DUKE UNIVERSITY MEDICAL CENTER LIBRARY HISTORY OF MEDICINE COLLECTIONS Gift of Michael R. McVaugh, PhD Digitized by the Internet Archive in 2016 https://archive.org/details/firstlinesofphys01oliv FIRST LINES OF PHYSIOLOGY; DESIGNED FOR THE USE OF STUDENTS OF MEDICINE. X BY DANIEL OLIVER, M. D. Professor of the Theory and Practice of Physic, &c. in Dartmouth College* Multa esse constat in corpore, quorum vim rationemque perspicere nemo, nisi qua fecit, potest .Lactant. de opific. Dei. BOSTON: MARSH, CAPEN & LYON ; JAMES MUNROE & CO. ; AND RUSSELL, SHATTUCK & CO. 1835 . Entered according to Act of Congress, in the year 1835, By Daniel Oliver, M. D. In the Clerk’s Office of the District of New-Hampshire. Printed by William A. Hall & Co. 122 Washington street. PREFACE. The following work had its origin in a request made to the author by the Medical Class of Dart- mouth College, of the year 1833, that he would pub- lish his Lectures on Physiology. He consented to take the subject into consideration, and if, upon a careful revision of his lectures, he should be able to satisfy himself, that they were, in any degree, worthy of the public eye, to comply with the wishes of his young friends. His final determination on the subject may be gathered without difficulty, from the appearance of the present work. Whether he has acted wisely in presenting himself to the public, in the capacity of an author, on a subject preoccupied by numerous respectable, and some cele- brated names, is a question which he will not venture to decide ; but will only suggest, that the work, being designed for students, makes no pretensions to origin- ality, or novelty, but is wholly derived from the co- pious sources of physiological knowledge, which have fertilized this department of science, and, from the nature of the case, can possess no higher merit than that of arrangement and correctness. But, with re- gard to the latter point, it is well known, that there are many questions, on which physiologists are by no means agreed ; and that what one holds to be sound IV PREFACE. doctrine, may be regarded as heretical by another ; and that, of course, it is impossible for any system of opinions to obtain universal approbation. On such questions, the author has exercised the common privi- lege of being guided by his own judgment, after carefully weighing the authorities and the evidence on opposite sides of the disputed points. In the collection of Iris materials, he has consulted all the works on the subject, which were accessible to him ; but the authors to whom he is principally indebted are the following ; viz. Adelon, Bourdon, Lepelletier, Magendie,Broussais, Mayo, Rudolphi,* * * § Berthold,t Mar- tini,^ Jacopi,§ Tieclemann, and Tiedemann and Gmelin, and the authors of the admirable articles on Physiology, in the Dictionaire de Medicine. From most of these sources he has drawn largely, and, in many instances, without particular acknowledgment, which, in an ele- mentary book, designed for students, appeared to be unnecessary. Some apology may be thought necessary for the chapter on animal magnetism. This, he trusts, may be found in the attention, which this subject has re- cently attracted, chiefly in consequence of the publi- cation of the Report of the Committee of the French Royal Academy, appointed to investigate the subject of animal magnetism, read before the Academy on the 21st and the 28th of June, 1831, and the extraordi- nary narrative of Jane Rider. The report mentioned above, signed by several distinguished French physi- * Grundriss der Physiologie, Berlin, ISIS, t Lehrbuch der Physiologie, Gottingen, 1S29. t Elementa Physiologies, Taurini, 1828. § Elementi di Fisiologia e Notoraia Comparativa, Livorno, 1S23. PREFACE. V cians, the author regards as sufficient of itself to justify the insertion of a chapter on the subject ; and the history of Jane Rider’s somnambulism, con- tains several authentic facts, almost as incredible as the mirabilia of animal magnetism. The Academy of Berlin, we are informed, in 1818, proposed a prize on this subject; and an ordinance of the Prussian government of 1817, prohibits the prac- tice of magnetism to all but licensed physicians. In Russia and Denmark similar regulations have been adopted. Many eminent physicians of France and Germany have become converts to Mesmerism ; and Hahnemann remarks, that none but madmen can en- tertain a doubt of its curative powers. The author expresses no opinion of his own upon the subject, but would merely remark, that a doctrine embraced by such men as Rostan, Georget, Guersent, Itard, Hufe- land, and many other distinguished names, ought not to be rejected with contempt, and without examina- tion, as a tissue of the grossest charlatanism and fraud. In conclusion, the author, though aware of numer- ous imperfections in his book, ventures to express his hope, that it may not be found wholly unworthy of the attention of the profession, especially of its younger members, and of students, for whose use it is exclu- sively designed. ERRATA. The distance of the author’s residence from the press, has given occasion to several errors to creep into the text. The reader is requested to correct the fol- lowing, as affecting the sense. The others, consisting of literal errors, and obvi- ous at the first glance, it was thought unnecessary to notice particularly. Page 144, line 21 — from top, dele, owing. 156, “ 22 — for riveted , lege, united. 160, “ 24 — for thin , 1. their. 211, “ 23 — for settled , 1. fitted . 238, “ 10 — for to, 1. depends on. 254, “ 9 — -for for instance, as, 1. as, for instance. 266, “ 21 — insert fluid, after gastric. 301, “ 19 — for Lown, 1. Lower. 310, “ 28 — for thin, 1. their. 312, “ 21 — for purgations, 1. purgatives. “ “ 25 — for appearance, 1. disappearance. 321, “ 32 — for muriate, 1. minute. 329, “ 39 — for the, 1. other. 353, “ 4 — for dogs, read days. 361, “ 12 — for cholestine , 1. cholesterine. 428, 2 — for then, 1. thus. 432, “ 41— for Jive hundred, 1. fifteen hundred. 508, “ 21— for the magnetic sleep then , 1. in magnetic sleep, there. 509, “ 10 — insert as, after necessary. “ “ 11 — for something, 1. sometimes. CONTENTS. CHAPTER I. Definition of Physiology. Page. Definition of Physiology 9 Two classes of bodies, viz. inorganic and organic 9 Two elements in each, viz. material and dynamic. Life inseparable from organization 10 Organic matter endued with two kinds of force, viz. physical and organic 10 CHAPTER II. Comparison between Organic and Inorganic Matter. Peculiarities of organic matter 11 Organic bodies possess determinate forms and magnitudes 11 They contain globular particles 12 — consist of solid and fluid matter, and systems of organs 13 — consist of two kinds of elements 14 — form ternary or quaternary, compounds 15 Conflict between chemical and organic power 18 Organized bodies react against the chemical forces of matter... 19 Their growth proceeds from within 20 — they possess the power of reproduction 20 — are subject to death 21 CHAPTER III. Relations of Organic Bodies to Heat, Light and Electricity. Organized bodies regulate, to a certain extent, their own temperature 21 Organip heat 22 Organized bodies have the power of resisting very high tem- Living beings idio-electric 24 Electrical organs of the torpedo and gymnotus 25 Analogy between them and the voltaic battery 26 The electricity of these animals, vital 26 Phosphorescence of inorganic substances 30 Do. of organic substances during decomposition .. 31 Do. of living substances 32 Phosphorescence of insects depends on peculiar animal matter. . 35 VIII CONTENTS. CHAPTER IV. Comparison of Animals and Vegetables. Organized beings divided into two classes, animals and plants Comparison between them . Page. . 36 . 36 CHAPTER V. Division of the Animal Kingdom. Animal kingdoms divided into vertebrated and invertebrated Human race belongs to the mammalia Peculiarities of mind .. 37 .. 38 39 , 40 CHAPTER VI. Anatomical Analysis, or, structure of the Human body. Structure of the human body. Consists of solids and fluids . • • Ultimate animal solid disposed in various modes. CHAPTER VII. 41 41 Fundamental Tissues. Solids of the body composed of three fundamental tissues, viz. cellular, muscular, and nervous Cellular tissue of two kinds — forms a connected whole — basis of all the membranes Serous membranes line the closed cavities. . •••••*’ ' j Mucous membranes more highly organized than the serous, an line the cavities which open outwardly Skin resembles mucous membrane Skin, an organ of relation •••"". ’11,7,1=" Fibrous membranes consist of condensed cellular tissue , * 5 - Cartilaginous tissue Osseous tissue Bones of three kinds — form a connected system Muscular fibre — fibrin Irritability Nervous fibre — albumen, sensibility 43 44 45 45 46 47 49 50 51 51 52 53 54 54 54 55 CHAPTER VIII. The Compound Structures of the System. 57 Muscles of two kinds, viz. animal and organic * ' -g Where situated .......... * - ’ -g Nervous system of two kinds, viz. animal and organic ....... . Vascular system divided into arterial, venous, and h mp a 1 Arteries and veins, how formed * " fi1 Structure of lymphatics Viseeral system CONTENTS. IX CHAPTER IX. Fluids of the System. Page. riuids divided into three kinds 61 Chyle and lymph , 62 The blood 63 Circulation of the blood 63 Serum, coagulates by heat, &c 64 Cruor — fibrin 65 Red globules, their shape, size 66 Arterial blood contains more globules than venous 67 Hematosine 68 Coagulation, how caused 69 Principles existing in the blood 71 chapter x. Chemical Analysis of the Organization. Ultimate elements of animal matter, metallic ai d non-metallic .. Oxygen exists in all the solids and fluids Hydrogen, also Carbon exists largely in bile and venous blood Azote, principal chemical characteristic 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 animal fluids Iron exists in the blood The organic elements are quaternary compounds — divided into two classes, viz. acids and oxyds Organic oxyds Quaternary compounds, the most important Albumen, the most generally diffused ■ — Fibrin, its properties ) Gelatin, do. $ Osmazome, its properties Mucus and Caseine, Urea . . | their properties . . 72 73 73 74 74 75 76 76 77 77 77 78 79 79 80 81 82 83 CHAPTER XI. Physiological Analysis of the Organization. Organized beings possess the property of being affected by exter- nal agents - Modifications of this property Sensibility Contractility Two kinds of contractility Expansibility 84 85 85 86 89 92 B X CONTENTS. Page. Erectile tissues 92 Alterative powers 94 Physical properties 96 Elasticity 96 Flexibility and extensibility 97 Imbibition 97 Endosmose and exosmose 98 CHAPTER XII. The Functions. Actions of life form a circle 99 Four classes of Functions 100 Vital 100 Nutritive 1 and > 10 L Sensorial ) Genital 102 CHAPTER XIII. First Class , or Vital Functions. Of innervation 102 Encephalic nervous system 103 Cerebrum 103 Cerebellum 105 Pons Varolii. 106 Medulla spinalis 106 Motions of the brain 108 Analysis of the brain 109 Envelopes of brain and spinal marrow 109 Dura mater 110 Pia mater Ill Encephalic nerves 112. Ganglionic nervous system 113 Functions of the nervous system 115 Sensation 117 Brain destitute of sensibility 120 The brain, the organ of voluntary motion 121 — of the intellectual and moral faculties 123 Effect of removing the cerebral lobes 125 Seat of vision threefold 126 Effect of wounding the cerebellum 127 — of mutilating the tubercula quadrigemina 128 Functions of the optic thalami 129 Lobes of the cerebrum subservient to flexion, those of the cere- bellum to extension 130 Influence of the brain over the organic functions , 131 Functions of the spinal cord 135 Medulla oblongata, the seat of consciousness 136 Functions of the anterior and posterior parts of the spinal cord 137 Opinions of Bellingeri 133 Influence of the spinal cord upon the organic functions ........ 140 CONTENTS. XI Page. Influence of the spinal cord upon respiration 140 Do. upon the circulation 142 Do. upon digestion 143 Do. upon nutrition 144 Cerebro-spinal nerves subservient to sensation and motion 145 Nerves of specific sensation 146 Nerves of voluntary motion 147 Nerves of mixed functions 148 Vertebral nerves ... 150 — distinguished by their symmetry 151 Irregular system of nerves 152 Great Sympathetic 153 CHAPTER XIV. The Circulation. The circulation, universal suspension of, instantly fatal 154 Organs of 155 The heart a double organ 156 The arteries form two systems 159 The veins, also 160 The capillary vessels 161 Circulation in reptiles, fishes, &c 162 Course of the circulation 163 Bichat’s division of the circulation 164 Circulation of black and of red blood 164 Capillary circulation 167 Action of the heart 169 Course of the blood in the arteries 171 Quantity of blood 172 Moving powers of the circulation 172 Functions of the heart 173 Functions of the arteries 175 Arteries possess a vital power of contraction 176 Functions of the capillaries 181 Influence of the heart felt in the capillary vessels 182 Functions of the veins 184 Veins exert a motive force 186 Suction power of the heart 188 Effect of inspiration 189 Influence of the nervous system . 190 Influence of the great Sympathetic 191 chapter xv. Respiration. Respiration completes the formation of the blood Lungs, description of — possess two circulations Thorax, how enlarged Inspiration Three degrees of 192 192 194 195 196 197 XII CONTENTS. Page. Expiration 199 T hree degrees of 199 A tion of the abdominal muscles 200 E asticity of the lungs 200 Action of the larynx, trachea and lungs 201 Chemical phenomena of respiration 202 Composition of the atmosphere 202 Analysis of air expired from the lungs 204 Nitrogen absorbed in respiration 206 Volume of air, inspired 206 Quantity of air contained in the lungs, when distended 208 Quantity of oxygen consumed in respiration 209 Consumption of oxygen variable 210 Vital part of respiration 211 Lungs digest air 211 Influence of respiration upon the blood 212 Theories of respiration 212 Oxygen combines with the earb u of me venous blood in the lungs 213 Oxygen absorbed by the blood 213 Do. by the radicles of the pulmonary veins 214 Do. by the lymphatics of the lungs 215 Influence of the par 216 Asphyxia produced by section of this nerve 217 Opinions as to the mode 218 Experiments of Brachet 219 CHAPTER XVI. The Nutritive Functions. Digestion peculiar to animals 221 Apparatus of digestion 222 Stomach 223 Intestines 224 Structure of the digestive canal 225 Motions of the oesophagus • 226 Hunger 228 Manducation 229 Deglutition 230 Chymosis „ 232 Motions of the stomach 233 Gastric fluid 234 — its properties 235 — secreted only when the stomach is excited 236 — its solvent powers 237 Chymification not merely chemical solution of food 23S Reducing, converting, and vitalizing powers of the stomach . . . 239 Chyme 240 Its passage out of the stomach 241 Influence of the par vagum upon digestion 242 Ph illips’ and Brodie’s opinion 243 Breschet’s do 243 LeuretandLassaigne’s do - 244 Brachet’s do. .... 246 CONTENTS. XIII Page. Chylosis 247 Intestinal fluid 248 Bile and pancreatic fluid 248 Appearance of albumen 249 Albumen contained in the pancreatic fluid 251 Analysis of the contents of the small intestines 252 Motions of the small intestines 254 Absorption of chyle 255 Chyle, its properties 256 Caecum, its functions 257 Defecation 258 Liver, found in all vertebrated animals, and in all the mollusca 260 Circulation of the liver 261 Secretion of bile 262 Whether from arterial or venous blood 263 Bile, its properties 265 — its uses 266 — an excrementitious fluid 266 The Pancreas 269 —found in the mammalia in birds— and in the amph.bia 270 Pancreatic fluid 270 Food 271 Animal principles, which contain azote, most nutritious 272 Fibrin 272 Albumen, gelatin, osmazome 273 Starch, mucilage, sugar 274 Saccharine group 275 Oily group 276 Albuminous group 276 Experiments of Magendie on articles o. food 277 CHAPTER XVII. Absorption. Absorption, apparatus of 278 Lymphatics 279 Lacteals 281 Conglobate glands 281 — where situated 282 Functions of the lymphatic system 284 Various kinds of absorption 285 Accidental absorption, internal and external 287 Cutaneous absorption 288 Absorption by mucous membranes 289 Absorption from all parts and surfaces 290 Accidental absorption, in what it differs from nutritive 291 Alimentary absorption 292 — continues after death 293 Chyle, constantly changing in its properties 294 Absorption from whole alimentary canal 295 Substances assimilated in the absorbents 296 Venous absorption 297 — experiments on it 297 Tiedemann and Gmelin’s researches 299 XIV CONTENTS. Page. Lawrence and Coates’, do. 300 Communication between the absorbents and the veins 301 Chyle may get into the circulation though the thoracic duct ob- structed 304 Passage of chyle into the left subclavian vein 305 Internal absorption 306 —effected by the lymphatics , 306 Do. by the veins 308 Imbibition 310 Accelerated by Galvanism 312 Lymph, its properties, and motion 313 Office of lymphatic glands 314 CHAPTER XVIII. Secretion. Secretion 315 — its vital character 315 — in its simplest form, the separation of substances existing in the blood 316 Many secreted substances not educts but products 318 Structure of the secretory organs 319 Glandular follicles 320 Conglomerate glands 321 Classification of the secreted fluids 323 Cutaneous exhalation 326 Quantity of this secretion 328 — varies with many circumstances 329 Mucous exhalations 33 L Internal exhalations 333 Follicular secretions 339 Glandular secretions 341 Secretion of milk 343 Secretion of urine 346 Composition of the urine 351 Uses of this secretion 353 CHAPTER XIX. Nutrition. Nutrition 356 Perpetual decomposition and reparation of the body' 356 Organs themselves, the agents of nutrition 359 Acidification of the organic elements 360 Nutrition influenced by innervation 362 chapter xx. Animal Heat. Animal heat 363 Opinions respecting its origin 363 CONTENTS. XV Page. Crawford’s opinion respecting it 364 Brodie’s do. do 365 Calorification connected with the vital actions of the capillary vessels 366 CHAPTER XXI. Functions of Relation. Functions of relation 369 Sensation 370 CHAPTER XXII. Sense of Touch. Sense of touch 371 Skin 372 Touch, active or passive 373 Most of the soft solids sensible to contact 374 CHAPTER XXIII. Vision. Vision 375 Apparatus of 375 The eye, description of 376 Nerves of the eye 379 Refraction of light 385 The eye, a dioptric instrument 386 Circumstances which regulate the direct on of refracted light . . 388 Refracting powers of the eye 390 Offices of different parts of the eye 394 Motions of the Iris 396 Uses of the choroid coat 399 Do. of the retina 400 Accommodating power of the eye 401 Cause of erect vision 403 Do. of single vision 405 Accidental colors 406 CHAPTER XXIV. Hearing. Hearing, apparatus of 408 Cavity of the tympanum 409 Internal ear 410 Auditory nerve 411 Sound, how excited 413 Physiology of hearing 416 XVI CONTENTS. CHAPTER XXV. Se?t,se of Smell. Page. Sense of smell 418 Organ of 419 Olfactory nerve, according to Magendie, not essential to smell. ■ 421 CHAPTER XXVI. Taste. Taste, apparatus of 422 Tongue, nerves of 423 — the principal organ of taste 424 Teeth, sensible to certain tastes 425 CHAPTER XXVII. Motion. Motion Muscular motion Muscles Composed of fibrin ^ Properties of $ Do muscles in contracting undergo any change of volume ? Velocity of muscular contraction Force of muscular contraction — greater during life than after death The order, in which the different muscles of the human body lose their contractility Causes of the vital contraction of the muscular fibre Causes that increase and diminish the energy of muscular contraction The energy of the brain, the proper stimulus of the voluntary muscles The effects of various other stimuli applied to them Whence the muscles derive their power of contraction .... Whence the muscles of animal and vegetative life derive their nerves Of the essence or immediate cause of muscular contractiori. . . . Mechanical disadvantages under which the locomotive muscles act Various attitudes and motions of the human body analyzed and explained Walking, running, jumping, swimming - Voluntary muscles may acquire a new sphere of contraction. . . Organic muscles — their arrangement and peculiar properties 426 427 428 429 431 432 433 434 436 437 438 438 439 440 440 441 443 447 449 450 451 CONTENTS. XVII CHAPTER XXVIII. Of the Voice. Of the voice Organ of the voice „ The modifications of the voice > — -how produced 5 " ’ ’ Theory of the formation of the voice Experiments of Magendie Page. . 452 . 452 . 453 - 454 . 455 CHAPTER XXIX. Generation. Generation 457 Organs of 458 Male 458 Female 463 Impregnation 467 — various opinions upon 468 — various experiments 470 Theories of generation 473 1. Epigenesis 474 2. Evolution 477 Two sects of the partizans of this system 477 Ovarists 477 Animalculists 480 Various opinions and experiments 481 CHAPTER XXX. Sleep. Sleep 485 — the approach of 486 — the state of, and its effects 487 — the duration of 488 Remote causes of sleep 488 Efficient cause unknown 489 Various opinions on the subject 490 Of the torpid state in animals 491 Dreams - 492 Somnambulism 493 V arious phenomena of 494 Remarkable case of Jane Rider 495 XVIII CONTENTS. CHAPTER XXXI. Animal Magnetism. Page. Animal magnetism 498 Method of producing magnetic sleep 498 Phenomena exhibited in this state 500 Remarkable case of a surgical operation performed during mag- netic sleep 504 State of the mental faculties during magnetic sleep 506 Double consciousness 506 Medical Report of the French Royal Academy 512 Remarks of Cuvier 513 Remarks of La Place 513 CHAPTER XXXlt. Death . Death 514 Natural 514 Accidental 515 Apoplexy, or death of the brain 516 Syncope, or death of the heart 516 Asphyxia, or death of the lungs 516 Physiology of sudden accidental death 517" Signs of death 519 FIRST LINES OF PHYSIOLOGY. CHAPTER I. Definition. Physiology is the science of life, or of the phenom- ena 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 referred to two great classes, viz : the organic, and the inorganic ; distinguished from each other by certain striking properties, and each embrac- ing an immense number of subdivisions, or subordinate 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 corpo- real mass ; the other, certain general properties belong- ing 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 wdiere find matter divested of physical properties, and it is only by mental abstraction that we can conceive of it, as existing without them. For any thing we know, the property of attraction may be as essential to matter, as the corporeal mass w r hich 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 dy- 2 10 FIRST LINES OF PHYSIOLOGY. namic 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 prop- erties 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 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 ex- ist separate from life, because we find by experience that all the external and sensible characters of organ- ization, 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 or- ganization which occasion death, are obvious on dis- section ; 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 condition of life. The powers or forces, which are connected with in- organic 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 transforma- tions of lifeless matter, which constitute these changes, are the results of the operation of these forces. In addition to these two, organized matter is en- dued with another kind of force, which may be term- ed organic , or vital , and which is of a higher order than the two former. It exists in connection with the mechanical and chemical forces, for wherever it is ORGANIC AND INORGANIC MATTER. 11 found, they are present likewise. It cannot exist without 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 with- in the domain of inorganic 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 remark- able contrast with that of inorganic matter. Their other characteristics are no less peculiar and distin- guishing. 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. 12 FIRST LINES OF PHYSIOLOGY. 2. All organized bodies, plants as well as animals, are distinguished by rounded forms, which approach the spherical, oval, or cylindrical, and sometimes are branching and articulated. They scarcely ever pre- sent 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 sur- faces. The forms of mineral substances, on the contra- ry, are bounded by plane surfaces, and straight lines, irregularly broken by. sharp angles. 3. The volume of organized bodies is no less de- termined than their form. Every species of annual and vegetable, has its own proper size, to which, with accidental exceptions, every full grown individual be- longing 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 mat- ter they contain, yet be absolutely identical in their nature or properties. The smallest fragment of a mineral substance has all the properties of the mass from which it was taken. 4. Upon examining organized bodies with a mi- croscope, they are found to contain minute particles of matter of a globular or oval, and sometimes flat- tened 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 con- ferva , the byssus , &c. are composed of them. In most of the animal fluids also, as the blood, chyle, saliva, pan- creatic fluid, the milk, the spermatic fluid, and the fat, globules have been discovered. They have also been observed in the peculiar juices of vegetables, particu- larly in those of the lactescent plants. They are found also in the cells of plants, and in the solid tissues of ani- mals, as the cellular, mucous, and serous ; in the brain, nerves, muscles, tendons and glands. These globules, to which there is nothing analo- gous in minerals, are considered by some physiologists ORGANIC AND INORGANIC MATTER. 13 as the elementary forms of organized bodies, as the ultimate organic molecules, from which, disposed in various modes, the different tissues of animal 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, synovial, 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, pre- sents another very striking characteristic, which distin- guishes them from common matter. Mineral substan- ces are formed of homogeneous parts, which are per- fectly similar in their physical and chemical proper- ties ; while organic bodies consist of various parts, which differ in their forms, properties and functions. A mineral substance 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. Or- ganized 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 influ- ence of the fluids and solids, upon each other. The various parts of which organized bodies consist, per- form different functions in the economy of the individ- ual ; 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 co- hesion. 14 FIRST LINES OF PHYSIOLOGY. 6. These two great classes of bodies, differ also in their chemical 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 together by chemical affinity, or by cohesive attraction. But or- ganized bodies never consist of less than three ele- ments; and animal substances contain at least four, viz. oxygen, carbon, hydrogen, and azote. Carbon may be considered as the characteristic element of one class of organized bodies, viz. vegetables ; and azote, of the other, or animal substances. Further; a mineral has a fixed chemical composi- tion, 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 continually changing the matter, of which they are formed. But, another striking peculiarity in the chemistry of organic bodies, is, that they consist of two kinds of el- ements ; one, which may be termed chemical , such as exist in mineral bodies, as oxygen, carbon, hydrogen, and azote ; and another, which may be called organ- ic , because they are the product exclusively of the or- ganic or vital forces, and are never found in inorganic matter ; such as albumen , gelatine , fibrin , &c. It is owing to the fact, that these last named elements are produced, not by the general powers of matter, but by the peculiar forces of organic life, that it is impossible for us to decompose, and to reform organic substances, as we can inorganic. It is only the general forces of matter, of which we can avail ourselves in our exper- iments upon bodies. These will enable us to reduce to their ultimate elements, all kinds of matter, both or- ganic and inorganic. But they will not enable us to recombine these elements in those arrangements, which constitute 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 ORGANIC AND INORGANIC MATTER, 15 power to create a single particle of vegetable or ani- mal matter ; and our analyses of these substances, are in fact nothing else than a more or less complete de- struction of their organization. Another important difference in the chemical com- position of organic and inorganic bodies, relates to the mode, in which the elements, which enter into their composition, are combined together. In organic sub- stances, the chemical composition is much more com- plex than in minerals, and from the same cause, less intimate and fixed. In mineral substances, the com- binations are for the most part binary, or their con- stituent elements are united by twos, and their affini- ties are completely saturated ; so that these substances are comparatively fixed in their compqsition, and have but little tendency to change. However numerous the elements of inorganic substances may be, we al- ways find them forming binary, or, double or triple binary compounds. Water, the earths, the oxyds, and chlorides of metals, the acids, and many other sub- stances, furnish examples of simple binary combina- tions. The carbonates of lime and of the alkalies, the earthy, alkaline, and metallic salts, glass, &c., are ex- amples of double binary compounds. Solutions of saline substances in water, or the same substances in a state of crystallization containing water, afford ex- amples 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 tivos. Take water, for example, 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 sparing- ly, with the simple gases. But it will readily dissolve all these substances, in some state of combination with other elements. Thus carbonic, sulphuric and phosphoric acids, readily combine with water. Sul- phuretted and phosphuretted hydrogen are also absorb- ed by water, though in very different proportions. The metallic salts, and the alkalies are soluble in water. 16 FIRST LINES OF PHYSIOLOGY. If we attempt to form a ternary compound’ by uniting a simple body to a substance composed of two ele- ments, 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 togeth- er any number of bodies, having 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 mat- ter ; but it never exists in it in sufficient proportion to saturate the combustible elements, carbon and hydro- gen, 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 car- bon.* In the ternary and other more complex combina- tions of organic matter, in which the combining ele- ments 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 energet- ic, and more perfectly saturated. Thus, the ternary combinations of oxygen, carbon, and hydrogen, are re- solved by spontaneous decomposition, 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 main- tained, 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 indi- * Tiedemann. ORGANIC AND INORGANIC MATTER. 17 vidual 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, actually employed in the formation of them, is much less than that of those, which exist in the latter. Vegetable matter is composed princi- pally of three elements, viz. carbon, hydrogen and oxygen ; and animal matter of four, containing, in ad- dition to the three former, another element, azote, from which it derives its principal chemical peculi- arity. Besides these four, which are the essential el- ements of organic matter, it contains several others, but in very inconsiderable quantities, making in the whole about nineteen, which is little more than one third of the whole number of elementary substances, which have as yet been discovered by chemical re- searches. It appears, then, that the structure of organized bodies presents the following characteristic features, viz. that they possess a determinate 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 quaternary 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 or- ganic bodies consist of solid and fluid parts ; that the solid parts are not compact and homogeneous, but pos- sess 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 or- gans, differing in their form, size, structure, and ac- tions, but all mutually dependent on one another, and 3 18 FIRST LINES OF PHYSIOLOGY. conspiring to produce the same result, the preserva- tion and welfare of the individual. 7. The general properties, by which organized bo- dies are distinguished from inorganic matter, are next to be considered. It has already been observed, that organized substances are not immediately subjected to the laws of chemical affinity, but that they are en- dued with a new species of force, by which these laws are modified, and which may be termed organic power. In consequence of this peculiar property, or- ganic substances react against the physical and chem- ical influences of the external world, in a peculiar 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 or- ganic and chemical power. The physical and chem- ical 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 general powers of mat- ter are, in every instance, sooner or later invariably successful. These forces are inherent in every form of matter, unwearied in their exercise, indestructible and inexhaustible ; 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 overcome and destroyed by the general powers of matter, it is constantly starting up and renewing the conflict elsewhere, and is successful for a tune, though, in the end, always overcome by the steady opposition of these powers. So long as an organ- ized. 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 ORGANIC AND INORGANIC MATTER. \\) or natural decay, the chemical affinities of its ele- ments 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 phenom- ena of incipient vegetable, or animal decomposition. This power of reacting against, and neutralizing the mechanical and chemical forces of matter, is ex- emplified in the faculty, possessed by animal bodies, of preserving a certain regular and invariable tem- perature, amid very great changes of temperature of the medium, in which they live ; in the pow er of elab- orating out of a vast variety of heterogeneous sub- stances, 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 va- rious external agents, of showing themselves sensible to the impressions which they thus receive, and of be- ing excited by these to certain actions, which inorganic substances never exert. The phenomena of nutrition and growth, under the influence of external agents, imply the aptitude of being affected by the impres- sions, received from them. Animals of all classes are excitable, their nutrition, and consequently the pre- servation of their lives, being effected under the in- fluence of external agents, and their voluntary motions being frequently excited by various impressions from without. The egg and the seed are capable of enter- ing upon a series of internal movements and develop- ments, under the influence of warmth, moisture, and atmospheric air. This property of being determined to certain move- ments or manifestations of force, under the influence of certain exciting causes or impressions from with- 20 FIRST LINES OF PHYSIOLOGY. out, is supposed, by some physiologists, not to he lim- ited 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 certain organic substances, as albu- men, fibrin, gelatin, starch, gluten, gum, &c. spontane- ously assume, 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 accre- tion. The surface, to which the new particles of mat- ter are applied, is internal in organic, but external in inorganic matter. Organized bodies grow by a se- ries of internal developments; inorganic increase by the addition of matter, applied externally to them. With the nutrition of organized bodies, which is accom- plished by the continual intussusception of new matter, is connected an antagonist process of organic decom- position, in which the worn out elements are removed, and discharged ; so that a perpetual round of compo- sition and decomposition is going on in all organized bodies. 10. Further; organized substances possess the power of producing beings similar to themselves, or, the fac- ulty of generation. This is a remarkable and exclu- sive prerogative of organized bodies, unless we admit, with some physiologists, that matter in certain forms and under particular circumstances, has the property organizing itself into some of the lower forms of ani- mal or vegetable life. 11. Organized bodies possess the power of being affected with, and of recovering from disease. 12. Organized substances have a determinate du- ration or period, beyond which it is impossible to pro- long their existence. This period varies for each species of organized being, animal, as well as veget- able. Some insects live but a day, some plants but RELATION OP ORGANIZED BODIES TO HEAT, ETC. 21 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 main- tained the organic structure ; and the destruction of the body itself by a separation of its elements, effect- ed by the exertion of their chemical affinities, which had been previously controlled and neutralized, as it were, by the vital powers. CHAPTER III Relation of Organized Bodies to Heat , Light , and Electricity. The relations of organized beings to the imponder- able elements, 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 phe- nomena 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 ex- tinction of the living principle,' with the exception that organic matter, in certain stages, or under certain cir- cumstances 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 tem- perature. Living bodies develop heat from the inte- 22 FIRST LINES OF PHYSIOLOGY. rior towards the exterior by their own peculiar pow- ers, instead of receiving it from surrounding objects. They do not receive , but produce it ; and they are ca- pable of resisting, to a certain extent, the tendency of caloric to an equilibrium. A part of a living animal, exposed to a considerable degree of cold, instead of having its own temperature reduced, like an inorgan- ic 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 differ- ent sources, are connected with such different forms of matter, and are subject to such dissimilar laws, there may be some essential difference in their nature and properties. Organized beings differ much in them power of pro- ducing 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 gen- erally, that those, which are the highest in the scale of development, possess it in the greatest degree. Thus, plants have a lower temperature than animals ; and the invertebrated animals a lower temperature than those, which possess a bony skeleton ; of the vertebra- ted animals, also, those which are lowest in the zoo- logical scale, viz. fishes and reptiles, have an inferi- or temperature to that of birds and the mamma- lia. 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. Ma- ny insects have a much higher temperature, than would correspond with their position in the zoological scale. Those exceptions, as we shall see hereafter, admit of an explanation, on other principles; par- ticularly that the degree of organic heat in ani- mals, depends on the degree of development of the respiratory organs, — those animals, whose respiratory system is most complicated and perfect, possessing the greatest degree of animal heat. This principle, RELATION OF ORGANIZED BODIES TO HEAT, ETC. 23 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 develop- ed nervous system, as in 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 sys- tems ; 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 appropri- ated to the organic or nutritive functions, and its ac- tivity is not absorbed in those higher functions of the nervous system, in which the mammiferous quadru- peds, and in a much higher degree, man, surpass the feathered tribe.* Organized bodies, also, have the power of resisting the heating influence of very high temperature, or of maintaining their own at nearly the same standard, under the two opposite circumstances 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, ex- cites the exhaling vessels of the skin to a copious se- cretion of perspirable fluid, which absorbs the excess of caloric, and flies off with it in the state of vapor. The development of organic heat is checked, un- der these circumstances, because an excess of ex- ternal temperature depresses and weakens those func- tions, 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 ; digestion, nutrition, secretion, and, in short, all the processes connected with the nutrition of the * Berthold. 24 FIRST LINES OF PHYSIOLOGY. 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 sufficient- ly high, a more active development of caloric takes place from within. All the operations of life are per- formed with increased energy, as respiration, the ac- tion of the nervous system, digestion, assimilation, and the secretion ; and with these, calorification. Plants possess the power of regulating their own temperature in a far less degree than animals. In- deed, some naturalists do not admit that they pos- sess such a power at all. Certain plants, however, especially several species of the arum , as the arum italicum , the arum cordifolium , and arum esculentum, develope 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° Reaumer, when the temperature of the air was only 21° R. The ger- mination of seeds, also, is accompanied with an evolu- tion of heat, a fact, which is exemplified in the pro- cess of malting. Electricity. — There is also an organic electricity, as there is an organic heat. Living beings are idioelec- tric, i e., capable of developing electricity, and of ex- hibiting electrical phenomena by the exertion of their vital powers. Many facts have been observed, by different physiologists, tending to establish the exist- ence of a vital fluid, bearing a very close analogy to physical electricity and galvanism. Beclard observed that needles, plunged into the middle of a nerve, acquir- ed 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 sub- stances, such as little fragments of paper; from which he inferred, that electricity is developed in the nerv- ous system under the influence of vitality. Another physiologist, Weinhold, asserts that a spark may be RELATIONS OF ORGANIZED BODIES TO HEAT, ETC. 25 obtained by approximating the two ends of a divided nerve towards each other.* But the most remarkable examples of electrical phenomena, developed under the influence of vitality, are furnished by certain fishes, which are provided with particular organs for that purpose. Of these fish- es there are several kinds, as the torpedo , of which there are two species, the torpedo marnxorata , and the torpedo ocellata ; the rhinobatus electricus , the tetrodon electricus , the gymnotus electricus , the trichurus elec- tricus , and the silurus electricus. The electrical organs of the torpedo consist of an ap- paratus, 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, stand- ing 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 trans- verse membranous partitions. 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 be- neath the former, separated from it by a thick tendi- nous membrane, a layer of fat, and muscles. The structure of both is similar. They are composed of horizontal membranous plates, separated by an inter- 4 * Lepellctier. 