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 education can be imagined to have exercised any influence on the mind, children exhibit various dispo- sitions, each presents some predominant propensity, or evinces a singular aptness in some study or pursuit; and it is a matter of daily observation that every one has his peculiar talent or propensity. But it is difficult to imagine how this could be the case, if the manifesta- tion of each faculty depended on the whole of the brain; different conditions of the whole mass might affect the mind generally, de- pressing or exalting all its functions in an equal-degree, but could not permit one faculty to be strongly and another weakly manifested. 3. The plurality of organs in the brain is supported by the pheno- mena of some forms of mental derangement. It is not usual for all the mental faculties in an insane person to be equally disordered; it often happens that the strength of some is increased, while that of others is diminished; and in many cases one function only of the mind is deranged, while all the rest are performed in a natural man- ner. 4. The same opinion is supported by the fact that the several mental faculties are developed to their greatest strength at different periods of life, some being exercised with great energy in childhood, others only in adult age; and that, as their energy decreases in old age, there is not a gradual and equal diminution of power in all of them at once, but on the contrary, a diminution in one or more, while others retain their full strength, or even increase in power. 5. The plurality of cerebral organs appears to be indicated by the phe- nomena of dreams, in which only a part of the mental faculties are at rest or asleep, while the others are awake, and, it is presumed, are exercised through the medium of the parts of the brain appropriated to them. 6. It is stated, that the examination of the brains of indi- viduals, each remarkable for some peculiar propensity or talent, has THE CORPUS CALLOSUM. 359 always demonstrated a corresponding development of a certain portion of the brain. These facts have been so illustrated and adapted by phrenologists, that the theory of the plurality of organs in the cerebrum thus made probable, has been commonly regarded as peculiar to phrenology, and as so essentially connected with it, that if the system of Gall and Spurzheim be untrue, this theory cannot be maintained. But it is plain that all the system of phrenology built upon the theory maybe false, and the theory itself true; for if the school of Gall and Spurz- heim assume, not only this theory, but also that they have deter- mined all the primitive faculties of which the mind consists, i. e., all the faculties to which special organs must be assigned, and the places of all those organs in the cerebral hemispheres and the cerebellum. Possibly this may be a system of error, founded on a true theory: the cerebrum may have many organs, and the mind as many facul- ties ; but what are the faculties that require separate organs, and where those organs are, may be subjects of which only the first or most general knowledge is yet attained. At any rate, the phrenolo- gical physiology of the brain could not be introduced here without more discussion and objection than is consistent with the plan of this work.1 Of the physiology of the other parts of the brain, little or nothing can be said. Of the offices of the corpus callosum, or great transverse and oblique commissure of the brain, nothing positive is known. But instances in which it was absent, or very deficient, either without any evident mental defect, or with only such as might be ascribed to coincident affections of other parts, make it probable that the office which is commonly assigned to it, of enabling the two sides of the brain to act in concord, is exercised only in the highest acts of which the mind, acting on the brain, is capable. And this view is confirmed by the very late period of its development, and by its absence in all but the placental Mammalia.2 To the fornix and other commissures no special function can be assigned; but it is a reasonable hypothesis that they connect the actions of the parts between which they are severally placed (Fig. 107, next page). 1 The phrenological writings of Mr. Combe, and the "Brain and its Phy- siology," by Mr. Noble, are, probably, the best for the medical student who desires to read the arguments in favor of the system. The objections against it may be read in an article in the British and Foreign Medical Review, Oct. 1846; and in the article " Phrenology," in the Penny Cyclopaedia, from which the above is chiefly taken. 2 See cases of congenital deficiency of the corpus callosum, by Mr. Paget and Mr. Henry, in the twenty-ninth and thirty-first volumes of the Medico- Chirurgical Transactions. » 360 THE NERVOUS SYSTEM. Fig. 107. This figure has been introduced with the view of assisting the student in his study of the relations of the inferior longitudinal commissure or fornix, which may be described as com- mencing in the centre of the thalamus nervi optici (t), proceeding from thence to the base of the brain, where it suddenly bends upwards and forwards, forming by this turn the knuckle (b), which is called corpus albicans or mammillare. This body receives a few fibres (a) from the locus niger (6) in the crus cerebri (5), running forward from thence towards the anterior commissure, receiving fibres from the convolutions at the base of the brain, crossing and as it were kneeling upon the anterior commissure (s), and ascending towards the great transverse commissure, forms the anterior pillar of the fornix (c), receiving fibres in its course from the under and front part of the anterior lobes, and thus forming the septum lucidum (d); running back from thence, passing in its course backwards over the thalamus nervi optici (l), it spreads laterally, constituting that portion which is called the body of the fornix (e); descending again at the back part of the brain it forms the descending or poste- rior pillar of the fornix tania hippocampi (f), some of its fibres running back to be connected with the posterior lobes (i); others crossing the projection called hippocampus major (o), to be connected with the middle lobe, and others again passing over the pes hippocampi (h) to be connected with the anterior portion of the middle lobe. Thus does this commissure con- nect different portions of the convoluted surface of the brain together, which are inferior to the great transverse commissure, and on the same side of the mesial line. a. Fibres of tho inferior longitudinal commissure, or fornix, from the locus niger. b. Corpus mammillare, c. Anterior pillars of inferior longitudinal commissure, or fornix, d. Septum lucidum. e. Body of the fornix, or centre of the commissure. F. Taenia hippocampi, or descending fibres of the inferior longitudinal commissure, g. Fibres covering the hippocampus major. H. Fibres covering the pes hippocampi. I. Fibres covering the hippocampus minor, k. Great transverse commissure divided in the mesial line. s. Posterior cerebral ganglion, or thalamus. I. Anterior commissure. 5. Section of the crus cerebri. 6. Locus niger. 7. Anterior cere- bral ganglion, or corpus striatum, partially scraped away. As little is known of the functions of the pineal and pituitary glands. Indeed, Oesterlen and others raise the question whether either their structure or functions are those of nervous organs, and class them among the glands without ducts (cii). PHYSIOLOGY OF THE CEREBRAL AND SPINAL NERVES. The cerebral nerves are twelve pairs, and the spinal nerves thirty- one pairs, symmetrically arranged on each side of what, reduced to PHYSIOLOGY OF THE THIRD CEREBRAL NERVE. 361 its simplest form, may be regarded as a column or axis of nervous matter, extending from the olfactory bulbs on the ethmoid bone, to the filum terminate of the spinal cord in the lumbar and sacral por- tion of the vertebral canal. The spinal nerves all present certain characters in common, such as their double roots; the isolation of the fibres of sensation in the posterior roots, and of those of motion in the anterior roots; the formation of the ganglia on the posterior root; and the subsequent mingling of the fibres in trunks and branches of mixed functions. Similar characters probably belong essentially to the cerebral nerves; but even when one includes the nerves of special sense, it is not possible to discern a conformity of arrangement in any besides the fifth or trifacial, which, from its many analogies to the spinal nerves, Sir Charles Bell designated as the spinal nerve of the head. According to their several functions, the cerebral or cranial nerves may be thus arranged : — Nerves of special sense....... Olfactory, optic, auditory, part of the glosso- pharyngeal, and the ungual branch of the fifth. Nerves of common sensation The greater portion of the fifth, and part of the glosso-pharyngeal. Nerves of motion.............. Third, fourth, lesser division of the fifth, sixth, facial, and hypoglossal. Mixed nerves................... Pneumogastric, and accessory. The physiology of the several nerves of the special senses will be considered with the organs of those senses. Physiology of the Third, Fourth, and Sixth Cerebral or Cranial Nerves. The physiology of these nerves may be in some degree combined, because of their intimate connection with each other in the actions of the muscles of the eye-ball, which they supply. They are pro- bably all formed exclusively of motor fibres: some pain is indicated when the trunk of the third nerve is irritated near its origin; but this may be because of some filaments of the fifth nerve running backwards to the brain in the trunk of the third, or because adjacent sensitive parts are involved in the irritation. The third nerve, or motor oculi (Fig. 108, next page), supplies the levator palpebrae superioris muscle, and, of the muscles of the eye-ball, all but the oblique superior or trochlearis, to which the fourth nerve is appropriated, and the rectus externus which receives the sixth nerve. Through the medium of the ophthalmic or lenti- cular ganglion, of which it forms what is called the short root, it also supplies tbe motor filaments to the iris. When the third nerve is irritated within the skull, all these 362 THE NERVOUS SYSTEM. Fig. 108. The drawing exhibits the cerebral connection of all the cerebral nerves except the first, It is from a sketch of Solly's, taken from two dissections of this part. D. Posterior optio tubercle. The generative bodies of the thalamus are just above it. e. Cerebellum, h. Spinal cord. i. Tuber cinereum. K. Optic thalamus divided perpendicularly, w. Corpus resti- forme. x. Pons Varolii. 66. Optic nerves: this nerve is traced on the left side back beneath the optic thalamus and round the crus cerebri. It divides into four roots; the first (gg) plunges into the substance of the thalamus, the next runs over the external geniculate body and surface of the thalamus, the third goes to the anterior optic tubercle, the fourth runs to d, the testis or posterior optic tubercle, c. Third pair common oculo« muscular, arising by two roots like the spinal roots of the spinal nerves, the upper from the grey neurine of the locus niger, the lower from the continuation of the pyramidal columns in the crus cerebri and Pons Varolii, pt. d. Fourth pair, apparently arising from the inter-cerebral commissure (ic), but really plunging down to the olivary tract (of) as it ascends to the optic tubercles, e m. Motor or non-ganglionic root of the fifth pair, arising from the posterior edge of the olivary tract, e. Sensory root of the fifth pair running down between the olivary tract and restiform body to the sensory tract, f. Sixth pair, or ab- ducens, arising from the pyramidal tract, g. Seventh pair, facial nerve, or portio dura, arising by an anterior portion from the olivary tract and by a posterior portion from the cerebellic fibres of the anterior columns as they ascend on the corpus restiforme, w. h. Eighth pair, portio mollis, or auditory nerve, with its two roots embracing the restiform body. i. Ninth pair, or glosso-pharyngeal; and j. Tenth pair, or par vagum, plunging into the restiform ganglion, j j. Fibres of the optic nerve plunging into the thalamus; immediately below these letters is the corpus geniculatum externum, k. Eleventh pair, or lingual nerve; the olivary body has been nearly sliced off and turned out of its natural position; some of the filaments of the lingual nerve are traced into the deeper portion of the ganglion, which is left in its situation; oth rs which are the highest are evidently connected with the pyra- midal tract. PHYSIOLOGY OF THE THIRD CEREBRAL NERVE. 363 muscles to which it is distributed are convulsed. When it is paralyzed or divided, the following effects ensue : first, the upper eye-lid can be no longer raised by the levator palpebrse, but drops, and remains gently closed over the eye, under"the unbalanced in- fluence of the orbicularis palpebrarum, which is supplied by the facial nerve : secondly, the eye is turned outwards by the unbalanced action of the rectus externus, to which the sixth nerve is appro- priated ; and hence, from the irregularity of the axes of the eyes, double-sight is often experienced when a single object is within view of both the eyes: thirdly, the eye cannot be moved either upwards, downwards, or inwards : fourthly, the pupil is dilated. The relation of the third nerve to the iris is of peculiar interest. In ordinary circumstances the contraction of the iris is a reflex action, which may be explained as produced by the stimulus of light on the retina being conveyed by the optic nerve to the brain (probably to the corpora quadrigemina), and thence reflected through the third nerve to the iris. Hence the iris ceases to act when either the optic or the third nerve is divided or destroyed, or when the cor- pora quadrigemina are destroyed or much compressed. But when the optic nerve is divided, the contraction of the iris maybe excited by irritating that portion of the nerve which is connected with the brain; and when the third nerve is divided, the irritation of its dis- tal portion will still excite contraction of the iris in which its fibres are distributed. The contraction of the iris thus shows all the character of a reflex act, and in ordinary cases requires the concurrent action of the optic nerve, corpora quadrigemina, and third nerve; and, probably also, seeing the peculiarities of its perfect mode of action, the ophthalmic ganglion. But, besides, both irides will contract their pupils under the reflected stimulus of light falling on only one retina or under irritation of one optic nerve. Thus in amaurosis of one eye, its pupil may contract when the other eye is exposed to a stronger light: and generally the contraction of each of the pupils appears to be in direct proportion to the total quantity of light which stimulates cither one or both retinas, according as one or both eyes are open. The iris acts also in association with certain other muscles supplied by the third nerve: thus, when the eye is directed inwards, or up- wards and inwards, by the action of the third nerve distributed in the rectus internus and rectus superior, the iris contracts, as if under direct voluntary influence. The will cannot, however, act on the iris alone through the third nerve; but this aptness to contract in association with the other muscles supplied by the third, may be sufficient to make it act even in total blindness and insensibility of the retina, whenever these muscles are contracted. The contraction of the pupils when the eyes are moved inwards, as in looking at a near object, has probably the purpose of excluding those outermost rays of light which would be too far divergent to be refracted to a 364 THE NERVOUS SYSTEM. clear image on the retina; and the dilatation in looking straight for- wards, as in looking at a distant object, permits the admission of the largest number of rays, of which none are too divergent to be so re- fracted.1 The fourth nerve, or Nervus trochlearis or paiheticus, is exclu- sively motor, and supplies only the trochlearis or obliquus superior muscle of the eyeball. This muscle acts spasmodically when the nerve is irritated, and is paralyzed when the nerve is divided or otherwise hindered from its function. From this paralysis results a very slight, if any, deviation of the eye from its normal direction; the pupil is directed a very little upwards and outwards by the un- balanced action of the obliquus inferior, and a peculiar kind of double vision is produced in which the same object appears as two, placed one above the other, but again appears single when the head is in- clined towards the shoulder of the opposite side to that on which the superior oblique is paralyzed (Szokalski; in Longet, cxxxvi. vol. ii. p. 398). These phenomena are explained by the peculiar actions of the oblique muscles, which as Hunter2 showed (i. vol. iv. p. 274), rotate the eye round its antero-posterior axis, or round such an ima- ginary line as would nearly correspond with the prolongation of the optic nerve. Thus, when the head is bent down for a certain dis- tance towards either (say the left) shoulder, the corresponding points of the retinae of both eyes may be held on a level horizontal line by the superior oblique of the right eye rotating the inner part of the eye downwards, and the inferior oblique of the left eye rotating the inner part of its eye upwards. Thus in health, the mind receives a similar and single impression from an object whether the head is erect or turned towards either side, through the action of the infe- rior oblique of one eye being associated with that of the superior ob- lique of the other. And thus in disease, when one superior oblique is paralyzed, the inner half of the retina of that eye is rotated up- wards, and when the image of any object falls on it, the mind refers that object to a point lower than that to which it refers the image of the same object on the other retina, though all the inner parts of the latter retina are really lower than tbe corresponding points of the re- tina on the paralyzed side. The sixth nerve, Nervus abducens or ocularis externus, is also, like the fourth, exclusively motor, and supplies only the rectus ex- ternus muscle.3 The rectus externus is, therefore, convulsed, and 1 On the contractions of the iris, and the functions of all its nerves, see Dr. Radclyffe Hall's essays (xciv. 1846). 2 And more lately Hueck (clxvi.); Volkmann (xv. art. Sehen.) ; and Dr. G. Johnson (lxxiii. art. Orbit.). 3 In several animals it sends filaments to the iris (Radclyffe Hall); and it has probably done so in man, in some instances in which the iris has not SIXTH CEREBRAL NERVE. 365 the eye is turned outwards, when the sixth nerve is irritated; and the muscle paralyzed when the nerve is disorganized, compressed, or divided. In all such cases of paralysis the eye squints inwards and cannot be moved outwards. In its course through the cavernous sinus, the sixth nerve forms larger communications with the sympathetic nerve than any other nerve within the cavity of the skull does; and, on this ground, used to be considered as giving origin to the sympathetic. But the im- port of these communications with the sympathetic, and the subse- quent distribution of its filaments after joining the sixth nerve, are quite unknown; and there is no reason to believe that the sixth nerve is, in function, more closely connected with the sympathetic than any other cerebral nerve is. The question has often suggested itself, why the six muscles of the eyeball should be supplied by three motor nerves when all of them are within reach of the branches of one nerve; and the true explana- tion would have more interest than attaches to the movements of the eye alone, since it is probable that we have, in this instance, within a small space, an example of some general rule according to which associate or antagonist muscles are supplied with motor nerves. Now, in the several movements of the eyes we sometimes have to act with symmetrically placed muscles, as when both eyes are turned upwards or downwards, inwards or outwards.1 All the symmetrically placed muscles are supplied with symmetrical nerves, i. e., with cor- responding branches of the same nerves on the two sides; and the action of these symmetrical muscles is easy and natural, as we have a natural tendency to symmetrical movement in most parts. But because of this tendency to symmetrical movements of muscles sup- plied by symmetrical nerves, it would appear as if, when the two eyes are to be moved otherwise than symmetrically, the muscles to effect such a movement must be supplied with different nerves. So, when the two eyes are to be turned towards one side, say the right, by the action of the rectus externus of the right eye and the rectus internus of the left, it appears as if the tendency to action through the similar branches of corresponding nerves (which would move both eyes inwards or outwards) were corrected, by one of these mus- cles being supplied by the sixth, and the other by the third nerve. So with the oblique muscles: the simplest and easiest actions would be through branches of the corresponding nerves, acting similarly as symmetrical muscles; but the necessary movements of the two eyes been paralyzed, while all the other parts supplied by the third nerve were (see Grant, in Longet, cxxxvi. t. ii. p. 888). 1 It is sometimes said that the external recti cannot be put in action simul- taneously : yet they are so when the 030s, having been both directed inwards, are restored to the position which they have in looking straight forwards. 31* -m THE NERVOUS SYSTEM. require the contraction of the superior oblique of one side, to be associated with the contraction of the inferior oblique and the relaxa- tion of the superior oblique, of the opposite side. For this, the fourth nerve of one side is made to act with a branch of the third nerve of the other side; as if thus the tendency to simultaneous action through the similar nerves of the two sides were prevented. At any rate, the rule of distribution of nerves here seems to be, that when, in frequent and necessary movements, any muscle has to act with the antagonist of its fellow on the opposite side it and its fel- low's antagonist are supplied from different nerves. Physiology of the Fifth or Trigeminal Nerve. The fifth, trigeminal, or trifacial nerve resembles, as already stated, the spinal nerves, in that its branches are derived through two roots; namely, the portio major, the filaments of which expand to receive the corpuscles that form the Casserian ganglion, and the portio minor, which has no ganglion, and passes under the ganglion of the portio major to join the third branch or division which issues from it. The first and second divisions of the nerve, which arise wholly from the ganglion of the portio major, are purely sensitive. The third divi- sion, which is formed in part by the portio minor, and in part from the Casserian ganglion, is, in its trunk and many of its branches, both motor and sensitive. Through the branches of the greater or ganglionic portion of the fifth nerve, all the anterior and antero-lateral parts of the face and head, with the exception of the skin of the parotid region (which derives branches from the cervical spinal nerves), acquire common sensibility; and among these parts may be included the organs of special sense, from which common sensations are conveyed through the fifth nerve, and their peculiar sensations through their several nerves of special sense. All the muscles, also, acquire musculai sensibility through the filaments of the ganglionic portion of the fifth nerve distributed to them with their proper motor nerves. Through branches of the lesser or non-ganglionic portion of the fifth the muscles of mastication, namely, the temporal, masseter, two pterygoid, anterior part of the digastric, and mylo-hyoid, derive their motor nerves. The motor function of these branches is proved by the violent contraction of all the muscles of mastication in experi- mental irritation of the third, or inferior maxillary, division of the nerve; by paralysis of the same muscles when it is divided or dis- organized, or from any reason deprived of power; and by the reten- tion of the power of these muscles when all those supplied by the facial nerve lose their power through paralysis of that nerve. The last instance proves best that, though the buccinator muscle gives passage to, and receives some filaments from, a buccal branch of the inferior division of the fifth nerve, yet it derives its motor power FIFTH OR TRIGEMINAL NERVE. 367 from the facial, for it is paralyzed together with the other muscles that are supplied by the facial, but retains its power when the other muscles of mastication are paralyzed. It is probable, therefore, that the buccal branch of the fifth contains only sensitive fibres; and that of these some are supplied to the buccinator muscle, as to all the other muscles some sensitive fibres are distributed to confer mus- cular sensibility. The sensitive function of the branches of the greater division of the fifth nerve is proved by all the usual evidences, such as their distribution in parts that are sensitive and not capable of muscular contraction, the exceeding sensibility of some of these parts, their loss of sensation when the nerve is paralyzed or divided, the pain without convulsions produced by morbid or experimental irritation of the trunk or branches of the nerve, and the analogy of this por- tion of the fifth to the posterior root of a spinal nerve. (See Longet and others.) But although formed of sensitive filaments exclusively, the bran- ches of the greater or ganglionic portion of the fifth nerve exercise a manifold influence on the movements of the muscles of the head and face, and other parts in which they are distributed. They do so, in the first place, by providing the muscles themselves with that sensibility without which the mind, being unconscious of their posi- tion and state, cannot voluntarily exercise them. It is, probably, for conferring this sensibility on the muscles, that the branches of the fifth nerve anastomose so frequently with those of the facial and hypoglossal, and the nerves of the muscles of the eye; and it is because of the loss of this sensibility that when the fifth nerve is divided, animals are always slow and awkward in the movements of the muscles of the face and head, or hold them still, or guide their movements by the sight of the objects towards which they wish to move. Again, the fifth nerve has an indirect influence on the muscular movements, by conveying sensations of the state and position of the skin and other parts; which the mind perceiving, is enabled to determine appropriate acts. Thus, when the fifth nerve, or its infra- orbital branch is divided, the movements of the lips in feeding may cease or be imperfect; a fact which led Sir Charles Bell into one of the very few errors of his physiology of the nerves. He supposed that tbe motion of the upper lip, in grasping food, depended directly on the infra-orbital nerve; for he found that after he had divided that nerve on both sides in an ass, it no longer seized the food with its lips, but merely pressed them against the ground, and used the tongue for the prehension of the food. Mr. Mayo corrected this error, lie found, indeed, that after the infra-orbital nerve had been divided, the animal did not seize its food with the lip, and could not use it well during mastication, but that it could open the lips. He, therefore, justly attributed the phenomeua in Sir C. Bell's experi- 368 THE NERVOUS SYSTEM. ments to the loss of sensation in the lips; the animal not being able to feel the food, and, therefore, although it had the power to seize it, not knowing bow or where to use that power. Lastly, the fifth nerve has an intimate connection with muscular movement through the many reflex acts of muscles of which it is the necessary excitant. Hence, when it is divided and can no longer convey impressions to the nervous centres to be thence reflected, the irritation of the conjunctiva produces no closure of the eye, the mechanical irritation of the nose excites no sneezing, that of the tongue no flowing of saliva; and although tears and saliva may flow naturally, their efflux is not increased by the mechanical or chemical or other stimuli, to the indirect or reflected influence of which it is liable in the perfect state of this nerve. The fifth nerve, through its ciliary branches and the branch which forms the long root of the ciliary or ophthalmic ganglion, exercises, also, some influence on the movements of the iris. When the trunk or the ophthalmic portion is divided, the pupil becomes, according to Valentin (iv. vol. ii. p. 666), contracted in men and rabbits, and dilated in cats and dogs; but, in all cases, becomes immovable, even under all the varieties of the stimulus of light. How the fifth nerve thus affects the iris is unexplained; according to Longet, the same effects are pro- duced by destruction of the superior cervical ganglion of the sympa- thetic, so that, possibly, they are due to the injury of those filaments of the sympathetic which, after joining the trunk of the fifth at and beyond the Casserian ganglion, proceed with the branches of its ophthalmic division to the iris; or, as Dr. B. Hall ingeniously sug- gests, the influence of the fiftb nerve on the movements of the iris may be ascribed to the affection of vision in consequence of the dis- turbed circulation or nutrition in the retina, when the normal influ- ence of the fifth nerve and ciliary ganglion is disturbed. In such disturbance, increased circulation making the retina more irritable might induce extreme contraction of the iris; or, under moderate stimulus of light, producing partial blindness, might induce dilata- tion : but it does not appear why, if this be the true explanation, the iris should in either case be immovable and unaffected by the various degrees of light. Furthermore, the complete paralysis or division of the fifth nerve, by the morbid effects which it produces in the organs of special sense, makes it probable that, in the normal state, the fifth nerve exercises some indirect influence on all these organs or their func- tions. Thus, after such complete paralysis, within a period varying from twenty-four hours to a week, the cornea begins to be opaque; then it grows completely white; a low destructive inflammatory process ensues in the conjunctiva, sclerotica, and interior parts of the eye; and within one or a few weeks, the whole eye may be quite disorganized, and the cornea may slough or be penetrated by a large ulcer. The sense of smell (and not merely that of mechanical irri- RELATION OF FIFTH NERVE TO THE SENSES. 369 tation in the nose), may be at the same time lost, or gravely im- paired ; so may the hearing; and commonly, whenever the fifth nerve is paralyzed, the tongue loses the sense of taste in its anterior and lateral parts, i. e., in the portion in which the lingual or gusta- tory branch of the inferior maxillary division of the fifth is distributed. The loss of the sense of taste may be due to the lingual branch of the fifth nerve being, really, a nerve of special sense; or it may be because it supplies, in the anterior and lateral parts of the tongue, a necessary condition for the proper nutrition of that part But, deferring this question till the glosso-pharyngeal nerve is to be con- sidered, it may be observed that in some brief time after complete paralysis, or division, of the fifth nerve, the power of all the organs of the special senses may be lost; they may lose not merely their sensibility to common impressions, for which they all depend directly on the fifth nerve, but also their sensibility to the several peculiar impressions for the reception and conduction of which they are pur- posely constructed and supplied with special nerves besides the fifth. The facts observed in these cases' can, perhaps, be only explained by the influence which the fifth nerve exercises on the nutritive pro- cesses in the organs of the special senses. It is not unreasonable to believe, that, in paralysis of the fifth nerve, their tissues may be the seats of such changes as are seen in the laxity, the vascular conges- tion, oedema, and other affections of the skin of the face and other tegumentary part which also accompany the paralysis; and that these changes, which may appear unimportant when they affect external parts, are sufficient to destroy that refinement of structure by which the organs of the special senses are adapted to their functions. In the chapter on Nutrition (p. 244), the question is mentioned whether of the two, the fifth or the sympathetic nerve, conveys the impression by which the nutrition of the parts is influenced; and it is stated that Magendie and Longet have observed, that the destruc- tion of the eye ensues more quickly after division of the trunk of the fifth beyond the Casserian ganglion, or after division of the ophthalmic branch, than after division of the roots of the fifth be- tween the brain and the ganglion. Hence it would appear as if the influence on nutrition were conveyed through the filaments of the sympathetic, which join the branches of the fifth nerve at and be- yond the Casserian ganglion, rather than through the filaments of the fifth itself; and this is confirmed by experiments in which ex- tirpation of the superior cervical ganglion of the sympathetic pro- duced the same destructive disease of the eye as commonly follows the division of the fifth nerve. And yet, that the filaments of the fifth nerve, as well as those of the sympathetic, may conduct such influence appears certain from the cases, including that by Mr. Stanley, in which the source of the 1 Two of the best cases are published, with analyses of others, by Mr. Dixon, in the Medico-Chirurgical Transactions, vol. xxviii. 370 THE NERVOUS SYSTEM. paralysis of the fifth nerve was near the brain, or at its very origin, before it receives any communication from the sympathetic nerve. The problem, therefore, cannot yet be certainly solved. The ex- istence of ganglia of the sympathetic in connection with all the principal divisions of the fifth nerve where it gives off those branches which supply the organs of special sense—for example, the connec- tion of the ophthalmic ganglion with the ophthalmic nerve at the origin of the ciliary nerves ; of the sphenopalatine ganglion with the superior maxillary division where it gives its branches to the nose and the palate; of the otic ganglion with the inferior maxillary near the giving off of filaments to the internal ear; and of the sub-maxil- lary ganglion with the lingual branch of the fifth—all these connec- tions suggest that a peculiar and probably conjoint influence of the sympathetic and fifth nerves is exercised in the nutrition of the or- gans of the special senses; and the results of experiment and disease confirm this by showing that the nutrition of the organs may be im- paired in consequence of impairment of the power of either of the nerves. A singular connection between the fifth nerve and the sense of sight is shown in cases of no unfrequent occurrence, in which blows or other injuries implicating the frontal nerve as it passes over the brow are followed by total blindness in the corresponding eye. The blindness appears to be the consequence of defective nutrition of the retina; for although, in some cases, it has ensued immediately, as if from concussion of the retina, yet in some it has come on gradu- ally like slowly progressive amaurosis, and in some with inflamma- tory disorganization followed by atrophy of the whole eye.1 And, again, the fifth nerve is shown intimately connected with the third by cases in which paralysis of the third has followed neuralgia of the fifth; and not less, by the influence of belladonna applied to the filaments of the fifth, and producing" a kind of paralysis of the iris through a reflected narcotising influence on the branches of the third. Physiology of the Facial Nerve. The facial, or portio dura of the seventh pair of nerves, is the motor nerve of all the muscles of the face, including the platysma, but not including any of the muscles of mastication already enume- rated (p. 366) ; it supplies, also, through the connection of its trunk with the Vidian nerve, by the petrosal nerves, some of the muscles, most probably the levator palati and azygos uvulae, of the soft pa- late; by its tympanic branches it supplies the stapedius and laxator tympani, and through the otic ganglion the tensor tympani; through the chorda tympani it supplies the lingualis and some other muscu- lar fibres of the tongue; and by branches given off before it comes 1 Such a case is recorded by Snabilie in the Nederlandsch Lancet. August, 1846. ° FACIAL NERVE. 371 upon the face, it supplies the muscles of the external ear, the poste- rior part of the digastricus, and the stylo-hyoideus.1 To all these muscles it is the sole motor nerve, and it is probably exclusively motor in its power; no pain is produced by irritating it near its origin (Valentin), and the indications of pain which are elicited when any of its branches are irritated may be explained by the abundant anastomoses which, in all parts of its course, it forms with sensitive nerves, whose filaments being mingled with its own are the true source of the pain. Such anastomoses are effected with the fifth nerve through the petrosal branches of the Vidian, and probably also through the chorda tympani, and with the pneumo- gastric nerve through its auricular branch, even before the facial leaves the cranium. When the facial nerve is divided, or in any other way paralyzed, the loss of power in the muscles which it supplies, wbile proving the nature and extent of its functions, displays also the necessity of its perfection for the perfect exercise of all the organs of the special senses. Thus, in paralysis of the facial nerve, the orbicularis palpe- brarum being powerless, the eye remains open through the unba- lanced action of the levator palpebrae, and the conjunctiva, thus continually exposed to the air and the contact of dust, is liable to repeated inflammation, which may end in thickening and opacity of both its own tissue and that of the cornea. These changes, how- ever, ensue much more slowly than those which follow paralysis of the fifth nerve, and never bear the same destructive character; both because the nutrition of the eye is not directly interfered with, and because the globe can still be moved upwards and inwards, so as to carry the cornea partially under the angle of the upper eyelid in winking and sleeping. In paralysis of the facial nerve, also, tears are apt to flow constantly over the face, apparently because of the paralysis of the tensor tarsi muscle, and the loss of the proper direc- tion and form of the orifice of the puncta lacrymalia. By these things the sense of sight is impaired. The sense of hearing, also, is impaired in many cases of paralysis of the facial nerve; not only in such as are instances of simultane- ous disease in the auditory nerves, but in such as may be explained by the loss of power in the muscles of the internal ear. The sense of smell is commonly at the same time impaired through the inabi- lity to draw air briskly towards the upper part of the nasal cavities, ia which part alone the olfactory nerve is distributed; because, to draw the air perfectly in this direction, the action of the dilators and compressors of the nostrils should be perfect. Lastly, the sense of taste is impaired, or may be wholly lost, in paralysis of the facial nerve, provided the source of the paralysis be in some part of the nerve between its origin and the giving off of 1 On the minute anatomy of the facial nerve, see especially Morganti (cxx. 1845, or an abstract in xxv. 1844, p. 53); and Beck (clxiv.). 372 THE NERVOUS SYSTEM. the chorda tympani. This result, which has been observed in many instances of disease of the facial nerve in man,1 appears explicable only by the influence which, through the chorda tympani, it exer- cises on the movements of the lingualis and the adjacent muscular fibres of the tongue; and, according to some, or probably in some animals, on the movements of the stylo-glossus. This result is not due to any gustatory fibres conveyed by the chorda tympani from the Vidian nerve to the tongue; for the loss of taste is observed when the facial is paralyzed by some affection behind the junction of the great petrosal branch of the Vidian, when, therefore, whatever fila- ments of the Vidian there may be in the chorda tympani, are un- affected. We can, therefore, only suppose that the accurate move- ment of these muscles of the tongue is essential to the exercise of taste; a fact, if it be so, which is the more singular, because the sense of taste is not materially impaired in cases of paralysis of all the other muscles of the tongue through injury of the hypoglossal nerve. Together with these effects of paralysis of the facial nerve, the muscles of the face being all powerless, the countenance acquires on the paralyzed side a characteristic, vacant look, from the absence of all expression: the angle of the mouth is lower, and the paralyzed half of the mouth looks longer than that on the other side; the eye has an unmeaning stare. All these peculiarities increase, the longer the paralysis lasts; and their appearance is exaggerated when at any time the muscles of the opposite side of the face are made active in any expression, or in any of their ordinary functions. In an attempt to blow or whistle, one side of the mouth and cheek acts properly, but the other side is motionless or flaps loosely, at the impulse of the expired air; so in trying to suck, one side only of the mouth acts; in feeding, the lip and cheek are powerless, and food lodges between the cheek and gum. The number of movements concerned in respiration which are performed under the control of the facial nerve, and the great share which it has in the movements most expressive of the states of the mind, led Sir Charles Bell to place the facial in his class of respiratory nerves. But there are no instances in which, when unable to act under ordinary stimuli or in other functions, the facial nerve has yet been capable of action in respiratory movements; its paralysis, when complete, is so in respect to every function alike. As a nerve of expression, it must not be considered independent of the fifth nerve, with which it forms so many anastomoses; for, although it is through the facial nerve alone that all the muscles of the face are put into their naturally expressive actions, yet the power 1 See especially C. Bernard (cxxii. 1844). See also Guarini (cxx. 1842), and Verga (xc. 1843); and for evidences against this view see Morganti (cxx. 1845 and 1846). He maintains that the chorda tympani is formed ex- clusively of sensitive fibres ; but in this he is most probably wrong. GLOSSO-PHARYNGEAL NERVE. 373 which the mind has of suppressing, controlling, and imitating or acting all these expressions, can only be exercised by voluntary and well-educated actions directed through the facial nerve with the guidance of the knowledge of the state and position of every mus- cle; which knowledge is acquired only through the fifth nerve, which confers sensibility on the muscles, and appears, for this pur- pose, to be more abundantly supplied to the muscles of the face than any other sensitive nerve is to those of other parts. It has been already said, that the facial nerve perhaps supplies the levator palati and azygos uvulas muscles with motor power; but the same is also ascribed, as probable, to the pneumogastric and ac- cessory nerves. The evidence for the facial is, chiefly, the fact that when it is paralyzed, the uvula often deviates to the opposite side, and recovers its medium position when the paralysis ceases; a con- dition which is also said to be sometimes observed when the petrosal nerves, through which alone the facial can supply the palate, are in- jured in fracture of the base of the skull. The middle posterior palatine nerve, also, passes into the levator palati and azygos uvulae, and may, through the petrosal nerves and sphenopalatine ganglion, receives filaments from the facial nerve. But, on the other hand, irritation of the trunk of the facial nerve produces no contractions of these muscles of the palate (Hein, lxxx. 1844; Valentin, iii.) • and the experiments of Hein seemed to show that such contractions did follow the irritation of the pneumogastric and accessory nerves from one or both of which, filaments pass to the palate through branches of the glosso-pharyngeal.1 Physiology of the Glosso-Pharyngeal Nerve. The glosso-pharyngeal nerves, in the enumeration of the cerebral nerves by numbers according to the position in which they leave the cranium, are considered as divisions of the eighth pair of nerves, in which term are included with them the pneumogastric and accessory nerves. But the union of the nerves under one term is inconve- nient, although in some parts the glosso-pharyngeal and pneumogas- tric are so combined in their distribution that it is impossible to separate them in either anatomy or physiology. The glosso-pharyngeal nerve appears to give filaments through its tympanic branch (Jacobson's nerve), to the fenestra ovalis, and fenestra rotunda, and the Eustachian tube; also, to the carotid plexus, and, through the lesser petrosal nerve, to the sphenopala- tine ganglion.2 After communicating, either within or without the cranium, with the pneumogastric, and, soon after it leaves the cra- nium, with the sympathetic, digastric branch of the facial, and the accessory nerve, the glosso-pharyngeal nerve parts into the two prin- 1 The sewral cases relating to this question are given in xxv. 1843-4-5. * See especially Beck (clxiv.). 32 374 THE NERVOUS SYSTEM. cipal divisions indicated by its name, and supplies the mucous mem- brane of the posterior and lateral walls of the upper part of the pha- rynx, the Eustachian tube, the arches of the palate, the tonsils and their mucous membrane, and the tongue as far forwards as the fora- men csecum in the middle line, and to near the tip at the sides and inferior part. Some experiments make it probable that the glosso-pharyngeal nerve contains, even at its origin, some motor fibres, together with those of common sensation and the sense of taste. For Volkmann (lxxx. 1840), and Hein (lxxx. 1844), when they divided the nerve within the skull, and then irritated its distal portion, saw movements of the pharynx and of the palate and its arches, which appeared to be due to contractions of the stylo-pharyngeus, and, perhaps also, of the palato-glossus muscles. And the recent experiments of Biffi and Morganti (lxxx. 1847, p. 360), confirm these, although their former ones (cxx. 1847) did not. Whatever motor influence, there- fore, is conveyed directly through branches of the glosso-pharyngeal may be ascribed to the filaments of the pneumogastric or accessory that are mingled with it. The experiments of Dr. John Beid (xciv. 1838), confirming those of Panizza and Longet, tend to the same conclusions; and their results probably express nearly all the truth regarding the part of the glosso-pharyngeal which is distributed to the pharynx. These results were that,—1. Pain was produced when the nerve, particu- larly its pharyngeal branches, were irritated. 2. Irritation of the nerve before the giving-off its pharyngeal branches, or of any of these branches, gave rise to extensive muscular motions of the throat and lower part of the face: but, when the nerve was divided, these motions were excited by irritating the upper or cranial portion, while irritation of the lower end, or that in connection with the muscles, was followed by no movement; so that these motions must have de- pended on a reflex influence transmitted to the muscles through other nerves by the intervention of the nervous centres. 3. When the functions of the brain and medulla oblongata were arrested by poisoning the animal with prussic acid, irritation of the glosso-pha- ryngeal nerve, before it was joined by any branches of the pneumo- gastric, gave rise to no movements in the muscles of the pharynx or other parts to which it was distributed; while, on irritating the pha- ryngeal branch of the pneumogastric, or the glosso-pharyngeal nerve, after it had received the communicating branches just alluded to, vigorous movements of all the pharyngeal muscles and of the upper part of the oesophagus followed. The most probable conclusion, therefore, may be that what motor influence the glosso-pharyngeal nerve may seem to exercise, is due either to the filaments of the pneumogastric or accessory that are mingled with it, or to impressions conveyed through it to the medulla oblongata, and thence reflected to muscles through motor nerves, GLOSSO-PHARYNGEAL NERVE: TASTE. 375 especially the pneumogastric, accessory, and facial. Thus, the glosso- pharyngeal nerve excites through the medium of the medulla oblon- gata the actions of the muscles of deglutition. It is the chief cen- tripetal nerve engaged in these actions; yet not the only one, for, as Dr. John Beid has shown, the acts are scarcely disturbed or re- tarded when both the glosso-pharyngeal nerves are divided. But besides being thus a nerve of common sensation in the parts which it supplies, and a centripetal nerve through which impressions are conveyed to be reflected to the adjacent muscles, the glosso-pha- ryngeal is also a nerve of special sensation; being the gustatory nerve, or nerve of taste, in all the parts of the tongue to which it is dis- tributed. After many discussions, the question, which is the nerve of taste ?—the lingual branch of the fifth, or the glosso-pharyngeal ? — may be most probably answered by stating that they are both nerves of this special function. For very numerous experiments and cases have shown that when the trunk of the fifth nerve or its lingual branch is paralyzed or divided, the sense of taste is com- pletely lost in the superior surface of the anterior and lateral parts of the tongue. The loss is instantaneous after division of the nerve; and, therefore, cannot be ascribed to the defective nutrition of the part, though to this, perhaps, may be ascribed the more complete and general loss of the sense of taste when the whole of the fifth nerve has been paralyzed. But, on the other hand, while the loss of taste in the part of the tongue to which the lingual branch of the fifth nerve is distributed proves that to be a gustatory nerve, the fact that the sense of taste is at the same time retained in the posterior and postero-lateral parts of the tongue, and in the soft palate and its anterior arch, to which (and to some parts of which exclusively) the glosso-pharyngeal is distributed, proves that this also must be a gustatory nerve. In a patient in St. Bartholomew's Hospital, the left lingual branch of the fifth nerve was divided in removing a portion of tbe lower jaw: she lost both common sensation and the sensation of taste in the tip and anterior parts of the left half of the tongue, but retained both in all the rest of the tongue. M. Lisfranc and others have noted similar cases; and the phenomena in them are so simple and clear, that there can scarcely be any fallacy in the conclusion that the lingual branches of both the fifth and the glosso-pharyngeal nerves are gustatory nerves in the parts of the tongue which they severally supply. This conclusion is confirmed by some experiments on animals;1 and, perhaps, more satisfactorily as concerns the sense of taste in 1 Namely, those of Magendie, Mayo, Miiller, and Kornfeld (see Miiller xxxii. p 822); and most completely by those of Dr. Alcock (lxxi., 1836), and of Morganti and Biffi (cxx., 1847). On the contrary are the experiments of Panizzi (recorded by Dr. Burrows, lxxi., vol. xvi.); of Valentin (iii. and iv.), and of Wagner (xxxviii., No. 75). Some explanation of the probable source of the contradiction is given by Morganti (I. c). 376 THE NERVOUS SYSTEM. man, by observation of the parts of the tongue and fauces in which the sense is most acute. According to Valentin's experiments made on thirty students, the parts of the tongue from which the clearest sensations of taste are derived, are the base, as far as the foramen caecum and lines diverging forwards on each side from it; the pos- terior palatine arches down to the epiglottis; the tonsils and upper part of the pharynx over the root of the tongue. These are the seats of the distribution of the glosso-pharyngeal nerve. The ante- rior dorsal surface, and parts of the anterior and inferior parts of the tongue, in which the lingual branch of the fifth is alone distributed, conveyed no sense of taste in the majority of the subjects of Valen- tin's experiments; but even if this were generally the case, it would not invalidate the conclusion that, in those who have the sense of taste in the anterior and upper part of the tongue, the lingual branch of the fifth is the nerve by which it is exercised. And the same may be said of the soft palate and uvula; in those who have the sense of taste in these parts its nerves must be branches of the fifth; for, unless it be through the minute branch which passes into the Jacobsonian plexus, and might thence pass through the inferior pe- trosal nerve and spheno-palatine ganglion, the glosso-pharyngeal nerve can send no filaments to the soft palate. Physiology of the Pneumogastric Nerve. The pneumogastric nerve, nervus vagus, or par vagum, has, of all the cranial and spinal nerves, the most various distribution, and in- fluences the most various functions, either through its own filaments or those which, derived from other nerves, are mingled in its branches. The parts supplied by the branches of the pneumogastric nerve are as follow: by its pharyngeal branches, which enter the pharyn- geal plexus, a large portion of the mucous membrane, and, probably, all the muscles of the pharynx; by the superior laryngeal nerve, the mucous membrane of the under surface of the epiglottis, the glottis, and the greater part of the larynx, and the crico-thyroid muscle; by the inferior laryngeal nerve, the mucous membrane and muscular fibres of the trachea, the lower part of the pharynx and larynx, and all the muscles of the larynx except the crico-thyroid; by oesopha- geal branches, the mucous membrane and muscular coats of the oeso- phagus. Moreover, the branches of the pneumogastric nerve form a large portion of the supply of nerves to the heart and the great arteries through the cardiac nerves, derived from both the trunk and the recurrent nerve; to the lungs, through both the anterior and the posterior pulmonary plexuses; and to the stomach by its terminal branches passing over the walls of that organ. From the parts thus enumerated as receiving nerves from the TnE PNEUMOGASTRIC NERVE. 377 pneumogastric, it might be assumed that it is a nerve of mixed func- tion, both sensitive and motor. Experiments prove that it is so from its origin, for the irritation of its roots, even within the cranial cavity, produces both pain and convulsive movements of the larynx and pharynx; and when it is divided within the skull, the same move- ments follow the irritation of the distal portion, showing that they are not due to reflex action. Similar experiments prove that, through its whole course, it contains both sensitive and motor fibres, but after it has emerged from the skull, and in some instances even sooner, it enters into so many anastomoses that it is hard to say whether the filaments it contains are, from their origin, its own, or whether they are derived from other nerves combining with it. This is particularly the case with the filaments of the sympathetic nerve, which are abun- dantly added to nearly all the branches of the pneumogastric. The likeness to the sympathetic which it thus acquires, is further in- creased by its containing many filaments derived, not from the brain, but from its own petrosal ganglia, in which filaments originate, in the same manner as in the ganglia of the sympathetic, so abun- dantly that the trunk of the nerve is visibly larger below the ganglia than above them (Bidder and Volkmann, xv., art. Nervenphysio- logie). Next to the sympathetic nerve, that which most importantly communicates with the pneumogastric is the accessory nerve, whose internal branch joins its trunk, and is lost in it. Properly, therefore, the pneumogastric might be regarded as a triple-mixed nerve; having, out of its own sources, motor, sensitive, and sympathetic or ganglionic nerve-fibres ; and to this natural com- plexity it adds that which it derives from the reception of filaments from the sympathetic, accessory, and cervical nerves, and, probably, the glosso-pharyngeal and facial. The most probable account of the particular functions which the branches of the pneumogastric nerve discharge in the several parts to which they are distributed may be drawn from Dr. John Beid's experiments on dogs (xciv. vols. xlix. and li.). They show that — 1. The pharyngeal branch is the principal, if not the sole, motor nerve of the pharynx and soft palate,1 and is most probably wholly motor; a part of its motor fibres being derived from the internal branch of the accessory nerve. 2. The inferior laryngeal nerve is the motor nerve of the larynx, irritation of it producing vigorous movements of the arytenoid cartilages; while irritation of the superior laryngeal nerve gives rise to no action in any of the muscles attached to the arytenoid cartilages, but merely to contractions of the crico- thyroid muscle. 3. The superior laryngeal nerve is chiefly sensitive; the inferior, for the most part, motor; for division of the recurrent nerves puts an end to the motions of the glottis, but without lessen- 1 On the probable influence of the facial in the movements of the palate, Beep. 372; and on the glosso-pharyngeal, see p. 374. 32* 378 THE NERVOUS SYSTEM. ing the sensibility of the mucous membrane; and division of the superior laryngeal nerves leaves the movements of the glottis un- affected, but deprives it of its sensibility. 