..„•»; ARMY MEDICAL LIBRARY FOUNDED 1836 WASHINGTON, D.C. FIRST LINES PHYSIOLOGY; DESIGNED FOR THE USE OF STUDENTS OF MEDICINE. BY DANIEL OLIVER, M.D., LL.D., A.A.S., LATE CORRESPONDING MEMBER OF THE ACADEMY OF SCIENCES AND FINE ARTS OF PALERMO, AND PROFESSOR OF MATERIA MEDICA IN THE MEDICAL COLLEGE OF OHIO. THIRD EDITION, WITH CORRECTIONS AND ADDITIONS. Multa esse constat in corpore, quorum vim rationemque perspicere nemo nisi qui fecit, potest—Lactant. de opific. Dei^ BOSTON: WILLIAM D. TICKNOR & CO., CORNER OP WASHINGTON AND SCHOOL STREETS. M DCCC XLIV. Entered according to Act of Congress, in the year 1840, By Daniel Oliver, M. D. In the Clerk's Office of the District Court for the District of Massachusetts. I. R. BUTTS, PRINTER, No. 2 SCHOOL STBEET. PREFACE TO THE SECOND EDITION. In offering a second edition of the First Lines of Physiology to the medical public, and especially to those who are preparing to enrol themselves among its numbers — for whose use the work was originally designed — the author thinks it proper briefly to state the principal alterations and improvements which have been made in the work. 1. No alteration has been made in the plan and general ar- rangement of the book, for none appeared on the whole preferable to that which was originally adopted. And here it may not be improper to remark, that the preliminary matter, constituting nearly one-fifth of the whole work, and comprising a description of the distinctive characters and of the elementary analysis of the organization,—anatomical, chemical, and physiological,—form, it is believed, an important and valuable part of the work, being fundamental to the whole subject of physiology, and being pre- sented in a more systematic form than will usually be found in elementary treatises on this subject, except in the works of the German physiologists. 2. An addition of probably one-fourth has been made to the materials of the work, drawn from the latest and best sources which were accessible to the author. These will be found inter- spersed throughout the book, incorporated in various parts with the original matter; or embodied by themselves in considerable masses, and filling up lacuna which existed in the first edition. Nearly every chapter of the work contains additions, more or less IV PREFACE. copious, of the first description, extending as far as consistent with the prescribed limits of the work, or as was practicable without destroying the symmetry of its parts. The principal ad- ditions of this description will be found in the chapters on the Blood, Innervation, the Circulation, Digestion, Nutrition, Animal Heat, the Senses, especially touch, taste, and vision, Sleep and Generation. Any one who will take the trouble to compare the corresponding chapters on these subjects, in the two editions, will perceive almost at a glance that those of the last have received copious, and it is hoped, important accessions of matter. Con- siderable masses of matter, constituting new sections, have also been added to several of the chapters, among which may be men- tioned the section on the psychological functions of the brain; several sections on fostai development and physiology in the chapter on Generation ; besides several shorter ones in the chap- ters on the Circulation, Digestion, Vision, Sleep, &c. On the whole, it is thought that the value of the work is materially in- creased by the copious accessions of matter which, distinguish this edition from the first. 3. Few retrenchments have been made in this edition, for no considerable ones appeared to be called for. Probably a more critical or a less partial eye would have been more successful in the search after exceptionable passages. Among such the chap- ter on Animal Magnetism will probably be enumerated by many readers. I am aware that a large majority of those into whose hands this book may fall, probably regard animal magnetism as unworthy of serious attention, and as a fitter subject of ridicule than of sober consideration. Perhaps they are right, and I do not undertake to assert that they are not so ; but I am not quite sure but it would be premature to assume this hypothesis for a certainty. My reasons for this hesitation are, that I find many intelligent men, after an examination of the subject, have been satisfied with the evidence in favour of its claims; men accus- tomed to the investigation of subjects of physical science, and at least as competent to judge correctly as those who have adopted the opposite opinion; and more so, I may add, than many of those who, without any experimental knowledge of the subject whatever, have held it up to ridicule and contempt. I repeat it, that* men quite as competent to judge as any of us, and with vastly better opportunities of observation than most of us, as able to weigh every fact, to appreciate every circumstance, to detect any imposture, and to reason soundly on the whole subject • men it may be added, who can have no conceivable motive to deceive or to impose upon others; many such men, I say, have become convinced, and have avowed their conviction, of the reality of Animal Magnetism. " I repeat it," says Rostan, in writing on this subject, " what I am about to describe I have seen, and have seen frequently. I have not been satisfied to witness it in a single per- PREFACE. V son, but have subjected numerous individuals to these investiga- tions. I have taken as subjects of my researches individuals of various classes, and of both sexes, — persons many of whom were ignorant even of the name of magnetism, men of letters, students of medicine, epileptics, ladies of fashion, young females, &c. I have continued these inquiries for many years, and, with very few exceptions, I have always obtained results worthy of the greatest attention; and in nearly all these cases the phenomena were ex- actly of the same kind, or strikingly similar. Among these phe- nomena there were some of a very extraordinary character, which always appeared, others more rarely, and some but seldom." He afterwards proceeds to observe, that in these experiments it was physically impossible that there could be any collusion, or any communication whatever, between the persons on whom they were made. Now what are we to do with such testimony as this ? And this is only a single specimen of what might be adduced. Are we to reject it with contempt, and to declare such men as the distinguished physician just cited, and many others who might be mentioned, to be fools or impostors, because they testify to facts which do not accord with a certain standard of truth or possibility which, in the plenitude of our knowledge and presumption, we have seen fit to set up, a standard derived from the little glimpses we have been able to catch of the secret operations of nature ? How much of the intimate and essential nature of the nervous system do we know ? How much of this terra incognita have we yet explored, which shall authorize us to say that nothing does or can lie beyond the reach of our own vision ? " But these stories about magnetism contradict experience, and therefore must be false!" The true expression of this fact is, that they do not fall within the sphere of common experience. But can we say that there is not and cannot be a field of experi- ence of more restricted limits, within which these facts may be as true as those which they appear to contradict are in the wide theatre of common observation ? Is no concurrence nor combi- nation of circumstances in physical or physiological nature possi- ble, which may so modify the ordinary operation of the laws of nature, as to produce new and paradoxical results, and which, so long as the combination lasts, may constitute a new, though lim- ited field of experience ? And is this so certain, that rather than admit the contrary, we must reject testimony which on any other subject we should never have dreamed of questioning, and charge with wickedness or gross folly men who we have no reason to doubt are quite as capable and as honest as ourselves? Is it for us to dogmatize on this subject at a time when every year is re- vealing to us new wonders, and bringing to light new powers in the physical and organic worlds; and while it is enlarging the little circle of our knowledge, is still more disclosing to us the boundless extent of the unknown regions beyond ? Is it for us, VI PREFACE. out of the fathomless depths of our own ignorance, to issue ordi- nances to nature, and to say how far her power extends and where it terminates ? Let us listen to the words of a consummate judge of human nature, and consider for a moment how well they ap- ply to ourselves in this matter. " But God be thanked," says Sir William Temple, in speaking of man, " his pride is greater than his ignorance, and what he wants in knowledge he supplies by sufficiency. When he has looked about him as far as he can, he concludes there is no more to be seen; when he is at the end of his line he is at the bottom of the ocean; when he has shot his best, he is sure none ever did or ever. can shoot better or beyond it. His own reason he holds to be the certain measure of truth, and his own knowledge, of what is possible in nature" Considerations such as these, as well as personal observation, have had their weight with many persons who have taken no part in the discussions and controversies to which this subject has led. Many individuals of fair and honest minds, and some of them of high intelligence, have, to my own knowledge, been impressed with the reality and truth of this matter, but have been backward to avow their conviction, because unwilling to incur the ridicule of their friends. In some parts of Europe, this subject, as is well known, has obtained a strong foothold among scientific men. A distinguish- ed foreigner from one of the most learned countries in Europe, a few years since, in reply to a question of the author, who asked him what was thought of animal magnetism at that time in Eu- rope, used the following words: " Sir, there is no doubt what- ever of its reality ; but it is a dangerous power, and the exercise of it ought to be forbidden except under the restrictions of law." It ought not to be forgotten, that the two most eminent phi- losophers of the age have treated the pretensions of animal mag- netism with respect, and have even admitted at least the great probability that they have a real foundation in the nature or properties of the nervous system. When I consider the sober and cautious language of science on this subject, coming from the lips of philosophers of vast abilities, trained to habits of the sever- est investigation, and whose genius was successfully employed for along series of years in unfolding the deepest mysteries of physical nature and of organization, I confess that the scoffs and sneers of ignorant or half-informed presumption are apt, by some hidden affinity of thought, to bring to my mind a certain sound which is described in the expressive language of Scripture as " the crackling of thorns under a pot." The discovery of the invisible thread of thought which leads to so singular a result, I would propose as a problem to the metaphysician. The disciples of the school of the infinitesimal medicine I would remind, that the great founder of their system — " that PREFACE. Vll fine old man," as I think Mr. Coleridge calls him —declares that none but fools or madmen can entertain a doubt of the curative powers of animal magnetism. The followers of Gall and Spurzheim should not forget that zoo-magnetism and craniology sprung from the same soil; and that if the latter has expatriated itself among the mists of Caledo- nia, and taken another name, and has long since been forgotten in the land of its nativity, while the former still clings to its native soil, they are still countrymen, and ought not to meet as stran- gers in a foreign land. The philosophers of the supersensual school also should be re- minded, that magnetism and transcendentalism have the same fatherland— the land of dreams and of mighty shadows, the land of the Hartz and the Brocken. The idolaters of nature will be slow to admit, that, whatever may transcend sense, any thing can transcend her power; though they will not deny that whether she speaks through master either lifeless or animated, or from the lips of her own inspired hierophants, she sometimes utters oracles which are hard to be understood. The reader will now understand why I have not expunged the chapter on Animal Magnetism. I am no advocate for its pre- tensions ; but I have so much respect for many of those who are or have been, that I wish to have it rescued from the hungry clutches of mountebanks and impostors, and placed under the pro- tection of science, until its claims shall have received a thorough investigation. In conclusion, I would only remark, that the book, in the main, is printed with great correctness; and that the errors or awkward expressions which may occasionally offend the reader's eye, will find a ready apology in the fact that the author's residence and the press are more than three hundred miles apart. Boston, August 31, 1840. ADVERTISEMENT TO THE THIRD EDITION. At the request of the immediate representatives of the lamented author of this Treatise, the present editor undertook the task of preparing it for the press. It did not enter into his intentions to make any important changes in the body of the work. He has aimed at nothing more than to remove such errors as he might detect, and to supply some additional knowledge upon those points which seemed most to require illustration. To remodel the work would not only have demanded a great amount of time and labour, but would have destroyed its unity and individuality, and thus deprived it of one of its chief at- tractions. Nor is it because the editor agrees with every state- ment or opinion here expressed, that his hand has been so sparingly exercised upon the text. Respect for the deliberate conclusions and opinions of a thoughtful and laborious inquirer into the truths of nature, would alone have withheld him from writing a running commentary of ingenious doubts and trivial criticisms. The work of the author is before the student as it was bequeathed him; an unpretending monument of the study and reflection of a sincere and candid scholar. The hours that have been devoted to its revision, if they have added but little to its value, may at least be accepted as a tribute to the memory of one who was loved and respected wherever he was known. Boston, Dec. 9, 1843. CONTENTS. CHAPTER I. DEFINITION OF PHYSIOLOGY. Definition of Physiology, . . .17 Two classes of bodies, viz. inorganic and organic, . . . . .17 Two elements in each, viz. material and dynamic, . . . .17 Life inseparable from organization, 18 Organic matter endued with two kinds of force, viz. physical and organic,.....18 CHAPTER II. COMPARISON BETWEEN ORGANIC AND INORGANIC MATTER 18 Conflict between chemical and or ganic power Peculiarities of organic matter, Organic bodies possess determinate forms and magnitudes, . They contain globular particles, They consist of solid and fluid matter and systems of organs, . They consist of two kinds of ele ments, ..... They form ternary or quaternary compounds, .... 19 19 20 21 21 Organized bodies react against the chemical forces of matter, Efforts of organized bodies to tain their integrity, Vis Medicatrix, Organized bodies possess the power of reproduction, Are subject to death, 23 24 25 26 26 26 CHAPTER III. RELATIONS OF ORGANIZED BODIES TO HEAT, LIGHT, AND ELECTRICITY. Organized bodies regulate, to a cer- tain extent, their own temperature, 28 Organic heat,.....28 Organized bodies have the power of resisting very high temperatures, 29 Living beings idio-electric, . . 30 Electrical sparks emitted by living beings,......31 Electrical organs of the torpedo and gymnotus......31 Analogy between them and the voltaic battery,.....31 Needles converted into magnets by discharge of the torpedo, . . 33 2 The electricity of these animals vital, Electrical currents in living bodies, . Electrical state of persons under dif- ferent circumstances, Phosphorescence of inorganic sub- stances, ..... Phosphorescence of organic substan- ces during decomposition, Phosphorescence of living substances, Phosphorescence of insects depends on peculiar animal matter, Phosphorescence of the retina from pressure, ..... 33 35 35 36 37 37 38 39 X CONTENTS. CHAPTER IV. COMPARISON OF ANIMALS AND VEGETABLES. Organized beings divided into two Comparison between them, classes, animals and plants, . . 40 CHAPTER V. DIVISION OF THE ANIMAL KINGDOM. Animal kingdom divided into verte- Human race belongs to the mammalia, brated and invertebrated, . . 41 Peculiarities of structure, &c. of man, CHAPTER VI. ANATOMICAL ANALYSIS, OR, STRUCTURE OF THE HUMAN BODY. Structure of the human body, . . 43 Ultimate animal solid disposed in Consists of solids and fluids, . . 43 various modes, .... Vesicular theory of Raspail, . . 45 CHAPTER VII. FUNDAMENTAL TISSUES. Solids of the body composed of three fundamental tissues, viz. cellular, muscular, and nervous, . . 46 Cellular tissue of two kinds, . . 47 ----forms a connected whole, . . 48 ----basis of all the membranes, . 48 Serous membranes line the closed cavities,.....49 Mucous membranes more highly or- ganized than the serous, and line the cavities which open outwardly, 49 Skin resembles mucous membrane, . 51 Fluids divided into three kinds . . 60 Chyle and lymph, . . . .61 The blood,.....61 Liquor sanguinis, . . . .61 Serum coagulates by heat, . . 62 Colour of the serum, . . .63 Cruror — fibrin, . . . .63 Difference between albumen and fibrin,.....65 Difference between fibrin and muscu- lar fibre,.....65 Skin an organ of relation, . . .51 Fibrous membranes consist of con- densed cellular tissue — Uses, . 51 Cartilaginous tissue, . . . .52 Osseous tissue, . . . . .53 Bones of three kinds, . . .53 Bones form a connected system, . 54 Muscular fibre — fibrin, irritability, . 54 The muscular fibre an imperforate vesicle, ...... 54 Nervous fibre — albumen, sensibility, 55 Vesicular origin of the nerves, . . 56 Blood owes its power of passing through the capillaries to fibrin, . 65 Hemorrhage from a deficiency of fibrin,......65 Red globules, their shape, size, . 66 Nucleus of the globules, . . .66 Motion of the globules, . . .67 Chemical analysis of the blood, . 71 Coagulation, how caused, . . .71 Expansion of the blood, . . ! 73 Principles existing in the blood, ' 74 CHAPTER Vm. THE COMPOUND STRUCTURES OF THE SYSTEM. Muscles of two kinds, viz. animal and Vascular system divided into arterial, organic,.....57 venous and lymphatic, . . .58 Where situated, . . . .57 Arteries and veins, how formed, . 59 Nervous system of two kinds, viz. Structure of lymphatics, . . .60 animal and organic, . . .58 Visceral system, . . . .60 CHAPTER IX FLUIDS OF THE SYSTEM. CONTENTS. XI CHAPTER X. CHEMICAL ANALYSIS OF THE ORGANIZATION. Ultimate elements of animal matter, metallic and non-metallic, Oxygen exists in all the solids and fluids,...... Hydrogen also, .... Carbon exists largely in bile and ve- nous blood, ..... Azote, principal chemical characteris- tic of animal matter, Phosphorus exists in nearly all parts of animal bodies, .... Sulphur exists in albumen and in muscular flesh, .... Chlorine is present in most of the ani- mal fluids, ..... Iron exists in the blood, . 75 75 75 76 76 76 77 77 78 The organic elements are quaternary compounds,.....78 Organic elements are divided into two classes, viz. acids and oxides, . 78 Organic oxides, . . . .78 Quaternary compounds the most im- portant, .....79 Albumen the most generally diffused, 79 Albumen composed of an organized tissue, and a liquid, . . ; 79 Fibrin, its properties, . . .80 Gelatin, do.....80 Osmazome, do. . . . ,81 Mucus and caseine, their properties, . 81 Urea,......82 CHAPTER XI. PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. Organized beings possess the property of being affected by external agents, Excitants of the living organization, . Corresponding kinds of excitabilities, Modifications of excitability, Sensibility, .... Imponderable agency of the nerves, Contractility, .... Two kinds of contractility, 83 84 84 85 85 87 88 89 Expansibility, . Erectile tissues, Alterative powers, . Physical properties, . Elasticity, , Flexibility and extensibility, Imbibition, Endosmose and exosmose, 91 91 92 94 94 95 95 95 Actions of life form a circle, Four classes of functions, . Vital, .... CHAPTER XII. THE FUNCTIONS. . 96 Nutritive and sensorial, . 97 Genital, . . 97 97 98 CHAPTER XIII. FIRST CLASS, OR THE VITAL FUNCTIONS. Of innervation, . . . .98 Encephalic nervous system, . . 99 Cerebrum,.....99 Cerebellum,.....100 Pons Varolii,.....101 Medulla spinalis, .... 101 Motions of the brain, . . . 102 Analysis of the brain, . . . 103 Envelops of brain and spinal marrow, 103 Dura mater,.....104 Pia mater,.....104 Encephalic nerves, .... 105 Ganglionic nervous system, . . 106 Functions of the nervous system, . 107 Sensation,.....108 Brain destitute of sensibility, . .111 The brain the organ of voluntary motion,......Ill The brain the organ of the intellectual and moral faculties, . . .113 Localization of the cerebral functions, 114 Effect of removing the cerebral lobes, 114 Seat of vision threefold, Effect of wounding the cerebellum, . Effect of mutilating the tubercula quadrigemina, . Functions of the optic thalami, . Lobes of the cerebrum subservient to flexion, those of the cerebellum to extension, Influence of the brain over the or ganic functions, Functions of the spinal cord, Medulla oblongata the seat of con sciousness, .... Functions of the anterior and poste rior parts of the spinal cord, Opinions of Bellingeri, 115 116 117 118 119 120 124 124 125 126 xn CONTENTS. Influence of the spinal cord upon the organic functions, .... 127 Its influence upon respiration, . . 127 Its influence upon the circulation, . 128 Its influence upon digestion, , . 130 Its influence upon nutrition, . . 131 Cerebro-spinal nerves subservient to sensation and motion, . . . 132 Nerves of specific sensation, . • 132 Nerves of voluntary motion, . . 133 Nerves of mixed functions, . . 134 Vertebral nerves, .... 135 The vertebral nerves distinguished by their symmetry.....136 Great sympathetic, .... 136 Irregular system of nerves, . . 137 Bell's classification of the nerves, . 137 Hall's classification of the nerves, . 138 Psychological functions of the brain,. 141 Faeulty of knowledge, . . . 142 Ideogenesis, ..... 142 Sensation not a cognitive faculty, . 143 Conception,.....143 Attention, a function of the will, . 144 Judgment, as a source of ideas, Relation and resemblance, Primitive judgments, . • • Judgment and reason, as sources ol knowledge, . Reasoning, • • • •. Different kinds of reason, viz. intui- tion, demonstration, and induction,. Belief,...... Succession of ideas, . Association of ideas, . Laws of association, . Faculty of feeling, . Emotions divided into immediate, re- trospective, and prospective, . Subjective and objective emotions, . Influence of emotions on organic func- tions, ....•• Will,......■ Influence of the will over sensation and internal consciousness, Instinct, ...... Difference between man and other animals, in relation to instinct, 145 145 147 148 150 150 151 151 151 151 153 154 154 154 155 156 156 156 CHAPTER XIV. THE CIRCULATION. The circulation, universal suspension of, instantly fatal, . . . .157 Organs of the circulation, . . . 158 The heart, a double organ, . . 158 The arteries form two systems, . . 161 The veins also, .... 161 The capillary vessels, . . . 162 Dispositions of the capillary vessels, . 162 Circulation in reptiles, fishes, &c. . 164 Course of the circulation, . . . 165 Bichat's division of the circulation, . 166 Circulation of black and of red blood, 166 Capillary circulation, . . . 168 Action of the heart, .... 169 Impulse of the apex of the heart against the left side, . . . 170 Course of blood in the arteries, . . 172 Different degrees of velocity of the globules in the central and external parts of the moving column, . . 173 Viscidity of the blood necessary to its motion in the capillaries, . . 173 Force of the heart, .... 174 Pressure of the blood on the vessels, . 174 Sounds of the heart, .... 175 Ascribed to various causes, . . 176 Hope's theory of, .... 177 Bouillaud's theory of, ... 177 Moving powers of the circulation, . 178 Functions of the heart, . . . 179 Functions of the arteries, . . . 180 Arteries possess a vital power of con- traction, ..... 181 Functions of the capillaries . . 186 Influence of the heart felt in the capillary vessels, .... 187 Functions of the veins, . . . 189 Veins exert a motive force, . . 190 Suction power of the heart, . . 191 The suction power denied by Arnott, 192 Effect of inspiration, .... 193 Influence of the nervous system, . 194 Influence of the great sympathetic, . 195 Weinhold's experiments, . . . 196 CHAPTER XV. RESPIRATION. Respiration completes the formation of blood,.....197 Lungs, description of, ... 197 The lungs possess two circulations, . 198 Thorax, how enlarged, . . . 199 Inspiration, three degrees of, . . 201 Expiration, three degrees of, . . 202 Action of the abdominal muscles, . 203 Elasticity of the lungs, . . .203 Action of the larynx, trachea, and lungs,......204 Chemical phenomena of respiration, . 205 Analysis of air expired from the lungs, ...... 206 Nitrogen absorbed in respiration, . 207 Volume of air inspired, . . . 208 Volume of air contained in lungs when distended, .... 209 Quantity of oxygen consumed in respi- ration, ......209 CONTENTS. Xlll Consumption of oxygen variable, Vital part of respiration, . Influence of respiration upon the blood, ...... Theories of respiration, 210 211 212 213 Influence of the par vagum, . . 216 Asphyxia produced by section of par vagum,......216 Opinions on the subject, . . . 217 CHAPTER XVI. NUTRITIVE FUNCTIONS. Digestion peculiar to animals, . Apparatus of digestion, Stomach,..... Intestines,..... Structure of the digestive canal, Motions of the oesophagus, Hunger,..... Manducation, .... Deglutition, Chymosis,..... Motions of the stomach, Gastric fluid, .... Chymification..... Chyme, ..... Influence of the par vagum upon gestion, ..... Various opinions respecting, Chylosis, ..... Intestinal fluid, .... di- 220 Bile and pancreatic fluid, . . . 243 220 Appearance of albumen, . . . 244 221 Analysis of the contents of the small 222 intestines,.....245 222 Motions of small intestines, . . 247 223 Chyle, its properties, . . . .248 225 Caecum, its functions, . . . 249 225 Defecation,.....250 226 Liver, circulation of, . . . . 252 228 Secretion of bile, . . . .253 228 ------its uses,.....256 230 Pancreas, pancreatic fluid, . . 258 235 Food.......260 231 Prout's views,.....264 Raspail's views, .... 264 237 The spleen,.....265 237 Its structure,.....265 242 Influenced by neighbouring parts, . 266 243 Use unknown,.....266 CHAPTER XVII. AESORPTION. Apparatus of absorption, . . . 267 Lymphatics, ..... 267 Lacteals, ,.....268 Conglobate glands, .... 269 Functions of the lymphatic system, . 270 Various kinds of absorption, . . 271 Accidental absorption, internal and external,.....273 Cutaneous absorption, . . . 273 Absorption by mucous membranes, . 274 Absorption from all parts and surfaces, 275 Alimentary absorption, . . . 276 Chyle constantly changes its proper- ties, ......278 Substances assimilated in the absorb- ents, ......279 Venous absorption, .... 280 Experiments upon it, ... 280 Tiedemann and Gmelin's researches, 281 Lawrence and Coates's researches, . 282 Passage of chyle into the left sub- clavian vein,..... Internal absorption, .... Internal absorption effected by the lymphatics,..... Internal absorption effected by the veins.......288 Imbibition,.....290 Accelerated by Galvanism, . . 292 Lymph, its properties and motion, . 293 Office of lymphatic glands, . . 293 285 286 286 CHAPTER XVIII. SECRETION. Secretion,......294 ------, its vital character, . . 294 ------, in its simplest form, the sepa- ration of substances existing in the blood, . • . . • -295 Many secreted substances not educts but products, .... 296 Structure of the secretory organs, . 297 Glandular follicles, . . . .297 Conglomerate glands, . . . 298 Classification of the secreted fluids, . 299 Cutaneous exhalation, . . . 302 Quantity of this secretion, . . 303 Quantity varies with many circum- stances, ......304 Mucous exhalations, .... 306 Internal exhalations, .... 308 Follicular secretions, ... . . 313 Glandular secretions,.... 314 Secretion of milk, .... 316 Secretion of urine, . . . . 318 Composition of urine, . . . 321 Uses of this secretion, . . . 323 XIV CONTENTS. CHAPTER XIX. NUTRITION. Nutrition.......325 The organs the agents of nutrition, . 328 Perpetual decomposition and repara- Acidification of the organic elements, 329 tion of the body, . . . .326 Nutrition influenced by innervation, 330 CHAPTER XX. ANIMAL HEAT. Animal Heat,.....331 action of the capillary vessels, . 333 Opinions respecting its origin, . . 331 Increased heat in fever, . . . 335 Crawford's theory, .... 332 Continuance of heat after death from Brodie's theory, .... 333 apoplexy and asphyxia, . . . 335 Calorification connected with the vital CHAPTER XXI. FUNCTIONS OF RELATION. Sensation, . .' . . . .338 External sensations, .... 340 Internal sensations, . . . . 338 CHAPTER XXII. SENSE OF TOUCH. Skin, the organ of touch, . . . 341 derived from touch, according to Touch active or passive, . . . 342 Brown, ...... 343 The idea of solidity or resistance not Remarks on this opinion, . . . 343 CHAPTER XXIII. VISION. Apparatus of vision, .... 345 Uses of the choroid coat, . Eye, description of, . . . . 346 Uses of the retina, Nerves of the eye, .... 348 Accommodating power of the eye,. Refraction of light, .... 353 Cause of erect vision, Refracting powers of the eye, . . 356 Cause of single vision, Offices of different parts of the eye, . 359 Accidental colours, . Motions of the iris, .... 362 Perceptions derived from vision, Iris not indispensable to vision, . . 364 364 364 366 368 369 370 371 CHAPTER XXIV. HEARING. Hearing, apparatus of, 374 Auditory nerve, ... 376 Cavity of the tympanum, . .374 Sound, how excited, .... 377 Internal ear,.....375 Physiology of hearing, . ] 330 CHAPTER XXV. SENSE OF SMELL. Organ of smell, . . . .383 Not essential to smell, . 385 Olfactory nerve, . . . .384 Uses of the sinuses, ..." 335 CONTENTS. XV CHAPTER XXVI. TASTE. Taste, apparatus of, Tongue, nerves of, 385 386 Panizza's experiments, Teeth sensible to certain tastes. 387 390 CHAPTER XXVII. Muscular motion. .... 391 Muscles,......391 Properties of,.....392 Do they undergo any change of vo- lume in contracting, . . . 394 Velocity and force of muscular con- traction, .....395 Strength of a muscle greater during life than after death, . . .396 Order in which different muscles loose their contractility, .... 397 Causes of the vital contraction of the muscular fibre .... 398 The energy of the brain the proper stimulus of the voluntary muscles, 399 The effects of various other stimuli applied to them, .... 400 Whence the muscles derive their power of contraction, . . . 400 The essence, or immediate cause of muscular contraction, . . . 401 The mechanical disadvantages under which the locomotive muscles act, . 402 Various motions and attitudes of the human body analyzed, . . 403 Walking, running, jumping, swim- ming, ...... 406 Organic muscles, .... 408 Curious experiment on lifting, . . 410 CHAPTER XXVIII. OF THE VOICE. Organ of the voice, . Modifications of the voice, how pro- duced, ..... 410 411 Theory of the formation of the voice, 411 Experiments of Magendie, . . 412 CHAPTER XXLX. GENERATION. Generation, organs of, Male, ...... Female,..... Impregnation, .... .------------, various opinions upon, -, various experiments, 415 415 419 423 424 425 427 427 428 Development of the foetus, Descent of the ovum into the uterus, First appearance of certain important parts,...... Embryo about the fifth or sixth week, 429 Embryo at the end of the second month,......429 Embryo at the fourth month, . . 430 Embryo at six months, . . ' 431 Embryo at nine months, . . • 432 Development of internal parts, . . 432 Brain and spinal cord, . . • 433 Development of parts sometimes arrested, ..... 434 Vascular system, .... 435 Heart and aorta, .... 435 Lungs, &c......435 Intestines, liver, &c. . . . 435 Spleen, kidneys, &c. Organs of generation, Muscles and bones, . Eyes and ears, . Appendages of the foetus, Chorion, . Amnion, . Umbilical vesicle, Allantois, Umbilical cord, Placenta, . Foetal nutrition, Foetal circulation, Gravid uterus, . Labour, Theories of generation, 1. Epigenesis, . 2. Evolution, Two sects of the partisans tem, Ovarists, . Animalculists, . Various opinions and experiments . 437 . 437 . 438 . 439 . 440 . 441 . 442 . 442 . 443 . 444 . 444 . 447 . 450 . 452 . 452 . 454 . 455 . 457 of this sys- 457 457 459 460 XVI CONTENTS. CHAPTER XXX. DYNAMIC CONNECTION OF THE FUNCTIONS. Synergy,......463 Examples of, in the eye, . . . 463 In the organs of respiration, . . 464 In the diaphragm, abdominal muscles, glottis, &c. . 464 In the limbs,,.....466 Sympathy, In the organs ot sense, Brain, diaphragm, &c. In the heart, liver, &c. In the sexual organs. 466 466 466 467 468 CHAPTER XXXI. SLEEP. Sleep, approach of, . State of sleep, and its effects, Duration of sleep, Remote causes of sleep, . Efficient cause unknown, . Various opinions on the subject, . 469 Torpid state of animals, . 473 . 469 Dreams, .... . 474 . 470 Various classes of, . 474 . 471 Somnambulism, . 478 . 471 Various phenomena of, . 478 . 471 Remarkable case of Jane Rider, . 479 CHAPTER XXXII. ANIMAL MAGNETISM. Method of producing magnetic sleep, 482 Phenomena of this state, . . . 483 Remarkable case of an operation per- formed during magnetic sleep, . 486 Double consciousness, . . . 488 Medical report of the French Royal Academy, ..... 491 Remarks of Cuvier .... 492 Remarks of Laplace, . . . 492 CHAPTER XXXIII. DEATH. Death, natural,.....493 Death, accidental, .... 494 Apoplexy, or death of the brain, . 494 Syncope, or death of the heart, . . 494 Asphyxia, or death of the lungs, . 495 Physiology of sudden accidental death, 495 Signs of death, .... 497 ADDENDA. Artificial formation of organic com- pounds, ...... 499 Origin of living tissues, . . . 499 Structure of the mucous membranes, 503 Structure of the skin, . . . 504 Structure of bone, .... 505 Structure of muscular fibre, . . 505 Structure of the nervous system, . 505 Structure of the arteries, . . . 506 Lymph and chyle, .... 506 Cause of the buffy crust, . . . 506 Relation of fibrin to albumen, . . 506 Blood corpuscles, .... 507 Composition of acetic and lactic acids, 508 Cause of the arterial pulse, . . 508 Vital contractility of the arteries, . 508 Sounds of the heart.....508 Nerves of the larynx, . . . 509 Structure of the liver, . . . 509 Nature of food, .... 510 Communication of the lacteals with the intestinal cavity, . . . 510 Mechanism of absorption by the lac- teal.......511 Secretion and nutrition, . . . 512 Source of animal heat, . . .513 Properties of the muscles, . . 514 Glands of the female vagina, . . 515 Development of the ovum, . . 515 FIRST LINES OF PHYSIOLOGY. CHAPTER I. DEFINITION. Physiology is the science of life, or of the phenomena of living bodies; or it may be defined the science of organization; this term being used to express the living or active organization, and not being separable from the idea of life. In contemplating the vast number of bodies which present themselves to our notice, we perceive that they may all be re- ferred to two great classes, viz.: the organic, and the inorganic ■ distinguished from each other by certain striking properties, and each embracing an immense number of subdivisions, or subordi- nate classes. In each of these two great departments of nature we observe two objects or elements essential to the class of beings we are considering ; one, a corporeal mass ; the other, certain general properties belonging to it; or, a material and a dynamic element; and these two are inseparably blended together, or only separable by an act of thought. We no where find matter divested of physical properties, and it is only by mental abstrac- tion that we can conceive of it as existing without them. For any thing we know, the property of attraction may be as essen- tial to matter, as the corporeal mass which it presents to our senses. Attraction or gravitation, as isolated from matter, we know is nothing but an abstraction of our minds, and probably a corporeal mass isolated from the dynamic element of matter, that is, from its physical or chemical properties, is no less so. The same is true of organized matter. It consists of two elements, a corporeal mass, and certain properties inseparably blended together. These properties, which in their aggregate we term life, we can separate in thought from the sensible mass, with which they are united, but they cannot be separated in 18 FIRST LINES OF PHYSIOLOGY. reality from it. When we speak of life or vital properties, we speak of mere mental abstractions, and we should never forget that this is the case, or we may be led into errors and absurdities in reasoning on the subject. It may perhaps be supposed that, though life cannot exist without organization, yet the latter may exist separate from life, because we find by experience that all the external and sensible characters of organization remain some time after the extinction of life. Yet, beyond all doubt, death is always accompanied with some essential change in the organization, though it may not be possible for us, in all cases, to determine what this is. In most instances, the lesions of the organization which occasion death are obvious on dissection ; and that they are not so in all, is probably owing to the fact, that science has never yet been able to penetrate into, and unravel the deeper mysteries of the organization, which constitute the immediate and essential conditions of life. The powers or forces which are connected with inorganic matter are of two kinds, mechanical and chemical ; and all matter, without exception, so far as our knowledge of it extends, is subject to the influence of these forces. The changes which take place in the physical world, and the motions and transfor- mations of lifeless matter, which constitute these changes, are the results of the operation of these forces. In addition to these two, organized matter is endued with an- other kind of force, which may be termed organic or vital, and which is of a higher order than the two former. It exists in connexion with the mechanical and chemical forces, for where- ever it is found, they are present likewise. It cannot exist with- out them, though they may exist without it. But wherever the organic force exists, it modifies, in a greater or less degree, the mere physical forces of matter, and sometimes appears almost to subvert them; but, as soon as the organic power has ceased to operate, the two former immediately resume their empire, and soon bring back the organized mass within the domain of inor- ganic nature. CHAPTER II. COMPARISON BETWEEN ORGANIC AND INORGANIC MATTER. A striking difference exists between the structure and general properties of organic and inorganic matter. The structure or material composition of organized bodies is so peculiar and specific, as to form a remarkable contrast with that of inorganic ORGANIC AND INORGANIC MATTER. 19 i matter. Their other characteristics are no less peculiar and dis- tinguishing. The most important differences between these two classes of substances, will be briefly noticed. 1. An organized body always possesses a certain determinate form, peculiar to the species to which it belongs. Every species has its own type, and this is so peculiar, that the systematic place of every plant and every animal in existence, might be determined by the manner in which it occupies space, or, in other words, by its external shape. Mineral substances, on the contrary, never possess a fixed and invariable form, though in a state of crystallization, they frequently present forms of great regularity. 2. All organized bodies, plants as well as animals, are distin- guished by rounded forms, which approach the spherical, oval, or cylindrical, and sometimes are branching and articulated. They scarcely ever present straight lines, or plane surfaces, or sharp angles, or ridges, but are almost always bounded by curved or undulating lines, and by concave or convex surfaces. The forms of mineral substances, on the contrary, are bounded by plane surfaces, and straight lines, irregularly broken by sharp angles. 3. The volume of organized bodies is no less determined than their form. Every species of animal and vegetable, has its own proper size, to which, with accidental exceptions, every full grown individual belonging to it conforms. But there are no fixed limits to the volume of mineral substances. They may be either great or small, according to the quantity of matter they contain, yet be absolutely identical in their nature or properties. The smallest fragment of a mineral substance has all the pro- perties of the mass from which it was taken. 4. Upon examining organized bodies with a microscope, they are found to contain minute particles of matter of a globular or oval, and sometimes flattened shape. The fluid, as well as the solid parts, both of animals and plants, abound in these minute globules. Some of the lowest classes of the animal world, as the infusory animalcula, and the polypus, as well as the most simple of the vegetable, e.g.; the conferva, the byssus, &c., are composed of them. In most of the animal fluids also, as the blood, chyle, saliva, pancreatic fluid, the milk, the spermatic fluid, and the fat, globules have been discovered. They have also been observed in the peculiar juices of vegetables, partic- ularly in those of the lactescent plants. They are found also in the cells of plants, and in the solid tissues of animals, as the cellular, mucous, and serous ; in the brain, nerves, muscles, ten- dons, and glands. These globules, to which there is nothing analogous in mine- rals, are considered by some physiologists as the elementary forms of organized bodies, as the ultimate organic molecules from which, disposed in various modes, the different tissues of animal 20 FIRST LINES OF PHYSIOLOGY. bodies result. Arranged in lines, they form the fibrous tissues of the nerves, muscles, and tendons. Extended in the form of sheets, they compose the various membranes, the serous, syno- vial, and mucous, and the coats of the vessels. United in masses, they form the solid substance of the glands, as the liver, pancreas, kidneys, salivary glands, &c. 5. The internal structure of organized bodies, presents another very striking characteristic, which distinguishes them from com- mon matter. Mineral substances are formed of homogeneous parts, which are perfectly similar in their physical and chemical properties ; while organic bodies consist of various parts, which differ in their forms, properties, and functions. A mineral sub- stance may exist either in a solid, liquid or gaseous form ; but it never presents a combination of these forms. It is either wholly solid, wholly liquid, or wholly gaseous. Whereas organic matter always presents a combination of solid and fluid parts. Organized bodies always consist of vascular or porous matter, with fluids contained in its vessels or interstices; and this composition is indispensable to the actions of living matter; for these result from the mutual influence of the fluids and solids upon each other. The various parts of which organized bodies consist, perform different functions in the economy of the individual; all of which however concur, each, in a peculiar manner, to the welfare and preservation of the whole. Every organized body is a system of organs, and can only exist by the association of these organs ; each of these being absolutely essential to the existence of all the others. Whereas, mineral bodies present no diversity of structure, and no reciprocal relations of different organs; and the parts into which they may be divided, can exist separately from their associates as well as when aggregated together by physical cohesion. 6. These two great classes of bodies differ also in their chemi- cal composition. A mineral may consist of a single element, or may form a simple body, as diamond, sulphur, &c. ; or, it may be composed of a great number of different elements, held to- gether by chemical affinity, or by cohesive attraction. But or- ganized bodies never consist of less than three elements; and animal substances contain at least four, viz. oxygen, carbon hydrogen, and azote.. Carbon may be considered as the charac- teristic element of one class of organized bodies, viz. vegetables ■ and azote of the other, or animal substances. Further ; a mineral has a fixed chemical composition, which undergoes scarcely any change under ordinary circumstances; while organized bodies are subject to incessant changes in their composition, in consequence of certain internal motions, which are essentially connected with the presence of life, and which are accompanied with a constant waste and replacement of the matter of which these bodies are composed. ORGANIC AND INORGANIC MATTER. 21 But another striking peculiarity in the chemistry of organic bodies is, that they consist of two kinds of elements ; one, which may be termed chemical, such as exist in mineral bodies, as oxy- gen, carbon, hydrogen, and azote; and another, which may be called organic, because they are the product exclusively of the organic or vital forces, and are never found in inorganic matter ; such as albumen, gelatin, fibrin, &c. It is owing to the fact that these last named elements are produced, not by the general pow- ers of matter, but by the peculiar forces of organic life, that it is impossible for us to decompose, and to reform organic, as we can inorganic substances. It is only the general forces of matter of which we can avail ourselves in our experiments upon bodies. These will enable us to reduce to their ultimate elements all kinds of matter, both organic and inorganic. But they will not enable us to recombine these elements in those arrangements which con- stitute the organic elements ; because this requires the agency of a new species of force, which is wholly out of the sphere of our control. It is not in our power to create a single particle of vege- table or animal matter ; and our analyses of these substances are in fact nothing else than a destruction, more or less complete, of their organization. Another important difference in the chemical composition of or- ganic and inorganic bodies, relates to the mode in which the ele- ments which enter into their composition are combined together. In organic substances the chemical composition is much more complex than in minerals, and from the same cause, less intimate and fixed. In mineral substances the combinations are for the most part binary, or their constituent elements are united by twos, and their affinities are completely saturated ; so that these substan- ces are comparatively fixed in their composition, and have but little tendency to change. However numerous the elements of inorganic substances may be, we always find them forming binary, or double or triple binary compounds. Water, the earths, the oxides and chlorides of metals, the acids, and many other sub- stances, furnish examples of simple binary combinations. The carbonates of lime and of the alkalies, the earthy, alkaline, and me- tallic salts, glass, &c, are examples of double binary compounds. Solutions of saline substances in water, or the same substances in a state of crystallization containing water, afford examples of triple binary compounds. It is difficult to form ternary compounds, on account of this strong tendency of the elements of matter to unite by twos. Let us take, for example, water, which is an inorganic fluid, composed of two elements, oxygen and hydrogen,' and we shall find that there are very few simple substances which it will dissolve. It will not combine with sulphur, carbon, phosphorus, nor with the metals; and but very sparingly with the simple gases. But it will readily dissolve all these substances in some state of combi- 22 FIRST LINES OF PHYSIOLOGY. nation with other elements. Thus, carbonic, sulphuric, and phos- phoric acids, readily combine with water. Sulphuretted and phosphuretted hydrogen are also absorbed by water, though in very different proportions. The metallic salts, and the alkalies are soluble in water. What is true of water, is true also of other binary compounds ; they refuse to unite, or they unite with diffi- culty, with simple substances; whereas simple bodies, as oxygen, chlorine, &c, combine with avidity with other simple substances, but not with bodies composed of two elements, except in certain special cases, or under peculiar circumstances. If we attempt to form a ternary compound, by uniting a simple body to a substance composed of two elements, the result is, either that no chemical action takes place between them, or, that the simple body exerts so strong an affinity for one of the elements of the compound, as to decompose it. If we add together any number of bodies, hav- ing affinities for one another, they never unite into one complex body, but always arrange themselves in binary compounds. Oxygen, e. g., is one of the elements of organic matter ; but it never exists in it in sufficient proportion to saturate the combusti- ble elements, carbon and hydrogen, with which it forms ternary compounds. Hence all organic matter is combustible. It burns when ignited in contact with the air, and then absorbs all the oxygen necessary to saturate its hydrogen and carbon.* In the ternary and other more complex combinations of organic matter in which the combining elements are held together by a feeble affinity, there is a constant tendency to separate and assume a binary arrangement, in which the affinities are more energetic, and more perfectly saturated. Thus, the ternary combinations of oxygen, carbon, and hydrogen, are resolved by spontaneous de- composition into the binary compounds, carbonic acid and water. If azote is one of the combining elements, as is the case with animal substances, it separates from the oxygen and carbon and unites with the hydrogen, for which it possesses a strong affinity, and forms ammonia, which is one of the characteristic results of animal decomposition. From this tendency of the elements of animal and vegetable substances, to pass into binary combinations, arises the facility with which they are decomposed. The nice equilibrium, in which their elements are held in these complex combinations, can no longer be maintained after the vital forces, which formed them have ceased to act. To adopt a familiar illustration, we may say, that the company breaks up, and each individual joins the friend for whom he has the strongest attachment. Though the composition of organized bodies is much more complex than that of inorganic, yet the number of elements actu- ally employed in the formation of them, is much less than that of * Tiedemann. ORGANIC AND INORGANIC MATTER. 23 those which exist in the latter. Vegetable matter is composed principally of three elements, viz. carbon, hydrogen, and oxygen ; and animal matter of four, containing, in addition to the three former, another element, azote, from which it derives its princi- pal chemical peculiarity. Besides these four, which are the essen- tial elements of organic matter, it contains several others, but in very inconsiderable quantities, making in the whole about nine- teen, which is little more than one-third of the whole number of elementary substances which have as yet been discovered by chemical researches. It appears, then, that the structure of organized bodies presents the following characteristic features, viz. that they possess a de- terminate form and volume; are composed of particles of matter of a spherical shape ; and possess a peculiar chemical composition, consisting, in almost all cases, of three or four ultimate elements, which are always the same, viz. oxygen, hydrogen, carbon, and azote ; that these are combined together into ternary, or quater- nary compounds, not by the operation of chemical forces alone, but by these modified by a new species of force, the organic, or vital powers ; and they are formed into certain organic elements, which the common powers of matter are wholly unable to form, and which, on the contrary, they are constantly endeavoring to subvert ; that organic bodies consist of solid and fluid parts ; that the solid parts are not compact and homogeneous, but possess a fibrous and vascular, or areolar structure, in which the fluid parts are contained; and, lastly, that an organized body consists of an assemblage of organs, differing in their form, size, structure, and actions, but all mutually dependent on one another, and conspiring to produce the same result, the preservation and welfare of the individual. 7. The general properties by which organized bodies are distin- guished from inorganic matter, are next to be considered. It has already been observed, that organized substances are not immedi- ately subjected to the laws of chemical affinity, but that they are endued with a new species of force, by which these laws are mod- ified, and which may be termed organic power. In consequence of this peculiar property, organic substances react against the physical and chemical influences of the external world in a pecu- liar mode, the intimate nature of which we are unable to discover, while its results are evident and extremely curious. There is a perpetual conflict between organic and chemical power. The physical and chemical forces of nature unite in their endeavors to reduce under the general laws of matter these isolated masses, which have been wrested from them by a foreign power, which has superseded their own authority, and which is extending its conquests in every part of their empire. In this struggle the gen- " eral powers of matter are, in every instance, sooner or later inva- riably successful. These forces are inherent in every form of 24 FIRST LINES OF PHYSIOLOGY. matter, unwearied in their exercise, indestructible and inexhausti- ble ; while the organic forces, are by their own nature limited in duration, exist only in connexion with particular forms of matter, isolated from the general mass, and maintained in a forced state of composition by the energy of these very powers, in opposition to the general laws of matter. But, if organic power is, in every instance, sooner or later over- come and destroyed by the general powers of matter, it is con- stantly starting up and renewing the conflict elsewhere, and is successful for a time, though in the end always overcome by the steady opposition of these powers. So long as an organized body is animated with organic power, so long it resists the chemical influences to which it is exposed. Even when its organic power is weakened by disease or natural decay, the chemical affinities of its elements are restrained within very narrow limits; and it is only on the invasion, or near approach, of death in particular parts, or in the whole system, that the chemical forces begin to be developed, in the phenomena of incipient vegetable or animal decomposition. The conflict between chemical and organic power consists in the attraction which the elements of physical nature exert towards those of living matter, and which is resisted by the vital affinities between the elements of the latter ; and, on the other hand, in the vital attraction of living matter towards certain elements of inorganic nature, an attraction which is counteracted by the chemical affinities which belong to the latter. But the seeds of discord exist also in the organic elements themselves. For both classes of powers, chemical and vital, exist in these ele- ments, giving them different tendencies to combination, and of course mutually limiting each other. In fact, these two classes of powers, the physical and organic, may be more properly con- sidered as mutually limiting, than as hostile powers. Each is restrained and kept in check by the other. This power of reacting against and neutralizing the mechanical and chemical forces of matter, is exemplified in the faculty, pos- sessed by animal bodies, of preserving a certain regular and inva- riable temperature amid very great changes of temperature of the medium in which they live ; in the power of elaborating out of a vast variety of heterogeneous substances, viz. the different kinds of matter used as food, the same homogeneous products, viz. the chyle and blood ; and in the power of moulding out of this fluid a great variety of curious tissues and organs, differing in their mechanical structure, in their composition and properties, and all compounded in opposition to the general laws of matter. All organized beings, both vegetable and animal, are endued with the property of being affected by various external agents of showing themselves sensible to the impressions which they thus receive, and of being excited by these to certain actions, which inorganic substances never exert. The phenomena of ORGANIC AND INORGANIC MATTER. 25 nutrition and growth, under the influence of external agents, imply the aptitude of being affected by the impressions received from them. Animals of all classes are excitable, their nutrition, and consequently the preservation of their lives, being effected under the influence of external agents, and their voluntary mo- tions being frequently excited by various impressions from with- out. The egg and the seed are capable of entering upon a series of internal movements and developments, under the influence of warmth, moisture, and atmospheric air. The irritating effects of many physical agents on living matter are the result of its endeavour to maintain its own integrity, and to assimilate to its own nature the agents which act upon it; and the nature of this reaction or excitement will depend on the properties of the agent, as well as on the powers of the living body. A cutting instrument is resisted by the living solid by the force of the vital affinity of the latter. Destroy the life of the part and the resistance is lessened ; a fact which proves that the mechanical power of the instrument is limited by the vital properties of the organization. Here the effect is confined to the effort of the living substance to maintain its own integrity. But if the effort be unsuccessful, and the vital resistance be not sufficient to overcome the mechan- ical power of the instrument, a new effort, of a different kind, consisting in a series of vital actions of a peculiar character, is made to repair the injury. The spasm of a muscle occasioned by pricking it, is, perhaps, another example of an effort of living matter to resist physical injury, by condensing itself. In these cases, no time is allowed for an effort at assimilation to be made on the part of the organized body. But if a foreign substance, soluble in the animal fluids, as a piece of iron, be left in the flesh, the assimilating power is then exerted, and the metal, if not discharged by suppuration, is corroded and absorbed into the blood. In like manner, knives, purposely swallowed, have been dissolved or digested in the stomach or bowels. Chemical agents, in like manner, as heat, acids, and alkalies, are resisted or limited in their action by vitality. Foreign sub- stances existing in the blood are so masked that it. is frequently impossible to detect their presence. It is evident, from these examples, that living bodies must be endued with various powers of resistance to injury ; for as different agents attack living matter in different modes, the resistance of the organization must be varied in order to overcome them. Besides the physical and chemical agents which may act injuriously upon the organization, there is a third and most important class of noxious agents, which act physiologically, and which are met by a different kind of resistance on the part of the 4 26 FIRST LINES OF PHYSIOLOGY. organization. These are various poisons, especially the organic, and the causes of disease, the destructive influence of which is resisted, and very frequently with success, by the vital powers of the organization. These conservative powers of the organization, are collectively termed the vis medicatrix natural, a property which it seems im- possible, without the grossest absurdity, to deny to living matter. All the instances just mentioned of resistance of the organiza- tion to mechanical, chemical, and physiological agents, of a noxious kind, are examples and illustrations of the same power of self-preservation. The same property is the basis of nutrition. This property of being determined to certain movements or manifestations of force, under the influence of certain exciting causes or impressions from without, is supposed, by some phy- siologists, not to be limited to matter already organized and endued with vitality, but to be inherent in organic matter, which is still amorphous and devoid of life. This opinion is founded on what is called spontaneous generation, a process in which cer- tain organic substances, as albumen, fibrin, gelatin, starch, gluten, gum, &c. spontaneously assume, [as some have believed,] under the influence of certain external circumstances, some of the lowest forms of animal and vegetable life. 9. Another distinctive property of organized bodies is, that their growth and increase proceed from within, while inorganic matter increases by external accretion. The surface to which the new particles of matter are applied, is internal in organic, but external in inorganic matter. Organized bodies grow by a series of internal developments; inorganic increase by the addi- tion of matter applied externally to them. With the nutrition of organized bodies, which is accomplished by the continual intus- susception of new matter, is connected an antagonist process of organic decomposition, in which the worn out elements are removed and discharged ; so that a perpetual round of composition and decomposition is going on in all organized bodies. 10. Further, organized substances possess the power of pro- ducing beings similar to themselves, or, the faculty of generation. This is a remarkable and exclusive prerogative of organized bodies, unless we admit, with some physiologists, that matter in certain forms and under particular circumstances, has the property of organizing itself into some of the lower forms of animal or vegetable life. 11. Organized bodies possess the power of being affected with, and of recovering from disease. 12. Organized substances have a determinate duration or period, beyond which it is impossible to prolong their existence. No power short of creative energy can prolong this duration beyond the period appointed by the laws of its own being. Its existence consists of a series of internal developments, each of ORGANIC AND INORGANIC MATTER. 27 which is the natural result of that which immediately preceded; and in a certain time the series, which in every species is un- alterably determined by the laws of its being, is exhausted, and it then ceases to exist. Originating in a minute portion of matter derived from a being similar to itself, when placed in certain circumstances, it immediately commences a series of internal evolutions by which it gradually enlarges in magnitude ; and its interior structure is more fully unfolded. A great variety of distinct parts, which were only imperfectly sketched out, or existed merely in a germinal state, are now gradually unfolded; and this process of internal development goes on without inter- ruption, until the organic mass reaches a certain magnitude, and acquires a certain form, which denote the zenith of its existence. This form and volume once attained, a certain period of time is consumed in consolidating its growth, and ripening its powers; after which a process of organic decay commences, and the individual, having fulfilled the object of its existence, is, by the inevitable laws of its own nature, conducted back, by a different route, to the world of physical nature from which it sprung. Its material elements are returned to the great magazine of nature, from which they were borrowed; its peculiar powers and pro- perties are decomposed and lost among the mass of dynamic principles; and while its organs and its powers are resolved into numerous primitive elements, its individuality perishes, and its unity, both of matter and of power, is lost by diffusion in the vast ocean of nature. The duration of life varies for each species of organized being, animal, as well as vegetable. Some insects live but a day, some plants but a year; while the life of man sometimes reaches to a century, and that of some trees to the term of many hundred, and even, it is supposed, several thousand, years. The destruction of organized beings is termed death, to which there is nothing analogous in the world of inorganic matter ; and it is distinguished by two remarkable circumstances, viz. the abolition of the vital forces, or that internal energy which maintained the organic structure ; and the destruction of the body itself by a separation of its elements, effected by the exertion of their chemical affinities, which had been previously controlled and neutralized, as it were, by the vital powers. 28 FIRST LINES OF PHYSIOLOGY. CHAPTER III. RELATION OF ORGANIZED BODIES TO HEAT, LIGHT, AND ELECTRICITY. The relations of organized beings to the imponderable ele- ments, Heat, Light, and Electricity, are of a peculiar kind, and worthy of particular notice. All organized bodies have, to a certain extent, the power of regulating their own temperature; many of them possess the faculty of exhibiting electrical phenomena of a peculiar kind ; and some of them the power of developing light, or of becoming luminous. All these powers are connected with the presence of life in organized beings. They cease with the extinction of the living principle, with the exception that organic matter, in cer- tain stages, or under certain circumstances of decomposition, is phosphorescent, or becomes luminous in the dark. Caloric. Living, or organized matter, possesses the power, to a certain extent, of regulating its own temperature. Living bodies develop heat from the interior towards the exterior by their own pecLiliar powers, instead of receiving it from surround- ing objects. They do not receive but produce it; and they are capable of resisting, to a certain extent, the tendency of caloric to an equilibrium. A part of a living animal, exposed to a con- siderable degree of cold, instead of having its own temperature reduced, like an inorganic substance, frequently becomes warmer than before ; the defect of physical heat being compensated by an excess of organic. It has been conjectured, that as these two kinds of heat are derived from such different sources, are con- nected with such different forms of matter, and are subject to such dissimilar laws, there may be some essential difference in their nature and properties. But in fact, caloric, however excited when brought within the sphere of vitality, loses something of its chemical character and relations. Its affinities are modified • it combines, separates, accumulates, &c, after different laws • and its effects in many respects are widely different from those which it produces in lifeless or inorganic matter. In short there is no example of pure mechanical or chemical action in the living animal body. All is animalized ; every thing bears the stamp and characters of life. Organized beings differ much in their power of producing heat. As this faculty is connected with the living powers and the exercise of it is one of the modes of their manifestations it may be stated generally, that those which are the highest in the scale of development, possess it in the greatest degree. Thus RELATIONS OF ORGANIZED BODIES TO HEAT, ETC. 29 plants have a lower temperature than animals ; and the inverte- brated animals a lower temperature than those which possess a bony skeleton : of the vertebrated animals, also, those which are lowest in the zoological scale, viz. fishes and reptiles, have an inferior temperature to that of birds and the mammalia. There are exceptions, however, to this general principle. Birds have a higher temperature than the mammiferous quadrupeds, though they stand lower in the scale of organization. Some of the mammalia, also, have a higher temperature than man. Many insects have a much higher temperature than would cor- respond with their position in the zoological scale. Those exceptions, as we shall see hereafter, admit of an explanation on other principles ; particularly that the degree of organic heat in animals, depends on the degree of development of the respira- tory organs — those animals whose respiratory system is most complicated and perfect, possessing the greatest degree of animal heat. This principle, however, requires some qualifications. Animal heat is greatest, not absolutely in those animals in which the organs of respiration alone are highly developed, but in those which, besides, possess a highly developed nervous system, as is the case with birds when compared with insects. The human race and the mammalia, however, do not possess so high a temperature as birds, though they have much more highly developed nervous systems ; from which it is inferred, that animal heat, as far as it is connected with the nervous system, does not depend upon the degree of development of this, absolutely, but only so far as this system is appropriated to the organic or nutritive functions, and its activity is not absorbed in those higher functions of the nervous system, in which the mammiferous quadrupeds, and in a much higher degree, man, surpass the feathered tribe.* Organized bodies, also, have the power of resisting the heat- ing influence of very high temperature, or of maintaining their own at nearly the same standard, under the two opposite circum- stances of a higher and a lower temperature of the surrounding medium. When exposed to a degree of heat superior to the standard of their own temperature, the development of organic heat from within is immediately checked, and the excess of caloric applied to the surface excites the exhaling vessels of the skin to a copious secretion of perspirable fluid, which absorbs the excess of caloric, and flies off with it in the state of vapour. The development of organic heat is checked, under these cir- cumstances, because an excess of external temperature depresses and weakens those functions, by the activity of which caloric is generated in the system. Thus, the nervous power is debilitated by extreme heat; respiration becomes slower and less perfect; * Berthold. 30 FIRST LINES OF PHYSIOLOGY. digestion, nutrition, secretion, and in short, all the processes con- nected with the nutrition of the system, and carried on in the capillary vessels, where the evolution of animal heat takes place, are more or less enfeebled. Under opposite circumstances, that is, when the surrounding temperature is not sufficiently high, a more active development of caloric takes place from within. All the operations of life are performed with increased energy, as respiration, the action of the nervous system, digestion, assimi- lation, and the secretions; and with these, calorification. Plants possess the power of regulating their own temperature in a far less degree than animals. Indeed, some naturalists do not admit that they possess such a power at all. Certain plants, however, especially several species of -the arum, as the arum italicum; the arum cordifolium and arum esculentum, develop a high degree of temperature at the period of inflorescence. Hubert found that the heat of the flowers of the arum cordifolium rose to 45° Reaumur when the temperature of the air was only 21° R. The germination of seeds, also, is accompanied with an evolution of heat, a fact which is exemplified in the process of malting. Electricity. There is also an organic electricity, as there is an organic heat. Living beings are idioelectric, i. e., capable of developing electricity, and* of exhibiting electrical phenomena by the exertion of their vital powers. Many facts have been observed, by different physiologists, tending to establish the existence of a vital fluid, bearing a very close analogy to physi- cal electricity and galvanism. Beclard observed that needles, plunged into the middle of a nerve, acquired magnetic properties. Beraudi pricked the crural nerve of a rabbit with two steel needles, isolated at their free extremities by a plate of lac, and found, at the expiration of fifteen minutes, that the needles had acquired the power of strongly attracting light substances, such as little fragments of paper ; from which he inferred, that elec- tricity is developed in the nervous system under the influence of vitality. Another physiologist, Weinhold, asserts that a spark may be obtained by approximating the two ends of a divided nerve towards each other.* All animals, probably, have more or less free electricity. The changes of form and combination, which are incessantly taking place in the matter of which their bodies are composed, must be constantly disturbing the electri- cal equilibrium, and releasing the electric fluid from its com- bined state. In the human race, electricity appears to be de- veloped with much greater facility in some individuals than in others. Persons of an irritable temperament, it is said, have more free electricity than those of a dull phlegmatic habit. The use of alcohol is said to increase it. Some remarkable facts are on record, illustrating the development of free electricity in the * Lepelletier. RELATIONS OF ORGANIZED BODIES TO HEAT, ETC. 31 human body. It is related of a lady of Verona, that she used to terrify her maids by emitting bright sparks, accompanied by a crackling noise, when her body was rubbed or touched by a linen cloth. Another remarkable case, of recent occurrence, was that of a young lady of Orford, N. H., who had suffered a long time under ill health. The electrical phenomena first appeared during a vivid Aurora, Borealis. When she was slightly insulated by a carpet, sparks passed between her and any conducting body which approached. These sparks were emitted by her fingers to the brass ball of a stove, at the distance of an inch and a half. The affection lasted several months. But the most remarkable examples of electrical phenomena developed under the influence of vitality, are furnished by certain fishes which are provided with electrical organs. In these fishes the electro-motive power, instead of being diffused throughout the solids and fluids of the animals, is centralized in a particular ap- paratus or set of organs, intimately connected with the nervous system. Of these fishes there are several kinds, as the torpedo, of which there are two species, the torpedo marmorata, and the torpedo ocellata ; the rhinobatus electricus, the tetrodon electricus, the gymnotus electricus, the trichurus electricus, and the silurus electricus. The electrical organs of the torpedo consist of an apparatus which may be compared to a battery of several hundred voltaic piles. This apparatus is formed of a great number of prisms, of from three to six sides, standing very close together, near the head and gills of the fish, and in a direction perpendicular to the surface. These prisms consist of membranous tubes, the sides of which are abundantly supplied with blood-vessels and nerves, and which are divided into cells by transverse membranous par- titions. The cells are filled with an albuminous fluid. These organs receive three large nerves on each side, one derived from the fifth pair of cerebral nerves; the two others from the eighth, or the par vagum. As the electrical apparatus of the torpedo resembles a battery of voltaic piles, that of the gymnotus may be compared to a battery of galvanic troughs. Two of these, a larger and a smaller, are found on each side of the spine, separated from each other by a long ligament, and by the superior muscles of the vertebral column. The larger is found immediately under the skin, along the muscles of the back, and extends to the extremity of the long tail of the fish, where it terminates at a point. A smaller organ is found beneath the former, separated from it by a thick tendinous membrane, a layer of fat, and muscles. The structure of both is similar. They are composed of horizontal membranous plates, separated by an interval of about one-third of a line from one another, and crossed in a perpendicular direc- tion by membranous partitions, in such a manner as to form a 32 FIRST LINES OF PHYSIOLOGY. great number of cells, which are filled with a gelatinous fluid. These organs receive numerous branches of nerves from the spinal marrow, which ramify minutely on the walls of the cells. The extent of surface of these organs is very great. Lacepede calculated that the discharging surface of the electric organs in a gymnotus four feet long, is at least 123 square feet in extent. The electrical apparatus of the silurus electricus, also re- sembles a galvanic trough. It is composed of a membrane situated immediately under the integuments on each side of the fish, arranged in the form of numerous rhomboidal cells, which extend from the head to the ventral fins. These small cells are filled with an albuminous fluid. The organ receives an abun- dance of nerves from a large branch of the par vagum,. The structure of these electrical organs, as well as the phe- nomena which they produce, point out a striking analogy be- tween them and the voltaic battery. These organs exhibit, in their structure, a great resemblance to voltaic piles of the second class, inasmuch as they are composed of alternate strata of moist conductors of different kinds ; i. e. membranous partitions, and a gelatinous or albuminous fluid. The electrical phenomena pro- duced by them, however, are by no means to be accounted for by their structure alone, or the mechanical arrangement of the parts which form them giving rise to electrical excitement merely by contact. For it is found that the division of the nervous trunks which supply them, immediately destroys their power of giving electrical shocks, although their mechanical structure remains unaffected. Humboldt says, that when the gymnotus is cut asunder, the anterior part alone, from its con- nexion with the brain, continues to give shocks. From these facts we must infer, that the electrical discharge of the organs of these fishes is a vital act, which depends immediately on the in- fluence of the nerves upon them ; while the electrical organs themselves can only be considered as a necessary physical con- dition, or, as contributing, in a secondary manner, to the excite- ment and discharge, by contact. The discharges seem to be under the control of the animal's will. The phenomena of these discharges point out a striking analogy between them and the effects of physical electricity. The sensation produced by the shock, is very similar to that of an electric discharge. The shocks may also be communicated, not only by contact, but by the intervention of substances which are conductors of electricity. Moistened thread, or cloth, con- ducts the shock; but the same substances when dry are non- conductors. According to Humboldt and Gay Lussac, however, metallic substances will not convey the shock of the torpedo. The same is true of water, according to the same philosophers; for they experienced no shock on immersing their hands in the water near the fish. The effect was produced only on actual RELATION OF ORGANIZED BODIES TO HEAT, ETC. 33 contact. In the gymnotus electricus, however, the propagation of electricity by intermediate substances, is much more evident. It sends its shock through the water to the hand placed near it, and small fishes, which are swimming by, are sometimes killed by its discharges at a considerable distance. Metallic substances, and even wood, placed in contact with the fish, will conduct the discharge ; but sealing-wax and bees-wax are non-conductors. Several persons, forming a connected chain, may receive a shock, as from a common electrical machine, if the person who forms one extremity of the chain, is in immediate contact with the electrical organs of the fish, or is connected with them by means of a conductor of electricity. If the chain is broken by a non- conductor, the effect does not take place. In some experiments, sparks have been observed to accompany the discharges. To these facts it may be added, that Dr. Davy, by the discharge of a torpedo six inches long, converted eight needles into magnets. He also decomposed solutions by passing discharges through them by means of gold and platina wires. Notwithstanding these and other facts, evidently of an elec- trical nature, there are others which point -out a difference be- tween physical electricity and that produced by the electrical organs of these animals. Many of the most common effects of electricity, it has been found impossible to produce by means of these organs. Thus, they do not influence, in the slightest de- gree, the most sensible electrometer. No attraction nor repulsion of light bodies is produced by them. It is impossible to charge a Leyden jar by means of them ; and Davy was unable to effect the slightest decomposition of water, by repeated discharges of a torpedo. The discharge of the electrical organs of these fishes is an act of the will. Unless the animal exerts a voluntary act, no discharge takes place. A strong and vigorous fish has sometimes been seized with both hands without giving a shock; while, at other times, the slightest contact has been sufficient to excite one. Humboldt is of opinion, that the torpedo has the power of sending his shock in whatever direction he pleases. My friend, Dr. Francis W. Cragin, of Surinam, informs me, that the discharge of the gymnotus electricus is propagated in every direction, in the water. If the hand be plunged into any part of the tub in which one of these eels is contained, it will receive a shock, whenever the animal is irritated to make a discharge. After giving a shock, electrical fishes have the power of speedily charging their battery again. But the frequent repe- tition of the discharges exhausts them, and their shocks become weaker, unless they have a period of repose to recruit their vigour. The division or tying of the nerves which supply the electrical organs, destroys their power of giving shocks. The destruction 5 34 FIRST LINES OF PHYSIOLOGY. of the brain of the animal produces the same effect; but the power of giving shocks survives, for some time, the excision of the heart. There are, however, two electrical phenomena exhibited by animals, which are not of a vital character. One is the produc- tion of sparks by the friction of the fur of certain animals par- ticularly the cat, the rabbit, the dog, the horse, &c. Of the same nature are the sparks which are frequently observed on pulling off the stockings in cold dry weather, and on combing the hair. In these cases, electricity is excited merely by friction. The galvanic phenomena exhibited by living animal organs, under certain circumstances, are examples of the other. Elec_ tricity excited in these cases is not of a vital character, but is produced by the mutual contact of heterogeneous animal sub- stances, as muscles and nerves, disposed in such a manner as to form a chain ; precisely as it is by the contact of different metals with each other, or with moistened substances arranged in the same manner. The effects are still more striking, if the muscles and nerves, which form the animal chain, are armed with metal- lic coatings, which are made to communicate by means of a metallic wire. In these cases, electricity is excited by the con- tact of heterogeneous substances. That electricity should be excited in living bodies, is what we should naturally expect from the fact, that most of the conditions which are necessary to the excitement of it in inorganic matter, exist in living substances; as, for example, the changes of form and composition which are constantly taking place in the vital processes of digestion, nutrition, respiration, secretion, the evapo- ration of liquids, &c. The living body is a laboratory, in which matter is undergoing incessant changes of form and aggregation ; fluids are passing into solids, and solids into fluids, and fluids into gases or vapours; and in all these processes, heterogeneous sub- stances, as fluids and solids, are brought into contact, and mutu- ally act upon each other. These circumstances are precisely those, which, in inorganic matter, give rise to electrical mani- festations. Most of the operations in nature, in which two heterogeneous substances enter into mutual action, occasion a disturbance of the electrical equilibrium, and the production of electrical phenomena. And, according to Donne, there are elec- trical currents in living bodies, which are caused by the acid and the alkaline states of certain membranes or organs, representing the opposite poles of a galvanic pile. Thus, the whole skin secretes an acid fluid ; while the lining membrane of the whole digestive canal from the mouth to the anus, except the stomach, secretes an alkaline mucus. The saliva, the mucus of the oesophagus, and that which is secreted by the whole intestinal canal, is alkaline. The serous and syno- vial membranes also, in a healthy state, secrete an alkaline liquor, which in certain diseases is liable to become acid. RELATION OF ORGANIZED BODIES TO HEAT, ETC. 35 According to Donne, the skin, which is an acid membrane, and the internal alkaline membranes, represent the two poles of a pile, between which electrical currents are determined, the effects of which are appreciable by the galvanometer. For if one of the conductors of the instrument be placed in contact with the mucous membrane of the mouth, and the other with the skin, the magnetic needle deviates fifteen, twenty, or even thirty degrees, according to the delicacy of the instrument; and its direction indicates that the alkaline or mucous membrane takes negative, and the skin positive, electricity. Similar polarities, or opposite chemical states, exist between other organs, especially the stomach and liver, between which, according to Donne, there are powerful electrical currents. The chemical nature of the secretions may be changed by disease, the acid becoming alkaline, and vice versa; and these changes, according to M. Donne, occasion modifications of the electrical currents which exist between different organs. Acidity is usually the result of inflam- mation, and the acid which is developed by inflammation is the hydrochloric. In relation to the electrical state of individuals of the human race, under different circumstances, Pfaff and Ahrens, by experi- ments made with a gold-leaf electrometer, upon persons placed on an insulating stool, obtained the following results: 1. In a state of health, the electricity of the human body is generally positive. 2. Irritable men, of a sanguine temperament, have more free electricity than those of a dull, sluggish, phlegmatic habit. 3. In the evening, the quantity of free electricity is greater than at any other time of the day. 4. Spirituous drinks increase the quantity of electricity. 5. Women are more frequently in a negatively electrical state than men. Gardini observed this electrical condition in females at the period of menstruation, and during gestation. 6. In rheumatic diseases the electricity sinks to zero; and as the disease disappears, gradually rises and becomes apparent again. Phosphorescence. Another example of the development of the imponderable elements by organized matter, is furnished by the phosphorescence of many animals and plants. Inorganic substances exhibit this phenomenon under the following circumstances, viz.* 1. Some have the property of shining in the dark, after having been exposed to solar or other light for a certain time. This is the case with the diamond, calcareous spar, marble, strontian, and some other bodies ; and, in a less degree, with alabaster, saltpetre, muriate of ammonia, galena, &c. The phosphorescence takes place in all transparent media, and even in a vacuum, with a sensible evolution of heat. * Tiedemann. 36 FIRST LINES OF PHYSIOLOGY. 2. Many substances shine in the dark, after having been ex- posed to a certain heat, as chalk, barytes, strontian, magnesia, rock crystal, quartz, topaz ; the filings of many metals ; as zinc, antimony, iron, silver, and gold. In these cases, heat appears to act by overcoming the affinity of these bodies for light, and setting this element free. 3. Friction, percussion, and compression, are accompanied with a disengagement of light in many substances, particularly in those which are rendered phosphorescent by insolation or exposure to heat. Certain fluids, as water and air, give out light when suddenly compressed. , 4. The crystallization of salts, in the water in which they were dissolved, is sometimes accompanied with a disengagement of light. This has been particularly observed in the sulphate of potash, and the jluate of soda. 5. Intense chemical action is generally accompanied with an evolution of light. 6. Electrical phenomena frequently give rise to a disengage- ment of light. Some bodies are rendered luminous by the trans- mission of an electric shock through them ; and the fluid itself frequently becomes visible, under the form of a vivid spark. Many organic substances destitute of life, give out light under circumstances exactly similar. 1. Some after exposure to solar light, as flour, starch, gum arabic, feathers, horn, coral, snail shells, teeth, pearls, bones, &c. 2. Some after exposure to heat, as volatile and fixed oils, sugar, wood, &c. 3. Some by friction, as sugar, manna, resins, &c.: olive and essential oils, when shaken in a vacuum. 4. All organic bodies during their combus- tion. 5. Resinous substances when electrically excited by friction. Many organic substances, also, are phosphorescent during the process of decomposition. Dead vegetable matter, particularly the wood of trees, and especially that of the roots, when decom- posing under the influence of a moderate heat, and of moisture, and without being fully exposed to the atmosphere, is frequently phosphorescent. It is remarkable, that great heat and a freezing temperature, are both destructive of the phosphorescence. The light becomes stronger, but continues a shorter time, in condensed air. In oxygen gas, the phosphorescence is not increased in intensity, but continues a longer time. It ceases in a few hours in azote, hydrogen gas, and the phosphuretted hydrogen, but reappears on the admission of atmospheric air. It disappears in a few minutes in carbonic acid, sulphuretted hydrogen, chlorine, ammonia, and muriatic acid gas. It is speedily extinguished in fixed oils and alcohol, ether, lime-water, and diluted acids. It disappears instantly in sulphuric acid. In oxygen, it occasions a loss of the gas, and a production of carbonic acid. From these facts, Gmelin inferred, that during the decomposition of wood, there is sometimes formed an organic and very inflammable com- RELATION OF ORGANIZED BODIES TO HEAT, ETC. 37 pound of carbon, hydrogen, and oxygen, which, like phosphorus, burns with an evolution of light at the ordinary temperature of the air. It is not improbable that phosphorus itself may be one of the ingredients of this compound, and contribute greatly to the effect.* Dead animal matter, however, much more frequently exhibits the phenomena of phosphorescence than vegetable. Dead fish, particularly the marine molluscous fish, in the incipient stage of putrefaction, often exhibits it in a high degree. It usually begins a day or two after death, when the animal is exposed to the atmosphere, or to oxygen gas, moisture, and a moderate tempera- ture. A freezing temperature, and the heat of boiling water, equally suspend it. The phosphorescence does not appear in a vacuum, in carbonic acid, hydrogen, or sulphuretted hydrogen gas. Lime-water, alcohol, ether, and strong solutions of alkalies, salts, and acids, destroy it. But it appears again when these solutions are diluted with a large quantity of water. On the surface of the fish, during its phosphorescence, a gelatinous fluid matter is obser- ved, which is the source of the luminous appearance. It may be washed off with water, which dissolves it, and becomes luminous itself. The phosphorescence ceases as soon as the decomposing fish exhales a fetid odour. From these facts it seems probable that the phosphorescence of dead animal matter is occasioned by its decomposition, followed by the formation of a combustible compound, which probably contains phosphorus, and which burns slowly with the evolution of light, in atmospheric air, or oxygen gas, at a moderate temperature.f But light is frequently given out by organized bodies, under the influence of vitality. It is asserted by some philosophers, that the flowers of several plants emit luminous sparks after sun- set, in clear warm summer evenings. Several of the cryptogam- ous plants are said to be phosphorescent. The appearance has been most frequently observed in those which grow in warm and humid situations, as in mines; particularly in a cryptogamous plant, called the rhizomorpha. The phosphorescence of this plant becomes more vivid in a temperature of 40° C. It does not give out light in a vacuum, nor in a gas which contains no oxygen. It shines brighter in oxygen gas than in atmospheric air, and con- sumes part of the oxygen, with the production of carbonic acid. The phenomenon ceases with the life of the plant. It seems to depend on the emanation of an inflammable vapour, which under- goes a slow combustion in atmospheric air, and oxygen gas. The dictamnus albus is said to diffuse around it, during warm summer evenings, an atmosphere which takes fire on the approach of a lamp, and burns with a brilliant flame. A great number of animals, also, both aquatic and aerial, exhibit * Tiedemann. t Ibid. 38 FIRST LINES OF PHYSIOLOGY. luminous phenomena. Most of the inferior classes of animals which inhabit the sea, as the infusoria, the medusa,, the radiaria, the annelides, many of the Crustacea, the mollusca, and even some of the fishes are phosphorescent. The luminous appearance of the ocean, which is frequently observed, particularly in the tropical climates, is derived from this source. The marine animalcula, contained in a vessel filled with sea water, have been observed to be phosphorescent, whenever the water is agitated by shaking the vessel. Diluted sulphuric acid, poured into a vessel containing luminous animalcula, has been found to occasion a sudden brilliant light, which immediately afterwards disappeared. The phosphorescence of the medusae has been observed to increase whenever the water containing them was warmed. In alcohol, also, their light became more vivid ; but this fluid soon killed them, and their phosphorescence disappeared. The phosphorescence takes place during the motions of the animal, and is more vivid in proportion to their vivacity and energy. The light emitted by some of the phosphorescent marine animals, is most vivid at the time of propagation ; and it is asserted by some observers, that even earth-worms are phosphorescent at the period of their amours. A viscid matter exudes from some of the phos- phorescent marine insects, which is also luminous, and which communicates a luminous appearance to the finger, and even to the mouth and saliva of those who eat them. The light disap- pears in a vacuum, but returns on the re-admission of the air. A moderate heat increases its vividness, but the heat of boiling water, or cold, equally destroys it. The phosphorescence continues some time in oil. A dilute solution of muriate of soda, or of nitrate of potash, or the spirit of sal ammoniac, increases its brilliancy; while concentrated solutions, vinegar, wine, alcohol, sulphuric acid, and corrosive sublimate, speedily destroy it. It continues some time after death, but is extinguished at the commencement of putrefaction. Among the animals which live in the air, the tribe of insects furnishes the greatest number of phosphorescent animals. The source of the light in insects, has its principal seat in the posterior rings of the abdomen. It seems to reside in a peculiar albumin- ous matter secreted by the animal, which is phosphorescent when exposed to a moderate heat, and to atmospheric air ; but ceases to emit light when coagulated by alcohol, ether, corrosive sublimate, or concentrated mineral and vegetable acids, &c. The phospho- rescence also disappears in the non-respirable gases, and in a vacuum, but returns on exposure to atmospheric air or oxygen gas. The phosphorescence usually commences at dusk, and at an earlier period if the insects be put in a dark place. It seems to be under the control of the animal's will; for a sudden noise will sometimes instantly cause it to cease. Some naturalists attribute the phenomenon to the action of the nerves ; others to the faculty possessed by insects of accelerating or retarding their respiration RELATION OF ORGANIZED BODIES TO HEAT, ETC. 39 with which they suppose the emission of light to be connected. It seems to be certain, that the motions of the insect increase the phosphorescence. The phenomena of phosphorescence require a certain tempera- ture of the air. At a certain degree of cold, the emission of light ceases, and, on the contrary, its vividness increases if the tempe- rature of the air be elevated within certain limits. If one of these insects, when not emitting light, be plunged into warm water, the phosphorescence commences ; and if the temperature of the water be raised, it increases until the heat reaches a certain point, at which the emission of light ceases. If living insects be plunged into water heated to a degree sufficient to kill them, they emit a very vivid light at the moment they perish. The phosphorescence requires the presence either of atmo- spheric air or oxygen gas. If luminous insects be placed in the receiver of an air-pump, the light which they emit gradually becomes fainter in proportion as the air is exhausted. In oxygen gas their light becomes very brilliant, and still more so, if the gas be heated. The protoxide of azote produces a similar effect. Chlorine gas destroys them instantly. In hydrogen gas, carbonic acid, sulphuretted and carburetted hydrogen, and azote, which soon kill the insects, the phosphorescence speedily ceases. The emission of light continues some time in warm water, but soon ceases in alcohol; and is instantly annihilated by the concentra- ted mineral acids. An electric or galvanic current, in some instances, has been found to excite a brilliant phosphorescence in the insects exposed to it. Mechanical and chemical irritations, productive of pain to the insect, have also been found to produce the same effect. Tiedemann supposes that the phosphorescence of insects depends on a peculiar animal matter, secreted by certain organs. This matter probably contains phosphorus, or some other com- bustible substance, which combines with the oxygen of the air, or with that contained in the water, at a medium temperature, and thus gives rise to the disengagement of light. The secretion of this substance is an operation of life, and is influenced by various external agents, which exert an influence upon the vital actions of these insects. But the phosphorescence itself is not of a vital character; it depends entirely on the composition and qualities of the luminous matter, and sometimes continues for several days after the death of the animals.* The only example of vital phosphorescence in the human system is furnished by the eye. In this organ the retina becomes luminous by pressure. It is well known that when the eyeball is pressed outwardly by the end of the finger applied near the inner angle of the eye, a luminous circle will be seen opposite to the point of pressure. A feeble light is produced by pressing upon the outer angle of * Tiedemann. 40 FIRST LINES OF PHYSIOLOGY. the eye. The effect may be produced even in total darkness ; and hence it follows that the retina, when compressed, is capable of emitting light, in the total absence of external light. It is to be observed, however, that this organic light is visible only to the eye which produces it. The production and the perception of the light are identical phenomena. CHAPTER IV. COMPARISON OF ANIMALS AND VEGETABLES. Organized beings are divided into two great classes, viz : animals and vegetables, distinguished from each other by certain characteristic features. Vegetables are organized living bodies, destitute of feeling and consciousness, and of the power of locomotion. They draw their nourishment from without by absorption at their surface, or by means of roots. They are composed of a homogeneous substance, forming roundish oblong cells, in which the solid or fluid matter of the plant is contained, without presenting any other kind of tissue. They reproduce themselves by temporary organs, which always die before the plants themselves. Animals are organized beings, endued with consciousness and feeling, and the power of locomotion. Most animals, from the zoophyte to man, are provided with an internal cavity for the reception and elaboration of the food. They are also much more complex in their organization, presenting a great variety of tissues and organs. They contain a much larger proportion of fluid, and a much smaller proportion of solid parts, than vege- tables. They are composed of a greater number of chemical elements, and always contain azote in addition to the principles which exist in vegetable bodies. CHAPTER V. DIVISION OF THE ANIMAL KINGDOM. The animal kingdom presents an immense variety of species, which are arranged in various classes, and subordinate divisions. One of the most general divisions of the animal world, is into DIVISION OF THE ANIMAL KINGDOM. 41 vertebrated and invertebrated ; the former embracing those ani- mals which are provided with an interior bony frame or skeleton ; the latter comprehending all such as are destitute of it. Again : the vertebrated animals are divided into two great sub-classes, the warm and the cold-blooded animals ; the former including those which possess a temperature considerably higher than the medium in which they live ; the latter those whose temperature exceeds but little that of the surrounding element. Further ; the warm-blooded animals either produce living young, which they suckle, or hatch their young from eggs. The former, or viviparous warm-blooded animals, constitute a great and im- portant division of the animal kingdom, under the name of the mammalia ; the latter, or the oviparous warm-blooded animals, form the immense family of birds. The cold-blooded vertebrated animals are also divided into two great sub-classes ; one includes those which breathe by means of lungs, and comprehends the reptiles, forming the four orders, serpents, tortoises, frogs, and lizards; the second em- braces the cold-blooded animals, which breathe, not by lungs, but by a different set of organs, called gills; these are the fishes. The invertebrated animals constitute the inferior division of the animal kingdom, embracing insects, worms, the molluscous animals, zoophytes, and the infusory animalcula. TABLE OF A CLASSIFICATION OF ANIMALS. Viviparous, and having breasts. 1. Mammalia. ( Oviparous. 2. Birds, e Breathing with lungs. 3. Reptiles. ( Do. with gills. 4. Fishes. f Articulations both of the ex- 5. Insects, Crustacea, Itremities, and of the body ; but Arachnids. chiefly of the former. < | Numerous annular articulations 6. Annulata. of the body. rBody naked, covered with a 7. Mollusca. I slimy membrane, or inclosed in a calcareous shell. Breath- ing by gills or lungs, with I sexes separate, or hermaphro- dite. Blood, white. Head, not distinct from the body. < I Having a stellated or radiated 8. Radiated Animals. disposition of the parts, both Sca-ncttlc, ' external and internal, and pro- Star-fish vided with organs of respira- Medusa' I tion. Holothuria, t(c. I Without organs of respiration. 9. Zoophytes. i Polypus, ^ Coral, Infusory Animalcula. § C Warm-blooded. | [ Cold-blooded. . t< With articulated bodies. l* I^Unarticulated bodies. 42 FIRST LINES OF PHYSIOLOGY. The human race belongs to the great class of the mammalia, i. e. of warm-blooded, viviparous animals. Some animals of this class approach so near to man in organization and external shape, that they have received the name of anthropomorphous animals. This is the case with the simia, or ape tribe. The points of difference, however, are so numerous, as to have led many naturalists to form the human into a distinct and separate class. Some of these distinguishing marks are the following, viz: 1. The upright position. That this is natural to man, is evi- dent from the structure of his body, particularly the great size of his head, and the absence of the strong ligament of the neck, with which quadrupeds are provided for the support of their heads ; the great comparative size of the lumbar region, the breadth of the pelvis, and of the os sacrum, evidently designed to support a great superincumbent weight ; the bulk of the glutai muscles, whose power is exerted in extending the pelvis on the thighs, and maintaining it in that state, in the erect position of the trunk. In the mammalia, even in the simia, the glutaus maximus, which in man is the largest muscle in the body, is very small and inconsiderable. The extensors of the knee joint, also, are much stronger in man than in the mammalia. The effect of the action of these muscles, is to preserve an extended state of the limbs, which is essential to the upright position. The gastroc- nemii muscles, are also much more highly developed in man. We find, accordingly, that no other animal has calves equal to those of man. These muscles are necessary to progression ; for, by raising the heel, they elevate the whole body in the act of walking. The large size of the feet, forming an ample basis for the body to rest upon; the angle which the soles of the feet form with the axis of the body; the concave form of the sole and the greater prominence of the heel, designed to give attach- ments to the strong muscles of the calf, and to support the back of the foot, are further proofs that the perpendicular position is natural to man. In other mammiferous animals, the os calcis does not touch the ground. Many animals, as the dog and cat, do not even rest on the tarsus, but merely on their toes. But in man, the whole surface of the tarsus, metatarsus, and toes, rests on the ground. To these peculiarities of structure may be added the position of the eyes, and the shortness of the upper extremi- ties, which evidently point out the erect position as natural to man. 2. The free use of both hands. This prerogative of man is evidently connected with the upright position. If two limbs are sufficient for the support and progression of an animal, the two others are left free for other uses. Man is the only two-handed animal. The simia, which approach the nearest to man, are strictly four-handed, or quadrumanous animals, and of course are neither bipeds nor quadrupeds. They have thumbs on their lower, as well as on their upper extremities ; and their feet are ANATOMICAL STRUCTURE OF THE HUMAN BODY. 43 instruments of prehension as well as their hands. In man, the difference in structure between the hands and feet, evidently proves that they were not intended to perform the same functions. One is organized for support, the other for prehension. 3. The prominence of the chin, the perpendicular direction of the inferior incisor teeth, and the absence of the intermaxillary bone, are also characteristic marks of man. Another circum- stance is, that in man the teeth are of the same length ; whereas, in other animals the various kinds of teeth differ in length, and are separated by intervals from one another. In inferior animals, the canine teeth are much longer than their neighbours, and are separated from them by a considerable interval. 4. Man is physically defenceless. He is not provided by nature with weapons either for attack or defence. He remains in a helpless state after birth longer than any other animal, and is indebted to reason alone for his instruments of aggression or self-defence. 5. In man the facial angle is greater than in any other animal. In the best formed human head it amounts to between 80° and 90°. In the ape tribe, the facial angle is vastly inferior to that of the least favourable specimens of the human species. The largeness of this angle in man, depends on the great development of the forehead and anterior part of the brain. 6. Man has the largest brain, in relation to the volume of the nerves. This position is generally true, but there are some exceptions to it. 7. The sexual instinct is equally active at all seasons, and is not an irresistible impulse, but is subjected to the dominion of reason. 8. Man is the only animal that sleeps on his back. 9. He is the only animal that laughs and weeps. 10. He is the only animal which possesses an articulate lan- guage, expressive of ideas or mental conceptions. 11. He is the only animal endued with reason, a moral sense, and a sentiment of religion. 12. He can adapt himself to greater varieties of climate, and is more widely diffused over the earth's surface than any other animal. CHAPTER VI. ANATOMICAL ANALYSIS, OR STRUCTURE OF THE HUMAN BODY. The human system is a very complicated machine. It con- sists both of solids and fluids, or, of containing and contained 44 FIRST LINES OF PHYSIOLOGY. parts. The fluids constitute much the larger portion of the whole, bearing to the solids the ratio of about nine to one, ac- cording to some physiologists ; or of only three to one, according to others. The first estimate is probably much the nearest the truth. The solids are composed of the same chemical principles as the fluids, and are reducible by analysis to the same ultimate elements. This follows as a natural consequence from the fact, that the solids are formed out of the fluids, by new combinations of their particles, under the direction of vital or organic affinity. In the formation of the solids, the particles of matter are arranged in various modes. If we may believe some microscopical ob- servers, the ultimate animal solid is a minute sphere or globule of matter of extreme minuteness, not exceeding in diameter the eight thousandth part of an inch. This is supposed to be the ul- timate mechanical element of the animal organization, from which, disposed in various modes, are formed a great variety of animal solids. These may be arranged in the order of their simplicity, into filaments, fibres, tissues, organs, apparatuses, and systems.'* A filament is composed of a series of the primitive molecules, arranged longitudinally or in a row. Several of these filaments united together in a bundle, form a fibre. In this manner are formed the muscular and nervous fibres. A tissue is composed of fibres disposed collaterally or in planes, so as to form an ex- pansion or membrane ; or, intersecting one another at various angles, in such a manner as to form spongy solids, with areola? or interstices dispersed throughout them. The cellular, serous, and mucous tissues are thus formed. Different tissues, disposed in a certain manner, so as to form a distinct piece of animal mechanism, designed to perform a particular office, constitute an organ. Thus a muscle, a nerve, a bone, the stomach, the brain, &c, are organs. Some of the organs are extremely complicated in their structure, as the eye, the ear ; the viscera contained in the great cavities, as the lungs, liver, intestines, &c. Sometimes several organs are associated together for the pur- pose of accomplishing a common object. Such an assemblage is called an apparatus. Thus, the apparatus of digestion consists of the mouth, teeth, oesophagus, stomach, intestines, liver, pan- creas, lacteals, &c.; all of which organs concur toward the same object, the assimilation of food. The term system is applied to an assemblage of organs which possess the same or a similar structure. Thus, the nervous sys- tem consists of a variety of organs which, however differing in figure, magnitude, and situation, agree together in possessing one common structure. The same is true of the muscular system that of the bones, ligaments, vessels, &c. The first step in organizing the animal frame out of the primi- * Library of Useful Knowledge ; Article, Physiology. ANATOMICAL STRUCTURE OF THE HUMAN BODY. 45 tive molecule, is the formation of the filament, which may be regarded as the elementary animal solid. The next is the forma- tion of the fibre, by the union of several filaments in a bundle. The fibres may be regarded as elementary, in relation to the tis- sues, which are all formed out of fibres. Such is the common view. That of Raspail, founded on microscopical observation, is widely different, but extremely plau- sible and ingenious. The organic vesicle is composed, according to Raspail, of a combination of carbon, oxygen, and hydrogen, in variable proportions, or of carbon and water, represented by the symbol (C+OH ), united with an earthy or volatile base. The vesicle thus organized becomes the germ and generating element of the organs. These vesicles contain within them the germs of others, possessed of the same structure and aptitudes, and en- closing a third order of germs, and so on in an indefinite series. Organization, therefore, says Raspail, may be considered as a kind of vesicular crystallization, endued with the power of indefinite development. This vesicular crystal has the power of imbibing gases or fluids in contact with it, and of converting them into organic fluids. At the moment of its formation, the organic mole- cule, according to Raspail, is an oily substance, resulting from the intimate union of hydrogen with six times its weight of carbon. In this state it possesses the power of imbibition, and if exposed to atmospheric air, it absorbs, eventually, oxygen enough to satu- rate its hydrogen, so that the molecule may then be represented by one portion of carbon and one of water. In this stage of its formation it takes the character of gum, assumes the spherical form when suspended in a fluid, and continues to absorb gases; and at the same time it acquires a tendency to combine with inorganic bases, especially earthy and alkaline substances, as lime, potash, soda, ammonia, and some others. In this state, says Raspail, the vesicle is an organ endued with life, and with the faculty of inde- finite reproduction, by organizing, after its own type, the fluid contained in it. Every organized being, in this view, is formed by vesicular evolution, and every organ may be considered as a vesicle in a certain stage of development, or modified in a certain manner. Thus, a bone is a vesicle elongated or otherwise modified in its shape, and incrusted with calcareous salts ; a muscle an elongated cell endued with the power of contraction ; a gland is a cell con- nected by a hilum to the parietes of the cavity which contains it. The vessels are canals formed in the interstices of the cells, by the fluid imbibed by the external cell forcing itself a passage be- tween contiguous cells by separating them from each other. A filament, according to this view, is composed of an elongated imperforate vesicle. A tissue, like the adipose or cellular, is form- ed by successive orders of vesicles, produced by a series of internal developments : a structure which may be illustrated by the me- 46 FIRST LINES OF PHYSIOLOGY. chanical division of a small piece of solid animal fat, as mutton or beef tallow. It will be found, says Raspail, that such a mass is composed of an external vesicle, with strong membranous coats ; that within it are contained smaller masses, easily separable from one another, and each invested by a vesicular membrane, with more delicate coats than those of the external one, and inclosing in its turn a certain number of still smaller masses, and so on successively until we arrive at the primitive vesicles, which con- tain the granules of fat. Each of these vesicles of an inferior order, is attached, by some point of its surface, to the internal face of the vesicle which contains it, and is the result of the develop- ment of the latter ; and the whole mass may be easily conceived to arise in this manner from a single vesicle, by a series of inter- nal developments. CHAPTER VII. FUNDAMENTAL TISSUES. The solid part of the body is formed out of three fundamental tissues, the cellular, the muscular, and the nervous. All the solids of the body, however numerous, and however widely they may differ one from another, as the bones, ligaments, cartilages; the vessels, muscles, nerves, &c. may be analyzed, anatomically, into one or more of these three. Of these tissues, the most generally diffused, and the simplest in structure, is the cellular. This tissue enters into the composi- tion of every organ, and is the basis of the solid structure of the body. It forms, in fact, a kind of frame-work of the body, so that if every other kind of animal matter were removed, the cellular tissue alone would preserve the exact figure, and present a perfect skeleton of the whole, and of every one of its parts. Into the areola, or interstices of the cellular membrane, all other kinds of animal matter may be considered as infused. Thus, the bones are formed of an earthy salt, the phosphate of lime, infused in cells formed of cellular tissue. The muscles are bundles of fibres, inclosed in a sheath formed of cellular membrane. Every fasciculus of these fibres has a sheath of this tissue ; and every individual fibre, which goes to the formation of a muscle, has an envelop of cellular membrane. The same tissue, also, forms sheaths for the nervous cords. These sheaths send fine processes within, which surround the bundles of nervous fibres, and connect them together. The greater part of the ligaments, tendons, and cartilages, are composed of cellular tissue. It even constitutes a very considerable part of the hair and nails. This tissue also FUNDAMENTAL TISSUES. 47 penetrates into the interior of the solid viscera, as the liver, pan- creas, and other glands, and the coats of the hollow organs, as the stomach, intestines, vessels, &c, where it serves the purpose of connecting and binding together the tissues of which they are composed. The cellular tissue, then, it appears, occurs in two forms. In one, it constitutes the basis of all the solids of the body ; in the other, it serves as a bond of union, by which the organs are con- nected together. The first, by some physiologists, is termed the parenchymatous; the second, the atmospheric cellular tissue. The latter fills up the intervals or spaces between the organs ; while the former enters into the texture of the organs themselves, and contains all the other tissues of which they are composed. The cellular tissue, however, though entering into the compo- sition of all the organs, which perform every variety of function, yet never loses its own character, which is every where the same ; nor participates in that of the organ which it contributes to form. Though present in the nerves, and penetrating into the very recesses of these organs, yet it does not share in the sensibility which is the peculiar attribute of the nerves ; and though it accompanies every muscle and every muscular fibre, it no where partakes of the irritability which belongs to these organs. Though it exists in the glands, it has no concern in the secretion of their peculiar products. The cellular tissue appears to be composed of fibres of extreme delicacy, intersecting one another in every direction, so as to leave between them interstices, or little cells, from which it derives its name. According to Raspail, it is composed of a congeries of vesicles developed in successive series ; those of cotemporaneous formation pressing on one another, and at length becoming ce- mented, so that their parietes become confounded together. The cellular structure, however, appears only where the tissue is sub- jected to a slight distension, and it entirely disappears when the distending cause ceases to act; for the cellular tissue is extremely elastic and contractile, except in plants, in which it forms cells of regular shape, with firm walls. In animals, in the living state, it appears as a soft, loose, elastic, semi-fluid substance, of a grayish colour ; sometimes it presents a slimy appearance. It gives pas- sage to some blood-vessels and nerves, which, however, are des- tined to other parts, and are not spent on the cellular tissue itself. It is abundantly supplied with colourless vessels, and particularly lymphatics, which absorb the aqueous or oily fluid contained in its cells. This tissue, as it exists in every part of the body, forms a con- nected whole, or an immense net-work, every where permeable to the air. If air be forced into its cells in any part of the body, with a moderate continued force, it gradually penetrates and per- vades the tissue, so that the whole of it becomes inflated. As 48 FIRST LINES OF PHYSIOLOGY. it exists in the living body, its cells, where it enters into the composition of the organs, are filled with the parenchyma of these, and in other places, either with a watery halitus, or an oily fluid. The uses of this tissue may be inferred from what has been said. It forms a basis for all the solid organs, and it connects the solid parts of the body together; and, by its softness and elasticity, and the oily fluid with which its cells are filled, it pro- motes the mobility of the parts on one another. Its fundamental physiological property is contractility, or animal elasticity, which it imparts to all the organs it contributes to form ; and its chemi- cal characteristic is its being composed chiefly of gelatin. Out of the cellular tissue are formed a great variety of others, which may be regarded as modifications of it. These are mem- branes of all kinds, the sheaths of the muscles and nerves, vessels, and other organs. The membranes, which are formed of the cellular tissue, con- stitute some of the most important structures of the body. The general covering of the body is formed of membrane. Each individual structure has its membranous covering. All the cavi- ties, in which the principal organs are enclosed, are lined by membrane. The vessels are composed chiefly of membrane. Even the solid organs, as already observed, are formed of a basis of membrane, into the areolae of which, as a mould, is in- fused the peculiar animal matter belonging to them respectively. Now, all these membranes are merely modifications of the cellu- lar tissue. The principal varieties of membrane, which require to be noticed, are the following, viz. the serous, the mucous, the dermoid, the fibrous, the cartilaginous, and the osseous. 