26 FIRST LINES OF PHYSIOLOGY. val of about one third of a line from one another, and crossed in a perpendicular direction by membranous partitions, in such a manner as to form a great num- ber 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 electrical apparatus of the silurus electricus, also, resembles a galvanic trough. It is composed of a membrane, situated immediately under the integu- ments 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 abundance of nerves from a large branch of the par vagum. The structure of these electrical organs, as well as the phenomena, which they produce, point out a strik- ing analogy between them and the voltaic battery. These organs exhibit, in their structure, a great re- semblance to voltaic piles of the second class, inas- much 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 produced by them, however, are by no means to be accounted for by their struc- ture alone, or the mechanical arrangement of the parts, which form them, giving rise to electrical ex- citement 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. From this we must infer, that the elec- trical discharge of the organs of these fishes is a vital act, which depends immediately on the influence of the nerves upon them ; while the electrical organs themselves can only be considered, as a necessary physical condition, or, as contributing, in a secondary manner, to the excitement and discharge, by contact. The discharges seem to be under the control of the animal’s will. RELATION OF ORGANIZED BODIES TO HEAT, ETC. 27 The phenomena of these discharges point out a striking analogy between them and the effects of phys- ical 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, conducts the shock ; but if dry, the same sub- stances 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 hsh. The effect was produced only on actual contact. In the gymnotus electricus, however, the propagation of electricity by intermedi- ate substances, is much more evident. It sends its shock through the water to the hand placed near it, and small ftshes, which are swimming by, are some- times killed by its discharges, at a considerable dis- tance. Metallic substances, and even wood, placed in contact with the hsh, will conduct the discharge ; but sealing-wax and bees-wax are non-conductors. Several persons, forming a connected chain, may re- ceive 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 hsh, or is connected with them by means of a con- ductor of electricity. If the chain is broken by a non-conductor, the effebt does not take place. In some experiments, sparks have been observed to ac- company the discharges. Notwithstanding these and other facts, evidently of an electrical nature, there are others, which point out a difference between 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 degree, 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 28 FIRST LINES OF PHYSIOLOGY. 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 fish- es 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 ex- cite one. Humboldt is of opinion, that the torpedo has the power of sending his shock in whatever direc- tion he pleases. My friend, Dr. Francis W. Cragin, of Surinam, informs me, that the discharge of the gym- notus 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 pow- er of speedily charging their battery again. But the fre uent repetition of the discharges exhausts them, and their shocks become weaker, unless they have a period of repose, to recruit their vigor. The division, or tying of the nerves, which supply the electrical organs, destroys their power of giving shocks. The destruction 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 ex- hibited by animals, which are not of a vital character. One is the production of sparks by the friction of the fur of certain animals, particularly 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 or- gans, under certain circumstances, are examples of the other. Electricity excited in these cases is not of a vital character, but is produced by the mutual contact of RELATION OF ORGANIZED BODIES TO HEAT, ETC. 29 heterogeneous animal substances, 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 ar- ranged in the same manner. The effects are still more striking, if the muscles and nerves, which form the animal chain, are armed with metallic coatings, which are made to communicate by means of a metal- lic wire. In these cases, electricity is excited by the contact 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 liv- ing substances ; as, for example, the changes of form and composition, which are constantly taking place in the vital processes of digestion, nutrition, respira- tion, secretion, the evaporation of liquids, &c. The living body is a laboratory, in which matter is under- going incessant changes of form and aggregation ; fluids are passing into solids, and solids into fluids, and fluids into gases or vapors ; and in all these processes, hetero- geneous substances, as fluids and solids, are brought into contact, and mutually act upon each other. These circumstances are precisely those, which, in in- organic matter, give rise to electrical manifestations. Most of the operations in nature, in which two hete- rogeneous substances enter into mutual action, occa- sion a disturbance of the electrical equilibrium, and the production of electrical phenomena. These con- siderations, however, will not explain the electricity sometimes developed in the nervous system, under the influence of vitality ; particularly the electrical phe- nomena exhibited by the gymnotus , torpedo , and other electrical fishes. Phosphorescence . — Another example of the devel- opment 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.* * Tiedemann. 30 FIRST LINES OF PHYSIOLOGY. 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, salt-petre, muriate of ammonia, galena, &c. The phosphor- escence takes place in all transparent media, and even in a vacuum, with a sensible evolution of heat. 2. Many substances shine in the dark, after having been exposed 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 over- coming the affinity of these bodies for light, and set- ting this element free. 3. Friction, percussion and compression, are accom- panied with a disengagement of light in many sub- stances, particularly in those, which are rendered phos- phorescent 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 fluate of soda. 5. Intense chemical action is generally accompanied with an evolution of light. 6. Electrical phenomena frequently give rise to a dis- engagement of light. Some bodies are rendered lumin- ous by the transmission 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 ara- bic, 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 RELATION OF ORGANIZED BODIES TO HEAT, ETC. 31 during their combustion; 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 decomposing under the influ- ence 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 inten- sity, but continues a longer time. It ceases in a few hours in azote, hydrogen gas, and the phosphu- retted hydrogen, but reappears on the admission of atmospheric air. It disappears in a few minutes in carbonic acid, sulphuretted hydrogen, chlorine, ammo- nia, and muriatic acid gas. It is speedily extin- guished in fixed oils and alcohol, ether, lime water, and diluted acids. It disappears instantly in sulphu- ric 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 compound of carbon, hydrogen and oxy- gen, 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 fre- quently 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 mod- erate temperature. A freezing temperature, and the * Tiedemann. 32 FIRST LINES OF PHYSIOLOGY. heat of boiling water, equally suspend it. The phos- phorescence 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 phos- phorescence, a gelatinous fluid matter is observed, 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 odor. 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 phos- phorus, and which burns slowly with the evolution of light, in atmospheric air, or oxygen gas at, amoderate temperature.* But light is frequently given out by organized bod- ies, 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 cryptogamous 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 ; particu- larly 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 at- mospheric air, and consumes 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 vapor, which un- dergoes a slow combustion in atmospheric air, and oxygen gas. The dictamnus albus is said to diffuse around it, during warm summer evenings, an atmos- * Tiedemann. RELATION OP ORGANIZED BODIES TO HEAT, ETC. 33 phere, 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 luminous phenomena. Most of the in- ferior 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 ap- pearance 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 phospho- rescent, whenever the water is agitated by shaking the vessel. Diluted sulphuric acid, poured into a ves- sel containing luminous animalcula, has been found to occasion a sudden brilliant light, which immediately afterwards disappeared. The phosphorescence of the medusai 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 propaga- tion ; 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 phosphorescent 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 disappears in a vacuum, but returns on the re-admission of the air. A moderate heat increases its vividness, but the heat of boiling wa- ter, 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 am- moniac, increases its brilliancy; while concentrated solutions, vinegar, wine, alcohol, sulphuric acid, and 5 34 FIRST LINES OF PHYSIOLOGY. corrosive sublimate, speedily destroy it. It continues some time after death, but is extinguished at the com- mencement of putrefaction. Among the animals which live in the air, the tribe of insects furnishes the great- est number of phosphorescent animals. The source of the light in insects, has its principal seat in the pos- terior rings of the abdomen. It seems to reside in a peculiar albuminous 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 subli- mate, or concentrated mineral and vegetable acids, &c. The phosphorescence also disappears in the non- respirable gases, and in a vacuum, but returns on ex- posure 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 ani- mal’s will ; for, a sudden noise will sometimes instantly cause it to cease. Some naturalists attribute the phe- nomenon to the action of the nerves; others, to the fac- ulty possessed by insects, of accelerating or retarding their respiration, 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 temperature of the air. At a certain degree of cold, the emission of light ceases, and, on the contrary, its viv- idness increases, if the temperature of the air be ele- vated within certain limits. If one of these insects, when not emitting light, be plunged into warm water, the phosphorescence commences ; and, if the tempera- ture 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 atmospheric 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 RELATION OP ORGANIZED BODIES TO HEAT, ETC. 35 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 hy- drogen gas, carbonic acid, sulphuretted and carburet- ted 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 concentrated 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 in- sects depends on a peculiar animal matter, secreted by certain organs. This matter probably contains phos- phorus, or some other combustible 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 charac- ter ; it depends entirely on the composition and qual- ities of the luminous matter, and sometimes continues for several days after the death of the animals.* * Tiedemann. 36 FIRST LINES OF PHYSIOLOGY. CHAPTER IV. Comparison of Animals and Vegetables. Organized beings are divided into two great class- es, 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 locomo- tion. 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 mat- ter 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 con- sciousness and feeling, and the powrnr of locomotion. All animals, from the zoophyte to man, are provided with an internal cavity for the reception and elabora- tion of the food. They are also much more complex in their organization, presenting a great variety of tis- sues and organs. They contain a much larger pro- portion of fluid, and a much smaller proportion of sol- id parts, than vegetables. They are composed of a greater number of chemical elements, and always con- tain azote in addition to the principles, which exist in vegetable bodies. DIVISION OF THE ANIMAL KINGDOM. 37 CHAPTER V. Division of the Animal Kingdom. The animal kingdom presents an immense variety nf species, which are arranged in various classes, and subordinate divisions. One of the most general divis- ions of the animal world, is into vertebrated and inver- tebrated ; the former, embracing those animals 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-blood- ed animals, constitute a great and important di- vision 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 di- vided 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 embraces 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, 38 FIRST LINES OF PHYSIOLOGY. worms, the molluscous animals, zoophytes, and the infusory animalcula. TABLE OF A CLASSIFICATION OF ANIMALS. Warm-blooded. Cold-blooded. f Viviparous, and hav- l w Mammalia. J ing breasts. I Oviparous. 2. Birds. f B reathing with lungs. 3. Reptiles. t Do. with gills. 4. Fishes. f Articulations, both of 5. Insects, Crustacea, ! the extremities, and Arachnid.®. of the body ; but chiefly of the former. Numerous annular ar- 6. Annulata. ticulations of the body. Unarticulated bodies. 'Body naked, covered 7. Mollcsca. with a slimy mem- brane, or inclosed in a calcareous shell. Breathing by gills or lungs, with sexes separate, or her- maphrodite. Blood, white. Head, not distinct from the body. Having a stellated or radiated disposition of the parts, both external and inter- nal, and provided with organs of re- spiration. Without organs of re- spiration. 8. Radiated Animals. Sea-nettle, Star-fish , Medusa, Holothuria , tf-c. 9. Zoophytes. Polypus, Coral, Infusory Animal- cula. 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 species DIVISION OP THE ANIMAL KINGDOM. 39 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 evident from the structure of his body, particu- larly 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 design- ed to support a great superincumbent weight ; the bulk of the glutaii 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 simioe, the glutoms max- imus , 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 mail 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 gas- trocnemii muscles, are also much more highly devel- oped in man. We find, accordingly, that no other an- imal has calves equal to those of man. These mus- cles are necessary to progression ; for, by raising the heel, they elevate the whole body in the act of walk- ing. The concave form of the sole of the foot, and the greater prominence of the heel, designed to give attachments 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 oth- er 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, metatar- sus, and toes, rests on the ground. 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 progres- sion of an animal, the two others are left free for other uses. Man is the only firo-handed animal. The sim- ioe , which approach the nearest to man, are strictly 40 FIRST LINES OF PHYSIOLOGY. 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 ex- tremities; and their feet are 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 , and the perpendicu- lar direction of the inferior incisor teeth, are also char- acteristic marks of man, and are found in no other animal. Another circumstance is, that in man the teeth are of the same length ; whereas, in other ani- mals the different kinds of teeth differ in length, and are separated by intervals from one another. In in- ferior animals, the canine teeth are much longer than their neighbors, and are separated from them by a considerable interval. 4. Man is physically defenceless. He is not provi- ded by nature with weapons either for defence, or of- fence. He remains in a helpless state after birth, longer than any other animal, and is indebted to his 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 favorable 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 vol- ume of the nerves. This position is generally true, but there are some exceptions to it. 7. Man is the only animal that sleeps on his back. 8. He is the only animal, which possesses an artic- ulate language, expressive of ideas or mental concep- tions. 9. He is the only animal endued with reason, and a moral sense. ANATOMICAL STRUCTURE OF THE HUMAN BODY. 41 10. 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 consists both of solids and fluids, or, of containing and contained parts. The fluids constitute much the larger portion of the whole, bearing to the solids the ratio of about 9 to 1, according to some physiologists ; or of only 3 to 1, according to others. The first es- timate is probably much the nearest the truth. The solids are composed of the same chemical prin- ciples as the fluids, and are, by analysis, reducible to the same ultimate elements. This follows as a nat- ural 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 affini- ty. In the formation of the solids, the particles of matter are arranged in various modes. If we may believe some microscopical observers, the ultimate animal solid is a minute sphere or globule of matter of extreme minuteness, not exceeding in diameter the 8000th part of an inch. This is supposed to be the ultimate mechanical element of the animal organiza- tion, from which, disposed in various modes, are form- ed a great variety of animal solids. These may be arranged in the order of their simplicity, into filaments, fibres, tissues, organs, apparatuses, and systems.* * Library of Useful Knowledge; Article, Physiology. 6 42 FIRST LINES OF PHYSIOLOGY. A filament is composed of a series of the primitive molecules, arranged longitudinally, or in a row. Sev- eral 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 areolae 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 hone, 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 purpose 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, pancreas, lacte- als, &c. ; . all of which organs concur tow T ard the same object, the assimilation of food. The term system is applied to an assemblage of or- gans, which possess the same, or a similar structure. Thus, the nervous system consists of a variety of or- gans, which, however differing in figure, magnitude, and situation, agree together in possessing one com- mon 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 primitive molecule, is the formation of the fila- ment, which may be regarded as the elementary ani- mal solid. The next is the formation of the fibre, by the union of several filaments in a bundle. The fibres may be regarded as elementary, in relation to the tissues, which are all formed out of fibres. FUNDAMENTAL TISSUES. 43 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 nu- merous, and however widely they may differ one from another, as the bones, ligaments, cartilages ; the ves- sels, muscles, nerves, &c. may be analyzed, anatom- ically, into one or more of these three. Of these tissues, the most generally diffused, and the simplest in structure, is the cellular. This tis- sue enters into the composition 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 areolae, 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 envelope of cellular membrane. The aime 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 considera- 44 FIRST LINES OF PHYSIOLOGY. ble part of the hair and nails. This tissue, also, pen- etrates into the interior of the solid viscera, as the liv- er, pancreas, 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 com- posed. 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 un- ion, by which the organs are connected together. The first, by some physiologists, is termed the pa- renchymatous; the second, the atmospheric cellular tis- sue. The latter fills up the intervals or spaces be- tween 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 composition of all the organs, which perform eve- ry variety of function, yet never loses its own charac- ter, which is everywhere 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 secre- tion 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. This structure, however, appears only where the tissue is subjected to a slight distention, and it entirely disap- pears, when the distending cause ceases to act; for the cellular tissue is extremely elastic and contrac- tile, 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 sub- FUNDAMENTAL TISSUES. 45 stance, of a grayish color ; sometimes it presents a slimy appearance. It gives passage to some blood- vessels and nerves, which, however, are destined to other parts, and are not spent on the cellular tissue itself. It is abundantly supplied with colorless ves- sels, 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 connected whole, or an immense net-work, every where permeable to air. If air be forced into its cells in any part of the body, with a moderate con- tinued force, it gradually penetrates and pervades the tissue, so that the whole of it becomes inflated. Aslit 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 or- gans, and it connects the solid parts of the body to- gether ; and, by its softness and elasticity, and the oily fluid with which its cells are filled, it promotes the mo- bility of the parts on one another. Its fundamental physiological property is contractility , or, animal elas- ticity , which it imparts to all the organs it contri- butes to form ; and its chemical 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 membranes of all kinds, the sheaths of the muscles and nerves, vessels, and other organs. The membranes , which are formed of the cellular tissue, constitute some of the most important struc- tures of the body. The general covering of the body is formed of membrane. Each individual structure has its membranous covering. All the cavities, in which the principal organs are enclosed, are lined by membrane. The vessels are composed chiefly of mem- brane. Even the solid organs, as already observed, are formed of a basis of membrane, into the areolae of which, as a mould, is infused the peculiar animal mat- 46 FIRST LINES OF PHYSIOLOGY. ter belonging to them respectively. Now, all these membranes are merely modifications of the cellular 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, brain, and joints are lined by serous membrane. These mem- branes 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 cav- ity of the chest, which contains the lungs ; between the lungs themselves, where the heart is situated ; in the ventricles of the brain, where th ejilexus choroicles s 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 sy- novial membranes, which line them, are classed with the serous membranes. The bursa mucosa belong to the same structure. The arachnoides, which lies be- tween, and separates the dura mater and pia mater of the brain and spinal marrow, is also regarded as a serous membrane. The serous membranes, it appears, enclose, chief- ly, the organs of automatic or involuntary motion. They envelope the heart, the lungs, and the in- testinal canal, and the glandular and other organs connected with it, and some of the organs of re- production. According to Rudolplii, serous mem- branes 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 FUNDAMENTAL TISSUES. 47 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 color, 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 cavi- ties 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 ves- sel. 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 tis- sues immediately subjacent to them. The uses of the serous membranes are to separate heterogeneous parts, or organs ; and to diminish fric- tion, 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 organization than the serous, are the mucous membranes , so called from the viscid fluid, which it is their proper office to secrete. These mem- branes line all the cavities, which open upon the sur- face of the body, as the digestive and urinary passa- ges, the nasal cavities, and the air tubes. They enter into the structure of the different organs, which are concerned in the prehension, and assimilation of the aliments, in aerial respiration, and the secretion, 48 FIRST LINES OF PHYSIOLOGY. and excretion, of the various fluids. They may he considered as the basis of the glands, into the sub- stance of which they everywhere penetrate; the inner tunic of the excretory ducts, even to their radicles, where they anastomose with the capillary parenchyma of the glands, being always formed of mucous membrane. According to Rudolphi, these membranes have no free surface, hut always lie be- tween two others, having on their inner surface a thin serous tissue. The mucous membranes, with scarcely an excep- tion, form a continuous whole. That, which lines the eyes and eye-lids, is connected by means of the nasal canal, with the membrane, which invests the cav- ities 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 fol- lows the route of the pharyx and oesophagus into the stomach and intestines, which it lines throughout their whole extent. In the small intestines, it sends de- tachments to the liver and pancreas, through the bil- iary 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 vcsiculce seminales , and thence through the spermatic cord into the testes. In the fe- male 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 connexion with that, which lines the alimentary canal. For, the per- ineum covered by the common integuments, intervenes FUNDAMENTAL TISSUES. 49 between the outlets of the digestive and urinary pas- sages. 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 mucous membrane. The mu- cous 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 color, and are largely supplied with blood-vessels and nerves. They are furnished with numerous small glandular 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 sheathe and protect the inner surfaces of the body, as the skin does the outer ; and, by means of the mu- cus secreted by them, to screen these 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 mem- branes are highly extensible and elastic. 3. The skm, or cutis , which forms the outer cover- ing 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 mem- branes. About the orifices of the internal canals, the skin and the mucous membranes pass into each oth- er, as in the lips, nostrils, eyelids, external ear, rec- tum, &c. Like the mucous membranes, the skin is largely supplied with blood-vessels and nerves, and in many parts with small glandular bodies, called se- baceous 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, externally, by the cuticle, or epidermis , an inorganic membrane, destitute of 7 50 FIRST LINES OF PHYSIOLOGY. 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-colored varieties of the hu- man species, according 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 color 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 sup- pleness and moisture. The skin is very extensible and contractile. This membrane is one of the principal organs of re- lation ; by means of which, a communication is estab- lished between us and the external world, and by which we obtain a great number of ideas of the qual- ities of external bodies, as heat, cold, hardness, form, distance, &c. To qualify it for this function, it pos- sesses great sensibility, which it derives from the cere- bro-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 con- tact 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 con- densed cellular tissue, are the fibrous , so called from their texture. To this structure belong the pcrios- teurn , the dura-mater , the ajioneuroses , 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 under another form, that of thick bun- dles of different shapes, as in the ligaments and ten- dons. FUNDAMENTAL TISSUES. 51 The color 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 connected together, so that it is difficult to separate them. It seems to con- sist principally of condensed cellular tissue. The fi- brous tissue is sparingly supplied with vessels, particu- larly in adult age ; but in the fetal 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 produc- tive 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 ligaments and tendons, are essentially mechanical. It chiefly serves to form bonds of connection, by which the bones are united together, and the joints strength- ened; 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 envelopes 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 cellular, appearing to consist of condensed cellu- lar membrane and gelatin. Cartilages are firm, smooth, highly elastic substances, of a pearly Avhite color, 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 red ves- sels, and neither nerves, nor lymphatics, have been discovered in them. They unite with great difficulty 52 FIRST LINES OF PHYSIOLOGY. 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 cartilaginous. The permanent are those, which are not destined to future ossifica- tion, though they are liable to a morbid process, by which they are converted into bone. Thus, the car- tilages of the ribs, those of the larynx and trachea, and even the epiglottis, are sometimes found ossified. Naturalists have, even, observed examples of ossifica- tion in the cartilaginous fishes, in which, in the nor- mal state, the skeleton remains cartilaginous during the life of the animal. The permanent cartilages are found in various sit- uations, 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 ad- mit of a certain degree of motion upon one another, as the intervertebral cartilages, and those between the bones of the pelvis ; they also tip the articular ex- tremities 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 pro- cess of ossification, in which the future bone always appears first in the form of cartilage. In the fetal state all the bones are cartilaginous. The structure FUNDAMENTAL TISSUES. 53 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 di- minish, and with them, its powers of nutrition and reparation. The bones are covered with a fibrous membrane, called the periosteum, which may be con- sidered 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 mem- brane 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 in- ternal periosteum. The inner surface of the hollow bones is lined with a serous membrane, called the peri- osteum 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 vertebrse ; the cylindrical or tubular bones, including those of the arms and 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 externally ; internally they present different kinds of structure. The broad flat bones consist of two tables, between which a cellular structure inter- venes. 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 mar- row. 54 FIRST LINES OF PHYSIOLOGY. The bones form a connected system, which consti- tutes the basis of the whole frame. They are the hardest part of the body, and serve as the frame- work and support of all the soft parts. They serve as points of attachment to the muscles, or moving pow- ers, and constitute levers of various kinds for the mus- cles to act upon, in executing the various motions which the body has the power of performing. Ossification is frequently a morbid process, occur- ring 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, some- times become bony. The same structures are some- times 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 fac- ulty of contracting or shortening itself on the applicat ion of certain stimuli. It is as peculiar, also, in its chemical constitution, as it is in its structure and its vital prop- erties, being formed almost wholly of concrete fibrin. The ultimate muscular filament is extremely mi- nute, not exceeding, 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 color, which is supposed to be owing to the blood which they contain. The ultimate 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 ill a sheath of cellular tissue, and the whole muscle has an envelope 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 thick- er and more condensed, and constitutes a larger pro- portion of the whole mass, while the muscular fibres FUNDAMENTAL TISSUES. 55 diminish, in receding from the middle and approaching 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 ex- tremities of the muscles, this tissue becomes more con- densed, and forms an increasing proportion of the whole mass of the organ, until the muscular fibres wholly disappear, and the whole cellular tissue be- longing 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 cylin- drical 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 des- titute 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 executed. III. The third constituent element of the structure of the body, is the nervous fibre. This consists essen- tially of albumen , as the muscular fibre consists of fibrin , and the cellular tissue of gelatin ; and it is en- dued with a distinct physiological property, sensibility. A nerve consists of two elements, viz. a pulpy or medullary matter, i. e. the peculiar matter of the nerve, and a sheath which invests it, formed of cellular tis- sue. The medullary substance consists of bundles of nervous fibres, each covered with its own sheath of cel- lular tissue or membrane, and each also being divisible into a finer series, until we arrive at the ultimate ner- vous filament. This appears to be destitute of a cel- lular 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 en- velope of cellular tissue ; and lastly, the nerve itself, formed by an aggregate of fasciculi, has a common sheath, which is called the neurileme. According to Fontana, the ultimate nervous filament is twelve times larger than the primitive muscular. 56 FIRST LINES OF PHYSIOLOGY. Of nervous matter is formed the nervous system, consisting of the brain, spinal marrow, the ganglions, and the nerves themselves. Its elementary physiolog- ical property, as before remarked, is sensibility, which it communicates to all parts of the system, to which nerves are distributed. The sensibility thus diffused throughout the sytem, has two principal centres or foci, viz. the brain, and the great solar plexus ; and it bestows unity and individuality upon the whole as- semblage 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 ner- vous, 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 cartila- ges, have already been sufficiently described, under the head of the osseous and cartilaginous tissues. The functions of these, together with those of the liga- ments and tendons, are essentially mechanical. The ligaments constitute a structure, the chief use of which is to connect the bones together into one sys- tem; though there are many other structures which resemble the ligaments, which are destined to ver different uses ; e. g. the sclerotica of the eye, the J dura-mater, the periosteum, the aponeuroses of the mus- cles, the fascice, the w hite tunic of the testes, and THE COMPOUND STRUCTURES. 57 ovaria, and the proper coat of the kidneys and spleen. These, with the ligaments, constitute collectively, the fibrous system. The common character 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 con- tain scarcely any blood-vessels, they are of a white shining color. 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 to- gether 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 mem- brane and are again inserted into it. In some few examples, however, they are connected, not with the periosteum, but with cartilages. The capsular ligaments, which enclose the artic- ulations, consist 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 into 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, mus- cles of voluntary, 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 ; de- rive 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. 8 58 FIRST LINES OF PHYSIOLOGY. 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 direct- ly to them. The heart, the stomach, intestines, blad- der, 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 capillary vessels and veins, that of the lymph and chyle in the lymphatics, that of the different secreted fluids in the ex- cretory ducts, the contractile motion of the cellular tis- sue 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 impor- tant system of organs, consisting of the brain, spinal marrow, ganglions and nerves. Like the muscular system, it is divided into two great sections, one term- ed 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 voluntary mo- tion. The nerves, belonging to it, are connected by their central extremity with the brain or spinal cord, and, by their peripheral, with the organs of sense, or the muscles of voluntary motion ; and they are chan- nels of communication -between the centre and the periphery of the nervous system of animal life. The nervous system of organic life, presides over organic sensibility 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 func- tions of the circulation, of nutrition, secretion, exhala- tion, absorption, &c., are supposed to be under the control of this part of the nervous system. THE COMPOUND STRUCTURES. 59 The vascular system constitutes another very es- sential part of the human body. It embraces various organs, which differ in structure and in functions, but which agree in general in this respect, that they con- sist of cylindrical canals or tubes with membranous 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 in- troduced into the body, where, after undergoing cer- tain changes, they are made to repair the waste in the organization, 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 sys- tem, 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 lym- phatic. The first, or the arterial, carries red blood from the heart to all parts of the body ; the second, or 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 col- orless fluids from the interstices 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 mammalia, birds, reptiles and fishes. They originate from the various membranes, the basis of which is con- densed cellular tissue, as the mucous, serous, synovial and dermoid, as well as from the cellular 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 regarded as an appendage of 60 FIRST LINES OF PHYSIOLOGY. the venous system. Their function is to absorb the nutritive fluid prepared by digestion in the alimentary canal, as well as other substances, which may come in contact with the external integuments of the body, and the mucous membranes. They, also, re-absorb certain parts of the various secreted fluids, and they are supposed to be the principal agents of the decom- position of the solid tissues and organs ; the molecules of which they detach and absorb, convert into a fluid state, and convey into the mass of the venous blood. The arteries are composed of three coats ; first, an external, formed of condensed cellular tissue, and pos- sessing 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 fibres, of a yellow color, and possessed of little or no irritability. According to Berzelius, it is wholly destitute of fibrin, in which respect it differs essen- tially from the muscular tissues. The third, or inter- nal 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 longitudinal fibres, but, according to Magendie, it contains a multitude of fibres interlacing one another in all directions. Like the middle tunic of the arte- ries, 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 * The middle coat of the blood-vessels, is regarded, by many anato- mists, as a distinct tissue of a fibrous structure and peculiar nature. It is either of a yellowish white, or pale reddish color, and is called the vascular fibre. It contains no fibrin, nor does it respond to many irrita- tions which excite muscular contraction, as galvanism, and mechanical 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 longitu- dinally- The lymphatics are destitute of it. FLUIDS OF THE SYSTEM. 61 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 distention, without being ruptured. It forms in the cavities of the veins, numerous folds, which perform the function of valves. The lacteals and lymphatics are composed of two coats only, viz. an external and an internal ; the ex- ternal, 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 abdo- men, as the lungs, the stomach, intestines, liver, spleen, pancreas, &c. The heart is excepted, as belonging to the vascular system, and the brain, as being part of the nervous ; and hence these two organs are not consid- ered 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. 62 FIRST LINES OF PHYSIOLOGY. 1. 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 aliment by the powers of digestion, and imbibed from the small intestines by a branch of the absorbent sys- tem, 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 lym- phatics. 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 solids, as well as of various fluids, absorbed from the differ- ent cavities and surfaces of the system. These fluids, which are formed and deposited by a perpetual pro- cess of secretion, are subject to the action of the ab- sorbents, so long as they remain in contact with any of the living tissues. Certain parts of them are im- bibed by the lymphatics and blended with the mol- ecules, 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 afterwards 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 combination with the chyle and venous blood, and the whole compound fluid is con- verted 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 de- scribed under the head of the secretions. FLUIDS OF THE SYSTEM. 63 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 cavi- ties of the heart. It is apparently homogeneous, hut 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, a saline taste, and a faint animal odor. It is well known, that the blood, soon after being drawn from the living vessels, loses its fluidity and concretes into a solid mass, and shortly after sepa- rates into two distinct portions. A yellowish trans- parent 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 coag- ulated part, which is of a red or dark bro wn color, is called the crassamentum , or cruor of the blood, and the fluid part, the serum. The coagulum , or cmor, also, is found to consist of two parts ; for, by ablution with water, it may be de- prived of its red color, a fact, which proves that this color depends on the presence of a separate principle. When thus separated from the two other constituent principles of the blood, viz. the serum and the coloring matter, the coagulum appears as a soft splid, of a whitish color, insipid and inodorous, and of a greater specific gravity than water ; and it sometimes presents a fibrous appearance, a circumstance from which it has received the name of fibrin. The coloring matter consists of minute globules of a red color, soluble in water, and which are visible in the blood when viewed through a microscope. 