4* *>.jf X MANUAL OP PHYSIOLOGY. BY WILLIAM S. KIRKES, M. D. MANUAL OF PHYSIOLOGY. BY WILLIAM SENHOUSE KIRKES, M.D., FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS; ASSISTANT PHYSICIAN TO, AND LECTURER ON BOTANY AND VEGETABLE PHYSIOLOGY AT, ST. BARTHOLOMEW'S HOSPITAL. A NEW AND REVISED AMERICAN, FROM THE LAST LONDON EDITION. WITH TWO HUNDRED ILLUSTRATIONS. PHILADELPHIA: BLANCHARD AND LEA. 185 7. QT Entered, according to Act of Congress, in the year 1857, by BLANCHARD & LEA, in the Clerk's Office of the District Court of the United States in and for the Eastern District of Pennsylvania. Printed by T. K. & P. G. Collins. AMERICAN PUBLISHERS' ADVERTISEMENT. The very recent and careful revision which this work has received at the hands of the author, has rendered unnecessary any extended additions in again preparing it for the American student. Such few notes as were deemed desirable have been added by Dr. J. Aitken Meigs, who has superintended the passage of the volume through the press, and who has introduced a large number of new and superior illustrations, which, it is hoped, will render the facts advanced more easy of comprehension. Care has been exer- cised, however, in these additions, not to interfere in any way with the intentions of the author to render the work simply a succinct "account of the facts and generally admitted principles of Phy- siology." The author's text has been preserved throughout without omis- sion or modification. Such notes as have been added will be found distinguished by enclosure in brackets [ ]. As in the former American Edition, the steel plates of the origi- nal have been engraved on wood, and scattered through the text, in their appropriate places, as more convenient for reference; and the title of "Manual" has been retained, in place of "Handbook," as being better suited to the character of the work. The editorial supervision to which it has been subjected in its passage through the press is a guarantee that the present edition will in no way detract from the reputation which the work has so deservedly attained. Philadelphia, April, 1857. 1* (v) PREFACE TO THE THIRD EDITION. In the preparation of the present Edition every portion of the work has been submitted to careful revision; and, in nearly all parts of it, additions and alterations have been introduced. No change, however, has been made in the general plan and arrano-e- ment of the book; and no more detailed account of the structure of the organs and tissues is given, because of the increased bulk which such an addition would have occasioned, and because of the number and excellence of the published works on General and Phy- siological Anatomy. The work therefore is, as before, essentially a Hand-book of Physiology. William Senhouse Kirkes. Lower Seymour-street, October, 1856. (vii) PREFACE TO THE FIRST EDITION. The publishers of Dr. Baly's edition of " Miiller's Elements of Physiology " had long designed to render that admirable work more available for the general use of students. They had proposed the reduction of its principal contents into a volume more nearly propor- tionate to the share of time which can be devoted to Physiology, as only one of many subjects to be studied in the period of pupillage. The present work was commenced with the intention of fulfilling their design; it was announced as a " Hand-book of Physiology on the Basis of Miiller's Elements;" and many of its chapters, namely those on Motion, Voice and Speech, the Senses, Generation, and Development, are chiefly abstracts of corresponding portions of that work, and of the Supplement by Dr. Baly and myself. But, in the rest of the subjects, it was found that the progress of Phy- siology, during seven years, had so increased or modified the facts, and some even of the principles of the science, that " Miiller's Ele- ments," and the notes added by Dr. Baly, could only be employed as among the best authorities and examples. The design was, there- fore, departed from, so far as it concerned the construction of a Hand-book on the basis of Muller. In writing the present work, the primary object has been to give such an account of the facts and generally admitted principles of Physiology as may be conveniently consulted by any engaged in the study of the Science; and, more especially, such an one as the stu- dent may most advantageously use during his attendance upon Lec- tures, and in preparing for examinations. The brevity essential to this plan required that only so much of Anatomy, Chemistry, and (ix) X PREFACE TO THE FIRST EDITION. the other sciences allied to Physiology, should be introduced as might serve to remind the reader of knowledge already acquired, or to be obtained, by the study of works devoted to these subjects. For the same end, it was necessary to omit all discussions of unset- tled questions, and expressions of personal opinion; but ample references are given, not only to works in which these may be read, but to those by which the study of Physiology may be, in its widest extent, pursued. For the convenience of students the subjects are arranged on a plan corresponding with that in which they are taught in the courses of Lectures on Physiology, delivered in the principal metro- politan schools of medicine. I cannot sufficiently express my obligations to Mr. Paget, from whom I have received the most liberal aid in every stage of the work; and who has, moreover, afforded me access to his manu- script notes of Lectures. I have also to offer my best thanks to Dr. Baly for many kind suggestions made by him in the course of the work. William Senhouse Kirkes. College of St. Bartholomew's Hospital, Sept. 29th, 1848. CONTENTS. Introduction, .... CHAPTER I. Chemical Composition of the Human Body, CHAPTER II. Structural Composition of the Human Body, CHAPTER III. Vital Properties of the Organs and Tissues Body, ..... CHAPTER IV. The Blood, ..... Coagulation of the Blood, Conditions affecting Coagulation, The Blood-Corpuscles, or Blood-Cells, The Serum, .... Chemical Composition of the Blood, . Vital Properties and Actions of the Blood, CHAPTER V. Circulation of the Blood, Of the Action of the Heart, Action of the Valves of the Heart, xii CONTENTS. Sounds and Impulse of the Heart, Frequency and Force of the Heart's Action, Cause of the Rhythmic Action of the Heart, Effects of the Heart's Action, The Arteries, . The Pulse, ..... Force of the Blood in the Arteries, The Capillaries, .... The size, number, and arrangement of Capillaries, Circulation in the Capillaries, The Veins, ...,•■ Peculiarities of the Circulation in Different Parts, Cerebral Circulation, .... Erectile Structures, . CHAPTER VI. Respiration, ...... Structure of the Lungs, .... Movements of Respiration, Movement of the Blood in the Respiratory Organs, . Changes of the Air in Respiration, Changes produced in the Blood by Respiration, Influence of the Nervous System in Respiration, Effects of the Suspension and Arrest of Respiration, CHAPTER VII. Animal Heat, ..... Sources and Mode of Production of Heat in the Body, CHAPTER VIII. Digestion, ...... Changes of the Food effected in the Mouth, . Passage of Food into the Stomach, Digestion of Food in the Stomach, . Structure of the Stomach, Secretion and Properties of the Gastric Fluid, Changes of the Food in the Stomach, Movements of the Stomach, . Influence of the Nervous System on Gastric Digestion Changes of the Food in the Intestines, Structure and Secretions of the Intestines, The Pancreas, and its Secretion, CONTENTS. xiii PAGE The Liver, and its Secretion, ..... 207 Changes of the Food in the Large Intestine, . . 222 Movements of the Intestines, ..... 223 CHAPTER IX. Absorption, ....... 225 Absorption by the Lacteal Vessels, .... 226 Absorption by the Lymphatics, .... 227 Properties of Chyle and Lymph, .... 229 Office of the Lacteal and Lymphatic Vessels and Glands, . 232 Absorption by the Blood-vessels, .... 237 CHAPTER X. Nutrition and Growth, ..... 244 Nutrition, ....... 244 Growth, ....... 255 CHAPTER XI. Secretion, ........ 257 Secreting Membranes, ..... 258 Secreting Glands, ...... 264 Process of Secretion, ..... 266 CHAPTER XII. Vascular Glands ; or Glands without Ducts, . . . 270 CHAPTER XIII. The Skin and its Secretions, ..... 275 Structure of the Skin, ...... 275 Excretion by the Skin, . . . . . 279 Absorption by the Skin, . . . .282 CHAPTER XIV. The Kidneys and their Secretion, .... 283 Structure of the Kidneys, ..... 283 Secretion of Urine, ...... 286 The Urino: its general Properties, . 288 Chemical Composition of the Urine, .... 290 2 XIV CONTENTS. CHAPTER XV. The Nervous System, . . . • Elementary Structures of the Nervous System, Functions of Nerve-Fibres, . ... Functions of Nervous Centres, Cerebro-spinal Nervous System, Spinal Cord and its Nerves, . Functions of the Spinal Cord, The Medulla Oblongata, Its Structure, . Its Functions, .... Structure and Physiology of the Meso-cephalon, or. Pons Varolii, ....... Structure and Physiology of the Cerebellum,. Structure and Physiology of the Cerebrum, . Physiology of the Cerebral and Spinal Nerves, . Physiology of the Third, Fourth, and Sixth Cerebral or Cranial Nerves, ..... Physiology of the Fifth or Trigeminal Nerve, Physiology of the Facial Nerve, Physiology of the Glosso-Pharyngeal Nerve, Physiology of the Pneumogastric Nerve, Physiology of the Accessory Nerve, . Physiology of the Hypoglossal Nerve, . Physiology of the Spinal Nerves, Physiology of the Sympathetic Nerve, . PAQB 301 301 311 318 322 326 337 337 340 344 346 350 360 361 366 370 373 376 380 382 382 383 CHAPTER XVI. Causes and Phenomena of.Motion, Ciliary Motion, . Muscular Motion, Muscular Tissue, Properties of Muscular Tissue, 391 391 398 393 396 CHAPTER XVII. Of Voice and Speech, .... Mode of Production of the Human Voice Applications of the Voice in Singing and Speaking, Speech, ...... 408 408 412 416 CONTENTS. XV CHAPTER XVIII. The Senses, ........ The Sense of Smell, ...... The Sense of Sight, ...... Of the Phenomena of Vision, .... Of the Reciprocal Action of different parts of the Retina on each other, ....... Of the Simultaneous Action of the two Eyes, Sense of Hearing, ..... Anatomy of the Organ of Hearing, . Physiology of Hearing, ..... Functions of the External Ear, Functions of the Middle Ear; the Tympanum, Ossicula, and Fe- nestra, ...... Functions of the Labyrinth, .... Sensibility of the Auditory Nerve, . Sense of Taste, ...... Sense of Touch, ..... PAGE 420 425 430 437 449 451 456 456 461 462 4G3 468 470 474 478 CHAPTER XIX. Generation and Development, Generative Organs of the Female, Unimpregnated Ovum, .... Discharge of the Ovum, .... Impregnation of the Ovum, Male Sexual Functions, .... Development, . Changes in the Ovum previous to the Formation of the Changes in the Ovum within the Uterus, Development of the Embryo, The Chorion and Placenta, Development of Organs, . Development of the Vertebral Column and Cranium, Development of the Face and Visceral Arches, Development of the Extremities, Development of the Vascular System, Development of the Nervous System, . 485 485 487 492 499 499 504 Embryo . 504 508 511 622 527 527 528 530 530 536 xvi CONTENTS. PAGE 538 540 543 543 547 Index, . g^_ List of Works Referred to, Development of the Organs of Sense, Development of the Alimentary Canal, . Development of the Respiratory Apparatus, . . The Wolffian Bodies, Urinary Apparatus, and Sexual Organs, At the end of the Volume is a numbered List of Authorities to which reference is made; and with the numbers of these the figures in parentheses, throughout the text, correspond. LIST OF ILLUSTRATIONS. no. 1. 2. 3. 4. 5. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. Corpuscles of human blood, .... Red particles of the blood of the common fowl, Fibres of unstriped muscle, .... Primary organic cell, .... Plan representing the formation of a cell and its nucleus Muscular fibre of animal life, Broken muscular fibre, ..... Fasciculi and fibres of cellular tissue, Development of the areolar tissue, Fibres of elastic tissue from the ligamentum flavum of the vertebrae, .... Portion of white fibrous tissue, Uniform coagulation of blood, Coagulation with contraction, . Cupped coagulum, .... Fibrils of healthy fibrin, entangling red and white blood puscles, ..... Fibrous membrane lining the egg-shell, Colorless blood-corpuscles, . Prismatic crystals from human blood, . Tetrahedral crystals from blood of guinea-pig, Hexagonal crystals from blood of squirrel, Development of first set of blood-corpuscles in Batrachian larva, Development of first set of blood-corpuscles in the Mammalian embryo, ....... Development of human lymph- and chyle-corpuscles into blood- corpuscles, ....... Diagram of the circulating apparatus in mammals and birds, Diagram of the semi-lunar valves of the aorta, Fibrous tissue of a semi-lunar valve beneath the endocardium, Sections of aorta to show the action of the semi-lunar valves, 2 * ( xvii ) PAGE 42 42 43 44 45 46 46 47 47 48 48 55 55 56 57 57 63 71 71 73 74 75 83 87 xviii LIST OF ILLUSTRATIONS. 28.* Vertical section through the aorta at its junction with the left ventricle, . 29. Hsemadynamometer of Poiseuille, . 30. Blood-vessels of an intestinal villus, . • • ' ' 31. Distribution of capillaries around follicles of mucous membrane, 118 32. Capillary network of nervous centres, . - • * 33. Capillary network of fungiform papilla of the tongue, 34. Capillaries in the web of the frog's foot, 35. Portion of the erectile tissue of the corpus cavernosum, 36. Slightly oblique gection through a bronchial tube, . • 137 . . lo7 138 138 64. 115 120 134 139 141 37. Ciliary epithelium of the human trachea, 38. Two small pulmonary lobules, . 39. Air-cells of the lung, . 40. Arrangement of the capillaries in the air-cells of the human lung, ....-•• 41. The changes of the thoracic and abdominal walls of the male during respiration, . 42. The respiratory movement in the female, . • • I4* 43. Lobule of parotid gland of a new-born infant, . • 173 44. Mucous membrane of the stomach, after Boyd, . • 180 45. Longitudinal section through the coats of a pig's stomach, near the pylorus, ...••• 46. One of the tubular follicles of the pig's stomach, after Wasmann, 182 47. Gastric gland from the stomach of a dog, . • .183 48. Section of the mucous membrane of the small intestine in the dog, 200 49 /a. Transverse section of Lieberkiihn's tubes or follicles, "> 200 I b. A single Lieberkiihn's tube, . / 50. Solitary gland of small intestine, after Boehm, . . 201 51. Part of a patch of the so-called Peyer's glands, . . 201 52. Side view of a portion of intestinal mucous membrane of a cat, showing a Peyer's gland, .... 202 53. Capillary plexus of the villi of the human small intestine, . 203 54. One of the intestinal villi with the commencement of a lacteal, 204 55. Intestinal villus of a kitten, ..... 204 56. Vertical section of the coats of the small intestine of a dog, showing the commencing portions of the portal vein and the capillaries, ...... 207 57. Transverse section of a lobule of the human liver, . . 208 58. A small lobule from the pig's liver, .... 208 59. Cells from the liver, ...... 209 60. Small branch of an inter-lobular duct, . . . 209 61. Capillary blood-vessels and lymphatics from the tail of a tadpole, 228 62. Lymphatic heart, ...... 234 63. Section of lymphatic gland,..... 235 a. One of the inguinal lymphatic glands, . . "I b. One of the superficial lymphatic trunks of the thigh, I c. One of the femoral lymphatic trunks, laid open to show | the valves, ..... J LIST OF ILLUSTRATIONS. XIX FIG. PA8E. 65. Endosmometer, ....... 240 66. Endosmometor of Power, ..... 241 67. Intended to represent the changes undergone by a hair towards the close of its period of existence, .... 246 68. Section of a portion of the upper jaw of a child, showing a new tooth in process of formation, .... 248 69. Scales of tessellated epithelium, .... 262 70. Cylinders of the intestinal epithelium; after Henle, . 263 71. Pulp in the human spleen, ..... 274 72. A perpendicular section of the skin of the sole of the foot, 276 73. Sweat gland and the commencement of its duct, . . 277 74. Sebaceous glands of the skin; after Gurlt, . . . 278 75. A section of the kidney surmounted by the suprarenal capsule, 284 76. Section of the cortical substance of the human kidney, . 284 77. Termination of a considerable arterial branch wholly in Malpig- hian tufts, ...... 285 78. Plan of the renal circulation in man and the mammalia, . 286 ' a. Portion of a secreting canal from the cortical substance of the kidney, ..... 79. ^ B. The epithelium or gland-cells, . . . 286 Portion of a canal from the medullary substance of the kidney, ...... 80. Appearance presented by the solid white portion of the urine of birds and reptiles, ..... 395 81. Linear masses of granules of urate of ammonia, . . 295 82. Uric acid crystals from human urine, .... 296 83. Thick lozenge-shaped crystals of uric acid, . . 296 84. Uric acid crystals in which the rhomboidal form is replaced by a square one, ...... 85. Accidental varieties of rhomboidal and square crystals of uric acid,.......296 86. Rhomboidal prisms of uric acid, .... 297 87. Aggregated lozenges of uric acid, .... 297 88. Hippuric acid, ....... 297 89. Mixed phosphates, ...... 299 90. Triple phosphate of magnesia and ammonia, . . . 299 91. Chloride of Sodium resulting from slow evaporation of healthy urine, ....... 92. Primitive nerve-tubules, ..... 302 93. Diagram of tubular fibre of a spinal nerve, 94. Roots of a dorsal spinal nerve, and its union with the sympa- thetic, . . • • • • .305 95. Distribution of the tactile nerves at the surface of the lip, 307 96. Terminal nerves on the sac of the second molar tooth of the lower jaw in the sheep, ..... 307 97. Extremities of a nerve of the finger, with Pacinian corpuscles attached, ....... 308 98. Pacinian corpuscles from the mesentery of a cat, . 296 300 302 303 308 XX LIST OF ILLUSTRATIONS. FIG. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113. 114. 115, 117. 118. 119. 120. 121. 122, 124. 125. 126. 127. 128. 129. 130. 131. 132. 133. 134. 135. 136. 137. 138. Nerve-corpuscles from a ganglion, . Various forms of ganglionic vesicles, Connection between nerve-fibres and nerve-corpuscles, Transverse section of the spinal cord, . Diagram to show the decussation of the fibres within the trunk of a nerve; after Valentin, . Front view of the medulla oblongata, . Posterior view of the medulla oblongata, Sensory and motor column in medulla oblongata, Dissection showing relation of fornix, Cerebral connection of all the cerebral nerves except the first, Vibratile or ciliated epithelium, .... Nucleated ciliary cells, . Stages of the development of striped muscular fibre, Muscular fibrils of the pig; after Sharpey, External and sectional views of the larynx, Bird's-eye view of larynx from above, . 116. Vocal cords; from Prof. Willis, Outer wall of the nasal fossa, with the three spongy bones and meatus, ...... Olfactory filaments of the dog, .... Nerves of the septum of the nose, Vertical section of the human retina and hyaloid membrane, The yellow spot of the retina occupying the axis of the eye after Soemmering, ..... 123. Diagrams illustrating the use of the foramen Soemmering Outer surface of the retina: after Jacob, Choroid and iris, exposed by turning aside the sclerotica; from Zinn, ....... f a. Vertical section of the human cornea, "t \ b. The posterior epithelium, . J Position of the lens in the vitreous humor, shown by an imagi- nary section ; after Arnold, .... Lens hardened in spirit, and partially divided along the three interior planes, as well as into lamellae; after Arnold, Vertical section of the eye from before backwards, Diagram to show the position and action of the ciliary muscle, Diagram to show inversion of image on the retina, Diagram illustrative of the results of "attention" to visual im- pressions, ...... A circle showing the various simple and compound colors of light, and those which are complemental of each other, Diagram illustrative of simultaneous action of two eyes, Section of eye showing the application, in man, " in quadrupeds, Diagram showing want of simultaneous action in eye of quad- ruped, ..... Hypothetical division of optic nerve in chiasm ; after Miiller, PAGE 309 310 310 323 326 338 338 339 360 362 391 391 395 396 409 410 411 427 427 428 431 432 432 433 434 435 436 436 438 442 444 448 449 452 453 454 454 455 LIST OF ILLUSTRATIONS. XXI FIO. PAGE 139. Union of correspondent fibres of optic nerves in sensorium, 455 140. Union of correspondent fibres in optic nerve, . . . 455 141. Stereoscopic drawing of a cube, .... 456 142. Interior of the osseous labyrinth; from Soemmering, . . 457 143. General view of the external, middle, and internal ear; from Scarpa, ....... 459 144. Ossicles of the left ear articulated, and seen from the outside and below; from Arnold, . . . . 460 145. Propagation of sound through ossicles, . . . 466 146. Tongue, seen on its upper surface; from Soemmering, . 475 147. Papillae of the palm, the cuticle being detached, . . 479 148. Vessels of papillae, from the heel, .... 479 149. Section of the Graafian vesicle of a mammal; after Von Baer, 488 150. Ovum of the sow; after Barry, .... 489 151. Diagram of a Graafian vesicle, containing an ovum, . . 490 152. Successive stages of the formation of the corpus luteum, in the Graafian follicle of the sow, .... 496 153. Corpora lutea of different periods; after Dr. Montgomery, . 497 164. Development of the spermatozoids of Certhia familiaris; after Wagner, ....... 500 155. Development of the spermatozoids of the rabbit, . . 501 (a. An ovarian ovum from a bitch in heat, . . -» b. The same ovum after the removal of most of the club- L 505 shaped cells, . . . . .J 157. Cleavage of the yelk in ovum of bitch; after Bischoff, . 506 158. Cleavage of the yelk after fecundation; after Bagge, . 507 159. Section of the lining membrane of a human uterus at the period of commencing pregnancy; after Weber, . . . 509 160. Two thin segments of human decidua after recent impregna- tion; from Dr. Sharpey, .... 510 161. A vertical section of the mucous membrane, showing uterine glands of the bitch; from Dr. Sharpey, . . . 511 162. Diagram of part of the decidua and ovum separated, to show their mutual relations; from Dr. Sharpey, . . 511 163. Portion of the germinal membrane of a bitch's ovum, with the area pellucida and rudiments of the embryo ; after Bischoff, 512 164. Portion of the germinal membrane, with rudiments of the em- bryo from the ovum of a bitch; after Bischoff, . . 514 165. Diagram showing vascular area in the chick, . . 515 166. Embryo of the chick at the commencement of the third day; after Wagner, ...... 515 167. Formation of arterise omphalo-mesentericae, . . .516 168. Embryo from a bitch at the 23d or 24th day; after Bischoff, 516 169. A longitudinal section of an embryo chick in the second day of incubation, . . . . . . .517 170. Formation of amnion, and vitelline duct, . . . 518 171. Further development of same, . . . . .518 172. Aborted ovum; after Sharpey, .... 520 XXli LIST OF ILLUSTRATIONS. PAGE no. 590 173. Mesentery and intestine of the embryo, • • ^ 174. Omphalomesenteric vein in foetus, • 175, 176, 177. Ovum and embryo ; after Miiller, . * " 178. The lower part of the body of a bitch's embryo; after Bischoff, 179. The lower extremity of an older embryo ; after Biscnott, . 180. Diagram of human ovum, at the time of formation of placenta, 181. The villi of the foetal portion of a mature human placenta; after Weber, 182. Extremity of the villus; after Weber, . • • 183. Transverse section of the uterus and placenta ; J. Reid, ^ . 184. Connection between the maternal and foetal vessels ; J. Reid, 185. Extremity of a placental villus; after Goodsir, 186. Development of the parts of the face in the embryo of Triton taeniatus; after Reichert, . 187. A human embryo of the fourth week, 188. Capillary bloodvessels of the tail of a young larval frog; after Kolliker, ...•■•• 532 189. Heart of the chick at the 45th, 65th, and 85th hours of incuba- tion ; after Thomson, ..... 190. Heart of a human embryo of about the fifth week; after Von Baer, ....... 191. Plan of the transformation of the system of aortic arches into the permanent arterial trunks in mammiferous animals; after Van Baer, ...... 535 192. Early forms of the brain in the embryo ; after Tiedemann, . 537 193. Development of the eye ; after Huschke, ... 539 194. An embryo dog ; after Bischoff, . . . .541 195. First appearance of parotid gland in the embryo of a sheep, 542 196. Lobules of the parotid, with the salivary ducts, in the embryo of the sheep at a more advanced stage, . . • 542 197. Rudiment of the liver on the intestine of a chick at the fifth day of incubation, . . . . . . 542 198. Development of the respiratory organs; after Rathke, . 543 199. Urinary and generative organs of human embryo ; after Miiller, 544 200. Urinary and generative organs of a human embryo measuring 31 inches in length; after Miiller, .... 545 522 522 523 525 525 52G 526 526 529 531 533 534 MANUAL OF PHYSIOLOGY. INTRODUCTION. Human Physiology is the science which treats of the conditions, phenomena, and laws of the life of the human body in the state of health. The phenomena of life manifested in the human body, as in that of all animals, may be arranged in two principal classes; the first comprehending those which are observed, in various degrees of per- fection and variously modified, in both vegetables and animals; the second, those which are peculiar to the members of the animal kingdom. The first class of the phenomena of life includes, 1st. The pro- cesses of digestion, absorption, secretion, excretion, circulation, and respiration, which, together with the offices of some parts not yet understood, fulfil their purpose in the formation, movement, and purification of the blood, with the materials for the nutrition of all the tissues of the body; 2nd. The processes of growth and nutrition, or nutritive assimilation, by which the several parts of the body, obtaining materials from the blood, repair the loss and waste to which they are subject in the discharge of their functions, or through their natural impairment and decay; 3d. The generative processes, for the formation, impregnation, and development of the ova. These are named processes, functions, or phenomena of organic or vegetative life. Those of the first two divisions maintain the existence of the individual being; those of the third maintain that of the species. The second class of vital phenomena includes the functions of sensation and voluntary motion, by which the mind of an animal acquires knowledge of things external to itself, and is enabled to act upon them. These are named phenomena of animal or relative life. But the division of the functions or phenomena of life into these, or anv similar classes, is artificial, and must not be taken as indicating 3 3 (25) 26 CHEMICAL COMPOSITION OF HUMAN absolute difference and dissociation. The organic and the animal hfe are knit together and mutually dependent; neither can be long maintained without the other. As all the processesof organic life are essential to the maintenance of the organs of animal life, so in an equal degree, the sensation and voluntary motion of animal life are elsential to the taking of food, the discharge of excretions, and other processes of organic life, by which the animal and the species are maintained. All the bodies in which the phenomena of life have been observed are formed of diverse mutually adapted parts, or organs; they are, therefore, called organisms, or organized bodies or parts; their com- position and structure, being peculiar, are named organic, and con- stitute their organization. While alive, also, they manifest certain peculiar vital properties and modes of action. A brief account, therefore, of the chemical composition, general anatomical structure, and vital properties of the several tissues and organs, will be a neces- sary preface to the consideration of their actions. CHAPTER I. CHEMICAL COMPOSITION OP THE HUMAN BODY. The following Elementary Substances may be obtained,by chemi- cal analysis, from the human body; Oxygen, Hydrogen, Nitrogen, Carbon, Sulphur, Phosphorus, Silicon, Chlorine, Fluorine, Potassium, Sodium, Calcium, Magnesium, Iron, and probably, or sometimes, Manganesium, Aluminium, and Copper. Thus, of the fifty-five elements of which all known matter is composed, nearly one-third exist in the human body. A few others have been detected in the bodies of other animals; but no element has yet been found in any living body which does not also exist in inorganic matter. Of the elements enumerated above, the first four, because they exist in nearly all animal substances and form the largest parts of all, are named essential elements; the rest, being less constant, and occurring often in only very small quantity, are named incidental elements. But the term incidental must not be understood to imply that any of these elements (except, perhaps, the last three) are less necessary to the right composition of the substances in which they exist than the essential elements are. Sulphur, for example, is as constant and necessary a constituent of albumen, and iron of hsema- tosine, as any of the elements are. The terms must be taken in only a general sense. No organic substance being known which has not at least three of the first four elements, they may be considered essential to the formation and existence of organic matter. But one CHIEF PECULIARITIES. 27 or more of the other elements added to these, in comparatively small proportions, contribute to determine, as it were incidentally, the pecu- liarities by which one kind of organic matter is distinguished from another. The elements composing organic and inorganic matter being thus the same, we must look to the modes in which they are combined for an explanation of the differences between the two classes of sub- stances. We cannot indeed draw an absolute rule of chemical distinction between the two classes, for there are substances which present every gradation of composition between those that are quite organic and those that are inorganic. Such substances of inter- mediate eomposition are many that are formed when inorganic matters, taken as nutriment by plants, gradually assume the characters of organic matter, under the influence of the vital properties of the plant; and such are those which are formed in both plants and animals, when, out of the well-organized tissues, or out of the sap or blood, materials are being separated, to form either tissues for mechanical service, or stores for nutriment, or purifying excretions. In both cases, the substances that are in the state of transition between the organic and the inorganic, or between the more and the less organized states, may proceed through changes so gradual that no natural line of demarcation between the two states can be discerned; and one cannot say when that which has been called inorganic has acquired the characters of an organic body, or when that which has been organic ceases to deserve the name. Alcohol, ether, acetic acid, urea, uric acid, and the fatty and oily matters, are such substances of organic origin, and intimately related to such as no one would hesitate to call organic, yet in their simplicity and mode of composi- tion they are like inorganic matters. But although no decided difference in chemical characters can be discerned in substances that thus stand, as it were, on the boundary between the organic and the inorganic world, yet, all the substances that form the proper component living tissues of animal bodies are as distinguished from inorganic substances as the actions of living bodies are from the passiveness of dead; and, as a general rule, it may be held that the more active the vital processes are that are carried on in any substance, the more widely do the chemical charac- ters of that substance differ from those of inorganic matter. The chief peculiarities in the chemical characters of animal sub- stances appear to be these three : — 1. The simplest of the compounds naturally formed in the body, — of those compounds which, from their being supposed to stand, in order of simplicity, nearest to the elements, are called proximate principles,—are composed of at least three elements. In the in- organic world, the most abundant substances are either in the ele- mental state, as the oxygen and nitrogen, by the mixture of which the atmosphere is formed; or, are formed by the union of only two 28 CHEMICAL COMPOSITION OF HUMAN BODY. elements, as water, of oxygen and hydrogen, the oxides of calcium aluminium, and others. In the organic world, the most abundant substances are, in plants, compounds of three elements as starch gum, su-ar, cellulose, and others composed of carbon, hydrogen, and oxyeen- and in animals, of four or five elements, as albumen, fib- rine, gelatine, and other compounds of the four essential elements and sulphur. . . 2. In the more compound inorganic substances, the several ele- ments of which they consist appear to be combined, or, as it were, put together, in pairs—each element seeming to have more affinity for on'e of the others than for all the rest. The elements are arranged in what is called a binary mode of combination. But, when any number of elements are combined in an organic compound, they ap- pear all held together as with one bond, as if each of them were united with equal force to all the others. Thus, for example, car- bonate of ammonia, which is regarded as an inorganic salt, is formed of the same four elements as compose most animal matters. Its constitution may be thus expressed :— Oxygen, } uniting, form carbonic acid |and thege twQ uniting> fom Nitrogren, 1 .A- -. • i carbonate of ammonia. ruuugeu, i uniting, form ammonia. J And in the analysis of this substance, the first pair of elements may be separated together in the form of carbonic acid, the second pair remaining as ammonia. But, in stating the composition of an organic body, these four elements would be all placed within one bond or bracket; and in the analysis of such a compound the ele- ments part asunder, and re-combine in compounds, which vary according to the circumstances in which the change takes place, and of which compounds there may be no reason to believe that any pre- viously existed in the substance analyzed. Thus, in the decompo- sition of albumen, carbonic acid, water, ammonia, carburetted and sulphuretted hydrogen, and other compounds, would be not merely separated, but formed out of the elements parting asunder, and com- bining again according to their several affinities and the circum- stances of the case. 3. Not only is a large number of elements combined in an organic compound, but a large number of equivalents or atoms of each of the elements are united to form an equivalent or atom of the compound. In the case of carbonate of ammonia, already referred to, one equi- valent of carbonic acid is united with one of ammonia; the equiva- lent or atom of carbonic acid consists of one of carbon with two of oxygen ; and that of ammonia of one of nitrogen with three of hydro- gen. But in an equivalent or atom of fibrine, or of albumen, there are of the same elements, respectively, 48, 15, 12, and 39 equiva- lents, according to Dumas, and nearly ten times as many according to Mulder. And, together with this union of large numbers of INSTABILITY OF ORGANIC COMPOUNDS. 29 equivalents in the organic compound, it is further observable, that the several numbers stand in no simple arithmetical relation one with another, as the numbers of equivalents combining in an organic compound do. With these peculiarities in the chemical composition of organic bodies we may connect two other consequent facts: the first, that of the large number of different compounds that are formed out of comparatively few elements; the second, that of their great prone- ness to decomposition. For it is a general rule, that the greater the number of equivalents or atoms of an element that enter into the formation of an atom of a compound, the less is the stability of that compound. Thus, for example, among the various oxydes of lead and other metals, the least stable in their composition are those in which each equivalent has the largest number of equivalents of oxygen. So, water, composed of one equivalent of oxygen and one of hydrogen, is not changed by any slight force; but peroxyde of hydrogen, which has two equivalents of oxygen to one of hydrogen, is among the substances most easily decomposed. The instability on this ground belonging to animal organic com- pounds is augmented; 1st, by their containing nitrogen, which, among all the elements, may be called the least decided in its affini- ties, that which maintains with least tenacity its combinations with other elements; and, 2ndly, by the quantity of water which, in their natural mode of existence, is combined with them, and the presence of which furnishes a most favorable condition for the decomposition of nitrogenous compounds. Such, indeed, is the instability of ani- mal compounds, arising from these several peculiarities in their con- stitution, that, in dead and moist animal matter, no more is requisite for the occurrence of decomposition than the presence of atmo- spheric air and a moderate temperature; conditions so commonly present that the decomposition of dead animal bodies appears to be, and is generally called, spontaneous. The modes of such decompo- sition vary according to the nature of the original compound, the temperature, the access of oxygen, the presence of microscopic or- ganisms, and other circumstances, and constitute the several pro- cesses of decay and putrefaction; in the results of which processes the only general rule seems to be, that the several elements of the original compound finally unite to form those substances whose com- position is, under the circumstances, most stable. ' i An interesting account of the nature of the so-called spontaneous decom- position of dead organic matter is given by Dr. Helmholtz (lxxx. 1843): for an abstract of the paper see xxv. 1843-4, p. 5. The experiments of Helm- holtz show, that although the results of spontaneous decomposition are modi- fied by the'presence of infusorial organisms, yet these are not, as has been supposed, essential to the occurrence of the process: their existence in large quantities in decomposing animal matters is due to the fact, that such decom- position furnishes the most favorable conditions to their development and life. Consult also, on this subject, Liebig, in the last edition of his Animal Chemistry. 30 CHEMICAL COMPOSITION OF HUMAN BODY. It is not known how far the process of decomposition which thus occurs in dead animal matter is imitated in the living body; but the facility of decomposition which it indicates may be considered in the study of those chemical changes which are constantly effected during life tranquilly, and without the intervention of any such compara- tively violent forces as are used in chemical art. The instability which organic compounds show when dead makes them amenable to the chemical forces exercised on them during life by the living tis- sues—forces inimitably gentle, so slight that their operation is not discernible by any effects besides those which they produce in the living body. What has been said respecting the mode in which the elements are combined in the composition of animal matter refers only to the four essential elements. Little or nothing is known of the mode in which the incidental elements, or their compounds, are combined with the compounds formed of the essential elements; only it is probable that they are combined chemically, and as necessary parts of the substances they contribute to form. Of the natural organic compounds existing in the human body, some occur almost exclusively in particular tissues or fluids; as the coloring matter of the blood and other fluids, the fatty matter of the nervous organs, etc. But many exist in several different parts, and may, therefore, be now described in general terms. They may be arranged in two classes, namely, the azotized, or ni- trogenous, and the non-azotized or non-nitrogenous principles. The non-azotized principles include the several fatty, oily, or ole- aginous substances, of which, in the human body, the most abundant are named margarine, elaine or oleine, stearine, cholestearine, and cerebrine. The fatty substances are, nearly all, compounds of carbon, hydro- gen, and oxygen. They burn with a bright flame, the proportion of oxygen being less than would be sufficient to form water with the hydrogen, or carbonic acid with the carbon, that they contain. They are all lighter than water, nearly all are fluid at the natural tempera- ture of the body, all are insoluble in water, soluble in ether and boil- ing alcohol, and most of them crystallize when deposited from solu- tion. They are nearly all of the kind named fixed oils ; none of them is what is called a drying oil, i. e., none so combines with oxygen as to form a resin-like varnish on the substance over which it is spread. The oily or fatty matter which, enclosed in minute cells, forms the essential part of the adipose or fatty tissue of the human body, and which is mingled in minute particles in many other tissues and fluids, consists of a mixture of margarine and oleine, the proportion of the former being the greater the higher the temperature at which the mixture congeals, and the firmer the mass is when concealed. GELATINOUS SUBSTANCES. 31 The animal fats, or suets, that are firmer than human fat, contain also a substance named stearine, which remains solid at or near 130° F. Margarine congeals at 120°, oleine at about 25°. Their mix- ture in human fat is a clear yellow oil, of which different specimens congeal at from 45° to 35° F. Margarine, when deposited from solution in alcohol, forms fine needle-shaped crystals; and micro- scopic tufts or balls of such crystals are often found in fat-cells after death, especially in the fat of diseased parts and old people. According to Schultze, oleine, when acted upon by sulphuric acid and sugar, assumes the same violet-red color as ensues in bile when similarly tested, while the firmer fats are not thus affected, neither are the solid vegetable fats, although vegetable oils are colored like animal oleine (lix. 1850, p. 101). Margarine and oleine, like all the fatty matters with which soaps may be made, and which are therefore named saponifiable, appear to consist of fatty acids combined with a base which is soluble in water.1 When one of these fats is long boiled with an alkali, it is decomposed : the fatty acid, which is named margaric or oleic, according to the substance employed, unites with the alkali, forming a neutral soapy substance, margarate or oleate of soda, or potash, as the case may be: and the base of the fat, a sweet syrupy substance named glycerine, remains. The fatty matter of human adipose tissue may therefore be regarded as a mixture of margarate and oleate of glycerine. Glycerine, moreover, is considered to be a hydrated oxyde of a substance called Glyceryl; and margaric acid a compound of a substance named margaryl with oxygen. The formula for mar- garine is C76H750I2; that for oleine C94Ha70,5; that for glycerine C6H706 +HO (cxi. vol. i. p. 70). Oholestearine or Cholesterine, a fatty matter which does not melt below 27*°, and is, therefore, always solid at the natural temperature of the body, may be obtained in small quantity from blood, bile, and nervous matter. It occurs abundantly in many biliary calculi; the pure white crystalline specimens of these concretions being formed of it almost exclusively. Minute rhomboidal scale-like crystals of it are also often found in morbid secretions, as in cysts, the puriform matter of softening and ulcerating tumors, etc. It is soluble in ether and boiling alcohol; but alkalies do not change it; it is one of those fatty substances which are not saponifiable. Its formula is C37H320 (lxxxii. vol. i. p. 70). The azodzed or nitrogenous principles in the human body include two chief classes of substances, namely, the gelatinous and the albu- minous. The gelatinous substances are contained in several of the tissues, especially those which servo a passive mechanical office in the econ- 1 See on this subject Mulder (lxi.), Berzelius (xxiv.), and Redtenbacher (x. Aug. 1S43). 32 CHEMICAL COMPOSITION OF HUMAN BODY. omy; as the cellular or fibro-cellular tissue in all parts of the body the tendons, ligaments, and other fibrous tissues, the cartilages and bones, the skin and serous membranes. These when boiled in water, yield a material, the solution of which remains liquid while it is hot, but becomes solid and jelly-like on cooling. Two varieties of these substances are described, gelatine and cnon- drine : the latter being derived from cartilages, the former from all the other tissues enumerated above, and, in its purest state, from isinglass, which is the swimming-bladder of the sturgeon, and which, with the exception of about 7 per cent, of its weight, is wholly redu- cible into gelatine. The most characteristic property of gelatine is that already mentioned, of its solution being liquid when warm, and solidifying or setting when it cools. The temperature at which it becomes solid, the proportion of gelatine which must be in solution, and the firmness of the jelly when formed, are various, according to the source, the quantity, and the quality of the gelatine; but, as a general rule, one part of dry gelatine dissolved in 100 of water, will become solid when cooled to 60°. The solidified jelly may be again made liquid by heating it; and the transitions from the solid to the liquid state by the alternate abstraction and addition of heat, may be repeated several times; but at length the gelatine is so far altered, and, apparently, oxydized by the process, that it no longer becomes solid on cooling. Gelatine in solutions too weak to solidify when cold, is distinguished by being precipitable with alcohol, creasote, tannic acid, and bichloride of mercury, and not precipitable with the ferrocyanide of potassium. The most delicate and striking of these tests is the tannic acid, which is conveniently supplied in an infu- sion of oak-bark or gall-nuts : it will detect one part of gelatine in 5000 of water; and if the solution of gelatine be strong it forms a singularly dense and heavy precipitate, which has been named tanno- gelatine, and is completely insoluble in water. Gelatine is also dis- tinguished from albuminous substances by assuming a yellowish- brown, instead of a red color, when tested by sulphuric acid and sugar (Schultze, lix. 1850, p. 102). When gelatine is boiled with caustic potash, or with sulphuric acid, it is decomposed, and among the products of its change are two substances named leucine and sugar of gelatine, of which the latter is remarkable for its similarity to the sugars produced from vegetable substances, and for being susceptible of crystallization (Simon, Ixxxii. vol. i. p. 33, and Prout, xxi. p. 455; see also lix. 1850, p. 96, and 1855, p. 116). Among the varieties of gelatine derived from different tissues, and from the same sources at different ages, much diversity exists as to the firmnessand other characters of the solid formed in the cooling of the solutions. The differences between isinglass, size, and "hie in these respects are familiarly known, and afford good examples of the varieties called weak and strong, or low and high, gelatines. ALBUMEN. 33 The differences are ascribed by Dr. Prout to the quantities of water combined in each case with the pure or anhydrous gelatine; and part of this water seems to be chemically combined with the gela- tine, for no artificial addition of water to glue would give it the cha- racter of size, nor would any abstraction of water from isinglass or size convert it into the hard dry substance of glue. But such a change is effected in the gradual process of nutrition of the tissues; for, as a general rule, the tissues of an old animal yield a much firmer or stronger jelly than the corresponding parts of a young ani- mal of the same species. A similar difference is observable in the leathers formed by the tanning of the skins of young and old ani- mals ; a fact which, together with the general similarity of the action of tannic acid upon skin and upon gelatine, makes it probable that gelatine is really (though some chemists hold the contrary), contained as such in the tissues from which it is obtained by boiling. The analysis of dry gelatine yields C. 5005, II. 647, N. 18-35, 0. 2513 parts in 100 : its formula is stated as C,6H18N4014 (lx. p. 509). Chondrine.—The variety of gelatine obtained from cartilages agrees with gelatine in that its solution in water solidifies on cooling, though less firmly, and is precipitable with alcohol, creasote, tannic acid,Tind bichloride of mercury. Like gelatine, also, it is distin- guished from the albuminous substances by not being precipitable with ferrocyanide of potassium; but, unlike gelatine, it is precipi- table with acetic and the mineral and other acids, and with the sulphate of alumina and potash, persulphate of iron and acetate of lead. The albuminous substances are more highly or perfectly organic, i. e., are more different from inorganic bodies than are any of the substances yet considered, or, perhaps, any in the body. The chief of them are albumen, fibrine, and caseine ; but the last being found almost exclusively in milk, will be described with that fluid. Prin- ciples essentially similar to them all are found also in vegetables, especially in the sap and fruits. And substances much resembling, though not classed with, the albuminous, are horny matter and extractive matter. In addition to the chemical properties severally manifested by albumen, fibrine, and caseine, albuminous substances generally are distinguished from the gelatinous by being changed into a violet-rod color when treated with sulphuric acid and sugar, as in Pettenkofer's test for bile. These substances indeed undergo changes in color exactly similar to those undergone by bile when exposed to this test. (Schultze, lix. 1850, p. 101.) Millon has also found that albuminous substances assume an intense red color when treated with a solution of quicksilver dissolved in an equal weight of sul- phuric acid, and four and a half parts of water. Gelatinous tissues, however, are similarly affected (xviii. vol. 28). Albumen exists in some of the tissues of the body, especially the nervous, in the lymph, chyle, and blood, and in many morbid fluids, 34 CHEMICAL COMPOSITION OF HUMAN BODY. as the serous secretions of dropsy, pus, and others. In the human body it is most abundant, and most nearly pure, in the serum of the blood. In all the forms in which it naturally occurs, it is combined with about six per cent, of fatty matter, phosphate of lime, chloride of sodium, and other saline substances. Its most characteristic pro- perty is, that both in solution, and in the half-solid state in which it exists in white of egg, it is coagulated by heat, and in thus becoming solid becomes insoluble in water. The temperature required for the coagulation of albumen is the higher the less the proportion of albu- men in the solution submitted to heat. Serum and such strong solutions will begin to coagulate at from 150° to 170°, and these, when the heat is maintained, become almost wholly solid and opaque. But weak solutions require a much higher temperature, even that of boiling, for their coagulation, and either only become milky or opaline, or produce flocculi which are precipitated.1 Albumen, in the state in which it naturally occurs, appears to be but little soluble in pure water, but is soluble in water containing a small proportion of alkali.2 In such solutions it is probably com- bined chemically with the alkali; it is precipitated from them by alcohol, ether, nitric, and other mineral acids (unless when thCT are very dilute), by ferrocyanide of potassium (if before or after adding it the alkali combined with the albumen be neutralized), by bichlo- ride of mercury, acetate of lead, and most metallic salts. These precipitates are not merely solidified albumen, but compounds of albumen, with the acid or base added to it. In the former case, the albumen takes the part of a base, as in nitrate of albumen; in the latter, it takes the part of an acid, as in albuminate of oxyde of mercury, lead, etc. The precipitates with the metallic salts are solu- ble in an excess of albumen, and in solutions of chloride of sodium and other alkaline salts; and it is, probably, by these means that the salts of iron, mercury, and other metals, taken into the blood, remain dissolved in it. Coagulated albumen, i. e., albumen made solid with heat, is soluble in solutions of caustic alkali, and in acetic acid if it be long digested or boiled with it. With the aid of heat, also, strong hydrochloric acid dissolves albumen previously coagulated, and the solution has a beautiful purple or blue color. The per-centage composition of albumen of blood, according to the experiments of Mulder (lix. 1847, p. 83), is, carbon, 53-4; hydro- gen, 7-1; nitrogen, 15-6; oxygen, 22-3; phosphorus, 0-3; sulphur, 1-3 : its formula is not yet certainly known. Fibrine exists, most abundantly, in solution in the blood and the 'For explanation of the conditions in which albumen in the urine and other fluids may not be coagulable by heat, see Dr. Bence Jones, lxxi vol. xxvii. p. 228. 2 On the mode of preparing albumen soluble in water without any addition, see Wurtz (xii. Oct. 1844). PROTEINE. 35 more perfect portions of the lymph and chyle; and in the solid state, in some part of the tissue of voluntary muscles, and occasionally in minute particles in the blood. (B. D. Thomson, xvii., April, 1846). The characteristic property of fibrine is, that in certain conditions (especially when the blood or other fluid containing it is taken from the living body), it separates from its solution, and spontaneously assumes the solid form, or coagulates.1 It is on this that the coagu- lation of the blood (a process to be further described hereafter) depends. If a common clot of blood be pressed in fine linen while a stream of water flows upon it, the whole of the blood-color is gra- dually removed, and strings and various pieces remain, of a soft, yet tough, elastic, and opaque-white substance, which consist of fibrine, impure with a mixture of fatty matter, lymph-corpuscles, shreds of the membranes of red blood-corpuscles, and some saline substances. Fibrine somewhat purer than this may be obtained by stirring blood while it coagulates, and collecting the shreds that attach themselves to the instrument, or by retarding the coagulation, and, while the red blood-corpuscles sink, collecting the fibrine unmixed with them. But in neither of these cases is the fibrine perfectly pure. Chemically, fibrine and albumen cannot be distinguished. All the changes, produced by various agents, in coagulated albumen may be repeated with coagulated fibrine, with no greater differences of result than may be reasonably ascribed to the differences in the mechanical properties of the two substances. Of such differences, the principal are that fibrine immersed in acetic acid swells up and becomes trans- parent like gelatine; while albumen undergoes no such apparent change; and that deutoxyde of hydrogen is decomposed when in contact with coagulated fibrine, but not with albumen. Proteine. It is the opinion of Mulder that animal albumen, fibrine, and caseine, and the corresponding substances derived from vegetables, are all compounds of a substance which he has named proteine, and believes to be composed of the four essential elements alone. He assigns for its composition, carbon 55, hydrogen 7 2, nitrogen 14*5, and oxygen 23-3 per cent.; and for its formula, CasHsoNgOio- Proteine may be obtained by dissolving albumen, fibrine, or caseine in a heated solution of caustic potash (the liquor potassse of the pharmacopoeia will suffice), and adding to the solution enough acetic acid to neutralize it. The proteine, being insoluble in the neutral salts, is thus precipitated, in the form of a light grey- 1 A very small quantity of fibrine may be so dissolved in serous fluid that it will not spontaneously coagulate. The fluid of common hydrocele does not of itself coagulate; but, as Dr. Buchanan (lxxi. 183G, pp. 52, and 90; 1845, p. 617) has shown, if a piece of washed clot of blood, or of muscle, or some other animal tissue be placed in it, a filmy coagulum of fibrine will form and attach itself to the substance introduced. The film has the filamentous ap- pearance of proper fibrine clot, and is not mixed with corpuscles, as that of blood-clot is. 36 CHEMICAL COMPOSITION OF HUMAN BODY. ish powdery-looking substance, whose reactions are very similar to those of coagulated albumen. Liebig, however, and Fleitmann (x. b. 61) deny the existence of any such substance as proteine, on the ground that what Mulder so called, and considered to be formed of none but the essential elements, always contains a certain quantity of sulphur, as the albumen or other substance from which it was prepared did. This question is still disputed; for since Liebig published his opinion, Mulder has repeated his own, and maintained that, though the proteine prepared as above describod does not contain sulphur, yet it is not in the form of elemental sulphur, but in that of hypo-sulphurous acid. He believes albumen, fibrine, and other principles of this group to be compounds of proteine with sulphamid and phosphamid, and that in dissolving them in potash-ley, these-compounds are decomposed with water, ammonia being formed and given off, while sulphurous and phosphorous acids combine with the proteine (lix. 1847, p. 82). The question must, as yet, be thus left; but in the doubt as to whether there be such a substance as proteine or not, we maybe jus- tified in still retaining the use of the term proteine-compounds, in speaking of the class, including fibrine, albumen, and others to which the name of albuminous compounds was originally applied.1 Horny Matter.—The substance of the horny tissues, including the hair and nails (with whale-bone, hoofs, and horns), probably con- sists, according to Mulder, of proteine with larger proportions of sulphamid than albumen and fibrine contain. Hair contains 10 per cent, and nails 6-8 per cent, of sulphamid. The composition of the latter is — c 50-1 of the former C 49-9 H 6-9 H 6-4 N 17-3 N 17-1 0 with ) 22-5 0 21.6 S 3-2 s 5-0 The horny substances, to which Simon applies the name of kera- tine, are insoluble in water, alcohol, or ether; soluble in caustic alkalies, and sulphuric, nitric, and hydrochloric acids; and not pre- cipitable from the solution in acids by ferrocyanide of potassium. Mucus, in some of its forms, is related to these horny substances, consisting, in great part, of epithelium detached from the surface of mucous membrane, and floating in a peculiar clear and viscid fluid. But, under the name of mucus, several various substances are in- cluded, of which some are morbid albuminous secretions containing mucus and pus-corpuscles, and others consist of the fluid secretion variously altered, concentrated, or diluted. But the true chemical characters of this fluid are as yet incompletely known. It is gene- «For a full and recent account of proteine compounds generally see Leli- mann's Physiological Chemistry, (Am. edit,, vol. I., pp. 290-356.) EXT P. ACTIVE MATTERS. 37 ally alkaline, and, when the cells and other corpuscles mingled with it have subsided, is a pellucid fluid, containing, according to Berze- lius, 5-33 per cent, of proper mucous matter. This is very little soluble in water; more soluble in water slightly alkaline, and from this solution is precipitated by alcohol, acetic, nitric, sulphuric, and hydrochloric acids. An excess of the last three acids redissolves the precipitates they severally throw down; and, in the acid solu- tion thus formed, ferrocyanide of potassium produces no precipitate. According to Scherer (x. b. 57), pure mucus, cleared of epithelium, and subtracting 4-1 per cent, of saline matter, contains carbon 52-17, hydrogen 7'01, nitrogen 12-64, oxygen 28-18. Extractive Matters.