-fourths of a Tone 271 
 
 Tempered Major Third (2 Tones) 2'37 
 
 The degree of damping of the resonator in the ear may be ascertained 
 by the following experiment: A shake, of which the beats recur ten times 
 in a second, can be heard with perfect distinctness at all parts of the scale 
 down to the low A (110 vibrations) without the impression of the alterna- 
 tion of the two tones being obliterated in the ear by the after-sounding of 
 the vibrating parts. Below A this is the case. Assuming then that the 
 intensity of the vibrations must sink to one-tenth in order that when the 
 same tone recurs, that is to say, after an interval of a fifth of a second, it is 
 no longer audible, it follows that the parts of the organ of hearing set into 
 vibration by A after a fifth of a second, i.e. 22 vibrations, continue to. 
 vibrate with only a tenth of their original intensity. The degree of damping 
 of the resonators in the ear must therefore correspond to about the second, 
 or perhaps the third or fourth degree of the Table given above ; and it is 
 actually observed that below A the shake becomes rough and confused. 
 Taking the third degree as the correct one, if the intensity of excitation of the 
 resonator, by its proper tone, is equal to 100, its excitation by other tones 
 approximating it in pitch will be as follows : 
 
 Difference of pitch in"] 
 
 fractions of a whole [> O'l 0'2 0'3 0-4 O'o 0'6 07 0'8 0'9 TO 
 Tone J 
 
 10 74 41 24 15 10 7 ' 2 5>4 4>2 3>3 27 
 
 The parts of the ear which are set into vibration by the note A are 
 therefore affected with only one-tenth of the intensity by any tone which is 
 removed half a tone from A in pitch ; hence the same resonators cannot be 
 called into action for A sharp and A. flat, as for A. This is another argu- 
 ment in favour of the theory above quoted (Helmholtz). 
 
 The occurrence of deafness for a series of tones, e.g. the deepest notes 
 (bass deafness), which is frequently observed, favours the opinion that there 
 exist in the ear separate organs for the preception of tones of different pitch 
 (Moos). According to this theory any simple tone would excite the 
 particular resonator in the ear of which the proper tone is nearest to it, 
 with the greatest intensity, those adjoining it, with less. 
 
 Theoretical considerations, however, indicate that if the membrana tym- 
 pani is excited by a simple tone, it vibrates at the same time with 
 
ANALYSIS OF COMPOUND TONES BY THE EAR. 443 
 
 the harmonic overtones of the exciting tone; so that the resonators 
 answering to these overtones are excited, as well as those answering to the 
 original tone, and therefore a simple tone is never heard (J. J. Miiller). 
 
 The analysis of compound tones in the ear can only be 
 effected by a system of resonators. It is still a matter of con- 
 jecture what part of the ear is to be regarded as constituting 
 such a system. The cochlea claims the first consideration in 
 this point of view. If we suppose the arches of Corti to be 
 resonators (Helmholtz), an obvious correspondence presents 
 itself between their gradually increasing dimensions and th& 
 graduation required in the numbers expressing their proper 
 vibrations. Or we may take the simpler view that the rays of 
 the membrana basilaris (Hensen), due to the greater tension of 
 the membrane in the radial than in the longitudinal direction, 
 correspond to a series of tense strings of gradually increasing 
 length. According to another view, the auditory cirrhi of the 
 labyrinth and cochlea may constitute a system of which the 
 graduation is dependent on the varied length or stiffness of 
 these organs (Hensen). 
 
 According to Kolliker, the cochlea contains about 3,000 arches of Corti. 
 Deducting 200 for tones which are musically unavailable, 2,800 remain for 
 the seven octaves that are musically audible (from C n. to H vi.) Hence 
 there are 400 arches to each octave, and 33 ( = *$) to each semitone. As 
 skilled musicians can distinguish an interval amounting to ^ of a semitone 
 (E. H. Weber), it may be assumed that a tone which is intermediate 
 between the proper tones of two adjoining Corti's elements will affect both 
 with unequal intensity, and that by this difference the pitch will be per- 
 ceived (Helmholtz). 
 
 At least two vibrations following one another with rapidity 
 are necessary to excite the sensation of a tone. A single 
 vibration causes only the impression of a tap. If, for example, 
 a card is held against the teeth of a revolving Savart's toothed 
 wheel, so as to produce sound, the tone is unaltered so long as 
 the rate of revolution remains the same. If, now, all the teeth 
 excepting the last two are gradually removed, the same tone con- 
 tinues to be heard, although it becomes duller, just as a colour 
 becomes duller when mixed with a good deal of ' black .' If the 
 last tooth but one is removed, the tone vanishes and only the 
 sensation of a tap remains, which is to be regarded as a rapidly 
 vanishing wave-system. 
 
 If many different simple tones are so combined that the 
 
444 NOISES. CONSONANCE AND DISSONANCE. 
 
 organ of hearing cannot analyse them, or if they follow each 
 other so rapidly that the after-tones of each preceding tone 
 are mingled with those of its s accessor, so that a confusion 
 arises which cannot be analysed by the ear, and in which no 
 periodicity can be perceived, the resulting sensation is commonly 
 called a noise. Many noises therefore are only very complicated 
 musical sounds, in which a fundamental or prime tone, having 
 often the timbre of a vowel, can be recognised. According to 
 the vowel sound heard, these noises receive names by onomato- 
 poiesis, such as clinking, thundering, clattering, crackling, &c. 
 Beside these apparently unperiodical sound vibrations (which, 
 however, must needs be possessed of periodicity, seeing that they 
 are composed of tones), there are others which are really un- 
 periodical, and to the impression on the ear of these the term 
 noise should be exclusively applied (Helmholtz). In what parts 
 of the organ of hearing the perception of taps and noises takes 
 place is at present matter only of conjecture without proof. 
 (Ampullae and Sacculus). 
 
 The mingling of successive tones would be much more constant, and 
 music -would be therefore impossible, if the damping of the vibrating parts 
 of the ear were not very complete. The damping apparatus has not yet 
 been thoroughly investigated. It has been supposed by some that the 
 otoliths and the membrana tectoria of the cochlea, which lies upon the organ 
 of Corti (p. 438), constitute damping apparatus (Waldeyer). 
 
 Harmony of Musical Sounds. 
 
 If several musical sounds reach the ear at the same time, an 
 agreeable or disagreeable impression is received, the nature of 
 which is ultimately connected with the relations of the 
 vibrational numbers of their prime tones. According to these 
 relations we distinguish consonant (agreeable) and dissonant 
 (disagreeable) combinations of sounds. The octave (1:2) and 
 t^e twelfth (1 : 3) are the most perfectly consonant sounds ; 
 then follow in order in the direction of dissonance, the fifth 
 (2 : 3), fourth (3 : 4), major sixth (3 : 5), major third (4 : 5), 
 minor sixth (5 : 8), minor third (5 : 6), &c. The explanation of 
 this phenomenon is that the disagreeable impression of a dis- 
 sonance consists in the beats caused by it, i.e. in the variations of 
 intensity produced by the interference of two wave-systems 
 which differ somewhat in their wave-lengths. Two simultaneous 
 
HARMONY OF SOUNDS. BEATS. 445 
 
 tones of different pitch strengthen each other whenever the wave 
 crests or the wave troughs between them coincide, and they 
 weaken or annul each other when crests coincide with troughs. 
 The periods of recurrence of beats must obviously be equal to- 
 the difference between the vibration numbers of the two 
 tones ; the smaller the interval between the two tones and 
 the lower the pitch, the less frequently do the beats occur. 
 If they are so frequent that they cannot be recognised separately 
 as beats, they give the impression of a painful discontinuity 
 (comparable to the flickering of a light). The maximum of 
 confusion and roughness is experienced when the beats recur 
 thirty-three times in a second. The more nearly the constituent 
 tones of two simultaneous compound tones coincide with each 
 other or with combinational tones (p. 440), so as to give rise to 
 beats of moderate frequency, the greater will be the discord. 
 
 For further explanation attention is directed to the Table, 
 which, starting from the prime tone C (256 vibrations), sets 
 forth the vibration numbers of its constituent tones, as well as 
 those of some of the tones derived from it. If all the con- 
 ditions of dissonance were given, the Table would also exhibit 
 the combinational tones, which are. however, not here taken into 
 consideration. The small figures denote the number of beats 
 which a constituent tone makes with the two constituent tones 
 of the fundamental compound tone (Grundklang) which are 
 nearest to it. 
 
 It is seen from the Table that in the sounds of the octave and twelfth 
 there are no constituent tones, except those which are also in the funda- 
 mental sound; here therefore no beats are possible the octave and 
 twelfth are in ' absolute ' consonance. In the sound of the fifth, constituent 
 tones exist which are not in the fundamental tone, but these are not brought 
 into such collision with those of the fundamental tone nearest to them 
 as to cause beats : the fifth therefore is a ( perfect ' consonant. The condi- 
 tions, however, for beats exist in the constituent tones of the fourth, major 
 sixth and major third (' medial ' consonances), and in an even greater 
 degree in those of the minor sixth and minor third (' imperfect ' concords), 
 and still more in those of seventh, second, &c. (dissonances). It is also 
 seen that the number of beats gradually approaches 33. Dissonance is 
 occasioned by any interval, the more readily the lower the pitch. (Com- 
 pare the statement above.) On these principles rest the sciences of harmony 
 and temperament, which cannot, however, be entered upon here. The rela- 
 tion of constituent tones (their l melodic relationship ') is also important with 
 regard to the succession of sounds which constitutes melody. If a sound is 
 followed by its octave, no new tone is heard, the attention is not attracted by 
 
446 
 
 DEGREES OF CONSONANCE. 
 
 
 Si a 
 
 o 
 
 o *-> 8 
 
 
 B 
 
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 K O 
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 ^ PH ^ 3s 
 
 
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 ^ ^ 
 
 
 la 
 
 CO CO CO t CO I CO 
 U7> (M >Q CO *O 1 # W5 *O 1C CO 
 J2 CM CM CM | CM 1 CM 
 
 
 8 
 
 II II II II 11 
 
 
 j 3 
 
 CO >0 -* J <M 
 
 
 
 * CM 
 
 
 
 ^"^ r ^"^N ' ^^^ 
 
 
 
 
 O O O 
 
 
 to 
 
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 CO "^ >O ""* >O ^ O "^ 
 
 
 
 co "^ ^ ^f 
 
 
 S 
 
 O O S rH ^ 
 
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 CO 
 
 CO CO rH ^ -^ 
 
 c* co o o^ 
 
 H 
 
 
 CO ^H >0 
 
 EAT-NUM 
 
 M 
 
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 CO CO ^So^^CO ^O 
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 ft 
 
 
 
 r-lOO r-ICj '~ < I;5 I ~ l c5 
 
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 t-3 ^S og coS 
 
 CO 
 
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 CO CM CM r-t 
 
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 S5 O5 " O5 O 
 
 
 
 
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 W 
 
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 CO CO OO rH O 13 
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 CO * r " < t-H ^ 
 CO - 1 CO CO CO c<, 
 
 
 M 
 
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 * -*rH .-(S t^CO O^ OS t O^3 
 
 
 
 CO -f CM CM^r-H O^CO 
 
 
 01 
 
 a - s gs 
 
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 M o 
 
 Jj^ P 00 M"* Ml-H M *^ ^O MO M^ M 
 
 o 
 
 
 
 H 
 
 
 
 p 
 
 
 a 
 
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 ^ 1- 1 1 1 
 
 Q 
 
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 53 -5 'S3 S 
 
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 CJ P --H O MtlpH i < k ' "~ 
 
 OEHt^iHMrsi^i^i^ 
 
SEATS. HEARING FROM OUTSIDE. 447 
 
 any new impression. The contrary is the case when a note is followed by 
 its fifth or fourth, &c. 
 
 If a compound tone, of which the prime tone makes n vibrations in a 
 second, is heard along with others, the smallest number of beats per second 
 depends on the relation between the two tones, as follows : The fundamental 
 tone in simultaneous vibration with the fifth gives |- beats, with the fourth 
 and major sixth J, with the major third J, with the minor sixth and minor 
 third -, with the major seventh and major second (a whole tone) -"-, with 
 the minor second (semitone) ~w, &c. This may be more generally expressed 
 as follows: If ft represents the vibrational number of the deeper ground 
 tone, and in that of the higher, and the fraction is reduced to the small- 
 est whole numbers ( 0, then the minimum, number of beats is = . In 
 other words, the smaller n is (that is, the lower the pitch) and the greater n l 
 is (that is, the more incommensurable the fraction which expresses the 
 interval), the smaller is the minimum number of beats per second. 
 
 The fraction is clearly f for the fifth, | for the fourth, | for the major 
 sixth, | for the major third, f for the minor sixth, f for the minor third, 
 a g 5 for the major seventh, J for the major second, ~~ for the minor second. 
 
 A simple experiment shows convincingly that the essence of dissonance 
 really lies in the beats. If one of two perfectly similar tuning-forks, stand- 
 ing on resonance cases, is put more and more out of tune by means of wax, 
 beats of increasing frequency are heard on sounding them ; when those 
 beats reach a certain rate of frequency the characteristic sensation of discord 
 is perceived. 
 
 Hearing from Outxide. 
 
 The cause of every sensation of sound which is transmitted 
 by the membrana tympani appears to the mind to come from 
 outside, whereas that which is conducted through bone appears 
 to arise in the head itself. If, e.g., the head is held under water 
 the impressions of hearing will only seem to come from outside 
 when the external ear is filled with air (Weber). As, however, 
 even in this case the principal conduction is by means of the 
 bones in the head, the impression of extrinsic origin is 
 occasioned by the sensibility of the membrana tympani, and is 
 not due to any particular form given to the labyrinth waves 
 emanating from the stapes. If this be so, one may suppose that 
 the sensibility of the membrana tympani gives information as 
 to the direction of the sound-waves which reach it, and perhaps 
 this is also the case as regards the pinna, which from its nume- 
 rous projections is peculiarly adapted to judge of the angle at 
 which the sound rays fall (Weber), especially when it is aided 
 by its movements. (Compare what follows.) 
 
448 SUBJECTIVE SENSATIONS. ENTOTIC IMPRESSIONS. 
 
 Subjective Sensations of Hearing. 
 
 In the organ of hearing, as in that of sight, there are certain 'subjective 
 sensations/ which depend either upon peculiarities in the excitation of 
 the nerve, or upon abnormal conditions of the nerve itself. These 
 impressions, however, appear to be of very limited occurrence, and have 
 been as yet but little investigated. With reference to after-tones, it may 
 with probability be concluded that when a series of tones succeed each other 
 with rapidity (as, for example, when the teeth of a Savart's wheel are so set 
 that instead of being equidistant throughout they are at different distances 
 from each other in successive segments of the circumference), a noise is 
 produced by the mixture of tones which is analogous to the mixture of 
 colours in the colour top (p. 401). ' After-sounds ' are to be regarded as 
 physical phenomena, as for example when a tone or a piece of music rings 
 in the ear long after the sound has ceased to be actually heard. This is also 
 true of other hallucinations of hearing. 
 
 Amongst subjective impressions may be mentioned ringing and humming 
 in the ears. These tones or noises are dependent upon the excitation of the 
 auditory nerves by unknown causes, and are particularly apt to occur when 
 their excitability is morbidly increased. The subjective musical tones which 
 are occasionally observed may probably be explained as arising from 
 abnormal excitation of the nerve fibre corresponding to a single element of 
 the organ of Corti (p. 438) ; for in these cases there is at the same time 
 excessive sensibility to the objective sounds which correspond to those 
 heard subjectively (Moos, Czerny, Samelson). The buzzing which is heard 
 when the auditory passages are closed is dependent on the fact that under 
 this condition we hear principally by conduction through bone ; conse- 
 quently the muscular sounds of the head, and the friction sounds produced 
 by the circulating blood, are perceived. 
 
 Entotic Impressions. 
 
 From subjective sensations may be distinguished those impressions which 
 have their source in the organ of hearing, and are therefore called entotic. 
 To these belong, 1, rushing sounds caused by vibrations of the air in the 
 external ear, or in the cavity of the tympanum, when their communication 
 with the atmosphere is interrupted in the case of the former by substances 
 covering it, or inserted into it, or by cerumen ; in that of the latter, by 
 occlusion of the Eustachian tube. These sounds in the external ear are par- 
 ticularly loud when a hollow body, such as a tube, in which the air vibrates, 
 is applied to the auditory passage, so as to lengthen it. 2. The crackling 
 sound caused by contraction of the tensor tympani, as to the signifi- 
 cance of which see p. 433. 3. Hammering sounds, caused by the pulsation 
 of the arteries either in the organ of hearing, or at a distance from it. 
 These become more audible when the head rests upon a hard body. 
 4. Friction sounds, caused by the circulating blood. 5. Muscular sounds, &c. 
 
HEARING WITH BOTH EARS. 449 
 
 I F 
 
 Hearing with both Earsk 
 
 By hearing with both ears, as by seeing with both eyes, the 
 two organs are enabled to assist each other mutually and to correct 
 each other's errors. We are also thereby aided in determining 
 the locality of sound-producing bodies. Whether the terminations 
 of the organ of hearing possess anything corresponding to the 
 6 identity ' which exists in the eyes, whether, for example, the ex- 
 citation of two corresponding fibres of both cochleae is perceived 
 as a single sensation, cannot at present be decided. A single tone, 
 although it is heard by both ears is heard only as one, in which case 
 we may assume that the elements in the two cochlese which are 
 affected by it correspond with each other. On the other hand, 
 we can distinguish two tones even when both ears are excited 
 simultaneously by tones of the same pitch, provided that either 
 their intensities are different or that the excitability of the two 
 corresponding elements is unequal. This last statement is 
 proved by the following experiment. If two similarly sounding 
 tuning-forks are held one before each ear, and one of them is 
 made to revolve round its axis in such a way that the tone shall 
 alternately vanish and reappear (four times in one revolution), 
 neither fork is heard continuously, but both sound alternately, 
 the fixed one being only audible when the revolving one is not 
 heard (Dove). The excitability naturally diminishes during the 
 continuance of the sound, but less on the side of the revolving 
 tuning-fork than on the other side. If the excitation is of 
 equal intensity, the impression of a tone will be perceived only 
 on the side on which the excitability is greater. (This result is 
 of course not obtained when the two tones are different.) From 
 this experiment it may be concluded either that the excitations 
 of two corresponding elements of both ears can be distinguished 
 from each other, or that the excitation is perceived as a single 
 one, but is referred to the side on which the excitation is 
 strongest. Both conclusions are opposed to the admission of an 
 analogy with the organ of sight. The value of the experiment 
 is, however, diminished by the circumstance that in all pro- 
 bability the sounds of the two forks are not absolutely identical. 
 Another fact which appears to militate against the notion that 
 we perceive excitations of both ears in common, is that in most 
 persons (Fessel, Fechner), and especially in pathological conditions 
 
450 APPRECIATION OF DIRECTION. PROTECTIVE ORGANS. 
 
 (v. Witticli) one ear perceives the same tone at a higher pitch 
 than the other. 
 
 Appreciation of Direction. 
 
 Two opposite membrange tympani and pinnae must naturally 
 afford a more accurate indication of the direction of a sound 
 than one alone, considering that by turning the head we can 
 alter the relation of the ears to the sounding body. It is indeed 
 conceivable that the different local relation of the two ears to 
 objects might enable us to judge of distance. 1 The position of 
 the ears is best adapted for the discrimination of sounds coming 
 from the sides. Those from before or behind can only be dis- 
 tinguished by turning the head or by the position of the pinnae 
 the situation of which is best adapted for the reception of waves 
 coming from the front. These are therefore heard more loudly 
 than those from behind. If the pinnae are pressed against the 
 head and the hands placed before the external meatus, so as to 
 form a kind of ear, sounds coming from behind are heard more 
 loudly than they would be otherwise. 
 
 Protective Organs of the Ear. 
 
 In a certain sense the pinnge, especially in animals where 
 they are mobile, may be regarded as protective organs for the 
 ears, inasmuch as the existence of projections (e.g. thetragus in 
 man) tends to hinder the penetration of dust or cold air into the 
 ear. Other protective organs are the stiff bristly hairs 
 (vibrissse) of the external meatus, and the ceruminous glands, the 
 secretion from which lubricates the wall of the meatus. The 
 purpose of the cerumen is uncertain. Its absence determines 
 difficulty of hearing and buzzing in the ears, the cause of which 
 is unknown. The internal ear, from its position inside the 
 petrous bone, is completely protected. 
 
 APPENDIX. Destruction of the membranous labyrinth (Flourens), as well 
 as section of the auditory nerve (Brown- Sequard) in animals, cause striking 
 rotatory movements of the head, abnormalities of the movements of loco- 
 motion, and movements which resemble the uncontrollable rotations (Zwangs- 
 bewegungen} which occur after certain injuries of the brain (Chap. XL). 
 
 1 We generally judge of the distance of a source of sound only by the quality 
 of intensity ; hence, the well-known acoustic illusion employed in theatres. 
 
FUNCTION OF SEMICIRCULAR CANALS. SMELL. 451 
 
 With regard to these statements controversies have arisen : the distur- 
 bance of equilibrium does not, according to Bottcher, occur in frogs after 
 complete destruction of the labyrinth ; it does occur, according to Lb'wenberg, 
 after removal of the brain, and is dependent on reflex actions, which are 
 occasioned by excitation of the labyrinth and have their centre in the 
 thalamus. 
 
 It is supposed by Goltz, that these disturbances are attributable to the 
 loss of the power of discrimination as to the position of the head, and that 
 this power has its seat in the membranous labyrinth and the auditory nerve, 
 and is dependent on the circumstance, that, whatever may be the position 
 of the head, every change in it occasions pressure of the endolymph on a new 
 part of the membranous labyrinth. According to another theory (that of 
 Breuer and Crum-Brown), every movement of the head in a given direction 
 determines a relative movement of the endolymph against the wall of the 
 membranous canal in the opposite direction, which movement is perceived 
 by the nerve-endings in the ampullae. 
 
 III. THE OLFACTOEY OKGAN. 
 
 The peripheral terminal organs of the olfactory nerves pass 
 as numerous branches through the foramina of the cribriform 
 plate of the ethmoid into the cavity of the nose, and are 
 expanded on a membrane, which, as a mucous membrane, lines 
 the upper part of the nasal cavity, and is distinguished from 
 the mucous membrane proper of the nose (Schneiderian mem- 
 brane) by its lighter colour and the absence of the ciliary 
 epithelium. These terminal organs are excited by certain 
 gaseous bodies in a manner at present totally unknown, nor 
 do we know the properties to which they owe their excita- 
 bility. The odorous particles are conducted to the olfactory 
 membrane by inspiration through the nose. The inspired 
 current is split up at the anterior prominent ridge of the inferior 
 turbinated bone, and a part of it, instead of passing directly 
 along the inferior rneatus to the posterior nares, takes a 
 circuitous course along the upper parts of the nasal cavity 
 (Bidder). The excitation, it appears, takes place only at the 
 first moment of contact, for to ensure a more permanent sensa- 
 tion it is necessary that fresh particles of the exciting body 
 should be brought continually in contact with the terminal 
 organs, or, in other words, that the particles should pass in a 
 current through the olfactory organ, and the effect is greater 
 the quicker the renewal of the particles takes place, i.e. 
 the more rapid the current. 
 
 a G 2 
 
452 STRUCTURE OF THE ORGAN OF SMELL. ODOURS. 
 
 The olfactory bulbs, which were formerly considered as a part of the 
 olfactory nerves, are now more properly considered to be parts of the brain. 
 The olfactory nerves proper are distinguished from other nerves by consisting- 
 of a number of small bundles, each of which again is composed of numerous, 
 extremely fine primitive nerve fibres, surrounded by a common areolar mem- 
 brane. The olfactory membrane which lines the two upper turbinated 
 bones and the upper part of the septum (' regio olfactoria ') has the follow- 
 ing construction (M. Schultze) : Between the cylindrical epithelial cells, 
 pointed at their basal end, there are found bipolar spindle cells, which send 
 one process to the surface and another into the interior ; the latter is said to 
 be identical with the delicate primitive nerve fibres of the olfactory nerve, 
 the other process is provided with a bundle of very long tender hairlets, 
 which project beyond the surface; the spindle-cells are thus considered to be 
 nerve-cells. According to recent researches (Exner), the cells found in the 
 frog, and formerly described as simple epithelial cells, are likewise nerve- 
 cells and are provided with hairs. 
 
 That gaseous bodies only possess the power of exciting the olfactory 
 organs is evident from the fact that the filling up of the nose with an 
 odoriferous (volatile) fluid, such as eau-de-Cologne, produces no sensation 
 of smell (Weber). It is well known also that the body to be smelled must 
 pass through the olfactory region in a current, for every sensation of smell 
 can be at once stopped by holding the breath or by inspiring exclusively 
 through the mouth, even if the atmosphere, and therefore also the air in 
 the nasal cavity, be filled with the odorous substance. On the other hand, 
 rapid and repeated respirations (< sniffing ') increase the impression of smell. 
 
 The necessity of the conveyance of the current to the olfactory region by 
 the anterior promontory of the inferior turbinated bone is seen from the fact 
 that the odorous body is not smelled when first passed into the mouth and 
 thence through the posterior nares into the nose (Bidder). Most of the 
 odorous substances act already even when diluted to an extraordinary extent, 
 so that an exceedingly small quantity mixed with the atmosphere of the 
 room can readily be perceived. Recently it has been shown that most of 
 the odorous vapours possess a large capacity for absorbing heat (Tyndall). 
 
 The Sensations of Smell. 
 
 Excitation of the terminal olfactory organs, possibly also an 
 excitation of any kind of the nerve trunks themselves, gives 
 rise to certain sensations, which we call odours. They are 
 distinguished both as regards their intensity and character. 
 The intensity seems to depend 1. On the quantity of odorous 
 body in the gaseous mixture. 2. On the velocity of the current 
 passing through the olfactory region. 3. On the number of 
 excited olfactory elements. It appears at least that those 
 animals possess the most delicate perception of smell, whose 
 olfactory organs cover a large surface. The cause of the special 
 
ODOURS. 453 
 
 character of an odour is totally unknown, and we possess no 
 division nor scale, nor even a name for the different odours, but 
 call them only after the body to which they belong, and of 
 which the same or similar character of the smell reminds us. 
 
 It is scarcely doubtful, after the analogy of all the other sense organs, 
 that mechanical, electrical, &c. irritation of the olfactory nerve produces 
 the sensation of smell ; experimentally, this has, however, as yet, not been 
 proved. The only sure way to direct electric currents to the olfactory 
 nerves would consist in filling the nasal cavity with water, into which one 
 of the two electrodes is inserted, but here the simultaneous, [irritation of 
 the sensible fibres of the trigeminus produces such violent pain, that we can- 
 not decide as to the sensations of smell produced at the same time (Rosen- 
 thai). In the excitation of the terminal organs of the olfactory nerve by 
 odorous substances, the hairs on the cells above described seem to take an 
 important part ; this seems probable from the fact that by filling the nasal 
 cavity with water l the sense of smell disappears for a short time (E. H. 
 "Weber) ; some have also observed that by the contact of these hairs with 
 water they swell up and are invisible for some time (Schultze). 
 
 The principle of specific energies (p. 343) would justify us in assuming 
 here also, the same as has been shown for the organs of sight and 
 hearing (pp. 391 and 441), the existence of different olfactory fibres, each of 
 which would be excited by a particular kind of olfactory stimulus and give 
 rise to a particular sensation ; we possess at present no clue whatever as to 
 how many such fibres are likely to exist. 
 
 From the olfactory sensations proper we have to distinguish those 
 impressions which depend on the irritation of the sensory fibres of the fifth 
 nerve present in the nasal mucous membrane; thus ammoniacal vapour acts 
 on the latter chiefly, and is therefore still perceived as a sensation after 
 the olfactory terminations have been destroyed, or it may cause reflex actions 
 (sneezing). 
 
 We know very little about subjective sensations of smell; in certain 
 pathological conditions of the nose (catarrh, &c.), the sense of smell is for 
 a time quite suspended, or even replaced by abnormal sensations of smell. 
 
 About ' after-smells ' we know next to nothing. The author observes that 
 for several hours after experiencing certain strong odours, such as cadaverous 
 odours, every unpleasant smell has, with him, most distinctly, the character 
 of the first. 
 
 As regards the relations of the two nasal cavities to each other, we only 
 know that the simultaneous irritation of the two by different odours does 
 not give rise to one impression, but causes a sort of race between the two 
 (Valentin). 
 
 1 In filling the nasal cavity with fluids, these are poured in through the nares, 
 the body taking up the recumbent posture, resting on the back. The fluid is pre- 
 vented from running out through the posterior nares by the velum palati, which 
 adapts itself to the wall of the pharynx. 
 
454 SEAT OF THE SENSE OF TASTE. 
 
 The nasal mucous membrane may be considered to act as 
 a protecting organ to the olfactory region, by liberating the 
 traversing air from its coarser noxious admixtures. On the 
 other hand, the olfactory organ may be considered as keeping- 
 guard for the respiration, inasmuch as many of the noxious 
 impurities of the atmosphere affect the sense of smell. 
 
 IV. THE ORGAN OF TASTE. 
 
 Our knowledge of the sense of taste is more fragmentary 
 than that of any other sense organ. The seat of this sense has 
 not even been accurately fixed, and for the following reasons : 
 1. Because it is difficult to separate this sensation from other 
 sensations which are evoked at the same time on the application 
 of the substance to be tasted, namely odorous and tactile sensa- 
 tions. 2. Because fluids which possess a taste pass so easily from 
 any one spot of the mouth, and therefore possibly from a spot 
 not endowed with taste to the proper taste organs. The special 
 seat of the gustatory sensibility has therefore been very diffe- 
 rently stated. Undoubtedly the root of the tongue plays an 
 important part, but it is doubtful whether it alone (Bidder^ 
 "Wagner), or also the tip and the borders of the tongue 
 (Schirmer, Klaatsch and Stich, Camerer), the soft palate (J. 
 Miiller, Drielsma), or at least a part of it (Schirmer, Klaatsch 
 and Stich), or even the hard palate (Drielsma), are seats of 
 gustatory sensation. Researches with limited electric irritation 
 (Neumann) show the tip of the tongue, and its borders over an 
 area of several lines to be capable of appreciating taste, though 
 not all qualities of taste (Lussana) ; the anterior part of the 
 upper surface, the whole of the lower surface, and the frsenum 
 are devoid of gustatory sensitiveness. 
 
 The nerves presiding over taste seem to belong to several 
 cranial nerves. Besides the glosso-pharyngeal nerve, about 
 whose function there can be no doubt, the lingual branch of the 
 fifth is considered by many to be a nerve of taste, though some 
 observers believe that it derives its > gustatory fibres from the 
 chorda tympani branch of the facial nerve ; the rami palatini 
 of the fifth are likewise considered to be gustatory. 
 
 In facial palsy disturbances of taste are very common. Against the 
 participation of the facial nerve it is asserted that after section of the chorda 
 
TERMINATIONS OF THE NERVES OF TASTE. 455 
 
 tympani, no degenerated nerve fibres are to be found in the lingual nerve 
 beyond the point of departure of the salivary nerves (Vulpian); others, 
 however, have found such degenerated nerve-fibres (Prevost) (in the dog 
 even, Vulpian). Since a case has been recorded, in which the intra-cranial 
 portion of the facial nerve was found totally degenerated, without there 
 having been any disturbance of taste (Wachsmuth), it is now assumed that 
 the gustatory fibres join the facial nerve only by the N. petrosus super- 
 ficialis major and enter the course of the trigeminus partly by the N. 
 petrosus superfioialis minor and the otic ganglion, and partly by the chorda 
 tyrnpani (Schiff). Since we may have paralysis of the fifth without dis- 
 turbances of taste, it is quite possible that fibres of the glosso-pharyngeal 
 nerve pass by means of Jacobson's anastomosis (N. petrosus superficialis 
 minor and the otic ganglion) into the fifth. 
 
 The terminal organs of the nerves of taste are found in the 
 papillae of the tongue. The furrow surrounding the circum- 
 vallate papillae at the root of the tongue dips down, and forms 
 a capillary space, the inner side of which is provided with the 
 terminal organs of the gustatory nerves, while the free surface 
 of the papillae shows the ordinary structure of the mucous 
 membrane of the tongue ; these terminal organs are the gusta- 
 tory bulbs, or ' gustatory goblets,' and consist of goblet-like 
 organs, open externally, and filled with cells ; of the cells 
 themselves those more centrally situated, ' the gustatory cells 
 proper,' terminate peripherically in a short rod, while their 
 central ends pass into fine nerve fibres, which, in the interior 
 of the papilla?, are connected with medullary nerve fibres 
 (Loven, Schwalbe). The fluid to be tasted must therefore first 
 enter the capillary space mentioned. These spaces containing 
 the gustatory bodies are found also in the form of plane 
 surfaces in the papillce foliatce of man, and most animals 
 (generally there is one at each border of the posterior part of 
 the tongue, while in man it consists again of five parallel lon- 
 gitudinal rows ; C. Mayer, Krause, and v. Wyss). The fungi- 
 form papillae ' possess gustatory bodies on their upper surface 
 (Loven), and, according to some, the free surface of the papillae 
 circumvallatae is also provided with them (Schwalbe, Honig- 
 schmied). 
 
 The gustatory nerves are excited by certain substances which 
 are fluid, or at least soluble in the fluids secreted in the oral 
 cavity; probably also most (Stich) gases which possess any 
 taste belong to this class. The process of excitation is totally 
 unknown. ' Grustatory sensations ' are the results of the excita- 
 
456 GUSTATORY SENSATIONS. 
 
 tion of the terminal organs as well as of the trunks of the 
 gustatory nerves themselves, and these are distinguished both 
 as to their intensity and character. The intensity of the sensa- 
 tion depends on the force and duration of the excitation, and the 
 number of excited nerve fibres. If the excitation be, therefore, 
 caused by a sapid substance, then the taste will be the more 
 intense 1, the more sapid the substance is ; 2, the more con- 
 centrated it is ; 3, the longer it acts ; 4, the larger the surface 
 of the taste organ it is in contact with; 5, the more easily 
 excited the nerve fibre. The properties are not known by 
 means of which the tasting substance produces the different 
 empirical and undefinable characters of taste which are known, 
 such as sweet, bitter, acid, alkaline, salty, putrid ; the different 
 sweet-tasting bodies (e.g. the different kinds of sugar, glycerin, 
 glyciue, salts of lead, beryll-salts, etc.) belong to the most 
 varied groups, and show no relations in their other properties. 
 
 As regards the taste of substances of the different chemical groups, the 
 following facts may be noticed : the sour taste of the soluble acids ; the sweet 
 taste of all polyatomic alcohols, which contain as many OH- groups as they 
 contain atoms (to this group belong C 2 H 4 ,(OII) 2 Glycol. ; C 3 H 5 (OH) 3 
 Glycerin ; C 4 H 6 (OH) 4 Lichen-sugar j C 6 Hg(OH) 6 Mannite [less 2 H grape 
 sugar]; the bitter taste of many compound sugars (glucosides), many 
 alkaloids, etc. 
 
 In man the excitation of the trunks of the gustatory nerves can only be 
 effected by electricity. If an ascending current be passed through the 
 gustatory nerves (as by putting the positive electrode to the tip of the 
 tongue, the negative 'electrode being in contact with any other part of the 
 body, say the hand), a distinctly acid taste is perceived; if the current 
 is a descending one, the taste becomes burning and 'alkaline.' If now, in 
 this case, we had a direct excitation of the nerves by the current, the 
 production of different tastes, according to the direction of the current, 
 would speak against the principle of specific energies (p. 344). It has, 
 therefore, been attempted to explain the results as due to the tasting of the 
 electrolytic products separated out on the tongue. The observation that the 
 results remain the same, when the current is passed to the tongue, not 
 by immediate metallic contact, but by the interposition of moist con- 
 ductors, does not disprove this explanation, because at the boundary of two 
 moist conductors, and especially, between nerve contents and membrane, 
 electrolytic products are deposited. 
 
 Besides gustatory sensations, the excitation of the nerves of 
 taste causes, in a reflex manner, secretion of the salivary glands. 
 (See p. 94.) 
 
END-ORGANS OF SENSORY NERVES. 457 
 
 We know nothing definite about subjective gustatory sensations, though 
 their existence is demonstrated (* after-taste/ etc.). Here, too, we have to 
 distinguish between the subjective gustatory sensations and those sensa- 
 tions which depend on certain conditions of the buccal mucous membrane 
 (' perverse ' tastes in catarrh, etc.). 
 
 V. THE REMAINING SENSE-ORGANS. 
 
 The perceptions produced by the other centripetal nerves 
 (excepting the optic, auditory, olfactory, and gustatory nerves) 
 are known as ' common sensations.' Sensory nerves are found in 
 almost every part of the body, but not to the same extent ; the 
 intestines seem to contain the least, and the muscles, bones, 
 fascise, etc. are but sparingly provided with them ; most 
 numerously, however, are they distributed over the skin and 
 the adjoining mucous membranes (the mucous membrane of 
 the oral and nasal cavities, the conjunctiva, etc.). 
 
 The terminations of the sensory nerves are only known for a few localities, 
 and their minute structure is, as yet, the subject of much contention. 
 The following forms have hitherto been described : 1. Pacinian ( Vater's) cor- 
 puscules; they are relatively large (0'5 4 mm ), and are situated in the sub- 
 cutaneous cellular tissue, especially of the hollow of the hand and foot; 
 they are also found in the genital organs, many muscles and joints, and in 
 the sympathic plexus of the abdomen (for instance, in the mesentery of the 
 cat). They are egg-shaped, and consist of many concentric lamellaa of areolar 
 tissue, enclosing a cylindrical body, consisting of protoplasm (inner bulb) ; 
 into this the nerve-fibre enters, runs along its interior as a simple axis-cylinder, 
 and terminates, often after splitting up into several branches, in a button- 
 like swelling extremity. The nerve-fibre, before it enters the corpuscule, is 
 surrounded by a lamellated neurilemma. 2. Terminal nerve bodies (Krause's 
 corpuscules) are oval, or more or less rounded vesicles of 0*03 0*06 mm , 
 consisting of an areolar sheath, with nuclei and soft homogeneous contents, in 
 which the nerve-fibre runs, terminating in a point ; they are found in many 
 organs, especially in the mucous membranes, where they occupy the areolar 
 mucosa. Possibly the organs mentioned under 1 and 2 are mere modifications 
 of the same form of which the last-mentioned most likely presents the primary 
 type. 3. ' Tactile corpuscules ' (Wagner and Meissner) . They are found in some 
 of the papillae of the cutis (the rest of the papillae contain capillary hoops), 
 more particularly in the hollow of the hand and sole of the foot ; they form 
 elongated, oval clubs, coarsely and irregularly striated, 0-05 Ol mm long, 
 which take up nearly the whole papilla, and into which one or two nerve-fibres 
 or parts of a nerve-fibre enter ; the mode of termination of the entering nerve 
 is, as yet, doubtful ; some believe that they split up into branches and that 
 each branch is again broken up into small transverse brauchlets, which are 
 
458 END-ORGANS OF SENSORY NERVES. PAIN. 
 
 the cause of the transverse striation ; a more recent view, however, is that the 
 tactile corpuscule consists only of a nerve-tube assuming the form of a skein ; 
 such * terminal nerve bundles ' are seen distinctly and well developed in the 
 glans penis (Tornsa). In the interior of the corpuscule, the branches of the 
 nerve-fibres are said to 'terminate in a manner similar to that observed in the 
 Pacinian body (Grandry). 4. l Terminal nerve-buds. 1 The terminations of 
 the sensory nerves of the cornea. Here the nerves break up into fine branches, 
 which form a network in the subepithelial layer, and thence send filaments, 
 sometimes branched again, into the epithelium, and which terminate on the 
 free surface, floating in the lacrymal fluid (Cohnheim); according to others, 
 these filaments terminate when yet within the epithelium in a small knob 
 (Hoyer). A similar mode of termination seems to hold good for the sensory 
 cutaneous nerves (Langerhans,Podcopaew,Eberth). The mode of termination 
 of the sensory (and reflex) nerves, in many places, is as yet unknown. 
 Ganglionic bodies are observed in the skin which may possibly be terminal 
 organs of sensory nerves (Tomsa). There are, also, special terminal organs, 
 some of which are connected with tactile hairs, as, for instance, in the web of 
 the bat, ear of the mouse, snout of mole, etc. 
 
 Qualities of the Sensations under consideration. 
 
 Any intense excitation of the nerves under consideration, 
 which are distinguished as the ' sensory nerves ' in the limited 
 sense of the word, from the preceding nerves of special sensibility, 
 is felt as an unpleasant sensation, asj>am, whether the terminal 
 organs or the trunks of the nerves be excited. A large portion 
 of these nerves, namely, those supplying the intestines, the 
 bones, the vessels, etc., seem excitable only by ' pathological ' 
 agencies, and then always to cause pain, if their function be not 
 to call forth reflex actions. The rest, however, give rise, when 
 their end organs are normally and not so- strongly excited, to 
 various sensations. The excitation of the end-organs may be 
 brought about by very different processes, by chemical, 
 mechanical, and thermal agents, but not by the vibrations of 
 light and sound. This harmony of the specific excitants 
 (p. 344) with the general nerve irritants, favours the idea 
 that the end organs of the sensory nerves are of simple construc- 
 tion, and not very different from the nerve trunks, and perhaps 
 only made more accessible to the exciting processes of the 
 external world by their position. The sensations which are 
 produced by mechanical irritation of the end-organs, are called 
 Tactile sensations : those which follow thermic irritation, 
 Sensations of temperature. 
 
TACTILE SENSATIONS. 450 
 
 Hecent observations heave made it very doubtful, whether painful irrita- 
 tions of the skin are merely due to a stronger irritation of the ordinary 
 nerve terminations, or whether rather to an irritation of special end organs. 
 For there seem, according to some observers, to be different roads of 
 conduction in the brain, both for tactile sensations and painful sensa- 
 tions, such, for instance, as are caused by chemical irritation of the skin 
 (tactile and pathic channels, see Chap. XL): it is possible, therefore, that in 
 these two cases, different peripheral apparatus may be concerned, and it has, 
 moreover, already been stated that the modes of termination of the nerves 
 in the skin are various. 
 
 The following experiment (E. H. Weber) proves that sensations of 
 temperature can only be caused by the thermic irritation of the end-organs. 
 If the elbow is dipped into a very cold fluid, the cold is only felt at the 
 immersed part of the body (where the fibres terminate) ; pain, however, is 
 felt in the terminal organs of the ulnar nerve, namely, in the finger-points ; 
 this pain, at the same time, deafens the local sensation of cold. This 
 experiment serves, likewise, to prove that the cause of excitation is referred 
 to the end organ (p. 345). 
 
 Tactile Sensations. 
 
 Tactile sensations are produced by mechanical irritation of 
 different degrees, by contact and by pressure. 
 