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 yellow- ish color, of a saline taste, and of the odor of blood. It owes its taste to the presence of earthy and alka- line salts, which it holds in solution. Besides these salts, it contains a free alkali, g.s is evident from its changing vegetable blue colors to a green. But the 64 FIRST LINES OF PHYSIOLOGY. property by which it is peculiarly distinguished, is that of becoming solid by exposure to heat. The temper- ature necessary to produce this effect, must be as high as 160 Q F. At this temperature, serum becomes a white opake solid, of a firm consistence, resembling the coagulated white of an egg. It preserves its property of coagulating, even when diluted with a large quan- tity 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 developes in it globules, which have a strong . analogy to those of the blood. The coagulation 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 albumen, it is supposed, may indirectly cause it to coagulate, by removing 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 appli- cation 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 combi- nation with the albumen, is transferred to the water, while the albumen is left to assume a solid form. The natural color of the serum, is liable to be changed by the presence of accidental substances. In jaundice, it is of a deep yellow color, which is derived from an impregnation with bile. It also acquires a ’yellow color, 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 color of turbid wdiey, owing, it is supposed, to the presence of chyle. In some cases it has been observed of a white color, like cream, and sometimes has been found to contain globules. This appearance has been FLUIDS OF THE SYSTEM. 65 observed in the blood of persons, whose digestive or- gans were disordered, and who had been subject to sickness, vomiting, and bad appetite. Berzelius and Marcet have, each, analyzed the serum of the blood, with the following results : Berzelius. Water, 905.0 Marcet. Water, 900.00 Albumen, 80.0 Albumen, - 86.80 Lactate and impure phos- U.O Extractive matter, Hydrochlorate of potash 4.00 phate of soda, | 6.60 Hydroehlorate of potash > 6.0 and soda, and soda, Sub-carbonate of soda, 1.65 Impure soda, 4.0 Sulphate of potash, - 0.35 Loss, ... 1.0 Earthy phosphate, 0.60 1000.00 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 sub- stance. The coagulum or cruor of the blood, is composed essentially of fibrin and coloring matter. When freed from the coloring matter, fibrin is a soft solid, of a whitish color, without smell or taste, insoluble in water, not affecting the blue vegetable colors, 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 properties. By distillation, it furnishes a large quantity of carbo- nate 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 carbo- nate of soda. One hundred parts of fibrin are composed of Carbon, - - 53.360 Oxygen, - - - 19.685 Hydrogen, - - 7.021 Azote, - - - 19.934 9 66 FIRST LINES OF PHYSIOLOGY. Fibrin is considered by some chemists, as a mere modification of albumen. It is the basis of muscular flesh. It possesses the power of spontaneous coagula- tion, and the blood owes its property of coagulating to the presence of this principle. The remaining constituent of the blood is the red globules. When examined by the microscope, the blood presents the appearance of a fluid, holding in suspen- sion minute particles of a spheroidal figure. According to some observers, these consist of a solid nucleus or central part, surrounded by a vesicle, which con- tains 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 mammalia, 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 glob- ules of the human blood, represent them as circular, flattened bodies, having a depression in the centre ; consisting of a central nucleus with an external en- velope of a red color. Raspail considers the globules as composed of albu- men, which has been dissolved in the serum of the blood by the aid of some menstruum, and is afterwards precipitated from it, by its neutralization, or by evap- oration. 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 albu- men will at first coagulate and become white, but will afterwards dissolve in the acid, and assume a violet color, which subsequently changes to a blue. If the acid be then decanted, or suffered to evaporate, a white powder will be precipitated, w’hich, when FLUIDS OF THE SYSTEM, 67 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 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 considers 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 succes- sive 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 ap- pearance 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. 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 mam- malia, 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 herbivo- rous. 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 physiolo- gists, the globules of the blood possess the faculty of spontaneous motion. Treviranus, with the assistance of a microscope, observed two kinds of motion in the 68 FIRST LINES OF PHYSIOLOGY. 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. Ac- cording to Copland, Professor Schultz of Berlin has more recently confirmed the fact respecting the intes- tine motion of the globules, which, as he asserts, move on spontaneously, keeping at a distance from one another, and surrounded by envelopes of coloring matter. This power of the globules, Copland at- tributes 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 repul- sion ; the latter tends to bring them to a state of re- pose, and is exerted in the organic structures them- selves, where the globules of the blood come into contact with them. The coloring matter of the blood, sometimes called hematosine, is supposed by some to reside in the en- velope of the red globules. By Brande it is considered as a peculiar animal principle, capable of combining with metallic oxyds.— He formed compounds of this coloring matter with oxyd of tin. But the best pre- cipitants of it are the nitrate of silver and corrosive sublimate. Woollen cloths impregnated with either of these metallic salts, and dipped in an aqueous solution of the coloring matter of the blood, became permanently dyed. Berzelius and Engelhart attribute the color of the blood to the presence of iron, in some unknown state of combination. The coloring matter is soluble in water. When dried and exposed to heat in contact with the air, it melts, swells up, and burns with a flame, leaving a coal of very difficult incineration. This ' coal burns with a disengagement of ammoniacal gas, and leaves FLUIDS OF THE SYSTEM. 69 the one-hundredth part of its weight of ashes, com- posed of Oxyd of iron, - - 55.0 Phosphate of lime and a trace ) g ^ of phosphate of magnesia, $ Lime, - - - ' 17.5 Carbonic acid, - - 19.0 The coloring principle of the blood is supposed to he 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, presents the following results : Water, .... 780.145 786 590 Fibrin, ----- 2.100 3.565 Albumen, - 65.090 69.415 Coloring matter, - 133.000 119.626 Crystallizable fatty matter, - - 2.430 4.300 Oily matter, .... 1.310 2.270 Extracted matter soluble in alcohol and water, 1.790 1.920 Albumen combined with soda, - - 1.265 2.010 Chloruret of sodium and potassium, alkaline ) g g~g - ggj phosphates, sulphates and sub-carbonates, $ /• 4 Sub-carbonate of lime and magnesia, phos- 1 phates of lime, magnesia and iron, per > 2.100 1.414 oxyd of iron, - - - 3 Loss, 2.400 2.586 1000.00 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, are sufficient to produce this effect. Hewson froze fresh blood by exposing it to a low temperature, and afterwards thawed it. It first resumed its fluidity, but afterwards coagulated in the usual manner. It has also been ascertained by ex- periment, that blood will coagulate, when deprived of the contact of the air, and subjected to agitation. In the exhausted receiver of an air-pump, its coagulation is even accelerated. Coagulation is influenced by the rapidity with which the blood flows from the body. According to Scudamore, blood slowly drawn from 70 FIRST LINES OF PHYSIOLOGY. a vein, coagulates more rapidly than when taken in a full stream. Exposure to oxygen gas accelerates it. During the coagulation of the blood, the tempera- ture of the mass is said to rise. Dr. Gordon estimated the rise of the thermometer at six degrees. Dr. Davy, however, regards the increase of temperature from this cause, as very trifling. Certain saline substances, as, a saturated 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 coag- ulated in the veins, in animals killed by powerful gal- vanic shocks. 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 in- superable difficulty. For, the carbonic acid of the atmosphere, and the carbonic acid, which is formed in the blood itself by the absorption of oxygen, combines with and saturates the menstruum of the albumen, which is consequently precipitated in the form of a coagulum. The evaporation of the ammonia, which is another menstruum of the albumen, and that of a part of the water of the blood, liberates another portion of dissolved albumen, and increases the quantity of the coagulum. Raspail, on the same principle, accounts for the pre- cipitation of the albumen in the form of the globules of the blood, which he considers as identical with albu- men. The absorption of the aqueous part of the blood, by the tissues nourished by it, and perhaps the satu- ration of the alkaline menstruum of the albumen, by the residue of nutrition constantly passing into the blood from the same tissues, occasion a regular pre- FLUIDS OF THE SYSTEM. 71 cipitation of albumen in the blood, in the form of small globules. The coagulation of the blood, however, is regarded by the most enlightened physiologists, as a vital phe- nomenon, and as not depending on any physical cause. “ The blood is supposed either to be endowed with a principle of vitality, or to receive from the living parts, with which it is in contact, a certain vital impression, which, together with constant motion, counteracts its tendency to coagulate.” Copland ascribes the coagulation of the blood prin- cipally 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 between the coloring envelopes and the cen- tral globules, contained in them. This attraction ceases soon after the blood is removed from the veins ; and the central bodies, freed from the colored envel- opes, are left to obey the attraction, which tends to unite them ; and in uniting, they form a net-work, in the meshes of which the coloring matter is entangled ; and the phenomena of coagulation are thus produced. 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 annual matter, of which the organs are composed. Vauquelin discovered in the blood, a considerable quantity of a fatty substance, which was at first supposed to be fat, but which was afterwards 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 con- taining azote. Prevost and Dumas demonstrated the existence of urea, a peculiar animal matter found in the urine, in the blood of animals, whose kidneys had been extirpated. Cholesterine, and some of the other ele- ments 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 72 FIRST LINES OF PHYSIOLOGY. basis of a great number of membranes and tissues : the fatty substance, before mentioned, 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 mat- ter consists of two classes of elements, viz. one chem- ical, 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 chemical powers of matter, but by the opera- tion of the organic forces. These are albumen, fibrin, gelatin, ozmazome, &c. All animal matter may be ana- lyzed proxiinately into these elements. The chemical forces tend to destroy these forms of matter, and to reduce them to the ultimate elements. The Ultimate Elements. The ultimate ponderable elements of animal matter may be divided into non-metallic and metallic sub- stances. I. The non-metallic elements are oxygen, hydrogen, carbon, azote, phosphorus, sulphur, chlorine, and fluo- rine. (Berthold.) CHEMICAL ANALYSIS OF THE ORGANIZATION. 73 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. mag- nesium, silicium, and aluminum. 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 proportion, and perhaps may be considered, as the only essential elements of animal matter. Oxygen enters very largely into the composition of animal matter. 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 be all divid- ed into organic oxyds and acids. In combination with hydrogen, it forms the watery basis of all the fluids, which constitute, as it has been computed, nine-tenths of the whole weight of the body. In union with car- bon it forms carbonic acid, which exists in the blood, and is exhaled abundantly from the lungs in respira- tion, and from the skin. With phosphorus it forms the phosphoric acid, which exists largely in the bones in combination with lime, and is one of the constitu- ents of healthy urine. With the metalloids it forms potash, soda, and lime. It also enters into the com- position of the organic elements, as albumen, fibrin, gelatin, 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 con- tained in the swimming vesicle, is pure oxygen gas. This is the case with the fishes, which live near the bottom of the water, and swim near the ground. Hydrogen is another principle which exists in all the fluids, and several of the solids of the body. It consti- tutes one element of the water basis of the fluids. It predominates in venous blood, as oxygen does in arterial. It exists largely in the bile ; is one of the ele- ments of fat and oil ; and is often developed in a 10 74 FIRST LINES OF PHYSIOLOGY. gaseous form in the intestinal canal, in enfeebled states of digestion. Combined with chlorine, it forms the hydrochloric acid, which exists in many of the animal fluids, in combination with soda. Hydrogen is introduced into the system by the aliments, and is eliminated by cutaneous and pulmonary exhala- tions, by the excretions of the kidneys, alimentary canal, and liver. In the process of putrefactive de- composition, it combines with sulphur, and sometimes with phosphorus, forming, with them, two fetid gases the sulphuretted and phosphuretted hydrogen. Carbon . — This element abounds in the vegetable kingdom, but is also found largely in animal sub- stances.. It is one of the elements of animal oil or fat, and of the quaternary animal oxyds, albumen, fibrin, gelatin, and mucus. It exists largely in the bile, and in venous blood. Most animal substances by combustion develope a considerable quantity of carbon. It is received by the aliments, and is elim- inated by respiration, by cutaneous transpiration, 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 charac- teristics. It is true, however, that a few plants contain it, particularly the mushroom tribe. It abounds, also, in the pollen of plants, and in the vegetable principle, gluten, and is one of the elements of the vegetable alka- loids, quinine, strychnine, &c. But, it exists almost uni- versally in animal substances, and may be regarded as one of its 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 pro- portion of azote. The peculiar smell of burning ani- mal matter is oAving chiefly to the presence of this principle. In the putrefaction of animal substances, CHEMICAL ANALYSIS OF THE ORGANIZATION. 75 the azote, disengaging itself from the other elements, combines with the hydrogen, forming a binary com* pound, ammonia , which is one of the characteristic results of animal decomposition. Azote is received into the system, chiefly w T ith the food, particularly 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 secretion of the kidneys, as it exists largely in healthy urine ; but partly by respiration, in which there appears to be an exhalation, as w r ell 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 sur- face 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 substance, to abandon the solid form, and re- sume their natural state as gases, an effort which is increased by the external heat, to which animal sub- stances are exposed, and by their own organic heat when in a living state, promotes the tendency to de- composition of animal matter. Phosphorus . — This principle exists both in animal and vegetable substances, but more abundantly in the former. It is present 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, with which it forms phospho- ric acid. It always exists in combination, generally in the state of phosphoric acid. It is evacuated chiefly by urine, which contains a considerable quantity of phosphoric acid, some of it free, and some in combi- nation with bases. During animal decomposition, a part of the phosphorus combines with hydrogen, form- ing the fetid gas, phosphuretted hydrogen. The phos- phorescence of putrefying animal matter, is supposed to 76 FIRST LINES OF PHYSIOLOGY. be owing to some inflammable compound of this kind. The extraordinary phenomenon of the spontaneous combustion of the human body, has been attributed, by Treviranus, to an accumulation of phosphorus in the system, owing to some obstacle to its regular ex- cretion by the kidneys and other outlets. The body, it is supposed, may at length become so highly charged with it, as to be rendered extremely combustible. Sulphur . — This is another principle of animal sub- stances, which always exists in combination with 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 with hydrogen, and then discharged from the system. It also, sometimes, passes off’ by cutane- ous transpiration. The fetor of foul ulcers is occa- sioned 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 com- bination with hydrogen, forming the hydrochloric acid. This is present in a free state in the gastric fluid, and in combination with 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 se- creted 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 with 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 carbonic, 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 CHEMICAL ANALYSIS OF THE ORGANIZATION. 77 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 animal matter. It exists as silex in the hu- man hair, and in the urine. Magnesium exists in animal and vegetable substan- ces, especially 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 pigrnentum nigrum. In what state it exists in the blood, is not known. It is supposed by some physiologists, in some indeterminate state of combination, to form the coloring 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 ele- ments, 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 ele- ments. The organic elements may be divided into two classes, viz. acids and oxyds. In addition to these, vegetables possess a peculiar kind of proximate prin- ciples, which are not found in animals. These are the recently discovered vegetable alkalies. 1. The organic acids found in the human system, are the acetic , 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 78 FIRST LINES OF PHYSIOLOGY. other animal fluids. The oxalic exists in some of the urinary calculi, particularly the mulberry calculus. The benzoic acid has been discovered in human urine. The uric acid consists of four elements, oxygen, carbon, hydrogen, 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 oxyds are numerous, both in the veg- etable and animal kingdoms, and differ widely from one another in their properties. Some of them con- sist of three elements, oxygen, carbon, and hydrogen ; others, of four, containing azote in addition to the three former. The ternary oxyds found in the animal kingdom, are sugar , resin , and fixed and volatile oils. Of sugar , there are two varieties found in the hu- man system. , One, the sugar of milk ; the other, a morbid product, existing in the urine of persons affect- ed with diabetes. The sugar ofi milk is obtained from the whey, by evaporating it to the consistence of syrup, and allow- ing it to cool. It is afterwards purified by means of albumen and crystallizing it again. In many re- spects it differs from the sugar of the cane, though possessing a sweet taste. It is not susceptible of the vi- nous fermentation ; 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 dia betic urine to the consistence of a syrup, and keeping it in a warm place for several days. In its properties and composition it appears to be iden- tical with vegetable sugar. A peculiar resin exists in the bile. Oi' fixed oils , fat and the marrow of the bones, are examples. Volatile oils are found in some of the inferior ani- mals, but not in man. The quaternary compounds, formed of oxygen, carbon, hydrogen, and azote, are the most important CHEMICAL ANALYSIS OF THE ORGANIZATION. 79 proximate principles of animal 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. Besides these, there are several others which are less common, as caseine , urea , hema- tine, the black matter of the eye, cholesterine, picrornel, &c. The first of these, albumen , is, of all substances, the most generally diffused in the animal economy. It exists both in a liquid and in a solid form. Combined with 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 con- stitutes 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 which is contained in the hydatid. It is a colorless, transparent substance, with- out taste or smell, coagulable by heat, by alcohol, ether, concentrated sulphuric acid, some of the metal- lic salts in solution, and an infusion of tannin. Ex- posed to a certain degree of heat, (about 160 F.) it coagulates into an insoluble mass. Solid albumen is a white, tasteless, elastic sub- stance, insoluble in water, 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 tumors are composed princi- pally of it. Albumen is composed of Carbon, Oxygen, Hydrogen, Azote, 52.883 or 17 equivalents. 23.872 6 do. 7.540 13 do. 15.705 2 do. 80 FIRST LINES OF PHYSIOLOGY. It also contains a small quantity of sulphur ; since it blackens silver, and, in a state of decomposition, ex- hales sulphuretted hydrogen gas. The physiological property, which corresponds with albumen, is sensi- bility. 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 owing 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 insoluble in water. It may be obtained by stirring fresh blood with a stick until it coagulates, and then washing the fibres which adhere to the stick, with cold water, so as to dissolve out the red globules. In its chemical com- position and many of its properties, it resembles albu- men, but differs from it, in coagulating at all tem- peratures. 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, w hat is remarkable, it exists in none of the fluids. It is a substance, distinguished from all other animal principles by its readily dissolv- ing in warm water, and forming a bulky, tremulous solid on cooling. When dried, it forms a hard, semi- transparent, brittle substance, with a shining fracture. One part of gelatin dissolved in one hundred parts of warm water, becomes solid on cooling, forming a hy- drate of gelatin. CHEMICAL ANALYSIS OP THE ORGANIZATION. 81 The well known 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 ising-glass 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 modifications, and exists in the skin, cartilages, liga- ments, 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 we have at present no sufficient means of answering. It is, probably, like fibrin, a mere modification of albumen. It is composed of The property which 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 flavor 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 water and alco- hol, either cold or hot, and by not forming a jelly, when its solution is concentrated by evaporation. According 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 Hydrogen, Azote, Carbon, Oxygen, 47.881 27.207 7.914 16.998 100.00 11 82 FIRST LINES OF PHYSIOLOGY. 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, which are destitute of sensibility, as the nails, hair, cuticle, and horny parts, which consist chiefly of inspissated mucus. The scales, feathers, and wool of different animals contain a good deal of mucus. The retc mucosum is supposed to be formed of compacted mucus. In union with water, mucus is a transparent, viscid, ropy fluid, without odor or taste. Nitric acid, at first, coagulates, but afterwards dis- solves it. In its dry state it is insoluble in w ater. 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 mammiferous animals, and is obtained from this fluid after it has been coagulated. After the removal of the cream, the curd must be well w ashed w ith 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 white, insipid, ino- dorous substance, of a greater specific gravity than water, 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, particularly in being coagulated by acids. It is composed of Carbon, Oxygen, Hydrogen, Azote, 59.781 11.409 7.429 21.381 100.000 CHEMICAL ANALYSIS OP THE ORGANIZATION. 83 Urea is a matter, which exists in human urine and in that of quadrupeds. It may be procured by evap- orating fresh urine to the consistence of a syrup, and gradually adding to it concentrated nitric acid, till it becomes a dark colored, crystallized mass. This is to be well washed 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 with pure alcohol, which dissolves only the urea. The alcoholic solution is afterwards to be concentrated by evaporation, and the urea is deposited in crystals. The crystals of urea are transparent, and colorless, and without odor. They leave a sensation of coldness on the tongue like nitre, and have a specific gravity greater than water. Urea is soluble in water and alcohol. Though not distinctly alkaline, it has the property of uniting with the nitric and oxalic acids. It is very highly azotized. It is composed of Oxygen, 26.40 Azote, - 43.40 Carbon, 19.40 Hydrogen, 10.80 100.00 The other quaternary oxyds are not of sufficient importance to be here particularly described. 84 FIRST LINES OF PHYSIOLOGY. 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 power 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 inter- nal movements, by which they are gradually developed, and their organization assumes the variety, complica- tion and form, demanded by the type of being, to which they respectively belong. This power, itself, assumes new properties or modifications in the different varie- ties of the organization thus developed ; each one re- acting in its own peculiar manner against the impres- sions made upon it ; every fibre, every tissue, every organ possessing its own specific excitability, and manifesting its own 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 own peculiar species of exci- tability, according to the difference of structure and constitution bestowed upon them at their original for- mation. The alimentary canal is excited by the presence of food, and by its own 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 PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 85 or internal impressions, conveyed 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 with this property, and are capable of exhibiting some modifi- cation of vital reaction, under the influence of external impressions of various kinds. Even the globules con- tained in the blood, and some of the other fluids, seem to be endued with this property; as their motions appear to be influenced by external excita- tions which act upon them. This property of living matter assumes three prin- cipal modifications 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 altera- tive, may be comprehended under the expression, vital affinity. These may be termed the physiological prop- erties of the organization, which 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 sensi- bility, 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 world, or from their own organization, im- pressions 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 mem- branes. In the interior of the body, it exists in all the soft solids, and its office appears to be, to convey to the mind a knowledge of the wants of the system ; and, in a pathological state, to apprize it, by means of the sensation of pain, of the disorders which exist in the organization. 86 FIRST LINES OF PHYSIOLOGY. Special sensibility is a property which is the basis of the relation existing between the organs of specific sensation, and the peculiar stimulants which act upon them. Thus the eye is endued with specific sensibility to light ; the ear, to the impressions of sound ; the pal- ate, 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 he 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 ex- cited by them. It is here, also, that sensation elab- orated 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 another 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 he the great solar plexus. Its mani- festations are independent of the brain, never, at least in the normal state, invoking the assistance of this organ, nor giving rise to the feeling of conscious- ness. 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 respective contents ; &c. ; but in all these cases, which are examples of organic sen- sibility, 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, however, that the existence of this species of sensibility stands on very different grounds from those on which the former rests. We have the highest possible evidence of the existence of cerebral sensibility, in our own feelings and consciousness; whereas that of organic sensibility is a mere hypothesis PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 87 which we are induced to make, to enable us to ex- plain certain phenomena, which appear to imply it. If, however, we admit of the existence of this species of sensibility, 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 jjlexus, is independent of the brain, and its exercise conveys no notice to the mind. Cerebral sensibility is displayed in all our sensations and perceptions, external and internal organic or vegetative , in the processes of digestion, circulation, secretion, absorption, nutrition, &c. In some parts of the system, according to Bichat, the presence of those fluids or solids, with which these parts are usually in contact, produces only organic im- pressions, which, in a healthy state, never give rise to animal sensation. This is the case with the mucous membranes, lining passages which open to the exter- nal 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 impres- sions, which these substances produce, are confined to the surface, with which they are in contact. But, if foreign bodies be brought into contact with them, cerebral sensation is immediately developed, and the individual becomes conscious of the impression. There are, also, certain parts of the body, which in a healthy state appear to be wholly destitute of cerebral sensibil- ity, though their growth and nutrition, in common with that of other parts of the system, prove that they possess organic. These are the bones, carti- lages, 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 alimentary canal possesses cerebral sensi- bility at its two extremities, but organic, in the inter- mediate parts. 88 FIRST LINES OF PHYSIOLOGY. The peculiar seats of cerebral sensibility, are the organs of animal 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 nour- ished and grow. 2. Contractility, or the faculty by virtue of which a living part contracts, is the principal motive force of the system. All the motions of the body have been sometimes traced up to this property, though there appears to exist a peculiar motive power in the system, which displays itself in the dilatation or erection of parts, and which cannot without difficulty be referred to contractility. Broussais, however, has attempted to trace up not only all the manifold movements, of the system, but, even all the vital manifestations whatever, to this single property of contractility. Living animal matter has the faculty of condens- ing itself, under the influence of certain external im- pressions. 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 de- grees in different 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 proportion of this principle. Accordingly, the muscles which are peculiarly distinguished by their power 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, as soon as the blood ceases to move. In the living state, the molecules of fibrin are kept in a state of mutual repulsion, perhaps by the vital influ- ence of the walls of the vessels, in which they move. But, as soon as they are withdrawn from this influ- ence, either by the death of the vessels, or by the removal of the blood from the body, the particles of PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 89 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 gela- tin or albumen, and are wholly destitute of fibrin, as the membranes, vessels, cartilages, &c., possess a cer- tain kind of contractility, i. e. they have the faculty of reacting against any distending force, and of recover- ing their former dimensions when 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 power of contracting on the application of stimuli ; an opinion, however, which is not strictly correct. Vital contractility exists in two modifications. One of them requires, for its exercise, the influ- ence of the brain, which is transmitted by means of nerves to the organs, in which it is called into action, viz. the locomotive and vocal muscles. All the vol- untary motions of the body, and all the muscular exertions employed in the various acts, which we consciously perform, are examples of the exercise of this power. The mechanical movements 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 immediate control of the will, and is attended with the consciousness of the individual. It may be termed cerebral contractility, because the influence of the brain is necessary, in the normal state, to excite it to action. The absence of cerebral contractility in a part nat- urally possessed of it, is called paralysis ; its morbid excess or exaltation, spasm or convulsion. By Bichat this power is denominated animal contractility ; by some others, locomotility. The second modification of contractility is termed organic , because it is a property which belongs to, and animates every part of the organization. It is inde- pendent of the brain, and its manifestations result from the immediate excitation of the organs themselves, 12 90 FIRST LINES OF PHYSIOLOGY. from stimuli applied directly to them. Its exercise is wholly uninfluenced by the will, and is not accompa- nied with consciousness. Organic contractility has been subdivided into two kinds, sensible and insensible , according as its phenom- ena are manifest, or obscure and latent. Thus certain organs, as the heart, the stomach, the bladder, and the uterus, possess an inherent power wholly independent of the brain or will, of contracting in a manifest and obvious manner under certain cir- cumstances, i. e. the application or presence of peculiar stimuli. The effect is wholly independent of the will and consciousness of the individual. Aliments excite contraction of the stomach and bowels; the presence of urine stimulates the bladder to contract ; the full grown foetus excites the uterus ; the stimulus of the blood, the heart, &c. This species of organic contractility is a prominent attribute of the holloAV muscles, or those which are placed out of the jurisdiction of the brain, as the heart, the stomach, intestines, &c. ; but it is not exclusively confined to them. It exists in the reser- voirs 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 circumstance, 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, we 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 passage of the secreted fluids through the fine canals of the glands which prepare them. The phenomena hardly admit of an explanation, without resorting to PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 91 the supposition of a power of contraction 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 contrac- tility. The motion of the blood in the two 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 forward as far as the fine ramifications of the arterial system, termed the capillary vessels, where the action of the heart is probably little felt. The motion of the blood, however, still continues, though it is propelled by other causes than the action of the heart. It is forced on by the insensible con- tractions of these hair-like vessels themselves, until it passes into the radicles of the veins. This insensible organic contractility exists in ani- mals destitute of a heart, or central moving power. 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 plants, and the motions of their fluids are maintained by it. In the animal body, the seats of this power 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 according to the structure of the part to which they are attached. They have been inge- niously compared to the hour and minute hands on the dial of a clock, which 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 * Diction, de Medicine. 92 FIRST LINES OF PHYSIOLOGY. which they produce, are not within the jurisdiction of the brain, and are wholly independent of the will. These effects are the result of various stimuli applied directly to the organs, which 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 dila- tation. This power differs from elasticity, which is purely a physical property, in not requiring the ap- plication 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, which become turgid, and gorged with blood, under the influence of venereal desire ; and in the nipple, which is similarly affected in the act of suckling. The same property is mani- fested in the skin, and the subcutaneous cellular tis- sue. Thus the face is said to swell with pleasure, the neck, to become tumid with anger ; the ends of the fingers experience a degree of erection in the act of touching, and the papillae 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, which are fur- nished 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 irritation. Thus, the internal membranes, as the serous, mucous, and synovial, when irritated, become turgid with blood, which accumulates in their vascular tissue. This is particularly exemplified in the gastric mucous membrane, when excited by the presence of aliment ; and in the serous and synovial membranes, when PHYSIOLOGICAL ANALYSIS OP THE ORGANIZATION. 93 exposed to the air, or subjected to any kind of irrita- tion. The glands exhibit similar phenomena under the same circumstances ; and even the muscles and nerves, and other parts provided with vessels, become turgescent with blood, when laid bare, and subjected to irritation. The parts which exhibit this phenomenon in the most conspicuous degree, as the organs of generation, and the nipples, are composed of a tissue of blood- vessels, interlaced with numerous ramifications of nerves. The erectile tissues are sometimes developed acci- dentally, or by disease. Aneurism by anastomosis is of this description. Hemorrhoidal tumors, also, some- times present all the characters of the accidental erectile tissues. The dilatation of the heart, which succeeds the systole of the organ, and the expansion of the iris, in the contraction of the pupil of the eye, are referred by some physiologists to this species of vital motion. During the dilatation of the heart, the organ swmlls up, and becomes harder, in expanding to receive or suck up, as it were, the next wave of blood from the veins. The expansion of the iris, which produces the con- traction of the pupil, is regarded as the active motion of the iris, because it is produced by the stimulus of light on the eye ; whereas the contraction 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 always greatest in cases of pa- ralysis or much debility of the organ. The structure of the iris, however, is a subject of controversy among anatomists. According to Magen- •die and others, it is unquestionably 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, which, by its contraction, diminishes this aperture. If this be admitted, the con- traction of the pupil is the effect of muscular action, and cannot be referred to the expansibility of the iris. 94 FIRST LINES OF PHYSIOLOGY. It has been conjectured that the act of absorption may he promoted by the exercise of this power in the absorbent vessels ; their inhaling radicles thus open- ing 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 penetrate and pervade all the organs, determine then* structure and composition, and the changes to which, in common with the fluids, they are constantly subjected. The numerous transformations which the fluids and solids of the body undergo, as in chymification, chylosis, lymphosis, hsematosis, the secretions, nutrition, calori- fication, 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 he refer- red to this power of vital affinity. The formation of the organic elements of the body, also, as fibrin, albumen, gelatin, &c., are the results of the operation of the same power. The exercise of this power of vital affinity, is con- fined principally to the fluids, and is manifested in the successive transformations which they undergo, from the state of crude aliment, as it is received into the system, to that of the nutritive fluids in the highest degree of assimilation. It is the most striking charac- teristic of this force of vital chemistry, to form com- pounds and aggregates, which could never he produced by chemical affinity. Under the influence of this power, the elements of animal matter are withdrawn from the jurisdiction of chemical laws, and are main- tained in their peculiar states of vital combination, in the midst of a variety of destructive forces, which are exerted in vain to subvert them. A new order of affinities seems to be developed in the elements of these combinations, by the influence of this vital force ; PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 95 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 indiffer- ence for all others.* Vital affinity, however, is not confined in its opera- tions to the production of changes and new combina- tions in the fluids of the system. The solid tissues, also, are subject to its power. The various structures, of which the body is composed, are formed and nour- ished 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 va- rious combinations and the different degrees of aggre- gation and cohesion of the elements which constitute the different tissues, must be determined by the chem- ico-vital forces, which operated in combining and arranging these elements. The type of the organs, however, by which their shape, size, and relative position in the system are determined, must be referred to some other power which was impressed upon the germ by the act of generation ; a power, which has received the name of the vis formativa, or force of for- mation. As the formation and nutrition of the different or- gans and tissues of the body are executed under the control of vital affinity, and as the different modifica- tions of vital power, with which they are respectively endued, result from their organization or vital compo- sition, it is evident that the power of vital affinity is primitive in relation to the other vital forces, or is, indirectly, the parent of them all. This power which is bestowed upon the germ by the act of generation, is excited to activity by the influence of external causes; and the movements, to which it gives rise, determine the developement of the different structures of the body, their organization, and their chemical composi- tion, and as a necessary consequence, the various modifications of vital power, with which they are respectively endued. * Diction, de Medicine. 96 FIRST LINES OF PHYSIOLOGY. II. The physical properties of the animal tissues are elasticity , extensibility, flexibility, imbibition, and evapo- ration. 1. The first of these, or elasticity, is possessed in the greatest degree by the cellular tissue and its modifi- cations. It is a force, which tends to restore parts, which have been subjected to mechanical extension, to their former state, as soon as the extending cause ceases to act. The cellular tissue enters so univer- sally 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 hollow viscera, and the vessels, are kept in a state of distension by the volume of their contents. If the different soft solids were not main- tained in this state by the rigidity of the skeleton, there would be a general shrinking 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 between 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 tunes 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 exer- tion of its elasticity, overcome at first by the muscular contraction of the ventricles, but acting with effect as PHYSIOLOGICAL ANALYSIS OF THE ORGANIZATION. 