—Under this name are included substances of mixed and uncertain composition, which form the residue of ani- mal matter when, from almost any of the fluids or solids of the body, the albuminous, gelatinous, and fatty principles, have been removed. The remaining animal matter is mixed with various salts, such as lactates, chlorides, and phosphates, and is divisible into two principal portions, of which one is soluble in water alone, the other in alcohol. Doubtless there are in these substances many distinct compounds, of which some exist ready-formed in the body, and some are formed in the changes to which the previous chemical examinations have given rise. Some of these substances have received specific names, according to their most striking characters, as osmazome and zonii- dine, on which the principal odour and taste of cooked meat appear to depend ; or, according to their source, as ptyaline and phymatine, from the saliva and pancreatic fluid ; and part of the extractive mat- ter of the blood appears to be a proteine-compound (Ludwig, x. 1845). But the true composition, origin, and nature of all these substances are unknown. Kreatine and kreatinine, two principles which used to be included among the extractive matters of muscular tissue, have been carefully studied by Liebig (liv.), who has found them also in the urine, and has thus given additional probability to the suggestion of Berzelius, that the extractive matters are generally the products of the chemical changes that take place in the natural waste and degeneration of the tissues, and are the substances that are to be separated from the tissues for excretion. Such are the chief substances of which the human body is com- posed. They are formed mainly of the four essential elements, and exhibit all those characters which have been mentioned as peculiar to organic bodies; but with the exception of the fatty matters, and perhaps proteine, all appear to contain, besides the four elements, other elements, or even compound substances, such as phosphate of lime chloride of sodium, or other salts. And all the fluids and tis- sues of the body appear to consist, chemically speaking, of mixtures of several of these principles, together with saline matters. Thus, 4 38 CHEMICAL COMPOSITION OF HUMAN BODY. for example, a piece of muscular flesh would yield fibrine, albumen, gelatine, fatty matters, salts of soda, potash, lime, magnesia, iron, and other substances which appear passing from the organic towards the inorganic states, as kreatine and others. This mixture of sub- stances may be explained in some measure by the existence of many different structures or tissues in the muscles; the gelatine may be referred principally to the cellular tissue between the fibres, the fatty matter to the adipose tissue in the same position, and part of the albumen to the blood and the fluid by which the tissue is kept moist. But, beyond these general statements, little can be said of the mode in which the chemical compounds are united to form an organized structure; or of how, in any organic body, the several inorganic and incidental substances are combined with those that are organic and essential. It must suffice, therefore, to mention the several parts in which each of the incidental elements and of their principal com- pounds occurs. Sulphur' is, probably, next to the essential ones, the most nearly constant element in organic compounds. It exists in albumen, fibrine, caseine, and gelatine, combined in all these, probably in the elemental state, with the other elements. In largest proportion it is found in taurine, one of the products of the decomposition of biliary matter, and in the morbid product, cystic oxyde: of both these it constitutes about 25 per cent. Among the tissues, and independent of the compounds above-named as containing it, sulphur is most abundant in the hair, cuticle, nails, and other horny tissues, and, according to Lassaigne (lv. Aug. 22, 1843), in fibrous and mucous membranes. Of the compounds of sulphur none are known to exist naturally, except the sulphocyanide of potassium in saliva, and the alkaline sulphates in the urine and sweat. The acid of the sulphates found in the ashes of other animal substances are formed during the burning, through the elemental sulphur combining with oxygen. Phosphorus is found together with sulphur, and probably similarly combined as an element, in albumen and fibrine, but not in caseine. It exists also in some tissues, especially in the substance of the brain, from which two fatty acids, containing phosphorus, and named olco- phosphoric and cerebric acid, have been obtained; but, most abun- dantly, it occurs as phosphoric acid in combination with alkaline and earthy bases — as in the tribasic phosphate of soda in the blood and saliva, the super-phosphates of the muscles and urine, the basic phosphate of lime and magnesia in the bones and teeth. Such phos- phates are also found in the ashes of nearly all burnt animal sub- stances, even in tissues so simple that one must assume the phosphate to be a necessary constituent of the substance of the primary cell; for it is probable that these phosphates exist in the tissues ready formed, lOn the quantity of sulphur in different animal substances, see Ruling and others in Liebig's Annalen der Chemie und Pharmacie, Bd. lviii., andCan- statt's Jahresbericht for 1846, p. 90 SILICON, CHLORINE, FLUORINE. 39 as they do in caseine, and that they are not, like the sulphates, found in the ashes of animal matters, produced in the combustion. Silicon.—A very small quantity of silica exists, according to Ber- zelius, in the urine, and, according to Henneberg (x. Bd. 41) and E. Millon (xviii. 1848), in the blood. Traces of it have also been found in bones by V. Bibra, in hair by Van Laer, and in some other parts of the body (lxv. p. 65). Chlorine is abundant in combination with sodium, potassium, am- monium, and other bases in all parts, fluids as well as solid, of the body. Chloride of sodium (common salt) is, indeed, probably the most abundant of all the inorganic compounds in organized bodies. It is also not improbable that chlorine may exist in the gastric fluid in the form of hydrochloric acid, either free or in combination with an organic principle (Schmidt, lix. 1847, p. 102). Fluorine.—After the observations of Berzelius had been much questioned, on which the existence of minute quantities of fluoride of calcium in the bones, teeth, and urine was admitted, they have been fully confirmed by Dr. Daubeny and Mr. Middleton (lxiii. vol. ii. pp. 07, 134), and more recently by Von Bibra (lxiv). The salt is found in the ashes of all bones and teeth; and increased in quan- tity in fossil bones. Potassium and sodium are constituents of the blood and all the fluids, in various quantities and proportions. They exist in the form of chlorides, sulphates, and phosphates, and probably, also, in com- bination with albumen, or certain organic acids. Liebig, in his work on the Chemistry of Food, has shown that the juice expressed from muscular flesh always contains a much larger proportion of potash-salts than of soda-salts; while in the blood and other fluids, except the milk, the latter salts always preponderate over the for- mer ; so that, for example, for every 100 parts of soda-salts in the blood of the chicken, ox, and horse, there are only 40-8, 5-9, and 9-5 parts of potash-salts; but for every 100 parts of soda-salts in their muscles there are 381, 279, and 285 parts of potash-salts. Calcium.—The salts of lime (oxide of calcium) are by far the most abundant of the earthy salts found in the human body. They exist in the lymph, chyle, and blood in combination with phosphoric acid, the phosphate of lime being probably held in solution by the presence of phosphate of soda. Perhaps no tissue is wholly void of phosphate of lime; but its especial seats are the bones and teeth, in which, together with carbonate and fluate of lime, it is deposited in minute granules, in a peculiar compound, named bone-earth, and containing 5155 parts of lime, and 48-45 of phosphoric acid. Phosphate of lime, probably the tribasic phosphate, is also found in the saliva, milk, bile, and most other secretions, and superphosphate in the urine, and probably in the gastric fluid. (Blondlot, xvi.) Magnesium appears to be always associated with calcium, and probably exists in the same forms as it; but its proportion is always 40 CHEMICAL COMPOSITION OF HUMAN BODY. much smaller, except in the juice expressed from muscles, in the ashes of which magnesia preponderates over lime. (Liebig, liv.) Jr0n%—The especial place of iron is in the hsematosine, the color- ing-matter of the blood, of which a further account will be given with the chemistry of the blood. Peroxyde of iron is found, in very small quantities, in the ashes of bones, muscles, and many tissues, and of lymph and chyle, albumen of serum, fibrine, bile, and other fluids; and a salt of iron, probably a phosphate, exists in consider- able quantity in the hair, black pigment, and other deeply colored epithelial or horny substances. Manganesium.—Vauquelin believed he found a trace of the per- oxyde of this metal in the ashes of hair and bones; but in the more accurate analysis of the former substance by V. Laer, and of the latter by V. Bibra, no mention of manganesium is made. It has been detected in gall-stones (lxxxii. vol. 1., p. 15). According to M. E. Millon (xviii. 1848), it exists naturally in blood: and M. Burin du Buisson (clx. Fevrier, 1852) confirms this observation, and states his belief that it belongs solely to the corpuscles, and not to the serum. Glenard, however, believes that it is an accidental and not a constant ingredient in the blood (lix. 1855, p. 112.) Aluminium also is stated (Henle, xxxvii. p. 4) to exist in the ashes of hair, bones, and enamel; but neither V. Laer nor V. Bibra mentions it. Copper.—After long disputes, the general existence of copper in the human liver may be regarded as proved by the experiments of Orfila, Heller, and others. It exists in especially large quantity in dark biliary calculi, and we may probably assume that it does not enter into the proper permanent substance of the liver, but is con- tained in the bile, within the bile-cells and ducts, and is destined with it to be excreted. It is true, that Harless and V. Bibra have found it constantly present in the blood, as well as in the liver, of many mollusca and fish : and that in their blood it takes the place of some proportion of the iron contained in the blood of other spe- cies, and may be regarded as a normal, necessary constituent; yet, it seems most likely that, in the human body, both copper, mangane- sium, and aluminium should be regarded as accidented elements, which, being taken in minute quantities with the food, and not ex- creted at once with the faeces, are absorbed and deposited in some tissue or organ, of which, however, they form no necessary part. In the same manner arsenic and lead, being absorbed, may be deposited in the liver and other parts. This view is confirmed by the fact ob- served by Heller, that although copper is frequently present in the bile of adults, yet it is never found in that of infants (ix. vol. ii. p. 321). The researches of Cattanei di Momo also seemed to prove that neither copper nor lead exists in the bodies of new-born children or infants (xxv. 1843-4, p. 3).1 [! In the Annales d'Hygiene publique et de me'decine legale, (t. 42, 1849) the student will find an excellent historical resume' by Chevalier and Cotte- reau, of the metallic substances found in organized bodies.] GRANULES. 41 CHAPTER II. STRUCTURAL COMPOSITION 6F THE HUMAN BODY. The component substances of the body are commonly divided into fluids and solids. The fluids are, 1st, formative fluids, from which are derived the materials for the formation of the solid tissues; and, 2d, secreted fluids, which are separated from the tissues and the blood, through, speaking generally, the operation of special organs, such as cells ar- ranged in glands or membranes. So little can be said that would apply to all the members of either of these classes of the fluids, that a general description of them would be useless; they will therefore be considered in their several more appropriate place.—[See chapters on Blood, Lymph, Chylk, the several Secretions, etc.] Among the solids of the body, some appear, even with the help of the best microscopic apparatus, perfectly uniform and simple; they show no trace of structure, i. e., of being composed of definitely arranged dissimilar parts. These are named simple, structureless, or amorphous solids. Such are the apparently structureless mass com- posing the albumen of eggs, and the substance called cytoblastema, or formative substance, in which the nuclei and cells are imbedded in many tissues in progress of development. Such also is the sim- ple membrane which forms the walls of most primary cells, of the finest capillary blood-vessels and gland-ducts, and of the sarcolemma of muscular fibre; and such the membrane enveloping the vitreous humor of the eye. Such also, having a dimly granular appearance, but no really granular structure, is the intercellular substance of the most perfect cartilage. In the solids which present determinate structure, certain primary forms may be distinguished, which, by their various modifications and modes of combination make up the tissues and organs of the body. Such are, 1. Granules or molecules, the simplest and minutest of the primary forms. They are particles of various size, from immeasurable minuteness to the 10,000th of an inch in diame- ter ; of various and generally uncertain composition, but usually so affecting light transmitted through them, that at different focal dis- tances their centre, or margin, or whole substance, appears black. From this character, as well as from their low specific gravity (for in microscopic examinations they always appear lighter than water), and from their solubility in ether when they can be favorably tested, it is probable that most granules are formed of fatty or oily matter; or, since they do not coalesce as minute drops of oil would, that they are particles of oil coated over with albumen deposited on them from 42 STRUCTURAL COMPOSITION OF HUMAN BODY. the fluid in which they float. (See Ascherson, lxxx. 1848). In any fluid that is not too viscid, they exhibit the phenomenon of molecular motion, shaking and vibrating incessantly, and sometimes moving through the fluid, under the influence of some unknown force. Granules are either free, as in milk, chyle, milky serum, yelk- substance, and most tissues containing cells with granules; or en- closed, as are the granules in nerve-corpuscles, gland-cells, and epi- thelium-cells, the pigment granules in the pigmentum nigrum and medullary substance of the hair; or imbedded, as are the granules of phosphate and carbonate of lime in bones and teeth. 2. Nuclei, or cytoblasts, appear to be the simplest elementary structures, next to granules. They were thus named in accordance with the hypothesis that they are always connected with cells, or tissues formed from cells, and that in the development of cells, each nucleus is the germ or centre around which the cell is formed. The hypothesis is only partially true, but the terms based on it are too familiarly accepted to make it advisable to change them till some more exact and comprehensive hypothesis is formed. Of the corpuscles called nuclei, or cytoblasts, the greater part are minute cellules or vesicles, with walls formed of simple membrane, enclosing a colorless pellucid fluid, and often one or more particles, like minute granules, called nucleus-corpuscles, or nucleoli. Such vesicular nuclei, without nucleoli, are those of the blood-corpuscles of oviparous vertebrate animals (Figs. 1 and 2 ); and such, with nu- Fig. 1. Fig. 2. *......ol Fig. 1. Corpuscles of human blood, magnified about 500 diameters.—(1) Single pp.rticles. 1,1. Their flattened face. 2. A particle seen edgewise. (2) Aggregation of particles in a columnar form. Fig. 2. Red particles of the blood of the common fowl. a. Ordinary appearance when the flat surface is turned towards the eye; 6, appearance which is sometimes presented by the particle when in the same position, and which suggests the idea of a furrow surrounding the central nucleus; c, d, different appearances of the particles when seen edgewise. cleoli, are those of epithelium-cells and pigment-cells. But some nuclei appear to be formed of an aggregate of granules imbedded in a pellucid substance, as, for examples, the nuclei of the lymph and chyle-corpuscles. The composition of the nucleus is uncertain. One of its most general characters, and the most useful in microscopic examinations, is, that it is neither dissolved nor made transparent by acetic acid, NUCLEI: FREE AND ATTACHED. 43 but acquires, when that fluid is in contact with it, a darker and more distinct outline. Nuclei may be either free or attached. Free nuclei are such as either float in fluid, like those in the gastric juice, which appear to be derived from the secreting cells of the gastric glands, or lie loosely imbedded in solid substance, as in the grey matter of the brain and spinal cord, and most abundantly in some quickly-growing tumours. Attached nuclei are either closely imbedded in homogeneous pellucid substance, as in rudimental cellular tissue; or are fixed on the surface of fibres, as on those of organic muscle (Fig. 3) and organic nerve-fibres; or are enclosed in cells, or in tissues formed by the extension or junction of cells. Nu- clei enclosed in cells appear to be attached to the inner surface of the cell-wall, projecting into the cavity. Their position in relation to the cen- tre or axis of the cell is uncertain; often, when the cell lies on a flat or broad surface, they appear central, as in blood-corpuscles, epithelium- cells, whether tesselated or cylindri- cal ; but, perhaps, more often their position has no regular relation to the centre of the cell. In most in- stances, each cell contains only a single nucleus; but in cartilage, es- pecially when it is growing or ossi- fying, two or more nuclei in each cell are common; and the develop- ment of new cells is often effected by a division or multiplication of nuclei in the cavity of a parent cell; as in biood-cells, the germinal vesi- cle, and others. When cells extend and coalesce, so that their walls form tubes or sheaths, the nuclei commonly remain attached to the inner surface of the wall. Thus they are seen imbedded in the wall of the minutest capillary blood-vessels of, for example, the retina and brain; in the sarcolemma of transversely striated muscular fibres; and in minute gland-tubes. In such cases their arrangement may be irregular, as in the capillaries; or regular, as in the single or alternating double rows of nuclei in different examples of the muscular fibre. Nuclei are most commonly oval or round, and do not generally conform themselves to the diverse shapes that the cells assume; they Fibres of unstriped muscle: c. In their natural state, a. Treated with acetic acid, showing the corpuscles, b. Cor- puscles, or nuclei, detached, showing their various appearances. 44 STRUCTURAL COMPOSITION OF HUMAN BODY. are, altogether, less variable elements, even in regard to size, than the cells are; of which fact one may see a good example in the uni- formity of the nuclei in cells so multiform as those of epithelium. But sometimes they appear to be developed into filaments, elongating themselves and becoming solid, and uniting end to end for greater length, or by lateral branches to form a network. So, according to Henle (xxxvii. p. 194), are formed the filaments of the striated and fenestrated coats of arteries, and the yellow or elastic filaments that are mingled with the common filaments of cellular tissue, and with organic muscular fibre, especially in the walls of arteries. The fila- ments of the cortical substance of hair, and the seminal filaments, or spermatozoids, appear to be also elongated and divided nuclei. Cells, Primary cells, or Elementary cells, are vesicles or scales of larger average size than nuclei, but, like them, composed, in the normal state, of membranous cell-walls, with, usually, liquid contents, and generally round or oval (Fig. 4). The cell-wall never presents any appearance of structure: it ap- pears sometimes to be a proteine-substance, as F'g- 4-_____in blood-cells; sometimes a horny matter, as in thick and dried cuticle. In almost all cases (the dry cells of horny tissue, perhaps, alone excepted) the cell-wall is made transparent by acetic acid, which also penetrates through it and distends it, so that it can hardly be dis- cerned. But in such cases the cell-wall is usually not dissolved ; it may be brought into view again by nearly neutralizing the acid Primary organic Cell, show- ^{fa g0(Ja or potash. ing the cell-membrane, the t • i. j.t_ j. j 1 j a x nucleus, and the nucleolus. „In s°me ""stances, the most developed state of a cell is that in which it has no nucleus, as in the mammalian blood-corpuscles, in which, as will be described, the substance of the nucleus of the lymph or chyle-corpuscle is gradually all appropriated and changed to the contents of the blood- corpuscle. But, in other instances, especially in old cells, as in those of the nails, the outer layers of epidermis, and the adipose tissue, the nucleus may disappear, wasting away; and this is, probably, always a sign of degeneration of the tissue,for a similar wasting of nuclei is commonly observed in all tissues in the state of fatty degeneration. With the exceptions just mentioned, all the cells of the human body appear to contain nuclei. Sometimes the nucleus nearly fills the cavity of the cell, as in lymph and chyle-corpuscles, in which the cell-wall lies so close round the nucleus, that it can hardly be seen till it is raised up by water or acetic acid insinuating itself be- tween it and the nucleus; and such is the proportion between the nucleus and cell in young epidermis-cells; but more often the nuc- SHAPE AND CONTENTS OF CELLS. 45 leus has a diameter from one-fourth to one-tenth less than that of the cell (Fig. 5). The simplest shape of cells, and that which is probably the normal Fig- 5< shape of the primary cell, is oval , g * g. or spheroidal, as in cartilage-cells «J and lymph-corpuscles; but in many instances they are flattened and dis* P1,an "*"»****« the formation of a .. k . . , . nucleus, and of a cell on the nucleus, ac- COld, as in the blood-COrpuSCles, or mrting to Schleiden's view. scale-like, as in epidermis and tes- selated epithelium. By mutual pressure they may become many- sided, as the pigment cells of the choroidal pigmentum nigrum and in close-textured adipose tissue; they may assume a conical or cylin- driform or prismatic shape, as in the varieties of cylinder-epithelium and the enamel-tubes; or be caudate, as in certain bodies in the spleen; they may send out exceedingly fine processes in the form of vibratile cilia, or larger processes, with which they become stellate, or variously caudate, as in the large nerve, or ganglion-corpuscles, and the epithelium of the choroid plexuses. The contents of cells, including under this term all but their nuclei, are almost infinitely various, according to the position, office, and ago of the cell. In adipose tissue they are the oily matter of the fat, the mixture of margarine and oleine; in gland-cells the contents are the proper substance of the secretion, bile, semen, etc., as the case may be; in pigment-cells they are the pigment granules that give the color; and in the numerous instances in which the cell-contents can be neither seen because they are pellucid, nor tested because of their minute quantity, they are yet, probably, peculiar in each tissue, and constitute the greater part of the proper substance of each. Commonly, when the contents are pellucid, they contain granules which float in them; and when water is added and the contents are diluted, the granules display an active molecular movement within the cavity of the cell. Such a movement may be seen by adding water to m-ucus, or pus-corpuscles, or to those of Lymph. In a few eases the whole cavity of the cell is filled with granules : it is so in yelk-cells and milk-corpuscles, in the large diseased corpuscles often found among the products of inflammation, and in some cells when they are the seat of extreme fatty degeneration. The peculiar con- tents of cells may be often observed to accumulate first around or directly over the nuclei, as in the cells of black pigment, in those me- lanotic tumours, and in those of the liver during the retention of bile. Intercelhdar substance is the material in which, in certain tissues, the cells are imbedded. Its quantity is very variable. In the finer epithelia, especially the columnar epithelium on the mucous mem- brane of the intestines, it can be just seen filling the interstices of the close-set cells; here it has no appearance of structure. In car- tilage and bone it forms a large portion of the whole substance of 46 STRUCTURAL COMPOSITION OF HUMAN BODY. the tissue, and is either homogeneous and finely granular, or osseous, or, as in fibro-cartilage, resembles tough tendinous tissue. In some cases, the cells are very loosely connected with the intercellular sub- stance, and may be nearly separated from it, as in fibro-cartilage; but in some their walls seem amalgamated with it. The foregoing may be regarded as the simplest, and the nearest to the primary, forms assumed in the organization of animal matter; as the state into which it passes in becoming a solid tissue, living or capable of life. By the further development of tissue thus far organized, according to rules which will be hereafter described, higher or secondary forms are produced, which it will be sufficient in this place merely to enumerate. Such are, 4, Filaments, or fibrils.— Threads of exceeding fineness, from ^o^ulA of an incn uPwards. Such filaments are either cylindriform, as are those of the striated muscular (Figs. 6 and 7) and the fibro-cellular or areolar tissue (Figs. 8 and 9; or flattened, as are those of the organic muscles (Fig. 3), the common elastic tissues (Figs. 10 and 11), and the finer variety of the same tissue, which is commonly associated with the proper white filaments of the fibro-cellular tissue. Filaments usually lie in parallel fasciculi, as in muscular and tendinous tissues; but in some instances are matted or reticular, with branches and intercommunications, as are the filaments of the middle coat, and of the longitudinally-fibrous coat of arteries; and in other instances, are spirally wound, or very tortuous, as in the common fibro-cellular tissue. Fig. 6. Musoular fibre of animal life (magnified 5 diameters), a. Small portion, natural size. b. Same, magnified 5 diameters, or larger and smaller fasciculi, seen in transverse section. Fig. 7. Portion of broken muscular fibre of animal life (magnified about 700 diameters.) 5. Fibres, in the instances to which the name is commonly ap- plied, are larger than filaments or fibrils, but are by no essential TUBULES. 47 general character distinguished from them. The flattened band-like fibres of the coarser varieties of organic muscles and elastic tissue are the simplest examples of this form; the toothed fibres of the crystalline lens are more complex; and more compound, so as hardly to permit of being classed as elementary forms, are the striated mus- cular fibres, which consist of bundles of filaments inclosed in sepa- rate membranous sheaths, and the cerebro-spinal nerve-fibres in which similar sheaths inclose apparently two varieties of nerve- substance. 6. Tubules are formed of simple membrane, such as the minute capillary lymph and blood-vessels, the investing sheaths of striated muscular and cerebro-spinal nerve-fibres, and the basement membrane or proper wall of the fine ducts of secreting-glands. Fig. 8. Fig. 9. Fig. 8. Fasciculi and fibres of cellular tissue.—The two erements of Areolar tissue, in their natural relations to one another; 1, the white fibrous element, with cell nuclei; 9, sparingly visible in it; 2, the yellow fibrous element, showing the branching or anastomosing character of its fibrillse; 3, fibrillse of the yellow element, far finer than the rest, but having a similar curly character; 8, nucleated cell-nuclei, often seen apparently loose.—From the areolar tissue under the pectoral muscle, magnified 320 diameters. Fig. 9. Development of the Areolar tissue (white fibrous element); 4, nucleated cells, of a rounded form; 5, 6, 7, the same, elongated in different degrees, and branching. At 7, the elongated extremities have joined others, and are already assuming a distinctly fibrous tissue character. (After Schwann.) Most of the tissues which are composed of these primary struc- tures will be briefly described in future chapters, and in connection 48 VITAL PROPERTIES OF ORGANS AND TISSUES. with the physiology of the organs that they help to form. The in- sertion of a system of general anatomy would not further the pur- pose of this work; and would be superfluous while the student has access to such admirable works devoted to the subject as the Intro- duction to Quain's Anatomy, by Dr. Sharpey; the Physiological Anatomy of Dr. Todd and Mr. Bowman; Kblliker's Manual of Human Histology, translated for the Sydenham Society; the Micro- scopic Anatomy of the Human Body, by Dr. Hassall, and the various articles on the tissues published in the Cyclopaedia of Anatomy and Physiology. Fig. 10. Fig. 11. Fig. 10. Fibres of Mastic issue from the ligamentum flavum of the vertebras. (Magnified d20 diameters.) Fig. 11. Portion of whit* fibrous tissue, magnified 320 diameters; 1, 2, straight appearance of the tissue when stretched; 3, 4, 5, various wavy appearances which the tissue exhibits when not stretched. CHAPTER III. VITAL PROPERTIES OP THE ORGANS AND TISSUES OP THE HUMAN BODY. Some of the actions observed in living bodies indicate the opera- tion of other properties and forces besides those which can be refer- red to the chemical and mechanical constitution of organized sub- stances. These properties being the sources of phenomena which are peculiar to living beings, are named vital properties; the forces DEVELOPMENT, GROWTH, ASSIMILATION. 49 issuing from them, vital forces ; the acts in which they are expressed, such as those enumerated at p. 25, are vital acts or vital processes ; and the state in which these processes are displayed is life. 1. The most general, perhaps an universal, property of living bodies, is that which is manifested in the ability to form themselves out of materials dissimilar from them; as when, for example, the ovule develops itself from the nutriment of the fluids of the parent, —or when a plant, or any part of one, grows by appropriating the elements of water, carbonic acid, and ammonia,—or when an animal subsists on vegetables, and its blood and various organs are formed from the materials of its food. The force which is manifested in these acts is termed formative force (assimilative, or plastic force); and the processes effected by it are named assimilative, nutritive, or formr ordinary cases, however, it may be held that the expired air is saturated with watery vapour, and hence is derivable a means of estimating the quantity exhaled in any given time : namely, by sub- tracting the quantity contained in the air inspired from the quantity which (at the same barometric pressure) would saturate the same air at the temperature of expiration, which is ordinarily about 99°. And, on the other hand, if the quantity of watery vapour in the ex- pired air be estimated, the quantity of air itself may from it be de- termined, being as much as that quantity of watery vapour would saturate at the ascertained temperature and barometric pressure. The quantity of water exhaled from the lungs in twenty-four hours ranges (according to the various modifying circumstances already mentioned) from about 3000 to 13,000 grains (6 to 27 ounces). Some of this is probably formed by the combination of the excess of oxygen absorbed in the lungs with the hydrogen of the blood; but the far larger proportion of it must be the mere exhalation of the water of the blood, taking place from the surfaces of the air-passages and cells, as it does from the free surfaces of all moist animal mem- branes, particularly at the high temperature of warm-blooded animals. It is exhaled from the lungs whatever be the gas respired, continuing to be expelled even in hydrogen gas. Changes produced in the Blood by Respiration. The most obvious change which the blood undergoes in its pas- sage through the lungs is that of color, the dark crimson of venous blood being exchanged for the bright scarlet of arterial blood. The circumstances whicb have been supposed to give rise to this change, the conditions capable of effecting it independent of respiration, and some other differences between arterial and venous blood, were dis- cussed in the chapter on Blood (page 69). The change in color is, indeed, the most striking, and may appear the most important, which the blood undergoes in its passage through the lungs; yet, perhaps, its importance is very little, except so far as it is an indication of other and essential alterations effected in the composition of the blood. Of these alterations the priucipal are, 1st, that the blood, after passing through the lungs, is 1° or 2° warmer than it was be- fore ; 2d, that it coagulates sooner and more firmly, and contains, apparently, more fibrine; 3d, that it contains more oxygen, less carbonic acid, and less nitrogen. The difference last named is, probably, the most important. It 154 RESPIRATION. might be assumed, from what has been said of the changes in the inspired air, and it is proved, at least in regard to the first two gases, by examination of the blood itself. The existence of carbonic acid in both arterial and venous blood has been proved by several experimenters, who have obtained appre- ciable, quantities of it by exposing the blood to the vacuum of the air-pump, or, more certainly, by agitating it with atmospheric air, oxygen, or other gases, such as hydrogen or nitrogen. By the lat- ter process carbonic acid may always be extracted from venous blood. Some, indeed, have failed to procure any gas from blood by means of the air-pump; but this may be explained by the fact observed by Magnus, that carbonic acid is not given out until the air in which the blood is placed is so rarefied that it supports only one inch of mercury. Heat, also, commonly fails to evolve carbonic acid from blood; probably because, as also observed by Magnus, a tempera- ture high enough to set free this gas coagulates the albumen of the blood, and if albumen, impregnated with carbonic acid, is once coagulated, the gas cannot be separated from it again by means of heat. The uncertainty of former experiments is corrected by the more recent researches of Magnus (xvii. 1845), from which it appears sure that carbonic acid, oxygen, and nitrogen exist, both in arterial and venous blood. Their relative proportions differ in the two kinds of blood. The quantity of oxygen contained in arterial blood is twice as great as that in venous blood: being equal to from 10 to 10^ per cent, of the volume of the former, and only about 5 per cent, of the volume of the latter. The quantity of carbonic acid, on the other hand, is less in arterial than in venous blood, amount- ing to about 20 volumes per cent, in the former, and 25 per cent, in the latter. The quantity of nitrogen contained in the blood varies from about 1-7 to 3-3 per cent. : its relative proportion in arterial and in venous blood does not appear* to differ much; but from its being commonly exhaled in small quantity from the lungs, it may be believed to be greater in the venous blood. These facts are supported by those already mentioned, concerning the exhalation of nitrogen by animals breathing in oxygen and hy- drogen, and of carbonic acid by frogs breathing in nitrogen. The gases could not be so exhaled did they not exist in solution in the blood. And there can therefore be little doubt which of the pro- posed theories of respiration should be chosen for the explanation of the process. Till the existence of the gases in the blood was clearly proved, the theory most favored was, that the oxygen of the atmo- spheric air permeates the membranous walls of the air-cells, enters the blood, and there at once combines with carbon derived from the disintegrated tissues, to form carbonic acid, which escapes, together with the greater part of the nitrogen previously absorbed from the atmosphere. It could be well objected, even when the existence of CHANGES DURING RESPIRATION. 155 gases in the blood was doubtful, that if this theory were true, the lungs ought to be much warmer than other parts of the body, through the quantity of heat given out in the quick union of the carbon with the oxygen of the atmosphere; and that such was not found to be the case : the temperature of blood in the left side of the heart being never more than one or two degrees higher than that in the right. Lagrange and Hassenfratz (xxxii. p. 350), impressed with this and other objections, proposed the theory which, with some modifi- cations, has been more recently advocated by Magnus and others, and has been shown by them to be sufficient for the explanation of most of the phenomena yet observed in this part of the respiratory process. According to this theory, the oxygen absorbed into the blood from the atmospheric air in the lungs, is in part dissolved, and probably, also, in part loosely combined chemically with one or other of its ingredients. In this condition, the oxygen is carried in the arterial blood to the various parts of the body, and with it, is, in the capillary system of vessels, brought into near relation or contact with the elementary parts of the tissues. Herein, co-operating pro- bably in the process of nutrition, or the removal of disintegrated parts of the tissues, about one-half of the oxygen which the arterial blood contains disappears, and a proportionate quantity of carbonic acid and water is formed. The venous blood, containing the new formed carbonic acid, returns to the lungs, where a portion of the carbonic acid is exbaled, and a fresh supply of oxygen is again taken in. Whether part, or the whole, of the oxygen absorbed during respi- ration, is at once united chemically with any of the constituents of the blood has not been determined. By some it is supposed to com- bine with the red corpuscles, by others with the fibrine. It appears most probable that the greater part of the gas is held in solution by the fluid part of the blood : if combined, it must be very loosely so, till it reaches the capillaries. The same may be said with respect to the carbonic acid. Some recent researches by Dr. Harley (cxxiii. 1856, p. 78) seem to render necessary a slight modification of this theory, since they tend to show that, although no doubt much, yet not all of the oxygen absorbed at the lungs is conveyed to the tissues and organs of the body, a portion appearing to enter at once into chemical combination with some of the organic constituents of the blood, perhaps, as Dr. Harley believes, the coloring matter of the corpuscles, and thus pro- ducing part of the carbonic acid exhaled in expiration. How the exchange of the gases is effected has been already con- sidered ; if the diffusion theory be not received, we must suppose the emission and imbibition to be effected after the plan of the secre- tion and absorption of fluids by other organs; a supposition which 156 RESPIRATION. is favored by the close analogy in structure between the lungs and the secreting glands. Influence of the Nervous System in Respiration. The respiratory functions are in two respects subject to the influ- ence of the nervous system : namely, 1st,.in the movements for the introduction and exit of air; and, 2dly, in the interchange _of the o-ases. These will be more particularly considered in the sections on the Medulla Oblongata and Pneumogastric Nerves. It may suffice to state here, that the respiratory movements, and their regu- lar rhythm, so far as they are involuntary and independent of con- sciousness (as in all ordinary occasions they are), are under the abso- lute governance of the medulla oblongata, which, as a nervous centre, receives the impression of the "necessity of breathing," and reflects it to the phrenic and such other motor nerves as will bring into co- ordinate and adapted action, the muscles necessary to inspiration. But the respiratory movements may be voluntarily performed or variously directed; and the mind may be conscious of the necessity of breathing, either when it attends to the sensations to which that necessity gives rise, or when those sensations are more than com- monly intense. In these cases, we may believe that the brain, as well as the medulla oblongata, is engaged in the process; for we have no evidence of the mind exercising either perception or will through any other organ than the brain. But even when the brain is thus in action, it appears to be the medulla oblongata which combines the several respiratory muscles to act together. In such acts, for exam- ple, as those of coughing and sneezing, the mind must first perceive the irritation at the larynx or nose, and exercise a certain degree of will in determining the actions, as, e. g., in the taking of the deep inspiration that always precedes them. But the mode in which the acts are performed, and the combination of muscles to effect them, are determined by the medulla oblongata, independent of the will, and have the peculiar character of reflex involuntary movements, in being always, and without practice or experience, precisely adapted to the end or purpose. In these, and in all the other extraordinary respiratory actions, such as are seen in dyspnoea, or in straining, yawning, hiccough, and others, the medulla oblongata brings into adapted combination of action many other muscles besides those commonly exerted in re- spiration. Almost all the muscles of the,body, in violent efforts of dyspnoea, coughing, and the like, may be brought into action at once, or in quick succession; but, more particularly, the muscles of the larynx, face, scapula, spine, and abdomen, co-operate in these efforts with the muscles of the chest. These, therefore, are often classed as secondary muscles of respiration; and the nerves supply- ing them, including, especially, the facial, pneumogastric, spinal accessory, and external respiratory nerves, were classed by Sir EFFECTS OF SUSPENDED RESPIRATION. 157 Charles Bell with the phrenic, as the respiratory system of nerves. There appears, however, no propriety in making a separate system of these nerves, since their mode of action is not peculiar, and many besides them co-operate in the respiratory acts. That which is pecu- liar in the nervous influence directing the extraordinary movements of respiration is, that so many nerves are combined towards one pur- pose by the power of a distinct nervous centre, the medulla oblon- gata. In other than respiratory movements, these nerves may act singly or together, without the medulla oblongata; but, after it is destroyed, no movement adapted to respiration can be performed by any of the muscles, even though the part of the spinal cord from which they arise be perfect. The phrenic nerves, for example, are unable to excite respiratory movements of the diaphragm when their connection with the medulla oblongata is cut off, though their con- nection with the spinal cord may be uninjured. The influence exercised through the pneumogastric nerves upon the^ functions of the lungs, cannot be considered separately from their relation to the muscles of the larynx, and must therefore be deferred to the section particularly treating of the nerves. Effects of the Suspension and Arrest of Respiration. These deserve some consideration because of the illustration which they afford of the nature of the normal processes of respiration and circulation. When the process of respiration is stopped, either by arresting the respiratory movements, or permitting them to continue in an atmosphere deprived of uncombincd oxygen, the circulation of blood through the lungs is retarded, and, at length, stopped. The immediate effect of such retarded circulation is an obstruction to the exit of blood from the right ventricle : this is followed by delay in the return of venous blood to the heart; and to this succeeds venous congestion of the nervous centres and all the other organs of the body. In such retardation, also, an unusually small supply of blood is transmitted through the lungs to the left side of the heart; and this small quantity is venous. The condition, then, in which a suffocated, or asphyxiated, animal dies is, commonly, that the left side of the heart is nearly empty, while the lungs, right side of the heart, and other organs, are gorged with venous blood. To this condition many things contribute. 1st. The obstructed passage of blood through the lungs, which appears to be the first of the events leading to suffocation, seems to depend on the cessation of the interchange of gases, as if blood charged with carbonic acid could not pass freely through the pulmonary capilla- ries. That such may be the case, is shown by Mr. Wharton Jones's observation, that the circulation in the web of the frog's foot may be retarded or arrested by directing on the web a stream of carbonic acid, under the influence of which the blood-corpuscles appear to 158 RESPIRATION. cluster and stagnate in the vessels. But the stagnation of blood in the pulmonory capillaries would not perhaps be enough to stop en- tirely the circulation, unless the actions of the heart were also weak- ened ; for Mr. Erichsen (xciv. vol. lxiii. p. 22), having pithed dogs, and tied the right bronchus, and maintained artificial respiration in the left lung,"found that, so long as the heart's action continued, black blood still flowed through a right pulmonary vein, though less freely than red blood through a left one. Therefore, 2dly, the fatal result is due, in some measure, to the weakened action of the right side of the heart, in consequence, pro- bably, of its over-distension by blood continually flowing into it, this flow probably being much increased by the powerful but fruitless efforts continually made at inspiration (Eccles. lxxi., vol. xliv., p 657). Thirdly, because of the obstruction at the right side of the heart, there must be venous congestion in the medulla oblongata and ner- vous centres: and this evil is augmented by the left ventricle re- ceiving and propelling none but venous blood. Hence, slowness and disorder of the respiratory movements and the movements of the heart may be added. But this alone does not explain asphyxia; for Mr. Erichsen found that a dog was asphyxiated in the ordinary time, although arterial blood was made to circulate through the ner- vous centres during the whole time. However, under all these con- ditions combined, the heart at length ceases to act. The time at which the complete cessation ensues is uncertain. The domestic mammalia usually perish, after submersion in water, in about three minutes : there are exceptional cases, in which animals and human beings have been revived after being under water for a longer pe- riod. According to Mr. Erichsen (1. c. p. 30), in dogs suffocated by drowning, the voluntary movement ceases in If minutes; the involuntary in 2j after submersion; the ventricular contractions continue for a period ranging from 6 J to 14 minutes, the average time being 9} minutes; and the blood in the arteries becomes as black as that in the veins in about 1£ minutes. In the human sub- ject, he thinks that the ventricular contractions always cease at or before the expiration of five minutes after complete submersion ; for persons are rarely, if ever, saved if they have been under water more than four minutes. The instances in which recovery has taken place after a longer immersion are probably to be explained by the occurrence of fainting at the moment of the accident; for, with the circulation enfeebled, the deprivation of air may be endured much longer than it can while the blood still circulates quickly and accu- mulates carbonic acid. It is to the accumulation of carbonic acid in the blood, and its conveyance into the organs that we must, in the first place, ascribe the phenomena of asphyxia. For when this does not happen, all the other conditions may exist without injury; as they do, for ex TEMPERATURE OF HUMAN BODY. 159 ample, in hybcrnating, warm-blooded animals. In these, life is sup- ported for many months in atmospheres in which the same animals, in their full activity, would be speedily suffocated. During the pe- riods of complete torpor, their respiration entirely ceases; the heart acts very slowly and feebly; the processes of organic life are all but suspended, and the animal may be with impunity completely deprived of atmospheric air. Spallanzani kept a marmot, in this torpid state, immersed for four hours in carbonic acid gas, without its suffering any apparent inconvenience. Dr. Marshall Hall kept a lethargic bat under water for sixteen minutes, and a lethargic hedgehog for 22J minutes: and neither of the animals appeared injured by the experiment (lxxiii. vol. ii. p. 771). CHAPTER VII. ANIMAL HEAT. Intimately associated with the process of respiration are the production of animal heat, and the maintenance of a uniform tempe- rature of the body; conditions as essential to the continuance of life in warm-blooded animals, as the extrication of carbonic acid and the absorption of oxygen are. The average temperature of the human body, in those internal parts which are most easily accessible, such as the mouth and rec- tum, may be estimated at from 98° to 103° F. Brown-Sequard fixes the standard at 103° F. In children, the temperature is com- monly as high as 102° F. In old persons it is about the same as in adults (Davy, xliii., 1844). [MM. Becquerel and Breschet have experimented on the temperature of the internal parts of the body, by means of a thermo-electric apparatus, composed of two wires of different metals soldered together, with their free ends attached to a thermo-electric multiplier, having an index graduated to lOths of a degree. The wire thrust into the calf of the leg to the depth of 1£ inches indicated a temperature of 98° F.; at the depth of i of an inch, the temperature was 94°, showing a difference of 4 degrees. They also found that the biceps muscle was 3° warmer than the su- perficial fascia, and that compression of the brachial artery instantly reduced the temperature several lOths of a degree.'] Of the exter- nal parts of the body the temperature becomes lower the further they are removed from the centre of the body; thus, in the human subjeet, a thermometer placed in the axilla was found by Mr. John Davy to stand at 98° F.; at the loins it indicated a temperature of 1 [Consult Annales des Sciences Naturelles, 2de. ser. t. 3, 4, et 9. See also Todd and Bowman's Fhysiological Anatomy, Amer. edit., Art. Animal Heat.] 160 ANIMAL HEAT. 96i° ; on the thigh 94°; on the leg 93° or 91° ; on the sole of the foot 90° (xliii., 1844). In disease, the temperature of the body may deviate several degrees above and below the average of health In some diseases, as scarlatina and typhus, it rises as high as 106° or 107° F.; and in children, M. Roger has observed the tempera- ture of the skin to be raised to 108-5° F. (cxxii., 1844). In the morbus caruleus, in which there is defective arterialization of the blood from malformation of the heart, the temperature of the body is often as low as 79° or 77 £°; in Asiatic cholera, a thermometer placed in the mouth sometimes rises only to 77° or 79°. M. Roger observed the temperature of the body in children to be sometimes reduced in disease to 74-3. [Occasionally, a remarkable rise in the temperature of the body takes place very soon after death. This phenomenon has been particularly observed in cases of yellow fever. Thus Dr. Dowler, of New Orleans, records an instance in which the temperature was elevated nine degrees in the short space of 15 minutes.] The temperature of the body, in health, is about \\° F. lower during sleep than while awake. According to Dr. Davy (cxxiii., June, 1845), it is highest in the morning after rising from sleep, continues high but fluctuating till evening, and is lowest about mid- night. Sustained mental exertion elevates it slightly; continued bodily exercise does so to a considerable extent; after feeding, also, it is somewhat raised. All these facts are important, both as show- ing variations in the temperature of the body correspondent with those in the production of carbonic acid in the same circumstances, and as proving that the influence which slight changes in the organic economy of warm-blooded animals have, is as great or greater than that exercised by even extreme variation in the external tem- perature to which they are exposed. For in warm climates, Dr. Davy found the temperature of the interior of the body only from 2-7° to 3-6° F. higher than in temperate climates; and during the voyage of the " Bonite," the French naturalists, who had an oppor- tunity of observing the influence of various climates on the same persons, found that the temperature of the human body rises and falls in only a slight degree, even in extremes of external tempera- tures ; that it falls slowly in passing from hot to cold climates, and rises more rapidly in returning towards the torrid zone: but that these changes in the temperature of the body are more considerable in some individuals than in others (xviii., 1838, p. 456). The temperature maintained by mammalia in an active state of life, according to the tables of Tiedemann and Rudolphi, averages 101°. The extremes recorded by them were 96° and 106°, the former in the narwhal, the latter in a bat (Vespertilio Pipistrella). In birds, the average is as high as 107° ; the highest temperature, 111-25°, being in the small species, the linnets, etc. (cxxv. p. 234). Among reptiles, Dr. John Davy found, that while the medium they AVERAGE TEMPERATURE OF ANIMAL BODY. 161 were in was 75°, their average temperature was 82-5°. As a gen- eral rule, their temperature, though it falls with that of the surround- ing medium, is, in temperate media, two or more degrees higher; and though it rises also with that of the medium, yet at very high degrees ceases to do so, and remains even lower than that of the medium. Fish, insects, and other Invertebrata, present, as a general rule, the same temperature as the medium in which they live, whether that be high or low : only, among fish, the tunny-tribe, with strong hearts, and red meat-like muscles, and more blood than the average of fish have, are generally 7° warmer than the water around them. The difference, therefore, between what are commonly called the warm and the cold-blooded animals, is not one of absolutely higher or lower temperature; for the animals which to us, in a temperate climate, feel cold (being like the air or water, colder than the surface of our bodies), would, in an external temperature of 100° or 200°,' have nearly tbe same temperature, and feel hot to us. The real dif- ference is, as Mr. Hunter expressed it (i. vol. iii. p. 16, and vol. iv. p. 131, et seq.), that what we call warm-blooded animals (birds and Mammalia), have a certain "permanent heat in all atmospheres," while the temperature of the others, which we call cold-blooded, is "variable with every atmosphere." The power of maintaining an uniform temperature, which Mammalia and birds possess, is combined with the want of power to endure such changes of temperature as are harmless to the other classes; and when their power of resisting change of temperature ceases, they suffer serious disturbances or die. M. Magendie has shown that birds and rabbits die when, being exposed to great external heat, their temperature is raised as much as 9° above the natural standard: but they bear a reduction of the temperature of the interior of the body to a much greater amount before very dangerous or fatal conse- quences ensue (exciii. 1850). In all the ordinary circumstances of life, the maintenance of uni- form temperature is effected by the production of heat sufficient to compensate for that which is constantly lost in radiation into the medium in which we live, or in combination with the fluids evapora- ting from the exposed surfaces of the body. The losses thus sustained are extremely various in different cir- cumstances; and the degrees of power which animals possess of adapting themselves to such differences are equally various. Some live best in cold regions, where they produce abundant heat for radia- tion, and cannot endure the heat of warm climates, where the heat that they habitually produce would, probably, be excessive, and by its continual, though perhaps small excess, would generate disease; others, naturally inhabiting warm climates, die if removed to cold 1 Humboldt and Bonpland saw fish thrown up from volcanoes alive, and apparently in health, along with water and vapor which raised the thermo- meter to 210°. 14* 162 ANIMAL HEAT. ones, as if because their power of producing heat were not quite sufficient to compensate for the constantly larger abstraction of it by radiation. Man, with the aid of intellect for the provision of arti- ficial clothing, and with command over food, is, in these respects, superior to all other creatures; possessing the greatest power of adaptation to external temperature, and being capable of enduring extreme degrees of heat as well as of cold without injury to health. His power of adaptation is sufficient for the maintenance of a uni- form temperature in a range of upwards of 200° Fahrenheit; a power which is only shared by some of the domestic animals who are his companions in his various abodes. Sources and Mode of Production of Heat in the Body. To explain the production of heat in the body, several theories have been advanced; but it now appears almost certain that the cor- rect one is that which refers the generation of heat, primarily and in general, to certain chemical processes going on in the system; but admits, at the same time, that as these chemical changes are carried on in parts whose functions are, to a certain extent, under the influ- ence of the nervous system, therefore the production of heat is liable to be modified, either locally or in every part, by the operation of that system. In explaining the chemical changes effected in the process of respiration (p. 155), it was stated that the oxygen of the atmosphere taken into the blood is, most probably, combined in the systemic capillary vessels with the carbon and the hydrogen of disintegrated and absorbed tissues, and certain elements of food which have not been converted into tissues. That such a combination, between the oxygen of the atmosphere and the carbon and hydrogen in the blood, is continually taking place, is made nearly certain by the fact, that a larger amount of carbon and hydrogen is constantly being added to the bipod from the food than is required for the ordinary purposes of nutrition, and that a quantity of oxygen is also constantly being absorbed from the air in the lungs, of the disposal of which no ac- count can be given except by regarding it as combining, for the most part, with the excess of carbon and hydrogen, and being evaporated in the form of carbonic acid and water. In other words, the blood of warm-blooded animals appears to be always receivin°- from the digestive canal and the lungs more carbon, hydrogen, and oxygen, than are consumed in the repair of the tissues : and to be always emitting carbonic acid and water, for which no other source can be ascribed than the combination of these elements. In the processes of such combination, heat must be continually produced in the animal body. The same amount of heat will be evolved in the union of any given quantities of carbon and oxygen, and of hydrogen and oxygen, whether the combination be rapid and evident as in ordinary combustion, or slow and imperceptible as in the chants CHEMICAL THEORY OF ITS PRODUCTION. 163 which are believed to occur in the living body. And since the heat thus arising will be generated wherever the blood is carried, every part of the body will be heated equally; or so nearly equally that the rapid circulation of the blood will quickly remove any diversities of temperature in different parts. To establish this theory, it needs to be shown, that the quantity of carbon and hydrogen which, in a given time, unites in the body with oxygen, is sufficient to account for the amount of heat generated in the animal within the same time: an amount capable of main- taining the temperature of the body at from 98° to 100°, notwith- standing a large loss by radiation and evaporation.1 An attempt to determine this point was made by Dulong and Despretz. Dulong introduced different mammiferous animals, car- nivorous as well as herbivorous, into a receiver, in which the changes produced in the air by respiration, and the volume of the different products, could be determined at the same time that the amount of heat lost by the animal could be ascertained. His experiments led him to conclude, among other points, that supposing all the oxygen, absorbed into the blood from the air in the lungs, were combined with carbon and hydrogen in the system, and that as much heat were thus generated as would be developed during the quick combustion of equal quantities of oxygen and carbon, and of oxygen and hydro- gen, still, the whole quantity of heat produced would amount to only from f to ^ of that which is developed during the same space of time by carnivorous as well as herbivorous animals. Despretz placed ani- mals in a vessel surrounded with water; an uninterrupted current of air to and from the vessel was maintained, and the volume and com- position of the air employed were ascertained both before and after the experiment (which was continued 1£ or 2 hours), as well as the increase in the temperature of the surrounding water during it: by this means it was found that the heat which should have been gene- rated, according to the chemical theory of respiration, would account for from 0'76 to 0-91 only of that which the animals really gave out durin"- the same time. The failure of these experiments to account for all the heat produced threw doubts on the chemical theory of animal heat (as the proposed explanation has been called), till Liebig lately showed that Dulong and Despretz were in error in their con- elusions, from having formed too low an estimate of the heat produced in the combustion of carbon and hydrogen. On repeating their experiments, and using the more accurate numbers to represent these combustion-heats, Liebig found reason to believe that the quantity of heat which would be generated, by the union of the oxygen absorbed 1 Some heat will also be generated in the combination of sulphur and phos- phorus with oxygen, to which reference has been made (p. 150); but the amount thus produced has not been estimated, and need not be considered in the exposition of a theory which can, at present, be stated in only the most general terms. 