4. The motions of the oesophagus are dependent on motor fibres of the pneumogastric, and are probably excited by impressions made upon sensitive fibres of the same; for irritation of its trunk excites motions of the oesophagus, which extend over the cardiac portion of the stomach; and division of the trunk paralyzes the oesophagus, which then becomes distended with the food. 5. The cardiac branches of the pneumogastric nerve are one, but not the sole, channel through which the influence of the central organs and of mental emotions is transmitted to the heart. 6. The pulmonary branches form the principal, but not the only, channel by which the impressions on the mucous surface of the lungs that excite respiration, are transmitted to the medulla oblongata. Dr. Beid was unable to determine whether they contain motor fibres; but reasons for believing that they do so, have been already given (p. 146). From these results, and referring to what has been said in former chapters, the share which the pneumogastric nerve takes in the functions of the several parts to which it sends branches may be understood:— 1. In deglutition, the motions of the pharynx are of the reflex kind. The stimulus of the food, or other substance to be swallowed, acting on the filaments of the glosso-pharyngeal, the filaments of the superior laryngeal given to the pharynx, and the cervical nerves, is conducted to the medulla oblongata, where it is reflected, chiefly, through the pneumogastric to the muscles of the pharynx and, per- haps, also of the soft palate (see further, pp. 178 and 343). 2. In the functions of the larynx, the sensitive filaments of the pneumogastric supply that acute sensibility by which the glottis is guarded against the ingress of foreign bodies, or of irrespirable gases. The contact of these stimulates the filaments of the superior laryn- geal branch of the pneumogastric; and the impression conveyed to the medulla oblongata, whether it produces sensation or not, is re- flected to the filaments of the recurrent or inferior laryngeal branch, and excites contraction of the muscles that close the glottis. Both these branches of the pneumogastric co-operate also in the produc- tion and regulation of the voice; the inferior laryngeal determining the contraction of the muscles that vary the tension of the vocal cords, and the superior laryngeal conveying to the mind the sensa- tions of the state of these muscles necessary for their continuous gui- dance. And both the branches co-operate in the actions of the larynx in the ordinary slight dilatation and contraction of the glottis in the acts of expiration and inspiration, and more evidently in those of coughing and other forcible respiratory movements (p. 157). 3. It is partly through their influence on the sensibility and mus- cular movements in the larynx, that the pneumogastric nerves exer- THE PNEUMOGASTRIC NERVE. 379 cise so great an influence on the respiratory process, and that the division of both the nerves is commonly fatal. To determine how death is in these cases produced has been the object of innumerable and often contradictory experiments. It is probably produced differently in different cases, and in many is the result of several co- operating causes. Thus, after division of both the nerves, the respi- ration at once becomes slower, the number of respirations in a given time being commonly diminished to one-half (Emmert, xxxii. p. 371; J. Bead, xciv. 1839); probably, because the pneumogastric nerves are the principal conductors of the impression of the necessity of breathing to the medulla oblongata. Bespiration does not cease; for it is probable, that the impression may be conveyed to the medulla oblongata through the sensitive nerves of all parts in which the im- perfectly aerated blood flows (see p. 196); yet the respiration being retarded adds to the other injurious effects of division of the nerves. Again, division of both pneumogastric trunks, or of both of their recurrent branches, is often very quickly fatal in young animals; but in old animals the division of the recurrent nerves is not generally fatal, and that of both the pneumogastric trunks is not always fatal (J. Beid, 1. c), and, when it is so, the death ensues slowly. This difference is probably because the yielding of the cartilages of the larynx in young animals permits the glottis to be closed by the atmospheric pressure in inspiration, and they are thus quickly suffo- cated unless tracheotomy is performed (Legallois, cxxxix.). In old animals, the rigidity and prominence of the arytenoid cartilages pre- vent the glottis from being completely closed by the atmospheric pressure; even when all the muscles are paralyzed, a portion at its posterior part remains open, and through this the animal continues to breathe. Yet, the diminution of the orifice for respiration may add to the difficulty of maintaining life. In the case of slower death after division of both the pneumogas- tric nerves, the lungs are commonly found gorged with blood, oede- matous, or nearly solid, or with a kind of low pneumonia, and with their bronchial tubes full of frothy, bloody fluid and mucus; changes to which, in general, the death may be proximately ascribed. These changes are due, perhaps in part to the influence which the pneumo- gastric nerves exercise on the chemical process of respiration in the lungs, and the movements of the air-cells and bronchi; yet, since they are not always produced in one lung when its pneumogastric nerve is divided, they cannot be ascribed wholly to the suspension of organic nervous influence (J. Beid). Bather, they may be ascribed to the hinderance to the passage of blood through the lungs in conse- quence of the diminished supply of air, and the excess of carbonic acid in the air-cells (see p. 158) : in part perhaps to paralysis of the blood-vessels, leading to congestion : and in part, also, as the experi- ments of Traube especially show (clxxi. 1846), they appear due to 380 THE NERVOUS SYSTEM. the passage of food and of the various secretions of the mouth and fauces through the glottis, which, being deprived of its sensibility, is no longer stimulated or closed in consequence of their contact. He says, that if the trachea be divided and separated from the oesopha- gus, or if only the oesophagus be tied, so that no food or secretion from above can pass down the trachea, no degeneration of the tissue of the lungs will follow the division of the pneumogastric nerves. So that, on the whole, death after division of the pneumogastric nerves may be ascribed, when it occurs quickly in young animals, to suffocation through mechanical closure of the paralyzed glottis : and, when it occurs more slowly, to the congestion and pneumonia pro- duced by the diminished supply of air, by paralysis of the blood- vessels, and by the passage of foreign fluids into the bronchi, and aggravated by the diminished frequency of respiration, the insensi- bility to the diseased state of the lungs, the diminished aperture of the glottis, and the loss of the due nervous influence upon the process of respiration. 4. Bespecting the influence of the pneumogastric nerves on the movements of the oesophagus and stomach, the secretion of gastric fluid, the sensation of hunger, absorption of the stomach, and the action of the heart, former pages may be referred to, especiallly pages 178, 343, 196 to 198, and 102-3. On all these parts the in- fluence is, as its structure (p. 481) would suggest, like that of the sympathetic more than that of a cerebro-spinal nerve; the move- ments that follow its irritation being in the stomach slow and con- tinuous, and in the heart rather tardily following the irritation. Physiology of the Accessory Nerve. In the preceding pages it is implied that all the motor influence which the pneumogastric nerves exercise, is conveyed through fila- ments which, from their origin, belong to them: and this is, per- haps, true. Yet a question may still be entertained, which has been often discussed, whether all or a great part of the motor filaments that appear to belong to the pneumogastric nerves are not given to them from the accessory nerves.1 The principal branch of the accessory nerve, its external branch, supplies the sterno-mastoid and trapezius muscles; and, though pain is produced by irritating it, is composed almost exclusively of motor fibres. It might appear very probable, therefore, that the internal branch, which is added to the trunk of the pneumogastric just before the giving off of the pharyngeal branch is also motor; and that through, it the pneumogastric nerve derives part of the motor fibres which it supplies to the muscles enumerated above. And, further, since the pneumogastric nerve has a ganglion just above the part at which the internal branch of the accessory nerve joins its 1 An abstract of nearly the whole discussion is given in xxv. 1843-4. PHYSIOLOGY OF THE ACCESSORY NERVE. 381 trunk, a close analogy may seem to exist between these two nerves and the spinal nerves with their anterior and posterior roots. In this view, Arnold and several later physiologists have regarded the accessory nerve as constituting a motor root of the vagus nerve; and, although this view cannot now be maintained, yet it is very probable that the accessory nerve gives some motor filaments to the pneumogastric. For, among the experiments on the point, many have shown that when the accessory nerve is irritated within the skull, convulsive movements ensue in some of the muscles of the larynx; all of which, as already stated, are supplied, apparently, by branches of the pneumogastric: and (which is a very significant fact) Vrolik states that in the chimpanse' the internal branch of the accessory does not join the pneumogastric at all, but goes direct to the larynx. On the whole, therefore, although in some of the ex- periments no movements in the larynx followed irritation of the ac- cessory nerve, yet it may be concluded that it gives to the pneumo- gastric nerve some of the motor filaments which pass, with the laryn- geal branches, to the muscles of the larynx, especially to the crico- thyroid (Bernard, cxxii. 1844). It is not certain whether, besides these, the accessory gives to the pneumogastric any other motor filaments; for the experiments to determine whether, on irritating the accessory within the skull, the muscles of the pharynx, oesophagus, or other parts besides the larynx are convulsed, are completely contradictory, and there appears no other means than that of experiment by which the difficulty may be solved. It is, however, certain that the accessory nerve does not supply all the motor filaments which the branches of the pneumogastric contain; for division of the pneumogastric pro- duces a much more extensive paralysis of motion in all the parts that it supplies, than division of the accessory or its internal branch does: especially in regard to the larynx, and other respiratory organs, almost the only effects of destruction of the accessory are loss of voice, and panting in great efforts (Bernard, cxxii. 1844.) Among the roots of the accessory nerve, the lower, arising from the spinal cord, appear to be composed exclusively of motor fibres, and to be destined entirely to the trapezius and sterno-mastoid muscles; the upper fibres, arising from the medulla oblongata, con- tain many sensitive as well as motor fibres, and these alone are in- cluded in the internal branch, which joins the pneumogastric (Bernard, Morganti). Of these, indeed, it is not rare to find some that are united with the pneumogastric at its ganglion, or even within the cranial cavity; and of these upper roots also, the com- municating branch is formed, which sometimes takes the place of the posterior root of the first cervical nerve. As a respiratory nerve, under the influence of the medulla oblon- gata, the accessory has been often observed to conduct impressions exciting movements necessary to respiration in the sterno-mastoid 382 THE NERVOUS SYSTEM. and trapezius muscles, after these muscles have ceased to move under the influence of the will. They may thus act whenever any of the parts of the brain above the medulla oblongata cease to be capable of conveying impressions; for then the will cannot act on these or any other muscles, though they are still amenable to the reflex influence of the medulla oblongata. Physiology of the Hypoglossal Nerve. The hypoglossal, or ninth nerve, or motor lingua', has a peculiar relation to the muscles connected with the hyoid bone, including those of the tongue. It supplies through its descending branch {descendens noni), the sterno-hyoid, sterno-thyroid, and omo-hyoid; through a special branch the thyro-hyoid, and through its lingual branches the genio-hyoid, stylo-glossus, hyo-glossus, and genio-hyo- glossus. It contributes, also, to the supply of the submaxillary gland. The function of the hypoglossal is, perhaps, exclusively, motor. Irritation of it within the skull produces little if any pain; but since pain is sometimes produced, it may be supposed that the nerve has either some sensitive fibres from its origin, or some which are taking a retrogade course through it to the brain. As a motor nerve, its influence on all the muscles enumerated above is shown by their convulsions when it is irritated, and by their loss of power when it is paralyzed. The effects of the paralysis of one hypoglossal nerve are, however, not very striking in the tongue. Often, in cases of hemiplegia involving the functions of the hypoglossal nerve, it is not possible to observe any deviation in the direction of the pro- truded tongue; probably because the tongue is so compact and firm that the muscles of either side, their insertion being nearly parallel to the median line, can push it straight forwards or turn it for some distance towards either side. The plexus formed between the branches of the descendens noni and those of the second and third cervical nerves serves not only to distribute filaments of the hypoglossal to the depressor muscles of the hyoid bone, but to admit into the descendens noni filaments of the cervical nerves which take a recurrent course through it, and of which some return to the medulla oblongata through the trunk of the hypoglossal, and others go to the tongue through its lingual branches (Volkmann, lxxx. 1840). Hence, and from other connec- tions with the cervical nerves higher up, the hypoglossal nerve has ample borrowed sensibility. Physiology of the Spinal Nerves. Little need be added to what is already said of these nerves (pp. 325 to 327). The anterior roots of the spinal nerves are formed ex- THE SYMPATHETIC NERVE. 383 clusively of motor fibres; the posterior roots exclusively of sensitive fibres. Beyond the ganglia all the spinal nerves appear to be mixed nerves, and to contain as well sympathetic filaments as those of sen- sation and motion derived through their own roots. Of the functions of the ganglia of the spinal nerves nothing very definite is known. That they are not the reflectors of any of the ascertained reflex actions through the spinal nerves, is shown by the reflex movements ceasing when the posterior roots are divided be- tween the ganglia and the spinal cord. rilYSIOLOGY OF THE SYMPATHETIC NERVE. The sympathetic nerve, or sympathetic system of nerves, obtained its name from the opinion that it is the means through which are effected the several sympathies in morbid action which distant organs manifest. It has also been called trisplanchnic nerve, because it is principally distributed among the organs of the three chief visceral systems, the thoracic, abdominal, and pelvic; and the nervous system of organic life, in the supposition that it alone, as a nervous system, influences the organic processes. All the terms are defective : for, there is sufficient reason to believe that the cerebro-spinal nervous system may influence the organic functions: the cerebro-spinal sys- tem is not excluded from the viscera, nor the trisplanchnic nerve excluded from other parts : the cerebro-spinal system is the medium of numerous sympathies, and the blood of as many or more. But, since the title sympathetic nerve has the advantage of long and most general custom in its favour, and is not more inaccurate than the others, it will be here employed.1 The general differences between the fibres of the cerebro-spinal and sympathetic nerves are already stated (p. 304); and it has been said, that although such general differences exist, and are sufficiently discernible in selected filaments of each system of nerves, yet they are neither so constant, nor of such a kind, as to warrant the suppo- sition, that the different modes of action of the two systems can be referred to the different structures of their fibres. Bather, it is pro- bable, that the laws of conduction by the fibres are in both systems the same, and that the differences manifest in the modes of action of the systems are due to the multiplication and separation of the ner- vous centres of the sympathetic: ganglia, or nervous centres, being 1 The title "ganglionic system of nerves," would be in every respect pre- ferable, if it were sure that the ganglia or the spinal nerves give origin to no nerve-filaments but such as are attached to the rest of the ganglionic system, and that no nerve-filaments attached to this system are derived from the brain and spinal cord. 384 THE NERVOUS SYSTEM. placed in connection with the fibres of the sympathetic in nearly all parts of their course. In the most general view, the sympathetic system may be described as arranged in two principal divisions, each of which consists of ganglia and connecting fibres. The first division may include the ganglia seated on, or close to, cerebral and spinal nerves, with the filaments issuing from them; the second may comprise the ganglia on the two main branches of the sympathetic, and on its branches in the visceral cavities. To the first belong the ophthalmic, spheno-palatine, otic, and sub- maxillary ganglia on the divisions of the fifth nerve; and probably the ganglia on the glosso-pharyngeal and pneumogastric nerves, and on the posterior roots of the spinal nerves; for from all these, fibres appear to originate which, in structure, resemble those derived from the proper ganglia of the sympathetic, and are distributed to the same parts. To the second division belong the ganglia arranged in a continuous line along the sides of the vertebrae, with their con- necting cords, which make up what have been generally called the trunks"of the sympathetic nerve; and all the ganglia placed irregu- larly on the branches of the sympathetic distributed to the viscera. Of the former the number and proportion correspond generally to the vertebrae; of the latter to the development of the viscera. The structure of all these ganglia appears to be essentially similar; all containing, 1st, nerve-fibres traversing them; 2dly, nerve-fibres originating in them; 3dly, nerve- or ganglion-corpuscles, giving ori- gin to these fibres; and 4thly, other corpuscles that appear free. And in the trunk, and thence proceeding branches of the sympathe- tic, there appear to be always, 1st, fibres which arise in its own gan- glia; 2dly, fibres derived from the ganglia of the cerebral and spinal nerves; 3dly, fibres transmitted from the brain and spinal cord through the roots of their nerves. Bespecting the course of the filaments belonging to the sympa- thetic, the following appears to have been determined. Of the fila- ments derived from the ganglia on the cerebral nerves, some may pass towards the brain; for, in the trunks of the nerves, between the ganglia and the brain, fine filaments like those of the sympathetic are found. But these may be proceeding from the brain to the ganglia; and on the whole, it is probable that nearly all the filaments origi- nating in the ganglia on cerebral nerves, go out towards the tissues and organs to be supplied, some of them being centrifugal, some cen- tripetal; so that each ganglion with its outgoing filaments may form a kind of special nervous system appropriated to the part in which its filaments are placed. Such, for example, may be the ophthalmic ganglion with the ciliary nerves: connected with the brain and the rest of the sympathetic system, by the branches of the third, fifth, and sympathetic nerves that form its roots; yet, by filaments of its THE SYMPATHETIC NERVE. 385 own, controlling in some mode and degree, the processes in the inte- rior of the eye. Of the fibres that arise in the spinal ganglia, some appear to pass into the posterior branches of the spinal nerves, and to be distributed with them; the rest pass through the branches by which the spinal nerves communicate with the trunks of the sympathetic, and then entering the sympathetic are distributed with its branches to the viscera. With these, also, a certain number of the large ordinary cerebro-spinal nerve-fibres, after traversing the ganglia, pass into the sympathetic. Of the fibres derived from the ganglia of the sympathetic itself, some go straightway towards the viscera, the rest pass through the branches of communication between the sympathetic and the ante- rior branches of the spinal nerves, and, joining these spinal nerves, proceed with them to their respective seats of distribution, especially to the more sensitive parts. Thus, through these communicating branches, which have been generally called roots or origins of the sympathetic nerve, an inter- change is effected between all the spinal nerves and the sympathetic trunks; all the ganglia, also, which are seated on the cerebral nerves, have roots (as they are called) through which filaments of the cere- bral nerves are added to their own. So that, probably all sympathe- tic nerves contain some intermingled cerebral or spinal nerve fibres; and all cerebral and spinal nerves some filaments derived from the sympathetic system or from ganglia. But the proportions in which these filaments are mingled are not uniform. The nerves of volun- tary muscles contain in their trunks a majority of large or cerebro- spinal nerve-fibres, but in their peripheral distribution either only, or a majority of, fine fibres, of which, however, the greater part are of course the cerebro-spinal fibres reduced in size. The nerves of the skin, and of most sensitive mucous membranes, contain, for the most part, equal numbers of both large and fine fibres, but the proportions often deviate in both directions; and in all, in their peripheral distri- bution, the fine fibres greatly preponderate. In the nerves of invo- luntary muscles, and in those of the less sensitive mucous membranes, there is a great predominance of the fine filaments.1 The physiology of the sympathetic nerve is still very obscure; there arc, however, certain statements which may be made in regard to it. . At first, it may be stated generally as nearly certain, that the sym- pathetic nerve-fibres are simple conductors of impressions, as those ' For au account of the minute anatomy of the sympathetic nerve, see Kol- liker (cxiv and xv. 1844-5, and ccvi. and ccxii.); Hannover (cxix.); Bidder and Volkmann (cxxvi.); Wagner (cxv.); Remak (clxxii.); Todd and Bow- man (xxxix.); Drummond (lxxiii., art. Sympathetic .\erve); and the reports in Canstatt's Jahresberichte to 1850. 33 386 THE NERVOUS SYSTEM. of the cerebro-spinal system are, and that the ganglionic centres have (each in its appropriate sphere) the like powers both of conducting and of communicating impressions. Their power of conducting im- pressions is sufficiently proved in ordinary diseases, as when any of the viscera, usually unfelt, gives rise to sensations of pain, or when a part not commonly subject to mental influence is excited or re- tarded in its actions by the various conditions of the mind; for in all these cases impressions must be conducted to and fro through the whole distance between the part and the spinal cord and brain. So, also, in experiments, now more than sufficiently numerous, irritations of the semilunar ganglia, the splanchnic nerves, the thoracic, hepatic, and other ganglia and nerves, have elicited expressions of pain, and have excited movements in the muscular organs supplied from the irritated part.1 In the case of pain excited, or movements affected by the mind, it may be supposed that the conduction of impressions is effected through the cerebro-spinal fibres which are mingled in all, or nearly all, parts of the sympathetic nerves. There are no means of deciding this; but if it be admitted that the conduction is effected through the cerebro-spinal nerve-fibres, then, whether or not they pass unin- terruptedly between the brain or spinal cord and the part affected, it must be assumed that their mode of conduction is modified by the ganglia. For, if such cerebro-spinal fibres conducted in the ordinary manner, the parts should be always sensible and liable to the influ- ence of the will, and impressions should be conveyed to and fro in- stantaneously. But this is not the case; on the contrary, through the branches of the sympathetic nerve and its ganglia none but in- tense impressions, or impression exaggerated by the morbid excita- bility of the nerves or ganglia, can be conveyed. Either, therefore, the nerve-fibres conduct differently in the sym- pathetic nerves (which is improbable), or else the ganglia have a power of modifying the method of conduction of impressions. It is as if the facility with which an impression may be communicated from one fibre to another in the ganglia were such that the whole force of ordinary impressions on the nerve-fibres is lost in diffusion among the rest of their contents. This seems not improbable; for some cases show that when fibres certainly belonging to cerebro- spinal nerves pass through ganglia of, or connected with, the sympa- thetic, they do not so rapidly, or so surely, transmit impressions as when they have no such relation to the ganglia. Thus, the iris is not under the direct or perfect influence of the will; though the passage of filaments of the third nerve to it is shown by its 1 See especially Longet (cxxxvi.); Valentin (iv., vol. ii., p. 107, etc.); Rad- clyffe Hall (xciv., July, 1846). The last-named observer says, that move- ments most constantly and actively ensue when the whiter parts of ganglia are irritated; and that they often fail of being produced when the ganglia irritated are grey and pellucid. THE SYMPATHETIC NERVE. 387 acting with the muscles supplied by the same nerve. Neither does it always cojitract when the third nerve is irritated, and when all the other muscles supplied by the same nerve are put in action. So, also, when all the other muscles supplied by the facial nerve contract on irritating its trunk, the levator palati and azygos uvulae, to which its filaments probably pass through the sphenopalatine ganglion, do not contract. We may explain these facts by believing that the impression, whe- ther of the mind, or of artificial irritation, which would be conveyed at once through nerve-fibres, unconnected with ganglia, is, in the ganglia of the sympathetic, communicated and diffused among the corpuscles and the other fibres; and thus, as one may say, is exhaus- ted without reaching the muscles, or, in the case of a centripetal nerve, the spinal cord or brain. Whether, then, the conduction be effected through proper sympa- thetic nerve-fibres, or through cerebro-spinal fibres mingled with them and traversing their ganglia, there is this peculiarity to be as- cribed either to the fibres or, more probably, to the ganglia — that the conduction is effected more slowly; so tbat when, for .example, a ganglion on a sympathetic nerve is irritated, the movements in the parts supplied from it do not immediately ensue, and pain is not in- dicated till after repeated irritations, or till, by exposure, or other- wise, the fibres and ganglia have become morbidly irritable. ^ But, with this exceptiou, it is probable that the laws of conduction of impressions are the same in both cerebro-spinal and sympathetic systems. Bespecting the general action of the ganglia of the sympathetic nerve little need be said here, since they were taken as examples by which to illustrate the common modes of action of all nervous centres (see p. 31S). Indeed, complex as the sympathetic system, taken as a whole, is, it presents in each of its parts a simplicity not to be found in the cerebro-spinal system : for each ganglion with afferent and efferent nerves forms a simple nervous system, and might serve for the illustration of all the nervous actions with which the mind is unconnected. But it will be more convenient to consider the ganglia now iu connection with the functions that they may be sup- posed to control, in the several organs supplied by the sympathetic system alone, or in conjunction with the cerebro-spinal. The general processes which the sympathetic appears to influence are those of involuntary motion, secretion, and nutrition. Many movements take place involuntarily in parts_supplied with cerebro-spinal nerves, as the respiratory and other spinal reflex mo- tions; but the parts principally supplied with sympathetic nerves are usually capable of none but involuntary movements, and when the mind acts on them at all, it is only through the strong excite- 388 THE NERVOUS SYSTEM. ment or depressing influence of some passion, or through some voluntary movement with which the actions of the involuntary part are commonly associated. The heart, stomach, and intestines are examples of these statements; for the heart and stomach, though supplied in large measure from the pneumogastric nerves, yet proba- bly derive through them few filaments except such as have arisen from their ganglia, and are therefore of the nature of sympathetic fibres. The parts which are supplied with motor power by the sympathetic nerve continue to move, though more feebly than before, when they are separated from their natural connections with the rest of the sympathetic system, and wholly removed from the body. Thus, the heart, after it is taken from the body, continues to beat in Mammalia for one or two minutes, in reptiles and Amphibia for hours; and the peristaltic motions of tbe intestines continue under the same circum- stances. Hence the motion of the parts supplied with nerves from the sympathetic are shown to be, in a measure, independent of the brain and spinal cord. Their movements, too, though accelerated, or at las* retarded and enfeebled, remain, even after their removal from the body, like those which are natural to them, retaining their character of adaptation to a purpose, and often their harmony and rhythm. They are in all these respects different from the quiverings and twitchings of muscles supplied with cerebro-spinal nerves, when they are similarly separated from the body. The same difference con- tinues when the muscles, having ceased to act spontaneously, are stimulated to fresh contractions by mechanical or other irritation. Of a muscle supplied with cerebro-spinal nerves, only that fasciculus acts to which the stimulus is applied; it instantly twitches once or twice in a disorderly, ineffective manner, and then lies at rest again. But of one supplied from the sympathetic nerve, the contraction commences more slowly, but continues longer; it is a more deliberate and more orderly contraction, more like the natural action of the muscle during life, and extending often far beyond the part to which the irritation was first applied. The difference is well shown (as will be mentioned in the chapter on Motion) with the electro- galvanic stimulus, and affords a nearly constant and characteristic distinction between the muscles severally supplied by the two nervous systems, and distinguished in their structure by their simple, or their transversely-striated, fibres. The difference here indicated must, probably, be ascribed to the influence of the ganglia of the sympathetic, which combine for regular and harmonious action the several fasciculi that act in the manner just described. It cannot be ascribed to the nerve-fibres, for all the parts are supplied with a mixture of both cerebro-spinal and ganglionic fibres; and it can hardly be supposed that a peculiar mode of action of the latter could quite counterbalance the tendency to the ordinary action of the former. Neither can the peculiarity be THE SYMPATHETIC NERVE. 389 ascribed to the muscular fibres; for the heart has fibres like those of voluntary muscle, yet they act, in this respect, like those of the other muscles supplied with sympathetic nerves and controlled by ganglia. Among the ganglia, to which this co-ordination of movements is to be ascribed, must be reckoned, not those alone which are on the principal trunks and branches of the sympathetic external to any organ, but those also which lie in the very substance of the organs; such as those discovered in the heart by Bemak, others like to which have been found also in the mesentery close by the intestines, in the kidneys, and other parts. The extension of discoveries of such ganglia will probably diminish yet further the number of instances in which the involuntary movements appear to be effected independ- ently of central nervous influence. It seems to be a general rule, at least in animals that have both cerebro-spinal and sympathetic nerves much developed, that the involuntary movements excited by stimuli conveyed through ganglia are orderly and like natural movements, while those excited through nerves without ganglia are convulsive and disorderly; and the pro- bability is that, in the natural state, it is through the same ganglia that natural stimuli, impressing centripetal nerves, are reflected through centrifugal nerves to the involuntary muscles. As the muscles of respiration are maintained in uniform rhythmic action by the reflecting and combining, power of the medulla oblongata, so, probably, are those of the heart, stomach, and intestines, by their several ganglia. And as with the ganglia of the sympatbetic and their nerves, so with the medulla oblongata and its nerves distributed to respiratory muscles,—if these nerves or the medulla oblongata itself be directly stimulated, the movements that follow are convul- sive and disorderly; but if the medulla be stimulated through a centripetal nerve, as when cold is applied to the skin, then the im- pressions are reflected so as to produce movements which, though they may be very quick and almost convulsive, are yet combined in the plan of the proper respiratory acts. Such, then, seems to be the peculiarity of the action of the sym- pathetic nerve, and especially of its ganglia, in determining the in- voluntary movements of the parts that it supplies. And, as first stated, this peculiarity seems to be due, not to an essentially different mode of aetiou in either the fibres or the ganglia of the sympathetic, but to the arrangement of those ganglia, which are inserted in or very near to the parts whose movements they control. Bespecting the influence of the sympathetic nerve in nutrition aud secretion, we may refer to the chapters on those processes (pp. 252 to 255, and pp. 269-70). The mode in which this influence is exercised is still obscure, though probably it is in great measure con- nected with the supply of blood to the parts. The experiments of Dr. Waller, Brown-Sequard, and others, leave little doubt that the 33 * 390 THE NERVOUS SYSTEM. sympathetic nerve possesses great influence over the contractile power of the blood-vessels, division of the trunk or branch of such nerve being followed by paralysis of the coats of the vessels supplied by the ramifications of the divided nerve, and by consequent congestion of the parts in which such vessels are distributed. Important though the influence of the sympathetic is over the processes of nutrition and secretion, yet it cannot be determined that the cerebro-spinal fibres do not also exercise some influence over these processes. The apparent distribution of both kinds of fibres to all sensitive and secreting parts, and the impossibility of isolating them, make the difficulty of deciding this point very great. The difficulty is much greater in the higher than in the lower Vertebrata; for it would appear that, in the same proportion as the centres of the cerebro- spinal system are developed, so is its connection with the processes of organic life more intimate. In frogs, for instance, all the organic functions may be carried on for several days after the removal of the brain and spinal cord, saving only the medulla oblongata for the maintenance of respiration; but in Mammalia, and most of all, in man, even a slight injury of either brain or spinal cord may disturb all the organic functions. The regular movements of the stomach and intestines, the heart, and urinary bladder, independently of the spinal cord or brain, is manifested by numerous experiments in reptiles and Amphibia; but in Mammalia, the separation of these organs from the spinal cord or brain, is sufficient to render their actions feeble and irregular, or, after a time, to stop them altogether. Probably, therefore, the safest view of the question at present is, still to regard all the processes of organic life, in man, as liable to the combined influences of the cerebro-spinal and the sympathetic systems; to consider that those influences may be so combined as that the sympathetic nerves and ganglia may be in man, as in the lower animals, the parts through which the ordinary and constant influence of tbe nervous force is exercised on the organic processes; while the cerebro-spinal nervous centres and their ganglia are the parts from which the proper sympathetic ganglia may derive supplies of nervous force, and from which, more often or more regularly than in the lower animals, the processes of the organic and the animal life are made to work in connection and mutual adaptation. Finally, in regard to the exercise of nervous influence upon the organic processes, it appears proper to consider it as exercised not only through the medium of the circulation, but also more directly; and as affecting, for instance, the organic chemical affinities of the molecules engaged in them; for the changes in the mode of nutri- tion and secretion in a part cannot be altogether explained by mere variations in the diameter of its blood-vessels, or in the quantity of blood supplied to it. Daily observation shows multiform results in secretion and nutrition in cases of disease, of which all have, for a common condition, the enlargement of the blood-vessels of the dis- CILIARY MOTION. 391 eased part; something, therefore, besides the enlargement of the blood-vessels must, in these cases, determine the different events; and so, when the various exercise of nervous influence in a part affects the size of its vessels and the supply of blood, this change cannot be considered as the only source of the change in its mode of secretion or nutrition. CHAPTER XVI. CAUSES AND PHENOMENA OF MOTION. The vital motions of the solid parts of animals present two prin- cipal kinds, differing in the organs of their production, in their phenomena, and in their causes : they are first, the oscillatory mo- tion or vibration of microscopic cilia, with which the surfaces of certain membranes are beset; and secondly, the motion from con- traction of fibres, which either have a longitudinal direction and are fixed at both extremities, or form circular bands : the contraction or shortening of the fibres bringing the fixed parts nearer to each other. CILIARY MOTION. As just said, this consists in the incessant vibration of fine, pellu- cid, blunt processes, about 5055th of an inch long, termed cilia, Fig. 109. Fig. 110. Ficr. 109. Vibratile or ciliated epithelium; a, nucleated cells, resting on their smaller extre- mities ; b, cilia. Fit;. HO. a. b, c, d, e, f. Nucleated ciliary cells: their free ends straight, and furnished with filamonts called cilia, of different shapes; ii, nucleus, a, cilia. situated on the free extremities of the cells of epithelium covering certain surfaces of the body. The form of epithelium on which cilia occur is most commonly of the cylindrical kind (Figs. 109 and 110; 392 CAUSES AND PHENOMENA OF MOTION. see also p. 263); but sometimes, as on the surface lining the cere- bral ventricles, it is of the tesselated variety (p. 263). In man, and probably in Mammalia generally, the ciliary epithe- lium lines the interior of the nasal cavity, except the olfactory re- gion (Todd and Bowman, xxxix. vol. ii. p. 5), and of the frontal and other sinuses communicating with it, the lachrymal canal and sac, and is spread over the mucous surface of both eyelids, but not over the conjunctiva covering the eye itself. From the posterior part of the nasal cavity, it passes to the upper part of the pharynx, which it lines to about opposite the lower border of the atlas : it is also spread over the upper surface of the soft palate, and laterally is continued to the orifice of the Eustachian tube, through which canal it extends into the cavity and membrane of the tympanum. Ciliary epithelium occurs also over the whole extent of the respiratory mu- cous tract, commencing at the larynx, and ceasing only near the terminations of the bronchi (pp. 137-8). It is met with also in the female generative apparatus, commencing about the neck of the uterus, extending along the Fallopian tubes to their fimbriated ex- tremities, and continued for a short distance along the peritoneal surface of the tubes; and in the male it occurs in the epididymis (Hassall). In Mammalia there is no instance of its occupying any part of the urinary mucous surface; but in reptiles it lines the uri- nary tubules to a greater or less extent, and sometimes, though not generally, proceeds within the Malpighian capsules (Bowman, xliii. 184.!; Valentin, xxxiv. bd. viii. p. 92; Kblliker, lxxx. 1845, p. 519). If a portion of ciliary mucous membrane from a living or recently dead animal be moistened, and examined with a microscope, the cilia are observed to be in constant motion, either whirling round their fixed extremities so that their ends describe circles, or waving continually backwards and forwards, and alternately rising and fall- ing with a lashing or fanning movement. During the lashing move- ments each of the cilia performs a motion somewhat similar to that performed during the feathering of an oar in rowing (Quekett, lxxi. May, 1844) : hence the general result of their movements is to pro- duce a continuous current in a determinate direction : and this di- rection is invariably the same on the same surface, being usually towards its external orifice. In the production of such current pro- bably consists the principal use of the cilia, which are thus enabled to propel the fluids or minute particles which come within the range of their influence, and to aid in their expulsion from the body. In the Fallopian tube the direction of the current excited by tbe cilia is towards the cavity of the uterus, and may thus be of service in aiding the passage of the ovum. Of the purposes served by the cilia covering the surface of the cerebral ventricles nothing is known. The nature of the ciliary motion, and the cause on which it de- MUSCULAR MOTION. 393 pends, arc equally obscure. It seems to be alike independent of the will, of the direct influence of the nervous system, and of muscular contraction; for it is involuntary, there is no nervous or muscular tissue in the immediate neighbourhood of the cilia, and it continues for several hours after death or removal from the body, provided the portion of examined tissue is kept moist. Its independence of the nervous system is shown also in its occurrence in the lowest inverte- brated animals apparently unprovided with anything analogous to a nervous system, in its persistence in animals killed by prussic acid, narcotic or other poisons, and after the direct application of narcotics to the ciliary surface, or the discharge of a Leyden jar, or of a gal- vanic shock through it. In their rhythmic action and its persistence after death or removal from the body, the ciliary movements bear a close analogy to those of the heart: and the analogy is made closer by both kinds of movements being diminished by cold and increased by heat.1 MUSCULAR MOTION. Muscular tissue is of two kinds, distinguished by structural pecu- liarities and mode of action. The first kind includes the muscles of organic life, which (with the exception of the fibres of the heart, the lymphatic hearts of birds and reptiles, and the stomach and in- testines of some fish), consist of simple, smooth filaments; the second comprises the muscles of animal life, and the heart, and other ex- ceptions just named, which consist of compound and apparently striated fibres, or tubes including fibrils. The muscles of organic life, or unstriped muscles as they are also called, consist of fibres, or ratber of elongated spindle-shaped fibre- cells, which in their most perfect form are flat, from 4?Yo~ *° 3750" of an inch broad, very clear, granular, and brittle, so that when they break they often have abruptly-rounded or square extremities. Some of them are uniform; many bear nuclei; many are marked along the middle, or, more rarely, along one of the edges, either by a fine, continuous dark streak, or by short, isolated, dark lines, or by dark points arranged in a row or scattered; and between these three kinds of marks there are such gradations as prove that they have all the same origin from nuclei. Fibres such as these are collected in divers numbers in fasciculi, upon which the dark lines just men- tioned sometimes form, by branches which they give off and receive, a sort of network, and sometimes run tortuously, like the nucleus- fibres of the fibro-cellular tissue (Fig. 3, p. 43). Fibres of organic muscle, sucb as are here described, form the proper contractile coats of the digestive canal from the middle of the 1 For the best accounts of Cilia, see Dr. Sharpey (lxxiii. art. Cilia), and Henle (xxxvii.) 394 CAUSES AND PHENOMENA OF MOTION. oesophagus to the external sphincter ani, of the urinary bladder, the trachea and bronchi, the ducts of glands, the gall-bladder, the vesi- culas seminales, the pregnant uterus, and the arteries. This form of tissue also enters largely into the composition of the tunica dartos, and is the principal cause of the wrinkling and con- traction of the scrotum on exposure to cold: the fibres of the cre- master assist in some measure in producing this effect, but are chiefly concerned in drawing up the testis and its coverings towards the inguinal opening. It occurs largely also in the cutis, being espe- cially abundant at the interspaces between the bases of the papillae. Hence, when it contracts under the influence of cold, fear, or any other stimulus, the papillae are made unusually prominent, and give rise to the peculiar roughness of the skin termed cutis anserina or goose-skin. Fibres of this tissue, also, constitute part of the walls of most gland-ducts and lymphatics, and are the chief agents con- cerned in the propulsion of the contents of these canals. The muscles of animal life, or striped muscles, include the whole class of voluntary muscles, the heart, the muscular tissue of the pha- rynx and upper part of the oesophagus, the lymphatic hearts of birds and reptiles, and the stomach and intestines of some fish. The vol- untary muscles are composed of fleshy bundles inclosed in coverings of fibro-cellular tissue, by which each is at once connected with, and isolated from, those adjacent to it. Each bundle is again divided into smaller ones, similarly ensheathed and similarly divisible; and so on, through an uncertain number of gradations, till, just beyond the reach of the unaided eye, one arrives at the primitive fasciculi, or the muscular fibres peculiarly so called. The primitive fasciculi consist of tubes of delicate structureless membrane, the sarcolemma of Mr. Bowman, inclosing a number of filaments. They are cylindriform or prismatic, with five or more sides, according to the manner in which they are compressed by adjacent fasciculi. Their breadth varies in different animals, from g^th to g^th of an inch; in man, from ¥ J0th to ^th, the average of the majority being about 4 ^th. Their most striking, though not constant, characteristics are their pale yellow color, and their being apparently marked by striae, which pass transversely round them, in slightly curved or wavy parallel lines, from T^^0TJth to T3^oth of an inch apart. Other, but generally more obscure, striae~also pass longitudinally over the tubes, and indicate the size and direction of the filaments or primitive fibrillae of which the primitive fasciculus is composed (Figs. 6 and 7, p. 46). The primitive fibrils are the proper contractile tissue of the mus- cle. Each of them is cylindriform, but somewhat flattened, and about TF ^th. of an inch in its greatest thickness. They are marked by transverse impressions, which are at exactly the same distance apart as the stria on the surface of the fasciculus. Hence it is gen- erally concluded, that the striated appearance of the primitive fasci- MUSCULAR TISSUE OF ANIMAL LIFE. 395 culi is produced by the filament being so apposed that the transverse marks on all those near tne surface lie at exactly the same levels. (Fig. 111.) Fig. 111. Stages of the development of striped muscular fibre. 1. Arrangement of the primitive cells in a linear series. After Schwann. 2. The cells united. The nuclei separated, and some broken up; longitudinal lines becom- ing apparent. From a foetal calf three inches long. 3, 4. Transverse stripes apparent. In 3, the nuclei are internal, and bulge the fibre. In 4, they are prominent on the surface. From a foetal calf of two months old. 5. Transverse stripes, fully formed and dark; nuclei disappearing from view. From the human infant at birth. 6. Elementary fibre from the adult, treated with acid; showing the nuclei. Magnified about 300 diameters. Each primitive fasciculus contains several hundreds of the primi- tive fibrils; and when fully formed, they fill all the cavity of the sarcolemma, with the exception of very small interspaces, which seem occupied with a glutinous pellucid fluid. It is only in immature fasciculi that there is an appearance of a central cavity, which is filled either with fluid or with minute granules. At present, there is much question of the true structure of the fibrils, and-of the source of their seeming constrictions, or transverse impressions. Some deny the existence of such constrictions, except when the muscle is contracted, or in some particular condition after death; while others believe that the fibrils are rows of corpuscles, or dises, connected by a homogeneous transparent substance. The trans- verse marks on the fibrils, and the ordinary striae on the fasciculus, correspond to the spaces between the discs. The most recent view on the subject is that published almost simultaneously by Dr. Sharpey (exlix.) and Dr. Carpenter (cl.), according to which the alternate dark and light particles, of which the fibril is composed, have each a quadrilateral, and generally a rectangular form. Every bright particle or space is marked across its centre by a fine, dark, trans- verse line or shadow, by which the space is divided into two 396 CAUSES AND PHENOMENA OF MOTION. Fig. 112. Muscular fibrils of the pig, mag- nified 720 diameters, a. An appa equal parts; and sometimes a bright border may be perceived on either side of the fibril, so that each of the rectangular dark bodies ap- pears to be surrounded with a bright area, having a similar quadrangular outline, as if the pellucid substance inclosed it on all sides (see Fig. 112). These appearances would seem to show that the elementary particles of which the fibril is made up, are little masses of pellucid substance, possibly nucleated cells, presenting a rec- tangular outline, and appearing dark in the centre. Properties of Muscular Tissue. The property of muscular tissue, by which its peculiar functions are exercised, is its contractility, through which the con- traction or shortening of muscles is excited by all kinds of stimuli, applied either directly to the muscles, or indirectly to rentTy'sing'ie^fibrii, showing The them through the medium of their motor quadrangular outline of the com- nerves. This property, although com- ponent particles, their dark central monl b ht int0 action through the part and bright margin, and their J o i_ • 1 . • lines of junction crossing the light nervous system, appears to be inherent in intervals. 6. a longitudinal seg- the muscular tissue, and not derived by ment of a fibre consisting of anum- ^ f th neryes , ggy y 1gt ber of fibrils still connected toge- . . „ v , .r J . ' . ,' ther. The dark cross stripes and it may be manifested in a muscle which light intervals on 6 are obviously is isolated from the influence of the ner- vous system by division of the nerves supplying it, so long as the natural tissue of the muscle is duly maintained by nu- trition ; 2d, it is manifest in a portion of muscle, in which, under the microscope, no nerve-fibre can be traced; and, 3d, it is retained in all the muscles when it may be supposed tbat the func- tion of their nerves is suspended by the inhalation of ether or of chloroform (Harless, lxxx. 1847). If the removal of nervous influence is long continued, as by divi- sion of the nerve supplying a muscle, or in cases of paralysis of long standing, the irritability, i. e., the power of both perceiving and re- sponding to a stimulus, may be lost; but this is chiefly because of the impaired nutrition of the muscular tissue, which ensues through its inaction (J. Beid). The irritability of muscles is also soon lost, unless a supply of arterial blood to them is kept up. Thus, after ligature of the main arterial trunk of a limb, the power of niovinc occasioned by the dark specks and intervening light spaces respec- tively corresponding in the differ- ent fibrils, c. Other smaller col- lections of fibrils. From a prepa- ration by Mr. Lealand. After Dr. Sharpey. CONTRACTION OF MUSCULAR TISSUE. 397 the muscles is partially or wholly lost, until the collateral circulation is established ; and when, in animals, the abdominal aorta is tied, the hind legs are rendered almost powerless (Segalas, xxxii. p. 895). So, also, it is to the imperfect supply of arterial blood to the muscu- lar tissue of the heart, that the cessation of the action of this organ in asphyxia is in some measure due (page 158). Besides the property of contractility, the muscles, especially those of animal life and striated, possess sensibility by means of the sensi- tive nerve-fibres distributed to them. The amount of common sen- sibility in muscles is not great; for they may be cut or pricked with- out giving rise to severe pain, at least in their healthy condition. But they have a peculiar sensibility, or at least a peculiar modifica- tion of common sensibility, which is shown in that their nerves can communicate to the mind an accurate knowledge of their states and position when in action. By this sensibility we are not only made conscious of the morbid sensations of fatigue and cramp in muscles, but acquire, through muscular action, a knowledge of the distance of bodies and their relation to each other, and are enabled to esti- mate and compare their weight and resistance by the effort of which we are conscious in measuring, moving, or raising them. Except with such knowledge of the position and state of each muscle, we could not tell how or when to move it for any required action; nor without such a sensation of effort could we maintain the muscles in contraction for any prolonged exertion*. The mode of contraction in the transversely-striated muscular tissue has been much disputed. The most probable account, which has been especially illustrated by Mr. Bowman (xliii. 1840-1841), is that the contraction is effected by an approximation of the con- stituent parts of the fibrils, which, at the instant of contraction, without any alteration in their general direction, become closer, flatter, and wider; a condition wbich is rendered evident by the approximation of the transverse striae seen on the surface of the fasciculus, and by its increased breadth and thickness. The ap- pearance of the zigzag lines into which it was supposed the fibres are thrown in contraction, is due to the relaxation of a fibre which has been recently contracted, and is not at once stretched again by some antagonist fibre, or whose extremities are kept close together by the contractions of other fibres. The contraction is therefore a simple, and, according to Ed. Weber, an uniform, simultaneous, and steady shortening of each fibre and its contents. What each fibril or fibre loses in length, it gains in thickness: the contraction is a change of form, not of size; it is, therefore, not attended with any diminution in bulk from condensation of the tissue. This has been proved for entire muscles, by making a mass of muscle, or many together, contract in a vessel full of water, with which a fine, jper- pcndicular, graduated tube communicates. Any diminution of the bulk of the contracting muscle would be attended by a fall of fluid ;;i 398 CAUSES AND PHENOMENA OF MOTION. in the tube; but when the experiment is carefully performed, the level of the water in the tube remains the same, whether the muscle be contracted or not (Barzelotti; Mayo, xxxii. p. 886; Valentin, iv., Matteucci, cxxiv.).1 In thus shortening, muscles appear to swell up, becoming rounder, more prominent, harder, and apparently tougher. But this hardness of muscle in the state of contraction is not due to increased firmness or condensation of the muscular tissue, but to the increased tension to which the fibres, as well as their tendons and other tissues, are subjected from the resistance ordinarily opposed to their contraction. When no resistance is offered, as when a muscle is cut off from its tendon, not only is no hardness perceived during contraction, but the muscular tissue is even softer, more extensile, and less elastic than in its ordinary uncontracted state. (Ed. Weber, xv. art Muskelbcwegung). Heat is developed in the contraction of muscles. Becquerel and Breschet found with the thermo-multiplier about 1° of heat pro- duced by each forcible contraction of a man's biceps; and when the actions were long continued, the temperature of the muscle in- creased 2°. It is not known whether this development of heat is due to chemical changes ensuing in the muscle, or to the friction of its fibres vigorously acting: in either case, we may refer to it a part of the heat developed in active exercise, especially by the lower animals. And Nasse suspects that to it is due the higher tempera- ture of the blood in the left ventricle; for he says it is always warmer in the left ventricle than in the left auricle, and that the blood in the latter is but little warmer than that on the right side of the heart. But these experiments need confirmation. Sound is produced when muscles contract forcibly. Dr. Wollas- ton showed that this sound might be easily heard by placing the tip of the little finger in the ear, and then making some muscles con- tract, as those of the ball of the thumb, whose sound may be con- ducted to the ear through the substance of the hand and finger. A low shaking or rumbling sound is heard, the height and loudness of the note being in direct proportion to the force and quickness of the muscular action, and the number of fibres that act together, or, as it were, in time. To this sound of muscular contraction may be as- signed, as already stated (p. 92), the first sound of the heart. In the smooth, or simple muscular fibres, scarcely any of the phe- nomena just described have been observed. The fibres are believed to contract with a simple shortening, but the exact mode, and the phenomena attending it, have not been satisfactorily determined. The two kinds of fibres have characteristic differences in the mode in which they act on the application of the same stimulus; diffe- 1 Edward Weber, however, states that a very slight diminution does take place in the bulk of a contracting muscle; but it is so slight as to be practi- cally of no moment. MUSCULAR IRRITABILITY AFTER DEATH. 