97 soon as the stimulus, which excited the organ to con- tract, 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 con- stantly reacting upon the column of blood, which 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 towards the termination of the arterial system. The contractility of the coats of the various canals which carry color- less and secreted fluids, 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 char- acter, as appears from several facts. The contrac- tility of the cellular tissue, e. g. is almost 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 stimula- ting agents. Moreover, it varies at different periods of life, in certain states of disease, and in short, according to a variety of circumstances, which 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 flexi- bility, as the free motions of these parts require. They are, also, possessed of some degree of extensibility. The tendons possess but little extensibility ; and for an obvious reason. As they are attached to mus- cles, and serve to conduct the moving force exerted by these organs, to the bones, it was evidently neces- sary, that they should not yield, themselves ; otherwise the moving force would be partly expended or ab- sorbed by them, before its arrival at the bones. 4. Imbibition . — Another important physical proper- ty of the animal tissues, is imbibition. 13 * Tiedemann. 98 FIRST LINES OF PHYSIOLOGY. 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 would into a sponge. All the soft animal tissues possess this power of imbi- bition. Some of the tissues absorb with great facility, as the serous membranes and the small vessels ; others, as, e. g. the epidermis are penetrated by fluids with much greater difficulty. The phenomena of imbibition are curious ; and they appear*to depend both on the nature of the fluid ab- sorbed, andthe texture of the absorbing tissue. Detrochet found, that on Ailing the intestine of a chicken with milk, or some other dense fluid, and plunging it into water, the milk passed out of the intestine through its coats, and the water into it, in the opposite direction ; and from repeated experiments of a similar kind, he deduced the conclusion that whenever 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 contained 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, the hydrogen in a short time will become contaminated with atmospheric air, which penetrates through the coats of the bladder. It appears, on the whole, 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 water which they imbibe, and retain. If they are deprived of this water, 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 with this fluid, their former properties are restored. THE FUNCTIONS. 99 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 circumstances favorable to evaporation, the aqueous part of the fluids begins to pass off in the form of vapor from the exposed surface, and the loss thus occasioned is greater or less, accord- ing as the surrounding circumstances are more or less favorable to evaporation. The losses of fluid thus occasioned may be so great under some circumstan- ces, 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 impossi- ble to find either beginning or end. Every thing is com- plicated 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. Now the motions of these organs, indispensably 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. Without the action of the lungs, an impure blood would be returned to the left side of the heart, by which its own vessels 100 FIRST LINES OF PHYSIOLOGY. would become penetrated, and its power of contrac- tion paralyzed ; and without the action of the heart, the functions of the lungs would instantly cease, be- cause no blood would 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, dependent both upon the heart and the lungs. If the lungs be deprived of the influence of the brain, their functions are instantly suspended ; respi- ration 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 transmit- ted 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, respi- ration, innervation, &c., are dependent upon digestion, and digestion indispensably requires the aid of the circulating, respiratory, and nervous systems. It ap- pears, therefore, that all the great functions of life are mutually dependent ; that they form a circle, in which it is equally impossible to distinguish a beginning or a termination, and of course to determine which are primitive, and which secondary 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 which is indispensable to that of those we are con- sidering ; and, consequently, every classification which can be adopted, must be more or less arbitrary and defective. The arrangement, 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, nutritive; 3, seasonal ; 4, genital. 1. Vital . — If we examine with attention the liv- ing system in organized beings, we perceive a class of functions, the exercise of which is absolutely THE FUNCTIONS. 101 indispensable, every moment, to maintain them in the living state. This first and most important class of func- tions 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 con- stitute what 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 nutrition, the assimilation of these to the various tissues and organs, and the expulsion from the system of heterogeneous or worn-out elements. This class embraces the four functions, digestion , absorption , nutrition , and secretion. The great object of this class of functions is to repair the waste in the organs inces- santly caused by the actions of life, and to maintain them in the state of nutrition, necessary to the sup- port of these actions. They may be termed the nutri- tive functions. The exercise of them is not so im- mediately necessary to life, as that of the first class. 3. Sensorial. — The third class may be called the sen- sorial functions , or functions of relation. These comprise the sensations, intellectual operations, and the volun- tary motions. They establish the relations between living beings and the external world; and become wider 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 wants; but in the human species, they present their greatest develope- ments. 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 which the brain is the common centre, are susceptible of great improvement by edu- cation, and are much influenced and modified by the power of habit. They are less necessary to life than 102 FIRST LINES OF PHYSIOLOGY. either of the two former classes, and their exercise may he suspended for a considerable time without danger. 4. Genital . — The fourth class of functions, is the geni- tal. 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 majority of organized beings, they require the concurrence of two individuals, or at least of two distinct organic apparatuses, one male, the other female. They are not unfolded, until the individual has attained that stage of constitutional developement, termed puberty; and in the human race, and some of the superior animals, 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 ani- mal organization, the functions of which are in the highest degree important 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 ; that is, the sensations, and the voluntary motions. But besides this, it ex- ercises an influence over the functions of organic or INNERVATION. 103 vegetative life, the degree and extent of which, how- ever, 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 0 applied ; while that, which it exercises over the two primary organs of this department, viz. the lungs and the heart, assigns to innervation a place among the vital functions, or those indispensably necessary to life. As presiding over sensation and voluntary motion, the functions of the nervous system fall under the third class, or those of relation. The nervous system is divided into two great sec- tions, which may be termed the encephalic, and the ganglionic ; the formei of which is sometimes called the nervous system of animal , the latter, that of or- ganic life. Encephalic JVervous System. The encephalic nervous system consists of the ence- phalon, 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 annular protuberance , and the spinal marrow. The cerebrum, cerebellum, and pons Varolii, are termed collectively the brain, that globular mass of nervous matter which fills the cavity of the cranium. The greatest length of this organ is about six inches ; its transverse and vertical dimen- sions, about five inches each. Its weight in the adult is between three and four pounds. 1. Cerebrum. — The cerebrum in man, constitutes much the most considerable part of the encephalon. The upper surface of it, which is convex, is divided lon- gitudinally by a deep fissure into two equal and sym- metrical halves, termed hemispheres, which are sepa- rated by a fold of the dura mater, called the falx. The fissure which separates the two hemispheres, is bound- 104 FIRST LINES OF PHYSIOLOGY. ed inferiorly by a kind of bridge of medullary matter, called the corpus callosum , which 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 convolutions, which exhibit a strik- ing resemblance to a mass of intestines. 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 brain to consist. The depth of these fissures is said to bear some ratio to the developement 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 trans- verse depression called the Jissura Sylcii. 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 prolongations, which are termed cornua. The anterior cornua are separa- ted by a transparent membranous partition, called the septum lucidum, composed of two laminae, the separa- tion of which leaves a small cavity between them, called the fossa Sylcii , or the fifth ventricle. The two lateral ventricles communicate with each other by an opening, called the foramen of Monro. In the lateral ventricles several parts are found, for a particular description of which, we 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 lower 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 ventricles, and, on being cut into obliquely, exhibiting a striated appearance, owing to alternate streaks of grayish and whitish matter ; the optic thalami , two oval eminences, lying INNERVATION. 105 between the diverging extremities of the corpora stri- ata, and their upper surface forming a part of the floor of the ventricles ; the commissure i mollis , a band of cineritious matter, which connects the convex surfaces of the optic thalami ; the tcenia semicircularis, a line of white matter running between 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, covering 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 the venae Galeni , which run backward and enter the sinus rectus. Between the optic thalami and the crura cerebri, is a deep fissure, which communicates with 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 lat- ter, 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 poste- rior lobes of the cerebrum, from which it is separated by the tentorium. Like the brain, it is divided into two lateral halves by the lesser falx, and it is com- posed of two hemispheres, united behind, by the ver- miform processes which rest upon the medulla oblon- gata , and before, by the pons Varolii. On its upper surface, it presents live fasciculated lobules, common to both lobes, and disposed in transverse concentric bands. The inferior part of the cerebellum presents a convex surface, on which may be distinguished four lobules disposed in concentric arches. When a sec- tion is made between the two hemispheres a beautiful arborescent appearance presents itself, formed by the peculiar arrangement of the white and gray matter of the brain, which is termed arbor vitce. In thh cere- bellum exists a cavity called the fourth ventricle. The sides of this cavity are formed by the crura cerebclli, the anterior part by the medulla oblongada, and the upper and back part, by the valve of Vieussens. The 106 FIRST LINES OF PHYSIOLOGY. third and fourth ventricles communicate with each other by an opening, termed the aqueduct of Sylvius. 3. The annular 'protuberance , or pons Varolii, is a large round eminence situated between the cerebrum and 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 two supe- rior, 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 groves, which separate the tubercles. 4. The medulla spinalis, or spinal marrow is a cylin- drical cord of nervous matter, which originates from the pons Varolii, passes downwards through the oc- cipital 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 enceph- alon, what is sometimes termed the cerebro-spinal axis. That part of it, which extends from the pons varolii to the occipital hole, is termed the medulla oblongata. On its surface, it presents four eminences, termed the corpo- ra pyramidalia, and the corpora olivaria. The two former are oblong bundles of medullary matter, lying contiguous to each other ; and on the outside side of these are the two others, which, from some resem- blance in shape to olives, are called corpora olivaria. The posterior surface of the medulla oblongata is contiguous with 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 two oblong eminences termed the corpora restiformia. The remaining part of the medulla spinalis is a long cylindrical cord, occupying the vertebral canal, and extending from the occipital foramen to about the level of the first lumbar vertebra. On its anterior sur- face, a deep fissure extends through its whole length, dividing it into two equal lateral parts. Its posterior surface, also, is divided by a median groove. INNERVATION. 107 The spinal cord is considered by some anatomists as consisting of four columns, two ascending to the cerebrum, and two descending from the cerebellum; by others as consisting of two only. According to Bellingeri, it consists, throughout its whole course, of six whitish 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 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 cor- pora pyramidalia, and the crura of the brain, and may be termed the cerebral strands of the cord. The late- ral columns are continuous with the corpora restifor- mia, and may be denominated the restiform strands. And the posterior column’s communicate directly with the cerebellum, and may be termed the cerebellic strands. The vertebral cord, instead of exhibiting the ap- pearance of a regular cylinder, presents two remark- able enlargements, one of which 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 developement of the cor- responding upper and lower extremities. This relation exists in the fetal state, and continues after birth, and according to Serres, the bulbs of the spinal cord, as well as the limbs which correspond with them, pro- gressively increase until 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 dis- tinct kinds of matter, one termed the cortical or cine- ritious, the other, the medullary or white. The first 108 FIRST LINES OF PHYSIOLOGY. 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 color, and of a firmer consistence than the medullary matter. The cortical substance is essentially vascular, and perhaps is designed to protect the brain from the impulse of the blood, by dividing the vessels sent to it into infinitely small twigs. It also serves, perhaps, to nourish the medul- lary part. The medullary or white matter is situated interi- orly. It constitutes much the larger portion of the whole mass of the brain, and is traversed by a great number of ramifications of blood-vessels. The mass of the brain seems to be formed of an expansion of the fasciculi of medullary fibres of the medulla oblon- gata, 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 cranium. The difference depends on the different degrees of activity of the brain, in these two states of the system. Another motion depends on respiration. The brain rises during expiration, but sinks in the act of inspira- tion. A third depends on the pulsations of the heart, with which it synchronizes. During the systole of the heart, the blood is propelled forcibly into the ar- teries of the brain, and communicates a pulsatory motion to the organ, which sinks again during the diastole of the heart. The spinal marrow is subject to similar motions. INNERVATION. 109 These motions of the brain are said to be a prerog- ative 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 arte- ries and the two internal carotids; the principal branches of which occupy the base of the brain. Numerous veins r&mify over the surface of the organ, and terminate in osseo-fibrous canals, which open into the jugular veins. The quantity of blood which it receives, is very great, amounting, it is supposed, to one-eighth of the whole quantity which issues from the heart. Chemical Analysis of the Brain. The analysis of the substance of the brain, exhibits the following results : Water, - 8.000 Albumen, - - - 700 White fatty matter, - - 453 Red do. do. - - 70 Osmazome, - - - 112 Phosphorus, - - - 150 Sulphur, - - - - 515 Traces of phosphates of potash, lime, and magnesia, and muriate of soda. 10.000 Envelopes 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, 110 FIRST LINES OF PHYSIOLOGY. the cerebellum, the pons Varolii, and the medulla ob- longata. The spine is a column, composed of twenty- four perforated bones, called vertebrae, piled one upon another, in such a manner as to form a continuous 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 hones, the os 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 arachnoids , and an inter- nal, or the pia mater. 1. The dura mater is the external envelope 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 lamina?. Its internal surface forms several folds or duplica- tures. One of these constitutes the falx cerebri , which separates the two hemispheres of the brain from each other. Its upper edge, extending from the frontal ridge to the middle groove of the occipital bone, con- tains 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 circum- ference contains the lateral sinuses. The falx cerebelli is another process of the dura mater , which lies between the lobes of the cerebellum. These different partitions appear designed to maintain the principal divisions of the encephalon in their re- spective situations, and to prevent them from being compressed by one another. In animals, whose habits of life lead them to spring down from elevated places, as the cat, there are bony partitions between the prin- cipal parts of the encephalon, instead of the membra- nous folds of the dura mater. INNERVATION. Ill 2. The arachnoides is situated between the dura ma- ter and pia mater. It is a serous membrane, and con- sequently forms a closed sac. It is expanded over the convolutions of the brain without dipping into the fissures which separate them, and over the cerebellum, and the base of the pons Yarolii. It forms a sheath for all the nerves and all the vessels which pass into, or out of, the cranium. It also passes downwards into the vertebral canal, envelopes the spinal marrow, and gives a sheath to each of the vertebral nerves. This membrane penetrates into the third ventricle by a small opening between the corpus callosum, and the tubercula quadrigemina ; it lines the third ventricle, and is continued over the parietes of the lateral and fourth ventricles, into which it penetrates through the aqueduct of Sylvius. 3. The pia mater is the third membrane of the ence- phalon. It is a loose cellulo-vascular membrane, which immediately invests the brain, dipping into the fissures which separate the convolutions, and covering the superior surface of the corpus callosum ; enveloping, interiorly the base of the brain, the pons Varolii, and the surface of the cerebellum. It penetrates into the third and lateral ventricles, where it forms the choroid web , and the plexus choroides. It appears to be a del- icate tissue of blood-vessels, connected and supported by soft cellular membrane. The pia mater, which invests the spinal marrow, is connected to the arachnoid membrane by a loose cel- lular tissue and by blood-vessels ; leaving, however, an interval between the two membranes, wdiich is filled by a liquid. This space communicates with the ventricles of the brain by means of the fourth ventri- cle. The fluid, which thus surrounds the spinal mar- row, it is conjectured, may serve the purpose of blunt- ing 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 laminae of the arach- noides itself. Magendie informs us that the spinal fluid exists in all the mammiferous animals as well as 112 FIRST LINES OF PHYSIOLOGY. man, and at every period of life, occupying the whole length of the vertebral canal. The encephalic nerves constitute the second part of the encephalic system. These nerves are white cords, extending from the brain or spinal marrow to every part of the system, and are the conductors of sensitive and motive impressions. They are disposed in symmetrical pairs, and are composed of filaments, connected together by cellular tissue. Of these nerves there are forty-three pairs. Two pairs originate from the cerebrum ; viz. the olfactory , and the optic. Five pairs from the pons Varolii and its peduncles, viz. the motores oculorurn. or third pair ; the pathetici, or fourth pair ; the trifacial , 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 marrow ; viz. five from the medulla oblongata ; viz. the auditory nerve, or eighth pair; the glosso- pharyngeal, or ninth pair; the pneumo- gastric, or tenth pair, sometimes called the eighth pair, and the par-vagum ; the hypoglossal ; and the spinal accesso- ry. Eight arise from the cervical part of the spinal marrow; 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 which they are destined, and which, for the most part, are the senses and the muscles of voluntary motion ; others form nu- merous 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 branch- es, interlaced together. The plexuses formed by the encephalic nerves, are four in number ; the cervical, brachial , lumbo-abdomi- nal, 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 fourth vertebrse, and INNERVATION. 113 gives rise to four principal nerves, which are distribu- ted 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 concealed, in a great measure, in the cavity of the axilla, and gives rise to eight principal branches, distributed to the thorax, shoulder and arm.. 3. The lumbo-abdominal plexus is formed by the anterior branches of the five lumbar nerves, lies be- hind the psoas muscle, and gives origin to six princi- pal 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 with 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 color, of a roundish, or elongated shape, varying in volume from the size of a hemp-seed to that of an almond ; most of them extending 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 dowmwards to the ganglions, nearest it, and others to anastomose with the cerebro-spinal nerves. Some of them furnish branches, which are distributed imme- diately to certain organs, as to the arterial coats, or 15 114 FIRST LINES OF PHYSTOLOUY. to particular viscera. Thus, the ophthalmic ganglion gives origin to the ciliary nerves ; the submaxillary , to the filaments which supply the salivary glands ; the spheno-palatine, the cavernous , and the naso-palatine , to branches which are distributed to the arteries and neighboring parts, &c. But most of the filaments proceeding from the ganglia, are destined to the for- mation 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 ganglions, 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 little splanchnic nerve. The ganglions are numerous, and are found in dif- ferent situations. Most of them extend in a series along the vertebral column ; six are found in the head, and several in the abdomen. The ganglions, which exist in the head, are the ophthalmic , the spheno-palatine , the cavernous , the naso- palatine, the sub-maxillary , and the otic , or the gan- glion of Arnold. Of those, which lie along the verte- bral column, three, or sometimes only two, are found in the neck, and are called the cervical ganglions; eleven or twelve, 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 semi-lunar ganglions, situated on each side of the aorta, on a level with the coeliac artery. By then’ 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 semi-lunar, and are connected with them by anasto- mosing filaments. This collection of ganglia and nervous filaments interlaced together, constitutes the solar plexus. Plexuses formed by the ganglionic nerves. — The nervous branches furnished by the ganglions, unite in INNERVATION. 115 a great number of points with branches of the ence- phalic nerves, forming inextricable plexuses. From these, originate numerous branches, some of which are distributed to the neighboring organs, but much the larger portion to the coats of the arteries, which they accompany in their principal divisions, forming secon- dary 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 pneumo-gastric nerve, and the anterior branches of the first thoracic ganglions : The solar plexus, formed by the great and little splanchnic nerves, and by numerous branches furnish- ed by the semi-lunar ganglion and its accessories. From this great centre spring branches which serve to form a great number of secondary plexuses, as the diaphragmatic plexus ; the coeliac, from which origi- nate 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 sympathetic 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 divi- ded intot wo general classes ; the first, those of relation , comprehending the sensations, voluntary motions, and the intellectual operations; the second, those by which it influences the other functions of the system, as the respiration, circulation, digestion, nutrition, se- cretion, calorification, &c. 116 FIRST LINES OF PHYSIOLOGY. The first class of these functions does not, in strict propriety, fall under consideration at present, because it constitutes the third general class, into which the functions of the system are distributed, viz. the senso- rial , or those of relation. It is the second class, viz. those by which the nervous system controls, or influ- ences the other functions most necessary to life, par- ticularly 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 organ- ized 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 cerebi'um , cerebellum , and f)ons Varolii , may be considered as the great cen- tre of this section of the nervous system, and one of the most important organs in the whole animal econ- omy. It is the great developement of the brain in the human race, which raises man so far above all other animals, even those, which from their near approach to man in external shape and internal organization, are termed anthropomorphous. The functions over which 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 individu- ality, the temple in which is enshrined the perceptive, thinking, and willing principle. The spinal marrow and nerves are subordinate organs, whose 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 important influence over many of the other functions of the system, particularly res- piration, and the circulation, as has been already INNERVATION. 117 observed. These two classes of the cerebral func- tions, though differing essentially from each other, I shall not separate, but consider together ; while under the third class of the functions, or those of relation, will be considered the senses, and the subject of volun- tary motion. 1. The sensorial functions of the brain . — These in- clude sensation, voluntary motion, and the intellectual and moral faculties. Sensation . — The organs of sense and the nerves are the immediate seats of sensation, but its ultimate seat is the brain. Every sensation we experience, from whatever cause it originates, and by whatever channel it is introduced, requires the intervention of 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 way or other modified, or digested, as it were, by this organ. Of this the proof is per- fectly conclusive. If the nerve, which connects an organ of sense with the brain, be divided or compress- ed, no sensation will be excited in the mind by im- pressions made upon the organ. The same physical effect will be produced as before by the external 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 excited. A circumstance truly curious in this process of sensation is, that, though the brain is the ultimate and real seat of sen- sation, yet every sensation is always referred to the organ of sense, on which the impression which gives rise to it, is made ; so that there would appear to be a double organic action in all cases of sensation, viz. one from the organ of sense to the brain, by which sensation is excited ; the other from the brain, towards the organ, bymeans 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, which sometimes occur in persons who have lost some 118 FIRST LINES OF PHYSIOLOGY. of their limbs, and who complain 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 which it is referred, actually existed. For the essence of a substance con- sists in being felt. When it is felt, it exists ; when it is not felt, it' does not exist. These sensations are delusive only in being referred by the mind to a part, which has no existence ; but this only proves that the reference itself is a cerebral action, and may be ex- erted even in the absence of the organ, to which 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, which are the recipients of the impressions, and the nerves proceeding from them to the brain are uninjured ; but no sensation isexcited, 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, impressions 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 power of being excited by external impressions, from their con- nection with this organ. No impression upon the senses is noticed or excites consciousness, merely be- cause the brain, in a state of repose, is incapable of receiving them, and of reacting upon them. If, how- ever, these impressions, whether made by external innervation. 119 causes, or produced by affections of the organs them- selves, 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 shadowy kind of consciousness, which 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 increased, the sensations excited by them, would be- come more vivid than under the ordinary degree of cerebral reaction. Now the fact is found strictly to accord with 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 atten- tion 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 dissipating the cerebral energy, become distinct and even vivid sensations, when the scattered rays of the mind are recalled, concentrated together in a focus, and thrown 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 sensation, may be noticed in this place. In certain affections of the brain, sensations are some- times excited by the mere action of the brain itself, without the corresponding impressions upon the senses. 120 FIRST LINES OF PHYSIOLOGY. We have examples of this curious fact in certain ner- vous diseases, as catalepsy, hypochondriasis, and ma- nia. Insane persons sometimes listen attentively to fancied strains of celestial music, to which they earnestly call the attention of others. In the same manner, tire tales of visions and apparitions, which have been so frequently told, and so generally dis- credited by all but the ignorant and the supersti- tious, admit of an explanation in perfect consistency with physiological principles. The brain has been, highly excited by the operation of fear and awe, upon ardent imaginations. The action of the brain has naturally corresponded with 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 according to the law which operates in all cases of actual sensation, it has been accompanied by a refer- ence to the appropriate organ of sense. The shape under which the hallucination will be embodied in such cases, will probably be determined by accidental cir- cumstances, 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 cerebel- lum themselves are destitute of sensibility. Wounds of these parts, as it seems to be established by experi- ments, do not excite pain. The whole of the hemis- pheres has been pared away, the cerebellum removed in the same manner, the corpora striata, and the optic thalami cut away, 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. Accord- ing 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 INNERVATION. 121 sides of the fourth ventricle ; hut this property dimin- ishes 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 mo- tions. The immediate instruments of motion are the muscles. It is by the contraction or shortening of these, that motions are impressed upon the moving parts of animal bodies. The muscles possess a peculiar power of contracting, upon the application of certain stimulants. Thus, mechanical irritation applied to mus- cular fibres, excites them to contract ; and without the application of some stimulant power, the contractility of the muscles remains in a dormant state, and the or- gan does not contract. Now the stimulus which acts upon the voluntary muscles, so as to excite their fac- ulty 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 without the agency of the brain. Of the mechanism of these actions we are totally ignorant. We are conscious only of the two extremes of the phenomena, the act of the will, which is an immaterial agent and which by an internal sentiment we refer to the brain, and the physical effect to which it 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 two phenomena. The energy of the brain is conveyed, as if by electricity, to the instruments of motion, which are instantly excited to their appropriate actions. The cerebral influence, however, may be set in motion by other causes besides the will, and contrac- tions of the voluntary muscles be excited not only without 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 devel- oped in it by disease, will frequently excite involun- tary contractions of the muscles, which usually act 16 122 FIRST LINES OF PHYSIOLOGY. 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 contractions, which are called convulsions or spasms. In such cases a person may retain his consciousness, and the power of the will may exist in full vigor ; 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 imma- terial, 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 communication between the brain and any organ of voluntary motion be cut off. by divid- ing, compressing, or stupifying by opium, the nerve which forms this communication, no act of the will can excite to motjon 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 two organs is no longer open. Certain diseases of the brain, or injuries inflicted upon the organ, abolish the power of volition. It is remarkable that, in these cases, the same cause which destroys the faculty of the will, and of course prevents voluntary contractions of the muscles, 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 illus- tration of the dependence of voluntary motion upon the brain. In this disease, some of the voluntary muscles lose their power of contracting under the in- fluence 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 condition in hemiplegia, and some INNERVATION. 123 other varieties of palsy, is generally connected with some lesion of the brain, which may be the effect of disease or of accident. It does not so far impair the 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 conse- quently are not excited to contraction. It would seem probable from this fact, that the faculty of volition has a distinct seat in the brain, and that its physical influence is exerted upon some other part of the organ, whence it is transmitted to the conductors of the cere- bral energy, the nerves. If the seat of the faculty itself be materially injured, no act of the will can be exerted. But if the seat of the injury be any part of the brain, on which the physical influence of the will is exerted, or through which 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 in- action, and the faculty of volition dormant, there is no contraction of the voluntary muscles. A person asleep, if placed on his feet, is unable to support him- self in an erect position, but obeys the law of gravi- tation, and sinks to the ground. If sleep overtakes him while sitting, its first approaches are indicated by nodding of the head forwards ; 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 be- hind 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 incontrovertible kind. The connection of the brain with the operations of the in- tellect, and of the moral faculty, is shown by numer- ous 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 124 FIRST LINES OF PHYSIOLOGY. 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 powers ; and accordingly we find that inju- ries of the head, frequently destroy or impair the fac- ulties of the mind. The same consequences result from certain diseases of the brain, a fact which is remarkably exemplified in apoplexy, and in insanity — two 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 patient 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 insensible, we may be equally sure, that this organ has suffered some physical change, which, in most cases, will be apparent on dissection. 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 ex- periences 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 devel- opement and growth ; if they are neglected, it proba- bly never attains the expansion of which it is capable. This circumstance 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 developed brain, and no volunta- ry efforts of the individual can overcome the obstacle; for it is a physical one, connected with the state of the organization. On the other hand, severe exer- cise imposed upon the brain in its tender state, in young children, is still more pernicious; for it INNERVATION. 125 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 blos- som, every thing gives hopes of an early and abundant harvest, but the fruit never ripens, but falls half-form- ed to the ground. 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 physiologists, ultimately, of all the sensations. Vertical pressure upon the hemispheres of the brain, occasions stupor, — an effect, however, which Mayo ascribes to the compression 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 durable 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 fol- lowed by blindness of the opposite eye, and by a paralytic weakness of the muscles of the opposite side of the body. If both lobes are removed, much injured or com- pressed, according to Flourens, there is from that moment neither sight, hearing, smell, taste, memory, thought, nor will. The animal subjected to the ope- ration, sinks into an apoplectic stupor ; a fact, from which Flourens infers, that the cerebral lobes consti- tute the organ of the memory, of the will, and, ulti- mately, of all the sensations. It is a curious fact, that although the sight of the opposite eye is destroyed when one of the cerebral lobes is removed, the contrac- tility of the iris remains unimpaired. If the conjunc- tiva, the optic nerve, or the tubercula quadrigemina, 126 FIRST LINES OF PHYSIOLOGY. 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 elsewhere. 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 odors, to sounds, and to tastes. He admits that vision is abolished by the ablation of the cerebral lobes ; but this fact he ac- counts 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 intervention 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 ap- pears 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 unim- paired, when the lobes of the brain are mutilated or wounded. Even deep wounds of the brain are not invariably followed by debility of sensation or motion, or of the mental faculties ; facts, which render it prob- able, that a portion of these lobes, perhaps the central part, may suffice for the exercise of these functions. The office of the cerebellum is supposed to be, to regulate and combine different motions to a determin- INNERVATION. 127 ate object. A wound of one side of the cerebellum is followed by a weakness of the same side of the ani- mal. If the wound be deep, the body on the injured side becomes paralytic. In the experiments of Flou- rens, however, wounds and injuries of the cerebellum were 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 power of combining the motions, necessary to the mode of progression which is proper to the species of the animal, subjected to the experiment. The animal appears to be intoxi- cated, and exhibits a singular propensity to go back- wards. Another remarkable phenomenon is a kind of rotation or whirling round, which is said to be some- times exhibited by persons, after wounds, or in dis- eases, of the cerebellum. Sometimes patients affected with disease of this organ, whirl round in their beds in a very extraordinary manner. Further, if a verti- cal incision be made into one side of the cerebellum, the animal rolls over and over, always turning itself towards the injured side ; at the same time a want of harmony is observed in the direction of the eyes, one of them being turned upwards and backwards, the other, downwards and forwards. On making a simi- lar incision in the opposite hemisphere parallel to the first, the motion of the animal ceases, and the harmo- ny of direction in the two eyes is immediately re- stored. Magendie observed that the same effect was pro- duced by dividing the crus cerebelli in a rabbit, as by dividing the cerebellum unequally. The animal sur- vived 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 opposite crus put a stop to the motion. If a section of the cerebellum on one side, gave rise to a constant revolution towards the same side, the division of the opposite crus cerebelli did not restore the equilibrium, but the animal began to revolve to- wards the side of the divided crus. 128 FIRST LINES OF PHYSIOLOGY. These curious phenomena Mayo ascribes to a sen- sation like vertigo, produced by the lesions of the cerebellum. Upon comparing the cerebrum and cerebellum to- gether in relation to the effect of injuries upon them, it appears that lesions of the cerebellum give rise to a want of harmony in the voluntary motions ; those of the cerebrum, implicate the senses, understanding, 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 symp- toms of narcotism ; in the latter, those of intoxication. Lesions of the cerebrum produce paralysis or immo- bility ; those of the cerebellum, agitation and disor- dered motions, and especially a disposition to go back- wards, and a rotation of the body. Diseases of the cerebrum destroy the harmony of ideas ; those of the cerebellum, the harmony of motions. The cerebellum influences chiefly the lower limbs ; the cerebrum, the upper.* The tubercula quad rig emina have been supposed chiefly to influence the voluntary motions of the body, the sense of vision, and the contraction of the iris. The removal of one of these bodies, weakens the sight, and the motions of the iris of the opposite eye, causing dilatation of the pupil. The total destruction of the tubercles, produces blindness, immobility of the iris, and dilatation of the pupils. Irritation applied to the tubercles, occasions convulsions and contractions of the iris. Magendie, however, remarks, that he had never seen that an injury of the optic tubercle affected the vision in the mammiferous animals, though this effect was very evident in birds. The destruction of the p>ons VaroEi, occasions im- mobility of the body, and the loss of all the senses. The respiration and circulation are not affected, unless the injury extends to the medulla oblongata. Ac- cording to Bourdon, the pons Varolii is situated be- tween the functions of the will and those of instinct, * Bourdon. INNERVATION. 