 The limit at which the intensity of the irritation becomes 
 painful is different for different parts of the body. By help of 
 the tactile sensation we are able to come to the following con- 
 clusions : 1. We conclude as to the existence of a foreign body 
 touching our body. 2. From the intensity of the sensation we 
 estimate the force of the pressure exerted, and from this we 
 estimate, under given circumstances, the weight, tension, etc., 
 of the touching body. The muscular sensation is an important 
 aid in these estimations (i.e. the sensation of the degree of 
 exertion in the muscles concerned in carrying, lifting, drawing, 
 pressing (see below). 3. We have always an idea of the state 
 of irritation of all our sensory fibres, and feel therefore our 
 whole body surface as a < tactile field, ' similar to the field of 
 vision (compare p. 395). We are thus enabled to determine 
 immediately the locality of each part touched, and thus also 
 the position of the touching body. 4. When a body touches a 
 cutaneous surface, or several cutaneous points simultaneously, 
 we are enabled, from the position of the different points of 
 contact, from the different pressure, and from the spaces not 
 touched, to draw conclusion as to the configuration of the touch- 
 ing body. This conclusion becomes still more positive when 
 
460 TACTILE SENSATIONS. 
 
 we pass the skin over the touching body, and thus create for 
 ourselves a number of tactile pictures. For this purpose those 
 cutaneous surfaces are best fitted which possess great mobility, 
 and contain numerous sensory end-organs, i.e. the finger-tips, 
 the point of tongue (see below). If different parts of the cuta- 
 neous surface touch the same body, a knowledge of the relative 
 position of the different cutaneous surfaces is necessary in order 
 to determine the configuration of the touching body. This 
 knowledge we obtain through the muscular sensation (see 
 below), because muscular movements are necessary for nearly 
 every change of the relative position. If this knowledge is 
 wanting, as, for instance, in abnormally distorted, displacements 
 of position, false conceptions arise about the configuration of 
 the body. The c experiment of Aristotle ' belongs to this class : 
 By placing the middle finger so over the index finger that a 
 small round body (pea, penholder) can be brought or rolled 
 about between the radial side of the index finger and the ulnar 
 side of the middle finger, the sensation of two round bodies is 
 produced, because one body cannot be brought in contact with 
 these two surfaces without producing distortion. By its very 
 uniform touch we conclude the presence of a fluid, and by the 
 more or less increasing pressure, when the tactile surface moves 
 about, we estimate the more or less soft or hard consistency of 
 a body, etc. These different conclusions are often enumerated as 
 specific ' senses ' (Sense of pressure, sense of locality, etc.). 
 
 The perceptive power of the sensory nerves depends, as 
 regards its sensitiveness for each part of the body, on the fol- 
 lowing : 1 . On the richer or poorer distribution of its end 
 organs. 2. On the absolute sensitiveness of the part. 
 
 The number of end organs in the different cutaneous sur- 
 faces can only be determined anatomically ; experimentally, 
 however, we can get relative data as to their distribution; the 
 method is the following (E. H. Weber, Czermak) : 1. Find 
 the smallest distance which can intervene between two bodies 
 touching the skin, either simultaneously or shortly after one 
 another, in order to produce two separate sensations ; the instru- 
 ment used consists in a pair of compasses with blunt points, 
 which can be placed on the skin at different, easily read off, dis- 
 tances (the eyes being shut). The distance is found to be smallest 
 on the tip of the tongue (M mm ), on the palmar side of the third 
 
TACTILE SENSATIONS. 461 
 
 phalanx (2-2 mm ), and the red surface of the lips (4-4 mm ) ; 
 largest on back, chest, neck, and extremities (35 66 mm ). 
 
 The smallest required distance is in some places, for instance 
 on the extremities, less in the transverse than in the longi- 
 tudinal direction; it is less also when the points are placed 
 on the skin one after the other; it is less, by beginning 
 with larger distances and gradually finding that distance at 
 which both impressions blend, than proceeding in the reverse 
 order, and beginning at a smaller distance and gradually finding 
 that distance at which the two separate sensations make their 
 appearance ; lastly, it becomes smaller the greater the attention 
 and the greater the practice (hence it is generally smaller in blind 
 people, Groltz) ; it is also said to become smaller by surrounding 
 the skin with indifferent fluids (oil, water), having the same 
 temperature as the body (Suslowa). Two impressions just felt 
 distinct from each other blend into one when the skin between 
 the two touched points is irritated by tickling or induction 
 currents (Suslowa); for the explanation of this see below. 
 2. Move the two separately felt points of the compass over the 
 skin in two parallel lines, keeping the same distance, and 
 determine the variations in the apparent distance and the dis- 
 tance at which the two separate sensations blend. 3. The eyes 
 being closed at the time, touch a point of the skin, and note 
 accurately the apparent place of touch. 
 
 The absolute sensitiveness of any cutaneous part is deter- 
 mined in the following way: 1. Two different weights are 
 placed on a cutaneous part, and the smallest difference in 
 weight which can yet be perceived is accurately determined. 
 The loading is done either by weights placed unsupported 
 on the part (Weber), or by loaded small plates (Aubert and 
 Kammler), or by a blunted point suspended on one beam of a 
 balance, the weight of the point being taken off, equalized, 
 in different degrees, by weights attached to the other beam 
 of the balance (Dohrn). Here also the sensibility is found 
 to be more delicate with the increase than the decrease of 
 the difference in the weights, and also with a smaller abso- 
 lute pressure than with a larger. 2. By determining the 
 smallest possible variation in pressure which a cutaneous part 
 can perceive (Groltz) ; an india-rubber tube, filled with water, 
 and to ensure a constant surface of contact, bent at one spot 
 
462 TACTILE SENSATIONS, 
 
 over a piece of cork, is touched at that spot by the cutaneous part 
 to be examined, and by rhythmically exerted pressure, waves, 
 analogous to those of the arterial pulse, are produced in the 
 tube. This method gives the same scale of results as Weber's 
 experiment with the compasses; the tip of the tongue only 
 forms a remarkable exception, inasmuch as its sensation for 
 pressure stands much lower than in the other scale for measur- 
 ing the sense of locality. 3. The smallest possible irritation 
 which can yet be felt is determined ; it has thus been found 
 that an impression or touch which can just be felt, ceases to be 
 so on passing weak unfelt induction currents through the cuta- 
 neous part touched (Suslowa.) 
 
 Of the last-mentioned three methods the second is the most decisive, for 
 we are naturally only sensitive to variations in pressure, and these take place 
 in the second method with greater rapidity and precision than in the first, 
 It is, however, to be observed, that in the second mode of experimentation 
 the sense of space is not altogether excluded, for with the positive variation 
 of pressure there is, most likely, also, a slight increase in the surfaces of 
 contact, as both the tube and the cutaneous part are mutually flattened, and 
 experience teaches us that we are able to feel the arterial pulsations in 
 many places, whilst the cutaneous part touched does not perceive it, though 
 the same variation of pressure acts on it too. Already, comparisons of this 
 kind may be used for the construction of a scale (Goltz). The third method 
 becomes most reliable by using an electromagnetic motor apparatus to pro- 
 duce irritation (Leyden) ; the results thus obtained are, however, only to be 
 used with caution, on account of the different resistances in the conductivity 
 of the mucous membranes and the epidermis of different parts of the cuta- 
 neous surface. 
 
 Lastly, there are methods for determining at the same time 
 the sensibility of the cutaneous parts in both directions, namely, 
 by finding the degree of perfection of our conclusions as to the 
 configuration or the course of touching bodies. 1. The skin is 
 touched with bodies of a definite configuration. 2. Different 
 figures (letters) are drawn on the skin with a point, and one now 
 states in the first case the apparent figure of the body, and in 
 the second that of the drawing. 
 
 In order to explain the above-stated facts about the separa- 
 tion in space of the tactile impressions, the following assumptions 
 are necesssary (Lotze, E. H. Weber, Meissner, Czermak). We 
 are continually conscious of the state of irritation of all the 
 cutaneous points in their given arrangement in space (our con- 
 sciousness perceives a field of tactile sensation, as already stated). 
 
TACTILE SENSATIONS. 463 
 
 Every irritation of a sensory end-organ is referred to a definite 
 spot in the field of tactile sensibility, that is, on the surface of 
 the skin. This spot is, however, not the point irritated, but 
 rather a circular or (on the extremities, p. 461) an oval plane, 
 the centre of which is formed by the irritated point, the so- 
 called circle of sensibility (see below). Two such circles, which 
 either touch or partly cover each other, can, however, not be 
 separately perceived ; the separation takes place then only when 
 between the two circles there is a non-irritated sensory element 
 and the apparent distance of the two irritations is the greater 
 the more numerous the non-irritated elements which remain 
 between the two circles. From this it follows that two neigh- 
 bouring impressions on the skin can only then be felt separate 
 when their distance is greater than the whole diameter of one 
 circle of sensibility. The numbers given on page 461 are 
 therefore the diameters of the circles of sensibility at the corre- 
 sponding cutaneous placdfe. It follows further, that two separate 
 impressions blend when the intervening sensory elements are 
 irritated (compare the observation on p. 461). 
 
 There still remains to be explained how it is that these 
 circles possess different sizes at the different parts of the skin. 
 A circle of sensation is evidently not an anatomical magnitude, 
 such as the district of distribution of a nerve-fibre, for, firstly : 
 it is altered by attention, practice and other influences ; and, 
 secondly, it would be possible for the two feet of the com- 
 passes, if their distance were smaller than the diameter of one 
 circle of sensation, in one case, both to fall within one 
 circle, in another case into two neighbouring circles 
 (these being considered fixed). We must therefore assume the 
 existence of a circle of sensation round each cutaneous point. 
 To the above explanation is further to be added, that the circles 
 are the smaller the more closely packed the sensory organs 
 (compare 461); from which it follows that the assumption, that 
 the circle of sensation is caused by the mechanical effect of 
 the irritation on a cutaneous surface, and not on a mere point 
 (circles of diffusion}, is not enough : for if so, then the size of 
 the circles would evidently be independent of the relative 
 number of the end-organs, and therefore would in general be 
 the same everywhere. It is rather to be assumed, that the 
 transmission of the irritation of one fibre to another sensory 
 
464 SENSATIONS OF TEMPERATURE. 
 
 fibre in the neighbourhood is a central process (irradiation, 
 associated sensation), and that it always extends from every 
 point, in every direction, to the same number of sensory fibres 
 (the distance of the two points of the compasses corresponds in 
 the mean to twelve tactile corpuscules, Krause), but that by 
 practice, attention, and acuteness of irritation, etc. it can be 
 diminished. This view (see Chap. XI., under Spinal Cord) 
 seems to correspond best with the observed facts. 
 
 Alterations in the normal amount of Wood in the skin (hyperaemia, 
 anaemia) diminish the tactile power (Alsberg) ; intense cooling of the skin 
 (for instance, ether-spray) may produce complete anaesthesia ; certain poisons 
 brought in contact with the skin act in the same way, 
 
 Sensations of Temperature. 
 
 Sensations of temperature are produced when the end-organs 
 of sensory nerves are irritated by variations of temperature 
 within the limits of about +10 to +47 C., particularly 
 when the skin is either warmed or cooled by bodies in contact 
 with it. The sensation caused by a positive variation we call 
 sensation of warmth, that caused by the negative variation, 
 sensation of cold. When the variation of temperature extends 
 over a large surface, or over the whole body, then the sensa- 
 tion of cold changes to a sensation of shivering, and the sensa- 
 tion of warmth gives rise to a sense of heat. The symptoms 
 mentioned at page 232 are connected with both (the shivering of 
 fever is caused by the sudden cooling of the skin in consequence 
 of the diminished flow of blood through the spasmodically 
 contracted cutaneous arteries, whilst fever heat is due to the 
 reverse process ; in both, however, the mean bodily temperature is 
 higher than normal). Variations of temperature between 27 and 
 33 C. are distinguished most acutely, then variations between 
 33-39C. and then variations between 14-27C. (Nothnagel). 
 The different regions of the body may be grouped as regards 
 their sensitiveness to changes of temperature (measured by the 
 smallest yet perceptible variation) as follows (leaving out 
 the extremities, which follow no law), (E. H. Weber) : 
 Tip of tongue, eyelids, cheeks, lips, neck, trunk. As the middle 
 line is approached the parts are less sensitive. The variation is 
 felt more intensely the more rapid its occurrence, and the larger 
 the affected cutaneous surfaces. Temperatures above or below 
 
SENSATIONS OF TEMPERATURE. MUSCULAR SENSE. 465 
 
 the limit given above produce pain (p. 458). Variations are 
 here no longer specifically felt. 
 
 Anaemia of the skin increases the sensitiveness for temperature ; hyper- 
 semia diminishes it (Alsberg). 
 
 If the principle of specific energies (compare p. 344) is to be a general one, 
 we must assume here, also, different fibres and different central organs for 
 the tactile and temperature sensations; though we know nothing definite 
 about this, it may be yet mentioned that the distances in the experiment 
 cited on p. 461 are smaller when the temperature of the two points of the 
 compasses differ (Czerrnak), and that in the experiments given on p. 461 a 
 colder weight is felt as heavier, so that the apparent difference of pressure 
 becomes greater when the heavier weight is at the same time colder, and 
 less when the lighter weight is colder, and that difference of pressure is 
 felt with equal weights of unequal temperature (Weber). 
 
 Other Specific Sensations. 
 
 The sensory nerves of certain parts of the skin and mucous 
 membrane of the genital organs (4th section), on being irritated, 
 give rise to peculiar sensations, different from the tactile and 
 temperature sensations, which are called voluptuous sensations* 
 
 We know very little about the specific sensations of those 
 nerve-fibres which do not terminate in the skin. Some of these 
 sensations, hunger and thirst, have already been considered 
 (p. 197). There only remain for consideration 
 
 The muscular sense (Weber). The presence of sensory 
 fibres, though not anatomically demonstrated with certainty, is 
 physiologically proved by the muscular pains observed under 
 certain conditions, and by the sense of fatigue which un- 
 doubtedly exists. The question is only whether these or other 
 nerve-fibres explain to us the state of activity of the muscles. 
 It is evident that many phenomena, such for instance as the 
 combination of complicated muscular movements, depend on 
 the intervention of centripetal fibres, for such movements 
 become very defective when the posterior roots of the spinal 
 nerves are divided (Bernard), or when the centripetally con- 
 ducting parts of the spinal cord (see Chap. XL) are injured or 
 degenerated (for instance, in the gray degeneration of the pos- 
 terior columns (locomotor ataxy). It is very improbable that 
 these defects depend on the loss of cutaneous sensibility, for 
 the movements are not at all or very little interfered with by 
 skinning the animal (Bernard). It seems therefore that con- 
 
 H H 
 
466 MUSCULAR SENSE. 
 
 sciousness itself is aware of the condition of the muscles, etc. 
 This may be brought about in the following ways. 1. Sensory 
 nerves of the muscles give information about the changes in 
 tension, pressure, and possibly also of the state of contraction. 
 2. Our consciousness judges of the voluntary impulse, which 
 is imparted to the motor nerves, and of the effects which neces- 
 sarily follow. 3. The sensorium is made aware of the effects 
 of muscular activity by the surrounding parts (muscles, areolar 
 tissue, etc.). Whether all these different ways or one of them 
 only exists, is not known. The various uses of such a muscular 
 sense are evident, partly from what has just been said estima- 
 tion of weights lifted, knowledge as to the configuration of the 
 surface of, and conclusions as to the form of bodies touching. 
 
 In the joints, periosteum, and more rarely in muscles, Pacinian bodies 
 (p. 457) have been found, which perhaps have some relation to the muscular 
 sense (sub 3 in the above paragraph), (Rauber.) 
 
467 
 
 CHAPTER XI. 
 
 THE CENTRAL END-ORGANS OF NERVES. (CENTRAL 
 NERVOUS ORGANS.) 
 
 A. GENERAL CONSIDERATIONS. 
 
 THE central end-organs of nerve-fibres are contained in certain 
 structures, which are called the ' central organs of the nervous 
 system.' The latter contain, in addition to the central end- 
 organs, numerous conducting fibres. Their function is, there- 
 fore, much complicated by the fact that they are able to act also 
 as conducting agents. Since the investigation of the central 
 nervous end-organs has never, hitherto, been possible apart from 
 the nerve-fibres with which they are mixed, a physiological con- 
 sideration of them is not possible in the present state of our 
 knowledge. We can, therefore, only give the discoveries which 
 have been made concerning the functions of the mixed organs 
 brain, spinal cord, and ganglia to serve as material for the future 
 physiology of the nervous end-organs which have not yet been 
 isolated. 
 
 The characteristics which go to constitute a central 
 nervous organ are, according to what was said in the introduc- 
 tion, the following: 1. The liberation of the active condition 
 in a ('centrifugal') nerve-fibre, without the apparent par- 
 ticipation of any external influence automatism. 2. The 
 liberation of the active condition in one (' centrifugal ') nerve- 
 fibre, brought about through another ( c centripetal ') fibre 
 reflex action. 3. The phenomena collectively called states of 
 consciousness or mental operations, which are connected with 
 the irritation of certain central organs. 
 
 All organs of the body which can be shown to possess the 
 above characteristics contain as necessary constituents ganglion- 
 
 H H 2 
 
468 PROPERTIES OF GANGLION-CELLS. 
 
 cells, which are immediately in communication with nerve- 
 fibres. Since no other structures, with the exception of the 
 peripheral end-organs previously mentioned, are known to be 
 in undoubted continuation with nerve-fibres, these ganglion- 
 cells must, in general, be regarded as the central end-organs of 
 nerve-fibres. It is, nevertheless, still doubtful (1) whether all 
 ganglion-cells ought to be considered as central organs, and 
 (2) whether there do not exist other central organs in addition 
 to ganglion-cells. 
 
 The former of these doubtful points seems to be settled in the negative 
 by the expression, in general use, of ' peripheral ganglion-cells.' That is to 
 say, in many organs, the functions of which are certainly not those of central 
 nervous organs, nerve-fibres are found to be provided with ganglion-cells or 
 cellular apparatus much resembling them. This is seen to be the case in 
 the organs of sense, in glands, &c. If, however, the power of transferring a 
 stimulus from one nerve-fibre to another be regarded as a general character- 
 istic of a central organ, it is quite possible to look upon the i peripheral 
 ganglion-cells/ the exact signification of which is yet entirely unknown, as 
 also belonging to the class of nervous central organs. Every fibre in the 
 course of which is interposed a ganglion-cell must, accordingly, be regarded 
 as a system of two fibres, of which one is provided with a peripheral 
 end-organ, while the other, like the numerous intercentral fibres of brain, 
 spinal cord, and sympathetic nervous system, connects together two central 
 organs. With respect to the second question, as to the use of ganglion-cells 
 only as central organs, it may be stated that there exist in the brain 
 numberless small cellular organs of manifold form, which have been distin- 
 guished from ganglion-cells, but whose nature appears essentially to agree 
 with that of the latter bodies to the extent that it is in general nervous. 
 
 Many anatomical peculiarities in the structure of the central organs can 
 only be made out in preparations in which, besides the changes accompany- 
 ing the death of the tissues, certain others, of the nature of coagulation, &c., 
 have been induced by means of reagents. Very little is therefore known of 
 the real structures of the organs during life. 
 
 Properties of Ganglion-Cells. 
 
 Of the properties of ganglion-cells almost nothing is known. 
 The nature of their chemical composition can only be imperfectly 
 and approximately gathered from analyses of the grey substance 
 of the brain. The white substance of the brain, which consists 
 essentially of nerve-fibres and a connecting substance (neuroglia), 
 is considered to be of the same composition as nerve-trunks ; 
 the constituents of the latter indeed have been chiefly deter- 
 mined by examinations of brain and spinal cord. While the 
 
CHEMICAL COMPOSITION OF NER VE SUBSTANCE. 469 
 
 reaction to test-paper of the white substance is neutral or 
 alkaline, the grey substance has been found to be acid 
 (Grscheidlen), a circumstance which is probably to be attri- 
 buted to the rapid changes occurring at the surface of section. 
 The chemical constituents of the white substance are lecithin, 
 protagon, and probably other lecithin-bodies ; albumin, potas- 
 sium-albuminate and globulins ; cholesterin and fats ; creatine, 
 xanthine, and hypoxanthine ; inosite and some anhydride of 
 sugar ; lactic acid (the ordinary modification according to 
 Oscheidlen) and volatile fatty acids ; salts and water. The 
 grey substance of the brain is distinguished chemically from 
 the white chiefly by containing more water, albumin, lecithin, 
 and lactic acid, and less cholesterin, fat and protagon. 
 
 A considerable number of substances which are now known to be either 
 the products of the decomposition of lecithin, or the mixtures of such pro- 
 ducts with other bodies, were formerly described as genuine constituents of 
 brain substance. Even the above-mentioned constituents may be them- 
 selves the results of the decomposition of more complicated pre-existing 
 compounds. One of them, protagon, has recently been regarded as a mixture 
 of lecithine and a nitrogenous glucoside, cerebrin (Hoppe-Seyler), a body 
 which chiefly occurs in the white substance (Petrowsky). The composi- 
 tion of grey and white brain-substance is given in the following Table 
 (Petrowsky) : 
 
 Grey substance. White substance. 
 
 Water 81-6 p.c. 684 p.c. 
 
 Solids 18-4 31-6 
 
 Consisting of 
 
 Albumins and gelatin . . 55-4 p.c. 24-7 p.c. 
 
 Lecithine .... 17-2 9-9 
 
 Cholesterin and fats . . 18-7 51-9 
 
 Cerebrine .... 0*5 9-5 
 
 Substances insoluble in ether . 6-7 3-3 
 
 Salts 1-5 0-6 
 
 It is in the highest degree probable that processes of oxida- 
 tion take place in ganglion-cells as in all other organs. It is, 
 however, still but a probability, unless we consider it evidenced 
 by the fact that the venous blood of the brain and spinal cord 
 is as poor in oxygen and as rich in carbonic acid (i.e. as dark 
 in colour), as the venous blood of any other region of the body. 
 We are equally ignorant as to whether such processes of oxidation 
 are concerned in the activity of the ganglion-cells, and, if so, 
 to what extent ; we cannot say whether that activity is not de- 
 
470 LIBERATION OF ENERGY IN NERVE-CELLS. 
 
 pendent upon processes of decomposition similar to those which 
 occur in muscles and nerves ; or what the results of such oxida- 
 tions or decompositions are. 
 
 Still less is known of the transformation of energy in 
 ganglion-cells. As far as can be judged the energies which 
 become kinetic or free in ganglion-cells are not of a nature 
 which admits of investigation by the means at our disposal. We 
 must suppose in general that molecular processes occur in them 
 similar to, and immediately connected with, those which are 
 assumed to occur in nerve-fibres (p. 342). If the active con- 
 dition of a nerve-fibre be imagined as a chain of successive 
 liberations of force, the manifestation of energy in the ganglion- 
 cell must be regarded as the initial or final link of that chain ; 
 and the question now arises : What, in the first place, is the 
 force which liberates the potential energy of the ganglion-cell, 
 and what, in the second, becomes of the force thus set free ? 
 
 The answer to these questions seems to be simplest in the 
 case where the cell is intermediate between two nerve-fibres, 
 i.e. in the case of reflex activities in the widest sense of the 
 term. Here the potential energy of the ganglion-cell is set 
 free by means of the energy, already liberated, of the stimulated 
 fibre ; and the energy thus become kinetic, in its turn sets free 
 the energy which is potential in the second fibre. In this case, 
 therefore, we have but a single chain of liberations, the initial 
 link of which (the original liberating force) is some influence 
 in the external medium, which operates upon a peripheral end- 
 organ (organ of sense); and the final link of which is the 
 liberation of the potential energy of some organ of work such 
 as a muscle, a gland, or a parenchyma. The ganglion-cell, in 
 such a case, performs a function which differs in no essential 
 respect from that of any portion of a simple conducting fibre. 
 
 But the process which takes place during stimulations which 
 are characterized as automatic is far more difficult to under- 
 stand. Under the title of automatic are included all those 
 stimulations proceeding from a ganglion-cell in which the 
 liberating force in the ganglion-cell is unknown. In this case 
 two possible theories present themselves. Either the liberation 
 of energy within the cell takes place without the aid of any 
 liberating force, or the automatism is only apparent, the libe- 
 ration being due to some operation of a reflex nature*. Possibly 
 
AUTOMATISM, RHYTHMICAL AND TONIC. 471 
 
 many apparently automatic stimulations are to be explained on 
 the latter supposition, as, indeed, has already been the case with 
 some, viz. with the liberation of the respiratory movements 
 (p. 168) ; with muscular tonus, &c. 
 
 In the former case, in which energy is supposed to be set 
 free without the aid of any liberating force, it would be 
 necessary to assume a continuous liberation of energy. 1 The 
 stimulation of the nerve-fibre brought about by it need not, 
 however, be continuous. Suppose, for instance, that the energy 
 liberated has to overcome a certain resistance before being able 
 to act as a stimulus upon the nerve-fibre, it would then be 
 necessary for the tension of the energy liberated to reach a 
 certain amount previous to stimulation, just as gas constantly 
 passed through a bent tube under water does not rise in the 
 tube in a continuous stream, but in an intermittent manner in 
 bubbles of a certain size, since it is necessary to accumulate a 
 certain pressure in the tube in order to overcome the resistance 
 due to the cohesion and weight of the water. In this manner 
 a rhythmical stimulation is accomplished. As a fact, all stimu- 
 lations, which have been shown to be automatic, are either 
 continuous (' tonic ') or rhythmical ; but here it is necessary to 
 remind the reader of the probability that even tonic stimula- 
 tions ought in truth to be regarded as rhythmical (tetanic, 
 p. 260). Any force which could increase or diminish this 
 hypothetical resistance would influence the frequency of the 
 rhythm and the strength of each stimulus, just as, in the above 
 illustration, an increase in the cohesiveness of the water brought 
 about by means of gum, &c. would render the bubbles less 
 frequent but greater, while a diminution, brought about by 
 using ether instead of water, would cause the bubbles to be- 
 come more frequent but smaller. If the resistance were made 
 exceedingly great, the stimuli would be discharged at long 
 intervals, while if it were much reduced the intervals would be 
 so slight as to render the stimulation tonic (tetanic). An influ- 
 
 1 Such a continuous liberation may be supposed to be caused by a continual 
 bringing together of energy-yielding materials, effected by extraneous means (e.g. 
 by the blood), in exactly the quantities in which they combine : or by the energy 
 liberated at any one moment so acting during the next upon the stored-up potential 
 energy as to perform the part of a liberating force, somewhat as the heat formed 
 during the burning of tinder by a spark first serves to maintain the combustion. 
 
472 REG ULA TING NER VES. STA TES OF CONS CIO USNESS. 
 
 ence of tliis kind appears, in fact, to be exerted in the case of 
 certain ganglion-cells characterized by a rhythmico-automatic 
 action, by means of the so-called c regulating ' nerves, of which 
 the ' inhibitory ' nerves form one class. 
 
 Certain phenomena, especially the action of some fibres of 
 the vagus on the heart, and others upon the medulla oblongata 
 (pp. 73 and 352), can only be explained in a very forced 
 manner by other theories. If it be established as a certainty 
 that the influence of those fibres upon the central organs 
 merely consists in a modifying action exerted by them upon the 
 organs in question, of such a nature that the activities of the 
 latter are differently distributed as to time, and hence that 
 the strength of every discharge of energy is inversely propor- 
 tional to its frequency (p. 168), it can only be explained by 
 assuming that the hypothetical resistance is increased by the 
 activity of certain fibres (inhibitory fibres) and diminished by 
 the activity of others (accelerating fibres). It is just as easy, 
 however, to imagine that accelerating and inhibitory nerves act, 
 the former by accelerating, and the latter by hindering, the 
 chemical processes which occur in the central organ, the resis- 
 tance meantime remaining constant. Such a theory would 
 imply that the sum total of the magnitudes of the discharges 
 did not remain constant, but varied, which is indeed the case 
 during the inhibition of the heart by the vagus (Ludwig and 
 Coats). 
 
 We understand nothing whatever of the processes of stimu- 
 lation in ganglion-cells, in which the initial or the final link 
 in the chain of liberations is a state of consciousness (Will, 
 Sensation) ; or of those mental operations which are not ap- 
 parently directly dependent upon the stimulations of the con- 
 ducting organs (Processes of Thought). It is exceedingly 
 doubtful whether any such mental operations occur which are 
 not connected with irritation of nerves, and therefore with 
 sensation or will. 
 
 A theory, which, although incapable of demonstration, has 
 been put forward in a modified form from other quarters, seems 
 not improbable. According to it, every mental operation forms 
 an unbroken series a c chain of thought ' the initial act of 
 which has connected with it a stimulation of nerve (Sensation), 
 and the final act of which is, in its turn, accompanied by a 
 
STATES OF CONSCIOUSNESS. RECAPITULATION. 473 
 
 state of consciousness (Will) which is also connected with 
 nervous stimulation. It is now but a step further to suppose 
 that an uninterrupted series or chain of successive liberations, 
 coincident with, and in some unknown way connected with the 
 above-mentioned series of mental operations, takes place in the 
 central nervous organ, uniting the initial and final nervous 
 stimulations concerned in Sensation and Will. With this 
 hypothesis the difficulty would be removed of seeking in the 
 central organ the beginning or end of an irregular and discon- 
 tinuous process of liberation ; for, according to it, the essential 
 operations occurring in the central organs, and concerned in 
 the phenomena of mind, would be distinguished from simple 
 reflex acts only by the greater amount of time and space ren- 
 dered necessary by the greater number of centres (organs of 
 the mind), whose stimulation is concerned in any mental ope- 
 ration. Consequently, the origin of every excitation of nerve 
 which is not automatic would have to be sought for, imme- 
 diately or mediately, in the stimulation of a peripheral nervous 
 end-organ. 
 
 This is not the place to mention the numerous philosophical views con- 
 cerning the dependence of the functions of mind upon material processes, or, 
 as it is here put, upon the forces liberated in a central organ. It must be 
 kept in mind that the hypothesis just brought forward has nothing whatever 
 to do with that question. 
 
 The properties which, according to what has been said 
 above, can be ascribed on hypothetical grounds to ganglion -cells 
 (with some reservations), are, therefore, the following : 1. A 
 continual liberation of forces, which, in their turn, act as libe- 
 rators upon the different nerve-fibres, either (a) without any 
 further interruption (true tonic automatism, if such exist) : or 
 (6) after overcoming a certain hypothetical resistance (rhyth- 
 mical and tetanic apparently tonic automatism), the extent 
 of the resistance, or, according to other views, the rapidity of 
 evolution of the force, depending in its turn upon the condition 
 as to excitation of certain different 'regulating'' fibres. 2. 
 The power of conducting from one nerve-fibre to another, con- 
 duction taking place from a centripetal fibre, through one or 
 more ganglion-cells, to a centrifugal fibre : if the change occur- 
 ring in the ganglion-cells during conduction is not associated 
 with states of consciousness, the process is characterized as 
 
474 GENERAL PROPERTIES OF GANGLION-CELLS. 
 
 reflex ; while, if it is so associated, the state of consciousness 
 coincident with excitation of the central organ by means of the 
 centripetal fibre is called Sensation, and that coincident with 
 excitation by means of the centrifugal fibre, "Will. 
 
 Whether we ought to add to the general properties of 
 ganglion-cells that of irritability when acted on by the common 
 nervous stimuli, is not yet decided. Certain experiments on 
 the non-irritability of the spinal cord under mechanical stimu- 
 lation, which will be discussed hereafter, indicate that ganglion- 
 cells differ from nerves in this respect, probably to a considerable 
 extent. The composition of the blood surrounding the cells has 
 a most important influence upon them. 
 
 Finally, there must, most probably, be added to the gene- 
 ral properties of ganglion-cells certain conditions of their 
 activity as to time. 1 . The number of vibrations of the ' bruit 
 musculaire' during tetanus produced by centric stimulation 
 (p. 260) is about 19*5 per second. Since muscle on artificial 
 stimulation, whether directly or indirectly applied, is capable 
 of a much quicker series of vibrations, the above number cannot 
 be due to any property of muscle or nerve, but is most probably 
 to be explained by supposing that the motor ganglion-cells, from 
 which the motor nerve immediately proceeds, imparts to the 
 nerve 19*5 impulses per second at every excitation, even when 
 artificially induced (p. 261). 2. The excitation of the optic 
 nerve is most intense when it takes place 17 18 times in a 
 second (p. 387). 3. The excitation of the auditory nerve is 
 most intense when it takes place 33 times in a second. The 
 last two circumstances are possibly explicable on the assump- 
 tion that in the sensory ganglion-cell, which is first excited by 
 means of a centripetal fibre, every excitation takes -^ or ^, 
 as the case may be, of a second to exhaust itself, in conse- 
 quence of which the succeeding excitation acts with greater 
 effect after that interval than it would if aroused earlier. The 
 total effect, therefore, must be greatest when excitation takes 
 place with the above-mentioned frequency. 
 
 The time taken up in conduction through the central organ 
 (ganglion-cells, grey network) may be determined in the case 
 of reflex actions by measuring the interval of time which elapses 
 between stimulation and the reflex action caused by it, and sub- 
 tracting therefrom the time occupied in conduction through the 
 
STRUCTURE OF THE SPINAL CORD. 475 
 
 sensory and motor nerves concerned, a knowledge of which may 
 be obtained by the method given on p. 336 (Helmholtz). In 
 this manner an interval of -^ T V of a second has been ob- 
 tained, with respect to which, however, it is unknown to what 
 extent or description of path through the central organ it refers. 
 The time taken up by conduction through the centres is shorter 
 the stronger the centripetal stimulation ; it is, moreover, in the- 
 region of the spinal cord, greater in the case of conduction 
 across the mesial plane, and it is increased by exhaustion of 
 the central organs (Eosenthal). 
 
 The measurements of time, with regard to mental activities, will be 
 given when discussing the Cerebrum. 
 
 B. SPECIAL PHYSIOLOGY OF THE CENTRAL 
 NERVOUS ORGANS. 
 
 There must now be described whatsoever has been discovered 
 concerning the functions, as centres and as conductors, of the 
 various central organs, viz., brain, spinal cord, and sympathetic 
 ganglia. It must be expressly borne in mind that only those 
 facts which have been established with some degree of certainty 
 will be noticed in this, the darkest, region of physiology. 
 
 1. Spinal Cord. 
 
 STEUCTUKE. The most important points, physiologically, in the structure 
 of the spinal cord are the following: In a cross section of the cord there are 
 distinguished, 1. The narrow central canal lined by epithelium. 2. The 
 grey substance which surrounds that canal, and projects in the form of horns 
 (anterior and posterior cornua) into the white substance. 3. The white 
 substance, in which one may distinguish on either side of the median 
 fissures, three columns, the anterior, lateral, and posterior; between the 
 anterior and lateral columns lies the anterior cornua of the grey substance, 
 and the fibres of the anterior root of the spinal nerve which enter it. In 
 like manner the posterior cornua and the fibres of the posterior root lie 
 between the posterior and lateral columns. The white substance, besides 
 the root fibres traversing it in an horizontal direction, consists of vertical 
 (longitudinal) fibres and a connecting substance (neuroglia). The grey 
 substance consists of ganglion-cells, and a homogeneous grey mass, in which 
 the majority of recent observers describe an interlacement of fine axis 
 cylinders running in all directions. 
 
 The ganglion-cells lie for the most part in the anterior and posterior 
 
476 COND UCTION OF SENSORY AND MOTOR IMPRESSIONS. 
 
 ornua. There is distinguished in every ganglion-cell (Deiters) a granular 
 mass (protoplasm), a large nucleus with neucleoli and processes. Among 
 the processes one the axis cylinder, which, as it seems, is in connection 
 with the nucleus may be at once detected by its appearance ; the remain- 
 ing processes are fine, numerously branched, pointed fibres (processes of 
 protoplasm), into which homogeneous fine simple fibres axis cylinders of 
 the second kind are inserted. The latter join the fine network of fibres of 
 which the n. ain mass of the grey substance consists (Gerlach), and from 
 which fibres, united so as to form thicker bundles, run into the white sub- 
 stance. According to recent theories (M. Schultze), the cells consist of 
 a fine fibrillar network, the processes also being fibrillated (p. 322); if 
 so, the cells are merely traversed by the fibrillse of the processes. 
 
 The large axis cylinders (those of the first kind) are the terminations of the 
 root-fibres of the spinal nerves. The cells into which the fibres of the anterior 
 root enter ('motor ganglion-cells') are larger and have more numerous pro- 
 toplasmic processes than the more spindle-shaped cells into which the pos- 
 terior root-fibres enter (' sensory ganglion-cells '). According to another view 
 (Gerlach), the fibres of the posterior roots do not in general enter into gang- 
 lion-cells, but pass directly into the fibrillar network of the grey substance, 
 so that the cells of the posterior cornua also are probably to be reckoned as 
 motor. 
 
 It is clear from the anatomical arrangement of the parts 
 that the spinal cord is, with the exception of the thin sympa- 
 thetic communications, the only connection between the brain 
 and the nerves of the trunk and extremities. The spinal cord 
 must therefore contain the paths for the conduction of all 
 voluntary movements of the trunk and extremities, for all 
 sensations in those parts, and for all actions not psychical of 
 other cranial centra (e.g. the respiratory centre). 
 
 It is, however, established on anatomical grounds that the 
 nerves of the trunk in the spinal cord do not simply run to the 
 brain, but that all of them, or at least the motor nerves, are first 
 of all connected with ganglion-cells. Moreover, there are phy- 
 siological reasons against the view of the direct entrance of the 
 nerves of the trunk into the brain, as will be seen on consulting 
 the sections on Eeflex Actions. 
 
 No well -ascertained anatomical facts have, as yet, been dis- 
 covered which throw light on the conduction of impressions 
 from motor and sensory ganglion-cells to the brain. It is most 
 probable that the cells are immediately connected with a com- 
 plicated network of fibres, which continues uninterruptedly to 
 the brain, but from which fibres continually separate and run to 
 the brain isolated in the white substance. In order to under- 
 
SENSATION. REFLEX ACTION. 477 
 
 stand the matter, it is necessary to assume that impressions only 
 travel along structurally continuous paths paths morphologi- 
 cally pre-existent but that they are able to pass along those 
 paths in every direction where continuity of the conducting 
 structure is established. According to this supposition a nervous 
 impression, when once it has gained the actual, anatomical 
 network of fibres, may pass along every individual fibre which 
 is fitted for conduction. 
 
 The result of an excitation of a sensory fibre of the trunk or 
 extremities is either a Sensation, which is referred with more 
 or less exactness to the peripheral termination of the fibre (p. 
 345), or a Reflex Action, i.e. an excitation of a motor fibre 
 without the aid of consciousness, i.e. an excitation which is 
 involuntary. 
 
 The production of a localised sensation implies that the 
 excitation has been conducted in an isolated manner to the mental 
 organs in the brain. But since all sensory fibres pass, either 
 directly or indirectly, through a sensory ganglion-cell, into the 
 frequently mentioned network of fibres, such an isolated conduc- 
 tion seems impossible. Equally unintelligible is that process 
 which may, in a certain sense, be looked upon as the reverse of 
 the preceding, viz. the voluntary production of isolated move- 
 ments. For since the excitation of a motor ganglion-cell can 
 apparently only be brought about by means of the grey network 
 of fibres, which is at the same time connected with every 
 other motor cell, it is by no means clear how excitation can be 
 confined to the one cell concerned. In order to explain these 
 phenomena it is necessary to have recourse to a hypothesis, 
 which will be treated of on p. 479. 
 
 The reflex acts following excitation of the same sensory fibre 
 may be of the most varied kinds. Individual muscles may 
 contract, whereby regular, and, in a certain sense, purpose-like 
 movements may be produced ; or apparently disorderly move- 
 ments may result, in more or less limited muscular regions, or 
 in all the muscles of the body. 
 
 Orderly reflex movements may be best observed in animals 
 the mental organs of which have been removed by separation of 
 the brain from the spinal cord ; and, for the latter operation, 
 frogs are the most convenient. Beheaded frogs when stimulated 
 make regular and purpose-like movements of defence, which 
 
478 ORDERLY REFLEX ACTS. 
 
 differ so little from voluntary movements having the same object 
 that some have ascribed them to mental organs situated in the 
 spinal cord (Pfliiger). Exactly similar reflex movements occur 
 when the mental organs of the brain are rendered inactive 
 during sleep; and involuntary and orderly reflex actions con- 
 tinually occur, even in a wakeful condition, for the purpose of 
 escaping some form or other of stimulation applied to the body. 
 
 A beheaded, or brainless, frog will take up a sitting posture like the un- 
 injured animal; if pinched with forceps it will press with the feet against 
 the instrument in order to push it away; if a drop of acid be placed 
 upon the skin, it whisks it off at once with its feet, &c. These protec- 
 tive movements are very regular, but they admit of variations. If, for 
 instance, that leg be cut off which is employed under ordinary circumstances 
 in the removal of an irritant from a certain spot of skin, another limb will 
 be brought into play, after some ineffectual movements of the stump, for the 
 accomplishment of the same object. In this case the stimulus is not indeed 
 the usual one ; but it has had time, during the vain attempts of the frog to 
 remove the irritant by means of the stump, to reach such an intensity that 
 a mechanical explanation of the phenomenon is still possible. During sleep 
 irritation by tickling, &c. produces unconscious but orderly and purpose-like 
 movements. 
 
 The attempt to explain these facts by assuming the existence of mental 
 organs in the spinal cord will be discussed below. 
 
 Orderly reflex acts have not all a defensive character, many 
 purposive reflex processes having other objects. Thus, it may 
 be observed in frogs whose cerebra have been separated from 
 their spinal cords (Goltz) : 1. That they croak regularly when 
 the skin in the neighbourhood of the back is gently stroked, or 
 when the nerves supplying that skin are mechanically irritated. 
 2. That, during the breeding season, the male will clasp the 
 female firmly and continuously if the back of the latter be 
 applied to the breast of the former, or if any other similarly 
 shaped structure, such as the finger of the experimenter, or the 
 back of a male frog, be similarly applied. On the other hand 
 an uninjured frog does not croak regularly on having its back 
 stroked, and will only clasp an object as it is accustomed to 
 clasp the female if copulation have been interrupted immediately 
 before (Groltz). The consideration of these differences will be 
 resumed hereafter. 
 
 For the performance of orderly reflex acts that portion of the cord with 
 which the implicated sensory and motor nerves are directly connected is all 
 that is necessary. For example, the second experiment above detailed may 
 be shown with only that portion of the trunk bearing the anterior extrerai- 
 
REFLEX MOVEMENTS OF DISORDERLY NATURE. 479 
 
 ties, viz. with the portion of the back between the skull and the fourth 
 vertebra, and the attached shoulder-girdle and arms. 
 