399 rences which may perhaps be ascribed as much to their respective modes of connection with the nervous system as to their structures (sec p. 388). When irritation is applied directly to a muscle with striated fibres, or to the motor nerve supplying it, contraction of the part irritated, and of that only, ensues; and this contraction is in- stantaneous, and ceases on the instant of withdrawing the irritation. But when any part with smooth-fibred muscles, e. g., the intes- tines, or bladder, or a duct is irritated, the subsequent contrac- tion ensues more slowly, extends beyond the part irritated, and, with alternating relaxations, continues for some time after the withdrawal of the irritation. Ed. Weber (xv. art. Muskelbewegung) has particularly illustrated the difference in the modes of contrac- tion of the two kinds of muscular fibres by the effects of the electro- magnetic stimulus. The rapidly succeeding shocks, given by this means to the nerves of muscles, excite in all the transversely- striated muscles a fixed state of tetanic contraction, which lasts as long as the stimulus is continued, and on its withdrawal instantly ceases: but in the muscles with smooth fibres they excite, if any movement, only one that ensues slowly, is comparatively slight, alternates with rest, and continues for a time after the stimulus is withdrawn. In their mode of responding to these stimuli, all the voluntary muscles, or those with transverse striae, are alike; but among those with simple fibres there are many differences,—a fact which tends to confirm the opinion, that their peculiarity depends as much or more on their connection with nerves and ganglia than on their own properties. According to Weber, the ureters and gall- bladder are the parts least excited by stimuli: they do not act at all till the stimulus has been long applied, and then contract feebly and in a small extent. The contraction of the caecum and stomach are quicker and wider spread : still quicker those of the iris, and of the urinary bladder if it be not too full. The actions of the small and large intestines, the vas deferens, and pregnant uterus are yet more vivid, more regular, and more sustained; and they require no more stimulus than that of the air to excite them. The heart is quickest and most vigorous of all the muscles of organic life in con- tracting upon irritation, and appears in this, as in nearly all other respects, like the connecting member of the two classes of muscles. All the muscles retain their property of contracting under the influence of stimuli applied to them, or to their nerves, for some time after death, the period being longer in cold-blooded than in warm-blooded Vertebrata, and shorter in birds than in Mammalia. It would seem as if the more a"ctive the respiratory process in the living animal, the shorter is the time of duration of the irritability in tbe muscles after death; and this is confirmed by the comparison of different species in the same order of Vertebrata. But the period during which this irritability lasts, is not the same in all persons, 400 CAUSES AND PHENOMENA OF MOTION. nor in all the muscles of the same persons. In man it ceases, according to Nysten, in the following order: — first, in the left ven- tricle, then in the intestines and stomach, the urinary bladder, right ventricle, oesophagus, iris: then in the voluntary muscles of the trunk, lower and upper extremities; lastly in tbe left and right auricle of the heart. After the muscles of the dead body have lost their irritability or capability of being excited to contraction by the application of a stimulus, they spontaneously pass into a state of contraction, appa- rently identical with that which ensues during life.1 It affects all the muscles of the body; and, where external circumstances do not prevent it, commonly fixes the limbs in that which is their natural posture of equilibrium or rest. Hence, and from the simultaneous contraction of all the muscles of the trunk, is produced a general stiffening of the body, constituting the rigor mortis or post-mortem rigidity. The muscles are not affected exactly simultaneously by the post- mortem contraction, but rather in succession. It affects the neck and lower jaw first; next, the upper extremities, extending from above downwards; and lastly reaches the lower limbs; in some rare instances only, it affects the lower extremities before, or simulta- neously with, the upper extremities. It usually ceases in the order in which it began; first at the head, then in the upper extremities, and, lastly, in the lower extremities. According to Sommer, it never commences earlier than ten minutes, and never later than seven hours, after death; and its duration is greater in proportion to the lateness of its accession. Since the rigidity does not ensue until muscles have lost the capacity of being excited by external stimuli, it follows that all circumstances wbich cause a speedy exhaustion of muscular irri- tability, induce an early occurrence of the rigidity, while conditions by which the disappearance of the irritability is delayed, are suc- ceeded by a tardy onset of this rigidity. Hence its speedy occur- rence and equally speedy departure in the bodies of persons exhausted by chronic diseases; and its tardy onset and long continuance after sudden death from acute diseases. In some cases of sudden death from lightning, violent injuries, or paroxysms of passion, the rigor mortis appears not to occur at all; but this is not always the case. (See lxxi. May 16, 1851.) It may indeed, perhaps, be doubted whether there is really a complete absence of the post-mortem rigidity in any such cases; for the experiments of M. Brown- Sequard with electro-magnetism, make it probable that the rigidity 1 If, however, arterial blood be made to circulate through the body or through a limb, the contraction of the muscles thus supplied with blood, may, according to Brown-Sequard, be suspended, and the muscles again admit of contracting on the application of a stimulus (cxc. Oct. 1851, p. 542; and cci). POST-MORTEM RIGIDITY. 401 may supervene immediately after death, and then pass away with such rapidity as to be scarcely observable. Thus he took five rab- bits, and killed them by removing their hearts. In the first, rigidity came on in ten hours, and lasted 102 hours; in the second, which was feebly electrified, it commenced in seven hours, and lasted 144; in the third, which was more strongly electrified, it came on in two, and lasted 72 hours; in the fourth, which was still more strongly electrified, it came on in one hour, and lasted 20; while in the last rabbit, which was submitted to a powerful electro-galvanic current, the rigidity ensued in seven minutes after death, and passed away in 25 minutes. From this it appears that the more powerful the electric current, the sooner docs the rigidity ensue, and the shorter is its duration; and as the lightning-shock is so much more powerful than any ordinary electric discharge, the rigidity may ensue so early after death and pass away so rapidly as to escape detection. The influence exercised on the onset and duration of post-mortem rigidity by causes which exhaust the irritability of the muscles was well illustrated in further experiments by the same physiologist, in which he found that the rigor mortis ensued far more rapidly, and lasted for a shorter period, in those muscles which had been power- fully electrified just before death, than in the rest which had not been thus acted upon (cxix. 1849). The occurrence of rigor mortis is not prevented by the previous existence of paralysis in a part, provided the paralysis has not been attended with very imperfect nutrition of the muscular tissue. The rigidity affects the involuntary as well as the voluntary muscles, whether they are constructed of striped or unstriped fibres. ^ The rigidity of involuntary muscles with striped fibres is shown in the contraction of the heart after death (p. 85), when it constitutes what has been called concentric hypertrophy. The contraction of the muscles with unstriped fibres is shown by an experiment of Valentin (iv. Bd. ii. p. J>6), who found that if a graduated tube be connected with a portion of intestine taken from a recently-slain animal, filled with water and tied at the opposite end, the water will in a few hours rise to a considerable height in the tube, owing to the con- traction of the intestinal walls. It is yet better shown in the arteries, of which all that have muscular coats contract after death, .and thus present the roundness and cord-like feel of the arteries of a limb lately removed, or a body recently dead. Subsequently they relax, as do all the other muscles, and feel lax and flabby, and lie as if flattened, and with their walls nearly in contact.1 Actions of Muscles.—The simplest division of muscular actions, and one which, for practical use, is most convenient, is into the voluntary and the involuntary actions. But it is comparatively » Several interesting points in relation to post-mortem rigidity may be found in the late Mr. W. F. Barlow's Papers on Muscular Contractions after Death from Cholera (lxxi. 1849-50). 84* 402 CAUSES AND PHENOMENA OF MOTION. useless and uninstructive in the consideration of the general physi- ology of muscular movements; for, as we have seen, the structure of muscles does not exactly correspond with their having habitually the voluntary or the involuntary mode of action; neither can any muscles be said, unconditionally, to be either voluntary, or invol- untary, since many involuntary movements are performed by muscles subject to the will, and many muscles that are commonly independent of the will are liable to be affected by it or other acts of the mind. More than all, whether a muscle is involuntary or not depends not on itself, but on the nervous system; for, if the brain be removed or inactive, all the muscles become involuntary ones. Neglecting, therefore, this distinction, it will be more instructive to follow Tvliiller in an enumeration of the modes in which move- ments may be excited, either in single muscles, or in groups of mus- cles combined for united or opposite actions. 1. The first class of movements may be named automatic, the parts seeming to "have in themselves the power of motion,"1 and not only the power, but the mode and plan. These may include all those muscular actions which are not de- pendent on the will or any other act of the mind; which are either persistent, or periodical with a regular rhythm; and are dependent on normal natural causes seated in the nerves or central organs of the nervous system. The cause of the rhythmic movements may be, as has been shown, either in the sympathetic or the cerebro-spinal nervous centres, but never in nerve-fibres. Of the automatic move- ments dependent chiefly on the sympathetic, the principal are those of the heart, the intestinal canal, uterus, and urinary bladder. The automatic movements of the heart are nearly like those of the animal muscles, quick, and succeeding each other quickly; those of the other organs are more gradual and more enduring, and their inter- vals of rest are much longer. Whether this difference be owing to the different structure of the muscle, or to the nature of the nervous influence, has been already considered but not decided. It is a characteristic of the automatic movements of all the viscera of organic life, that a certain order of succession is observed in the contractions; one part of the viscus contracts before another, and the motipn thus traverses the organ in a determinate direction during each period of the rhythm. In the heart, the motion commences in the venae cavae, and proceeds through the auricles and ventricles, and then, after an interval, is resumed in the venae cavae (p. 84). In the intestine, the movement travels in a vermicular manner from above downwards; and a second movement, beginning at the upper part of the intestine before the first has completed its course, affects the parts in the same order. The action of stimuli on these organs xWhat Miiller names "movements excited by heterogeneous stimuli," are here omitted, because of the doubt whether any such occur naturally. AUTOMATIC MUSCULAR MOVEMENTS. 403 endowed with automatic motion does not generally alter the order of the contractions, unless it be excessive and abnormal; but it influ- ences the rapidity and force of the contractions; thus stimuli, whether external or internal, acting on the heart, cause it to beat quicker and ulore forcibly, and motions of the intestinal canal are rendered both more energetic and quicker by external irritation, as when the intes- tine is exposed to the air; or by internal irritation of its mucous membrane, as in diarrhoea. Such irritation, also, may proceed from the nervous centres; so disorder of the spinal cord may produce spasmodic automatic movements of the intestinal canal and uterus : and irritation of the cceliac ganglion may accelerate the movements of the intestines, but generally in all these cases, the natural mode, i. e., the plan and order of the movements is maintained. As already stated, the constant and primary cause of the rhythmic contractions of these and of all the organic muscles is probably con- nected with the mode of action of the sympathetic nerve and its ganglia. Their continuance, when the organs are removed from the body, proves that they do not depend on the brain or spinal cord; and their purposive and orderly character indicates that they are directed through nervous centres, such as are found only in the sympathetic system. The supposed mode of action of the sympa- thetic ganglia in determining such movements is stated at pp. 100, 225, etc. But there are also automatic movements which are dependent on the central organs of the cerebro-spinal nervous system. Such are the involuntary movements of respiration, the nervous centre govern- ing which is in the medulla oblongata. These have been sufficiently considered (pp. 157, 342). Such also are the motions of the muscles of the eye and of the iris during sleep, in which the eye is generally turned somewhat inwards and upwards, and the iris is con- tracted, although light is excluded; and such, probably, the normal and habitual winking of the eye-lids for the purpose apparently of maintaining the moisture of the conjunctiva. All these movements have some kind of time or rhythm. Other automatic movements controlled by the cerebro-spinal centres are persistent: such are those of the sphincters. For, although we have voluntary power over these muscles to strengthen their contraction, yet their action continues independently of volition, during sleep as well as in the waking state, and it cannot be voluntarily interrupted, except by everting a counter pressure against it by their antagonist muscles. The principal sphincter among the animal muscles is the sphincter ani, the force and impulse to the contraction of which are derived from the spinal cord (p. 331), from which a constant motor impulse seems to be directed to it. 2. The second class of muscular movements may be named antagonistic movements. There are groups of muscles opposed to each other iu their action in almost all parts of the body. The ex- 404 CAUSES AND PHENOMENA OF MOTION. tremities have flexors and extensors, supinators and pronators, abduc- tors and adductors, and rotators inwards and rotators outwards. When the muscles of one lateral half of the face are paralyzed, those of the opposite half of it draw the features towards their side. The tongue, when one half of it is paralyzed, may be drawn to the opposite side. Hence it would appear that the muscular fibres, especially those of animal life, are constantly in a state of slight contraction; and that the state of inaction of the different parts of our body does not indi- cate an absolutely relaxed condition of the muscles, but rather that the different groups of muscles antagonize and balance each other; and that when the position of a part is changed from the medium state of apparent rest, one or more of the muscles, already in a state of antagonistic action, are merely thrown into more powerful con- traction. When muscles have few or no antagonists, they always tend to give to the parts on which they act a determinate position. Thus there are numerous muscles which rotate the thigh outwards, while the rotation inwards can be effected but feebly by the tensor vaginae femoris. Hence arises the involuntary tendency to the turning out- wards of the whole limb in walking, sitting, or lying. The sphincters are also muscles which have no proper antagonists. The constant occlusion of the orifices of the viscera by the sphincters can be ac- counted for, therefore, by the fact of the contraction of muscles not wholly ceasing in the state of apparent rest, and of their having no antagonizing muscles ; without its being necessary to suppose that a constant current of nervous influence is transmitted specially to them. 3. Reflex Movements.—The character of the reflected movements has been already explained (pp. 317, etc.). They include all muscu- lar actions which arise from impressions on centripetal nerves exci- ting motor nerves to action through the intervention of the nervous centres; and arrange themselves into two principal groups, of which the first may include the reflex movements determined by the brain and spinal cord. 4 Of the Associate or Consensual Movements, the peculiarity con- sists in the voluntary impulse to one motion giving rise to the pro- duction of other motions contrary to, or independently of, the will; thus, whenever the eye is voluntarily directed inwards, the iris con- tracts. The less perfect the action of the nervous system, the more frequently do associate movements occur. It is only by education that we acquire the power of confining the influence of volition, in the production of voluntary motions, to a certain number of nervous fibres issuing from the brain. An awkward person in performing one voluntary movement makes many others, which are produced involuntarily by consensual nervous action. In the piano forte player we have an example, on the other hand, of the faculty of in- sulation of the nervous influence in its highest perfection. The MOVEMENTS DEPENDENT ON STATES OF MIND. 405 motions most prone to be associated involuntarily are those of the corresponding parts of the two sides of the body : as the motions of the hides, of the muscles of the ear, of the eye-lids, and of the ex- tremities in the attempt to effect opposed motions. Some of the most remarkable facts illustrating the association and antagonism of muscular actions are presented by the muscles which move the eyes (pp. 305—0). The organic muscles also are, in some measure, subject to the laws of association. The increased frequency and force of the heart's action during muscular exertions of the body, are probably, in some measure, owing to this cause. The action of the voluntary muscles has an influence on that of the intestinal canal, and on that of the urinary bladder. Every one is aware how beneficial muscular exer- cise is in preserving the regularity of the muscular action of the in- testines, and the regularity of excretion. 5. Of the movements dependent on certain states of the mind, there are three classes: those dependent on mere ideas passing through the mind; those arising from the passions, emotions, or affections; and voluntary movements. Certain groups of muscles of the animal system are in a constant state of proneness to involuntary motion, owing to the susceptibility of their nerves, or rather of the parts of the brain from which they arise, to be excited by ideas. Thus all the respiratory muscles, in- cluding those supplied by the facial nerve, may be excited to action merely by particular states of the mind. Any sudden change in the state of the mind, a sudden change of thought, such as occurs when the idea of the ridiculous arises in the mind, without any passion being excited, is capable of giving rise to a corresponding action of the nerves, evidenced in the muscles of the face and the respiratory muscles. Yawning, inasmuch as it can be excited by the mere idea, or by seeing or hearing another yawn, belongs to the same class of movements. The disposition to the movements of the features and the respiratory muscles that constitute laughing and yawning, exists previously; and is manifested when the idea gives to the nervous force the determinate direction. Ideas of fearful or detestable objects suddenly excited, even when called up by mere fictions, occasion, in persons of excitable temperament, the motion of shuddering; and the same occurs, sometimes, from the mere thought of a disgusting medicine: vomiting, indeed, may be produced by the mere recollec- tion of a disagreeable taste. . It is, again, principally the respiratory portion of the nervous sys- tem which is involuntarily excited to the production of muscular actions by the passions and emotions of the mind. The change in the state of the brain seems to be propagated to the medulla oblon- gata, which causes a change of action in the respiratory muscles, through the medium of their nerves, including the facial nerve, which is preeminently the nerve of expression. 406 CAUSES AND PHENOMENA OF MOTION. The exciting passions give rise to spasms, and frequently even to convulsive motions, affecting the muscles supplied by the respiratory and facial nerves. Not only are the features distorted, but the actions of the respiratory muscles are so changed as to produce the move- ments of crying, sighing, and sobbing. During the sway of depres- sing passions, such as fear, or terror, all the muscles of the body be- come relaxed,—the motor influence of the brain and spinal cord being depressed. The feet will not support the body, the features hang as without life, the eye is fixed, the look is completely vacant, and void of expression, the voice feeble or extinct. Frequently the state of the feelings, under the influence of passion, is of a mixed character; the mind is unable to free itself from the depressing idea ; yet the effort to conquer this gives rise to an exciting action in the brain. In these mixed passions, the expression of relaxation in cer- tain muscles,—in the face, for example,—may be combined with the active state of others; so that the features are distorted, whether in consequence merely of the antagonizing action of the opposite mus- cles being paralyzed, or by a really convulsive contraction. Disor- orderly as the mode in which these emotional influences are exercised may seem to be, yet to each emotion certain combined movements are appropriated, and become expressive of it. The nerves of certain groups of muscles seem to be naturally combined to act together when the appropriate emotion is felt, as the respiratory nerves are for the common respiratory movements. Like these movements, also, the emotional movements may be controlled by the will, though essen- tially independent of it, and though, when the stimulus exciting them is very strong, they may occur in opposition to the effort of the will. With these actions of the muscles of animal life, those of organic life are often associated; the disturbed action of the heart during mental emotions is an instance of such association. Of the voluntary movements we have already spoken in connection with the physiology of the motor nerves and the brain. In all the former instances, we are scarcely, or not at all, conscious of the move- ments that take place, or are only conscious of them by other senses than the muscular sense, as by seeing the movement. And this may be connected with the probability that the central organs determin- ing these movements are not the organs in which the mind can either clearly discern sensations, or deliberately exercise the will (see p. 354). In the voluntary motions we have both consciousness and intention; though not in all cases an equal degree of either, for in movements habitually performed we are hardly either conscious or intent. We have have no knowledge how the will acts in the brain, through which alone its full influence can be directed to the nerves (see p. 354); but the influence of the will on the motor fibres is not a soli- tary fact of its kind. Through the brain we have the power of voluntarily directing the mind to all the cerebral and spinal nerves, VOLUNTARY MOVEMENTS. 407 even to the nerves of common sensation, and the nerves of special sense; we exercise this power whenever we attend to sensations. If two persons are addressing different words to our opposite ears, we can by attention follow what is said by the one, while we leave what the other says unnoticed. The same circumstance is observed in the case of simultaneous impressions on different senses. Accord- ing to the direction we give our attention, we cease to see distinctly while we exert the power of hearing to a greater degree, and vice versa; for only one object at a time can be taken cognizance of by the faculty of attention (see p. 314). Thus, we have the power of directing the attention according to our will; the will has here the same influence as in the production of voluntary motions. The only difference is, that in the latter case the motor nerve-fibres, previously in a state of repose, are excited to action; while in attending to the impressions on the sensitive nerves, the action of the will consists in rendering the sensation more intense or distinct. Neither is the power of the will limited to the motor and sensitive nerves; it also influences the mental operations; we have the power of voluntarily directing our thoughts. In short, we see that the voluntary effort of the mind can be directed upon motor or sensitive nerves, or made to affect the mental operations: an act of volition is nothing else than the voluntary and conscious direction of the nervous forces in the brain upon different cerebral apparatus; and on the part of the brain subjected to this voluntary action of the nervous principle it depends, whether the effect shall be a muscular movement, a more distinct perception, or an idea connected with some sensible object. As a general rule, a voluntary movement is more difficult the smaller the number of nervous fibres required to be excited, and the smaller the part to be moved. The nervous force more readily ex- cites many than few nervous fibres to action; hence the tendency to the associate movements described at page 404. It is doubtful whe- ther distinct portions of a long muscle can be voluntarily excited to independent and separate action. The action of the nervous force is therefore less capable of localization when excited by volition than when determined by accidental involuntary stimuli. From external causes very small parts of a muscle, for example, of the biceps of the arm, are seen to contract separately; but this never occurs from voluntary influence. The power of confining the voluntary excite- ment of the nervous principle to distinct groups of fibres is increased by much exercise, and the more frequently certain groups of fibres are excited to action by the influence of the will, the more capable do they become of isolated action; this is exemplified in performers on the piano-forte, etc. .Motions very frequently performed occur at last whenever the nervous influence in the brain receives, in the slightest degree, the direction necessary to produce them; as if the conducting power of the nervous fibres, and the combining power of the nervous 408 VOICE AND SPEECH. centros, increased with the frequency of their excitement. Hence the facility of the habitual movements; hence the mimic move- ments of the hands in speaking; and thus obscure ideas, without any distinct consciousness, often give rise to determinate and ap- propriate motions, provided these motions have been previously many times excited in the same manner; the effort of the will in producing these movements being as obscurely felt as the sensation or idea that led to them. CHAPTEB XVII. OF VOICE AND SPEECH. In nearly all air-breathing vertebrate animals there are arrange- ments for the production of sound, or voice, in some part of the respiratory apparatus. In many animals, the sound admits of being variously modified and altered during and after its production ; and, in man, one of the results of such modification is speech. Mode of Production of the Human Voice. It has been proved, by observations on living subjects, as well as by experiments on the larynx taken from the dead body, that the sound of the human voice is the result of the inferior laryngeal ligaments, or vocal cords, which bound the glottis, being thrown into vibrations by currents of expired air impelled over their edges. Thus, if a free opening exists in the trachea, the sound of the voice ceases, but returns on the opening being closed. An opening into the air-passages above the glottis, on the contrary, does not prevent the voice being formed. M. Magendie, also, has shown that the voice is not lost, though the epiglottis, the superior ligaments of the larynx, and the upper part of the arytenoid cartilages be injured. The same may be observed in cases of disease; and in injuries, when the vocal cords are exposed, they may be seen vibrating during the emission of sound. Injury of the laryngeal nerves supplying the muscles which move the vocal cords puts an end to the formation of vocal sounds; and when these nerves are divided on both sides, the loss of voice is complete. Moreover, by forcing a current of air through the larynx in the dead subject clear vocal sounds are pro- duced, though the epiglottis, the upper ligaments of the larynx, the ventricles between them and the inferior or vocal ligaments, and the upper part of the arytenoid cartilages, be all removed; provided the vocal cords remain entire, with their points of attachment, and are kept tense and so approximated that the fissure of the glottis may be narrow. STRUCTURE OF THE VOCAL APPARATUS.1 409 The vocal ligaments, therefore, may be regarded as the proper organs of the mere voice: the modifications of the voice are effected by other parts as well as by them. Their structure is adapted to enable them to vibrate like tense membranes, for they contain a large quantity of elastic tissue; and they are so attached to the cartilaginous parts of the larynx that they can be made tense either by the depression of the thyroid cartilage (Fig. 113, E cg), towards Fig. 113. External and sectional views of the larynx. A n b, the cricoid cartilage; e c G, the thyroid cartilage; a, its upper horn; c, its lower horn, where it is articulated with the cricoid; f, the arytenoid cartilage; e p, the vocal ligament; A K, crico-thy roideus muscle; rem, thyro-aryte- noidcus muscle; xe, cricoary tenoideus lateralis; s, transverse section of arytenoideus trans- versus; mn, space between thyroid and cricoid; bl, projection of axis of articulation of arytenoid with thyroid. the cricoid cartilage (Fig. 113, AnB), by means of the crico-thyroid muscles (Fig. 113, A k) ; or by the retraction of the arytenoid carti- lages (Fig. 114, N F, N F, p. 411), which are moved backwards by the posterior crico-arytenoid muscles (Fig. 114, N x), at the same time that they are approximated by the posterior arytenoid (Fig. 113, s). The length of the fissure of the glottis (Fig. 114, be- tween vv) depends on the degree to which the cords are thus stretched; and their degree of tension probably depends not only on the degree in which their stretching is resisted by their proper tissue, but also, in some measure, on the action of the thyroaryte- noid muscles (Fig. 114, v kf), which are closely connected to them along their whole length. 35 410 VOICE AND SPEECH. Fig. 114. Bird's-eye view of larynx from above. G e h, the thyroid cartilage, embracing the ring of the cricoid ruxw, and turning upon the axis x z, which passes through the lower horn c, Fig. 113; n f, n F, the arytenoid cartilages connected by the ary tenoideus transversus; iv,it, the vocal ligaments; Nx, the right crico-arytenoideus lateralis (the left being removed); vfc/, the left thyro-arytenoideus (the right being removed); N I, N I, the crico-arytenoidei postici; B b, the crico-arytenoid ligaments. The aperture of the glottis is narrowed by the approximation of the arytenoid cartilages, which is effected by the arytenoid muscles: it is dilated by the lateral crico-arytenoid (nx), which draw the arytenoid cartilages asunder. The experiments of the Bev. Mr. Willis (cxliii. 1832), on instru- ments made in imitation of the larynx, have shown that, besides being made tense, the vocal cords, in order to produce a proper vocal sound, must have their inner edges parallel. In the ordinary position of the glottis, during respiration without vocalization, he supposes that the lips of the glottis are inclined from each other (as at a a Fig. 116, p. 411, which is an imaginary transverse perpendicular section of the vocal tube), and that to produce voice they must assume the parallel state (as at aa, Fig. 115, p. 411); and he attributes to the thyro-arytenoid muscles the office of placing the ligaments in this position. In vocalizing, the ligaments vibrate in their entire breadth, and with them the thyro-arytenoid muscles, and (to an extent corres- ponding to the force with which they vibrate) the adjacent elastic tissues of the larynx and other parts, and the air in and beyond the respiratory passages. For the deepest notes, the vocal ligaments are much relaxed by the approximation of the thyroid to the arytenoid cartilages. The lips or margins of the glottis are, in this state of the larynx, not only devoid of tension—tbey are, when at rest, even wrinkled—but they become stretched by the current of air, and thus ACTION OF THE VOCAL CORDS. 411 Fie;. 115. Fig- 116. a--- Figs. 115,116. a a. Vocal cords. (From Prof. Willis.) acquire the degree of tension necessary for vibration. From the deepest note thus produced, the vocal sounds may be raised about an octave by allowing the vocal cords to have the slight degree of ten- sion which the elastic crico-thyroid ligament can give them, by draw- ing the thyroid cartilage towards the cricoid. The medium state, in which the cords are neither relaxed and wrinkled nor stretched, is the condition for the middle notes of the natural voice, and those which are most easily produced in singing. (The ordinary tones of the voice in speaking are intermediate between these and the deep bass notes). The higher notes of the natural voice are produced by the lateral compression of the vocal cords, and the narrowing of the space between them by means of the thyro-arytenoid muscles; and further, by increasing the force of the current of air.1 In the quiescent state, the aperture of the glottis is widely open and somewhat triangular, the base of the triangle corresponding to the space between the separated arytenoid cartilages. In inspiration the glottis is slightly dilated, in expiration contracted; and at the moment of the emission of sound it is more narrowed, the margins of the arytenoid cartilages being brought into contact, and the edges of the vocal cords approximated and made parallel. The degree of approximation usually corresponds to the height of the note pro- duced ; but probably not always, for the width of the aperture has no essential influence on the height of the note, as long as the vocal cords have the same tension; only, with a wide aperture, the tone is more difficult to produce, and is less perfect, the rushing of the air through the aperture being heard at the same time. No true vocal sound is produced at the posterior part of the aper- ture of the glottis, that, viz., which is formed by the space between the arytenoid cartilages. For, as Miiller's experiments showed, if 1 For the laws regulating the vibration of membranous tongues, and other sounding bodies, and for further details of the mode of production of the voice and of the circumstances by which it is modulated, consult Miiller. 412 VOICE AND SPEECH. the arytenoid cartilages be approximated in such a manner that their anterior processes touch each other, but yet leave an opening behind them as well as in front, no second vocal tone is produced by the passage of the air through the posterior opening, but merely a rust- ling or bubbling sound; and tbe height or pitch of the note pro- duced is the same whether the posterior part of the glottis be open or not, provided the vocal cords maintain the same degree of tension. Vocal sounds can be produced not only when the lips of the glottis are separated by a narrow interval, but even when to the eye they appear to be in contact, especially if the vocal cords are much relaxed; in which case the vibrations of the lips of the glottis are very strong. The notes emitted in such a condition of the glottis are stronger and fuller; but, provided the length of the cords be the same, and the tension in both cases equally slight, the height of the note is not influenced by the cords being in contact, or by their being separated by a narrow interval. The epiglottis, by being pressed down so as to cover the superior cavity of the larynx, serves to render the notes deeper in tone, and at the same time somewhat duller, just as covering the end of a short tube placed in front of caoutchouc tongues lower the tone. In utter- ing very deep tones during life, we evidently employ the epiglottis in this way; at least, such seems to be the object of the retraction and depression of the tongue while we press down the head in front, in endeavoring to produce very deep notes. In no other respect does the epiglottis appear to have any effect in modifying the vocal sounds.1 Application of the Voice in Singing and Speaking. The notes of the voice thus produced may observe three different kinds of sequence. The first is the monotonous, in which the notes have all nearly the same pitch, as in ordinary speaking; the variety of the sounds of speech being owing to articulation in the mouth. In speaking, however, occasional syllables generally receive a higher intonation for the sake of accent. In poetry there is rhythm in ad- dition to the accent, but the modulation of music is wanting. The second mode of sequence is the successive transition from high to low notes, and vice versa, without intervals; such as is heard in the sounds, which, as expressions of passion, accompany crying in men, and in the howling and whining of dogs. The third mode of sequence of the vocal sounds is the musical, in which each sound has a determinate number of vibrations, and the number of vibra- 1 The influence which the two portions of the vocal tube, viz., that fur- nished by the trachea and that by the air-passages in front of the larynx, exercise in modulating the voice is not yet satisfactorily determined. For observations on the subject consult Miiller (I. c); Mr. Bishop (clxxxi. 1836); and Mi Willis (cxliii. 1832). VARIETIES ACCORDING TO SEX AND AGE. 413 tions in the successive sounds have the same relative proportions as characterize the notes of the musical scale. The compass of the voice in different individuals comprehends one, two, or three octaves; in singers,—that is, in persons apt for singing, —it extends to two or three octaves. But the male and female voices commence and end at different points of the musical scale. The lowest note of the female voice is about an octave higher than the lowest of the male voice; the highest note of the female voice about an octave higher than the highest of the male. The compass of the male and female voices taken together, or the entire scale of the human voice, includes about four octaves. The principal difference between the male and the female voice is, therefore, in their pitch; but they are also distinguished by their tone,—the male voice is not so soft. The voice presents other varieties besides the male and female; there are two kinds of male voice, technically called the bass and tenor, and two kinds of female voice, the contr'alto and soprano, all differing from each other in tone. The bass voice usually reaches lower than the tenor, and its strength lies in the low notes; while the tenor voice extends higher than the bass. The contr'alto voice has generally lower notes than the soprano, and is strongest in the lower notes of the female voice; while the soprano voice reaches higher in the scale. But the difference of compass, and of power in different parts of the scale, are not the essential distinctions between the different voices; for bass singers can sometimes go very high, and the contr'alto frequently sings the high notes like soprano singers. The essential difference between the bass and tenor voices, and between the contr'alto and soprano, consists in their tone or "timbre," which distinguishes them even when they are singing the same note. The qualities of the barytone and mezzo-soprano voices are less marked; the barytone being intermediate between the bass and tenor, the mezzo-soprano between the contr'alto and soprano. They have also a middle position as to pitch in the scale of the male and female voices. The different pitch of the male and the female voice depends on the different length of the vocal cords in the two sexes; their rela- tive length in men and women being as three to two. The difference of the two voices in tone or " timbre" is owing to the different nature and form of the resounding walls, which in the male larynx are much more extensive, and form a more acute angle anteriorly. The different qualities of the tenor and bass, and of the alto and soprano voices, probably depend on some peculiarities of the lio-a- ments and the membranous and cartilaginous parietes of the laryn- geal cavity, which are not at present understood, but of which we may form some idea, by recollecting that musical instruments made of different materials, e. g., metallic and gut-strings, may be tuned 414 VOICE AND SPEECH. to the same note, but that each will give it with a peculiar tone or " timbre." The larynx of boys resembles the female larynx ; their vocal cords before puberty have not two-thirds the length which they acquire at that period; and the angle of their thyroid cartilage is as little pro- minent as in the female larynx. Boys' voices are alto and soprano, resembling in pitch those of women, but differing somewhat from those in tone, and louder. But, after the larynx bas undergone the change produced during the period of development at puberty, the boys' voice becomes bass or tenor. While the change of form is taking place, the voice is said to crack; it becomes imperfect, fre- quently hoarse and crowing, and is unfitted for singing until the new tones are brought under command by practice. In eunuchs, who have been deprived of the testes before puberty, the voice does not undergo this change. The voice of most old people is deficient in tone, unsteady, and more restricted in extent: the first defect is owing to the ossification of the cartilages of the larynx and the altered condition of the vocal cord; the want of steadiness arises from the loss of nervous power and command over the muscles; the result of which is here, as in other parts, a tremulous motion. These two causes combined render the voice of old people void of tone, unsteady, bleating, and weak. In any class of persons arranged, as in an orchestra, according to the characters of voices, each would possess, with the general charac- teristics of a bass, or tenor, or any other kind of voice, some pecu- liar character by which his voice would be recognised from all the rest. The conditions that determine these distinctions are, how- ever, quite unknown. They are probably inherent in the tissues of the larynx, and as indiscernible as the minute differences that cha- racterize men's features; in likeness to which one often observes hereditary and family peculiarities of voice as well marked as those of the limbs or face. Most persons, particularly men, have the power, if at all capable of singing, of modulating their voices through a double series of notes of different character; namely, the notes of the natural voice, or chest-notes, and the falsetto notes. The natural voice, which alone has been hitherto considered, is fuller, and excites a distinct sensa- tion of much stronger vibration and resonance than the falsetto voice, which has more a flute-like character. The deeper notes of the male voice can be produced only with the natural voice, the highest with the falsetto only; the notes of middle pitch can be produced either with the natural or falsetto voice; the two registers of the voice are, therefore, not limited in such manner that one ends when the other begins, but they run in part side by side. The natural, or chest-notes, are produced by the ordinary vibra- tions of the vocal cords. The mode of production of the falsetto notes is still obscure. By Midler they are thought to be due to VARIETIES IN STRENGTH OF VOICE. 415 vibrations of only the inner borders of the vocal cords. In the opinion of Petrequin and Diday (xix.), they do not result from vibrations of the vocal cords at all, but from vibration of the air passing through the aperture of the glottis, which they believe as- sumes, at such times, the contour of the embouchure of a flute. Others (considering some degree of similarity which exists between the falsetto notes and the peculiar tones, called harmonic, which are produced when, by touching or stopping a harp-string at a particular point, only a portion of its length is allowed to vibrate) have supposed that, in the falsetto notes, portions of the vocal ligaments are thus isolated and made to vibrate while the rest are held still. The question cannot yet be settled: but any one in the habit of singing may assure himself, both by the difficulty of passing smoothly from one set of notes to the other, and by the necessity of exercising himself in both registers lest he should become very de- ficient in one, that there must be some great difference in the modes in which their respective notes are produced. The strength of the voice depends partly on the degree of capa- bility of vibration of the vocal cords; and partly on the fitness for resonance of the membranes and cartilages of the larynx, of' the parietes of the thorax, lungs, and cavities of the mouth, nostrils, and communicating sinuses. It is diminished by anything which interferes with such capability of vibration. The intensity or loud- ness of a given note cannot be rendered greater by merely increasing the force of the current of air through the glottis; for increase of the force of the current of air, cceteris paribus, raises the pitch both of the natural and the falsetto notes. Yet, since a singer pos- sesses the power of increasing the loudness of a note from the faintest "piano" to "fortissimo" without its pitch being altered, there must be some means of compensating the tendency of the vocal cords to emit a higher note when the force of the current of air is increased. This means evidently consists in modifying the tension of the vocal cords. When a note is rendered louder and more intense, the vocal cords must be relaxed by remission of the muscular action, in proportion as the force of the current of the breath through the glottis is increased. When a note is rendered fainter, the reverse of this must occur. The length of the larynx and trachea below the vocal ligaments has, according to Miiller, no perceptible influence in the tone or pitch of the voice;—be thinks that the elongation of the vocal tube in front of the glottis by the descent of the larynx, only facilitates the formation of the deep notes, and the shortening of the tube by the ascent of the larynx that of the high notes. Mr. Bishop states, however, that the trachea is not really lengthened by the ascent of the larynx; he finds that it is raised out of the thorax nearly to the same extent as the larynx is elevated; he therefore concludes, that an absolute shortening of the entire vocal tube, including the trachea 416 VOICE AND SPEECH. and the cavities above the glottis, is produced by the elevation of the larynx towards the base of the skull. But the variation in the length of the tube being insufficient to render it capable of adjust- ing itself to the whole range of vocal tones, both he and Mr. Wheat- stone (clxxxii. p. 373) suppose that the defect is supplied by the varying tension of the walls of the trachea, and by the diminished diameter of the trachea during the ascent of the larynx. A still further influence on the voice is attributed to the trachea by Mr. W'heatstone. He has observed that a column of air may not only vibrate, by reciprocation with another body whose vibrations are isochronous with its own, but also when the number of its own vibra- tions are any multiple of those of the sounding body. Such would be the vibrations of the column of air in the trachea divided into harmonic lengths, with relation to the vibrations of the vocal cords. The falsetto notes, he suggests, may be the result of the vibrations of the harmonic subdivisions of the column of air in the trachea. The arches of the palate and the uvula become contracted during the formation of the higher notes: but their contraction is the same for a note of given height, whether it be falsetto or not: and in either case the arches of the palate may be touched with the finger, without the note being altered. Their action, therefore, in the pro- duction of the higher notes, seems to be merely the result of involun- tary associate nervous action, excited by the voluntarily increased exertion of the muscles of the larynx. If the palatine arches con- tribute at all to the production of the higher notes of the natural voice and the falsetto, it can only be by their increased tension strengthening the resonance. The office of the ventricles of the larynx is evidently to afford a free space for the vibrations of the lips of the glottis : they may be compared with the cavity at the commencement of the mouth-piece of trumpets, which allows the free vibration of the lips.1 SPEECH. Besides the musical tones formed in the larynx, a great number of other sounds can be produced in the vocal tube, between the glot- tis and the external apertures of the air-passages, the combination of which sounds into different groups to designate objects, proper- ties, actions, etc., constitutes language. The languages do not em- ploy all the sounds which can be produced in this manner, the com- bination of some with others being often difficult. Those sounds 1 Many of the conclusions respecting the physiology of the human voice which are stated in the foregoing pages are derived from, or illustrated by, experiments with apparatus made in imitation of the larynx; for the com- plete account of these, and for suggestions how they may be yet further applied to the study of this part of physiology, consult the elaborate chapters by Miiller; and the papers of Willis (cxliii. 1832); Wheatstone (clxxxii.) ; Bishop (clxxxi. 1836); and the earlier writers to whom Miiller refers. SPEECH: CONSONANTS AND VOWELS. 417 which are easy of combination enter, for the most part, into the for- mation of the greater number of languages. Each language contains a certain number of such sounds, but in no one are all brought to- gether. On the contrary, different languages are characterized by the prevalence in them of certain classes of these sounds, while others are less frequent or altogether absent. The sounds produced in speech, or articulate sounds, are com- monly divided into vowels and consonants; the distinction between which arc that the sounds for the former are generated in the larynx, while those for the latter are produced by interruption of the cur- rent of air in some part of the air-passages above the larynx. The term consonant has been given to these because several of them are not properly sounded, except consonantly with a vowel. Thus, if it be attempted to pronounce aloud the consonants, b, h, and g, or their modifications p, t, k, the intonation only follows them, in their combination with a vowel. To recognise the essential properties of the articulate sounds, we must, according to Miiller, first examine them as they are produced in whispering, and then investigate which of them can also be uttered in a modified character conjoined with vocal tone. By this procedure we find two series of sounds : in one the sounds are mute, and cannot be uttered with a vocal tone; the sounds of the other series can be formed independently of voice, but are also capable of being uttered in conjunction with it. All the vowels can be expressed in a whisper without vocal tone, that is, mutely. These mute vowel-sounds differ, however, in some measure, as to their mode of production, from the consonants. All the mute consonants are formed in the vocal tube above the glottis, or in the cavity of the mouth or nose, by the mere rushing of the air between surfaces differently modified in disposition. But the sound of the vowels, even when mute, has its source in the glottis, though the vocal cords are not thrown into the vibrations necessary for the production of voice; and the sound seems to be produced by the passage of the current of air between the relaxed vocal cords. The same vowel-sound- can be produced in the larynx when the mouth is closed, the nostrils being open, and the utterance of all vocal tone avoided. This sound, when the mouth is open, is so modified by varied forms of the oral cavity, as to assume the cha- racters of the vowels a, e, i, o, u, in all their modifications. The cavity of the mouth assumes the same form for the articula- tion of each of the mute vowels as for the corresponding vowel when vocalized; the only difference in the two cases lies in the kind of sound emitted by the larynx. Kratzenstein and Kempelen have pointed out that tbe conditions necessary for changing one and the same sound into the different vowels, are differences in the size of two parts__the oral canal and the oral opening; and the same is the case with roo-ard to the mute vowels. By oral canal, Kempelen 418 VOICE AND SPEECH. means here the space between the tongue and palate: for the pro- nunciation of certain vowels both the opening of the mouth and the space just mentioned are wide; for the pronunciation of other vowels both are contracted; and for others one is wide, the other contracted. Admitting five degrees of size, both of the opening of the mouth and of the space between the tongue and palate, Kempelen thus states the dimensions of these parts for the following vowel sounds:— Vowel. Sound. Size of oral opening. Size of oral canal. a as in 'far' 5.......................................3 a " 'name' 4.......................................2 e " 'theme' 3.......................................1 o " 'go' 2.......................................4 oo " 'cool' 1.......................................5 Another important distinction in articulate sounds is, that the utterance of some is only of momentary duration, taking place during a sudden change in the conformation of the mouth, and being inca- pable of prolongation by a continued expiration. To this class be- long b, p, d, and the hard g. In the utterance of other consonants the sounds may be continuous; they may be prolonged, ad libitum, as long as a particular disposition of the mouth and a constant expi- ration are maintained. Among these consonants are h, m, n, f, s, r, I. Corresponding differences in respect to the time that may be occu- pied in their utterance exist in the vowel-sounds, and principally constitute the differences of long and short syllables. Thus, the a as in " far" and " fate," the o as in " go" and " fort," may be in- definitely prolonged; but the same vowels (or more properly differ- ent vowels expressed by the same letters), as in " can" and "fact," in "dog" and "rotten," cannot be prolonged.1 All sounds of the first or explosive kind are insusceptible of com- bination with vocal tone ("intonation"), and are absolutely mute; nearly all the consonants of the second or continuous kind may be attended with " intonation." The peculiarity of speaking, to which the term ventriloquism is applied, appears to consist merely in the varied modification of the sounds produced in the larynx, in imitation of the modifications which voice ordinarily suffers from distance, etc. From the obser- vations of Miiller and Colombat (xxxviii. 1840) it seems that the essential mechanical parts of the process of ventriloquism consist in taking a full inspiration, then keeping the muscles of the chest and neck fixed, and speaking with the mouth almost closed, and the lips and lower jaw as motionless as possible, while air is very slowly ex- pired through a very narrow glottis; care being taken also, that none of the expired air passes through the nose. But, as observed 1 The minuter physiology of speech may be best studied in Miiller (xxxii.); or in the remarkable work by Ammann (from which even Miiller has been iustructed), entitled " Dissertatio de Loquela," 1700. INTONATION AND VENTRILOQUISM. 