164 ANIMAL HEAT. into the blood from the atmosphere with the carbon and hydrogen taken into the system as food, is sufficient to account for the whole of the caloric formed in the animal body.1 Many things observed in the economy and habits of animals are explicable by this theory, and are, therefore, evidence for its truth. Thus, as a general rule, in the various classes of animals, as well as in individual examples of each class, the quantity of heat generated in the body is in direct proportion to the activity of the respiratory process. The highest animal temperature, for example, is found in birds, in whom the function of respiration is most actively performed. In Mammalia, the process of respiration is less active, and the ave- rage temperature of the body less, than in birds. In reptiles, both the respiration and the heat are at a much lower standard; whilst in animals below them, in which the function of respiration is at the lowest point, a power of producing heat is, in ordinary circum- stances, hardly discernible. Among these lower animals, however, the observations of Mr. Newport (xliii. 1837) supply confirmatory evidence. He shows that the larva, in which the respiratory organs are smaller in comparison with the size of the body, has a lower temperature than the perfect insect. Volant insects have the highest temperature, and they have always the largest respiratory organs and breathe the greatest quantity of air; while among terrestrial insects, those also produce the most heat which have the largest respiratory organs and breathe the most air. During sleep, hybernation, and other states of inaction, respiration is slower or suspended, and the temperature is proportionably diminished; while on the other hand, when the insect is most active and respiring most voluminously, its amount of temperature is at its maximum, and corresponds with the quantity of respiration. Neither the rapidity of the circulation nor the size of the nervous system, according to Mr. Newport, presents such a constant relation to the evolution of heat. Similar evidence in favor of this theory of animal heat is furnished by the fact that heat is sometimes evolved by plants, in a quantity which appears to be in direct proportion to the amount of oxygen they at the same time absorb and convert into carbonic acid. For example, their evolution of heat is most evident during flowering and the germination of seeds, the times at which the largest amount of carbonic acid is exhaled. The quantity and quality of food consumed by man and animals in the different climates and seasons, also appear to be adapted to the production of various amounts of heat by the combination of carbon and hydrogen with oxygen. In northern regions, for ex- ample, and in the colder seasons of more southern climes, the quan- tity of food consumed is (speaking very generally) greater than is consumed by the same men or animals in opposite conditions of 'Liebig's estimates and calculations may be referred to in the "Lancet" (Feb. 1845). INFLUENCE OF NERVOUS SYSTEM. 165 climate and seasons. And the food which appears naturally adapted to the inhabitants of the coldest climates, such as the several fatty and oily substances, abounds in carbon and hydrogen, and is fitted to combine with the large quantities of oxygen which, breathing cold dense air, they absorb from their lungs. The influence of the nervous system in modifying the production of heat has been already referred to. The experiments and obser- vations which best illustrate it are those showing first, that when the supply of nervous influence to a part is cut off, the temperature of that part falls below its ordinary degree; and, secondly, that when death is caused by severe injury to or removal of the nervous centres, the temperature of the body rapidly falls, even though artificial re- spiration be performed, the circulation maintained, and to all ap- pearance the ordinary chemical changes of the body be completely effected. It has been repeatedly noticed that, after division of the nerves of a limb, its temperature falls: and this diminution of heat has been remarked still more plainly in limbs deprived of nervous influence by paralysis. For example, Mr. Earle (xli. vol. vii. p. 1 73) found the temperature of the hand of a paralyzed arm to be 70°, while that of the sound side had a temperature of 92° F. On electrifying the paralyzed limb, the temperature rose to 77°. In another case, the temperature of the paralyzed finger was 56° F., while that of the unaffected hand was 62°. Sir B. C. Brodie (xliii. 1811 and 1812) found, that if artificial respiration was kept up in animals killed by decapitation, division of the medulla oblongata, destruction of the brain, or poisoning with Worara poison, the action of the heart continued, and the blood underwent the usual changes in the lungs, as shown by the analysis of the air respired, but that the heat of the body was not maintained : on the contrary, being cooled by the air forced into the lungs, it became cold more rapidly than the body of an animal in which artificial respiration was not kept up. With equal certainty, though less definitely, the influence of the nervous system on the production of heat is shown in the rapid and momentary increase of temperature, sometimes general, at other times quite local, which is observed in states of nervous ex- citement; in the general increase of warmth of the body, sometimes amounting to perspiration, which is excited by passions of the mind; in the sudden rush of heat to the face, which is not a mere sensa- tion ; and in the equally rapid diminution of temperature in the depressing passions. But none of these instances suffices to prove that heat is generated by mere nervous action, independent of any chemical change; all are as well explicable on the supposition that the influence of the nervous system alters, in some way, the chemical processes from which the heat is commonly generated. There are ample proofs that the nervous system, especially in the most highly organized animals, does so modify all the functions of organic life; 166 ANIMAL HEAT. and it appears more reasonable to suppose that it thus influences the production of heat, than to ascribe to it any more direct agency. _ The temporary increase of heat in a part under nervous excite- ment, may, in part, be due to a larger afflux of blood to the part, in consequence of temporary relaxation of the walls of the small arteries through nervous agency. M. Bernard, for example, found that when^he divided, on one side of the neck, the trunk which unites the sympathetic ganglia, or when he removed th'e superior cervical ganglion, an increase of temperature at once took place on the cor- responding side of the face, and continued for many months (ccvii. p. 418).1 ° [Dr. Brown-Sequard has observed the same remarkable phenomena as those detailed by M. CI. Bernard. He regards them as mere results of the paralysis, and of the consequent dilatation of the blood- vessels. In consequence of this dilatation, the blood reaches the part supplied by the nerve in larger quantities; the nutrition is therefore more active. The increased sensibility is a result of the augmented vital properties of the nerves when their nutrition is in- creased. Dr. Brown-Sequard has likewise noticed the increase of temperature of the ear over that of the rectum, to the amount of one or two degrees Fahr.; but it must be remembered that the tempera- ture of the rectum is a little lower than that of the blood, and as the ear is gorged with that fluid, it is easy to understand why it should possess its temperature. Many facts prove that the degree of tem- perature and sensibility in a part are in direct ratio with the amount of blood circulating in it. If galvanism be applied to the superior portion of the sympathetic nerve after it has been cut in the neck, the vessels of the face and ear, after a short time, begin to contract, and subsequently resume their normal condition, if they do not even diminish. Coincidently with this diminution, there is a decrease of the temperature and sensibility of the face and ear, until the palsied and sound side are alike in this respect. When the galvanic current ceases to act, the vessels again dilate, and all the phenomena discovered by 31. Bernard reappear. It hence appears that the only direct effect of section of the cervical portion of the sympathetic is the paralysis and consequent dilatation of the blood-vessels. Another deduction from these experiments is, that the sympathetic sends motor fibres to many of the blood-vessels of the head.2] In the foregoing pages, the illustrations of the power of maintain- ing an uniform temperature have had reference to the ordinary case of man living in a medium colder than his body and therefore losing heat both by radiation and evaporation. The losses in these two i [Gazette Me'dicale, Fevr. 21, 1852. 2 Vide Phil. Med. Exam., N. S., vol. viii., No. viii., August, 1852.] EFFECTS OF AGE. 167 ways will bear, in general, an inverse proportion to one another; the small loss of heat in evaporation in cold climates may go far to com- pensate for the greater loss by radiation; as, on the other hand, the great amount of fluid evaporated in hot air may remove nearly as much heat as is commonly lost by both radiation and evaporation in ordinary temperatures. Thus, it is possible, that the quantities of heat required for the maintenance of an uniform proper temperature in various climates and seasons are not so different as they may, at first thought, seem : but on these points no accurate information has yet been obtained.1 Neither, as to the maintenance of the temperature of the body in hot air is more known than that great heat can for a time be borne with little change in the proper temperature of the body, provided the air be dry. Sir Charles Blagden and others supported a tempe- rature varying between 198° and 211° F. in dry air for several min- utes ; and in a subsequent experiment he remained eight minutes in a temperature of 260°. Delaroche and Berger (exxxii.) observed that the temperature of rabbits was raised only a few degrees when they were exposed to heat varying from 122° to 194°. But such heats are not tolerable when the air is moist as well as hot, so as to prevent evaporation from the body. 31. C. James (xix. April, 1844) states, that in the vapour-baths of Nero he was almost suffocated in a temperature of 112°, while in the caves of Testaccio, in which the air is dry, he was but little incommoded by a temperature of 176°. In the former, evaporation from the skin was impossible; in the latter, it was, probably, abundant, and the layer of vapour which would rise from all the surface of the body would by its very slowly conducting power, defend it for a time from the full action of the external heat. It remains to notice certain conditions by which the production of heat is modified. The effects of age are noticeable. 31. Edwards found the power of generating heat to be less in old people: and the same was observed by Dr. Davy (xliii., 1844), who, in eight people, between eighty-seven and ninety-five years old, found that, although the ave- rage temperature of the body was not lower than that of younger persons, yet the power of resisting cold was less in them — exposure to a low temperature causing a greater reduction of heat than in young persons. i Vierordt has made estimates of the heat given out, per minute, from the lungs in warming the inspired air, and in combination with the evaporated water; it would be enough to heat (at the most) 90-34 grains of water from 32° to'2120 (ex. p. 23G). At this rate the loss by evaporation from the skin and lungs together may be roughly estimated at enough to heat nearly 4000 grains of water from 32° to 212°. 168 ANIMAL HEAT. The same rapid diminution of temperature was observed by 3L Edwards in the new-born young of most carnivorous and rodent ani- mals when they were removed from the parent, the temperature of the atmosphere being between 50° and 531° F.; whereas, while lying close to the body of the mother, their temperature was only 2 or 3 degrees lower than hers. The same law applies to the young of birds. Young sparrows, a week after they were hatched, had a temperature of 95° to 97°, while in the nest; but when taken from it, their temperature fell in one hour to 66§°, the temperature of the atmosphere being at the time 62£°- It appears from his investiga- tions, that, in respect of the power of generating heat, some mam- malia are born in a less developed condition than others; and that the young of dogs, cats, and rabbits, for example, are inferior to the young of those animals which are not born blind. The need of ex- ternal warmth to keep up the temperature of new-born children is well known; the researches of 31. Edwards show that the want of it is, as Hunter suggested, a much more frequent cause of death in new-born children than is generally supposed, and furnish a strong argument against the idea that children, by early exposure to cold, can soon be hardened into resisting its injurious influence. Active exercise, as already stated, raises the temperature of the body. This may be partly ascribed to the fact that every muscular contraction is attended by the development of one or two degrees of heat in the acting muscle; and that the heat is increased according to the number and rapidity of these contractions, and may be quickly diffused by the blood circulating from the heated muscles. Possibly, also, some heat may be generated in the various movements, stretch- ings, and recoilings of tbe other tissues, as the arteries, whose elastic walls, alternately dilated and contracted, may give out some heat, just as caoutchouc alternately stretched and recoiling becomes hot. But the heat thus developed cannot be so much as some have sup- posed (Winn, xvii. Ser. 3, vol. xiv., p. 174. Winter, xxx., 1843, p. 794). The influence of external coverings for the body must not be un- noticed. In warm-blooded animals they are always adapted, among other purposes, to the maintenance of uniform temperature; and man adapts for himself such as are, for the same purpose, fitted to the various climates to which he is exposed. By their means, and by his command over food and fire, perhaps as much as by his capacity of developing appropriate amounts of heat, he maintains his tempe- rature on all accessible parts of the surface of the earth. DIGESTION. 169 CHAPTER VIII. DIGESTION. Digestion is the process by which those parts of our food which may be employed in the formation and repair of the tissues, or in the production of heat, are made fit to be absorbed and added to the blood. Food may be considered in its relation to the two purposes above- mentioned ; and the various articles of food may be artificially clas- sified according as they are chiefly subservient to one or the other of these purposes. All articles of food that are to be employed in the production of heat, must contain a larger proportion of carbon and hydrogen than is sufficient to form water with the oxygen that they contain; and none are appropriate for the maintenance of any tissues (except the adipose) unless they contain nitrogen, and are capable of conversion into the nitrogenous principles of the blood. The name of nutritive or plastic is given to those principles of food which admit of conversion into the albumen or fibrine of the blood, and of being subsequently assimilated, through the medium of the blood, by the tissues. And those principles, comprising the greater part of the non-nitrogenous materials of food, in the form of fat, starch, sugar, gum, and other similar substances, which are believed to be employed in the production of heat, are named calori- faeioit, or sometimes respiratory food. An easier division of foods than this according to their destina- tion, is derived from their origins; for all consist of either animal or vegetable substances. No substance can afford nutriment, even though it contain all the elements of organic bodies, unless it have all the natural peculiarities of organic composition, and contain, in- corporated with its other elements, some of those derived from the mineral kingdom, which, as incidental elements (p. 26), are found in the organized tissues; such as sulphur, iron, lime, magnesia, etc. Man is supported as well by food constituted wholly of animal substances, as by that which is formed entirely of vegetable matters; and the structure of his teeth, as well as experience, seems to point out that he is destined for a mixed kind of aliment. In the case of carnivorous animals, the food upon which they exist, consisting as it docs of the flesh and blood of other animals, not only contains all the elements of which their own blood and tissues are composed, but contains them combined, probably, in the same forms. Therefore, little more may seem requisite, in the preparation of this kind of food for the nutrition of the body, than that it should be dissolved and conveyed into the blood in a condition capable of being re- organized. But in the case of the herbivorous animals, which feed 15 170 DIGESTION exclusively upon vegetable substances, it might seem as if there would be creator difficulty in procuring food capable of assimilation into their blood and tissues. But the chief ordinary articles of vege- table food contain substances identical, in composition^ with the albumen, fibrine, and caseine, which constitute the principal nutri- tive materials in animal food. Albumen is abundant in the juices and seeds of nearly all vegetables ; the gluten which exists, especially in corn, and other seeds of grasses, as well as in their juices, is identical in composition with fibrine, and is commonly named vegetable fibrine; and the substance named legumm, which is obtained especially from peas, beans, and other seeds of legumin- ous plants, and from the potato, is identical with the caseine of milk. All these vegetable substances are, equally with the corresponding animal principles, and in the same manner, capable of conversion into blood and tissues; and, like the blood and tissues in both classes of animals, the nitrogenous food of both may be regarded as in essen- tial respects similar. An apparently more considerable difference between animal and vegetable foods consists in the different kind, and proportionately larger quantity, of the non-nitrogenous principles contained in the latter. The only non-nitrogenous organic substances in animal food are furnished by the fat; and, in some instances, by the vegetable matters that may chance to be in the digestive canals of such animals as are eaten whole. The amount of these is far less than that of the non-nitrogenous substances consumed by herbivorous animals, in their quantities of starch, sugar, gum, oil, and other ternary com- pounds. Yet, that the final destination of the ternary principles is the same in both classes, is almost proved by the ability of man and many other animals to subsist, and, apparently, to_maintain an iden- tical composition and an uniform temperature, with food of either kind. Again, the several alimentary substances, from both animal and vegetable substances, may be arranged, according to the system of Dr. Prout, in three classes, under the names of albuminous, sac- charine, and oleaginous principles. In the albuminous group are included all the nitrogenous principles, whether derived from the animal or from the vegetable kingdom. These comprise albumen, fibrine, caseine, gelatine, and chondrine; the two latter substances being classed under this head on account of their bearing a closer resemblance to the albuminous than to any other principles of food. The saccharine group comprises substances derived exclusively from the vegetable kingdom, viz., sugar itself, and the various principles capable of being converted into it, as starch, gum, pectine, and lignine, or woody fibre: all of which are composed of carbon, hydrogen, and oxygen, with the two latter in the proportion in which they form water. The oleaginous group includes the various kinds of fatty and oily principles, which occur abundantly in both the animal and vege- PRINCIPLES OF FOOD. 171 table kingdoms. All are composed principally of carbon and hydro- gen : the quantity of the former element usually exceeding that of the latter; and both being more than sufficient to form water with the oxygen they contain. Besides these three principal divisions, Dr. Prout makes a fourth division for the aqueous part of food. For, besides that water constitutes nearly four-fifths of the total weight of the animal body, and must, therefore, enter largely into the com- position of food, it is highly probable that it plays an important part in the various transformations undergone in the system; and thus contributes materially to the nutrition of the different textures. It has been already said, that animals cannot subsist on any but organic substances, and that these must contain the incidental elements and compounds which are naturally combined with them : in other words, not even organic compounds are nutritive unless they are sup- plied in their natural state. The most singular instance of this fact is, perhaps, that of the production of scurvy by the want of vegetable food, and its cure by giving vegetables; which, however, must be either raw, or simply preserved, or so cooked that their saline constituents may not be removed from them. Pure fibrine, pure gelatine, and other principles purified from the substances naturally mingled with them, are incapable of supporting life for more than a brief time. Moreover, health cannot be maintained by any number of sub- stances derived exclusively from one of the three groups of alimen- tary principles. A mixture of nitrogenous and non-nitrogenous sub- stances, together with the inorganic principles which are severally contained in them, is essential to the well-being, and, generally, even to the existence of an animal. The truth of this is demonstrated by experiments performed for the purpose, and is illustrated by the composition of the food prepared by nature as the exclusive source of nourishment to the young of 31ammalia, namely milk. In milk, the albuminous group 'of aliments is represented by the caseine, the oleaginous by the butter, the aqueous by the water, the saccharine by the sugar of milk.1 Milk, likewise, contains phosphate of lime, alkaline and other salts, and a trace of iron; so that it may be briefly said to include all the substances which the tissues of the growing animal need for their nutrition, and which are required for the pro- duction of animal heat. The yelk and albumen of eggs are in the same relation, as food for the embryoes of oviparous animals, as milk is to the young of 31ammalia, and afford another example of mixed food being provided as the most perfect for nutrition. The experiments illustrating the same principle have been chiefly performed by 3Iagendie (cxxxiii.). Dogs were fed exclusively on sugar and distilled water. During the first seven or eight days they >At least it is so in the milk of herbivorous animals; but, according to Dumas (xix. Oct. 1845), sugar does not exist in the milk of Carnivora, except when some saccharine or farinaceous principle is mixed with their food; its place in their natural milk is filled, as it is in their food, by the fatty matter. 172 DIGESTION. were brisk and active, and took their food and drink as usual; but in the course of the second week they began to get thin, although their appetite continued good and they took daily between six and eio-ht ounces of sugar. The emaciation increased during the third week, and they became feeble, and lost their activity and appetite. At the same time an ulcer formed on each cornea, followed by an escape of the humors of the eye; this took place in repeated experi- ments. The animals still continued to eat three or four ounces of su°-ar daily; but became at length so feeble as to be incapable of motion, and died on a day varying from the 31st to the 34th. On dissection their bodies presented all the appearances produced by death from starvation; indeed, dogs will live almost the same length of time without any food at all. When dogs were fed exclusively on gum, results almost similar to the above ensued. AVhen they were kept on olive-oil and water, all the phenomena produced were the same, except that no ulceration of the cornea took place : the effects were also the same with butter. Tiedemann and G-melin obtained very similar results. They fed dif- ferent geese, one with sugar and water, another with gum and wa- ter, and a third with starch and water. All gradually lost weight. The one fed with gum died on the sixteenth day; that fed with sugar on the twenty-second; the third, which was fed with starch, on the twenty-fourth, and another on the twenty-seventh day; hav- ing lost, during these periods, from one sixth to one half of their weight. The experiments of Chossat (xix. Oct. 1843) and Letellier (xii. 1844) prove the same; and in men the same is shown by the various diseases to which they who consume but little nitrogenous food are liable, and especially, as Dr. Budd has shown, by the affec- tion of the cornea which is observed in Hindus feeding almost ex- clusively on rice. But it is not only the non-nitrogenous substances, which, taken alone, are insufficient for the maintenance of health. The experiments of the Academies of France and Amsterdam were equally conclusive that gelatine alone soon ceases to be nutritive (xxv. 1843-4, p. 35). These facts prove the necessity of a mixture of elementary prin- ciples in the food; and, beyond this, 3Iagendie's further experi- ments appear to prove, that animals cannot live long if fed exclu- sively on any single article of food (except milk), even although it contains principles belonging to each of the three groups of alimen- tary substances. For example (to mention only some of his results), a dog fed on white bread, wheat, and water, did not live more than fifty days; rabbits and guinea-pigs fed on any one of the following substances,—wheat, oats, barley, cabbage, or carrots,—died with all the signs of inanition in fifteen days; wbile, if the same substances were given simultaneously, or in succession, the animals suffered no ill effect. CHANGES OF FOOD IN THE MOUTH. 173 Fig. 43. Changes of the Food effected in the Month. The first of the series of changes to which the food is subjected in the digestive canal takes place in the cavity of the mouth; the solid articles of food are here submitted to the action of the teeth, whereby they are divided and crushed, and, by being at the same time mixed with the fluids of the mouth, are reduced to a soft pulp capable of being easily swallowed. The fluids with which the food is mixed in the mouth consist of the secretion of the salivary glands, and the mucus secreted by the lining membrane of the whole buccal cavity. The glands concerned in the production of saliva are very exten- sive, and, in man and 3Iammalia generally, are presented in the form of four pairs of large glands, the pa- rotid, (Fig. 43) submaxillary, sublingual, and intralingual, and numerous smaller bodies, of similar structure and with sepa- rate ducts, which are scattered thickly beneath the mucous membrane of the lips, cheeks, soft palate, and root of the tongue. These all havo the structure common to what are termed conglomerate glands, which will be spoken of in the chapter on Secretion. Saliva, as it commonly flows from the mouth, is mixed with the secre- tion of the mucous membrane, and often with air-bubbles, which, being retained by its viscidity, make it frothy. When obtained from the parotid-ducts, and free from mucus, saliva is a transpa- rent watery fluid, the specific gravity of which varies from 1-006 to 1-009, aud in with the microscope, are found floating a number of minute particles, derived from the secreting ducts and vesicles of the glands. In the impure or mixed saliva are found, besides these particles, numerous epithelial scales separated from the surface of the mucous membrane of the mouth and tongue, and mucus-corpuscles, discharged for^ the most part from the tonsils, which when the saliva is collected in a deep vessel, and left at rest, subside in the form of a white opaque matter, leaving the supernatant salivary fluid transparent and color- less, or with a pale blueish-gray tint. In reaction the saliva, when first secreted, appears to be always alkaline; and that from the parotid gland is said to be more strongly alkaline than that from the other salivary glands. This alkaline condition is most evident when digestion is going on, and, according to Dr. Wright (xxx. 1842-3), the decree of alkalinity of the saliva bears a direct proportion to the acidit °of the gastric fluid secreted at the same time 15* Fte. 43. Lolmle of parotid gland of a new-born Infant, injected with mercury. Mag- nified 50 diameters. which, when examined During- fast- 174 D IGESTION. ing, the saliva, although secreted alkaline, shortly becomes acid; and it does so especially when secreted slowly, and allowed to mix with the acid mucus of the mouth, by which its alkaline reaction is destroyed. According to Dr. Wright (xxx. March, 1842), whose analysis does not materially differ from the more recent analyses of Frerichs (lix. 1850, p. 136), Jacubowitsch (ccviii. p. 7 e. s.), and others, the composition of saliva is— Water................................9881 Ptyaline.............................. 1-8 Fatty matter....................... -5 Albumeu (with soda)............. 17 Mucus................................... 2-6 Ashes....................................41 Loss.....................................1-2 1000 0 Ptyaline is the name given to a peculiar nitrogenous substance, which is insoluble in alcohol. By 3Iialhe it is stated to be closely analogous to the vegetable substance termed diastase; according to Lehmann (cciii. vol. ii. p. 15) it closely resembles both albumen and caseine, though it is not identical with either of them. The ashes of saliva have been analyzed by Enderlin (x. 1844), who found that they consist of substances very similar to those in the ashes of blood, and he believes that the alkalinity of the saliva, like that of the blood, is due to the tribasic phosphate of soda. The other salts which he found in it were chlorides of sodium and potas- sium, sulphate of soda, and phosphates of lime, magnesia, and of iron. Saliva also contains a small quantity of sulpho-cyanogen, in the form of sulpho-cyanide of potassium; its presence is indicated by a deep red color when saliva is mixed with a neutral solution of a salt of the peroxide of iron. See, on this point, Pettenkofer (lix. 1846, p. 115), Strahl (lix. 1847, p. 100), and Bidder and Schmidt (ccviii. p. 10). Its use is still unknown. The tartar which collects on the human teeth consists almost entirely of the earthy phosphates, combined with about 19 per cent, of animal matter, and containing shells of infusoria, and other accidental mixtures. The rate at which saliva is secreted is subject to considerable va- riation. When the tongue and muscles concerned in mastication are at rest, and the nerves of the mouth are subject to no unusual stimulus, the quantity secreted is not more than sufficient, with the mucus, to keep the mouth moist. But the flow is much accelerated when the movements of mastication take place, and especially when they are combined with the presence of food in the mouth. It may be excited also, even when the mouth is at rest, by the mental im- pressions produced by the sight or thought of food. Under these varying circumstances, the quantity of saliva secreted in twenty-four hours varies also; its average amount is thought to range from fif- teen to twenty ounces. In a man who had a fistulous opening of the parotid duct, 31itscherlich found that the quantity of saliva dis- ACTION OF SALIVA. 175 charged from it during twenty-four hours, was from two to three ounces; and the saliva collected from the mouth during the same period, and derived from the other salivary glands, amounted to six times more than that from the one parotid. Bidder and Schmidt, however, estimate the amount much higher than this, believing that the average daily excretion in man is upwards of three pounds (ccviii. p. 14). The purposes served by saliva are of several kinds. In the first place, acting mechanically, it keeps the mouth in a due condition of moisture, facilitating the movements of the tongue in speaking, and the mastication of food. Thus also it serves in dissolving sapid substances, and rendering them capable of exciting the nerves of taste. But the principal mechanical purpose of the saliva is that, by mixing with the food during mastication, it makes it a soft pulpy mass, such as maybe easily swallowed. To this purpose the saliva is adapted both by quantity and quality. For, speaking generally, the quantity secreted during feeding is in direct proportion to the dry- ness and hardness of the food : as 31. Lassaigne has shown, by a table of the quantity produced in the mastication of a hundred parts of each of several kinds of food; thirty parts suffice for a hundred parts of crumb of bread; but not less than 120 for the crusts; 42-5 parts of saliva are produced for the hundred of roast meat; 3-7 for as much of apples; and so on, according to the general rule above- stated. The quality of saliva is equally adapted to this end. It is easy to see how much more readily it mixes with most kinds of food than water alone does; and 31. Bernard has rendered probable from his experiments and observations, that the saliva from the parotid, labial, and other small glands, being more aqueous than the rest, is that which is chiefly braided and mixed with the food in mastica- tion ; while the more viscid mucoid secretion of the submaxillary, palatine, and tonsillitic glands, is spread over the surface of the soft- ened mass to enable it to slide more easily through the fauces and oesophagus. This view obtains confirmation from the interesting fact, pointed out by Professor Owen, that, in the great ant-eater, whose enormously elongated tongue is kept moist by a large quantity of viscid saliva, the submaxillary glands are remarkably developed, while the parotids are not of unusual size (ccvii. p. 76, note). Beyond these, its mechanical purposes, there are reasons for be- lieving that saliva performs some chemical part in the digestion of the food. The chief of these reasons are, the number and size of the glands engaged in the secretion; the variety of substances which enter into its composition, and which can scarcely be supposed to be of use so far as its mechanical properties are concerned; the quan- tity which is secreted, not only during mastication, but after the food has passed into the stomach, especially in old persons, who, from their loss of teeth, frequently swallow their food in an imperfectly 176 DIGESTION. masticated state; the fact that the saliva secreted during digestion is more alkaline than at other times; and, lastly, the results of cer- tain experiments. . Among the experiments are those of Spallanzani and Beaumur, who found that food inclosed in perforated tubes, and introduced into the stomach of an animal, was more quickly digested when it had been previously impregnated with saliva than when it was moist- ened with water. Dr. Wright, also, found thaUf the oesophagus of a dog is tied, and food mixed with water alone is placed in the sto- mach, the food will remain undigested, though the stomach may secrete abundant acid fluid; but if the same food were mixed with saliva, and the rest of the experiment similarly performed, the food was readily digested. But although it may hence appear that the saliva has more than a mechanical influence in promoting digestion, yet the nature of the chemical part it takes is uncertain. Its composition, as traced by chemical analysis, offers no certain guide. Its alkalinity, though, as already stated, it appears to increase in the same proportion as the acidity of the secretion of the stomach both in health and disease, is never sufficient to neutralize the gastric fluid; the contents of the stomach, including as they do the saliva swallowed, are always acid. The very short time during which the saliva remains in contact with the food before it is neutralized by the acid of the stomach, precludes the notion that the alkali is the principal constituent by which it assists in digestion. Its organic principle, ptyaline, however, has probably more power; for numerous experiments, easily repeated, show that when saliva or a portion of the salivary gland is added to starch-paste, the starch is quickly transformed into dextrine, and grape-sugar; and when common raw starch is masticated and mingled with saliva, and kept with it at a temperature of 90° or 100°, the starch-grains are cracked or eroded, and their contents are trans- formed in the same manner as the starch-paste.1 Changes similar to these are effected on the starch of farinaceous food (especially after cooking) in the stomach; and it is reasonable to refer them to the action of the saliva, because the acid of the gastric fluid tends to retard or prevent, rather than favour, the transformation of the starch. It may therefore be held that a purpose served by the saliva in the digestive process is that of assisting in the transformation of the starch, which enters so largely into the composition of most arti- cles of vegetable food, and which (being naturally insoluble) is con- verted into the soluble dextrine or grape-sugar, and made fit for absorption. 1 See on these points, Leuchs (xxxii. p. 577), Mialhe (xii. 1845), Wright (xxx. 1842-3), Lehmann (xiv. 1843, and cciii. vol. ii. p. 10, c. s.), a report of the Academy of Sciences, translated in the Medical Gazette, vol. xxxvii. p. 788, Valentin's Reports in Canstatt's Jahresberichte to 185G, Bidder and Schmidt (ccviii.), and various Essays by M. Claude Bernard. SALIVA ON FOOD . 177 It appears from the experiments of 3Iagendie (xviii. July, 1846) and Bernard (lix. 1X47, p. 117), that, besides saliva, many azotized substances, especially ii' in a state of incipient decomposition, may excite this transformation of starch, such as pieces of the mucous membrane of the mouth, bladder, rectum, and other parts, various animal and vegetable tissues, and even morbid products; but the gastric fluid will not produce the same effect. The property there- fore cannot be exclusively assigned to the saliva, though, on the other hand, it seems proved by the experiments of Bidder and Schmidt (ccviii. pp. 17-18) that the transformation in question is effected much more rapidly by this fluid than by any of the other fluids or substances experimented with, except the pancreatic secre- tion, which, as will be presently shown, is very analogous to saliva. The actual process by which these changes are effected is still obscure. Probably the azotized substance, ptyaline, acts as a kind of ferment, like diastase in the process of malting, and excites molecular changes in the starch, which result in its transformation, first into dextrine and then into sugar: and it would seem that this transfor- mation continues even after the food has entered the stomach. On this latter point, however, there is still much difference of opinion, Bidder and Schmidt believing that the process is arrested on the entrance of the food into the stomach. According to Bernard, 31a- gendie, Frerichs, and others, the part of the salivary fluid which is most active in thus transforming starch, is that secreted by the small glands of the mucous membrane of the mouth. Bidder and Schmidt, however, deny this, and believe that a mixture of the secretion of all the parts concerned in the formation of saliva is necessary to the perfect accomplishment of the metamorphosis (ccviii. P. 19). Starch appears to be the only principle of food upon which saliva acts chemically: it has no apparent influence on any of the other ternary principles, such as sugar, gum, mucus, or cellulose; and seems to be equally destitute of power over albuminous and gelatin- ous substances, so that we have as yet no information respecting any purpose it can serve in the digestion of Carnivora beyond that of softening or macerating the food; though, since such animals masti- cate their food very little, usually " bolting" it, the saliva has probably but little use, even in this respect, in the process of digestion.1 1 On the chemistry and action of Saliva, as well as on other points con- nected with the physiology of digestion, the student will find much valuable information in an analysis of Bidder and Schmidt's work by Dr. Day, in the British and Foreign Medico-Chirurgical Review, vol. xii. p. 107, and in Dr. Bence Jones's Lectures on Digestion, in the Medical Times, 1851-2. 178 DIGESTION. PASSAGE OF FOOD INTO THE STOMACH. When properly masticated, the food is transmitted in successive portions to the stomach by the act of deglutition or swallowing. This act, for the purpose of description, may be divided into three parts. In the first, particles of food collected to a morsel glide between the surface of the tongue and the palatine arch, till they have passed the anterior arch of the fauces; in the second, the morsel is carried through the pharynx; and in the third, it reaches the stomach through the oesophagus. These three acts follow each other rapidly. The first is performed voluntarily by the muscles of the tongue and cheeks. The second also is effected with the aid of muscles which are in part endued with voluntary motion, such as the muscles of the soft palate and pharynx; but it is, nevertheless, an involuntary act, and takes place without our being able to prevent it, as soon as a morsel of food, drink, or saliva is carried backwards to a certain point of the tongue's surface. When we appear to swallow voluntarily, we only convey, through the first act of deglutition, a portion of food or saliva beyond the anterior arch of the palate; then, the substance acts as a stimulus, which in accordance with the laws of reflex move- ments hereafter to be described, is carried by the sensitive nerves to the medulla oblongata, where it is reflected to the motor nerves, and an involuntary adapted action of the muscles of the palate and pharynx ensues. The third act of deglutition takes place in the oesophagus, the muscular fibres of which are entirely beyond the influence of the will. The second act of deglutition is the most complicated, because the food must pass by the posterior orifice of the nose and tbe rima glot- tidis of the larynx, without touching them. When it has been brought, by the first act, behind the anterior arches of the palate, it is moved onwards by the tongue being carried backwards, and by the muscles of the anterior arches contracting behind it. The root of the tongue being retracted, and the larynx being raised with the pharynx and carried forwards under the tongue, the epiglottis is pressed over the rima glottidis, and the morsel glides past it; the closure of the glottis being additionally secured by the simultaneous contraction of its own muscles; so that, even when the epiglottis is destroyed, there is little danger of food or drink passing into the larynx, so long as its muscles can act freely. At the same time, the approximation of the sides of the posterior palatine arch, which move quickly inwards like side-curtains, closes the passage into the upper part of the pharynx and the posterior nares, and forms an inclined plane, along the under surface of which the morsel descends; then the pharynx, raised up to receive it, in its turn contracts, and forces it onwards into the oesophagus. In the third act, in which the food passes through the oesophagus, every part of that tube, as it receives the morsel, and is dilated by STRUCTURE OF THE STOMACH. 179 it, is stimulated to contract; hence an undulatory contraction of the oesophagus, which is easily observable in horses while drinking, pro- ceeds rapidly along the tube. It is only when the morsels swallowed are large, or taken too quickly in succession, that the progressive contraction of the oesophagus is slow, and attended with pain. Besides the actions ensuing in the oesophagus during the passage of food, certain rhythmic contractions have been observed at its lower part, independently of deglutition. They are produced by the fibres near the cardiac orifice of the stomach, which fibres are usually in a state of contraction, especially when the stomach is full, and ap- pear to act as a kind of sphincter to prevent the regurgitation of food. During vomiting they are relaxed; and at the same time, the whole muscular tissue of the tube is said to perform an anti-peristaltic motion, the reverse of that which it executes during deglutition. When vomiting has been produced by the injection of tartar emetic into the veins, these anti-peristaltic motions of the oesophagus are said to be continued, even though the tube is separated from the stomach. DIGESTION OF FOOD IN THE STOMACH. Structure of the Stomach. It appears to be an universal character of animals, that they have an internal cavity for the production of a chemical change in the aliment—a cavity for digestion : and when this cavity is compound, the part in which the food undergoes its principal and most impor- tant changes is the stomach. In man, and those Mammalia which are provided with a single stomach, its walls consist of three distinct layers or coats, viz., an external peritoneal, an internal mucous, and an intermediate muscu- lar coat, with blood-vessels, lymphatics, and nerves distributed in and between them. In relation to the physiology of the stomach in digestion, only the muscular and mucous coats need be considered. The muscular coat of the stomach consists of three separate layers, or sets of fibres, which, according to their several directions, are named the longitudinal, circular, and oblique. The longitudinal set are the most superficial; they are continuous with the longitudinal fibres of the oesophagus, and spread out in a diverging manner over the great end and sides of the stomach. They extend as far as the pylorus, being especially distinct at the lesser or upper curvature of the stomach, along which they pass in several strong bands. The next set are the circular or transverse fibres, which more or less com- pletely encircle all parts of the stomach; they are most abundant at the middle and in the pyloric portion of the organ, and some form the chief part of the thick projecting ring of the pylorus. The next and consequently deepest set of fibres are the oblique; they are com- paratively few in number, and are placed only at the cardiac orifice and portion of the stomach, over both surfaces of which they are 180 DIGESTION. Fig. 44. spread, some passing obliquely from left to right, others fromnight to left around the cardiac orifice, to which by their interlacingrthey form a kind of sphincter, continuous with that round the lower end of the oesophagus. « , ,___, The fibres of which the several muscular layers of the stomach, and of the intestinal canal generally, are composed, belong to the class of organic muscle, being smooth, or unstnped, elongated, spindle- shaped fibre-cells, a fuller description of which will be given under the head of Muscular tissue. The mucous membrane of the stomach rests upon a layer ot loose cellular membrane, or submucous tissue, which connects it with the muscular coat, and contains its principal blood-vessels. Ex- amined when the stomach is distended, it is smooth, level, soft, and velvety; in the con- tracted state, it is thrown into numerous, chiefly longitudinal, folds or rugae. When examined with a lens, the internal or free surface, as was first accurately pointed out by Dr. Sprott Boyd (xciv. vol. xvi.), presents a peculiar honeycomb appearance produced by shallow, polygonal depressions or cells (Fig. 44, A.) the diameter of which varies generally from 2foth to ^th of an inch; but near the pylorus is as much as TUUth of an inch. They are separated by slightly elevated ridges which sometimes, especially in certain morbid states of the stomach, bear minute, narrow, vascular processes that look o^lJX^Cri Hke villi, and have given rise to the erroneous Ceils of human stomach—open supposition, that the stomach has absorbing mouths of tubes seen at the bot- viHi like those of the small intestines. In ^X£XZT££. the bottom of the cells minute openings are membrane of the stomach in tbe visible (Fig. 44, A), which are the OriuCeS pig,-the cellular coat on which 0f perpendicularly-arranged tubular glands ^^^^17^ imbedded side by side in sets or bundles, in 20 diameters. the substance of the mucous membrane, and composing (b) nearly the whole structure. These tubular glands (Fig. 45, a) vary in length from one-fourth of a line to nearly a line ; they are longer and more thickly set^ to- wards the pylorus than elsewhere; their length is equal to the various thickness of the mucous membrane of the stomach at different parts. At their bases, which rest on the submucous tissue, or an intervening layer of muscular tissue (Fig. 45, b) they measure about 355th of an inch in diameter, and at their orifices about jooth- Sometimes their blind dilated extremities, instead of being rounded off, have an uneven, or varicose, or pouched appearance, and sometimes they are GLANDS OF THE STOMACH. 181 Blightly branched. Occasionally, two above, and open on the surface of the stomach by a common orifice or duct. Their walls consist, essentially, of tu- bular inflections of the basement mem- brane of the mucous coat of the sto- mach. This membrane, in the upper third of the tube, is lined by an epi- thelial layer of cylindrical cells, con- tinuous with that of the surface of the stomach: in the lower two-thirds, in- stead of a layer of cylindrical epithe- lium, the tube is filled by numerous roundish, or oval, or polygonal nucle- ated cells, in various stages of devel- opment, containing much finely granu- lar material, and engaged in the secre- tion of the gastric fluid, which, when fully elaborated, is discharged by the cells, and mixes with the food in the stomach. The cylindrical cells in the upper part of the tube appear to take no direct share in the secretion of the acid gastric juice, but assist in forming the neutral or slightly alkaline mucus which covers the surface of the stomach after fasting (Kolliker, ccvi. p. 399). In the intervals between successive pe- riods of digestion, when the stomach is empty, the lower secreting parts of the tubules appear to be at rest, and are said to be nearly empty: they are called into activity on the fresh introduction of food. The elaboration of the gastric or digestive fluid in the cells seems to be perfected only as they reach the surface; for, according to Bernard (xix. 31arch, 184.4), the mucous membrane is not. acid a little below the surface. On their outside, these tubular glands are covered by capillary blood-vessels derived from arteries, whose principal trunks lie in the submucous tissue, and send up vertical branches through the inter- spaces between the several bundles of glands (Fig. 46, b) ; while branches form anastomoses in the ridges between the polygonal spaces on the internal surface of the stomach. In animals, the tubular glands of the stomach, which at their blind extremities are almost always branched, and much more so than in man, appear to be of two distinct kinds. In one kind the tubules, situated almost exclusively about the pylorus, are lined throughout by cylindrical epithelium (Fig. 46), and appear to take '"" 16 contiguous tubules coalesce Fig. 45. — Longitudinal section through the coats of a pig's stomach, near the pylorus; magnified 30 dia- meters.—a. Tubular glands of the mucous membrane.—6. A layer of muscular tissue.—c. Submucous tis- sue, containing nerves and blood- vessels, two of the latter cut across. —d. Transverse muscular coat.—e. Longitudinal muscular coat.—■/. Se- rous layer. (After Kolliker.) 182 DIGESTION. no part in the secretion of proper gastric fluid, but to be concerned in the formation of simple mucus; in the other kind, the tubules, which occupy the rest of the mucous membrane, ex- cept in the stomach of the pig, where they occur only about the middle (Kolliker), are lined by cylindrical epithelium only in their upper part, and throughout the rest of their extent are filled with true glandular cells, like those in the lower part of the gastric glands in the human subject, only much larger, and, in con- sequence of their large size, giving a peculiar beaded ap- pearance to the narrow branch- es into which the terminations of the tubules are divided (Fig. 47). Some recent observa- tions by Kolliker (cxc. vol. xiii. p. 544) make it probable that in the human stomach also there are two, if not more, kinds of tubular glands, the one lined by cylindrical epithelium throughout, and not concerned in the formation of gastric juice; the other, as described, lined by cylindrical epithelium only at the upper part, the rest of the tube being filled with gland- cells engaged in the elaboration of gastric fluid.1 Besides the tubular or proper gastric glands, certain other glandular structures are frequently met with in the stomach both of man and ani- mals. These are small opaque-white sacculi, like the Peyer's glands of the intestines, filled with minute cells and granules, situated chiefly alon"- the lesser curvature of the stomach, beneath the mucous mem- brane, sometimes in the pyloric regions also. They are said to be only found during digestion in man; and it is probable that, having 1 For the best recent account of the structure of the mucous membrane of the stomach, see Kblliker (ccvi. p. .'308, and ccxii.), and Brinton (lxxiii. Art. " Stomach and Intestines"), who confirms Kolliker's description, and adds much original matter. Fig. 46.—One of the tubular follicles of the pig's stomach, after Wasmann, cut ob- liquely so as to dis- play the upper part of its cavity, with the cylindrical epithe- lium forming its wall. At the lower part of the follicle, the external nucle- ated extremities of the cylinders of epi- thelium are seen. Fig. 47.—Gastricgland from the stomach of dog. a. Upper part of the tube,lined by cylindrical epithelium. 6. Primary branches, with similar epithelium, c. Termi- nal branches filled with secreting gland-cells, and exhibiting a central canal for the escape of the secreted fluid. (After Kolliker.) PROPERTIES OF THE GASTRIC FLUID. 183 elaborated certain materials of importance to the digestive process, they burst, discharge their contents, and disappear. According to Brinton, they are rarely absent in children. Secretion and Properties of the Gastric Fluid. While the stomach contains no food, and is inactive, no gastric fluid is secreted; and mucus, which is either neutral or slightly alka- line, covers its surface. But immediately on the introduction of food or other foreign substance into the stomach, the mucous membrane, previously quite pale, becomes slightly turgid and reddened with the influx of a larger quantity of blood; the gastric glands commence secreting actively, and an acid fluid is poured out in minute drops, which gradually run together and flow down the walls of the sto- mach, or soak into the substances introduced. The nature of the gastric fluid, thus secreted, was till lately in- volved in complete obscurity. The first accurate analysis of it was made by Dr. Prout; but it does not appear that it was collected in any large quantity, or pure and separate from food, until the time when Dr. Beaumont (cxxxviii.) was enabled by a fortunate circum- stance to obtain it from the stomach of a man, named St. 3Iartin, in whom there existed, as the result of a gunshot wound, an opening leading directly into the stomach, near the upper extremity of the great curvature, and three inches from the cardiac orifice. The external opening was situated two inches below the left mamma, in a line drawn from that part to the spine of the left ilium. The bor- ders of the opening into the stomach, which was of considerable size, had united, in healing, with the margins of the external wound; but the cavity of the stomach was at last separated from the exterior by a fold of mucous membrane, which projected from the upper and back part of the opening, and closed it like a valve, but could be pushed back with the finger. The introduction of any mechanical irritant, such as the bulb of a thermometer, into the stomach, excited at once the secretion of gastric fluid. This could be drawn off with a caoutchouc tube, and could often be obtained to the extent of nearly an ounce. The introduction of alimentary substances caused a much more rapid and abundant secretion of pure gastric fluid than the presence of other mechanical irritants did. No increase of tem- perature could be detected during the most active secretion; the thermometer introduced into the stomach always stood at 100° Fah., except during muscular exertion, when the temperature of the sto- mach, like that of other parts of the body, rose one or two degrees higher. 31. Blondlot (xvi.), and subsequently, 31. Bernard (xix., June, 1844\ and since then, several others, by maintaining fistulous open- ings into the stomachs of dogs, have confirmed most of the facts dis- covered by Dr. lleaumont. From their observations, also, it appears 184 DIGESTION. that pepper, salt, and other soluble stimulants excite a more rapid discharge of gastric fluid than mechanical irritation does ; so do alka- lies generally, but acids have a contrary effect. When mechanical irritation is carried beyond certain limits, so as to produce pain, the secretion, instead of being more abundant, diminishes or ceases en- tirely, and a ropy mucus is poured out instead. Very cold water or small pieces of ice, at first render the mucous membrane pallid, but soon a kind of reaction ensues, the membrane becomes turgid with blood, and a larger quantity of gastric juice is poured out. The application of too much ice is attended by diminution in the quan- tity of fluid secreted, and by consequent retardation of the process of digestion. The quantity of the secretion seems to be influenced also by impressions made on the mouth; for 31. Blondlot found that when sugar was introduced into the dog's stomach, either alone or mixed wTth human saliva, a very small secretion ensued; but when the dog had himself masticated and swallowed it, the secretion was abundant. Dr. Beaumont described the secretion of the human stomach as " a clear, transparent fluid, inodorous, a little saltish, and very per- ceptibly acid. Its taste is similar to that of thin mucilaginous water slightly acidulated with muriatic acid. It is readily diffusible in water, wine, or spirits; slightly effervesces with alkalies; and is an effectual solvent of the materia alimentaria. It possesses the pro- perty of coagulating albumen in an eminent degree; is powerfully antiseptic, checking the putrefaction of meat; and effectually resto^ rative of healthy action, when applied to old foetid sores and foul, ulcerating surfaces " (p. 76). Dr. Dunglison found in this gastric fluid free hydrochloric and acetic acids, phosphates and hydrochlorates of potash, soda, lime, and magnesia, and an animal matter which was soluble in cold, but inso- luble in hot water. The quantity of free hydrochloric acid which he obtained by distillation seems to have been large; and Dr. Prout, as well as other chemists, have satisfied themselves of the existence of this acid in the gastric fluid of the rabbit, hare, horse, calf, and dog. Acetic acid also is said to have been found in the gastric secretion of horses and dogs, as well as by Dr. Beaumont in tbat of the human subject. But the results of more recent experiments by 31. Blondlot (xvi.), Dr. B. D. Thompson (xvii., May, 1845), 3131. Bernard and Barreswil (xviii., Dec, 1844), and Lehmann (lix., 1847, p. 102), cast doubt on the opinion that/Vee hydrochloric, acetic, or any other volatile acid, exists in this fluid; at least in the case of the dog and pig, the -animals experimented on. Having obtained large quantities of pure gastric fluid from the stomach of a dog, and carefully distilled portions of it on the sand-bath, Blondlot found not the slightest trace of acidity in the product of the distillation ; but the residue in the retort was intensely acid, and became more so the more it was con- centrated by continuing the distillation. The non-existence of both ANIMAL MATTER. . 185 hydrochloric and acetic acids seeming to be thus demonstrated, Blond- lot was I'd to believe that the acidity of the gastric fluid depends on an acid phosphate of lime. For he observed no effervescence on the addition of carbonate of lime to the acid gastric fluid; neither when carbonate of lime was placed in the gastric fluid, was the fluid neu- tralized, or the carbonate dissolved. By further investigation he demonstrated the existence of a super-phosphate of lime in the gastric fluid. But he seems to have been in error in attributing the whole of the acidity of the gastric fluid to this salt; for 31M. Bernard and Barreswil have found that if the gastric fluid be sufficiently concen- trated by evaporation, distinct effervescence occurs on the addition of carbonate of lime ; proving the presence of some free acid, which they, as well as Dr. 11. D. Thompson, Lehmann (lix., 1847, p. 102), and Frcrichs (lix., 1850, p. 134), consider to be the lactic, an opin- ion to which Liebig (liv. p. 138) also gives his sanction. 