 Besides orderly reflex movements, movements of a disorderly 
 .nature, without any definite object, may occur : such movements 
 are described as reflex convulsions. They only take place under 
 abnormal conditions, as, for example, on very powerful stimula- 
 tion, or after the operation of certain poisons (strychnia), or of 
 certain pathological processes (traumatic and rheumatic tetanus, 
 hydrophobia). They consist of transitory tetanic contractions 
 of single groups of muscles, or of all the muscles of the body, 
 on the application of a sensory stimulus. The less developed the 
 abnormal condition of the spinal cord is, the more limited are 
 the convulsions, and the stronger is the stimulus necessary to 
 induce them. When, owing to an increased development in 
 the abnormal condition, or to an increase in the strength of the 
 stimulus (the stimulus being supposed to be applied to a limited 
 portion of the skin), the reflex convulsions extend over a wider 
 and wider area, they take the following course (Pfliiger) : They 
 are first manifest in the muscles, the motor fibres of which arise 
 in the cord on the same side and at the same level ; then they 
 spread to the muscles supplied by the fibres of the opposite side, 
 but still only to those which are symmetrical with the muscles 
 of the side first affected, and they are never more intense in the 
 latter than in the former ; afterwards the convulsions affect 
 muscles supplied by fibres given off at levels which are nearer 
 and nearer to that of the medulla oblongata ; and, finally, the 
 muscles supplied by all fibres enter into general tetanic convul- 
 sions, which, owing to the superior strength of the extensors, give 
 rise to the appearance known as stretching convulsions. The 
 fibres proceeding from the medulla oblongata may, without any 
 such great extension of the reflex processes, be implicated in 
 convulsions of a reflex nature, as will be shown below. 
 
 In poisoning by strychnia, the slightest disturbance of the patient, such 
 as by a draught of air or a vibration of the couch, is enough to induce a 
 paroxysm. It has recently been observed that, during the condition of 
 apno3a, the reflex convulsions characteristic of strychnia and similar 
 poisons do riot occur (Rosenthal and Leube, Uspensky). 
 
 In order to understand reflex activity, it is necessary to sup- 
 pose a union of motor and sensory ganglion-cells, and, moreover, 
 a union in manifold ways. As direct anastomoses of these cells 
 
480 PATHS OF MORE OR LESS PERFECT CONDUCTIVITY. 
 
 do not occur (Deiters), this union can only be effected by means 
 of the above-mentioned grey network of fibres. But since this 
 network apparently unites all the ganglion-cells of the spinal 
 cord together, while it is certainly possible to understand the 
 extension of the reflex process to all the muscles of the body, 
 as occurs in the general convulsions of strychnine poisoning, it 
 is as difficult to see how the reflex process is ever limited and local- 
 ised, or how it results in orderly acts, as it is to understand the 
 isolated conduction of sensations to the brain, or the voluntary 
 production of isolated movements in the trunk, to which 
 reference was made on p. 477. 
 
 In order, therefore, to reconcile the physiological possibilities 
 with the anatomical facts, it is necessary to assume that under 
 ordinary circumstances there exists throughout the network of 
 fibres a very great resistance to conduction, so that the exci- 
 tation or impression, even at a short distance from the sensory 
 cell, which had been directly stimulated, becomes reduced to an 
 almost imperceptible strength. In consequence, excitation can 
 only be distributed (a) in the neighbourhood of the stimulated 
 cell, causing limited reflex actions, (6) along paths where con- 
 ductivity is more perfect, and which do not originate in the fibrous 
 network at too great a distance from the point of stimulation. 
 Such paths of more perfect conductivity are, apparently, the 
 fibres which were described as emerging from the network and 
 running in the white substance to the brain. In this way the 
 isolated conduction of sensibility, as well as that of voluntary 
 impulses to movement, become intelligible. The latter sort of 
 impressions might be supposed to descend along a fibre of the 
 white substance and to pass into the grey network, where they 
 would be able to enter those motor cells only which were in 
 the immediate neighbourhood of the point of entrance. 
 
 The production of orderly, purpose-like reflex movements 
 remains unexplained on this theory, since it is not certain 
 that, in such movements, the impressions are transferred to the 
 motor cells in the immediate vicinity. It must at least be first 
 shown that the situation of the cells is such that the motor cells 
 respond to the stimulation of the sensory cells nearest them by 
 the most perfect movements for the purposes of defence, an 
 arrangement which is, of course, quite possible. It is, however, 
 quite as probable that, by an inherited perfection of organization, 
 
REFLEX ACTION. INHIBITION OF REFLEX ACTIVITY. 481 
 
 conduction from every sensory cell in the network is especially 
 favoured in certain directions (by a diminution of resistance in 
 those directions), whereby purpose-like movements are subserved 
 or that combinations are formed, more readily capable of con- 
 ducting, by means of the fibres of the white substance. 
 
 The abnormal extension of the reflex process, first of all to 
 neighbouring motor cells, then to motor cells more remote, and 
 finally to the whole number of them, would further be explained 
 by supposing a diminution of the above-mentioned resistance 
 to conduction, which strychnia and the pathological causes of 
 tetanus might be able to bring about in an extraordinary degree. 
 If this were the true explanation, the power of referring 
 sensations to definite localities, and of producing, voluntarily, 
 local movements, would also be prejudiced; but concerning this 
 we have no exact information. 
 
 This hypothesis admits, on the other hand, the possibility of 
 the existence of influences capable of increasing the resistance 
 to conduction, and therefore, of (1) rendering more difficult the 
 production of reflex acts, and (2) rendering keener the powers 
 of localising sensations and voluntary movements ; and such in- 
 fluences have in fact been demonstrated. 
 
 After it had been noticed that the power of reflex action in 
 the region belonging to the spinal cord became more regular 
 and stronger after separation of the brain, certain organs were 
 discovered to exist in the latter which constantly act prejudicially 
 upon the reflex power of the cord, viz. Setschenow's ' inhibitory 
 centres for reflex movements? If, by means of a metronome, 
 the time be measured which elapses between the application of 
 a continuous (chemical) stimulus and the commencement of the 
 resulting reflex action, it will be found to be greater, with the 
 same stimulation, according as the reflex powers of the central 
 organ are slighter, since the stimulus does not acquire an 
 intensity sufficient to liberate the reflex movement until after 
 it has been applied for some time. It will be found that the 
 time between stimulation and the movement induced by it is- 
 less, or, in other words, that the reflex power of the cord is 
 greater, after separation of the brain at a point below the optic 
 lobes; but that the reverse obtains on stimulation of the 
 brain, and especially of the optic lobes, by means of salt 
 solution, or blood, which, according to Setschenow, acts as. 
 
 II 
 
482 INHIBITION BY SETSCHENOW S CENTRES. 
 
 a stimulant to the central organs. The optic lobes, there- 
 fore, exert a constant inhibitory action upon the reflex powers 
 of the spinal cord, which, according to the above hypothesis, 
 must be due to an increase in the resistance to conduction 
 along the grey fibres of the network. Similar inhibitory 
 centres may be demonstrated to exist in mammals (Simonoff). 
 
 The operation of certain depressers of reflex power (morphia, digitaline, 
 etc.) depends upon the stimulation of these centres which they are able to 
 bring about (Setschenow, Weil). Increased venosity of the blood, pro- 
 duced by suffocation, or stagnation in the vessels of the brain, also acts as a 
 stimulus upon them (Rosenthal and Weil). 
 
 The exalted activity of the reflex powers, which is seen after 
 section of the spinal cord in all parts below the line of section, 
 and which is especially noticeable by comparison of the two 
 sides of the body after unilateral section of the cord, was 
 formerly described as < hypersesthesia and hyperkinesia.' It 
 cannot depend entirely upon the removal of the inhibitory 
 centres, since the act of section, during which a stimulation of 
 the nerves which usually convey the inhibitory impression is 
 unavoidable, does not first depress and then exalt the reflex 
 function of the cord, as might have been expected, but, on the 
 contrary, first exalts and afterwards depresses it. It must, 
 therefore, be assumed that section, and the subsequent presence 
 of blood at the surface of section, and other, partially unknown, 
 stimulants, first of all excite and finally exhaust the reflex 
 apparatus (Herzen, Setschenow and Paschutin). This action is 
 one upon the grey substance, while the paths of conduction, 
 which descend from the inhibitory organs, run in the white an- 
 terior columns. 
 
 Hence we are not fully entitled to ascribe to the apparatus 
 inhibitory of the power of reflex action, a constant (tonic) 
 operation. But it follows from what was previously said that 
 the brain has an inhibitory influence upon that power in some 
 other way. While a brainless animal performs with regularity 
 definite movements on the application of a certain stimulus, an 
 animal whose brain is uninjured has the power, evidently by 
 means of its will, of suppressing those movements as it pleases. 
 Just as an uninjured frog is not compelled to croak when its back 
 is stroked, so a man when awake can voluntarily suppress reflex 
 acts which he invariably performs when asleep, and to which, 
 
INHIBITION OF REFLEX ACTIVITY. 483 
 
 even when he is awake, he feels c an almost irresistible impulse.' 
 Such acts are scratching the skin when the latter is irritated by 
 itching ; closing the eyelids when the conjunctiva is touched. 
 (Exactly similar relationships exist in the domain of the brain.) 
 There are, however, reflex actions upon which the will exerts no 
 influence, as, for example, ejaculatio seminis on irritation of the 
 penis, such acts being invariably those which cannot be induced 
 by the will alone without the aid of the reflex power. 
 
 Another kind of inhibition of reflex movements occurs, 
 according to recent observations (Groltz, Setschenow, Nothnagel, 
 Lewisson ), on powerful irritation of the sensory nerves even of 
 animals whose brains have been previously destroyed. For 
 example, the before-mentioned reflex croaking does not take 
 place if the skin of the frog be powerfully stimulated at any 
 point. There must exist, therefore, fibres inhibitory of reflex 
 movements which run from the periphery to the spinal cord. 
 
 Orderly reflex acts do not follow on strong stimulation of the trunks of 
 sensory nerves, owing, probably, to the simultaneous irritation of the 
 inhibitory fibres contained in the nerves (Fick and Erlenmeyer). 
 
 There are, then, three kinds of influence inhibitory of 
 reflex movement : firstly, that exerted by Setschenow's centres j 
 secondly, that exerted by the mental organs ; and, thirdly, that 
 exerted by centripetal fibres. There is no reason to suppose, 
 with Danilewsky, that the first and second kinds are identical, 
 for, in the first place, the centres of Setschenow in the frog do 
 not form part of the cerebrum, which is undoubtedly the seat of 
 consciousness ; and, in the second place, the two kinds of inhi- 
 bitory influence are essentially different, the will either allowing 
 or preventing the production of orderly reflex acts, while 
 Setschenow's centres seem only capable of influencing the de- 
 gree and extent of irregular reflex movements. 
 
 All kinds of reflex movement presuppose that the blood in 
 the vessels of the spinal cord is, to a certain extent, venous ; 
 hence apnoea prevents the occurrence of reflex movements 
 (Eosenthal). 
 
 It has recently been sought to classify reflex acts according to the 
 method of their liberation (Setschenow, Danilewsky). Those induced by 
 means of touching are called ' tactile reflex movements/ to distinguish them 
 from ' pathetic reflex movements/ or such as follow the chemical or 
 otherwise destructive and painful irritation of the skin. These two sorts of 
 
 i i 2 
 
484 NON-IRRITABILITY OF SPINAL CORD. 
 
 inducing, or liberating, impressions have, moreover, been thought to travel 
 along different centripetal paths, since the reflex movements induced by them 
 differ in their nature. Such a distinction which may possibly be supported 
 on anatomical grounds would, at the same time, explain the difference 
 which exists in the power of the mind to refer to their exact locality 
 impressions of a tactile and of a painful nature the former being local- 
 ised by the mind with far more exactness than the latter, which appear 
 to radiate or extend over a considerable surface beyond the point of appli- 
 cation of the irritant. (This difference may, however, be explained in the 
 manner given on p. 486). It would appear, further, that it is only reflex 
 movements of a l pathetic ' nature which are capable of inhibition by means 
 of Setschenow's centres ; while { tactile ' reflex movements, on the other 
 hand, can only be inhibited by means of the will. These differences will be 
 again spoken of. 
 
 The slight knowledge which we possess concerning the paths 
 in the spinal cord along which the characteristic operations of 
 that organ proceed, has been gained partly by direct experiment, 
 partly from observations of pathological conditions, and partly 
 from a study of anatomical arrangement. The experiments 
 referred to consist mainly in observing the effects of partial 
 section of the cord, such as unilateral section, section of in- 
 dividual white or grey columns, section at different levels on the 
 same or on opposite sides, etc. The method mentioned on p. 
 346 for the discovery of paths of conduction, viz. by stimulation ,. 
 cannot be applied in the case of the spinal cord, if it be true, 
 as some observers state, that the cord is not irritable to direct 
 mechanical and electrical stimuli (Brown-Sequard, Schiff, Van 
 Deen, S. Meyer). It must be remembered, however, that this 
 statement is opposed by others (Fick and Engelken, Griannuzzi). 
 For, assuming the statement to be true, no stimuli applied to 
 the spinal cord, except those of a chemical nature, which 
 appear to be partially active, will produce any results if 
 they do not directly excite the root-fibres of some spinal nerve 
 which happens to be traversing the cord at the point of stimu- 
 lation. 
 
 The fibres of the cord proceeding from the vaso-motor centre must be 
 excepted in the above statement, as every stimulation of spinal cord produces 
 narrowing of all the arteries supplied by fibres given off below the point of 
 stimulation (Ludwig and Thiry). Moreover, all stimulations of the 
 substance of the cord, as was mentioned on p. 76, cause reflex irritation 
 of the vaso-motor centre, and raise the blood-pressure (Ludwig and 
 Dittmar). Should the apparent inability of electrical and mechanical 
 stimuli to irritate the cord be really established, notwithstanding the 
 
PATHS OF CONDUCTION IN THE CORD. 485 
 
 assertions to the contrary of Fick and Giannuzzi, it ought rather to be 
 ascribed to an overpowering irritation of such inhibitory fibres as happen to 
 come in the way of the stimulus than to an absolute inability on the part 
 of any conducting portion of the cord to respond to stimulation. In the 
 latter case, it must be supposed that only axis cylinders of the first kind 
 have the general properties of extra-central nerve-fibres, and that the re- 
 maining, specially central, fibres cannot be irritated by the most important 
 nervous stimuli. In order to express that the conducting substance of 
 the cord is only capable of conduction and not of irritation, the terms 
 * sesthesodic * (capable of conducting sensory impressions) and f kinesodic ' 
 (capable of conducting motor impressions) have been applied to it. 
 
 From the effects of partial division of the cord in various 
 ways (Brown-Sequard, Schiff, Setschenow, and others) the 
 following conclusions have been drawn. 1. The conduction of 
 localised sensory impressions, and of motor impressions which are 
 voluntarily restricted to definite sets of muscles, is effected 
 through the white substance. Partial section of the latter severs 
 the connection between the mind and individual regions of the 
 skin and individual groups of muscles. Hence result insensi- 
 bility to tactile impressions anaesthesia, and paralysis of vo- 
 luntary motion. The paths which subserve conduction remain 
 on the same side of the cord as far as the brain, i.e. they do 
 not cross the middle line of the cord. The conduction of sen- 
 sory impressions takes place through the posterior white columns, 
 that of motor impressions through the anterior and lateral white 
 columns. 2. The 'pressor' fibres, which proceed from the pos- 
 terior extremities, course along the lateral columns, and cross 
 the cord partially (Ludwig and Miescher). 3. The conduc- 
 tion of painful impressions, and of involuntary (and especially 
 reflex) motor impulses, takes place through the grey substance, 
 in its whole extent, without any distinctions of sensory and 
 motor tracts. Section of the grey substance, therefore, produces, 
 among other things, a condition in which painful operations 
 cause sensations of touch, but not of pain ' analgesia.' Such 
 a condition frequently supervenes during the narcosis of 
 chloroform, in which case the knife of the surgeon is felt, but 
 no sensation of pain is experienced. This result of section of 
 the grey substance is not restricted to sharply defined regions 
 of the body, as are the results of section of the white substance, 
 but is somewhat regular in all the parts supplied by nerves 
 which enter the cord below the point of section; and it is the 
 
486 COORDINATION. 
 
 more complete according as section has included more of the 
 grey substance. 
 
 These experiments agree well with the phenomena of reflex 
 action and with the discoveries of anatomists. According to all 
 that has been said, a normal, sensory stimulation, a 'tactile 
 stimulus,' after leaving the sensory ganglion-cell, would not 
 travel for any distance in the grey network of fibres, but would 
 speedily make its way into a fibre of the white posterior columns, 
 along which it would be conducted to the organs of the mind, 
 and would there give rise to a localised sensation. The conduc- 
 tion of an impulse along the fibres of the grey network, in addi- 
 tion, stimulates a number of motor cells and, mediately through 
 them, their attached fibres, by which means an orderly reflex 
 act is produced. This reflex act may be inhibited, in some un- 
 known way, by a descending excitation from the will travelling 
 down the white anterior columns from the brain. In like manner, 
 the will, by means of an impulse transmitted down the white 
 anterior and lateral columns, may induce in the grey fibrous 
 network an excitation of limited extent, by which certain 
 motor cells and fibres can be rendered active, and a voluntary 
 and restricted movement produced. 
 
 Violent (' pathetic ') stimulations, on the contrary, produce 
 a stronger excitation of sensory ganglion-cells, an excitation 
 which is capable of more extended conduction through the 
 grey substance than that induced by a more moderate 
 stimulation, and which may even affect the whole of the 
 fibrous network. In the first place a far greater number of the 
 fibres of the posterior columns derived from the network will, 
 consequently, be stimulated, though not all to the same degree, 
 since those fibres which are nearest the excited cell will be more 
 powerfully stimulated than those more remote, on account of 
 the resistance offered by the grey network. Hence results a 
 less exact localisation in consciousness of the sensation (diffused 
 sensations). In the second place an extended conduction of the 
 state of excitation through the fibrous network must call into 
 activity a greater number of motor apparatuses, and, in conse- 
 quence, produce extended, irregular, reflex movements, an effect 
 which may be prevented by an inhibitory impression proceeding 
 from Setschenow's centres and descending in the white substance. 
 Finally, the transmission of the state of excitation through the 
 
TONUS OF VOLUNTARY MUSCLES. 487 
 
 grey substance to the brain seems (though it is still doubtful) 
 to cause a sensation of pain. 
 
 In order to explain the phenomenon of orderly reflex move- 
 ment it is necessary to assume the existence of certain com- 
 binations of ganglion-cells, in which an especially slight 
 resistance is opposed to conduction. In this way arise certain 
 co-ordinations of motor elements, which can apparently be 
 called into activity, not only in a reflex manner, but also by the 
 will, so that the will, in intentional, purposive movements, 
 need not have stimulated each individual fibre supplying the 
 muscles, but may have simply rendered active the same appara- 
 tus as would have been brought into play in the reflex produc- 
 tion of the same movement. If this were not so the mind 
 would have more work than it could accomplish in the produc- 
 tion of the innumerable muscular movements required in such 
 an apparently simple operation as walking. 
 
 It is not yet satisfactorily settled whether the spinal cord 
 possesses automatic apparatuses in addition to those already 
 mentioned. The following automatic functions, which have 
 been ascribed to the spinal cord, will now be discussed. 
 
 1. The Maintenance of the Tonus of Voluntary Muscles. 
 
 By ' muscular tonus ' is understood a constant, slight, and 
 involuntary contraction of all the muscles of the body, but 
 especially of those of animal life, which is dependent upon the 
 nervous system. All the appearances which are usually received 
 as proof of the existence of this constant tonus are, however, 
 capable of explanation in other ways. Thus, the retraction 
 of severed muscles, which was supposed to be due to it, 
 takes place when the nerves supplying the muscles have 
 been previously divided, and is merely due to the fact that 
 muscles in the body are extended somewhat beyond their 
 natural length (p. 242). Again, distortion of the face after 
 paralysis of the facial nerve on one side need not depend upon a 
 deficiency of muscular tonus on that side, but upon the fact 
 that, after contraction of the muscles of the opposite side has 
 once occurred, there are no means of re-extending the muscles 
 to their original shape (p. 257). But the assumption of any 
 such real automatic tonus may be directly disproved by first 
 
488 TONUS OF VOLUNTARY MUSCLES. 
 
 of all making a preparation in which an extended muscle is 
 still connected with its motor nerve and the central nervous 
 system, and then dividing the nerve, when it will be noticed 
 that the muscle does not become in the slighest degree elon- 
 gated (Auerbach, Heidenhain). 
 
 On the other hand, individual voluntary muscles may, under 
 certain conditions, be shown to be under an involuntary and 
 weak contraction, which is not, however, automatic, but reflex 
 in its nature. If a frog be vertically suspended, after having 
 its brain separated from its spinal cord, and the nerves of one 
 of its hinder legs be divided, it will be noticed that the in- 
 jured leg hangs more loosely than the uninjured one. The 
 same results follow if, instead of dividing the whole sciatic 
 plexus of nerves, the posterior roots alone be cut. Hence it 
 must be concluded that the slight flexion of the uninjured limb 
 'is not due to an automatic, but to a reflex action which is 
 liberated by means of the sensory fibres of the limb (Brondgeest), 
 and the necessary irritation of which appears to proceed from 
 the skin (Cohnstein). This contraction does not affect all the 
 muscles of the limb, nor has it been shown to exist at all in the 
 ordinary posture of the body. In the first place, as may be 
 proved, it only affects the flexors ; and in the second it is but 
 another form of the better known phenomenon that a brainless 
 frog strives, in all positions of body, to retract its legs. It 
 has not yet been proved that, after the legs have been drawn 
 up as in sitting, contraction of the flexors continues in the 
 same manner as during suspension, when retraction, on account 
 of the weight, cannot be maintained, except to a slight extent, 
 for any length of time (Hermann). Hence Brondgeest's 
 phenomenon is to be regarded merely as the special continuance, 
 under abnormal circumstances, of a contraction of reflex origin, 
 which is usually transitory. We must conclude, therefore, that 
 the existence of a ' muscular tonus ' is not yet established. 
 
 The influence of section of the posterior roots in diminishing the 
 irritability of the anterior (p. 353), which has recently been contested by 
 Griinhagen and G. Heidenhain, may be explained by reference to the above- 
 mentioned phenomenon (Steinmann and Cyon). 
 
TONUS OF SMOOTH MUSCLES. 489 
 
 2. The Maintenance of the Tonus of Smooth Muscles. 
 
 A. The tonic contraction of the dilatator-fibres of the 
 pupil (p. 377) and the smooth optic muscles of Miiller, which 
 ceases on section of the sympathetic cord in the neck, is said 
 to be under the influence of the spinal cord. The automatic 
 centre for this influence is said to lie in the neighbourhood of 
 the lower cervical and upper thoracic vertebrse (' centrum 
 ciliospinale,' Budge ; c centrum occulo-spinale,' Bernard) ; 
 because, in the first place, as may be shown, the sympathetic 
 cord derives the fibres concerned from the anterior root of the 
 spinal nerve of that locality ; and, in the second place, a con- 
 dition of paralysis or of irritation of the cord in that vicinity is 
 accompanied by corresponding phenomena in the eye ; paralysis, 
 for example, being marked by contraction of the pupil, etc. 
 These circumstances, however, as is easily seen, merely prove 
 that the region of the cord referred to is concerned in the con- 
 duction of the necessary impressions, and not that it is their place 
 of origin. Moreover, since section of the cervical portion of the 
 cord causes contraction of the pupils (Schiff), and prevents 
 dyspnceic dilatation of them (Salkowski), it is evident that some 
 portion of the fibres concerned in the production of this result, 
 and the cause of their tonic excitation, must be above the 
 spinal cord, somewhere in the medulla oblongata. The cilio- 
 spinal centre, therefore, is analogous in function to the rest of the 
 grey substance of the cord, and must be regarded merely as the 
 proximate origin of the fibres to the eye, and, possibly, as reflex 
 in function. 
 
 B. The tonus of arteries (p. 75) is also known to be depen- 
 dent upon the integrity of fibres which are derived from the spinal 
 cord, for unilateral section of the cord causes dilatation of all the 
 arteries of the same side below the level of section. A centre 
 for all these fibres is situated in the medulla oblongata, as will 
 be explained below ; but in this case also the grey substance 
 appears to contain proximate centra of a reflex nature, to which 
 the descending vaso-motor fibres first proceed. The cord must 
 even be supposed to have a share in the tonic excitation of the 
 fibres, for the arterial dilatation following division of the cord 
 below the level of section is not permanent, but soon gives place 
 
490 TONUS OF SMOOTH MUSCLES. 
 
 again to contraction; and permanency of dilatation is not secured 
 until the cord below the point of section is destroyed, when the 
 animals experimented on die, if the area over which dilatation 
 has taken place be sufficiently large (Le Gallois, Groltz). More- 
 over, poisoning by means of strychnia causes contraction of 
 the arteries which have been previously dilated by dividing the 
 cord above (Schlesinger). The vaso-motor nerves descending 
 from the medulla oblongata, as well as the 'pressor' fibres pro- 
 ceeding to it, are contained in the lateral columns of the cord 
 (Dittmar). 
 
 C. The tonus of sphincters. The sphincter ani is con- 
 stantly contracted, for, in order to overcome its resistance, it is 
 necessary to distend the rectum with fluids to a greater extent 
 when the nerves supplying it are intact than when they are 
 divided (GKannuzzi and Nawrocki). The central nervous organ 
 concerned in this constant contraction ('centrum ano-spinale') 
 is situated in the spinal cord, in the dog opposite the lower 
 third of the fifth lumbar vertebra (Budge, Griannuzzi, Masius), in 
 rabbits between the sixth and seventh lumbar vertebrae (Masius). 
 The sphincter of the bladder and its tonus have already been 
 discussed on p. 118, where it was stated that neither the tonus 
 nor even the sphincter-muscle itself have been distinctly proved 
 to exist. The chief cause of the closure of the bladder, viz. 
 the contraction of the urethral muscles (Budge), is most pro- 
 bably reflex in its nature. The central organ concerned in this 
 closure ( c centrum vesico-spinale ') is situated immediately be- 
 low the ano-spinal centre (Masius). The tonic closure of 
 rectum and bladder is regulated by fibres proceeding from the 
 brain (Masius), just as are the other regular reflex acts over 
 which the spinal cord presides. 
 
 Not a single automatic centre, therfore, can with certainty, 
 or even with probability, be assumed to exist in the spinal cord; 
 all the phenomena supposed to depend upon such centres are 
 capable of explanation as processes of the nature of ' orderly 
 reflex actions.' 
 
 The schema of the construction of the spinal cord, represented in the 
 diagram, may serve to make clearer what has been said concerning the 
 physiology of this portion of the nervous system. The figure represents an 
 antero-posterior vertical section, taken a little to one side of the middle line. 
 
SCHEMA OF SPINAL CORD. ENCEPHALON. 
 
 491 
 
 2. Encephalon. 
 
 The continuation upwards of the spinal cord, consisting of 
 medulla oblongata, cerebellum, the so-called cerebral ganglia 
 (corpora quadrigemina, thalami optici, corpora striata, etc.), and 
 
 -^a. 
 
 G s grey substance, "w v white anterior column, w H -white posterior column, v sp. 
 anterior root-fibres, and H sp. posterior root-fibres, of spinal nerves. M G 
 motor ganglion-cell of grey anterior cornu, s G sensory ganglion-cell (?) of grey 
 posterior cornu, 1111 sensory fibres, 2 2 motor fibres, 3 inhibitory fibres, 4 4 
 co-ordinating fibres (?). 
 
 the cerebral hemispheres, contains a great number of central 
 organs concerning the functions and combinations of which 
 extremely little has been discovered. The cerebral hemispheres 
 contain the organs concerned in the psychical functions, as will 
 be shown hereafter. 
 
492 GENERAL ARRANGEMENT OF PARTS. 
 
 One of the chief objects of the physiology of the central 
 nervous system is to investigate the connections between the 
 organ of the mind and the peripheral end-organs, viz. sense- 
 organs and muscles. As far as spinal nerves are concerned it 
 has already been shown that they do not proceed directly to the 
 surface of the cerebral hemispheres ; but that they first enter the 
 grey substance of the cord. This substance is then connected 
 with the brain but still, as will be presently explained, not 
 with the surface of the cerebrum by means of the longitudinal 
 fibres of the white columns. 
 
 Cranial nerves, also, do not communicate directly with the 
 surface of the cerebrum, but first enter certain intermediate 
 central organs, a general view of which is contained in the 
 following statements. 
 
 The grey mass covering the cerebral hemispheres gives off 
 the following systems of fibres, which form the white substance 
 of the hemispheres: 1. Fibres uniting together various regions 
 of the surface on one side (so-called ' associating fibres '). 2. 
 Fibres uniting symmetrical, and perhaps also unsymmetrical, 
 regions of surface of the two hemispheres (so-called ' commissural 
 fibres' passing through the corpus callosum and the anterior 
 commissure). 3. Eadiating fibres running towards the above- 
 mentioned cerebral ganglia or grey masses lying in the interior 
 of the brain (' peduncular fibres '). The third system must con- 
 stitute the bond between the organ of mind and the external 
 world, that is to say, if there is not yet another system (which 
 Broadbent maintains) consisting of fibres which run uninter- 
 ruptedly from the posterior part of the grey matter through the 
 crura cerebri into the white substance of the cord. 
 
 The ganglia at the base of the brain are directly connected 
 with nerves (anterior cranial nerves) and with one another. 
 Finally, the strongest bonds of union pass, by means of the 
 peduncles of the brain, to the cerebellum, and to the grey sub- 
 stance of the medulla oblongata and the spinal cord, and, there- 
 fore, to the proximate termination of almost all peripheral 
 nerves. 
 
 If we regard as the object of all nervous combinations the projection 
 of the surface of the body, in its motor and sensory aspects, upon the plane 
 of the mental organs, the following schema of this projection may be drawn 
 (Meynert) : The first system of projection, perhaps better described as the 
 
SCHEMA OF THE CENTRAL NERVOUS ORGANS. 493 
 
 inner, unites the cerebral cortex with the large ganglia at the base of the 
 brain (the radial system of fibres) ; the second system of projection, or the 
 middle system (the peduncles, etc.), unites the basal ganglia with the grey 
 substance of the spinal cord and the analogous portion of the medulla oblon- 
 gata (viz. the ' central grey tube,' so called because the substance composing 
 it lies about the central canal of the cord and its continuation the calamus 
 sci-iptorius, floor of the fourth ventricle, aqueduct of Sylvius, and third 
 ventricle) ; the third system of projection, or the external, is constituted by 
 the peripheral nerves. The second is weaker than the others ; hence at the 
 points of union of the three systems there is noticed between the internal 
 and middle a reduction, and between the middle and external again an in- 
 crease, in the number of fibres. In the middle system a crossing, probably 
 of all the fibres, takes place, i.e. the fibres cross the middle plane to reach 
 the opposite side of the body. 
 
 This schema, as might be expected, does not hold in its entirety; 
 deviations from it are observable especially in the case of the anterior 
 cranial nerves, in which there appears to be no organ corresponding to the 
 central grey tube, and, therefore, no middle system of projection. 1 Moreover, 
 the fibres above mentioned, which pass from the grey matter of the cortex 
 direct to the central grey matter, would offer an example of deficiency of the 
 middle system of projection. 
 
 The cerebellum forms a centre, laterally situated, which communicates 
 with all the rest, and from which, also, arise nerve-fibres of the external 
 system (portions of the trigeminus and acoustic nerve). 
 
 Fig. 41. 
 
 The annexed diagram serves to explain the three systems of projection : 
 B is the grey substance of the cerebral cortex, G the ganglia at the base 
 of the brain, H is the central grey tube, 1, 2, 3 are the fibres of three systems 
 
 1 Many observers believfe that, in the nerves of special sense, the peripheral 
 ganglion>cells are the organs -which correspond to the central grey tube, considering, 
 for example, the optic fibres as the middle system of projection and the radial fibres 
 of the retina as the external series. 
 
494 FIBROUS TRACTS OF THE ENCEPHALON. 
 
 of projection, a are associating, and c are commissural fibres. The dotted 
 fibres represent the above-mentioned deviations ; for example, 3 represents 
 the optic fibres, and la the combining fibres of Broadbent. 
 
 The combinations of the ganglia at the base of the brain one 
 with another and with the grey substance of the spinal cord, 
 and with its cerebral analogue, are the most difficult to deter- 
 mine, and form the weakest portion of the anatomy of the 
 encephalon. Where the spinal cord becomes medulla oblongata 
 the central canal of the former makes its way to the surface 
 posteriorly in the calamus scriptorius, and forms a shallow groove 
 in the floor of the fourth ventricle. The grey substance sur- 
 rounding the canal, at the same time, reaches the posterior 
 surface and lies spread out on the floor of the groove, the ante- 
 rior cornua being external to the posterior. More superiorly 
 the grey substance assumes the form of scattered grey masses, 
 the so-called 'nuclei' of the posterior cranial nerves, which are 
 clearly the analogues of the grey substance of the spinal cord. 
 The main body of the medulla oblongata consists of white 
 columns, the continuations of the white columns of the cord, 
 which run in part to the ganglia at the base of the brain, viz. 
 to the corpora quadrigemina and through the crura cerebri to 
 the thalami optici, corpora striata, and lenticular nucleus, and 
 in part to the cerebellum. From the white posterior columns 
 of the spinal cord those fibres contained in the funiculi graciles 
 and processus cuneati pass through the crura cerebelli to the 
 cerebellum ; the rest pass through the external bundles of the 
 pyramids and the crura cerebri into the cerebrum (some, as was 
 mentioned above, passing directly to the cortex of the posterior 
 portion); and a small number of fibres run directly into the 
 trigeminal nerve, which thus gets a spinal root. The anterior 
 and lateral columns run partly through the pyramids and crura 
 cerebri to the corpora striata and lenticular nucleus (and, 
 possibly, in part direct to the cortex of the cerebrum), partly to 
 the corpora quadrigemina and through the tegmentum to the 
 optic thalami, and partly through the corpora restiformia and 
 the crura cerebelli to the cerebellum. The cerebellar hemi- 
 spheres, which, according to what has just been said, communi- 
 cate with all the white columns of the cord through their 
 peduncles, are in addition united with the pons, and hence with 
 each other, by means of the crura cerebelli ad pontem; and 
 
ORIGIN OF CRANIAL NERVES. 495 
 
 also to the cortex of the cerebrum, by the crura cerebelli ad 
 corpora quadrigemina, which do not really communicate with 
 the grey substance of the corpora. The medulla oblongata 
 contains, in addition, the hemispherical olivary bodies, about 
 the relations of which little is certainly known. 
 
 The following statements embody what has been discovered concerning 
 the origins of the cranial nerves : 
 
 First pair {Olfactory}. The olfactory tracts lying at the base of the 
 anterior lobe of the brain, and becoming continuous with the olfactory 
 bulbs, are the rudiments of the olfactory lobes of the lower animals largely 
 developed lobes of the brain analogous in structure to the cerebral hemi- 
 spheres. Their white fibres communicate with various portions of the cortex 
 of the cerebrum, and, according to some, with the corpora striata also. 
 From the bulbs arise the olfactory nerves proper, which perforate the cribri- 
 form plate. 
 
 Second pair (Optic}. The optic tracts arise in part from the corpora 
 geniculata extern a and from the thalami optici, and in part from the corpora 
 geniculata interna, and from the anterior corpora quadrigemina. Bending 
 round the crura cerebri, they then form the optic chiasma, in which, accord- 
 ing to some, one half, and according to others, all, the fibres of each tract 
 cross over to the opposite side (p. 417). 
 
 Third pair (Motores oculi) and 
 
 Fourth, pair ( Troclilear or pathetic) arise on each side in the neighbour- 
 hood of the aqueduct of Sylvius, from a grey nucleus, common to both, 
 which communicates with the above-mentioned corpora quadrigemina, and 
 also through the crus with the lenticular nucleus. While the third nerve, 
 piercing the crus to its under surface, emerges close to the pons, the 
 fourth passes upwards, perforates the roof of the aqueduct, crossing at the 
 same time to the opposite side, and bends round the crus, after the fashion 
 of the optic tract, to appear on the surface below. 
 
 Fifth pair (TrigeminaT). The fibres of this nerve have very various 
 origins, a. On a level with the point of exit from the pons is the co-called 
 4 trigeminal sensory nucleus,' the ganglionic cells of which are small, which 
 is analogous to the posterior cornu of the grey substance of the cord ; from 
 it certain of the fibres originate, b. The ascending root is derived from 
 the posterior column of the cord and from a portion at least as low down 
 as the middle of the neck, the fibres springing from the grey substance of 
 the posterior cornu and running in the white posterior columns. At the 
 side of the medulla the fibres run for some distance very superficially. 
 This very sensitive part, situated close behind the processus cuneatus, and 
 sometimes but slightly developed, is the tuberculum Rolandi. c. Descending 
 roots, viz. (1) from the large-celled ' trigeminal motor nucleus,' in the neigh- 
 bourhood of the corpora quadrigemina, concerning the further connections 
 of which with the ganglia of the brain nothing is known; (2) from a 
 collection of large vesicular cells (similar to the cells of the spinal ganglia) 
 -at the side of the aqueduct of Sylvius ; (3) from the locus cseruleus which 
 
496 ORIGIN OF CRANIAL NERVES. 
 
 lies beneath the substantia ferruginea in the upper part of the floor of the 
 fourth ventricle, the fibres being crossed, d. Fibres from the cerebellum, 
 running in the crura cerebelli ad corpora quadrigemina. 
 
 Sixth pair (Abducens). The fibres of this nerve arise from a large-celled 
 nucleus at the bottom of the groove in the floor of the fourth ventricle, 
 at its anterior part. The further connections of this nucleus, which supplies 
 fibres to the facial, are unknown. 
 
 Seventh pair (Facial). This nerve is derived from a nucleus similar 
 to the one last mentioned, though situated somewhat lower, but receives 
 a number of fibres also from the nucleus of the sixth nerve. Another, 
 descending, set of fibres comes from the lenticular nucleus of the opposite 
 side of the body. The connections of the nucleus of this nerve are unknown. 
 
 Eighth pair (Auditory}. This nerve receives fibres chiefly from threo 
 interdependent nuclei, which lie on a level with the broadest (middle) 
 portion of the floor of the fourth ventricle, between and in front of the 
 corpora restiformia. Fibres both from these nuclei and from the trunk of 
 the auditory nerve may be traced into the crura cerebelli and into the cere- 
 bellum, but the other relations of the fibres of the auditory nerve are not as 
 yet known. A portion of the fibres cross between their nucleus of origin 
 and their place of exit. 
 
 Ninth pair (Glosso-pharyngeat) and 
 
 Tenth pair (Par vagum, pneumogastric or Vftfftti) arises from nuclei, which 
 are, in part, common to both, situated in the lower half of the floor of th& 
 fourth ventricle, and in the substance of the medulla oblongata near the 
 olivary bodies. These nuclei supply fibres to the spinal accessory also* 
 Their connections are not known. 
 
 Eleventh pair (Spinal accessory). In addition to the fibres from the 
 nuclei just mentioned, this nerve is supplied from an elongated nucleus lying 
 along the external surface of the anterior cornu and reaching as far down as 
 the fifth cervical vertebra. The fibres leave this nucleus in a great number 
 of roots, which lie in a special line down the lateral column of the spinal 
 cord between the anterior and posterior roots of the cervical spinal nerves. 
 This line is somewhat spiral, being more posterior below. 
 
 Twelfth pair (Hypoglossal'). The fibres of this nerve arise, for the most 
 part, from two large-celled nuclei, situated deeply in the substance of 
 the medulla oblongata, on a level with the lowest portion of the floor 
 of the fourth ventricle. Some of the fibres appear to arise higher up in the 
 brain without touching the nuclei. Certain observers have maintained the 
 existence also of connections with the olivary bodies. 
 
 The statements of anatomists are too incomplete and in- 
 secure for the establishment of any theory concerning the 
 functions of the various parts of the brain. Theories have, 
 however, been set up notwithstanding the deficiency of facts at 
 our disposal. Such a one, for example, is that of Meynert, 
 according to which that division of the crura cerebri which is 
 known as the basis or pedunculus (in the limited sense) which 
 
MEDULLA OBLONGATA. 497 
 
 is connected with the lenticular nucleus and corpora striata, and 
 which is developed in the various members of the animal series 
 proportionately to the cerebral hemispheres, is concerned in the 
 conscious reception of sensations and in the production of 
 movements ; while that portion of the cms which is known as 
 the tegmentum (Haube), and which communicates with the 
 optic thalami and the corpora quadrigemina is concerned in 
 the reflection of impressions from the optic nerves into the 
 motor apparatus. 
 
 Physiological experiments conducted in these regions are 
 most indefinite. The usual plan of investigation, viz. that of 
 applying stimuli to the brain-substance, leads either to negative 
 results (p. 484 ), or, if electrical stimulation is used, to results 
 which, owing to the unavoidable dispersal of the currents in 
 numerous directions, are not sufficiently localised to form the 
 basis for trustworthy conclusions. In the place of exact obser- 
 vations after section and stimulation of different regions, we 
 have here the far less refined method of observation after 
 lesions, lesions induced in the most delicate and complicated 
 organ of the body by means so absurdly rough that, as Lud- 
 wig has forcibly put it, they may be compared to injuries to 
 a watch by means of a pistol shot. The results obtained in 
 this way are attributable to the most diverse causes ; for, apart 
 from the fact that it is impossible to localise the lesion itself, 
 the results may be due to irritation of centres, paralysis of 
 centres, stimulation of conducting apparatus, or paralysis of 
 conducting apparatus, without our being able to say to which* 
 Hence the interpretation of even those phenomena which are 
 constant in their occurrence is always uncertain. 
 
 The third and best method of investigation which is possi- 
 ble is the observation of cases of disease in which the exact 
 nature of the lesions is accurately ascertained after death. 
 
 The facts which may be considered in some degree established 
 are the following : 
 
 A. Medulla Oblongata. 
 
 In the medulla oblongata essentially the same arrangement 
 of parts is noticed as in the spinal cord. The grey substance,, 
 the connections of which with that of the spinal cord, and witli 
 
 K K 
 
498 RESPIRATORY CENTRE. 
 
 the cranial nerves from the sixth (abducens) downwards, have 
 already been described, is, without doubt, the seat of manifold 
 reflex processes in which those nerves are implicated, and of a 
 number of motor impulses, some of which (if not all, as some 
 think) are to be regarded as reflex in their nature, others as 
 automatic. The functions in which the medulla is concerned 
 are of such importance to the whole organism that injuries of 
 this portion of the encephalon are more dangerous to life than 
 those of any other region of brain or spinal cord. 
 
 1. The Centre for the Involuntary Movements of Respira-* 
 tion, and for the Convulsions of Dyspnoea. Lesion of a 
 limited region of the floor of the fourth ventricle at the apex 
 of the calamus scriptorius causes sudden cessation of respira- 
 tion, and instant death to warm-blooded animals. This region 
 is called le no3ud vital, or point vital (Flourens). It extends 
 on both sides of the middle line ; and, if the lesion affect one 
 side only, the respiratory symptoms affect the corresponding side 
 of the body alone. 
 
 According to more recent statements (Gierke) the structure, injury to 
 which abolishes respiration, does not consist of a mass of ganglia, but of two 
 bundles of fine nerve-fibres, which spring in part from the vagus-fibres 
 entering them, and in part from the nuclei of the vagus and trigeminus, and 
 which run towards the spinal cord, whence the proper respiratory nerves 
 arise. While extirpation of the individual nuclei is not alone sufficient to 
 cause respiration to cease, destruction of this, partly intercentral and partly, 
 even, merely centripetal, combination between vagus, trigeminus, and spinal 
 origin of respiratory motor nerves, produces paralysis of respiration. The 
 view that this nervous union constitutes essentially the ' respiratory centre ' 
 seems, however, inadmissible, for the rhythmical character of the excitation 
 can scarcely originate otherwise than in some ganglionic apparatus. It is quite 
 possible that this ganglionic apparatus is situated in the spinal cord itself, 
 if, as is stated, animals poisoned by strychnia still breathe after section of 
 the cord in the cervical region. (P. Rokitansky.) 
 