419 by Miiller, much of the ventriloquist's skill in imitating the voices coming from particular directions, consists in deceiving other senses than hearing. We never distinguish very readily the direction in which sounds reach our ear; and, when our attention is directed to a particular point, our imagination is very apt to refer to that point whatever sounds we may hear. [Stammering is a temporary inability to enunciate, freely and dis- tinctly, certain letters at the commencement of one or more of the syllables of a word. There is a broken or interrupted emission of the voice in the act of articulation, and a consequent disconnexion of the sounds. The consonants afford great obstacles to the stam- merer, as they do, also, to children learning to talk; inasmuch as they are necessarily more difficult of enunciation than the vowels, in consequence of being dependent upon an ever-varying disposition and arrangement of the parts composing the vocal tube. Especially is this the case with that class of consonants known as explosives__ as b, d, t, g, k, &c. These letters have of themselves no sound, or are mutes. They do not admit of a continuous pronunciation like the h, m, n, f s, r, I, but require to be associated with a vowel sound, before they can be enunciated. Much difference of opinion has existed in regard to the essential cause of stammering; and views have occasionally been entertained, which are certainly far from tenable. Many of the earlier writers have attributed all the varieties of this form of defective speech to some organic affection of the vocal apparatus, or malformation of the parts that compose the mouth and fauces; as, for example, hyper- trophy of the tongue, a too low position of that organ in the mouth, enlargement of the tonsils, uvula, &c. A more accurate knowledge of the anatomy and physiology of the organs of phonation led to an improvement on these restricted conjectures. Schulthess, Arnott, Miiller, and several other very eminent physiologists, maintained that stammering is dependent for its immediate cause upon a spas- modic closure of the glottis, producing a sudden arrestation of the issuing column of air.1 Later researches, however, have shown that this is true of the guttural sounds only. Dr. Carpenter2 is disposed to consider that the proximate cause, in the majority of cases, is a disordered action of the nervous centres of a centric origin. This is proved by the close analogy which pre- vails between the phenomena of stammering and those of the gene- ral disease, chorea. The great difficulty, in by far the largest num- ber of cases, is to be sought for in the spasmodic action of certain of the muscles concerned in the production of voice and in articula- tion, which spasmodic action impedes or entirely arrests the column 1 [Miiller.—Elements of Physiology. 2 Carpenter's Principles of Human Physiology.] 420 THE SENSES. of sounding breath. This view is particularly conteuded for by Dr. Dunglison. ■ Often, as in chorea or St. Vitus's dance, the slightest agitation serves to aggravate, in the most painful degree, the abnormal action. Indeed, the affection may not improperly be—as it has been—called, " chorea" or " St. Vitus's dance" of the voice. The stammerer, on attempting to enunciate a word or syllable, experiences difficulty or resistance at the commencement, and having but an imperfect con- trol over the voluntary muscles of the vocal apparatus, he at once loses all confidence in his ability to produce the sound required, and there consequently results an irregular or spasmodic action of those muscles, which, for a longer or shorter period, and determined by the degree of spasm, effectually prevents enunciation. In the case of the explosive consonants, the total interruption of the breath, and the badly regulated and insufficient volition, give occasion to the most painful spasmodic efforts on the part of the muscles more im- mediately concerned in articulation. This may be even extended to the whole body, which is thrown into a most distressing state of agitation to overcome the obstacle. At length the spasm ceases with the accomplishment of the act of expiration. It will now, therefore, be understood, why the complete interruption to expira- tion in the enunciation of the explosive consonants should be the most common phenomenon observed in stammerers. In the case, however, of the continuous consonants, an additional phenomenon occurs, in the sound being prolonged by spastic action for a much longer time than necessary.] CHAPTER XVIII. THE SENSES. Sensation consists in the mind receiving, through the medium of the nervous system, and, usually, as the result of the action of an external cause, a knowledge of certain qualities or conditions, not of external bodies but of the nerves of sense themselves; and these qualities of the nerves of sense are in all different, the nerve of each sense having its own peculiar quality. There are two principal kinds of sensation, named common and special. The first is the consequence of the ordinary sensibility or feeling possessed by most parts of the body, and is manifested when a part is touched, or in any ordinary manner is stimulated. Accord- 1 [Medical Examiner, July, 1852. See also Braithwaite's Retrospect, January, 1853.] THE SENSES GENERALLY. 421 ing to the stimulus, the mind perceives a sensation of heat, or cold, of pain, of the contact of hard, soft, smooth, or rough objects, etc. From this, also, in morbid states, the mind perceives itching, ting- ling, burning, aching, and the like sensations. In its greatest per- fection common sensibility constitutes touch or tact. Touch is, in- deed, usually classed with the special senses, and will be considered in the same group with them; yet it differs from them in being a property common to many nerves, e. g., all the sensitive spinal nerves, the pneumogastric, glosso-pharyngeal, and fifth cerebral nerves, and in its impressions being communicable through many organs. Including the sense of touch, the special senses are five in num- ber : the senses of smell, sight, hearing, taste, and touch. The manifestation of each of the first three depends on the existence of a special nerve: the optic for the sense of sight, the auditory for that of hearing, and tbe olfactory for that of smell. The sense of taste appears to be a property common to branches of the fifth and of the glosso-pharyngeal nerves. The senses, by virtue of the peculiar properties of their several nerves, make us acquainted with the states of our own body; and thus, indirectly, inform us of such qualities and changes of external matter as can give rise to changes in the condition of the nerves. That which through the medium of our senses is actually perceived by the mind is, indeed, merely a property or change of condition of our nerves; but the mind is accustomed to interpret these modifications in the state of the nerves produced by external influences as proper- ties of the external bodies themselves. This mode of regarding sensations is so habitual in the case of the senses which are more rarely affected by internal causes, that it is only on reflection that we perceive it to be erroneous. In the case of the sense of feeling or touch, on the contrary, where the peculiar sensations of the nerves perceived by the sensorium are excited as frequently by internal as by external causes, we more readily apprehend the truth. For it is easily conceived that the feeling of pain or pleasure, for example, is due to a condition of the nerves, and is not a property of the things which excite it. What is true of these is true of all other sensa- tions ; the mind perceives conditions of the optic, olfactory, and other nerves specifically different from that of their state of rest; these conditions may be excited by the contact of external objects, but they may also be the consequence of internal changes : in the former case the mind, having knowledge of the object through either in- stinct or instruction, recognises it by the appropriate changes which it produces in the state of the nerves. ]. The special susceptibility of the different nerves of sense for certain influences,—as of the optic nerve for light, of the auditory nerves for vibrations, and so on,—is not due entirely to those nerves having each a specific irritability for such influences exclusively. For although in the ordinary events of life the optic nerve is excited 3(5 422 THE SENSES. only by the undulations or emanations of which light may consist, the auditory only by vibrations of the air, and the olfactory only by odorous particles, yet each of these nerves may have its peculiar pro- perties called forth by other conditions. In fact, in whatever way, and to whatever degree a nerve of special sense is stimulated, the sensation produced is essentially of the same kind; irritation of the optic nerve invariably producing a sensation of light, of the auditory nerve a sensation of some modification of sound. The phenomenon must therefore be ascribed to a peculiar quality belonging to each nerve of special sense. It has been supposed, indeed, that irritation of a nerve of special sense when excessive may produce pain; but expe- riments seem to have proved that none of these nerves possess the faculty of common sensibility. Thus Magendie observed that when the olfactory nerves laid bare in a dog were pricked, no signs of pain were manifested : and others of his experiments seemed to show that both the retina and optic nerve are insusceptible of pain (lxii. t. iv. p. 180). 2. External impressions on a nerve can give rise to no kind of sensation which cannot also be produced by internal causes exciting changes in the condition of the same nerve. In the case of the sense of touch, this is at once evident. The sensations of the nerves of touch (or common sensibility), excited by causes acting from without, are those of cold and heat, pain and pleasure, and innume- rable modifications of these, which have the same kind of sensation as their element. All these sensations are constantly being produced by internal causes in all parts of our body endowed with sensitive nerves. The sensations of the nerves of touch are therefore states or qualities proper to themselves, and merely rendered manifest by exciting causes, whether external or internal. The sensation of smell, also, may be perceived independently of the application of any odorous substance from without, through the influence of some in- ternal condition of the nerve of smell. The sensations of the sense of vision, namely, colour, light and darkness, are also often perceived independently of all external exciting causes. So, also, whenever the auditory nerve is in a state of excitement, the sensations peculiar to it, as the sounds of ringing, humming, etc., are perceived. 3. The same cause, whether internal or external, excites in the different senses different sensations; in each sense the sensations pe- culiar to it. For instance, one uniform internal cause, which may act on all the nerves of the senses in the same manner, is the accu- mulation of blood in their capillary vessels, as in congestion and in- flammation. This one cause excites in the retina, while the eyes are closed, the sensation of light and luminous flashes; in the audi- tory nerve, the sensation of bumming and ringing sounds; in the olfactory nerve, the sense of odors; and in the nerves of feeling, the sensation of pain. In the same way, also, a narcotic substance in- troduced into the blood, excites in the nerves of each sense peculiar ACTION OF STIMULI ON NERVES OF SENSE. 423 symptoms: in the optic nerve, the appearance of luminous sparks before the eyes; in the auditory nerves, "tinnitus aurium;" and in the common sensitive nerves, the sensation of creeping over the sur- face. So, also, among external causes, the stimulus of electricity, or the mechanical influence of a blow, concussion, or pressure, ex- cites in the eye the sensation of light and colors; in the ear, a sense of a loud sound or of ringing; in the tongue, a saline or acid taste; and at the other parts of the body, a perception of peculiar jarring or of the mechanical impression, or shock like it. 4. Although in the cases just referred to, and in all ordinary con- ditions, sensations are derived from peculiar conditions of the nerves of sense, whether excited by external or by internal causes, yet the mind may have the same sensations independently of changes in the conditions of at least the peripheral portions of the several nerves, and even independently of any connection with the external organs of the senses. The causes of such sensations are seated in the parts of the brain in which the several nerves of sense terminate. Thus pressure on the brain has been observed to cause the sensation of light; luminous spectra may be excited by internal causes after com- plete amaurosis of the retina: and Humboldt states that, in a man who had lost one eye, he produced, by means of galvanism, luminous appearances on the blind side. Many of the various morbid sensa- tions attending diseases of the brain, the vision of spectra, and the like, are of the same kind. 5. Again, although the immediate objects of the perception of our senses are merely particular states induced in the nerves, and felt as sensations, yet, inasmuch as the nerves of the senses are material bodies, and therefore participate in the properties of matter generally, occupying space, being susceptible of vibratory motion, and capable of being variously changed chemically as well as by the action of heat and electricity, they make known to the mind, by virtue of the different changes thus produced in them by external causes, not merely their own condition, but also some of the different properties and changes of condition of external'bodies; as, e. g., " extension," progressive and tremulous motion, chemical change, etc. The information concerning external nature thus obtained by the senses, varies in each sense, having a relation to the peculiar qualities or energies of the nerve. All the senses are not equally adapted to impart the idea of exten- sion. The nerve of vision and the nerves of touch, being capable of an exact perception of this property in themselves, make us ac- quainted with it in external bodies : and it is by these senses that we best, by seeing and feeling bodies, learn their extension and their relation to other objects and to ourselves. In the nerves of taste, the sensation of extension is less distinct, but not altogether deficient; for we are capable of distinguishing whether the seat of a bitter or 424 THE SENSES. sweet taste be the tongue, the palate, or the fauces. The sense of hearing is almost totally incapable of perceiving the quality of exten- sion ; for the organ of hearing has no conception of its own extension, or of the part at which the sound is heard. The mind can perceive at loast the organ on which odors are impressed, and is conscious of the whole cavity of the nostrils being occupied by a penetrating odor; but we cannot make the odorous substance act on less than the entire nasal cavity. The sensation of motion is, like motion itself, of two kinds,—pro- gressive and vibratory. The faculty of the perception of progressive motion is possessed by the senses of vision, touch, and taste. Thus an impression is perceived travelling from one part of the retina to another, and the movement of the image is interpreted by the mind as motion of the object. The same is the case in the sense of touch ; so also the movement of a sensation of taste over the surface of the organ of taste can be recognised. The motion of tremors, or vibra- tions, is perceived by several senses, but especially by those of hear- ing and touch. For the sense of hearing, vibrations constitute the ordinary stimulus, and so give rise to the perception of sound. By the sense of touch vibrations are perceived as tremors, occasionally attended with the general impression of tickling; for instance, when a vibrating body, such as a tuning-fork, is approximated to a very sensible part of the surface, the eye can communicate to the mind the image of a vibrating body, and can distinguish the vibrations when they are very slow; but the vibrations are not communicated to the optic as to the auditory nerve in such a manner that it repeats them, or receives their impulses. We are made acquainted with chemical actions principally by taste, smell, and touch, and by each of these senses in the mode proper to it. Volatile bodies disturbing the conditions of the nerves by a chemical action, exert the greatest influence upon the organ of smell; and many matters act on that sense which produce no impression upon the organs of taste and touch,—for example, many odorous substances, as the vapors of metals, of lead for instance, and of many minerals. Some volatile substances, however, are perceived not only by the sense of smell, but also by the senses of touch and taste, pro- vided they are of a nature adapted to disturb chemically the condi- tion of these organs, and in the case of the organ of taste, can be dissolved by the fluids covering it. Thus, the vapors of horse-radish and mustard, and acrid suffocating gases, act upon the conjunctiva and the mucous membrane of the lungs, exciting through the com- mon sensitive nerves merely modifications of common feeling; and at the same time they excite the sensations of smell and of taste. 7. Sensations are referred from their proper seat towards the ex- terior; but this is owing, not to anything in the nature of the nerves themselves, but to the accompanying idea derived from experience. THE SENSE OF SMELL. 425 For in the perception of sensations there is a combined action both of the mind and of the nerves of sense; and the mind, by educa- tion or experience, has learned to refer the impressions it receives to objects external to the body. Even when it derives impressions from internal causes, it commonly refers them to external objects. The light perceived in congestion of the retina seems external to the body : the ringing of the ears in diseases is felt as if the sound came from some distance : the mind referring it to the outer world from which it is in the habit of receiving the like impression (see p. 315). 8. Moreover, the mind not only perceives the sensations and inter- prets them according to ideas previously obtained, but it has a diroct influence upon them, imparting to them intensity by its faculty of attention. Without simultaneous attention, all sensations are only obscurely, if at all, perceived. If the mind be torpid in indolence, or if the attention be withdrawn from the nerves of sense in intel- lectual contemplation, deep speculations, or an intense passion, the sensations of the nerves make no impression upon the mind; they are not perceived,—that is to say, they are not communicated to the conscious " self," or with so little intensity, that the mind is unable to retain the impression, or only recollects it some time after, when it is freed from the preponderating influence of the idea which had occupied it. This power of attention to the sensations derived from a single organ, may also be exercised in a single portion of a sentient organ, and thus enable one to discern the detail of what would otherwise be a single sensation. For example, by well-directed attention, one can distinguish each of the many tones simultaneously emitted by an orchestra, and can even follow the weaker tones of one instru- ment apart from the other sounds, of which the impressions, being not attended to, are less vividly perceived. So, also, if one endea- vors to direct attention to the whole field of vision at the same time nothing is seen distinctly; but when the attention is directed to this, then to that part, and analyzes the detail of the sensation, the part to which the mind is directed is perceived with more distinctness than the rest of the same sensation. THE SENSE OF SMELL. The sense of smell ordinarily requires, for its excitement to a state of activity, the action of external matters, which produces certain changes in the olfactory nerve; and this nerve is susceptible of an infinite variety of states dependant on the nature of the external stimulus. 36* 426 THE SENSES. The first condition essential to the sense of smell is the existence of a special nerve, the changes in whose condition are perceived as sensations of odor; for no other nerve is capable of these sensations, even though acted on by the same causes. The same substance which excites the sensation of smell in the olfactory nerves, may cause another peculiar sensation through the nerves of taste, and may produce an acrid and burning sensation on the nerves of touch; but the sensation of odor is yet separate and distinct from these, though it may be simultane- ously perceived. The second condition of smell is a peculiar con- dition of the olfactory nerve, or a peculiar change produced in it by the stimulus or odorous substance. The material causes of odors are, in the case of animals living in the air, substances suspended in a state of extremely fine division in the atmosphere; or gaseous exhalations, often of so subtile a nature that they can be detected by no other reagent than the sense of smell itself. In fishes, the odorous matters are contained in the water; but in what form, — whether dissolved in the same manner as the gases absorbed by water—is uncertain. The matters of odor must, in all cases, be dissolved in the mucus of the mucous membrane before they can be immediately applied to, or affect, the olfactory nerves; therefore, a further condition necessary for the perception of odors is, that the mucorft membrane of the nasal cavity be moist. When the Schneiderian membrane is dry, the sense of smell is lost; in the first stage of catarrh, when the secretion of mucus within the nostrils is lessened, the faculty of perceiving odors is either lost, or renderod very imperfect. In animals living in the air, it is also requisite that the odorous matters should be transmitted in a current through the nostrils. This is effected by the respiratory movements : hence we have vol- untary influence over the sense of smell; for by interrupting respira- tion we prevent the perception of odors, and by repeated quick inspirations assisted, as in the act of sniffing, by slight contraction of the nostrils, we render the impression more intense. The human organ of smell is essentially formed by the filaments of the olfactory nerves distributed, in minute arrangement, in the mucous membrane covering the superior three-fourths of the septum of the nose, the superior turbinated or spongy bone, the upper half of the middle turbinated bone, and the upper wall of the nasal cavities beneath the cribriform plates of the ethmoid bone (Fig. 117, p. 427). This olfactory region is covered by tesselated epithelium (Todd and Bowman). In all their distribution, the branches of the olfactory nerves retain much of the same soft and greyish texture which distinguishes their trunks (as the olfactery lobes of the brain are called) within the cranium. Their individual filaments, also, are peculiar, more resembling those of the sympathetic nerve than the filaments of the other cerebral nerves do, containing no outer DISTRIBUTION OF THE OLFACTORY NERVE. Fig. 117. 427 Outer wall of the nasal fossa, with the three spongy bones and meatus: the nerves being shown as they would appear through the membrane if it were transparent, a. Olfactory process. 6. Olfactory bulb (represented rather too short) resting on the cribriform plate. Below is seen the plexiform arrangement of the olfactory filaments on the upper and middle Bpongy bones, c. Fifth nerve within the cranium with its Gasserian ganglion, d. Its supe- rior maxillary division, sending branches to Meckel's ganglion, and through that to the three spongy bones, wliere they anastomose with the olfactory filaments, and with s, branches of the nasal division of the ophthalmic nerve, o. Posterior palatine twigs from Meckel's ganglion, supplying the soft and hard palate, t. Orifice of the Eustachian tube on the side of the pharynx, behind the lower spongy bone.—From Soemmering, two-thirds diameter. white substance, and being finely granular and nucleated1 (Fig. 118). The branches are dis- tributed principally in close plexuses; but the mode of ter- mination of the filaments is not yet satisfactorily determined. The sense of smell is derived exclusively through those parts of the nasal cavities in which the olfactory nerves are dis- tributed; the accessory cavities or sinuses communicating with the nostrils seem to have no relation to it. Air impregnated with the vapor of camphor was injected by Deschamps into the frontal sinus through a fistulous opening, and Richerand injected 1 See Todd and Bowman (xxxix. vol. ii): the -work -which, before all minute anatomy of the organs of sense, the student should consult. Olfactory filaments of the dog: a. In water. b. In acetic acid.—Magnified 250 diameters. on the 428 THE SENSES. odorous substances into the antrum of Highmore; but in neither case was any odor perceived by the patient. The purposes of these sinuses appear to be that the bones, necessarily large for the action of the muscles and other parts connected with them, may be as light as possible, and that there may be more room for the resonance of the air in vocalizing. The former purpose, which is in othter bones obtained by filling their cavities with fat, is here attained, as it is in many bones of birds, by their being filled with air. All parts of the nasal cavi- Fig. 119. ties, whether they can be the seats of the sense of smell or not, are endowed with com- mon sensibility by the nasal branches of the first and second divisions of the fifth nerve. (Fig. 119.) Hence the sensations of cold, heat, itching, tickling, and pain; and the sensation of tension or pressure in the nostrils. That these nerves cannot perform the function of the olfactory nerves, is proved by cases in which the sense of smell is lost, while the mucous membrane of the nose remains susceptible of the various modifications of common sensation or touch. But it is often difficult to distinguish the sensation of smell from that of mere feel- ing, and to ascertain what belongs to each separately. This is the case particularly with the sensations excited in the nose by acrid vapors, as of ammonia, horse-radish, and mustard, etc., which resemble much the sensations of the nerves of touch; and the difficulty is the greater when it is remembered that these acrid vapors have nearly the same action upon the mucous membrane of the eyelids. It was because the common sensibility of the nose to these irritating substances remained, after the destruction of the olfactory nerves, that Magendie was led to believe the fifth nerve might exercise the special sense. Animals do not all equally perceive the same odors; the odors perceived by an herbivorous animal and by a carnivorous animal are different. The Carnivora have the power of detecting most accu- Nerves of the septum of the nose. a. Olfactory bulb resting on the cribriform plate, below which its branches may be traced on the septum, about half way down. Behind, the naso-palatine nerve from Meckel's ganglion is seen descending to the naso-palatine canal. In front, the nasal twig of the ophthalmic nerve descends towards the tip of the nose, dividing into two principal branches. p. Roof of the mouth, e. Orifice of the Eustachian tube.—From Arnold, one-half diameter THE SENSE OF SMELL. 429 rately by the smell the special peculiarities of animal matters, and of tracking other animals by the scent; but have apparently no sensibility to the odors of plants and flowers. Herbivorous animals are peculiarly sensitive to the latter, and have a narrower sensibility to animal odors, especially to such as proceed from other individuals than their own species. Man is far inferior to many animals of both classes in respect of the acuteness of smell; but his sphere of sus- ceptibility to various odors is more uniform and extended. The cause of this difference must lie in the endowments of the central parts of the olfactory apparatus. Opposed to the sensation of an agreeable odor is that of a dis- agreeable or disgusting odor, which corresponds to the sensations of pain, dazzling and disharmony of colors, and dissonance, in the other senses. The cause of this difference in the effect of different odors is unknown; but this much is certain, that odors are pleasant or offensive in a relative sense only, for many animals pass their existence in the midst of odors which to us are highly disagreeable. A great difference in this respect is, indeed, observed amongst men : many odors generally thought agreeable are to some persons intoler- able ; and different persons describe differently the sensations that they severally derive from the same odorous substances. There seems also to be in some persons an insensibility to certain odors, comparable with that of the eye to certain colors; and among dif- ferent persons, as great a difference in the acuteness of the sense of smell as among others in the acuteness of sight. We have no exact proof that a relation of harmony and disharmony exists between odors as between colors and sounds; though it is probable that such is the case, since it certainly is so with regard to the sense of taste; and since such a relation would account in some measure for the different degrees of perceptive power in different persons; for as some have no ear for music (as it is said), so others have no clear appreciation of the relations of odors, and, therefore, little pleasure in them. It is also not certain that sensations of odors continue after the impression of the odorous matter has ceased, though we can scarcely imagine that such is not the case. It is difficult to ascertain this point by direct observation; because the odor that is frequently retained in the nose may arise from some of the odorous matter remaining dissolved in the mucus of the nostrils. The sensations of the olfactory nerves, independent of the external application of odorous substances, have hitherto been little studied. It has been found that solutions of inodorous substances, such as salts, excite no sensation of odor when injected into the nostrils. The friction of the electrical machine is, however, known to produce a smell like that of phosphorus. Bitter, too, has observed, that when galvanism is applied to the organ of smell, besides the impulse to sneeze, and the tickling sensation excited in the filaments of the fifth nerve, a smell like that of ammonia was excited by the negative 430 THE SENSES. pole, and an acid odor by the positive pole; whichever of these sensations was produced, it remained constant as long as the circle was closed, and changed to the other at the moment of the circle being opened. Frequently a person smells something which is not present, and which other persons cannot smell; this is very frequent with nervous people, but it occasionally happens to every one. In a man who was constantly conscious of a bad odor, the arachnoid was found after death, by MM. Cullerier and Maignault, to be beset with deposits of bone; and in the middle of the cerebral hemi- spheres were scrofulous cysts in a state of suppuration. Dubois was acquainted with a man who, ever after a fall from his horse, which occurred several years before his death, believed that he smelt a bad odor. THE SENSE OF SIGHT. The eye, or the organ of vision, consists essentially in a membra- nous expansion of the peripheral extremity of the nerve of sight, the optic, for the purpose of receiving the impressions of the rays of light from luminous bodies. This expansion of the optic nerve is termed the retina. It is a delicate membrane, concave, with the concavity directed forwards; semi-transparent when fresh, but soon becoming clouded and opaque, with a pinkish tint from the blood in its minute vessels. It results from a sudden spreading out or ex- pansion of the optic nerve, of whose terminal fibres, apparently de- prived of their'external white substance, it is almost entirely com- posed. At first the fibres of the optic nerve run in distinct bundles, which radiate from the point at which the trunk of the nerve termi- nates, and then pursue a tolerably straight course towards the anterior margin of the retina. As they proceed in this course, how- ever, the bundles shortly break up into their component fibres, which then interlace and form a fine membranous sheath, towards the anterior margin of which all trace of fibrous arrangement disappears. The mode in which the nerve-fibres of the retina terminate, is still involved in obscurity, in spite of the many efforts to determine the question. According to some observers, the fibres terminate in loops, according to others, in free extremities, and according to others, again, they become continuous with prolongations from nerve- cells, which are found abundantly in the tissue of the retina. That the latter is not an unfrequent mode of termination seems to have been fully proved by Kolliker, H. Miiller, and others (cxc. vol. xiii. p. 547). Nearly all who have recently examined the minute structure of the retina, concur in describing the existence of numerous cells and globules lying on both sides of the fibrous expansion of this mem- brane, and chiefly along its internal surface and within the meshes formed by the interlacing of the individual nerve-fibres. These cellular bodies appear to be of different kinds, although, as Henle STRUCTURE OF THE RETINA. 431 observes, it is probable that the several varieties met with, are only the same cells in different stages of development. The larger and more perfect developed cells are nearest to the fibrous layer (Fig. 120). By Valentin (xxxiv. 1837, p. 25), who first accurately Fig. 120. Vertical section of the human retina and hyaloid membrane, h. Hyaloid membrane, h' Nuclei on its inner surface, c. Layer of transparent cells, connecting the hyaloid and re- tina, c'. Separate cell enlarged by imbibition of water, n. Gray nervous layer, with its capillaries. 1. Its fibrous lamina. 2. Its vesicular lamina. 1'. Shred of fibrous lamina de- tached. 2'. Vesicle and nucleus detached, g. Granular layer. 3. Light lamina frequently seen. g'. Detached nucleated particle of the granular layer, to. Jacob's membrane, m'. Appearances of its particles, when detached, m". Its outer surface. Magnified 320 diameters. described them, they were considered as identical with the ganglion- corpuscles of nervous substance: and the fact that many of them present radiating processes or prolongations, which, as just stated, not unfrequently become directly continuous with the nerve-fibres of the retina, substantiates this opinion. Very shortly after death, these cells and the place which they occupied becomes a confused granular mass, in which are scattered, often in a linear direction, numerous oil-like globules, which are probably the nuclei of the dis- integrated cells. Exactly in the centre of the retina, and at a point thus corres- ponding to the axis of the eye, in which the sense of vision is most perfect, is a round yellowish elevated spot, about 54th of an inch in diameter, having a minute aperture at its summit, and called after its discoverer the yellow spot of Soemmering (Fig. 121, p. 432). It is not covered by the fibrous part of the retina, but a layer of closely-set cells passes over it (xxxix. Am. Ed., p. 415). The use of this spot is quite unknown. [Dr. Learning has recently offered the following explanation of the use of the foramen Soemmering. " If we close one eye and look upon the page of a book, we shall 432 THE SENSES. Fig. 121. notice that the word in the axis of the eye, as well as the words immediately above and below it, are distinct, while the rest of the page is illegible. Perfectly distinct vision is confined to a very small space of the retina, and is bounded by the limits of the foramen in the centre of the yellow spot. But an opening in the retina, instead of perfecting, would destroy vision; we must necessarily conclude that, under the cir- cumstances alluded to, the foramen is closed. Now, the foramen has sometimes been found The yellow spot of closed by anatomists, but then the bifurcated the retina occupying fold has disappeared, and the only mark of its the axis of the eye; and previoug existence was a dent in the vitreous the entrance of the op- i j • ., j.i r i j a tic nerve, with the ar- bumour corresponding precisely to the fold. An teria centralis retinae open foramen with a fold of the retina; a closed on the inner side of the foramen, and no fold of the retina; all this implies axis.-After Soemmer- motion Qf thfi partg " If we look at a distant object with both eyes open, and pass an ordinary ruler before one of them so as to exclude the distant object, the central part of the ruler will be invisible to that eye; that is, the central part of the retina has become insen- sible to light. The bounds of this insensibility can easily be defined, and they will be found to correspond with those of the yellow spot of Soemmering. The following diagram will illustrate this suffici- ently, the ruler being held about 12 or 15 inches distant, and made to pass before the left eye : — Fig. 122. Fig. 123. r //' '/A. B C T " Fig. 122, A, represents the ruler seen by the right eye; B, that by the left; the outline of the extremity being faintly visible; the central part as far as C is transparent or invisible, while the dis- tant object appears at D. " The ruler may now be passed further to the right, when the ex- tremity at B will become visible again; showing that the power of becoming insensible to light, under these circumstances, is possessed only by the yellow spot of Soemmering, and not by the retina at large. It is curious to watch the play of sensibility; sometimes the transparency expanding widely and in a moment contracting to a mere point. "The use of all this is evident. When two objects are presented (a very frequent occurrence), one in the axis of each eye, the mind THE RETINA AND CHOROID COAT. 433 is not perplexed by the blending of the two objects, but contem- plates the one while the other is withdrawn. This may be further illustrated by Wheatstone's Stereoscope. Place before the glasses a printed page on which two pencil marks have been drawn vertically about two inches apart. Let the lines be thrown into one by the action of the eyes, and fix the attention on any word the lines appear to run through. At first, perhaps, there will be a blending of letters, so that no word can be made out, both foramina being closed and sensitive; presently a word will be distinct, and either be retained or alternate with a word through which the other pencil mark passes. We may infer that this is owing in the latter case to the alternate action of the foramina, and not to the alternate action of the eyes, for the vertical pencil marks remain blended.1] At about an eighth of an inch to the inner side of the yellow spot, and consequently of the axis of the eye, is the point at which the optic nerve spreads out its fibres to form the retina. This is the only point of the surface of the retina from which the power of vision is absent. On the outside, the retina is surrounded by the membrana Jacobi (Fig. 124), composed of cylindrical, or staff-shaped, transparent, and highly refractive bodies, arranged per- pendicularly to the surface of the re- tina, with their outer extremities im- bedded, to a greater or less depth, in a layer of black pigment of the cho- roid coat. Recent researches seem to have determined that this mem- brane, instead of being, as was for- merly considered, an independent covering, is intimately associated, both in structure and function, witb the sensitive part of the retina: for the conical and staff-shaped bodies, of which it is composed, appear to Outer surface of the retina, showing \,e connected by means of delicate tbe membrane of Jacob, partially de- fibreg issuin„ from them with the tached.—After Jacob. . , ° „ ,, ,. , nerve-vesicles of the retina, and even to become continous with the radiating processes which some of these vesicles present (ccvii. p. 706). Concerning the use of these bodies, Briicke was of opinion that they may serve to conduct back to the sensitive portion of the retina, those rays of light, which having traversed that membrane, are not entirely absorbed by the black pigment of the choroid; but the discovery of their connection with the~sensitive part of the retina supports the opinion entertained by Kolliker and H. Miiller, that their special office is to receive and transmit impressions of light. > [American Journal of the Medical Sciences, July, 1852.] 37 434 THE SENSES. The chloroid which is the next tunic of the eye, and surrounds the membrana Jacobi, consists of a thin and highly vascular mem- brane, of which the internal surface is covered by a layer of black pigment-cells in which, as just said, the staff-shaped bodies of the membrana Jacobi are imbedded (Fig. 125). The principal use of Fig. 125. Choroid and iris, exposed by turning aside the sclerotica: c, c. Ciliary nerves branching in the iris. d. Smaller ciliary nerve, e, e. Vasa vorticosa. h. Ciliary ligament and muscle, h. Converging fibres of the greater circle of the iris. I. Looped and knotted form of these near the pupil, with the converging fibres of the lesser circle of the iris within them. o. The optio nerve.—From Zinn. , the choroid is to absorb, by means of its pigment, those rays of light which pass through the transparent retina, and thus to prevent their being thrown again upon the retina so as to interfere with the dis- tinctness of the images there formed. Hence animals in which the choroid is destitute of pigment, and human Albinoes, are dazzled by daylight, and see best in the twilight. By means of the retina and the other parts just described, a pro- vision is afforded for enabling the terminal fibres of the optic nerve to receive the impression of rays of light, and to communicate them to the brain, in which they excite the sensation of vision. But that light should produce in the retina images of the objects from which it comes, it is necessary that when emitted or reflected from deter- minate parts of external objects, it should stimulate only correspond- ing parts of the retina. For as light radiates from a luminous body in all directions, when the media offer no impediment to its trans- mission, a luminous point will necessarily illuminate all parts of a THE CORNEA AND AQUEOUS HUMOR. 435 surface, such as the retina, opposed to it, point. A retina, therefore, without any front of it to separate the light of diffe- rent objects, would see nothing distinctly, but would merely perceive the general impression of daylight, and distinguish it from the night. Accordingly, we find that in man, and most vertebrate animals, certain transparent refracting media are placed in front of the retina for the pur- pose of collecting together into one point the different diverging rays emitted by each point of the external body, and of giving them such directions that they shall fall on corresponding points of the retina, and thus produce an exact image of the object from which they proceed. These refracting media are, in the order of succession from without inwards, the cornea, the aqueous humor, the crystal- line lens, and the vitreous humor. The cornea is a dense perfectly trans- parent substance, convex anteriorly, con- cave posteriorly, and composed of fibrous tissue arranged in numerous distinct la- minae (Fig. 126). It is in a two-fold manner capable of refracting and causing convergence of the rays of light that fail upon and traverse it. It thus affects them, first, by its density; for it is a law in optics that when rays of light pass from a rarer into a denser medium, if they impinge upon the surface in a di- rection removed from the perpendicular, they are bent out of their former direc- tion towards that of a line perpendicular to the surface of the denser medium; and, secondly, by its convexity—for it is another law in optics that rays of light impinging upon a convex transparent surface are refracted towards the centre, those being most refracted which are far- thest from the centre of the convex sur- face. Behind the cornea is a space con- taining a thin watery fluid, the aque- and not merely one single optical apparatus placed in Fig. 126. A. Vertical section of the human cornea, a. Coujunctival epithelium. 6. Anterior elastic lamina, from which there pass off a number of fibres into c, the layers of the cor- nea proper, among which the nu- clei are apparent, d. Posterior elastic lamina, e. Posterior epithe- lium.—Magnified 80 diameters. b. The posterior epithelium, o, seen in section; p, seen in face.— Magnified 300 diameters. 436 THE SENSES. ous humor, holding in solution a small quantity of chloride of sodium and extractive matter. The space containing the aqueous humor is divided into an anterior and posterior chamber by a mem- branous partition, the iris, to be presently again mentioned. The effect produced by the aqueous humor on the rays of light traversing it is not yet fully ascertained. Its chief use, probably, is that of enabling the cornea to maintain its proper convexity; and at the same time to furnish a medium in which the movements of the iris can take place. Behind the aqueous humor and the iris, and imbedded in the ante- rior part of the medium next to be described, viz., the vitreous humor, is seated a doubly-convex body, the crystalline lens, which is the most important refracting structure of the eye (Fig. 127). The structure of the lens is very complex. It consists essentially of fibres united side by side to each other, and arranged together in very numerous laminae, which are so placed upon one another that when hardened in spirit the lens splits into three portions, in the form of sectors, each of which is composed of superimposed concentric laminae (Fig. 128). The lens increases in density and, consequently, in power of Fig. 127. Fig. 128. Fig. 127. Position of the lens in the vitreous humor, shown by an imaginary section. The dark triangular space on each side of the lens is intended to indicate the position of the canal of Petit.—After Arnold. Fig. 128. Lens, hardened in spirit, and partially divided along the three interior planes, as well as into lamellae. Magnified S%. diameters.—After Arnold. refraction, from without inwards; the central part, usually termed the nucleus, being the most dense. The density of the lens increases with age; it is comparatively soft in infancy, but very firm in ad- vanced life : it is also more spherical at an early period of life than in old age. The vitreous humor constitutes nearly four-fifths of the whole globe of the eye. It fills up the space between the retina and the lens, and its soft jelly-like substance consists essentially of numerous layers, formed of delicate, simple membrane, the spaces between which are filled with a watery, pellucid fluid. It probably exercises some share in refracting the rays of light to the retina; but its prin- PHENOMENA OF VISION. 437 cipal use appears to be that of giving the proper distension to the globe of the eye, and of keeping the surface of the retina at a proper distance from the lens. Such are the transparent media by which the rays of light undergo the necessary refraction in their course from an external object to the sensitive retina. They and the other contents of the ball of the eye are surrounded and kept in position by a dense fibrous, external investment, termed the sclerotica, which, besides thus encasing the contents of the eye, serves to give attachment to the various muscles by which the movements of the eye-ball are effected. These muscles, and the nerves supplying them, have been already considered (p. 361). As already observed, the space occupied by the aqueous humor is divided into two portions by a vertically-placed membranous dia- phragm, termed the iris, provided with a central aperture, the pupil, for the transmission of light. The iris is composed of organic mus- cular fibres imbedded in ordinary fibro-cellular or connective tissue. The muscular fibres of the iris have a direction, for the most part, radiating from the circumference towards the pupil; but as they ap- proach the pupillary margin, they assume a circular direction, and at the very edge form a complete ring. By the contraction of the ra- diating fibres, the size of the pupil is enlarged: by the contraction of the circular ones, which resemble a kind of sphincter, it is di- minished. The object effected by the movements of the iris is the regulation of the quantity of light transmitted to the retina; the quantity of which is, cceleris paribus, directly proportioned to the size of the pupillary aperture. The posterior surface of the iris is coated with a layer of dark pigment, so that no rays of light can pass to the retina except such as are admitted through the aperture of the pupil.' Of the Phenomena of Vision. The essential constituents of the optical apparatus of the eye may thus be enumerated : a nervous expansion to receive and transmit to the brain the impression of light; certain refracting media for the purpose of so disposing of the rays of light traversing them as to throw a correct image of an external body on the retina; and a con- tractile diaphragm with a central aperture for regulating the quantity of light admitted into the eye. With the help of the subjoined diagram (Fig. 129), representing a vertical section of the eye from before backwards, the mode in which, by means of the refracting media of the eye, an image of an 1 For the best account of the structure of the various parts of the eye, see, besides Todd and Bowman (xxxix. vol. ii.), the Lectures on Ophthalmic Surgery, by Mr. Bowman (lxxi. 1847 and 1848); Arnold (clxv.); Lawrence (clxxxv.); Wharton Jones (clxix. and lxxiii., art. Eye); Briicke (clxx.); and Kolliker (ccvi. and ccxii.). 37* 438 THE SENSES. Fig. 129. object of sight is thrown on the retina, may be rendered intelligible. The rays of the cones of light emitted by the points A B, and every other point of an object placed before the eye, are first refracted, that is, are bent towards the axis of the cone, by the cornea c c, and the aqueous humor contained between it and the lens. The rays of each cone are again refracted and bent still more towards its central ray or axis by the anterior surface of the lens E e; and again as they pass out through its posterior surface into the less dense medium of the vitreous humor. For a lens has the power of refracting, and causing the convergence of, the rays of a cone of light, not only on their entrance from a rarer medium into its anterior convex surface, but also at their exit from its posterior convex surface into the rarer medium. In this manner the rays of the cones of light issuing from the points A and B are again collected to points at a and b; and, if the retina F be situated at a and b, perfect, though reversed, images of the points A and B will be perceived : but if the retina be not at a and b, but either before or behind that situation,—for instance, at n or G,—circular luminous spots c and f or e and o, instead of points, will be seen; for at H the rays have not yet met, and at G they have already intersected each other, and are again diverging. The retina must therefore be situated at the proper focal distance from the lens, otherwise a defined image will not be formed; or, in other words, the rays emitted by a given point of the object will not be collected into a corresponding point of focus upon the retina. The means by which distinct and correct images of objects are formed in the retina, in the various conditions in which the eye is placed in relation to external objects, may be separately considered under the following heads :—1, the means for preventing indistinct- ness from aberration; 2, the means for preventing it when objects are viewed at different distances; 3, the means by which the reversed image of an object on the retina is perceived as in its right position by the mind. 1. Since the retina is concave, and from its centre towards its SPHERICAL ABERRATION CORRECTED. 439 margins gradually approaches the lens, it follows that the images of objects situated at the sides cannot be so distinct as those of objects nearer to the middle of the field of vision, and of which the images are formed at a distance behind the lens exactly corresponding to the situation of the retina. Moreover, the rays of a cone of light from an object situated at the side of a field of vision do not meet all in the same point, owing to their unequal refraction; for the refraction of the rays which pass through the circumference of a lens is greater than that of those traversing its central portion. The concurrence of these two circumstances would cause indistinctness of vision, un- less corrected by some contrivance. Such correction is effected, in both cases, by tbe iris, which forms a kind of annular diaphragm to cover the circumference of the lens, and to prevent the rays from passing through any part of the lens but its centre, which corresponds to the pupil. The image of an object will be most defined and distinct when the pupil is narrow, the object at the proper distance for vision, and the light abundant; so that, while a sufficient number of rays are ad- mitted, the narrowness of the pupil may prevent the production of indistinctness of the image by this spherical aberration or unequal refraction just mentioned. But even the image formed by the rays passing through the circumference of the lens, when the pupil is much dilated, as in the dark, or in a feeble light, may, under certain circumstances, be well defined; the image formed by the central rays being then indistinct or invisible, in consequence of the retina not receiving these rays where they are concentrated to a focus. Distinctness of vision is further secured by the inner surface of the choroid, immediately external to the retina itself, as well as the posterior surface of the iris and the ciliary processes, being coated with black pigment, which absorbs any rays of light that may be reflected within the eye, and prevents their being thrown again upon the retina so as to interfere with the images there formed. The pig- ment of the choroid is especially important in this respect; for the retina is very transparent, and if the surface behind it were not of a dark color, but capable of reflecting the light, the luminous rays winch had already acted on the retina would be reflected back again through it, and would fall upon other parts of the same membrane, producing both dazzling from excessive light, and indistinctness of the images. In the passage of light through an ordinary convex lens, decom- position of each ray into its elementary colored parts commonly ensues, and a colored margin appears around the image owing to the unequal refraction which the elementary colors undergo. In the optical instruments this, which is termed chromatic aberration, is corrected by the use of two or more lenses, differing in shape and density, the second of which continues or increases the refraction of the rays produced by the first, but by recombining the individual parts of 440 THE SENSES. each ray into its original white light, corrects any chromatic aberra- tion which may have resulted from the first. It is probable that the unequal refractive power of the transparent media in front of the retina, may be the means by which the eye is enabled to guard against the effect of chromatic aberration. The human eye is achro- matic however, only so long as the image is received at its focal dis- tance upon the retina, or so long as the eye adapts itself to the different distances of sight. If either of these conditions be inter- fered with, a more or less distinct appearance of colors is produced. 2. The distinctness of the image formed upon the retina is mainly dependent on the rays emitted by each luminous point of the object being brought to a perfect focus upon the retina. If this focus oc- curs at a point either in front of, or behind the retina, indistinctness of vision ensues, with the production of a halo. The focal distance, i. e., the distance of the point at which the luminous rays from a lens are collected, besides being regulated by the degree of convexity and density of tbe lens, varies with the distance of the object from the lens, being greater as this is shorter, and vice versa. Hence, since objects placed at various distances from the eye can, within a certain range, different in different persons,1 be seen with almost equal dis- tinctness, there must be some provision by which the eye is enabled to adapt itself; so that whatever length the focal distance may be, the focal point may always fall exactly upon the retina. This power of adaptation of the eye to vision at different distances has received the most varied explanations. It is obvious that the effect might be produced in either of two ways; viz., by altering the convexity or density, and thus the refracting power, either of the cornea or lens; or, by changing the position either of the retina or of the lens, so that whether the object viewed is near or distant, and the focal distance thus increased or diminished, the focal point to which the rays are converged by the lens, may always be at the place occupied by the retina. The amount of either of these changes required in even the widest range of vision, is extremely small. For, from the refrac- tive powers of the media of the eye it has been calculated by Olbers, that the difference between the focal distances of the images of an object at such a distance that the rays are parallel, and of one at the distance of four inches, is only about 0-143 of an inch. On this calculation, the change in the distance of the retina from the lens required for vision at all distances, supposing the cornea and lens to maintain the same form, would not be more than about one line, which might be effected either by elongation of the eye, or by a change in the position of the lens. Dr. Young estimated the necessary change at one-sixth of the length of the axis of the eye. Olbers also calculated the amount of change in the convexity of the cornea 1 An ingenious instrument for measuring the distances at which each person may have a distinct sight of objects has been invented by Mr. Smee, who names it the Optometer (clxxxvi.). VISION AT DIFFERENT DISTANCES. 