1. The serous membranes. The serous membranes line all the closed cavities, or sacs of the body, and are reflected over the organs, contained in them. Thus, the cavities of the chest, the abdomen, the brain, and joints are lined by serous membrane. These membranes separate dissimilar or heterogeneous parts from each other. Wherever a cavity exists in the body, containing parts or organs differing in structure from the walls of the cavity, such cavity, as well as the contained parts, are lined by a serous membrane. Thus, in the cavity of the abdomen, which contains the great organs subservient to digestion; in the cavity of the chest, which contains the lungs ; between the lungs themselves, where the heart is situated ; in the ventricles of the brain, where the plexus choroides is found, we find, severally, a lining of serous membrane, which is reflected from the walls of the cavity, over the organs contained in it. The cavities of the joints belong to the same category, and, accordingly, the synovial membranes which line them, are classed with the serous membranes. The bursa muscosa belong to the same structure. The arachnoides, which lies between, and separates the dura mater and pia mater of FUNDAMENTAL TISSUES. 49 the brain and spinal marrow, is also regarded as a serous mem- brane. The serous membranes, it appears, enclose, chiefly, the organs of automatic or involuntary motion. They envelop the heart, the lungs, and the intestinal canal, and the glandular and other organs connected with it, and some of the organs of reproduc- tion. According to Rudolphi, serous membranes line, not only the closed cavities of the body, but the interior of the vessels also, and the canals which open outwardly, as the alimentary canal and the air passages, forming a cuticle over the mucous membranes, which line these passages, analogous to that which covers the external skin. These membranes are of a shining whitish colour, and smooth on their free or inner surface, which is moistened with a watery halitus, from which they derive their name. On their attached, or external surface, they are rough, like condensed cellular mem- brane, and are connected with the walls of the cavities which they line by means of cellular tissue. They are extremely elastic and extensible, as appears from the shrinking of serous sacs after the removal of collections of water, or of any other cause which has distended them, They are said to be destitute of blood- vessels and nerves, and to consist merely of condensed cellular membrane, in which, it is asserted, the microscope cannot detect the least trace of a vessel. The serosity which exhales from, and moistens them, is merely an exudation from the vessels beneath them, and is probably transmitted by inorganic pores. The intense inflammation sometimes affecting the walls of the cavities which are lined by them, and which is usually referred to the serous membrane, is supposed, by some anatomists, to be seated in the tissues immediately subjacent to them. The uses of the serous membranes are to separate heteroge- neous parts or organs; and to diminish friction, and facilitate the motion or gliding of these parts upon one another by means of their moist and polished surfaces. 2. Mucous membranes. Another class of membranes, formed out of the cellular tissue, and possessing a higher degree of or- ganization than the serous, are the mucous membranes, so called from the viscid fluid which it is their proper office to secrete. These membranes line all the cavities which open upon the sur- face of the body, as the digestive and urinary passages, the nasal cavities and the air tubes. They enter into the structure of the different organs which are concerned in the prehension and assi- milation of the aliments, in aerial respiration, and the secretion and excretion of the various fluids. They may be considered as the basis of the glands, into the substance of which they every where penetrate: the inner tunic of the excretory ducts, even to their radicles, as far as their termination, being always formed 7 50 FIRST LINES OF PHYSIOLOGY. of mucous membrane. According to Rudolphi, these mem- branes have no free surface, but always lie between two others, having on their inner surface a thin serous tissue. The mucous membranes, with scarcely an exception, form a continuous whole. That which lines the eyes and eyelids, is connected by means of the nasal canal, with the membrane which invests the cavities of the nose. In the throat, the lining membranes of the mouth and nose pass into each other ; and they detach a process which passes through the canal of Eustachius into the cavity of the tympanum. In the fauces, the mucous membrane divides into two great branches, one of which passes through the larynx and trachea into the lungs, and furnishes a lining to the air tubes in all their branchings ; the other follows the route of the pharynx and oesophagus into the stomach and intestines, which it lines throughout their whole extent. In the small intestines, it sends detachments to the liver and pancreas, through the biliary and pancreatic ducts, which penetrate, by the ramifications of these ducts, into the very parenchyma of these glands. Another branch of the mucous membrane lines the passages of the urinary and sexual organs. In the male it invests the urethra, and bladder, and passes thence through the ureters into the kidneys ; another branch passes into the vesicula seminales, and thence through the spermatic cord into the testes. In the female it lines the vagina and uterus, and passes thence through the fallopian tubes into the ovaries. The branch of the mucous membrane which invests the urinary organs, apparently has no connection with that which lines the alimentary canal. For the perineum, covered by the common integuments, intervenes between the outlets of the digestive and urinary passages. In some animals, however, these canals have a common outlet, and consequently the mucous mem- branes which line them are continuous with each other. This is the case with birds. In the mammalia, also, the skin which covers the perineum approaches, in its organization, to the mu- cous membrane. The mucous membranes which line the excretory ducts of the breast and the external ear, are isolated from the rest. The mucous membranes, as before remarked, are more highly organized than the serous. They are of a loose, spongy texture, and of a reddish colour, and are largely supplied with blood-ves- sels and nerves. They are furnished with numerous small glan- dular bodies, called mucous glands or follicles. In a healthy state, these membranes are always covered with a slimy sub- stance, which is secreted by them, and from which they derive their name. The uses of these membranes are to sheath and protect the inner surfaces of the body, as the skin does the outer • and, by means of the mucus secreted by them, to screen these FUNDAMENTAL TISSUES. 51 surfaces from the contact of irritating substances, which may either be introduced from without, or generated in the body itself. Like the cellular tissue, the mucous membranes are highly ex- tensible and elastic. 3. The skin or cutis, which forms the outer covering of the body, forms another variety of membrane, which is a modification of the cellular tissue, and which bears a close analogy to the mucous membranes. About the orifices of the internal canals, the skin and the mucous membranes pass into each other, as in the lips, nostrils, eyelids, external ear, rectum, &c. Like the mucous membranes, the skin is largely supplied with blood-ves- sels and nerves, and in many parts with small glandular bodies, called sebaceous glands. On the face, and many other parts, it is thin and delicate ; in the palms of the hands, and soles of the feet, and some other places, much thicker. It is covered, ex- ternally, by the cuticle, or epidermis, an inorganic membrane, destitute of vessels and nerves, wholly insensible, and easily re- newed, if removed or destroyed. The inner surface of the cuticle is lined by a fine tissue, called the rete mucosum, by which it is united to the cutis, and which, by some, is regarded as a distinct membrane ; by others, merely as compacted mucus. It is very soluble ; and in the Ethiopian race, in which it is thicker than in the light-coloured varieties of the human species, accord- ing to Blumenbach, it may be completely separated both from the cutis and cuticle, and made to appear as a distinct membrane. It is the seat of colour in the human race, the cutis itself being white, and the cuticle, semi-transparent. The sebaceous glands of the cutis secrete a thin oily fluid, which is diffused over the skin, and preserves its suppleness and moisture. The skin is very extensible and contractile. This membrane is one of the principal organs of relation ; by means of which, a communication is established between us and the external world, and by which we obtain a great number of ideas of the qualities of external bodies, as heat, cold, hardness, form, distance, &c. To qualify it for this function, it possesses great sensibility, which it derives from the cerebro-spinal nerves, with which it is plentifully supplied. It also gives passage to fluids from the system under the form of insensible perspiration, or sweat, and is an absorbing, as well as an exhaling organ. It seems, also, to protect the system against the irritating contact of external bodies, and to modify the impressions received from them, so as to disarm them of their hurtful properties. 4. Another class of membranes, formed out of condensed cellular tissue, are the fibrous, so called from their texture. To this structure belong the periosteum,, the dura mater, the aponeu- roses, the fascia, the perichondrium, the tunica albuginea of the testes and of the ovaries, the coverings of the kidneys and spleen, and the sclerotica of the eye. The fibrous structure also appears 52 FIRST LINES OF PHYSIOLOGY. under another form, that of thick bundles of different shapes, as in the ligaments and tendons. The colour of this tissue is generally of a pearly white, with a satin-like or argentine lustre. Its texture is essentially fibrous. The fibres which compose it are delicate and intimately con- nected together, so that it is difficult to separate them. It seems to consist principally of condensed cellular tissue. The fibrous tissue is sparingly supplied with vessels, particularly in adult age ; but in the foetal state, and in infancy, its vessels are much more abundant and conspicuous. Certain parts of this tissue, also, are highly vascular, as, for example, the periosteum and dura mater; while, in certain other parts, it seems to be wholly destitute of vessels. The existence of nerves in the fibrous tissue has not been clearly demonstrated. This tissue possesses but little elasticity, and scarcely any extensibility; but its strength and tenacity are very great. It possesses no irritability, and, in a normal state, no perceptible sensibility. Yet the distension which precedes the rupture of the ligaments, and the wrenching of the same parts, in injuries, are productive of violent pain. In morbid states, the fibrous tissue is sometimes the seat of very acute sensibility. The functions of this tissue, as it exists in the form of liga- ments and tendons, are essentially mechanical. It chiefly serves to form bonds of connexion, by which the bones are united to- gether, and the joints strengthened ; and firm solid conductors of muscular motion to the bones, which the muscles are designed to move. In the form of membrane it furnishes strong sheaths or envelops to many parts, as the corpora cavernosa, the eye, the kidneys, spleen, testicles, the tendons, bones, and cartilages. 5. The cartilaginous tissue is another modification of the cel- lular, appearing to consist of condensed cellular membrane and gelatin. Cartilages are firm, smooth, highly elastic substances, of a pearly white colour, and which become semi-transparent by drying. With the exception of the bones, they are the hardest parts of the animal frame. They are destitute of blood-vessels, and neither nerves nor lymphatics have been discovered in them. They unite with great difficulty after wounds. Cartilages are invested with a fibrous membrane, called perichondrium. They differ from bones in containing no phosphate of lime, and in the want of cells and cavities for containing marrow. Cartilages are divided into two kinds, the permanent and the temporary. The temporary are those which are destined to be converted into bone ; for all the bones were originally cartila- ginous. The permanent are those which are not destined to future ossification, though they are liable to a morbid process, by which they are converted into bone. Thus, the cartilages of the ribs, those of the larynx and trachea, and even the epiglottis are sometimes found ossified. Naturalists have even observed exam- FUNDAMENTAL TISSUES. 53 pies of ossification in the cartilaginous fishes, in which, in the normal state, the skeleton remains cartilaginous during the life of the animal. The permanent cartilages are found in various situations, and perform various offices in the system. In some instances, they constitute the basis of organs ; of which we have examples in the cartilage of the ear, that of the nose, and those of the larynx and trachea. Sometimes they exist between bones which are not susceptible of motion upon each other, as between the bones of the cranium; sometimes, between such as admit of a certain degree of motion upon one another, as the intervertebral carti- lages, and those between the bones of the pelvis; they also tip the articular extremities of the long bones which move freely upon each other in the cavities of the joints. To these may be added the cartilaginous prolongations of the ribs. 6. The osseous tissue, which constitutes the bones, is the hardest part of the human body. The basis of it is cellular tissue, which is infiltrated with an earthy salt, the phosphate of lime. If this be removed, the bones appear as cartilages, and, by long maceration, they are at last reduced to cellular tissue. The bones are formed from cartilages, as is evident from the process of ossification, in which the future bone always appears first in the form of carti- lage. In the foetal state all the bones are cartilaginous. The structure of bones belongs to that variety of the cellular tissue which is called fibrous. The fibres follow no regular course, but intersect each other in every direction. The osseous tissue, like the cartilaginous, is said to have no proper nerves ; yet Mr. Swan has given us the view of a nervous cord passing directly into a bone. The blood-vessels of this tissue, which, in its early period of development, are numerous, gradually diminish, and with them its powers of nutrition and reparation. The bones are covered with a fibrous membrane, called the periosteum, which may be considered as an expansion of the tendons of the muscles over the bones. The muscles are attached to the bones by means of the periosteum only. Into this membrane pass the nutritive blood- vessels of the bones, some of which branch over the periosteum, and others penetrate into the substance of the bones. In certain places, where no muscles are attached to bones, and no periosteum is formed, a distinct membrane is provided to supply its place. This is the case with the inner surface of the cranium, where a strong fibrous membrane supplies the place of an internal perios- teum. The inner surface of the hollow bones is lined with a serous membrane, called the periosteum internum, or medullary web, which secretes the marrow. This is plentifully supplied with blood-vessels. The bones may be divided into three kinds, the roundish or spongy bones, as those of the hands and feet, and the vertebras; the cylindrical or tubular bones, including those of the arms and 51 FIRST LINES OF PHYSIOLOGY. legs; and the flat bones, as the shoulder-blades and the bones of the cranium. The bones are of a yellowish white color, and smooth exter- nally ; internally they present different kinds of structure. The broad flat bones consist of two tables, between which a cellular structure intervenes. In the cylindrical bones, the middle part is hollow, forming a tube, with firm, hard walls, but the two extremities are spongy or cellular. The cells and cavities are filled with an oily substance called marrow. The bones form a connected system, which constitutes the basis of the whole frame. They are the hardest part of the body, and serve as the framework and support of all the soft parts. They serve as points of attachment to the muscles or moving powers, and constitute levers of various kinds for the muscles to act upon, in executing the various motions which the body has the power of performing. Ossification is frequently a morbid process, occurring in a variety of structures, and impeding the functions of the parts. Thus the coats of the arteries, the valves of the heart, the tendons, and even certain muscular parts, as the substance of the heart, sometimes become bony. The same structures are sometimes converted into cartilage. II. Another constituent part of the system is the muscular fibre. To this appertains another of the elementary properties of life, viz. irritability, or the faculty of contracting or shortening itself on the application of certain stimuli. It is as peculiar, also, in its chemical constitution, as it is in its structure, and its vital properties, being formed almost wholly of concrete fibrin. Ras- pail applies his vesicular theory to the structure of the muscles, as well as to that of the cellular tissue. A muscular fibre he considers as an elongated imperforate vesicle, developed in the interior of one of a higher order, which has a similar origin. In this manner the whole organ may be considered as composed of different orders of vesicles, successively developed, and springing- ultimately from a single vesicular germ. In the large bulky muscles of a stout man, Raspail conceives that the process of development has proceeded further than in those of an emaciated subject; and that the increase in volume of these organs is owing, not merely to the deposition of interstitial adipose matter, but also to a development of their own proper substance. Thus, if we suppose that in a muscle of an emaciated subject, we must pass through five successive orders of vesicles, before reaching the elementary muscular cylinder or fibre, it is easy to conceive that in a robust subject, the same muscle may have proceeded one step further in its development, and that the fifth order, which constituted the ultimate filament in the extenuated muscle^ has, in the full-sized bulky organ, given birth to a sixth, which constitutes now the elementary fibres. It also appears, that each FUNDAMENTAL TISSUES. 55 cylindrical cell not only reproduces its type by its internal surface, but may also germinate by its external. Hence we find in the same aponeurotic sheath, muscular fibres of different lengths. By using a high magnifying power, Raspail discovered that each muscular fibre, consisting of an imperforate tube, contains within its cavity a spiral filament, which serves to keep its parietes apart, and by the approximation of its coils, to produce muscular contraction, a structure analogous to that of the ligneous fibres of vegetables. The ultimate muscular filament is extremely minute, not ex- ceeding, according to some physiologists, the fifth part of the diameter of a red globule of blood. The visible fibres into which the bundles of muscular flesh may be mechanically divided, are cylindrical in their shape, and of a reddish colour, which is sup- posed to be owing to the blood which they contain. The ulti- mate fibres are united into bundles, called fasciculi, or lacerti ; and these, by their aggregation, form the fleshy masses which are called muscles. Every fibre and fasciculus is enclosed in a sheath of cellular tissue, and the whole muscle has an envelop of the same ; so that the cellular tissue is largely incorporated into the substance of the muscles, to which it imparts its own peculiar property, animal elasticity. The cellular substance, which thus exists between the fibres and fasciculi of the muscles, becomes thicker and more condensed, and constitutes a larger proportion of the whole mass, while the muscular fibres diminish, in receding from the middle and ap- proaching the extremities of the muscles, where they terminate in tendons. And it is in this mode that the tendons are formed out of cellular tissue. For towards the extremities of the muscles this tissue becomes more condensed, and forms an increasing pro- portion of the whole mass of the organ, until the muscular fibres wholly disappear, and the whole cellular tissue belonging to each fibre and fasciculus, prolonged beyond the termination of the muscle, and condensed together, appears in the form of a silvery white cord, of a cylindrical or flattened shape, called tendon. The tendons then, it is evident, must be connected with every fibre of the muscles to which they belong. They are destitute of the irritability of the muscles, but are elastic like the cellular tissue, of which they are formed, and they consist principally of gelatin. The muscles are the instruments by which most of the sensible motions of the system, both voluntary and involuntary, are exe- cuted. III. The third constituent element of the structure of the body, is the nervous fibre. This consists essentially of albumen, as the muscular fibre consists of fibrin, and the cellular tissue of gelatin ; and it is endued with a distinct physiological property, sensibility. A nerve consists of two elements, viz. a pulpy or medullary 56 FIRST LINES OF PHYSIOLOGY. matter, i. e. the peculiar matter of the nerve, and a sheath which invests it, formed of cellular tissue. The medullary substance consists of bundles of nervous fibres, each covered with its own sheath of cellular tissue or membrane, and each also being divis- ible into a finer series, until we arrive at the ultimate nervous filament. This appears to be destitute of a cellular sheath ; but the primitive nervous fibre, formed by an aggregate of filaments, is invested with a sheath, and every fasciculus in like manner has its own envelop of cellular tissue ; and lastly, the nerve itself, formed by an aggregate of fasciculi, has a common sheath, which is called the neurilenia. According to Fontana, the ultimate ner- vous filament is twelve times larger than the primitive muscular. The nervous system, according to Raspail, has a vesicular origin. Every nervous branch is organized and developed exactly in the same manner as the branches of a plant. It is an elongated vesi- cle, which takes its origin from the external surface of the mater- nal branch, in which it is implanted. And the articulation of the two branches, viz. the maternal and the secondary, constitutes a ganglion, which, like the vegetable nodus, is a new centre of vitality. Of nervous matter is formed the nervous system, consisting of the brain, spinal marrow, the ganglions, and the nerves themselves. Its elementary physiological property, as before remarked, is sensi- bility, which it communicates to all parts of the system to which nerves are distributed. The sensibility thus diffused throughout the system, has two principal centres or foci, viz. the brain and the great solar plexus ; and it bestows unity and individuality upon the whole assemblage of organs and functions of which the living system is composed. CHAPTER VIII. THE COMPOUND STRUCTURES OF THE SYSTEM. Out of the elementary tissues, which have thus been briefly described, viz. the cellular, muscular, and nervous, are formed the various organs which compose the system of the animal. The principal of these are the bones, cartilages, ligaments, muscles, nerves, vessels, viscera, and organs of sense. The two first of these, viz. the bones and cartilages, have al- ready been sufficiently described, under the head of the osseous and cartilaginous tissues. The functions of these, together with those of the ligaments and tendons, are essentially mechanical. The ligaments constitute a structure, the chief use of which is THE COMPOUND STRUCTURES. 57 to connect the bones together into one system ; though there are many other structures which resemble the ligaments, which are destined to very different uses ; as, e. g., the sclerotica of the eye, the dura mater, the periosteum, the aponeuroses of the muscles, the fascia, the white tunic of the testes and ovaria, and the pro- per coat of the kidneys and spleen. These, with the ligaments, constitute collectively, the fibrous system. The common char- acter belonging to all these tissues, is a distinctly fibrous structure. In consequence of a deficiency of nerves, they possess scarcely any sensibility, except to mechanical violence of a certain kind, as, e. g., wrenching; and, as they contain scarcely any blood- vessels, they are of a white shining colour. They are very firm and compact in their texture. The proper ligaments are of different shapes ; some being round, some broad, and others forming sacs, as the capsular ligaments. They serve to connect together the articular ends of the bones in forming the joints. The ligaments are intimately connected with the periosteum of the bones, as they spring from this membrane and are again in- serted into it. In some few examples, however, they are con- nected, not with the periosteum, but with cartilages. The capsular ligaments, which enclose the articulations, con- sist of two coats, of which the outer is fibrous, and the inner serous. The serous forms a closed sac, and is a secretory membrane, by which is prepared the synovial liquor. The muscles constitute another very important class of organs, consisting of muscular fibres collected together in bundles by the intervention of cellular membrane, and plentifully supplied with blood-vessels and nerves. They are the organs of motion, and of the voice, and are divided into two classes — first, muscles of vol- untary, and secondly, those of involuntary motion ; or, as they are sometimes termed, muscles of animal and those of organic life. Those of the first class constitute the fleshy parts of the body. They lie more exteriorly, or towards the periphery ; derive their nerves principally from the spinal marrow ; act in the normal state only under the control of the will; are attached by both extremities to bones ; and are the organs of the voluntary motions of the body. The second class, or the muscles of organic life, are found in the interior of the body. These receive their nerves principally from the ganglionic system. They are not attached to bones, and are hollow organs, which do not contract under the influence of the will, but in consequence of certain natural stimuli, applied directly to them. The heart, the stomach, intestines, bladder, and, according to some physiologists, the air tubes of the lungs, belong to this class of muscles. Animal motion, however, is not, in all instances, executed by muscles. The motions of the blood in the 8 58 FIRST LINES OF PHYSIOLOGY. capillary vessels and veins, that of the lymph and chyle in the lymphatics, that of the different secreted fluids in the excretory ducts, the contractile motion of the cellular tissue and of several of the membranes formed out of it, as the skin, the serous and mucous tissues, &c, are not executed by a muscular structure. The nervous system constitutes another very important system of organs, consisting of the brain, spinal marrow, ganglions, and nerves. Like the muscular system, it is divided into two great sections, one termed the nervous system of animal, the other that of organic life. The first consists of the brain and spinal marrow and the nerves proceeding from them ; the second, of the system of ganglions and the nerves to which they give rise. The nervous system of animal life presides over cerebral sensation and volun- tary motion. The nerves belonging to it, are connected, by their central extremity, with the brain or spinal cord, and by their peri- pheral, with the organs of sense, or the muscles of voluntary mo- tion ; and they are channels of communication between the centre and the periphery of the nervous system of animal life. The nervous system of organic life, presides over organic sensi- bility and involuntary motion. Its nerves are distributed to the hollow viscera of the thorax and abdomen, and to the coats of the blood-vessels, which they accompany to all parts of the body. The functions of the circulation, of nutrition, secretion, exhalation, absorption, &c, are supposed to be under the control of this part of the nervous system. ^ The vascular system constitutes another very essential part of the human body. It embraces various organs, which differ in structure and in functions, but which agree in general in this re- spect, that they consist of cylindrical canals or tubes with mem- branous coats, which contain some kind of fluid, and do not open outwardly. By means of this system, certain substances, designed for nourishment or respiration, as aliment and the oxygen of the atmosphere, are introduced into the body, where, after undergoing certain changes, they are made to repair the waste in the organi- zation occasioned by the operations of life. By the same system, materials unfit for nutrition, whether introduced from without, or developed in the body itself, are conducted to some excretory organ, by which they are afterwards discharged. By the vascular system, the blood, the great excitant of the organs, and the source from which are derived the materials employed in the various processes of life, is distributed to all parts of the body, which are nourished and excited by it. The vascular system is divided into three great branches, viz. the arterial, the venous, and the lymphatic. The first, or the'arte- rial, carries red blood from the heart to all parts of the body • the seconder venous,brings back purple blood from all parts of the body to the heart again ; and the third, the lymphatic, also called the absorbent system, carries white or colourless fluids from the inter- THE COMPOUND STRUCTURES. 59 stices and periphery of the body, and from all the organs, into a large trunk, which opens into the venous system near the heart. The lymphatics, as yet, have been discovered only in the mam- malia, birds, reptiles, and fishes. They originate from the various membranes, the basis of which is condensed cellular tissue, as the mucous, serous, synovial, and dermoid, as well as from the cellu- lar membrane itself, which fills the interstices and forms the basis of the organs. They communicate with the venous system by means of the great lymphatic trunks, and, as some physiologists assert, by direct anastomosis with the veins ; so that they are re- garded as an appendage of the venous system. Their function is to absorb the nutritive fluid prepared by digestion in the aliment- ary canal, as well as other substances, which may come in contact with the external integuments of the body, and the mucous mem- branes. They also re-absorb certain parts of the various secreted fluids, and they are supposed to be the principal agents of the decomposition of the solid tissues and organs ; the molecules of which they detach and absorb, convert into a fluid state, and con- vey into the mass of the venous blood. The arteries are composed of three coats ; first, an external, formed of condensed cellular tissue, and possessing considerable strength and elasticity ; second, a middle, or the proper coat of the arteries, the real character of which is a subject of some controversy. It is a very firm, thick, and elastic tunic, composed of circular fibjres, of a yellow colour, and possessed of little or no irritability. According to Berzelius, it is wholly destitute of fibrin, in which respect it differs essentially from the muscular tissues. The third or internal coat, is smooth and polished, and is said to be lubricated with a kind of serous exhalation. The veins in their structure differ somewhat from the arteries. Like these, they are composed of three coats, an external, middle, and inner. The external consists of cellular substance, is dense, and difficult to rupture. The second, or middle, is considered as the proper coat of the veins. It is said to be composed of longi- tudinal fibres, but, according to Magendie, it contains a multitude of fibres interlacing one another in all directions. Like the mid- dle tunic of the arteries, it is insensible to the galvanic influence, and is not supposed to be muscular. It seems to be doubtful whether it contains fibrin or not.* The third or interior coat, is extremely thin and smooth, and serves to facilitate the motion of the blood by diminishing its friction. It is susceptible of great distension without being ruptured. It forms in the cavities of the veins numerous folds, which perform the function of valves. * The middle coat of the blood-vessels, is regarded, by many anatomists, as a distinct tissue of a fibrous structure and peculiar nature. It is either of a yellowish white, or pale reddish colour, and is called the vascular fibre. It contains no fibrin, nor does it respond to many irritations which excite muscular contraction, as galvanism, and me- chanical irritation. It appears, however, to possess a peculiar vital contractility, which differs from muscular irritability. In the arteries, this tissue embraces these vessels circularly ; in the veins, it is disposed longitudinally. The lymphatics are destitute of it. 60 FIRST LINES OF PHYSIOLOGY. The lacteals and lymphatics are composed of two coats only, viz. an external and an internal ; the external, of a firm, fibrous nature ; the internal, very thin and delicate. Like the veins, the lymphatics are supplied with numerous valves. The visceral system comprehends the large organs contained in the great cavities of the thorax and abdomen, as the lungs, the stomach, intestines, liver, spleen, pancreas, &c. The heart is ex- cepted, as belonging to the vascular system, and the brain, as being part of the nervous ; and hence these two organs are not considered as being strictly viscera. The viscera are the most complicated parts of the animal system, with the exception of the organs of sense, which are properly appendages of the nervous system. They are the seats and the instruments of the great functions of digestion and respiration. CHAPTER IX. FLUIDS OF THE SYSTEM. The fluids constitute much the larger proportion of the whole system. They are of various kinds, and perform very different offices in the animal economy. They may be distributed under three general heads, viz. I. those which serve for the preparation of the blood ; II. those which are formed out of the blood ; and III. the blood itself. I. Those which serve for the preparation of the blood, are two, viz. the chyle and the lymph. The chyle is a thick, cream-like fluid, prepared from the ali- ment by the powers of digestion, and imbibed from the small in- testines by a branch of the absorbent system, viz. the lacteals, and carried into the circulation by the thoracic duct. It is destined to repair the losses of the blood, to which fluid it bears a close analogy in its constitution and properties. Its final conversion into blood is consummated in the lungs. 2. By the lymph is meant a fluid which is formed in another part of the absorbent system, the proper lymphatics. As these vessels spring from all parts of the body, and are supposed to be the principal agents of the decomposition of the organs, the fluid contained in them must consist partly of the debris of all the sol- ids, as well as of various fluids absorbed from the different cavi- ties and surfaces of the system. These fluids, which are formed and deposited by a perpetual process of secretion, are subject to the action of the absorbents, so long as they remain in contact with any of the living tissues. Certain parts of them are imbibed FLUIDS OF THE SYSTEM. 61 by the lymphatics and blended with the molecules detached from the decomposing organs, and both are elaborated together into the fluid called lymph. This fluid is conveyed by the lymphatics into the common trunk of the absorbent system, the thoracic duct, where it is mixed with the chyle, and both are immediately after- wards carried into the torrent of the venous blood, near the heart. Like the chyle, the lymph contributes to repair the losses of the blood; but it is first subjected to the action of the lungs, in com- bination with the chyle and venous blood, and the whole com- pound fluid is converted by respiration into arterial blood. Like the chyle, too, the lymph bears a strong analogy to the blood in its composition and properties. These two fluids will be more particularly described hereafter. II. The fluids formed out of the blood will be described under the head of the secretions. III. The blood is the most important of the animal fluids. This name is given to the scarlet or purple fluid, contained in the arteries and veins, and the cavities of the heart. It is apparently homogeneous, but is in fact a fluid of a very compound nature, consisting of various ingredients, possessed of peculiar chemical and physical properties. It has a specific gravity somewhat greater than that of water, viz. from 1.053 to 1.126, according to Berzelius, a saline taste, and a faint animal odour. The colour of the blood, when flowing from a vein, is influenced by circumstances. If the arm has been long compressed by the bandage, it is darker than under other circumstances. The same is the case in persons afflicted with asthma or dyspnoea. In in- flammatory and rheumatic affections, and in pulmonary consump- tion, it is of a brighter red. As it exists in the blood-vessels, the blood is composed of numerous red particles, of a lenticular form, swimming in a colourless fluid, or of a solid and a liquid part. The latter has been called the liquor sanguinis. The former, to which the blood is indebted for its colour, has received the name of the red globules. The liquor sanguinis is, also, as will be presently seen, a complex substance. When kept at rest this fluid coagulates, forming a gelatinous mass of the same volume as when it was liquid, and which receives the shape of the containing vessel. Shortly after, the solid mass contracts in volume, forcing out of its surface and sides a yellowish liquid, which is the serum of the blood. In certain diseases, as rheumatic and inflammatory affec- tions, the liquor sanguinis coagulates very slowly, giving time for the red globules, which have a greater specific gravity, in some measure to subside. The stratum of nearly colourless fluid which floats above, is the pure liquor sanguinis, cleared of the colouring principle, and may be removed and examined by itself. So when the entire blood drawn from a healthy person is suf- fered to rest, in a short time it loses its fluidity, concretes into a 62 FIRST LINES OF PHYSIOLOGY. solid mass, and soon afterwards begins to separate into two dis- tinct portions. A yellowish transparent fluid oozes out of the coagulated mass, and, when the process is completed, is found to constitute two-thirds or three-fourths of the whole. The coagu- lated part, which is of a red or dark brown colour, is called the crassamentum or cruor of the blood, and the fluid part the serum. The coagulum or cruor, also, is found to consist of two parts; for, by ablution with water, it may be deprived of its red colour, a fact which proves that this colour depends on the presence of a separate principle. When thus separated from the two other con- stituent principles of the blood, viz. the serum and the colouring matter, the coagulum appears as a soft solid, of a whitish colour, insipid and inodorous, and of a greater specific gravity than wa- ter ; and it sometimes presents a fibrous appearance, a circumstance from which it has received the name of fibrin. The colouring matter consists of minute disks of a red colour, soluble in wa- ter, and which are visible in the blood when viewed through a microscope. Besides the constituent principles of the blood, already men- tioned, this fluid contains a volatile matter, which is peculiar in every species of animal. This halitus, according to Berzelius, is a proximate element dissolved in serum. It is stronger and more abundant in men than in women and children; but in eunuchs, and in persons affected with tabes dorsalis, it is said to be absent. At the moment of its coagulation, small bubbles of gas escape from the blood, which force a passage through the coagulum on their way to the surface. The serum is a transparent liquid, of a light yellowish colour, of a saline taste, and of the odour of blood. It owes its taste to the presence of earthy and alkaline salts, which it holds in solu- tion. Besides these salts, it contains a free alkali, as is evident from its changing vegetable blue colours to a green. But the property by which it is peculiarly distinguished, is that of be- coming solid by exposure to heat. The temperature necessary to produce this effect, must be as high as 160° F. At this tempera- ture, serum becomes a white, opaque solid, of a firm consistence, resembling the coagulated white of an egg. This property of be- coming solid by exposure to heat, the serum owes to the presence of albumen ; and a curious experiment of Magendie may serve to illustrate the affinity of the albumen of eggs with the serum of the blood. He injected the whites of five eggs, diluted with five times their volume of water, into the veins of a dog. The solu- tion was somewhat viscid, yet the animal suffered no inconveni- ence from the experiment, and his blood, on examination, pre- sented the usual characters of healthy blood. But a drachm of a very viscid solution of the same substance, injected into the carotid artery of the same animal, occasioned death in a few minutes. FLUIDS OF THE SYSTEM. 63 Serum preserves its property of coagulating, even when diluted with a large quantity of water. Several other agents besides heat are capable of coagulating serum, as the mineral acids, alcohol, and some of the metallic salts. The action of the galvanic pile, also, coagulates it, and at the same time develops in it globules, which have a strong analogy to those of the blood. The coagu- lation of serum has been differently accounted for. By some chemists, it has been referred to the abstraction of its free alkali. Serum is a compound of albumen and soda, the latter of which is supposed to maintain the albumen in a liquid state. All agents, therefore, which are capable of abstracting the soda from the albu- men, it is supposed, may indirectly cause it to coagulate, by re- moving the force which overcame its cohesive attraction. If we suppose the albumen to be kept in solution by means of the soda, it will be easy to understand why acids and alcohol coagulate serum. The action of heat is a little different. On the applica- tion of heat, the equilibrium of affinities, by which these elements are held together, is deranged; and the soda, which before was in a state of chemical combination with the albumen, is transferred to the water, while the albumen is left to assume a solid form. The natural colour of the serum is liable to be changed by the presence of accidental substances. In jaundice it is of a deep yel- low colour, which is derived from an impregnation with bile. It also acquires a yellow colour in persons who have been taking rhubarb. In blood drawn from a person who has recently eaten a hearty meal, the serum has been found to exhibit the colour of turbid whey, owing, it is supposed, to the presence of chyle. In some cases it has been observed of a white colour, like cream, and sometimes has been found to contain globules. This appear- ance has been observed in the blood of persons whose digestive organs were disordered, and who had been subject to sickness, vomiting, and bad appetite. In young unweaned animals, as sucking puppies and kittens, the serum of the blood has some- times been observed to be milk-white. Even white blood has also been seen to flow from the vessels of unweaned puppies. The blood of a goose was observed to be white by Ledel and Gendrin ; Christison and others have witnessed the same fact; and Raspail mentions a phial of blood, which had the appearance of milk marbled with chocolate. This phenomenon he ascribes to the development of an acid in the blood, (which in its ordinary state is alkaline,) causing a partial coagulation of the albumen in grumes, which, enveloping the colouring matter, clarifies the re- maining liquid albumen, marbling it of a chocolate colour. The acid state of the blood in these cases, is proved by dropping a little upon the carbonate of lime, when it effervesces, and assumes a chocolate colour. The persons whose blood presents this ap- pearance, Raspail observes are subject to vertigo. Alcohol, it seems, has in some instances produced the same effects, which 64 FIRST LINES OF PHYSIOLOGY. Raspail ascribes to its developing acetic acid in the blood, by its action on the albumen. Sometimes the white colour depends unequivocally on the presence of milk in the blood, as in the case of a man who had drunk a large quantity of this fluid before losing blood. Here chemical examination detected the presence of perfect milk in the blood drawn. The same appearance has sometimes been owing to the pre- sence of fat in the blood. In very fat persons, so much of this substance has sometimes been found in the blood as to form a crust on its surface, and even to admit of being removed by a tea- spoon.* Alcohol, as before mentioned, coagulates albumen ; and Ma- gendie says, that if an animal be made to swallow a large dose of alcohol, solidified albumen is found in his vessels after death. But it is a curious and important fact, connected with this sub- ject, that alcohol may exist largely in the blood of living animals, without producing coagulation of the albumen ; thus, the blood drawn from a man who had been drinking a large quantity of spirits, took fire on applying the flame of a lamp to it, and con- tinued to burn several minutes. Berzelius and Marcet have each analyzed the serum of the blood, with the following results : Berzelius. Marcet. Water,........ 905.0 Water,........900.00 Albumen,....... 80.0 Albumen,....... 86.80 Lactate and impure phos- } . „ Extractive matter, .... 4.00 phaleofsoda, 5 " Hydrochlorate of potash and > Ilydrochlorate of potash and) fi „ soda, } b,b0 soda> ) Subcarbonate of soda, . . . 1.65 Impure soda,..... 4.0 Sulphate of potash, . . . 0.35 Loss,........ 1.0 Earthy phosphate, .... 0.60 1000.0 1000.00 A more recent analysis of serum by Le Canu, does not differ materially from the two former, except in the discovery of two new principles in this fluid ; one a fatty, crystallizable matter • the other an oily substance. The coagulum or cruor of the blood, is composed essentially of fibrin and colouring matter. When freed from the colouring matter, fibrin is a soft solid, of a whitish colour, without smell or taste, insoluble in water, not affecting the blue vegetable colours and containing about four-fifths of its weight of water. Exposed to the air, it becomes dry, semi-transparent and brittle ; and if in this state it be plunged into water, it gradually absorbs as much as it has before lost by desiccation, and resumes its former pro- perties. By distillation, it furnishes a large quantity of carbonate * Thackrah and Adams. FLUIDS OF THE SYSTEM. 65 of ammonia, and a voluminous charcoal, which is very difficult to incinerate, and which leaves a residue containing a good deal of phosphate of lime, a little phosphate of magnesia, carbonate of lime, and carbonate of soda. One hundred parts of fibrin are composed of Carbon,.............53.360 Oxygen..............19.685 Hydrogen,.....•......7.021 Azote,.............19.934 Fibrin is the basis of muscular flesh. It possesses the power of spontaneous coagulation, and the blood owes its property of coagulating to the presence of this principle. Fibrin is considered by some chemists as a mere modification of albumen. According to Denis, it is albumen combined with different salts ; but Ma- gendie remarks, that an essential difference between albumen and fibrin consists in this : that a variety of substances solidify the form- er, whereas few possess the property of liquifying it, and that pre- cisely the contrary is the fact in the case of fibrin. Thus, nitrate of copper coagulates albumen, but prevents the coagulation of fibrin. Fibrin is the basis of muscular flesh, but, according to Magendie, the fibrin of the blood differs from that of the muscles in being but slightly nutritive : whereas the latter is highly so. Magendie asserts, that the blood owes its power of passing through the capillary system to the presence of fibrin, which renders it coagulable. Hence the coagulability of this element of the blood is necessary to the support of life. If any substance possessing the property of destroying the coagulability of the fibrin be injected into the veins, the blood will no longer be able to traverse the capillary vessels, but will become obstructed, either in the pulmonary capillaries, or in some others of still greater tenuity, producing local engorgements and extravasation in the tissues, and, in short, all the consequences of capillary stagnation. A similar condition of the blood is a consequence of many fatal epidemics ; it exists in asphyxia from carbonic acid, and is pro- duced by the action of the hydrocyanic acid, and of some other poisons. The same physiologist expresses the singular opinion, that the fibrin is suspended in the serum in the form of minute vascular arborizations, forming the first degree or incipient state of organization. The coagulation of the fibrin he considers as a higher degree of organization, and the clot of blood as an arborescent mass, form- ing a kind of delicately organized parenchyma, differing essentially from the albumen, the coagulation of which is the result of phy- sical or chemical agency. The same property of fibrin is exem- plified in the coagulum which obliterates the cavities of divided blood-vessels, in the formation of adhesions and false membranes, in all of which fibrin exists in an organized state. The cicatriza- 9 66 FIRST LINES OF PHYSIOLOGY. tion of wounds is effected by the same element of the blood, and hence, when there is a deficiency of it in the vital fluid, wounds assume an unfavourable character, and refuse to heal. The well known influence of pure air and generous diet in promoting the healing of wounds and ulcers in such circumstances, is ascribed by Magendie to the power which these agents exert in increasing the fibrin or organizable element of the blood. The disposition to hemorrhage, and the difficulty of checking it, is probably to be ascribed in many cases to a deficiency of fibrin in the vital fluid. According to Meyer, the fibrin possesses a peculiar power of crystallizing. Under favourable circumstances, the red mass or crassamentum crystallizes in conical needles. It is a remarkable fact, that in inflammation the proportion of fibrin in the blood is invariably increased ; and acute rheuma- tism is the form of inflammation in which this increase is the greatest. The remaining constituent of the blood is the red globules. When examined by the microscope, the blood presents the ap- pearance of a fluid holding in suspension minute particles of a spheroidal or lenticular figure. According to some observers, these consist of a solid nucleus or central part, surrounded by a vesicle, which contains a fluid. It appears that the blood of all animals contains globules. These differ in shape and size in the different species of animals. In the human species and the mam- malia, in some of the fishes, in many of the mollusca, and in insects, they are round; in birds, in the amphibia, and in many of the fishes, they are of an elliptical shape. In the human blood the diameter of the globules is variously estimated by different observers; the estimates varying from one seventeen-hundredth to one six-thousandth part of an inch. Perhaps their diameter may be assumed at about one four-thousandth of an inch. The latest microscopical observations on the globules of the human blood, represent them as circular, flattened bodies, having a depression in the centre; consisting of a central nucleus with an external envelop of a red colour. Raspail considers the globules as composed of albumen, which has been dissolved in the serum of the blood by the aid of some menstruum, and is afterwards precipitated from it by its neutral- ization, or by evaporation. To illustrate their formation, he states that if a certain quantity of the white of eggs be put into an excess of concentrated hydrochloric acid, the albumen will at first coagulate and become white, but will afterwards dissolve in the acid, and assume a violet colour, which subsequently changes to a blue. If the acid be then decanted, or suffered to evaporate, a white powder will be precipitated, which, when viewed through a microscope, presents the appearance of very small spherical particles, of the same size with the globules of the blood and which might easily be confounded with them. The number of FLUIDS OF THE SYSTEM. 67 the globules, he observes, will vary according to the quantity of the menstruum which evaporates in a given time, and many other circumstances. The appearance of the central nucleus in each globule, he con- siders as, in most cases, the effect of an optical illusion; but that which is observed in the blood of frogs, he supposes to be owing to the successive solution of the different layers of the albuminous globule in the water in which they are diffused in making the experiment. As the external layers of the albuminous globule are the first to imbibe the water, they acquire a less refractive power than the central layers, which hence present a more opaque appearance than the external. When the most external layer is wholly dissolved, the next undergoes the same change, and so on till the globule is entirely dissolved and disappears. Magendie, also, denies the existence of the central nucleus in the globules of human blood, though he admits of their presence in the globules of the blood of fishes and reptiles. If you take, he observes, some of the blood of one of these orders of animals, and examine the globules it contains Avith a microscope, you will distinctly perceive a swelling in the centre; afterwards dissolve the globules and examine the solution, and no globules will be visible, but only the minute bodies which formed their nuclei, for these are insoluble in water. But water completely dissolves the globules of human blood ; no vestige of them remains. The chemical relations of the globules, according to Raspail, are identical with those of albumen. They are soluble in water, in ammonia, in the acetic and concentrated hydrochloric acids ; and are coagulable by other acids, by heat, and by alcohol. Arterial blood contains a greater number of globules than venous. The blood of birds also contains more than that of any other class of animals. The mammalia in this respect stand next to birds ; and the blood of carnivorous animals appears to possess a greater number of globules than that of the herbivorous. In general, the quantity bears a certain relation to the degree of heat possessed by animals ; the cold-blooded animals being those whose blood contains the smallest proportion. According to Treviranus and some other physiologists, the globules of the blood possess the faculty of spontaneous motion. Haller says that the red globules possess three kinds of motion ; viz. 1. Backwards and forwards in the vessels. 2. Towards wounded parts. 3. Towards large masses of red globules. Tre- viranus, with the assistance of a microscope, observed two kinds of motion in the blood while flowing from the veins of a living animal. One consisted in a whirling or rotatory motion of the globules, while the other manifested itself by a kind of tremulous contraction of the whole coagulum. According to Copland, Pro- fessor Schultz of Berlin has more recently confirmed the fact respecting the intestine motion of the globules, which, as he 68 FIRST LINES OF PHYSIOLOGY. asserts, move on spontaneously, keeping at a distance from one another, and surrounded by envelops of colouring matter. 1 his power of the globules Copland attributes to the influence exerted by the ganglial nerves, which are plentifully distributed on the coats of the vessels. Another force which Copland supposes to act upon them and to influence their motions, is the attraction exerted by the different tissues with which they are brought into contact while circulating in the capillary vessels. The former of these forces keeps the globules in a state of constant motion and repulsion ; the latter tends to bring them to a state of repose, and is exerted in the organic structures themselves, where the globules of the blood come into contact Avith them. These tAvo forces acting upon the globules, are also noticed by Andral, who remarks, that the blood when examined in the paren- chyma of the organs by the aid of a microscope, has been com- pared to a kind of vortex, from which molecules are constantly seen detaching themselves. These unite Avith and are lost in the solid tissues, while others are at the same time separating them- selves from the solids and passing into the torrent of the blood. These motions of the red globules have been observed by several other physiologists, and of their existence there can be no doubt: but Avhether they are of a vital or mechanical kind, is a question on which there is much difference of opinion. Raspail regards them as the effects of currents in the serum, effects which, he says, may be imitated by suffering Avater, holding minute globules of the farina of potatoes, to Aoav through a fine tube, when, he observes, an innumerable multitude of limpid monads will be seen performing in all directions the most surprising evolutions. Magendie ridicules the idea of spontaneous motion in the red globules as a chimera. Another extraordinary kind of motion in the globules of the blood, has been observed several days after it has been drawn from the veins. These motions are rendered more conspicuous, by diluting the serum in Avhich the globules float with a little water. The globules are then observed to move about in all directions, sometimes appearing to coalesce, then separating, and passing over and by the side of each other ; in short, constantly altering their shape, position, and appearance. It is remarkable that these motions are not visible until a few days after the blood is draAvn ; a fact, which seems to be wholly irreconcilable with the idea of their being of a vital character. Yet Messrs. Emerson and Reader, Avho witnessed and have accu- rately described these motions, ascribe them to a peculiar living action of the globules themselves. A curious discovery of Ma- gendie seems to have ascertained their real nature. The French physiologist remarks, that Avhen the globules are left to them- selves for twenty-four or thirty-six hours, they assume a puckered look, and a multitude of monads or vibrions make their appear- FLUIDS OF THE SYSTEM. 69 ance in the serum and on the globules of the blood, moving on their surface, penetrating into their substance, and issuing from it by the edges. These globules gradually diminish in size, and at length disappear, as if devoured by the infusoria. These ani- malcula give rise to evident motions in the red globules, and were undoubtedly the cause of the motions observed by Emerson and Reader. When some fresh globules, extracted from neAvly drawn blood, were put into serum containing great numbers of infusoria, Magendie observes that the latter pounced on them with a sort of fury, and totally destroyed them in a very short time. Magendie also noticed another curious fact connected with this subject. In some blood mixed with sulphuretted hydrogen, he observed globules affected with a variety of extraordinary motions, oscilla- ting in various directions with great rapidity, describing curved, straight, or irregular lines, just like the microscopic monad. The cause of these motions he does not attempt to explain. According to Poli, the red globules are affected with a kind of turgescence, which is greater or less according to the vigorous or enfeebled state of the animal, and of course must be of a vital character. The red globules are the heaviest constituent part of the blood • a quality for which they are probably indebted to the presence of iron. An excess of them in the blood indicates an inflammatory or febrile diathesis. Their use is unknown, though it should seem that they are the most highly elaborated part of the vital fluid, for of all the elements of the blood, they are reproduced with the greatest difficulty. Hence the pale and exsangueous appearance, which is sometimes permanent, of persons who have experienced profuse or repeated losses of blood. Besides the red globules there exists also in the blood, as one of its normal constituents, a considerable quantity of large white or colourless globules of a flattened or lenticular form, which adhere to the glass on which they are laid, while the coloured glob- ules float about and oscillate in various directions. They are not affected by water, acetic acid, or ammonia, which dissolve the red globules. According to Burdach, there is another kind of minute globules visible in the blood under the microscope. They present the appearance of a colourless, transparent, central part, of a vitreous look, surrounded by a dark red or blackish circumference, looking like a perforated disc, or like an iris with a light-coloured back- ground behind the pupil. Sometimes they appear like minute glass spheres with dark rings around them. Their form is gene- rally globular, but sometimes elliptical. Burdach regards them as air vesicles arising from the destruction of the red globules by water. In perfectly fresh blood he remarks they are gene- rally wanting. 70 FIRST LINES OF PHYSIOLOGY. The colouring matter of the blood, sometimes called hematostnc, is supposed by some to reside in the envelop of the red globules. By Brande it is considered as a peculiar animal principle, capable of combining with metallic oxides. He formed compounds of this colouring matter with oxide of tin. But the best precipitants of it are the nitrate of silver, and corrosive sublimate. Woollen cloths impregnated Avith either of these metallic salts, and dipped in an aqueous solution of the colouring matter of the blood, be- came permanently dyed. Berzelius and Engelhart attribute the colour of the blood to the presence of iron, in some unknown state of combination. The existence of a large quantity of iron in the blood is Avell established ; yet neither the gallic acid, the infusion of nutgalls, nor the prussiate nor hydrocyanate of potash, produces in this fluid any precipitate, nor any change of colour, from which the presence of iron might be inferred. Hence Berzelius concluded that iron exists in the blood only in a metallic state. But the fact seems to be established by Rose and Raspail, that organic coagulable fluids are capable of AvithdraAving a metallic substance from the most powerful action of a reagent. Thus, a mixture of oil and the salts of iron, presents no signs of the presence of the metal, until several days after the mixture has been placed in the ferro-prussiate of potash, sharpened Avith an acid. Rose obtained the same result by mixing albumen or gelatin with the peroxide of iron. The colouring matter is soluble in water. Soluble hematosine when perfectly dry is black, with a lustre like that of jet. In thin laminae or in powder, it is of a red colour, and destitute both of smell and taste. With cold water, in which it readily dissolves, it forms a red liquor, which may be kept without change for months. When dried and exposed to heat in contact with the air, it melts, sAvells up, and burns with a flame, leaving a coal of very difficult incineration. This coal burns Avith a disengagement of ammoniacal gas, and leaves the one-hundredth part of its weight of ashes, composed of Oxide of iron,..........55.0 Phosphate of lime and a trace ) „,k of phosphate of magnesia, y ' * * Lime,.............17.5 Carbonic acid,..........19.0 The colouring principle of the blood is supposed to be derived from respiration, because the globules of chyle and lymph, which are converted into blood by respiration, are destitute of it. The analysis of the integral blood, according to Le Canu, pre- sents the following results: FLUIDS OF THE SYSTEM. 71 Water,.............780.145 Fibrin,............. 2.100 Albumen,............65 090 Colouring matter, . . ■......133.000 Crystallizable fatty matter,...... 2.430 Oily matter,........... 1 310 Extractive matter soluble in alcohol and water, 1.790 Albumen combined with soda,..... 1265 Chlorides of sodium and potassium, alkaline 7 r, o-rn phosphates, sulphates and sub-carbonates, $ Sub-carbonate of lime and magnesia, phos- "} phates of lime, magnesia and iron, per- > 2.100 oxide of iron, } Loss, .............2.400 1000.00 The coagulation of the blood has been attributed to various causes, as e. g. its cooling on being drawn from the vessels, the contact of the air, rest, &c. None of these causes, however, is sufficient to produce this effect. Hewson froze fresh blood by exposing it to a Ioav temperature, and aftenvards thaAved it. It first resumed its fluidity, but aftenvards coagulated in the usual manner. But Magendie found that blood exposed to a tempera- ture of 14° Reaumur, coagulated into a very firm clot before con- gelation took place, but on raising its temperature it did not regain its fluidity. It has also been ascertained by experiment, that blood Avill coagulate Avhen deprived of the contact of the air, and subjected to agitation. In the exhausted receiver of an air-pump its coagulation is even accelerated. But if a bottle be completely filled with blood, recently drawn, and the mouth then accurately closed with a tight stopper, coagulation is retarded. Coagulation is influenced by the rapidity Avith which the blood Aoavs from the body. According to Scudamore, blood slowly draAvn from a vein coagulates more rapidly than Avhen taken in a full stream. He also found that coagulation is hastened by heat, and retarded by cold. The action of oxygen upon the blood promotes coagulation, Avhile that of carbonic acid retards, Avithout preventing it. The division of the 8th pair, according to Magendie, deprives the blood of its power of coagulating. Certain saline substances, as, a solution of common salt, muriate of ammonia, nitre, or a solution of potash, prevent a coagulation of the blood ; while alum, and the sulphates of zinc and of copper, promote it. Electricity, according to Scudamore, does not pre- vent coagulation. Blood, subjected to electric shocks, was found to coagulate as quickly as that which was not electrified; and the blood was always found coagulated in the veins, in animals killed by poAverful galvanic shocks. Scudamore considers coagulation as connected with the disen- gagement of carbonic acid, which is most active at the commence- ment of coagulation, and ceases when this process is completed. Hence, whatever retards the extrication of carbonic acid, obstructs coagulation. The blood coagulates more rapidly in proportion as 786.590 3.565 69 415 119.626 4 300 2.270 1.920 2.010 7.304 1.414 2 586 1000.00 72 FIRST LINES OF PHYSIOLOGY. it is heavier and richer in coagulable matter, as in strong healthy persons. A firm texture of the coagulum indicates great vascular activity. During the coagulation of the blood, the temperature of the mass is said to rise. Dr. Gordon estimated the rise of the ther- mometer at six degrees. Dr. Davy, hoAvever, regards the increase of temperature from this cause as very trifling. Raspail accounts for the coagulation of the blood, by referring it to the neutralization or evaporation of some menstruum, which maintained the albumen in a liquid state. This menstruum he supposes to be soda and ammonia. On this principle, he observes, the spontaneous coagulation of the blood presents no insuperable difficulty. For, the carbonic acid of the atmosphere, and the car- bonic acid Avhich is formed in the blood itself by the absorption of oxygen, combines with and saturates the menstruum of the al- bumen, Avhich is consequently precipitated in the form of a coag- ulum. The evaporation of the ammonia, Avhich is another men- struum of the albumen, and that of a part of the Avater of the blood, liberates another portion of dissolved albumen, and increases the quantity of the coagulum. Raspail, on the same principle, accounts for the precipitation of the albumen in the form of the globules of the blood, which he con- siders as identical Avith albumen. The absorption of the aqueous part of the blood by the tissues nourished by it, and perhaps the saturation of the alkaline menstruum of the albumen by the resi- due of nutrition constantly passing into the blood from the same tissues, occasion a regular precipitation of albumen in the blood, in the form of small globules. Raspail then regards the blood as analogous to vegetable fluids, and containing essentially the same principles, viz. albumen, wa- ter, and various saline substances, with a colouring principle. The albumen exists in two states, viz.. in solution, in which it is held by an alkaline menstruum, but coagulable by the saturation of the menstruum, and secondly, in the form of globules.* The coagulation of the blood, however, is regarded by the most enlightened physiologists, as a vital phenomenon, and as not de- pending on any physical cause. " The blood is supposed-"either to be endoAved with a principle of vitality, or to receive from the liv- ing parts, with which it is in contact, a certain vital impression, * The following table exhibits his views of the composition of the blood : BLOOD. 1. Globular albumen. 2. Albumen in solution, but coagulable by the saturation of the menstruum 3. Oil in small quantity. "u«i. 4. Hydrochlorates, acetates, and phosphates of ammonia, soda, potash limp m,ffnP sia, and iron. r ' ll,uc> '"««gue COLOURING MATTER. 5. Iron and potash combined with albumen, which holds it in solution. FLUIDS OF THE SYSTEM. 73 which, together with constant motion, counteracts its tendency to coagulate." Copland ascribes the coagulation of the blood principally to the agency of the red globules, resulting chiefly from the loss of the vital motion which these globules possess in the vessels, and that of the attraction existing betAveen the colouring envelops and the central globules contained in them. This attraction ceases soon after the blood is removed from the veins ; and the central bodies, freed from the coloured envelops, are left to obey the attraction, which tends to unite them; in uniting, they form a network, in the meshes of Avhich the colouring matter is entangled; and thus the phenomena of coagulation are produced. The blood exhibits a pulsating motion in the incubated egg before the formation of the heart, so that it possesses a power of motion in this initial stage of foetal life Avholly independent of the heart, and perhaps derived from its own inherent nature. Indeed, some time after the heart is formed out of the blood, it appears pale and bloodless, nor does it pulsate or move like the rest of the body of the embryo. The speck of blood which is thus discern- ed four or five days after incubation, is so minute that it disap- pears during its contraction, and is only visible during its expan- sion, when it appears of the size of the point of a needle, and of a red colour. According to Burdach, the blood also possesses a great power of expansion, as is evinced by several facts. This expansive power is connected Avith its vitality; for after death the whole mass of the blood appears to occupy much less space than during life. For example, in the dead body the arteries are empty, the heart and capillaries contain but little blood, and the veins less than in the living state ; and the great, venous trunks, into Avhich the blood appears to be chiefly collected, are by no means much dis- tended. Noav during life the Avhole vascular system is full of blood, a fact from Avhich, when compared Avith the preceding one, it seems to folloAV that the blood is more expanded, and occupies more space in its living state, than after death. The folloAving experiment by Rosa appears to confirm this conclusion. He tied up an artery in a living animal when filled with blood. He after- wards cut out the enclosed part, and found that Avhen it was cold, it shrunk to one-third of its former diameter, so that the volume of the dead compared with that of the living blood, was in the ratio of one to nine. So in the living state, the volume of the blood, he says, appears to observe the same ratio with that of the activity of the living poAver. Bellengeri made some interesting experiments on the electricity of the blood, of which some of the results are the folloAving, viz. In the phlegmasia?, the electricity of the blood is evidently diminished, but increases again as the disease abates. In chronic 10 74 FIRST LINES OF PHYSIOLOGY. diseases the opposite condition obtains. In many cases of intense inflammation the electricity is negative. When the blood forms the inflammatory crust, its electricity is less than in its healthy state. When the blood shoAvs a higher degree of electricity than m its normal state, the buffy coat never forms on it. At the commence- ment of venesection the blood is darker, thicker, less fluid, and less electrical than at the end of the process. The blood furnishes the elements of nutrition to all the tissues and organs of the body ; and recent analyses of this fluid have ascertained in it the presence of many of the peculiar forms of animal matter of Avhich the organs are composed. Vauquelin discovered in the blood a considerable quantity of a fatty sub- stance, which was at first supposed to be fat, but which was after- wards ascertained by Chevreul to be the peculiar substance of the brain and nerves. It differs from fat, and all other substances of the same nature, in containing azote. Prevost and Dumas demonstrated the existence of urea, a pecu- liar animal matter found in the urine, in the blood of animals whose kidneys had been extirpated. Cholesterine, and some of the other elements of the bile, have been discovered in the serum of the blood. The fibrin which exists in this fluid is identical with the muscular fibre ; its albumen is the basis of a great num- ber of membranes and tissues : the fatty substance, before men- tioned, combined with albumen and ozmazome, forms the nervous system; and the phosphates of lime and magnesia, which exist in the blood, constitute a great portion of the substance of the bones. CHAPTER X. CHEMICAL ANALYSIS OF THE ORGANIZATION. It has already been observed, that organized matter consists of two classes of elements, viz. one chemical, the other organic. The chemical, are the ultimate elements into which organized substances may be reduced by destructive analysis ; as, oxygen, hydrogen, carbon, azote, &c. The organic are the proximate elements, which are formed out of the ultimate, not by the chemi- cal powers of matter, but by the operation of the organic forces. These are albumen, fibrin, gelatin, ozmazome, &c. All animal matter may be analyzed proximately into these elements. The chemical forces tend to destroy these forms of matter, and to re- duce them to the ultimate elements. CHEMICAL ANALYSIS OF THE ORGANIZATION. 75 The Ultimate Elements. The ultimate ponderable elements of animal matter may be divided into non-metallic and metallic substances. I. The non-metallic elements are oxygen, hydrogen, carbon, azote, phosphorus, sulphur, chlorine, and fluorine. (Berthold.) II. The metallic elements are, 1. The bases of the alkalies, viz., potassium, or kalium, sodium, and calcium. 2. The metallic bases of some of the earths, viz. magnesium, silicium, and alumi- num. 3. The ponderous metals, iron, manganese, and copper. Of these, the four first of the non-metallic elements, viz. oxygen, hydrogen, carbon, and azote, exist in vastly the greatest propor- tion, and perhaps may be considered, as the only essential elements of animal matter. Oxygen enters very largely into the composition of animal mat- ter. It is a constituent part of all the fluids and solids of the body. It is an essential element of all the proximate elements, for these may all be divided into organic oxides and acids. In combination with hydrogen, it forms the Avatery basis of all the fluids, which constitute, as it has been computed, nine-tenths of the weight of the body. In union Avith carbon it forms carbonic acid, which exists in the blood, and is exhaled abundantly from the lungs in respiration, and from the skin. With phosphorus it forms the phosphoric acid, Avhich exists largely in the bones in combination with lime, and is one of the constituents of healthy urine. With the metalloids it forms potash, soda, and lime. It also enters into the composition of the organic elements, as albumen, fibrin, gela- tin, and mucus. The oxygen which exists in the body, is derived partly from the food and drink, and partly from respiration. It is eliminated from the system by all the excretions, particularly by sweat, urine, and respiration. It is remarkable, that in certain fishes, the air contained in the swimming vesicle, is pure oxygen gas. This is the case with the fishes, which live near the bottom of the Avater, and SAvim near the ground. Hydrogen is another principle Avhich exists in all the fluids, and several of the solids of the body. It constitutes one element of the watery basis of the fluids. It predominates in venous blood, as oxygen does in arterial. It exists largely in the bile; is one of the elements of fat and oil ; and is often developed in a gaseous form in the intestinal canal, in enfeebled states of digestion. Com- bined with chlorine, it forms the hydrochloric acid, Avhich exists in many of the animal fluids, in combination with soda. Hydro- gen is introduced into the system by the aliments, and is elimina- ted by cutaneous and pulmonary exhalations, by the excretions of the kidneys, alimentary canal, and liver. In the process of putre- factive decomposition, it combines Avith sulphur, and sometimes with phosphorus, forming, with them, two fetid gases, the sulphu- retted and phosphuretted hydrogen. 76 FIRST LINES OF PHYSIOLOGY. Carbon. This element abounds in the vegetable kingdom, but is also to be found largely in animal substances. It is one of the elements of animal oil or fat, and of the quaternary animal oxides, albumen, fibrin, gelatin, and mucus. It exists largely in the bile, and in venous blood. Most animal substances by combustion de- velop a considerable quantity of carbon. It is received by the aliments, and is eliminated by respiration, by cutaneous transpira- tion, and by the secretion of the liver. It is constantly developed by the processes of life, accumulates in the venous blood, and is discharged from it principally by respiration. Azote. This principle exists largely in animal matter, and is regarded as one of its principal chemical characteristics. It is true, however, that a feAv plants contain it, particularly the mushroom tribe. It abounds also in the pollen of plants, and in the vegeta- ble principle, gluten, and is one of the elements of the vegetable alkaloids, quinine, strychnine, &c. But it exists almost universally in animal substances, and may be regarded as one of the essential elements. All the organic elements of animal matter contain azote; but it exists most abundantly in fibrin, and, consequently, in the muscular flesh, which is formed principally of this element. The substance of the brain and nerves contains a less proportion of azote. The peculiar smell of burning animal matter is owing chiefly to the presence of this principle. In the putrefaction of animal substances, the azote, disengaging itself from the other elements, combines with the hydrogen, forming a binary compound, ammonia, which is one of the characteristic results of animal de- composition. Azote is received into the system chiefly with the food, partic- ularly with that which is derived from the animal kingdom, and from the leguminous plants, and the seeds of the cerealia. It is also believed to be introduced into the blood by respiration, in which, it appears to be ascertained, there is an absorption of azote. Its discharge from the system is effected principally by the secre- tion of the kidneys, as it exists largely in healthy urine ; but partly by respiration, in which there appears to be an exhalation, as well as absorption, of azote. It always exists in combination with other elements in the animal system, except in the vesicle of certain fishes which swim near the surface of the water, in which it is found in a pure state. Of these four essential elements of animal matter, three, when in an uncombined state, are aeriform bodies ; and the effort which they make, as they exist in animal substances, to abandon the solid form, and resume their natural state as gases, an effort which is increased by the external heat to which animal substances are exposed, and by their own organic heat when in a living state, promotes the tendency to decomposition of animal matter. Phosphorus. This principle exists both in animal and vegeta- ble substances, but more abundantly in the former. It is present CHEMICAL ANALYSIS OF THE ORGANIZATION. 77 in the blood and the brain, and, indeed, in nearly all parts of animal bodies, but is contained in the greatest proportion in the bones, combined with oxygen, Avith Avhich it forms phosphoric acid. It ahvays exists-in combination, generally in the state of phosphoric acid. It is evacuated chiefly by urine, which contains a consider- able quantity of phosphoric acid, some of it free, and some in combination with bases. During animal decomposition, a part of the phosphorus combines with hydrogen, forming the fetid gas, phosphuretted hydrogen. The phosphorescence of putrefying an- imal matter, is supposed to be oAving to some inflammable com- pound of this kind. The extraordinary phenomenon of the spon- taneous combustion of the human body, has been attributed by Treviranus, to an accumulation of phosphorus in the system, OAving to some obstacle to its regular excretion by the kidneys and other outlets. The body, it is supposed, may at length become so highly charged Avith it, as to be rendered extremely combustible. Sulphur. This is another principle of animal substances which ahvays exists in combination Avith other elements, as soda and potash. It exists particularly in albumen, and in the hair and nails, and also in muscular flesh. It is extricated in the intestines in combination Avith hydrogen, and then discharged from the system. It also, sometimes, passes off by cutaneous transpiration. The fetor of foul ulcers is occasioned partly by an evolution of sulphuretted hydrogen ; and the same gas is supposed by some to be the vehicle of infection in the hospital gangrene. Chlorine exists in most of the animal fluids in combination with hydrogen, forming the hydrochloric acid. This is present in a free state in the gastric fluid, and in combination Avith soda and potash in the blood and bile. It exists, also, in the urine, in the sweat, milk, saliva, synovial fluid, &c. Kalium or Potassium exists very sparingly in the system, and always in combination with oxygen, i. e. in the state of potash. Combined with muriatic acid, potash is present in the blood, and several of the secreted fluids, as the bile, urine, sweat, milk, &c. In combination with the phosphoric acid, it exists in the brain. It is much more abundant in plants than animals. Sodium. This metalloid, in combination Avith oxygen, is much more abundant in animal substances than kalium. As soda, it exists in the blood, mucus, saliva, bile, muscular flesh, bones, milk, and other animal substances, in combination with the car- bonic, phosphoric, sulphuric, muriatic, and lactic acids. It is more common in animals than in plants. Calcium, in the form of lime, exists largely in the bones, and sparingly in the muscles and brain. It is generally combined with the phosphoric acid, as in the bones, but sometimes with the carbonic acid, forming the phosphate and carbonate of lime. Silicium is found, though very sparingly, in some kinds of ani- mal matter. It exists as silex in the human hair, and in the urine. 78 FIRST LINES OF PHYSIOLOGY. Magnesium exists in animal and vegetable substances, espe- cially in bones, and in some animal fluids. In combination with phosphoric acid it is found in the blood, in the substance of the brain, and in human milk. Iron. This metal is pretty extensively diffused in animal bodies; especially in the blood of red-blooded animals, and in the pigmentum nigrum. In what state it exists in the blood is not known. It is supposed by some physiologists, in some indeter- minate state of combination, to form the colouring principle of the red globules of the blood. The Organic or Proximate Elements. The proximate principles of animal matter are formed by various combinations of the ultimate elements, by the influence of the vital or organic forces. These principles are, for the most part, quaternary compounds of oxygen, hydrogen, carbon, and azote. Some of the acids found in animals, form an exception to this general fact, being formed of only three elements. The organic elements may be divided into tAvo classes: viz. acids and oxides. In addition to these, vegetables possess a peculiar kind of proximate principles, which are not found in animals. These are the recently discovered vegetable alkalies. 1. The organic acids found in the human system, are the ace- tic, the oxalic, the benzoic, and the uric. The three first are common to the animal and vegetable kingdoms, and consist of three elements only, viz : oxygen, hydrogen, and carbon. The acetic, called also the lactic acid, exists in milk, urine, and in many other animal fluids. The oxalic exists in some of the uri- nary calculi, particularly the mulberry calculus. The benzoic acid has been discovered in human urine. The uric acid consists of four elements, oxygen, carbon, hydro- gen, and azote. It is a constituent part of human urine, and of that of many other animals, as birds, reptiles, and insects. 2. The organic oxides are numerous, both in the vegetable and animal kingdoms, and differ Avidely from one another in their properties. Some of them consist of three elements, oxygen, car- bon, and hydrogen; others, of four, containing azote in addition to the three former. The ternary oxides found in the animal kingdom, are sugar, resin, and fixed and volatile oils. Of sugar, there are tAvo varieties found in the human system. One, the sugar of milk; the other, a morbid product, existing in the urine of persons affected with diabetes. The sugar of milk is obtained from the whey, by evaporating it to the consistence of syrup, and allowing it to cool. It is after- wards purified by means of albumen and crystallizing it again. In many respects it differs from the sugar of the cane, though pos- sessing a sweet taste. It is not susceptible of the vinous fermenta- CHEMICAL ANALYSIS OF THE ORGANIZATION. 79 tion; and may be converted, by the action of the nitric acid, into the saccholactic acid; a property in which it differs from every other kind of sugar. The sugar of diabetes exists in the urine of persons affected with this disease. It may be obtained by evaporating diabetic urine to the consistence of a syrup, and keeping it in a warm place for seA^eral days. In its properties and composition it appears to be identical with vegetable sugar. A peculiar resin exists in the bile. Of fixed oils, fat and the marroAV of the bones are examples. Volatile oils are found in some of the inferior animals, but not in man. The quaternary compounds, formed of oxygen, carbon, hydro- gen, and azote, are the most important proximate principles of ani- mal matter. Among those which are most generally diffused, and which enter more or less into the composition of almost all animal bodies, are albumen, fibrin, gelatin, mucus, and ozmazome. Be- sides these, there are several others Avhich are less common, as caseine, urea, hematine, the black matter of the eye, choleste- rine, picromel, &c. The first of these, albumen, is, of all substances, the most gen- erally diffused in the animal economy. It exists both in a liquid and in a solid form. Combined Avith a greater or less proportion of water and a little saline matter, it constitutes the white of eggs, from which it derives its name, albumen; it forms, also, the serum of the blood, the aqueous fluid of the cavities and cellular tissue, and the fluid of dropsies. It constitutes the principal part of the synovial fluid, and it exists in the chyle and lymph. It forms the fluid of blisters and burns, and that Avhich is contained in the hy- datid. It is a colourless, transparent substance, without taste or smell, coagulable by heat, by alcohol, ether, concentrated sulphu- ric acid, some of the metallic salts in solution, and an infusion of tannin. Exposed to a certain degree of heat, (about 160° F.) it coagulates into an insoluble mass. According to Raspail, albumen is composed of two heterogene- ous substances, one an organized insoluble tissue of a cellular struc- ture, the other a liquid contained in the cells of the former. This, he says, may be verified by the simple experiment of shaking to- gether distilled Avater and the fresh white of an egg. The agita- tion will make the water milky, and there Avill be visible, even to the naked eye, a considerable quantity of fragments of white mem- branous tissues. These membranous flakes may be easily sepa- rated by filtering the Avater, Avhich Avill pass through the filter per- fectly limpid, carrying with it the soluble parts of the albumen, but leaving behind the organized tissue in the form of a Avhite, elastic, and glutinous mass, insoluble in Avater. The filtered wa- ter, exposed to evaporation, leaves behind a solid residue of a yel- lowish colour. If exposed to heat it becomes milky and coagu- 80 FIRST LINES OF PHYSIOLOGY. lates, and in short presents all the characters of liquid albumen. In common air it putrefies, and generates multitudes of infusory animalcula of the genus monad. The insoluble tissue is not visible until the albumen is shaken Avith Avater, because it possesses the same refractive power as the soluble part contained in its cells. But Avater, by diluting the liquid part, communicates to it a different refractiAre poAver from that of the tissue, and then becomes milky, because it contains two substances, Avhich refract unequally the rays of light. Solid albumen is a Avhite, tasteless, elastic substance, insoluble in Avater, alcohol and oils, but readily dissolved by alkalies. It constitutes the basis of the substance of the nerves, and brain, and is contained in several of the tissues of the body, as, e. g. the skin, glands, and vessels. It exists in the hair and nails; and morbid growths and tumours are composed principally of it. Albumen is composed of Carbon,..........52.S83 or 17 equivalents. Oxygen,..........23.872 6 do. Hydrogen,.........7 540 13 do.- Azote,.......• . . . 15.705 2 do. It also contains a small quantity of sulphur; since it blackens silver, and, in a state of decomposition, exhales sulphuretted hy- drogen gas. The physiological property which corresponds with albumen is sensibility. Fibrin is a principle which enters largely into the composition of the blood, chyle, and lymph, and is the basis of muscular flesh. It possesses the property of spontaneously coagulating, and it is ow- ing to the presence of fibrin that the blood coagulates when drawn from the living vessels. In its coagulated state fibrin is a solid whitish substance of a fibrous appearance, and may be easily drawn into threads. It is destitute of smell and taste, and insolu- ble in Avater. It may be obtained by stirring fresh blood with a stick until it coagulates, and then Avashing the fibres Avhich adhere to the stick with cold water, so as to dissolve out the red globules. In its chemical composition and many of its properties it resembles albumen, but differs from it in coagulating at all temperatures. Fibrin is composed of Carbon,.........53.360 or 18 equivalents. Oxygen,.........19.685 5 do. Hydrogen,........7.021 14 do. Azote,.........19.934 3 do. From this analysis it appears that fibrin is more highly azotized than albumen. The physiological property which corresponds to it is irritability. Gelatin is another element of almost all the solid parts of the body: but, what is remarkable, it exists in none of the fluids. It is a substance distinguished from all other animal principles by its readily dissolving in warm water, and forming a bulky, tremu- CHEMICAL ANALYSIS OF THE ORGANIZATION. 81 lous solid on cooling. When dried, it forms a hard, semi-trans- parent, brittle substance, with a shining fracture. One part of gelatin dissolved in one hundred parts of warm water becomes solid on cooling, forming a hydrate of gelatin. The well-knoAvn cement, glue, which is prepared from the skins and hoofs of animals by boiling them in water, and evaporating the solution, is an impure gelatin. The isinglass of commerce, prepared from the sounds of the sturgeon, is a very pure species of this principle. Gelatin forms the basis of the cellular tissue and its modifica- tions, and exists in the skin, cartilages, ligaments, tendons, and bones. As it is not present in the blood, nor indeed in any of the animal fluids, it is a question by what means it is formed in the system. This question Ave have at present no sufficient means of ansAvering. It is probably, like fibrin, a mere modification of albumen. Raspail conceives that it does not exist as such in the system, but is the result of the action of heat on the tissues em- ployed in preparing it. It is composed of Carbon................47.881 Oxygen, . . •............27.207 Hydrogen...............7.914 Azote,.......'........16.998 100.000 The property Avhich corresponds to gelatin in the system is animal elasticity. Osmazome. This is another element which is found in all the animal fluids, and in some of the solid parts of the body, as the brain and the muscular fibre. It exists in the flesh of most adult animals. It is a reddish brown substance, of an aromatic smell, and of a strong and agreeable taste. The flavour and smell of beef-soup are owing to the presence of osmazome. The strong taste of roasted meat, also, is supposed to depend on osmazome. It is distinguished from other animal principles by its solubility in Avater and alcohol, either cold or hot, and by not forming a jelly when its solution is concentrated by evaporation. Accord- ing to Orfila, it possesses no nutritious powers, but is tonic and stimulating. By some physiologists, osmazome is regarded as a peculiar extractive matter of flesh ; but by Berzelius it is considered as a compound formed of a peculiar animal matter, combined with lactate of soda, and by Raspail, as an impure combination of albumen and acetic acid. Mucus. This is a secreted fluid, which lubricates the surface of the mucous membranes. In a solid state it enters into the composition of some of the hard parts of the body, Avhich are des- 11 82 FIRST LINES OF PHYSIOLOGY. titute of sensibility, as the nails, hair, cuticle, and horny parts, Avhich consist chiefly of inspissated mucus. The scales, feathers, and wool of different animals contain a good deal of mucus. The rete mucosum is supposed to be formed of compacted mucus. In union with Avater, mucus is a transparent, viscid, ropy fluid, without odour or taste. Nitric acid at first coagulates, but after- wards dissolves it. In its dry state it is insoluble in water. In hot water it imbibes so much of the fluid as to swell and become softened. The acids are its true solvents. It contains a good deal of azote. Caseine. This substance exists only in the milk of the mam- miferous animals, and is obtained from this fluid after it has been coagulated. After the removal of the cream, the curd must be Avell washed with water, drained on a filter, and dried; and it then constitutes the caseine. This principle derives its name from its being the basis of cheese. It is a Avhite, insipid, inodor- ous substance, of a greater specific gravity than Avater, and is highly azotized, and very nutritious. When decomposed by fire, it yields a large quantity of carbonate of ammonia. Caseine appears to have a strong resemblance to albumen, par- ticularly in being coagulated by acids. It is composed of Carbon,...............59.781 Oxygen,...............11.409 Hydrogen,..............7.429 Azote,................21.381 100.000 Urea is a matter which exists in human urine and in that of quadrupeds. It may be procured by evaporating fresh urine to the consistence of a syrup, and gradually adding to it concentrated nitric acid, till it becomes a dark coloured, crystallized mass. This is to be well Avashed with ice-cold water, and then dried by pressure between folds of blotting paper. The nitrate of urea is afterwards to be decomposed by a strong solution of carbonate of potash or soda. The solution is then to be evaporated almost to dryness, and the residue to be treated Avith pure alcohol, Avhich dissolves only the urea. The alcoholic solution is afterAvards to be concentrated by evaporation, and the urea is deposited in crystals. The crystals of urea are transparent and colourless, and without odour. They leave a sensation of coldness on the tongue like nitre, and have a specific gravity greater than Avater. Urea is soluble in water and alcohol. Though not distinctly alkaline, it has the property of uniting Avith the nitric and oxalic acids. It is very highly azotized. It is composed of PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 83 Oxygen................26.40 Azote,................43.40 Carbon,................19.40 Hydrogen,...............10.80 100.00 The other quaternary oxides are not of sufficient importance to be here particularly described. CHAPTER XI. PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. All organized beings, vegetable as well as animal, are endued with the property of being affected by various external agents, and of being excited to action by them. All the manifestations of life in organized matter are the effect of impressions made upon it by external or internal agents, giving rise to vital reaction under the influence of this property. It is this poAver in the seed, the egg, and the germ, which, reacting against impressions made upon them by certain external circumstances, gives rise to a series of in- ternal movements, by which they are gradually developed, and their organization assumes the variety, complication, and form, demanded by the type of being to which they respectively belong. This poAver itself assumes new properties or modifications in the different varieties of the organization thus developed; each one reacting in its own peculiar manner against the impressions made upon it; every fibre, every tissue, every organ possessing its own specific excitability, and manifesting its OAvn mode of activity when excited by appropriate impressions. Thus, the cellular tissue, the muscles, the nerves, the vessels, the bones, the organs of sense, enjoy each their OAvn peculiar species of excitability according to the difference of structure and constitution bestowed upon them at their original formation. The alimentary canal is excited by the presence of food, and by its OAvn secreted fluids. Every gland is solicited by its appropriate stimuli to secrete its peculiar product. The organs of sense are excited by certain external impressions, each in a mode peculiar to itself. The brain is roused to action by external or internal impressions, con- veyed to it by means of the nerves, and the muscles are excited to contraction, by excitations derived from the nerves. In short, all the solid parts of the living system are endued Avith this prop- erty, and are capable of exhibiting some modification of vital reac- 84 FIRST LINES OF PHYSIOLOGY. tion, under the influence of external impressions of various kinds. Even the globules contained in the blood and some of the other fluids, seem to be endued Avith this property ; as their motions ap- pear to be influenced by external excitations which act upon them. The excitants Avhich act upon the living organization, and give rise to the exercise of the functions, are of various kinds, and may be divided into two classes, external and internal. 1. External. The external excitants are those physical in- fluences Avhich are constantly or periodically applied to the sys- tem, and are indispensable to support the activity of life. These are, air, food, heat, electricity, moisture, climate, &c. 2. Internal. The internal are : (a) The blood, and other fluids contained in the vessels and re- ceptacles of the body, Avhich they excite to contract, and thus to impress upon themsehres incessant or periodical motion. The blood, the various secreted fluids, the chyle, the lymph, are examples. (b) The solid matter of the different tissues, which act as ex- citants to the lymphatic and absorbent vessels, the result of which is, the disintegration of the organs, and the conversion of the solid matter of the body into a fluid state, which is necessary to facili- tate its removal from the system. (c) The functions of the organs, which are reciprocally ex- citants to one another. So intimate is the association of the nu- merous organs of which the human system is composed, and so closely are their respective functions connected together, that the actions of every organ are excitants more or less directly to all the others. This intimate connection and mutual subordination of all parts of the system constitute the complex unity of life; and are the source of that universal sympathy which pervades all parts of the organization, and which causes a single impression, made on any part of the system, to resound, as it Avere, in diversified tones from the innumerable chords of this many-stringed harp. (d) The immaterial stimulus of the soul, acting either con- sciously and Avith determinate aim, or blindly and without the cognizance of the individual. Thus the stimulus of the will act- ing upon the brain, excites the contraction of the voluntary mus- cles ; and the passions and emotions influence unconsciously the actions of the heart and blood-vessels, and also excite fibrous con- tractions of many other organs of involuntary motion. Thus they influence many of the secretions, as the biliary, urinary, cutaneous, intestinal, and lachrymal. The excitability of the system is of different kinds, correspond- ing with the diversified nature of the excitants which act upon it. 1. That which responds to the impression of external agents, is found in the great surfaces of the body, exposed to external influ- ences. Thus the skin is excited by the influence of air, tempera- ture, and moisture ; the lungs by the atmosphere ; the stomach by food. PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 85 2. The excitability which is acted upon by internal excitants is: (a) That of the heart and blood-vessels responding to the stim- ulus of the blood. (6) That of the internal surfaces of other canals and cavities answering to the stimulus of their respective contents. This kind of excitability is exemplified in the secretory and excretory vessels, and in the receptacles of various secreted fluids. (c) Excitability of the lymphatics answering to the stimulus of the molecules of the organs. (d) That of the organs in respect to the stimulus of function of other organs. This in the physiological state is the source of normal, and in the pathological, of morbid sympathy. (e) The excitability of the muscles, which responds to the stimulus of the Avill, or rather to that of the nervous power set in motion by the Avill; and that of the fibrous structure of the invol- untary muscles, as the heart, stomach, and secretory organs, to the immaterial stimulus of the passions. (/) The excitability of the brain to the immaterial stimulus of the soul, and (g) That of the nerves to the stimulus of the brain and to other excitants which act upon them, viz. impressions of various kinds from external and internal causes, which, when made upon the nerves, give rise to sensation, open or latent, or some other mode of nervous re-action. This property of living matter assumes three principal modifi- cations in the different solids and fluids, and may be analyzed into three distinct forces, viz. sensitive, motive, and alterative. The sensitive powers are sensibility, and its modifications ; the motive, are contractility, and expansibility, or erectility ; the alterative may be comprehended under the expression, vital affinity. These may be termed the physiological properties of the organization, Avhich distinguish it in a peculiar manner from lifeless matter. In addition to these, living matter possesses certain physical proper- ties in common with inanimate bodies, as elasticity, extensibility, flexibility, imbibition, and evaporation. I. Physiological or vital properties. 1. The first of the physiological properties is sensibility, which is the exclusive attribute of the nervous system. It is peculiar to animals provided with nerves, and its office is to enable them to receive from the external Avorld, or from their own organization, impressions of which they are conscious. Sensibility presides over all our sensations, external and internal, and may be divided into two kinds, viz. general and special. General sensibility animates the whole periphery of the body, the skin, and the origin of the mucous membranes. In the inte- rior of the body, it exists in all the soft solids, and its office ap- pears to be, to convey to the mind a knowledge of the wants of the system ; and, in a pathological state, to apprise it by means of the 86 FIRST LINES OF PHYSIOLOGY. sensation of pain, of the disorders which exist in the organiza- tion. Special sensibility is a property which is the basis of the rela- tion existing betAveen the organs of specific sensation and the peculiar stimulants which act upon them. Thus the eye is en- dued with specific sensibility to light; the ear to impressions of sound ; the palate to tastes; &c. Sensibility, both general and special, has a common centre, which is the brain. This organ is the great focus of sensation, to which all impressions must be transmitted before they can be felt. Its own action is indispensable to sensation; for, if it be rendered by any cause incapable of reacting upon the impressions transmitted to it from the senses, no sensation is excited by them. It is here, also, that sensation, elaborated by the intellect, gives rise, directly or indirectly, to all the modes of perception and thought. According to Bichat and some other physiologists, there is ano- ther species of sensibility, which does not require the intervention of the brain, and which has received the name of organic. It resides in the organs where it is called into exercise, and its centre is supposed to be the great solar plexus. Its manifestations are independent of the brain, never, at least, in the normal state, in- voking the assistance of this organ, nor giving rise to the feeling of consciousness. According to Bichat, the stomach may be said to be sensible to the presence of food ; the heart to the stimulus of the blood; the excretory vessels to the presence of their re- spective contents, &c.; but in all these cases, Avhich are examples of organic sensibility, the feeling is either confined to the organ where it is excited, or it perhaps extends to the great ganglionic centre. It is not propagated to the brain, and is not accompanied with the consciousness of the individual. It is evident, hoAvever, that the existence of this species of sensi- bility stands on very different grounds from those on which the former rests. We have the highest possible evidence of the exist- ence of cerebral sensibility, in our own feelings and consciousness; whereas that of organic sensibility is a mere hypothesis which we are induced to make, to enable us to explain certain phenomena which appear to imply it. If, however, Ave admit of the existence of this species of sensi- bility, we may divide the faculty into two kinds, viz. cerebral, and organic or vegetative. The first has a common centre, the brain, the intervention of which is indispensable to its manifestations, and its exercise is necessarily accompanied with consciousness. The second, also, has a common centre, viz. the solar plexus, is inde- pendent of the brain, and its exercise conveys no notice to the mind. Cerebral sensibility is displayed in all our sensations and per- ceptions, external and internal; organic or vegetative, in the pro- cesses of digestion, circulation, secretion, absorption, nutrition, &c. PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 87 In some parts of the system, according to Bichat, the presence of those fluids or solids Avith which these parts are usually in con- tact, produces only organic impressions, Avhich, in a healthy state, never give rise to animal sensation. This is the case with the mucous membranes lining passages which open to the external air. The presence of the fluids secreted by these membranes, and the transit of the substances to which they are designed to give passage, in general excite little sensation of which we are conscious. The impressions Avhich these substances produce, are confined to the surface with Avhich they are in contact. But if foreign bodies be brought into contact Avith them, cerebral sensa- tion is immediately developed, and the individual becomes con- scious of the impression. There are also certain parts of the body, which in a healthy state appear to be wholly destitute of cerebral sensibility, though their growth and nutrition, in common with that of other parts of the system, prove that they possess organic. These are the bones, cartilages, and ligaments, parts which are wholly destitute of feeling in a healthy state. But when they are affected with disease, animal sensibility is sometimes developed in them, and they become the seats of acute pain. The aliment- ary canal possesses cerebral sensibility at its two extremities, but organic in the intermediate parts. The peculiar seats of cerebral sensibility, are the organs of ani- mal life, or of relation, as they are termed; as the skin, and the organs of sense, the nerves, muscles, and, in a less degree, the membranes and viscera. All the solid parts, without exception, are endued with organic sensibility, for all parts are nourished and grow. Sensation, or nervous reaction, differs from all others in not being accompanied with motion of ponderable matter. All the other actions of the economy, are performed by the agency of some kind of appreciable motion, as muscular contraction in all its varieties, respiration, circulation of the blood, digestion of food, secretion, absorption, nutrition. All these processes are attended with a change of place of masses of matter, either fluid or solid, or with molecular changes implying motion, though not always perceptible to the senses. Nervous reaction, on the other hand, is accompanied with mo- tion of imponderable matter. When an impression is made upon an organ of sense, the brain instantly perceives it, and the effect implies a transfer of the impression to the brain by means of some kind of motion, analogous, probably, to that of the electric fluid. And the acts of the Avill Avhich excite muscular motion by means of the nerves, produce the effect apparently by the instantaneous passage of imponderable matter from the brain to the organs which are excited to. action. This imponderable agency of the nerves is, by some physiolo- gists, supposed in all cases to precede and to be introductory to 88 FIRST LINES OF PHYSIOLOGY. the visible motions of matter, with which the vital functions are accompanied. Since nervous matter is every where present in the solid parts of the body, it is evident that all impressions made upon the organs, Avhether external or internal, are immediately received by nerves, when it is supposed they receive a certain degree of assimilation before they act upon the organs themselves. They are thus undoubtedly modified in some degree, and digested as it were by the nervous system, and brought to a condition more homogeneous to the system and to each other, and in this state of assimilation they act upon the organs ; so that, however differ- ent in their nature, they are all reduced in their influence upon the organs to an imponderable agency, homogeneous to the spirit of life. They are brought much nearer in their nature to the properties on Avhich they are to act; and the effect of these assimi- lated impressions, or the results to Avhich they lead, are either physical motion of masses of animal matter, solid or fluid, as mus- cles, blood, &c, or it is chemico-vital motion of the molecules of matter, resulting in those changes of combination of which most of the vital functions consist. As the stomach and lungs therefore digest food, and assimilate it to the nature of the economy, so the nervous system may be said to digest certain powers or properties of matter, when applied to, and acting upon the system, and the result of these two diges- tions, is respectively the invisible and imponderable agency of the nervous power, and the blood — the two grand factors of all vital action. 2. Contractility, or the facility by virtue of which a living part contracts, is the principal motive force of the system. All the mo- tions of the body have been sometimes traced up to this property, though there appears to exist a peculiar motive poAver in the sys- tem, which displays itself in the dilatation or erection of parts, and which cannot without difficulty be referred to contractility. Brous- sais, however, has attempted to trace up, not only all the manifold movements of the system, but even all vital manifestations what- ever, to this single property of contractility. Living animal matter has the faculty of condensing itself under the influence of certain external impressions. In a single fibre, this condensation manifests itself in a shortening of the fibre, or the approximation of its two extremities. This tendency to contraction exists in various degrees in differ- ent kinds of animal matter. The organic element which possesses it in the most eminent degree is fibrin. Hence those tissues which possess the greatest degree of contractility, contain the largest pro- portion of this principle. Accordingly, the muscles, Avhich are pe- culiarly distinguished by their poAver of contraction, are composed almost wholly of fibrin. It is, perhaps, owing to this property that the fibrin, which is maintained in a fluid state in the blood when moving in the living vessels, becomes coagulated and condensed PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 89 as soon as the blood ceases to move. In the living state, the mole- cules of fibrin are kept in a state of mutual repulsion, perhaps by the vital influence of the Avails of the vessels in Avhich they move. But as soon as they are Avithdrawn from this influence, either by the death of the vessels, or by the removal of the blood from the body, the particles of fibrin approach one another by virtue of this property of attraction, and unite together into a concrete mass. When organized into muscles, fibrin contracts on the application of certain stimuli, either transmitted by nerves from the brain, or applied directly to them. Those tissues which are formed chiefly out of gelatin or albu- men, and are Avholly destitute of fibrin, as the membranes, vessels, cartilages, &c, possess a certain kind of contractility, i. e. they have the faculty of reacting against any distending force, and of recovering their former dimensions Avhen this is removed; but they have not been supposed to be contractile in the same sense as the fibrinous tissues, i. e. to possess the poAver of contracting on the application of stimuli; an opinion, however, which is not strictly correct. Vital contractility exists in tAvo modifications. One of them requires for its exercise the influence of the brain, which is transmitted by means of nerves to the organs in Avhich it is called into action, viz. the locomotive and vocal muscles. All the voluntary motions of the body, and all the muscular exertions employed in the various acts Avhich Ave consciously perform, are examples of the exercise of this power. The mechanical move- ments of respiration, those subservient to the voice and to speech, with all the numerous gestures and motions of the body, have their foundation in this power. Its exercise is under the imme- diate control of the will, and is attended Avith the consciousness of the individual. It may be termed cerebral contractility, be- cause the influence of the brain is necessary, in the normal state, to excite it to action. The absence of cerebral contractility in a part naturally possessed of it, is called paralysis ; its morbid excess or exaltation, spasm, or convulsion. By Bichat this power is denominated animal con- tractility; by some others, locomotility. The second modification of contractility is termed organic, be- cause it is a property Avhich belongs to, and animates every part of the organization. It is independent of the brain, and its mani- festations result from the immediate excitation of the organs them- selves, from stimuli applied directly to them. Its exercise is wholly uninfluenced by the will, and is not accompanied with conscious- ness. Organic contractility has been subdivided into two kinds, sensi- ble and insensible, according as its phenomena are manifest, or ob- scure and latent. 12 90 FIRST LINES OF PHYSIOLOGY. Thus, certain organs, as the heart, the stomach, the bladder, and the uterus, possess an inherent power Avholly independent of the brain or will, of contracting in a manifest and obvious manner under certain circumstances, i. e. the application or presence of peculiar stimuli. The effect is Avholly independent of the will and conciousness of the individual. Aliments excite contraction of the stomach and bowels; the presence of urine stimulates the bladder to contract; the full groAvn foetus excites the uterus; the stimulus of the blood the heart, &c. This species of organic contractility is a prominent attribute of the hollow muscles, or those Avhich are placed out of the jurisdic- tion of the brain, as the heart, the stomach, intestines, &c.; but it is not exclusively confined to them. It exists in the reservoirs and canals belonging to some of the secreted fluids, and, according to some physiologists, in the skin and cellular membrane, tissues which are not muscular in their structure, and contain no fibrin, but consist almost wholly of gelatin. Insensible organic contractility. This property is of the same nature as the preceding, and differs from it chiefly in the circum- stance that its effects are much less conspicuous. In fact, the very admission of it as a distinct property is rather a deduction of reason, than the immediate result of observed facts. That is, Ave are compelled to resort to the supposition of a force of this kind, in order to account for many of the vital phenomena, especially the motion of the blood in the capillary system of the circulation ; that of the absorbed fluids in the lymphatics and lacteals ; and the pas- sage of the secreted fluids through the fine canals of the glands which prepare them. The phenomena hardly admit of an expla- nation, without resorting to the supposition of a poAver of contrac- tion in the walls of the canals or vessels which are the seats of these phenomena. But as its effects are not of a manifest kind, like the contractions of the heart, or stomach, or bladder, it may be termed insensible organic contractility. The motion of the blood in the tAvo extremes of the circulating system, may serve as an illustration of these two kinds of organic contractility, sensible and insensible. In the larger vessels the blood is propelled by the sensible organic contractility of the heart. This force pushes it fonvard as far as the fine ramifications of the arterial system, termed the capillary vessels, Avhere the action of the heart is probably little felt. The motion of the blood, hoAV- ever, still continues, though it is propelled by other causes than the action of the heart. It is forced on by the insensible contrac- tions of these hair-like vessels themselves, until it passes into the radicles of the veins. This insensible organic contractility exists in animals destitute of a heart or central moving poAver. The motions of their fluids must be maintained by a propulsive force of this kind existing in the vessels themselves. A similar force exists in the vessels of PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 91 plants, and the motions of their fluids are maintained by it. In the animal body, the seats of this poAver are the capillary vessels of the circulation, the lymphatic system, including the lacteals, and the fine canals by which the secreted fluids pass out from the place of their formation. These two modifications of organic contractility are regarded as, at bottom, the same, but differing in their manifestations ac- cording to the structure of the part to Avhich they are attached. They have been ingeniously compared to the hour and minute hands on the dial of a clock, Avhich are both moved by the same power; yet the motion of one is insensible to the eye, while that of the other is distinctly visible.