 It is not yet established whether this centre liberates the 
 rhythmical movements of respiration automatically, or whether 
 its activity is dependent upon the excitation of centripetal 
 nerves, and is, therefore, reflex in its nature (p. 169). The 
 respiratory centre is the only centre concerning which the con- 
 ditions of the automatism (or of the reflex powers) are at all 
 fully understood. Its activity requires : 1. The presence of 
 oxygenated blood, without which irritability disappears. 2. A 
 certain relationship among the gases of the blood, which rela- 
 
RESPIRATORY CENTRE. 499 
 
 tionship acts as a stimulus ; the smaller the amount of oxygen, 
 and the larger the amount of carbonic acid, present in the blood, 
 the more intense becomes the activity of the centre, and the 
 greater the number of muscles which are brought into play 
 (Dyspnoea) ; if the amount of carbonic acid present sinks below 
 ti certain point, the activity ceases altogether (Apncea). More 
 exactly speaking, the respiratory centre consists of two centres, 
 the rhythmical activities of which, although apparently inde- 
 pendent as to strength, alternate as to the time of their phases, 
 viz. one being connected with the inspiratory and the other 
 with the expiratory muscles. Each supplies a definite group 
 of muscles, the members of which, however, are not all equally 
 implicated in movement, more or fewer being rendered active 
 according to the strength of the exciting cause, which varies in 
 proportion as reflex processes are extended in the spinal cord 
 (pp. 479,486). Moreover, these centres possess accelerating and 
 inhibitory nerves, in the sense in which the terms were explained 
 on p. 483. Stimulation of those nerves, whose course has already 
 been given (p. 167), does not seem in general to increase or 
 diminish the activity of the centre, but merely to modify the 
 distribution of the activity in time. The fibres which produce 
 on irritation slowing of the movements of inspiration cause at 
 the same time quickening of those of expiration, and vice versa. 
 With the aid of the conception developed at page 480 we may 
 form the following conjecture as to the influence exerted by these 
 respiratory nerves (Rosenthal) : Both in the case of inspiration 
 and expiration a resistance to the discharge of the energy tending 
 to excite movement must be supposed, which brings about 
 the rhythm of the action. If, now, it be assumed that an in- 
 crease of resistance in the one case increases the force of stimu- 
 lation in the other ; and that, further, stimulation of the vagus- 
 fibres weakens the inspiratory resistance, while that of the superior 
 laryngeal fibres strengthens it, all the phenomena mentioned 
 in Chapter IV. may be accounted for. The normal inspiratory 
 resistance must be supposed to be so slight that no stimulation 
 to expiration, and, hence, no active expiratory movements, occur. 
 If the inspiratory resistance be increased, by stimulation of the 
 slowing, or section of the quickening fibres, in the first place 
 inspiration becomes seldomer and deeper, and in the second, 
 
 K K 2 
 
500 RESPIRATORY CENTRE. 
 
 owing to the activity of expiratory stimulation, expiratory 
 resistance is overcome, and active expiratory movements follow 
 a result which is more marked, both in the number and strength 
 of the expirations, the stronger the stimulus. If, on the con- 
 trary, the inspiratory resistance is diminished, by stimulation of 
 the vagus, in the first place inspiration becomes quicker and 
 shallower, and finally tetanic, and, in the second, if expiration 
 have previously been effected by active (muscular) movements, 
 such active movements entirely disappear. Finally, if stimula- 
 tion be increased, i.e. if the blood become poorer in oxygen 
 or richer in carbonic acid, it is clear that both inspiration and 
 expiration must increase in frequency, strength, and in the 
 number of muscular movements involved ; or, in other words, 
 the condition of dyspnoea supervenes, in which active expira- 
 tory movements occur, such as did not previously take place (p. 
 169). 
 
 The above conditions may be best illustrated by the example already given 
 of gas conducted through a tube under water, only, in this case, the gas must 
 be supposed to be led through a forked tube, the limbs of which dip into 
 different fluids. One of these fluids that representing the normal resist- 
 ance to inspiration must be supposed to be considerably less cohesive than 
 the other, representing that of expiration. Irritation of the vagus corre- 
 sponds to diminution, and irritation of the laryngeus to increase, in the 
 cohesiveness of the first fluid. Dyspnoea corresponds to increase of the 
 pressure under which the gas is forced through the tube. The bubbles which 
 stream up through the first fluid represent the nervous impulses transmitted 
 to the inspiratory apparatus ; those which ascend in the latter to the impulses 
 transmitted to the expiratory mechanism. The illustration shows at the 
 same time that, for simple reasons, in the case when bubbles rise in both 
 tubes (i.e. when inspiration and expiration are both active), they ascend 
 alternately, first in the one and then in the other. 
 
 The increase in the frequency of respiration under increased 
 temperature (p. 167) may be produced by raising the tempe- 
 rature of the brain alone, which is accomplished by placing the 
 carotids in heated tubes (Fick and Groldstein). It is therefore 
 considered to be dependent upon changes occurring in the respi- 
 ratory centre. At high temperatures artificial respiration does 
 not produce apncea (Ackermann). 
 
 If excitation of the respiratory centre reaches an abnormal 
 strength, other muscles besides the normal and accessory muscles 
 of respiration are brought into play, viz., in the first place, the 
 muscles of the jaws, as in gasping, and finally almost all the 
 
CENTRE REGULATING THE HEARTS ACTION. 501 
 
 muscles of the body, as in the general epileptiform convulsions 
 attendant upon suffocation. This is clearly a mere case of ex- 
 tension of the condition of excitation throughout the grey sub- 
 stance of the medulla, and perhaps also of the cord ; and, as a 
 fact, other nervous centres in the medulla are implicated, as the 
 centre for the dilatation of the pupils, the vaso-motor centre, 
 and the cardiac-inhibitory centre. Some observers explain the 
 phenomenon by assuming the existence of a special 6 convulsion- 
 centre ' in the medulla. 
 
 According to recent researches, in which the medulla was directly stimu- 
 lated, the above-mentioned convulsions occur on irritation of a region which 
 (in rabbits) is bounded above by the corpora quadrigemina, below by the 
 alae cinerese, externally by the locus caeruleus, and acoustic tubercle, and 
 internally by the eminentiee teretes. This region, which is stimulated to 
 activity by the presence of asphyxial blood, is not supposed to be the real 
 ' convulsion-centre,' but merely a point from which radiate impulses to 
 movement, which are derived from a reflex convulsion-centre situated in the 
 pons (Nothnagel). 
 
 These convulsions occur not only when the interchange of 
 the gases of the blood is prevented, but also when the blood, or 
 the substance of the brain, is deprived of oxygen or is saturated 
 with carbonic acid, as, for example, when the blood in the blood- 
 vessels of the brain stagnates in consequence of ligature of all 
 the afferent arteries, or when excessive bleeding has occurred. 
 These observations (Kussmaul and Tenner) have led to the 
 designation of ' convulsions of anaemia,' a term which is 
 now no longer admissible when the true nature of the process 
 is understood (Rosenthal), and when it has been found possible 
 to produce the same convulsions by causing venous blood to 
 stagnate in the vessels (Hermann and Escher). 
 
 2. The Centre for the Regulation of the Heart's Action. 
 The centre whence the inhibitory vagus-fibres for the heart 
 receive their stimulation (which, as was explained on p. 72, is 
 possibly rhythmical in its nature) lies somewhere in the medulla 
 oblongata, but its precise situation is not yet known. In 
 warm-blooded animals the centre is constantly active, not, 
 however, as has hitherto been assumed, automatically, but as 
 a consequence of reflex stimulations; for section of certain 
 centripetal nerves releases the 'tonus' of the vagus (p. 78), 
 and, according to Groltz and Bernstein, irritation of them 
 increases its inhibiting powers. It has not yet been determined 
 
502 VASO-MOTOR CENTRE. 
 
 whether the accelerating nerves of the heart also, which will be 
 described when the sympathetic system is treated of, have their 
 centre in the medulla oblongata. 
 
 It is evident that some connection exists between the cardiac inhibitory 
 and the respiratory centres ; for during every respiratory act there occurs a 
 stimulation of inhibitory vagus-fibres (Bonders), which probably coincides 
 with the close of inspiration, but the effects of which, on account of the ' period 
 of latent stimulation ' (p. 257), do not become manifest until the commence- 
 ment of expiration (Pfliiger, Bonders.) 
 
 3. The Vaso-motor Centre. The general vaso-motor centre 
 lies certainly higher than the commencement of the cord, for 
 section of the cord in the cervical region paralyses all the arte- 
 ries of the body (Ludwig and Thiry). It extends in rabbits from 
 about 3 mm above the calamus scriptorius to the upper portion 
 of the floor of the fourth ventricle, but its upper boundary can- 
 not exactly be determined ; and is situated bilaterally, at some 
 distance from the middle line, in that portion of the medulla 
 which contains the continuation of the lateral spinal columns^ 
 in which, as has been already stated, the vaso-motor andpressor 
 fibres run. It contains some large multipolar ganglion -cells 
 (Owsjannikow, Dittmar). It is constantly in action, and its 
 activity is either automatic or, perhaps, merely reflex. The 
 facts in connection with this activity and the influence exerted 
 upon it by the gases of the blood and by the regulating nerves 
 have been already stated (p. 79). The fibres proceeding from 
 the centre pass into the cord, and, after having probably been 
 first interrupted by the grey substance in the manner indicated 
 in the section on arterial tonus, leave it again, set by set, in 
 order to be distributed to the arteries, for the most part along* 
 with fibres from the sympathetic system. Hence, section of 
 the spinal cord causes dilatation of all the arteries in the regions 
 below the point of section, while its irritation produces the 
 opposite condition of contraction (Ludwig and Thiry), the 
 former diminishing and the latter increasing the blood-pressure 
 and temperature of the organism, and acting on the heart in a 
 corresponding manner (p. 234). 
 
 Irritation of the crura cerebri causes contraction of all arteries (Budge). 
 This circumstance does not disprove the former statement that the proper 
 vaso-motor centre lies in the medulla ; it merely shows that the cerebrum 
 can exert some influence upon that centre blushing and growing pale, due 
 
OTHER CENTRES IN THE MEDULLA OBLONGATA. 503 
 
 to psychical causes (Budge) ; the reader should refer also to the effects of 
 removal of the cerebrum upon the action of sensory nerves (p. 79). 
 
 4. The Centre for the Dilatation of the Pupils, and for 
 the Movements of the other Smooth Muscles of the Eye. The 
 exact position of the centre which gives off fibres to the oculo- 
 spinal region of the spinal cord is not known. The centre itself, 
 wherever it he, is constantly active, and, possibly, owing to 
 reflex stimulation. It is under similar influences to the respi- 
 ratory and vaso-motor centres, dyspneea, for example, being 
 accompanied by dilatation of the pupils whilst the optic vessels 
 become pale. 
 
 Many circumstances already alluded to seem to indicate a close connec- 
 tion between the four centres just discussed, especially their stimulation by 
 a certain condition of the blood as to gaseous contents, the coincidence in 
 the rhythm of their action, where such rhythm occurs, &c. (compare pp. 79, 
 169, and 379.) 
 
 5. The Centre for the Movements of Swallowing. The 
 proof that this centre is situated in the medulla oblongata 
 chiefly rests upon the occurrence of convulsive movements of 
 swallowing when that portion of the nervous system is under 
 stimulation, and upon the anatomical fact that the nerves con- 
 cerned in the act are derived from the medulla. The exact 
 situation of the centre is not yet determine^. The centre is 
 only called into activity by reflex stimulations, and must there- 
 fore be put into the same category with the numerous appa- 
 ratuses in the spinal cord for orderly reflex actions (p. 146). 
 
 6. The Centre for the Movements of Mastication. The 
 proofs of the existence of this centre in the medulla 
 are similar to those in the last-mentioned centre, viz. the 
 occurrence of trismus or cramps of the masticatory muscles 
 under similar circumstances to those mentioned above. The 
 centre resembles the spinal apparatuses for orderly reflex actions 
 which are capable of use in regular voluntary movements. 
 
 7. The Diabetic Centre. Lesions of a portion of the floor 
 of the fourth ventricle near the middle line, and extending 
 from a little above the calamus scriptorius to the broadest part 
 of the groove, cause transitory diabetes (p. 189), or sometimes 
 merely increased secretion of urine diabetes insipidus 
 (Bernard). The supposition which was formerly held that this 
 
504 GANGLIA AT BASE OF BRAIN. 
 
 was due to irritation (or, according to others, to paralysis) of 
 a centre for the nerves regulating the formation of sugar in the 
 liver, and which was connected with the vagus, is rendered 
 doubtful in consequence of the altered views of physiologists 
 concerning the processes occurring in the liver (p. 187). Many 
 suppose, as is elsewhere recorded, that it is due to injuries 
 inflicted upon the vaso-motor centre in this region of such a 
 nature as to cause dilatation of the vessels of the liver, 
 kidneys, &c. 
 
 The other functions of the medulla oblongata are not well 
 understood, with the exception of those concerned in the reflex 
 actions already mentioned, in which the lower cranial nerves 
 play a part, as, for example, in the reflex operations in the pro- 
 duction of saliva (p. 96). The use of the olivary bodies is 
 entirely enigmatical. The crossing of the fibrous tracts in the 
 medulla, as well as certain kinds of involuntary movements 
 which follow injuries to it, will be discussed below. 
 
 B. Ganglia at the Base of the Brain, and White Substance 
 of the Brain. 
 
 The region between the medulla oblongata and the surface 
 of the cerebral hemispheres contains a number of extensive 
 grey masses the ganglia already enumerated and a highly 
 complicated system of white fibres, the general distribution of 
 which has also been given. 
 
 In the lower vertebrates, e.g. in frogs, it may be shown 
 that, after the power of conscious action has been abolished by 
 removal of the cerebral hemispheres, the possibility of a number 
 of complicated movements still remains, but that these cease 
 when the other parts of the encephalon situated above the 
 medulla are removed. The animals experimented upon. are, 
 more particularly, enabled to maintain their equilibrium under 
 varying conditions, and (for example) to prevent themselves, by 
 properly adapted movements, from slipping down a plane the 
 inclination of which to the horizontal is gradually increased 
 (Goltz). Moreover, in these regions, in frogs chiefly in the 
 optic lobes which correspond to the corpora quadrigemina and 
 thalami optici, are situated the arrangements whereby the reflex 
 
GANGLIA AT BASE OF BRAIN. 505 
 
 powers of the spinal cord are inhibited (Setschenow). The 
 ganglia at the base of the brain are not only in communication 
 with the grey substance of the cord and medulla, and, through 
 these, with almost all the peripheral organs of the body, but 
 are also connected with the nerves of the higher senses, whereby 
 they are concerned in much more manifold and complicated 
 centripetal excitations than are the simpler reflex apparatuses 
 of the cord ; hence it would seem that they are the seat of 
 reflex operations and co-ordinations of correspondingly greater 
 complexity ; for the complexity of the efferent or centrifugal 
 impulses to activity must increase with the number of afferent 
 or centripetal stimulations. The importance of this region is 
 apparently still further increased by the fact that, besides pos- 
 sessing the means of bringing about excitations in the sub- 
 ordinate groups of centra which it contains, it has the power 
 of inhibiting reflex action. The above-mentioned power of 
 adjusting equilibrium is probably but one slight indication of 
 the functional powers possessed by these organs. The parti- 
 cipation of the higher nerves of sense in those powers will be 
 understood when it is remembered that, in the first place, the 
 objects in the field of vision, as well as the muscular sense of the 
 muscles of the eye, influence powerfully our movements ; l and 
 that, in the second, the auditory nerve is most probably con- 
 nected with peripheral apparatuses which serve to explain the 
 position of the head ; and to these circumstances may be added 
 the centripetal impressions from the whole skin, and from the 
 muscles, the influence of which upon the posture of the body 
 has already been stated (p. 488). 
 
 With the above properties of the portions of the brain now 
 being considered must probably be connected the circumstance 
 that unilateral lesions of them give rise to extremely abnormal 
 movements, ' uncontrollable movements.' The chief forms of 
 these abnormal movements are : (1) movement forwards at the 
 periphery of a circle like that of a horse galloping round a 
 
 1 After observing objects in continual motion, or after rotation of the body, the 
 eyes being kept open, the well-known ' dizziness ' supervenes when the eye is again 
 fixed upon objects at rest. The reason of this lies in the fact that during move- 
 ment the eye has to be rotated in a definite direction in order to remain fixed on a 
 point and that this rotation is afterwards continued by habit when the eye 
 endeavours to become fixed upon a point in repose, thus causing the point to seem 
 to move in the opposite direction (Helmholtz). 
 
 
506 GANGLIA AT BASE OF BRAIN. 
 
 ring; (2) rotation about the longitudinal axis of the body, 
 rolling or wallowing movements ; (3) movement of the an- 
 terior portion of the body about the fixed posterior portion. 
 They follow injuries to the corpora striata, optic thalami, cms 
 cerebri, pons Varolii, and certain portions of the medulla oblon- 
 gata and cerebellum. More exact statements as to the form 
 and direction of the movements cannot with certainty be given. 
 Their direction changes, in consequence of the crossing of fibres, 
 according as the plane of the section is more anterior or pos- 
 terior. The older explanation which assumed the existence of 
 centres for the production of movement in a certain direction 
 which were stimulated by these injuries, is inadmissible, because 
 the movements frequently occur merely as abnormal expressions 
 of an intentional movement, such as of flight. Moreover, lesion 
 of white fibres, viz. of the crura, is sufficient to produce them, 
 and they have been sometimes observed to follow injuries to 
 the cortical portion of the cerebrum. Mere paralysis of indi- 
 vidual groups of muscles for instance, in the case of the first 
 class of abnormal movements previously referred to, of the 
 muscles of the side of the body turned towards the imaginary 
 centre of the circle of movement is also insufficient to explain 
 the phenomena, for this paralysis frequently does not exist. 
 The most probable explanation is the following : Since move- 
 ments are directed in accordance with sensory stimulations from 
 without, assisted by a knowledge of the situation of the parts of 
 the body, especially of the head and of the eyeballs, all injuries 
 which lead to false judgments concerning those matters for 
 example, such as cause misrepresentation as to the position of 
 the head and even injuries to motor tracts which disturb the 
 innervation of the muscles of the head and eyeball, without 
 leading to corresponding impressions, may produce abnormal 
 movements. As a fact, abnormal carriage of the head frequently 
 occurs during such peculiar involuntary movements. Moreover, 
 in the case of movements directed by purely reflex means with- 
 out the intervention of the mind, injuries to the conducting 
 paths may, under certain circumstances, result in similar 
 movements. Galvanisation of the head also causes dizziness, 
 which may even give place to movements of the above-men- 
 tioned description (Purkinje, Hitzig). 
 
 Our knowledge of the special functions of individual ganglia 
 
GANGLIA AT BASE OF BEAIN. 507 
 
 is exceedingly incomplete. The fcorpora quadrigemina, which 
 communicate on the one side with the optic nerve and on the 
 other with the nucleus of the motor oculi, may be shown, both 
 anatomically and experimentally, to form an important reflex 
 centre between the retina and the internal and external muscles 
 of the eye. After destruction of these organs, reflex contraction 
 of the pupils ceases ; irritation of them produces contraction of 
 the pupil of the opposite side, or, according to others, of both 
 sides (Flourens, Longet, Budge). According to more recent 
 statements (Knoll) the above results are said to occur only when 
 the optic tract is implicated, in which case the corpora quadri- 
 gemina would not be a centre for the reflex contraction of the 
 iris. On the contrary, stimulation of the anterior corpus quadri- 
 geminum is asserted to cause dilatation of the pupil of the same 
 side, as long as the cervical sympathetic cord remains intact, 
 and therefore to stimulate the centrum ciliospinale. Stimula- 
 tion of the anterior corpus quadrigeminum also causes rotation of 
 both eyeballs towards the opposite side (Adamiik). 
 
 The thalami optici, which also communicate with the options, 
 do not admit of experimental investigation without the most 
 extensive injury of other parts of the brain. As lesions of the 
 optic thalami produce the peculiar movements above referred to, 
 it is supposed to be through them that the eye influences co- 
 ordinated movements. Pigeons whose cerebra have been 
 extirpated without injury to the thalami optici follow by 
 movement of the head the direction of a light which is carried 
 round them in a circle (Longet). The intimate connection of 
 the optic thalami with the cortex of the cerebrum indicate, in 
 addition, functions concerned in the conscious perception of 
 visual impressions. 
 
 Scarcely any i'acts, save those of an anatomical nature, are 
 known respecting the corpora striata and lenticular nucleus. 
 These organs, which, like the fibres of the crura proceeding to 
 them, have a proportionate development to the cerebrum in the 
 various classes of animals, probably take a part in the produc- 
 tion of conscious sensations and movements, which is, however, 
 quite unknown. Lesions of the lenticular nucleus invariably 
 cause hemiplegia. A species of spasmodic attempt at flight has 
 been recently noticed to follow injuries to the corpora striata 
 (Nothnagel). 
 
508 WHITE SUBSTANCE OF THE BRAIN. 
 
 Nothing' whatever has been discovered with regard to the 
 physiological position and function of the numerous grey tracts 
 of the pons Varolii. 1 
 
 In the mass of white substance extending between the 
 ganglia at the base of the brain and the central grey substance 
 an apparently complete crossing of the fibres from one side 
 to the other takes place. The physiological proof of this lies in 
 the circumstance that pathological changes and injuries situ- 
 ated in one of the cerebral hemispheres are followed by anaes- 
 thesia, or paralysis of voluntary motion only in portions of the 
 opposite side of the body. Not until the lesion has affected, 
 by pressure, &c., the cranial nerves situated at the base of the 
 brain, do symptoms manifest themselves in portions of the 
 head situated on the same side as that of the seat of injury. 
 As to the exact situation where the crossing takes place, the 
 discoveries of anatomists and physiologists do not quite agree. 
 For example, while dissection shows an intercrossing of fibres of 
 the white columns in the anterior white commissure of the cord, 
 unilateral sections of those columns are only followed by 
 paralysis of the same side (Volkmann, von Bezold). The 
 crossed commissural fibres are, therefore, possibly merely co- 
 ordinative in function, like those marked 4 in Fig. 40. Fibres 
 cross over from one side to the other in various situations of the 
 spinal cord : firstly, between the pyramids, where, to judge 
 from the connection with the columns of the spinal cord, both 
 motor and sensory fibres are concerned in the crossing, the 
 former, however, passing over at a lower point ; secondly, in 
 the white raphe or white lamina occupying the mesial plane of 
 the medulla, where occurs, especially, the crossing of the con- 
 necting columns between the grey nuclei of the cranial nerves 
 and the cerebellum, as well as of the fibres running from the 
 nuclei to the peduncles of the brain ; and, thirdly, in the pons 
 Varolii, about the crossing of the fibres of which but little is 
 known. The crossing is completed in the peduncles of the brain. 
 
 The olfactory, optic, and trochlear nerves form very remark- 
 able exceptions to the general rule of the intercrossing of 
 nerves. The olfactory fibres are entirely unilateral. The optic 
 fibres cross outside the brain in the chiasma. According to 
 
 1 It may be here mentioned that nothing is known of the physiological 
 significance of the pituitary body and pineal gland. 
 
CEREBELLUM. 509 
 
 some the crossing is only partial, extending to half the number 
 of fibres ; but it has recently been stated, in support of the 
 view of the entire crossing, that section of the optic nerve 
 causes dilatation of the pupil of the same side, while section of the 
 optic tract causes dilatation of that of the opposite side (Knoll). 
 The same author also states that section of the optic nerve 
 completely releases the tonus of the sphincter iridis, so that 
 section of the motor oculi nerve no longer causes dilatation of 
 the pupil ; and that, therefore, the tonus of the sphincter 
 muscle must be regarded as of reflex origin. The trochlear 
 nerve crosses the middle line after its exit from its nucleus, as 
 well as while within the substance of the brain ; if the crossing 
 of the fibres within the brain is complete, the twofold crossing 
 will of course constitute the nerve practically unilateral. The 
 physiological and pathological facts, which might serve to 
 throw light upon this point, are still wanting. 
 
 C. Cerebellum. 
 
 The cerebellum was formerly, but on insufficient grounds, 
 thought to be the seat of certain psychical functions, as of the 
 sexual instinct (Grail) and certain other voluntary acts. Patho- 
 logical facts and the results of extirpation seem to indicate 
 that it rather resembles the above-described organs in contain- 
 ing a great co-ordinating centre for orderly movements (Flourens, 
 Longet, E. Wagner). Awkwardness in performing movements, 
 frequent falling, and, in birds, the loss of the power of flight, 
 are consequences of its removal, or of disease in its tissues. The 
 connection of the cerebellum with all the columns of the cord, 
 with the ganglia at the base of the brain, and with the cortex of 
 the cerebrum, but especially its intimate relations with the 
 auditory nerve, also renders the above function to a certain ex- 
 tent plausible. It is possible that the auditory nerve, the 
 influence of which in judging of the position of the head has 
 already been repeatedly mentioned, plays a similar part to that 
 of the optic nerve in the co-ordinating apparatus of the middle 
 brain. Deafness does not follow on removal of the cerebellum. 
 In disease of the cerebellum affecting one side only, the disturb- 
 ances of movement appear chiefly to concern the opposite side 
 
510 CEREBRAL CORTEX. 
 
 of the body. Irritation of the cerebellum causes neither move- 
 ments nor, as far as can be judged, sensations of pain. 
 
 D. Cortex of the Cerebrum. 
 
 The cortex of the cerebrum must be regarded as the chief, 
 if not the exclusive, seat of psychical activity. The essential 
 proofs of this are the following : 1. In the animal series the cere- 
 brum is found to be more fully developed in comparison with the 
 mass of the body, and with the encephalon as a whole, in those 
 classes in which the individuals approach, in mental powers, the 
 condition of man. The degree of development is judged of by 
 the weight of the cerebrum and by the number of gyri or ' con- 
 volutions,' for an increase in the latter increases the extent of 
 the superficies, and hence the amount of grey substance. 2. 
 In cases where the cerebrum is abnormally small from birth 
 (microcephalus, cretinismus), or where it is diseased (hydro- 
 cephalus, &c.), there is noticed a corresponding diminution in 
 the higher mental powers, or idiotcy. 3. Injuries, compression, 
 and diseases of the cerebrum are almost always accompanied by 
 mental disturbance peculiarity of demeanour, insensibility, 
 somnolence, or excitement. 4. Kemoval of the cerebral hemi- 
 spheres (which is best accomplished in birds) induces a condition 
 resembling that of sleep, in which all voluntary movement ceases. 
 Nevertheless, movements of a reflex nature occur in response to 
 the stimulation of sense-organs ; but they are so regular in the 
 order of their occurrence that they may be predicted. When 
 the cerebrum is removed in slices, a gradual loss of all the 
 powers of the mind is said to take place (Flourens). 
 
 It has been also maintained that the various degrees of mental ability in 
 man are dependent upon the size, development, and weight of the cerebrum ; 
 the results obtained by weighing are far from supporting this supposition. 
 The height, breadth, and prominence of the forehead are regulated by 
 the development of the cerebrum ; and a measure of the prominence is 
 obtained in the l facial angle,' or angle formed by the intersection of two 
 lines, one of which touches the most prominent point of the forehead, and the 
 symphysisof the two halves of the upper jaw, and the other passes through 
 the base of the skull. The more acute is this angle, the more nearly the face 
 resembles the type of that of the lower animals. The relative development 
 of the cerebral hemispheres is best estimated in animals by comparing them 
 with the corpora quadrigemina, the size of which has evidently no connection 
 whatever with the degree of psychical development. The cerebra of Mono- 
 
STATES OF CONSCIOUSNESS OR MENTAL OPERATIONS. 511 
 
 tremata and Marsupialia amongst mammals are distinguished by the circum- 
 stance that they want a corpus callosum. Of the sulci the fissure of Sylvius, 
 which separates inferiorly and laterally the temporal and frontal lobes, is the 
 most constantly found ; in many mammals (in mice, moles, shrews, and bats) 
 it is the only one present, while in others (in hares, guinea-pigs, beavers, &c.) 
 a few longitudinal furrows and convolutions are added on to the convex 
 surface. In dogs the fissure of Sylvius is surrounded by three concentric 
 furrows, whereby four ' primary convolutions' are formed 5 at the same time 
 a transverse sulcus occurs in the anterior part of the brain, which runs from 
 the upper part of the longitudinal fissure, and is called the ' fissure of Ro- 
 lando,' or ' sulcus cruciatus,' and which is surrounded by the fourth primary 
 sulcus. In many mammalian brains, possessed of a great number of convo- 
 lutions, the primary convolutions are more difficult to make out. 
 
 It is impossible here to enter upon the description and nomenclature of 
 the complicated convolutions of the human brain. 
 
 The nature of psychical operations requires discussion here 
 only in one of its aspects. States of consciousness, or mental 
 operations, which are connected in some unknown way with the 
 material processes of the encephalic organs, entirely elude defi- 
 nition, as has already been said in the Introduction. But it is 
 another question, and one which may engage our attention here, 
 -whether the material processes of those organs form connecting 
 chains between centripetal and centrifugal excitations a species 
 of complicated reflex actions which are independent of the 
 states of consciousness, or mental operations, and to which the 
 latter are attached merely as passive concomitants ; or whether 
 the. latter can actively interfere in the material processes, 
 and so of themselves produce excitation in an organ. The 
 first view seems not to be in agreement with the existence 
 of a free will ; for it has not yet been determined whether 
 the same series of centripetal impressions would not constantly 
 induce in the same organism exactly the same effects, i.e. would 
 call forth the same apparently voluntary movements. The 
 second view presents the difficulty of requiring the assumption 
 that a scientifically undefinable process acts upon material par- 
 ticles which obey physical laws. 
 
 An essential difference between psychical processes and 
 orderly reflex acts lies in the fact that in the latter it is only 
 centripetal stimulations acting at the time which are of effect in 
 inducing them, while, in the former, centripetal excitations 
 which have long gone by may also operate. It is therefore 
 necessary, from the materialistic point of view, to assume the 
 
512 PSYCHICAL PROCESSES AND REFLEX ACTION. 
 
 existence of apparatuses in the mental organs in which centri- 
 petal excitations leave behind them a lasting change. As to 
 the nature of these changes, there exists no ground whatever 
 for supposition. 
 
 On the other hand, we are only entitled to assume the 
 existence of psychical functions in cases where the motor reac- 
 tion following sensory stimulation may be recognised as the 
 associated effect of an excitation which is passed. The other 
 means of deciding the point, viz. the existence or non-existence 
 of states of consciousness, is impracticable, as, strictly speaking, 
 it is impossible to know whether such states occur or not in 
 foreign organisms. Hence we are not justified in ascribing 
 psychical functions to the spinal cord on account of the purpo- 
 sive reactions of headless animals, or of animals asleep, which 
 were previously referred to; for these actions are evidently 
 merely the result of a momentary stimulus, as is shown by 
 the regularity of their occurrence, and are to be regarded, 
 therefore, as pure reflex actions. 
 
 From what has been already stated, a general schema of the 
 central nervous system may be constructed : A centre ( c the 
 central grey matter of the cord '), having apparently no direct 
 connection with the nerves of the higher senses, provides for the 
 simplest reflex acts, in which, essentially, the organs in the 
 vicinity of the body take a part when excited : this the simplest 
 kind of reflex actions might be described as ' plane reflex acts, 
 or reflex acts in one plane.' A second centre of a higher nature 
 (' ganglia at the base of the brain, cerebellum (?) '), which is 
 connected with all the regions dependent upon the first centre, 
 and in addition with the higher nerves of sense, and which 
 possesses also inhibitory fibres controlling the first-named centre, 
 provides for more complicated actions and reflex actions, in 
 which distant parts of the body are concerned, e.g. reactions of 
 the extremities following visual impressions, locomotions which 
 are directed by the eye, &c. A third centre of the highest kind 
 ( c cortex of the brain '), which is in connection with the others, 
 has the property, on the application of certain centripetal 
 impressions during the waking state (?), of becoming so changed 
 for considerable periods, or for ever, that unequal complicated 
 actions may result ; for, in addition to the manifold combina- 
 tions of momentary centripetal impressions, numerous impres- 
 
APHASIA. 513 
 
 sions of the past also have a distinct action in centrifugal exci- 
 tation. The number of the possible combinations is, therefore, 
 so immensely great that there is ample scope for theory to ex- 
 plain all actions as the results of centripetal influences. Ex- 
 citation of this highest centre is accompanied by states of con- 
 sciousness, and here is the limit of physiological observation. 
 
 It is not possible to give more detailed statements as to the 
 arrangements in the centres of the cortex of the cerebrum. The 
 entirely gratuitous phrenological division of the mental func- 
 tions according to f impulses,' and the equally baseless localisa- 
 tion of them in regions of the cerebral cortex, have long been 
 recognised as meaningless and false. It is also impossible to 
 assign any individual spot in the cerebrum as the seat of con- 
 sciousness, since cases are known, in connection with almost every 
 part, in which, when that part was destroyed or was wanting, 
 consciousness still remained. Local defects in the cerebrum 
 merely separate certain regions of the body situated on the 
 opposite side from connection with the mind, while conscious- 
 ness may still remain after destruction of one hemisphere. 
 Unfortunately, we possess no trustworthy experience as to 
 whether, after such destruction, any portion of the images im- 
 pressed on the memory have been effaced, or as to the connec- 
 tion which exists eventually between the place of injury and the 
 loss of memory. 
 
 Unilateral injuries, induced by rupture of the white sub- 
 stance of either hemisphere indicate that the mind communi- 
 cates with the various regions of the body by means of definite 
 fibres. The question now arises, Do these groups of fibres 
 spring from definite regions of the cerebral cortex, or from 
 diverse regions, or even from all portions ? The first of these 
 possibilities seems to be supported by the circumstances that 
 pathological changes affecting a certain anterior portion of the 
 brain, namely, the Island of Reil (which is situated at the 
 bottom of the Sylvian fissure, and which is discovered projecting 
 downwards between the two branches of the fissure), as well as 
 lesions of the grey lamina of the claustrum which is situated 
 between the Island and the lenticular nucleus, induce a condition 
 called c Aphasia,' in which the patient is unable to speak words 
 while retaining the power of writing them. The knowledge 
 derived from experiment concerning the individual sensory and 
 
 LL 
 
514 ELECTRICAL STIMULATION OF THE BRAIN. 
 
 motor functions of the cortex is in the highest degree indefinite. 
 Mechanical lesions occasion, according to most authors, neither 
 pain nor movements. The movements which have recently been 
 induced (Fritsch and Hitzig, Ferrier) by electrical stimulation, 
 since they do not occur after mechanical or chemical stimula- 
 tion, may very well be set down to the irritation of more deeply 
 seated regions, for the latter, are unavoidably exposed to the 
 diffusion of currents. This explanation is especially probable 
 in the case of Ferrier's experiments. According to the results 
 obtained by the observers just mentioned, the anterior parts of 
 the cerebral cortex in particular are connected with the motor 
 arrangements. Experiments with destruction of small parts of 
 the cortex by excision (Fritsch and Hitzig), or by cauterisation 
 by means of injections into the tissue (^Nothnagel, Fournie), 
 resulted for the most part in abnormal postures and movements 
 of individual members, which are attributed (Nothnagel) to loss 
 of muscular sense. No results as to the nature and distri- 
 bution of the functions of the cortex, even of the value of 
 approximations, can be deduced from these experiments. 
 
 Most cases of the above-mentioned ' Aphasia ' depend upon lesions of 
 the left hemisphere, and are accompanied by paralysis of the right half of 
 the trunk (right-sided hemiplegid). It has therefore been concluded, not 
 without opposition, that the so-called f centre of speech ' is un symmetrical 
 unilateral. Cases are, however, known of Aphasia following lesion on the 
 right side (Bouillaud), and the greater frequency of the former kind is 
 referred to circulatory agencies. 
 
 The results of electrical stimulation of the cortex are the following 
 {Fritsch and Hitzig) : Within the arch circumscribed by the four primary 
 convolutions and the sulcus cruciatus (in the dog) is situated, in the anterior 
 region, a spot the irritation of which induces contraction of the cervical 
 muscles ; in the lateral region a similar spot exists for the extensors and 
 adductors, and a little way behind is another for the flexors and rotators of 
 the fore limb, while a fourth for the muscles of the hind limb is found at the 
 posterior part of the space. At the posterior part of the convolution which 
 surrounds the fourth, is found a spot for the muscles supplied by the facial 
 nerve. In spite of the close approximation of the electrodes one to the 
 other, it is impossible to prevent a diversion of the current through the deeper 
 portions of the brain. This surmise is not out of harmony with the fact that 
 slight changes of the position of the electrodes induce changes in the results, 
 for the direction of the diverted currents is very much altered as the elec- 
 trodes are shifted even over small areas. 
 
 We must not omit to mention that there exists in rabbits, in the 
 neighbourhood of the posterior apex of the hemisphere, a spot on injuring 
 which violent but transitory forward and sideward movements result after 
 
CO-ORDINATED AND ASSOCIATED MOVEMENTS. 515 
 
 some time (Nothnagel). In this case it would seem that the movements 
 were due to some hallucination on the part of the animal rather than to a 
 direct motor influence. 
 
 Direct combinations of the cerebral cortex with sensory or 
 motor nerve-fibres of the external system are rendered doubtful 
 on the anatomical grounds above mentioned, and at most only 
 occur in special regions. It seems more probable that the same 
 apparatuses are made use of in the production of conscious 
 sensation and voluntary movement as in the production of 
 reflex acts ot a lower or a higher order. As in the latter 
 motor nerve-centres are so combined that the muscles co- 
 operate in orderly manner to cause reflex action, so it is possible 
 that in orderly voluntary movements also these co-ordinating 
 systems are brought into activity as a whole, whereby the mind 
 is, as it were, spared much labour. This is rendered all the 
 more probable as we cannot voluntarily contract each indi- 
 vidual muscle alone. It is probable that the mental organs are 
 provided not only with inciting fibres, but also with inhibitory 
 fibres, for these centres. Whether intermediate apparatuses, 
 concerned in similar influences exerted on the organs of the 
 mind, are present in the case of centripetal excitations also, is 
 still more doubtful, and such would, at least, be far less 
 intelligible. 
 
 In addition to the above-described purposive co-ordinations 
 of movements, there exist others, which might be described as 
 defects or weaknesses ; in contradistinction to ' co-ordinated,' 
 these are called ' associated ' movements, to the category of 
 which belongs, e.g., the wrinkling of the skin of the forehead 
 during strong bodily (or mental) excitement. It is possible 
 to render oneself, by an act of will, temporarily and, by 
 frequent repetition, permanently, free from these ' movements 
 of association,' as is shown in the independence of the two hands 
 of a pianist. 
 
 Sensations in the region of other fibres than those which have been 
 objectively excited are called 'associated sensations.' One illustration has 
 already previously been given (p. 464), viz. the phenomenon of ' Irradiation/ 
 or the apparent implication in stimulation of regions which were not them- 
 selves excited, in the neighbourhood of an excited cutaneous nerve-fibre, 
 which is owing to the various connections of the grey substance of the cord. 
 In other cases remote fibres also may appear to the mind to have been 
 stimulated, probably because of the closeness of the stimulated and the 
 
 L L 2 
 
516 TIME OCCUPIED BY PSYCHICAL ACTS. 
 
 non-stimulated fibres at their origin in the grey substance j for example, 
 the sensation of tickling in the larynx which follows when the external 
 auditory meatus is touched near the tympanum, both regions being supplied 
 by the vagus. f Irradiation ' also may be diminished by practice, as shown 
 by the more acute perception of the touch (due to the diminution of the 
 areas of sensation) in blind persons. 
 
 By means of the method described on p. 336, and similar contrivances, 
 the rapidity of certain simple psychical processes may be determined. In 
 these experiments (Bonders, De Jaagrr) it appeared that a signal prearranged 
 to be given on a certain stimulation occurred later, the more complicated 
 the psychical operation which was necessary for the production of the signal, 
 and that, in addition, the time varied according to the way in which the* 
 stimulus acted. For example, as a means of experiments, (1) the time 
 which elapsed between a cutaneous stimulus, and the giving of a signal, 
 which had to be varied by the person experimented upon according as the- 
 one or the other of two localities of the skin had been stimulated (i.e. 
 decision had first to be made as to which of the localities had received 
 the stimulus) was 0-066 sec. ; (2) when light was used as a stimulus, a, 
 decision between two colours took 0-122 0-184 sec. ; I, decision between 
 two letters of the alphabet took 0-166 sec., c, decision between five letters 
 took 0*170 sec., the signal consisting in pronouncing the name of the letter 
 which was suddenly exhibited; (3) when the stimulus was auditory, a, 
 distinguishing between two vowels took 0*056 sec., 6, distinguishing between 
 five vowels took 0-069 0*088 sec., the signal consisting in repeating the 
 name of the vowel. 
 
 If objects be allowed to act upon the eye for only a very short time, they 
 are not recognised ; the time during which the eye must be stimulated in 
 order to ensure recognition is, for large letters, about 0-0005 sec., and it is 
 longer the smaller the object and the less it differs from the ground on 
 which it rests. If a second object is presented to the eye immediately on 
 the disappearance of the first, the first must be observed for a longer time in 
 order to be recognised, and the longer according as the second object is a 
 more powerful stimulus, and as the first object is more complicated in 
 form (Helmholtz and Baxt). If, prior to the momentary illumination of 
 an object, the attention be directed to a certain part of it, that part is 
 perceived even though, without having the attention so directed, the 
 illumination would be of too short duration for it to be possible (Helmholtz). 
 
 Psycho-Physical Relations. 
 
 As it is impossible to define the nature of states of con- 
 sciousness, there exists, of course, no measure for them. Never- 
 theless in recent times, in the more exact consideration of those 
 states of consciousness which are most accessible to investigation, 
 viz. the sensations, a method of measurement has, by an artifice, 
 been introduced. By this method a definite relationship appears 
 
FECHNEKS PSYCHO-PHYSICAL LAW. 517 
 
 to have been established between the increase of the state of exci- 
 tation of the mental organ and the increase of the state of con- 
 sciousness (sensation). It must not be overlooked, however, 
 that between the material process in the organ of sense and that 
 in the organs of mind there intervenes a whole series of libera- 
 tions, concerning the relations of which nothing is yet known; 
 we are, therefore, entirely ignorant as to where to localise this 
 relationship, which has been termed ' psycho-physical ' (Fechner). 
 These psycho-physical discoveries were made by determining 
 the slightest increase of stimulus which was perceptible as a 
 sensation, i.e. the increase of stimulus which occasioned the 
 smallest possible increase of sensation. The increase of stimulus 
 is within certain limits constantly proportional to the strength 
 of stimulus already applied (E. H. Weber), i.e. ' the stronger 
 the stimulus (as, for instance, a pressure) already in action, the 
 more must it be increased, in order that the increase may be 
 perceived.' This law holds true in the case of all the organs of 
 sense (Fechner, Volkmann). It follows therefrom that sen- 
 sations increase proportionately to the logarithms of the 
 strength of the stimulus (Fechner). 
 