441 which would be required for distinct vision at different distances, and finds it to be extremely small, though greater than it appeared pro- pable could be produced by any power of the eye or of its muscles. Both the above conditions, as well as several others, have been supposed sufficient alone to account for the power of adaptation of the eye. Thus, by Sir E. Home and others, it has been attributed exclusively to a change in the convexity of the cornea, produced by the muscles of the eye-ball. But the calculations of Olbers showed that the necessary change was greater than could be produced by the muscles of the eye; and Hueck has recently adduced evidence to prove that no alteration at all in the convexity of the cornea ensues when the eye looks first at a distant and then at a near body. By others the power of adaptation has been ascribed to alterations in the form of the whole globe of the eye, by the action of the muscles. But the action of tbe straight muscles is merely to retract the eye, and, if resistance were afforded by the cushion of fat behind it, to flatten rather than elongate it; their action might therefore have the effect of adapting the eye to the vision of distant objects: but it is in looking at very near objects, on the contrary, that we are conscious of an effort within the orbit. Moreover, as observed by Volkmann, we do not seem to possess sufficient power over the recti muscles to produce the combined action of all the four at one time; and except by such combined action, either of all four, or at least of two opposite ones, retraction of the eye-ball could not be effected. Injury of the third pair of nerves, also, whereby paralysis of three of the recti muscles is produced, is not followed by any material disturbance of the power of adaptation; and evidence has been furnished by Hueck to show that neither the oblique nor straight muscles can in any way exer- cise sufficient pressure on the eye to effect appreciable alteration in its form, or in the distinctness of an image formed on the retina. The movements of the iris have been considered the means of adaptation by some physiologists, chiefly from the fact that when distant objects are viewed, the pupil becomes dilated; when near ob- jects, contracted. In general, such movements in the iris might be regarded as merely associate movements, the pupil contracting when the eye is turned inwards, as in the act of looking at a near ob- ject, and dilating when the eyes are turned outwards. But con- traction of the pupil may ensue when by a voluntary effort, without any change in the position of the axes of the eyes, a near object is regarded; and dilatation of the pupil when a distant object is re- garded. The iris may therefore co-operate for the production of dis- tinct vision at different distances; but sufficient evidence that it is not the chief organ for adaptation, is furnished by the fact, that individuals in whom the iris is wholly wanting may have perfect vision for near as well as distant objects. Hueck, also, states that, without altering the direction of the axes of his eyes, or the quantity of light admitted, but merely by fixing his attention on a side object, 442 THE SENSES. he was able to widen his pupils as much as one-half more than their former diameter, without there ensuing any indistinctness of the ob- ject towards which the eyes were directed. The opinion now most commonly entertained of the adapting power of the eye, is, that it is mainly due to some alteration either in posi- tion or form, or in both, undergone by the crystalline lens. The ar- guments stated by Hueck in favor of this view, are, first, that if the eye is watched attentively from the side, the iris will be observed to be bent forwards in the middle, and approximated closer to the cor- nea, when a near object is viewed, and to become flattened again when the sight is fixed upon a distant object: secondly, that when the fresh eye of a dog is removed and placed before a window, so that through an opening in the sclerotica, a distinct image of the window frame, and an indistinct one of a smaller object, such as a key, held nearer to the eye, are perceived, the latter may be rendered distinct, and the former indistinct, by drawing the lens forward with a needle, inserted through the margin of the cornea. With respect to the mode in which such an approximation of the lens towards the cornea during the vision of near objects may be effected, different explanations are offered. By some it is supposed to be produced by vascular turgescence of the ciliary processes; the recedence of the lens ensuing on the ces- sation of the turgescence. By others, and with greater probability, it is supposed to be effected by the contraction of muscular tissue situated in the neighborhood of the ciliary body and processes.1 [An examination of the diagram (Fig. 130) will show that the action of the cili- ary muscle must have the effect of ad- vancing the ciliary processes, and with them the lens, towards the cornea. The muscular nature of their structure is con- firmed by its anatomy in birds, where it is largely developed. Its fibres are of the striped variety, and are supplied with nerves from the ciliary. That this muscle is concerned in adapt- ing the eye to distances seems proved by the fact that this power is lost by the ap- plication of belladonna, by which it is para- lyzed, and from the circumstance that after the operation for cataract the adapting power also disappears. When the eye is employed in the examination of near ob- 1 For an analysis of the various opinions on this subject, consult the Sup- plement to Miiller's Physiology. Fig. 130. Diagram to show the position and action of the ciliary muscle: a. Sclerotic. 6. Cornea, c. Cho- roid, separated a little from the sclerotic, d. Situation of the ci- liary ligament, and point from which the ciliary muscle radi- ates, e. Iris. n. Lens, connected with the ciliary processes by the anterior wall of the canal of Pe- tit, the situation of which is marked by the *. Magnified 3 diameters. VISION AT DIFFERENT DISTANCES. 443 jects, the pupil contracts, as do also the internal recti, and by the action of the ciliary muscles the lens is drawn forwards; all of which actions are performed by the influence of the third pair. The feel- ing of fatigue that is experienced under these circumstances is fami- liar to all, and arises from the effort made by the muscle above named. Whilst in the examination of distant objects, no such feel- ings are experienced, the lens retiring to the condition of repose, where it is maintained without muscular effort.] This view is supported by the fact that the adapting power of the eye can by many persons be exerted, and often rapidly, by a volun- tary effort, quite independent of any alteration in the direction of the axes of the eyes; for it is inconceivable how such an effect can be produced, except by muscular fibres. The observations of Volkmann and Hueck, and others, are also favorable to this view; since they show that in its quiescent state the eye is adapted to the vision of objects situated at the furthest point of distinct sight, and that, therefore, in order to accommodate itself to the vision of an object placed at any distance within this far point, the eye will require but one act, that, namely, of increas- ing its focal distance in proportion to the nearness of the object under view : an act of which the mind seems conscious by the effort which it has to make in adapting the eye to the vision of near ob- jects. No act is requisite to adapt the eye to the perception of dis- tant objects, for, in reverting to its state of rest, it at once resumes its capacity for distant vision, and retains it so long as its quiescent state continues. The range of distances through which persons can adapt their power of vision is not in all cases the same. Some persons possess scarcely any power of adaptation, and of this defect of vision there are two kinds: one, in which the person can see objects distinctly only when brought close to the eye, having little power to discern distant objects: another, in which distant objects alone can be dis- tinctly perceived, a small body being almost invisible except when held at a considerable distance from the eye. In the one case the person is said to be short-sighted or myopic: in the other, long-sighted or presbyopic. Myopia is caused by anything, such as undue con- vexity of the cornea, which increases the refracting power of the eye, and so causes the image of an object to be formed at a point anterior to the retina: the defect is remedied by the use of concave glasses. Presbyopia or long-sightedness is the result of conditions the reverse of the above, and is remedied by the use of convex glasses, which diminish the focal distance of an image formed in the eye.1 3. The direction given to the rays by their refraction is regulated by that of the central ray, or axis of the cone^ towards which the 1 For details on this subject consult Miiller (xxxii.), and the various trea- tises on the Physiology and Defects of Vision. 444 THE SENSES. rays are bont. The image of any point of an object is, therefore, as a rule (the exceptions to which need not here be stated), always formed in a line identical with the axis of the cone of light, as in the line B a, or a b, Fig. 131: so that the spot where the image of any point will be formed upon Fig. 131. the retina may be deter- mined by prolonging the central ray of the cone of light, or that ray which traverses the centre of the pupil. Thus, A b is the axis or central ray of the cone of light issuing from A; B a, the central ray of the cone of light issuing from B; the image of A is formed at b, the image of B at a, in the inverted position; therefore what in tbe object was above, is in the image below, and vice versd,—the right-hand part of the object is in the image to the left, the left-hand to the right. If an opening be made in an eye at its superior surface, so that the retina can be seen through the vitreous humor, this reversed image of any bright ob- ject, such as the windows of the room, may be perceived at tbe bot- tom of the eye. Or still better, if the eye of any albino animal, such as a white rabbit, in which the coats, from the absence of pig- ment, are transparent, is dissected clean, and held with the cornea towards a window, a very distinct image of the window completely inverted is seen depicted on the posterior translucent wall of the eye. Volkmann (xv. art. Sehen, p. 286) has also shown that a similar ex- periment may be successfully performed in a living person possessed of large, prominent eyes, and an unusually transparent sclerotica. No completely satisfactory explanation has yet been offered, to ac- count for the mind being able to form a correct idea of the erect position of an object of which an inverted image is formed on the retina. Miiller and Volkmann are of opinion that the mind really perceives an object as inverted but needs no correction, since every- thing is seen alike inverted, and the relative position of the objects therefore remains unchanged; and the only proof we can possibly have of the inversion is by experiment and the study of the laws of optics. It is the same thing as the daily inversion of objects conse- quent on the revolution of the entire earth, which we know only by observing the position of the stars; and yet it is certain that, within twenty-four hours, that which was below in relation to the stars, comes to be above. Hence it is, also, that no discordance arises be- tween the sensations of inverted vision and those of touch, which perceives everything in its erect position; for the images of all ob- jects, even of our own limbs, in the retina, are equally inverted, and therefore maintain the same relative position. Even the image of IDEAL SIZE OF FIELD OF VISION. 445 our hand, while used in touch, is seen inverted. The position in which we see objects, we call tberefore the erect position. A mere lateral inversion of our body in a mirror, where the right band occu- pies the left of the image, is indeed scarcely remarked : and there is but little discordance between the sensations acquired by touch in regulating our movements by the image in the mirror, and those of sight, as, for example, in tying a knot in the cravat. There is some want of harmony here, on account of the inversion being only lateral, and not complete in ail directions. The perception of the erect position of objects appears, therefore, to be the result of an act of the mind. And this leads us to a con- sideration of the several other properties of the retina, and of the co- operation of the mind in the several other parts of the act of vision. To these belong not merely the act of sensation itself, and the per- ception of the changes produced in the retina, as light and colors, but also the conversion of the mere images depicted in the retina into ideas of an extended field of vision, of proximity and distance, of the form and size of objects, of the reciprocal influence of dif- ferent parts of the retina upon each other, the simultaneous action of the two eyes, and some other phenomena. To speak first of the ideal size of the field of vision.—The actual size of the field of vision depends on the extent of the retina, for only so many images can be seen at any one time as can occupy the retina at the same time; and thus considered, the retina, of which the affections are perceived by the mind, is itself the field of vision. But to the mind of the individual the size of the field of vision has no determinate limits; sometimes it appears very small, at another time very large; for the mind has the power of projecting the im- ages on the retina towards the exterior. Hence the mental field of vision is very small when the sphere of the action of the mind is limited by impediments near the eye: on the contrary, it is very extensive when the projection of the images on the retina towards the exterior by the influence of the mind is not impeded. It is very small when we look into a hollow body of small capacity held before the eyes; large when we look out upon a landscape through a small opening; more extensive when we look at the landscape through a window; and most so when our view is not confined by any near object. In all these cases the idea which we receive of the size of the field of vision is very different, although its absolute size is in all the same, being dependent on the extent of the retina. Hence it follows, that the mind is constantly co-operating in the acts of vision, so that at last it becomes difficult to say what belongs to mere sensation, and what to the influence of the mind. By a mental operation of this kind, we obtain a correct idea of the size of individual objects, as well as of the extent of the field of vision. To understand this, it will be necessary to refer again to Fig. 131, p. 444. 38 446 THE SENSES. The angle x, included between the decussating central rays of two cones of light issuing from different points of an object, is called the optical angle—angulus opticus seu visorius. This angle be- comes larger, the greater the distance between the points A and b ; and since the angles x and y are equal, the distance between the points a and b in the image on the retina increases as the angle x becomes larger. Objects at different distances from the eye, but having the same optical angle, x — for example, the objects, c, d, and e — must also throw images of equal size upon the retina; and, if they occupy the same angle of the field of vision, their image must occupy the same spot in the retina. Nevertheless, these images appear to the mind of very unequal size when the ideas of distance and proximity come into play; for, from the image a b, the mind forms the conception of a visual space extending to e, d, or c, and of an object of the size which that re- presented by the image on the retina appears to have when viewed close to the eye, or under the most usual circumstances. A land- scape depicted on the retina, as a 6,and viewed under the angle x, is therefore conceived by the mind to have an extent of two miles, perhaps, if we know that its extent is such, or if we infer it to be so from the number of known objects seen at the same time. And in the same way that the images of several different objects, viewed under the same angle, thus appear to the mind to have a different size in the field of vision, so the whole field of vision, which has always the same absolute size, is interpreted by the mind as of ex- tremely various extent; and, for this reason also, the image viewed in the camera obscura is regarded as a real landscape—as the true field of vision — although only a small image depicted upon paper. The same mental process gives rise to the idea of depth in the field of vision; this idea being fixgd in our mind principally by the cir- cumstance that, as we ourselves move forwards, different images in succession become depicted on our retina, so that we seem to pass between these images, which to the mind is the same thing as pass- ing between the objects themselves. The action of the sense of vision in relation to external objects is, therefore, quite different from that of the sense of touch. The ob- jects of the latter sense are immediately present to it; and our own body, with which they come into contact, is the measure of their size. The part of a table touched by the hand appears as large as the part of the hand receiving an impression from it, for a part of our body in which a sensation is excited is here the measure by which we judge of the magnitude of the object. In the sense of vision, on the contrary, the images of objects are mere fractions of the objects themselves realized upon the retina, the extent of which remains constantly the same. But the imagination which analyzes the sensations of vision, invests the images of objects, together with the whole field of vision, in the retina, with very varying dimen- VISUAL DIRECTION. 447 sions; the relative size of the images in proportion to the whole field o vtsion, or of the affected parts of the retina to the whole retina alone remaining unaltered. The direction in which an object is seen, the direction of vision, or visual direction, depends on the part of the retina which receives the image and on the distance of this part from, and its relation to the central point of the retina. Thus, objects of which the images all upon the same parts of the retina lie in the same visual direc- tion; and when, by the action of the mind, the images or affections ot the retina are projected into the exterior world, the relation of the images to each other remains the same. The estimation of the form of bodies by sight is the result partly of the mere sensation, and partly of the association of ideas. Since t he form of the images perceived by the retina depends wholly on the outline of the part of the retina affected, the sensation alone is adequate to the distinction of only superficial forms from each other, as of a square from a circle. But the idea of a solid body, as a sphere, or a body of three or more dimensions, e. g., a cube, can only be attained by the action of the mind constructing it from the different superficial images seen in different positions of the eye with regard to the object; and, as shown by Mr. Wheatstone and illustrated in the stereoscope, from two different perspective projec- tions of the body being presented simultaneously to the mind by the two eyes. Hence, when in adult age sight is suddenly restored to persons blind from infancy, all objects in the field of vision appear at first as if painted flat on one surface; and no idea of solidity is formed until after long exercise of the sense of vision combined with that of touch. . We judge of the motion of an object, partly from the motion of its image over the surface of the retina, and partly from the motion of our eyes following it. If the image upon the retina moves while our eyes and our body are at rest, we conclude that the object is changing its relative position with regard to ourselves. In such a case the movement of the object may be apparent only, as when we are standing upon a body which is in motion, such as a ship. If, on the other hand, the image does not move with regard to the retina, but remains fixed upon the same spot of that membrane, while our eyes follow the moving body, we judge of the motion of the object by the sensation of the muscles in action to move the eye. If the imao-e moves over the surface of the retina while the muscles of the eye are acting at the same time in a manner corresponding to this motion, as in reading, we infer that the object is stationary, and we know that we are merely altering the relation of our eyes to the object. Sometimes the object appears to move when both object and eye are fixed, as in vertigo. The mind can, by the faculty of attention, concentrate its activity more or less exclusively upon the senses of sight, hearing, and touch 448 THE SENSES. alternately. When exclusively occupied with the action of one sense, it is scarcely conscious of the sensations of the others. The mind, when deeply immersed in contemplations of another nature, is indif- ferent to the actions of the sense of sight, as of every other sense. We often when deep in thought have our eyes open and fixed, but see nothing owing to the action of the fibres of the optic nerves being unable to excite the mind to perception when otherwise engaged. The attention which is thus necessary for vision, is neces- sary also to analyze what the field of vision presents. The mind does not perceive all the objects presented by the field of vision at the same time with equal acuteness, but directs itself first to one and then to another. The sensation becomes more intense according as the particular object is at the time the principal subject of mental con- templation. Any compound mathematical figure produces a differ- ent impression, according as the attention is directed exclusively to one or the other part of it. Thus, in (Fig. 132,) we may in suc- cession have a vivid perception of the whole, or of dis- Fig. 132. tinct parts only; of the six triangles near the outer circle, of the hexagon in the middle, or of the three large triangles. Tbe more numerous and varied the parts of which a figure is composed, the more scope does it afford for the play of the attention. Hence it is that architectural ornaments have an enlivening effect on the sense of vision, since they afford constantly fresh subject for the action of the mind. The duration of the sensations of the retina is much longer than that of the impressions which produce them: according to Plateau, the sensation persists 0-32 to 0-35 of a second after the impression has ceased; and the duration of the after-sensation or spectrum, is greater in a direct ratio with the duration of the impression which caused it. Hence the image of a bright object, as of the panes of a window through which the light is shining, may be perceived in the retina for a considerable period, if we have previously kept our eye fixed for some time on them. The color of the spectrum varies with that of the object which produced it. The spectra left by the images of white or luminous objects are ordinarily white or luminous ; those left by dark objects are dark. Sometimes, however, the relation of the light and dark parts in the image may, under certain circumstances, be reversed in the spectrum; what was bright may be dark, and what was dark may appear light. This occurs whenever the eye, which is the seat of the spectrum of a luminous object, is not closed, but fixed upon another bright or white surface, as a white wall or a sheet of white paper. Hence the spectrum of the sun, which, while light is ex- cluded from the eye, is luminous, appears black or grey when the eye is directed upon a white surface. The explanation of this is that the part of the retina which has received the luminous image ACTION OF PARTS OF RETINA ON EACH OTHER. 449 remains for a certain period afterwards in an excited state, while that which has received a dark image is in an unexcited, and there- fore much more excitable, condition. The ocular spectra which remain after the impression of colored objects upon the retina are always colored; and their color is not that of the object, or of the image produced directly by the object, but the opposite, or complemental color. The spectrum of a red object is, therefore, green; that of a green object, red; that of violet, yel- low; that of yellow, violet, and so on. The colors which thus reciprocally excite each other in the retina are those placed at oppo- site points of the circle in Fig. 133. Fig. 133. A oircle showing the various simple and compound colors of light, and those which are complemental of each other, i. e., which, when mixed, produce a neutral grey tint. The three simple colors, red, yellow, and blue, are placed at the angles of an equilateral triangle, which are connected together by means of a circle; the mixed colors, green, orange, and violet, are placed intermediate between the corresponding simple or homogeneous colors; and the com- plemental colors, of which the pigments when mixed would constitute a grey, and of which the prismatic spectra would together produce a white- light, will be found to be placed in each oase opposite to each other, but connected by a line passing through the centre of the circle- The figure is also useful in showing the further shades of color which are complementary of each other. If the circle be supposed to contain every transition of color between the six marked down, those which, when united, yield a white or grey color, will always be found directly opposite to each other; thus, for example, the intermediate tint between orange and red is complemental of the middle tint between green and blue. Of the reciprocal Action of different Parts of the Retina on each other. Although each elementary part of the retina represents a distinct portion of the field of vision, yet the different elementary parts, or sensitive points, of that membrane have a certain influence on each other; the particular condition of one influencing that of another, so that the image perceived by one part is modified by the image depicted in the other. The phenomena, which result from this rela- tion between the different parts of the retina, may be arranged in two classes; the one including those where the condition existing in the greater extent of the retina is imparted to the remainder of that membrane; the other consisting of those in which the condition of 38* 450 THE SENSES. the larger portion of the retina excites in the less extensive portion the opposite condition. 1. When two opposite impressions occur in contiguous parts of an image on the retina, the one impression is, under certain circum- stances, modified by the other. If the impressions occupy each one- half of the image, this does not take place; for in that case, their actions are equally balanced. But if one of the impressions occupies only a small part of the retina, and the other the greater part of its surface, the latter may, if long continued, extend its influence over the whole retina, so that the opposite less extensive impression is no longer perceived, and its place becomes occupied by the same sensa- tion as the rest of the field of vision. Thus, if we fix the eye for some time upon a strip of colored paper lying upon a white surface, the image of the colored object, especially when it falls on the lateral parts of the retina, will gradually disappear, and the white surface be seen in its place. The disappearance of images which fall on the point of entrance of the optic nerve is also attributed by Miiller to this property pos- sessed by the retina of imparting the condition affecting its larger part to the remainder. The more common explanation of the pheno- menon, however, is, that the retina corresponding to the point of entrance of the optic nerve is completely insensible to the impres- sions of light. The phenomenon itself is very readily shown. If we direct one eye, the other being closed, upon a point at such dis- tance to the side of any object that the image of the latter must fall upon the retina at the point of entrance of the optic nerve, this image is lost either instantaneously or very soon. If, for example, we close the left eye, and direct the axis of O >j, the right eye steadily towards the circular spot here represented, while the page is held at a distance about five times greater than that of the objects from each other, the cross will vanish, and the color of the paper will be seen in its place. That this phenomenon arises from the image falling on the point of entrance of the optic nerve, is shown by fixing the same eye upon the cross instead of upon the round dot; the latter object then docs not disappear, or only after long persistence of the im- pression. 2. In the second class of phenomena, the affection of one part of the retina influences that of another part not in such a manner as to obliterate it, but so as to cause it to become the contrast or opposite of itself. Thus a grey spot upon a white ground appears darker than the same tint of grey would do if it alone occupied the whole field of vision, and a shadow is always rendered deeper when the light which gives rise to it becomes more intense, owing to the greater contrast. The former phenomena ensue gradually, and only after the images have been long fixed on the retina; the latter are instantaneous in their production, and are permanent. SIMULTANEOUS ACTION OF BOTH EYES. 451 In the same way, also, colours may be produced by contrast. Thus, a very small dull-grey strip of paper, lying upon an extensive surface of any bright colour, does not appear grey, but has a faint tint of the colour which is tbe contrast of that of the surrounding surface (see page 449). A strip of grey paper upon a green field, for example, often appears to have a tint of red, and when lying upon a red surface, a greenish tint; it has an orange-coloured tint upon a bright blue surface, and a blueish tint upon an orange- colored surface; a yellowisb colour upon a bright violet, and a violet tint upon a bright yellow surface. The colour excited thus, as a contrast to the exciting colour, being wholly independent of any rays of the corresponding colour acting from without upon the re- tina, must arise as an opposite or antagonistic condition of that mem- brane ; and the opposite conditions of which the retina thus becomes the subject would seem to balance each other by their reciprocal reaction. A necessary condition for the production of the contrasted colours is, that the part of the retina in which the new colour is to be excited, shall be in a state of comparative repose; hence the small object itself must be grey. A second condition is, that the colour of the surrounding surface shall be very bright, that is, it shall contain much white light. Of the Simultaneous Action of the two Eyes. Although the sense of sight is exercised by two organs, yet the impression of an object conveyed to the mind is single. Various theories have been advanced to account for this phenomenon. By Gall, it was supposed that we do not really employ both eyes simul- taneously in vision, but always see with one only at a time. This especial employment of one eye in vision certainly occurs in persons whose eyes are of very unequal focal distance, but in the majority of individuals both eyes are simultaneously in action in the percep- tion of the same object; this is shown by the double images seen under certain conditions. If two fingers be held up before the eyes, one in front of the other, and vision be directed to the more distant, so that it is seen singly, the nearer will appear double; while, if the nearer one be regarded, the more distant will be seen double; and one of the double images in each case will be found to belong to one eye, the other to the other eye. Single vision results only when certain parts of the two retinae are affected simultaneously; if different parts of the retinas receive the image of the object, it is seen double. The parts of the retinae in the two eyes which thus correspond to each other in the property of referring the images which affect them simultaneously, to the same spot in the field of vision, are in man just those parts which corres- pond to each other if one retina were placed exactly in front of, and over, the other (as in Fig. 134, c). Thus the outer lateral por- 452 THE SENSES. tion of one eye corresponds to, or, to use a better term, is identical with, the inner portion of the Fig- 134. other eye; or a of the eye A (fig. 134) with a' of the eye B. The ' upper part of one retina is also identical with the upper part of the other; and the lower parts of the two eyes are identical with each other. This is proved by a single ex- periment. Pressure upon any part of the ball of the eye, so as to affect the retina, produces a luminous circle seen at the opposite side of the field of vision to that on which the pressure is made. If, now, in a dark room, we press with the finger at the upper part of one eye, and at the lower part of the other, two luminous circles are seen, one above the other, so, also, two figures are seen, when pressure is made simultaneously on the two outer or the two inner sides of both eyes. It is certain, therefore, that neither the upper part of one retina and the lower part of the other are identical, nor the outer lateral parts of the two retinae, nor their inner lateral portions. But if pressure be made with the fingers upon both eyes simultaneously at their lower part, one luminous ring is seen at the middle of the upper part of the field of vision; if the pressure be applied to the upper part of both eyes, a single luminous circle is seen in the middle of the field of vision below. So, also, if we press upon the outer side a of the eye A, and upon the inner side a' of the eye B, a single spectrum is produced, and is apparent at the extreme right of the field of vision; if upon the point b of one eye, and the point b' of the other, a single spectrum is seen to the extreme left. The spheres of the two retinae may, therefore, be regarded as lying one over the other, as in c, Fig. 134; so that the left portion of one eye lies over the identical left portion of the other eye, the right portion of one eye over the identical right portion of the other eye; and with the upper and lower portions of the two eyes, a lies over a', b over V', and c over c'. The points of the one retina in- termediate between a and c, are again identical with the corres- pondent points of the other retina between a' and c'; those between b and c of the one retina, with those between V and c' of the other. In short, all other parts are non-identical: and, when they are ex- cited to action, the effect is the same as if the impressions were made on different parts of the same retina: and the double images belong- ing to the eyes A and B, are seen at exactly the same distance from each other as exists between the image of the eye A and the part of the retina of the eye A which corresponds to, or is identical with, the seat of the second image in the eye b; or, to return the figure already used in illustration (fig. 134), if a of one eye be affected, and \U DIVERGENCE OF AXES IN QUADRUPEDS. 453 V of the other, the distances of the two images a and V will, inas- much as a is identical with a', and b with V, lie at exactly the same distance from each other as images produced by impressions on the points a b of the one eye, or a! U of the other. In application of these results to the phenomena of vision, if the position of the eyes with regard to a luminous object be such that similar images of the same object fall on identical parts of the two retime, as occurs when the axes meet in some one point, the object is seen single; if otherwise, as in the various forms of squinting, two images are formed, and double vision results. If the axes of the eyes, A and b (Fig. 135), be so directed that they meet at a, an object at a will be seen singly, for the point a of the one retina, and a' of the other, are identical. - So, also, if the object /3 be so situated that its image falls in both eyes at the same distance from the central point of the retina,—namely, at b in the one eye, and at b' in the other, —a will be seen single, for it affects identical parts of the two retinae. The same will apply to the object «. In quadrupeds, the relation between the identical and non- identical parts of the retinae cannot be the same as in man; for the axes of their eyes gene- rally diverge, and can never be made to meet in one point of an object. When an ani- mal regards an object situated directly in front of it, the image of the object must fall in both eyes on the outer portion of the retinae. Thus the image of the object a (Fig. 136) will fall at a' in one eye, and at a" in the other: and these points a' and a" must be identi- cal. So, also, for distinct and single vision of objects, b or c, the points V and b", or c' and c", in the two retinae, on which the im- ages of these objects fall, must be identical. All points of the re- tina in each eye which receive rays of light from lateral objects only, can have no correspondent identical points in the retina of the other eye; for otherwise two objects, one situated to the right and the other to the left, would appear to lie in the same spot of the field of vision. It is probable, therefore, that there are in the eyes of ani- mals parts of the retinae which are identical, and parts which are not identical, i. &^A)ll is united to the incus at right angles. These u several changes in the direction of the chain of \ ^__ bones have, however, no influence on that of the \ undulations, which remains the same as it was in "<5T~ the meatus externus and long process of the mal- \ leus, so that the undulations are communicated by \ a the stapes to the fenestra ovalis in a perpendicular \ direction. Increasing tension of the membrana tympani diminishes the facility of transition of sonorous undulations from the air to it. M. Savart observed that the dry membrana tympani, on the ap- proach of a body emitting a loud sound, rejected particles of sand strewn upon it more strongly when lax than when very tense; and inferred, therefore, that hearing is rendered less acute by increasing 1 Eduard Weber (cxxxv. 1846) has shown, however, that the existence of the membrane over the fenestra rotunda will permit of such approximation and removal of the stapes to and from the labyrinth. When by the stapes the membrane of the fenestra ovalis is pressed towards the labyrinth, the mem- brane of the fenestra rotunda may, by the pressure communicated through the fluid of the labyrinth, be pressed towards the cavity of the tympanum. OFFICE OF THE EUSTACHIAN TUBE. 467 the tension of the membrana tympani. Miiller has confirmed this by experiments with small membranes arranged so as to imitate the membrana tympani: and it may be confirmed also by observation on one's self. For the membrana tympani in one's own person may be rendered tense at will in two ways, namely, by a strong and con- tinued effort of expiration or of inspiration, while the mouth and nostrils are closed. In the first case, the compressed air is forced with a whizzing sound into the tympanum, the membrana tympani is made tense, and immediately hearing becomes indistinct. The same temporary imperfection of hearing is produced by rendering the membrana tympani tense, and convex towards the interior, by the effort of inspiration. The imperfection of hearing, produced by the last-mentioned method, may continue for a time even after the mouth is opened, in consequence of the previous effort at inspiration having induced collapse of the walls of the Eustachian tubes-, which prevents the restoration of equilibrium of pressure between the air within the tympanum and that without: hence we have the oppor- tunity of observing that even our own voice is heard with less intensity when the tension of the membrana tympani is great. If the pressure of the external air or atmosphere be very great, while, on account of collapse of the walls of the Eustachian tube, the air in the interior of the tympanum fails to exert an equal counter-pressure, the membrana tympani will of course be forced inwards, and imperfect deafness be produced. Thus it may be explained why, in a diving-bell, voices sound faintly. In all cases, the effect of the increased tension of the membrana tympani is not to render both grave and acute sounds equally fainter tban before. On the contrary, as observed by Dr. Wollaston, the increased tension of the membrana tympani produced by exhausting the cavity of the tympanum, makes one deaf to grave sounds only. The principal office of the Eustachian tube, in Miiller's opinion, has relation to the prevention of these effects of increased tension of the membrana tympani. Its existence and openness will provide for the maintenance of the equilibrium between the air within the tympanum and the external air, so as to prevent the inordinate tension of the membrana tympani which would be produced by too great or too little pressure on either side. While discharging this office, however, it will serve to render sounds clearer, as (Henle suggests) the apertures in violins do; to supply the tympanum with air; and to be an outlet for mucus: and the ill effects of its obstruction may be referred to the hinderance of all these its offices, as well as of that ascribed to it as its principal use. The influence of the tensor tympani muscle in modifying hearing may also be probably explained in connection with the regulation of the tension of the membrana tympani. If, through reflex nervous action, it can be excited to contraction by a very loud sound, just as the iris and orbicularis palpebrarum muscle are by a very intense 468 THE SENSES. light, then, it is manifest that a very intense sound would, through the action of this muscle, induce a deafening or muffling of the ears. It is in favor of this supposition that a loud sound excites, by reflection, nervous action, winking of the eyelids, and, in persons of irritable nervous system, a sudden contraction of many muscles. The influence of the stapedius muscle in hearing is unknown. It acts upon the stapes in such a manner as to make it rest obliquely in the fenestra ovalis, depressing that side of it on which it acts, and elevating the other side to the same extent. When the fenestra ovalis and fenestra rotunda exist together with a tympanum, the sound is transmitted to the fluid of the internal ear in two ways,—namely, by solid bodies and by membrane; by both of which conducting media sonorous vibrations are communicated to water with considerable intensity. The sound being conducted to the labyrinth by two paths will, of course, produce so much the stronger impression; for undulations will be thus excited in the fluid of the labyrinth from two different though contiguous points, and by the crossing of these undulations, stationary waves of increased inten- sity will be produced in the fluid. Miiller's experiments show that the same vibrations of the air act upon the fluid of the labyrinth with much greater intensity through the medium of the chain of auditory bones and the fenestra ovalis, than through the medium of the air of the tympanum and the membrane closing the fenestra rotunda: but the cases of disease in which the ossicula have been lost without loss of hearing, prove that sound may also be well con- ducted through the air of the tympanum and the membrane of the fenestra rotunda. Functions of the Labyrinth. The fluid of the labyrinth or perilymph is the most general and constant of the acoustic provisions of the labyrinth. In all forms of organs of hearing, the sonorous vibrations affect the auditory nerve through the medium of a fluid : and the reason for this provision is probably to be found in the following circumstances. The ultimate purpose of the organ of hearing is to impart, as perfectly as possible, the impulses of the sonorous vibrations to the fibres of the auditory nerve. This nerve being soft, and, like all nerves, impregnated with water, sonorous undulations, if directly communicated to it from solid parts, would be partly converted into undulations of a fluid, before producing their impression on the fibres. Besides, however, the im- pregnation of the nervous fibres with water, on which their softness depends, all the interspaces between the fibres are, as in all soft tissues, filled with fluid matters, either blood or the fluid of cellular membrane. Hence the auditory nerve, in receiving the sonorous undulations through the medium of the fluid of the labyrinth, receives them from a medium of the same kind as that which occupies all USE OF THE SEMICIRCULAR CANALS. 469 the pores and interstices of the nervous fibres themselves. On this account, the vibration of the particles in the nerve itself will proba- bly be much more uniform in character than if the surfaces of the nerve had been in contact with solid parts: in which case, the more internal particles of the nerve, being distant from the surface of the solid bone, would be acted on in a different manner from the more superficial particles. The function usually ascribed to the semicircular canals is the collecting, in their fluid contents, the sonorous undulations from the bones of the cranium. They have probably, also, in some degree the power of conducting sounds in the direction of their curved cavities more easily than the sounds are carried off by the surround- ing hard parts in the original direction of the undulations, though this conducting power is in them much less perfect than in tubes containing air. Admitting that they have these powers, the increased intensity of the sonorous vibrations thus attained will be of advantage in acting on the auditory nerve where it is expanded in the ampullae of the canals, and in the utriculus. Where the membranous canals are in contact with the solid parietes of the tubes, this action must be much more intense. But the membranous semicircular canals must have a function independent of the surrounding hard parts; for in the Petromyzon they are not separately enclosed in solid substance, but lie in one common cavity with the utriculus. The crystalline pulverulent masses in the labyrinth would reinforce the sonorous vibrations by their resonance, even if they did not actually touch the membranes upon which the nerves are expanded; but, inasmuch as these bodies lie in contact with the membranous parts of the labyrinth, and the vestibular nerve-fibres are imbedded in them, they communicate to these membranes and the nerves vibratory impulses of greater intensity than the fluid of the labyrinth can impart. This appears to be the office of the otoconia. Sonorous undulations in water are not perceived by the hand itself immersed in the water, but are felt distinctly through the medium of a rod held in the hand. The cochlea seems constructed for the'spreading out of the nervous fibres over a wide extent of surface, upon a solid lamina communica- ting with the solid walls of the labyrinth and cranium, at the same time that it is in contact with the fluid of the labyrinth ; and which, beside exposing the nervous fibres to the influence of sonorous undu- lations by two media, is itself insulated by fluid on either side. The connection of the lamina spiralis with the solid walls of the labyrinth adapts the cochlea for the perception of the sonorous undu- lations propagated by the solid parts of the head and the walls of the labyrinth. The membranous labyrinth of the vestibule and semi- circular canals is suspended free in the perilymph, and is destined more particularly for the perception of sounds through the medium 40 470 THE SENSES. of that fluid, whether the sonorous undulations are imparted to the fluid through the fenestrae, or by the intervention of the cranial bones, as when sounding bodies are brought into communication with the head or teeth. The spiral lamina on which the nervous fibres are expanded in the cochlea is, on the contrary, continuous with the solid walls of the labyrinth, and receives directly from them the im- pulses which they transmit. This is an important advantage; for the impulses imparted by solid bodies have, ceteris paribus, a greater absolute intensity than those communicated by water. And, even when a sound is excited in the water, the sonorous undulations are more intense in the water near the surface of the vessel containing it than in other parts of the water equally distant from the point of origin of the sound : hence we may conclude that, cceteris paribtis, the sonorous undulations of solid bodies act with greater intensity than those of water. Hence we perceive at once an important use of the cochlea. This is not, however, the sole office of the cochlea; the spiral lamina, as well as the membranous labyrinth, receives sonorous im- pulses through the medium of the fluid of the labyrinth from the cavity of the vestibule and from the fenestra rotunda. The lamina spiralis is, indeed, much better calculated to render the action of these undulations upon the auditory nerve efficient than the mem- branous labyrinth is; for, as a solid body insulated by a different medium, it is capable of resonance. Lastly, it may be observed, that the fibres of the nerve being spread out singly upon the lamina spiralis is advantageous, because, in the first place, it ensures a more complete participation of the fibres in the impulses communicated by the solid parts of the coch- lea ; and, secondly, the intensity with which the sonorous undulations are communicated to a body is proportionate to the extent of surface over which they can act on it. Sensibility of the Auditory Nerve. Most frequently, several undulations or impulses on the auditory nerve concur in the production of the impressions of sound. But that a single impulse may be sufficient to excite the sensation, we have an example in the sound produced by an explosion or the sudden division of air, by the coming together of two previously separated bodies of air, as in cracking a whip, etc. There is, at all events, nothing to refute this opinion; although it must be admitted that a single shock to the air will very readily excite a succession of undu- lations. By the rapid succession of several impulses at unequal intervals, a noise or rattle is produced; from a rapid succession of several im- pulses at equal intervals, a musical sound results, the height or DISTINCTION OF DIFFERENT SOUNDS. 471 acuteness of which increases with the number of the impulses com- municated to the ear within a given time. A sound of definite mu- sical value is also produced when each of the impulses, succeeding each other thus at regular intervals, is itself compounded of several undulations, in such a way that it would alone give the impression of an unmusical sound; that is to say, by sufficiently rapid succes- sion of short unmusical sounds at regular intervals a musical sound is generated. It would appear that two impulses, which are equivalent to four single or half vibrations, are sufficient to produce a definite note audible as such through the auditory nerve. The note produced by the shocks of the teeth of a revolving wheel at regular intervals upon a solid body, is still heard when the teeth of the wheel are re- moved in succession until two only are left; the sound produced by the impulses of these two teeth has still tbe same definite value in the scale of music. The maximum and minimum of the intervals of successive im- pulses still appreciable through the auditory nerve as determinate sounds, have been determined by M. Savart. If their intensity is sufficiently great, sounds are still audible which result from the suc- cession of 48,000 half vibrations, or 24,000 impulses in a second; and this, probably, is not the extreme limit in acuteness of sounds perceptible by the ear. For the opposite extreme, he has succeeded in rendering sounds audible which were produced by only fourteen or eighteen half vibrations, or seven or eight impulses, in a second; and sounds still deeper might probably be heard, if the individual impulses could be sufficiently prolonged. By removing one or several teeth from the toothed wheel before mentioned, M. Savart was also enabled to satisfy himself of the fact that, in the case of the auditory nerve, as in that of the optic nerve, the sensation continues longer than the impression which causes it; for the removal of a tooth from the wheel produced no interruption of the sound. The gradual cessation of the sensation of sound ren- ders it difficult, however, to determine its exact duration beyond that of the impression of the sonorous impulses. The power of perceiving the direction of sounds is not a faculty of the sense of hearing itself, but is an act of the mind judging on experience previously acquired. From the modifications which the sensation of sound undergoes according to the direction in which the sound reaches us, the mind infers the position of the sounding body. Tbe only true guide for this inference is the more intense action of the sound upon one than upon the other ear. But even here there is room for much deception by the influence of reflexion or resonance, and by the propagation of sound from a distance with- out loss of intensity through curved conducting-tubes filled with air. By means of such tubes, or of solid conductors which convey the 472 THE SENSES. sonorous vibrations from their source to a distant resonant body, sounds may be made to appear to originate in a new situation. The direction of sound may also be judged of by means of one ear only; the position of the ear and head being varied, so that the sonorous undulations at one moment fall upon the ear in a perpen- dicular direction, at another moment obliquely. But when neither of these circumstances can guide us in distinguishing the direction of sound, as when it falls equally upon both ears, its source being, for example, either directly in front or behind us, it becomes impos- sible to determine whence the sound comes. Ventriloquists take advantage of the difficulty with which the direction of sounds is recognised, and also of the influence of the imagination over our judgment, when they direct their voice in a certain direction, and at the same time pretend themselves to hear the sounds coming from thence. The distance of the source of sounds is not recognised by the sense itself, but is inferred from their intensity. The sound itself is always seated but in one place, namely, in our ear; but it is in- terpreted as coming from an exterior soniferous body. When the intensity of the voice is modified in imitation of the effect of dis- tance, it excites the idea of its originating at a distance; and this also is taken advantage of by ventriloquists. The experiments of Savart, already referred to, prove that the effect of the action of sonorous undulations upon tbe nerve of hear- ing endures somewhat longer than the period during which the un- dulations are passing through the ear. If, however, the impression of the same sound be very long continued, or constantly repeated for a long time, then the sensation produced may continue for a very long time, more than twelve or twenty-four hours even, after the original cause of the sound has ceased. This must have been expe- rienced by every one who has travelled several days continuously; for some time after the journey the rattling noises are heard when the ear is not acted on by other sounds. We have here a proof that the perception of sound as sound, is not essentially connected with the existence of undulatory pulses; and that the sensation of sound is a state of the auditory nerve, which, though it may be excited by a succession of impulses, may also be produced by other causes. The sensations of the retina re- maining after the external impression of light has ceased, have been attributed to a retention of some of the matter of light for a certain time by the retina, as in the absorption of light by dark bodies; but in the case of the sense of hearing, such an hypothesis is evidently untenable. No irritating matter and no impulse can be here re- tained ; and, even if it be supposed that undulations excited by the impulse are kept up in the auditory nerve for a certain time, they must be undulations of the nervous principle itself, which, being excited, continue until the equilibrium is restored. SUBJECTIVE SOUNDS. 