3131. 31elsens and Dumas (lix., 1844, p. 109), have also proved the exist- ence of a free acid by the gradual solution of portions of carbonate of lime placed in gastric fluid. But since, even after long contact, the carbonate of lime does not completely neutralize the acid of the gastric fluid, it is most probable that there is, together with a free acid, some acid phosphate of lime, as maintained by M. Blondlot. Bcspecting the nature of the free acid, whose presence is thus proved, the discrepant results suggest a supposition that the source of the acidity of the gastric fluid may vary in different animals, or at different times in tbe same animal. The existence of hydrochloric acid in the human gastric fluid seems to have been clearly deter- mined by Prout, Dunglison, Enderlin (lix., 1843, p. 149), and others (see, especially, Hubbenet, cxciv.), and more recently by Pro- fessor Grabam (ccvii., p. 82); its non-existence, and the existence of lactic acid, as clearly in the fluid of pigs and dogs by the other analysts just quoted; possibly all are right. The results of experi- ments in artificial digestion make it probable that the digestive pro- perties of the gastric fluid require only the existence of a certain degree of acidity, which is equally effective whatever be the acid em- ployed, provided this acid does not decompose the active animal principle of the digestive fluid.1 The animal matter mentioned in the analysis of the gastric fluid by Dr. Dunglison has been since named pepsinc, from its power in the process of digestion. It is an azotized substance, the composition of which, according to Bidder and Schmidt (ccviii. p. 46), consists of C-)3II6.,Nn.8 and ()2,.5. It is best procured by digesting portions of the mucous membrane of the stomach in cold water, after they have been macerated for some time in water at a temperature between 80° 1 An excellent summary of our knowledge on this subject is given by Dr. Brinton in his elaborate article on the Stomach and Intestines, in Todd's Cyclopaedia of Anatomy and Physiology, June, 1855. 16* 186 DIGESTION. and 100° F. The warm water dissolves various substances as well as some of the pepsine, but the cold water takes up little else than pepsine, which, on evaporating the cold solution, is obtained in a greyish-brown viscid fluid. The addition of alcohol throws down the pepsiue in greyish-white flocculi; and one part of the principle thus prepared, if dissolved in even 60,000 parts of water, will digest meat and other alimentary substances. The digestive power of the gastric fluid is manifested in its soften- ing, reducing into pulp, and partially or completely dissolving vari- ous articles of food placed in it at a temperature of from 90° to 100°. This, its peculiar property, requires the presence of both the pepsine and the acid; neither of them can digest alone, and, when they are mixed, either the decomposition of the pespine, or the neutralization of the acid, at once destroys the digestive property of the fluid. For the perfection of the process, also, certain conditions are required, which are all found in the stomach; namely, first, a temperature of about 100° F.; secondly, such movements as the food is subjected to by the muscular actions of the stomach, which bring in succession every part of it in contact with the mucous mem- brane, whence the fresh gastric fluid is being secreted; thirdly, the constant removal of those portions of food which are already digested, so that what remains undigested may be brought more completely into contact with the solvent fluid; and fourthly, a state of softness and minute division, such as that to which the food is reduced by mastication previous to its introduction into the stomach. The chief circumstances connected with the mode in which the gastric fluid acts upon food during natural digestion, have been de- termined by watching its operations on different alimentary sub- stances, when removed from the stomach and placed in conditions as nearly as possible like those under which it acts while within that viscus. The fact that solid food, immersed in gastric fluid out of the body, and kept at a temperature of about 100°, is gradually con- verted into a thick fluid similar to chyme, was shown by Spallanzani, Dr. Stevens, Tiedemann and Grmelin, and others. They used the gastric fluid of dogs,—obtained by causing the animals to swallow small pieces of sponge, which were subsequently withdrawn soaked with the fluid,—and proved nearly as much as the later experiments with the same kind of gastric fluid by Blondlot, Bernard, and others. But these need not be particularly referred to, while we have the more satisfactory and instructive observations which Dr. Beaumont made with the fluid obtained from the stomach of St. 31artin. After the man had fasted seventeen hours, Dr. Beaumont took one ounce of gastric fluid, put into it a solid piece of boiled recently salted beef weighing three drachms, and placed the vessel which contained them in a water-bath heated to 100°. " In forty minutes, digestion had distinctly commenced over the surface of the meat; in fifty minutes, the fluid had become quite opaque and cloudy, the external texture ACTION OF THE GASTRIC FLUID. 187 began to separate and become loose; and in sixty minutes chyme began to form. At 1 p. m." (two hours after the commencement of the experiment) " the cellular texture seemed to be entirely de- stroyed, leaving the muscular fibres loose and unconnected, floating about in small fine shreds, very tender and soft" (exxxviii. p. 120). In six hours, they were nearly all digested—a few fibres only re- maining. After the lapse of ten hours, every part of the meat was completely digested. The gastric juice, which was at first transpa- rent, was now about the color of whey, and deposited a fine sediment of the color of meat. A similar piece of beef was, at the time of the commencement of this experiment, suspended in the stomach by means of a thread; at the expiration of the first hour it was changed in about the same degree as the meat digested artificially; but, at the end of the second hour, it was completely digested and gone. In other experiments Dr. Beaumont withdrew, through the open- ing in the stomach, some of the food which had been taken twenty minutes previously, and which was completely mixed with the gas- tric juice. He continued the digestion, which had already com- menced, by means of artificial heat in a water-bath. In a few hours, the food thus treated was completely chymified; and the artificial seemed in this, as in several other experiments, to be exactly similar to, though a little slower than, the natural digestion. The apparent identity of the process within and out of the stomach thus manifested, while it shows that we may regard digestion as essentially a chemical process, when once the gastric fluid is formed, justifies the belief that Dr. Beaumont's other experiments with the digestive fluid may exactly represent the modifications to which, under similar conditions, its action in the stomach would be liable He found that, if the mixture of food and gastric fluid were exposed to a temperature of 34° F., the process of digestion was completely arrested. In another experiment, a piece of meat which had been macerated in water at the temperature of 100° for several days, till it acquired a strong putrid odor, lost, on the addition of some fresh gastric juice, all signs of putrefaction, and soon began to be digested. From other experiments he obtained the data for estimates of the degrees of digestibility of various articles of food, and the modes in which the digestion is liable to be affected, to which reference will again be made. When natural gastric juice cannot be obtained, many of these experiments may be performed with an artificial digestive fluid, the action of which, probably, very closely resembles that of the fluid secreted by the stomach. It is made by macerating in water por- tions of fresh dried mucous membrane of the stomach of a pig' or 1 The best portion of the stomach of the pig for this purpose is that be- tween the cardiac and plyoric orifices ; the cardiac portion appears to furnish the least active digestive fluid. 188 DIGESTION. other omnivorous animal, or of the fourth stomach of the calf, and adding to the infusion a few drops of hydrochloric acid—about 3-3 grains to half an ounce of the mixture, according to _ Schwann. Portions of food placed in such fluid, and maintained with it at a temperature of about 100°, arc, in an hour or more, according to the toughness of the substance, softened and changed in just the same manner as they would be in the stomach. The nature of the action by which the mucous membrane of the stomach, and its secretion, work these changes in organic matter, is exceedingly obscure. The action of the pepsine may be compared with that of a ferment, which at the same time that it undergoes change itself, induces certain changes also in the organic matters with which it is in contact. Or its mode of action may belong to that class of chemical processes termed " catalytic/' in which a sub- stance excites, by its mere presence, and without itself undergoing change as ordinary ferments do, some chemical action in the sub- stances with which it is in contact. So, for example, spongy plati- num, or charcoal, placed in a mixture, however voluminous, of oxygen'and hydrogen, make them combine to form water; and diastase makes the starch in grains undergo transformation, and sugar is produced. And that pepsine acts in some such manner appears probable from the very minute quantity capable of exerting the peculiar digestive action on a large quantity of food, and appa- rently with little diminution in its active power. The process dif- fers from ordinary fermentation in being unattended with the formation of carbonic acid, in not requiring the presence of oxygen, and in being unaccompanied by the production of new quantities of the active principle, or ferment. It agrees with the processes of both fermentation and organic catalysis, in that whatever alters the composition of the pepsine (such as heat above 100°, strong alcohol, or strong acids), destroys the digestive power of the fluid. Changes of the Food in the Stomach. The general effect of digestion in the stomach is the conversion of the food into chyme, a substance of various composition according to the nature of the food, yet always presenting a characteristic thick, pultaceous, grumous consistence, with the undigested portions of the food mixed in a more fluid substance, and a strong disagreeable acid odor and taste. Its color depends on the nature of the food, or on mixtures of yellow or green bile which may, apparently even in health, pass into the stomach. Reduced into such a substance, all the various materials of a meal may be mingled together, and near the end of the digestive process hardly admit of recognition; but the experiments of artificial diges- tion, and the examination of stomachs with fistulae, have illustrated many of the changes through which the chief alimentary principles CHANGES OF FOOD IN THE STOMACn. 189 pass, and the times and modes in which they are severally disposed of. These must now be traced. The readiness with which the gastric fluid acts on the several arti- cles of food is, in some measure, determined by the state of division, and the tenderness and moisture of the substance presented to it. By minute division of the food, the extent of surface with which the digestive fluid can come in contact is increased, and its action pro- portionably accelerated. Tender and moist substances offer less resistance to the action of the gastric juice than tough, hard, and dry ones do, because they may be thoroughly penetrated with it, and thus be attacked by it, not only at the surface, but at every part at once. Tbe readiness with which a substance is acted upon by the gastric fluid does not, however, necessarily imply the degree of its nutritive property; for a substance may be nutritious, yet, on account of its toughness or other qualities, hard to digest; and many soft, easily-digested substances contain comparatively a small amount of nutriment. But for a substance to be nutritive it must be capable of being assimilated to the blood; and to find its way into the blood, it must, if insoluble, be digestible by the gastric fluid or some other secretion in the intestinal canal. There is, therefore, thus far, a necessary connection between the digestibility of a substance and its power of affording nutriment. Those portions of food which are liquid when taken into the sto- mach, or which are easily soluble in the fluids therein, are probably at once absorbed by the blood-vessels in the mucous membrane of the stomach. 31agendie's experiments, and, better still those of Dr. Beaumont, have proved this quick absorption of water, wine, weak saline solutions, and the like; that they are absorbed without mani- fest change by the digestive fluid; and that, generally, the water of such liquid food as soups is absorbed at once, so that the substances suspended in it are concentrated into a thicker material, like the chyme from solid food, before the digestive fluid acts upon them. The action of the gastric fluid on the several kinds of solid food has been studied in various ways. In the earliest experiments, per- forated metallic' and glass tubes, filled with the alimentary substances, were introduced into the stomachs of animals, and after the lapse of a certain time withdrawn, to observe the condition of the contained substances ; but such experiments are fallacious, because gastric fluid has not ready access to the food. A better method was practised in a series of experiments by Tiedmann and Gmelin, who fed dogs with different substances, and killed them in a certain number of hours afterwards. But the results they obtained are of less interest than those of the experiments of Dr. Beaumont, on his patient, St. 3Iartin, and of Dr. (Josse (exxxvii.) who had the power of vomiting at will. Dr. Beaumont's observations show, that the process of digestion in the stomach, during health, takes place so rapidly, that a full meal, consisting of animal and vegetable substances, may nearly all be con- 190 DIGESTION. verted into chyme in about an hour, and the stomach left empty in two hours and a half. The detail of two days' experiments will be sufficient examples:— Exp. 42. April 7th, 8 A. M. St. 31artin breakfasted on three hard-boiled eggs, pancakes, and coffee. At half-past eight o'clock, Dr. Beaumont examined the stomach, and found a heterogeneous mixture of the several articles slightly digested. ... At a quarter past ten, no part of the breakfast remained in the stomach. Exp. 43.—At eleven o'clock the same day, he ate two roasted eggs and three ripe apples. In half an hour they were in an inci- pient state of digestion; and at a quarter past twelve no vestige of them remained. Exp. 44.—At two o'clock p. m. same day, he dined on roasted pig and vegetables. At three o'clock they were half chymified, and at half-past four nothing remained but a very little gastric juice. Again, Exp. 46. April 9th. At three o'clock p. M. he dined on boiled dried codfish, potatoes, parsnips, bread, and drawn butter. At half-past three o'clock examined, and took out a portion about half- digested ; the potatoes the least so. The fish was broken down into small filaments; the bread and parsnips were not to be distinguished. At four o'clock examined another portion. Very few particles of fish remained entire. Some of the few potatoes were distinctly to be seen. At half-past four o'clock took out and examined another por- tion ; all completely chymified. At five o'clock stomach emptv Cn. 158). J * Many circumstances besides the nature of the food are apt to in- fluence the process of chymification. Among them are, the quantity of food taken; the stomach should be fairly filled, not distended: the time that has elapsed since the last meal, which should be at least enough for the stomach to be quite clear of food: the amount of exercise previous, and subsequent to the meal, gentle exercise being favorable, over-exertion injurious to digestion; the state of mind, tranquillity of temper being apparently essential to a quick and due digestion :_ the bodily health : the state of the weather. But under ordinary circumstances, from three to four hours may be taken as the average time occupied by the complete digestion of a meal. Dr. Beaumont constructed a table showing the times required for the digestion of all usual articles of food in St. 3Iartin's stomach, ' and in his gastric fluid taken from the stomach. Among the sub- stances most quickly digested were rice and tripe, both of which were chymified in an hour; eggs, salmon, trout, apples, and venison, were digested in an hour and a half; tapioca, barley, milk, liver, fish, in two hours; turkey, lamb, potatoes, pig, in two hours and a half; beef and mutton required from three hours to three and a half, and both were more digestible than veal; fowls were like mutton in their degree of digestibility. Animal substances were, in general con- verted into chyme more rapidly than vegetables. ; CHANGES OF FOOD IN THE STOMACH. 191 Dr. Beaumont's experiments were all made on ordinary articles of food. A minuter examination of the changes produced by gastric digestion on various tissues has been lately made by Dr. Bawitz (xxvi.), who examined microscopically the products of the artificial digestion of different kinds of food, and the contents of the faeces after eating the same kinds of £)od. The general results of his examinations, as regards animal food, show that muscular tissue breaks up into its constituent fasciculi, and that these again are divided transversely; gradually the transverse striae become indistinct, and then disappear; and finally, the sarcolemma seems to be dis- solved, and no trace of the tissue can be found in the chyme, except a few fragments of fibres. These changes ensue most rapidly in the flesh of fish and hares, less rapidly in that of poultry and other animals. The fragments of muscular tissue which remain after the continued action of the digestive fluid, do not appear to undergo any alteration in their passage through the rest of the intestinal canal, for similar fragments may be found in faeces even twenty-four hours after the introduction of the meat into the stomach. The cells of cartilage and fibro-cartilage, except those of fish, pass unchanged through the stomach and intestines, and may be found in the faeces. The interstitial tissues of these structures are converted into pulpy, textureless substances in the artificial digestive fluid, and are not discoverable in the fiseccs. Elastic fibres are unchanged in the diges- tive fluid. Fatty matters also are unchanged; fat-cells are sometimes found quite unaltered in the faeces: and crystals of cholestearine may usually be obtained from faeces, especially after the use of pork-fat. As regards vegetable substances, Dr. Bawitz states, that he fre- quently found large quantities of cell-membranes uncbanged in the faeces; also starch-cells, commonly deprived of only part of their contents. The green coloring principle, chlorophyll, was usually unchanged. The walls of the sap-vessels and spiral-vessels were quite unaltered by the digestive fluid, and were usually found in large quantities in the faeces; their contents, probably, were re- moved. From these experiments we may understand the structural changes which the chief alimentary substances undergo in their conversion into chyme; and the proportions of each which are not reducible to chyme, nor capable of any further act of digestion. The chemical changes undergone in and by the proximate principles are less easily traced. Of the albuminous principles, the caseine of milk, and, according to Dr. Beaumont, fluid albumen, are coagulated by the acid of the gastric fluid; and thus, before they are digested, come into the con- dition of the other solid principles of the food. These, including solid albumen and fibrine, in the same proportion as they are brokeu up and anatomically disorganized by the gastric fluid, appeared to be reduced or lowered in their chemical composition (see Prout, xxi. 192 DIGESTION. p. 463). This chemical change is probably produced, as suggested by Dr. Prout, by the principles entering into combination with wa- ter. It is sufficient to conceal nearly all their characteristic pro- perties; the albumen is made scarcely coagulable by heat; the gelatine, even when its solution is evaporated, does not congeal in cooling; the fibrine and caseine cannot be found by their characte- ristic tests. It would seem, indeed, that all these various substances are converted into one and the same principle, a low form of albu- men, now generally termed albuminose or peptone, from which, after being absorbed, they are again raised in the elaboration of the chyle and blood to which they are assimilated. Whatever be the mode in which the gastric secretion affects these principles, it, or something like it, appears essential, in order that they may be assimilated to the blood and tissues. For, when Ber- nard and Barreswil injected albumen dissolved in water into the jugular veins of dogs, they always, in about three hours after, found it in the urine. But if, previous to injection, it was mixed with gastric fluid, no trace of it could be detected in the urine. The influence of the liver seems to be almost as efficacious as that of the gastric fluid, in rendering albumen assimilable; for Bernard found that, if diluted egg-albumen, unmixed with gastric fluid, is injected into the portal vein, it no longer makes its appearance in the urine, and is, therefore, no doubt, assimilated by the blood (xix. 1850, p. 889). The saccharine including the amylaceous principles are at first, probably, only mechanically separated from the vegetable substances within which they are contained, by the action of the gastric fluid. The soluble portions, viz., sugar, gum, and pectine are probably at once absorbed. The insoluble ones, viz., starch and lignine (or some parts of it) are rendered soluble and capable of absorption, by being converted into dextrine or grape-sugar. It is probable that this change is carried on to some extent in the stomach; for many experiments, including those of Dr. Percy (lxxi. April, 1843), show that starch is absorbed from the stomach, being, of course, previ ously rendered soluble. This change is probably effected, however, not by the gastric fluid, but by the saliva introduced with the food, or subsequently swallowed; for Frerichs found that it was arrested if, by tying the oesophagus, the continued introduction of salivary secretion into the stomach was prevented (xv. Bd. 3, Art. Ver- dauung). The transformation of starch is continued in the intestinal canal, probably, as will be shown, by the secretion of the pancreas, and by that of the intestinal glands and mucous membrane. And, further, respecting the action of the stomach in the digestion of starch, it may be doubted whether the human stomach has any power over it in a raw state; for both by man and Caruivora, when starch has been taken raw, as in corn and rice, large quantities of the granules are passed unaltered with the excrements. Cooking, MOVEMENTS OF THE STOMACH. 193 by expanding or bursting the envelopes of the granules, renders their interior more amenable to the action of the digestive organs; and the abundant nutriment furnished by bread, and the large propor- tion that is absorbed of the weight of it consumed, afford proof of the completeness of their power to make its starch soluble and pre- pare it for absorption.1 Of the oleaginous principles, as to their changes in the stomach, no more can be said than that they appear to be reduced to minute particles, and pass into the intestines mingled with the other con- stituents of the chyme. Being further changed in the intestinal canal, they are rendered capable of absorption by the lacteals.2 Movements of the Stomach. It has been already said, that the gastric fluid is assisted towards accomplishing its share in digestion by the movements of the stomach. In granivorous birds, for example, the contraction of the strong mus- cular gizzard affords a necessary aid to digestion by grinding and triturating the hard seeds which constitute part of the food. But in the stomachs of man and 3Iammalia the motions of the muscular coat are too feeble to exercise any such mechanical force on the food; neither are they needed, for mastication has already done the mechanical work of a gizzard; and the experiments of Beaumur and Spallanzani have demonstrated that substances enclosed in perfo- rated tubes, and consequently protected from mechanical influence, are yet digested. The normal actions of the muscular fibres of the human stomach appear to have a three-fold purpose; first, to adapt the stomach to the quantity of food in it, so that its walls may be in contact with the food on all sides, and, at the same time, may exercise a certain amount of compression upon it; secondly, to keep the orifices of the stomach closed until the food is digested, and then, permitting the pyloric orifice to open, to expel the chyme through it into the intes- tines; and, thirdly, to produce certain movements among the con- tents of the stomach whereby the thorough intermingling of the food and gastric fluid may be facilitated. 1 A new theory respecting the digestion of starch has just been advanced by M. Blondlot, who believes that the component particles of starch-grains are held together by an azotized substance analogous to gelatine; that the gastric fluid dissolves this substance, and that the liberated minute particles of starch are not further chemically acted upon in the alimentary canal, but, with the fatty, albuminous, and other molecules of chyle, are taken up by the intestinal villi (lix. 1856, p. 172). [2 Upon the subject of Gastric Digestion, the student may consult Bernard (Lecons de Physiologie Expe"rimentale appliquee a la Medicine, 1855 and 1S56); Longet (Gazette Hebdomadaire for April, 1855); Dalton (Amer. Journ. of Med. Sciences for Oct., 1854 and Oct., 1856); Smith (Philad. Med. Exami- ner for July 1856); Carpenter (Human Physiology 6th Amer. edit); and Chambers (Digestion and its Derangements, Amer. edit., ^ew York, 1856). 1 17 194 DIGESTION. When digestion is not going on, the stomach is uniformly con- tracted, its orifices not more firmly than the rest of its walls; but, if examined shortly after the introduction of food, it is found closely encircling its contents, and its orifices are firmly closed like sphinc- ters. The cardiac orifice, every time food is swallowed, opens to admit its passage to the stomach, and immediately again closes. The pyloric orifice, during the first part of gastric digestion, is usually so completely closed, that even when the stomach is sepa- rated from the intestines, none of its contents escape. But towards the termination of the digestive process, the pylorus seems to offer less resistance to the passage of substances from the stomach; first it yields to allow the successively digested portions to go through it; and then it allows the transit of even undigested substances. From the observations of Dr. Beaumont on the man St. Martin, it appears that food, as soon as it enters the stomach, is subjected to the action of the muscular coat, whereby it is moved through the fundus and along the great curvature from left to right, and then along the lesser curvature from right to left. He perceived the effect of the same motions in the changes of position which the stem of a thermometer, whose bulb was introduced into the stomach, under- went. Each of these circular motions occupied from one to three minutes. They increased in rapidity as the process of chymification advanced, and continued until it was completed. The contraction of the fibres situated towards the pyloric end of the stomach, seems to be more energetic and more decidedly peris- taltic than those of the cardiac portion. Thus, Dr. Beaumont found that when the bulb of the thermometer was placed about three inches from the pylorus, it was tightly embraced from time to time and drawn towards the pyloric orifice for a distance of three or four inches. The object of this movement appears to be to carry the food towards the pylorus as fast as it is formed into chyme, and to propel the chyme into the duodenum; the undigested portions of food being kept back until they also are reduced into chyme, or until all that is digestible has passed out. The action of these fibres is often seen in the contracted state of the pyloric portion of the stomach after death, when it alone is contracted and firm, while the cardiac portion forms a dilated sac. Sometimes, by a predominant action of strong circular fibres placed between the cardia and pylorus, the two portions, or ends, as they are called, of the stomach, are separated from each other by a kind of hour-glass contraction. These actions of the stomach are peculiar to it and independent. But it is, also, adapted to act in concert with the abdominal muscles, in certain circumstances which can hardly be called abnormal, as in vomiting and eructation. It has, indeed, been frequently stated, that the stomach itself is quite passive during vomiting, and that the ex- pulsion of its contents is effected solely by the pressure exerted upon it when the capacity of the abdomen is diminished by the contraction CHANGES OF FOOD IN THE STOMACH. 195 of the diaphragm and abdominal muscles: and this opinion has been especially supported by 31. 3Iagendie (xxxii. p. 554). After having injected tartar emetic into the veins of dogs, and in other instances given it by the mouth, he states that he never saw the stomach itself contract; and that if in such cases he drew the stomach out of the abdominal cavity, vomiting was prevented until he returned the viscus to its natural situation, when vomiting immediately ensued. Pressure with the hand had the same influence as the abdominal muscles; and even the action of the diaphragm alone, pressing against the linea alba, was sufficient to produce vomiting when the abdominal muscles had been cut away. When the stomach was removed, and a pig's bladder connected with the oesophagus in its stead, vomiting was produced in the same way as when the stomach itself remained uninjured. The latter observation, however, only proves that the pressure exerted by the contracting abdominal muscles upon an unresisting bag, is sufficient to expel its contents. And the others do not show more than that a considerable share in the act of vomiting is exercised by the abdominal muscles. On the other hand, many facts seem to prove that the stomach takes an active part in the expulsion of its own contents. In a case, for example, which fell under the notice of 31. Lepine (lv. 1844), the abdomen of the patient was torn open by a horn, and the stomach was wholly protruded. For half an hour, it was seen repeatedly and forcibly contracting itself, till by its own efforts it expelled all its contents except the gases. 3Ioreover, during vomiting, the contrac- tion of the stomach can usually be distinctly felt by the patient; though, at least in animals, it appears to be often so slight and rapid, that even when the stomach is exposed, its occurrence might be over- looked. Besides taking this share by its contraction, the stomach also es- sentially contributes to the act of vomiting, by the relaxation of the oblique fibres around the cardiac orifice, coincidently with the con- traction of the abdominal muscles and of the rest of its own fibres. For, until the relaxation of these fibres, no vomiting can ensue; when contracted, they can as well resist all the force of the contract- ing abdominal and other muscles, as the muscles by which the glottis is closed can resist the same force in the act of straining. Doubtless we may refer many of the acts of retching and ineffectual attempts to vomit to the want of concord between the relaxation of these muscles and the contraction of the rest. The muscles with which the stomach co-operates in contraction during vomiting, are chiefly and primarily those of the abdomen; the diaphragm also acts, but not as the muscles of the abdominal walls do. They contract and compress the stomach more and more towards the back and upper parts of the diaphragm; and the dia- phragm (which is usually drawn down in the deep inspiration that precedes each act of vomiting) holds itself fixed in contraction, and 196 DIGESTION. presents an unyielding surface against which the stomach may be pressed. It is enabled to act thus, and probably only thus, because the inspiration which precedes the act of vomiting, is terminated by closure of tbe glottis; after which the diaphragm can neither descend further, except by expanding the air in the lungs; nor, exceptby compressing the air, ascend again until, the act of vomiting having ceased, the glottis is opened again. Some persons possess the power of vomiting at will, without ap- plying any undue irritation to the stomach, but simply by a voluntary effort. It seems, also, that this power may be acquired by those who do not naturally possess it, and by continual practice may become a habit. Cases are also of no rare occurrence in which persons habitu- ally swallow their food hastily, and nearly unmasticated; and then, at their leisure, regurgitate it, piece by piece, into their mouth, re- masticate, and again swallow it, exactly as is done by the ruminant order of Mammalia. Influence of the Nervous System on Gastric Digestion. This influence is manifold; and is evidenced, 1st, in the sensa- tions which induce to the taking of food; 2d, in the secretion of the gastric fluid; 3d, in the movements of the food in and from the stomach. The sensation of hunger is manifested in consequence of deficiency of food in the system. The mind refers the sensation to the stomach; yet, since the sensation is relieved by the introduction of food either into the stomach itself, or into the blood through other channels than the stomach, it would appear not to depend on the state of the sto- mach alone. This view is confirmed by the fact that the division of both pneumogastric nerves, which are the principal channels by which the mind is cognizant of the condition of the stomach, does not appear to allay the sensations of hunger (Beid, lxxiii. vol. iii. p. 899). But that the stomach has some share in this sensation, is proved by the relief afforded, though only temporarily, by the introduction of even non-alimentary substances into this organ. It may, there- fore, be said that the sensation of hunger is derived from the system generally, but chiefly from the condition of the stomach; the nerves of which, we may suppose, are more affected by the state of the in- sufficiently replenished blood than those of other organs are. The sensation of thirst, indicating the want of fluid, is referred to the fauces, although, as in hunger, this is merely the local declara- tion of a general condition existing in the system. For thirst is relieved for only a very short time by washing the dry fauces; but may be relieved completely by the introduction of liquids into the blood, either through the stomach, or by injections into the blood- vessels, or by absorption from the surface of the skin, or the intes- tines. The sensation of thirst is perceived most naturally whenever ON THE SECRETION OF GASTRIC FLUID. 197 there is a disproportionately small quantity of water in the blood : as well, therefore, when water has been abstracted from the blood, as when saline, or any solid matters have been abundantly added to it. We can express the fact (even if it be not an explanation of it), by saying that the nerves of the mouth and fauces, through which the sense of thirst is chiefly derived, are more sensitive to tbis condition of the blood than other nerves are. And the cases of hunger and thirst are not the only ones in which the mind derives, from certain organs, a peculiar predominant sensation of some condition affecting the whole body. Thus, the sensation of the " necessity of breath- ing," is referred especially to the lungs; but, as Volkmann's experi- ments show, it depends on the condition of the blood which circu- lates everywhere, and is felt even after the lungs of animals are removed; for they continue, even then, to gasp and manifest the sensation of want of breath. So, perhaps, it may be added, the dis- ordered blood of fever, and other affections of the blood, circulates everywhere, but produces peculiar sensations in only certain parts. And, as with respiration, when the lungs are removed, the mind may still feel the body's want of breath, so in hunger and thirst, even when the stomach has been filled with innutritious substances, or the pneumogastric nerves have been divided, and the mouth and fauces are kept moist, the mind is still aware, by the more obscure sensa- tions in other parts, of the whole body's need of food and water. The influence of the nervous system on the secretion of gastric fluid is shown plainly enough in the influence of the mind upon digestion in the stomach; and is, in this regard, well illustrated by several of Dr. Beaumont's observations. 31. Bernard, also, watching the act of gastric digestion in dogs, who had fistulous openings into their stomachs, saw that on the instant of dividing their pneumogastric nerves, the process of digestion was stopped, and the mucous mem- brane of the stomach, previously turgid witb blood, became pale, and ceased to secrete. These, however, and the like experiments show- ing the instant effects of division of the pneumogastric nerves, may prove no more than the effect of a severe shock, and that influences affecting digestion may be conveyed to the stomach through those nerves. From other experiments it may be gathered that, although, as in 31. Bernard's, the division of both pneumogastric nerves always temporarily suspends the secretion of gastric fluid, and so arrests the process of digestion, and is occasionally followed by death from inanition, yet the digestive powers of the stomach may be completely restored after the operation, and the formation of chyme and the nutrition of the animal may be carried on almost as per- fectly as in health (Beid, lxxiii., vol. iii., p. 900, and Hubbenet, cxciv.). It has been said, that after the division of the pueumogastric nerves the absorption of poisons by the stomach does not take place, or is more slowly effected. But in thirtv experiments on mammalia, 17* 198 DIGESTION. which 31. Wernscheidt performed under Miiller's direction, not the least difference could be perceived in the action of narcotic poisons introduced into the stomach, whether the pneumogastric had been divided on both sides or not, provided the animals were of the same species and size. It appears, however, that such poisons as are capable of being rendered inert by the action of the gastric fluid, may, if taken into the stomach shortly after division of both pneu- mogastric nerves, produce their poisonous effects, in consequence, apparently, of the temporary suspension of the secretion of gastric fluid. Thus, in one of his experiments, 31. Bernard gave to each of two dogs, in one of which he had divided the pneumogastric nerves, a dose of emulsine, and, half an hour afterwards, a dose of amygdaline, substances which are innocent alone, but when mixed produce hydrocyanic acid. The dog whose nerves were cut, died in a quarter of an hour, the substances being absorbed unaltered, and mixing in the blood; in the other, the emulsine was decomposed by the gastric fluid before the amygdaline was administered; therefore, hydrocyanic acid was not formed in the blood, and the dog survived. The results of these experiments have been recently confirmed by Frerichs (xv. art. Verdauung). The influence of the nervous system on the movements of the sto- mach has been often seen in the retardation or arrest of these move- ments after division of the pneumogastric nerves. The results of irritating the same nerves were ambiguous; but the experiments of Longet (cxxxvi. vol. i. p. 323) and Bischoff (lxxx. 1843, Jahresbe- richt, p. civ.) have shown that the different results depended on whether the stomach were digesting or not at the time of the experi- ment. In the act of digestion, the nervous system of the stomach appears to participate in the excitement which prevails through the rest of its organization, and a stimulus applied to the pneumogastric nerves is felt intensely, and active movements of the muscular fibres of the stomach follow; but in the action of fasting, the same stimulus produces no effect. So, while the stomach is digesting, the pylorus is too irritable to allow anything but chyme to pass; but when diges- tion is ended, the undigested parts of the food, and even large bodies, coins and the like, may pass through it. Experiments have done little to explain the influence of the sym- pathetic nerves and their ganglia on the movements and secretions of the stomach. CHANGES OF THE FOOD IN THE INTESTINES. In the intestines, the passage of the chyme into which has been just described, the food thus far acted on and digested is exposed to the influence of the bile, the pancreatic fluid, and the secretions of the several glands imbedded in, and forming the intestinal mucous membrane. By the action of these various secretions the chyme STRUCTURE OF THE INTESTINES. 199 undergoes further changes ; after which, being more perfectly sepa- rated from the innutritions parts of the food, it is absorbed by the blood-vessels and lacteals, and the rest of the food, with portions of the above-named secretions, is ejected in faeces. Structure and Secretions of the Intestines. The intestinal canal is divided into two chief portions, named, from their differences in diameter, the small and the large intestine, which are separated from each other by a muscular valvular struc- ture, the ileo-caecal valve. The distinction is much less marked in Caraivora than in Herbivora; the large intestine in the latter class of animals being very wide and long. The small intestine, for con- venience of description, has been further divided into three portions, viz., the duodenum, which extends for eight or ten inches beyond the pylorus; the jejunum, which occupies two-fifths, and the ileum, which occupies three-fifths, of the rest of this portion of the canal. The large intestine also is subdivided into three portions, viz., the ccBcum, a short, wide pouch, separated from the small intestines by the ileo-caecal valve; the colon, which occupies the principal part of the large intestine, and is divided into an ascending, transverse, and descending portion; and the rectum, which terminates at the anus. The caecum is said to be absent in all animals which hybernate: it is small in Caraivora, and very large and long in the Solidungula, Bu- minantia, and Bodentia, in which there is reason to believe that it performs an especially active part in the digestion of the food which has not been perfectly transformed in the stomach. The intestines, like the stomach, are constructed of three princi- pal coats, viz., the serous, muscular, and mucous. The fibres of the muscular coat of the small intestine are arranged in two layers; those of the outer layer being disposed longitudinally; those of the inner layer transversely, or, in portions of circles encompassing the canal. In the enocum and colon, besides those longitudinal fibres which, as in the small intestines, are thinly disposed on all parts of the walls, others are collected into three strong bands, which are so connected with the other coats of the intestine, especially with the peritoneal coats, that they hold the canal in folds bounding intermediate sacculi. At the rectum, the fasciculi of these longitudinal bands, or ligaments of the colon as they are called, spread out and mingle with the other longitudinal fibres, forming with them a thicker layer of longitudinal fibres than exists on any other part of the intestinal canal. The mucous membrane of the small intestine has its surface greatly extended l>v being formed in transverse folds, termed valvulse conni- ventcs. These commence in the duodenum, are largely developed therein directly beyond the orifice of the bile-duct, and retaining the same large size and closely placed, are continued through the whole of the jejunum, a-nd then, gradually diminishing in size and close- 200 DIGESTION. ness of juxtaposition, they cease near the middle of the ileum. No similar folds exist in any part of the large intestine. In the substance of the mucous membrane of the small intestine numerous glands are imbedded; its surface is studded with minute processes termed villi; and it is covered throughout with cylindrical epithelium. The glands of the small intestine are of three principal kinds, named after their describers, the glands of Lieberkuhn (lxxv.), of Peyer (lxxvi.), and of Brunn or Brunner (Ixxvii.). The glands or follicles of Lieberkuhn are simple tubular depressions of the intestinal mucous membrane, thickly distributed over the whole surface, both of the large and small intestines.' (Fig. 48.) In the small intestine, these Fig. 48. Fig. 49. Fig. 48. Section of the mucous membrane of the smajl intestine in the dog, showing Lieberkiihn's follicles and villi, a. Villi. 6. Lieberkiihn's follicles, c. Other coats of the intestine. Fig. 49. a. Transverse section of Lieberkiihn's tubes or follicles, showing the basement membrane and subcolumnar epithelium of their walls, with the areolar tissue which connects the tubes, a. Basement membrane and epithelium, constituting the wall of the tube. 61 Cavity or lumen of the tube. Magnified 200 diameters. B. A single Lieberkiihn's tube, highly magnified. A happy accidental section in the oblique direction has served to display very distinctly tbe form and mode of packing of the epithelial particles, the cavity of the tube, and the mosaic pavement of its exterior, a. Basement- membrane, c. Internal surface of the wall of the tube. Magnified 200 diameters. are visible only with the aid of a lens, and their orifices appear as minute dots scattered between the villi. They are larger in the large intestine, and increase in size the nearer they approach the anal end of the intestinal tube, and in the rectum their orifices may be visible to the naked eye. Each tubule or follicle is constructed of the same 1 Lieberkuhn only described them as existing in the small intestine; Boehm (Ixxvii.) first pointed out their existence over the whole extent of the large intestine also. GLANDS OF THE SMALL INTESTINE. 201 essential parts as the intestinal mucous membrane, viz., a fine struc- tureless membraua propria or basement-membrane, a layer of cylin- drical epithelium lining it, and capillary blood-vessels covering its exterior. (Fig. 49.) Their contents appear to vary, even in health; the varieties being dependent, probably, on the period of time in relation to digestion at which they are examined. At the bottom of the follicle the contents usually consist of a granular material, in which a few cytoblasts or nuclei are imbedded : these cytoblasts, as they ascend towards the surface, are supposed to be gradually devel- oped into nucleated cells, some of which are discharged into the intestinal cavity. The purpose served by the material secreted by these glands is still doubtful. Their large number and the extent of surface occupied by them seem, however, to indicate that they are con- cerned in other and higher offices than the mere production of fluid to moisten the surface of the mucous membrane. The glands of Peyer occur exclusively in the small intestine. They are found in the greater abundance the'nearer to the ileo-caecal valve. They are met with in two conditions, viz., either scattered singly, in which case they are termed glandulse solitariai, or aggre- gated in groups of various sizes, chiefly of an oval form, and situated opposite the attachment of the mesentery. In this state they are named glandulce agminate, the groups being commonly called Peyer's patches. In structure, and probably in function, there is no Fig. 51. Fig. 50. Solitary gland of small intestine, after Boehm. Fig. 51. Part of a patch of the so-called Peyer's glands magnified, showing the various forms of the sacculi, with their zone of foramina. The rest of the membrane marked with Lk iHTkiilin's follicle and sprinkled with villi. (After Boehm.) essential difference between the solitary glands and the individual bodies of which each group or patch is made up; but the surface of the solitary glands (big. 50) is beset with villi, from which those forming the agminate patches (Fig. 51) are usually free. In the 202 DIGESTION. Fig. 52. condition in which they have been most commonly examined, each gland appears as a circular, opaque, white sacculus, from half a line to a line in diameter, and, according to the degree in which it is developed, either sunk beneath, or more or less prominently raised on, the surface of a depression or fossa in the mucous membrane. Each gland is surrounded by openings like those of Lieberkiihn's follicles (see Fig. 51), except that they are more elongated; and the direction of the long diameter of each opening is such that the whole produce a radiated appearance around the white sacculus. These openings appear to belong to tubules like Lieberkiihn's follicles; they have no communication with the sacculus, and none of its contents escape through them on pressure. Neither can any permanent opening be detected in the sacculus or Pey- er's gland itself (see Fig. 52). According to Henle's view, each of these glands may be regarded as a secreting cell, which, when its con- tents are fully matured, forms a com- munication with the cavity of the intestine by the absorption or burst- ing-»of its own cell-wall, and of the portion of mucous membrane over it; thus it discharges its secretion into the intestinal tube. A small shallow cavity or space remains for a time, after this absorption or dehiscence, but shortly disappears, together with all trace of the previous gland. According to Briicke (clxxxix., Nov., 1850), Kblliker (ccvi., p. 409, e. s.), and others, however, these bodies should not be regarded as temporary gland-cells, which thus discharge their elaborated con- tents into the intestines, but as analogous to absorbent glands, their probable office being to take up certain materials from the chyle, elaborate and subsequently discharge them into the lacteals, with which they are evidently closely connected, for Briicke has been able to inject the glands through these vessels. According to this view, Peyer's glands constitute a kind of appendage to the lacteal system, analogous to the mesenteric and lymphatic glands, and have no share in the production of any part of the intestinal fluid. The opaque-white contents of the glands consist of minute granules of fatty and albuminous matter, mingled with which are nucleated cells in various stages of development; and, if the view just stated be Fig. 52. Side-view of a portion of intes- tinal mucous membrane of a cat, showing a Peyer's gland (a) : it is imbedded in the submucous tissue (/), the line of separa- tion between which and the mucous mem- brane passes across the gland; b, one of the tubular follicles, the orifioes of which form the zone of openings around the gland; c, the fossa in the mucous mem- brane ; d. villi; e, follicles of Lieberkuhn. After Bendz (lxxix.). DIGESTION: INTESTINAL VILLI. 203 correct, these cells are, no doubt, actively engaged in the elaboration of material destined to be conveyed away by the lacteals. Brunner's glands are confined to the duodenum; they are most abundant and thickly set at the commencement of this portion of the intestine, diminishing gradually as the duodenum advances. They are situated beneath the mucous membrane, imbedded in the sub- mucous tissue, minutely lobulated bodies, visible to the naked eye, like detached small portions of pancreas, and provided with perma- nent gland-ducts, which pass through the mucous membrane and open on the internal surface of the intestine. As in structure, so probably in function, they resemble the pancreas; or at least stand to it in a similar relation to that which the small labial and buccal glands occupy in relation to the larger salivary glands, the parotid and sub-maxillary. The Villi are confined exclusively to the mucous membrane of the small intestine. They are minute vascular processes, (Fig. 53), Fig. 53. Capillary plexus of the villi of the human small intestine, as seen on the surface, after a successful injection, magnified 50 diameters. from a quarter of a line to a line and two-thirds in length (Miiller, xxxii. p. 271, Am. ed.), covering, in the proportion of about twenty- five on every square line, the surface of the mucous membrane (Lie- berkiihn, lxxv.), and giving it a peculiar velvety, fleecy appearance. They vary in form even in the same animal, and differ according as the vessels they contain are empty or full of chyle; being usually, in the former case, flat and pointed at their summits, in the latter cylindrical or clavate. Into the base of each villus there enter one or more lacteal vessels, which pass up the middle, and extend nearly to the tip, where they terminate cither by a closed and somewhat 204 DIGESTION. dilated extremity, or by Fig-. 5-1. One of the intestinal villi, with the commencement of a lacteal. Fig. 55. Fig. 55. Intestinal villus of a kitten, deprived of epithelium, treated with acetic acid, and magnified 350 diameters; a, base- ment membrane: b. subjaoent nuclei: c, nuclei of the organic muscular fibres: d, roundish nu- clei in the centre of the villus. After Kolliker. forming a kind of network (Fig. 54); in no case do they terminate in perforated or open extremities. (Krause, lxxx. 1837; Valentin, lxxx. 1839; E. H. Weber, lxxx. 1847, p. 400; Kolliker, ccvi. p. 404; and ccxii.). Two or more minute arteries are distributed within each villus; and, from their capillaries, which form a dense net- work, proceed one or two small veins, which pass out at the base of the villus (see Fig. 30, p. 117). Being a process of the mucous membrane, each villus possesses an invest- ing basement-membrane, the outer surface of which is covered with a layer of cylindri- cal epithelium, similar to that which invests every other part of the intestinal mucous membrane, and lines the tubular follicles of Lieberkuhn. Another important con- stituent of the villus has lately been discovered, namely, a layer of organic muscular fibres, which forms a kind of thin hollow cone immediately around the central lacteal, and is, therefore, situ- ated beneath the blood-vessels and much of the granular basis of the villus. The addition of acetic acid to the villus brings out the characteristic nuclei of the mus- cular fibres, and shows the size and posi- tion of the layer most distinctly (Fig. 55). Its use is still unknown, though it is impossible to resist the belief, that it is instrumental in the propulsion of chyle along the lacteals. The office of the villi is the absorption of chyle from the completely digested food in the intestines. The mode in which they effect this will be considered in the chapter on Absorption. The glands of the large intestine are of two kinds, viz., the tubular follicles of Lieberkuhn already described, and certain solitary glands which are scat- tered over the whole length of this part of the intestines, but are most numerous in the caecum and its vermiform appen- dix. Boehm described these solitary glands as simple flask-shaped cavities, THE PANCREAS, AND ITS SECRETION. 205 provided with a permanent orifice at the apex of the cavity. But l)r» Baly (Ixxi. March, 1847) has shown that they have not al- ways a permanent opening, but are sometimes closed, resembling in this respect the solitary glands of the small intestine. When closed, the existence of tbese glands can only be recognised by the absence of the orifices of the tubular follicles at the spots which they occupy. When a gland is emptied of its contents, it often happens that a number of the adjoining tubular follicles appear to be drawn inwards, and present a radiated arrangement around the centre of the gland. In the midst of these radiating tubular follicles the orifice of the gland may be discerned. Of the functions of these intestinal glands, as of the others already mentioned, nothing is known with certainty. The difficulty of de- termining the function of any single set of the intestinal glands must, indeed, seem almost insuperable : while so many fluids are discharged together into the intestine, and all acting, probably, at once, produce a general effect upon the food, it is almost impossible to discern the share of each. On this ground, the changes that the food undergoes in the intestines must be deferred till all the fluids that act upon it have been described. The Pancreas, and its Secretion. The pancreas is situated within the curve formed by the duodenum, and its main duct opens into that intestine, either through a small opening or through a duct common to itself and to the liver. The pancreas, in its minute anatomy, closely resembles the salivary glands; and the fluid elaborated by it appears almost identical with saliva. When obtained pure, in all the different animals in which it has been hitherto examined, it has been found colorless, transparent, and slightly viscid. The most recent investigations tend to confirm the account given by Leuret and Lassaigne, that when fresh it is alka- line, and contains an animal matter and certain salts, both of which are similar to those fouud in saliva, except in that there is no sulpho- cyanogen. Like saliva, the pancreatic fluid, shortly after its escape, becomes neutral and then acid. Most of the earlier, and some of the recent examiners, state that it contains a certain quantity of albumen; but it is probable that this was only an accidental ingre- dient in the specimens examined; for M. Blondlot (xvi. p. 124), who obtained a considerable quantity of pure secretion from the pancreas of a dog, states that he could not find a trace of albumen in it. See also Frerichs, xv. art. Verdauungy Numerous experiments have shown that starch is acted upon by the pancreatic fluid, or by portions of pancreas put in starch-paste, in the same manner as, and even more powerfully than, it is by saliva and portions of the salivary glands. And although, as before stated (p. 177\ many substances besides those glands can excite the transformation of starch into dextrine and grape sugar, yet it 206 DIGESTION. appears not improbable that the pancreatic fluid, exercising this power of transformation, is subservient to the purpose of digesting starch. MM. Bouchardat and Sandras (xix. Jan, 1845) have shown that the raw starch-granules which have passed unchanged through the crops and gizzards of granivorous birds, or through the stomachs of herbivorous Mammalia, are, in the small intestine, disorganized, eroded, and finally dissolved, as they are when exposed, in experi- ment, to the action of the pancreatic fluid. The bile cannot effect such a change in starch; but it remains yet to be proved whether the pancreas or the intestinal mucous membrane has the greater share in it, for both seem to possess the powers of converting the starch into sugar. (On the Action of the Intestinal Secretion alone on Starch, see Hubbenet, cxiv.) Moreover, the existence of a pancreas in the Caraivora indicates that it must serve some purpose besides that of digesting starch. Perhaps it may assist in the digestion of fat, or in rendering it fit for absorption ; for numerous cases are recorded in which the pan- creatic duct being obstructed so that the secretion could not be dis- charged, fatty or oily matter was abundantly discharged from the intestines (xli. vol. xviii. p. 57). In nearly all these cases, indeed, the liver was coincidently diseased, and the change or absence of the bile might appear to contribute to the result: but in at least one1 the liver was healthy, and there appeared nothing but the absence of the pancreatic fluid from the intestines to which the excretion or non-absorption of fatty matter could be ascribed. Moreover, Claude Bernard has lately stated, and has brought for- ward abundant evidence in support of his statement, that the express use of the pancreatic fluid is to render the fatty matters capable of absorption by the lacteals, by transforming them into a kind of emul- sion exactly like chyle. Evidence of a contrary nature, however, has been more recently advanced by Dr. Lenz (cxcvi.), and Dr. Frerichs (xv. art. Verdauungy They tied the pancreatic duct in cats, and after keeping them fasting for some time, to allow of the entire removal of the pancreatic fluid which migbt have passed into the intestine, they fed them with milk and fat meat, and found, on killing them and opening their intestinal canal, that the lacteals were filled with ordinary milky chyle. Moreover, in young dogs, Frerichs applied a ligature around the upper part of the small intestine below the entrance of the pancreatic duct, and then injected milk and oil into the lower part of the intestine, and found that the oily matters were completely absorbed by the lacteals. These and other argu- ments must make us hesitate, at least for the present, to give full credence to M. Bernard's statement. At the same time, however, it should be observed, that the fact of other secretions in the intes- tinal canal possessing the property of emulsifying fat is by no means 1 Museum, St. Bartholomew's Hospital. Series XX. No. 2. THE LIVER AND ITS SECRETION. 