 If /3 represent a stimulus, y the sensation which corresponds to it, dy the 
 smallest perceptible increase of sensation, and e?/3 the increase of stimulus 
 necessary to produce that increase of sensation, then, according to Weber's 
 law, dy is not proportional to the absolute increase of stimulus dj3, but to the 
 relative increase of stimulus, measured according to the strength of stimulus 
 /3, i.e. to dg. Therefore if & be a constant 
 
 If this equation be integrated, the sensation y being considered as a sum 
 of numerous small increases of sensation, then 
 
 y = k. log. nat. + const. 
 
 If the constant of integration be so chosen that when y =0 18 is equal to b 
 that is to say, if b is the intensity which the stimulus must already have in 
 order to be perceived (' initial ' or ( liminal ' intensity, ' Schwellenwerth ' of 
 Fechner) then 
 
 which expresses that y commences to be positive when /3>J. The formula 
 for y (the l Maassformel ' of Fechner), which becomes valid for every lo- 
 garithmic system by changing the value of Jc, therefore, shows that sensations 
 increase with the logarithms of the stimulus (considered in relation to the 
 1 liminal intensity '), and shows that, in general, with increasing stimuli the 
 
518 FECHNERS LAW. SLEEP. 
 
 sensations (corresponding to the logarithms) increase, at first quickly, and 
 then more and more slowly. 
 
 The resistance which was (p. 480) assumed to be offered by 
 the grey network of the spinal cord, and the magnitude of 
 which determines the extent of the circle of irradiation (p. 464), 
 may, with the aid of certain hypotheses, serve as the starting- 
 point of another deduction from Fechner's formula. 
 
 If it be assumed (1) that the resistance is so constituted that 
 in being propagated the excitation is constantly diminished by 
 an equal fraction of its own value ; (2) that the imperceptible 
 value which it finally attains is equal to the liminal intensity 
 of the stimulus ; and (3) that the intensity of the sensation is 
 proportionate to the magnitude of the area of the circle of 
 irradiation, the same relation between strength of stimulus, 
 liminal intensity, and intensity of sensation is found as is ex- 
 pressed by ' Fechner's formula ' (Maassformel). On the other 
 hand, the empirical determination of the ' formula of intensity * 
 may, by Weber's law, serve for the verification of the above 
 assumptions. It is thus at once found that k in the formula 
 of intensity is inversely proportional to the central resistance 
 (Bernstein). 
 
 It is impossible to enter here upon the further simplification 
 and application of 'Fechner's formula' to special cases. As 
 regards the ' liminal intensity ' of the stimulus it may, how- 
 ever, be remarked that, since the effect of a stimulus depends 
 on many circumstances (intensity, duration, distribution over 
 many or few sensitive elements, suddenness of action, &c.), the 
 4 liminal intensity ' also may be represented in various ways. 
 The stimulus of a musical tone, for instance, may be considered 
 as the product of the number and of the intensity of the com- 
 ponent vibratory stimuli, so that the ' liminal intensity ' of a 
 high tone will correspond to a smaller degree of intensity than 
 the ' liminal intensity ' of a low tone. 
 
 Sleep. 
 
 In the mental organs two states, the physical difference 
 between which is not understood, hold alternate sway with a 
 certain regularity ; these are the waking and the sleeping states. 
 
SLEEP. 519 
 
 There appears to be a kind of sleep in which no mental action 
 whatever takes place, so that the only central organs in operation 
 are those of an automatic and reflex nature. The functions 
 depending upon the central organs of this character, viz. 
 circulation, respiration, secretion, digestion, &c., go on as 
 usual. The reactions to external stimuli which still manifest 
 themselves, and which proceed exactly like those of animals 
 whose cerebra have been extirpated, must be regarded simply 
 as undisturbed orderly reflex movements ; for, as was explained 
 on p. 512, we have no grounds for regarding them as the results 
 of still remaining mental activity, having its seat either in the 
 cerebrum or perhaps in special mental organs (as of the spinal 
 cord, &c.) not in the sleeping state. 
 
 Whether states of consciousness or mental operations occur 
 during sleep can only be decided by one means, that of the 
 memory. From it we learn that incomplete mental actions do 
 very frequently take place in the form of dreams. These are 
 marked by sensations without objective causes (hallucinations), 
 volitions without effect (disappointments in intended but im- 
 possible movements), and processes of thought without the usual 
 logic of the waking state (apparent solutions of problems which 
 seem afterwards when remembered to be absurd). No means 
 exist of determining the duration of dreams. An observation 
 which has frequently been made leads to the belief that possibly 
 most dreams occur only at the moment of awakening or, at least, 
 at the moment of a sudden and momentary release from sleep ; 
 for a dream often ends with a sensation occasioned by some 
 objective cause which, at the same time, brings about the 
 awaking of the sleeper. Hence the fact that extraordinary 
 delusions as to time are an accompaniment of dreams. 
 
 Awaking from sleep appears for the most part to be caused 
 by sensations which must be stronger the deeper the sleep. 
 The depth of sleep may be expressed by Fechner's formula given 
 above, by making the liminal intensity b (i.e. the value which 
 a stimulus must have in order to induce a state of conscious- 
 ness) so great that 7 becomes negative on ordinary stimulations. 
 Direct measurements have shown (Kohlschiitter) that 6, and 
 consequently the intensity of sleep, increases from the com- 
 mencement of sleep, at first quickly, then more slowly, 
 until about the end of the first hour, after which it again 
 
520 SLEEP. CEREBRAL CIRCULATION. 
 
 diminishes, at first quickly and then very slowly, reaching 
 its usual value at awaking-time. Frequently, and without any 
 apparent cause, sleep becomes suddenly less intense, relapsing 
 again to its former depth. As a general statement, the deeper 
 the sleep the longer it lasts. The deeper the sleep, and the 
 greater, therefore, is 6, the stronger must the stimulus /3 be 
 which is requisite to call forth a sensation and cause awaking. 
 
 The chief condition of sleep is the removal as far as possible 
 of all stimuli : hence the stillness and darkness of night are 
 conducive to sleep. Sleep, moreover, seems to come more 
 readily and to be deeper the greater the preceding exertions 
 of the mental organs. During sleep the mental organs are 
 restored to vigour, and the exhausted muscles, which are for 
 the most part relaxed during its continuance, become refreshed. 
 The numerous and well-known phenomena of sleep and dreaming 
 may be passed over without further comment. Concerning 
 the material changes in the brain during sleep, the alterations 
 of blood-pressure, nutrition, &c., we have as yet mere hypothesis 
 unsupported by facts. 
 
 APPENDIX. Circulatory and Nutritive Conditions of the Brain and Spinal 
 Cord. The activity of the central organs is dependent in a high degree 
 upon their blood-circulation, as the consequences of anaemia, hypei'cemia, 
 stagnation, &c., show (p. 501). Special arrangements appear to exist with 
 a view to regulate the blood-pressure. As such may be mentioned : 1. The 
 fact that brain and spinal cord are enclosed in a bony case which they, 
 together with the cerebro-spinal fluid, completely fill. On account of the 
 incompressibility of these parts, and of the unyielding nature of the enclosing- 
 case, cardiac and respiratory variations in the vascular areas appear to be 
 impossible. In order that such variations should occur, either the case must 
 be opened (thus, the brain shows respiratory pulsations when the skull is 
 opened ; and a manometer communicating with the interior of the cranium 
 exhibits respiratory and cardiac oscillations) or the cerebro-spinal fluid 
 must flow out (thus, in injuries to the spine, the brain shows respiratory 
 movements which, as it seems, induce basilar meningitis by "friction, 
 Kosenthal). Artificial or pathological increase of intracranial pressure 
 causes much disturbance of function, presumably depending upon circulatory 
 mischief. 2. The brain, by means of the circle of Willis, is secure from any 
 sudden interruption to circulation by the closure of an artery. 3. Changes 
 of blood-pressure in the brain, which might result from sudden changes in 
 the position of the body (as, for instance, on rising from the horizontal 
 position), are said to be prevented by the thyroid body which forms a 
 collateral blood-reservoir (Liebermeister). If the change of position occurs 
 suddenly a transitory faintness follows. The thyroid body is said to 
 
 ulate blood-pressure in the brain in another way also, since, when 
 
SYMPATHETIC CENTRES AND NERVES. 521 
 
 * 
 
 swollen by the strong influx of arterial blood, it compresses the carotid 
 (Guy on) j that is to say, when the muscles are powerfully excited, the 
 carotids sometimes exhibit no pulsation (Maignien). 4. The vaso-motor 
 nerves of the brain, which traverse the highest cervical ganglion, but do not 
 wholly lie in the sympathetic cord (Nothnagel), are the media for the 
 general regulatory influences such as are described at p. 79. , 
 
 MB&A R y 
 
 I I/ X J V V 
 
 3. Sympathetic Centres and Nerves. 
 
 v CALifrnp\rri 
 
 In general those nerves are described \^s sympathetic,'* ^M^i. 
 irrespective of their origin, which supply the viscera and the 
 vessels. Moreover, the non-medullated nerve-fibres, which 
 are present in such large numbers in sympathetic nerves, are 
 called ' sympathetic fibres.' The origin of these sympathetic 
 fibres is not exactly determined. The numerous ganglion- cells 
 which are aggregated in the large somatic cavities, or are 
 scattered singly through the parenchymata of many viscera, are 
 to be regarded as the principal central organs of the sympathetic 
 system ; but it has been shown anatomically and physiologically 
 that many sympathetic fibres are in communication with the 
 cerebro-spinal organs, partly by means of the rami communi- 
 cantes of the spinal nerves, and partly by means of unions formed 
 with the cranial nerves. This communication has been already 
 alluded to in the description of the oculo-spinal centre (pp. 489, 
 507) and of the origin of the vaso-motor nerves (p. 502). 
 Nevertheless no sympathetic nerve has ever been proved to be 
 in connection with the will, for all the movements of the viscera 
 are completely involuntary. The sensibility of the viscera, 
 also, is so extremely slight that it is supposed to be due to the 
 few medullated (' cerebro-spinal ') fibres which the sympathetic 
 nerve-trunks contain. Smooth muscles are regulated only by 
 sympathetic fibres, and hardly any instance is known of other 
 descriptions of muscles being supplied from this system of nerves. 
 
 The ganglion-cells of the sympathetic and spinal ganglia are surrounded 
 by a capsule covered with squamous epithelium (Frantzel). They give offj as a 
 rule, a straight fibre, and a spiral one which twists round the former (Arnold, 
 Beale) ; hence they are to be regarded as bipolar. It is, however, stated 
 that, in the spinal ganglia, only unipolar cells are found (Courvoisier, 
 Schwalbe). 
 
 The functions of the sympathetic central organs are, as far 
 
522 FUNCTIONS OF CENTRAL SYMPATHETIC ORGANS. 
 
 as is known, the following: 1. To subserve reflex action, which, 
 so far as muscular movements are concerned, is of the pur- 
 poselike, orderly character previously described (p. 477) ; hence 
 co-ordinating arrangements must exist in connection with them. 
 In addition to motor reflex actions we get also secretory. 2. To 
 subserve automatism (motor and secretory). Possibly many 
 of these apparently automatic excitations ought to be classed 
 as reflex: the cerebro-spinal organs cannot be concerned in 
 such excitations, as the functions ('vegetative') which really 
 depend upon the sympathetic system continue for a long time 
 after destruction of these organs (Bidder). In the case of 
 automatic, as of reflex, actions co-ordinating arrangements 
 are recognisable. The rhythmical automatism in sympathetic 
 nerves is under the regulation of inhibitory and accelerating 
 fibres, just as was the case with nerves of the cerebro-spinal 
 system (p. 472). 
 
 The following may be taken as a more particular statement 
 of the functions of the sympathetic organs : 
 
 1. The Ganglia of Parenchymata. Many organs contain in 
 their substance ganglion-cells, by means of which their functions 
 are in part regulated. Such organs are especially the heart, 
 and, according to most authors, the stomach, intestines, uterus, 
 &c. The ganglia of the heart are most easily studied. They 
 possess a rhythmical automatism in virtue of which isolated 
 fragments of the heart pulsate of themselves. In addition, 
 co-ordinating arrangements are present whereby the various 
 segments of the isolated and uninjured viscus contract in 
 regular sequence. Moreover, the rhythm is under the control 
 of accelerating and retarding fibres, both of which sets arise from 
 the cerebro-spinal organs, but the former of which run in 
 sympathetic courses (viz. through the lowest cervical and upper- 
 most thoracic ganglia), while the latter pass along the vagus. 
 The customary assumption that the heart also contains (in the 
 auricle) inhibitory central organs is doubtful. 
 
 The stimulus which produces automatic excitation of the cardiac ganglia 
 is unknown. In the frog's heart it appears to be the oxygen of the air or of 
 the blood, since regular pulsation ceases on excluding the oxygen (Goltz, 
 Cyon), although direct stimulation still induces contraction, the muscles them- 
 selves, therefore, remaining irritable. On the other hand, the presence of car- 
 bonic acid appears to excite the inhibitory system (Traube, Cyon). In the 
 
GANGLION. CERVICAL SYMPATHETIC. 523 
 
 case of mammals the conditions are more difficult to grasp, as it is impossible 
 to experiment with the isolated heart. 
 
 Intestinal peristaltis affords another example of automatic 
 co-ordinated movement brought about by parenchymatous 
 ganglia. In this case also an inhibitory mechanism (for the 
 small intestine) is found in the splanchnic nerves, while it 
 would seem that accelerating fibres reach the intestine from the 
 sympathetic plexuses of the abdomen. The stimulus for this- 
 automatism is also unknown. 
 
 The presence of air increases the movements, as does also an increased 
 venous condition of the blood, caused, for example, locally by stagnation, 
 (p. 148). 
 
 Concerning the innervation of the uterus Chap. XII. may 
 be consulted. 
 
 2. Ganglia, Plexuses, and Sympathetic Cord. Nothing is 
 known about the action of the numerous ganglion- cells found in 
 these structures. Experiments in which stimulation and section 
 have been made use of have merely led to a knowledge of the 
 fibres, derived apparently from the cerebro-spinal organs which 
 chanced to pass through them. The only apparently established 
 fact indicating the existence of reflex powers in a ganglion, viz. 
 the secretion of saliva induced in a reflex manner through the 
 submaxillary ganglion (p. 96), has recently been doubted 
 (Eckhard); for the result follows on electrical stimulation only^ 
 and may be due to a diffusion of the current, which may thus 
 affect the secreting nerves themselves. 
 
 In the cervical portion of the sympathetic the following 
 fibres have been shown to exist : 
 
 1. Vaso-motor fibres for the corresponding half of the head : 
 these have their origin in the cerebro-spinal organ. 
 
 2. Fibres for the dilatator pupillse : these also take origin 
 in the cerebro-spinal organ. 
 
 3. Fibres for the smooth orbital muscle of Miiller, and also,, 
 apparently, for the rectus externus muscle, since section of 
 the cervical sympathetic induces internal strabismus. 
 
 4. Secreting fibres for the salivary glands, and for the 
 lachrymal glands : the origin of these is unknown. 
 
 5. Accelerating fibres for the heart (von Bezold). 
 
 6. The lowest cervical ganglion, besides the highest thoracic 
 
624 THORACIC DIVISION OF THE SYMPATHETIC. 
 
 ganglion (ganglion stellatum\ with which it is frequently 
 united, conducts accelerating fibres to the heart through the 
 third branch of the ganglion (E. and M. Cyon) ; the first and 
 second branches are the roots of the depressor nerve. 
 
 7. Fibres proceeding to the cerebro-spinal organ which call 
 into activity the cardiac inhibitory mechanism. 
 
 8. Fibres proceeding to the cerebro-spinal organ, which 
 stimulate the vaso-motor centre (pressor fibres). 
 
 In the thoracic portion of the sympathetic but few clearly 
 established experimental results have been obtained. The 
 superior thoracic ganglion (ganglion stellatum) conducts to 
 the heart accelerating fibres, which reach the ganglion 
 by way of the cervical sympathetic cord (von Bezold) and 
 the root accompanying the vertebral artery (von Bezold and 
 Bever). 
 
 The plexus cardiacus, belonging to this part of the sym- 
 pathetic system, is constituted of fibres passing to and from the 
 heart and belonging to the vagus, depressor, and sympathetic 
 nerves. In the thoracic portion also arise the splanchnics, 
 major and minor, to which the following fibres may be assigned 
 (spl. major) : 1. Inhibitory fibres for the intestine (p. 148). 
 2. Accelerating fibres for the intestine (surmised from the effect 
 of post-mortem stimulation, p. 148). 3. Fibres inhibiting the 
 renal secretion. 4. Vaso-motor fibres for the extensive vascular 
 region of the abdomen. 5. Centripetal fibres which inhibit the 
 heart in a reflex manner (situated in the frog in the sympathetic 
 cord (Bernstein). 6. Fibres, irritation of which causes an 
 abnormal appearance of sugar in the urine (von Grafe, Eckhard, 
 Ploch). 
 
 Concerning the abdominal portion of the sympathetic we 
 have but few trustworthy statements. Irritation of the cord 
 and the plexuses (coeliac,mesenteric, renal, suprarenal, spermatic, 
 hypogastric) causes for the most part movements, or increased 
 movements, of neighbouring organs, viz. intestine, bladder, 
 ureters, uterus, vesiculae seminales, and spleen (induced, in the 
 last-mentioned organ, by irritation of the plexus lienalis, a 
 branch of the cceliac plexus, Jaschkowitz). Section or extir- 
 pation of the sympathetic cord and plexuses cause chiefly 
 circulatory and nutritive disturbance. It may be mentioned 
 that extirpation of the coeliac ganglia produced, in one well- 
 
THE SUPRARENAL CAPSULES. 525 
 
 established case, a disturbance of digestion, in which undigested 
 food was voided per anum (Lamansky). 
 
 The discoveries which have been made concerning the 
 uterus will be given in Chap. XII., when considering parturition. 
 
 The suprarenal capsules are very rich in nerves and contain 
 in their interior cells resembling ganglion-cells; on this 
 account their function has been supposed to be nervous, but 
 this is as yet unsupported by facts. Other suppositions as to- 
 their nature have already been stated on p. 178. 
 
527 
 
 PART IV. 
 
 ORIGIN, DEVELOPMENT, AND DEATH OF 
 THE ORGANISM. 
 
 CHAPTER XII. 
 
 A. GENERAL OBSERVATIONS. 
 
 THE origin of new organisms is always associated with the 
 existence of others which have preceded them. Since the 
 belief in the free formation of cells has been almost universally 
 abandoned,~one may affirm that no organic form originates in 
 shapeless matter, but that each form is derived from a pre- 
 existing one. The general plan of new formation is either a de- 
 composition of an organism into parts which henceforward 
 develop independently, or the separation of a part which develops 
 individually from an older organism which continues to exist ; the 
 new part may either remain in connection with the old or may 
 separate from it. 
 
 The doctrine of spontaneous or equivocal generation, which ever finds 
 defenders the doctrine which affirms that organised beings do spring from 
 shapeless matter, as in fermenting or decomposing fluids is opposed to the 
 statements made above. 
 
 The apparent proofs of such spontaneous generations are : 
 
 1. The development of vegetable and animal organisms (fungi, 
 infusoria) in infusions of organic substances. 
 
 2. The development of organisms (entozoa) within completely shut 
 cavities. In both cases, however, the organisms spring, as may be proved, 
 from the numerous germs contained in the air; as the infusion remains 
 barren if the air reach it without any germs (these being separated by 
 filtration from it), or if the germs contained in the air be destroyed before 
 
528 SPONTANEOUS GENERATION. 
 
 it reaches the infusion, as by conducting the air through red-hot tubes. 
 The development of entozoa is unquestionably due to the germs which are 
 introduced with the nutriment, and which can in certain stages of their 
 existence wander into the closed cavities of the body. 
 
 Notwithstanding what has been said in opposition to the present 
 occurrence of spontaneous generation, science teaches us that the tem- 
 perature of our globe was once so high that no organised being can have 
 existed upon it, so that at some period in its history a true primordial gene- 
 ration must have taken place. 
 
 The resemblance between the parent organism and its offspring not only 
 extends to the general form, but to peculiarities of formation, which charac- 
 terize not merely the genus, or the species, but even the variety or race to 
 which it belongs, so that peculiarities in form which have arisen acciden- 
 tally can easily be transmitted. 
 
 This constitutes the basis of the attempt to explain the origin of species 
 and genera through inherited and ever increasing varieties in form 
 (Darwin). In order to explain the fact that a variety in form, once present, 
 develops further and further, an assumption suffices, upon which the Darwinian 
 theory is based, viz. that of all existing organisms only a fraction meets with the 
 conditions necessary to continued existence, and that consequently a struggle 
 for existence is going on amongst living beings. In this struggle those 
 beings will always be the conquerors which are endowed with properties 
 which render them adapted to the local conditions in which they are placed. 
 If, therefore, in any animal species a certain variety of form has arisen, which 
 renders the individuals concerned more suited to the existing conditions 
 than their fellows (as, e.g., more able to procure nourishment, to bear par- 
 ticular temperatures, to vanquish foes, to allure the opposite sex for purposes 
 of reproduction), then these individuals will, under the given circumstances, 
 hold the upper hand in the struggle for existence, their peculiarities will bo 
 maintained by inheritance, and by further variation in the same direction 
 will establish a wider and wider separation from the original form. In this 
 way it is possible that from the same stock there may be developed in 
 different localities such deviations that out of varieties there may spring 
 new species, and out of species new genera. 
 
 The inability to discover the transition-forms between two species is 
 easily seen to depend upon the fact that, of all the forms which result from 
 one stem, the extreme forms least of all come into collision in the struggle 
 for existence, whilst the mean forms most easily are destroyed in the 
 process. 
 
 By carrying the same principle further, but in an opposite direction, the 
 surmise is formed that all animal (and vegetable) forms spring but from a 
 few, perhaps even from a single parent form. The Darwinian hypothesis has, 
 also, another fruitful side, in that it destroys specially all teleological specula- 
 tions, by showing that of all possible forms which can exist, only those most 
 adapted to their uses can survive, whilst the others must succumb. 
 
 Seeing that in the breeding of animals the hereditability of certain 
 peculiarities is taken advantage of, and these peculiarities are thereby 
 further developed, the individuals which possess them in a pre-eminent 
 
FISSIPAROUS AND OVIPAROUS REPRODUCTION. 529 
 
 degree being specially cared for and employed in propagation, the principle 
 above alluded to has by its expositor been denominated f natural selection/ 
 
 Forms of Reproduction. 
 
 The fundamental forms of reproduction are the following : 
 
 1. Fission of the existing organism into several pieces (of 
 equal value), which continue to live independently, either 
 united or separated, and which grow to the size of the original 
 organism. This is spoken of as the fissiparous mode of repro- 
 duction. Closely connected to this is the separate continued 
 existence of the pieces of animals which have been artificially 
 divided, and which has often been observed. 
 
 2. Scission of a constituent part of the parent organism. 
 The constituent part may either remain joined to the parent 
 or may separate from it ; in either case it develops indepen- 
 dently of it, whilst the parent continues to exist. If the part 
 which separates is an important multicellular constituent of 
 the parent organism which remains united with it for a time 
 or for ever, the process is termed ' gemmiparous re-produc- 
 tion.' If, however, the separating portion be but a single cell, 
 which develops independently of any connection with the parent 
 organism, the process is termed c oviparous reproduction,' and 
 the cell concerned in this process is called ' germ-cell,' or 4 egg,' 
 or ' ovum.' 
 
 The fissiparous and gemmiparous modes of reproduction 
 only occur in the lowest animal forms. The oviparous mode, 
 on the contrary, occurs throughout the rest of the animal king- 
 dom, even in man, and in many of the lower animals in 
 addition to the first-named processes of reproduction. 
 
 The ovum is the product of a special organ, 'the ovary/ 
 It is only in a few animals that the development of the egg 
 proceeds alone to the very end ('parthenogenesis '). 
 
 In order that development may occur, or at any rate pro- 
 ceed beyond a certain limit, the egg requires, as a rule, contact 
 with a peculiar element. The peculiar element is ' semenj the 
 product of another organ, the ' testicle.' The ovary and the 
 testicle are either (as in the higher animals) found in separate in- 
 dividuals or they are both present in the same individual. In 
 the first case the individual furnished with the ovary is termed 
 female, as distinguished from the male, which is provided 
 
 M M 
 
530 PARTHENOGENESIS. 
 
 with the testicle; in the second case the creature (as in 
 many of the lower animal forms) is said to be 'herma- 
 phrodite.' The contact of semen and ovum is called 
 ' fertilisation ' or c impregnation,' and reproduction by means 
 of eggs which have to be fertilised is spoken of as c sexual re- 
 production ; ' the fissiparous and gemmiparous modes of repro- 
 duction, as well as parthenogenesis, constitute, on the other 
 hand, c non-sexual ' modes of reproduction. 
 
 Undoubtedly parthenogenesis has, hitherto, only been certainly deter- 
 mined to occur in a few species, and in them it only occurs side by side 
 with true sexual reproduction, and yields invariably only individuals of one 
 sex (e.g. in bees and in a species of wasp, only males, in the psychidce 
 females). 
 
 The best known example, that of bees, may here be specially considered. 
 In a bee-hive there occur three classes of individuals, viz. males (which are 
 called the drones), females incapable of reproduction (the working bees), 
 and one female capable of reproducing (the queen bee). The queen bee 
 once in the year, in what may be termed the nuptial flight, is impregnated 
 by one of the drones which surround her, and returns with a full ' recepta- 
 culum seminis.' She is now in a position either to fertilise the eggs which 
 she lays or to leave them unfertilised. Both these events occur, and they 
 are governed by the cell in which the egg is deposited ; in the cells of the 
 drones are placed the non-fertilised, and in the cells of the working bees the 
 fertilised eggs. The emission or non-emission of the semen which is stored 
 up depends either upon the will (instinct) of the queen bee or upon the 
 mechanical relations of the cell into which she thrusts the posterior part of 
 lier body. 
 
 Whether the fertilised ovum develops into a sterile female (working- 
 bee) or into a fully developed female (queen bee) depends upon the feeding 
 of the larvae by the working bees, perhaps also upon the. form and size of 
 the cells. 
 
 A momentary parthenogenetic development occurs in some animals, in 
 Tvhich the non-fertilised egg goes through the early stages of development 
 (first stages of cleavage), and then an arrest occurs ; such a process has 
 Tiitherto been observed in the sow (BischofF), in the rabbit (Hensen), and in 
 the hen (Oellacher). 
 
 Sexual Maturity. Fertility. 
 
 In the case of all organisms the conditions required for re- 
 production first occur at a particular stage of their develop- 
 ment, generally only when their growth is completed, so that 
 the excess of ' the receipts ' over * the expenditure ' of the body 
 which has hitherto served the purposes of growth may thence- 
 forward be used in the production of generative materials, or 
 
FERTILITY. 531 
 
 even (in the case of viviparous creatures) in the nutrition of the 
 developing egg. It is only at this particular period (period of 
 puberty) that in animals of different sexes the complete de- 
 velopment of the germ-preparing organs (ovary and testicle) 
 occurs. Henceforward, however, for long periods of time, often 
 until death, the reproductive process proceeds, generally at 
 regular intervals. The number of the progeny of one indi- 
 vidual, or of one pair of individuals, i.e. their c fertility,' varies 
 very greatly throughout the animal kingdom. In making such 
 a quantitative determination one may start from two different 
 stand-points. If reproduction be looked upon as a function of 
 the maternal organism in relation to other functions, viz. as an 
 expenditure in relation with the other sources of expenditure and 
 income which constitute the whole exchanges of the matter of 
 the body, then we must determine the relation between the 
 weight of the animal and the weight of the reproductive 
 material yielded by it in the condition in which it leaves the 
 body (as eggs in the oviparous, young creatures in the viviparous, 
 semen in male animals). Such determinations (Leuckart) 
 exhibit enormous differences in the expenditure of generative 
 matters ; thus, for example, the yearly generative expenditure 
 of the female organism is, in the human female, about -~ of 
 the body weight, in the sow about J, in the mouse about three 
 times the body weight, in the hen five times, and in the queen 
 bee 110 times the body weight. If now we consider reproduc- 
 tion in relation to the maintenance of the species, we must 
 compare, instead of the weight, the number of the real progeny 
 resulting. The first kind of determination alluded to cannot 
 be utilised for this purpose, for, firstly, the same weight of 
 generative material represents in different species a widely 
 differing number of possible individuals ; and, secondly, a 
 great number of circumstances must concur in order that 
 fertilisation and development should occur, and these circum- 
 stances are relatively only rarely present, so that in general only 
 a small fractional part of the generative material really accom- 
 plishes its end. 
 
 The number of the progeny can, however, only be very rarely 
 determined ; as one may, however, venture to assume that the 
 object of reproduction is to maintain the number of individuals 
 of the species approximately constant, it follows that the 
 
 M M 2 
 
532 FERTILITY. THE OVUM. 
 
 number of the progeny stands in a certain relation to the mean 
 duration of life of the species. If we designate the number 
 of years of the latter by n, the constant number of individuals 
 by a, the number of individuals which must be born in a year 
 
 will be . For each individual being of the species, there will 
 n 
 
 be yearly born in the mean of progeny. How much of this 
 
 Tit 
 
 production falls upon each reproductive individual depends 
 principally on, 1, whether the new creature originates sexually, 
 i.e. by the concurrence of two parents ; 2, the number of re- 
 producing individuals in relation to the total number, as well 
 as the duration of the period of fecundity in relation to the 
 duration of life. The number of germs produced will, in 
 general, exceed the numbers obtained by the above methods, 
 the rarer are the conditions realised necessary for fertilisation 
 and development. 
 
 Sexual Reproduction. 
 
 The egg (ovum) in its simplest form is a globular cell, the 
 granular lecithin-containing protoplasm of which is called the 
 yolk (vitellus). Besides this, many eggs possess a (secondly 
 deposited) secondary yolk (Nebendotter), which occasionally 
 consists of immigrated cells. The vesicular nucleus of the 
 ovum is called the germinal vesicle (vesicula germinativa), and 
 the nucleolus which is seen in the vesicle is called the germinal 
 spot (macula germinativa). In many eggs a cell-membrane 
 cannot distinctly be made out, and in the majority of cases the 
 cell is found surrounded by an envelope of different form and 
 not belonging to it, which, when a vitelline membrane is 
 present, is deposited upon it. This envelope is in its simplest 
 form a structureless, tolerably thick, membrane, so that seen in 
 profile it appears as a bright ring (zona pellucida of mammalia 
 and man). In the majority of eggs it is perforated by numerous 
 canals ; in some it is covered by villus-like processes, the most 
 diverse forms being observed in invertebrate animals. In many 
 animals the envelope possesses a tolerably large opening, which 
 is of importance in the process of fertilisation, and which is 
 called 4 the micropyle ' (Keber) ; this is especially the case in 
 
CHEMICAL CONSTITUENTS OF THE OVUM. 533 
 
 numerous invertebrata and fishes, probably also in higher verte- 
 brata. 
 
 The chemical constituents of the yolk of the egg are princi- 
 pally derivations of lecithin (vitellin, ichthin, protagon (?), see 
 p. 36), various albuminous bodies, a colouring matter related to 
 hsematoidin (p. 28), an amylaceous body, salts and water. 
 
 In many cases the egg possesses accessory envelopes, which it partly 
 brings with it from the seat of its formation in the ovary (as the discus 
 proligerus ; the yellow of the bird's egg is to be looked upon as the en- 
 tire ovarian follicle, and only the germ-disc is the ovum proper), partly 
 it receives on its way through the excretory passages; thus the white 
 and the shell of the bird's egg are formed around it in its passage through 
 the oviduct a passage which is effected by peristaltic movements. In this 
 way are produced the spiral twists of the clialaza. The ovum of the rabbit 
 receives in a similar manner an envelope of albumen as it passes along the 
 Fallopian tube. 1 
 
 The liberation of the mature ovum from the seat of its 
 formation in the ovary occurs at certain periods, the periods of 
 rut or heat, which occur once or several times in the year ; the 
 number of eggs which are liberated at one time varies from a 
 single one (in man) to many thousands. In general, sexual 
 intercourse is only fruitful when taking place during the period 
 of heat or rut. 
 
 The semen consists of a large number of corpuscles, which 
 are of a form peculiar to each species, and which are suspended 
 in a highly albuminous fluid, and which generally move through 
 it in a particular manner. The form of these seminal cor- 
 puscles (zoo-sperms, spermatozoa, or spermatozoids) is similar 
 in all vertebrata and in many invertebrata ; they consist of a 
 globular, oval, or cylindrical (sometimes corkscrew-shaped) body 
 or head and a fine tolerably long thread or tail, which is con- 
 tinually engaged in a whip-like movement. In invertebrate 
 animals numerous other, in part motionless, forms are seen. 
 
 Impregnation consists in contact of the semen with the 
 liberated ovum. This contact happens either within the female 
 
 1 According to recent researches (His) the yolk of the bird's egg consists, in 
 addition to ovum proper (principal yolk) and the germinal vesicle and the accessory 
 yolk, of cells of the membrana granulosa of the follicle which have wandered through 
 the zona. In the mammalian egg, at least, only a small part of the cells of the mem- 
 brana granulosa wander into the egg, the remainder forming the epithelium of 
 the follicle and the ' discus proligerus.' 
 
534 IMPREGNATION. SEGMENTATION. 
 
 organs of generation, into which the semen is conducted, or 
 outside of them, by the semen being poured over the previously 
 extruded ova, or by being accidentally brought in contact with 
 the eggs, as by the surrounding water. Even artificial fertilisa- 
 tion is possible. Very small quantities of semen appear 
 sufficient to fertilise, provided that they contain spermatozoa 
 (Spallanzani). 
 
 The union of the male and female bodies which is required 
 in the first-mentioned mode of impregnation is denominated 
 sexual intercourse or copulation. In the majority of animals it 
 occurs during the period of rut, during which time, along with 
 the special condition of the germ-preparing organs, in both 
 sexes the desire for intercourse, ' sexual appetite,' awakens. 
 Probably in all animals the act of copulation is accompanied 
 by voluptuous sensations. 
 
 The nature of impregnation is as yet unknown. In all pro- 
 bability it is, above all, essential, in order that it should occur, 
 that one or more spermatozoa should penetrate the ovum. 
 At any rate spermatozoa have been found within the fecundated 
 eggs of the most diverse species of animals. The entrance of 
 the spermatozoa occurs, in eggs which possess a micropyle, pro- 
 bably through it, otherwise perhaps by an active penetration of 
 the ovi-sac ; both processes have been observed to occur. 
 
 The development of the embryo commences soon after the 
 contact or penetration of the semen, being brought about, or 
 at any rate furthered by it, in an inexplicable manner. The 
 spermatozoa which have penetrated disappear after a short time ; 
 nothing definite is known in reference to the changes which 
 they undergo. 
 
 Development of the Impregnated Egg. 
 
 The development of the egg begins in all cases with the 
 formation of numerous cells, through a progressive division of 
 the ovum ; this is known as segmentation. Out of the cells 
 which are formed originate the organs of the embryo in so 
 many ways that no general principles applicable to all animals 
 can be laid down. In ova which possess a food-yolk (birds, 
 amphibia, fishes, strictly even mammalia) only a partial segmen- 
 tation occurs, i.e. the whole of the yolk does not take part in 
 
CONDITIONS FOR DEVELOPMENT OF OVUM. 535 
 
 the process, but only that part of it which contains the germinal 
 vesicle, which is called the principal yolk or formative yolk. 
 The non-segmenting food-yolk, which is derived from the gra- 
 nulosa cells of the follicle, undergoes no morphological changes, 
 but it yields its chemical constituents to the embryo so as to 
 build it up, hence its name. 
 
 The development of the ovum takes place in the majority 
 of cases outside the maternal organism, in the most different 
 localities suitable to the process. In the majority of cases a 
 certain temperature is requisite for development, which is 
 partly obtained by the choice of the locality in which the egg 
 is deposited, partly afforded by the sun's heat, and, lastly, 
 partly by the maternal body, given whilst it covers the eggs 
 (hatching); this can also be artificially applied (artificial 
 hatching). 
 
 The second condition necessary to development is the 
 access of oxygen. In the developing egg, as in the already 
 developed organism, processes of oxidation occur, which con- 
 sume oxygen and yield carbonic acid. The exchanges of the 
 gases with the atmosphere, or with the water which contains 
 gases, takes place through porous openings. In many cases 
 the development of the ovum takes place within the maternal 
 organism in a dilatation of the efferent generative apparatus, 
 i.e. in the uterus, as in mammalia and in man. The two con- 
 ditions requisite for development are here realised in a very 
 complete manner ; the temperature is maintained by the sojourn 
 in the equally heated maternal body; the respiration takes 
 place by means of the very early developed vessels of the em- 
 bryo, which form a capillary system in connection with a part 
 of the uterine wall ; the walls of the foetal capillary system 
 come into immediate contact with the maternal capillaries, 
 which are also strongly developed at the above-mentioned 
 part. 
 
 At this spot in the c placenta ' there occurs a passage of 
 oxygen from the blood of the mother into that of the embryo, 
 and of carbonic acid in the reverse direction. The same organ 
 is the medium of the passage of nutritive matters from the 
 body of the mother to that of the embryo. After development 
 has proceeded to a certain point, the egg is expelled through 
 the genital aperture, the process being denominated ' birth.' 
 
536 ALTERNATE GENERATION. 
 
 Modifications of Development. 
 
 The development of the ovum into a complete organism 
 similar to the one from which it is derived does not always take 
 place continuously. In certain classes of animals development 
 is arrested for considerable periods at certain stages ; at these 
 stages of development the organism manifests similar functions 
 to those which are observed when it is completely developed, viz. 
 voluntary motion, capacity to take food, to digest, &c. This is 
 called the ' larval condition,' and the best known examples are 
 afforded by the larval stage in the ' metamorphosis ' of insects. 
 Even reproduction occurs in such larval conditions, by fission and 
 budding ; when this occurs the process is termed ' alternate 
 generation.' As larvae generally possess a thoroughly different 
 form, and as their life cannot be distinguished from that of the 
 fully formed organism, numerous larvae have been described as 
 separate species before their origin and further development 
 were discovered. This has specially occurred in cases of alter- 
 nate generation ; the larvaB which possess the functions of a 
 fully developed animal, including the power of reproduction, 
 and the forms of which differ in an extraordinary degree from 
 that which they ultimately assume, have for long periods of 
 time been held to be distinct animal forms, even to be animals 
 belonging to different classes or orders. 
 
 The leaf-louse may be cited as offering the simplest example of alternate 
 generation. From the fertilised ova of this creature, early in the spring, 
 non-sexual young are developed, and these produce animals similar to 
 themselves which are born alive ; the latter, in their turn, give birth to a new 
 viviparous generation, and the process is repeated during several generations, 
 until finally, later in the autumn, young are born which are partly male 
 and partly female j these copulate and produce fertilised ova which remain 
 inactive during the winter j in spring the cycle of changes again commences. 
 The viviparous generations cannot be looked upon as composed of partheno- 
 genetic females, because they never change into the egg-producing females 
 of the final generation (Leuckart). 
 
 A more complete example is furnished by intestinal worms belonging to 
 the cestode class, e.g. by tape-worms (tcmia soliuni). 
 
 The living tape-worm existing in the intestine of man consists of a head 
 with suckers and booklets, and of a chain of segments (joints), which are 
 smallest near the head and then grow longer and broader. The smallest are 
 the youngest, and these originate continually by a process of budding from 
 the so-called neck. Every joint is to be looked upon as an individual, and 
 
DURATION OF UTERO-GESTATION IN MAN. 537 
 
 contains male and female organs of generation, which develop with age. 
 Sexual congress takes place between these joints, so that the oldest always 
 contain fertilised eggs already in a state of development. These joints 
 (proglottides) are from time to time thrown off, and leave the body with 
 the excrement. Presumably the ova, when they again directly reach a 
 human intestine, can again develop into the heads of tape-worms and 
 generate new joints; there would then be an alternation between two ge- 
 nerations, one increasing by budding and one by a sexual process 
 (hermaphroditic). 
 
 The usual process, however, consists in this, that the ova, previously 
 referred to, find a host in one of the numerous animals into whose bodies 
 they can be introduced with the food, and nearly always by preference the 
 host, in the case of the tcenia solium, is a particular animal species the pig. 
 
 Here the hook-provided embryo bores its way to parts suited for its 
 residence (the liver, the brain, the muscles, the taenia solium in the pig 
 -specially reaching the sub-cutaneous cellular tissue; possibly a part of the 
 way to the organs is travelled over by the embryo finding its way into the 
 blood, giving rise to an embolism and being liberated again), and there 
 develops a bladder-like appendage (cyst) into which it can occlude itself. 
 Thus out of the teenia solium is formed the cystercus cellulosse of the pig 
 (measley pork), which, when the flesh is consumed by man, reaches his 
 alimentary canal, where, by the action of the digestive fluids, it loses its bladder 
 and acquires joints. In other cases, as in the echinococcus hominis (found 
 in the liver, kidneys, &c., and derived from the tsenia echinococcus of the dog's 
 intestine), there originate within a headless bladder, ' acephalocyst,' which 
 develops from the embryo, many small cysts with the heads of tseniee, and 
 within these there often occur new generations. 
 
 In this case two different kinds of non-sexual alternate with sexual 
 reproduction, of which the one, which can pass through many generations, 
 is by budding from the embryo bladder, the other by budding from the 
 ta3nia-heads. 
 
 B. EEPEODUCTION IN MAN. 
 
 The propagation of the human race is effected by a sexual 
 process of reproduction, impregnation taking place internally, 
 and the development of the embryo being intra-uterine. Birth 
 occurs about 280 days after the impregnation* of the ovum. 
 Usually only one ovum, rarely two, still more seldom three or 
 more ova develop at once. 
 
 The period of sexual maturity (puberty) generally com- 
 mences in man between the ages of 13 and 17, being somewhat 
 earlier in woman than in man, and somewhat earlier in hot 
 than in cold climates. In addition to the development of the 
 organs of generation and their appendices (as, e.g., the hair which 
 
538 DURATION OF THE PERIOD OF FECUNDITY. 
 
 covers the pudenda), and the display of the functions connected 
 with this development (menstruation in woman, seminal emis- 
 sions in man ;, there appear at this period many other cor- 
 poreal changes, such as the development of the mammary glands 
 and the growth of the panniculus adiposus in woman, the 
 changes in the voice and the growth of the beard in man. At 
 the same time there occur also certain psychical changes, and 
 the sexual passion manifests itself. 
 
 The period of fecundity continues in woman until about 45 
 or 50 years of age ; in man no certain limit has been ascer- 
 tained to exist. In woman the close of the period of fecundity 
 and the arrest of menstruation are associated with certain bodily 
 changes, especially of the generative apparatus, which are c com- 
 prehended ' in the term fc involution,' but in which the normal 
 cannot yet be sufficiently distinguished from the morbid 
 changes. 
 