473 Corresponding to the double vision of the same object with the two eyes, is the double hearing with the two ears; and analogous to the double vision with one eye, dependent on unequal refraction, is the double hearing of a single sound with one ear, owing to the sound coming to the ear through media of unequal conducting power. The first kind of double hearing is very rare; instances of it are recorded, however, by Sauvages and Itard. The second kind, which depends on the unequal conducting power of two media through which the same sound is transmitted to the ear, may easily be experienced. If a small bell be sounded in water, while the ears are closed by plugs, and a solid conductor is interposed between the water and the ear, two sounds will be heard, differing in intensity and tone; one being conveyed to the ear through the medium of the atmosphere, the other through the conducting-rod. The sense of vision may vary in its degree of perfection as regards either the faculty of adjustment to different distances, the power of distinguishing accurately the particles of the retina affected, sensibi- lity to light and darkness, or the perception of the different shades of color. In the sense of hearing there is no parallel to the faculty by which the eye is accommodated to distance, nor to the perception of the particular part of the nerve affected; but just as one person sees distinctly only in a bright light, and another only in a mode- rate light, so in different individuals the sense of hearing is more perfect for sounds of different pitch: and just as a person, whose vision for the forms of objects, etc., is acute, nevertheless distin- guishes colors with difficulty, and has no perception of the harmony and disharmony of colors, so one, whose hearing is good as far as regards the sensibility to feeble sounds, is sometimes deficient in the power of recognising the musical relation of sounds, and in the sense of harmony and discord; while another individual, whose hearing is in other respects imperfect, has these endowments. The causes of these differences are unknown. Subjective sounds are the result of a state of irritation or excite- ment of the auditory nerve produced by other causes than sonorous impulses. A state of excitement of this nerve, however induced, gives rise to the sensation of sound. Hence the ringing and buzzing in the ears heard by persons of irritable and exhausted nervous_ sys- tem, and by patients with cerebral disease, or disease of the auditory nerve itself; hence also the noise in the ears heard for some time after a long journey in a rattling noisy vehicle. Bitter found that electricity also excites a sound in the ears. From the above truly subjective sounds we must distinguish those dependent, not on a state of the auditory nerve itself merely, but on sonorous vibrations excited in the auditory apparatus. Such are the buzzing sounds attendant on vascular congestion of the head and ear, or on aneu- rismal dilatation of the vessels. Frequently, even the simple pul- satory circulation of the blood in the ear is heard. To the sounds 474 THE SENSES. of this class belong also the snapping sound in the ear produced by a voluntary effort, and the buzz or hum heard during the contrac- tion of the palatine muscles in the act of yawning; when air is forced into the tympanum, so as to make tense the membrana tym- pani; and in the act of blowing the nose, as well as during the forcible depression of the lower jaw. Irritation or excitement of the auditory nerve is capable of giving rise to movements in the body, and to sensations in other organs of sense. In both cases it is probable that the laws of nervous reflec- tion, through the medium of the brain, come into play. An in- tense and sudden noise excites, in every person, closure of the eye- lids, and in nervous individuals a start of the whole body, or an un- pleasant sensation like that produced by an electric shock through- out the body, and sometimes a particular feeling in the external ear. Various sounds cause in many people a disagreeable feeling in the teeth, or a sensation of cold trickling through the body; and, in some people, intense sounds are said to make the saliva collect. The sense of hearing may in its turn be affected by impressions on many other parts of the body; especially in diseases of the abdo- minal viscera, and in febrile affections. Here, also, it is probable that the central organs of the nervous system are the media through which the impression is transmitted. SENSE OF TASTE. The conditions for the perception of taste are : — 1, the presence of a nerve with special endowments; 2, the irritation of this nerve by the sapid matters; 3, the solution of these matters in the secre- tions of the organ of taste. The nerves concerned in the produc- tion of the sense of taste have been already considered (pp. 375-6). The mode of action of the substances which excite taste probably consists in the production of a change in the internal condition of the gustatory nerves, and, according to the difference of the sub- stances, an infinite variety of changes of condition, and consequently of tastes, may be induced. It is not, however, necessary for the manifestation of taste that sapid substances in solution should be brought into contact with its nerves. For the nerves of taste, like the nerves of other special senses, may have their peculiar properties excited by various other kinds of irritation, such as electricity and mechanical impressions. Thus Henle observed that a small current of air directed upon the tongue gives rise to a cool saline taste, like that of saltpetre; and Dr. Baly has shown that a distinct sensation of taste, similar to that caused by electricity, may be produced by a smart tap applied to the papillae of the tongue. Moreover, the mechanical irritation of the fauces and palate produces the sensation of nausea, which is probably only a modification of taste. The matters to be tasted must either be in solution or be soluble STRUCTURE OF THE TONGUE. 475 Fig. 146. in the moisture covering the tongue; hence insoluble substances are usually tasteless, and produce merely sensations of touch. More- over, for a perfect action of a sapid, as of an odorous substance, it is necessary that the sentient surface should be moist. Hence, when the tongue and fauces are dry, sapid substances, even in solution, are with difficulty tasted. The principal, but not exclusive, seat of the sense of taste is the fauces and tongue. The tongue is a muscular organ whose use in relation to mastication and deglutition has already been considered (p. 178). The free surface is covered with structures analogous to those of the skin, namely, a cutis or corium, on which are placed papillae, and which, together with them, is invested by epithelium. The cutis is thinner and less dense than that of the skin, but is constructed of similar tissue, serves as a ground-work for the ramifica- tion of the abundant blood- vessels and nerves which the tongue receives, and affords insertion to the extremities of the muscular fibres of which the chief substance of the organ is composed. The papillae of the tongue are thickly set over its whole upper surface, giving to it its characteristic roughness (Fig. 14G). Their greater promi- nence than those of the skin is due to their interspaces not being filled up with epithe- lium, as the interspaces of the papilla? of the skin are. The papillae of the tongue present several diversities of form; but three principal varieties, differing both in seat and general characters, may usually be distinguished. 1st. Cir- cumvallate or calyciform pa- pilla?, eight or ten in number, situate in two V-shaped lines at the base of the organ. These are circular elevations from .,Lth to T\jth of an inch wide, each with a central de- Tongue, seen on its upper surface: a. One of the circumvallate papillre. b. One of the fungi- form papillae. Numbers of the conical papillaa are seen about d, and elsewhere, e. Glottis, epiglottis, and glosso-epiglottidean folds of mucou- membrane.—From Soemmering, 476 THE SENSES. pression, and surrounded by a circular fissure, at the outside of which again is a slightly-elevated ring; both the central elevation and the ring being formed of close-set simple papilla?. 2d. Fungi- form papillae, scattered chiefly over the sides and tip, and sparingly over the middle of the dorsum, of the tongue; their name is derived from their being usually narrower at their base than their summit. These also consist of groups of simple papillae, each of which con- tains in its interior a loop of capillary blood-vessels, and a nerve- fibre. 3d. Conical or filiform papillae: these, which are the most abundant, are scattered over the whole surface, but especially over the middle of the dorsum. Their name denotes their shape. The epithelium of the tongue is of the tessellated kind, like that of the epidermis (p. 262). It covers every part of the surface, but over the fungiform papilla? forms a thinner layer than elsewhere, so that these papillae stand out more prominently than the rest. The epithelium covering the conical papillae has been shown by Todd and Bowman (xxxix. Am. Ed., p. 382), to have a singular arrangement; being extremely dense and thick, and projecting from their sides and summits in the form of long, stiff, hair-like processes. Many of these processes bear a close resemblance in structure to hairs, and some actually contain minute hair-tubes. Each of the three varieties of papilla? just described have been commonly regarded as simple processes, like the papilla? of the skin, but Todd and Bowman have shown that the surface of each is studded by minute conical processes of mucous membrane, which thus form secondary papilla?. These secondary papilla? also occur over most other parts of the tongue, not occupied by the compound papilla?. They are commonly buried beneath the epithelium; hence have been hitherto overlooked. Such, in outline, is the structure of the sensitive surface of the tongue. But the tongue is not the only seat of the sense of taste, for the results of experiments as well as ordinary experience show that the soft palate and its arches, the uvula, tonsils, and probably the upper part of the pharynx are endowed with taste. These parts, together with the base and posterior parts of the tongue, are supplied with branches of the glosso-pharyngeal, and evidence has been already adduced (p. 375) that the sense of taste is con- ferred upon them by this nerve. In most, though not in all, persons, the anterior part of the tongue, especially the edges and tip, are supplied with taste. The middle of the dorsum is only feebly endowed with this sense, probably be- cause of the density and thickness of the epithelium covering the filiform papillae of this part of the tongue, which will prevent the sapid substances from penetrating to their sensitive parts. The use of these papilla? is, therefore, probably less for taste than for mecha- nical purposes in the act of mastication. The gustatory property THE TONGUE: TASTE AND TOUCH. 477 of the anterior part of the tongue is due, as already said (pp. 368, 375), to the lingual branches of the fifth nerve. Besides the sense of taste, the tongue, by means also of its pa- pillae, is endued, especially at its sides and tip, with a very delicate and accurate sense of touch, which renders it sensible of the im- pressions of heat and cold, pain, and mechanical pressure, and con- sequently of the form of surfaces. The tongue may lose its common sensibility, and still retain the sense of taste, and vice versa. This fact renders it probable that, although the senses of taste and of touch may be exercised by tbe same papillae supplied by the same nerves, yet the nervous conductors for these two different sensations are distinct, just as the nerves for smell and common sensibility in the nostrils are distinct; and it is quite conceivable that the same nervous trunk may contain fibres differing essentially in their specific properties. Facts already detailed (p. 375) seem to prove that the lingual branch of the fifth nerve is the seat of sensations of taste in the anterior part of the tongue: and it is also certain, from the marked manifestations of pain to which its division in animals gives rise, that it is likewise a nerve of common sensibility. The glosso- pharyngeal also seems to contain fibres both of common sensation and of the special sense of taste. The concurrence of common and special sensibility in the same part makes it sometimes difficult to determine whether the impression produced by a substance is perceived through ordinary sensitive fibres, or through those of the sense of taste. In many cases, in- deed, it is probable that both sets of nerve-fibres are concerned, as when irritating acrid substances are introduced into the mouth. The impressions on the mind leading to the perception of taste seem to result, as already said, from certain changes in the internal condition of the nerves produced by the contact of sapid substances with the papillae in which the fibres of these nerves are distributed. This explanation, obscure though it be, may account generally for the sense; but the variations of taste produced by different sub- stances are as yet inexplicable. In the case of hearing, we know that sounds differ from one another according to the differences in the number of undulations producing them; and in the case of vi- sion it is reasonably inferred that different colors result from differ- ences in the number of undulations, or in the rate of transit, of the imponderable principle of light. But, in the cases of taste and smell, no such probable explanation has yet been offered. It would appear, indeed, from the experiments of Horn (clxxiii.), that while some substances taste alike in all regions of the tongue's surface, others excite different tastes, according as they are applied to dif- ferent papilla? of the tongue. This observation, if confirmed, would seem to show that, in some cases at least, different fibres are capable of receiving different impressions from the same sapid substance. Much of the perfection of the sense of taste is often due to the 478 THE SENSES. sapid substances being also odorous, and exciting the simultaneous action of the sense of smell. This is shown by the imperfection of the taste of such substances when their action on the olfactory nerves is prevented by closing the nostrils. Many fine wines lose much of their apparent excellence if the nostrils are held close while they are drunk. Very distinct sensations of taste are frequently left after the sub- stances which excited them have ceased to act on the nerve; and such sensations often endure for a long time, and modify the taste of other substances applied to the tongue afterwards. Thus, the taste of sweet substances spoils the flavor of wine, the taste of cheese improves it. There appears, therefore, to exist the same relation between tastes as between colors, of which those that are opposed or complementary render each other more vivid, though no general principles governing-this relation have been discovered in the case of tastes. In the art of cooking, however, attention has at all times been paid to the consonance or harmony of flavors in their combina- tion or order of succession, just as in painting and music the funda- mental principles of harmony have been employed empyrically while the theoretical laws were unknown. Frequent and continued repetition of the same taste renders the perception of it less and less distinct, in the same way that a color becomes more and more dull and indistinct, the longer the eye is fixed upon it. Thus, after frequently tasting first one and then the other of two kinds of wine, it becomes impossible to discriminate between them. The simple contact of a sapid substance with the surface of the gustatory organ seldom gives rise to a distinct sensation of taste; it needs to be diffused over the surface and brought into intimate con- tact with the sensitive parts by compression, friction, and motion between the tongue and palate. The sense of taste seems capable of being excited also by internal causes, such as changes in the conditions of the nerves or nervous centres produced by congestion or other causes which excite subjec- tive sensations in the other organs of sense. But, little is known of the subjective sensations of taste; for it is difficult to distinguish the phenomena from the effects of external causes, such as changes in the nature of the secretions of the mouth. SENSE OP TOUCH. The sense of touch is not confined to particular parts of the body of small extent, like the other senses; on the contrary, all parts ca- pable of perceiving the presence of a stimulus by ordinary sensation are, in various degrees, the seat of this sense; for touch is simply a modification or exaltation of common sensation or sensibility. The nerves on which the sense of touch depends are, therefore, the same STRUCTURE OF SENSITIVE PAPILLA. 479 as those which confer ordinary sensation on the different parts of the body, viz., the posterior ganglionic roots of the nerves of the spinal cord and the sensitive cerebral nerves. But, although all parts of the body supplied with sensitive nerves are thus, in some degree, organs of touch, yet the sense is exercised in perfection in only those parts the sensibility of which is extremely delicate, e.g., the skin, the tongue,and the lips, which are provided with abundant papilla?. The structure of the tongue and of its papillae has been already considered. A general account has also been given of the structure of the skin and of its functions as an organ for excretion and ab- sorption (p. 275); its peculiarities as a sensitive integument, and especially as an organ of touch, have now to be considered. By means of its toughness, flexibility, and elasticity, the skin is emi- nently qualified to serve as the general integument of the body, for defending the internal parts from external violence, and readily yielding and adapting itself to their various movements and changes of position. But, from the abundant supply of sensitive nerve- fibres which it receives, it is enabled to fulfil a not less important purpose in serving as the principal organ of the sense of touch. The entire surface of the skin is extremely sensitive, but its tactile properties are due, chiefly to the abundant papilla? with which it is studded. These papilla? have already been described as conical ele- vations of the corium, more prominent and more densely set at some parts than at others (p. 275). The parts on which they are most abundant and most prominent are the palmar surface of the hands and fingers, and the soles of the feet—parts, therefore, in which the sense of touch is most acute. Over other parts of the skin they are more or less thinly scattered, and are scarcely elevated above the Fig. 147. Fig. 148. Fig. 147. Papillae of the palm, the cuticle being detached. Magnified 35 diameters. Fig. 148. Vessels of papilla, from the heel: a, terminal arterial twig; v, commencing vein. Magnified 80 diameters. surface. Their average length is about y^f-h of an inclb an(J at their base they measure about ^th of an inch in diameter. Each papilla is abundantly supplied with blood, receiving from the vascu- lar plexus in the cutis one or more minute arterial twigs, which di- 480 THE SENSES. vide into capillary loops in its substance, and then reunite into a minute vein, which passes out at its base. The abundant supply of blood which the papilla? thus receive explains the turgescence or kind of erection which they undergo when the circulation through the skin is active. Each papilla contains also one or more terminal nerve-fibres, from the ultimate ramifications of the cutaneous plexus, on which its exquisite sensibility depends. The exact mode in which these nerve-fibres terminate is not yet satisfactorily determined. In some parts, especially those in which the sense of touch is highly developed, as, for example, the palm of the hand and the lips, the fibres appear to terminate, in many of the papillae, by one or more free ends in the interior of a dilated oval-shaped body, not unlike a Pacinian corpuscle, occupying the principal part of the interior of the papilla, and termed, by Kblliker, an "axis-body." The nature of tbis body is obscure. Kblliker, Huxley, and others, regard it as little else than a mass of fibrous, or connective tissue, surrounded by elastic fibres, and formed, according to Huxley, by an increased de- velopment of the neurilemma of the nerve-fibres entering the papilla. Wagner, however, to whom seems to belong the merit of first de- scribing these bodies, and who named them "corpuscula tactus," believes that, instead of thus consisting of a homogeneous mass of connective tissue, they are special and peculiar bodies of laminated structure, directly concerned in the sense of touch. They do not occur in all the papilla? of the parts where they are found, and, ac- cording to Wagner, those papilla? which possess them contain no blood-vessels, while, on the other hand, into the vascular papillae no nerve-fibres enter. Kblliker and Huxley, however, have seen both blood-vessels and axis-bodies within the same papillae; so that, although Wagner's statement on this point may be generally, yet it is not invariably, true. Since these peculiar bodies in which the nerve-fibres end are only met with in the papillae of highly sensitive parts, it may be inferred that they are specially concerned in the sense of touch, yet their absence from the papilla? of other tactile parts, shows that they are not essential to this sense.' In those in- stances in which the nerve-fibres do not thus terminate, they appear to form loops and return. Although destined especially for the sense of touch, the papilla? are not so placed as to come into direct contact with external objects, but, like tbe rest of the surface of the skin, are covered by one or more layers of epithelium, forming the cuticle or epidermis (p. 278). The papilla? adhere very intimately to the cuticle, which is thickest in the spaces between tbem, but tolerably level on its outer surface: 1 For the best account of these bodies, the nature of which, as said, is still obscure, the student is referred to Wagner (lxxx. 1852, p. 493), Kolliker (ccvi. p. 86, and ccxii. vol. ii.), Meissner (xiv. 1853, p. 342), and Huxley (ccxvii. vol. ii. p. 1). THE SENSE OF TOUCH. 481 hence, when stripped off from the cutis, as after maceration, its in- ternal surface presents a series of pits and elevations corresponding to the papillae and their interspaces, of which it thus forms a kind of mould. Besides affording by its impermeability a check to undue evaporation from the skin, and providing the sensitive cutis with a protecting investment, the cuticle is of service in relation to the sense of touch. For, by being thickest in the spaces between the papilla?, and only thinly spread over the summits of these processes, it may serve to subdivide the percipient surface of the skin into a number of isolated points, each of which is capable of receiving a distinct impression from an external body. By covering the pa- pilla? it renders the sensation produced by external bodies more ob- tuse, and in this manner also is subservient to touch : for unless the very sensitive papilla? were thus defended, the contact of sub- stances would give rise to pain, instead of the ordinary impressions of touch. This is shown in the extreme sensitiveness and loss of tactile power in a part of the skin when deprived of its epidermis. If the cuticle is very thick, however, as on the heel, touch becomes imperfect, or is lost, through the inability of the tactile papillae to receive impressions through the dense and horny layer covering them. The sensations of the common sensitive nerves have as peculiar a character as those of any other organ of sense. The sense of touch renders us conscious of the presence of a stimulus, from the slightest to the most intense degree of its action, neither by sound, nor by light, nor by color, but by that indescribable something which we call feeling, or common sensation. The modifications of this sense often depend on the extent of the parts affected. The sensation of pricking, for example, informs us that the sensitive particles are in- tensely affected in a small extent; the sensation of pressure indicates a slighter affection of the parts in a greater extent, and to a greater depth. It is by the depth to which the parts are affected, that the feeling of pressure is distinguished from that of mere contact. By the sense of touch the mind is made acquainted with the size, form, and other external characters of bodies. And in order that these characters may be easily ascertained, the sense of touch is especially developed on those parts which can be readily moved over the surface of bodies. Touch, in its more limited sense, or the act of examining a body by the touch, consists merely in a voluntary employment of this sense combined with movement, and stands in the same relation to the sense of touch or common sensibility, gene- rally, as the act of seeking, following, or examining odors does to the sense of smell. Every sensitive part of the body which can, by means of movement, be brought into different relations of contact with external bodies, is an organ of "touch." No one part, conse- quently, has exclusively this function. The hand, however, is best adapted for it, by reason of its peculiarities of structure,—namely, 41 482 THE SENSES. its capability of pronation and supination, which enables it, by the movement of rotation, to examine the whole circumference of a body; the power of opposing the thumb to the rest of the hand; and the relative mobility of the fingers. In forming a conception of the figure and extent of a surface, the mind multiplies the size of the hand or fingers used in the inquiry by the number of times which it is contained in the surface tra- versed ; and by repeating this process with regard to the different dimensions of a solid body, acquires a notion of its cubical extent. The perfection of the sense of touch on different parts of the sur- face is proportioned to the power which such parts possess of dis- tinguishing and isolating the sensations produced by two points placed close together. This power depends, at least in part, on the number of primitive nerve-fibres distributed to the part; for the fewer the primitive fibres which an organ receives, the more likely is it that several impressions on different contiguous points will act on only one nervous fibre, and hence be confounded, and perhaps produce but one sensation. Experiments to determine the tactile properties of different parts of the skin, as measured by this power of distinguishing distances, were made by E. H. Weber. The ex- periment consisted in touching the skin, while the eyes were closed, with the points of a pair of compasses sheathed with cork, and in ascertaining how close the points of the compasses might be brought to each other, and still be felt as two bodies. He examined, in this manner, nearly every part of the surface of the body, and has given tables showing the relative degrees of sensibility of different parts. Experiments of a similar kind have been performed also by Valentin (iv. vol. ii. p. 566): and, among the numerous results obtained by both these investigators, it appears that the extremity of the third finger and the point of the tongue are the parts most sensitive: a distance of as little as half a line being here distinguished. Next in sensitiveness to these is the mucous surface of the lips, which can perceive the two points of the compass when separated to the dis- tance of about a line and a half: on the dorsum of the tongue they require to be separated two lines. The parts in which the sense of touch is least acute are the neck, the middle of the back, the mid- dle of the arm, and the middle of the thigh, on which the points of the compass have to be separated to the distance of thirty lines to be perceived as distinct points (Weber). Other parts of the body possess various degrees of sensibility intermediate between the above extremes. (For Weber's table see xxxii. p. 546, Am. ed.; for Va- lentin's, iv. vol. ii. p. 566). A sensation in a part endowed with touch appears to the mind to be, cceteris paribus, more intense when it is excited in a large extent of surface than when it is confined to a small space. The tempera- ture of water, into which he dipped his whole hand, appeared to Weber to be bigher than that of water of really higher temperature, THE SENSE OF TOUCH. 483 in which he immersed only one finger of the other hand. Simi- lar observations may be made by persons bathing in warm or cold water. Part of the ideas which we obtain of the conditions of external bodies is derived through the peculiar sensibility with which muscles are endowed—the sensibility by which we are made acquainted with their position, and the degree of their contraction. By this sensa- tion we are enabled to estimate the degree of force exerted in resist- ing pressure or in raising weights. The estimate of weight by mus- cular effort is more accurate than that by pressure on the skin, ac- cording to Weber, who states that by the former a difference between two weights may be detected when one is only one-twentieth or one- fifteenth less than the other. It is not the absolute, but the relative, amount of the difference of weight which we have thus the faculty of perceiving. It is not, however, certain that our idea of the amount of muscular force used is derived solely from sensation in the muscles. We have the power of estimating very accurately beforehand, and of regula- ting, the amount of nervous influence necessary for the production of a certain degree of movement. When we raise a vessel, with the contents of which we are not acquainted, the force we employ is determined by the idea we have conceived of its weight. If it should happen to contain some very heavy substance, as quicksilver, we shall probably let it fall; the amount of muscular action, or of ner- vous energy, which we had exerted, being insufficient. The same thing occurs sometimes to a person descending stairs in the dark; he makes the movement for the descent of a step which does not exist. It is possible that in the same way the idea of weight and pressure in raising bodies, or in resisting forces, may in part arise from a con- sciousness of the amount of nervous energy transmitted from the brain, rather than from a sensation in the muscles themselves. The mental conviction of the inability longer to support a weight must also be distinguished from the actual sensation of fatigue in the muscles. So, with regard to the ideas derived from sensations of touch com- bined with movements, it is doubtful how far the consciousness of the extent of muscular movement is obtained from sensations in the muscles themselves. The sensation of movement attending the motions of the hand is very slight; and persons who do not know that the action of particular muscles is necessary for the production of given movements do not suspect that the movement of the fingers, for example, depends on an action in the forearm. The mind has, nevertheless, a very definite knowledge of the changes of position produced by movements; and it is on this that the ideas which it conceives of the extension and form of a body are in great measure founded. In order that an impression made on a sensitive surface may be 484 THE SENSES. perceived, it is necessary that there should exist a reciprocal influ- ence between the mind and the sense of touch; for, if the mind does not thus co-operate, the organic conditions for the sensation may be fulfilled, but it remains unperceived. Moreover, the distinctness and intensity of a sensation in the nerves of touch depend, in great measure, on the degree in which the mind co-operates for its percep- tion. A painful sensation becomes more intolerable the more the attention is directed to it: thus, a sensation in itself inconsiderable, as an itching in a very small spot of the skin, may be rendered very troublesome and enduring. As every sensation is attended with an idea, and leaves behind it an idea in the mind which can be reproduced at will, we are enabled to compare the idea of a past sensation with another sensation really present. Thus we can compare the weight of one body with another which we had previously felt, of which the idea is retained in our mind. Weber was, indeed, able to distinguish in this manner between temperatures experienced one after the other better than between temperatures to which the two hands were simultaneously subjected. This power of comparing present with past sensations diminishes, however, in proportion to the time which has elapsed between them. The after-sensations left by impressions on nerves of common sen- sibility or touch are very vivid and durable. As long as the condi- tion into which the stimulus has thrown the organ endures, the sensa- tion also remains, though the exciting cause should have long ceased to act. Both painful and pleasurable sensations afford many examples of this fact. The law of contrast, which we have shown to modify the sensations of vision (p. 450), prevails here also. After the body has been ex- posed to a warm atmosphere, a degree of temperature a very little lower, which would under other circumstances be warm, produces the sensation of cold; and a sudden change to the extent of a few degrees from a cold temperature to a warm one, will produce the sen- sation of warmth. Heat and cold are, therefore, relative terms; for a particular state of the sentient organs causes what would otherwise be warmth to appear cold. So, also, a diminution in the intensity of a long-continued pain gives pleasure, even though the degree of pain that remains would in the healthy state have seemed intolerable. Subjective sensations, or sensations dependent on internal causes, are in no sense more frequent than in the sense of touch. All the sensations of pleasure and pain, of heat and cold, of lightness and weight, of fatigue, etc., may be produced by internal causes. Neu- raulgic pains, the sensation of rigor, formication or the creeping of ants, and the states of the sexual organs occurring during sleep, afford striking examples of subjective sensations. The mind, also, has a remarkable power of exciting sensations in the nerves of common sensibility; just as the thought of the nauseous GENERATION AND DEVELOPMENT. 485 excites sometimes the sensation of nausea, so the idea of pain gives rise to the actual sensation of pain in a part predisposed to it. The thought of anything horrid excites the sensation of shuddering; the feelings of eager expectation, of pathetic emotion, of enthusiasm, excite in some persons a sensation of " concentration " at the top of the head, and of cold trickling through the body; fright causes sen- sations to be felt in many parts of the body; and even the thought of tickling excites that sensation in individuals very susceptible of it, when they are threatened with it by the movements of another person. These sensations from internal causes are most frequent in persons of excitable nervous systems, such as the hypochondriacal and the hysterical, of whom it is usual to say that their pains are imaginary. If by this is meant that their pains exist in their imagination merely, it is certainly quite incorrect. Pain is never imaginary in this sense; but is as truly pain when arising from internal as from external causes; the idea of pain only can be unattended with sensation, but of the mere idea no one will complain. Still, it is quite certain that the imagination can render pain that already exists more intense, and can excite it when there is a disposition to it. CHAPTER XIX. GENERATION AND DEVELOPMENT. The several organs and functions of the human body, which have been considered in the previous chapters, have relation to the indi- vidual being. We have now to consider these organs and functions which are destined for the propagation of the species. These com- prise the several provisions made for the formation, impregnation, and development of the ovum, from which the embryo or foetus is produced and gradually perfected into a living human being. The organs concerned in effecting these objects are named the generative organs, or sexual apparatus, since part belongs to the male and part to the female sex. Generative Organs of the Female. The female organs of generation consist of two Ovaries for the formation of ova; of a Fallopian tube, or oviduct, connected with each ovary, for the purpose of conducting the mature ovum to the uterus or cavity in which, if impregnated, it is retained until the embryo is fully developed and fitted to maintain its existence inde- pendent of internal connection with the parent; and, lastly, of a 41* 486 GENERATION AND DEVELOPMENT. passage, or vagina, with its appendages, for the reception of the male generative organ in the act of copulation, and for the subsequent discharge of the foetus. The ovaries are two oval compressed bodies, situated in the cavity of the pelvis, one on each side, enclosed in the folds of the broad ligament. Each ovary is attached to the uterus by a narrow fibrous cord (the ligament of the ovary), and, more slightly, to the Fallopian tube by one of the fimbria? into which the walls of the extremity of the tube expand. The ovary is enveloped by a capsule of dense fibro-cellular tissue, which again is surrounded by peritoneum. The internal structure of the organ consists of a peculiar soft fibrous tissue, or stroma, abundantly supplied with blood-vessels, and having imbedded in it, in various stages of development, numerous minute follicles or vesicles, the Graafian vesicles, or sacculi containing the ova. A further account of the Graafian vesicles and of their con- tained ova will be presently given. The Fallopian tubes are about four inches in length, and extend between the ovaries and the upper angles of the uterus. At the point of attachment to the uterus the Fallopian tube is very narrow, but in its course to the ovary it increases to about a line and a half in thickness; at its distal extremity, which is free and floating, it bears a number of fimbriae, one of which, longer than the rest, is attached to the ovary. The canal by whicfi each Fallopian tube is traversed is narrow, especially at its point of entrance into the uterus, at which it will scarcely admit a bristle; its other extremity is wider, and opens into the cavity of the abdomen, surrounded by the zone of fimbria?. Externally, the Fallopian tube is invested with peri- toneum ; internally, its canal is lined with mucous membrane covered with ciliary epithelium (p. 392): between the peritoneal and mucous coats the walls are composed of fibrous tissue similar to that of the uterus. The uterus is a somewhat pyriform, fibrous organ, with a central cavity lined with mucous membrane. In the unimpregnated state it is about three inches in length, two in breadth at its upper part or fundus, but at its lower pointed part or neck, only about half an inch. Tbe part between the fundus and neck is termed the body of the uterus: it is about an inch in thickness. The walls of the organ are composed of dense fibro-cellular tissue, with which are intermingled fibres of organic muscle : in the impregnated state the latter are much developed and increased. The cavity of the uterus corresponds in form to that of the organ itself: it is very small in the unimpregnated state; the sides of its mucous surface being almost in contact, and probably only separated from each other by mucus. Into its supper part, at each side, opens the canal of the corresponding Fallopian tube : below, it communicates with the vagina by a fissure-like opening in its neck, the os uteri, the mar- gins of which are distinguisbed into two lips, an anterior and THE HYMEN, CLITORIS, AND LABIA. 487 posterior. At the mucous membrane of the cervix are found several mucous follicles, termed Ovula or glandula? Nabothi: they probably form the jelly-like substance by which the os uteri is usually found closed.1 The vagina is a membranous canal, six or eight inches long, ex- tending obliquely downwards and forwards from the neck of the uterus, which it embraces, to the external organs of generation. It is lined with mucous membrane, which in the ordinary contracted state of the canal is thrown into transverse folds. External to the mucous membrane the walls of the vagina are constructed of fibro- cellular tissue, within which, especially around the lower part of the tube, is a layer of erectile tissue. The anterior extremity of the vagina is embraced by an orbicular muscle, the constrictor vagina?; its external orifice is, in the virgin, partially closed by a fold or ring of mucous membrane termed the hymen. The external organs of generation consist of the clitoris, a small elongated body, situated above and in the middle line, and constructed, like the male ponis, of two erectile corpora cavernosa, and surmounted by an imperforate glans and prepuce : of two folds of mucous membrane, termed labia interna or nymphcv ; and in front of these, two other folds, the labia externa or pudenda, formed of the external integument, and lined internally by mucous membrane. Between the nympha? and beneath the clitoris is an angular space, termed the vestibule, at the centre of whose base is the orifice of the meatus urinarius. Numerous mucous follicles are scattered beneath the mucous membrane, com- posing these parts of the external organs of generation; and at the side of the fore part of the vagina, are two larger lobulated glands, named vulvo-vaginal, or Duvernoy's glands, which are analogous to Cowper's glands in the male. Having given this general outline of the several parts which, in the female, contribute to the reproduction of the species, it will now be necessary to examine successively the formation, discharge, im- pregnation, and development of the ovum, to which these several parts are subservient. Unimpregnated Ovum. If the structure and formation of the human ovary be examined at any period between early infancy and advanced age, but especially durina: that period of life in which the power of conception exists, it will be found to contain, on an average, from fifteen to twenty small vesicles or membranous sacs of various sizes; these have been already alluded to as the follicles or vesicles of De Graafi the ana- 1 For an account of the arrangement of the fibres of the uterus, see xxxvi. Jan. 1845. 488 GENERATION AND DEVELOPMENT. tomist who first accurately described them. At their first formation, the Graafian vesicles are small and deeply-seated in the substance of the ovary; but as they increase in size, they make their way towards the surface; and when mature they form little prominences on the exterior of the ovary covered only by the peritoneum. Each fol- licle is formed with an external mem- branous envelope composed of fine fibro cellular tissue, and connected with the surrounding stroma of the ovary by networks of blood-vessels. (Fig. 149.) This envelope or tunic is lined with a layer of nucleated cells, forming a kind of epithelium or in- ternal tunic, and named membrana granulosa. The cavity of the follicle is filled with an albuminous fluid in which microscopic granules float; and it contains also the ovum or ovule. The ovum is a minute spherical body situated, in immature follicles, near their centre; but in those nearer ma- turity, in contact with the membrana granulosa, at that part of the follicle which forms a prominence on tbe surface of the ovary. The cells of the membrana granulosa are at that point more numerous than elsewhere, and are heaped around the ovum, forming a kind of granular zone, the discus proligerus (Fig. 149). In order to examine an ovum, one of the Graafian vesicles, it matters not whether it be of small size or arrived at maturity, should be pricked, and the contained fluid received upon a piece of glass. The ovum then, being found in the midst of the fluid by means of a simple lens, may be further examined with higher microscopic powers. Owing to its globular form, however, its struc- ture cannot be seen until it is subjected to gentle pressure. The human ovum is extremely small, measuring, according to Bischoff, from 5|^ to ^^ of an inch. Its external investment is a transparent membrane, about ^G'O °^ an *ncn iQ thickness, which, under the microscope, appears as a bright ring (Fig. 150), bounded externally and internally by a dark outline: it is called the zona pellucida, or vitelline membrane, and corresponds with the chorion of the impregnated ovum. It adheres externally to the heap of cells constituting the discus proligerus. Within this transparent investment or zona pellucida, and usually in close contact'with it, lies the yelk or vitellus, which is composed of granules and globules of various sizes, imbedded in a more or less fluid substance. The smaller granules, which are the more numerous, resemble in their appearance as well as their constant Fig. 149. Section of the Graafian vesicle of a mammal, after Von Baer. 1. Stroma of the ovary with blood-vessels. 2, Peritoneum. 3 and 4. Layers of the external coat of the Graafian vesicle. 5. Membrana granulosa. 6. Fluid of the Graafian vesicle. 7. Granular zone or discus proligerus, containing the ovum (8). THE GERMINAL VESICLE AND GERMINAL SPOT. 489 motion, pigment granules. The larger granules er globules which have the aspect of fat globules, are in greatest number at the periphery of the yelk. The number of the granules is, according to Bis- choff, greatest in the ova of carnivorous animals. In the human ovum their quantity is comparatively small. The substance that combines the globules and granules of the yelk is, in many animals, quite fluid. The yelk then completely fills the cavity of the zona pellucida, and escapes in a liquid form when that membrane is ruptured: Ovum of the sow, after i , • /. ii i i • i Barry. 1. Germinal spot. but in ova of the human subject and some 2 G;rmiDal vesicle. 3. animals the yelk is much more consistent, and yeik. 4. zona pellucida. sometimes escapes as a solid globular mass when 5. Discus proligerus. 6. the zona pellucida is torn. It is, according to A is empty. ^ u the cells. One of these belongs to the maternal margm of the pellucid villus. 526 GENERATION AND DEVELOPMENT. Fig. 183. Transverse section of the uterus and placenta; a and 6, uterine sinuses, with tufts of foetal placental vessels prolonged into them; c, curling artery passing through decidua vera; d, decidua vera; e, tufts of placental vessels.—J. Reid. Fig. 184. Connection between the maternal and foetal vessels: a, curling artery; b, uterine vein; c, placenta; d, placental tufts, with inner coat of vascular system of the mother enveloping them.—J. Beid. portion of the placenta, is placed between the membrane of the villus and that of the vascular system of the mother, and is probably designed to separate from the blood of the parent the materials des- tined for the blood of the foetus; the other belongs to the foetal portion of the placenta, is situated between the membrane of the villus and the loop of vessels contained within, and probably serves for the absorption of the material secreted by the other sets of cells, and for its conveyance into the blood-vessels of the foetus. (See Fig. 185.) Between the two sets of cells with their investing membrane Fig. 185. Extremity of a placental villus: a, external memhrane of the villus continuous with the lining membrane of the vascular system of the mother; b, external cells of the villus belong- ing to the placental decidua; cc, germinal centres of external cells; d, the space between the maternal and foetal portions of the villus; e, the internal membrane of the villus, continuous with the external membrane of the chorion; /, the internal cells of the villus, belonging to the chorion; g, the loop of umbilical vessels.—After Goodsir. there exists a space, d, into which it is probable that the materials secreted by the one set of cells of the villus are poured, in order that they may be absorbed by the other set, and thus conveyed into the foetal vessels.1 1 Although, in the text, mention is made only of the passage of materials from the blood of the mother into that of the foetus, yet there can be no doubt of the existence of a mutual interchange of materials between the blood of both foetus and parent, the latter supplying the former with nutriment, and in turn abstracting from it materials which require to be removed. (See on the sub- ject Dr. A. Harvey, excix.) DEVELOPMENT. 527 DEVELOPMENT OF ORGANS. It remains now to consider in succession the development of the several organs and systems of organs in the further progress of the embryo. Development of the Vertebral Column and Cranium. The primitive part of the vertebral column in all the Vertebrata is the gelatinous chorda dorsalis, which consists entirely of cells (p. 515). This cord tapers to a point at the cranial and caudal extremities of the animal. In the progress of its development it is found to become inclosed in a membranous sheath, which at length acquires a fibrous structure, composed of transverse annular fibres. The chorda dorsalis is to be regarded as the azygous axis of the spinal column, and, in particular, of the future bodies of the vertebra?, although it never itself passes into the cartilaginous or the osseous state, but remains enclosed as in a case within the persistent parts of the vertebral column which are developed around it. It is perma- nent, however, only in a few animals : in the majority it disappears at an early period. The cartilaginous or osseous vertebrae are always first developed in pairs of lateral elements at the sides of the chorda dorsalis. From these lateral elements are formed the bodies and the arches of the vertebra?. In some animals, as the sturgeon, however, the lateral elements of the vertebrae undergo no further development, and it is here that the chorda dorsalis is persistent through life. In the myxinoid fishes the spinal column presents no vertebral segments, and there exists merely the chorda dorsalis with the fibrous layer surrounding its sheath, which is the layer in which the skelefon originates. This fibrous layer also forms superiorly the membranous covering of the vertebral canal. In reptiles, birds, and mammals, the mode in which the vertebrae are formed around the chorda dorsalis seems to be different. The peculiarity of this type is, at all events, distinct in the class of birds. Here the vertebrae, in that part of the spinal column which belongs to the trunk, are developed from a single pair of elementary parts. When the formation of these parts from the blastema commences, there appears at each side of the chorda dorsalis a series of quad- rangular figures, the rudiments of the future vertebrae. (Fig. 166, p. 515). These gradually increase in number and size, so as to sur- round the chorda both above and below, sending out, at the same time, superiorly, processes to form the arches destined to enclose the spinal cord. In this primitive condition the body and arches of each vertebra are formed by one piece on each side, xit a certain period these two primary elements, which have become cartilaginous, unite 528 GENERATION AND DEVELOPMENT. inferiorly by a suture. The chorda is now enclosed in a case, formed by the bodies of the vertebrae, but it gradually wastes and disappears. Before the disappearance of the chorda, the ossification of the bodies and arches of the vertebrae begins at distinct points. The ossification of the body is first observed at the point where the two primitive elements of the vertebrae have united inferiorly. Those vertebrae which do not bear ribs, such as the cervical vertebrae, have generally an additional centre of ossification in the transverse process, which is to be regarded as an abortive rudiment of a rib. In the foetal bird, these additional ossified portions exist in all the cervical vertebrae, and gradually become so much developed in the lower part of the cervical region as to form the upper false ribs of this class of animals. The same parts exist in Mammalia and man; those of the last cervical vertebrae are the most developed, and in children may, for a considerable period, be distinguished as a sepa- rate part on each side, like the root or head of a rib. Tbe true cranium is a prolongation of the vertebral column, and is developed at a much earlier period than the facial bones. Origi- nally, it is formed of but one mass, a cerebral capsule, the chorda dorsalis being continued into its base, and ending there with a taper- ing point. This relation of the chorda dorsalis to the basis of the cranium is persistent through life in some fish, e.g., the sturgeon. The first appearance of a solid support at the base of the cranium observed by Miiller in fish, consists of two elongated bands of car- tilage, one on the right, and the other on the left side, which are connected with the cartilaginous capsule of the auditory apparatus, and united with each other in an arched manner anteriorly beneath the anterior end of the cerebral capsule. Hence, in the cranium, as in the spinal column, there are at first developed at the sides of the chorda dorsalis two symmetrical elements, which subsequently coalesce, and may wholly enclose the chorda. At a later period the base of the cranium contains three parts analogous to the bodies of vertebrae; the most anterior of which, in the majority of animals, is small, and its development frequently abortive, whilst in man and mammiferous animals the three are very distinct. These parts are developed by the formation of three dis- tinct points of ossification, one behind the other, in the basilar car- tilage. The three ossified portions become united by sutures, and in mammals form a rod-like body, tapering towards its anterior ex- tremity, and giving attachment at its sides to the lateral parts of the three vertebrae. Development of the Face and Visceral Arches. Before the development of the face, the visceral cavity of the cephalic region is formed superiorly by the primitive rudimentary structure which contains the encephalon, the cerebral capsule; whilst DEVELOPMENT OF THE FACE. 529 the lower and lateral walls of that cavity are formed by the anterior " visceral arch." At this period there is no nasal cavity, and the visceral cavity of the head extends uninterruptedly from the first visceral arch to the cerebral capsule. In birds and mammiferous ani- mals there are three visceral arches, and also three visceral clefts. The first cleft becomes converted into the external auditory passage, the tympanum, and the Eustachian tube; the second and the third are obliterated. The face is originally formed of a middle portion proceeding from the forehead, or frontal process, and of a lateral portion on each side, derived from the superior extremity of the first visceral arch. These parts are at first separate. The lateral and the inferior parts, des- tined to form the superior and inferior maxillary apparatus, are both derived from the first visceral arch, in which an angular bend ap- pears ; the part above this bend being converted into the superior maxillary mass, and that below it into the inferior maxillary appara- tus (see Fig. 186). The superior maxillary mass, in its growth, Fig. 186. Development of the parts of the face in the embryo of Triton treuiatus. A. An embryo four lines long, magnified; b, another embryo further advanced in development. After Keichert. 1, the first visceral arch, or inferior arch of the first cephalic vertebra (incorrectly marked 2 in the figure A); 2, the second visceral arch; 3, the second visceral process; 4, the first visceral cleft; 5, the second visceral cleft; 6, the nasal or anterior frontal process; 7, ru- diments of the superior maxilla; 8, rudiments of the superior intermaxillary hone; 9. the cleft between the nasal or anterior frontal processes; 10, the external nasal opening; 11, the eye; 12, the small elevation of the lachrymal bone ; 13, the opening of the cephalic visceral cavity or mouth; 14, the external branchiae; 15, the membranous branchial operculum; 16, elevated ridge pushed forward by the heart and its aortic arches. approaches the frontal process, and unites with it; a cavity being left beneath that process and between the two superior maxillary masses, which becomes the nasal cavity. By the union of the superior max- illary masses (the superior maxilla and palate bone) of opposite sides 45 530 GENERATION AND DEVELOPMENT. beneath this cavity, the separation of the nose from the mouth by the palate is effected. The mode of development of the face affords an explanation of the anormal cleft palate and the congenital cleft between the upper maxillary and the intermaxillary bone, and of those congenital fis- sures which pass between the intermaxillary bone and upper jaw, as far upwards as the orbital cavity. Congenital clefts of this kind are the results of an arrest of development occurring during the primi- tive conditions of the parts. The first visceral arch, according to Beichert, produces the supe- rior maxillary apparatus, the under jaw, and a part of the ossicula auditus, namely, the malleus and the incus. From the second visce- ral arch are formed the stapes of the ear, and the suspensory appa- ratus of the hyoid bone, i. e., the styloid process of the temporal bone, the ligamentum stylo-hyoideum, and the smaller cornu of the os hyoidcs. The posterior cornua, and the body of the hyoid bone, are developed from a cartilaginous band contained in the third visce- ral arch. Development of the Extremities. The extremities are developed in an uniform manner in all verte- brate animals. They appear in the form of leaf-like elevations from the parietes of the trunk (see Fig. 187), at points where more or less of an arch will be produced for them within. The primitive form of the extremitiy is nearly the same in all Vertebrata, whether it be destined for swimming, crawling, walking, or flying. In the human foetus the fingers are at first united as if webbed for swim- ming ; but this is to be regarded not so much as an approximation to the form of aquatic animals, as the primitive form of the hand, the individual parts of which subsequently become more completely isolated. Development of the Vascular System. The first development of the vascular system and heart in the ger- minal membrane has been already alluded to. The earliest form of the heart presents itself as a solid compact mass of embryonic cells, similar to those of which the other organs of the body are consti- tuted. It is at first unprovided with a cavity: but this shortly makes its appearance, resulting apparently from the separation from each other of the cells of the central portion. A liquid is now formed in the still closed cavity, and the central cells may be seen floating within it. These contents of the cavity are soon observed to be propelled to and fro with a tolerable degree of regularity, owing to the commencing pulsations of the heart. These pulsations take place even before the appearance of a cavity, and immediately after DEVELOPMENT OF THE BLOOD-VESSELS. 531 Fig. 187. A human embryo of the fourth week, 31 lines in length. 