* They possess one character in common, viz. that the effects Avhich they produce are not Avithin the jurisdiction of the brain, and are Avholly independent of the will. These effects are the result of various stimuli applied di- rectly to the organs Avhich are the seats of them. Thus, the blood, the aliments, the urine, put in play respectively the organic contractility of the heart, the stomach, the bladder; the bile, the tears, the lymph, that of the excretory ducts of the liver, the lachrymal ducts, the lymphatics, &c. Expansibility. Another of the motive forces is expansibility, a property, by the exercise of which a part becomes the seat of a turgescence or active dilatation. This poAver differs from elasticity, Avhich is purely a physical property, in not requiring the applica- tion of an expanding force. It is directly opposed in its nature and effects to the faculty of contractility. The property of expansibility is exemplified in the phenomena of vital turgescence in the erectile tissues, as the male'and female organs of generation, both external and internal, Avhich become turgid and gorged Avith blood, under the influence of venereal de- sire; and in the nipple, Avhich is similarly affected in the act of suckling. The same property is manifested in the skin, and the subcutaneous cellular tissue. Thus the face is said to SAvell Avith pleasure, the neck to become tumid Avith anger, the ends of the fingers experience a degree of erection in the act of touching, and the papilla? of the tongue in tasting. In a state of inaction these papillae are small, soft, pale, and indistinct. In a state of erection, on the contrary, they are enlarged, erect, red and turgid with blood. In fact, any of the soft solids, Avhich are furnished with blood- vessels, may become the seat of this phenomenon. Any of them may become the focus of a fluxion of blood, if subjected to irrita- tion. Thus, the internal membranes, as the serous, mucous, and synovial, Avhen irritated, become turgid Avith blood, Avhich accu- mulates in their vascular tissue. This is particularly exemplified in the gastric mucous membrane Avhen excited by the presence of aliment; and in the serous and synovial membranes, Avhen exposed * Diction, de Medecine. 92 FIRST LINES OF PHYSIOLOGY. to the air, or subjected to any kind of irritation. The glands ex- hibit similar phenomena under the same circumstances ; and even the muscles and nerves, and other parts provided Avith vessels, become turgescent Avith blood when laid bare and subjected to irritation. The parts which exhibit this phenomenon in the most conspic- uous degree, as the organs of generation and the nipples, are com- posed of a tissue of blood-vessels, interlaced with numerous rami- fications of nerves. The erectile tissues are sometimes developed accidentally, or by disease. Aneurism by anastomosis is of this description. Hem- orrhoidal tumours, also, sometimes present all the characters of the accidental erectile tissues. The dilatation of the heart, Avhich succeeds the systole of the organ, and the expansion of the iris, in the contraction of the pu- pil of the eye, are referred by some physiologists to this species of vital motion. During the dilatation of the heart, the organ swells up, and becomes harder, in expanding to receive or suck up, asit were, the next Avave of blood from the veins. The expansion of the iris, Avhich produces the contraction of the pupil, is regarded as the active motion of the iris, because it is pro- duced by the stimulus of light on the eye ; whereas the contrac- tion of the iris, by which the pupil is enlarged, is occasioned by the absence or diminished energy of the proper stimulus of the eye, and is ahvays greatest in cases of paralysis or much debility of the organ. The structure of the iris, however, is a subject of controversy among anatomists. According to Magendie and others, it is un- questionably muscular, and is composed of two sets of fibres, one of which is exterior and radiated, and by its action dilates the pupil; while the other, which is interior, or next the pupil, is cir- cular, forming a sphincter, Avhich, by its contraction, diminishes this aperture. If this be admitted, the contraction of the pupil is the effect of muscular action, and cannot be referred to the expan- sibility of the iris. It has been conjectured that the act of absorption may be pro- moted by the exercise of this power in the absorbent vessels ; their inhaling radicles thus opening to receive and suck in the fluids which they are destined to absorb. The extent and limits of this force, however, are not accurately defined. 3. The alterative, or chemico-vital powers of the living system may be comprehended under the expression, vital affinity. It is in these powers that the changes which take place in the composition of the solids and fluids of the living body originate. They pene- trate and pervade all the organs, determine their structure and composition, and the changes to Avhich, in common with the fluids, they are constantly subjected. The numerous transforma- tions which the fluids and solids of the body undergo, as in chymi- PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 93 fication, chylosis, lymphosis, hsematosis, the secretions, nutrition, calorification, and fecundation; and the preservation of a certain degree of cohesion or fluidity in the various animal solids and fluids, in spite of the counteracting influence of ordinary chemical agency, must be referred to this power of vital affinity. The formation of the organic elements of the body, also, as fibrin, al- bumen, gelatin, &c, are the results of the operation of the same power. The exercise of this power of vital affinity is confined princi- pally to the fluids, and is manifested in the successive transforma- tions which they undergo, from the state of crude aliment, as it is received into the system, to that of the nutritive fluids in the high- est degree of assimilation. It is the most striking characteristic of this force of vital chemistry, to form compounds and aggregates, which could never be produced by chemical affinity. Under the influence of this poAver, the elements of animal matter are with- drawn from the jurisdiction of chemical laws, and are maintained in their peculiar states of vital combination, in the midst of a va- riety of destructive forces, Avhich are exerted in vain to subvert them. A new order of affinities seems to be developed in the el- ements of these combinations, by the influence of this vital force ; affinities which cannot be satisfied by the common properties of matter, but which mutually saturate one another, and leave the compound in a state of indifference for all others.* Vital affinity, however, is not confined in its operations to the productions of changes and new combinations in the fluids of the system. The solid tissues, also, are subject to its poAver. The various structures of Avhich the body is composed, are formed and nourished by the influence of vital affinity. The structure of a living solid is determined by the same laws as those which fixed its chemical constitution. The various combinations and the dif- ferent degrees of aggregation and cohesion of the elements which constitute the different tissues, must be determined by the chemi- co-vital forces Avhich operated in combining and arranging these elements. The type of the organs, hoAvever, by Avhich their shape, size, and relative position in the system are determined, must be referred to some other power, Avhich Avas impressed upon the germ by the act of generation; a powder which has received the name of the vis formativa or force of formation. As the formation and nutrition of the different organs and tis- sues of the body are executed under the control of vital affinity, and as the different modifications of vital power, with which they are respectively endued, result from their organization or vital composition, it is evident that the power of vital affinity is primi- tive in relation to the other vital forces, or is indirectly the parent of them all. This power, which is bestowed upon the germ by * Diction, de Medecine. 94 FIRST LINES OF PHYSIOLOGY. the act of generation, is excited to activity by the influence of external causes ; and the movements to which it gives rise, deter- mine the development of the different structures of the body, their organization and their chemical composition, and, as a necessary consequence, the various modifications of vital poAver Avith Avhich they are respectively endued. II. The physical properties of the animal tissues are elasticity, extensibility, flexibility, imbibition, and evaporation. 1. The first of these, or elasticity, is possessed in the greatest degree by the cellular tissue and its modifications. It is a force which tends to restore parts which have been subjected to me- chanical extension, to their former state, as soon as the extending cause ceases to act. The cellular tissue enters so universally into the composition of the organs and tissues, that, with the exception of the bones, they are all endued, though in different degrees, with this property. And the organs and membranes are so disposed in the system, that they are kept in a constant state of extension. Thus the extensor and flexor muscles of the same parts counteract each other's elasticity, so that in a state of inaction they are in a condition of mutual extension. The holloAv viscera and the ves- sels are kept in a state of distension by the volume of their con- tents. If the different soft solids were not maintained in this state by the rigidity of the skeleton, there would be a general shrink- ing and collapse of the organs, by the exertion of this elastic force. If a muscle be divided, the two parts recede from each other, leaving an interval betAveen the two divided ends. When the hollow organs are evacuated, they contract by their elasticity, until their cavities are obliterated. The cartilages are highly elastic ; and this property in the sterno-costal cartilages is one of the forces by which the movements of expiration are accomplished. The elasticity of the pulmonary tissue also contributes to the same effect. The elasticity of the intervertebral cartilages occasions a difference in the length of the vertebral column, and consequently in the height or stature of the body, at different times of day. Hence a person is usually a little taller in the morning than in the evening. The dilatation of the heart, which alternates with the systole of the organ, is ascribed by some physiologists to the ex- ertion of its elasticity, overcome at first by the muscular contrac- tion of the ventricles, but acting Avith effect as soon as the stimulus, which excited the organ to contract, is removed by the expulsion of the blood from its cavities. The elasticity of the arterial tissues is an essential force in the circulation of the blood. This force constantly reacting upon the column of blood, Avhich is projected into these vessels by the heart, and keeps them distended, maintains the motion of the blood in the arteries, and propels the vital fluid toAvards the ter- mination of the arterial system. The contractility of the coats of the various canals which carry colourless and secreted fluids, PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 95 is of a vital character, but is probably assisted by the elasticity of these tunics. The elasticity of the animal tissues, though regarded as a mere physical property, is partly of a vital character, as appears from several facts. The contractility of the cellular tissue, e. g. is al- most wholly destroyed by death. It is also excited to action by certain impressions, especially by heat and cold, in some instances by light,* and by some other stimulating agents. Moreover, it varies at different periods of life, in certain states of disease, and in short, according to a variety of circumstances Avhich influence the state of nutrition. 2 and 3. Flexibility and Extensibility. These physical powers exist in various degrees in different parts. The ligaments of the joints are endued with great flexibility, as the free motions of these parts require. They are also possessed of some degree of exten- sibility. The tendons possess but little extensibility ; and for an obvious reason. As they are attached to muscles, and serve to conduct the moving force exerted by these organs to the bones, it Avas evidently necessary that they should not yield themselves ; other- wise the moving force Avould be partly expended or absorbed by them before its arrival at the bones. 4. Imbibition. Another important physical property of the animal tissues is imbibition. If a liquid be placed in contact with an animal tissue, after a certain time it will be found to have penetrated into the latter, as it Avould into a sponge. All the soft animal tissues possess this power of imbibition. Some of the tissues absorb Avith great fa- cility, as the serous membranes and the small vessels ; others, as, e. g. the epidermis, are penetrated by fluids Avith much greater difficulty. The phenomena of imbibition are curious ; and they appear to depend both on the nature of the fluid absorbed, and the texture of the absorbing tissue. Dutrochet found, that on filling the intestine of a chicken Avith milk, or some other dense fluid, and plunging it into water, the milk passed out of the intestine through its coats, and the Avater into it, in the opposite direction ; and from repeated experiments of a similar kind, he deduced the conclusion, that Avhenever an organized cavity containing a fluid is immersed in another fluid less dense than the former, there is a tendency in the membrane to expel the denser fluid, and to absorb the rarer. And if the con- tained fluid be the rarer, then the passage of the two fluids occurs in the opposite directions. The same phenomena are exhibited by the gases. If a bladder be filled with pure hydrogen gas and exposed to atmospheric air, * Tiedemann. 96 FIRST LINES OF PHYSIOLOGY. the hyrdrogen in a short time will become contaminated with at- mospheric air, Avhich penetrates through the coats of the bladder. It appears, on the Avhole, that substances formed of organic matter imbibe or are penetrated by fluids of various kinds, and all kinds of gases ; and that every animal and vegetable tissue is possessed of this property. According to Chevreul, many of the animal tissues are indebted for their physical properties to the Avater which they imbibe and retain. If they are deprived of this Avater, their properties are so much changed that they are rendered unfit for their proper offices in the animal economy ; but if they are placed in contact with water, and become again impregnated Avith this fluid, their former properties are restored. 5. Evaporation. This is another physical property which the animal tissues and organs possess in common with inorganic bodies. Whenever the body or any of the organs is placed in circumstan- ces favourable to evaporation, the aqueous part of the fluids begins to pass off in the form of vapour from the exposed surface, and the loss thus occasioned is greater or less according as the sur- rounding circumstances are more or less favourable to evaporation. The losses of fluid thus occasioned may be so great under some circumstances, as, in some animals, to cause speedy death. CHAPTER XII. THE FUNCTIONS. By the functions are meant the vital actions. The phenomena of life consist in an assemblage of actions, forming an uninterrupted circle, in which it is impossible to find either beginning or end. Every thing is complicated in the vital functions. Every thing depends on something which precedes it; and the antecedent, in many cases, is equally dependent on that which follows. The circulation of the blood, e. g. is an effect of the motion of the heart and blood-vessels. Noav the motions of these organs indis- pensably require the presence of blood circulating in them; that is, the circulation presupposes itself. The heart is enabled to beat and to maintain the circulation only by means of the blood which circulates in its own vessels. The heart requires the action of the lungs, and the lungs no less the action of the heart. With- out the action of the lungs, an impure blood would be returned to the left side of the heart, by which its own vessels Avould become penetrated, and its power of contraction paralyzed; and without THE FUNCTIONS. 97 the action of the heart, the functions of the lungs Avould instantly cease, because no blood Avould be sent to these organs, either for their own nutrition or to be purified by respiration. The lungs are no less under the influence of the brain, and the brain depend- ent both upon the heart and the lungs. If the lungs be deprived of the influence of the brain, their functions are instantly sus- pended ; respiration ceases; the dark blood brought to the lungs by the pulmonary artery is no longer purified by these organs, but is returned to the heart in the foul state of venous blood, and thence a portion of it transmitted to the brain, which, like the heart, soon becomes paralyzed by its poisonous influence. The heart, it is true, is not immediately dependent on the brain ; but it is so indirectly, through the medium of the lungs. All the functions of the system, the circulation, respiration, innervation, &c, are dependent upon digestion, and digestion indispensably requires the aid of the circulating, respiratory, and nervous sys- tems. It appears, therefore, that all the great functions of life are mutually dependent; that they form a circle, in Avhich it is equally impossible to distinguish a beginning or a termination, and of course to determine which are primitive, and which sec- ondary phenomena. This mutual dependence and subordination of the functions, renders it impracticable to establish any natural order in treating of them. Begin where we will, there are antecedent phenomena, the knowledge of Avhich is indispensable to that of those we are considering ; and, consequently, every classification which can be adopted must be more or less arbitrary and defective. The ar- rangement which will be adopted in this work, as, on the whole, less objectionable than any other, is that of Chaussier. Chaussier admits four classes of functions; 1, vital; 2, nutri- tive ; 3, sensorial; 4, genital. 1. Vital. If Ave examine Avith attention the living system in organized beings, Ave perceive a class of functions, the exercise of which is absolutely indispensable, every moment, to maintain them in the living state. This first and most important class of functions may properly be termed the vital functions, and they are three in number, viz. innervation, circulation, and respiration, or the functions of the nervous system, those of the heart, and those of the lungs. These constitute Avhat has been fancifully called the tripod of life ; they are three great columns which support the whole fabric of the living system. 2. Nutritive. A second class of functions has for its object the introduction into the system of the materials of growth and nu- trition, the assimilation of these to the various tissues and organs, and the expulsion from the system of heterogeneous or Avorn-out elements. This class embraces the four functions, digestion, ab- sorption, nutrition and secretion. The great object of this class 13 98 FIRST LINES OF PHYSIOLOGY. of functions is to repair the waste in the organs incessantly caused by the actions of life, and to maintain them in the state of nutri- tion necessary to the support of these actions. They may be termed the nutritive functions. The exercise of them is not so immediately necessary to life as that of the first class. 3. Sensorial. The third class may be called the sensorial func- tions, or functions of relation. These comprise the sensations, intellectual operations, and the voluntary motions. They estab- lish the relations betAveen living beings and the external world; and become Avider in their sphere in proportion as organized beings ascend in the scale of existence. In the vegetable world they can hardly be supposed to exist at all. In the inferior animals they are limited to the narrow circle of mere physical Avants : but in the human species they present their greatest developments. They confer upon man an intellectual and moral existence, and extend his relations to objects and beings which are elevated far above the sphere of his physical necessities. These functions, of Avhich the brain is the common centre, are susceptible of great improvement by education, and are much influenced and modified by the power of habit. They are less necessary to life than either of the tAvo former classes, and their exercise may be suspended for a considerable time Avithout danger. 4. Genital. The fourth class of functions, is the genital. These have no concern with the preservation of the individual, but relate solely to the perpetuation of the species. They are distinguished from the others by several peculiarities. In a ma- jority of organized beings, they require the concurrence of tAvo individuals, or at least of two distinct organic apparatuses, one male, the other female. They are not unfolded until the indi- vidual has attained that stage of constitutional development termed puberty; and in the human race, and some of the superior ani- mals, they cease in the female at a certain epoch of life. CHAPTER XIII. FIRST CLASS, OR THE VITAL FUNCTIONS. Innervation. By the term innervation is meant the physiological action of the nervous system. The nervous system is an integral part of the animal organiza- tion, the functions of which are in the highest degree important INNERVATION. 99 and interesting; but of the precise nature and extent of these, much difference of opinion exists among physiologists. One great office of the nervous system, about which there is no dispute, is to preside over the sensorial functions, or those of relation j that is, the sensations, and the voluntary motions. But besides this, it exercises an influence over the functions of organic or vegetative life, the degree and extent of which, however, is not well defined, and is a subject of much controversy among physiologists. It is to this influence of the nervous system upon organic life in general, that the term innervation is, in strictness, applied; while that Avhich it exercises over the tAvo primary organs of this department, viz. the lungs and the heart, assigns to innervation a place among the vital functions, or those indis- pensably necessary to life. As presiding over sensation and vol- untary motion, the functions of the nervous system fall under the third class, or those of relation. The nervous system is divided into tAvo great sections, Avhich may be termed the encephalic, and the ganglionic ; the former of which is sometimes called the nervous system of animal, the latter, that of organic life. Encephalic Nervous System. The encephalic nervous system consists of the encephalon, and the conductors of sensation and of motion, called nerves. By the encephalon is meant the medullary mass contained in the cranium, and its prolongation, the vertebral canal. It is formed of four parts, viz. the cerebrum, the cerebellum, the annu- lar protuberance, and the spinal marrow. The cerebrum, cere- bellum, and pons Varolii, are termed collectively the brain, that globular mass of nervous matter Avhich fills the cavity of the cranium. The greatest length of this organ is about six inches ; its transverse and vertical dimensions, about five inches each. Its weight in the adult is betAveen three and four pounds. 1. Cerebrum. The cerebrum in man, constitutes much the most considerable part of the encephalon. The upper surface of it, Avhich is convex, is divided longitudinally by a deep fissure into two equal and symmetrical halves, termed hemispheres, which are separated by a fold of the dura mater, called the falx. The fissure which separates the two hemispheres, is bounded inferiorly by a kind of bridge of medullary matter, called the corpus callosum, Avhich reunites the two hemispheres of the brain below. The whole periphery of the cerebrum is intersected by deep fissures, and presents numerous winding eminences, termed con- volutions, which exhibit a striking resemblance to a mass of in- testines. The fissures between the convolutions are from twelve to fifteen lines deep, and, according to Gall, they result from the packing or folding up of the membrane of which he supposes the 100 FIRST LINES OF PHYSIOLOGY. brain to consist. The depth of these fissures is said to bear some ratio to the development of the intellectual powers. The inferior surface of the brain is divided into three distinct regions on each side, termed lobes. The anterior and middle lobes are separated by a transverse depression called the fissura Sylvii. In the substance of the brain are found four cavities, termed ventricles. Two of these are called lateral ventricles, one of which is situated in the central part of each hemisphere. They are irregular in their shape, and each has three winding prolonga- tions, Avhich are termed cornua. The anterior cornua are separa- ted by a transparent membranous partition, called the septum lucidum, composed of two laminae, the separation of Avhich leaves a small cavity betAveen them, called the fossa Sylvii, or the fifth ventricle. The two lateral ventricles communicate Avith each other by an opening, called the foramen of Monro. In the lateral ventricles several parts are found, for a particular description of Avhich, Ave must refer to books on anatomy. Among them are the fornix, which is a flat body of a triangular shape, supporting the septum lucidum, having its upper surface contigu- ous to the corpus callosum, and its loAver resting upon the choroid plexus, and the optic thalami ; the corpora striata, which are two smooth eminences, situated in the anterior part of the lateral ven- tricles, and, on being cut into obliquely, exhibiting a striated ap- pearance, OAving to alternate streaks of grayish and Avhitish matter; the optic thalami, tAvo oval eminences, lying between the diverg- ing extremities of the corpora striata, and their upper surface, forming a part of the floor of the ventricles; the commissura mollis, a band of cineritious matter, which connects the convex surfaces of the optic thalami; the tania semicircularis, a line of white matter running betAveen the convex surfaces of the optic thalami, and the corpora striata; the plexus choroides, situated under the fornix, consisting of a plexus of tortuous vessels, cover- ing the optic thalami, and the corpora striata, and extending into the inferior cornua of the lateral ventricles. This plexus returns its blood, by two veins, called vena Galeni, Avhich run backAvard and enter the sinus rectus. BetAveen the optic thalami and the crura cerebri, is a deep fissure, which communicates Avith the lateral ventricles by a small aperture at its upper and fore part. This is called the third ventricle. 2. The cerebellum or little brain, is, next to the latter, the most voluminous part of the encephalon. In the adult, its weight is about one-eighth or ninth part of that of the cerebrum. It is situated under the posterior lobes of the cerebrum, from Avhich it is separa- ted by the tentorium. Like the brain, it is divided into two lateral halves by the lesser falx, and it is composed of two hemispheres united behind by the vermiform processes Avhich rest upon the me- dulla oblongata, and before by the pons Varolii. On its upper sur- face, it presents five fasciculated lobules, common to both lobes, and INNERVATION. 101 disposed in transverse concentric bands. The inferior part of the cerebellum presents a convex surface, on Avhich may be distin- guished four lobules disposed in concentric arches. When a section is made between the two hemispheres a beautiful arbo- rescent appearance presents itself, formed by the peculiar arrange- ment of the white and gray matter of the brain, Avhich is termed arbor vita. In the cerebellum exists a cavity called the fourth ventricle. The third and fourth ventricles communicate Avith each other by an opening, termed the aqueduct of Sylvius. 3. The annular protuberance, or pons Varolii, is a large round eminence situated betAveen the cerebrum and the cerebellum, and apparently formed by the union of processes from them, termed the crura cerebri, and crura cerebelli. The posterior surface of the pons Varolii presents, on its upper part, four tubercles, termed the tubercula quadrigemina. The tAvo superior, which are larger and more prominent than the inferior, are termed the nates; the two others, the testes. The pineal gland corresponds to the point of intersection of the two grooves Avhich separate the tubercles. 4. The medulla spinalis, or spinal marroAv, is a cylindrical cord of nervous matter, which originates from the pons Varolii, passes doAvnwards through the occipital foramen, and extends through the vertebral canal as far as the first vertebra of the loins, where it terminates; forming with the other parts of the encephalon, what is sometimes termed the cerebro-spinal axis. The part of it Avhich extends from the pons Varolii to the occipital hole, is termed the medulla oblongata. On its surface it presents four eminences, termed the corpora pyramidalia, and the corpora oliva- ria. The tAvo former are oblong bundles of medullary matter lying contiguous to each other; and on the outside of these are the two others, which, from some resemblance in shape to olives, are called corpora olivaria. The posterior surface of the medulla oblongata is contiguous Avith the pons Varolii, and contributes to form the fourth ventricle. On each side of the upper and back part of the medulla oblongata. are situated tAvo oblong eminences termed the corpora restiformia. The remaining part of the medulla spinalis is a long cylindri- cal cord, occupying the vertebral canal, and extending from the occipital foramen to about the level of the first lumbar vertebra. On its anterior surface, a deep fissure extends through its whole length, dividing it into two equal lateral parts. Its posterior sur- face, also, is divided by a median groove. The spinal cord is considered by some anatomists as consisting of four columns, two ascending to the cerebrum, and two de- scending from the cerebellum; by others as consisting of two only According to Bellingeri, it consists, throughout its whole course, of six Avhitish or medullary strands ; viz. two anterior, two lateral, and two posterior. The two anterior are separated from each other by the anterior median furrow, and from the lateral 102 FIRST LINES OF PHYSIOLOGY. strands by the anterior horns of the gray matter. The posterior strands are separated from each other by the posterior median furrow, and from the lateral strands either by the posterior horns of the gray matter, or by the posterior collateral furrows. The anterior strands are continuous with the corpora pyramida- lia, and the crura of the brain, and may be termed the cerebral strands of the cord. The lateral columns are continuous with the corpora restiformia, and may be denominated the restiform strands. And the posterior columns communicate directly with the cerebel- lum, and may be termed the cerebellic strands. The vertebral cord, instead of exhibiting the appearance of a regular cylinder, presents tAvo remarkable enlargements, one of Avhich extends from the second cervical nerve to the first dorsal; the second is comprised between the first lumbar and the third sacral nerve. The first of these is larger than the second, and the volume of each of them appears to be in the direct ratio with the developments of the corresponding upper and loAver extremities. This relation exists in the fcetal state, and continues after birth, and, according to Serres, the bulbs of the spinal cord, as well as the limbs which correspond with them, progressively increase un- til the age of thirty years; and on the approach of old age they begin to diminish, and this diminution is accompanied with an atrophy of the upper and lower extremities. The substance of the encephalon presents two distinct kinds of matter, one termed the cortical or cineritious, the other, the medul- lary or Avhite. The first constitutes the external part of the brain, covering the subjacent matter to the depth of about one-sixth of an inch, and entering deep between the convolutions. It is of a grayish colour, and of a firmer consistence than the medullary matter. The cortical substance is essentially vascular, and per- haps is designed to protect the brain from the impulse of the blood, by dividing the vessels sent to it into infinitely small tAvigs. It also serves, perhaps, to nourish the medullary part. The medullary or Avhite matter is situated interiorly. It con- stitutes much the larger portion of the Avhole mass of the brain, and is traversed by a great number of ramifications of blood-ves- sels. The mass of the brain seems to be formed of an expansion of the fasciculi of medullary fibres of the medulla oblongata, and especially to originate from the corpora pyramidalia and olivaria. The fibres of the former from each side decussate each other, and contribute to the formation of the opposite part of the brain. Be- sides this lateral decussation of the brain, there exists, according to some physiologists, an antero-posterior one; since the effects of a lesion of the corpora striata are said to be manifested in the legs, and those of an injury of the optic thalami, in the arms. The brain is subject to several motions. During sleep it is said to become less turgid, and to suffer a degree of collapse ; but, on waking, it rises again, and fills more completely the cavity of the INNERVATION. 103 cranium. The difference depends on the different degrees of ac- tivity of the brain, in these tAvo states of the system. Another motion depends on respiration. The brain rises during expiration, but sinks in the act of inspiration. A third depends on the pulsa- tions of the heart, with which it synchronizes. During the sys- tole of the heart, the blood is propelled forcibly into the arteries of the brain, and communicates a pulsatory motion to the organ, which sinks again during the diastole of the heart. The spinal marroAV is subject to similar motions. These motions of the brain are said to be a prerogative of the higher classes of animals, the mammalia ; for they are not observed either in birds, reptiles, or fishes. The brain receives its blood by the vertebral arteries and the two internal carotids, the principal branches of which occupy the base of the brain. Numerous veins ramify over the surface of the organ, and terminate in osseo-fibrous canals, which open into the jugular veins. The quantity of blood Avhich it receives is very great, amounting, it is supposed, to one-eighth of the whole quan- tity which issues from the heart. Chemical Analysis of the Brain. The analysis of the substance of the brain, exhibits the follow- ing results: Water,...................8.000 Albumen........... White fatty matter........ Red do do........ Ozmazome,.......... Phosphorus.......... Sulphur........... Traces of phosphates of potash, lime, and magnesia, and muriate of soda Envelops of the Brain and Spinal Marrow. The encephalon is contained in a large, roundish case, formed of bones, and prolonged inferiorly into a cylindrical canal. The globular case is termed the cranium, and its prolongation, the spine. The cranium is formed of eight bones, viz. the frontal, the ethmoid, the sphenoid, the occipital, the two parietal, and the two temporal bones; and it contains the cerebrum, the cerebel- lum, the pons Varolii, and the medulla oblongata. The spine is a column, composed of twenty-four perforated bones, called ver- tebrae, piled one upon another, in such a manner as to form a con- tinuous canal, and distinguished into three kinds, according to their position in the column; viz. seven cervical, twelve dorsal, and five lumbar. It is terminated by two other bones, the os .......700 .......453 ....... 70 .......112 .......150 .......515 10.000 104 FIRST LINES OF PHYSIOLOGY. sacrum, and the os coccygis, and it contains the vertebral part of the spinal cord. Within its bony case, the encephalon is enveloped by three membranes, viz. an external, termed the dura mater, a middle called the arachnoides, and an internal, called the pia mater. 1. The dura mater is the external envelop of the brain. It is a strong fibrous membrane, which forms the internal periosteum of the cranium, adhering loosely to the bones of the skull, except at the sutures and foramina. By maceration it is divisible into two or more laminse. Its internal surface forms several folds or duplicatures. One of these constitutes the falx cerebri, Avhich separates the tAvo hemi- spheres of the brain from each other. Its upper edge, extending from the frontal ridge to the middle groove of the occipital bone, contains the superior longitudinal sinus. Its lower edge, which passes over the corpus callosum, contains the inferior longitudinal sinus. Another process of the dura mater, is the tentorium cerebelli, which is a membranous partition, separating the cerebrum from the cerebellum. Its outer circumference contains the lateral sinuses. The falx cerebelli is another process of the dura mater, which lies between the lobes of the cerebellum. These different parti- tions appear designed to maintain the principal divisions of the encephalon in their respective situations, and to prevent them from being compressed by one another. In animals, Avhose habits of life lead them to spring down from elevated places, as the cat, there are bony partitions betAveen the principal parts of the ence- phalon, instead of the membranous folds of the dura mater. 2. The arachnoides is situated between the dura mater and pia mater. It is a serous membrane, and consequently forms a closed sac. It is expanded over the convolutions of the brain without dipping into the fissures Avhich separate them, and over the cere- bellum, and the base of the pons Varolii. It forms a sheath for all the nerves and all the vessels which pass into, or out of, the cranium. It also passes doAvmvards into the vertebral canal, en- velops the spinal marroAV, and gives a sheath to each of the ver- tebral nerves. This membrane penetrates into the third ventricle by a small opening between the corpus callosum, and the tuber- cula quadrigemina; it lines the third ventricle, and is continued over the parietes of the lateral and the fourth ventricles, into which it penetrates through the aqueduct of Sylvius. 3. The pia mater is the third membrane of the encephalon. It is a loose cellulo-vascular membrane, Avhich immediately invests the brain, dipping into the fissures which separate the convolu- tions, and covering the superior surface of the corpus callosum; enveloping, inferiorly, the base of the brain, the pons Varolii, and the surface of the cerebellum. It penetrates into the third and INNERVATION. 105 lateral ventricles, Avhere it forms the choroid web, and the plexus choroides. It appears to be a delicate tissue of blood-vessels, con- nected and supported by soft cellular membrane. The pia mater, Avhich invests the spinal marrow, is connected to the arachnoid membrane by a loose cellular tissue and by blood- vessels ; leaving, however, an interval betAveen the two mem- branes, which is filled by a liquid. This space communicates with the ventricles of the brain by means of the fourth ventricle. The fluid, Avhich thus surrounds the spinal marrow, it is conjec- tured, may serve the purpose of blunting the shocks or concussions accidentally impressed upon the spine, and thus of preserving the cord from mechanical injury. According to Ollivier, a spinal fluid also exists between the two laminee of the arachnoides itself. Magendie informs us that the spinal fluid exists in all the mam- miferous animals as well as man, and at every period of life, occu- pying the whole length of the vertebral canal. The encephalic nerves constitute the second part of the ence- phalic system. These nerves are white cords, extending from the brain or spinal marroAV to every part of the system, and are the conductors of sensitive and motive impressions. They are dis- posed in symmetrical pairs, and are composed of filaments, con- nected together by cellular tissue. Of these nerves there are forty-three pairs. Two pairs origi- nate from the cerebrum; viz. the olfactory, and the optic. Five pairs from the pons Varolii and its peduncles, viz. the motores oculorum, or third pair; the pathetici, or fourth pair; the tri- facial, or fifth pair ; the external motory nerves of the eye, or sixth pair ; and the facial nerve, or seventh pair. The remaining thirty-six pairs originate from the spinal mar- roAV; viz. five from the medulla oblongata; viz. the auditory nerve or eighth pair; the glossopharyngeal, or ninth pair : the pneumogastric, or tenth pair, sometimes called the eighth pair, or the par vagum; the hypoglossal; and the spinal accessory. Eight arise from the cervical part of the spinal marroAV ; twelve from the dorsal; five from the lumbar ; and six from the sacral. All these nerves furnish numerous filaments, some of which pass directly to the organs to Avhich they are destined, and Avhich, for the most part are those of the senses, and the muscles of voluntary motion ; others form numerous anastomoses between the encephalic and the ganglionic nervous systems ; and a third class are em- ployed in the formation of plexuses, which consist of a net-work of filaments proceeding from different branches, interlaced together. The plexuses formed by the encephalic nerves, are four in number • the cervical, brachial, lumbo-abdominal, and sacral. 1. The cervical plexus is formed by the anterior branches of the second, third, and fourth cervical nerves, is situated in the lateral part of the neck on a level with the second, third, and 14 106 FIRST LINES OF PHYSIOLOGY. fourth vertebras, and gives rise to four principal nerves, which are distributed to the head, neck, and the superior parts of the thorax. 2. The brachial plexus is formed by the anterior branches of the four last cervical, and the first dorsal nerves. It lies con- cealed, in a great measure, in the cavity of the axilla, and gives rise to eight principal branches, distributed to the thorax, shoul- der, and arm. 3. The lumbar abdominal plexus is formed by the anterior branches of the five lumbar nerves, lies behind the psoas muscle, and gives origin to six principal nerves, the five first of which are distributed to the parietes of the pelvic cavity, and most of the organs contained in it; and the last, termed the lumbo-sacral nerve, descends into the pelvis, and unites Avith the sciatic or sacral plexus. 4. The sacral plexus is formed by the anterior branches of the four first sacral nerves, occupies the sides of the pelvic face of the sacrum, and gives off three principal branches, the two first of which are distributed to the cavity of the pelvis, and the viscera contained in it, and the third, an immense nerve termed the sciatic, is distributed to the lower limbs. Ganglionic Nervous System. The second grand section of the nervous system is called the ganglionic, and sometimes the nervous system of organic life. By ganglions are meant small bodies of a grayish white colour, of a roundish, or elongated shape, varying in volume from the size of a hemp-seed to that of an almond ; most of them extend- ing in a series along the sides of the vertebral column, from the base of the cranium to the superior extremity of the coccyx, and connected together by nervous filaments. Each ganglion transmits nerves both upwards and doAvnwards to the ganglions nearest it, and others to anastomose with the cerebro-spinal nerves. Some of them furnish branches, which are distributed immediately to certain organs, as to the arterial coats, or to particular viscera. Thus, the ophthalmic ganglion gives origin to the ciliary nerves ; the submaxillary, to the fila- ments which supply the salivary glands ; the sphenopalatine, the cavernous, and the naso-palatine, to branches which are distributed to the arteries and neighbouring parts, &c. But most, of the fila- ments proceeding from the ganglia, are destined to the formation of the numerous plexuses belonging to this system. Thus the cervical ganglions supply filaments, which form the three cardiac nerves, superior, middle, and inferior, which terminate in the cardiac plexus. The thoracic gangiions, from the fifth to the eighth or ninth, inclusive, send off filaments which contribute to the formation of the great splanchnic nerve ; and the tenth and eleventh furnish branches which form the lesser splanchnic nerve. The ganglions are numerous, and are found in different situa- INNERVATION. 107 tions. Most of them extend in a series along the vertebral column ; six are found in the head, and several in the abdomen. The ganglions, Avhich exist in the head, are the ophthalmic, the spheno-palatine, the cavernous, the naso-palatine, the submaxil- lary, and the otic, or the ganglion of Arnold. Of those Avhich lie along the vertebral column, three, or sometimes only two, are found in the neck, and are called the cervical ganglions; eleven or tAvelve, in the dorsal region ; five, four, or sometimes only three, in the lumbar ; and three in the sacral. In the abdomen, are found the great semilunar ganglions, situated on each side of the aorta, on a level Avith the cceliac ar- tery. By their superior extremity, these ganglions receive the great splanchnic nerves, and by their inferior, they communicate with each other. A number of smaller ganglia surround the two semilunar, and are connected with them by anastomosing fila- ments. This collection of ganglia and nervous filaments inter- laced together, constitutes the solar plexus. Plexuses formed by the ganglionic nerves. The nervous branches furnished by the ganglions, unite in a great number of points with branches of the encephalic nerves, forming inextri- cable plexuses. From these originate numerous branches, some of Avhich are distributed to the neighbouring organs, but much the larger portion to the coats of the arteries, Avhich they accom- pany in their principal divisions, forming secondary plexuses. The principal of these plexuses are the following, viz : The cardiac plexus, formed by the three nerves of the same name. From this plexus branches arise, which form the coronary plexus: The pulmonary plexus, formed by filaments of the pneumogas- tric nerve, and the anterior branches of the first thoracic ganglions : The solar plexus, formed by the great and lesser splanchnic nerves, and by numerous branches furnished by the semilunar ganglion and its accessories. From this great centre spring branches which serve to form a great number of secondary plex- uses, as the diaphragmatic plexus; the coeliac, from which originate the coronary of the stomach, the hepatic, and the splenic; the superior and inferior mesenteric, the renal, whence is formed the spermatic, &c. The ganglionic system is termed collectively, the great sym- pathetic nerve. It seems to arise from the sixth cerebral nerve, and from the vidian branch of the fifth. It receives filaments from the seventh, eighth, and ninth, and all the spinal nerves, to the lumbar region, and extends to the pelvis, where it terminates. Functions of the Nervous System. The functions of the nervous system may be divided into two general classes ; the first, those of relation, comprehending the 108 FIRST LINES OF PHA'SIOLOGY. sensations, voluntary motions, and the intellectual operations ; the second, those by Avhich it influences the other functions of the system, as the respiration, circulation, digestion, nutrition, secre- tion, calorification, &c. The first class of these functions does not, in strict propriety, fall under consideration at present, because it constitutes the third general class into Avhich the functions of the system are dis- tributed, viz. the sensorial, or those of relation. It is the second class, viz. those by Avhich the nervous system controls, or influences the other functions most necessary to life, particularly respiration, and the circulation, which finds a place among the vital functions ; though it is proper to state, that several distinguished physiologists have embraced the opinion, that innervation is the first and most indispensable condition of life ; that it constitutes the very essence of vitality ; is common to all organized beings, without exception, and is essential to every manifestation of life. In treating of the functions of the nervous system, we shall consider separately the different parts of which it is composed, viz. the brain, spinal marrow, and nerves. I. The brain, comprehending the cerebrum, cerebellum, and pons Varolii, may be considered as the great centre of this section of the nervous system, and one of the most important organs in the whole animal economy. It is the great development of the brain in the human race, Avhich raises man so far above all other ani- mals, even those, Avhich from their near approach to man in external shape and internal organization, are termed anthropomorphous. The functions over Avhich the brain presides, are the sensations, the voluntary motions, and the intellectual and moral faculties, It is the seat of consciousness, and of the feeling of individuality, the temple in which is enshrined the perceptive, thinking, and willing principle. The spinal marrow and nerves are subordinate organs, Avhose office it is to transmit impressions from the organs of sense to the brain, and the cerebral influence in the contrary direction, to the muscles of locomotion and voice. Besides these, which are the sensorial functions of the brain, it exercises an im- portant influence over many of the other functions of the system, particularly respiration, and the circulation, as has been already observed. These tAvo classes of the cerebral functions, though differing essentially from each other. I shall not separate, but consider together ; Avhile, under the third class of the functions, or those of relation, will be considered the senses, and the subject of voluntary motion. I. The sensorial functions of the brain. These include sensa- tion, voluntary motion, and the intellectual and moral faculties. Sensation. The organs of sense and the nerves are the imme- diate seats of sensation, but its ultimate seat is the brain. Every sensation Ave experience, from Avhatever cause it originates, and by whatever-channel it is introduced, requires the intervention of INNERVATION. 109 the brain before it can be felt. The impression itself is made upon some organ or sensible part, more or less remote from the brain; but before sensation can be excited by it, the impression must be conveyed to the brain, and in some Avay or other modi- fied, or digested, as it were, by this organ. Of this the proof is perfectly conclusive. If the nerve, which connects an organ of sense with the brain, be divided or compressed, no sensation will be excited in the mind by impressions made upon the organ. The same physical effect will be produced as before by the ex- ternal agent; but the channel between the organ of sense and the brain being obstructed, the impression is no longer conveyed to this great focus of sensation, and no feeling, consequently, is ex- cited. A circumstance truly curious in this process of sensation is, that, though the brain is the ultimate and real seat of sensation, yet every sensation is always referred to the organ of sense on which the impression that gives rise to it is made ; so that there would appear to be a double organic action in all cases of sensa- tion, viz. one from the organ of sense to the brain, by which sensation is excited; the other from the brain towards the organ, by means of which it is referred to the latter. The agency of the brain in sensation is strikingly illustrated by those curious cases of delusive sensation, Avhich sometimes occur in persons Avho have lost some of their limbs, and Avho com- plain of pain or some other sensation in a part which no longer exists. Here the brain is evidently the only seat of the sensation ; and this is as real as if the part to Avhich it is referred actually existed. For the essence of a sensation consists in being felt. When it is felt it exists ; Avhen it is not felt, it does not exist. These sensations are delusive only in being referred by the mind to a part Avhich has no existence ; but this only proves that the reference itself is a cerebral action, and may be exerted even in the absence of the organ, to Avhich the reference is made. In certain diseases or injuries of the brain, by which the organ is rendered incapable of exerting its usual powers, impressions upon the organs of sense excite no sensation in the mind. The organs of sensation Avhich are the recipients of the impressions, and the nerves proceeding from them to the brain are uninjured; but no sensation is excited, because the brain is unable to react upon, and to digest the impressions received from them. In such circumstances, as a person receives no sensations from any of his senses, external or internal, he is in a state of general insensibility. A similar torpor of the brain may be produced by the action of opium, alcohol, and other narcotics ; and, accordingly, we find that persons completely under the influence of these agents, are in a great measure insensible to external impressions. There is another state of the system in which the action of the brain is suspended, while this organ, as well as the organs of sense and the nerves retain their integrity, but in which, impres- 110 FIRST LINES OF PHYSIOLOGY. sions made upon the senses, excite no sensation in the mind. This state is sleep. In this periodical inaction of the brain, the senses partake, because they derive their poAver of being excited by ex- ternal impressions, from their connection with this organ. No impression upon the senses is noticed or excites consciousness, merely because the brain, in a state of repose, is incapable of re- ceiving them, and of reacting upon them. If, however, these impressions, whether made by external causes, or produced by affections of the organs themselves, are of a certain degree of strength, they may so far excite the action of the brain, as to give rise to an imperfect sort of sensation, or to that shadoAvy kind of consciousness Avhich we term dreaming. On the other hand, the activity of the brain may be so absorbed by its own peculiar functions, as profound meditation, or exclusive attention to some engrossing subject of thought, that impressions upon the senses are not perceived, because the cerebral power is already fully occupied, and none can be spared to give audience to these messages from the senses. In the cases enumerated above, sensation is not excited, because the brain does not react upon the impressions transmitted from the senses. It might be conjectured from this, that if the action of the brain directed to these impressions, could in any way be in- creased, the sensations excited by them would become more vivid than under the ordinary degree of cerebral reaction. Now the fact is found strictly to accord Avith theory in this case. We have the power of increasing the activity of the brain, by an effort of the will, or by an energetic concentration of the attention upon the impressions received from the senses; and when we exert this power, we find that the increased cerebral energy adds strength and distinctness to the resulting sensations. Slight impressions, and such as, perhaps, would scarcely have been perceived under the circumstances which are constantly distracting and dissipa- ting the cerebral energy, become distinct and even vivid sensations, when the scattered rays of the mind are recalled, concentrated to- gether in a focus, and throAvn directly upon them. The action of the brain is, therefore, as essential an element of sensation, as the impressions made upon the organs of sense. One further proof that the brain is the ultimate organ of sensa- tion, may be noticed in this place. In certain affections of the brain, sensations are sometimes excited by the mere action of the brain itself, without the corresponding impressions upon the senses. We have examples of this curious fact in certain nervous diseases, as catalepsy, hypochondriasis, and mania. Insane persons some- times listen attentively to fancied strains of celestial music, to which they earnestly call the attention of others. In the same manner, the tales of visions and apparitions, which have been so frequently told, and so generally discredited by all but the igno- rant and the superstitious, admit of an explanation in perfect con- INNERVATION. Ill sistency with physiological principles. The brain has been highly excited by the operation of fear and aAve, upon ardent imagina- tions. The action of the brain has naturally corresponded Avith the state of feeling which gave rise to it, and has, accordingly, been such as the actual impression of some fearful object upon the senses, would naturally have produced in the brain ; and ac- cording to the law Avhich operates in all cases of actual sensation, it has been accompanied by a reference to the appropriate organ of sense. The shape under Avhich the hallucination Avill be em- bodied in such cases, will probably be determined by accidental circumstances, and the habitual or prevailing associations of the individual. It is remarkable, that though the brain is the ultimate seat of sensation, yet both the cerebrum, and cerebellum themselves are destitute of sensibility. Wounds of these parts, as it seems to be established by experiments, do not excite pain. The whole of the hemispheres has been pared aAvay, the cerebellum removed in the same manner, the corpora striata, and the optic thalami cut aAvay, and yet the animal subjected to this shocking experiment, remained perfectly passive, exhibiting no indications by cries or struggles, that it was suffering pain. But as soon as the operator reached the tubercula quadrigemina, trembling and convulsions immediately took place. The medulla oblongata, and spinalis are highly sensible. According to Magendie, sensibility exists in an exquisite degree in the spinal marrow, particularly on its pos- terior surface ; while on the anterior it is much more feeble. Very acute sensibility also exists in the sides of the fourth ventricle ; but this property diminishes in approaching the anterior part of the medulla oblongata, and becomes very feeble in the tubercula quadrigemina. Voluntary Motion. The brain is also the organ of the will, the point of departure of all our voluntary motions. The imme- diate instruments of motion are the muscles. It is by the con- traction or shortening of these, that motions are impressed upon the moving parts of animal bodies. The muscles possess a pecu- liar poAver of contracting, upon the application of certain stimu- lants. Thus, mechanical irritation applied to muscular fibres, excites them to contract; and Avithout the application of some stimulant power, the contractility of the muscles remains in a dor- mant state, and the organ does not contract. Now the stimulus which acts upon the voluntary muscles, so as to excite their faculty of shortening themselves to exert itself, is the influence of the brain set in motion by an act of the will. No voluntary action can be performed Avithout the agency of the brain. Of the me- chanism of these actions we are totally ignorant. We are con- scious only of the tAvo extremes of the phenomena, the act of the will, which is an immaterial agent, and which by an internal sen- timent we refer to the brain, and the physical effect to Avhich it 112 FIRST LINES OF PHYSIOLOGY. leads, viz. the motion we will to produce; and, notwithstanding the distance which separates the two places where the cause ope- rates, and where the effect is produced, we are not conscious of any interval of time between the tAvo phenomena. The energy of the brain is conveyed, as if by electricity,. to the instruments of motion, Avhich are instantly excited to their appropriate actions. The cerebral influence, however, may be set in motion by other causes besides the will, and contractions of the voluntary muscles be excited not only Avithout the agency of volition, but even in spite of the strongest efforts of this faculty to prevent them. Thus, any irritation applied to the brain, or developed in it by disease, will frequently excite involuntary contractions of the muscles, which usually act only under the will. Irritations, also, seated in other parts of the body, as the alimentary canal, may excite the brain sympathetically, and determine the cerebral influence to the muscles of voluntary motion, giving rise to those involuntary con- tractions, Avhich are called convulsions or spasms. In such cases a person may retain his consciousness, and the power of the will may exist in full vigour ; and yet, it is wholly unable to restrain the contractions of the muscles excited by the influence of a more powerful stimulus. The physical stimulus of the brain is more energetic than the immaterial, and the organ acted upon, by two opposite forces, yields to that whose action is most powerful. The proofs that the brain is the seat of the will, the source of voluntary action, are of the same kind and equally conclusive with those that it is the organ of sensation. If the communica- tion between the brain and any organ of voluntary motion be cut off, by dividing, compressing, or stupifying by opium, the nerve which forms this communication, no act of the will can excite to motion the part so isolated from the brain. In these cases the brain is as capable as ever of exerting its powers of volition ; but the acts of the will can no longer influence the muscle to contract, because the channel of communication between the tAvo organs is no longer open. Certain diseases of the brain, or injuries inflicted upon the organ, abolish the poAver of volition. It is remarkable, that in these cases, the same cause Avhich destroys the faculty of the will, and of course prevents A^oluntary contractions of the mus- cles, may act as a physical or morbid irritation to the brain, and give rise to spasmodic or involuntary contractions of them. The disease termed paralysis, affords another illustration of the dependence of voluntary motion upon the brain. In this disease, some of the voluntary muscles lose their poAver of contracting under the influence of the will. The brain still retains its power of exerting an act of the will, but is unable to give effect to the act by exciting the paralyzed muscles to contraction. This con- dition in hemiplegia, and some other varieties of palsy, is gene- rally connected Avith some lesion of the brain, which may be the effect of disease or of accident. It does not so far impair the INNERVATION. 113 power of the brain, as to abolish the faculty of volition; but it destroys the physical influence of the acts of this faculty upon the organ, so that the nervous energy is not transmitted to the affected muscles, which consequently are not excited to contrac- tion. It would seem probable, from this fact, that the faculty of volition has a distinct seat in the brain, and that its physical influ- ence is exerted upon some other part of the organ, whence it is transmitted to the conductors of the cerebral energy, the nerves. If the seat of the faculty itself be materially injured, no act of the Avill can be exerted. But if the seat of the injury be any part of the brain, on Avhich the will is exerted, or through Avhich it must be transmitted, in its passage to the muscles of voluntary motion, then though an act of the faculty may be exerted by the individual, yet no corresponding contraction of the voluntary muscles will follow it. During sleep, in which the brain is in a state of inaction, and the faculty of volition dormant, there is no contraction of the vol- untary muscles. A person asleep, if placed on his feet, is unable to support himself in an erect position, but obeys the law of grav- itation, and sinks to the ground. If sleep overtakes him while sitting, its first approaches are indicated by nodding of the head forward ; because the strong muscles of the back of the neck are no longer able to support it; and not being poised exactly on its centre of gravity, but resting on the vertebral column behind this centre, its anterior part preponderates. Intellectual and moral faculties. The brain is the organ of the intellectual and moral faculties. The proofs of this are of an in- controvertible kind. The connection of the brain with the opera- tions of the intellect, and of the moral faculty, is shoAvn by nu- merous facts. An internal sentiment leads us irresistibly to refer the acts of the mind and of the moral faculty, to the brain or head. No one ever imagined that he carried on his reasoning operations in his lungs, stomach, or liver. These organs, like all others, have certain functions peculiar to themselves. The same is true of the brain. A healthy state of certain parts of this organ is necessary to the exercise of the rational and moral poAvers; and accordingly we find that injuries of the head frequently destroy or impair the faculties of the mind. The same consequences result from certain diseases of the brain, a fact which is remarkably exemplified in apoplexy and in insanity — tAvo diseases which are, probably in all cases connected with some physical change in the state of the brain. In general, in all cases of acute disease, in which the pa- tient preserves his mental faculties unclouded to the last, we may be pretty certain that the brain is unaffected; and, on the other hand, whenever we find him become drowsy, stupid, or insensi- ble, we may be equally sure that this organ has suffered some physical change, which, in most cases, will be apparent on dissec- 114 FIRST LINES OF PHYSIOLOGY. tion. Opium, alcohol, and other narcotics, which exert so striking an influence upon the mental faculties, owe this property to their power of producing certain changes in the brain. Like all the other organs of the body, the brain experiences the effects of the exercise of its functions, in an increase of its volume. If the intellectual powers are duly cultivated, the organ acquires its full development and growth ; if they are neglected it probably never attains the expansion of which it is capable. This circum- stance is important; for it explains the fact, that the neglect of early intellectual culture, in many cases, can never be compensated by subsequent education. The brain, in these cases, has not been sufficiently developed, in its organization and volume, by necessary exercise. It is incapable of acting with the energy of a fully de- veloped brain, and no voluntary efforts of the individual can over- come the obstacle, for it is a physical one, connected Avith the state of the organization. On the other hand, severe exercise im- posed upon the brain in its tender state, in young children, is still more pernicious; for it prematurely exhausts the energy of the organ, and brings on its early decrepitude. The brain, at first, under the influence of artificial excitements, is rapidly unfolded, the intellectual faculties soon bud and blossom, every thing gives hopes of an early and abundant harvest; but the fruit never ripens, but falls half formed to the ground. Localization of the Cerebral Functions. Numerous experimental researches have been made, in order to determine the functions which respectively belong to different parts of the brain; but as yet, without very satisfactory results. The cerebral lobes are supposed to be the seats of the faculties of thinking, memory, and the will; and according to some physi- ologists, ultimately, of all the sensations. Vertical pressure upon the hemispheres of the brain, occasions stupor, — an effect, however, which Mayo ascribes to the com- pression of the medulla oblongata. Lateral pressure is said to be followed by no sensible effect. The lobes of the brain appear to be that portion of the organ in which all the sensations assume a distinct shape, and leave dura- ble traces in the memory; a property, by which they furnish the materials of knowledge and judgment. The ablation of one of the cerebral lobes, or a profound lesion of it, is followed by blindness of the opposite eye, and by a para- lytic weakness of the muscles of the opposite side of the body. If both lobes are removed, much injured, or compressed, ac- cording to Flourens, there is from that moment neither sight, hearing, smell, taste, memory, thought, nor will. The animal subjected to the operation sinks into an apoplectic stupor; a fact from which Flourens infers, that the cerebral lobes constitute the INNERVATION. 115 organ of the memory, of the will, and, ultimately, of all the sen- sations. It is a curious fact, that although the sight of the oppo- site eye is destroyed when one of the cerebral lobes is removed, the contractility of the iris remains unimpaired. If the conjunc- tiva, the optic nerve, or the tubercula quadrigemina, be irritated, the iris contracts with convulsive force; a fact, from which it appears, that while the principle of vision resides in the cerebral lobes, that of the contractility of the iris exists elseAvhere. Magendie, on the contrary, asserts that neither the cerebrum, nor the cerebellum, is the principal seat of sensibility, or of the special senses. He affirms that if the lobes of the cerebrum, and those of the cerebellum, be removed in one of the mammalia, the animal still remains sensible to strong odours, to sounds, and to tastes. He admits that vision is abolished by the ablation of the cerebral lobes; but this fact he accounts for by observing, that vision does not consist in the simple perception of light; but that the action of the apparatus of vision, is almost always connected with an intellectual or instinctive operation, by which we form ideas of the distance, size, shape, and motion of objects ; and this intellectual element of vision, he supposes, requires the interven- tion of the cerebral hemispheres. On this subject Magendie remarks, that the sense of vision has a threefold seat in the brain; viz. the cerebral lobes in the sense just explained, the optic thalami and the fifth pair of nerves. An injury of one of the thalami is followed by a loss of sight in the opposite eye, and a section of the fifth pair occasions blindness of the eye on the same side. Hence it appears that the influence of the hemispheres and of the optic thalami upon vision, is transverse or exerted upon the opposite sides, while that of the fifth pair is direct. Admitting, however, that the cerebral lobes are the seats of memory, of the will, and of the sense of vision, it is certain that these faculties may continue unimpaired, when the lobes of the brain are mutilated or wounded. Even deep Avounds of the brain are not invariably followed by debility of sensation or motion, or of the mental faculties ; facts, which render it probable, that a por- tion of these lobes, perhaps the central part, may suffice for the exercise of these functions. In some cases, a lesion of one hemi- sphere will give rise to disorder of the intellectual faculties; in others, intelligence continues unimpaired. In the first case, the intellect sometimes halts, as it were, in consequence of the tAvo hemispheres acting unequally. By the unimpaired action of the sound one, the patient seems to be conscious of the crippled state of the other. He understands perfectly well the questions ad- dressed to him, and perhaps meditates a rational answer; but when he attempts to express himself, he talks nonsense, or says something entirely different from what he intended, and perhaps, conscious of the incoherence and absurdity of his words, he stops 116 FIRST LINES OF PHYSIOLOGY. and endeavours to recollect himself, and makes another attempt with the same success. In such cases the iavo hemispheres do not, and cannot act in harmony. The powers of intelligence ap- pear to rally to the sound hemisphere, leaving to the crippled one the inferior office of giving expression to its thoughts. An extensive lesion of both hemispheres, it is supposed, can scarcely exist without materially impairing the intellectual pow- ers. Yet I have known extensive disorganization of the brain in the form of numerous large tubercles, the largest of Avhich equalled a small pullet's egg in size, interspersed throughout the brain and cerebellum, yet accompanied during the Avhole course of the dis- ease with uncommon clearness and even acuteness of mind. The patient Avas a young girl of very great promise. The disease was of three years' standing at the time of her death, Avhich occurred at the age of nine. It was accompanied with complete amaurosis for the two last years of her life, and with paralysis of both loAver extremities. During this time, her appetite was good, she greAV fast, and her intellect was unclouded. The office of the cerebellum is suppposed to be, to regulate and combine different motions to a determinate object. A wound of one side of the cerebellum is folloAved by a Aveakness of the same side of the animal. If the Avound be deep, the body on the injured side becomes paralytic. Serres, hoAvever, affirms that lesions of one of the lobes of the cerebellum occasion paralysis of the limbs on the opposite side. If the lesion of the cerebellum is on the left, the paralysis affects the right side, and vice versa. Of the truth of this opinion he adduces several proofs from pathology, and experimental physiol- ogy. The division of the one side of the cerebellum he found to produce a flexure of the body towards the same side, in conse- quence of the muscles of the opposite side being no longer able to counterbalance those of the other. The disposition to turn in the same direction, seems to proceed from the greater strength of the muscles on the side corresponding Avith that of the lesion. The animal is evidently weaker on the opposite side, seeks to be sup- ported, and is apt to fall on the same side. In the experiments of Flourens, wounds and injuries of the cerebellum Avere found to cause a discord, or want of harmony, rather than a weakness, of the voluntary motions. The ablation of it occasioned a loss of the poAver of combining the motions, necessary to the mode of progressing which is proper to the species of the animal subjected to the experiment. The animal appears to be intoxicated, and exhibits a singular propensity to go backwards. Another remarkable phenomenon is a kind of rota- tion or whirling round, Avhich is said to be sometimes exhibited by persons, after wounds, or in diseases, of the cerebellum. Sometimes patients affected with diseases of this organ, whirl round in their beds in a very extraordinary manner. Further, if INNERVATION. 117 a vertical incision be made into one side of the cerebellum the animal rolls over and over, always turning itself toAvards the in- jured side ; at the same time a Avant of harmony is observed in the direction of the eyes, one of them being turned upwards and back- wards, the other, doAvnwards and forwards. On making a similar incision in the opposite hemisphere parallel to the first, the motion of the animal ceases, and the harmony of direction in the two eyes is immediately restored. Magendie observed that the same effect was produced by di- viding the cms cerebelli in a rabbit, as by dividing the cerebellum unequally. The animal survived the experiment eight days ; and during the whole time it continued to revolve upon its long axis, except when arrested by some obstacle. The division of the op- posite crus put a stop to the motion. If a section of the cerebellum on one side gave rise to a con- stant revolution towards the same side, the division of the opposite crus cerebelli did not restore the equilibrium, but the animal began to revolve towards the side of the divided crus. These curious phenomena Mayo ascribes to a sensation like vertigo, produced by the lesions of the cerebellum. Upon comparing the cerebrum and the cerebellum together, in relation to the effect of injuries upon them, it appears that lesions of the cerebellum give rise to a Avant of harmony in the voluntary motions ; those of the cerebrum, implicate the senses, understand- ing, and will. Compression of the brain produces the effect of opium; alterations of the cerebellum, the effects of the abuse of alcohol. In the former case there are symptoms of narcotism ; in the latter those of intoxication. Lesions of the cerebrum produce paralysis or immobility; those of the cerebellum, agitation and disordered motions, and especially a disposition to go backAvards, and a rotation of the body. Diseases of the cerebrum destroy the harmony of ideas ; those of the cerebellum, the harmony of mo- tions. The cerebellum influences chiefly the loAver limbs ; - the cerebrum, the upper.* The tubercula quadrigemina have been supposed chiefly to in- fluence the voluntary motions of the body, the sense of vision, and the contraction of the iris. The removal of one of these, weakens the sight, and the motions of the iris of the opposite eye, causing dilatation of the pupil. The total destruction of the tuber- cles produces blindness, immobility of the iris, and dilatation of the pupils. Serres, however, states that he has seen these bodies dis- organized, but had never Avitnessed in these cases, a loss of vision. Irritation applied to the tubercles occasions convulsions and con- tractions of the iris. Magendie, however, remarks, that he had never seen that an injury of the optic tubercle affected the A'ision in the mammiferous animals, though this effect was very evident in birds. * Bourdon. 118 FIRST LINES OF PHYSIOLOGY. The destruction of the pons Varolii, occasions immobility of the body, and the loss of all the senses. The respiration and circulation are not affected, unless the injury extends to the me- dulla oblongata. Artificial irritation of the pons on one side, causes contraction of the pupil on the same side, but convulsions of the opposite side of the body. General irritation applied to it, produces contraction of the pupils, general convulsions, or universal paralysis, paralysis of the muscles of inspiration, and vomiting. Inflammation of the pons causes rigidity of all the limbs, and permanent contraction of the pupils. If it is inflamed more on one side than the other, the contraction of the pupil is greater on the same side, and the rigidity of the limbs on the opposite. Sometimes there is trismus. According to Bourdon, the pons Varolii is situated between the functions of the will and those of instinct, exactly on the limits of intelligence and life. Above it, all is voluntary ; below it, all is spontaneous and automatic. The optic thalami are believed by some physiologists, to influ- ence the motions of the arms, and the corpora striata, those of the lower extremities ; so that lesions of the former, it is supposed, may occasion paralysis of the arms, and those of the latter, para- plegia, or palsy of the loAver extremities. Paralyses of the arms are said to be more obstinate than those of the legs, because the lesions of the optic thalami are generally the profounder and more durable. Further, as the thalami are nearer the medulla oblongata, morbid affections of them more frequently affect respiration. Hence paralysis or convulsions of the arms, are oftener accompanied with oppressed respiration than those of the legs. According to Bourdon, paraplegia is often accompanied with, or preceded by, a pain in the temples ; a fact which is explained by the anterior situation of the corpora striata. The optic thalami, also, like the tubercula quadrigemina, are subservient to the sense of vision, and the corpora striata to that of smell. So that the same parts of the brain Avhich are instru- mental in vision, are subservient to the sense of touch, in regu- lating the motions of the arm; and the organs of locomotion are allied to the sense of smell by means of the corpora striata, which are subservient to both. According to Serres, it is only a certain part of the optic thalami which is instrumental in vision. He says that he has seen the whole superior surface destroyed without impairing this sense, and even if the injury penetrates deeper, vision is not lost, unless it reaches as far as the level of the commissura mollis, which he regards as the boundary of the sense. In these affections, vision, instead of being destroyed or im- paired, sometimes becomes double ; and Avhat is still more re- INNERVATION. 119 markable, in some cases the patients see objects double Avith one eye, and single with the other ; and cases have occurred, in which the double vision in one eye has become single, and in the other the reverse. The optic thalami, and the corpora striata, according to Serres, exercise a special influence upon the voice, speech, and articulation. The parts of the encephalon which seem to be particularly destined to motion, are the corpora striata, the optic thalami, in their inferior part, the crura cerebri, the pons Varolii, the pe- duncles of the cerebellum, the lateral parts of the medulla ob- longata, and the anterior part of the spinal marrow. And accord- ing to Serres, it is established by facts, that the medulla oblongata and the pons Varolii exert an equal influence over the motions of the limbs; that the lobes of the cerebellum have a greater influence over the lower than the superior extremities; while, on the con- trary, the cerebral lobes influence the superior more than the inferior limbs. It may be proper here to mention the opinions of a celebrated Italian physiologist, Bellingeri, respecting some of the functions of the different parts of the brain. Bellingeri endeavours to prove that the cerebral lobes, the anterior strands of the spinal cord, and the anterior roots of the spinal nerves, are subservient to motion; and that the cerebellum, the posterior strands of the spinal cord, and the posterior roots of the spinal nerves, also pre- side over motions. In proof of the first proposition, he refers to numerous authorities to show, that while injuries and diseases of the superior part of the brain affect chiefly the intellectual facul- ties, lesions of the middle lobes and corpora striata affect princi- pally the motions of the abdominal or sacral extremities; and that injuries and diseases of the optic thalami, and posterior lobes of the brain, affect chiefly the motions of the thoracic ex- tremities. He also adduces experimental proof of the subservience of the anterior strands of the spinal cord, and the anterior roots of the spinal nerves, to the motions of the limbs. In proof of the subservience of the cerebellum, &c, to motion, he adduces the experiments of various physiologists, which show that sections of the cerebellum produce paralysis of the muscles of the opposite side. He also refers to numerous cases in which morbid states of the cerebellum gave rise to tetanic rigidity of the muscles, trismus, rigid tension of the extremities, general convulsive mo- tions, and priapism ; and others, in which palsy of various muscles was produced by diseases of the cerebellum. Bellingeri further endeavours to prove that the lobes of the brain are subservient to the motions of flexion ; and the cerebel- lum, to those of extension. In proof of the first position, he adduces various experiments of different physiologists, as Magendie, Flourens, &c. Thus, Serres found that the removal or injury of one of the anterior 120 FIRST LINES OF PHYSIOLOGY. lobes of the brain, Avas followed by flexion of the opposite abdo- minal extremity ; and the removal of both anterior lobes produced the flexion of both abdominal extremities. On the contrary, the division or removal of the posterior lobes of the brain is folloAved by flexion of the thoracic extremities. The removal or destruc- tion of the hemispheres of the brain, causes an irresistible motion of progression forAvards ; while wounds or destruction of the cere- bellum produce a retrogressive motion. From pathological in- vestigations, Bellingeri infers that inflammation or any irritation of the cerebral lobes produces spasm, which assumes the form of flexion, and sometimes, also, of adduction of the extremities; from which he infers that the cerebral lobes preside over the mo- tions of flexion and adduction of the extremities. In proof of the proposition that the cerebellum presides over the motions of extension, he adduces various experiments from different physiolo- gists ; the general result of which is, that irritations excited in the cerebellum induce opisthotonos or spasmodic extension of the head, trunk, and posterior extremities; that in some instances of lesions inflicted on the cerebellum, these spasmodic motions may be so violent as to throAv the animal completely backwards ; and, that the motion of retrogression observed by Magendie in injuries or irritations of the cerebellum, is owing to the spasmodic action thus induced in the extensor muscles, by Avhich the animals are compelled involuntarily to move backwards. In support of the same position, Bellingeri adduces a variety of pathological facts.* 2. Influence of the brain over the organic functions. The influ- ence of the brain over the organic functions is comparatively inconsiderable, being far inferior to that of the spinal marrow. Most of the great functions of the system, hoAvever, appear to be more or less influenced by cerebral innervation ; as respiration, the circulation, digestion, secretion, nutrition, calorification, &c. Thus respiration is, in some degree, subject to the influence of the brain, because the external muscles of respiration belong to the class of the voluntary muscles, Avhich derive their nervous influence directly or indirectly from the brain. The internal sentiment of the want of respiration, Avhich produces the cerebral reaction upon the external muscles of respiration, must be referred to the seat of consciousness in the encephalon, wherever this may be. This internal sentiment, hoAvever, is by no means necessary to respiration; for this function goes on without intermission when consciousness is suspended, as e. g. during sleep, and in certain cerebral diseases. And where the latter are accompanied with stertorous or embarrassed respiration, the effect is to be as- cribed to compression or lesion of the medulla oblongata. The action of the brain, therefore, is not necessary to respiration ; and accordingly we find that the removal of the whole organ does not * Edinb. Med. and Surg. Journ. No. cxx. INNERVATION. 121 destroy this function, provided that the medulla oblongata be left uninjured. Acephalous infants have lived some days after birth. In an account of an acephalous child by Mr. Lawrence, it is stated that the brain and the cranium Avere deficient, and the basis of the latter Avas covered by the common integuments, except over the foramen magnum, Avhere there existed a soft tumour about the size of the end of the thumb. This child lived four days, and breathed naturally, and Avas not observed to be deficient in warmth until its poAvers declined. The medulla spinalis was found to extend about an inch above the foramen magnum, swell- ing out into a small bulb, Avhich formed the soft tumour upon the basis of the skull. All the nerves, from the fifth to the ninth, Avere connected Avith this. The most extensive organic disease may exist in different parts of the brain without affecting respira- tion. Yet, that this function is influenced by the brain, appears from the fact, that certain emotions of the mind produce an evi- dent effect on the movements of respiration. The action of the heart, also, is considerably influenced by the brain. It is well knoAvn that violent emotions, and all strong moral affections poAverfully influence the action of the heart. A sudden emotion of surprise frequently occasions palpitation. A vivid sensation of joy has, in many instances, occasioned sudden death, by paralyzing the heart. It is related of the painter Francia, that he Avas struck with such admiration by a painting of Raphael, that he SAvooned and expired on the spot. The passion of fear, also, produces a strong depressing effect upon the circulation. Terror has, in some instances, caused a mortal syncope ; and aneurisms of the heart have been often produced by this cause. According to Desault, the Reign of Terror in France, in the year 1793, Avas uncommonly fruitful in this disease. Diseases and injuries of the brain, also affect the circulation. Compression of this organ from extravasated blood, or effused serum, in many cases renders the pulse preternaturally slow, or irregular. In these examples, it is true, respiration is frequently much disordered, and the affection of the circulation may be considered as an indirect and secondary effect. But there are cases of morbid affection of the brain, which point out a more immediate action of this organ upon the heart. For example, I have known symptoms of cerebral disease which seemed to threaten hydrocephalus, but from Avhich the patient recovered, accompanied Avith an intermittent or irregular pulse, which continued during the Avhole course of the affection. Con- cussion of the brain, also, is attended Avith great depression of the action of the heart, and of the capillary circulation, together with coldness of the surface. The Avell known power of digitalis in causing a slow or intermitting pulse, is probably connected with its sedative influence upon the brain. Though it is true that 16 122 FIRST LINES OF PHYSIOLOGY. the injection of an infusion of this plant into the veins, produces the same effect, partly perhaps from its direct action on the heart. The removal of the brain, according to Dr. Philip and others, does not diminish the action of the heart; but if it be suddenly destroyed, as by crushing it, the motion of this organ is immedi- ately enfeebled. Digestion, also, is influenced in some degree by the brain, as appears by the effects upon the function, produced by certain mental emotions. The effect produced by the division of the pneumogastric nerves upon digestion, is to be ascribed to the in- terception, not of the influence of the brain, but of that of the medulla oblongata. With respect to the other organic functions, which for the most part are exercised in the parenchyma of the organs, and the capil- lary vessels, and which derive their poAvers principally from the ganglionic system, the influence of the brain may be inferred from the disturbance occasioned in these functions by moral causes, such as violent passions, or emotions. These causes take their rise in the brain, and the effects which they produce in modifying the organic functions, are illustrative of the influence of cerebral innervation over the department of vegetative life. The passions affect the capillary circulation and calorification; for the skin be- comes red or pale, and hot or cold, under the influence of certain passions. The secretions, also, manifest the influence of cerebral innerva- tion. Grief increases the secretion of tears; fear, that of the kid- neys. A cold sAveat sometimes starts out from the skin under the influence of the same moral cause. The peculiar state of the nervous system Avhich exists in hysterical affections, frequently occasions a copious secretion of pale urine, but sometimes produces the opposite effect, and suppresses the secretion. A fit of anger has been known to change the qualities of the milk, so as to give rise to colic and diarrhoea in infants nourished by it. Boerhaave re- lates a case of this kind, in Avhich epilepsy Avas excited by this cause, and continued to return during the whole life of the patient. The cerebral influence, also affects absorption, and probably nutrition likeAvise. It is well known, that persons under the in- fluence of fear are peculiarly liable to be attacked by contagious, or epidemic disease ; while those who are calm and fearless in the general panic, are much less liable to suffer. This fact renders it probable that the passion of fear promotes absorption, as some other debilitating causes undoubtedly do ; and that the morbific principle, whatever it be, is thus more easily introduced into the system of persons affected by it. The paralysis of a limb often tends to atrophy or Avithering ; a fact which appears to evince the influence of encephalic innervation upon nutrition. Paralytic parts also sometimes swell or become oedematous. These facts, and numerous others of a similar kind, appear to INNERVATION. 123 leave no doubt, that the parenchyma of the organs, as well as the capillary system, is supplied with nerves, Avhich subject them in some degree, to the influence of the brain. The brain is also believed, by many physiologists, to be the instrument of that mysterious vital relation, Avhich exists between, and connects together, the different organs; in other words, it is supposed to be the principal agent of the sympathies. On the Avhole, the brain is the organ of intelligence ; it directs the means by which Ave react upon the external world ; it exer- cises an important influence over the functions of internal life ; and, as the great, centre of the nervous system, is probably the principal organ of sympathy. These functions of the brain, especially the two latter, render this organ indispensable to life in the higher classes of animals; and accordingly Ave find that injuries of this organ from accident or disease, are generally, though not invariably, fatal. Though it be true, hoAvever, that the functions of internal life are more or less influenced by cerebral innervation, yet it must not be inferred that they are dependent on this organ; since it is well known that full grown foetuses have been born, destitute of every trace of a brain, and even of a spinal marrow. From this, it should seem, that during foetal life the innervation of the gang- lionic system is sufficient to maintain the nutritive and vital func- tions, in their imperfect and rudimentary state ; but that after birth, when the individual commences a new and more elevated existence, when all the phenomena of animal or external life start at once into existence, and the brain, their common centre, is roused to the exertion of all its sleeping energies ; when two of the most important of the organic functions Avhich are immediately dependent on encephalic innervation, viz. digestion and respira- tion, first begin their exercise ; the empire of the brain is extended over all the functions of life, connecting them together in a bond of reciprocal dependence and sympathy ; and cerebral innervation then becomes indispensable to their regular exercise, and conse- quently to animal life. A curious conclusion to which Hall has been led by his experimental researches is, that this process of nervous development may, in some of the lower orders of animals be reversed, as it were, by the successive removal of portions of the nervous system. He remarks, that if such a part of the ner- vous masses be removed as can be spared without the immediate destruction of life, the animal is reduced to a loAver degree in the scale of organized beings. It lives, but degraded below the level to which it properly belongs, and it acquires an increased power of enduring further mutilations. In this manner, Hall believes the whole brain and spinal marrow might be removed, and the animal live, supported by the ganglionic nervous system, and cu- taneous respiration. 124 FIRST LINES OF PHYSIOLOGY. Functions of the Spinal Cord. The influence which this part of the nervous system exercises upon some of the most important functions, places it in the first rank of organs most necessary to life. The spinal marrow is found in all the higher classes of animals, under different forms, and the more highly developed, in proportion as their whole organization is more perfect. By its direct communication with the brain on the one hand, and on the other with the different parts of the body, it becomes the principal channel of communication between the common centre of sensation and voluntary motion, and the imme- diate instruments of these functions, viz. all the sensible parts of the trunk and limbs, and the muscles of voluntary motion. It exercises, also, an important influence over many of the organic functions, particularly respiration, calorification, cutaneous trans- piration, the digestive functions, and the motions of the heart. In treating of the functions of the spinal cord, I shall consider first, its sensorial functions; secondly, those by which it influen- ces the vital and organic ones. I. Sensorial functions. According to Mayo, it appears from Magendie's experiment of removing the cerebrum, optic tubercles, and cerebellum in a living animal, that the brain may be taken away by successive portions, and yet the animal survive, and ex- hibit sensation and instinct. But if the mutilation be carried a line further, so as to comprise that small segment of the medulla oblongata, in which the fifth and eighth nerves originate, con- sciousness is at once instantly extinguished. From this experi- ment it would seem to folloAV, that this portion of the medulla oblongata, instead of the cerebral lobes, is the seat of conscious- ness. Mayo remarks, further, that the rest of the nervous system derives its vitality, or rather its participation in the phenomena of consciousness, from its continuity with this small portion of the medulla oblongata. In proof of Avhich, he states that in cold- blooded animals, as the frog or turtle, consciousness will continue some time after the head has been severed from the body ; and it Avill remain either in the head or the body, according as the section of the medulla oblongata has been made below or above the spot just described. If the section be made below this vital part, the body is deprived of sensibility while the head continues to exhibit marks of consciousness. But if the section be made just above the origin of the fifth and eighth nerves, the result is directly opposite ; for the head is deprived of life, while the body remains alive. According to Mayo, the stupor occasioned by ver- tical pressure upon the hemispheres of the brain, is owing to the compression of the medulla oblongata. The same author observes in connection Avith this subject, that when vomiting has been ex- cited by an emetic, it is arrested by pressure applied to the medulla oblongata. INNERVATION. 125 The spinal marrow may be regarded as a common centre of the nerves, distributed to the muscles of voluntary motion, and of those subservient to general sensibility. It is not, however, inde- pendent of the brain. It is only a conductor, and perhaps we may say a prime conductor, of sensific impressions from the limbs and trunk of the body to the brain in one direction; and of motive impulses from the seat and source of volition, the cerebral lobes, to the muscles of voluntary motion in the other. It has been knoAvn from the infancy of medicine, that injuries of the spinal marrow occasion a paralysis, both of sensation and motion, of the parts situated below the injured portion of the cord. A division of the cord in any part of its course, always paralyses the limbs, and that portion of the trunk of the body situated below the seat of the injury, leaving the parts above, Avholly unaffected, If the injury occur high up in the neck, it causes almost instant death. The involuntary discharge of urine and fecal matter, Avhich is frequently the consequence of injuries of the spine, was referred by Galen to a paralysis of the nervous filaments Avhich are distributed upon the sphincters of the bladder and rectum. It is also Avell known, that irritations applied to the spinal marroAV, excite convulsions of the trunk and limbs beloAv the seat of the irritation. The researches of Bell, Magendie, and others, appear also to have established the fact, that the anterior part of the spinal cord presides over voluntary motion, and the posterior over sensation. The spinal nerves originate by double roots, one anterior, the other posterior ; and Magendie found that dividing the posterior roots of the spinal nerves, which supplied one of the hind legs, completely destroyed the sensibility of the limb, without affecting its power of motion ; and, on the other hand, that the section of the anterior roots abolished the muscular power, Avithout impair- ing the sensibility of the limb. A striking evidence of the same fact is furnished by the nux vomica, a poison, which, in some animals, excites the most violent spasms, but which produces no such effect, if the anterior roots of the spinal nerves be previously divided. It appears, however, that the isolation of these two properties in the anterior and posterior roots of the spinal nerves, is not com- plete. If an irritation be applied to the posterior roots, contrac- tions are produced in the muscles to Avhich the nerves are dis- tributed, though they are much less violent than when the anterior roots are irritated. In like manner, slight indications of sensibility are observed, when an irritation is applied exclusively to the anterior roots. The isolation of these two properties, sensibility and motility, from each other, in the double roots of the spinal nerves, will enable us to account for those cases of paralysis, in which the loss of power is confined exclusively to the sensibility or the motility of the paralyzed part. 126 FIRST LINES OF PHYSIOLOGY. The gray central part of the spinal cord, appears to be the principal seat of these two properties; for the roots of the spinal nerves, are found to penetrate into this central portion of the cord. There is still, hoAvever, much difference of opinion respecting the functions of these parts of the spinal marrow. According to Bellingeri, the posterior strands preside over the movements of ex- tension, and the anterior over those of flexion; Avhence there results an antagonism between these tAvo parts of the spinal cord. The posterior strands produce a relaxation of the sphincter of the blad- der, and the contraction of that of the rectum ; the anterior, on the contrary, preside over the contraction of the sphincter of the bladder, and the relaxation of that of the rectum. The anterior and posterior strands exert no influence upon sensibility, but only on motion. The Avhite matter of the spinal cord is the exclusive seat of motility ; while the influence of the gray matter, is con- fined to the sense of touch. Experiments also seem to have ascertained, not only that the spinal cord is the source of sensation and motion of the trunk and limbs generally, but that the sensibility and powers of motion of any part of the trunk and limbs, depend on that portion of the spinal marrow from which it receives its nerves. If an animal is made to take strychnine, and the spinal marroAV be laid bare, the convulsions in any part occasioned by the poison, are arrested by compressing that part of the spinal cord which corresponds with it; while compression of the brain, or of the medulla oblongata, neither suspends nor checks them in the slightest degree. This fact appears to prove, that the spinal marrow is not merely a chan- nel of communication betAveen the brain and the organs of motion, but that the principle of motion resides in this part itself. Experiments also make it probable, that the different portions of the spinal cord are capable of acting independently of one another ; a fact which confirms the opinion that the spinal mar- row has a power of its OAvn, independent of the brain. Mayo remarks, that the spinal cord consists of an assemblage of inde- pendent segments ; that each segment, from which a pair of nerves arises, has in itself a mechanism of sensitive and instinc- tive action, similar to that of analogous parts in the invertebrated animals. In proof of this he adduces the following experiments. If the spinal cord be divided in the middle of the neck, and again in the middle of the back in a body, a few seconds after it has been deprived of life, upon irritating a sentient organ connected with either isolated segment, muscular action is produced. If, e. g. the sole of the foot is pricked, the foot is suddenly retracted in the same manner as it would have been during life. In this experiment a sentient organ is irritated, and the irritation is pro- pagated through the sentient nerve to the isolated segment of the spinal cord, and gives rise to some change, followed by a motific impulse along the voluntary nerves to the muscles of the part. INNERVATION. 127 Still, the peculiar energy of the spinal marroAV, is subordinate to the influence of the brain, which perceives and appreciates the impressions conveyed to it from the sense of touch through the spinal cord, and which reacts in such a manner, that its influence is transmitted through the same channel to the locomotive organs. Without the action of the cerebral lobes, no voluntary motion could be originated, and probably no sensation be distinctly and consciously felt. Influence of the Spinal Marrow over the Organic Functions. The spinal cord also exercises an important influence upon some of the organic functions most necessary to life. The su- perior part of the spinal cord, or the medulla oblongata, may be regarded as a kind of focus of vitality in the superior classes of animals. In this limited portion of the cerebro-spinal system are concentrated all the nervous forces immediately necessary to life; particularly the nerves which give energy to the lungs, the larynx, the heart, and the stomach, and those Avhich supply the external muscles of respiration; and any cause Avhich should at the same time suspend the action of all these nerves, would im- mediately annihilate life.* Hence, the instant death occasioned by an injury of this part of the spinal cord. According to Bel- lingeri, the lateral strands of the medulla, Avhich are continuous with the corpora restiformia, preside over the organic and instinc- tive functions. Respiration, especially, is under the influence of the superior part of the medulla spinalis; and lesions of this part of the cord are ahvays accompanied by symptoms which point out the de- pendence of respiration upon it. Lesions of the medulla ob- longata instantly annihilate respiration. Injuries of the spinal cord opposite to the second vertebra, also, occasion instantaneous death; because all the respiratory nerves are then injured simul- taneously, so that respiration is instantly destroyed by a paralysis of the external and internal muscles of the chest, and those of the neck and nostrils, and by the inaction of the aerial passages and lungs. If the spinal marroAV be Avounded opposite to the fifth cervical vertebra, or a little higher, respiration becomes laborious, and the motions of respiration are executed only by the muscles of the neck and shoulders, the diaphragm becoming nearly motionless, and the intercostal muscles paralyzed ; and death soon follows from asphyxia. If a lesion be inflicted upon the dorsal portion of the spinal cord, it is folloAved by immobility of the ribs, because the intercostal muscles derive their nervous influence from this part of the cord. Respiration, however, is still carried on imperfectly by the action of the diaphragm, and * Ollivier. 128 FIRST LINES OF PHYSIOLOGY. the respiratory muscles, accompanied by the elevation of the shoulders, expanding of the nostrils, opening of the mouth, &c. It may be asked Avhy a simple section of the spinal marrow at the occiput produces death, Avhen no other injury is inflicted upon the medulla spinalis, than the mere separation of its vertebral from its cerebral portion. Brachet answers this question by ob- serving that the pneumogastric nerves, Avhich originate in the medulla oblongata, receive in the lungs the impression of the want of respiration, and transmit it to the medulla oblongata. In the normal state, the medulla oblongata reacts upon those parts of the spinal cord Avhich give rise to the respiratory nerves of the chest. But if the communication between the medulla oblongata and the vertebral parts of the cord be intercepted, the former can no lon- ger transmit its influence to the latter, which, consequently, do not excite the respiratory muscles to action. The effect upon respiration of dividing the pneumogastric nerves, is another illustration of the influence of the medulla ob- longata on this function. The division of these nerves in the neck, produces a paralysis of the lungs, which soon terminates in asphyxia and death. It also occasions a paralysis of the muscles which dilate the larynx, in consequence of which the aperture of the larynx becomes closed, and opposes an insurmountable obsta- cle to the introduction of air in the lungs. It is supposed, also, to prevent the transmission of the sentiment of the want of respira- tion to the medulla oblongata, and consequently the reaction of this upon that part of the spinal cord Avhich furnishes the respira- tory muscles of the chest Avith nerves. The influence of the spinal marrow upon the circulation of the blood, is by no means so great as upon respiration. Even the total destruction of the cord does not occasion an immediate sus- pension of this function. Experiments, however, have ascertain- ed that the circulation of the blood is considerably influenced by the spinal column. The destruction of the spinal marrow, or of any considerable portion of it, has been found to enfeeble the ac- tion of the heart. If the lumbar part of it be destroyed, the cir- culation is enfeebled in the posterior extremities, but is not affect- ed in other parts of the body, which derive their nervous influence from that part of the cord Avhich is situated above the injury. And, in general, when any portion of the spinal cord is destroyed, the circulation becomes more feeble in the parts situated below the injured portion of the spine, than in those above. On the whole, it is ascertained that the action of the heart is independent of spinal innervation, but is much influenced by it. The heart may act without the spinal cord, but yet is subjected in some de- gree to this nervous centre. If the heart be deprived at once of the influence both of brain and spinal cord, the action of the or- gan, according to Hall, is enfeebled from that, moment. The heart, like the muscles of voluntary motion, possesses a degree of irrita- INNERVATION. 129 bility independent of the great nervous centres ; but if separated from them, it gradually loses this power. From the moment of the removal of the brain and spinal marrow, its irritability begins to fail. The circulation becomes weaker, and then ceases, first in the remoter parts of the system, then in those nearer the seat of the moving power. Flourens was of opinion that the circulation depends upon the medulla oblongata, and that the poAver of the heart is impaired by the destruction of this portion of the nervous system, only because respiration is annihilated. But Hall found that the medulla ob- longata in a frog might be destroyed so as to annihilate respiration, yet the circulation, though at first enfeebled by the shock, recov- er itself and continue perfectly vigorous for many hours. But the capillary circulation appears to be immediately depend- ent upon the innervation of the spinal cord. The destruction of any part of this nervous centre, always produces a suspension of the circulation of the capillary vessels of the parts which receive their nerves from the destroyed portion. Hence in paraplegia from an injury of the spine, the capillary circulation is sometimes al- most wholly suspended ; the skin is purple or mottled, from a stasis of venous blood in the small A^essels. The cutaneous veins are much enlarged and croAvded Avith dark-coloured blood, from the loss of their contractile poAver; there is a total absence of cuta- neous transpiration ; the skin is dry, and there is a constant ex- foliation of the cuticle. There is also a sensible diminution in the temperature of the paralyzed parts. The development of caloric in the system seems to take place in the tAvo capillary sys- tems, the pulmonary and the general; and both these systems de- rive their nervous influence in a great measure from the spinal cord. Hence, in chronic affections of this organ, attended with a loss of sensation and motion, there is a sensible diminution of temperature, of which the patient complains. Calorification, hoAvever, is not under the exclusive control of spinal innervation. The whole nervous system is probably concerned in it. It may perhaps be contended that the suspension of the capillary circu- lation in such cases, is owing to an enfeebled action of the arteries of the part. This might be admitted, if Ave suppose, with Hall, that the arterial trunks possess muscular coats, or proper irritabil- ity. In fact, the explanation of the phenomenon, depends on the question Avhether the vascular irritability, the power which is de- stroyed, in the examples under consideration, appertains to the arterial canals, or the capillaries ; for the action of the heart is ob- viously out of the question in the solution of the phenomenon. But the most important circumstance in these cases, in relation to the functions of the spinal cord is, that the part of the vascular system below the seat of the lesion of the spine, is paralyzed and 17 130 FIRST LINES OF PHYSIOLOGY. deprived of its power of moving the blood; a fact which demon- strates not only a certain general dependence of the circulating vessels upon the spinal cord, independently of the heart, but the influence of different portions of the cord upon the vessels of the parts which they respectively supply with nervous power. That the spinal cord exerts an influence upon digestion, is as- certained by pathological facts, and by experiments on living ani- mals. Thus, it has been observed, that the digestive functions are performed slowly and imperfectly in individuals affected with chronic diseases of the spine. According to Bourdon, lesions of the dorsal portion of the cord, are almost always accompanied or followed by colics, indigestion, obstinate affections of the kidneys, spleen, liver, ovaria, &c. Obstinate constipation, followed by in- voluntary evacuations, is a common symptom of affections of the spinal cord. The section of the cord between the fifth and sixth dorsal vertebrae in a dog, was found to destroy the power of evac- uating the bowels, an effect which was undoubtedly owing, in part, to the paralysis of the abdominal muscles, but which was partly to be ascribed to a loss of power in the muscular coat of the intestines, produced by the section of the cord.* From its power of stimulating the spinal cord, Serres recommends the tinc- ture of nux vomica in injections and frictions on the abdomen and lumbar region, in lead colic, and in protracted parturition from torpor of the uterus. The influence of the medulla oblongata upon digestion, is illus- trated by the effect upon chymification, produced by the division of the pneumogastric nerves. This operation in living animals has been found to produce a paralysis of the stomach, by which the muscular contractions of the organ are annihilated, and chym- ification brought to a stand. It appears, therefore, that the con- tractions of the muscular coat of the stomach, as well as those of the fibrous tissue of the bronchial tubes, depend on the influence of the medulla oblongata, transmitted by the pneumogastric nerves. The functions of the kidneys, also, are subject to the influence of the spinal marrow. In certain cases of injury or disease of the latter, the secretion of urine is totally suspended, and in others, it is more or less changed. The division of the spinal cord in the neighbourhood of the dorsal and lumbar vertebras, or the total destruction of it below the last cervical vertebra, has been found entirely to change the qualities of the urine, which has become perfectly limpid, like water, containing little or no animal extractive matter, but much of the saline and acid principles. The destruction of the medulla oblongata, and of the cervical portion of the cord, has occasioned an immediate suspension of the urinary function, though respiration was maintained by artificial means. Chronic affections of the cord are sometimes accompanied by a morbid * Ollivier. INNERVATION. 131 state of the bladder; as, chronic inflammation, or a copious se- cretion of vesical mucus. It has also been remarked, that para- plegia is a disease which, of all others, is most apt to occasion saline incrustations on sounds left in the bladder. The inferior part of the spinal cord appears to be necessary to the contraction of the uterus in parturition. Females who had previously borne children, have subsequently lost the power of giving birth to children, by an attack of paraplegia. No dilata- tion of the neck of the uterus, no expulsive pains, nor contraction of the organ has occurred at the time of pregnancy, and instru- mental aid has become necessary. The division of the lumbar part of the cord in rabbits, bitches, and some other animals, some time before the period of parturi- tion, has been found to prevent this process; and the animals die undelivered. If the section of the cord be made after parturition has com- menced, the uterine efforts suddenly cease, and delivery is pre- vented. On the other hand, the irritation of the spinal marrow in this region, produces abortion. Even in pregnant animals, abortion has been produced after decapitation by passing a wire downwards into the spinal canal. As soon as the stylet has reached the lum- bar region, uterine contractions, terminating in delivery, have taken place. In female rabbits and guinea pigs, the injection of the tincture of nux vomica into the crural veins, produces the same effect. According to some physiologists, the spinal marrow presides over the functions of nutrition. Rachetti * remarks, that the en- ergy of nutrition in animals, is in the inverse ratio to the mass of the brain, and in the direct proportion to the volume of the spinal marrow. It is to the predominance of this part of the nervous system, according to the same physiologist, that the Crustacea, insects, and worms, owe the remarkable property which they pos- sess, of reproducing parts which have been removed, or acciden- tally destroyed. The numerous connections of the spinal marrow with the great sympathetic, which has been generally considered as the nervous system of organic or vegetative life, strengthen the opinion that the former exercises some influence upon the organic functions. The connections of the great sympathetic and the spinal marrow are so intimate as to have led some physiologists to the opinion, that this nerve has its origin in the spinal marrow, or derives from the latter the greatest part of its nervous energy; and, in con- firmation of this opinion, it has been observed, that the develop- ment of the great sympathetic, in different classes of animals, is always in the direct ratio to that of the spinal marrow. On the ■gga.^.a 'Ollivier. 132 FIRST LINES OF PHYSIOLOGY. whole, it may be observed, that of all parts of the nervous system, the spinal marrow is most indispensable to life. Of the Nerves. It has already been observed that there are forty-three pairs of nerves which originate from the cerebro-spinal system, viz. two from the cerebrum, five from the pons Varolii, five from the me- dulla oblongata, and the remaining thirty-one from the vertebral spinal column. The structure of these cords has already been described. The cerebro-spinal nerves are subservient to sensation and mo- tion ; some of them to one of these functions only, the others to both. Thus the nerves of sight, hearing, and smell, are nerves of sensation only ; the oculo-motory, the trochlearis, the abducens, and some branches of the fifth pair, and the facial, are nerves of motion. But, with these exceptions, the nerves are both sensitive and motive ; or, as the German physiologists express it, indifferent. In their peripheral extremities, the nerves either retain their distinct and independent character, as is the fact with the optic, acoustic, &c.; or they become amalgamated with the other tis- sues. The more highly a nerve is endoAved with power, the more independent and isolated it is from the other soft parts. Thus, the nerves of specific sensation, as the olfactory, the acous- tic, and the optic, preserve their individuality in their peripheral expansions. While the nerves of common sensation, as those of the skin, are confounded and melted, as it were, with the tissues of this membrane, so as not to be separable or distinguishable from it. The periphery of the nervous system, however, is not confined to the outer skin, or the external parts of the body, but exists everywhere, where nerves are expanded, as in the muscles, the parenchyma of most of the organs, and some of the membranes. Cranial Nerves. The nerves which originate from the base of the brain are tAvelve pairs, and are called cerebral or cranial nerves ; the remain- ing thirty-one, which arise from the spinal marrow, are termed vertebral nerves. Of the cranial nerves, some are possessed of specific sensibility, as the olfactory, the optic, and the auditory. There are others subservient to voluntary motion, as the third, the fourth, the sixth, perhaps the seventh, and the eleventh; and a third class, whose functions are of a mixed character, as the fifth, the tenth, and perhaps the ninth, or the glosso-p/laryngeal. 