129 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 physiolo- gists, to influence 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, paraple- gia or palsy of the lower 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 oblon- gata, morbid affections of them, more frequently affect respiration. Hence paralysis or convulsions of the arms, are oftener accompanied with oppressed respira- tion than those of the legs. According to Bourdon, paraplegia is often accom- panied 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 quadrige- mina , are subservient to the sense of vision, and the corpora striata to that of smell. So that the same parts of the brain which are instrumental in vision, are subservient to the sense of touch, in regulating 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. The parts of the encephalon, which seem to be partic- ularly destined to motion, are the corpora striata, the optic thalami in their inferior part, the crura cerebri, the pons Varolii, the peduncles of the cerebellum, the lat- eral parts of the medulla oblongata, and the anterior part of the spinal marrow. 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 endeavors 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 ; 17 130 FIRST LINES OF PHYSIOLOGY. and that the cerebellum, the posterior strands of the spinal cord, and the posterior roots of the spinal nerves, also, preside 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 principally the motions of the abdominal or sacral extremities ; and that injuries and diseases of the optic chambers, and posterior lobes of the brain, affect chiefly the motions of the thoracic extremities. He, also, adduces experimental proof of the subservi- ence 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 cere- bellum, &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 motions, and priapism ; and others, in which palsy of various mus- cles was produced by diseases of the cerebellum. Bellingeri, further, endeavors to prove that the lobes of the brain are subservient to the motions of flexion ; and the cerebellum, to those of extension. In proof of the first position, he adduces various ex- periments of different physiologists, as Magendie, Flourens, &c. Thus, Serres found that the removal or injury of one of the anterior lobes of the brain, was followed by flexion of the opposite abdominal extrem- ity; and the removal of both anterior lobes produced the flexion of both abdominal extremities. On the con- trary, the division or removal of the posterior lobes of the brain is followed by flexion of the thoracic ex- tremities. The removal or destruction of the hemis- pheres of the brain causes an irresistible motion of progression forwards ; while wounds or destruction of the cerebellum produce a retrogressive motion. — From pathological investigations, Bellingeri infers that INNERVATION. 131 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 motions of flexion and adduction of the ex- tremities. In proof of the proposition that the cere- bellum 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 spas- modic 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 throw the animal completely backwards ; and, that the motion of retrogression observed by Ma- gendie in injuries or irritations of the cerebellum, is owing to the spasmodic action thus induced in the extensor muscles, by which the animals are compelled involuntarily to move backwards. In support of the same position, Bellingeri adduces a variety of patho- logical facts.* 2. Influence of the brain over the organic functions. — The influence of the brain over the organic func- tions is comparatively inconsiderable, being far inferior to that of the spinal marrow. Most of the great functions of the system, however, appear to be more or less influenced by cerebral innervation ; as respira- tion, 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 mus- cles, which derive their nervous influence directly or indirectly from the brain. The internal sentiment of the want of respiration, which 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, however, is by no means necessary to Edinb. Med. and Surg. Journ. No. cxx. 132 FIRST LINES OF PHYSIOLOGY. respiration ; for, this function goes on without intermis- sion, 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 ascribed 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 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 were deficient, and the basis of the latter was covered by the common integuments, except over the foramen magnum, where there existed a soft tumor about the size of the end of the thumb. This child lived four days, and breathed naturally , and was not observed to be deficient in warmth until its powers declined. The medulla spi- nalis was found to extend about an inch above the foramen magnum, swelling out into a small bulb, which formed the soft tumor upon the basis of the skull. All the nerves, from the fifth to the ninth, were connected with this. The most extensive organic disease may exist in different parts of the brain with- out affecting respiration. Yet, that this function is influenced by the brain, appears from the fact, that certain emotions of the mind produce an evident effect on the movements of respiration. The action of the heart , also, is considerably influ- enced by the brain. It is well known that violent emotions, and all strong moral affections powerfully 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 was struck with such admiration by a painting of Raphael, that he swooned and expired on the spot. The passion of fear, also, produces a strong depressing effect upon the circula- tion. Terror has, in some instances, caused a mortal INNERVATION. 133 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, was un- commonly fruitful in this disease. Another fact which tends to the same conclusion is, that concussion of the brain is attended with great depression of the action of the heart, and of the capil- lary circulation, together with coldness of the surface. 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 pneumo-gastric nerves upon digestion, is to be ascribed to the interception, 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 capillary vessels, and which de- rive their powers principally from the ganglionic sys- tem, 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 func- tions, are illustrative of the influence of cerebral in- nervation over the department of vegetative life. The passions affect the capillary circulation and calorifi- cation ; for, the skin becomes red or pale, and hot or cold, under the influence of certain passions. The secretions , also, manifest the influence of cere- bral innervation. Grief increases the secretion of tears; fear, that of the kidneys. A cold sweat some- times starts out from the skin under the influence of the same moral cause. The peculiar state of the ner- vous system which exists in hysterical affections, fre- quently 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 diarrhea in infants nourished by it. Boerhaave relates a case of this kind, in which epilepsy was excited by 134 FIRST LINES OF PHYSIOLOGY. this cause, and continued to return during the whole life of the patient. The cerebral influence, also, affects absorption , and probably nutrition likewise. It is well known, that persons under the influence of fear are peculiarly liable to be attacked by contagious, or epidemic dis- ease ; 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 pro- motes 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 withering; a fact, which appears to evince the influence of encephalic innervation upon nutrition. These facts, and numerous others of a similar kind, appear to leave no doubt, that the parenchyma of the organs, as well as the capillary system, are supplied with nerves, which 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, which exists between, and connects together, the dif- ferent organs ; in other words, it is supposed to be the principal agent of the sympathies. On the whole, the brain is the organ of intelligence ; it directs the means by which we react upon the external world ; it exercises 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 according we find that injuries of this organ from accident or disease, are generally, though not invariably, fatal. Though it be true, however, that the functions of in- ternal 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 INNERVATION. 135 that full grown fetuses have been born, destitute of every trace of a brain, and even of a spinal marrow. From this, it should seem, that during fetal life the innervation of the ganglionic system is sufficient to maintain the nutritive and vital functions, in their im- perfect and rudimentary state ; but that after birth, when the individual commences a new and more ele- vated 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 which are immediately de- pendent on encephalic innervation, viz. digestion and respiration, first begin their exercise ; the empire of the brain is extended over all the functions of life, con- necting them together in a bond of reciprocal depen- dence and sympathy ; and cerebral innervation then becomes indispensable to their regular exercise, and consequently to animal life. 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 class- es of animals, under different forms, and the more high- ly 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 immediate instruments of these functions, viz. all the sensible parts of the trunk and limbs, and the muscles of vol- untary motion. It exercises, also, an important influ- ence over many of the organic functions, particularly respiration, calorification, cutaneous transpiration, 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, 136 FIRST LINES OF PHYSIOLOGY. those by which it influences the vital and organic ones. I. Sensorial f unctions . — According to Mayo, it ap- pears from Magendie’s experiment of removing the cerebrum, optic tubercles, and- cerebellum in a living animal, that the brain may be taken away by succes- sive portions, and yet the animal survive, and exhibit sensation and instinct. But if the mutilation be car- ried a line further, so as to comprise that small seg- ment of the medulla oblongata, in which the fifth, and eighth nerves originate, consciousness is at once in- stantly extinguished. From this experiment it would seem to follow, that this portion of the medulla oblon- gata, instead of the cerebral lobes, is the seat of con- sciousness. Mayo remarks, further, that the rest of the nervous system derives its vitality, or rather its par- ticipation in the phenomena of consciousness, from its continuity with this small portion of the medulla ob- longata. In proof of which, he states that in cold- blooded animals, as the frog or turtle, consciousness will continue some time after the head has been sev- ered from the body ; and it will 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 con- sciousness. 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 vertical pressure upon the hemispheres of the brain, is owing to the compression of the medulla oblongata. The same author observes in connection with this subject, that when vomiting has been excited by an emetic, it is arrested by pres- sure applied to the medulla oblongata. 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, independent of the INNERVATION. 137 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 known 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 paralyzes the limbs, and that portion of the trunk of the body, situated hcloic the seat of the injury, leaving the parts above , wholly unaffected. If the injury occur high up in the neck, it causes almost instant death. The involuntary discharge of urine and fecal matter, which is frequently the consequence of injuries of the spine, was referred by Galen to a paralysis of the nervous filaments, which are distributed upon the sphincters of the bladder and rectum. It is also well known, that irritations applied to the spinal marrow, excite con- vulsions of the trunk and limbs below the seat of the irritation. The researches of Bell, Magendie and others, ap- pear also to have established the fact, that the ante- rior 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 sensi- bility of the limb, without affecting its power of mo- tion ; and, on the other hand, that the section of the anterior roots abolished the muscular power, without impairing the sensibility of the limb. A striking evi- dence of the same fact is furnished by the mix 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. 18 138 FIRST LINES OF PHYSIOLOGY. It appears, hoAvever, that the isolation of these two properties in the anterior and posterior roots of the spinal nerves, is not complete. If an irritation he ap- plied to the posterior roots, contractions are produced in the muscles, to which the nerves are distributed, though they are much less violent than when the an- terior roots are irritated. In like manner, slight indi- cations 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 con- fined exclusively to the sensibility or the motility of the paralyzed part. 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, however, much difference of opinion re- specting the functions of these parts of the spinal mar- row. According to Bellingeri, the posterior strands pre- side over the movements of extension, and the anterior over those of flexion ; whence there results an antag- onism between these two parts of the spinal cord. The posterior strands produce a relaxation of the sphincter of the bladder, and the contraction of that of the rectum ; the anterior on the contrary, preside over the contraction of the sphincter of the blad- der, and the relaxation of that of the rectum. The anterior and posterior strands exert no influence upon sensibility, but only on motion. The white matter of the spinal cord is the exclusive seat of motility ; while the influence of the gray matter, is confined 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, depends on that portion of the spinal marrow from which it receives its nerves. If INNERVATION. 139 an animal is made to take strychnine, and the spinal marrow be laid hare, the convulsions in any part oc- casioned 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 channel of communica- tion between 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 differ- ent portions of the spinal cord are capable of acting independently of one another; a fact, which confirms the opinion that the spinal marrow has a power of its own. independent of the brain. Mayo remarks, that the spinal cord consists of an assemblage of indepen- dent segments ; that each segment, from which a pair of nerves arises, has in itself a mechanism of sensitive and instinctive action, similar to that of analogous parts in the invertebrated animals. In proof of this he ad- duces 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, muscu- lar 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 irri- tation is propagated 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. Still, the peculiar energy of the spinal marrow, is subordinate to the influence of the brain, which per- ceives 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 locomo- tive organs. Without the action of the cerebral lobes, no voluntary motion could be originated, and probably no sensation be distinctly and consciously felt. 140 FIRST LINES OF PHYSIOLOGY. Influence of the Spinal Marrow over the Organic Functions. The spinal cord, also, exercises an important influ- ence upon some of the organic functions most neces- sary to life. The superior part of the spinal cord, or the medulla oblongata, may he 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 neces- sary to life ; particularly the nerves which give energy to the lungs, the larynx, the heart, and the stomach, and those which supply the external muscles of respi- ration ; and any cause, which should at the same time suspend the action of all these nerves, would imme- diately annihilate life.* Hence, the instant death oc- casioned by an injury of this part of the spinal cord. According to Bellingeri, the lateral strands of the medulla, which are continuous with the corpora resti- formia , preside over the organic and instinctive func- tions. Respiration , especially, is under the influence of the superior part of the medulla spinalis ; and lesions of this part of the cord, are always accompanied by symptoms, which point out the dependence of respira- tion upon it. Lesions of the medulla oblongata in- stantly annihilate respiration. Injuries of the spinal cord opposite to the second vertebra, also, occasion instantaneous death ; because all the respiratory nerves are then injured simultaneously, so that respi- ration 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 marrow be wounded 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 * Ollivier. INNERVATION. 141 becoming nearly motionless, and the intercostal mus- cles, paralyzed ; and death soon follows from asphyx- ia. If a lesion be inflicted upon the dorsal portion of the spinal cord, it is followed by immobility of the ribs, because the intercostal muscles derive their ner- vous influence from this part of the cord. Respira- tion, however, is still carried on imperfectly by the action of the diaphragm, and the other respiratory muscles, accompanied by the elevation of the shtml- ders, expanding of the nostrils, opening .of the mouth, &c. It may be asked why a simple section of the spinal marrow at the occiput, produces death, when 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 observing that the pneumo-gastric nerves, which originate in the medulla oblongata, receive in the lungs the impression of the want of respiration, and transmit it to the me- dulla oblongata. In the normal state, the medulla oblongata reacts upon those parts of the spinal cord which give rise to the respiratory nerves of the chest. But, if the communication between the medulla oblon- gata and the vertebral parts of the cord, be intercepted, the former can no longer transmit its influence to the latter, which, consequently, do not excite the respira- tory muscles to action. The effect upon respiration, of dividing the pneumo- gastric nerves, is another illustration of the influence of the medulla oblongata on this function. The di- vision 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 obstacle to the introduction of air into 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 which furnishes the respiratory muscles of the chest with nerves. 142 FIRST LINES OF PHYSIOLOGY. The influence of the spinal marrow upon the circu- culation of the blood, i,s by no means so great, as upon respiration. Even the total destruction of the cord does not occasion an immediate suspension of this function. Experiments, however, have ascertained, that the circulation of the blood is considerably influ- enced by the spinal column. The destruction of the spinal marrow, or of any considerable portion of it, has*been found to enfeeble the action of the heart. If the lumbar part of it be destroyed, the circulation is enfeebled in the posterior extremities, but is not af- fected in other parts of the body, which derive their nervous influence from that part of the cord, which 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. Oh the whole, it is ascertained that the action of the heart is independent of spinal innervation, but is much in- fluenced by it. The heart may act without the spinal cord, but yet is subjected in some degree to this ner- vous centre. But the capillary circulation appears to be immedi- ately dependent 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 paraple- gia from an injury of the spine, the capillary circula- tion is sometimes almost wholly suspended ; the skin is purple or mottled, from a stasis of venous blood in the small vessels ; there is a total absence of cutane- ous transpiration ; the skin is dry, and there is a con- stant exfoliation of the cuticle. There is, also, a sen- sible diminution in the temperature of the paralyzed parts. The developement of caloric in the system, seems to take place in the two capillary systems, the pulmonary and the general ; and both these systems derive 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. INNERVATION. 143 there is a sensible diminution of temperature, of which the patient complains. Calorification, however, is not under the exclusive control of spinal innervation. The whole nervous system is probably concerned in it. That the spinal cord exerts an influence upon di- gestion , is ascertained by pathological facts, and by experiments on living animals. 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, ova- ria, &c. Obstinate constipation, followed by involun- tary 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 evacuating the bowels, an effect which was undoubtedly owing, in part, to a paralysis of the abdominal muscles, but which was partly to be ascribed to a loss of power in the muscu- lar coat of the intestines, produced by the section of the cord.* The influence of the medulla oblongata upon diges- tion, is illustrated by the effect upon chymification, produced by the division of the pneumo-gastric nerves. This operation in living animals, has been found to produce a paralysis of the stomach, by which the mus- cular contractions of the organ are annihilated, and chymification brought to a stand. It appears, there- fore, that the contractions 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 pneumo-gastric 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 * Ollivier. 144 FIRST LINES OF PHYSIOLOGY. neighborhood of the dorsal and lumbar vertebrae, or the total destruction of it below the last cervical ver- tebra, has been found entirely to change the qualities of the urine, which has become perfectly limpid, like water, containing little or no animal extractive mat- ter, but much saline and acid principles. The de- struction of the medulla oblongata, and of the cervical portion of the cord, has occasioned an immediate sus- pension of the urinary function, though respiration was maintained by artificial means. Chronic affec- tions of the cord are sometimes accompanied by a morbid state of the bladder ; as, chronic inflammation, or a copious secretion of vesical mucus. It has also been remarked, that paraplegia is a disease which, of all others, is most apt to occasion saline incrustations on sounds, left in the bladder. According to some physiologists, the spinal marrow presides over the functions of nutrition. Rachetti * remarks, that the energy 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 owing to the predominance of this part of the nervous system, according to the same physiologist, that the Crustacea, insects, and worms, owe the re- markable property which they possess, of reproducing parts which have been removed or accidentally de- stroyed. The numerous connections of the spinal marrow with the great sympathetic, which has been generally considered as the nervous system of organic or vege- tative 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 greater part of its nervous energy ; and, in confir- mation of this opinion, it has been observed, that the developement of the great sympathetic, in different * Ollivier. INNERVATION. 145 classes of animals, is always in the direct ratio to that of the spinal marrow. On the whole, it may be ob- served, 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 medulla 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 sensa- tion and motion ; some of them to one of these func- tions only, the others to both. Thus the nerves of sight, hearing, 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 physi- ologists express it, indifferent. In their peripheral extremities, the nerves either retain their distinct and independent character, as is the fact with the optic acustic, &c. ; or they become amalgamated with the other tissues. The more high- ly a nerve is endowed with power, the more indepen- dent and isolated it is from the other soft parts. Thus, the nerves of specific sensation, as the olfactory, the acustic, and the optic, preserve their individuality in their peripheral expansions. While the nerves of common sensation, as those of the skin, are confound- ed and melted, as it were, with the tissue of this membrane, so as not to be separable or distinguish- able from it. The periphery of the nervous system, however, is not confined to the outer skin, or the ex- ternal parts of the body, but exists every where, where nerves are expanded, as in the muscles, the paren- chyma of most of the organs, and some of the mem- branes. 19 146 FIRST LINES OF PHYSIOLOGY. Cranial Nerves. The nerves, which originate from the base of the brain are twelve pairs, and are called cerebral or cranial nerves ; the remaining 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 audito- ry. 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-pharyngeal. 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 numerous 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 connected to the optic thal- ami 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 pitui- tary fossa, and afterwards separate, and pass through the optic foramina, arrive at the posterior and inner part of the eye-ball, 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, which are distrib- uted to the cochlea, vestibule, and semi-circular ca- nals. INNERVATION. 147 These three nerves, together with the fourth pair, are isolated and have no anastomoses. They commu- nicate only with the brain, and the organs to which they are respectively distributed ; having no connection with the spinal marrow, nor with the great sympa- thetic. All the other nerves are connected together by communications, more or less numerous. 2. Nerves of voluntary motion. — The cranial nerves, subservient 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 filaments from the back part of the crura ce- rebri. This nerve is distributed to five muscles in the orbit of the eye, and sends a filament to the lenticular ganglion. By this ganglion it communicates 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, beneath the tubercula quad- rigemina and the lateral part of the valve of Vieus- sens. 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, ex- cept 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 into 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 term- ed the portio dura of the seventh, rises apparently between the corpora olivaria and restiformia. It enters the internal auditory foramen with the acustic nerve, then leaves the latter, and passes out of the cranium by the stylo-mastoid foramen. It receives a 148 FIRST LINES OF PHYSIOLOGY. filament of the Vidian nerve, which enters the cavity of the tympanum, under the name of the corda tympa- ni. The facial nerve furnishes filaments 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 integu- ments of the face. The seventh, according to Bell, is a nerve of instinctive , but according to Mayo, of vol- untary 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 V arolii in two fasciculi or roots, upon the larger of which, or the posterior, is formed a ganglion termed the Gasserian. Each nerve afterwards separates into three divisions, viz. the ophthalmic, the superior maxillary, and the in- ferior maxillary. The first branch is distributed to the eye-ball, the iris, the lachrymal gland, the Schneiderian membrane, and the muscles and integuments 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 dis- tributed to the alveoli of the lower jaw, the submax- illary, and sublingual glands, the tongue, the masse- ter, the pterygoid, the temporal, and the buccinator muscles, and to the integuments of the temple and chin. The fifth pair communicates with the third, the sixth, the seventh, 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 mus- cles and integuments, are, like the spinal nerves sub- servient to sensation and voluntary motion, jointly ; but Mayo contends, that the facial branches of the INNER YATION. 149 fifth are exclusively sentient nerves ; while the twigs, which supply the masseter, the temporal, the 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 sensation, viz. to the face, and to the organs of specific sensation the eyes, nostrils, mouth, &c. ; but its third branch, the inferior maxillary, furnishes the tongue with a nerve, which is considered as the gus- tatory nerve, or the peculiar nerve of taste. The tenth pair , or the pneumo- gastric nerves , com- monly 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, or glosso- pharyngeal nerves, and the twelfth, or accessory nerves; and descend on the lateral parts of the neck, with the great sympathetic on the outer side of the primitive carotid, and posterior to the jugular vein. They dis- tribute branches to the larynx, trachea, lungs, pharynx, oesophagus, stomach, duodenum, liver, spleen, and kid- neys. This important nerve establishes the principal con- nection between 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 principal connection between the organs, subjected to the will and those which are not under the control of this principle. In a word, it unites the two lines of Bichat, the animal, and organ- ic. In its whole course it gives twigs to the gangli- ons, and contributes to form with their own proper filaments, the principal plexuses of this system. The branches of the pneumo-gastric nerves, which are distributed to the larynx, lungs, oesophagus, and stomach, appear to be nerves both of sensation and of involuntary motion. 150 FIRST LINES OF PHYSIOLOGY. 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 auditory canal, and receives one from the facial, and another from the pneumo-gastric 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 branch- es 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 occip- ital bone, and passes out by the foramen lacerum pos- terius, with the pneumo-gastric, to which 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 bestows the power of motion. It appears, also, to be a nerve of sensation ; for, irritating it ex- cites pain, and consequently in its functions, it resem- bles the spinal nerves. The Vertebral Nerves. The vertebral nerves are more uniform in the manner of their origin, and regular in their distribu- tion, than those which originate at the base of the brain. Each vertebral nerve arises by two distinct 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 ante- rior to make up the entire spinal nerve. These nerves, INNERVATION. 151 thus springing from two roots, possess the double property of conveying, in opposite directions, sensific and motive impressions. If a vertebral nerve is divi- ded in any part of its course, the parts, to which it is distributed, are deprived both of their sensibility and of their power 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 im- pairing its sensibility ; while the section of the poste- rior roots, without affecting the power of motion, abolishes the sensibility. Each of these nerves, there- fore, consists of two orders of filaments, which per- form different offices, one conveying sensific impres- sions from the parts, to which 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, viz. 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. 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, ac- cording to Bell, another system, which he terms the superadded or irregular , which he considers as forming a complex associated system, subservient to 152 FIRST LINES OF PHYSIOLOGY. respiration. Sir C. Bell remarks, that the motions dependent on respiration, extend nearly over the whole body, while they more directly affect the trunk, neck, and face. This is particularly true of respira- tion 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 connected with respiration, and which re- quire the aid of the respiratory muscles, such as coughing, sneezing, laughing, swallowing, vomiting, and speaking. Now all these actions, though not subservient 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 pecu- liarly destined to them ; and this connexion establish- es 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 ac- tivity. 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 move- ments of inspiration, or when it is intended to perform some voluntary action, which requires the aid of respi- ration, as smelling or speaking, it requires the aid of volition. In dyspnoea, violent efforts are made to ex- pand the thorax, by elevating the shoulders; and in highly excited respiration, the movements are not con- fined to the chest, but affect simultaneously the abdo- men, thorax, neck, throat, lips and nostrils. It is evident, then, that whatever may be the design of this exten- sive connexion of respiration with other functions of the system, it must be effected by an association of a great variety of muscles, animated by some common influence ; and the nerves concerned in establishing this connexion, are termed by Bell the respiratory nerves, and form a system distinguished from the spi- nal, by the irregularity of their distribution. They originate, also, from one root only, and are destitute of ganglions at their origin. INNERVATION.. 153 These nerves arise very nearly together 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 downwards, 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, supposes that the branches of the intercostal and lum- bar nerves, which influence the intercostal muscles, and the muscles of the abdomen in the act of respira- tion, are derived from the continuation of the same cord or slip of medullary matter. The respiratory, or superadded system of nerves, therefore, consists of the portio dura of the seventh, or the facial nerve, the tenth or pneumo-gastric, the phrenic, which is distrib- uted to the diaphragm, the spinal-accessory, which supplies the muscles of the shoulder, and the external respiratory, which is spent on the outside of the chest. Functions of the Sympathetic Nerve. The functions of the great sympathetic are not known. In the neck, and the canalis caroticus, it fur- nishes branches to the great vessels, and to the heart ; in the chest, branches which are distributed to the viscera of the abdomen, and in the abdomen, others to the pelvic viscera. The same organs, however, are supplied with nerves from the encephalic system. The common opinion seems to be, that the great sympa- thetic presides over the organic or involuntary func- tions, as secretion, nutrition, absorption, calorification, &c. It is also supposed to be, as its name imports, the source of the numerous sympathies, which unite the viscera of organic life into one great connected system. By some physiologists, the ganglions of this nerve are supposed to render the organs, which are supplied with nerves from them, independent of the will. In herbivorous animals, which employ most of their time in eating, the sympathetic nerve is very large, 20 154 FIRST I^INES OF PHYSIOLOGY. corresponding with the voluminous viscera of these animals. The sympathetic is possessed of scarcely any sen- sibility. 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. 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 sud- den 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 mo- ment its nutrition ceases, and it loses the power of executing its peculiar functions ; and it is obvious that an universal suspension of the circulation, which dis- tributes 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 ab- THE CIRCULATION. 155 sorbed into the system, instead of being immediately employed in nourishing it, are first converted into a distinct fluid, the blood, which furnishes the immediate elements of nutrition ; and in which, also, there exists a local respiration; i. e. the absorption of air takes place separately from that of the other nutritive prin- ciples, and,, in a separate organ, or apparatus. Two different kinds of matter are absolutely necessary to the nutrition of animals, viz. air, and certain solid and 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 nutrition. 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 carried from this organ to all parts of the body, to furnish the materials for their nutrition, and vital excitation. Hence, a local respi- ration is always accompanied with a circulation ; while in those animals, in which respiration is dissem- inated, i. e. is not concentrated in a particular organ, as in insects, there is no circulation.* The organs of the circulation are the heart , the ar- teries , the veins , and the capillary vessels. These or- gans, collectively, represent two trees of unequal size, whose trunks are united at the heart, and whose 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 cir- culation, the heart. The motion of the blood in this apparatus is a cir- culatory one. This fluid is forced out of the heart by the contraction of the organ, and propelled to every * Adelon. 156 FIRST LINES OF PHYSIOLOGY. part of the body through elastic tubes, called arteries. From the extremities of these it passes into the mi- nute organs of another set of tubes, termed A r eins, and by them is returned to the hea rt. According to some physiologists, there exists between the termination of the arteries and the commencement of the veins, an intermediate order of fine hair-like 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 which returns from all parts of the body, and transmits it to the lungs, where it is con- verted by respiration into scarlet-colored arterial blood. This may lie termed the venous , or the pul- monary heart. The other heart receives from the lungs 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 riveted 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 cavities, by which the heart receives the blood, are called auricles ; and those which 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 direc- tions, interlacing one another, and forming an inextri- cable 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 mem- brane, reflected over it from the pericardium, a sac of a fibro-serous structure. This membrane secretes a THE CIRCULATION. 157 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 pneumo-gastric and the great sympathetic nerves, and they follow the ramifi- cations of the coronary arteries. The heart is situated in the thorax, in the lower part of the anterior mediastinum. Its position is oblique, being inclined forwards, downwards, and outwards, and from right to left. Its posterior sur- face is nearly horizontal, and rests upon the aponeu- rotic centre of the diaphragm. Its anterior is turned a little upwards, 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 vertebra?, 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 direc- tion 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 called 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 con- nected by their common septum, and by fibres pass- ing from one to the other, that it is impossible for either to contract alone. The same is true of the two ventricles. They have a common septum, and there are whole layers of fibres common to both. On the contrary, the auricles and ventricles are connected with each other only by cellular tissue, vessels, and nerves. No muscular fibres pass from one to the oth- er, and by maceration they may be easily separated from each other. 158 FIRST LINES OF PHYSIOLOGY. According to some physiologists, the right ventricle has a greater capacity than the left, because the venous system to which it belongs, is more capacious than the arterial. But others assert, that the superior capacity of the right side of the heart, is a cadaveric phenome- non, 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 trans- parent membrane, which is continued from the ven- tricles into the corresponding arteries, and from the auricles into the veins which open into them. It is usually classed with the serous membranes. Between each auricle and the corresponding ven- tricle is placed a valve, which is formed by a duplica- tion of the inner membrane, strengthened by interve- ning 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 chordae tendiueoe. The margin of the valves is strengthened by little granular bodies, term- ed corpora sesamordea. These valves prevent the refluence of the blood from the ventricles into the auricles, during the contraction of the former. Valves exist, also, at the origin of the two great arteries, the pulmonary artery, and the aorta, where these vessels communicate with the right and the left ventricles. These valves differ widely from the for- mer. They are formed by folds of the inner mem- brane of the arteries, are of a semi-lunar shape, and are attached by their convex margin to the circum- ference of the artery, each occupying a third part of it. These are termed the semi-lunar, or sigmoid valves, and their office is to prevent a reflux of the blood from the aorta and pulmonary artery, into the corres- ponding ventricles. THE CIRCULATION. 159 The orifice of the inferior vena cava is also furnish- ed 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 fetal state, and its office is to direct the blood of the inferior cava through the foramen ovale , an ap- erture by which, during fetal 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 which 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 pul- monary veins into the left. r The Arteries . — The vessels into which the blood is propelled by the action of the heart, and distributed to all parts of the body, are termed arteries. These vessels form two 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 col- ored blood, which it distributes by its ramifications throughout all parts of the system, terminating in minute twigs at the periphery of the body, and in the limbs and internal organs. The main trunk of the pulmonary arterial system which arises from the right ventricle, is called the pulmonary artery. It carries dark colored or venous blood, and its ramifications are distributed throughout the lungs. Where an artery divides, its branches have an area greater than that of the trunk, and they generally di- verge at acute angles. In general, the arterial and venous trunks are distributed together ; the larger ar- teries 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 with one anoth- er, permitting the blood to pass freely from one branch 160 FIRST LINES OF PHYSIOLOGY. to another, and these communications increase, as the arteries become more distant from the heart. These vessels are nourished by minute arterial branches, dis- tributed through these tunics, and which are termed vasa vasorum. They are also supplied with nerves, which are derived principally from the great sympa- thetic. The structure of these vessels has already been described. The Veins . — The veins , which return the blood to the heart from all parts of the body, constitute, like the arteries, two systems ; one of which corresponds to the arterial system of the aorta, and conveys dark colored or venous blood from the periphery of the body, from the head, trunk and limbs, and from all the internal organs, to the right auricle of the heart, into which it opens by the two great trunks, called the vence cavce , superior and inferior. The other, which corresponds to the pulmonary arterial system, conveys scarlet colored 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 are very strong and flexible tubes, though possessed of little elasticity. They are furnished with numerous valves, formed by semilunar folds of thin in- terior tunic, the office of which is to prevent the reflux of the blood. Like the arteries, they are furnished with vasa vasorum, and with nerves derived from the great sympathetic. The Capillary Vessels . — The capillary system, which is intermediate between the terminations of the arte- ries and the origins of the veins, presents two modifi- cations. In one, it consists of canals, furnished with proper coats or walls, which carry blood from the ex- treme 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 en- large, 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 THE CIRCULATION. 