2, the chorion; 3, part of the amnion; 4, umbilical vesicle with its long pedicle passing into the abdomen; 7, the heart; 8, the liver; 9, the visceral arch destined to form the lower jaw, beneath which are two other visceral arches separated by the branchial clefts: 10, rudiment of the upper extremity; 11, that of the lower extremity; 12, the umbilical cord; 15, the eye; 16, the ear; 17, the cerebral hemispheres; 18, the optic lobes or corpora quadrigemina. the first "laying down" of the cells from which the heart is formed. At first they seldom exceed from fifteen to eighteen in the minute. The fluid within the cavity of the heart shortly assumes the charac- ters of blood. At the same time the cavity itself forms a communi- cation with the great vessels in contact with it, and the cells of which its walls are composed are transformed into fibrous and muscular tis- sues, and into epithelium. Blood-vessels appear to be developed in two ways, according to the size of the vessels. In the formation of large blood-vessels, masses of embryonic cells similar to those from which the heart and other structures of the embryo are developed, arrange themselves in the position, form and thickness of the developing vessel. Shortly the cells in the interior of a column of this kind seem to be developed into blood-corpuscles, while the external layer of cells is converted into the walls of the vessel. In the development of capillaries, another plan is pursued. This has been well illustrated by Kolliker (xxxi. August, 1846), as ob- served in the tails of tadpoles. The first lateral vessels of the tail have the form of simple arches, passing between the main artery and vein, and are produced by the junction of prolongations sent from both the artery and vein, with certain elongated or star-shaped cells, in the substance of the tail. When these arches are formed, and are permeable to blood, new prolongations pass from them, join other radiated cells, and thus form secondary arches. In this manner, the capillary net-work extends in proportion as the tail increases in length and breadth, and it, at the same time, becomes more dense by the 532 GENERATION AND DEVELOPMENT. formation, according to the same plan, of fresh vessels within its meshes. The prolongations by which the vessels communicate with the star-shaped cells, consist at first of narrow pointed projections from the side of the vessels, which gradually elongate until they come in contact with the radiated processes of the cells. The thickness of such a prolongation often does not exceed that of a fibril of fibrous Fig. 188. Capillary blood-vessels of the tail of a young larval frog. Magnified 350 times. After Kblliker. a. Capillaries permeable to blood; 6. fat granules attached to the walls of the ves- sels, and concealing the nuclei; c. hollow prolongation of a capillary, ending in a point; d. a branching cell with nucleus and fat-granules; it communicates by three branches with pro- longations of capillaries already formed; e. blood-corpuscles still containing granules of fat. tissue, and at first it is perfectly solid; but by degrees, especially after its junction with a cell, or with another prolongation, or with a vessel already permeable to blood, it enlarges, and a cavity then forms in its interior (see Fig. 188). With Kolliker's account our DEVELOPMENT OF THE HEART. 533 own observations made on the fine gelatinous tissue conveying the umbilical vessels of a sheep's embryo to the uterine cotyledons, com- pletely accord. This tissue is well calculated to illustrate the various steps in the development of blood-vessels from elongating and branch- ing cells (see clxxi. p. 104). About the time that the heart at its lower extremity receives the venous trunks, and at its upper extremity divides into the arterial trunks or aortic arches, it becomes curved from a straight into a horse-shoe form, and shortly divides into three cavities (Fig. 189). Fig. 189. Heart of the chick at the 45th, 65th, and 85th hours of incubation. 1. The venous trunks; 2, the auricle; 3, the ventricle; 4, the bulbus arteriosus. After Ur. Allen Thomson. Of these three cavities, which are developed in all Vertebrata, the most posterior is the simple auricle; the middle one the simple ven- tricle ; and the most anterior the bulbus arteriosus. These three parts of the heart contract in succession. The auricle and the bulbus arteriosus at this period lie at the extremities of the horse-shoe. The bulging out of the middle portion inferiorly gives the first indication of the future form of the ventricle. (See Fig. 189). The great curvature of the horse-shoe by the same means becomes much more developed than the smaller curvature between the auricle and bulbus; and the two extremities, the auricle and bulb, approach each other superiorly, so as to produce a greater resemblance to the later form of the heart, whilst the ventricle becomes more and more developed inferiorly. The heart of fishes retains these three cavities, no fur- ther division by internal septa into right and left chambers taking place. In Amphibia also the heart throughout life consists of the three muscular divisions which are so early formed in the embryo; but the auricle is divided internally by a septum into a pulmonary and a systemic auricle. In reptiles, not merely the auricle is thus divided into two cavities, but a similar septum is more or less developed in the ventricle. In birds, mammals, and the human subject, both auricle and ventricle undergo complete division by septa; whilst in these animals, as well as in reptiles, the bulbus aortae is not permanent, but becomes lost in the ventricles. The septum dividing the ventricle commences at the apex and extends upwards. (See Fig. 190). When it is complete, a septum is deve- loped in the bulbus aortae separating the roots of the proper aorta and the pulmonary artery. The septum of the auricles is developed from a semilunar fold, which extends from above downwards. In 45* 534 GENERATION AND DEVELOPMENT. Fig. 190. Heart of a human embryo of about the fifth week. a. The heart opened on the abdominal aspect: 1, the bulbus arteriosus; 2, two aortic arches which unite posteriorly to form the aorta; 3, the auricle; 4, the opening from the auricle into the ventricle (6), which is laid open; 5, the septum rising from the lowest part of the cavity of the ventricle; 7, the vena cava inferior, b. The same heart viewed from behind: 1, the trachea; 2, the lungs; 3, the ven- tricle ; 4,5, the large atrium cordis or auricle; 6, the diaphragm ; 7, the aorta descendens; 8, the nervus vagus; 9, its branches; 10, continuation of the nervus vagus. After Von Baer. man, the septum between the ventricles, according to Meckel, begins to be formed about the fourth week, and at the end of eight weeks is complete. The septum of the auricles, in man and ail animals which possess it, remains imperfect throughout foetal life. When the partition of the auricles is first commencing, the two venae cavas have different relations to the two cavities. The superior cava enters, as in the adult, into the right auricle; but the inferior cava is so placed, that it appears to enter the left auricle, and the posterior part of the septum of the auricles is formed by the Eustachian valve, which extends from the point of entrance of the inferior cava. Sub- sequently, however, the septum, growing from above downwards, becomes directed more and more to the left of the vena cava inferior. During the entire period of foetal life, there remains an opening in the septum, which the valve of the foramen ovale, developed in the third month, imperfectly closes. Aortic Arches and Pulmonary Vessels. — In the early embryoes of all vertebrate animals the blood is distributed from the bulbous aortae in arches towards either side, and, after passing round the circumference of the visceral cavity, is again collected in front of the vertebral column into a single vessel, the aorta descendens. The aortic arches are always several in number, and at first lie in connec- tion with the visceral arches. In those animals which breathe by branchiae, and in which the visceral arches partly serve for the for- mation of the branchial apparatus, each of the aortic arches is re- solved into two parallel vessels, one arterial, which comes from the heart and ramifies wholly in the branchiae, and the other venous, which arises in the branchial laminae, and unites with the veins of the other branchiae in front of the aorta, to form the descending aorta. In the Amphibia the same structure exists for a certain f DEVELOPMENT OF VEINS. 535 period; but afterwards the branchial vessels are again transformed into three aortic arches, which, when the branchial apparatus has ceased to exist, sink deeper into the thoracic cavity, and become permanent. In Mammalia the aortic arches are soon reduced to three, one of which is the persistent arch of the aorta, whilst the other two are the ductus arteriosi of the pulmonary artery. Of these ductus arte- riosi the right also disappears ; so that during the remainder of foetal life only two aortic arches exist, one arising from the right, and the other from the left ventricle (Fig. 191). The former of these gives Fig. 191. Plan of the transformation of the system of aortic arches into the permanent arterial trunks in mammiferous animals; after Von Baer. 1, situation of the original single trunk which arose from the single ventricle, and which has become divided into two tubes: it gave off five pairs of aortic arches, which terminated in the two roots of the aorta (2, 2'). Those of the arches which are obliterated at a very early period, are marked by dotted lines. The first arch of the right side, with the root of the aorta of that side (2) which remains longer, and forms the right ductus arteriosus, is drawn as a very narrow vessel, with a dotted line on each side. The vessels which still exist at birth, are drawn of the full size. These are the first arch of the left side, constituting the ductus arteriosus Botalli, which is in greater part obliterated soon after birth, and the second arch of the left side, constituting the perma- nent arch of the aorta (3). The subclavian arteries (4) and the carotid arteries (5) are formed from parts of the other primtive aortic arches. After the obliteration of the left ductus arte- riosus, the pulmonary arteries are the only remains of the first pair of aortic arches. off the arteries to the lungs, the latter the vessels to the upper parts of the body. These two arches are of equal size, and so remain until the foetus has attained its maturity. After birth the posterior portion of the arch which arises from the right ventricle (the ductus arteriosus Botalli) rapidly becomes narrowed, and in the course of the first few weeks after birth its cavity is entirely obliterated : the anterior portion becomes the trunk of the independent arteriae pul- monales. At the same time the closure of the foramen ovale takes place. . Veins.__The conformation of the venous system also is at first the same in the embryoes of all vertebrate animals, and subsequently departs in various ways, from the common primitive type. In the 536 GENERATION AND DEVELOPMENT. original condition there are two anterior venous trunks (the jugular veins), and two posterior trunks, the cardinal veins. One of the anterior trunks, and one of the posterior, unite on each side and form a transverse canal,—the ductus Cuvieri. The two ductus Cuvieri unite beneath the oesophagus to form a shorter main canal which enters the auricle, — at that time a simple cavity. The car- dinal veins are originally formed by the caudal veins, branches from the kidneys and Wolffian bodies, and others from the dorsal parietes of the trunk, which are, at a later period, the intercostal and lumbar veins; and in animals which have lower extremities, the two cardinal veins also receive the crural veins. The omphalo-mesenteric vein, vena omphalo-meseraica, which receives the veins of the mesentery, is common to all vertebrate animals. It passes with the two ductus Cuvieri to the auricle. When the liver is formed, this vein gives branches to it, and re- ceives from it others, the venae hepaticae. Between the two sets of hepatic veins the trunk of the omphalo-mesenteric becomes ob- literated, and then the vena portae is formed as an independent vessel conveying blood to the liver, while the same blood is carried out of the organ by the distinct venae hepaticae. The umbilical vehi originally terminates in that part of the omphalo-mesenteric vein which is about to enter the heart, and which subsequently forms the most anterior or superior part of the vena cava inferior. At a later period it sends branches to the liver, while its trunk and the inferior vena cava remain connected by the ductus venosus. Tlie circulation of the foetus is essentially distinguished from that of the adult human subject by the mingling of the blood of the two auricles, which takes place through the opening in their septum, also by the further mixture of the blood of the two sides of the heart, which is effected through the medium of the ductus arteriosus Botalli, and further by the circumstance of part only of the blood of the right ventricle being sent to the lungs. All the blood of the body, or all the blood which the two ventricles emit, except the small quantity which the lungs receive from the right ventricle, is returned to the right auricle. The blood of the left ventricle is sent to the upper parts and also to the lower parts of the body; that of the right ventricle passes chiefly through the ductus Botalli, and supplies the lower parts of the body. All this blood returns to the right auricle. Only the fractional portion which the right ventricle sends to the lungs is collected from those organs in the left auricle. Development of the Nervous System. The mode in which the rudimentary structures of the cerebro- spinal nervous system are formed has been already stated (p. 513). The dorsal laminae, the inner borders of which close in and form the DEVELOPMENT OF THE BRAIN. 537 canal of the spinal cord, seem to leave a fissure in the situation of the medulla oblongata. Between this and the most anterior ex- tremity of the canal, several vesicular enlargements, the vesicles of Fig. 192. Early forms of the brain in the embryo, after Tiedemann. a. Brain and spinal cord of an embryo of the seventh week: 1, spinal cord; 2, enlargement of the spinal cord where it makes a bend forwards; 3, cerebellum; 4, optic lobes; 5, optic thalami; 6, membranous hemispheres of the cerebrum; 7, prominence analogous to the corpus striatum, b. Brain of au embryo of the ninth week: 1, spinal cord; 2, cerebellum; 3, optio lobes; 4, optic thalami, enclosing the third ventricle; 5, cerebral hemispheres, e. Brain of an embryo of the twelfth week, viewed from above, the membranous walls of the hemispheres being reflected to either side: 1, spinal cord; 2, cerebellum; 3, optic lobes; 4, optic thalami, between which the third ventricle lies; 5, tbe walls of the hemispheres ; 6, corpora striata; 7, commencement of the corpus callosum. f. perpendicular section of the same brain : 1, spinal cord; 2, bend of the cord forwards; 3 second bend of the cord upwards; 4, cerebellum ; 5, thin laminae connecting the cerebellum with the optic lobes; 6, orura cerebri; 7, optic lobes or corpora quadrigemina; 8, cavity of the third ventricle; 9, the infundibulum; 10, optic lobe; 11, optic nerves; 12, margin of the fis- sure leading into the lateral ventricle; 13, corpus callosum, at this period perpendicular in its direction. the brain, are developed. (See Fig. 164, p. 514). As observed by Yon Baer in the chick, the cerebellum is formed early; to produce 538 GENERATION AND DEVELOPMENT. it, the laminae, after having formed the fourth ventricle, meet again superiorly and anteriorly, and enclose a short canal leading into the vesicle of the optic lobes or corpora quadrigemina, the largest of the cerebral vesicles. The vesicle in front of that of the optic lobes is the vesicle of the third ventricle, the first formed, and at first the most anterior. In front of it are developed the vesicles of the cere- brum (see Fig. 192, A and b). The nerves of special sense are originally hollow processes of the ventricles, the auditory nerve arising from the fourth, the optic nerve from the third, and the olfactory nerve from the lateral ventricle. The most essential parts of the organs of special sense are, therefore, in their origin, diver- ticula, or parts protruded, from the brain. After a certain period, the vesicle of the corpora quadrigemina does not increase in size equally with the other parts, whilst the cerebral hemispheres become more rapidly developed, and extend backwards so as to cover the parts situated behind them (see Fig. 192, c. D.). The cerebral ganglia are produced by thickening of the walls of the primary vesicles; the corpora striata in the most anterior or cere- bral vesicle, and the optic thalami in the vesicle of the third ventricle (Fig. 193, E, f). According to Professor Betzius (exxxv. 1846) the three lobes or portions of the cerebral hemispheres in the human embryo are de- veloped, not at once, but at three separate periods. In the first of these periods, which extends from the second to the third month, the anterior lobes are formed; in the second period, comprised be- tween the end of the third and the beginning of the fifth month, the middle lobes are formed; last of all, the posterior lobes are deve- loped. The inferior horns of the lateral ventricles and the hippo- campi do not appear until the second period; at this period also the optic thalami make their appearance, and after these the tubercula quadrigemina. Development of the Organs of Sense. The eye is in part developed as a protruded portion of the vesicle of the third ventricle of the brain, and it contains part of the mem- branes of the brain, namely, the fibrous and the vascular tunic. Ac- cording to Huschke, the retina is originally a vesicle-like protrusion of the brain, with the cavity of which it communicates through the medium of the tubular optic nerve (Fig. 193, a). The sac of the transparent media which the eye afterwards contains communicates at no period with the cavity of the brain. The capsule of the lens appears to be developed from an inverted portion of the common in- teguments, and consequently is at a certain period open externally (Fig. 193, b). The inversion of the tegument from without, de- presses the external convex surface which the vesicle of the retina DEVELOPMENT OF THE EYE. 539 Fig. 193. Development of the eye; after Husrhkc. A, longitudinal section of an eye of an embryo chick of two days, enlarged thirty times. The cavities of the retina and optic nerves are seen, the whole being covered by the external tegument, c, the cephalic part of an embryo chick of the first half of the third day of incubation, magnified seven times; showing the eye with the capsule of the lens still open, surrounded by the retina, which is folded so as to con?i?t of two layers, and presents the cleft inferiorly. There are also seen the tubular looped heart, three branchial or visceral arches, and the labyrinth of the ear still open. B, is«a section of the eye of the same embryo, through the middle of the lens, enlarged thirty times. The semicircular layers of membrane are seen. The most internal is the very thick capsule of the lens; the next is the true retina, the most external is Jacob's membrane. D, the eyo of a chick of the third day of incubation, showing the same parts as figure c on a larger scale, e, is the section of an eye at the fourth day of incubation of the chick, magnified thirty times. The capsule of the lens is now closed, is covered with conjunctiva, and contains a conical nucleus, the lens. The vitreous humor is developed between the capsule of the lens and the retina: external to the two layers of the retina is the sclerotic coat. has, on the second day of incubation, towards the canal of the optic nerve, and the anterior half of the vesicle is thus reflected inwards upon itself in the manner of a serous sac. The inverted layer be- comes the future retina; the external layer, the membrana Jacobi: The more recent and extended observations of Mr. H. Gray on the development of the retina and optic nerve in the chick, are at variance in some respects with the account given by Huschke. Mr. Gray was never able to see satisfactorily any doubling-in of the re- tina so as to form two layers, and he maintains that Jacob's mem- brane is not developed until a much later period (xliii. 1850, p. 189). The iris is formed rather late, but its circle is complete at its first development. In the eye of the foetus of Mammalia and man, the pupil is closed by a delicate membrane, the membrana pupillaris, 540 GENERATION AND DEVELOPMENT. the blood-vessels of which are derived from the anterior surface of the iris. From the pupillary margin of the iris there likewise ex- tends backwards the vascular membrana capsulo-pupillaris, which connects the margin of the capsule of the lens with the margin of the iris. The eyelids of the human subject and mammiferous animals, like those of birds, are first developed in the form of a ring. They then extend over the globe of the eye until they meet and become firmly agglutinated to each other. But before birth, or in the Carnivora after birth, they again separate. The ear likewise, according to Huschke, consists of a part deve- loped from within, and of one formed externally. The labyrinth is developed upon tbe hollow protruded part of the brain which forms the auditory nerve. It appears first in the form of an elongated vesicle at the hinder part of the head of very young embryoes above the second so-named branchial cleft. From it is developed a second vesicle, the rudiment of the cochlea, the convolutions of which are then formed. The semicircular canals are produced, as diverticula of the vestibule, which terminate by again communicnting with the same cavity. The Eustachian tube, the cavity of the tympanum, and the ex- ternal auditory passage, are remains of the first branchial cleft. The membrana tympani divides the cavity of this cleft into an internal space, the tympanum, and the external meatus. The mucous mem- brane of the mouth, which is prolonged in the form of a diverticu- lum through the Eustachian tube into the tympanum, and the exter- nal cutaneous system come into relation with each other at this point, the two membranes being separated only by the proper membrane of the tympanum. Development of Alimentary Canal. The alimentary canal, which, as already described, is a kind of diverticulum from the umbilical vesicle, is at first an uniform straight tube, which gradually becomes divided into its special parts, stomach, small intestine, and large intestine (Fig. 194). The stomach originally has the same direction as the rest of tbe canal; its cardiac extremity being superior, its pylorus inferior. The first changes of position which the alimentary canal undergoes consists in the stomach assuming an oblique direction, and in the small intestine taking a new course from the stomach towards the navel, and, after making an abrupt bend there, returning towards the middle of the body in order to make its final curve to reach the anus. The limit between the small and the large intestine lies in the part returning from the umbilicus, the ductus omphalo-mesente- DEVELOPMENT OF ALIMENTARY CANAL. 541 ricus beinjr connected with the lower part of the small intestine (see Fig. 174, p. 521). The part of the small intestine near the Fig. 194. An embryo dog, representing the junction of the umbilical vesicle with the intestinal canal. a, rudimentary nostrils; b, rudimentary eyes; c, the first visceral arch ; d, the second visceral arch; e, the right, /, the left auricular appendage; g, the right, k, the left ventricle of the heart; i, the aorta; k, the liver, between the two lobes of which is perceived the divided ori- fice of the omphalo-mesenteric vein; I, the stomach; m, the intestine, communicating with the umbilical vesicle, n; o, the Wolffian bodies; p, the allantois; q, the upper extremities! r, the lower extremities.—After Bischoff. umbilicus gradually becomes elongated and convoluted (see Fig. 173), and at the same time the large intestine rises so as to form its great arch round the greater part of the small intestine. The principal glands in connection with the intestinal canal are the salivary, pancreas, and the liver. In Mammalia, each salivary gland first appears as a simple canal with bud-like processes (Fig. 195) lying in a gelatinous nidus or blastema, and communicating with the cavity of the mouth. As the development of the gland advances, the canal becomes more and more ramified, increasing at the expense of the blastema in which it is still enclosed. The 40 542 GENERATION AND DEVELOPMENT. Fig. 195. Fig. 196. Fig. 195. First appearance of parotid gland in the embryo of a sheep. Fig. 196. Lobules of the parotid, with the salivary ducts, in the embryo of the sheep at a more advanced stage. branches or salivary ducts constitute an independent system of closed tubes (Fig. 196). The pancreas is developed exactly as the salivary glands. The liver in the embryo of the bird is developed by the pro- trusion, as it were, of a part of the walls of the intestinal canal, in the form of two conical hollow branches which embrace the common Fig. 197. Rudiment of the liver on the intestine of a chick at the fifth day of incubation, a, heart; &, intestine; c, diverticulum of the intestine in the coats of which the liver (d) is envelope 1; e, part of the mucous layer of the germinal membrane. venous stem (Fig. 197). The cones increase in length, pushing before them ramifications of blood-vessels, while their base becomes DEVELOPMENT OF THE URINARY ORGANS. 543 gradually narrowed, and assumes the form of a cylindrical duct. At the same time, internal ramifications are developed in the cavities of the cones, and these become united at their base, in consequence of more and more of the surrounding part of the intestinal parietes being taken up to form them, till at last the part that separated them is removed to a distance from the intestine; and the cavities, ori- ginally double, open by one mouth into the intestine. The gall- bladder is developed as a diverticulum from the hepatic duct. Development of the Respiratory Apparatus. The lungs, at their first development, appear as small tubercles or diverticula from the abdominal surface of the oesophagus. They are united at the anterior part of their circumference, and here a pedicle is formed which becomes elongated into the trachea (see Fig. 198, A, b). Soon afterwards, the lung is seen to consist of a mass of Fig. 198. ABC J/1 *G1_I 7 \ it* M V"v 4 This Fig. illustrates the development of the respiratory organs. A. is the oesophagus of a chick on the fourth day of incubation, with the rudiments of the trnohea and the lungs of the left side viewed laterally: 1, the inferior wall of oesophagus; 2, the upper wall of the same tube; 3, the rudimentary lung; 4, the stomach. B, is the same object seen from below, so that both lungs are visible. C, shows the tongue and respiratory organs of the embryo of a horse: 1, the tongue; 2, the larynx; 3, the trachea; 4, the lungs viewed from the upper side.—After Rathke. caecal tubes issuing from the branches of the trachea (Fig. 198, c). The diaphragm is early developed. The Wolffian Bodies, Urinary Apparatus, and Sexual Organs. The Wolffian bodies have been already several times mentioned. They are organs peculiar to the embryonic state, and may be re- garded as temporary, though not rudimental, kidneys; for they seem to discharge the functions of these latter organs, though they are not developed into them. They probably bear the same relation to the persistent kidneys, as the branchiae of Amphibia do to the luno's which succeed them. 544 GENERATION AND DEVELOPMENT. In Mammalia the Wolffian bodies are bean-shaped, and are com- posed of transverse cascal canals, united by an excretory duct which leads from the lower extremity of the organ to the sinus urogenitalis or cloaca of the foetus. (See Fig. 199, 4). The kidneys (2) and supra- renal capsules (1) are developed behind them. Their size is at first so great, that they entirely conceal the kidneys; but in proportion as the latter bodies increase in size, they grow relatively smaller, and come to be placed more inferiorly. Along the outer border of the gland runs the efferent part of the generative.apparatus (5), viz., the Fallopian tube, or the vas deferens, which at first has the same conformation, and terminates by a free extremity; whilst the tes- ticle or ovary (2) is formed independently at the internal excavated border of the organ. Sub- sequently the efferent tube and the testicle in the male become connected by transverse vessels, whilst in the female the extremity of the efferent tube merely acquires an open mouth. In both sexes the Wolffian bodies entirely dis- appear, and are not converted into any other organ. The epididymis is developed indepen- dently, that part which consists of the coni vas- culosi being formed of the communicating tubes which connect the efferent tube with the testis, and the rest being constituted by the convolu- tions of the efferent tube itself. All that part of the efferent tube of the generative apparatus which is thrown into strongly marked convolu- tions along the outer border of the Wolffian body, contributes to the formation of the epidi- dymis, and from the point where the convolutions cease, a band or ligament, the gubernaculum testis Hunteri, which was developed before the convolutions of the tube were visible, and contains fibres of the cremaster muscle, passes off to the inguinal canal, and sub- sequently serves to guide the testis into the scrotum. In the female the tube remains free from convolutions, but from the same point as in the male, a ligament, afterwards the round ligamentum of the uterus, extends to the inguinal ring. The part of the tube which lies below the point of attachment of this ligament becomes the horn of the uterus. In those animals in which a middle portion or body of the uterus exists, this part is formed by the coalescence of the two horns. In the human uterus, the two horns gradually become shorter, and are lost in the body or fundus of tbe uterus which is at the same time developed. (See Fig. 200, A, c). Magnified representa- tion of the urinary and generative organs of human embryo meas- uring eight lines in length. 1, the supra- renal capsule of the right side, totally con- cealing the correspond- ing kidney which lies behind it; 2, kidney and ureter of the left side exposed by the re- moval of the suprare- nal capsule; 3, testis or ovary of the right side; 4, Wolffian body; 5, Fallopian tube, or vas deferens. — After Miil- ler. DEVELOPMENT OF THE SEXUAL ORGANS. 545 Fig. 200. Urinary and generative organs of human embryo measuring 3& inches in length, a general view of these parts: 1, suprarenal capsules; 2, kidneys; 3, ovary; 4, Fallopian tube; 5, uterus; 6, intestine; 7, the bladder, b, bladder and generative organs of the same embryo, viewed from the side: 1, the urinary bladder; 2, urethra; 3, uterus (with two cornua); 4, vagina; 5, part as yet common to the vagina and urethra; 6, common orifice of the urinary and generative organs; 7, the clitoris, c, internal generative organs of the same embryo: 1, the uterus; 2, the round ligaments; 3, the Fallopian tubes; 4, the ovaries; 5, the remains of the Wolffian bodies, d, external generative organs of the same embryo: 1, the labia majora; 2 the nympha?; 3, the clitoris.—After Miiller. The sinus urogenitalis, which has been mentioned, is a cavity or canal, opening externally, in which the excretory ducts of the Wolffian bodies, the ureters, and the efferent parts of the generative apparatus terminate internally. This canal is also prolonged into the urachus. Subsequently it becomes divided by a process of division extending from before backwards, or from above down- wards, into a " pars urinaria," and a " pars genitalis." The former, extending towards the urachus, is converted into the urinary bladder, whilst from the latter are formed the vesiculae seminales in the male, and the middle portion of the uterus in the female (see Fig. 200, B). The external parts of generation are at first the same in both sexes. The opening of the genito-urinary apparatus is, in both 46* 546 GENERATION AND DEVELOPMENT. sexes, bounded by two folds of skin, whilst in front of it there is formed a penis-like body surmounted by a glans, and cleft or fur- rowed along its under surface. The borders of the furrow diverge posteriorly, running at the sides of the genito-urinary orifice inter- nally to the cutaneous folds just mentioned (see Fig. 200, B, d). In the female, tkis body becoming retracted, forms the clitoris, and the margins of the furrow on its under surface are converted into the nymphae, or labia minora, the labia majora pudendae being consti- tuted by the great cutaneous folds. In the male foetus, the margins of the furrow at the under surface of the penis unite at about the fourteenth week, and form that part of the urethra which is in- cluded in the penis. The large cutaneous folds form the scrotum, and at a later period, namely, in the eighth month of development, receive the testicles, which descend into them from the abdominal cavity. Sometimes the urethra is not closed, and the deformity called hypospadia then results. The appearance of hermaphro- ditism may, in these cases, be increased by the testes being re- tained within the abdomen. INDEX. A. Abdominal type of respiration, 140. Aberration, spherical and chromatic, 439-440. Absorbents. See Lymphatics. Absorption, general purposes of, 225. different kinds of, 22G. by lacteal vessels, ib. in villi, 227. cells developed for, ib. by lymphatics, 228. by blood-vessels, 236. rapidity of, 243. by the skin, 282. of gases by lungs, 150. elective, 227, 237. nutritive, 2.16. interstitial, ib. process of, by endosmose, 238-241. see lymph, chyle, lymphatics, lac- teals. Accessory nerve, 380. Accidental elements, 40. Acetic acid in gastric fluid, 184. Acid. See Hydrochloric. Acetic, etc., influence of, in digestion, 185. Acini of glands, 265. Action of capillaries, 123. Adaptation of eye to different dis- tances, 440. Adipose tissue, composition of, 30. Afferent lymphatics, 235. nerve fibres, 311. After-sensations, 429, 478, 481. Age, in relation to pulse, 97. Age, continued. in relation to breathing, 144. influence of, on production of car- bonic acid, 148. in relation to heat of body, 159, 167. in relation to excretion of urea, 292. Aggregated glands, 265. Agminate glands, 201. Air, atmospheric, composition of, 146. changes by breathing, 147. quantity breathed, 142. purity of, influencing production of carbonic acid, 149. diffusion of, in lungs, 145. favorable to coagulation of blood, 60. Air-cells, 139-140. Air-tubes. See Bronchi. Albumen, characters of, 33. composition of, 35. coagulated, properties of, 35. relation to fibrine, ib. not coagulated by heat, note, 35. of blood, 66. of chyle, 230. tissues and secretions in which it exists, 38. products of decomposition of, 28. action of gastric fluid on, 184. coating oily matter, 230. Albuminose, 192. Albuminous substances, 33. food, 170. principles, digestion of, 191. (547) 548 IND EX. Aliments. See Food. Alimentary canal, development of, 540. See Stomach, Intestines, etc. Alkalies, fats decomposed by boiling with, 31. Alkaline reaction of blood, 71. Alkali of saliva, effects of, 176. Allantois, 522. vessels of, ib. office of, 523. Aluminium, parts of body in which found, 40. Amativeness, organ of, 348. Amaurosis, action of iris in, 363-64. after injury of the fifth nerve, 369. Ammonia, a product of the decomposition of albumen, 28. cyanate of, 292. urate of, 295. from skin, 280. Amnion, 517. Ampulla, 457. Amputation, sensations after, 316. Amylaceous principles, digestion of, 192. Anastomoses of nerves, 305. of veins, 126. Aneurism, coagulation of blood in, 31. Ani, sphincter. See Sphincter. Anima. See Mind. Animal fats, 30. fluids, various kinds of, 41. food, 169. digestion of, 190. in relation to urine, 293. heat, see Temperature and Heat, 159. life, its phenomena, 26. solids, various kinds of, 41. substances, chemical characters of, 28. Antagonistic movements, 403. Anterior pyramids, 337. Antiperistaltic movements, 224. Aorta, valves of, 86. its elasticity, 106. pressure of blood in, 116. Aortic arches, 534. Apoplexy, effects of, 356. with cross-paralysis, 341. Apoplexy, continued. continued breathing in, 344. Aqueductus cochleae, 457. vestibuli, ib. Aqueous humour, 435. part of food, 171. Arantii, corpora, 89. Arches, visceral, 528-9. Arciform processes, 345. Area pellucida, 512. vasculosa, ib. Arterial blood, organization of, 59. Arteries, their structure, 104. their elasticity, 106. its advantages, ib. their muscularity, 108. its purpose, 110. their office, 111. their pulse, ib. force of blood in them, 114. its variations, 116. effects of exposure, 108. of division, ib. of cold, 108, 109. of electro-magnetism, 110. contraction after death, 108. dilatation, ib. large and small, distinctions in structure of, 106. minute, arrangement of, 117-120. small, their action, 123. three states of, 111. enlargement in the pulse, 111. change of form in the pulse, ib. influence of sympathetic nerve on, 111. Artery, organization of blood in, 30. Articulate, sounds, classification of, 416. vowels and consonants, ib. whispered sounds, 417. mute vowels, ib. mute consonants, ib. continuous consonants, 418. Artificial digestive fluid, 187. Asphyxia, 157. Assimilation or maintenance, nature of the process, 49. nutritive, 244. of blood, 79. Assimilative force, 49. Associate movements, 404. INDEX. 549 Atmospheric air. See Air. pressure, effects on cerebral-circu- lation, 133. on lungs, etc., 140. Atrophy, from deficient blood, 251. from diseased brain, 255. Attention, influence of, 407, 425. Auditory nerve, 459_ sensibility of, 470. Auricles of heart, their action, 85. their dilatation, 98. capacity, ib. force of contraction, ib. formation of septum between, 533. Automatic movements, 402. dependent on sympathetic system, ib. on cerebro-spinal system, 403. rhythmic, 402. persistent, 403. Axis-cylinder of nerve-fibre, 303 Azote. See Nitrogen. Azotized, food. See Food. principles, divisions of, 31. B. Baritone, 413. Basement-membrane, 258, 261. Bass-voice, 413. Bicuspid valve, 89. Bile, its composition, 209. its elementary composition, 211. quantity secreted, 213. purpose of, 214. excrementitious, ib. directly and indirectly excremen- titious, 215. digestive properties of, 216. antiseptic properties of, 217. excretion of, necessary to life, 215. mixture with chyme, 188. making chyme capable of absorp- tion, 216. re-absorption of, 214. formation of ammonia in its de- composition, 217. a natural purgative, ib. coloring serous secretions, 260 duct, passage of bile in, 212. Biliary resin, 210. Biline, and the products of its decomposi- tion, 210. compared with blood, 211. Bilipyrrhine and Biliphseine, 211. Biliverdine and Bilifulvine, ib. Binary compounds, 28. Birds, their high temperature, 164. Bladder, urinary, evacuation of, a reflex act, 333. Bleeding; effects on water in blood, 66 Blood, general character of, 53. specific gravity of, 54. temperature of, 54, 154. color of, arterial and venous, 54, 69-70. reaction of, 55, 71. odor or halitus of, 55 coagulation of, 55-59. circumstances influencing, 59. water in, 66. its fibrine, ib. separation of fibrine from, 35. its albumen, 66. globuline, 67. hsematine, 68. extractive matter of, 37. its fatty matters, 70. its inorganic constituents, 71. gases in, 200. containing urea, 293. relation of lymph to, 229. compared with lymph and chyle, 231. compared with bile, 212. reabsorption of bile into, 214. changes by respiration, 153, 156. hepatic, characters of, 208. portal, characters of, 208. menstrual, 55, 495. state of, in hunger and thirst, 196. its vital properties, 73. organization of, 57. conditions favoring its organization, 59. its growth and maintenance, 79. its development, 74—79. development from lymph and chyle, 232. \ repetition of production of, 250. formed in the liver, 214, note. office of vascular glands, 271. 550 INDEX. Blood, continued. highest parts of organic life, 31. its purpose, 80. right condition of, necessary to nutrition, 251. its relation to tissues, 123-4. to nutrition, 251. to secretions, 278-79. adaptation to parts, 251. quantity to each part regulated, 109. varieties of supply to parts, 128. its increase may favor growth in a part, 267. deficient a cause of atrophy 251. a cause of mortification, ib. circulation of. See Circulation, 82. force in circulating, 103. velocity in the veins, 129. average velocity, 122, 130. movement in capillaries, 120. resistance to movement, 121. effects of gravitation, 125. quantity required to dilate the arteries, 114. statical pressure in arteries, ib. Blood-corpuscles, two forms of, 62. red, 62-63. white, 63. term of life, 249. degeneration of, 78. sinking, 57. movement in capillaries, 122. Blood-crystals, 72. Blood-vessels, absorption by, 236. substances absorbed by, 237. their fulness hindering absorption, 244. communication with lymphatics, 228. share in nutrition, 251. Bone-earth, composition of, 39. Bones, vascular and non-vascular, 252. Brain, divisions of, 344. See Pons, Cerebrum, etc. duality of, 357. acids, containing phosphorus in, 39. circulation of blood in, 132. its capillaries, 119. relation of blood to, 81. its influence on heart's action, 100. development of, 537-8. compression of, continued breathing in, 344. Brain, continued. disease of, with atrophy, 255. coagula in its membranes, 58. Branchiae, relation to development of blood-corpuscles, 76, note. Branchial arches and clefts, 527-8. Breathing air, 142. Breathing, capacity of, 143. Bronchi, arrangement and structure, 137. their muscularity, 144. Bronchial arteries and veins, 146. Brunner's glands, 192. Buccinator muscle, motor power de- rived from facial nerve, 366. Buffy coat, mode of formation of, 57, 63. Bulbus arteriosus, 533. Bursse mucosse, 259. c. Caecum, 199, 222. changes of food in, 222. acid fluid in, ib. large in Herbivora, ib. Calcium, parts of body in which found, 40. fluoride of, in bones, teeth, and urine, 39. Calculi, biliary, containing cholestea- rine, 31. containing copper, 40. Calculus, radiation of sensation from, 320, 330. Calorifacient food, 169. Calyces of the kidney, 284. Canal of the spinal cord, 350. Capacity of arteries, 107. vital, of chest, 143. Capillaries, their arrangement, 117. diameter, 118. networks, ib. number, 119. nature, 120. structure, ib. circulation in, ib. velocity of, 121. variations of, 122. their contractions, 123. development of, 532-3. of lungs, 138. Capsules of Malpighi, 284. Carbon, union of, with oxygen, pro- ducing heat, 162. its combustion-heat, 164. INDEX. 551 Carbonic acid in atmosphere, 146. increase of in breathed air, 147. diffusion of, 151. in lungs, 145. in blood, 154. effect on color of blood, 70. influence on coagulation, 60. increase of blood in asphyxia, 159. influence on circulation, 158. effect of, on pulmonary circulation, 123. in relation to heat of body, 160. exhaled from skin, 280-282. hybernating animals in, 159. Carbonate, alkaline in blood, 71. Cardia, action of, 193. sphincter of, 180. relaxation in vomiting, 195. Cardiac branches of pneumogastric, 378. Cartilage, chondrine the animal basis of, 33. Casein, absence of phosphorus in, 38. Casserian ganglion, 366. Catalysis, process of, 188. Cauda equina, 322. Caudate, ganglion-corpuscles, 307. Cells, primary or elementary, 44-6. the formation of, 49. examples of formative power, 50. action in secretion, 266. importance of, in inorganic pro- cesses, 50. of glands, 266. embryo, 74. air, 170-2. See Pulmonary, Hepa- tic, Renal, etc. Centres nervous. See Nervous centres. Centrifugal nerve-fibres, 311. Centripetal nerve-fibres, ib. Cerebellum, its structure, 356. its commissure, the pons, ib. its functions, 347. in relation to sensation, ib. in relation to motion, ib. effects of removal, ib. effects of disease, 348. relative size of, ib. organ of muscular sensibility, ib. organ of ainativeness, 349. cross action of, 350. injuries and diseases of its crura, ib. connection with testes, 349. Cerebral ganglia, their office, 354. in relation to will and sensation, 355. Cerebral ganglia, continued. in relation to emotions and emo- tional acts, ib. hemispheres, development of, 538. one sufficient for ordinary acts, 357. destruction of one, ib. Cerebral nerves, 360. third, 361. relation of, to iris, ib. to lenticular ganglion, ib. fourth, 864. fifth, 366. relation of, to senses, 366-8. a nerve of taste, 368. relation of, to nutrition, 369. sixth, 364. communication of, with sympa- thetic, 365. seventh, 370. See Portio Dura and Portio Mollis. eighth, 373. See Glosso-pharyngeal, Pneumo- gastric, and spinal Accessory. Cerebral and spinal nerves, 360. Cerebro-spinal nervous system, 322. See Spinal Cord, Brain, etc. Cerebro-spinal fluid: relation to cir- culation, 133. Cerebrum, its structure, 350. its functions, 354-357. development of, 357. defects of, ib. effects of injury of, ib. Chalk-stones, 294. Charcoal, absorption of, 243. Chemical characters of animal sub- stances, 28. composition of the human body, 26. sources of heat, 162. Chest, its capacity, 143. its construction, 139. elasticity of its walls, 142. Chest-notes, 414. Chloride of sodium in albumen, 34. Chlorine, action on negro's skin, 283. parts in which found, 39. Chloroform, effects of, 344. Choleic and cholinic acids, 210. Cholestearine, properties of, 31. in bile, 211. Cholepyrrhine, ib. Chondrine, properties of, 33. Chorda dorsalis, 515. Chorda tympani, 370. 552 INDEX. Chorion, 588. first appearance of, 505. formation and structure of, 522. villi of, ib. Choroid coat of eye, 433. use of pigment of, 439. Chromatic aberration, ib. Chyle, its general characters, 229. fatty matter, molecules, fibrine, etc., ib. analysis of, 231. compared with lymph, ib. quantity found, 232. elaboration of, 230. Chyle-corpuscles, ib. structure of, 76. development into blood-corpuscles, 76-9 Chyme, 188. changes in intestines, 198. Cicatrix, assimilation of, 255. Cilia and ciliary motion, 391. action of, in lungs, 145. Ciliary epithelium, 263. of urine tubes, 286, note. Circulation of blood, 82. general purpose, ib. general mode, 82-84. systemic pulmonary, and portal, 83. action of the heart, 84. in the arteries, 104. capillaries, 117. veins, 124. rate of, 129. peculiarities in different parts, 132. resistance to it, 121. in foetus, 536. Cleaving of yelk, process of, 506. Clefts, visceral, 529. Climate, effects on heat of body, 160. Clitoris, 487. structure of, 134. Clot, or coagulum of blood, 55. contraction of, 56. changes in the living body, ib. conical mode of formation of (see Coagulation), ib. Clothes in relation to heat, 168. Coagulation, of blood, 55. the process described, ib. conditions affecting, 59. of albumen, 34. See Blood, Fi- brine. Coagulated albumen, properties of, 35. Coagulum of chyle, 230. Cochlea of the ear, 457. office of, 470. Cold-blooded animals, 161. extent of reflex movements in, 331. Cold, influence on secretion by sto- mach, 184. retards coagulation of blood, 59. Collateral circulation in veins, 126. Colon, 199, 222. Color of blood, source of, 69. changes of, 153. Coloring matter of bile, 211. of urine, 297. Columnse carnese, their action, 86-90. Columns of medulla oblongata, func- tions of, 340. Columns of spinal cord, 322. their functions, 326. effects of dividing, 328. cases of disease and injury of, 325. Combination of muscles in reflex acts, 322. Combinations of sensations, 357. Combined movements, office of cere- bellum in, 348. Combustion-heats, 164. Commissures of cerebrum, 351. offices of, 359. spinal cord, 322. Commissural fibres of spinal cord, 323. Communication of impressions, 320. Compass of the voice, 412. Complemental air, 142. Composition, chemical, of the human body, 26. Concha, 461. Conduction of impressions, 52. in spinal cord, 325. along it, 326. across it, 328-9. in medulla oblongata, 340. in sympathetic nerve, 319. in nervous centres, ib. Conductors, nerve-fibres are, 313. Cone, fibrous (brain), 351. Conglomerate glands, 265. Coni vasculosi, 499. Conical clot, mode of formation of, 58. epithelium, 263. Conscience, 356. supremacy of, 358. Consensual movements, 404. Consonants and vowels, 416. Contact, points of, influence on coagu- lation of blood, 61. INDEX. 553 Continuous fibres, note, 337. Contractility, 50. influence of nerves on, 61. of muscular tissue, 396. Contraction of coagulated fibrine, 56. muscular tissue, mode of, 397. muscular, of arteries, 108. Contralto voice, 413. Convoluted glands, 266. Convolutions, cerebral, 352. Co-ordination of movements, office of cerebellum in, 348. Copper, always an accidental element in the body, 40. in bile, 40, 211. Cord, spinal; see Spinal cord. Cords, tendinous, in heart, 89 vocal, see Vocal cords. Corium, 275. Cornea, 434. nutrition of, 120. ulceration of, in imperfect nutrition, 171. Corpora Arantii, 89. geniculata, 352. olivaria, 337. pyramidalia, 337. quadrigemina, 351. their function, 352. relation to heart, 103. restiformia, 338. striata, their structure, 351-2. their function, 354. Corpus callosum, office of, 359. defects of, 360. cavernosum penis, 134. dentatum, 346. luteum, 496. structure and mode of forma- tion, ib. as a sign of pregnancy, 498. spongiosum urethrae, 134. Corpuscles of blood, 54. their development, 74. first set, 74-77. second set, 77-79. degeneration of, 81. of lymph, 54, 230. of lymph-glands, 235. of Malpighi, 284. see Blood, Chyle, etc. Cortical substance of kidney, 284. Coughing, influence on blood's pres- sure, 117. sensation in larynx before, 320. 47 Cowper's glands, 499. office uncertain, 503. Craniological examination of Cero- bellum, 348. Craniology, 358. Cranium, development of, 528. Crassamentum, 55. Cross-paralysis, 341. Cruor, 67. Crura cerebelli, 346. effects of irritating, 347.. effects of disease of, 350. cerebri, 351-2. their office, 353. effects of dividing, ib. Crystalline lens, 435. in relation to vision at different distances, 442. Crystals in blood, 72. Cupped appearance of blood-clot, 57 Curves of arteries, 111. Cutaneous perspiration, 280. Cuticle, see Epidermis, Epithelium. Cutis anserina, 394. vera, 275. Cuvier, ducts of, 535. Cyanate of ammonia, 292. Cylindrical epithelium, 263. Cystic duct, passage of bile in, 213. oxyde, sulphur in, 38. Cytoblasts, 42. in developing and growing parts, 249. Cytoblastema, or formative substance, D. Day, time of, influence on carbonic acid, 149. Death, natural, of particles, 245. instantaneous, from injury to me- dulla oblongata, 342. Decapitated animals, reflex acts in, 331. temperature of, 166. Decay of dead organic matter, see Decomposition. natural, of particles, 245. Decidua, 508. vera, 510. reflexa, ib. serotina, 511. in relation to the ovum, 510. Decomposition, spontaneous, 29. explanation of, ib. circumstances influencing, ib. 554 INDEX. Decomposition, continued. proneness of organic compounds to, ib. Decussation of fibres in medulla ob- longata, 340. Degeneration of blood corpuscles, 78. Deglutition, 178. a reflex act, 330. independent of brain, 393. connection with medulla oblongata, 393. centripetal nerves exciting, ib. relation of nerves to, 374. relation of pneumogastric nerve to, 378. Delirium, phenomena of, 358. Derangement, phenomena of, 359. Derma, 275. Descendens noni, 382. Development, nature of the process, 49. repeated in nutrition, 250. of organs, 527-546. of vertebral column and cranium, 527. of face and visceral arches, 258. of extremities, 530. of heart and vessels, 531. of blood, 74-79. of fibrine, 78. of vascular system, 531. of nervous system, 513, 537. of organs of sense, 538. of intestinal canal, 540. of respiratory apparatus, 543. of Wolffian bodies, urinary appa- ratus, and sexual organs, 543. Diaphragm, action of, in inspiration, 140. action of, in vomiting, 195. Diffusion of carbonic acid and oxygen, 151. of impressions^ 320. Digestion, general nature of, 169. See Gastric Fluid, Food, and Sto- mach. Digestive fluid, see Gastric fluid. Digestive property of saliva, 175. tract of mucous membrane, 260. Discus proligerus, 438. Disease in relation to heat of body, 159. Diseased parts, assimilation in, 255. Diseases, occurring only once, 255. frequently, ib. Diseases, continued. symmetrical, 251. reflex acts in, 334. Division of nerve-roots, effects of, 325. of nerves in neuralgia, 316. of spinal cord, effects of, 330. and subdivision of yelk, 496. Dorsal laminae, 512. Dreams, phenomena of, 359. Dropsy, serous fluid of, contains albu- men, 33. Drowning, time in which fatal, 159. Duality of mind, 358-9. Duct, vitelline or omphalo-mesenteric, 619. Ducts of glands, their office, 268. temporary, 264. permanent, 264. contraction of, 268. morbid affections of, ib. Duodenum, 199. Duvernoy's glands, 487. Dyslysin, 210. E. Ear, internal, 456. Ectopia vesicae, observations on, 286. Eel, capillary circulation in, 121. Efferent nerve-fibres, 311. lymphatics, 235. Egg-shell, microscopic characters of membrane of, 57. Eighth cerebral nerve, 373. Elastic tissue, its arteries, 105. tissues, heat developed in, 168. Elasticity, of arteries, 105-108. of veins, 124. employed in expiration, 142. Electric organs, nerve-fibres in, 307. Electro-magnetism, effect on arteries, 110. Elementary substances of the human body, 26. Elements, accidental, 40. essential, 26. incidental, ib. Embryo, see Development. blood of, 74-79. cells forming blood, 74. Emission of semen a reflex act, 333. INDEX. 555 Emotions, connection of, with cerebral ganglia, 355. Encephalon, divisions of, 344. See Pons Varolii, etc. Fndosmosis, process of, 240. Endosmometer, ib. Enlargement of spinal cord, 324. Epidermis, increased growth of, 256. in relation to secretion, 278. as integument, ib. hinderance to absorption, 242. development, etc., of, 248. Epididymis, 499. Epiglottis, action in swallowing, 178. influence of, on voice, 411. Epilepsy, reflex acts in, 322. Epithelium, varieties of, 262-3. tesselated, 262. cylindrical, 263. ciliary, ib. parts unoccupied by, 491. motion, phenomena of, 492. general purpose of, 264. relation to gland-cells, 262. of air-passages, 139-145. of urine tubes, 285. of serous membranes, 258. in urine, 297. in bile, 211. in saliva, 172. a chief ingredient in mucus, 36. Equivalents, mode of combination in organic bodies, 28. Erectile tissues, 134. Erection, of penis, a reflex act, 334. influence of nerves in, 135. of muscular tissue in, ib. connection of, with cerebellum, 348. Essential elements, 26. Ether, effects of, 344. Eutmchs, voice of, 414. Excito-motory acts and nerves, 331, note. Excretion, general nature of, 258. direct and indirect, 215. Excretory organs, general function of, 136. Excretory office of tissues, 80. Exercise, effects of, on venous circulation, 127. Exercise, continued. effects of, on muscles, 245. in relation to heat, 168. influence on production of carbonic acid, 150. Exosmosis, 240. Expiration, act of, 142. influence on pressure of blood, 116. Expiratory movements, effects on cir- culation, 127. Extension of muscles in relation to spinal cord, 335. External ear, parts of, 461. functions of, 462. Extractive matters, varieties of, 36. Bubstances included among, 37. probably products of waste of tis- sues, ib. Extremities, development of, 530. Eye, structure of Beveral parts of, 430. refracting media of, 434. adaptation of to vision at different distances, 440. position of, during sleep, 403. capillary vessels of, 119. disorganization of, after division of fifth nerve, 369. ball, action of muscles of, 351- 366. lash, development, etc., of, 246. Eyes, simultaneous action of, in vision, 451. F. Face, development of, 528. Facial nerve, 360. effects of paralysis of, 361. relation of, to expression, 862-3. Faculties, higher mental, relation to cerebrum, 355. Faeces, character and composition, 253. quantity of, 252. analysis of, in children and adults, 214. absence of biline from, ib. Fallopian tube, 486. opening into abdomen, 259. movements of cilia in, 392. reflex action of, 334. Falsetto notes, 414. Fasting, saliva during, 173. influence on secretion of bile, 212. 556 INDEX. Fat, probable action of pancreas on, 205. Fatty substances, composition and de- scription of, 30. in relation to heat of body, 165. absorbed by lacteals, 226. in blood, 70. of chyle, 229. of bile, 211. combined with albumen, 34. Fellinic acid, 210. Fenestra ovalis, 457. office of, 464. rotunda, 457. office of, 464. Fermentation, analogy of digestion to, 188. Fibres, various forms of, 47. Fibrils or filaments, varieties of, 46. Fibrine, 35, 56. similar in composition to. albumen, 35. development of, 78. sources and properties of, 35. coagulation of, a process of organi- zation, 57. conditions under which not sponta- neouslycoagulable, 35, note. microscopic character of, 57. in blood, 66. the coagulating principle in the blood, 57. weight of, in blood, includes that of white corpuscles, 66. in chyle, 230. as food, 169. Fibrous cone (bi*ain), 351. Field of vision, actual and ideal size of, 445. Fifth nerve, see Nerve fifth. Filament or Fibrils, varieties of, 46. Fillet of Reil, 351. Filum terminale, 322, 360. Fimbriae of Fallopian tube, 486. Fish, warm-blooded, 161. their cerebella, 349. Flesh, analyses of, 65. Fleshy columns, and their action, 86- 90. Flexion of muscles, in relation to spi- nal cord, 335. Fluids, animal, divisions of, 41. secreted, ib. formative, ib. Fluoride of calcium, in bones, teeth, and urine, 39. Fluorine, parts of animal body in which found, 39. Foetal placenta, 525. Foetus, circulation of, 536. office of bile in, 214. faeces of, 215. Foetal life, vascular glands in, 271. Follicles, Graafian, 488. Food, general purposes of, 169. nutritive or plastic, ib. calorifacient, or respiratory, ib. animal and vegetable, 170. necessary composition of, ib. appropriate for man, ib. proximate principles in, 170. nitrogenous and non-nitrogenous, ib. albuminous, saccharine, and oleagi- nous, ib. milk, as natural, 171. necessity of mixture of, 170-1. changes effected in the mouth, 172. in the stomach, 188. in the intestines, 198. digestibility of articles of, 190. animal, digestion of, ib. vegetable, digestion of, 191. relation of, to saliva, 175. mixed with saliva, 176. effects of gastric fluid on, 189. structural changes by digestion, 190. chemical changes by digestion, 191. movement along intestines, 222. changes of, in large intestine, 222. indigestible parts excreted, ib. influence on secretion of bile, 212, influence on production of carbonic acid, 149. in relation to heat of body, 165. relation of urine to, 289. relation to nitrogen exhaled, 152. in relation to phosphates in urine, 300. Force, nervous, 52. of ventricles of heart, 98. of respiratory movements, 144. Forces, vital, 49. engaged in the circulation, 84. Formative force and process, nature and varieties of, 49. power, in blood, 80. substance, or cytoblastema, 41. fluids, ib. Fornix, office of, 360. IND EX. 557 Fourth ventricle, 338-9, 350. cerebral nerve, 364. Freezing, effect of, on blood, 69. Functions, of parts, variations, 111. discharge of, attended with impair- ment of parts, 244-5. in relation to vascularity, 120. Fundus of uterus, 487. G. Gall-bladder, passage of bile into, 213. passage of bile from, ib. Ganglia, mode of action. See Nervous centres. cerebral or sensory, 354. of the sympathetic, functions of, 384-7. in relation to involuntary move- ments, 388. to nutrition and secretion, 389. in heart, 100. Ganglion, Casserian, 366. corpuscles. See Nerve-corpuscles. Ganglionic nervous system. See Sym- pathetic nerve. Gases, absorbed by the skin, 283. Gastric fluid, Becretion of, 183. excitement of secretion, 183-4. characters of, 184. acids in, ib. pepsin and other animal matter in, 186. digestive power of, 186. conditions of action, ib. experiments with, 186-7. artificial, 187. nature of action, 188. relation of, to saliva, 176. essential to digestion, 192. Gastric glands, their structure, 180-3. their office, ib. Gelatinous substances, 32. tissues, ib. Gelatine, properties of, 32. sugar of, 33. varieties of, 32. exists naturally in certain tissues, ib. relation to blood, 81. 