207 irreconcilable with the opinion that this power is, as M. Bernard appears to have proved, largely, if not principally resident in the pan- creatic fluid. It appears quite clear, from the experiments of Bidder, Schmidt, b rericbs, and others, that the pancreatic secretion has no solvent action on albuminous substances. The Liver and its Secretion. Structure of the Liver.—The liver receives blood through two vessels, the hepatic artery and the portal vein. The former, con- veying arterial blood, appears to be destined chiefly for the nutrition of the coats of the large vessels, the ducts, and the investing mem- branes belonging to the liver, supplying these parts with blood as the bronchial artery does the corresponding parts in the lungs (see p. 146). Through the latter, which cawies venous blood, are supplied the materials for the formation of bile. Fig. 56. Vertical section of the coats of the small intestine-of a dog, showing only tbe commencing portions of the portal vein and the capillaries. The injection has been thrown into the portal vein, but has not penetrated to the arteries, a. Vessels of the villi, b. Those of Lieberkiihn's tubes, c. Those of the muscular coat. The tributary branches, by the convergence and junction of which the main trunk of the portal vein is formed, comprise the veins which receive the blood from the stomach and intestinal canal, the spleen, pancreas, and gall-bladder (Fig. 56). The trunk thus formed branches, like an artery, in the liver, and its minutest divisions (short of the capillaries) are so arranged that they divide, or, as it were, map out, the whole liver into minute, nearly oval, portions or lobules, 208 DIGESTION. from Ath to ^tb. of an inch in diameter (Fig. 57). From these Fig. 57. Fig. 57. Transverse section of a lobule of the human liver, showing the reticular arrange- ment of the Bile-ducts, with some of the branches of the Hepatic Vein in the centre, and those of the Portal System at the periphery. Fig. 58. Fig. 58. A small lobule from the pig's liver, showing a, the interlobular branches of the portal vein, and 6, a portion of the lobular capillary net-work within the capsule injected. Each branch is seen to give o£f small branches on either side to the adjacent lobules. After Beale. interlobular veins (as they are called) proceed on every side minute capillaries (Fig. 58), which form dense net-works that seem to make STRUCTURE OF THE LIVER. 209 Fig. 59. up nearly the whole substance of the lobules. Through the capil- laries, the blood passes into intra-lobular veins, of which one, with its outspread branches, occupies the centre, or axis, of each lobule; and these intra-lobular veins, by successive junction and conflux, make up the trunks of the hepatic veins, by which the blood of the portal vein, after secreting the bile, is carried from the liver. The interspaces left in the plexuses of capillaries in every lobule of the liver appear filled with nucleated cells (hepatic or bile-cells, Fig. 59, A). These l£?<^ are rounded or polygonal cells, from 5^5th to y^Qth of an incb in diameter, contain- ing well-marked nuclei and granules, and having, sometimes, a yellowish tinge, especially about their nuclei, derived from the bile, which appears to be first formed in them; frequently they contain various-sized particles of fat (b, Fig. 59), though this fatty matter is probably not one of the natural constituents of healthy cells. In what relation these cells stand to the minutest bile-ducts is still unsettled: according to some observers, they form or line ducts, arranged in plexuses like those of the capillary blood-vessels, and interlacing with them (Kiernan, xliii. 1833, Kronenberg, lxxx. 1844, E. II. Weber, lxxx. 1844, Backer, cxlvi., Retzius, lxxx. 1850, Lionel Beale, cxxiii. 1856, p. 454, and ccxiv. Fig. 60. Cells from the liver. Magnified. Fig. 59. a. Small branch of inter-lobular duct, o, Most superficial part of cell containing net-work, with cells filled with oil, and free oil globules, c. Narrowest portions of the duct, magnified 125 diameters. The shaded parts show the points to which the injection reached. After Dr. Beale. 1856); (Fig. 60.) but according to others, they are only packed in among the blood-vessels, and by temporary communications discharge IS* 210 DIGESTION. their contents into the minute bile-ducts which line the spaces between the lobules, and never enter within them (Henle, xxxvii., Handfield Jones, lxxi. vol. xxxix. p. 387, and xliii. 1846-9, and 1853, Kolliker, ccvi. p. 418, etc.).1 The blood which the portal vein conveys to the liver is supplied from two chief sources; namely, that in the gastric and mesenteric veins, which contains the soluble elements of food absorbed from the stomach and intestines during digestion, and that in the splenic vein: it must therefore combine the qualities of the blood from each of these sources. The blood from the gastric and mesenteric veins will vary much according to the stage of digestion and the nature of the food taken, and can therefore seldom be exactly the same. The blood from the splenic vein is probably more definite in composition, though also liable to alterations according to the stage of the digestive pro- cess and other circumstances. Speaking generally, and without con- sidering the sugar, dextrine, and other soluble matters which may have been absorbed from the alimentary canal, the blood in the gastric and mesenteric veins appears to be deficient in solid matters, especially in red corpuscles, owing to dilution by the quantity of water absorbed, to contain an excess of albumen, though chiefly of a lower kind than usual, resulting from the digestion of nitrogenized substances, and termed albuminose (p. 192), and to yield a less tena- cious kind of fibrine than that of blood generally. The blood of the splenic vein seems generally to be deficient in red corpuscles, and to contain an unusually large proportion of albumen: the fibrine seems to vary in relative amount, sometimes greater, sometimes less, but, like that in the mesenteric veins, is said to be deficient in tena- city. The quantity of solid matter is, by some observers, said to be much reduced, by others to be scarcely below the average. The blood of the portal vein, combining the peculiarities of its two factors, the splenic and mesenteric venous blood, is usually of lower specific gravity than blood generally, more watery, contains fewer red cor- puscles, more albumen, chiefly in the form of albuminose, and yields a less firm clot than tbat yielded by other blood, owing to the defi- cient tenacity of its fibrine. These characteristics of portal blood refer to the composition of the blood itself, and have no reference to the extraneous substances, such as the absorbed materials of the food, which it may contain; neither, indeed, has any complete analysis of these been given. Comparative analyses of blood in the portal vein and blood in the hepatic veins have also been frequently made, with the view of deter- 1 On the structure of the Liver, the student may advantageously read the original papers of Kiernan (xliii. 1832, and lxxi. vol. xv.), or the description by Erasmus Wilson in the Cyclopaedia of Anatomy, or that in Dr. Budd's Treatise on Diseases of the Liver, as well as the more modern accounts re- ferred to in the text. [The student is also referred to the article of Dr. Leidy on the Structure of the Liver, in the Amer. Journ. of Med. Sciences, for Jan. 1848.] PORTAL AND HEPATIC VENOUS BLOOD. 211 mining the changes which this fluid undergoes in its transit through the liver. G reat diversity, however, is observable in the analyses of these two kinds of blood by different chemists. Part of this diver- sity is no doubt attributable to the fact pointed out by Bernard, that unless the portal vein is tied before the liver is removed from the body, hepatic venous blood is very liable to regurgitate into the portal vein, and thus vitiate the result of the analysis. Guarding against this source of error, recent observers seem to have determined that hepatic venous blood contains less water, albumen, and salts, than that of the portal vein; but that it yields a much larger amount of extractive matter, among which is a constant element, namely, grape-sugar, which is found equally the same, whether saccharine or farinaceous matter have been present in the food or not.1 The Secretion of Bile, of which we will now speak, is the most obvious, and one of the chief functions which the liver has to per- form ; but, as will be presently shown, it is not the only one, for recent discoveries have shown that important changes are effected in certain constituents of the blood in its transit through this gland, whereby they are rendered more fit for their subsequent purposes in the animal economy. Composition of the Bile.—The bile is a somewhat viscid fluid, of a yellow or greenish-yellow color, a strongly bitter taste, and a pecu- liar nauseous smell; its specific gravity is from 1026 to 1030. Its color and degree of consistence vary much, apparently independent of disease ; but, as a rule, it becomes gradually more deeply colored and thicker while it advances along its ducts, or remains long in the gall-bladder, wherein, at the same time, it becomes more viscid and ropy from being mixed with the mucus. The bile has been always described as having naturally a slightly alkaline reaction; but the investigations of Gorup-Besanez (Ixxxii.), and Bidder and Schmidt (ccviii.), show that in man, oxen, and pigs, it is always, when first secreted, exactly neutral; but, in the early stages of its decomposition, is apt to become acid, and subsequently alkaline. Numerous analyses of the bile of man and animals have been published; that of the bile of the ox by Berzelius (xv. art. Galle, p. 518), is perhaps one of the most correct, and the researches of Gorup-Besanez, Strecker, and others, show that the composition of human bile is essentially similar. The analysis by Berzelius gives— Water.......................................................... 904-4 Biline (with fat and coloring principles)............. 80-0 Mucus, chiefly from the gall-bladder................. 03.0 Salts........................................................... 12-6 1000-0 !For the latest observations on the composition of the portal and hepatic venous blood, see Scherer's Report in Canstatt's Jahresbericht, 1855, p. 171, ct soq.; see also on the subject, Gray (ccxii.), Carpenter (ccvii. p. 168), and Lelnnann (cciii.). 212 DIGESTION. The Biline or biliary matter described by Berzelius, when freed by ether from the fat with which it is combined, is a resinoid_ sub- stance, soluble in water, alcohol, and alkaline solutions, and giving to the watery solution the taste and general characters of bile. Mulder (xiv. 1847), whose account of biline accords very closely with that of Berzelius, describes it as being neutral, and without the tendency to unite with bases, solid but not crystallizable. Berzelius and Mulder both consider biline to be a single substance, which, in decom- position, yields various materials that have been regarded as natural constituents of bile, such as the biliary resin and picromel of The- nard (xiii. t. i. p. 23), the taurine found by Gmelin, the dyslysin, choleic, fellinic, and other acids of as many other writers.1 Accord- ing to Mulder, this decomposition of biline begins in the gall-bladder of the living animal, and continues out of the body until the whole of the biline is decomposed; and because both of its quickness and the variety of its results, the exact composition of pure biline cannot be determined. According to Lehmann, Streckcr, and Bidder and Schmidt, how- ever, biliary matter is not the single substance supposed by Berzelius and Mulder, but is a compound of soda combined with one or both of two resinous acids, which by Strecker are named cholic and choleic, by Lehmann, glycocholic and taurocholic, because the former consists, he believes, of cholic acid conjugated with glycine (or sugar of gelatine), the latter of the same acid conjugated with taurine. In the bile of most Mammalia, according to Lehmann, both these acids, combined with soda, exist, and constitute about 75 per cent, of the solid matter. In the dog, there is no glycocholic, but only tauro- cholic acid united with soda (ccx. p. 157). The Fatty matter of bile consists chiefly of the crystalline sub- stances named cholestearine (see p. 31). Other fatty substances are usually found in various small proportions, such as oleine and mar- garine, or their acids, oleic and margaric acids, combined with potash and soda. The coloring matter has not yet been obtained pure from the bile, owing to the facility with which it is decomposed. It oc- casionally deposits itself in the gall-bladder as a yellow substance mixed with mucus, and in this state has been frequently examined. Berzelius (xv. art. Galfe) gave it the name of cholepyrrhine or bili- pyrrhine; Simon (Ixxxii. vol. i. p. 43) named it bilipho^ine. Ber- zelius also thought it composed of two coloring matters: because if, to the solution of cholepyrrhine in caustic soda, or potash, an acid is added, a green substance is deposited in flocculi, which bas all the properties of chlorophyll, the green coloring matter of plants; this 1 The principal writers on the chemistry of the bile, besides those just quoted, are Kemp, in various parts of the Chemical Gazette and London Medical Gazette; Demarcay (xii. 67, p. 177); Liebig (xi. 3d edit.); Prout (xxi. p. 393, Am. Ed.); Griffith (cii.); Strecker (x. bd. 66, 1. —43); Leh- mann (cciii. and ccx.); Bidder and Schmidt (ccviii.) CHEMICAL CONSTITUENTS OF BILE. 213 he called hilive.rdin. After its separation, a yellow substance still remains, which he named bilifuloine. But it is probable, as main- tained by Gorup-Besanez (lxxxiii.), that these substances are only the products of the decomposition of a single coloring matter, the original cholepyrrhine of Berzelius, the biliphjeine of" Simon; and that the various colors presented by bile depend upon modifications of this principle. Gorup-Besanez states, also, that there is a con- siderable analogy between it and the coloring matter of blood; a view which has been maintained also by Polli (vii. 1846), and more recently by others. The addition of a mineral acid to the coloring matter of bile produces singular transformations of tint, converting the yellowish color successively into green, blue, violet, red, and brown, and thus affords a ready means of detecting the presence of bile or of its coloring matter. The mueus in bile is derived chiefly from the mucous membrane of the gall-bladder, but in part also from the hepatic ducts and their branches. It constitutes the residue after bile is treated with alcohol. The epithelium with which it is mixed may be detected in the bile withthe microscope in the form of cylindrical cells, either scattered or still held together in layers. To the presence of this mucus is probably to be ascribed the rapid decomposition undergone by the biline; for, according to Berzelius, if the mucus be separated, bile will remain unchanged for many days. The saline or inorganic constituents of the bile are similar to those found in most other secreted fluids, including the chlorides of sodium and potassium, and the phosphates and sulphates of soda, potash, lime, and magnesia. It has generally been supposed that the bile contains free soda, or an alkaline salt of this substance, such as the carbonate or tribasic phosphate; but Gorup-Besanez having shown, as already stated, that the bile is really neutral, it is probable that the carbonate and tribasic phosphate of soda, found in the ashes of bile, are formed in the incineration, and do not exist as such in the fluid. Oxide of iron, also, is a common constituent of the ashes of bile (Gorup-Besanez, lxxxiii.); and copper is generally found in healtby bile, and constantly in biliary calculi (Gorup-Besanez, lxxxiii., and see p. 40). Such are the principal chemical constituents of bile; but its phy- siology is, perhaps, more illustrated by its ultimate elementary com- position. According to Liebig's analysis, the biliary matter — con- sisting of biline and the products of its spontaneous decomposition— yields, on analysis, 76 atoms of carbon, 66 of hydrogen, 22 of oxy gen, 2 of nitrogen, and a certain quantity of sulphur.1 Comparing 1 The sulphur is combined with the taurine—one of the substances yielded by the decomposition of biline. According to Redtenbacher's analysis (x. Feb., 184ti), the general correctness of which is confirmed by Dr. Gregory (vii. p. 566) and others, the quantity of sulphur in taurine is about 26°per 214 DIGESTION. this with the ultimate composition of the organic parts of blood — which may be stated at C48H36N60H with sulphur and phosphorus- it is evident that bile contains a large preponderance of carbon and hydrogen, and a deficiency of nitrogen. The import of this will presently appear. The process of secreting bile is probably continually going on, but appears to be retarded during fasting, and accelerated on taking food. This was shown by Blondlot (xx. p. 62), who, having tied the com- mon bile-duct of a dog, and established a fistulous opening between the skin and gall-bladder, whereby all the bile secreted was dis- charged at the surface, noticed that, when the animal was fasting, sometimes not a drop of bile was discharged for several hours; but that, in about ten minutes after the introduction of food into the stomach, the bile began to flow abundantly, and continued to do so during the whole period of digestion. Bidder and Schmidt's obser- vations are quite in accordance with this. The bile is probably formed first in the hepatic cells; then, beiDg discharged (in some unknown way—perhaps, Kblliker suggests, by transmission from cell to cell) into the minutest hepatic ducts, it passes into the larger trunks, and from the main hepatic duct may be carried at once into the duodenum.1 But, probably, this happens only while digestion is going on; during fasting it flows from the common bile-duct into the cystic duct, and thence into the gall- bladder, where it accumulates till, in the next period of digestion, it is discharged into the intestine. The gall-bladder thus fulfils what appears to be its chief or only office, that of a reservoir; for it ena- bles bile to be constantly secreted for the purification of the blood, yet insures that it shall all be employed in the service of digestion, although digestion is periodic and the secretion of bile is constant. The mechanism by which the bile passes into the gall-bladder is simple. The orifice through which the common bile-duct commu- nicates with the duodenum is narrower than the duct, and appears to be closed, except when there is sufficient pressure behind to force the bile through it. The pressure exercised upon the bile secreted during the intervals of digestion, appears insufficient to overcome the force with which the orifice of the duct is closed; and the bile in the common duct, finding no exit in the intestine, traverses the cystic duct, and so passes into the gall-bladder, being probably aided in this retrograde course by the peristaltic action of the ducts. The bile is discharged from the gall-bladder, and enters the duodenum cent. According to Dr. Kemp (vi. No. 99, 1846), the sulphur in the bile of the ox, dried and freed from mucus, coloring matter, and salts, constitutes about 3 per cent. 1 It should be observed, however, that according to Dr. Handfield Jones, the hepatic cells have little if any share in the secretion of bile, their office being chiefly to form the sugar which the liver contains (xliii. 1853). AMOUNT OF BILE SECRETED. 215 on the introduction of food into the small intestine: being pressed on by the contraction of the coats of the gall-bladder, and probably of the common bile-duct also; for both these organs contain organic muscular fibre-cells. Their contraction is excited by the stimulus of the food in the duodenum acting so as to produce a reflex move- ment, the force of which is sufficient to open the orifice of the com- mon bile-duct. \rarious estimates have been made of the quantity of bile dis- charged into the intestines in twenty-four hours : the quantity doubt- less varies, like that of the gastric fluid, in proportion to the amount of food taken. The usual estimate has been that, in man, the quantity of bile daily secreted is from seventeen to twenty-four ounces (xi. 1st edit., p. 64); but Blondlot's investigations make it probable that this estimate is too high. The quantity discharged through the fistulous opening of the gall-bladder in one of his dogs amounted, on the average, to twelve and a half drachms in twenty-four hours. And if with Haller we suppose that the liver of man secretes from four to five times the quantity secreted by the liver of a dog, this would give from six to eight ounces as the average quantity of bile poured into the intestinal canal in twenty-four hours (xx. p. 61). On the other hand, however, it must be observed, that Bidder and Schmidt estimate the daily quantity secreted by man at about 54 ounces. The purposes served by the secretion of bile may be considered to be of two principal kinds, viz. : excrement itious and digestive.1 As an excrementitious substance, the bile is destined especially for the preparation of portions of carbon and hydrogen, in order that they may be removed from the blood: and its adaptation to this purpose is well illustrated by the peculiarities attending its secretion and disposal in the foetus. During intra-uterine life, the lungs and the intestinal canal are almost inactive: there is no respiration of open air or digestion of food; these are unnecessary, because of the supply of well-elaborated nutriment received by the vessels of the foetus at the placenta. The liver, during the same time, is propor- tionally larger than it is after birth, and the secretion of bile is active, 1 In birds, e.g., in the chick, during about the last three days of incuba- tion, the liver is made bright yellow by the absorption of the yelk, which fills and clogs all the minute branches of the portal veins, But in time the ma- terials of the yelk disappear, part being developed into blood-corpuscles, which enter the circulation, the rest forming bile, and being discharged into the intestines (E. II. Weber, xxxiii. 1846; see also an essay by him on a cor- responding development of blood-corpuscles in the liver of the frog, lix., 18 IS, p. ;>S). It is possible that, in a very early period of its development, blood may be thus formed in the liver of the mammalian embryo out of the absorbed contents of its umbilical vesicle ; but there is only analogy to make this probable; and there is no evidence that any such blood-making function ever belongs to the liver in extra-uterine life, or after a placenta is deve- loped 216 DIGESTION. although there is no food in the intestinal canal upon which it can exercise any digestive property. At birth the intestinal canal is full of thick bile, mixed with intestinal secretion ; for the meconium, or faeces of the foetus, is shown, by the analyses of Simon (Ixxxii., vol. ii. p. 367), and of Frerichs (xxii., vol. iii. p. 314), to contain all the essential principles of bile.1 In the foetus, therefore, the main purpose of the secretion of bile must be the purification of the blood by direct excretion, i. e., by separation from the blood, and ejection from the body without further change. Probably, all the bile secreted in foetal life is incorporated in the meconium, and with it discharged ; and thus the liver may be said to discharge a function in some sense vicarious of that of the lungs. For, in the foetus, nearly all the blood coming from the placenta passes through the liver previous to its distribution to the several organs of the body; and the abstraction of carbon, hydrogen, and other elements of bile will purify it, as in extra-uterine life the separation of carbonic acid and water at the lungs does. This evident disposal "of the fcetal bile by excretion makes it highly probable that the bile in extra-uterine life is also, at least for the most part, destined to be discharged as excrement. But the analysis of the faeces of both children and adults shows that (except when rapidly discharged in purgation) they contain very little of the bile secreted, probably not more than one-sixteenth part of its weight, and that this portion includes only its coloring and some of its fatty matters, but none of its essential principle, the biline (Berzelius, xxiv., Gorup-Besanez, lxxxiii., p. 51, Pettenkofer, x., 1844, p. 90, and Bidder and Schmidt, ccviii.). All the biline is again absorbed from the intestines into the blood. But the elementary composition of biline (see p. 213) shows such a preponderance of carbon and hydrogen that it cannot be appropriated to the nutrition of the tis- sues ; therefore, it may be presumed that, after absorption, the car- bon and hydrogen of the biline combining with oxygen are excreted in carbonic acid and water. The destination of the bile is, on this theory, essentially the same in both foetal and extra-uterine life; only, in the former, it is directly excreted, in the latter indirectly, being, before final ejection, modified in its absorption from the in- testines and mingled with blood. The change from the direct to the indirect mode of excretion of the bile may, with much probability, be connected with a purpose in relation to the development of heat. The temperature of the foetus is maintained by that of the parent, and needs no source of heat 1 Analysis of Meconium by Frerichs:— Biliary resin ..... .................................................... 15-6 Cholestearine, oleine, and margarine........................... 15-4 Epithelium, mucus, pigment, and salts........................ 69. 100- THE BILE VIEWED AS AN EXCRETION. 217 within the body of the foetus itself; but, in extra-uterine life, there is (as one may say) a waste of material for heat when any excretion is discharged unoxydized: the carbon and hydrogen of the biline, therefore, instead of being ejected in the faeces, are reabsorbed, in order that they may be combined with oxygen, and that in the com- bination heat may be generated. That ejection is the final destination of the bile, and that whatever other purposes it may serve are not essential to the maintenance of life, appear from facts mentioned by Blondlot (xx). He found that dogs may live in health for at least several months, even though the bile is prevented from passing into the intestines by removing a portion of the common bile-duct, provided all the bile that is secreted can be discharged from the body by keeping open a fistulous com- munication between the skin and the gall-bladder. It must not, however, _ be thought indifferent whether the bile be reabsorbed or not, provided it be ejected; for, in experiments similar to those of Blondlot, Schwann (lxxx., 1844) found that the animals always died with the signs of inanition; such signs, it may be supposed, as would be produced by the deficiency of carbon and hydrogen in the blood. Though the chief purpose of the secretion of bile may thus appear to be the purification of the blood by excretion, yet there is reason to believe that, while it is in the intentines, it serves in the process of digestion. In nearly all animals the bile is discharged, not through an excretory duct communicating with the external surface, or with a simple reservoir, as most excretions are, but is made to pass into the intestinal canal, so as to be mingled with the chyme directly after it leaves the stomach; an arrangement, the constancy of which clearly indicates that the bile has some important relations to the food with which it is thus mixed. A similar indication is furnished also by the fact that the secretion of bile is more active, and the quantity discharged into the intestines much greater, during diges- tion, than at any other time (Blondlot, xx. p. 62). ■ Moreover, the bile is a very elaborated fluid, formed of materials which do not pre- exist in the same condition in the blood, and secreted by cells in a highly organized gland; in which respects it resembles the higher kinds of secretions which are destined to serve some important pur- poses in the economy, and differs from those which, like carbonic acid and the urine, are straightway discharged from the body. Respecting the nature of the influence exercised by the bile in digestion, there is, however, very little at present known. It is sup- posed that the bile assists, in some way, in converting the chyme into chyle, and in rendering it capable of being absorbed by the lacteals. 1 This activity of secretion during digestion may, however, be in part ascribed to the fact that a greater quantity of blood is sent through the portal ■^yein to the liver at this time, and that this blood contains some of the mate- rials of the food absorbed from the stomach and intestines. 19 218 DIGESTION. For it has appeared in some experiments in which the common bile- duct was tied, that, although the process of digestion in the stomach was unaffected, chyle was no longer well-formed; the contents of the lacteals consisting of clear, colorless fluid, instead of being opaque and white, as they ordinarily are, after feeding (Sir B. Brodie, v., 1S23, Tiedemann and Gmelin, xxix.). Similar experiments by Blondlot (xx.) have not yielded the same result: though more recent observations by Bidder and Schmidt, seem to show that less fat is disgested and absorbed when bile is prevented entering the intes- tines, than when it is freely mingled with the intestinal contents (ccviii. pp. 215-234). The bile has a strongly antiseptic power, and may serve to prevent the decomposition of food during the time of its sojourn in the in- testines. The experiments of Tiedemann and Gmelin show that the contents of the intestines are much more fetid after the common bile- duct has been tied than at other times; and the experiments of Bidder and Schmidt on animals with an artificial biliary fistula, confirm this observation; moreover, it is found that the mixture of bile with a fermenting fluid stops or spoils the process of fermen- tation. Again, the contents of the small intestine are alkaline, though the chyme is acid. The bile, with the pancreatic fluid, and the secretion of the intestinal glands, is supposed to make this acid fluid alkaline, and the bile was formerly thought to do so by the free soda, or the carbonate or tribasic phosphate of soda, said to be among its inor- ganic constituents; but, as already stated (p. 211), the bile is neu- tral, and it is more probable that, as Valentin suggests (iv. vol. i. p. 338), the chyme is made alkaline by the ammonia which is one of the products of the spontaneous decomposition of bile in the intes- tines. The bile has also been considered to act as a kind of natural pur- gative by promoting an increased secretion of the intestinal glands, and by stimulating the intestines to the propulsion of their contents. This view receives support from the constipation which ordinarily exists in jaundice, from the diarrhoea which accompanies excessive secretion of bile, and from the purgative properties of ox-gall. The above observations express nearly all that is known, and most of what is reasonably supposed, of the influence of the bile on the contents of the small intestine; but it is evident that there is no certainty of more than the general fact that some influence is exer- cised. Nothing is really known of the changes effected by the mix- ture of the bile with the food. By itself, it certainly seems to produce no material effect on any of the principal elements of food, for on submitting various substances to its influence out of the body it has been found that starch is unchanged, that albuminous sub- stances are unacted upon even though the bile be acidulated, and that even fatty matters undergo no chemical change, being, at the INFLUENCE OF BILE IN DIGESTION. 219 most, converted into a kind of emulsion less perfect than that formed when similar fatty matters are mixed with the pancreatic fluid. (Beuce Jones, lxxxviii. July 5, 1851). Experiments like these, however, made on bile alone and out of the body should be very cautiously received as evidence concerning the digestive function of this fluid when placed under natural conditions, and especially when mixed with the other secretions poured into the intestinal canal. For the observations of Zander (exev.) show very clearly that much more powerful effects are produced on the chyle by these several secretions when mixed than when left to act separately: and it is therefore probably to their combined rather than to their separate eftect that the most important changes ensuing in the alimentary matters must be ascribed, the share which each takes in the general result being quite unknown. Again, nothing is known with certainty respecting the changes which the reabsorbed portions of the bile undergo in either the in- testines or the absorbent vessels. That they are much changed appears from the impossibility of detecting them in the blood; and that part of this change is effected in the liver (through which these portions of the reabsorbed bile must pass with all the other materials absorbed from the digestive canal) is probable from an experiment of Magendie, who found that when he injected bile into the portal vein the dog was unharmed, but was killed when he injected the bile into one of the systemic vessels. The secretion of bile, as already observed, is only one of the pur- poses fulfilled by the liver. Another very important function ap- pears to be that of so acting upon certain constituents of the blood passing through it, as to render some of them capable of assimilation with the blood generally, and to prepare others for being duly eli- minated in the process of respiration. From the labors of M. C. Bernard, to whom we owe most of what we know on this subject, it appears that the low form of albuminous matter, or albuminose, con- veyed from the alimentary canal by the blood of the portal vein, requires to be submitted to the influence of the liver before it can be assimilated by the blood; for if such albuminous matter is in- jected into the jugular vein, it speedily appears in the urine; but if introduced into the portal vein, and thus allowed to traverse the liver, it is no longer ejected as a foreign substance, but is probably incorporated with the albuminous part of the blood. An important influence seems also to be exerted by the liver upon the saccharine matters derived from the alimentary canal. The chief purpose of the saccharine and amylaceous principles of food is in relation to respiration and the production of animal heat; but in order that they may fulfil this their main office, it seems to be essential that they should undergo some intermediate change, which is effected in the liver, and which consists in their conversion into a peculiar form of saccharine matter, analogous to glucose or diabetic sugar, 220 DIGESTION. and usually termed " liver-sugar." That such influence is exerted by the liver seems proved by the fact, that when cane or grape sugar is injected into the jugular vein, it is speedily thrown out of the system, and appears in the urine; but when injected into the portal vein, and thus enabled to traverse the liver, it ceases to be excreted at the kidneys: and, what is still more to the point, a very large quantity of glucose, or liver-sugar, may be injected into the venous system without any trace of it appearing in the urine. So that it may be concluded, that the saccharine principles of the food undergo in their passage through the liver some transformation necessary to the subsequent purpose they have to fulfil in relation to the respi- ratory process, and without which such purpose probably could not be properly accomplished, and the substances themselves would be eliminated as foreign matters by the kidneys. Then, again, it has been discovered by Bernard, and the discovery has been amply confirmed by Lehmann and other distinguished ani- mal chemists, that the liver possesses the remarkable property of forming sugar out of principles in the blood which contain no trace of saccharine or amylaceous matter. In animals fed exclusively on flesh, as well as in those living on mixed food, the liver is continu- ally engaged in producing large quantities of sugar, which passes into the blood of the hepatic vein, and is thence carried off, appa- rently to be consumed in the process of respiration; for although found in the blood of the right cavities of the heart, it is rarely, and then only in small amount, found in the blood proceeding from the left side of this organ. That the sugar in the case of flesh-feeding animals is formed within the liver itself, and not as part of the digestive process in the alimentary canal, is proved by the fact, that while an abundant quantity is found in the tissue of the liver and in the hepatic venous blood, none can be detected in the chyle, or even in the blood of the portal vein, when proper precautions are taken to prevent any reflux of the hepatic venous blood into the portal stream. There is still much doubt as to which constituents of the blood, when this fluid is destitute of saccharine principles, furnish the ma- terial out of which the liver-sugar is formed. Fat being a ternary non-nitrogenous compound like sugar, it is not unreasonable to sup- pose that it may be readily transformed into the latter substance; and this supposition is strongly supported by the result of one of Poggiale's experiments (lix. 1856, p. 177), in which the hepatic venous blood of a dog, fed for ten days exclusively on fat and but- ter, yielded nearly as much sugar as that of another dog fed for the same length of time on flesh alone. The fact, however, that a diet composed entirely of fatty matter does not lead to the formation of more sugar than a diet of fat and flesh together, or of flesh alone, supports the view entertained by Bernard, that much of the liver- sugar may be derived from some of the albuminous principles of the FUNCTIONS OF THE LIVER. 221 blood by the separation of their nitrogen. The nitrogenous sub- stances thus thought to be transformed into sugar in the liver, may consist either of albuminous constituents of food, or of disintegrating materials resulting from the waste of nitrogenous tissues, which, preparatory to their final ejection from the system, may pass througb the intermediate state of sugar, which fits them for ready oxydation in the respiratory process. But as yet this is mere speculation, and the real source and nature of the materials out of which the liver forms sugar, especially in animals fed exclusively on flesh, must be still considered as undetermined.1 Many of Bernard's experiments seem to show that fat, as well as sugar, may be formed by the liver, especially in herbivorous animals, out of the albuminous and other constituents of the blood : but there is still much uncertainty on this point.2 With regard, then, to the functions of the liver, it may be con- cluded that they consist, first, in the secretion of bile, for purification of the blood, for purposes in relation to digestion, and for the prepa- ration of hydro-carbonaceous principles for subsequent elimination or combustion in the respiratory process; and, secondly, in the produc- 1 Lehmann has lately advanced the opinion that part of the liver-sugar is derived from decomposition of the htcmatine of the blood-corpuscles, which he believes to ensue in the liver (lix. 1856, p. 176); and this is quite con- sistent with Valentin's interesting observation, that even in hybernating animals, in whom there can be very little waste of tissue, and no fresh intro- duction of food, the production of su immersed in chlo- rine; and Abernethy observed that when he held his hands in oxy- gen, nitrogen, carbonic acid, and other gases contained in jars over mercury, the volume of the gases became considerably diminished. The share which the evaporation from the skin has in the main- tenance of the uniform temperature of the body, and as one of the conditions to which the production of heat needs to be adapted, is already mentioned (p. 161). CHAPTEB XIV. THE KIDNEYS AND THEIR SECRETION. Structure of the Kidneys. The kidneys, provided especially for the excretion of the refuse nitrogen, phosphorus and sulphur, lime and magnesia, have the general structures of glands arranged in a manner distinguishing them from all other excretory organs. In each kidney numerous secreting tubes (tubuli uriniferi) are collected in bundles, in from ten to twenty separated conical or pyramidal portions (pyramids or cones of Malpighi), which together constitute the tubular por- tion of the kidney. The apices of the cones converge, and project into calyces, which are branches of a large cavity called the pelvis of the kidney, that leads to the ureter, its excretory duct (Fig. 75). The trunks of the urine-tubes open at the extremities or papillae of the pyramids, and their branches running in a straight and some- what divergent course towards the surface of the kidney, as they approach it, become tortuous, and, winding in various directions, terminate in, or bear on small pedicles proceeding from their walls, dilated, flask-shaped sacculi, named capsules of Malpighi. Those 284 THE KIDNEYS AND THEIR SECRETION. Fig. 75. that bear capsules at their sides, probably unite with one another in loops, or terminate in simply closed ends. The small branches of the renal arteries ramify very abundantly in the parts of the kidney near its surface, and between the several pyramids; and predominating over the tubules, have obtained for these corti- cal parts of the kidney the name of vascu- lar portion. Before dividing into capil- laries, they form vascular tufts or little balls, called Malpighian corpuscles or glo- merules (Fig. 76). In the formation of these, each minute artery divides into four or more small tortuous branches, which run on the surface of the corpuscles, and give off many branches that fill up the spaces between and within them, and lead to a small vein which usually emerges from the corpuscle at the same part as the artery enters it. Thus, each Malpighian corpuscle appears as if suspended by a small short pedicle, formed of its artery and vein. Each lies within a Malpighian capsule, or attached to its exterior (Hyrtl, lxxxviii. April, 1846; Bidder, lxxx. 1845), and from the vein of each proceed capillaries, which ramify in close networks over the urine-tubes (Fig. 77). Thus, therefore, the circulation of the kidney is peculiar in that the capillaries, from which the blood is chiefly derived to form the A section of the Kidney, sur- mounted by the suprarenal cap- sule; the swellings upon the surface mark the original consti- tution of the organ, as made up of distinct lobules.—1. The supra- renal capsule. 2. The vascular portion of the kidney. 3, 3. Its tubular portion, consisting of cones. 4, 4. Two of the papillae projecting into their correspond- ing calyces. 5, 5, 5. The three infundibula; the middle 5 is eituated in the mouth of a calyx. 6. The pelvis. 7. The ureter. Fig. 76. Section of the cortical substance of the human Kidney:—a a, tubuli uriniferi divided transversely, showing the spheroidal epithelium in their interior; B, Malpighian capsule • a, its afferent branch of the renal artery; 6, its glomerulus of capillaries; c, c, secreting plexus, formed by its efferent vessels; d d, fibrous stroma. STRUCTURE OF THE KIDNEYS. 285 Fig. 77. From the human subject. This specimen exhibits the termination of a considerable arte- rial branch wholly in Malpbigian tufts; a, arterial branch with its terminal twigs. At a, the injection has only partially filled the tuft; at b it has entirely filled it, and has also passed out along the efferent vessel ef without any extravasation; at y it has burst into the capsule, and escaped along the tube t, but has also filled the efferent vessel ef; at d and e it has extravasatcd, and passed along the tube; at m and m, the injection, on escaping into the capsule, has not spread over the whole tuft. Magnified about 45 diameters. urine, are like the divisions of a vein rather than of an artery: for the branchings of the arteries in the Malpighian tufts or cor- puscles, and the collection of their branches again into the small efferent vessel, give that vessel the character of a vein, and make the capillary circulation over the urine-tubes, analogous to the portal circulation through the liver, (Fig. 78) an analogy which is the closer, because in fish and Amphibia the kidney receives not only a renal artery, whose branches form the Malpighian bodies, but also a large renal (or renal-portal) vein, bringing, for the secretion of urine, the venous blood of the hinder parts of the body, and giving off the capillaries which ramify upon the urine-tubes (Bowman, xliii., 1842). 286 THE KIDNEYS AND THEIR SECRETION. The urine-tubes are minute canals of about ^th of jn inch m diameter, formed of pellucid, simple or basement-membrane and lined throughout with nucleated gland-cells arranged ike, aa^epithe- lium, of spheroidal form, and darkly dotted or grated (see Frg 79). Not unfrequently, portions of tubes, especially of those that Fig. 79. Fig. 78. Plan of the renal circulation in man and the Mammalia, a, terminal branch of the artery, giving the terminal twig 1, to the Malphigian tuft m.from which emerges the efferent or portal vessel 2. Other efferent vessels, 2, are seen entering the plexus of capillaries, sur- rounding the uriniferous tube, t. From the plexus, the emulgent vein, v, springs. Fig. 79. A. Portion of a secreting canal from the cortical substance of the kidney. B. The epithelium or gland-cells, more highly magnified (700 times), c. Portion of a canal from the medullary substance of the kidney. At one part the basement-membrane has no epithelium lining it. are convoluted or tortuous, appear nearly filled with such cells, or thin separated nuclei, as if the urine were filtered through them on its way to the pelvis. The same kind of epithelium is continued into the Malpighian capsules, and lines their whole internal surface, and if they contain Malpighian tufts, is reflected over them like a serous membrane.1 Secretion of Urine. The separation of urine from the blood is probably effected, like other secretions, by the agency of the gland-cells, and equally in all parts of the urine-tubes. The urea and uric acid, and perhaps some 1 In the frog, triton, and probably most or all other naked Amphibia, the epithelium at and just within the neck or commencing dilatation of the Mal- pighian capsule is ciliated. This fact (first observed by Mr. Bowman) is, perhaps, connected with the peculiar arrangement of the seminal tubes or branches of the vasa deferentia, which open into one end of the Malpighian capsulos, while the urine-tubes open into the others. The cilia work towards the seminal tubes, and would prevent the seminal fluid from mingling with the urine (seeBidder, cliv., and Ludwig, lix. 1847). SECRETION OF URINE. 287 of the other constituents existing ready formed in the blood, may need only separation, that is, they may pass from the blood to the urine without further elaboration; but this is not the case with some of the other principles of the urine, such as the acid phosphates and the sulphates, for these salts do not exist in the blood, and must be formed by the chemical agency of the cells. The large size of the renal arteries and veins permits so rapid a transit of the blood through the kidneys, that the whole of the blood is purified by them. The secretion of urine is rapid in comparison with other secretions, and as each portion is secreted it propels those already in the tubes onwards into the pelvis. Thence through the ureter the urine passes into the bladder, into which its rate and mode of entrance have been watched in cases of ectopia vesicae, i. e., of such fissures in the anterior and lower part of the walls of the abdomen, and of the front wall of the bladder, that its hinder wall with the orifices of the ureters is exposed to view. The best obser- vations on such cases were made by Mr. Erichsen (lxxi., 1845). The urine does not enter the bladder at any regular rate, nor is there a synchronism in its movement through the two ureters. During fasting, two or three drops enter the bladder every minute, each drop as it enters first raising up the little papilla on which, in these cases, the ureter opens, and then passing slowly through its orifice, whicb at once again closes like a sphincter. In the recumbent posture, the urine collects for a little time in the ureters, then flows gently, and if the body be raised, runs from them in a stream till they are empty. Its flow is increased in deep inspiration, or straining, and in active exercise, and in fifteen or twenty minutes after a meal. The same observations, also, showed how fast some substances pass from the stomach through the circulation, and through the ves- sels of the kidneys. Ferrocyanate of potash so passed on one occa- sion in a minute: vegetable substances, such as rhubarb, occupied from sixteen to thirty-five minutes; neutral alkaline salts with vege- table bases, which were generally decomposed in transitu, made the urine alkaline in from twenty-eight to forty-seven minutes. But the times of passage varied much; and the transit was always slow when the substances were taken during digestion. The urine collecting in the urinary bladder is prevented from re- gurgitation into the ureters by the mode in which they pass through the walls of the bladder, namely, by their lying for between half and three quarters of an inch between the muscular and mucous coats, and then turning rather abruptly forwards, and opening through the latter. It collects till the distension of the bladder is felt either by direct sensation, or, in ordinary cases, by a transferred sensation at and near the orifice of the urethra. Then, the effort of the will being directed primarily to the muscles of the abdomen, and through them (by reason of its tendency to act with them, to the urinary bladder), the latter, though its muscular walls are really composed 288 THE KIDNEYS AND THEIR SECRETION. of involuntary muscle, contracts, and expels the urine. The muscular fibres behind the ureters, where they lie between the muscular and mucous coats of the bladder, compress these canals as they contract for the expulsion of the urine; and the vesical orifice of the urethra, which appears to be closed only by the elasticity of the surrounding parts, is forced open by the pressure of the urine while the bladder is contracting, and again closes by the same elasticity when the bladder ceases to contract. The Urine : its General Properties. Healthy urine is a clear limpid fluid, of a pale yellow or amber color, with a peculiar faint aromatic odor, which becomes pungent and ammoniacal when decomposition takes place. The urine, though usually clear and transparent at first, often, as it cools, becomes opaque and turbid from the deposition of part of its constituents pre- viously held in solution; and this may be consistent with health, though it is only in disease that, in the temperature of 98° or 100°, at which it is voided, the urine is turbid even when first expelled. Al- though ordinarily of a pale amber color, yet, consistently with health, the urine may be nearly colorless, or of a brownish or deep orange tint; and between these extremes, it may present every shade of color. When secreted, and, most commonly, when first voided, the urine has a distinctly acid reaction in man and all carnivorous animals, and it thus remains till it is neutralized or made alkaline by the ammonia developed in it by decomposition. In most herbivorous animals, on the contrary, the urine is alkaline and turbid. The dif- ference depends, not on any peculiarity in the mode of secretion, but on the differences in the food on which the two classes subsist; for when carnivorous animals, such as dogs, are restricted to a vegetable diet, their urine becomes pale, turbid, and alkaline, like that of an herbivorous animal, but resumes its former acidity on the return to an animal diet; while the urine voided by herbivorous animals, e.g., rabbits, fed for some time exclusively upon animal substances, pre- sents the acid reaction and other qualities of the urine of Carnivora, its ordinary alkalinity being restored only on the substitution of a vegetable for the animal diet (Bernard, xviii. 1846). Human urine is not usually rendered alkaline by vegetable diet, but it becomes so after the free use of alkaline medicines, or of the alkaline salts with carbonic or vegetable acids; for these latter are changed into alka- line carbonates previous to elimination by the kidneys. Except in these cases it is very rarely alkaline, unless ammonia has been deve- loped in it by decomposition commencing before it is evacuated from the bladder. The average specific gravity of the human urine is stated by Br. Prout to be 1020 (xxi. p. 403, Am. ed.), by Becquerel, as the mean GENERAL PROPERTIES OF URINE. 289 in the two sexes, 1017 (l. p. 148).' Probably no other animal fluid presents so many varieties in density within twenty-four hours as the urine does; for the relative quantity of water and of solid constitu- ents of which it is composed is materially influenced by the condi- tion and occupation of the body during the time at which it is secreted, by the length of time which has elapsed since the last meal, and by several other accidental circumstances. The existence of these causes of difference in. the composition of the urine has led to the secretion being described under the three heads of urina san- guinis, urinct potds, and urina cibi. The first of these names sig- nifies the urine, or that part of it which is secreted from the blood at times in which neither food nor drink has been recently taken, and is applied especially to the urine which is evacuated in the morning before breakfast. The urina potHs indicates the urine secreted shortly after the introduction of any considerable quantity of fluid into the body : and the urina cibi the portions secreted during the period immediately succeeding a meal of solid food. The latter kind contains a larger quantity of acid matter than either of the others; the former, being largely diluted with water, possesses a compara- tively low specific gravity. Of these three kinds, the morning-urine is the best calculated for analysis, since it represents the simple se- cretion unmixed with the elements of food or drink; if it be not used, the whole of the urine passed during a period of twenty-four hours should be taken. In accordance with the various circum- stances above-mentioned, the specific gravity of the urine may, con- sistently with health, range widely on both sides of the usual average. The average healthy range may be stated at from 1015 in the winter to 1025 in the summer (Prout, xxi. p. 403, Am. ed.), and variations of diet and exercise may make as great a difference. In disease, the variation may be greater; sometimes descending, in albuminuria, to 1004, and frequently ascending, in diabetes, when the urine is loaded with sugar, to 1050, or even to 1060 (Watson, xlviii. p. 170, Am. edit.). The whole quantity of urine secreted in twenty-four hours is sub- ject to variation according to the amount of fluid drank, and the quantity secreted by the skin. It is because the secretion of the skin is more active in summer than in winter, that the quantity of urine is smaller, and its specific gravity proportionately higher. According to Prout, the quantity voided in summer may be esti- mated at 30 ounces daily; that in winter at 40 ounces : this will give a mean of 35 ounces as the average amount of the urinary secre- tion by an adult healthy man. 1 The specific gravity indicates only the proportionate, not the absolute quantity of solid matter in a given bulk of urine. For determining the latter point, various tables have been constructed; see Christison, xlix. vol. iv. p. 248; Becquerel, l. p. 17 ; Prout, xxi. p. 407, Am. ed.; Day, xxx. 1844, p. 370; and Golding Bird, ii. p. 57, Am. edit. 290 THE KIDNEYS AND THEIR SECRETION. Chemical Composition of the Urine. The urine consists of water, holding in solution certain animal and saline matters as its ordinary constituents, and occasionally various matters taken into the stomach as food — salts, coloring- matters, and the like. The quantities of the several natural and constant ingredients of the urine are stated somewhat differently by the different chemists who have analysed it; but many of the dif- ferences are not important, and the well-known accuracy of the several chemists renders it almost immaterial which of the analyses is adopted. The analysis by A. Becquerel (l. p. 7) being adopted by Dr. Prout (xxi. p. 404, Am. Ed.), and by Dr. Golding Bird (li. p. 59, Am. Ed.), will be here employed. The older analysis by Berzelius (xxiv. p. 342), adopted by Miiller (xxxii. p. 460, Am. Ed.), includes all the principal solid constituents of the urine, and probably states correctly the proportions that they bear to one another; but, as pointed out by Dr. Prout, it is probable that Ber- zelius examined urine of very high specific gravity, and has, in consequence, overstated the quantity of solid ingredients; for he sets them down at more than double the amount found to exist by more recent analysts. If the mean specific gravity of human urine be taken at 1020, and the average quantity passed in twenty-four hours be estimated at thirty-five ounces, it will be found, according to the analysis of M. Becquerel, that 1000 parts of urine contain 33 parts of solid matter dissolved in 967 parts of water. Its more exact composition is as follows : — Water................................................................................ 967- Urea............................................................................... 14-230 Uric acid........................................................................... -468 Coloring-matter............................1 inseparable from"! 10167 Mucus, and animal extractive matter / each other J Sulphates { |jf*gh Salts f Lime Bi-phosphates < , r v v 1 Magnesia [ Ammonia ni.i -a f Sodium Chlorides | potassium Hippurate of soda............ 8135 Fluate of potash Silica...................................................................... traces. 1000-000 From these proportions, however, most of the constituents are, even in health, liable to variations. Especially, the water is so. COMPOSITION AND PROPERTIES OF UREA. 291 Its variations in different seasons, and according to the quantity of drink and exercise, are already mentioned. It is also liable to be influenced by the condition of the nervous system, being sometimes greatly increased in hysteria, and some other nervous affections; and at other times diminished. In some diseases it is enormously increased; and its increase may be either attended with an aug- mented quantity of solid matter, as in ordinary diabetes, or may be nearly the sole change, as in the affection termed diabetes insipidus. In other diseases, e. g., the various forms of albuminuria, the quantity may be considerably diminished. A febrile condition almost always diminishes the quantity of water; and a like diminution is caused by any affection which draws off a large quantity of fluid from the body through any other channel than that of the kidneys, e. g., the bowels and the skin. Urea. — Urea is the principal solid constituent of the urine, forming nearly one-half of the whole quantity of solid matter. It is also the most important ingredient, since it is the chief substance by which the nitrogen of decomposed tissues and superfluous food is excreted from the body. For its removal the secretion of urine seems especially provided; and by its retention in the blood the most pernicious effects are produced. Urea, like the other solid constituents of the urine, exists in a state of solution. But it may be procured in the solid state, and then appears in the form of delicate silvery acicular crystals, which, under the microscope, appear as four-sided prisms. It is obtained in this state by evaporating urine carefully to the consistence of honey, acting on the inspissated mass with four parts of alcohol, then evaporating the alcoholic solution, and purifying the residue by repeated solution in water or alcohol, and finally allowing it to crystallize. It readily combines with an acid, like a weak base; and may thus be conveniently procured in the form of a nitrate, by adding about half a drachm of pure nitric acid to double that quantity of urine in a watch-glass. The crystals of nitrate of urea are formed more rapidly if the urine have been previously concen- trated by evaporation. Urea is colorless when pure; when impure, yellow or brown: without smell, and of a cooling, nitre-like taste; has neither an acid nor an alkaline reaction, and deliquesces in a moist and warm atmosphere. At 59° F., it requires for its solution less than its weight of water; it is dissolved in all proportions by boiling water: but it requires five times its weight of cold alcohol for its solution. At 248° F., it melts without undergoing decomposition; at a still higher temperature, ebullition takes place, and carbonate of ammonia sublimes; the melting mass gradually acquires a pulpy consistence; and, if tbe heat is carefully regulated, leaves a grey-white powder, cyanic acid. Urea is identical in composition with cyanate of ammonia; its ulti- 292 THE KIDNEYS AND THEIR SECRETION. mate analysis yielding 2 atoms of carbon, 2 of nitrogen, 2 of oxygen, and 4 of hydrogen, which is the composition of hydrated cyanate of ammonia (cyanic acid = C^NO; water=HO; ammonia = NH3). This cyanate of ammonia, or artificial urea, as discovered by Wbhler, may be formed by the mutual action of ammonia, cyanic acid, and water; or by decomposing cyanate of silver with hydrochlorate of ammonia, or cyanate of lead with a solution of ammonia (liii. xxvii. 