161 a single globule of blood to pass out at a time. They are also subject to great changes, some of them disap- pearing and closing up, and new ones being formed. The formation of these vessels is caused by the fine arterial canals gradually losing their coats, and be- coming confounded with the parenchyma of the or- gans. The capillary vessels have numerous anasto- moses, and they are the theatre of the functions of nutrition, secretion, calorification, hematosis, &c. The capillary system is divided into two sections or departments, one called the general, the other the pul- monary. The first of these is intermediate, between the ultimate branches of the aorta, and the origins of the vense cav*. It is the theatre of nutrition, and se- cretion, and of the conversion of arterial into venous blood. The second exists only in the lungs, and is intermediate between 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 sys- tem, in which the mass of the blood undergoes the op- posite changes. It appears from this, that the lungs have two capil- lary systems, viz. one connected with their peculiar function, or respiration ; and another, which 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 termi- nate and are lost in the tissues and organs, and the veins originate anew. Most physiologists, on the con- trary, contend for the immediate passage of the arte- ries into the veins, and Rudolphi asserts that the pla- centa affords the only exception to this structure. In the invertebrated animals however, or at least in many of them, it is said to be impossible to force injections from the arteries into the veins. 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 21 162 FIRST LINES OF PHYSIOLOGY. the lungs, to become endued with the arterial princb pie ; these animals being so constituted, that the aera- tion of a portion of the blood is sufficient for the reno- vation 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 reno- vated 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 au- ricles. 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 two branches, one of which carries a portion of the blood to the lungs, to be sub- jected to respiration; the other distributes the remain- ing 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, com- prehending the worms, the mollusca, the Crustacea, and fishes, the organs of the circulation present differ- ent dispositions. Worms have no heart ; and the cir- culation, which consists in the passage of the blood from the organs of respiration to all parts of the ani- mal, 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 conveying 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 animals, 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 de’signed to circulate both kinds of blood, as in the reptiles, nor arterial blood alone, as in the crus- taceous and some of the molluscous animals. Its office THE CIRCULATION. 163 is to propel the venous blood to the gills, while the arte- rial 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, which pro- ceed 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 circu- lation ; the other, or the venous heart, is the organ of the lesser, or the pulmonary. In the general circula- tion, 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 follows. 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 which it is projected into the pulmonary artery, and by the ramifications 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 164 FIRST LINES OF PHYSIOLOGY. corresponding ventricle, by the contraction of which it is projected into the aorta, and by the ramifications of this vessel distributed to all parts of the system. In the capillary vessels of these it loses its arterial character, and then passes into another system of ves- sels, the veins, by which 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 circdlation is quite complete ; for, in neither does the blood return to the same point from which its course commenced. In or- der 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 which are effected in the capillary systems of the two, i. e. the change from arterial to venous, and that from venous to arterial blood. It appears, then, that the two parts of which the heart is com- posed 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 its left ventricle and its right auricle. The right ventricle and the left auricle, therefore, are the two extremes, be- tween which is comprehended the pulmonary or lesser circulation ; while the left ventricle and the right au- ricle bound the arterial or the greater circulation. Besides this division of the circulation into aortal and pulmonary, 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 phe- nomena, viz. the passage of the blood from the ca- THE CIRCULATION. 165 pillaries of the lungs where it assumes its arterial properties, to the general capillary system where it furnishes the elements of nutrition and of the secre- tions, and acts as the universal excitant of all the or- gans ; and, secondly, the passage of the blood from the general capillary system to the pulmonary capil- laries, where the properties of the vital fluid are reno- vated by respiration. In this view, the two capillary systems, 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 ca- pillary system of the lungs, where the blood acquires the peculiar characters which distinguish arterial blood. From the capillary system of the lungs it passes into the pulmonary veins, which 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 he considered as the termination of the circulation 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 pas- sage, 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, therefore, be- longs to the circulation of arterial blood. The circulation of the black, or venous blood, com- mences where the former terminated, i. e. in the gen- eral capillary system. Here the blood is converted from arterial into venous, from scarlet to purple-color- ed blood. From the general capillary system it pass- es into the veins, which convey it to the pulmonary or venous heart. From this it is distributed by the pul- monary 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 166 FIRST LINES OF PHYSIOLOGY. of this side of the heart, therefore, belongs to the cir- culation of venous blood. Each of these circulations begins with veins, and terminates with arteries, and each of them, in its course, passes through both cavi- ties of one side of the heart. Each of them consists of two segments of circles of unequal size ; the larger being a moiety of the general or aortal circulation, the smaller, a division of the pulmonary. The circula- tion of red or arterial blood, consists of the venous part of the pulmonary, and of the arterial part of the general circulation ; and the circulation of venous, or purple blood, consists of the venous segment of the aortal or general circulation, and of the arterial seg- ment of the pulmonary. The two circulations are entirely independent of each other, except at their origins and terminations, the two capillary systems, where the arterial and ve- nous blood are reciprocally transformed into each other; and they intersect each other at the heart, through which they both pass, yet without communi- cating 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 impulse, or excitation, indispensable to life and to the func- tions of the organs. A part of the arterial blood re- mains in the organs, to replace the materials removed by vital decomposition ; another part is expended in the secreted fluids, and passes into the canals belong- ing to this function in the different secretory organs. Of course, a part only, and perhaps but a small part of the blood, returns 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 ven- tricle of the heart. In the circulation of black or venous blood, this fluid passes from the general capillary system to that THE CIRCULATION. 167 of the lungs, in order to be renovated and converted again into arterial blood by respiration. In its pas- sage to the pulmonary heart, it is reinforced by the addition of a considerable quantity of chyle and lymph, which are on then* way to the lungs, to be converted into blood by respiration. These two fluids, the chyle and lymph, are gathered up and conveyed into the blood by an order of vessels called absorbents. These vessels, collecting the materials of renovation from the organs, by vital decomposition, and from all the 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, with which they are transmitted through the lungs, where the whole compound fluid is converted by respiration into arterial blood. The ve- nous 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 carbonic acid, the blood is said to be much darker than in asphyxia from other causes. The motion of the venous blood is first impressed by the action of the general capillaries, which 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, when 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 im- pulse by tliQ 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 tw'o kinds, viz. the gene- ral , and the 'pulmonary capillary circulation. In the former, the blood furnishes the organs with the mate- rials of nutrition, and of the secretions; caloric is evolved, the blood becomes charged with carbonic 168 FIRST LINES OF PHYSIOLOGY. acid, and perhaps loses some of the oxygen it had ac- quired in respiration, and is converted from arterial into venous blood. The capillary circulation of the lungs may be con- sidered as opposed to the former. It has, for its ob- ject, 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 circulation possesses no central organ of impulsion, like the two others, hut depends on the vital contractility of the minute vessels, which exe- cute it ; and it does not present the same regularity as the cardiac circulation. In the normal state, the general 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 increased or di- minished. By increasing it in one place we 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, an- imals may be said to possess two 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 peri- pheral 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 liga- ture of large arteries ; the circulation , being then maintained by the numerous anastomoses of the peri- pheral 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 consequence of which it THE CIRCULATION. 169 contracts with great force upon the blood, which flows into it from the veins, and propels it into the mouths of the great arteries, which communicate with 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 re- ceive the blood returned from the general circulation and the lungs, by the vense cavae and the pulmonary veins, they contract upon it and force it into the ven- tricles, which dilate at the same moment to receive it; and immediately afterwards, when the distended ven- tricles are contracting to force the blood into the aor- ta and the pulmonary artery, the auricles dilate in order to receive a new supply from the veins. Hence the contraction of the auricles and the dilatation of the ventricles, take place at the same time, and vice versa. The two auricles contract, and dilate, simulta- neously, and the same is true of the two ventricles. This is probably owing to the fact that the two auricles have a common muscular septum, so that one cannot contract without the other ; a structure, which exists also in the ventricles ; while the auricles are connect- ed to the ventricles only by cellular tissue, vessels, and nerves. When the auricles contract, the blood expelled by their action is thrown back partly upon the veins, producing, in some cases, a venous pulse ; but the greater part of it enters the ventricles, which sponta- neously dilate to receive it. A pulse in the jugular veins is sometimes perceptible in persons of spare habits, and in morbid affections of the lungs, owing 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, producing 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 action of the auricles is gentle, and is some- times repeated before the contraction of the ventricles 22 170 FIRST LINES OF PHYSIOLOGY. takes place. The action of the ventricles is sudden and powerful. The dilatation of the ventricles occu- pies thrice as much time as the contraction. Accord- ing to some physiologists, during the contraction of the auricles, one of the tricuspid valves closes the ori- fice 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, to enable it more thoroughly to blend together the chyle, the lymph, and the venous blood. The systole of the auricles is succeeded by that of the ventricles, during which the tissue of the heart hardens and shortens itself, is displaced a little, and its apex curls upwards and strikes the left wall of the chest, between the sixth and seventh ribs. This phe- nomenon has been referred to the impulse, which the aorta and pulmonary artery receive from the ivave of blood projected into them, which displaces them a little, and produces a reaction upon the heart, by which the point of the organ is pushed forward 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 ap- pears, however, that these circumstances are not ne- cessary to produce this effect ; for if the heart of an animal recently killed, be placed, while yet palpitat- ing, upon a table, the apex continues to be tilted up by each contraction of the ventricles. 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 pulmonan artery, and, through these canals, distributed through- out the general system and the lungs. It is then tak- en up by the radicles of the corresponding veins, and THE CIRCULATION. 171 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 appears from the feeble jets of blood emitted bv the small arteries. In arteries of a certain degree of mi- nuteness the jets disappear; a fact which proves, that the force of the heart is much lessened in these re- mote vessels. Thfs gradual retardation of the veloci- ty of the blood is owing, partly, to the increasing resistances 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 accelerated velocity, to- wards the heart. The course of the blood in the arteries is an inter- mittent one. It is alternately more and less rapid ; more so during the systole of the heart, because then the blood moves under the influence of the most pow- erful of the moving forces; less rapid during the dias- tole, because it then moves only under the contractile reaction of the arteries. In the first moment it flows by jets, which coincide 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 between the jets, issues out by the elasticity of the arterial tunics. Attempts have been made to compute the force with which the ventricles of the heart contract. Hales estimated the force exerted by the left ventricle of a horse, in propelling 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 Le Pelletier, 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 172 FIRST LINES OF PHYSIOLOGY, 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. The whole quantity of the blood in the body of an adult, is estimated at between thirty and forty pounds, and this, it is computed, performs more than five hun- dred and fifty revolutions through the body every twenty-four hours. A complete revolution 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 in- fants, the heart contracts about one hundred and forty times in a minute, a rate which gradually diminishes until the period of adult age. In old age, the contrac- tions of the heart diminish in frequency, the pulse not exceeding sixty in a minute. Moving Powers of the Circulation. Some physiologists, as Harvey, Haller, and Spallan- zani, consider the heart as the only moving power of the circulation. Others, as Hunter, Blumenbach, Ssemmering, Senac Martini, &c. are of opinion, that, besides the propel- ling 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 Dar- win, deny that the arteries possess an active power of contracting ; but they assume a vital contractility in the capillary vessels, a kind of absorbing and propel- ling force, which moves the blood in the capillary system, which they consider as removed from the in- fluence of the heart. There is another class, among whom are Trevira- nus, Cams, and some others, who ascribe 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. THE CIRCULATION. 173 Another opinion, almost as singular, is that of Burns, who regards the arteries as the principal moving powers of the circulation, while he limits the office of the heart merely to the regular delivery 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 with os- sification of the aortal valves. He says, that it is a well known fact, that, in this disease, the heart sometimes contracts twice for each pulsation of the arteries, which he affirms could not happen, if the heart propelled the blood through the arterial sys- tem by its own unassisted powers. For, in that case, the arterial pulsations being the effect of the con- tractions of the heart, would necessarily, in every instance, exactly synchronize with the latter, and could in no case be either more or less. The phenome- non, he says, may be easily explained, by considering, that, when the aortal valves become rigid by ossifica- tion, they oppose an obstacle to the free passage of the blood from the heart to the aorta ; so that a suffi- cient 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. These opinions we 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 which 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 water, it will con- tinue to contract and dilate with great energy, throw- ing jets of the fluid to some distance for a considera- ble time. It even exerts this self-moving power, when empty, and placed in a vacuum, so that its ac- tion is independent of the contact of air and blood. 174 FIRST LINES OF PHYSIOLOGY. 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 re- sponded to very active irritation, four days after the death of the animal. The heart of a sturgeon was cut out and laid on the ground, and after it ceased to beat was blown up, in order to be dried. It was then hung up, when it began to move again, and con- tinued to pulsate regularly, though more slowly, for ten hours ; and it even continued to contract, where the auricles had become so dry, as to rustle with the motion * 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 sur- face, 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 alternation of action and repose, Mayo remarks, seems to be natural to its irri- table 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 observed in the heart taken from a living animal; but they are uniformly found con- tracted upon themselves. Nor do irritations applied 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. 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 bra- chial artery, and by the other in the open carotid of a large living dog, the heart of the animal will instant- ly 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 metallic tube, the portion of the * Mitchell, Am. Journ. Med. Scien. No. 13. THE CIRCULATION. 175 artery beyond the tube will pulsate just as if the ves- sel had remained entire. Bichat observes, that it the arteries give rise to the pulse by their own powers of contraction, there ought to be a defect or irregularity in the arterial pulsations below an aneurismal tumor ; since the arterial texture, being altered and partly de- stroyed, it must necessarily lose its living powers, and, consequently, its vital contractility. Bichat further ob- serves, that the jets of blood from an open artery, cor- respond with the dilatation of these vessels, and the subsiding of the jets, with their contraction; which is exactly the reverse of what we should expect, if the pulsations were occasioned by the action of the arte- ries 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 them- selves. The pulse, in all parts of the body, is ex- actly synchronous with the systole of the ventri- cles. According to Dr. Young, the velocity of the pulsa- tions is sixteen feet in a second, which would diffuse them simultaneously throughout every part of the system. The pulse seems to be caused, not by the dilatation of the arteries, but by a slight movement 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 bloocl. This occupies the interval between the pulsations. Even when 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 Bi- chat, is the physical property of elasticity or con- tractility of tissue. In his view of the circulation, the power of the heart projects the blood into the arte- ries, 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, which was first dilated, being relieved of the 176 FIRST LINES OF PHYSIOLOGY. distension, contracts by its elasticity upon the de- creasing column of blood. In this view the contrac- tile power of the arteries, merely serves the purpose of adapting their capacity to the volume of their con- tents, and, in short, of keeping the arteries constantly full, whatever may be the quantity of blood which they contain. And if we keep in mind the fact, that the arteries, notwithstanding the perpetually varying quantity of their blood, 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 re- moved 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 water 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 constant- ly full, by adapting their capacity to the volume of their contents. Many facts, however, are inconsistent with this doctrine, and tend to prove that the arteries are en- dued, not merely with the physical property of elasti- city, but with a vital power of contractility , 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 between the ligatures, the blood will immediately spirt out with considerable force, and the artery become much contracted. As, in this ex- periment, the force of the heart is intercepted by the lower ligature, the blood must be forced out of the THE CIRCULATION. 177 artery by its own contractile power. If the experi- ment be performed after death, the blood, instead ol spirting out to some distance, will flow out with little or no jet. Magendie compressed with 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 arteries 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 capillary 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 sup- plied them. He separated by a probe the par vagum, and the sympathetic nerve, from the carotid artery, in dogs and rabbits; and then, touching these nerves with caustic alkali, in one minute and a half he ob- served the pulsations of the artery gradually to in- crease, and in two minutes, to become still stronger. In another experiment he w T rapped the wrist of one man in ice, and enveloped that of another in cloths dipped in hot water ; in consequence of which, in the first individual, the pulse in the wrist operated on, be- came stronger than that of the opposite wrist ; and in the second, weaker. 4. The shrinking of arteries, from exposure to the air, demonstrates a power of contraction in them, differ- ent from mere elasticity, and which must be of a vital character. Dr. Parry found that the artery of a liv- ing animal, if exposed to the air, would sometimes con- tract in a few minutes to a great extent ; and in some 23 178 FIRST LINES OF PHYSIOLOGY. instances, only a single fibre of the artery was affected, narrowing 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 unimpaired ; and, according to Martini, Nassius relates the case of a man, who died in a fit of syncope, in which a very sensible pulsation of the ar- teries, continued a quarter of an hour after the motion of the heart was entirely extinct. 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 pathol- ogist 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, when 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 rare- ly, in which the pulsations of the arteries did not cor- respond with the systole of the heart. The instances referred to by Burns, are of this description. Accord- ing to Rudolphi, Zimmerman saw a woman, in whose right arm the artery generally beat only fifty-five strokes, while that of the left beat ninety or ninety- two. A venerable medical friend mentioned to the author a similar case, which he had witnessed him- self. On this subject Martini makes the following re- mark : “ Ad hoc arteriarum micatus sacpenumero fre- quentiores deprehenduntur, quin cordis motus nihi- lum quidem increverint.” The same author further states the following fact: “ Corde osseam firmitatem adepto, pergit sanguis per arterias promo veri." 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 CIRCULATION. 179 the arterialized blood is moved solely by vessels. The aorta is formed by the union of branches proceeding from the gills. 9. After the removal of the heart from a living ani- mal, the blood may still be seen to flow in the small vessels. Mayo states, that in an experiment 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 fetuses are sometimes destitute of a heart. In these the circula- tion must be carried on wholly by the action of the arteries and veins. It may not be amiss to mention, in this place, a cu- rious fact, which has sometimes been observed, in cases of amputation of the lower extremities, viz. that scarcely any blood has escaped from the incision of the soft parts ; and, upon examination, it has been dis- covered that the main artery of the limb was ossified, or converted into a rigid tube of bone. If it were cer- tain, in these cases, that the ossified artery was pervious throughout its whole extent, the fact would form a curious counterpart to that cited above, from Martini, viz. that in ossification of the heart, the blood still continues to circulate in the arteries. The true ex- planation of the phenomenon, however, we have prob- ably yet to learn. 10. To the facts and considerations above mention- ed, may be added the experiments of Hastings, which appear to establish, beyond a doubt, the irritability of the arterial canals. In these experiments the larger arteries of different animals, the aorta, femoral, and carotid, were laid bare, and subjected to different irri- tations, 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 180 FIRST LINES OF PHYSIOLOGY. irritation produced a contraction in it, or rendered its pulsations more perceptible, or occasioned an irregula- rity in the surface of the artery, which appeared to arise from a permanent contraction of the fibres of the middle coat. In some instances, a contraction was produced, which remained after the death of the ani- mal. 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 measurement to have shrunk one eighth in cir- cumference, by the application of ammonia. In other experiments, it increased the action of these vessels ; for, arteries which, when first exposed, scarcely pul- sated, were very evidently contracted, and dilated immediately after being touched by the liquor ammo- nice. The nitric acid, also, occasioned a considerable contraction of the arteries. 11. 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- vessels, perhaps, is to subject the blood to ganglionic innervation; another possibly may be, to render the ves- sels themselves excitable by the stimulus of the blood. 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 apply- ing the finger to the vessel, the pulsation is readily perceived. According to Magendie, however, the di- latation of the aorta, during the systole of the heart, is manifest to the eye ; and the same effect takes place in the divisions of the aorta of a certain magni- tude ; but the dilatation continually decreases in pro- portion as the arteries become smaller; and ceases wholly in those of a very small diameter. Mayo also asserts, that if an animal, in which the carotid artery THE CIRCULATION. 181 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 pulse- less and motionless, 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; because the impulse of the blood projected into them, tends to straighten or extend them, which produces a sensible motion in the vessels. The cur- vature of the aorta is the place, where this effect is most considerable. Mayo states, that a partial dilatation of an artery may be produced, 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, treat- ed in this manner, becomes sensibly enlarged in the part subjected to the friction, assuming an ampulla- ted appearance, which 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 mi- croscope, and the capillary vessels were distinctly ob- served 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 ani- mal. Dr. Philip also found, that the motion of the blood in the capillaries is influenced by the applica- tion of stimulants to certain parts of the nervous sys- tem, 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, when the blood reaches the capillaries. The motion 182 FIRST LINES OF PHYSIOLOGY. of the blood gradually becomes slower, and the vital fluid ceases to move by jerks. Besides, the capillary vessels are the seats of the vital operations of nutri- tion, calorification, 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 micro- scopic observations 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 di- rection, with astonishing velocity and for a long time. If a part be irritated, the blood is seen to flow to- wards it suddenly in the capillary vessels, as if these exercised an attraction for it. The portal circulation furnishes a strong argument in favor of the doctrine of the vital contractility of the capillaries. It is impossible to conceive that the pow- er of the heart, can extend through two capillary sys- tems, 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 circula- tion, that the larger arteries 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 annihi- lated 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 slowly 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 capillaries under a three- THE CIRCULATION. 183 fold 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 which the blood is sub- jected in the capillary vessels, and which 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 ap- pears 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 capil- laries themselves draws it in the other. Any irrita- tion applied to these vessels, increases the flow of blood towards them ; a principle which is illustrated in inflammation. Hence, the attractive influence of the capillary vessels, regulates the quantity of blood which traverses the other parts of the circle of the cir- culation. They may either attract more or less blood to themselves, or refuse to receive it, and thus ma- terially influence the course of the blood in the great vessels, change the pulse, and determine the quanti- ty of blood which passes into the veins, and, conse- quently, of that which 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 improba- ble, that the principal office of the heart is to propel the blood into the great arteries, which is thence drawn 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 neighboring vessels, and from them gradually to the larger arterial trunks. Hence the increased action of the arteries which 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 184 FIRST LINES OF PHYSIOLOGY. part, the capillary circulation varies in its activity, ac- cording to the degree of excitement which happens to prevail. Every morbid condition of an organ is ac- companied with a change in its capillary circulation. Further, there are some organs, whose functions are intermittent, as the uterus ; and these must attract more blood into their vessels, when in a state of ac- tivity, than when at rest. All these considerations go to establish the importance of the functions of the ca- pillary vessels, and appear to justify the opinion of Broussais, who considers the great vessels as a reser- voir, to furnish the capillary system with blood ; from which these last named vessels draw out only the quantity which they require. It is difficult to determine the relative proportions of moving power, which the heart, arteries, and ca- pillary vessels respectively contribute to the circula- tion. In genera], the further we advance from the heart, the irritability of the arteries appears to in- crease ; 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, where, of course, it is least needed ; but in the capillary vessels, where the action of the heart is but little felt, this deficiency is compensated by a high de- gree 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 dilata- ble, 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 contributing any contractile power, either physical or vital, to the circulation. It has, therefore, been' supposed that the vis a ter go, derived from the heart, arteries and capillaries, continues to operate in propelling the blood in the veins, while these vessels are regarded as mere passive tubes. This opinion, how- ever, is liable to strong objections. THE CIRCULATION. 185 The quantity of Mood contained in the veins, ap- pears to be too greav to he sustained in the ascend- ing 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 hydrostatics, 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 ter go 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 ter go were sufficient to propel the blood in the ascending veins, it is evident that these vessels would always be in a state of great distension. In the lower extremities, especially, they would have to sus- tain 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 dis- tended, 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, would be accumulat- ing in, and distending them ; and not until them sides were distended to the utmost, would the propulsive power behind be enabled to force the blood upwards. Another force, which has been considered as one of the moving powers of the venous blood, is the con- traction of muscles in contact with the veins, or through 24 186 FIRST LINES OF PHYSIOLOGY. which 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 with them, and force the blood from the parts immediately sub- jected to their pressure. The blood, then, has a ten- dency to move in all directions from the centre of pressure, hut is prevented from flowing in a retrograde direction, by the valves with which the vessels are provided ; and, of course, is necessarily directed to- wards the heart. When the muscle is relaxed, the vein is relieved from the pressure, and receives a new supply of blood from the capillaries. It is evident, however, that muscular contraction must be a second- ary, and by no means a principal 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 impetu- ous, as after violent exercise. And, besides, it appears extremely improbable that nature 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 he most necessary, to pro- mote 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 enlarge- ments of the hemorrhoidal vessels, are the natural con- sequences 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. In- deed it is said, that true irritability exists in the great venous trunks, as the vena cava inferior, especially in * Carson. THE CIRCULATION. 187 cold-bloocled animals. Every one has noticed the shrinking of the external veins ; as, of those in the back of the hand, in cold weather. They contract, perhaps, to one third of their ordinary diameter. Hastings found, that both the capillary veins and the large venous trunks, readily and sometimes vio- lently contracted, on the application of certain stimu- li. The oil of turpentine, applied to small veins, oc- casioned a great contraction of their diameters. The nitric acid produced so strong a contraction, in veins irritated by it, that the passage of the blood was al- most wholly prevented. On applying nitric acid to a trunk of one of the pulmonary veins in the thorax of 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 became white from the con- tact of the acid, but suffered no contraction of their coats. These facts demonstrate a vital power of con- traction 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 con- nections with the neighboring 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 power, which some physiologists have sup- posed to assist in giving motion to the venous blood, is the active dilatation of the heart, by which it is conceived the blood is sucked up in the veins, like water in a pump. 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 relaxation 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, throwing jets of the fluid to some distance. Another fact, which is favorable to the same opinion, is, that after death, the ventricles are 188 FIRST LINES OF PHYSIOLOGY. generally found distended with blood, from which it seems to follow, that the state of dilatation is the natural condition 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 which its elasticity would maintain it ; but, after the stimulating cause is removed by the con- traction of the ventricle, the elasticity being no longer counteracted, is left at liberty to exert itself, and re- stores the heart to its former volume. The suction power of the heart, however, is not ad- mitted by all physiologists. Dr. Arnott denies it, and asserts, that, even admitting it to exist, it could not promote the motion of the blood in the veins, because these vessels, being pliant, flexible tubes, would col- lapse 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 draw- ing the piston of the syringe, the water nearest the mouth of the syringe, Arnott observes, will be drawn in, and then the sides of the tube will collapse, acting as a valve to the mouth of the instrument, and putting a stop to the experiment. This experiment of Ar- not.t’s, however, is not a fair representation of the ac- tual 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 experi- ment, in order to be satisfactory, ought to be perform- ed in a different manner. Into a piece' of intestine, or eel-skin, filled with water, 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 propor- tion, so as to keep the vessel constantly full. Then the atmospheric pressure could not make the tube col- lapse, but would be exerted upon the column of fluid contained in it, and force it into the upper syringe. THE CIRCULATION. 189 The expansion of the thorax during inspiration, is another force, which promotes the flow of venous blood towards the heart. Inspiration establishes a kind of focus of suction in the chest, by which both air and blood are drawn into it. When the chest is dilated by inspiration, the jugular veins are observed to empty themselves and collapse ; but during expiration they rise, and become turgid with blood. Magendie intro- duced 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 was ob- served to flow from the open extremity of the tube, only at the time of expiration. During inspiration, the suction power drew 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 with colored fluid. Dur- ing inspiration, the fluid Avas draAvn from the A r essel into the vein, but, at the time of expiration, it remain- ed 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, obstruct- ing the flow of blood to the chest, and engorging the periphery of the circulation. It must be considered, liOAvever, in reference to the influence of the expansion of the chest upon the cir- culation, that there is only one act of respiration, for every five or six pulsations of the heart ; and, conse- quently, that the blood passes five or six times into the auricles of the heart, while respiration takes place but once. In the fetal 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 giving motion to the venous blood, viz. the vis a Ur go derwed from the action of the heart, the arteries, and the capillary vessels; the contractile power of the veins themselves ; the aspiratory action 190 FIRST LINES OF PHYSIOLOGY. of the heart ; the expansion of the lungs in inspira- tion ; 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. Tli.ey 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 JYervous System upon the Heart. The heart is more independent of the great nervous centres, particularly of the brain, than many other or- gans. Acephalous fetuses frequently live until birth, and sometimes a few’ days longer. Reptiles have lived six months without a head ; and mammiferous ani- mals may live some time after the loss of the head, if the vessels of the neck be tied to prevent 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 through- out its substance, derived from the ganglionic system and thenar vagum and the innervation of the cere- bro-spinal axis, particularly of the dorsal part, is sup- posed to be necessary to the motions of the heart, in their perfect developement. The influence of the nervous system upon the cir- culation is established by many facts. After a con- siderable 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 de- stroyed, 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 becomes feebler by degrees, and at length wholly ceases in the lower extremity of the same side ; but remains unim- paired, or nearly so, in the other parts of the body. The heart’s action is impaired by the division of the prin- THE CIRCULATION. 191 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 in- fluence of the nervous system upon the living blood itself, transmitted by the coats of the blood-vessels, is supposed by some physiologists to be sufficient to maintain the circulation of the blood in particular parts, without the aid of the heart. 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 Hufe- land’s journal/some experiments of Bartels, on persons who had been beheaded. Six highway robbers had lost their heads near Marbourg, and on opening the bodies of the whole six, a few minutes after their exe- cution, the heart was observed to contract and dilate alternately, with considerable force, and in a regular manner. The motions, however, gradually diminish- ed in strength, for the space of half an hour, but were instantly re-excited, by irritating a filament of the great sympathetic ; while the irritation of the spinal marrow, merely gave rise to contractions of the mus- cles of the trunk, without producing any effect what- ever upon the heart. The influence of the sympathetic upon .the action of the heart, was demonstrated, in a very conclusive manner, by experiments on dogs, performed by Bra- chet himself. In these experiments Brachet succeed- ed, after many failures, in isolating, on each side, the inferior cervical ganglions, and, upon dividing all the filaments which proceeded from them, he found that the action of the heart, after a few irregular contrac- tions, was almost immediately annihilated, and the circulation ceased. 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 with a pair of scis- sors; upon which, the circulation instantly stopped, the heart ceased to contract, and the animal became 192 FIRST LINES OF PHYSIOLOGY. rigid, and expired. From these experiments, Brachet inferred, that the heart derives its principle of motion from the ganglionic system. CHAPTER XV. Respiration. The third and last of the vital functions, is respira- tion, a function which is indispensable to animal, and even vegetable existence. By respiration, the assimi- lation of aliments, which commenced 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 administering to the various operations of life, is again reanimated by the influence of atmospheric ah, and prepared anew to dispense life and nutrition throughout the system. In the human species, and the higher classes of ani- mals, respiration is accomplished by certain organs, called the lungs ; two viscera, which 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 with that of the cavity of the thorax, with 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 al- ways penetrated with 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 hummer- THE RESPIRATION. 