 Formation of the Ovum. 
 
 The mature human ovum is globular, and has a diameter of 
 O18-0*2 mm . The external envelope is a tolerably thick, clear, 
 structureless membrane, which presents the appearance of a 
 clear ring (zona pellucida). No membrane has been discovered 
 below this. The yolk is a tough granular protoplasm, probably 
 contractile ; within it, situated usually excentrically, is the 
 germinal vesicle, presenting the appearance of a clear bladder 
 with a dark germinal spot. The existence of a food-yolk sur- 
 rounding the principal yolk is probable. The chemical con- 
 stituents of the human ovum are probably those mentioned at 
 p. 533. 
 
 The formation of the egg takes place in the Graafian follicles 
 of the ovary ; these are spherical bladders, which, when ripe, 
 are about the size of a pea, and are embedded in the stroma of 
 the ovary. Their wall is composed of a vascular capsule, com- 
 posed of connective tissue, which is coated on its inner surface 
 by a stratified epithelium (' membrana granulosa' seu 'germina- 
 tiva'). This epithelium is at a certain spot massed into a mound 
 of cells (cumulus s. discus proligerus), in which the ovum lies 
 embedded. The hollow space in the follicle is filled with a 
 yellow albuminous fluid. 
 
 According to recent researches (Pfliiger, His, Waldeyer, Koster, and' 
 
DEVELOPMENT OF THE OVUM. 53 
 
 others) the development of ova and follicles probably takes place in mam- 
 malia and man in the following manner : 
 
 The connective-tissue rudiment of the ovary, which is a part of the con- 
 nective tissue of the Wolffian body, is covered by a layer of cylindrical cells 
 distinct from the peritoneal epithelium; this very early growing thicker 
 inserts itself into the simultaneously growing stroma of connective tissue 
 By this simultaneous growth there is formed in the ovarian stroma 
 cavernous system of tubes quite filled with cells (Valentin), the so-called 
 egg- tubes (* Eischla'uche '). 
 
 Some of these cells distinguish themselves soon by their size and 
 appearance from the remainder j these are the ovum-cells (according to 
 Pfliiger primordial eggs, which by further division form ova). Later on, 
 the tubes separate into divisions, of which each contains one, a few several 
 egg-cells, surrounded by the smaller cells of the granulosa ; in these divisions, 
 i.e. in the rudiments of the follicles, between the cells, there is formed a 
 cavity filled with liquid, which extends around and divides the cells into 
 one set which lies in contact with the wall of the follicle (inembrana granu- 
 losa), and into another which remains in relation with the other, but which 
 surrounds the ovum (cumulus proligerus) which is now placed peripherically. 
 
 During their maturation the ova acquire their zona pellucida and food- 
 yolk, both of which are presumably products of the layer of cells of the 
 granulosa which lie immediately in contact with the egg (this layer is- 
 distinguished by the cylindrical form of the cells). 
 
 In cases where the food-yolk consists of cells, these are derived from the 
 membrana granulosa, and have wandered through the zona. In the bird's 
 egg all the cells of the membrana granulosa wander, and the yolk represents 
 the entire follicle. 
 
 At determined intervals one or more of the follicles of the 
 ovary reach maturity, i.e. their size and the distension of 
 their walls increase so much, in consequence of the augmenta- 
 tion of their fluid contents, that they burst. As the follicles in 
 ripening always approach the surface of the ovary, and as they 
 lie before their rupture immediately beneath the capsule of 
 connective tissue which invests the organ, the fluid contents, 
 together with the ovum embedded in the cells of the cumulus 
 proligerus, would be extruded immediately into the abdominal 
 cavity. As, however, before the rupture of the follicle, the 
 fimbriated extremity of the Fallopian tube is so apposed to the 
 surface of the ovary that, cup-like, it embraces the follicle, the 
 ovum enters the canal of the Fallopian tube, and is impelled 
 through it into the uterus by the outwardly directed movements 
 of the cilia of the epithelium which lines the tube. 
 
 The process of liberation of the ovum is associated with a 
 capillary hemorrhage from the uterine mucous membrane, 
 
5r 540 MENSTRUATION. CORPORA LUTE A. 
 
 c which, constitutes the phenomenon of 'menstruation.' The 
 T liberation of ova occurs in woman during the whole period of 
 c her sexual life, except during pregnancy and lactation, at inter- 
 -, vals of twenty-eight days, the haemorrhage continuing for seve- 
 ai ral days. Usually only one ovum is extruded at one time ; 
 
 two or more are liberated. 
 In mammalia the liberation of ova (rut or heat) occurs more 
 seldom, viz. once or several times in the year, but in them several 
 ova are generally thrown off within a short period ; in their 
 case, too, a discharge of blood takes place from the organs of 
 generation. 
 
 The object of the haemorrhage appears to be to stimulate 
 the uterine mucous membrane, so as to favour the reception of 
 the ovum in the event of its being impregnated (Pfliiger). 
 In support of this view may be cited the fact that, in animals 
 which possess several placental sites, at the time of 6 heat,' blood 
 merely exudes from those sites. 
 
 The broken and emptied Graafian follicle, which, at most, 
 contains a drop of blood which has entered it during the process 
 of rupture, undergoes special changes, some of which commence 
 before the rupture. The cells of the membrana granulosa 
 increase first, and become filled with a yellow fat, whilst the 
 capsule becomes less and less distinguishable from the stroma of 
 the ovary. 
 
 Thus originates the coi^pus luteum, which progressively re- 
 cedes into the interior of the ovary. After it has attained a 
 certain size (generally before the commencement of the suc- 
 ceeding menstruation, for one generally finds but one corpus 
 luteum in the ovary) it shrivels into a cicatrix, which soon 
 becomes imperceptible, and which sometimes contains crystals 
 of hsematoidin, which are derived from the extravasated blood. 
 At the place where the ovarian capsule was broken there also re- 
 mains a cicatrix, so that, as life advances, the originally smooth 
 surface of the ovary becomes more and more puckered. During 
 pregnancy the last formed corpus luteum is developed much 
 more slowly, and reaches a much greater size, so that before the 
 periodical liberation of ova was known such were alone spoken 
 of as ' corpora lutea vera.' 
 
 The blood which is separated during menstruation is mixed 
 with uterine mucus, with epithelium cells, and mucous corpus- 
 
THE SEMEN. STRUCTURE OF SPERMATOZOIDS. 541 
 
 cles ; it is probably to this admixture that the menstrual blood 
 owes its decided alkalinity, and its inability to coagulate. 
 
 The processes which go on during menstruation are yet, in many respects, 
 obscure j no sufficient explanation has yet been given of the cause of the 
 periodic maturation of the follicles, nor of its relation to the external 
 haemorrhage, nor of the peculiar course which the follicles follow in the ovary 
 before and after their rupture, but especially concerning the mode in which 
 the apposition of the Fallopian tube to the ovary takes place. The discovery 
 of specially arranged unstriped muscular fibres in the fold of peritoneum which 
 supports the uterus, the Fallopian tubes, and the ovaries (Rouget) appears to 
 offer an explanation for the majority of these phenomena. These muscular 
 fibres must, in the first place, bring about the apposition of the orifices of the 
 tubes to the ovary, and in the second place, by compressing the venous 
 trunks, lead to a stasis of blood in the organs of generation ; the conse- 
 quence of this must be to cause a kind of erection in the vessels the structure 
 of which is similar to that of the corpora cavernosa, leading to a haemorrhage 
 within the uterus, but in the ovary to an increase in the contents of a follicle 
 due to the transudation, and ultimately to the bursting of the follicle. 
 
 The further changes which the liberated ova undergo will 
 be discussed farther on, when the results brought about by im- 
 pregnation are considered. 
 
 Formation of Semen. 
 
 Human semen in the condition in which it is evacuated 
 is a very tough, white, alkaline fluid, possessed of peculiar 
 odour, and assuming a more fluid consistence when exposed to 
 air. It is a mixture of the secretions of the glands which 
 empty themselves in the excretory passages, with the original 
 secretion from the testicles ; the latter is alkaline or neutral, is 
 destitute of smell, and dries more readily. 
 
 The semen contains a large number of seminal corpuscles,, 
 about O05 mm long, the body of which is almond-shaped and 
 terminates in a tapering tail. The movements of the sperma- 
 tozoids are pendulum-like or wave-like vibrations of the tail, 
 by which the body is driven forward in a straight line, at a rate 
 varying between O05 mm and 0-1 5 mm in the second, until, meeting 
 with an obstacle, its direction is altered. The movement of 
 spermatozoa is most rapid in semen which has just been evacu- 
 ated ; it is slow or absent in semen from the testicle. The 
 duration of the movement depends upon a variety of circum- 
 
M2 DEVELOPMENT OF SPERMATOZOIDS. 
 
 stances, which, in general, are the same as those which influence 
 the ciliary motion. 
 
 The motion of spermatozoids continues longest in fluids the 
 concentration of which is the same, or very nearly the same, as 
 that of semen, and is especially active in the secretion of the 
 seminal passages (as in the prostatic secretion, Cowper's secre- 
 tion, &c.), as well as in that of the female genital organs. The 
 motion very soon ceases in very dilute fluids, in water and in 
 saliva. Quite independently of the state of concentration, the 
 following substances arrest the secretion : many metallic salts, 
 mineral acids, alcoholic and ethereal substances, &c. On the 
 contrary, the caustic alkalies under certain circumstances 
 restore the arrested movements of spermatozoa. The cause of 
 these movements is quite unknown ; some consider the head to 
 be the active organ of movement (Grohe), and others the tail 
 (Schweigger-Seidel, v. La Valette St. Greorge) ; the relations 
 between the movements of spermatozoa and those of protoplasm 
 and of cilia have already been spoken of in Chapter VIII. 
 
 The principal chemical constituents of the semen are : 
 albuminous bodies, protagon, fats, water, and salts (potassium 
 salts, phosphates). 
 
 The formation of semen takes place in the testicle, the cells of the 'seminal 
 tubes ' furnishing the spermatozoa. The statements relating to the for- 
 mation of the latter in man are not yet certain. Most probably several or 
 many spermatozoa originate in one cell, from nucleated oval vesicles, 
 of which each one develops at one end the tail of a spermatozoon ; 
 ultimately the parent cell falls to pieces, setting free the spermatozoa ; 
 occasionally fragments of the cell remain connected with the spermatozoa 
 and admit of being recognised (Kolliker). According to other observers 
 the semen-forming cells possess but one nucleus, and the nucleus grows as 
 the head of the spermatozoid out of one side of the cell, whilst opposite to it 
 the protoplasm of the cell grows out as the tail of the spermatozoid (v. La 
 Valette St. George). The semen-forming cells originate by division from 
 the glandular cells, which lie in the axis of the tubuli seminiferi (lately 
 different statements have been made on this matter, which are, however, 
 doubtful). The fluid part of the semen originates by unknown secretory pro- 
 cesses in the tubuli seminiferi ; in all probability the specific constituents of 
 the fluid proceed from the same cells which furnish the spermatozoa. The 
 spermatozoa of the tubuli seminiferi exhibit either no movements or only 
 slight ones. The formation of semen appears to proceed continuously. 
 Nothing is known in reference to the nerves which preside over this secre- 
 tion. 
 
 The semen, when formed, after it has passed through the 
 
THE MECHANISM OF ERECTION. 543 
 
 spongy cavities of the c corpus Highmori' and the canals of the 
 epididymis, is carried by the vas deferens into the vesiculce 
 seminales, where it accumulates. On its way it mixes with the 
 secretion of the mucous membrane of the vas deferens, the 
 inferior extremity of which presents racemose glands, as well 
 as with the secretion of the vesiculaa seminales. 
 
 The emission of semen takes place by reflex action through 
 irritation of the penis, during sexual intercourse, during sleep 
 under the influence of weak irritation? associated with volup- 
 tuous dreams (seminal emissions caused by pressure of urine). 
 
 Under normal circumstances, erection of the penis must pre- 
 cede emission of semen, i.e. the three corpora cavernosa become 
 filled with blood, so that the penis becomes lengthened and 
 stiffened, and assumes a rounded prismatic form ; at the same 
 time it becomes erect, and slightly concave on its dorsal sur- 
 face. The nature of erection has not yet been sufficiently made 
 out. 
 
 The corpora cavernosa constitute a communicating system 
 of cavities, in which open the finest twigs of the arteries which 
 run in the septa, and from which the veins proceed. As the 
 septa contain smooth muscular fibres, and can therefore actively 
 alter the lumen of the corpora cavernosa, two explanations of 
 erection are possible, viz. : 1. The flow of blood out of the 
 corpora cavernosa may be hindered by compression of the effe- 
 rent veins. 2. An increased flow of blood into the corpora 
 cavernosa may occur by the cessation of a tonic contraction 
 which is present during rest (Kolliker). 
 
 Both phenomena appear actually to occur, as the following 
 experiments prove : 1. Diminution of a tonic contraction of 
 blood-vessels ; in the dog irritation of the nervi erigentes (fibres 
 which proceed from the sciatic to the hypogastric plexus) 
 causes erection (Eckhard). During this irritation any arteries 
 of the penis which may have been cut across bleed more freely 
 (Loven); erection can therefore not merely be due to a 
 hindered efflux of blood, but it must depend upon the abolition 
 of a contraction of vessels, the mechanism of which is not 
 known ; the pressure of blood in the vessels of the penis, even 
 during the strongest erection, only amounts to one- sixth of the 
 pressure in the carotid artery (Loven). The action of the 
 nerves which influence erection may be placed side by side with 
 
544 THE MECHANISM OF ERECTION. EMISSION. 
 
 that which the fibres of the chorda tympani exert on the salivary 
 glands. 
 
 The vaso-motor nerves of the penis are contained in the 
 pudendal nerve and in the nervi dor sales penis; a section of 
 these alone does not cause erection ; it however prevents erec- 
 tion in the future (Hausmann and Grunther). 
 
 2. A compression of the efferent veins appears to occur, 
 especially when erection is at its height ; this is effected (a) 
 by the m. transversus perinsei, through which the venae pro- 
 fundse pass (Henle); (b) by trabecular projections, composed of 
 smooth muscular fibres, into the veins which compose the plexus 
 Santorini (Langer) ; (c) by the vense proiundse themselves 
 passing through the corpora cavernosa (Langer). The imme- 
 diate centre which presides over erection appears to exist in the 
 lumbar portion of the spinal cord (Groltz). After cutting across 
 the cord between the cervical and dorsal regions, mechanical 
 irritation of the penis of dogs still leads to reflex erection 
 (strong irritation of sensory nerves prevents this, as it does 
 other reflex actions), though not after destruction of the lumbar 
 portion of the cord. The brain is in connection with this 
 centre, as results from the fact that erection of the penis is 
 brought about by psychical conditions, further that it follows 
 irritation of the crura cerebri, of the cervical portion of the 
 cord (Segalas, Budge, Eckhard). Erection often occurs in per- 
 sons who die by hanging. 
 
 The arteries which lead to the corpora cavernosa (' helicine arteries ') 
 follow a very curved course, so that a great increase in the volume of the 
 penis may occur without any dragging of the arteries. 
 
 Sexual Intercourse. 
 
 Whenever the sexual passion is excited, erection sets in, and 
 it precedes the emission of semen. The latter phenomenon only 
 occurs after mechanical irritation of the penis, as occurs during 
 sexual intercourse by its friction against the rugose walls of the 
 vagina. It therefore occurs as a reflex movement. 
 
 The emission of semen from the vesiculae seminales into the 
 urethra probably occurs by peristaltic contraction of the vas 
 deferens and vesiculse seminales, whilst the emission from the 
 urethra is the result of rhythmical contractions of the bulbo- 
 
COITUS. IMPREGNATION. 545 
 
 and ischio-cavernous muscles. The passage to the bladder is 
 shut off by the erection of the c caput gallinaginis,' which at the 
 same time prevents the passage of urine during erection. The 
 secretions from the prostate and from Cowper's glands mingle 
 with the semen which is excreted. Even in the genital organs 
 of woman, as a result of the sensory irritation which takes place 
 during coitus, certain reflex movements occur, which probably 
 further the passage of semen into the most internal organs. 
 Amongst such movements have been surmised the assumption 
 of a more perpendicular position by the uterus, which is perhaps 
 due to an erection of this organ (Kouget), and, probably, peri- 
 staltic movements of the uterus and Fallopian tubes, taking 
 place in the direction of the ovaries (such movements have at 
 any rate been observed to occur in the lower animals). Such 
 movements would explain how a portion of the semen is con- 
 ducted to the ovary, in spite of the movements of the ciliated 
 epithelium, which are opposed to its passage, as the irregular 
 movements of the spermatozoa could not be utilised in effecting 
 the passage upwards. After emission of semen erection very 
 soon ceases, as well as the psychical and physical excitement 
 which accompanies it ; the latter disappears^ more rapidly in 
 man than in woman. In both sexes there ensues an exhaus- 
 tion, which continues for some time. 
 
 Impregnation. 
 
 The seat of contact between ovum and semen has not yet 
 been determined with certainty, but in all probability it occurs 
 generally in the ovary itself, or in the vicinity of the Fallopian 
 tubes, seeing that in mammalia, after intercourse has taken 
 place, the surface of the ovaries is generally covered with sper- 
 matozoids (Bischoff) ; in this way is to be explained the occa- 
 sional occurrence of ovarian and abdominal pregnancies. Closely 
 connected with this question is the one as to whether, with 
 sexual intercourse, there is associated a liberation of ova similar 
 to that which occurs during menstruation, or whether, in fertile 
 coitus, only the ova which are liberated before or after menstru- 
 ation are impregnated. In favour of the latter view is the ana- 
 logy with mammalian animals which can only be impregnated 
 during the 6 period of heat.' As the human female can be 
 
 N N 
 
546 IMPREGNATION. DEC1DUJ?. 
 
 impregnated at any time, we must, if intercourse cannot effect 
 a liberation of ova, suppose that either the still present ovum 
 of the last menstruation remains capable of fertilisation, and 
 is actually impregnated, or that the semen remains in the female 
 generative organs, perhaps even in contact with the ovary, until 
 the next ovum is liberated, and is still able to fertilise it. Pro- 
 bably both processes occur. Concerning the process of im- 
 pregnation and the first stages of development, there exist, in 
 the case of man, no direct observations. We are therefore here 
 compelled to reason by analogy from the other mammalia, as 
 must necessarily be done in the exposition which is to follow of 
 the processes of development. The youngest fecundated ova 
 obtained as a result of miscarriage, or of the death of the mother, 
 exhibit only tolerably advanced stages of development. 
 
 The impregnated egg is most probably impelled by the 
 ciliary motion of the mucous membrane of the Fallopian tube 
 into the uterus, to the mucous membrane of which it attaches 
 itself, and in which it is usually found embedded. Presumably 
 the process proceeds in such a manner that the surrounding 
 parts of the mucous membrane increase in size, and grow over the 
 ovum, the portion which has grown over, which is called the 
 4 decidua reflexa,' increasing in size with the ovum. 
 
 According to another view the ovum places itself behind the 
 uterine mucous membrane (decidua vera), and thrusts it before 
 itself ; according to Funke, the process consists in the ovum 
 sinking into a uterine gland, as is really the case in the guinea- 
 pig, and perforating its base. 
 
 At a later stage of development, after the embryonal vessels 
 have been formed, an intimate interlacement with those of the 
 mother takes place (placenta). The excessive development of a 
 corpus luteum (verum) during pregnancy points to the periodic 
 liberation of ova being interrupted by it. The interruption 
 usually continues during lactation, as is evidenced by the fact 
 that menstruation usually is absent, and especially because 
 fresh corpora lutea are usually not formed in suckling women. 
 
 An incipient formation of a decidua appears to occur with each libera-* 
 tion of an ovum, the uterine mucous membrane being swollen; and this 
 appears to be the cause of the menstrual haemorrhage (Pfliiger). 
 
SEGMENTATION. GERM-VESICLE. 547 
 
 C. DEVELOPMENT OF THE OVUM IN THE 
 MAMMALIA AND MAN. 
 
 Segmentation. 
 
 The first process in the development of the ovum is that 
 of segmentation. 
 
 It begins in mammalia as early as a few hours after the 
 contact of the semen with the ovum, or after the entrance of 
 the spermatozoids into the yolk (perhaps even earlier), so that 
 the ovum only reaches the uterus at a tolerably late stage of 
 development. Segmentation consists in a progressive cell- 
 division, by which each spherical cell splits up into two half- 
 spheres. Whether the first cell is identical with the ' germ-cell ' 
 (with the principal yolk), or whether it first originates by 
 transformations of that cell is doubtful, and the same remark 
 applies to the germinal vesicle, which is invisible before seg- 
 mentation, as well as to the manner of cell-division and the 
 division of the nucleus. 
 
 Segmentation proceeds very rapidly (its duration in man is 
 unknown ; in the rabbit it lasts some days, and in the dog more 
 than eight days) and furnishes in the end a large number of 
 small, spherical, strongly refracting cells, which together 
 present a mulberry-like appearance. 
 
 During segmentation the ovum, whilst in the Fallopian tube, loses the 
 discus proligems, and either surrounds itself, as the rabbit's ovum, with 
 accessory envelopes, or the zona pellucida first receives in the uterus (as in 
 the human subject) the first envelope of fine radially arranged villi, which 
 ramify and form a thick villous covering around the ovum ; the zona then 
 receives the name of chorion (frondosum). 
 
 Rudiment of the Embryo. 
 
 The disposal of the cells which have been produced in the 
 process of segmentation for the purpose of building up the 
 embryo commences with the deposition of their greater part on 
 the inside of the zona pellucida, to form a closed membrane 
 which is called the germ-vesicle (' UmhullungshautJ Keichert). 
 At a certain part of the membrane a more considerable accumu- 
 lation of cells takes place, destined directly for the formation 
 
 K N 2 
 
548 GERMINAL AREA. FORMATION OF VESICLE. 
 
 of the embryo, and this is called 6 the germinal area.' The 
 cavity which results from the deposition of cells, as well as from 
 the enlargement of the ovum, is filled with fluid, or in eggs 
 which possess a food-yolk, contains the latter. 
 
 In order to understand the development of the embryo a 
 somewhat different consideration of the fully developed animal 
 body than that usually given by descriptive anatomists is 
 requisite. Let us conceive a mammal with a short straight 
 alimentary canal, and let us lose sight of all glandular organs ; 
 the body may then be considered as a tube, the lumen of which 
 is the lumen of the alimentary canal and the wall of which is 
 composed of many concentric layers, viz. (from within outwards) : 
 intestinal mucous membrane, muscular coat of intestine, serous 
 coat of intestine, parietal layer of peritoneum, muscular layer 
 of trunk, osseous layer of trunk, skin covering trunk. All these 
 layers grow together ; only between the visceral and parietal 
 layers of the peritoneum, up to the mesentery situated in the 
 middle line behind, there is no fusion, but a cavity, the pleuro- 
 peritoneal cavity, which is, however, empty, so that its walls 
 are always completely in contact with one another. The ideal 
 tube which we are imagining possesses complete symmetry. Its 
 extremities, which have no openings, may be looked upon as 
 bulky outgrowths from the external wall of the tube. 
 
 The embryonic development of the tube takes place in 
 general in the following manner : the wall arises in the com- 
 mencement as a flat thickening of the first-formed germ vesicle 
 which everywhere surrounds the ovum; this thickened spot 
 splits up by degrees into the different layers which correspond 
 to the strata in the wall of the ideal tube. 
 
 The cavity, however (the intestinal cavity), is a part of the 
 germ-vesicle, which separates from the rest by the thickened 
 portion of the vesicle that which is to form the wall of the 
 embryo partly shutting itself off from the rest of the vesicle, 
 in the form of a lengthened tube. The main portion of the 
 germ-vesicle (which is not included within the embryo) is then 
 called the umbilical vesicle, and the canal-shaped communica- 
 tion which by the ever increasing constriction becomes progres- 
 sively narrower, and establishes a communication between the 
 cavity in the embryo (intestinal cavity) and that of the 
 umbilical vesicle, is called the umbilical duct or ; ductus vitello- 
 
THE THREE LAYERS OF THE BLASTODERM. 549 
 
 intestinalis seu omphalo-entericus.' The ultimately ring-shaped 
 place of constriction is the navel; as the thickening and even 
 the division into layers of the germ-vesicle does not limit itself 
 to the portion which becomes constricted, but extends beyond 
 the point of constriction towards the peripheral parts of the 
 vesicle, it follows that even the wall of the navel consists of 
 several embryonic layers. 
 
 The formation of layers over the germinal area of the germ- 
 vesicle, which, in great part, begins even before the commence- 
 ment of the shutting off of the embr} T onic cavity, is variously 
 described. Only one view, which in the main is Remak's, will 
 here be given ; the others will be, however, cursorily examined. 
 
 Three layers the three layers of the blastoderm form in 
 the smooth at first oval, then hour-glass-shaped thickening of 
 the germ-vesicle. The most external or uppermost 'the 
 epiblastj the sensory layer, is the seat of the cutaneous epithe- 
 lium with its appendages, the glands of the skin, and of the 
 central organs of the nervous system (brain and spinal cord) 
 with its appendages, the organs of the senses. 
 
 The central nervous system originates in the central (axial) 
 part of this layer in the so-called medullary folds; the 
 epithelium of the skin is formed from the peripheral part or 
 * corneal layer ' of the epiblast. 
 
 The innermost of the three layers of the blastoderm c the 
 hypoblast' is the seat of the intestinal epithelium with its 
 appendages, viz. the epithelium and the glandular cells of the 
 glands which open into the intestine. Between the epiblast 
 and the hypoblast lies the mesoblast, the motor and germi- 
 native layer from which all the rest all the parts of the body 
 which consist of connective tissue, muscles, vessels, and nerves, 
 as well as the urinary and generative organs are formed. 
 This layer splits up very early into two plates ; the external 
 forms the wall of the trunk, the internal forms the wall of the 
 intestine, with the exception of the epithelium ; the space 
 between these secondary layers constitutes the already men- 
 tioned ' pleuro-peritoneal cavity.' Inasmuch as the division 
 into these two layers is arrested in the middle line, there is 
 here established a fusion between the wall of the trunk and of 
 the intestine, and this is the seat of the mesentery. (Compare 
 below, Fig. 42, II., IIL, IV.) 
 
550 THE EPIBLAST. 
 
 Processes of Development in the Germinal Area. 
 
 In each of the three layers of the blastoderm there 
 follow, in addition to the already mentioned process of con- 
 striction, certain processes of development by which they 
 undergo transformation. 
 
 The chief of these processes are : 1 . In the epiblast the 
 lamince dorsales or medullary folds separate from the corneal 
 layer and form a tube. 2. In the mesoblast the first commence- 
 ment of a skeleton takes place ; further, the division already 
 alluded to and the formation of a vascular system commences. 
 8. From the epiblast and hypoblast processes of epithelium 
 grow into the tissues from out of the middle layer, so that there 
 are formed hollow processes which are in part enclosed in the 
 body cavity, and form glands. 
 
 Epiblast. 
 
 1. The first process to be mentioned is the one which first 
 occurs. In the centre of the medullary fold a longitudinal 
 groove is formed, dividing it into two symmetrical halves, which 
 curve towards one another, drawing over themselves the corneal 
 plates which are attached to them. The cause of this is the 
 growing forwards of the processes of the middle layer, which 
 tend to press themselves between the medullary plates, which 
 are curved towards one another, and the corneal plate. 
 Ultimately the medullary folds are closed, so as to form the 
 medullary tube, and the corneal plates still attached to the 
 point of union are, finally, completely separated from it by 
 the union of the two lateral appendages of the middle layer, 
 in such a manner that the medullary tube is thenceforward 
 entirely enveloped in a prolongation of that layer. This 
 envelope forms the spinal arch, together with the muscles, the 
 ligaments, and the skin of the back (which last receives a 
 covering from the corneal layer, viz. the epidermis), and at the 
 anterior extremity (head) the cranial capsule. 
 
 The medullary tube becomes the spinal cord and brain ; its 
 interior is converted into the central canal of the cord, with its 
 connection in the brain the so-called ventricles of the brain. 
 Compare below, Fig. 42, II., III., IV.) 
 
MESOBLAST. FORMATION OF SPLANCHNOPLEURE. 551 
 
 Mesoblast. 
 
 2. The simultaneous phenomena of development which 
 take place in the mesoblast concern the vertebral system. 
 
 The centre of this system is a streak which is very early 
 developed, and which runs in the median plane of the embryo, 
 and which is called the 'chorda dorsalis.' On each side of 
 this there appear two longitudinal plates, the protovertebral 
 plates, which by transverse lines subdivide themselves into a 
 number of protovertebrce. The remainder of the mesoblast, 
 so far as it belongs to the germinal area, forms ' the lateral 
 plates.' The protovertebrce undergo the following changes : they 
 develop 'spinal processes,' the influence of which upon the 
 formation of the canal of the cerebro-spinal organs and upon 
 the union between this and the separated corneal plates has 
 already been mentioned. Internally the proto vertebrae grow 
 around the chorda dorsalis. (See below, Fig. 42, II., and fol- 
 lowing.) 
 
 Their substance is converted into various tissues, viz. into 
 the vertebral column with its appendages, into the ribs and the 
 muscles pertaining to them, into the spinal nerves and the skin 
 of the back. The bodies of the vertebrae originate in the part 
 which surrounds the notochord, in such a manner that in the 
 middle section of each protovertebra there is formed an inter- 
 vertebral cartilage, and from the fusion of adjacent halves of 
 the protovertebrse a persistent vertebral body originates. 
 
 In the lateral plates there occurs further the already men- 
 tioned splitting up of the embryonal wall into the two layers ; 
 the internal attaches itself to the hypoblast, and forms with it 
 the splanchnopleure, the external attaches itself to the epi- 
 blast, and forms with it the somatopleure. The separation 
 between these two layers forms the pleuro-peritoneal cavity ; 
 the internal undivided edges of the lateral plates, advancing 
 together little by little on the ventral side of the vertebral 
 column, form the so-called middle plates, which are the founda- 
 tion of the mesentery, and foetal urinary and generative organs. 
 The former of these two sets of organs originate as a string- 
 like thickening of the middle plates, which later on becomes 
 hollow ; according to some as an invagination of the pleuro 
 
552 DEVELOPMENT OF THE VASCULAR SYSTEM. 
 
 peritoneal cavity the Wolffian canal. For the further develop- 
 ment of this organ, and the other urino-generative organs, see 
 below. 
 
 The third process which takes place in the mesoblast is the 
 development of the vascular system. 
 
 This system first originates in that layer of the mesoblast 
 which goes to form the splanchnopleure, and makes its way 
 outwards in the yet undivided peripheral part of the mesoblast. 
 The manner in which the vessels and the blood are formed has 
 not been accurately determined, yet, according to the majority 
 of statements, it occurs as follows : cellular trabeculos are inter- 
 woven so as to form a network ; the peripheral layers of cells are 
 then converted into vascular parietes, and the contained cells 
 become at first colourless nucleated blood-corpuscles. Accord- 
 ing to a new view (Klein) the vessels originate in cells which 
 become hollow, which lengthen out and run together, and from 
 the nuclei of which the blood-corpuscles are formed. 
 
 The area over which blood-vessels are formed is consider- 
 able, occupying an important circularly-bordered portion of 
 the germ-vesicle, which is called the area vasculosa. 
 
 Of all vessels the first formed is the Heart ; it originates in 
 the most anterior part of the splanchno-pleure which has 
 already become closed into a tube. 
 
 The following may serve to explain the position of the heart: the 
 amnion-fold is formed more rapidly at the head and tail than at the sides. 
 At a certain stage of development the embryonal wall -which is shutting 
 itself off from the germ vesicle resembles a shoe somewhat trodden down at 
 heel (see Fig. 42, 1.), the free borders of which pass into the main part of the 
 germ-vesicle. The opening of the shoo represents the still widely open 
 navel; the shoe cavity represents the interior of the intestine. Along the 
 middle line of the sole of the shoe (which represents the dorsal surface of 
 the embryo) the cerebro-spinal tube would be situated. The wall of the 
 shoe is throughout double, up to a streak in the middle line of the sole (the 
 mesentery) ; at the end of the shoe and on the uppermost part of the anterior 
 layer (the shoe being supposed to be suspended vertically with the heel 
 downwards, but with the opening towards the observer) the wall is also 
 single, the body and intestinal wall being united. This unsplit upper 
 part of the anterior wall is called the l pharynycal plate? From the cavity 
 of the germ-vesicle one may pass through the navel, into the anterior part 
 of the cavity of the embryo, which has now already assumed the shape of 
 a tube (this part, which is transformed into the foregut, is called the 'fovea 
 cardiaca '), as well as into the posterior, shallower, 'foveola posterior.' That 
 part of the wall of the l fovea cardiaca ' which is directed towards the 
 
DEVELOPMENT OF THE HEART. 653 
 
 //m?z-vesicle (the anterior wall of the hypothetical shoe) is, below the 
 ^ pliaryngeal plate] also double like the main part of the sole. Of the two 
 layers the inner one represents the anterior wall of the foregut, and the 
 external that portion of the pleuro-peritoneal cavity which ties in front of 
 the intestine. (Kefer to Fig. 42, L, V., VIII.) 
 
 The heart originates in the median line anteriorly, accord- 
 ing to some (Eemak), as a cylindrical thickening of the anterior 
 wall of the foregut (see Fig. 42, V., VI.), which thickening 
 soon becomes hollowed out, and appears to be in connection 
 with the remaining vessels ; according to others (Schenk, 
 Oellacher), as a process of the wall of the foregut, which shuts 
 itself off and grows forwards into the cavity lying in front of 
 the intestine referred to in the preceding paragraph. The 
 vessels which are connected with the heart are to be followed 
 in two directions. The arterial vessels commence with two 
 aortic arches starting from the anterior extremity of the heart, 
 which curve inwards and backwards along the pharyngeal 
 plate and which, separated at first throughout the length of 
 the chorda dorsalis, later on unite to form the aorta, and termi- 
 nate in the arterise iliacse communes. 
 
 Instead of one there are generally several (three) aortic 
 trunks on each side, which, however, again unite on each side 
 to form an aorta or aortic root. On each side there springs 
 from the aortas a series of vertically ascending arteries, which 
 run on the sides of the splanchnopleure, and which go to the 
 area vasculosa, where they ramify; these are called the 
 omphalo-meseraic arteries. Two venous trunks pass into the 
 posterior end of the heart through a short common trunk ; these 
 vessels also are distributed over the area vasculosa and are 
 called the omphalo-meseraic veins. 
 
 Both the above sets of vessels communicate through a cir- 
 cular vessel which limits the area vasculosa and which is termed 
 the sinus terminalis (see Fig. 42, I.) This system of vessels 
 probably serves as a first respiratory apparatus, as well as to 
 convey to the foetus the nourishment which is yielded by the 
 contents of the germ- vesicle. It disappears early in proportion 
 as the contents of the vesicle are of little importance in 
 nutrition, and is at a later stage replaced by the allantois, 
 which subserves the same functions. As soon as it is formed, 
 the heart begins to pulsate, so that the blood corpuscles com- 
 
554 DEVELOPMENT OF INTESTINAL GLANDS, LIVER, ETC. 
 
 mence at once a somewhat irregular circulation through the 
 newly-formed vessels. 
 
 Hypoblast. 
 
 From the inner layer, the development of which commences 
 latest, processes are protruded which grow into that part of 
 the mesoblast which is contained in the splanchnopleure, 1 and 
 form the small glands of the alimentary canal, as well as the 
 liver, the pancreas, and, in addition, the lungs and the perma- 
 nent kidneys. It is easy to see how the protrusion of the hy- 
 poblast must form the epithelium, or the cells of a glandular 
 canal, whilst the invaginated splanchnopleure must form the 
 connective tissue, the blood-vessels, the nervous and the mus- 
 cular surroundings (the basis of the gland). If the protrusion 
 proceeds so far that even the splanchnopleure is protruded, as 
 in all large glands, the protruded intestinal wall must evidently 
 project into the pleuroperitoneal cavity, as is the case in 
 reality with all the glands which open into the intestine and 
 which are surrounded by peritoneum. 
 
 The liver originates by the protrusion of two hollow processes 
 (primitive hepatic ducts) from the foregut, close to the navel; the finest 
 branches form the very complex network of hepatic canals, which, with 
 the blood-vessels, constitute the parenchyma of the hepatic lobules. The 
 larger canals are the biliary ducts, and a projection from one of the primordial 
 canals forms the gall-bladder. The liver grows around the trunk of the 
 omphalo-meseraic vein, which communicates with its vessels. One of the 
 intestinal veins which enter into it, and which is permanent, forms later 
 on with those branches the portal vein. 
 
 Opposite to the liver, and starting from the posterior intestinal wall, there 
 arises by ramifications, and afterwards hollowing out, an outgrowth which is 
 at first solid, the pancreas. 
 
 A further double projection from the anterior wall of the intestine, but 
 above the heart, and which penetrates the pleuro-peritoneal cavity, forms the 
 lungs, with their bronchial system, the entrance to the lungs being therefore 
 situated in the foregut (later the pharynx). For the development of the 
 kidneys see p. 561. Lastly, the thyroid and thymus glands have to be con 
 sidered ; the first arises as a vesicular outgrowth from the anterior wall of the 
 foregut, which shuts itself off, then by further processes of development 
 
 1 By this it is not intended to ascribe in any way an active part to the epi- 
 thelium ; it is indeed more probable that the in-growth of epithelium is conditioned 
 by the growth of the splanchnopleure. 
 
AMNION. 555 
 
 divides into two symmetrical cavities, which respectively give rise to secon- 
 dary cavities. The thymus gland is formed in a similar manner. The 
 spleen, lymphatic gland and follicles, and the suprarenal capsules, originate- 
 from the mesoblast, 
 
 Peripheral Processes of Development. 
 
 Side by side with all the processes of development which 
 have been described as proceeding in the germinal area there- 
 are other processes taking place in the peripheral part of the- 
 germ-vesicle, which have for their object to permit the embryo 
 to develop freely on all sides, by embedding it in a fluid 
 (amnion), and also to bring the foetal blood into relations per- 
 mitting of diffusion-changes taking place between it and the- 
 maternal blood, whereby nutrition and respiration are rendered 
 possible (' allantois '). 
 
 1. Development of the Amnion. 
 
 It has already been mentioned that a cleavage of the ger- 
 minal area into blastodermic layers proceeds beyond the em- 
 bryonal area to the peripheral parts of the germ-vesicle, and 
 that the same is true of the cleavage of the mesoblast. The 
 latter cleavage, however, does not extend over the whole germ- 
 vesicle, but only so far as the area vasculosa extends. Hero 
 the superficial layer ceases, so that at this spot, provided that 
 the epiblast has been broken through, the space between the 
 two layers of the mesoblast, and ultimately the pleuro-peri- 
 toneal cavity, may be reached. The peripheral parts of the 
 external portion of the mesoblast (' Hautplatte ') now rise up 
 from the germ-vesicle, and arch backwards on all sides of the 
 embryo, driving the epiblast before them, and coming from 
 all sides join above the embryo, enclosing it in a sac which is 
 called the amnion ; the layer of the epiblast which is enclosed 
 lines the inner surface of the amniotic sac. 
 
 The amnion is filled with a serous fluid, by which the embryo 
 is surrounded on all sides ; besides the normal constituents of 
 transudations, it contains secretions from the skin and nitro- 
 genous products of oxidation, presumably as a result of diffusion 
 from the allantois. 
 
556 FORMATION OF ALL AN TO IS. PLACENTA. 
 
 2. Formation of the Allantois. 
 
 Near to the caudal end of the embryo in the region of the 
 navel there originate two solid accumulations of cells, which 
 grow from the external layer of the mesoblast, and which soon 
 unite. Into this out-growth, which lies close to the splanchno- 
 pleure, there grows a process of the posterior part of the intes- 
 tine in such a manner that a vesicular cavity is formed ; this 
 bladder, the allantois., grows out of the embryo between the 
 somatopleure and the splanchnopleure, reaching the space be- 
 tween the amnion and the germ-vesicle ; growing always more 
 and more extensive, it envelops the ammion, and reaches the 
 inner wall of the chorion, with which it becomes connected 
 over a greater or smaller surface. The communication between 
 the posterior part of the intestine and the allantois forms the 
 cloaca., into which empty themselves the foetal urinary organs. 
 The part of the allantois which becomes small, and which passes 
 through the umbilical orifice, is called the urachus. The 
 allantois is highly vascular. The arteries, the umbilical 
 arteries spring from the common iliacs ; they lead to a well- 
 developed capillary system, the loops of which enter the cho- 
 rionic villi ; the veins unite to form the single umbilical vein, 
 which, returning to the embryo, opens into the omphalo-meseraic 
 vein, and thus communicates (as the portal vein) with the 
 blood-vessels of the liver ; it sends a branch directly to the vena 
 cava inferior (ductus venosus). 
 
 The well-developed villi of the chorion. which contain the 
 blood-vessels of the allantois, grow into the interior of the 
 uterine mucous membrane, in which, at the corresponding spot, 
 corresponding capillary loops are formed. The two sets of 
 vessels together form the placenta, in which an exchange by 
 diffusion proceeds between foetal and maternal blood, for the 
 purposes of respiration and nutrition; the blood of the umbilical 
 vein is therefore necessarily brighter (more arterial) than that 
 of the corresponding arteries, exactly as at a later period 
 of existence the blood of the pulmonary arteries and veins 
 differ. The umbilical vesicle and the area vasculosa now lose 
 their importance; and, together with their blood-vessels and the 
 umbilical duct, shrivel together so as to form a thin string. The 
 
VISCERAL CLEFTS. BRANCHIAL ARCHES. 557 
 
 fluid which the allantois contains is a transudation containing 
 the secretion of the primordial kidneys, with some nitrogenous- 
 products of oxidation. 
 
 Whilst in man only one placenta is developed, animals possess several 
 placental sites, so that the villi of the chorion enter the villi of the decidua 
 in many places. 
 
 Final Stages of Development of the Embryo. 
 
 If we imagine the body cavity of the embryo to have been 
 shut off from the germ-vesicle, the umbilicus will consist of two 
 concentric tubes ; the inner (the omphalo-meseraic duct) con- 
 nects the intestine with the umbilical vesicle; the outer is 
 formed by skin, and connects the abdominal wall of the embryo 
 with the amnion. Between these concentric tubes there exists 
 a circular space, through which the pleuro-peritoneal cavity 
 may be reached, and through which the urachus comes. 
 
 By a simple process of separation by constriction, an intes- 
 tinal tube, closed on all sides, is formed, which is united in 
 the median line posteriorly to the body cavity (by the mesen- 
 tery), and to the whole upper end of the body. Subsequently 
 there are formed an anterior and a posterior intestinal opening. 
 In the anterior part of the centre of the pharyngeal plate, close 
 below the fore-brain, there is formed a depression into which the 
 epiblast passes. This depression becomes deeper and deeper, 
 and ultimately opens by a fissure into the upper end of the fore- 
 gut (pharynx), forming the buccal and nasal cavities. 
 