196). The action of heat upon urea in evolving carbonate of ammonia, and leaving cyanic acid, is thus explained. A similar decomposition of the urea with development of carbonate of am- monia ensues spontaneously when urine is kept for some days after being voided, and explains the ammoniacal odor then evolved. It is probable, that this spontaneous decomposition is accelerated by the mucus and other animal matters in the urine, which, by becoming putrid, act the part of a ferment and excite a change of composition in the surrounding compounds. It is chiefly thus that the urea is sometimes decomposed before it leaves the bladder, when the mucous membrane is diseased, and the mucus secreted by it is both more abundant and, probably, more prone than usual to become putrid (Dumas, Iii. p. 39). The same occurs also in some affections of the nervous system, particularly in paraplegia. Assuming 35 ounces of urine to be passed in twenty-four hours, the total amount of urea excreted within the same period, at the rate of fourteen parts and a quarter in every 1000 parts of urine, will be 227 grains, or nearly half an ounce. The amount of this substance excreted is, however, like that of the urine itself, subject to considerable variation. It is materially influenced by diet, being greater when animal food is exclusively used, less when the diet is mixed, and least of all with a vegetable diet (Lehmann, Ixxxii. p. 416). As a rule, men excrete a larger quantity than women, and persons in the middle periods of life, a larger quantity than infants or old people (Lecanu, lvi. t. 25, p. 261). The quantity of urea does not neces- sarily increase and decrease with that of the urine, though on the whole it would seem that whenever the amount of urine is much augmented, the quantity of urea also is usually increased (Bec- querel, L.). In various diseases, as albuminuria, the quantity is reduced considerably below the healthy standard, while in other affections it is raised above it. The urea appears to be derived from two different sources. That it is derived in part from the unassimilated elements of nitrogenous food, circulating with the blood, is shown in the increase which en- sues on substituting an animal or highly nitrogenous for a vegetable diet (see especially Lehmann, cciii. vol. ii. pp. 450-2). And that it is in larger part derived from the disintegration of the azotized animal tissues, is shown by the fact that it continues to be excreted, though in smaller quantity than usual, when all nitrogenous sub- stances are strictly excluded from the food, as when the diet consists URIC ACID. 293 for several days of sugar, starch, gum, oil, and similar non-azotized vegetable substances (Lehmann, loc. cit., and Ixxxii., and Bischoff, ccxvi.). It is excreted also even although no food at all is taken for a considerable time; thus it is found in the urine of reptiles which have fasted for months; and in the urine of a madman who had fasted eighteen days, Lassaigne found both urea and all the compo- nents of healthy urine (lvii. p. 272). For these and other reasons, Bischoff believes that urea is exclusively derived from the metamor- phosis of tissues, and that no part of it is furnished by unassimilated elements of food. According to Dr. Prout (xxi. p. 411, Am. Ed.), the urea is derived chiefly from the gelatinous tissues; according to Liebig (xi. p. 137), all the nitrogenous tissues furnish a share of it by their decomposition; and that the muscles do so is nearly proved by the close relation between urea and the kreatine and the kreati- nine which both they and urine contain, and by the increased excre- tion of urea after active exercise. [The theory of Liebig finds further confirmation in the fact that in lions, tigers, dogs, and other carnivorous animals which lead active lives and inspire large quantities of oxygen, the urine abounds in urea, but contains little uric acid — this latter being converted into urea by oxidation. According to Dr. Frick, the convicts of the Maryland Penitentiary, who took little exercise, discharged uric acid in excess, while those who underwent much physical exertion elimi- nated urea by the kidneys more freely than uric acid. Dr. F. informs us that one of the effects of the administration of cod liver oil was to diminish the quantity of urea. On the other hand, Wohler found an increased amount of urea in the urine of rabbits into whose veins urate of potash had been injected. The views of Liebig are to some extent favored by the results of a series of experiments on the rela- tions existing between urea and uric acid, recently performed by Dr. Hammond.1] Urea exists ready-formed in the blood, and is simply abstracted therefrom by the kidneys. It may be detected in small quantity in the blood (ix. 1848), and in some other parts of the body, e. g., the humors of the eye (Millon, xviii. 1843), even while the functions of the kidneys are unimpaired; but when, from any cause, especially extensive disease or extirpation of the kidneys, the separation of urine is imperfect, the urea is found largely in the blood and most other fluids of the body. Uric Acid.—This, which is another nitrogenous animal substance, and was formerly termed lithic acid on account of its existence in many forms of urinary calculi, is rarely absent from the urine of man or animals, though in the feline tribe it seems to be sometimes entirely replaced by urea (Gr. Bird, lxxi., vol. xli., p. 1106). Its 1 [See Amer. Jour. Med. Sciences for Jan., 1855, and April, 1856.] 25 * 294 THE KIDNEYS AND THEIR SECRETION. proportionate quantity varies considerably in different animals. In man, and Mammalia generally, especially the Herbivora, it is com- paratively small, not exceeding, in the human subject, one part in 2000 parts of urine. In the whole tribe of birds and of serpents, on the other hand, the quantity is very large, greatly exceeding that of urea. In the urine of graminivorous birds, indeed, urea is rarely if ever found, its place being entirely supplied by uric acid. The quantity of uric acid, like that of urea, in human urine, is increased by the use of animal food, and decreased by the use of food free from nitrogen, or by an exclusively vegetable diet. In most febrile dis- eases, and in plethora, it is formed in unnaturally large quantities; and in gout it is deposited in, and in the tissues around, joints, in the form of urate of soda, of which the so-called chalk-stones of this disease are principally composed. The condition in which uric acid exists in solution in the urine, has formed the subject of much discussion, because of its difficult solubility in water. Dr. Prout found that it required 10,000 times its weight of water, at the temperature of 60° F. for solution; whereas in urine, one part of it is retained in solution by only 2000 parts of water. He was led to believe that uric acid does not exist in the free state in urine, but is combined with ammonia in the form of the more soluble salt of urate of ammonia. This view is sup- ported by the fact that urine, when evaporated, deposits not crystals of uric acid, as would probably be the case if this acid existed in its free state, but urate of ammonia. It is supported also by the facts that the addition of an acid to urine causes the deposition of crys- tals of uric acid, and that the uric acid in the excrement of birds and serpents is not in the free state, but is combined with ammonia. It may, therefore, be considered highly probable that the principal part at least of the uric acid exists in the urine in the form of urate of ammonia; and Dr. Bence Jones has shown that the solubility of this salt is increased by the presence of chloride of sodium, of which a proportion is present in the urine (lxxi., Dec, 1843). Liebig (xxx., June, 1844), however, maintains that the uric acid exists as urate of soda, produced, he supposes, by the uric acid, as soon as it is formed, combining with part of the base of the alkaline phosphate of soda of the blood. Hippuric acid, which exists in human urine also, he believes, acts upon the alkaline phosphate in the same way, and increases still more the quantity of acid phosphate, on the presence of which it is probable that a part of the natural acidity of the urine depends. It is scarcely possible to say whether the union of uric acid with the bases soda and ammonia takes place in the blood, or in the act of secretion in the kidney: the latter is the more probable opinion, but the quantity of either uric acid or urates in the blood, is probably too small to allow of this question being solved. According to Dr. Prout, the source of uric acid is in the disinte- CHARACTERS OF URIC ACID. 295 grated elements of albuminous tissues : while by Liebig it is assumed that uric acid is the first-formed product of the decay of all azotized tissues, and that if a due supply of oxygen is afforded, it is resolved into urea and carbonic acid. The fact, however, that in birds, whose rapid respiration and circulation ensures a large supply of oxygen, the uric acid is excreted in the form of urate of ammonia, and is rarely converted into urea, is quite opposed to such a view. The relation which uric acid and urea bear to each other is therefore still obscure. The fact that they often exist together in the same urine seems to make it probable that they have different origins or different offices to perform; but the entire replacement of either by the other, as of urea by uric acid in the urine of birds, serpents, and many insects, and of uric acid by urea, in the urine of the feline tribe of Mammalia, shows that each alone may discharge all the important functions of the two. Owing to its existing in combination in healthy urine, uric acid, for examination, must generally be precipitated from its bases by a stronger acid. Frequently, however, when excreted in excess, it is deposited in a crystalline form, mixed with large quantities of urate of ammonia or soda. In such cases, it may be procured for micro- scopic examination, by gently warming the portion of urine contain- ing the sediment: this dissolves urate of ammonia and soda, while the comparatively insoluble crystals of uric acid subside to the bot- tom. In larger quantity, this acid may be obtained from the urine of birds or serpents, which consists almost exclusively of urate of ammonia. The thick, white, urinary secretion of these animals is to be dried, dissolved in warm water, filtered, and then decomposed with nitric or hydrochloric acid (Fig. 80). The most common form in which uric acid is deposited in urine is Fig. 80. Fig. Sir- Fig. 80. Appearance presented by the solid white portion of the urine of birds and reptiles, under a magnifying power of 210 diameters. To the naked eye, this resembles chalk; under the microscope it consists of innumerable minute granules of the urate of ammonia. Fig. 81. Linear masses of granules of urate of ammonia. 296 THE KIDNEYS AND THEIR SECRETION. that of a brownish or yellowish powdery substance, consisting of granules of urate of ammonia or soda (Fig. 81). When deposited in crystals it is most frequently in rhombic or diamond-shaped la- minae (Figs. 82, 83), not unlike scales of epithelium, their resem- Fig. 82. Fig. 83. Fig. 82. Uric Acid Crystals from human urine. Fig. 83. Uric Acid. Thick lozenges, often found mixed with urate of ammonia and oxalate of lime. blance to which is often further increased by the existence of inter- nal markings, which look like nuclei. The laminae are sometimes of considerable thickness; and, when lying on their sides, they often appear like flattened cylinders; but their true form is made manifest as they roll over. Occasionally the rhombic form of the crystals is replaced by the square (Figs. 84, 85). Various other shapes (Figs. Fig. 84. Fig. 85. Fig. 84. Uric Acid Crystals in which, when the deposit is of long continuance, the rhom- boidal form is replaced by a square one. Fig. 85. Uric Acid. Accidental varieties of the rhomboid and square forms. 86, 87,) are also occasionally presented, and will be found described in works on the subject (see especially Prout, xxi.; G. Bird, li.; Simon, Ixxxii.; Griffith, cii.). When deposited from urine the HIPPURIC ACID. 297 crystals are generally more or less deeply colored by being combined with the coloring principles of the urine. Fig. 86. Fig. 87. Rhomboidal prisms of uric acid. Aggregated lozenges of uric acid. Uric acid is insoluble in ether and alcohol. It contains about 31 per cent, of nitrogen; its analysis yielding, according to Dr. Prout, nitrogen 31-12, carbon 39-87, hydrogen 2-22, oxygen 26-77. Its formula is C10H4N4O6. Hippuric Acid (Fig. 88) has long been known to exist in the urine of herbivorous animals in com- bination with soda. Liebig has shown that it also exists naturally in the urine of man, in quantity equal to the uric acid (xxx. June 1844) ; but, according to Dr. G-. Bird, its quantity is not more than one-third of the uric acid. It is a nitrogenous compound, and contains as much as 63 per cent, of carbon; 100 parts, according to Liebig, consisting of C 63-032, H 5-000, N 7337, O 24-631. It is closely allied to benzoic acid; and this substance, when introduced into the system, is excreted by the kidneys as hippuric acid (Ure, xli. vol. xxiv). Its source is in some parts of vegetable diet, though man has no hip- puric acid in his food, nor, commonly, any benzoic acid that might be converted into it. The nature and composition of the coloring matter of urine is involved in considerable obscurity. It is usually supposed that there are two distinct kinds, a yellow and a red, by the varying proportions of which the different tints of urine are produced. (See on the subject G-. Bird, li. p. 52; Heller, ix. 1846-7; Simon, Ixxxii.; and, for a full account, Scherer, x. Bd. 57, p. 180, or for an abstract of the paper there given, lix. 1846, p. 130). Fig. 88. Hippuric Acid. 298 THE KIDNEYS AND THEIR SECRETION. The mucus in the urine consists principally of the epithelial debris of the mucous surface of the urinary passages. Particles of epithe- lium, in greater or less abundance, may be detected in most samples of urine, especially if it has remained at rest for some time, and the lower strata are then examined. As urine cools, the mucus is some- times seen suspended in it as a delicate opaque cloud, but generally it falls. In inflammatory affections of the urinary passages, especially of the bladder, mucus in large quantities is poured forth, and speedily undergoes decomposition. The presence of the decomposing mucus excites (as already stated) chemical changes in the urea, whereby ammonia, or carbonate of ammonia, is formed, which, combining with the excess of acid in the super-phosphates in the urine, pro- duces insoluble neutral or alkaline phosphates of lime and magnesia, and phosphate of ammonia and magnesia. These, mixing with the mucus, constitute the peculiar white, viscid, mortar-like substance which collects upon the mucous surface of tbe bladder, and is often passed with the urine, forming a thick, tenacious sediment. Besides mucus and coloring matter, urine contains a considerable quantity of animal matter, usually described under the obscure name of animal extractive. The investigations of Liebig (liv.), Heintz (lix. 1847, p. 105), and others, have shown that some of this ill- defined substance consists of kreatine and kreatinine, two substances derived from the metamorphosis of muscular tissue. These sub- stances appear to be intermediate between the proper elements of the muscles, and perhaps of other azotized tissues, and urea: the first products of the disintegrating tissues probably consisting not of urea, but of kreatine and kreatinine, which subsequently are partly resolved into urea, partly discharged, without change, in the urine. Scherer's analysis shows, also, that much of the substance classed as extractive matter of the urine, is a peculiar coloring matter, probably derived from the haematine of the blood. Salts.—The saline substances in urine constitute about one-fourth of the solid ingredients. They consist of the various saline matters found in the other fluids and tissues of the body, together with some that are peculiar to the urine. The Sulphates are the most abundant; they exist as the sulphates of soda and potash: salts which are taken in very small quantity with the food, and are scarcely found in other fluids or tissues of the body; for the sulphates commonly enumerated among the constitu- ents of the ashes of the tissues and fluids are, for the most or entirely, produced by the changes that take place in the burning. Hence it is probable that the sulphuric acid which the sulphates in the urine contain, as soon as it is formed in the blood, or in the act of secre- tion of urine, is combined with the soda and potash which are in excess in the blood, and make it alkaline. The sulphur of which the acid is formed, is probably derived from the decomposing nitro- genous tissues, the other elements of which are resolved into urea PHOSPHATES IN URINE. 299 and uric acid. The oxygen is supplied through the lungs, and the heat generated during combination with the sulphur, is one of the subordinate means by which the animal temperature is maintained. Besides the sulphur in these salts, some also appears to be in the urine, uncombined with oxygen; for after all the sulphates have been removed from urine, sulphuric acid may be formed by drying and burning it with nitre. Mr. Bonalds believes that from three to five grains of sulphur are thus daily excreted (xvii. 1846). The combination in which it exists is uncertain: possibly it is in some compound analogous to cystine or cystic oxyde, which contains as much as 25 per cent, of sulphur. The Phosphates (Figs. 89 and 90,) are more numerous, though less abundant, than the sulphates. From Jth to T'gth part of them are phosphates with alkaline bases; from fths to -j-gths, with earthy Fig. 89. Fig. 90. Fig. 89. Mixed phosphates. The minute dots represent the amorphous particles of phosphate of lime. Fig. 90. Varieties of crystalline forms. The triple or neutral phosphate of magnesia and ammonia. bases (Bence Jones, xliii. 1845). In blood, saliva, and other alka- line fluids of the body, phosphates exist in the form of alkaline, probably tribasic, salts. In the urine they are acid salts, viz., the bi-phosphates of soda, ammonia, lime, and magnesia, the excess of acid being, according to Liebig (xxx. June, 1844), due to the ap- propriation of the alkali with which the phosphoric acid in the blood is combined, by the several new acids which are formed or discharged at the kidneys, namely, the uric, hippuric, and sulphuric acids, all of which he supposes to be neutralized with soda. The presence of the acid phosphates account, in great measure, or, according to Liebig, entirely, for the acidity of the urine. The phosphates are taken largely in both vegetable and animal food; some, thus taken, are excreted at once; others, after being trans- formed and incorporated with the tissues. Phosphate of lime forms the principal earthy constituent of bone, and from the decomposition of the osseous tissue the urine derives a large quantity of this salt. The decomposition of other tissues also, but especially of the brain 300 THE KIDNEYS AND THEIR SECRETION. and nerve-substance, furnishes large supplies of phosphorus to the urine, which phosphorus is supposed, like the sulphur, to be united with oxygen, and then combined with bases. According to Bec- querel, 1000 parts of urine contain on an average -373 of phosphoric acid in the state of combination ; so that a person in health will pass about 5-72 grains in twenty-four hours. This quantity is, however, liable to considerable variation. Any undue exercise of the mind, and all circumstances producing nervous exhaustion, increase it. The earthy phosphates are more abundant after meals, whether on animal or vegetable food, and are diminished after long fasting. The alkaline phosphates are increased after animal food, diminished after vegetable food. Exercise increases the alkaline, but not the earthy phos- phates (Bence Jones). Phosphorus uncom- bined with oxygen appears, like sulphur, to be excreted in the urine (Bonalds, 1. c), and it is said that the quantity is sometimes so large as to render objects dipped in the urine luminous in the dark (liii., Feb., 1S14). The Chlorides occur as chlorides of potas- sium and sodium (Fig. 91). As they exist largely in food, and in most of the animal flu- ids, their occurrence in the urine is easily un- derstood. Occasionally the urine contains flu- ate of potash, and a small quantity of silica; but neither of these appears to be a constant constituent.1 1 In addition to the various works already quoted, see, for further details on the Chemistry of the Urine, Dr. Garrods's lectures, in the Lancet for 1848; Dr. Golding Bird's lectures in the forty-second volume of the Medical Ga- zette; Dr. Day's several reports in Ranking's Abstract, and in the British and Foreign Medico-Chirurgical Review; Scherer's Reports in Canstatt's Jahresberichte to 1856; and among others, the works of Dr. Griffith (cii.), Dr. Bence Jones (exeviii.), J. E. Bowman (cexv.), and Lehmann (cciii.). [The student may also consult the paper of Dr. Jones on the Kidney and its Ex- cretions in the Amer. Jour. Med. Sciences for April, 1855.] Chloride of sodium resultin healthy urine. from slow evaporation of THE NERVOUS SYSTEM. 301 CHAPTER XV. THE NERVOUS SYSTEM. The general nature of the functions of the nervous system, its connection with the mind on the one hand, and the contractile and sensitive parts on the other, and its influence on the functions of organic life, have been already referred to (pp. 51-53). The following pages will be devoted to a fuller exposition of these subjects. The nervous system consists of two portions or constituent sys- tems, the cerebro-spinal, and the sympathetic or ganglionic, each of which (though they have many things in common) possess certain peculiarities in structure, mode of action, and range of influence. The cerebrospinal system includes the brain and spinal cord, with the nerves proceeding from them, and the several ganglia seated upon these nerves, or forming part of the substance of the brain. It was denominated by Bichat the nervous system of animal life; and includes all the nervous organs in and through which are performed the several functions with which the mind is more immediately con- nected ; namely, those relating to sensation and volition, and the mental acts connected with sensible things. The sympathetic or ganglionic portion of the nervous system, which Bichat named the nervous system of organic life, consists essentially of a chain of ganglia connected by nervous cords, which extend from the cranium to the pelvis, along each side of the verte- bral column, and from which nerves with ganglia proceed to the viscera in the thoracic, abdominal, and pelvic cavities. By its dis- tribution, as well as by its peculiar mode of action, this system is less immediately connected with the mind, either as sensiferous or as receiving the impulses of the will; it is more closely connected than the cerebro-spinal system is witb the processes of organic life. But the differences between these two systems are not essential: their actions differ in degree and object more than in kind or mode: in the lower animals all the nervous functions are performed by one system corresponding with the cerebro-spinal of the Vertebrata; and among the Vertebrata many of the functions which, in the warm- blooded animals, are controlled by the sympathetic nerves, are in fish under the control of the pneumogastric cerebral nerves. Elementary Structures of the Nervous System. The organs of the nervous system, or systems, are composed essen- tially of two kinds of structure, vesicular and fibrous; both of which 26 302 THE NERVOUS SYSTEM. appear essential to the construction of even the simplest nervous sys- tem The vesicular structure is usually collected in masses and min- gled with the fibrous structure, as in the brain, spinal cord and the several ganglia; and these masses constitute what are termed nervous centres, being the organs in which it is supposed that nervous force may be o-enerated, and in which are accomplished all the various reflections, and other modes of disposing of impressions when they are not simply conducted along nerve-fibres. The fibrous nerve- substance, besides entering into the composition of the nervous cen- tres, forms alone the nerves, or cords of communication, which con- nect the various nervous centres, and are distributed in the several parts of the body for the purpose of conveying nervous force to them, or of transmitting to the nervous Fig. 92. centres the impressions made by stimuli. Along the nerve-fibres impressions or conditions of excitement are simply con- ducted : in the nervous centres they may be made to deviate from their direct course, and be variously diffused, reflected, or otherwise disposed of. Nerves are constructed of minute fibres or tubules full of nervous matter, arranged in parallel or interlacing bundles, which bundles are connected by intervening fibro-cellular tissue, in which their prin- cipal blood-vessels ramify. A layer of the same, or of strong fibrous tissue also sur- rounds the whole nerve, and forms a sheath or neurilemma for it. In most nerves, two kinds of fibres are mingled; those of one kind being most numerous in, and charac- teristic of, nerves of the cerebro-spinal sys- tem; those of the other, most numerous in nerves of the sympathetic system. The fibres of the first kind appear to con- sist of tubules of a pellucid simple mem- brane, within which is contained the pro- per nerve-substance, consisting of transpa- rent oil-like and apparently homogeneous material, which gives to each fibre the appearance of a fine glass tube filled with a clear transparent fluid (Fig. 92, a). This simplicity of composition is, however, only a perfectly fresh nerve; for, shortly after z;es which make it probable that their con- different materials. The internal, or cen- Primitive nerve-tubules. A. A perfectly fresh tubule with a single dark outline. B. A tu- bule of fibre with a double con- tour from commencing post- mortem change, c. The changes further advanced, producing a varicose or beaded appearance. d. A tubule or fibre, the central part of which, in consequence of still further changes, has ac- cumulated in separate portions within the sheath. After Wag- ner (cxv). apparent in the fibres of death, they undergo chan: tents are composed of two STRUCTURE OF NERVES. 303 tral part, occupying the axis of the tube, becomes greyish, while the outer, or cortical portion, becomes opaque and dimly granular or grumous, as if from a kind of coagulation. At the same time, the fine outline of the previously transparent cylindrical tube is ex- changed for a dark double contour (Fig. 92, B), the outer line being formed by the sheath of the fibre, tbe inner by the margin of curdled or coagulated medullary substance. The granular material shortly collects into little masses, which distend portions of the tubular membrane, while the intermediate spaces collapse, giving the fibres a varicose, or beaded appearance (Fig. 92, c and d), instead of their previous cylindrical form. The difference produced in the contents of the nerve-fibres when Fig. 93. A. Diagram of tubular fibre of a spinal nerve, a. Axis-cylinder, b. Inner border of white substance, c c. Outer border of white substance, d d. Tubular membrane. B. Tubular fibres ; e, in a natural state, showing the parts as in A. /. The white substance and axis cylin- der, interrupted by pressure while the tubular membrane remains, g. The same, with vari- cosities. A. Various appearances of the white substance, and axis-cylinder forced out of the tubular membrane by pressure, i. Broken end of a tubular fibre, with the white substance closed over it. k. Lateral bulging of white substance and axis-cylinder from pressure. I. The same, more complete, g'. Varicose fibres of various sizes, from the cerebellum, c. Gela- tinous fibres from the solar plexus, treated with acetic acid to exhibit their cell nuclei, b and 0 magnified :>20 diameters. exposed to the same conditions, has, with other facts, led to the opinion, now generally adopted, that the central part of each nerve- 304 THE NERVOUS SYSTEM. fibre differs from the circumferential portion: and the former has been named by Rosenthal and Purkinje (xxxiv., 1840, p. 7(>), the axis-cylinder ; by Remak (xxxviii., June, 1838), the primitive band. The outer portion is usually called the medullary or white substance of Schwann, being that to which the peculiar white aspect of cerebro- spinal nerves is principally due. The whole contents of the nerve- tubules appear to be extremely soft, for when subjected to pressure they readily pass from one part of the tubular sheath to another, and often cause a bulging at the side of the membrane. They also rea- dily escape on pressure from the extremities of the tubule, in the form of a grumous or granular material. (Fig. 93, p. 303.) The size of the nerve-fibres varies, and the same fibres do not pre- serve the same diameter through their whole length, being largest in their course within the trunks and branches of the nerves, in which the majority measure from ^^th to ^oVofb of an inch in diameter. As they approach the brain or spinal cord, and generally also in the tissues in which they are distributed, they gradually become smaller. In the grey or vesicular substance of the brain or spinal cord, they generally do not measure more than from jo-g^th to y^o-ijoth of an inch (cxiii. Heft. ii.). The fibres of the second kind, which constitute the principal part of the trunk and branches of the sympathetic nerves, and are mingled in various proportions in the cerebro-spinal nerves, differ from the preceding, chiefly in their fineness, being only about | or J as large in their course within the trunks and branches of the nerves; in the absence of the double contour; in their contents being apparently uniform ; and in their having, when in bundles, a yellowish-grey hue instead of the whiteness of the cerebro-spinal nerves. These peculia- rities make it probable that they differ from the other nerve-fibres in not possessing the outer layer of white or medullary nerve-substance; and that their contents are composed exclusively of the substance corre- sponding with the central portion, or axis-cylinder of the larger fibres. (Fig. 94.) Yet since many nerve-fibres may be found which appear intermediate in character between these two kinds, and since the large fibres, as they approach both their central and their peripheral ends, gradually diminish in size, and assume many of the other characters of the fine fibres of the sympathetic system, it is not ne- cessary to suppose that there must be a material difference in the office or mode of action of the two kinds of fibres.1 Every nerve-fibre in its course proceeds uninterruptedly from its JFor the best account of the structure of nerve-fibres, see xxv., 1842, in which is an analysis of the descriptions by Valentin, Henle, Remak. Pur- kinje, Wagner, Krause, Ehrenberg, and other continental writers; also the notices of more recent investigations, by Will, Hannover, Kolliker, and others, in the subsequent reports ; and the various reports in Canstatt's Jahresbericht; see also Dr. Todd and Mr. Bowman in their Physiological Anatomy, and Kolliker, in his Manual of Human Histology. STRUCTURE OF NERVES. 305 Fig. 94. Boots of a dorsal spinal nerve, and its union with sympathetic; cc. Anterior fissure of the spinal cord. a. Anterior root. p. Posterior root with its ganglion, a'. Anterior branch, pf. Posterior branch, s. Sympathetic, e. Its double junction with the anterior branch of the spinal nerve by a white and gray filament. origin at a nervous centre to its destination, whether this be the periphery of the body, in another nervous centre, or in the same centre whence it issued. In the whole of its course, also, however long, there is no branching, or anastomosis or union with the sub- stance of any other fibres. Bundles, or fasciculi, of fibres run together in the nerves, but merely lie in apposition with each other; they do not unite: even where the fasciculi appear to anastomose, there is no union of fibres, but only an interchange of fibres between the anastomosing fasciculi. Hence the central extremity of each fibre is connected with the peripheral extremity of a single nervous fibre only; and this peri- pheral extremity is in direct relation with only one point of the brain, spinal cord, or other nervous centre: so that, corresponding to the many millions of primitive fibres which are distributed to peripheral parts of the body, there are the same number of periphe- 26* 306 THE NERVOUS SYSTEM. ral points of the body represented in the nervous centres. Although each nerve-fibre is thus single and undivided through its whole course, yet, in the terminal ramifications, individual fibres sometimes break up into several subdivisions, as in the distribution of nerves in striped muscular tissue in the frog. At certain parts of their course, nerves form plexuses, in which they anastomose with each other, and interchange fasciculi, as in the case of the brachial and lumbar plexuses. The object of such inter- change of fibres is, probably, to give to each nerve passing off from the plexus a wider connection with the spinal cord than it would have if it proceeded to its destination without such communication with other nerves. Thus, since the brachial plexus is formed by the intermingling of fasciculi from the four last cervical, and the first dorsal nerves, it is possible that each trunk coming off from it may contain fibres derived from several parts of the cord interme- diate between the roots of the fourth cervical and those of the first dorsal. By this means, the parts supplied from the brachial plexus are enabled to have wider relations with the nervous centres, and more extensive sympathies; and, by this means, too, groups of muscles may be associated for combined actions (Gull, lxxxviii., 1849). The terminations of nerve-fibres are their modes of distribution and connection in the nervous centres, and in the parts which they supply : the former are called their central, the latter their peripheral terminations. As they approach their final and minutest distribution in the several tissues, the small bundles of nerve-fibres commonly form delicate plexuses, the terminal plexuses. These, then dividing or breaking up, give off the primitive fibres, which appear to be dis- posed of in various ways in different tissues. It is exceedingly diffi- cult to determine how they terminate: but examples of each of the following modes have been observed. 1. In loops. In this (which can only conventionally be called a mode of termination), each fibre, after issuing from a branch in a terminal plexus, runs over the ele- mentary structures of the containing tissue, then turns back, and joins the same or a neighbouring branch, in which it probably pur- sues its way back to a nervous centre. This arrangement has been found in the internal ear (Hannover, cxix.), in the papillae of the tongue (Todd and Bowman, xxxix. p. 440) and of the skin (Fig. 95,) Kblliker, ccvi. p. 65), in the tooth-pulp (Valentin, xxxix., p. 221,) (Fig. 96), and, in a modified form, in striped muscular tissue (Kolliker, ccvi. p. 184). 2. By branching. In the muscular tissue of the frog and the lower Vertebrata, it not unfrequently happens that each ultimate nerve-fibre breaks up into several branches, which spread out over the muscular fibres (Wagner, cxv. ; Volkmann, cxxvi. p. 70; Kolliker, ccvi. p. 184). A similar termination by division or branching of the ultimate fibres seems to occur in the PACINIAN CORPUSCLES. 307 retina, and in some other parts. A modification of this mode of ter- Fig. 0."). Fig. 96. Terminal nerves on the sac of the se- cond molar tooth of the lower jaw in the sheep, showing the arrangement in loops. After Valentin. Distribution of the tactile nerves at the surface of the lip; as seen in a thin perpendicular section of the akin. mination has been described by Wag- ner (cxv.) as occurring in the electric organ of the ray. A large nerve-fibre suddenly breaks up into from twelve to fifteen branches, each of which again divides into two secondary branches. Some of these secondary branches anastomose and form a net- work ; while others divide again di- chotomously, each of these branches again anastomosing and subdividing, until a very fine network is formed, from which branches pass off, and seem to be lost in the substance of the electric organs. 3. In plexuses. Thus, nerve-fibres appear to terminate in certain serous membranes. According to Mr. Rainey (xli. vol. xxix. p. 85), the arachnoid membrane of the brain and spinal cord is traversed by innumerable delicate nerve-fibres, arranged in minute plexuses; and a similar mode of arragement ap- pears to be observed by the nerve-fibres in other serous membranes, e.g., the peritoneum (Bourgery, xix., 1845; Pappenheim, xviii., 1845). 4. By free ends. It is not improbable that this mode of termination exists in several parts : it is best seen in the Pacinian corpuscles, and in some of the papillae of the skin. The Pacinian corpuscles are little elongated, oval bodies, situated on some of the cerebro-spinal and sympathetic nerves, especially the cutaneous nerves of the hands and feet (Figs. 97, 98). They are named Pacinian, after their discoverer, Pacini.1 Each corpuscle is 1 See for a description of these bodies an abstract of Henle and Kolliker's essay on them (xxv. 184o-4, p. 46); Mr. Bowman in the Cyclopedia of Ana- tomy and Physiology; Kolliker (ccvi. p. 318); and Huxley (cexvii. vol. i.). 308 THE NERVOUS SYSTEM. Fig. 98. Fig. 97. Extremities of a nerve of the finger with Pacinian corpuscles attached. A. Nerve from the finger, natural size; showing the Pacinian corpuscles, b. Ditto, magnified two diameters, showing their different size and shape. Fig. 98. Pacinian corpuscles from the mesentery of a cat; intended to show the general construction of these bodies. The stalk and body, the outer and inner system of capsules with the central cavity are seen. a. Arterial twig, ending in capillaries, which form loops in some of the inter-capsular spaces, and one penetrates to the central capsule. 6. The fibrous tissue of the stalk, prolonged from the neurilemma, n. Nerve-tube advancing to the central capsule, there losing its white substance, and stretching along the axis to the opposite end, where it is fixed by a tubercular enlargement. attached by a narrow pedicle to the nerve on which it is situated; it is formed of several concentric layers of fine membrane, with intervening spaces containing fluid; through its pedicle passes a single nerve-fibre, which, after traversing the several concentric layers and their inter- mediate spaces, enters a central cavity, and gradually losing its dark border, and becoming smaller, terminates at or near the distal end of the cavity, in a knob-like enlargement, or by bifurcating. The enlargement commonly found at the end of the fibre, is said by Pacini (cxx., 1845, p. 208) to resemble a ganglion-corpuscle; but this VESICULAR NERVOUS SUBSTANCE. 309 observation has not been confirmed. In some of the tactile papillae of the skin, nerve-fibres terminate in a small oval body, not unlike in form and structure the Pacinian corpuscles : they will be described when speaking of the sense of touch. 5. In nerve-corpuscles. This has been determined in the retina and in the lamina spiralis of the internal ear, and probably exists in other parts. The central termination of nerve-fibres can be better considered after the account of the vesicular nerve-substance. The vesicular nervous substance is composed, as its name implies, of vesicles or corpuscles, which are commonly called nerve-corpuscles, or ganglion-corpuscles. These are found only in the nervous centres, i. e., the brain, spinal cord, and the various ganglia; they are min- gled with nerve-fibres, and imbedded in a dimly-shaded or granular substance; they give to the ganglia and to certain parts of the brain and spinal cord the peculiar greyish or reddish grey aspect by which these parts are characterized. They are large nucleated cells, filled with a finely-granular material, some of which is often dark like pig- ment : the nucleus, which is vesicular, contains a nucleolus (Fig. 99). Besides varying much in shape, partly in consequence of mu- tual pressure, they present such other varieties as make it probable either that there are two different kinds, or that in the stages of their develop- ment they pass through very different forms. Some of them are small, gene- rally spherical or ovoid, and have a regular uninterrupted outline (Fig. 99). These simple nerve-corpuscles are most numerous in the sympathetic ganglia. Others, which are called caudate or stellate nerve-corpuscles (Fig. 100), are larger, and have one, two, or more long processes issuing from them, which processes often di- vide and subdivide, and appear tubular, and filled with the same kind of granular material as is contained within the corpuscles. Of these processes some appear to taper to a point, and terminate at a greater or less distance from the corpuscle; others may be traced until each of them, gradually losing its granular appearance, becomes continuous with, and acquires all the cbaracters of, a perfect nerve- fibre (Fig. 101). It is probable that many nerve-fibres, when they enter a nervous centre, terminate, or perhaps, more correctly, originate in this mode of connection with nerve-corpuscles. As they enter, the fibres gra- dually become finer; some, possibly, form simple loops; but many enter into connection with nerve-corpuscles. In the most common Nerve-corpuscles from a ganglion: after A'alentin. In one a second nucleus is visible. The nucleus of several con- tains one or two nucleoli. 310 THE NERVOUS SYSTEM. Fig. 100. A B Various forms of ganglionic vesicles: A, B, large stellate cells, with their prolongations, from the anterior horn of the gray matter of the spinal cord; C, nerve-cell with its connected fibra, from the anastomosis of the facial and auditory nerves in the meatus auditorius internus of the ox; a, cell-wall; b, cell-contents; c, pigment; d, nucleus; e, prolongation forming the sheath of the fibre; /, nerve-fibre; D, nerve-cell from the substantia ferruginea of man; e, smaller cell from the spinal cord, magnified 350 diameters. form of such connection, the outer substance of the fibre gradually disappears, the pellucid membranous sheath dilates, as if to envelope a nerve-corpuscle which occupies the dilated part; the sheath again contracts, and then, unless the fibre thus ends in the corpuscle (as at A, Fig. 101), its sheath is continued over to the other side of the corpuscle, and is gradually filled again with its proper substance (Fig. 101, B). Fig. 101. Connection between nerve-fibres and nerve-corpuscles, from the roots of a spinal nerve of the ray. After Wagner (cxv.). a. A nerve-corpuscle, escaped by pressure from the capsule formed around it by the dilated sheath of the nerve-tubule; it shows also the gradual disappearance of the outer portion of tbe substance of the nerve as it comes into relation with the corpus- cles, b. A nerve-corpuscle enclosed within a dilated portion of the sheath of a nerve; part of the granular material of the corpuscle is continuous with the central substance of the nerve in the course of which it is inserted. FUNCTIONS OF NERVE-FIBRES. 311 A prolongation of the granular substance of the corpuscle which thus appears to be inserted or received within the sheath of the fibre, extends for some distance along each part of the nerve-tube, taking the place of part of the proper substance of the fibre.1 Among the many questions yet to be decided on this subject of the connection of nerve-fibres with the corpuscles in the nervous centres, the principal are whether, in each centre, many fibres thus arise from corpuscles, or whether the corpuscles are more generally inserted in the course of fibres that have some other mode of termi- nation. In several instances more fibres have been counted leaving than entering a ganglion : the surplus, therefore, may be supposed to arise from the ganglion-corpuscles. It is, also, still to be deter- mined whether this relation to ganglion-corpuscles is common to all kinds of nerve-fibres, or limited to those of certain functions. It does not belong exclusively to either the cerebro-spinal or the sym- pathetic nerves, for it has been seen in the spinal cord as well as in the sympathetic ganglia. Both large and small nerve-fibres, also, have been seen to issue from the corpuscles, and Wagner and Bid- der mention having several times observed a fibre of both kinds arising from the same corpuscle. They are of opinion that sensi- tive fibres alone are brought into this intimate relation with nerve- corpuscles (xv. Bd. iii. p. 455, and cxxvi.), but the evidence for believing that the motor fibres have not a similar relation, is insuffi- cient. Functions of Nerve-Fibres. The office of the nerves as simple conveyers or conductors of ner- vous impressions is of a twofold kind. First, they serve to convey to the nervous centres the impressions made upon their peripheral extremities, or parts of their course; and in this way the mind, through the medium of the brain, may become conscious of external objects. Secondly, they serve to transmit impressions from the brain and other nervous centres to the parts to which the nerves are distributed; and these impressions seem to be of at least two kinds, those, namely, which excite muscular contractions, and those whicb influence the secretion, nutrition, and other organic functions of a part. For this twofold office of the nerves two distinct sets of nerve- fibres are provided, in both the cerebro-spinal and sympathetic sys- tems. Those which convey impressions from the periphery to the centre are classed together as centripetal or afferent nerves, or, when 1 On this origin of nerve-fibres in ganglia, consult Bidder and Volkmann (cxxvi.); and for nearly all that has been written on the connection of nerve- fibres with ganglion-corpuscles, see, in addition to Bidder's account, Wagner (cxv. and xv., art. Sympathischer Nerven); Hannover (cxix.); Todd and Bow- man (xxxix.); Kolliker (cxiv. and ccxii.); and for a summary of the obser- vations of these and other physiologists refer to Henle's report in Canstatt's Jahresbericht for 1817, p. 58, and his subsequent reports to 1856. 312 THE NERVOUS SYSTEM. speaking exclusively of cerebro-spinal nerves, nerves of sensation, or sensitive nerves. Those fibres, on the other hand, which are em- ployed to transmit central impulses to the muscles are classed as centrifugal, efferent, or motor nerves, or nerves of motion. The nervous influence by which secretion and nutrition are controlled seems to be conveyed (as already stated, pp. 255-270) along both sensitive and the centrifugal sympathetic nerves. With this difference in the functions of nerves, there is no appa- rent difference in the structure of the nerve-fibres by which it might be explained. Among the cerebro-spinal nerves, the fibres of the olfactory, optic, and auditory nerves are finer than those of the nerves of common sensation, and more like the fibres in the brain: but with these exceptions no centripetal fibres can be distinguished in their microscopic or general characters from those of motor nerves. Neither can the difference in functions be due to the kind of tissue to which a nerve is distributed; for although the nerves supplying muscles are principally motor, yet the muscular tissue contains sen- sitive fibres also, for pain is felt when it is injured, and, as will be hereafter shown, much of the exactness and precision of muscular action is determined by the power which the muscular tissue has of communicating to the mind the sensation of its own contraction, and of the effects produced by it. Nerve-fibres appear to possess no power of generating force in themselves, or of originating impulses to action : for the manifesta- tion of their peculiar endowments they require to be stimulated. They possess a certain property of conducting impressions, a pro- perty which has been named excitability; but this is never mani- fested till some stimulus is applied (see pp. 51, 52). Under ordinary circumstances nerves of sensation are stimulated by external objects acting upon their extremities; and the nerves of motion by the will, or by some force generated in the nervous centres. But almost all things that can disturb the nerves from their passive state act as stimuli, and agents the most dissimilar produce the same kind, though not the same degree of effect, because that on which they act pos- sesses but one kind of excitable force. Thus all stimuli, as well the internal organic as the inorganic,—the chemical, mechanical, and electric,—when applied to parts endowed with sensation, or to sen- sitive nerves (the connection of the latter with the brain and spinal cord being uninjured) produce sensations; and when applied to the nerves of muscles excite contractions. Muscular contraction is pro- duced as well when the motor nerve is still in connection with the brain, as when its communication with the nervous centres is cut off by dividing it; nerves, therefore, have, by virtue of their excitabi- lity, the property of exciting contractions in muscles to which they are distributed; and the part of the divided motor nerve which is connected with the muscle, will still retain this power however much FUNCTIONS OF NERVE-FIBRES. 313 we may curtail it; but irritation of the other portion, which is in connection with the brain, never excites contractions of the muscles. Mechanical irritation, when so violent as to injure the texture of the primitive nerve-fibres, deprives the centripetal nerves of their power of producing sensations when irritation is again applied at a point more distant from the brain than the injured spot; and in the same way, no irritation of a motor nerve will excite contraction of the muscle to which it is distributed, if the nerve has been com- pressed and bruised between the point of irritation and the muscle; the effect of such an injury being the same as that of division. The action of nerves is also excited by temperature. Thus, when heat is applied to the nerve going to a muscle, or to the muscle itself, contractions are produced. These contractions are very vio- lent when the flame of a candle is applied to the nerve, while less elevated degrees of heat,—for example, that of a piece of iron merely warmed,—do not irritate sufficiently to excite action of the muscles. The application of cold has the same effect as that of heat. The effect of the local action of excessive or long-continued cold or heat on the nerves, is the same as that of destructive me- chanical irritation. The sensitive and motor power in the part is destroyed, but the other parts of the nerve retain their excitability; and, after the extremity of a divided nerve going to a muscle has been burnt, contractions of the muscle may be excited by irritating the nerve below the burnt part. Chemical Stimuli excite the action of both sensitive and motor nerves as mechanical irritants do; provided their effect is not so strong as to destroy the structure of the nerve to which they are applied. A like manifestation of nervous power is produced by electricity and by magnetism. Some of these laws regulating the excitability of nerves and their power of manifesting their functions, require further notice, with several others which have not yet been alluded to. Certain of the laws and conditions of actions relate to nerves both of sensation and of motion, being dependent on properties common to all nerve-fibres; while of others, some are peculiar to nerves of motion, some to nerves of sensation. It is a law of action in all nerve-fibres, and corresponds with the continuity and simplicity of their course, that an impression made on any fibre is simply and uninterruptedly transmitted along it, with- out being imparted or diffused to any of the fibres lying near it. In other words, all nerve-fibres are mere conductors of impressions. Their adaptation to this purpose is, perhaps, due to the contents of each fibre being completely isolated from those of adjacent fibres by the membrane or sheath in which each is enclosed, and which acts, it may be supposed, just as silk or other non-conductors of electri- city, when covering a wire, prevent the electric condition of the wire from being conducted into the surrounding medium. 314 THE NERVOUS SYSTEM. Nervous force travels along nerve-fibres with an immeasurable velocity. A certain period of time probably does elapse in the transit of an impression from one end of a fibre to the other; but its length is inappreciable, and will probably never be ascertained, while we have not the opportunity of tracing the passage through distances as vast as those through which the passage of light is cal- culated. (See, however, Helmholtz, lxxi. vol. x. n. s. p 472.) It has been supposed, indeed, that the velocity is less in some persons than in others; chiefly because the impression of an object on the retina is sometimes perceived rather later by one person than by another — the difference amounting to one-third, or one-half, or even a whole second. The cases in which this difference has been chiefly observed are those in which the two senses of sight and hearing are simultaneously engaged in noting the exact moment at which a star passes before the thread crossing the field of a telescope. While the constant motion of the star across the field is followed with the eye, the ear notes each stroke of the pendulum-clock which stands near, marking the seconds. Now, it frequently happens, when two per- sons are thus engaged in making the same observation, that one of them notes the transit of the star later than the other; as if either the velocity with which the impression of the star passes along the optic nerve were less in one than in the other; or, as if one nerve conveyed impressions more rapidly than anotber, so that the one person would see before he hears, the other hear before seeing. But, a more probable explanation is, that both impressions are con- veyed with the same immeasurable velocity, but the mind does not at the same instant take cognizance of both—for the mind does not readily perceive with equal distinctness two different simultaneous impressions, but, rather, when several impressions are made on the nerves at the same time, takes cognizance of only one at a time, and perceives the rest in succession. When, therefore, both hearing and sight are directed simultaneously to different objects, the mind may first hear and then see, and the interval of time between the two perceptions may be. greater in some persons than in others; or some persons may be conscious at the same moment of many impres- sions, between which others require a considerable interval. No nerve-fibre can convey more than one kind of impression. Thus, a motor fibre can convey only motor impulses, that is, such as may produce movements in contractile parts: a sensitive fibre can transmit none but such as may produce sensation if they are propagated to the brain. Moreover, the fibres of a nerve of special sense, as the optic or auditory, can convey only such impressions as may produce a peculiar sensation, e. g., that of light or sound. While the rays of light, and the sonorous vibrations of the air, are without influence on the nerves of common sensation, the other stimuli which may produce pain when applied to them, produce, VELOCITY OF NERVOUS FORCE. 315 when applied to these nerves of special sense, only morbid sensa- tions of light, or sound, or taste, according to the nerve impressed. Of the laws of action peculiar to nerves of sensation and of motion respectively, many can be ascertained only by experiments on the roots of the nerves. For, it is only at their origin that the nerves of sensation and of motion are distinct; their filaments, shortly after their departure from the nervous centres, are mingled together, so that nearly all nerves, except those of the special senses, consist of both sensitive and motor filaments, and are hence termed mixed nerves. Among the laws of action of nerves of sensation is, 1st, that these nerves appear able to convey impressions only from the parts in which they are distributed, towards the nervous centre from which they arise, or to which they tend. Thus, when a sensitive nerve is divided, and irritation is applied to the end of the proximal portion, i. e., of the portion still connected with the nervous centre, sensa- tion is perceived, or a reflex action ensues; but, when the end of the distal portion of the divided nerve is irritated, no effect appears. The absence of effect in the latter case is, perhaps, not to be ascribed to the distal portion of the nerve being completely cut off from con- nection with the nervous centre, for it may contain fibres which, after reaching their destination, return through loops back to a nervous centre; rather, it may be believed, that the sensitive fibres cannot convey impressions in any direction except towards the nervous centres. When an impression is made upon any part of the course of a sensitive nerve, the mind may perceive it as if it were made, not only upon the point to which the stimulus is applied, but also upon all the points in which the fibres of the irritated nerve are dis- tributed : in other words, the effect is the same as if the irritation were applied to the parts supplied by the branches of the nerve. When the whole trunk of the nerve is irritated, the sensation is felt at all the parts which receive branches from it: but, when only indi- vidual portions of the trunk are irritated, the sensation is perceived at those parts only which are supplied by the several portions. Thus, if we compress the ulnar nerve where it lies at the inner side of the elbow-joint, behind the internal condyle, we have the sensation of "pins and needles," or of a shock, in the parts to which its fibres are distributed; namely, in the palm and back of the hand, and in the fifth and ulnar half of the fourth finger. When stronger pressure is made, the sensations are felt in the fore-arm also; and, if the mode and direction of the pressure be varied, the sensation is felt by turns in the fourth finger, in the fifth, in the palm of the hand, or in the back of the hand, according as different fibres or fasciculi of fibres are more pressed upon than others. It is in accordance with this law, that when parts are deprived 316 THE NERVOUS SYSTEM. of sensibility by compression or division of the nerve supplying them, irritation of the portion of the nerve connected with the brain still excites sensations which are felt as if derived from the parts to which the peripheral extremities of the nerve-fibres are distributed. Thus, there are cases of paralysis in which the limbs are totally insensible to external stimuli, yet are the seat of most violent pain, resulting, apparently, from irritation of the sound part of the trunk of the nerve still in connection with the brain, or from irritation of those parts of the nervous centre from which the sensitive nerve or nerves supplying the paralyzed limbs originate. An illustration of the same law is also afforded by the cases in which division of a nerve for the cure of neuralgic pain is use- less, and in which the pain continues or returns, though portions of the nerve be removed. In such cases, the disease is probably seated nearer the nervous centre than the part at which the division of the nerve is made, or it may be in the nervous centre itself. When the cause of the neuralgia is seated in the trunk of the nerve — for example, of the facial or infra-orbital nerve — division of the branches can be of no service; for the stump remaining in connection with the brain, and containing all the fibres distributed in the branches of the nerve to the skin, continues to give rise, when irritated, to the same sensations as are felt when the peri- pheral parts themselves are affected. Division of a nerve prevents the possibility of external impressions on the cutaneous extremities of its fibres being felt; for these impressions can no longer be com- municated to the brain : but the same sensations which were before produced by external impressions may arise from internal causes. In the same way may be explained the fact, that when part of a limb has been removed by amputation, the remaining portions of the nerves which ramified in it may give rise to sensations which the mind refers to the lost part. When the stump and the divided nerves are inflamed, or pressed, the patient complains of pain felt as if in the part which has been removed. When the stump is healed, the sensations which we are accustomed to have in a sound limb are still felt; and tingling and pains are referred to the parts that are lost, or to particular portions of them, as, to single toes, to the sole of the foot, to the dorsum of the foot, etc. But (as Volkmann shows) it must not be assumed, as it often has been, from these examples, that the mind has no power of discrimi- nating the very point in the length of any nerve-fibre to which an irritation is applied. Even in tbe instances referred to, the mind perceives the pressure of a nerve at the point of pressure, as well as in the seeming sensations derived from the extremities of the fibres: and in stumps, pain is felt in the stump as well as, seemingly, in the parts removed. In the natural state of parts, also, the mind dis- cerns the very part of a nerve-fibre that is irritated. Thus, if a needle's point be drawn in a straight line across the back, or the LAWS OF ACTION OF NERVES OF SENSATION. 