1. Nerves of specific sensation. These are the first, second, and the eighth, or portio mollis of the seventh. The first, or the olfactory nerve, rises by three roots from the fore and under part of the corpus striatum, and, dividing into nu- INNERVATION. 133 merous fibrils, passes through the foramina of the ethmoid bone and is distributed on the septum narium, and the adjacent surface of the upper turbinated bone. This is considered as the nerve of smell. The second, or optic, is conducted to the optic thalami and the tubercula quadrigemina by two bands, which are extended from these eminences to the optic thalami. The two nerves unite in front of the pituitary fossa, and afterwards separate, and pass through the optic foramina, arrive at the posterior and inner part of the eyeball, and, piercing the sclerotica and choroides, terminate in the retina. This is the nerve of vision. The auditory, or eighth nerve, frequently called the portio mollis of the seventh, rises by two roots from the medulla oblongata. It accompanies the facial or the seventh, as long as it is contained in the cranium, and the internal auditory canal. At the bottom of this canal, it divides into branches, Avhich are distributed to the cochlea, vestibule, and semi-circular canals. These three nerves, together with the fourth pair, are isolated and have no anastomoses. They communicate only with the brain, and the organs to which they are respectively distributed; having no connection with the spinal marrow, nor with the great sympathetic. All the other nerves are connected together by communications, more or less numerous. 2. Nerves of voluntary motion. The cranial nerves, subser- vient to voluntary motion, are the third, the fourth, the sixth, the seventh, and the eleventh. The third pair, or the motores oculorum, arise by several fila- ments from the back part of the crura cerebri. This nerve is dis- tributed to five muscles in the orbit of the eye, and sends a fila- ment to the lenticular ganglion. By this ganglion it communi- cates with the fifth pair, and with the great sympathetic. The fourth pair, or the pathetic, are the slenderest nerves in the body. Each of these is attached by three or four filaments, be- neath the tubercula quadrigemina and the lateral part of the valve of Vieussens. They supply the superior oblique muscle of the eye. The sixth nerve takes its apparent origin from the outside of the anterior pyramid at the edge of the pons Varolii, and supplies the abductor muscle of the eye. It communicates with the third and the fifth pairs, and by means of these, with all the other nerves, except the four which have been mentioned as isolated from the rest. The eleventh, or hypoglossal nerve, arises from the fore part of the olivary tubercle by several filaments. These are collected together in two fasciculi, which unite to form one nerve. This nerve supplies the flesh of the tongue and several muscles of the throat, on which it bestows the power of motion. The seventh pair, or facial nerve, frequently termed the portio dura of the seventh, rises apparently betAveen the corpora olivaria 134 FIRST LINES OF PHYSIOLOGY. and restiformia. It enters the internal auditory foramen with the acoustic nerve, then leaves the latter, and passes out of the cra- nium by the stylo-mastoid foramen. It receives a filament of the Vidian nerve, Avhich enters the cavity of the tympanum, under the name of the corda tympani. The facial nerve furnishes fila- ments to the muscles of the tympanum, and the integuments of the ear. Upon emerging from the cranium, it enters the parotid gland, and is distributed to the muscles and integuments of the face. The seventh, according to Bell, is a nerve of instinctive, but according to Mayo, of voluntary motion. 3. Nerves of a mixed function. These are the fifth, the tenth, and perhaps the ninth, and the twelfth. The fifth, or trifacial, are the largest of the cranial nerves. They emerge from the sides of the pons Varolii in two fasciculi or roots, upon the larger of which, or the posterior, is formed a ganglion termed the Gasse- rian. Each nerve afterAvards separates into three divisions, viz. the ophthalmic, the superior maxillary, and the inferior maxillary. The first branch is distributed to the eyeball, the iris, the lach- rymal gland, the Schneiderian membrane, and the muscles and in- teguments of the forehead. The second division, or the superior maxillary, is distributed to the Schneiderian membrane, to the cheek, the nostrils, the palate, and the alveoli of the upper jaw. The third division, or the inferior maxillary, is distributed to the alveoli of the lower jaw, the submaxillary, and sublingual glands, the tongue, the masseter, the pterygoid, the temporal, and the buc- cinator muscles, and to the integuments of the temple and chin. The fifth pair communicates with the third, the sixth, the sev- enth, the eleventh, and with the great sympathetic ; forming of itself a kind of sympathetic nerve, by which all parts of the head are connected with each other, and with all other parts of the body. According to Sir C. Bell, the branches of the fifth pair, which emerge upon the face to supply the muscles and integuments, are, like the spinal nerves, subservient to sensation and voluntary mo- tion, jointly; but Mayo cantends that the facial branches of the fifth are exclusively sentient nerves ; while the twigs Avhich supply the masseter, the temporal, two pterygoids, and the circumflexus palati, derived from the smaller fasciculus of the fifth, which is destitute of a ganglion, are nerves of voluntary motion. The sentient branches of the fifth, are nerves of common sensa- tion, viz. to the face, and to the organs of specific sensation, the eyes, nostrils, mouth, &c.; but its third branch, the inferior max- illary, furnishes the tongue with a nerve, which is considered as the gustatory nerve, or the peculiar nerve of taste. The tenth pair, or the pneumogastric nerves, commonly called the eighth pair, arise from the medulla oblongata, immediately beneath the glosso-pharyngeal. They emerge from the cranium through the foramina lacera posteriora, in company with the ninth, INNERVATION. 135 or glosso-pharyngeal nerves, and the twelfth, or accessory nerves ; and descend on the lateral parts of the neck, with the great sym- pathetic, on the outer side of the primitive carotid, and posterior to the jugular vein. They distribute branches to the larynx, trachea, lungs, pharynx, oesophagus, stomach, duodenum, liver, spleen, and kidneys. This important nerve establishes the principal connection be- tween the two departments of the nervous system, and is the bond which unites together the vital, nutritive, and animal functions. It forms a communication between the organs contained in the three great cavities of the body, viz. the brain, heart, lungs, and stomach. With the fifth and the seventh, it constitutes the prin- cipal connection between the organs subjected to the will, and those Avhich are not under the control of this principle. In a word, it unites the two lives of Bichat, the animal and organic. In its whole course it gives twigs to the ganglions, and contri- butes to form, with their own proper filaments, the principal plexuses of this system. The branches of the pneumogastric nerves, Avhich are distributed to the larynx, lungs, oesophagus, and stomach, appear to be nerves both of sensation and of involuntary motion. The ninth, or glosso-pharyngeal nerve, is attached by several filaments in the line which separates the corpora olivaria from the corpora restiformia. These filaments unite into a single cord, which, after its exit from the cranium, sends a filament to the au- ditory canal, and receives one from the facial, and another from the pneumogastric nerve. It furnishes branches to the root of the tongue, and to the upper part of the pharynx, and bestows the power of motion on the muscles of these parts. According to Mayo, the branches sent to the root of the tongue are sentient only, but those distributed to the upper part of the pharynx, are subservient both to sensation and voluntary motion; an opinion founded on the fact, that, on irritating the glosso-pharyngeal nerve in an animal recently killed, the muscular fibres about the pharynx were found to act, but not those of the tongue. The twelfth pair, or the accessory nerve of Willis, arises from the lateral part of the spinal cord in the upper part of the neck, by numerous filaments, then ascends and enters the foramen magnum of the occipital bone, and passes out by the foramen lacerum pos- terius, with the pneumogastric, to Avhich it sends a filament. It furnishes fibrils to the pharynx, but the greater part of it assists the spinal nerves in supplying the sterno-cleido-mastoid, and the trapezius muscles, on which it bestoAvs the power of motion. It appears also to be a nerve of sensation; for, irritating it excites pain, and consequently in its functions it resembles the spinal nerves. The Vertebral Nerves. The vertebral nerves are more uniform in the manner of their 136 FIRST LINES OF PHYSIOLOGY. origin, and regular in their distribution, than those which originate at the base of the brain. Each vertebral nerve arises by two dis- tinct roots, an anterior and a posterior, and each of these roots is composed of several filaments. The posterior filaments form a ganglion before they join the anterior to make up the entire spinal nerve. These nerves, thus springing from two roots, possess the double property of conveying, in opposite directions, sensific and motive impressions. If a vertebral nerve is divided in any part of its course, the parts to Avhich it is distributed are deprived both of their sensibility and of their poAver of motion. But if the two roots are divided separately, different effects are produced. The division of the anterior roots destroys the power of motion of the parts supplied by the nerve, without impairing its sensibility; Avhile the section of the posterior roots, without affecting the power of motion, abolishes the sensibility. Each of these nerves, therefore, consists of tAvo orders of filaments, which perform dif- ferent offices, one conveying sensific impressions from the parts to Avhich they are distributed to the spinal marrow: the other, transmitting motive impressions from the cord to the muscles of voluntary motion. The vertebral nerves, then, are distinguished by the regularity of their origin and distribution, from those which originate at the base of the brain. They differ from the latter, also, in originating by double roots, and in the circumstance that one of their roots swells out into a ganglion. One of the cranial nerves, and one only, Ariz. the fifth, resembles the vertebral nerves in these respects. On this account, the fifth pair of cerebral nerves is classed by Sir C. Bell with the vertebral; and is supposed to resemble them in its functions, as it does in its structure. Functions of the Sympathetic Nerve. The functions of the great sympathetic are not known. In the neck, and the canalis caroticus, it furnishes branches to the great vessels, and to the heart; in the chest, branches which are dis- tributed to the viscera of the abdomen, and in the abdomen, others to the pelvic viscera. The same organs, however, are supplied Avith nerves from the encephalic system. The common opinion seems to be, that the great sympathetic presides over the organic or involuntary functions, as secretion, nutrition, absorption, calori- fication, &c. It is also supposed to be, as its name imports, the source of the numerous sympathies Avhich unite the viscera of organic life into one great connected system. By some physiolo- gists, the ganglions of this nerve are supposed to render the organs which are supplied Avith nerves from them independent of the will. In herbivorous animals, which employ most of their time in eating, the sympathetic nerve is very large, corresponding with the voluminous viscera of these animals. INNERVATION. 137 The sympathetic is possessed of scarcely any sensibility. Whatever may be the functions of this nerve, every part of the body must be under the influence of its innervation by means of the branches with which the blood-vessels are supplied, and which penetrate with them into the interior of all the organs. BelVs Classification of the Nerves. From the regularity of their origin and distribution, the spinal nerves, including the fifth cerebral, are termed, by Sir. C. Bell, the regular, or the symmetrical nerves. They are distributed laterally to the two halves of the body, including both limbs and trunk, are subservient to common sensation, and to voluntary motion, and, as we are instructed by comparative anatomy, are common to every class of animals. Most of the other encephalic nerves constitute, according to Bell, another system, which he terms the superadded or irregular, which he considers as forming a complex associated system, sub- servient to respiration. Sir C. Bell remarks, that the motions de- pendent on respiration, extend nearly over the whole body, while they more directly affect the trunk, neck, and face. This is par- ticularly true of respiration when in a state of unusual activity, or while the individual is under the influence of strong passion or emotion. There is, also, a great variety of actions which are con- nected with respiration, and Avhich require the aid of the respira- tory muscles, such as coughing, sneezing, laughing, sAvalloAving, vomiting, and speaking. Now all these actions, though not sub- servient to respiration, are so connected with this function, that they necessarily require the aid of the muscles of respiration, as well as that of others peculiarly destined to them; and this con- nection establishes associations of the respiratory muscles with many others, and extends the influence of respiration over many other functions of the system. Respiration, also, exists in various degrees of activity. In its ordinary state, and in sleep, it is an involuntary action. But, in many cases, as, e. g. when any obstruction exists to the ordinary movements of inspiration, or when it is intended to perform some voluntary action, Avhich requires the aid of respiration, as smell- ing, or speaking, it requires the aid of volition. In dyspnoea, vio- lent efforts are made to expand the thorax, by elevating the shoul- ders • and in highly excited respiration, the movements are not confined to the chest, but affect simultaneously the abdomen, tho- rax neck throat, lips, and nostrils. It is evident, then, that what- ever may be the design of this extensive connection of respiration with other functions of the system, it must be effected by an asso- ciation of a great variety of muscles, animated by some common influence ; and the nerves concerned in establishing this connec- 18 138 FIRST LINES OF PHYSIOLOGY. tion, are termed by Bell the respiratory nerves, and form a system distinguished from the spinal, by the irregularity of their distribu- tion. They originate also from one root only, and are destitute of ganglions at their origin. These nerves arise very nearly to- gether in a series, from a tract of medullary matter on the side of the medulla oblongata, between the motor and sensitive columns. From this fasciculus, or column, arise in succession, from above dowmvards, the portio dura of the seventh, the glosso-pharyngeal, the par vagum, or tenth pair, the spinal accessory, and, as Bell thinks, the phrenic, and the external respiratory. Bell also sup- poses that the branches of the intercostal and lumbar nerves, which influence the intercostal muscles, and the muscles of the abdomen in the act of respiration, are derived from the continuation of the same cord or slip of medullary matter. The respiratory, or super- added system of nerves, therefore, consists of the portio dura of the seventh or the facial nerve; the tenth or pneumogastric ; the phrenic, which is distributed to the diaphragm; the spinal acces- sory, which supplies the muscles of the shoulder; and the exter- nal respiratory, which is spent on the outside of the chest. HalVs Classification. Hall has made a new classification of the nerves and nervous system, which appears to have a foundation in physiological truth. He divides the nervous system into, 1. The cerebral, or sentient and voluntary. 2. The true spinal, or excito-motory. 3. The gangli- onic, or nutrient, secretory, &c. The second class, or the excito- motory, he claims the merit of having first pointed out himself. The 1st class comprehends all parts of the nervous system which are concerned in sensation and volition, the nerves of specific sensa- tion and of touch; and those of voluntary motion. The cerebrum and cerebellum are the centre; its sentient nerves proceed from the organs of sense and from the external surfaces, imvardly to- wards the centre ; its voluntary nerves pursue a course the reverse of this, from this centre to the muscles of voluntary motion. The sentient nerves belonging to this class are : the first; sec- ond ; fifth; eighth, or auditory; the ninth, glosso-pharyngeal or gustatory ; and the posterior spinal. The voluntary are : the third, or oculo-motory ; the minor portion of the fifth ; the myo-glossal, or twelfth ; and the anterior spinal. The 2d class, the excito-motory, or true spinal, comprises the tu- bercula quadrigemina, the medulla oblongata, the medulla spinalis, and the true spinal nerves, embracing the excitors and the motors. (a) The excitors belong chiefly to the fifth, the pneumogastric, and the posterior spinal nerves. The excitor branches of the fifth, going to the eyelid, nostril, fauces, and face; those of the pneu- mogastric, to the larynx, pharynx, lungs, and stomach; those of INNERVATION. 139 the posterior spinal nerves, to the anus, cervix vesicae, cervix uteri, and general surface of the body. (b) The motor or reflex branches are : the seventh, to the orbi- cularis ; the fourth and sixth, to the eyeball; the tenth, or pneu- mogastric, to the larynx and pharynx; the spinal accessory, the phrenic, and the inferior external respiratory, to the muscles of respiration; the spinal nerves, to the sphincters, ejaculators, and uterus. Spinal nerves are also distributed to the general muscu- lar system, as nerves of tone. The 3d class is composed of two divisions, an internal and ex- ternal. The internal includes the sympathetic, and probably fila- ments of the pneumograstic. The external ganglionic embraces the fifth and the posterior spinal nerves. The existence of the 2d class, or division, which forms the chief peculiarity of Hall's classification, is founded upon various facts and experiments. In an animal stunned by a blow with an axe on the head, and deprived of sensation and voluntary power, mechanical irritation by a sharp instrument, as pricking or lace- rating the face or surface of the body with a nail or pin, excited no motion, nor any evidence of sensation; but when the eyelash Avas touched with a straw, the eyelid was forcibly closed by the action of the orbicularis ; and when the cornea was touched, the eyeball rolled outwardly by the action of the abducens. When the margin of the anus was touched, the sphincter contracted forcibly, the tail was raised, and the vulva was drawn towards the anus; motions which were executed after the abolition of con- sciousness and volition; and which Hall terms excito-motory. Respiration also continued. The upper part of the medulla ob- longata was then destroyed, when, after some convulsions, respira- tion ceased, and the eyelid and eyeball remained motionless on the application of stimuli. In like manner, the division of the spinal marrow below the occiput, in a frog, instantly abolishes all traces of sensation and of voluntary poAver. All is still. But on pinch- ing a toe with the forceps, both posterior extremities are excited to motion. If the integuments be pinched, the excito-motory phe- nomena are immediately produced. But on destroying the spinal marrow with a probe, these results are no longer obtained; the limbs remain motionless notwithstanding the toes are pinched. Cerebral diseases confirm these conclusions. In apoplexy there is complete insensibility, blindness, deafness, &o., yet respiration continues, and the sphincters do their office. In hydrocephalus there is perhaps total blindness, with dilatation of the pupil; and the eye does not wink on the near approach of a finger to the cor- nea ; yet a slight touch of the tip of the eyelid produces an imme-. diate closure of the eye. Filaments of the fifth pair are the excitors of the edges of the eyelids and surface of the eyeball, of the nostrils, face, and per- haps the fauces; and are the agents first concerned in causing 140 FIRST LINES OF PHYSIOLOGY. closure of the eyelids, in sneezing, vomiting, and sobbing, when the eyelash is touched, the nostrils irritated, the fauces stimulated, or cold Avater is dashed in the face. Other nerves convey the reflex influence from the medulla oblongata to the orbicularis, and the respiratory muscles in these cases. Filaments of the pneumogastric are the excitors of the larynx and bronchia, the pharynx, and stomach, in the irritation produced by carbonic acid or a drop of water coming in contact with the larynx ; in the dyspnoea caused by inhaling the dust of ipecac ; in deglutition ; in ordinary respiration ; and in vomiting produced by antimony, or by calculi in the gall duct or ureter. It is a curious fact, Avhich serves to illustrate the functions of the excitory filaments of the fifth and the pneumogastric, that irritating the former in the fauces induces vomiting, while exciting the lat- ter in the pharynx occasions sAvallowing. Hence it has sometimes happened that a feather employed to excite vomiting by tickling the fauces, has, by being carried into the pharynx, excited an act of deglutition, and been drawn into the oesophagus. A similar result has sometimes occurred in the introduction of instruments or irritating substances into the urinary passages and into the rectum. Respiration is regarded by Hall as belonging to the class of func- tions depending on the excito-motory system of nerves. He thinks it probable, from facts, that the acts of inspiration are excited by the contact of carbonic acid with the filaments of the pneumogastric in the lungs. It appears that after repeated deep inspirations, by which the air in the lungs, and of course the carbonic acid, is completely exhausted, respiration can be suspended longer than under ordinary circumstances. Hence the impossibility of suspending respiration beyond a certain time. Pinching the pneumogastric nerve in an experiment, produces an act of inspiration ; but the fifth and the spinal nerves are also excitor nerves of this function. Hence dash- ing cold water in the face, and plunging into the sea or cold water, excites an act of inspiration. The medulla oblongata combines the action of the different muscles together in the acts of respiration. Deglutition is also an excited act, requiring the presence of some stimulus or substance to be swallowed. Hence it is impossible to swallow several times in rapid succession, without taking something into the mouth. Yet the contact of the finger with the pharynx of a dog, by passing it through an incision into the throat, excited deglutition very evidently, in an experiment of Magendie. Cold water dashed on the surface of the body excites other func- tions belonging to this class besides respiration. Applied in this manner to the feet and legs, it will sometimes cause a relaxation of the sphincters, and the expulsion of the urine and fasces. The first act of respiration after birth may be explained on the same principle. The whole tone of the muscular system, Hall infers to be the result of an excito-motory function. He observes that the limbs of an animal, separated from their connection with the cerebrum, INNERVATION. 141 become relaxed on destroying the spinal marrow. The limbs and tail of a turtle, whose head had been cut off, were irritated by a pointed instrument, or taper, and were instantly excited to rapid motion. The sphincter remained closed, and perfectly circular; and contracted still more forcibly on the application of a stimulus.' On removing the spinal marrow from its canal, the limbs lost their firmness and tone, became perfectly flaccid, and no longer responded to stimuli applied to them ; the sphincter lost its circular form and its contracted state, and became flaccid and relaxed; the tail in like manner 1 ost its tone, and was unaffected by stimuli. Similar effects are produced in separate portions of the animal, as the head, lower or upper extremities, and tail, when separated from the body. The 3d division of the nervous system embraces the ganglionic nerves. Hall divides it into external and internal, the latter inclu- ding the sympathetic, and perhaps a part of the pneumogastric; the former embracing all the other ganglionic nerves, especially the fifth and the posterior spinal. These last Hall supposes to be provided with ganglia like the sympathetic, because they are des- tined to a similar office ; viz. nutrition. Hence he terms them external nutrient nerves, as the sympathetic constitutes the nutri- ent nerve for internal parts. In short, the fifth and posterior spi- nal nerves he regards as the external part of the ganglionic system. But these external ganglionic nerves involve sentient and excitory nerves with the nutrient; and hence their ganglia differ in appear- ance from the ganglia of the sympathetic, partaking in some degree of the character of plexuses. Hall adduces in proof of his views of the nutrient function of the fifth, the fact that if sensation in the face be abolished by disease or compression of the fifth within the cranium, the eye ceases to be nourished and is destroyed. If the loss of sensation be the effect of disease of the brain, the eye is not involved. Psychological Functions of the Brain. The psychological functions of the brain require a more extended notice in this place, although it is impossible even to touch upon them, Avithout trespassing upon the domains of another science, In- tellectual Philosophy. Some defect of method is unavoidable, and in itself of little consequence. In fact, in relation to the functions in question, Physiology and Intellectual Philosophy contemplate the same phenomena from different points of view ; and in both cases it may assist us in obtaining clearer ideas of the objects we are contemplating, if we shift our position and view them under a different aspect. The psychological functions of the brain may be divided into three classes, viz. the faculty of knowledge ; the feelings or emo- tions ; and the desires; or the cognitive, affective, and appetitive faculties. 142 FIRST LINES OF PHYSIOLOGY. I. Faculty of Knowledge. This faculty, as may be inferred from its name, comprehends all those powers which are employed in acquiring knowledge. Knowledge, though referring to objects which exist out of the mind, or to the mind itself, regarded as the object of its own pow- ers, is itself purely a mental phenomenon; consisting in certain modes or affections of consciousness, which on an ultimate analy- sis, will be found to be composed of certain internal perceptions, which Ave term ideas, and of various connections or relations existing between them. The acquisition of ideas then, and the discovery of the relations between them, and of the laws which regulate their succession, is the great office of the faculty of knowledge. The acquisition or formation of ideas may be called ideogenesis ; the discovery of the relations or connections between them is the office of judgment and reason. The order in Avhich they succeed each other is determined by a law which has been called the association of ideas. Ideogenesis, judgment, and rea- son, and association, therefore, are the three grand functions of the faculty of knowledge. 1. Ideogeny. The first of these powers, ideogenesis, is com- posed of several sub-faculties, all of which are called into exer- cise in the formation of ideas. But. a faculty preliminary in its exercise to them all, and which, instead of belonging to their num- ber, only furnishes materials or occasions for their exertion, re- quires first to be noticed. This is the power of sensation. Sen- sation is that affection of consciousness which is produced by the impressions made on the senses by external objects. Two things are to be carefully distinguished in sensation, viz. the physical and the psychological part of the process. External objects act upon or impress our organs of sense by their physical properties, and the impression itself is purely of a physical character. But a remarkable and inexplicable consequence of this impression is, that a certain feeling is excited in our minds, which has a strict correspondence with the nature of the impression, and of course, with the sensible qualities of the object which produces it, but which has not, and, from the nature of the case, cannot possibly have, any conceivable resemblance to the latter. This feeling is termed sensation. The number of sensations which are excited in our minds by material objects are almost unlimited, and when illuminated by the powers of the understanding, furnish us with the most ample materials of knowledge, yet the whole world of sensation by itself, is incapable of imparting to us a single ray of knowledge. These varying states of consciousness must be brought under the cognizance of the intellectual faculty, to enable us to form from them a single idea, or to learn a single truth. In short, our sen- sations must be intellectualized before they can be converted into INNERVATION. 143 knowledge. As we are constituted, indeed, the senses are con- stantly exciting the faculty of judgment into action, so that sen- sation at a very early period of life becomes almost inseparably blended Avith perception. But the tAvo powers are totally distinct in their origin, and may be clearly discriminated in their nature and results. A being endued with the mere powers of sensation, even in the highest possible degree, Avould be incapable of know- ing or of learning any thing Avhatever. He would be simply con- scious of certain sensations, or of various modifications of his own existence, and of nothing more. This consciousness would neither acquaint him with the existence of external objects, nor of him- self ; nor even with that of the sensations, of which he was con- scious ; for the knowledge of these facts necessarily involves ideas and perceptions, which sensation alone can never furnish. But if we now suppose him to be suddenly inspired with this subtle in- tellectual sense, and the phenomena of his consciousness to be brought under the eye of his own understanding, he would in- stantly perceive the objects which he only felt before; and not only these, but a multitude of others, which he had not before observed, because they are not visible to the eye of sense. New objects would be occasionally starting up from among those he had been contemplating, where they had been lurking, as it were, before, until the light of the understanding shone in upon them, and laid open their hiding-places to his view. Among the earliest truths he thus would acquire, would be the knowledge of his own existence, and that of the existence of external objects, as the cause of his sensations ; besides numerous other ideas, Avhich would immediately spring Lip in his mind, wholly unlike his sensations, and Avhich by no power of analysis could be deduced from them. It appears, therefore, that sensation is not one of the cognitive or intellectual faculties. Its proper office is to furnish materials or occasions for the exercise of these powers. 2. Conception. The actual formation of ideas may be said to commence with conception. By this is understood the faculty of reviving the states of mind, or of consciousness produced by sen- sible impressions, in the absence of the objects which occasioned them ; or rather, it is the power of thinking of our sensations. This is the first and simplest exercise of the ideopoietic faculty. It furnishes us with all our sensible ideas, and in a certain sense, is the avenue by which all knowledge enters the mind. Our conceptions are faint images or copies of our sensations, and they form the first step in intellectualizing sensations, or in converting them into knowledge. Without this power, knowledge would be impossible. We should be merely subjects of various sensible impressions, which would be constantly giving place to others, and vanishing away without leaving a trace in the mind, by which they could be recalled. By means of this power, we are able to multiply copies of our sensations to any extent, to be employed 144 FIRST LINES OF PHYSIOLOGY. afterwards as materials in various intellectual processes. Memory, imagination, and association, are modes of this power. Of the physical part of this process Ave know nothing. But as in every case of sensation, there is a certain configuration of the organs of sense, produced by the impression of the external object, and a certain change also in the physical state of the brain, it seems probable, that in conception, a similar condition, both of the organ of sense and of the brain, exists, since the state of our con- sciousness in conception is a kind of shadow or faint image of that which exists in sensation. That such is the fact, seems to be proved by the phenomena of spectral illusions, which appear to originate not merely in the state of the mind, but also in the physical condition of the brain and nervous system, and some- times in that of the organs of vision alone. 3. Attention. Another faculty, of essential importance in the production of ideas, is attention, or the power of directing the mind to a sensation or idea, or any of its elements ; or of keeping the object we are viewing steadily before the mind, to the exclu- sion of all others. This faculty is one of the functions of the will. When an idea, or any of its elements, is made the object of attention, it starts out in strong relief from the cluster with which it was associated, and takes its place in the very focal point of the intellectual eye. It is to be remembered, that solitary im- pressions are never made upon us: we are constantly surrounded by multitudes of objects, all of which are appealing to our senses, and producing collectively very complex and mingled impressions, which without the power of attention could never be separated into their constituent parts, and converted into ideas. In this analysis, it is true, the poAver of attention is aided by the senses, as Avell as by certain powers of internal perception. Thus, a sin- gle object, as a peach, e. g., may address itself to several of the senses, as the sight, touch, smell, and taste, at the same time. The object is one, and is recognised to be such, yet the senses uncon- sciously analyze the collective impression produced by it into four distinct elements, Avhich, diverging, as it were, from the object, and exciting their appropriate sensations in the different organs of sense, afterwards converge from these towards the centre of per- ception, where they reunite, and receiving certain intellectual elements from the mind, are organized into an idea of the object. These intellectual elements are necessary to complete the idea of the object, and they constitute the basis of many judgments which we form respecting it. Without them we could never know that the peach Avas any thing more than a collection of certain proper- ties, without any basis or bond of union; or rather, we could know nothing whatever about it. By this power, directed towards the phenomena of our own con- sciousness, we obtain the knowledge of our mental operations, states of feeling, and intellectual faculties. But in every case of INNERVATION. 145 this kind, to the results of the analysis of the phenomena of con- sciousness, affected by attention, there is ahvays superadded an element furnished by the mind itself, which is necessary to con- vert the sentiment into an idea ; and until this is accomplished, nothing can be predicated of them by the mind, and no judgment whatever formed of them. We are necessarily conscious of all our mental acts and feelings. We are conscious of seeing, hear- ing, willing, thinking ; of pain, pleasure, hope, joy, &c. By the exercise of attention, we are able to detach the idea of the men- tal act or feeling, from the confused and mingled field of con- sciousness, and by a certain mental abstraction, to bestow individ- uality and a kind of personal existence upon it, under the shape of a distinct idea. In this manner, we acquire ideas of our men- tal operations and affections, and by a further process, in which another faculty, judgment, is concerned, we obtain a knowledge of our mental faculties ; ideas which consciousness alone could never furnish. It is probable that all the varying states of con- sciousness, sensation, Abolition, perception, &c, are accompanied each with a corresponding physical change in the state of the brain. And if this be admitted, it will not be difficult to conceive that the reflex, or intellectual act of the mind, may be exerted on any portion of this physical process, which will then become a special object of attention ; and perhaps be performed with greater energy, or reiterated, so as to produce a stronger consciousness of itself; two circumstances in which perhaps the essence of at- tention as to its physiological and intellectual condition consists. In this manner the intellectual elements of an idea, as well as the sensible, may become objects of attention, and be isolated from their associates. 4. Judgment. Another important faculty employed in forming ideas is judgment, which is defined to be the poAver of perceiving the relations betAveen objects or phenomena, or rather between the ideas we form of them. Noav these relations constitute a dis- tinct class of ideas, wholly different from those, betAveen which they are perceived to exist. They are not derived from sensation, nor are they copies of any thing. They are the offspring of the mind itself, springing from a peculiar internal power of perception, which is termed judgment. An immense number of ideas is derived from this source, for scarcely any two objects can be mentioned, between which some kind of relation will not be perceived to exist. The number of these relations, and of the ideas derived from them, is absolutely unlimited and they constitute an inexhaustible source of knowl- edge. Let us take a single relation, e. g., that of resemblance, and contemplate for a moment its prodigious fecundity in ideas and materials of knowledge. Take any number of objects, the most dissimilar that can be conceived of, as, e. g., a steam engine, the 19 146 FIRST LINES OF PHYSIOLOGY. moral essence, justice, a fit of the gout, and the idea of nothing, and though at first we might be puzzled to conjecture any shadow of resemblance or analogy between them, yet a moment's reflec- tion will teach us that they all agree, at least in one respect, viz. in being objects of thought to the same thinking mind ; an agree- ment, or resemblance, Avhich enables us to apply the same denom- ination (things quasi thinked of) to all of them, however dissim- ilar they may be to the same mind under every other point of view. And this agreement or resemblance is precisely as real, as far as it goes, as that between sensible objects which make simi- lar impressions on the senses, as trees, floAvers, quadrupeds, &c. In the above-mentioned example, the resemblance consists in the sameness of relation of these objects to the human understanding. In descending from the most general relation of objects to the mind, Ave shall find that they assume other relations to the un- derstanding, superadded to the universal one of being objects of thought; relations which are sources of other resemblance be- tween them. Some have objective, others only subjective exist- ence ; i. e. some exist out of the mind ; others exist only in it. The former include matter and spirit; the latter, mathematical and other kinds of intellectual truth. To pursue the descending series still lower, things Avhich have a real or objective existence, may be divided into corporeal and incorporeal. The former, in addi^ tion to the two more general resemblances mentioned above, have another superadded to them, viz. they all possess body ; the latter have the common resemblance of being all destitute of it. In descending a step loAver in the scale of this relation, we shall discover, that as hitherto resemblance appeared to consist in the sameness of relation to the human intellect, Avhen we arrive at the class of corporeal substances, a neAV resemblance is superadded, which consists in the sameness of relation to the senses. For all corporeal substances possess certain relations to the senses, by means of Avhich they produce certain impressions upon them, be- tween Avhich the judgment recognises the relation of resemblance. In relation to the sense of vision, corporeal substances may be classed into visible and invisible ; in relation to touch, into palpa- ble and impalpable, and so on. These resemblances, consisting in similarity of relation to the senses, will be constantly accumu- lating as we pursue the division of the objects of thought in the descending scale. Thus, visible objects may be divided into col- oured or colourless ; coloured, into red, blue, green, &c. ; palpable, into hard, soft, solid, liquid, &c. By a similar process, we dis- cover resemblances betAveen certain powers or properties of mind which enable us to class them together, and to bestow upon them certain common appellations. In the exercise of the senses, the judgment recognises the similarity of the processes, and all the acts of the senses are thus connected together by the relations of resemblance. So in perception, in willing, and in the acts of judg- INNERVATION. 147 ment itself. It is apparent then that this single relation of resem- blance is pregnant with the most important results in the acquisition of human knowledge. It is the basis of all classification and all general knoAvledge ; it is indispensable to the formation of lan- guage ; and it is the germ of the vast science of mathematics. All general knowledge is founded upon it; for it is only so far as objects resemble one another that the same things can be pre- dicated of them. Objects are arranged in classes only in conse- quence of certain resemblances perceived to exist between them. Hence without this relation no classification would be possible ; and all knowledge would be limited to particular truths. Language is also founded upon this relation. All Avords in any language, except proper names, express general ideas ; that is, ideas of objects, or their qualities and relations, Avhich so far resemble each other as to receive the same common appellation. All names of objects, their qualities, actions, and relations, are general terms, and Avithout the poAver of perceiving the relations of resemblance betAveen the objects of thought, so as to lay a foundation for clas- sification, language could never have been invented, for no intelli- gible language Avould have been possible. No word would admit of more than a single application, and hence it would be manifestly impossible to learn the signification of any Avord until it had be- come worthless and incapable of further application. The idea of number, also, is derived from this perception of resem- blance. The basis of number is unity. But the idea of one could never be detached from the idea of a single object, but by com- paring it Avith one more object at least. The idea of unity is an intellectual element added to our idea of an object; but it cannot be disengaged from it but by repetition of the idea. The very essence of unity consists in its involving the idea of plurality, i. e., in its being convertible into plurality merely by repetition. The repetition of an impression or idea, therefore, is absolutely necessary to enable us to perceive the oneness of a single impres- sion or idea, or to detach from it the intellectual element, unity, superadded by the mind. It is impossible for us to apply the term one to any words but such as are expressive of general ideas. Objects must be generalized by the relation of resemblance, before they can be individualized by annexing to them the conception of unity. Noav number is the basis of the science of mathematics, which may therefore be traced to a single relation, that of resem- blance betAveen the objects of thought — as the power of abstraction is derived from the faculty of attention, so generalization is the result of the same faculty, aided by the judgment in the perception of resemblance. There is one important class of conceptions or ideas of a very peculiar kind, which are formed by certain primitive and intuitive judgments. In the ordinary exercise of judgment, the comparison of two ideas is necessary to enable the mind to perceive the rela- 148 FIRST LINES OF PHYSIOLOGY. tion between them. But in the case in question, a single idea only is presented to the mind, and it immediately excites another totally different from the first, but connected with it by an indis- soluble relation. The idea itself instantly suggests or rather in- volves the relation, which leads by a fine film of thought, forming a kind of intellectual bridge, to a second idea or conception, wholly unlike the first, and especially distinguished by its irresistible ne- cessity. Thus a single sensation or act of consciousness instantly suggests the idea and belief of our OAvn existence, Avith a force of conviction which no power of reasoning can either increase or di- minish. The idea of body, however formed, leads to the concep- tion of space in Avhich it exists ; for space is the logical condition of the existence of body. It is impossible to conceive of body but as existing someAvhere, that is, in space ; and the moment this idea is formed, we feel an irresistible conviction of its absolute ne- cessity, that is, we feel the impossibility of conceiving of the non- existence of space. The idea once formed, becomes wholly inde- pendent of that which suggested it, and from the narrow dimen- sions of the particular substance which -first aAvakened it in our minds, it instantly swells to an illimitable and inconceivable extent, and becomes one of the most immovable convictions of the human mind. The idea of body, then, which is that of something both contingent and limited, leads to the conception of space, or of something which is of unlimited extent and of absolute necessity. In a similar manner are formed the idea of time, of infinity, of cause and effect, of substance, personal identity, and some others. One most important idea, viz, that of right and wrong, and of merit and demerit, the former referring to certain actions, the lat- ter to the agents who respectively performed them, may be traced to a similar origin. In performing certain actions we feel a certain sentiment, viz. that Ave have done right ; in performing certain others, Ave are conscious that Ave have done wrong. In attending to this consciousness, we separate the sentiment of right involved in it from the action which produced it, and this sentiment is then converted into the idea of right; we become sensible of the distinction of right and wrong, and we feel that it is engraved in indelible characters on the human mind. It imme- diately becomes a universal and necessary idea, and constitutes the basis of the science of morals. As this class of ideas is distinguished by peculiar characters, and as it is the result of a special function of judgment, the faculty by which they are produced is referred by some metaphysicians to a separate and higher power of the mind, viz. reason. Reason has been defined by one of its most zealous advocates, as a distinct faculty, " the power of universal and necessary con- victions, the source and substance of truths above sense, and hav- ing their evidence in themselves." It transcends experience, and, as Coleridge remarks, " it avails itself of a past experience, to su- INNERVATION. 149 persede its necessity in all future time; and affirms truths which no sense could perceive, nor experiment verify, nor experience con- firm." Stewart also suggests the appropriation of the term reason to the faculty by which these truths are learned. From this brief analysis of the sources of our ideas, it will ap- pear, that in relation to their origin, they may be divided into three classes, viz. 1. Ideas of sensation, or sensible ideas. 2. Ideas of judgment, or of relation. 3. Ideas of reason, or transcendental ideas. A single impression made upon the senses by an external object, is sufficient to excite ideas of all the three classes. Thus, for ex- ample, let a person receive a blow upon the head from a hard sub- stance, as a stone, and let us consider what ideas might be excited in his mind by this impression. 1. The idea of the impression. 2. The idea of himself as the subject of it. 3. That of the ex- ternal substance Avhich produced it. 4. The idea of causation, from considering the external body as the cause of the sensation. 5. The idea of space, as necessarily involved in that of the body. 6. That of time, derived from the idea of the duration of the im- pression ; and several others. Now none of these but the first are derived from sensation ex- cept chronologically. But by the constitution of the mind, the first suggests the others by a kind of primitive judgment; and thus an idea of sensation begets a numerous progeny of others, which bear no resemblance whatever to the parent idea. This serves merely to fecundate the mind, which contains innumerable germs of thought, which otherwise Avould never be developed. II. Judgment and Reason. From what has been said, it appears that judgment and reason are sources of ideas only indirectly; their true functions are to discover the connections and affinities of thought; to perceive, but not to individualize the relations betAveen ideas. They connect ideas by a fine film of thought, a sort of intellectual bridge, which is termed a relation. By an act of attention, this is detached from the two ideas which it serves to connect, contemplated by itself, and converted into an idea. The process of the judgment then is synthetic. Ideas are placed in a mental juxtaposition by this faculty, but they are afterAvards separated by an act of attention, which seizes upon the intermediate or connecting idea, and be- stows upon it a separate existence. Before this analysis has indi- vidualized the connecting idea, the relation is felt, but not, strictly speaking, perceived. But after the sentiment of relation has been converted into an idea by the attention, then, in a subsequent ex- ercise of the judgment, the relation is not only felt, but perceived; and if expressed in language, it is then affirmed. 150 FIRST LINES OF PHYSIOLOGY. The office of judgment and reason then, is not the discovery of ideas, but of truths; they present us new ideas, not in a sepa- rate state, but folded up as it Avere with other ideas, in the form of mental propositions. From these the ideas of relation are disen- tangled by the faculty of attention, and then first assume the character of independent ideas. A connected series or chain of judgments is termed reasoning, Avhich is a progressive evolution of truth from certain premises or propositions. In all sound reasoning, the last proposition or con- clusion is contained in the first. For example : 1. Man is a rational but selfish being. 2. A selfish being will seek his own interest, even at the expense of others. 3. A being Avho will seek his own interest even at the expense of others, needs some restraint for the security of others. 4. A rational being.Avho needs to be restrain- ed for the security of others, must live under laws. 5. Man must live under laws. This last proposition, it will be perceived, is involved in the first, rom which it is unfolded by a progressive analysis or series of judgments. This property of eliciting truth by linking a series of judgments together, is considered as one of the functions of reason, and is termed reasoning or demonstration. A third pro- cess employed by reason in the acquisition of truth, is induction. Intuition, demonstration, and induction, then, are the three means of Avhich reason avails herself in the discovery of truth. By intuition we have an immediate perception of truth, an irresistible conviction, neither requiring nor admitting the interven- tion of any media of proof. For example, we intuitively perceive our own existence, and our personal identity ; we believe that every event must have a cause ; that the testimony of our senses does not deceive us, &c. Demonstration is the development of an idea from one Avhich is more general, and which contains it. It is the discovery of a connection between tAvo ideas, by means of a third Avhich is more general than the two others, so as to comprehend them both, and connect them together. To demonstrate is to deduce the partic- ular from the general, as in the example of reasoning adduced above. The scholastic form of demonstrative reasoning, is the syllogism. Induction is a process which is the reverse of demonstration, i. e., it proceeds from the particular to the general. The field of inductive reasoning is physical inquiry, in which we aim to estab- lish general laws from particular facts. We resolve particular facts into others more general and comprehensive. " When, by com- paring a number of cases, agreeing in some circumstances, but differing in others, and all attended with the same result, a phil- osopher connects, as a general laAV of nature, the event Avith its physical cause, he is said to proceed according to the method of induction." In this process Ave generalize the particular character INNERVATION. 151 of the phenomena, and this general character we call a law. We evidently proceed from the particular to the general, and not as in demonstrative reasoning, from the general to the particular. The immense acquisitions of modern physical science are trophies of the inductive reasoning. Belief is but another name for judgment. We may indeed feel it to be the conviction of the mind, that Avhat the judgment per- ceives it perceives truly, that is, that the judgment is not mistaken or in an error. But it is difficult to discriminate between the sig- nifications of the tAvo terms. We judge or perceive that one man is taller or stouter than another, and Ave believe him to be so. The belief is ahvays precisely as strong as the judgment. Every judgment is an element of knowledge. The collective judgments which we form on any subject, constitute our know- ledge of it, which will be more or less complete in proportion as our judgments are more extensive and numerous. A complete system of judgments on any subject of knowledge, constitutes a science. The Order or Succession of Ideas. The order or succession of ideas, so far as it is spontaneous, is regulated by a law which has been erroneously termed the asso- ciation of ideas. There is an uninterrupted current of thoughts, feelings, desires, sensations, and acts of the Avill, sweeping through the mind during our waking hours. It is absolutely impossible to stop it, though Ave have a certain control over the direction in which it moves. The very effort is only a new state of mind, which immediately mixes with the others, and is irresistibly hur- ried along with the stream. If we separate from this mingled and moving stream of consciousness, our sensations and volitions, which are constantly giving it a new direction, and suffer it to pursue its own spontaneous course, it will appear, upon examina- tion, that this, instead of being wholly fortuitous and uncertain, is determined by certain fixed laws of thought, which are collec- tively termed the association of ideas. These laws will be briefly enumerated. 1st. The law of coexistence. When several ideas or feelings have been excited in the mind at the same time, if any one of them afterwards return, it is almost always in company with some of its former associates. This law seems to be founded in the unity of the mind, by virtue of which, states of mind which have formerly coexisted, whether consisting of ideas, emotions, judg- ments, &c. have a tendency to recur together. 2d. The law of succession. Ideas or states of mind which have once or repeatedly occurred in a certain order of succession, have a tendency to recur in the same, and never in the contrary order. Any one of the series may bring along Avith it the neighbour 152 FIRST LINES OF PHYSIOLOGY. which immediately folloAved, but scarcely ever the one which Avent before in the original order. The difficulty of repeating the Lord's Prayer, of singing some familiar air, or of boxing the compass, backwards, is a familiar illustration of this law. Upon a moment's reflection it will appear that the first law may be in- cluded under this. 3d. The law of resemblance. Every one is acquainted with the fact, that when an object is presented to the mind, it frequent- ly recalls the idea of some other entirely different, to which, how- ever it bears some resemblance, as when a portrait recalls the idea of the original, or a child which we see for the first time, brings to mind the image of his father. On the same principle, physi- cal objects sometimes excite moral ideas, and vice versa ; thus, the white and stainless snow, may suggest the idea of spotless purity and innocence; affliction and distress, that of gloomy and over- spreading clouds; while the curling Avaves and ripples of the ocean, sparkling and glancing in the sunlight, may picture them- selves, on a poetical mind, as smiles and dimples on the visage of the ocean-god, as in the exquisite image of the Greek poet, tiovziw ze xv/uazwv 'avrjgiduov yth<6ua. Illustrations may be multiplied to any extent. It is evident that this law will be more or less ex- tensive in its operation, according to the greater or less aptitude in the mind to discover among different objects the relations of re- semblance or analogy. The ground of the law lies in the fact, that objects that are recognised as similar, affect the mind in a similar manner; and that similar states of mind possess certain common elements, which form an easy medium of transition from one to the other. 4th. The law of contrast. Contrast or opposition of qualities, is another principle of suggestion ; that is, there is a tendency in the mind to pass from objects to their opposites. Thus a dwarf may suggest the idea of a giant, a fact of such common occur- rence, that a very diminutive person is sometimes jocularly or in derision called a giant. On the same principle, a very ugly or de- formed person may be called an Apollo; a blockhead, a NeAVton; &c. A palace may excite the idea of a hovel; wealth, that of poverty ; light, of darkness, &c. The source of this tendency of the mind lies in this, that opposites are contrary extremes; and that an object or quality is extreme only in comparison with its opposite, which of course it naturally suggests, or rather implies. The very idea of degree, involves the coexistence in the mind of the ideas between which it exists. One extreme, therefore, natu- rally suggests the opposite, for in fact it virtually involves the idea of it. The very idea of extreme, implies the greatest possible distance which separates an object or idea from another of the same kind, with which it is therefore necessarily brought into comparison. In fact, this law may be resolved into the preceding, or that of resemblance; one extreme naturally suggests another. INNERVATION. 153 In relation to the mind, the law seems to be founded in its tendency to oscillate from one point to the opposite one, before it regains its natural state of indifference. 4th. The law of causality. Any phenomenon, regarded as an effect, suggests to the mind the idea of its cause, and vice versa. 6th. The general law of relation. This comprehends all the preceding, and embraces some others. It is apparent that any object whatever may suggest the idea of any other with which it is connected, by any relation perceived by the mind. The rela- tion will form a bridge, which will easily conduct the mind from one idea to another, whether the relation be that of resemblance, contrast, coexistence, succession, or any other. All primitive or intuitive judgments furnish examples which fall under this gen- eral law. In fact, all the particular laws above alluded to, may be united under one general la\v, that of relation ; and, consequently, association may be ultimately resolved into judgment. The current of association is turned out of its natural channel by the occasional intrusion of sensation, and sometimes by acts of the will. The occurrence of certain ideas Avhich we have previously ex- perienced, accompanied Avith the additional idea of their former existence, is ascribed to memory. It is, in fact, an example of association or suggestion, either spontaneous, or influenced by vo- lition, but connected with the idea of past existence. III. Faculty of Feeling or Emotion. Sensations and ideas frequently excite certain vivid feelings entirely unlike themselves, and dissimilar to our intellectual states, which are termed emotions or affections; as, anger, joy, love, wonder, fear, &c. These feelings result from a perception or sen- timent of certain qualities in the objects which excite our sensa- tions, or which are represented by certain ideas excited in the mind. If a person receives a bodily injury from another, he feels perhaps physical pain, and nothing more. But if he supposes the injury intentional, he experiences, besides bodily pain, a vivid emo- tion of the mind, impelling him to retort the injury upon the offender, a feeling which, if not gratified at the time, sometimes settles down into a cooler but deeper sentiment, Avhich aims at the same result. Inanimate objects very often give rise to some of these feelings. Much of the scenery of nature, e. g., is calculated to excite in our minds the most diversified and powerful emotions; as, feelings of wonder, delight, of sublimity, beauty, cheerfulness, gloom, &c. Certain ideas of the imagination, also, as those which are suggested by reading an affecting narrative, may give rise to the most delightful or the most painful emotions, as joy, love, admi- ration, cheerfulness, &c, or, anger, contempt, disappointment, pity, 20 154 FIRST LINES OF PHYSIOLOGY. &c. Certain states of the organization also are productive of these feel ings. These feelings are exceedingly numerous, and may be variously classed. There are some which do not relate to any particular object or time, such as cheerfulness and melancholy. There are others which relate to certain objects as existing at the present time, such as feelings of Avonder, sublimity, and beauty. These Brown denominates immediate emotions. There are some which regard their objects as past, and necessarily involve this idea of the past; as remorse, revenge, gratitude, &c. These he terms retro- spective emotions. There is a third class, which relate to future objects, or Avhich look forward instead of backward. These are the prospective emotions. They comprehend the whole tribe of our desires and aversions, and of course belong to the third head. In regard to the objects which excite them, the emotions may be divided into subjective and objective.. The subjective relate to or centre in ourselves. The objective relate to other persons. The subjective emotions are divisible into three classes. 1. Pride, love of power or wealth, vanity, shame, humility, cheerfulness, relate to the present time. 2. A good or evil conscience, repent- ance, remorse, relate to the past. 3. Hope, fear, courage, anxiety, suspense, despair, &c, refer to the future. The objective emotions relate to other persons, and may be divided into two classes, of directly opposite characters, viz. love, friendship, approbation, gratitude, respect; and envy, jealousy, revenge, anger, contempt, hatred, cruelty, &c. These feelings constitute the principal sources of the enjoyment as well as of the sufferings of man; and on their due regulation most of the happiness and true value of human life depends. When they acquire a certain degree of permanence and strength, so as to get the mastery of the reason and judgment, they are termed passions. Some of them, however, are of too mild and placid a character ever to receive this name ; as cheerfulness, contentment. The passions have a very conspicuous influence upon many of the functions of life, and in reference to the opposite characters of this influence, have been divided into the two classes ; viz. exci- ting and depressing passions. The former, as hope, joy, love, anger, &c, in a moderate de- gree, increase the nervous and muscular energy, promote the cir- culation of the blood, augment animal heat and cutaneous exhala- tion, and in certain enfeebled states of the system, from sickness or other causes, may act as beneficial tonics. But when violent or excessive they are capable of producing very injurious and even fatal consequences. Sometimes they stimulate the system to such a degree as to excite fever ; and some of them, as excessive joy or ungovernable rage, may prove suddenly fatal, by paralyzing the brain or the heart, or by causing a rupture of the latter, or INNERVATION. 155 some large blood-vessel, especially in the brain, and thus causing or giving rise to apoplexy. The depressing passions, as fear, sorroAV, anxiety, home-sick- ness, shame, despair, ahvays enfeeble the poAvers of the brain and heart, and, in an excessive degree, may produce paralysis of these organs, or of some part of the muscular system. Thus vertigo, swooning, and temporary paralysis of the organs of locomotion or speech, may be the effects of these passions. But it is a curi- ous fact, that, under certain circumstances, Avhen suddenly excited, these passions have sometimes operated as poAverful stimulants to the brain and muscular system. Thus a sudden fright has been knoAvn to restore to a person the use of his limbs or his speech ; and feeble persons have been so much invigorated by fear, that they have acquired strength to move burdens which required the united strength of several men. But this temporary excitement of the nervous and muscular power has usually been succeeded by still deeper depression. Faculty of Desire. Objects, or their ideas, frequently excite a wish to possess or a desire to avoid them. If an object be agreeable to the senses or the imagination, the idea of it also is grateful, and its valuable qualities are often exaggerated by the faculty last mentioned, Avhen reason is frequently called upon to make a sober estimate of its real value. If both agree in their report, a third faculty of the mind is called upon to enable us to obtain or avoid the object. This is the will. If the tAvo other poAvers — reason, and imagi- nation or inclination — disagree, the mind of the individual be- comes the theatre of a conflict betAveen them, the result of which will determine, quoad hoc, whether the person is a rational being or not. The absolute authority of reason constitutes the highest freedom of the will. The greater the power and dominion of reason in our moral determinations, and the less the influence of our irrational inclinations, the freer is the will, or rather they who exercise it; and vice versa. The will then is the term of our desires and inclinations as well as of reason. Volition is a conscious attempt to do something which Ave feel or think we have power to do. The result of it is generally sup- posed to be limited to muscular action. The contraction of the muscles of voluntary motion in the natural or healthy state, takes place exclusively under the influence of this power. Locomotion, respiration, and speech, are examples of voluntary action. Re- spiration, however, is carried on without any conscious effort on our part; though we have the power of suspending it for a short time by a voluntary effort. It also continues Avithout interruption during sleep, though consciousness and volition are then slum? bering with the other animal functions. Respiration is therefore 156 FIRST LINES OF PHYSIOLOGY. only in part a voluntary function ; i. e. the influence of the will over it is very limited. But there is another theatre besides muscular contraction for the display of this power ; viz. the field of sensation and of in- ternal consciousness. The will is exerted not only in exciting the action of the voluntary muscles, but in scrutinizing our sen- sations, and in fixing the mind on certain ideas or feelings, or in directing the current of our thoughts into new channels. When we listen attentively to certain sounds; e. g. fix the attention on a certain voice or instrument among the mingled sounds of a concert of music; when Ave examine the colours and shape of some beautiful visible object, &c.; when Ave analyze by the palate the scientific results of refined cookery; when we direct our attention to some idea as it is floating away on the current of consciousness, and seize upon and secure it before it disap- pears ; when we purposely set about some intellectual investiga- tion, or form some moral determination, &c.; in all these cases, our will is as much concerned as in lifting our legs in walking or dancing, exercising our jaws in eating, or even in exerting our muscular power in the most emphatic manner, as in raising a heavy burden. In fact, our voluntary muscular actions are fre- quently the result of two distinct volitions, which belong respec- tively to the two classes above mentioned. The mere muscular action which is accomplished by an act of the will, is only a consummation of a previous intellectual or moral act, which is no less the effect of the same power. A murderer first forms a deliberate determination, which is an act of the will, to perpetrate the deed; he then exerts another act of the same faculty to give effect to his design. Instinct. There is another faculty, which remains to be noticed among the functions of the brain, which is instinct. Instinct is a blind impulse to certain actions necessary to the physical well- being of the individual, the continuance of the species, and the safety of the young. We know little about it except its results, many of which are very curious and admirable. It may be accounted for, however, by supposing that at particular times or periods, certain feelings or states of the nervous system are phy- siologically developed, which by the laws of the organization are communicated to the centre of the nervous system, and give rise automatically to certain acts, of the aim and nature of which the animal is unconscious, but which are necessary to the attainment of certain important objects. It is, in fact, an example of exqui- site physiological mechanism. In man, there intervenes between the feelings which prompt to actions analogous to the instinctive actions of brutes, and the actions themselves, the light of the understanding, imparting a knowledge of the aim or end of the action, and also suggesting means by which it may be accomplished. In proportion, there- THE CIRCULATION. 157 fore, to the development of the understanding, instinct is super- seded or confined Avithin narrow limits. Yet there are instincts in man, and there is understanding in other animals. A faint light of the understanding sometimes glimmers between the in- stinctive feelings and actions of animals, apparently giving some knowledge of the aim or object of the actions, and suggesting means of bringing them to pass. And it is worthy of remark, that this resource in the understanding comes to their aid only when it is needed; i. e. only when the ordinary means of attain- ing the object fails and instinct is at fault. In instinct, a physical impulse is the sole spring of the act, directly influencing the organization. In man, the physical im- pulse may exist, and may be irresistible by acting directly upon the organization ; but there may also coincide an intellectual in- centive or a rational motive acting upon the will, and impelling it to the same action, which will then cease to be purely an instinctive one, and become partly rational; or the rational or psychological impulse may wholly supersede the physical, and thus take the action entirely out of the domain of instinct. The organic and automatic nature of instinct is evident from the fact that instinct can never be improved; vvrieis £oxot/ ddtdaxzoi. CHAPTER XIV. THE CIRCULATION. The circulation of the blood is another of the vital functions, or one which is immediately necessary to life. The universal suspension of it throughout the body, is instantly fatal. Hence, diseases of the heart, and of the great vessels, are apt to terminate in sudden death, while morbid affections of the other vital organs, the brain and the lungs, however violent and acute, scarcely ever, if ever, occasion immediate death. Life, or vital excitement, is maintained in all the organs by the presence of arterial blood. This fluid is the source of the nutrition of all the organs and tissues, and its presence is an indispensable condition to the performance of every function of the system. If an organ is deprived of arterial blood, from that moment its nutri- tion ceases, and it loses the power of executing its peculiar func- tions ; and it is obvious that a universal suspension of the circu- lation, which distributes the blood to every part of the system, must instantly abolish every function of life. The circulation does not exist in all animals, but only in those in which the alimentary matter is absorbed into the system instead 158 FIRST LINES OF PHYSIOLOGY. of being immediately employed in nourishing it, and first converted into a distinct fluid, the blood, Avhich furnishes the immediate ele- ments of nutrition ; and in Avhich there also exists a local respira- tion ; i. e. the absorption of air takes place separately from that of the other nutritive principles, and in a separate organ or apparatus. Two different kinds of matter are absolutely necessary to the nu- trition of animals, viz. air, and certain solid or liquid substances, which are called food. The latter, or the food, is not capable of being converted into blood, before the former, i. e. the air, has acted upon it by one of its principles, oxygen. Now, if these two elements of the blood are not introduced into the system in the same place, but by separate organs, it is evidently impossible, that they can, immediately after their absorption, be employed in nutri- tion. It is necessary that one of them, after its absorption, be conveyed to the organ where the other is absorbed, and that the nutritive fluid, formed by their mutual action, be afterwards car- ried from this organ to all parts of the body, to furnish the mate- rials for their nutrition, and vital excitation. Hence, a local res- piration is always accompanied with a circulation ; while in those animals in which respiration is disseminated, i. e. is not concen- trated in a particular organ, as in insects, there is no circulation.* The organs of the circulation are the heart, the arteries, the veins, and the capillary vessels. These organs collectively repre- sent tAvo trees of unequal size, whose trunks are united at the heart, and Avhose branches are infinitely ramified; those of the larger tree, throughout all parts of the system; and those of the smaller, throughout the lungs. At the union of the two trunks is found the central organ of the circulation, the heart. The motion of the blood in this apparatus is a circulatory one. This fluid is forced out of the heart by the contraction of the or- gan, and propelled to every part of the body through elastic tubes, called arteries. From the extremities of these it passes into the minute organs of another set of tubes, termed veins, and by them is returned to the heart. According to some physiologists, there exists between the termination of the arteries and the commence- ment of the veins, an intermediate order of fine hairlike vessels, termed capillaries. The course of the blood, from and to the heart, is called the circulation. The Heart. In the human species, in that class of the animal kingdom called the mammalia, and in birds, the heart is a double organ, consisting, in fact, of two single hearts, each of which gives motion to a distinct species of blood. One of them receives the dark venous blood Avhich returns from all parts of the body, and transmits it to the lungs, where it is converted by respiration into scarlet-coloured arterial blood. This may be termed the venous, or the pulmonary heart. The other heart receives from the lungs * Adelon. THE CIRCULATION. 159 the arterial blood, and conveys it to all parts of the system. This may be called the arterial or aortic heart. And these two hearts are united together into a single organ. Each of these two hearts contains two cavities, one designed to receive the returning blood from the veins ; the other to propel it in the opposite direction into the arteries, and through them to all parts of the body. The cav- ities, by which the heart receives the blood, are called auricles ; and those Avhich contract upon this fluid and force it out of the heart into the arteries, are termed the ventricles. The walls of the heart are composed of a muscular substance, the fibres of which run in various directions, interlacing one another, and forming an inextricable tissue. The parietes of the ventricles are much thicker than those of the auricles. The cavities are lined by a thin membrane, forming, by its folds, valves which sentinel the different apertures and outlets of the organ. The heart is covered externally by a serous membrane, reflected over it from the pericardium, a sac of a fibro-serous structure. This membrane secretes a fluid called the liquor pericardii, the use of which is to lubricate the organ. The nerves of the heart are derived from a plexus formed by filaments of the pneumogastric and the great sympathetic nerves, and they follow the ramifications of the coronary arteries. The heart is situated in the thorax, in the lower part of the an- terior mediastinum. Its position is oblique, being inclined fonvards, downwards, and outAvards, and from right to left. Its posterior sur- face is nearly horizontal, and rests upon the aponeurotic centre of the diaphragm. Its anterior is turned a little upAvards, and exhibits a groove passing from left to right obliquely downwards, in which is lodged the anterior coronary artery and veins. The base of the organ is directed backwards, and to the right towards the bodies of the dorsal vertebras, from which it is separated by the aorta and the oesophagus. The apex is inclined forwards and to the left, and during life its pulsations are felt between the cartilages of the fifth and sixth ribs. The figure of the heart is somewhat conical. The septum which separates its cavities, runs in the direction of its long axis, but in such a manner that the apex of the heart falls exclusively to the left ventricle. The chambers of the pulmonary or venous heart, more usually termed the right side of the heart, are trian- gular in their shape; while those of the arterial, which is also ealled the left side of the heart, are oval. Each of these cavities is capable of containing about two ounces of blood. The two auricles are so connected by their common septum, and by fibres passing from one to the other, that it is impossible for either to contract alone. The same is true of the tAvo ventricles. They have a common septum, and there are whole layers of fibres com- mon to both. On the contrary, the auricles and ventricles are con- nected with each other only by cellular tissue, vessels, and nerves. 160 FIRST LINES OF PHYSIOLOGY. No muscular fibres pass from one to the other, and by maceration they may be easily separated from each other. According to some physiologists, the right ventricle has a greater capacity than the left, because the venous system to which it be- longs, is more capacious than the arterial. But others assert, that the superior capacity of the right side of the heart, is a cadaveric phenomenon, owing to the accumulation of blood in it, which occurs in the last moments of life; while the left side, in a state of vacuity, contracts to a smaller volume. Each cavity of the heart is lined with a thin transparent mem- brane, which is continued from the ventricles into the correspond- ing arteries, and from the auricles into the veins which open into them. It is usually classed with the serous membranes. BetAveen each auricle and the corresponding ventricle is placed a valve, which is formed by a duplication of the inner membrane, strengthened by intervening fibrous substance. The free margin of these valves is irregular, and in the right side of the heart it presents three apices, but two only in the left. Whence the right auriculo-ventricular valve is termed the tricuspid valve, and the left, the bicuspid or mitral. The floating edge of the valves is attached to the fleshy columns of the ventricles by short tendinous threads, called chorda tendinea. The margin of the valves is strengthened by little granular bodies, termed corpora sesamoidea. These valves prevent the refluence of the blood from the ventri- cles into the auricles, during the contraction of the former. Valves exist also at the origin of the two great arteries, the pul- monary artery, and the aorta, where these vessels communicate with the right and the left ventricles. These valves differ widely from the former. They are formed by folds of the inner membrane of the arteries, are of a semilunar shape, and are attached by their convex margin to the circumference of the artery, each occupying a third part of it. These are termed the semilunar, or sigmoid valves, and their office is to prevent a reflux of the blood from the aorta and pulmonary artery, into the corresponding ventricles. The orifice of the inferior vena cava is also furnished with a duplication of its inner membrane, which projects into the cavity of the auricle, and is called the Eustachian valve. This valve is useful only in the fostal state, and its office is to direct the blood of the inferior cava through the foramen ovale, an aperture by which, during fostal life, the two auricles communicate with each other. This aperture closes after birth, leaving an oval depression in the septum of the auricle, termed the fossa ovalis. At the opening of the coronary vein also, a valve is found formed by a semilunar fold of membrane, and Avhich prevents the reflux of blood from the auricle into the vein. There are no valves at the entrance of the superior cava into the right auricle, nor of the pulmonary veins into the left. The Arteries. The vessels into which the blood is propelled by THE CIRCULATION. 161 the action of the heart, and distributed to all parts of the body, are termed arteries. These vessels form tAvo distinct systems, the aortal and the pulmonary ; the former connected with the left, the latter with the right ventricle of the heart. The main trunk of the aortal system, which opens into the left ventricle, is called the aorta. It contains scarlet-coloured blood, which it distributes by its ramifications throughout all parts of the system, terminating in minute tAvigs at the periphery of the body, and in the limbs and internal organs. The main trunk of the pulmonary arterial sys- tem, which arises from the right ventricle, is called the pulmonary artery. It carries dark-coloured or venous blood, and its ramifica- tions are distributed throughout the lungs. Where an artery, divides, its branches have an area greater than that of the trunk, and they generally diverge at acute angles. In general, the arterial and venous trunks are distributed together; the larger arteries having an accompanying vein, the smaller ones two. The capacity of the venous system is much greater than that of the arterial. The arteries frequently inosculate Avith one another, permitting the blood to pass freely from one branch to another, and these communications increase as the arteries become more distant from the heart. Hall, however, says, that in no instance was he able to detect an anastomosis betAveen the minute or extreme arte- rial branches. These vessels are nourished by minute arterial branches, distributed through these tunics, and which are termed vasa vasorum. They are also supplied Avith nerves, Avhich are derived principally from the great sympathetic. The structure of these vessels has already been described. The Veins. The veins, Avhich return the blood to the heart from all parts of the body, constitute, like the arteries, two sys- tems ; one of which corresponds to the arterial system of the aorta, and conveys dark-coloured or venous blood from the periphery of the body, from the head, trunk, and limbs, and from all the inter- nal organs, to the right auricle of the heart, into which it opens by the two great trunks, called the vena cava superior and infe- rior. The other, which corresponds to' the pulmonary arterial system, conveys scarlet-coloured or arterial blood from the lungs to the left auricle of the heart, into which it opens by four large trunks, called the pulmonary veins. The veins have several origins. The most general is from ar- teries, either directly or through the medium of capillaries. The blood in living animals, and the substances used for injecting the vessels, pass from the arteries to the veins by continuous canals. If the arteries of the pia mater be injected with tallow and ver- milion, the veins will be filled Avith the tallow without the ver- milion ; the superficial veins in the hand or foot may be injected with quicksilver, from the arteries, facts which prove the continuity 21 162 FIRST LINES OF PHYSIOLOGY. of the two kinds of canals. A second origin is from cells, of which in the human body, the corpora cavernosa of the penis and clito- ris, and the maternal part of the placenta furnish examples. In these parts, at least, the veins must be supposed to exercise the function of absorption. A third origin is from sinuses, as from those of the dura mater. A fourth, is from other veins, as in the liver, Avhere the hepatic veins originate in part from the extreme ramifications of the vena portas. Anastomoses are not uncommon betAveen the radicles of the veins, presenting the curious and interesting phenomenon of two currents of blood in the same vessel, flowing in opposite directions. The veins are very strong and flexible tubes, though possessed of little elasticity. They are furnished with numerous valves, formed by semilunar folds of the thin interior tunic, the office of Avhich is to prevent the reflux of the blood. Like the arteries, they are furnished with vasa vasorum, and Avith nerves derived from the great sympathetic. The Capillary Vessels. The capillary system, which is inter- mediate betAveen the terminations of the arteries and the origins of the veins, presents two modifications. In one, it consists of canals furnished with proper coats or walls, which carry blood from the extreme arteries into the origins of the veins. But in many parts of the body, the coats of these fine vessels disappear, and the globules of blood find a passage for themselves, in various directions, in the parenchyma of the organs; and these passages at length begin to enlarge, acquire walls, and assume the character of the finest veins. The capillary canals of this species are much smaller than the first, and it is said, permit only a single globule of blood to pass out at a time. They are also subject to great changes, some of them disappearing and closing up, and neAv ones being formed. The formation of these vessels is caused by the fine arterial canals gradually losing their coats, and becoming con- founded Avith the parenchyma of the organs. The capillary ves- sels have numerous anastomoses, and they are the theatre of the functions of nutrition, secretion, calorification, hematosis, &c. The transition from arteries to veins presents different disposi- tions. Sometimes a fine arterial twig merely bends round and reverses its direction, and is at once converted into a vein. Some- times these parallel vessels communicate by lateral branches pass- ing transversely from one to the other. But in general, the ulti- mate arterial branches form numerous ramifications, which inos- culate with each other, so as at last to form a delicate network; and from this network originate similar ramifications, which, uniting together form the commencement of the veins, and the fine arteries and veins leading respectively to and from this net- work, run parallel and almost in contact with each other. In the liver the same capillary network receives twigs from the hepatic artery, and the vena portas, and gives origin to the radicles of the THE CIRCULATION. 163 hepatic veins, as appears from injections. In the capillary system of the lungs there is a similar disposition. Twigs both from the pulmonary and from the bronchial arteries contribute to the forma- tion of the same capillary network; and branches of no incon- siderable size, of these two different sorts of vessels are known to communicate together. The capillary system is divided into two sections or depart- ments, one called the general, the other the pulmonary. The first of these is intermediate between the ultimate branches of the aorta, and the origins of the venae cavae. It is the theatre of nutrition, and secretion, and of the conversion of arterial into venous blood. The second exists only in the lungs, and is inter- mediate betAveen the pulmonary artery and the pulmonary veins. It is the seat of hematosis, or of the conversion of venous into arterial blood, and may be considered as opposed to the general capillary system, in which the mass of the blood undergoes the opposite changes. It appears from this, that the lungs have two capillary systems, viz. one connected with their peculiar function, or respiration ; and another, Avhich is a branch of the general capillary system, and is connected with the nutrition of these organs. Some physiologists do not admit a distinct capillary system. According to Wilbrand, the arteries terminate and are lost in the tissues and organs, and the veins originate anew. Most phy- siologists, on the contrary, contend for the immediate passage of the arteries into the veins, and Rudolphi asserts that the placenta affords the only exception to this structure. Hall says that he had never seen an instance of the immediate termination of an artery in a vein. Capillary vessels are gene- rally, if not invariably, interposed. These vessels may be dis- tinguished from the minute arteries and Areins, by their retaining a uniform diameter during their continual divisions, conjunctions, and inosculations, Avhile the minute arteries continually subdivide into smaller branches, and the minute veins unite into larger. Another distinguishing character betAveen the minute arteries and the capillaries is, that in the former, the pulsatory movement of the blood is distinctly visible, but in the normal .state of the circu- lation, never extends to the capillaries. These vessels, Hall says, are formed by the subdivision of the ultimate arterial branches into others of equal size with itself, a structure which, by increasing the capacity of the vessels, produces a more diffused and slower circulation. Placed between the minute arteries and veins, they always retain the same diameter, hoAvever frequently they may divide, subdivide, unite, anastomose, and even form circles. In fact, they form a complete netAvork of vessels, which constantly retain the same dimensions and character. In the higher orders of animals, injections readily pass from arteries into veins ; although in the invertebrated animals, or at 164 FIRST LINES OF PHYSIOLOGY. least in many of them, it is said to be impossible to force injec- tions from the former into the latter vessels. Milk injected into an artery, has been seen in the blood of the veins. Even foreign substances injected into the system of the vena cava have been observed in the blood of the aortal system, and even in the fluids secreted from it, and of course must have passed from the pul- monary artery to the pulmonary veins. In one experiment Mayer observed in the blood of the aorta, and of the vena porta, milk which he had injected into the jugular vein of a rabbit. In this case the milk had passed not only from the pulmonary artery to the pulmonary veins, but from the arteries to the veins of the in- testines, and hence had traversed tAvo capillary circulations. Such is a brief account of the general structure of the heart and blood-vessels, in the human species, the mammalia, and birds. In another class of animals, the reptiles, a part only of the blood passes through the lungs, to become endued with the arterial principle; these animals being so constituted, that the aeration of a portion of the blood is. sufficient for the renovation of the whole mass. In the reptiles, therefore, it is not necessary that the two kinds of blood should be kept separate. Indeed, if they were so, the renovated portion could not impart its "animating influence to the other. Hence, these animals have only a single heart, consisting of one ventricle, and one or two auricles. The auricle receives both arterial blood from the lungs, and venous blood from all parts of the body ; and in its cavity these two kinds of blood are mixed together. From the ventricle arises a single arterial trunk, which divides into tAvo branches, one of which carries a portion of the blood to the lungs, to be. subjected to res- piration ; the other distributes 'the remaining portion to all parts of the body. In the other classes of animals, the two kinds of blood are not mixed together, but remain distinct; and, of course, one and the same heart is not sufficient to circulate both. In these classes of animals, comprehending the worms, the mollusca, the Crustacea, and fishes, the organs of the circulation present different disposi- tions. Worms have no heart; and the circulation, which con- sists in the passage of the blood from the organs of respiration to all parts of the animal, and its return- to these organs again, is carried on exclusively by vessels, In the Crustacea, and most, of the mollusca, there is a single heart only, but it is designed to circulate only arterial blood. Its office is limited to the convey- ing of arterial blood to the various parts of the body ; and this blood after its conversion to venous blood in the different organs, is returned to the organs of respiration by vessels. These ani- mals, therefore, possess an arterial heart. In the cephalopodes there are three hearts, two venous and one aortic. In fishes also there exists only a single heart; but this is not designed to circulate both kinds of blood, as in the reptiles, nor THE CIRCULATION. 165 arterial blood alone, as in the crustaceous and some of the mol- luscous animals. Its office is to propel the venous blood to the gills, while the arterial blood is conveyed from these organs to all parts of the system, not by another heart, but wholly by vessels. Fishes, therefore,-have properly only a venous heart. Their aorta is a vessel formed by arteries Avhich proceed from the gills. The Circulation. It has already been observed, that the heart is a double organ, being composed of two distinct hearts united together. Each of these is the organ of a distinct circulation. One of them, viz. the arterial heart, is the agent of the greater, or the general cir- culation ; the other, or the venous heart, is the organ of the lesser, or the pulmonary. In the general circulation, in which the course of the blood forms a larger circle, arterial blood is projected from the arterial heart, through the aorta and its branches, to all parts of the body, and, having lost its arterial character in the various organs, is returned as venous blood, to the pulmonary or venous heart. The venous heart is. the origin or point of departure of the lesser or pulmonary circulation, which forms a much smaller circle than the aortic. It consists in the passage of the venous blood through the lungs, where it loses its venous character by the influence of respiration ; and in its return from the lungs, as arterial blood, to the arterial or aortic heart. Beginning at any given point in the circulation, as e. g. at the auricle of the pulmonary or venous heart, the course of the blood is as folioavs. The pulmonary auricle, receives the venous blood on its return from all parts of the system. From the auricle it passes into, the corresponding ventricle, by the contraction of Avhich it is projected into the pulmonary artery, and by. the rami-' fications of this vessel is conveyed to the capillary system of the lungs. Here it loses its venous character, and is converted into arterial blood. It is then taken up by the pulmonary veins, and conveyed to the auricle of the arterial heart, and thence into the corresponding ventricle, by the contraction of which it is pro- jected into the aorta, and by the ramifications of this vessel dis- tributed to all parts of the system. In the capillary vessels of these it loses its arterial character, and then passes into another system of vessels, the veins, by Avhich it is returned as venous blood to the auricle of the pulmonary heart, from which its course was supposed to commence. It appears from this, that neither circulation is quite complete ; for, in neither does the blood return to the same point from which its course commenced. In order to arrive at this point, wherever it be assumed, the blood must pass the round of both circulations, arterial and pulmonary, and undergo both of the changes Avhich are effected in the capillary systems of the tAvo, i. e. the change 166 FIRST LINES OF PHYSIOLOGY. from arterial to venous, and that from venous to arterial blood It appears, then, the two parts of which the heart is composed are so related to each other, that the ventricle of one forms the commencement, and the auricle of the other the termination, of a distinct circulation. The heart has the lungs between its right ventricle and its left auricle ; and all the organs of the body, in- cluding the lungs and the heart itself, between Tts left ventricle and its right auricle. The right ventricle and the left auricle, therefore, are the two extremes, between which is comprehended the pulmonary or lesser circulation; while the left ventricle and the right auricle bound the arterial or the greater circulation. Besides this division of the circulation into aortal and pulmo- nary, or greater and lesser, another was proposed by Bichat, founded on the qualities of the blood, and the changes which it undergoes in the lungs, and the general capillary system. Bichat divides the circulation into arterial and venous, or the circulation of red, and that of black blood. In the first, the blood passes from the lungs to all parts of the body ; in the second, it returns from all parts of the body to the lungs again. According to this view, the circulation may be reduced to two phenomena, viz. the passage of the blood from the capillaries of the lungs, where it assumes its arterial properties, to the general capillary system, where it furnishes the elements of nutrition and of the secretions, and acts as the universal excitant of all the organs ; and, secondly, the passage of the blood from the general capillary system to the pulmonary capillaries, Avhere the properties of the vital fluid are renovated by respiration. In this view, the two capillary sys- tems, the general and the pulmonary, are the points of departure of the two circulations, instead of the aortal and pulmonary sides of the heart. The circulation of red blood commences in the capillary sys- tem of the lungs, Avhere the blood acquires the peculiar characters which distinguish arterial blood. From the capillary system of the lungs it passes into the pulmonary veins, Avhich convey it into the left auricle, or that of the arterial heart. From this it passes into the corresponding ventricle, which projects it into the aortal system. Through this it is distributed to the general capillary system, which may be considered as the termination of the cir- culation of red or arterial blood. In this, then, the arterial blood is constantly passing from the capillary system of the lungs, to the general capillary system; and, in its passage, it is transmitted through the arterial heart, or what is commonly called the left side of the heart. The whole of the left side of the heart, there- fore belongs to the circulation of arterial blood. The circulation of the black or venous blood, commences where the former terminated, i. e. in the general capillary system. Here the blood is converted from arterial into venous, from scarlet to purple-coloured blood. From the general capillary system it THE CIRCULATION. 167 passes into the veins, which convey it to the pulmonary or venous heart. From this it is distributed by the pulmonary artery, to the capillary system of the lungs, which is the termination of the circulation of venous blood. This circulation, then, consists in the passage of venous blood, from the general capillary system to that of the lungs, in the course of which it passes through the pulmonary or venous heart. The whole of this side of the heart, therefore, belongs to the circulation of venous blood. Each of these circulations begins Avith veins, and terminates with arteries, and each of them, in its course, passes through both cavities of one side of the heart. Each of them consists of tAvo segments of circles of unequal size ; the larger being a moiety of the gene- ral or aortal circulation, the smaller, a division of the pulmonary. The circulation of red or arterial blood, consists of the venous part of the pulmonary, and of the arterial part of the general cir- culation ; and the circulation of venous, or purple blood, consists of the venous segment of the aortal or general circulation, and of the arterial segment of the pulmonary. The two circulations are entirely independent of each other, except at their origins and terminations, the tAvo capillary systems, where the arterial and venous blood are reciprocally transformed into each other ; and they intersect each other at the heart, through which they both pass, yet without communicating together. In the circulation of red, or arterial blood, the vital fluid is sent to the general capillaries, and traverses all the organs, furnishing in its passage the elements of nutrition, and of the secretions. It also communicates to all the organs a peculiar species of vital im- pulse, or excitation, indispensable to life and to the functions of the organs. A part of the arterial blood remains in the organs, to replace the materials removed by vital decomposition : another part is expended in the secreted fluids, and passes into the canals belonging to this function in the different secretory organs. Of course, a part only, and perhaps but a small part of the blood, re- turns to the heart, robbed of its vital and nutritious principles, and presenting the characters of venous blood. The first impulse of the blood in this circulation, is received in the capillary vessels of the lungs, but its principal moving power is the left ventricle of the heart. In the circulation of black or venous blood, this fluid passes from the general capillary system to that of the lungs, in order to be renovated and converted again into arterial blood by respira- tion. In its passage to the pulmonary heart, it is reinforced by the addition of a considerable quantity of chyle and lymph, which are on their Avay to the lungs, to be converted into blood by respiration. These two fluids, the chyle and the lymph, are gathered up and conveyed into the blood by an order of vessels called absorbent. These vessels, collecting the materials of ren- ovation from the organs, by vital decomposition, and from all the 168 FIRST LINES OF PHYSIOLOGY. free surfaces of the body, internal and external, convey them by two principal trunks into the great veins near the heart. These materials are unfit for the purposes of the economy, some of them by defect of animalization, others, perhaps, by an excess of it. They are, therefore, blended together, and mixed with the venous blood, Avith Avhich they are transmitted through the lungs, where the Avhole compound fluid is converted by respiration into arterial blood. The venous blood appears to owe its principal characters to an excess of carbonic acid, and, perhaps, to the loss of oxygen, expended in nutrition and the secretions. In asphyxia from car- bonic acid, the blood is said to be much darker than in asphyxia from other causes. The motion of the venous blood is first im- pressed by the action of the general capillaries, Avhich forces the vital fluid into the radicles of the veins, where it clears the first set of valves. These sustain the column of blood, and prevent its retrograding, Avhen the Veins, excited by the stimulus of the blood, contract upon it, and force it beyond the next series of valves. When it reaches the pulmonary heart, it receives a new impulse by the contraction of the right ventricle. . The passage of the blood through the two capillary systems, may be considered as constituting a distinct circulation, which may be termed the capillary. This may be divided into two kinds, viz. the general, and the pulmonary capillary circulation. In the former, the blood fur- nishes the organs with the materials of nutrition, and of the se- cretions ; caloric is evolved, the blood becomes charged with car- bonic acid, and perhaps loses some of the oxygen it had acquired in respiration, and is converted from arterial into venous blood. The capillary circulation of the lungs may be considered as op- posed to the former. It has for its object, the renovation of the blood, or its conversion from venous to arterial, by respiration ; an effect which seems to be produced by the loss of carbonic acid, and the acquisition of oxygen. The capillary system possesses no central organ of impulsion like the two others, but depends on the vital contractility of the minute vessels which execute it; and it does not.present the same regularity as the cardiac circulation. In the normal state, the gen- eral sum of its activity remains nearly the same; since the same quantity of blood must traverse the capillary system in a given time. But the activity of particular parts of it may be much in- creased or diminished. By increasing it in one place Ave may les- sen it in another, and vice versa; a principle on which depends the effect of counter-irritation. The capillary circulation survives the cardiac, and is the last to cease at death. Admitting the existence of the capillary system, animals may be said to possess tAvo circulatory systems ; one a peripheral, which constitutes a circle, the other, a central, which forms the radii of this. The lower we descend in the zoological scale, the more the THE CIRCULATION. 169 peripheral or capillary predominates; and the higher we ascend, the more does the central or cardiac. Hence, the more easy re- establishment of the circulation in the lower than in the higher animals, after the ligature of large arteries ; the circulation being then maintained by the numerous anastomoses of the peripheral system. Mechanism of the Circulation. The motion of the blood is maintained principally by the action of the heart. This organ is endued with great irritability, in con- sequence of which it contracts Avith great force upon the blood, which flows into it from the veins, and propels it into the mouths of the great arteries, which communicate Avith its ventricles. The action of the heart consists of an alternate contraction and dilatation, or systole and diastole, of the auricles and ventricles. When the auricles receive the blood returned from the general circulation and the lungs, by the venas cavae and the pulmonary veins, they contract upon it and force it into the ventricles, which dilate at the same moment to receive it; and immediately after- wards, when the distended ventricles are contracting to force the blood into the aorta and the pulmonary artery, the auricles dilate in order to receive a neAV supply from the vems. Hence the con- traction of the auricles and the dilatation of the ventricles take place at the same time, and vice versa. The two auricles con- tract and dilate simultaneously, and the same is true of the two ventricles. This is probably owing to the fact that the two auri- cles have a common muscular septum, so that one cannot contract without the other ; a structure Avhich exists also in the ventricles ; Avhile the auricles are connected to the ventricles only by cellular tissue, vessels, and nerves. When the auricles contract, the blood expelled by their action is throAvn back partly upon the veins, producing, in some cases, a venous pulse; but the greater part of it enters the ventricles, which spontaneously relax to receive it. A pulse in the jugular veins is sometimes perceptible in persons of spare habits, and in morbid affections of the lungs, OAving to a reflux of blood into these veins at the time of the contraction of the right ventricle. In some cases this reflux extends to the veins of the liver, pro- ducing an engorgement of this organ. So, where there is an ob- stacle to the passage of the blood into the aorta, there is sometimes a reflux into the pulmonary veins, by which the lungs become engorged. The experiments of Hope, confirmed by those of Bouillaud, appear to have established the following facts respecting the rythm of the heart's action." The first motion of the heart Avhich succeeds the interval of 22 170 FIRST LINES OF PHYSIOLOGY. repose, is the systole of the auricles. This moA'-ement consists in a slight contraction, which is most conspicuous in the auricular appendage, and which is propagated rapidly by a kind of vermic- ular motion to the ventricle. The motion, though rapid, is not so quick but that it can be easily folloAved by the eye. The systole of the ventricle which succeeds, commences sud- denly, and consists in a sudden energetic jerking movement, ac- companied by a depression of the centre or body of the ventricle, and the elevation and impulse of its apex against the side. The shock of the heart against the ribs, and the pulsations of the arte- ries near the heart, are simultaneous with the ventricular systole. In the arteries more distant from the heart, the pulse is not exact- ly synchronous Avith the systole, but follows it at a scarcely ap- preciable interval. The systole is succeeded by the diastole of the ventricles, which is an instantaneous motion of expansion, accompanied with an influx of blood into the ventricles, while the apex of the heart collapses and retires from the side. To the diastole succeeds the interval of rest, in which the ven- tricles remain quiescent and in a state of fulness, but not disten- tion, until again excited by the auricular contraction, which intro- duces anew the same series of movements. A complete revolution of these movements occupies, in an adult, about the space of a second. Of this time the ventricular systole occupies about one half; the diastole about one-fourth, or a little more ; the interval of rest one-fourth, or rather less. The auricular systole occurs during the latter part of the period of repose, and occupies of course only about one-eighth of a beat. As the contraction of the ventricles occupies only one-half of the time of the Avhole beat, it appears that the ventricles enjoy tAvelve hours rest out of each twenty-four. This is true, hoAvever, only on the supposition that the diastole is a state of repose. Hope estimates the interval of rest enjoyed by the ventricles at only six hours out of the twenty-four, falling, in each beat, between the diastole of the ventricles and the next auricular systole. The re- pose of the auricles he estimates at about the same; for though the systole of the auricles occupies only about one-eighth of a whole beat, the remaining seven-eighths, Hope remarks, is not de- voted to repose; for during most of this time the auricle is in a state of greater or less distention, which is not repose. The action of the auricles is gentle, and is sometimes repeated before the contraction of the ventricles takes place. The extent of the auricular contraction is very inconsiderable, says Hope, not amounting probably to one-third of its volume, and of course the quantity of blood throAvn by it into the ventricle is but small; yet sufficient, as the ventricle is already full in consequence of its diastole, to bring it to a degree of distention necessary to excite it to contraction. It is further to be observed, that the auricles con- THE CIRCULATION. 171 tract twice or more for every ventricular systole. In a rabbit Hope saw the auricle make tAvo or three contractions without exciting the ventricle, when a fourth, of about the same degree of energy, caused the heart to start up with the usual appearances of the ventricular systole. The auricles expel but a small portion of their contents at a time, and are constantly full; their motions ranging between fulness and distention. In small animals, as the frog, the ventricles expel the Avhole of their blood, as appears by their becoming pale during the systole; but in large animals, as the ass, they do-not appear to expel the whole, to judge from their diminution of volume. According to some physiologists, during the contraction of the auricles, one of the tricuspid valves closes the orifice of the pulmonary artery, and one of the bicuspid that of the aorta, so as to prevent the entrance of the blood into these vessels, during the dilatation of the ventricles. The right auricle has more fleshy columns than the left, perhaps to enable it more thoroughly to blend together the chyle, the lymph, and the venous blood. During the systole of the ventricles, the tissue of the heart har- dens and shortens itself, and is displaced a little ; and its apex, curling upwards, strikes the left Avail of the chest, between the sixth and seventh ribs. This phenomenon has been referred to the impulse which the aorta and pulmonary artery receive from the wave of blood projected into them, Avhich displaces them a little, and produces a reaction upon the heart, by which the point of the organ is pushed forAvard and to the left. The dilatation of the auricles also, which takes place during the contraction of the ventricles, must contribute to carry the latter forwards. It appears, however, that these circumstances are not necessary to produce this effect; for if the heart of an animal recently killed, be placed, while yet palpitating, upon a table, the apex continues to be tilted up by each contraction of the ventricles. Hope explains this phe- nomenon in the folloAving manner. During the state of relaxation, the heart lies collapsed and flattened, Avith a large extent of its inferior surface resting upon the table. On contracting, it starts up, and assuming a more globular form, is supported by a much smaller surface. Hence the apex is elevated, and the more so, because the base, from its greater Aveight, is the less movable part. Ac- cording to Hope, the mechanism of this action is very similar in the living subject. The auricles, especially the left, are attached to the posterior part of the base, and the aorta and pulmonary artery spring from its anterior part. The auricles being in a state of distention during the systole of the ventricles, form an unyield- ing fulcrum under the ventricles ; the fibres of which contracting towards the aorta and pulmonary artery in front, draw up the rounded body of the heart upon the auricles behind. In this view of the phenomenon, the auricles represent the fulcrum of the lever, 172 FIRST LINKS OF FHYSIOLOGA'. the apex of the heart its long arm, Avhile the moving power is applied at the aorta and pulmonary artery. The walls of the left ventricle are thicker and stronger than those of the right, because it has a greater distance to project the blood ; and, according to Berthold, the right ventricle has a greater capacity than the left, because the venous system, to which it belongs, is more capacious than the arterial. By the systole of the ventricles, the blood is projected with great force and velocity into the aorta and pulmonary artery, and, through these canals, dis- tributed throughout the general system and the lungs. It is then taken up by the radicles of the corresponding veins, and returned by the trunks of these vessels to the auricles of the heart. The motion of the blood is more rapid, as the arteries are larger and nearer the heart. Its velocity gradually diminishes as the arterial canals become smaller, and recede farther from the heart, as ap- pears from the feeble jets of blood emitted by the small arteries. In arteries of a certain degree of minuteness the jets disappear ; a fact which proves that the force of the heart is much lessened in these remote vessels. This gradual retardation of the velocity of the blood is OAving partly to the increasing resistance which this fluid has to encounter in its passage through the arterial tubes, from friction and other causes, and partly to the increasing capacity . of the vessels as they become more distant from the heart. In the veins, on the other hand, the blood moves with a constantly accel- erated velocity toAvards the heart. According to Hall, the natural circulation is rapid and slightly pulsatory in the minute arteries, but in the true capillaries and venous system, slow and equable. But if the circulation be in the slightest degree impeded, the pulsatory motion at each contraction of the heart becomes very manifest, and is visible in all the three systems of vessels, arterial, capillary, and venous. In the arteries, the motion of the globules is alternately more and less rapid at each systole and diastole of the heart. In the capillaries and veins, the flow of the blood is often completely arrested during the dias- tole, and again proceeds by a pulsatory movement during the sys- tole of the heart. The course of the blood in the arteries is an intermittent one. It is alternately more or less rapid ; more so during the systole of the heart, because then the blood moves under the influence of the most powerful of the moving forces; less rapid during the diastole, because it then moves only under the contractile reaction of the arteries. In the .first movement it Aoavs by jets, which co- incide with the contraction of the ventricles, and which are greater as the artery is nearer the heart. In the second, it flows from an open vessel in a continued stream in consequence of the reaction of the arterial walls. The blood which flows from an artery be- tween the jets, issues out by the elasticity of the arterial tunics. The motion of the blood in the small vessels is much promoted THE CIRCULATION. 173 by a high temperature. Hales found that hot water injected into the mesenteric artery returned by the corresponding vein, with a velocity thirty-two times as great as that of a lukewarm fluid, in- jected into the same vessel. When he injected cold water, the velocity of its motion was only one-eighteenth as great as that of the same volume of fluid of a medium temperature, under the same pressure. For this reason, during very hot weather, a greater quantity of blood is constantly passing through the vessels, and the exhalations from the skin and lungs, are much increased. Hence, as Magendie observes, in persons affected with organic disease of the heart, cold damp weather is sure to bring on fits of suffocation, as well as infiltration and sAvelling of the lower ex- tremities. If now the temperature of tlje weather rises, even if the change be small, the circulation immediately becomes freer, and the symptoms above mentioned disappear. It has been ascertained that the column of blood passing through a vessel moves with different velocities in the central and the ex- terior parts of the current. Upon examining the motion of the blood in an artery under the microscope, if the coats of the vessels are thin enough to admit of the passage of light, it will be seen that the globules move with the greatest rapidity in the axis of the vessel, and the velocity gradually diminishes in passing from the centre to the periphery of the canal. It appears also that, contiguous to the internal sur- face of the vessel, there is a space, about one-tenth or one-eighth of the diameter of the tube in breadth, which is filled with the serum of the blood, and in which this fluid is nearly motionless ; for when red globules leave the central current, as they approach this external stratum, their motion becomes less rapid, and if they get entangled in it, almost wholly ceases ; if they come into con- tact with the sides of the vessel, they become stationary. In mi- nute vessels the influence of this motionless stratum of -serum, and of these different degrees of velocity of the current, will be very considerable ; for a greater relative quantity of the blood will be motionless, and the diameter of the central moving column will be extremely small. If the calibre of the vessel be very small, the central current will be reduced to a mere thread, and in tubes still more minute, fluids can scarcely move at all. It is a very curious fact, noticed by Magendie, that the viscidity of the blood, instead of being unfavourable to its passage through the capillary vessels, is an indispensable condition to its motion in these minute tubes. If it be deprived of this quality, it becomes unfit to circulate in these living canals. A certain degree of vis- cidity indeed has been found to promote the passage of liquids through inorganic capillary tubes. Very pure water, e. g. will pass either not at all, or with great difficulty through very minute tubes, but if a little albumen be added to it, it traverses with ease the same canals. 