 Further, there are formed on the lateral parts of the pha- 
 ryngeal plate three gutter-shaped cavities of the hypoblast, 
 which run from before backwards ; these ultimately break 
 through the pharyngeal plate, and form on each side three 
 visceral or branchial clefts, and later on yet a fourth, by the 
 hypoblast making a border, as the mucous membrane gives an 
 external mucous edge to the lips ; between each pair of pharyn- 
 geal plates there remains a pharyngeal or branchial arch, which 
 is so arranged that on its inner side an aortic arch runs from 
 before backwards. Along the pharyngeal arches thickenings 
 arise from before backwards, and ultimately meet. The space 
 between the skull and the first pharyngeal arch is taken up by 
 the buccal and nasal cavities ; the first pair of branchial arches 
 is converted into a lower jaw and the neighbouring parts of the 
 
58 FORMATION OF CEREBRAL VESICLES. 
 
 cranium ; as, however, it sends two branches into the common 
 buccal and nasal cavity, which grow so as to meet, and which 
 develop into the upper jaw and gums, a separation between 
 the buccal and nasal cavities is ultimately effected. (It is from 
 an arrest in the development of these processes that hare lip 
 and cleft palate result.) 
 
 The remaining visceral clefts unite, the branchial arches 
 furnishing the hyoid bone, a portion of the laryngeal cartilages, 
 the skin of the neck, &c., by processes which cannot here be 
 examined in detail. The tongue originates as an outgrowth 
 from the inner side of the lower jaw. The posterior intestinal 
 opening originates in a perforation of the cloaca, which is the 
 common termination of the intestine and the allantois. 
 
 This common aperture is afterwards subdivided by a bridge, 
 the perinceum (which is an outgrowth of the wall which sepa- 
 rates the intestine from the allantois), into one connected with 
 the bowel, viz. the anus, and into one communicating with the 
 -allantois (opening of the uro-genital sinus). 
 
 The first pair of visceral clefts unite, except where an open- 
 ing is left, which is the rudiment of the external auditory 
 meatus. The second, third, and fourth clefts unite completely ; 
 as the aortic arches bend back from the inner side of the 
 branchial arches, and take with them the mesoblast, the third 
 and fourth clefts grow deeper. 
 
 Of the remaining processes of development the following 
 must be mentioned : 
 
 1. The ' medullary or neural tube,' the cavity of which con- 
 tinually diminishes by an increase of the thickness of its walls, 
 very early shows, at its dilated cerebral end, two transverse de- 
 pressions which mark off three cerebral vesicles. Each vesicle 
 carries on either side a vesicular outgrowth, which subsequently 
 becomes pedunculated, which represents the rudiments of the 
 three higher organs of special sense with their respective nerves 
 
 the first is the olfactory, the second the optic, and the third 
 
 the auditory ; the vesicles are the rudiments of the peripheral 
 nerve distribution. In the optic vesicle, which is immediately 
 beneath the corneal layer, a vesicular involution of the latter 
 takes place, which ultimately becomes shut off and forms the 
 lens with its capsule. The optic vesicle thus invaginated in 
 itself becomes converted into an hemispherical body, by the 
 
THE EYE. THE INTESTINAL CANAL. 559 
 
 anterior half (the retina) being placed in close apposition with 
 the posterior (the choroid). Between the lens and the retina 
 there then originates the vitreous body, and around, by a pro- 
 cess from the mesoblast, the sclerotic, which unites with the 
 portion of the skin which covers the eye so as to form the 
 cornea. 
 
 The three cerebral vesicles represent, from before back- 
 wards, the third ventricle, the aqtwductus Silvii, and the fourth 
 ventricle. The first gives off a new vesicle on each side, the 
 interior of which represents the lateral ventricles (the com- 
 munication between these and the primitive vesicle is formed 
 by the foramen of Munro\ and their walls represent the 
 cerebral hemispheres ; the lateral vesicles in man outgrow all 
 the others. 
 
 In a similar manner the third cerebral vesicle sends out two 
 cerebellar vesicles. Between the first and the second vesicle 
 there arises early a tolerably sharp constriction, so that the 
 former bends around the anterior extremity of the embryo. 
 
 The cerebral ganglia (optic thalami, &c.) arise as a thick- 
 ening of the vesicular walls. 
 
 Statements vary as to the origin of peripheral nerves and ganglion-cells. 
 The majority of authorities believe them to originate in the mesoblast; 
 others (Hensen) believe the axis cylinders to arise as outgrowths from the 
 p:anglionic cells of the central nervous system into the mesoblast, which 
 furnishes, however, the sheath and white substance of Schwann. 
 
 2. The intestinal canal forms at first a simple tube, which 
 is only slightly bent in the centre, where the mesentery is 
 longest. 
 
 In the vicinity of the liver a dilatation of this tube occurs, 
 marking the position of the stomach, which subsequently, by a 
 movement of rotation, takes up its persistent transverse position 
 and thus presents a fundus and two curvatures. By an 
 elongation of the intestinal tube, and a simultaneous elon- 
 gation of the mesentery are formed the coils of the small 
 intestine and the curves of the large intestine. That piece of 
 the omphalomesenteric duct which lies within the embryo 
 breaks at the navel and forms a rudimentary appendage of the 
 lower part of the ilium. 
 
 3. The heart, which in the beginning is a straight tube 
 situated in the middle line, very early alters its form, so that its 
 
560 DEVELOPMENT OF HEART AND LARGE VESSELS. 
 
 venous (posterior and inferior) end bends itself towards its 
 arterial end, so that the whole organ, with the origin of the 
 veins, takes the form of an S (see below, Fig. 42, I.). The 
 cause of this is that during a certain time the aortic arches in- 
 crease in number posteriorly, whilst those situated anteriorly dis- 
 appear ; hence the anterior part of the heart is thrust backwards, 
 whilst the venous end retains its original position. Three parts 
 of the heart, which contract one after the other, may now be 
 recognised, viz. sinus venosus (from which the two auricles 
 afterwards spring), ventricle, and bulbus aortce. A longitu- 
 dinal partition wall is now formed, at first in the ventricle 
 and afterwards in the auricle (being incomplete here), whereby 
 two separate ventricles are formed, and two auricles communi- 
 cating through the foramen ovale. Of the three remaining 
 pairs of aortic roots, the first forms the carotid and subclavian 
 (on the right side the common trunk persists); the second 
 forms on the left side the permanent aortic arch, which leads to 
 the primitive descending aorta, and from which the vessels of 
 the first pair spring ; the right branch disappears. 
 
 The third pair furnishes the pulmonary arteries ; the right 
 arch disappears, except its pulmonary branch, and the left 
 remains connected with the descending aorta, the connecting 
 piece forming the ductus arteriosus (duct of Botal). Ulti- 
 mately the bulbus arteriosus divides itself in such a manner that 
 the section which gives off the pulmonary arteries remains con- 
 nected with the right ventricle, whilst the remainder, with the 
 arch of the aorta, remains attached to the left ventricle. Even 
 then all the blood can pass from the right heart into the aorta, 
 partly through the foramen ovale, and partly through the ductus 
 arteriosus. It is only after birth, when respiration through the 
 lungs has commenced, that both these communications are 
 closed, and thenceforward the whole of the blood of the right 
 heart is carried to the lungs. 
 
 4. The internal urinary organs are developed in the 
 following manner : the structure in which they originate, the 
 Wolffian duct, is at its upper end closed, and communicates 
 below with the posterior part of the intestine (foveola posterior). 
 The anterior end of the duct sends inwards a row of little blind 
 canals, which are in part furnished with glomeruli (derived from 
 the mesoblast). Thus arises the Wolffian body, of which one 
 
URINARY AND GENERATIVE ORGANS. 561 
 
 part, the primordial kidney, discharges the functions of a kidney, 
 whilst the remainder (the sexual part) goes to form the organs 
 of generation. 
 
 The permanent kidneys are formed (Kupffer) by a tubular 
 protrusion from the tail-end of the Wolffian duct ; this protrusion 
 pursues a course parallel to that of the primordial kidneys, and 
 grows upwards as the rudiment of the ureters ; the upper end 
 grows into a mass of cells derived from the mesoblast (paren- 
 chyma of the kidney), and thus originate the pelvis of the 
 kidney and the calyces. The tubuli uriniferi are either (Remak) 
 further outgrowths from the calyces, the dilated ends of which 
 (capsules) surround the glomeruli, or (Kupffer) they originate 
 independently in the kidneys (from the periphery outwards), 
 and only afterwards open into the calyces. (For the develop- 
 ment of the urinary bladder, the reader must refer to the 
 paragraph relating to the external organs of generation.) 
 
 5. The internal organs of generation are originally 
 hermaphroditically disposed in both sexes. The peritoneal 
 squamous epithelium which invests the free surface of the 
 Wolffian duct is sharply separated from a layer of cylindrical 
 epithelium which is placed upon the middle and the lateral 
 angles ; this epithelium (germinal epithelium)., which probably 
 is derived from the epiblast, is the rudiment of the female 
 generative apparatus, viz., in the middle, of the ova and the 
 cells of the in. granulosa, and laterally of the epithelium which 
 lines the Fallopian tubes and the uterus. The union of the 
 median part with the connective tissue of the Wolffian bodies,, 
 which leads to the formation of the ovary, has already been 
 spoken of. The lateral layer of epithelium is similarly sur- 
 rounded by connective tissue and presents the appearance of 
 a longitudinal cord, which later becomes hollow and gives rise 
 to Mullers duct, which occupies the position of the future 
 Fallopian tubes. 
 
 The two Muller's ducts open not far from the Wolffian ducts. 
 into the hindgut. Later on, their lower ends unite to form a 
 common chamber, the uterus and vagina. Above, in the vicinity 
 of the ovary, an opening forms in the ducts, and this opening 
 is surrounded by fringes. The piece of the duct above the open- 
 ing becomes reduced to the condition of a vesicle. In the male 
 embryo the testicle arises from the genital part of the Wolffian 
 
 O 
 
562 URINARY AND GENERATIVE ORGANS. 
 
 bodies ; the canals of which becoming very much elongated and 
 arranged in coils, are converted into the tubuli seminiferi, 
 which penetrate the connective tissue of the testicle ; that 
 portion which has not penetrated forms the epididymis, and 
 the ducts of the primordial kidneys form the vets deferens, 
 with the vesiculce seminales. The tubuli which do not form a 
 part of the testicle are the vasa aberrantia of Haller. In the 
 female the genital part of the Wolffian bodies remains as 
 Rosenmuller's organ, or the parovcurium, the efferent passage 
 being converted into the round ligament of the uterus. In 
 both sexes the renal part of the Wolffian bodies becomes reduced 
 to the condition in which it is known as the organ of Gir aides 
 or the parepidldymis, and in the female as a separate structure 
 situated close to the parovarium. 
 
 In the male, further, the seat of the ovary persists as a non- 
 pedunculated cyst (Fleischl), whilst the ducts of Miiller ter- 
 minate below in the uterus masculinus (E. H. Weber) or 
 vesicula prostatica, their upper end being represented by 
 pedunculated cysts. 
 
 6. The external urinary and sexual organs. When with the 
 closure of the navel, the urachus is shut off, the portion of the 
 allantois which remains in the embryo forms the urinary bladder 
 (the vertex of which remains connected with the navel by the 
 urachus). The lowest part of the allantois, which contains 
 the openings both of the urinary and the sexual organs, is called 
 the sinus urogenitalis. On each side of the opening of the 
 latter there arises two cutaneous projections, which in woman 
 give rise to the labia majora, but which in man grow together 
 above the opening, to form the scrotum, closing by a persistent 
 seam which is called the raphe. In front of the opening, further, 
 there arises an elongated body, which bears on its lower surface a 
 furrow, which posteriorly runs into the sinus urogenitalis. 
 The edges of this furrow unite in man to form the canal-shaped 
 urethra, which opens at the apex of the elongated body, the 
 penis ; the posterior part of the urethra is formed by the uro- 
 genital sinus itself. In woman, however, the furrow remains 
 open, and its edges grow into the labia minora or nymphce 
 whilst the original body itself forms the clitoris. The tiro- 
 genital sinus becomes, however, so short that it merely forms 
 a depression between the labia, into which the vagina and the 
 
OLDER THEORIES OF DEVELOPMENT. 563 
 
 urinary bladder with a short urethra separately open. In the 
 male embryo the descent of the testes takes place into the 
 scrotum at the eighth month ; on this matter anatomical text- 
 books are to be consulted. 
 
 Nothing is known in reference to the circumstances which influence the 
 sex of the embryo. By statistics some have pretended to show that the 
 relative ages of the parents have a certain influence in leading to a preponder- 
 ance of males or females, still even this influence has been differently 
 stated by different writers. Lately it has been asserted (Thury) that the 
 sex depends upon the stage of maturit}^ which the ovum has attained before 
 impregnation ; according to this view ova are at first only capable of 
 developing embyros of the female sex, and only after having undergone a 
 change are they capable of producing males. But this is by no means 
 generally proved. 
 
 7. The extremities originate as warty processes from the 
 sides of the trunk, which only subsequently increase in length. 
 
 The development of the tissues, which is one of the most 
 important sections in the history of development, is usually 
 treated of as a part of Histology, and the reader is therefore 
 referred, on this subject, to the works which specially treat of 
 that branch of Anatomy. 
 
 The older theories of Pander, v. Baer, and Bischoff, assumed principally 
 the existence of only two layers of the blastoderm an external or l animal,' 
 corresponding to the somatopleure, and an internal ' vegetative,' correspond- 
 ing to the splanchnopleure ; between these two that vascular system was 
 supposed to originate from a separate vascular layer. A similar theory has 
 lately been advanced by His, according to which, however, the whole system 
 of connective tissues, the vessels, and the blood, are derived from the so- 
 called ' white-yolk ' (of the bird's egg), which has quite a different origin 
 from the 'principal yolk ' (archiblast, neuroblast). It (i.e. the white yolk) 
 originates in the cells of the m. granulosa which have migrated through the 
 vitelline membrane into the principal yolk. The elements of the white yolk 
 serve either for building up the embryo (' parablast,' ' haemoblast ') by 
 migrating between the two layers of the blastoderm, or merely as ( food- 
 yolk.' Another theory (Reichert's) accepts the process of splitting up of the 
 mesoblast (' stratum intermedium '), but differs from Remak's theory in not 
 distinguishing a sensory (corneal) layer, and maintains that the original 
 blastoderm persists as an enveloping membrane (' Umhiillungshaut '), whilst 
 the proper layers are deposited within it afterwards. Between the envelop- 
 ing membrane and the stratum intermedium originates the medullary plate 
 as a special ' upper ' layer, limited to the germinal area. That portion of 
 the enveloping membrane which becomes shut off in the amnion forms the 
 epidermis of the skin of the embryo, and furnishes an epithelial covering to 
 
 o o 2 
 
564 
 
 OLDER THEORIES OF DEVELOPMENT. 
 
 the inner uirface of the amnion (/ endaranion '). Other recent modifications 
 of the theory of Kemak adopted in the text could not be here referred to 
 without entering in a more special manner into the study of embryology. 
 
 The appended diagrammatic representations may serve to ex- 
 plain some of the fundamental points in development. With the 
 exception of I., they are transverse sections of the embryo. 
 
 -is 
 
 d' in 
 
 FIG. 42. 
 
 I. is a superficial view seen from the interior of the germ- 
 vesicle ; it shows the shoe-shaped embryo with the vessels of the 
 area vasculosa. Across the anterior layer of the shoe, the already 
 S-shaped heart is seen, from which superiorly there proceed two 
 aortic roots, inferiorly, the two omphalo-meseraic veins. Through 
 the opening of the shoe (the navel) the two still separated aortse 
 are seen, with the omphalo-meseraic arteries ; in the area vas- 
 culosa the arteries are feebly, the veins strongly delineated. 
 
 The remaining figures are in part cross-sections (II., III.,, 
 IV., VI., VII.), partly longitudinal sections of the embryo (V. 
 and VIII.). 
 
 Section VI. corresponds to the line AB in the longitu- 
 dinal section V.; the transverse section VII. corresponds similarly 
 
BIRTH. 565 
 
 to the line VW in VIII. The letters of reference are the 
 same in all the drawings. 
 
 ih Epiblast hn Cutaneous navel 
 
 m Medullary or neural tube Fc Fovea cardiaca (foregut) 
 
 nig Mesoblast Fp Fovea posterior (hindgut) 
 
 <L Hypoblast a Amnion (peripheral part of the 
 
 e Chorda dorsalis external part of the mesoblast 
 
 n Protovertebral plates detached and inverted ; in Fig IV. 
 
 s Lateral plates on the left, it is yet connected 
 
 p Pleuroperitoneal cavity with the internal part of the 
 
 H External part of mesoblast mesoblast ; on the right it is 
 
 D Internal part of mesoblast detached). 
 
 M Mesentery Al Allantois 
 
 S Pharyngeal plate ur Urachus 
 
 Ch Chorion frondosum cl Cloaca 
 
 nb Umbilical vesicle vo Omphalo-meseraic veins 
 
 C Heart ao Omphalo-meseraic arteries 
 
 T Aortic arches st Sinus terminalis 
 
 dn Omphalo-meseraic duct L Liver 
 
 So as to make the diagrams as intelligible as possible, in 
 IV. and VII., the sections of the two aortse and of the two 
 Wolffian bodies are not shown. 
 
 Birth. 
 
 By the development of the ovum the uterus is more and 
 more stretched, so that at the same time the cervix becomes 
 obliterated. The uterine walls increase in thickness by the 
 growth and by the new formation of its muscular fibres, as 
 well as by the considerable development of its blood-vessels. 
 At last, about 280 days after impregnation, by the operation 
 of causes which are entirely unknown to us, the expulsion of the 
 now developed ovum takes place. This expulsion is brought 
 about by rhythmical and painful contractions of the muscular 
 fibres of the uterus, which are technically known as c pains,' 
 and which are aided by the compression of the abdomen. 
 
 The following facts are known in reference to the innervation of the 
 uterus : 
 
 Irritation of the hypogastric plexus gives rise to uterine contractions, and 
 the same result is obtained by exciting the spinal cord up to the cerebellum ; 
 the fibres which pass from the spinal cord to the uterus leave it in the 
 vicinity of the last thoracic, and the third and fourth lumbar vertebrae. 
 They pass along sympathetic paths, traverse the inferior mesenteric ganglion 
 and run in one of the nerves which lie over the aorta, until they reach the 
 uterus (Frankenhauser). 
 
566 FOETAL ENVELOPES. UMBILICAL COED. 
 
 In addition to the nervous supply derived from the spinal cord, the uterus 
 appears to possess nerve centres in its more immediate vicinity, perhaps- 
 scattered in part through its parenchyma. These centres are excited by the- 
 blood of dyspnoea (Oser and Schlesinger), like the centres in the medulla 
 oblongata, and in the intestines, so that suffocation, compression of the- 
 aorta (Spiegelberg), haemorrhage, &c. bring about uterine contractions. 
 Even the centre presiding over uterine contractions, which is seated in the- 
 brain, is excited by the blood during dyspnoea, as well as by the circumstance* 
 previously mentioned (Oser and Schlesinger). 
 
 In the human being the ovum is not thrown off uninjured, 
 but the embryo is first expelled, after the envelopes which sur- 
 rounded it have been torn, and it is followed by the rest of the 
 ovum. These envelopes are from without inwards 1. The 
 decidua reflexa (p. 546). 2. The chorion, which, at the place 
 where the allantois is situated (normally not at the orifice of 
 exit of the uterus) forms the placenta, and which is free from 
 villi over the os uteri. 3. The amnion (the umbilical vesicle 
 forms an imperceptible structure in the placenta, compare p. 556). 
 
 As a result of the pressure of the first ' pains,' these mem- 
 branes protrude in an arched form through the os uteri, and 
 ultimately tear at one spot ; after a large part of the liquor 
 amnii has escaped, a part of the foetus, usually the head, is 
 set free. Now, with more or less rapidity, the process of ex- 
 pulsion sets in, hindered in part by the narrowness of the 
 pelvis, in part by that of the os uteri, of the vagina and the 
 vulva. Simultaneously, the placenta not only its foetal, but 
 also its maternal part taking with it a portion of the uterine 
 mucous membrane detaches itself from the contracting uterine 
 wall, a process which is naturally accompanied by haemorrhage. 
 After the birth of the foetus, the placenta, with the membranes 
 which formed the walls of the ovum attached to its margins, 
 though already detached, is still contained within the uterus, 
 and the foetus is united to it by means of the long umbilical 
 cord. The latter contains the following structures: 1. The 
 stalk of the allantois (a prolongation of the urachus), with 
 the umbilical vessels, viz. the two arteries, which continue to 
 pulsate, and the vein, which by the early intra-uterine rotations 
 of the foetus, is nearly always spirally twisted. 2. The shri- 
 velled omphalo-meseraic duct with the umbilical vesicle. 3. 
 Everything else which surrounds the tubular peduncle of the 
 
COMMENCEMENT OF EXTRA-UTERINE LIFE. 567 
 
 amnion projecting from the navel, and which thus covers the 
 inner side of the placenta, and passes over its margin to those 
 of the chorion. The principal bulk of the umbilical cord is, 
 however, formed by the three umbilical vessels, imbedded in a 
 white connective tissue (mucous tissue), which is called ' Whar- 
 ton's jelly.' 
 
 As soon as the detachment of the placenta commences, 
 foetal respiration through the intermediation of the maternal 
 blood ceases, and in consequence of this a change in the gases 
 of the blood commences, which leads to the first respiration 
 through the lungs (Schwartz). The placenta which is con- 
 tained in the uterus is no longer of service to the child, and 
 the umbilical cord, of which the arteries cease to pulsate, can, 
 after previous ligature of its foetal end, be cut across, unless the 
 expulsion of the placenta with the fcetal envelopes (' after- 
 birth ') be awaited. The skin of the newly-born child is covered 
 with a sebaceous layer, which constitutes the vernix cascosa. 
 After the expulsion of the afterbirth, and the arrest of the 
 haemorrhage by the continuing contractions of the uterus 
 ( 6 after-pains '), a regeneration of the uterine mucous membrane 
 sets in, which is accompanied by a diminution of its muscular 
 coat, and a new formation of muscular fibre cells ; the first of 
 these processes is associated with a mucous, and, at first, bloody 
 discharge, which constitutes ' the lochiaS 
 
 At birth the mammary glands of the mother begin to se- 
 crete (p. 121), and usually it is only on the cessation of the 
 secretion, which takes place about ten months afterwards, that 
 the process of menstruation, which had been arrested by impreg- 
 nation, again becomes re-established. 
 
 D. DEVELOPMENT OF THE CHILD AFTER BIRTH. 
 
 At birth, neither the development of the structures nor of 
 the functions of the young creature is arrested. The commence- 
 ment of extra-uterine life, and the period which succeeds it up 
 to puberty, are especially characterized by important processes 
 of development. During this period (infancy and childhood) 
 the development of the bones, and of the first and second teeth 
 takes place, and growth is most energetic ; above all, it is the 
 period of the development of the mental powers, which from the 
 
568 GROWTH. PERIOD OF LIFE. 
 
 first low stages, when they approximate in their nature reflex ac- 
 tions, under the influence of the multiplicity of external influences, 
 such as experience and education, develop ever more and more. 
 
 Growth is the term which is applied to express the increase 
 in the dimensions of the body in all directions, as well as the 
 increase of weight, due to the excess of the income of the body 
 over its expenditure. The whole of the tissues and parts of the 
 body take a part in this process, so that in general the propor- 
 tions of the growing body are maintained. The most general 
 conception of growth would treat it as being due to an increase in 
 the number of tissue-forming elements, brought about in gene- 
 ral as a result of cell-division, rather than as being due to an 
 increase in the size of those which already exist, although this 
 mode of growth also occurs. 
 
 The usual measure of its growth is the increase in the length 
 of the body, and this is chiefly associated with the growth in 
 length of the bones, which continues until about the twenty- 
 second year. The growth in other dimensions, and the increase 
 in weight, continues until about the fortieth year. 
 
 A diminution in weight occurs during the first days of life, 
 and then again after from forty to fifty years of age ; at the 
 latter age this is associated with a diminution in the length 
 of the body. 
 
 The life of man may be divided into the following periods : 1. ' Infancy,' 
 which lasts from birth until the first dentition (the first 7 or 9 months) ; 
 this is a period of most energetic growth, the length of the body increasing 
 by two-thirds (20 cm ) 2. ' Childhood/ which lasts until the second dentition 
 (from 9 months until 7 years). The growth of the body in the second year 
 amounts to about ten centimetres, in the third to about seven, and in each 
 succeeding year about 5 cm . 3. Boyhood and Girlhood, which last until 
 puberty (from 7 to 15 years). 4. Adolescence, which extends to the com- 
 pletion of the growth of the body (15 to 22 years). 5. Period of maturity 
 (adult age), which lasts until * involution ' occurs in woman, and until retro- 
 grade changes occur in man, i.e. from the twenty-second until the forty-fifth 
 year. 6. Age of gradual retrograde changes (old age), commencing about 
 the forty-fifth year and lasting until death. 
 
 The retrograde changes which occur in the later periods of 
 life consist in manifold processes of wear and contraction and 
 destruction, in which that which is diseased is so little separated 
 from that which is healthy as to preclude any detailed allusion 
 to the phenomena in this place. 
 
CAUSES OF DEATH. 569 
 
 E. DEATH. 
 
 Death puts an end to those processes of the organism which 
 are characteristic of 'Life,' and with death there sets in an 
 assemblage of processes which are comprehended in the term 
 Putrefaction. 
 
 There may be great difference of opinion as to which is the 
 act which marks the close of life. Most naturally the energies 
 of the body, its movements and its heat-production, especially 
 the former, on account of their being easily recognised, appear 
 to be conspicuous characteristics of life. It is obvious, how- 
 ever, that amongst movements, only one which is automatic can 
 serve as an index of life, and of such automatic movements the 
 most regular as well as the most conspicuous are those of the 
 heart. Usually then the standing-still of the heart is looked 
 upon as a sign of death. 
 
 Although it may be urged that the cessation of a single 
 function cannot be taken as a sign of the cessation of all others, 
 yet a continued cessation of the movements of the heart is a 
 certain sign of approaching death, as the function of every 
 organ is associated with a supply of arterialised blood, and this 
 cannot be afforded without the heart. The standing-still of the 
 heart is, therefore, one of the most certain causes of death. 
 
 The inquiry into the causes of death leads to the following- 
 conclusions. As the activities of the body are the result of 
 oxidation processes, there are three forms of general (somatic) 
 death, which may be due to : 1. Deficiency in the material to be 
 oxidized or of those inorganic matters which are indispensable 
 to the vital processes, therefore, defective nutrition. 2. De- 
 ficiency in the supply of oxygenized blood. 3. An absence of 
 the conditions necessary to the oxidizing action of oxygen. 
 
 Now as these circumstances can exert their action upon one 
 or all of the parts of the body, there may be either a general or 
 only a local death. The latter (necrosis, gangrene) may, in 
 its turn, lead to general death, when it implicates an organ, the 
 destruction of which is incompatible with life. The interlace- 
 ment of the various processes of life renders it impossible to 
 effect a strict separation between these three kinds of death ; 
 each of the three circumstances nearly always drags the others 
 
570 CAUSES OF DEATH. 
 
 after it ; it is, therefore, only necessary to examine these indi- 
 vidually in so far as they furnish the primary causes of death. 
 
 I. Defective nutrition constitutes a very frequent, though 
 always a remote, cause of death (cessation of the action of 
 the heart or respiratory muscles being the proximate cause). 
 According to its nature it leads to a gradual death. Death 
 from hunger (p. 207), death which follows the inanition of old 
 people, and also in part local death, due to local disturbances of 
 the circulation, come under this category. 
 
 II. The supply of arterialised blood may be defective or 
 cease altogether: 1. In consequence of the absence of blood, as 
 when haemorrhage occurs through the opening of large vessels 
 or of the heart itself. If the haemorrhage be not fatal, a re- 
 storation may be brought about by the action of water, yet the 
 amount of the red blood corpuscles may be so small as to be 
 insufficient to keep up the necessary exchanges of oxygen. 2. 
 By cessation of the circulation : this occurs (a) locally, by 
 closure of the arteries going to a part (as by ligature, throm- 
 bosis, embolism, or by their being cut), or by a hindrance to 
 the flow of blood, due to obstacles in the veins ; the consequence 
 may be local, or it may even be general, death, if the disturb- 
 ance of circulation affect the principal vascular trunks ; (6) 
 generally, by a positive pressure in the thorax (p. 67), or by 
 an arrest of the heart; this may occur in consequence of 
 injury or defective nutrition (atrophy) of the substance of the 
 heart, of cessation of the circulation in the coronary arteries, 
 of powerful irritation of the medulla oblongata or of the vagi, 
 or of defective supply of oxygen. A cessation of the circula- 
 tion is conceivable in consequence of the cardiac movements 
 being completely ineffective, e.g. by an injury to, or inefficiency 
 of, the cardiac valves. 3. By a hindrance to the absorption 
 and retention of oxygen by the blood. To this category 
 belong all the influences mentioned at page 158, which lead 
 to suffocation, of which some, viz. the cessation of the 
 active movements of respiration, must now be examined 
 more closely. The following circumstances lead to this : a. 
 Paralysis of the respiratory centre in the medulla oblongata, 
 due either to injury or destruction (e.g. by apoplexy) ; defective 
 supply of blood or of oxygen due to circumstances which 
 have already been mentioned ; lastly, the action of paralysing 
 
DEATH. PUTREFACTION. 571 
 
 poisons (such as chloroform), b. Impediments to the con- 
 ducting power of nerves supplying the respiratory muscles,. 
 e.g. section or compression of the phrenic nerves and poisoning 
 by curare, c. Paralysis of the respiratory muscles of the 
 diaphragm. d. Tetanus of the respiratory muscles, as by 
 strychnia-poisoning, or by irritation of the vagi. e. Mechanical 
 hindrances to the expansion of the thorax, as pressure. 4. By 
 expulsion of the oxygen of the blood (poisoning by carbonic 
 oxide), or by a consumption of the oxygen of the blood (by 
 means of reducing agents). 
 
 III. Very little is yet known concerning the circumstances 
 required for the oxidation-processes of the body. It has already 
 been mentioned (p. 231), that the mean temperature of the body 
 is indispensable to life. Great or, at any rate, continuous rises 
 and depressions of the temperature (heating or cooling with 
 simultaneous abolition of the means of heat-regulation) lead 
 to death. Possibly there are poisons which, like those which 
 prevent putrefaction, render processes of oxidation impossible. 
 
 It belongs to the province of pathological science to inves- 
 tigate the modes in which diseases, injuries, and abnormal 
 external circumstances, occasion death. Death from old age is 
 usually designated as the physiological ( or natural ' mode of 
 death ; this is a mode of death of which the proximate cause 
 is unknown, but of which the remote causes are to be sought 
 for in the diminished capacity for action of the organs of the 
 body as a whole, and which is partly due to atrophy, partly to- 
 degeneration. 
 
 After the phenomena of ' rigor mortis ' have passed away, the dead body 
 falls a prey to putrefaction, unless this be prevented by very rapid desicca- 
 tion or by the use of agents which oppose putrefaction. Putrefaction, con- 
 cerning which little is yet known, consists in a slow oxidation of the organic 
 constituents, brought about by the oxygen of the air, under the influence of 
 a ferment, such as vibrios must probably be considered (Pasteur). 
 
 The marks of post-mortem lividity (suggilations, livores) are precursors 
 of putrefaction, which, in addition to cadaveric rigidity, afford an almost 
 certain proof of death ; these marks are occasioned by the blood-colouring 
 matter diffusing out of the blood-corpuscles, first into the serum, and after- 
 wards into the fluids moistening the arterial walls, the parenchyma of 
 organs and the skin. 
 
ADDENDUM. 
 
 Appendix to the Mechanism of Respiration (p. 170). 
 
 THE introductory passages concerned in respiration are the nasal apertures, 
 the pharyngo-nasal cavity, the larynx, and the trachea. Eespiration by the- 
 mouth, although frequently voluntary, as a rule merely serves to replace 
 that by the nose, when the passages of the latter are from any cause 
 obstructed. The above-mentioned channels in part subserve the purposes 
 of respiration by means of suitable arrangements with which they are pro- 
 vided, and in part are the seat of certain movements which are induced in 
 them by the motions of respiration. The inspired air, in passing along them 
 to the lungs, is warmed, and deprived, by contact with the walls, of the 
 coarser solid impurities which it may contain. These particles, as well as- 
 superfluous mucus, &c., are driven outwards by the waving cilia which are 
 present on nearly every portion of the walls. 
 
 The larynx further possesses in the vocal cords an apparatus for prevent- 
 ing the entrance into the trachea of foreign bodies, such as saliva, small 
 portions of food, &c., as well as of certain irritating gases j for every 
 stimulus causes reflex closure of the glottis. If the glottidean muscles be 
 paralysed by section of the vagi, or of the inferior laryngeal branches of the 
 vagi, such foreign bodies gain entrance into the lungs easily, and induce 
 fatal inflammations (Traube). 
 
 The expulsion of foreign particles which have either found their way 
 into the respiratory passages, or have arisen there as pathological products 
 (mucus), is brought about by the stimulation of the mucous membrane 
 which they cause, and which induces, in a reflex manner, an explosive ex- 
 piratory blast of air, by which they are driven out. Such explosive expira- 
 tion is called sneezing when the nasal cavities are concerned, and coughing 
 when the irritant is in the larynx. Each is accompanied by a noise pro- 
 duced by the sudden bursting open of a closed aperture, which in sneezing^ 
 is formed by the apposition of the velum palati to the pharyngeal wall, and 
 in coughing by the apposed vocal cords. Coughing may be induced by 
 mechanical irritation of any portion of the respiratory mucous membrane 
 from the lower surface of the upper vocal cords to the alveoli, but it is 
 especially violent when the irritant is applied at the larynx, or at the place 
 of bifurcation of the trachea below (Nothnagel). The sensory nerves im- 
 
74 ADDENDUM. 
 
 plicated in the reflex act of sneezing are the trigeminal nerve, and possibly 
 ^also the olfactory nerve, and in coughing- probably the superior laryngeal 
 branches of the vagi especially. Coughing may also be voluntary. It is 
 quite possible that the bronchial muscles referred to previously (p. 161) may 
 assist in expelling mucus, &c. from the finer bronchial tubes. 
 
 Expired air may be used voluntarily for purposes similar to those just 
 discussed. For example, mucus may be driven from the nose, the nostrils 
 being voluntarily compressed from without in the process of what is called 
 4 blowing the nose ; ' or through the isthmus of the fauces, which is nar- 
 rowed by muscular action, as in ' clearing the throat.' Fluids which it is 
 desired to keep in the throat for some time without swallowing are pre- 
 vented from entering into the air-passages by keeping up a stream of expired 
 air, which, as it escapes through the fluid in bubbles, causes the character- 
 istic noise of ' gargling.' Warm and moist air expired through the widely- 
 opened mouth may be used for the purposes of heating and moistening. 
 Finally, vocal cords, uvula, tongue, lips, or any of the other apparatuses of 
 the mouth for the purpose of vocalising, may be set in sonorous vibration, 
 as in ' singing,' ' speaking,' ' blowing.' (Voice and speech are discussed in 
 Chapter VIII.) 
 
 If the glottis be closed after a deep inspiration, and the abdominal 
 muscles then powerfully contracted, the viscera of the abdomen become 
 strongly compressed, and such pressure may aid in the expulsion of the 
 contents of the various abdominal organs rectum, uterus, and bladder 
 {abdominal pressure). 
 
NOTES 
 
 BY THE A U T H B. 
 
 PAGE 36. 
 
 According to more recent researches (Hoppe-Seyler and Diaconow), 
 pvotagon must be regarded as a combination in which lecithin is contained 
 in addition to cerebrin. Cerebrin (W. Miiller), C 17 H 33 N0 3 (?), is a glucoside, 
 and exhibits the property, ascribed to protagon, of swelling up on the addi- 
 tion of water. When decomposed by means of mineral acids it yields, in 
 addition to other, as yet uninvestigated, products, a body of the sugar-group 
 which deflects the plane of polarisation to the left. 
 
 PAGE 73. 
 
 The hypothesis given in the text, in consequence especially of researches 
 on certain poisons, now appears to have become as untenable as the older 
 view, according to which there exist in the heart, and particularly in the 
 auricles, inhibitory centres in connection with the vagus, but possessing a 
 tonus of their own. There are certain poisons, of which muscarine is the 
 chief, which induce, even after section of the vagi, a stand-still of the heart 
 in diastole, during which condition every stimulus is followed by a single con- 
 traction. Atropia, on the contrary, causes the heart to beat more quickly, 
 and interferes in the results of vagus-irritation and in the action of muscarine. 
 It is not sufficient to explain these effects as due to irritation or paralysis of the 
 inhibitory vagus-endings ; for nicotine (which operates like atropia, except 
 at the onset, when its action seems to be the reverse) does not prevent the 
 stand-still due to muscarine, and therefore paralyses portions of the nerve 
 nearer to the centre than those acted on by atropia. The portions cf the 
 nerve in the latter case are probably the vagus-ending, while muscarine 
 and atropia act upon the ganglionic inhibitory apparatus (Schmiedeberg, 
 Bohm). 
 
 Hence Stannius's experiment would have to be explained by assuming 
 that, after the separation of the sinus-ganglion, the inhibitory centres in the 
 whole separated portion (auricles and ventricles) overcome the motor centra, 
 while in the ventricle by itself the latter kind only are present (von Bezold). 
 
576 NOTES. 
 
 That the vagus contains accelerating as well as inhibitory fibres is 
 established by this fact, among others, that in poisoning by atropia irritation 
 of the vagus causes the heart to beat more quickly (Schmiedeberg). 
 
 PAGE 111. 
 
 According to later researches (Heidenhain), easily recognisable sub- 
 stances which pass into the urine, such as sulph-indigotate of sodium, do not 
 appear in the capsules and in the straight uriniferous tubules, but only in the 
 convoluted tubules, after they have been injected into the blood-vessels. This 
 shows that the capsules effect the separation of water alone, and perhaps 
 also of salts, the specific constituents of the urine being secreted from the 
 blood by the epithelium of the convoluted tubules. This circumstance sup- 
 ports the theory of Bowman against that of Ludwig concerning the secretion 
 of urine, as does also the observation of von Wittich, referred to in the text, 
 respecting the kidneys of birds, which observation may be confirmed in the 
 case of mammalia after the injection of sodium urate. Additional impor- 
 tance must be attached to these facts, since, after the functions of the capsule 
 have been abolished by cauterising the cortex, the tubuli still take up 
 colouring matter, which, however, on account of the deficient supply of 
 water, remain in them (Heidenhain). 
 
INDEX. 
 
 ABD 
 
 ABDUCENS (6th) nerve, 349 ; origin 
 of, 496 
 
 Absolute muscular force, 265 
 
 Absorbed materials, destination of, 134 
 
 Absorption, 127; methods of, 128; 
 forces concerned in, 130; seats of, 
 131 
 
 Accelerating nerves of heart, 74; of 
 respiratory movements, 167 
 
 Accommodation, 372 ; changes in the 
 form of the lens during, 373 ; changes 
 in the optical constants of the eye 
 which occur during, 374 ; participation 
 of the iris in, 375; nerves concerned 
 in, 375; rate at which it occurs, 375; 
 influence of Calabar bean upon, 375 ; 
 power of, diminishes with age, 377 
 
 Acetic acid, 1 3 
 
 anhydride, 18 
 
 ether, 18; decomposition of, 19 
 Acidification of the blood, 51 ; of mus- 
 cle, 250 
 
 Acidity of urine, 110 
 Acids, aromatic, 16 
 
 cholic, 16 
 
 fatty, 13 
 
 glycollic, 14 
 
 inorganic, 12 
 
 oleic, 16 
 
 oxalic, 15 
 Acrylic acid, 16 
 
 ' Adelomorphous ' cells of gastric glands, 
 
 99 
 After-images, 400 
 
 tastes, 457 
 
 tones, 448 
 
 smells, 454 
 
 Ages of man, the, 5.68 
 
 Albumen, 33 
 
 Albuminoid bodies, 31 
 
 Albuminous bodies, in their relation to 
 
 fats, 193 
 Alcohols, 17 
 
 ATM 
 
 Alimentary secretions, 92 
 
 Allantoin, 28 
 
 Allantois, the, 566 
 
 Alloxan, 23 
 
 Alloxantin, 24 
 
 Alto voice, range of, 311 
 
 Amides, 22 
 
 Ami do-acetic acid, 24 
 
 Amido-acids, 24 
 
 Amines, 21 
 
 Ammonia and ammoniacal derivatives, 
 20 
 
 Amnion, development of the, 555 
 
 Ampullse, nerves ending in the, 437 
 
 Amylolytic ferments, 35 
 
 Anelectrotonus, 325 
 
 Angelic acid, 16 
 
 Anhydrides of sugar, 20 
 
 Anisic acid, 17 
 
 Ankle-joint, relation of, to the erect 
 posture, 298 
 
 Antagonism of muscles, 289 
 
 Aphasia, 513 
 
 Apno3a, 270 
 
 Arachidic acid, 13 
 
 Area rasculosa, 552 
 
 Arterial system, systemic, 55 ; pulmo- 
 nary, 55 ; development of, 553, 560 
 
 Articulate sounds, classified, 311 
 
 Ascending and descending currents, 
 effects of, on nerves, 328 
 
 Asphyxia, 170, 171 ; definition of, 17 S 
 
 Aspirates (see Consonants), 315 
 
 Aspiration of the thorax, 66 ; its in- 
 fluence on the circulation of lymph, 
 136 
 
 Assimilation, 37; chief processes of, 184 ; 
 seat of, 185 
 
 Associating fibres, 492 
 
 Astigmatism, 382 
 
 Atmospheric air, composition of, 149 
 
 Atmospheric pressure, part played by, 
 in respiration, 159 
 
 P P 
 
678 
 
 INDEX. 
 
 ATE 
 
 CIL 
 
 Atropia, action of, upon accommodatioo, 
 
 372 ; action of, on pupil, 375 
 Auditory cirrhi, 437 
 Auditory nerve, 350, 496 
 Automatic rhythmical contractions, 72 
 Automatism, 467, 470 
 Axis-cylinder, 321 
 
 BAKBITUKIC acid, 23 
 Bass voice, 311 
 
 Beats, 444 et seq. 
 