317 thigh, or any part in which nerve-fibres are widely placed, the mind perceives the line of irritation as a straight one; whereas, if it re- ferred all impressions to the ends of irritated fibres, this mode of irritation should be felt in sensations variously scattered about the line, in the points at which the nerve-fibres crossed by the needle terminate. So, in the case of the retina, it is certain that its whole inner surface is not so covered with the ends of nerve-fibres that the images of any two points or lines which appear distinct must always fall on different fibres; but if, in any case, the two images fall on different parts of the same fibres, and the mind perceives them as distinct objects, it must be because the mind can discern the very point or points of a nerve-fibre on which an impression falls. The conclusions from both these sets of facts may be, that in the natural state of the parts, and on the application of ordinary stimuli, the mind can so distinctly discern an impression made on any point in the length of a nerve-fibre as to refer it to that point, and, even when, as in the case of impressions on the retina, two or more arc made at the same instant on different points of the same fibre, can discriminate and perceive them both as distinct and as proceeding from definitely related objects; but that in morbid states of the nerves, and, in the case of unusual stimuli, the impressions made on nerve-fibres in their course are referred by the mind rather to parts from which it is in the habit of receiving impressions through those nerves, than to the parts of the nerve-fibres on which the stimulus or irritation is applied. The habit of the mind to refer impressions received through the sensitive nerves to the parts from which impressions through those nerves are, or were, commonly received, is further exemplified when the relative position of the peripheral extremities of sensitive nerves is changed artificially, as in the transposition of portions of skin. When, in the restoration of a nose, a flap of skin is turned down from the forehead and made to unite with the stump of the nose, the new nose thus formed has, as long as the isthmus of skin by which it maintains its original connections remains undivided, the same sensations as if it were still on the forehead; in other words, when the nose is touched, the patient feels the impression as if it were derived from the forehead. When the communication of the nervous fibres of the new nose with those of the forehead is cut off by division of the isthmus of skin, the sensations are no longer referred to the forehead; the sensibility of the nose is at first absent, but is gradually developed. When, in a part of the body which receives two sensitive nerves, one is paralyzed, the other is inadequate to maintain the sensibility of the entire part; the extent to which the sensibility is preserved corresponds to the number of the fibres unaffected by the paralysis. This is a consequence of the isolation and simplicity of the several 27* 318 THE NERVOUS SYSTEM. nerve-fibres, so that, as already observed, even when nerves appear to anastomose, their several fibres continue separate and distinct, as isolated conductors of impressions. Thus, when the ulnar nerve, which supplies the fifth and a part of the fourth finger, is divided, the sensibility of those parts is not supplied through the medium of the branches which the ulnar derives from the median nerve; but the fourth and fifth fingers are permanently deprived of sensibility. Several of the laws of action in motor nerves correspond with the foregoing. Thus, the motor influence is propagated only in the direction of the fibres going to the muscles ; by irritation of a motor nerve, contractions are excited in all the muscles supplied by the branches given off by the nerve below the point irritated, and in those muscles alone: the muscles supplied by the branches which come off from the nerve at a higher point than that irritated, are never directly excited to contractions. No contraction, for instance, is produced in the frontal muscle by irritating the branches of the facial nerve that ramify upon the face; because that muscle derives its motor nerves from the trunk of the facial previous to these branches. So, again, because the isolation of motor nerve-fibres is as complete as that of sensitive ones, the irritation of a part of the fibres of a motor nerve does not affect the motor power of the whole trunk, but only that of the portion to which the stimulus is applied. And it is because of the same fact that when a motor nerve enters a plexus, and contributes with other nerves to the formation of a ner- vous trunk proceeding from the plexus, it does not impart motor power to the whole of that trunk, but only retains it isolated in the fibres which form its continuation in the branches of that trunk. Functions of Nervous Centres. As already observed (p. 309), the term nervous centre is applied to all those parts of the nervous system which contain ganglion- corpuscles, or vesicular nerve-substance, /. e., the brain, spinal cord, and the several ganglia which belong to the cerebro-spinal and the sympathetic systems. Each of these nervous centres has a proper range of functions, the extent of which bears a direct proportion to the number of nerve-fibres that connect it with the various organs of the body, and with other nervous centres; but they all have cer- tain general properties and modes of action common to them as nervous centres. It is generally regarded as the property of nervous centres, that they originate the impulses by which muscles may be excited to action, and by which the several functions of organic life maybe maintained. Hence, they are often called sources or originators of nervous power or force. But, the instances in which these expres- sions can be strictly used are few. It is possible that the ganglia of the heart are the spontaneous sources of the nervous force that ex- CONDUCTION THROUGH NERVOUS CENTRES. 319 cites its rhythmical contractions; that the medulla oblongata may originate the force exciting the co-ordinate and adapted acts of the first respirations; and that from the spinal cord is derived the force under which the sphincter ani is held in uniform contraction; but with these exceptions (if they are such) few or no motor impulses proceed spontaneously from the nervous centres.1 The brain does not issue any except when itself impressed by the will, or stimulated by an impression from without; neither without such previous im- pressions do the other nervous centres produce or issue motor impulses. The intestinal ganglia, for example, do not give out the nervous force necessary to the contractions of the intestines except when they receive, through their centripetal nerves, the stimuli of substances in the intestinal canal. So, also, the spinal cord; for a decapitated animal lies motionless so long as no irritation is applied to its centripetal nerves, though the moment it is touched movements ensue. The more certain and general office of all the nervous centres is that of variously disposing and transferring the impressions that reach them through their several centripetal nerve-fibres. In nerve- fibres, as already said, impressions are only conducted in the simple isolated course of the fibre; in all the nervous centres an impression may be not only conducted, but also communicated: in the brain alone it may be perceived (see p. 53). Conduction in or through nervous centres may be thus simply illustrated. The food in a given portion of the intestines, acting as a stimulus, produces a certain impression on the nerves in the mucous membrane, which impression is conveyed through them to the adja- cent ganglia of the sympathetic. In ordinary cases, the consequence of such an impression on the ganglia is the movement of the mus- cular coat of that and the near adjacent portions of the canal. But, if irritant substances be mingled with the food, the sharper stimulus produces a stronger impression, and this is conducted through the nearest ganglia to others more and more distant; and, from all these, motor impulses issuing, excite a wide-extended and more forcible action of the intestines. Or, even through all the sympathetic ganglia, the impression may be further conducted to the ganglia of the spinal nerves, and through them to the spinal cord, whence may issue motor impulses to the abdominal and other muscles, producing cramp. And yet further, the same morbid impression may be con- ducted through the spinal cord to the brain, where the mind may perceive it. In the opposite direction, mental influence may be con- ducted from the brain through a succession of nervous centres—the spinal cord and ganglia, and one or more ganglia of the sympathetic — to produce the influence of the mind on the digestive and other 1 The case of that modification of tone which consists in a permanent, and seemingly passive, slight contraction of the muscles, is not here in view. 320 THE NERVOUS SYSTEM. organic functions. In short, in all cases in which the mind either has cognizance of, or exercises influence on, the processes carried on in any part supplied with sympathetic nerves, there must be a con- duction of impressions through all the nervous centres between the brain and that part. It is probable that in this conduction through nervous centres the impression is not propagated through uninter- rupted nerve-fibres, but is conveyed through successive nerve-vesicles and connecting nerve-filaments. In some instances, and when the stimulus is exceedingly powerful, the conduction may be effected as quickly as through continuous nerve-fibres; but with less stimulus it may occupy some minutes in its transit. Thus, e.g., in stimulating the semilunar ganglia of the stomach, movements slowly ensue in the stomach; on touching the heart, all its fibres very soon contract, yet not in that instantaneous manner in which the fibres of a voluntary muscle contract when its nervous trunk is irritated. But instead of, or as well as, being conducted, impressions made on nervous centres may be communicated, from the fibres that brought them, to others; and in this communication may be either trans- ferred, diffused, or reflected. The transference of impressions may be illustrated by the pain in the knee, which is a common sign of disease of the hip. Here the impression made by the disease on the nerves of the hip-joint, is conveyed to the spinal cord; there it is transferred to the central ends or connections of the nerve-fibres of the knee-joint. Through these the transferred impression is conducted to the brain, and the mind, referring the sensation to the part from which it usually through these fibres receives impressions, feels as if the disease and the source of pain were in the knee. At the same time that it is transferred, the primary impression may be also conducted, and in this case, pain is felt in both the hip and the knee. So, not unfre- quently, if one touches a small pimple that may be seated in the trunk, a pain will be felt in as small a spot on the arm, or some other part of the trunk. And so, in whatever part of the respiratory organs an irritation may be seated, the impression it produces is transferred to the nerves of the larynx; and then the mind perceives the peculiar sensation of tickling in the glottis, which best, or almost alone, excites the act of coughing. Or, again, when the sun's light falls strongly on the eye, a tickling may be felt in the nose, exciting sneezing. In all these cases the primary impression may be con- ducted as well as transferred; and in all it is transferred to a certain set of nerves which generally appear to be in some purposive relation with the nerves first impressed. The diffusion or radiation of impressions is shown when an im- pression received at a nervous centre is diffused to many other fibres in the same centre, and produces sensations extending far beyond, or in an indefinite area around, the part from which the primary im- PHENOMENA OF REFLEX ACTION. 321 pression was derived. Hence, as in the former cases, result various kinds of what have been denominated sympathetic sensations. Sometimes such sensations are referred to almost every part of the body; as in the shock and tingling of the skin produced by some startling noise. Sometimes only the parts immediately surrounding tbe point first irritated participate in the effects of the irritation : thus, the aching of a tooth may be accompanied by pain in the ad- joining teeth, and in all the surrounding parts of the face; the ex- planation of such a case being, that the irritation conveyed to the brain by the nerve-fibres of the diseased tooth is radiated to the central ends of adjoining fibres, and that the mind perceives this secondary impression as if it were derived from the peripheral ends of the fibres. Thus, also, the pain of a calculus in the ureter is diffused far and wide. All the preceding examples represent impressions communicated from one sensitive fibre to others of the same kind; or from fibres of special sense to those of common sensation. A similar communi- cation of impressions from sensitive to motor fibres, constitutes re- flection of impressions, displays the important function common to all nervous centres as reflectors, and produces reflex movements. In the extent and direction of such communications also, phenomena corresponding to those of transference and diffusion to sensitive nerves, are observed in the phenomena of reflection. For, as in transference, the reflection may take place from a certain limited set of sensitive nerves to a corresponding and related set of motor nerves; as when, in consequence of the impression of light on the retina, the iris contracts, but no other muscle moves. Or, as in diffusion or radia- tion, the reflection may bring widely-extended muscles into action; as when an irritation in the larynx brings all the muscles engaged in expiration into coincident movement. It will be necessary hereafter to consider in detail so many of the instances of the reflecting power of the several nervous centres that it may be sufficient here to mention only the most general rules of reflex action. 1. For the manifestation of every reflex action, three things are necessary; first, one or more perfect centripetal nerve-fibres, to con- vey an impression; 2dly, a nervous centre to which this impression may be conveyed, and in which it may be reflected; 3dly, one or more centrifugal nerve-fibres, upon which this impression may be reflected, and by which it may be conducted to the contracting tissue. In the absence of either of these three conditions, a proper reflex movement could not take place; and whenever impressions made by external stimuli on sensitive nerves give rise to motions, these are never the result of the direct reaction of the sensitive and motor fibres of the nerves on each other; in all such cases the impression is conveyed by the sensitive fibres to a nervous centre, and is therein communicated to the motor fibres. 322 THE NERVOUS SYSTEM. 2. All reflex actions are essentially involuntary; all may be ac- complished independent of the will, though most of them admit of being modified, controlled, or prevented by a voluntary effort. All are perfectly performed without education or previous experience, although some, as coughing and the like, are not well performed unless the will have previously made some preparatory movement. 3. All reflex actions performed in health have a distinct purpose, and are adapted to secure some end desirable for the well-being of the body; but, in disease, many of them are irregular and purpose- less. As an illustration of the first point may be mentioned move- ments of the digestive canal, the respiratory movements, the con- traction of the eyelids and the pupil to exclude many rays of light when the retina is exposed to a bright glare. These, and all other normal reflex acts afford, also, examples of the mode in which the nervous centres combine and arrange co-ordinately the actions of the nerve-fibres, so that many muscles may act together for the common end. Another instance of the same kind is furnished by the spas- modic contractions of the glottis on the contact of carbonic acid, or any foreign substance, with the internal surface of the epiglottis or larynx. Examples of the purposeless, irregular nature of morbid reflex actions are seen in the convulsive movements of epilepsy, and in the spasms of tetanus and hydrophobia. 4. Beflex muscular acts are commonly more sustained than those produced by the direct stimulus of muscular nerves. As Volkmann relates (lxxx. 1845), the irritation of a muscular organ, or its motor nerve, produces contraction, lasting only so long as the irritation con- tinues ; but irritation applied to a nervous centre through one of its centripetal nerves, excites reflex and harmonious contractions, which last some time after the withdrawal of the stimulus. CEREBRO-SPINAL NERVOUS SYSTEM. The physiology of the cerebro-spinal nervous system includes that of the spinal cord, medulla oblongata and brain, of the several nerves given off from each, and of the ganglia on those nerves. It will be convenient to speak first of the spinal cord and its nerves. Spinal Cord and its Nerves. The spinal cord is a cylindriform column of nerve-substance, con- nected above with the brain through the medium of the medulla oblongata, terminating below, about the first or second lumbar verte- bra, in a slender filament of grey or vesicular substance, the fllum terminale, which lies in the midst of the roots of many nerves form- ing the cauda equina. The cord is composed of fibrous and vesicu- lar nervous substance, of which the former is situated externally, and constitutes its chief portion, while the latter occupies its central or STRUCTURE OF THE SPINAL CORD. 323 Fig. 102. axial portion, and is so arranged, that on the surface of a transverse section of the cord it appears like two some- what crescentic masses connected together by a narrower portion, or isthmus. The spinal cord consists of two exactly sym- metrical halves united in the middle line by a commissure, but separated anteriorly and posteriorly by a vertical fissure ; the posterior fissure being deeper, but less wide and distinct than the anterior. Each half of the spinal cord is marked on the sides (obscurely at the lower part, but distinctly above,) by two longitudinal furrows, which divide it into three portions, columns, or tracts, an anterior, middle or late- ral, and posterior. From the groove between the anterior and lateral columns spring the an- terior roots of the spinal nerves; and just in front of the groove between the lateral and posterior column arise the posterior roots of the same : a pair of roots on each side correspond- ing to each vertebra. The fibrous part of the cord contains con- tinuations of the innumerable fibres of the spi- nal nerves issuing from it, or entering it; but is, probably, not formed of them exclusively; nor a mere trunk, like a great nerve, through which they may pass to the brain. (Fig. 102.) It is, indeed, among the most difficult things in structural anatomy to determine the course of individual nerve-fibres, or even of fasciculi of fibres, through even a short distance of the spinal cord: and it is only by the examination of transverse and longitudinal sections through the substance of the cord, such as those so suc- cessfully made by Mr. Lockhart Clarke (xliii., ls.31 and 1853), that we can obtain anything like a correct idea of the direction taken by the fibres of the roots of the spinal nerves within the cord. From the information afforded by such sections, it would appear, that of the root-fibres of the nerves which enter the cord, some assume a transverse, others a longitudinal direction : the fibres of the former pass hori- zontally or obliquely into the substance of the cord, in which many of them appear to become continuous with fibres entering the cord from other roots, others pass into the columns of the cord, while Transverse section of the spinal cord. A. Immediately below the decussation of the pyramids, b. At mid- dle of cervical bulb. c. Mid- way between cervical and lumbar bulbs, d. Lumbar bulbs. E. An inch lower. p. Very near the lower end. a. Anterior surface, p. Posterior surface. The points of emergence of the anterior and posterior roots of the nerves are also seen. 324 THE NERVOUS SYSTEM. some, perhaps, terminate at or near the part which they enter: of the fibres of the second set, which usually first traverse a portion of the grey substance, some pass upwards, and others, at least of the posterior roots, turn downwards, but how far they proceed in either direction, or in what manner they terminate, are questions still un- determined. It is probable, that of these latter, many constitute longitudinal commissures, connecting different segments of the cord with each other, while others, probably, pass directly to the brain. That all, or even many, do not pass to the brain, is rendered proba- ble by many circumstances. First, if they did so, the thickness of the spinal cord ought to increase from below upwards, in the same proportion as fresh fasciculi of fibres are added to it by each pair of spinal nerves; and the portion nearest the medulla oblongata ought to be thicker than any part below it. But this is certainly not the case: the upper part of the cervical portion of the cord is smaller than the lower part; and both it and the middle of the dorsal por- tion are smaller than the lumbar portion. The general rule respect- ing the size of different parts of the cord appears to be, that the size of each part bears a direct proportion to the size and number of nerve-roots given off from itself, and has but little relation to the size or number of those given off below it. Thus, the cord is very large in the middle and lower part of its cervical portion, whence arise the large nerve-roots for the formation of the brachial plexuses and the supply of the upper extremities, and again enlarges at the lowest part of its dorsal portion and the upper part of its lumbar, at the origins of the large nerves which, after forming the lumbar and sacral plexuses, are distributed to the lower extremities. Together with this increase of the white substance, there is, however, a corre- sponding increase in the quantity of grey matter to which the greater thickness of the cord, at such parts, is also in some measure due. That such enlargements, occurring at parts of the cords which give off nerves of unusual size, are due to actual increase of nervous substance, has been proved by Volkmann (xv., art. Nervenphysiolo- gie). He weighed four pieces of a horse's spinal cord, each seven centimetres long, and taken respectively from below the second, the eighth, the nineteenth, and the thirtieth pairs of nerves, and found that their weights, in this order, were 219, 293,163, and 281 grains. On measurement, he found that the areas of the transverse sections of the grey matter in them were (in the same order) 13, 28, 11, and 25 square lines; and those of the white matter 109, 142, 89, and 121 square lines. It thus appeared, that the quantity of white or fibrous substance of the cord is absolutely less at the cervical than at the lowest part of the lumbar portion; which it could not be, if the cord, in its progress from below upwards, retained any quantity of the fibres successively received from the roots of the spinal nerves. On the other hand, the enlargement and increased weight of the NERVES OF SPINAL CORD. 325 cord at parts exactly corresponding to tbe origin of the larger and most numerous nerves, and its diminution immediately above and below such parts, make it most probable that the fibres composing the roots of those nerves arise directly from the largest parts of the cord, and not from any parts higher up. Although, however, this statement by Volkmann may be in great measure true for the horse and other animals, yet the observations of Kblliker and others make it probable that, in the case of man, the white or fibrous substance of the cord does regularly and progres- sively increase from below upwards, in consequence, no doubt, of the continual addition of fresh fasciculi from each pair of nerves; and that, therefore, as already said, many of the fibres proceed through the cord in simple and uninterrupted continuity to the brain. It may be added, however, that there is no sufficient evidence for the supposition, that an uninterrupted continuity of nerve-fibres is essential to the conduction of impressions on the spinal nerves to and from the brain : such impressions may be as well transmitted through the nerve-vesicles of the cord as by the nerve-fibres; and the experiments of Brown-Sequard, again to be alluded to, make it probable that the grey substance of the cord is the only chan- nel through whicb sensitive impressions are conveyed to the brain.1 The Nerves of the Spinal Cord consist of thirty-one pairs, issuing from the sides of the whole length of the cord; their numbers cor- responding with the intervertebral foramina, through which they pass. Each nerve arises by two roots, an anterior and posterior, the latter being the largest. The roots emerge through separate aper- tures of the sheath of dura mater surrounding the cord; and directly after their emergence, while the roots lie in the intervertebral fora- men, a ganglion is formed on the posterior root. The anterior root lies in contact with the anterior surface of the ganglion, but none of its fibres intermingle with those in the ganglion. But imme- diately beyond the ganglion, the two roots coalesce, and, by the mingling of their fibres, form a compound or mixed spinal nerve, which, after issuing from the intervertebral canal, divides into an anterior and posterior branch, each containing fibres from both the roots (Fig. 103, p. 326). The anterior root of each spinal nerve arises by numerous sepa- rate and converging fasciculi from the anterior column of the cord; the posterior root by more numerous parallel fasciculi, from the posterior column, or, rather, from the posterior part of the lateral column; for if a fissure be directed inwards from the.groove 1 On the anatomy of the spinal cord consult any of the principal syste- matic treatises; or Grainger (ciii.); Todd (lxxiii. art. Nervous centres); Longet (exxxvi.); Stilling and AVallach (clvii); J. L. Clarke (xliii. 1851 and 1853): Kolliker (ccvi. and ccxii.). 326 THE NERVOUS SYSTEM. Fig. 103. Diagram to show the decussation of the fibres within the trunk of a nerve.— (After Valentin.) between the middle and posterior columns, the posterior roots will remain attached to the former. The anterior roots of each spinal nerve consist exclusively of motor fibres; the posterior as exclusively of sensitive fibres. For the knowledge of this important fact, and much of the consequent progress of the phy- siology of the nervous system, science is indebted to Sir Charles Bell. The fact is proved in vari- ous ways. Division of the anterior roots of one or more nerves is followed by complete loss of motion in the parts supplied by the fibres of such roots; but the sensation of the same parts re- mains perfect. Division of the posterior roots destroys the sensibility of the parts supplied by their fibres, while the power of motion continues unimpaired. Moreover, irritation of the ends of the distal portions of the divided anterior roots of a nerve excites muscular movements; irritations of the ends of the proximal portions, which are still in connection with the cord, are followed by no effect. Irritation of the distal portions of the divided posterior roots, on the other hand, produces no muscular movements, and no mani- festation of pain; for, as already stated, sensitive nerves convey impressions only towards the nervous centres: but irritation of the proximal portions of these roots elicits signs of intense suffering. Occasionally, also, under this last irritation, muscular movements ensue; but these are either voluntary, or the result of the irritation being reflected from the sensitive to the motor fibres. As an example of the experiments of which the preceding para- graph gives a summary account, this may be mentioned : If in a frog the three posterior roots of the nerves going to the hinder ex- tremity be divided on the left side, and the three anterior roots of the corresponding nerves on the right side, the left extremity will be deprived of sensation, tho right of motion. If the foot of the right leg, which is still endowed with sensation but not with the power of motion, be cut off, the frog will give evidence of feeling pain by movements of all parts of the body except the right leg itself, in which he feels the pain. If, on the contrary, the foot of the left leg which has the power of motion, but is deprived of sen- sation, is cut off, the frog does not feel it, and no movement follows except the twitching of the muscles irritated by cutting them or their tendons. Functions of the Spinal Cord. The spinal cord manifests all the properties already assigned to nervous centres (see p. 318). FUNCTIONS OF THE SPINAL CORD. 327 1. It is capable of conducting impressions, or states of nervous excitement. Through it, the impressions made upon the peripheral extremities or other parts of the spinal sensitive nerves are con- ducted to the brain, where alone they can be perceived by the mind. Through it, also, the stimulus of the will, applied to the brain, is capable of exciting the action of the muscles supplied from it with motor nerves. And for all these conductions of impressions to and fro between the brain and the spinal nerves, the perfect state of the cord is necessary; for when any part of it is destroyed, and its com- munication with the brain is interrupted, impressions on the sensi- tive nerves given off from it below the seat of injury, cease to be propagated by the brain; and the mind loses the power of volunta- rily exciting the motor nerves proceeding from the portion of cord isolated from the brain. Illustrations of this are furnished by various examples of paraly- sis, but by none better than by the common paraplegia, or loss of sensation and voluntary motion in the lower part of the body, in consequence of destructive disease or injury of a portion, including the whole thickness, of the spinal cord. Such lesions destroy the communication between the brain and all parts of the spinal cord below the seat of injury, and consequently cut off from their con- nection with the mind, the various organs supplied with nerves issuing from those parts of the cord. But if this lower portion of the cord preserves its integrity, the various parts of the body sup- plied with nerves from it, though cut off from the brain, will never- theless be subject to the influence of the cord, and, as presently to be shown, will indicate its other powers as a nervous centre. From what has been already said, it will appear probable that the conduction of impressions along the cord is effected (at least, for the most part) through the gray substance, i. e., through the nerve-cor- puscles and filaments connecting them. But there is reason to be- lieve that all parts of the cord are not alike able to conduct all im- pressions ; and that, rather, as there are separate nerve-fibres for motor and for sensitive impressions, so, in the cord, separate and determinate parts serve to conduct the same impressions. The con- sideration of this point involves the question of the functions of the columns of the cord. The question is whether the anterior and pos- terior columns correspond to the anterior and posterior roots re- spectively: whether the anterior columns contain only motor, the posterior only sensitive fibres. Experiments, especially those of Longet (cxxxvi.) and Van Deen (clviii.), have shown that irritations of the anterior columns of the spinal cord are followed by convulsive movements of all the parts supplied with motor nerves from and below the irritated part, but give rise to no manifestations of pain: while irritation of the poste- rior columns appears to cause excruciating pain, without producing any muscular movement besides such as may be the result of voli- 328 THE NERVOUS SYSTEM. tion, or the reflection of the stimulus from the irritated cord to the roots of motor nerves. Again, when the spinal cord is completely divided, irritation of the posterior columns of the lower part which is cut off from the brain produces no effect: irritation of the ante- rior columns of the same part excites violent movements. And, in the same experiment, irritation of the divided anterior columns of the portion of the cord still connected with the brain produces no effect: but irritation of the divided posterior columns of the same portion produces acute pain and reflex movements (Longet). Again, when both the anterior columns of the cord are divided, the power of voluntary movement in the parts supplied with nerves below the point of division is completely lost: the sensibility of the same parts being unimpaired. When both posterior columns are divided, sen- sation in the parts supplied by nerves from below the injured point is lost, while the power of movement over such parts remains per- fect (Van Deen). [It has been shown by Dr. Brown-Sequard, that when the posterior column on one side is cut, there is a loss of sen- sibility in the opposite side of the body, thus proving a crossing of the fibres of the sensory, as well as of the motor tract.] The results of these experiments would seem to prove that the effects of the division of the anterior or posterior columns of the cord are exactly the same as those of division of the anterior or posterior roots of the spinal nerves, and that therefore one might be justified in calling the anterior the motor, and the posterior the sensitive, columns of the cord. Yet there are reasons for hesitation. For the posterior roots of the spinal nerves are connected (as already stated) not with the posterior columns, but with the posterior part of the lateral columns; and neither tbe injuries in experiments, nor the results of disease, can be so precisely limited as to discern the dif- ference of the effects of injury of the posterior columns, from those of the immediately-adjacent portions of the lateral columns. Neither is it likely that the fibres of the columns are the sole, or even the principal, conductors of impressions: at the most, therefore, we should not be justified in assuming more than that the posterior half of the cord corresponds with the sensitive roots, and the anterior with the motor. And even this statement, though there may be little doubt of its general truth, should be held as likely to require modi- fications : for the results of diseases and injuries of different parts of the human cord are not always in accordance with it. Though many cases have seemed confirmatory of it,' yet some have been observed directly contrary to it; cases, for example, in which com- 1See especially a case by Begin, quoted, with others, by Longet (cxxxvi. vol. i. p. 331). A man was stabbed at the back of the neck, and the point of the knife passed obliquely forwards between the sixth and seventh cer- vical vertebrae, dividing the corresponding anterolateral and anterior columns of the cord on the right side. During the six days in which he survived the injury, there existed a complete paralysis of motion in the right lower ex- tremity, and incomplete paralysis of motion in the right upper extremity but sensibility was perfect. CONDUCTION BY THE SPINAL CORD. 329 plcte loss of motion, without any impairment of sensation, was an accompaniment of lesion of the posterior columns of the cord, the anterior being apparently entire (Stanley, xli. vol. xxiii.; Webster, xli. vol. xxvi.). The recent experiments of M. Brown-Sequard on the functions of the spinal cord, bear especially on this part of the subject. They render nearly certain, that, although the posterior columns of the cord are essentially sensitive, yet that they do not in themselves con- vey impressions direct to the brain, but conduct them to the grey substance of the cord, by which alone they are transmitted onwards to the brain. His experiments show, also, that sensitive impressions reaching the cord pass downwards for a short distance, probably along the descending fibres delineated by Mr. Lockhart Clarke, and ultimately pass across to the opposite side of the spinal cord; so that, on division of one posterior column of the spinal cord, sensa- tion is lust, not in parts on the corresponding, but in those on the opposite, side of the body. In the case of tbe anterior columns no such crossing takes place in the cord, the fibres and impulses passing directly to and from the cerebrum, their crossing being effected at the medulla oblongata.1 That impressions may be conducted across as well as along the cord may also be proved in other ways. Thus, if the brain and medulla oblongata be removed, irritation of either posterior column of the upper end of the cord will cause general movements of mus- cles, the impression being conveyed across to the anterior columns and roots; for the movements do not happen if the anterior roots are divided. If one half of the cord be divided at a certain part, and the other half at a certain distance from that part, impressions (at least sensitive ones) may be conducted through the intermediate por- tion of the cord from one side to the other (Van Deen); and this may be effected though only a portion of the grey substance be left to connect the portions of cord above and below. But impressions do not seem to be conveyed from the anterior columns to the posterior, nor from one anterior column to the other; so that, as in the case already cited from Begin after the division of one anterior column, including the anterior part of the grey matter in it, the will has no power over the muscles deriving nerves from or below the injured part of the column.2 *For a resumS of M. Brown-Se"quard's experiments on the functions of the spinal cord, see a clever essay by Mr. Thomas Smith in the British and Foreign Medico-Chirurgical Review, April, 1856. 2 For a complete discussion of this subject, and for the arguments in favor of the posterior columns of the cord being composed of fibres forming com- missural connections between its several parts, see Todd (lxxiii. art. Nervous Centres: and clix.). The best evidence for the sensitive and motor functions being appropriate to the posterior and anterior columns is in Longet (cxxxvi.). Many interesting facts are in Sir Charles Bell's works (cxlii.); Miiller (xxxii.); Gruinger (clii.); and Brown-S6quard (cxc. April, 1856). 28* 330 THE NERVOUS SYSTEM. 2. In the second place, the spinal cord as a nervous centre, or rather, as an aggregate of many nervous centres, has the power of communicating impressions from fibre to fibre in the several ways already mentioned (p. 319). Examples of the transference and radiation of impressions in the cord have been given; and that the transference at least takes place in the cord, and not in the brain, is nearly proved by the case of pain felt in the knee, and not in the hip, in diseases off he hip; of pain felt in the urethra or glans penis, and not in the bladder, in calculus; for, if both the primary, and the secondary or transferred, impressions, were in the brain, both should be always felt. Of radia- tion of impressions there are, perhaps, no means of deciding whether they take place in the spinal cord or in the brain: but the analogy of the cases of transference makes it probable that the communica- tion is, in this, also, effected in the cord. The power, as a nervous centre, of communicating impressions from sensitive to motor, or, more strictly, from centripetal to centri- fugal nerve-fibres, is what is usually discussed as the reflex function of the spinal cord. Its general mode of action, its general, though incomplete, independence of consciousness, the will, and the brain, and the conditions necessary for its perfection have been already stated (p. 321). These points, and the extent in which the power operates in the production of the natural reflex movements of the body, have now to be further illustrated. They will be described in terms adapted to the general rules of reflections of impressions in nervous centres, avoiding all such terms as might seem to imply that the power of the spinal cord in reflecting is different in kind from that of all other nervous centres. The occurrence of movements under the influence of the spinal cord, and independent of the will, is well exemplified in the acts of swallowing, in which a portion of food carried by voluntary efforts into the fauces, is conveyed by successive involuntary contractions of the constrictors of the pharynx and muscular walls of the oeso- phagus into the stomach. These contractions are excited by the stimulus of the food on the centripetal nerves of the pharynx and oesophagus being first conducted to the spinal cord and medulla oblongata, and thence reflected through the motor nerves of these parts.1 All these movements of the pharynx and oesophagus are •It is customary to call the nerves thus conducting impressions to be re- flected, excilo-motory; and the nerves by which the impressions are reflected, reflecio-motory; and corresponding terms are applied in explanation of the reflex acts of the cord. They are here avoided, both for the reason given in the preceding paragraph, and because they are apt to lead the student to believe that the nerves contain one set of fibres for the conduction of im- pressions to and from the brain, and another for the conduction of them to and from the spinal cord; the improbability of which will appear from what is said of the structure of the cord in p. 323. REFLEX FUNCTIONS OF SPINAL CORD. 331 involuntary; the will cannot arrest them or modify them; and though tbe mind has a certain consciousness of the food passing, which becomes less as the food passes further; yet that this is not necessary to the act of deglutition, is shown by its occurring when the influence of the mind is completely removed; as when food is introduced into the fauces or pharynx during a state of complete coma, or in a brainless animal (Grainger, clii.). So, also, for example, under the influence of the spinal cord the involuntary and unfelt muscular contraction of the sphincter ani is maintained when the mind is completely inactive, as in deep sleep, but ceases when the lower part of the cord is destroyed, and cannot be maintained by the will. The independence of the mind manifested by the reflecting power of the cord, is further shown in the most perfect occurrence of the reflex movements when the spinal cord and the brain are discon- nected, as in decapitated animals, and in cases of injuries or diseases so affecting the spinal cord as to divide or disorganize its whole thickness at any part whose perfection is not essential to life. Thus, when the head of a lizard is cut off, the trunk remains standing on the feet, and the body writhes when the skin is irritated. If the animal is cut in two, the lower portion can be excited to motion as well as the upper portion; the tail may be divided into several seg- ments, and each segment, in which any portion of spinal cord is contained, contracts on the slightest touch; even the extremity of the tail moves as before, as soon as it is touched. All the portion of the animal in which these movements can be excited, contain some part of the spinal cord; and it is evidently the cause of the motions excited by touching the surface; for they cannot be excited in parts of the animal, however large, if no cord is contained in them. Mechanical irritation of the skin excites not the slightest motion in the leg when it is separated from the body; yet the ex- tremity of the tail moves as soon as it is touched. With the same power of the spinal cord in reflecting impressions, an eel, or a frog, or any other cold-blooded animal, will move long after it is deprived of its head, and when, however much the movements may indicate purpose, it is not probable that consciousness or will has any share in them. And so, in the human subject, or any warm-blooded animal, when the cord is completely divided across, or so diseased at some part that the influence of the mind cannot be conveyed to the parts below it, the irritation of any part of the surface supplied by nerves given off from the cord below the seat of injury, is com- monly followed by spasmodic and irregular reflex movements, even though in the healthy state of the cord such involuntary movements could not be excited when the attention of the mind was directed to the irritating cause. In the fact last mentioned is an illustration of an important dif- ference between the warm-blooded and the lower animals in regard 332 THE NERVOUS SYSTEM. to the reflecting power of the spinal cord (or its homologue in the Invertebrata), and the share which it and the brain have respectively, in determining the several natural movements of the body. When, for example, a frog's head is cut off, the limbs remain in or assume a natural position; resume it when disturbed; and when the abdo- men or back is irritated, the feet are moved with the manifest pur- pose of pushing away the irritation. It is as if the mind of the animal were still engaged in the acts.1 But, in division of the human spinal cord, the lower extremities fall into any position that their weight and the resistance of surrounding objects combine to give them; if the body is irritated they do not move towards the irritation ; and if themselves are touched the consequent movements are disorderly and purposeless. Now, if we are justified by analogy in assuming that the will of the frog cannot act more than the will of man, through the spinal cord separated from the brain, then it must be admitted, that many more of the natural and purposive movements of the body can be performed under the sole influence of the cord in the frog than in man ; and what is true in the instances of these two species is generally true also of the whole class of cold- blooded as distinguished from warm-blooded animals. It may not, indeed, be assumed that the acts of standing, leaping, and other movements, which decapitated cold-blooded animals can perform, are also always, in the entire and healthy state, performed invol- untarily and under the sole influence of the cord; but it is probable that such acts may be, and commonly are, so performed, the mind of the animal having only the same kind of influence in modifying and directing them, as the mind of man has in modifying and directing the movements of the respiratory muscles. The fact that such movements as are produced by irritating the skin of the lower extremities in the human subject, after division or disorganization of a part of the spinal cord, do not follow the same irritation when the mind is active and connected with the cord through the brain, is, probably, due to the mind ordinarily per- ceiving the irritation and instantly controlling the muscles of the irritated and other parts; for, even when the cord is perfect, such involuntary movements will often follow irritation if it be applied when the mind is wholly occupied. When, for example, one is anxiously thinking, even slight stimuli will produce involuntary and reflex movements. So, also, during sleep such reflex move- ments may be observed when the skin is touched or tickled; for 1 The evident adaptation and purpose in the movements of the cold-blooded animals have led some to think that they must be conscious and capable of will without their brains. But purposive movements are no proof of consciousness or will in the creature manifesting them The movements of the limbs of head- less frogs are not more purposive than the movements of our own re-spiratory muscles are: in which we know that neither will nor consciousness is at all times concerned. REFLEX FUNCTIONS OF SPINAL CORD. 333 example, when one touches with a finger the palm of the hand of a sleeping child, the finger is grasped — the impression on the skin of the palm producing a reflex movement of the muscles which close the hand. But when the child is awake no such effect is produced by a similar touch. On the whole, it may, from these and like facts, be concluded, that the proper reflex acts, performed under the influence of the reflecting power of the spinal cord, are essentially independent of the brain, and may be performed perfectly when the brain is sepa- rated from the cord : that these include a much larger number of the natural and purposive movements of the lower animals than of the warm-blooded animals and man : and that dver nearly all of them the mind may exercise, through the brain, some control; determining, directing, hindering, or modifying them, either by direct action or by its power over associated muscles. In this fact, that the reflex movements from the cord may be perfectly performed without the intervention of consciousness or will, yet are amenable to the control of the will, we may see their admirable adaptation to the well-being of the body. Thus, for example, the respiratory movements may be performed while the mind is, in other things, fully occupied, or in sleep powerless; yet, in an emergency, the mind can direct and strengthen them; and it can adapt them to the several acts of speech, effort, etc. Being, for ordinary purposes, independent of the will and consciousness, they are performed perfectly, without experience or education of the mind; yet they may be employed to other and extraordinary uses when the mind wills, and so far as it acquires power over them. Being commonly independent of the brain, their constant continuance does not produce weariness; for it is only in the brain that it or any other sensation can be perceived. The subjection of the muscles to both the spinal cord and the brain, makes it difficult to determine in man what movements or what share in any of them can be assigned to the reflecting power of the cord. The fact, that after division or disorganization of a part of the cord, movements, and even forcible though purposeless ones, are produced in the lower limbs when the skin is irritated, proves that the spinal cord can supply nervous force for the action of the muscles that are, naturally, most under the control of the will: and it is, therefore, not improbable, that, for even the voluntary action of those muscles, when the cord is perfect, it may supply the force, and the will the direction. As instances in which it supplies both force and direction, that is, both excites and determines the combination of muscles, may be mentioned the acts of the abdominal muscles iu vomiting and voiding the contents of the bladder and rectum: in both of which, though, after the period of infancy, the mind may have the power of postponing or modifying the act, there are all the evidences of reflex action; namely, the necessary prece- 334 THE NERVOUS SYSTEM. dence of a stimulus, the independence of the will, and, sometimes, of consciousness, the combination of many muscles, the perfection of the act without the help of education or experience, and its failure or imperfection in disease of the lower part of the cord. The emis- sion of semen is equally a reflex act governed by the spinal cord: the irritation of the glans penis conducted to the spinal cord, and thence reflected, excites the successive and coordinate contractions of the muscular fibres of the vasa deferentia and vesiculae seminales, and of the bulbo-cavernosi and other muscles of the urethra; and a forcible expulsion of semen takes place, over which the mind has little or no control, and which, in paraplegia, may be unfelt. The erection of the penis also, as already explained (page 135), appears to be in part the result of a reflex contraction of the muscles by which the veins returning the blood from the penis are composed. Irritation of the vagina in sexual intercourse appears also to be propagated in the spinal cord, and thence reflected to the motor nerves supplying the Fallopian tubes. The involuntary action of the uterus in expelling its contents during parturition, is also of a purely reflex kind, dependent in part on the spinal cord, though in part also upon the sympathetic system: its independence of the brain and the mind was proved by cases of delivery in paraplegic women, and is now more abundantly shown in the use of chloroform. Besides these acts, regularly performed under the influence of the reflecting power of the spinal cord, others are manifested in accidents, such as the movements of the limbs and other parts, to guard the body against the effects of sudden danger. When, for example, a limb is pricked or struck, it is instantly and involuntarily withdrawn from the instrument of injury; a threatened blow on the face causes involuntary closure of the eye. And the preservative tendency of the reflex power of the cord is shown in the outstretched arms when falling forwards, and their reversed position when falling backwards. To these instances of spinal reflex action some add yet many more, including nearly all the acts which seem to be performed uncon- sciously, such as those of standing, walking, and the like. But those are not involuntary acts; they are not accomplished without the active cooperation of the brain, for they are impossible in coma, sleep, paraplegia, and complete mental abstraction; they all require educa- tion for their perfection; their force is not proportioned to any ex- ternal stimulus exciting them; they produce weariness; in short, they appear to be only examples how small an amount of attention and will are necessary for the performance of habitual acts. The phenomena of spinal reflex actions in man are much more striking and unmixed in cases of disease. In some of these, the effect of a morbid irritation, or a morbid irritability of the cord, is very simple; as when the local irritation of the sensitive fibres, bein°- propagated to the spinal cord, excites merely local spasms,—spasms° REFLEX FUNCTION OF SPINAL CORD. 335 namely, of those muscles, the motor fibres of which arise from the same part of the spinal cord as the sensitive fibres that are irritated. Of such a case we have instances in the spasms and tremors of limbs on which a severe burn is inflicted, etc. _ In other instances, in which we must assume that the cord is mor- bidly more irritable, i. e., apt to issue more nervous force than is proportionate to the stimulus applied to it, a slight impression on a sensitive nerve produces extensive reflex movements. This appears to be the condition in tetanus, in which a slight touch on the skin may throw the whole body into convulsion. A similar state is in- duced by the introduction of strychnia, and, in frogs, of opium into the blood; and numerous experiments on frogs thus made tetanic have shown that the tetanus is wholly unconnected with the brain, and depends on the state induced in the spinal cord. It may have seemed to be implied that the spinal cord, as a single nervous centre, reflects alike from all parts all the impressions con- ducted to it. But it is more probable that it should be regarded as a collection of nervous centres united in a continuous column. This is made probable by the fact that segments of the cord may act as distinct nervous centres, and excite motions in the parts supplied with nerves given off from them; as well as by the analogy of cer- tain cases in which the muscular movements of single organs are under the control of certain circumscribed portions of the cord. Thus Volkmann (lxxx., 1844,) has shown that the rhythmical move- ments of the anterior pair of lymphatic hearts in the frog depend upon nervous influence derived from the portion of spinal cord cor- responding to the third vertebra, and those of the posterior pair on influence supplied by the portion of cord opposite the eighth verte- bra. The movements of the hearts continue, though the whole of the cord, except the above portion, be destroyed; but on the instant of destroying either of these portions, though all the rest of the cord is untouched, the movements of the corresponding hearts cease. What appears to be thus proved in regard to two portions of the cord, may be inferred to prevail in other portions also; and the inference is reconcilable with most of the facts known concerning the physi- ology of the cord. It might be supposed that each portion of the cord is, as the nervous centre of a certain region, receiving and issuing impressions from and to the several nerve-fibres immediately connected with it. But some experiments by Engelhardt and Harless have made it pro- bable (if the case of frogs may be taken as an example of general truth), that different portions of the length of the cord are assigned for the government of different kinds of movements. The results of Harless' experiments may be thus expressed in a scheme in which each number represents that of the vertebra opposite to which the irritation was applied to the spinal cord: — 336 THE NERVOUS SYSTEM. Irritation at the . . Flexion of upper ex- tremities decreas- ing as the irritation is applied higher. Extension of upper extremities decreas- ing as the irritation is applied higher. 1st vertebra. 2d 3d 4th 5th 6th 7th 8th No movement. Flexion of lower extre- mities decreasing as the irritation is ap- plied lower. Less or no effect. Extension of lower ex- tremities decreasing as the irritation is ap- plied lower. Other of Harless' experiments appeared to show that the only portion of the frog's cord capable of reflecting. impressions to the motor nerves of tbe extremities, is that between the third and fifth vertebraj. For, by cutting away the cord from below upwards, the power of reflecting so as to produce movements in the lower extremi- ties is lost when the section comes to the sixth vertebra, and that of reflecting to the upper extremities, when the section reaches the fourth vertebra. The influence of the spinal cord on the sphincter ani has been already mentioned (p. 331). It maintains this muscle in permanent contraction, so that, except in the act of defecation, the orifice of the anus is always closed. This influence of the cord resembles its common reflex action in being involuntary, although the will can act on the muscle to make it contract more, or to permit its dilatation, and in that the constant action of the muscle is not felt, nor dimin- ished in sleep, nor productive of fatigue. But the act is different from ordinary reflex acts in being nearly constant. In this respect, it resembles that condition of muscles which has been called Tone,1 or passive contraction; a state in which they always appear to be when not active in health, and in which, though called inactive, they appear to be in slight contraction, and certainly are not relaxed, as they are long after death, or when the spinal cord is destroyed. This tone of all the muscles of the trunk and limbs seems to depend on the spinal cord, as the contraction of the sphincter ani does. If an animal is killed by injury or removal of the brain, the tone of the muscles may be left, and the limbs feel firm as during sleep; but if the spinal cord be destroyed, the sphincter ani relaxes, and all the muscles feel loose, and flabby, and atonic, and remain so till the rigor mortis commences. 1 This kind of tone must be distinguished from that mere firmness and tension which it is customary to ascribe with the name of tone to all tissues that feel robust and not flabby, as well as to muscles. The tone peculiar to muscles has in it a degree of vital contraction: that of other tissues is only due to their being well nourished, and therefore compact and tense THE MEDULLA OBLONGATA. 337 For the further study of the functions of the spinal cord, it need scarcely be said, that the works of Sir Charles Bell and Dr. Marshall Hall are the most important. The other principal writings are those of I'rochaska (cliii.); Magendie (civ.); Miiller (xxxii ); Grainger (clii.); Newport (xliii. 