174 FIRST LINES OF PHYSIOLOGY. Attempts have been made to compute the force Avith Avhich the ventricles of the heart contract. It has been found that the action of the heart is capable of supporting in a tube connected Avith the arteries, a column of blood eight feet high, producing a pressure of about four pounds to the square inch on the inner surface of the arterial coats ; adding to this, the inertia of the injected fluid, and of the blood already contained in the artery, as also the yielding of the coats of the vessel, the force Avith which the heart acts may be estimated at six pounds the square inch. Noav the left ventri- cle when distended has about ten square inches of internal surface, and hence the whole force exerted by it may be about sixty pounds. This corresponds nearly Avith the calculation of Hales, who esti- mated the force exerted by the left ventricle of a horse, in pro- pelling the blood, at 113.22 pounds, and that which is exerted by the left ventricle of a man's heart, at 51.5 pounds. According to Lepelletier, the systole of the left ventricle overcomes the whole pressure of the atmosphere upon the body, equal to 35,000 or 40,000 pounds.* The resistance which the systole of the heart has to overcome, arises from the inertia of the mass of blood which it propels, and the friction of this fluid against the walls of the vessels, through which it passes. Poiseuille ascertained by experiment that the pressure acting upon the inner surface of the arteries of an animal, is the same in every part of the system. There is an exact equality of pressure in all parts of the arterial system, whatever may be the difference of diameter in the arteries, or in their distance from the heart. He also discovered the remarkable fact, that his hasmadynamom- eter indicated the same arterial pressure in a horse and dog, show- ing that a heart which Aveighs only three or four ounces, exerts the same amount of pressure on the Avails of the vessels, as one which weighs six or seven pounds. In the veins the pressure is much less than in the arteries, in consequence of their superior capacity. The pressure diminishes during inspiration and increases during respiration. The injection of water into the veins, Aveakens the contractile energy of the left ventricle, and the general pressure of the blood throughout the whole vascular system. Hence perhaps, in part, the beneficial effects of aqueous drinks in febrile diseases. When an artery is tied, the pressure of the blood which is removed from its internal surface, is distributed throughout the remainder of the arterial system. The force of the contractions of the left ventricle being resisted by the ligature, is divided among the other vascular tubes which remain open, and increases the pressure of the blood in every part of the arterial system. Hence the amputation of one of the extremities, which diminishes very considerably the circle of the circulation, is followed by in- *Is not the effect partly owing to the superior energy of contraction of the left ventricle' THE CIRCULATION. 175 creased pressure and tension of the whole arterial system. The effect is partly to be ascribed to the diminished surface on Avhich the force of the left ventricle acts, and partly to the relative in- crease of the volume of the blood, compared Avith the diminished capacity of the vascular system. Poiseuille found that pain increases the internal pressure of the vessels, probably by augmenting the energy of the contractions of the heart. I have knoAvn an apoplectic affection occur in a young lady immediately after the extirpation of a small tumour from the neck. The operation Avas borne Avith the utmost pa- tience and tranquillity, but as soon as it Avas completed, she began to yawn in a very extraordinary manner, and soon became speech- less, and nearly insensible. This state continued about two days, when it terminated in death. In this case the pain of the opera- tion, and the effort to Suppress any manifestation of it, may be supposed to have increased the vascular pressure to such a degree, that the vessels of the brain could not sustain it. The father of this lady, a learned president of one of our most distinguished universities, died of apoplexy. The whole quantity of the blood in the body of an adult, is estimated at between thirty and forty pounds, and this, it is com- puted, performs more than five hundred and fifty revolutions through the body every twenty-four hours. A complete revolu- tion of the blood, it is estimated, is accomplished in about three minutes. The contractions of the ventricles take place at equal intervals, and in adults from seventy to seventy-five times in a minute. In new-born infants, the heart contracts about one hun- dred and forty times in a minute, a rate which gradually dimin- ishes until the period of adult age. In old age, the contractions of the heart diminish in frequency, the pulse not exceeding sixty in a minute. Sounds of the Heart. Upon applying the ear to the region of the heart, a double sound, consisting of two successive sounds folloAved by an inter- val of silence, is distinctly heard. This double sound, which has been compared to the ticking of a watch, Avill be found to coincide Avith the beating of the heart and the pulsation of the arteries, and of course to recur with the same frequency. The first sound is duller and more prolonged than the second, in which it terminates Avithout any appreciable interval. The second, which is shorter, clearer, and more sonorous than the first, re- sembles the flapping of a bellows' valve ; or the sound of a dog lapping water, or that produced by gently striking the surface of a fluid with the flat of the hand. This sound succeeds the first so rapidly as almost to be confounded with it. The interval of silence then folloAVS, the length of which will depend on the 176 FIRST LINES OF PHYSIOLOGY. slowness or infrequency of the heart's contraction. This inter- val is interrupted by the first sound, which commences the series anew. This double sound is owing to the action of the heart beyond all question, but as to the mechanism of it, many opinions have been entertained by physiologists, and the subject is still in an unsettled state. It is ascertained, however, that the first or dull sound occurs during the ventricular systole. It is synchronous Avith the impulse of the heart against the side and with the pulse ; and in the experiments on animals, has been observed to occur at the moment the ventricle was seen to contract, Experiment has also determined that the second or clearer flapping sound occurs during the diastole of the ventricles. The most prominent opinions as to the causes of these sounds are the following. 1st. That which refers them to the contraction and active dila- tation of the ventricles. It is well known that muscular contrac- tion produces sound. If the fist be clenched and applied to the ear, a sound is heard similar to that of a distant carriage rolling rapidly along. This obscure rumbling or roaring noise is com- posed of a series of sounds, following one another in rapid suc- cession ; and it immediately ceases when the muscular contrac- tion is discontinued. If the contraction becomes more forcible, the vibrations which constitute the sound become more frequent; in the opposite hypothesis, less so ; or if the ear be rested upon a cushion, and the person clenches the jaws forcibly, as by biting the knot in a handkerchief, the same result is obtained. The introduction of the point of the finger into the ear also gives rise to this sound. Muscular contraction, hoAvever, is not in all cases productive of this sound. This is true for the most part of the spasm of tetanus. The opinion that the sounds of the heart are owing to a similar cause is untenable, for they are entirely unlike in their character, and the former are vastly louder than any muscular sounds; be- sides all which, the sounds of the heart are generally louder, as Hope remarks, in direct proportion as the ventricular walls are thinner. A second opinion, which is that of Dr. Hope, ascribes these sounds to the impulse given to the molecules of the blood, by the contraction of the ventricles. This impulse is first given to the particles of blood in contact with the ventricles, and is propaga- ted from particle to particle through the mass of the fluid, the collision between them producing sound. The irregularity of the internal surface of the ventricles, occasioned by the columnar carneas, seems calculated to favor the production of sound; for the external stratum of blood, which is entangled as it were in the sinuosities or the columnas, is thrown into innumerable con- flicting currents by the contraction of the ventricles. Hence the collision of the particles is more extensive and violent, than if it THE CIRCULATION. 177 were occasioned by a simple direct impulse. The central mass at the same time is tending towards the mouths of the aorta and pulmonary artery; and as it is composed of a multitude of con- flicting currents, reflected on all sides from the walls of the ven- tricles, and converging toAvards these orifices, the collision thus produced in the molecules of the blood occasions the sound. The second sound, or that of the diastole of the ventricles, is occasioned, as Hope supposes, by the sudden reaction of the walls of the ventricles upon the blood at the completion of the diastole. The particles of this fluid, Avhich shoots Avith great velocity from the auricles into the ventricles, are suddenly arrested in their course by the abrupt termination of the ventricular diastole, and the reaction of the ventricles produces the sound. The auricles do not contribute to either sound, nor indeed, according to Hope, do the auricular contractions produce any sound whatever. On this theory Bouillaud remarks, that if it were well founded, these sounds ought to continue, or at least not wholly disappear, in indurations or other lesions of the valves. But in fact, accord- ing to Bouillaud, these lesions, especially indurations of various kinds of the valves, put a complete, or nearly complete stop to the normal sounds of the heart, and give rise to certain acciden- tal sounds, known under the name of the bellows or rasping sound, &c. A third opinion is that of Rouanet and Bouillaud, which ex- plains the sounds of the heart by the action of the valves, on the principle in which sound is produced by the play of the valves in machinery. The first sound, or that of the systole of the ventricles, is sup- posed to be caused, 1. By the sudden and energetic closure of the auriculo-ventricular valves, which are drawn toAvards each other by the contraction of the columnas carneas, so as to come smartly together. 2. By the sudden depression of the semilunar valves, by the column of blood projected into the aorta and pul- monary artery by the systole of the ventricles. The second sound, or that of the dilatation of the ventricles, is caused, 1. By the forcible elevation of the sigmoid valves by the Avave of blood which the aorta and pulmonary artery forces against them, and the sudden collision of their opposing faces ; 2. Sudden depression of the auriculo-ventricular valves, Avhich is produced by the diastole of the ventricles, aided by the contrac- tion of the auricles, propelling the blood into them. The chief cause of this second sound, is supposed to be the sudden impulse of the column of blood against the aortic and pulmonary valves. The chief argument in favor of this theory of the sounds of the heart is, that whatever diseases this organ may be affected with, so long as the play of the valves is free and unobstructed, 23 178 FIRST LINES OF PHYSIOLOGY. the sounds of the heart undergo no material change ; and on the contrary, in all affections of this organ Avhich are accompanied Avith an impeded or abnormal action of the valves, the natural sounds of the heart are essentially changed, and sometimes wdiolly disappear, giving place to a variety of morbid sounds, as that of the bellows, rasp, saAv, file, &c. Moving Powers of the Circulation. Some physiologists, as Harvey, Haller, and Spallanzani, con- sider the heart as the only moving power of the circulation. Others, as Hunter, Blumenbach, Soemmering, Senac, Martini, &c, are of opinion, that besides the propelling force of the heart, a muscular contractility of the arteries, is one of the moving forces of the circulation. A third class, including Bichat, Weitbrecht, and DarAvin, deny that the arteries possess an active power of contracting ; but they assume a vital contractility in the capillary vessels, a kind of ab- sorbing and propelling force, which moves the blood in the capil- • Iary system, which they consider as removed from the influence of the heart. There is another class, among whom are Treviranus, Cams, and some others, who ascrib.e the motion of the blood, chiefly, to a self-moving power existing in the blood itself, while they consider the heart as only an auxiliary force, and deny all power to the arteries and the capillary vessels. Another opinion, almost as singular, is that of Burns, who re- gards the arteries as the principal moving powers of the circulation, while he limits the office of the heart merely to the regular de- livery of the blood to the aorta, to be afterwards distributed by the contractions of the arteries to all parts of the system. Burns' opinion 'is founded on a phenomenon, which he alleges is often observed in patients affected Avith ossification of the aortal valves. He says that it is a Avell knoAvn fact, that in this disease the heart sometimes contracts tAvice for each pulsation of the arteries, which he affirms could not happen if the heart propelled the blood through the arterial system by its own unassisted powers. For in that case, the arterial pulsations being the effect of the con- tractions of the heart, Avould necessarily, in every instance, exact- ly synchronize with the latter, and could in no case be either more or less. The phenomenon, he says, may be easily explain- ed, by considering, that when the aortal valves become rigid by ossification, they oppose an obstacle to the free passage of the blood from the heart to the aorta ; so that a sufficient quantity of blood is not projected into the artery by a single contraction of the heart, to fill the vessel; and the latter, consequently, does not react upon the blood, until it receives an additional supply by a second contraction of the heart. THE CIRCULATION. 179 These opinions Ave shall not stop to examine, but shall proceed to consider the functions of the different parts of the circulatory apparatus. Functions of the Heart. . The heart is the principal moving power of the circulation; a doctrine Avhich rests on many facts and considerations. One of these is the astonishing irritability of the heart. When this organ is removed from the thorax of a living animal, as, e. g. a frog, and put into warm Avater, it Avill continue to contract and dilate with great energy, throAving jets of the fluid to some distance for a considerable time. It even exerts this self-moving poAver when empty, and placed in a vacuum, so that its action is independent of the contact of air and blood.* In some animals, particularly in some of the reptiles and fishes, the heart retains this power of contracting some time after death. The heart of' a snake has responded to very active irritation, four days after the death of the animal. Harvey states that if the heart of an eel, and that of certain fishes, be removed from the thorax and cut into pieces, the separate parts Avill alternately con- tract, and become relaxed. The heart of a sturgeon Avas cut out and laid on the ground, and after it ceased to beat was bloAvn up, in order to be dried. It Avas then hung up, when it began to move again, and continued to pulsate regularly, though more slow- ly, for ten hours; and it even continued to contract Avhen the auricles had become so dry as to rustle with the motion.-^ Mr. SAvan relates, that after tying the principal arteries of a puppy, he removed the heart and lungs, and placed them on a table exposed to the air, and the heart continued to pulsate for several days! Mayo states, that if the heart be taken from the body of an animal immediately after death, and the blood be carefully washed from its internal surface, or, if the auricular portion be separated from the ventricles by a clean section, the alternate states of action and relaxation continue to recur as before ; and for a short period, no stimulus seems to be required to excite it to contract. The alter- nation of action and repose, Mayo remarks, seems to be natural to its irritable fibre, or to result immediately from its structure. Nothing of this kind is observed in the arteries. They never undergo the alternate contractions and dilatations which are ob- served in the heart taken from a living animal; but they are uni- formly found contracted upon themselves. Nor do irritations ap- plied to them excite them to contraction after death. If the finger be inserted into the open aorta, it does not feel itself compressed by the contraction of the vessel, as it does when thrust into the heart. * An old chronicle, purporting to be a contemporary account of the murder of James I. of Scotland, in describing the execution of one of the conspirators, relates that " they boweld and quarterd him all quyke, and drewe out his harte* of his body; the which harte lepe thrise more than a fote of heghte, after hit was drawen owte of his body." t Mitchell, Am. Journ. Med. Scien. No. 13. 180 FIRST LINES OF PHYSIOLOGY. If an arm of a dead body be cut off, and immersed some time in a warm bath to make it pliable, and a small tube be then fixed by one extremity in the brachial artery, and by the other in the open carotid of a large living dog, the heart of the animal will instantly drive blood into the lifeless arm, and produce a feeble pulsation in the artery. So if several inches of an artery be cut out, and the continuity of the canal be re-established by a metal- lic tube, the portion of the artery beyond the tube will pulsate just as if the vessel had remained entire. Bichat observes, that if the arteries give rise to the pulse by their own powers of con- traction, there ought to be a defect or irregularity in the arterial pulsations below an aneurismal tumour; since the arterial texture being altered and partly destroyed, it must necessarily lose its liv- ing powers, and consequently its vital contractility. Bichat further observes, that the jets of blood from an open artery, correspond with the dilatation of these vessels, and the subsiding of the jets with their contraction; which is exactly the reverse of Avhat we should expect, if the pulsations were occasioned by the action of the arteries themselves. On the whole there can be no doubt, that the pulse is occasioned by the systole of the heart, and not by the action of the arteries themselves. The pulse, in all parts of the body; is exactly synchronous with the systole of the ven- tricles. According to Dr. Young, the velocity of the pulsations is six- teen feet in a second, which would diffuse them almost simulta- neously throughout every part of the system. The pulse seems to be caused, not by the dilatation of the arteries, but by a slight move- ment of locomotion, or vibration, occasioned by the stroke of the ventricles and simultaneous with it, followed by reaction of the arterial coats upon the column of blood. This occupies the in- terval between the pulsations. Even Avhen ossified and incapable of being dilated, it is said that they still pulsate. Sometimes the aorta forms a long bony tube, yet the pulse is not obliterated. No pulse exists in animals destitute of a heart. Functions of the Arteries. The only power which the arteries exert in the circulation, according to Bichat, is the physical prop- erty of elasticity or contractility of tissue. In his view of the circulation, the poAver of the heart projects the blood into the arteries, which at first yield, though very little, to the impulse; but, as the blood advances farther on in the arterial system, the part of the latter nearest the heart, Avhich was first dilated, being relieved of the distention, contracts by its elasticity upon the de- creasing column of blood. In this view, the contractile power of the arteries merely serves the purpose of adapting their capacity to the volume of their contents, and, in short, of keeping the arte- ries constantly full, Avhatever may be the quantity of blood which they contain. And if we keep in mind the fact, that the arteries, notAvithstanding the perpetually varying quantity of their blood, THE CIRCULATION. 181 are constantly full, it is easy to conceive that the contraction of the left ventricle, forcing an additional quantity of blood into them, will be felt, at the instant it takes place, throughout the whole arterial system; and that a quantity of blood, equal to that which is propelled into the aorta by each contraction of the left ventricle, will be removed by the same stroke from the further extremity of the arterial system. If the arteries of a dead body be injected with water, and a syringe filled with the same fluid be fixed in the aorta, at the moment the piston of the syringe is pressed down, the Avater will spirt out of any artery that happens to be open, no matter how remote it may be from the propelling force. In this view, the contraction of the arteries contributes not a particle of power to the circulation, but merely serves to keep the arterial tubes constantly full, by adapting their capacity to the volume of their contents. Many facts, hoAvever, are inconsistent with this doctrine, and tend to prove that the arteries are endued, not merely Avith the physical property of elasticity, but with a vital power of contrac- tility, by which they contribute to the sum of the moving forces of the circulation. 1. If the carotid artery of a living animal be laid bare for a few inches, and two ligatures be applied to it at some distance from each other, on making a small incision into the artery be- tween the ligatures, the blood will immediately spirt out with considerable force, and the artery become much contracted. As, in this experiment, the force of the heart is intercepted by the lower ligature, the blood must be forced out of the artery by its own contractile poAver. If the experiment be performed after death, the blood, instead of spirting out to some distance, will flow out with little or no jet. Magendie compressed Avith his fingers the crural artery, in a dog, and saw it contract below the pressure, so as to expel from its cavity all the blood it contained. 2. In hemorrhage, the bleeding arteries contract in proportion to the loss of blood; but if the hemorrhage prove fatal, the same vessels return to their original dimensions. Their contraction, in the first instance, is evidently not owing to elasticity, but must be of a vital character, because, after death it ceases, and the arte- ries become enlarged, and resume their original diameters. 3. Arteries may be influenced by stimulants applied to their nerves. Philip found that the motion of the blood, in the capil- lary system, was influenced by stimulants applied to the brain. But Sir E. Home ascertained that even the large arteries were capable of being excited, by irritating the nerves which supplied them. He separated by a probe the par vagum, and the sympa- thetic nerve, from the carotid artery, in dogs and rabbits; and then, touching these nerves with caustic alkali, in one minute and a half he observed the pulsations of the artery gradually to in- 182 FIRST LINES OF PHYSIOLOGY. crease, and in two. minutes to become still stronger. In another experiment he Avrapped the Avrist of one man in ice, and envel- oped that of another in cloths dipped in hot water ; in consequence of which, in the first individual, the pulse in the wrist operated on, became stronger than that of the opposite wrist; and in the second, weaker. 4. The shrinking of arteries, from exposure to the air, demon- strates a power of contraction in them different from mere elas- ticity, and Avhich must be of a vital character. Dr. Parry found that the artery of a living animal, if exposed to the air, would sometimes contract in a few minutes to a great extent; and in some instances, only a single fibre of the artery was affected, nar- rowing the channel of the vessel, as if a string were tied round it. 5. Hoffman observes, that in paralytic limbs, there is in many instances, no pulse, although the power of the heart is unimpair- ed ; and, according to Martini, Nassius relates the case of a man, who died in a fit of syncope, in Avhich a very sensible pulsation of the arteries continued a quarter of an hour after the motion of the heart was entirely extinct. In paraplegia, I have known an almost complete suspension, not only of the capillary circulation, but even of that in the large veins, below the seat of the lesion in the spine. Just below the line dividing the healthy from the paralyzed part, it Avas impossible to. obtain blood by cupping; although, just above this line, blood escaped freely from the incis- ions of the scarificator. Some of the cutaneous veins of the thigh AArere very large and prominent, and apparently distended Avith a dark blood. Yet upon plunging a lancet into one of them of the size of a goosequill, only a single drop of very black blood escaped from the puncture. Here a part of the vascular system was abso- lutely paralyzed, together with the powers of sensation and motion, by a lesion of the spine, and the blood was almost motionless in the vessels of the affected part, though the powers of the heart Avere not essentially impaired. Why Avas not the blood propelled through these vessels by the vis a tergo ? 6. A fact mentioned by Laennec, and which has probably been observed by many other physicians, is worthy of notice in this place. This eminent pathologist asserts, that in diseases of the heart the pulse is often feeble, and indeed almost imperceptible, although the contractions of the heart, and especially those of the left ventricle, are much more energetic than usual. In apoplexy, on the contrary, the pulse is frequently strong, Avhen the impulse or contraction of the heart is very feeble ; facts which, according to Laennec, seem to be inexplicable, except, by supposing that the arteries act independently of the heart. 7. Further : cases have occurred, though very rarely, in Avhich the pulsations of the arteries did not correspond Avith the systole of the heart. The instances referred to by Burns are of this description. According to Rudolphi, Zimmerman saAV a woman, THE CIRCULATION. 183 in whose right arm the artery generally beat only fifty-five strokes, while that of the left beat ninety or ninety-two. Dr. Elisha Bar- tlett has briefly reported a case of the same kind in the American Journal of Medical Sciences, May, 1836. The patient was a young female affected with chlorosis. She was subject to a strong and painful pulsation in the temporal arteries, which was not synchronous with the action of the heart. The average num- ber of pulsations at the Avrist was found by repeated counting to be one hundred and six; that of the pulsations of the temporal artery was eighty. A venerable medical friend mentioned to the author a similar case, Avhich he had witnessed himself. On this subject Martini makes the folloAving remark : "Ad hoc arteriarum micatus saepenumero frequentiores deprehenduntur, quin cordis motus' nihilum quidem increverint." The same author further states the following fact: " Corde osseam firmitatem adepto, per- git sanguis per arterias promoveri.". 8. There are some animals, in which a circulation exists, although they are destitute of a heart. And in fishes, which have only a venous or pulmonary heart, the arterialized blood is moved solely by vessels. The aorta is formed by the union of branches proceeding from the gills. To these facts may be added, a curi- ous discovery made by Hall, of an artery in the frog and toad, Avhich pulsates distinctly after the removal of the heart. 9. After the removal of the heart from a living animal, the blood may still be seen to flow in the small vessels. Mayo states, that in an experirnent of Hall, a ligature was tied round all the vessels passing to and from the heart of a frog; yet the blood continued to flow with some rapidity into the. arteries of the web of the foot; but after a few seconds it became slower, then stopped, when a retrograde rush of blood took place. After this, its ordinary flow was resumed, then a reflux again took place, and so on alternately, for a considerable time. Imperfect human foetuses are sometimes destitute of a heart. In these the1 circulation must be carried on wholly by the action of the arteries and veins. An important fact connected Avith this subject, which is men- tioned by an old anatomist, I shall make no apology for citing in his own language : " Quanta arteriarum in protrudendo sanguine sit potentia, manifeste ab injecta ligatura, patet; vix enim ea, in vivente arteiia etiam magna constringitur, quin statim ultra vincu- lum, tempore quo vix tres quatuorve pulsationes peragerentur, omriino inanitur quamvis a corde, impediente fascia, nullum pro- cedentem sentiat impulsum." * It may not be amiss to mention, in this place, a curious fact, Avhich has sometimes been observed, in cases of amputation of the loAver extremities, viz. that scarcely any blood has escaped from the incision of the soft parts; and, upon examination, it has been * De Back, Dissertatio de Corde. 184 FIRST LINES OF PHYSIOLOGY. discovered that the main artery of the limb was ossified, or con- verted into a rigid tube of bone. If it Avere certain, in these cases, that the ossified artery was pervious throughout its Avhole extent, the fact would form a curious counterpart to that cited above from Martini, viz. that in ossification of the heart, the blood still con- tinues to circulate in the arteries. The true explanation of the phenomenon, however, we have probably yet to learn. 10. There is still another remarkable class of cases, in some respects analogous to those just mentioned, and still more irrecon- cilable Avith the doctrine of Harvey and Haller, that the heart is the sole moving power of the circulation. In these cases there is a cessation of pulsation in some of the large arteries in the upper or loAver extremities, no appreciable disease existing in the arterial coats, and the action of the heart being perfectly natural. A remarkable case of this kind is reported in the Medico-Chirurgical Review, for April, 1836. The patient was a young female aged 22, who had suffered a severe attack of pneumonia, from the effects of which she had not fully recovered. Three years after- wards, she was affected with pains in the legs and arms, and epi- gastrium, chills and febrile heat, furred tongue, confined bowels; the pulse ninety, and small. A few days after the reporter first saw her, she had no pulse at either wrist, while the heart and carotid arteries were acting strongly. At a subsequent visit, a few days later, the pulsation was found to have ceased about an inch below each clavicle, while pain was elicited by pressure along the course of the main arteries of the arm. Some days after, a slight vibration Avas perceptible in the left radial artery, while all pulsation had disappeared from the dorsal arteries of the left foot. Shortly afterwards, no pulsation could be found in any artery of the extremities. Severe pains were felt at the same time in some of the limbs, especially the left leg, which exhibited signs of incipient mortification, and was, therefore, removed by amputa- tion. On loosing the tourniquet, very little blood escaped from the large arteries, and this without jet; while the smaller arteries bled freely, and several of them required the ligature. Upon slitting up the large arteries of the amputated limb, no trace of disease could be found in them. But they appeared smaller than usual. A very remarkable circumstance in this case, Avas the return of the pulse in arteries in which it had wholly ceased. This occurred repeatedly in the left radial artery. Another cir- cumstance Avorthy of attention, was the pain and tenderness along the course of the large arteries of the arm, a fact Avhich appears to point to a morbid state of these vessels themselves, as the cause of the absence of pulsation, for the action of the heart continued un- altered. This curious case suggests many interesting reflections, which it must be left to the reader to make. It will be found to be a problem of no easy solution, to reconcile it to the doctrine of THE CIRCULATION. 185 Harvey and Haller. Cases of a similar kind are recorded by Parry and others. 11. To the facts and considerations above mentioned, may be added the experiments of Hastings, Avhich appear to establish, beyond a doubt, the irritability of the arterial canals. In these experiments the larger arteries of different animals, the aorta, femora], and carotid, were laid bare, and subjected to different irritations, of a mechanical and chemical nature; and the result, in general, was increased contraction of the vessel operated upon. When the vessel was scraped with the scalpel, the irritation pro- duced a contraction in it, or rendered its pulsations more percepti- ble, or occasioned an irregularity in the surface of the artery, which appeared to rise from a permanent contraction of the fibres of the middle coat. In some instances, a contraction Avas produced, which remained after the death of the animal. The application of ammonia produced similar effects, notwithstanding the assertion of Bichat, that no contraction can be produced in arteries by means of alkalies. In one experiment, an artery was proved by measure- ment to have shrunk one-eighth in circumference by the applica- tion of ammonia. In other experiments, it increased the action of these vessels; for arteries which Avhen first exposed scarcely pul- sated, Avere very evidently contracted, and dilated immediately after being touched by the liquor ammonia. The nitric' acid, also, occasioned a considerable contraction of the arteries. 12. The ganglionic nerves distributed upon the coats of the arteries and veins, probably confer upon these vessels some vital endowment. In other organs, as the heart, the intestines, and stomach, we find that this nervous influence is connected with a susceptibility to the influence of stimulants, and is, perhaps, the cause of it. One use of the nerves in the coats of the blood-ves- sels, perhaps, is to subject the blood to ganglionic innervation; another possibly may be, to render the vessels themselves excita- ble by the stimulus of the blood. Mr. Swan remarks that the nerves have considerable power over the arteries independently of the heart, a fact which he says, "we have frequent opportunities of Avitnessing in diseases." In illustration of it, he mentions the case of a patient who complained of numbness in the left side, attended Avith coldness and slightly diminished muscular action; the pulse on that side was weaker than on the right, where it was perfectly free and natural. The symptoms Avent off and returned several times within a few days, and had no connection with organic disease. According to Mr. S., the common opinion that the blood-vessels are furnished with nerves almost entirely by the great sympathetic, is a mistake. The aorta, it is true, is supplied by it, but many of the arteries receive contributions from the nearest branches of other nerves, by Avhich means their actions, he remarks, become more 24 186 FIRST LINES OF PHYSIOLOGY. readily associated with the actions of the parts to which they are distributed, and the supply of blood made to depend on the exi- gencies of the organs, and not merely on the action of the heart. The pain produced by tying up arteries, seems to show that they receive other nerves than those of the sympathetic. When an arterial trunk, the direction of which is straight, is exposed in a living animal, in general no dilatation and no motion are perceptible to the eye during the systole of the left ventricle. But on applying the finger to the vessel, the pulsation is readily perceived. According to Magendie, however, the dilatation of the aorta, during the systole of the heart, is manifest to the eye j and the same effect takes place in the divisions of the aorta of a certain magnitude; but the dilatation continually decreases in proportion as the arteries become smaller; and ceases wholly in those of a very small diameter. Mayo also asserts, that if an ani- mal, in Avhich the carotid artery is exposed, be excited or alarmed, as by holding its nostrils for a few seconds, the heart will contract with violence, and the artery, instead of lying pulseless and motion- less, will leap from its place at every systole of the left ventricle, becoming elongated, and assuming a tortuous appearance. In the arteries which are curved the pulsations are visible; he- cause the impulse of the blood projected into them tends to straighten or extend them, which produces a sensible motion in the vessels. The curvature of the aorta is the place where this effect is most considerable. Mayo states, that a partial-dilatation of an artery may be produ- ced, by exposing it in a living animal, and rubbing it for half a minute between the finger and thumb. A large artery in a living animal, as the carotid of an ass, or the crural artery of a dog, treated in this manner, becomes sensibly enlarged in the part sub- jected to the. friction, assuming an ampullated appearance, Avhich subsides in a quarter of an hour, if the wound be closed. Functions of the Capillaries. The irritability of the capillary vessels has been demonstrated, in the most conclusive manner, by the experiments of Dr. W. Philip. In some of these experiments, the blood was observed to move in the capillary vessels, after the excision of the heart, and even after death. The web of a frog's foot was placed in the field of a microscope, and the capillary vessels were distinctly observed, to contract on the application of stimuli. The capillary vessels of the mesentery were observed to move the blood some time after the death of the animal. Dr. Philip also found, that the motion of the blood in the capillaries is influenced by the application of stimulants to certain parts of the nervous system, in the same manner as the motions of the heart, and wholly independently of any control exerted upon them by this organ. There are reasons for believing that the force of the heart and of the arteries is nearly exhausted Avhen the blood reaches the THE CIRCULATION. 187 capillaries. The motion of the blood gradually becomes sloAver, and the vital fluid ceases to move by jerks. Besides, the capillary vessels are the seats of the vital operations of nutrition, calorifica- tion, secretion, and hematosis ; and it seems difficult to conceive that these processes, which are extremely variable in their activity, should not directly influence the quantity and the motion of the blood which supplies them with materials. In microscopic obser- vations the blood has been observed to hesitate in its motion, to stop, as if uncertain what course to take, and even to move in a retrograde direction, with astonishing velocity and for a long time. If a part be irritated, the blood is seen to flow towards it suddenly in the capillary vessels, as if these exercised an attraction for it. The portal circulation furnishes a strong argument in favour of the doctrine of the vital contractility of the capillaries. It is impossible to conceive that the power of the heart, can extend through two capillary systems, which the portal blood is obliged to traverse. The capillary vessels themselves must be the princi- pal agents of this circulation. It appears to be owing to the contractility of the capillaries surviving the other powers of the circulation, that the larger arte- ries in dead animals are found empty. In most cases the capillaries remain alive and active throughout the system, for a considerable time after respiration has ceased, working, as Dr. Arnott expresses it, like innumerable little pumps, drawing the blood out of the arteries, and forcing it into the veins. The influence of the heart, however, is not annihilated in the capillary vessels, but extends through the capillary system into the veins. Magendie found, that when he compressed the femoral artery in an animal, the blood flowed out more sloAvly from the femoral vein; and as soon as the pressure was removed from the artery, again spirted out in a larger curve. When the action of the heart is feeble, the remote parts of the system are pale and cold. It appears, on the whole, that the blood moves in the capil- laries under a threefold impulse, viz. the action of the heart, that of the arteries, and that of the capillaries themselves. This last is probably the chief cause. But besides this impulse, to Avhich the blood is subjected in the capillary vessels, and Avhich impels it forwards in the course of the circulation, and causes it to pass from the arteries into the veins, it is subject to another, which attracts it into the parenchyma of the organs, to be employed in nutrition, secretion, &c. Between these two impulses, the blood sometimes appears to hesitate, as if it were at a loss which to obey. The action of the heart moves it in the first direction; the peculiar action of the nutrient and secretory capillaries themselves draws it in the other. Any irrita- tion applied to these vessels, increases the Aoav of blood towards them ; a principle Avhich is illustrated in inflammation. Hence, the attractive influence of the capillary vessels, regulates the quan- 188 FIRST LINES OF PHYSIOLOGY. tity of blood Avhich traverses the other parts of the circle of the circulation. They may either attract more or less blood to them- selves, or refuse to receive it, and thus materially influence the course of blood in the great vessels, change the pulse, and de- termine the quantity of blood Avhich passes into the veins, and, consequently, of that Avhich moves in the heart and arteries. The arteries and veins become larger in an organ which is the seat of a chronic irritation. From these, and many other similar facts, it appears not improbable, that the principal office of the heart is to propel the blood into the great arteries, which is thence draAvn out, as it were, by the attractive power of the capillary vessels, determined by the wants of those parts of the system to which they belong. When a part of the capillary system attracts to it more blood than usual, the fluxion extends to the neighbouring vessels, and from them gradually to the larger arterial trunks. Hence the increased action of the arteries Avhich go to an inflamed part. Each organ attracts from the great vessels different quantities of blood, according to its degree of vitality, and the activity of its functions. Even in the same part, the capillary circulation varies in its activity, according to the degree of excitement which hap- pens to prevail. Every morbid condition of an organ is accom- panied with a change in its capillary circulation. Further, there are some organs, Avhose functions are intermittent, as the uterus; and these must attract more blood into their vessels, when in a state of activity, than when at rest. All these considerations go to establish the importance of the functions of the capillary vessels, and appear to justify the opinion of Broussais, who considers the great vessels as a reservoir, to furnish the capillary system with blood ; from which these last named vessels draw out only the quantity which they require. The motion of the blood in the minute and capillary vessels is subject to various modifying influences. A slight obstacle to the circulation, as the pressure of a ligature applied very gently to the limb ; a very slight tension of the mem- brane submitted to the microscope, even a very trifling degree of dryness of the web of the frog's foot, will produce a pulsatory mo- tion, consisting of a more and less rapid flow alternately, or of alternate motion and rest of the blood in these small vessels. When the poAvers of the circulation fail or become very feeble, the blood in these vessels becomes affected with a movement of oscillation, in which, during its systole, the heart appears to propel the blood into the extreme vessels, but during its diastole, the contractile and elastic power of the coats of the vessels, and the pressure of the contiguous parts, force the blood back in the oppo- site direction, the two powers thus impressing upon the vital fluid an alternate progressive and retrograde movement. This oscilla- tory motion becomes very striking if the action of the heart be THE CIRCULATION. 189 entirely-intercepted, either by the excision of the organ, or by a ligature round the aorta. In this case, says Hall, the globules flow along the minute arteries in an uninterrupted stream for several seconds, in consequence, as he supposes, of the contraction of its successive portions. It then suddenly reverses its motion and flows in the opposite direction, an effect which he ascribes to the diastole of the vessel. It is difficult to determine the relative proportions of moving power which the heart, arteries, and capillary vessels respectively contribute to the circulation. In general, the further we advance from the heart the irritability of the arteries appears to increase ; and in the capillary vessels it is so great as to be sufficient to give motion to the blood, in some measure independently of the heart. The irritability of the arteries, then, is most inconsiderable nearest the heart, Avhere, of course, it is least needed ; but in the capillary vessels, where the action of the heart is but little felt, this defi- ciency is compensated by a high degree of irritability of the vessels. Functions of the Veins. The causes of the motion of the blood in the veins, also, have been a subject of much controversy among physiologists. These vessels possess little or no elasticity; for, though very dilatable, they appear to have little power of reaction upon their contents. They also appear to be endued with little, if any, irritability; and hence they seem to be incapable of con- tributing any contractile power, either physical or vital, to the circulation. It has therefore been supposed that the vis a tergo, derived from the heart, arteries, and capillaries, continues to operate in propelling the blood in the veins, Avhile these vessels are regarded as mere passive tubes. This opinion, however, is liable to strong objections. The quantity of blood contained in the veins appears to be too great to be sustained in the ascending branches, and kept in motion by the contractions of the heart and arteries, and the vital action of the capillaries, alone. The veins are supposed to contain at least twice as much blood as the arteries; and a circumstance which, from the laws of hy- drostatics, appears to be calculated to increase the pressure of this column of blood in the ascending veins is, that the fluid is con- stantly passing into a narrower channel in its ascent towards the heart. The contracting sides of the cone along which the blood moves, oppose a resistance to the motion of the fluid, which a considerable part of the moving force is expended in overcoming. So that the vis a tergo has not only to sustain and propel twice the column of blood contained in the arteries, but also to overcome a degree of resistance arising from the structure of the venous tubes, the amount of which it is difficult to estimate. But setting aside this difficulty, and supposing that the vis a tergo Avere sufficient to propel the blood in the ascending veins, it is evident that these vessels would always be in a state of great 190 FIRST LINES OF PHYSIOLOGY. distention. In the lower extremities especially, they would have to sustain such a degree of lateral pressure as would keep their coats constantly on the stretch. Yet we do not find that this is the actual condition of the veins of the feet and legs. They never become so much distended as to be converted into rigid tubes; which, however, would necessarily be the case with these vessels if the blood moving in them were propelled solely by a force from behind. For so long as the "veins yielded to the pressure of the blood, this fluid, instead of rising in these vessels, Avould be accu- mulating in and distending them; and not until their sides were distended to the utmost, would the propulsive poAver behind be enabled to force the blood upAvards. Another force, which has been considered as one of the moving powers of the venous blood, is the contraction of muscles in con- tact with the veins, or through Avhich these vessels pass. This has been inferred from the quickened circulation, and the strong pulsations of the heart and arteries,, which follow great muscular exertions. The muscles during their contraction swell and press upon the veins in contact Avith them, and force the blood from the parts immediately subjected to their pressure. The blood, then, has a tendency to move in all directions from the centre of pressure, but is prevented from flowing in a retrograde direction, by the valves with which the. vessels are provided ; and, of course, is necessarily directed towards the heart. When the muscle is relaxed, the vein is relieved from the pressure, and receives anew supply of blood from the capillaries. It is evident, however, that muscular contraction must be a secondary, and by no means a prin- cipal agent; for there are certain diseases, as fever, in which the muscles are perfectly at rest, and yet the circulation, and of course the motion of the venous blood, is as impetuous as after violent exercise. And besides, it appears extremely improbable that na- ture would have relied for the continuance of a function which cannot be suspended for.a moment without destruction, upon an agent so precarious and uncertain as the action of the voluntary muscles.* Muscular action seems to be most necessary to promote the flow of the venous blood in those parts of the system where the veins are destitute of valves, as in the abdomen. Hence a congestion of venous blood in the portal system, engorgement of the liver, and enlargements of the hemorrhoidal vessels, are the natural consequences of inactive and sedentary habits of life. The veins themselves also exert a motive action upon the blood. This action is different from that of the heart, but is not simple elasticity ; for if a vein be punctured between two ligatures, the blood spirts out with greater force during life than after death. Indeed, it is said that true irritability exists in the great venous * Carson. THE CIRCULATION. 191 trunks, as the vena cava inferior, especially in cold-blooded ani- mals. Every one has noticed the shrinking of the external veins, as of those in the back of the hand, in cold weather. They con- tract perhaps to one-third of their ordinary diameter. A singular fact mentioned by Hall, Avhich seems to favour the opinion of the contractile power of the veins, deserves to be no- ticed in this place. He states that Avhen the course of the blood along a large vein is arrested, the "vessel immediately assumes the character of an artery, apparently giving off branches instead of receiving roots; the globules of the blood pursuing a retrograde course." . Further: Hastings found that both the capillary veins and the large venous trunks, readily and sometimes violently contracted on the application of certain stimuli. The oil of turpentine ap- plied to small veins, occasioned a great contraction of their diame- ters. The nitric acid produced so s.trong a contraction in veins irritated by it, that the passage of the blood was almost wholly prevented. On applying nitric acid to a trunk of one of the pulmonary veins in the thorax pf a cat, the vessel with all its branches became much contracted. A similar effect was produced in the abdominal cava of a cat, by the application of nitrous acid. When the experiment was performed after death, the vessels be- came white from the contact of the acid, but suffered no contrac- tion of their coats. These facts demonstrate a vital power of contraction in the veins, from which it may be inferred, that they are not mere passive tubes in the function of the circulation. In some situations, however, the veins cannot contract upon the blood, from their connections with the neighbouring parts. This is the case with the. veins of the liver, and those which pass through the substance of bones. The sinuses of the dura mater are in the same predicament. Another force, which has been supposed to assist in giving motion to the venous-blood, is an aspiratory power existing near the source of the circulation, which draws or sucks the blood into the heart. That such a power exists it seems impossible to deny. What else is it Avhich empties the veins into the heart, when a •ligature which intercepts the vis a tergo, is applied to them ? An experiment described by Harvey sets this fact in a strong light. " Sed in serpentibus et piscibus quibusdam, ligando venas per aliquod spatium infra cor, videbis spatium inter ligaturam et cor valde cito inaniri. " This aspiratory power consists of two forces, viz. the active dilatation of the heart, and the expansion of the thorax in inspiration. On opening the thorax of a living animal, and applying the finger to the heart, it will be perceived that the dilatation of the organ, is an active operation, and not a mere re- laxation of its muscular fibres. So, where the heart of a frog is cut out and put into warm water, it will continue to contract and dilate with great energy, throAving jets of the fluid to some distance 192 FIRST LINES OF PHYSIOLOGY. CEsterreicher witnessed a fact showing the great power with which the heart dilates. He saw the heart of a young dog which weighed scarcely half a pound, throw up a Aveight of six and a half pounds to some height (in der hohe); and Magendie says that Avhen the ventricles dilate it is with very great force, a force Avhich, in animals recently dead, he had many times observed to be capable of raising a Aveight of twenty pounds. Another fact which is favourable to the same opinion is, that after death, the ventricles are generally found distended with blood, from Avhich it seems to follow that the state of dilatation is the natural condi- tion of the organ. Dr. Bostock regards the dilatation of the heart as the effect of the elasticity of the organ, overcome at first by its irritability, which from the contact of the blood causes it to contract to a smaller volume than that at Avhich its elasticity Avould maintain it; but after the stimulating cause is removed by the contraction of the ventricle, the elasticity being no longer counteracted is left at liberty to exert itself, and restores the heart to its former volume. The suction power of the heart, hoAvever, is not admitted by all physiologists. Dr. Arnott denies it, and asserts that, even ad- mitting it to exist, it could not promote the motion of the blood in the veins, because these vessels being pliant flexible tubes, Avould collapse by the atmospheric pressure, instead of suffering the blood to be pumped up in them, by the suction of the heart. If the point of a syringe be inserted into a piece of intestine or eel skin, or a vein filled with water, on attempting to pump up the water, by draAving the piston of the syringe, the water near- est the mouth of the syringe, Arnott observes, Avill be drawn in, and then the sides of the tube Avill collapse, acting as a valve to the mouth of the instrument, and putting a stop to the experi- ment. This experiment of Arnott's, hoAvever, is not a fair repre- sentation of the actual condition of the veins in the living body. For while the circulation is going on, the capillary vessels are constantly forcing blood into the veins, as fast as it is flowing out of them by other causes. The experiment, in order to be satis- factory, ought to be performed in a different manner. Into a piece of intestine, or eel skin, filled with Avater, should be inserted not only one syringe to draw the water out, but another at the opposite extremity to force it in, in the same proportion, so as to keep the vessel constantly full. Then the atmospheric pressure could not make the tube collapse, but Avould be exerted upon the column of fluid contained in it, and force it into the upper syringe. But even if the principle of Arnott's reasoning be admitted, there is a circumstance in the structure and attachments of many of the larger veins which makes it inapplicable to them. It seems that some of the veins are prevented from collapsing either THE CIRCULATION. 193 by their attachment to the neighbouring parts, or by some pecu- liarity of mechanism. This has long been knoAvn to be the case Avith the sinuses of the brain, and the hepatic veins. But accord- ing to M. Berard, there are certain peculiarities in the structure of some of the other veins, by Avhich the same object is accomplish- ed. Thus the mouth of the superior vena cava is kept patulous, and in a state of constant tension, by the process of the pericar- dium Avhich extends over it: and the subclavian veins, and the junction of the jugulars with them, as also the axillary veins along their whole course', from the scaleni muscles to the arm-pit, are maintained in a similar state by their attachment to various apo- neurotic membranes, at the bottom of the neck. These veins, therefore, Avhen divided do not collapse, unless separated-from the parts Avhich keep them on the stretch. The inferior cava may be considered as placed in similar circumstances by its connec- tion with the diaphragm, through which it passes. Accordingly, it always remains extended, and never collapses, even Avhen empty. Hence, according to M. Berard, as the principal veins are thus prevented from collapsing, and are. enabled to resist the pressure of the atmosphere, the suction poAver of inspiration is exerted Avith effect in pumping the blood from the veins into the heart, and in promoting the motion of the venous blood through the liver. The absence of a similar structure in the great veins leading to the extremities, it is supposed must render this poAver Avholly useless in the venous circulation of the other branches of the in- ferior cava, and this might be admitted Avere not these vessels kept from collapsing by the blood constantly passing into them through the vis a tergo. It is OAving to this structure that air is sometimes sucked into a large venous trunk at the bottom of the neck, Avhen Avounded in surgical operations. The expansion of the thorax during inspiration, is another force, Avhich promotes the Aoav of venous blood toAvards the heart. Inspiration establishes a kind of focus of suction in the chest, by Avhich both air and blood are drawn into it. When the chest is dilated, by inspiration, the jugular Areins are observed to empty themselves and collapse ; but during expiration they rise, and be- come turgid Avith blood. Magendie introduced a gum elastic tube into the jugular vein of a living animal, so as to penetrate into the vena cava, and even into the right auricle, and the blood Avas observed to flow from the open extremity of the tube only at the time of expiration. During inspiration, the suction poAver dreAV the blood into the chest, and prevented its rising in the tube. Barry inserted one end of a spiral tube into the jugular vein, and plunged the other into a vessel filled Avith coloured fluid. During inspiration, the fluid Avas drawn from the vessel into the vein, but, 25 194 FIRST LINES OF PHYSIOLOGY. at the time of expiration, it remained stationary in the tube, or was repelled into the vessel. On the whole, the effect of inspiration is to promote the flow of blood towards the chest, and, of course, to empty the remote parts of the circulating system; while expiration produces the opposite effect, obstructing the flow of blood to the chest, and engorging the periphery of the circulation. During expiration the blood moves Avith greater force in the arteries than during inspiration. It appears from experiments that the influence of respiration on the motion of the venous blood is greatest near the heart, and gradually diminishes as the distance from that organ increases. It must be considered, however, in reference to the influence of the expansion of the chest upon the circulation, that there is only one act of respiration, for every five or six pulsations of the heart; and, consequently, that the blood passes five or six times into the auricles of the heart, Avhile respiration takes place but once. In the fostal state, respiration does not exist, yet the circulation has a much greater velocity than after birth. It appears, on the whole, that a variety of causes concur in giv- ing motion to the venous blood, viz. the vis a tergo derived from the action of the heart, the arteries, and the capillary vessels ; the contractile poAver of the veins themselves; the aspiratory action of the heart; the expansion of the lungs in inspiration; and the contraction of the muscles in contact with the veins. Some of the German physiologists assume a self-moving power in the blood, by virtue of which it exerts an effort to diffuse itself throughout the body. They assert, that the blood seeks out or makes new passages for itself in the organs. So in the incubated egg, globules of blood, it is said, may be seen moving in currents, before the vessels are formed. Influence of the Nervous System upon the Heart. The heart is more independent of the great nervous centres particularly of the -brain, than many other organs. If the thorax of a cold-blooded animal be opened, and the nerves which are dis- tributed to the heart be subjected to any kind of irritation the action of this organ is neither accelerated, nor sensibly affected in any mode. Acephalous foetuses frequently live until birth, and sometimes a few days longer. Reptiles have lived six months without a head; and mammiferous animals may live some time after the loss of the head, if the vessels of the neck be tied to pre- vent death by hemorrhage, and respiration be maintained artificially. The principle of the heart's action appears to reside in the organ itself, though some physiologists suppose it to be derived from the nerves distributed throughout its substance, derived from the gang- lionic system and the par vagum; and the innervation of the cere- THE CIRCULATION. 195 bro-spinal axis, particularly of the dorsal part, is supposed to be necessary to the motions of the heart, in their perfect development. The influence of the nervous system upon the circulation is established by many facts. After a considerable injury to any part of this system, as the spinal cord, the brain, or the nerves themselves, the circulation of the blood is enfeebled or partially destroyed, in the part whose nerves have been isolated from the rest of the nervous system. For example ; if the sciatic nerve be divided, the circulation, it is said, becomes feebler by degrees, and at length wholly ceases in the loAver extremity of the same side; but remains unimpaired, or nearly so, in the other parts of the body. The heart's action is impaired by the division of the prin- cipal nerves proceeding from the spinal marrow, and the more so as more of these nerves are divided. Very severe injuries of the brain, or spinal cord, sometimes occasion a total cessation of the circulation. The influence of the nervous system upon the living blood itself, transmitted by the coats of the blood-vessels, is sup- posed by some physiologists to be sufficient to maintain the circu- lation of the blood in particular parts, without the aid of the heart. A celebrated doctrine on this subject was that of Legallois, who attempted to demonstrate that the heart derives its principle of action from the spinal marroAV. It appears, however, from the experiments of Philip, Clift, and Brachet, that the action of the heart survives the destruction of the spinal cord, especially in young animals, and if the operation be performed slowly. The absence of this part of the nervous system, it appears further, does not prevent the action of the heart in foetuses destitute of it. But it should seem from facts mentioned by Brachet, that the great sympathetic exerts the greatest nervous influence over the heart. This writer cites from Hufeland's journal, some experi- ments of Bartels on persons who had been beheaded. Six high- way robbers had lost their heads near Marbourg, and on opening the bodies of the whole six, a Asav minutes after their execution, the heart Avas observed to contract and dilate alternately, Avith considerable force, and in a regular manner. The motions, hoAV- ever, gradually diminished in strength, for the space of half an hour, but Avere instantly re-excited, by irritating a filament of the great sympathetic; while the irritation of the spinal marroAV, merely gave rise to contractions of the muscles of the trunk, Avithout producing any effect whatever upon the heart. The influence of the sympathetic upon the action of the heart Avas demonstrated in a very conclusive manner by experiments on dogs, performed by Brachet himself. In these experiments Brachet succeeded, after many failures, in isolating, on each side, the infe- rior cervical ganglions, and, upon dividing all the filaments which proceeded from them, he found that the action of the heart, after a few irregular contractions, Avas almost immediately annihilated, and the circulation ceased. 196 FIRST LINES OF PHYSIOLOGY. In another experiment, he exposed the cardiac nerves, and followed them into the chest until he reached the cardiac plexus. Having succeeded in isolating this body, he divided it Avith a pair of scissors ; upon Avhich the circulation instantly stopped, the heart ceased to contract, and the animal became rigid, and expired. From these experiments, Brachet inferred, that the heart derives its principle of motion from the ganglionic system. Bouillaud inclines to the same opinion. Some very curious experiments of Weinhold deserve • to be mentioned in this place, though doubts may exist as to some of the inferences to be legitimately draAvn from them. He beheaded a cat, and after the complete cessation of the pulsation of the arteries, and of muscular action, he removed the spinal marroAV, and substituted in its place an amalgam of mercury, zinc, and silver. The pulsations of the arteries immediately recommenced, and muscular action was reneAved, the animal executing several leaps. After the irritability seemed to be exhausted, Weinhold established a communication between the heart and voluntary muscles, and the amalgam in the spinal canal, by means of a me- tallic arc, and succeeded in again reviving general though feeble contractions. In another experiment, he filled Avith the same amalgam the cranial and vertebral canal of a cat, which exhibited no sign of life ; when the animal raised its head, opened its eyes, looked steadily, attempted to walk, and even to raise itself, after repeat- edly falling down. The circulation and arterial pulsations were very active during all this time, and continued for a quarter of an hour after the chest and abdomen Avere opened. In a dog, whose cranium only was filled with the amalgam, he observed that the pupil contracted on the approach of light; .and Avhen a lighted candle Avas placed near it, the dog manifested a desire to avoid it. The animal also listened when a person made a noise by striking with a key upon a table. These experiments are infinitely curious and remarkable, but it. is hardly possible to read the account of them, without feeling a shade of doubt pass, over the mind, whether they are to be con- sidered so much experiments upon brainless cats and dogs, as upon certain brainless animals of a higher order. The heart is wholly exempt from the jurisdiction of the will, though poAverfully influenced by the passions or mental emotions. There is one remarkable case on record. hoAvever, that of a Cap- tain Townsend, who could stop the action of the heart, and re- store it again at will. The story is so marvellous as very natu- rally to have excited some distrust among physiologists; yet a few years since I knew a young man, Avho possessed in a slight degree a similar poAver. He could accelerate or retard the mo- tions of his heart by a mental effort. If the pulse were sixty in a minute, he could raise it to eighty or lessen it to forty. The RESPIRATION. 197 effort Avas purely a mental one, and Avas not accompanied by any muscular action. The change of the pulse took place imme- diately; but on the cessation of the effort, the pulse did not re- turn immediately to its previous state. The effort produced a feeling of weakness, and he made it reluctantly. In this case organic lesion of the heart was suspected to exist. CHAPTER XV. RESPIRATION. The third and last of the vital functions, is respiration, a func- tion Avhich is indispensable to animal, and even vegetable exist- ence. By respiration, the assimilation of aliments, which com- menced in the stomach and intestines, is finally completed in the lungs, by their conversion into blood; and this fluid itself, after being drained of its nutritive and vivifying-principles, in adminis- tering to the various operations of life, is again reanimated by the influence of atmospheric air, and prepared anew to dispense life and nutrition throughout the system. In the human species, and the higher classes of animals, respi- ration is accomplished by certain organs, called the lungs ; two viscera, Avhic.h fill the cavity of the thorax, of a spongy texture, extremely vascular, and divided into lobes. The two lungs are separated from each other, by the mediastinum and the heart, and are enveloped by membranes, termed the pleura. Their figure corresponds Avith that of the cavity of the thorax, Avith the walls of which they are always in contact, so that no air can intervene between them. In consequence of their tissue, after birth, being always penetrated Avith a great quantity of air, their specific gravity is less than that of water, and they swim when placed in this fluid. The substance of the lungs is composed of innumerable fine cells, connected together by a delicate cellular membrane. Each lung is divided by deep fissures into sections, termed lobes, of which the right lung contains three, the left only two. Each of these lobes is subdivided into smaller lobes, or lobules, and these, again, into the fine cells above mentioned. Each lobule is sur- rounded by a thin layer of cellular tissue, Avhich separates it from the adjoining lobules. Each lung is attached to the spine by its root, Avhere blood-A^essels, nerves, lymphatics, and a branch of the Avindpipe enter it. The lungs are covered by a transparent mem- brane, termed the pleura, Avhich is reflected from the root of the 198 FIRST LINES OF PHYSIOLOGY. lungs, over the spine and sternum, ribs, intercostal muscles, and diaphragm. Air is admitted into the lungs, by means of the trachea or windpipe, a tube eight or ten inches long, composed of cartilagi- nous arches, or imperfect rings, deficient on the posterior side; of cellular and muscular coats, and a lining of mucous membrane.* The canal is completed behind by a fibrous membrane. The trachea is situated before the vertebral column, in the posterior mediastinum, resting on the oesophagus, and extending from the lower parts of the larynx, to the level of the second or third dor- sal vertebra. Here it bifurcates, or divides into two branches, termed bronchia, one of which passes to the right lung, and the other to the left. Each of the bronchia subdivides, as it enters the lung; the right into three branches, which are severally distributed to the three lobes of the right lung; the left into two, corresponding with the two lobes of the left lung. As they penetrate into the lungs, they subdivide more and more, branching throughout the whole pulmonary tissue, until their extreme divisions terminate in the fine vesicles Avhich constitute the principal part of the sub- stance of the lungs. Each ramification of the bronchia is con- nected with a particular cluster of these cells, and if air be forced gently into it, it will inflate this, but none of the neighbouring cells, unless the force employed be so great as to rupture the sides of the cells. The air cells are said to be about the one-hundredth of an inch in diameter. The trachea and bronchia are lined by a mucous membrane, Avhich is a continuation of the membrane of the larynx, and ex- tends to the termination of the bronchia. It is lubricated with mucus, secreted by mucous follicles interspersed throughout it. The outer membrane of the tracheo-bronchial tube consists of longitudinal and parallel fibres, and is considered by some as analo- gous to the muscular tunic of the intestines, but by Beclard, as identical Avith the yellow tissue of the arteries. This membrane connects together the cartilages of the trachea posteriorly, filling up the deficiency of the cartilaginous rings, and completing the formation of the tracheal tube. In the smaller divisions of the bronchia, the cartilaginous arches wholly disappear, and the fine aerial canals consist merely of the fibrous and the mucous membranes. The lungs are supplied with two distinct circulations, one of which is destined to the nutrition of the organs, the other is con- nected with their peculiar functions, viz. respiration, or hematosis. * It is a curious fact, that birds can live several hours with the trachea tied, provided one of the hollow bones, into which the air penetrates in respiration, be sawed open so as to admit the air. But if a vessel containing carbonic acid, or azote, be adapted to such an opening, the bird soon dies. RESPIRATION. 199 They receive first, arteries which spring from the aorta, and con- vey arterial blood for the nutrition of the lungs, ramifying over the bronchia, and termed the bronchial arteries ; and secondly, the pulmonary artery, a large vessel which arises from the right ventricle of the heart, and conveys venous blood to the pulmona- ry capillary system, in order to be converted into arterial blood by respiration. These organs also possess two capillary systems; viz. one, which is a part of the general capillary system, is the seat of the nutrition of the lungs, and of the transformation of arterial into venous blood, and intermediate betAveen the bronchial arteries and veins; the other, or the pulmonary capillary system, is the seat of the peculiar functions of the lungs, or of the conversion of venous into arterial blood. This is intermediate, between the pulmonary artery and the pulmonary veins. The extreme branches of the bronchial arteries anastomose freely with one another, and also Avith the minute ramifications of the pulmonary artery and Arein. The bronchial veins open for the most part into the pulmonary veins. The lungs are abundantly supplied Avith lymphatics and con- globate glands. The latter are situated at the bifurcation of the trachea, around the bronchia, and some of them are found in the interior of the lungs. The nerves of these organs are derived from the pulmonary plexus, formed by branches of the pneumo- gastric, and the great sympathetic. The thorax, or chest, in Avhich the lungs are situated, is a box of bones, formed anteriorly by the sternum, laterally by the ribs, of Avhich there are twelve on each side; and posteriorly by the dorsal vertebrae. The seven superior ribs are termed true ribs, the five loAver ones, false. The true ribs are attached posteriorly to the vertebrae, by movable articulations, and anteriorly with the sternum, by cartilaginous prolongations. The ribs are connected together by tAvo strata of muscles, Avhich are termed intercostal. BeloAv, the thorax is bounded by the midriff, or diaphragm, which separates it from the cavity of the abdomen. This muscular par- tition, though dividing the trunk of the body transversely, does not form a horizontal plane, but arches upAvards into the thorax forming a considerable concavity, when vieAved from the abdomen. All the parts of the thorax are movable, and are so arranged that its cavity may be enlarged in every direction. It may be enlarged vertically, by the contraction of the diaphragm; for in contracting this muscle loses in some measure its arched form, and becomes depressed and flattened toAvards the abdomen, so as to diminish this cavity, and enlarge, in the same measure, that of the thorax. Laterally, the thorax may be enlarged by the eleva- tion and abduction of the ribs, the arches of Avhich*are drawn upwards and outwards, by the contraction of the intercostal mus- 200 FIRST LINES OF PHYSIOLOGY. cles; and, in the antero-posterior direction, its cavity may be in- creased, by the elevation of the sternum. There are several muscles employed in giving motion to the walls of the thorax. These are, besides the diaphragm and inter- costal muscles, the serrati, the scaleni, the subclavius, the Icvatores costarum, the pectoral muscles, the abdominal muscles, &c. The phenomena of respiration may be divided into three classes, mechanical, chemical,. and vital. The mechanical phenomena comprehend the mechanism by which air is alternately drawn into and forced out of the lungs; the chemical relate to the changes which the air undergoes in the lungs; and the vital, to those which are effected in the blood by the contact of the air. Mechanical part of Respiration. The mechanism of respiration may be reduced to the two phe- nomena of inspiration and expiration, or the alternate introduction of air into the lungs, and its expulsion from these organs. Inspiration, or the introduction of air into the lungs, is effected by the dilatation of the thorax, which is accomplished by the de- pression of the diaphragm, and the elevation and abduction of the ribs and sternum. By these motions, the cavity of the chest is enlarged in its three principal diameters, vertical, lateral, and antero- posterior. The vertical diameter, extending from the centre of the diaphragm to the top of the chest, is seven or eight inches in length, and this is increased by the contraction of the diaphragm, from tAvo to four inches, according to the depth of the inspiration. It is chiefly the lateral parts of this muscle, Avhich become de- pressed in inspiration, its centre being tendinous and incapable of contraction, and besides, being fixed by its attachment to the ster- num and to the pericardium. According to Lenhossek, the increase of the capacity of the thorax, caused by the contraction of the diaphragm, is five times greater than that Avhich is produced- by the action of the other muscles of inspiration. The lateral, or transverse diameter, is nine or ten inches in length, and is increased by the ascent of the ribs to eleven or twelve. The arches of the ribs are drawn outAvards as well as upwards, during their elevation ; an effect Avhich is OAving to the obliquity of the planes which pass through their arches, in rela- tion to the spinal column, with which they are articulated. From the- same cause, the sternal extremities of the ribs advance for- Avards in their ascent, carrying the sternum Avith them, and thus increasing the depth of the chest from before, backAvards. This diameter is five or six inches in length, and may be increased by the elevation of the ribs, from an inch to an inch and a half. The increase off the transverse diameter of the chest is the greatest about the seventh and eighth ribs, Avhere the horizontal diameter is the largest. In females a greater range of motion is bestOAved RESPIRATION. 201 on the ribs, on account of the impediment to the free descent of the diaphragm, occasioned by the gravid uterus in pregnancy. The elevation of the ribs is accomplished, in ordinary inspira- tion, by the contraction of the intercostal muscles. The first rib is made a fixed point, by the action of the scaleni and subclavian muscles, and all the others are raised towards the first, by a gen- eral and simultaneous movement, caused by the action of the in- tercostal muscles. In difficult or excited respiration, several other muscles contri- bute their aid, in elevating the ribs ; as the great serrati, the su- perior serrati postici, the pectoral muscles, the latissimus dorsi, the sterno-cleido-mastoid, &c. According to Magendie, there are Avell marked degrees of inspi- ration, viz. 1. Ordinary inspiration, Avhich is effected by the depression of the diaphragm, and a very gentle and scarcely per- ceptible elevation of the thorax. 2. Full inspiration, in Avhich there is a very evident elevation of the thorax, as well as depres- sion of the diaphragm. 3. Forced inspiration, in Avhich the di- mensions of the chest are enlarged to the utmost, in every direction. In the first, or ordinary degree of inspiration, the air penetrates only a part of the pulmonary tissue ; in the second, it inflates a larger portion of the lungs; but it is only in the third, that the Avhole extent of these organs is pervaded by it. In the third de- gree of inspiration, several muscles are employed, Avhich are at- tached by one of their extremities to the arms ; in consequence of Avhich, it becomes necessary that the arms be previously fixed, or made a point of support for these muscles to act upon. Hence in violent dyspnoea, from asthma, or any other cause, the sufferer instinctively seizes the arms of his chair, or any other solid body in his efforts to elevate the ribs and expand the thorax. In ma- king violent efforts, on the contrary, as in raising heavy burdens pushing, &c. in evacuating the bladder, or the rectum, and in the efforts of parturition, the walls of the thorax are made a fixed point for the muscles of the arms or abdomen, by taking a deep inspira- tion, and then closing the glottis, to prevent the escape of the air from the lungs. If the muscles which close the glottis be para- lyzed, by dividing the laryngeal nerve, or the glottis be kept open by the introduction of a canula, a strong effort becomes imprac- ticable. The condition of the lungs in the thorax has been compared to that of a bladder enclosed in a receptacle having movable Avails, in such a manner that no air can penetrate between the tAvo, and that the mouth of the bladder opens to the external air. In these circumstances, if the Avails of the receptacle be separated farther from each, the effect Avill be to remove the pressure of the atmosphere from the external surface of the bladder, Avhile its in- ternal surface will remain exposed to it, by means of its mouth 26 202 FIRST LINES OF PHYSIOLOGY. which opens externally. The Aveight of the atmosphere thus acting upon the internal surface of the bladder, and not being counteracted by any external pressure, Avill keep this membranous sac in close apposition Avith the walls of the receptacle, and oblige it to folloAV all the motions of the latter. The situation of the lungs enclosed in the thorax is very simi- lar ; and, consequently > Avhen the chest is. expanded by the action of the inspiratory muscles,'all pressure is removed from the ex- ternal surface of the lungs, the "air contained in these organs ex- pands by its elasticity, and, keeps their external surface in close contact Avith the Avails of the chest; and a volume of air, at the same time; rushes through the glottis and windpipe into the lungs, sufficient to restore the equilibrium betAveen the rarefied air con- tained in these organs, and the external atmosphere. The first act of inspiration, after birth, may be accounted for in the same manner. The inspiratory muscles of the new-born infant are excited to action, either by the. irritation of the exter- nal air, or by an instinctive feeling then first developed; the chest is expanded, air rushes in through the windpipe and unfolds the lungs, and respiration commences. Expiration, or the contraction of the thorax, which succeeds inspiration, is the result of several forces, These are of two kinds, passive and active. The passive are the Aveight of the ribs and parietes of the chest; the resilience, or elastic reaction of the sterno-costal cartilages Avhich had been put-on the stretch, and subjected to a degree of torsion in inspiration; and the elas- ticity of the bronchial tubes. The active poAvers are the abdo- minal muscles, Avhich force the viscera against the diaphragm and thus diminish the vertical diameter of the chest. Another effect of the action of the abdominal muscles, is to fix the infe- rior ribs, so as to make them a point of- support, toAvards Avhich the superior may be draAvn by the intercostal muscles, Avhichmay thus be rendered instruments of expiration. The sacro-lumbalis, the longissimus dorsi/ the serrati postici inferiores, the quadmtus lumborum, the triangularis sterni, contribute to the same effect, that of depressing the inferior-ribs, and diminishing the transverse and antero-posterior diameters of the thorax. According to Magendie, expiration, like inspiration, presents three degrees, viz. 1. ordinary ; 2. large; and, 3. forced expira- tion. In the first degree, or ordinary expiration, there is a diminution of the vertical diameter, produced by the relaxation and ascent of the diaphragm into the thorax; this muscle being pushed up by the abdominal viscera, which are compressed by the anterior muscles of the abdomen. The second degree, or large expira- tion, is the effect of the relaxation of the muscles Avhich elevate the chest, permitting the ribs and sternum to sink down by their own Aveight, and to resume their ordinary relative situation, in RESPIRATION. 203 respect to the vertebral column. Forced expiration is the result of a powerful contraction of the abdominal and the other expira- tory muscles, pushing the diaphragm up into the chest, and pro- ducing the utmost possible depression of the ribs. The oblique and transverse muscles of the abdomen, hoAvever, which are considered as the antagonists of the diaphragm and the principal agents of ordinary expiration, are not essential to this function, and perhaps have less concern in it than has been gene- rally supposed. If the ribs were draAvn doAvn by the contraction of these muscles, we should expect that they would feel teiise and rigid during expiration, Avhich is not the fact. Besides, in extensive wounds of the abdomen, Avhere the boAvels are pro- truded, respiration could not be carried on, if expiration Avere effected by or required the pressure of.the abdominal viscera against the diaphragm ; for in these cases the intestines instead of being pressed up against the diaphragm are ahvays protruded through the Avound; and Avhat is Avorthy of notice, this protru- sion takes place during inspiration ; a fact which proves that it is at this time that the intestines suffer the greatest pressure, and not during expiration, Avhen they are supposed to be so strongly compressed by the action of the abdominal muscles. To these considerations, it may be added, that in certain experiments, these muscles have been divided transversely, or even altogether re- moved,- and yet respiration has continued for a considerable time.* Carson considers the elasticity of the lungs as an important agent in expiration. The lungs have a strong tendency to col- lapse, and they are prevented from obeying this tendency, only by the pressure of the air within them. But if an opening be made into the cavity of the chest, so as to expose the external surface of the lungs to the atmosphere, and thus equalize the pressure on their external and internal surfaces, then the lungs are left at liberty to exert their collapsing poAver and to assume the dimensions Avhich their structure and their elasticity make natural to them. Hence, Avounds penetrating into the thorax are followed by a collapse of the lungs and cessation of respiration on the injured side of .the chest. Carson found, by experiments on calves, sheep,'and dogs, that, the collapsing effort of the lungs Avas equal to the pressure of a column of Avater from a foot to a foot and a half in height. It should seem from this, that the lungs are in a forced state of expansion during life, and that they have a constant tendency to collapse, and to recede from the Avails of the thorax. When the inspiratory muscles cease to act, and to maintain the chest in a state of dilatation, the collapsing power of the lungs may be exerted Avith effect, to a certain extent; because then there is nothing to prevent it. The lungs then shrink to their former volume, forcing out the air Avhich had been * Carson. 204 FIRST LINES OF PHASIOLOGY. admitted by the preceding act of inspiration; and, as the lungs shrink, the diaphragm and intercostals, noAV passive, offer no re- sistance to the external air Avhich presses upon the Avails of the thorax, keeping them in contact with the collapsing lungs, so as to prevent the formation of a vacuum in the chest. According to Rudolphi, the larynx, trachea, and lungs them- selves, take an active part in respiration. The larynx, he remarks, is in incessant motion in the act of breathing. In inspiration, the arytenoid cartilages are drawn apart by the muscles, which go to them from the thyroid and cricoid cartilages, and the glottis is thus opened. In expiration, on the contrary, the arytenoid carti- lages are drawn toAvards each other again by their own proper mus- cles, and the glottis is thus closed. In birds, and the amphibia, Avhich are destitute of an epiglottis, these motions, according to Rudolphi, may easily be seen by drawing the tongue forward, or bending back the lower jaw. With the larynx, the trachea, with all its branches, or the lungs themselves, are in simultaneous action. While the arytenoid car- tilages are separated from each other in inspiration, the inner or longitudinal fibres, which run the whole length of the trachea and its ramifications, contract, by Avhich means all these parts are raised and dilated so as to offer an easy admission to the air. These fibres afterwards become relaxed, and the air passages are contracted — an effect to Avhich the transverse muscles of the trachea contribute-; and the air is thus expelled. Treviranus asserts that an evident motion may be observed in the lungs of quadrupeds, after the removal of the intercostal mus- cles and diaphragm; and in reptiles, if the thorax be opened and the heart removed, the lungs may be observed alternately to con- tract and expand, and their motions may even be accelerated by stimulants. Another fact which affords a strong argument in favour of the irritability of the lungs is, that they are liable to spasmodic affections and to paralysis. The first condition appears in the form of nervous asthma, or dyspnoea; and sudden death sometimes appears to result from the second.* According to this vieAv, all these parts are active in respiration, and of course the comparison of the lungs to a bladder, which is partially expanded and contracted by the ingress and egress of air, is wholly unsuitable. The fibres of the lungs, according to Ru- dolphi, can even act Avhen these organs have grown to the side, and externally are wholly immovable. These are some of the principal facts relating to the physical or mechanical part of respiration. * Lenhossek. \f RESPIRATION. 205 Chemical phenomena of Respiration. The chemical phenomena relate to the changes Avhich the air received into the lungs undergoes in respiration. The atmosphere is that invisible elastic fluid which surrounds the earth to the height of about forty miles, and which is abso- lutely necessary to the existence of all organized living beings, vegetable as well as animal. Its specific gravity, compared to that of water, is as 1 to 770. A column of it, extending to the top of the atmosphere, is equal in weight to a column of water of the same diameter, thirty-tAvo feet, or to a column of mercury tAventy- eight inches in height. The pressure Avhich it exerts upon the human body is consequently enormous, amounting to betAveen thirty and forty thousand pounds on a middle-sized adult. Atmospheric air is composed essentially of three elements, viz. oxygen, azote, and carbonic acid — in the proportion of 20 or 21 per cent, of oxygen, 78 or 79 of azote, and 1 or 2 of carbonic acid. Oxygen is an invisible aeriform body, rather heavier than at- mospheric air, possessing a strong tendency to combine Avith many other substances in nature, and forming Avith them certain com- pounds called acids and oxides; it enters into the composition of air, Avater, and of all vegetable and animal substances ; is the prin- cipal supporter of combustion, and is an element essential to the formation and renovation of the blood, both in aerial and aquatic animals. Azote is an invisible, gaseous body, lighter than oxygen and atmospheric air, and incapable of supporting combustion. In most animals, it is incapable of supporting respiration, though according to Vauquelin, it is the element Avhich supports it in several of the inferior classes of animals. It is one of the essential elements of animal matter, and exists in some families of plants. Experiments seem to have proved, that it is both absorbed and exhaled in res- piration. Carbonic acid, also, is an invisible aeriform substance, of a slightly acid taste, of a greater specific gravity than azote or oxy- gen, capable of forming salts by combining with salifiable oxides, irrespirable by animals, and extinguishing burning bodies. Though it occasions asphyxia in animals who inhale it, it seems to be essen- tial to the respiration of plants. It is always present in atmospheric air, though in a very minute proportion. Atmospheric air contains also, the imponderable elements, light, heat, and electricity; more or less of watery vapour ; exhalations from plants and animals; and many other accidental admixtures. The presence of the essential, as well as the accidental ingre- dients of the atmosphere, may be determined without difficulty. The presence of oxygen is ascertained by the combustion of a lighted taper in air; that of carbonic acid by its making lime- Avater turbid; and that of azote, by the formation of ammonia 206 FIRST LINES OF PHYSIOLOGY. with hydrogen, in the conditions requisite to the combination of the Lavo elements. Caloric and light become sensible, by subject- ing the air to sudden compression in a glass condenser — Avater by the moisture deposited by a mass of air, Avhen suddenly cooled, &c. Such is the composition of atmospheric air, Avhich is so indis- pensable to respiration, and consequently to the support of animal life. Upon analyzing a portion of air, Avhich issues from the lungs in expiration, it is found that the proportion of its elements has un- dergone a considerable change ; and this change is found to con- sist-hi an increase of the carbonic acid, a diminution of the oxygen, and the addition of a large quantity of watery, vapour, containing some animal matter in solution. Thus, instead of consisting of twenty or twenty-one parts of oxygen, seventy-eight of azote, and one or two of carbonic acid, like atmospheric air, the air of expi- ration contains only about fourteen per cent, of oxygen ; its car- bonic acid is increased to about eight per cent., or according to Dr. Apjohn only to about 3.6 per cent.; while the proportion of its azote remains nearly unaltered. It appears then that the portion of air, which has been employed in respiration, loses about seven per cent, of oxygen, and acquires about an equal quantity of car- bonic acid, Avhile the quantity of its azote undergoes little or no change.* Now, if it be admitted that the volume of carbonic acid, which is formed by respiration is exactly equal to that of the oxygen Avhich has disappeared, it suggests a very simple theory of the changes which the air undergoes in respiration. As carbonic acid is formed by a combination of carbon and oxygen, and as a certain volume of oxygen gas disappears in respiration, and its place -is supplied by an equal volume of carbonic acid, it seems natural to infer, that the air introduced into the lungs has furnished the oxy- gen, and the blood in the lungs, the carbon, of Avhich this carbonic acid is composed. According to this vieAV, the whole of the oxygen Avhich has disappeared, is still present in the air of respiration, but it exists in a state of chemical union Avith carbon, under the form of carbonic acid. It has been ascertained, however, by the researches of Lavoisier and Seguin, of Davy, and more recently "by those of Dr.- EdAvards, that a quantity of oxygen disappears in respiration, Avhich exceeds what is necessary for the formation of the carbonic acid Avhich is generated. Edwards estimates this excess of oxygen consumed in respiration above the volume of carbonic acid formed, when at its maximum, at nearly one-third of the oxygen which has disap- peared, and as varying from this almost down to nothing. The * It appears to be owing to the increased proportion of carbonic acid, rather than to the loss of oxygen, that air, which has been respired, loses its fitness for inspiration.' According to Lepelletier, it appears from experiments, that an air composed of forty per cent, oxygen, forty-five of azote, and.fifteen of carbonic acid, will not effect hema- tosis, though it contains twice the proportion of oxygen which exists in common air. RESPIRATION. 207 variation of this excess depends on a variety of circumstances, as the age, the species, or the peculiar constitution of the animal em- ployed in the experiment. Noav if it be true that more oxygen is consumed in respiration than can be accounted for.by the carbonic acid Avhich is formed and is present in the air of respiration, it must be supposed that a part of the oxygen, at least, which has disappeared, has been ab- sorbed by the lungs, Avhile the remaining part may be supposed to have combined with the carbon of the blood, to form carbonic acid. But if a part of the oxygen is actually absorbed by the lungs, some physiologists have been disposed to believe that the Avhole of it is, ' and that the carbonic acid expired is not formed by a union of oxygen and carbon in the lungs, but is secreted and ready formed from the blood. This opinion is adopted by Dr. EdAvards, and is corroborated by some of his experiment's. He found that if frogs, in the month of March, Avere confined for eight hours in pure hy- drogen gas, after their lungs -Avere exhausted of air by'pressure, they continued to breathe, though less and.less vigorously, and expired a volume of carbonic acid gas nearly equal to their own bulk.* Similar results Avere obtained in experiments upon kittens. A kitten three or four days old, Avas placed in a receiver filled with pure hydrogen gas, and in nineteen minutes, performed about an equal number of inspirations. Upon aftenvards examining the air contained in the receiver, it Avas found to contain twelve times as much carbonic acid as could be accounted for by the air con- tained in the lungs of the animal at the beginning of the experi- ment. EdAA'-ards's experiments also proved that nitrogen is sometimes absorbed in respiration, or at least, that a variable proportion of this principle disappears in. this process; a fact which had been previously asserted by Cuvier and Davy. EdAvards found, also, that when small birds Avere immersed in a large quantity of air for a limited time, there Avas in many instances, an evident increase in the quantity of nitrogen, Avhile in others, there was a loss of this principle. He observed, that these different results had some con- nection Avith the season of the year, Avhen the experiments Avere performed. In Avinter, a deficiency of azote Avas observed in the air respired, but in spring and summer, the quantity of this prin- ciple Avas found to be increased. EdAvards inferred from his ex- periments, that both absorption and exhalation of azote are con- stantly going on in the lungs during respiration, and that, according to the predominance of one or the other of these processes, or their exact equality, there is a deficiency or excess of azote in the air expired, or the volume of this principle remains unaltered. The quantity of air received into the lungs in inspiration is exceedingly variable, and has been very differently estimated by * Rudolphi, however, is of opinion, that the carbonic acid, produced by a frog con- tained in a globe of hydrogen gas, is not exhaled from the lungs, but from the skin. 208 FIRST LINES OF PHYSIOLOGY. different physiologists. Gregory estimated it at only tAvo cubic inches. According to Rudolphi, the naturalist Abildgaard states of himself, that Avith a small chest he inspired, in ordinary respi- ration three cubic inches of atmospheric air; but about every sixth or seventh inspiration, his breathing Avas deeper, and he in- spired from six to seven, and sometimes even fifteen cubic inches. Herthold, Avith a more capacious chest, inhaled, in every act of re- spiration, from twenty to twenty-nine cubic inches; Avhile Keutch inspired only from six to tAvelve. GoodAvyn estimates the volume of air inspired at about fourteen cubic inches; Davy, at from thirteen to seventeen; Cuvier, at sixteen; Allen and Pepys, at sixteen and a half; Menzies, at 43.77. It is estimated by late observers, that the greatest quantity of air, Avhich can be drawn into the lungs in forced inspiration, is about seventy cubic inches. It is not probable, that the air inspired reaches at once the ulti- mate ramifications of the bronchia. The air-cells are constantly filled with a certain quantity of air, left by preceding inspirations It is probable that the air last inspired, is mixed by degrees Avith the residual air present in the cells, and that it serves to keep this in a fit state to arterialize the blood. The quantity of air con- tained in the lungs after an ordinary or a forced inspiration, and after an ordinary or a forced expiration, has been differently esti- mated. According to Berthold, the lungs of an adult, after a forced inspiration, contain about two hundred and fourteen cubic inches of air ; after a common inspiration, one hundred and twen- ty-six cubic inches ; after a common expiration, one hundred and six cubic inches ; and after a forced expiration, only eighty-five. Mr. Dalton found that after a forced inspiration, he could bloAv out tAvo hundred cubic inches of air from his lungs. His ordinary inspi- rations and expirations amounted each to about thirty cubic inches. Menzies says, that many men are able, after ordinary expira- tion, to expel seventy cubic inches more from their lungs. He thinks from this, that the lungs can hold tAvo hundred and nine- teen cubic inches, and, after a common expiration, still contain one hundred and seventy-nine cubic inches. Allen and Pepys estimate the quantity of air, contained in the lungs after an ordinary expiration, at only one hundred and three cubic inches. They state, as the results of their experiments, that the lungs of a man of common size, contain, after death, more than one hundred cubic inches of, air. Rudolphi thinks, that Allen and Pepys's estimate of the volume of the air respired, may be admitted as correct, in ordinary respiration ; and in women and children, that it may be loAvered. But betAveen the ordinary acts of respiration he observes, there occur, from time to time, fuller inspirations and expirations; and in healthy labouring men, with capacious chests, he thinks Menzies' estimate not too high. In four subjects, Avho died natural deaths, and of course after expiration, GoodAvyn found that the lungs contained severally one RESPIRATION. 209 hundred and twenty; one hundred and tAvo; ninety; one hun- dred and twenty-five cubic inches of air. The average of these is one hundred and nine. In the lungs of hanged persons, Avho inspire deeply before death, he found, in one case, two hundred and seventy-two; in another tAvo hundred and fifty ; and in a third, two hundred and sixty-two cubic inches of air. It is said that Ave can expel one hundred and seventy cubic inches of air by forced expiration, and that one hundred and twenty cubic inches will still remain in the lungs. If this be true, the volume of air, which these organs contain in their quiescent state, must be the sum of these tAvo quantities, or two hundred and ninety cubic inches. Noav if it be assumed that Ave inhale forty cubic inches in in- spiration, the Avhole volume of air, Avhich the lungs contain in a distended state, is three hundred and thirty cubic inches, and con- sequently only one-eighth of the contents of the lungs is changed by every act of respiration. But if Ave inhale only about fifteen cubic inches in ordinary respiration, which is probably near the truth, the quantity of air contained in the distended lungs is three hundred and five cubic inches, and only about one-tAventieth part of their contents is changed m every act of respiration. Such is. the uncertainty, hoAvever, that reigns on this subject, that some physiologists are of opinion, that the air in the lungs is complete- ly reneAved in four acts of respiration. The volume of the air' inhaled in every act of respiration is diminished in the lungs about one-eightieth part of its bulk. If Ave inspire forty cubic inches, one half cubic inch disappears; a loss, Avhich, perhaps, is occa- sioned by the absorption of a quantity of oxygen, above Avhat is necessary for the production of the carbonic acid Avhich is formed in respiration. If an adult inhales forty cubic inches of air in inspiration, he must inspire eight cubic inches of oxygen- gas. If one-fifth of this be consumed in respiration, one and three-fifths cubic inches of oxygen gas disappear in every act of respiration. If, then, Ave respire tAventy times a minute, Ave must consume thirty-tAvo cubic inches of oxygen gas in the same time. It is probable, hoAvever, that forty-cubic inches is much too high an estimate of the vol- ume of the air inspired in ordinary respiration. If we assume it at fifteen cubic inehes, Avhich is not far from the average of several estimates made by different observers, it Avill folloAv that, if the quantity of oxygen consumed by respiration in a minute is thirty cubic inches, one half of that which is inspired disappears in every act of respiration. For fifteen cubic inches of atmospheric air contain three cubic inches of oxygen. If half .of this, i. e. one and a half cubic inches, disappear, and we respire tAventy times a minute, we shall consume thirty cubic inches in the same space 27 210 FIRST LINES OF PHYSIOLOGY. of time. Davy estimates the quantity of oxygen consumed in a minute by respiration at 31.6 cubic inches. This Avould amount to nearly tAvo thousand cubic inches in an hour, and forty-five thousand cubic inches in twenty-four hours. According to Lavoi- sier and Seguin, a man consumes in an hour, one cubic foot of oxygen, or in twenty-four hours, tAvo pounds, one ounce, and one grain. The quantity of carbonic acid discharged in every act of respi- ration, is very variable. By GoodAvyn it is estimated at eleven per cent, of the whole volume of air expired ; by Menzies, at only five per cent.; by Davy and Gay-Lussac at three or four; by Coutanceau at six or eight. Allen and Pepys estimated the quan- tity of carbonic acid emitted from the lungs of a healthy man, in ordinary unexcited respiration, at 26.6 cubic inches at the temper- ature of 50°. They also found that in a pigeon confined in oxy- gen gas, the production of carbonic acid Avas only half as great as Avhen it breathed common air ; and the loss of oxygen Avas exactly equal to the united volumes of carbonic acid and nitrogen Avhich Avere disengaged. When the bird was placed in a mixture of oxygen and hydrogen gases, rather more carbonic acid was formed than in common air, and its volume was found to be exactly equal to the loss of the oxygen. The hydrogen was considerably dimin- ished, but its loss was supplied by an equal volume of nitrogen. These experiments then prove, that nitrogen may be secreted and hydrogen absorbed by the lungs. The quantity of carbonic acid which is formed by respiration in tAventy-four hours, is estimated at seventeen thousand, eight hundred and eleven grains, which Avould contain about five thou- sand grains, or nearly eleven ounces of carbon. This, in a year, would amount to about tAvo hundred and fifty pounds solid car- bon excreted from the body by the lungs. This estimate, how- ever, there is reason to think, is much too high. Prout supposes that the conversion of albuminous matter into gelatin is one of the principal sources of the carbonic acid Avhich is expelled from the lungs in respiration, and Avhich he supposes to exist in the venous blood. Gelatin contains three or four per cent, less of car- bon than albumen, and it enters into the structure of every solid part of the body, but exists neither in the blood, nor in any other of the animal fluids. The skin, especially, consists almost wholly of gelatin ; a fact, from which Prout conjectures that a large part of the carbonic acid of venous blood is formed in the skin, and in the other gelatinous tissues. Accordingly, we find that the skin gives off carbonic acid, and consumes oxygen. The consumption of oxygen and the production of carbonic acid, are extremely variable under different circumstances, even in the same person. Whenever respiration is very active, more oxy- gen is consumed, and more carbonic acid formed. More carbonic acid is formed during digestion and during exercise; animal food RESPIRATION. 211 and Avine, and mental agitation increase it. According to Nysten, more carbonic acid is formed by respiration, in inflammatory fevers, and less, in atonic diseases. If pure oxygen gas be respired, a larger quantity of oxygen is consumed, and more carbonic acid expired, than in the respiration of atmospheric air. More carbonic acid is formed during the day than in the night. The maximum quantity is formed betAveen eleven o'clock, A. M. and one o'clock, P. M. ; the minimum, about eight o'clock in the evening; from Avhich time until half past three in the morning, there is no change. The air expired from the lungs is loaded Avith a large quantity of watery vapour, derived partly from the lungs, and partly from the mouth, fauces, and trachea. The quantity of it Avas estimated by Hales, at about tAventy ounces in tAventy-four hours ; more re- cently by Menzies, at six ; by Abernethy, at nine ; and by Thom- son, at nineteen ounces. The breath frequently becomes impregnated Avith the odour of substances Avhich have been sAvalloAved. If odoriferous substances are injected into the veins, or a serous cavity, the breath acquires this odour. If a solution of phosphorus in oil be injected into the veins of an animal, its breath becomes luminous in the dark, and in the light is loaded Avith dense Avhite fumes of phosphoric acid. In fact, it appears an important function of the lungs, to act as an excretory organ for the venous blood. Hence these organs per- form an important part in the process of assimilation and nutri- tion, not merely in effecting the necessary exchange of principles betAveen the component parts of the inspired air and those of the venous blood, but also by depurating the blood from unassimilable substances of the volatile kind, taken Avith the food, or otherwise introduced into the system. It is manifest therefore that the pul- monary vapour must be exceedingly variable, according to the nature of the food, drink, and medicines, which have been taken, and also according to the condition of the vital actions, and the variable circumstances of health and disease. Thus musk, the juice of garlic, alcohol, camphorated spirits, sulphuret of carbon, injected into the veins, become sensible by their odour in the pul- monary vapour almost immediately. Vital part of Respiration. By the vital part of respiration, is meant the changes produced in the blood by the influence of atmospheric air. The lungs digest air, as the stomach digests food; and, as the digestion of food is designed to form a nutritive fluid, the blood, out of aliment received into the stomach, the digestion of air contributes to the same object, the formation of blood. It completes Avhat the stomach had begun. The nutritive fluid, formed by the stomach and its appendages and carried into the blood-vessels, is still im- perfect until it has passed through the lungs and received the in- 212 FIRST LINES OF PHYSIOLOGY. fluence of respiration. In the lungs it is supposed to lose a large quantity of carbon under the form of carbonic acid, and to absorb oxygen from the air, and to acquire its peculiar scarlet colour; and it then becomes adapted for all the purposes of life, and not before. The organization of the blood is probably completed in the lungs, perhaps by the addition of the red colouring matter, or hematosine. Respiration is therefore essential to the formation of the blood, which is the great excitant of the system, the fluid which keeps all the machinery of life- in action, and which sup- plies the materials out of Avhich all this machinery itself is manu- factured. This is one essential purpose of respiration. Another, equally important, and indeed closely connected with the first, is to produce certain changes upon the blood already formed, after it.has circulated through the system, and been em- ployed in the various functions of life. While the florid arterial blood is administering to the various operations of life, it is gra- dually changing its colour, and becoming darker, and at last, what remains of it, assumes the purple colour of venous blood. In this condition it is no longer fit for the purposes of the animal econo- my. It is robbed of the principles most essential to life, and it must be reneAved and prepared afresh, before it is fit to be em- ployed again. For this purpose it is returned from all parts of the body to the heart, by the veins, and instead of being again transmitted to the various parts of the system by the arteries, it passes into the lungs, having received, just before its entrance into the heart, a supply of fresh prepared nutritious matter, the chyle, mixed with the result of the vital decomposition of the organs and tissues of the system, part of Avhich is probably de- signed to be remoulded again into the living tissues, and part to be eliminated from the system by the various excretions. In the lungs it loses a large quantity of carbon, and watery vapour, and perhaps absorbs oxygen, and is changed back to its former scar- let colour, and is then again fitted for the uses^ of the animal economy. The coloration and perhaps arterialization of the blood, how- ever, requires other conditions than the mere contact of atmos- pheric air. It has been ascertained that the saline substances existing in the serum are necessary to this effect. A variety of salts, as chlorate of potash, nitre, common salt, and bicarbonate of soda, have the property of communicating to the blood a florid colour, far brighter than that of arterial blood. A solution of one of these substances, of the proper strength, will give to venous blood the arterial colour, even without exposure to the air. A clot of venous blood, if its serum be carefully removed, is not made florid by oxygen gas; and arterial blood, deprived of its serum by pure water, assumes the dark colour of venous blood. Hence it appears that the arterialization of the blood depends on two causes, essentially different, viz. the influence of the oxy- RESPIRATION. 213 gen of the atmosphere, and the effect of the saline substances contained in the serum. A curious fact suggested by this subject is that the blood taken from a vein is sometimes of a very dark purple, and at others of a bright florid red, very similar to arterial blood. From this also it seems probable that the coloration of the blood is influenced by other causes than respiration. Another circumstance which I have repeatedly noticed is, that in some instances the florid blood issues from the veins Avith great impetuosity, and even a pulsatory motion, resembling very nearly a jet of arterial blood. Dr. Christison was led to the conclusion that the coloration of the blood in respiration is a chemical process, from finding that Avhen venous blood acquires the arterial colour by agitation with atmospheric air, a considerable portion of oxygen disappears and carbonic acid is formed. From what.has been said it appears that respiration, in relation to its influence upon the blood, is a complex function. It com- pletes the formation of the new blood; it renovates the old, pre- paring it again for the purposes of life ; and it reconverts into blood the molecules detached from all the organs by vital decom- position, and which have consequently existed, at least once before, under the form of blood. It incorporates the Avorn-out venous blood, both Avith matter imperfectly animalized, and with matter animalized to excess, and combines the heterogeneous mass into one homogeneous fluid highly impregnated with vital- ity,, arterial blood. Theory of Respiration. There is still much difference of opinion among physiologists in regard to the mode in Avhich the changes produced in the blood are effected by respiration. An opinion, Avhich prevailed for some time, assumed that the oxygen of the air inspired, combines in the lungs Avith the carbon of the venous blood, and that the latter is converted into arterial blood- by the loss of this carbon. This opinion was founded on the fact that the volume of .carbonic acid formed in respiration, is almost exactly equal to the oxygen which disappears ; and as car- bonic acid contains its OAvn volume of oxygen gas, it was inferred that the oxygen Avhich disappears is converted into carbonic acid, by combining Avith carbon in the lungs. This carbon Mr. Ellis supposed to be separated from venous blood by a kind of secretion. Another opinion which has been maintained by several distin- guished physiologists is, that the oxygen is absorbed by the blood, and the carbonic acid is gradually formed in the course of the circulation, and is afterwards exhaled by the venous blood in a subsequent act of respiration^ As the quantity of oxygen gas which disappears is rather greater than sufficient for the produc- 214 FIRST LINES OF PHYSIOLOGY. tion of the carbonic acid Avhich is formed, it must be supposed that at least a part of the oxygen consumed is absorbed by the blood ; and if so, it seems probable that the Avhole of it is, and consequently, that the carbonic acid is not formed in the lungs at the expense of this oxygen, but is exhaled, ready-formed, from the venous blood. A consideration which affords some confirma- tion to this opinion is, that the inhalation of oxygen is not neces- sary to the production of carbonic acid, as was ascertained by the experiments of Dr. Edwards on frogs and kittens;—for these animals, when confined in hydrogen gas, exhaled carbonic acid. Nysten and Coutanceau, also, after inhaling azote, found in the air of expiration seven or eight per cent, of carbonic acid, just as when common air is respired. It is possible, however, as Rudolphi supposes, that this carbonic acid Avas formed from the atmospheric air present in the lungs at the time of the experiments. Edwards's experiments, also, seem to have ascertained the fact, that the blood circulating in the lungs is capable of absorbing oxygen as Avell as hydrogen and azote ; and Nysten found that oxygen gas might be injected into the veins of dogs without injury, provided but small doses were injected at a time; while the injection of azote and hydrogen soon occasioned death. Some experiments of Girtan- ner seem to establish the presence of oxygen in arterial blood. He put some arterial blood of sheep under a receiver filled Avith pure azote ; and at the expiration of thirty hours, the a^- in the receiver contained oxygen enough to support the combustion of a candle about two hours.* That carbonic acid exists in venous blood, seems to be render- ed probable from the fact that carbonic acid may be injected in considerable quantity into the veins Avithout injury. An experi- ment of Danvin has a bearing upon this subject, in proving that gaseous substances may probably exist in the blood in a state of loose combination. He found that venous blood, when exposed in an exhausted receiver, swelled to ten times its original bulk. On this subject, hoAvever, physiologists are not agreed. Tiede- mann and Gmelin found that no carbonic acid nor any other per- manent gas was extricated from blood taken from the femoral artery and vein of a dog, and placed in different tubes under the receiver of an air-pump. Arterial blood, however, was found to absorb carbonic acid pretty largely. Upon adding vinegar to each kind of blood, which as before was placed under a receiver, a quantity of carbonic acid escaped from both, but more from the venous than from the arterial. Whence it followed, that combined though not free carbonic acid exists in the blood. The conclusions of these physiologists on the nature of changes in respiration, were : That the oxygen is absorbed by the blood, • * Lepelletier. RESPIRATION. 