47* Gelatine, continued. as food, 172. digestion of, 192. Generation and development, 585. Generative organs of the female, 586. Geniculata, corpora, 352. Genito-urinary tract of mucous mem- brane, 261. Germinal area, development of blood in, 75. membrane, 508. serous layer, 512. mucous layer, ib. vesicle, 489. development of, 491. disappearance of, 504. spot, 489. development of, 491. Gizzard, action of, 193. Gland-cells, agents of secretion, 266. relation to epithelium, 262. Gland-ducts, minute arrangements of, 265, 266. Gland, prostate, 499. Glands, secreting. See Secreting Glands. their modes of discharge, 268. relation between growth and secre- tion of, 267. removal of particles, 244. vascular, 270. lymphatic. See Lymphatic. of intestines, 199. vulvo-vaginal, 487. Cowper's, 503. Globuline, composition of, 67. Glomerules of kidney, 284. Glossopharyngeal nerve, 373. relation of, to taste, 375-6. Glottis, forms which it assumes, 410. dilated in inspiration, ib. contracted in expiration, ib. degree of narrowing proportioned to height of note, 411. closure in vomiting, 195. Glue, a variety of gelatine, 32. Gluten as food, 169. Glyceryl, 31. Glycerine, ib. Graafian vesicles, formation of, 488. relation of ovum to, 488. rupture of, 492. analogy to glands, 264. 558 INDEX. Granules or molecules, 42. free and imbedded, ib. molecular movements of, ib. Granule-cells of blood, 77. Gravitation of blood, and its effects 125. Grey matter of spinal cord, 322. function of, 329. of cerebrum, 352. Grooves on spinal cord, 322. Growth, 49, 255. its general nature, 355. coincident with development, 356. continuous through life, ib. increased or renewed, ib. always a healthy process, 357. as hypertrophy, ib. with development, ib. conditions of, ib. increased by afflux of blood, ib. of blood, 79. Gum, as food, 170. Gustatory nerves, 375-6. H. Habitual movements, 334, 407. Haematoidin, 73. Hsemato-crystalline, ib. Haemato-globulin, 67. Haematosine or Haematine, 68. Hsemadynamometer, 115. Hair, development, etc., of, 246. structure of, 246. casting of, 246-7. growth near old ulcers, 257. chemical composition of 36. follicles, 277. their secretion, 279. Halitus or odor of blood, 55. Hamulus, 458. Hand, principal seat of sense of touch, 479. Hearing, organ of, 456. influence of the membrana tym- pani and auditory nerves upon, 465-7. influence of tension of the mem- brana tympani on, 464. double, 473. impaired by lesion of facial nerve, 361. See Sound, Vibrations, &c. Heart, its action, 84. action of the auricles, 85. action of the ventricles, 86. action of fleshy columns, ib. order of action, ib. order of sounds, ib. action of its valves, ib. its arterial valves, ib. its auriculo-ventricular valves, _ 89. action of tendinous cords, ib. sounds of, 91. 1st sound, 92. 2d sound, 93. impulse, 94. frequency of action, 96. force of action, 98. capacity of ventricles, 99. cause and method of rhythmic ac- tion, 100. effects of action, 103. general connection with nerves, 102. influenced by sympathetic nerve, 101. influenced by pneumogastric, 102. effects of electro-magnetic stimulus, ib. its action after removal, 101. its ganglia, sources of force, 319. its action weakened in asphyxia, 158. sounds of, in relation to the pulse, 113. its continuous growth, 256. hypertrophy of, 256. and vessels, development of, 531. first pulsations of, ib. development of its several cavities and septa, 533. Hearts, lymphatic, see Lymphatic hearts. Heat, animal, production of, 162. adaptation to climate, ib. evolved in plants, 164. lost by radiation, etc., 166. development of, in relation to bile, 215. developed in contraction of muscles, 398. external effects of, 166-7. Heat or rut, 493. period of, coincident with discharge of ova, ib. INDEX. 559 Height, relation to capacity of chest, 143. Hemispheres, Cerebral (see Cere- brum). Hepatic cells, 207. veins, 84. characters of blood in, 208. ducts, 207. vessels, arrangement of, ib. Herbivorous animals, their alkaline urine, 288. Hip-joint, pain in its diseases, 320, 330. Hippuric acid, 297. Horny matter, natural composition of, 36. tissue, ib. Horse's blood, peculiar coagulation, 63. spinal cord, measurement of, 324. cerebella, 349. Hour-glass contraction of stomach, 194. Hunger, sensation of, 196. Hybernation, retarded respiration, etc., in, 159. temperature in, 164. Btate of thymus in, 272. Hydrochloric acid in gastric fluid, 188. Hydrogen, union of, with oxygen pro- ducing heat, 162. its combustion-heat, 164. Hymen, 482. Hypertrophy, 256. Hypoglossal nerve, 382. I. Ideas, connection of, with cerebrum, 355. Heum, 199. Ileo-caecal valve, ib. structure and action, 224. Imbibition from vessels, in nutrition, etc., 120. of fluids, 238. Impressions, conduction of, 52, 318. retained and reproduced in cere- brum, 355. Impulses of heart (see Heart). Incidental elements, 26. Incus, 460. Inferior costal type of respiration, 142. Inflammatory blood, corpuscles in, 63. Infusoria, presence of, not essential to decomposition, note, 30. Injections into blood, 130. Hiorganic bodies, distinction from organic, 27. elements, parts of the body in which they severally occur, 38. constituents of blood, 71. Inspiration, act of, 140. force employed in, ib. enlargement of chest in, ib. effects on circulation, 128. influence on pressure of blood, 116. Instability of organic compounds, 29. Intellectual faculties, relation to cere- brum, 355. Intercellular substance, 46. Intercellular passages in lungs, 138. Intestines, general functions of, 198. structure of, 199. glands of, ib. villi of, 199-202. movements of, 223. in relation to the nerves, 319. mode of contraction of, 403. absorption in, 226. gases in, 222. fatty discharges from, 205. Intestinal canal, development of, 540. Intonation, 419. Diversion of images on retina, 444. corrected by the mind, 445. Involucrum capitis, 516. Involuntary character of reflex acts, 321. movements (see Movements). Iris, structure and offices of, 436. relation of, to third nerve, 363. relation of, to optic nerve, ib. action of, 364. relation of, 368. connection of, with corpora quad- rigemina, 353. contracted during sleep, 403. in relation to vision at different dis- tances, 442. contracts when eye turns inwards, 404. Iron, in blood, 69. parts of body in which found, 40. 560 INDEX. Irritability of muscular tissue, 397. Isinglass, source of, 32. Iter a tertio ad quartum ventriculum, 350. J. Jacob's membrane, 433. Jacobson's nerve, 373. Jejunum, 199. Jetting flow of blood in arteries, 107. K. Keratine or horny substance, 36. Kidneys, their structure, 283. their functions (see Urine), 286. capillaries of, 119. Knee, pain of, in diseased hip, 320, 330. Kreatine and Kreatinine, principles extracted from muscular tissue, 37. present in urine, 298. L. Labyrinth of the ear, 456. Lacteals, their distribution, 226. in villi, 202. contain lymph in fasting, 229. absorption by, 226. Lactic acid in gastric fluid, 184. Lamina spiralis, 458. use of, 470. Laminae dorsales, 512. viscerales or ventrales, 515. Large intestine, glands in, 204. Larynx, construction of, 408-9. vocal ligaments of, 409. ventricles of, 416. actions of muscles of, 409. irritation referred to, 820. Laryngeal nerves, 378. Lateral tracts, 337. Layer, still, of blood in capillaries, 122. Lens, crystalline, see Crystalline lens. Lenticular ganghon, relation of third nerve to, 361. Leucine, and sugar of gelatine, 82. Levator palpebrae superioris, nerve supplying, 361. Lieberkiihn's glands, 199. Life, state of, 49. the phenomena, 25. dependence on medulla oblongata, 341. natural term of, for each particle, 245, 249. Lightning, condition of blood in per- sons killed by, 62. Lime, salts of, in human body, 40. phosphate of, in albumen, 34. in blood, 71. in tissues, 40. in bones and teeth, 39. Lingual branch of fifth nerve, 368. Liquor sanguinis, 54, 56. coagulation of, 63. lymph derived from, 229. Liver, vessels of, 206. ducts of, 207. cells of, ib. general purposes of, ib. secretion of, 209. process of secretion by, 212. purposes of secretion of, 213, (see also Bile). formation of sugar by, 219. circulation in, 83. development of, 541. in the foetus, 213. a blood-making organ, ib. note. its vessels filled with yelk, ib. note. Living bodies, properties of, 49. Lobules of lungs, 137. Locus niger, 361. Loops, capillary, 119. terminal, of nerves, 306. Love, physical, cerebellum in relation to, 348. Lungs, their structure, 137. lobules of, ib. intercellular passages in, 138. their cells, 138-9. their capillaries, 138. . their elasticity, 142. circulation in, 88. pressure of blood in, 116. enlargement in inspiration, 140. development of, 543. Luteum corpus, see Corpus luteum. Lymph, its general characters, 280. its corpuscles, ib. analysis of, 231. INDEX. 561 Lymph, continued. comparison with chyle, ib. with blood, 232. relation to blood, 229. organization of, 57. quantity formed, 232. effused in inflammation, 57. corpuscles, structure of, 76. in blood, 63. development into blood-corpus- cles, 77, 78. movement in capillaries, 122. weighed with fibrine, 66. Lymphatics, their distribution, 228. origin of, ib. parts in which not found, ib. communication with blood-vessels, 229. substances absorbed by, 229, 238. Lymphatic vessels, 232. their structure, ib. valves, ib. propulsion of lymph by, 233. contraction of, ib. hearts, 234. structure and action, ib. relation of, to spinal cord, ib. 186. glands, 234. their structure, 234-5. vessels of, 235. blood-vessels of, ib. cells of, ib. office of, 236. plexuses, 235. M. Magnesia, phosphate of, in bones and teeth, 39. Magnesium, parts of body in which found, 40. Maintenance or assimilation, nature of the process, 49. nutritive, 244. of blood, 79. Malleus, 460. Malpighi, pyramids of, 284. capsules of, ib. corpuscles or glomerules of, ib. Manganesium, parts of body in which found, 40. Margarine and margaric acid, pro- perties of, 30. Margarine, formula of, 31. Margaryl, ib. Mastication, 173. Meconium, 214. Medulla oblongata, structure of, 337. its tracts, 338. origin of nerves in, 339. analogy to spinal cord, ib. its nerves analogous to spinal nerves, 340. functions of, ib. mode of conduction in, ib. division and irritation of, ib. decussation of fibres in, ib. as a nervous centre, 341. centre of respiratory movements, 156, 342. effects of injury and disease, 342. seat of respiratory centre in, ib. reflecting power of, ib. wide connection of, 343. action in deglutition, ib. not seat of sensation or voluntary power, ib. maintenance of power in, 344. immunity from action of ether and chloroform, ib. influence on swallowing, 330. a source of force, 319. congestion in asphyxia, 158. Membrana decidua, 508. granulosa, 488. development of, into corpus lu- teum, 498. changes in cells of, previous to discharge of ovum, 504. Jacobi, 433. pupillaris, 540. capsulo-pupillaris, ib. tympani, 460. office of, 464. Membrane, primary or basement, 258, 261. Membrane, Vitelline, 488. Membranes, mucous. See Mucous membranes. Membranes, serous. See Serous membranes. Membranes, mixtures of fluids through, 239. Membranous labyrinth of ear, 458. Memory, relation to cerebrum. 355. Menstruation, 493. analogous with heat, 494. period of, coincident with discharge of ova, 494. 562 IND EX. Menstruation, continued. period of, first occurrence, 494. usually absent in pregnancy, 450. in suckling, ib phenomena of, ib. time of life when it ceases. Menstrual discharge, composition of, 55, 495. Mental exertion, effect on heat of body, 160. excretion of phosphates after, 300. Mental faculties, development of, 356. Mercury, absorption of, 243, 282. Mesenteric arteries, contraction of, 109. Meshes of capillary network, 117. Mesocephalon (see Pons Varolii), 344. Mezzo-soprano voice, 413. Milk, as food, 171. its composition, ib. Mind, hypothesis of, 356. varieties in children, 358. varieties in different ages, 359. connection of, with cerebrum, 356. duality of, 357-8. combines two sensations in one, 357. perception of two impressions by, 314. refers morbid impressions to peri- pheral ends of nerves, 316. can discriminate the point of a nerve so irritated, 817. influence of, in action of contractile tissues, 52. on heart's action, 100. on digestion, 196. on intestines, 225. on nutrition, 253. on secretion, 270. on reflex movements, 331-2. Mitral valve, 89. Mixed food, for man, 169, 171. Modiolus, 444. Molecules, or granules, 42. movement of, in cells, 45. Molecular base of chyle, 229. Monotonous voice, 412. Mortification from deficient bh 251. Motion, 391. ciliary, 391. muscular (see Movements), 393. | Motor columns of cord, 327. nerve-fibres, 311. linguae, or hypoglossal nerve, 882. oculi, or third nerve, 361. Mouth, orifice in relation to food, 173. moistened with saliva, 175. Movements of muscles, 401. automatic, 402. antagonistic, 365-6, 403. reflex, see reflex acts, 330, 404. associate or consenual, 365-6, 404. dependent on mind, 405. voluntary, 406. habitual, 334, 407. excited by ideas, 405. of expression, 406. excited by passion or emotion, ib. symmetrical, 405-6. of respiration, 139. respiratory, influence on carbonic acid, 148. influence of cerebellum, 350. dependent on the sympathetic nerve, 387-8. connection of, with optic thalami, 353. Mucous membranes, general characters, 260, divided into tracts, ib. component structures, 261. primary membrane, ib. epithelium-cells, 262. gland-cells of, ib. effects on starch, 176, Mucus, nature of, 36. resemblance to horny matter, ib. various substances included under the term, ib. in bile, 211. acid of vagina, 55. of urine, 297. corpuscles of, in saliva, 173. Muscles, of organic life, 393. animal life, 394. actions of (see Movements), 401. organic, peculiarities in contraction of, 399. flexion and extension of, 335. effects of their pressure on the veins, 126. impairment and removal of parti- cles, 245. changed by exercise, ib. INDEX. 563 Muscles, continued. layer of organic, in walls of vesi- cula3 seminales, 503. assisting erection, 135. Muscular tissue, 393. properties of, 396. irritability of, 397. peculiar sensibility of, 397. mode of contraction, 397. heat developed in contraction of, 398. Bound produced, ib. substances yielded on analysis of, 37. nerve-fibres in, 307. double supply of nerves, 811. sense, 368-397, 483. cerebellum, the organ of, 348. fibres of the heart, 95. tissue in arteries, 105, 108. in large veins, 124. Muscular coat of stomach, 179. fibres of stomach, action of, 193. coat of intestines, 199. Muscularity of lymphatics, 232. of lymph-hearts, 234. Musical sounds, 412, 471. Myopia or short-sightedness, 443. N. Nabothi glandulae, 486. Nails, chemical composition of, 36. Nates (brain), 351. Natural organic compounds, 28. classification of, 30. Necessity of breathing, 156. Nerve-corpuscles, their structure, 309. simple, ib. caudate or stellate, ib. connection with fibres, ib. Nerve-fibres, their structure, 302. cerebro-spinal, ib. sympathetic, 304, their course, 305. continuity of, 337. in plexuses, 305. their terminations, 306. in loops, ib. in plexuses, 307. by free ends, ib. by division, ib. in nerve-corpuscles, 309. Nerve-fibres, continued. origin of, 311. general purpose, ib. distinctions of, 311. action of stimuli on, 312 laws of action in, 313. effects of injury and division, 312, 316. mere conductors, 313 rate of conduction, 314. conduct one kind of impression, 315. sensitive, laws of action, ib, effects of division, ib. existence of loops in, 315. mind refers impressions to peri- phery, ib. illustrations of, 315-6. mind perceives the very point irri- tated, 317. one cannot discharge the function of another, ib. motor, laws of action, 318. Nerves, cerebral, physiology of (see Cere- bral nerves). excito-motory and reflecto-motory, 331, note. fifth, effects of division, 254. motor, 318. olfactory, cases of absence of, 253. pneumogastric, influence in diges- tion, 196-7. in absorption, 197. on movements of stomach, 198. influence on respiratory process, 156, 342. connection with respiration, 342, 343. influence on bronchi, 145. in relation to hunger, 196. effects of dividing. 343. respiratory, 154. sensitive, 311, 315. spinal, number and origin, 325. their roots, ib. specific functions, 325. effects of dividing, ib. sympathetic, influence on nutrition, 254. connection with intestines, 225. ulnar, division of, 317. effects of compression, 316. Nervous centres, 309. functions of, 318. sources of power, 319. 564 INDEX. Nervous centres, continued. conduction in, 319. communication in, 320. transference of impressions in, ib. diffusion or radiation in, 320. reflexion in, ib. conditions of, 321. congestion of asphyxia, 158. irritation of, produces sustained movements, 322. participation in reflex acts, 321. Nervous force, 52. velocity of, 319. Nervous system, 301. cerebro-spinal, ib. sympathetic, ib. elementary structure, 301. fibres, 302. vesicular structure, 309, functions of fibres, 311. of centres, 318. conduction in centres, 319. transference in, 320. diffusion or radiation, ib. reflection, ib. relation to the mind, 52. relation of blood to, 81. in relation to heat, 165. influence in erection, 135. connection with heart, 102. influence on respiration, 156. influence on digestion, 196. connection with movements of in- testines, 225. influence of nutrition, 253. influence on secretion, 269. influence of contractility, 42. development of, 527. first appearance, 513. Nervous tissue, in relation to urine, 300. Nervus Vagus, see Pneumogastric. Network, capillary, see Capillaries, 117. Neuralgia, division of nerves for, 316. New-born animals, heat of, 167. Nipple, structure of, 134. Nitrate of albumen, 34. of urea, 300. Nitrogen, influence of, in decomposi- tion, 29. changed in respiration, 151. of atmospheric air, 146, 151, absorbed by the skin, 283. in blood, 154. Nitrogenous principles, division of, 31. food, 170. in relation to urine, 293. Nose. See smell. restoration of, 317. irritation referred to, 320. Non-azotized, organic principles, 30. Non-vascular tissues, 120. Non-vascular parts, nutrition of, 251. Nucleated cells, see Cells. Nuclei, description of, 42-44. in developing and growing parts, 249. Nucleus, present in most cells, 44. metamorphoses of, 44. disappearance of, in degenerating tissue, 44. in Mammalian blood-corpuscles, ib. corpuscles, or nucleoli, 43. Nutrition, general nature of, 244. illustrated, 246. conditions of healthy, 250. of vascular and non-vascular parts, 251. influence of nervous system upon, 253, 369. in paralyzed parts, 253. Nutritive food, 169. process, 49. repetition, 250. reproduction, ib. Nymphae, 487. 0. Oblique muscles of the eye, action of, 364. Ocular spectrum, 448. Odour of blood, etc., 75, 71. (Esophagus, action in deglutition, 198. reflex movements of, 330. action in vomiting, 198. Oil, absorption of, 243. Oils, fixed, 30. Oily matter, coated with albumen. 230. Oleaginous food, 170. Oleaginous principles, digestion of, 192. Oleine and oleic acid, properties of, 30. Oleine, formula of, 31. Olfactory nerve, 426. Olivary bodies, 337. INDEX. 565 Omphalo-mesenteric duct, 519. vessels, 516. Ophthalmic ganglion, relation of third nerve to, 337. Optic lobes, their function, 352—5. Optic nerves (see Vision). Optic nerve, decussation of, 454-5. Optic thalami, relation of, to sight, 353. Organs, organisms, organization, 26. Organic and inorganic bodies, dis- tinctions between, 27. compounds prone to decomposition, 28. compounds, cause of instability of, 29. food, 169. life, its phenomena, 25. life, nervous system of, 383. processes, influence of sympathetic nerves upon, 397. processes, influenced by cerebro- spinal and sympathetic nerves, ib. Organization of fibrine, 67. Organs, plurality of cerebral, 358. Organs of sense, development of, 448. Osmazome, 37. Ossicula auditus, 460. office of, 465-6. Otoconia, or ear powder, 459. use of, 469. Ovaries, 486. Ovula Nabothi, 487. Ova, discharged periodically, 494. Ovum, structure of, 498. formation of, 490. changes in ovary, 491. discharge of, from ovary, 492. impregnation of, 499. development of, 504. changes in, previous to formation of embryo, 504. cleaving of yelk, 506. changes subsequent to cleaving, 507.. impregnated, changes of, in lower half of Fallopian tube, 505. changes of, in uterus, 506. connection of, with uterus, 522. impregnated, in relation to the de- cidua, 493-4. Oviduct, or Fallopian tube, 486. Oxygen, consumed in breathing, 150-155. 48 Oxygen, continued. proportion of, to carbonic acid, . 150-1. diffusion-volume of, 151 in blood, 154. union with other elements of blood, 155. union of with carbon, etc., pro- ducing heat, 162. effects on color of blood, 70. effect of, on pulmonary circulation, 123. P. Pacinian corpuscles, 307. Pain in paralyzed parts, 316. Palate and uvula in relation to voice, 416. Pancreas, 205. development of, 541. Pancreatic fluid, 205. Papillse, of the kidney, 284. of the skin, 275, 479. Par vagum, see Pneumogastric. Paralyzed parts, painful, 316. nutrition of, 253. limbs, temperature of, 164. Paralysis, cross, 341. Paraplegia, from disease or injury of the spinal cord, 327. reflex movements in, 331. delivery in, 334. state of intestines in, 225. Parotid gland, saliva from, 173. Particles, changes in nutrition, 244. removal when impaired or effete, ib. duration of life in each, 249. subject to circumstances, ib. natural decay and death, 245. process for forming new ones, 249. Patheticus, or fourth nerve, 364. Pause in Heart's action, see Heart, 85. Pavement-epithelium, 262. Peduncles, of the cerebellum, 346. of cerebrum, 350-352. Pelvis of the kidney, 284. Penis, corpus cavernosum, 134. 566 IND EX. Penis, continued. erection of, a reflex act in part, 834. Pepsine, 185. action^of, 188. Peptone, 192. Perception, 52. Perilymph, or fluid of labyrinth of ear, 458. use of, 468. Peristaltic movements, 223. Peritoneum, peculiarities of, 259. Permanent glands, 264. Perspiration, cutaneous, 280. insensible and sensible, ib. Peyer's glands, 200. Pharynx, action in swallowing, 178. reflex movements of, 330. Phlebolithes, 59. Phosphamid, relation of, to proteine, 36. Phosphates, exist ready-formed in tissues, 39. parts in which they are found, ib. present in albumen, 34. in blood, 71. acid, in gastric fluid, 184. Phosphorus, in organic compounds, 38. in urine, 299. union of with oxygen producing heat, 163, note. Phrenology, 358. Phymatine, 37. Physical forces, share in organic pro- cesses, 50. Pia mater, circulation in, 133. Picromel, 205. Pigment, of hair, 246. Pigment-cells, form and contents of, 45. Pineal gland, 360. Pituitary gland, ib. Placenta, formation and structure, 524. foetalis and uterina, 525. in relation to the liver, 214. Plants, heat evolved in, 164. Plastic food, 169. force, 49. Plexuses. nervous, 305. terminal, 306. conduction through, 318. brachial, relation to spinal cord, 324. Plexuses, continued. lumbar, ditto, ib. Plurality of cerebral organs, 358. Pneumogastric nerve, 376. relations of, to functions of larvnx 378. J to functions of oesophagus, 378. to respiration, 378. to functions of stomach, 380. to action of heart, ib. Poisoned wounds, absorption from. 243. Polygamous birds, their cerebella, 349. Pons Varolii, its structure, 344. its functions, 345. organ of sensation and will, 346. experiments showing its power, ib. Ponticulus, 345. Portal blood, characters of, 198-9. circulation, 83. veins, arrangement of, 207. Portio major, of fifth nerve, 366. minor, of fifth nerve, ib. mollis, of seventh nerve, 459. dura, of seventh nerve, 360. Position, efl'ect of, on the blood in parts, 133. Post-mortem rigidity, 399-400. affects all classes of muscles, 401. Posterior pyramids, 338. Posture, effects on the pulse, 97. Potash, salts of, in muscles, 40. in animal fluids, ib. Potassium, parts of body in which found, ib. Pregnancy, absence of menstruation during, 495. Presbyopia, or short-sightedness, 443. Primary membrane, 258-261. Primitive groove, 512. fasciculi and fibres of muscle, 394. band of nerve-fibre, 303. Principle, mental, 356. Principles, proximate, of animal sub- stances, 28. nitrogenous, 31. non-nitrogenous, 30 fatty, their composition, ib. of food. See Albuminous, etc. Processus gracilis, 460. a cerebello ad testes, 346 arciformes, 345. Properties, vital, 49. INDEX. 567 Prostate gland. 499. functions of secretion unknown, 503. Proteine, 35, 36. mode of obtaining, 35. compounds, 36. tritoxyde of, 65. in muscular coat of arteries, 105. Proximate principles of animal com- pounds, 28. Ptyaline, 37, 173. Puberty indicated in the female by menstruation, 494 Pudic nerves, 135. Pulmonary artery, valves of, 86. circulation, 83, 146. velocity of, 122. influence of carbonic acid on, 158. branches of pneumogastric, 378. Pulp of hair, 246-7. Pulse, 111. explained, 113. its frequency, 97. its variations, 97-8. its relation to respiration, 98. in capillaries, 421. in contracted arteries, 111. Pulsation in veins, 91. Pulsations, first, of heart, 531. Pupil of eye, office of, 436. Purpose of the blood, 80. Pus, contains albumen, 33. Putrefaction. See Decomposition. influence of gastric fluid on, 187. Pylorus, structure of, 180. action of, 193. Pyramids of Malpighi, 284. Pyramids. See Medulla Oblongata. R. Radiation of impressions, 320. Reason, 355, note. supremacy of, 357. Rectum, 199. evacuation of, a reflex act, 333. Reflection of impressions, 320. Reflecto-motory acts and nerves, note, 331. nature of, 320. conditions of, 321. essentially involuntary, ib. characters of, ib. Reflecto-motory acts, continued. influences of will in, 321, 332. purposive, 322. combined acts, ib. purposeless, ib. sustained, ib. illustrated, 404. in swallowing, 330. in decapitated animals, 331. after injury of cord, 331. difference in different classes, ib. greater extent of, in cold-blooded animals, 332. independent of brain or mind, 333. adaptation of, ib. what to be so regarded in man, 333. preservative, 334. relation of fifth nerve to, 368. Reflex acts, see Reflecto-motory acts. Refraction, laws of, 437. Refracting media of eye, ib. Relative life, its phenomena, 26. Renal arteries, arrangement of, 284. capsules, 272. cells, 285. portal vein, ib. Repair, retarded in paralysis, 253. after injury of cord, ib. Repetition, nutritive, 250. Reproduction, nutritive, ib. Reserve air, 142. Residual air, ib. Resin, biliary, 210. Respiration, general purpose, 136. structure of organs of, 137-139. movements of, 139. quantity of air changed in, 142. frequency of, 144. force of, ib. movements of air-tubes in, 144. movements of air in, 145. movements of blood in, 146. changes of air in, 146. carbonic acid increased by, 147. oxygen diminished by, 150. nitrogen, alterations in, 151. water exhaled by, 153. changes of blood by, 153. theories of, 155. influence of nervous system, 156. effects of suspending, 157. types of, 140-142. 568 INDEX. Respiration, continued. its relation to the pulse, 98. connection with medulla oblongata, 342. Respiratory food, 169. movements reflex, 333. movements of, automatic, 403. voluntary, 156. extraordinary, 156-1. excited by various stimuli, 342-3. excitement through nerves, 343. effects on the venous circulation, 127. nerves, 137. process, influence of pneumogastric nerves on, 378. tract of mucous membrane, 260-1. Respired air, temperature of, 147. Rest, favorable to coagulation, 60. Restiform bodies, 338. tradts, effects of irritating, 347. Retching, explanation of, 195. Rete testis, 499. Retina, structure of, 430. discernment of impressions on, 317. inversion of images on, 444. duration of sensations on, 458. Rigor mortis, 400. in arteries, 110. Rigidity of involuntary muscles, 401. Roots of spinal nerves, 325. Rotations, following injury of crura cerebelli, 350. produced by dividing the crura ce- rebri, 352 produced byinjury of optic thalami, 353. explanations of, 354. of yelk, 505. Round tracts, 338. Rumination, 196. Rhythm of heart. See Heart, 99. Rhythmic movements, 403. s. Saccharine food, 173. principles, digestion of, 192. action of the bile on, 218. Sacculus, 458. Safety-valve action of tricuspid valve, 91. Saline solutions, absorption of, 243. Saliva, organs for production of, 173. its composition, ib. epithelium mixed with, ib. ashes of, ib. mode of secretion, 174. quantity secreted, ib. purpose of, 176. for mastication, ib. chemical and digestive properties, 176. action on starch, ib. its relation to gastric fluid, ib. Salivary glands, development of, 541, Salts, action of, on blood, 70. Saponifiable substances, 31. Sarcolemma, 394. Scala vestibuli, 458. tympani, ib. Sclerotica, 436. Scurvy, influence of food in, 171. Sebaceous glands, 277. their secretions, 279. Secreted fluids, 41. Secreting glands, general characters, 264-266. temporary, 264. permanent, ib. tubular, simple, 265. aggregated, ib. convoluted tubular, 266. Secretion, general nature of, 258. necessary apparatus for, 258. by membranes, 258. by serous membranes, ib. by synovial membranes, 258. by mucous membranes, 260. process of, 267. resemblance to nutrition, 267. discharge of, 268. circumstances influencing, 268. influence of nervous system, 269. vicarious, 258. process by cells and nuclei, 266. antagonist, 270. mixed with exudations, 266. relation to supply of blood, 268, 270. Selection of materials for absorption, 227. Self-formation, characteristic of life, 49. Semen, emission of, a reflex act, 383. Semicircular canals of ear, 457 use of, 569. INDEX. 569 Semilunar valves, see Heart. Seminal fluid, 499. composition of, 503. influence exerted on other ova than those impregnated, ib. corpuscles and granules, 500. filaments, 501. tubes, 499. communicating with urine tubes, note, 286. Sensation, meaning of, 52. definition of, 420. and perception, mind alone capable of, 53. common and special, 420 subjective, in cerebrum, 355. perceived in pons, 346. perfect, perceived in cerebrum, 355. nerves of, laws of action, 315. simultaneous, 314. general, referred to particular or- gans, 196-7. combination of, in one, 357. in stumps, 316. Sense, of hearing; see Hearing, Sound. of sight; see Vision. of smell; see Smell. of taste ; see Taste. of touch ; see Touch. muscular, 368, 397, 483. Bpecial, nerves of, 315. organs of, development of, 538. Senses, special, general properties of, 420. nerves of each sense have special properties, ib. in relation to external nature, 421, 423. qualities of nerves of sense, 421. action of external and internal sti- muli on, 422. same stimulus excites different sen- sations in each, 423. influence of attention on impres- sions upon the senses, 425. impairment of, from division of the fifth nerve, 368. impairment of, from division of fa- cial nerve, 371. Sensibility, muscular; see Muscular sense. Sensible things, relation of mind to, 355. Sensitive columns of cord, 328. nerve-fibres, 311. 48* Sensory ganglia, 354. Septum between ventricles; formation of, 533. between auricles, formation of, ib. Seroline, 70. Serosity of blood, 65. Serous membranes, structure of, 258. epithelium of, ib. lining visceral cavities, 259. lining joints, etc., ib. their arrangement, ib. their purpose, ib. fluid secreted by, 260. nerves of, 307. Serum, of blood, 64. chief source of albumen, 34. temperature at which it coagu- lates, ib. colored by red corpuscles, 68. separation of, 55. Seventh cerebral nerve, 370. Sex, influence on production of car- bonic acid, 148. relation to breathing, 144. Sexual organs and functions of, in the female, 486. in the male, 499. Sexual passion, connection of, with cerebellum, 348. Shock, effect on heart's action, 100. influence on digestion, 197. Sight, see Vision. relation of corpora quadrigemina to, 352. impaired by lesion of fifth nerve, 369. Sigmoid valves, see Heart, 86. SiUcon and silica, parts in which found, 39. Singing, 412. Sinus terminalis, 515. uro-genitalis, 544. Sinuses of Morgagni, 87. of dura mater, 133. Sixth cerebral nerve, 364. Size, a variety of gelatine, 32. Skin; its structure, 275, 278. capillaries of, 119. excretion by, 279, 282. translation from, 281. absorption by, 282. gases exhaled from, 281. respiratory function of, 282. evaporation from, 283. 570 INDEX. Skin, continued. as an organ of touch, 478. parts in which sense most acute, 479. structure of papillae of, ib. epithelum, uses of, in relation to touch, 480. Sleep, influence in production of carbonic acid, 150. in relation to heat of body, 160. Smell, sense of, 425. conditions of, ib. different kinds of odours, 428. impaired by lesion of fifth nerve, 368. Sneezing, caused by sun's light, 320. Sniffing, act of, 426. Soap, fatty matter, which can be con- verted into, 31. Soda, tribasic phosphate in blood and saliva, 39, 71. urate of, 295. Sodium, parts of body in which found, 40. chloride of, in albumen, 34. Sole of foot, papillaa, etc., 275. Solids, auimal, varieties of, 41. Solids, simple, structureless, or amor- phous, 41. Solitary glands, 200, 204. Sommering, yellow spot of, 431. Sonorous substances, their intensity, 471. Soprano voice, 413. Sound, produced by contraction of muscle, 398. perception of, 470. perception of the direction of, 472. perception of distance of source of, 472. permanence of sensation of, ib. reflection of, by external ear, 462. subjective, 474. Sounds, of heart. See Heart. musical, 412, 471. conduction of, by external auditory passage, 462. Sources of nervous force, 319. Spasms, reflex acts, 334. Special sense, nerves of, 315, 420. Spectrum, or after-sensation on re- tina, 448. Speech, 416. Spermatozoids, development of, 500. Spermatozoids, continued. form and structure of, 501. motion of, ib. conditions influencing, ib. in impregnating fluids of all ani- mals, ib. function of, ib. Spherical aberration, how corrected in the eye, 439. Sphincter ani, action of, 224, 403. influence of cord on, 224, 331, 336. Spinal accessory nerve, 380. Spinal cord, 322. its construction, ib. commissure of, ib. fissures in, ib. tracts of, ib. course of fibres in, ib. size of parts of, 323. enlargements of, 324. its proportion to the cerebellum, 348. functions of, 326. as a conductor, 326. functions of its columns, 327. conduction across, 329-330. conduction through grey substance of, 329. communicating impression, 330. transference in, ib. radiation in, ib. reflex function of, ib. examples of, ib. independent of brain and mind, 331. different in higher and lower animals, 332. influence of mind in, 333. in disease, 334. parts of, that reflect in particular directions or modes, ib. influence on sphincter ani, 336. influence on tone, ib. effects of various divisions of, 330. effects of injuries of, on nutrition, 253. special power, of parts of, 234. its influence on heart's action, 100. in relation to intestines, 253. irritated from intestines, 319. influence on lymph hearts, 234, 335. connection with genital organs, 348. nerves, see Nerves spinal, 325. Spiral canal, cochlea, 457. IND EX. 571 Spirit, 355, note. Spleen, 270-273. Spontaneous decomposition, explana- tion of, 29. Spot, germinal, 489. Stapedius muscle, 461. office of, 468. Stapes, 460. Starch, effect of saliva on, 176. of other substances on, ib. digestion in stomach, 192. action of pancreas on, 205. changes in caecum, 222. effects of cooking on, 192. Statical pressure of blood, 115. Stature, relation to capacity of chest, 143. Stereoscope, 456. Still layer of blood, 122. Stimuli, as excitants of contractility, 51. Stimulus to nerve-fibres, 312. various kinds of, ib. St. Martin, Alexis, case of, 183. Stomach, its structure, 179. secretion of, see Gastric Fluid, 183. digestive power in, 192. digestive process in, 188. movements of, 193. in vomiting, 194. influence of nervous system on, 198. absorption from, 199. its temperature, 183. in relation to hunger, 196. examined through fistulae, 183. secretion influenced by state of mouth, 184. passage of substances from, to urine, 288. Striped and unstriped muscular fibres, 393-4. Structural composition of human body, 40. Stumps, sensations in, 816. Sudoriparous glands, 275. their distribution, 276. number, ib. their secretion, 274. Suets, or animal fat, 30. Suffocation, 157. Sugar, as food, 170. digestion of, 192. changes in caecum, 222. Sugar, continued. in liver, 219. of gelatine, 32. Sulphates, source of, in ashes of ani- mal substances, 38. in urine, 299. Sulphocyanide of potassium, 38. Sulpho-cyanogen in saliva, 174. Sulphur, in proteine compounds, 36. in organic compounds, 38. parts of the body in which it oc- curs, ib. union of, with oxygen, producing heat, 163, note. in urine, 299. difficulty of separating from pro- teine, 24. Superior costal type of respiration, 142. Supra-renal capsules, 270, 272. Swallowing, 128. a reflex act, 330. Sweat, analysis of, 280. Symmetrical diseases, 251. Sympathetic nerve, 382. ganglia of, 384. fibres of, ib. their course, 385. relation of, to cerebro-spinal sys- tem, ib. conduction by, ib. communications of, with sixth nerve, 365. influence on heart's action, 100. influence on arteries, 111. See Nerve, Sympathetic. Synovial fluid, secretion of, 260. membranes, 259. Systemic circulation, 83. affected by respiratory movements, 127. T. Tannic acid, test for gelatine, 32. Tanno-gelatine, 32. Tartar of teeth, 174. Taste, conditions for the perceptions of, 474. seat of, 475. connection of, with sense of smell, 477. permanence of impressions, 478. subjective sensations, ib. 572 INDEX. Taste, continued. variations of, 477. sense of, relation of fifth nerve to, 368. relation of facial nerve to, 371. nerves on which the sense depends, 375-6. Taurine, 210-11. quantity of sulphur in, 38. Teeth, reproduction of, 250. repetition of production of, ib. Temperature, average, of body, 159. average in diseases, ib. variations in sleep, etc., 160. relations to carbonic acid, ib. of Mammalia, birds, etc., 161. of cold-blooded and warm-blooded animals, ib. means of maintaining, 162. loss by radiation, etc., ib. sources and production of heat, ib. theory of animal heat, ib. in relation to food, etc., 165. in relation to the nervous system, ib. effects of increased, 166. modified by age, etc., 167. influence of, in exciting decomposi- tion, 29. of respired air, 147. influence on amount of carbonic acid produced, 148. of stomach, 183. Temporary glands, 264. in stomach, 183. Tendinous cords, 89. Tenor voice, 413. Tensor tympani muscle, 460. office of, 448. Tesselated epithelium, 262. Testes (brain), 351. Testes, connection with cerebellum, 348. Testicle, structure of, 499. Tetanus, 334. Thalami optici, see Optic Thalami. their structure, see Cerebrum. their function, 353. Theories of respiration, 155. Third cerebral nerve, 361. Thirst, sensation of, 196. Thoracic duct, its contents, 231-2. development of lymph and chyle in, 232. Thymus gland, 270-272. Thyroid gland, ib. Timbre of voice, 413. Tissues, absorption, of 228. animal, reference to accounts of, 47. erectile, 134. fatty, 30. gelatinous, 32. growth in proportion to water in, 66. moistened with watery part of blood, ib. muscular, 393. mutation of particles in, 245. mutually excretory, 80. nitrogenous, in relation to urea, 293. re-formation of, 249. their relation to blood, 123. vascular and non-vascular, 120. Tone, its nature, 336, and note. in relation to the spinal cord, ib. Tongue, structure of, 475. papillae of, ib. epithelium of, 276. part most sensitive to taste, 477. an organ of touch, ib. action in deglutition, 178. motor nerve in, 382, Tooth, development of, 248. Tooth-ache, radiation of sensation in, 320. Tooth-fang, absorption of, 248. Tooth-pulp, nerve-fibres in, 307. Touch, sense of, 478. modification of common sensation, ib. part of nervous system dependent on, ib. characters of external bodies ascer- tained by, 481. conditions for perfection of, 482. connection of, with muscular sense, 483. co-operation of mind with, 484. subjective sensations of, ib. sensations of, excited by mind, ib. Trachea in relation to the voice, 444. Tracts of medulla oblongata, 337-8. of mucous membrane, 260. of spinal cord, 322. Tragus, 461. Transference of impressions, 320. Transplantation of skin, 317. Transudation from skin, 280. 1 Tricuspid valve, 89. I N D EX. 573 Trifacial, trigeminal, orfifthnerve,366. Trisplanchnic or sympathetic nerve, 382. Trochlearis nerve, 364. Tubular glands, 265. of stomach, 180. Tubules, general structure of, 47. Tubuli seminiferi, 499. uriniferi, 284. Tunica albuginea of testicle, 499. Turgescence, in erectile and other organs, 135. of gastric mucous membrane, 183. Tympanum or middle ear, structure, 459. functions, 463. use of air in, 467. Types of respiration, 140-2 u. Ulnar nerve, effects of compression of, 316. effects of division, 317. Umbilical arteries, contraction of, 108. vesicle, 518. small size in mammalian ovum, ib. office and destination of, ib. Umbilicus, 517. Understanding, relation to cerebrum, 355. Uniform temperature, maintenance of, 162. Urachus, 522. Urate of ammonia, 296. of soda, ib. Urea, 291. Ureter, arrangement of, 287. radiation of pain in, 320. Urethra, its corpus spongiosum, 134. Uric acid, 294. Urinary bladder, hypertrophy of, 256. action of, 288. tubules, 284. Urine, secretion of, 286. rate of, ib. effects of posture, etc., 287. its general properties, 288. color, ib. reaction of, ib. Urine, continued. made alkaline by diet, 289. specific gravity of, ib. variations of, ib. quantity secreted, 290. chemical composition, ib. its several constituents, 291. coloring matter of, 297. spontaneous decomposition, 292. decomposition by mucus, 298. Uterine placenta, 525. Uterus, 487. follicular glands of, 509. simple and compound glands of, in bitch, 510. development of, in pregnancy, 233. reflex action of, 334. and vagina, their mucus, 52. contractions of its arteries, 108. Utriculus, 458. V. Vagina, 487. Vagus nerve (see Pneumogastric). Valve, ileo-caecal, 224. of Vieussens, 350. Valves, see Veins and Heart. Valvulae conniventes, 199. Varolii, pons, see Pons. Vasa deferentia, reflex movements of, 333. lutea, 520. Vascular glands, 270. analogous to secreting glands, 270. in relation to blood, 271. in early life, ib. several offices of, 272. relation to lymphatic glanls, 273. ! parts, nutrition of, 251. system, first appearance, 512. Vascularity, degrees of, 119. Vegetable food, 169. digestion of, 191. Vegetative life, its phenomena, 25. Veins, their structure, 124. in muscular parts, ib. valves of, 84, 124. influence of gravitation in, 125. force of blood in, 125. assistance to circulation in, 126. effects of muscular pressure on, ib. 574 INDEX. Veins, continued. effects of respiration on, 127. velocity of blood in, 129. absorption by, 236. pulsation in, 91 their muscular coats, 85. reflux of blood into, ib. in erectile tissues, 134. cranium, 133. Vein-stones, 59. Velocity of blood, 129. in arteries, 113, 122. in capillaries, 122. in veins, 129. of nervous force, 314. Vena portae, its arrangement, 83. Venous blood, organization of, 53. system, conformation of, in embryo, 535. Ventilation, in relation, to carbonic acid, 149. Ventral laminae, 515. Ventricles of heart, effect of, on arteries, 106. force in the veins, 125. their dilatation, 98. their capacity, ib. force of contraction, ib. their action, 86. of larynx, office of, 416. cerebral, 350. Ventriloquism, 419. Vermicular movement of intestines, 223. Vermiform process, 346. Vertebrae, formation of, 515. Vertebral column and cranium, de- velopment, 527. Vesicle, germinal, 489. Graafian, 488. Vesicula blastodermica, 508. seminales, 503. functions of, 503. reflex movements of, 333. Vesicular nervous substance, 309. Vestibule of the ear, 456. Vibrations of vocal cords, 408-410. Vidian nerve, 370. Vieussens, valve of, 350. Villi of intestines, 202, 227. cells developed in, 227. action of blood-vessels of, ib. epithelium of, ib. their blood-vessels, 117. on intestinal glands, 201. Villi of chorion, 522. Vis nervosa, 52. Visceral arches, development, 529. laminae, 515. Vision, organ of, 430. phenomena of, 437. conditions for formation of correct images, 438. at different distances, adaptation of eye to, 440. field of, ideal size, 445. its relation to the external world, 446. erect, accounted for, 444-5. direction of, 447. estimation of the form of objects, ib. estimation of the size of objects, 446. estimation of their distance, ib. estimation of their motion, 447. influence of attention on, ib. influence of contrast on the percep- tions of, 450. single, with two eyes, 451. its cause, 454-5. single, in quadrupeds, 453. Visual direction, 448. Vital capacity of chest, 143. properties, 26. Vital properties of blood, 73. of living bodies, 49. Vitelline duct, 518. membrane, 488. development of blood in 74. Vitellus, or yelk, 498. Vitreous humor, 446. Vocal cords, vibrations of, cause of voice, 408. structure and attachments of, 409- 410. longer in males than in females, 413. Voice and speech, 408. human, generated at the glottis, 408. in speaking, 412. compass of, ib. sexual difference, 413. varieties of, as the base, tenor, etc., ib. tone or pitch uninfluenced by length of larynx or trachea, 415. conditions on which strength of, de- pends, ib. influence of age upon, 414. IND EX. 575 Voice and speech, continued. in eunuchs, ib. influence of trachea on, 415, 416. Voluntary movements, 406. Vomiting, act of, 194. action of stomach in, ib. movement of oesophagus in, 178. influence of spinal cord in, 333. a reflex act, ib. Voluntary and acquired, 195. Vowels and consonants, 416. Vulvo-vaginal glands, 487. w. Warm-blooded animals, 161. Water, in blood, 66. deficient in thirst, 196. in various tissues, 66. influence of, in exciting decomposi- tion, 29. absorbed by the skin, 282. vapor of, in atmosphere, 147. exhaled from skin, 280. from lungs, 153, 280. Wave of blood in the pulse, 113. Weight, relation to capacity of breath- ing, 143. White corpuscles, see Lymph-corpus- cles. White substance of nerve-fibre, 303. Will, exercised through pons, 346. deliberate, exercised through cere- brum, 355. Willis, circle of, 133. Wolffian bodies, 543. Wounds, poisoned, absorption from, 243. Y. Yelk, or vitellus, 488. rotation of, within zona pellucida, 505. contraction of, in Fallopian tube, ib. absorption of, 218, note. Yelk-sac, 518. Yellow spot of Soemmering, 431. z. Zomidine, 37. Zona pellucida, 498. LIST OF WORKS REFERRED TO. I. John Hunter. Works of, Edited by Mr. Palmer. London. Longmans. 1835. II. Goodsir. Anatomical and Pathological Observations, by John and H. D. S. Goodsir. 1845. III. Valentin. De Functionibus Nervorum Cerebralium et Nervi Sympathetici. Berne, 1839. IV. Valentin. Lehrbuch Der Physiologie des Menschen. Braun- schweig, 1844. V. Quarterly Journal of Science and Arts. VI. Chemical Gazette. VII. Annali di Chimica applicata alia Medicina. Gennago. VIII. Oesterreichische Medicinische Wochenschrift. Wien. IX. 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Edited by Dr. Tweedie. Vol. VI. A System of Midwifery, by Dr. Rigby. Philada., 1847. L. A. Becquerel. Semeiotique des Urines. Paris, 1841. LI. Goldirrg Bird. Urinary Deposits. Philadelphia, 1854. LII. Dumas. Lecon sur la Statique Chgmique des Etres Orga- nises. Paris, 1841. LIII. Annales de Chimie et de Pharmacie. LIV. Liebig. Chemistry of Food. Walton and Maberly. 1847. LV. Bulletin de l'Acad^mie Royale de M6decine. LVI. Journal de Pharmacie. LVII. Journal de Chimie M£dicale. LVIII. Guy's Hospital Reports. LIX. Canstatt's Jahresberichte, fiber die Fortschritte in der Bio- logic Erlangen. LX. Fownes. A Manual of Chemistry. Amer. edit., Philadelphia. LXI. Mulder. Proeve Eener Algemeene physiolgische Scheikunde. Rotterdam, 1845. LXII. Magendie. Journal de Physiologie. LXIII. Memoirs and Proceedings of the Chemical Society of London. LXIV. Von Bibra. Chemische Untersuchungen fiber die Knochen und Z'ahne. Schweinfurt, 1844. LXV. Hoffman. Grundlinien der physiolog. und patholog. Chemie. 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De Glandularum Intestinalium Structura Peni- tiori. Berol. 1835. LXXIX. H. C. B. Bendz. Haandbog i den Almindenige Anatomie. Kjobenhavn, 1847. LXXX. Miiller's Archiv fur Anatomie, Physiologie, und wissenschaft- liche Medecin. Berlin. LXXXI. Schultz. Das System der Circulation in seiner Entwickelung durch die Thier-Reihe. Stuttgard, 1836. LXXXII. F. Simon's Animal Chemistry. Translated by Dr. Day for the Sydenham Society. Philadelphia, 1846. LXXXIII. Gorup-Besanez. Untersuchungen fiber Galle Erlangen, 1846. LXXXIV. Kolliker. Entwickelungs-Geschichte der Cephalopoden. LXXXV. John Davy. Anatomical and Physiological Researches. LXXXVI. Whitehead. On Sterility and Abortion. Philadelphia, 1848. LXXXVII. Annales d'Hygiene Publique et de Me*decine Legale. LXXXVIII. The Medical Times. LXXXIX. H. Zwicky. Die Metamorphose des Thrombus. Zurich, 1845. 4to. XC. Gazetta Medica de Milano. XCI. Signor Polli. Researches and Experiments upon the Human Blood. Noticed in the Medico-Chirurgical Review, Oct. 1847. XCIL Me*moires de l'Acade'mie de Chirurgie. XCIII. Report of the Proceedings of the British Association. XCIV. Edinburgh Medical and Surgical Journal. XCV. Burrows. Disorders of the Cerebral Circulation. Philadel- phia. 1848. XCVI. Meckel. Archiv. fur Anatomie und Physiologie. XCVII. Dublin Hospital Reports. XCVIII. Travers. Further Inquiry concerning Constitutional Lrritation. XCIX. Tiedemann. Zeitschrift fur Physiologie. C. Oesterreicher. Lehre vom Krieslauf des Blutes. Niiremburg, 1826. CI. British and Foreign Medical Review, Edited by J. Forbes, M. D CII. Griffiths. On the Chemical and Microscopical Characters of the Blood and Urine. Philadelphia. CHI. E. Harless. Ueber den Einfluss der Gase auf die Form der Blut-Kcerperchen. Erlangen, 1846. 580 LIST OF AUTHORS. CIV. C. Vogt. Histoire Naturelle des Poissons d'Eau douce, by M. Agassiz. Tom. 1, 1842. CV. C. Vogt. Untersuchungen fiber die Entwickeluug der Geburt- shelferkroete. Solothurn, 1841. CVI. Fahrner. De Globulorum Sanguinis in Mammal. Embryon. et Adultis Origine. CVII. J. Miiller. Handbuch der Physiologie des Menschen. 4to. ed. 1844. CVIII. Hollandische Beitrage. CIX. Andral et Gavarret. Recherches sur la quantite d'Acide Car- bonique exhale- par le Poumon. Paris, 1843. CX. Vierordt. Physiologie des Athmens. 1845. CXI. Gmelin. Handbuch der Theoretischen Chemie. Frankfort, 1827. CXII. Retzius. Om Mekanismen af Semi-lunar-Valvlernes tillolut- ning. CXIII. G. Treviranus. Beitrage zur Aufklarung der Erscheinung des Lebens. CXIV. Kolliker. Die Selbst'andigkeit und Abhangigkeit des Sympa- tischen Nervensystems. Zurich, 1844. CXV. R. Wagner. Neue Untersuchungen fiber den Bau und die En- digung der Nerven, etc. 1847. CXVI. Doublin Journal of Medical Science. CXVII. Hope. Treatise on Diseases of the Heart. Philadelphia. CXVIII. C. J. B. Williams. Pathology and Diagnosis of Diseases of tho Chest. Philadelphia. CXIX. Hannover. Recherches Microscopiques sur le Systeme Ner- veux, 1844. CXX. Annali Universali di Medicini. Luglio. CXXI. Moleschott. De Vesiculis Pulmonum Malpighianis. Halse, 1845. CXXII. Archives Ge'ne'rales de Medicine. CXXIII. Proceedings of the Royal Society. CXXIV. Erdmann's Journal. CXXV. Tiedemann's Physiology, translated by Gully and Lane. CXXVI. F. H. Bidder. Zur Lehre von dem Verh'altniss der Ganglien- kb'rper den Nervenfadern. Leipsic, 1847. CXXVII. Kobelt. Die M'annlichen und Weiblichen WollustorgUne des Menschen, etc. Freiburg, 4to., 1844. CXXVIII. Oesterreicher Jahrbucher. CXXIX. Ecker. Physiolog. Untersuchungen fiber die Bewegungen des Gehirns und Ruckenmarks. Stuttgard, 1843. LIST OF AUTHORS. 581 CXXX. Medicinische Zeitung des Vereins fur Heilkunde in Preus- sen. CXXXI. Carpenter. Principles of Human Physiology. Amer. Ed., Philadelphia. CXXXII. Delaroche et Berger. Exp. sur les Effets qu'une forte Cha- leur produit dans l'Economie Animale. Paris, 1806. CXXXIII. Magendie's Physiology; translated by Milligan. Amer. Ed. CXXXIV. Herbst. Des Lymphagef ass-system und seine Verrichtungen. Gdttingen, 1844. CXXXV. Archives d'Anatomie Ge"ne"rale et de Physiologie. CXXXVI. Longet. Anatomie et Physiologie du Systeme Nerveux, etc. Paris, 1842. CXXXVII. SpaUanzani. Versuche fiber das Verdauungsgeschaft. Leip- zig, 1785. CXXXVIII. Experiments and Observations on the Gastric Juice, and the Physiology of Digestion, by W. Beaumont. U. S., 1834. Reprinted with notes by Dr. A. Combe. Edinburgh, 1838. CXXXIX. Legallois. QSuvres completes, edited by M. Pariset. Paris, 1830. CXL. Flourens. Recherches Expe*rimentales sur les Fonct. du Sys- teme Nerveux, etc. Paris. CXLI. Magendie. Lecons sur les Fonctions du Systeme Nerveux. CXLII. Sir Charles Bell. Various Works on the Nervous System. See also Mr. Shaw's interesting " Narrative of the Dis- coveries of Sir Charles Bell in the Nervous System," and his more recent Essay " On Sir C. Bell's researches in the Nervous System." CXLIII. Transactions of the Cambridge Philosophical Society. CXLIV. C. Matteucci. Lectures on the Physical Phenomena of Living Beings. Philadelphia, 1849. CXLV. Liebig. Researches into the Motion of the Juices in the Ani- mal Body. Walton and Maberly, 1848. CXLVI. Backer. De Structura Hepatis. Leyden. CXLVII. J. Miiller. De Glandularum Structura, etc. Translated by Mr. Solly. CXLVIII. Vogel. Ueber die Gesetze nach welchen die Mischung von Flussigkeiten. ... in permeable substanzen erfolgt. Got- tingen, 1846. CXLIX. Quain's Elements of Anatomy, 5th Edition, by Mr. R. Quain * and Dr. Sharpey. Am. Ed., Philadelphia, 1849. CL. Carpenter. Elements of Physiology. Philadelphia. CLI. CEsterlen. Beitrage zur Physiologie. 1843. 49* 582 LIST OF AUTHORS. CLII. Grainger. Observations on the Spinal Cord. London, 1837. CLIII. Prochaska. Annotat. Academicae, 1784. Opera Minora, 1800. Lehrsiitze aus der Physiologie. Wien, 1797. CLIV. Bidder. Ueber die M'annlichen Geschlechts und Harnwerk- zeuge der Amphibien, 1840. CLV. Magendie. Lecons sur les Fonctions et les Maladies du Sys- teme Nerveux. Paris, 1841. CLVI. Brodie. Lectures on Pathology and Surgery. Longman, 1846. CLVII. Stilling and Wallach. Untersuchungen Ueber den Bau des Nervensystems. CLVIII. Van Deen. Nadere Entdekkingen over die Eigenschappen von het Ruggming, etc. Leiden, 1839. CLIX. Todd. Anatomy of the Brain, Spinal Cords and Ganglions. CLX. Revue Me*dicale. CLXI. Foville. Traite" Complet du Systeme Nerveux. 1844. CLXII. Schiff. De Vi Motoria Baseos Encephali. 1845. CLXIII. Mayo. Anatomical Commentaries. CLXIV. Beck. Anatomische Untersuchungen uber viito- viii,e- und ix" Hirnnervenpaares. Heidelberg, 1847, CLXV. Arnold. F. Icones Nervorum Capitis. Heidelberg. CLXVI. Hueck. Die Achsendrehung des Auges. Dorpat, 1838. CLXVII. Holland, Dr. Medical Notes and Reflections. Philada., 1856. CLXVIII. Mackenzie. Physiology of Vision. CLXIX. Wharton Jones. Lectures on Ophthalmic Surgery. Philada. CLXX. Briicke. Various papers in Miiller's Archiv.; and a published work on the Microscopic Structure of the Eye. CLXXI. Traube. Beitrage zur experimentellen Pathologie und Phy- siologie. Berlin, 1846. CLXXII. Remak. Ueber ein Selbst'andiges Darmnervensystem. Berlin, 1847. CLXXIII. Horn. Ueber den Geschmacks-Sinn des Menschen. Heidel- berg, 1835. CLXXIV. Dr. Baly and Dr. Kirkes. Supplement to the Second Volume of Mutter's Elements of Physiology. CLXXV. Hausmann. Ueber die Zeugung des wahren weiblichen Eies. Hannover, 1840. CLXXVI. Boullaud. Recherches Cliniques et Experimentales sur le Cervelet; referred to by Longet, cxxxvi. t. i. p. 740. CLXXVII. Bischoff. Beweis der von die Begattung unabhangigen periodischen Reifung und Loslosung der Eier. 1844. LIST OF AUTHORS. 583 CLXXVIII. Raciborski. De la Puberte" et de l'Age Critique chez la Femme, etc. Paris, 1844. CLXXIX. Pouchet. Th£orie Positive d'Evolution Spontan. Paris, 1847. CLXXX. Bagge. De Evolutione Strongyli auric, et Ascarid. vivip. Erlangen, 1841. CLXXXI. London and Edinburgh Philosophical Magazine. CLXXXII. Mayo. Elements of Physiology. CLXXXIII. E. H. Weber. Zus'atze vom Baue und Verricht. des Gesch- lechte Organe. CLXXXIV. Bischoff. Entwickelungs-Gescbichte des Hunde-Eies. CLXXXV. Lawrence. Treatise on Disease of the Eye. Philada. CLXXXVI. Smee. Vision in Health and Disease. 1847. CLXXXVII. Bischoff. Entwickelungs-Geschichteder Saugethiere und des Menschen. 1842. CLXXXVIII. The Human Brain. Its Structure, Physiology, and Diseases. By Samuel Solly, F. R. S. Philada., 1848. CLXXXIX. Monthly Journal of Medical Science. Edinburgh. CXC. British and Foreign Medico-Chirurgical Review. CXCI. Das anatomische und physiologische Verhalten der cavernoser Korper der Sexual organe. 1851. CXCII. Kolliker und Siebald's Zeitschrift. CXCIII. L'Union Me"dicale. CXCIV. Disquisitiones de Succo Gastrico. Diss. Inaug. By Antonius Hiibbenet. Dorpat, 1850. CXCV. De Succo Enterico. Inaug. Diss. By Robertus Zander. Dorpat, 1850. CXCVI. De Adipis Concoctione et Absorptione. Diss. Inaug. By Ed. Lenz. Dorpat, 1850. CXC VII. De Subtiliore Pulmonum Structura. By Arius Adriani, 1847. CXCVIII. Dr. Bence Jones. On Animal Chemistry in its application to Stomach and Renal Diseases. H. Bailliere. New York, 1850. CXCIX. On a remarkable effect of Cross-breeding. By Dr. Alexander Harvey. Blackwood and Sons, 1851. CC. Dr. Radclyffe Hall. On the Action of the Muscular Coat of the Bronchial Tubes. Pamphlet, 1851. CCI. Brown-Sequard. Recherches sur le R6tablissement de l'lrii- tabilite' Musculaire chez un Supplied treize heures apres la Mort. Paris, 1851. CCII. Dr. Carpenter. Principles of Physiology, general and com- parative. Third Edition. Philada. CCIII. Lehmann. Physiological Chemistry, translated by Dr. Day, for the Cavendish Society. Am. Ed. Philada., 1855. 584 LIST OF AUTHORS. CCIV. Funke. Atlas der physiologischen Chemie. Leipzig, 1853. CCV. W. S. Savory. Observations on the Structure and Con- nections of the Valves of the Human Heart. Pamphlet, 1851. CCVI. Kolliker. Handbuch der Gewebelehren des Menschen. Leip- zig, 1852. CCVII. Dr. Carpenter. Principles of Human Physiology, fifth Am. Edition. 1855. CCVIII. Bidder and Schmidt. Die Verdauungssafte und der Stoff- wechsel. Leipzig, 1852. CCIX. Paget. Lectures on Surgical Pathology. American Edition. 1853. CCX. C. G. Lehmann. Handbuch der physiologische Chemie. Leipzig, 1854. Translated by Morris. Philada., 1856. CCXI. Kolliker. Manual of Human Histology. Translated for the Sydenham Society, by G. Busk and T. Huxley. American Edition. CCXII. Gray. On the Structure and Use of the Spleen. CCXIII. The Medical Times and Gazette. CCXIV. J. E. Bowman. Practical Handbook of Medical Chemistry. Philadelphia, 1849. CCXV. Bischoff. Der Harnstoff als Maas der Stoffwechsels. Giessen, 1853. CCXVI. Quarterly Journal of Microscopical Science. Churchill. THE END. 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