1844); Volkmann (lxxx. 1838); Dr. W. Budd (xli. vol. xxii.); Carpenter (cxxxi.); Todd (lxxiii. art. Ner- vous Centres); Barlow (lxxi. vol. xli.) ; Brown-Sequard (cxc. April, 185G). THE MEDULLA OBLONGATA. Its Structure. The medulla oblongata is a mass of grey and white nervous sub- stance contained within the cavity of tbe cranium, forming part of the cephalic prolongation of the spinal cord, and connecting it with the brain, The grey substance which it contains is situated in the interior, variously divided into masses and laminae by the white or fibrous substance which is arranged, partly in external columns, and partly in fasciculi traversing the central grey matter. The medulla oblongata is larger than any part of the spinal cord. Its columns are pyriform, enlarging as they proceed towards the brain, continuous with those of the spinal cord, more prominent than they are, and separated from one another by deeper grooves. In front are two, corresponding with the anterior columns of the cords, and named anterior pyramids or corpora pyramidalia; they are separated from each other by a deep, anterior, median fissure, at the bottom of which fibres appear decussating, i. e., crossing one another and changing sides. In this manner, nearly all the fibres of each pyramid pass over, and, turning backwards become continuous with the opposite lateral columns of the cord; those which do not decussate are directly continuous with the anterior column of the cord. Traced upwards, the fibres of the anterior pyramids pass through the inferior part of the pons Varolii; and then, forming the lower part of the crura cerebri, proceed through the optic thalami and corpora striata, to be distributed in the substance of the cerebral hemispheres1 (Fig. 102). External to each anterior pyramid is a prominent oval body (the olivary body), the fibres in and around which are continuous below with those of the corresponding anterior tracts of the cord, while 1 The expressions " continuous fibres," and the like, appear to be usually understood as meaning that certain primitive nerve-fibres pass without inter- ruption from one part to the other of those named. But such continuity of primitive fibres through long distances in the nervous centres is very far from proved. The apparent continuity of fasciculi (which is all that dissection can yet trace) is explicable on the supposition that many comparatively short fibres lie parallel, with the ends of each inlaid among many others. In such a case, there would be an apparent continuity of fibres; just as there is, for example, when one untwists and picks out a long cord of silk or wool, in which each fibre is short, and yet each fasciculus appears to be continued through the whole cord. 29 338 THE NERVOUS SYSTEM. above they pass into the deeper longitudinal fibres of the medulla oblongata, along which they may be traced through the crura cerebri into the lower parts of the optic thalami and corpora striata. The corpora olivaria are formed of portions of grey substance imbedded in fibres, and elevating them. Immediately behind the corpora olivaria, on each side, is a small, depressed tract, of fibrous matter, distinguished from the olivary tract because its fibres, instead of passing onwards longitudinally to the cerebrum, go outwards transversely through the pons into the cerebellum (Fig. 104). These tracts are named the lateral tracts, and are interesting in that the facial nerve emerges through them, and probably derives from them its connection with the motor portion of the medulla oblongata and cord. Behind the lateral tract on each side is the corpus restiforme, a large column of nerve-fibres, which, with its continued fibres below, forms the restiform tract (Fig. 105). It is continuous below with Fig. 104. Fig. 105. Fig. 104. Front view of the medulla oblongata: p, p. Pyramidal bodies, decussating at d. o, o. Olivary bodies, r, r. Restiform bodies, a, a. Arciform fibres, v. Lower fibres of the Pons Varolii. Fig. 105. Posterior view of the medulla oblongata: p,p. Posterior pyramids, separated by the posterior fissure, r, r. Restiform bodies, composed of c, c, posterior columns, and d, d, lateral part of the antero-lateral columns of the cord, a, a. Olivary columns, as seen on the floor of the fourth ventricle, separated by s, the median fissure, and crossed by some fibres of origin of n, n, the seventh pair of nerves. the posterior columns of the cord, while above, its fibres may be traced transversely through the pons into the cerebellum. Those of each body form a large portion of the corresponding eras cerebelli, and are distributed to the corresponding hemisphere of the cerebel- STRUCTURE OF THE MEDULLA OBLONGATA. 339 lum, whence it is probable that continuations from them pass into the cerebrum. The restiform bodies are separated from each other posteriorly by two narrow columns, the posterior pyramids, or posterior pyramidal tracts, one on each side of the posterior fissure; and by the lower angle of the fourth ventricle. The fibres of these tracts are con- tinuous below with a narrow column, which about the middle of the cervical portion of the cord begins to be, as it were, set off from the posterior columns by a narrow groove. They seem to pass upwards, longitudinally, through the pons, and thence in connection with the processes that unite the cerebrum with the cerebellum, under the corpora quadrigemina, and into the crus cerebri of the opposite side (Fig. 106). Fig. 106. This drawing is from a dissection made on a piece of brain, which had been hardened ia spirits. It exhibits the course of the sensory columns from the medulla oblongata to the thalamus, c. Anterior optic tubercle, d. Posterior ditto i & c. Inler-cerebral commissure, or processus e cerebello ad testes. H. Spinal cord. K. Thalamus optici. M. Corpus striatum. u. Crus cerebri, w. Corpus restiforme. x, x. Pons Varolii. 6. Optic nerve, c. Third pair! 6 c. Locus niger. p t. Pyramidal, or motor tract, s t, s t, s t. Sensory tract—The posterior third of the antero-lateral column, s c. Sensory root of the fifth pair of nerves. Deeper than the posterior pyramidal tracts, and forming slight elevations on each side of the middle line of the fourth ventricle, are other two, named the round tracts. They appear to be composed of the middle or axial portions of the anterior and lateral columns, which, as they pass upwards, are, as it were, exposed from behind by the divergence of the restiform and posterior pyramidal tracts. The round tracts pass longitudinally through the pons, and thence proceed, decussating, under the corpora quadrigemina to the fibres of the crura cerebri. The continuation of the grey matter of the cord into the medulla oblongata forms the grey matter covering the floor of the fourth ven- 340 THE NERVOUS SYSTEM. tricle, and diffused beneath its surface. The separation of the pos- terior internal and restiform tracts leaves open, in the fourth ventricle, the upper portion of the canal which, in the early foetal state, extends through the whole length of the grey matter of the spinal cord, and is continuous above with the cerebral ventricles. It is unfortunate that even a much deeper study than is here sketched of the anatomy of the medulla oblongata, affords very little insight into its physiology. The interest connected with the tracing of the continuities of its several columns with those of the spinal cord lies, chiefly, in the fact that nerves of similar function arise from botb. Thus, from the anterior pyramids, and their continua- tion in the crura cerebri, arise the motor third and sixth pairs of cerebral nerves. From the groove between the anterior pyramids and the olivary tracts (a groove continuous with that in which all the motor roots of the spinal nerves emerge), arises the motor hy- poglossal nerve. From the lateral and the round tracts, formed of fibres continuous with the anterior and lateral columns of the cord, arise the motor facial, and fourth or trochlear, nerves; while from the front of the restiform tracts, in a line continuous with the groove between the posterior and lateral columns of the cord, spring the roots of the sensitive glosso-pharyngeal and pneumogastric nerves. There is, thus, the closest analogy in structure and, probably also, in the general endowments of their several parts, between the me- dulla oblongata and the spinal cord. The difference in size and form appears due, chiefly, first, to the divergence, enlargement, and decussation of the several columns, as they pass to be connected with the cerebellum or the cerebrum; and, secondly, to the inser- tion of new quantities of grey matter, in the olivary bodies and other parts, in adaptation to the higher office, and wider range of influence, which the medulla oblongata as a nervous centre exer- cises. Functions of the Medulla Oblongata. In its functions, the medulla oblongata differs from the spinal cord chiefly in the importance and extent of the actions that it governs. Like the cord, it may be regarded first, as conducting impressions, in which office it has a wider extent of function than any other part of the nervous system, since it is obvious that all impressions passing to and fro between the brain and the spinal cord, and all nerves arising below the pons, must be transmitted through it. The modes of conduction through the medulla oblongata are probably similar to those through the cord. In the same degree as it is probable that the spinal cord transmits motor impressions in its anterior columns, and sensitive impressions chiefly along its poste- rior columns, so is it that the medulla oblongata conducts motor impressions along its anterior pyramidal and olivary tracts, and sen- sitive ones along its posterior and restiform tracts. This, which FUNCTIONS OF THE MEDULLA OBLONGATA. 341 might be expected from the continuity of the columns in the two parts, and the similarity of the nerves arising from them, is further rendered probable by experiments and the results' of disease. Ma- gendie divided one of the anterior pyramidal tracts of the medulla oblongata, and observed complete loss of the motor power over one half of the body, while its sensation seemed to be unimpaired (cxli. t. i. p. '285). In Longet's experiments on dogs and rabbits, irrita- tion of the anterior pyramids appeared to be unproductive of pain, but the slightest touch of the restiform bodies elicited signs of acute suffering (cxxxvi. t. i. p. 400). Among the corresponding evi- dences furnished by disease, Lebert mentions a case in which great disorder of the power of motion with unimpaired sensation, resulted from an affection of the anterior portion of the medulla oblongata: tbe posterior portion being apparently unharmed (cxxxvi. t. i. p. 407). The decussation of part of the fibres of the anterior pyramids of the medulla oblongata, and their crossing into the lateral tracts of the opposite side of the cord, make it probable that the motor im- pressions proceeding from the brain would, by traversing one pyra- mid, pass across to the opposite side of the spinal cord. Thus are explained the phenomena of cross-paralysis, as it is termed, i. e., of the loss of motion, in cerebral apoplexy, being always on the side opposite to that on which the effusion of blood has taken place. Looking only to the anatomy of the medulla oblongata, it was not possible to explain why the loss of sensation also is on the side op- posite the injury or disease of the brain : for there is no evidence of a decussation of posterior fibres like that which ensues among the anterior fibres of the medulla oblongata. But the discoveries of Brown-Sequard have shown that the crossing of sensitive impres- sions occurs in the spinal cord (see p. 329). The functions of the medulla oblongata as a nervous centre, are more immediately important to the maintenance of life than those of any other part of the nervous system, since from it alone issues the nervous force necessary for the performance of respiration and deglutition. It has been proved by repeated experiments, especially by those of Legallois (cxxxix. t. i. p. 64), Flourens (cxl.), and Longet (cxxxvi.), that the entire brain may be gradually cut away in successive portions, and yet life may continue for a considerable time, and the respiratory movements be uninterrupted. Life may, also, continue when the spinal cord is cut away in successive por- tions from below upwards as high as the point of origin of the phre- nic nerve, or in animals without a diaphragm, such as birds or reptiles, even as high as the medulla oblongata. In Amphibia, these two experiments have been combined : the brain being all re- moved from above, and the cord from below; and so long as the medulla oblongata was intact, respiration and life were maintained. But if, in any animal, the medulla oblongata is wounded, particularly 29* 342 THE NERVOUS SYSTEM. if it is wounded in its central part, opposite the origin of the pneu- mogastric nerves, the respiratory movements cease, and the animal dies as if asphyxiated. And this effect ensues even when all parts of the nervous system, except the medulla oblongata, are left in- tact.1 Injury and disease in men prove the same as these experiments on animals. Numerous instances are recorded, especially by Sir Charles Bell (cxlii.), in which injury to the human medulla oblon- gata has produced instantaneous death; and, indeed, it is through injury of it, or of the part of the cord connecting it with the origin of the phrenic nerve, that death is commonly produced in fractures and diseases with sudden displacement of the upper cervical ver- tebrae. The centre whence the nervous force for the production of com- bined respiratory movements appears to issue is in the interior of that part of the medulla oblongata from which the pneumogastric nerves arise; for with care the medulla oblongata may be divided to within a few lines of this part, and its exterior may be removed, without the stoppage of respiration ; but it immediately ceases when this part is invaded. This is not because the integrity of the pneu- mogastric nerves is essential to the respiratory movements; for both these nerves may be divided without more immediate effect than a retardation of these movements. The conclusion, therefore, may safely be, that this part of the medulla oblongata is the nervous centre wherein the impulses producing the respiratory movements originate, and whence they issue in rhythm and adaptation. The power by which the medulla oblongata governs and combines the action of various muscles for the respiratory movements is an instance of the power of reflection, which it possesses in common with all nervous centres. Its general mode of action, as well as the degree in which the mind may take part in respiration, and the number of nerves and muscles which, under the governance of the medulla oblongata, may be combined in the forcible respiratory movements, have been already briefly described (see p. 157). That which seems most peculiar in this centre of respiratory action is its wide range of connection, the number of nerves by which the cen- tripetal impression to excite motion may be conducted, and the num- ber and distance of those through which the motor impulse may be directed. The principal centripetal nerves engaged in respiration are the pneumogastric, whose branches supplying the lungs appear to convey the most acute impression of the " necessity of breathing." When they are both divided the respiration becomes slower (J. Beid, xciv. 1838), as if the necessity were less acutely felt: but it does not cease, and therefore other nerves besides them must have the 1 Death in such cases may not be immediate, especially if the temperature of the animal be previously reduced. (Brown-S€quard, xix. December, CENTRE OF THE RESPIRATORY MOVEMENTS. 343 power of conducting the like impression. The experiments of Volk- mann make it probable that all centripetal nerves possess it in some degree, and that the existence of imperfectly aerated blood in con- tact with any of them acts as a stimulus, which, being conveyed to the medulla oblongata, is reflected to the nerves of the respiratory muscles : so that respiratory movements do not wholly cease so long as any centripetal nerves, and any nerves supplying muscles of re- spiration, are both in continuous connection with the respiratory centre of the medulla oblongata. The wide extent of connection which belongs to the medulla oblongata as the centre of the respiratory movements, is further shown by the fact that impressions, by mechanical and other ordi- nary stimuli, made on many parts of the external or internal surface of the body, may induce respiratory movements. Thus involuntary inspirations are induced by the sudden contact of cold with any part of the skin, as in dashing cold water into the face; irritation of the mucous membrane of the nose produces sneezing; irritation in the pharynx, oesophagus, stomach, or intestines, excites the con- currence of the respiratory movements to produce vomiting; violent irritation in the rectum, bladder, or uterus, gives rise to a concurrent action of the respiratory muscles, so as to effect the expulsion of the faeces, urine, or foetus. The medulla oblongata is also the centre whence are derived the motor impulses enabling the muscles of the palate, pharynx, and oesophagus to produce the successive co-ordinate and adapted move- ments necessary to the act of deglutition (see p. 178). This is proved by the persistence of the power of swallowing after destruc- tion of the cerebral hemispheres and cerebellum; its existence in anencephalous monsters; the power of swallowing possessed by marsupial embryoes before the brain is developed; and by the complete arrest of the power of swallowing when the medulla oblongata is injured in experiments. But the reflecting power herein exercised by the medulla oblongata is of a much simpler and more restricted kind than that exercised in respiration; it is, indeed, not more than a simple instance of reflex action by a seg- ment of the spinal axis, receiving impressions for this purpose from only a few centripetal nerves, and reflecting them to the motor nerves of the same organ. The incident or centripetal nerves in this case are the branches of the glossopharyngeal and, in a sub- ordinate degree, those of the cervical nerves, which combine to form the pharyngeal plexus; and the nerves through which the motor impressions to the fauces and pharynx are reflected are the pharyngeal branches of the vagus, and, in subordinate degrees, or as supplying muscles accessory to the movements of the pharynx, the branches of the hypoglossal, facial, cervical, recurrent and fifth nerves. For the oesophageal movements, so far as they are con- nected with the medulla oblongata, the filaments of the pneumo- 344 THE NERVOUS SYSTEM. gastric nerve alone appear to be sufficient (see John Beid, xciv. 1838). Though respiration and life continue while the medulla oblongata is perfect and in connection with respiratory nerves, yet, when all the brain above it is removed, there is no more appearance of sensa- tion, or will, or of any mental act in the animal the subject of the experiment, than there is when only the spinal cord is left. The movements are all involuntary and unfelt; and the medulla ob- longata has therefore no claim to be considered as an organ of the mind, or as the seat of sensation or voluntary power. These are connected with parts next to be described. It may be here observed, that the part of the medulla oblongata which acts as a nervous centre, may continue to discharge its func- tion after the part which is only a conductor has ceased to act. Thus, patients with apoplexy or compression of the brain may go on breathing, though, if they have any sensibility or voluntary power, it is so little, that we cannot suppose any impressions to be con- veyed, in either direction, through the medulla oblongata. And so, when ether or chloroform has been inhaled, patients breathe very well, though they are wholly insensible, and have so completely lost all voluntary power, that we cannot suppose the medulla oblongata to conduct either to or from the pons or any other part of the brain. Moreover, it appears, that by such inhalation much of the reflect- ing power of the medulla oblongata may be destroyed; and yet its power in the respiratory movements may remain. Thus, in patients completely affected with chloroform, the winking of the eye-lids ceases, and irritation of the pharynx will not produce the usual movements of swallowing, or the closure of the glottis (so that blood may run quietly into the stomach, or even into the lungs); yet, with all this, they may breathe steadily, and show that the power of the medulla oblongata to combine in action all the nerves of the respiratory muscles is perfect (see Longet, cxxii. 1847). STRUCTURE AND PHYSIOLOGY OP THE MESO-CEPHALON, OR PONS VAROLII. The encephalon, or brain, is usually divided, in anatomical de- scription, into four parts, namely, the medulla oblongata, the meso- cephalon (pons, pons Varolii, or tuber annulare), the cerebellum, and the cerebrum. The meso-cephalon, or pons, is composed prin- cipally of transverse fibres connecting the two hemispheres of the cerebellum, and forming its principal commissure. But it includes, interlacing with these, numerous longitudinal fibres which connect the medulla oblongata with the cerebrum, and transverse fibres which connect it with the cerebellum. Among the longitudinal fibres of the pons, the inferior and some of the superior connect the FUNCTIONS OF THE PONS VAROLII. 345 anterior pyramidal, the olivary, and the round tracts of the medulla oblongata with the cerebrum; while others of the superior fibres connect with it the posterior and internal columns of the medulla. By the transverse fibres of the pons, a part of the anterior and lateral tracts, and, apparently, the whole of the restiform tracts of the me- dulla oblongata, are connected with the cerebellum; so that the pons may be regarded as containing the several means, 1st, by which the cerebrum is connected with all the tracts of the medulla oblongata, except the restiform and lateral; 2d, by which the cere- bellum is connected with these two tracts; 3d, those by which its two hemispheres are united; and, lastly (if we may reckon the processus arciformes or pontieulus as part of the pons), the fibres by which the anterior pyramidal and the restiform tracts of the medulla oblongata are connected with each other. And among the fasciculi of nerve-fibres by which these several parts are con- nected, the pons also contains abundant grey or vesicular substance, which appears irregularly placed among the fibres, and fills up all the interstices. As a conductor of impressions, we may consider the pons, as its anatomy would suggest, to contain the continuation of the con- ducting portion of the medulla oblongata to the cerebrum and cerebellum. Longet (cxxxvi. t. i. p. 427) says, that acute pain is produced by touching its posterior part; but, by irritation of its interior, no pain, but convulsions of the face, limbs, and other parts ensue. But the results of experiments respecting its conducting power are confused by those of the injuries of the crura cerebri and crura cerebelli, which will be presently referred to. As a nervous centre, it appears probable that the pons may be regarded as the first, or lowest portion of the encephalon, in which, when the rest of the brain is removed, the mind may have sensation of impressions or exercise the will. When all the encephalon above the medulla oblongata is removed from a warm-blooded animal, it appears absolutely insensible, and deprived of all voluntary power; it only breathes and has other, generally purposeless, reflex movements of the trunk and limbs. But experiments of Flourens and Longet show that when the pons is left, with the medulla oblongata, indica- tions of sensibility may be elicited, and the movements that follow them are characteristic of purpose and will. Thus, in the experi- ments on rabbits and puppies, the cerebrum and cerebellum being removed, with the corpora striata, and all other parts down to the pons, when the tail was pinched the creature cried out, when ammo- nia was held to its nose it put up its foot to remove the irritation. So long as it was not irritated, it remained passive and motionless; but it resisted irritation, and when disturbed from an apparently easy posture, resumed it. All these movements ceased as soon as the pons was removed. It must, therefore, be assumed either that 346 THE NERVOUS SYSTEM. the pons is an organ through which the mind may receive and trans- mit impressions, or that it is a nervous centre for higher and more purposive reflex acts, than the medulla oblongata or any part of the spinal cord. The latter may be the true explanation of the move- ments above-described, for they are not more indicative of sensation and will than are those of the decapitated frog, in which there is sufficient reason to believe that neither of these mental faculties sub- sists ; but, to believe that these movements are voluntary and expres- sive of sensations, appears more accordant with the general fact of the subordination of the reflex function to the power of the will in the warm-blooded animals. STRUCTURE AND PHYSIOLOGY OF THE CEREBELLUM. The more one ascends towards the highest organs of the cerebro- spinal system, the more does it become difficult to trace any struc- ture beyond that of external form and connection, and much the more difficult to connect even the manifest structure with any of the functions of the part. With reference to the cerebellum, there ap- pears, at present, so complete a want of connection between its anat- omy and its physiology, that it would not assist in the design of this work to say more of the former than that each of the halves or hemi- spheres of which it consists appears formed on the prolongations of fibres combined in a crus cerebelli; that these fibres are derived from three sources, namely: 1st. The restiform tracts of the medulla oblongata forming the inferior crus or peduncle; 2d. Interchanging or commissural fibres which, together with fibres going outwards from the lateral tracts of the medulla oblongata, form the middle crus or peduncle; 3d. Fibres interchanging between the cerebellum and cerebrum, which form the superior crus, or processus a cerebello ad testem. Further, that the prolongation of the crus cerebelli, in which these three fasciculi are combined, contains, imbedded in it, a mass of grey matter, the corpus dentatum, and sends off lamellae, which separate and are arranged like the nervules of a leaf, and are overlaid with layers of grey matter, folded and closely adjusted over the ends of the nervules. The pons, as already said, forms the infe- rior and principal commissure connecting the two hemispheres of the cerebellum; but they are also united above, by a continuity of both grey and white substance, arranged on the same general plan as in themselves, in the vermiform processes. The physiology of the cerebellum may be considered in its rela- tion to sensation, voluntary motion, and the instincts or higher facul- ties of the mind. It is itself insensible to irritation, and may be ah1 cut away without eliciting signs of pain (Longet, cxxxvi. t. i. 733, and others). Yet, if any of its crura be touched, pain is indicated; and, if the restiform tracts of the medulla oblongata be irritated, the most acute suffering is produced. Its removal or disorganization by FUNCTIONS OF THE CEREBELLUM. 347 disease is, also, generally unaccompanied with loss or disorder of sen- sibility ; animals from which it is removed can smell, see, hear, and feel pain, to all appearance, as perfect as before (Flourens, cxl.; Ma- gendie, cxli. etc.). So that, although the restiform tracts of the medulla oblongata, which are themselves so sensitive, and the con- tinuations of the especially sensitive columns of the spinal cord, enter the cerebellum, it cannot be regarded as a principal organ of sensibility. In reference to motion, the experiments of Longet and most others agree that no irritation of the cerebellum produces movement of any kind; and these are probably correct, though Valentin says that irri- tation of it (as of some other parts of the encephalon) produces move- ment of the stomach, intestines, urinary bladder, and vasa deferentia. More uniform and remarkable results are produced by removing parts of the cerebellum. Flourens (whose experiments have been abun- dantly confirmed by those of Bouillaud (clxxvi.), Longet (cxxxvi., t. i. 740), and others, extirpated the cerebellum in birds by succes- sive layers. Feebleness and want of harmony of the movements were the consequence of removing the superficial layers. When he reached the middle layers, the animals became restless without being convulsed; their movements were violent and irregular, but their sight and hearing were perfect. By the time that tbe last portion of the organ was cut away, the animals had entirely lost the powers of springing, flying, walking, standing, and preserving their equili- brium. When an animal in this state was laid upon its back, it could not recover its former posture; but it fluttered its wings, and did not lie in a state of stupor; it saw the blow which threatened it, and endeavored to avoid it. Volition, sensation, and memory, there- fore were not lost, but merely the faculty of combining the actions of the muscles; and the endeavors of the animal to maintain its balance were like those of a drunken man. The experiments afforded the same results when repeated on all classes of animals, and, from them and the others before referred to, Flourens inferred that the cerebellum belongs neither to the sensi- tive nor the intellectual apparatus; and that it is not the source of voluntary movements, although it belongs to the motor apparatus: but is the organ for the co-ordination of the voluntary movements, or for the excitement of the combined action of muscles. Some cases of disease of the cerebellum confirm this view; but the majority afford only negative evidence (see Longet, cxxxvi. t. i. p. 742). On the whole, also, it is confirmed by comparative ana- tomy. The tables of M. Serrez show that, although with some ex- ceptions, in the ascending scale of the Vertebrata, the cerebellum undergoes a general increase of size, and acquires an increasing pre- ponderance over the size of the spinal cord, so that we cannot say that its development is unconditionally proportionate to the faculty of combining muscular movements, yet, in each of the four classes 348 THE NERVOUS SYSTEM. of Vertebrata, the species whose natural movements require most frequent and exact combinations of muscular actions, are those whose cerebella are most developed in proportion to the spinal cord. On the strength of all these evidences, the view of M. Flourens has been generally adopted. But M. Foville holds that the cere- bellum is the organ for the perception of muscular sensibility, i. e., of the sensations derived from muscles, through which the mind acquires that knowledge of their actual state and position which is essential to the exercise of the will upon them. It must be admitted that all the facts just referred to are as well explained on this hypo- thesis as on that of the cerebellum being the organ for combining movements; and this hypothesis is, perhaps, more consistent than M. Flourens', with the very close connection between the cerebellum and the posterior columns of the cord. Grail was led to believe, that the cerebellum is the organ of physi- cal love, or, as Spurzheim called it, of amativeness; and this view is generally received by phrenologists. The facts favouring it are, first, several cases in which atrophy of the testes and loss of sexual passion have been the consequence of blows over the cerebellum or wounds of its substance; secondly, cases in which disease of the cerebellum has been attended with almost constant erection of the penis, and frequent seminal emissions; and, thirdly, that it has seemed possible to estimate the degree of sexual passion in different persons by an external examination of the region of the cerebellum. With regard to the first class of facts, they are open to the objection that the loss of the sexual passion may have been the consequence of the loss of the testes, and that the latter loss may have been due to some connection in the process of nutrition between the cerebel- lum and testes, similar to that which exists between the testes and the hair and other parts, whose growth indicates the attainment of puberty, and, for a time, the maintenance of virility. These facts have little bearing on tbe question, unless it is shown that the loss of sexual passion followed the injury of the cerebellum before the testes began to diminish. The cases of disease of the cerebellum do not prove more; for the same affections of the genital organs are more generally observed in diseases, and in experimental irritations, of the medulla oblongata and upper part of the spinal cord. (See Longet, cxxxvi. t. i. 762). The facts drawn from craniological examination will receive the credit given to the system of which they are a principal evidence. But, in opposition to them, it must be stated, that there has been a case of complete disorganization or absence of the cerebellum with- out loss of sexual passion (Combiette, clx. 1831, Longet, and Cru- veilhier); that the cocks from whom M. Flourens removed the cere- bellum showed sexual desire, though they were incapable of gratify- ing it; and that among animals there is no proportion observable between the size of the cerebellum and the development of the sexual FUNCTIONS OF THE CEREBELLUM. 349 passion. On the contrary, many instances may be mentioned in which a larger sexual appetite co-exists with a smaller cerebellum; as, e. g., that rays and eels, which are among the fish that copulate, have no laminae on their almost rudimental cerebella; and that cod- fish, that do not copulate, but deposit their generative fluids in the water, have comparatively well-developed cerebella. Among the Ampbibia, the sexual passion is exceedingly strong in frogs and toads; yet the cerebellum is only a narrow bar of nervous substance. Among birds there is no enlargement of the cerebellum in the males that are polygamous; the domestic cock's cerebellum is not larger than the hen's, though his sexual passion must be estimated at many times greater than hers. Among Mammalia the same rule holds; and in this class the experiments of M. Lassaigne have plainly shown, that the abolition of the sexual passion by removal of the testes in early life is not followed by any diminution of the cerebel- lum ; for in mares and stallions the average absolute weight of the cerebellum is 61 grains, and in geldings 70 grains; and its propor- tionate weight, compared with that of the cerebrum, is, on an average, as 1 :659 in mares; as 1:597 in geldings; and only as 1 : 7'07 in stallions. On the whole, therefore, it appears advisable to wait for more evidence before concluding that there is any peculiar and direct connection between the cerebellum and the sexual instinct or sexual passion.1 From all that has been observed, no other office is mani- fest in it than that of regulating and combining muscular move- ments, or of enabling them to be regulated and combined by so in- forming the mind of the state and position of the muscles that the will may be definitely and aptly directed to them. The influence of each half of the cerebellum is directed to mus- cles on the opposite side of the body; and it would appear that, for the right ordering of movements, the actions of its two halves must be always mutually balanced and adjusted. For, if one of its crura, or, if the pons on either side of the middle line, be divided, so as to cut off from the medulla oblongata and spinal cord the influence of one of the hemispheres of the cerebellum, strangely disordered movements ensue. The animals fall down on the side opposite to that on which the crus cerebelli has been divided, and then roll over continuously and repeatedly; the rotation being always round the long axis of their bodies, and from the side on which the injury has been inflicted.2 The rotations sometimes take place with much 1 See, on this subject, an interesting discussion at a meeting of the Medico-Chirurgical Society: the Lancet, 1849, vol. i. p. 320. 2 Miigendie, and Miiller, and others following him, say the rotation is towards the injured side; but Longet and others more correctly give the statement as in the test. The difference has probably arisen from using the words right and left, without saying whose right and left are meant, whether those of the observer or those of the observed. When, for example, an animal's right crus cerebelli is divided, he rolls from his own right to his 30 350 THE NERVOUS SYSTEM. rapidity; as often, according to M. Magendie, as sixty times in a minute, and may last for several days. Similar movements have been observed in men; as by M. Serres, in a man in whom there was an apoplectic effusion in the right crus cerebelli; and by M. Belhomme in a woman, in whom an exostosis pressed on the left crus.1 They may, perhaps, be explained by assuming that the division or injury of the crus cerebelli produces paralysis, or imperfect and disorderly movements, of the opposite side of the body; the animal falls, and then, struggling with the disordered side on tbe ground, and striving to rise with the other, pushes itself over; and so, again and again, with the same act, rotates itself. Such movements cease when the other crus cerebelli is divided; but probably only because the paralysis of the body is thus made almost complete. STRUCTURE AND PHYSIOLOGY OP THE CEREBRUM. The cerebrum is placed in connection with the pons and medulla oblongata by its two crura or peduncles: it is connected with the cerebellum, by the processes called superior crura of the cerebellum, or processus a cerebello ad teste, and by a layer of grey matter, called the valve of Vieussens, which lies between these processes, and extends from the inferior vermiform process of the cerebellum to the corpora quadrigemima of the cerebrum. These parts, which thus connect tbe cerebrum with the other principal divisions of the cerebro-spinal nervous centre, form parts of the walls of a cavity (the fourth ventricle) and a canal (the iter a tertio ad quartum ventriculum), which are the continuation of the canal that in the foetus extended through the whole length of the spinal cord and brain. They may therefore be regarded as the continuation of the cerebro-spinal axis or column; on which, as a development from the simple type, the cerebellum is placed; and, on the further continuation of which, structures both larger and more numerous are raised, to form the cerebrum. . The crura cerebri are principally formed of nerve-fibres, of which the inferior are continuous with those of the anterior pyra- midal and olivary tracts, and the superior with the round and pos- terior pyramidal tracts of the medulla oblongata. They may there- fore be regarded as, principally, conducting organs : but each of them manifests also the character of a nervous centre, in that it contains a mass of vesicular substance, the locus niger, wbose nerve-corpuscles abound in pigment-granules, and afford some of the best examples of the caudate structure. The office of the crura cerebri as conduc- tors will appear in speaking of the relation of the cerebrum to voluntary motion, and the peculiar effects of their division : as centres, own left, but from the left to the right of one who is standing in front of him. 1 See such cases recorded and collected by Dr. Paget (xciv. 1847). GANGLIA ON THE CRURA CEREBRI. 351 they are probably connected with the functions of the third nerve, which arises from their inner margins, and through which are directed the chief of the numerous and complicated movements of the eyeball and iris. On their upper part the crura cerebri bear three pairs of small ganglia, or masses of mingled grey and white nerve-substance, namely, the corpora gcniculata externa, and interna, and the corpora quad- rigemina, or nates and testes. Beneath or through the corpora quad- rigemina pass the continuations of the round and posterior pyramidal tracts of the medulla oblongata, decussating as they proceed onwards : and nearer to the upper surface of the same ganglia pass the fibres of the superior crura of the cerebellum, mingling with the fibres that form the chief part of the origin of the optic nerves, with the func- tions of which nerves these ganglia appear intimately connected. In its further course, each crus cerebri, enlarged by the addition of many fibres, forms, as it proceeds, a kind of fibrous cone, with its truncated apex in the pons. On it are placed in succession two other ganglia, the optic thalamus and corpus striatum, in which its fibres, and those that are continually added to them, traverse vari- ously-shaped masses and layers of grey substance, and from the an- terior part of which, diverging in all directions, and bending back- wards, they pass into the substance of the corresponding cerebral hemisphere. These several organs on each side of the cerebrum are connected by commissures, formed principally of nerve-fibres; namely, the cor- pora quadrigemina by part of the fibres of the round tract which form - the fillet of Reil, and meet in the middle line; the optic thalami by the anterior and posterior commissures formed of fibres, and the mid- dle or soft commissure of grey substance; part of the corpora striata and the cerebral hemispheres, by the anterior commissure and cor- pus callosum. The several parts of each of the hemispheres are also connected by longitudinal and oblique fibres passing beneath the con- volutions from one part to another; and, in the median part of the fornix, connecting the middle cerebral lobe with the optic thalamus. The cerebral convolutions appear to be formed of nearly parallel plates of fibres, the ends of which are turned towards the surface of the brain, and are overlaid and mingled with successive layers of grey nerve-substance. Some have supposed that the euds of the fibres are connected in loops, of which loops-parts are continued from tbe diverging fibres of the cone, and others from the fibres of the corpus cailosum; but this is uncertain. The external grey matter is so arranged in layers that a vertical section of a convolution generally presents the appearance of three layers of grey, with two intervening layers of white substance, a grey layer being most external. In these grey layers, the outer is formed principally of granular matter and 352 THE NERVOUS SYSTEM. nuclei, like those of nerve-corpuscles; in the deeper layers are more perfectly formed cells.1 The Crura, Cerebri appear as the principal conductors of impres- sions to and from the cerebrum, and division of one of them produces singular effects on the movements. When one is cut across, the ani- mal moves round and round, rotating round a vertical axis, from the injured towards the sound side, as if from a partial paralysis of the side opposite to the injury. The effect may be supposed due to the interruption of the voluntary impulses from the cerebrum ; for even though the cerebellum may have the office of combining the muscles whose co-operation is necessary for each action, yet it is probable that the deliberate effort of the will must proceed from tbe cerebrum. The movements of an animal are more disordered when the cerebel- lum is removed and the cerebrum is left, than when both cerebrum and cerebellum are removed; as if, in the latter case, the voluntary power were weak but not disordered, but in the former acted with full strength but with disorder. The Corpora Quadrigemina (from which, in function, the corpora geniculata are not distinguished), are the homologues of the optic lobes in the birds, Amphibia, and fishes, and may be regarded as the principal nervous centres for the sense of sight. The experiments of Flourens, Longet, and Hertwig, show that removal of the corpora quadrigemina wholly destroys the power of seeing; and diseases in which they are disorganized are usually accompanied with blindness. Atrophy of them is also often a consequence of atrophy of the eyes. Destruction of one of the corpora quadrigemina (or of one optic lobe in birds), produces blindness of the opposite eye. The loss of sight thus produced is not only because the corpora quadrigemina contain continuations of the optic tracts, or roots of the optic nerves, but because they are the organs in which the mind perceives the sen- sations of light. As Longet's experiments show, when the cerebral hemispheres of a pigeon are removed, and its optic thalami and optic lobes are left, it not only exhibits the reflex movements of the con- traction of the iris and the closure of the eyelids when a candle is held to the eye, but when the candle is moved round before the eye, moves its head after it, manifestly because it sees and watches it. It appears, indeed, not to see many things, and runs against obstacles; but this is because though it may see them it cannot recognise them, having lost all memory of objects through the loss of its cerebrum. The loss of sight is the only apparent injury of sensibility sustained by the removal of the corpora quadrigemina. The removal of one 1 For further descriptions of the structure of the brain the student should refer to Mayo (clxiii.); Quain (cxlix.); Foville (clxi.) ; Longet (cxxxvi.); Todd (clix.); or Solly (clxxxviii.). In these works, he will find sufficient guidance to the previous less perfect treatises. THE OPTIC THALAMI. 353 of them affects the movements of the body, so that animals rotate, as after division of the crus cerebri, only more slowly: but this is pro- bably due to giddiness and partial loss of sight. The more evident and direct influence is that produced on the iris. It contracts when the corpora quadrigemina are irritated: it is always dilated when they are removed : so that they may, perhaps, be regarded as the nervous centres governing its movements, and adapting them to the impressions derived from the retina through the optic nerves and tracts. There is no evidence that the corpora quadrigemina are, in any sense, organs of the intellectual faculties, or of the affections. Yet it may be questioned if their connection with vision be their only function, seeing their large size in fish whose iris is not movable, and that generally neither their absolute nor their proportionate size in different animals bears any simple relation to the acuteness or extent of their several powers of vision. The Optic Thalami probably participate in a small degree in the visual function of the corpora quadrigemina, for part of the fibres of the optic tract may be traced to their surfaces; and in a recent exa- mination of the brain of a child born without eyes, the optic thalami as well as the corpora quadrigemina were found extremely small (cxc. 1851, p. 543). But the results of experiments prove nothing on this point. They only show disturbances of the power of movement. Irritation of the optic thalami produces no convulsions, and only little pain (Longet and Flourens) : destruction of one has effects very similar to those of division of one crus cerebri, namely, a rotation, in which the animal, remaining standing, turns continually round. Schiff, by whom a series of experiments on these various rotations has been made (clxii), has shown that no such effect follows the removal of any other part of the brain; and Longet points out, as a strong contrast, that after removing all the cerebral hemispheres and the corpora striata, the animal can still stand and walk, but that on removing one of the optic thalami it falls down paralyzed on the opposite side, or commences the rotatory movement. The evidence of apoplexy and other diseases is similar: all such cases manifest a loss of power of part or the whole of the opposite side of the body. Concerning the functions of the Corpora Striata, experiments, and tbe effects of diseases, permit none but negative conclusions — such as that they are not the central organs for the sense of smell, nor peculiarly concerned in sensation or movement. The recent experiments of Schiff (clxii.) confirming and, in many respects, correcting those of Magendie and others, show that when they are removed in rabbits sensation is unimpaired, and the power of move- ment complete; so that although at first the creature remains at rest, it will, after irritation, or spontaneously, in about half an hour, begin to move, at first slowly, and then with increasing speed and larger 354 THE NERVOUS SYSTEM. leaps, till it strikes against some obstacle, when it falls, and again for a time remains torpid. Various explanations are offered of these and other strange modes of movements which ensue when the several parts just considered are mutilated, such as that particular masses or tracts in the brain determine the impulses to move in this or that direction, and that, by destroying any part, the balance in which its impulse holds that of the corresponding part of the opposite side is lost. But no such explanations guide to the true physiology of these parts. Taking together all the parts yet considered, i. e., all the parts of the cerebro-spinal nervous system except the cerebral hemispheres, they appear to include the apparatus, 1st, for the direction and government of all the unfelt and involuntary movements of the parts which they supply; 2d, for the perception of sensations; and 3d, for the direction of sucb instinctive and habitual movements as do not require the exercise of judgment, deliberation, memory, or any other intellectual act. The medulla oblongata and spinal cord have their office in none but involuntary and unconscious movements; but above the medulla oblongata, the pons, and other organs appear capa- ble of such conditions as the mind may perceive, and of being, by the will, excited to the production of voluntary and orderly move- ments. But these parts cannot be regarded as organs of the higher faculties of the mind: with them alone an animal appears to possess neither memory of former sensations, nor judgment to determine and control its actions. Mere sensations and will, acting according to instinctive impulse and instinctive knowledge or habit, constitute the whole mind of the animal deprived of its cerebral hemispheres. But seeing what manifestations of mind subsist in animals after the removal of the cerebral hemispheres, it is reasonable to suppose that these lower organs, the cerebral or sensory ganglia, naturally discharge the functions of which they then appear capable, and that the cerebral hemispheres are engaged in only the higher mental acts. This appears the more probable when it is considered that all the cerebral nerves are in direct connection with these ganglia; and are only through the medium of the highest of them (including herein the olfactory ganglia as part of the brain) connected with the cere- bral hemispheres; so that whatever acts are performed through these nerves, independently of the higher faculties of the mind, may be fairly ascribed to the power of these several ganglia. Again the homologues of these organs, that is, of the corpora quadrigemina, the optic thalami, and corpora striata, and the olfactory lobes or ganglia, maintain in the descending scale of the vertebrate animals a large size, and are proportionate to the development of their organs of sense ; while the cerebral hemispheres regularly diminish in their proportion, till in the highest fish they are not larger than these ganglia, and in the lower fish are not larger than the optic or olfac- tory lobes alone. Now, in the same descending series, the intellec- FUNCTIONS OF THE CEREBRAL HEMISPHERES. 355 tual powers seem to diminish commensurately with the decrease of the cerebral hemispheres; but their is no corresponding decrease of the lower powers of the mind, in the exercise of simple perception and will adapted to the instincts of which these ganglia at the base of the brain are supposed to be the organs.1 Neither perhaps can any such diminution be traced in those emo- tions and emotional acts, or expressions, which belong to the instincts that all animals appear to have in common, such as fear, anger, etc.; of these also it is not improbable that the cerebral ganglia may be the organs; _ but this can only be suspected while we know so little of the emotions to which lower animals are subject. If it be probable that the functions of the parts already considered are correctly indicated in the preceding paragraphs, it will be in the same decree probable that the functions of the cerebral hemispheres, thus determined by "way of exclusion," are those of the organs by which the mind, 1st, perceives those clear and more impressive sensa- tions wbich it can retain, and judge according to; 2dly, performs those acts of will each of which requires a deliberate, however quick, determination; 3dly, retains impressions of sensible things, and re- producesthem in subjective sensations and ideas; 4thly, manifests itself in its higher and peculiarly human emotions and feelings, and in its faculties of judgment, understanding,2 memory, reflection, in- duction, and imagination, and others of the like class. The cerebral hemispheres appear thus to be the organs in and through which the mind acts, in all these its operations, which have immediate relation to external and sensible things; and this view may be held without fear, while it is held, also, that the mind has other and higher parts or faculties, by which it has or may attain to knowledge of things above the senses; namely, the conscience and the pure reason, which may be instructed otherwise than through the senses, and exercised independently of the brain. The evidences that the cerebral hemispheres are, in the sense and degree indicated above, the organs of the mind, are chiefly these :— 1. That any severe injury of them, such as a general concussion, or 1 The whole of this subject is well discussed by Dr. Carpenter (ccvii. p. 503, et seq.), who regards the "series of ganglionic centres which have been enumerated as constituting the real sensorium; each ganglion having the power of rendering the mind conscious of the impression derived from the organ with which it is connected. 2 By understanding or intellect is here meant the " faculty of judging ac- cording to sense;" a faculty, therefore, which has to do with none but sensi- ble things, and the ideas derived from them. It is often called "reason," or the reasoning faculty; but the term "reason" is here applied only to the higher faculty, whicli has cognizance of necessary truths, and of things above the senses—that which Scripture designates, or includes in the designation, the •' Spirit of man."—In the use and adaptation of the terms here employed, the example of Coleridge is followed. See his "Aids to Reflection." 356 THE NERVOUS SYSTEM. sudden pressure by apoplexy, may instantly deprive a man of all power of manifesting externally any mental faculty. 2. That in the same general proportion as the higher sensuous mental faculties are developed in the vertebrate animals, and in man at different ages, the more are the size of the cerebral hemispheres developed in compari- son with the rest of the cerebro-spinal system. 3. That no other part of the nervous system bears a corresponding proportion to the deve- lopment of the mental faculties. 4. That congenital and other mor- bid defects of the cerebral hemispheres are, in general, accompanied with corresponding deficiency in the range or power of the intellec- tual faculties and the higher instincts. To explain such facts, no hypothesis (if it must be so called while we have regard only to the facts of science) is so sufficient as that which supposes an immaterial principle, not necessarily dependent for its existence on the brain, but incapable of external manifestation or of knowledge of external things, except through the medium of the brain, and the nervous organs connected therewith. Such a principle would remain itself unchanged, in the case of injury or disease of the brain; but its external manifestations, and all its acts performed in connection with the brain, would be hindered or dis- turbed ; as, for example, the work of any artist might be stopped or spoiled through deficiency or badness of his implements of art. And in the operations of such a principle, it might well be supposed that the power with which its several faculties are manifested would bear a direct proportion to the size of the organs through which they are manifested; for whether we suppose or not that the principle itself may, in different individuals, have different degrees of power, yet its power of manifestation or perception through the cerebral hemi- spheres, may vary as those organs do. But while this may be true respecting those parts of the mind which have to do with the things of sense, it would require much more and different evidence and arguments to make it probable that the cerebral hemispheres, or any other parts of the brain, are, in any meaning of the term, the organs of those parts or powers of the mind which are occupied with things above the senses. The reason or Spirit of man which has knowledge of divine truths, and the con- science, with its natural discernment of moral right and wrong, can- not be proved to have any connection with the brain. In the com- plex life we live, they are, indeed, often exercised on questions in which the intellect or some other lower mental faculty is also con- cerned ; and in all such cases men's actions are determined as good or bad according to the degree in which they are guided by the higher or by the lower faculties. But the reason and the conscience must be exercised independently of the brain when they are engaged in the contemplation of things which have not been learned through the senses, or through any intellectual consideration of sensible things. All that a man feels in himself, and can observe in others, FUNCTIONS OF THE CEREBRAL HEMISPHERES. 357 of the subjects in which his reason and his conscience are most natu- rally engaged; of the mode in which they are exercised, and the disturbance to which they are liable by the perceptions or ideas of sensible things; of the manner and sources of their instruction; of their natural superiority and supremacy over all the other faculties of the mind ; and of his consciousness of responsibility for their use; all teaches him that these faculties are wholly different, not in degree only, nor as different members of one order, but in kind and very nature from all else of which he is composed; all, if rightly consi- dered, must incline him to receive and hold fast the clearer truth which Bevelation has given of the nature and destinies of the Spirit to which these, his highest faculties, belong. Bespecting the mode in which the mental principle operates in its connection with the brain, there is no evidence whatever. But it appears that, for all but its highest intellectual acts, one of the cere- bral hemispheres is sufficient. For numerous cases are recorded in which no mental defect was observed, although one cerebral hemi- sphere was so disorganized or atropbied, that it could not be sup- posed capable of discharging its functions. The remaining hemi- sphere was in these cases adequate to the functions generally dis- charged by both; but the mind does not seem in any of these cases to have been tested in very high intellectual exercises; so that it is not certain that one hemisphere will suffice for these. In general, the mind combines, as one sensation, the impressions which it derives from one object through both hemispheres, and the ideas to which the two such impressions give rise are single; and in general, also, the mind acts alike in and through both the bemispheres: fts actions being, if one may so speak, symmetrical as the hemispheres are. But it would appear that when one hemisphere is disordered, the same object may produce two sensations, and suggest simulta- neously different ideas : or, at the same time, two trains of thought may be carried on by the one mind acting, and being acted upon, differently in the two hemispheres. Thus are explicable some of the incoherences of dreaming and delirium; and, especially, those singu- lar eases in which a person in delirium, puzzled by the two different, and seemingly simultaneous, trains of thought in which he is engaged, fancies himself two persons, and, as another, holds conversation with himself.1 In relation to common sensation and the effort of the will, the impressions to and from the hemispheres of the brain are carried across the middle line : so that in destruction or compression of xSee Dr. Holland's essay on this subject (clxvii.); and Dr. Wigan's essay, and other works, on the Duality of the Mind, or, as it would be better called, of the Brain, for every reasonable person is as conscious of his unity as of his identity ; indeed, the idea of personal identity involves that of unity. 358 THE NERVOUS SYSTEM. either hemisphere, whatever effects are produced in loss of sensation or voluntary motion, are observed on the side of the body opposite to that on which the brain is injured. In speaking hitherto of the cerebral hemispheres as the organs of the mind, they have been regarded as if they were single organs, of which all parts are equally appropriate for the exercise of each of the mental faculties. But it is a more probable theory that each faculty has a special portion of the brain appropriated to it as its proper organ. For this theory, the principal evidences among those col- lected by Drs. Gall and Spurzheim are as follows : 1. That it is in accordance with the physiology of the other compound organs or systems in the body, in which each part has its special function; as, for example, of the digestive system, in which the stomach, liver, and other organs perform each their separate share in the general process of the digestion of the food. 2. That in different individuals, the several mental functions are manifested in very different degrees. Even in early childhood, before educa