215 and combines partly Avith carbon and hydrogen, forming carbonic acid and Avater, and partly unites Avith the solid organic com- pounds contained in the blood. From these proceed acetic or lactic acid, Avhich combines with a portion of carbonate of soda contained in the blood, and expels its carbonic acid into the cells. The acetate of soda thus formed loses, in its course through the different secreting organs, its acetic acid, and the soda com- bines again with carbonic acid, in its passage through the body with the mass of blood, and again returns to the lungs in the form of carbonate of soda. This vieAV supposes that acetic acid is formed by respiration, and that this acid expels from the alkaline carbonate of the venous blood a portion of its carbonic acid, converting it into an acetate. Another very plausible theory of respiration assumes that the oxygen is absorbed by the radicles of the pulmonary veins; and that the carbonic acid and Avatery vapour are exhaled from the pulmonary mucous membrane. But the exhalation of aqueous vapour and of carbonic acid is not regarded as peculiar to the lungs, and of course not as the essential and characteristic part of respiration ; because the skin is constantly performing precisely the same office ; since the matter of insensible perspiration con- tains both aqueous vapour and carbonic acid combined Avith some animal matter. The exhalation of carbonic acid in respiration is not necessarily connected with the absorption of oxygen. Like other secretions, it is supposed to be formed from arterial, and not venous blood; to be secreted, not from the venous blood of the pulmonary artery, but from the branches of the bronchial arte- ries, distributed over the mucous membrane of the bronchia. While the essential and characteristic part of respiration is sup- posed to consist in the absorption of oxygen by the radicles of the pulmonary veins. In this vieAV the air drawn into the lungs in respiration is decomposed; part of its oxygen is absorbed into the venous blood, and changes it to arterial. The roots of the pulmonary veins are the instruments of this absorption, and bring the oxygen into immediate contact with the venous blood. The carbonic acid, and the aqueous animal vapour, Avhich exist in the air expired, are the product of a secretion from the mucous mem- brane of the bronchia, a secretion from arterial blood, and perfectly similar to the exhalation from the skin. This secretion is not supposed to have any influence upon the arterialization of the blood in the lungs, because being formed from arterial blood, the effect of it should rather be to convert this into venous, as is the case with the other secretions, than to change the venous into arterial blood. The lungs, in this vieAV, are the seats of two opposite functions, absorption and exhalation. By the first, an aerial principle, necessary to life, is incessantly introduced into the animal economy, and constitutes the great and essential pur- pose of respiration. The pulmonary capillary system is the seat 216 FIRST LINES OF PHYSIOLOGY. of this absorption. The second, Avhich has its seat in the gene- ral capillary system, and Avhich consists in the exhalation of car- bonic acid, and a Avatery vapour, with a little animal matter from the lungs, is not peculiar to these organs, but is shared equally by the skin. It may not be amiss to notice in this place the theory of Chaus- sier, who supposes that the oxygen is absorbed by the lymphatics of the lungs, vessels Avith Avhich these organs are very abundantly supplied; that it is conveyed by the lymphatics into the thoracic duct, and there blended Avith the chyle and lymph; and after- Wards, in combination .with these fluids, conveyed to the right side of the heart, and thence transmitted to the lungs; and that it is in the extreme divisions of the pulmonary artery that the' combination becomes perfect. The change of colour of the blood in the lungs, his theory supposes to be occasioned merely by the separation of carbonic acid already existing in the venous blood. This theory, it Avill be perceived, transfers the process of hema- tosis from the lungs to the thoracic. duct. It assumes that the oxygen, before combining with the blood, passes through a great extent of the absorbent system, besides a part of the circulating, which is inconsistent Avith the suddenness of the change which takes place in the blood'in respiration. The venous blood ac- quires instantly the arterial color in the lungs — as Avas demon- strated by an experiment of Bichat. It also assumes that the coloration of the blood in the lungs is occcasioned by the exhala- tion of carbonic acid. . Now, according to Coutanceau, during the respiration of any other gas than oxygen, especially of azote, the exhalation of carbonic acid and watery vapour continues, yet-the- venous blood retains its dark colour. Influence of Innervation upon Respiration. The external organs of respiration, the nose, the mouth, the muscles about the chest, the diaphragm, and the abdominal mus- cles, are supplied with nervous influence by the fifth pair of nerves, the facial, the accessory, the spinal nerves, and the phre- nic ; Avhile the proper organs of respiration, the larynx, the tra- chea, and its ramifications, constituting the mass of the lungs, are supplied by the pneumogastric nerve, and the pulmonary plexus, which is formed by filaments of the pneuniogastric nerve, and the anterior branches of the first thoracie ganglions. The pneumogastric nerves, as might be inferred from their sup- plying all the internal organs of respiration Avith branches, exert an important influence upon respiration, though it still remains a subject of controversy with physiologists, Avhat the precise na- ture of this influence is. The section of these nerves, on both sides, about the middle of the neck, soon occasions extreme dyspnoea, followed in a feAV hours by death; and, on dissection, RESPIRATION. 217 the lungs are found overloaded with blood, and the bronchial tubes filled with a white frothy fluid. Death, in these cases, is OAving to a paralysis of the muscles which open the glottis, Avhile those Avhich close this aperture re- main unaffected. The dilating muscles of the larynx receive their nerves from the inferior laryngeal, or the recurrent branch of the pneumogastric ; the constrictors, from the superior laryn- geal. The section of this nerve paralyzes the constrictors, and the glottis remains open; while the section of the recurrent branch paralyzes the dilators, and the glottis remains closed. It is said that the section of the recurrent nerve, is more dangerous than the division of the par vagum, in the neck. If, after the section of the pneumogastric nerve, an opening be made in the trachea, so as to admit the air freely into the lungs, the dyspnoea is relieved, and life may be prolonged for three or four days. Yet the animal inevitably dies from increasing dysp- noea, sometimes accompanied with vomiting. The blood in the arteries assumes a darker colour, and, according to Mr. Brodie, less carbonic acid is evolved in respiration. Upon dissection, the lungs are found engorged with dark blood, and the bronchial cells and tubes, and frequently the trachea itself, are filled with a frothy, and sometimes bloody fluid. In some cases there is also an effusion of serum, or blood, in the parenchyma of the lungs. Different opinions have been entertained respecting the manner in Avhich asphyxia is produced by the section of the par vagum. It may be OAving to one of two causes. Either the division of these nerves prevents the penetration of air into the bronchial cells, or it prevents the mutual action of the blood and air upon each other, and consequently, the arterialization of the blood. This latter opinion is adopted by Dupuytren, who thinks that animals die after the division of these nerves, because the air, though it still penetrates freely into the lungs, and comes in con- tact with the blood, is unable to combine Avith this fluid, since this combination requires the vital action of the pneumogastric nerves. He endeavoured to establish this opinion by experiment. He found that if an artery in an animal in Avhich the par vagum was divided, were opened, the blood, which at first spirted out of the bright arterial colour, gradually became darker, and assumed the appearance of venous blood. The compression of the nerves produced the same effect. Legallois found that an opening into the trachea, after the section of the pneumogastric nerves, did not prevent the arterial blood from becoming venous, though it permitted the free ingress of air into the lungs. Dumas, hoAvever, found that if air Avere forced into the lungs after the section of the par vagum, arterial blood continued to be formed ; from which he inferred that, in this experiment, asphyxia is occasioned by some obstruction to the entrance of air into the 28 218 FIRST LINES OF PHYSIOLOGY. lungs; so that without some external force this fluid is unable to penetrate into the bronchial cells. The fact that after decapita- tion life may be maintained for some time by artificial respiration appears to be irreconcilable Avith Dupuytren's opinion. A fact stated by Magendie deserves to be noticed in this place. From his experiments, it appears that the section of the vagi de- stroys the coagulability of the fibrin, a property Avhich he regards as indispensable to life. The most probable opinion, on the Avhole, seems to be that of Brachet, viz. that the division of the par vagum annihilates the appetite of respiration, and paralyzes the fibres of the bronchia; permitting an accumulation of the bronchial secretions in the cells and fine tubes of the lungs, and thus gradually preventing the contact of the air with the blood in the pulmonary vessels. The experiments of Brachet appear to prove, that the pneumo- gastric nerves convey from the lungs to the brain a knowledge or sentiment of the Avant of respiration, in consequence of which the brain reacts upon the external muscles of respiration, by means of the cerebro-spinal nerves distributed to these muscles; and upon the muscles and • fibrous coat of the larynx, trachea, and bronchia, through the medium of the pneumogastric. Brachet, in some of his experiments, found that the section of the par vagum. appeared to annihilate the appetite for respiration. In one of these, after the division of these nerves in a puppy three days old, he plunged the muzzle of the animal into Avarm water, so as entirely to prevent the entrance of air into his lungs. The animal made an effort to raise his head out of the water, and died in a state of asphyxia, after a feAv slight motions, which were Avholly unlike the struggles for breath of a suffocating animal. The muzzle of another puppy of the same litter, was in like man- ner plunged in Avater, Avithout the previous division of the. par va- gum. Unlike the first, he made violent efforts to withdraw his nose from the Avater and to respire, and the asphyxia came on with difficulty, and was accompanied with convulsive struggles. In two other comparative experiments, two puppies of the same litter were placed under two receivers, filled Avith atmos- pheric air, one of them having previously undergone the section of the pneumogastric nerves, and had an opening made in the trachea; the other Avithout any preparation. In the latter, respi- ration soon became larger and more frequent, the animal raised his head, and breathed Avith his mouth open and his nostrils ex- panded, and died Avith the symptoms Avhich usually accompany this kind of asphyxia. The former, in which the par vagum had been divided, breathed in the usual manner, and died quietly at the expiration of forty-six minutes, without agitation, and without expanding his nostrils or opening his mouth. From these experiments Brachet infers, that the section of the par vagum intercepts the impression produced by the privation of RESPIRATION. 219 atmospheric air, in its passage to the brain; since one animal Avhich has been subjected to this experiment, dies of asphA^xia without manifesting any feeling of the want of respiration. The continuation of the movements of respiration, after the appetite has been annihilated, Brachet attributes to the habit Avhich the respiratory muscles have acquired of contracting, and which sur- vives the sentiment of the want of respiration. The convulsive struggles Avhich sometimes occur in this kind of asphyxia, he attributes to the influence of the black blood on the heart and other organs. Brachet also attempts to establish, that the par vagum apprises the brain of the presence of mucus, or any foreign substance in the bronchia, and that by means of the same nerves, the fibres of the bronchia react upon -and expel these substances. He divided the tAvo pneumogastric nerves in a dog, and then made an opening into the trachea, through Avhich he introduced a little ball of orris (boule d'iris) fastened to a thread. The breathing became labori- ous, but the animal exhibited no sign that he experienced any dis- agreeable sensation. He then held an open jar of muriatic acid to the opening in the trachea for several minutes, and even let some drops of it fall into the interior of it, but Avithout eliciting from the dog any signs of sensation. In another experiment, he made an opening in the trachea of a dog Avithout dividing the par vagum. A feAv drops -of blood fell into the trachea and excited coughing. The ball of orris excited violent coughing, which pushed it forcibly towards the larynx. The muriatic acid occasioned paroxysms of coughing, which obliged him to AvithdraAv it. On applying it again, the cough was reneAved —- upon which Brachet divided the par vagum, when the cough suddenly ceased, respiration became rattling, and in less than an hour, the dog died Avithout having expectorated any thing. That these nerves react upon the fibres of the bronchia, causing them to contract, Brachet endeavours to prove by experiment. He injected Avarm water into the trachea of a dog, Avhich excited violent coughing, by which the water was expectorated. The irritation, however., provoked an abundant secretion, Avhich kept up the cough and expectoration for several hours. Upon repeat- ing the experiment, the next day, on the same dog, the same phe- nomena occurred ; but after the dog had apparently ejected all the water from his lungs, Brachet divided the par vagum, upon which expectoration immediately ceased, respiration became rattling, and in about two hours the dog died. Lepelletier also remarks, that the section of the par vagum, or a suspension or diminution of its power, causes a debility or inac- tion of the air vesicles, and a stagnation in them of the air altered by hematosis; and it explains the occurrence of asphyxia in cer- tain cases, Avhere the great phenomena of inspiration and expira- tion continue to be carried on. For the air may continue to be 220 FIRST LINES OF PHYSIOLOGY. renewed in the principal divisions of the bronchia, by the mechan- ical movements of respiration ; but its renovation in their ultimate branches, is impossible Avithout the vital contraction of the air vesi- cles themselves. CHAPTER XVI. THE NUTRITIVE FUNCTIONS. The nutritive functions are four in number, viz. Digestion, Absorption, Secretion, and Nutrition. Digestion. Digestion is a function peculiar to animals; and the existence of a separate set of organs devoted to digestion, has been regarded as one of the characteristics by which animals are distinguished from plants. Vegetables, it is true, are nourished and grow ; but they do not, properly speaking, digest. Their nutrition and groAvth are the result of an external absorption from the atmosphere and the soil, effected at their surface, and by means of roots; while animals first receive the materials of their nutrition into a central cavity, where they are subjected to a series of remarkable changes, and their nutritive elements are afterwards carefully selected, and imbibed by a set of internal roots. Nutritive matter, therefore, is absorbed in a crude state by plants; but in a digested state, by animals. In vegetables, and the loAvest orders of the animal king- dom, the absorbing vessels themselves exercise an assimilating poAver over the matters absorbed as nourishment, and this prepara- tion is the only digestion which the food of these kinds of organ- ized beings undergoes; but in all the animal kingdom, with the exception of the very lowest orders in the zoological scale, diges- tion is centralized in a particular apparatus, more or less compli- cated, according to the position of the species in the scale of animal life. In its simplest or rudimental state, the digestive apparatus con- sists of a membranous sac, provided with a single opening, which serves both for mouth and anus. In its first stage of complica- tion, it assumes the form of a straight canal, the length of which is less than that of the animal to which it belongs, and is provided with two orifices, one destined for the reception of the food, the other to the expulsion of the refuse matter of nutrition. In its higher stages of complication, it progressively acquires a greater relative length, in some of the higher orders of animals exceeding, DIGESTION. 221 by nearly thirty times, the length of the body, and presenting numerous convolutions. Its tAvo orifices are guarded by circular muscles, which act under the control of the will; and several auxiliary organs are connected Avith it, Avhich contribute to give greater variety and complication to its functions. In the mammalia, the digestive canal presents its greatest or last degree of complication. In the human species it consists of a tube about six times as long as the body, extending from the mouth, through the chest and abdomen, to its inferior orifice, the anus; unequal in its diameter, being much larger in some places than in others, and in one part swelling out into a capacious sac ; presenting, in a great part of its course, irregular convolutions, and terminating at each extremity by one orifice, closed by a circular muscle, which acts under the control of the Avill. The digestive canal is found partly in the head, Avhere it forms the cavity of the mouth; partly in the neck and thorax, where it takes the names of the pharynx and the asophagus ; but princi- pally in the abdomen, Avhere it forms the stomach and intestines, Avhich, with the associated viscera, the liver, the pancreas, the spleen, and the mesentery, occupy nearly the whole of this great cavity. The mouth is formed by the tAvo lips. Its cavity is bounded above by the palate, beloAV by the tongue, before by the teeth, laterally by the cheeks, and posteriorly by the curtain of the pal- ate, which separates the cavity of the mouth from the pharynx. The pharynx is a funnel-shaped cavity, Avhich terminates in the asophagus. It opens into the mouth by the isthmus of the fauces; into the nasal cavities by the posterior nares ; into the trachea, by the superior opening of the larynx ; and into each ear, by a funnel- shaped canal, called the Eustachian tube. The asophagus, or gul- let, is a continuation of the pharynx. It is a long, straight, fleshy tube, Avhich passes doAvn the chest, behind the trachea, lying upon the vertebral column; and it opens into the stomach by an orifice which is called the cardia. The pharynx and oesophagus, or the pharyngo-oesophageal cavity, is the organ of deglutition. The stomach is a large pouch, situated beloAV the diaphragm, and lying obliquely across the epigastric region, and a part of the left hypochondriac. Above, it is bounded by the liver and the diaphragm ; below, by the transverse colon; behind, by a part of the vertebral column, and the great centre of the ganglionic nerves; before by the false ribs of the left side, with their carti- lages ; on the left, by the spleen. The stomach has two orifices, a superior and an inferior. By the former, which is also called the cardiac, it communicates with the oesophagus; by the latter, also termed the pyloric, it opens into the first of the small intestines, or the duodenum. Two curved lines, a superior and an inferior, extend from one of these orifices to the other. The superior, which is concave, is much 222 FIRST LINES OF PHYSIOLOGY. shorter than the inferior, Avhich is convex; i. e. the inferior arch of the stomach is much greater than the superior. The situation of the organ, as well as its volume, varies much, according to its state of emptiness or repletion. When empty, it is flaccid and depending, and its greater curvature inclines doAvnward. But when distended, its greater curvature is raised forAvard. The stomach is the organ of chymification, or gastric digestion. The intestines extend from the pylorus to the anus, forming a mass of convolutions, Avhich fill most of the abdominal cavity. They are usually divided into tAvo portions, viz. the large and the small intestines ; a distinction founded on their relative diameters. The small intestines,, or the upper portion, are subdivided into three parts, viz. the duodenum, the jejunum, and the ileum. The first receives its name from its length, which is equal to twelve fingers' breadths. It is the seat of chylific'ation, or duodenal diges- tion. The jejunum, or hungry gut, is so called from its being generally found empty; and the ileum, i. e. the twisted gut, de- rives its name from the numerous convolutions Avhich it exhibits. The small intestines have a less diameter and thinner coats than the other portions of the intestinal canal; but their length is much greater, amounting in an adult to four or five times the length of the whole body. They are attached to the superior lumbar ver- tebras by a duplicatyre of the peritoneum, called the mesentery. The large intestines commence Avhere the small terminate. A circular fold of the mucous membrane of the ileum, penetrating by its free border into the large intestine, and called, the ileo-cascal valve, separates the two great divisions of the intestinal canal from each other. The large intestines are divided into three portions, viz. the cacum, the colon, and the rectum, which last terminates in the anus. In the greater part of its extent,'the digestive canal consists of three membranes, viz. a mucous, a muscular, and a serous. Only the two first, however,-are essential to it; the mucous, or internal tunic, constituting a secreting and absorbing surface; and the muscular, or middle, executing the various motions to which the food is subjected after its reception into the mouth. The exter- nal, or serous tunic, is merely accessary, as it is wanting in many parts of the digestive tube, and no Avhere completely envelops it. The soft parts of the mouth are composed almost wholly of muscles, lined internally by a mucous membrane. These muscles execute the different motions of the mouth, by which this cavity is enlarged or diminished, and variously modified in its shape, in the processes of mastication and insalivation, and the food is after- wards forced from the mouth into the pharynx. The membrane which lines the mouth secretes, a mucus Avhich lubricates this cav- ity, and is blended with the food in mastication. The muscular part of the pharynx is composed of six constric- tor muscles, which contract this cavity and compress its contents, DIGESTION. 223 forcing them into the oesophagus in the act of deglutition. The fibres of these muscles form planes or sheets, Avhich cross each other in various directions. The pharynx is lined internally by a mucous membrane of a deep red colour. The oesophagus, in like manner, is composed of a muscular coat and a mucous membrane. The former consists of tAvo strata of muscles, viz. one external, Avhich is composed of longitudinal fibres, of considerable thickness and strength; and one internal, consisting of circular fibres, considerably thinner than the former. Near the stomach the longitudinal fibres diverge, and may be traced extending over its cardiac extremity ; but the circular fibres wholly disappear at the termination of the oesophagus. The mucous membrane is continuous Avith that which lines the pha- rynx. It presents numerous longitudinal folds, which are owing to the contraction of the muscular coat. According to Magendie, the inferior third of the oesophagus, is subject to an uninterrupted alternate motion of contraction and relaxation. The contraction commences at the upper part of the inferior third, and proceeds, Avith a certain degree of rapidity, to the insertion of the oesophagus into the stomach. Its duration is variable, but on an average amounts to about thirty seconds. The part thus contracted is hard and elastic, like a tense cord. The relaxation which succeeds, takes place suddenly and simulta- neously irl the contracted fibres. This motion of the oesophagus is under the influence of the par vagum. If these nerves are di- vided in an animal, the oesophagus ceases to contract in the man- ner just described, arid assumes a state intermediate betAveen con- traction and relaxation.* The oesophagus is furnished Avith mucous follicles, which are sparingly distributed over it. The stomach, also, is composed of tAvo principal coats, or mem- branous laminas. The internal is a soft, spongy, mucous mem- brane, Avhich is extremely vascular, or plentifully supplied Avith blood-vessels. Except Avhen the stomach is distended, the mucous membrane is draAvn into folds or wrinkles, so that its surface is much greater than that of. the other coats. It is smeared with mucus, secreted by numerous follicles, seated in its mucous coat. The second coat of the stomach is muscular, and is composed of fibres disposed in three different directions, viz. longitudinally^ circularly, and obliquely. The longitudinal fibres form the exte- rior muscular plane. Immediately beneath this are the circular fibres, Avhich run parallel to one another; and subjacent to the latter are the oblique, which form broad fasciculi at the tAvo ex- tremities of the stomach. Besides these two principal coats, the stomach receives an external tunic, formed by a duplicature of the peritoneum. This coat is united to the muscular, by cellular tissue. * Magendie. 224 FIRST LINES OF PHYSIOLOGY. The stomach is plentifully supplied with blood-vessels and nerves. The blood is chiefly designed to furnish materials for the secretion of the gastric fluid, Avhich is supposed to be the princi- pal agent in chymification. The arteries of the stomach are very large and numerous, and they all spring, directly or indirectly, from a large trunk called the coeliac artery. The nerves of the stomach originate from both nervous systems, the cerebro-spinal and the ganglionic. From the former it receives branches by means of the pneumogastric; and from the latter, by the coeliac plexus. The structure of the intestines resembles, very nearly, that of the stomach. They are composed, essentially, of two coats, viz. a mucous and a muscular ; the former constituting a secreting and absorbing surface ; the latter, or muscular, executing the various motions, which are necessary in propelling the contents of the intestines regularly through the canal. There is a third tunic, which is external, and Avhich is derived from the- peritoneum. This is termed the serous, or peritoneal coat. The mucous coat is sometimes termed villous, from the villosi- ties Avhich its internal surface exhibits, resembling the pile of velvet. These villi are extremely numerous, presenting the ap- pearance of small spongy masses, adhering to the mucous coat. They are very vascular, and their bases are surrounded by small bodies of a glandular structure, termed mucous follicles, which are destined to secrete the mucus Avhich smears the inner surface of the intestines. The mucous coat of the small intestines is gathered into folds or plicas, presenting when dried a lunated appearance and denom- inated the valvula conniventes. These appear to be designed to increase the internal surface of the intestines, and to retard the passage of the alimentary matter, so as to give more time for the necessary changes to be wrought upon it, and also for its absorp- tion by the lacteals. The muscular coat consists of two orders of fibres, one longi- tudinal, or running parallel to the axis of the canal; the other circular, or embracing it like rings. In the large intestines, the longitudinal fibres are collected into bundles, or fasciculi, Avhich have the effect of puckering up the intestines, forming numerous prominent cells, in which feculent matter is sometimes retained a long time. The arteries of the intestines are derived from the mesenteric arteries ; their nerves almost Avholly from the solar plexus. Into the first of the small intestines, the duodenum, open the excretory ducts of two important glands, the liver and the pancreas. The necessity of taking food arises from the losses Avhich the body is constantly undergoing by the different secretions and excretions, and which amount to several pounds in the space of twenty-four hours. These losses immediately affect the blood, DIGESTION. 225 Avhich becomes impoverished by the demands upon its principles, which nutrition, and the various secretions and excretions, are constantly making. But, indirectly, the solids feel the effects of this incessant drainage, because. they are undergoing, Avithout intermission, the process of organic decomposition, and the mole- cules detached from them, are passing into the venous blood, and are afterwards eliminated from the system by the urinary and other excretions. We are incited to take food by certain internal sensations, Avhich are termed hunger and thirst. Neither the seat nor the efficient causes of these sensations are Avell known. Hunger has been frequently referred to a peculiar affection of the nerves of the stomach; an opinion Avhich in itself seems sufficiently proba- ble, as sensation is a phenomenon of the nervous system, and as the sensation of hunger is referred directly to the stomach. The experiments of Brachet, in Avhich the section of the pneumo- gastric nerves appeared to annihilate the appetite for food, tend to corroborate this opinion. It is observed hoAvever, by Mayo, that nausea is referred to the stomach upon the same grounds with the sensation of hunger; and yet, according to the experi- ments of Magendie, nausea and retching may be produced after the removal of the stomach of an animal, by injecting .tartar emetic into the A*eins. Thirst has been referred to a certain impression upon the nerves of the fauces and pharynx. But in the case of a man Avho had cut through the oesophagus, several buckets full of Avater Avere swalloAved daily, and discharged through the wound, Avithout quenching the thirst,—Avhich Avas afterwards allayed by inject- ing spirit, diluted Avith water, into the stomach. From these facts Mayo observes, that- jt is not impossible, that a person might be hungry without a stomach, and thirsty Avithout a throat. Digestion, from the first reception of aliment into the mouth, to the rejection of the refuse of it, by the inferior extremity of the intestinal canal, is composed of the following processes, viz. 1. manducation and insalivation, performed by the mouth • 2. deglutition, by the pharynx and oesophagus ; 3. chymosis, by the stomach ; 4. chylosis, by the duodenum ; 5. intestinal absorption, by the small intestines ; and 6. defecation, by the large. I. Manducation is the mechanical division of the food, Avhich is broken and ground' doAvn by the action of the teeth, pressed against it by the motions of the jaws. These motions are of three kinds, viz. one vertical, consisting of the elevation and de- pression of the lower jaw, and two horizontal, in one of Avhich the loAver jaAv is moved backAvards and fonvards, and in the other laterally, or from side to side. These motions are executed by the action of "several muscles, viz. the temporal, the masseter, the external and internal pterygoid, the zygomatic, the digastric, and 29 226 FIRST LINES OF PHYSIOLOGY. some others. The temporal, masseter, and internal pterygoid muscles, elevate the loAver jaw, the temporal moving it somewhat backwards as Avell as upAvards ; the masseter, forwards and up- wards ; and the pterygoid, from side to side. In carnivorous ani- mals, these muscles, particularly the temporal, possess prodigious power. The loAver jaw is moved horizontally forward, by the combined action of the tAvo external pterygoid muscles, aided by the masseter and the internal pterygoid. The pterygoid muscles, when they act singly, move the jaAV obliquely, from side to side, and communicate a grinding motion to the teeth. The loAver jaw is depressed, and the mouth thus opened, by the action of several muscles, especially the digastric, and various others, attached to the os hyoides. During the operation of mastication, in which the food is di- vided and ground down by the teeth, it is intimately penetrated and impregnated with the saliva, a fluid which is secreted by three pairs of glands, viz. the parotids, the submaxillary, and the sublingual. These glands are stimulated to an increased secre- tion of saliva by the taste or smell, and frequently by the mere idea, of food. These glands will be described hereafter. The quantity of saliva secreted during an ordinary meal, is probably very considerable. In a case of division of the oesopha- gus, described by Dr. Gairdner, from six to eight ounces of saliva were observed to be discharged during a meal, which consisted of broth, injected into the stomach through the wound. Under the stimulus of mastication, as Mayo remarks, the quantity se- creted is probably much greater. The minute division of the food by mastication, and its pene- tration by the saliva, appear to be designed, chiefly, to promote its solution in the stomach, and to facilitate deglutition. Hence, a leisurely and sufficiently prolonged mastication, in .general, ren- ders digestion easier and more prompt. II. Deglutition. After the morsel is sufficiently masticated, it is pushed into the pharynx by the action of the tongue, which is raised and pressed against the palate by the stylo-glossal muscles. At the same time, the pharynx is draAvn upwards to receive the morsel by the action of the muscles, Avhich raise the os hyoides, and by the stylo-pharyngens. The pharynx is embraced by the fibres of three muscles, Avhich are termed its upper, middle, and lower constrictors; the contraction of Avhich tends to diminish its cavity and to compress its contents; and their successive action gradually forces the bolus into the oesophagus. Its return into the mouth is prevented by the pressure of the tongue ; its entrance into the posterior nares is precluded by the velum pendulum palati, which is forced before the bolus, and becomes horizontal and tense by the action of the levator and the circumflexus of the palate; and its passage into the larynx is prevented by the epiglottis, which is pressed down by the food upon the orifice of the larynx. DIGESTION. 227 According to Magendie, hoAvever, the epiglottis is not necessary to deglutition ; for, in some of his experiments, it Avas removed from animals, and it has sometimes been destroyed by disease in the human subject, without materially impairing deglutition. The passage of food into the larynx, according to Magendie, is prevented by the action of the muscles which close the rima glottidis, viz. the arytanoideus transversus, and the arytanoidei obliqui. As long as these muscles preserve their poAver of con- traction, food is prevented from passing into the larynx, even in the absence of the epiglottis. But if the power of contraction in these muscles be destroyed or enfeebled, as appears to be the fact in some cases of palsy, deglutition is liable to be interrupted by violent fits of coughing, occasioned by the entrance of a part of the food into the larynx—although the epiglottis remains entire. The secretions of the mouth and fauces, the saliva to dilute the aliment, the mucus to lubricate the surfaces over which it is to pass, are almost indispensable to the deglutition of dry substan- ces. It has been observed that the use of belladonna occasions in some instances, so great a diminution of the salivary and mu- cous secretions, that the individual is unable to mould dry sub- stances, such as bread, into a bolus, and can with difficulty swallow them. As soon as the food has reached the oesophagus, the muscular contraction of this fleshy tube is excited, by means of Avhich the bolus is gradually forced into the stomach. The poAver of gravi- tation contributes but little to the descent of food into the stomach ; for it is found that funambulists can swallow Avithout difficulty, with their heads doAvnward. The motion of the oesophagus in deo'lutition, consists in a successive contraction of its circular fibres, from above doAvmvards. The upper part of the tube is dilated by the bolus, Avhich is forced into it by the contraction of the pharynx. Its superior circular fibres are then excited to con- tract, and the food is pushed further doAvn into the tube, dilating the parts immediately beneath, which react upon it, and force it still further doAvn, until it reaches the stomach. The longitudi- nal fibres, in contracting, shorten and relax the oesophagus, and in this mode promote the descent of its contents. Mayo supposes that the longitudinal fibres of the tAvo extremities of the alimen- tary canal, viz. the oesophagus and the rectum, are designed to strengthen these parts, and to prevent their elongation and rupture by the volume of their solid contents. Deglutition is divided by Magendie into three stages, viz. 1. The passage of the food from the mouth into the pharynx. 2. From the pharynx into the oesophagus. And, 3. From the oesophagus into the stomach. The first stage is voluntary; the second partakes of the nature both of voluntary and involuntary action. Magendie considers pharyngeal deglutition as involun- tary ; yet Mayo remarks, that it may at any time be performed 228 FIRST LINES OF PHYSIOLOGY. by a deliberate exertion of the ■■will.. The third stage, or oesopha- geal deglutition, is removed from the jurisdiction of the will. Yet, as Mayo remarks, the oesophagus appears to partake of the nature of both the voluntary and involuntary muscles; for Avhen the.nervi vagi are pinched, a sudden action ensues in its fibres, Avhich is presently after succeeded by a second action of a slower kind. III. Chymosis. Gastric digestion, or chymosis, consists in the conversion of food in the stomach into a soft pulpy mass, termed chyme. The aliment, previously masticated and thoroughly blended Avith the saliva, descends through the pharynx and oesophagus into the stomach, in-the manner just described. . Some physiologists suppose that the stomach.is not mechanically dis- tended by the mass of the aliments, but that it exercises the poAver of self-dilatation in the reception of the food. However this may be, the organ enlarges in proportion to the. volume of the food Avhich is sAvalloAved. Its coats are distended, the plicae of its mucous membrane are unfolded, and the sinuosities of its arteries and veins disappear. The increased volume of the stom- ach pushes the diaphragm up into the thorax, distends the walls. of the abdomen anteriorly, and presses against the contiguous viscera, particularly the liver and spleen. The position of the stomach undergoes a change, the organ performing, as it were, part of a revolution on its axis, by which its anterior face becomes superior, its posterior inclines doAviiAvard, its inferior arch is raised forward, and its superior turned backward. Motions of the Stomach. The stomach, stimulated by the presence of food,' reacts upon and compresses it ; for being a hollow muscular organ, it contracts upon its contents, and under some circumstances Avith very'con- siderable force. It has been ascertained by observation, that the human stomach is capable of contracting to such a degree, as to expel from its cavity hairs, needles, and other smaller bodies. The fleshy stomachs of birds possess' vastly greater mechanical poAvers, so as even to be able to break down very hard substances. The muscular action of the stomach consists of a kind of vermic- ular motion, produced by the alternate contractions of its trans- verse and longitudinal fibres, the former diminishing its diameter, the latter shortening its length, by approximating its splenic and pyloric extremities. Tiedemann and Gmelin remark, that the muscular coat of the stomach does not contract simultaneously throughout its whole extent, but one part contracts a little, while another dilates, and vice versa ; the place Avhere contractions take place becoming thicker and rugous. According to the same physiologists, these undulatory movements proceed from the oeso- phagus towards the pylorus, and from this back again to the oeso- DIGESTION. 229 phagus. In some cases, they observed these motions to begin at the same time at both extremities of the stomach, and to meet at the middle of the organ. They appeared to be most energetic in the pyloric part of the stomach, where the muscular coat is thickest. .Hence the motions' of the- stomach during digestion have a predominant tendency toAvards the pylorus. Dr" Beaumont found that the bulb of a thermometer introduced into the stomach during this period, was draAvn doAvn with a considerable and steady force. The most vigorous contractions are occasioned by the most stimulating food. These successive contractions of the muscular fibres occasion a sIoav movement of the aliments in the stomach, by which they are brought successively into contact with all parts of its surface, and thoroughly penetrated Avith the gastric fluid. According to Beaumont, the contractions of the muscular coat of the stomach produce a constant sIoav revolution of the food round the interior of the organ, from one extremity to the other. After its entrance into the stomach, the ordinary course of the food, in these revolutions, is first from right to left, thence, along the large curvature, from left to' right. " The bolus, as it enters the cardia, turns to the left, passes the aperture, descends into the splenic extremity, and folloAvs the great curvature towards the pyloric end. It then returns in the course of the smaller curvature, makes its appearance again at the aperture, in its descent into the great curvature, to perform similar revolutions."* From one to three minutes are occupied in completing one of these revolutions. During these motions, the cardiac and pyloric orifices of the stomach are closed, so as to prevent the escape of the food. The contraction of these apertures continues, even if the stomach be cut out of a living animal, during digestion. According to Home, the stomach, during these contractions, forms a kind of double sac, by the action of a transverse band, situated three or four in- ches from the pyloric extremity. The contraction of this band during digestion, divides the sac of the stomach into two parts, one of which, viz. the splenic, contains the food that is but little digested ; the other, or the pyloric, that part of it which is further advanced in chymification. This opinion, Beaumont's experi- ments confirm. Besides the active motion of the stomach, this organ is subjected to the alternate movements of the abdominal muscles and the diaphragm in respiration. That these motions may afford some aid to the organ in executing its functions, is the more probable from the fact that weak stomachs are frequently assisted by the mechanical support of a belt. * Beaumont. 230 FIRST LINES OF PHYSIOLOGY. Secretions of the Stomach. Not only the muscular action of the stomach is excited by the stimulus of food, but its circulation and its secretions are increased. There is a concentration of vital activity in the organ, an in- creased afflux of blood toAvards it, a greater evolution of heat, and an increase of its follicular and perspiratory secretions. The latter of these, the gastric fluid, is exhaled in abundance, and the pro- cess of digestion commences. In the process of chymification the food undergoes a remarka- ble change ; for the properties of chyme are entirely different from those of the aliment out of which it is prepared. The taste, smell, and other sensible properties of the food, are altered or disappear, and new ones are acquired. It is evident, therefore, that the chemical affinities of the food have been totally subverted, and its elements have entered into neAv combinations. Whether this change is confined to the proximate principles of the food, or ex- tends to its ultimate elements, it is not easy to determine. This remarkable change in the properties of the food is produced by a fluid secreted by the stomach, called the gastric liquor. This fluid is secreted abundantly during digestion, but not Avhen the stomach is empty. It has already been observed that the stomach is large- ly supplied Avith blood vessels. It receives much more blood than is necessary for its oavu nutrition ; and the destination of this ex- cess of blood, probably, is to furnish materials for the secretion of the gastric fluid. The gastric liquor is produced not by a follicu- lar secretion, but arterial exhalation, Like all the other secretions, it maybe increased, diminished, or changed in its qualities by various causes. Thus the division of the pneumogastric nerves, the use of narcotics, the excessive use of stimulating drinks, vio- lent emotions of the mind, &c. diminish the secretion of this fluid ; and, on the other hand, condiments and high-seasoned food increase it. The gastric fluid, according to Beaumont's observations, is a clear transparent fluid, perceptibly acid to the taste, and a little saltish, but destitute of odour. It effervesces slightly Avith the alkalies; possesses in a high degree the property of coagulating albumen, and is poAverfully antiseptic. According to Beaumont, pure gastric fluid will keep unchanged for almost any length of time ; and it appears from Spallanzani that meat may be preserved in it Avithout taint for five or six weeks, or even longer. Its acid properties are owing to the presence of free muriatic and acetic acids. According to Tiedemann and Gmelin, the gastric fluid contains the hydrochloric and acetic acids, and, in horses, the butyric ; saliva, osmazome, chloruret, and sulphate of soda, and a little carbonate and phosphate of lime. The degree of its acidity corresponds to the less or greater digestibility of the food; those aliments which are the most difficult of digestion causing a greater DIGESTION. 231 degree of acidity in the gastric fluid. Thus bones, cartilages, fibrin, concrete albumen, meat, gluten, oats, and bread, are more difficult to digest than starch, potatoes, rice, gelatin, and liquid albumen; and they were found to occasion the secretion of a more acid gastric fluid in dogs and cats. In horses, oats caused the secretion of very acid gastric liquor. It appears, then, that the degree of acidity of this fluid depends on the degree of exci- tation of the stomach, produced by the food. The gastric liquor appears to be secreted only when the stomach is excited by the stimulus of aliment; and, consequently, no conclusion respecting its properties, can be draAvn from experiments on the fluid, taken from the stomach during fasting, as this consists chiefly of gastric mucus, mixed Avith saliva; a consideration Avhich may account for many contradictory results in the researches of physiologists on the gastric fluid. This fluid appears to be the principal agent in chymification or gastric digestion. Its most remarkable property is its power of dissolving alimentary substances; a power Avhich it retains some time after death ; for alimentary matter introduced into the stom- ach of an animal recently killed is more or less perfectly digested. The poAvers of the gastric fluid in dissolving alimentary substances Avere first satisfactorily ascertained by some experiments performed by Spallanzani and Stephens, in the last century. Stephens in his experiments inclosed various alimentary substances in hollow metallic balls pierced with holes, to admit the gastric fluid; and he found that the balls, when voided by stool, were empty, the substances they had contained being digested, having escaped by the holes in their sides. These experiments Avere performed on men and other animals. Spallanzani obtained similar results ; and pursuing the idea, he exposed certain aliments, properly masticated and impregnated Avith saliva, to the action of the gastric fluid out of the stomach. They were kept in the axilla for several hours; and upon examination afterwards were found to be chymified. Beaumont's experiments appear to establish, conclusively, the poAver of the gastric liquor in dissolving alimentary substances out of the stomach. The process is rather sloAver perhaps, because the exact temperature of the stomach cannot be maintained by arti- ficial means, and because it is impossible to subject the food to the same mechanical agitation, by exactly imitating the motions of the stomach. The results-, however, are in both cases apparently the same ; the chyme, prepared by artificial digestion, presenting the same sensible properties as that which is found in the stomach. The solvent powers of the gastric fluid in respect to alimentary matter are very great. The hardest bones are dissolved and digested by it in the stomachs of dogs; and Beaumont found that it would dissolve even bones out of the body. It coagulates milk and the serum of the blood, and other kinds of albumen; and afterwards dissolves the coagula. The energy of this men- 232 FIRST LINES OF PHYSIOLOGY. struum appears to observe an inverse ratio to the mechanical poAv- ers of the teeth and stomach, employed in the comminution of the food. Hence in animals which masticate their food, or are pos- sessed of thick fleshy stomachs,- the gastric fluid is endued with feebler powers; Avhile in those which are destitute of teeth and have membranous stomachs, its solvent energy is very great. But these extraordinary properties of the gastric fluid are exerted almost exclusively upon organic substances. And it is a remark- able fact that these substances, Avhen endued Avith life, effectually resist its power. Hence the living Avails of the stomach itself, and intestinal Avorms Avhich sometimes ascend into the stomach, are invulnerable to the action of this fluid. The poAvers of the gastric liquor, as might be supposed, are adapted- in every species of animal to the nature of the food on Avhich it subsists. Hence the gastric fluid of herbivorous animals will digest only vegetables ; and that of carnivorous animals only animal substances. A curious example of this is furnished by the fact that when a haAvk or an owl has SAvallowed a small bird hav- ing seeds in its stomach, these have passed unaltered through the intestines of the bird of prey. Its properties, hoAvever, are sus- ceptible of essential modification, by the qualities or nature of the substances employed as food,—so that herbivorous animals may by degrees become accustomed to, and even thrive upon, animal food, and vice versa. This change hoAvever is always gradual, arid hence the danger or inconvenience at least, of making sudden changes in the nature of the food. The solvent properties of the gastric fluid appear to be only a special example of a general assimilative poAver possessed by the animal fluids. Thus animal substances, even bones introduced into the abdomen of a living animal, or inserted under the cuticle, in some.instances are Avholly dissolved. A temperature of about 98° or 100°.is very favourable to the solution of the food in the gastric fluid. Beaumont found that while a phial of this fluid, at a temperature of 99°, completely dis- solved a portion of masticated fresh beef, the same quantity in another phial in Avhich an equal Aveight of cheAved beef Avas placed, and exposed to a temperature of 34° in the open air, had in the same time produced only a macerated or softened appearance in the beef. According to Lenhossek, the animal temperature is raised during digestion, and the region of the stomach becomes a kind of focus of heat. Hence taking food diminishes the danger of freezing in persons exposed to severe cold. In most of Beaumont's expe- riments, hoAvever, the temperature of the stomach was not raised by digestion; but in tAvo or three of them it Avas somewhat in- creased. The ordinary temperature of the stomach is about 100°, and Beaumont, in some instances, found it to be higher at the pylorus than at the cardiac extremity. DIGESTION. 233 During digestion a small quantity of gaseous matter is usually present in the stomach, which is found to consist of oxygen, car- bonic acid, hydrogen, and azote. Sometimes it is Avholly absent. Some of it is probably derived from the air sAvallowed Avith the food ; but a portion of it doubtless is extricated during the changes which the aliment undergoes in the stomach. The solvent poAvers of this secretion, in relation to alimentary substances, may be understood, in part, by a reference to its composition. Thus the water Avhich it contains dissolves several simple alimentary principles, as liquid albumen, gelatin, osma- zome, sugar, gum, and starch. The hydrochloric and acetic acids, dissolve several other principles, Avhich are not soluble in water; as concrete-albumen, fibrin, coagulated caseum, gluten, and gliadine, a. substance analogous to gluten.. These acids dis- solve, also, cellular tissue, membranes, tendons, cartilages, and bones. Their solvent poAver is assisted by heat; and hence, the temperature of the stomach is an important agent in gastric diges- tion. From the fact that alimentary-substances, Avhen subjected to the action of the gastric fluid out of the stomachy are converted into a substance presenting the characters of chyme, some physi- ologists have embraced the opinion, that gastric digestion is noth- ing but a chemical solution of the aliment in the gastric fluid. Tiedemann and Gmelin, who adopt this opinion, admit hoAVever, ■ that Avith respect to some alimentary substances, a peculiar kind of decomposition is produced by the action of the gastric fluid. Starch, for instance, Avhen . dissolved in the stomach, loses its peculiar property of giving a deep blue colour to iodine, and is converted into sugar and gum. It would follow, from this theory of digestion, that the digesti- bility of alimerits is in proportion to the facility Avith Avhich they are dissolved in the gastric liquor, and of course depends upon their peculiar composition. The substances most easy of diges- tion are such as are .soluble in Avarm Avater, or contain a large proportion of soluble principles, as sugar, gum, liquid albumen, and gelatin. Those Avhich require the aid of acids to dissolve them, as those Avhich contain much gluten, concrete albumen, fibrin, caseum, cartilage, or bone, are of more difficult digestion ; Avhile some are insoluble in the gastric fluid, and of course indi- gestible ; as the fibres of wood, or of plants, the skin of some of the leguminous plants, the kernels of fruits, feathers, hairs, &c. Chvmification, hoAvever, is not to be regarded merely as a chemi- cal solution of alimentary matter in the gastric fluid. It is true that the process of gastric digestion may be imitated out of the body, by macerating alimentary substances in the gastric fluid. No doubt a solution more or less perfect may be effected in this Avay, by the solvent poAvers of this fluid over substances of an alimentary kind. This is established by the experiments of Spal- 30 - 234 FIRST LINES OF PHYSIOLOGY. lanzani, and more fully by those of Beaumont. But it is not so certain that they become endued Avith all the properties of chyme, especially Avith those Avhich assimilate them to the nature of the living animal body, by undergoing this process. It is indeed difficult to conceive how a mere chemical solution of aliment can endue it with living properties, or vitalize it; for undoubtedly chyme is in the first stage of animalization. It cannot become invested Avith living poAvers, if placed out of the atmosphere of vitality. Vital affinity can operate only within the sphere of vital poAver. If then the gastric fluid is a mere chemical solvent of alimentary substances, it seems probable that the living coats of the stomach, Avith Avhich all parts of the food are brought successively into contact, may impart to the latter certain proper- ties, which may assimilate it to the nature of the living organi- zation ; properties which it is impossible to conceive that it can acquire, Avhen removed from the contact of living matter. Life is a unit ; its properties cannot be separated from the source whence they originate. It is as impossible to conceive of bottling up a portion of vitality Avith a feAv ounces of gastric fluid, as it Avould be to think of corking up a phial of sunshine, and keeping it in the dark. The analysis of digestion, proposed by Prout, corresponds in the main with this vieAV. Prout attributes to the stomach, three distinct poAvers; Avhich are all exerted in digestion ; viz. a reduc- ing, a converting, and a vitalizing poAver. By the reducing poAver he means the faculty which the stomach possesses of dis- solving alimentary substances, or of bringing them to a semifluid state. This operation he supposes to be altogether chemical. By the converting power of the stomach, he means the faculty of changing simple alimentary principles into one another, as starch into sugar and gum. Without such a power, Prout thinks that the uniformity in the composition of the chyle, Avhich he sup- poses to be indispensable to the existence of animals, could not be preserved. This process of conversion he considers, also, as chemical, but as of more difficult accomplishment than the re- ducing. The vitalizing, or organizing poAver, is that by which alimentary substances are brought into such a condition as adapts them for an intimate union Avith the living body. This poAver, he says, cannot be chemical, but is of a vital character, and its nature is entirely unknoAvn. The vital properties Avhich the chyme acquires in the stomach, Avhatever these properties be, it is the prerogative of the living or the nervous poAvers of the stomach to confer. The influence of these poAvers in digestion is illustrated by numerous facts, especially by the influence of those medicinal agents Avhich depress the nervous energy, as opium and other narcotics.; the effect of passions of the mind, and the sud- den accession of disease ; and intercepting the nervous influence by the ligature, or section of the par vagum; causes Avhich can DIGESTION. 235 hardly be supposed competent to destroy the chemical or solvent powers of the gastric fluid, but which, nevertheless, are well knoAvn by physiologists, to interrupt or Aveaken the process of gastric digestion. The substance into Avhich aliment is converted in the stomach is called chyme. This is a semifluid, homogeneous matter, of a grayish colour, sourish smell, and insipid or disagreeable taste, but varying considerably in its sensible properties, according to the qualities of the food out of Avhich it is prepared. According to Beaumont, it is invariably homogeneous, but its colour par- takes slightly of the colour of the food. " It is always of a lightish or grayish colour, varying in its shades and appearance from that of cream to a grayish or dark-coloured gruel. It is, also, more consistent at one time than at another; modified in this respect, hj the kind of diet used. It is invariably distinctly acid." Its acidity, according to Tiedemann, is derived from that of the gastric fluid. Leuret and Lassaigne, found the chyme in an epileptic, Avho died five hours after taking food, to present the appearance of a pale saffron-coloured pap, of a strong and repul- sive smell, containing lactic acid, a white crystalline animal mat- ter, similar to sugar of milk ; a fat yelloAvish acid matter, resem- bling rancid butter; another animal substance, like caseum; albumen, phosphate of lime, muriate and phosphate of soda. According to Raspail, chyme is a kind of paste formed of a mixture of the debris of the vegetable and animal tissues used as food, and of a solution in acetic acid of albumen, gum, and oil, together Avith all the salts existing in the tissues, Avhich the acetic acid can dissolve. The acidity of the chyme, therefore, is due, as he asserts, not as Pont supposes, to the presence of the hydro- chloric, but to that of the acetic acid, Avhich he says may be obtained abundantly from the chyme by distillation. This acetic acid is derived, not from the gastric fluid, but from the fermenta- tion of alimentary principles in the stomach. Raspail remarks that gastric digestion requires the presence and the mutual action of at least tAvo substances, viz. sugar, or a substance convertible into sugar, and albumen or gluten. When a mixture of these two principles is left to itself, they react upon each other, and become the subject of an intestine motion, called fermentation. The result of this mutual action is alcohol, Avhich remains in the liquid, and hydrogen and carbonic acid, which escape with effer- vescence in the form of gas. If a portion of gluten remains after the disappearance of the sugar, a neAV reaction takes place be- tween this residual gluten and the alcohol, and the result of it is the formation of the acetic acid, at the expense of the tAvo ele- ments of this neAV fermentation. The acidity of the chyme then in this vieAV is developed by fermentation, and is derived, not from the muriatic, but the acetic acid. The acetic acid thus developed holds in solution or renders 236 FIRST LINES OF PHYSIOLOGY. soluble the vegetable gluten :or animal albumen and oil, which may still be present in the alimentary mass. If we suppose this solution of albumen, &'c in acetic acid to be sufficiently diluted Avith water to assume a liquid form, and to be separated from the debris of the tissues used as food, it Avould represent, according to Raspail, an acid' and rudimentary blood, requiring only to be rendered alkaline by the action of the. bile to be converted into chyle, a-fluid which differs in its composition'from blood only in the absence of colouring matter. The carbonic acid and. hydrogen .gases extricated during the gastric fermentation, Raspail supposes to.be absorbedby the walls of the stomach. The time required for the conversion of food into chyme, va- ries according to the greater or less degree of digestibility of the latter. In Beaumont's experiments, the average time employed in gastric digestion Avas about' three hours and a half. If the food is of a soft consistence, and well divided by mastication, it is speedily penetrated by the gastric fluid, and rapidly dissolved. But if it possesses a certain degree of consistence, or has been SAvallowed in large masses, its solution goes on sloAvly, and from the surface to the centre. The external layers are frequently softened, and almost dissolved, while the parts within are almost wholly unchanged. Those parts of the aliments which are near- est the surface of the stomach, are most exposed to the action of the gastric fluid, as well as to the vitalizing influence of the stomach, and of course are the soonest dissolved, and chymified. By the successive contractions of the muscular coat, the dis- solved portions are carried towards the pylorus, and gradually pass out of the stomach into the duodenum. The passage of the chyme from the stomach takes place during the expansion of the circular fibres of the pyloric extremity, perhaps by the contrac- tion of the longitudinal. It is at first slow, but becomes more rapid in the latter stages of chymification, as the formation of chyme becomes more abundant. According to Rudolphi, the chyme passes out of the stomach by drops, and the more rapidly as the degree of its fluidity is greater. The sensibility of the pylorus appears to bear a strict relation to the digested condition of the food ; so that any undigested por- tion, which happens to approach this outlet of the stomach, is de- nied an exit. The pylorus contracts so as to prevent its escape. Hence food of difficult digestion may be retained in the stomach a considerable time, as for example, even a week or more, and then be vomited up unchanged, or pass off by stool. For a simi- lar reason, chyme is always present in the greatest quantity at the pyloric end of the stomach, whither it is regularly carried as fast as it is formed. While at the cardiac end, where digestion com- mences, it is found much more sparingly. In general, the peris- taltic action of the stomach continues until the aliment is Avholly DIGESTION. 237 dissolved by the gastric fluid, and has passed out of the stomach. The organ then resumes a state of contraction and quiescence natural to it when empty. Fluids pass out of the stomach very speedily, chiefly perhaps by absorption. Influence of Innervation upon Chymification. That the par vagum or pneumogastric nenre exercises some important influence over digestion, has- long been known to physi- ologists, though it is not yet fully ascertained Avhat this influence is. The results of experimental researches on the uses of these nerves, by different, physiologists, have not been uniform,. but sometimes directly contradictory. But it seems to be pretty gen- erally agreed, that the division of these nerves in the neck causes a suspension of the process of digestion. Blainville passed a ligature round the nerve above the lungs, and the effect Avas a suspensiori of respiration and chymification. The ligature was afterwards AvithdraAvn, and the tAvo functions were restored. The same physiologist and Legallois, performed the experiment on pigeons; and it Avas found that the corn sAval- loAved by the birds remained unaltered in the crop. Dupuy per- formed a similar experiment on horses. The animals ate and drank, but died on the sixth day ; and on dissection no chyle was found in the lacteals. These experiments have been performed by several other physiologists, with similar results. The functions which have been ascribed to the pneumogastric nerve, by different physiologists, in relation to gastric digestion, are of three kinds. 1. That it presides over the secretion of the gastric fluid. 2. That it animates the muscular motions of the stomach and oesophagus. 3. That it is the seat of sensation in the stomach, bestoAving upon this organ both common sensibility, and the appetites of hunger and thirst. The first opinion is adopted by Philip and Brodie, and, to a certain extent, by Tiedemann and Gmelin. Brodie found that in . animals killed with arsenic, after the section of the pneumogastric nerves, no trace of gastric fluid could be discovered in the stomach. Philip referred the suspension of digestion after the division of these nerves, in his experiments upon animals, to a suspension of the secretion of gastric fluid. Tiedemann and Gmelin ascribe the check Avhich digestion experiences from the section of these nerves, to a paralysis of the muscular coat of the stomach; but they are also of opinion, that the secretion of the gastric fluid, and its acid qualities, are dependent on the influence of these nerves ; and hence, that the division of them may retard digestion, by preventing the secretion of this fluid, as Avell as by paralyzing the muscular fibres of the stomach. The formation of this acid 238 FIRST LINES OF PHYSIOLOGY. secretion out of the blood, Avhich is an alkaline fluid, they sup- pose, requires an energetic action of the nervous poAver on the blood Avhich penetrates into the capillary network of the stomach; and they conjecture that this influence operates by causing a de- composition of the salts contained in the blood, viz. the muriates of potash and soda, and the acetate of soda, the acids of which, they suppose are secreted into the stomach, freed from their bases, and become integrant parts of the gastric fluid. This opinion is founded on an experiment, in which the stomach of a dog in which both pneumogastric nerves had been divided Avith a loss of sub- stance, and which had aftenvards eaten the boiled Avhite of eggs, exhibited no mark of acidity, its contents not reddening the tinc- ture of turnsole. It seems probable, hoAvever, that the branches of the great sympathetic, which penetrate Avith the arteries into the coats of the stomach, have a considerable, if not the principal share, in the secretion of the gastric fluid. 2. Breschet inferred from his experiments, that digestion is re- tarded by the section of the par vagum, not in consequence of a suspension of the secretion of gastric fluid, but by a paralysis of the muscular fibres of the oesophagus and stomach, resulting from this operation ; in consequence of Avhich, the mechanical motions of the stomach, necessary to chymification, are no longer exe- cuted, and the food lies motionless in the holloAv sac. Breschet found that this operation retards but does not destroy digestion. Leuret and Lassaigne also performed the experiment on a horse, by cutting out a piece from the vagus four or five inches long, on each side of the neck; and then performing tracheotomy to pre- vent asphyxia, they suffered the animal to eat. They found, how- ever, that the oesophagus was paralyzed by the operation, and the food forced back into it and vomited up. To prevent this they tied the oesophagus, and eight hours after the animal had eaten, it was killed; and they found that digestion had taken place, and the food was completely chymified. The experiment Avas after- wards repeated Avith the same results; and the conclusion Avhich Leuret and Lassaigne dreAV from it Avas, that digestion may take place independently of the par vagum. In fact, the vagus spends most of its inferior branches upon the oesophagus, sending but few to the stomach, Avhich is supplied Avith nerves from the gang- lionic system; and hence, the section of the vagus only retards digestion, Avhich is still carried on under the influence of the great sympathetic. It is a curious fact, that the influence of the pneumogastric nerves on digestion may be supplied by galvanism and electricity, and even by mechanical irritation. If the nerve be merely di- vided, and the ends be suffered to remain in contact Avith each other, digestion is not suspended. The tAvo ends must be removed from each other, or a piece cut out, to insure the effect; and in that case, if the inferior or gastric end of the divided nerve, be DIGESTION. 239 stimulated by a galvanic current, or even by mechanical irrita- tion, digestion recommences. From this fact, Breschet inferred that electricity operates in restoring digestion by exciting the muscular movements of the Avails of the stomach, by means of Avhich the food is brought successively into contact Avith all parts of its inner surface ; and that mechanical irritation operates on the same principle. This view is strikingly corroborated by a fact mentioned by Tiedemann and Gmelin, viz. that they had frequently witnessed, in experiments, that mechanical and chemi- cal irritations, applied to the pneumogastric nerves, occasioned contractions in the muscular coats of the stomach. 3. Experiments make it probable, that the stomach derives cerebral sensibility from the par vagum ; and that the sense of hunger also depends on the influence of these nerves.* Bell states, that animals killed by acrid poisons die Avithout pain, if the par vagum be divided, but hoAvling Avith agony if these nerves are left uninjured. The section, or the compression by ligature, of these nerves, a little above the stomach, appears Avholly to destroy the feeling of hunger. Brachet divided the pneumogas- tric nerves in a dog Avhich had been kept from food tAventy-four hours, and Avas ravenously hungry. The animal before the ope- ration Avas extremely impatient for food, but became indifferent to it aftenvards, and went and lay quietly doAvn. When meat Avas offered him, he began to eat; and continued to eat till both the stomach and oesophagus became distended with food. The feeling of satiety was evidently annihilated, as Avell as that of hunger ; and the animal ate merely to gratify the sense of taste. Similar experiments on horses, performed by Leuret and Las- saigne, Avere folloAved by like results. Two inches of the par vagum Avere cut out, and the animals continued to eat as before; from Avhich these physiologists inferred, that the appetite was not affected by the division of these nerves. It was remarkable, hoAvever. that they continued to eat after the stomach Avas very much distended Avith food, a fact Avhich makes it probable that the feeling of satiety Avas destroyed by the experiment, and the animals continued to eat automatically, as it Avere, Avithout being prompted by appetite to begin, or by the sense of fulness to leave off. The feeling of thirst also appears to be destroyed, as Avell as that of hunger and the appetite of respiration. The subjects of these experiments, probably, not only eat but drink also and respire automatically. It should be remembered, that the pleasure of eating does not consist exclusively in the gratification of the appetite, which resides in the stomach, but that much, if not most of it, is purely gustatory, and is seated in the palate and fauces. The physical * Secetur nrrvus pneumogastricus. Cessat illico fames; non cessat illico digestio. —Martinii Element. Physiol. 240 FIRST LINES OF PHYSIOLOGY. incentives to taking food are tAVofold, having their seats in distinct portions of the alimentary canal, and deriving their origin from separate arid independent parts of the nervous system. It is true these are intimately connected together, yet not so closely but that considerable pleasure may be taken in eating Avhen no real hunger exists. Even infants, Avhose natural tastes have not been corrupted by artificial habits, frequently gorge themselves with their natural food, and are obliged to get rid of the excess by vomiting. There can be no doubt that the same is true, to a cer- tain extent, of the inferior animals, and hence, from the fact that animals continue to eat after the section of the pneumogastric nerves, Ave cannot infer that the feeling of hunger is not derived from these nerves. A fact mentioned by Swan may seem to be at variance with this alleged function of the pneumogastric nerve. He relates that in a gentleman who died after suffering great dyspnoea, the par vagum Avas found to be smaller than usual, and softer in its consistence. This patient had enjoyed a great appetite for seve- ral months before his death, but had never felt satisfied with eating, nor experienced any sense of fulness, Avhatever quantity of food he might have taken. This case will perhaps be found to prove quite as much for, as against, the sensiferous function of the pneumogastric nerve. The nerve "Avas diseased, and the consequence Avas, that-one modification of gastric sensibility, the feeling of satiety, and ful- ness after eating, Avas annihilated or. very much diminished; while another, viz. the sense of hunger, was morbidly excited. Either of these affections of the sensibility of the stomach, might have resulted from a diseased state of the nerve, from which this organ derives this property, and Avho can undertake to say that a certain degree or state of .disease in this nerve, might not destroy or diminish one kind of gastric sensibility, and morbidly increase another? It is worthy of remark that Mr. Swan himself attrib- uted both affections to the diminished energy of the nerves. For he says, that it appeared to him that the pneumogastric nerves suffered from the action of the cplchicum, of Avhich the patient had made a free use, and I think, he goes on to say, " the craving for food, and the want of a sensation of fulness after eating ever so much, shoAved the nerves at least had lost their sensitive qualities." The pains Avhich are sometimes experienced in paralyzed limbs furnish examples somewhat analogous ; for in these cases Ave have impaired nervous poAver diminishing one kind of sensibility, and increasing another. Both of the symptoms in Mr. SAvan's pa- tient, obviously point to an affection of the instrument of sensa- tion in the stomach, Avhatever this may be; and the diseased condition in which the par- vagum Avas found, gives probability to the conclusion that this nerve is that instrument itself. DIGESTION. 241 The analogy of the lingual branch of the fifth pair, which bestows common and special sensibility on the tongue, may be alleged in favour of this view of the functions of the par vagum. It is here proper to mention the assertion of Magendie, that if the section of the pneumogastric nerves be made in the thorax, below the place where the branches Avhich supply the lungs are given off, the food which is afterwards taken, is regularly con- verted into chyme, and furnishes abundant chyle ; and he is dis- posed to attribute the suspension of digestion, when the nerves are divided in the neck, to the influence of disturbed respiration upon the action of the stomach. Brachet, however, regards Magendie's experiments inconclusive, on account of the great difficulty of making a complete division of the pneumogastric nerves beloAV the origin of the pulmonary branches, without dividing the oesophagus itself. In his experiments to determine this point, he found that if the complete section of the par vagum was effected by the division of the oesophagus a little above the cardia, the stomach of the animal remained distended with the food taken just before the experiment; a very slight alteration only being perceptible in the contents of the stomach, several hours after the section of the oesophagus. On the Avhole, it appears to be established by experiment, that the pneumogastric nerves not only give activity to the muscular fibres of the stomach and oesophagus, but also bestow cerebral sensibility upon the organ, and are the immediate seat of thesen- sations of hunger and thirst. It is probable, also, that the secre- tions of the stomach are influenced by the state of its sensibility, and that the section of these nerves, by impairing or destroying this power, may indirectly occasion a change in the qualities of the gastric fluid, or a diminished secretion of it, and in this man- ner, likewise, impair or suspend chymification. It appears, also, that digestion is suspended by other operations by Avhich the nervous poAver is Aveakened. Wilson found that chymification- Avas arrested by a section of the spinal cord in the lumbar region; and EdAvards and Vavasseur witnessed the same effect, from the removal of part of the cerebral hemispheres. An injection of opium into the veins was found to produce the same effect. According to Brachet, the par vagum is the channel which transmits the impressions of medicinal and poisonous substances from the stomach to the brain. If a narcotic be administered in a sufficient dose, its effect upon the brain is perceived almost immediately, and long before the poison could be digested and absorbed. But if the par vagum be previously divided, the effect is -prevented. Brachet gave to each of tAvo dogs six grains of opium, having in one previously divided the par vagum. The dog which had not undergone the operation, fell into a state of 31 242 FIRST LINES OF PHYSIOLOGY. profound narcotism, while the other lay doAvn quietly, and mani- fested no other symptom than the dyspnoea Avhich always results from the section of the pneumogastric nerves. The nux vomica in like manner, which acts so violently and rapidly as a poison on dogs, produces no such effect if the par vagum be divided. The poison may be given in a double or triple dose, and yet in- toxication Avill not be produced at once, as is commonly the case • but will manifest itself at a much later period, with much less intensity than common. Emetics, and purgatives also, admin- istered to dogs which have suffered the division of these nerves according to Brachet, produce none of their usual effects. This statement, however, it is proper to mention, is at variance with the fact related by Magendie, that tartar emetic, introduced into the stomach of an animal, in which both branches of these nerves had been divided, occasioned vomiting; Avhence it is inferred that an irritation must have existed in the stomach, implying the presence of some kind of sensibility in the organ, after the section of the par vagum. But if vomiting always implies irritation or sensation of any kind in the stomach, what, it may be asked, is the seat of this sensation, in animals made to vomit by tartar emetic injected into the veins after the stomach has been cut out, and a bladder substituted in its place ? If vomiting can occur in one case without the aid of gastric sensibility, it may in the other; and the effect in both, is doubtless to be referred to the same cause, viz. the introduction of the tartar emetic into the circulation, in the one case by injection, in the other by absorp- tion from the coats of the stomach. The poisonous effects of alcohol are,/first communicated to the brain through the same channel. -^ \ IV. Chylosis. The duodenum receives the chyme from the stomach, and has generally been believed to accomplish the sec- ond digestion, or the conversion of chyme into chyle. In the duo- denum it meets with the bile, pancreatic and intestinal fluids, loses its acid properties, and becomes alkaline, probably by the agency of the soda of the bile ; and by this change, according to Raspail, it is converted into chyle, and thus advances another step towards the formation of blood, from which it now differs in composition only in the absence of colouring matter. In this state it is greed- ily imbibed by the coats of the intestines, leaving a residual mass, Avhich is destined, after having been sloAvly conducted through a very long and Avinding passage, to be dismissed by the postern of the system. The duodenum, like the other parts of the intestinal canal, is composed of three tunics, viz. a serous or peritoneal, a muscular, and a mucous. The first, however, covers only the anterior part of the intestine, and can hardly be considered as essential to it. The second, or muscular, is formed almost Avholly of circular fibres. The third or mucous, exhibits a great number of transverse folds, termed the valvula conniventes. It DIGESTION. 243 exercises a double secretion, one follicular, or mucous, the other perspiratory, or exhaling. The arteries of the duodenum are derived from the right gastro-epiploic, and the splenic ; its nerves, almost Avholly from the solar plexus. The situation of the duo- denum is deep in the abdomen, on a level Avith the third or fourth lumbar vertebra; having behind it the vertebral column, the aorta, and the vena cava inferior; before it, the stomach, and transverse mesocolon; above, the liver; and below, the small intestines. In the duodenum the chyme is exposed to the action of three neAV agents, by which its nutritious parts are further elaborated, and the constituent principles of chyle are developed. These agents are the intestinal fluid, the bile, and the pancreatic secre- tion. The irritation excited by the acid chyme on the inner sur- face of the duodenum, occasions a copious afflux of these fluids into the intestine. According to Tiedemann and Gmelin, the gall-bladder is ahvays empty during digestion, but full during fasting. The pancreatic fluid is secreted in increased abundance ; and the stimulus of these tAvo fluids, particularly of the acrid bile, in addition to that of the chyme, produces an increased secretion of the intestinal fluids, both the mucous or follicular, and the aqueous or perspiratory. The intestinal fluid of the duodenum has some resemblance to the gastric liquor. According to Tiedemann and Gmelin, it is acid in the duodenum and the superior part of the small intestines, though less so than the gastric fluid ; and it becomes gradually less and less acid, until at last, in the inferior part of the small intestines, its acidity disappears, and it becomes neutral. The free acid contained in the intestinal fluid is chiefly the acetic; the hydrochloric, Avhich exists in the gastric fluid, being rarely present in the intestinal. The quantity of the intestinal liquor is said to be in proportion to the degree of indigestibility of the food. The bile is a viscid fluid, secreted by the liver, of a greenish brown colour, extremely bitter taste, and possessed of alkaline properties. It will be more particularly described hereafter. The pancreatic fluid is a Avhitish semi-transparent fluid, of a slightly saline taste, and coagulable by heat. It contains a large proportion of albumen and caseine ; and, according to Tiedemann and Gmelin, a free acid. The mixture of these fluids with the chyme in the duodenum, effected by the contraction of this intestine, soon occasions a sensi- ble change in its appearance. After passing the mouth of the ductus choledochus, it loses the homogeneous appearance which it presented in the stomach, and becomes more or less deeply coloured Avith yellow, its central portion presenting a deeper hue than the parts nearer the intestine. The external part adheres to the duodenum, so that its motion through the intestine is less rapid than that of the central portion. The sour smell and taste of the chyme gradually lessen and disappear; and, according to the 241 FIRST LINES OF PHYSIOLOGY. experiments of Marcet and Prout, albumen, which is an essential part of the chyle, is copiously developed. This substance begins to appear a feAv inches from the pylorus, and disappears in the inferior portion of the small intestines. According to Prout, if the food contained no albuminous matter, no albumen is developed in the stomach ; but immediately on the entrance of the chyme into the duodenum, and its mixture with the biliary and pancreatic secretions, albumen and other principles of chyle begin to appear. This albumen is supposed, by Tiede- mann and Gmelin, to be derived partly from the pancreatic fluid, which contains a large proportion of this principle ; but most of it, probably, is developed from the food itself, by the changes which it undergoes in the duodenum. The albumen and the other chylous principles, are absorbed by the lacteals; and, combined together, they constitute the chyle. According to Tiedemann and Gmelin, and some other physiol- ogists, chyle is not formed in the duodenum; for they assert that it is impossible to extract a particle of this fluid from the contents of this intestine. If this be true, the office of the duodenum is more completely to animalize the chyme, and to develop these principles or materials, necessary to the formation of the chyle. Leuret and Lassaigne, hoAvever, assert that all the essential prin- ciples of chyle pre-exist in the chyme. Albumen, Avhich is the basis of the chyle, exists abundantly in the chyme of the duo- denum ; and particles of fibrin also, they affirm, may be detected in it. If chyme be examined Avith the microscope, globules may be perceived in it, which exactly resemble the globules of fibrin which exist in the chyle. These globules are not present in the gastric juice, intestinal fluid, bile, or pancreatic secretion ; and, consequently, can be derived only from the food. In what man- ner the acidity of the chyme diminishes, as it descends in the small intestines, is not fully determined. Many physiologists suppose, that it is neutralized by the soda of the bile. Leuret and Lassaigne remark, that in chylification, the bile and the pan- creatic fluid prevent the fermentation of the chyme, by neutral- izing its acid principles; and that fat substances, which had not been completely converted into chyme, are dissolved by the bile, and rendered suitable for nutrition. Tiedemann and Gmelin, on the contrary, maintain that the bile is wholly incapable of dis- solving fat* They also suppose, that the soda of the bile unites with and neutralizes a part of the hydrochloric and acetic acids of the chyme ; and that the free acid, still remaining in the latter, precipitates the mucus of the bile in a state of coagulation, and with this, a great part of the colouring principles of the bile; as appears from the fact, that the mucus Avhich is precipitated is of * La bile n'est pas capable de dissoudre le plus petit atome de graisse. Elle ne peut> done, contribuer a sa resorption que d'une maniere mechanique en la tenant en suspen- sion, quand elle est tres divisee.— Tiedemann et Gmelin, Recherches, fyc. DIGESTION. 245 a brown colour. Besides this mucus, several other principles are precipitated from the bile, as cholesterine, margaric acid, and resin, which Tiedemann and Gmelin found in the insoluble contents of the small intestines, and Avhich contribute to the formation of the fasces. The German physiologists, as well as Leuret and Las- saigne, found that digestion and the formation of chyle, continued after tying the ductus choledochus; from which they inferred, in opposition to Mr. Brodie, that the bile has no agency in chylifi- cation. According to Beaumont, bile is seldom present in the stomach ; but Avhen fat or oily food has been used for some time, this fluid passes into the stomach and mingles Avith the gastric liquor. The pancreatic fluid, Avhich contains a large quantity of albu- men, a substance resembling caseine, and another, Avhich has the property of becoming red by the action of chlorine, Tiedemann and Gmelin suppose, contributes to the assimilation of the chyme in the small intestines by the admixture of its principles, which contain a large quantity of azote. That these principles contri- bute to the assimilation of the chyme in the small intestines, ap- pears probable from the fact that they progressively decrease, as the contents of the intestines proceed in their course, being, undoubtedly, absorbed Avith the assimilated part of the aliment. Thus, according to Tiedemann and Gmelin, the contents of the small intestines contain a constantly decreasing proportion of albumen, of caseous matter, and of the peculiar substance Avhich becomes red by the action of chlorine, in their progress through this portion of the intestinal canal. The office of the pancreatic fluid in animalizing the food, the German physiologists also infer from the greater comparative size of the pancreas in animals which live on vegetables, than in such as feed on animal matter. The wild cat, which is Avholly carnivorous, has a much smaller pan- creas than the domestic cat, Avhich lives partly on vegetable food, though the latter is a much smaller animal. The uses of the intestinal fluid are various. It probably com- pletes the solution of those parts of the aliment Avhich were im- perfectly dissolved by the gastric fluid. It also dilutes the chyme, and facilitates its progress through the intestinal canal, and lubri- cates the inner surface of the tube. Tiedemann and Gmelin also suppose that it serves them as a medium by which the chyme is united with the bile and pancreatic fluid. The analysis of the contents of the small intestines, furnished Tiedemann and Gmelin with the following ingredients, viz: 1. A free acid, the acetic, and sometimes the butyric. This is, perhaps, derived chiefly from the gastric fluid. 2. Albumen. This principle, as already observed, is found in considerable abundance in the duodenum, and gradually dimin- ishes in the inferior portion of the small intestines. The albu- men Prout supposed to be formed out of the chyme only, in the 246 FIRST LINES OF PHYSIOLOGY. duodenum, by the agency of the bile and the pancreatic fluid; for he says he never observed any trace of it in the chyme, or the aliments dissolved by the gastric fluid. Tiedemann and Gmelin, however, observe, that Avhen the food consists of liquid Avhite of eggs, or when it contains albumen, this principle is dissolved by the gastric fluid, and passes into the duodenum Avith the chyme unchanged. Not only liquid Avhite of eggs, but flesh, glue, and bread made of spelt, bones in dogs, and oats in horses, furnished an abundance of albumen; while fibrin, boiled Avhite of eggs, gluten, milk and cheese, furnished but little. As the pancreatic fluid contains a great quantity of albumen, it is also probable that this principle, in the contents of the small intestines, is derived partly from the former. It is gradually absorbed by the lymphat- ics of the small intestines, and forms the basis of the chyle. 3. Caseine. Tiedemann and Gmelin almost ahvays found in the filtered fluid of the small intestines, a matter which was pre- cipitated by distilled vinegar and the other acids, and Avhich re- sembled caseine. This matter they suppose to be produced, partly by the secretion of the intestinal canal, and partly to be derived from the pancreatic fluid, which contains a matter resembling it. They suppose it to exercise an important part in the assimilation of alimentary substances, and in their conversion into animal mat- ter by imparting azote. It is a more highly azotized principle than albumen, and is absorbed by the lacteals. 4. A matter precipitated by • chloruret of tin, and composed chiefly of ozmazome and saliva. This also is absorbed. 5. A substance which becomes coloured of a rose or peach- flower red by chlorine, is almost ahvays found in the small intes- tines. An excess of chlorine destroys the colour. It Avas found, in dogs, horses, and sheep, in the duodenum and the small intes- tines. Tiedemann and Gmelin suppose, that it is derived from the pancreatic fluid, in which it exists. It is never found in the stomach ; but the ligature of the biliary ducts does not prevent its appearance. Consequently it is not derived from the bile. It is absorbed, and perhaps contributes to the assimilation of the food. 6. Besides the foregoing, several substances were extracted by alcohol, which Avere insoluble in water, as fat, stearine, the colour- ing principle and the resin of bile, and cholesterine. 7 and 8. Carbonate of ammonia, and alkaline carbonates, phos- phates, and sulphates; Avith carbonate and phosphate of lime. On the Avhole, upon considering the changes which the food undergoes in the stomach and intestines, so far as they can be traced, it appears that its conversion into albuminous matter, which forms the basis of chyle and blood, is the great business of digestion. It is true that no albumen is developed in gastric digestion; for none can be detected in the chyme, except when the food consists of albuminous matter. But albumen is formed DIGESTION. 247 abundantly in the duodenum, and diminishes rapidly in the infe- rior parts of the small intestines, in consequence of its being absorbed by the lacteals; and Dr. Prout is of opinion that the change which the aliment undergoes in the stomach consists in an approach to the nature of albumen, though none of this prin- ciple can be discovered in the chyme of the stomach, Avhen it has not existed in the food. Motions of the small intestines. During digestion the peris- taltic motions of the intestinal canal are performed Avith energy. These motions consist in alternate contractions and relaxations of the muscular fibres. The passage of the chyme through the duodenum, hoAvever, is slow ; a fact Avhich is OAving to several causes, as, for instance, the deficiency of the peritoneal coat, ad- mitting of an easier dilatation of this intestine ; its greater dimen- sions than those of the other small intestines; the weakness of its longitudinal fibres, and its various curvatures; and finally, the great number of its valvulas conniventes, or transverse folds of its mucous membrane. According to Brachet, the motions of the duodenum, like those of the stomach, depend on the influence of the pneumogastric nerves ; for the section of these nerves a few hours after taking food, paralyzes the duodenum and the superior part of the small intestines, in consequence of Avhich the alimentary mass is ar- rested in its progress. The influence of the par vagum, hoAvever, does not extend through the whole of the small intestines; for the inferior part has been found to empty itself of alimentary matter injected into it after the section of these nerves, while the aliment injected at the same time into the superior parts, has been found partially digested in the same places. The inferior part of the small intestines appears to be under the influence of the spinal marrow, for the section of this medullary cord in the lower part of the back, arrests the progress of the chyme, suffering it to accumulate in the lower part of the small intestines, and in the large intestines. It appears then, according to Brachet, that the muscular coat of the small intestines receives the nervous influ- ence which stimulates it from the cerebro-spinal system ; and that, in respect to its power of contraction, it is under the influence of this system. V. Absorption. The contents of the small intestines, consisting of a mixture of chyme, the mucus of the intestines, and the in- testinal liquor, of bile and pancreatic fluid, become more and more consistent, as they advance further in the canal by the con- traction of its muscular tunic. The fluid parts are imbibed by numerous lymphatic vessels, originating in its mucous membrane, and conveyed under the form of chyle, into the thoracic duct, and thence into the torrent of the venous blood near the heart. The subject of absorption will be considered hereafter. The in- testinal mucus, rendered more consistent, and combined with the 248 FIRST LINES OF PHYSIOLOGY. insoluble and indigestible parts of the food, and Avith the fat,, the resin, the colouring matter and mucus of the bile, which form the incipient excrementitious mass, first assumes a distinct character in the last third of the small intestines. They arrive at length, by degrees, at the caseum, Avhere they remain some time, and Avhere, as Tiedemann and Gmelin think, a last effort is made by nature to extract from the undissolved parts of the aliment, Avhat- ever they may contain capable of affording nourishment. Before considering further the functions of this part of the alimentary canal, it may be proper to describe the result of duodenal diges- tion, the nutritious fluid called chyle, though it is asserted by several physiologists that this fluid does not exist in the intestines, but that it is formed by the action of the absorbent, vessels, exer- cised upon the nutritious principles developed by the second digestion. Chyle is the fluid contained in the lacteals. It is absorbed by these vessels from the aliment, after it has been digested in the stomach and duodenum, and is destined to the renovation of the' blood. It is a fluid of a milk-white colour ; but it varies in its consistence and appearance in different classes of animals, and according to the qualities of the food, and the quantity of the drinks. In carnivorous animals it is opaque; in herbivorous, transparent and of a greenish colour; in birds and fishes, thin, serous, and transparent. It is said to have a spermatic odour, and a sAveetish or saltish taste, wholly unlike that of the aliments from which it is formed. Its specific gravity is superior to that of water, but less than that of blood. According to Tiedemann and Gmelin, and Magendie, it is alkaline. In its chemical composition it has a strong analogy Avith blood. If left to itself, it coagulates, and separates into three parts, viz. a fluid, a coagulum, and a peculiar fatty substance. The first is an albuminous fluid, like the serum of the blood, and coagulable by heat, alcohol, and acids, contains the same salt in solution, and differs from the serum of the blood only in containing a peculiar fatty matter. The coagulum, like that of the blood, is formed of fibrin and a colouring matter. This latter substance, hoAvever, is Avhite, instead of being red. The coagulum also contains a peculiar fatty matter not found in the blood. According to Bauer, Dumas and Prevost, chyle exhibits, under the- microscope, the same globules as the blood, Avith the only difference that the globules are not surrounded with a coloured envelop. Leuret and Lassaigne affirm, that among all animals, whatever their food may consist of, the chyle contains fibrin, albumen, and a fat matter, muriate of soda, and phosphate of lime, in variable pro- portions. They also observe, that the fibrin is not in proportion to the azote contained in the food ; and that the chyle of animals fed upon gum and sugar, contains as much fibrin as that of those Avhich are nourished exclusively upon meat. The same, they DIGESTION. 249 affirm, is true respecting the albumen contained in the serous part of the chyle. Magendie, on the contrary, asserts that chyle formed from flesh contains more fibrin ; that from sugar, com- paratively little ; while that which is produced from oil, contains more of the fatty matter. According to Marcet, chyle produced from vegetable aliments contains three times as much carbon as that formed out of animal substances ; this last is always milky, and its coagulum opaque and rose-coloured, and covered with a layer of cream-like fluid ; while vegetable chyle is destitute of this principle, is transparent, and has a colourless coagulum. Tiedemann and Gmelin affirm, that chyle does not coagulate before it has passed through the mesenteric ganglions; and are of opinion, from this fact, that the fibrin in the chyle is not de- rived immediately from the food. The white colour of the chyle is attributed by some physiologists to the fatty matter present in it. Leuret and Lassaigne found the chyle milky and opaque, from the presence of this matter in the absorbents; but limpid, colourless, and destitute of fat, in the thoracic duct. In the tho- racic duct in dogs, it has been observed of a reddish colour, OAving, according to Tiedemann and Gmelin, to the mixture of some of the colouring matter of the blood with it. In its passage from the intestines through the absorbent system, the chyle evidently undergoes considerable changes in its sensible and other proper- ties, and probably becomes more completely assimilated and ani- malized. Leuret and Lassaigne say, that it is clearer and more aqueous as it issues from the ganglions. Vauquelin observes, that it assumes a rose colour in its progress in the lymphatic sys- tem, and Tiedemann and Gmelin, Emmert and Reuss assert, that it presents, in its exit from the mesenteric glands, a redder colour, contains more fibrin, and is more coagulable, sometimes deposit- ing a scarlet-coloured cruor ; changes which are ascribed, Avith apparent reason, to the action of the mesenteric glands. It is said to become red by exposure to oxygen or even atmospheric air. Out of the body it putrefies in a few days, if formed out of animal food ; but vegetable chyle, it is said, Avill resist putrefac- tive decomposition several weeks. The analogy of chyle with the blood, in its composition and properties, is evident, from the history of the fluid, and it may properly be considered as blood in a rudimentary state. Functions of the Cacum. This intestine is considered, by Tiedemann and Gmelin, as a reservoir, having some analogy with the stomach, especially in animals Avhich feed on coarse vege- table matter, as ruminating animals, horses, the rodentes, and the pachyderms, in which this intestine has a large capacity, Avhile in the carnivorous animals, as cats and dogs, it is small, and is entirely Avanting in those animals Avhich feed on fruits and the sweet roots of plants, as the bear and the badger. The large 250 FIRST LINES OF PHYSIOLOGY. and numerous glands of this intestine secrete an acid fluid, which mixes with and dissolves the remains of the undigested aliment, that continues some time in the caseum. This secretion also contains a little albumen, which is found in greatest abundance in animals which feed on vegetable matter. This albumen is supposed, by Tiedemann and Gmelin, to contribute to the assimi- lation of the aliments dissolved by the acid secretion. In this intestine also first appears the excrementitious matter of the in- testines, under the form of a soft-brownish or yelloAvish-brown paste, with the peculiar feculent odour, which Tiedemann and Gmelin suppose is derived from a volatile oil secreted principally by the caseum. Schultz's views of the functions of the caseum, founded on ex- periments, are similar to those of Tiedemann and Gmelin. He maintains that there are two digestions, one of which is effected in the stomach, the other in the caseum. The latter he supposes, to be especially active in the assimilation of vegetable food. He infers from his experiments that the residue of gastric digestion, when it reaches the caseum, becomes acid a second time in this intestine, and that this secondary acid chyme is there neutralized by bile, exactly as the gastric chyme was in the duodenum. Hence there is a twofold consumption of bile ; which he says is ahvays present in the course of the.small intestines. For it is a mistake to suppose that all the bile secreted by the liver during fasting is laid up in reserve in the gall-bladder. Much the larger part flows into the intestines, during the empty state of the stomach. During fasting, however, this bile does not enter the caseum, but collects above the cascal valve, where it remains until the acidification of the contents of the caseum, when the valve opens and admits it into the intestine. Schultz conceives that there is an antagonism between the gastric and cascal digestions. For when the bile is chiefly consumed on the gastric chyme, the cascal digestion is im- perfect ; and on the other hand, when the bile Aoavs freely into the caseum, the acidity of the chyme in the duodenum cannot be neutralized. In those animals in which this function is most per- fectly developed, each digestion has its appropriate period, and no interference takes place betAveen them. The period of action of one coincides with that of repose of the other. These vieAvs of the functions of the caseum, however, are not entertained by other physiologists, though it is in this intestine that a feculent character first appears in the contents of the ali- mentary canal. Defecation. The passage of the fasces through the large in- testines is sIoav, but varies, according to a variety of circumstances, from ten, twenty, or twenty-four hours, to several days. In some instances substances have remained several months in the cells of the colon. During its sojourn in the large intestines, the feculent mass becomes more consistent by the absorption of its thinner DIGESTION. 251 parts; its saline principles increase ; the resinous and colouring matter, derived from the bile, become more concentrated, and im- part a more stimulant quality to the mass. The fact that the body may be nourished and supported for a considerable time, by nutritive injections, appears to prove, not only that active absorp- tion is exercised by the large intestines, but also, either that a sort of digestion is performed by this portion of the alimentary canal, or that the absorbent vessels of the rectum and colon, exert an assimilating power upon the crude aliment absorbed by them. In the rectum the fasces become more dense by the absorption of their aqueous part, and assume the shape under which they are excreted. The large intestines differ from the small in the disposition of their muscular fibres ; the longitudinal ones being disposed in three bands, and shorter than the intestine, so that they pucker it up, forming numerous pouches or cells. The mucous membrane pre- sents no trace of valvulas conniventes, but is furnished with a great number of mucous follicles. Its nerves are derived from the hypogastric and lumbar plexuses and its arteries from the superior and inferior mesenteric. The contractions of the mus- cular fibres of the large intestine are Avholly without the domain of the will. But in defecation, or the expulsion of the fasces from the rectum, several accessory muscles are employed, Avhich are under the control of this poAver, as the diaphragm above, the ischio-coccygeal muscles, the levator ani, and the abdominal mus- cles. Astruc, and some others, suppose that defecation was per- formed exclusively by the efforts of the rectum; an error Avhich called forth the witticism of Pitcairn — Ast credo Astruccium nunquam cacdsse. The concurrence of the voluntary muscles with the action of the intestine itself, is indispensable to over- come the contraction of the sphincter of the rectum, particularly in the expulsion of feces of a hard consistence, which sometimes requires a strong effort of the will. The act is finally accom- plished, principally by a contraction of the abdominal muscles upon a full and sustained inspiration, with the glottis closed, so that it is impossible to speak during the expulsive effort. According to Berzelius, fasces afford the folloAving ingredients, viz. water, 73.3; remains of animal and vegetable substances, 7.0 ; bile, 0.9 ; albumen, 0.9 ; extractive matter, 2.7 ; substances, formed of altered bile, resin, animal matter, &c. 14; salts, 1.2. These salts are the carbonate, the muriate, and the sulphate of soda; ammoniaco-magnesian phosphate, and phosphate of lime. The Liver. This voluminous gland is one of the most important organs in the whole system, not only on account of its functions, but of its 252 FIRST LINES OF PHYSIOLOGY. peculiar structure and circulation, and its sympathies with other important viscera. It is found in all the vertebrated animals, and in the mollusca, in many of the Crustacea, and the arachnides. In birds, reptiles, and fishes, its volume is greater in proportion to the size of the body, than in the human species and the mammalia. In man it is the most voluminous of the viscera, especially in the fostal state. It is situated in the right hypochondriac region, and the corres- ponding part of the epigastrium, having above it the diaphragm, to which it is connected by a fold of the peritoneum, called the suspensory ligament of the liver ; the right kidney, and the trans- verse colon and the stomach below ; the last dorsal vertebras be- hind ; and the anterior part of the base of the chest before it. Attached to the lower part of the liver, and partly imbedded in it, is a pyriform sac, called the gall-bladder, having its fundus or larger extremity placed forward, in a groove of the anterior border of the liver, and frequently projecting beyond it; and its neck and smaller extremity turned backwards and terminating in a canal, called the cystic duct. It is composed of iwo membranes or coats, viz. a cellular or muscular, as it is considered by some anatomists, and an interior mucous one. Besides these, it is partly covered by the peritoneum, by which it is attached, and the liver. The colour of the liver is a reddish-brown ; but in a diseased state it varies a good deal, becoming darker or lighter, according to the nature of the disease. In some cases it becomes universally of a cream colour. According to Rudolphi, the very dark colour of the organ is connected with a softness of its texture, and with a dark-coloured bile ; and, on the other hand, an unusually light colour of its substance, with a firmer texture and a light-coloured bile. The substance of the liver is formed of a glandular paren- chyma, the granulations of which become apparent by lacerating its tissue. The importance of the liver is manifest from the immense sup- ply of blood which it receives, and from the extraordinary distribu- tion of its vessels. It differs from all the other glands in receiving a large supply of venous blood in addition to the arterial blood which is sent to it in common with all other parts of the body. Its arterial blood it receives principally by a branch of the coeliac artery, called the hepatic. It also receives some branches from the coronary artery of the stomach, and the inferior diaphragmatic arteries. Sometimes a branch of the superior mesenteric is sent to the right lobe. Its venous blood is derived from the viscera of the abdomen ; the veins of Avhich in their course to the liver unite into a large trunk, called the vena porta. On entering the liver, this great vein divides and subdivides into innumerable branches, in the manner of an artery, and is distributed to every part of the gland. The system of the vena portas is a curious anomaly in the circulation, and was compared by Galen to a tree whose roots were DIGESTION. 253 dispersed throughout the abdomen, and its branches in the liver. This organ thus possesses tAvo distinct vascular systems, an arterial and a venous, a character in which it resembles the lungs. The extreme divisions of these two vessels, the hepatic artery and the vena portas, terminate in the radicles of the hepatic veins, which gradually unite into large venous trunks, that enter the vena cava inferior, and convey the returning blood to the heart. From the extremities of these vessels, also, and communicating with them, spring the minute radicles of the biliary duct, called the pori bilia- rii, Avhich secrete the bile from the blood; and by their union in a large trunk, constitute the hepatic duct. Haller says, that the radicles of the biliary ducts communicate immediately with the last divisions of the vena portas, a structure from Avhich he explains the passage of the bile into the blood in jaundice, when an obsta- cle in the hepatic duct prevents the passage of this fluid into the intestines. The hepatic duct, which is formed by the union of all the excretory ducts of the liver, is a canal about the size of a writing- quill, and an inch and a half in length. It is joined at a very acute angle by the duct of the gall-bladder, called the cystic duct, and forms with it the ductus choledochus, a canal eighteen or twenty lines long, which pierces the coats of the duodenum, and terminates on the inner surface of that intestine, three or four inches from the stomach. The gall-bladder is Avanting in many animals. It is sometimes absent in man, Avithout any apparent injury to health.* The ductus choledochus is Avanting in many of the amphibia, in Avhich the hepatic and cystic ducts open separately into the duodenum. In fishes this duct arises immediately from the gall- bladder. The nerves of the liver, which are feAv in number compared Avith its volume, are derived principally from the solar plexus, and follow the course and branchings of the hepatic artery. Some of its nerves, however, it derives from the pneumogastric. It is abundantly supplied with lymphatics; these originate in the pa- renchyma of the organ, and contain a yellowish-coloured lymph ; the colour being derived from an admixture of bile absorbed by them. The great office of the liver is the secretion of bile. In regard to this secretion, however, several questions have arisen which have led to much controversy among physiologists. One relates to the source of this secretion ; another to the uses of it. With regard to the source of the bile, it has been a question with physi- ologists, whether this fluid is secreted out of venous or arterial blood ; since the liver is supplied with both kinds, by the hepatic artery and the vena portas. Some physiologists have contended, * Lepelletier. 254 FIRST LINES OF PHYSIOLOGY. that the hepatic artery supplies the materials from which the bile is secreted, from the analogy of the other secretions, which are all formed from arterial blood. To this, however, it is replied, that carbon is secreted in the lungs from the venous blood of the pul- monary artery, which ramifies through the lungs as the vena portas branches in the liver; and therefore that it is possible that bile, which contains a large proportion of carbon, may also be secreted from venous blood. Comparative physiology also furnishes a reply to this argument, in the fact, that in some of the lower ani- mals, as the reptiles, the urine is secreted in a great measure out of venous blood. Another argument is founded on the dispropor- tion between the vast quantity of venous blood which the liver receives, and the inconsiderable quantity of bile secreted by the organ. A disproportion, hoAvever, quite as great if not greater, exists betAveen the vena portas and the hepatic veins, which must nevertheless convey, not only the residual blood of the vena portas, but that of the hepatic artery also, into the vena cava inferior. Besides, it is probable, and indeed certain, that a part of the bile secreted is immediately absorbed by the lymphatics, and conveyed into the thoracic duct. Mr. Abernethy describes a remarkable case, in which the vena portas opened directly into the inferior vena cava. The hepatic artery was larger than usual. In this case the bile found in the biliary ducts must have been secreted from the blood of the hepatic artery. Lawrence describes a case in which a similar anomaly existed. To this it may be added, that the vena portas does not exist in the invertebrated animals; and yet these possess a liver, which secretes bile. Injections pass from the hepatic artery into the biliary ducts, proving a direct anastomosis of the ultimate branches of the hepatic artery Avith the radicles of the biliary ducts. Tying the hepatic artery is said to cause a cessation of the secretion of bile. This, however, is inconclusive, because the liver is nourished by the arterial blood of this vessel; and if its nourishment is Avithheld from it, and the stimulus of arterial blood withdrawn, it is not surprising that its secretory functions should be suspended. The fact, however, is denied, and needs confirmation. That the bile is secreted from the portal blood, is inferred, on the other hand, from the following considerations, viz: The vena portas conveys a much larger quantity of blood into the liver, than the hepatic veins can carry out. The excess, it is reasonable to suppose, is employed in the formation of bile. If it be not so disposed of, it is difficult to imagine Avhat becomes of it. Injections pass very easily from the vena portas into the biliary ducts. It is alleged, also, that the venous blood is more analogous to bile, in its constitution and properties, than arterial, as it con- DIGESTION. 255 tains more carbon and hydrogen, principles which abound in bile, but less azote ; and is darker coloured and more consistent. The peculiar properties of the blood of the vena portas, may also be considered as favourable to this opinion. It appears, from the researches of Schultz, that the portal blood differs in its constitu- tion, in several respects, from that of the arteries and other Areins. It is blacker than other venous blood; and it is not reddened by the neutral salts, by atmospheric air, nor even by the action of oxygen gas. It does generally coagulate, and in those cases in Avhich coagulation takes place, it becomes liquid again, either partially or Avholly, at the end of from twelve to twenty-four hours. It contains less fibrin than the arterial and ordinary venous blood, as might have been inferred from its inferior coagulability, but almost twice as much fat. Some physiologists have recog- nised in these peculiarities an approximation to the qualities of the bile. Tying the vena portas occasions a suspension of the secretion of bile. According to Rudolphi, there is a free communication between all the blood-vessels of the liver, viz., the branches of the hepatic artery, those of the vena portas, and of the hepatic veins, and the biliary ducts; from which he infers, that the principles out of which the bile is formed are easily separated from the blood. He affirms, that he has seen coloured water injected into the vena portas readily pass into the hepatic artery. Perhaps this free com- munication is an argument in favour of bile being secreted from both kinds of blood. The excretory duct of the liver terminates in the duodenum, three or four inches from the pylorus. But before it arrives at this intestine, it is joined by the duct of the vesicula fellis. Of course, at this point, the bile from the liver can pass in one of tAvo directions, viz., either directly into the duodenum, or by turning a very acute angle, into the gall-bladder. During digestion in the duodenum, when this intestine is stimulated by the presence of chyme, and is in a state of vital erection, the stimulus is com- municated to the mouth of the common duct, and propagated along both its branches, to the liver and gall-bladder; so that the hepatic and cystic bile are solicited, at the same time, to pass into the duodenum; and the gall-bladder and the hepatic duct both empty themselves of bile. But when the duodenum is not en- gaged in the work of digestion, the hepatic bile is diverted into the other channel, and passes into the gall-bladder, where it re- mains until called for, and undergoes some change in its proper- ties, becoming more concentrated, bitter, and viscid, in conse- quence of the absorption of its aqueous parts by the lymphatics; and probably, receiving some addition from the secretion of the mucous membrane of the gall-bladder. If it be retained a long time in the vesicula fellis, its bitterness becomes excessive, and 256 FIRST LINES OF PHYSIOLOGY. its colour of a deep green, by the great concentration of its pecu- liar principles. Bile differs more from the blood than most of the other secreted fluids. It is a fluid of a greenish-brown colour, extremely bitter and viscid. It consists of water, albumen, resin, and soda, both free and united with the phosphoric, sulphuric, and hydro-chloric acids, and a yellow colouring matter. It derives its leading pro- perties from a colouring fatty substance, called cholesterine, which forms the basis of biliary concretions; picromel, a resin which gives the bile its bitterness; albumen, which causes it to froth on being agitated ; free soda, to which it owes its alkaline properties; and various salts, composed chiefly of soda, combined with phos- phoric, sulphuric, and hydrochloric acids. The secretion of bile appears to be unintermitting. It has been found in experiments, in Avhich the orifice of the common duct was laid bare, that the bile issued drop by drop, and gradually diffused itself over the intestine. The lymphatics of the liver contain a lymph coloured with bile, Avhich they convey into the thoracic duct. Berthold sup- poses that the bile contained in this lymph, contributes to the assimilation of the chyle. The uses of the bile have already been considered in part. It probably acts as a stimulant to the mucous and the muscular coats of the intestines, soliciting a flow of the intestinal fluids, and ex- citing the peristaltic contraction of the canal. Hence the unusual dryness of the fasces, and the constipation of the bowels in jaun- dice, and in animals in which the biliary duct has been tied. Tiedemann and Gmelin also suppose that it contributes to animal- ize those articles of food which do not contain azote, by imparting to them its own principles, which are highly charged with azote; that it neutralizes a part of the acid contained in the chyme, which is derived from the gastric fluid; and that it counteracts the putrefaction of the contents of the intestines, which they infer from the fact that the fasces are unusually foetid in dogs in which the ductus choledochus has been tied. But the German physiologists also vieAV the bile as an impor- tant excretion, designed to maintain the blood in a state of com- position necessary to qualify it for nutrition, in the different organs. The reasons on Avhich this opinion rests are briefly the following, viz. 1. Most of the constituent principles of the bile, as the resin, the colouring matter, the mucus, and the salts, concur to the for- mation of the fasces, and are rejected from the system Avith the latter. 