193 able fine cells, connected together by a delicate cel- lular membrane. Each lung is divided by deep fis- sures 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 surrounded by a thin layer of cellular tissue, which separates it from the adjoining lobules. Each lung is attached to the spine by its root, where blood- vessels, nerves, lymphatics, and a branch of the wind- pipe enter it. The lungs are covered by a transparent membrane, termed the pleura, which is reflected from the root of the lungs, over the spine and sternum, ribs, intercostal muscles, and diaphragm. Air is admitted into the lungs, by means of the tra- chea or windpipe, a tube eight or ten inches long, composed of cartilaginous arches, or imperfect rings, deficient on the posterior side ; of cellular and muscu- lar 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 oesopha- gus, and extending from the lower parts of the larynx to the level of the second or third dorsal vertebra. Here it bifurcates, or divides into two branches, term- ed 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 seve- rally 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, which constitute the principal part of the substance of the lungs. Each * It is a curious fact, that birds can live several hours with the tra- chea tied, provided one of the hollow bones, into which the air pene- trates in respiration, be sawed open so as to admit the air. Eut if a vessel containing carbonic acid, or azote, be adapted to such an opening, the bird soon dies. 25 194 FIRST LINES OF PHYSIOLOGY. ramification of the bronchia is connected with a par- ticular cluster of these cells, and if air be forced gently into it, it will inflate this, hut none of the neighbor- ing cells, unless the force employed he 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, which is a continuation of the membrane of the larynx, and extends 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 analogous to the muscular tunic of the intes- tines, but by Bedard, as identical with the yellow tis- sue of the arteries. This membrane connects togeth- er the cartilages of the trachea posteriorly, filling up the deficiency of the cartilaginous rings, and complet- ing the formation of the tracheal tube. In the smaller divisions of the bronchia, the carti- laginous arches wholly disappear, and the fine aerial canals consist merely of the fibrous and the mucous membranes. The lungs are supplied with two distinct circula- tions, one of which is destined to the nutrition of the organs, the other is connected with then' peculiar func- tions, viz. respiration, or hematosis. They receive, first, arteries which spring from the aorta, and con- vey arterial blood for the nutrition of the lungs, ram- ifying 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 ar- terial blood by respiration. These organs also possess two capillary systems ; viz. one, which is a part of the general capillary sys- tem, is the seat of the nutrition of the lungs, and of the transformation of arterial into venous blood, and in- termediate between the bronchial arteries and veins ; the other, or the 'pulmonary capillary system, is the THE RESPIRATION. 195 seat of the peculiar functions of the lungs, or of the conversion of venous into arterial blood. This is in- termediate, between the pulmonary artery and the pulmonary veins. The lungs are abundantly supplied with lymphat- ics and conglobate 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, w or chest, in which the lungs are situat- ed, is a box of bones, formed anteriorly by the ster- num, laterally by the ribs, of which there are twelve on each side ; and posteriorly by the dorsal vertebrae. The seven superior ribs are termed true ribs, the five lower ones, false. The true ribs are attached poste- riorly to the vertebrae, by moveable articulations, and anteriorly with the sternum, by cartilaginous prolon- gations. The ribs are connected together by two strata of muscles, which are termed intercostal. Be- low, the thorax is bounded by the midriff, or dia- phragm, which separates it from the .cavity of the abdomen. This muscular partition, though dividing the trunk of the body transversely, does not form a horizontal plane, but arches upwards into the thorax, forming a considerable concavity, when viewed from the abdomen. All the parts of the thorax are moveable, and are so arranged, that its cavity may be enlarged in every direction. It may be enlarged vertically, by the con- traction of the diaphragm ; for, in contracting, this muscle loses in some measure its arched form, and be- comes depressed and flattened towards 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 elevation and abduction of the ribs, the arches of which are drawn upwards and outwards, by the contraction of the intercostal mus- cles ; and, in the antero-posterior direction, its cavity may be increased, by the elevation of the sternum. 196 FIRST LINES OF PHYSIOLOGY. There are several muscles, employed in giving mo- tion to the walls of the thorax. These are, besides the diaphragm and intercostal muscles, the serrati , the scaleni , the suhclavius, the levatores cost a rum , the pec- toral muscles, the abdominal muscles, &,c. The phenomena of respiration may be divided in- to 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 phenomena 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 ac- complished by the depression 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 sev- en or eight inches in length, and this is increased by the contraction of the diaphragm, from two to four inches, according to the depth of the inspiration. It is chiefly the lateral parts of this muscle, which become depress- ed in inspiration, its centre being tendinous and inca- pable of contraction, and besides, being fixed by its at- tachment to the sternum and to the pericardium. 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 outwards as well as upwards, during their ele- vation; an effect which is owing to the obliquity of the planes which pass through their arches, in relation to THE RESPIRATION. 197 the spinal column, with which they are articulated. From the same cause, the sternal extremities of the ribs advance forwards in their ascent, carrying the sternum with them, and thus increasing the depth of the chest from before, backwards. 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 elevation of the ribs is accomplished, in ordi- nary inspiration, 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 general and simultaneous movement, caused by the action of the intercostal muscles. In difficult or excited respiration, several other muscles contribute their aid, in elevating the ribs ; as the great serrati , the superior serrati postici , the pec- toral muscles, the latissimus dorsi, the sterno-cleido- mastoid , &c. According to Magendie, there are well-marked de- grees of inspiration, viz. 1 . ordinary inspiration, which is effected by the depression of the diaphragm, and a very gentle and scarcely perceptible elevation of the thorax ; 2. full inspiration, in which there is a very evident elevation of the thorax, as well as depression of the diaphragm ; and, 3. forced inspiration, in which the dimensions 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 pul- monary tissue ; in the second, it inflates a larger por- tion of the lungs ; but it is only in the third, that the whole extent of these organs is pervaded by it. In the third degree of inspiration, several muscles are employed, which are attached by one of their extrem- ities to the arms ; in consequence of which, 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 198 FIRST LINES OF PHYSIOLOGY. ribs and expand the thorax. In making violent efforts, on the contrary, as in raising heavy burdens, in push- ing, &c. in evacuating the bladder, or the rectum, and in the efforts of parturition, the walls of the thorax are made a fixed point fdr the muscles of the arms or ab- domen, by taking a deep inspiration, 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 impracticable. The condition of the lungs in the thorax has been compared to that of a bladder, enclosed in a recepta- cle, having moveable walls, in such a manner that no air can penetrate between the two, and that the mouth of the bladder opens to the external air. In these circumstances, if the walls of the receptacle be separated farther from each, the effect will be to re- move the pressure of the atmosphere from the exter- nal surface of the bladder, while its internal surface will remain exposed to it, by means of its mouth, which opens externally. The weight of the' atmos- phere, thus acting upon the internal surface of the bladder, and not being counteracted by any external pressure, will keep this membranous sac in close ap- position with the walls of the receptacle, and oblige it to follow all the motions of the latter. The situation of the lungs enclosed in the thorax, is very similar ; and, consequently, when the chest is expanded by the action of the inspiratory muscles, all pressure is removed from the external surface of the lungs, the air contained in these organs expands by its elasticity, and keeps their external surface in close contact with the walls 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 equi- librium between the rarified air contained in these or- gans, and the external atmosphere. The first act of inspiration, after birth, may be ac- counted for in the same manner. The inspiratory muscles of the new-born infant are excited to action. THE RESPIRATION. 199 either by the irritation of the external air, or by an instinctive feeling then first developed; the chest is expanded, air rushes in through the windpipe and un- folds 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 pas- sive are the weight of the ribs and parietes of the chest ; the resilience, or elastic reaction of the sterno- costal cartilages, which had been put on the stretch, and subjected to a degree of torsion in inspiration; and the elasticity of the bronchial tubes. The active powers are the abdominal muscles, which 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 inferior ribs, so as to make them a point of support, towards which the superior may be drawn by the intercostal muscles, which may thus be rendered instruments of expiration. The sacro-lumbalis, the longissinms dorsi , the serrati postici infer lores, the quadratics lumbar-urn , 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 expiration. 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 tho- rax ; 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 which elevate the chest, permitting the ribs and ster- num to sink down by their own weight, and to re- sume their ordinary relative situation, in respect to the vertebral column. Forced expiration is the result of a powerful contraction of the abdominal and the other expiratory muscles, pushing the diaphragm up 200 FIRST LINES OF PHYSIOLOGY. into the chest, and producing the utmost possible de- pression of the ribs. The oblique and transverse muscles of the abdo- men, however, which are considered as the antago- nists of the diaphragm, and the principal agents of or- dinary expiration, are not essential to this function, and perhaps have less concern in it, than has been generally supposed. If the ribs were drawn down by the contraction of these muscles, we should expect that they would feel tense and rigid during expiration, which is not the fact. Besides, in extensive wounds of the abdomen, where the bowels are protruded, re- spiration could not be carried on, if expiration were 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 dia- phragm, are always protruded through the wound ; and, what is worthy of notice, this protrusion 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, when 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 alto- gether removed, 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 collapse, 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 exter- nal 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 power, and to assume the dimensions which their structure and their elasticity make natural to them. Hence, wounds penetrating into the thorax. * Carson. THE RESPIRATION. 201 are followed by a collapse of the lungs, and cessation of respiration on the injured side of the chest. Car- son found, by experiments on calves, sheep, and dogs, that the collapsing effort of the lungs was equal to the pressure of a column of water, 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 dur- ing life, and that they have a constant tendency to collapse, and to recede from the walls of the thorax. When the inspiratory muscles cease to act, and to maintain the chest in a state of dilatation, the collaps- ing power of the lungs may be exerted with 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 which had been admitted by the preceding act of inspiration; and, as the lungs shrink, the diaphragm and intercostals, now passive, offer no resistance to the external air which presses upon the walls of the thorax, keeping them in contact with the collapsing lungs, so as to prevent the forma- tion of a vacuum in the chest. According to Rudolphi, the larynx, trachea, and lungs themselves, take an active part in respiration. The larynx, he remarks, is in incessant motion, in the act of breathing. In inspiration, the arytenoid carti- lages are drawn apart by the muscles, who go to them from the thyroid and cricoid cartilages, and the glot- tis is thus opened. In expiration, on the contrary, the arytenoid cartilages are drawn towards each oth- er again by their own proper muscles, and the glottis is thus closed. In birds, and the amphibia, which 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 cartilages 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 which means all these parts are raised and ’dilated, so as to offer an 26 202 FIRST LINES OF PHYSIOLOGY. easy admission to the air. These fibres afterwards become relaxed, and the air passages are contracted — an effect to which the transverse muscles of the tra- chea contributes ; and the air is thus expelled. According to this view, all these parts are active in respiration, and of course the comparison of the lungs to a bladder, which is partially expanded and con- tracted by the ingress and egress of air, is wholly un- suitable. The fibres of the lungs, according to Ru- dolphi, can even act. when these organs have grown to the side, and externally are wholly immoveable. These are some of the principal facts relating to the physical or mechanical part of respiration. Chemical 'phenomena of Respiration. The chemical phenomena, relate to the changes, which 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 absolutely 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-two feet, or to a column of mercury twenty-eight inches in height. The pressure which it exerts upon the human body, is consequently enormous, amounting to between 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 atmospheric air, possessing a strong tendency to combine with many other substances in nature, and forming with them certain compounds, called acids, and oxyds ; it enters into the composi- 1’HE RESPIRATION. 203 tive of air, water, and of all vegetable and animal substances ; is the principal 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 sup- porting combustion. In most animals, it is incapable of supporting respiration, though according to Van- quelin, it is the element which 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 respiration. Carbonic acid , also, is an invisible aeriform sub- stance, of a slightly acid taste, of a greater specific gravity than azote or oxygen, capable of forming salts by combining with salifiable oxyds, irrespirable by animals, and extinguishing burning bodies. Though it occasions asphyxia in animals who inhale it, it seems to be essential 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 vapor ; exhalations from plants and animals ; and many other accidental admixtures. The presence of the essential, as well as the acci- dental ingredients of the atmosphere, may be deter- mined 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 water turbid ; and that of azote, by the formation of ammo- nia with hydrogen, in the conditions requisite to the combination of the two elements. Caloric and light become sensible, by subjecting the air to sudden com- pression in a glass condenser — water by the moisture deposited by a mass of air, when suddenly cooled, &c. Such is the composition of atmospheric air, which is so indispensable to respiration, and consequently to the support of animal life. 204 FIRST LINES OF PHYSIOLOGY. Upon analyzing a portion of air, which issues from the lungs in expiration, it is found, that the proportion of its elements has undergone a considerable change: and this change is found to consist in an increase of the carbonic acid, a diminution of the oxygen, and the addition of a large quantity of watery vapor, con- taining 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 expiration con- tains only about fourteen per cent, of oxygen ; its car- bonic acid is increased to about eight 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 carbonic acid, while the quantity of its azote un- dergoes little or no change.* Now, if it be admitted that the volume of carbonic acid, which is formed in respiration, is exactly equal to that of the oxygen, which has disappeared, it suggests a very simple theory of the changes which the air undergoes in respiration. As carbonic acid is formed by a combi- nation 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 oxygen, and the blood in the lungs, the carbon, of which this carbonic acid is composed. According to this view, the whole of the oxygen, which has disappeared, is still present in the air of respiration, but it exists in a state of chemical union with carbon, under the form of carbonic acid. It has been ascertained, however, by the researches of Lavoisier, and Seguin, of Davy, and more recently * 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 respiration. According to Le Pelletier, 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 hematosis, though it contains twice the proportion of oxygen, which exists in common air. THE RESPIRATION. 205 by those of Dr. Edwards, that a quantity of oxygen disappears in respiration, which exceeds what is ne- cessary for the formation of the carbonic acid which is generated. Edwards estimates this excess of ox- ygen consumed in respiration, above the volume of carbonic acid formed, when at its maximum, at nearly one third of the oxygen which has disappeared, and as varying from this, almost down to nothing. The variation of this excess depends on a variety of cir- cumstances, as the age, the species, or the peculiar constitution of the animal employed in the experi- ment. Now, if it be true, that more oxygen is consumed in respiration, than can be accounted for by the car- bonic acid which 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 absorbed by the lungs, while 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 physi- ologists have been disposed to believe that the whole of it is, and that the carbonic acid expired is not formed by an union of oxygen and carbon in the lungs, but is secreted and ready formed from the blood. This opinion is adopted by Dr. Edwards, and is corroborated by some of his experiments. He found that if frogs, in the month of March, were confined for eight hours in pure hydrogen gas, after their lungs were 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 were ob- tained in experiments upon kittens. A kitten three or four days old, was placed in a receiver filled with pure hydrogen gas, and in nineteen minutes, per- formed about an equal number of inspirations. Upon afterwards examining the air contained in the re- * Rudolphi, however, is of opinion, that the carbonic acid, produced by a frog contained in a globe of hydrogen gas, is not exhaled from the lungs, but from the skin. 206 FIRST LINES OF PHYSIOLOGY. ceiver, it was found to contain twelve times as much carbonic acid as could be accounted for by the air contained in the lungs of the animal at the beginning of the experiment. Edwards’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 as- serted by Cuvier and Davy. Edwards found, also, that when small birds were immersed in a large quantity of air for a limited time, there was, in many instances, an evident increase in the quantity of nitro- gen, while, in others, there was a loss of this princi- ple. He observed, that these different results had some connection with the season of the year, when the experiments were performed. In winter, a defi- ciency of azote was observed in the air respired, but in spring and summer, the quantity of this principle was found to be increased. Edwards inferred from his experiments, that both absorption and exhalation of azote are constantly 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 re- mains unaltered. The quantity of air received into tlue lungs in inspiration is exceedingly variable, and has been very differently estimated by different physiologists. Gregory estimated it at only two cubic inches. Ac- cording to Rudolphi, the naturalist. Abildgaard states of himself, that with a small chest he inspired, in ordinary respiration, three cubic inches of atmospheric air ; but about every sixth or seventh inspiration, his breathing was deeper, and he inspired from six to seven, and sometimes even fifteen cubic inches. Hert- hold, with a more capacious chest, inhaled, in every act of respiration, from twenty to twenty-nine cubic inches; while Keutch, inspired only from six to twelve. Goodwyn estimates the volume of air in- spired at about 14 cubic inches; Davy, at from 13 to THE RESPIRATION. 207 17 — (Cuvier at 16; Allen, and Pepys at 16|; Menzies at 43.77. It is estimated, by late observers, that the greatest quantity of air, which 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 ultimate ramification 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 with 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 contained in the lungs after an ordinary or a forced inspiration , and after an ordinary or a forced expiration , has been differently estimated. 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 twenty cubic inches ; after a common expiration, one hundred and six cubic inches ; and after a forced expiration, only eighty-five. Menzies says, that many men are able, after ordi- nary expiration, to expel seventy cubic inches more from their lungs. He thinks from this, that the lungs can hold two hundred and nineteen cubic inches, and, after a common expiration, still contain one hundred and seventy-nine cubic inches. Allen and Pepys estimate the quantity of air, con- tained 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. Rudol- phi 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 lowered. But between the ordinary acts of respiration he observes, there occur, from time to time, fuller inspirations and expirations; and in healthy laboring men, with capacious chests, he thinks Menzies’ estimate not too high. 208 FIRST LINES OF PHYSIOLOGY. In four subjects, who died natural deaths, and of course after expiration , Goodvvyn found that the lungs contained severally one hundred and twenty ; one hundred and two ; ninety ; one hundred and twenty- five cubic inches of air. The average of these is one hundred and nine. In the lungs of hanged persons, who inspire deeply before death, he found, in one case, two hundred and seventy-two; in another two hundred and fiftv; and in a third, two hundred and sixtv-two cubic inches of air. It is said that we 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 two quantities, or two hundred and ninety cubic inches. Now, if it be assumed, that we inhale forty cubic inches in inspiration, the whole volume of air, which the lungs contain in a distended state, is three hun- dred and thirty cubic inches, and consequently only one eighth of the contents of the lungs, is changed by every act of respiration. But, if we 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 twentieth part of their contents is changed in every act of respiration. Such is the uncertainty, however, that reigns in this sub- ject, that some physiologists are of opinion, that the air in the lungs is completely renewed 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 we inspire forty cubic inches, one half cubic inch disappears; a loss which, perhaps, is occasioned by the absorption of a quantity of oxygen, above what is necessary for the production of the carbonic acid which is formed in respiration. If an adult inhales forty cubic inches of air in THE RESPIRATION. 209 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 oxy- gen gas disappear in every act of respiration. If, then, we respire twenty times a minute, we must consume thirty-two cubic inches of oxygen gas in the same time. It is probable, however, that forty cubic inches is much too high an estimate of the volume of the air inspired in ordinary respiration. If we assume it at fifteen cubic inches, which is not far from the average of several estimates made by different ob- servers, it will follow 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 twenty times a minute, we shall consume thirty cubic inches in the same .space of time. Davy estimates the quantity of oxygen, consumed in a minute by respiration, at 31.6 cubic inches. This would amount to nearly two thousand cubic inches in an hour, and forty-five thousand cubic inches in twenty-four hours. Accord- ing to Lavoisier and Seguin, a man consumes in an hour, one cubic foot of oxygen, or in twenty-four hours, two pounds, one ounce, and one grain. The quantity of carbonic acid discharged in every act of respiration, is very variable. By Goodwyn 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 Luscac at three or four ; by Contan- ceau at six or eight. The quantity of carbonic acid, which is formed by respiration in twenty- four hours, is estimated at seventeen thousand, eight hundred and eleven grains, which would contain about five thousand grains, or nearly eleven ounces of carbon. This, in a year, would amount to about two hundred and fifty pounds solid carbon excreted from the body by the lungs. This estimate, however, there is reason to think, is 210 FIRST LINES OF PHYSIOLOGY. much too high. Prout supposes that the conversion of albuminous matter into gelatin is one of the prin- cipal sources of the carbonic acid, which is expelled from the lungs in respiration, and which he supposes to exist in the venous blood. Gelatin contains three or four per cent, less of carbon than albumen, and it en- ters 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 oxygen is consumed, and more carbonic acid formed. More carbonic acid is formed during digestion and during exercise ; ani- mal food and wine, 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 at- mospheric air. More carbonic acid is formed during the day, than in the night. The maximum quantity is formed between eleven o'clock, A. M. and one o’clock, P. M. ; the minimum, about eight o’clock in the evening; from which time until half past three in the morning, there is no change. The air expired from the lungs, is loaded with a large quantity of watery vapor, derived partly from the lungs, and partly from the mouth, fauces, and trachea. The quantity of it was estimated by Hales, at about twenty ounces in twenty-four hours ; more recently by Menzies, at six ; by Abernethy at nine ; and by Thompson at nineteen ounces. The breath frequently becomes impregnated with the odor of substances which have been swallowed. THE RESPIRATION. 211 If odoriferous substances are injected into the veins, or a serous cavity, the breath acquires this odor. 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 with dense white fumes of phosphoric acid. 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 stom- ach 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 what the stomach had begun. The nutritive fluid, formed by the stomach and its append- ages and carried into the blood-vessels, is still imper- fect, until it has passed through the lungs and received the influence of respiration. In the lungs it is sup- posed' 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 color ; and it then becomes settled for all the purposes of life, and not before. The organization of the blood is proba- bly completed in the lungs, perhaps by the addition of the red coloring matter, or hematosine. Respira- tion 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 supplies the materials out of which all this machinery itself is manufactured. This is one essen- tial purpose of respiration. Another, equally important, and indeed closely con- nected with the first, is to produce certain changes upon the blood already formed, after it has circulated through the system, and been employed in the various functions of life. While the florid arterial blood is administering to the various operations of life, it is gradually changing its color, and becoming darker, 212 FIRST LINES OF PHYSIOLOGY. and at last, what remains of it, assumes the purple color of venous blood. In this condition it is no longer fit for the purposes of the animal economy. It is robbed of the principles most essential to life, and it must be renewed and prepared afresh, before it is fit to be employed again. For this purpose it is re- turned 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 which is probably designed 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 vapor and perhaps absorbs oxygen, and is changed back to its former scarlet color, and is then again fitted for the uses of the animal economy. Respiration, therefore, in relation to its influence upon the blood, it appears, is a complex function. It completes the formation of the new blood; it renovates the old, preparing it again for the purposes of life ; and it reconverts into blood the molecules detached from all the organs by vital decomposition, and which have consequently existed at least once before, under the form of blood. It incorporates the worn-out venous blood, both with matter imperfectly animalized. and with matter animalized to excess, and combines the heterogeneous mass into one homogeneous fluid highly impregnated with vitality, arterial blood. Theory of Respiration . There is still much difference of opinion among physiologists in regard to the mode, in which the changes produced in the blood, are effected by re- spiration. An opinion, which prevailed for some time, as- sumed that the oxygen of the air inspired, combines THE RESPIRATION. 213 in the lungs with 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 carbonic acid contains its own volume of oxygen gas, it was inferred that the oxygen which disappears, is converted into carbonic acid, by combining with 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 distinguished 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 subse- quent act of respiration. As the quantity of oxygen gas which disappears, is rather greater than sufficient for the production of the carbonic acid which 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 whole of it is, and consequently, that the carbonic acid is not formed in the lungs at the expense of this oxygen, but is ex- haled, ready formed, from the venous blood. A con- sideration which affords some confirmation to this opinion is, that the inhalation of oxygen is not necessary 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 Contanceau, 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 Rudolplii supposes, that this carbonic acid was formed from the atmospheric air, present in the ' lungs at the time of the experiments. Edwards’s experiments, also, seem to have ascer- tained the fact, that the blood circulating in the lungs, is capable of absorbing oxygen as well as hydrogen and azote ; and Nysten found that oxygen 214 FIRST LINES OF PHYSIOLOGY. gas might he 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 Girtanner seems to establish the presence of oxygen in arterial blood. He put some arterial blood of sheep under a receiver filled with pure azote ; and at the expiration of thirty hours, the air in the receiver- contained oxy- gen enough to support the combustion of a candle about two hours.* That carbonic acid exists in venous blood, seems to be rendered probable from the fact, that carbonic acid may be injected in considerable quantity into the veins without injury. An experiment of Darwin 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 re- ceiver, swelled to ten times its original bulk. Another very plausible theory of respiration as- sumes, that the oxygen is absorbed by the radicles of the pulmonary veins ; and that the carbonic acid and watery vapor are exhaled from the pulmonary mucous membrane. But the exhalation of aqueous vapor and of carbonic acid, is not regarded as pe- culiar 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 vapor and carbonic acid, combined with some animal matter. The exhalation of car- bonic acid in respiration is not necessarily connected with the absorption of oxygen. Like other secre- tions, 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 arteries, distributed over the mucous membrane of the bronchia. While the essential and characteristic part of respiration, is supposed to consist * Le Pelletier. THE RESPIRATION. 215 in the absorption of oxygen by the radicles of the pulmonary veins. In this view, 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 oxy- gen into immediate contact with the venous blood. The carbonic acid, arid the aqueous animal vapor, which exist in the air expired, are the product of a secretion from the mucous membrane of the brochia, 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 arteri- alization 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 view, are the seats of two opposite functions, absorption and ex- halation. By the first, an aerial principle, necessary to life, is incessantly introduced into the animal economy, and constitutes the great and essential purpose of respiration. The pulmonary capillary system is the seat of this absorption. The second, which has its seat in the general capillary system, and which consists in the exhalation of carbonic acid, and a watery vapor, 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 Chaussier, who supposes that the oxygen is absorbed by the lymphatics of the lungs, vessels with which these organs are very abundantly supplied; that it is conveyed by the lymphatics into the tho- racic duct, and there blended with the chyle and lymph; and afterwards, 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 color of the blood in the lungs, his theory supposes to be 216 FIRST LINES OF PHYSIOLOGY. occasioned merely by the separation of carbonic acid already existing in the venous blood. This theory, it will be perceived, transfers the process of liematosis 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, be- sides a part of the circulating, which is inconsistent with the suddennes of the change, which takes place in the blood in respiration. The venous blood ac- quires instantly the arterial color in the lungs — as was demonstrated by an experiment of Bichat. It also assumes, that the coloration of the blood in the lungs, is occasioned by the exhalation of carbonic acid. Now, according to Contanceau, during the respiration of any other gas than oxygen, especially of azote, the exhalation of carbonic acid and watery vapor continues, yet the venous blood retains its dark color. Influence of Innervation upon Respiration. The external organs of respiration, the nose, the mouth, the muscles about the chest, the diaphragm, and the abdominal muscles, are supplied with nervous influence by the fifth pair of nerves ; the facial, the accessory, the spiral nerves, and the phrenic ; while the proper organs of respiration, the larv#t, 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 fila- ments of the pneumogastric nerve, and the anterior branches of the first thoracic ganglions. The pneumogastric nerves, as might be inferred from their supplying all the internal organs of respira- tion with branches, exert an important influence upon respiration, though it still remains a subject of con- troversy with physiologists, what the precise nature of this influence is. The section of these nerves, on both sides, about the middle of the neck, soon occasions extreme dyspnea, followed, in a few hours, by death ; and, on dissection, the lungs are found in a THE RESPIRATION. 217 state of great engorgement with blood, and the bron- chial tubes filled with a white frothy fluid. Death, in these cases, is owing to a paralysis of the muscles which open the glottis, while those which close this aperture remain 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 laryngeal. 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, or that of the pneumo- gastric, between the superior and inferior laryngeal nerves, 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 dyspnea is relieved, and life may be prolonged for three or four days. Yet the animal inevitably dies from increasing dyspnea, sometimes accompanied with vomiting. The blood in the arteries assumes a darker color, and, according to Mr. Brodie, less carbonic acid is evolved in respira- tion. 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 which asphyxia is produced by the section of the par vagum. It may be owing 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 arteri- alization 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 28 218 FIRST LINES OF PHYSIOLOGY. contact with the blood, is unable to combine with this fluid, since this combination requires the vital action of the pneumogastric nerves. He endeavored to establish this opinion by experiment. He found that, if an artery in an animal in which the par vagum was divided, were opened, the blood which at first spirted out, of the bright arterial color, gradually became darker, and assumed the appearance of ve- nous blood. The compression of the nerves produced the same effect. Le Gallois found, that an opening into the trachea, after the section of the pneumo- gastric nerves, did not prevent the arterial blood from becoming venous, though it permitted the free ingress of air into the lungs. Dumas, however, found that, if air were forced into the lungs, after the section of the par vagum, arterial blood continued to be formed ; from which he infer- red that, in this experiment, asphyxia is occasioned by some obstruction to the entrance of air into the lungs ; so that without some external force, this fluid is unable to penetrate into the bronchial cells. The fact, that after decapitation, life may be maintained for some time by artificial respiration, appears to be irreconcileable with Dupuytren’s opinion. The most provable opinion 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 accumula- tion 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 pneumogastric nerves convey, from the lungs to the brain, a knowledge or sentiment of the want 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. THE RESPIRATION. 219 Bracket, 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 warm 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 few slight motions, which were wholly unlike the struggles for breath of a suffocating animal. The muzzle of another puppy of the same litter, was in like manner plunged in water, without the previous division of the per vagum. Unlike the first, he made violent efforts to withdraw his nose from the water, and to respire, and the asphyxia came on with diffi- culty, and was accompanied with convulsive strug- gles. In two other comparative experiments, two puppies of the same litter were placed under two receivers, filled with atmospheric air, one of them having pre- viously undergone the section of the pneumogastric nerves, and had an opening made in the trachea ; the other without any preparation. In the latter, respira- tion soon became larger and more frequent, the ani- mal raised his head, and breathed with his mouth open and his nostrils expanded, and died with the symptoms which 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 atmospheric air, in its passage to the brain ; since one animal who has been subjected to this experiment, dies of asphyxia, without manifesting any feeling of the want of re- spiration. The continuation of the movements of respiration, after the appetite has been annihilated, Brachet attributes to the habit, which the respiratory 220 FIRST LINES OF PHYSIOLOGY. muscles, have acquired of contracting, and which survives the sentiment of the want of respiration. The convulsive struggles which 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 apprizes 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 two pneumogastric nerves in a dog, and then made an opening into the trachea, through which he introduced a little ball of orris (boule d iris) fas- tened to a thread. The breathing became laborious, but the animal exhibited no sign, that he experienced any disagreeable 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 without eliciting from the dog any signs of sensation. In another experiment, he made an opening in the trachea of a dog, without dividing the par vagum. A few 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 withdraw it. On applying it again, the cough was renewed — upon which Brachet divided the par vagum, when the cough suddenly ceased, respiration became rattling, and in less than an hour, the dog died without having expectorated any thing. That these nerves react upon the fibres of the bron- chia, causing them to contract, Brachet endeavors to prove by experiment. He injected warm water into the trachea of a dog, which excited violent coughing, by which the water was expectorated. The irrita- tion, however, provoked an abundant secretion, which kept up the cough and expectoration for several hours. Upon repeating the experiment, the next day, on the same dog, the same phenomena occurred ; but after THE NUTRITIVE FUNCTIONS. 22 1 the dog had apparently rejected 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. Le Pelletier also remarks, that the section of the par vagum, or a suspension or diminution of its power, causes a debility or inaction of the air vesicles, and a stagnation in them of the air, altered by hematosis ; and it explains the occurrence of asphyxia in certain cases, where the great phenomena of inspiration and expiration continue to be carried on. For the air may continue to be renewed in the principal divisions of the bronchia, by the mechanical movements of re- spiration ; but its renovation in their ultimate branch- es, is impossible, without the vital contraction of the air vesicles 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 character- istics, by which animals are distinguished from plants. Vegetables, it is true, are nourished and grow ; but they do not, properly speaking, digest. Their nutri- tion and growth are the result of an external absorp- tion from the atmosphere and the soil, effected at 222 FIRST LINES OF PHYSIOLOGY. 