 ' Belegzellen ' of gastric glands, 99 
 
 Benzoic acid, 17 
 
 Benzol, 17 
 
 Bidder's ganglion, 73 
 
 Bile, 101 ; its secretion, 102 ; its use in 
 digestion, 105^__ 
 
 Bilicyanin, 29 
 /-Bilifuscin, 29 
 
 Biliphaein, 28 
 
 Biliprasin, 29 
 
 Bilirubin, 28 ; its derivatives, 29 
 
 Biliverdin, 29 
 
 Birth, 565 
 
 Bladder, changes which the urine under- 
 goes in the, 118 
 
 Blastoderm, layers of the, 549 ; different 
 
 views as to, 563 
 
 / Blood, 39 ; coloured corpuscles of the, 
 39 ; colourless, 42 ; composition of 
 coloured corpuscles of, 40 ; composi- 
 tion of colourless corpuscles of, 42 ; 
 plasma of, 42 ; chemical composition 
 of plasma of, 50 ; arterial and venous 
 varieties of, 48 ; gases of, 43 ; acidi- 
 fication of, 51 ; deoxygenation of, 51 ; 
 quantity of, in the body, 49; circu- 
 lation of the, 54 
 
 Blood-crystals, 41 
 
 Blood-vessels, innervation of, 75 
 
 Boracic acid, action of, on the coloured 
 blood-corpuscles, 40 
 
 Branchial arches, 557 
 
 clefts, 557 
 
 ' Bruit musculaire,' 260, 267 
 
 Bursse mucosae, fluids of, 92 
 
 Butter, 124 
 
 Butter-milk, 124 
 
 Butylactic acid, 14 
 
 Butyric acid, 13; its oxidation, 2 
 
 PALABAK BEAN, action of, upon the 
 
 \J accommodation of the eye and upon 
 
 the iris, 375 
 
 Calorification of the blood at death, 51 
 Capri c acid, 13 
 Caproic acid, 13 
 
 
 Caprylic acid, 13 
 
 Carbamide or urea, 22 
 
 Carbohydrates, 18; of food, in relation 
 to the fats of the body, 195 
 
 Carbon, 9 
 
 Carbonic acid, 14, 15; its presence in ^ 
 the blood, 47 ; its formation in mus- 
 cle, 250 
 
 Cardinal points of the eye, 366 
 
 Carmine, 27 
 
 Casein, 33 ; its presence in milk, 123 ... 
 
 Catelectrotonus, 325 
 
 Cellulose, 20, 
 
 Central nervous organs, 467 
 
 Centrifugal chains, 6 
 
 Centripetal chains, 6 
 
 Cereals, considered as articles of diet, 
 196 
 
 Cerebellum, 509 
 
 Cerebral vesicles, the, 5-58 
 
 Cerebrin, 575 
 
 Cerebrum, cortex of, 510 ; proofs that 
 it is the seat of psychical activity, 
 510; effects of electrical stimulation 
 of, 514 
 
 Cerumen, 119 
 
 Chains, centrifugal, 6 
 
 centripetal, 6 
 
 liberating, 6 
 
 Check-mechanism of joints, 293 
 Chemical constituents of red blood-cor- 
 puscles, 40 ; of colourless blood-cor- 
 puscles, 42 ; of the plasma or liquor 
 sanguinis, 42 ; of the blood, 50 ; of 
 osseous tissue, 90 ; of cartilaginous 
 tissues, 91 ; of connective tissue, 91 ;: 
 of synovia, 92; of the fluids of 
 tursse mucosse, synovial sheathes, 
 92 ; of saliva, 94 ; of gastric juices, 
 99; of bile, 102; of pancreatic juice,. 
 107; of coagulated beef-muscle, 241 
 
 Chenocholic acid, 16 
 
 Chiasma nervorum opticorum, 417 ^ 
 
 arrangement of fibres in, 509 
 Chitin, 37 
 Chlorine, 9 
 
 Chlorobenzoic acid, 17 
 Cholepyrrhin, 28 
 Choletelin, 29 
 Cholic acid, 16 
 
 acids, series of, 16 
 Choline, or neurine, 21 
 Choloidic acid, 16 
 Chondrin, 36 
 
 Chondrogenous substance, 91 
 Chorion, the, 556 
 Chromatic aberration, 380 
 Chyle, 135 
 
 Chyme, 139 
 Cilia, 285 
 
INDEX. 
 
 579 
 
 CIL 
 
 ELE 
 
 Ciliated cells, 285 ; circumstances which 
 influence movement of, 285 
 
 Circles of diffusion, 371 ; of sensibility 
 in the skin, 463 
 
 Circulation, of the matter of the organ- 
 ism, 3 
 
 velocity of, 69 
 Cirrhi, auditory, 437 
 Cloaca, the, 558 
 Coagulation of the blood, 50 
 Cochlea, structure of the, 438 ; analysis 
 
 of compound tones by, 443 
 
 Co-efficient of absorption, 43 ; of ven- 
 tilation, 165 
 
 Coitus, 534, 544 
 
 Colloids, 85 
 
 Coloured or red blood-corpuscles, 39 
 / Colouring matters, 28 
 >Colourless or white blood-corpuscles, 42 ; 
 origin of, 178 
 
 Commissural fibres, 492 
 
 Complementary air, definition of, 165 
 
 Compounds, chemical, of the body, 10 
 
 Conduction by nerves, 335 
 
 Conductivity, paths of more or less 
 perfect, in cord, 480 
 
 Conjugate focal distances, 360 
 
 foci, 360 
 
 planes, 363 
 
 Consciousness, 7 ; states of, 472 
 Consonance and dissonance, 444 et seq. 
 Consonants, 311, 314; their classifica- 
 tion, 315 
 
 Constancy of the amount of blood in the 
 body, 185 
 
 Contractility, muscular, its indepen- 
 dence, 247 
 
 Contraction, single muscular, 257 ; 
 analysed, 257 ; time occupied by, how 
 measured, 258; 'secondary,' defined, 
 260 ; Pfliiger's law of, 327 
 
 Contrast, simultaneous, 402 
 
 Contrasting colours, 401 
 
 Convulsions, reflex, 479 
 
 Copper, its occurrence in the body, 9 
 
 Corpora quadrigemina, functions of, 507 
 
 lutea, 540 
 
 striata, functions of, 507 
 Corresponding or identical points, 410, 
 
 417 
 
 Corti, organ of, 438 
 
 Coughing, 573 
 
 Cranial nerves, enumeration and func- 
 tions of, 347 ; origin of, 495 
 
 Cream, 124 
 
 Creatine, 26 
 
 Creatinine, 28 
 
 Crotonic acid, 16 
 
 Crystalloids, 85 
 
 * Currents of inclination' defined, 273 ; 
 
 weak, defined, 272 ; strong, defined, 
 
 272 
 
 ' Cutaneous currents,' 274 
 Cyanamide, 26 
 Cystine, 25 
 
 "TvAMPING- of the resonators in the 
 
 Lf ear, 441 
 
 Darwinian theory, the, 528 
 
 Death, 569 
 
 Decompositions which occur in the living 
 
 body, 2 
 
 Definition of Physiology, 1 
 Deglutition, 143 
 ' Delomorphous ' cells of gastric glands, 
 
 99 
 Deoxygenation of the blood, at death, 
 
 51 
 Depressor branch of the vagus (nerve of 
 
 Ludwig and Cyon), 79 
 Development, modifications of, 536 
 Dextrin, 20 
 Diabetes and the circumstances which 
 
 induce it, 188 ; centre in the medulla 
 
 oblongata, lesion of which induces, 
 
 503 
 
 Dialuric acid, 23, 24 
 Diapedesis, 81 
 
 Diastole of auricles and ventricles, 57 
 Diffusion, in relation to secretion, 85 ; 
 
 in relation to absorption, 130 
 Digestion, 136; chemistry of, 137; 
 
 mechanism of, 142 
 Diphthongs, nature of, 314 
 Direction, lines of, or visual rays, 368 
 Disdiaclasts, 239 
 Distance of objects, estimation of, by 
 
 the eye, 425 
 
 Distribution of the blood in the body, 71 
 Dolium galea, secretion of, 12 
 Dot/ere, prominence of, 239 
 Ductus arteriosus, 560 
 Dynamogenous constituents of food, 224 
 Dyslysin, 16 
 Dyspnoea, 172 
 
 ECONOMY of the organism, the, 199 
 Eggs, considered as an article of 
 diet, 195 
 Elastin, 34 
 
 Electric currents (a) of muscles, 270 ; 
 negative variation of, 275 ; electro- 
 motive force of, 273; theories to 
 explain the occurrence of, 276 
 
 (b) of nerves, 338; electromotive 
 force of, 338 ; negative variation of, 
 339 ; theories to explain the occur- 
 rence of, 340 
 
 Electromotive force (a) of muscular 
 current, 273 ; of nerve current, 338 
 
580 
 
 INDEX. 
 
 ELE 
 
 GLT 
 
 Electrotonus, 325 
 Embryo, rudiment of the, 547 
 Emigration of blood-corpuscles, 81 
 Emmetropic eye, the, 376 
 Emydin, 36 
 Encephalon, 491 
 Endosmose, 85 
 Endosmotic force, 85 
 Energies of the body, the, 215 
 Energy, potential, of the body, intro- 
 duction of, 216 ; kinetic, 217 ; forms 
 which it assumes in the body, 4; 
 expenditure of, in body, 220 ; compa- 
 rison between income and expenditure 
 of, 221 ; influence of conversion of, on 
 the exchanges of matter, 222 
 
 yielding material of the organism, 
 
 2 
 
 Entoptic phenomena, 402 
 Entotic phenomena, 448 
 Epiblast, the, 549, 550 
 Equator, of a muscle, 272 ; of the eye 
 
 defined, 404 
 Equilibrium of the body, conditions of 
 
 the, 295 
 
 Erect posture, the, 295 
 Erection, mechanism of. 543 
 Ethers and anhydrides, 18 
 Eustachian tube, function of the, 433, 
 
 436 
 
 Exchanges of the matter of the organ- 
 ism, 9, 190 
 
 Excretions defined, 83 
 Exhaustion, of muscle, 249; of nerve, 
 
 324 
 
 Expenditure of the organism, 198 ; con- 
 trasted with its income and stock, 
 199 
 
 Expiration, mechanism of, 163 
 Explosives, 315 
 
 Eye, the, 354 ; schema of, 355 ; forma- 
 tion of images in, 358 ; refracting 
 media of, 355 ; indices of refraction 
 of refractive media of, 357 ; cardinal 
 points of, 366 ; accommodation of, 372 ; 
 anomalies and peculiarities of, 380 ; 
 illumination of, and examination of, 
 by means of ophthalmoscope, 383 ; 
 movements of, 403 ; muscles of, 407 ; 
 organs which protect, 426 
 
 T7ACETTED eyes of insects, 428 
 
 X! Facial (7th) nerve, 349, 496 
 
 Faeces, evacuation of, 146 
 
 Falsetto voice, 309 
 
 Fat, its presence in milk, 124 
 
 Fatigue or exhaustion of muscle, 249, 
 
 266 
 Fats, neutral, constitution of, 19; their 
 
 enumeration, 19; their decomposition, 
 19 ; their presence in milk, 122, 124; 
 of the body, whence derived? 193 
 
 Fatty acids, homologous series of, 13 
 
 Fechners formula, 517 
 
 Ferments, hydrolytic, 35 
 
 Fernet' 's views on the state of the car- 
 bonic acid of the blood, 47 
 
 Fertility, 530 
 
 Fibrin, 33, 50 
 
 Fibroin, 35 
 
 Field of vision, 395 
 
 Filtration, influence of, in secretion, 84 ; 
 influence of in absorption. 130 
 
 Flesh, as an article of diet, 195 
 
 Fluids of cavities, 91 
 
 Fluorescence, 382 
 
 Fluorine, 9 
 
 Food, organic constituents of, 2 ; inor- 
 ganic constituents of, 3 ; defined, 190 ; 
 classified, 191, 224 
 
 Foramen ovale, the, 560 
 
 Formic acid, 13 
 
 Friction, internal, of liquids, 61 (foot- 
 note) ; of air, in bronchial tubes, 166 
 
 Fundus of the eye, image of, how ob- 
 tained, 384 
 
 A, at the base of the brain, 
 U relation of the, 494 ; functions of, 
 
 504 ; sympathetic, 522 
 Ganglion-cells, 467; properties of, 468 
 
 et seq. ; summary of hypothetical 
 
 properties of, 473 ; conditions of the 
 
 activity of, 474 
 
 Gaseous exchanges of the body, 156 
 Gases, classified in respect to their action 
 
 on respiration, 174; of the blood, 43 
 Gastric-juice, 97 ; the glands which 
 
 secrete it, 99 ; influence of nerves 
 
 upon secretion of, 100 
 Gelatiginous substance, 90 
 Gelatin or Glutin, 34 
 Germinal area, 548 
 
 epithelium, 561 
 
 spot, 532 
 
 - vesicle, 532, 547 
 Glands, definition of, 88 ; classification 
 
 of, 88 
 
 Glandular secretions, 92 
 Globulin, 33, 42 
 Glomerulus of kidney, 112 
 Glosso-pharyngeal (9th) nerve, 350, 496 
 Glucosicles, 20 
 Glutin or gelatin, 34 
 Glyceric acid, 25 
 
 ethers, 19 
 Glycerin, 17, 19 
 Glycerin-phosphoric acid, 19 
 
INDEX. 
 
 581 
 
 GLT 
 
 IER 
 
 Glyco-benzoic (hippuric) acid, 25 
 
 Glycocholic acid, 25 
 
 Glycocine, 24 
 
 Glycogen, 20; how prepared, 186 
 action of ferments on, 187 ; whenc 
 derived, 188 ; destination of, 188 
 
 Glycollic acid, its formula, 14 
 
 acids, series of, 14 
 Grape-sugar, 17 
 
 Grey substance of brain, chemical com 
 
 position of, 469 
 Growth, 568 
 Guanidine, 22 
 Guanine, 28 
 Guano-gallic acid, 16 
 Gum, 20 
 Gustatory bulbs, 455 
 
 sensations, 466 
 
 H^EMATIN, 29, 41 
 Hsematoidin, 28, 41 
 Hsemin, 41 
 Hsemochromogen, 41 
 Hsemodromometer, the, of Volkmann, 
 
 70 
 
 Hemoglobin, 36, 40 
 Harmony of musical sounds, 444 
 ' Hauptzellen ' of gastric glands, 99 
 Hearing, the organ of, 429 ; from out- 
 side, 447 ; with both ears, 449 
 Heart, 56 ; muscular fibres of, 56 ; 
 rhythmical movements of, 57, 72, 77 ; 
 valves of, 58 ; sounds of, 60 ; work 
 done by, 64 ; innervation of, 72 ; 
 development of, 552, 559 
 Heat, development of, in the body, 218, 
 226 ; absolute amount of, generated 
 in the unit of time by unit weight of 
 any organ, 226 ; whether controlled 
 by nervous system, 227 ; losses of, 
 228; arrangements concerned in regu- 
 lating, 233 ; development of, in 
 muscle, 268 ; how measured, 269 ; de- 
 velopment of, during rigor, 269 ; of 
 combustion of various proximate 
 principles, 217 
 Heat-unit, 4 
 
 Hemiopia, explanation of, 417 
 Hepatic artery, influence of blood of, on 
 
 secretion of the bile, 103 
 - lobule, structure of, 102 
 Hermann's ' inogene ' theory of the mus- 
 cular economy, 253 
 
 Hip-joint, mechanism of the, 293, 297 
 Hippuric acid, 25 
 Homo-thermous, or warm-blooded, 
 
 animals, 228 
 Horopter, the, 411 
 ' Hubhoke,' defined, 262 
 
 Hunger, 197 
 
 Hyalin, 37 
 
 Hybernating animals, 234; peculiarity 
 
 of muscular current in, 274 
 Hydro-bilirubin, 29 
 Hydrochloric acid, 12; presence of, in 
 
 gastric juice, 97 
 Hydrogen, 10; peroxide of, 12 
 Hydrolytic decompositions, 2, 19, 30 
 ferments, 34 
 Hyocholic acid, 16 
 Hyodyslysin, 16 
 Hypermetropia, 377 
 Hypoblast, the, 549, 554 
 Hypoglossal (12th) nerve, 353, 496 
 Hypo xan thine, 27 
 
 TCTHIN, 36 
 -L Icthydin, 36 
 Idio-muscular contractions, 262 
 Illumination of the eye, 383 
 Images, formation of, 358 ; real and 
 virtual, 360 ; formation of, on retina 
 when the eye is passive, 370 ; sub- 
 jective, 400 ; persistent or after-, 400 
 Impregnation, 533, 545 
 Income and expenditure, of the blood, 
 
 149; of the body, 199 
 Index of refraction of the ocular media, 
 
 357 
 
 Ingestion of food, 196 ; effects of ex- 
 cessive, 200, 210; effects of insuffi- 
 cient, 206 
 
 Inhibitory centres, 78, 481 
 nerves of heart, 73 ; of respiration, 
 
 167 
 
 Innervation of heart, 72 
 Inogene substance, 253 
 Inosinic acid, 28 
 Inosite, 18 
 
 Inspiration, mechanism of, 162 
 Inter-central nerve fibres, 346 
 Intestinal juice, 108 
 Intestines, changes which food under- 
 goes in, 139; development of the, 559 
 Intra-cardiac nerve centres, 72 
 Iris, 377; fibres of, 377; supply of 
 nerves to, 378 ; effect of irritating 
 optic nerve on, 378 ; action of atropia 
 and Calabar bean on, 375 
 Iron, 9 
 
 Irradiation, 401 
 
 Irritability, (a) muscular, 247 ; facts 
 proving independence of, 274 ; varia- 
 tion of, 248 ; circumstances which 
 lead to its diminution, 249 ; means of 
 restoring, 249. 
 
 (b) ner vous, 323 ; effects of elec- 
 ical currents upon, 325 
 
INDEX. 
 
 JOI 
 JOINTS, classification of, 291 
 
 T7ERATIN, 34 
 
 1\. Kidney, structure of the, 112; 
 
 development of the, 561 
 ' Kinesogenous ' constituents of food, 
 
 224 
 
 Kinetic energy, of the body, 14 
 Knee-joint, mechanism of the, 294, 298 
 Krause's corpuscles, 457 
 Kumiss, 125 
 Kymographion, Ludwig's, Fick's and 
 
 Marey's, 65 
 Kynuretic acid, 28 
 
 T ACHRYMAL apparatus, the, 427 
 
 Jj Lacteals, 129 
 
 Lactic acid, 14 
 
 Lake- coloured blood, 40, 48 
 
 Larynx, 305 ; constituent parts of the, 
 305 ; muscles of the, 306 ; nerves of 
 the, 307 ; observations on, how con- 
 ducted, 309 ; relation of development 
 of, to sexual powers, 311 
 
 Latent period, 257 
 
 Laughing, 167 
 
 Laurostearic acid, 13 
 
 Lead, occurrence of, in body, 9 
 
 Lecithin, 21 ; presence of in milk, 122; 
 in brain, 469 ; in the ovum, 532 
 
 Lenses, optical, properties of, 368 
 
 Leucic acid, 14 
 
 Leucin, 25 
 
 Liberating apparatus, the, 319 
 
 chains, G 
 
 force, definition of, 5 
 Liberation, of the movements of the 
 
 digestive apparatus, 146 ; of the 
 respiratory movements, 166; of mus- 
 cular activity, 247 
 
 "Lift, the' (' Hiibhohe'), 262 
 
 Liminal intensity, 519 
 
 Lines of separation, 411 
 
 Liquor amnii, 555 
 
 sanguinis, 42 
 
 ' Listing's ' law, 405 
 
 Lithofellic acid, 14 
 
 Liver, lobules of, 102 ; development of, 
 
 554 
 Losses of the body, enumeration of the 
 
 various necessary, and their reparation 
 
 by food, 202 
 
 Lungs, development of the, 554 . 
 * Luxus-consumption,' definition of the 
 
 term, 213 
 
 MIL 
 
 Lymph, 135; pressure under which it 
 circulates, 135; the forces concerned 
 in its circulation, 136 
 
 Lymph-cells, 134, 135 
 
 Lymph-sacs, 129 
 
 Lymph-spaces, 128 
 
 Lymphatic glands, 134 
 
 vessels, 128 
 
 MAGNESIUM, 9 
 Magnifying power of optical 
 instruments, 398 
 
 Magnitude of objects, estimation of, by 
 the eye, 425 
 
 Malonic acid, 15 
 
 Malpighian bodies of kidney, 112 
 
 Manganese, 9 
 
 Margaric acid, 13 
 
 Marrow of bone, structure of, and re- 
 lation of, to blood-corpuscles, 179 
 
 Mastication, 142 ; nerves concerned in, 
 143 ; nerve centre presiding over 
 movements of, 503 
 
 Material exchanges of the organism, 3 
 
 Mean temperature of animal bodies, 
 228, 231 ; arrangements concerned in 
 maintenance of, 231; fluctuations in, 
 233 
 
 Mechanical equivalent of heat, 4, 220 
 
 work of muscle, 256 ; usual expression 
 of, 256 
 
 Mechanism of the skeleton, 289 
 Medulla oblongata, 497 ; various centres 
 
 in, 498 
 Medullary folds, 549, 550 
 
 sheath of nerve fibres, 321 
 
 tube, the, 550, 558 
 Meibomian glands, secretion of, 121 
 Melanin, 29 
 
 Membrana basilaris, 438 
 
 tectoria, 438, 444 
 
 tympani, 431 ; action of tensor tym- 
 pani upon, 432 ; vibration of, with 
 the harmonic overtones of the exciting 
 tone, 443 
 
 Membrane of Eeissner, 438 
 
 Menstruation, 539 
 
 Mesoblast, the, 549, 551 
 
 Metamorphosis, progressive and retro- 
 grade, 37 ; of insects, 536 
 
 Methylamine, 21 
 
 Methyl-guanidine, 26 
 
 Methyluramine, 22 
 
 Milk, 121 ; physical properties of, 
 122 ; secretion of, 123; 'circumstances 
 which affect secretion of, 124 ; amount 
 of, 125 ; considered as an article of 
 diet, 195 
 
INDEX. 
 
 583 
 
 MIL 
 
 OEG 
 
 Milk-sugar, 18, 122, 123 
 
 Mind, definition of, 7 
 
 Motor oculi (3rd) nerve, 347; effects 
 
 which follow division of, 348; origin 
 
 of, 495 
 
 Motor roots of spinal nerves, 353 
 Movable joints, 290 
 Movements, of the body, 236 ; voluntary 
 
 and involuntary, 296 ; compulsory, 
 
 505 
 Mucin, 34 ; presence in the nuclei of 
 
 blood-corpuscles, 42 ; occurrence of, 
 
 in saliva, 93 
 Mucus, 92 
 Miiller's duct, 561 
 Muscle, 
 
 A. striated structure of, 238 ; termi- 
 nations of nerves in, 239 ; chemical 
 constituents of, 240 ; different condi- 
 tions of, 242 ; tone of, 487 ; mechanical 
 properties of, when in a state of rest, 
 242 ; exchanges of matter in, when 
 in a state of rest, 243 ; the various 
 kinds of rigor of, 244; essential 
 nature of the process of rigor of, 245 ; 
 nature of the influences which occasion 
 the state of activity of, 247 ; stimuli 
 to the contraction of, classified, 248 ; 
 circumstances which affect the action 
 of stimuli of, 248 ; chemical processes 
 which occur in, 250 ; theories to 
 account for the phenomena which 
 accompany contraction of, 251 ; 
 changes in the form of contracting, 
 256 ; amount of work done by con- 
 tracting, 262, 267 ; thermic pheno- 
 mena of, 268; electrical phenomena 
 of, 270 ; hypotheses to explain the 
 latter, 276 
 
 B. Unstriped, 281 
 Muscle-curve, 257 
 
 plasma, 240 
 
 prisms, 238 
 
 tubes, or fibres, 238 
 
 Muscular current, the, 270 ; demon- 
 stration of, 271 ; 'negative deflection' 
 of, 275 ; theories to explain occurrence 
 of, 276 
 
 Muscular fatigue, or exhaustion, 249; 
 influence of, on the absolute force of 
 muscle, 260 
 
 Muscular fibres of heart, 56 
 
 murmur, 260, 267 
 
 sense, the, 465 
 
 Myopia, 376; correction of, by glasses, 
 
 377 
 
 Myosin, 34, 240 
 Myotics, definition of, 380 
 Myristic acid, 13 
 
 "YTATUKAL selection, 529 
 
 ll ' Near point ' and ' far point,' 376 
 
 Negative deflection, of muscular current, 
 275 ; wave of, 276 
 
 Nerve-fibres, medullated and non-medul- 
 lated, 321; classification of, according 
 to functions, 343 ; centripetal, centri- 
 fugal and inter-central, 343 ; mode of 
 determining function of, 346 
 
 Nerves, structure of, 321; chemical 
 constituents of, 322; various condi- 
 tions of, 322 ; irritability of, 323 ; 
 circumstances affecting irritability of, 
 323 ; electrical stimuli of, 326 ; 
 chemical stimuli of, 331 ; thermal 
 stimuli of, 331; mechanical stimuli of, 
 332 ; natural stimuli of, 332 ; centri- 
 fugal and centripetal, 333; conduction 
 by, 336 ; determination of rapidity of 
 conduction of, 336 ; resistance of, to 
 passage of electricity, 337; inhibitory, 
 ' of heart, 73; secretory, 89, 95 ; vaso- 
 motor, 75 ; trophic, 90 
 
 Nervous activity, theories concerning 
 342 
 
 system, influence of, upon conversion 
 of potential into kiaetic energy, 4; 
 influence of upon the circulation of 
 the blood, 72 ; classification of the- 
 organs of, into five groups, 317 
 
 'Nervus depressor' of Ludwig and 
 Cyon, 79 
 
 Neurilemma, 321 
 
 Neurine or choline, 21 
 
 Nitrogen, 10 ; presence of, in the blood, 
 48 
 
 'Nceud Vital,' 167 
 
 ' Non-polarisable electrodes,' employed 
 in researches in animal electricity, 
 271 
 
 OECOID, the, 40 
 (Enanthylic acid, 13 
 Oleicacid, 16 
 
 acids, series of, 16 
 Olfactory mucous membrane, 452 
 
 nerve, 347 ; origin of, 495 
 
 organ, the, 451 
 Omphalo-meseraic arteries and vein 
 
 553 
 
 Ophthalmometer, the, 358 
 Ophthalmoscope (Helmholtz's), 383 
 Optic nerve, 347 ; origin of, 495 
 Optometer, the, 377 
 Organ of Corti, 438 
 
 of sight, 355 et seq. 
 
 of taste, 454 
 
 Organic constituents of food, 2 
 
584 
 
 INDEX. 
 
 OKG 
 
 BE A 
 
 Organs, definition of, 4 ; of work, 6 ; of 
 the senses, 355 et scq. 
 
 Osmose, 85 
 
 Osseous tissue, 90 
 
 Ossicula auditus, 434 
 
 Otolith, the, 437 
 
 Ovary, development of the, 539 
 
 Ovum, the, 529 ; formation of, 538 
 
 Oxalic acid, 15 
 
 acids, series of, 15 
 
 Oxaluric acid, 23 
 
 Oxidation, 2 ; decompositions dependent 
 upon, 2 
 
 Oxygen, 9 ; presence of, in the blood, 
 45; tension of, in blood, 153; con- 
 sumption of, by the human body, per 
 hour, 156 
 
 Ozone, 9 ; inquiry into presence of, in 
 blood, 437 
 
 "HACINIAN corpuscles, 457 
 
 JL Palmitic acid, 13 
 
 Pancreas, development of the, 554 
 
 Pancreatic juice, 106; secretion of, 107; 
 influence of nerves on, 108 
 
 Parabanic acid, 23 
 
 Parenchymatous tissues and their secre- 
 tions, 89 
 
 Parthenogenesis, 529 
 
 Pelargonic acid, 13 
 
 Pepsin, 97 
 
 Peptones, and their anhydrides, 31, 98 
 
 Period of latent excitation of muscle, 257 
 
 Peristaltic movements, 143 ; of oeso- 
 phagus, 144; of stomach, 145; of 
 small intestine, 146; of large intestine, 
 146; central nervous organs presiding 
 over, 147 ; arrested by a low tem- 
 perature, 147 ; inhibited by irritation 
 of the splanchnic nerves, 148 
 
 jyiuger's ' law of contraction,' 327 ; 
 application of to muscle, 330 
 
 Pharyngeal plate, the, 552 
 
 Phosgene gas, synthesis of urea from, 
 23 
 
 Phosphoric acid, 13; salts of, 13 
 
 Phosphorus, 9 
 
 Physiology, definition of, 1 ; province 
 of, 7 
 
 Planes, conjugate, 363 ; principal, 363; 
 equatorial, 404 
 
 Plants, relation of, to matter and energy, 
 and to animals, 3 
 
 Plasma, or liquor, sanguinis ; chemical 
 constituents of, 42 ; coagulation of, 52 ; 
 the fibrin-generators contained in, 52 
 Plastic constituents of food, 224 
 Pleuroperitoneal cavity, the, 549 
 
 Pneumogastric nerve, 350, 496 
 
 Pneumograph of Marey, 166 
 
 Poikilothermous, or cold-blooded, ani- 
 mals, 228 
 
 Polarisation, 382 ; of electrodes,' 271 
 
 Portal vein, influence of blood of, on 
 secretion of bile, 103 
 
 Post-mortem lividity, 571 
 
 Potential energy, 1 
 
 Pressor nerves, 79 
 
 Pressure of the blood, 63; amount o^, 
 in the arteries of man, 63 ; its fluctua- 
 tion in the arteries occasions the 
 arterial pulse, 63 ; its amount in 
 capillaries and veins, 66 
 
 Primary position of the eye, defined, 404 
 
 Principal ray, or line of direction, defin cd, 
 360 
 
 Processes characteristic of living beings, 
 1 
 
 Propionic acid, 1 3 
 
 Protagon, 36, 469 
 
 Proteids, 31 
 
 Protoplasm, 236, 283 
 
 Protoplasmic structures, 283 ; contrac- 
 tility the general feature of, 283; 
 partial contractions exhibited by, 
 283 ; stimuli which excite, 284 
 
 Proto- vertebrae, 551 
 
 Pseudoscope, the, 423 
 
 Psychical processes, 510; rapidity of 
 certain simple, 516 
 
 Psycho-physical law, 517 
 
 Ptyalin, 93 
 
 Puberty, 537 
 
 Pulse, 64; how investigated, 65; fre- 
 quency of, 80 
 
 Pupil of the eye, 377 ; influence of mus- 
 cular fibres of iris upon the size of, 
 377 ; effect of irritation of cilio-spinal 
 region of the cord on, 378 ; effect of 
 irritation of optic nerve on, 378 ; con- 
 traction of, follows accommodation 
 for near vision, 378 ; contraction of, 
 follows an inward rotation of the eye- 
 ball, 378; dilatation of, follows power- 
 ful irritation of sensory nerves, 379, 
 and violent muscular efforts, 379, and 
 occurs during dyspnoea, 379 ; changes 
 in size of, accompanying pulse-beats 
 and respiration, 379; action of various 
 poisons on, 380; centre presiding 
 over, 503 
 
 PurJeinje's figures, 403 
 Pylorus, its condition during digestion, 
 345 
 
 p ADDKEHUNGSWINKEL; 4oe 
 
 Xt Eeaction of the blood, 39 
 
INDEX. 
 
 585 
 
 EEF 
 
 SPI 
 
 Eeflex action, 477 
 
 Keflex movements, 477 ; orderly, 477 ; 
 
 disorderly, 479 ; inhibition of, 482 ; 
 
 influence of condition of the blood 
 
 upon, 483 
 
 Kefracting media of the eye, 355 
 Eegion of distinct vision, 376 
 Regulating nerves, 74 
 Eeissner, membrane of, 438 
 Romaic's ganglia, 73 
 Reproduction, forms of, 529 ; sexual, 
 
 532 
 
 Reserve air, definition of, 165 
 Residual air, definition of, 165 
 Resonants (see Consonants), 315 
 Resonators, 303, 314, 431 
 Respiration, 149; chemistry of, 150; 
 
 mechanism of, 158 ; of foreign gases, 
 
 174; methods used in the study of 
 
 the total gas-exchanges which occur 
 
 in, 158; of muscles, 243 
 Respiratory air, definition of, 165 
 
 movements, muscles concerned in, 
 162; nerves which accelerate, 167; 
 nerves which inhibit, 167 ; exciting 
 cause of, 168 
 
 murmurs, 166 
 
 secretions, 109 
 
 Retractor muscles of Miiller, 427 
 Rhythm of the respiratory movements, 
 
 166 
 Rhythmical contractions of the heart, 72 ; 
 
 circumstances affecting, 77 
 Rigor of muscle, 244 ; essential nature 
 
 of, 245 ; two stages of, 245 ; chemical 
 
 processes which occur in, 252 
 
 mortis, 571 
 'Ritter's' tetanus, 329 
 
 Rods and cones, the, of the retina, 385 ; 
 
 structure of, 394 
 Roots of spinal nerves, 353 
 Rosenmullers organ, or Parovarium, 
 
 562 
 
 Running, 301 
 Rut, period of, 533 
 
 SACCIJLUS and utriculus, nerve- 
 endings in, 437 
 Salicylic acid, 17 
 Saliva, 93 ; varieties of, 93 ; influence 
 
 of nervous system on secretion of, 95 ; 
 
 influence of, in digestion, 138 
 Sarcine, or hypoxanthine, 27 
 Sarcolactic acid, 14, 15 ; formation of, in 
 
 muscle, 241, 253 
 Sarcosine, 26, 112 
 Sarcosine-carbami c acid, 112 
 Sarcosine-sulphamic acid, 112 
 
 Sarcous elements, 238 
 
 Schema, Weber's, of the circulation, 61; 
 of the eye, 355; of the crystalline 
 lens, 366 ; of the spinal cord, 490 ; 
 of the central nervous system, 512 
 
 Schneiderian membrane, the, 451 
 
 Sebaceous secretion, 121 
 
 Secondary positions of the eye, 405 
 
 tetanus, 275 
 
 Secretion, 83 ; physical processes of, 84 ; 
 chemical processes of, 86; organs 
 engaged in, 87 ; influence of nerves 
 on, 88; classification of, into (1) 
 parenchymatous and (2) free, 83, 84 ; 
 evolution of heat during, 87 
 
 Secretory nerves, 89, 95, 96, 343 
 
 Segmentation, 534, 547 
 
 Semen, 533 ; formation of the, 541 ; 
 movements of spermatozoa in, 541 ; 
 chemical constituents of, 542 
 
 Semicircular canals, supposed function 
 of, 451 
 
 Sensations, common, 457 ; tactile, 459 
 
 Sericine, 34 
 
 Serin, 25 
 
 Serous sacs, 128 
 
 Setschenow 1 s centres, 481 
 
 Sexual intercourse, 544 
 
 Sighing, 167 
 
 Silicic acid, 13 
 
 Silicon, 9 
 
 Sinus terminalis, 353 
 
 urogenitalis, 562 
 
 venosus, 560 
 Sitting posture, the, 299 
 Sleep, 518 
 
 Smell, sensations of, 453 
 
 Sneezing, 573 
 
 Sobbing, 167 
 
 Sodium, 9 
 
 Somatopleure, the, 551 
 
 Sound, conduction of, to the tympanic 
 cavity, 430 ; conduction of, through 
 the tympanic cavity, 434 ; conduction 
 of, through the labyrinth, 435 ; 
 intensity of, 439 ; pitch of, 439 
 
 'Specific energies,' the principle of, 344 
 et seq. 
 
 Speech defined, 311 
 
 Spermaceti, constituents of, 20 
 
 Spermatozoids, 533 ; in their relation to 
 cilia, 285 
 
 Spherical aberration, 380 
 
 Spices, use of, in digestion, 191 
 
 Spinal accessory nerve, 350, 496 
 
 cord, 475 ; structure of, 475 ; paths 
 of conduction of in, 484; conduction 
 of localised sensory impressions by, 
 485 ; pressor fibres of, 485 ; conduc- 
 tion of painful impressions by, 485 
 
 QQ 
 
586 
 
 INDEX. 
 
 SPI 
 
 TUB 
 
 conduction of involuntary motor im- 
 pulses by, 485 ; schema of, 490 
 
 Spirometer (Hutchinson's), 165 
 
 Splanchnic nerves, 76, 148 
 
 Splanchnopleure, the, 551 
 
 Spleen, plan of structure of, 178; results 
 following extirpation of, 179 
 
 Spontaneous generation, doctrine of, 
 527 
 
 Stannius's experiment, 72, 575 
 
 Starch, 20 
 
 Starvation, exchanges of the matter of 
 the body during, 207 
 
 Stearic acid, 13 
 
 Stearin, hydrolytic decomposition of, 3 
 
 Stereoscope, the, 422 
 
 Stereoscopic brilliancy, 424 
 
 vision, 419 
 
 Stimulation, rhythmical and tonic, 471 
 Stimuli for muscle, 247; classified ac- 
 cording to their nature, 248 
 ' Stoifwechsel des Organismus,' 3 
 Stomach, structure of glands of, 99 ; 
 changes which the food undergoes in, 
 138 ; movements of, 145 ; development 
 of the, 559 
 Stomata, 128 
 
 Stroma of blood-corpuscles, 40 
 ' Stromuhr,' the, of Ludwig, 70 
 Subjective images, 400 
 
 sensations of hearing, 448 
 Submaxillary ganglion, 96 
 Succinic acid, 15 
 
 Succus entericus, 108 
 
 Sugar of milk, 18 
 
 Sulphocyanides, presence of in saliva, 93 
 
 Sulphur, 9 
 
 Sulphuric acid, 12 
 
 Suprarenal capsules, plan of structure 
 
 of, 178 
 Swallowing, 143 ; nerves engaged in, 
 
 146 ; centre in medulla presiding over 
 
 movements of, 503 
 Sweat, 119; secretion of, 120; function 
 
 of in the regulation of temperature, 
 
 232 
 Sympathetic centres and nerves, 521 
 
 et seq. 
 
 vibration, range of, 441 
 Synchondroses and symphyses, 289 
 Synovia, 92, 292 
 
 Systole of auricles and ventricles, 57 
 
 rpACHOMETEE, the, of Vierordt, 70 
 JL Tactile sensations, 459 
 Tsenia solium, development of, 536 
 Tartronic (oxy-malonic) acid, 27 
 Tartronyl-amide, 27 
 Tartronyl-cyanamide (uric acid), 27 
 
 Taste, organ of, 455; nerves presiding 
 over, 455 ; terminal organs of nerves 
 of, 455 ; affection of, in facial palsy, 
 455 
 
 Taurine, 25, 125 
 Taurine-carbamic acid, 112 
 Taurocholic acid, 26 
 Tears, 126 
 
 Telestereoscope, of Helmholtz, 423] 
 Temperature, of the body, 228 ; variation 
 of, in different parts, 229 ; mean, and 
 maintenance of, 231 ; fluctuations in 
 the mean, 233 ; post-mortem, 235 ; 
 sensations of, 464 ; of blood of portal 
 and hepatic veins contrasted, 104 ; 
 effect of, on cardiac contractions, 77 ; 
 on nervous irritability, 324 
 Tenor-voice, 311 
 
 Tension, of gases, 44 ; of the gases of 
 the blood, 151 ; of the oxygen of the 
 blood, 152 ; of carbonic acid of the 
 air in the pulmonary alveoli, 152 ; of 
 the gases of the tissues, 155 ; of the 
 carbonic acid of the lymph, 155 
 
 Tertiary positions of the eye, 405, 406 
 
 Testicle, structure of the, 542 ; develop- 
 ment of the, 561 
 
 Tetanus, 260; artificial induction of, 
 261 ; 'secondary' defined, 275 
 
 Thalami optici, functions of, 507 
 
 Thaumatrope, the, explained, 400 
 
 Thirst, 197 
 
 Thiry's method of obtaining pure succus 
 entericus, 108 
 
 Thoracometer of Sibson, 165 
 
 Thorax, aspiration of, 66 
 
 Thymus gland, plan of structure of, 178 
 
 ' Timbre,' or quality, of musical sounds, 
 303, 440 
 
 Tissues, respiration of, 155 
 
 ' Tone' of blood-vessels, 75 ; of the vaso- 
 motor centre, 79; of voluntary mus- 
 cles, 487 ; of involuntary muscles, 
 489 ; of arteries, 489 ; of sphincters, 
 490 
 
 Tones, simple and compound, 302 ; 
 prime, 303 ; combinational, differen- 
 tial, and summational, 440 
 
 Tongue, movements of, 144 
 
 Touch-bodies of Wagner and Meissner, 
 458 
 
 Transudations, 86 and 91 
 
 Triacetyl, 19 
 
 Trigeminal (5th) nerve, 348 ; origin of, 
 495 
 
 Trimethylamin, 21 
 
 Trochlear (4th) nerve, 348; origin of, 
 495 
 
 Trophic nerves, the, 343 
 
 Tubuli uriniferi, 112 
 
INDEX. 
 
 587 
 
 TTM 
 
 ZOO 
 
 Tympanic cavity, conduction of sound 
 
 in, 430 
 
 membrane, see Membrana tympani 
 Tyrosin, 26 
 
 TTMBILICAL cord, the, 566 
 U duct, the, 548 
 
 vesicle, the, 548 
 Unit of heat, 4 
 Urea, 22, 110 
 Uric acid, 22, 110 
 
 Urinary colouring matters, 29, 110 
 
 secretion, 109; constituents of, 110; 
 apparatus engaged in, 112; circum- 
 stances affecting, 113; influence of 
 nervous system upon, 116 
 
 Urobilin, 29 
 
 Uses of muscles, the, 286 
 
 Uterus, nervous supply of the, 565 
 
 masculinus, or vesicula prostatica, 
 562 
 
 VAGUS, 350 ; inhibitory influence of, 
 on heart, 73 
 
 Valerianic acid, 13 
 
 Valerolactic acid, 14 
 
 Valves of the heart, 58 
 
 Vascular system, development of, 552 
 
 Vasomotor centre, 76, 502 
 
 nerves, 75 ; influence of, on secretion, 
 89 
 
 Velocity of circulation, 69 
 
 Ventricles of Morgagni, function of, 307 
 
 Vertebral column, arrangement of arti- 
 cular surfaces of, 297. 
 
 Vibratory sounds, 316 
 
 Vision, 385 et seq ; 
 
 Visual angle, 368, 397 
 
 Visual rays, 363 
 
 'Vital capacity' of the lungs, 164 
 
 ' Vital force,' 1 
 
 Vitelline, 36 
 
 Vocal cords, 305 ; movements of, in" the 
 
 production of voice, 308 
 Vocal organs, sounds produced by, 307 
 Voice, 302 ; production of, 307 ; falsetto, 
 
 309 ; compass of the, 310. 
 Voluptuous sensations, 465 
 Vomiting, mechanism of, 148 
 Vowels, nature of, 311; analysis of, 
 
 312 and 314; shape of the buccal 
 
 cavity in the production of, 313; 
 
 synthesis of, 314 
 
 WALKING, 300 
 Water, 12 
 
 "Wave of muscular contraction, 261 ; of 
 negative deflexion, 276 
 
 ' Weak- currents,' as distinguished from 
 * strong-currents,' 272 
 
 Weber's schema of the circulation, 61 
 
 Whey, 125 
 
 White substance of the brain, chemical 
 composition of, 468 
 
 Wolffian body, the, 560 
 
 canal, the, 551, 560 
 
 Work, organs of, 6 ; of the heart, 64 ; 
 of muscles of frog, 265 ; of the body 
 is greater than corresponds to oxida- 
 tion of albuminous bodies, 225 
 
 VANTHINE, 2, 27 
 
 A 
 
 YAWNING, 167 
 
 JL Yolk, the, 532; chemical consti- 
 tuents of, 533 
 
 700ID, the, 40 
 
 L 
 
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