2. When the bile by any cause is prevented from passing into the intestinal canal, as in animals in which the biliary duct has been tied, or in persons affected with jaundice, the materials of the bile are separated from the blood by means of other secretory DIGESTION. 257 organs, particularly by the kidneys, but partly by the serous and mucous membranes, and by the skin. The principles. of this fluid are also deposited in the cellular tissue, in the coats of the arteries, veins and lymphatics, and even in the dense fibrous tis- sues, the cartilages and bones, which all assume a yellow hue. 3. The liver appears.to perform a function analogous to that of the lungs ; since it separates from the venous blood a large quantity of carbon, in the form of resin, colouring matter, fatty matter, and mucus. In the lungs the excess of carbon, derived from the vegetable part of the food, is excreted in the form of a gas, and in a state of oxidation ; but in the liver it is throAvn off in the form of a liquid, and in combination with hydrogen, con- stituting the resin and fatty matter of the bile, and still in a com- bustible state. A fact favourable to the opinion that the liver is auxiliary to the lungs in decarbonizing the blood, is that the resin of the bile, which exists so largely in this fluid, and is excreted from the body with the fasces, exists in the greatest proportion in herbivorous animals. Thus the bile of the ox contains much more of it than human bile, or that of the dog ; and Tiedemann and Gmelin infer that this resin is derived chiefly from vegetable aliment. These physiologists also remark that the lungs and- liver, in different species of animals, are in a state of antagonism to each other. If the lungs are largely developed, if the system frees itself of a large quantity of oxidated combustible matter, by the respiratory organs, the liver is small, arid the secretion of bile inconsiderable. But if the lungs are small, or imperfectly developed, the liver is large, and the biliary secretion copious. Thus the liver is proportionally large in reptiles Avhich respire by means of lungs with large cells, like sacs or bladders, and Avhose pulmonary circulation is incornplete, and which decar- bonizes the blood slowly. On the other hand, warm-blooded animals with well-developed lungs, as the mammalia and birds, which consume the largest proportion of oxygen in a given time and throw off the greatest quantity of carbonic acid, have the smallest livers in proportion to.the size of their bodies. In fishes on the contrary, Avhich live in the water, and breathe by means of gills, the liver is comparatively large. In these animals re- spiration is very imperfect, being maintained only by the small quantity of air combined Avith the Avater in which they live, and being performed by gills, the structure of which is less favour- able than that of the lungs to the absorption of oxygen. The enormous size of the liver in the mollusca, which breathe by gills or by small, imperfectly developed lungs, tends to corroborate the same opinion. It is also worthy of remark, that the system of the vena portas is more highly developed, and much more com- plicated in its structure in reptiles and fishes, than in the mam- malia and birds. For while this great venous trunk in the latter 33 258 FIRST LINES OF PHYSIOLOGY. is formed only by the veins of the stomach and intestinal canal, the spleen and pancreas, in reptiles and fishes it receives several other veins. Thus in tortoises, not only the veins of the spleen and of the intestinal canal, but those of the posterior extremities, of the pelvis, of the tail, and even the azygos, unite Avith the vena portas. In serpents, this vein also receives the right renal vein, and the intercostals. In fishes, the vena portas receives the veins of the tail, of the kidneys, and of the genital organs ; so that the quantity of venous blood Avhich arrives at the liver is proportionally much greater than in the other classes ; and indeed the greater part of the venous blood traverses the liver and con- tributes to the secretion of the bile, before it arrives at the heart and the organs of respiration. 4. The great comparative size of the foetal liver furnishes an- other argument in favour of the vieAV that the bile is an excre- mentitious fluid. During the foetal state, the greater part of the blood Avhich is brought from the placenta by the umbilical vein arrives at the system of the vena portas, and circulates in the liver before it is conveyed to the heart by the inferior vena cava. The bile also is secreted abundantly, as appears from the great quantity of meconium Avhich exists in the intestines in the later period of utero-gestation. It is evident, that in the foetus the bile cannot be subservient to chylification; and the probability is, that the office of the liver in this stage of existence is to purify the blood of the umbilical vein from such organic principles as are injurious to the animal economy, and to maintain the composition of the blood in a state suitable for the nutrition of the body. It is prob- able, therefore, that in the fostal state the liver acts in part as a substitute for the lungs, which, after birth, perform the office of purifying the blood of noxious principles, by a kind of combus- tion with the oxygen of the air. 5. Another fact Avhich is revelant to the subject is, that the se- cretion of bile continues in the hybernating mammalia, the rep- tiles, and the mollusca, although these animals take no nourish- ment during the whole course of their winter sleep. 6. Tiedemann and Gmelin also adduce some pathological facts to corroborate their opinion. In general, they remark, the secre- tion of bile is augmented in derangements of respiration; and whenever an air is respired which is vitiated by putrid animal or vegetable emanations. The Pancreas. This is a gland five or six inches in length, of a whitish colour, and lying transversely across the body of the twelfth dorsal ver- tebra, covered by the stomach, and almost circumscribed by the three curvatures of the duodenum. It receives numerous blood- vessels from the splenic, the right gastro-epiploic, the superior DIGESTION. 259 mesenteric, the coronary of the stomach, the hepatic and the in- ferior diaphragmatic. It derives its nerves from the ganglionic system, by the hepatic, the superior mesenteric, and the splenic plexuses. This gland is of a granulated texture, consisting of small gra- nules, or acini, united together by cellular membrane ; these acini being aggregated into smaller, and these again into larger lobes. These lobes give origin to the fine pancreatic ducts, Avhich unite together into one large excretory, called the duct of Wirsungius. This canal runs the Avhole length of the pancreas, and opens, by its larger extremity, into the duodenum, near the end of its second curvature, sometimes by a separate orifice, and sometimes by a common mouth, Avith the ductus choledochus. In some cases its mouth has been found two inches distant from the orifice of this duct. Its passage through the coats of the intestine is oblique, running under the mucous membrane in such a manner as to leave a free border of the latter, Avhich exercises the functions of a valve. Sometimes there are two pancreatic ducts. This gland is found in all the mammalia, in birds, and in the amphibia. It exists in some fishes, but in others it is Avanting. The pancreatic fluid is a white, or light yellowish, someAvhat viscid fluid, inodorous and semi-transparent, and of a slightly sa- line taste. It becomes frothy by agitation, and coagulates by heat; and Avhen it is putrefying diffuses an ammoniacal odour. Physiol- ogists have differed a good deal as to its constitution and proper- ties. Some consider it as an acid, others as an alkaline fluid, Leuret and Lassaigne, and many other physiologists, consider it as very similar to saliva; while Tiedemann and Gmelin say that it differs essentially from saliva, in containing a free acid, a large proportion of albumen and caseine, of which the saliva offers only slight traces; and in the absence of mucus, of salivary matter, and of the sulphocyanate of potash. The secretion of this fluid appears to be slow. Magendie ex- posed the orifice of the pancreatic duct in dogs, and Avipcd the mucous membrane of the intestine dry Avith a piece of fine linen ; and he observed that the pancreatic fluid issued only in drops, Avhich scarcely appeared once in half an hour, and sometimes not so often. In birds the quantity Avhich issues is much greater. Leuret and Lassaigne obtained from the pancreatic duct of a horse, in half an hour, three ounces of fluid. Tiedemann and Gmelin obtained from a large dog only about ten grammes, or one-third of an ounce, in four hours. A drop issued out every six or seven seconds. When the animal made a deep inspiration, and the ab- dominal viscera were strongly compressed by the diaphragm, the discharge Avas more copious, sometimes several drops issuing in a second. Schuyl obtained two ounces in about three hours. It appears from these experiments that the quantity of this secretion varies much at different times, and probably under different cir- 260 FIRST LINES OF PHYSIOLOGY. cumstances. The stimulus of chyme in the duodenum, propa- gated from the mouth of the duct to the interior of the gland, gives rise to an increased flow of blood to it, and a more copious secretion of the pancreatic fluid. From the position of the gland, in relation fo the stomach,-it must be exposed to pressure when- ever this organ is distended with food, and probably is stimulated by the pressure to increased secretion. This gland, as before re- marked, is proportionally larger in herbivorous than carnivorous animals; a fact which seems to indicate its importance in the as- similation of aliment of difficult digestion. It appears, however, that the pancreas may be extirpated in dogs without fatal conse- quences, or even serious injury to health. Brunner extirpated the gland in several dogs, ahd observed a voracious appetite and the most obstinate constipation as the consequences. Food. The food of man is derived both from the animal and the vegetable kingdoms. Prout remarks, that organized beings adopt as aliments, substances lower.than themselves in the scale of or- ganization. Thus, plants and the loAvest kinds of animals have the poAver of assimilating inorganic substances, such as water and carbonic acid. In ascending the zoological scale, we find that animals generally prey upon those Avhich are inferior to them- selves in organization, in magnitude, or intelligence, until Ave arrive at man himself. " By this beautiful arrangement in the mode of their nutrition," Prout remarks, ''animals,are exonerated from the toil of the initial assimilation of the materials composing their frame ; as in their food, the elements are already in the order Avhich is adapted for their purpose. Hence, the assimilating or- gans do not require that complication which otherwise they would have needed, and much elaborate organization is saved." Animal food is more easily and speedily digested than vege- table, because it approaches much more nearly to the nature of the system it is destined to nourish. Probably every kind of animal matter is capable of being converted into nutriment. Food is derived from every department of animated nature, to supply the wants, or to gratify the appetite of man. The mam- miferous quadrupeds, birds, fishes, reptiles, insects, and the crus- taceous and molluscous animals, are all greedily sought after and devoured by man. Fibrin. Of the animal principles, those which contain the greatest proportion of azote are, perhaps, the most nutritious, as Avell as most stimulating. This is particularly true of fibrin, which forms the basis of muscular flesh, and is a constituent principle of the blood. It contains about twenty per cent, of azote, and is highly nutritious. The same is probably true of cheese, Avhich the experiments of Sir A. Cooper Avould lead us to DIGESTION. 261 conclude is a substance of easy digestion, and is highly nutri- tious. It is highly azotized, containing about tAventy-one per cent, of azote. Londe remarks, that of all aliments, the fibrinous are those Avhich remain the longest in the alimentary canal, Avhich exact the greatest labour of digestion, excite the greatest animal heat in the stomach, stimulate the blood-vessels of the mucous membrane, and the general circulation, and cause the most copious secretion of the gastric and intestinal fluids. It is one of those which undergo the greatest alteration by digestion, and leave the smallest residue. When fibrinous aliment contains ozmazome, it is of all kinds of food, the most exciting, and the most nu- tritious. Albumen is another animal principle which is extremely nutri- tious, and of easy digestion. According to Tiedemann and Gme- lin, the liquid Avhite of eggs is dissolved by the gastric liquor, and passes into the duodenum without undergoing any sensible change. It is coagulated, hoAvever, by the gastric fluid before it is dissolved. Albumen exists in the blood, in the matter of the brain and nerves, and in other forms of animal matter. Caseine appears to be a modification of albumen ; and the Avhite of eggs consists of this principle. It contains about fifteen per cent, of azote. Albumen, if uncoagulated, is rapidly digested, and excites but little heat. Aliments containing it pass out of the stomach so much the more speedily, as they have been less altered by cookery. It is very nutritious, and leaves but little residue. Gelatin is a highly nutritious principle. It is extracted from the tendinous, and ligamentous, and cartilaginous part of animals ; and constitutes the basis of soups. It is found in none of the animal fluids. The flesh of young animals contains more gelatin but less fibrin than that of old ones. Gelatin excites so little the local action of the stomach, that, according to Londe, it requires the aid of stimulants in order to be digested. - It passes rapidly through the alimentary canal, and, by some authors, is considered as laxative. It produces little or no excitation of animal heat, or of the circulation, and leaves little residue. Ozmazome, according to Orfila, is stimulating, but possesses no nutritious properties. Animal fat and oils. These principles are very nutritious, and are wholly convertible into chyme; but if separated from other animal principles, are not very digestible. But, as they exist inter- spersed betAveen the fibrinous parts of animals, they render the latter more tender and easy of digestion. Even the substance of the bones cannot resist the poAvers of digestion, The spongy bones are more easily digestible than the hard ; but they all con- tain gelatin, and many of them oil or marrow ; both of which are very nutritious. The vegetable principles Avhich afford nourish- ment by being converted into chyme, are starch, mucilage, sugar, oil and fats, and gluten. 262 FIRST LINES OF PHYSIOLOGY. Starch is found in a variety of vegetables, particularly in several of the nutritious grains, as Avheat, oats, barley, rye ; and it consti- tutes most of the nutritious parts of rice, barley, and maize; it exists also largely in potatoes. Sago, tapioca, salep, and arrow- root, consist almost Avholly of starch. It is a curious fact, that as soon as starch is dissolved by the gastric fluid, it loses the property of assuming a blue colour by the action of iodine. Londe asserts, that aliments in Avhich starch predominates, pass more speedily through the stomach than those in which fibrin, albumen, or gel- atin abounds. The digestion of the amylaceous elements pro- duces but little elevation of heat, and no sensible acceleration of the pulse. Of all vegetable aliments they are the most nutritious. Mucilage abounds in many of the garden plants, as carrots, beets, turnips, cabbages, lettuce, melons, &c, combined in some of them Avith sugar, &c, and Avith woody fibre. The various gums, as for example, gum arabic, consist of some modification of mucilage in a solid form. Wherever it exists it is nutritious. Mucilaginous aliments excite little or no heat, or increased activity of the circulation; on the contrary, they produce a general relax- ation of the tissues, and diminish the energy of all the functions. Gum is extensively used as an aliment by the Moors of Lybia and Senegal. Sugar abounds in the saccharine fruits, as grapes, raisins, figs, dates, the sugar-cane; pears, apples, peaches, berries, &c. In these last, it is combined Avith the malic acid. It also exists largely in the beet, the parsnip, the sap of the maple and of the ash. It is very nutritious; but according to Magendie, though it is easily digested, and leaves no residue, it is incapable of furnish- ing a chyle which can support life more than thirty or forty days. From the experiments of Magendie, it appears that an exclusive use of sugar produces ulcerations of the cornea. Oil exists in the cocoa, chocolate, olives, almonds, and other nuts. It is very nutritious, being Avholly convertible into chyme; but it is not very easy of digestion. But the most nutritious of the vegetable principles is gluten. This differs from the other proximate elements of vegetable mat- ter, in approaching pretty nearly to the constitution of animal matter, especially in containing a considerable proportion of azote. It is the most highly animalized of vegetable principles. It exists in the farinaceous grains, particularly in wheat, in which it is very abundant; and on the presence of this principle depends the prop- erty in Avheat of undergoing the panary fermentation, or of making bread. Wheat flour makes the best bread, from its containing more of this principle than any other grain. Substances destitute of gluten, as rice, maize, barley, are incapable of the panary fermen- tation, and of making good bread. It is highly nutritious. Gluten is found, though sparingly, in various parts of the vege- table kingdom ; as in certain floAvers, fruits, the leaves of certain DIGESTION. 263 plants, cabbages, and some roots. Combined with starch, it is extremely nutritious. Dr. Prout has reduced the various nutritious principles of ani- mal and vegetable matter under three general heads, viz. the sac- charine, the oleaginous, and the albuminous. The first, or the saccharine, comprehends sugar, starch, gums, acetic acid, and some other analogous principles ; the second, or the oleaginous, oils, fats, alcohol, &c. ; the third, or the albuminous, other animal substances, particularly albumen, fibrin, and gelatin; and the vegetable principle, gluten.* The saccharine group embraces tAvo classes of "substances, viz. the crystallizable and the uncrystallizable. The crystallizable are sugar and the acetic acid. Sugar is a triple compound of hydro- gen, oxygen, and carbon. But it is worthy of remark that the hydrogen and oxygen are combined exactly in the proportion in Avhich they form water; from Avhich it is inferred, that sugar is a compound of water and carbon, or is a hydrate of carbon. Vinegar is another proximate principle Avhich is crystallizable ; and like sugar is formed of carbon and water, though the proportions of the carbon and water are different from those that form sugar. They differ, hoAvever, in the circumstance, that Ave can form vinegar artificially, but not sugar. The uncrystallizable substances belonging to the saccharine group are starch, and lignin, or woody fibre. The former of these, or starch, in its composition, very nearly coincides Avith sugar; i. e. it is composed of Avater and carbon, and the propor- tions in which they are combined are very nearly the same as in sugar. The second, or lignin, in all its varieties has been found to pos- sess very nearly the same essential composition. It is a hydrate of carbon, consisting of equal weights of this principle and Avater. The affinity of these four substances appears not only from their similarity of composition, but from the fact that they are converti- ble into one another. Thus, both starch and Avood may by arti- ficial processes be converted either into sugar or into vinegar: Avood may also be converted into a kind of starch ; and sugar into vinegar; though we cannot reverse the process, and convert vine- gar into sugar, or starch into Avood. The oily group in all their varieties are all essentially the same in their composition, being composed of olefiant gas and Avater. Alcohol is referred to the same group by Prout, as its composition is the same. . The albuminous group comprehends albumen, gelatin, and fibrin of which the animal tissues are chiefly composed, and caseine, or the curd of milk. The vegetable principle, gluten, is referred by Prout to the same class. All of the albuminous group * Prout. 264 FIRST LINES OF PHYSIOLOGY. differ from the saccharine and the oleaginous, in containing a fourth principle, viz. azote. One of them, viz. gelatin, is easily convertible into a kind of sugar. " Such," says Prout, " are the three great staminal principles from which all organized beings are essentially constituted," — "and, as all the more perfect organized beings feed on other or- ganized beings, their food must necessarily consist of one or more of the above three staminal principles. Hence, it not only fol- lows, as before observed, that in the more perfect animals, all the antecedent labour of preparing these compounds de novo, is avoid- ed ; but that a diet, to be complete, must contain more or less of all the three staminal principles. Such at least must be the diet of the higher classes of animals, and especially of man." This view of the nature of aliments, Prout remarks further, is illustrated and confirmed by the composition of milk; the only substance expressly designed and prepared by nature as food; and in which, therefore, we should expect to find the model and pro- totype of nutritious matter in general. Now, every sort of milk, Prout remarks, is a mixture of the three staminal principles above described ; for milk ahvays contains a saccharine ; a butyraceous, or oily; and a caseous, or albuminous principle. These vieAvs of Prout receive some confirmation from certain experiments of Magendie, on the effects of particular kinds of diet on animals. A dog was fed exclusively on Avhite sugar and water, and for seven or eight days he appeared to thrive upon this diet. In the second week he begari to lose flesh, though his ap- petite continued good. In the third he lost his spirits, and his appetite failed ; and an ulcer formed on the middle of each cornea, which penetrated into the chamber of the eye, and the humours of the eye escaped. The dog died at the thirty-second day of the experiment. Similar results ensued with dogs fed on olive oil and distilled Avater, except that ulceration of the cornea did not take place. Another dog, fed upon white bread, made of pure wheat, and with water, died at the expiration of fifty days. An ass fed upon boiled rice, lost his appetite, and died in fifteen days. According to Raspail, digestion requires the presence of at least two alimentary principles in the food, viz. a saccharine or saccha- rifiable ; and albumen or gluten. Each of these substances is in- digestible by itself, because it requires the influence of one of the other class to excite the digestive fermentation. This is the true ground of the fact established by Magendie, that animals cannot be sustained on a single alimentary principle. Bread contains an abundance of both principles, viz. sugar or saccharifiable starch, and gluten. Hence its highly nutritious qualities. Flesh also contains sugar united with its albuminous tissues. Hay, which is the bread of graminivorous animals, is rich in sugar and gluten. The sugar cane is the type of this class, the other graminacese being diminutives of the former. DIGESTION. 265 On the whole, it appears to be established by experiment, that a certain variety in the food is necessary to the health of man, and of other animals. The experiments of Dr. Stark upon the effects of various simple kinds of food, when used exclusively for a considerable time, appear to prove, that the system is reduced to a state of great debility and emaciation by such a course of diet; and that there is not a single article of food, however nutri- tious, capable, of itself, of supporting the vigour of the system. The Spleen. The spleen is a spongy vascular organ, of a flattened oblong shape, and of a livid colour, situated in the left hypochondriac region, beloAV the diaphragm,-behind the descending colon, and directly over the left kidney, adhering to the fundus of the stomach. It is supplied Avith blood by the splenic artery, one of the three branches of the coeliac, a large and tortuous vessel, which, before it enters the spleen, divides into several branches, from Avhich five or six very'short branches are detached to the stomach, and dis- tributed upon its large extremity. The spleen derives its nerves from the coeliac plexus. It is attached loosely to the neighbour- ing parts by folds of the peritoneum and by vessels, and to the stomach especially by the vasa brevia. The texture of this organ is extremely spongy, brittle and vas- cular. It contains a large quantity of blood, apparently extrava- sated in numerous membranous cells, of which the organ seems to be chiefly composed. But according to some anatomists, on the most careful examination, no cells containing blood can be found interposed betAveen the arteries and veins. Others on. the contrary assert, that the organ is chiefly composed of an infinite number of little cells Avhich communicate freely Avith one another, and Avith the splenic, vein. The primary branches of the splenic vein, Avhen examined on their internal surface, appear to be per- forated Avith a great number of orifices, through which a stylet may be passed directly into the cells of which the parenchyma of the organ is composed. At a greater distance from the trunk, the orifices, with Avhich the coats of these vessels are perforated, become larger; and ultimately the parietes of the latter lose their continuity and separate into filaments, which become confounded Avith the walls of the cells before mentioned. The splenic artery almost immediately after entering the organ diminishes rapidly in volume, subdividing into minute branches, Avhich, according to some anatomists, disappear on the parietes of the cells. These branches divide into extremely delicate vessels, Avhich are disposed like the hairs of a pencil, but do not inosculate with one another; Avhile the veins anastomose freely together. Injections readily pass from the arteries to the veins. Besides its blood-vessels, the 266 FIRST LINES OF PHYSIOLOGY. spleen contains a great number of lymphatics. In addition to these constituent parts, anatomists describe a multitude of soft grayish Avhite nodules or granulations, of about one-sixth of a line in diameter, dispersed through the substance of the spleen, the nature and uses of Avhich are unknown. They are said to become very tumid in animals immediately after drinking. The position and volume of the spleen are much influenced by the state of the neighbouring parts. The motions oi the da- phragm in respiration are constantly changing its place ; and it is also much affected by the state of the stomach. When this organ is distended by food or gas, the spleen almost comes into contact with its great extremity, and assumes a very oblique position. But Avhen the stomach is empty, the spleen is more distant from it, and its position is nearly vertical. The volume of the spleen is lessened when the stomach is full, but augmented Avhen that organ is empty ; a fact which is accounted for by the dimin- ished influx of blood into the spleen in the one case, and the in- creased, in the other. The Arolume of this organ is liable to be affected by several causes. It.is said to be smaller in those who perish suddenly, and larger in such as die a lingering death. It frequently becomes much enlarged by repeated attacks of inter- mittent fever : and it is said to have been found ruptured from excessive distention, in persons who have died in the cold stage of that disease. Its office is unknown. Many physiologists have conjectured that it is subservient, in some mode or other, to the formation of bile, an opinion which derives some probability from the fact that the splenic vein contributes to the formation of the vena portas. Whatever may be the functions of the spleen, hoAvever, it appears that it is not necessary to life ; for animals Avhich have been de- prived of it, have not been found to suffer any inconvenience from its loss. In some instances they have even become fatter. It is said that this organ is almost invariably absent in acepha- lous foetuses. CHAPTER XVII. ABSORPTION. After the chyme has been subjected to the second digestion in the duodenum, its nutritious parts are absorbed and carried into the circulation, and, almost immediately afterAvards, are subjected to respiration in the lungs, Avhere their conversion into blood is completed. The route which the chyle takes in its passage from ABSORPTION. 267 the intestines to the circulation, is through a part of the absorbent system ; and the functions of this system, or the physiology of absorption, are next to be considered. The absorbent system consists of the lymphatic vessels, the conglobate glands, and the thoracic duct. The lymphatics are fine pellucid vessels, which exist in all parts of the body, and terminate in the venous system, into Avhich they convey the fluids Avhich they absorb. The lymphatics con- sist of tAvo coats, of Avhich the external is cellular, and capable of considerable extension ; while the internal, like the inner coat of the blood-vessels, is smooth, and possessed of little extensi- bility, and forms numerous folds or valves, Avhich, in general, are arranged in pairs. These valves are disposed in such a manner, with their bases directed towards the origins of the vessels, and their free margins towards the heart, as to permit the free passage of their contents toAvards the veins, but to prevent it in the oppo- site direction. The lymphatics are endued Avith considerable irritability, Avhich continues several hours after death. If an animal be killed about the close of the process of digestion, upon opening the abdomen the lacteals will be found turgid Avith chyle. But these vessels, irritated by the contact of the air, gradually contract; and, in the course of a minute or two, Avholly disappear. A similar result may be obtained Avithin the space of twenty hours after death. But, after this time, the irritability of these vessels is annihilated, and they continue distended with chyle, notAvithstanding the contact of the air. If the thoracic duct, or any other lymphatic trunk, be tied in a living animal, and a puncture be made in the vessel below the ligature, the lymph spirts out in a jet; but if the experiment be performed some time after death, the fluid escapes from the vessel sloAAdy. The lymphatics are very elastic and possessed of great poAvers of resistance. A lymphatic Avhich is so fine as to be scarcely perceptible Avhen empty, may acquire a diameter of half a line when distended by an injection; and, if again emptied, it will resume its original dimensions. Their powers of resistance are much superior to those of blood-vessels of the same diameter. The lymphatics originate in two sources, viz. the surfaces of all the membranes, and the parenchyma, or internal tissue of all the organs. Thus, they originate, 1. From the areola of the cellular tissue, throughout its whole extent. 2. From the serous membranes, as the peritoneum, the pleura, the pericardium, the cavities of the joints, and, perhaps, those of the brain. 3. From all the mucous membranes, as the inner surface of the organs of respiration and digestion, and of the sexual and urinary organs. To this branch of the lymphatic system, the lacteals may be referred, as they spring from the mucous membrane of the diges- tive canal. 4. From the outer skin. They originate also, from 268 FIRST LINES OF PHYSIOLOGY. the tissues of all the organs themselves, as the muscles, the glands, bones, &c. Hence, it appears that all parts of the organism, with the exception of the hair, the nails, the epidermis, and the enamel of the teeth, are furnished with these vessels. They have not been detected, hoAvever, it is said, in the brain, the spinal marrow, the eye, and the internal ear ; though, according to Rudolphi, Mascagni and Schreger saw lymphatics in some parts of the eye; and Fohman detected them in the cornea, conjunctiva, serous membranes, inner coats of the vessels, and in the placenta and umbilical cord. Rudolphi even affirms that they have often been seen in the brain. It is a disputed point among physiologists, Avhether the absorbent vessels originate by open mouths or not. Some suppose that they commence in small spongy masses; others, that they originate in erectile ampullae ; others, in vesicles susceptible of transudation. But Bichat and some others think that they commence by small absorbing mouths, like those of the puncta lachrymalia. In the limbs, the lymphatics form two sets, viz. a superficial, and a deep-seated. The former is situated in the cellular tissue, beneath the skin, and accompanies the subcutaneous veins; the latter is found principally, in the intermuscular spaces, round the nerves, and the great vessels. Both sets ascend from their origins towards the upper parts of the limbs, gradually diminishing in number, but increasing in volume, and at length, enter the lym- phatic ganglions of the groin and axilla. In general, several ab- sorbent vessels enter every conglobate gland, on the side remote from the heart, and a smaller number issue from it in the direc- tion towards this organ. In the trunk, also, the lymphatic vessels are distributed in two sets, one superficial, or subcutaneous; the other, situated on the internal surface of the walls of the great cavities. In the thoracic and abdominal viscera likewise, these vessels form tAvo orders, an external and internal; the former occupying the surface of these organs, the latter apparently originating in their parenchyma. The absorbent vessels of the small intestines, and of the me- sentery, are termed lacteals. They originate by imperceptible orifices, at the surface of the villi of the mucous coat of the small intestines, and pass betAveen the two laminae of the mesentery, to a double series of small ganglions, called mesenteric glands. From these ganglions arise numerous vessels, of the same nature as the lacteals, Avhich unite into larger trunks, and these termi- nate eventually in the thoracic duct. Some physiologists are of opinion, that the lacteals do not terminate exclusively in the tho- racic duct. According to CoAvper, and Tiedemann and Gmelin, there are numerous anastomoses betAveen the chyliferous vessels and the meseraic veins. Meckel, Lobstein, and others, have ob- served similar communications with the vena portas; and other ABSORPTION. 269 physiologists have asserted their existence in various other parts: The chyliferous vessels Avhich issue from the mesenteric gan- glions, sometimes anastomose Avith the radicles of the mesenteric veins. This alleged direct communication between the lacteals and the veins, has an important relation to the physiology of ab- sorption, as Avill appear hereafter. The conglobate glands, or lymphatic ganglions, are small flat- tened bodies, of an oval or circular shape, of different sizes, vary- ing in.diameter from the one-twentieth of an inch to an inch. They are extremely vascular, are supplied with-nervous fila- ments, and receive lymphatic vessels, Avhich subdivide in their substance, forming inextricable plexuses, interwoven Avith innu- merable blood-vessels. The lymphatics Avhich enter them are termed vasa inferentia; those Avhich issue from them, in the direction towards the heart, are called vasa efferentid. If mer- cury be Injected into the vasa inferentia it is observed to fill a series of cells in the gland, and afterAvards escapes by the vasa efferentia. If a lymphatic gland be injected with Avax, the Avhole substance of the gland assumes the appearance of a mass of con- voluted absorbents, irregularly dilated, and which reciprocally communicate.* The lymphatic glands are not numerous in the extremities, but are found in abundance in the thorax and abdomen. They gene- rally exist in places where there is an accumulation of fat, as in the folds of the great articulations, about the anterior part of the ver- tebral column, and in the places Avhere the blood-vessels penetrate the viscera. Their number is very considerable, amounting, as has been computed, to six or seven hundred ; .but it appears to diminish in old age. Two or three small absorbent glands are found at the inner ankle, four or five in the ham, and from eight to twelve in the groin. These last receive absorbents from the leg and thigh, from the pudenda, the parietes of the abdomen, the nates, and the loins. Several, also, are found in the lateral parts of the cavity of the pelvis, and about the internal iliac vessels; others, on the outside of the pelvis, in the course of the glutasal and ischiatic arteries; and several minute glands are situated upon the bladder, the uterus, and the vesiculae seminales. Numerous lymphatic glands are situated in the course of the external iliac vessels, forming a chain Avhich extends from the crural arch to the inferior part of the .vertebral column. Others are found in the holloAv of the sacrum, between the laminae of the mesorectum. Large and numerous lymphatic glands occur, also, in the lumbar region, surrounding the aorta, and the inferior vena cava. They are found, also, upon the crura of the diaphragm, over the renal arte- ries, round the vena porta?, and along the splenic artery. The * Mayo. 270 FIRST LINES OF PHYSIOLOGY. mesenteric glands which receive the lacteals, are numerous, amounting sometimes to a hundred or more. They lie between the tAvo laminas of the mesentery, and are of considerable size. Opposite to the second lumbar vertebra, the absorbents of the mesentery, after passing through the mesenteric glands, unite into an oval sac, termed the receptaculum chyli. This reservoir, which receives also the absorbents of the lower extremities, is the com- mencement of the thoracic duct, a tortuous canal, about the size of a goosequill, which ascends betAveen the aorta and the right crus of the diaphragm, into the posterior cavity of the mediastinum. It then ascends behind the arch of the aorta, as high as the sev- enth cervical vertebra, and then arches doAvnwards, and opens into the left subclavian vein at the angle where this vessel joins the internal jugular. Its embouchure is provided with a valve, derived from the internal membrane of the A^ein. The thoracic duct, in its course to the subclavian vein, is joined by absorbents from the viscera and the neighbouring parts. It occasionally divides and unites again, particularly Avhere it crosses from right to left, in the cavity of the thorax. The structure of this duct is similar to that of the lymphatic and chyliferous vessels ; its parietes consisting of tAvo membranes, an internal and external, — the former of which is thin and delicate, the latter is a strong, fibrous membrane, capa- ble of opposing great resistance to a distending force. In the thorax, lymphatic glands are found upon the diaphragm and pericardium, and around the thymus gland, and the large ves- sels at the base of the heart. Besides these, there are numerous glands, situated before the division of the trachea, around the bronchia, and in the interior of the lungs. In the superior extremities, these bodies are found at the bend of the elbow joint, and clusters of them surround the axillary ves- sels, and their branches, and the subclavian and carotid arteries. Several small glands, also, are found behind the ear, some upon the buccinator muscle, and along the base of the jaAV. None have been found within the cavity of the cranium. The absorbent ves- sels of the left side of the head, and of the left upper extremity, terminate for the most part, in the thoracic duct, but partly in the left subclavian vein itself by tAvo or three separate orifices. But the absorbents of the right upper extremity, open either into the right subclavian vein, or the internal jugular of the same side, and are frequently joined by the lymphatics of the right side of the head, and those from the right lung, forming a great lymphatic trunk on the right side. This, hoAvever, is very short, being sel- dom more than an inch in length. The Function of Absorption. The lymphatic system is a great apparatus, pervading, Avith few exceptions, every part of the body, and instrumental in a function ABSORPTION. 271 indispensable to nutrition, and, consequently to animal life. The function of absorption is chiefly concerned in tAvo processes, dia- metrically opposite to each other, but each equally indispensable to the regular repair of the organization. One of them is the introduction of foreign substances into the circulation to be after- wards assimilated and identified Avith the living organs ; the other, is the decomposition of the organs, and the regular removal of their debris, or detached molecules, in order to make Avay for the depo- sition of the neAV elements of nutrition. The lymphatics which originate in the mucous membranes of the alimentary canal, and the lungs, furnish the means by Avhich the elements necessary to the repair of the organization, are introduced; Avhile those which spring from the parenchyma of the organs, are the instruments by Avhich these are regularly taken to pieces, to make room for their reconstruction by the nutrient vessel^ Besides these functions, subservient to nutrition, the lymphatics absorb certain parts of the secreted fluids, both of those Avhich are deposited upon surfaces which have no external outlet, and such as are secreted upon membranes, or in sacs, and canals, which are exposed to, or com- municate Avith, the external air. It appears, then, that the various absorptions which are regu- larly executed in the system, may be divided into the five follow- ing kinds, viz. alimentary, respiratory, interstitial, recrementitial, and excrementitial absorption. 1. The first, or alimentary absorption, is executed at the inner surface of the small intestines. It is employed in the introduction of nutritious matter, obtained from the aliments and drinks, and its result is the formation of chyle. 2. The second or respiratory absorption, is concerned in the introduction of an aerial principle, essential to life, into the mass of the blood. The consideration of it belongs to the history of respiration. By these tAvo absorptions, all the materials intro- duced from without, for the support of life, are received into the system. These tAvo species of absorption may be termed, collect- ively, absorption of composition. 3. Interstitial absorption is employed in regularly detaching from every organ a certain number of molecules, to counter-bal- ance the action of its nutrient vessels, and thus to prevent an indefinite increase of its volume ; or to preserve a proper equili- brium between composition and decomposition. It is this absorp- tion which occasions the changes of volume in the organs, at the different periods of life ; and when it predominates over nutrition, produces atrophy of particular parts of the body. It occasions the shrinking and disappearance of the thymus gland, the removal of exostoses and other tumours, and the disappearance of the red colour of the bones, in animals Avhich have been fed for a certain time Avith madder. It is this, also, Avhich hollows out a canal in the callus Avhich unites a fractured bone. This absorp- 272 FIRST LINES OF PHYSIOLOGY. tion varies in every organ, and is of as many kinds as there are different tissues; Interstitial. absorption may also be termed ab- sorption of decomposition. 4. Recremcntitial absorption. This takes up the fluids secreted upon surfaces which have no external outlet, Avhich fluids would increase indefinitely if they were not removed by. absorption, as fast as they are secreted. The matters taken up by this species of absorption are very various, as the serous fluids, the synovia of the joints, the serosity of the cellular tissue, the fat, the marrow, the colouring matter of the skin, that of the iris, and'of the cho- roides, the humours of the eye, the lymph of Cotunnius, and the fluids'exhaled into the interior of the lymphatic glands, and of the thymus and thyroid glands. The reality of this absorption cannot be denied, and is demonstrated by numerous facts. The quantity of the fat and the marrow of the bones, varies according to the age, and state of health, and various other circumstances. Dropsies disappear by absorption. . If foreigri substances, solid, liquid, or gaseous, be "placed in contact Avith the surfaces Avhich secrete these recrementitious fluids, they diminish, or totally dis- appear, by absorption ; a fact Avhich affords a presumption, that the peculiar secretions of these surfaces must, in like manner, be subject to absorption. 5. Excrementitial absorption. The excreted fluids, also, are subject to absorption, by which they are deprived of certain parts which, perhaps may be usefully employed in the system ; or by the loss of Avhich, they are rendered more fit themselves for the uses to Avhich they are destined in the animal economy. A great variety of fluids are subject to this species of absorption, as, for example, the fluids exhaled by the skin, and the mucous mem- branes, the matter secreted by the-sebaceous follicles, the mucus, the cerumen of the ear, the saliva, the bile, the gastric and pan- creatic fluid, the spermatic liquor, the milk, and urine. Adelon remarks, that nature chooses to subject the materials of decompo- sition to a useful revision, before rejecting them finally from the body. By this absorption the excreted fluids become more con- centrated and stimulating; hepatic bile is converted into cystic by absorption, the urine is rendered more acrid and concentrated; and the spermatic fluid becomes more stimulating by long reten- tion. In general, only certain principles are absorbed from the excreted fluids ; but if any obstacle prevents their excretion,.they are absorbed entire, and may then.be sometimes detected in the blood; and, in some instances, they are deposited, by a neAV se- cretion, in places remote from the organ by which they were originally secreted. The absorptions Avhich have thus been described, are carried on Avithout intermission in the system; and they impress certain changes upon the fluids absorbed, by Avhich these are prepared to contribute to the formation of the common nutritive fluid, the ABSORPTION. 273 blood ; for this fluid is the final result of the five species of ab- sorption just enumerated. In each of these absorptions the mat- ter absorbed is elaborated and changed in its properties. Thus, chyme is converted into chyle, by absorption. The oxygen ab- sorbed in respiration is assimilated to the blood, so that it is im- possible to detect its presence in this fluid. In like manner, the molecules detached from the tissues and organs by decomposing absorption, and the principles absorbed from the recrementitious and excrementitious fluids, do not preserve their proper characters in the lymphatics, but undergo an elaboration by which they are converted into lymph. But absorption sometimes occurs accidentally, or occasionally ; as for example, Avhere certain substances Avhich are not of an alimentary or assimilable nature, are introduced into the system, or placed in contact Avith any absorbing surfaces. Substances so circumstanced are frequently absorbed, and they may sometimes be detected in the blood, in the secreted fluids, or even in the parenchyma of the organs, for they undergo no elaboration, and their properties are unchanged by the action of the absorbents. These accidental absorptions are of tAvo kinds, viz. External and Internal. The seats of the first, or of external absorption, are the two great surfaces, the skin and mucous membranes. Substances of various kinds, placed in contact with either of these great expan- sions are subject to absorption, and may thus be introduced into the blood. 1. Solid, liquid, and gaseous substances, placed in contact with the skin, may be absorbed by this tissue, as is demonstrated by many facts. For example, thirst may be quenched by the appli- cation of moist cloths to the skin, or by bathing. Adelon cites the case of a patient in fever, in Avhich so much Avater Avas absorbed during the use of a foot-bath, that the level of the fluid in the vessel was sensibly lowered. It is also asserted that the body increases in Aveight after using the bath, and that the urinary secretion is augmented, to carry off the water which has been absorbed. Cruikshanks Avitnessed the thirst quenched by bathing, and the secretion of urine, which had ceased in consequence of Avant of drink, restored by the bath. Falconer found that his hand, immersed to the Avrist in Avarm Avater, had absorbed in a quarter of an hour ninety-eight grains of fluid. Hamilton observes that the saliva has become intolerably bitter from an absorption of sea-water. Paracelsus states, that he has supported patients by nutritive baths of milk or broth. Fontana and others assert that the body absorbs moisture Avhen exposed to a humid atmosphere. The experiments of Professor Mussey, performed several years ago at Philadelphia, demonstrate the absorption of the colouring matter of madder and other substances, by the skim 35 274 FIRST LINES OF PHYSIOLOGY. Medicinal substances, applied to the skin, are frequently absorbed into the circulation, and exert their peculiar effect upon the sys- tem. From the experiments of Chaussier, it appears that the hydrosulphuric acid gas is capable of producing asphyxia in dogs, when applied to an extensive surface of the skin. A plaster of garlic, applied to the skin, has been found to impart a strong smell of garlic to the breath and the urine, which continued seve- ral, hours, though the individual breathed through a tube Avhich passed out of the apartment. In. general, however, the cuticle is previously removed, or the substance is applied by friction, or rubbed in ; othenvise the absorption is much less considerable, for the cuticle appears to present an obstacle to the absorbing action of the skin. The cuticle, however, it should be remem- bered, opposes no resistance to the passage of fluids from within; and Avhy, it may be asked, should it hinder the entrance of fluids from Avithout. Metallic quicksilver has been found in the bones of persons who had been subjected to mercurial frictions ; it has been found, for example, in a carious skull, and in some Other of the bones. Autenrieth and Zeller obtained quicksilver by dis- tilling the blood of rabbits, dogs, and cats, which had been rubbed with this mineral. Schubarth had, a large quantity of quicksilver rubbed into a horse, from the fifth of July to the third of August, Avhen the animal died, and, on distilling his blood, small globules of quicksilver Avere discovered in it.* Canter obtained from the sediment of sixty pounds of urine, subjected to distillation, more than twenty grains of quicksilver. Quicksilver has been found, not only in the blood and-urine, but in the saliva and SAveat of persons Avho have been severely salivated. Many animals are nourished by cutaneous absorption, and the same may be true of the foetus, in the first periods of pregnancy, before the mouth is formed by Avhich fluids can be received, and Avhen the intimate connection between the foetus and the mother-does not yet exist. Gases also are absorbed by the skin.' Thus, the putrid miasms of a dissecting-room have been absorbed by this membrane, as has been ascertained by experiment, in Avhich precautions were used to prevent their introduction by pulmonary absorption. In a Avord, Westrumb inferred from his experiments that the skin possesses a faculty of absorption so extensive, that it can imbibe all kinds of substances, from the least to the highest degree of fluidity, provided they are soluble. 2. The mucous membranes also exercise an absorbing poAver upon various foreign substances placed in contact Avith.them. Alimentary substances and air are constantly absorbed by the in- testinal and the pulmonary mucous membranes. But other prin- ciples besides chyle and oxygen are absorbed from, the aliments and the air Avhich we breathe ; as, for example, those parts of * Rudolphi. ABSORPTION. 275 our food and drinks which are incapable of chylification, and the vapours or gases with which the air we inhale becomes acciden- tally impregnated. Substances not of an alimentary kind, also, introduced accidentally, or purposely; into the alimentary canal, such as medicines, colouring, odoriferous, saline, and other sub- stances, are frequently absorbed. Chaussier produced asphyxia - by injecting sulphuretted hydrogen gas. into the intestines. Accidental pulmonary absorption also is very active. Sub- stances in a state of vapoiir,-or fine dust, drawn into the lungs Avith the air of inspiration, are readily imbibed — such as metallic va- pours, odoriferous substances,' miasmatic exhalations, &c. Pul- monary absorption is, probably, one of the most frequent means by Avhich contagious effluvia are introduced into the system. Liquids/also, injected into the lungs, are absorbed by these.or- gans ; a fact Avhich has been established by repeated experiments. The mucous membrane of the urinary and genital, organs is also an absorbing surface. Fluids injected into the bladder are frequently absorbed ;' and the virus of syphilis is introduced into the system by the same Channel of the genito-urinary mucous membrane. But accidental absorption may take place from surfaces, or parts of the body, Avhich have no communication with the external air. In fact, every part of the body seems to possess the poAver of .absorbing substances placed in contact Avith it, as for example, the serous surfaces, the cellular tissue, and the parenchyma of the organs. Experiments have demonstrated that various substances, either in a solid, liquid, or gaseous form, are subject to absorption, if placed in contact with any tissue of the body, or even buried in the very substance of the organs. Chaussier inserted a cal- culus in a Avound Avhich he had made in an animal, and which afterAvards healed over the foreign substance. After a time, the calculus became corroded, and finally disappeared by absorption.* Dupuytren and Magendie injected various liquid substances into the serous cavities and cellular. tissue, and found that they were absorbed. Achard, Nysten, Chaussier, and others, had observed the same fact Avith respect to gases, as oxygen, carbonic acid, sulphuretted hydrogen, &c. introduced into different parts of the body. The air Avhich escapes into the cellular tissue in emphy- sema sometimes disappears by absorption. The excrementitious fluids, also, Avhen their regular excretion is prevented by any obstacle, are subject to absorption. In jaun- dice, the bile is absorbed into the blood, and imparts a yellow tinge to all parts of the body. In paralysis of the bladder, and in the experiment of tying the ureters in a living, animal, the urine is absorbed into the blood, and impregnates all the fluids and tissues of the system. Even the contents of the large intes- * Adelon. 276 FIRST LINES OF PHYSIOLOGY. tines, if retained a long time, are partially absorbed, and impart a feculent odour to the cutaneous exhalation. Morbid excremen- titious fluids, also, as pus, if long retained, are absorbed into the blood. The blood extravasated in the brain in apoplexy, or in any other part of the system, is sometimes absorbed. The crys- talline lens is absorbed after the operation of couching in cataract; and even the foetus, in extra-uterine pregnancy, is sometimes re- moved by absorption. According to Adelon, accidental absorption is distinguished from nutritive, by the circumstance that in the former there is little or no change in the properties of the substances absorbed; whereas, in the latter, the matter absorbed is ahvays elaborated in such a manner that its properties are disguised, and it cannot be detected in the fluids or solids of the system. Medicinal sub- stances Avhich are introduced into the system by accidental ab- sorption from the skin or mucous membrane of the alimentary canal, retain their medicinal properties nearly or Avholly un- changed. Of this the folloAving fact is a remarkable instance. Metallic silver was obtained by M. Brande from the plexus cho- roides and pancreas of an individual Avho had been cured of epilepsy by taking the nitrate of silver. The skin of the patient, who afterAvards died of another disease, was coloured blue, and all the internal viscera were more or less stained with the same hue. If this Avere not the case, if medicinal substances were assimilated by absorption to the nature of the animal fluids, it is eArident that they could not exert their specific effects upon the system. So the excrementitious fluids, Avhen accidentally ab- sorbed, retain their properties Avith little alteration. When the bile is absorbed in jaundice, or the urine, in retention of this fluid from paralysis of the bladder, or any other cause, these excretions impregnate the animal fluids and tissues with their own peculiar qualities. Particular Absorptions. It has already been observed, that there are five species of nutritive absorption, viz. digestive or alimentary, respiratory, in- terstitial, absorption of the recrementitious and that of the excre- mentitious fluids. The second belongs to the history of respira- tion, and the three last may be comprehended under a single title, viz. internal absorption. 1. Alimentary or digestive absorption, is executed in the small intestines. It is exercised upon the food and drink, after these have been subjected to the action of the digestive organs. The instruments of this absorption are the lymphatics of the small intestines, or lacteals, as they are called. These vessels originate in the villi of the mucous coat of the intestinal canal, and passing between the serous and muscular coats of the intestines, they ABSORPTION. 277 proceed to the mesenteric ganglions. From these bodies there arise a second series of lacteals, fewer in number, but of a larger size, which unite together into larger trunks, and terminate, eventually, in the thoracic duct. There is a free communication between the lacteals which enter, and those which issue from the mesenteric glands, through these bodies; for. a mercurial injec- tion passes from one to the other without distending the glands. It is doubtful whether the lacteals open directly into the cavity of the intestines, or, Avhether some kind of tissue exists inter- mediate between their extremities and the surface of the villi of the small intestines. HoAvever this may be, these vessels exert a peculiar vital action upon the chyme in the intestinal cavity, selecting, absorbing, and combining its nutritive principles, and converting them into a much more highly animalized fluid, termed chyle. This white, cream-like fluid, it is said, does not pre-exist ready formed in the chyme, but is the result of the action of the lacteals upon the nutrient principles contained in it. It is affirmed, that chyle has never been discovered in the intestines, and that it is impossible to obtain it from chyme by expression or any other means. It is formed by the elaborating action of the lacteals themselves, Avhich, at the same moment that they absorb, impress certain vital changes upon the nutritive parts of the chyme, which hence assume the properties of chyle. In the same manner, the sap of plants does not pre-exist in the soil in Avhich they groAV, but is formed by the peculiar action of the roots, which absorb the materials of it from the ground. No other substance but chyme Avhich has been acted upon by the bile and pancreatic fluid, is capable of being converted into chyle ; and such sub- stances as find their Avay into the small intestines without being reduced to the state of chyme, do not contribute to the formation of chyle. During digestion the lacteals become filled and turgid Avith chyle. Various theories have been proposed to explain the mode in Avhich this absorption is accomplished. Some physiologists have referred it to imbibition or capillary attraction; some, to en- dosmose and exosmose, or the motion of heterogeneous fluids across a membranous diaphragm, separating them from each other ; some, to electrical or galvanic agency; others, in fine, to a peculiar, in- scrutable vital action. This last opinion, though it explains no- thing, is, probably, the true one. The action of the absorbents continues a considerable time after death, or the cessation of the circulation. After emptying some of the lacteals in an animal, soon after death, by pressing out their contents, they soon become filled again; and the expe- riment has been found to succeed tAvo hours after the extinction of life. Mascagni observed absorption in infants to continue six hours after death, and in adults, tAventy-four; and Desgenettes found it to take place sixty hours after the cessation of life, even 278 FIRST LINES OF PHYSIOLOGY. in very young subjects. Valentin found chyle in the lacteals as late as three days after death.* The quantity of chyle Avhich is formed in a given time is un- certain. Magendie found, that in a dog of a common size, Avhich had eaten heartily of animal food, more than half an ounce of chyle issued from an opening in the thoracic duct in five minutes, and it continued to Aoav out for several hours'. This would im- ply a pretty rapid formation and motion of the chyle ; for, at this rate, six ounces must have entered the circulation in an hour. Emmert estimated the quantity Avhich flowed from the thoracic duct of a horse, at a pound in half an hour. In man, the quantity formed must be proportionally large, but it is evidently impracti- cable to arrive at any precision in estimating it. The chyle appears to be constantly undergoing changes in its properties in its passage through the absorbent system. Its albu- minous qualities seem to diminish, while the proportion of its fatty matter, and of its fibrin and cruor, appears to increase. Its tendency to coagulate also increases as it approaches the venous system, and becomes very considerable in the thoracic duct.. In the large lymphatic trunks, or those between the mesenteric glands and the thoracic duct, the chyle gradually loses its opaque and milky or cream-like appearance, and becomes clearer and more transpa- rent. It is also remarked by Emmert, that, in the smaller lacteals, near the origins of these vessels, the chyle is more homogeneous in its appearance and properties ; but, in the larger trunks, it gradu- ally becomes more heterogeneous. In the thoracic.duct, it has sometimes been observed of a reddish colour. Chyle obtained from the smaller lacteals of a horse was found to be milk-Avhite; while that from the larger trunks, and the receptaculum ch'yli, was yelloAvish; and the chyle of the thoracic duct still more so. Exposed to the air it assumed a pink or -peach-blossom colour. These changes are probably produced, partly by the vital influence of the lacteals themselves, exerted upon the chyle, and partly by the action of the mesenteric glands. It is, however, impossible to determine, what are the functions of these bodies. It is con- jectured, by some physiologists, that the chyle undergoes some peculiar modification in traversing these glands. Some are of opinion, that they produce a more intimate combination of the elements of the chyle ; others, that they secrete a peculiar fluid, which is destined to dilute it; Avhile some suppose that their office is to purify this fluid, by separating from it certain heterogeneous principles. Absorption takes place throughout the whole alimentary canal. Even in the mouth the absorbents imbibe some part of the food, as is evident from the effects of Avine or spirits held in the mouth. It is probable, also, that the absorbents of the oesophagus imbibe * Lepelletier. ABSORPTION. 279 something from the aliment during its passage through this tube. The lymphatics of the stomach are found, to be turgid during digestion. But the chyliferous absorbents of the small intestines are particularly active during digestion, in imbibing the nutritious chyle. These vessels diminish in number in the inferior portion of the small intestines ; but some are found in the large intestines, and their effects are evident in the increasing density and consis- tency of the contents of the loAver part of the alimentary canal. In horses and some other animals, the absorbents of the large in- testines are observed to be filled Avith -a chyle-like fluid. As chyle is found only in the lacteals, and yet, as just observed, absorption of nutritious substances takes place from the Avhole sur- face of the alimentary canal, it appears that alimentary matter may be.imbibed from the intestines, Avithout having undergone the pre- paratory process of gastric digestion. Per3ons have been nourished for many days, and even Aveeks, by injections of milk, broth, and other nutritive fluids, thrown up the rectum. The author had a patient who Avas supported four Aveeks, almost exclusively, upon injections of animal decoctions and Avine. No food whatever could be taken the greater part of this time. A few drops of sage tea, or even pure Avater, Avould occasion the most dreadful anguish ; and it is a question Avith the author, Avhether food enough Avas sAval- loAved, during this whole period, to form one gill of chyle. This patient completely recovered, and is noAV in the enjoyment of good health. Now, it is evident that alimentary substances,'directly absorbed from the intestines, pan undergo no assimilation previous ■ to their reception into the circulation, except that which they re- ceive in their passage through the absorbent system ; a considera- tion Avhich appears to establish the conclusion, that the absorbents exert an elaborating influence upon the substances absorbed, which, under some circumstances, may serve as a substitute for digestion in the stomach and small intestines ; and it affords some corrobo- ration of the principle that every living animal substance, solid as Avell as fluid, poss?sses a power of assimilation, by virtue of which it constantly tends to subdue to its oavh nature substances applied to or mixed Avith it, and to communicate to them its OAvn proper- ties. In cases of extreme inanition, it would seem that alimentary matter is sometimes absorbed so greedily as not to alloAv time either for chylification or any other considerable change to be effected. We are told of a young man almost dead of hemorrhage, supported by broth, in whom the last discharge of blood had the smell, taste, arid even colour of this substance. He eventually recovered and greAV fat. ' Lepelletier expresses the opinion, that hematosis, or the formation of blood out of the aliments, commences at the ori- gin of the absorbents, that it is continued by the action of these vessels, by that of the mesenteric ganglions, and by the veins, and that it is finally consummated in the capillaries of the lungs, by the influence of respiration. 280 FIRST LINES OF PHYSIOLOGY. It has already been observed, that, after long fasting, the lac- teals, instead of containing chyle, are filled with real lymph. But, according to Magendie, after twelve, twenty-four, or even thirty- six hours of total abstinence, the lacteals of a dog contain a small quantity of semi-transparent fluid, of a slightly milky appearance, which he supposes to be chyle, formed by the digestion of the saliva and the mucus of the stomach. But, if the fasting be pro- longed beyond three or four days, the lacteals are found sometimes filled with lymph, and sometimes entirely empty. Venous absorption. Many physiologists of the present day, have adopted the opinion, founded on various facts and considerations, that the absorption of the chyle, and of other substances from the alimentary canal, is not effected, exclusively, by the lacteals. Some of the experiments and facts on Avhich this opinion is founded will be noticed. Magendie gave a dog four ounces of an infusion of rhubarb, and half an hour afterwards, not a trace of it coidd be discovered in the thoracic duct, though the urine of the animal indicated its presence, and half of it had disappeared from the alimentary canal. Segalas injected an infusion of nux vomica into a part of the intestines, iso- lated by two ligatures, having tied the blood-vessels of the part, but left the lacteals untouched. In one hour no appearance of poisoning had taken place ; but in six minutes after removing the ligatures from the blood-vessels, symptoms of poisoning appeared. Berthold injected water, coloured Avith ink, into a piece of intes- tine of a puppy, isolated in like manner by tAvo ligatures, and in ten minutes the fluid had partly disappeared from the intestine, and the veins of the part were filled with it, but the lacteals were entirely empty. According to Boerhaave, the blood of the mesen- teric veins becomes more fluid during the digestion of fluids; and Flandrin thought that he perceived an herbaceous smell in the blood of these vessels, in a horse Avhich had been eating food of this kind. Kaaw Boerhaave injected warm water into .the stom- ach and intestines of a dog, just killed, and, by a little pressure, this Avater passed into the meseraic veins, so that these vessels became pale, and, at last, clear water flowed out of the vena cava inferior. The result was similar with coloured Avater. Lieber- kuhn pushed an injection into the vena portas, and saAV the matter of it ooze out of the villi of the intestines. Ribes obtained the same result. Avith essence of turpentine, coloured black, and with mercury — facts from which it appears, that the meseraic veins have open orifices in the cavity of the intestines. Flandrin gave a horse a mixture of honey and asafoetida, and the venous blood of the stomach and intestines exhaled the peculiar odour of the asafoetida, Avhile the chyle and the arterial blood were wholly free from it. Magendie caused a dog to take diluted alcohol, a solu- tion of camphor, and other odorous substances, and on examining the chyle half an hour afterwards, no trace of these substances ABSORPTION. 281 could be detected in it; while the blood exhaled the odour of alcohol, camphor, &c. and these substances could be even obtained from the portal blood by distillation. The same physiologist gave a dog two ounces of a decoction of nux vomica, after tying the tho- racic duct, and death took place as speedily as'in another Avhich had sAvalloAved the same poison Avithout having had the duct.obstructed by a ligature. In another dog, he isolated a piece of intestine by two ligatures, and divided, Avith the utmost care, all the vessels of the part, arterial, venous, lymphatic, and chyliferous, with the exception of a single artery and vein, Avhich Avere left undivided. He then separated the piece of intestine from the rest of the canal, so that it was connected. with it only by a single artery and vein, and injected into it a decoction of nux vomica, and, in . six minutes, the effects of the poison manifested themselves.. Flandrin sometimes found the substances injected, in veins only ; sometimes in the lacteals only, and sometimes in neither, but only in the urine. Haller found that the blue juice of the heliotrope, Avhich he had injected into the stomach, was present in the chyle, but not the red colouring matter of madder, nor the yellow of saffron. Emmert shoAved that madder, curcuma, prussiate of pot- ash, nitrate of silver, &c. are received into the chyle. The researches of Tiedemann and Gmelin, of Germany, and of LaAvrence and Coates, of our OAvn country, corroborate the conclusion, that absorption from the alimentary canal, is not ex- clusively the function of the lymphatics, but is shared Avith them by the mesenteric veins. In the experiments of Tiedemann and Gmelin, various colouring, odorous, and saline substances, Avere introduced into the stomach, and the urine, the portal blood, and the chyle of the thoracic duct, were afterAvards submitted to the proper tests, or the presence or absence of the substances absorbed' was ascertained by their colour or smell. It appeared from these experiments, that colouring substances were not absorbed by the lymphatics or lacteals, as they could in no instance be detected in the. chyle of the lacteals, or that of the thoracic duct, either by their smell, or by the aid of chemical tests, though they Avere detected in the urine, and in the serum of the blood of the vena porta '; facts which demonstrated that they entered the circulation by venous absorption. The same results were obtained with odorous substances. They were detected in the urine, and in the portal blood; but in no instance were they discovered in the chyle of the lacteals or thoracic duct. Saline substances, of which several were employed, as the prussiate of potash, the muriate of barytes, the muriate and sul- phate of iron, and the acetate of lead, Avere discovered in the urine, and several of them in the blood of the mesenteric veins ; a very few of them, also, were detected in the chyle of the tho- racic duct. 36 282 FIRST LINES OF PHYSIOLOGY. On the whole, they inferred from these experiments that the office of the lacteals is to absorb the nutritious matter, formed by digestion, and to convey it to the thoracic duct ; Avhile the roots of the mesenteric veins absorb substances Avhich are not of an alimentary nature, as saline, colouring, odorous, and metallic, and, probably, medicinal and poisonous substances. Rudolphi, hoAv- ever, remarks in answer to these conclusions of Tiedemann and Gmelin, that nothing exists in the urine Avhich did not previously exist in the blood. Now it is certain, that many substances can be detected in the urine Avhich cannot be discovered in the blood. So in the chyle, many principles may be present, but not suffi- ciently concentrated to be detected by chemical or other tests. Roose proved, that the serum of the blood, as well as a filtered solution of the white of eggs, might contain a considerable quan- tity of oxide of iron in solution, Avithout the possibility of de- tecting it by the usual agents; and he established the following principles, viz. that all organic substances, soluble in Avater, which are decomposed by exposure to a high temperature, possess the property of preventing the precipitation of the oxide of iron, and of other oxides, by alkalies ; and on the contrary, all organic substances, soluble in water, which are completely or partially volatilized, without decomposition, by a high temperature, do not possess this poAver.* The experiments of LaAvrence and Coates led to results simi- lar in the main to those of Tiedemann and Gmelin. The prus- siate of potash Avas introduced into the stomach, and the blood of the vena porta afterAvards examined. On the addition of a salt of iron, the portal blood assumed a blue colour, more or less intense, indicating the formation of the Prussian blue. The chyle of the thoracic duct Avas also found to contain the prussiate of potash, evrincing that the absorption of the salt had been effected partly by the lymphatics. In some of the experiments, the portal blood was found exclusively to contain the salt, the chyle of the thoracic duct presenting no trace of it; in some others, precisely the reverse of this occurred. But the authors remark, that the general weight of evidence Avas strongly in favour of the princi- pal absorption having taken place through the vena porta. The fact Avas more conclusively established by tying the thoracic duct, and thus intercepting the communication betAveen the lymphatics and the circulation. In one experiment, in order to stop every knoAvn communication betAveen the absorbent system and the circulation, the thoracic duct and the trunk of the lymphatics on the right side of the neck Avere both secured by ligature, yet the blue colour Avas produced in the serum of the blood, taken from the right side of the heart, in tAventy minutes. On the whole, it appears that the lacteals absorb chyle much * Rudolphi. ABSORPTION. 283 more readily than other substances. Colouring, odorous, and mineral substances, perhaps poisons, and, in general, matters not of an assimilable nature, are absorbed Avith difficulty by the lac- teals, and much more easily by the veins. Some unchymified substances, of an alimentary nature, as milk, are absorbed by these vessels. Rudolphi says, that he has seen a Avhitish blood flow from the vessels of the head, in sucking puppies, on cutting into the diploe, from Avhich blood a large quantity of bluish Avhite fluid, perfectly like milk, soon separated itself. Lower also found milk in the blood drawn from a vein sc^bn after food had been taken ; and Veridet mentions a case, in Avhich a person in an at- tack of fever drank a quart of milk, and on bleeding him soon after, a stratum of milk formed on the blood. In cases of long fasting, the lacteals absorb the animal juices, and become filled with intestinal fluid, bile, &c. and frequently with true lymph. Several distinguished physiologists assert a direct communication betAveen the absorbent vessels and the veins. Blizard and Meckel observed lymphatics terminate directly in veins. Ribes, in in- jecting the supra-hepatic veins, saw the matter pass into the super- ficial lymphatics of the liver. According to Mertins, a considerable part of the chyle is carried directly into the vena azygos, and the lumbar veins, and others by the lacteals. Meckel, Lobstein, and others, have observed similar communications with the vena portas ; and other physiologists have asserted their existence in various other parts. Lizars remarks, that some of the lymphatics, almost as soon as they originate, join the veins in the capillary tissue ; others anastomose with the veins in the lymphatic glands, Avhile a third class concentrate to form the thoracic duct. Aselli, the original discoverer of the absorbent system, was persuaded that the lacteals terminated in the vena portas ; an opinion Avhich, according to Mayo, the observations of Fohman have proved to be partially true, shoAving that many of the lacteals open into the branches of the visceral veins. It is also said that a Dr. Dubled of Paris has succeeded in injecting the tAvo inferior thirds of the thoracic duct, and some of the neighbouring lymphatics, by forc- ing an injection through the inferior vena cava. He also found, in an animal in Avhich he had tied the vena cava beloAV the diaphragm, that the thoracic duct, and some of the lymphatics, a few hours afterwards, contained blood. But an Italian anatomist, Lippi, has carried this opinion to a much greater extent. He has endeavoured to prove, that the absorbent vessels of the abdomen open freely into the iliac, the spermatic, the emulgent, and lum- bar veins, and the vena cava, as Avell as into the branches of the portal system; and that they communicate with the venous sys- tem, not only by opening into the great venous trunks, but by anastomosing with the small veins Avhich issue from the conglo- bate glands, and by direct continuity with the capillary veins. He also affirms, that several absorbent trunks in the abdomen 284 FIRST LINES OF PHYSIOLOGY. terminate directly in the pelvis of the kidneys. He does not think that any communication exists between the absorbents and veins in the limbs. This alleged communication between the absorbents and. the veins, is regarded by many physiologists as imaginary. Rudolphi treats the opinion Avith contempt, but Mayo observes, that he thinks it not unlikely that such communications do exist, even in the limbs; for he has sometimes seen mercury throAvn into the absorbents of the limbs unaccountably make its way into the veins. He also states, that on injecting the arteries of the mesentery of a Aog with ink, he observed the veins next to become filled Avith a black fluid, and then the lacteals; and he further says; that he has certainly seen, in one instance, the absorbents of the liver filled Avith coloured injection from the hepatic artery. Adelon doubts the reality of this communication; and regards it as a cadaveric phenomenon. According to Camper, and Tiedemann and Gmelin, there are numerous anastomoses betAveen the chyliferous vessels arid the meseraic veins. In ex- periments performed by these two last named physiologists on two dogs, a horse, a cow, and three human bodies, the lacteals were injected Avith quicksilver ; and in all of them the metal reached the branches of the mesenteric veins, and the vena portas, without the application of any external force. On close exami- nation, it Avas discovered that the communication of the lacteals with the veins of the intestines, took place in the mesenteric glands, and that all the veins proceeding from a gland filled Avith quicksilver, also became, filled with the rnetal ; a fact which proved, that it passed from the lacteals through the gland directly into the veins proceeding from it. In several of their experi- ments, these physiologists observed in the portal blood, white streaks resembling chyle,.and Avhich they supposed to be really such; an. appearance Avhich Avas readily explained by their dis- covery of a communication betAveen. the lacteals and the meseraic veins, in the glands'of the mesentery. The chyle, thus entering the portal circulation, and conveyed Avith it to the liver, they supposed to be elaborated in this gland, by the separation of its heterogeneous principle in the secretion of bile. Rudolphi, however, gives no Aveight to the experiments in which quicksilver has been observed to pass out Of a gland into a vein. He supposes, in these cases, that this ponderous metal forced for itself new passages. He admits that quicksilver, in- jected into an absorbent, frequently passes into a vein; but he explains the fact by asserting that either the vein lying under or near the absorbent has been Avounded by the injecting tube, or, what he says is most frequently the case, that the quicksilver has passed from the absorbent vessel into the thoracic duct, left sub- clavian vein, through the superior vena cava into the inferior, and thence to the place where the injection was made. This passage of the injected quicksilver through the thoracic duct, ABSORPTION. 2Q5 superior and inferior 'cava, &c, takes place, he asserts, in a mo- ment. Rudolphi further objects, that if such communication really existed betAveen the veins and lymphatics it Avould be im- possible to inject the latter with quicksilver, for all the metal would pass into the veins. He admits that in birds, anatomists at present regard the immediate communication of the absorbents with the veins as fully established. When the lymphatics in a duck's foot are injected Avith quicksilver, the metal is always soon found in the lumbar veins. But he says that it is impossible to discover the communication. On opening the vein no orifice of a lymphatic can be detected in it; but the lymphatic may be traced to the kidney; and here, he thinks, the connection exists by Avhich the quicksilver gets into the veins. He supposes that, in the kidneys of birds, Avhich are very large, a particular con- nection may exist betAveen these tAvo orders of vessels. This important question cannot yet be considered as settled; though, to the author, the arguments in favour of the communication of the absorbents and the veins appear to preponderate. It appears that the thoracic duct may be obstructed, and yet chyle find its way into the circulation. In tAvo instances, Sir A. Cooper found this canal obstructed in human subjects ; but in both collateral vessels ascended from beloAV the obstruction, and opened into the duct above it. Dupuytren tied the thoracic duct in horses, some of Avhich died, Avhile others survived the opera- tion. In one, Avhich was opened six Aveeks after the operation, the canal Avas found perfectly closed at the place Avhere the liga- ture was applied ; but there Avere found connecting vessels, Avhich passed from the part of the duct beloAV the ligature to the subcla- vian vein. But in an experiment performed by Leuret and Las- saigne, the thoracic duct of a dog Avas tied, and the animal lived and even thrived fifty-eight days, at the end of Avhich time he was killed; and upon opening him, the thoracic duct, which was single, was found perfectly closed. The accuracy of this state- ment seems to be doubted by Rudolphi, and very naturally, as, if admitted, it appears decisive of the question of the passage of chyle into the circulation by other channels than the thoracic duct. Flandrin repeated the experiment of tying the thoracic duct on tAvelve horses, Avhich lived and retained their flesh and appetite. On killing and opening them a fortnight afterwards, he found that the thoracic duct was not double. The passage of the chyle into the left subclavian vein, it is said, takes place only by drops; and the conversion of chyle into blood is effected, not at once, but by degrees, and after many revolutions of the blood through the circulating system. Haller' thought that eighty thousand revolutions of the blood were necessary to complete the conversion of chyle into this fluid. Plocquet says, that chyle requires ten or twelve hours in order to be converted into red blood; and Autenrieth adds, that in blood 286 FIRST LINES OF PHYSIOLOGY. drawn from man or other animals, within 'this time, the serum is sometimes found milk-Avhite. In this view, it is apparent that the secretions and excretions, particularly urine, by removing the unassimilable principles from the imperfect blood, may contribute essentially during its circulation through the body to its complete sanguification. The opinion, that the chyle is not immediately converted into blood, is founded partly on the appearance' of white streaks and flakes Avhich have sometimes been observed in the blood a few hours after digestion. These streaks Haller took to be chyle. He had even seen, in living animals, white chyle, floating in the blood, issue from a wound or enter the heart. This white appearance, however, disappeared some hours after eating, and the Avhole mass of the blood resumed its usual red colour. In some instances, instead of the blood presenting the appear- ance of white streaks or flakes, the Avhole mass of it has been observed to be colored Avhite, presenting the appearance of milk # or cream, for a longer or shorter time. This appearance of the blood has been observed in individuals of scorbutic or cachectic habits, or of corpulent persons. These appearances of the blood probably depend on different causes. When occurring a feAv hours, after eating, the white streaks are, perhaps, owing to unassimilated chyle, especially when fat, oily, or milky food has been eaten, and the powers of digestion and hematosis are enfeebled. In other cases, they may be owing to pathological states of the blood, as in scurvy, chlo- rosis, or, as Hewson supposed, to the absorption of fat, milk, pus, or other substances. Emmert regards this appearance, not as chyle, but as a sign of an inflammatory condition of the blood, and analogous to the pleuritic crust. Internal absorption. From the analogy in structure of the lymphatics with the lacteals, Avhich unquestionably absorb a nutri- tive matter from the intestines, from the lymphatics constituting a part of the same system of vessels, and from the universality of their distribution, it has been inferred that their office is to ab- sorb and to convey to the circulation the elements detached from the organs, and certain principles separated from the secreted and excreted fluids. The direct proofs of this function of the lym- phatics, hoAvever, are not perfectly conclusive ; and one of the most eminent physiologists of the age considers the general doc- trine as resting on insufficient grounds. Some of the most im- portant facts in favour of lymphatic absorption are the following : Whenever acrid or poisonous substances, as, for example, the 'venereal virus, are imbibed into the system, or Avhen a person, in dissecting a dead body, is accidentally inoculated with the septic poison, Avith which corpses are sometimes tainted, it is generally the lymphatic system which first discovers marks of irritation. The lymphatic vessels, originating near the part to ABSORPTION. 287 which the poison is applied, frequently become inflamed, present- ing the appearance of red lines, and the lymphatic glands, to Avhich they lead, sometimes become enlarged and tender. Mascagni found in animals Avhich had died of pulmonary or abdominal hemorrhage, the lymphatics of the lungs and perito- neum full of blood. He also observed, in one instance, all the lymphatic vessels filled Avith the fluid of a dropsy. Desgenettes observed the lymphatics of the liver to contain a bitter lymph, and those of the kidneys lymph impregnated Avith urine. Soem- mering saw the lymphatics of the liver filled Avith bile, and those of the axilla Avith milk. And Dupuytren observed the lymphat- ics and the lymphatic glands, in the neighbourhood of a large suppurating tumour, situated at the internal part of the thigh filled with a fluid which had the characters of pus.* In caries of the bones, according to Soemmering, the lymphatics, in that vicinity have been seen filled Avith calcareous earth. Hunter injected water, coloured Avith indigo, into the peritoneum ; and saw the lymphatics of the abdomen assume a blue colour. The extirpa- tion of the lymphatic ganglions, if practised immediately after the insertion of certain poisons, or infectious matters, prevents the absorption of the latter in the corresponding parts. So, in cases of extravasation, the lymphatic vessels, which originate in the seats of the extravasated fluid, become engorged with it. In the experiments of Lawrence and Coates, which consisted in injecting certain substances, as the prussiate of potash, into the cavity of the abdomen, the chyle of the thoracic duct Avas found to contain this salt. When it Avas injected into the trachea of a living ani- mal, its presence Avas detected in one case in the thoracic duct; and in tAvo or three instances, indications of its presence were de- tected in the right side of the heart. In another curious experiment, a saturated solution of prussiate of potash was injected into the cellular tissue, over one side of the abdomen, and the same quan- tity of a strong solution of sulphate of iron Avas throAvn into the cavity of the abdomen, on the opposite side. In thirty-five min- utes the animal Avas bled to death ; and on examination the lungs Avere found to be of a deep blue colour throughout their whole texture. The thoracic duct, in its course in the thorax, was of a deep blue ; the chyle contained in it, the urine, and the coagulable lymph of the blood, Avere all blue. The day after, the chyle had thrown doAvn a blue deposit. Mascagni mentions an experiment which he made upon himself, and which appears decisive of the question of lymphatic absorption. Having immersed his feet several hours in water, he observed a slightly painful tumefaction of the inguinal glands, and a transudation of the fluid through the gland. From these and other similar facts, the absorbing function of * Adelon, 288 FIRST LINES 'OF PHYSIOLOGY. the lymphatics is almost universally admittea; but several distin- guished physiologists have revived the ancient doctrine of venous absorption, contending that the veins share this function with the lymphatics; and one eminent experimentalist has attempted to prove, that absorption is the exclusive prerogative of the veins. The subject of absorption, in relation to the mesenteric veins, has already been considered. If it be true that these veins partake with the lacteals in the office of absorbing substances from the alimentary canal, analogy would justify us in concluding, that the veins in other parts of the system must- participate with the lym- phatics in the same function. A well-knOAvn experiment of Magendie, has been considered as placing the doctrine of venous absorption beyond controversy. He separated the thigh of a dog from the body, dividing all the parts except the femoral artery and vein. Into each of these vessels, he introduced the barrel of a small quill, upon Avhich each of the vessels AA^ere secured by two ligatures, and then divided, in a circular direction, between the ligatures ; so that the two columns of blood, floAving in oppO- ' site directions in the femoral artery and vein, constituted the only vital connection between the limb and body of the animal. Tavo grains of a very subtle poison, Avere then forced into the cellular substance of the foot, and in about four minutes, the poison man- ifested its peculiar effects upon the animal. This experiment, however, does not appear absolutely decisive of the question, be- cause in forcing the poison by a blunt instrument into the cellular substance of the foot, some of the small veins must unavoidably have been lacerated; and in this Avay a portion of the poison directly introduced into the returning blood. Or, the poison might have been imbibed by the coats of the veins. The experiments of Lawrence and Coates demonstrate the absorption of the prus- siate of potash from the lungs,.by the pulmonary veins, the salt being detected in the left side of the heart in a Asav minutes after being injected into the trachea. According to Mayer, also, the prussiate of potash, injected into the lungs, is found in the blood sooner than in the chyle, and sooner in the left than, in the right side of the heart. Yet Avhen large quantities were injected, it was found largely in the venous blood of the right side of the heart, and in the inferior vena cava.* Absorption from the cellular tissue by veins, was also demon- strated by Lawrence and Coates, by repeating the experiment of Magendie, Avith the variation of substituting.the prussiate of pot- ash for a powerful poison. The result was equally striking, but like the other, perhaps, not wholly free from fallacy. In their experiment upon the prussiate of potash, injected into serous cavities, they found that absorption Avas accomplished prin- cipally, if not exclusively, by the lymphatics. * Rudolphi. ABSORPTION. 289 Magendie states that himself and Dupuytren had made more than one hundred and fifty experiments, in Avhich they had exposed a great number of different fluids to absorption, by the serous mem- branes, and that they had never seen them find their way into the lymphatics. The substances thus introduced into the serous cav- ities, produced their peculiar effects upon the system, with the same promptitude Avhen the thoracic duct was tied, as Avhen this canal was left unobstructed. Opium stupefied; wine intoxi- cated, &c. To these facts it may be added, that foreign substances applied to a granulating surface, have afterwards been discovered in the blood of the veins, but not in the lymphatics. One important fact remains to be noticed, viz. that pus is some- times found in veins coming from the vicinity of an abscess, a fact which appears to prove that it Avas absorbed by these vessels. Bourdon relates a remarkable case of this kind, in a man who died shortly after undergoing amputation of one of his thighs, on account of a fall which shattered his limbs to pieces. His peri- toneum Avas found highly inflamed ; and on examining the ampu- tated limb, the vena saphena was discovered to be full of pus, or rather it contained more pus than blood. In the iliac vein the proportion of blood Avas greater, yet even in this vessel there was found a good deal of pus. The veins on the opposite side also Avere filled with pus along the Avhole course of the leg and thigh. In pursuing the dissection of the Avhole limb very carefully, on arriving at the foot, a considerable effusion of pus Avas discovered, which was beyond all doubt the source of that found in the veins of the leg and thigh, and Avhich reached as high up as the iliac vein. Adelon is of opinion, that both veins and lymphatics are con- cerned in internal absorption, interstitial, recrenientitious, and excrementitious. These tAvo orders of vessels, he observes, are equally extended from the parts Avhere absorption takes place, to the centre of the circulation. They are both returning systems of vessels, and have their origins at the external and internal sur- faces, Avhere absorption occurs. An injection thrown into a vein or lymphatic, equally penetrates into the parenchyma of the organs, and oozes out at the surfaces, Avhich are the seats of the recrenientitious function. The lymph and the venous blood, Avhich circulate in these two orders of vessels, have the same des- tination, viz. after being blended writh the chyle, which is another product of absorption, to be converted in the lungs into arterial blood, The lymphatics and the veins have equally a capacity superior to that of the arteries; and hence there are the same rea- sons to believe that both of these orders of vessels return to the centre of the circulation something more than the residue of the arterial blood. Both of them also are provided with valves; and 37 290 FIRST LINES OF PHYSIOLOGY. they are connected Avith each other by numerous anastomoses. All that seems to be necessary to complete the analogy betAveen these two orders of vessels, is to suppose that their essential func- tions are the same, and that on the one hand the veins participate in what has .usually been regarded as the peculiar function of the lymphatics, viz. absorption, and on the other, that the lymphatics exercise an office analogous to that of the veins. The grounds of the first of these opinions have already been noticed, and they have proved satisfactory to the minds of many physiologists. The second, viz. that the lymphatics are not only absorbents, but veins, has also been adopted by some physiologists, and supported Avith very plausible reasons. This opinion regards the lymphatics as the veins of the Avhite or colourless tissues, as cartilage, tendon, ligament, the serous membranes, &c. These tissues in the healthy state are not supplied Avith red blood. They receive only colour- less vessels circulating a Avhite albuminous fluid. If the white tissues, however, are attacked with inflammation, these colourless vessels become sufficiently enlarged to carry red blood, and are then visible to the naked eye. Noav the doctrine of the venous function of the lymphatics supposes that these vessels carry back the residue of the colourless fluids from the white fluids, just as the veins return the residual or venous blood from the red. Ade- lon is of opinion that the materials of internal absorption are not merely imbibed, but are changed into lymph and venous blood at the moment of their absorption. Venous blood, he says, is as much formed by venous absorption out of the materials absorbed by the veins, as chyle is by the lacteals out of chyme. Neither lymph nor venous blood exists before the action of absorption. Several distinguished physiologists, hoAvever, are of opinion, that substances which find an entrance into the veins, are not absorbed by the mouths of these Aressels, but penetrate through their coats by imbibition. Mayo mentions the folloAving facts, most of them taken from Magendie, in favour of this opinion. A piece of fresh meat put in common salt, in a few days becomes penetrated throughout its Avhole mass Avith salt. In an animal opened some time after death, the parts in the vicinity of the gall-bladder are found deeply tinged with bile. If the theca vertebralis be opened in a living animal, or soon after death, it is found to contain a cer- tain quantity of fluid ; but a like quantity of fluid is not found in it if the examination be delayed till some time after death. If half an ounce of acidulated Avater be throAvn into the pericardium of a dog killed tAvelve hours before, and a continual stream of warm water be injected into the coronary arteries, so as to flow into the right auricle, in four or five minutes it gives unequivocal evidence of containing an acid. In an animal killed by a poi- soned arrow, the parts near the Avound become impregnated, to the depth of several lines, Avith a brownish yelloAV colour, and with the bitter taste belonging to the poison. ABSORPTION. 291 That imbibition takes place in living animal matter also, is established by many facts. If a drop of ink be put on the peri- toneum of a living animal, it soaks into it, and forms a large cir- cular stain, which penetrates through the membrane, and after a considerable time, to the subjacent tissues. If a small quantity of ink be introduced into the pleura of a puppy, in the course of an hour the pleura, the pericardium, the intercostal muscles, and the surface of the heart itself, assume a blackish tinge. If the jugular vein of a living puppy be raised from its place and sepa- rated from the neighbouring parts by a piece of card, and the vessel be carefully denuded of the surrounding cellular textures, and a strong aqueous solution of the alcoholic extract of nux vomica be placed upon the middle of the card, so as to surround and bathe the vein, the usual effects of the poison manifest them- selves in less than four minutes. Magendie found the same re- sults to folloAV when the experirnent Avas made on a large arterial trunk; only they Avere much less prompt, owing to the greater thickness of the arterial coats, and the superior compactness of their texture. More than a quarter of an hour was necessary for the passage of the nux vomica through the coats of the artery. Emmert saw all the symptoms of poisoning Avith prussic acid pro- duced in a couple of rabbits, by applying the oil of bitter almonds to the sound skin of the back. The muscles under the skin, even as deep as the bones, had the smell of the prussic acid. The effect of suction, of ligatures, and of the application of cupping glasses in preventing the absorption of poison, are all favourable to the idea, that it finds a passage into the system by imbibition. Magendie ascertained the fact, that a state of distention of the vessels is unfavourable to imbibition. He injected a large quan- tity of Avater into the veins of a dog, and having introduced a poison into the cavity of the pleura, he Avaited nearly half an hour to Avitness its effects, which in other cases required only about two minutes to manifest themselves. He then bled the animal largely in the jugular vein, and as the blood flowed, the poison began to manifest its effects. Hence he concluded that absorp- tion is inversely as the distention of the vessels. On the same principle, perhaps, absorption is promoted by inanition, exhausting discharges, and all causes Avhich diminish the mass of the fluids, or retard the motion of the blood. Hence medicines act with most power if given in the morning on an empty stomach. Ex- posure to contagion is said to be most dangerous under the same circumstances. Absorption is very active after long sickness, after the operation of purgatives, after blood-letting, and long fasting. Intoxication is most apt to occur cet. par. in hungry, feeble, and exhausted persons. On this principle, probably, depends the quicker disappearance of extravasated blood, dropsical effusion, &c. under a scanty diet. 292 FIRST LINES OF PHYSIOLOGY. Magendie conjectures that the cause of imbibition is the affinity of the coats of the vessels for the substances absorbed. The serous membranes, and the cellular tissue, according to the same physiologist, are, particularly during life, the best agents of im- bibition. Fodera ascertained that iriibibition is very much accelerated by galvanism. A solution of prussiate of potash was injected into the pleura, and a solution of sulphate of iron, into the abdo- men of a living animal. Under ordinary circumstances, five or six minutes are required for the two substances to come into con- tact, by imbibition through the diaphragm. But if a light gal- vanic current Avere transmitted through the diaphragm, the passage took place instantaneously. The same result was obtained, when one of the solutions was placed in the bladder, and the other in the abdomen; or one in the lungs, and the other in the cavity of the pleura. It appears, on the whole, that the subject of venous absorption is involved in no little obscurity, though the facts and considera- tions in favour of this alleged function of the veins, appear to preponderate over those of a contrary tendency. Whether, how- ever, substances which obtain an entrance into these vessels are absorbed by open orifices, or are imbibed by their coats; or whether they find their way thither by both these avenues, is a question of secondary importance. The great fact seems to be fully established, that many foreign substances find their way into the system, principally, if not exclusively, by this channel, and whether they owe this prerogative to a vital or a physical cause, is evidently of no consequence ; since, in either case, the result, as far as we know, is the same, and the means of effecting it were undoubtedly not a matter of accident, but of choice. Admitting the reality of venous absorption, Ave shall have three classes of vessels endoAved with the function of absorption, viz. the lacteals, lymphatics, and veins; and from the Avise frugality of nature in the use of means in accomplishing her intentions, it may be rationally inferred, that each of these systems of vessels performs a distinct and peculiar office in the general function of absorption. Dr. Handyside of Edinburgh, accordingly, has at- tempted to allot to each its appropriate office in the folloAving positions, founded on experiments made either by himself or by other physiologists: 1. That the lacteals absorb aliment, and nothing else. 2. That the lymphatics absorb the debris of the body, or the molecules which have become useless, and must be removed to make room for the deposition of new matter. 3. That the veins, besides returning the blood to the heart, absorb various foreign substances. Lymph is obtained with difficulty from the lymphatic vessels, on account of the tenuity and transparency of these vessels, and ABSORPTION. 293 the circumstance that they are not always filled with this fluid. It may, however, be obtained from the thoracic duct of an ani- mal which has been kept from food for three or four days. It then presents the following characters. It is a nearly transparent colourless fluid, or, according to some physiologists, of a slightly opaline colour, tinged •with red. Its rose colour is said to be deeper the longer the animal from Avhich it is taken has fasted. It has a strong spermatic odour, and a saline taste. The motion of the lymph is slow. When one of these vessels is punctured, the lymph is said to issue out very sloAvly. The lymphatics possess a contractile poAver, and frequently empty themselves as soon as they are exposed to the air. Hence they are almost always found empty in an animal recently dead. Their contractile power may probably be assisted by the me- chanical compression, Avhich they undergo from the contraction of the neighbouring muscles; from the pulsation of the arteries with which they are in contact; from the pressure of the dis- tended holloAv organs, and other causes ; and. the motions there impressed upon them, and communicated to their contents, are determined by the disposition of their valves in the direction of the thoracic duct. Avhere the lymph mingles Avith the chyle. The conglobate glands have been supposed to perform the office of more completely assimilating the heterogeneous princi- ples which enter into the composition of the lymph, and perhaps of arresting and separating any noxious ingredient, so as to pre- vent its passage into the blood-vessels. In favour of this last conjecture, may be mentioned the swelling of the conglobate glands, which lie in the course of branches of the lymphatics, by Avhich poisonous or noxious substances have been absorbed. In these cases, Avhich are of common occurrence, the poisonous sub- stance appears to be arrested in its course to the circulation, by the lymphatic gland, Avhich it irritates and inflames, and which sometimes suppurates, a process by Avhich the poison may be de- stroyed or evacuated. Or, if suppuration should not take place, the noxious principle may be neutralized or assimilated, by the peculiar action of the gland, and thus disarmed of its power of doing mischief. In certain situations, or under particular circumstances, the lym- phatic glands become coloured. Thus the glands which receive the lymphatics of the liver are of a yelloAvish colour, derived probably from the colouring matter of the bile. The bronchial glands are black ; the mesenteric glands of animals fed with mad- der become red ; facts Avhich render it probable that the colouring matter is arrested in its course to the circulation, and perhaps, after a time, assimilated or destroyed by the peculiar action of the gland. 294 FIRST LINES OF PHYSIOLOGY. CHAPTER XVIII. SECRETION. ^ In speaking of the fluids of the system, it Avas observed that they might be divided into three classes, viz : 1. those which serve for the preparation of the blood, 2. those which are formed out of the blood ; and 3. the blood itself. The first and the last of these, viz. the chyle, lymph, and the blood, have already been described. It remains in this place to consider the second class, viz. those formed out of the blood, or the secreted fluids, and the process by which they are prepared, or the function of secre- tion. Secretion may be defined the vital action of the secretory organs upon the blood, by which they extract from it, and com- bine together, the elements of a fluid which had no existence in the blood previous to this elaboration. This function is one of the most obscure and mysterious in the animal economy. The vessels subservient to it Mr. Hunter used to call the architects and chemists of the system, expressing by these terms the plastic powers of these agents, Avhich, out of the same homogeneous fluid, the blood, could construct such a variety of wonderful fabrics, and compound such a diversity of chemical products. The vital nature of the function of secretion is evident from many facts and considerations. The division or compression of the nerves, distributed to a secretory organ, is said to suspend this function, and the peculiar fluid prepared by the organ, we are told, is no longer secreted. The secretions are also liable to great variations in their degrees of activity, and in their results, from the peculiar condition of the vital poAvers of the secretory organs. Hence the secreted fluids are constantly changing, not only in quantity, but in their qualities, in consequence of the fluctuations occurring in the state of the vital poAvers of the glands, Avhich prepare them. Moral causes, as is well known, have a powerful influence upon the secretions. SorroAv and profound grief per- vert the qualities of the bile. A fit of anger sometimes causes an increased secretion of this fluid. The same passion has also been known to produce such a change in the qualities of the milk, in a nurse, that the child Avhich she suckled was frequently seized with vomiting and convulsions; a fact Avhich Lepelletier says he had often witnessed. Morbid states of the secretory organs materially affect the qual- ities of the fluids prepared by them. Thus the cellular membrane, and several of the other surfaces, when inflamed, secrete pus; the pleura and peritoneum, when in the same morbid state, secrete SECRETION. 295 fibrin, and sometimes pus. The bile in a diseased state of the liver, differs materially from the healthy fluid; and the secretion of the kidneys becomes exceedingly depraved in certain diseases of these organs. In its simplest form secretion seems to be merely a separation of some element or principle already existing in the blood. In this manner a serous fluid is separated from the blood, and deposited upon certain surfaces by a kind of arterial exhalation. This kind of secretion may be illustrated by a fact, which is observed when the body is injected Avith size and vermilion throAvn into the aorta; for then there is found in the serous cavities a quantity of colourless size, Avhich must have been strained through very mi- nute orifices.* That this is not a mere mechanical filtration, however, is evident from the fact, that when membranes, which in their healthy state are lubricated by a serous exudation, be- come diseased, the fluid exhaled by them differs materially in its properties from the healthy secretion. Warm water injected into the veins, also, filters through serous surfaces. It has been ascertained by experiment that the blood contains, ready formed, some of the principles Avhich exist in certain of the secretions, as well as some of the peculiar kinds of animal matter of which the organs are composed. Thus fibrin, or the basis of muscular flesh, is one of the elements of the blood. A peculiar substance, ascertained to be the basis of nervous matter, has also been detected in the blood. Some of the elements of the bile, also, have been discovered in the serum of the blood. Another curious fact discovered by Prevost and Dumas is, that after the extirpation of the kidneys, a sensible quantity of urea may be found in the blood ; from which it has been inferred that the kid- neys do not form this substance, but only separate it from the blood. If this Avere the case, hoAvever, it seems difficult to ac- count for the fact, that not a trace of urea can be found in the blood of animals Avho have not undergone this operation. An- other curious fact of a similar kind is, that the blood of a frog, after the extirpation of the testicles, has been found capable of fecundating the female spaAvn. From the imperfect state of ani- mal chemistry, it is probable that several principles may exist in the blood, Avhich our present means of analysis will not enable us to detect, Dupuytren injected tAvo ounces of bile into the veins of a dog, but the blood of the animal, which Avas analyzed a feAv moments afterwards by Thenard, exhibited not a trace of bile.f If it could be proved, hoAvever, that all the substances of Avhich the secreted fluids consist, pre-existed in the blood, it Avould not folloAV that the process of secretion is a mere mechanical separa- tion of these substances from the blood. It would still be neces- * Mayo. t Lepelletier. 296 FIRST LINES OF PHYSIOLOGY. sary to suppose some peculiar elective power in the vessels of the secretory organs, by which the peculiar secretion of each gland should be separated from the mass of the blood, and collected in the excretory vessels of the gland. No mechanical filtration Avould be adequate to separate the neurine or cholesterine from the blood; or to select the numerous principles which are formed in the urine, and to combine them together into this fluid. The process must be a chemico-vital, or dynamic one, even in the sim- plest case of secretion; a conclusion which is confirmed by the fact, that secretion is so much influenced by the state of the vital or nervous power of the system at large, or of the secreting organ itself. But with respect to much the greater part of the secreted fluids, we have no evidence that they pre-exist in the blood. They cannot, therefore be considered as educts, but must be regarded as the products of secretion. We must consider them as formed by the secretory vessels, out of principles furnished by the blood, which these vessels themselves have the power of selecting out of the general mass, and of combining together into new com- pounds. Of the nature of the process, or the means employed by the secretory vessels in accomplishing it, we are wholly in the dark. Wollaston conjectured that electricity may have some agency in secretion, an idea Avhich he illustrated by a very inge- nious experiment. He took a glass tube, about tAvo inches long, and three quarters of an inch in diameter, and closed one extrem- ity with a piece of bladder. He then poured into the tube a little water, containing, in solution, a minute quantity of muriate of soda. After moistening the bladder, he placed it on a bit of silver; then bent a fine zinc Avire, so that one of its extremities touched the piece of silver, and the other penetrated into the tube, to the depth of about an inch. At the same moment the external surface of the bladder indicated the presence of pure soda. There was, therefore, from this \^ery weak action of the electric fluid, a decomposition of the marine salt, by which the soda was separa- ted from the acid, passed through the bladder, and Avas deposited on its external surface. Dr. Young suggests an explanation of the mode in which elec- tricity may be supposed to act in the process of secretion. "We may imagine," he observes, "that at the-subdivision of a minute artery a nervous filament pierces it on one side, and affords a pole positively electrical, and another opposite filament, a negative pole ; then the particles of oxygen and nitrogen, contained in the blood, being most attracted by the positive point, tend towards the branch Avhich is nearest to it, Avhile those of the hydrogen and carbon take the opposite channel; and that both these por- tions may again be subdivided, if it be required, and the fluid, thus analyzed, may be recombined into new forms, by the reunion of a certain number of each of the kinds of minute ramifications. SECRETION. 297 In some cases the apparatus may be someAvhat more simple than this; in others, perhaps, much more complicated."* The structure, or organization, by Avhich secretion is effected, is of three kinds : 1. The first and simplest consists merely of capillary vessels, minutely ramified. This kind of structure is employed in the separation of those fluids Avhich are designed to moisten and lubricate certain cavities and surfaces of the body. Thus, the pleura and peritoneum are kept moist by a serous fluid, separated from the blood by this simple kind of structure. There is some difference of opinion among anatomists respecting the disposition and nature of these vessels. Some suppose that they consist of the ultimate divisions of the arterial branches. Others suppose that these vessels are pierced Avith a great number of lateral pores, through which the secreted fluids exude. But Bichat, and many other modern anatomists, assume the existence of a particular order of vessels, proceeding from the capillary arteries, denominated exha- lants, of a peculiar texture and properties, and giving passage, in the healthy state, only to Avhite or colourless fluids. These exha- lant vessels are supposed to possess some peculiarities of structure and properties, in each of the different tissues of Avhich they form a part. Hence the differences which exist in the fluids exhaled from the skin, the mucous, serous, and synovial, &c. membranes, viz. the sweat, the exhalations in the mucous cavities, the serosity which lubricates the serous sacs, &c. The fluids exhaled by these vessels are deposited either on surfaces which communicate Avith the external air, and are eliminated from the system, in the form of a fluid or vapour, — or, in closed cavities, from Avhich they are again taken into the system by absorption. The fluids thus separated by exhalation, or perspiration, from the blood, may be reduced to the folloAving heads: 1. cutaneous; 2. mucous; 3. serous; 4. synovial; 5. cellular; 6. medullary; 7. ocular; 8. vascular. 2. Another kind of structure, one degree more complicated, is that of the glandular follicles. These are small, bottle-shaped sacs, lodged in the substance of the membranes in Avhich they are situated, with their mouths opening on the surface of these mem- branes. Their cavities are lined by a continuation of the mucous membrane, which is supplied Avith a considerable number of nerves and blood-vessels. The external coat of the follicles appears to possess a certain degree of contractility, since the expulsion of the matter secreted by them is accomplished by the contraction of these bodies themselves. Indeed, Haller supposed that they pos- sessed muscular fibres analogous to those Avhich exist in the uri- nary bladder. The fluid secreted in these cavities remains some * Med. Literat. p. 109. 38 298 FIRST LINES OF PHYSIOLOGY- time, during which its consistency is gradually increased by the absorption of its more fluid parts. But Avhen the membrane in which they are seated is irritated, and requires to be moistened, they contract and expel the fluid they had secreted. Mucous follicles, or crypts, are found only in the membranes of relation, viz. the mucous membranes, and the skin. They open only on the free surfaces of these membranes, and this circum- stance, together Avith the unctuous quality of the follicular secre- tions, sufficiently proves that they are designed to lubricate these membranes, and to screen them in some degree from the contact of foreign substances, to which, as membranes of relation, they are constantly subject. There are three kinds of fluids prepared by follicular secretion, viz. mucus, sebaceous matter, and the ceru- men of the ears. • 3. The third, and most complicated kind of structure, subser- vient to secretion, is that of the conglomerate glands. These are large organs of a peculiar structure, which constitute several of the viscera. They are formed by a large number of arteries, veins, nerves, and lymphatics, disposed in a peculiar manner, and connected together by a tissue of cellular membrane. When con- tained in a cavity, they are invested on their external surface Avith a coat derived from the membrane Avhich lines the cavity; and they are provided Avith a canal, called the excretory duct. This duct, throughout all its ramifications in the gland, is lined Avith mucous membrane. With regard to the ultimate structure of glands, anatomists have been divided in opinion. Malpighi maintained that the parenchyma of glands is formed of hollow globules, or acini, each of Avhich might be considered as a follicle, intermediate between the ter- mination of the blood-vessels of the gland, and the origins of the excretory ducts. Ruysch, on the contrary, contended, that these acini Avere nothing more than inextricable plexuses of blood-ves- sels, and excretory ducts continuous Avith them, and that secretion is accomplished at the place of their communication. The opin- ion of Rusych, according to Bhimenbach, is much the most con- sistent Avith microscopical observations, and the effects of minute injections. Still, some anatomists are of opinion that some pecu- liar kind of structure, or parenchyma, exists in the glands inter- mediate between the blood-vessels and excretory ducts; and that this parenchyma presents the peculiar and characteristic part of the organ in which its secretory function is performed; and that it varies in its structure and physiological properties in each spe- cies of gland. Besides this fundamental tissue of the glands, arte- ries, veins, lymphatics, nerves, excretory ducts, and cellular tissue, to connect the whole together, enter into the structure of these organs. Some of the glands are provided with a reservoir, or mem- branous sac, in which the product of their secretion is deposited SECRETION. 