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 ab- sorbed in a crude state by plants ; but in a digested state, by animals. In vegetables, and the lowest orders of the animal kingdom, the absorbing vessels themselves, exercise an assimilating power over the matters absorbed as nourishment, and this prepara- tion is the only digestion which the food of these kinds of organized matter, undergoes ; but in all the animal kingdom, with the exception of the very low- est orders in the zoological scale, digestion is central- ized 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 consists of a membranous sac, provided with a single opening, which serves both for mouth and anus. In its first stage of complication, it as- sumes the form of a straight canal, the length of which is less than that of the animal to which it be- longs, and is provided with two orifices, one destined for the reception of the food, the other to the expul- sion 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, by nearly thirty tunes, the length of the body, and presenting numerous convo- lutions. Its two orifices are guarded by circular muscles, which act under the control of the will; and several auxiliary organs are connected with it, which contribute to give greater variety and compli- cation to its functions. In the mammalia , the digestive canal presents its greatest or last degree of complication. In the hu- man 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 THE NUTRITIVE FUNCTIONS. 223 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 will. The digestive canal is found partly in the head, where it forms the cavity of the mouth ; partly in the neck and thorax, where it takes the names of the 'pharynx and the oesophagus ; but principally in the abdomen, where it forms the stomach and intestines, which, with the associated viscera, the liver, the pan- creas, the spleen, and the mesentery, occupy nearly the whole of this great cavity. The mouth is formed by the two lips. Its cavity is bounded above by the palate, below by the tongue, before by the teeth, laterally by the cheeks, and pos- teriorly by the curtain of the palate, which separates the cavity of the mouth from the pharynx. The pha- rynx is a tunnel-shaped cavity, which terminates in the oesophagus. It opens into the mouth by the isth- mus 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 fun- nel-shaped canal, called the Eustachian tube. The oesophagus , or gullet, is a continuation of the pharynx. It is a long, straight, fleshy tube, which passes down the chest, behind the trachea, lying upon the verte- bral column ; and it opens into the stomach by an orifice, which is called the cardia. The pharynx and oesophagus, or the pharyngo-cesophageal cavity, is the organ of deglutition. The stomach is a large pouch, situated below 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 gangli- onic nerves ; before, by the false ribs of the left side, with their cartilages ; on the left, by the spleen. The stomach has two orifices, a superior and an 224 FIRST LINES OF PHYSIOLOGY. inferior. By the former, which is also called the cardiac , it communicates with the oesophagus ; by the latter, also termed the jjyloric, 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 shorter than the inferior, which 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 downward. But, when distended, its greater curvature is raised forward. The stomach is the or- gan of chymification, or gastric digestion. The intestines extend from the pylorus to the anus, forming a mass of convolutions, which fill most of the abdominal cavity. They are usually divided into two 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 ilium. The first receives its name from its length, which is equal to twelve fingers’ breadths. It is the seat of chylijication, or duodenal digestion. The jeju- num, or hungry gut, is so called from its being gen- erally found empty; and the ilium , i. e. the twisted gut, derives its name from the numerous convolutions which 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 vertebra' by a duplicature of the peritoneum, called the mesentery. The large intes- tines commence where the small terminate. A cir- cular fold of the mucous membrane of the ileum, penetrating, by its free border, into the large intes- tine, and called the ileo-csecal valve, separates the two great divisions of the intestinal canal from each other. The large intestines are divided into three THE NUTRITIVE FUNCTIONS, 225 portions, viz. the caecum , 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 muscu- lar, and a serous. Only the two first, however, are essential to it ; the mucous, or internal tunic, consti- tuting 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 external, or serous tunic, is merely accessary, as it is wanting in many parts of the di- gestive tube, and no where completely envelopes it. The soft parts of the mouth are composed almost wholly of muscles, lined internally by a mucous mem- brane. 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 afterwards forced from the mouth into the pharynx. The membrane which lines the mouth, secretes a mucus, which lubricates this cavity, and is blended with the food in mastication. The muscular part of the pharynx is composed of six constrictor muscles, which contract this cavity and compress its contents, forcing them into the cesophagus in the act of deglutition. The fibres of these muscles form planes or sheets, which cross each other in various directions. The pharynx is lined internally by a mucous .membrane, of a deep red color. The oesophagus, in like manner, is composed of a muscular coat and a mucous membrane. The former consists of two strata of muscles, viz. one external, which is composed of longitudinal fibres, of consid- erable thickness and strength ; and one internal, con- sisting 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 cesophagus. The mucous mem- brane is continuous with that which lines the pharynx. 29 226 FIRST LINES OF PHYSIOLOGY. 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 contrac- tion commences at the upper part of the inferior third, and proceeds, with 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 simultane- ously in the contracted fibres. This motion of the oesophagus is under the influence of the par vagum. If these nerves are divided in an animal, the oesopha- gus ceases to contract in the manner just described, and assumes a state intermediate between contrac- tion and relaxation.* The oesophagus is furnished with mucous follicles, which are sparingly distributed over it. The stomach, also, is composed of two principal coats, or membranous lamina?. The internal is a soft, spongy, mucous membrane, which is extremely vas- cular, or plentifully supplied with blood-vessels. Ex- cept when the stomach is distended, the mucous membrane is drawn 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 folli- cles, seated in its mucous coat. The second coat of the stomach is muscular, and is composed of fibres, disposed in three different direc- tions, viz. longitudinally, circularly, and obliquely. The longitudinal fibres form the exterior muscular plane. Immediately beneath this are the circular fibres, which run parallel to one another ; and subja- cent to the latter are the oblique, which form broad fasciculi at the two extremities of the stomach. Be- sides these two principal coats, the stomach receives an external tunic, formed by a duplicature of the THE NUTRITIVE FUNCTIONS. 227 peritoneum. This coat is united to the muscular, by cellular tissue. 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, which is supposed to be the principal agent in chymi- fication. The arteries of the stomach are very large and numerous, and they all spring, directly or indi- rectly, from a large trunk, called the cceliac artery. The nerves of the stomach originate from both nerv- ous 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 muscu- lar ; the former constituting a secreting and absorbing surface ; the latter, or muscular, executing the various motions, which are necessary in propelling the con- tents of the intestines regularly through the canal. There is a third tunic, which is external, and which is derived from the peritoneum. This is termed the serous, or peritoneal coat. The mucous coat is sometimes termed villous , from the villosities which its internal surface exhibits, re- sembling the pile of velvet. These villi are extremely numerous, presenting the appearance 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 folli- cles, which are destined to secrete the mucus, which smears the inner surface of the intestines. The mucous coat of the small intestines is gathered into folds or plica, presenting, when dried, a lunated appearance, and denominated the valvulce 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 absorption by the lacteals. 228 FIRST LINES OF PHYSIOLOGY. The muscular coat consists of two orders of fibres, one longitudinal, 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, which have the effect of puckering up the intestines, forming numer- ous prominent cells, in which feculent matter is some- times retained a long time. The arteries of the intestines are derived from the mesenteric arteries ; their nerves almost wholly from the solar plexus. Into the first of the small intestines, the duodenum, open the excretory ducts of two im- portant glands, the liver and the pancreas. The necessity of taking food arises from the losses, which the body is constantly undergoing by the differ- ent secretions and excretions, and which amount to several pounds in the space of twenty-four hours. These losses immediately affect the blood, which be- comes impoverished by the demands upon its princi- ples, 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, without 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, which are termed hunger and thirst. Nei- ther the seat nor the efficient causes of these sensa- tions are well known. Hunger has been frequently referred to a peculiar affection of the nerves of the stomach ; an opinion which in itself seems sufficiently probable, as sensation is a phenomenon of the nervous system, and as the sensation of hunger is referred di- rectly to the stomach. The experiments of Brachet, in which the section of the pneumogastric nerves ap- peared to annihilate the appetite for food, tend to corroborate this opinion. It is observed, however, by Mayo, that nausea is referred to the stomach upon the saifie grounds with the sensation of hunger ; and yet, THE NUTRITIVE FUNCTIONS. 229 according to the experiments of Magendie, nausea and retching may be produced after the removal of the stomach of an animal, by injecting tartar emetic into the veins. Thirst has been referred to a certain impression upon the nerves of the fauces and pharynx. But in the case of a man, who had cut through the oesopha- gus, several buckets full of water were swallowed daily, and discharged through the wound, without quenching the thirst, — which was afterwards allayed by injecting spirit, diluted with water, into the stom- ach. From these facts Mayo observes, that it is not impossible, that a person might be hungry without a stomach, and thirsty without 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, which is broken and ground down 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 in the elevation and depression of the lower jaw, and two horizontal, in one of which the lower jaw is moved backwards and forwards, and in the other laterally, or from side to side. These motions are executed by the action of several mus- cles, viz. the temporal, the masseter, the external and internal pterygoid, the zygomatic, the digastric, and some others. The temporal, masseter and in- ternal pterygoid muscles, elevate the lower jaw, the temporal moving it somewhat backwards as well as upwards; the masseter, forwards and upwards, and the pterygoid, from side to side. In carniverous ani- mals, these muscles, particularly the temporal, pos- sess prodigious power. The lower jaw is moved 230 FIRST LINES OF PHYSIOLOGY. horizontally forward, hy the combined action of the two external pterygoid muscles, aided by the masse- ter and the internal pterygoid. The pterygoid mus- cles, when they act singly, move the jaw obliquely, from side to side, and communicate a grinding motion to the teeth. The lower 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 divided and ground down by the teeth, it is in- timately 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 secretion 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 oesophagus, 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 secreted is probably much greater. The minute division of the food by mastication, and its penetration by the saliva, appear to be designed, chiefly, to promote its solution in the stomach, and to facilitate deglutition. Hence, a leisurely and suffi- ciently prolonged mastication, in general, renders di- gestion 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 drawn upwards to re- ceive the morsel by the action of the muscles, which raise the os hyoides , and by the stylo-pharyngeus. The pharynx is embraced by the fibres of three mus- THE NUTRITIVE FUNCTIONS. 231 cles, which are termed its upper, middle, and lower constrictors ; the contraction of which, tends to dimin- ish 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. According to Magendie, however, the epi- glottis is not necessary to deglutition ; for, in some of his experiments, it was removed from animals, and it has sometimes been destroyed by disease in the hu- man 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 arytamoideus transversus , and the ary tamo idei obliqui. As long as these muscles preserve their power of contraction, 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 enfee- bled, 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. As soon as the food has reached the oesophagus, the muscular contraction of this fleshy tube is excited, by means of which the bolus is gradually forced into the stomach. The power of gravitation contributes but little to the descent of food into the stomach ; for it is found that funambulists can swallow without diffi- culty, with their heads downward. The motion of the cesophagus in deglutition, consists in a successive contraction of its circular fibres, from above down- wards. The upper part of the tube is dilated by the bolus, which is forced into it by the contraction of 232 FIRST LINES OF PHYSIOLOGY. the pharynx. Its superior circular fibres are then excited to contract, and the food is pushed further down into the tube, dilating the parts immediately beneath, which react upon it, and force it still further down, until it reaches the stomach. The longitudinal fibres, in contracting, shorten and relax the oesopha- gus, and in this mode promote the descent of its con- tents. Mayo supposes that the longitudinal fibres of the two extremities of the alimentary canal, viz. the oesophagus and the rectum, are designed to strengthen these parts, and to prevent their elongation and rup- ture by the volume of their solid contents. Deglutition is divided by Magendie, into three sta- ges, viz. — 1. the passage of the food from the mouth into the pharynx ; 2. from the pharynx into the oeso- phagus ; 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 invol- untary ; yet Mayo remarks, that it may at any time be performed by a deliberate exertion of the will. The third stage, or oesophageal deglutition, is removed from the jurisdiction of the will. Yet, as Mayo re- marks, the oesophagus appears to partake of the nature both of the voluntary and involuntary muscles ; for when the nervi vagi are pinched, a sudden action en- sues in its fibres, which is presently after succeeded by a second action of a slower kind. III. Chymosis. Gastric digestion, or chymosis, con- sists in the conversion of food in the stomach, into a soft, pulpy mass, termed chyme. The aliment, previ- ously masticated and thoroughly blended with the saliva, descends through the pharynx and oesophagus into the stomach, in the manner just described. Some physiologists suppose, that the stomach is not mechan- ically distended by the mass of the aliments, but that it exercises the power of self-dilatation in the recep- tion of the food. However this may be, the organ enlarges in proportion to the volume of the food which is swallowed. Its coats are distended, the plica of its mucous membrane are unfolded, and the sinuosities of THE NUTRITIVE FUNCTIONS. 233 its arteries and veins disappear. The increased vol- ume of the stomach pushes the diaphragm up into the thorax, distends the walls of the abdomen anteriorly, and presses against the contiguous viscera, particu- larly the liver and spleen. The position of the stom- ach 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 downward, 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. Its muscular coat exerts a kind of vermicular motion, by the alternate contractions of its transverse and longitudinal fibres, the former diminishing its diameter, the latter short- ening its length, by approximating its splenic and pyloric extremities.' Tiedemami and Gmelin remark, that the muscular coat of the stomach does not con- tract simultaneously throughout its whole extent, but one part contracts a little, while another dilates, and vice versa ; the place where contractions take place becoming thicker and rugous. According to the same physiologists, these undulatory movements pro- ceed from the oesophagus towards the pylorus, and from this back again to the oesophagus. 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. The most vigorous contractions were occasioned by the most stimulating food. These successive contractions of the muscular fibres occasion a slow movement of the aliments in the stomach, by which they are brought successively into contact with all parts of its surface, and thoroughly penetrated with the gastric fluid. According to Beaumont, the contractions of the muscular coat of the stomach produce a constant, 30 234 FIRST LINES OF PHYSIOLOGY. slow 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, along the small arch, thence along the large curva- ture, from left to right. “ The bolus, as it enters the cardia, turns to the left, passes the aperture, descends into the splenic extremity, and follows the great curvature towards the pyloric end. It then returns in the course of the smaller curvature, makes its appearance again at the aperture, in its descent into the great curvature, to perform similar revolutions.” * From one to three minutes are occupied in com- pleting one of these revolutions. During these mo- tions, 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, bv the action of a transverse band, situated three or four inches 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. Secretions of the Stomach. Not only the muscular action of the stomach is ex- cited by the stimulus of food, but its circulation and its secretions are increased. There is a concentration of vital activity in the organ, an increased afflux of blood towards 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 process of digestion commences. * Beaumont. THE NUTRITIVE FUNCTIONS. 235 In the process of chymification, the food undergoes a remarkable 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 disap- pear, and new ones are acquired. It is evident, there- fore, that the chemical affinities of the food have been totally subverted, and its elements have entered into new combinations. Whether this change is confined to the proximate principles of the food, or extends 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 when the stomach is empty. It has already been observed, that the stomach is largely supplied with blood-vessels. It receives much more blood than is necessary for its own nutrition ; and the destination of this excess 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 may be increased, diminished, or changed in its qualities, by various causes. Thus the division of the pneumogastric nerves, the use of nar- cotics, the excessive use of stimulating drinks, violent emotions of the mind, &c. diminish the secretion of this fluid ; and, on the other hand, condiments and high seasoned food increases it. The gastric fluid, according to Beaumont’s observa- tions, is a clear transparent fluid, perceptibly acid to the taste, and a little saltish, but destitute of odor. It effervesces slightly with the hlkalies ; possesses, in a high degree, the property of coagulating albumen ; is powerfully antiseptic, resisting the putrefaction of ani- mal matter ; and is an effectual solvent of alimentary substances. Its acid properties are owing to the pres- ence of free muriatic and acetic acids. According to Tiedemann and Gmelin, the gastric fluid contains the hydrochloric and acetic acids, and in horses, the bu- tyric ; saliva, osmazome, chloruret, and sulphate of 236 FIRST LINES OF PHYSIOLOGY. 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 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 a very acid gastric liquor. It appears, then, that the degree of acidity of* this fluid, depends on the degree of excitation of the stomach, produced by the food. The gastric liquor appears to be secre- ted only when the stomach is excited by the stimulus of aliment ; and, consequently, no conclusion respect- ing its properties, can be drawn from experiments on the fluid, taken from the stomach during fasting, as this consists chiefly of gastric mucus, mixed with saliva ; a consideration, which may account for many contradictory results in the researches of physiolo- gists on the gastric fluid. Now, this fluid appears to be the principal agent in gastric digestion, or chymi- fication. Its powers in dissolving alimentary sub- stances, were first satisfactorily ascertained, by some experiments performed by Spalanzani and Stephens, in the last century. Stephens, in his experiments, inclosed various alimentary substances in hollow me- tallic 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' were performed on men and other animals. Spalanzani obtaine.d similar results; and pursuing the idea, he exposed certain aliments, properly masticated and impregnated with 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 estab- lish, conclusively, the power of the gastric liquor in THE NUTRITIVE FUNCTIONS. 237 dissolving alimentary substances out of the stomach. The process is rather slower, perhaps, because the exact temperature of the stomach cannot be accu- rately maintained by artificial means, and because it is impossible to subject the food to the same mechan- ical agitation, by exactly imitating the motions of the stomach. The results, however, are in both cases apparently the same; the chyme, prepared by arti- ficial digestion, presenting the same sensible proper- ties, as that which is found in the stomach. The solvent powers of the gastric fluid, in respect to ali- mentary 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. A certain degree of heat is necessary to its action, and it ope- rates with more energy, the more minutely the food is divided. The solvent powers of this secretion, in relation to alimentary substances, may be understood, in part, by a reference to its composition. Thus, the water which it contains dissolves several simple alimentary principles, as liquid albumen, gelatin, osmazome, sugar, gum, and starch. The hydrochloric and acetic acids, dissolve several other principles, which are not soluble in water; as concrete albumen, fibrin, coagu- lated caseum, gluten, and gliadine, a substance analo- gous to gluten. These acids dissolve, also, cellular tissue, membranes, tendons, cartilages and bones. Their solvent power is assisted by heat ; and hence, the temperature of the stomach is an important agent in gastric digestion. From the fact, that alimentary substances, when subjected to the action of the gas- tric fluid out of the stomach, ard converted into a substance presenting the characters of chyme, some physiologists have embraced the opinion, that gastric digestion is nothing but a chemical solution of the aliment in the gastric fluid. Tiedemann and Gmelin, who adopt this opinion, admit however, that, with 238 FIRST LINES OF PHYSIOLOGY. respect to some alimentary substances, a peculiar kind of decomposition is produced by the action of the gastric fluid. Starch, for instance, when dissolved in the stomach, loses its peculiar property of giving a deep blue color to iodine, and is converted into sugar and gum. It would follow, from this theory of digestion, that the digestibility of aliments, is in proportion to the facility with which they are dissolved in the gastric liquor, and, of course, to their peculiar composition. The substances most easy of digestion, are such as are soluble in warm water, or contain a large propor- tion of soluble principles, as sugar, gum, liquid albu- men, and gelatin. These which require the aid of acids to dissolve them, as those which contain much gluten, concrete albumen, fibrin and caseum, cartilage, bone, are of more difficult digestion ; while some are insoluble in the gastric fluid, and of course indigesti- ble ; as the fibres of wood, or of plants, the skin of some of the leguminous plants, the kernels of fruits, feathers, hairs, &c. Chymilication, however, is not to be regarded merely as a chemical 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 bq effected in this way, by the solvent powers of this fluid over substances of an alimentary kind. This is established by the experiments of Spa- lanzani, and more fully by those of Beaumont. But it is not so certain, that they become endued with all the properties of chyme, especially with those which assimilate them to the nature of the living animal body, by undergoing this process. Le Pelletier af- firms, that in the experiments, which he had made with food, thoroughly masticated, and blended with saliva, penetrated with gastric fluid, and placed in favorable circumstances out of the stomach, he always found the food either reduced to a pulpy mass, or simply softened, or in the incipient stage of acid or putrid fermentation ; but never in a state of perfect THE NUTRITIVE FUNCTIONS. 239 chyme; as was proved by introducing the artificial chyme into the duodenum of living animals, when it was found that not a particle of real chyle was ever formed from it. 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 can- not become invested with living powers, if placed out of the atmosphere of vitality. Vital affinity can oper- ate only within the sphere of vital power. If, then, the gastric fluid is a mere chemical solvent of alimen- tary substances, it seems probable that the living- coats of the' stomach, with which all parts of the food are brought successively into contact, may impart to the latter certain properties, which may assimilate it to the nature of the living organization ; properties which it is impossible to conceive that it can acquire, when 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 with a few ounces of gastric fluid, as it would be to think of corking up a phial of sunshine, and keeping it in the dark. The analysis of digestion, proposed by Front, cor- responds in the main with this view. Prout attrib- utes to the stomach, three distinct powers; which are all exerted in digestion ; viz. a reducing, a converting , and a vitalizing power. By the reducing power, 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 ali- mentary 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, which he supposes 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 reducing. The 240 FIRST LINES OF PHYSIOLOGY. vitalizing, or organizing power, is that by which ali- mentary substances are brought into such a condition, as adapts them for an intimate union with the living body. This power, he says, cannot be chemical, but is of a vital character, and its nature is entirely un- known. The vital properties which the chyme ac- quires in the stomach, whatever these properties be, it is the prerogative of the living or the nervous pow- ers of the stomach to confer. The influence of these powers in digestion, is illustrated by numerous facts, especially by the influence of these medieinal agents which depress the nervous energy, as opium and other narcotics ; the effect of passions of the mind, and the sudden accession of disease; and intercepting the nervous influence by the ligature, or section of the parvagum ; causes, which can hardly be supposed competent to destroy the chemical or solvent powers of the gastric fluid, but which, nevertheless, are well known by physiologists, to interrupt or weaken the process of gastric digestion. The substance into which aliment is connected in the stomach, is called chyme. This is a semifluid, homogeneous matter, of a grayish color, sourish smell, and insipid or disagreeable taste, but varying con- siderably in its sensible properties, according to the qualities of the food out of which it is prepared. Ac- cording to Beaumont, it is invariably homogeneous, but its color partakes slightly of the color of the food. “ It is always of a lightish or grayish color, varying in its shades and appearance, from that of cream, to a grayish or dark-colored ground. It is, also, more consistent at one time, than at another ; modified in this respect, by 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, who died five hours after taking food, to present the appearance of a pale saffron-colored pap, of a strong and repul- sive smell, containing lactic acid, a white crystaline animal matter, similar to sugar of milk, a fat yellow- ish acid matter, resembling rancid butter ; another THE NUTRITIVE FUNCTIONS. 241 animal substance, like caseum, albumine, phosphat of lime, muriate and phospliat of soda. The time re- quired for the conversion of food into chyme, varies according to the greater or less degree of digestibility of the latter. In Beaumont’s experiments; the aver- age time employed in gastric digestion, was 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 con- sistence, or has been swallowed in large masses, its solution goes on slowly, 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 ali- ments, which are nearest the surface of the stomach, are most exposed to the action of the gastric fluid, as well as to the vitalizing influence of the stom- ach, and of course are the soonest dissolved, and ch y milled. By the successive contractions of the muscular coat, the dissolved portions are carried towards the pylorus, and gradually pass out of the stomach into the duo- denum. The passage of the chyme from the stom- ach takes place during the expansion of the circular fibres of the pyloric extremity, perhaps by the con- traction of the longitudinal. It is at first slow, but becomes more rapid in the later stages of chymifica- tion, as the formation of chyme becomes more abun- dant. According to Rudolphi, the chyme passes out of the stomach by drops, and the more rapidly as the degree of its fluidity is greater. Food of difficult solution, remains a longer time in the stomach, and in some instances, even a week or more, and may then be vomited up unchanged, or pass off by stool. In general, the peristaltic action of the stomach con- tinues, until the aliment is wholly dissolved by the gastric fluid, and has passed out of the stomach. The organ then resumes the state of contraction and qui- escence, natural to it when empty. Fluids pass out 31 242 FIRST LINES OF ^PHYSIOLOGY. of the stomach very speedily, chiefly perhaps, hv absorption. Influence of innervation upon chymiflcation. That the par vagum or pneu mo-gastric nerve exer- cises some important influence over digestion, has long been known to physiologists, though it is not yet fully ascertained what this influence is. The results of ex- perimental researches on the uses of these nerves, by different physiologists have not been uniform; but sometimes directly contradictory. But it seems to be pretty generally 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 was a suspension of respira- tion and chymiflcation. The ligature was afterwards withdrawn, and the two functions were restored. The same physiologist and Legallois, performed the ex- periment on pigeons ; and it was found, that the corn swallowed by the birds, remained unaltered in the crop. Dupuy performed 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 re- lation 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, bestowing 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 THE NUTRITIVE FUNCTIONS. 243 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 ani- mals, to a suspension of the secretion of gastric fluid. Tiedemann and Gmelin ascribe the check which di- gestion 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 well as by paralysing the muscular fibres of the stomach. The formation of this acid secretion out of the blood, which is an alkaline fluid, they suppose, requires an energetic action of the nervous power on the blood, which penetrates into the capillary net work of the stom- ach ; and they conjecture that this influence operates by causing a decomposition 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 with a loss of substance, and which had afterwards eaten the boiled white of eggs, ex- hibited no mark of acidity, its contents not reddening the tincture of turnsole. It seems probable, however, that the branches of the great sympathetic, which penetrate with the arteries into the coats of the stomach, have a very considerable, if not the prin- cipal share in the secretion of the gastric fluid. 2. Breschet. inferred from his experiments, that di- gestion is retarded 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 which, the mechanical motions of the stomach, necessary to chymification, 244 FIRST LINES OF PHYSIOLOGY. are no longer executed, and the food lies motionless in the hollow sac. Breschet found that this operation retards, but does not destroy digestion. Leuret and Laissaigne, also, performed the experi- ment 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 prevent asphyxia, and then suffered the animal to eat. They found, however, that the oesophagus was paralysed by the operation, and the food forced back into it, and vomited up. To prevent this, they tied the oesopha- gus, 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 was afterwards repeated, with the same results ; and the conclusion which Leuret and Lais- saigne drew from it was, that digestion may take place independently of the par vagum. In fact, the vagus spends most of its inferior branches upon the oesophagus, sending hut few to the stomach, which is supplied with nerves from the ganglionic system; and hence, the section of the vagus only retards digestion, which is still carried on under the influence of the great sympathetic. It is a curious fact, that the influence of the pneu- mogastric nerves on digestion, may be supplied by galvanism and electricity, and eAen by mechanical irritation. If the nerve be merely divided, and the ends be suffered to remain in contact with each other, digestion is not suspended. The two 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 stimulated by a galvanic current, or even by mechanical irritation, digestion recommences. From this fact, Breschet inferred that electricity operates in restoring digestion, by exciting the muscular movements of the walls of the stomach, by means of which, the food is brought successively into contact with all parts of its inner surface; and that mechanical irritation operates on the same prin- ciple. This view is strikingly corroborated by a THE NUTRITIVE FUNCTIONS. 245 fact, mentioned l>y Tiedemann and Gmelin ; viz. that they had frequently witnessed, in experiments, that mechanical and chemical 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 without pain, if the par vagum are divided, hut howling with agony, if these nerves are left uninjured. The section, or the compression by ligature, of these nerves, a little above the stomach, appears wholly to destroy the feeling of hunger. It is true that Leuret and Laissaigne cut out two inches of the par vagum in horses, and the animals continued to eat as before ; from which these physiologists in- ferred, that the appetite was not affected by the di- vision of these nerves. It was remarkable, however, that they continued to eat after the stomach was very much distended with food, a fact which makes it probable that the feeling of satiety was destroyed by the experiment, and the animals continued to eat automatically, as it were, without being prompted by appetite, to begin, or by the gratification of it, to leave off. The feeling of thirst, also, appears to be destroyed, as well 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 is here proper to mention the assertion of Ma- gendie, that if the section of the pneumogastric nerves be made in the thorax, below the place where the branches, which supply the lungs, are given off, the food, which is afterwards taken, is regularly converted into chyme, and furnishes abundant chyle ; and he is disposed to attribute the suspension of digestion, when the nerves are divided in the neck, to the influence of * Secetur nervous pneumogastricus. Cessat illico fames; non cessat illico digestio. ' Martinius Elevient. Physiol. 246 FIRST LINES OF PHYSIOLOGY. 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 pneuinogastric nerves below the origin of the pulmonary branches, without dividing the oesophagus itself. In his experi- ments 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 con- tents of the stomach, several hours after the section of the oesophagus. On the whole, it appears to be established by experiment, that the pneuinogastric 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 the sensations of hunger and thirst. It is probable, also, that the secretions 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 manner, likewise, impair or suspend chymifi- cation. It appears, also, that digestion is suspended by other operations, by which the nervous power is weakened. Wilson found that chymification was ar- rested by a section of the spinal cord, in the lumbar region ; and Edwards 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 chan- nel, 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 ab- THE NUTRITIVE FUNCTIONS. 247 sorbed. But, if the par vagum be previously divided, the effect is prevented. Brachet gave to each of two dogs six grains of opium, having in one previously divided the par vagum. The dog which had not un- dergone the operation, fell into a state of profound narcotism, while the other lay down quietly, and manifested no other symptom than the dyspnoea, which always results from the section of the pneu- mogastric 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 intoxication will 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, produce none of their usual effects. 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 second digestion, or the conversion of chyme into chyle. This intestine, like the other parts of the intestinal canal, is composed of three tunics, viz. a serous or peritoneal, a muscular, and a mu- cous. 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 wholly of circular fibres. The third, or mu- cous, exhibits a great number of transverse folds, termed the valvulce conniventes. It exercises a double secretion, one follicular, or mucous, the other per- spiratory, or exhaling. The arteries of the duodenum are derived from the right g astro-epiploic, and the splenic; its nerves, almost wholly from the solar plexus. The situation of the duodenum is deep in the abdomen, on a level with the third or fourth lum- bar vertebra ; having behind it the vertebral column, the aorta, and the vena cava inferior ; before it, the 248 FIRST LINES OF PHYSIOLOGY. stomach, and transverse mesocolon ; above, the liver ; and below, the small intestines. In the duodenum, the chyme is exposed to the action of three new agents, by which its nutritious parts are further elaborated, and the constituent prin- ciples of chyle are developed. These agents are the intestinal fluid, the bile and the pancreatic secretion. The irritation, excited by the acid chyme on the inner surface of the duodenum, occasions a copious afflux of these fluids into the intestine. According to Tiede- mann and Gmelin, the gall bladder is always empty during digestion, but full during fasting. The pan- creatic fluid is secreted in increased abundance ; and the stimulus of these two 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 per- spiratory. The intestinal fluid of the duodenum has some re- semblance to the gastric liquor. According to Tiede- mann 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, which 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 indigesti- bility of the food. The bile is a viscid fluid, secreted by the liver, of a greenish brown color, extremely bitter taste, and possessed of alkaline properties. It will be more par- ticularly described hereafter. The pancreatic fluid is a whitish 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 NUTRITIVE FUNCTIONS. 249 The mixture of these fluids with the chyme in the duodenum, effected by the contraction of this intestine; soon occasions a sensible change in its ap- pearance. 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 colored with yellow, its central portion presenting a deeper hue than the parts nearer the intestine. The external part adheres to the duo- denum, 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 experiments of Marcet and Prout, albumen, which is an essential part of the chyle, is copiously developed. This sub- stance begins to appear a few inches from the pylo- rus, and disappears in the inferior portion of the small intestines. According to Prout, if the food contained no albu- minous matter, no albumen is developed in the storm ach ; but, immediately on the entrance of the chyme into the duodenum, and its mixture with the biliary and pancreatic secretions, albumen and other prin- ciples of chyle begin to appear. This albumen is supposed, by Tiedemann 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 ab- sorbed by the lacteals ; and, combined together, they constitute the chyle. According to Tiedemann and Gmelin and some other physiologists, chyle is not formed in the duode- num ; for, they assert, that it is impossible to extract a particle of this fluid from the contents of this intes- tine. If this be true, the office of the duodenum is more completely to animalize the chyme, and to de- velope these principles or materials, necessary to the formation of the chyle. Leuret and Laissaigne, how- 32 250 FIRST LINES OF PHYSIOLOGY. ever, assert that all the essential principles of chyle preexist in the chyme. Albumen, which is the basis of the chyle, exists abundantly in the chyme of the duodenum; and particles of fibrin, also, they affirm, may be detected in it. If chyme be examined with 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 secre- tion ; and, consequently, can be derived only from the food. In what manner the acidity of the chyme dimin- ishes, 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 Laissaigne remark, that in chylification the bile and the pancreatic fluid prevent the fermentation of the chyme, by neutralizing its acid principles, and that fat substances, which had not been completely con- # verted into chyme, are dissolved by the bile, and ren- dered suitable for nutrition. Tiedemann and Gmelin, on the contrary, maintain that the bile is wholly in- capable of dissolving fat.'* They also suppose, that the soda of the bile unites with and neutralizes a part of the hydro-chloric 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 col- oring principles of the bile ; as appears from the fact, that tlie mucus which is precipitated, is of a brown color. Besides this mucus, several other principles are precipitated from the bile, as cholesterine, mar- garic acid, and resin, which Tiedemann and Gmelin found in the insoluble contents of the small intestines, and which contribute to the formation of the feces. The German physiologists, as well as Leuret and Laissaigne, found that digestion and the formation of * La bile n’est pas capable de dissoudre le plus petit atome de graisse. Elle ne peut, done contribuer a sa rdsorption que d'une manidre mdchanique en la tenant en suspension, quand elle est tres divisde. Tiedemann and Gmelin , Recherches,