299 for a time, and its essential principles concentrated by the absorp- tion of its aqueous parts. These sacs are lined interiorly by a mucous membrane, and externally they are formed of a mem- brane which some anatomists have considered as of a muscular nature, since it possesses the poAver of contracting, and thus of expelling from its caviiy the secreted fluid deposited in it. The phenomena of glandular secretion may be reduced to the four folloAving. 1. Excitation of the gland, during Avhich the blood flows to it in increased quantity. 2. The peculiar action of the glandular parenchyma, or secretion, a chemico-vital process sui generis. 3. The deposit of the fluid, secreted in the reservoir of the secretion. This fluid immediately after its secretion is absorbed by the radicles of the excretory duct, is transmitted through this canal by means of its insensible contractility, and deposited in the reservoir, if one exist; othenvise, it is conveyed by the excretory duct to the place, of its destination. 4. Excre- tion. While the secreted fluid is detained in the receptacle, it becomes more concentrated by the absorption of its thinner parts, by Avhich it is rendered more exciting to the Avails of this cavity; Avhile, by its increasing accumulation, it acts as a physical stim- ulus. The parietes of the receptacle at length react, by their contractility, upon the secreted fluid, Avhich is gradually forced out of the cavity; and, in some instances, certain muscles, sub- servient to the excretion, are excited sympathetically into action, to promote the expulsion of the secreted matter. In some cases, excretion as Avell as secretion is excited by a stimulus, acting upon the interior of the canal into Avhich.the excretory duct opens. The glandular secretions may be divided into the seven fol- lowing kinds, viz. the lachrymal, salivary, pancreatic, biliary, lactic, urinary, and spermatic. Classification of the Secreted Fluids. The secreted fluids have been classified on different principles. 1. According to their composition, or chemical nature. 2. Ac- cording to their destination and uses in the animal economy. 3. According to their degree of cohesion or consistency. 4. Accord- ing to the structure of the organ by which they are secreted. I. In relation to their composition, the secreted fluids may be divided into five classes, viz.— 1. The serous, or watery, resembling the serum of the blood, and composed of a large proportion of water, a little albumen in solution, and salts, existing in the latter. To this class belong the serosity of the serous membranes, and of the articulations, that of the cellular tissue, of the chambers of the eye, of the cap- sule of the crystalline lens, and of the labyrinth of the ear. 2. The albuminous, distinguished by the presence of a large quantity of albumen. To this class belong the pancreatic and 300 FIRST LINES OF PHYSIOLOGY. spermatic fluids, and the milk, Avhich contains, besides a serous fluid, an oily matter, and several salts. 3. The mucous, Avhich are characterized by the presence of a large proportion of animal mucus ; as the mucus of the mucous membranes, that of the mouth, fauces, stomach, intestinal canal, nose, air-passages of the lungs, and urinary and genital organs; and, in most animals Avhich live in the water, the fluid which lubricates the surface of the skin. 4. The fat or oily, as the fat of the cellular tissue, the marrow of the bones, the fluid secreted by the crypts, or follicles of the skin, the cerumen of the ears, the secretion of the meibomian glands, and the sebaceous matter of the prepuce. 5. The mixed, as the saliva, the bile, the urine, the tears, which contain several salts and peculiar animal principles. II. In respect to their uses in the animal economy, the secreted fluids have been divided into two classes, viz. the recrementitious, and the excrementitious; the first, including those Avhich are destined to be absorbed, and returned into the mass of blood, and which are deposited in cavities Avhich have no external outlet; the second, comprehending those Avhich are designed, after their formation, to be expelled from the system, and which are depo- sited in cavities, or on surfaces, Avhich communicate with the ex- ternal air. To the first class, or that of the recrenientitious secretions, belong the exhalations into the cellular membrane, and the serous cavities; the synovial fluid, the oily fluid of the cellular tissue, and that of the round bones, and the aqueous humour of the eye. The excrementitious secretions may be divided into two orders, viz. those which, though destined to be discharged from the sys- tem, are yet designed to perform certain offices before their re- moval ; and, secondly, such as are strictly and exclusively excre- mentitious, and which serve no other purpose than to depurate the blood. The first order embraces the saliva, the gastric fluid, the bile, milk, and several others. The latter comprehends the urine, and the exhalations from the skin and lungs. Berzelius has made the interesting remark, that the secretions, or the fluids destined to be employed within the system for par- ticular purposes, are alkaline; while the excretions, or those des- tined to be evacuated, are all acid. To the excretions, Berzelius refers the urine, the fluid of perspiration, and the milk. All the others belong to the class of secretions. This observation of Berzelius, however, has been contradicted by Schultze, who says, that he has not found it verified in any species of animal. The same secreted fluid, he says, in one kind of animal is acid, in another alkaline, in a third indifferent, as he has ascertained by more than a hundred experiments ; whence he conceives it impossible to establish any general law on the subject. SECRETION. 301 Thus, of the secretions ; the bile is an alkaline fluid, contain- ing, besides various salts, and some animal principles^ a small quantity of uncombined soda. The spermatic fluid also contains about one per cent, of free soda. The tears, the saliva, and the pancreatic fluid, all contain the same alkali. On the other hand, the excreted fluids, the urine, the matter of perspiration, and the milk, are all characterized by possessing acid properties. They all contain a free acid, which, according to Berzelius, is the lactic. Milk contains six parts in one thou- sand of this acid, besides various salts, in some of which, it exists in a state of combination. The matter of perspiration also con- tains a small portion of acid, Avhich Thenard considers as the acetic, but Berzelius conceives it to be the lactic acid. The skin, also, exhales carbonic acid. That the urine is an acid fluid, is evident from the fact, that recent human urine reddens litmus paper, an effect Avhich, according to Berzelius, is OAving to the presence of lactic and uric acids, in a free state ; but, according to Dr. Prout, depends on two super-salts, which exist in the urine, viz. the superlithate, and superphosphate of ammonia. The halitus of pulmonary exhalation, which may be regarded as one of the excretions, affords another exemplification of the principle of Berzelius. This ATapour contains carbonic acid; and this, as it is generally supposed, is produced by the acidification of the carbon of the venous blood. A curious fact, first men- tioned by Bichat, may be referred to the same principle. If a solution of phosphorus be injected into the veins of an animal, fumes of phosphoric acid are poured forth from the lungs, formed by the acidification of the phosphorus in the pulmonary exhalants. Tiedemann observes, that, betAveen the secreted and excreted fluids, there exists this difference, viz. that the former contain globules, or organic molecules, of Avhich no traces can be dis- covered in the latter. Thus, globules have been found in the saliva, the pancreatic and the spermatic fluids, and the milk, which he ranks among the secretions ; Avhile none have been discovered in the urine, the bile, the tears, &c. The bile and tears, it will be observed, Tiedemann assigns to the excretions. III. In relation to their degree of cohesion and consistency, the secreted fluids may be divided into the aeriform and the liquid. To the first class belong the exhalations from the skin, and the organs of respiration. All the other secretions belong to the second, or that of the liquid secretions. These, however, differ exceedingly in their consistency. Some of them, as the serosity of the serous membranes, and that of the cellular tissue, the aqueous humour of the eye, and the liquor of Cotunnius, are nearly as fluid as water, though their specific gravity is greater. Next to these in cohesion, may be ranked the tears, the urine, and sweat. The saliva, the pancreatic fluid, the bile, the mucus, synovia, milk, and the spermatic liquor, possess a still greater 302 FIRST LINES OF PHYSIOLOGY. degree of consistency, and some of them are viscid and ropy. But the oily secretions, as the fat, the marrow of the bones, the cerumen, and the matter secreted by the follicles of the skin, are still more consistent, and even require a certain degree of heat to render them fluid. IV. The secreted fluids, considered in reference to the structure of the organs by which they are. prepared, may be divided into three classes, viz. the perspiratory, or, the exhalations, the follic- ular and the glandular. The perspiratory secretions, or the exhalations, take place either in cavities Avhich have no external opening, or on the skin, or mucous membranes. Hence, they have been divided into exterior and interior exhalations. The exterior exhalations comprehend those of the mucous membranes and of the skin; the interior, the serous, synovial, cellular, medullary, ocular, and some others. The exterior exhalations Avill be considered first. Cutaneous Exhalation, or Perspiration. The secretion from the skin is an albuminous halitus, or vapour, Avhich is perpetually exhaled from its outer surface, and is termed, the insensible perspiration, though it possesses qualities Avhich frequently fall under the notice of the senses.* It often has a sensible odour, and frequently instead of assuming the form of an invisible vapour, it is deposited on the skin in drops of a colour- less liquid, which is called sweat. The instruments of this ex- halation, are the numerous exhalant arteries, wThich enter into the texture of the skin, and open upon the surface of this membrane. According to Breschet and De Vauzeme, the skin is provided-Avith a distinct apparatus for the secretion of the cutaneous fluid, con- sisting of a glandular parenchyma, and of canals for conveying the secretion to the surface of the body. These excretory canals are disposed in a spiral form, and open obliquely under the scales of the epidermis. The process of cutaneous exhalation goes on Avithout intermission during life. The fluid is constantly issuing from the skin in the form of a vapour, which is immediately dis- solved by the air, or absorbed by the clothing, and forms a kind of atmosphere round the body. When condensed into a liquid, the matter of perspiration is a colourless fluid, heavier than water; and is composed of water, a small quantity of free acetic acid, hydrochlorate of soda and pot- ash, a little phosphate of lime, a little animal matter, and carbonic * Dr. Edwards has shown, that the skin performs a function analogous to respiration; and that animals of the frog kind will live longer deprived of their lungs than of their skin. Under the former mutilation they were found to live several days ; in two cases out of three, thirty-three days; under the latter, or the loss of the skin, they lived only a few hours. SECRETION. 303 acid; and according to Thenard, a trace of oxide of iron.* The presence of a free acid in it is sometimes very evident, from its rank sourish smell. The matter Avith which the skin becomes incrusted, where habits of cleanliness are neglected, Avas analyzed by Vauquelin and Fourcroy, and found to consist almost Avholly of phosphate of lime. The animal matter is the source of the peculiar odour Avhich distinguishes different animals, and which varies, probably, in every individual of each species. This odour is subject to many variations, from a variety of circumstances, as the age, temperament, sex, nature of the aliments, use of medi- cine, healthy or pathological state, &c. In jaundice, it is said that the cutaneous transpiration has.the odour of musk; in scrophu- lous persons that of sour mucilage ; in scurvy, the smell of sul- phuretted hydrogen ; and in the latter stages of many fatal dis- eases, that of animal matter in a state of putrefaction ; f characters, Avhich might perhaps be turned to account in the diagnosis of many diseases. The peculiar odour, with Avhich the cutaneous perspiration becomes tainted in certain diseases, is owing to the presence of certain principles Avhich become accidentally com- bined Avith it. Thus Orfila, according to Lepelletier, demonstra- ted the presence of bile in the sweat of patients affected with the jaundice. The cutaneous transpiration in putrid fevers, contains, according to Deyeux and Parmentier, ammonia, and in milk fever, according to Berthollet, a free acid. A very curious fact in rela- tion to the odour of the cutaneous exhalation, is mentioned by Speranza, an Italian physician. A man of a robust constitution, after a hard day's work, perceived that his left fore-arm exhaled from its internal surface, a peculiar aromatic odour, like- that, of the Peruvian balsam, or the vapour of amber or benzoin throAvn upon ignited coals. This odour Avas extremely powerful, so as even to impregnate the chamber in Avhich he slept; arid it Avas increased by friction. It continued tAvo months and then disap- peared after a violent attack of fever. It is difficult to ascertain the amount of this secretion. Many experiments have been made on the subject, but Avith contradic- tory results. It is unquestionably one of the most abundant of the excretions, and some have estimated it to exceed all the rest collectively. According to Dodard, it averages in France, an ounce every hour; and bears to the solid excretions the ratio of seven to one, and to all the excretions together, that of tAvelve to fifteen. According to Robinson, in Scotland the cutaneous per- spiration in youth bears to the urine the ratio of 1340 to 1000, "It appears that not only carbonic acid, hut azote also, is exhaled by the skin; and according to Abernethy, in the proportion of two parts of the former, to one of the lat- ter • anifwe are informed by Collard de Al.irtigny, that a full diet of animal food in- creases the proportion of azote, while a diet of vegetable food, or ot white meats, causes an increased proportion of carbonic acid. t Lepelletier. 304 FIRST LINES OF THYSIOLOGY. or about 3£ to 10, and in old age, that of 967 to 1000. Sauvages states that sixty ounces of ingesta furnish five ounces of fasces, twenty-two of urine, and thirty-three of cutaneous perspiration. It is much influenced in its amount by season, climate, age, man- ner of life, sickness, health, and probably other circumstances. Thus, in the Avarm months of the year, the cutaneous secretion has been found to bear to the urine the proportion of five to three ; but in the cold months not to exceed that of two to three. In the temperate months, the tAvo excretions have been observed to balance each other. In old age, the urinary secretion exceeds that of the skin, and the reverse is true in infancy. The cuta- neous exhalation exceeds the pulmonary in the ratio of about eleven to seven. According to Lavoisier and Seguin, the greatest quantity of the insensible perspiration is thirty-two grains a minute ; equal to three ounces, tAvo drachms, and forty-eight grains an hour; and five pounds a day. Its smallest amount is eleven grains a minute, or one pound eleven and a half ounces a day. Its average quan- tity is estimated at eighteen grains a minute, of which eleven are furnished by the skin, and seven by the lungs. Several other estimates, founded on observation, have been made by other physiologists, which do not differ materially from those of Lavoisier and Seguin. Mr. Dalton, however, in a series of experiments Avhich he performed on this subject, arrived at very different results. Mr. Dalton found that in the month of March, his daily con- sumption of solid food Avas thirty-eight ounces, and of fluid, fifty- three ounces; amounting in the whole to ninety-one ounces, or nearly six pounds. During this time he eA^acuated daily forty- eight and a half ounces of urine, and five ounces of fasces, leaving thirty-seven and a half ounces, or about two-fifths of the whole to be accounted for, Avhich must have been lost by cutaneous and pulmonary exhalation. In the month of June a similar series of experiments gave some- Avhat different results. The solids consumed per day amounted to thirty-four ounces; the fluids, to fifty-six ounces; total, ninety ounces. Daily evacuations of urine, forty-tAvo ounces, of fasces, four and a half ounces; leaving nearly forty-four ounces, or almost one half, for the daily loss by cutaneous and pulmonary exhalation. According to Mr. Dalton's estimate, the Avhole amount of the insensible perspiration from the Avhole surface of the body, is only one-fifth of the quantity exhaled from the lungs. He found that he exhaled from his lungs 2.8 lbs. troy, of carbonic acid, con- taining nearly ten ounces and a quarter of carbon, in twenty-four hours. He also ascertained that he exhaled not exceeding tAventy and a half ounces of aqueous vapour, making the Avhole amount of water and carbon discharged from the lungs in one day thirty SECRETION. 305 ounces and three quarters. This taken from thirty-seven and a half ounces, the total of cutaneous and pulmonary exhalation, leaves only six ounces and three quarters per day for the insen- sible perspiration, consisting of six ounces and a half of water, and a quarter of an ounce of carbon. In Dalton's experiments, about an ounce and a half of azote were taken into the stomach daily, in the form of flesh, cheese, and milk ; and nearly the whole of it, or rather about the same quantity must have passed off by the kidneys and intestinal canal. It appears, therefore, that Dalton differs very widely in his estimate of the amount of the insensible perspiration, from other physiologists who have investigated the subject. While the latter estimate it at more than thirty ounces, Mr. Dalton reduces it to less than one quarter of this quantity; and while they calculate that the cutaneous exhalation exceeds the pulmonary in the ratio of eleven to seven, Mr. Dalton infers that the pulmonary is five times as great as the cutaneous. The cutaneous exhalation, it appears, attains its maximum during the six hours before noon ; it falls to its loAvest point im- mediately after eating, and again increases during digestion. Ac- cording to EdAvards, it is increased by sleep, by a dry state of the air, and by exposure to heat. He also supposes it to be in- fluenced by atmospheric pressure. Impaired digestion is said to diminish it very much ; yet the author has known a case of very severe and obstinate dyspepsia, in which during digestion the sweat Avould fall in large drops from the ends of the fingers. Here it may be observed, that Avhatever quantity of food a person may take, and Avhatever increase of Aveight he may acquire after eating, if he has attained his full groAvth, and is in good health, he always returns, after the expiration of twenty-four hours, to the same Aveight. In general, insensible perspiration is most abundant in infancy, Avhen it is sourish to the smell; and least so in old age. It is more abundant in men than in Avomen, in whom it becomes acid during menstruation. It increases in summer, diminishes in Avin- ter, and is much more copious in hot than in cold climates. It also varies much with the degree of excitation of the skin. When this organ is directly excited by friction, or sympathetically, from its connection Avith the organs, the cutaneous exhalation is much increased. When the blood contains a large proportion of water, this function frequently becomes more active; and the same is true Avhen some of the other excretions are not performed with their usual activity; the defects being compensated by the in- creased activity of the cutaneous exhalation. If the quantity of the insensible perspiration increases, that of the urinary and in- testinal excretions is diminished. The quantity of the blood is another circumstance Avhich influences this secretion. Plethoric 39 306 FIRST LINES OF PHYSIOLOGY. persons frequently perspire copiously. Exercise, by increasing the velocity of the blood, is frequently accompanied and folloAved by SAveating. Magendie mentions a person Avho could always bring on SAveating Avhile in bed, merely by forcibly contracting his muscles for a feAv moments. Taking Avarm drink is often followed by sweating. A circumstance which points out the in- fluence of the nervous system upon this function is, that certain mental emotions, as fear and great perplexity of mind, are some- times attended Avith profuse sweating. Certain parts of the body perspire more easily and more copi- ously than others ; as for example, the hands and feet, the axillas, the groins, the forehead, &c. These parts receive proportionably a greater quantity of blood than others, and some of them are secured from the contact of the air, as the axillas and the soles of the feet. This exhalation also differs in its odour, and per- haps in its composition, in different parts of the body. Its acidity seems to be greatest in the axillas, as appears from the red stain it frequently communicates to blue garments, under the arm-pits. As certain circumstances, especially a dry state of the air, and a diminished barometrical pressure promote both physical evapo- ration and insensible cutaneous perspiration, Edwards has been led to distinguish in this function of the skin, two elements, viz. a vital and a physical one, or secretion and evaporation. On placing frogs at a loAver temperature both in a dry and a moist air, and comparing the losses of weight Avhich they suffered in these different circumstances, the fluid lost by secretion, compared Avith that Avhich disappeared by transpiration, appeared to be in the ratio of one to six ; from Avhich it may be inferred that we lose much more fluid from the skin by evaporation than by secretion. The uses of this function in the animal economy are various. It is evident that it is subservient to the decomposition of the body. It depurates the blood of carbonic acid, and many saline ingredients, like respiration and the renal secretion, and Avith this last it has an intimate connection. In many animals it is the only excretion subservient to the decomposition of the organs; as no apparatus for the secretion of the urine exists in them. Another important use of this secretion is, to absorb and carry off the excess of animal heat, and to prevent the elevation of the temperature of the body above the natural standard. It serves also to maintain the epidermis in a state of suppleness favourable to the exercise of the sense of touch. Its importance in the animal economy may be estimated from the fact that its suspension is a frequent source of disease, and its restoration one of the most usual signs of return- ing health. \^? Mucous Exhalation or Perspiration. The mucous membranes are the seat of an exhalation analogous SECRETION. 307 to that of the skin. These membranes are the seat of tAvo orders of secretions, one perspiratory or exhaling, the other follicular. The instruments of the first, or the exhalations, are the capillary vessels, termed the mucous exhalants, which open upon the sur- face of these membranes, and which must be carefully distin- guished from the follicles, Avhich secrete the mucus Avith Avhich these surfaces are lubricated. The perspiratory fluid of the mu- cous membranes has a close analogy Avith the serum of the blood. It is a thin diaphanous fluid, of a greater specific gravity than Avater, and of a slightly saline taste, consisting of muriates and phosphates of potash and soda, albumen, and a little mucus dis- solved in a large quantity of water. This humour is constantly exhaled at the surfaces of the mucous membranes, Avhich it con- tributes to moisten and lubricate ; and perhaps aids at the same time in depurating the blood. Examples frequently occur of a morbid increase of this secretion, as, for instance, at the com- mencement of nasal and pulmonary catarrhs, in Avhich the dis- charge is generally thin and serous ; and in serous diarrhoea and choleras, in Avhich the quantity of serous fluid discharged is some- times uncommonly great. The perspiratory exhalation of the conjunctiva, a perfectly transparent fluid, mingles with and dilutes the tears, serves to moisten the conjunctiva, and prevent its irritation by the contact of the air, and facilitates the motion of the eyeball, and of the palpebras upon each other. In the serous ophthalmia it is in- creased ; in the dry, suppressed. That of the nasal passage performs a similar office in guarding the mucous membrane of the nose from the irritating contact of the air, maintaining it in a requisite degree of moistness and sup- pleness for the sense of smelling, and perhaps dissolving the odor- ous particles which are drawn into the nose in the act of smelling. This exhalation is frequently increased at the commencement of coryza ; and diminished or suppressed at the invasion of an acute inflammation of the mucous membrane of the nose, and of many other acute phlegmasias. The cavity of the tympanum is lined by a detachment of the mucous membrane of the fauces, Avhich is also the seat of a per- spiratory secretion, designed to keep the parts contained in this cavity in a condition favourable to the exercise of their functions. An increase of this exhalation produces dropsy of the tympanum ; a suppression occasions a preternatural dryness of it. The membrane Avhich lines the interior of the excretory ducts of the mamma, is the seat of an active exhalation, particularly during the process of lactation. It unites with and dilutes the milk secreted by the glands, and facilitates its excretion. In some cases this membrane becomes the seat of a sanguineous discharge, vicarious of the menstrual secretion. In the sexual and urinary organs, both male and female, the 308 FIRST LINES OF PHYSIOLOGY. perspiratory secretion of the mucous membranes which lines them, serves to moisten these passages, and to facilitate the various func- tions of which they are the seats. In the female organs, this exha- lation is much augmented after parturition, and takes the name of the lochial discharge. In chronic inflammation of the uterus or vagina, it is frequently increased, producing a discharge, termed fluor albus or leucorrhaa. Sometimes the membrane which lines the uterus becomes the seat of a gaseous exhalation, which escapes from its cavity Avith an explosive noise. The mucous membrane of the alimentary canal, in its whole extent, is the seat of an active exhalation, by which these passages are moistened and lubricated, their contents diluted, and their vari- ous functions facilitated. This exhalation is much increased during the processes of mastication, deglutition, and gastric and intestinal digestion. In the stomach, the product of this exhalation is termed the gastric fluid, which is possessed of peculiar properties, and is the great agent of chymification. In certain, morbid affections of the stomach this exhalation is increased, and gives rise to Vomit- ing or eructations of serous fluid. In the small intestines it takes the name of the intestinal fluid, serves to dilute their contents, and probably to promote the solution of the nutritious parts, which were not digested in the stomach. A morbid increase of it gives rise to serous diarrhoeas. In the large, intestines, the fluid exhaled by their mucous membranes serves to dilute the feculent matter, and to facilitate defecation. A morbid increase of it may occasion serous diarrhoea; its diminution, a hard and dry state of the fasces, accompanied with obstinate constipation. . The lungs, also, are the seat of a mucous exhalation Avhich keeps the pulmonary passages constantly moist, though exposed to the drying influence of the air. Like the dermoid exhalation, it assumes the form of a vapour by absorbing a. large quantity of caloric, and is probably one of the means of preventing the tem- perature of the lungs from rising too high, from the animal heat generated in respiration. In certain diseases of the lungs, as the humoral asthma and serous catarrh, the pulmonary exhalation is increased. The dermoid and pulmonary exhalatioris are probably vicarious of each other. If either is diminished, the defect may be compensated by the increased activity of the other. Thus Delaroche and Berger, having covered the whole skin Avith a var- nish impermeable to the sweat, found that the loss of weight Avas not diminished, by obstructing the exhalation from the skin. Internal Exhalations. 1. The serous. The serous membranes, or those which line the serous cavities, are the seats of a constant exhalation, destined to keep these membranes moist, to facilitate the gliding motions of their contiguous surfaces upon each other, and to prevent their SECRETION. 309 adhesion. The exhaling vessels, which open upon the free sur- face of these membranes, are. the 'sources of this exhalation. It is a transparent, colourless fluid, having- a greater specific gravity than water, with little taste ; and is composed'of albumen, hy- drochlorates, subcarbonafes, and subphosphates of potash and soda, and a gelatinous mucus, dissolved in-a large quantity of Avater; It differs from the serum of the blood, according to Bostock, principally in containing a less proportion of albumen and of Avater. A trace of ozmazoriie has been found in the serum of the ventricles of the brain in hydrocephalus,,and in the cephalo- spinal fluid of a horse.* A inorbid increase of this exhalation gives rise to dropsies of the serous cavities. In inflammations of the serous, membranes, this exhalation frequently becomes so much loaded Avith albumen, that -it forms layers of coagulated matter over the inflamed surfaces, Avhich sometimes become or- ganized into false membranes, arid frequently cement the con- tiguous surface's together. The serous membranes secrete from the blood' Avith great promptness foreign substances introduced into it.. This was found to be the-case Avith the hydrocyanated ferruret of potass, introduced into the jugular vein of a horse by Herring, It ap- peared first on the internal surfaee of the pericardium, then suc- cessively on the pleura, the peritoneum, and lastly on the articular capsules of the.extremities. No trace of the solution' Avas found in the ventricles of the brain in the feAv instances in which they Avere examined. From two fifteen minutes elapsed before it made its appearance in the other serous cavities. The cavities in which this exhalation takes place are those of the arachnoides, the pleura, the pericardium,', the peritoneum, and the tunica vaginalis. The cephalo-spinal exhalation, according to Magendie, is one of the most abundant and most important, though least known. It is found beneath the arachnoides, covering the whole surface of the brain, filling up the depressions Avhich this presents, and forming a layer of variable thickness, Avhich extends from the cranium to the extremity of the sacrum. It also exists in the ventricles of the brain and cerebellum, which are lined by a pro- longation; of -the arachnoides. ' The quantity of .this fluid, according to Magendie, varies Avith a variety of •circumstances. In general, it is in the inverse ratio to the volume of the brain. In atrophy of this organ, from old age, or any other, .cause, the quantity of the cerebro-spinal fluid is augmented, so as to keep the cranio-spinal cavity constantly full, and when any part of the brain is Avanting, its place is oc- cupied by this fluid. The morbid increase of it in the ventricles * Magendie. 310 FIRST LINES OF PHYSIOLOGY. of the brain constitutes the disease termed hydrocephalus; its accumulation in the cerebro-spinal canal is called hydrorachis. In the cavities of the pleura, the serous exhalation serves to maintain the moisture of the free surfaces of those membranes, and to facilitate their motions upon one another, in the play of the lungs in respiration. Its morbid accumulation constitutes the disease termed hydrothorax. The pericardium, also, is moistened by a serous exhalation, designed to facilitate the motions of the heart. Dropsy of the pericardium is the result of its morbid increase. In the cavity of the abdomen, the exhalation from the perito- neum maintains the surfaces of all the organs, contained in this great cavity, in a state of humidity favourable to their free mo- tions, and prevent adhesion between contiguous surfaces. The morbid increase of this exhalation, gives rise to one of the most frequent and most incurable forms of dropsy, ascites. The tunica vaginalis, also, is moistened by a serous exhalation, Avhich, Avhen morbidly increased, gives rise to hydrocele. 2. The Synovial. The synovial membranes lining the mova- ble articulations, and the sheaths of the tendons, have a close analogy Avith the serous membranes, and are the seat of an ex- halation designed to facilitate the motions of the joints, and the play of the tendons in their sheaths. The product of this exhala- tion is called the synovia. It is a Avhite or yellowish viscid fluid, having some resemblance to the Avhite of an egg, of a slightly saline taste, and is composed of a large proportion of albumen, a fatty matter, a peculiar animal substance soluble in Avater, soda, muriates of soda and potash, and phosphate and carbonate of lime. Its use is to lubricate the joints, for Avhich purpose its smoothness and viscidity admirably adapt it, performing the same office in animal mechanics, as the oil Avhich Ave apply to those parts of artificial machines Avhich are exposed to friction. It is sometimes morbidly increased, giving rise to hydrarthrosis, or dropsy of the articulations. 3. Cellular. The cellular tissue, so generally diffused through- out the system, is the seat of a double exhalation, one serous, the other adipose. The plates of Avhich this tissue is composed, are constantly exhaling into the cells Avhich they form, a fluid which has a close analogy with that of the serous membranes, and which, probably, is subservient to the same uses, viz. to facilitate the play of these plates upon one another, and thus to favour the motions of the various organs Avhich are connected together by cellular tissue. In some parts of the system, Avhere the fat might be inconvenient or injurious, Ave meet with the cellular tissue wholly isolated from the adipose system; as, for example, in the cranium, the spine, the eyelids, the organs of generation, round the vessels, &c. A morbid increase of this exhalation constitutes that form of dropsy called anasarca or adema. SECRETION. 311 Besides the serosity of the cellular tissue, there is found, in many parts of it, a fluid of a very different nature, called the fat. Magendie remarks, that some parts of the cellular tissue always contain this substance ; other parts, sometimes only; and others again, never. The orbit of the eye, the soles of the feet, the pulp of the fingers, and that of the toes, always contain fat. The subcutaneous cellular tissue, and that Avhich surrounds the heart, the kidneys, &c. frequently contain it; Avhile that of the eyelids, the scrotum, and of the interior of the brain, are always destitute of it. The fat is contained in distinct cells, Avhich have no communi- cation Avith those adjoining them ; a circumstance Avhich, Magen- die observes, has led to the opinion, that the tissue Avhich secretes the fat is different from that which exhales the serosity. The correctness of this opinion he thinks doubtful. The size, the form, and the disposition of these cells are extremely variable, and the whole quantity of fat which they contain, not less so. In some individuals it amounts to a feAv ounces only; in others, to some hundred pounds. According to Chevreuil, human fat is ahvays of a yellowish colour, inodorous, lighter than Avater, and insoluble in this fluid; of an unctuous consistence, and becoming concrete at variable temperatures. It is very inflammable, and becomes rancid by the action of air and light. To the microscope it presents the appear- ance of polyhedral granules, enveloped in a very fine diaphanous membrane. Animal fat is composed of tAvo parts, one fluid, at common temperatures, the other concrete, composed of two prox- imate principles, in different proportions, termed by Chevreuil, elaine and stearine. According to the relative proportions of these tAvo elements, the fat is more or less fluid at a common tem- perature. The uses of this substance, in the animal economy, are chiefly of a physical kind. It lubricates the solids, and facilitates their movements. In the orbit of the eye it forms a soft, elastic cushion, on Avhich the eyeball moves Avith facility. In the soles of the feet, and on the buttocks, also, it forms a cushion, Avhich diminishes the effect of pressure, to Avhich these parts are so much exposed. It is also supposed to contribute to maintain the animal heat, and to guard against the effect of severe cold ; since fat sub- stances are bad conductors of caloric. The seat of the sensation of cold, however, is not the parts Avithin the subcutaneous adipose matter, but the skin, Avhich, of course, cannot be protected from the influence of a cold temperature, by a non-conductor situated on its internal surface. The adipose matter under the skin, may, however prevent the penetration of cold to the internal parts; and, in fact, corpulent persons appear to suffer less from cold than those Avith lean, dry frames. In some animals, the fat forms a magazine of nutriment, to which they have recourse during the 312 FIRST LINES OF PHYSIOLOGY period of hybernation, being supported during their long winter's sleep by the absorption of their: fat. An excessive accumulation of fat is considered as a disease, and.is termed polysarcia. The development of this substance is influenced by a variety of cir- cumstances, as age, manner of life, diet, &c. In general, it in- creases after middle age, particularly in persons of sedentary hab- its, and those who use a full diet. The abdomen becomes prom- inent, the buttocks enlarged in size, and the' female mammas become more voluminous. Castration in the inferior animals, and in man, increases the disposition to the formation of this substance. 4. Medullary. The cavities of the long bones, and the cells of the spongy ones, are lined by membranes, called the internal periosteum. . They are the seats of an exhalation of an oily fluid, called the marrow, which fills the cavities and interstices of the bones, and which resembles the adipose matter of the cellular system. The uses of it are not well knoAvn ; but by some it is considered as a mere deposit of superfluous nutritious matter. Haller and Blumenbach were of opinion, that its use Avas.to ren- der the bones more flexible. In persons Avho die. of chronic dis- eases, in a state of extreme emaciation, the cavities of the bones, it is said,- are found completely empty.'- 5. Exhalation of the interior of the eye.. The eyeball is formed of membranes, Avhich inclose several humours. These humours are the product of an exhalation, of which the membranes are the seats. The humours of the eye are the aqueous, secreted by a fine membrane Avhich lines the two chambers of the eye; the crystal- line, secreted by the crystalline membrane, which is a closed sac, of a lenticular form ; the vitreous, Avhich is exhaled by a mem- brane of extreme delicacy and transparency, and of a cellular structure, called the hyaloid membrane ; the black matter of the choroides; and that Avhich lines the posterior face of the iris, both secreted by the choroides. The first of these, or the aqueous humour, is a perfectly limpid fluid, consisting of a large proportion of water, of albumen, and some salts. It fills the tAvo chambers of the eye, and if evacuated is speedily reneAved, as for example, after the operation for cata- ract by extraction. The crystalline humour is a dense, gelatinous body, of ex- quisite transparency, having the form of a double convex, lens. Its central parts are denser than those near the surface. It is contained in a thin capsule, and is composed of Avater, albumen, and gelatin. It differs from the aqueous humour, in containing a larger proportion of the two latter animal principles. The vitreous humour is a fluid composed of albumen, gelatin, and several salts, dissolved in a large proportion of Avater. It is secreted by a very delicate membrane, called the hyaloid, in the cells of Avhich it is contained. A morbid increase of it, consti- SECRETION. 313 tutes the disease termed hydrophthalmia, or dropsy of the eye. The pigmentum nigrum, or black matter of the choroides and posterior part of the iris, is secreted by the choroid membrane. It is composed of water, gelatin, several salts, and a peculiar colouring matter. The aqueous and vitreous humours are reneAved Avith rapidity, when evacuated by accident, or in operations on the eye; and, according to the experiments of Leroy d'Etiole and Coiteau, it appears that the crystalline, Avhen extracted from the eye, is re- produced by exhalation.* Follicular Secretions. The follicular secretions are those Avhich are effected by the small secretory sacs, Avhich have already been described under the name of follicles, or crypts. These bodies are found only in the mucous membrane and the skin, on the free surfaces of which they open. The viscid, or unctuous fluid, Avhich they secrete, is designed to lubricate these membranes, and to enable them to support, Avithout inconvenience, the habitual contact of foreign bodies, to Avhich, as organs of relation, the skin and mucous mem- branes are exposed. 1. Mucous follicular secretions. The mucous follicles are found in all the mucous membranes, sometimes isolated from one another, and sometimes aggregated together in clusters. The first class, or the simple follicles, are dispersed over the palate, tongue, trachea, oesophagus, stomach, and intestinal canal. They are also found in the mucous membrane Avhich lines the biliary and cystic ducts, in the ureters and bladder, and in the mucous membrane of the vagina. The conglomerated mucous follicles are the tonsils, Peyerian glands of the intestinal canal, the prostate gland, and the glands of Cowper. The fluid secreted by the follicles is termed mucus. It is a viscid, colourless, transparent, and insipid fluid, heavier than water, soluble in the acids, insoluble in alcohol, not coagulable like albumen, precipitated by acetate of lead, and becoming, by desiccation in the air, a semi-transparent, brittle solid, of a yel- lowish colour. It is very similar, in its properties, to vegetable mucilage, but differs from it in containing azote. Bostock and Vauquelin consider it as a proximate principle ; but Berzelius thinks that it is composed of lactate of soda, combined Avith an animal matter. A morbid increase of this secretion in the nasal passages constitutes the affection termed coryza; in the lungs, bronchial catarrh ; in the intestines, diarrhoea or dysentery ; in the urinary passages, blennonhagia, 6lc. * Magendie. 40 314 FIRST LINES OF PHYSIOLOGY. 2. Cutaneous follicular secretion. The follicular secretion of the skin is effected by little hollow bodies, Avith membranous walls, dispersed throughout the skin, and termed sebaceous folli- cles. These bodies bear a close resemblance to the crypts of the mucous membranes; but they are never clustered together, as the latter are in certain situations. They exist at the roots of the hairs, and generally the hairs traverse the cavities of the follicles on their Avay to the surface of the skin. The fluid secreted by them is a thick, unctuous matter, which, diffused over the epider- mis and the hair, serves to lubricate and soften them, to defend the skin from the effects of friction, and perhaps to protect it from the influence of moisture. The number of the sebaceous follicles dispersed over the skin is immense. Mr. Chevalier counted one hundred and forty in the space of a quarter of an inch, Avhich Avould amount to one hundred and tAventy millions over the Avhole surface of the body. The matter secreted by these follicles is the vehicle of the pecu- liar animal odour which emanates from certain individuals, forming an atmosphere round them, into which it is so disagreeable for others to enter. The meibomian glands, or ciliary follicles, belong to the class of the sebaceous follicles. These are small granular bodies, situated in the thickness of the tarsal cartilages, and secrete a peculiar sebaceous matter, which lubricates the margins of the eyelids, and prevents the irritation which their motions might otherwise produce. It may perhaps also prevent the escape of tears from betAveen the eyelids.. The ceruminous glands of the ear also belong to the same class. They are situated in the external auditory passage, and secrete a yelloAV, bitter, unctuous matter, of a semi-fluid con- sistence, called the cerumen of the ear. The uses of it are to sheathe and protect the Avails of this passage. It sometimes be- comes hard and dry, by the absorption of its thinner parts, and then is a common cause of deafness, which, hoAvever, is easily relieved by carefully removing the hardened matter. Glandular Secretions. Several of these have been considered already. Those Avhich remain to be noticed, are the salivary, the lacteal, and the urinary; or the secretions of saliva, of milk, and of the urine. 1. Salivary secretion. The salivary glands are six in number, viz. the two parotid, situated in front of the ears, in the hollow between the mastoid process of the temporal bone and the branch of the lower jaw. These glands are composed of granulations, united into lobules and lobes by cellular membrane. Their arteries are furnished by the carotid, the facial, and the temporal. The granulations of which they are composed give origin to SECRETION. 315 excretory ducts, which, by their union, form the stenonian duct, which passes across the masseter muscle, perforates the buccina- tor, and opens into the mouth opposite to the middle molar tooth of the upper jaw. The portio dura traverses the substance of this gland. The tAvo submaxillary glands. These are situated on the inner side of the ramus of the loAver jaAV, betAveen the two por- tions of the digastric muscle. Their ducts are termed the ducts of Wharton, and open at the sides of the frenum linguas. The nerves of their glands are derived from the gustatory, by means of Avhich their functions are closely connected with im- pressions on the organ of taste. The tAvo sublingual glands axe situated under the anterior part of the tongue. They are.smaller than the submaxillary glands, and their excretory ducts, Avhich are several in number, open upon the sides of the frenum linguas. These glands, like the submaxillary, derive their nerves from the gustatory. The fluid secreted by these glands is termed the saliva. It is constantly flowing into the mouth, and mingles with the fluids secreted by the membrane Avhich lines this cavity, and by the mucous follicles. It is composed of Water,..................992.9. Peculiar animal matter called ptyaline,........2.9 Mucus....................1.4 Hydrochlorate of potash and soda,........... 1.7 Lactate of soda, and animal matter..........0.9 Free soda,.................. 0.2 1080.0 According to Mitscherlich, the saliva is most generally a little acid, sometimes neutral, and at other times strongly alkaline. It is acid betAveen meals. During mastication it is alkaline, and sometimes its acidity disappears at the very first mouthful of food. Its acidity is OAving to the presence of the hydrochloric, phos- phoric, sulphuric, and lactic acids. The concretions formed on the teeth, commonly called tartar, are supposed to be deposited by the saliva, as this matter is found in the greatest abundance near the openings of the salivary ducts. It is composed of phosphate of lime, of mucus, and some animal matter. According to Haller, from six to eight ounces of saliva are secreted during a meal. The whole quantity secreted in twenty- four hours has been estimated at about tAvelve ounces. The se- cretion is constantly going on, but is much more active sometimes than at others. During sleep very little is secreted. But in eat- ing, particularly during mastication, and in speaking, the secretion is much increased. Acids, spices, stimulants, high-seasoned ali- ments, all promote the secretion of the saliva. The sight, and 316 FIRST LINES OF PHYSIOLOGY. even the idea of savoury food, frequently produces the same effect, Sometimes, under these excitations, the saliva is projected in a jet into the mouth. The action of sialagogues, especially the mercurial preparations, excites a morbid increase of this secre- tion, termed salivation, or ptyalism, in which the quantity of this fluid secreted is sometimes enormous. It has in some instances amounted to twenty-three pounds in a day. In hydrophobia this secretion is so much perverted, that the saliva, if introduced into the blood-vessels, becomes a most dreadful poison. Under the influence of terror or rage, also, it sometimes acquires venomous properties, causing gangrene in the part bitten by the frightened or enraged individual or animal; and sometimes exciting a fatal affection of the nervous system, analogous to hydrophobia. Secretion of Milk. fc The organs which secrete the milk, are the mamma, or breasts. These are tAvo glands, situated on the anterior part of the thorax, below the clavicles, and before the great pectoral muscle, of a hemispherical form, covered by a smooth, delicate skin, and com- posed of an assemblage of lobes, each of Avhich is formed of sev- eral lobules, and these of acini, or granulations. The lobes are connected together by a dense cellular tissue, and are buried in a dense mass of fat. These acini appear to consist of minute vesi- cles, and an organized tissue, and they give origin to the radicles of the lactiferous ducts, which, gradually uniting, form larger trunks, corresponding in number Avith the lobes, and amounting to about fifteen in each breast. These trunks do not anastomose Avith one another, but converge toAvards the centre of the gland, Avhere they terminate in delicate excretory canals, Avhich are col- lected into a bundle, and enveloped in a kind of erectile sheath. This constitutes the nipple, the small body Avhich projects from the centre of the mamma, surrounded by a pink-coloured or red- dish-broAvn areola. The nipple, Avhich is of the same colour, presents on its surface numerous fine papillas, in Avhich are the orifices of the lactiferous ducts. The skin of the areola and nip- ple contains a number of sebaceous glands, which secrete an unctuous matter, designed to screen these parts from the saliva of the child. The arteries of the mammas are derived from the internal mam- mary, the axillary, the first intercostals, and the thoracic; its nerves, from the brachial plexus and the intercostals. These glands are abundantly supplied Avith lymphatics. The product of the secretion of the mammas, the milk, is a fluid of a Avell known colour and taste ; and, according to Ber- zelius, is composed of milk, properly so called, and cream. The milk consists of the folloAving principles, viz. — SECRETION. 317 Water,..................928.75 Cheese, with a trace of sugar,..........2S.00 Su»ar of milk,.......•.......35.00 Hydrochlorate of potash,............ 1.70 Phosphate do............. . 0.25 Lactic acid, acetate of potash, and lactate of iron, .... 6.00 Phosphate of lime,.............. 0.30 1000.00 Cream is composed of Butter,.................. 4.5 Cheese,.................. 3.5 Whey,................, . 92.0 100.0 Whey contains 4.4 of sugar of milk and salts. Human milk differs from that of the coav in containing less caseine, and a much larger proportion of sugar of milk. The qualities of the milk are much influenced by the nature and quantity of the aliments. Under a diet of animal food, it is more abundant, of a thicker consistence, and less acid; Avhile a vege- table diet diminishes the quantity of this secretion, and renders it thinner and more acid. The quantity of this secretion depends also very much upon that of the ingesta. A Avoman Avho con- sumes five or six pounds of solid and liquid aliment within twen- ty-four hours, Avill furnish in the same period from tAvo to three pounds of milk, or even more. The increase of the secretion occurs too soon after taking food to allow time for the digestion of the latter, and its conversion into blood, or even chyle. It easily acquires the flavour and the peculiar properties of substances taken into the stomach, either as food or medicine. Hence, the disagreeable flavour Avhich coav's milk frequently acquires, Avhen this animal has fed upon certain kinds of plants. In like manner purgative substances, as salts or rhubarb, taken by the nurse, fre- quently operate upon the boAvels of the infant. Its qualities, also, are sometimes affected by mental emotions. It has been a sub- ject of controversy Avhether the milk is secreted from the blood or from the chyle; or, as some physiologists have supposed, from the lymph. The question seems to be decided by the analogy of the other secretions, as well as by the fact that mercurial in- jections, throAvn into the mammary arteries, readily pass into the lactiferous ducts, and vice versa. Another fact, which seems to be conclusive of the question is, that blood is sometimes drawn into the lactiferous ducts, Avhen the infant has completely drained the breast of milk, and yet continues to suck with force* Before the age of puberty the mammas are imperfectly deve- loped, being small and flat; but at puberty, Avhen the catamenia appear, they enlarge and become prominent. Until the period of * Vesalius states that he has seen the mammary veins in a nurse full of milk. 318 FIRST LINES OF PHYSIOLOGY. fecundation, however, they remain inactive ; but as soon as preg- nancy has taken place they begin to swell, and become affected with pricking and shooting pains. Towards the close of utero- gestation, they secrete a serous fluid, Avhich is termed colostrum, and the secretion sometimes retains the same character two or three days after parturition. The secretion of the milk continues until the end of the period of nursing, and ceases in the course of the second year. In some rare examples milk has been secreted by the mammas of young virgins, and even of men. Secretion of Urine. The glands Avhich secrete the urine are the kidneys. These are two bodies, four or five inches long, and two or three in breadth, in shape resembling the kidney-bean. They are situated on the sides of the vertebral column, before the psoa and quad- rati lumborum muscles, opposite the tAvo last dorsal and the tAvo first lumbar vertebras, imbedded in fat. The right kidney lies at the under and back part of the large lobe of the liver ; the left is situated under the posterior part of the spleen, and behind the left part of the stomach, pancreas, and colon. Sometimes one kidney is Avanting, and in some instances there are three. They are cov- ered on their anterior part by the peritoneum, reflected from the liver and the spleen. These glands are composed of tAvo distinct substances, an exter- nal, termed the cortical, and an internal, called the tubular. The eortical substance is about two lines in thickness, is of a lighter red and softer consistence than the tubular, and consists almost entirely of blood-vessels and [acini] granulations, Avhich are the commencements of the tubuli uriniferi. It is supposed to consti- tute the secretory part of the gland. The tubular part consists of a number of conical bodies, varying from seven to twenty, Avith their bases directed toAvards the cir- cumference, and their summits toAvards the centre, or pelvis, of the kidneys. The tubular part is of a darker colour, and firmer consistence than the cortical. It is composed almost wholly of convergent uriniferous canals, which originate in the cortical sub- stance, and Avhich terminate in small apertures at the summits of the cones. The orifices of the uriniferous canals are less nume- rous than the canals themselves. The rounded summits of the cones, Avhich are perforated with the orifices of the uriniferous ducts, are termed the mamillary processes. Each of these is enclosed in a loose conical sac, termed an infundibulum. The pelvis of the kidney is a membranous sac formed by the union of the infundibula. At its inferior part it contracts, and is continued into the ureter or excretory duct of the kidney. The ureters are long, membranous canals, about the size of a Avriting- quill, lined like the pelvis of the kidney with mucous membrane, SECRETION. 319 very dilatable, and opening into the inferior and posterior surface of the bladder. The kidneys receive their blood by the renal or emulgent arte- ries, two large vessels Avhich spring immediately from the aorta. No other organs in the body, in proportion to their volume, receive so large a quantity of blood. A free communication exists between the renal arteries and the veins, and the tubular part, of the kidneys. Injections thrown into the renal artery pass into the veins and into the cortical substance, and thence into the pelvis of the gland. The renal nerves are derived from the great sympathetic. The urinary bladder, into Avhich the ureters open, and convey the urine from the kidneys, is a membranous sac, situated in the cavity of the pelvis, betAveen the pubis and the rectum. In females, it lies betAveen the pubis and the uterus. Its posterior and upper surface is covered by the peritoneum, and is in contact Avith the inferior part of the small intestines. The bladder is composed of four tunics, viz. a serous, cellular, muscular, and mucous. The serous, deriAred from the peritoneum, invests only the superior part of the bladder. The cellular is sit- uated immediately beneath the peritoneal, but is much more exten- sive, as it completely encircles the bladder. It is very loose, and loaded with adipose matter. The muscular coat consists of muscular fibres Avhich run in various directions over the bladder, and, by their contraction, diminish the capacity of this reservoir, and effect the evacuation of its contents. The inner coat is a mucous membrane, Avhich is continuous Avith that which lines the ureters. The bladder has three apertures, tAvo of them being the orifices of the ureters, and the third, the mouth of the bladder, or, the commencement of the urethra. This last is a canal, tAvelve or fifteen lines long in females, and opening betAveen the clitoris and the vagina; but in males it is eight or nine inches in length, extending from the mouth of the bladder to the glans penis. It is formed of a long fibrous membrane, lined on its interior by a mucous coat. The nerves of the bladder are derived from the hypogastric plexus. The posterior extremity of the urethra is surrounded in three- fourths of its circumference by a collection of mucous follicles, commonly called the prostate gland. Before the prostate gland there are tAvo small glandular bodies, about the size of a pea, which open into the urethra, and Avhich are termed Cowper's glands. These, together with the prostate, secrete a mucus which passes into the urethra. In a case mentioned by Lieutaud, the urinary bladder did not exist. The ureters, Avhich Avere as large as the small intestine, opened directly into the urethra. Secretion. If an incision be made into the pelvis of the kidney of a living animal, the urine may be seen to exude sloAvly from 320 FIRST LINES OF PHYSIOLOGY. the summits of the excretory cones. It passes thence into the pelvis, from Avhich it enters the ureters, and from these canals it distils sloAvly into the bladder, gradually filling and distending this reservoir. If the uriniferous cones be slightly compressed, a considerable quantity of urine is forced out, Avhich, hoAvever, is not limpid like the natural secretion, but thick and turbid. The passage of the urine from the ureter into the bladder, ac- cording to Magendie, is not continual. But at short and regular intervals, the ureters, distended by the urine, open their lower orifices and suffer the fluid to enter the bladder. The ureters then collapse and their orifices close, and the passage of the urine into the bladder ceases for several seconds, and then recommences in the same manner as before. In general, the passage of the urine into the bladder coincides with the act of inspiration. The urine accumulated in the bladder, cannot ascend into the ureters, for these tubes open obliquely into the bladder, so that the pressure of the fluid Avhich distends it, tends to close the orifices of the ureters, and to prevent any reflux of the urine towards the kidneys. That it does not continually escape from the urethra, according to Magendie, is owing to several causes; as, the dispo- sition of the urethra, particularly toAvards its vesical extremity, to maintain a contracted state ; a tendency Avhich depends on the circumstance, that the membranous part of the urethra is com- posed exteriorly of muscular fibres which are endued Avith a strong contractile power. But the principal cause Magendie states to be the action of the muscles Avhich elevate the anus, including the compressor urethra of Wilson, Avhich, by this contraction, press the urethra upAvards, keeping its parietes forcibly in contact, and thus closing its poste- rior orifice. When the bladder has become distended with urine, to a cer- tain degree, a peculiar sensation is excited in the organ, with a desire to evacuate it. The bladder is susceptible of great disten- tion. In its natural state it is capable of containing about two pounds of urine; but it sometimes becomes so much distended that its fundus extends up above the umbilicus, and more than two gallons of urine have been found in it. The excretion of the urine is accomplished by the contractile poAver of the bladder, assisted by the action of the abdominal muscles. The habitual disposition of the muscular coats of the bladder to contract, is resisted by the external extremity of the urethra. But under the influence of the sensation Avhich solicits the evacuation of the urine, the voluntary poAver excites the abdominal muscles to con- tract, and the action of these muscles assists the contraction of the bladder in overcoming the resistance. The will also relaxes the muscles Avhich elevate the anus, and Avhich, by this contrac- tion, close the urethra. As soon as the resistance of this canal is overcome, the urine is evacuated by the contraction of the blad- SECRETION. 321 der, Avhich is generally aided by the abdominal muscles, in which case the fluid is evacuated with a much more vehement jet. We can instantly arrest the discharge by the voluntary contraction of the levators of the anus. The excretion is partly a voluntary, partly an involuntary act. The contraction of the bladder is in- voluntary ; that of the abdominal muscles is dependent on the will. The contraction of the bladder, however, is sufficient to expel the urine ; for in experiments in Avhich the abdomen in living animals has been opened, and the bladder removed from the action of the abdominal muscles, and even when the bladder with the prostate, and a small portion of the membranous part of the urethra, has been detached from the animal, the urine has been discharged by the action of the bladder alone. The small quantity of urine Avhich remains in the urethra after the bladder has ceased to contract, is expelled by the contraction of the peri- neal muscles, particularly of the bulbo-cavernosus. The product of the secretion of the kidneys, the urine, is a fluid of a yelloAvish colour, of a peculiar, sometimes ammoniacal odour, and an acrid bitter taste. Its specific gravity is variable, being from one thousand and five to one thousand and thirty-three, that of water being one thousand. When recent, it reddens the vege- table blue colours, but in the act of decomposing it changes them to a green. The first of these properties is attributed, by different chemists, to the presence of various acids. Vauquelin ascribes it to the phosphoric, Thenard to the acetic, Berzelius to the lactic, Scheele to the benzoic, particularly in infants ; Prout to the superlithate and superphosphate of ammonia. Its poAver of con- verting blue colours to a green, is owing to the development of ammonia, during the decomposition of the urine. The composi- tion of urine, according to Berzelius, is as follows, viz. Water,..................933.00 Urea, ..................30.00 Uric acid,.................1.00 Lactic do., lactate of ammonia, and animal matter combined with them,...............17.14 Mucus of the bladder,.............0.32 Sulphate of potash,..............3.71 Sulphate of soda,...............3.16 Phosphate of soda,..............2.94 Hydrochlorate of soda,.............4.45 Phosphate of ammonia,............. 1-65 Hydrochlorate of ammonia,...........150 Earthy matter, with a trace of fiuate of lime,.....1.00 Silex,...................0.03 1000.00 The principal properties of the urine are owing to the urea, a peculiar animal matter, Avhich contains a large proportion of azote, and is strongly disposed to putrefaction. By the decomposition 41 322 FIRST LINES OF PHYSIOLOGY. of the urea and of the mucus, ammonia is formed, Avhich gives to decomposing urine its alkaline properties. The acid properties of recent urine depend on the presence of the free acids, which enter into its composition. One of these, the uric, is frequently deposited, in the form of a reddish matter, on the sides of the vessels into Avhich the fluid is received. This acid, also, fre- quently gives rise to sabulous or calculous concretions. The composition and the physical properties of the urine are subject to great varieties. Under the free use of Avatery drinks, its quantity increases, and it becomes paler and more diluted.* The proportion of uric acid increases under a full animal diet, accompanied Avith sedentary or inactive habits of life. The same acid diminishes in quantity, and sometimes wholly disap- pears, under a diet of vegetable matter, or of substances Avhich contain no azote, as sugar, gum, butter, oil, &c. According to Chevreuil and Magendie, the urine in dogs may be rendered at pleasure either acid or alkaline, by confining these animals to a diet exclusively animal or vegetable. Certain colouring sub- stances, taken into the stomach, as rhubarb and madder, commu- nicate a deep yelloAV or red tinge to the urine. The same effect is produced by immersion in a bath, formed by an infusion of these substances. The urine also frequently becomes impreg- nated with the odour of certain substances which have been eaten or sAvallowed, particularly asparagus and the turpentines. Many substances, either introduced into the stomach, or injected into the veins, find their way to the kidneys, and may be detected in the urine. If a few grains of the nitrate or prussiate of potash, for example, be taken into the stomach, the presence of the salt may be discovered in the urine a short time after ; but what is worthy of remark, not a trace of it can be detected in the blood. Magendie also ascertained that Avhen the prussiate of potash Avas injected into the veins, or was absorbed either from the intestinal canal, or from a serous membrane, it soon found its way into the urine, Avhere its presence might be readily detected. If the quan- tity of the salt injected Avere considerable, its presence in the blood might be ascertained by the proper chemical tests; but if very little were injected, it Avas found impossible to detect it in the blood by the usual means. The same results were obtained when the prussiate Avas mixed Avith blood draAvn from the veins; Avhile the presence of the salt could always be detected in the urine, in Avhatever proportion it existed in this fluid. It appears, therefore, that substances may exist in the blood, on their route to the kidneys, Avithout the possibility of our detecting them in this fluid; while their presence in the urine, as soon as they reach this secretion, may readily be discovered by ordinary chemical means. * The average quantity secreted daily is estimated at three or four pounds. SECRETION. 323 The extirpation of one of the kidneys in dogs, according to Magendie, does not affect the health of the animal, but the loss of both is inevitably fatal in a feAv days, varying from tAvo to five. The same physiologist remarks, that in these cases there is an extraordinary increase of the secretion of bile, the stomach and intestines of the animal becoming filled Avith the fluid. A curious fact, relating to the excision of the kidneys, which has already been mentioned, is, that after the extirpation of these glands, a considerable quantity of urea can be detected in the blood, though not a trace of it can be found in the fluid before the experiment. Prevost and Dumas estimate the quantity of urea which a healthy dog habitually produces, at a drachm in tAventy-four hours. After the excision of the kidneys five ounces of the blood of the animal were found to contain one scruple of this substance. The probability seems to be, that the urea pre- exists in the blood, and is merely separated by the kidneys ; but that after the extirpation of these organs, as its elimination from the blood is prevented, it accumulates in this fluid, until it amounts to a quantity Avhich may be recognised by chemical analysis. The introduction of urea into the blood has been found to pro- duce an increase of the secretion of urine. Uses of the Urinary Secretion. The secretion of the urine differs, in one respect, from all the other secretions, viz. that it is not designed for any local use. It is subservient to two general purposes, viz. the depuration of the blood, and the decompositiori of the body ; and in this twofold respect, it is one of the functions most necessary to life. Some idea of the importance of this function may be formed from the calculation that ten thousand ounces, or nearly eighty gallons of blood are brought to the kidneys every hour by the renal arteries. Many foreign substances are constantly entering the mass of the blood, Avhich alter the qualities of this fluid, from which it is necessary it should be regularly purified. The digestive and respiratory organs, and the great surface of the skin, are the three avenues by which extraneous substances may enter the blood. Further, many of the secreted fluids, even the excrementitious, if any obstacle prevent their excretion, are reabsorbed and carried back into the circulation. This is the case with the bile, and milk, and probably with all the others. Even pus, the fluid of dropsies, and other morbid products, and even fascal matter, are sometimes absorbed, and enter the mass of the blood. Noav the secretion of urine is the means appointed by nature to purify the blood from these and other foreign substances. Accordingly, we find the urine saffron-coloured in jaundice, in consequence of the admixture of bile, and of a red or deep yellow colour, after the 324 FIRST LINES OF PHYSIOLOGY. ingestion of madder or rhubarb. Many foreign substances, also, which are taken into the stomach, but are incapable of chylifica- tion, soon find their way to the kidneys, and are secreted Avith the urine , and the celerity Avith which some of them find their way from the stomach or the blood-vessels into this secretion is truly remarkable. Home discovered that rhubarb could be de- tected in the urine seventeen minutes after it had been sAvalloAved. And Fodera, having injected a solution of hydrocyanated ferruret of potash into the stomach of an animal, found that the urine gave indications of the presence of the salt in five or six minutes. He then killed the animal, and upon examining the blood discov- ered the salt in this fluid also. In another experiment, in Avhich the hydrocyanated ferruret of potash was injected into the jugular vein of a horse, the kidneys gave decided indications of its presence in the course of one min- ute. The superfluous part of our drinks folloAvs the same route, and is thus discharged from the system. Foreign substances, ab- sorbed in respiration, are in many instances discharged by the same channel. Thus the urine of a person Avho breathes an atmos- phere impregnated Avith the vapour of oil of turpentine, acquires a peculiar odour, which has been compared to that of violets. From the fact that the urine is the vehicle by which these foreign matters are removed from the blood, and is in part composed of these impurities of the vital fluid, it has sometimes been aptly termed faces sanguinis. Further, it is Avell known that part of the materials Avhich compose the solid structure of the body are regularly taken up by internal absorption and carried into the circulation; and this pro- cess is as incessant as nutrition, the parts removed by absorption making room for the fresh materials to be deposited by the nutri- ent vessels. Our organs are decomposed as fast as they are re- composed or nourished, and of this decomposition the renal secre- tion is an essential instrument. The peculiar principle, urea, contained in the urine, has been supposed to be derived from the old elements of nutrition, combined together in a peculiar mode in the blood-vessels, or by the vital poAver of the kidneys. Of the tAvo offices of the renal secretion which have been men- tioned, the depuration of the blood, and the removal of the de- composed matter of nutrition, the first seems to be executed by a kind of filtration ; for it is found that, under certain circumstances, foreign matters are sometimes separated from the blood by other strainers. Thus, the fluid of dropsies sometimes manifests the qualities of the aliments Avhich have been taken, and sometimes the presence of bile ; facts which evince that the secretory struc- ture of the kidneys is not essential to the separation of these sub- stances, and that they may be secreted by a simpler apparatus. So the bones become coloured red after the use of aliments con- taining madder ; the colouring matter, instead of being secreted NUTRITION. 325 from the blood by the kidneys, being deposited in the bones with the matter of nutrition. The kidneys, hoAvever, are the organs which are particularly charged Avith the office of removing for- eign substances from the blood; and are to the drinks Avhat defe- cation is to the solid aliments. It is Avorthy of remark, that, after the old matter of nutrition is taken up by interstitial absorption, and conveyed into the blood, this fluid is subjected to the influence of respiration, before it is carried to the kidneys; and after being purified by respiration, and converted into arterial blood, it is transmitted to the kidneys, to be further purified, by the separation of the principles of the urine. It is a curious circumstance, that the kidneys, though depurating organs, operate upon arterial blood, which has shortly before been purified in the lungs; and this blood, when purified by the separation of the foreign matters which may have been introduced into it, as well as of the old elements of nutrition, furnished by the detritus of the organs, becomes venous blood, Avhich must again be subjected to the action of the lungs, before it can be employed for any other purposes in the animal economy. The blood, as it issues from the lungs, is perfectly adapted to the uses of the system ; for Ave find that it is immediately transmitted to all the organs, to furnish the elements of nutrition, and of the secretions, and the necessary vital excitement. Yet we find that one-eighth of this blood is diverted into a particular channel, by which it passes to the kidneys, where it parts Avith certain prin- ciples Avhich are noxious to it, and if retained in the blood, are inevitably fatal in a short time. It is not very apparent Avhy this particular portion of the arterial blood only should be subjected •to the action of the kidneys, Avhile all the remaining, and vastly the larger part, though equally impregnated Avith these noxious principles, is transmitted, Avithout this depuration, to all parts of the body. Nor is it more apparent, why, after undergoing this purification in the kidneys, and parting with these noxious ingre- dients, it is rendered more unfit than it was before to administer to the Avants of the economy, in being converted into venous blood, and again requiring the action of the lungs to prepare it to subserve the uses of the system. CHAPTER XIX. NUTRITION. The nutriti\re functions, Avhich have so far been considered, have all one and the same aim, viz. that of preparing materials, 326 FIRST LINES OF PHYSIOLOGY. which may become incorporated Avith the living system, and re- pair the losses Avhich it is constantly sustaining, from exercise of the functions of life. Digestion, absorption, respiration, circula- tion, and the secretions, are only preliminary functions, subser- vient to nutrition, Avhich may be regarded as the consummation of the assimilating functions. That the fabric of the body is undergoing a perpetual decom- position and renovation, cannot be doubted. The immense losses which the system is constantly sustaining from the numerous secretions and excretions, particularly from the renal and cuta- neous, the first of Avhich contains a very large quantity of animal matter, derived in all probability from the debris, or rubbish, of the decomposing organs ; — the necessity of frequent and ample supplies of aliment, and the extreme emaciation Avhich is the consequence of a few days' abstraction from it; the changes of volume, which the organs and the Avhole body undergo, in passing through the successive periods of life, which can only be ac- counted for, on the supposition of an entire remoulding of the whole, from time to time, by the nutritive poAvers ; — these, and many other considerations, leave no reasonable doubt, that the process of decomposition is perpetually going on, taking to pieces the solid fabric of the body, and that the Avork of nutrition fol- lows close upon its footsteps, in repairing the losses which are thus made. A well-known experiment with madder has usually been considered as decisive of the point, that there is a perpetual decomposition of animal matter. If this substance be mixed with the food of animals, it is found that in a short time the bones of the animals become of a red colour; and if the madder be then withdraAvn from their food, the red colour in a short time wholly disappears, evidently from the absorption of the madder, which had been previously deposited in the bones. From this experi- ment, it has been inferred, that even the hard substance of the bones, during life, undergoes continual decomposition, and of course, that the losses which they sustain must be repaired by the deposition of new ossific matter; and if this be true, the soft solids which have less cohesion, must probably undergo a more rapid decomposition. This experiment, hoAvever, in strict logic, proves nothing more than that the colouring matter of madder is deposited on the bones, if the substance be taken a certain time with the food; and that this colouring matter is afterwards ab- sorbed and carried out of the system. It proves, in fact, nothing more than the deposition and absorption of madder itself, and not that of the bones, or the other animal textures; and as madder is not an alimentary substance, and is incapable of perfect assimila- tion, (for otherAvise it would not communicate its colour to the bones,) no inference can logically be made, from the fact of its absorption, to the absorption of the assimilated matter of which the living solids are actually composed. NUTRITION. 327 Many facts have led some physiologists to the opinion, that while many, if not most of the solids are subject to this perpetual change of matter, there are some which, when once formed and fully developed, remain unalterably the same. Blumenbach is of opinion, that only those solids undergo this successive change, which possess the reproductive poAver, i. e. the property which certain parts of the bones, and nails,* and epidermis possess of repairing, not only the natural losses of matter, from the Avear and tear of life, but. even the removal of considerable portions of their substances from external injuries. While in those parts whose vital poAvers are of a higher order, the parenchyma Avhich forms their base appears to be permanent, and is liable only to this change, viz. that the interstices of the tissue, Avhile nutrition is active, are constantly full of nutrient animal gelatine ; but when nutrition languishes, they are deprived of their gelatine, collapse, and become extenuated. This view Avould confine the change of matter in the body, to the parts endued with the lowest degrees of vitality, as the bones, nails, and epidermis. That the cutis vera is not really reproduced, and of course must be a stranger to this change of matter, Blumenbach remarks, is probable from the fact that scars are frequently permanent, and that the marks im- printed upon the skin in the operation of tattooing, in which charcoal, ashes, soot, the juices of plants, &c. are pricked in by a pointed instrument, remain ever afterAvards. Bourdon infers from these facts, that there exists in the organs a fundamental tissue which undergoes no change. Other physiologists are of opinion that all parts of the body, without exception, are incessantly undergoing a renovation of their substance, by an uninterrupted movement of nutrition. The volume, the consistency, the composition, the configuration, the texture of the body, and of all its parts, the cellular tissue, mem- branes, vessels, nerves, muscles, cartilages, bones, tendons, liga- ments, &c. all are supposed to be subject to incessant changes, more or less rapid. All animals, Tiedemann observes, live in an uninterrupted circle of formation and of transformation, of de- struction and of renovation. This, in all probability, is the true doctrine. There is beyond all question a constant waste of the elements of the organization by the operations of life. Every function in its exercise occasions a consumption both of materials and of power; and not a single action of life, however inconsid- erable, but demands the presence, and occasions the expenditure of blood. Not a fibre contracts, not a sensitive filament expe- riences an impression, Avithout undergoing some change in its own organic condition, some deterioration of the perfection of its vital mechanism. Not a single ray of light falls upon the eye, - According to Blumenbach, the nails, after the loss of the first phalanx of the finger, have been known to be reproduced on the middle phalanx. 328 FIRST LINES OF PHYSIOLOGY. not a transient thought or momentary feeling flits through the brain, but it carries aAvay with it some element of poAver, leaving the exquisite organization of the part in a lower degree of vital endowment. No part therefore that is not condemned to a state of absolute inaction in the system, can be exempted from the necessity of constant reparation; and no such part is known, or can be supposed to exist. To supply the great Avaste occasioned by the numerous and complicated actions of the living system, there is a constant influx of crude materials and power from the physical world into the vortex of life. Here these elements, by a higher or transcenden- tal chemistry, are converted into that mysterious fluid the blood, in which are stored up all the elements both of structure and of power, employed in the formation of the diversified organs of the body. Noav every part of the system is supplied either with red or colourless blood by receiving vessels, and sends back the residue charged with the debris of its OAvn nutrition, by corresponding returning vessels. The returning fluid differs from that which the organ received. Its properties are altered, and its constituent parts are n Med. Rev. April, 1840, pp. 505 — 6.] 502 ADDENDA- Function of the Nucleus. It was stated by Schleiden that in vegetables the nucleus is usually reabsorbed. In the tissues of animals, hoAvever, its'per- sistence was remarked -by Schwann, but he seems to have con- sidered its function as relating mainly to the formation of the primary cell arising from it. Dr. Barry h.as shoAvn that it has reference also to the formation of the secondary cells Avhich are developed within the first or parent cell. This development of one cell within another, though very common if not universal in vegetables, was thought by Schwann to be comparatively rare in animals. Dr. Barry's embryo!ogical researches have shown the error of this opinion. Exceptions to the law of development from cells. A feAv of the tissues seem to be produced more directly, by the simple consolidation of the fluid plasma (organizable fluid) into fibrillas and'membranous lamellas; and soriie, (as Avould appear from Henle's observations,) are formed by the coalescence of* the elements of cells, whose development into cells has. been arrested. (Carpenter's Report.) SchAvann . acknowledged the existence of one or tAvo exceptions to the law of development from cells. The most striking example is. found in the inter- cellular substance of the cartilages, which shoAvs a distinct fibrous structure including cells in its meshes, these cells appearing to be independent of the tissue by Avhich they are surrounded, and not to have contributed to its formation, unless, as has been suggested, they may "diffuse such a plastic influence on their exterior^ as in muscle and the vegetable tissues they seem to exert on the depo- sitions within their cavities." [B. fy F. Med. Rev. April, 1840.] Extension of these doctrines. The original conclusions respecting the formation and function of cells have been in many respects greatly developed, as the fol- lowing statements from Dr. Carpenter's report will sufficiently show. — " Not only does it now appear that nearly all the animal tissues,- however great the alterations they may have undergone in structure and properties, have their immediate origin in cells ; but that in animals, as in plants, all the changes in which organic life essentially consists, are performed by cells, scarcely distin- guishable from each other by any well marked characters.'''' The author proceeds to explain that he does not mean to in- clude purely animal functions, such as those of the brain and muscular systems, nor those of a merely physical character, as the resistance and support of the solid and elastic tissues. ADDENDA, 503 " We knoAv of no animal," he continues, " so simple as the lowest cryptogamian plant; but there is reason, to'believe that there are many in Avhich no vessels exist, their tissue being every where in near contact with the nutrient fluid, and absorbing directly from it ; and it is certain that there are many in Avhich a few scattered muscular fibres and nervous filaments constitute the only departure from the general type of cellular tissue. Here, ' then, there is no difficulty in understanding that all the functions of organic life, absorption, assimilation, nutrition, respiration, secretion, and reproduction, must be performed by cells. Again, in the early condition of the embryo, Avhich is at first'nothing more than a mass of cells, precisely the same holds good. For some time its life is entirely vegetative ; it absorbs its nutriment by cells spread over the yolk; and this nutriment is at first applied solely to the development of neAV cells, some of which gradually undergo metamorphosis into other tissues. But the same will be found true of this function in the adult state of the highest animal; for nutritive absorption is in it also performed by cells, which appear destined to this function alone. In like man- ner it Avill appear that another set of cells have for their office the assimilation of the nutriment, that is, the preparation of it for entering into the composition of the living organized body. Further, it seems certain that thie first 'development of nearly all the tissues takes place from cells, Avhich are produced at the ex- pense of this assimilated nutriment. Again, the separation from the circulating fluid of those products which are. to be cast off from it, is also accomplished by cells. With regard to the sim- ple exhalation of fluid, it may be remarked that this, like imbibi- tion, is a physical function, dependent upon the permeability of membrane ; and that the vital action of cells is therefore not necessary for it. The same may perhaps be said of respiration ; but we shall find that in this the action of cells is concerned. Lastly, in regard to reproduction, it appears that the essential part of this process consists, among animals as among plants, of the multiplication of cells under peculiar conditions."— [Carpenter's Report on the Origin and Function of Cells, in the British and Foreign Medical Review, for January, 1843. Schwann and Schleiden on the Identical Structure of Plants and Animals, in the same Review, for April, 1840. Midler's Physiology.] 9 Structure of the Mucous Membranes, (p. 49.) These membranes are lined by a thin cuticle, corresponding to the epidermis. Recent microscopic investigations have shown that this cuticle or epithelium, as it is called, is formed by an aggregation of nucleated cells, formed at the surface of the mem- brane, Avhich assume several appearances, according to the part Avhere they are found. The most common kind is that Avhich 504 ADDENDA. lines the mouth, the conjunctiva of the globe of the eye, the va- gina, etc., and is similar to the lining membrane of the synovial and serous membranes, the blood and lymph vessels, and to the epidermis. This is called tesselated or plaster-epithelium, from the flattened shape of its superficial layers. The next variety is called cylinder-epithelium, and is composed of conical, pyramidal, or cylindrical cells, Avhose apices are attached, and whose bases are free. This is found in the stomach and intestines, the male genito-urinary apparatus, etc. The third variety is the ciliary epithelium, in which cells like those of the second variety have attached to their free extremities several cilia, or hair-like processes, which by some unknown power are during life constantly whirl- ing round their fixed extremities, or waving backwards and for- wards. Examples of this are found in the respiratory mucous membrane, the palpebral conjunctiva, etc. [Paget's Report on AnaL fy Phys. in B. fy F. Med. Rev. for July, 1842.] Structure of the Skin. (pp. 51, 341.) The researches of Breschet and Roussel profess to have shown the existence of certain organs situated in this compound struc- ture not previously described. They recognise : 1. The dermis or fibrous layer. 2. The papillae. 3. The organs of exhalation, consisting of a glandular parenchyma, (contorted tubes; Wagner,) situated in the substance of the dermis, (beneath the dermis ac- cording to Muller, Wilson and Carpenter,) and of spiral canals which open by minute pores through the epidermis. 4. Rami- fied inhalent vessels. 5. The glandular organs which secrete the mucous substance, which, by hardening becomes the epidermis, consisting of the secreting bodies situated at the deepest part of the dermis, and their excretory canals. These constitute what is called by Breschet the blennogenous apparatus. 6. The chromato- genous apparatus, or that which secretes the colouring matter of the skin, consisting of glandular bodies and excretory ducts. To these must be added the accessory parts, as the hair, the nails, the mucous, adipose and sebaceous follicles, etc. These anatomical views have excited much attention, but do not appear in all points to have been confirmed, while in others they are opposed by subsequent observation. The existence of the spiral sudoriferous ducts, and the glands in which they have their origin, is generally agreed upon. The former are easily seen in a very thin lamina shaved from the skin of the sole of the foot, or palm of the hand, in a direction perpendicular to its surface. The epidermis is shown to consist of nucleated cells, formed by the fluid exudation from the surface of the dermis, the outer lay- ers of which become flattened and hardened, while the inner soft ones constitute Avhat Avas formerly called the rete mucosum. The hair and nails have a similar origin, like the epithelium of ADDENDA. 505 the mucous membranes, Avhich corresponds to the epidermis. The colouring matter has a similar origin in cells formed at the surface of the cutis. [Nouvelles Recherches, etc. Par. M. G. Breschet, etc., Paris, 1835. — 'Wilson's Anatomists' Vade Mecum. — Midler's Physiology. — Carpenter's Physiology. — Paget's Report in B. fy F. Med. Rev. for July, 1842T] Structure of Bone. (p. 53.) The general disposition of the structure is that of lamellas, which are disposed around tubes and cellular cavities. The tubes are called Haversian canals, from the name of the anatomist Avho first described them. Each of them contains an artery and a vein. The cellular cavities, though imperfectly described by LeuAven- hoeck and others, and though obvious enough through an ordi- nary microscope in a thin slice of bone, have not been satisfac- torily examined until within a feAv years. These cavities, or as they Avere formerly called, bone corpuscles, are round or oval, and flattened, having jagged Avails, from which proceed delicate branch- ing tubes, (calcigerous canals) Avhich terminate in the Havers- ian canals. It seems probable that these canals and their branches are empty. An excellent figure of them is given in the second edition of Wilson's Anatomists' Vade Mecum, p. 4. Structure of Muscular Fibre, (pp. 54, 57.) A remarkable difference betAveen the muscular fibres of organic and of animal life, consists in the appearance of transverse striae upon the latter. Those of organic life are Avithout these marks, flat, and sometimes containing nuclei. Microscopic observers have been unable to agree as to the cause of the strias, and the ultimate arrangement of the molecules of the animal fibre. Mr. BoAvman's view of the cause of contraction is similar to that of Raspail, mentioned at p. 402. [Paget's Report.] Structure of the Nervous System, (p. 56.) The cineritious, gray, cortical, or ganglionic portion, is found to consist of spherical or oval globules, containing one or more nuclei Avith subordinate nucleoli. Each of them is contained in a fine filamentous sheath, and is constituted mainly of a red or reddish-gray granular material, held together by a clear, soft, gela- tinous substance. The intimate structure of the primitive ele- ments of the medullary portion, beyond the fact of its tube-like character arising from the existence of a sheath and a softer con- tained matter is not perfectly understood. [Ibid.] 64 506 ADDENDA. Structure of the Arteries, (pp. 59, 178.) The observations of Henle would show that the arteries pos- sess a coat of circular fibres, Avhich in respect of development and microscopic structure is similar to the layers of organic muscle in the stomach. Externally to this he recognises a coat of genuine elastic tissue, which exists, hoAvever, only in the larger arteries, the muscular coat becoming more and more evident as the size of the arteries decreases. [Ibid.] Lymph and Chyle, (pp. 60, 278, 293.) Both these fluids contain globules, the relation of which to those of blood does not appear to be yet determined. Colourless corpuscles are found in the blood, (p. 69) but it is not certain that these are identical with chyle or lymph globules. It has been conjectured that the red corpuscles are formed from those of the chyle. It has also been supposed that the globules of the chyle and lymph may be the nuclei, or cytoblasts of the primordial cells from which all the tissues are developed. [Paget's Report. — Carpenter's Physiology. — Muller's Physiology.] Cause of the Buffy Crust. The stratum of liquor sanguinis, free from red globules, which forms the upper portion of the clot of inflammatory blood, as mentioned at page 61, is commonly called the buffy coat, or the inflammatory crust. Its formation is ascribed to the slowness with which coagulation takes place, Avhich gives the red particles time to subside. It has been shoAvn by Dr. Stokes's experiments, that this is not the true cause of the phenomenon in question. The observations of Professor Nasse, of Marburg, confirmed by those of Mr. Wharton Jones, tend to shoAv that it is owing to an in- creased power of aggregation in the red globules, which by their closer union press out the liquor sanguinis from the kind of sponge- work which they form, and becoming specifically heavier by this condensation, subside to the bottom, leaving the liquor sanguinis they squeeze out from their meshes to accumulate at the surface, where by its coagulation it forms the yelloAvish crust in question. [ Observations, etc. by T. Wharton Jones, in the Brit. 6f For. Med. Rev. for Oct., 1842.] Relation of Fibrin to Albumen, (pp. 65, 80.) " Chemical analysis has led to the remarkable result, that fibrin and albumen contain the same organic elements united in the ADDENDA. 507 same proportion, so that two analyses, the one of fibrin, and the other of albumen, do not differ more than two analyses of fibrin or two of albumen respectively do, in the composition of one hundred parts." [Liebig's Animal Chemistry, p. 39.] But if no important chemical difference can be detected in the composition of these two substances, their properties are very dif- ferent. Dr. Carpenter ingeniously suggests the analogy which this phenomenon presents to that of isomerism in inorganic chemistry. It is now well known, that two substances which are isomeric with relation to each other, — that is, which have the same elements in the same proportions, — may possess very different qualities. The mode of combination is no doubt differ- ent in the two cases. Fibrin appears to be more highly organized than albumen, its particles being ready to take the form of a regular structure, so soon as they are separated from the circulating fluid and left in contact with a living tissue. Even when with- drawn from the body, the coagulum it forms presents, according to Mr. Gulliver, distinct traces of organization. [Carpenter, Op. Cit.] Blood Corpuscles, (p. 66.) The flattened, disk-like form of the blood corpuscles, as they should be called, rather than globules, is seen Avith perfect ease by the inexperienced observer, as they roll over in the field of the microscope. To examine them, a little serum, or a solution of salt or sugar, may be placed on the object-glass, and a minute drop of blood from a prick of the finger mingled with it. Water im- mediately destroys the form of the corpuscles. These bodies are now very commonly regarded as nucleated cells, each having an independent life and assisting in one or more important functions. Thus, while they are considered by Whar- ton Jones and others in the light of swimming glands, the object of Avhich is to elaborate the " organizable plasma" — in other words, to change albumen into fibrin,—it is Avell known that Liebig treats of them principally as the agents by which oxygen is carried from the lungs through the rest of the system. [Whar- ton Jones. — Liebig. — Carpenter.] The experiment mentioned upon the 73d page, which Avas thought to show an extraordinary diminution in the volume of the dead as compared Avith the living blood, can hardly be thought sufficient to establish an opinion so entirely opposed to Avhat we know of the nature of fluids in general and of the blood in par- ticular. 503 ADDENDA. Composition of Acetic and Lactic Acids, (p. 7S.) ACETIC ACID. LACTIC ACID. Carbon, . . 40.00 Carbon, - . 44.92 Hydrogen, . 6.67 Hydrogen, . 6.11 Oxygen, . . 53.33 Oxygen, . . 48.97 {Liebig's Animal Chemistry.] Cause of the Arterial Pulse, (p. 180.) The experiments of Poiseuille have demonstrated that an actual dilatation of the arteries takes place at every pulsation, amounting to about -^ of their capacity. [Mutter, i. 212.] Vital Contractility of the Arteries, (p. 181.) It is evident that the arteries possess a power of altering their calibre independent of simple elasticity, but there is every reason to suppose this is exercised in regulating and riot in propelling the current of blood. The asserted existence of a muscular coat distinct from the elastic tunic, Avhich has been already mentioned, (p. 506) would account for the existence of these powers in differ- ent degrees in the larger and smaller arteries, according as one or the other coat predominates. The supposed artery in the frog and toad, which pulsates after the removal of the heart, is, as we believe, identical with the lymphatic heart of these reptiles, a description of Avhich is given in Muller's Physiology, i. 292. Sounds of the Heart, (p. 184.) The second sound is now generally attributed altogether to the sudden depression of the sigmoid valves of the aorta and pul- monary artery. The causes of the first sound are less certainly established. Dr. Hope's conclusion is in these Avords. — " The first sound is compound, viz. consisting 1st, of valvular sound: 2d, of the sound of extension — a loud smart sound, produced by the abstract act of sudden, jerking extension of the braced muscular walls; 3d, a prolongation, and possibly an augmentation, by bruit musculaire," (muscular sound). [On Dis. of Heart, etc. Pen- nock's edit. p. 79.] The London and Dublin committees conclude that valvular action is not a cause of the first sound. [Ibid, pp. 78, 79.] Drs. Pennock and Moore are of opinion, that the auriculo-ventricular valves, (to which, if any, it must be attribu- ted) "aid but slightly in its production." [Ibid. p. 65.] Dr. Williams appears to consider the " sound of extension," men- tioned by Dr. Hope, as identical Avith the sound of contraction. ADDENDA. 509 Finally, Drs. Pennock and Moore are disposed to think that the contraction of the auricles, and the rush of blood from the ven- tricles may contribute to make up the sound. Thus, it will be seen, that the only cause on which all agree, is muscular contraction. But there is good reason for believing that some other causes are concerned, of which valvular extension seems to us among the most probable. Nerves of the Larynx, (pp. 217, 412.) The recurrent nerve " is distributed to all the muscles of the larynx, Avith the exception of the crico-thyroid." [Wilson.] Cruveilhier describes particularly a branch distributed to the ary- tenoid muscle, which is the chief contractor of the larynx. [Anat. Descriptive, iv. 863.] The experiments of Dr. J. Reid, " have established, that Avhilst the inferior laryngeal (recurrent) is the motor nerve of nearly all the laryngeal muscles, the supe- rior laryngeal is the exciter or efficient nerve, conveying to the medulla oblongata the impressions by which muscular movements are excited." [Carpenter.] The suffocation which follows the section of the recurrents, Avhen the respiration is excited, as by a struggle, is attributed to the falling in of the lips of the glottis, the muscles of which are paralyzed, and close the opening during inspiration like a pair of valves. [Ibid.] The loss of voice, attributed to the existence of tubercular cavities, (p. 412,) is commonly, if not always OAving to ulceration of the larynx, often affecting the chordae vocales. This is a most frequent complication of phthisis. Structure of the Liver, (p. 251, et seq.) The investigations of Mr. Kiernan, have cast neAV light on the disposition of the ultimate elements of this organ. The student will find these vieAVs explained and illustrated by figures in several of the recent Avorks on anatomy and more extended physiological treatises. Mr. Kiernan considers the gland as made up of minute granules which he calls lobules. Each of these lobules rests upon a branch of the hepatic vein, a twig from Avhich enters the lobule, to Avhich it holds the relation of the stem to a leaf. The portal vein ramifies in the intervals of the lobules, and sends branches into their substance, which there form a venous plexus. The blood of these plexuses is collected by the branches of the hepatic vein, arising from the stem which supports the lobule. The hepatic artery sends its branches among the lobules, and their extremities open into the venous plexuses formed by the portal vein. Thus the hepatic vein receives the blood of the por- tal vein directly from its venous plexuses, and also receives that 510 ADDENDA. of the hepatic artery mediately through these plexuses, into which, as stated, it Avas poured by the arterial extremities. The biliary ducts appear to begin by loops, or blind extremi- ties, and to form a plexus in the interior of each lobule. These branches or plexuses form the proper substance of the lobule. There is no reason to suppose there is any other communication between these ducts and any of the vessels, than such as exists between similar parts in other secreting organs, depending upon primeability of the membranous walls, and not " direct anasto- mosis." (p. 263.) [See p. 512.] The bile is thought to be secreted from the branches of the portal vein, which form a plexus in the interior of each lobule. But as this plexus receives the terminal branches of the hepatic artery, it might be said that the secretion is formed from a mixture of ar- terial and venous blood. It has been answered to this, that the fact of the blood of the artery having passed through its capillaries into the portal vein, shows that it must have undergone a change into the venous character. The point appears to be yet unsettled. As the portal vein forms its plexuses in the more external por- tion of the lobules, and the hepatic vein occupies its centre, the appearance produced by congestion in these two vessels will be different. If there is congestion of the portal system, while it does not exist in the hepatic vein, the liver will present the ap- pearance of yellowish spots upon a red ground. But if the hepatic vein is the seat of congestion, while the portal system is free from it, the appearance will be that of red spots upon a yel- lowish ground. If both veins are congested, a uniform red will prevail, and a uniform yellowish tinge if both are free from the usual quantity of blood. [ Wilson's Anatomists' Vade Mecum, — Carpenter's Physiology.] Nature of Food. (p. 260.) The researches of modern chemistry have shewn that the nu- tritious portions of vegetables, are only modifications of one azo- tized principle, to which its discoverer, Muller, gave the name of proteine, from the Greek word expressive of its preeminent im- portance. It is also established that the three animal principles, fibrin, albumen, and casein are only modifications of this same principle. The essential element of the blood and the milk, and consequently of all the tissues, is therefore elaborated in vegetable organims. [See Liebig's Chemistry, pp. 46. 48. 101, etc., Cam- bridge edition.] Communication of the Lacteals with the Intestinal Cavity. (p. 277.) There appears to be no direct communication by means of open mouths. [Muller, i, 287— 8, and plate 1, fig. 9, 2d edition.] ADDENDA. 511 Mechanism of absorption by the Lacteals. (p. 277.) The following is the description of this process by Mr. Good- sir, as given in the Edinburgh New Philosophical Journal. " Having fed a dog with oatmeal, milk, and butter, the author examined the intestinal villi three hours afterwards, when the lacteals were turgid Avith chyle, and the gut full of milky chyme, mingled with a bilious looking fluid. In the white portion of the fluid, which was situated principally towards the mucous mem- brane, numerous epithelium cells were found, some of which had evidently (from their form) been detached from the surface of the villi, whilst others had been thrown off from the interior of the follicles of Lieberkuhn. The villi Avere turgid, and destitute of epithelium except around their bases. Each villus was covered by a very fine smooth membrane, continuous with what Mr. Bowman terms the basement membrane of the mucous surface, which is reflected from the follicles. The villi Avere semi-trans- parent except at their free or bulbous extremities, Avhere they were Avhite and nearly opaque. The summit of each villus was crowded beneath the enveloping membrane, with a number of perfectly spherical vesicles, varying in size from TttW to ?5Vd of an inch; the matter in the interior of Avhich had an opalescent milky appearance. At the part Avhere these vesicles approach- ed the granular texture of the substance of the villus, minute granular or oily particles Avere situated in great numbers. The trunks of tAvo lacteals could be easily traced up to the centre of the villus; and as they approached the vesicular mass, they sub- divided and looped ; but in no instance could they be seen to communicate directly with any of the vesicles. " These vesicles can scarcely be considered in any other light than as cells, Avhose lives have but a very brief duration, selecting from and appropriating the materials in contact with the surface of the villi into their own substance, and then liberating them, by solution or disruption of the cell-wall, in a situation where they can be absorbed by the lacteals. When the gut contains no more chyme, the development of new vesicles ceases, the lacteals empty themselves, and the villi become flaccid. During this inter- val of repose, the epithelium is renewed, for the protection of the surface of the villi, and for the secreting function of the follicle of Lieberkuhn. It is considered by Mr. Goodsir, that the epithelium cells have their origin in certain nuclei, Avhich he detects scattered through the basement membrane. " There appears to be a strong resemblance between the process of absorption in animals, as thus explained, and that which takes place in plants through the medium of the spongiole." [B. 6f F. Med. Rev. for Oct., 1812.] 512 ADDENDA. Secretion and Nutrition, (pp. 291, 325.) The principal laAvs of glandular structure, as laid doAvn by Mal- pighi and Muller, are the following : " 1st, That a general unity of plan prevails in the seemingly manifold varieties of glandular structure in the different organs, and classes of animals; 2nd, That all secretory glands are composed of tubes opening on a free surface, and either simple, or variously ramified, so as to present in a small solid space a very great extent of surface for secretion; 3d, That Avhile the excretory end of the gland-duct opens on a free surface, its opposite or secretory end is always closed; 4th, That aggregations of these blind ends of a ramified gland-duct form the acini, Avhich Avere long supposed to be the proper agents of se- cretion ; 5th, That there is no open communication between gland-ducts and other vessels, and that the blood vessels do not open into the ducts or acini, but ramify in a capillary network in their walls and interspaces, and these supply the materials of the secretion." [Paget's Report.] But there are certain secreting bodies which seem to be excep- tions to these rules. Such are the grouped (Peyer's) and isolated glands of the small intestines, which consist of simple sacculi without any orifice, and which having matured their contents, discharge them by rupture or absorption of their parietes. The (Graafian) vesicles of the ovary, (p. 419,) which, after having alloAved the development of the ovum in their cavity, discharge it by bursting into the Fallopian tube, may be considered as analo- gous to the closed glandular bodies just mentioned. But the agency of closed cells has been alleged by some recent distinguished observers, to be concerned in every proper act of secretion. (The mere exhalation of Avatery fluid from the ex- ternal or internal surfaces, is to be considered only as a physical phenomenon.) In the account given by Mr. Goodsir of the me- chanism of absorption of the chyle by the lacteals, we have seen that the true agents in this process are probably the cells which are found at the summit of the villi, beneath its enveloping mem- brane and around the terminations of the lacteals. These cells, as we have seen, are thought, first, to absorb the chyle from the intestine, and then to discharge it by rupture or dissolution into the lacteals, or, in other words, to take certain materials from a free surface and pour them into the circulating fluids. The process of secretion is simply the reverse of absorption; the materials are taken from the circulating fluid and poured out on the free surface. The researches of Purkinje, Henle, and the more recent ones of Mr. Goodsir, tend to shoAV that the nucleated cells which line the ducts of glandular organs, and constitute their epithelium, are the true agents in secretion, elaborating certain constituents from the blood, Avhich they discharge by rupture or otherwise upon the ADDENDA. 513 surface of the du<^t. Mr. Goodsir remarks that, " there are not, as has hitherto been supposed, two vital processes going on at the same time in the gland, growth and secretion; but only one, viz. groAvth. The only difference between this kind of groAvth and that which occurs in other organs being, that a portion of the product is, from the anatomical condition of the part, thrown out of the system." That is to say, the materials appropriated from the circulating fluid by the cells Avill be deposited in the midst of the tissues, or thrown out upon a free surface, according to the situation of the cells, in the same Avay as the coagulable lymph of dysentery being formed in an open canal, is evacuated as a secretion, Avhile that of pleurisy being deposited in a shut sac, is organized, like the materials added to the healthy tissues by the ordinary process of nutrition. But the power of selection which causes the secreting cells of the kidney to elaborate urine, those of the liver to form bile, and those of the tissues generally to appro- priate the proper materials for their growth, depends upon some difference wholly unexplained by any thing as yet observed in their microscopic or chemical characters, and may probably al- ways remain without explanation. [Paget's Report. — Goodsir on the Ultimate Secreting Structure, etc., as cited in the Brit. 8f For. Med. Rev. for Oct. 1842.] Source of Animal Heat. (p. 342.) The doctrines of Liebig, with the experiments upon which they are based, have been so widely made known by his work on Animal Chemistry, and his " Familiar Letters," Avith the analyses, reviews, and discussions without number to Avhich they have giv- en origin, that it can be only necessary here to recall the leading principles which he has taught, referring to the sources mentioned for further details. These principles are 1st, that " The mutual action betAveen the elements of the food and the oxygen convey- ed by the circulation of the blood to every part of the body is the source of animal heat." 2nd, That the combination of car- bon Avith oxygen always produces a given amount of heat, wheth- er that combination takes place rapidly or slowly, at a high or a low temperature. Thus the carbon of the food changed to car- bonic acid in the body, gives out just as much heat as if it had been burned in the air or in oxygen gas ; the amount of heat evolved is less intense in the first case than in the second or third, but it is produced for a proportionally longer time. 3d, Whatev- er intermediate forms the food may assume, its last change is uni- formly the conversion of its carbon into carbonic acid and its hydrogen into Avater (in other words their combustion,) the unas- similated nitrogen and unoxidized carbon being expelled in the urine or solid excrements. 4th, The quantity of heat generated in 65 514 addenda. the body, will therefore be proportionate, fir^, to the quantity of oxygen received into the system, and second, to that of the food, or rather the carbori 'and hydrogen Avhich it contains. In cold climates a given volume of air contains more oxygen than in warm climates ; the nature of the soil arid the effect of the atmosphere prompt to more active exercise,.Avhich.excites the activity of the respiration. The food employed • in these climates contains a much larger proportion of carbon than the natural food of the in- habitants of the south, and is consumed in much larger quantities. Thus the two conditions of a high animal temperature are furnish- ed to the inhabitant of the northern regions. 5th, If food is not supplied, the oxygen introduced by respiration consumes the tis- sues of the body itself. In the progress of starvation, first, the fat disappears, the'n the other parts 'in succession are acted upon, and converted into oxidized products (carbonic acid and water) which are given off by the* skin and lungs. The animal heat is maintained at the expense of this oxidation or sIoav combustion of the body itself. "A starving man.is soon frozen to death; and .every one knoAvs, that the animals of prey in the arctic regions far exceed in voracity those of the torrid zone." According to Liebig's" calculations 13.9 oz. of carbon derived from the food are daily converted into carbonic acid, — that is, ox- idized or burned, —in the body of a healthy adult. By computing the number of degrees of heat evolved in this act of combination, he arrives at the conclusion, that "no doubt can be entertained, that when all the concomitant circumstances are included in the calculation, the heat evolved in the process of combustion, to which the food is subjected in the body, is amply sufficient to ex- ' plain the constant temperature of the body, as Avell as the evap- oration from the skin and lungs." This process of oxidation or combustion is always going on simultaneously in the lungs, Avhere the oxygen of the atmosphere combines with the red corpuscles, and in the capillaries, Avhere the oxygen of the red corpuscles combines with the elements of the food and certain portions of the tissues themselves, which are thus removed to make room for neAV depositions of organized matter. If food is not supplied, the whole process, as Ave have seen, goes on at the expense of the living tissues, which are rapidly wasted. The only influence, according to Liebig, which the nerves have in the production of animal heat is in enabling the organs to form those substances with Avhich the oxygen enters into combination. Properties of the Muscles, (p. 392.) The distinction betAveen " contractility of tissue" or " animal elasticity" and what is called lone is not insisted upon in this connection. If the reader will turn back to page 140, he will find the latter property is spoken of, and shown by Dr. Hall's ex- ADDENDA. 515 penments to be dependent upon the integrity of the spinal mar- row. It is therefore evidentlv different from mere mechanical elasticity depending on the "large quantity of cellular tissue in- corporated in their substance." It is also evidently different from the contraction of a muscle, in obedience to the will or to any di^ rect irritation. The one is an occasional action which the rhuscle can keep up only for a limited time, after Avhich it "becomes painful and difficult, and can no longer be maintained ;" the other is the permanent and natural condition of the muscles in the healthy system, and constitutes in fact their state of repose in op- position to the state of activity. Glands of the Female Vagina, (pp. 421, 424.) Two remarkable glands situated at the entrance of the female vagina, Avere described by several distinguished anatomists of the 17th and 18th centuries, but Haller, having failed to detect them, denied their existence, and they Avere long forgotten, until at length Mr. Taylor rediscovered them, and described them in the Dublin Journal, (vol. xiii.) They are also briefly alluded to in Mr. Guthrie's Avork on Diseases of the Bladder. Professor Tiedemann, of Heidelberg, has recently published a monograph relating to these bodies, (On the Glands of Duverney, Bartholinus, or Cowper, in the human female, etc., Heidelberg and Leipsic, 1840). His description is as follows. " These glands are situated at each side of the entrance of the vagina, beneath the skin covering the posterior or inferior part of the labia. They are likewise covered by the superficial fascia of the perineum, and by the fibres of the constrictor vaginas. They here occupy a space included between the loAver end of the vagina and the ascending ramus of the ischium,